Comparison of the different approaches to generate holograms from data acquired with a Kinect sensor

NASA Astrophysics Data System (ADS)

Kang, Ji-Hoon; Leportier, Thibault; Ju, Byeong-Kwon; Song, Jin Dong; Lee, Kwang-Hoon; Park, Min-Chul

2017-05-01

Data of real scenes acquired in real-time with a Kinect sensor can be processed with different approaches to generate a hologram. 3D models can be generated from a point cloud or a mesh representation. The advantage of the point cloud approach is that computation process is well established since it involves only diffraction and propagation of point sources between parallel planes. On the other hand, the mesh representation enables to reduce the number of elements necessary to represent the object. Then, even though the computation time for the contribution of a single element increases compared to a simple point, the total computation time can be reduced significantly. However, the algorithm is more complex since propagation of elemental polygons between non-parallel planes should be implemented. Finally, since a depth map of the scene is acquired at the same time than the intensity image, a depth layer approach can also be adopted. This technique is appropriate for a fast computation since propagation of an optical wavefront from one plane to another can be handled efficiently with the fast Fourier transform. Fast computation with depth layer approach is convenient for real time applications, but point cloud method is more appropriate when high resolution is needed. In this study, since Kinect can be used to obtain both point cloud and depth map, we examine the different approaches that can be adopted for hologram computation and compare their performance.

Distributed computing feasibility in a non-dedicated homogeneous distributed system

NASA Technical Reports Server (NTRS)

Leutenegger, Scott T.; Sun, Xian-He

1993-01-01

The low cost and availability of clusters of workstations have lead researchers to re-explore distributed computing using independent workstations. This approach may provide better cost/performance than tightly coupled multiprocessors. In practice, this approach often utilizes wasted cycles to run parallel jobs. The feasibility of such a non-dedicated parallel processing environment assuming workstation processes have preemptive priority over parallel tasks is addressed. An analytical model is developed to predict parallel job response times. Our model provides insight into how significantly workstation owner interference degrades parallel program performance. A new term task ratio, which relates the parallel task demand to the mean service demand of nonparallel workstation processes, is introduced. It was proposed that task ratio is a useful metric for determining how large the demand of a parallel applications must be in order to make efficient use of a non-dedicated distributed system.

Nonparallel linear stability analysis of unconfined vortices

NASA Astrophysics Data System (ADS)

Herrada, M. A.; Barrero, A.

2004-10-01

Parabolized stability equations [F. P. Bertolotti, Th. Herbert, and P. R. Spalart, J. Fluid. Mech. 242, 441 (1992)] have been used to study the stability of a family of swirling jets at high Reynolds numbers whose velocity and pressure fields decay far from the axis as rm-2 and r2(m-2), respectively [M. Pérez-Saborid, M. A. Herrada, A. Gómez-Barea, and A. Barrero, J. Fluid. Mech. 471, 51 (2002)]; r is the radial distance and m is a real number in the interval 0

Simulation of Nonlinear Instabilities in an Attachment-Line Boundary Layer

NASA Technical Reports Server (NTRS)

Joslin, Ronald D.

1996-01-01

The linear and the nonlinear stability of disturbances that propagate along the attachment line of a three-dimensional boundary layer is considered. The spatially evolving disturbances in the boundary layer are computed by direct numerical simulation (DNS) of the unsteady, incompressible Navier-Stokes equations. Disturbances are introduced either by forcing at the in ow or by applying suction and blowing at the wall. Quasi-parallel linear stability theory and a nonparallel theory yield notably different stability characteristics for disturbances near the critical Reynolds number; the DNS results con rm the latter theory. Previously, a weakly nonlinear theory and computations revealed a high wave-number region of subcritical disturbance growth. More recent computations have failed to achieve this subcritical growth. The present computational results indicate the presence of subcritically growing disturbances; the results support the weakly nonlinear theory. Furthermore, an explanation is provided for the previous theoretical and computational discrepancy. In addition, the present results demonstrate that steady suction can be used to stabilize disturbances that otherwise grow subcritically along the attachment line.

An analytical and experimental study of sound propagation and attenuation in variable-area ducts. [reducing aircraft engine noise

NASA Technical Reports Server (NTRS)

Nayfeh, A. H.; Kaiser, J. E.; Marshall, R. L.; Hurst, L. J.

1978-01-01

The performance of sound suppression techniques in ducts that produce refraction effects due to axial velocity gradients was evaluated. A computer code based on the method of multiple scales was used to calculate the influence of axial variations due to slow changes in the cross-sectional area as well as transverse gradients due to the wall boundary layers. An attempt was made to verify the analytical model through direct comparison of experimental and computational results and the analytical determination of the influence of axial gradients on optimum liner properties. However, the analytical studies were unable to examine the influence of non-parallel ducts on the optimum linear conditions. For liner properties not close to optimum, the analytical predictions and the experimental measurements were compared. The circumferential variations of pressure amplitudes and phases at several axial positions were examined in straight and variable-area ducts, hard-wall and lined sections with and without a mean flow. Reasonable agreement between the theoretical and experimental results was obtained.

Method to improve optical parametric oscillator beam quality

DOEpatents

Smith, Arlee V.; Alford, William J.; Bowers, Mark S.

2003-11-11

A method to improving optical parametric oscillator (OPO) beam quality having an optical pump, which generates a pump beam at a pump frequency greater than a desired signal frequency, a nonlinear optical medium oriented so that a signal wave at the desired signal frequency and a corresponding idler wave are produced when the pump beam (wave) propagates through the nonlinear optical medium, resulting in beam walk off of the signal and idler waves, and an optical cavity which directs the signal wave to repeatedly pass through the nonlinear optical medium, said optical cavity comprising an equivalently even number of non-planar mirrors that produce image rotation on each pass through the nonlinear optical medium. Utilizing beam walk off where the signal wave and said idler wave have nonparallel Poynting vectors in the nonlinear medium and image rotation, a correlation zone of distance equal to approximately .rho.L.sub.crystal is created which, through multiple passes through the nonlinear medium, improves the beam quality of the OPO output.

Optical parametric osicllators with improved beam quality

DOEpatents

Smith, Arlee V.; Alford, William J.

2003-11-11

An optical parametric oscillator (OPO) having an optical pump, which generates a pump beam at a pump frequency greater than a desired signal frequency, a nonlinear optical medium oriented so that a signal wave at the desired signal frequency and a corresponding idler wave are produced when the pump beam (wave) propagates through the nonlinear optical medium, resulting in beam walk off of the signal and idler waves, and an optical cavity which directs the signal wave to repeatedly pass through the nonlinear optical medium, said optical cavity comprising an equivalently even number of non-planar mirrors that produce image rotation on each pass through the nonlinear optical medium. Utilizing beam walk off where the signal wave and said idler wave have nonparallel Poynting vectors in the nonlinear medium and image rotation, a correlation zone of distance equal to approximately .rho.L.sub.crystal is created which, through multiple passes through the nonlinear medium, improves the beam quality of the OPO output.

A risk hedging strategy under the nonparallel-shift yield curve

NASA Astrophysics Data System (ADS)

Gong, Pu; He, Xubiao

2005-08-01

Under the assumption of the movement of rigid, a nonparallel-shift model in the term structure of interest rates is developed by introducing Fisher & Weil duration which is a well-known concept in the area of interest risk management. This paper has studied the hedge and replication for portfolio immunization to minimize the risk exposure. Throughout the experiment of numerical simulation, the risk exposures of the portfolio under the different risk hedging strategies are quantitatively evaluated by the method of value at risk (VaR) order statistics (OS) estimation. The results show that the risk hedging strategy proposed in this paper is very effective for the interest risk management of the default-free bond.

Light propagation in the averaged universe

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

Bagheri, Samae; Schwarz, Dominik J., E-mail: s_bagheri@physik.uni-bielefeld.de, E-mail: dschwarz@physik.uni-bielefeld.de

Cosmic structures determine how light propagates through the Universe and consequently must be taken into account in the interpretation of observations. In the standard cosmological model at the largest scales, such structures are either ignored or treated as small perturbations to an isotropic and homogeneous Universe. This isotropic and homogeneous model is commonly assumed to emerge from some averaging process at the largest scales. We assume that there exists an averaging procedure that preserves the causal structure of space-time. Based on that assumption, we study the effects of averaging the geometry of space-time and derive an averaged version of themore » null geodesic equation of motion. For the averaged geometry we then assume a flat Friedmann-Lemaître (FL) model and find that light propagation in this averaged FL model is not given by null geodesics of that model, but rather by a modified light propagation equation that contains an effective Hubble expansion rate, which differs from the Hubble rate of the averaged space-time.« less

The Aeroacoustics of Turbulent Flows

NASA Technical Reports Server (NTRS)

Goldstein, M. E.

2008-01-01

Aerodynamic noise prediction has been an important and challenging research area since James Lighthill first introduced his Acoustic Analogy Approach over fifty years ago. This talk attempts to provide a unified framework for the subsequent theoretical developments in this field. It assumes that there is no single approach that is optimal in all situations and uses the framework as a basis for discussing the strengths weaknesses of the various approaches to this topic. But the emphasis here will be on the important problem of predicting the noise from high speed air jets. Specific results will presented for round jets in the 0.5 to 1.4 Mach number range and compared with experimental data taken on the Glenn SHAR rig. It is demonstrated that nonparallel mean flow effects play an important role in predicting the noise at the supersonic Mach numbers. The results explain the failure of previous attempts based on the parallel flow Lilley model (which has served as the foundation for most jet noise analyses during past two decades).

Improving Thermal Ablation Delineation With Electrode Vibration Elastography Using a Bidirectional Wave Propagation Assumption

PubMed Central

DeWall, Ryan J.; Varghese, Tomy

2013-01-01

Thermal ablation procedures are commonly used to treat hepatic cancers and accurate ablation representation on shear wave velocity images is crucial to ensure complete treatment of the malignant target. Electrode vibration elastography is a shear wave imaging technique recently developed to monitor thermal ablation extent during treatment procedures. Previous work has shown good lateral boundary delineation of ablated volumes, but axial delineation was more ambiguous, which may have resulted from the assumption of lateral shear wave propagation. In this work, we assume both lateral and axial wave propagation and compare wave velocity images to those assuming only lateral shear wave propagation in finite element simulations, tissue-mimicking phantoms, and bovine liver tissue. Our results show that assuming bidirectional wave propagation minimizes artifacts above and below ablated volumes, yielding a more accurate representation of the ablated region on shear wave velocity images. Area overestimation was reduced from 13.4% to 3.6% in a stiff-inclusion tissue-mimicking phantom and from 9.1% to 0.8% in a radio-frequency ablation in bovine liver tissue. More accurate ablation representation during ablation procedures increases the likelihood of complete treatment of the malignant target, decreasing tumor recurrence. PMID:22293748

Improving thermal ablation delineation with electrode vibration elastography using a bidirectional wave propagation assumption.

PubMed

DeWall, Ryan J; Varghese, Tomy

2012-01-01

Thermal ablation procedures are commonly used to treat hepatic cancers and accurate ablation representation on shear wave velocity images is crucial to ensure complete treatment of the malignant target. Electrode vibration elastography is a shear wave imaging technique recently developed to monitor thermal ablation extent during treatment procedures. Previous work has shown good lateral boundary delineation of ablated volumes, but axial delineation was more ambiguous, which may have resulted from the assumption of lateral shear wave propagation. In this work, we assume both lateral and axial wave propagation and compare wave velocity images to those assuming only lateral shear wave propagation in finite element simulations, tissue-mimicking phantoms, and bovine liver tissue. Our results show that assuming bidirectional wave propagation minimizes artifacts above and below ablated volumes, yielding a more accurate representation of the ablated region on shear wave velocity images. Area overestimation was reduced from 13.4% to 3.6% in a stiff-inclusion tissue-mimicking phantom and from 9.1% to 0.8% in a radio-frequency ablation in bovine liver tissue. More accurate ablation representation during ablation procedures increases the likelihood of complete treatment of the malignant target, decreasing tumor recurrence. © 2012 IEEE

Separated flows near the nose of a body of revolution

NASA Technical Reports Server (NTRS)

Lin, S. P.

1986-01-01

The solution of the Navier-Stokes equations for the problem of cross-flow separataion about a deforming cylinder was achieved by iteration. It was shown that the separation starts at the rear stagnation point and the point of primary separation moves upstram along the cylinder surface. A general method of linear stability analysis for nonparallel external flows was constructed, which consists of representing the eigenfunctions with complete orthogonal sets and forms characteristic equations with the Galerkin method. The method was applied to the Kovasznay flow which is an exact solution of the Navier-Stokes equation. The results show that when the critical parameter is exceeded, there are only a few isolated unstable eigen-frequencies. Another exact solution is shown to be absolutely and monotonically stable with respect to infinitesimal disturbances of all frequencies. The flow is also globally, asymptotically, and monotonically stable in the mean with respect o three-dimensional disturbances. This result forms the sound foundation of rigorous stability analysis for nonparallel flows, and provides an invaluable test ground for future studies of nonparallel flows in which the basic states do not posses exact solutions. The application of this method to the study of the formation of spiral vorticies near the nose of a rotating body of revolution is underway. The same method will be applied to the stability analysis of reversed flow over a plate with suction.

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

Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.

The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E. R. Tracy and A. N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. A cold-plasma model is introduced in this paper whichmore » exhibits ray helicity in conversion regions where the density and magnetic field gradients are significantly nonparallel. For illustration, such regions are identified in a model of the poloidal plane of a deuterium-tritium tokamak plasma. In each conversion region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. A detailed analytic and numerical study of helical rays in this sector is developed for a 'symmetric-wedge' model.« less

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

Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.

The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E.R. Tracy and A.N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. In this paper we show that a cold plasma model willmore » exhibit ray helicity in conversion regions where the density and magnetic field gradients are significantly non-parallel. For illustration, we examine a model of the poloidal plane of a deuterium-tritium tokamak plasma, and identify such a region. In this region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. We introduce a ''symmetric-wedge'' model, to develop a detailed analytic and numerical study of helical rays in this sector.« less

Virtual fringe projection system with nonparallel illumination based on iteration

NASA Astrophysics Data System (ADS)

Zhou, Duo; Wang, Zhangying; Gao, Nan; Zhang, Zonghua; Jiang, Xiangqian

2017-06-01

Fringe projection profilometry has been widely applied in many fields. To set up an ideal measuring system, a virtual fringe projection technique has been studied to assist in the design of hardware configurations. However, existing virtual fringe projection systems use parallel illumination and have a fixed optical framework. This paper presents a virtual fringe projection system with nonparallel illumination. Using an iterative method to calculate intersection points between rays and reference planes or object surfaces, the proposed system can simulate projected fringe patterns and captured images. A new explicit calibration method has been presented to validate the precision of the system. Simulated results indicate that the proposed iterative method outperforms previous systems. Our virtual system can be applied to error analysis, algorithm optimization, and help operators to find ideal system parameter settings for actual measurements.

Application of the Linux cluster for exhaustive window haplotype analysis using the FBAT and Unphased programs.

PubMed

Mishima, Hiroyuki; Lidral, Andrew C; Ni, Jun

2008-05-28

Genetic association studies have been used to map disease-causing genes. A newly introduced statistical method, called exhaustive haplotype association study, analyzes genetic information consisting of different numbers and combinations of DNA sequence variations along a chromosome. Such studies involve a large number of statistical calculations and subsequently high computing power. It is possible to develop parallel algorithms and codes to perform the calculations on a high performance computing (HPC) system. However, most existing commonly-used statistic packages for genetic studies are non-parallel versions. Alternatively, one may use the cutting-edge technology of grid computing and its packages to conduct non-parallel genetic statistical packages on a centralized HPC system or distributed computing systems. In this paper, we report the utilization of a queuing scheduler built on the Grid Engine and run on a Rocks Linux cluster for our genetic statistical studies. Analysis of both consecutive and combinational window haplotypes was conducted by the FBAT (Laird et al., 2000) and Unphased (Dudbridge, 2003) programs. The dataset consisted of 26 loci from 277 extended families (1484 persons). Using the Rocks Linux cluster with 22 compute-nodes, FBAT jobs performed about 14.4-15.9 times faster, while Unphased jobs performed 1.1-18.6 times faster compared to the accumulated computation duration. Execution of exhaustive haplotype analysis using non-parallel software packages on a Linux-based system is an effective and efficient approach in terms of cost and performance.

Application of the Linux cluster for exhaustive window haplotype analysis using the FBAT and Unphased programs

PubMed Central

Mishima, Hiroyuki; Lidral, Andrew C; Ni, Jun

2008-01-01

Background Genetic association studies have been used to map disease-causing genes. A newly introduced statistical method, called exhaustive haplotype association study, analyzes genetic information consisting of different numbers and combinations of DNA sequence variations along a chromosome. Such studies involve a large number of statistical calculations and subsequently high computing power. It is possible to develop parallel algorithms and codes to perform the calculations on a high performance computing (HPC) system. However, most existing commonly-used statistic packages for genetic studies are non-parallel versions. Alternatively, one may use the cutting-edge technology of grid computing and its packages to conduct non-parallel genetic statistical packages on a centralized HPC system or distributed computing systems. In this paper, we report the utilization of a queuing scheduler built on the Grid Engine and run on a Rocks Linux cluster for our genetic statistical studies. Results Analysis of both consecutive and combinational window haplotypes was conducted by the FBAT (Laird et al., 2000) and Unphased (Dudbridge, 2003) programs. The dataset consisted of 26 loci from 277 extended families (1484 persons). Using the Rocks Linux cluster with 22 compute-nodes, FBAT jobs performed about 14.4–15.9 times faster, while Unphased jobs performed 1.1–18.6 times faster compared to the accumulated computation duration. Conclusion Execution of exhaustive haplotype analysis using non-parallel software packages on a Linux-based system is an effective and efficient approach in terms of cost and performance. PMID:18541045

Model-Based IN SITU Parameter Estimation of Ultrasonic Guided Waves in AN Isotropic Plate

NASA Astrophysics Data System (ADS)

Hall, James S.; Michaels, Jennifer E.

2010-02-01

Most ultrasonic systems employing guided waves for flaw detection require information such as dispersion curves, transducer locations, and expected propagation loss. Degraded system performance may result if assumed parameter values do not accurately reflect the actual environment. By characterizing the propagating environment in situ at the time of test, potentially erroneous a priori estimates are avoided and performance of ultrasonic guided wave systems can be improved. A four-part model-based algorithm is described in the context of previous work that estimates model parameters whereby an assumed propagation model is used to describe the received signals. This approach builds upon previous work by demonstrating the ability to estimate parameters for the case of single mode propagation. Performance is demonstrated on signals obtained from theoretical dispersion curves, finite element modeling, and experimental data.

Gravity Waves in the Atmosphere: Instability, Saturation, and Transport.

DTIC Science & Technology

1995-11-13

role of gravity wave drag in the extratropical QBO , destabilization of large-scale tropical waves by deep moist convection, and a general theory of equatorial inertial instability on a zonally nonuniform, nonparallel flow.

Rockfall travel distances theoretical distributions

NASA Astrophysics Data System (ADS)

Jaboyedoff, Michel; Derron, Marc-Henri; Pedrazzini, Andrea

2017-04-01

The probability of propagation of rockfalls is a key part of hazard assessment, because it permits to extrapolate the probability of propagation of rockfall either based on partial data or simply theoretically. The propagation can be assumed frictional which permits to describe on average the propagation by a line of kinetic energy which corresponds to the loss of energy along the path. But loss of energy can also be assumed as a multiplicative process or a purely random process. The distributions of the rockfall block stop points can be deduced from such simple models, they lead to Gaussian, Inverse-Gaussian, Log-normal or exponential negative distributions. The theoretical background is presented, and the comparisons of some of these models with existing data indicate that these assumptions are relevant. The results are either based on theoretical considerations or by fitting results. They are potentially very useful for rockfall hazard zoning and risk assessment. This approach will need further investigations.

Linear and nonlinear stability of the Blasius boundary layer

NASA Technical Reports Server (NTRS)

Bertolotti, F. P.; Herbert, TH.; Spalart, P. R.

1992-01-01

Two new techniques for the study of the linear and nonlinear instability in growing boundary layers are presented. The first technique employs partial differential equations of parabolic type exploiting the slow change of the mean flow, disturbance velocity profiles, wavelengths, and growth rates in the streamwise direction. The second technique solves the Navier-Stokes equation for spatially evolving disturbances using buffer zones adjacent to the inflow and outflow boundaries. Results of both techniques are in excellent agreement. The linear and nonlinear development of Tollmien-Schlichting (TS) waves in the Blasius boundary layer is investigated with both techniques and with a local procedure based on a system of ordinary differential equations. The results are compared with previous work and the effects of non-parallelism and nonlinearity are clarified. The effect of nonparallelism is confirmed to be weak and, consequently, not responsible for the discrepancies between measurements and theoretical results for parallel flow.

HCG-. beta. -subunit radioimmunoassay: potential error in HCG measurement related to choice of labeled antigen. [/sup 125/I

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

Tyrey, L.; Hammond, C.B.

1976-05-15

Antiserum generated against the hormone-specific ..beta..-subunit of hCG was used with different labeled antigens to measure circulating hCG in patients having trophoblastic disease. When /sup 125/I-hCG..beta.. served as the labeled antigen, a small number of patient sera failed to show parallelism with the second IS-hCG reference and erroneous estimates of hormone concentrations were obtained. Replacement of the /sup 125/I-hCG..beta.. with labeled hCG corrected the nonparallelism exhibited by these samples. Inhibition curves obtained with purified hCG and hCG..beta.. suggested that both the nonparallelism and its correction with the change in labeled antigen would be consistent with the possibility that this assaymore » aberration may result from the presence of free hCG..beta.. in these sera. (auth)« less

Unidirectional transmission realized by two nonparallel gratings made of isotropic media.

PubMed

Ye, Wei-Min; Yuan, Xiao-Dong; Zeng, Chun

2011-08-01

We realize a unidirectional transmission by cascading two nonparallel gratings (NPGs) made of isotropic, lossless, and linear media. For a pair of orthogonal linear polarizations, one of the gratings is designed as a polarizer, which is a reflector for one polarization and a transmitter for the other; another grating is designed as a polarization converter, which converts most of one polarized incident wave into another polarized transmitted wave. It is demonstrated by numerical calculation that more than 85% of the incident light energy can be transmitted with less than 1% transmission in the opposite direction for linearly polarized light at normal incidence, and the relative bandwidth of the unidirectional transmission is nearly 9%. The maximum transmission contrast ratio between the two directions is 62 dB. Unlike one-way diffraction grating, the transmitted light of the NPGs is collinear with the incident light, but their polarizations are orthogonal. © 2011 Optical Society of America

Effect of nonparallel placement of in-circle bipolar radiofrequency ablation probes on volume of tissue ablated with heat sink.

PubMed

Pillai, Krishna; Al-Alem, Ihssan; Akhter, Javed; Chua, Terence C; Shehata, Mena; Morris, David L

2015-06-01

Percutaneous bipolar radiofrequency ablation (RFA) is a minimally invasive technique for treating liver tumors. It is not always possible to insert the bipolar probes parallel to each other on either side of tumor, since it restricts maneuverability away from vital structures or ablate certain tumor shape. Therefore, we investigated how nonparallel placement of probes affected ablation. Bipolar RFA in parallel and in divergent positions were submerged in tissue model (800 mL egg white) at 37°C and ablated. Temperature probes, T1 and T2 were placed 8.00 mm below the tip of the probes, T3 in between the probe coil elements and T4 and T5 at water inlet and outlet, respectively. Both models with heat sink (+HS) and without (-HS) were investigated. The mean ablated tissue volume, mass, density and height increased linearly with unit angle increase for -HS model. With +HS, a smaller increase in mean volume and mass, a slightly greater increase in mean density but a reduction in height of tissue was seen. The mean ablation time and duration of maximum temperature with +HS was slightly larger, compared with -HS, while -HS ablated at a slightly higher temperature. The heat sink present was minimal for probes in parallel position compared to nonparallel positions. Divergence from parallel insertion of bipolar RFA probes increased the mean volume, mass, and density of tissue ablated. However, the presence of large heat sinks may limit the application of this technique, when tumors border on larger vessels. © The Author(s) 2014.

Modification of VanWagner's canopy fire propagation model

Treesearch

James Dickinson; Andrew Robinson; Richy Harrod; Paul Gessler; Alistair Smith

2007-01-01

The conditions necessary for the combustion of canopy fuels are not well known but are assumed to be highly influenced by the volume through which the canopy fuels are dispersed, known as canopy bulk density (CBD). Propagating crown fire is defined as a continuous wall of flame from the bottom to the top of the canopy, implying crown fire propagation is actually...

An implementation of cellular automaton model for single-line train working diagram

NASA Astrophysics Data System (ADS)

Hua, Wei; Liu, Jun

2006-04-01

According to the railway transportation system's characteristics, a new cellular automaton model for the single-line railway system is presented in this paper. Based on this model, several simulations were done to imitate the train operation under three working diagrams. From a different angle the results show how the organization of train operation impacts on the railway carrying capacity. By using the non-parallel train working diagram the influence of fast-train on slow-train is found to be the strongest. Many slow-trains have to wait in-between neighbouring stations to let the fast-train(s) pass through first. So the slow-train will advance like a wave propagating from the departure station to the arrival station. This also resembles the situation of a highway jammed traffic flow. Furthermore, the nonuniformity of travel times between the sections also greatly limits the railway carrying capacity. After converting the nonuniform sections into the sections with uniform travel times while the total travel time is kept unchanged, all three carrying capacities are improved greatly as shown by simulation. It also shows that the cellular automaton model is an effective and feasible way to investigate the railway transportation system.

Microstructure of enamel.

PubMed

Boyde, A

1997-01-01

Enamel is a composite material consisting of mineral and organic phases. The properties of the mineral phase are modulated dramatically by its division into microscopic crystals, cemented together by the organic matrix protein polymer. A good concept of the 3D orientations of the crystals derives from visualizing their growth perpendicular to the surface in which they develop, which is pitted by the secretory poles of the ameloblasts. The arrangement of the crystals is the cause of the discontinuities, known as the prism boundaries or junctions, in the otherwise continuous structure. These locations acquire a more concentrated organic matrix during maturation, and they are both crack stoppers and crack propagation tracks in the adult tissue. Any tendency of prisms to cleave may be reduced by their varicosities, which reflect daily variations in the rate of production; their cross-sectional shape; the non-parallelism of adjacent groups, which develops through translocation of groups of cells across the surface during development; and the support of any one microscopic tissue element by other tissue, including dentine, placed to resist an applied load. Incremental growth lines are preferential cleavage planes within the enamel. Failure patterns of enamel in normal and abnormal use can be explained by these parameters, with additional consideration of functional variation and fatigue.

Parallel workflow manager for non-parallel bioinformatic applications to solve large-scale biological problems on a supercomputer.

PubMed

Suplatov, Dmitry; Popova, Nina; Zhumatiy, Sergey; Voevodin, Vladimir; Švedas, Vytas

2016-04-01

Rapid expansion of online resources providing access to genomic, structural, and functional information associated with biological macromolecules opens an opportunity to gain a deeper understanding of the mechanisms of biological processes due to systematic analysis of large datasets. This, however, requires novel strategies to optimally utilize computer processing power. Some methods in bioinformatics and molecular modeling require extensive computational resources. Other algorithms have fast implementations which take at most several hours to analyze a common input on a modern desktop station, however, due to multiple invocations for a large number of subtasks the full task requires a significant computing power. Therefore, an efficient computational solution to large-scale biological problems requires both a wise parallel implementation of resource-hungry methods as well as a smart workflow to manage multiple invocations of relatively fast algorithms. In this work, a new computer software mpiWrapper has been developed to accommodate non-parallel implementations of scientific algorithms within the parallel supercomputing environment. The Message Passing Interface has been implemented to exchange information between nodes. Two specialized threads - one for task management and communication, and another for subtask execution - are invoked on each processing unit to avoid deadlock while using blocking calls to MPI. The mpiWrapper can be used to launch all conventional Linux applications without the need to modify their original source codes and supports resubmission of subtasks on node failure. We show that this approach can be used to process huge amounts of biological data efficiently by running non-parallel programs in parallel mode on a supercomputer. The C++ source code and documentation are available from http://biokinet.belozersky.msu.ru/mpiWrapper .

Development of a Three-Dimensional PSE Code for Compressible Flows: Stability of Three-Dimensional Compressible Boundary Layers

NASA Technical Reports Server (NTRS)

Balakumar, P.; Jeyasingham, Samarasingham

1999-01-01

A program is developed to investigate the linear stability of three-dimensional compressible boundary layer flows over bodies of revolutions. The problem is formulated as a two dimensional (2D) eigenvalue problem incorporating the meanflow variations in the normal and azimuthal directions. Normal mode solutions are sought in the whole plane rather than in a line normal to the wall as is done in the classical one dimensional (1D) stability theory. The stability characteristics of a supersonic boundary layer over a sharp cone with 50 half-angle at 2 degrees angle of attack is investigated. The 1D eigenvalue computations showed that the most amplified disturbances occur around x(sub 2) = 90 degrees and the azimuthal mode number for the most amplified disturbances range between m = -30 to -40. The frequencies of the most amplified waves are smaller in the middle region where the crossflow dominates the instability than the most amplified frequencies near the windward and leeward planes. The 2D eigenvalue computations showed that due to the variations in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the most amplified disturbances are shifted to 120 degrees compared to 90 degrees for the parallel theory. It is also observed that the nonparallel amplification rates are smaller than that is obtained from the parallel theory.

High-Speed Research: 1994 Sonic Boom Workshop: Atmospheric Propagation and Acceptability Studies

NASA Technical Reports Server (NTRS)

Mccurdy, David A. (Editor)

1994-01-01

The workshop proceedings include papers on atmospheric propagation and acceptability studies. Papers discussing atmospheric effects on the sonic boom waveform addressed several issues. It has long been assumed that the effects of molecular relaxation are adequately accounted for by assuming that a steady state balance between absorption and nonlinear wave steepening exists. It was shown that the unsteadiness induced by the nonuniform atmosphere precludes attaining this steady state. Further, it was shown that the random atmosphere acts as a filter, effectively filtering out high frequency components of the distorted waveform. Several different propagation models were compared, and an analysis of the sonic boom at the edge of the primary carpet established that the levels there are bounded. Finally, a discussion of the levels of the sonic boom below the sea surface was presented.

Boundary-Layer Receptivity and Integrated Transition Prediction

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan

2005-01-01

The adjoint parabold stability equations (PSE) formulation is used to calculate the boundary layer receptivity to localized surface roughness and suction for compressible boundary layers. Receptivity efficiency functions predicted by the adjoint PSE approach agree well with results based on other nonparallel methods including linearized Navier-Stokes equations for both Tollmien-Schlichting waves and crossflow instability in swept wing boundary layers. The receptivity efficiency function can be regarded as the Green's function to the disturbance amplitude evolution in a nonparallel (growing) boundary layer. Given the Fourier transformed geometry factor distribution along the chordwise direction, the linear disturbance amplitude evolution for a finite size, distributed nonuniformity can be computed by evaluating the integral effects of both disturbance generation and linear amplification. The synergistic approach via the linear adjoint PSE for receptivity and nonlinear PSE for disturbance evolution downstream of the leading edge forms the basis for an integrated transition prediction tool. Eventually, such physics-based, high fidelity prediction methods could simulate the transition process from the disturbance generation through the nonlinear breakdown in a holistic manner.

Broadband Ultrasonic Transducers

NASA Technical Reports Server (NTRS)

Heyser, R. C.

1986-01-01

New geometry spreads out resonance region of piezoelectric crystal. In new transducer, crystal surfaces made nonparallel. One surface planar; other, concave. Geometry designed to produce nearly uniform response over a predetermined band of frequencies and to attenuate strongly frequencies outside band. Greater bandwidth improves accuracy of sonar and ultrasonic imaging equipment.

Numerical Study of Interaction of a Vortical Density Inhomogeneity with Shock and Expansion Waves

NASA Technical Reports Server (NTRS)

Povitsky, A.; Ofengeim, D.

1998-01-01

We studied the interaction of a vortical density inhomogeneity (VDI) with shock and expansion waves. We call the VDI the region of concentrated vorticity (vortex) with a density different from that of ambiance. Non-parallel directions of the density gradient normal to the VDI surface and the pressure gradient across a shock wave results in an additional vorticity. The roll-up of the initial round VDI towards a non-symmetrical shape is studied numerically. Numerical modeling of this interaction is performed by a 2-D Euler code. The use of an adaptive unstructured numerical grid makes it possible to obtain high accuracy and capture regions of induced vorticity with a moderate overall number of mesh points. For the validation of the code, the computational results are compared with available experimental results and good agreement is obtained. The interaction of the VDI with a propagating shock wave is studied for a range of initial and induced circulations and obtained flow patterns are presented. The splitting of the VDI develops into the formation of a non-symmetrical vortex pair and not in a set of vortices. A method for the analytical computation of an overall induced circulation Gamma(sub 1) as a result of the interaction of a moving VDI with a number of waves is proposed. Simplified, approximated, expressions for Gamma(sub 1) are derived and their accuracy is discussed. The splitting of the VDI passing through the Prandtl-Meyer expansion wave is studied numerically. The obtained VDI patterns are compared to those for the interaction of the VDI with a propagating shock wave for the same values of initial and induced circulations. These patterns have similar shapes for corresponding time moments.

Viscoelastic characterization of dispersive media by inversion of a general wave propagation model in optical coherence elastography

NASA Astrophysics Data System (ADS)

Zvietcovich, Fernando; Rolland, Jannick P.; Grygotis, Emma; Wayson, Sarah; Helguera, Maria; Dalecki, Diane; Parker, Kevin J.

2018-02-01

Determining the mechanical properties of tissue such as elasticity and viscosity is fundamental for better understanding and assessment of pathological and physiological processes. Dynamic optical coherence elastography uses shear/surface wave propagation to estimate frequency-dependent wave speed and Young's modulus. However, for dispersive tissues, the displacement pulse is highly damped and distorted during propagation, diminishing the effectiveness of peak tracking approaches. The majority of methods used to determine mechanical properties assume a rheological model of tissue for the calculation of viscoelastic parameters. Further, plane wave propagation is sometimes assumed which contributes to estimation errors. To overcome these limitations, we invert a general wave propagation model which incorporates (1) the initial force shape of the excitation pulse in the space-time field, (2) wave speed dispersion, (3) wave attenuation caused by the material properties of the sample, (4) wave spreading caused by the outward cylindrical propagation of the wavefronts, and (5) the rheological-independent estimation of the dispersive medium. Experiments were conducted in elastic and viscous tissue-mimicking phantoms by producing a Gaussian push using acoustic radiation force excitation, and measuring the wave propagation using a swept-source frequency domain optical coherence tomography system. Results confirm the effectiveness of the inversion method in estimating viscoelasticity in both the viscous and elastic phantoms when compared to mechanical measurements. Finally, the viscoelastic characterization of collagen hydrogels was conducted. Preliminary results indicate a relationship between collagen concentration and viscoelastic parameters which is important for tissue engineering applications.

Influence of viscous dissipation on a copper oxide nanofluid in an oblique channel: Implementation of the KKL model

NASA Astrophysics Data System (ADS)

Ahmed, Naveed; Adnan; Khan, Umar; Mohyud-Din, Syed Tauseef; Manzoor, Raheela

2017-05-01

This paper aims to study the flow of a nanofluid in the presence of viscous dissipation in an oblique channel (nonparallel plane walls). For thermal conductivity of the nanofluid, the KKL model is utilized. Water is taken as the base fluid and it is assumed to be containing the solid nanoparticles of copper oxide. The appropriate set of partial differential equations is transformed into a self-similar system with the help of feasible similarity transformations. The solution of the model is obtained analytically and to ensure the validity of analytical solutions, numerically one is also calculated. The homotopy analysis method (HAM) and the Runge-Kutta numerical method (coupled with shooting techniques) have been employed for the said purpose. The influence of the different flow parameters in the model on velocity, thermal field, skin friction coefficient and local rate of heat transfer has been discussed with the help of graphs. Furthermore, graphical comparison between the local rate of heat transfer in regular fluids and nanofluids has been made which shows that in case of nanofluids, heat transfer is rapid as compared to regular fluids.

The Effect of Freezing on the Dynamics of Dike Propagation

NASA Astrophysics Data System (ADS)

Tait, S.; Taisne, B.

2007-12-01

When magma-filled cracks propagate close to the Earth's surface, host rock temperature is well below the magma solidus. Solidification and substantial increase in magma viscosity can occur, are most pronounced near the propagating tip and can slow or arrest the progress of the dike. Quantitative analysis is required to predict whether a given dike will reach the surface to erupt and the duration of the precursor sequence. This challenging physical problem mixes elasticity, fracture mechanics, heat transfer and fluid flow with strong rheologic gradients due to cooling. We describe the propagation behaviour of such a hydraulic fracture using a laboratory experimental system of a crack fed by a constant flux of paraffin wax from a source reservoir propagating through gelatin below the solidus of the wax. The most novel behaviour is an intermittent regime in which cracks periodically stop advancing due to solidification, then swell at constant length while enhancing the elastic deformation in the surrounding solid before propagation resumes. We present a physical model of this system, based on different balances between driving and resistive forces: the former are elastic stress and liquid buoyancy, the latter are fracture resistance at the tip and viscous resistance. The fracture is represented as a head, behind the propagating tip, connected to the source by a narrow tail. Freezing of liquid close to the tip is assumed to enhance fracture resistance according to a cooling law, and propagation is assumed to occur only when the stress exerted by the liquid is enough to overcome fracture resistance. Our theoretical model reproduces intermittent propagation with precise behaviour depending on the controlling stress balances, and provides a tool to analyse natural systems.

Forward and backward uncertainty propagation: an oxidation ditch modelling example.

PubMed

Abusam, A; Keesman, K J; van Straten, G

2003-01-01

In the field of water technology, forward uncertainty propagation is frequently used, whereas backward uncertainty propagation is rarely used. In forward uncertainty analysis, one moves from a given (or assumed) parameter subspace towards the corresponding distribution of the output or objective function. However, in the backward uncertainty propagation, one moves in the reverse direction, from the distribution function towards the parameter subspace. Backward uncertainty propagation, which is a generalisation of parameter estimation error analysis, gives information essential for designing experimental or monitoring programmes, and for tighter bounding of parameter uncertainty intervals. The procedure of carrying out backward uncertainty propagation is illustrated in this technical note by working example for an oxidation ditch wastewater treatment plant. Results obtained have demonstrated that essential information can be achieved by carrying out backward uncertainty propagation analysis.

Reply to Comment on "Fringe projection profilometry with nonparallel illumination: a least-squares approach"

NASA Astrophysics Data System (ADS)

Chen, Lujie; Quan, Chenggen

2006-07-01

We have confirmed that a mathematical expression in our previous Letter [Chen and Quan, Opt. Lett.30, 2101 (2005)] should be modified. The modification, however, does not affect the validity of the method reported, the results obtained and the subsequent conclusions made.

GALLAUDET'S NEW HEARING AND SPEECH CENTER.

ERIC Educational Resources Information Center

FRISINA, D. ROBERT

THIS REPROT DESCRIBES THE DESIGN OF A NEW SPEECH AND HEARING CENTER AND ITS INTEGRATION INTO THE OVERALL ARCHITECTURAL SCHEME OF THE CAMPUS. THE CIRCULAR SHAPE WAS SELECTED TO COMPLEMENT THE SURROUNDING STRUCTURES AND COMPENSATE FOR DIFFERENCES IN SITE, WHILE PROVIDING THE ACOUSTICAL ADVANTAGES OF NON-PARALLEL WALLS, AND FACILITATING TRAFFIC FLOW.…

Laser machining wood composites

Treesearch

Vladimir Barnekov; Henry A. Huber; Charles W. McMillin

1989-01-01

This practical, nonstatistical experiment using commercial equipment demonstrated that nominal 3/4-inch compositep anelsf or furniture consisting of a particleboard core,h igh density melamine crossbands, and walnut veneer face plies can be cut with a carbon dioxide/airjet-assisted laser to produce surfaces with minimal nonparallelism and char compared to previous...

Impact of pumping configuration on all-fibered femtosecond chirped pulse amplification

NASA Astrophysics Data System (ADS)

Lecourt, Jean-Bernard; Duterte, Charles; Bertrand, Anthony; Liégeois, Flavien; Hernandez, Yves; Giannone, Domenico

2008-04-01

We experimentally compared the co- and counter-propagative pumping scheme for the amplification of ultra-short optical pulses. According to pumping direction we show that optical pulses with a duration of 75 fs and 100mW of average output power can be obtained for co-propagative pumping, while pulse duration is never shorter than 400 fs for the counter-propagative case. We show that the impact of non-linear effects on pulse propagation is different for the two pumping configurations. We assume that Self Phase Modulation (SPM) is the main effect in the copropagative case, whereas the impact of Stimulated Raman Scattering is bigger for the counter-propagative case.

Rubber-coated bellows improves vibration damping in vacuum lines

NASA Technical Reports Server (NTRS)

Hegland, D. E.; Smith, R. J.

1966-01-01

Compact-vibration damping systems, consisting of rubber-coated metal bellows with a sliding O-ring connector, are used in vacuum lines. The device presents a metallic surface to the vacuum system and combines flexibility with the necessary stiffness. It protects against physical damage, reduces fatigue failure, and provides easy mating of nonparallel lines.

Benchmark Lisp And Ada Programs

NASA Technical Reports Server (NTRS)

Davis, Gloria; Galant, David; Lim, Raymond; Stutz, John; Gibson, J.; Raghavan, B.; Cheesema, P.; Taylor, W.

1992-01-01

Suite of nonparallel benchmark programs, ELAPSE, designed for three tests: comparing efficiency of computer processing via Lisp vs. Ada; comparing efficiencies of several computers processing via Lisp; or comparing several computers processing via Ada. Tests efficiency which computer executes routines in each language. Available for computer equipped with validated Ada compiler and/or Common Lisp system.

Research in Parallel Algorithms and Software for Computational Aerosciences

NASA Technical Reports Server (NTRS)

Domel, Neal D.

1996-01-01

Phase I is complete for the development of a Computational Fluid Dynamics parallel code with automatic grid generation and adaptation for the Euler analysis of flow over complex geometries. SPLITFLOW, an unstructured Cartesian grid code developed at Lockheed Martin Tactical Aircraft Systems, has been modified for a distributed memory/massively parallel computing environment. The parallel code is operational on an SGI network, Cray J90 and C90 vector machines, SGI Power Challenge, and Cray T3D and IBM SP2 massively parallel machines. Parallel Virtual Machine (PVM) is the message passing protocol for portability to various architectures. A domain decomposition technique was developed which enforces dynamic load balancing to improve solution speed and memory requirements. A host/node algorithm distributes the tasks. The solver parallelizes very well, and scales with the number of processors. Partially parallelized and non-parallelized tasks consume most of the wall clock time in a very fine grain environment. Timing comparisons on a Cray C90 demonstrate that Parallel SPLITFLOW runs 2.4 times faster on 8 processors than its non-parallel counterpart autotasked over 8 processors.

Nonlinear Tollmien-Schlichting/vortex interaction in boundary layers

NASA Technical Reports Server (NTRS)

Hall, P.; Smith, F. T.

1988-01-01

The nonlinear reaction between two oblique 3-D Tollmein-Schlichting (TS) waves and their induced streamwise-vortex flow is considered theoretically for an imcompressible boundary layer. The same theory applies to the destabilization of an incident vortex motion by subharmonic TS waves, followed by interaction. The scales and flow structure involved are addressed for high Reynolds numbers. The nonlionear interaction is powerful, starting at quite low amplitudes with a triple-deck structure for the TS waves but a large-scale structure for the induced vortex, after which strong nonlinear amplification occurs. This includes nonparallel-flow effects. The nonlinear interaction is governed by a partial differential system for the vortex flow coupled with an ordinary-differential one for the TS pressure. The solution properties found sometimes produce a breakup within a finite distance and sometimes further downstream, depending on the input amplitudes upstream and on the wave angles, and that then leads to the second stages of interaction associated with higher amplitudes, the main second stages giving either long-scale phenomena significantly affected by nonparallelism or shorter quasi-parallel ones governed by the full nonlinear triple-deck response.

Research in Parallel Algorithms and Software for Computational Aerosciences

NASA Technical Reports Server (NTRS)

Domel, Neal D.

1996-01-01

Phase 1 is complete for the development of a computational fluid dynamics CFD) parallel code with automatic grid generation and adaptation for the Euler analysis of flow over complex geometries. SPLITFLOW, an unstructured Cartesian grid code developed at Lockheed Martin Tactical Aircraft Systems, has been modified for a distributed memory/massively parallel computing environment. The parallel code is operational on an SGI network, Cray J90 and C90 vector machines, SGI Power Challenge, and Cray T3D and IBM SP2 massively parallel machines. Parallel Virtual Machine (PVM) is the message passing protocol for portability to various architectures. A domain decomposition technique was developed which enforces dynamic load balancing to improve solution speed and memory requirements. A host/node algorithm distributes the tasks. The solver parallelizes very well, and scales with the number of processors. Partially parallelized and non-parallelized tasks consume most of the wall clock time in a very fine grain environment. Timing comparisons on a Cray C90 demonstrate that Parallel SPLITFLOW runs 2.4 times faster on 8 processors than its non-parallel counterpart autotasked over 8 processors.

Motion of a liquid bridge between nonparallel surfaces.

PubMed

Ataei, Mohammadmehdi; Tang, Tian; Amirfazli, Alidad

2017-04-15

Bulk motion of a liquid bridge between two nonparallel identical solid surfaces undergoing multiple loading cycles (compressing and stretching) was investigated numerically and experimentally. The effects of the following governing parameters were studied: the dihedral angle between the two surfaces (ψ), the amount of compressing and stretching (Δh), and wettability parameters i.e. the advancing contact angle (θ a ) and Contact Angle Hysteresis (CAH). Experiments were done using various combinations of ψ, Δh and on surfaces with different wettabilities to understand the effect of each parameter individually. Additionally, a numerical model using Surface Evolver software was developed to augment the experimental data and extract information about the shape of the bridge. An empirical function was proposed and validated to calculate the minimum amount of Δh needed to initiate the bulk motion (i.e. to overcome the initial lag of the motion in response to the compressing of the bridge), at a given dihedral angle ψ. The effect of governing parameters on magnitude and precision of the motion was investigated. The magnitude of the motion was found to be increased by increasing ψ and Δh, and/or by decreasing θ a and CAH. We demonstrated the possibility of modulating the precision of the motion with θ a . Additionally, it was shown that the magnitude of the motion (in one loading cycle) increases after each loading cycle, if the contact lines depin only on the narrower side of the bridge during compressing and only on the wider side during stretching (asymmetric depinning). Whereas, depinning on both sides of the bridge (symmetric depinning) reduced the magnitude of bridge motion in each cycle under cyclic loading. A larger ψ was found to convert symmetric depinning into asymmetric depinning. These findings not only enhance the understanding of bridge motion between nonparallel surfaces, but also are beneficial in controlling magnitude, precision, and lag of the motion in practical applications. Copyright © 2016 Elsevier Inc. All rights reserved.

2024 Unmanned Undersea Warfare Concept

DTIC Science & Technology

2013-06-01

mine. Assumptions are that the high-tech mine would have a 400 - meter range that spans 360 degrees, a 90% probability of detecting a HVU, and a 30...motor volume – The electric propulsion motor is assumed to be 0.127 cubic meters . A common figure of 24” x 18” x 18” is assumed. This size will allow...regard to propagation loss is assumed to be 400 HZ. Using Excel spreadsheet modeling, the maximum range is determined by finding that range resulting in

Adaptive and Nonadaptive Feedback Control of Global Instabilities with Application to a Heated 2-D Jet

DTIC Science & Technology

1992-04-01

Hannemann & Oertel (1989) and many others. If the the mean flow is weakly nonparallel, i.e. evolves slowly on the scale of a typical instability wave... HANNEMANN , K. & OERTEL, H. Jr. 1989 Numerical simulation of the absolutely and convectively unstable wake. J. Fluid Mech. 199, 55-88. HUERRE, P. & MONKEWITZ

76 FR 5646 - Self-Regulatory Organizations; NYSE Amex LLC; Order Granting Approval of Proposed Rule Change...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-01

... strike prices and non-parallel strikes in different expiration months of the same issue. The Commission... Listing of Options Series With $1 Strike Prices January 25, 2011. I. Introduction On November 24, 2010... Strike Price Program. The proposed rule change was published for comment in the Federal Register on...

Modeling, Simulation, and Analysis of a Decoy State Enabled Quantum Key Distribution System

DTIC Science & Technology

2015-03-26

through the fiber , we assume Alice and Bob have correct basis alignment and timing control for reference frame correction and precise photon detection...optical components ( laser , polarization modulator, electronic variable optical attenuator, fixed optical attenuator, fiber channel, beamsplitter...generated by the laser in the CPG propagate through multiple optical components, each with a unique propagation delay before reaching the OPM. Timing

Invertible propagator for plane wave illumination of forward-scattering structures.

PubMed

Samelsohn, Gregory

2017-05-10

Propagation of directed waves in forward-scattering media is considered. It is assumed that the evolution of the wave field is governed by the standard parabolic wave equation. An efficient one-step momentum-space propagator, suitable for a tilted plane wave illumination of extended objects, is derived. It is expressed in terms of a propagation operator that transforms (the complex exponential of) a linogram of the illuminated object into a set of its diffraction patterns. The invertibility of the propagator is demonstrated, which permits a multiple-shot scatter correction to be performed, and makes the solution especially attractive for either projective or tomographic imaging. As an example, high-resolution tomograms are obtained in numerical simulations implemented for a synthetic phantom, with both refractive and absorptive inclusions.

Ballistic pulse propagation in quantum wire waveguides: Toward localization and control of electron wave packets in space and time

NASA Astrophysics Data System (ADS)

Hayata, K.; Tsuji, Y.; Koshiba, M.

1992-10-01

A theoretical formulation of electron pulse propagation in quantum wire structures with mesoscopic scale cross sections is presented, assuming quantum ballistic transport of electron wave packets over a certain characteristic length. As typical mesoscopic structures for realizing coherent electron transmission, two traveling-wave configurations are considered: straight quantum wire waveguides and quantum wire bend structures (quantum whispering galleries). To estimate temporal features of the pulse during propagation, the walk off, the dispersion, and the pulse coherence lengths are defined as useful characteristic lengths. Numerical results are shown for ultrashort pulse propagation through rectangular wire waveguides. Effects due to an external electric field are discussed as well.

Ponderomotive and weakly relativistic self-focusing of Gaussian laser beam in plasma: Effect of light absorption

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

Patil, S. D., E-mail: sdpatilphy@gmail.com; Takale, M. V.

2016-05-06

This paper presents an influence of light absorption on self-focusing of laser beam propagation in plasma. The differential equation for beam-width parameter is obtained using the Wentzel-Kramers-Brillouin and paraxial approximations through parabolic equation approach. The nonlinearity in dielectric function is assumed to be aroused due to the combined effect of weakly relativistic and ponderomotive regime. To highlight the nature of propagation, behavior of beam-width parameter with dimensionless distance of propagation is presented graphically and discussed. The present work is helpful to understand issues related to the beam propagation in laser plasma interaction experiments where light absorption plays a vital role.

Hybrid Monte Carlo-Diffusion Method For Light Propagation in Tissue With a Low-Scattering Region

NASA Astrophysics Data System (ADS)

Hayashi, Toshiyuki; Kashio, Yoshihiko; Okada, Eiji

2003-06-01

The heterogeneity of the tissues in a head, especially the low-scattering cerebrospinal fluid (CSF) layer surrounding the brain has previously been shown to strongly affect light propagation in the brain. The radiosity-diffusion method, in which the light propagation in the CSF layer is assumed to obey the radiosity theory, has been employed to predict the light propagation in head models. Although the CSF layer is assumed to be a nonscattering region in the radiosity-diffusion method, fine arachnoid trabeculae cause faint scattering in the CSF layer in real heads. A novel approach, the hybrid Monte Carlo-diffusion method, is proposed to calculate the head models, including the low-scattering region in which the light propagation does not obey neither the diffusion approximation nor the radiosity theory. The light propagation in the high-scattering region is calculated by means of the diffusion approximation solved by the finite-element method and that in the low-scattering region is predicted by the Monte Carlo method. The intensity and mean time of flight of the detected light for the head model with a low-scattering CSF layer calculated by the hybrid method agreed well with those by the Monte Carlo method, whereas the results calculated by means of the diffusion approximation included considerable error caused by the effect of the CSF layer. In the hybrid method, the time-consuming Monte Carlo calculation is employed only for the thin CSF layer, and hence, the computation time of the hybrid method is dramatically shorter than that of the Monte Carlo method.

Hybrid Monte Carlo-diffusion method for light propagation in tissue with a low-scattering region.

PubMed

Hayashi, Toshiyuki; Kashio, Yoshihiko; Okada, Eiji

2003-06-01

The heterogeneity of the tissues in a head, especially the low-scattering cerebrospinal fluid (CSF) layer surrounding the brain has previously been shown to strongly affect light propagation in the brain. The radiosity-diffusion method, in which the light propagation in the CSF layer is assumed to obey the radiosity theory, has been employed to predict the light propagation in head models. Although the CSF layer is assumed to be a nonscattering region in the radiosity-diffusion method, fine arachnoid trabeculae cause faint scattering in the CSF layer in real heads. A novel approach, the hybrid Monte Carlo-diffusion method, is proposed to calculate the head models, including the low-scattering region in which the light propagation does not obey neither the diffusion approximation nor the radiosity theory. The light propagation in the high-scattering region is calculated by means of the diffusion approximation solved by the finite-element method and that in the low-scattering region is predicted by the Monte Carlo method. The intensity and mean time of flight of the detected light for the head model with a low-scattering CSF layer calculated by the hybrid method agreed well with those by the Monte Carlo method, whereas the results calculated by means of the diffusion approximation included considerable error caused by the effect of the CSF layer. In the hybrid method, the time-consuming Monte Carlo calculation is employed only for the thin CSF layer, and hence, the computation time of the hybrid method is dramatically shorter than that of the Monte Carlo method.

A wide-angle high Mach number modal expansion for infrasound propagation.

PubMed

Assink, Jelle; Waxler, Roger; Velea, Doru

2017-03-01

The use of modal expansions to solve the problem of atmospheric infrasound propagation is revisited. A different form of the associated modal equation is introduced, valid for wide-angle propagation in atmospheres with high Mach number flow. The modal equation can be formulated as a quadratic eigenvalue problem for which there are simple and efficient numerical implementations. A perturbation expansion for the treatment of attenuation, valid for stratified media with background flow, is derived as well. Comparisons are carried out between the proposed algorithm and a modal algorithm assuming an effective sound speed, including a real data case study. The comparisons show that the effective sound speed approximation overestimates the effect of horizontal wind on sound propagation, leading to errors in traveltime, propagation path, trace velocity, and absorption. The error is found to be dependent on propagation angle and Mach number.

Three-dimensional boundary layer stability and transition

NASA Technical Reports Server (NTRS)

Malik, M. R.; Li, F.

1992-01-01

Nonparallel and nonlinear stability of a three-dimensional boundary layer, subject to crossflow instability, is investigated using parabolized stability equations (PSEs). Both traveling and stationary disturbances are considered and nonparallel effect on crossflow instability is found to be destabilizing. Our linear PSE results for stationary disturbances agree well with the results from direct solution of Navier-Stokes equations obtained by Spalart (1989). Nonlinear calculations have been carried out for stationary vortices and the computed wall vorticity pattern results in streamwise streaks which resemble remarkably well with the surface oil-flow visualizations in swept-wing experiments. Other features of the stationary vortex development (half-mushroom structure, inflected velocity profiles, vortex doubling, etc.) are also captured in our nonlinear calculations. Nonlinear interaction of the stationary amplitude of the stationary vortex is large as compared to the traveling mode, and the stationary vortex dominates most of the downstream development. When the two modes have the same initial amplitude, the traveling mode dominates the downstream development owing to its higher growth rate, and there is a tendency for the stationary mode to be suppressed. The effect of nonlinear wave development on the skin-friction coefficient is also computed.

Estimating amplitude ratios in boundary layer stability theory: a comparison between two approaches

NASA Astrophysics Data System (ADS)

Govindarajan, Rama; Narasimha, R.

2001-07-01

We first demonstrate that, if the contributions of higher-order mean flow are ignored, the parabolized stability equations (Bertolotti et al. 1992) and the ‘full’ non-parallel equation of Govindarajan & Narasimha (1995, hereafter GN95) are both equivalent to order R[minus sign]1 in the local Reynolds number R to Gaster's (1974) equation for the stability of spatially developing boundary layers. It is therefore of some concern that a detailed comparison between Gaster (1974) and GN95 reveals a small difference in the computed amplitude ratios. Although this difference is not significant in practical terms in Blasius flow, it is traced here to the approximation, in Gaster's method, of neglecting the change in eigenfunction shape due to flow non-parallelism. This approximation is not justified in the critical and the wall layers, where the neglected term is respectively O(R[minus sign]2/3) and O(R[minus sign]1) compared to the largest term. The excellent agreement of GN95 with exact numerical simulations, on the other hand, suggests that the effect of change in eigenfunction is accurately taken into account in that paper.

The influence of foot position on scrum kinetics during machine scrummaging.

PubMed

Bayne, Helen; Kat, Cor-Jacques

2018-05-23

The purpose of this study was to investigate the effect of variations in the alignment of the feet on scrum kinetics during machine scrummaging. Twenty nine rugby forwards from amateur-level teams completed maximal scrum efforts against an instrumented scrum machine, with the feet in parallel and non-parallel positions. Three-dimensional forces, the moment about the vertical axis and sagittal plane joint angles were measured during the sustained pushing phase. There was a decrease in the magnitude of the resultant force and compression force in both of the non-parallel conditions compared to parallel and larger compression forces were associated with more extended hip and knee angles. Scrummaging with the left foot forward resulted in the lateral force being directed more towards the left and the turning moment becoming more clockwise. These directional changes were reversed when scrummaging with the right foot forward. Scrummaging with the right foot positioned ahead of the left may serve to counteract the natural clockwise wheel of the live scrum and could be used to achieve an anti-clockwise rotation of the scrum for tactical reasons. However, this would be associated with lower resultant forces and a greater lateral shear force component directed towards the right.

Remarks on Chern-Simons Invariants

NASA Astrophysics Data System (ADS)

Cattaneo, Alberto S.; Mnëv, Pavel

2010-02-01

The perturbative Chern-Simons theory is studied in a finite-dimensional version or assuming that the propagator satisfies certain properties (as is the case, e.g., with the propagator defined by Axelrod and Singer). It turns out that the effective BV action is a function on cohomology (with shifted degrees) that solves the quantum master equation and is defined modulo certain canonical transformations that can be characterized completely. Out of it one obtains invariants.

Spatial bandwidth considerations for optical communication through a free space propagation link.

PubMed

Tyler, Glenn A

2011-12-01

This Letter concentrates on the transverse limitations imposed by a finite aperture optical propagation link that supports free space optical communication. Here it is assumed that a series of states, which are the spatial component of the message, are sent through the communication channel. The spatial bandwidth of the propagation link expressed as bits per transmitted photon is computed as the product of the average link efficiency times the entropy of the link. To facilitate the evaluation, it is assumed that the transmitted states are minimum energy loss orbital angular momentum states expressed in the form of f(nm)(r)exp(imθ), where the radial function is controlled to ensure that, for each quantum number denoted by the values of n and m, the minimum energy loss is obtained. The results illustrate that the bandwidth in units of bits per transmitted photon is very nearly equal to log(2)(N(2)(f)here log(2)(·) denotes the logarithm in base 2 and the Fresnel number, N(f)=(π/4)D(1)D(2)/(λz), where D(1) is the diameter of the transmitting aperture, D(2) is the diameter of the receiving aperture, λ is the wavelength of the light used, and z is the propagation distance. © 2011 Optical Society of America

Simulation of wave propagation in three-dimensional random media

NASA Astrophysics Data System (ADS)

Coles, Wm. A.; Filice, J. P.; Frehlich, R. G.; Yadlowsky, M.

1995-04-01

Quantitative error analyses for the simulation of wave propagation in three-dimensional random media, when narrow angular scattering is assumed, are presented for plane-wave and spherical-wave geometry. This includes the errors that result from finite grid size, finite simulation dimensions, and the separation of the two-dimensional screens along the propagation direction. Simple error scalings are determined for power-law spectra of the random refractive indices of the media. The effects of a finite inner scale are also considered. The spatial spectra of the intensity errors are calculated and compared with the spatial spectra of

Shear Wave Speed Estimation Using Reverberant Shear Wave Fields: Implementation and Feasibility Studies.

PubMed

Ormachea, Juvenal; Castaneda, Benjamin; Parker, Kevin J

2018-05-01

Elastography is a modality that estimates tissue stiffness and, thus, provides useful information for clinical diagnosis. Attention has focused on the measurement of shear wave propagation; however, many methods assume shear wave propagation is unidirectional and aligned with the lateral imaging direction. Any deviations from the assumed propagation result in biased estimates of shear wave speed. To address these challenges, directional filters have been applied to isolate shear waves with different propagation directions. Recently, a new method was proposed for tissue stiffness estimation involving creation of a reverberant shear wave field propagating in all directions within the medium. These reverberant conditions lead to simple solutions, facile implementation and rapid viscoelasticity estimation of local tissue. In this work, this new approach based on reverberant shear waves was evaluated and compared with another well-known elastography technique using two calibrated elastic and viscoelastic phantoms. Additionally, the clinical feasibility of this technique was analyzed by assessing shear wave speed in human liver and breast tissues, in vivo. The results indicate that it is possible to estimate the viscoelastic properties in each scanned medium. Moreover, a better approach to estimation of shear wave speed was obtained when only the phase information was taken from the reverberant waves, which is equivalent to setting all magnitudes within the bandpass equal to unity: an idealization of a perfectly isotropic reverberant shear wave field. Copyright © 2018 World Federation for Ultrasound in Medicine and Biology. Published by Elsevier Inc. All rights reserved.

Hypergeometric Gaussian beam and its propagation in turbulence

NASA Astrophysics Data System (ADS)

Eyyuboğlu, Halil Tanyer; Cai, Yangjian

2012-10-01

We study propagation characteristics of hypergeometric Gaussian beam in turbulence. In this context, we formulate the receiver plane intensity using extended Huygens-Fresnel integral. From the graphical results, it is seen that, after propagation, hypergeometric Gaussian will in general assume the shape of a dark hollow beam at topological charges other than zero. Increasing values of topological charge will make the beam broader with steeper walls. On the other hand, higher values of hollowness parameter will contract into a narrower shape. Raising the topological charge or the hollowness parameter individually will cause outer rings to appear. Both increased levels of turbulence and longer propagation distances will accelerate the beam evolution and help reach the final Gaussian shape sooner. At lower wavelengths, there will be less beam spreading.

New approach to analyzing soil-building systems

USGS Publications Warehouse

Safak, E.

1998-01-01

A new method of analyzing seismic response of soil-building systems is introduced. The method is based on the discrete-time formulation of wave propagation in layered media for vertically propagating plane shear waves. Buildings are modeled as an extension of the layered soil media by assuming that each story in the building is another layer. The seismic response is expressed in terms of wave travel times between the layers, and the wave reflection and transmission coefficients at layer interfaces. The calculation of the response is reduced to a pair of simple finite-difference equations for each layer, which are solved recursively starting from the bedrock. Compared with commonly used vibration formulation, the wave propagation formulation provides several advantages, including the ability to incorporate soil layers, simplicity of the calculations, improved accuracy in modeling the mass and damping, and better tools for system identification and damage detection.A new method of analyzing seismic response of soil-building systems is introduced. The method is based on the discrete-time formulation of wave propagation in layered media for vertically propagating plane shear waves. Buildings are modeled as an extension of the layered soil media by assuming that each story in the building is another layer. The seismic response is expressed in terms of wave travel times between the layers, and the wave reflection and transmission coefficients at layer interfaces. The calculation of the response is reduced to a pair of simple finite-difference equations for each layer, which are solved recursively starting from the bedrock. Compared with commonly used vibration formulation, the wave propagation formulation provides several advantages, including the ability to incorporate soil layers, simplicity of the calculations, improved accuracy in modeling the mass and damping, and better tools for system identification and damage detection.

Advertisement-call preferences in diploid-tetraploid treefrogs (Hyla chrysoscelis and Hyla versicolor): implications for mate choice and the evolution of communication systems.

PubMed

Gerhardt, H Carl

2005-02-01

Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. Two-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor.

High-frequency source radiation during the 2011 Tohoku-Oki earthquake, Japan, inferred from KiK-net strong-motion seismograms

NASA Astrophysics Data System (ADS)

Kumagai, Hiroyuki; Pulido, Nelson; Fukuyama, Eiichi; Aoi, Shin

2013-01-01

investigate source processes of the 2011 Tohoku-Oki earthquake, we utilized a source location method using high-frequency (5-10 Hz) seismic amplitudes. In this method, we assumed far-field isotropic radiation of S waves, and conducted a spatial grid search to find the best fitting source locations along the subducted slab in each successive time window. Our application of the method to the Tohoku-Oki earthquake resulted in artifact source locations at shallow depths near the trench caused by limited station coverage and noise effects. We then assumed various source node distributions along the plate, and found that the observed seismograms were most reasonably explained when assuming deep source nodes. This result suggests that the high-frequency seismic waves were radiated at deeper depths during the earthquake, a feature which is consistent with results obtained from teleseismic back-projection and strong-motion source model studies. We identified three high-frequency subevents, and compared them with the moment-rate function estimated from low-frequency seismograms. Our comparison indicated that no significant moment release occurred during the first high-frequency subevent and the largest moment-release pulse occurred almost simultaneously with the second high-frequency subevent. We speculated that the initial slow rupture propagated bilaterally from the hypocenter toward the land and trench. The landward subshear rupture propagation consisted of three successive high-frequency subevents. The trenchward propagation ruptured the strong asperity and released the largest moment near the trench.

Diffusion of strongly magnetized cosmic ray particles in a turbulent medium

NASA Technical Reports Server (NTRS)

Ptuskin, V. S.

1985-01-01

Cosmic ray (CR) propagation in a turbulent medium is usually considered in the diffusion approximation. Here, the diffusion equation is obtained for strongly magnetized particles in the general form. The influence of a large-scale random magnetic field on CR propagation in interstellar medium is discussed. Cosmic rays are assumed to propagate in a medium with a regular field H and an ensemble of random MHD waves. The energy density of waves on scales smaller than the free path 1 of CR particles is small. The collision integral of the general form which describes interaction between relativistic particles and waves in the quasilinear approximation is used.

Effects of the Atmosphere on the Propagation of 10.6-micro Laser Beams.

PubMed

Hayes, J N; Ulrich, P B; Aitken, A H

1972-02-01

This paper gives an overview of the use of a wave optics computer code to model the propagation of high power CO(2) laser beams in the atmosphere. The nonlinear effects of atmospheric heating and kinetic cooling phenomena are included in the analysis. Only steady-state, nonturbulent cases are studied. Thermal conduction and free convection are assumed negligible compared to other effects included in the calculation. Results showing the important effect of water vapor concentration on beam quality are given. Beam slewing is also studied. Comparison is made with geometrical optics results, and good agreement is found with laboratory experiments that simulate atmospheric propagation.

Generation of Acoustic Self-bending and Bottle Beams by Phase Engineering

DTIC Science & Technology

2014-07-03

projectile under the action of gravity . We synthesize an acoustic beam propagating along a free-form Bézier curve in air33 by employing a planar speaker...the axial radiation force can be negative, indicating the existence of a pulling force against the beam propagation direction as well as the gravity ...use Legendre transformations to construct the geometric wavefront from a preset beam trajectory. Assume that the geometric wavefront W corresponding to

An introduction of component fusion extend Kalman filtering method

NASA Astrophysics Data System (ADS)

Geng, Yue; Lei, Xusheng

2018-05-01

In this paper, the Component Fusion Extend Kalman Filtering (CFEKF) algorithm is proposed. Assuming each component of error propagation are independent with Gaussian distribution. The CFEKF can be obtained through the maximum likelihood of propagation error, which can adjust the state transition matrix and the measured matrix adaptively. With minimize linearization error, CFEKF can an effectively improve the estimation accuracy of nonlinear system state. The computation of CFEKF is similar to EKF which is easy for application.

Propagation of electromagnetic waves parallel to the magnetic field in the nightside Venus ionosphere

NASA Technical Reports Server (NTRS)

Huba, J. D.; Rowland, H. L.

1993-01-01

The propagation of electromagnetic waves parallel to the magnetic field in the nightside Venus ionosphere is presented in a theoretical and numerical analysis. The model assumes a source of electromagnetic radiation in the Venus atmosphere, such as that produced by lightning. Specifically addressed is wave propagation in the altitude range z = 130-160 km at the four frequencies detectable by the Pioneer Venus Orbiter Electric Field Detector: 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz. Parameterizations of the wave intensities, peak electron density, and Poynting flux as a function of magnetic field are presented. The waves are found to propagate most easily in conditions of low electron density and high magnetic field. The results of the model are consistent with observational data.

Nano transfer and nanoreplication using deterministically grown sacrificial nanotemplates

DOEpatents

Melechko, Anatoli V [Oak Ridge, TN; McKnight, Timothy E [Greenback, TN; Guillorn, Michael A [Ithaca, NY; Ilic, Bojan [Ithaca, NY; Merkulov, Vladimir I [Knoxville, TX; Doktycz, Mitchel J [Knoxville, TN; Lowndes, Douglas H [Knoxville, TN; Simpson, Michael L [Knoxville, TN

2012-03-27

Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. An apparatus, includes a substrate and a nanoconduit material coupled to a surface of the substrate. The substrate defines an aperture and the nanoconduit material defines a nanoconduit that is i) contiguous with the aperture and ii) aligned substantially non-parallel to a plane defined by the surface of the substrate.

Factors confounding impedance catheter volume measurements in vitro.

PubMed

Bielefeld, M R; Cabreriza, S E; Spotnitz, H M

1993-06-01

The impedance catheter allows continuous measurement of ventricular volume. External influences have been described as causing parallel shifts in impedance-measured volumes; however, factors affecting impedance measurements in a nonparallel manner have not been fully characterized. Accordingly, an impedance catheter was placed inside a latex balloon into which known volumes of normal saline solution were injected. Conductive and nonconductive materials were individually placed within the balloon. Impedance was measured with materials touching (T) or not touching (NT) the catheter. Impedance-measured volumes were plotted versus actual volumes. Compared with the line of identity (LID), a statistical difference (p < 0.05) was found in the slopes in the presence of metallic objects only. These included a pacing lead (T, NT) (mT = 1.32m mNT = 1.29 versus mLID = 1.00), titanium (T) (mT = 1.68 versus mLID = 1.00), and aluminum (NT) (mNT = 0.72 versus mLID = 1.00). These changes in slope indicate nonparallel effects on impedance that confound the ability of the impedance catheter to determine volumes in vitro. These observations imply that serial calibration of both the slope constant (alpha) and the intercept (parallel conductance) of impedance may be necessary for in vivo measurements of ventricular volume based on impedance in the presence of metallic objects.

Steady Boundary Layer Disturbances Created By Two-Dimensional Surface Ripples

NASA Astrophysics Data System (ADS)

Kuester, Matthew

2017-11-01

Multiple experiments have shown that surface roughness can enhance the growth of Tollmien-Schlichting (T-S) waves in a laminar boundary layer. One of the common observations from these studies is a ``wall displacement'' effect, where the boundary layer profile shape remains relatively unchanged, but the origin of the profile pushes away from the wall. The objective of this work is to calculate the steady velocity field (including this wall displacement) of a laminar boundary layer over a surface with small, 2D surface ripples. The velocity field is a combination of a Blasius boundary layer and multiple disturbance modes, calculated using the linearized Navier-Stokes equations. The method of multiple scales is used to include non-parallel boundary layer effects of O (Rδ- 1) ; the non-parallel terms are necessary, because a wall displacement is mathematically inconsistent with a parallel boundary layer assumption. This technique is used to calculate the steady velocity field over ripples of varying height and wavelength, including cases where a separation bubble forms on the leeward side of the ripple. In future work, the steady velocity field will be the input for stability calculations, which will quantify the growth of T-S waves over rough surfaces. The author would like to acknowledge the support of the Kevin T. Crofton Aerospace & Ocean Engineering Department at Virginia Tech.

Numerical modeling of the exterior-to-interior transmission of impulsive sound through three-dimensional, thin-walled elastic structures

NASA Astrophysics Data System (ADS)

Remillieux, Marcel C.; Pasareanu, Stephanie M.; Svensson, U. Peter

2013-12-01

Exterior propagation of impulsive sound and its transmission through three-dimensional, thin-walled elastic structures, into enclosed cavities, are investigated numerically in the framework of linear dynamics. A model was developed in the time domain by combining two numerical tools: (i) exterior sound propagation and induced structural loading are computed using the image-source method for the reflected field (specular reflections) combined with an extension of the Biot-Tolstoy-Medwin method for the diffracted field, (ii) the fully coupled vibro-acoustic response of the interior fluid-structure system is computed using a truncated modal-decomposition approach. In the model for exterior sound propagation, it is assumed that all surfaces are acoustically rigid. Since coupling between the structure and the exterior fluid is not enforced, the model is applicable to the case of a light exterior fluid and arbitrary interior fluid(s). The structural modes are computed with the finite-element method using shell elements. Acoustic modes are computed analytically assuming acoustically rigid boundaries and rectangular geometries of the enclosed cavities. This model is verified against finite-element solutions for the cases of rectangular structures containing one and two cavities, respectively.

Adaptive spatial filtering of daytime sky noise in a satellite quantum key distribution downlink receiver

NASA Astrophysics Data System (ADS)

Gruneisen, Mark T.; Sickmiller, Brett A.; Flanagan, Michael B.; Black, James P.; Stoltenberg, Kurt E.; Duchane, Alexander W.

2016-02-01

Spatial filtering is an important technique for reducing sky background noise in a satellite quantum key distribution downlink receiver. Atmospheric turbulence limits the extent to which spatial filtering can reduce sky noise without introducing signal losses. Using atmospheric propagation and compensation simulations, the potential benefit of adaptive optics (AO) to secure key generation (SKG) is quantified. Simulations are performed assuming optical propagation from a low-Earth-orbit satellite to a terrestrial receiver that includes AO. Higher-order AO correction is modeled assuming a Shack-Hartmann wavefront sensor and a continuous-face-sheet deformable mirror. The effects of atmospheric turbulence, tracking, and higher-order AO on the photon capture efficiency are simulated using statistical representations of turbulence and a time-domain wave-optics hardware emulator. SKG rates are calculated for a decoy-state protocol as a function of the receiver field of view for various strengths of turbulence, sky radiances, and pointing angles. The results show that at fields of view smaller than those discussed by others, AO technologies can enhance SKG rates in daylight and enable SKG where it would otherwise be prohibited as a consequence of background optical noise and signal loss due to propagation and turbulence effects.

Energy approach to brittle fracture in strain-gradient modelling.

PubMed

Placidi, Luca; Barchiesi, Emilio

2018-02-01

In this paper, we exploit some results in the theory of irreversible phenomena to address the study of quasi-static brittle fracture propagation in a two-dimensional isotropic continuum. The elastic strain energy density of the body has been assumed to be geometrically nonlinear and to depend on the strain gradient. Such generalized continua often arise in the description of microstructured media. These materials possess an intrinsic length scale, which determines the size of internal boundary layers. In particular, the non-locality conferred by this internal length scale avoids the concentration of deformations, which is usually observed when dealing with local models and which leads to mesh dependency. A scalar Lagrangian damage field, ranging from zero to one, is introduced to describe the internal state of structural degradation of the material. Standard Lamé and second-gradient elastic coefficients are all assumed to decrease as damage increases and to be locally zero if the value attained by damage is one. This last situation is associated with crack formation and/or propagation. Numerical solutions of the model are provided in the case of an obliquely notched rectangular specimen subjected to monotonous tensile and shear loading tests, and brittle fracture propagation is discussed.

Wave propagation in a quasi-chemical equilibrium plasma

NASA Technical Reports Server (NTRS)

Fang, T.-M.; Baum, H. R.

1975-01-01

Wave propagation in a quasi-chemical equilibrium plasma is studied. The plasma is infinite and without external fields. The chemical reactions are assumed to result from the ionization and recombination processes. When the gas is near equilibrium, the dominant role describing the evolution of a reacting plasma is played by the global conservation equations. These equations are first derived and then used to study the small amplitude wave motion for a near-equilibrium situation. Nontrivial damping effects have been obtained by including the conduction current terms.

Sensor Analytics: Radioactive gas Concentration Estimation and Error Propagation

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

Anderson, Dale N.; Fagan, Deborah K.; Suarez, Reynold

2007-04-15

This paper develops the mathematical statistics of a radioactive gas quantity measurement and associated error propagation. The probabilistic development is a different approach to deriving attenuation equations and offers easy extensions to more complex gas analysis components through simulation. The mathematical development assumes a sequential process of three components; I) the collection of an environmental sample, II) component gas extraction from the sample through the application of gas separation chemistry, and III) the estimation of radioactivity of component gases.

Modeling of Waves Propagating in Water with a Crushed Ice Layer on the Free Surface

NASA Astrophysics Data System (ADS)

Szmidt, Kazimierz

2017-12-01

A transformation of gravitational waves in fluid of constant depth with a crushed ice layer floating on the free fluid surface is considered. The propagating waves undergo a slight damping along their path of propagation. The main goal of the study is to construct an approximate descriptive model of this phenomenon.With regard to small displacements of the free surface, a viscous type model of damping is considered, which corresponds to a continuous distribution of dash-pots at the free surface of the fluid. A constant parameter of the dampers is assumed in advance as known parameter of damping. This parameter may be obtained by means of experiments in a laboratory flume.

Methods of determining electron concentrations in the magnetosphere from nose whistlers

NASA Technical Reports Server (NTRS)

Park, C. G.

1972-01-01

Whistler propagation in the magnetosphere was studied in detail to find accurate and economical means of determining the path latitude and the electron concentration along the path from whistler parameters of nose frequency and travel time at the nose. Longitudinal propagation in field aligned whistler ducts of cold plasma was assumed, and the earth's magnetic field was approximated by a centered dipole. The effects of whistler propagation in the earth-ionosphere waveguide and through the conjugate ionospheres were treated as small perturbations. Several alternative methods are described so that the most economical method may be chosen depending on the desired accuracy and the availability of a computer or a calculator.

Secretion of full-length Tau or Tau fragments in cell culture models. Propagation of Tau in vivo and in vitro.

PubMed

Pérez, Mar; Medina, Miguel; Hernández, Félix; Avila, Jesús

2018-03-05

The microtubule-associated protein Tau plays a crucial role in stabilizing neuronal microtubules. In Tauopathies, Tau loses its ability to bind microtubules, detach from them and forms intracellular aggregates. Increasing evidence in recent years supports the notion that Tau pathology spreading throughout the brain in AD and other Tauopathies is the consequence of the propagation of specific Tau species along neuroanatomically connected brain regions in a so-called "prion-like" manner. A number of steps are assumed to be involved in this process, including secretion, cellular uptake, transcellular transfer and/or seeding, although the precise mechanisms underlying propagation of Tau pathology are not fully understood yet. This review summarizes recent evidence on the nature of the specific Tau species that are propagated and the different mechanisms of Tau pathology spreading.

Constraints on cosmic ray propagation in the galaxy

NASA Technical Reports Server (NTRS)

Cordes, James M.

1992-01-01

The goal was to derive a more detailed picture of magnetohydrodynamic turbulence in the interstellar medium and its effects on cosmic ray propagation. To do so, radio astronomical observations (scattering and Faraday rotation) were combined with knowledge of solar system spacecraft observations of MHD turbulence, simulations of wave propagation, and modeling of the galactic distribution to improve the knowledge. A more sophisticated model was developed for the galactic distribution of electron density turbulence. Faraday rotation measure data was analyzed to constrain magnetic field fluctuations in the ISM. VLBI observations were acquired of compact sources behind the supernova remnant CTA1. Simple calculations were made about the energies of the turbulence assuming a direct link between electron density and magnetic field variations. A simulation is outlined of cosmic ray propagation through the galaxy using the above results.

Attenuation characteristics of the fundamental modes that propagate in buried iron water pipes.

PubMed

Long, R; Lowe, M; Cawley, P

2003-09-01

The attenuation of the fundamental non-torsional modes that propagate down buried iron water pipes has been studied. The mode shapes, mode attenuation due to leakage into the surrounding medium and the scattering of the modes as they interact with pipe joints and fittings have been investigated. In the low frequency region the mode predicted to dominate over significant propagation distances approximates a plane wave in the water within the pipe. The established acoustic technique used to locate leaks in buried iron water pipes assumes that leak noise propagates as a single non-dispersive mode at a velocity related to the low frequency asymptote of this water borne mode. Experiments have been conducted on buried water mains at test sites in the UK to verify the attenuation and velocity dispersion predictions.

Encoding dependence in Bayesian causal networks

USDA-ARS?s Scientific Manuscript database

Bayesian networks (BNs) represent complex, uncertain spatio-temporal dynamics by propagation of conditional probabilities between identifiable states with a testable causal interaction model. Typically, they assume random variables are discrete in time and space with a static network structure that ...

Streamline-curvature effect in three-dimensional boundary layers

NASA Technical Reports Server (NTRS)

Reed, Helen L.; Lin, Ray-Sing; Petraglia, Media M.

1992-01-01

The effect of including wall and streamline curvature terms in swept-wing boundary-layer stability calculations is studied. The linear disturbance equations are cast on a fixed, body-intrinsic, curvilinear coordinate system. Those nonparallel terms which contribute mainly to the streamline-curvature effect are retained in this formulation and approximated by their local finite-difference values. Convex-wall curvature has a stabilizing effect, while streamline curvature is destabilizing if the curvature exceeds a critical value.

3D numerical simulation of the long range propagation of acoustical shock waves through a heterogeneous and moving medium

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

Luquet, David; Marchiano, Régis; Coulouvrat, François, E-mail: francois.coulouvrat@upmc.fr

2015-10-28

Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength,more » the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D aspect, the code was massively parallelized using the single program, multiple data paradigm with the Message Passing Interfaces (MPI) for distributed memory architectures. This allows us to handle problems in the order of a thousand billion mesh points in the four dimensions (3 dimensions of space plus time). The validity of the method has been thoroughly evaluated on many cases with known solutions: linear piston, scattering of plane wave by a heterogeneous sphere, propagation in a waveguide with a shear flow, scattering by a finite amplitude vortex and nonlinear propagation in a thermoviscous medium. This validation process allows for a detailed assessment of the advantages and limitations of the method. Finally, applications to atmospheric propagation of shock waves will be presented.« less

3D numerical simulation of the long range propagation of acoustical shock waves through a heterogeneous and moving medium

NASA Astrophysics Data System (ADS)

Luquet, David; Marchiano, Régis; Coulouvrat, François

2015-10-01

Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D aspect, the code was massively parallelized using the single program, multiple data paradigm with the Message Passing Interfaces (MPI) for distributed memory architectures. This allows us to handle problems in the order of a thousand billion mesh points in the four dimensions (3 dimensions of space plus time). The validity of the method has been thoroughly evaluated on many cases with known solutions: linear piston, scattering of plane wave by a heterogeneous sphere, propagation in a waveguide with a shear flow, scattering by a finite amplitude vortex and nonlinear propagation in a thermoviscous medium. This validation process allows for a detailed assessment of the advantages and limitations of the method. Finally, applications to atmospheric propagation of shock waves will be presented.

Terahertz beam propagation measured through three-dimensional amplitude profile determination

NASA Astrophysics Data System (ADS)

Reiten, Matthew T.; Harmon, Stacee A.; Cheville, Richard Alan

2003-10-01

To determine the spatio-temporal field distribution of freely propagating terahertz bandwidth pulses, we measure the time-resolved electric field in two spatial dimensions with high resolution. The measured, phase-coherent electric-field distributions are compared with an analytic model in which the radiation from a dipole antenna near a dielectric interface is coupled to free space through a spherical lens. The field external to the lens is limited by reflection at the lens-air dielectric interface, which is minimized at Brewster's angle, leading to an annular field pattern. Field measurements compare favorably with theory. Propagation of terahertz beams is determined both by assuming a TEM0,0 Gaussian profile as well as expanding the beam into a superposition of Laguerre-Gauss modes. The Laguerre-Gauss model more accurately describes the beam profile for free-space propagation and after propagating through a simple optical system. The accuracy of both models for predicting far-field beam patterns depend upon accurately measuring complex field amplitudes of terahertz beams.

Thermal mechanisms responsible for the irreversible degradation of superconductivity in commercial superconductors

NASA Astrophysics Data System (ADS)

Romanovskii, V. R.

2017-08-01

Conditions for the irreversible propagation of thermal instabilities in commercial superconductors subjected to intense and soft cooling have been formulated. An analysis has been conducted using two types of the superconductor's I-V characteristics, i.e., an ideal I-V characteristic, which assumes a step superconducting-to-normal transition, and a continuous I-V characteristic, which is described by a power law. The propagation rate of thermal instabilities along the superconducting composite has been determined. Calculations have been made for both subcritical and supercritical values of the current. It has been shown that they propagate along a commercial superconductor in the form of a switching wave. In rapidly cooled commercial superconductors, the steady-state rate of thermal instability propagation in the longitudinal direction can only be positive because there is no region of steady stabilization. It has been proved that, in the case of thermal instability irreversible propagation, the rise in the commercial superconductor temperature is similar to diffusion processes that occur in explosive chain reactions.

The Speed of Axial Propagation of a Cylindrical Bubble Through a Cylindrical Vortex

NASA Technical Reports Server (NTRS)

Shariff, Karim; Mansour, Nagi N. (Technical Monitor)

2002-01-01

Inspired by the rapid elongation of air columns injected into vortices by dolphins, we present an exact inviscid solution for the axial speed (assumed steady) of propagation of the tip of a semi-infinite cylindrical bubble along the axis of a cylindrical vortex. The bubble is assumed to be held at constant pressure by being connected to a reservoir, the lungs of the dolphin, say. For a given bubble pressure, there is a modest critical rotation rate above which steadily propagating bubbles exist. For a bubble at ambient pressure, the propagation speed of the bubble (relative to axial velocity within the vortex) varies between 0.5 and 0.6 of the maximum rotational speed of the vortex. Surprisingly, the bubble tip can propagate (almost as rapidly) even when the pressure minimum in the vortex core is greater than the bubble pressure; in this case, solutions exhibit a dimple on the nose of the bubble. A situation important for incipient vortex cavitation, and one which dolphins also demonstrate, is elongation of a free bubble, i.e., one whose internal pressure may vary. Under the assumption that the acceleration term is small (checked a posteriori), the steady solution is applied at each instant during the elongation. Three types of behavior are then possible depending on physical parameters and initial conditions: (A) Unabated elongation with slowly increasing bubble pressure, and nearly constant volume. Volume begins to decrease in the late stages. (B1) Elongation with decreasing bubble pressure. A limit point of the steady solution is encountered at a finite bubble length. (B2) Unabated elongation with decreasing bubble pressure and indefinite creation of volume. This is made possible by the existence of propagating solutions at bubble pressures below the minimum vortex pressure. As the bubble stretches, its radius initially decreases but then becomes constant; this is also observed in experiments on incipient vortex cavitation.

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

Liu, Ying D.; Luhmann, Janet G.; Moestl, Christian

We investigate how coronal mass ejections (CMEs) propagate through, and interact with, the inner heliosphere between the Sun and Earth, a key question in CME research and space weather forecasting. CME Sun-to-Earth kinematics are constrained by combining wide-angle heliospheric imaging observations, interplanetary radio type II bursts, and in situ measurements from multiple vantage points. We select three events for this study, the 2012 January 19, 23, and March 7 CMEs. Different from previous event studies, this work attempts to create a general picture for CME Sun-to-Earth propagation and compare different techniques for determining CME interplanetary kinematics. Key results are obtainedmore » concerning CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of fast CMEs can be approximately formulated into three phases: an impulsive acceleration, then a rapid deceleration, and finally a nearly constant speed propagation (or gradual deceleration); (2) the CMEs studied here are still accelerating even after the flare maximum, so energy must be continuously fed into the CME even after the time of the maximum heating and radiation has elapsed in the corona; (3) the rapid deceleration, presumably due to interactions with the ambient medium, mainly occurs over a relatively short timescale following the acceleration phase; and (4) CME-CME interactions seem a common phenomenon close to solar maximum. Our comparison between different techniques (and data sets) has important implications for CME observations and their interpretations: (1) for the current cases, triangulation assuming a compact CME geometry is more reliable than triangulation assuming a spherical front attached to the Sun for distances below 50-70 solar radii from the Sun, but beyond about 100 solar radii we would trust the latter more; (2) a proper treatment of CME geometry must be performed in determining CME Sun-to-Earth kinematics, especially when the CME propagation direction is far away from the observer; and (3) our approach to comparing wide-angle heliospheric imaging observations with interplanetary radio type II bursts provides a novel tool in investigating CME propagation characteristics. Future CME observations and space weather forecasting are discussed based on these results.« less

Low-momentum ghost dressing function and the gluon mass

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

Boucaud, Ph.; Leroy, J. P.; Le Yaouanc, A.

2010-09-01

We study the low-momentum ghost propagator Dyson-Schwinger equation in the Landau gauge, assuming for the truncation a constant ghost-gluon vertex, as it is extensively done, and a simple model for a massive gluon propagator. Then, regular Dyson-Schwinger equation solutions (the zero-momentum ghost dressing function not diverging) appear to emerge, and we show the ghost propagator to be described by an asymptotic expression reliable up to the order O(q{sup 2}). That expression, depending on the gluon mass and the zero-momentum Taylor-scheme effective charge, is proven to fit pretty well some low-momentum ghost propagator data [I. L. Bogolubsky, E. M. Ilgenfritz, M.more » Muller-Preussker, and A. Sternbeck, Phys. Lett. B 676, 69 (2009); Proc. Sci., LAT2007 (2007) 290] from big-volume lattice simulations where the so-called ''simulated annealing algorithm'' is applied to fix the Landau gauge.« less

Simulation study of axial ultrasound transmission in heterogeneous cortical bone model

NASA Astrophysics Data System (ADS)

Takano, Koki; Nagatani, Yoshiki; Matsukawa, Mami

2017-07-01

Ultrasound propagation in a heterogeneous cortical bone was studied. Using a bovine radius, the longitudinal wave velocity distribution in the axial direction was experimentally measured in the MHz range. The bilinear interpolation and piecewise cubic Hermite interpolation methods were applied to create a three-dimensional (3D) precise velocity model of the bone using experimental data. By assuming the uniaxial anisotropy of the bone, the distributions of all elastic moduli of a 3D heterogeneous model were estimated. The elastic finite-difference time-domain method was used to simulate axial ultrasonic wave propagation. The wave propagation in the initial model was compared with that in the thinner model, where the inner part of the cortical bone model was removed. The wave front of the first arriving signal (FAS) slightly depended on the heterogeneity in each model. Owing to the decrease in bone thickness, the propagation behavior also changed and the FAS velocity clearly decreased.

On focusing of a ring ripple on a Gaussian electromagnetic beam in a plasma

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

Misra, Shikha; Mishra, S. K.

In this communication the authors have investigated the focusing of a ring ripple on a Gaussian electromagnetic beam propagating in a plasma, considering each of the three kinds of basic nonlinearities, namely, ponderomotive, collisional, and relativistic. In this analysis, the electric field profile of the propagating beam is assumed to be composed of the radial electric field distribution of the Gaussian beam as well as that of the ring ripple; a paraxial like approach has been adopted to analyze the characteristics of the propagation. Thus, one considers a unique dielectric function for the beam propagation and a radial field sensitivemore » diffraction term, appropriate to the vicinity of the maximum of the irradiance distribution of the ring ripple. Further, the variation of the phase associated with the beam on account of the r independent terms in the eikonal has also been accounted for.« less

Shock Structure Analysis and Aerodynamics in a Weakly Ionized Gas Flow

NASA Technical Reports Server (NTRS)

Saeks, R.; Popovic, S.; Chow, A. S.

2006-01-01

The structure of a shock wave propagating through a weakly ionized gas is analyzed using an electrofluid dynamics model composed of classical conservation laws and Gauss Law. A viscosity model is included to correctly model the spatial scale of the shock structure, and quasi-neutrality is not assumed. A detailed analysis of the structure of a shock wave propagating in a weakly ionized gas is presented, together with a discussion of the physics underlying the key features of the shock structure. A model for the flow behind a shock wave propagating through a weakly ionized gas is developed and used to analyze the effect of the ionization on the aerodynamics and performance of a two-dimensional hypersonic lifting body.

Simulation of wave propagation in three-dimensional random media

NASA Technical Reports Server (NTRS)

Coles, William A.; Filice, J. P.; Frehlich, R. G.; Yadlowsky, M.

1993-01-01

Quantitative error analysis for simulation of wave propagation in three dimensional random media assuming narrow angular scattering are presented for the plane wave and spherical wave geometry. This includes the errors resulting from finite grid size, finite simulation dimensions, and the separation of the two-dimensional screens along the propagation direction. Simple error scalings are determined for power-law spectra of the random refractive index of the media. The effects of a finite inner scale are also considered. The spatial spectra of the intensity errors are calculated and compared to the spatial spectra of intensity. The numerical requirements for a simulation of given accuracy are determined for realizations of the field. The numerical requirements for accurate estimation of higher moments of the field are less stringent.

Collision of Identical Solitary Waves in Hertzian Chains

NASA Astrophysics Data System (ADS)

Sen, Surajit; Manciu, Marian; Hurd, Alan J.

2000-03-01

We consider a chain of elastic beads, which repel upon contact according to the non-linear Hertz potential. We further assume that the chain is under zero loading, i.e., the grains have zero initial overlap. We show via careful numerical solution of the equations of motion that an impulse propagates as a solitary wave and that the collision of identical solitary waves propagating in opposite directions along the chain spawns a hierarchy of multiple weak solitary waves [1]. [1] M. Manciu, S. Sen and A.J. Hurd, Phys Lett A (submitted).

Cosine-Gaussian Schell-model sources.

PubMed

Mei, Zhangrong; Korotkova, Olga

2013-07-15

We introduce a new class of partially coherent sources of Schell type with cosine-Gaussian spectral degree of coherence and confirm that such sources are physically genuine. Further, we derive the expression for the cross-spectral density function of a beam generated by the novel source propagating in free space and analyze the evolution of the spectral density and the spectral degree of coherence. It is shown that at sufficiently large distances from the source the degree of coherence of the propagating beam assumes Gaussian shape while the spectral density takes on the dark-hollow profile.

Design of a solar concentrator considering arbitrary surfaces

NASA Astrophysics Data System (ADS)

Jiménez-Rodríguez, Martín.; Avendaño-Alejo, Maximino; Verduzco-Grajeda, Lidia Elizabeth; Martínez-Enríquez, Arturo I.; García-Díaz, Reyes; Díaz-Uribe, Rufino

2017-10-01

We study the propagation of light in order to efficiently redirect the reflected light on photocatalytic samples placed inside a commercial solar simulator, and we have designed a small-scale prototype of Cycloidal Collectors (CCs), resembling a compound parabolic collector. The prototype consists of either cycloidal trough or cycloidal collector having symmetry of rotation, which has been designed considering an exact ray tracing assuming a bundle of rays propagating parallel to the optical axis and impinging on a curate cycloidal surface, obtaining its caustic surface produced by reflection.

Is There a Dark Matter Signal in the Galactic Positron Annihilation Radiation?

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

Lingenfelter, R. E.; Rothschild, R. E.; Higdon, J. C.

2009-07-17

Assuming Galactic positrons do not go far before annihilating, a difference between the observed 511 keV annihilation flux distribution and that of positron production, expected from beta{sup +} decay in Galactic iron nucleosynthesis, was evoked as evidence of a new source and signal of dark matter. We show, however, that the dark matter sources cannot account for the observed positronium fraction without extensive propagation. Yet with such propagation, standard nucleosynthetic sources can fully account for the spatial differences and positronium fraction, leaving no new signal for dark matter to explain.

Nanoconduits and nanoreplicants

DOEpatents

Melechko, Anatoli V [Oak Ridge, TN; McKnight, Timothy E [Greenback, TN; Guillorn, Michael A [Ithaca, NY; Ilic, Bojan [Ithaca, NY; Merkulov, Vladimir I [Knoxville, TN; Doktycz, Mitchel J [Knoxville, TN; Lowndes, Douglas H [Knoxville, TN; Simpson, Michael L [Knoxville, TN

2007-06-12

Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. An apparatus includes a substrate and a nanoconduit material coupled to a surface of the substrate, where the substrate defines an aperture and the nanoconduit material defines a nanoconduit that is i) contiguous with the aperture and ii) aligned substantially non-parallel to a plane defined by the surface of the substrate. An apparatus includes a substrate and a nanoreplicant structure coupled to a surface of the substrate.

Evolutionary Processes in Multiple Systems

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

Eggleton, P P; Kisseleva-Eggleton, L

There are several ways in which triple stars can evolve in somewhat unusual ways. They discuss two situations where Case A Roche-lobe overflow, followed by a merger, can produce anomalous wide binaries such as {gamma} Per; and Kozai cycles in triples with non-parallel orbits, which can produce merged rapidly-rotating stars like AB Dor, and which can also lead to the delayed ejection of one component of a multiple, as may have been observed in T Tau in 1998.

Beneficial Combination of Lacosamide with Retigabine in Experimental Animals: An Isobolographic Analysis.

PubMed

Luszczki, Jarogniew J; Zagaja, Mirosław; Miziak, Barbara; Kondrat-Wrobel, Maria W; Zaluska, Katarzyna; Wroblewska-Luczka, Paula; Adamczuk, Piotr; Czuczwar, Stanislaw J; Florek-Luszczki, Magdalena

2018-01-01

To isobolographically determine the types of interactions that occur between retigabine and lacosamide (LCM; two third-generation antiepileptic drugs) with respect to their anticonvulsant activity and acute adverse effects (sedation) in the maximal electroshock-induced seizures (MES) and chimney test (motor performance) in adult male Swiss mice. Type I isobolographic analysis for nonparallel dose-response effects for the combination of retigabine with LCM (at the fixed-ratio of 1:1) in both the MES and chimney test in mice was performed. Brain concentrations of retigabine and LCM were measured by high-pressure liquid chromatography (HPLC) to characterize any pharmacokinetic interactions occurring when combining these drugs. Linear regression analysis revealed that retigabine had its dose-response effect line nonparallel to that of LCM in both the MES and chimney tests. The type I isobolographic analysis illustrated that retigabine combined with LCM (fixed-ratio of 1:1) exerted an additive interaction in the mouse MES model and sub-additivity (antagonism) in the chimney test. With HPLC, retigabine and LCM did not mutually change their total brain concentrations, thereby confirming the pharmacodynamic nature of the interaction. LCM combined with retigabine possesses a beneficial preclinical profile (benefit index ranged from 2.07 to 2.50) and this 2-drug combination is worth recommending as treatment plan to patients with pharmacoresistant epilepsy. © 2017 S. Karger AG, Basel.

Test of a hypothesis of realism in quantum theory using a Bayesian approach

NASA Astrophysics Data System (ADS)

Nikitin, N.; Toms, K.

2017-05-01

In this paper we propose a time-independent equality and time-dependent inequality, suitable for an experimental test of the hypothesis of realism. The derivation of these relations is based on the concept of conditional probability and on Bayes' theorem in the framework of Kolmogorov's axiomatics of probability theory. The equality obtained is intrinsically different from the well-known Greenberger-Horne-Zeilinger (GHZ) equality and its variants, because violation of the proposed equality might be tested in experiments with only two microsystems in a maximally entangled Bell state |Ψ-> , while a test of the GHZ equality requires at least three quantum systems in a special state |ΨGHZ> . The obtained inequality differs from Bell's, Wigner's, and Leggett-Garg inequalities, because it deals with spin s =1 /2 projections onto only two nonparallel directions at two different moments of time, while a test of the Bell and Wigner inequalities requires at least three nonparallel directions, and a test of the Leggett-Garg inequalities requires at least three distinct moments of time. Hence, the proposed inequality seems to open an additional experimental possibility to avoid the "contextuality loophole." Violation of the proposed equality and inequality is illustrated with the behavior of a pair of anticorrelated spins in an external magnetic field and also with the oscillations of flavor-entangled pairs of neutral pseudoscalar mesons.

Clustering and flow around a sphere moving into a grain cloud.

PubMed

Seguin, A; Lefebvre-Lepot, A; Faure, S; Gondret, P

2016-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains far from any boundaries and without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size. The key point is that the upstream cluster size increases with the initial solid fraction [Formula: see text] but the cluster packing fraction takes an about constant value independent of [Formula: see text]. Although the upstream cluster size around the moving sphere diverges when [Formula: see text] approaches a critical value, the drag force exerted by the grains on the sphere does not. The detailed analysis of the local strain rate and local stress fields made in the non-parallel granular flow inside the cluster allows us to extract the local invariants of the two tensors: dilation rate, shear rate, pressure and shear stress. Despite different spatial variations of these invariants, the local friction coefficient μ appears to depend only on the local inertial number I as well as the local solid fraction, which means that a local rheology does exist in the present non-parallel flow. The key point is that the spatial variations of I inside the cluster do not depend on the sphere velocity and explore only a small range around the value one.

Collapse of optical wave arrested by cross-phase modulation in nonlinear metamaterials

NASA Astrophysics Data System (ADS)

Zhang, Jinggui; Li, Ying; Xiang, Yuanjiang; Lei, Dajun; Zhang, Lifu

2016-03-01

In this article, we put forward a novel strategy to realize the management of wave collapse through designing probe-pump configuration where probe wave is assumed to propagate in the positive-index region of metamaterials (MMs), while pump wave is assumed to propagate in the negative-index region. We disclose that cross-phase modulation (XPM) in MMs as a new physical mechanism that can be used to arrest the collapse of probe wave in the positive-index region by copropagating it together with pump wave in the negative-index region. Further, we observe that pump wave will evolve into a ring while probe wave will develop a side lob in the wings during the course of coupled waves propagation, different from the corresponding counterpart in the ordinary positive-index materials (OMs) where they simultaneously exhibit the catastrophic self-focusing behavior. Meanwhile, we also discuss how to control the collapse of probe wave by adjusting intensity-detuned pump wave. Our analysis is performed by directly numerically solving the coupled nonlinear Schrödinger equations, as well as using the variational approximation, both showing consistent results. The finding demonstrates XPM as a specific physical mechanism in MMs can provide us unique opportunities unattainable in OMs to manipulate self-focusing of high-power laser.

On the characteristics of obliquely propagating electrostatic structures in non-Maxwellian plasmas in the presence of ion pressure anisotropy

NASA Astrophysics Data System (ADS)

Adnan, Muhammad; Qamar, Anisa; Mahmood, Shahzad; Kourakis, Ioannis

2017-03-01

The dynamical characteristics of large amplitude ion-acoustic waves are investigated in a magnetized plasma comprising ions presenting space asymmetry in the equation of state and non-Maxwellian electrons. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low theory. An excess in the superthermal component of the electron population is assumed, in agreement with long-tailed (energetic electron) distribution observations in space plasmas; this is modeled via a kappa-type distribution function. Large electrostatic excitations are assumed to propagate in a direction oblique to the external magnetic field. In the linear (small amplitude) regime, two electrostatic modes are shown to exist. The properties of arbitrary amplitude (nonlinear) obliquely propagating ion-acoustic solitary excitations are thus investigated via a pseudomechanical energy balance analogy, by adopting a Sagdeev potential approach. The combined effect of the ion pressure anisotropy and excess superthermal electrons is shown to alter the parameter region where solitary waves can exist. An excess in the suprathermal particles is thus shown to be associated with solitary waves, which are narrower, faster, and of larger amplitude. Ion pressure anisotropy, on the other hand, affects the amplitude of the solitary waves, which become weaker (in strength), wider (in spatial extension), and thus slower in comparison with the cold ion case.

A Unified Model of Cloud-to-Ground Lightning Stroke

NASA Astrophysics Data System (ADS)

Nag, A.; Rakov, V. A.

2014-12-01

The first stroke in a cloud-to-ground lightning discharge is thought to follow (or be initiated by) the preliminary breakdown process which often produces a train of relatively large microsecond-scale electric field pulses. This process is poorly understood and rarely modeled. Each lightning stroke is composed of a downward leader process and an upward return-stroke process, which are usually modeled separately. We present a unified engineering model for computing the electric field produced by a sequence of preliminary breakdown, stepped leader, and return stroke processes, serving to transport negative charge to ground. We assume that a negatively-charged channel extends downward in a stepped fashion through the relatively-high-field region between the main negative and lower positive charge centers and then through the relatively-low-field region below the lower positive charge center. A relatively-high-field region is also assumed to exist near ground. The preliminary breakdown pulse train is assumed to be generated when the negatively-charged channel interacts with the lower positive charge region. At each step, an equivalent current source is activated at the lower extremity of the channel, resulting in a step current wave that propagates upward along the channel. The leader deposits net negative charge onto the channel. Once the stepped leader attaches to ground (upward connecting leader is presently neglected), an upward-propagating return stroke is initiated, which neutralizes the charge deposited by the leader along the channel. We examine the effect of various model parameters, such as step length and current propagation speed, on model-predicted electric fields. We also compare the computed fields with pertinent measurements available in the literature.

Reinventing potato as a diploid inbred line-based crop

USDA-ARS?s Scientific Manuscript database

The third most important food crop worldwide, potato, is a tetraploid outcrossing species propagated from tubers. Breeders have long been challenged by polyploidy, heterozygosity, and asexual reproduction. It has been assumed that tetraploidy is essential for high yield, the creation of inbred potat...

Magnetogasdynamics shock waves in a rotational axisymmetric non-ideal gas with increasing energy and conductive and radiative heat-fluxes

NASA Astrophysics Data System (ADS)

Nath, Gorakh

2016-07-01

Self-similar solutions are obtained for one-dimensional adiabatic flow behind a magnetogasdynamics cylindrical shock wave propagating in a rotational axisymmetric non ideal gas with increasing energy and conductive and radiative heat fluxes in presence of an azimuthal magnetic field. The fluid velocities and the azimuthal magnetic field in the ambient medium are assume to be varying and obeying power laws. In order to find the similarity solutions the angular velocity of the ambient medium is taken to be decreasing as the distance from the axis increases. The heat conduction is expressed in terms of Fourier's law and the radiation is considered to be the diffusion type for an optically thick grey gas model. The thermal conductivity and the absorption coefficient are assumed to vary with temperature and density. The effects of the presence of radiation and conduction, the non-idealness of the gas and the magnetic field on the shock propagation and the flow behind the shock are investigated.

Evaluation of Lightning Incidence to Elements of a Complex Structure: A Monte Carlo Approach

NASA Technical Reports Server (NTRS)

Mata, Carlos T.; Rakov, V. A.

2008-01-01

There are complex structures for which the installation and positioning of the lightning protection system (LPS) cannot be done using the lightning protection standard guidelines. As a result, there are some "unprotected" or "exposed" areas. In an effort to quantify the lightning threat to these areas, a Monte Carlo statistical tool has been developed. This statistical tool uses two random number generators: a uniform distribution to generate origins of downward propagating leaders and a lognormal distribution to generate returns stroke peak currents. Downward leaders propagate vertically downward and their striking distances are defined by the polarity and peak current. Following the electrogeometrical concept, we assume that the leader attaches to the closest object within its striking distance. The statistical analysis is run for 10,000 years with an assumed ground flash density and peak current distributions, and the output of the program is the probability of direct attachment to objects of interest with its corresponding peak current distribution.

Evaluation of Lightning Incidence to Elements of a Complex Structure: A Monte Carlo Approach

NASA Technical Reports Server (NTRS)

Mata, Carlos T.; Rakov, V. A.

2008-01-01

There are complex structures for which the installation and positioning of the lightning protection system (LPS) cannot be done using the lightning protection standard guidelines. As a result, there are some "unprotected" or "exposed" areas. In an effort to quantify the lightning threat to these areas, a Monte Carlo statistical tool has been developed. This statistical tool uses two random number generators: a uniform distribution to generate the origin of downward propagating leaders and a lognormal distribution to generate the corresponding returns stroke peak currents. Downward leaders propagate vertically downward and their striking distances are defined by the polarity and peak current. Following the electrogeometrical concept, we assume that the leader attaches to the closest object within its striking distance. The statistical analysis is run for N number of years with an assumed ground flash density and the output of the program is the probability of direct attachment to objects of interest with its corresponding peak current distribution.

Simple and flexible SAS and SPSS programs for analyzing lag-sequential categorical data.

PubMed

O'Connor, B P

1999-11-01

This paper describes simple and flexible programs for analyzing lag-sequential categorical data, using SAS and SPSS. The programs read a stream of codes and produce a variety of lag-sequential statistics, including transitional frequencies, expected transitional frequencies, transitional probabilities, adjusted residuals, z values, Yule's Q values, likelihood ratio tests of stationarity across time and homogeneity across groups or segments, transformed kappas for unidirectional dependence, bidirectional dependence, parallel and nonparallel dominance, and significance levels based on both parametric and randomization tests.

Propagation dynamics of successive emissions in laboratory and astrophysical jets and problem of their collimation

NASA Astrophysics Data System (ADS)

Kalashnikov, I.; Chardonnet, P.; Chechetkin, V.; Dodin, A.; Krauz, V.

2018-06-01

This paper presents the results of numerical simulation of the propagation of a sequence of plasma knots in laboratory conditions and in the astrophysical environment. The physical and geometric parameters of the simulation have been chosen close to the parameters of the PF-3 facility (Kurchatov Institute) and the jet of the star RW Aur. We found that the low-density region formed after the first knot propagation plays an important role in the collimation of the subsequent ones. Assuming only the thermal expansion of the subsequent emissions, qualitative estimates of the time taken to fill this area with the surrounding matter and the angle of jet scattering have been made. These estimates are consistent with observations and results of our modeling.

Preventing Unofficial Information Propagation

NASA Astrophysics Data System (ADS)

Le, Zhengyi; Ouyang, Yi; Xu, Yurong; Ford, James; Makedon, Fillia

Digital copies are susceptible to theft and vulnerable to leakage, copying, or manipulation. When someone (or some group), who has stolen, leaked, copied, or manipulated digital documents propagates the documents over the Internet and/or distributes those through physical distribution channels many challenges arise which document holders must overcome in order to mitigate the impact to their privacy or business. This paper focuses on the propagation problem of digital credentials, which may contain sensitive information about a credential holder. Existing work such as access control policies and the Platform for Privacy Preferences (P3P) assumes that qualified or certified credential viewers are honest and reliable. The proposed approach in this paper uses short-lived credentials based on reverse forward secure signatures to remove this assumption and mitigate the damage caused by a dishonest or honest but compromised viewer.

The deformation of the front of a 3D interface crack propagating quasistatically in a medium with random fracture properties

NASA Astrophysics Data System (ADS)

Pindra, Nadjime; Lazarus, Véronique; Leblond, Jean-Baptiste

One studies the evolution in time of the deformation of the front of a semi-infinite 3D interface crack propagating quasistatically in an infinite heterogeneous elastic body. The fracture properties are assumed to be lower on the interface than in the materials so that crack propagation is channelled along the interface, and to vary randomly within the crack plane. The work is based on earlier formulae which provide the first-order change of the stress intensity factors along the front of a semi-infinite interface crack arising from some small but otherwise arbitrary in-plane perturbation of this front. The main object of study is the long-time behavior of various statistical measures of the deformation of the crack front. Special attention is paid to the influences of the mismatch of elastic properties, the type of propagation law (fatigue or brittle fracture) and the stable or unstable character of 2D crack propagation (depending on the loading) upon the development of this deformation.

Radiation from a current filament driven by a traveling wave

NASA Technical Reports Server (NTRS)

Levine, D. M.; Meneghini, R.

1976-01-01

Solutions are presented for the electromagnetic fields radiated by an arbitrarily oriented current filament located above a perfectly conducting ground plane and excited by a traveling current wave. Both an approximate solution, valid in the fraunhofer region of the filament and predicting the radiation terms in the fields, and an exact solution, which predicts both near and far field components of the electromagnetic fields, are presented. Both solutions apply to current waveforms which propagate along the channel but are valid regardless of the actual waveshape. The exact solution is valid only for waves which propagate at the speed of light, and the approximate solution is formulated for arbitrary velocity of propagation. The spectrum-magnitude of the fourier transform-of the radiated fields is computed by assuming a compound exponential model for the current waveform. The effects of channel orientation and length, as well as velocity of propagation of the current waveform and location of the observer, are discussed. It is shown that both velocity of propagation and an effective channel length are important in determining the shape of the spectrum.

Effects of UGTs on the ionosphere

NASA Astrophysics Data System (ADS)

Argo, P. E.; Fitzgerald, T. J.

The processes that propagate local effects of underground nuclear tests from the ground into the upper atmosphere, and produce a detectable signal in the ionosphere are described. Initially, the blast wave from a underground test (UGT) radially expands, until it reaches the surface of the earth. The wave is both reflected and transmitted at this sharp discontinuity in propagation media. Tne reflected wave combines with the incident wave to form an 'Airy surface,' at which very strong ripping forces tear the earth apart. This broken region is called the 'spat zone,' and is launched into ballistic motion. The resultant ground motion launches an acoustical wave into the atmosphere. This acoustic wave, with overpressures of a few tenths of one percent, propagates upwards at the speed of sound. Assuming purely linear propagation, the path of the acoustic energy can be tracked using raytracing models. Most of the wave energy, which is radiated nearly vertically, tends to propagate into the upper atmosphere, while wave energy radiated at angles greater than about 30 degrees to the vertical will be reflected back to earth and is probably what is seen by most infrasonde measurements.

Coupling of electrostatic ion cyclotron and ion acoustic waves in the solar wind

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

Sreeraj, T., E-mail: sreerajt13@iigs.iigm.res.in; Singh, S. V., E-mail: satyavir@iigs.iigm.res.in; Lakhina, G. S., E-mail: gslakhina@gmail.com

2016-08-15

The coupling of electrostatic ion cyclotron and ion acoustic waves is examined in three component magnetized plasma consisting of electrons, protons, and alpha particles. In the theoretical model relevant to solar wind plasma, electrons are assumed to be superthermal with kappa distribution and protons as well as alpha particles follow the fluid dynamical equations. A general linear dispersion relation is derived for such a plasma system which is analyzed both analytically and numerically. For parallel propagation, electrostatic ion cyclotron (proton and helium cyclotron) and ion acoustic (slow and fast) modes are decoupled. For oblique propagation, coupling between the cyclotron andmore » acoustic modes occurs. Furthermore, when the angle of propagation is increased, the separation between acoustic and cyclotron modes increases which is an indication of weaker coupling at large angle of propagation. For perpendicular propagation, only cyclotron modes are observed. The effect of various parameters such as number density and temperature of alpha particles and superthermality on dispersion characteristics is examined in details. The coupling between various modes occurs for small values of wavenumber.« less

An algorithm for U-Pb isotope dilution data reduction and uncertainty propagation

NASA Astrophysics Data System (ADS)

McLean, N. M.; Bowring, J. F.; Bowring, S. A.

2011-06-01

High-precision U-Pb geochronology by isotope dilution-thermal ionization mass spectrometry is integral to a variety of Earth science disciplines, but its ultimate resolving power is quantified by the uncertainties of calculated U-Pb dates. As analytical techniques have advanced, formerly small sources of uncertainty are increasingly important, and thus previous simplifications for data reduction and uncertainty propagation are no longer valid. Although notable previous efforts have treated propagation of correlated uncertainties for the U-Pb system, the equations, uncertainties, and correlations have been limited in number and subject to simplification during propagation through intermediary calculations. We derive and present a transparent U-Pb data reduction algorithm that transforms raw isotopic data and measured or assumed laboratory parameters into the isotopic ratios and dates geochronologists interpret without making assumptions about the relative size of sample components. To propagate uncertainties and their correlations, we describe, in detail, a linear algebraic algorithm that incorporates all input uncertainties and correlations without limiting or simplifying covariance terms to propagate them though intermediate calculations. Finally, a weighted mean algorithm is presented that utilizes matrix elements from the uncertainty propagation algorithm to propagate random and systematic uncertainties for data comparison between other U-Pb labs and other geochronometers. The linear uncertainty propagation algorithms are verified with Monte Carlo simulations of several typical analyses. We propose that our algorithms be considered by the community for implementation to improve the collaborative science envisioned by the EARTHTIME initiative.

Propagating modes in gain-guided optical fibers.

PubMed

Siegman, A E

2003-08-01

Optical fibers in which gain-guiding effects are significant or even dominant compared with conventional index guiding may become of practical interest for future high-power single-mode fiber lasers. I derive the propagation characteristics of symmetrical slab waveguides and cylindrical optical fibers having arbitrary amounts of mixed gain and index guiding, assuming a single uniform transverse profile for both the gain and the refractive-index steps. Optical fibers of this type are best characterized by using a complex-valued v-squared parameter in place of the real-valued v parameter commonly used to describe conventional index-guided optical fibers.

Dynamics of short pulses and phase matched second harmonic generation in negative index materials.

PubMed

Scalora, Michael; D'Aguanno, Giuseppe; Bloemer, Mark; Centini, Marco; de Ceglia, Domenico; Mattiucci, Nadia; Kivshar, Yuri S

2006-05-29

We study pulsed second harmonic generation in metamaterials under conditions of significant absorption. Tuning the pump in the negative index range, a second harmonic signal is generated in the positive index region, such that the respective indices of refraction have the same magnitudes but opposite signs. This insures that a forward-propagating pump is exactly phase matched to the backward-propagating second harmonic signal. Using peak intensities of ~500 MW/cm(2), assuming chi((2))~80pm/V, we predict conversion efficiencies of 12% and 0.2% for attenuation lengths of 50 and 5microm, respectively.

Ion-acoustic double-layers in a magnetized plasma with nonthermal electrons

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

Rios, L. A.; Galvão, R. M. O.; Instituto de Física, Universidade de São Paulo, 05508-900 São Paulo

2013-11-15

In the present work we investigate the existence of obliquely propagating ion-acoustic double layers in magnetized two-electron plasmas. The fluid model is used to describe the ion dynamics, and the hot electron population is modeled via a κ distribution function, which has been proved to be appropriate for modeling non-Maxwellian plasmas. A quasineutral condition is assumed to investigate these nonlinear structures, which leads to the formation of double-layers propagating with slow ion-acoustic velocity. The problem is investigated numerically, and the influence of parameters such as nonthermality is discussed.

Cardiac conduction velocity estimation from sequential mapping assuming known Gaussian distribution for activation time estimation error.

PubMed

Shariat, Mohammad Hassan; Gazor, Saeed; Redfearn, Damian

2016-08-01

In this paper, we study the problem of the cardiac conduction velocity (CCV) estimation for the sequential intracardiac mapping. We assume that the intracardiac electrograms of several cardiac sites are sequentially recorded, their activation times (ATs) are extracted, and the corresponding wavefronts are specified. The locations of the mapping catheter's electrodes and the ATs of the wavefronts are used here for the CCV estimation. We assume that the extracted ATs include some estimation errors, which we model with zero-mean white Gaussian noise values with known variances. Assuming stable planar wavefront propagation, we derive the maximum likelihood CCV estimator, when the synchronization times between various recording sites are unknown. We analytically evaluate the performance of the CCV estimator and provide its mean square estimation error. Our simulation results confirm the accuracy of the proposed method and the error analysis of the proposed CCV estimator.

Understanding the Behaviour of Infinite Ladder Circuits

ERIC Educational Resources Information Center

Ucak, C.; Yegin, K.

2008-01-01

Infinite ladder circuits are often encountered in undergraduate electrical engineering and physics curricula when dealing with series and parallel combination of impedances, as a part of filter design or wave propagation on transmission lines. The input impedance of such infinite ladder circuits is derived by assuming that the input impedance does…

Angular distribution and polarization of atomic radiative emission in electric and magnetic fields

NASA Astrophysics Data System (ADS)

Jacobs, V. L.; Filuk, A. B.

1999-09-01

A density-matrix approach has been developed for the angular distribution and polarization of radiative emission during single-photon atomic transitions for a general set of steady-state excitation processes in an arbitrary arrangement of static (or quasistatic) electric and magnetic fields. Particular attention has been directed at spectroscopic observations in the intense fields of the high-power ion diodes on the Particle Beam Fusion Accelerator II (PBFA II) and SABRE devices at Sandia National Laboratories and at magnetic-field measurements in tokamak plasmas. The field-dependent atomic eigenstates are represented as expansions in a complete basis set of field-free bound and continuum eigenstates. Particular emphasis has been given to directed-electron collisional excitations, which may be produced by an anisotropic incident-electron velocity distribution. We have allowed for the possibility of the coherent excitation of the nearly degenerate field-dependent atomic substates, which can give rise to a complex spectral pattern of overlapping Stark-Zeeman components. Coherent excitations may be produced by a beam of electrons that are spin-polarized at an angle with respect to the propagation direction or by nonparallel electric and magnetic fields. Our main result is a general expression for the matrix elements of the photon-polarization density operator representing the total intensity, angular distribution, and polarization of the atomic radiative emission. For the observation of radiative emission in the direction of the magnetic field, the detection of linearly polarized emission, in addition to the usual circularly polarized radiation, can reveal the presence of a perpendicular electric field or a coherent excitation mechanism.

Angular distribution and polarization of atomic radiative emission in electric and magnetic fields

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

Jacobs, V.L.; Filuk, A.B.

A density-matrix approach has been developed for the angular distribution and polarization of radiative emission during single-photon atomic transitions for a general set of steady-state excitation processes in an arbitrary arrangement of static (or quasistatic) electric and magnetic fields. Particular attention has been directed at spectroscopic observations in the intense fields of the high-power ion diodes on the Particle Beam Fusion Accelerator II (PBFA II) and SABRE devices at Sandia National Laboratories and at magnetic-field measurements in tokamak plasmas. The field-dependent atomic eigenstates are represented as expansions in a complete basis set of field-free bound and continuum eigenstates. Particular emphasismore » has been given to directed-electron collisional excitations, which may be produced by an anisotropic incident-electron velocity distribution. We have allowed for the possibility of the coherent excitation of the nearly degenerate field-dependent atomic substates, which can give rise to a complex spectral pattern of overlapping Stark-Zeeman components. Coherent excitations may be produced by a beam of electrons that are spin-polarized at an angle with respect to the propagation direction or by nonparallel electric and magnetic fields. Our main result is a general expression for the matrix elements of the photon-polarization density operator representing the total intensity, angular distribution, and polarization of the atomic radiative emission. For the observation of radiative emission in the direction of the magnetic field, the detection of linearly polarized emission, in addition to the usual circularly polarized radiation, can reveal the presence of a perpendicular electric field or a coherent excitation mechanism.« less

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.

Efficiency arcjet thruster with controlled arc startup and steady state attachment

NASA Technical Reports Server (NTRS)

Smith, William W. (Inventor); Knowles, Steven C. (Inventor)

1989-01-01

An improved efficiency arcjet thruster has a constrictor and electrically-conductive nozzle anode defining an arc chamber, and an electrically-conductive rod having a tip spaced upstream from the constrictor and defining a cathode spaced from the anode by a gap generally coextensive with the arc chamber. An electrical potential is applied to the anode and cathode to generate an electrical arc in the arc chamber from the cathode to anode. Catalytically decomposed hydrazine is supplied to the arc chamber with generation of the arc so as to produce thermal heating and expansion thereof through the nozzle. The constrictor can have a electrically insulative portion disposed between the cathode tip and the nozzle anode, and an electrically-conductive anode extension disposed along the insulative portion so as to define an auxiliary gap with the cathode tip substantially smaller than the gap defined between the cathode and nozzle anode for facilitating startup of arc generation. The constrictor can also include an electrically-conductive electrode with a variable electrical potential to vary the shape of the arc generated in the arc chamber. Also, the cathode is mounted for axial movement such that the gap between its tip and the nozzle anode can be varied to facilitate a generally nonerosive generation of the electrical arc at startup and reliable steady state operation. Further, the arc chamber can have a nonparallel subsonic-to-supersonic transition configuration, or alternatively solely a nonparallel supersonic configuration, for improved arc attachment.

Crack propagation and arrest in pressurized containers

NASA Technical Reports Server (NTRS)

Erdogan, F.; Delale, F.; Owczarek, J. A.

1976-01-01

The problem of crack propagation and arrest in a finite volume cylindrical container filled with pressurized gas is considered. It is assumed that the cylinder contains a symmetrically located longitudinal part-through crack with a relatively small net ligament. The net ligament suddenly ruptures initiating the process of fracture propagation and depressurization in the cylinder. Thus the problem is a coupled gas dynamics and solid mechanics problem the exact formulation of which does not seem to be possible. The problem is reduced to a proper initial value problem by introducing a dynamic fracture criterion which relates the crack acceleration to the difference between a load factor and the corresponding strength parameter. The results indicate that generally in gas filled cylinders fracture arrest is not possible unless the material behaves in a ductile manner and the container is relatively long.

Propagation of the state change induced by external forces in local interactions

NASA Astrophysics Data System (ADS)

Lu, Jianjun; Tokinaga, Shozo

2016-10-01

This paper analyses the propagation of the state changes of agents that are induced by external forces applied to a plane. In addition, we propose two models for the behavior of the agents placed on a lattice plane, both of which are affected by local interactions. We first assume that agents are allowed to move to another site to maximise their satisfaction. Second, we utilise a model in which the agents choose activities on each site. The results show that the migration (activity) patterns of agents in both models achieve stability without any external forces. However, when we apply an impulsive external force to the state of the agents, we then observe the propagation of the changes in the agents' states. Using simulation studies, we show the conditions for the propagation of the state changes of the agents. We also show the propagation of the state changes of the agents allocated in scale-free networks and discuss the estimation of the agents' decisions in real state changes. Finally, we discuss the estimation of the agents' decisions in real state temporal changes using economic and social data from Japan and the United States.

A two dimension model of the uterine electrical wave propagation.

PubMed

Rihana, S; Lefrançois, E; Marque, C

2007-01-01

The uterus, usually quiescent during pregnancy, exhibits forceful contractions at term leading to delivery. These contractions are caused by the synchronized propagation of electrical waves from the pacemaker cells to its neighbors inducing the whole coordinated contraction of the uterus wall leading to labor. In a previous work, we simulate the electrical activity of a single uterine cell by a set of ordinary differential equations. Then, this model has been used to simulate the electrical activity propagation. In the present work, the uterine cell tissue is assumed to have uniform and isotropic propagation, and constant electrical membrane properties. The stability of the numerical solution imposes the choice of a critical temporal step. A wave starts at a pacemaker cell; this electrical activity is initiated by the injection of an external stimulation current to the cell membrane. We observe synchronous wave propagation for axial resistance values around 0.5 GOmega or less and propoagation blocking for values greater than 0.7 GOmega. We compute the conduction velocity of the excitation, for different axial resistance values, and obtain a velocity about 10 cm/sec, approaching the one described by the literature for the rat at end of term.

Fluid-driven fracture propagation in heterogeneous media: Probability distributions of fracture trajectories

NASA Astrophysics Data System (ADS)

Santillán, David; Mosquera, Juan-Carlos; Cueto-Felgueroso, Luis

2017-11-01

Hydraulic fracture trajectories in rocks and other materials are highly affected by spatial heterogeneity in their mechanical properties. Understanding the complexity and structure of fluid-driven fractures and their deviation from the predictions of homogenized theories is a practical problem in engineering and geoscience. We conduct a Monte Carlo simulation study to characterize the influence of heterogeneous mechanical properties on the trajectories of hydraulic fractures propagating in elastic media. We generate a large number of random fields of mechanical properties and simulate pressure-driven fracture propagation using a phase-field model. We model the mechanical response of the material as that of an elastic isotropic material with heterogeneous Young modulus and Griffith energy release rate, assuming that fractures propagate in the toughness-dominated regime. Our study shows that the variance and the spatial covariance of the mechanical properties are controlling factors in the tortuousness of the fracture paths. We characterize the deviation of fracture paths from the homogenous case statistically, and conclude that the maximum deviation grows linearly with the distance from the injection point. Additionally, fracture path deviations seem to be normally distributed, suggesting that fracture propagation in the toughness-dominated regime may be described as a random walk.

Fluid-driven fracture propagation in heterogeneous media: Probability distributions of fracture trajectories.

PubMed

Santillán, David; Mosquera, Juan-Carlos; Cueto-Felgueroso, Luis

2017-11-01

Hydraulic fracture trajectories in rocks and other materials are highly affected by spatial heterogeneity in their mechanical properties. Understanding the complexity and structure of fluid-driven fractures and their deviation from the predictions of homogenized theories is a practical problem in engineering and geoscience. We conduct a Monte Carlo simulation study to characterize the influence of heterogeneous mechanical properties on the trajectories of hydraulic fractures propagating in elastic media. We generate a large number of random fields of mechanical properties and simulate pressure-driven fracture propagation using a phase-field model. We model the mechanical response of the material as that of an elastic isotropic material with heterogeneous Young modulus and Griffith energy release rate, assuming that fractures propagate in the toughness-dominated regime. Our study shows that the variance and the spatial covariance of the mechanical properties are controlling factors in the tortuousness of the fracture paths. We characterize the deviation of fracture paths from the homogenous case statistically, and conclude that the maximum deviation grows linearly with the distance from the injection point. Additionally, fracture path deviations seem to be normally distributed, suggesting that fracture propagation in the toughness-dominated regime may be described as a random walk.

Behavior of dusty real gas on adiabatic propagation of cylindrical imploding strong shock waves

NASA Astrophysics Data System (ADS)

Gangwar, P. K.

2018-05-01

In this paper, CCW method has been used to study the behavior of dusty real gas on adiabatic propagation of cylindrical imploding strong shock waves. The strength of overtaking waves is estimated under the assumption that both C+ and C- disturbances propagate in non-uniform region of same density distribution. It is assumed that the dusty gas is the mixture of a real gas and a large number of small spherical solid particles of uniform size. The solid particles are uniformly distributed in the medium. Maintaining equilibrium flow conditions, the expressions for shock strength has been derived both for freely propagation as well as under the effect of overtaking disturbances. The variation of all flow variables with propagation distance, mass concentration of solid particles in the mixture and the ratio of solid particles to the initial density of gas have been computed and discussed through graphs. It is found that the presence of dust particles in the gases medium has significant effects on the variation of flow variables and the shock is strengthened under the influence of overtaking disturbances. The results accomplished here been compared with those for ideal gas.

Experimental and calculative estimation of femtosecond laser induced-impulsive force in culture medium solution with motion analysis of polymer micro-beads

NASA Astrophysics Data System (ADS)

Yamakawa, Takeshi; Maruyama, Akihiro; Uedan, Hirohisa; Iino, Takanori; Hosokawa, Yoichiroh

2015-03-01

A new methodology to estimate the dynamics of femtosecond laser-induced impulsive force generated into water under microscope was developed. In this method, the position shift of the bead in water before and after the femtosecond laser irradiation was investigated experimentally and compared with motion equation assuming stress wave propagation with expansion and collapse the cavitation bubble. In the process of the comparison, parameters of force and time of the stress wave were determined. From these results, dynamics of propagations of shock and stress waves, cavitation bubble generation, and these actions to micro-objects were speculated.

Multiple rotation assessment through isothetic fringes in speckle photography

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

Angel, Luciano; Tebaldi, Myrian; Bolognini, Nestor

2007-05-10

The use of different pupils for storing each speckled image in speckle photography is employed to determine multiple in-plane rotations. The method consists of recording a four-exposure specklegram where the rotations are done between exposures. This specklegram is then optically processed in a whole field approach rendering isothetic fringes, which give detailed information about the multiple rotations. It is experimentally demonstrated that the proposed arrangement permits the depiction of six isothetics in order to measure either six different angles or three nonparallel components for two local general in-plane displacements.

Anti-backlash gear bearings

NASA Technical Reports Server (NTRS)

Vranish, John M. (Inventor)

2009-01-01

A gear bearing having a first gear and a second gear, each having a plurality of teeth. Each gear operates on two non-parallel surfaces of the opposing gear teeth to perform both gear and bearing functions simultaneously. The gears are moving at substantially the same speed at their contact points. The gears may be roller gear bearings or phase-shifted gear bearings, and may be arranged in a planet/sun system or used as a transmission. One preferred embodiment discloses and describes an anti-backlash feature to counter ''dead zones'' in the gear bearing movement.

Closed timelike curves produced by pairs of moving cosmic strings - Exact solutions

NASA Technical Reports Server (NTRS)

Gott, J. Richard, III

1991-01-01

Exact solutions of Einstein's field equations are presented for the general case of two moving straight cosmic strings that do not intersect. The solutions for parallel cosmic strings moving in opposite directions show closed timelike curves (CTCs) that circle the two strings as they pass, allowing observers to visit their own past. Similar results occur for nonparallel strings, and for masses in (2+1)-dimensional spacetime. For finite string loops the possibility that black-hole formation may prevent the formation of CTCs is discussed.

Receptivity and Bypass Dynamics

NASA Technical Reports Server (NTRS)

Lasseigne, D. G.; Criminale, W. O.; Joslin, R. D.; Jackson, T. L.

1999-01-01

Problems concerning laminar-turbulent transition are addressed by solving a series of initial value problems. Solutions to the temporal, initial-value problem .with an inhomogeneous forcing term imposed upon the flow are sought. It is shown that: (1) A transient disturbance lying located outside of the boundary layer can lead to the growth of an unstable Tollmein-Schlicting wave; (2) A resonance with the continuous spectrum may provide a mechanism for bypass transition; and (3) The continuum modes of a disturbance feed directly into the Tollmein-Schlicting wave downstream through non-parallel effects.

Parallel Lattice Basis Reduction Using a Multi-threaded Schnorr-Euchner LLL Algorithm

NASA Astrophysics Data System (ADS)

Backes, Werner; Wetzel, Susanne

In this paper, we introduce a new parallel variant of the LLL lattice basis reduction algorithm. Our new, multi-threaded algorithm is the first to provide an efficient, parallel implementation of the Schorr-Euchner algorithm for today’s multi-processor, multi-core computer architectures. Experiments with sparse and dense lattice bases show a speed-up factor of about 1.8 for the 2-thread and about factor 3.2 for the 4-thread version of our new parallel lattice basis reduction algorithm in comparison to the traditional non-parallel algorithm.

3-D Spontaneous Rupture Simulations of the 2016 Kumamoto, Japan, Earthquake

NASA Astrophysics Data System (ADS)

Urata, Yumi; Yoshida, Keisuke; Fukuyama, Eiichi

2017-04-01

We investigated the M7.3 Kumamoto, Japan, earthquake to illuminate why and how the rupture of the main shock propagated successfully by 3-D dynamic rupture simulations, assuming a complicated fault geometry estimated based on the distributions of aftershocks. The M7.3 main shock occurred along the Futagawa and Hinagu faults. A few days before, three M6-class foreshocks occurred. Their hypocenters were located along by the Hinagu and Futagawa faults and their focal mechanisms were similar to those of the main shock; therefore, an extensive stress shadow can have been generated on the fault plane of the main shock. First, we estimated the geometry of the fault planes of the three foreshocks as well as that of the main shock based on the temporal evolution of relocated aftershock hypocenters. Then, we evaluated static stress changes on the main shock fault plane due to the occurrence of the three foreshocks assuming elliptical cracks with constant stress drops on the estimated fault planes. The obtained static stress change distribution indicated that the hypocenter of the main shock is located on the region with positive Coulomb failure stress change (ΔCFS) while ΔCFS in the shallow region above the hypocenter was negative. Therefore, these foreshocks could encourage the initiation of the main shock rupture and could hinder the rupture propagating toward the shallow region. Finally, we conducted 3-D dynamic rupture simulations of the main shock using the initial stress distribution, which was the sum of the static stress changes by these foreshocks and the regional stress field. Assuming a slip-weakening law with uniform friction parameters, we conducted 3-D dynamic rupture simulations by varying the friction parameters and the values of the principal stresses. We obtained feasible parameter ranges to reproduce the rupture propagation of the main shock consistent with those revealed by seismic waveform analyses. We also demonstrated that the free surface encouraged the slip evolution of the main shock.

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

Erkaev, N. V.; Semenov, V. S.; Biernat, H. K.

Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the ''kink'' and ''sausage'' flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating alongmore » the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity.« less

Review of critical flow rate, propagation of pressure pulse, and sonic velocity in two-phase media

NASA Technical Reports Server (NTRS)

Hsu, Y.

1972-01-01

For single-phase media, the critical discharge velocity, the sonic velocity, and the pressure pulse propagation velocity can be expressed in the same form by assuming isentropic, equilibria processes. In two-phase mixtures, the same concept is not valid due to the existence of interfacial transports of momentum, heat, and mass. Thus, the three velocities should be treated differently and separately for each particular condition, taking into account the various transport processes involved under that condition. Various attempts are reviewed to predict the critical discharge rate or the propagation velocities by considering slip ratio (momentum change), evaporation (mass and heat transport), flow pattern, etc. Experimental data were compared with predictions based on various theorems. The importance is stressed of the time required to achieve equilibrium as compared with the time available during the process, for example, of passing a pressure pulse.

Local Infrasound Variability Related to In Situ Atmospheric Observation

NASA Astrophysics Data System (ADS)

Kim, Keehoon; Rodgers, Arthur; Seastrand, Douglas

2018-04-01

Local infrasound is widely used to constrain source parameters of near-surface events (e.g., chemical explosions and volcanic eruptions). While atmospheric conditions are critical to infrasound propagation and source parameter inversion, local atmospheric variability is often ignored by assuming homogeneous atmospheres, and their impact on the source inversion uncertainty has never been accounted for due to the lack of quantitative understanding of infrasound variability. We investigate atmospheric impacts on local infrasound propagation by repeated explosion experiments with a dense acoustic network and in situ atmospheric measurement. We perform full 3-D waveform simulations with local atmospheric data and numerical weather forecast model to quantify atmosphere-dependent infrasound variability and address the advantage and restriction of local weather data/numerical weather model for sound propagation simulation. Numerical simulations with stochastic atmosphere models also showed nonnegligible influence of atmospheric heterogeneity on infrasound amplitude, suggesting an important role of local turbulence.

Airway reopening: Steadily propagating bubbles in buckled elastic tubes

NASA Astrophysics Data System (ADS)

Heil, Matthias; Hazel, Andrew L.

2001-11-01

Many pulmonary diseases result in the collapse and occlusion of parts of the lung by viscous fluid. The subsequent airway reopening is generally assumed to occur via the propagation of an air finger into the collapsed, fluid-filled part of the airway. The problem has some similarity to the scenario of the `first breath' when air has to enter the fluid-filled lungs of a newborn baby for the first time. We have developed the first three-dimensional computational model of airway reopening, based on a finite-element solution of the free-surface Stokes equations, fully coupled to the equations of large-displacement shell theory. Following a brief discussion of the numerical method, we will present results that illustrate the 3D flow field by which the steadily propagating air finger reopens the non-axisymmetrically collapsed airway. Finally, we will contrast the system's behaviour to predictions from earlier two-dimensional models.

Sgr A* as Source of the Positrons Observed in the Galactic Center Region

NASA Astrophysics Data System (ADS)

Jean, Pierre; Guessoum, Nidhal; Ferrière, Katia

2017-01-01

We explore the possibility that a substantial fraction of the positrons observed to annihilate in the central region of our Galaxy come from the supermassive black hole Sgr A* that lies at the center. This idea was proposed by several authors, but the propagation of the emitted positrons into the bulge and beyond remained a serious problem for models of the origin of GC positrons. We assume models of positron production with different energies. The propagation of positrons from their production site is followed in detail with Monte-Carlo simulations, taking into account the physical conditions of the propagation regions as well as various physical interactions. Using the known physics of positron annihilation in astrophysical environments, we calculate the properties of the annihilation emission (time evolution and spatial distribution) for the different models under consideration. We present the results of these simulations and the conclusions/constraints that can be inferred from them.

Statistical Orbit Determination using the Particle Filter for Incorporating Non-Gaussian Uncertainties

NASA Technical Reports Server (NTRS)

Mashiku, Alinda; Garrison, James L.; Carpenter, J. Russell

2012-01-01

The tracking of space objects requires frequent and accurate monitoring for collision avoidance. As even collision events with very low probability are important, accurate prediction of collisions require the representation of the full probability density function (PDF) of the random orbit state. Through representing the full PDF of the orbit state for orbit maintenance and collision avoidance, we can take advantage of the statistical information present in the heavy tailed distributions, more accurately representing the orbit states with low probability. The classical methods of orbit determination (i.e. Kalman Filter and its derivatives) provide state estimates based on only the second moments of the state and measurement errors that are captured by assuming a Gaussian distribution. Although the measurement errors can be accurately assumed to have a Gaussian distribution, errors with a non-Gaussian distribution could arise during propagation between observations. Moreover, unmodeled dynamics in the orbit model could introduce non-Gaussian errors into the process noise. A Particle Filter (PF) is proposed as a nonlinear filtering technique that is capable of propagating and estimating a more complete representation of the state distribution as an accurate approximation of a full PDF. The PF uses Monte Carlo runs to generate particles that approximate the full PDF representation. The PF is applied in the estimation and propagation of a highly eccentric orbit and the results are compared to the Extended Kalman Filter and Splitting Gaussian Mixture algorithms to demonstrate its proficiency.

47 CFR 80.767 - Propagation curve.

Code of Federal Regulations, 2010 CFR

2010-10-01

... land (smooth earth); transmitting antena heights of 4,800, 3,200, 1,600, 800, 400, 200, and 100 feet; based on a receiving antenna height of 9 meters (30 feet), for the 156-162 MHz band. The use of this is... antenna heights lower than 9 meters (30 feet), assume that the field strength is the same as at 9 meters...

A cellular automaton model of wildfire propagation and extinction

Treesearch

Keith C. Clarke; James A. Brass; Phillip J. Riggan

1994-01-01

We propose a new model to predict the spatial and temporal behavior of wildfires. Fire spread and intensity were simulated using a cellular automaton model. Monte Carlo techniques were used to provide fire risk probabilities for areas where fuel loadings and topography are known. The model assumes predetermined or measurable environmental variables such as wind...

Strong Coupling of Single Emitters to Surface Plasmons

DTIC Science & Technology

2007-07-01

however, we can make an eikonal approximation,39 assuming that the plas- mons are emitted completely into the end of the tip z=0 and that the propagative...restricts the re- gimes of validity to ki w, ki d1. An additional set of as- sumptions is made in using the eikonal approximation to arrive at Eq. 49

Surface acoustic wave diffraction driven mechanisms in microfluidic systems.

PubMed

Fakhfouri, Armaghan; Devendran, Citsabehsan; Albrecht, Thomas; Collins, David J; Winkler, Andreas; Schmidt, Hagen; Neild, Adrian

2018-06-26

Acoustic forces arising from high-frequency surface acoustic waves (SAW) underpin an exciting range of promising techniques for non-contact manipulation of fluid and objects at micron scale. Despite increasing significance of SAW-driven technologies in microfluidics, the understanding of a broad range of phenomena occurring within an individual SAW system is limited. Acoustic effects including streaming and radiation force fields are often assumed to result from wave propagation in a simple planar fashion. The propagation patterns of a single SAW emanating from a finite-width source, however, cause a far richer range of physical effects. In this work, we seek a better understanding of the various effects arising from the incidence of a finite-width SAW beam propagating into a quiescent fluid. Through numerical and experimental verification, we present five distinct mechanisms within an individual system. These cause fluid swirling in two orthogonal planes, and particle trapping in two directions, as well as migration of particles in the direction of wave propagation. For a range of IDT aperture and channel dimensions, the relative importance of these mechanisms is evaluated.

The effect of wealth-based anti-expectation behaviors on public cooperation

NASA Astrophysics Data System (ADS)

Wang, Le; Chen, Tong; You, Xinshang; Wang, Yongjie

2018-03-01

Wealth difference is a common sense in our society. It is unreasonable to assume people have the same capability to donate money to the common pool in public goods game (PGG). Individuals have behavioral expectation towards their neighbors. In this paper, we introduce wealth-based anti-expectation mechanism to explore cooperation. Through numerical simulation results, we are glad to find that the anti-expectation mechanism could stimulate cooperation when the positive effects are equal to or larger than the negative effects from anti-expectation behaviors. Based on this mechanism, we propose propagation mechanism which aims to propagate the positive effects from the poor to inspire more people to choose cooperative strategies. When individuals are tolerant towards defectors, The fraction of cooperators increases with the increment of propagation distance. Enlarging the distance is not wise when individuals are harsh towards defectors. Additionally, we find that the more tolerant towards defectors we are, the higher the cooperation rate is in general. Therefore in PGG, we could consider one's anti-expectation towards others' behaviors and improve cooperation by propagating the poor's anti-expectation effects.

Nonlinear guided wave propagation in prestressed plates.

PubMed

Pau, Annamaria; Lanza di Scalea, Francesco

2015-03-01

The measurement of stress in a structure presents considerable interest in many fields of engineering. In this paper, the diagnostic potential of nonlinear elastic guided waves in a prestressed plate is investigated. To do so, an analytical model is formulated accounting for different aspects involved in the phenomenon. The fact that the initial strains can be finite is considered using the Green Lagrange strain tensor, and initial and final configurations are not merged, as it would be assumed in the infinitesimal strain theory. Moreover, an appropriate third-order expression of the strain energy of the hyperelastic body is adopted to account for the material nonlinearities. The model obtained enables to investigate both the linearized case, which gives the variation of phase and group velocity as a function of the initial stress, and the nonlinear case, involving second-harmonic generation as a function of the initial state of stress. The analysis is limited to Rayleigh-Lamb waves propagating in a plate. Three cases of initial prestress are considered, including prestress in the direction of the wave propagation, prestress orthogonal to the direction of wave propagation, and plane isotropic stress.

Modeling Propagation of Shock Waves in Metals

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

Howard, W M; Molitoris, J D

2005-08-19

We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P {approx} 300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and shear modulus depend on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. Atmore » melt the yield strength and shear modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that give the correct detonation velocity and C-J pressure (P {approx} 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov.« less

Modeling Propagation of Shock Waves in Metals

NASA Astrophysics Data System (ADS)

Howard, W. M.; Molitoris, J. D.

2006-07-01

We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P ˜ 300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and shear modulus depend on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and shear modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that give the correct detonation velocity and C-J pressure (P ˜ 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov.

Real-time 3-D space numerical shake prediction for earthquake early warning

NASA Astrophysics Data System (ADS)

Wang, Tianyun; Jin, Xing; Huang, Yandan; Wei, Yongxiang

2017-12-01

In earthquake early warning systems, real-time shake prediction through wave propagation simulation is a promising approach. Compared with traditional methods, it does not suffer from the inaccurate estimation of source parameters. For computation efficiency, wave direction is assumed to propagate on the 2-D surface of the earth in these methods. In fact, since the seismic wave propagates in the 3-D sphere of the earth, the 2-D space modeling of wave direction results in inaccurate wave estimation. In this paper, we propose a 3-D space numerical shake prediction method, which simulates the wave propagation in 3-D space using radiative transfer theory, and incorporate data assimilation technique to estimate the distribution of wave energy. 2011 Tohoku earthquake is studied as an example to show the validity of the proposed model. 2-D space model and 3-D space model are compared in this article, and the prediction results show that numerical shake prediction based on 3-D space model can estimate the real-time ground motion precisely, and overprediction is alleviated when using 3-D space model.

On the wall-normal velocity of the compressible boundary-layer equations

NASA Technical Reports Server (NTRS)

Pruett, C. David

1991-01-01

Numerical methods for the compressible boundary-layer equations are facilitated by transformation from the physical (x,y) plane to a computational (xi,eta) plane in which the evolution of the flow is 'slow' in the time-like xi direction. The commonly used Levy-Lees transformation results in a computationally well-behaved problem for a wide class of non-similar boundary-layer flows, but it complicates interpretation of the solution in physical space. Specifically, the transformation is inherently nonlinear, and the physical wall-normal velocity is transformed out of the problem and is not readily recovered. In light of recent research which shows mean-flow non-parallelism to significantly influence the stability of high-speed compressible flows, the contribution of the wall-normal velocity in the analysis of stability should not be routinely neglected. Conventional methods extract the wall-normal velocity in physical space from the continuity equation, using finite-difference techniques and interpolation procedures. The present spectrally-accurate method extracts the wall-normal velocity directly from the transformation itself, without interpolation, leaving the continuity equation free as a check on the quality of the solution. The present method for recovering wall-normal velocity, when used in conjunction with a highly-accurate spectral collocation method for solving the compressible boundary-layer equations, results in a discrete solution which is extraordinarily smooth and accurate, and which satisfies the continuity equation nearly to machine precision. These qualities make the method well suited to the computation of the non-parallel mean flows needed by spatial direct numerical simulations (DNS) and parabolized stability equation (PSE) approaches to the analysis of stability.

The nonlinear evolution of modes on unstable stratified shear layers

NASA Technical Reports Server (NTRS)

Blackaby, Nicholas; Dando, Andrew; Hall, Philip

1993-01-01

The nonlinear development of disturbances in stratified shear flows (having a local Richardson number of value less than one quarter) is considered. Such modes are initially fast growing but, like related studies, we assume that the viscous, non-parallel spreading of the shear layer results in them evolving in a linear fashion until they reach a position where their amplitudes are large enough and their growth rates have diminished sufficiently so that amplitude equations can be derived using weakly nonlinear and non-equilibrium critical-layer theories. Four different basic integro-differential amplitude equations are possible, including one due to a novel mechanism; the relevant choice of amplitude equation, at a particular instance, being dependent on the relative sizes of the disturbance amplitude, the growth rate of the disturbance, its wavenumber, and the viscosity of the fluid. This richness of choice of possible nonlinearities arises mathematically from the indicial Frobenius roots of the governing linear inviscid equation (the Taylor-Goldstein equation) not, in general, differing by an integer. The initial nonlinear evolution of a mode will be governed by an integro-differential amplitude equations with a cubic nonlinearity but the resulting significant increase in the size of the disturbance's amplitude leads on to the next stage of the evolution process where the evolution of the mode is governed by an integro-differential amplitude equations with a quintic nonlinearity. Continued growth of the disturbance amplitude is expected during this stage, resulting in the effects of nonlinearity spreading to outside the critical level, by which time the flow has become fully nonlinear.

Physically Based Failure Criteria for Transverse Matrix Cracking

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Camanho, Pedro P.

2003-01-01

A criterion for matrix failure of laminated composite plies in transverse tension and in-plane shear is developed by examining the mechanics of transverse matrix crack growth. Matrix cracks are assumed to initiate from manufacturing defects and can propagate within planes parallel to the fiber direction and normal to the ply mid-plane. Fracture mechanics models of cracks in unidirectional laminates, embedded plies and outer plies are developed to determine the onset and direction of propagation for unstable crack growth. The models for each ply configuration relate ply thickness and ply toughness to the corresponding in-situ ply strength. Calculated results for several materials are shown to correlate well with experimental results.

Propagation of sound waves through a linear shear layer: A closed form solution

NASA Technical Reports Server (NTRS)

Scott, J. N.

1978-01-01

Closed form solutions are presented for sound propagation from a line source in or near a shear layer. The analysis was exact for all frequencies and was developed assuming a linear velocity profile in the shear layer. This assumption allowed the solution to be expressed in terms of parabolic cyclinder functions. The solution is presented for a line monopole source first embedded in the uniform flow and then in the shear layer. Solutions are also discussed for certain types of dipole and quadrupole sources. Asymptotic expansions of the exact solutions for small and large values of Strouhal number gave expressions which correspond to solutions previously obtained for these limiting cases.

Mathematical Modeling of Torsional Surface Wave Propagation in a Non-Homogeneous Transverse Isotropic Elastic Solid Semi-Infinite Medium Under a Layer

NASA Astrophysics Data System (ADS)

Sethi, M.; Sharma, A.; Vasishth, A.

2017-05-01

The present paper deals with the mathematical modeling of the propagation of torsional surface waves in a non-homogeneous transverse isotropic elastic half-space under a rigid layer. Both rigidities and density of the half-space are assumed to vary inversely linearly with depth. Separation of variable method has been used to get the analytical solutions for the dispersion equation of the torsional surface waves. Also, the effects of nonhomogeneities on the phase velocity of torsional surface waves have been shown graphically. Also, dispersion equations have been derived for some particular cases, which are in complete agreement with some classical results.

A three-dimensional refractive index model for simulation of optical wave propagation in atmospheric turbulence

NASA Astrophysics Data System (ADS)

Paramonov, P. V.; Vorontsov, A. M.; Kunitsyn, V. E.

2015-10-01

Numerical modeling of optical wave propagation in atmospheric turbulence is traditionally performed with using the so-called "split"-operator method, when the influence of the propagation medium's refractive index inhomogeneities is accounted for only within a system of infinitely narrow layers (phase screens) where phase is distorted. Commonly, under certain assumptions, such phase screens are considered as mutually statistically uncorrelated. However, in several important applications including laser target tracking, remote sensing, and atmospheric imaging, accurate optical field propagation modeling assumes upper limitations on interscreen spacing. The latter situation can be observed, for instance, in the presence of large-scale turbulent inhomogeneities or in deep turbulence conditions, where interscreen distances become comparable with turbulence outer scale and, hence, corresponding phase screens cannot be statistically uncorrelated. In this paper, we discuss correlated phase screens. The statistical characteristics of screens are calculated based on a representation of turbulent fluctuations of three-dimensional (3D) refractive index random field as a set of sequentially correlated 3D layers displaced in the wave propagation direction. The statistical characteristics of refractive index fluctuations are described in terms of the von Karman power spectrum density. In the representation of these 3D layers by corresponding phase screens, the geometrical optics approximation is used.

Investigations of Vacuum Ultraviolet and Soft X-Ray Lasers.

DTIC Science & Technology

1984-03-01

be achieved. A similar situation has been with the excitation energy of an excited level b referred to as excited state beta-decay in astro - -. of...we assumed that the laser field propagates in the x3 -direction. The corresponding momenta are B( fx )) = Z6(x - xn)llf’(X)l, Pu t( pO+p3)lv/, P- = (pO_

Heterodyne efficiency of a coherent free-space optical communication model through atmospheric turbulence.

PubMed

Ren, Yongxiong; Dang, Anhong; Liu, Ling; Guo, Hong

2012-10-20

The heterodyne efficiency of a coherent free-space optical (FSO) communication model under the effects of atmospheric turbulence and misalignment is studied in this paper. To be more general, both the transmitted beam and local oscillator beam are assumed to be partially coherent based on the Gaussian Schell model (GSM). By using the derived analytical form of the cross-spectral function of a GSM beam propagating through atmospheric turbulence, a closed-form expression of heterodyne efficiency is derived, assuming that the propagation directions for the transmitted and local oscillator beams are slightly different. Then the impacts of atmospheric turbulence, configuration of the two beams (namely, beam radius and spatial coherence width), detector radius, and misalignment angle over heterodyne efficiency are examined. Numerical results suggest that the beam radius of the two overlapping beams can be optimized to achieve a maximum heterodyne efficiency according to the turbulence conditions and the detector radius. It is also found that atmospheric turbulence conditions will significantly degrade the efficiency of heterodyne detection, and compared to fully coherent beams, partially coherent beams are less sensitive to the changes in turbulence conditions and more robust against misalignment at the receiver.

Fully kinetic Biermann battery and associated generation of pressure anisotropy

NASA Astrophysics Data System (ADS)

Schoeffler, K. M.; Loureiro, N. F.; Silva, L. O.

2018-03-01

The dynamical evolution of a fully kinetic, collisionless system with imposed background density and temperature gradients is investigated analytically. The temperature gradient leads to the generation of temperature anisotropy, with the temperature along the gradient becoming larger than that in the direction perpendicular to it. This causes the system to become unstable to pressure anisotropy driven instabilities, dominantly to the electron Weibel instability. When both density and temperature gradients are present and nonparallel to each other, we obtain a Biermann-like linear-in-time magnetic field growth. Accompanying particle-in-cell numerical simulations are shown to confirm our analytical results.

Theoretical and Computational Studies of Stability, Transition and Flow Control in High-Speed Flows

DTIC Science & Technology

2011-02-22

A. H. Nayfeh. Nonparallel stability of boundary layers with pressure gradients and suction. Technical Report AGARD - CP -224, 1977. [Squ33] H. B. Squire...only. µ = µr ( T Tr )3/2 Tr + Ts T + Ts , (2.13) 8 K = µcp Pr , (2.14) where µr = 1.7894 × 10−5 Ns/m2, Tr = 288.0 K, Ts = 110.33 K, and cp is the...fraction of species s Cpf = frozen specific heat, cal/g-mole-K Cp ,s = specific heat at constant pressure of species s, cal/g-mole Dij = binary diffusion

Seventy years of pancreatic physiology: take a look back.

PubMed

Morisset, Jean

2014-11-01

This review article has 4 major objectives to follow pancreatic physiology development more than close to 70 years of intensive and productive basic research. At first, the review will focus on secretion of the pancreatic enzymes with (1) the controls involved, (2) the interrelations existing between secretion and synthesis of these enzymes, (3) the enzymes' adaptation to the constituents of the diet, and (4) whether secretion of the different enzymes is parallel or nonparallel. Second, growth and regeneration of the pancreatic gland will be looked at in relation to the factors involved and the target cells implicated.

Study of the surface wave off-great-circle propagation based on dense seismic array: a case study in Northeast China

NASA Astrophysics Data System (ADS)

Chen, H.; Chong, J.

2016-12-01

The traditional surface wave tomography is based on the ray theory, which assumes that surface wave propagates along the great-circle. The great-circle assumption is valid only when the size of the anomaly is larger than the width of the Fresnel zone and the lateral variation is relatively smooth. However, off-great-circle propagation may occur when the surface wave travels across tectonic boundaries with strong heterogeneity and sharp velocity change, e.g., continental margin, mid-ridge and sea trench, resulting in arrival angle anomaly and multi-pathing effect. The off-great-circle propagation may deviate the result of surface wave tomography based on great-circle approximation, so it is of great importance to study the off-great-circle propagation. In this study, we used the teleseismic waveforms from September 2009 to August 2011, recorded by the NECESSArray in Northeast China, to study the off-great-circle propagation of Rayleigh wave by the Beamforming method. Our results show that the off-great-circle effect increases with decreasing period. At the period of 60 s, the off-great-circle effect is relatively weak and the Rayleigh wave propagates approximately along the great-circle. While at the period of 20 s, the off-great-circle effect becomes strong, the arrival angle anomaly measured from some events can be as large as 20º, and obvious multi-pathing effect is also observed. Lateral variations of the arrival angle anomaly and phase velocity have also been found in the study region, which may be correlated with the lithosphere heterogeneity in Northeast China. Our results demonstrate the necessity to study the surface wave off-great-circle propagation. Acknowledgement: This study is financially supported by National Natural Science Foundation of China under Grant No. 41590854.

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

Conroy, Aindriú; Mazumdar, Anupam; Koshelev, Alexey S., E-mail: a.conroy@lancaster.ac.uk, E-mail: alexey@ubi.pt, E-mail: a.mazumdar@lancaster.ac.uk

Einstein's General theory of relativity permits spacetime singularities, where null geodesic congruences focus in the presence of matter, which satisfies an appropriate energy condition. In this paper, we provide a minimal defocusing condition for null congruences without assuming any ansatz -dependent background solution. The two important criteria are: (1) an additional scalar degree of freedom, besides the massless graviton must be introduced into the spacetime; and (2) an infinite derivative theory of gravity is required in order to avoid tachyons or ghosts in the graviton propagator. In this regard, our analysis strengthens earlier arguments for constructing non-singular bouncing cosmologies withinmore » an infinite derivative theory of gravity, without assuming any ansatz to solve the full equations of motion.« less

Influence of off-great-circle propagation of Rayleigh waves on event-based surface wave tomography in Northeast China

NASA Astrophysics Data System (ADS)

Chen, Haopeng; Ni, Sidao; Chu, Risheng; Chong, Jiajun; Liu, Zhikun; Zhu, Liangbao

2018-05-01

Surface waves are generally assumed to propagate along great-circle paths in most surface-wave tomography. However, when lateral heterogeneity is strong, off-great-circle propagation may occur and deteriorate surface wave tomography results based on the great-circle assumption. In this study, we used teleseismic waveforms recorded by the NECESSArray in Northeast China to study off-great-circle propagation of Rayleigh waves using the beamforming method and evaluated the influence of off-great-circle propagation on event-based surface wave tomography. The results show that arrival angle anomalies generally increase with decreasing period. The arrival angle anomalies at 60 and 50 s periods are smaller than that at 40 and 30 s periods, which indicates that the off-great-circle propagation is relatively weak for longer periods. At 30 s period, the arrival angle anomalies are relatively larger and some of the measurements can exceed 20°, which represents a strong off-great-circle propagation effect. In some areas, the arrival angle anomalies of adjacent events differ significantly, which may be attributed to multipathing propagation of surface waves. To evaluate the influence of off-great-circle propagation on event-based surface wave tomography, we used measured arrival angle anomalies to correct two-station phase velocity measurements, and performed azimuthal anisotropy tomography using dispersion datasets with and without the arrival angle correction. At longer periods, such as 60 s, the influence of off-great-circle propagation on surface wave tomography is weak even though the corrected model has better data fit than the uncorrected model. However, the influence of off-great-circle propagation is non-negligible at short periods. The tomography results at 30 s period show that the differences in phase velocity, the strength of anisotropy and the fast direction can be as large as 1.5 per cent, 1.0 per cent and 30°, respectively. Furthermore, the corrected phase velocity is systematically lower than that without correction. This study illustrates the necessity of studying the off-great-circle propagation of surface waves to improve the accuracy of event-based surface wave tomography, especially for shorter periods.

Practical and adequate approach to modeling light propagation in an adult head with low-scattering regions by use of diffusion theory.

PubMed

Koyama, Tatsuya; Iwasaki, Atsushi; Ogoshi, Yosuke; Okada, Eiji

2005-04-10

A practical and adequate approach to modeling light propagation in an adult head with a low-scattering cerebrospinal fluid (CSF) region by use of diffusion theory was investigated. The diffusion approximation does not hold in a nonscattering or low-scattering regions. The hybrid radiosity-diffusion method was adopted to model the light propagation in the head with a nonscattering region. In the hybrid method the geometry of the nonscattering region is acquired as a priori information. In reality, low-level scattering occurs in the CSF region and may reduce the error caused by the diffusion approximation. The partial optical path length and the spatial sensitivity profile calculated by the finite-element method agree well with those calculated by the Monte Carlo method in the case in which the transport scattering coefficient of the CSF layer is greater than 0.3 mm(-1). Because it is feasible to assume that the transport scattering coefficient of a CSF layer is 0.3 mm(-1), it is practical to adopt diffusion theory to the modeling of light propagation in an adult head as an alternative to the hybrid method.

Practical and adequate approach to modeling light propagation in an adult head with low-scattering regions by use of diffusion theory

NASA Astrophysics Data System (ADS)

Koyama, Tatsuya; Iwasaki, Atsushi; Ogoshi, Yosuke; Okada, Eiji

2005-04-01

A practical and adequate approach to modeling light propagation in an adult head with a low-scattering cerebrospinal fluid (CSF) region by use of diffusion theory was investigated. The diffusion approximation does not hold in a nonscattering or low-scattering regions. The hybrid radiosity-diffusion method was adopted to model the light propagation in the head with a nonscattering region. In the hybrid method the geometry of the nonscattering region is acquired as a priori information. In reality, low-level scattering occurs in the CSF region and may reduce the error caused by the diffusion approximation. The partial optical path length and the spatial sensitivity profile calculated by the finite-element method agree well with those calculated by the Monte Carlo method in the case in which the transport scattering coefficient of the CSF layer is greater than 0.3 mm^-1. Because it is feasible to assume that the transport scattering coefficient of a CSF layer is 0.3 mm^-1, it is practical to adopt diffusion theory to the modeling of light propagation in an adult head as an alternative to the hybrid method.

Modeling the Propagation of Shock Waves in Metals

NASA Astrophysics Data System (ADS)

Howard, W. Michael

2005-07-01

We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P ˜300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and bulk modulus depends on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and bulk modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that gives the correct detonation velocity and C-J pressure (P ˜ 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov. We also discuss the dependence of our results upon our material model for aluminum.

Numerical simulation of premixed flame propagation in a closed tube

NASA Astrophysics Data System (ADS)

Kuzuu, Kazuto; Ishii, Katsuya; Kuwahara, Kunio

1996-08-01

Premixed flame propagation of methane-air mixture in a closed tube is estimated through a direct numerical simulation of the three-dimensional unsteady Navier-Stokes equations coupled with chemical reaction. In order to deal with a combusting flow, an extended version of the MAC method, which can be applied to a compressible flow with strong density variation, is employed as a numerical method. The chemical reaction is assumed to be an irreversible single step reaction between methane and oxygen. The chemical species are CH 4, O 2, N 2, CO 2, and H 2O. In this simulation, we reproduce a formation of a tulip flame in a closed tube during the flame propagation. Furthermore we estimate not only a two-dimensional shape but also a three-dimensional structure of the flame and flame-induced vortices, which cannot be observed in the experiments. The agreement between the calculated results and the experimental data is satisfactory, and we compare the phenomenon near the side wall with the one in the corner of the tube.

A DERATING METHOD FOR THERAPEUTIC APPLICATIONS OF HIGH INTENSITY FOCUSED ULTRASOUND

PubMed Central

Bessonova, O.V.; Khokhlova, V.A.; Canney, M.S.; Bailey, M.R.; Crum, L.A.

2010-01-01

Current methods of determining high intensity focused ultrasound (HIFU) fields in tissue rely on extrapolation of measurements in water assuming linear wave propagation both in water and in tissue. Neglecting nonlinear propagation effects in the derating process can result in significant errors. In this work, a new method based on scaling the source amplitude is introduced to estimate focal parameters of nonlinear HIFU fields in tissue. Focal values of acoustic field parameters in absorptive tissue are obtained from a numerical solution to a KZK-type equation and are compared to those simulated for propagation in water. Focal waveforms, peak pressures, and intensities are calculated over a wide range of source outputs and linear focusing gains. Our modeling indicates, that for the high gain sources which are typically used in therapeutic medical applications, the focal field parameters derated with our method agree well with numerical simulation in tissue. The feasibility of the derating method is demonstrated experimentally in excised bovine liver tissue. PMID:20582159

A derating method for therapeutic applications of high intensity focused ultrasound

NASA Astrophysics Data System (ADS)

Bessonova, O. V.; Khokhlova, V. A.; Canney, M. S.; Bailey, M. R.; Crum, L. A.

2010-05-01

Current methods of determining high intensity focused ultrasound (HIFU) fields in tissue rely on extrapolation of measurements in water assuming linear wave propagation both in water and in tissue. Neglecting nonlinear propagation effects in the derating process can result in significant errors. A new method based on scaling the source amplitude is introduced to estimate focal parameters of nonlinear HIFU fields in tissue. Focal values of acoustic field parameters in absorptive tissue are obtained from a numerical solution to a KZK-type equation and are compared to those simulated for propagation in water. Focal wave-forms, peak pressures, and intensities are calculated over a wide range of source outputs and linear focusing gains. Our modeling indicates, that for the high gain sources which are typically used in therapeutic medical applications, the focal field parameters derated with our method agree well with numerical simulation in tissue. The feasibility of the derating method is demonstrated experimentally in excised bovine liver tissue.

A DERATING METHOD FOR THERAPEUTIC APPLICATIONS OF HIGH INTENSITY FOCUSED ULTRASOUND.

PubMed

Bessonova, O V; Khokhlova, V A; Canney, M S; Bailey, M R; Crum, L A

2010-01-01

Current methods of determining high intensity focused ultrasound (HIFU) fields in tissue rely on extrapolation of measurements in water assuming linear wave propagation both in water and in tissue. Neglecting nonlinear propagation effects in the derating process can result in significant errors. In this work, a new method based on scaling the source amplitude is introduced to estimate focal parameters of nonlinear HIFU fields in tissue. Focal values of acoustic field parameters in absorptive tissue are obtained from a numerical solution to a KZK-type equation and are compared to those simulated for propagation in water. Focal waveforms, peak pressures, and intensities are calculated over a wide range of source outputs and linear focusing gains. Our modeling indicates, that for the high gain sources which are typically used in therapeutic medical applications, the focal field parameters derated with our method agree well with numerical simulation in tissue. The feasibility of the derating method is demonstrated experimentally in excised bovine liver tissue.

Three-dimensional elastic-plastic finite-element analysis of fatigue crack propagation

NASA Technical Reports Server (NTRS)

Goglia, G. L.; Chermahini, R. G.

1985-01-01

Fatigue cracks are a major problem in designing structures subjected to cyclic loading. Cracks frequently occur in structures such as aircraft and spacecraft. The inspection intervals of many aircraft structures are based on crack-propagation lives. Therefore, improved prediction of propagation lives under flight-load conditions (variable-amplitude loading) are needed to provide more realistic design criteria for these structures. The main thrust was to develop a three-dimensional, nonlinear, elastic-plastic, finite element program capable of extending a crack and changing boundary conditions for the model under consideration. The finite-element model is composed of 8-noded (linear-strain) isoparametric elements. In the analysis, the material is assumed to be elastic-perfectly plastic. The cycle stress-strain curve for the material is shown Zienkiewicz's initial-stress method, von Mises's yield criterion, and Drucker's normality condition under small-strain assumptions are used to account for plasticity. The three-dimensional analysis is capable of extending the crack and changing boundary conditions under cyclic loading.

A parametric analysis of waves propagating in a porous solid saturated by a three-phase fluid.

PubMed

Santos, Juan E; Savioli, Gabriela B

2015-11-01

This paper presents an analysis of a model for the propagation of waves in a poroelastic solid saturated by a three-phase viscous, compressible fluid. The constitutive relations and the equations of motion are stated first. Then a plane wave analysis determines the phase velocities and attenuation coefficients of the four compressional waves and one shear wave that propagate in this type of medium. A procedure to compute the elastic constants in the constitutive relations is defined next. Assuming the knowledge of the shear modulus of the dry matrix, the other elastic constants in the stress-strain relations are determined by employing ideal gedanken experiments generalizing those of Biot's theory for single-phase fluids. These experiments yield expressions for the elastic constants in terms of the properties of the individual solid and fluids phases. Finally the phase velocities and attenuation coefficients of all waves are computed for a sample of Berea sandstone saturated by oil, gas, and water.

Propagation of a Gaussian-beam wave in general anisotropic turbulence

NASA Astrophysics Data System (ADS)

Andrews, L. C.; Phillips, R. L.; Crabbs, R.

2014-10-01

Mathematical models for a Gaussian-beam wave propagating through anisotropic non-Kolmogorov turbulence have been developed in the past by several researchers. In previous publications, the anisotropic spatial power spectrum model was based on the assumption that propagation was in the z direction with circular symmetry maintained in the orthogonal xy-plane throughout the path. In the present analysis, however, the anisotropic spectrum model is no longer based on a single anisotropy parameter—instead, two such parameters are introduced in the orthogonal xyplane so that circular symmetry in this plane is no longer required. In addition, deviations from the 11/3 power-law behavior in the spectrum model are allowed by assuming power-law index variations 3 < α < 4 . In the current study we develop theoretical models for beam spot size, spatial coherence, and scintillation index that are valid in weak irradiance fluctuation regimes as well as in deep turbulence, or strong irradiance fluctuation regimes. These new results are compared with those derived from the more specialized anisotropic spectrum used in previous analyses.

Amplitude variations during SIDs in 10.2 and 13.6 kHz waves propagating long distances in the subionospheric waveguide - Theoretical interpretation

NASA Astrophysics Data System (ADS)

Charcosset, G.; Tixier, M.

1981-12-01

During sudden ionospheric disturbances (SIDs), vertical electric field amplitude variations of waves emitted at 10.2 and 13.6 kHz in Norway and Liberia and observed in France were found to result in a regular decrease at the former wavelength and more complex behavior at the latter, where amplitude behavior depends on the importance of the SID. A theoretical interpretation employing a waveguide mode hypothesis of long distance wave propagation is presented, in which it is assumed that the D-region ionization enhancement produced by the solar X-ray flux during SID can be represented by a decrease of the waveguide height in which the shape of the density profile remains unchanged.

Electric dipole radiation at VLF in a uniform warm magneto-plasma.

NASA Technical Reports Server (NTRS)

Wang, T. N. C.; Bell, T. F.

1972-01-01

Use of a linear full electromagnetic wave theory to calculate the input impedance of an electric antenna embedded in a uniform, lossless, unbounded warm magnetoplasma, which is assumed to consist of warm electrons and cold ions. In calculating the dipole radiation resistance for the thermal modes and the thermally modified whistler mode the analysis includes the finite temperature only for the electrons. In deriving the formal solution of the warm plasma dipole input impedance a full-wave analysis is used and two antenna orientations are considered, parallel and perpendicular to the static magnetic field. A general dispersion equation governing the modes of propagation is derived and a detailed analysis is made of the propagation characteristics of these modes.

Solar flare particle propagation: Comparision of a new analytic solution with spacecraft measurements. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Lupton, J. E.

1972-01-01

An analytic solution was obtained to the complete Fokker-Planck equation for solar flare particle propagation including the effects of convection, energy-change, corotation, and diffusion. It is assumed that the particles are injected impulsively at a single point in space, and that a boundary exists beyond which the particles are free to escape. Several solar flare particle events were observed with solar and galactic cosmic ray experiment aboard OGO 6. Detailed comparisons of the predictions of the solution with observations of 1 to 70 MeV protons show that the model adequately describes both the rise and decay times. The solution also yields a time evolution for the vector anisotropy which agrees well with reported observations.

Electromagnetic plasma wave propagation along a magnetic field. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Olson, C. L.

1970-01-01

The linearized response of a Vlasov plasma to the steady-state excitation of transverse plasma waves along an external magnetic field is examined. Assuming a delta-function excitation mechanism, and performing a detailed Vlasov-Maxwell equation analysis using Fourier-Laplace transforms, the plasma response is found to consist of three terms: a branch-cut term, a free-streaming term, and a dielectric-pole term. Also considered is the phenomenon of plasma wave echoes. The case of longitudinal electrostatic waves is extended to the case of transverse plasma waves that propagate along an external magnetic field. It is shown that a transverse echo results in lowest order only when one excitation is transverse and the other is longitudinal.

Parallel and nonparallel behavioural evolution in response to parasitism and predation in Trinidadian guppies.

PubMed

Jacquin, L; Reader, S M; Boniface, A; Mateluna, J; Patalas, I; Pérez-Jvostov, F; Hendry, A P

2016-07-01

Natural enemies such as predators and parasites are known to shape intraspecific variability of behaviour and personality in natural populations, yet several key questions remain: (i) What is the relative importance of predation vs. parasitism in shaping intraspecific variation of behaviour across generations? (ii) What are the contributions of genetic and plastic effects to this behavioural divergence? (iii) And to what extent are responses to predation and parasitism repeatable across independent evolutionary lineages? We addressed these questions using Trinidadian guppies (Poecilia reticulata) (i) varying in their exposure to dangerous fish predators and Gyrodactylus ectoparasites for (ii) both wild-caught F0 and laboratory-reared F2 individuals and coming from (iii) multiple independent evolutionary lineages (i.e. independent drainages). Several key findings emerged. First, a population's history of predation and parasitism influenced behavioural profiles, but to different extent depending on the behaviour considered (activity, shoaling or boldness). Second, we had evidence for some genetic effects of predation regime on behaviour, with differences in activity of F2 laboratory-reared individuals, but not for parasitism, which had only plastic effects on the boldness of wild-caught F0 individuals. Third, the two lineages showed a mixture of parallel and nonparallel responses to predation/parasitism, with parallel responses being stronger for predation than for parasitism and for activity and boldness than for shoaling. These findings suggest that different sets of behaviours provide different pay-offs in alternative predation/parasitism environments and that parasitism has more transient effects in shaping intraspecific variation of behaviour than does predation. © 2016 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2016 European Society For Evolutionary Biology.

Brittle fracture in viscoelastic materials as a pattern-formation process

NASA Astrophysics Data System (ADS)

Fleck, M.; Pilipenko, D.; Spatschek, R.; Brener, E. A.

2011-04-01

A continuum model of crack propagation in brittle viscoelastic materials is presented and discussed. Thereby, the phenomenon of fracture is understood as an elastically induced nonequilibrium interfacial pattern formation process. In this spirit, a full description of a propagating crack provides the determination of the entire time dependent shape of the crack surface, which is assumed to be extended over a finite and self-consistently selected length scale. The mechanism of crack propagation, that is, the motion of the crack surface, is then determined through linear nonequilibrium transport equations. Here we consider two different mechanisms, a first-order phase transformation and surface diffusion. We give scaling arguments showing that steady-state solutions with a self-consistently selected propagation velocity and crack shape can exist provided that elastodynamic or viscoelastic effects are taken into account, whereas static elasticity alone is not sufficient. In this respect, inertial effects as well as viscous damping are identified to be sufficient crack tip selection mechanisms. Exploring the arising description of brittle fracture numerically, we study steady-state crack propagation in the viscoelastic and inertia limit as well as in an intermediate regime, where both effects are important. The arising free boundary problems are solved by phase field methods and a sharp interface approach using a multipole expansion technique. Different types of loading, mode I, mode III fracture, as well as mixtures of them, are discussed.

A Workflow to Improve the Alignment of Prostate Imaging with Whole-mount Histopathology.

PubMed

Yamamoto, Hidekazu; Nir, Dror; Vyas, Lona; Chang, Richard T; Popert, Rick; Cahill, Declan; Challacombe, Ben; Dasgupta, Prokar; Chandra, Ashish

2014-08-01

Evaluation of prostate imaging tests against whole-mount histology specimens requires accurate alignment between radiologic and histologic data sets. Misalignment results in false-positive and -negative zones as assessed by imaging. We describe a workflow for three-dimensional alignment of prostate imaging data against whole-mount prostatectomy reference specimens and assess its performance against a standard workflow. Ethical approval was granted. Patients underwent motorized transrectal ultrasound (Prostate Histoscanning) to generate a three-dimensional image of the prostate before radical prostatectomy. The test workflow incorporated steps for axial alignment between imaging and histology, size adjustments following formalin fixation, and use of custom-made parallel cutters and digital caliper instruments. The control workflow comprised freehand cutting and assumed homogeneous block thicknesses at the same relative angles between pathology and imaging sections. Thirty radical prostatectomy specimens were histologically and radiologically processed, either by an alignment-optimized workflow (n = 20) or a control workflow (n = 10). The optimized workflow generated tissue blocks of heterogeneous thicknesses but with no significant drifting in the cutting plane. The control workflow resulted in significantly nonparallel blocks, accurately matching only one out of four histology blocks to their respective imaging data. The image-to-histology alignment accuracy was 20% greater in the optimized workflow (P < .0001), with higher sensitivity (85% vs. 69%) and specificity (94% vs. 73%) for margin prediction in a 5 × 5-mm grid analysis. A significantly better alignment was observed in the optimized workflow. Evaluation of prostate imaging biomarkers using whole-mount histology references should include a test-to-reference spatial alignment workflow. Copyright © 2014 AUR. Published by Elsevier Inc. All rights reserved.

Final Report on Scientific Activities Pursuant to the Provisions of AFOSR Grant 79-0018-A during the Period November 1, 1982 to October 31, 1983.

DTIC Science & Technology

1983-10-31

nonparallel line segments, itand it2’ with unit exterior normals vIand v 2- Proceeding as before we can show, applying the Rolmgren theorem together...application of (2.7) readily shows that z) le -tg(t) , Re(z) > P. (2.9) Re(z)-A L 2 [0 0) Let rr,p denote the positively oriented D-shaped contour consisting of...dedness of p in strips I le (z) 4- p . Proof of Theorem 4.6. From Theorem 4.3 the functions ezkt form a Schauder basis for L2 [-,wJ; equivalently, the

Turbine airfoil with an internal cooling system having vortex forming turbulators

DOEpatents

Lee, Ching-Pang

2014-12-30

A turbine airfoil usable in a turbine engine and having at least one cooling system is disclosed. At least a portion of the cooling system may include one or more cooling channels having a plurality of turbulators protruding from an inner surface and positioned generally nonorthogonal and nonparallel to a longitudinal axis of the airfoil cooling channel. The configuration of turbulators may create a higher internal convective cooling potential for the blade cooling passage, thereby generating a high rate of internal convective heat transfer and attendant improvement in overall cooling performance. This translates into a reduction in cooling fluid demand and better turbine performance.

Wake excited in plasma by an ultrarelativistic pointlike bunch

DOE PAGES

Stupakov, G.; Breizman, B.; Khudik, V.; ...

2016-10-05

We study propagation of a relativistic electron bunch through a cold plasma assuming that the transverse and longitudinal dimensions of the bunch are much smaller than the plasma collisionless skin depth. Treating the bunch as a point charge and assuming that its charge is small, we derive a simplified system of equations for the plasma electrons and show that, through a simple rescaling of variables, the bunch charge can be eliminated from the equations. The equations demonstrate an ion cavity formed behind the driver. They are solved numerically and the scaling of the cavity parameters with the driver charge ismore » obtained. As a result, a numerical solution for the case of a positively charged driver is also found.« less

Limits on the critical length of damage in weak snowpack layers from en-echelon slab fracture spacing observed during avalanche release

NASA Astrophysics Data System (ADS)

Gauthier, D.; Hutchinson, D. J.

2012-04-01

We present simple estimates of the maximum possible critical length of damage or fracture in a weak snowpack layer required to maintain the propagation that leads to avalanche release, based on observations of 'en-echelon' slab fractures during avalanche release. These slab fractures may be preserved in situ if the slab does not slide down slope. The en-echelon fractures are spaced evenly, normally with one every one to ten metres or more. We consider a simple two-dimensional model of a slab and weak layer, with upslope fracture propagating the weak layer, and examine the relationship between the weak layer and en-echelon slab fractures. We assume that the slab fracture occurs in tension, and initiates at either the base or surface of the slab in the area of peak tensile stress at the tip of the weak layer fracture. We also assume that if at the time the slab is completely bisected by fracture the propagation in the weak layer will arrest spontaneously if it has not advanced beyond the critical length. In this scenario, en-echelon slab fractures may only form when the weak layer fracture repeatedly exceeds the critical length; otherwise, there could be only a single slab fracture. We estimate the position of the weak layer fracture at the time of slab bisection using the slab thickness and ratio between the fracture speeds in the weak layer and slab. We show that in the simple model en-echelon fractures only form if the slab thickness multiplied by the velocity ratio is greater than the critical length. Of course, the critical length must also be less than the en-echelon spacing. It follows that the first relationship must be valid independent of the occurrence of en-echelon fractures, although the speed ratio may be process-dependent and difficult to estimate. We use this method to calculate maximum critical lengths for propagation in actual avalanches with and without en echelon fractures, and discuss the implications for comparing competing propagation models. Furthermore, we discuss the possible applications to other cases of progressive basal failure and en-echelon fracturing, e.g. the ribbed flow bowls or so-called 'thumbprint' morphology which sometimes develops during landsliding in sensitive clay soils.

Graviton propagation within the context of the D-material universe.

PubMed

Elghozi, Thomas; Mavromatos, Nick E; Sakellariadou, Mairi

2017-01-01

Motivated by the recent breakthrough of the detection of Gravitational Waves (GW) from coalescent black holes by the aLIGO interferometers, we study the propagation of GW in the D-material universe , which we have recently shown to be compatible with large-scale structure and inflationary phenomenology. The medium of D-particles induces an effective mass for the graviton, as a consequence of the formation of recoil-velocity field condensates due to the underlying Born-Infeld dynamics. There is a competing effect, due to a super-luminal refractive index, as a result of the gravitational energy of D-particles acting as a dark-matter component, with which propagating gravitons interact. We examine conditions for the condensate under which the latter effect is sub-leading. We argue that if quantum fluctuations of the recoil velocity are relatively strong, which can happen in the current era of the universe, then the condensate, and hence the induced mass of the graviton, can be several orders of magnitude larger than the magnitude of the cosmological constant today. Hence, we constrain the graviton mass using aLIGO and pulsar-timing observations (which give the most stringent bounds at present). In such a sub-luminal graviton case, there is also a gravitational Cherenkov effect for ordinary high-energy cosmic matter, which is further constrained by means of ultra-high-energy cosmic ray observations. Assuming cosmic rays of extragalactic origin, the bounds on the quantum condensate strength, based on the gravitational Cherenkov effect, are of the same order as those from aLIGO measurements, in contrast to the case where a galactic origin of the cosmic rays is assumed, in which case the corresponding bounds are much weaker.

Air Blast Calculations

DTIC Science & Technology

2013-07-01

composition C-4 (C4), a polymer-bonded explosive (PBXN-109), and nitromethane (NM). Each charge diameter (CD) is assumed to be 17.46 cm (equivalent to a 10-lb... explosive detonates, the rapid expansion of reaction gases generates a shock wave that propagates into the surrounding medium. The pressure history at a...spherical explosive charge suspended in air. A comparison of the results obtained using CTH are made to ones generated using the Friedlander

Force-free electromagnetic pulses in a laboratory plasma

NASA Technical Reports Server (NTRS)

Stenzel, R. L.; Urrutia, J. M.

1990-01-01

A short, intense current pulse is drawn from an electrode immersed in a magnetized afterglow plasma. The induced magnetic field B(r,t) assumes the shape of a helical double vortex which propagates along B(0) through the uniform plasma as a whistler mode. The observations support a prediction of force-free (J x B + neE = 0) electromagnetic fields and solitary waves. Energy and helicity are approximately conserved.

A novel multi-segment path analysis based on a heterogeneous velocity model for the localization of acoustic emission sources in complex propagation media.

PubMed

Gollob, Stephan; Kocur, Georg Karl; Schumacher, Thomas; Mhamdi, Lassaad; Vogel, Thomas

2017-02-01

In acoustic emission analysis, common source location algorithms assume, independently of the nature of the propagation medium, a straight (shortest) wave path between the source and the sensors. For heterogeneous media such as concrete, the wave travels in complex paths due to the interaction with the dissimilar material contents and with the possible geometrical and material irregularities present in these media. For instance, cracks and large air voids present in concrete influence significantly the way the wave travels, by causing wave path deviations. Neglecting these deviations by assuming straight paths can introduce significant errors to the source location results. In this paper, a novel source localization method called FastWay is proposed. It accounts, contrary to most available shortest path-based methods, for the different effects of material discontinuities (cracks and voids). FastWay, based on a heterogeneous velocity model, uses the fastest rather than the shortest travel paths between the source and each sensor. The method was evaluated both numerically and experimentally and the results from both evaluation tests show that, in general, FastWay was able to locate sources of acoustic emissions more accurately and reliably than the traditional source localization methods. Copyright © 2016 Elsevier B.V. All rights reserved.

A new wave front shape-based approach for acoustic source localization in an anisotropic plate without knowing its material properties.

PubMed

Sen, Novonil; Kundu, Tribikram

2018-07-01

Estimating the location of an acoustic source in a structure is an important step towards passive structural health monitoring. Techniques for localizing an acoustic source in isotropic structures are well developed in the literature. Development of similar techniques for anisotropic structures, however, has gained attention only in the recent years and has a scope of further improvement. Most of the existing techniques for anisotropic structures either assume a straight line wave propagation path between the source and an ultrasonic sensor or require the material properties to be known. This study considers different shapes of the wave front generated during an acoustic event and develops a methodology to localize the acoustic source in an anisotropic plate from those wave front shapes. An elliptical wave front shape-based technique was developed first, followed by the development of a parametric curve-based technique for non-elliptical wave front shapes. The source coordinates are obtained by minimizing an objective function. The proposed methodology does not assume a straight line wave propagation path and can predict the source location without any knowledge of the elastic properties of the material. A numerical study presented here illustrates how the proposed methodology can accurately estimate the source coordinates. Copyright © 2018 Elsevier B.V. All rights reserved.

Comparison of measured and computed Strehl ratios for light propagated through a channel flow of a He N 2 mixing layer at high Reynolds numbers

NASA Astrophysics Data System (ADS)

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

1997-04-01

A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after they propagated through a He N 2 mixing layer in a rectangular channel. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Phase structure functions, computed from the reconstructed phase surfaces, were stationary in first increments. A five-thirds power law is shown to fit streamwise and cross-stream slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence, which describes the structure function with a single parameter. Strehl ratios were computed from the phase structure functions and compared with a measured experiment obtained from simultaneous point-spread function measurements. Two additional Strehl ratios were calculated by using classical estimates that assume statistical isotropy throughout the flow. The isotropic models are a reasonable estimate of the optical degradation only within a few centimeters of the initial mixing, where the Reynolds number is low. At higher Reynolds numbers, Strehl ratios calculated from the structure functions match the experiment much better than Strehl ratio calculations that assume isotropic flow.

Simulation of Crack Propagation in Engine Rotating Components under Variable Amplitude Loading

NASA Technical Reports Server (NTRS)

Bonacuse, P. J.; Ghosn, L. J.; Telesman, J.; Calomino, A. M.; Kantzos, P.

1998-01-01

The crack propagation life of tested specimens has been repeatedly shown to strongly depend on the loading history. Overloads and extended stress holds at temperature can either retard or accelerate the crack growth rate. Therefore, to accurately predict the crack propagation life of an actual component, it is essential to approximate the true loading history. In military rotorcraft engine applications, the loading profile (stress amplitudes, temperature, and number of excursions) can vary significantly depending on the type of mission flown. To accurately assess the durability of a fleet of engines, the crack propagation life distribution of a specific component should account for the variability in the missions performed (proportion of missions flown and sequence). In this report, analytical and experimental studies are described that calibrate/validate the crack propagation prediction capability ]or a disk alloy under variable amplitude loading. A crack closure based model was adopted to analytically predict the load interaction effects. Furthermore, a methodology has been developed to realistically simulate the actual mission mix loading on a fleet of engines over their lifetime. A sequence of missions is randomly selected and the number of repeats of each mission in the sequence is determined assuming a Poisson distributed random variable with a given mean occurrence rate. Multiple realizations of random mission histories are generated in this manner and are used to produce stress, temperature, and time points for fracture mechanics calculations. The result is a cumulative distribution of crack propagation lives for a given, life limiting, component location. This information can be used to determine a safe retirement life or inspection interval for the given location.

Ageostrophic winds and vertical motion fields accompanying upper level jet streak propagation during the Red River Valley tornado outbreak

NASA Technical Reports Server (NTRS)

Moore, J. T.; Squires, M. F.

1982-01-01

Preliminary results are shown relating the ageostrophic wind field, through the terms of a semigeostrophic wind equation (assuming adiabatic conditions and the geostrophic momentum approximation) to both air parcel trajectories and their vertical motion fields computed from the parcels' displacement on isentropic surfaces, with respect to pressure. The analysis of results considers both upper-level (324 K) ageostrophic fields and low-level (304 K) fields. Preliminary results tend to support Uccellini and Johnson's (1979) hypothesis concerning upper-level-jet/low-level-jet (ULJ/LLJ) coupling in the exit region of the ULJ. Future plans are described briefly for research intended to clarify the mechanism behind ULJ streak propagation, LLJ development and their relationship to the initiation of severe convection.

Propagation of an ultrashort, intense laser pulse in a relativistic plasma

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

Ritchie, B.; Decker, C.D.

1997-12-31

A Maxwell-relativistic fluid model is developed for the propagation of an ultrashort, intense laser pulse through an underdense plasma. The separability of plasma and optical frequencies ({omega}{sub p} and {omega} respectively) for small {omega}{sub p}/{omega} is not assumed; thus the validity of multiple-scales theory (MST) can be tested. The theory is valid when {omega}{sub p}/{omega} is of order unity or for cases in which {omega}{sub p}/{omega} {much_lt} 1 but strongly relativistic motion causes higher-order plasma harmonics to be generated which overlap the region of the first-order laser harmonic, such that MST would not expected to be valid although its principalmore » validity criterion {omega}{sub p}/{omega} {much_lt} 1 holds.« less

Shock wave propagation in a magnetic flux tube

NASA Astrophysics Data System (ADS)

Ferriz-Mas, A.; Moreno-Insertis, F.

1992-12-01

The propagation of a shock wave in a magnetic flux tube is studied within the framework of the Brinkley-Kirkwood theory adapted to a radiating gas. Simplified thermodynamic paths along which the compressed plasma returns to its initial state are considered. It is assumed that the undisturbed medium is uniform and that the flux tube is optically thin. The shock waves investigated, which are described with the aid of the thin flux-tube approximation, are essentially slow magnetohydrodynamic shocks modified by the constraint of lateral pressure balance between the flux tube and the surrounding field-free fluid; the confining external pressure must be balanced by the internal gas plus magnetic pressures. Exact analytical solutions giving the evolution of the shock wave are obtained for the case of weak shocks.

Fisher waves and front roughening in a two-species invasion model with preemptive competition.

PubMed

O'Malley, L; Kozma, B; Korniss, G; Rácz, Z; Caraco, T

2006-10-01

We study front propagation when an invading species competes with a resident; we assume nearest-neighbor preemptive competition for resources in an individual-based, two-dimensional lattice model. The asymptotic front velocity exhibits an effective power-law dependence on the difference between the two species' clonal propagation rates (key ecological parameters). The mean-field approximation behaves similarly, but the power law's exponent slightly differs from the individual-based model's result. We also study roughening of the front, using the framework of nonequilibrium interface growth. Our analysis indicates that initially flat, linear invading fronts exhibit Kardar-Parisi-Zhang (KPZ) roughening in one transverse dimension. Further, this finding implies, and is also confirmed by simulations, that the temporal correction to the asymptotic front velocity is of O(t(-2/3)).

Role of geomechanically grown fractures on dispersive transport in heterogeneous geological formations.

PubMed

Nick, H M; Paluszny, A; Blunt, M J; Matthai, S K

2011-11-01

A second order in space accurate implicit scheme for time-dependent advection-dispersion equations and a discrete fracture propagation model are employed to model solute transport in porous media. We study the impact of the fractures on mass transport and dispersion. To model flow and transport, pressure and transport equations are integrated using a finite-element, node-centered finite-volume approach. Fracture geometries are incrementally developed from a random distributions of material flaws using an adoptive geomechanical finite-element model that also produces fracture aperture distributions. This quasistatic propagation assumes a linear elastic rock matrix, and crack propagation is governed by a subcritical crack growth failure criterion. Fracture propagation, intersection, and closure are handled geometrically. The flow and transport simulations are separately conducted for a range of fracture densities that are generated by the geomechanical finite-element model. These computations show that the most influential parameters for solute transport in fractured porous media are as follows: fracture density and fracture-matrix flux ratio that is influenced by matrix permeability. Using an equivalent fracture aperture size, computed on the basis of equivalent permeability of the system, we also obtain an acceptable prediction of the macrodispersion of poorly interconnected fracture networks. The results hold for fractures at relatively low density.

Propagating mass accretion rate fluctuations in black hole X-ray binaries: quantitative tests

NASA Astrophysics Data System (ADS)

Rapisarda, S.; Ingram, A.; van der Klis, M.

2017-10-01

Over the past 20 years, a consistent phenomenology has been established to describe the variability properties of Black Hole X-ray Binaries (BHBs). However, the physics behind the observational data is still poorly understood. The recently proposed model PROPFLUC assumes a truncated disc/hot inner flow geometry, with mass accretion rate fluctuations propagating through a precessing inner flow. These two processes give rise respectively to broad band variability and QPO. Because of propagation, the emission from different regions of the disc/hot flow geometry is correlated. In our study we applied the model PROPFLUC on different BHBs (including XTE J1550-564 and Cygnus X-1) in different spectral states, fitting jointly the power spectra in two energy bands and the cross-spectrum between these two bands. This represents the first study to utilize quantitive fitting of a physical model simultaneously to observed power and cross-spectra. For the case of XTE J1550-564, which displays a strong QPO, we found quantitative and qualitative discrepancies between model predictions and data, whereas we find a good fit for the Cygnus X-1 data, which does not display a QPO. We conclude that the discrepancies are generic to the propagating fluctuations paradigm, and may be related to the mechanism originating the QPO.

Simulation of light propagation in the thin-film waveguide lens

NASA Astrophysics Data System (ADS)

Malykh, M. D.; Divakov, D. V.; Sevastianov, L. A.; Sevastianov, A. L.

2018-04-01

In this paper we investigate the solution of the problem of modeling the propagation of electromagnetic radiation in three-dimensional integrated optical structures, such as waveguide lenses. When propagating through three-dimensional waveguide structures the waveguide modes can be hybridized, so the mathematical model of their propagation must take into account the connection of TE- and TM-mode components. Therefore, an adequate consideration of hybridization of the waveguide modes is possible only in vector formulation of the problem. An example of three-dimensional structure that hybridizes waveguide modes is the Luneburg waveguide lens, which also has focusing properties. If the waveguide lens has a radius of the order of several tens of wavelengths, its variable thickness at distances of the order of several wavelengths is almost constant. Assuming in this case that the electromagnetic field also varies slowly in the direction perpendicular to the direction of propagation, one can introduce a small parameter characterizing this slow varying and decompose the solution in powers of the small parameter. In this approach, in the zeroth approximation, scalar diffraction problems are obtained, the solution of which is less resource-consuming than the solution of vector problems. The calculated first-order corrections of smallness describe the connection of TE- and TM-modes, so the solutions obtained are weakly-hybridized modes. The formulation of problems and methods for their numerical solution in this paper are based on the authors' research on waveguide diffraction on a lens in a scalar formulation.

Infrasound data inversion for atmospheric sounding

NASA Astrophysics Data System (ADS)

Lalande, J.-M.; Sèbe, O.; Landès, M.; Blanc-Benon, Ph.; Matoza, R. S.; Le Pichon, A.; Blanc, E.

2012-07-01

The International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) continuously records acoustic waves in the 0.01-10 Hz frequency band, known as infrasound. These waves propagate through the layered structure of the atmosphere. Coherent infrasonic waves are produced by a variety of anthropogenic and natural sources and their propagation is controlled by spatiotemporal variations of temperature and wind velocity. Natural stratification of atmospheric properties (e.g. temperature, density and winds) forms waveguides, allowing long-range propagation of infrasound waves. However, atmospheric specifications used in infrasound propagation modelling suffer from lack and sparsity of available data above an altitude of 50 km. As infrasound can propagate in the upper atmosphere up to 120 km, we assume that infrasonic data could be used for sounding the atmosphere, analogous to the use of seismic data to infer solid Earth structure and the use of hydroacoustic data to infer oceanic structure. We therefore develop an inversion scheme for vertical atmospheric wind profiles in the framework of an iterative linear inversion. The forward problem is treated in the high-frequency approximation using a Hamiltonian formulation and complete first-order ray perturbation theory is developed to construct the Fréchet derivatives matrix. We introduce a specific parametrization for the unknown model parameters based on Principal Component Analysis. Finally, our algorithm is tested on synthetic data cases spanning different seasonal periods and network configurations. The results show that our approach is suitable for infrasound atmospheric sounding on a regional scale.

Impact on a Compressible Fluid

NASA Technical Reports Server (NTRS)

Egorov, L. T.

1958-01-01

Upon impact of a solid body on the plane surface of a fluid, there occurs on the vetted surface of the body an abrupt pressure rise which propagates into both media with the speed of sound. Below, we assume the case where the speed of propagation of sound in the body which falls on the surface of the fluid may be regarded as infinitely large in comparison with the speed of propagation of sound in the fluid; that is, we shall assume that the falling body is absolutely rigid. IN this case, the entire relative speed of the motion which takes place at the beginning of the impact is absorbed by the fluid. The hydrodynamic pressures arising thereby are propagated from the contact surface within the fluid with the speed of sound in the form of compression and expansion waves and are gradually damped. After this, they are dispersed like impact pressures, reach ever larger regions of the fluid remote fran the body and became equal to zero; in the fluid there remain hydrodynamic pressures corresponding to the motion of the body after the impact. Neglecting the forces of viscosity and taking into account, furthermore, that the motion of the fluid begins from a state of rest, according to Thomson's theorem, we may consider the motion of an ideal compressible fluid in the process of impact to be potential. We examine the case of impact upon the surface of a ccmpressible fluid of a flat plate of infinite extent or of a body, the immersed part of the surface of which may be called approximately flat. In this report we discuss the first phase of the impact pressure on the surface of a fluid, prior to the appearance of a cavity, since at this stage the hydrodynamic pressures reach their maximum values. Observations, after the fall of the bodies on the surface of the fluid, show that the free surface of the fluid at this stage is almost completely at rest if one does not take into account the small rise in the neighborhood of the boundaries of the impact surface.

Intrasystem Analysis Program (IAP) Structural Design Study.

DTIC Science & Technology

1981-06-01

accuracy constraints, and user competence . This report is designed to serve as a guide in con- structing procedures and identifying those aspects of the...parameters. 3.3.3 Userability The term "Userability" refers here to the level of competence assumed for an IAP analyst in need of a procedure. There...media the wires pass through is homogeneous along the length of the wires. Under these assumptions the wave propagation is predominantly tranverse

On Acceptable Exposures to Short Pulses of Electromagnetic Fields

DTIC Science & Technology

2015-09-01

in the comparisons given in this report, the electric and magnetic field strengths are assumed to be related as for a propagating wave . In the...adequacy of current standards is far from a settled issue. 15. SUBJECT TERMS International Commission on Non- Ionizing Radiation Protection, Institute...a source, the electric and magnetic fields are approximately related to each other in the same way as in a radiating wave far from the source. That

Two Dimensional Acoustic Propagation Through Oceanic Internal Solitary Waves: Weak Scattering Theory and Numerical Simulation

DTIC Science & Technology

2006-06-01

ψ ρ ψ = = − ∑ ∫ (32) The last integral in Equation (29), mnH has the form 20 ( ) ( )( ) ( ) 0 2 ( , ) sin 2 ( ) 2 mn mn R i l k r mn i l k R mn...should be noted that in evaluating mnH , it is assumed that R is very large and that both the initial point 0r = and the final range R are well

Supplemental Student Support: Detection and Identification of Buried Targets using Time Reversal Acoustics

DTIC Science & Technology

2009-11-04

simulated result generated from the partial wave series model described in Chapter 2. Finally, the acoustic properties of the sediment phantom...the appropriate acoustic properties and propagation models for the sediment medium, that is, whether to assume the sediment is a fluid, an elastic...viscoelastic medium, or a poroelastic medium. 141 In this study, the sediment phantom employed is treated as a fluid. Its acoustic properties are

Conical Lens for 5-Inch/54 Gun Launched Missile

DTIC Science & Technology

1981-06-01

Propagation, Interferenceand Diffraction of Light, 2nd ed. (revised), p. 121-124, Pergamon Press, 1964. 10. Anton , Howard, Elementary Linear Algebra , p. 1-21...equations is nonlinear in x, but is linear in the coefficients. Therefore, the techniques of linear algebra can be used on equation (F-13). The method...This thesis assumes the air to be homogenous, isotropic, linear , time indepen- dent (HILT) and free of shock waves in order to investigate the

Clutter characterization within segmented hyperspectral imagery

NASA Astrophysics Data System (ADS)

Kacenjar, Steve T.; Hoffberg, Michael; North, Patrick

2007-10-01

Use of a Mean Class Propagation Model (MCPM) has been shown to be an effective approach in the expedient propagation of hyperspectral data scenes through the atmosphere. In this approach, real scene data are spatially subdivided into regions of common spectral properties. Each sub-region which we call a class possesses two important attributes (1) the mean spectral radiance and (2) the spectral covariance. The use of this attributes can significantly improve throughput performance of computing systems over conventional pixel-based methods. However, this approach assumes that background clutter can be approximated as having multivariate Gaussian distributions. Under such conditions, covariance propagations can be effectively performed from ground through the atmosphere. This paper explores this basic assumption using real-scene Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data and examines how the partitioning of the scene into smaller and smaller segments influences local clutter characterization. It also presents a clutter characterization metric that helps explain the migration of the magnitude of statistical clutter from parent class to child sub-classes populations. It is shown that such a metric can be directly related to an approximate invariant between the parent class and its child classes.

Electron acoustic nonlinear structures in planetary magnetospheres

NASA Astrophysics Data System (ADS)

Shah, K. H.; Qureshi, M. N. S.; Masood, W.; Shah, H. A.

2018-04-01

In this paper, we have studied linear and nonlinear propagation of electron acoustic waves (EAWs) comprising cold and hot populations in which the ions form the neutralizing background. The hot electrons have been assumed to follow the generalized ( r , q ) distribution which has the advantage that it mimics most of the distribution functions observed in space plasmas. Interestingly, it has been found that unlike Maxwellian and kappa distributions, the electron acoustic waves admit not only rarefactive structures but also allow the formation of compressive solitary structures for generalized ( r , q ) distribution. It has been found that the flatness parameter r , tail parameter q , and the nonlinear propagation velocity u affect the propagation characteristics of nonlinear EAWs. Using the plasmas parameters, typically found in Saturn's magnetosphere and the Earth's auroral region, where two populations of electrons and electron acoustic solitary waves (EASWs) have been observed, we have given an estimate of the scale lengths over which these nonlinear waves are expected to form and how the size of these structures would vary with the change in the shape of the distribution function and with the change of the plasma parameters.

Particle propagation, wave growth and energy dissipation in a flaring flux tube

NASA Technical Reports Server (NTRS)

White, S. M.; Melrose, D. B.; Dulk, G. A.

1986-01-01

Wave amplification by downgoing particles in a common flare model is investigated. The flare is assumed to occur at the top of a coronal magnetic flux loop, and results in the heating of plasma in the flaring region. The hot electrons propagate down the legs of the flux tube towards increasing magnetic field. It is simple to demonstrate that the velocity distributions which result in this model are unstable to both beam instabilities and cyclotron maser action. An explanation is presented for the propagation effects on the distribution, and the properties of the resulting amplified waves are explored, concentrating on cyclotron maser action, which has properties (emission in the z mode below the local gyrofrequency) quite different from maser action by other distributions considered in the context of solar flares. The z mode waves will be damped in the coronal plasma surrounding the flaring flux tube and lead to heating there. This process may be important in the overall energy budget of the flare. The downgoing maser is compared with the loss cone maser, which is more likely to produce observable bursts.

Stability properties of a thin relativistic beam propagation in a magnetized plasma

NASA Astrophysics Data System (ADS)

Jovanović, Dušan; Fedele, Renato; Belić, Milivoj; De Nicola, Sergio; Akhter, Tamina

2018-05-01

A self-consistent nonlinear hydrodynamic theory is presented of the propagation of a long and thin relativistic electron beam through a plasma that is relatively strongly magnetized. Such situation is encountered when the gyro-frequency is comparable to the plasma frequency, i.e. |Ω e | ω pe . In addition, it is assumed the plasma density is much bigger than that of the beam. In the regime when the solution propagates in the comoving frame with a velocity that is much smaller than the thermal speed, a nonlinear stationary beam structure is found in which the electron motion in the transverse direction is negligible and whose transverse localization comes from the nonlinearity associated with its 3-D adiabatic expansion. Conversely, when the parallel velocity of the structure is sufficiently large to prevent the heat convection along the magnetic field, a helicoidally shaped stationary solution is found that is governed by the transverse convective nonlinearity. The profile of such beam is determined from a nonlinear dispersion relation and depends on the transverse size of the beam and its pitch angle to the magnetic field.

Finite element approximation of the radiative transport equation in a medium with piece-wise constant refractive index

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

Lehtikangas, O., E-mail: Ossi.Lehtikangas@uef.fi; Tarvainen, T.; Department of Computer Science, University College London, Gower Street, London WC1E 6BT

2015-02-01

The radiative transport equation can be used as a light transport model in a medium with scattering particles, such as biological tissues. In the radiative transport equation, the refractive index is assumed to be constant within the medium. However, in biomedical media, changes in the refractive index can occur between different tissue types. In this work, light propagation in a medium with piece-wise constant refractive index is considered. Light propagation in each sub-domain with a constant refractive index is modeled using the radiative transport equation and the equations are coupled using boundary conditions describing Fresnel reflection and refraction phenomena onmore » the interfaces between the sub-domains. The resulting coupled system of radiative transport equations is numerically solved using a finite element method. The approach is tested with simulations. The results show that this coupled system describes light propagation accurately through comparison with the Monte Carlo method. It is also shown that neglecting the internal changes of the refractive index can lead to erroneous boundary measurements of scattered light.« less

Steady propagation of Bingham plugs in 2D channels

NASA Astrophysics Data System (ADS)

Zamankhan, Parsa; Takayama, Shuichi; Grotberg, James

2009-11-01

The displacement of the yield-stress liquid plugs in channels and tubes occur in many biological systems and industrial processes. Among them is the propagation of mucus plugs in the respiratory tracts as may occur in asthma, cystic fibrosis, or emphysema. In this work the steady propagation of mucus plugs in a 2D channel is studied numerically, assuming that the mucus is a pure Bingham fluid. The governing equations are solved by a mixed-discontinuous finite element formulation and the free surface is resolved with the method of spines. The constitutive equation for a pure Bingham fluid is modeled by a regularization method. Fluid inertia is neglected, so the controlling parameters in a steady displacement are; the capillary number, Ca, Bingham number ,Bn, and the plug length. According to the numerical results, the yield stress behavior of the plug modifies the plug shape, the pattern of the streamlines and the distribution of stresses in the plug domain and along the walls in a significant way. The distribution along the walls is a major factor in studying cell injuries. This work is supported through the grant NIH HL84370.

Azimuthal Directivity of Fan Tones Containing Multiple Modes

NASA Technical Reports Server (NTRS)

Heidelberg, Laurence J.; Sutliff, Daniel L.; Nallasamy, M.

1997-01-01

The directivity of fan tone noise is generally measured and plotted in the sideline or flyover plane and it is assumed that this curve is the same for all azimuthal angles. When two or more circumferential (m-order) modes of the same tone are present in the fan duct, an interference pattern develops in the azimuthal direction both in the duct and in the farfield. In this investigation two m-order modes of similar power were generated in a large low speed fan. Farfield measurements and a finite element propagation code both show substantial variations in the azimuthal direction. Induct mode measurement were made and used as input to the code. Although these tests may represent a worst case scenario, the validity of the current practice of assuming axisymmetry should be questioned.

Structured pedigree information for distributed fusion systems

NASA Astrophysics Data System (ADS)

Arambel, Pablo O.

2008-04-01

One of the most critical challenges in distributed data fusion is the avoidance of information double counting (also called "data incest" or "rumor propagation"). This occurs when a node in a network incorporates information into an estimate - e.g. the position of an object - and the estimate is injected into the network. Other nodes fuse this estimate with their own estimates, and continue to propagate estimates through the network. When the first node receives a fused estimate from the network, it does not know if it already contains its own contributions or not. Since the correlation between its own estimate and the estimate received from the network is not known, the node can not fuse the estimates in an optimal way. If it assumes that both estimates are independent from each other, it unknowingly double counts the information that has already being used to obtain the two estimates. This leads to overoptimistic error covariance matrices. If the double-counting is not kept under control, it may lead to serious performance degradation. Double counting can be avoided by propagating uniquely tagged raw measurements; however, that forces each node to process all the measurements and precludes the propagation of derived information. Another approach is to fuse the information using the Covariance Intersection (CI) equations, which maintain consistent estimates irrespective of the cross-correlation among estimates. However, CI does not exploit pedigree information of any kind. In this paper we present an approach that propagates multiple covariance matrices, one for each uncorrelated source in the network. This is a way to compress the pedigree information and avoids the need to propagate raw measurements. The approach uses a generalized version of the Split CI to fuse different estimates with appropriate weights to guarantee the consistency of the estimates.

Critical Parameters of the Initiation Zone for Spontaneous Dynamic Rupture Propagation

NASA Astrophysics Data System (ADS)

Galis, M.; Pelties, C.; Kristek, J.; Moczo, P.; Ampuero, J. P.; Mai, P. M.

2014-12-01

Numerical simulations of rupture propagation are used to study both earthquake source physics and earthquake ground motion. Under linear slip-weakening friction, artificial procedures are needed to initiate a self-sustained rupture. The concept of an overstressed asperity is often applied, in which the asperity is characterized by its size, shape and overstress. The physical properties of the initiation zone may have significant impact on the resulting dynamic rupture propagation. A trial-and-error approach is often necessary for successful initiation because 2D and 3D theoretical criteria for estimating the critical size of the initiation zone do not provide general rules for designing 3D numerical simulations. Therefore, it is desirable to define guidelines for efficient initiation with minimal artificial effects on rupture propagation. We perform an extensive parameter study using numerical simulations of 3D dynamic rupture propagation assuming a planar fault to examine the critical size of square, circular and elliptical initiation zones as a function of asperity overstress and background stress. For a fixed overstress, we discover that the area of the initiation zone is more important for the nucleation process than its shape. Comparing our numerical results with published theoretical estimates, we find that the estimates by Uenishi & Rice (2004) are applicable to configurations with low background stress and small overstress. None of the published estimates are consistent with numerical results for configurations with high background stress. We therefore derive new equations to estimate the initiation zone size in environments with high background stress. Our results provide guidelines for defining the size of the initiation zone and overstress with minimal effects on the subsequent spontaneous rupture propagation.

Anisoplanatic image propagation along a slanted path under lower atmosphere phase turbulence in the presence of encrypted chaos

NASA Astrophysics Data System (ADS)

Chatterjee, Monish R.; Mohamed, Ali A.

2017-05-01

In recent research, anisoplanatic electromagnetic (EM) wave propagation along a slanted path in the presence of low atmosphere phase turbulence (modified von Karman spectrum or MVKS) has been investigated assuming a Hufnagel-Valley (HV) type structure parameter. Preliminary results indicate a strong dependence on the slant angle especially for long range transmission and relatively strong turbulence. The investigation was further divided into two regimes, viz. (a) one where the EM source consisted of a plane wave modulated with a digitized image, which is propagated along the turbulent path and recovered via demodulation at the receiver; and (b) transmit the plane wave without modulation along the turbulent path through an image transparency and a thin lens designed to gather the received image in the focal plane. In this paper, we reexamine the same problem (part (a) only) in the presence of a chaotic optical carrier where the chaos is generated in the feedback loop of an acousto-optic Bragg cell. The image information is encrypted within the chaos wave, and subsequently propagated along a similar slant path and identical turbulence conditions. The recovered image extracted via heterodyning from the received chaos is compared quantitatively (through image cross-correlations and mean-squared error measures) for the non-chaotic versus the chaotic approaches. Generally, "packaging" the information in chaos improves performance through turbulent propagation, and results are discussed from this perspective. Concurrently, we will also examine the effect of a non-encrypted plane EM wave propagation through a transparency-lens combination. These results are also presented with appropriate comparisons with the cases involving lensless transmission of imagery through corresponding turbulent and non-turbulent layers.

Propagation of an ultra-short, intense laser in a relativistic fluid

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

Ritchie, A.B.; Decker, C.D.

1997-12-31

A Maxwell-relativistic fluid model is developed to describe the propagation of an ultrashort, intense laser pulse through an underdense plasma. The model makes use of numerically stabilizing fast Fourier transform (FFT) computational methods for both the Maxwell and fluid equations, and it is benchmarked against particle-in-cell (PIC) simulations. Strong fields generated in the wake of the laser are calculated, and the authors observe coherent wake-field radiation generated at harmonics of the plasma frequency due to nonlinearities in the laser-plasma interaction. For a plasma whose density is 10% of critical, the highest members of the plasma harmonic series begin to overlapmore » with the first laser harmonic, suggesting that widely used multiple-scales-theory, by which the laser and plasma frequencies are assumed to be separable, ceases to be a useful approximation.« less

Interaction of finite-amplitude sound with air-filled porous materials

NASA Technical Reports Server (NTRS)

Nelson, D. A.

1985-01-01

The propagation of high intensity sound waves through an air-filled porus material was studied. The material is assumed: (1) to be rigid, incompressible, and homogeneous, and (2) to be adequately described by two properties: resistivity r and porosity. The resulting wave equation is still nonlinear, however, because of the u sgn(u) term in the resistivity. The equation is solved in the frequency domain as an infinite set of coupled inhomogeneous Helmholtz equations, one for each harmonic. An approximate but analytical solution leads to predictions of excess attenuation, saturation, and phase speed reduction for the fundamental component. A more general numerical solution is used to calculate the propagation curves for the higher harmonics. The u sgn(u) nonlinearity produces a cubic distortion pattern; when the input signal is a pure tone, only odd harmonic distortion products are generated.

Measuring the speed resolution of extensive air showers at the Southern Pierre Auger Observatory

NASA Astrophysics Data System (ADS)

Gesterling, Kathleen; Sarazin, Fred

2009-10-01

Ultra-high energy cosmic rays induce extensive air showers (EASs) in Earth's atmosphere which are assumed to propagate at the speed of light. The fluorescence detector (FD) at the Southern Pierre Auger Observatory detects the light signal from the EAS and directly measures the energy of the cosmic ray. When two or more FD sites observe an event, the geometry of the shower can be calculated independently of the velocity it is traveling. It is then possible to fit the time profile recorded in the FD using the shower speed as a free parameter. The analysis of a collection of stereo events allowed us to determine with what speed resolution we can measure EASs with sensitivity to subluminal components. Knowing the speed resolution we can look for objects propagating significantly below the speed of light.

Lattice strains and load partitioning in bovine trabecular bone.

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

Akhtar, R.; Daymond, M. R.; Almer, J. D.

2012-02-01

Microdamage and failure mechanisms have been well characterized in bovine trabecular bone. However, little is known about how elastic strains develop in the apatite crystals of the trabecular struts and their relationship with different deformation mechanisms. In this study, wide-angle high-energy synchrotron X-ray diffraction has been used to determine bulk elastic strains under in situ compression. Dehydrated bone is compared to hydrated bone in terms of their response to load. During compression, load is initially borne by trabeculae aligned parallel to loading direction with non-parallel trabeculae deforming by bending. Ineffective load partitioning is noted in dehydrated bone whereas hydrated bonemore » behaves like a plastically yielding foam« less

Dynamics of charges and solitons

NASA Astrophysics Data System (ADS)

Barros, Manuel; Ferrández, Ángel; Garay, Óscar J.

2018-02-01

We first show that trajectories traced by charges moving in rotational magnetic fields are, basically, the non-parallel geodesics of surfaces of revolution with coincident axis. Thus, people living in a surface of revolution are not able to sense the magnetic Hall effect induced by the surrounding magnetic field and perceive charges as influenced, exclusively, by the gravity action on the surface of revolution. Secondly, the extended Hasimoto transformations are introduced and then used to identify trajectories of charges moving through a Killing rotational magnetic field in terms of non-circular elastic curves. As a consequence, we see that in this case charges evolve along trajectories which are obtained as extended Hasimoto transforms of solitons of the filament equation.

Capillary-tube-based extension of thermoacoustic theory for a random medium

NASA Astrophysics Data System (ADS)

Roh, Heui-Seol; Raspet, Richard; Bass, Henry E.

2005-09-01

Thermoacoustic theory for a single capillary tube is extended to random bulk medium on the basis of capillary tubes. The characteristics of the porous stack inside the resonator such as the tortuosity, dynamic shape factor, and porosity are introduced for the extension of wave equation by following Attenborough's approach. Separation of the dynamic shape factor for the viscous and thermal effect is adopted and scaling using the dynamic shape factor and tortuosity factor is demonstrated. The theoretical and experimental comparison of thermoviscous functions in reticulated vitreous carbon (RVC) and aluminum foam shows reasonable agreement. The extension is useful for investigations of the properties of a stack with arbitrary shapes of non-parallel pores.

Stresses in Solder Joints of Electronic Packages

DTIC Science & Technology

1991-12-31

soldering process. The device is soldered to the circuit board at a temperature of +185zc and this tempature is assumed to propagate only to the lead wire...tri-material assembly, showing the notation used hereafter, is shown in Figure 7. The Suhir model is applicable to assemblies with continuous...therefore the radii of curvature of layers are all equal. Using equilibrium equation (7) and moment-curvature equation (9) yields ()D D Xp (x) D T() -m 3 x

High-power laser interaction with low-density C–Cu foams

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

Pérez, F.; Colvin, J. D.; May, M. J.

2015-11-15

We study the propagation of high-power laser beams in micro-structured carbon foams by monitoring the x-ray output from deliberately introduced Cu content. In particular, we characterize this phenomenon measuring absolute time-resolved x-ray yields, time-resolved x-ray imaging, and x-ray spectroscopy. New experimental results for C–Cu foams show a faster heat front velocity than simulation that assumed homogeneous plasma. We suggest the foam micro-structure may explain this trend.

High-power laser interaction with low-density C–Cu foams

DOE PAGES

Pérez, F.; Colvin, J. D.; May, M. J.; ...

2015-11-19

Here, we study the propagation of high-power laser beams in micro-structured carbon foams by monitoring the x-ray output from deliberately introduced Cu content. In particular, we characterize this phenomenon measuring absolute time-resolved x-ray yields, time-resolved x-ray imaging, and x-ray spectroscopy. New experimental results for C–Cu foams show a faster heat front velocity than simulation that assumed homogeneous plasma. We suggest the foam micro-structure may explain this trend.

Adaptive Beamforming Algorithms for High Resolution Microwave Imaging

DTIC Science & Technology

1991-04-01

frequency- and phase -locked. With a system of radio camera size it must be assumed that oscillators will drift and, similarly, that electronic circuits in...propagation-induced phase errors an array as large as the one under discussion is likely to experience differ- ent weather conditions across it. The nominal...human optical system. Such a passing-scene display with human optical resolving power would be available to the air - man at night as well as during the

Exploring extra dimensions with scalar fields

NASA Astrophysics Data System (ADS)

Brown, Katherine; Mathur, Harsh; Verostek, Mike

2018-05-01

This paper provides a pedagogical introduction to the physics of extra dimensions by examining the behavior of scalar fields in three landmark models: the ADD, Randall-Sundrum, and DGP spacetimes. Results of this analysis provide qualitative insights into the corresponding behavior of gravitational fields and elementary particles in each of these models. In these "brane world" models, the familiar four dimensional spacetime of everyday experience is called the brane and is a slice through a higher dimensional spacetime called the bulk. The particles and fields of the standard model are assumed to be confined to the brane, while gravitational fields are assumed to propagate in the bulk. For all three spacetimes, we calculate the spectrum of propagating scalar wave modes and the scalar field produced by a static point source located on the brane. For the ADD and Randall-Sundrum models, at large distances, the field looks like that of a point source in four spacetime dimensions, but at short distances, it crosses over to a form appropriate to the higher dimensional spacetime. For the DGP model, the field has the higher dimensional form at long distances rather than short. The behavior of these scalar fields, derived using only undergraduate level mathematics, closely mirror the results that one would obtain by performing the far more difficult task of analyzing the behavior of gravitational fields in these spacetimes.

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

Farmer, W. A.; Koning, J. M.; Strozzi, D. J.

Here, we present radiation-hydrodynamic simulations of self-generated magnetic field in a hohlraum, which show an increased temperature in large regions of the underdense fill. Non-parallel gradients in electron density and temperature in a laser-heated plasma give rise to a self-generated field by the “Biermann battery” mechanism. Here, HYDRA simulations of three hohlraum designs on the National Ignition Facility are reported, which use a partial magnetohydrodynamic (MHD) description that includes the self-generated source term, resistive dissipation, and advection of the field due to both the plasma flow and the Nernst term. Anisotropic electron heat conduction parallel and perpendicular to the fieldmore » is included, but not the Righi-Leduc heat flux. The field strength is too small to compete significantly with plasma pressure, but affects plasma conditions by reducing electron heat conduction perpendicular to the field. Significant reductions in heat flux can occur, especially for high Z plasma, at modest values of the Hall parameter, Ω eτ ei≲1, where Ω e = eB/m ec and τ ei is the electron-ion collision time. The inclusion of MHD in the simulations leads to 1 keV hotter electron temperatures in the laser entrance hole and high- Z wall blowoff, which reduces inverse-bremsstrahlung absorption of the laser beam. This improves propagation of the inner beams pointed at the hohlraum equator, resulting in a symmetry shift of the resulting capsule implosion towards a more prolate shape. The time of peak x-ray production in the capsule shifts later by only 70 ps (within experimental uncertainty), but a decomposition of the hotspot shape into Legendre moments indicates a shift of P 2/P 0 by ~20%. As a result, this indicates that MHD cannot explain why simulated x-ray drive exceeds measured levels, but may be partially responsible for failures to correctly model the symmetry.« less

Simulation of self-generated magnetic fields in an inertial fusion hohlraum environment

DOE PAGES

Farmer, W. A.; Koning, J. M.; Strozzi, D. J.; ...

2017-05-09

Here, we present radiation-hydrodynamic simulations of self-generated magnetic field in a hohlraum, which show an increased temperature in large regions of the underdense fill. Non-parallel gradients in electron density and temperature in a laser-heated plasma give rise to a self-generated field by the “Biermann battery” mechanism. Here, HYDRA simulations of three hohlraum designs on the National Ignition Facility are reported, which use a partial magnetohydrodynamic (MHD) description that includes the self-generated source term, resistive dissipation, and advection of the field due to both the plasma flow and the Nernst term. Anisotropic electron heat conduction parallel and perpendicular to the fieldmore » is included, but not the Righi-Leduc heat flux. The field strength is too small to compete significantly with plasma pressure, but affects plasma conditions by reducing electron heat conduction perpendicular to the field. Significant reductions in heat flux can occur, especially for high Z plasma, at modest values of the Hall parameter, Ω eτ ei≲1, where Ω e = eB/m ec and τ ei is the electron-ion collision time. The inclusion of MHD in the simulations leads to 1 keV hotter electron temperatures in the laser entrance hole and high- Z wall blowoff, which reduces inverse-bremsstrahlung absorption of the laser beam. This improves propagation of the inner beams pointed at the hohlraum equator, resulting in a symmetry shift of the resulting capsule implosion towards a more prolate shape. The time of peak x-ray production in the capsule shifts later by only 70 ps (within experimental uncertainty), but a decomposition of the hotspot shape into Legendre moments indicates a shift of P 2/P 0 by ~20%. As a result, this indicates that MHD cannot explain why simulated x-ray drive exceeds measured levels, but may be partially responsible for failures to correctly model the symmetry.« less

Simulation of self-generated magnetic fields in an inertial fusion hohlraum environment

NASA Astrophysics Data System (ADS)

Farmer, W. A.; Koning, J. M.; Strozzi, D. J.; Hinkel, D. E.; Berzak Hopkins, L. F.; Jones, O. S.; Rosen, M. D.

2017-05-01

We present radiation-hydrodynamic simulations of self-generated magnetic field in a hohlraum, which show an increased temperature in large regions of the underdense fill. Non-parallel gradients in electron density and temperature in a laser-heated plasma give rise to a self-generated field by the "Biermann battery" mechanism. Here, HYDRA simulations of three hohlraum designs on the National Ignition Facility are reported, which use a partial magnetohydrodynamic (MHD) description that includes the self-generated source term, resistive dissipation, and advection of the field due to both the plasma flow and the Nernst term. Anisotropic electron heat conduction parallel and perpendicular to the field is included, but not the Righi-Leduc heat flux. The field strength is too small to compete significantly with plasma pressure, but affects plasma conditions by reducing electron heat conduction perpendicular to the field. Significant reductions in heat flux can occur, especially for high Z plasma, at modest values of the Hall parameter, Ωeτei≲1 , where Ωe=e B /mec and τei is the electron-ion collision time. The inclusion of MHD in the simulations leads to 1 keV hotter electron temperatures in the laser entrance hole and high-Z wall blowoff, which reduces inverse-bremsstrahlung absorption of the laser beam. This improves propagation of the inner beams pointed at the hohlraum equator, resulting in a symmetry shift of the resulting capsule implosion towards a more prolate shape. The time of peak x-ray production in the capsule shifts later by only 70 ps (within experimental uncertainty), but a decomposition of the hotspot shape into Legendre moments indicates a shift of P2/P0 by ˜20 % . This indicates that MHD cannot explain why simulated x-ray drive exceeds measured levels, but may be partially responsible for failures to correctly model the symmetry.

Simulation of ultrasonic pulse propagation, distortion, and attenuation in the human chest wall.

PubMed

Mast, T D; Hinkelman, L M; Metlay, L A; Orr, M J; Waag, R C

1999-12-01

A finite-difference time-domain model for ultrasonic pulse propagation through soft tissue has been extended to incorporate absorption effects as well as longitudinal-wave propagation in cartilage and bone. This extended model has been used to simulate ultrasonic propagation through anatomically detailed representations of chest wall structure. The inhomogeneous chest wall tissue is represented by two-dimensional maps determined by staining chest wall cross sections to distinguish between tissue types, digitally scanning the stained cross sections, and mapping each pixel of the scanned images to fat, muscle, connective tissue, cartilage, or bone. Each pixel of the tissue map is then assigned a sound speed, density, and absorption value determined from published measurements and assumed to be representative of the local tissue type. Computational results for energy level fluctuations and arrival time fluctuations show qualitative agreement with measurements performed on the same specimens, but show significantly less waveform distortion than measurements. Visualization of simulated tissue-ultrasound interactions in the chest wall shows possible mechanisms for image aberration in echocardiography, including effects associated with reflection and diffraction caused by rib structures. A comparison of distortion effects for varying pulse center frequencies shows that, for soft tissue paths through the chest wall, energy level and waveform distortion increase markedly with rising ultrasonic frequency and that arrival-time fluctuations increase to a lesser degree.

Simulation and measurement of nonlinear behavior in a high-power test cell.

PubMed

Harvey, Gerald; Gachagan, Anthony

2011-04-01

High-power ultrasound has many diverse uses in process applications in industries ranging from food to pharmaceutical. Because cavitation is frequently a desirable effect within many high-power, low-frequency systems, these systems are commonly expected to feature highly nonlinear acoustic propagation because of the high input levels employed. This generation of harmonics significantly alters the field profile compared with that of a linear system, making accurate field modeling difficult. However, when the short propagation distances involved are considered, it is not unreasonable to assume that these systems may remain largely linear until the onset of cavitation, in terms of classical acoustic propagation. The purpose of this paper is to investigate the possible nonlinear effects within such systems before the onset of cavitation. A theoretical description of nonlinear propagation will be presented and the merits of common analytical models will be discussed. Following this, a numerical model of nonlinearity will be outlined and the advantages it presents for representing nonlinear effects in bounded fields will be discussed. Next, the driving equipment and transducers will be evaluated for linearity to disengage any effects from those formed in the transmission load. Finally, the linearity of the system will be measured using an acoustic hydrophone and compared with finite element analysis to confirm that nonlinear effects are not prevalent in such systems at the onset of cavitation. © 2011 IEEE

Geometrical modeling of optical phase difference for analyzing atmospheric turbulence

NASA Astrophysics Data System (ADS)

Yuksel, Demet; Yuksel, Heba

2013-09-01

Ways of calculating phase shifts between laser beams propagating through atmospheric turbulence can give us insight towards the understanding of spatial diversity in Free-Space Optical (FSO) links. We propose a new geometrical model to estimate phase shifts between rays as the laser beam propagates through a simulated turbulent media. Turbulence is simulated by filling the propagation path with spherical bubbles of varying sizes and refractive index discontinuities statistically distributed according to various models. The level of turbulence is increased by elongating the range and/or increasing the number of bubbles that the rays interact with along their path. For each statistical representation of the atmosphere, the trajectories of two parallel rays separated by a particular distance are analyzed and computed simultaneously using geometrical optics. The three-dimensional geometry of the spheres is taken into account in the propagation of the rays. The bubble model is used to calculate the correlation between the two rays as their separation distance changes. The total distance traveled by each ray as both rays travel to the target is computed. The difference in the path length traveled will yield the phase difference between the rays. The mean square phase difference is taken to be the phase structure function which in the literature, for a pair of collimated parallel pencil thin rays, obeys a five-third law assuming weak turbulence. All simulation results will be compared with the predictions of wave theory.

Ultrasound wave propagation in tissue and scattering from microbubbles for echo particle image velocimetry technique.

PubMed

Mukdadi, Osama; Shandas, Robin

2004-01-01

Nonlinear wave propagation in tissue can be employed for tissue harmonic imaging, ultrasound surgery, and more effective tissue ablation for high intensity focused ultrasound (HIFU). Wave propagation in soft tissue and scattering from microbubbles (ultrasound contrast agents) are modeled to improve detectability, signal-to-noise ratio, and contrast harmonic imaging used for echo particle image velocimetry (Echo-PIV) technique. The wave motion in nonlinear material (tissue) is studied using KZK-type parabolic evolution equation. This model considers ultrasound beam diffraction, attenuation, and tissue nonlinearity. Time-domain numerical model is based on that originally developed by Lee and Hamilton [J. Acoust. Soc. Am 97:906-917 (1995)] for axi-symmetric acoustic field. The initial acoustic waveform emitted from the transducer is assumed to be a broadband wave modulated by Gaussian envelope. Scattering from microbubbles seeded in the blood stream is characterized. Hence, we compute the pressure field impinges the wall of a coated microbubble; the dynamics of oscillating microbubble can be modeled using Rayleigh-Plesset-type equation. Here, the continuity and the radial-momentum equation of encapsulated microbubbles are used to account for the lipid layer surrounding the microbubble. Numerical results show the effects of tissue and microbubble nonlinearities on the propagating pressure wave field. These nonlinearities have a strong influence on the waveform distortion and harmonic generation of the propagating and scattering waves. Results also show that microbubbles have stronger nonlinearity than tissue, and thus improves S/N ratio. These theoretical predictions of wave phenomena provide further understanding of biomedical imaging technique and provide better system design.

Propagation of Torsional Alfvén Waves from the Photosphere to the Corona: Reflection, Transmission, and Heating in Expanding Flux Tubes

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

Soler, Roberto; Terradas, Jaume; Oliver, Ramón

It has been proposed that Alfvén waves play an important role in the energy propagation through the solar atmospheric plasma and its heating. Here we theoretically investigate the propagation of torsional Alfvén waves in magnetic flux tubes expanding from the photosphere up to the low corona and explore the reflection, transmission, and dissipation of wave energy. We use a realistic variation of the plasma properties and the magnetic field strength with height. Dissipation by ion–neutral collisions in the chromosphere is included using a multifluid partially ionized plasma model. Considering the stationary state, we assume that the waves are driven belowmore » the photosphere and propagate to the corona, while they are partially reflected and damped in the chromosphere and transition region. The results reveal the existence of three different propagation regimes depending on the wave frequency: low frequencies are reflected back to the photosphere, intermediate frequencies are transmitted to the corona, and high frequencies are completely damped in the chromosphere. The frequency of maximum transmissivity depends on the magnetic field expansion rate and the atmospheric model, but is typically in the range of 0.04–0.3 Hz. Magnetic field expansion favors the transmission of waves to the corona and lowers the reflectivity of the chromosphere and transition region compared to the case with a straight field. As a consequence, the chromospheric heating due to ion–neutral dissipation systematically decreases when the expansion rate of the magnetic flux tube increases.« less

Linear theory of plasma Čerenkov masers

NASA Astrophysics Data System (ADS)

Birau, M.

1996-11-01

A different theoretical model of Čerenkov instability in the linear amplification regime of plasma Čerenkov masers is developed. The model assumes a cold relativistic annular electron beam propagating through a column of cold dense plasma, the two bodies being immersed in an infinite magnetic guiding field inside a perfect cylindrical waveguide. In order to simplify the calculations, a radial rectangular distribution of plasma and beam density is assumed and only azimuthal symmetric modes are under investigation. The model's difference consists of taking into account the whole plasma and beam electromagnetic structures in the interpretation of the Čerenkov instability. This model leads to alternative results such as the possibility of emission at several frequencies. In addition, the electric field is calculated taking into account its radial phase dependence, so that a map of the field in the interaction region can be presented.

The effect of convection and shear on the damping and propagation of pressure waves

NASA Astrophysics Data System (ADS)

Kiel, Barry Vincent

Combustion instability is the positive feedback between heat release and pressure in a combustion system. Combustion instability occurs in the both air breathing and rocket propulsion devices, frequently resulting in high amplitude spinning waves. If unchecked, the resultant pressure fluctuations can cause significant damage. Models for the prediction of combustion instability typically include models for the heat release, the wave propagation and damping. Many wave propagation models for propulsion systems assume negligible flow, resulting in the wave equation. In this research the effect of flow on wave propagation was studied both numerically and experimentally. Two experiential rigs were constructed, one with axial flow to study the longitudinal waves, the other with swirling flow to study circumferential waves. The rigs were excited with speakers and the resultant pressure was measured simultaneously at many locations. Models of the rig were also developed. Equations for wave propagation were derived from the Euler Equations. The resultant resembled the wave equation with three additional terms, two for the effect of the convection and a one for the effect of shear of the mean flow on wave propagation. From the experimental and numerical data several conclusions were made. First, convection and shear both act as damping on the wave propagation, reducing the magnitude of the Frequency Response Function and the resonant frequency of the modes. Second, the energy extracted from the mean flow as a result of turbulent shear for a given condition is frequency dependent, decreasing with increasing frequency. The damping of the modes, measured for the same shear flow, also decreased with frequency. Finally, the two convective terms cause the anti-nodes of the modes to no longer be stationary. For both the longitudinal and circumferential waves, the anti-nodes move through the domain even for mean flow Mach numbers less than 0.10. It was concluded that convection causes the spinning waves documented in inlets and exhausts of gas turbine engines, rocket combustion chambers, and afterburner chambers. As a result, the effects of shear must be included when modeling wave propagation, even for mean flows less than < Mach 0.10.

New Priorities for a Changing U.S. Economy

DTIC Science & Technology

1999-01-08

Stockholm, Sweden, 1991. [73] R . Malladi , J. Sethian, B. and Vermuri, "Shape modelling with front propagation: a level set approach," IEEE PAMI17...represented as n x n matrices of operators in £(£), and r (") is represented by a diagonal matrix, with diagonal entries equal to T. Denote by An...also has independent interest. Theorem 1 Assume that A’ is a *-algebra of finite dimension n. Then fa(A) = ^..(Art) for every A 6 £(£)~ r ~ Remark

Nonthermal Particles and Radiation Produced by Cluster Merger Shocks

DTIC Science & Technology

2003-09-10

NONTHERMAL PARTICLES AND RADIATION PRODUCED BY CLUSTER MERGER SHOCKS Robert C. Berrington and Charles D. Dermer Naval Research Laboratory, Code 7653...of the merging cluster and is assumed to be constant as the shock propagates outward from the cluster center. In this paper , we model the cluster ...emission in the60–250 eV band for a number of clus- ters. These clusters include Virgo , Coma, Fornax, A2199, A1795, and A4059 (Lieu et al. 1996a, 1996b

Evaluation of Acoustic Doppler Current Profiler measurements of river discharge

USGS Publications Warehouse

Morlock, S.E.

1996-01-01

The standard deviations of the ADCP measurements ranged from approximately 1 to 6 percent and were generally higher than the measurement errors predicted by error-propagation analysis of ADCP instrument performance. These error-prediction methods assume that the largest component of ADCP discharge measurement error is instrument related. The larger standard deviations indicate that substantial portions of measurement error may be attributable to sources unrelated to ADCP electronics or signal processing and are functions of the field environment.

Acoustic propagation in a thermally stratified atmosphere

NASA Technical Reports Server (NTRS)

Vanmoorhem, W. K.

1988-01-01

Acoustic propagation in an atmosphere with a specific form of a temperature profile has been investigated by analytical means. The temperature profile used is representative of an actual atmospheric profile and contains three free parameters. Both lapse and inversion cases have been considered. Although ray solutions have been considered, the primary emphasis has been on solutions of the acoustic wave equation with point source where the sound speed varies with height above the ground corresponding to the assumed temperature profile. The method used to obtain the solution of the wave equation is based on Hankel transformation of the wave equation, approximate solution of the transformed equation for wavelength small compared to the scale of the temperature (or sound speed) profile, and approximate or numerical inversion of the Hankel transformed solution. The solution displays the characteristics found in experimental data but extensive comparison between the models and experimental data has not been carried out.

Hierarchical Active Inference: A Theory of Motivated Control.

PubMed

Pezzulo, Giovanni; Rigoli, Francesco; Friston, Karl J

2018-04-01

Motivated control refers to the coordination of behaviour to achieve affectively valenced outcomes or goals. The study of motivated control traditionally assumes a distinction between control and motivational processes, which map to distinct (dorsolateral versus ventromedial) brain systems. However, the respective roles and interactions between these processes remain controversial. We offer a novel perspective that casts control and motivational processes as complementary aspects - goal propagation and prioritization, respectively - of active inference and hierarchical goal processing under deep generative models. We propose that the control hierarchy propagates prior preferences or goals, but their precision is informed by the motivational context, inferred at different levels of the motivational hierarchy. The ensuing integration of control and motivational processes underwrites action and policy selection and, ultimately, motivated behaviour, by enabling deep inference to prioritize goals in a context-sensitive way. Copyright © 2018 The Author(s). Published by Elsevier Ltd.. All rights reserved.

Nonlinear waves in electron-positron-ion plasmas including charge separation

NASA Astrophysics Data System (ADS)

Mugemana, A.; Moolla, S.; Lazarus, I. J.

2017-02-01

Nonlinear low-frequency electrostatic waves in a magnetized, three-component plasma consisting of hot electrons, hot positrons and warm ions have been investigated. The electrons and positrons are assumed to have Boltzmann density distributions while the motion of the ions are governed by fluid equations. The system is closed with the Poisson equation. This set of equations is numerically solved for the electric field. The effects of the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle are investigated. It is shown that depending on the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle, the numerical solutions exhibit waveforms that are sinusoidal, sawtooth and spiky. The introduction of the Poisson equation increased the Mach number required to generate the waveforms but the driving electric field E 0 was reduced. The results are compared with satellite observations.

Acoustic propagation in a thermally stratified atmosphere

NASA Technical Reports Server (NTRS)

Vanmoorhem, W. K.

1987-01-01

Acoustic propagation in an atmosphere with a specific form of temperature profile has been investigated by analytical means. The temperature profile used is representative of an actual atmospheric profile and contains three free parameters. Both lapse and inversion cases have been considered. Although ray solution have been considered the primary emphasis has been on solutions of the acoustic wave equation with point force where the sound speed varies with height above the ground corresponding to the assumed temperature profile. The method used to obtain the solution of the wave equation is based on Hankel transformation of the wave equation, approximate solution of the transformed equation for wavelength small compared to the scale of the temperature (or sound speed) profile, and approximate or numerical inversion of the Hankel transformed solution. The solution displays the characteristics found in experimental data but extensive comparison between the models and experimental data has not been carried out.

The influence of polarization on millimeter wave propagation through rain. Ph.D Thesis. Interim Report

NASA Technical Reports Server (NTRS)

Wiley, P. H.; Bostian, C. W.; Stutzman, W. L.

1973-01-01

The influence of polarization on millimeter wave propagation is investigated from both an experimental and a theoretical viewpoint. First, previous theoretical and experimental work relating to the attenuation and depolarization of millimeter waves by rainfall is discussed. Considerable detail is included in the literature review. Next, a theoretical model is developed to predict the cross polarization level during rainfall from the path average rain rate and the scattered field from a single raindrop. Finally, data from the VPI and SU depolarization experiment are presented as verification of the new model, and a comparison is made with other theories and experiments. Aspects of the new model are: (1) spherical rather than plane waves are assumed, (2) the average drop diameter is used rather than a drop size distribution, and (3) it is simple enough so that the effect which changing one or more parameters has on the crosspolarization level is easily seen.

Error Analysis and Validation for Insar Height Measurement Induced by Slant Range

NASA Astrophysics Data System (ADS)

Zhang, X.; Li, T.; Fan, W.; Geng, X.

2018-04-01

InSAR technique is an important method for large area DEM extraction. Several factors have significant influence on the accuracy of height measurement. In this research, the effect of slant range measurement for InSAR height measurement was analysis and discussed. Based on the theory of InSAR height measurement, the error propagation model was derived assuming no coupling among different factors, which directly characterise the relationship between slant range error and height measurement error. Then the theoretical-based analysis in combination with TanDEM-X parameters was implemented to quantitatively evaluate the influence of slant range error to height measurement. In addition, the simulation validation of InSAR error model induced by slant range was performed on the basis of SRTM DEM and TanDEM-X parameters. The spatial distribution characteristics and error propagation rule of InSAR height measurement were further discussed and evaluated.

A simulation of high energy cosmic ray propagation 1

NASA Technical Reports Server (NTRS)

Honda, M.; Kifune, T.; Matsubara, Y.; Mori, M.; Nishijima, K.; Teshima, M.

1985-01-01

High energy cosmic ray propagation of the energy region 10 to the 14.5 power - 10 to the 18th power eV is simulated in the inter steller circumstances. In conclusion, the diffusion process by turbulent magnetic fields is classified into several regions by ratio of the gyro-radius and the scale of turbulence. When the ratio becomes larger then 10 to the minus 0.5 power, the analysis with the assumption of point scattering can be applied with the mean free path E sup 2. However, when the ratio is smaller than 10 to the minus 0.5 power, we need a more complicated analysis or simulation. Assuming the turbulence scale of magnetic fields of the Galaxy is 10-30pc and the mean magnetic field strength is 3 micro gauss, the energy of cosmic ray with that gyro-radius is about 10 to the 16.5 power eV.

Elastic spheres can walk on water.

PubMed

Belden, Jesse; Hurd, Randy C; Jandron, Michael A; Bower, Allan F; Truscott, Tadd T

2016-02-04

Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys.

Elastic spheres can walk on water

PubMed Central

Belden, Jesse; Hurd, Randy C.; Jandron, Michael A.; Bower, Allan F.; Truscott, Tadd T.

2016-01-01

Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys. PMID:26842860

Relativistic theory of the falling retroreflector gravimeter

NASA Astrophysics Data System (ADS)

Ashby, Neil

2018-02-01

We develop a relativistic treatment of interference between light reflected from a falling cube retroreflector in the vertical arm of an interferometer, and light in a reference beam in the horizontal arm. Coordinates that are nearly Minkowskian, attached to the falling cube, are used to describe the propagation of light within the cube. Relativistic effects such as the dependence of the coordinate speed of light on gravitational potential, propagation of light along null geodesics, relativity of simultaneity, and Lorentz contraction of the moving cube, are accounted for. The calculation is carried to first order in the gradient of the acceleration of gravity. Analysis of data from a falling cube gravimeter shows that the propagation time of light within the cube itself causes a significant reduction in the value of the acceleration of gravity obtained from measurements, compared to assuming reflection occurs at the face. An expression for the correction to g is derived and found to agree with experiment. Depending on the instrument, the correction can be several microgals, comparable to commonly applied corrections such as those due to polar motion and earth tides. The controversial ‘speed of light’ correction is discussed. Work of the US government, not subject to copyright.

Acoustic propagation in a thermally stratified atmosphere

NASA Technical Reports Server (NTRS)

Vanmoorhem, W. K.

1985-01-01

This report describes the activities during the fifth six month period of the investigation of acoustic propagation in the atmosphere with a realistic temperature profile. Progress has been achieved in two major directions: comparisons between the lapse model and experimental data taken by NASA during the second tower experiment, and development of a model propagation in an inversion. Data from the second tower experiment became available near the end of 1984 and some comparisons have been carried out, but this work is not complete. Problems with the temperature profiler during the experiment have produced temperature profiles that are difficult to fit the assumed variation of temperature with height, but in cases where reasonable fits have been obtained agreement between the model and the experiments are close. The major weaknesses in the model appear to be the presence of discontinuities in some regions, the low sound levels predicted near the source height, and difficulties with the argument of the Hankel function being outside the allowable range. Work on the inversion model has progressed slowly, and the rays for that case are discussed along with a simple energy conservation model of sound level enhancement in the inversion case.

Uncertainties propagation and global sensitivity analysis of the frequency response function of piezoelectric energy harvesters

NASA Astrophysics Data System (ADS)

Ruiz, Rafael O.; Meruane, Viviana

2017-06-01

The goal of this work is to describe a framework to propagate uncertainties in piezoelectric energy harvesters (PEHs). These uncertainties are related to the incomplete knowledge of the model parameters. The framework presented could be employed to conduct prior robust stochastic predictions. The prior analysis assumes a known probability density function for the uncertain variables and propagates the uncertainties to the output voltage. The framework is particularized to evaluate the behavior of the frequency response functions (FRFs) in PEHs, while its implementation is illustrated by the use of different unimorph and bimorph PEHs subjected to different scenarios: free of uncertainties, common uncertainties, and uncertainties as a product of imperfect clamping. The common variability associated with the PEH parameters are tabulated and reported. A global sensitivity analysis is conducted to identify the Sobol indices. Results indicate that the elastic modulus, density, and thickness of the piezoelectric layer are the most relevant parameters of the output variability. The importance of including the model parameter uncertainties in the estimation of the FRFs is revealed. In this sense, the present framework constitutes a powerful tool in the robust design and prediction of PEH performance.

Does laser-driven heat front propagation depend on material microstructure?

NASA Astrophysics Data System (ADS)

Colvin, J. D.; Matsukuma, H.; Fournier, K. B.; Yoga, A.; Kemp, G. E.; Tanaka, N.; Zhang, Z.; Kota, K.; Tosaki, S.; Ikenouchi, T.; Nishimura, H.

2016-10-01

We showed earlier that the laser-driven heat front propagation velocity in low-density Ti-silica aerogel and TiO2 foam targets was slower than that simulated with a 2D radiation-hydrodynamics code incorporating an atomic kinetics model in non-LTE and assuming initially homogeneous material. Some theoretical models suggest that the heat front is slowed over what it would be in a homogeneous medium by the microstructure of the foam. In order to test this hypothesis we designed and conducted a comparison experiment on the GEKKO laser to measure heat front propagation velocity in two targets, one an Ar/CO2 gas mixture and the other a TiO2 foam, that had identical initial densities and average ionization states. We found that the heat front traveled about ten times faster in the gas than in the foam. We present the details of the experiment design and a comparison of the data with the simulations. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract No. DE-AC52-07NA27344, and the joint research project of ILE Osaka U. (contract Nos. 2014A1-04 and 2015A1-02).

Eruption mass estimation using infrasound waveform inversion and ash and gas measurements: Evaluation at Sakurajima Volcano, Japan

NASA Astrophysics Data System (ADS)

Fee, David; Izbekov, Pavel; Kim, Keehoon; Yokoo, Akihiko; Lopez, Taryn; Prata, Fred; Kazahaya, Ryunosuke; Nakamichi, Haruhisa; Iguchi, Masato

2017-12-01

Eruption mass and mass flow rate are critical parameters for determining the aerial extent and hazard of volcanic emissions. Infrasound waveform inversion is a promising technique to quantify volcanic emissions. Although topography may substantially alter the infrasound waveform as it propagates, advances in wave propagation modeling and station coverage permit robust inversion of infrasound data from volcanic explosions. The inversion can estimate eruption mass flow rate and total eruption mass if the flow density is known. However, infrasound-based eruption flow rates and mass estimates have yet to be validated against independent measurements, and numerical modeling has only recently been applied to the inversion technique. Here we present a robust full-waveform acoustic inversion method, and use it to calculate eruption flow rates and masses from 49 explosions from Sakurajima Volcano, Japan. Six infrasound stations deployed from 12-20 February 2015 recorded the explosions. We compute numerical Green's functions using 3-D Finite Difference Time Domain modeling and a high-resolution digital elevation model. The inversion, assuming a simple acoustic monopole source, provides realistic eruption masses and excellent fit to the data for the majority of the explosions. The inversion results are compared to independent eruption masses derived from ground-based ash collection and volcanic gas measurements. Assuming realistic flow densities, our infrasound-derived eruption masses for ash-rich eruptions compare favorably to the ground-based estimates, with agreement ranging from within a factor of two to one order of magnitude. Uncertainties in the time-dependent flow density and acoustic propagation likely contribute to the mismatch between the methods. Our results suggest that realistic and accurate infrasound-based eruption mass and mass flow rate estimates can be computed using the method employed here. If accurate volcanic flow parameters are known, application of this technique could be broadly applied to enable near real-time calculation of eruption mass flow rates and total masses. These critical input parameters for volcanic eruption modeling and monitoring are not currently available.

Measurement system and model for simultaneously measuring 6DOF geometric errors.

PubMed

Zhao, Yuqiong; Zhang, Bin; Feng, Qibo

2017-09-04

A measurement system to simultaneously measure six degree-of-freedom (6DOF) geometric errors is proposed. The measurement method is based on a combination of mono-frequency laser interferometry and laser fiber collimation. A simpler and more integrated optical configuration is designed. To compensate for the measurement errors introduced by error crosstalk, element fabrication error, laser beam drift, and nonparallelism of two measurement beam, a unified measurement model, which can improve the measurement accuracy, is deduced and established using the ray-tracing method. A numerical simulation using the optical design software Zemax is conducted, and the results verify the correctness of the model. Several experiments are performed to demonstrate the feasibility and effectiveness of the proposed system and measurement model.

Artificial photosynthetic systems: assemblies of slipped cofacial porphyrins and phthalocyanines showing strong electronic coupling.

PubMed

Satake, Akiharu; Kobuke, Yoshiaki

2007-06-07

This paper reviews selected types of structurally well defined assemblies of porphyrins and phthalocyanines with strong electronic coupling. Face-to-face, head-to-tail, slipped cofacial, and non-parallel dimeric motifs constructed by covalent and non-covalent bonds are compared in the earlier sections. Their molecular orientation, electronic overlap, and absorption and fluorescence properties are discussed with a view towards the development of artificial photosynthetic systems and molecular electronics. Complementary coordination dimers are fully satisfactory in terms of structural stability, orientation factor, pi-electronic overlap, and zero fluorescence quenching. In later sections, several polymeric and macrocyclic porphyrin assemblies constructed by a combination of covalent bonds and complementary coordination bonds are discussed from the viewpoint of light-harvesting antenna functions.

Seniority Number in Valence Bond Theory.

PubMed

Chen, Zhenhua; Zhou, Chen; Wu, Wei

2015-09-08

In this work, a hierarchy of valence bond (VB) methods based on the concept of seniority number, defined as the number of singly occupied orbitals in a determinant or an orbital configuration, is proposed and applied to the studies of the potential energy curves (PECs) of H8, N2, and C2 molecules. It is found that the seniority-based VB expansion converges more rapidly toward the full configuration interaction (FCI) or complete active space self-consistent field (CASSCF) limit and produces more accurate PECs with smaller nonparallelity errors than its molecular orbital (MO) theory-based analogue. Test results reveal that the nonorthogonal orbital-based VB theory provides a reverse but more efficient way to truncate the complete active Hilbert space by seniority numbers.

Continuous-feed electrochemical cell with nonpacking particulate electrode

DOEpatents

Cooper, John F.

1995-01-01

An electrochemical cell providing full consumption of electrochemically active particles in a nonpacking, electrolyte-permeable bed has a tapered cell cavity bounded by two nonparallel surfaces separated by a distance that promotes bridging of particles across the cavity. The gap/particle size ratio is maintained as the particles are consumed, decrease in size, and travel from the point of entry to the narrower end of the cell. A cell of this configuration supports a bed of low packing density maintained in a dynamic steady state by alternate formation and collapse of particle bridges across the gap and associated voids over the entire active area of the cell. The cell design can be applied to refuelable zinc/air cells and zinc/ferrocyanide storage batteries.

Continuous-feed electrochemical cell with nonpacking particulate electrode

DOEpatents

Cooper, J.F.

1995-07-18

An electrochemical cell providing full consumption of electrochemically active particles in a nonpacking, electrolyte-permeable bed has a tapered cell cavity bounded by two nonparallel surfaces separated by a distance that promotes bridging of particles across the cavity. The gap/particle size ratio is maintained as the particles are consumed, decrease in size, and travel from the point of entry to the narrower end of the cell. A cell of this configuration supports a bed of low packing density maintained in a dynamic steady state by alternate formation and collapse of particle bridges across the gap and associated voids over the entire active area of the cell. The cell design can be applied to refuelable zinc/air cells and zinc/ferrocyanide storage batteries. 6 figs.

Hypersonic Boundary Layer Instability Over a Corner

NASA Technical Reports Server (NTRS)

Balakumar, Ponnampalam; Zhao, Hong-Wu; McClinton, Charles (Technical Monitor)

2001-01-01

A boundary-layer transition study over a compression corner was conducted under a hypersonic flow condition. Due to the discontinuities in boundary layer flow, the full Navier-Stokes equations were solved to simulate the development of disturbance in the boundary layer. A linear stability analysis and PSE method were used to get the initial disturbance for parallel and non-parallel flow respectively. A 2-D code was developed to solve the full Navier-stokes by using WENO(weighted essentially non-oscillating) scheme. The given numerical results show the evolution of the linear disturbance for the most amplified disturbance in supersonic and hypersonic flow over a compression ramp. The nonlinear computations also determined the minimal amplitudes necessary to cause transition at a designed location.

A rapid calculation system for tsunami propagation in Japan by using the AQUA-MT/CMT solutions

NASA Astrophysics Data System (ADS)

Nakamura, T.; Suzuki, W.; Yamamoto, N.; Kimura, H.; Takahashi, N.

2017-12-01

We developed a rapid calculation system of geodetic deformations and tsunami propagation in and around Japan. The system automatically conducts their forward calculations by using point source parameters estimated by the AQUA system (Matsumura et al., 2006), which analyze magnitude, hypocenter, and moment tensors for an event occurring in Japan in 3 minutes of the origin time at the earliest. An optimized calculation code developed by Nakamura and Baba (2016) is employed for the calculations on our computer server with 12 core processors of Intel Xeon 2.60 GHz. Assuming a homogeneous fault slip in the single fault plane as the source fault, the developed system calculates each geodetic deformation and tsunami propagation by numerically solving the 2D linear long-wave equations for the grid interval of 1 arc-min from two fault orientations simultaneously; i.e., one fault and its conjugate fault plane. Because fault models based on moment tensor analyses of event data are used, the system appropriately evaluate tsunami propagation even for unexpected events such as normal faulting in the subduction zone, which differs with the evaluation of tsunami arrivals and heights from a pre-calculated database by using fault models assuming typical types of faulting in anticipated source areas (e.g., Tatehata, 1998; Titov et al., 2005; Yamamoto et al., 2016). By the complete automation from event detection to output graphical figures, the calculation results can be available via e-mail and web site in 4 minutes of the origin time at the earliest. For moderate-sized events such as M5 to 6 events, the system helps us to rapidly investigate whether amplitudes of tsunamis at nearshore and offshore stations exceed a noise level or not, and easily identify actual tsunamis at the stations by comparing with obtained synthetic waveforms. In the case of using source models investigated from GNSS data, such evaluations may be difficult because of the low resolution of sources due to a low signal to noise ratio at land stations. For large to huge events in offshore areas, the developed system may be useful to decide to starting or stopping preparations and precautions against tsunami arrivals, because calculation results including arrival times and heights of initial and maximum waves can be rapidly available before their arrivals at coastal areas.

On the behavior of return stroke current and the remotely detected electric field change waveform

NASA Astrophysics Data System (ADS)

Shao, Xuan-Min; Lay, Erin; Jacobson, Abram R.

2012-04-01

After accumulating a large number of remotely recorded negative return stroke electric field change waveforms, a subtle but persistent kink was found following the main return stroke peak by several microseconds. To understand the corresponding return stroke current properties behind the kink and the general return stroke radiation waveform, we analyze strokes occurring in triggered lightning flashes for which have been measured both the channel base current and simultaneous remote electric radiation field. In this study, the channel base current is assumed to propagate along the return stroke channel in a dispersive and lossy manner. The measured channel base current is band-pass filtered, and the higher-frequency component is assumed to attenuate faster than the lower-frequency component. The radiation electric field is computed for such a current behavior and is then propagated to distant sensors. It is found that such a return stroke model is capable of very closely reproducing the measured electric waveforms at multiple stations for the triggered return strokes, and such a model is considered applicable to the common behavior of the natural return stroke as well. On the basis of the analysis, a number of other observables are derived. The time-evolving current dispersion and attenuation compare well with previously reported optical observations. The observable speed tends to agree with optical and VHF observations. Line charge density that is removed or deposited by the return stroke is derived, and the implication of the charge density distribution on leader channel decay is discussed.

Investigating Plasma Motion of Magnetic Clouds at 1 AU through a Velocity-modified Cylindrical Force-free Flux Rope Model

NASA Astrophysics Data System (ADS)

Wang, Y.; Shen, C.; Liu, R.; Zhou, Z.

2014-12-01

Magnetic clouds (MCs) are the interplanetary counterparts of coronal mass ejections (CMEs). Due to the very low value of Can't connect to bucket.int.confex.com:4201 (Connection refused) LWP::Protocol::http::Socket: connect: Connection refused at /usr/local/lib/perl5/site_perl/5.8.8/LWP/Protocol/http.pm line 51. in MCs, they are believed to be in a nearly force-free state and therefore are able to be modeled by a cylindrical force-free flux rope. However, the force-free state only describes the magnetic field topology but not the plasma motion of a MC. For a MC propagating in interplanetary space, the global plasma motion has three possible components: linear propagating motion of a MC away from the Sun, expanding motion and circular motion with respect to the axis of the MC. By assuming the quasi-steady evolution and self-similar expansion, we introduced the three-component motion into the cylindrical force-free flux rope model, and developed a velocity-modified model. Then we applied the model to 73 MCs observed by Wind spacecraft to investigate the properties of the plasma motion of MCs. It is found that (1) some MCs did not propagate along the Sun-Earth line, suggesting the direct evidence of the CME's deflected propagation and/or rotation in interplanetary space, (2) the expansion speed is correlated with the radial propagation speed and 62%/17% of MCs underwent a under/over-expansion at 1 AU, and (3) the circular motion does exists though it is only on the order of 10 km s-1. These findings advance our understanding of the MC's properties at 1 AU as well as the dynamic evolution of CMEs from the Sun to interplanetary space.

Galactic synchrotron radiation from radio to microwaves, and its relation to cosmic-ray propagation models: past, present and future

NASA Astrophysics Data System (ADS)

Orlando, Elena

2016-04-01

Galactic synchrotron radiation observed from radio to microwaves is produced by cosmic-ray (CR) electrons propagating in magnetic fields (B-fields). The low-frequency foreground component separated maps by WMAP and Planck depend on the assumed synchrotron spectrum. The synchrotron spectrum varies for different line of sights as a result of changes on the CR spectrum due to propagation effects and source distributions. Our present knowledge of the CR spectrum at different locations in the Galaxy is not sufficient to distinguish various possibilities in the modeling. As a consequence uncertainties on synchrotron emission models complicate the foreground component separation analysis with Planck and future microwave telescopes. Hence, any advancement in synchrotron modeling is important for separating the different foreground components.The first step towards a more comprehensive understanding of degeneracy and correlation among the synchrotron model parameters is outlined in our Strong et al. 2011 and Orlando et al. 2013 papers. In the latter the conclusion was that CR spectrum, propagation models, B-fields, and foreground component separation analysis need to be studied simultaneously in order to properly obtain and interpret the synchrotron foreground. Indeed for the officially released Planck maps, we use only the best spectral model from our above paper for the component separation analysis.Here we present a collections of our latest results on synchrotron, CRs and B-fields in the context of CR propagation, showing also our recent work on B-fields within the Planck Collaboration. We underline also the importance of using the constraints on CRs that we obtain from gamma ray observations. Methods and perspectives for further studies on the synchrotron foreground will be addressed.

Elastic Reverse Time Migration (RTM) From Surface Topography

NASA Astrophysics Data System (ADS)

Akram, Naveed; Chen, Xiaofei

2017-04-01

Seismic Migration is a promising data processing technique to construct subsurface images by projecting the recorded seismic data at surface back to their origins. There are numerous Migration methods. Among them, Reverse Time Migration (RTM) is considered a robust and standard imaging technology in present day exploration industry as well as in academic research field because of its superior performance compared to traditional migration methods. Although RTM is extensive computing and time consuming but it can efficiently handle the complex geology, highly dipping reflectors and strong lateral velocity variation all together. RTM takes data recorded at the surface as a boundary condition and propagates the data backwards in time until the imaging condition is met. It can use the same modeling algorithm that we use for forward modeling. The classical seismic exploration theory assumes flat surface which is almost impossible in practice for land data. So irregular surface topography has to be considered in simulation of seismic wave propagation, which is not always a straightforward undertaking. In this study, Curved grid finite difference method (CG-FDM) is adapted to model elastic seismic wave propagation to investigate the effect of surface topography on RTM results and explore its advantages and limitations with synthetic data experiments by using Foothill model with topography as the true model. We focus on elastic wave propagation rather than acoustic wave because earth actually behaves as an elastic body. Our results strongly emphasize on the fact that irregular surface topography must be considered for modeling of seismic wave propagation to get better subsurface images specially in mountainous scenario and suggest practitioners to properly handled the geometry of data acquired on irregular topographic surface in their imaging algorithms.

Elastic Reverse Time Migration (RTM) From Surface Topography

NASA Astrophysics Data System (ADS)

Naveed, A.; Chen, X.

2016-12-01

Seismic Migration is a promising data processing technique to construct subsurface images by projecting the recorded seismic data at surface back to their origins. There are numerous Migration methods. Among them, Reverse Time Migration (RTM) is considered a robust and standard imaging technology in present day exploration industry as well as in academic research field because of its superior performance compared to traditional migration methods. Although RTM is extensive computing and time consuming but it can efficiently handle the complex geology, highly dipping reflectors and strong lateral velocity variation all together. RTM takes data recorded at the surface as a boundary condition and propagates the data backwards in time until the imaging condition is met. It can use the same modeling algorithm that we use for forward modeling. The classical seismic exploration theory assumes flat surface which is almost impossible in practice for land data. So irregular surface topography has to be considered in simulation of seismic wave propagation, which is not always a straightforward undertaking. In this study, Curved grid finite difference method (CG-FDM) is adapted to model elastic seismic wave propagation to investigate the effect of surface topography on RTM results and explore its advantages and limitations with synthetic data experiments by using Foothill model with topography as the true model. We focus on elastic wave propagation rather than acoustic wave because earth actually behaves as an elastic body. Our results strongly emphasize on the fact that irregular surface topography must be considered for modeling of seismic wave propagation to get better subsurface images specially in mountainous scenario and suggest practitioners to properly handled the geometry of data acquired on irregular topographic surface in their imaging algorithms.

Partially coherent isodiffracting pulsed beams

NASA Astrophysics Data System (ADS)

Koivurova, Matias; Ding, Chaoliang; Turunen, Jari; Pan, Liuzhan

2018-02-01

We investigate a class of isodiffracting pulsed beams, which are superpositions of transverse modes supported by spherical-mirror laser resonators. By employing modal weights that, for stationary light, produce a Gaussian Schell-model beam, we extend this standard model to pulsed beams. We first construct the two-frequency cross-spectral density function that characterizes the spatial coherence in the space-frequency domain. By assuming a power-exponential spectral profile, we then employ the generalized Wiener-Khintchine theorem for nonstationary light to derive the two-time mutual coherence function that describes the space-time coherence of the ensuing beams. The isodiffracting nature of the laser resonator modes permits all (paraxial-domain) calculations at any propagation distance to be performed analytically. Significant spatiotemporal coupling is revealed in subcycle, single-cycle, and few-cycle domains, where the partial spatial coherence also leads to reduced temporal coherence even though full spectral coherence is assumed.

Nonsimilar Solution for Shock Waves in a Rotational Axisymmetric Perfect Gas with a Magnetic Field and Exponentially Varying Density

NASA Astrophysics Data System (ADS)

Nath, G.; Sinha, A. K.

2017-01-01

The propagation of a cylindrical shock wave in an ideal gas in the presence of a constant azimuthal magnetic field with consideration for the axisymmetric rotational effects is investigated. The ambient medium is assumed to have the radial, axial, and azimuthal velocity components. The fluid velocities and density of the ambient medium are assumed to vary according to an exponential law. Nonsimilar solutions are obtained by taking into account the vorticity vector and its components. The dependences of the characteristics of the problem on the Alfven-Mach number and time are obtained. It is shown that the presence of a magnetic field has a decaying effect on the shock wave. The pressure and density are shown to vanish at the inner surface (piston), and hence a vacuum forms at the line of symmetry.

Generation and propagation of electromagnetic waves in the magnetosphere. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Taylor, W. W. L.

1973-01-01

Characteristics of broadband ELF, VLF, and LF emissions in the magnetosphere were calculated assuming incoherent Cerenkov radiation from magnetospheric electrons with energies from 50 eV to 50 keV. Calculations were included to determine the ray paths of the emitted waves. A diffusive equilibrium model of the magnetosphere with an ionosphere, plasmapause, and a centered dipole magnetic field was used. Ray path calculations were done in three dimensions. Using simultaneous energetic electron and VLF data, comparisons were made between calculated and observed VLF hiss. Assuming a wave normal angle six degrees from the resonance cone angle, the calculated spectral densities are both two orders of magnitude below the observed spectral densities. It seems unlikely that VLF hiss is produced by incoherent Cerenkov radiation. The observed spectral shape of V-shaped VLF hiss is similar to that calculated from incoherent Cerenkov radiation.

Signatures of photon-scalar interaction in astrophysical situations

NASA Astrophysics Data System (ADS)

Ganguly, Avijit K.; Jaiswal, Manoj K.

2018-01-01

Dimension-5 photon ( γ) scalar ( ϕ) interaction term usually appear in the Lagrangians of bosonic sector of unified theories of electromagnetism and gravity. This interaction makes the medium dichoric and induces optical activity. Considering a toy model of an ultra-cold magnetized compact star (white dwarf (WD) or neutron star (NS)), we have modeled the propagation of very low energy photons with such interaction, in the environment of these stars. Assuming synchro-curvature process as the dominant mechanism of emission in such environments, we have tried to understand the polarimetric implications of photon-scalar coupling on the produced spectrum of the same. Further more assuming the `emission-energy vs emission-altitude' relation, that is believed to hold in such ( i.e., cold magnetized WD or NS) environments, we have tried to point out the possible modifications to the radiation spectrum when the same is incorporated along with dimension-5 photon-scalar mixing operator.

Characterizing cosmic-ray propagation in massive star-forming regions: The case of 30 Doradus and the large Magellanic cloud

DOE PAGES

Murphy, E. J.; Porter, T. A.; Moskalenko, I. V.; ...

2012-04-24

We investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using infrared, radio, and γ-ray data and a phenomenological model based on the radio-far-infrared correlation within galaxies. By employing a correlation analysis, we derive an average propagation length of ~100-140 pc for ~3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed γ-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and γ-ray data, wemore » estimate a ~20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for ~3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is ~4 times higher, scaling as (R/GV) δ with δ ≈ 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include ~70 GeV CR nuclei traced by the 3-10 GeV γ-ray data (δ ≈ 0.66 ± 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D R ≈ (0.9-1.0) × 10 27(R/GV) 0.7 cm 2 s –1. We also compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor.« less

Measuring and engineering the atomic mass density wave of a Gaussian mass-polariton pulse in optical fibers

NASA Astrophysics Data System (ADS)

Partanen, Mikko; Tulkki, Jukka

2018-02-01

Conventional theories of electromagnetic waves in a medium assume that only the energy of the field propagates inside the medium. Consequently, they neglect the transport of mass density by the medium atoms. We have recently presented foundations of a covariant theory of light propagation in a nondispersive medium by considering a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces [Phys. Rev. A 95, 063850 (2017)]. In particular, we have shown that the mass is transferred by an atomic mass density wave (MDW), which gives rise to mass-polariton (MP) quasiparticles, i.e., covariant coupled states of the field and matter having a nonzero rest mass. Another key observation of the mass-polariton theory of light is that, in common semiconductors, most of the momentum of light is transferred by moving atoms, e.g., 92% in the case of silicon. In this work, we generalize the MP theory of light for dispersive media and consider experimental measurement of the mass transferred by the MDW atoms when an intense light pulse propagates in a silicon fiber. In particular, we consider optimal intensity and time dependence of a Gaussian pulse and account for the breakdown threshold irradiance of the material. The optical shock wave property of the MDW, which propagates with the velocity of light instead of the velocity of sound, prompts for engineering of novel device concepts like very high frequency mechanical oscillators not limited by the acoustic cutoff frequency.

Evolution of solitary density waves in stellar winds of early-type stars: A simple explanation of discrete absorption component behavior

NASA Technical Reports Server (NTRS)

Waldron, Wayne L.; Klein, Larry; Altner, Bruce

1994-01-01

We model the evolution of a density shell propagating through the stellar wind of an early-type star, in order to investigate the effects of such shells on UV P Cygni line profiles. Unlike previous treatments, we solve the mass, momentum, and energy conservation equations, using an explicit time-differencing scheme, and present a parametric study of the density, velocity, and temperature response. Under the assumed conditions, relatively large spatial scale, large-amplitude density shells propagate as stable waves through the supersonic portion of the wind. Their dynamical behavior appears to mimic propagating 'solitary waves,' and they are found to accelerate at the same rate as the underlying steady state stellar wind (i.e., the shell rides the wind). These hydrodynamically stable structures quantitatively reproduce the anomalous 'discrete absorption component' (DAC) behavior observed in the winds of luminous early-type stars, as illustrated by comparisons of model predictions to an extensive International Ultraviolet Explorer (IUE) time series of spectra of zeta Puppis (O4f). From these comparisons, we find no conclusive evidence indicative of DACs accelerating at a significantly slower rate than the underlying stellar wind, contrary to earlier reports. In addition, these density shells are found to be consistent within the constraints set by the IR observations. We conclude that the concept of propagating density shells should be seriously reconsidered as a possible explanation of the DAC phenomenon in early-type stars.

Strong Ionospheric Disturbances Observed by a Dense GPS Array After Large Earthquakes: Case Study of the 2003 Tokachi-oki Earthquake and its Geophysical Mechanism

NASA Astrophysics Data System (ADS)

Heki, K.; Ping, J.

2004-12-01

Ionospheric disturbances have been detected after, e.g. Northridge (Calais and Minster, 1995) and Denali (Ducic et al., 2003) earthquakes. Similar signals observed after the 2003 Tokachi-Oki Earthquake, the largest earthquake in Japan after the completion of GEONET, a nationwide array composed of over 1000 CGPS stations. We followed a standard procedure: applying a band-pass filter for the ionospheric combination of the L1 and L2 phase signals and calculating subioonospheric points (SIP) assuming thin ionosphere at the height of 350 km. Owing to the high density of SIP, many interesting features are observed and several important parameters were constrained, e.g. (1) apparent propagation speed, (2) directivity of disturbance signals, (3) decay during propagation, etc. As for (1), the observed speed of about 1 km/sec is significantly smaller than the Rayleigh Wave velocity, significantly faster than Travelling Ionospheric Disturbances (TID), but is consistent with the sound velocity at the ionospheric heights. The acoustic wave generated by sudden vertical movement of the Earth's surface first propagate upward. Then it will be refracted by height-dependent velocity structure resulting in horizontally propagating wave through the ionosphere. The observed TEC variation, with a wavelength of a few hundred km, may reflect electron density oscillation caused by the passage of such an acoustic wave. Regarding (2), there was a clear indication that the wave does not propagate northward. As first suggested by Calais et al. (1998), such a blocking is considered to be due to interaction between the geomagnetic field and the movement of charged particles comprising the ionosphere associated with the acoustic wave propagation. The model predicts that there will be no southward propagation of ionospheric disturbances caused by earthquakes in southern hemisphere mid-latitudes, which needs be confirmed by future earthquakes. The point (3) enabled the authors to define the empirical equation to calculate "Ionospheric disturbance magnitude" using the focal distance and disturbance amplitudes. Because the ionospheric disturbance monitoring does not require precise orbit information, such magnitudes could be determined near real time. This may help us, e.g. issue early warning message of Tsunami.

A viscoelastic model for the prediction of transcranial ultrasound propagation: application for the estimation of shear acoustic properties in the human skull

NASA Astrophysics Data System (ADS)

Pichardo, Samuel; Moreno-Hernández, Carlos; Drainville, Robert Andrew; Sin, Vivian; Curiel, Laura; Hynynen, Kullervo

2017-09-01

A better understanding of ultrasound transmission through the human skull is fundamental to develop optimal imaging and therapeutic applications. In this study, we present global attenuation values and functions that correlate apparent density calculated from computed tomography scans to shear speed of sound. For this purpose, we used a model for sound propagation based on the viscoelastic wave equation (VWE) assuming isotropic conditions. The model was validated using a series of measurements with plates of different plastic materials and angles of incidence of 0°, 15° and 50°. The optimal functions for transcranial ultrasound propagation were established using the VWE, scan measurements of transcranial propagation with an angle of incidence of 40° and a genetic optimization algorithm. Ten (10) locations over three (3) skulls were used for ultrasound frequencies of 270 kHz and 836 kHz. Results with plastic materials demonstrated that the viscoelastic modeling predicted both longitudinal and shear propagation with an average (±s.d.) error of 9(±7)% of the wavelength in the predicted delay and an error of 6.7(±5)% in the estimation of transmitted power. Using the new optimal functions of speed of sound and global attenuation for the human skull, the proposed model predicted the transcranial ultrasound transmission for a frequency of 270 kHz with an expected error in the predicted delay of 5(±2.7)% of the wavelength. The sound propagation model predicted accurately the sound propagation regardless of either shear or longitudinal sound transmission dominated. For 836 kHz, the model predicted accurately in average with an error in the predicted delay of 17(±16)% of the wavelength. Results indicated the importance of the specificity of the information at a voxel level to better understand ultrasound transmission through the skull. These results and new model will be very valuable tools for the future development of transcranial applications of ultrasound therapy and imaging.

Metabolite ratios to assumed stable creatine level may confound the quantification of proton brain MR spectroscopy.

PubMed

Li, Belinda S Y; Wang, Hao; Gonen, Oded

2003-10-01

In localized brain proton MR spectroscopy ((1)H-MRS), metabolites' levels are often expressed as ratios, rather than as absolute concentrations. Frequently, their denominator is the creatine [Cr], which level is explicitly assumed to be stable in normal as well as in many pathologic states. The rationale is that ratios self-correct for imager and localization method differences, gain instabilities, regional susceptibility variations and partial volume effects. The implicit assumption is that these benefits are worth their cost(w)-(w) propagation of the individual variation of each of the ratio's components. To test this hypothesis, absolute levels of N-acetylaspartate [NAA], choline [Cho] and [Cr] were quantified in various regions of the brains of 8 volunteers, using 3-dimensional (3D) (1)H-MRS at 1.5 T. The results show that in over 50% of approximately 2000 voxels examined, [NAA]/[Cr] and [Cho]/[Cr] exhibited higher coefficients of variations (CV) than [NAA] and [Cho] individually. Furthermore, in approximately 33% of these voxels, the ratios' CVs exceeded even the combined constituents' CVs. Consequently, basing metabolite quantification on ratios and assuming stable [Cr] introduces more variability into (1)H-MRS than it prevents. Therefore, its cost exceeds the benefit.

The Effect of a Pulsed Interference Signal on an Adaptive Array.

DTIC Science & Technology

1981-04-01

eigenvectors exist.) Using a spectral decomp- osition formula [10,11], we may write e-kM in the form -kM -k(T- )-kpo 3 -kg i (e -k = e a : .iZ e eie i , (28...N 0 (No/T b) In addition, for this analysis we shall assume the interference power at the array output has the same effect on detector performance... Sensitive Adaptive Array," to appear in IEEE Trans. Antennas and Propagation. 7. R.T. Compton, Jr., "The Tripole Antenna - An Adaptive Array with Full

A numerical study of three-dimensional diurnal variations within the thermosphere.

NASA Technical Reports Server (NTRS)

Volland, H.; Mayr, H. G.

1973-01-01

A thermosphere model with a realistic temperature profile is assumed. Heat conduction waves are introduced in addition to gravity waves. The temporal and spatial distribution of ion-neutral collisions is taken into account. However, the influence of viscosity waves is neglected. Viscosity-wave effects are simulated by an effective height-dependent collision number. Numerical calculations are conducted of the generation and propagation of two of the most important symmetric tidal waves at thermospheric heights. The influence of the solar EUV-heat upon the generation of the two tidal modes is investigated.

Space ethics to test directed panspermia

NASA Astrophysics Data System (ADS)

Makukov, Maxim A.; shCherbak, Vladimir I.

2014-10-01

The hypothesis that Earth was intentionally seeded with life by a preceding extraterrestrial civilization is believed to be currently untestable. However, analysis of the situation where humans themselves embark on seeding other planetary systems motivated by survival and propagation of life reveals at least two ethical issues calling for specific solutions. Assuming that generally intelligence evolves ethically as it evolves technologically, the same considerations might be applied to test the hypothesis of directed panspermia: if life on Earth was seeded intentionally, the two ethical requirements are expected to be satisfied, what appears to be the case.

Ion tracking in photocathode rf guns

NASA Astrophysics Data System (ADS)

Lewellen, John W.

2002-02-01

Projected next-generation linac-based light sources, such as PERL or the TESLA free-electron laser, generally assume, as essential components of their injector complexes, long-pulse photocathode rf electron guns. These guns, due to their design rf pulse durations of many milliseconds to continuous wave, may be more susceptible to ion bombardment damage of their cathodes than conventional rf guns, which typically use rf pulses of microsecond duration. This paper explores this possibility in terms of ion propagation within the gun, and presents a basis for future study of the subject.

Two-dimensional optical architectures for the receive mode of phased-array antennas.

PubMed

Pastur, L; Tonda-Goldstein, S; Dolfi, D; Huignard, J P; Merlet, T; Maas, O; Chazelas, J

1999-05-10

We propose and experimentally demonstrate two optical architectures that process the receive mode of a p x p element phased-array antenna. The architectures are based on free-space propagation and switching of the channelized optical carriers of microwave signals. With the first architecture a direct transposition of the received signals in the optical domain is assumed. The second architecture is based on the optical generation and distribution of a microwave local oscillator matched in frequency and direction. Preliminary experimental results at microwave frequencies of approximately 3 GHz are presented.

Chinese-English Electronics and Telecommunications Dictionary. Volume 2

DTIC Science & Technology

1976-11-01

cA fS] i^ W ^- bearing pin 01 axial 02 axial symmetry; rotational 03 synmetry axle weight 0« shaft clip 05 collar; burr CM axial ...terminal strips 07 J<A# three-way Joint ; triple Joint 08 K#frtt three-wattmeter method. 09 *t*Ü«f*f* three-dimensional wave propagation 10...design load ; assumed load ; 29 load rating 1040 •hejl genju wttt mm •hejl gongahl sir«* •h«Ji jlauan Äjtrt» •hejl Jlsuanblao ■ it it * /< •h«Jl

Dispersion relation of a surface wave at a rough metal-air interface

DOE PAGES

Kotelnikov, Igor; Stupakov, Gennady

2016-11-28

Here, we derived a dispersion relation of a surface wave at a rough metal-air interface. In contrast to previous publications, we assumed that an intrinsic surface impedance due to a finite electric conductivity of the metal can be of the same order as the roughness-induced impedance. We then applied our results to the analysis of a long-standing problem of the discrepancy between the experimental data on the propagation of surface waves in the terahertz range of frequencies and the classical Drude theory.

Upper-surface-blowing flow-turning performance

NASA Technical Reports Server (NTRS)

Sleeman, W. C., Jr.; Phelps, A. E., III

1976-01-01

Jet exhaust flow-turning characteristics were determined for systematic variations in upper-surface blowing exhaust nozzles and trailing-edge flap configuration variables from experimental wind-off (static) flow studies. For conditions with parallel flow exhausting from the nozzle, jet height (as indicated by nozzle exit height) and flap radius were found to be the most important parameters relating to flow turning. Nonparallel flow from the nozzle, as obtained from an internal roof angle and/or side spread angle, had a large favorable effect on flow turning. Comparisons made between static turning results and wind tunnel aerodynamic studies of identical configurations indicated that static flow-turning results can be indicative of wind-on powered lift performance for both good and poor nozzle-flap combinations but, for marginal designs, can lead to overly optimistic assessment of powered lift potential.

Method for targetless tracking subpixel in-plane movements.

PubMed

Espinosa, Julian; Perez, Jorge; Ferrer, Belen; Mas, David

2015-09-01

We present a targetless motion tracking method for detecting planar movements with subpixel accuracy. This method is based on the computation and tracking of the intersection of two nonparallel straight-line segments in the image of a moving object in a scene. The method is simple and easy to implement because no complex structures have to be detected. It has been tested and validated using a lab experiment consisting of a vibrating object that was recorded with a high-speed camera working at 1000 fps. We managed to track displacements with an accuracy of hundredths of pixel or even of thousandths of pixel in the case of tracking harmonic vibrations. The method is widely applicable because it can be used for distance measuring amplitude and frequency of vibrations with a vision system.

Robotic inspection of fiber reinforced composites using phased array UT

NASA Astrophysics Data System (ADS)

Stetson, Jeffrey T.; De Odorico, Walter

2014-02-01

Ultrasound is the current NDE method of choice to inspect large fiber reinforced airframe structures. Over the last 15 years Cartesian based scanning machines using conventional ultrasound techniques have been employed by all airframe OEMs and their top tier suppliers to perform these inspections. Technical advances in both computing power and commercially available, multi-axis robots now facilitate a new generation of scanning machines. These machines use multiple end effector tools taking full advantage of phased array ultrasound technologies yielding substantial improvements in inspection quality and productivity. This paper outlines the general architecture for these new robotic scanning systems as well as details the variety of ultrasonic techniques available for use with them including advances such as wide area phased array scanning and sound field adaptation for non-flat, non-parallel surfaces.

[Pathogenicity of artificial mineral fibers: are they as dangerous as asbestos?].

PubMed

Renzi, P M; Mantha, J; Matar, N; Renzi, G D

1990-01-01

Man-Made Mineral Fibres (MMMF) are starting to replace asbestos in the insulation industry. The popularity of these fibres has increased since the demonstration, in man, of the fibrogenicity and carcinogenicity of asbestos. A fear of human toxicity of MMMF has followed the demonstration of toxicity in animals after injection or instillation. This review of the litterature discusses the toxicity and side effects of MMMF. These fibres seem to have less toxicity than asbestos for the following reasons: 1. A lower concentration of fibres found in the air of the MMMF industry. 2. The cleavage of fibres in a perpendicular and non-parallel way. 3. The dissolution of fibres in the lung. Very fine fibreglass and mineral wool seem to be more toxic than continuous filaments and ordinary fibreglass.

Progressive evolution of deformation band populations during Laramide fault-propagation folding: Navajo Sandstone, San Rafael monocline, Utah, U.S.A.

NASA Astrophysics Data System (ADS)

Zuluaga, Luisa F.; Fossen, Haakon; Rotevatn, Atle

2014-11-01

Monoclinal fault propagation folds are a common type of structure in orogenic foreland settings, particularly on the Colorado Plateau. We have studied a portion of the San Rafael monocline, Utah, assumed to have formed through pure thrust- or reverse-slip (blind) fault movement, and mapped a particular sequence of subseismic cataclastic deformation structures (deformation bands) that can be related in terms of geometry, density and orientation to the dip of the forelimb or fold interlimb angle. In simple terms, deformation bands parallel to bedding are the first structures to form, increasing exponentially in number as the forelimb gets steeper. At about 30° rotation of the forelimb, bands forming ladder structures start to cross-cut bedding, consolidating themselves into a well-defined and regularly spaced network of deformation band zones that rotate with the layering during further deformation. In summary, we demonstrate a close relationship between limb dip and deformation band density that can be used to predict the distribution and orientation of such subseismic structures in subsurface reservoirs of similar type. Furthermore, given the fact that these cataclastic deformation bands compartmentalize fluid flow, this relationship can be used to predict or model fluid flow across and along comparable fault-propagation folds.

Waves propagating over a two-layer porous barrier on a seabed

NASA Astrophysics Data System (ADS)

Lin, Qiang; Meng, Qing-rui; Lu, Dong-qiang

2018-05-01

A research of wave propagation over a two-layer porous barrier, each layer of which is with different values of porosity and friction, is conducted with a theoretical model in the frame of linear potential flow theory. The model is more appropriate when the seabed consists of two different properties, such as rocks and breakwaters. It is assumed that the fluid is inviscid and incompressible and the motion is irrotational. The wave numbers in the porous region are complex ones, which are related to the decaying and propagating behaviors of wave modes. With the aid of the eigenfunction expansions, a new inner product of the eigenfunctions in the two-layer porous region is proposed to simplify the calculation. The eigenfunctions, under this new definition, possess the orthogonality from which the expansion coefficients can be easily deduced. Selecting the optimum truncation of the series, we derive a closed system of simultaneous linear equations for the same number of the unknown reflection and transmission coefficients. The effects of several physical parameters, including the porosity, friction, width, and depth of the porous barrier, on the dispersion relation, reflection and transmission coefficients are discussed in detail through the graphical representations of the solutions. It is concluded that these parameters have certain impacts on the reflection and transmission energy.

Capacity of MIMO free space optical communications using multiple partially coherent beams propagation through non-Kolmogorov strong turbulence.

PubMed

Deng, Peng; Kavehrad, Mohsen; Liu, Zhiwen; Zhou, Zhou; Yuan, Xiuhua

2013-07-01

We study the average capacity performance for multiple-input multiple-output (MIMO) free-space optical (FSO) communication systems using multiple partially coherent beams propagating through non-Kolmogorov strong turbulence, assuming equal gain combining diversity configuration and the sum of multiple gamma-gamma random variables for multiple independent partially coherent beams. The closed-form expressions of scintillation and average capacity are derived and then used to analyze the dependence on the number of independent diversity branches, power law α, refractive-index structure parameter, propagation distance and spatial coherence length of source beams. Obtained results show that, the average capacity increases more significantly with the increase in the rank of MIMO channel matrix compared with the diversity order. The effect of the diversity order on the average capacity is independent of the power law, turbulence strength parameter and spatial coherence length, whereas these effects on average capacity are gradually mitigated as the diversity order increases. The average capacity increases and saturates with the decreasing spatial coherence length, at rates depending on the diversity order, power law and turbulence strength. There exist optimal values of the spatial coherence length and diversity configuration for maximizing the average capacity of MIMO FSO links over a variety of atmospheric turbulence conditions.

Simulation of crack propagation in rock in plasma blasting technology

NASA Astrophysics Data System (ADS)

Ikkurthi, V. R.; Tahiliani, K.; Chaturvedi, S.

Plasma Blasting Technology (PBT) involves the production of a pulsed electrical discharge by inserting a blasting probe in a water-filled cavity drilled in a rock, which produces shocks or pressure waves in the water. These pulses then propagate into the rock, leading to fracture. In this paper, we present the results of two-dimensional hydrodynamic simulations using the SHALE code to study crack propagation in rock. Three separate issues have been examined. Firstly, assuming that a constant pressure P is maintained in the cavity for a time τ , we have determined the P- τ curve that just cracks a given rock into at least two large-sized parts. This study shows that there exists an optimal pressure level for cracking a given rock-type and geometry. Secondly, we have varied the volume of water in which the initial energy E is deposited, which corresponds to different initial peak pressures Ppeak. We have determined the E- Ppeak curve that just breaks the rock into four large-sized parts. It is found that there must be an optimal Ppeak that lowers the energy consumption, but with acceptable probe damage. Thirdly, we have attempted to identify the dominant mechanism of rock fracture. We also highlight some numerical errors that must be kept in mind in such simulations.

Bolt beam propagation analysis

NASA Astrophysics Data System (ADS)

Shokair, I. R.

BOLT (Beam on Laser Technology) is a rocket experiment to demonstrate electron beam propagation on a laser ionized plasma channel across the geomagnetic field in the ion focused regime (IFR). The beam parameters for BOLT are: beam current I(sub b) = 100 Amps, beam energy of 1--1.5 MeV (gamma =3-4), and a Gaussian beam and channel of radii r(sub b) = r(sub c) = 1.5 cm. The N+1 ionization scheme is used to ionize atomic oxygen in the upper atmosphere. This scheme utilizes 130 nm light plus three IR lasers to excite and then ionize atomic oxygen. The limiting factor for the channel strength is the energy of the 130 nm laser, which is assumed to be 1.6 mJ for BOLT. At a fixed laser energy and altitude (fixing the density of atomic oxygen), the range can be varied by adjusting the laser tuning, resulting in a neutralization fraction axial profile of the form: f(z) = f(sub 0) e(exp minus z)/R, where R is the range. In this paper we consider the propagation of the BOLT beam and calculate the range of the electron beam taking into account the fact that the erosion rates (magnetic and inductive) vary with beam length as the beam and channel dynamically respond to sausage and hose instabilities.

DE-Sync: A Doppler-Enhanced Time Synchronization for Mobile Underwater Sensor Networks.

PubMed

Zhou, Feng; Wang, Qi; Nie, DongHu; Qiao, Gang

2018-05-25

Time synchronization is the foundation of cooperative work among nodes of underwater sensor networks; it takes a critical role in the research and application of underwater sensor networks. Although numerous time synchronization protocols have been proposed for terrestrial wireless sensor networks, they cannot be directly applied to underwater sensor networks. This is because most of them typically assume that the propagation delay among sensor nodes is negligible, which is not the case in underwater sensor networks. Time synchronization is mainly affected by a long propagation delay among sensor nodes due to the low propagation speed of acoustic signals. Furthermore, sensor nodes in underwater tend to experience some degree of mobility due to wind or ocean current, or some other nodes are on self-propelled vehicles, such as autonomous underwater vehicles (AUVs). In this paper, we propose a Doppler-enhanced time synchronization scheme for mobile underwater sensor networks, called DE-Sync. Our new scheme considers the effect of the clock skew during the process of estimating the Doppler scale factor and directly substitutes the Doppler scale factor into linear regression to achieve the estimation of the clock skew and offset. Simulation results show that DE-Sync outperforms existing time synchronization protocols in both accuracy and energy efficiency.

Dynamic crack propagation in a 2D elastic body: The out-of-plane case

NASA Astrophysics Data System (ADS)

Nicaise, Serge; Sandig, Anna-Margarete

2007-05-01

Already in 1920 Griffith has formulated an energy balance criterion for quasistatic crack propagation in brittle elastic materials. Nowadays, a generalized energy balance law is used in mechanics [F. Erdogan, Crack propagation theories, in: H. Liebowitz (Ed.), Fracture, vol. 2, Academic Press, New York, 1968, pp. 498-586; L.B. Freund, Dynamic Fracture Mechanics, Cambridge Univ. Press, Cambridge, 1990; D. Gross, Bruchmechanik, Springer-Verlag, Berlin, 1996] in order to predict how a running crack will grow. We discuss this situation in a rigorous mathematical way for the out-of-plane state. This model is described by two coupled equations in the reference configuration: a two-dimensional scalar wave equation for the displacement fields in a cracked bounded domain and an ordinary differential equation for the crack position derived from the energy balance law. We handle both equations separately, assuming at first that the crack position is known. Then the weak and strong solvability of the wave equation will be studied and the crack tip singularities will be derived under the assumption that the crack is straight and moves tangentially. Using the energy balance law and the crack tip behavior of the displacement fields we finally arrive at an ordinary differential equation for the motion of the crack tip.

Complementary hydro-mechanical coupled finite/discrete element and microseismic modelling to predict hydraulic fracture propagation in tight shale reservoirs

NASA Astrophysics Data System (ADS)

Profit, Matthew; Dutko, Martin; Yu, Jianguo; Cole, Sarah; Angus, Doug; Baird, Alan

2016-04-01

This paper presents a novel approach to predict the propagation of hydraulic fractures in tight shale reservoirs. Many hydraulic fracture modelling schemes assume that the fracture direction is pre-seeded in the problem domain discretisation. This is a severe limitation as the reservoir often contains large numbers of pre-existing fractures that strongly influence the direction of the propagating fracture. To circumvent these shortcomings, a new fracture modelling treatment is proposed where the introduction of discrete fracture surfaces is based on new and dynamically updated geometrical entities rather than the topology of the underlying spatial discretisation. Hydraulic fracturing is an inherently coupled engineering problem with interactions between fluid flow and fracturing when the stress state of the reservoir rock attains a failure criterion. This work follows a staggered hydro-mechanical coupled finite/discrete element approach to capture the key interplay between fluid pressure and fracture growth. In field practice, the fracture growth is hidden from the design engineer and microseismicity is often used to infer hydraulic fracture lengths and directions. Microseismic output can also be computed from changes of the effective stress in the geomechanical model and compared against field microseismicity. A number of hydraulic fracture numerical examples are presented to illustrate the new technology.

Photoacoustic sounds from meteors

DOE PAGES

Spalding, Richard; Tencer, John; Sweatt, William; ...

2017-02-01

Concurrent sound associated with very bright meteors manifests as popping, hissing, and faint rustling sounds occurring simultaneously with the arrival of light from meteors. Numerous instances have been documented with –11 to –13 brightness. These sounds cannot be attributed to direct acoustic propagation from the upper atmosphere for which travel time would be several minutes. Concurrent sounds must be associated with some form of electromagnetic energy generated by the meteor, propagated to the vicinity of the observer, and transduced into acoustic waves. Previously, energy propagated from meteors was assumed to be RF emissions. This has not been well validated experimentally.more » Herein we describe experimental results and numerical models in support of photoacoustic coupling as the mechanism. Recent photometric measurements of fireballs reveal strong millisecond flares and significant brightness oscillations at frequencies ≥40 Hz. Strongly modulated light at these frequencies with sufficient intensity can create concurrent sounds through radiative heating of common dielectric materials like hair, clothing, and leaves. This heating produces small pressure oscillations in the air contacting the absorbers. Calculations show that –12 brightness meteors can generate audible sound at ~25 dB SPL. As a result, the photoacoustic hypothesis provides an alternative explanation for this longstanding mystery about generation of concurrent sounds by fireballs.« less

Low-frequency pulse propagation over 510 km in the Philippine Sea: A comparison of observed and theoretical pulse spreading.

PubMed

Andrew, Rex K; Ganse, Andrew; White, Andrew W; Mercer, James A; Dzieciuch, Matthew A; Worcester, Peter F; Colosi, John A

2016-07-01

Observations of the spread of wander-corrected averaged pulses propagated over 510 km for 54 h in the Philippine Sea are compared to Monte Carlo predictions using a parabolic equation and path-integral predictions. Two simultaneous m-sequence signals are used, one centered at 200 Hz, the other at 300 Hz; both have a bandwidth of 50 Hz. The internal wave field is estimated at slightly less than unity Garrett-Munk strength. The observed spreads in all the early ray-like arrivals are very small, <1 ms (for pulse widths of 17 and 14 ms), which are on the order of the sampling period. Monte Carlo predictions show similar very small spreads. Pulse spread is one consequence of scattering, which is assumed to occur primarily at upper ocean depths where scattering processes are strongest and upward propagating rays refract downward. If scattering effects in early ray-like arrivals accumulate with increasing upper turning points, spread might show a similar dependence. Real and simulation results show no such dependence. Path-integral theory prediction of spread is accurate for the earliest ray-like arrivals, but appears to be increasingly biased high for later ray-like arrivals, which have more upper turning points.

Lightning leader models of terrestrial gamma-ray flashes

NASA Astrophysics Data System (ADS)

Dwyer, J. R.; Liu, N.; Ihaddadene, K. M. A.

2017-12-01

Terrestrial gamma-ray flashes (TGFs) are bright sub-millisecond bursts of gamma rays that originate from thunderstorms. Because lightning leaders near the ground have been observed to emit x-rays, presumably due to runaway electron production in the high-field regions near the leader tips, models of TGFs have been developed by several groups that assume a similar production mechanism of runaway electrons from lightning leaders propagating through thunderclouds. However, it remains unclear exactly how and where these runaway electrons are produced, since lightning propagation at thunderstorm altitudes remains poorly understood. In addition, it is not obvious how to connect the observed behavior of the x-ray production from lightning near the ground with the properties of TGFs. For example, it is not clear how to relate the time structure of the x-ray emission near the ground to that of TGFs, since x-rays from stepped leaders near the ground are usually produced in a series of sub-microsecond bursts, but TGFs are usually observed as much longer pulses without clear substructures, at sub-microsecond timescales or otherwise. In this presentation, spacecraft observations of TGFs, ground-based observations of x-rays from lightning and laboratory sparks, and Monte Carlo and PIC simulations of runaway electron and gamma ray production and propagation will be used to constrain the lightning leader models of TGFs.

Upper-mantle origin of the Yellowstone hotspot

USGS Publications Warehouse

Christiansen, R.L.; Foulger, G.R.; Evans, J.R.

2002-01-01

Fundamental features of the geology and tectonic setting of the northeast-propagating Yellowstone hotspot are not explained by a simple deep-mantle plume hypothesis and, within that framework, must be attributed to coincidence or be explained by auxiliary hypotheses. These features include the persistence of basaltic magmatism along the hotspot track, the origin of the hotspot during a regional middle Miocene tectonic reorganization, a similar and coeval zone of northwestward magmatic propagation, the occurrence of both zones of magmatic propagation along a first-order tectonic boundary, and control of the hotspot track by preexisting structures. Seismic imaging provides no evidence for, and several contraindications of, a vertically extensive plume-like structure beneath Yellowstone or a broad trailing plume head beneath the eastern Snake River Plain. The high helium isotope ratios observed at Yellowstone and other hotspots are commonly assumed to arise from the lower mantle, but upper-mantle processes can explain the observations. The available evidence thus renders an upper-mantle origin for the Yellowstone system the preferred model; there is no evidence that the system extends deeper than ???200 km, and some evidence that it does not. A model whereby the Yellowstone system reflects feedback between upper-mantle convection and regional lithospheric tectonics is able to explain the observations better than a deep-mantle plume hypothesis.

Modeling of sub-ionospheric VLF signal perturbations associated with total solar eclipse, 2009 in Indian subcontinent

NASA Astrophysics Data System (ADS)

Pal, Sujay; Chakrabarti, Sandip K.; Mondal, Sushanta K.

2012-07-01

During the total solar eclipse of 2009, a week-long campaign was conducted in the Indian sub-continent to study the low-latitude D-region ionosphere using the very low frequency (VLF) signal from the Indian Navy transmitter (call sign: VTX3) operating at 18.2 kHz. It was observed that in several places, the signal amplitude is enhanced while in other places the amplitude is reduced. We simulated the observational results using the well known Long Wavelength Propagation Capability (LWPC) code. As a first order approximation, the ionospheric parameters were assumed to vary according to the degree of solar obscuration on the way to the receivers. This automatically brought in non-uniformity of the ionospheric parameters along the propagation paths. We find that an assumption of 4 km increase of lower ionospheric height for places going through totality in the propagation path simulate the observations very well at Kathmandu and Raiganj. We find an increase of the height parameter by h'=+3.0 km for the VTX-Malda path and h'=+1.8 km for the VTX-Kolkata path. We also present, as an example, the altitude variation of electron number density throughout the eclipse time at Raiganj.

Radiometric analysis of the longwave infrared channel of the Thematic Mapper on LANDSAT 4 and 5

NASA Technical Reports Server (NTRS)

Schott, John R.; Volchok, William J.; Biegel, Joseph D.

1986-01-01

The first objective was to evaluate the postlaunch radiometric calibration of the LANDSAT Thematic Mapper (TM) band 6 data. The second objective was to determine to what extent surface temperatures could be computed from the TM and 6 data using atmospheric propagation models. To accomplish this, ground truth data were compared to a single TM-4 band 6 data set. This comparison indicated satisfactory agreement over a narrow temperature range. The atmospheric propagation model (modified LOWTRAN 5A) was used to predict surface temperature values based on the radiance at the spacecraft. The aircraft data were calibrated using a multi-altitude profile calibration technique which had been extensively tested in previous studies. This aircraft calibration permitted measurement of surface temperatures based on the radiance reaching the aircraft. When these temperature values are evaluated, an error in the satellite's ability to predict surface temperatures can be estimated. This study indicated that by carefully accounting for various sensor calibration and atmospheric propagation effects, and expected error (1 standard deviation) in surface temperature would be 0.9 K. This assumes no error in surface emissivity and no sampling error due to target location. These results indicate that the satellite calibration is within nominal limits to within this study's ability to measure error.

Propagation of spectral characterization errors of imaging spectrometers at level-1 and its correction within a level-2 recalibration scheme

NASA Astrophysics Data System (ADS)

Vicent, Jorge; Alonso, Luis; Sabater, Neus; Miesch, Christophe; Kraft, Stefan; Moreno, Jose

2015-09-01

The uncertainties in the knowledge of the Instrument Spectral Response Function (ISRF), barycenter of the spectral channels and bandwidth / spectral sampling (spectral resolution) are important error sources in the processing of satellite imaging spectrometers within narrow atmospheric absorption bands. The exhaustive laboratory spectral characterization is a costly engineering process that differs from the instrument configuration in-flight given the harsh space environment and harmful launching phase. The retrieval schemes at Level-2 commonly assume a Gaussian ISRF, leading to uncorrected spectral stray-light effects and wrong characterization and correction of the spectral shift and smile. These effects produce inaccurate atmospherically corrected data and are propagated to the final Level-2 mission products. Within ESA's FLEX satellite mission activities, the impact of the ISRF knowledge error and spectral calibration at Level-1 products and its propagation to Level-2 retrieved chlorophyll fluorescence has been analyzed. A spectral recalibration scheme has been implemented at Level-2 reducing the errors in Level-1 products below the 10% error in retrieved fluorescence within the oxygen absorption bands enhancing the quality of the retrieved products. The work presented here shows how the minimization of the spectral calibration errors requires an effort both for the laboratory characterization and for the implementation of specific algorithms at Level-2.

Methods of approaching decoherence in the flavor sector due to space-time foam

NASA Astrophysics Data System (ADS)

Mavromatos, N. E.; Sarkar, Sarben

2006-08-01

In the first part of this work we discuss possible effects of stochastic space-time foam configurations of quantum gravity on the propagation of “flavored” (Klein-Gordon and Dirac) neutral particles, such as neutral mesons and neutrinos. The formalism is not the usually assumed Lindblad one, but it is based on random averages of quantum fluctuations of space-time metrics over which the propagation of the matter particles is considered. We arrive at expressions for the respective oscillation probabilities between flavors which are quite distinct from the ones pertaining to Lindblad-type decoherence, including in addition to the (expected) Gaussian decay with time, a modification to oscillation behavior, as well as a power-law cutoff of the time-profile of the respective probability. In the second part we consider space-time foam configurations of quantum-fluctuating charged-black holes as a way of generating (parts of) neutrino mass differences, mimicking appropriately the celebrated Mikheyev-Smirnov-Wolfenstein (MSW) effects of neutrinos in stochastically fluctuating random media. We pay particular attention to disentangling genuine quantum-gravity effects from ordinary effects due to the propagation of a neutrino through ordinary matter. Our results are of interest to precision tests of quantum-gravity models using neutrinos as probes.

Dynamic Granger-Geweke causality modeling with application to interictal spike propagation

PubMed Central

Lin, Fa-Hsuan; Hara, Keiko; Solo, Victor; Vangel, Mark; Belliveau, John W.; Stufflebeam, Steven M.; Hamalainen, Matti S.

2010-01-01

A persistent problem in developing plausible neurophysiological models of perception, cognition, and action is the difficulty of characterizing the interactions between different neural systems. Previous studies have approached this problem by estimating causal influences across brain areas activated during cognitive processing using Structural Equation Modeling and, more recently, with Granger-Geweke causality. While SEM is complicated by the need for a priori directional connectivity information, the temporal resolution of dynamic Granger-Geweke estimates is limited because the underlying autoregressive (AR) models assume stationarity over the period of analysis. We have developed a novel optimal method for obtaining data-driven directional causality estimates with high temporal resolution in both time and frequency domains. This is achieved by simultaneously optimizing the length of the analysis window and the chosen AR model order using the SURE criterion. Dynamic Granger-Geweke causality in time and frequency domains is subsequently calculated within a moving analysis window. We tested our algorithm by calculating the Granger-Geweke causality of epileptic spike propagation from the right frontal lobe to the left frontal lobe. The results quantitatively suggested the epileptic activity at the left frontal lobe was propagated from the right frontal lobe, in agreement with the clinical diagnosis. Our novel computational tool can be used to help elucidate complex directional interactions in the human brain. PMID:19378280

Bending, longitudinal and torsional wave transmission on Euler-Bernoulli and Timoshenko beams with high propagation losses.

PubMed

Wang, X; Hopkins, C

2016-10-01

Advanced Statistical Energy Analysis (ASEA) is used to predict vibration transmission across coupled beams which support multiple wave types up to high frequencies where Timoshenko theory is valid. Bending-longitudinal and bending-torsional models are considered for an L-junction and rectangular beam frame. Comparisons are made with measurements, Finite Element Methods (FEM) and Statistical Energy Analysis (SEA). When beams support at least two local modes for each wave type in a frequency band and the modal overlap factor is at least 0.1, measurements and FEM have relatively smooth curves. Agreement between measurements, FEM, and ASEA demonstrates that ASEA is able to predict high propagation losses which are not accounted for with SEA. These propagation losses tend to become more important at high frequencies with relatively high internal loss factors and can occur when there is more than one wave type. At such high frequencies, Timoshenko theory, rather than Euler-Bernoulli theory, is often required. Timoshenko theory is incorporated in ASEA and SEA using wave theory transmission coefficients derived assuming Euler-Bernoulli theory, but using Timoshenko group velocity when calculating coupling loss factors. The changeover between theories is appropriate above the frequency where there is a 26% difference between Euler-Bernoulli and Timoshenko group velocities.

Propagation Dynamics of Successive, Circumnavigating MJO Events in MERRA2 Reanalysis

NASA Astrophysics Data System (ADS)

Powell, Scott

2017-04-01

Propagation speeds of strong circumnavigating successive MJO events are investigated in MERRA2 reanalysis. Coherent, statistically significant circumnavigating signals in parameterized latent heating and modeled adiabatic cooling associated with large-scale vertical motion are detected and tracked. The signals appear to be associated with propagation of a first baroclinic Kelvin wave, but they obviously moved at a rate much slower than the theoretical phase speed for a dry first baroclinic Kelvin wave. ( 45-50 m/s). The goal is to determine what factors primarily control the variable propagation speed of the MJO signal as a function of longitude. Following theory of Neelin and Held (1987) and Emanuel et al. (1994), the climatological offset (i.e. cancellation) between column integrated diabatic heating and adiabatic cooling in MERRA2 is used to the estimate the wave propagation speed if a reduction of "effective static stability" governed the phase speed. The offset is robust from year to year at all longitudes. A first baroclinic mode based on applying the theory to reanalysis output would propagate between 20-25 m/s over much of the Western Hemisphere, between 20-35 m/s over the eastern Atlantic and Africa, and between 5-20 m/s over the tropical warm pool. The theoretically predicted velocities closely match the propagation speed of the circumnavigating convective signal seen in reanalysis over regions of the tropics where the weak temperature gradient (WTG) approximation is apparently inapplicable (i.e. where deep convection is not prevalent and the offset between diabatic heating and adiabatic cooling is small enough to allow a non-negligible temperature tendency). However, in places where deep convection is prevalent and the offset is large (greater than about 0.9), such as over the warm pool, the theory greatly overestimates propagation speed of the MJO signal. Rather, the moisture wave theory of Adames and Kim (2016), which assumes a WTG, accurately predicts the speed of the MJO signal. Thus, two distinct dynamic regimes, one in which gravity waves dominate and another in which moisture wave dynamics are more applicable, govern MJO propagation depending on where the signal is located. In the East Pacific, the offset has seasonal dependence. It is small (about 0.7) during boreal winter, and a reduction of effective static stability adequately describes propagation of the MJO signal. During boreal summer, the offset approaches 0.9, meaning that the WTG dynamic regime is prevalent like over the warm pool. However, no known theory for MJO propagation can explain the propagation speed of the signal, 8-9 m/s. In the East Pacific, convection tends to have a second baroclinic vertical structure, and it is centered off the equator. This highlights the need for extension of moisture wave/moisture mode theories to incorporate the second convective vertical mode and convection that is not centered latitudinally at the equator.

Tsunami propagation modelling - a sensitivity study

NASA Astrophysics Data System (ADS)

Dao, M. H.; Tkalich, P.

2007-12-01

Indian Ocean (2004) Tsunami and following tragic consequences demonstrated lack of relevant experience and preparedness among involved coastal nations. After the event, scientific and forecasting circles of affected countries have started a capacity building to tackle similar problems in the future. Different approaches have been used for tsunami propagation, such as Boussinesq and Nonlinear Shallow Water Equations (NSWE). These approximations were obtained assuming different relevant importance of nonlinear, dispersion and spatial gradient variation phenomena and terms. The paper describes further development of original TUNAMI-N2 model to take into account additional phenomena: astronomic tide, sea bottom friction, dispersion, Coriolis force, and spherical curvature. The code is modified to be suitable for operational forecasting, and the resulting version (TUNAMI-N2-NUS) is verified using test cases, results of other models, and real case scenarios. Using the 2004 Tsunami event as one of the scenarios, the paper examines sensitivity of numerical solutions to variation of different phenomena and parameters, and the results are analyzed and ranked accordingly.

Understanding the spectral hardenings and radial distribution of Galactic cosmic rays and Fermi diffuse γ rays with spatially-dependent propagation

NASA Astrophysics Data System (ADS)

Guo, Yi-Qing; Yuan, Qiang

2018-03-01

Recent direct measurements of Galactic cosmic ray spectra by balloon/space-borne detectors reveal spectral hardenings of all major nucleus species at rigidities of a few hundred GV. The all-sky diffuse γ -ray emissions measured by the Fermi Large Area Telescope also show spatial variations of the intensities and spectral indices of cosmic rays. These new observations challenge the traditional simple acceleration and/or propagation scenario of Galactic cosmic rays. In this work, we propose a spatially dependent diffusion scenario to explain all these phenomena. The diffusion coefficient is assumed to be anticorrelated with the source distribution, which is a natural expectation from the charged particle transportation in a turbulent magnetic field. The spatially dependent diffusion model also gives a lower level of anisotropies of cosmic rays, which are consistent with observations by underground muons and air shower experiments. The spectral variations of cosmic rays across the Galaxy can be properly reproduced by this model.

The influence of ground conductivity on the structure of RF radiation from return strokes

NASA Technical Reports Server (NTRS)

Levine, D. M.; Gesell, L.

1984-01-01

The combination of the finite conductivity of the Earth plus the propagation of the return stroke current up the channel which results in an apparent time delay between the fast field changes and RF radiation for distant observers is shown. The time delay predicted from model return strokes is on the order of 20 micro and the received signal has the characteristics of the data observed in Virginia and Florida. A piecewise linear model for the return stroke channel and a transmission line model for current propagation on each segment was used. Radiation from each segment is calculated over a flat Earth with finite conductivity using asymptotics approximations for the Sommerfeld integrals. The radiation at the observer is processed by a model AM radio receiver. The output voltage was calculated for several frequencies between HF-UHF assuming a system bandwidth (300 kHz) characteristic of the system used to collect data in Florida and Virginia. Comparison with the theoretical fast field changes indicates a time delay of 20 microns.

Attitude Determination Algorithm based on Relative Quaternion Geometry of Velocity Incremental Vectors for Cost Efficient AHRS Design

NASA Astrophysics Data System (ADS)

Lee, Byungjin; Lee, Young Jae; Sung, Sangkyung

2018-05-01

A novel attitude determination method is investigated that is computationally efficient and implementable in low cost sensor and embedded platform. Recent result on attitude reference system design is adapted to further develop a three-dimensional attitude determination algorithm through the relative velocity incremental measurements. For this, velocity incremental vectors, computed respectively from INS and GPS with different update rate, are compared to generate filter measurement for attitude estimation. In the quaternion-based Kalman filter configuration, an Euler-like attitude perturbation angle is uniquely introduced for reducing filter states and simplifying propagation processes. Furthermore, assuming a small angle approximation between attitude update periods, it is shown that the reduced order filter greatly simplifies the propagation processes. For performance verification, both simulation and experimental studies are completed. A low cost MEMS IMU and GPS receiver are employed for system integration, and comparison with the true trajectory or a high-grade navigation system demonstrates the performance of the proposed algorithm.

Multimodal Deep Autoencoder for Human Pose Recovery.

PubMed

Hong, Chaoqun; Yu, Jun; Wan, Jian; Tao, Dacheng; Wang, Meng

2015-12-01

Video-based human pose recovery is usually conducted by retrieving relevant poses using image features. In the retrieving process, the mapping between 2D images and 3D poses is assumed to be linear in most of the traditional methods. However, their relationships are inherently non-linear, which limits recovery performance of these methods. In this paper, we propose a novel pose recovery method using non-linear mapping with multi-layered deep neural network. It is based on feature extraction with multimodal fusion and back-propagation deep learning. In multimodal fusion, we construct hypergraph Laplacian with low-rank representation. In this way, we obtain a unified feature description by standard eigen-decomposition of the hypergraph Laplacian matrix. In back-propagation deep learning, we learn a non-linear mapping from 2D images to 3D poses with parameter fine-tuning. The experimental results on three data sets show that the recovery error has been reduced by 20%-25%, which demonstrates the effectiveness of the proposed method.

Rayleigh wave behavior in functionally graded magneto-electro-elastic material

NASA Astrophysics Data System (ADS)

Ezzin, Hamdi; Mkaoir, Mohamed; Amor, Morched Ben

2017-12-01

Piezoelectric-piezomagnetic functionally graded materials, with a gradual change of the mechanical and electromagnetic properties have greatly applying promises. Based on the ordinary differential equation and stiffness matrix methods, a dynamic solution is presented for the propagation of the wave on a semi-infinite piezomagnetic substrate covered with a functionally graded piezoelectric material (FGPM) layer. The materials properties are assumed to vary in the direction of the thickness according to a known variation law. The phase and group velocity of the Rayleigh wave is numerically calculated for the magneto-electrically open and short cases, respectively. The effect of gradient coefficients on the phase velocity, group velocity, coupled magneto-electromechanical factor, on the stress fields, the magnetic potential and the mechanical displacement are discussed, respectively. Illustration is achieved on the hetero-structure PZT-5A/CoFe2O4; the obtained results are especially useful in the design of high-performance acoustic surface devices and accurately prediction of the Rayleigh wave propagation behavior.

A model for wave propagation in a porous solid saturated by a three-phase fluid.

PubMed

Santos, Juan E; Savioli, Gabriela B

2016-02-01

This paper presents a model to describe the propagation of waves in a poroelastic medium saturated by a three-phase viscous, compressible fluid. Two capillary relations between the three fluid phases are included in the model by introducing Lagrange multipliers in the principle of virtual complementary work. This approach generalizes that of Biot for single-phase fluids and allows to determine the strain energy density, identify the generalized strains and stresses, and derive the constitutive relations of the system. The kinetic and dissipative energy density functions are obtained assuming that the relative flow within the pore space is of laminar type and obeys Darcy's law for three-phase flow in porous media. After deriving the equations of motion, a plane wave analysis predicts the existence of four compressional waves, denoted as type I, II, III, and IV waves, and one shear wave. Numerical examples showing the behavior of all waves as function of saturation and frequency are presented.

Role of location-dependent transverse wind on root-mean-square bandwidth of temporal light-flux fluctuations in the turbulent atmosphere.

PubMed

Chen, Chunyi; Yang, Huamin

2017-11-01

The root-mean-square (RMS) bandwidth of temporal light-flux fluctuations is formulated for both plane and spherical waves propagating in the turbulent atmosphere with location-dependent transverse wind. Two path weighting functions characterizing the joint contributions of turbulent eddies and transverse winds at various locations toward the RMS bandwidth are derived. Based on the developed formulations, the roles of variations in both the direction and magnitude of transverse wind velocity with locations over a path on the RMS bandwidth are elucidated. For propagation paths between ground and space, comparisons of the RMS bandwidth computed based on the Bufton wind profile with that calculated by assuming a nominal constant transverse wind velocity are made to exemplify the effect that location dependence of transverse wind velocity has on the RMS bandwidth. Moreover, an expression for the weighted RMS transverse wind velocity has been derived, which can be used as a nominal constant transverse wind velocity over a path for accurately determining the RMS bandwidth.

Hydrogen Lines in Mira Stars Through Interferometry and Polarimetry

NASA Astrophysics Data System (ADS)

Fabas, N.; Chiavassa, A.; Millour, F.; Wittkowski, M.

2015-12-01

Balmer lines in emission are the most prominent features in Mira stars spectra and have a strong potential as a proxy to study the lower atmosphere's dynamics. In Fabas et al. ([1]), we accumulated spectropolarimetric observations of Balmer lines in emission. As the shock is propagating outwards, linear polarization rate increases and the angle of this polarization evolves. Assuming that linear polarization arises from anisotropic scattering, it has the potential of telling us about the geometric structure of the shock as it propagates and the study of such atmospheric structures can typically be performed with interferometry. In 2012, AMBER data on the Mira star omicron Ceti were collected in which the Brackett γ line is studied. The data show signatures in the interferometric observables around this line. Olivier Chesneau was in the jury evaluating the PhD thesis of N. Fabas and he was seduced by the idea to study these shock waves with interferometry and use polarimetry as a complementary study.

Omori Law After Exogenous Shocks on Supplier-Customer Network

NASA Astrophysics Data System (ADS)

Fujiwara, Yoshi

We study the relaxation process of a supplier-customer network after mass destruction due to two giant earthquakes, Kobe 1995 and East Japan 2011, by investigating the number of chained failures. Firstly, a mass destruction and intervention of business activities in the damaged areas can be considered as a main shock. The exogenous shock was propagated on the supplier-customer network deteriorating financial states of other firms, even if they are not located in geographical neighbors. To quantify such aftershocks, we use chained failures on the network assuming that they indicate the trace of propagation of shocks. We show that the number of chained failures in its temporal change obeys an Omori-law, a power-law relaxation. This finding implies that the relaxation is much more sluggish than one would naively expect, and that it might be possible to estimate the extent and duration of aftershocks by using the empirical law. Several issues are discussed including the origin of the long-time relaxation.

Radiation from long pulse train electron beams in space plasmas

NASA Technical Reports Server (NTRS)

Harker, K. J.; Banks, P. M.

1985-01-01

A previous study of electromagnetic radiation from a finite train of electron pulses is extended to an infinite train of such pulses. The electrons are assumed to follow an idealized helical path through a space plasma in such a manner as to retain their respective position within the beam. This leads to radiation by coherent spontaneous emission. The waves of interest in this region are the whistler slow (compressional) and fast (torsional) Alfven waves. Although a general theory is developed, analysis is then restricted to two approximations, the short and long electron beam. Formulas for the radiation per unit solid angle from the short beam are presented as a function of both propagation and ray angles, electron beam pulse width and separation and beam current, voltage, and pitch angle. Similar formulas for the total power radiated from the long beam are derived as a function of frequency, propagation angle, and ray angle. Predictions of the power radiated are presented for representative examples as determined by the long beam theory.

Improved intraseasonal variability in the NASA GEOS AGCM with 2-moment microphysics and a shallow cumulus parameterization

NASA Astrophysics Data System (ADS)

Arnold, N.; Barahona, D.

2017-12-01

Atmospheric general circulation models (AGCMs) have long struggled to realistically represent tropical intraseasonal variability. Here we report progress in simulating the Madden Julian Oscillation (MJO) with the NASA Goddard Earth Observing System (GEOS) AGCM, in free-running simulations utilizing a new two-moment microphysics scheme and the University of Washington shallow cumulus parameterization. Lag composites of intraseasonal signals show significantly improved eastward propagation over the Indian Ocean and maritime region, with increased eastward precipitation variance and more coherent large-scale structure. The dynamics of the MJO are analyzed using a vertically resolved moisture budget, assuming weak temperature gradient conditions. We find that positive longwave radiative heating anomalies associated with high clouds contribute to low-level ascent and moistening, coincident with intraseasonal precipitation anomalies. Horizontal advection generally damps intraseasonal moisture anomalies, but at some longitudes contributes to their eastward tendency. Shallow convection is enhanced to the east of the intraseasonal precipitation maximum, and its associated moistening of the lower free troposphere encourages eastward propagation of deep convection.

Shallow Mantle Anisotropy Beneath the Juan de Fuca Plate

NASA Astrophysics Data System (ADS)

VanderBeek, Brandon P.; Toomey, Douglas R.

2017-11-01

The anisotropic fabric of the oceanic mantle lithosphere is often assumed to parallel paleo-relative plate motion (RPM). However, we find evidence that this assumption is invalid beneath the Juan de Fuca (JdF) plate. Using travel times of seismic energy propagating through the topmost mantle, we find that the fast direction of P wave propagation is rotated 18° ± 3° counterclockwise to the paleo-spreading direction and strikes between Pacific-JdF relative and JdF absolute plate motion (APM). The mean mantle velocity is 7.85 ± 0.02 km/s with 4.6% ± 0.4% anisotropy. Synthesis of the plate-averaged Pn anisotropy signal with measurements of Pn anisotropy beneath the JdF Ridge and SKS splits across the JdF plate suggests that the anisotropic structure of the topmost mantle continues to evolve away from the spreading center to more closely align with APM. We infer that the oceanic mantle lithosphere may record the influence of both paleo-RPM and paleo-APM.

Effect of kappa distribution on the damping rate of the obliquely propagating magnetosonic mode

NASA Astrophysics Data System (ADS)

Imran, Ali KHAN; G, MURTAZA

2018-03-01

Data from spacecrafts suggest that space plasma has an abundance of suprathermal particles which are controlled by the spectral index κ when modeled on kappa particle velocity distribution. In this paper, considering homogeneous plasma, the effect of integer values of κ on the damping rate of an obliquely propagating magnetosonic (MS) wave is studied. The frequency of the MS wave is assumed to be less than ion cyclotron frequency, i.e., ω \\ll {ω }{{i}}. Under this assumption, the dispersion relation is investigated both numerically and analytically, and it is found that the real frequency of the wave is not a sensitive function of κ, but the imaginary part of the frequency is. It is also shown that for those values of κ where a large number of resonant particles participate in wave-particle interaction, the wave is heavily damped, as expected. The possible application of the results to the solar wind is discussed.

Epidemic spreading in networks with nonrandom long-range interactions

NASA Astrophysics Data System (ADS)

Estrada, Ernesto; Kalala-Mutombo, Franck; Valverde-Colmeiro, Alba

2011-09-01

An “infection,” understood here in a very broad sense, can be propagated through the network of social contacts among individuals. These social contacts include both “close” contacts and “casual” encounters among individuals in transport, leisure, shopping, etc. Knowing the first through the study of the social networks is not a difficult task, but having a clear picture of the network of casual contacts is a very hard problem in a society of increasing mobility. Here we assume, on the basis of several pieces of empirical evidence, that the casual contacts between two individuals are a function of their social distance in the network of close contacts. Then, we assume that we know the network of close contacts and infer the casual encounters by means of nonrandom long-range (LR) interactions determined by the social proximity of the two individuals. This approach is then implemented in a susceptible-infected-susceptible (SIS) model accounting for the spread of infections in complex networks. A parameter called “conductance” controls the feasibility of those casual encounters. In a zero conductance network only contagion through close contacts is allowed. As the conductance increases the probability of having casual encounters also increases. We show here that as the conductance parameter increases, the rate of propagation increases dramatically and the infection is less likely to die out. This increment is particularly marked in networks with scale-free degree distributions, where infections easily become epidemics. Our model provides a general framework for studying epidemic spreading in networks with arbitrary topology with and without casual contacts accounted for by means of LR interactions.

Epidemic spreading in networks with nonrandom long-range interactions.

PubMed

Estrada, Ernesto; Kalala-Mutombo, Franck; Valverde-Colmeiro, Alba

2011-09-01

An "infection," understood here in a very broad sense, can be propagated through the network of social contacts among individuals. These social contacts include both "close" contacts and "casual" encounters among individuals in transport, leisure, shopping, etc. Knowing the first through the study of the social networks is not a difficult task, but having a clear picture of the network of casual contacts is a very hard problem in a society of increasing mobility. Here we assume, on the basis of several pieces of empirical evidence, that the casual contacts between two individuals are a function of their social distance in the network of close contacts. Then, we assume that we know the network of close contacts and infer the casual encounters by means of nonrandom long-range (LR) interactions determined by the social proximity of the two individuals. This approach is then implemented in a susceptible-infected-susceptible (SIS) model accounting for the spread of infections in complex networks. A parameter called "conductance" controls the feasibility of those casual encounters. In a zero conductance network only contagion through close contacts is allowed. As the conductance increases the probability of having casual encounters also increases. We show here that as the conductance parameter increases, the rate of propagation increases dramatically and the infection is less likely to die out. This increment is particularly marked in networks with scale-free degree distributions, where infections easily become epidemics. Our model provides a general framework for studying epidemic spreading in networks with arbitrary topology with and without casual contacts accounted for by means of LR interactions.

Effects of small variations of speed of sound in optoacoustic tomographic imaging

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

Deán-Ben, X. Luís; Ntziachristos, Vasilis; Razansky, Daniel, E-mail: dr@tum.de

2014-07-15

Purpose: Speed of sound difference in the imaged object and surrounding coupling medium may reduce the resolution and overall quality of optoacoustic tomographic reconstructions obtained by assuming a uniform acoustic medium. In this work, the authors investigate the effects of acoustic heterogeneities and discuss potential benefits of accounting for those during the reconstruction procedure. Methods: The time shift of optoacoustic signals in an acoustically heterogeneous medium is studied theoretically by comparing different continuous and discrete wave propagation models. A modification of filtered back-projection reconstruction is subsequently implemented by considering a straight acoustic rays model for ultrasound propagation. The results obtainedmore » with this reconstruction procedure are compared numerically and experimentally to those obtained assuming a heuristically fitted uniform speed of sound in both full-view and limited-view optoacoustic tomography scenarios. Results: The theoretical analysis showcases that the errors in the time-of-flight of the signals predicted by considering the straight acoustic rays model tend to be generally small. When using this model for reconstructing simulated data, the resulting images accurately represent the theoretical ones. On the other hand, significant deviations in the location of the absorbing structures are found when using a uniform speed of sound assumption. The experimental results obtained with tissue-mimicking phantoms and a mouse postmortem are found to be consistent with the numerical simulations. Conclusions: Accurate analysis of effects of small speed of sound variations demonstrates that accounting for differences in the speed of sound allows improving optoacoustic reconstruction results in realistic imaging scenarios involving acoustic heterogeneities in tissues and surrounding media.« less

Modelling the energy dependence of black hole binary flows

NASA Astrophysics Data System (ADS)

Mahmoud, Ra'ad D.; Done, Chris

2018-01-01

We build a full spectral-timing model for the low/hard state of black hole binaries assuming that the spectrum of the X-ray hot flow can be produced by two Comptonization zones. Slow fluctuations generated at the largest radii/softest spectral region of the flow propagate down to modulate the faster fluctuations produced in the spectrally harder region close to the black hole. The observed spectrum and variability are produced by summing over all regions in the flow, including its emission reflected from the truncated disc. This produces energy-dependent Fourier lags qualitatively similar to those in the data. Given a viscous frequency prescription, the model predicts Fourier power spectral densities and lags for any energy bands. We apply this model to archival Rossi X-ray Timing Explorer data from Cyg X-1, using the time-averaged energy spectrum together with an assumed emissivity to set the radial bounds of the soft and hard Comptonization regions. We find that the power spectra cannot be described by any smooth model of generating fluctuations, instead requiring that there are specific radii in the flow where noise is preferentially produced. We also find fluctuation damping between spectrally distinct regions is required to prevent all the variability power generated at large radii being propagated into the inner regions. Even with these additions, we can fit either the power spectra at each energy or the lags between energy bands, but not both. We conclude that either the spectra are more complex than two zone models, or that other processes are important in forming the variability.

Influence of water mist on propagation and suppression of laminar premixed flame

NASA Astrophysics Data System (ADS)

Belyakov, Nikolay S.; Babushok, Valeri I.; Minaev, Sergei S.

2018-03-01

The combustion of premixed gas mixtures containing micro droplets of water was studied using one-dimensional approximation. The dependencies of the burning velocity and flammability limits on the initial conditions and on the properties of liquid droplets were analyzed. Effects of droplet size and concentration of added liquid were studied. It was demonstrated that the droplets with smaller diameters are more effective in reducing the flame velocity. For droplets vaporizing in the reaction zone, the burning velocity is independent of droplet size, and it depends only on the concentration of added liquid. With further increase of the droplet diameter the droplets are passing through the reaction zone with completion of vaporization in the combustion products. It was demonstrated that for droplets above a certain size there are two stable stationary modes of flame propagation with transition of hysteresis type. The critical conditions of the transition are due to the appearance of the temperature maximum at the flame front and the temperature gradient with heat losses from the reaction zone to the products, as a result of droplet vaporization passing through the reaction zone. The critical conditions are similar to the critical conditions of the classical flammability limits of flame with the thermal mechanism of flame propagation. The maximum decrease in the burning velocity and decrease in the combustion temperature at the critical turning point corresponds to predictions of the classical theories of flammability limits of Zel'dovich and Spalding. The stability analysis of stationary modes of flame propagation in the presence of water mist showed the lack of oscillatory processes in the frames of the assumed model.

Influence of global heterogeneities on regional imaging based upon full waveform inversion of teleseismic wavefield

NASA Astrophysics Data System (ADS)

Monteiller, Vadim; Beller, Stephen; Operto, Stephane; Virieux, Jean

2015-04-01

The current development of dense seismic arrays and high performance computing make feasible today application of full-waveform inversion (FWI) on teleseismic data for high-resolution lithospheric imaging. In teleseismic configuration, the source is often considered to first order as a planar wave that impinges the base of the lithospheric target located below the receiver array. Recently, injection methods coupling global propagation in 1D or axisymmetric earth model with regional 3D methods (Discontinuous Galerkin finite element methods, Spectral elements methods or finite differences) allow us to consider more realistic teleseismic phases. Those teleseismic phases can be propagated inside 3D regional model in order to exploit not only the forward-scattered waves propagating up to the receiver but also second-order arrivals that are back-scattered from the free-surface and the reflectors before their recordings on the surface. However, those computation are performed assuming simple global model. In this presentation, we review some key specifications that might be considered for mitigating the effect on FWI of heterogeneities situated outside the regional domain. We consider synthetic models and data computed using our recently developed hybrid method AxiSEM/SEM. The global simulation is done by AxiSEM code which allows us to consider axisymmetric anomalies. The 3D regional computation is performed by Spectral Element Method. We investigate the effect of external anomalies on the regional model obtained by FWI when one neglects them by considering only 1D global propagation. We also investigate the effect of the source time function and the focal mechanism on results of the FWI approach.

Buoyancy Waves in Earth's Magnetosphere: Calculations for a 2-D Wedge Magnetosphere

NASA Astrophysics Data System (ADS)

Wolf, R. A.; Toffoletto, F. R.; Schutza, A. M.; Yang, J.

2018-05-01

To improve theoretical understanding of the braking oscillations observed in Earth's inner plasma sheet, we have derived a theoretical model that describes k∥ = 0 magnetohydrodynamic waves in an idealized magnetospheric configuration that consists of a 2-D wedge with circular-arc field lines. The low-frequency, short-perpendicular-wavelength mode obeys a differential equation that is often used to describe buoyancy oscillations in a neutral atmosphere, so we call those waves "buoyancy waves," though the magnetospheric buoyancy force results from magnetic tension rather than gravity. Propagation of the wave is governed mainly by a position-dependent frequency ωb, the "buoyancy frequency," which is a fundamental property of the magnetosphere. The waves propagate if ωb > ω but otherwise evanesce. In the wedge magnetosphere, ωb turns out to be exactly the fundamental oscillation frequency for poloidal oscillations of a thin magnetic filament, and we assume that the same is true for the real magnetosphere. Observable properties of buoyancy oscillations are discussed, but propagation characteristics vary considerably with the state of the magnetosphere. For a given event, the buoyancy frequency and propagation characteristics can be determined from pressure and density profiles and a magnetic field model, and these characteristics have been worked out for one typical configuration. A localized disturbance that initially resembles a dipolarizing flux bundle spreads east-west and also penetrates into the plasmasphere to some extent. The calculated amplitude near the center of the original wave packet decays in a few oscillation periods, even though our calculation includes no dissipation.

Behavior of a Liquid Bridge between Nonparallel Hydrophobic Surfaces.

PubMed

Ataei, Mohammadmehdi; Chen, Huanchen; Amirfazli, Alidad

2017-12-26

When a liquid bridge is formed between two nonparallel identical surfaces, it can move along the surfaces. Literature indicates that the direction of bridge movement is governed by the wettability of surfaces. When the surfaces are hydrophilic, the motion of the bridge is always toward the cusp (intersection of the plane of the two bounding surfaces). On the other hand, the movement is hitherto thought to be always pointing away from the cusp when the surfaces are hydrophobic. In this study, through experiments, numerical simulations, and analytical reasoning, we demonstrate that for hydrophobic surfaces, wettability is not the only factor determining the direction of the motion. A new geometrical parameter, i.e., confinement (cf), was defined as the ratio of the distance of the farthest contact point of the bridge to the cusp, and that of the closest contact point to the cusp. The direction of the motion depends on the amount of confinement (cf). When the distance between the surfaces is large (resulting in a small cf), the bridge tends to move toward the cusp through a pinning/depinning mechanism of contact lines. When the distance between the surfaces is small (large cf), the bridge tends to move away from the cusp. For a specific system, a maximum cf value (cf max ) exists. A sliding behavior (i.e., simultaneous advancing on the wider side and receding on the narrower side) can also be seen when a liquid bridge is compressed such that the cf exceeds the cf max . Contact angle hysteresis (CAH) is identified as an underpinning phenomenon that together with cf fundamentally explains the movement of a trapped liquid between two hydrophobic surfaces. If there is no CAH, however, i.e., the case of ideal hydrophobic surfaces, the cf will be a constant; we show that the bridge slides toward the cusp when it is stretched, while it slides away from the cusp when it is compressed (note sliding motion is different from motion due to pinning/depinning mechanism of contact lines). As such, the displacement is only related to geometrical parameters such as the amount of compression (or stretching) and the dihedral angle between the surfaces.

Do mesoscale faults in a young fold belt indicate regional or local stress?

NASA Astrophysics Data System (ADS)

Kokado, Akihiro; Yamaji, Atsushi; Sato, Katsushi

2017-04-01

The result of paleostress analyses of mesoscale faults is usually thought of as evidence of a regional stress. On the other hand, the recent advancement of the trishear modeling has enabled us to predict the deformation field around fault-propagation folds without the difficulty of assuming paleo mechanical properties of rocks and sediments. We combined the analysis of observed mesoscale faults and the trishear modeling to understand the significance of regional and local stresses for the formation of mesoscale faults. To this end, we conducted the 2D trishear inverse modeling with a curved thrust fault to predict the subsurface structure and strain field of an anticline, which has a more or less horizontal axis and shows a map-scale plane strain perpendicular to the axis, in the active fold belt of Niigata region, central Japan. The anticline is thought to have been formed by fault-propagation folding under WNW-ESE regional compression. Based on the attitudes of strata and the positions of key tephra beds in Lower Pleistocene soft sediments cropping out at the surface, we obtained (1) a fault-propagation fold with the fault tip at a depth of ca. 4 km as the optimal subsurface structure, and (2) the temporal variation of deformation field during the folding. We assumed that mesoscale faults were activated along the direction of maximum shear strain on the faults to test whether the fault-slip data collected at the surface were consistent with the deformation in some stage(s) of folding. The Wallace-Bott hypothesis was used to estimate the consistence of faults with the regional stress. As a result, the folding and the regional stress explained 27 and 33 of 45 observed faults, respectively, with the 11 faults being consistent with the both. Both the folding and regional one were inconsistent with the remaining 17 faults, which could be explained by transfer faulting and/or the gravitational spreading of the growing anticline. The lesson we learnt from this work was that we should pay attention not only to regional but also to local stresses to interpret the results of paleostress analysis in the shallow levels of young orogenic belts.

Demonstration of repeatability in a high-energy-density planar shear mixing layer experiment

DOE PAGES

Merritt, Elizabeth Catherine; Doss, Forrest William; Di Stefano, Carlos A.; ...

2017-03-11

On laser-driven platforms the assumption of experiment repeatability is particularly important due to a typically low data acquisition rate that doesn’t often allow for data redundancy. If the platform is repeatable, then measurements of the repeatable dynamics from multiple experiments can be treated as measurements of the same system. In high-energy-density hydrodynamic instability experiments the interface growth is assumed to be one of the repeatable aspects of the system. In this paper we demonstrate the repeatability of the instability growth in the counter-propagating shear experiment at the OMEGA laser facility, where the instability growth is characterized by the tracer layermore » thickness or mix-width evolution. Furthermore, in our previous experiment campaigns we have assumed the instability growth was repeatable enough to identify trends, but in this work we explicitly show that the mix-width measurements for nominally identical experiments are repeatable within the measurement error bars.« less

Relativistic Jets from Collapsars

NASA Astrophysics Data System (ADS)

Aloy, M. A.; Müller, E.; Ibáñez, J. M.; Martí, J. M.; MacFadyen, A.

2000-03-01

Using a collapsar progenitor model of MacFadyen & Woosley, we have simulated the propagation of an axisymmetric jet through a collapsing rotating massive star with the GENESIS multidimensional relativistic hydrodynamic code. The jet forms as a consequence of an assumed (constant or variable) energy deposition in the range of 1050-1051 ergs s-1 within a 30 deg cone around the rotation axis. The jet flow is strongly beamed (approximately less than a few degrees), spatially inhomogeneous, and time dependent. The jet reaches the surface of the stellar progenitor (R*=2.98x1010 cm) intact. At breakout, the maximum Lorentz factor of the jet flow is 33. After breakout, the jet accelerates into the circumstellar medium, whose density is assumed to decrease exponentially and then become constant, ρext=10-5 g cm-3. Outside the star, the flow begins to expand laterally also (v~c), but the beam remains very well collimated. At a distance of 2.54 R*, where the simulation ends, the Lorentz factor has increased to 44.

Forward modeling of an atmospheric scenario: path characterization in terms of scattering intensity

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

Bosisio, Ada Vittoria; Cadeddu, Maria P.; Fionda, Ermanno

The knowledge of possible impairments due to atmospheric propagation is of importance in the framework of future 5G mobile networks that use spectrum resource up to the W band. Here, the authors propose the scalar Scatter Indicator (SI), defined as the difference between the simulated TB at 72 GHz and the TB value at the same frequency estimated from a combination of TBs values at 23.8 and 31.4 GHz under assumed scatter-free condition. On the basis of radiosonde profiles observed in Milan, Linate (Italy) in 2005, clear-sky scenarios are used as reference to define a scatter-free TB’s database. A secondmore » database of simulated TBs including scattering effects is generated with ARTS to build the SI. Numerical results show that the SI assumes significant positive values with increasing drop effective radius and total liquid water LWP and it can be used to identify the scattering due to hydrometeor« less

Uncertainties associated with parameter estimation in atmospheric infrasound arrays.

PubMed

Szuberla, Curt A L; Olson, John V

2004-01-01

This study describes a method for determining the statistical confidence in estimates of direction-of-arrival and trace velocity stemming from signals present in atmospheric infrasound data. It is assumed that the signal source is far enough removed from the infrasound sensor array that a plane-wave approximation holds, and that multipath and multiple source effects are not present. Propagation path and medium inhomogeneities are assumed not to be known at the time of signal detection, but the ensemble of time delays of signal arrivals between array sensor pairs is estimable and corrupted by uncorrelated Gaussian noise. The method results in a set of practical uncertainties that lend themselves to a geometric interpretation. Although quite general, this method is intended for use by analysts interpreting data from atmospheric acoustic arrays, or those interested in designing and deploying them. The method is applied to infrasound arrays typical of those deployed as a part of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization.

High-current, relativistic electron-beam transport in metals and the role of magnetic collimation.

PubMed

Storm, M; Solodov, A A; Myatt, J F; Meyerhofer, D D; Stoeckl, C; Mileham, C; Betti, R; Nilson, P M; Sangster, T C; Theobald, W; Guo, Chunlei

2009-06-12

High-resolution coherent transition radiation (CTR) imaging diagnoses electrons accelerated in laser-solid interactions with intensities of approximately 10;{19} W/cm;{2}. The CTR images indicate electron-beam filamentation and annular propagation. The beam temperature and half-angle divergence are inferred to be approximately 1.4 MeV and approximately 16 degrees , respectively. Three-dimensional hybrid-particle-in-cell code simulations reproduce the details of the CTR images assuming an initial half-angle divergence of approximately 56 degrees . Self-generated resistive magnetic fields are responsible for the difference between the initial and measured divergence.

Maneuver Planning for Conjunction Risk Mitigation with Ground-track Control Requirements

NASA Technical Reports Server (NTRS)

McKinley, David

2008-01-01

The planning of conjunction Risk Mitigation Maneuvers (RMM) in the presence of ground-track control requirements is analyzed. Past RMM planning efforts on the Aqua, Aura, and Terra spacecraft have demonstrated that only small maneuvers are available when ground-track control requirements are maintained. Assuming small maneuvers, analytical expressions for the effect of a given maneuver on conjunction geometry are derived. The analytical expressions are used to generate a large trade space for initial RMM design. This trade space represents a significant improvement in initial maneuver planning over existing methods that employ high fidelity maneuver models and propagation.

Born approximation, multiple scattering, and butterfly algorithm

NASA Astrophysics Data System (ADS)

Martinez, Alex; Qiao, Zhijun

2014-06-01

Many imaging algorithms have been designed assuming the absence of multiple scattering. In the 2013 SPIE proceeding, we discussed an algorithm for removing high order scattering components from collected data. In this paper, our goal is to continue this work. First, we survey the current state of multiple scattering in SAR. Then, we revise our method and test it. Given an estimate of our target reflectivity, we compute the multi scattering effects in our target region for various frequencies. Furthermore, we propagate this energy through free space towards our antenna, and remove it from the collected data.

Acoustic Model Testing Chronology

NASA Technical Reports Server (NTRS)

Nesman, Tom

2017-01-01

Scale models have been used for decades to replicate liftoff environments and in particular acoustics for launch vehicles. It is assumed, and analyses supports, that the key characteristics of noise generation, propagation, and measurement can be scaled. Over time significant insight was gained not just towards understanding the effects of thruster details, pad geometry, and sound mitigation but also to the physical processes involved. An overview of a selected set of scale model tests are compiled here to illustrate the variety of configurations that have been tested and the fundamental knowledge gained. The selected scale model tests are presented chronologically.

An intermediate-level course on Biological Physics

NASA Astrophysics Data System (ADS)

Nelson, Phil

2004-03-01

I describe both undergraduate and graduate 1-semester courses designed to give a survey of Biological Physics. The courses cover classical as well as recent topics. The undergraduate version requires calculus-based first-year physics as its prerequisite. With this level of assumed background, we can arrive at topics such as molecular motors, manipulation of single molecules, and the propagation of nerve impulses. Students majoring in physics, chemistry, biochemistry, and every engineering major (as well as a few in biology), end up taking this course. The graduate course covers the same material but includes exercises with symbolic mathematics packages and data modeling.

Non-linear wave interaction in a plasma column

NASA Technical Reports Server (NTRS)

Larsen, J.-M.; Crawford, F. W.

1979-01-01

Non-linear three-wave interaction is analysed for propagation along a cylindrical plasma column surrounded by an infinite dielectric, in the absence of a static magnetic field. An averaged-Lagrangian method is used, and the results are specialized to parametric interaction and mode conversion, assuming an undepleted pump wave. The theory for these two types of interactions is extended to include imperfect synchronism, and the effects of loss. Computations are presented indicating that parametric growth rates of the order of a fraction of a decibel per centimeter should be obtainable for plausible laboratory plasma column parameters.

Spiral-Bevel-Gear Damage Detected Using Decision Fusion Analysis

NASA Technical Reports Server (NTRS)

Dempsey, Paula J.; Handschuh, Robert F.

2003-01-01

Helicopter transmission integrity is critical to helicopter safety because helicopters depend on the power train for propulsion, lift, and flight maneuvering. To detect impending transmission failures, the ideal diagnostic tools used in the health-monitoring system would provide real-time health monitoring of the transmission, demonstrate a high level of reliable detection to minimize false alarms, and provide end users with clear information on the health of the system without requiring them to interpret large amounts of sensor data. A diagnostic tool for detecting damage to spiral bevel gears was developed. (Spiral bevel gears are used in helicopter transmissions to transfer power between nonparallel intersecting shafts.) Data fusion was used to integrate two different monitoring technologies, oil debris analysis and vibration, into a health-monitoring system for detecting surface fatigue pitting damage on the gears.

Flux concentrations on solar dynamic components due to mispointing

NASA Technical Reports Server (NTRS)

Rylicki, Daniel S.

1992-01-01

Mispointing of the solar dynamic (SD) concentrator designed for use on Space Station Freedom (SSF) causes the optical axis of the concentrator to be nonparallel to the incoming rays from the Sun. This causes solar flux not to be focused into the aperture hole of the receiver and may position the flux on other SSF components. A Rocketdyne analysis has determined the thermal impact of off-axis radiation due to mispointing on elements of the SD module and photovoltaic (PV) arrays. The conclusion was that flux distributions on some of the radiator components, the two-axis gimbal rings, the truss, and the PV arrays could present problems. The OFFSET computer code was used at Lewis Research Center to further investigate these flux distributions incident on components. The Lewis study included distributions for a greater range of mispoint angles than the Rocketdyne study.

Photovoltaic module and module arrays

DOEpatents

Botkin, Jonathan; Graves, Simon; Lenox, Carl J. S.; Culligan, Matthew; Danning, Matt

2013-08-27

A photovoltaic (PV) module including a PV device and a frame, The PV device has a PV laminate defining a perimeter and a major plane. The frame is assembled to and encases the laminate perimeter, and includes leading, trailing, and side frame members, and an arm that forms a support face opposite the laminate. The support face is adapted for placement against a horizontal installation surface, to support and orient the laminate in a non-parallel or tilted arrangement. Upon final assembly, the laminate and the frame combine to define a unitary structure. The frame can orient the laminate at an angle in the range of 3.degree.-7.degree. from horizontal, and can be entirely formed of a polymeric material. Optionally, the arm incorporates integral feature(s) that facilitate interconnection with corresponding features of a second, identically formed PV module.

Photovoltaic module and module arrays

DOEpatents

Botkin, Jonathan [El Cerrito, CA; Graves, Simon [Berkeley, CA; Lenox, Carl J. S. [Oakland, CA; Culligan, Matthew [Berkeley, CA; Danning, Matt [Oakland, CA

2012-07-17

A photovoltaic (PV) module including a PV device and a frame. The PV device has a PV laminate defining a perimeter and a major plane. The frame is assembled to and encases the laminate perimeter, and includes leading, trailing, and side frame members, and an arm that forms a support face opposite the laminate. The support face is adapted for placement against a horizontal installation surface, to support and orient the laminate in a non-parallel or tilted arrangement. Upon final assembly, the laminate and the frame combine to define a unitary structure. The frame can orient the laminate at an angle in the range of 3.degree.-7.degree. from horizontal, and can be entirely formed of a polymeric material. Optionally, the arm incorporates integral feature(s) that facilitate interconnection with corresponding features of a second, identically formed PV module.

Multi-processing on supercomputers for computational aerodynamics

NASA Technical Reports Server (NTRS)

Yarrow, Maurice; Mehta, Unmeel B.

1990-01-01

The MIMD concept is applied, through multitasking, with relatively minor modifications to an existing code for a single processor. This approach maps the available memory to multiple processors, exploiting the C-FORTRAN-Unix interface. An existing single processor algorithm is mapped without the need for developing a new algorithm. The procedure of designing a code utilizing this approach is automated with the Unix stream editor. A Multiple Processor Multiple Grid (MPMG) code is developed as a demonstration of this approach. This code solves the three-dimensional, Reynolds-averaged, thin-layer and slender-layer Navier-Stokes equations with an implicit, approximately factored and diagonalized method. This solver is applied to a generic, oblique-wing aircraft problem on a four-processor computer using one process for data management and nonparallel computations and three processes for pseudotime advance on three different grid systems.

Numerical investigation of supersonic turbulent boundary layers with high wall temperature

NASA Technical Reports Server (NTRS)

Guo, Y.; Adams, N. A.

1994-01-01

A direct numerical approach has been developed to simulate supersonic turbulent boundary layers. The mean flow quantities are obtained by solving the parabolized Reynolds-averaged Navier-Stokes equations (globally). Fluctuating quantities are computed locally with a temporal direct numerical simulation approach, in which nonparallel effects of boundary layers are partially modeled. Preliminary numerical results obtained at the free-stream Mach numbers 3, 4.5, and 6 with hot-wall conditions are presented. Approximately 5 million grid points are used in all three cases. The numerical results indicate that compressibility effects on turbulent kinetic energy, in terms of dilatational dissipation and pressure-dilatation correlation, are small. Due to the hot-wall conditions the results show significant low Reynolds number effects and large streamwise streaks. Further simulations with a bigger computational box or a cold-wall condition are desirable.

Effect of curvature on stationary crossflow instability of a three-dimensional boundary layer

NASA Technical Reports Server (NTRS)

Lin, Ray-Sing; Reed, Helen L.

1993-01-01

An incompressible three-dimensional laminar boundary-layer flow over a swept wing is used as a model to study both the wall-curvature and streamline-curvature effects on the stationary crossflow instability. The basic state is obtained by solving the full Navier-Stokes (N-S) equations numerically. The linear disturbance equations are cast on a fixed, body-intrinsic, curvilinear coordinate system. Those nonparallel terms which contribute mainly to the streamline-curvature effect are retained in the formulation of the disturbance equations and approximated by their local finite difference values. The resulting eigenvalue problem is solved by a Chebyshev collocation method. The present results indicate that the convex wall curvature has a stabilizing effect, whereas the streamline curvature has a destabilizing effect. A validation of these effects with an N-S solution for the linear disturbance flow is provided.

Automatic Dictionary Expansion Using Non-parallel Corpora

NASA Astrophysics Data System (ADS)

Rapp, Reinhard; Zock, Michael

Automatically generating bilingual dictionaries from parallel, manually translated texts is a well established technique that works well in practice. However, parallel texts are a scarce resource. Therefore, it is desirable also to be able to generate dictionaries from pairs of comparable monolingual corpora. For most languages, such corpora are much easier to acquire, and often in considerably larger quantities. In this paper we present the implementation of an algorithm which exploits such corpora with good success. Based on the assumption that the co-occurrence patterns between different languages are related, it expands a small base lexicon. For improved performance, it also realizes a novel interlingua approach. That is, if corpora of more than two languages are available, the translations from one language to another can be determined not only directly, but also indirectly via a pivot language.

A probabilistic approach for the estimation of earthquake source parameters from spectral inversion

NASA Astrophysics Data System (ADS)

Supino, M.; Festa, G.; Zollo, A.

2017-12-01

The amplitude spectrum of a seismic signal related to an earthquake source carries information about the size of the rupture, moment, stress and energy release. Furthermore, it can be used to characterize the Green's function of the medium crossed by the seismic waves. We describe the earthquake amplitude spectrum assuming a generalized Brune's (1970) source model, and direct P- and S-waves propagating in a layered velocity model, characterized by a frequency-independent Q attenuation factor. The observed displacement spectrum depends indeed on three source parameters, the seismic moment (through the low-frequency spectral level), the corner frequency (that is a proxy of the fault length) and the high-frequency decay parameter. These parameters are strongly correlated each other and with the quality factor Q; a rigorous estimation of the associated uncertainties and parameter resolution is thus needed to obtain reliable estimations.In this work, the uncertainties are characterized adopting a probabilistic approach for the parameter estimation. Assuming an L2-norm based misfit function, we perform a global exploration of the parameter space to find the absolute minimum of the cost function and then we explore the cost-function associated joint a-posteriori probability density function around such a minimum, to extract the correlation matrix of the parameters. The global exploration relies on building a Markov chain in the parameter space and on combining a deterministic minimization with a random exploration of the space (basin-hopping technique). The joint pdf is built from the misfit function using the maximum likelihood principle and assuming a Gaussian-like distribution of the parameters. It is then computed on a grid centered at the global minimum of the cost-function. The numerical integration of the pdf finally provides mean, variance and correlation matrix associated with the set of best-fit parameters describing the model. Synthetic tests are performed to investigate the robustness of the method and uncertainty propagation from the data-space to the parameter space. Finally, the method is applied to characterize the source parameters of the earthquakes occurring during the 2016-2017 Central Italy sequence, with the goal of investigating the source parameter scaling with magnitude.

3-D dynamic rupture simulations of the 2016 Kumamoto, Japan, earthquake

NASA Astrophysics Data System (ADS)

Urata, Yumi; Yoshida, Keisuke; Fukuyama, Eiichi; Kubo, Hisahiko

2017-11-01

Using 3-D dynamic rupture simulations, we investigated the 2016 Mw7.1 Kumamoto, Japan, earthquake to elucidate why and how the rupture of the main shock propagated successfully, assuming a complicated fault geometry estimated on the basis of the distributions of the aftershocks. The Mw7.1 main shock occurred along the Futagawa and Hinagu faults. Within 28 h before the main shock, three M6-class foreshocks occurred. Their hypocenters were located along the Hinagu and Futagawa faults, and their focal mechanisms were similar to that of the main shock. Therefore, an extensive stress shadow should have been generated on the fault plane of the main shock. First, we estimated the geometry of the fault planes of the three foreshocks as well as that of the main shock based on the temporal evolution of the relocated aftershock hypocenters. We then evaluated the static stress changes on the main shock fault plane that were due to the occurrence of the three foreshocks, assuming elliptical cracks with constant stress drops on the estimated fault planes. The obtained static stress change distribution indicated that Coulomb failure stress change (ΔCFS) was positive just below the hypocenter of the main shock, while the ΔCFS in the shallow region above the hypocenter was negative. Therefore, these foreshocks could encourage the initiation of the main shock rupture and could hinder the propagation of the rupture toward the shallow region. Finally, we conducted 3-D dynamic rupture simulations of the main shock using the initial stress distribution, which was the sum of the static stress changes caused by these foreshocks and the regional stress field. Assuming a slip-weakening law with uniform friction parameters, we computed 3-D dynamic rupture by varying the friction parameters and the values of the principal stresses. We obtained feasible parameter ranges that could reproduce the characteristic features of the main shock rupture revealed by seismic waveform analyses. We also observed that the free surface encouraged the slip evolution of the main shock.[Figure not available: see fulltext.

A Theoretical Investigation of the Input Characteristics of a Rectangular Cavity-Backed Slot Antenna

NASA Technical Reports Server (NTRS)

Cockrell, C. R.

1975-01-01

Equations which represent the magnetic and electric stored energies are derived for an infinite section of rectangular waveguide and a rectangular cavity. These representations which are referred to as being physically observable are obtained by considering the difference in the volume integrals appearing in the complex Poynting theorem. It is shown that the physically observable stored energies are determined by the field components that vanish in a reference plane outside the aperture. These physically observable representations are used to compute the input admittance of a rectangular cavity-backed slot antenna in which a single propagating wave is assumed to exist in the cavity. The slot is excited by a voltage source connected across its center; a sinusoidal distribution is assumed in the slot. Input-admittance calculations are compared with measured data. In addition, input-admittance curves as a function of electrical slot length are presented for several size cavities. For the rectangular cavity backed slot antenna, the quality factor and relative bandwidth were computed independently by using these energy relationships. It is shown that the asymptotic relationship which is usually assumed to exist between the quality bandwidth and the reciprocal of relative bandwidth is equally valid for the rectangular cavity backed slot antenna.

Economic and Environmental Assessment of Seed and Rhizome Propagated Miscanthus in the UK.

PubMed

Hastings, Astley; Mos, Michal; Yesufu, Jalil A; McCalmont, Jon; Schwarz, Kai; Shafei, Reza; Ashman, Chris; Nunn, Chris; Schuele, Heinrich; Cosentino, Salvatore; Scalici, Giovanni; Scordia, Danilo; Wagner, Moritz; Clifton-Brown, John

2017-01-01

Growth in planted areas of Miscanthus for biomass in Europe has stagnated since 2010 due to technical challenges, economic barriers and environmental concerns. These limitations need to be overcome before biomass production from Miscanthus can expand to several million hectares. In this paper, we consider the economic and environmental effects of introducing seed based hybrids as an alternative to clonal M. x giganteus ( Mxg ). The impact of seed based propagation and novel agronomy was compared with current Mxg cultivation and used in 10 commercially relevant, field scale experiments planted between 2012 and 2014 in the United Kingdom, Germany, and Ukraine. Economic and greenhouse gas (GHG) emissions costs were quantified for the following production chain: propagation, establishment, harvest, transportation, storage, and fuel preparation (excluding soil carbon changes). The production and utilization efficiency of seed and rhizome propagation were compared. Results show that new hybrid seed propagation significantly reduces establishment cost to below £900 ha -1 . Calculated GHG emission costs for the seeds established via plugs, though relatively small, was higher than rhizomes because fossil fuels were assumed to heat glasshouses for raising seedling plugs (5.3 and 1.5 kg CO 2 eq. C Mg [dry matter (DM)] -1 ), respectively. Plastic mulch film reduced establishment time, improving crop economics. The breakeven yield was calculated to be 6 Mg DM ha -1 y -1 , which is about half average United Kingdom yield for Mxg ; with newer seeded hybrids reaching 16 Mg DM ha -1 in second year United Kingdom trials. These combined improvements will significantly increase crop profitability. The trade-offs between costs of production for the preparation of different feedstock formats show that bales are the best option for direct firing with the lowest transport costs (£0.04 Mg -1 km -1 ) and easy on-farm storage. However, if pelleted fuel is required then chip harvesting is more economic. We show how current seed based propagation methods can increase the rate at which Miscanthus can be scaled up; ∼×100 those of current rhizome propagation. These rapid ramp rates for biomass production are required to deliver a scalable and economic Miscanthus biomass fuel whose GHG emissions are ∼1/20th those of natural gas per unit of heat.

Economic and Environmental Assessment of Seed and Rhizome Propagated Miscanthus in the UK

PubMed Central

Hastings, Astley; Mos, Michal; Yesufu, Jalil A.; McCalmont, Jon; Schwarz, Kai; Shafei, Reza; Ashman, Chris; Nunn, Chris; Schuele, Heinrich; Cosentino, Salvatore; Scalici, Giovanni; Scordia, Danilo; Wagner, Moritz; Clifton-Brown, John

2017-01-01

Growth in planted areas of Miscanthus for biomass in Europe has stagnated since 2010 due to technical challenges, economic barriers and environmental concerns. These limitations need to be overcome before biomass production from Miscanthus can expand to several million hectares. In this paper, we consider the economic and environmental effects of introducing seed based hybrids as an alternative to clonal M. x giganteus (Mxg). The impact of seed based propagation and novel agronomy was compared with current Mxg cultivation and used in 10 commercially relevant, field scale experiments planted between 2012 and 2014 in the United Kingdom, Germany, and Ukraine. Economic and greenhouse gas (GHG) emissions costs were quantified for the following production chain: propagation, establishment, harvest, transportation, storage, and fuel preparation (excluding soil carbon changes). The production and utilization efficiency of seed and rhizome propagation were compared. Results show that new hybrid seed propagation significantly reduces establishment cost to below £900 ha-1. Calculated GHG emission costs for the seeds established via plugs, though relatively small, was higher than rhizomes because fossil fuels were assumed to heat glasshouses for raising seedling plugs (5.3 and 1.5 kg CO2 eq. C Mg [dry matter (DM)]-1), respectively. Plastic mulch film reduced establishment time, improving crop economics. The breakeven yield was calculated to be 6 Mg DM ha-1 y-1, which is about half average United Kingdom yield for Mxg; with newer seeded hybrids reaching 16 Mg DM ha-1 in second year United Kingdom trials. These combined improvements will significantly increase crop profitability. The trade-offs between costs of production for the preparation of different feedstock formats show that bales are the best option for direct firing with the lowest transport costs (£0.04 Mg-1 km-1) and easy on-farm storage. However, if pelleted fuel is required then chip harvesting is more economic. We show how current seed based propagation methods can increase the rate at which Miscanthus can be scaled up; ∼×100 those of current rhizome propagation. These rapid ramp rates for biomass production are required to deliver a scalable and economic Miscanthus biomass fuel whose GHG emissions are ∼1/20th those of natural gas per unit of heat. PMID:28713395

Excitation of Accelerating Plasma Waves by Counter-Propagating Laser Beams

NASA Astrophysics Data System (ADS)

Shvets, Gennady

2001-10-01

The conventional approach to exciting high phase velocity waves in plasmas is to employ a laser pulse moving in the direction of the desired particle acceleration. Photon downshifting then causes the momentum transfer to the plasma and wave excitiation. We describe a novel approach to plasma wake excitation, colliding-beam accelerator (CBA), which involves the photon exchange between the long and short counter-propagating laser beams. Depending on frequency detuning Δ ω between beams and duration τL of the short pulse, there are two approaches to CBA. First approach assumes (τL ≈ 2/ω_p). Photons exchanged between the beams deposit their recoil momentum in the plasma driving the plasma wake. Frequency detuning between the beams determines the direction of the photon exchange, thereby controlling the phase of the plasma wake. This phase control can be used for reversing the slippage of the accelerated particles with respect to the wake ^1. It can also be used for developing an injector/pulse compressor for the particles of either sign (electrons or positrons)^2. In the second approach, one utilizes a longer pulse with τL >> ω_p-1, which is detuned by Δ ω ~ 2 ωp from the counter-propagating beam. While the parametric excitation of plasma waves by the electromagnetic beatwave at 2 ωp of two co-propagating lasers was first predicted by Rosenbluth and Liu in 1972, we realized, for the first time, that the two excitation beams can be counter-propagating^4. The advantages of using this geometry (lower threshold laser intensity, insensitivity to plasma inhomogeneity) will be explained, and the results of the numerical simulations presented. footnotetext[1]G. Shvets, N. J. Fisch, A. Pukhov, and J. Meyer-ter-Vehn, Phys. Rev. E 60, 2218 (1999). footnotetext[2]G. Shvets, N. J. Fisch, and A. Pukhov, 28, 1194 (2000). footnotetext[5]G. Shvets and N. J. Fisch, Phys. Rev. Lett. 86, 3328 (2001).

Three-dimensional direct numerical simulation study of conditioned moments associated with front propagation in turbulent flows

NASA Astrophysics Data System (ADS)

Yu, R.; Lipatnikov, A. N.; Bai, X. S.

2014-08-01

In order to gain further insight into (i) the use of conditioned quantities for characterizing turbulence within a premixed flame brush and (ii) the influence of front propagation on turbulent scalar transport, a 3D Direct Numerical Simulation (DNS) study of an infinitely thin front that self-propagates in statistically stationary, homogeneous, isotropic, forced turbulence was performed by numerically integrating Navier-Stokes and level set equations. While this study was motivated by issues relevant to premixed combustion, the density was assumed to be constant in order (i) to avoid the influence of the front on the flow and, therefore, to know the true turbulence characteristics as reference quantities for assessment of conditioned moments and (ii) to separate the influence of front propagation on turbulent transport from the influence of pressure gradient induced by heat release. Numerical simulations were performed for two turbulence Reynolds numbers (50 and 100) and four ratios (1, 2, 5, and 10) of the rms turbulent velocity to the front speed. Obtained results show that, first, the mean front thickness is decreased when a ratio of the rms turbulent velocity to the front speed is decreased. Second, although the gradient diffusion closure yields the right direction of turbulent scalar flux obtained in the DNS, the diffusion coefficient Dt determined using the DNS data depends on the mean progress variable. Moreover, Dt is decreased when the front speed is increased, thus, indicating that the front propagation affects turbulent scalar transport even in a constant-density case. Third, conditioned moments of the velocity field differ from counterpart mean moments, thus, disputing the use of conditioned velocity moments for characterizing turbulence when modeling premixed turbulent combustion. Fourth, computed conditioned enstrophies are close to the mean enstrophy in all studied cases, thus, suggesting the use of conditioned enstrophy for characterizing turbulence within a premixed flame brush.

Effect of thermal pressurization on dynamic rupture propagation under depth-dependent stress

NASA Astrophysics Data System (ADS)

Urata, Y.; Kuge, K.; Kase, Y.

2009-12-01

Fluid and pore pressure evolution can affect dynamic propagation of earthquake ruptures owing to thermal pressurization (e.g., Mase and Smith, 1985). We investigate dynamic rupture propagation with thermal pressurization on a fault subjected to depth-dependent stress, on the basis of 3-D numerical simulations for spontaneous dynamic ruptures. We put a vertical strike-slip rectangular fault in a semi-infinite, homogenous, and elastic medium. The length and width of the fault are 8 and 3 km, respectively. We assume a depth-dependent stress estimated by Yamashita et al. (2004). The numerical algorithm is based on the finite-difference method by Kase and Kuge (2001). A rupture is initiated by increasing shear stress in a small patch at the bottom of the fault, and then proceeds spontaneously, governed by a slip-weakening law with the Coulomb failure criteria. Coefficients of friction and Dc are homogeneous on the fault. On a fault with thermal pressurization, we allow effective normal stress to vary with pore pressure change due to frictional heating by the formulation of Bizzarri and Cocco (2006). When thermal pressurization does not work, tractions drop in the same way everywhere and rupture velocity is subshear except near the free surface. Due to thermal pressurization, dynamic friction on the fault decreases and is heterogeneous not only vertically but horizontally, slip increases, and rupture velocity along the strike direction becomes supershear. As a result, plural peaks of final slip appear, as observed in the case of undrained dip-slip fault by Urata et al. (2008). We found in this study that the early stage of rupture growth under the depth-dependent stress is affected by the location of an initial crack. When a rupture is initiated at the center of the fault without thermal pressurization, the rupture cannot propagate and terminates. Thermal pressurization can help such a powerless rupture to keep propagating.

Advances in edge-diffraction modeling for virtual-acoustic simulations

NASA Astrophysics Data System (ADS)

Calamia, Paul Thomas

In recent years there has been growing interest in modeling sound propagation in complex, three-dimensional (3D) virtual environments. With diverse applications for the military, the gaming industry, psychoacoustics researchers, architectural acousticians, and others, advances in computing power and 3D audio-rendering techniques have driven research and development aimed at closing the gap between the auralization and visualization of virtual spaces. To this end, this thesis focuses on improving the physical and perceptual realism of sound-field simulations in virtual environments through advances in edge-diffraction modeling. To model sound propagation in virtual environments, acoustical simulation tools commonly rely on geometrical-acoustics (GA) techniques that assume asymptotically high frequencies, large flat surfaces, and infinitely thin ray-like propagation paths. Such techniques can be augmented with diffraction modeling to compensate for the effect of surface size on the strength and directivity of a reflection, to allow for propagation around obstacles and into shadow zones, and to maintain soundfield continuity across reflection and shadow boundaries. Using a time-domain, line-integral formulation of the Biot-Tolstoy-Medwin (BTM) diffraction expression, this thesis explores various aspects of diffraction calculations for virtual-acoustic simulations. Specifically, we first analyze the periodic singularity of the BTM integrand and describe the relationship between the singularities and higher-order reflections within wedges with open angle less than 180°. Coupled with analytical approximations for the BTM expression, this analysis allows for accurate numerical computations and a continuous sound field in the vicinity of an arbitrary wedge geometry insonified by a point source. Second, we describe an edge-subdivision strategy that allows for fast diffraction calculations with low error relative to a numerically more accurate solution. Third, to address the considerable increase in propagation paths due to diffraction, we describe a simple procedure for identifying and culling insignificant diffraction components during a virtual-acoustic simulation. Finally, we present a novel method to find GA components using diffraction parameters that ensures continuity at reflection and shadow boundaries.

Demonstration of improved seismic source inversion method of tele-seismic body wave

NASA Astrophysics Data System (ADS)

Yagi, Y.; Okuwaki, R.

2017-12-01

Seismic rupture inversion of tele-seismic body wave has been widely applied to studies of large earthquakes. In general, tele-seismic body wave contains information of overall rupture process of large earthquake, while the tele-seismic body wave is inappropriate for analyzing a detailed rupture process of M6 7 class earthquake. Recently, the quality and quantity of tele-seismic data and the inversion method has been greatly improved. Improved data and method enable us to study a detailed rupture process of M6 7 class earthquake even if we use only tele-seismic body wave. In this study, we demonstrate the ability of the improved data and method through analyses of the 2016 Rieti, Italy earthquake (Mw 6.2) and the 2016 Kumamoto, Japan earthquake (Mw 7.0) that have been well investigated by using the InSAR data set and the field observations. We assumed the rupture occurring on a single fault plane model inferred from the moment tensor solutions and the aftershock distribution. We constructed spatiotemporal discretized slip-rate functions with patches arranged as closely as possible. We performed inversions using several fault models and found that the spatiotemporal location of large slip-rate area was robust. In the 2016 Kumamoto, Japan earthquake, the slip-rate distribution shows that the rupture propagated to southwest during the first 5 s. At 5 s after the origin time, the main rupture started to propagate toward northeast. First episode and second episode correspond to rupture propagation along the Hinagu fault and the Futagawa fault, respectively. In the 2016 Rieti, Italy earthquake, the slip-rate distribution shows that the rupture propagated to up-dip direction during the first 2 s, and then rupture propagated toward northwest. From both analyses, we propose that the spatiotemporal slip-rate distribution estimated by improved inversion method of tele-seismic body wave has enough information to study a detailed rupture process of M6 7 class earthquake.

Longitudinal nonlinear wave propagation through soft tissue.

PubMed

Valdez, M; Balachandran, B

2013-04-01

In this paper, wave propagation through soft tissue is investigated. A primary aim of this investigation is to gain a fundamental understanding of the influence of soft tissue nonlinear material properties on the propagation characteristics of stress waves generated by transient loadings. Here, for computational modeling purposes, the soft tissue is modeled as a nonlinear visco-hyperelastic material, the geometry is assumed to be one-dimensional rod geometry, and uniaxial propagation of longitudinal waves is considered. By using the linearized model, a basic understanding of the characteristics of wave propagation is developed through the dispersion relation and in terms of the propagation speed and attenuation. In addition, it is illustrated as to how the linear system can be used to predict brain tissue material parameters through the use of available experimental ultrasonic attenuation curves. Furthermore, frequency thresholds for wave propagation along internal structures, such as axons in the white matter of the brain, are obtained through the linear analysis. With the nonlinear material model, the authors analyze cases in which one of the ends of the rods is fixed and the other end is subjected to a loading. Two variants of the nonlinear model are analyzed and the associated predictions are compared with the predictions of the corresponding linear model. The numerical results illustrate that one of the imprints of the nonlinearity on the wave propagation phenomenon is the steepening of the wave front, leading to jump-like variations in the stress wave profiles. This phenomenon is a consequence of the dependence of the local wave speed on the local deformation of the material. As per the predictions of the nonlinear material model, compressive waves in the structure travel faster than tensile waves. Furthermore, it is found that wave pulses with large amplitudes and small elapsed times are attenuated over shorter spans. This feature is due to the elevated strain-rates introduced at the end of the structure where the load is applied. In addition, it is shown that when steep wave fronts are generated in the nonlinear viscoelastic material, energy dissipation is focused in those wave fronts implying deposition of energy in a highly localized region of the material. Novel mechanisms for brain tissue damage are proposed based on the results obtained. The first mechanism is related to the dissipation of energy at steep wave fronts, while the second one is related to the interaction of steep wave fronts with axons encountered on its way through the structure. Copyright © 2013 Elsevier Ltd. All rights reserved.

Mesoscale variability observed in the Northern Adriatic in autumn 2016

NASA Astrophysics Data System (ADS)

Pasaric, Zoran; Iva, Medjugorac; Nastjenka, Supic; Tamara, Djakovac; Mirko, Orlic

2017-04-01

Quasi-synoptic measurements of hydrographic properties were performed in the Northern Adriatic along the transect extending from Rovinj to the Po River mouth in an approximately east-west direction. The depth along the transect slowly varies between 30 and 40 m. Three one-day cruises were conducted, the first on 12 Nov, the second on 18 Nov, and the third on 25 Nov 2016. During the first and the third cruise the sampling was done with a CTD probe lowered from the surface to the bottom, at eleven stations placed nearly equidistantly along the transect. Average distance between the stations was 6 km. The second cruise was conducted with a towed yo-yo profiler equipped with the CTD probe and continuously undulating between the surface and some 4 m above the bottom. With roughly three undulations per kilometer, horizontal resolution along the transect was about 200 m. The data suggest that three processes occurred during the cruises: 1) surface cooling and related vertical mixing, 2) intrusion of high-salinity waters into the western part of the transect, and 3) propagation of a mesoscale formation in a westward direction. The existence and propagation of the mesoscale feature is supported by a simple analytical model of topographic Rossby waves. By assuming that the bottom varies linearly in the direction perpendicular to the transect, the propagation speed of O(1 km/day) is obtained - in agreement with the observations.

On the spatial distribution of decameter‒scale subauroral ionospheric irregularities observed by SuperDARN radars

NASA Astrophysics Data System (ADS)

Larquier, S.; Ponomarenko, P.; Ribeiro, A. J.; Ruohoniemi, J. M.; Baker, J. B. H.; Sterne, K. T.; Lester, M.

2013-08-01

The midlatitude Super Dual Auroral Radar Network (SuperDARN) radars regularly observe nighttime low‒velocity Sub‒Auroral Ionospheric Scatter (SAIS) from decameter‒scale ionospheric density irregularities during quiet geomagnetic conditions. To establish the origin of the density irregularities responsible for low‒velocity SAIS, it is necessary to distinguish between the effects of high frequency (HF) propagation and irregularity occurrence itself on the observed backscatter distribution. We compare range, azimuth, and elevation data from the Blackstone SuperDARN radar with modeling results from ray tracing coupled with the International Reference Ionosphere assuming a uniform irregularity distribution. The observed and modeled distributions are shown to be very similar. The spatial distribution of backscattering is consistent with the requirement that HF rays propagate nearly perpendicular to the geomagnetic field lines (aspect angle ≤1°). For the first time, the irregularities responsible for low‒velocity SAIS are determined to extend between 200 and 300 km altitude, validating previous assumptions that low‒velocity SAIS is an F‒region phenomenon. We find that the limited spatial extent of this category of ionospheric backscatter within SuperDARN radars' fields‒of‒view is a consequence of HF propagation effects and the finite vertical extent of the scattering irregularities. We conclude that the density irregularities responsible for low‒velocity SAIS are widely distributed horizontally within the midlatitude ionosphere but are confined to the bottom‒side F‒region.

Electromagnetic coupling and array packing induce exchange of dominance on complex modes in 3D periodic arrays of spheres with large permittivity

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

Campione, Salvatore; Capolino, Filippo

In this study, we investigate the effect on wave propagation of array packing and electromagnetic coupling between spheres in a three-dimensional (3D) lattice of microspheres with large permittivity that exhibit strong magnetic polarizability. We report on the complex wavenumber of Bloch waves in the lattice when each sphere is assumed to possess both electric and magnetic dipoles and full electromagnetic coupling is accounted for. While for small material-filling fractions we always determine one dominant mode with low attenuation constant, the same does not happen for large filling fractions, when electromagnetic coupling is included. In the latter case we peculiarly observemore » two dominant modes with low attenuation constant, dominant in different frequency ranges. The filling fraction threshold for which two dominant modes appear varies for different metamaterial constituents, as proven by considering spheres made by either titanium dioxide or lead telluride. As further confirmation of our findings, we retrieve the complex propagation constant of the dominant mode(s) via a field fitting procedure employing two sets of waves (direct and reflected) pertaining to two distinct modes, strengthening the presence of the two distinct dominant modes for increasing filling fractions. However, given that one mode only, with transverse polarization, at any given frequency, is dominant and able to propagate inside the lattice, we are able to accurately treat the metamaterial that is known to exhibit artificial magnetism as a homogeneous material with effective parameters, such as the refractive index. Results clearly show that the account of both electric and magnetic scattering processes in evaluating all electromagnetic intersphere couplings is essential for a proper description of the electromagnetic propagation in lattices.« less

Electromagnetic coupling and array packing induce exchange of dominance on complex modes in 3D periodic arrays of spheres with large permittivity

DOE PAGES

Campione, Salvatore; Capolino, Filippo

2016-01-25

In this study, we investigate the effect on wave propagation of array packing and electromagnetic coupling between spheres in a three-dimensional (3D) lattice of microspheres with large permittivity that exhibit strong magnetic polarizability. We report on the complex wavenumber of Bloch waves in the lattice when each sphere is assumed to possess both electric and magnetic dipoles and full electromagnetic coupling is accounted for. While for small material-filling fractions we always determine one dominant mode with low attenuation constant, the same does not happen for large filling fractions, when electromagnetic coupling is included. In the latter case we peculiarly observemore » two dominant modes with low attenuation constant, dominant in different frequency ranges. The filling fraction threshold for which two dominant modes appear varies for different metamaterial constituents, as proven by considering spheres made by either titanium dioxide or lead telluride. As further confirmation of our findings, we retrieve the complex propagation constant of the dominant mode(s) via a field fitting procedure employing two sets of waves (direct and reflected) pertaining to two distinct modes, strengthening the presence of the two distinct dominant modes for increasing filling fractions. However, given that one mode only, with transverse polarization, at any given frequency, is dominant and able to propagate inside the lattice, we are able to accurately treat the metamaterial that is known to exhibit artificial magnetism as a homogeneous material with effective parameters, such as the refractive index. Results clearly show that the account of both electric and magnetic scattering processes in evaluating all electromagnetic intersphere couplings is essential for a proper description of the electromagnetic propagation in lattices.« less

About a flame propagation by a premixed gas mixture at high turbulence

NASA Astrophysics Data System (ADS)

Gaponov, Sergey A.

2018-03-01

In the paper the new model of the turbulent flame propagation in a premixed gas is offered. In its basis the diffusion equation of combustion products with a source, which is proportional to the contact surface of combustion products with a fresh mixture and an expansion coefficient is put. It is shown that the dependence of the generation rate of combustion products on their mass concentration satisfies conditions of the KPP (Kolmogorov, Petrovsky, Piskounov). In this case, the flame propagation speed depends on the flame surface in a unit volume near the leading front. But at turbulent motion the isolated fragments of combustion products surrounded with fresh mix can be formed on the forward front. It is assumed that the isolated fragments are the sphere shape at the weak turbulence, and with increase in intensity of turbulent pulsations the flame surface of each center is proportional to the pulsations velocity and inversely proportional to the flame speed relatively combustion products, i.e. it is inversely proportional to the product of normal flame speed and expansion coefficient. As a result the formula for the propagation speed calculation of the turbulent flame is proposed which includes not only traditional values of a pulsations velocity and normal flame speed, but also values of an expansion coefficient. On its basis it is explained why the turbulent flame speed exceeds the pulsations velocity by many times at moderate turbulence. It is shown that at the power dependence the turbulent flame speed on the pulsation velocity exponent can vary from 0.5 to unit. The received dependence can be improved if to replace the flat laminar flame with average on the surface of the curved flame, i.e. to take into account the Markstein theory.

Observations and modeling of EMIC wave properties in the presence of multiple ion species as function of magnetic local time

NASA Astrophysics Data System (ADS)

Lee, Justin H.; Angelopoulos, Vassilis

2014-11-01

Electromagnetic ion cyclotron (EMIC) wave generation and propagation in Earth's magnetosphere depend on readily measurable hot (a few to tens of keV) plasma sheet ions, elusive plasmaspheric or ionospheric cold (sub-eV to a few eV) ions, and partially heated warm ions (tens to hundreds of eV). Previous work has assumed all low-energy ions are cold and not considered possible effects of warm ions. Using measurements by multiple Time History of Events and Macroscale Interactions during Substorms spacecraft, we analyze four typical EMIC wave events in the four magnetic local time sectors and consider the properties of both cold and warm ions supplied from previous statistical studies to interpret the wave observations using linear theory. As expected, we find that dusk EMIC waves grow due to the presence of drifting hot anisotropic protons and cold plasmaspheric ions with a dominant cold proton component. Near midnight, EMIC waves are less common because warm heavy ions that suppress wave growth are more abundant there. The waves can grow when cold, plume-like density enhancements are present, however. Dawn EMIC waves, known for their peculiar properties, are generated away from the equator and change polarization during propagation through the warm plasma cloak. Noon EMIC waves can also be generated nonlocally and their properties modified during propagation by a plasmaspheric plume combined with low-energy ions from solar and terrestrial sources. Accounting for multiple ion species, measured wave dispersion, and propagation characteristics can explain previously elusive EMIC wave properties and are therefore important for future studies of EMIC wave effects on energetic particle depletion.

A computational model for histone mark propagation reproduces the distribution of heterochromatin in different human cell types.

PubMed

Schwämmle, Veit; Jensen, Ole Nørregaard

2013-01-01

Chromatin is a highly compact and dynamic nuclear structure that consists of DNA and associated proteins. The main organizational unit is the nucleosome, which consists of a histone octamer with DNA wrapped around it. Histone proteins are implicated in the regulation of eukaryote genes and they carry numerous reversible post-translational modifications that control DNA-protein interactions and the recruitment of chromatin binding proteins. Heterochromatin, the transcriptionally inactive part of the genome, is densely packed and contains histone H3 that is methylated at Lys 9 (H3K9me). The propagation of H3K9me in nucleosomes along the DNA in chromatin is antagonizing by methylation of H3 Lysine 4 (H3K4me) and acetylations of several lysines, which is related to euchromatin and active genes. We show that the related histone modifications form antagonized domains on a coarse scale. These histone marks are assumed to be initiated within distinct nucleation sites in the DNA and to propagate bi-directionally. We propose a simple computer model that simulates the distribution of heterochromatin in human chromosomes. The simulations are in agreement with previously reported experimental observations from two different human cell lines. We reproduced different types of barriers between heterochromatin and euchromatin providing a unified model for their function. The effect of changes in the nucleation site distribution and of propagation rates were studied. The former occurs mainly with the aim of (de-)activation of single genes or gene groups and the latter has the power of controlling the transcriptional programs of entire chromosomes. Generally, the regulatory program of gene transcription is controlled by the distribution of nucleation sites along the DNA string.

Nucleation and arrest of slow slip earthquakes: mechanisms and nonlinear simulations using realistic fault geometries and heterogeneous medium properties

NASA Astrophysics Data System (ADS)

Alves da Silva Junior, J.; Frank, W.; Campillo, M.; Juanes, R.

2017-12-01

Current models for slow slip earthquakes (SSE) assume a simplified fault embedded on a homogeneous half-space. In these models SSE events nucleate on the transition from velocity strengthening (VS) to velocity weakening (VW) down dip from the trench and propagate towards the base of the seismogenic zone, where high normal effective stress is assumed to arrest slip. Here, we investigate SSE nucleation and arrest using quasi-static finite element simulations, with rate and state friction, on a domain with heterogeneous properties and realistic fault geometry. We use the fault geometry of the Guerrero Gap in the Cocos subduction zone, where SSE events occurs every 4 years, as a proxy for subduction zone. Our model is calibrated using surface displacements from GPS observations. We apply boundary conditions according to the plate convergence rate and impose a depth-dependent pore pressure on the fault. Our simulations indicate that the fault geometry and elastic properties of the medium play a key role in the arrest of SSE events at the base of the seismogenic zone. SSE arrest occurs due to aseismic deformations of the domain that result in areas with elevated effective stress. SSE nucleation occurs in the transition from VS to VW and propagates as a crack-like expansion with increased nucleation length prior to dynamic instability. Our simulations encompassing multiple seismic cycles indicate SSE interval times between 1 and 10 years and, importantly, a systematic increase of rupture area prior to dynamic instability, followed by a hiatus in the SSE occurrence. We hypothesize that these SSE characteristics, if confirmed by GPS observations in different subduction zones, can add to the understanding of nucleation of large earthquakes in the seismogenic zone.

Causal inference in biology networks with integrated belief propagation.

PubMed

Chang, Rui; Karr, Jonathan R; Schadt, Eric E

2015-01-01

Inferring causal relationships among molecular and higher order phenotypes is a critical step in elucidating the complexity of living systems. Here we propose a novel method for inferring causality that is no longer constrained by the conditional dependency arguments that limit the ability of statistical causal inference methods to resolve causal relationships within sets of graphical models that are Markov equivalent. Our method utilizes Bayesian belief propagation to infer the responses of perturbation events on molecular traits given a hypothesized graph structure. A distance measure between the inferred response distribution and the observed data is defined to assess the 'fitness' of the hypothesized causal relationships. To test our algorithm, we infer causal relationships within equivalence classes of gene networks in which the form of the functional interactions that are possible are assumed to be nonlinear, given synthetic microarray and RNA sequencing data. We also apply our method to infer causality in real metabolic network with v-structure and feedback loop. We show that our method can recapitulate the causal structure and recover the feedback loop only from steady-state data which conventional method cannot.

Raster microdiffraction with synchrotron radiation of hydrated biopolymers with nanometre step-resolution: case study of starch granules

PubMed Central

Riekel, C.; Burghammer, M.; Davies, R. J.; Di Cola, E.; König, C.; Lemke, H.T.; Putaux, J.-L.; Schöder, S.

2010-01-01

X-ray radiation damage propagation is explored for hydrated starch granules in order to reduce the step resolution in raster-microdiffraction experiments to the nanometre range. Radiation damage was induced by synchrotron radiation microbeams of 5, 1 and 0.3 µm size with ∼0.1 nm wavelength in B-type potato, Canna edulis and Phajus grandifolius starch granules. A total loss of crystallinity of granules immersed in water was found at a dose of ∼1.3 photons nm−3. The temperature dependence of radiation damage suggests that primary radiation damage prevails up to about 120 K while secondary radiation damage becomes effective at higher temperatures. Primary radiation damage remains confined to the beam track at 100 K. Propagation of radiation damage beyond the beam track at room temperature is assumed to be due to reactive species generated principally by water radiolysis induced by photoelectrons. By careful dose selection during data collection, raster scans with 500 nm step-resolution could be performed for granules immersed in water. PMID:20975219

Moderately nonlinear ultrasound propagation in blood-mimicking fluid.

PubMed

Kharin, Nikolay A; Vince, D Geoffrey

2004-04-01

In medical diagnostic ultrasound (US), higher than-in-water nonlinearity of body fluids and tissue usually does not produce strong nonlinearly distorted waves because of the high absorption. The relative influence of absorption and nonlinearity can be characterized by the Gol'dberg number Gamma. There are two limiting cases in nonlinear acoustics: weak waves (Gamma < 1) or strong waves (Gamma > 1). However, at diagnostic frequencies in tissue and body fluids, the nonlinear effects and effects of absorption more likely are comparable (Gol'dberg number Gamma approximately 1). The aim of this work was to study the nonlinear propagation of a moderately nonlinear US second harmonic signal in a blood-mimicking fluid. Quasilinear solutions to the KZK equation are presented, assuming radiation from a flat and geometrically focused circular Gaussian source. The solutions are expressed in a new simplified closed form and are in very good agreement with those of previous studies measuring and modeling Gaussian beams. The solutions also show good agreement with the measurements of the beams produced by commercially available transducers, even without special Gaussian shading.

Time-reversal transcranial ultrasound beam focusing using a k-space method

PubMed Central

Jing, Yun; Meral, F. Can; Clement, Greg. T.

2012-01-01

This paper proposes the use of a k-space method to obtain the correction for transcranial ultrasound beam focusing. Mirroring past approaches, A synthetic point source at the focal point is numerically excited, and propagated through the skull, using acoustic properties acquired from registered computed tomograpy of the skull being studied. The received data outside the skull contains the correction information and can be phase conjugated (time reversed) and then physically generated to achieve a tight focusing inside the skull, by assuming quasi-plane transmission where shear waves are not present or their contribution can be neglected. Compared with the conventional finite-difference time-domain method for wave propagation simulation, it will be shown that the k-space method is significantly more accurate even for a relatively coarse spatial resolution, leading to a dramatically reduced computation time. Both numerical simulations and experiments conducted on an ex vivo human skull demonstrate that, precise focusing can be realized using the k-space method with a spatial resolution as low as only 2.56 grid points per wavelength, thus allowing treatment planning computation on the order of minutes. PMID:22290477

The Distance to the Heliospheric VLF Emission Region

NASA Technical Reports Server (NTRS)

McNutt, R. L., Jr.; Lazarus, A. J.; Belcher, J. W.; Lyon, J.; Goodrich, C. C.; Kulkarni, R.

1995-01-01

Two major episodes of heliospheric VLF emissions near 3 kHz have been observed by the Voyager spacecraft in 1983-1984 and 1992-1993. This higher-frequency component is apparently triggered by solar wind transients with sufficiently large spatial extents and energies to continue to propagate as shocks in the heliosheath. Entrainment of previously unshocked material and changed flow conditions in the heliosheath both tend to slow the shock propagation. The shock evolution is not self-similar. Rather, it is intermediate to two blast-wave similarity solutions in the moving solar wind frame. In one solution the shock moves as time to the 2/3 power and in the other as time to the 4/5 power. Using these models, the shock/Forbush decrease observed at Voyager 2 in September, 1991 and the turn-on of the 1992 emission is consistent with an emission region distance of approx. 130 AU (assuming no additional slowing of the shock in the heliosheath). If the termination shock was at approx. 70 AU when the transient shock collided with it, the true distance to the source region was probably closer to approx. 115 AU.

The distance to the heliospheric VLF emission region

NASA Technical Reports Server (NTRS)

Mcnutt, R. L., Jr.; Lazarus, A. J.; Belcher, J. W.; Lyon, J.; Goodrich, C. C.; Kulkarni, R.

1995-01-01

Two major episodes of heliospheric VLF emissions near 3 kHz have been observed by the Voyager spacecraft in 1983/84 and 1992/3. This higher-frequency component is apparently triggered by solar wind transients with sufficiently large spatial extents and energies to continue to propagate as shocks in the heliosheath. Entrainment of previously unshocked material and changed flow conditions in the heliosheath both tend to slow the shock propagation. The shock evolution is not self-similar. Rather, it is intermediate to two blast-wave similarity solutions in the moving solar wind frame. In one solution the shock moves as time to the 2/3 power and in the other as time to the 4/5 power. Using these models, the shock/Forbush decrease observed at Voyager 2 in September, 1991 and the turn-on of the 1992 emission is consistent with an emission region distance of approximately 130 AU (assuming no additional slowing of the shock in the heliosheath). If the termination shock was at approximately 70 AU when the transient shock collided with it, the true distance to the source region was probably closer to approximately 115 AU.

Chiral current generation in QED by longitudinal photons

NASA Astrophysics Data System (ADS)

Acosta Avalo, J. L.; Pérez Rojas, H.

2016-08-01

We report the generation of a pseudovector electric current having imbalanced chirality in an electron-positron strongly magnetized gas in QED. It propagates along the external applied magnetic field B as a chiral magnetic effect in QED. It is triggered by a perturbative electric field parallel to B, associated to a pseudovector longitudinal mode propagating along B. An electromagnetic chemical potential was introduced, but our results remain valid even when it vanishes. A nonzero fermion mass was assumed, which is usually considered vanishing in the literature. In the quantum field theory formalism at finite temperature and density, an anomaly relation for the axial current was found for a medium of massive fermions. It bears some analogy to the Adler-Bell-Jackiw anomaly. From the expression for the chiral current in terms of the photon self-energy tensor in a medium, it is obtained that electrons and positrons scattered by longitudinal photons (inside the light cone) contribute to the chiral current, as well as the to pair creation due to longitudinal photons (out of light cone). In the static limit, an electric pseudovector current is obtained in the lowest Landau level.

Relativistic features and time delay of laser-induced tunnel ionization

NASA Astrophysics Data System (ADS)

Yakaboylu, Enderalp; Klaiber, Michael; Bauke, Heiko; Hatsagortsyan, Karen Z.; Keitel, Christoph H.

2013-12-01

The electron dynamics in the classically forbidden region during relativistic tunnel ionization is investigated. The classical forbidden region in the relativistic regime is identified by defining a gauge-invariant total-energy operator. Introducing position-dependent energy levels inside the tunneling barrier, we demonstrate that the relativistic tunnel ionization can be well described by a one-dimensional intuitive picture. This picture predicts that, in contrast to the well-known nonrelativistic regime, the ionized electron wave packet arises with a momentum shift along the laser's propagation direction. This is compatible with results from a strong-field approximation calculation where the binding potential is assumed to be zero ranged. Further, the tunneling time delay, stemming from Wigner's definition, is investigated for model configurations of tunneling and compared with results obtained from the exact propagator. By adapting Wigner's time delay definition to the ionization process, the tunneling time is investigated in the deep-tunneling and in the near-threshold-tunneling regimes. It is shown that while in the deep-tunneling regime signatures of the tunneling time delay are not measurable at remote distance, they are detectable, however, in the latter regime.

[Basic research on vocal fold dynamics: three-dimensional vibration analysis of human and canine larynges].

PubMed

Döllinger, M; Rosanowski, F; Eysholdt, U; Lohscheller, J

2008-12-01

The understanding of normal and pathological vocal fold dynamics is the basis for a pathophysiological motivated voice therapy. Crucial vocal fold dynamics concerning voice production occur at the medial part of the vocal fold which is seen as the most critical region of mucosal wave propagation. Due to the limited size of the larynx the possibilities of laryngeal imaging by endoscopic techniques are limited. This work describes an experimental set-up that enables quantification of the entire medial and superior vocal fold surface using excised human and in vivo canine larynges. The data obtained enable analysis of vocal fold deflections, velocities, and mucosal wave propagation. The reciprocal dependencies can be examined and different areas of vocal fold dynamics located. The vertical components obscured in clinical endoscopy can be visualized. This is not negligible. In particular it is shown that the vertical deflection, which cannot be observed by clinical examination, plays an important part in the dynamics and therefore cannot be omitted for therapeutic procedures. The theoretically assumed entrainment and influence of the two main vibration modes enabling normal phonation is confirmed.

A theoretical study for the propagation of rolling noise over a porous road pavement

NASA Astrophysics Data System (ADS)

Keung Lui, Wai; Ming Li, Kai

2004-07-01

A simplified model based on the study of sound diffracted by a sphere is proposed for investigating the propagation of noise in a hornlike geometry between porous road surfaces and rolling tires. The simplified model is verified by comparing its predictions with the published numerical and experimental results of studies on the horn amplification of sound over a road pavement. In a parametric study, a point monopole source is assumed to be localized on the surface of a tire. In the frequency range of interest, a porous road pavement can effectively reduce the level of amplified sound due to the horn effect. It has been shown that an increase in the thickness and porosity of a porous layer, or the use of a double layer of porous road pavement, attenuates the horn amplification of sound. However, a decrease in the flow resistivity of a porous road pavement does little to reduce the horn amplification of sound. It has also been demonstrated that the horn effect over a porous road pavement is less dependent on the angular position of the source on the surface of tires.

Experimental studies of rock fracture behavior related to hydraulic fracture

NASA Astrophysics Data System (ADS)

Ma, Zifeng

The objective of this experimental investigation stems from the uncontrollable of the hydraulic fracture shape in the oil and gas production field. A small-scale laboratory investigation of crack propagation in sandstone was first performed with the objective to simulate the field fracture growth. Test results showed that the fracture resistance increased with crack extension, assuming that there was an interaction between crack faces (bridging, interlocking, and friction). An acoustic emission test was conducted to examine the existence of the interaction by locating AE events and analyzing waveform. Furthermore, the effects of confining stress, loading rate, stress field, and strength heterogeneous on the tortuosity of the fracture surface were experimentally investigated in the study. Finally, a test was designed and conducted to investigate the crack propagation in a stratified media with permeability contrast. Crack was observed to arrested in an interface. The phenomenon of delamination along an interface between layers with permeability contrast was observed. The delamination was proposed to be the cause of crack arrest and crack jump in the saturated stratified materials under confinement test.

Interplanetary Radio Transmission Through Serial Ionospheric and Material Barriers

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

Fields, David; Kennedy, Robert G; Roy, Kenneth I

2013-01-01

A usual first principle in planning radio astronomy observations from the earth is that monitoring must be carried out well above the ionospheric plasma cutoff frequency (~5 MHz). Before space probes existed, radio astronomy was almost entirely done above 6 MHz, and this value is considered a practical lower limit by most radio astronomers. Furthermore, daytime ionization (especially D-layer formation) places additional constraints on wave propagation, and waves of frequency below 10-20 MHz suffer significant attenuation. More careful calculations of wave propagation through the earth s ionosphere suggest that for certain conditions (primarily the presence of a magnetic field) theremore » may be a transmission window well below this assumed limit. Indeed, for receiving extraterrestrial radiation below the ionospheric plasma cutoff frequency, a choice of VLF frequency appears optimal to minimize loss. The calculation, experimental validation, and conclusions are presented here. This work demonstrates the possibility of VLF transmission through the ionosphere and various subsequent material barriers. Implications include development of a new robust communications channel, communications with submerged or subterranean receivers / instruments on or offworld, and a new approach to SETI.« less

Laser-induced extreme magnetic field in nanorod targets

NASA Astrophysics Data System (ADS)

Lécz, Zsolt; Andreev, Alexander

2018-03-01

The application of nano-structured target surfaces in laser-solid interaction has attracted significant attention in the last few years. Their ability to absorb significantly more laser energy promises a possible route for advancing the currently established laser ion acceleration concepts. However, it is crucial to have a better understanding of field evolution and electron dynamics during laser-matter interactions before the employment of such exotic targets. This paper focuses on the magnetic field generation in nano-forest targets consisting of parallel nanorods grown on plane surfaces. A general scaling law for the self-generated quasi-static magnetic field amplitude is given and it is shown that amplitudes up to 1 MT field are achievable with current technology. Analytical results are supported by three-dimensional particle-in-cell simulations. Non-parallel arrangements of nanorods has also been considered which result in the generation of donut-shaped azimuthal magnetic fields in a larger volume.

A Novel General Imaging Formation Algorithm for GNSS-Based Bistatic SAR.

PubMed

Zeng, Hong-Cheng; Wang, Peng-Bo; Chen, Jie; Liu, Wei; Ge, LinLin; Yang, Wei

2016-02-26

Global Navigation Satellite System (GNSS)-based bistatic Synthetic Aperture Radar (SAR) recently plays a more and more significant role in remote sensing applications for its low-cost and real-time global coverage capability. In this paper, a general imaging formation algorithm was proposed for accurately and efficiently focusing GNSS-based bistatic SAR data, which avoids the interpolation processing in traditional back projection algorithms (BPAs). A two-dimensional point target spectrum model was firstly presented, and the bulk range cell migration correction (RCMC) was consequently derived for reducing range cell migration (RCM) and coarse focusing. As the bulk RCMC seriously changes the range history of the radar signal, a modified and much more efficient hybrid correlation operation was introduced for compensating residual phase errors. Simulation results were presented based on a general geometric topology with non-parallel trajectories and unequal velocities for both transmitter and receiver platforms, showing a satisfactory performance by the proposed method.

Note: long range and accurate measurement of deep trench microstructures by a specialized scanning tunneling microscope.

PubMed

Ju, Bing-Feng; Chen, Yuan-Liu; Zhang, Wei; Zhu, Wule; Jin, Chao; Fang, F Z

2012-05-01

A compact but practical scanning tunneling microscope (STM) with high aspect ratio and high depth capability has been specially developed. Long range scanning mechanism with tilt-adjustment stage is adopted for the purpose of adjusting the probe-sample relative angle to compensate the non-parallel effects. A periodical trench microstructure with a pitch of 10 μm has been successfully imaged with a long scanning range up to 2.0 mm. More innovatively, a deep trench with depth and step height of 23.0 μm has also been successfully measured, and slope angle of the sidewall can approximately achieve 67°. The probe can continuously climb the high step and exploring the trench bottom without tip crashing. The new STM could perform long range measurement for the deep trench and high step surfaces without image distortion. It enables accurate measurement and quality control of periodical trench microstructures.

Robust Stabilization of T-S Fuzzy Stochastic Descriptor Systems via Integral Sliding Modes.

PubMed

Li, Jinghao; Zhang, Qingling; Yan, Xing-Gang; Spurgeon, Sarah K

2017-09-19

This paper addresses the robust stabilization problem for T-S fuzzy stochastic descriptor systems using an integral sliding mode control paradigm. A classical integral sliding mode control scheme and a nonparallel distributed compensation (Non-PDC) integral sliding mode control scheme are presented. It is shown that two restrictive assumptions previously adopted developing sliding mode controllers for Takagi-Sugeno (T-S) fuzzy stochastic systems are not required with the proposed framework. A unified framework for sliding mode control of T-S fuzzy systems is formulated. The proposed Non-PDC integral sliding mode control scheme encompasses existing schemes when the previously imposed assumptions hold. Stability of the sliding motion is analyzed and the sliding mode controller is parameterized in terms of the solutions of a set of linear matrix inequalities which facilitates design. The methodology is applied to an inverted pendulum model to validate the effectiveness of the results presented.

Mutually unbiased coarse-grained measurements of two or more phase-space variables

NASA Astrophysics Data System (ADS)

Paul, E. C.; Walborn, S. P.; Tasca, D. S.; Rudnicki, Łukasz

2018-05-01

Mutual unbiasedness of the eigenstates of phase-space operators—such as position and momentum, or their standard coarse-grained versions—exists only in the limiting case of infinite squeezing. In Phys. Rev. Lett. 120, 040403 (2018), 10.1103/PhysRevLett.120.040403, it was shown that mutual unbiasedness can be recovered for periodic coarse graining of these two operators. Here we investigate mutual unbiasedness of coarse-grained measurements for more than two phase-space variables. We show that mutual unbiasedness can be recovered between periodic coarse graining of any two nonparallel phase-space operators. We illustrate these results through optics experiments, using the fractional Fourier transform to prepare and measure mutually unbiased phase-space variables. The differences between two and three mutually unbiased measurements is discussed. Our results contribute to bridging the gap between continuous and discrete quantum mechanics, and they could be useful in quantum-information protocols.

A Novel General Imaging Formation Algorithm for GNSS-Based Bistatic SAR

PubMed Central

Zeng, Hong-Cheng; Wang, Peng-Bo; Chen, Jie; Liu, Wei; Ge, LinLin; Yang, Wei

2016-01-01

Global Navigation Satellite System (GNSS)-based bistatic Synthetic Aperture Radar (SAR) recently plays a more and more significant role in remote sensing applications for its low-cost and real-time global coverage capability. In this paper, a general imaging formation algorithm was proposed for accurately and efficiently focusing GNSS-based bistatic SAR data, which avoids the interpolation processing in traditional back projection algorithms (BPAs). A two-dimensional point target spectrum model was firstly presented, and the bulk range cell migration correction (RCMC) was consequently derived for reducing range cell migration (RCM) and coarse focusing. As the bulk RCMC seriously changes the range history of the radar signal, a modified and much more efficient hybrid correlation operation was introduced for compensating residual phase errors. Simulation results were presented based on a general geometric topology with non-parallel trajectories and unequal velocities for both transmitter and receiver platforms, showing a satisfactory performance by the proposed method. PMID:26927117

Eddy Current Minimizing Flow Plug for Use in Flow Conditioning and Flow Metering

NASA Technical Reports Server (NTRS)

England, John Dwight (Inventor); Kelley, Anthony R. (Inventor)

2015-01-01

An eddy-current-minimizing flow plug has an outer radial wall with open flow channels formed between the plug's inlet and outlet. The plug has a central region coupled to the inner surface of the outer radial wall. Each open flow channel includes (i) a first portion originating at the inlet and converging to a location in the plug where convergence is contributed to by changes in thickness of the outer radial wall and divergence of the central region, and (ii) a second portion originating in the plug and diverging to the outlet where divergence is contributed to by changes in thickness of the outer radial wall and convergence of the central region. For at least a portion of the open flow channels, a central axis passing through the first and second portions is non-parallel with respect to the given direction of the flow.

Metalenses based on the non-parallel double-slit arrays

NASA Astrophysics Data System (ADS)

Shao, Hongyan; Chen, Chen; Wang, Jicheng; Pan, Liang; Sang, Tian

2017-09-01

Metalenses based on surface plasmon polaritons have played an indispensable role in ultra-thin devices designing. The amplitude, phase and polarization of electromagnetic waves all can be controlled easily by modifying the metasurface structures. Here we propose and investigate a new type of structure with Babinet-inverted nano-antennas which can provide a series of unit-cells with phase-shifts covering 2π and ensure almost same transmittance simultaneously. As a result, the wavefront can be manipulated by arraying the units in course. Metalenses with the linear asymmetrical double slit unit-cell arrays are designed and the simulative results exhibit their perfect focusing characteristics, including single-focus lenses and multi-focus lenses. The small focus size and high numerical aperture make them stand out from the traditional counterparts in application of precision sensing devices. We expect our designs will provide new insights in the practical applications for metasurfaces in data storages, optical information processing and optical holography.

Experimental postseismic recovery of fractured rocks assisted by calcite sealing

NASA Astrophysics Data System (ADS)

Aben, F. M.; Doan, M.-L.; Gratier, J.-P.; Renard, F.

2017-07-01

Postseismic recovery within fault damage zones involves slow healing of coseismic fractures leading to permeability reduction and strength increase with time. To better understand this process, experiments were performed by long-term fluid percolation with calcite precipitation through predamaged quartz-monzonite samples subjected to upper crustal conditions of stress and temperature. This resulted in a P wave velocity recovery of 50% of its initial drop after 64 days. In contrast, the permeability remained more or less constant for the duration of the experiment. Microstructures, fluid chemistry, and X-ray microtomography demonstrate that incipient calcite sealing and asperity dissolution are responsible for the P wave velocity recovery. The permeability is unaffected because calcite precipitates outside of the main flow channels. The highly nonparallel evolution of strength recovery and permeability suggests that fluid conduits within fault damage zones can remain open fluid conduits after an earthquake for much longer durations than suggested by the seismic monitoring of fault healing.

Damage assessment in reinforced concrete using nonlinear vibration techniques

NASA Astrophysics Data System (ADS)

Van Den Abeele, K.; De Visscher, J.

2000-07-01

Reinforced concrete (RC) structures are subject to microcrack initiation and propagation at load levels far below the actual failure load. In this paper, nonlinear vibration techniques are applied to investigate stages of progressive damage in RC beams induced by static loading tests. At different levels of damage, a modal analysis is carried out, assuming the structure to behave linearly. At the same time, measurement of resonant frequencies and damping ratios as function of vibration amplitude are performed using a frequency domain technique as well as a time domain technique. We compare the results of the linear and nonlinear techniques, and value them against the visual damage evaluation.

Computation of Propagation Speed and Reflection of Axially Symmetric Waves in Composite Cylinders, with Application to Impedance Tube and Calibrator.

DTIC Science & Technology

1982-08-25

where w is the angular frequency and k the wave number; the phase speed c is related by W - kc. Because of the geometry, it is assumed that the field...PSA Phase of sample PST Phase of standard STEP Step size TEMP Temperature (C) THICK Length of sample (cm) VSA Voltage of sample VST Voltage of standard...VSA/ VST 0)027 W=4001.*RS69+.8*(TEMP-24 .0)- .037*( TEMFP-24 .0) **2.*0 00o29 E=(PSA-PST)/57.2958 0030 G=E-O 0031 IF (ABS(G)-2*3.14159 *LE. 0) GO TO 50

Spectral Density of Laser Beam Scintillation in Wind Turbulence. Part 1; Theory

NASA Technical Reports Server (NTRS)

Balakrishnan, A. V.

1997-01-01

The temporal spectral density of the log-amplitude scintillation of a laser beam wave due to a spatially dependent vector-valued crosswind (deterministic as well as random) is evaluated. The path weighting functions for normalized spectral moments are derived, and offer a potential new technique for estimating the wind velocity profile. The Tatarskii-Klyatskin stochastic propagation equation for the Markov turbulence model is used with the solution approximated by the Rytov method. The Taylor 'frozen-in' hypothesis is assumed for the dependence of the refractive index on the wind velocity, and the Kolmogorov spectral density is used for the refractive index field.

An association of magnetospheric whistler dispersion characteristics with changes in local plasma density.

NASA Technical Reports Server (NTRS)

Scarf, F. L.; Chappell, C. R.

1973-01-01

We use OGO 5 measurements made within the plasmapause on May 15, 1969, to investigate the possible association between changes in lightning whistler dispersion characteristics and local density fluctuations. It is shown that groups of whistlers with relatively constant dispersions tended to be detected in regions where the local ion concentration was significantly enhanced. It is assumed that these local density fluctuations represent characteristics of large-scale field-aligned variations. The results are then compared with ray refraction estimates appropriate for low-frequency whistler mode propagation (wave components with frequencies comparable to the local lower hybrid frequency) in a nonuniform medium.

An anisotropic lens for transitioning plane waves between media of different permittivities

NASA Astrophysics Data System (ADS)

Stone, Alexander P.; Baum, Carl E.

1988-11-01

A particularly simple geometry is considered in which an inhomogeneous and anisotropic lens is specified for the transition of plane waves between media of different permittivities. The permittivities of the regions outside of the lens can be constant, but the permittivity of the lens region depends on position. Results are presented for a plane wave in the second medium propagating normally to the assumed plane boundary of that medium. The results for the case of normal incidence are then generalized to the case of nonnormal incidence. The conditions of transit time conservation and impedance matching are related to the Brewster angle.

Scalar wave-optical reconstruction of plenoptic camera images.

PubMed

Junker, André; Stenau, Tim; Brenner, Karl-Heinz

2014-09-01

We investigate the reconstruction of plenoptic camera images in a scalar wave-optical framework. Previous publications relating to this topic numerically simulate light propagation on the basis of ray tracing. However, due to continuing miniaturization of hardware components it can be assumed that in combination with low-aperture optical systems this technique may not be generally valid. Therefore, we study the differences between ray- and wave-optical object reconstructions of true plenoptic camera images. For this purpose we present a wave-optical reconstruction algorithm, which can be run on a regular computer. Our findings show that a wave-optical treatment is capable of increasing the detail resolution of reconstructed objects.

Spatial features of synaptic adaptation affecting learning performance.

PubMed

Berger, Damian L; de Arcangelis, Lucilla; Herrmann, Hans J

2017-09-08

Recent studies have proposed that the diffusion of messenger molecules, such as monoamines, can mediate the plastic adaptation of synapses in supervised learning of neural networks. Based on these findings we developed a model for neural learning, where the signal for plastic adaptation is assumed to propagate through the extracellular space. We investigate the conditions allowing learning of Boolean rules in a neural network. Even fully excitatory networks show very good learning performances. Moreover, the investigation of the plastic adaptation features optimizing the performance suggests that learning is very sensitive to the extent of the plastic adaptation and the spatial range of synaptic connections.

The Impact of Discontinuity Front Orientation on the Accuracy of L1 Space Weather Forecasting

NASA Astrophysics Data System (ADS)

Szabo, A.

2013-12-01

Current space weather forecasting from the Sun-Earth first Lagrange (L1) point assumes that all observed solar wind discontinuity fronts (interplanetary shocks, ICME boundaries) are perpendicular to the Sun-Earth line and are propagating radially out from eh Sun. In reality, these weather fronts can have significantly tilted orientation. Combined ACE, Wind and Soho observations allow the quantification of this effect. With the launch of the DSCOVR spacecraft in early 2015, dual real-time solar wind measurements will become available (at least at some time). Algorithms and their impact exploiting this unique scenario will be discussed.

Radiative capture of cold neutrons by protons and deuteron photodisintegration with twisted beams

NASA Astrophysics Data System (ADS)

Afanasev, Andrei; Serbo, Valeriy G.; Solyanik, Maria

2018-05-01

We consider two basic nuclear reactions: capture of neutrons by protons, n + p → γ + d, and its time-reversed counterpart, photodisintegration of the deuteron, γ + d → n + p. In both of these cases we assume that the incoming beam of neutrons or photons is ‘twisted’ by having an azimuthal phase dependence, i.e., it carries an additional angular momentum along its direction of propagation. Taking a low-energy limit of these reactions, we derive relations between corresponding transition amplitudes and cross sections with plane-wave beams and twisted beams. Implications for experiments with twisted cold neutrons and twisted photon beams are discussed.

Higher derivative field theories: degeneracy conditions and classes

NASA Astrophysics Data System (ADS)

Crisostomi, Marco; Klein, Remko; Roest, Diederik

2017-06-01

We provide a full analysis of ghost free higher derivative field theories with coupled degrees of freedom. Assuming the absence of gauge symmetries, we derive the degeneracy conditions in order to evade the Ostrogradsky ghosts, and analyze which (non)trivial classes of solutions this allows for. It is shown explicitly how Lorentz invariance avoids the propagation of "half" degrees of freedom. Moreover, for a large class of theories, we construct the field redefinitions and/or (extended) contact transformations that put the theory in a manifestly first order form. Finally, we identify which class of theories cannot be brought to first order form by such transformations.

Minimal scales from an extended Hilbert space

NASA Astrophysics Data System (ADS)

Kober, Martin; Nicolini, Piero

2010-12-01

We consider an extension of the conventional quantum Heisenberg algebra, assuming that coordinates as well as momenta fulfil nontrivial commutation relations. As a consequence, a minimal length and a minimal mass scale are implemented. Our commutators do not depend on positions and momenta and we provide an extension of the coordinate coherent state approach to noncommutative geometry. We explore, as a toy model, the corresponding quantum field theory in a (2+1)-dimensional spacetime. Then we investigate the more realistic case of a (3+1)-dimensional spacetime, foliated into noncommutative planes. As a result, we obtain propagators, which are finite in the ultraviolet as well as the infrared regime.

A combustion model of vegetation burning in "Tiger" fire propagation tool

NASA Astrophysics Data System (ADS)

Giannino, F.; Ascoli, D.; Sirignano, M.; Mazzoleni, S.; Russo, L.; Rego, F.

2017-11-01

In this paper, we propose a semi-physical model for the burning of vegetation in a wildland fire. The main physical-chemical processes involved in fire spreading are modelled through a set of ordinary differential equations, which describe the combustion process as linearly related to the consumption of fuel. The water evaporation process from leaves and wood is also considered. Mass and energy balance equations are written for fuel (leaves and wood) assuming that combustion process is homogeneous in space. The model is developed with the final aim of simulating large-scale wildland fires which spread on heterogeneous landscape while keeping the computation cost very low.

Self similar flow behind an exponential shock wave in a self-gravitating, rotating, axisymmetric dusty gas with heat conduction and radiation heat flux

NASA Astrophysics Data System (ADS)

Bajargaan, Ruchi; Patel, Arvind

2018-04-01

One-dimensional unsteady adiabatic flow behind an exponential shock wave propagating in a self-gravitating, rotating, axisymmetric dusty gas with heat conduction and radiation heat flux, which has exponentially varying azimuthal and axial fluid velocities, is investigated. The shock wave is driven out by a piston moving with time according to an exponential law. The dusty gas is taken to be a mixture of a non-ideal gas and small solid particles. The density of the ambient medium is assumed to be constant. The equilibrium flow conditions are maintained and energy is varying exponentially, which is continuously supplied by the piston. The heat conduction is expressed in the terms of Fourier's law, and the radiation is assumed of diffusion type for an optically thick grey gas model. The thermal conductivity and the absorption coefficient are assumed to vary with temperature and density according to a power law. The effects of the variation of heat transfer parameters, gravitation parameter and dusty gas parameters on the shock strength, the distance between the piston and the shock front, and on the flow variables are studied out in detail. It is interesting to note that the similarity solution exists under the constant initial angular velocity, and the shock strength is independent from the self gravitation, heat conduction and radiation heat flux.

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

Li, Gen; Lee, Martin A., E-mail: gjk44@wildcats.unh.edu

The effects of scatter-dominated interplanetary transport on the spectral properties of the differential fluence of large gradual solar energetic particle (SEP) events are investigated analytically. The model assumes for simplicity radial constant solar wind and radial magnetic field. The radial diffusion coefficient is calculated with quasilinear theory by assuming a spectrum of Alfvén waves propagating parallel to the magnetic field. Cross-field transport is neglected. The model takes into consideration several essential features of gradual event transport: nearly isotropic ion distributions, adiabatic deceleration in a divergent solar wind, and particle radial scattering mean free paths increasing with energy. Assuming an impulsivemore » and spherically symmetric injection of SEPs with a power-law spectrum near the Sun, the predicted differential fluence spectrum exhibits at 1 AU three distinctive power laws for different energy domains. The model naturally reproduces the spectral features of the double power-law proton differential fluence spectra that tend to be observed in extremely large SEP events. We select nine western ground-level events (GLEs) out of the 16 GLEs during Solar Cycle 23 and fit the observed double power-law spectra to the analytical predictions. The compression ratio of the accelerating shock wave, the power-law index of the ambient wave intensity, and the proton radial scattering mean free path are determined for the nine GLEs. The derived parameters are generally in agreement with the characteristic values expected for large gradual SEP events.« less

The Propagation of Cosmic Rays from the Galactic Wind Termination Shock: Back to the Galaxy?

NASA Astrophysics Data System (ADS)

Merten, Lukas; Bustard, Chad; Zweibel, Ellen G.; Becker Tjus, Julia

2018-05-01

Although several theories exist for the origin of cosmic rays (CRs) in the region between the spectral “knee” and “ankle,” this problem is still unsolved. A variety of observations suggest that the transition from Galactic to extragalactic sources occurs in this energy range. In this work, we examine whether a Galactic wind that eventually forms a termination shock far outside the Galactic plane can contribute as a possible source to the observed flux in the region of interest. Previous work by Bustard et al. estimated that particles can be accelerated to energies above the “knee” up to R max = 1016 eV for parameters drawn from a model of a Milky Way wind. A remaining question is whether the accelerated CRs can propagate back into the Galaxy. To answer this crucial question, we simulate the propagation of the CRs using the low-energy extension of the CRPropa framework, based on the solution of the transport equation via stochastic differential equations. The setup includes all relevant processes, including three-dimensional anisotropic spatial diffusion, advection, and corresponding adiabatic cooling. We find that, assuming realistic parameters for the shock evolution, a possible Galactic termination shock can contribute significantly to the energy budget in the “knee” region and above. We estimate the resulting produced neutrino fluxes and find them to be below measurements from IceCube and limits by KM3NeT.

Modelling of deep gaps created by giant planets in protoplanetary disks

NASA Astrophysics Data System (ADS)

Kanagawa, Kazuhiro D.; Tanaka, Hidekazu; Muto, Takayuki; Tanigawa, Takayuki

2017-12-01

A giant planet embedded in a protoplanetary disk creates a gap. This process is important for both theory and observation. Using results of a survey for a wide parameter range with two-dimensional hydrodynamic simulations, we constructed an empirical formula for the gap structure (i.e., the radial surface density distribution), which can reproduce the gap width and depth obtained by two-dimensional simulations. This formula enables us to judge whether an observed gap is likely to be caused by an embedded planet or not. The propagation of waves launched by the planet is closely connected to the gap structure. It makes the gap wider and shallower as compared with the case where an instantaneous wave damping is assumed. The hydrodynamic simulations show that the waves do not decay immediately at the launching point of waves, even when the planet is as massive as Jupiter. Based on the results of hydrodynamic simulations, we also obtained an empirical model of wave propagation and damping in cases of deep gaps. The one-dimensional gap model with our wave propagation model is able to reproduce the gap structures in hydrodynamic simulations well. In the case of a Jupiter-mass planet, we also found that the waves with a smaller wavenumber (e.g., m = 2) are excited and transport the angular momentum to a location far away from the planet. The wave with m = 2 is closely related with a secondary wave launched by a site opposite from the planet.

Reaction-diffusion waves in neuronal tissue and the window of cortical excitability

NASA Astrophysics Data System (ADS)

Dahlem, M. A.; Müller, S. C.

2004-07-01

Spreading depression (SD) is a dynamic wave phenomenon occurring in all gray matter regions of the central nervous systems (CNS). It is characterized by a sudden breakdown of neuronal activity and accompanied by a massive influx and efflux of ions across the membrane of neurons. The retina is a constituent of the CNS in which one can easily observe the dynamic behavior of the SD wave fronts, because SD changes the optical properties of the tissue. There is ample evidence that SD belongs to the self-organization processes due to the coupling of reaction with diffusion in excitable medium. It is assumed that the occurrence of SD is associated with some neurological symptoms of migraine with aura. A frequently reported aura symptom is a traveling visual blind region (scotoma) with a preceding figure of scintillating line segments. The characteristic form and development of the scotoma suggests that the underlying phenomenon is a wave propagating through the primary visual cortex, most likely the cortical spreading depression. In this article we discuss similarities between SD waves and the migraine aura on the basis of properties of reaction-diffusion waves known from other excitable media. In particular, the propagation velocities, the shape and the dynamics of the waves are compared with each other. We find that the assumption of the neuronal tissue to be in a state of only weak excitability explains some properties of the migraine aura, such as the confined appearance and its propagation with a stable velocity.

Alfvén Wave Reflection and Turbulent Heating in the Solar Wind from 1 Solar Radius to 1 AU: An Analytical Treatment

NASA Astrophysics Data System (ADS)

Chandran, Benjamin D. G.; Hollweg, Joseph V.

2009-12-01

We study the propagation, reflection, and turbulent dissipation of Alfvén waves in coronal holes and the solar wind. We start with the Heinemann-Olbert equations, which describe non-compressive magnetohydrodynamic fluctuations in an inhomogeneous medium with a background flow parallel to the background magnetic field. Following the approach of Dmitruk et al., we model the nonlinear terms in these equations using a simple phenomenology for the cascade and dissipation of wave energy and assume that there is much more energy in waves propagating away from the Sun than waves propagating toward the Sun. We then solve the equations analytically for waves with periods of hours and longer to obtain expressions for the wave amplitudes and turbulent heating rate as a function of heliocentric distance. We also develop a second approximate model that includes waves with periods of roughly one minute to one hour, which undergo less reflection than the longer-period waves, and compare our models to observations. Our models generalize the phenomenological model of Dmitruk et al. by accounting for the solar wind velocity, so that the turbulent heating rate can be evaluated from the coronal base out past the Alfvén critical point—that is, throughout the region in which most of the heating and acceleration occurs. The simple analytical expressions that we obtain can be used to incorporate Alfvén-wave reflection and turbulent heating into fluid models of the solar wind.

Kelvin-Voigt model of wave propagation in fragmented geomaterials with impact damping

NASA Astrophysics Data System (ADS)

Khudyakov, Maxim; Pasternak, Elena; Dyskin, Arcady

2017-04-01

When a wave propagates through real materials, energy dissipation occurs. The effect of loss of energy in homogeneous materials can be accounted for by using simple viscous models. However, a reliable model representing the effect in fragmented geomaterials has not been established yet. The main reason for that is a mechanism how vibrations are transmitted between the elements (fragments) in these materials. It is hypothesised that the fragments strike against each other, in the process of oscillation, and the impacts lead to the energy loss. We assume that the energy loss is well represented by the restitution coefficient. The principal element of this concept is the interaction of two adjacent blocks. We model it by a simple linear oscillator (a mass on an elastic spring) with an additional condition: each time the system travels through the neutral point, where the displacement is equal to zero, the velocity reduces by multiplying itself by the restitution coefficient, which characterises an impact of the fragments. This additional condition renders the system non-linear. We show that the behaviour of such a model averaged over times much larger than the system period can approximately be represented by a conventional linear oscillator with linear damping characterised by a damping coefficient expressible through the restitution coefficient. Based on this the wave propagation at times considerably greater than the resonance period of oscillations of the neighbouring blocks can be modelled using the Kelvin-Voigt model. The wave velocities and the dispersion relations are obtained.

INTERACTION BETWEEN TWO CORONAL MASS EJECTIONS IN THE 2013 MAY 22 LARGE SOLAR ENERGETIC PARTICLE EVENT

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

Ding, Liu-Guan; Xu, Fei; Gu, Bin

We investigate the eruption and interaction of two coronal mass ejections (CMEs) during the large 2013 May 22 solar energetic particle event using multiple spacecraft observations. Two CMEs, having similar propagation directions, were found to erupt from two nearby active regions (ARs), AR11748 and AR11745, at ∼08:48 UT and ∼13:25 UT, respectively. The second CME was faster than the first CME. Using the graduated cylindrical shell model, we reconstructed the propagation of these two CMEs and found that the leading edge of the second CME caught up with the trailing edge of the first CME at a height of ∼6 solar radii. Aftermore » about two hours, the leading edges of the two CMEs merged at a height of ∼20 solar radii. Type II solar radio bursts showed strong enhancement during this two hour period. Using the velocity dispersion method, we obtained the solar particle release (SPR) time and the path length for energetic electrons. Further assuming that energetic protons propagated along the same interplanetary magnetic field, we also obtained the SPR time for energetic protons, which were close to that of electrons. These release times agreed with the time when the second CME caught up with the trailing edge of the first CME, indicating that the CME-CME interaction (and shock-CME interaction) plays an important role in the process of particle acceleration in this event.« less

Quickprop method to speed up learning process of Artificial Neural Network in money's nominal value recognition case

NASA Astrophysics Data System (ADS)

Swastika, Windra

2017-03-01

A money's nominal value recognition system has been developed using Artificial Neural Network (ANN). ANN with Back Propagation has one disadvantage. The learning process is very slow (or never reach the target) in the case of large number of iteration, weight and samples. One way to speed up the learning process is using Quickprop method. Quickprop method is based on Newton's method and able to speed up the learning process by assuming that the weight adjustment (E) is a parabolic function. The goal is to minimize the error gradient (E'). In our system, we use 5 types of money's nominal value, i.e. 1,000 IDR, 2,000 IDR, 5,000 IDR, 10,000 IDR and 50,000 IDR. One of the surface of each nominal were scanned and digitally processed. There are 40 patterns to be used as training set in ANN system. The effectiveness of Quickprop method in the ANN system was validated by 2 factors, (1) number of iterations required to reach error below 0.1; and (2) the accuracy to predict nominal values based on the input. Our results shows that the use of Quickprop method is successfully reduce the learning process compared to Back Propagation method. For 40 input patterns, Quickprop method successfully reached error below 0.1 for only 20 iterations, while Back Propagation method required 2000 iterations. The prediction accuracy for both method is higher than 90%.

KINETIC EVOLUTION OF CORONAL HOLE PROTONS BY IMBALANCED ION-CYCLOTRON WAVES: IMPLICATIONS FOR MEASUREMENTS BY SOLAR PROBE PLUS

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

Isenberg, Philip A.; Vasquez, Bernard J.

We extend the kinetic guiding-center model of collisionless coronal hole protons presented in Isenberg and Vasquez to consider driving by imbalanced spectra of obliquely propagating ion-cyclotron waves. These waves are assumed to be a small by-product of the imbalanced turbulent cascade to high perpendicular wavenumber, and their total intensity is taken to be 1% of the total fluctuation energy. We also extend the kinetic solutions for the proton distribution function in the resulting fast solar wind to heliocentric distances of 20 solar radii, which will be attainable by the Solar Probe Plus spacecraft. We consider three ratios of outward-propagating tomore » inward-propagating resonant intensities: 1, 4, and 9. The self-consistent bulk flow speed reaches fast solar wind values in all cases, and these speeds are basically independent of the intensity ratio. The steady-state proton distribution is highly organized into nested constant-density shells by the resonant wave-particle interaction. The radial evolution of this kinetic distribution as the coronal hole plasma flows outward is understood as a competition between the inward- and outward-directed large-scale forces, causing an effective circulation of particles through the (v{sub ∥}, v{sub ⊥}) phase space and a characteristic asymmetric shape to the distribution. These asymmetries are substantial and persist to the outer limit of the model computation, where they should be observable by the Solar Probe Plus instruments.« less

Numerical and Experimental Determination of the Geometric Far Field for Round Jets

NASA Technical Reports Server (NTRS)

Koch, L. Danielle; Bridges, James; Brown, Cliff; Khavaran, Abbas

2003-01-01

To reduce ambiguity in the reporting of far field jet noise, three round jets operating at subsonic conditions have recently been studied at the NASA Glenn Research Center. The goal of the investigation was to determine the location of the geometric far field both numerically and experimentally. The combination of the WIND Reynolds-Averaged Navier-Stokes solver and the MGBK jet noise prediction code was used for the computations, and the experimental data was collected in the Aeroacoustic Propulsion Laboratory. While noise sources are distributed throughout the jet plume, at great distances from the nozzle the noise will appear to be emanating from a point source and the assumption of linear propagation is valid. Closer to the jet, nonlinear propagation may be a problem, along with the known geometric issues. By comparing sound spectra at different distances from the jet, both from computational methods that assume linear propagation, and from experiments, the contributions of geometry and nonlinearity can be separately ascertained and the required measurement distance for valid experiments can be established. It is found that while the shortest arc considered here (approx. 8D) was already in the geometric far field for the high frequency sound (St greater than 2.0), the low frequency noise due to its extended source distribution reached the geometric far field at or about 50D. It is also found that sound spectra at far downstream angles does not strictly scale on Strouhal number, an observation that current modeling does not capture.

Modeling of temporal variation of very low frequency radio waves over long paths as observed from Indian Antarctic stations

NASA Astrophysics Data System (ADS)

Sasmal, Sudipta; Basak, Tamal; Chakraborty, Suman; Palit, Sourav; Chakrabarti, Sandip K.

2017-07-01

Characteristics of very low frequency (VLF) signal depends on solar illumination across the propagation path. For a long path, solar zenith angle varies widely over the path and this has a significant influence on the propagation characteristics. To study the effect, Indian Centre for Space Physics participated in the 27th and 35th Scientific Expedition to Antarctica. VLF signals transmitted from the transmitters, namely, VTX (18.2 kHz), Vijayanarayanam, India, and NWC (19.8 kHz), North West Cape, Australia, were recorded simultaneously at Indian permanent stations Maitri and Bharati having respective geographic coordinates 70.75°S, 11.67°E, and 69.4°S, 76.17°E. A very stable diurnal variation of the signal has been obtained from both the stations. We reproduced the signal variations of VLF signal using solar zenith angle model coupled with long wavelength propagation capability (LWPC) code. We divided the whole path into several segments and computed the solar zenith angle (χ) profile. We assumed a linear relationship between the Wait's exponential model parameters effective reflection height (h'), steepness parameter (β), and solar zenith angle. The h' and β values were later used in the LWPC code to obtain the VLF signal amplitude at a particular time. The same procedure was repeated to obtain the whole day signal. Nature of the whole day signal variation from the theoretical modeling is also found to match with our observation to some extent.

Influence of the light propagation models on a linearized photoacoustic image reconstruction of the light absorption coefficient

NASA Astrophysics Data System (ADS)

Okawa, Shinpei; Hirasawa, Takeshi; Kushibiki, Toshihiro; Ishihara, Miya

2015-03-01

Quantification of the optical properties of the tissues and blood by noninvasive photoacoustic (PA) imaging may provide useful information for screening and early diagnosis of diseases. Linearized 2D image reconstruction algorithm based on PA wave equation and the photon diffusion equation (PDE) can reconstruct the image with computational cost smaller than a method based on 3D radiative transfer equation. However, the reconstructed image is affected by the differences between the actual and assumed light propagations. A quantitative capability of a linearized 2D image reconstruction was investigated and discussed by the numerical simulations and the phantom experiment in this study. The numerical simulations with the 3D Monte Carlo (MC) simulation and the 2D finite element calculation of the PDE were carried out. The phantom experiment was also conducted. In the phantom experiment, the PA pressures were acquired by a probe which had an optical fiber for illumination and the ring shaped P(VDF-TrFE) ultrasound transducer. The measured object was made of Intralipid and Indocyanine green. In the numerical simulations, it was shown that the linearized image reconstruction method recovered the absorption coefficients with alleviating the dependency of the PA amplitude on the depth of the photon absorber. The linearized image reconstruction method worked effectively under the light propagation calculated by 3D MC simulation, although some errors occurred. The phantom experiments validated the result of the numerical simulations.

Understanding large SEP events with the PATH code: Modeling of the 13 December 2006 SEP event

NASA Astrophysics Data System (ADS)

Verkhoglyadova, O. P.; Li, G.; Zank, G. P.; Hu, Q.; Cohen, C. M. S.; Mewaldt, R. A.; Mason, G. M.; Haggerty, D. K.; von Rosenvinge, T. T.; Looper, M. D.

2010-12-01

The Particle Acceleration and Transport in the Heliosphere (PATH) numerical code was developed to understand solar energetic particle (SEP) events in the near-Earth environment. We discuss simulation results for the 13 December 2006 SEP event. The PATH code includes modeling a background solar wind through which a CME-driven oblique shock propagates. The code incorporates a mixed population of both flare and shock-accelerated solar wind suprathermal particles. The shock parameters derived from ACE measurements at 1 AU and observational flare characteristics are used as input into the numerical model. We assume that the diffusive shock acceleration mechanism is responsible for particle energization. We model the subsequent transport of particles originated at the flare site and particles escaping from the shock and propagating in the equatorial plane through the interplanetary medium. We derive spectra for protons, oxygen, and iron ions, together with their time-intensity profiles at 1 AU. Our modeling results show reasonable agreement with in situ measurements by ACE, STEREO, GOES, and SAMPEX for this event. We numerically estimate the Fe/O abundance ratio and discuss the physics underlying a mixed SEP event. We point out that the flare population is as important as shock geometry changes during shock propagation for modeling time-intensity profiles and spectra at 1 AU. The combined effects of seed population and shock geometry will be examined in the framework of an extended PATH code in future modeling efforts.

DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM

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

Zhao, Lulu; Zhang, Ming; Rassoul, Hamid K., E-mail: lzhao@fit.edu

2016-04-10

A double power law or a power law with exponential rollover at a few to tens of MeV nucleon{sup −1} of the event-integrated differential spectra has been reported in many solar energetic particle (SEP) events. The rollover energies per nucleon of different elements correlate with a particle's charge-to-mass ratio (Q/A). The probable causes are suggested as residing in shock finite lifetimes, shock finite sizes, shock geometry, and an adiabatic cooling effect. In this work, we conduct a numerical simulation to investigate a particle's transport process in the inner heliosphere. We solve the focused transport equation using a time-backward Markov stochasticmore » approach. The convection, magnetic focusing, adiabatic cooling effect, and pitch-angle scattering are included. The effects that the interplanetary turbulence imposes on the shape of the resulting SEP spectra are examined. By assuming a pure power-law differential spectrum at the Sun, a perfect double-power-law feature with a break energy ranging from 10 to 120 MeV nucleon{sup −1} is obtained at 1 au. We found that the double power law of the differential energy spectrum is a robust result of SEP interplanetary propagation. It works for many assumptions of interplanetary turbulence spectra that give various forms of momentum dependence of a particle's mean free path. The different spectral shapes in low-energy and high-energy ends are not just a transition from the convection-dominated propagation to diffusion-dominated propagation.« less

Asymmetry of light absorption upon propagation of focused femtosecond laser pulses with spatiotemporal coupling through glass materials

NASA Astrophysics Data System (ADS)

Zhukov, Vladimir P.; Bulgakova, Nadezhda M.

2017-05-01

Ultrashort laser pulses are usually described in terms of temporal and spatial dependences of their electric field, assuming that the spatial dependence is separable from time dependence. However, in most situations this assumption is incorrect as generation of ultrashort pulses and their manipulation lead to couplings between spatial and temporal coordinates resulting in various effects such as pulse front tilt and spatial chirp. One of the most intriguing spatiotemporal coupling effects is the so-called "lighthouse effect", the phase front rotation with the beam propagation distance [Akturk et al., Opt. Express 13, 8642 (2005)]. The interaction of spatiotemporally coupled laser pulses with transparent materials have interesting peculiarities, such as the effect of nonreciprocal writing, which can be used to facilitate microfabrication of photonic structures inside optical glasses. In this work, we make an attempt to numerically investigate the influence of the pulse front tilt and the lighthouse effect on the absorption of laser energy inside fused silica glass. The model, which is based on nonlinear Maxwell's equations supplemented by the hydrodynamic equations for free electron plasma, is applied. As three-dimensional solution of such a problem would require huge computational resources, a simplified two-dimensional model has been proposed. It has enabled to gain a qualitative insight into the features of propagation of ultrashort laser pulses with the tilted front in the regimes of volumetric laser modification of transparent materials, including directional asymmetry upon direct laser writing in glass materials.

Acoustic waves in the solar atmosphere at high spatial resolution. II. Measurement in the Fe I 5434 Å line

NASA Astrophysics Data System (ADS)

Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O.; Shchukina, N.

2010-11-01

Aims: We investigate the energy supply of the solar chromosphere by acoustic waves. Methods: A time sequence with high spatial and temporal resolution from the quiet Sun disc centre in Fe i 5434 Å (Landé factor g = 0) is analysed. We used models from a numerical simulation of granular convection and apply NLTE spectral line transfer to determine the height of formation. For estimates of acoustic energy flux, we adopted wave propagation with inclinations of the wave vector with respect to the vertical of 0°, 30°, and 45°. For a granular and an intergranular model, the transmissions of the atmosphere to high-frequency waves were determined for the three inclination angles. Wavelet and Fourier analyses were performed and the resulting power spectra were corrected for atmospheric transmission. Results: We find waves with periods down to ~40 s. They occur intermittently in space and time. The velocity signal is formed at a height of 500 km in the granular model and at 620 km in the intergranule. At periods shorter than the acoustic cutoff (~190 s), ~40% of the waves occur above granules and ~60% above intergranules. By adopting vertical propagation, we estimate total fluxes above granules of 2750-3360 W m-2, and of 910-1 000 W m-2 above intergranules. The weighted average is 1730-2 060 W m-2. The estimates of the total fluxes increase by 15% when inclined wave propagation of 45° is assumed.

Implications of Gamma-Ray Transparency Constraints in Blazars: Minimum Distances and Gamma-Ray Collimation

NASA Technical Reports Server (NTRS)

Becker, Peter A.; Kafatos, Menas

1995-01-01

We develop a general expression for the gamma - gamma absorption coefficient, alpha(sub gamma(gamma)) for gamma-rays propagating in an arbitrary direction at an arbitrary point in space above an X-ray-emitting accretion disk. The X-ray intensity is assumed to vary as a power law in energy and radius between the outer disk radius, R(sub 0), and the inner radius, R(sub ms) which is the radius of marginal stability for a Schwarzschild black hole. We use our result for alpha(sub gamma(gamma)) to calculate the gamma - gamma optical depth, tau(sub gamma(gamma)) for gamma - rays created at height z and propagating at angle Phi relative to the disk axis, and we show that for Phi = 0 and z greater than or approx equal to R(sub 0), tau(sub gamma(gamma)) proportional to Epsilon(sup alpha)z(sup -2(alpha) - 3), where alpha is the X-ray spectral index and Epsilon is the gamma - ray energy. As an application, we use our formalism to compute the minimum distance between the central black hole and the site of production of the gamma-rays detected by EGRET during the 1991 June flare of 3C 279. In order to obtain an upper limit, we assume that all of the X-rays observed contemporaneously by Ginga were emitted by the disk. Our results suggest that the observed gamma - rays may have originated within less than or approx equal to 45 GM/sq c from a black hole of mass greater than or approx equal to 10(exp 9) solar mass, perhaps in active plasma located above the central funnel of the accretion disk. This raises the possibility of establishing a direct connection between the production of the observed gamma - rays and the accretion of material onto the black hole. We also consider the variation of the optical depth as a function of the angle of propagation Phi. Our results indicate that the "focusing" of the gamma - rays along the disk axis due to pair production is strong enough to explain the observed degree of alignment in blazar sources. If the gamma - rays are produced isotropically in gamma - ray blazars, then these objects should appear as bright MeV sources when viewed along off-axis lines of sight.

The estimation of lower refractivity uncertainty from radar sea clutter using the Bayesian—MCMC method

NASA Astrophysics Data System (ADS)

Sheng, Zheng

2013-02-01

The estimation of lower atmospheric refractivity from radar sea clutter (RFC) is a complicated nonlinear optimization problem. This paper deals with the RFC problem in a Bayesian framework. It uses the unbiased Markov Chain Monte Carlo (MCMC) sampling technique, which can provide accurate posterior probability distributions of the estimated refractivity parameters by using an electromagnetic split-step fast Fourier transform terrain parabolic equation propagation model within a Bayesian inversion framework. In contrast to the global optimization algorithm, the Bayesian—MCMC can obtain not only the approximate solutions, but also the probability distributions of the solutions, that is, uncertainty analyses of solutions. The Bayesian—MCMC algorithm is implemented on the simulation radar sea-clutter data and the real radar sea-clutter data. Reference data are assumed to be simulation data and refractivity profiles are obtained using a helicopter. The inversion algorithm is assessed (i) by comparing the estimated refractivity profiles from the assumed simulation and the helicopter sounding data; (ii) the one-dimensional (1D) and two-dimensional (2D) posterior probability distribution of solutions.

Leaky GFD problems

NASA Astrophysics Data System (ADS)

Chumakova, Lyubov; Rzeznik, Andrew; Rosales, Rodolfo R.

2017-11-01

In many dispersive/conservative wave problems, waves carry energy outside of the domain of interest and never return. Inside the domain of interest, this wave leakage acts as an effective dissipation mechanism, causing solutions to decay. In classical geophysical fluid dynamics problems this scenario occurs in the troposphere, if one assumes a homogeneous stratosphere. In this talk we present several classic GFD problems, where we seek the solution in the troposphere alone. Assuming that upward propagating waves that reach the stratosphere never return, we demonstrate how classic baroclinic modes become leaky, with characteristic decay time-scales that can be calculated. We also show how damping due to wave leakage changes the classic baroclinic instability problem in the presence of shear. This presentation is a part of a joint project. The mathematical approach used here relies on extending the classical concept of group velocity to leaky waves with complex wavenumber and frequency, which will be presented at this meeting by A. Rzeznik in the talk ``Group Velocity for Leaky Waves''. This research is funded by the Royal Soc. of Edinburgh, Scottish Government, and NSF.

Effect of current on spectrum of breaking waves in water of finite depth

NASA Technical Reports Server (NTRS)

Tung, C. C.; Huang, N. E.

1987-01-01

This paper presents an approximate method to compute the mean value, the mean square value and the spectrum of waves in water of finite depth taking into account the effect of wave breaking with or without the presence of current. It is assumed that there exists a linear and Gaussian ideal wave train whose spectrum is first obtained using the wave energy flux balance equation without considering wave breaking. The Miche wave breaking criterion for waves in finite water depth is used to limit the wave elevation and establish an expression for the breaking wave elevation in terms of the elevation and its second time derivative of the ideal waves. Simple expressions for the mean value, the mean square value and the spectrum are obtained. These results are applied to the case in which a deep water unidirectional wave train, propagating normally towards a straight shoreline over gently varying sea bottom of parallel and straight contours, encounters an adverse steady current whose velocity is assumed to be uniformly distributed with depth. Numerical results are obtained and presented in graphical form.

Metastable sound speed in gas-liquid mixtures

NASA Technical Reports Server (NTRS)

Bursik, J. W.; Hall, R. M.

1979-01-01

A new method of calculating speed of sound for two-phase flow is presented. The new equation assumes no phase change during the propagation of an acoustic disturbance and assumes that only the total entropy of the mixture remains constant during the process. The new equation predicts single-phase values for the speed of sound in the limit of all gas or all liquid and agrees with available two-phase, air-water sound speed data. Other expressions used in the two-phase flow literature for calculating two-phase, metastable sound speed are reviewed and discussed. Comparisons are made between the new expression and several of the previous expressions -- most notably a triply isentropic equation as used, a triply isentropic equation as used, among others, by Karplus and by Wallis. Appropriate differences are pointed out and a thermodynamic criterion is derived which must be satisfied in order for the triply isentropic expression to be thermodynamically consistent. This criterion is not satisfied for the cases examined, which included two-phase nitrogen, air-water, two-phase parahydrogen, and steam-water. Consequently, the new equation derived is found to be superior to the other equations reviewed.

Acceleration and heating of heavy ions in high speed solar wind streams

NASA Technical Reports Server (NTRS)

Gomberoff, L.; Gratton, F. T.; Gnavi, G.

1995-01-01

Left hand polarized Alfven waves generated in coronal holes propagate in the direction of high speed solar wind streams, accelerating and heating heavy ions. As the solar wind expands, the ratio between the frequency of the Alfven waves and the proton gyrofrequency increases, due to the decrease of the interplanetary magnetic field, and encounter first the local ion gyrofrequency of the species with the largest M(sub l) = m(sub l)/z(sub l)m(sub p) (m(sub l) is the mass of species l, m(sub p) is the proton mass and z(sub l) is the degree of ionization of species l). It is shown that the Alfven waves experience there strong absorption and cannot propagate any further until the ions are accelerated and heated. Once this occurs, the Alfven waves continue to propagate until they meet the gyrofrequency of the next species giving rise to a similar phenomenon. In order to show this contention, we use the linear dispersion relation of ion cyclotron waves in a multicomponent plasma consisting of oxygen ions, alpha particles and protons. We assume that at any distance from the sun, the Alfven waves follow the local dispersion relation of electromagnetic ion cyclotron waves. To illustrate the results, we solve the dispersion relation for oxygen ions and alpha particles drifting relative to the protons. The dispersion relation has three branches. The first branch starts at zero frequency and goes to the Doppler-shifted oxygen ion gyrofrequency. The second branch starts close to the oxygen gyrofrequency, and goes to the Doppler-shifted alpha particle gyrofrequency. The third branch starts close to the alpha particle gyrofrequency, and goes to the proton gyrofrequency. The Alfven waves propagate following the first branch of the dispersion relation. When they reach the Doppler-shifted oxygen ion gyrofrequency, the ions are accelerated and heated to some definite values. When these values are reached, the dispersion relation changes, and it is now the first branch of the dispersion relation, the one which goes to the Doppler-shifted alpha particle gyrofrequency. The Alfven waves continue to propagate along the first branch of the dispersion relation and proceed to accelerate and heat the alpha particles.

Fracture propagation in Indiana Limestone interpreted via linear softening cohesive fracture model

NASA Astrophysics Data System (ADS)

Rinehart, Alex J.; Bishop, Joseph E.; Dewers, Thomas

2015-04-01

We examine the use of a linear softening cohesive fracture model (LCFM) to predict single-trace fracture growth in short-rod (SR) and notched 3-point-bend (N3PB) test configurations in Indiana Limestone. The broad goal of this work is to (a) understand the underlying assumptions of LCFM and (b) use experimental similarities and deviations from the LCFM to understand the role of loading paths of tensile fracture propagation. Cohesive fracture models are being applied in prediction of structural and subsurface fracture propagation in geomaterials. They lump the inelastic processes occurring during fracture propagation into a thin zone between elastic subdomains. LCFM assumes that the cohesive zone initially deforms elastically to a maximum tensile stress (σmax) and then softens linearly from the crack opening width at σmax to zero stress at a critical crack opening width w1. Using commercial finite element software, we developed LCFMs for the SR and N3PB configurations. After fixing σmax with results from cylinder splitting tests and finding an initial Young's modulus (E) with unconfined compressive strength tests, we manually calibrate E and w1 in the SR model against an envelope of experimental data. We apply the calibrated LCFM parameters in the N3PB geometry and compare the model against an envelope of N3PB experiments. For accurate simulation of fracture propagation, simulated off-crack stresses are high enough to require inclusion of damage. Different elastic moduli are needed in tension and compression. We hypothesize that the timing and location of shear versus extensional micromechanical failures control the qualitative macroscopic force-versus-displacement response in different tests. For accurate prediction, the LCFM requires a constant style of failure, which the SR configuration maintains until very late in deformation. The N3PB configuration does not maintain this constancy. To be broadly applicable between geometries and failure styles, the LCFM would require additional physics, possibly including elastoplastic damage in the bulk material and more complicated cohesive softening models.

Investigating dynamic underground coal fires by means of numerical simulation

NASA Astrophysics Data System (ADS)

Wessling, S.; Kessels, W.; Schmidt, M.; Krause, U.

2008-01-01

Uncontrolled burning or smoldering of coal seams, otherwise known as coal fires, represents a worldwide natural hazard. Efficient application of fire-fighting strategies and prevention of mining hazards require that the temporal evolution of fire propagation can be sufficiently precise predicted. A promising approach for the investigation of the temporal evolution is the numerical simulation of involved physical and chemical processes. In the context of the Sino-German Research Initiative `Innovative Technologies for Detection, Extinction and Prevention of Coal Fires in North China,' a numerical model has been developed for simulating underground coal fires at large scales. The objective of such modelling is to investigate observables, like the fire propagation rate, with respect to the thermal and hydraulic parameters of adjacent rock. In the model, hydraulic, thermal and chemical processes are accounted for, with the last process complemented by laboratory experiments. Numerically, one key challenge in modelling coal fires is to circumvent the small time steps resulting from the resolution of fast reaction kinetics at high temperatures. In our model, this problem is solved by means of an `operator-splitting' approach, in which transport and reactive processes of oxygen are independently calculated. At high temperatures, operator-splitting has the decisive advantage of allowing the global time step to be chosen according to oxygen transport, so that time-consuming simulation through the calculation of fast reaction kinetics is avoided. Also in this model, because oxygen distribution within a coal fire has been shown to remain constant over long periods, an additional extrapolation algorithm for the coal concentration has been applied. In this paper, we demonstrate that the operator-splitting approach is particularly suitable for investigating the influence of hydraulic parameters of adjacent rocks on coal fire propagation. A study shows that dynamic propagation strongly depends on permeability variations. For the assumed model, no fire exists for permeabilities k < 10-10m2, whereas the fire propagation velocity ranges between 340ma-1 for k = 10-8m2, and drops to lower than 3ma-1 for k = 5 × 10-10m2. Additionally, strong temperature variations are observed for the permeability range 5 × 10-10m2 < k < 10-8m2.

Detection of Propagating Fast Sausage Waves through a Detailed Analysis of a Zebra Pattern Fine Structure in a Solar Radio Burst

NASA Astrophysics Data System (ADS)

Kaneda, K.; Misawa, H.; Iwai, K.; Masuda, S.; Tsuchiya, F.; Katoh, Y.; Obara, T.

2017-12-01

Recent observations have revealed that various modes of magnetohydrodynamic (MHD) waves are ubiquitous in the corona. In imaging observations in EUV, propagating fast magnetoacoustic waves are difficult to observe due to the lack of time resolution. Quasi-periodic modulation of radio fine structures is an important source of information on these MHD waves. Zebra patterns (ZPs) are one of such fine structures in type IV bursts, which consist of several parallel stripes superimposed on the background continuum. Although the generation mechanism of ZPs has been discussed still, the most favorable model of ZPs is so-called double plasma resonance (DPR) model. In the DPR model, the frequency separation between the adjacent stripes (Δf) is determined by the plasma density and magnetic field in their source. Hence, the variation of Δf in time and frequency represents the disturbance in their source region in the corona. We report the detection of propagating fast sausage waves through the analysis of a ZP event on 2011 June 21. The variation of Δf in time and frequency was obtained using highly resolved spectral data from the Assembly of Metric-band Aperture Telescope and Real-time Analysis System (AMATERAS). We found that Δf increases with the increase of emission frequency as a whole, which is consistent with the DPR model. Furthermore, we also found that irregularities in Δf are repetitively drifting from the high frequency side to the low frequency side. Their frequency drift rate was 3 - 8 MHz/s and the repetitive frequency was several seconds. Assuming the ZP generation by the DPR model, the drifting irregularities in Δf correspond to propagating disturbances in plasma density and magnetic field with speeds of 3000 - 8000 km/s. Taking account of these facts, the observed modulations in Δf can be explained by fast sausage waves propagating through the corona. We will also discuss the plasma conditions in the corona estimated from the observational results.

A high-energy-density, high-Mach number single jet experiment

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

Hansen, J. F.; Dittrich, T. R.; Elliott, J. B.

2011-08-15

A high-energy-density, x-ray-driven, high-Mach number (M{>=} 17) single jet experiment shows constant propagation speeds of the jet and its bowshock into the late time regime. The jet assumes a characteristic mushroom shape with a stalk and a head. The width of the head and the bowshock also grow linearly in time. The width of the stalk decreases exponentially toward an asymptotic value. In late time images, the stalk kinks and develops a filamentary nature, which is similar to experiments with applied magnetic fields. Numerical simulations match the experiment reasonably well, but ''exterior'' details of the laser target must be includedmore » to obtain a match at late times.« less

Wave scattering in spatially inhomogeneous currents

NASA Astrophysics Data System (ADS)

Churilov, Semyon; Ermakov, Andrei; Stepanyants, Yury

2017-09-01

We analytically study a scattering of long linear surface waves on stationary currents in a duct (canal) of constant depth and variable width. It is assumed that the background velocity linearly increases or decreases with the longitudinal coordinate due to the gradual variation of duct width. Such a model admits an analytical solution of the problem in hand, and we calculate the scattering coefficients as functions of incident wave frequency for all possible cases of sub-, super-, and transcritical currents. For completeness we study both cocurrent and countercurrent wave propagation in accelerating and decelerating currents. The results obtained are analyzed in application to recent analog gravity experiments and shed light on the problem of hydrodynamic modeling of Hawking radiation.

Burn Propagation in a PBX 9501 Thermal Explosion

NASA Astrophysics Data System (ADS)

Henson, B. F.; Smilowitz, L.; Romero, J. J.; Sandstrom, M. M.; Asay, B. W.; Schwartz, C.; Saunders, A.; Merrill, F.; Morris, C.; Murray, M. M.; McNeil, W. V.; Marr-Lyon, M.; Rightley, P. M.

2007-12-01

We have applied proton radiography to study the conversion of solid density to gaseous combustion products subsequent to ignition of a thermal explosion in PBX 9501. We apply a thermal boundary condition to the cylindrical walls of the case, ending with an induction period at 205 C. We then introduce a laser pulse that accelerates the thermal ignition and synchronizes the explosion with the proton accelerator. We then obtain fast, synchronized images of the evolution of density loss with few microsecond resolution during the approximately 100 microsecond duration of the explosion. We present images of the solid explosive during the explosion and discuss measured rates and assumed mechanisms of burning the role of pressure in this internal burning.

Combination tones along the basilar membrane in a 3D finite element model of the cochlea with acoustic boundary layer attenuation

NASA Astrophysics Data System (ADS)

Böhnke, Frank; Scheunemann, Christian; Semmelbauer, Sebastian

2018-05-01

The propagation of traveling waves along the basilar membrane is studied in a 3D finite element model of the cochlea using single and two-tone stimulation. The advantage over former approaches is the consideration of viscous-thermal boundary layer damping which makes the usual but physically unjustified assumption of Rayleigh damping obsolete. The energy loss by viscous boundary layer damping is 70 dB lower than the actually assumed power generation by outer hair cells. The space-time course with two-tone stimulation shows the traveling waves and the periodicity of the beat frequency f2 - f1.

P-adic valued models of swarm behaviour

NASA Astrophysics Data System (ADS)

Schumann, Andrew

2017-07-01

The swarm behaviour can be fully determined by attractants (food pieces) which change the directions of swarm propagation. If we assume that at each time step the swarm can find out not more than p - 1 attractants, then the swarm behaviour can be coded by p-adic integers. The main task of any swarm is to logistically optimize the road system connecting the reachable attractants. In the meanwhile, the transporting network of the swarm has loops (circles) and permanently changes, e.g. the swarm occupies some attractants and leaves the others. However, this complex dynamics can be effectively coded by p-adic integers. This allows us to represent the swarm behaviour as a calculation on p-adic valued strings.

Deterministic Impulsive Vacuum Foundations for Quantum-Mechanical Wavefunctions

NASA Astrophysics Data System (ADS)

Valentine, John S.

2013-09-01

By assuming that a fermion de-constitutes immediately at source, that its constituents, as bosons, propagate uniformly as scalar vacuum terms with phase (radial) symmetry, and that fermions are unique solutions for specific phase conditions, we find a model that self-quantizes matter from continuous waves, unifying bosons and fermion ontologies in a single basis, in a constitution-invariant process. Vacuum energy has a wavefunction context, as a mass-energy term that enables wave collapse and increases its amplitude, with gravitational field as the gradient of the flux density. Gravitational and charge-based force effects emerge as statistics without special treatment. Confinement, entanglement, vacuum statistics, forces, and wavefunction terms emerge from the model's deterministic foundations.

Orbital Debris Shape Characterization Project Abstract

NASA Technical Reports Server (NTRS)

Pease, Jessie

2016-01-01

I have been working on a project to further our understanding of orbital debris by helping create a new dataset previously too complex to be implemented in past orbital debris propagation models. I am doing this by creating documentation and 3D examples and illustrations of the shape categories. Earlier models assumed all orbital debris to be spherical aluminum fragments. My project will help expand our knowledge of shape populations to 6 categories: Straight Needle/Rod/Cylinder, Bent Needle/Rod/Cylinder, Flat Plate, Bent Plate, Nugget/Parallelepiped/Spheroid, and Flexible. The last category, Flexible, is still up for discussion and may be modified. These categories will be used to characterize fragments in the DebriSat experiment.

Near-toll quality digital speech transmission in the mobile satellite service

NASA Technical Reports Server (NTRS)

Townes, S. A.; Divsalar, D.

1986-01-01

This paper discusses system considerations for near-toll quality digital speech transmission in a 5 kHz mobile satellite system channel. Tradeoffs are shown for power performance versus delay for a 4800 bps speech compression system in conjunction with a 16 state rate 2/3 trellis coded 8PSK modulation system. The suggested system has an additional 150 ms of delay beyond the propagation delay and requires an E(b)/N(0) of about 7 dB for a Ricean channel assumption with line-of-sight to diffuse component ratio of 10 assuming ideal synchronization. An additional loss of 2 to 3 dB is expected for synchronization in fading environment.

Combustion of Gaseous Mixtures

NASA Technical Reports Server (NTRS)

Duchene, R

1932-01-01

This report not only presents matters of practical importance in the classification of engine fuels, for which other means have proved inadequate, but also makes a few suggestions. It confirms the results of Withrow and Boyd which localize the explosive wave in the last portions of the mixture burned. This being the case, it may be assumed that the greater the normal combustion, the less the energy developed in the explosive form. In order to combat the detonation, it is therefore necessary to try to render the normal combustion swift and complete, as produced in carbureted mixtures containing benzene (benzol), in which the flame propagation, beginning at the spark, yields a progressive and pronounced darkening on the photographic film.

Support for the existence of invertible maps between electronic densities and non-analytic 1-body external potentials in non-relativistic time-dependent quantum mechanics

NASA Astrophysics Data System (ADS)

Mosquera, Martín A.

2017-10-01

Provided the initial state, the Runge-Gross theorem establishes that the time-dependent (TD) external potential of a system of non-relativistic electrons determines uniquely their TD electronic density, and vice versa (up to a constant in the potential). This theorem requires the TD external potential and density to be Taylor-expandable around the initial time of the propagation. This paper presents an extension without this restriction. Given the initial state of the system and evolution of the density due to some TD scalar potential, we show that a perturbative (not necessarily weak) TD potential that induces a non-zero divergence of the external force-density, inside a small spatial subset and immediately after the initial propagation time, will cause a change in the density within that subset, implying that the TD potential uniquely determines the TD density. In this proof, we assume unitary evolution of wavefunctions and first-order differentiability (which does not imply analyticity) in time of the internal and external force-densities, electronic density, current density, and their spatial derivatives over the small spatial subset and short time interval.

FDTD Modeling of LEMP Propagation in the Earth-Ionosphere Waveguide With Emphasis on Realistic Representation of Lightning Source

NASA Astrophysics Data System (ADS)

Tran, Thang H.; Baba, Yoshihiro; Somu, Vijaya B.; Rakov, Vladimir A.

2017-12-01

The finite difference time domain (FDTD) method in the 2-D cylindrical coordinate system was used to compute the nearly full-frequency-bandwidth vertical electric field and azimuthal magnetic field waveforms produced on the ground surface by lightning return strokes. The lightning source was represented by the modified transmission-line model with linear current decay with height, which was implemented in the FDTD computations as an appropriate vertical phased-current-source array. The conductivity of atmosphere was assumed to increase exponentially with height, with different conductivity profiles being used for daytime and nighttime conditions. The fields were computed at distances ranging from 50 to 500 km. Sky waves (reflections from the ionosphere) were identified in computed waveforms and used for estimation of apparent ionospheric reflection heights. It was found that our model reproduces reasonably well the daytime electric field waveforms measured at different distances and simulated (using a more sophisticated propagation model) by Qin et al. (2017). Sensitivity of model predictions to changes in the parameters of atmospheric conductivity profile, as well as influences of the lightning source characteristics (current waveshape parameters, return-stroke speed, and channel length) and ground conductivity were examined.

Determination of the thermal stress wave propagation in orthotropic hollow cylinder based on classical theory of thermoelasticity

NASA Astrophysics Data System (ADS)

Shahani, Amir Reza; Sharifi Torki, Hamid

2018-01-01

The thermoelasticity problem in a thick-walled orthotropic hollow cylinder is solved analytically using finite Hankel transform and Laplace transform. Time-dependent thermal and mechanical boundary conditions are applied on the inner and the outer surfaces of the cylinder. For solving the energy equation, the temperature itself is considered as boundary condition to be applied on both the inner and the outer surfaces of the orthotropic cylinder. Two different cases are assumed for solving the equation of motion: traction-traction problem (tractions are prescribed on both the inner and the outer surfaces) and traction-displacement (traction is prescribed on the inner surface and displacement is prescribed on the outer surface of the hollow orthotropic cylinder). Due to considering uncoupled theory, after obtaining temperature distribution, the dynamical structural problem is solved and closed-form relations are derived for radial displacement, radial and hoop stress. As a case study, exponentially decaying temperature with respect to time is prescribed on the inner surface of the cylinder and the temperature of the outer surface is considered to be zero. Owing to solving dynamical problem, the stress wave propagation and its reflections were observed after plotting the results in both cases.

The Role of Retained Austenite on the Mechanical Properties of a Low Carbon 3Mn-1.5Ni Steel

NASA Astrophysics Data System (ADS)

Chen, Jun; Zhang, Wei-na; Liu, Zhen-yu; Wang, Guo-dong

2017-12-01

The present studies focus on the correlation between retained austenite characteristics and the cryogenic temperature Charpy impact toughness, strength, and plasticity. The steels with different volume fractions and stabilities of retained austenite were prepared by quenching followed by intercritical heat treatment, and the microstructure was characterized using scanning electron microscope, electron back-scattered diffraction, and X-ray diffraction. The grain size, dislocation density, crack initiation energy, and crack propagation energy were quantified. It has been demonstrated that the volume fraction of retained austenite plays a significant role in the reduction of the measured yield strength and the effect of tempered martensite/ferrite matrix on cryogenic temperature impact toughness can be assumed to be similar due to the similar grain size, dislocation density and element content in solution for different heat treatments. It was found that the stability of retained austenite plays a determining role in the increase of cryogenic temperature impact toughness. Furthermore, the dependence of the crack propagation energy on retained austenite is much greater than that of the crack initiation energy. Generally, an excellent UTS × TEL does not produce good cryogenic temperature impact toughness.

Advection and dispersion of bed load tracers

NASA Astrophysics Data System (ADS)

Lajeunesse, Eric; Devauchelle, Olivier; James, François

2018-05-01

We use the erosion-deposition model introduced by Charru et al. (2004) to numerically simulate the evolution of a plume of bed load tracers entrained by a steady flow. In this model, the propagation of the plume results from the stochastic exchange of particles between the bed and the bed load layer. We find a transition between two asymptotic regimes. The tracers, initially at rest, are gradually set into motion by the flow. During this entrainment regime, the plume is strongly skewed in the direction of propagation and continuously accelerates while spreading nonlinearly. With time, the skewness of the plume eventually reaches a maximum value before decreasing. This marks the transition to an advection-diffusion regime in which the plume becomes increasingly symmetrical, spreads linearly, and advances at constant velocity. We analytically derive the expressions of the position, the variance, and the skewness of the plume and investigate their asymptotic regimes. Our model assumes steady state. In the field, however, bed load transport is intermittent. We show that the asymptotic regimes become insensitive to this intermittency when expressed in terms of the distance traveled by the plume. If this finding applies to the field, it might provide an estimate for the average bed load transport rate.

Constrained Kinematics of ICMEs from Multi-point in Situ and Heliospheric Imaging Data

NASA Astrophysics Data System (ADS)

Rollett, T.; Temmer, M.; Moestl, C.; Veronig, A. M.; Lugaz, N.; Vrsnak, B.; Farrugia, C. J.; Amerstorfer, U.

2013-12-01

The constrained harmonic mean (CHM) method is used to calculate the direction of motion of ICMEs and their kinematical profiles. Combining single spacecraft white-light observations from STEREO/HI with supplementary in situ data, it is possible to derive the propagation speed varying with heliocentric distance. This is a big advantage against other single-viewpoint methods, i.e. fitting methods, which assume a constant propagation speed. We show two different applications for the CHM method: first, an analysis of the interaction between the solar wind and ICMEs, and second, the interaction between two ICMEs. For analyzing interaction processes it is crucial to use a method that has the ability to investigate the corresponding effects on ICME kinematics. Additionally, we show the analysis of an outstanding fast ICME event of March 2012, which was detected in situ by Venus Express, Messenger and Wind and also observed by STEREO-A/HI. Due to these multiple in situ measurements it was possible to constrain the ICME kinematics by three different boundary values. These studies are fundamental in order to deepen the understanding of ICME evolution and to enhance existing forecasting methods. This work has received funding from the European Commission FP7 Project COMESEP (263252).

Invasive advance of an advantageous mutation: nucleation theory.

PubMed

O'Malley, Lauren; Basham, James; Yasi, Joseph A; Korniss, G; Allstadt, Andrew; Caraco, Thomas

2006-12-01

For sedentary organisms with localized reproduction, spatially clustered growth drives the invasive advance of a favorable mutation. We model competition between two alleles where recurrent mutation introduces a genotype with a rate of local propagation exceeding the resident's rate. We capture ecologically important properties of the rare invader's stochastic dynamics by assuming discrete individuals and local neighborhood interactions. To understand how individual-level processes may govern population patterns, we invoke the physical theory for nucleation of spatial systems. Nucleation theory discriminates between single-cluster and multi-cluster dynamics. A sufficiently low mutation rate, or a sufficiently small environment, generates single-cluster dynamics, an inherently stochastic process; a favorable mutation advances only if the invader cluster reaches a critical radius. For this mode of invasion, we identify the probability distribution of waiting times until the favored allele advances to competitive dominance, and we ask how the critical cluster size varies as propagation or mortality rates vary. Increasing the mutation rate or system size generates multi-cluster invasion, where spatial averaging produces nearly deterministic global dynamics. For this process, an analytical approximation from nucleation theory, called Avrami's Law, describes the time-dependent behavior of the genotype densities with remarkable accuracy.

A Unified Computational Model for Solar and Stellar Flares

NASA Technical Reports Server (NTRS)

Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats

2015-01-01

We present a unified computational framework that can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how flare-accelerated charged particles propagate down one-dimensional flux tubes and heat the stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere. These effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

Lesion contrast and detection using sonoelastographic shear velocity imaging: preliminary results

NASA Astrophysics Data System (ADS)

Hoyt, Kenneth; Parker, Kevin J.

2007-03-01

This paper assesses lesion contrast and detection using sonoelastographic shear velocity imaging. Shear wave interference patterns, termed crawling waves, for a two phase medium were simulated assuming plane wave conditions. Shear velocity estimates were computed using a spatial autocorrelation algorithm that operates in the direction of shear wave propagation for a given kernel size. Contrast was determined by analyzing shear velocity estimate transition between mediums. Experimental results were obtained using heterogeneous phantoms with spherical inclusions (5 or 10 mm in diameter) characterized by elevated shear velocities. Two vibration sources were applied to opposing phantom edges and scanned (orthogonal to shear wave propagation) with an ultrasound scanner equipped for sonoelastography. Demodulated data was saved and transferred to an external computer for processing shear velocity images. Simulation results demonstrate shear velocity transition between contrasting mediums is governed by both estimator kernel size and source vibration frequency. Experimental results from phantoms further indicates that decreasing estimator kernel size produces corresponding decrease in shear velocity estimate transition between background and inclusion material albeit with an increase in estimator noise. Overall, results demonstrate the ability to generate high contrast shear velocity images using sonoelastographic techniques and detect millimeter-sized lesions.

Biomechanics Analysis of Pressure Ulcer Using Damaged Interface Model between Bone and Muscle in the Human Buttock

NASA Astrophysics Data System (ADS)

Slamet, Samuel Susanto; Takano, Naoki; Tanabe, Yoshiyuki; Hatano, Asako; Nagasao, Tomohisa

This paper aims at building up a computational procedure to study the bio-mechanism of pressure ulcer using the finite element method. Pressure ulcer is a disease that occurs in the human body after 2 hours of continuous external force. In the very early stage of pressure ulcer, it is found that the tissues inside the body are damaged, even though skin surface looks normal. This study assumes that tension and/or shear strain will cause damage to loose fibril tissue between the bone and muscle and that propagation of damaged area will lead to fatal stage. Analysis was performed using the finite element method by modeling the damaged fibril tissue as a cutout. By varying the loading directions and watching both tensile and shear strains, the risk of fibril tissue damage and propagation of the damaged area is discussed, which may give new insight for the careful nursing for patients, particularly after surgical treatment. It was found that the pressure ulcer could reoccur for a surgical flap treatment. The bone cut and surgical flap surgery is not perfect to prevent the bone-muscle interfacial damage.

Microbial Diversity of Type I Sourdoughs Prepared and Back-Slopped with Wholemeal and Refined Soft (Triticum aestivum) Wheat Flours.

PubMed

Taccari, Manuela; Aquilanti, Lucia; Polverigiani, Serena; Osimani, Andrea; Garofalo, Cristiana; Milanović, Vesna; Clementi, Francesca

2016-08-01

The fermentation of type I sourdough was studied for 20 d with daily back-slopping under laboratory and artisan bakery conditions using 1 wholemeal and 2 refined soft wheat (Triticum aestivum) flours. The sourdough bacterial and yeast diversity and dynamics were investigated by plate counting and a combination of culture-dependent and culture-independent PCR-DGGE approach. The pH, total titrable acidity, and concentration of key organic acids (phytic, lactic, and acetic) were measured. Three flours differed for both chemical and rheological properties. A microbial succession was observed, with the atypical sourdough species detected at day 0 (i.e. Lactococcus lactis and Leuconostoc holzapfelii/citreum group for bacteria and Candida silvae and Wickerhamomyces anomalus for yeasts) being progressively replaced by taxa more adapted to the sourdough ecosystem (Lactobacillus brevis, Lactobacillus alimentarius/paralimentarius, Saccharomyces cerevisiae). In mature sourdoughs, a notably different species composition was observed. As sourdoughs propagated with the same flour at laboratory and artisan bakery level were compared, the influence of both the substrate and the propagation environment on microbial diversity was assumed. © 2016 Institute of Food Technologists®

Propagation of acoustic-gravity waves in arctic zones with elastic ice-sheets

NASA Astrophysics Data System (ADS)

Kadri, Usama; Abdolali, Ali; Kirby, James T.

2017-04-01

We present an analytical solution of the boundary value problem of propagating acoustic-gravity waves generated in the ocean by earthquakes or ice-quakes in arctic zones. At the surface, we assume elastic ice-sheets of a variable thickness, and show that the propagating acoustic-gravity modes have different mode shape than originally derived by Ref. [1] for a rigid ice-sheet settings. Computationally, we couple the ice-sheet problem with the free surface model by Ref. [2] representing shrinking ice blocks in realistic sea state, where the randomly oriented ice-sheets cause inter modal transition at the edges and multidirectional reflections. We then derive a depth-integrated equation valid for spatially slowly varying thickness of ice-sheet and water depth. Surprisingly, and unlike the free-surface setting, here it is found that the higher acoustic-gravity modes exhibit a larger contribution. These modes travel at the speed of sound in water carrying information on their source, e.g. ice-sheet motion or submarine earthquake, providing various implications for ocean monitoring and detection of quakes. In addition, we found that the propagating acoustic-gravity modes can result in orbital displacements of fluid parcels sufficiently high that may contribute to deep ocean currents and circulation, as postulated by Refs. [1, 3]. References [1] U. Kadri, 2016. Generation of Hydroacoustic Waves by an Oscillating Ice Block in Arctic Zones. Advances in Acoustics and Vibration, 2016, Article ID 8076108, 7 pages http://dx.doi.org/10.1155/2016/8076108 [2] A. Abdolali, J. T. Kirby and G. Bellotti, 2015, Depth-integrated equation for hydro-acoustic waves with bottom damping, J. Fluid Mech., 766, R1 doi:10.1017/jfm.2015.37 [3] U. Kadri, 2014. Deep ocean water transportation by acoustic?gravity waves. J. Geophys. Res. Oceans, 119, doi:10.1002/ 2014JC010234

Retraction: New aspects of photon propagation in expanding universes

NASA Astrophysics Data System (ADS)

Fahr, H.-J.; Heyl, M.

2017-12-01

According to present cosmological views the energy density of CMB (Cosmic Microwave Background) photons, freely propagating through the expanding cosmos, varies proportional to 1/S^4 with S being the scale factor of the universe. This behavior is expected, because General Theory of Relativity, in application to FLRW- (Friedmann-Lemaitre-Robertson-Walker) cosmological universes, leads to the conclusion that the photon wavelengths increase during their free passage through the spacetime metrics of the universe by the same factor as does the scale factor S. This appears to be a reasonable explanation for the presently observed Planckian CMB spectrum with its actual temperature of about 2.7 K, while at the time of its origin after the last scattering during the recombination phase its temperature should have been about 3000 K, at an epoch of about 380 ky after the Big Bang, when the scale of the universe S_r was smaller by roughly a factor of S/S_r = 1+z_r = 1100 compared to the present scale S = S_0 of the universe. In this paper we start from putting the question whether the scale-behavior of the CMB energy density that enters the energy-momentum tensor of the field equations describing the expanding universe is really falling off like 1/S^4 and, if in fact a deviation from a behavior according to 1/S^4 would occur, why do we nevertheless presently observe a CMB energy density which appears to be in accordance with such a 1/S^4-scaling? This question arises from another basic and fundamental question, namely: Can we really assume that the wavelength of the freely propagating photon during its travel all the way along its light geodetic is permanently affected by the expansion of the universe, i.e continuously recognizes the expansion of the cosmic scale S? With other words: Do freely propagating photons ........

Growth Kinematics of Opening-Mode Fractures

NASA Astrophysics Data System (ADS)

Eichhubl, P.; Alzayer, Y.; Laubach, S.; Fall, A.

2014-12-01

Fracture aperture is a primary control on flow in fractured reservoirs of low matrix permeability including unconventional oil and gas reservoirs and most geothermal systems. Guided by principles of linear elastic fracture mechanics, fracture aperture is generally assumed to be a linear function of fracture length and elastic material properties. Natural opening-mode fractures with significant preserved aperture are observed in core and outcrop indicative of fracture opening strain accommodated by permanent solution-precipitation creep. Fracture opening may thus be decoupled from length growth if the material effectively weakens after initial elastic fracture growth by either non-elastic deformation processes or changes in elastic properties. To investigate the kinematics of fracture length and aperture growth, we reconstructed the opening history of three opening-mode fractures that are bridged by crack-seal quartz cement in Travis Peak Sandstone of the SFOT-1 well, East Texas. Similar crack-seal cement bridges had been interpreted to form by repeated incremental fracture opening and subsequent precipitation of quartz cement. We imaged crack-seal cement textures for bridges sampled at varying distance from the tips using scanning electron microscope cathodoluminescence, and determined the number and thickness of crack-seal cement increments as a function of position along the fracture length and height. Observed trends in increment number and thickness are consistent with an initial stage of fast fracture propagation relative to aperture growth, followed by a stage of slow propagation and pronounced aperture growth. Consistent with fluid inclusion observations indicative of fracture opening and propagation occurring over 30-40 m.y., we interpret the second phase of pronounced aperture growth to result from fracture opening strain accommodated by solution-precipitation creep and concurrent slow, possibly subcritical, fracture propagation. Similar deformation mechanisms are envisioned to govern fracture growth over shorter timescales in reactive chemical subsurface environments including CO2 reservoirs, organic-rich shales, and geothermal systems.

Dominance of debonding defect of CFST on PZT sensor response considering the meso-scale structure of concrete with multi-scale simulation

NASA Astrophysics Data System (ADS)

Xu, Bin; Chen, Hongbing; Mo, Y.-L.; Zhou, Tianmin

2018-07-01

Piezoelectric-lead-zirconate-titanate(PZT)-based interface debonding defects detection for concrete filled steel tubulars (CFSTs) has been proposed and validated through experiments, and numerical study on its mechanism has been carried out recently by assuming that concrete material is homogenous. However, concrete is composed of coarse and fine aggregates, mortar and interface transition zones (ITZs) and even initial defects and is a typical nonhomogeneous material and its mesoscale structure might affect the wave propagation in the concrete core of CFST members. Therefore, it is significantly important to further investigate the influence of mesoscale structure of concrete on the stress wave propagation and the response of embedded PZT sensor for the interface debonding detection. In this study, multi-physical numerical simulation on the wave propagation and embedded PZT sensor response of rectangular CFST members with numerical concrete core considering the randomness in circular aggregate distribution, and coupled with surface-mounted PZT actuator and embedded PZT sensor is carried out. The effect of randomness in the circular aggregates distribution and the existence of ITZs are discussed. Both a local stress wave propagation behavior including transmission, reflection, and diffraction at the interface between concrete core and steel tube under a pulse signal excitation and a global wave field in the cross-section of the rectangular CFST models without and with interface debonding defects under sweep frequency excitation are simulated. The sensitivity of an evaluation index based on wavelet packet analysis on the embedded PZT sensor response on the variation of mesoscale parameters of concrete core without and with different interface debonding defects under sweep frequency voltage signal is investigated in details. The results show that the effect of the interface debondings on the embedded PZT measurement is dominant when compared to the meso-scale structures of concrete core. This study verified the feasibility of the PZT based debonding detection for rectangular CFST members even the meso-scale structure of concrete core is considered.

On the formation of tilted flux ropes in the Earth's magnetotail observed with ARTEMIS

NASA Astrophysics Data System (ADS)

Kiehas, S. A.; Angelopoulos, V.; Runov, A.; Moldwin, M. B.; Möstl, C.

2012-05-01

On 21 October 2010, ARTEMIS spacecraft P2, located at about -57 REGSM in the Earth's magnetotail, observed a series of flux ropes during the course of a moderate substorm. Subsequently, ARTEMIS spacecraft P1, located about 20 RE farther downtail and farther into the lobe than P2, observed a series of TCRs, consistent with the flux ropes observed by P2. The dual-spacecraft configuration allows simultaneous examination of these phenomena, which are interpreted as an O-line, followed by a series of flux ropes/TCRs. An inter-spacecraft time of flight analysis, assuming tailward propagation of cross-tail aligned ropes, suggests propagation speeds of up to ˜2000 km/s. A principal axis investigation, however, indicates that the flux ropes were tilted between 41° and 45° in the GSM x-y-plane with respect to the noon-midnight meridional plane. Taking this into account, the tailward propagation speed of the different flux ropes is determined to be between 900 and 1400 km/s. The same timing analysis also reveals that the flux rope velocity increased progressively from one flux rope to the next. A clear correlation between the magnetic field and plasma flow components inside the flux ropes was observed. As possible mechanisms leading to the formation of tilted flux ropes we suggest (a) a progressive spreading of the reconnection line along the east-west direction, leading to a boomerang-like shape and (b) a tilting of flux ropes during their formation by non-uniform reconnection with open field lines at the ends of the flux ropes. The progressive increase in the propagation velocity from the first to the last flux rope may be evidence of impulsive reconnection: initially deep inside the plasma sheet the reconnection rate is slow but as reconnection proceeds at the plasma sheet boundary and possibly lobes, the reconnection rate increases.

Analytical Solution for Transport with Bimolecular Reactions in Fracture-Matrix Systems with Application to In-Situ Chemical Oxidation

NASA Astrophysics Data System (ADS)

Rajaram, H.; Arshadi, M.

2016-12-01

In-situ chemical oxidation (ISCO) is an effective strategy for remediation of DNAPL contamination in fractured rock. During ISCO, an oxidant (e.g. permanganate) is typically injected through fractures and is consumed by bimolecular reactions with DNAPLs such as TCE and natural organic matter in the fracture and the adjacent rock matrix. Under these conditions, moving reaction fronts form and propagate along the fracture and into the rock matrix. The propagation of these reaction fronts is strongly influenced by the heterogeneity/discontinuity across the fracture-matrix interface (advective transport dominates in the fractures, while diffusive transport dominates in the rock matrix). We present analytical solutions for the concentrations of the oxidant, TCE and natural organic matter; and the propagation of the reaction fronts in a fracture-matrix system. Our approximate analytical solutions assume advection and reaction dominate over diffusion/dispersion in the fracture and neglect the latter. Diffusion and reaction with both TCE and immobile natural organic matter in the rock matrix are considered. The behavior of the reaction-diffusion equations in the rock matrix is posed as a Stefan problem where the diffusing oxidant reacts with both diffusing (TCE) and immobile (natural organic matter) reductants. Our analytical solutions establish that the reaction fronts propagate diffusively (i.e. as the square root of time) in both the matrix and the fracture. Our analytical solutions agree very well with numerical simulations for the case of uniform advection in the fracture. We also present extensions of our analytical solutions to non-uniform flows in the fracture by invoking a travel-time transformation. The non-uniform flow solutions are relevant to field applications of ISCO. The approximate analytical solutions are relevant to a broad class of reactive transport problems in fracture-matrix systems where moving reaction fronts occur.

The effect of dissipative inhomogeneous medium on the statistics of the wave intensity

NASA Technical Reports Server (NTRS)

Saatchi, Sasan S.

1993-01-01

One of the main theoretical points in the theory of wave propagation in random medium is the derivation of closed form equations to describe the statistics of the propagating waves. In particular, in one dimensional problems, the closed form representation of the multiple scattering effects is important since it contributes in understanding such problems like wave localization, backscattering enhancement, and intensity fluctuations. In this the propagation of plane waves in a layer of one-dimensional dissipative random medium is considered. The medium is modeled by a complex permittivity whose real part is a constant representing the absorption. The one dimensional problem is mathematically equivalent to the analysis of a transmission line with randomly perturbed distributed parameters and a single mode lossy waveguide and the results can be used to study the propagation of radio waves through atmosphere and the remote sensing of geophysical media. It is assumed the scattering medium consists of an ensemble of one-dimensional point scatterers randomly positioned in a layer of thickness L with diffuse boundaries. A Poisson impulse process with density lambda is used to model the position of scatterers in the medium. By employing the Markov properties of this process an exact closed form equation of Kolmogorov-Feller type was obtained for the probability density of the reflection coefficient. This equation was solved by combining two limiting cases: (1) when the density of scatterers is small; and (2) when the medium is weakly dissipative. A two variable perturbation method for small lambda was used to obtain solutions valid for thick layers. These solutions are then asymptotically evaluated for small dissipation. To show the effect of dissipation, the mean and fluctuations of the reflected power are obtained. The results were compared with a lossy homogeneous medium and with a lossless inhomogeneous medium and the regions where the effect of absorption is not essential were discussed.

A one-dimensional model for the propagation of transient pressure waves through the lung.

PubMed

Grimal, Quentin; Watzky, Alexandre; Naili, Salah

2002-08-01

The propagation of pressure waves in the lung has been investigated by many authors concerned with respiratory physiology, ultrasound medical techniques or thoracic impact injuries. In most of the theoretical studies, the lung has been modeled as an isotropic and homogeneous medium, and by using Hooke's constitutive law (see e.g. Ganesan et al. Respir. Physiol. 110 (1997) 19; Jahed et al. J. Appl. Physiol. 66 (1989) 2675; Grimal et al. C.R. Acad. Sci., Paris 329 (IIb) (2001) 655-662), or more elaborated material laws (see, e.g. Bush and Challener (Proceedings of the International Research Council on Biokinetics Impacts (IRCOBI), Bergish-gladbach, 1988); Stuhmiller et al. J. Trauma 28 (1988) S132; Yang and Wang, Finite element modeling of the human thorax. Web page: http://wwwils.nlm.nih.gov/research/visible/vhpconf98/AUTHORS/YANG/YANG.HTM.). The hypothesis of homogeneous medium may be inappropriate for certain problems. Because of its foam-like structure, the behavior of the lung-even if the air and the soft tissue are assumed to behave like linearly elastic materials-is susceptible to be frequency dependent. In the present study, the lung is viewed as a one-dimensional stack of air and soft tissue layers; wave propagation in such a stack can be investigated in an equivalent mass-spring chain (El-Raheb (J. Acoust. Soc. Am. 94 (1993) 172; Int. J. Solids Struct. 34 (1997) 2969), where the masses and springs, respectively, represent the alveolar walls and alveolar gas. Results are presented in the time and frequency domains. The frequency dependence (cutoff frequency, variations in phase velocity) of the lung model is found to be highly dependent on the mean alveolar size. We found that short pulses induced by high velocity impacts (bullet stopped by a bulletproof jacket) can be highly distorted during the propagation. The pressure differential between two alveoli is discussed as a possible injury criterion.

Simulation of quasi-static hydraulic fracture propagation in porous media with XFEM

NASA Astrophysics Data System (ADS)

Juan-Lien Ramirez, Alina; Neuweiler, Insa; Löhnert, Stefan

2015-04-01

Hydraulic fracturing is the injection of a fracking fluid at high pressures into the underground. Its goal is to create and expand fracture networks to increase the rock permeability. It is a technique used, for example, for oil and gas recovery and for geothermal energy extraction, since higher rock permeability improves production. Many physical processes take place when it comes to fracking; rock deformation, fluid flow within the fractures, as well as into and through the porous rock. All these processes are strongly coupled, what makes its numerical simulation rather challenging. We present a 2D numerical model that simulates the hydraulic propagation of an embedded fracture quasi-statically in a poroelastic, fully saturated material. Fluid flow within the porous rock is described by Darcy's law and the flow within the fracture is approximated by a parallel plate model. Additionally, the effect of leak-off is taken into consideration. The solid component of the porous medium is assumed to be linear elastic and the propagation criteria are given by the energy release rate and the stress intensity factors [1]. The used numerical method for the spatial discretization is the eXtended Finite Element Method (XFEM) [2]. It is based on the standard Finite Element Method, but introduces additional degrees of freedom and enrichment functions to describe discontinuities locally in a system. Through them the geometry of the discontinuity (e.g. a fracture) becomes independent of the mesh allowing it to move freely through the domain without a mesh-adapting step. With this numerical model we are able to simulate hydraulic fracture propagation with different initial fracture geometries and material parameters. Results from these simulations will also be presented. References [1] D. Gross and T. Seelig. Fracture Mechanics with an Introduction to Micromechanics. Springer, 2nd edition, (2011) [2] T. Belytschko and T. Black. Elastic crack growth in finite elements with minimal remeshing. Int. J. Numer. Meth. Engng. 45, 601-620, (1999)

Particle Filter with State Permutations for Solving Image Jigsaw Puzzles

PubMed Central

Yang, Xingwei; Adluru, Nagesh; Latecki, Longin Jan

2016-01-01

We deal with an image jigsaw puzzle problem, which is defined as reconstructing an image from a set of square and non-overlapping image patches. It is known that a general instance of this problem is NP-complete, and it is also challenging for humans, since in the considered setting the original image is not given. Recently a graphical model has been proposed to solve this and related problems. The target label probability function is then maximized using loopy belief propagation. We also formulate the problem as maximizing a label probability function and use exactly the same pairwise potentials. Our main contribution is a novel inference approach in the sampling framework of Particle Filter (PF). Usually in the PF framework it is assumed that the observations arrive sequentially, e.g., the observations are naturally ordered by their time stamps in the tracking scenario. Based on this assumption, the posterior density over the corresponding hidden states is estimated. In the jigsaw puzzle problem all observations (puzzle pieces) are given at once without any particular order. Therefore, we relax the assumption of having ordered observations and extend the PF framework to estimate the posterior density by exploring different orders of observations and selecting the most informative permutations of observations. This significantly broadens the scope of applications of the PF inference. Our experimental results demonstrate that the proposed inference framework significantly outperforms the loopy belief propagation in solving the image jigsaw puzzle problem. In particular, the extended PF inference triples the accuracy of the label assignment compared to that using loopy belief propagation. PMID:27795660

The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

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

Ulaganathan, Jaganathan, E-mail: jagan.ulaganathan@mail.utoronto.ca; Newman, Roger C., E-mail: roger.newman@utoronto.ca

2014-06-01

The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously withinmore » the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved.« less

Fundamental structure of steady plastic shock waves in metals

NASA Astrophysics Data System (ADS)

Molinari, A.; Ravichandran, G.

2004-02-01

The propagation of steady plane shock waves in metallic materials is considered. Following the constitutive framework adopted by R. J. Clifton [Shock Waves and the Mechanical Properties of Solids, edited by J. J. Burke and V. Weiss (Syracuse University Press, Syracuse, N.Y., 1971), p. 73] for analyzing elastic-plastic transient waves, an analytical solution of the steady state propagation of plastic shocks is proposed. The problem is formulated in a Lagrangian setting appropriate for large deformations. The material response is characterized by a quasistatic tensile (compression) test (providing the isothermal strain hardening law). In addition the elastic response is determined up to second order elastic constants by ultrasonic measurements. Based on this simple information, it is shown that the shock kinetics can be quite well described for moderate shocks in aluminum with stress amplitude up to 10 GPa. Under the later assumption, the elastic response is assumed to be isentropic, and thermomechanical coupling is neglected. The model material considered here is aluminum, but the analysis is general and can be applied to any viscoplastic material subjected to moderate amplitude shocks. Comparisons with experimental data are made for the shock velocity, the particle velocity and the shock structure. The shock structure is obtained by quadrature of a first order differential equation, which provides analytical results under certain simplifying assumptions. The effects of material parameters and loading conditions on the shock kinetics and shock structure are discussed. The shock width is characterized by assuming an overstress formulation for the viscoplastic response. The effects on the shock structure of strain rate sensitivity are analyzed and the rationale for the J. W. Swegle and D. E. Grady [J. Appl. Phys. 58, 692 (1985)] universal scaling law for homogeneous materials is explored. Finally, the ability to deduce information on the viscoplastic response of materials subjected to very high strain rates from shock wave experiments is discussed.

Theory of helix traveling wave tubes with dielectric and vane loading

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

Freund, H.P.; Zaidman, E.G.; Antonsen, T.M. Jr.

1996-08-01

A time-dependent nonlinear analysis of a helix traveling wave tube (TWT) is presented for a configuration where an electron beam propagates through a sheath helix surrounded by a conducting wall. The effects of dielectric and vane loading are included in the formulation as is efficiency enhancement by tapering the helix pitch. Dielectric loading is described under the assumption that the gap between the helix and the wall is uniformly filled by a dielectric material. The vane-loading model describes the insertion of an arbitrary number of vanes running the length of the helix, and the polarization of the field between themore » vanes is assumed to be an azimuthally symmetric transverse-electric mode. The field is represented as a superposition of azimuthally symmetric waves in a vacuum sheath helix. An overall explicit sinusoidal variation of the form exp({ital ikz}{minus}{ital i}{omega}{ital t}) is assumed (where {omega} denotes the angular frequency corresponding to the wave number {ital k} in the vacuum sheath helix), and the polarization and radial variation of each wave is determined by the boundary conditions in a vacuum sheath helix. The propagation of each wave {ital in} {ital vacuo} as well as the interaction of each wave with the electron beam is included by allowing the amplitudes of the waves to vary in {ital z} and {ital t}. A dynamical equation for the field amplitudes is derived analogously to Poynting{close_quote}s equation, and solved in conjunction with the three-dimensional Lorentz force equations for an ensemble of electrons. Electron beams with a both a continuous and emission-gated pulse format are analyzed, and the model is compared with linear theory of the interaction as well as with the performance of a TWTs operated at the Naval Research Laboratory and at Northrop{endash}Grumman Corporation. {copyright} {ital 1996 American Institute of Physics.}« less

RAPID DETERMINATION OF FOCAL DEPTH USING A GLOBAL NETWORK OF SMALL-APERTURE SEISMIC ARRAYS

NASA Astrophysics Data System (ADS)

Seats, K.; Koper, K.; Benz, H.

2009-12-01

The National Earthquake Information Center (NEIC) of the United States Geological Survey (USGS) operates 24 hours a day, 365 days a year with the mission of locating and characterizing seismic events around the world. A key component of this task is quickly determining the focal depth of each seismic event, which has a first-order effect on estimates of ground shaking used in the impact assessment applications of emergency response activities. Current methods of depth estimation used at the NEIC include arrival time inversion both with and without depth phases, a Bayesian depth constraint based on historical seismicity (1973-present), and moment tensor inversion primarily using P- and S-wave waveforms. In this study, we explore the possibility of automated modeling of waveforms from vertical-component arrays of the International Monitoring System (IMS) to improve rapid depth estimation at NEIC. Because these arrays are small-aperture, they are effective at increasing signal to noise ratios for frequencies of 1 Hz and higher. Currently, NEIC receives continuous real-time data from 23 IMS arrays. Following work done by previous researchers, we developed a technique that acts as an array of arrays. For a given epicentral location we calculate fourth root beams for each IMS array in the distance range of 30 to 95 degrees at the expected slowness vector of the first arrival. Because the IMS arrays are small-aperture, these beams highlight energy that has slowness similar to the first arrival, such as depth phases. The beams are rectified by taking the envelope and then automatically aligned on the largest peak within 5 seconds of the expected arrival time. The station beams are then combined into network beams assuming a range of depths varying from 10 km to 700 km in increments of 1 km. The network beams are computed assuming both pP and sP propagation, and a measure of beam power is output as a function of depth for both propagation models, as well as their sum. We validated this approach using several hundred seismic events in the magnitude range 4.5-6.5 mb that occurred in 2008 and 2009. In most cases, clear spikes in the network beam power existed at depths around those estimated by the NEIC using traditional location procedures. However, in most cases there was also a bimodality in the network beam power because of the ambiguity between assuming pP or sP propagation for later arriving energy. There were only a handful of cases in which a seismic event generated both sP and pP phases with sizes large enough to resolve the ambiguity. We are currently working to include PKP arrivals into the network beams and experimenting with various tuning parameters to improve the efficiency of the algorithm. This promising approach will allow NEIC to significantly and systematically improve the quality of hypocentral locations reported in the PDE and provide NEIC with additional valuable information on seismic source parameters needed in emergency response applications.

The origin of infrasonic ionosphere oscillations over tropospheric thunderstorms

NASA Astrophysics Data System (ADS)

Shao, Xuan-Min; Lay, Erin H.

2016-07-01

Thunderstorms have been observed to introduce infrasonic oscillations in the ionosphere, but it is not clear what processes or which parts of the thunderstorm generate the oscillations. In this paper, we present a new technique that uses an array of ground-based GPS total electron content (TEC) measurements to locate the source of the infrasonic oscillations and compare the source locations with thunderstorm features to understand the possible source mechanisms. The location technique utilizes instantaneous phase differences between pairs of GPS-TEC measurements and an algorithm to best fit the measured and the expected phase differences for assumed source positions and other related parameters. In this preliminary study, the infrasound waves are assumed to propagate along simple geometric raypaths from the source to the measurement locations to avoid extensive computations. The located sources are compared in time and space with thunderstorm development and lightning activity. Sources are often found near the main storm cells, but they are more likely related to the downdraft process than to the updraft process. The sources are also commonly found in the convectively quiet stratiform regions behind active cells and are in good coincidence with extensive lightning discharges and inferred high-altitude sprites discharges.

A fuzzy mathematical model of West Java population with logistic growth model

NASA Astrophysics Data System (ADS)

Nurkholipah, N. S.; Amarti, Z.; Anggriani, N.; Supriatna, A. K.

2018-03-01

In this paper we develop a mathematics model of population growth in the West Java Province Indonesia. The model takes the form as a logistic differential equation. We parameterize the model using several triples of data, and choose the best triple which has the smallest Mean Absolute Percentage Error (MAPE). The resulting model is able to predict the historical data with a high accuracy and it also able to predict the future of population number. Predicting the future population is among the important factors that affect the consideration is preparing a good management for the population. Several experiment are done to look at the effect of impreciseness in the data. This is done by considering a fuzzy initial value to the crisp model assuming that the model propagates the fuzziness of the independent variable to the dependent variable. We assume here a triangle fuzzy number representing the impreciseness in the data. We found that the fuzziness may disappear in the long-term. Other scenarios also investigated, such as the effect of fuzzy parameters to the crisp initial value of the population. The solution of the model is obtained numerically using the fourth-order Runge-Kutta scheme.

Particle acceleration at shocks in the presence of a braided magnetic field

NASA Astrophysics Data System (ADS)

Kirk, J. G.; Duffy, P.; Gallant, Y. A.

1997-05-01

The theory of first order Fermi acceleration at shock fronts assumes charged particles undergo spatial diffusion in a uniform magnetic field. If, however, the magnetic field is not uniform, but has a stochastic or braided structure, the transport of charged particles across the average direction of the field is more complicated. Assuming quasi-linear behaviour of the field lines, the particles undergo sub-diffusion ( ~ t^1/2) on short time scales. We investigate this process analytically, using a propagator approach, and numerically, with a Monte-Carlo simulation. It is found that, in contrast to the diffusive case, the density of particles at the shock front is lower than it is far downstream which is a consequence of the partial trapping of particles by structures in the magnetic field. As a result, the spectrum of accelerated particles is a power-law in momentum which is steeper than in the diffusive case. For a phase-space density f ~ p^-s, we find s =s_diff [1 + 1/(2rho_c)], where rho_c is the compression ratio of the shock front and s_diff is the standard result of diffusive acceleration:s_diff = 3rho_c/(rho_c - 1).

AMS-02 fits dark matter

NASA Astrophysics Data System (ADS)

Balázs, Csaba; Li, Tong

2016-05-01

In this work we perform a comprehensive statistical analysis of the AMS-02 electron, positron fluxes and the antiproton-to-proton ratio in the context of a simplified dark matter model. We include known, standard astrophysical sources and a dark matter component in the cosmic ray injection spectra. To predict the AMS-02 observables we use propagation parameters extracted from observed fluxes of heavier nuclei and the low energy part of the AMS-02 data. We assume that the dark matter particle is a Majorana fermion coupling to third generation fermions via a spin-0 mediator, and annihilating to multiple channels at once. The simultaneous presence of various annihilation channels provides the dark matter model with additional flexibility, and this enables us to simultaneously fit all cosmic ray spectra using a simple particle physics model and coherent astrophysical assumptions. Our results indicate that AMS-02 observations are not only consistent with the dark matter hypothesis within the uncertainties, but adding a dark matter contribution improves the fit to the data. Assuming, however, that dark matter is solely responsible for this improvement of the fit, it is difficult to evade the latest CMB limits in this model.

Experiments to verify nonparallel stability theory at Virginia Polytechnic Institute and State University, Blacksburg, Virginia

NASA Technical Reports Server (NTRS)

Saric, William S.

1988-01-01

The effects of normal mass injection and suction on boundary-layer stability and transition are studied on a flat plate. Titanium panels, in which 0.063 mm diameter holes were drilled on 0.635 mm centers, are inserted in the plate. Suction level and distribution are variable. Disturbances are introduced by means of a vibrating ribbon and measurements of both mean- and disturbance-flow velocities are made with a hot wire. Disturbance amplitudes are measured as a function of Reynolds number, frequency, and suction characteristics, and are compared with the previous results obtained over a Dynapore surface. Transition measurements under natural and forced conditions are also made. The stabilizing effects of suction are documented. It is also shown that very high local flow rates through the suction holes (which approach a hole Reynolds number of 300) do not destabilize the flow. On the other hand, weak blowing lowers the transition Reynolds number, but is found not to cause serious problems.

A path-level exact parallelization strategy for sequential simulation

NASA Astrophysics Data System (ADS)

Peredo, Oscar F.; Baeza, Daniel; Ortiz, Julián M.; Herrero, José R.

2018-01-01

Sequential Simulation is a well known method in geostatistical modelling. Following the Bayesian approach for simulation of conditionally dependent random events, Sequential Indicator Simulation (SIS) method draws simulated values for K categories (categorical case) or classes defined by K different thresholds (continuous case). Similarly, Sequential Gaussian Simulation (SGS) method draws simulated values from a multivariate Gaussian field. In this work, a path-level approach to parallelize SIS and SGS methods is presented. A first stage of re-arrangement of the simulation path is performed, followed by a second stage of parallel simulation for non-conflicting nodes. A key advantage of the proposed parallelization method is to generate identical realizations as with the original non-parallelized methods. Case studies are presented using two sequential simulation codes from GSLIB: SISIM and SGSIM. Execution time and speedup results are shown for large-scale domains, with many categories and maximum kriging neighbours in each case, achieving high speedup results in the best scenarios using 16 threads of execution in a single machine.

Factors Influencing the Incidence of Obesity in Australia: A Generalized Ordered Probit Model.

PubMed

Avsar, Gulay; Ham, Roger; Tannous, W Kathy

2017-02-10

The increasing health costs of and the risks factors associated with obesity are well documented. From this perspective, it is important that the propensity of individuals towards obesity is analyzed. This paper uses longitudinal data from the Household Income and Labour Dynamics in Australia (HILDA) Survey for 2005 to 2010 to model those variables which condition the probability of being obese. The model estimated is a random effects generalized ordered probit, which exploits two sources of heterogeneity; the individual heterogeneity of panel data models and heterogeneity across body mass index (BMI) categories. The latter is associated with non-parallel thresholds in the generalized ordered model, where the thresholds are functions of the conditioning variables, which comprise economic, social, and demographic and lifestyle variables. To control for potential predisposition to obesity, personality traits augment the empirical model. The results support the view that the probability of obesity is significantly determined by the conditioning variables. Particularly, personality is found to be important and these outcomes reinforce other work examining personality and obesity.

3-D Dynamic Rupture Simulations of the 2016 Kumamoto, Japan, Earthquake

NASA Astrophysics Data System (ADS)

Fukuyama, E.; Urata, Y.; Yoshida, K.

2016-12-01

On April 16, 2016 at 01:25 (JST), an M7.3 main shock of the 2016 Kumamoto, Japan, earthquake sequence occurred along the Futagawa and Hinagu faults. A few days before, three M6-class foreshocks occurred: M6.5 on April 14 at 21:26, M5.8 on April 14 at 22:27, and M6.4 on April 15 at 00:03 (JST). The focal mechanisms of the first and third foreshocks were similar to those of the main shock; therefore, the extensive stress shadow should have been generated on the fault plane of the main shock. The purpose of this study is to illuminate why the rupture of the main shock propagated successfully under such stress conditions by 3-D dynamic rupture simulations, assuming the fault planes estimated by the distributions of aftershocks.First, we investigated time evolution of aftershock hypocenters relocated by the Double Difference method (Waldhauser & Ellsworth, 2000). The result showed that planar distribution of the hypocenters was formed after each M6 event. It allows us to estimate fault planes of the three foreshocks and the main shock.Then, we evaluated stress changes on the fault planes of the main shock due to the three foreshocks. We obtained the slip distributions of the foreshocks by using Eshelby (1957)'s solution, assuming elliptical cracks with constant stress drops on the estimated fault planes. The stress changes on the fault planes of the main shock were calculated by using Okada (1992)'s solution. The obtained stress change distribution showed that the hypocenter of the main shock existed on the region with positive ΔCFF while ΔCFF in the shallower regions than the hypocenter was negative. Therefore, the foreshocks could encourage the initiation of the main shock rupture and could hinder the rupture propagating toward the shallow region.Finally, we conducted 3-D dynamic rupture simulations (Hok and Fukuyama, 2011) of the main shock under the initial stresses, which were the sum of the stress changes by these foreshocks and the regional stress field estimated by Yoshida et al. (2016, submitted). We used slip-weakening law with uniform friction parameters. We conducted many simulations varying unknown parameters (the friction parameters and the values of the principal stresses), and we will discuss the conditions for the rupture propagation of the main shock and the effects of the foreshocks on the main shock.

An ice-cream cone model for coronal mass ejections

NASA Astrophysics Data System (ADS)

Xue, X. H.; Wang, C. B.; Dou, X. K.

2005-08-01

In this study, we use an ice-cream cone model to analyze the geometrical and kinematical properties of the coronal mass ejections (CMEs). Assuming that in the early phase CMEs propagate with near-constant speed and angular width, some useful properties of CMEs, namely the radial speed (v), the angular width (α), and the location at the heliosphere, can be obtained considering the geometrical shapes of a CME as an ice-cream cone. This model is improved by (1) using an ice-cream cone to show the near real configuration of a CME, (2) determining the radial speed via fitting the projected speeds calculated from the height-time relation in different azimuthal angles, (3) not only applying to halo CMEs but also applying to nonhalo CMEs.

Short-range wakefields generated in the blowout regime of plasma-wakefield acceleration

NASA Astrophysics Data System (ADS)

Stupakov, G.

2018-04-01

In the past, calculation of wakefields generated by an electron bunch propagating in a plasma has been carried out in linear approximation, where the plasma perturbation can be assumed small and plasma equations of motion linearized. This approximation breaks down in the blowout regime where a high-density electron driver expels plasma electrons from its path and creates a cavity void of electrons in its wake. In this paper, we develop a technique that allows us to calculate short-range longitudinal and transverse wakes generated by a witness bunch being accelerated inside the cavity. Our results can be used for studies of the beam loading and the hosing instability of the witness bunch in plasma-wakefield and laser-wakefield acceleration.