Start-to-end global imaging as a sunward propagating, SAPS-associated giant undulation event
Henderson, Michael G; Donovan, Eric F; Foster, John C; Mann, Ian R; Immel, Thomas J
2009-01-01
We present high-time resolution global imaging of a sunward propagating giant undulation event from start to finish. The event occurred on November 24, 2001 during a very disturbed storm interval. The giant undulations began to develop at around 13UT and persisted for approximately 2 hours. The sunward propagation speed was on the order of 0.6 km/s (relative to SM coordinate system). The undulations had a wavelength of {approx} 750 km, amplitudes of {approx} 890 km and produced ULF pulsations on the ground with a period of {approx} 1108s. We show that the undulations were associated with SAPs flows that were caused by the proton plasma sheet penetrating substantially farther Earthward than the electron plasma sheet on the duskside. The observations appear to be consistent with the development of a shear flow and/or ballooning type of instability at the plasmapause driven by intense SAPS-associated shear flows.
SUNWARD PROPAGATING ALFVÉN WAVES IN ASSOCIATION WITH SUNWARD DRIFTING PROTON BEAMS IN THE SOLAR WIND
He, Jiansen; Pei, Zhongtian; Wang, Linghua; Tu, Chuanyi; Zhang, Lei; Marsch, Eckart; Salem, Chadi
2015-06-01
Using measurements from the WIND spacecraft, here we report the observation of sunward propagating Alfvén waves (AWs) in solar wind that is magnetically disconnected from the Earth's bow shock. In the sunward magnetic field sector, we find a period lasting for more than three days in which there existed (during most time intervals) a negative correlation between the flow velocity and magnetic field fluctuations, thus indicating that the related AWs are mainly propagating sunward. Simultaneous observations of counter-streaming suprathermal electrons suggest that these sunward AWs may not simply be due to the deflection of an open magnetic field line. Moreover, no interplanetary coronal mass ejection appears to be associated with the counter-streaming suprathermal electrons. As the scale goes from the magnetohydrodynamic down to the ion kinetic regime, the wave vector of magnetic fluctuations usually becomes more orthogonal to the mean magnetic field direction, and the fluctuations become increasingly compressible, which are both features consistent with quasi-perpendicular kinetic AWs. However, in the case studied here, we find clear signatures of quasi-parallel sunward propagating ion-cyclotron waves. Concurrently, the solar wind proton velocity distribution reveals a sunward field-aligned beam that drifts at about the local Alfvén speed. This beam is found to run in the opposite direction of the normally observed (anti-sunward) proton beam, and is apparently associated with sunward propagating Alfvén/ion-cyclotron waves. The results and conclusions of this study enrich our knowledge of solar wind turbulence and foster our understanding of proton heating and acceleration within a complex magnetic field geometry.
NASA Astrophysics Data System (ADS)
Wu, H.; Wang, X.; Wang, L.; Tu, C.; He, J.; Marsch, E.
2015-12-01
According to several theories, the beam instability induced by shock-accelerated ions can generate upstream-propagating Alfvén waves (UPAWs) with a bump near 0.03 Hz in the power spectrum, while the nonlinear wave-wave interaction favors an inverse cascade to create a power-law spectrum. Here we present the first observational evidence for the upstream-propagating Alfvénic fluctuations (UPAFs) with power-law spectra by using measurements from the WIND spacecraft in year 1995. We utilize a new criterion to identify the upstream-propagating Alfvénic intervals: the propagation direction is opposite to that of solar wind strahl electron outflow. Besides 35 UPAWs, we find 47 UPAFs with power-law spectra, and ~47% of these UPAFs are associated with energetic ion events (>30 keV). These UPAWs and UPAFs are mostly observed in the slow solar wind. However, their occurrence rate and power behave differently in dependence on the radial distance from the Earth. The spectral indices of UPAFs are between -3 and -2. These power-law spectra cannot be explained by the linear ion-beam instability. The results provide new clues on understanding the dynamic equilibrium between the non-linear inverse cascade and the linear ion-beam instability.
Sunward convection in both polar caps
Reiff, P.H.
1982-08-01
The geomagnetic storm of July 29, 1977 has been the object of concentrated study. The latter part of the day (1800--2300 UT) is particularly interesting because it is a period of extremely strong, almost directly northward interplanetary magnetic fields (IMF). Such northward IMF's have been related to periods of reversed (i.e., sunward) convection in the polar cap, and this day is no exception. Zanetti et al. (1981), using Triad magnetometer data, show magnetic perturbations implying reversed convection in the northern polar cap, while the Birkeland currents in the southern polar cap are very weak. They give two possible interpretations: (1) merging occurs preferentially in the northern cusp region, and therefore reversed convection is restricted to the northern polar cap or (2) the currents flow predominantly in the sunlit northern polar cap because its conductivity is higher. This paper shows convection data from both the northern polar cap (S3-3) and the southern polar cap (AE-C). In both cases, regions of reversed convection are seen. Therefore the asymmetry of the Birkeland currents is more likely caused by a conductivity asymmetry than a convection asymmetry. It is likely that the low-energy ions seen deep in the polar cap may be traped on closed field lines after merging on both tail lobe boundaries.
Seasonal effect for polar cap sunward plasma flows at strongly northward IMF Bz
NASA Astrophysics Data System (ADS)
Koustov, A. V.; Yakymenko, K. N.; Ponomarenko, P. V.
2017-02-01
We use Super Dual Auroral Radar Network data to study polar cap ionospheric flow under strongly dominant positive interplanetary magnetic field Bz component. We show that the near-noon flow along the magnetic meridian is predominantly sunward in summer. The sunward velocity increase with intensification of the external driver (the reverse convection electric field) is also faster in summer, and the rate of the increase is slightly larger for the Southern Hemisphere. The sunward flows simultaneously detected in both hemispheres are faster in the summer hemisphere. In addition, while sunward flows are aligned with the midnight-noon line in a winter hemisphere, they are oriented toward earlier magnetic local hours in a summer hemisphere.
Spatial distribution of the neutral carboneus compounds glow in the sunward Halley comet coma
NASA Astrophysics Data System (ADS)
Guineva, V.; Stoeva, P.; Werner, R.
The C2, C3, CH and CN glow in the Halley coma in sunward direction is studied in this work. For that reason, the 1035 spectra in the in the near UV and visible region registered by the Three-Channel spectrometer on board Vega-2 station on the 9 March 1986 are used. An improved method of the dust continuum extraction in the visible region is applied. The ``dust regions'' in the Halley comet spectra are re-examined. The spectral index u and a normalization coefficient of the continuum are computed for each spectrum by the least squares method on the basis of a linear regression. The index u is obtained to lay in the interval 3div 3.4. For all the spectra the average u and du values are: uav=3.2126, duav= 0.1197. Thus, the dust continuum evaluation is more reliable which conduce to a more precise separation of the gas emissions. The radial profiles presenting the carboneous compounds column intensities as a function of the projected distance to the nucleus are examined. The obtained profiles correspond very well to the Hazer's distribution when the optical thickness in the inner coma environment is taken into account. The deviation from Hazer's model for CN and C3 in the p<1000 km region, obtained in previous investigations, is not seen now. Possibly this deviation had been the result of a not perfectly subtracted dust continuum in this zone. The observed until now peculiarities of the C2, C3, CH and CN glow are confirmed. Thanks to the scanning of the Three-Channel spectrometer in a region of 7 rows and 15 columns spatial distributions of the examined radical intensities are computed using their emissions separated from the spectra in different scanner positions. From these distributions, complex intensity distributions for each carboneous compound are constructed, covering a larger space region. The obtained distributions are similar. The intensities decrease with the increase of the distance to the nucleus. Two jets are observed and discussed.
Alfvén Mach number and IMF clock angle dependencies of sunward flow channels in the magnetosphere
NASA Astrophysics Data System (ADS)
Eriksson, S.; RastäTter, L.
2013-04-01
Interplanetary coronal mass ejections associated with strong interplanetary magnetic field (IMF) By have been shown to enhance the neutral density in low Earth orbit. The enhancement has been linked to strong downward Poynting fluxes embedded within ionospheric channels of significant sunward ExB drift (2000-3000 m/s). Here we present MHD results describing the magnetospheric counterpart of the ionospheric flow channel that Defense Meteorological Satellite Program (DMSP) encountered on 15 May 2005. It is shown that the clock angle of maximum sunward flow (θFC) depends on the IMF clock angle θFC = α * θIMF - 1.3° with α = (0.30, 0.38, 0.43, 0.45) at X = (4, 2, 0, -2) RE. This is poleward of the magnetic null point region. The flow also depends on the solar wind Alfvén Mach number Vx = Vx0 - δv * MA. The critical MA = Vx0 / δV for Vx = 0 decreases from MA = 3.42 (X = 4 RE) to MA = 2.40 (X = -2 RE). The low MA and θIMF conditions that characterized the X = 2 RE flow and resulted in strong Poynting flux occurred for 16% of all 167 h in 1998-2008 with Dst < -180 nT.
NASA Technical Reports Server (NTRS)
Kelly, T. J.; Crooker, N. U.; Siscoe, G. L.; Russell, C. T.; Smith, E. J.
1984-01-01
Magnetospheric studies often require knowledge of the orientation of the IMF. In order to test the accuracy of using magnetometer data from a spacecraft orbiting the sunward libration point for this purpose, the angle between the IMF at ISEE 3, when it was positioned around the libration point, and at ISEE 1, orbiting Earth, has been calculated for a data set of two-hour periods covering four months. For each period, a ten-minute average of ISEE 1 data is compared with ten-minute averages of ISEE 3 data at successively lagged intervals. At the lag time equal to the time required for the solar wind to convect from ISEE 3 to ISEE 1, the median angle between the IMF orientation at the two spacecraft is 20 deg, and 80% of the cases have angles less than 38 deg. The results for the angles projected on the y-z plane are essentially the same.
He, Jiansen; Tu, Chuanyi; Wang, Linghua; Pei, Zhongtian; Marsch, Eckart; Chen, Christopher H. K.; Zhang, Lei; Salem, Chadi S.; Bale, Stuart D.
2015-11-10
Magnetohydronamic turbulence is believed to play a crucial role in heating laboratory, space, and astrophysical plasmas. However, the precise connection between the turbulent fluctuations and the particle kinetics has not yet been established. Here we present clear evidence of plasma turbulence heating based on diagnosed wave features and proton velocity distributions from solar wind measurements by the Wind spacecraft. For the first time, we can report the simultaneous observation of counter-propagating magnetohydrodynamic waves in the solar wind turbulence. As opposed to the traditional paradigm with counter-propagating Alfvén waves (AWs), anti-sunward AWs are encountered by sunward slow magnetosonic waves (SMWs) in this new type of solar wind compressible turbulence. The counter-propagating AWs and SWs correspond, respectively, to the dominant and sub-dominant populations of the imbalanced Elsässer variables. Nonlinear interactions between the AWs and SMWs are inferred from the non-orthogonality between the possible oscillation direction of one wave and the possible propagation direction of the other. The associated protons are revealed to exhibit bi-directional asymmetric beams in their velocity distributions: sunward beams appear in short, narrow patterns and anti-sunward in broad extended tails. It is suggested that multiple types of wave–particle interactions, i.e., cyclotron and Landau resonances with AWs and SMWs at kinetic scales, are taking place to jointly heat the protons perpendicular and in parallel.
NASA Technical Reports Server (NTRS)
Embleton, Tony F. W.; Daigle, Gilles A.
1991-01-01
Reviewed here is the current state of knowledge with respect to each basic mechanism of sound propagation in the atmosphere and how each mechanism changes the spectral or temporal characteristics of the sound received at a distance from the source. Some of the basic processes affecting sound wave propagation which are present in any situation are discussed. They are geometrical spreading, molecular absorption, and turbulent scattering. In geometrical spreading, sound levels decrease with increasing distance from the source; there is no frequency dependence. In molecular absorption, sound energy is converted into heat as the sound wave propagates through the air; there is a strong dependence on frequency. In turbulent scattering, local variations in wind velocity and temperature induce fluctuations in phase and amplitude of the sound waves as they propagate through an inhomogeneous medium; there is a moderate dependence on frequency.
2003-09-30
Electro - Optic Propagation Stephen Doss-Hammel SPAWARSYSCEN San Diego code 2858 49170 Propagation Path San Diego, CA 92152-7385 phone: (619...scenarios to extend the capabilities of TAWS to surface and low altitude situations. OBJECTIVES The electro - optical propagation objectives are: 1...development of a new propagation assessment tool called EOSTAR ( Electro - Optical Signal Transmission and Ranging). The goal of the EOSTAR project is to
Simulation of Magnetic Cloud Erosion and Deformation During Propagation
NASA Astrophysics Data System (ADS)
Manchester, W.; Kozyra, J. U.; Lepri, S. T.; Lavraud, B.; Jackson, B. V.
2013-12-01
We examine a three-dimensional (3-D) numerical magnetohydrodynamic (MHD) simulation describing a very fast interplanetary coronal mass ejection (ICME) propagating from the solar corona to 1 AU. In conjunction with it's high speed, the ICME evolves in ways that give it a unique appearance at 1AU that does not resemble a typical ICME. First, as the ICME decelerates in the solar wind, filament material at the back of the flux rope pushes its way forward through the flux rope. Second, diverging nonradial flows in front of the filament transport azimuthal flux of the rope to the sides of the ICME. Third, the magnetic flux rope reconnects with the interplanetary magnetic field (IMF). As a consequence of these processes, the flux rope partially unravels and appears to evolve to an entirely open configuration near its nose. At the same time, filament material at the base of the flux rope moves forward and comes in direct contact with the shocked plasma in the CME sheath. We find evidence such remarkable behavior has occurred when we examine a very fast CME that erupted from the Sun on 2005 January 20. In situ observations of this event near 1 AU show very dense cold material impacting the Earth following immediately behind the CME sheath. Charge state analysis shows this dense plasma is filament material, and the analysis of SMEI data provides the trajectory of this dense plasma from the Sun. Consistent with the simulation, we find the azimuthal flux (Bz) to be entirely unbalanced giving the appearance that the flux rope has completely eroded on the anti-sunward side.
NASA Technical Reports Server (NTRS)
Wakana, Hiromitsu
1991-01-01
L-band propagation measurements for land-mobile, maritime, and aeronautical satellite communications have been carried out by using the Japanese Engineering Test Satellite-Five (ETS-5) which was launched in Aug. 1987. This paper presents propagation characteristics for each of the mobile satellite communication channels.
NASA Propagation Information Center
NASA Technical Reports Server (NTRS)
Smith, Ernest K.; Flock, Warren L.
1989-01-01
The NASA Propagation Information Center became formally operational in July 1988. It is located in the Department of Electrical and Computer Engineering of the University of Colorado at Boulder. The Center is several things: a communications medium for the propagation with the outside world, a mechanism for internal communication within the program, and an aid to management.
2016-06-07
Shallow- Water Propagation William L. Siegmann Rensselaer Polytechnic Institute 110 Eighth Street Troy, New York 12180-3590 phone: (518) 276...ocean_acoustics LONG-TERM GOALS Develop methods for propagation and coherence calculations in complex shallow- water environments, determine...intensity and coherence. APPROACH (A) Develop high accuracy PE techniques for applications to shallow- water sediments, accounting for
Millimeter wavelength propagation studies
NASA Technical Reports Server (NTRS)
Hodge, D. B.
1974-01-01
The investigations conducted for the Millimeter Wavelength Propagation Studies during the period December, 1966, to June 1974 are reported. These efforts included the preparation for the ATS-5 Millimeter Wavelength Propagation Experiment and the subsequent data acquisition and data analysis. The emphasis of the OSU participation in this experiment was placed on the determination of reliability improvement resulting from the use of space diversity on a millimeter wavelength earth-space communication link. Related measurements included the determination of the correlation between radiometric temperature and attenuation along the earth-space propagation path. Along with this experimental effort a theoretical model was developed for the prediction of attenuation statistics on single and spatially separated earth space propagation paths. A High Resolution Radar/Radiometer System and Low Resolution Radar System were developed and implemented for the study of intense rain cells in preparation for the ATS-6 Millimeter Wavelength Propagation Experiment.
Gear crack propagation investigations
NASA Technical Reports Server (NTRS)
Lewicki, David G.; Ballarini, Roberto
1996-01-01
Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.
Gear Crack Propagation Investigation
NASA Technical Reports Server (NTRS)
1995-01-01
Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios
Propagation of Environmental Noise
ERIC Educational Resources Information Center
Lyon, R. H.
1973-01-01
Solutions for environmental noise pollution lie in systematic study of many basic processes such as reflection, scattering, and spreading. Noise propagation processes should be identified in different situations and assessed for their relative importance. (PS)
McCandless, Kathleen; Petersson, Anders; Nilsson, Stefan; Sjogreen, Bjorn
2007-01-08
WPP is a massively parallel, 3D, C++, finite-difference elastodynamic wave propagation code. Typical applications for wave propagation with WPP include: evaluation of seismic event scenarios and damage from earthquakes, non-destructive evaluation of materials, underground facility detection, oil and gas exploration, predicting the electro-magnetic fields in accelerators, and acoustic noise generation. For more information, see Users Manual [1].
NASA Astrophysics Data System (ADS)
Urrutxua, H.; Sanjurjo-Rivo, M.; Peláez, J.
2013-12-01
In year 2000 a house-made orbital propagator was developed by the SDGUPM (former Grupo de Dinámica de Tethers) based in a set of redundant variables including Euler parameters. This propagator was called DROMO. and it was mainly used in numerical simulations of electrodynamic tethers. It was presented for the first time in the international meeting V Jornadas de Trabajo en Mecánica Celeste, held in Albarracín, Spain, in 2002 (see reference 1). The special perturbation method associated with DROMO can be consulted in the paper.2 In year 1975, Andre Deprit in reference 3 proposes a propagation scheme very similar to the one in which DROMO is based, by using the ideal frame concept of Hansen. The different approaches used in references 3 and 2 gave rise to a small controversy. In this paper we carried out a different deduction of the DROMO propagator, underlining its close relation with the Hansen ideal frame concept, and also the similarities and the differences with the theory carried out by Deprit in 3. Simultaneously we introduce some improvements in the formulation that leads to a more synthetic propagator.
Elevated Temperature Crack Propagation
NASA Technical Reports Server (NTRS)
Orange, Thomas W.
1994-01-01
This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.
Elevated temperature crack propagation
Orange, T.W.
1994-02-01
This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.
Turbofan Duct Propagation Model
NASA Technical Reports Server (NTRS)
Lan, Justin H.; Posey, Joe W. (Technical Monitor)
2001-01-01
The CDUCT code utilizes a parabolic approximation to the convected Helmholtz equation in order to efficiently model acoustic propagation in acoustically treated, complex shaped ducts. The parabolic approximation solves one-way wave propagation with a marching method which neglects backwards reflected waves. The derivation of the parabolic approximation is presented. Several code validation cases are given. An acoustic lining design process for an example aft fan duct is discussed. It is noted that the method can efficiently model realistic three-dimension effects, acoustic lining, and flow within the computational capabilities of a typical computer workstation.
NASA Astrophysics Data System (ADS)
Urrutxua, Hodei; Sanjurjo-Rivo, Manuel; Peláez, Jesús
2016-01-01
In the year 2000 an in-house orbital propagator called DROMO (Peláez et al. in Celest Mech Dyn Astron 97:131-150, 2007. doi: 10.1007/s10569-006-9056-3) was developed by the Space Dynamics Group of the Technical University of Madrid, based in a set of redundant variables including Euler-Rodrigues parameters. An original deduction of the DROMO propagator is carried out, underlining its close relation with the ideal frame concept introduced by Hansen (Abh der Math-Phys Cl der Kon Sachs Ges der Wissensch 5:41-218, 1857). Based on the very same concept, Deprit (J Res Natl Bur Stand Sect B Math Sci 79B(1-2):1-15, 1975) proposed a formulation for orbit propagation. In this paper, similarities and differences with the theory carried out by Deprit are analyzed. Simultaneously, some improvements are introduced in the formulation, that lead to a more synthetic and better performing propagator. Also, the long-term effect of the oblateness of the primary is studied in terms of DROMO variables, and new numerical results are presented to evaluate the performance of the method.
PROPER: Optical propagation routines
NASA Astrophysics Data System (ADS)
Krist, John E.
2014-05-01
PROPER simulates the propagation of light through an optical system using Fourier transform algorithms (Fresnel, angular spectrum methods). Distributed as IDL source code, it includes routines to create complex apertures, aberrated wavefronts, and deformable mirrors. It is especially useful for the simulation of high contrast imaging telescopes (extrasolar planet imagers like TPF).
NASA Technical Reports Server (NTRS)
Nessel, James
2013-01-01
NASA Glenn Research Center has been involved in the characterization of atmospheric effects on space communications links operating at Ka-band and above for the past 20 years. This presentation reports out on the most recent activities of propagation characterization that NASA is currently involved in.
A Database for Propagation Models
NASA Technical Reports Server (NTRS)
Kantak, Anil V.; Rucker, James
1997-01-01
The Propagation Models Database is designed to allow the scientists and experimenters in the propagation field to process their data through many known and accepted propagation models. The database is an Excel 5.0 based software that houses user-callable propagation models of propagation phenomena. It does not contain a database of propagation data generated out of the experiments. The database not only provides a powerful software tool to process the data generated by the experiments, but is also a time- and energy-saving tool for plotting results, generating tables and producing impressive and crisp hard copy for presentation and filing.
Propagating Instabilities in Solids
NASA Astrophysics Data System (ADS)
Kyriakides, Stelios
1998-03-01
Instability is one of the factors which limit the extent to which solids can be loaded or deformed and plays a pivotal role in the design of many structures. Such instabilities often result in localized deformation which precipitates catastrophic failure. Some materials have the capacity to recover their stiffness following a certain amount of localized deformation. This local recovery in stiffness arrests further local deformation and spreading of the instability to neighboring material becomes preferred. Under displacement controlled loading the propagation of the transition fronts can be achieved in a steady-state manner at a constant stress level known as the propagation stress. The stresses in the transition fronts joining the highly deformed zone to the intact material overcome the instability nucleation stresses and, as a result, the propagation stress is usually much lower than the stress required to nucleate the instability. The classical example of this class of material instabilities is L/"uders bands which tend to affect mild steels and other metals. Recent work has demonstrated that propagating instabilities occur in several other materials. Experimental and analytical results from four examples will be used to illustrate this point: First the evolution of L=FCders bands in mild steel strips will be revisited. The second example involves the evolution of stress induced phase transformations (austenite to martensite phases and the reverse) in a shape memory alloy under displacement controlled stretching. The third example is the crushing behavior of cellular materials such as honeycombs and foams made from metals and polymers. The fourth example involves the axial broadening/propagation of kink bands in aligned fiber/matrix composites under compression. The microstructure and, as a result, the micromechanisms governing the onset, localization, local arrest and propagation of instabilities in each of the four materials are vastly different. Despite this
NASA Technical Reports Server (NTRS)
Cook, R. K.
1969-01-01
The propagation of sound waves at infrasonic frequencies (oscillation periods 1.0 - 1000 seconds) in the atmosphere is being studied by a network of seven stations separated geographically by distances of the order of thousands of kilometers. The stations measure the following characteristics of infrasonic waves: (1) the amplitude and waveform of the incident sound pressure, (2) the direction of propagation of the wave, (3) the horizontal phase velocity, and (4) the distribution of sound wave energy at various frequencies of oscillation. Some infrasonic sources which were identified and studied include the aurora borealis, tornadoes, volcanos, gravity waves on the oceans, earthquakes, and atmospheric instability waves caused by winds at the tropopause. Waves of unknown origin seem to radiate from several geographical locations, including one in the Argentine.
NASA Technical Reports Server (NTRS)
Helmken, Henry; Henning, Rudolf
1994-01-01
One of the key goals of the Florida Center is to obtain a maximum of useful information on propagation behavior unique to its subtropical weather and subtropical climate. Such weather data is of particular interest when it is (or has the potential to become) useful for developing and implementing techniques to compensate for adverse weather effects. Also discussed are data observations, current challenges, CDF's, sun movement, and diversity experiments.
Transionospheric Propagation Code (TIPC)
Roussel-Dupre, R.; Kelley, T.A.
1990-10-01
The Transionospheric Propagation Code is a computer program developed at Los Alamos National Lab to perform certain tasks related to the detection of vhf signals following propagation through the ionosphere. The code is written in Fortran 77, runs interactively and was designed to be as machine independent as possible. A menu format in which the user is prompted to supply appropriate parameters for a given task has been adopted for the input while the output is primarily in the form of graphics. The user has the option of selecting from five basic tasks, namely transionospheric propagation, signal filtering, signal processing, DTOA study, and DTOA uncertainty study. For the first task a specified signal is convolved against the impulse response function of the ionosphere to obtain the transionospheric signal. The user is given a choice of four analytic forms for the input pulse or of supplying a tabular form. The option of adding Gaussian-distributed white noise of spectral noise to the input signal is also provided. The deterministic ionosphere is characterized to first order in terms of a total electron content (TEC) along the propagation path. In addition, a scattering model parameterized in terms of a frequency coherence bandwidth is also available. In the second task, detection is simulated by convolving a given filter response against the transionospheric signal. The user is given a choice of a wideband filter or a narrowband Gaussian filter. It is also possible to input a filter response. The third task provides for quadrature detection, envelope detection, and three different techniques for time-tagging the arrival of the transionospheric signal at specified receivers. The latter algorithms can be used to determine a TEC and thus take out the effects of the ionosphere to first order. Task four allows the user to construct a table of delta-times-of-arrival (DTOAs) vs TECs for a specified pair of receivers.
2009-02-09
of parameters. Hence one expects that the solutions of the two equations , PES and NLS, are comparable. In Fig. 3 we plot the two solutions for...power saturated term, in the PES equation ) have stable soliton solutions or mode-locking evolution. In general the solitons are found to be unstable...literature. Generally speaking, the above lattice equations omitting nonlinear terms have solutions propagating along z direction, i.e., ψ(r, z) = e−iµzϕ(r
Olympus propagation experiments
NASA Technical Reports Server (NTRS)
Arbesser-Rastburg, Bertram
1994-01-01
A summary of the activities of the OPEX (Olympus Propagation EXperimenters) group is given and some of the recent findings are presented. OLYMPUS, a telecommunication satellite owned by the European Space Agency, was launched on 12 June 1989. After the in-orbit tests were completed (in September 1989) the first propagation experiments started. Throughout 1990 the spacecraft functioned very well and a large number of experimenters received the beacon signals. On 29 May 1991 the spacecraft became inoperational after a major technical problem. With a series of complicated procedures OLYMPUS was recovered on 15 August 1991 - the first time in history that a civilian telecommunications satellite was brought back to service after losing power and telemetry. The propagation experiments were back on track. However, the recovery had used up so much fuel that the North-South station keeping had to be abandoned, which led to a natural increase of inclination at a rate of about 0.8 deg per year. On 10 October 1992 the second 30 GHz beacon tube failed, causing a loss of this beacon signal. The other two beacon frequencies continued to deliver a stable signal for more than two years. On 12 August 1993 the spacecraft experienced another problem with the altitude control, but this time there was not enough fuel left for a recovery maneuver and thus the mission came to an end.
Temporal scaling in information propagation
NASA Astrophysics Data System (ADS)
Huang, Junming; Li, Chao; Wang, Wen-Qiang; Shen, Hua-Wei; Li, Guojie; Cheng, Xue-Qi
2014-06-01
For the study of information propagation, one fundamental problem is uncovering universal laws governing the dynamics of information propagation. This problem, from the microscopic perspective, is formulated as estimating the propagation probability that a piece of information propagates from one individual to another. Such a propagation probability generally depends on two major classes of factors: the intrinsic attractiveness of information and the interactions between individuals. Despite the fact that the temporal effect of attractiveness is widely studied, temporal laws underlying individual interactions remain unclear, causing inaccurate prediction of information propagation on evolving social networks. In this report, we empirically study the dynamics of information propagation, using the dataset from a population-scale social media website. We discover a temporal scaling in information propagation: the probability a message propagates between two individuals decays with the length of time latency since their latest interaction, obeying a power-law rule. Leveraging the scaling law, we further propose a temporal model to estimate future propagation probabilities between individuals, reducing the error rate of information propagation prediction from 6.7% to 2.6% and improving viral marketing with 9.7% incremental customers.
Temporal scaling in information propagation.
Huang, Junming; Li, Chao; Wang, Wen-Qiang; Shen, Hua-Wei; Li, Guojie; Cheng, Xue-Qi
2014-06-18
For the study of information propagation, one fundamental problem is uncovering universal laws governing the dynamics of information propagation. This problem, from the microscopic perspective, is formulated as estimating the propagation probability that a piece of information propagates from one individual to another. Such a propagation probability generally depends on two major classes of factors: the intrinsic attractiveness of information and the interactions between individuals. Despite the fact that the temporal effect of attractiveness is widely studied, temporal laws underlying individual interactions remain unclear, causing inaccurate prediction of information propagation on evolving social networks. In this report, we empirically study the dynamics of information propagation, using the dataset from a population-scale social media website. We discover a temporal scaling in information propagation: the probability a message propagates between two individuals decays with the length of time latency since their latest interaction, obeying a power-law rule. Leveraging the scaling law, we further propose a temporal model to estimate future propagation probabilities between individuals, reducing the error rate of information propagation prediction from 6.7% to 2.6% and improving viral marketing with 9.7% incremental customers.
Transport with Feynman propagators
White, R.H.
1990-11-06
Richard Feynman's formulation of quantum electrodynamics suggests a Monte Carlo algorithm for calculating wave propagation. We call this the Sum Over All Paths (SOAP) method. The method is applied to calculate diffraction by double slits of finite width and by a reflection grating. Calculations of reflection by plane and parabolic mirrors of finite aperture and from several figured surfaces are shown. An application to a one-dimensional scattering problem is discussed. A variation of SOAP can be applied to the diffusion equation. 2 refs., 8 figs.
Beam Propagation Experimental Study.
1982-03-01
30- -40- -50 I 0 100 200 300 Time (ns) Figure 2. FX-100 diode voltage and current. The gas- insulated coax was charged to 4.2 MV in order to produce...limit the usable gradient. The voltage standoff capability will be further limited by electron bombardment of the insulators , which may lead to flashover ...the low-pressure window for stable propagation has been inferred from measurements of the time delay for the beam arrival at a given axial position. 8
Desertification by front propagation?
Zelnik, Yuval R; Uecker, Hannes; Feudel, Ulrike; Meron, Ehud
2017-04-07
Understanding how desertification takes place in different ecosystems is an important step in attempting to forecast and prevent such transitions. Dryland ecosystems often exhibit patchy vegetation, which has been shown to be an important factor on the possible regime shifts that occur in arid regions in several model studies. In particular, both gradual shifts that occur by front propagation, and abrupt shifts where patches of vegetation vanish at once, are a possibility in dryland ecosystems due to their emergent spatial heterogeneity. However, recent theoretical work has suggested that the final step of desertification - the transition from spotted vegetation to bare soil - occurs only as an abrupt shift, but the generality of this result, and its underlying origin, remain unclear. We investigate two models that detail the dynamics of dryland vegetation using a markedly different functional structure, and find that in both models the final step of desertification can only be abrupt. Using a careful numerical analysis, we show that this behavior is associated with the disappearance of confined spot-pattern domains as stationary states, and identify the mathematical origin of this behavior. Our findings show that a gradual desertification to bare soil due to a front propagation process can not occur in these and similar models, and opens the question of whether these dynamics can take place in nature.
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.
NASA Technical Reports Server (NTRS)
Bringi, V. N.; Chandrasekar, V.; Mueller, Eugene A.; Turk, Joseph; Beaver, John; Helmken, Henry F.; Henning, Rudy
1993-01-01
Papers on Ka-band propagation measurements using the ACTS propagation terminal and the Colorado State University CHILL multiparameter radar and on Space Communications Technology Center Florida Propagation Program are discussed. Topics covered include: microwave radiative transfer and propagation models; NASA propagation terminal status; ACTS channel characteristics; FAU receive only terminal; FAU terminal status; and propagation testbed.
Retroelements: propagation and adaptation.
Hull, R; Covey, S N
1995-01-01
Retroelements are genetic entities that exist in both DNA and RNA forms generated by cyclic alternation of transcription and reverse transcription. They have in common a genetic core (the gag-pol core), encoding conserved functions of a structural protein and a replicase. These are supplemented with a variety of cis-acting nucleic acid sequences controlling transcription and reverse transcription. Most retroelements have additional genes with regulatory or adaptive roles, both within the cell and for movement between cells and organisms. These features reflect the variety of mechanisms that have developed to ensure propagation of the elements and their ability to adapt to specific niches in their hosts with which they co-evolve.
Gauge engineering and propagators
NASA Astrophysics Data System (ADS)
Maas, Axel
2017-03-01
Beyond perturbation theory gauge-fixing becomes more involved due to the Gribov-Singer ambiguity: The appearance of additional gauge copies requires to define a procedure how to handle them. For the case of Landau gauge the structure and properties of these additional gauge copies will be investigated. Based on these properties gauge conditions are constructed to account for these gauge copies. The dependence of the propagators on the choice of these complete gauge-fixings will then be investigated using lattice gauge theory for Yang-Mills theory. It is found that the implications for the infrared, and to some extent mid-momentum behavior, can be substantial. In going beyond the Yang-Mills case it turns out that the influence of matter can generally not be neglected. This will be briefly discussed for various types of matter.
ACTS mobile propagation campaign
NASA Technical Reports Server (NTRS)
Goldhirsh, Julius; Vogel, Wolfhard J.; Torrence, Geoffrey W.
1994-01-01
Preliminary results are presented for three propagation measurement campaigns involving a mobile receiving laboratory and 20 GHz transmissions from the Advanced Communications Technology Satellite (ACTS). Four 1994 campaigns were executed during weekly periods in and around Austin, Texas in February and May, in Central Maryland during March, and in Fairbanks, Alaska and environs in June. Measurements tested the following effects at 20 GHz: (1) attenuation due to roadside trees with and without foliage, (2) multipath effects for scenarios in which line-of-sight paths were unshadowed, (3) fades due to terrain and roadside obstacles, (4) fades due to structures in urban environs, (5) single tree attenuation, and (6) effects of fading at low elevation angles (8 deg in Fairbanks, Alaska) and high elevation angles (55 deg in Austin, Texas). Results presented here cover sampled measurements in Austin, Texas for foliage and non-foliage cases and in Central Maryland for non-foliage runs.
Propagation Terminal Design and Measurements
NASA Technical Reports Server (NTRS)
Nessel, James
2015-01-01
The NASA propagation terminal has been designed and developed by the Glenn Research Center and is presently deployed at over 5 NASA and partner ground stations worldwide collecting information on the effects of the atmosphere on Ka-band and millimeter wave communications links. This lecture provides an overview of the fundamentals and requirements of the measurement of atmospheric propagation effects and, specifically, the types of hardware and digital signal processing techniques employed by current state-of-the-art propagation terminal systems.
Interferometric Propagation Delay
NASA Technical Reports Server (NTRS)
Goldstein, Richard
1999-01-01
Radar interferometry based on (near) exact repeat passes has lately been used by many groups of scientists, worldwide, to achieve state of the art measurements of topography, glacier and ice stream motion, earthquake displacements, oil field subsidence, lava flows, crop-induced surface decorrelation, and other effects. Variations of tropospheric and ionospheric propagation delays limit the accuracy of all such measurements. We are investigating the extent of this limitation, using data from the Shuttle radar flight, SIR-C, which is sensitive to the troposphere, and the Earth Resources Satellites, ERS-1/2, which are sensitive to both the troposphere and the ionosphere. We are presently gathering statistics of the delay variations over selected, diverse areas to determine the best accuracy possible for repeat track interferometry. The phases of an interferogram depend on both the topography of the scene and variations in propagation delay. The delay variations can be caused by movement of elements in the scene, by changes in tropospheric water vapor and by changes of the charge concentrations in the ionosphere. We plan to separate these causes by using the data from a third satellite visit (three-pass interferometry). The figure gives the geometry of the three-pass observations. The page of the figure is taken to be perpendicular to the spacecraft orbits. The three observational locations are marked on the figure, giving baselines B-12 and B-13, separated by the angle alpha. These parameters are almost constant over the whole scene. However, each pixel has an individual look angle, theta, which is related to the topography, rho is the slant range. A possible spurious time delay is shown. Additional information is contained in the original.
Join-Graph Propagation Algorithms
Mateescu, Robert; Kask, Kalev; Gogate, Vibhav; Dechter, Rina
2010-01-01
The paper investigates parameterized approximate message-passing schemes that are based on bounded inference and are inspired by Pearl's belief propagation algorithm (BP). We start with the bounded inference mini-clustering algorithm and then move to the iterative scheme called Iterative Join-Graph Propagation (IJGP), that combines both iteration and bounded inference. Algorithm IJGP belongs to the class of Generalized Belief Propagation algorithms, a framework that allowed connections with approximate algorithms from statistical physics and is shown empirically to surpass the performance of mini-clustering and belief propagation, as well as a number of other state-of-the-art algorithms on several classes of networks. We also provide insight into the accuracy of iterative BP and IJGP by relating these algorithms to well known classes of constraint propagation schemes. PMID:20740057
Modeling turbulent flame propagation
Ashurst, W.T.
1994-08-01
Laser diagnostics and flow simulation techniques axe now providing information that if available fifty years ago, would have allowed Damkoehler to show how turbulence generates flame area. In the absence of this information, many turbulent flame speed models have been created, most based on Kolmogorov concepts which ignore the turbulence vortical structure, Over the last twenty years, the vorticity structure in mixing layers and jets has been shown to determine the entrainment and mixing behavior and these effects need to be duplicated by combustion models. Turbulence simulations reveal the intense vorticity structure as filaments and simulations of passive flamelet propagation show how this vorticity Creates flame area and defines the shape of the expected chemical reaction surface. Understanding how volume expansion interacts with flow structure should improve experimental methods for determining turbulent flame speed. Since the last decade has given us such powerful new tools to create and see turbulent combustion microscopic behavior, it seems that a solution of turbulent combustion within the next decade would not be surprising in the hindsight of 2004.
Kocia, Lucas; Heller, Eric J
2015-09-28
We offer a more formal justification for the successes of our recently communicated "directed Heller-Herman-Kluk-Kay" (DHK) time propagator by examining its performance in one-dimensional bound systems which exhibit at least quasi-periodic motion. DHK is distinguished by its single one-dimensional integral--a vast simplification over the usual 2N-dimensional integral in full Heller-Herman-Kluk-Kay (for an N-dimensional system). We find that DHK accurately captures particular coherent state autocorrelations when its single integral is chosen to lie along these states' fastest growing manifold, as long as it is not perpendicular to their action gradient. Moreover, the larger the action gradient, the better DHK will perform. We numerically examine DHK's accuracy in a one-dimensional quartic oscillator and illustrate that these conditions are frequently satisfied such that the method performs well. This lends some explanation for why DHK frequently seems to work so well and suggests that it may be applicable to systems exhibiting quite strong anharmonicity.
NASA Astrophysics Data System (ADS)
Kocia, Lucas; Heller, Eric J.
2015-09-01
We offer a more formal justification for the successes of our recently communicated "directed Heller-Herman-Kluk-Kay" (DHK) time propagator by examining its performance in one-dimensional bound systems which exhibit at least quasi-periodic motion. DHK is distinguished by its single one-dimensional integral—a vast simplification over the usual 2N-dimensional integral in full Heller-Herman-Kluk-Kay (for an N-dimensional system). We find that DHK accurately captures particular coherent state autocorrelations when its single integral is chosen to lie along these states' fastest growing manifold, as long as it is not perpendicular to their action gradient. Moreover, the larger the action gradient, the better DHK will perform. We numerically examine DHK's accuracy in a one-dimensional quartic oscillator and illustrate that these conditions are frequently satisfied such that the method performs well. This lends some explanation for why DHK frequently seems to work so well and suggests that it may be applicable to systems exhibiting quite strong anharmonicity.
NA
2002-03-04
The purpose of this Analysis and Model Report (AMR) supporting the Site Recommendation/License Application (SR/LA) for the Yucca Mountain Project is the development of elementary analyses of the interactions of a hypothetical dike with a repository drift (i.e., tunnel) and with the drift contents at the potential Yucca Mountain repository. This effort is intended to support the analysis of disruptive events for Total System Performance Assessment (TSPA). This AMR supports the Process Model Report (PMR) on disruptive events (CRWMS M&O 2000a). This purpose is documented in the development plan (DP) ''Coordinate Modeling of Dike Propagation Near Drifts Consequences for TSPA-SR/LA'' (CRWMS M&O 2000b). Evaluation of that Development Plan and the work to be conducted to prepare Interim Change Notice (ICN) 1 of this report, which now includes the design option of ''Open'' drifts, indicated that no revision to that DP was needed. These analyses are intended to provide reasonable bounds for a number of expected effects: (1) Temperature changes to the waste package from exposure to magma; (2) The gas flow available to degrade waste containers during the intrusion; (3) Movement of the waste package as it is displaced by the gas, pyroclasts and magma from the intruding dike (the number of packages damaged); (4) Movement of the backfill (Backfill is treated here as a design option); (5) The nature of the mechanics of the dike/drift interaction. These analyses serve two objectives: to provide preliminary analyses needed to support evaluation of the consequences of an intrusive event and to provide a basis for addressing some of the concerns of the Nuclear Regulatory Commission (NRC) expressed in the Igneous Activity Issue Resolution Status Report.
Review of aircraft noise propagation
NASA Technical Reports Server (NTRS)
Putnam, T. W.
1975-01-01
The current state of knowledge about the propagation of aircraft noise was reviewed. The literature on the subject is surveyed and methods for predicting the most important and best understood propagation effects are presented. Available empirical data are examined and the data's general validity is assessed. The methods used to determine the loss of acoustic energy due to uniform spherical spreading, absorption in a homogeneous atmosphere, and absorption due to ground cover are presented. A procedure for determining ground induced absorption as a function of elevation angle between source and receiver is recommended. Other factors that affect propagation, such as refraction and scattering due to turbulence, which were found to be less important for predicting the propagation of aircraft noise, are also evaluated.
Photon propagator for axion electrodynamics
Itin, Yakov
2007-10-15
The axion modified electrodynamics is usually used as a model for description of possible violation of Lorentz invariance in field theory. The low-energy manifestation of Lorentz violation can hopefully be observed in experiments with electromagnetic waves. It justifies the importance of studying how a small axion addition can modify the wave propagation. Although a constant axion does not contribute to the dispersion relation at all, even a slowly varying axion field destroys the light cone structure. In this paper, we study the wave propagation in the axion modified electrodynamics in the framework of the premetric approach. In addition to the modified dispersion relation, we derive the axion generalization of the photon propagator in Feynman and Landau gauge. Our consideration is free of the usual restriction to the constant gradient axion field. It is remarkable that the axion modified propagator is Hermitian. Consequently, the dissipation effects are absent even in the phenomenological model considered here.
Propagation Limitations in Remote Sensing.
Contents: Multi-sensors and systems in remote sensing ; Radar sensing systems over land; Remote sensing techniques in oceanography; Influence of...propagation media and background; Infrared techniques in remote sensing ; Photography in remote sensing ; Analytical studies in remote sensing .
A database for propagation models
NASA Technical Reports Server (NTRS)
Kantak, Anil V.; Suwitra, Krisjani S.
1992-01-01
In June 1991, a paper at the fifteenth NASA Propagation Experimenters Meeting (NAPEX 15) was presented outlining the development of a database for propagation models. The database is designed to allow the scientists and experimenters in the propagation field to process their data through any known and accepted propagation model. The architecture of the database also incorporates the possibility of changing the standard models in the database to fit the scientist's or the experimenter's needs. The database not only provides powerful software to process the data generated by the experiments, but is also a time- and energy-saving tool for plotting results, generating tables, and producing impressive and crisp hard copy for presentation and filing.
Reconstruction of nonlinear wave propagation
Fleischer, Jason W; Barsi, Christopher; Wan, Wenjie
2013-04-23
Disclosed are systems and methods for characterizing a nonlinear propagation environment by numerically propagating a measured output waveform resulting from a known input waveform. The numerical propagation reconstructs the input waveform, and in the process, the nonlinear environment is characterized. In certain embodiments, knowledge of the characterized nonlinear environment facilitates determination of an unknown input based on a measured output. Similarly, knowledge of the characterized nonlinear environment also facilitates formation of a desired output based on a configurable input. In both situations, the input thus characterized and the output thus obtained include features that would normally be lost in linear propagations. Such features can include evanescent waves and peripheral waves, such that an image thus obtained are inherently wide-angle, farfield form of microscopy.
Propagating plasmons on silver nanowires
NASA Astrophysics Data System (ADS)
He, Weidong; Wei, Hong; Li, Zhipeng; Huang, Yingzhou; Fang, Yurui; Li, Ping; Xu, Hongxing
2010-08-01
Chemically synthesized Ag nanowires (NWs) can serve as waveguides to support propagating surface plasmons (SPs). By using the propagating SPs on Ag NWs, the surface-enhanced Raman scattering of molecules, located in the nanowire-nanoparticle junction a few microns away from the laser spot on one end of the NW, was excited. The propagating SPs can excite the excitons in quantum dots, and in reverse, the decay of excitons can generate SPs. The direction and polarization of the light emitted through the Ag NW waveguide. The emission polarization depends strongly on the shape of the NW terminals. In branched NW structures, the SPs can be switched between the main NW and the branch NW, by tuning the incident polarization. The light of different wavelength can also be controlled to propagate along different ways. Thus, the branched NW structure can serve as controllable plasmonic router and multiplexer.
Propagating rifts on midocean ridges
NASA Astrophysics Data System (ADS)
Hey, Richard; Duennebier, Frederick K.; Morgan, W. Jason
1980-07-01
Spreading center jumps identified west of the Galapagos Islands near 95°W occur in a pattern consistent with the propagating rift hypothesis. A new rift is gradually breaking through the Cocos plate. Each successive jump is slightly longer than the preceding jump. The new spreading center grows at a new azimuth toward the west as the old one dies. The jumps are a manifestation of rift propagation. We extend the analysis of propagating rifts to the case of continuous propagation and predict patterns of magnetic anomalies and bathymetry consistent with the observed patterns. In particular, we correctly predict the trends of fossil spreading centers and V patterns of magnetic anomaly offsets required by the propagating rift hypothesis. Similar V patterns have been observed on many other spreading centers and have been interpreted in various ways. The propagating rift hypothesis appears to offer a simple explanation, consistent with rigid plate tectonics, for each of these patterns. This hypothesis may also have important implications for continental rifting.
The physical theory and propagation model of THz atmospheric propagation
NASA Astrophysics Data System (ADS)
Wang, R.; Yao, J. Q.; Xu, D. G.; Wang, J. L.; Wang, P.
2011-02-01
Terahertz (THz) radiation is extensively applied in diverse fields, such as space communication, Earth environment observation, atmosphere science, remote sensing and so on. And the research on propagation features of THz wave in the atmosphere becomes more and more important. This paper firstly illuminates the advantages and outlook of THz in space technology. Then it introduces the theoretical framework of THz atmospheric propagation, including some fundamental physical concepts and processes. The attenuation effect (especially the absorption of water vapor), the scattering of aerosol particles and the effect of turbulent flow mainly influence THz atmosphere propagation. Fundamental physical laws are illuminated as well, such as Lamber-beer law, Mie scattering theory and radiative transfer equation. The last part comprises the demonstration and comparison of THz atmosphere propagation models like Moliere(V5), SARTre and AMATERASU. The essential problems are the deep analysis of physical mechanism of this process, the construction of atmospheric propagation model and databases of every kind of material in the atmosphere, and the standardization of measurement procedures.
The geometry of propagating rifts
NASA Astrophysics Data System (ADS)
McKenzie, Dan
1986-03-01
The kinematics of two different processes are investigated, both of which have been described as rift propagation. Courtillot uses this term to describe the change from distributed to localised extension which occurs during the early development of an ocean basin. The term localisation is instead used here to describe this process, to distinguish it from Hey's type of propagation. Localisation generally leads to rotation of the direction of magnetisation. To Hey propagation means the extension of a rift into the undeformed plate beyond a transform fault. Detail surveys of the Galapagos rift have shown that the propagating and failing rifts are not connected by a single transform fault, but by a zone which is undergoing shear. The principal deformation is simple shear, and the kinematics of this deformation are investigated in some detail. The strike of most of the lineations observed in the area can be produced by such deformation. The mode of extension on the propagating rift appears to be localised for some periods but to be distributed for others. Neither simple kinematic arguments nor stretching of the lithosphere with conservation of crust can account for the observed variations in water depth.
User needs for propagation data
NASA Technical Reports Server (NTRS)
Sullivan, Thomas M.
1993-01-01
New and refined models of radio signal propagation phenomena are needed to support studies of evolving satellite services and systems. Taking an engineering perspective, applications for propagation measurements and models in the context of various types of analyses that are of ongoing interest are reviewed. Problems that were encountered in the signal propagation aspects of these analyses are reviewed, and potential solutions to these problems are discussed. The focus is on propagation measurements and models needed to support design and performance analyses of systems in the Mobile-Satellite Service (MSS) operating in the 1-3 GHz range. These systems may use geostationary or non-geostationary satellites and Frequency Division Multiple Access (FDMA), Time Division Multiple Access Digital (TDMA), or Code Division Multiple Access (CDMA) techniques. Many of the propagation issues raised in relation to MSS are also pertinent to other services such as broadcasting-satellite (sound) at 2310-2360 MHz. In particular, services involving mobile terminals or terminals with low gain antennas are of concern.
Wave propagation in ballistic gelatine.
Naarayan, Srinivasan S; Subhash, Ghatu
2017-01-23
Wave propagation characteristics in long cylindrical specimens of ballistic gelatine have been investigated using a high speed digital camera and hyper elastic constitutive models. The induced transient deformation is modelled with strain rate dependent Mooney-Rivlin parameters which are determined by modelling the stress-strain response of gelatine at a range of strain rates. The varying velocity of wave propagation through the gelatine cylinder is derived as a function of prestress or stretch in the gelatine specimen. A finite element analysis is conducted using the above constitutive model by suitably defining the impulse imparted by the polymer bar into the gelatine specimen. The model results are found to capture the experimentally observed wave propagation characteristics in gelatine effectively.
Dynamical Realism and Uncertainty Propagation
NASA Astrophysics Data System (ADS)
Park, Inkwan
In recent years, Space Situational Awareness (SSA) has become increasingly important as the number of tracked Resident Space Objects (RSOs) continues their growth. One of the most significant technical discussions in SSA is how to propagate state uncertainty in a consistent way with the highly nonlinear dynamical environment. In order to keep pace with this situation, various methods have been proposed to propagate uncertainty accurately by capturing the nonlinearity of the dynamical system. We notice that all of the methods commonly focus on a way to describe the dynamical system as precisely as possible based on a mathematical perspective. This study proposes a new perspective based on understanding dynamics of the evolution of uncertainty itself. We expect that profound insights of the dynamical system could present the possibility to develop a new method for accurate uncertainty propagation. These approaches are naturally concluded in goals of the study. At first, we investigate the most dominant factors in the evolution of uncertainty to realize the dynamical system more rigorously. Second, we aim at developing the new method based on the first investigation enabling orbit uncertainty propagation efficiently while maintaining accuracy. We eliminate the short-period variations from the dynamical system, called a simplified dynamical system (SDS), to investigate the most dominant factors. In order to achieve this goal, the Lie transformation method is introduced since this transformation can define the solutions for each variation separately. From the first investigation, we conclude that the secular variations, including the long-period variations, are dominant for the propagation of uncertainty, i.e., short-period variations are negligible. Then, we develop the new method by combining the SDS and the higher-order nonlinear expansion method, called state transition tensors (STTs). The new method retains advantages of the SDS and the STTs and propagates
Wave equations for pulse propagation
Shore, B.W.
1987-06-24
Theoretical discussions of the propagation of pulses of laser radiation through atomic or molecular vapor rely on a number of traditional approximations for idealizing the radiation and the molecules, and for quantifying their mutual interaction by various equations of propagation (for the radiation) and excitation (for the molecules). In treating short-pulse phenomena it is essential to consider coherent excitation phenomena of the sort that is manifest in Rabi oscillations of atomic or molecular populations. Such processes are not adequately treated by rate equations for excitation nor by rate equations for radiation. As part of a more comprehensive treatment of the coupled equations that describe propagation of short pulses, this memo presents background discussion of the equations that describe the field. This memo discusses the origin, in Maxwell's equations, of the wave equation used in the description of pulse propagation. It notes the separation into lamellar and solenoidal (or longitudinal and transverse) and positive and negative frequency parts. It mentions the possibility of separating the polarization field into linear and nonlinear parts, in order to define a susceptibility or index of refraction and, from these, a phase and group velocity. The memo discusses various ways of characterizing the polarization characteristics of plane waves, that is, of parameterizing a transverse unit vector, such as the Jones vector, the Stokes vector, and the Poincare sphere. It discusses the connection between macroscopically defined quantities, such as the intensity or, more generally, the Stokes parameters, and microscopic field amplitudes. The material presented here is a portion of a more extensive treatment of propagation to be presented separately. The equations presented here have been described in various books and articles. They are collected here as a summary and review of theory needed when treating pulse propagation.
Gap soliton propagation in optical fiber gratings
NASA Astrophysics Data System (ADS)
Mohideen, U.; Slusher, R. E.; Mizrahi, V.; Erdogan, T.; Kuwata-Gonokami, M.; Lemaire, P. J.; Sipe, J. E.; Martijn de Sterke, C.; Broderick, Neil G. R.
1995-08-01
Intense optical pulse propagation in a GeO2 -doped silica glass fiber grating results in nonlinear pulse propagation velocities and increased transmission at wavelengths where the grating reflects light in the linear limit. These nonlinear pulse propagation effects are predicted by numerical simulations of gap soliton propagation. The large linear refractive-index variations used for the fiber gratings in these experiments permit the propagation of gap solitons in short lengths of fiber.
Propagators in polymer quantum mechanics
NASA Astrophysics Data System (ADS)
Flores-González, Ernesto; Morales-Técotl, Hugo A.; Reyes, Juan D.
2013-09-01
Polymer Quantum Mechanics is based on some of the techniques used in the loop quantization of gravity that are adapted to describe systems possessing a finite number of degrees of freedom. It has been used in two ways: on one hand it has been used to represent some aspects of the loop quantization in a simpler context, and, on the other, it has been applied to each of the infinite mechanical modes of other systems. Indeed, this polymer approach was recently implemented for the free scalar field propagator. In this work we compute the polymer propagators of the free particle and a particle in a box; amusingly, just as in the non polymeric case, the one of the particle in a box may be computed also from that of the free particle using the method of images. We verify the propagators hereby obtained satisfy standard properties such as: consistency with initial conditions, composition and Green's function character. Furthermore they are also shown to reduce to the usual Schrödinger propagators in the limit of small parameter μ0, the length scale introduced in the polymer dynamics and which plays a role analog of that of Planck length in Quantum Gravity.
Microwave Propagation in Dielectric Fluids.
ERIC Educational Resources Information Center
Lonc, W. P.
1980-01-01
Describes an undergraduate experiment designed to verify quantitatively the effect of a dielectric fluid's dielectric constant on the observed wavelength of microwave radiation propagating through the fluid. The fluid used is castor oil, and results agree with the expected behavior within 5 percent. (Author/CS)
Sound propagation in choked ducts
NASA Technical Reports Server (NTRS)
Hersh, A. S.; Liu, C. Y.
1976-01-01
The linearized equations describing the propagation of sound in variable area ducts containing flow are shown to be singular when the duct mean flow is sonic. The singularity is removed when previously ignored nonlinear terms are retained. The results of a numerical study, for the case of plane waves propagating in a one-dimensional converging-diverging duct, show that the sound field is adequately described by the linearized equations only when the axial mean flow Mach number at the duct throat M sub th 0.6. For M sub th 0.6, the numerical results showed that acoustic energy flux was not conserved. An attempt was made to extend the study to include the nonlinear behavior of the sound field. Meaningful results were not obtained due, primarily, to numerical difficulties.
Exact propagators in harmonic superspace
NASA Astrophysics Data System (ADS)
Kuzenko, Sergei M.
2004-10-01
Within the background field formulation in harmonic superspace for quantum N = 2 super-Yang-Mills theories, the propagators of the matter, gauge and ghost superfields possess a complicated dependence on the SU(2) harmonic variables via the background vector multiplet. This dependence is shown to simplify drastically in the case of an on-shell vector multiplet. For a covariantly constant background vector multiplet, we exactly compute all the propagators. In conjunction with the covariant multi-loop scheme developed in arxiv:hep-th/0302205, these results provide an efficient (manifestly N = 2 supersymmetric) technical setup for computing multi-loop quantum corrections to effective actions in N = 2 supersymmetric gauge theories, including the N = 4 super-Yang-Mills theory.
Atmospheric propagation of THz radiation.
Wanke, Michael Clement; Mangan, Michael A.; Foltynowicz, Robert J.
2005-11-01
In this investigation, we conduct a literature study of the best experimental and theoretical data available for thin and thick atmospheres on THz radiation propagation from 0.1 to 10 THz. We determined that for thick atmospheres no data exists beyond 450 GHz. For thin atmospheres data exists from 0.35 to 1.2 THz. We were successful in using FASE code with the HITRAN database to simulate the THz transmission spectrum for Mauna Kea from 0.1 to 2 THz. Lastly, we successfully measured the THz transmission spectra of laboratory atmospheres at relative humidities of 18 and 27%. In general, we found that an increase in the water content of the atmosphere led to a decrease in the THz transmission. We identified two potential windows in an Albuquerque atmosphere for THz propagation which were the regions from 1.2 to 1.4 THz and 1.4 to 1.6 THz.
Fracture propagation, pipe deformation study
Aloe, A.; Di Candia, A.; Bramante, M.
1983-04-15
Shear fracture propagation has become an important research subject connected with design aspects of gas pipelines. Difficulties involved in predicting safe service conditions from pure theoretical studies require 1:1 scale experiments. Through these tests, semiempirical design criteria was formulated where the minimum level of material quality, indicated by Charpy V energy in the ductile range, is determined as a function of pipe geometry and hoop stress. Disagreements exist among these criteria. Different arrest energy predictions at high hoop stresses and different effects ascribed to the thickness have called for further research in the field. Some interesting indications were obtained about shape and size of the plastic zone ahead of the propagating crack. Burst tests have been conducted and are discussed.
Special Topics in HF Propagation
1979-11-01
data for the prediction of auroral absorption experienced by high-frequency radio waves: Basler (1965), Gorbushina et al. (1969), Agy (1970), Vargas ...Thomas (1959), Studies in polar blackout morphology, URSI-AGI, Com- mittee Report. Vargas -Vila, R. (1972), Auroral absorption predictions for high...cuide wa]ls in mho/m permeability of the propagation medium in henry /m E. permittivity of the propagat.on medium iiu fa-ad/m. For TE. modes, thi-s
A database for propagation models
NASA Technical Reports Server (NTRS)
Kantak, Anil V.; Suwitra, Krisjani; Le, Chuong
1995-01-01
A database of various propagation phenomena models that can be used by telecommunications systems engineers to obtain parameter values for systems design is presented. This is an easy-to-use tool and is currently available for either a PC using Excel software under Windows environment or a Macintosh using Excel software for Macintosh. All the steps necessary to use the software are easy and many times self explanatory.
A database for propagation models
NASA Technical Reports Server (NTRS)
Kantak, Anil V.; Suwitra, Krisjani; Le, Choung
1994-01-01
A database of various propagation phenomena models that can be used by telecommunications systems engineers to obtain parameter values for systems design is presented. This is an easy-to-use tool and is currently available for either a PC using Excel software under Windows environment or a Macintosh using Excel software for Macintosh. All the steps necessary to use the software are easy and many times self-explanatory; however, a sample run of the CCIR rain attenuation model is presented.
A database for propagation models
NASA Astrophysics Data System (ADS)
Kantak, Anil V.; Suwitra, Krisjani; Le, Chuong
1995-08-01
A database of various propagation phenomena models that can be used by telecommunications systems engineers to obtain parameter values for systems design is presented. This is an easy-to-use tool and is currently available for either a PC using Excel software under Windows environment or a Macintosh using Excel software for Macintosh. All the steps necessary to use the software are easy and many times self explanatory.
UHF Radiowave Propagation through Forests
1982-09-01
sde It nece sary and Identify b block number) " A model for UHF radiowave propagation thzough a forest of tree trunks, branches, and leaves is...all having prescribed location and orientation statistics. Tree trunks are modelled as infinitely-long, circular, lossy-di- electric cylinders...results. An anisotropic half-space model of the forest is developed based upon the effective dyadic susceptibility and the direct-, reflected-, and
GOES dynamic propagation of attitude
NASA Technical Reports Server (NTRS)
Markley, F. Landis; Seidewitz, ED; Chu, Don; Rowe, John N.
1988-01-01
The spacecraft in the next series of Geostationary Operational Environmental Satellites (GOES-Next) are Earth pointing and have 5-year mission lifetimes. Because gyros can be depended on only for a few years of continuous use, they will be turned off during routine operations. This means attitude must, at times, be determined without benefit of gyros and, often, using only Earth sensor data. To minimize the interruption caused by dumping angular momentum, these spacecraft have been designed to reduce the environmental torque acting on them and incorporate an adjustable solar trim tab for fine adjustment. A new support requirement for GOES-Next is that of setting the solar trim tab. Optimizing its setting requires an estimate of the unbalanced torque on the spacecraft. These two requirements, determining attitude without gyros and estimating the external torque, are addressed by replacing or supplementing the gyro propagation with a dynamic one, that is, one that integrates the rigid body equations of motion. By processing quarter-orbit or longer batches, this approach takes advantage of roll-yaw coupling to observe attitude completely without Sun sensor data. Telemetered momentum wheel speeds are used as observations of the unbalanced external torques. GOES-Next provides a unique opportunity to study dynamic attitude propagation. The geosynchronous altitude and adjustable trim tab minimize the external torque and its uncertainty, making long-term dynamic propagation feasible. This paper presents the equations for dynamic propagation, an analysis of the environmental torques, and an estimate of the accuracies obtainable with the proposed method.
Jet propagation through energetic materials
Pincosy, P; Poulsen, P
2004-01-08
In applications where jets propagate through energetic materials, they have been observed to become sufficiently perturbed to reduce their ability to effectively penetrate subsequent material. Analytical calculations of the jet Bernoulli flow provides an estimate of the onset and extent of such perturbations. Although two-dimensional calculations show the back-flow interaction pressure pulses, the symmetry dictates that the flow remains axial. In three dimensions the same pressure impulses can be asymmetrical if the jet is asymmetrical. The 3D calculations thus show parts of the jet having a significant component of radial velocity. On the average the downstream effects of this radial flow can be estimated and calculated by a 2D code by applying a symmetrical radial component to the jet at the appropriate position as the jet propagates through the energetic material. We have calculated the 3D propagation of a radio graphed TOW2 jet with measured variations in straightness and diameter. The resultant three-dimensional perturbations on the jet result in radial flow, which eventually tears apart the coherent jet flow. This calculated jet is compared with jet radiographs after passage through the energetic material for various material thickness and plate thicknesses. We noted that confinement due to a bounding metal plate on the energetic material extends the pressure duration and extent of the perturbation.
Turbofan Acoustic Propagation and Radiation
NASA Technical Reports Server (NTRS)
Eversman, Walter
2000-01-01
This document describes progress in the development of finite element codes for the prediction of near and far field acoustic radiation from the inlet and aft fan ducts of turbofan engines. The report consists of nine papers which have appeared in archival journals and conference proceedings, or are presently in review for publication. Topics included are: 1. Aft Fan Duct Acoustic Radiation; 2. Mapped Infinite Wave Envelope Elements for Acoustic Radiation in a Uniformly Moving Medium; 3. A Reflection Free Boundary Condition for Propagation in Uniform Flow Using Mapped Infinite Wave Envelope Elements; 4. A Numerical Comparison Between Multiple-Scales and FEM Solution for Sound Propagation in Lined Flow Ducts; 5. Acoustic Propagation at High Frequencies in Ducts; 6. The Boundary Condition at an Impedance Wall in a Nonuniform Duct with Potential Flow; 7. A Reverse Flow Theorem and Acoustic Reciprocity in Compressible Potential Flows; 8. Reciprocity and Acoustics Power in One Dimensional Compressible Potential Flows; and 9. Numerical Experiments on Acoustic Reciprocity in Compressible Potential Flows.
Sound Propagation in the Atmosphere
NASA Astrophysics Data System (ADS)
Attenborough, Keith
Propagation of sound close to the ground outdoors involves geometric spreading, air absorption, interaction with the ground, barriers, vegetation and refraction associated with wind and temperature gradients. After a brief survey of historical aspects of the study of outdoor sound and its applications, this chapter details the physical principles associated with various propagation effects, reviews data that demonstrate them and methods for predicting them. The discussion is concerned primarily with the relatively short ranges and spectra of interest when predicting and assessing community noise rather than the frequencies and long ranges of concern, for example, in infrasonic global monitoring or used for remote sensing of the atmosphere. Specific phenomena that are discussed include spreading losses, atmospheric absorption, diffraction by barriers and buildings, interaction of sound with the ground (ground waves, surface waves, ground impedance associated with porosity and roughness, and elasticity effects), propagation through crops, shrubs and trees, wind and temperature gradient effects, shadow zones and incoherence due to atmospheric turbulence. The chapter concludes by suggesting a few areas that require further research.
Transequatorial Propagation and Depletion Precursors
NASA Astrophysics Data System (ADS)
Miller, E. S.; Bust, G. S.; Kaeppler, S. R.; Frissell, N. A.; Paxton, L. J.
2014-12-01
The bottomside equatorial ionosphere in the afternoon and evening sector frequently evolves rapidly from smoothly stratified to violently unstable with large wedges of depleted plasma growing through to the topside on timescales of a few tens of minutes. These depletions have numerous practical impacts on radio propagation, including amplitude scintillation, field-aligned irregularity scatter, HF blackouts, and long-distance transequatorial propagation at frequencies above the MUF. Practical impacts notwithstanding, the pathways and conditions under which depletions form remain a topic of vigorous inquiry some 80 years after their first report. Structuring of the pre-sunset ionosphere---morphology of the equatorial anomalies and long-wavelength undulations of the isodensity contours on the bottomside---are likely to hold some clues to conditions that are conducive to depletion formation. The Conjugate Depletion Experiment is an upcoming transequatorial forward-scatter HF/VHF experiment to investigate pre-sunset undulations and their connection with depletion formation. We will present initial results from the Conjugate Depletion Experiment, as well as a companion analysis of a massive HF propagation data set.
Calculations of precursor propagation in dispersive dielectrics.
Bacon, Larry Donald
2003-08-01
The present study is a numerical investigation of the propagation of electromagnetic transients in dispersive media. It considers propagation in water using Debye and composite Rocard-Powles-Lorentz models for the complex permittivity. The study addresses this question: For practical transmitted spectra, does precursor propagation provide any features that can be used to advantage over conventional signal propagation in models of dispersive media of interest? A companion experimental study is currently in progress that will attempt to measure the effects studied here.
Confining crack propagation in defective graphene.
López-Polín, Guillermo; Gómez-Herrero, Julio; Gómez-Navarro, Cristina
2015-03-11
Crack propagation in graphene is essential to understand mechanical failure in 2D materials. We report a systematic study of crack propagation in graphene as a function of defect content. Nanoindentations and subsequent images of graphene membranes with controlled induced defects show that while tears in pristine graphene span microns length, crack propagation is strongly reduced in the presence of defects. Accordingly, graphene oxide exhibits minor crack propagation. Our work suggests controlled defect creation as an approach to avoid catastrophic failure in graphene.
Japanese propagation experiments with ETS-5
NASA Technical Reports Server (NTRS)
Ikegami, Tetsushi
1989-01-01
Propagation experiments for maritime, aeronautical, and land mobile satellite communications were performed using Engineering Test Satellite-Five (ETS-5). The propagation experiments are one of major mission of Experimental Mobile Satellite System (EMSS) which is aimed for establishing basic technology for future general mobile satellite communication systems. A brief introduction is presented for the experimental results on propagation problems of ETS-5/EMSS.
Understanding and Predicting Urban Propagation Losses
2009-09-01
available, the vast variety of physical cond Propagation Loss Tool will also be entered into a variety of examples, to test a few of the propagation loss...Model for Urban Areas. Rep. Silva, Junior, Edgar, and Gilberto A. Carrijo. "A Vectorial Istanbul: Bogazici University. Analysis of UHF Propagation
49 CFR 195.111 - Fracture propagation.
Code of Federal Regulations, 2014 CFR
2014-10-01
... 49 Transportation 3 2014-10-01 2014-10-01 false Fracture propagation. 195.111 Section 195.111... PIPELINE Design Requirements § 195.111 Fracture propagation. A carbon dioxide pipeline system must be designed to mitigate the effects of fracture propagation....
49 CFR 195.111 - Fracture propagation.
Code of Federal Regulations, 2012 CFR
2012-10-01
... 49 Transportation 3 2012-10-01 2012-10-01 false Fracture propagation. 195.111 Section 195.111... PIPELINE Design Requirements § 195.111 Fracture propagation. A carbon dioxide pipeline system must be designed to mitigate the effects of fracture propagation....
49 CFR 195.111 - Fracture propagation.
Code of Federal Regulations, 2013 CFR
2013-10-01
... 49 Transportation 3 2013-10-01 2013-10-01 false Fracture propagation. 195.111 Section 195.111... PIPELINE Design Requirements § 195.111 Fracture propagation. A carbon dioxide pipeline system must be designed to mitigate the effects of fracture propagation....
49 CFR 195.111 - Fracture propagation.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 49 Transportation 3 2011-10-01 2011-10-01 false Fracture propagation. 195.111 Section 195.111... PIPELINE Design Requirements § 195.111 Fracture propagation. A carbon dioxide pipeline system must be designed to mitigate the effects of fracture propagation....
49 CFR 195.111 - Fracture propagation.
Code of Federal Regulations, 2010 CFR
2010-10-01
... 49 Transportation 3 2010-10-01 2010-10-01 false Fracture propagation. 195.111 Section 195.111... PIPELINE Design Requirements § 195.111 Fracture propagation. A carbon dioxide pipeline system must be designed to mitigate the effects of fracture propagation. [Amdt. 195-45, 56 FR 26926, June 12, 1991]...
Cutting line determination for plant propagation
NASA Astrophysics Data System (ADS)
Lo, Li-Yun; Hsia, Chi-Chun; Sun, Hua-Hong; Chen, Hsiang-Ju; Wu, Xin-Ting; Hu, Min-Chun
2014-01-01
Investigating an efficient method for plant propagation can help not only prevent extinction of plants but also facilitate the development of botanical industries. In this paper, we propose to use image processing techniques to determine the cutting-line for the propagation of two kinds of plants, i.e. Melaleuca alternifolia Cheel and Cinnamomum kanehirai Hay, which have quite different characteristics in terms of shape, structure, and propagation way (e.g. propagation by seeding and rooting, respectively). The proposed cutting line determination methods can be further applied to develop an automatic control system to reduce labor cost and increase the effectiveness of plant propagation.
Wave Propagation in Bimodular Geomaterials
NASA Astrophysics Data System (ADS)
Kuznetsova, Maria; Pasternak, Elena; Dyskin, Arcady; Pelinovsky, Efim
2016-04-01
Observations and laboratory experiments show that fragmented or layered geomaterials have the mechanical response dependent on the sign of the load. The most adequate model accounting for this effect is the theory of bimodular (bilinear) elasticity - a hyperelastic model with different elastic moduli for tension and compression. For most of geo- and structural materials (cohesionless soils, rocks, concrete, etc.) the difference between elastic moduli is such that their modulus in compression is considerably higher than that in tension. This feature has a profound effect on oscillations [1]; however, its effect on wave propagation has not been comprehensively investigated. It is believed that incorporation of bilinear elastic constitutive equations within theory of wave dynamics will bring a deeper insight to the study of mechanical behaviour of many geomaterials. The aim of this paper is to construct a mathematical model and develop analytical methods and numerical algorithms for analysing wave propagation in bimodular materials. Geophysical and exploration applications and applications in structural engineering are envisaged. The FEM modelling of wave propagation in a 1D semi-infinite bimodular material has been performed with the use of Marlow potential [2]. In the case of the initial load expressed by a harmonic pulse loading strong dependence on the pulse sign is observed: when tension is applied before compression, the phenomenon of disappearance of negative (compressive) strains takes place. References 1. Dyskin, A., Pasternak, E., & Pelinovsky, E. (2012). Periodic motions and resonances of impact oscillators. Journal of Sound and Vibration, 331(12), 2856-2873. 2. Marlow, R. S. (2008). A Second-Invariant Extension of the Marlow Model: Representing Tension and Compression Data Exactly. In ABAQUS Users' Conference.
Energy propagation throughout chemical networks.
Le Saux, Thomas; Plasson, Raphaël; Jullien, Ludovic
2014-06-14
In order to maintain their metabolism from an energy source, living cells rely on chains of energy transfer involving functionally identified components and organizations. However, propagation of a sustained energy flux through a cascade of reaction cycles has only been recently reproduced at a steady state in simple chemical systems. As observed in living cells, the spontaneous onset of energy-transfer chains notably drives local generation of singular dissipative chemical structures: continuous matter fluxes are dynamically maintained at boundaries between spatially and chemically segregated zones but in the absence of any membrane or predetermined material structure.
LCMV: Propagation, quantitation, and storage
Seedhom, Mina O.
2011-01-01
Lymphocytic choriomeningitis virus (LCMV) is an enveloped ambisense RNA virus and the prototypic virus of the arenavirus group. It can cause viral meningitis and other ailments in humans, but it's natural host is the mouse. The LCMV/mouse model has been useful for examining mechanisms of viral persistence and basic concepts of virus-induced immunity and immunopathology. Here we discuss strain differences and biosafety containment issues for LCMV. Recommendations are made for techniques to propagate LCMV to high titers, to quantify it by plaque assay and PCR techniques, and to preserve its infectivity by appropriate storage. PMID:18770534
ACTS and OLYMPUS propagation experiments
NASA Technical Reports Server (NTRS)
Bostian, Charles W.; Baker, Kenneth R.
1988-01-01
The OLYMPUS and ACTS satellites both provide opportunities for 10 to 30 GHz propagation measurements. The spacecraft are sufficiently alike that OLYMPUS can be used to test some prototype ACTS equipment and experiments. Data are particularly needed on short term signal behavior and in support of uplink power control and adaptive forward error correction (FEC) techniques. The Virginia Tech Satellite Communications Group has proposed a set of OLYMPUS experiments including attenuation and fade rate measurements, data communications, uplink power control, rain scatter interference, and small-scale site diversity operation. A digital signal processing receiver for the OLYMPUS and ACTS beacon signals is being developed.
Mode II fatigue crack propagation.
NASA Technical Reports Server (NTRS)
Roberts, R.; Kibler, J. J.
1971-01-01
Fatigue crack propagation rates were obtained for 2024-T3 bare aluminum plates subjected to in-plane, mode I, extensional loads and transverse, mode II, bending loads. These results were compared to the results of Iida and Kobayashi for in-plane mode I-mode II extensional loads. The engineering significance of mode I-mode II fatigue crack growth is considered in view of the present results. A fatigue crack growth equation for handling mode I-mode II fatigue crack growth rates from existing mode I data is also discussed.
Modeling of Transionospheric Radio Propagation
1975-08-01
sin cpj dcp dq (17) where and VXz = Fresnel-zone radius at scattering layer 2 2 7 (0,0’) = [l + tan e cos (0 - «(*)] ß...y /nai, - 7 «T MODELING OF JRANSIONOSPHKir RADIO PROPAGATION RADI ^ja By: E. J. TREMOUW C L. RINO (£>. Augm IB?5 Prepared for: ROME A|R...following three relationships arise from Eqs. (1) and (2) 2 Ro cos (26) ( 7 ) R [ r. 2 o 0 = y ^ll + ^^cos (26) 2 L
Ultrasound propagation measurements and applications
NASA Technical Reports Server (NTRS)
Lynnworth, L. C.; Papadakis, E. P.; Fowler, K. A.
1977-01-01
This paper reviews three systems designed for accurately measuring the propagation of ultrasonic pulses. The three systems are presented in order of velocity-measuring precision: + or - 100 ns, + or - 1 ns, + or - 0.2 ns. Also included is a brief discussion of phase and group velocities, with reference to dispersive, highly attenuating materials. Measurement of attenuation by pulse-echo buffer rod techniques is described briefly. These techniques and instruments have been used to measure sound velocity and attenuation in a variety of materials and shapes, over a wide temperature range.
Propagation modelling in microcellular environments
NASA Astrophysics Data System (ADS)
Sharples, P. A.; Mehler, M. J.
This paper describes a microcellular model, based on ray tracing techniques. Ray tracing is a stationary phase technique which relies on the quasi-optical properties of radio waves in regions where any obstacles are large in terms of a wavelength. The model described is a very versatile implementation which can be used to study both indoor and outdoor propagation phenomena for a number of different types of service. In its fullest form it requires input data of a sophistication that is not commercially available. However, this allows the model to be used to assess the implications in terms of the achievable accuracy when using commercial building databases.
Light Propagation through Anisotropic Turbulence
2011-03-01
Kolmogorov stratospheric turbulence on star image motion,” Proc. SPIE 3126, 113–123 (1997). 5. B. E . Stribling, B. M . Welsh, and M . C. Roggemann...746407 (2009). 10. M . Chang, C. O. Font, F. Santiago, Y. Luna, E . Roura, and S. Restaino, “Marine environment optical propagation measure- ments,” Proc...Anisotropic factor as a function of alpha for several zeta values. Toselli et al. Vol. 28, No. 3 / March 2011 / J. Opt. Soc. Am. A 487 14. M . S
Continuous propagation of microalgae. III.
NASA Technical Reports Server (NTRS)
Hanson, D. T.; Fredrickson, A. G.; Tsuchiya, H. M.
1971-01-01
Data are presented which give the specific photosynthetic rate and the specific utilization rates of urea and carbon dioxide as functions of specific growth rate for Chlorella. A mathematical model expresses a set of mass balance relations between biotic and environmental materials. Criteria of validity are used to test this model. Predictive procedures are complemented by a particular model of microbial growth. Methods are demonstrated for predicting substrate utilization rates, production rates of extracellular metabolites, growth limiting conditions, and photosynthetic quotients from propagator variables.
Light propagation through anisotropic turbulence.
Toselli, Italo; Agrawal, Brij; Restaino, Sergio
2011-03-01
A wealth of experimental data has shown that atmospheric turbulence can be anisotropic; in this case, a Kolmogorov spectrum does not describe well the atmospheric turbulence statistics. In this paper, we show a quantitative analysis of anisotropic turbulence by using a non-Kolmogorov power spectrum with an anisotropic coefficient. The spectrum we use does not include the inner and outer scales, it is valid only inside the inertial subrange, and it has a power-law slope that can be different from a Kolmogorov one. Using this power spectrum, in the weak turbulence condition, we analyze the impact of the power-law variations α on the long-term beam spread and scintillation index for several anisotropic coefficient values ς. We consider only horizontal propagation across the turbulence cells, assuming circular symmetry is maintained on the orthogonal plane to the propagation direction. We conclude that the anisotropic coefficient influences both the long-term beam spread and the scintillation index by the factor ς(2-α).
OPEX propagation measurements and studies
NASA Technical Reports Server (NTRS)
Arbesser-Rastburg, Bertram
1990-01-01
With the launch of the telecommunications Olympus satellite a new area began for the Olympus Propagation Experiments (OPEX) group. The years of preparations are now paying off - the experiments are underway and the co-operative effort is now turning its attention to the processing and analysis of data and to the interpretation of results. The aim here is to give a short review of the accomplishments made since NAPEX 13 and the work planned for the future. When ESA's Olympus was launched in summer of 1989 it carried a payload producing three unmodulated beacons at 12.5, 19.8, and 29.7 GHz. The main purpose of these beacons is to enable scientists to carry out long term slant path propagation experiments at these frequencies. The OPEX group, which was set up under ESA auspices in 1980, had been preparing for this event very carefully. The specifications for the equipment to be used and the elaboration of standard procedures for data processing and analysis have been worked out jointly. Today the OPEX community includes approximately 30 groups of experimenters. Immediately after achieving platform stability at the orbital location at 341 degrees east, ESA performed the In-Orbit Tests. Most measurements were carried out in Belgium using terminals specially developed for this purpose. A summary of the test results is given.
Simplified propagation of standard uncertainties
Shull, A.H.
1997-06-09
An essential part of any measurement control program is adequate knowledge of the uncertainties of the measurement system standards. Only with an estimate of the standards` uncertainties can one determine if the standard is adequate for its intended use or can one calculate the total uncertainty of the measurement process. Purchased standards usually have estimates of uncertainty on their certificates. However, when standards are prepared and characterized by a laboratory, variance propagation is required to estimate the uncertainty of the standard. Traditional variance propagation typically involves tedious use of partial derivatives, unfriendly software and the availability of statistical expertise. As a result, the uncertainty of prepared standards is often not determined or determined incorrectly. For situations meeting stated assumptions, easier shortcut methods of estimation are now available which eliminate the need for partial derivatives and require only a spreadsheet or calculator. A system of simplifying the calculations by dividing into subgroups of absolute and relative uncertainties is utilized. These methods also incorporate the International Standards Organization (ISO) concepts for combining systematic and random uncertainties as published in their Guide to the Expression of Measurement Uncertainty. Details of the simplified methods and examples of their use are included in the paper.
Joint Acoustic Propagation Experiment (JAPE)
NASA Technical Reports Server (NTRS)
Carnes, Benny L.; Olsen, Robert O.; Kennedy, Bruce W.
1993-01-01
The Joint Acoustic Propagation Experiment (JAPE), performed under the auspices of NATO and the Acoustics Working Group, was conducted at White Sands Missile Range, New Mexico, USA, during the period 11-28 Jul. 1991. JAPE consisted of 220 trials using various acoustic sources including speakers, propane cannon, various types of military vehicles, helicopters, a 155mm howitzer, and static high explosives. Of primary importance to the performance of these tests was the intensive characterization of the atmosphere before and during the trials. Because of the wide range of interests on the part of the participants, JAPE was organized in such a manner to provide a broad cross section of test configurations. These included short and long range propagation from fixed and moving vehicles, terrain masking, and vehicle detection. A number of independent trials were also performed by individual participating agencies using the assets available during JAPE. These tests, while not documented in this report, provided substantial and important data to those groups. Perhaps the most significant feature of JAPE is the establishment of a permanent data base which can be used by not only the participants but by others interested in acoustics. A follow-on test was performed by NASA LaRC during the period 19-29 Aug. 1991 at the same location. These trials consisted of 59 overflights of supersonic aircraft in order to establish the relationship between atmospheric turbulence and the received sonic boom energy at the surface.
Microwave propagation on acupuncture channels.
Krevsky, Michael A; Zinina, Ekaterina S; Koshurinov, Yuri; Ovechkin, Aleck M; Tkachenko, Yuri A; Han, Wantaek; Lee, Sang-Min; Yoon, Gilwon
2006-01-01
Quantitative studies on functional state of acupuncture points and meridians have been done mostly by electrical measurement that requires the contact of the electrode on skin and is subject to pressure, humidity, etc. In this study, a new modality of using microwave was investigated. Microwave energy in the frequency range of 250 approximately 550MHz was irradiated on an acupuncture point. Transmitted microwave energy along the meridian was measured at the next acupuncture point of the same meridian. Diabetic and cancer patients were compared with healthy persons. Normal group consisted of 50 healthy persons. Diabetic group included 50 diabetic patients. Breast cancer group had also 50 patients. All 12 meridians on both right and left hands and feet were measured. For the diabetic group, the microwave energy propagation in this frequency range was 1.417 dB lower along Lung channel and 1.601 dB higher along Spleen channel compared with the normal group regardless of sex and diabetic types. For cancer patients, the propagation was 1.620 dB lower along Liver channel and 1.245 dB higher along Kidney channel compared with the normal group. Microwave energy proved to be a potential diagnostic method.
Vibration Propagation in Spider Webs
NASA Astrophysics Data System (ADS)
Hatton, Ross; Otto, Andrew; Elias, Damian
Due to their poor eyesight, spiders rely on web vibrations for situational awareness. Web-borne vibrations are used to determine the location of prey, predators, and potential mates. The influence of web geometry and composition on web vibrations is important for understanding spider's behavior and ecology. Past studies on web vibrations have experimentally measured the frequency response of web geometries by removing threads from existing webs. The full influence of web structure and tension distribution on vibration transmission; however, has not been addressed in prior work. We have constructed physical artificial webs and computer models to better understand the effect of web structure on vibration transmission. These models provide insight into the propagation of vibrations through the webs, the frequency response of the bare web, and the influence of the spider's mass and stiffness on the vibration transmission patterns. Funded by NSF-1504428.
Light propagation in nanorod arrays
NASA Astrophysics Data System (ADS)
Rahachou, A. I.; Zozoulenko, I. V.
2007-03-01
We study the propagation of TM- and TE-polarized light in two-dimensional arrays of silver nanorods of various diameters in a gelatin background. We calculate the transmittance, reflectance and absorption of arranged and disordered nanorod arrays and compare the exact numerical results with the predictions of the Maxwell-Garnett effective-medium theory. We show that interactions between nanorods, multipole contributions and formations of photonic gaps affect strongly the transmittance spectra that cannot be accounted for in terms of the conventional effective-medium theory. We also demonstrate and explain the degradation of the transmittance in arrays with randomly located rods as well as the weak influence of their fluctuating diameter. For TM modes we outline the importance of the skin effect, which causes the full reflection of the incoming light. We then illustrate the possibility of using periodic arrays of nanorods as high-quality polarizers.
Light propagation in inhomogeneous universes
NASA Technical Reports Server (NTRS)
Schneider, Peter; Weiss, Achim
1988-01-01
Refsdal's (1970) method is generalized to study the propagation of light rays through an inhomogeneous universe. The probability distribution for the linear component of the cumulative shear (CS) along light rays is derived, and it is shown that the CS can be dominated by nonlinear components, espcially for light rays in empty cones. The amplification tail of the amplification probability distribution is compared with analytic results; these linear investigations are shown to underestimate the high-amplification probability and hence the importance of the amplification bias in source counts. The distribution of the ellipticity of images of infinitesimal circular sources is derived, and it is shown that this can be dominated by the nonlinear contributions to the CS.
ETS-V propagation experiments in Japan
NASA Technical Reports Server (NTRS)
Ohmori, Shingo
1988-01-01
Propagation experiments on ship, aircraft, and land mobile earth stations were carried out using the Engineering Test Satellite-V (ETS-V), which was launched in August 1987. The propagation experiments are one of the missions of the Experimental Mobile Satellite System (EMSS). Initial experimental results of ETS-V/EMSS on propagation using ship, aircraft, and land mobiles with ETS-V are given.
Multipath Propagation over Snow at Millimeter Wavelengths,
1980-02-01
Propagation Branch Electromagnetic Sciences Division APPROVED: ALLAN C. SCHELL , Chief Electromagnetic Sciences Division FOR THE COMANDER: JOHN P...type of snow cover. A computer program was developed in order to model the reflection as a specular process, with the underlying terrain represented...data. 2,B’ 3II Contents 1. INTRODUCTION 9 2. ANALYSIS OF MULTIPATH PROPAGATION 10 2. 1 Propagation Mechanisms 12 2.2 Model Calculations for Flat Terrain
GALPROP: New Developments in CR Propagation Code
NASA Technical Reports Server (NTRS)
Moskalenko, I. V.; Jones, F. C.; Mashnik, S. G.; Strong, A. W.; Ptuskin, V. S.
2003-01-01
The numerical Galactic CR propagation code GALPROP has been shown to reproduce simultaneously observational data of many kinds related to CR origin and propagation. It has been validated on direct measurements of nuclei, antiprotons, electrons, positrons as well as on astronomical measurements of gamma rays and synchrotron radiation. Such data provide many independent constraints on model parameters while revealing some contradictions in the conventional view of Galactic CR propagation. Using a new version of GALPROP we study new effects such as processes of wave-particle interactions in the interstellar medium. We also report about other developments in the CR propagation code.
ACTS Propagation Measurements in Maryland and Virginia
NASA Technical Reports Server (NTRS)
Dissanayake, Asoka; Lin, Kuan-Ting
1996-01-01
Rapid growth in new satellite services incorporating very small aperture terminals (VSAT) and ultra small aperture terminals (USAT) is expected in the coming years. Small size terminals allow for widespread use of satellite services in small business and domestic applications. Due to congestion of lower frequency bands such as C and Ku, most of these services will use Ka-band (2/20 GHz) frequencies. Propagation impairments produced by the troposphere is a limiting factor for the effective use of the 20/30 GHz band and the use of smaller Earth terminals makes it difficult to provide sufficient link margins for propagation related outages. In this context, reliable prediction of propagation impairments for low margin systems becomes important. Due to the complexity of propagation phenomena propagation modeling is mainly attempted on an empirical basis. As such, the availability of reliable measured data that extend to probability levels well in excess of the traditional limit of 1 percent is of great importance in the development, validation, and refinement of propagation models. The beacon payload on the Advanced Communications Technology Satellite (ACTS) together with the propagation measurement terminals developed under the NASA ACTS propagation program provide an excellent opportunity to collect such data on a long-term basis. This paper presents the results of ACTS propagation measurements conducted in the Washington, DC metropolitan area by COMSAT Laboratories.
A stochastic model for propagation through tissue.
Lacaze, Bernard
2009-10-01
Attenuation of ultrasonic waves is often assumed linear with respect to frequency in biological applications whereas it is considered quadratic when the propagation occurs in the atmosphere or the water. In the latter case, other studies show that a Gaussian propagation duration can explain this attenuation behavior and provide a model for the energy loss in the stationary limit. The present paper defines an equivalent random propagation duration with Cauchy distribution, which is appropriate for the propagation of ultrasound through tissue. The model adds an unobserved noise that represents the signal deterioration. In addition, the model agrees with the mode downshift in the case of a narrowband signal.
Quench propagation velocity for highly stabilized conductors
Mints, R.G. |; Ogitsu, T. |; Devred, A.
1995-05-01
Quench propagation velocity in conductors having a large amount of stabilizer outside the multifilamentary area is considered. It is shown that the current redistribution process between the multifilamentary area and the stabilizer can strongly effect the quench propagation. A criterion is derived determining the conditions under which the current redistribution process becomes significant, and a model of effective stabilizer area is suggested to describe its influence on the quench propagation velocity. As an illustration, the model is applied to calculate the adiabatic quench propagation velocity for a conductor geometry with a multifilamentary area embedded inside the stabilizer.
Explosion propagation in inert porous media.
Ciccarelli, G
2012-02-13
Porous media are often used in flame arresters because of the high surface area to volume ratio that is required for flame quenching. However, if the flame is not quenched, the flow obstruction within the porous media can promote explosion escalation, which is a well-known phenomenon in obstacle-laden channels. There are many parallels between explosion propagation through porous media and obstacle-laden channels. In both cases, the obstructions play a duel role. On the one hand, the obstruction enhances explosion propagation through an early shear-driven turbulence production mechanism and then later by shock-flame interactions that occur from lead shock reflections. On the other hand, the presence of an obstruction can suppress explosion propagation through momentum and heat losses, which both impede the unburned gas flow and extract energy from the expanding combustion products. In obstacle-laden channels, there are well-defined propagation regimes that are easily distinguished by abrupt changes in velocity. In porous media, the propagation regimes are not as distinguishable. In porous media the entire flamefront is affected, and the effects of heat loss, turbulence and compressibility are smoothly blended over most of the propagation velocity range. At low subsonic propagation speeds, heat loss to the porous media dominates, whereas at higher supersonic speeds turbulence and compressibility are important. This blending of the important phenomena results in no clear transition in propagation mechanism that is characterized by an abrupt change in propagation velocity. This is especially true for propagation velocities above the speed of sound where many experiments performed with fuel-air mixtures show a smooth increase in the propagation velocity with mixture reactivity up to the theoretical detonation wave velocity.
Visualizing the Propagation of Acute Lung Injury
Cereda, Maurizio; Xin, Yi; Meeder, Natalie; Zeng, Johnathan; Jiang, YunQing; Hamedani, Hooman; Profka, Harrilla; Kadlecek, Stephen; Clapp, Justin; Deshpande, Charuhas G.; Wu, Jue; Gee, James C.; Kavanagh, Brian P.; Rizi, Rahim R.
2015-01-01
Background Mechanical ventilation worsens acute respiratory distress syndrome (ARDS), but this secondary ‘ventilator-associated’ injury is variable and difficult to predict. We aimed to visualize the propagation of such ventilator-induced injury, in the presence (and absence) of a primary underlying lung injury, and to determine the predictors of propagation. Methods Anesthetized rats (n=20) received acid aspiration (HCl) followed by ventilation with moderate tidal volume (VT). In animals surviving ventilation for at least two hours, propagation of injury was quantified using serial computed tomography (CT). Baseline lung status was assessed by oxygenation, lung weight, and lung strain (VT/expiratory lung volume). Separate groups of rats without HCl aspiration were ventilated with large (n=10) or moderate (n=6) VT. Results In 15 rats surviving longer than two hours, CT opacities spread outwards from the initial site of injury. Propagation was associated with higher baseline strain (propagation vs. no propagation, mean ± SD: 1.52 ± 0.13 vs. 1.16 ± 0.20, p<0.01), but similar oxygenation and lung weight. Propagation did not occur where baseline strain <1.29. In healthy animals, large VT caused injury that was propagated inwards from the lung periphery; in the absence of preexisting injury, propagation did not occur where strain was <2.0. Conclusions Compared with healthy lungs, underlying injury causes propagation to occur at a lower strain threshold and, it originates at the site of injury; this suggests that tissue around the primary lesion is more sensitive. Understanding how injury is propagated may ultimately facilitate a more individualized monitoring or management. PMID:26536308
Rapid vegetative propagation method for carob
Technology Transfer Automated Retrieval System (TEKTRAN)
Many fruit species are propagated by vegetative methods such as budding, grafting, cutting, suckering, layering etc. to avoid heterozygosity. Carob trees (Ceratonia siliqua L.) are of highly economical value and it is among the most difficult-to-propagate fruit species. In this study, air-layering p...
Propagation of major plant-virus hosts.
Hull, Roger
2009-08-01
Plant viruses are propagated in host plants, which are usually grown in glasshouses, screen houses, or growth cabinets. In most cases, the plants are grown from seed; in some cases, they are propagated as cuttings. This unit describes the basic techniques of growing suitable plants from seed and cuttings.
Nondestructive evaluation of pyroshock propagation using hydrocodes
NASA Astrophysics Data System (ADS)
Lee, Juho; Hwang, Dae-Hyeon; Jang, Jae-Kyeong; Lee, Jung-Ryul; Han, Jae-Hung
2016-04-01
Pyroshock or pyrotechnic shock generated by explosive events of pyrotechnic devices can induce fatal failures in electronic payloads. Therefore, understanding and estimation of pyroshock propagation through complex structures are necessary. However, an experimental approach using real pyrotechnic devices is quite burdensome because pyrotechnic devices can damage test structures and newly manufactured test structures are necessary for each experiment. Besides, pyrotechnic experiments are quite expensive, time-consuming, and dangerous. Consequently, nondestructive evaluation (NDE) of pyroshock propagation without using real pyrotechnic devices is necessary. In this study, nondestructive evaluation technique for pyroshock propagation estimation using hydrocodes is proposed. First, pyroshock propagation is numerically analyzed using AUTODYN, a commercial hydrocodes. Hydrocodes can handle stress wave propagation including elastic, plastic, and shock wave in the time domain. Test structures are modeled and pyroshock time history is applied to where the pyroshock propagation originates. Numerical NDE results of pyroshock propagation on test structures are analyzed in terms of acceleration time histories and acceleration shock response spectra (SRS) results. To verify the proposed numerical methodology, impact tests using airsoft gun are performed. The numerical analysis results for the impact tests are compared with experimental results and they show good agreements. The proposed numerical techniques enable us to nondestructively characterize pyroshock propagation.
Vehicular sources in acoustic propagation experiments
NASA Technical Reports Server (NTRS)
Prado, Gervasio; Fitzgerald, James; Arruda, Anthony; Parides, George
1990-01-01
One of the most important uses of acoustic propagation models lies in the area of detection and tracking of vehicles. Propagation models are used to compute transmission losses in performance prediction models and to analyze the results of past experiments. Vehicles can also provide the means for cost effective experiments to measure acoustic propagation conditions over significant ranges. In order to properly correlate the information provided by the experimental data and the propagation models, the following issues must be taken into consideration: the phenomenology of the vehicle noise sources must be understood and characterized; the vehicle's location or 'ground truth' must be accurately reproduced and synchronized with the acoustic data; and sufficient meteorological data must be collected to support the requirements of the propagation models. The experimental procedures and instrumentation needed to carry out propagation experiments are discussed. Illustrative results are presented for two cases. First, a helicopter was used to measure propagation losses at a range of 1 to 10 Km. Second, a heavy diesel-powered vehicle was used to measure propagation losses in the 300 to 2200 m range.
Propagation testing multi-cell batteries.
Orendorff, Christopher J.; Lamb, Joshua; Steele, Leigh Anna Marie; Spangler, Scott Wilmer
2014-10-01
Propagation of single point or single cell failures in multi-cell batteries is a significant concern as batteries increase in scale for a variety of civilian and military applications. This report describes the procedure for testing failure propagation along with some representative test results to highlight the potential outcomes for different battery types and designs.
PROPHET: An applicaton of propagation forecasting principles
NASA Technical Reports Server (NTRS)
Argo, P. E.; Rothmuller, I. J.
1979-01-01
A propagation assessment and forecasting terminal, PROPHET, is described. The terminal is a key element of the environmental prediction and assessment system which uses real time solar/geophysical data to provide real time knowledge of propagation conditions. The terminal uses models to translate data from satellite and ground based sources into performance predictions for specific systems.
Uncertainty Propagation in an Ecosystem Nutrient Budget.
New aspects and advancements in classical uncertainty propagation methods were used to develop a nutrient budget with associated error for a northern Gulf of Mexico coastal embayment. Uncertainty was calculated for budget terms by propagating the standard error and degrees of fr...
Propagation of almond rootstocks and trees
Technology Transfer Automated Retrieval System (TEKTRAN)
Millions of almond trees in production in California and elsewhere were propagated by nurseries using the grafting technique called budding. This gives a uniform orchard and allows the grower to select nut cultivar (scion) and rootstock combinations. Grafting is a form of clonal propagation and resu...
Crack propagation driven by crystal growth
A. Royne; Paul Meaking; A. Malthe-Sorenssen; B. Jamtveit; D. K. Dysthe
2011-10-01
Crystals that grow in confinement may exert a force on their surroundings and thereby drive crack propagation in rocks and other materials. We describe a model of crystal growth in an idealized crack geometry in which the crystal growth and crack propagation are coupled through the stress in the surrounding bulk solid. Subcritical crack propagation takes place during a transient period, which may be very long, during which the crack velocity is limited by the kinetics of crack propagation. When the crack is sufficiently large, the crack velocity becomes limited by the kinetics of crystal growth. The duration of the subcritical regime is determined by two non-dimensional parameters, which relate the kinetics of crack propagation and crystal growth to the supersaturation of the fluid and the elastic properties of the surrounding material.
Uncertainty propagation in nuclear forensics.
Pommé, S; Jerome, S M; Venchiarutti, C
2014-07-01
Uncertainty propagation formulae are presented for age dating in support of nuclear forensics. The age of radioactive material in this context refers to the time elapsed since a particular radionuclide was chemically separated from its decay product(s). The decay of the parent radionuclide and ingrowth of the daughter nuclide are governed by statistical decay laws. Mathematical equations allow calculation of the age of specific nuclear material through the atom ratio between parent and daughter nuclides, or through the activity ratio provided that the daughter nuclide is also unstable. The derivation of the uncertainty formulae of the age may present some difficulty to the user community and so the exact solutions, some approximations, a graphical representation and their interpretation are presented in this work. Typical nuclides of interest are actinides in the context of non-proliferation commitments. The uncertainty analysis is applied to a set of important parent-daughter pairs and the need for more precise half-life data is examined.
S-Band propagation measurements
NASA Technical Reports Server (NTRS)
Briskman, Robert D.
1994-01-01
A geosynchronous satellite system capable of providing many channels of digital audio radio service (DARS) to mobile platforms within the contiguous United States using S-band radio frequencies is being implemented. The system is designed uniquely to mitigate both multipath fading and outages from physical blockage in the transmission path by use of satellite spatial diversity in combination with radio frequency and time diversity. The system also employs a satellite orbital geometry wherein all mobile platforms in the contiguous United States have elevation angles greater than 20 deg to both of the diversity satellites. Since implementation of the satellite system will require three years, an emulation has been performed using terrestrial facilities in order to allow evaluation of DARS capabilities in advance of satellite system operations. The major objective of the emulation was to prove the feasibility of broadcasting from satellites 30 channels of CD quality programming using S-band frequencies to an automobile equipped with a small disk antenna and to obtain quantitative performance data on S-band propagation in a satellite spatial diversity system.
VPSim: Variance propagation by simulation
Burr, T.; Coulter, C.A.; Prommel, J.
1997-12-01
One of the fundamental concepts in a materials control and accountability system for nuclear safeguards is the materials balance (MB). All transfers into and out of a material balance area are measured, as are the beginning and ending inventories. The resulting MB measures the material loss, MB = T{sub in} + I{sub B} {minus} T{sub out} {minus} I{sub E}. To interpret the MB, the authors must estimate its measurement error standard deviation, {sigma}{sub MB}. When feasible, they use a method usually known as propagation of variance (POV) to estimate {sigma}{sub MB}. The application of POV for estimating the measurement error variance of an MB is straightforward but tedious. By applying POV to individual measurement error standard deviations they can estimate {sigma}{sub MB} (or more generally, they can estimate the variance-covariance matrix, {Sigma}, of a sequence of MBs). This report describes a new computer program (VPSim) that uses simulation to estimate the {Sigma} matrix of a sequence of MBs. Given the proper input data, VPSim calculates the MB and {sigma}{sub MB}, or calculates a sequence of n MBs and the associated n-by-n covariance matrix, {Sigma}. The covariance matrix, {Sigma}, contains the variance of each MB in the diagonal entries and the covariance between pairs of MBs in the off-diagonal entries.
Twist Propagation in Dinucleosome Arrays
Dobrovolskaia, Irina V.; Kenward, Martin; Arya, Gaurav
2010-01-01
We present a Monte Carlo simulation study of the distribution and propagation of twist from one DNA linker to another for a two-nucleosome array subjected to externally applied twist. A mesoscopic model of the array that incorporates nucleosome geometry along with the bending and twisting mechanics of the linkers is employed and external twist is applied in stepwise increments to mimic quasistatic twisting of chromatin fibers. Simulation results reveal that the magnitude and sign of the imposed and induced twist on contiguous linkers depend strongly on their relative orientation. Remarkably, the relative direction of the induced and applied twist can become inverted for a subset of linker orientations—a phenomenon we refer to as “twist inversion”. We characterize the twist inversion, as a function of relative linker orientation, in a phase diagram and explain its key features using a simple model based on the geometry of the nucleosome/linker complex. In addition to twist inversion, our simulations reveal “nucleosome flipping”, whereby nucleosomes may undergo sudden flipping in response to applied twist, causing a rapid bending of the linker and a significant change in the overall twist and writhe of the array. Our findings shed light on the underlying mechanisms by which torsional stresses impact chromatin organization. PMID:21081084
Fluctuation-controlled front propagation
NASA Astrophysics Data System (ADS)
Ridgway, Douglas Thacher
1997-09-01
the symmetry of the absorbing state, but which is unsuccessful at capturing the behavior of diffusion-limited growth. In an effort to find a simpler model system, we turned to modelling fitness increases in evolution. The work was motivated by an experiment on vesicular stomatitis virus, a short (˜9600bp) single-stranded RNA virus. A highly bottlenecked viral population increases in fitness rapidly until a certain point, after which the fitness increases at a slower rate. This is well modeled by a constant population reproducing and mutating on a smooth fitness landscape. Mean field theory of this system displays the same infinite propagation velocity blowup as mean field diffusion-limited aggregation. However, we have been able to make progress on a number of fronts. One is solving systems of moment equations, where a hierarchy of moments is truncated arbitrarily at some level. Good results for front propagation velocity are found with just two moments, corresponding to inclusion of the basic finite population clustering effect ignored by mean field theory. In addition, for small mutation rates, most of the population will be entirely on a single site or two adjacent sites, and the density of these cases can be described and solved. (Abstract shortened by UMI.)
MPPE (Multiple Pulse Propagation Experiment) results
Chambers, F.W.; Caporaso, G.J.; Chong, Y.P.; Deadrick, F.J.; Guethlein, G.; Fawley, W.M.; Orzechowski, T.J.; Renbarger, V.L.; Rogers, D. Jr.; Weir, J.T. ); Lee, P. ); Struve, K.W. ); Hubbard, R. ); Feinstein, L.; Keeley, D. (Science Applicatio
1990-10-01
The Multiple Pulse Propagation Experiment (MPPE) was conducted by the Beam Research Group of the Lawrence Livermore National Laboratory from September 1989, through January 1990, using the Advanced Test Accelerator (ATA). This experiment represents the culmination of the three previous beam propagation experiments conducted at the ATA over the past half decade. Highlights of this experiment were the multiple pulse operation of ATA, and the diagnosis of the beam propagation, and channel production at the higher repetition rates. A large database was collected on beam propagation in uniform gas and channels including m = 0 beam size and net current measurements; and m = 1 hose measurements. The generation and evolution of the electron beam driven channels was well documented. A key result of this experiment was that the beam was dominated by hose instability which limited propagation ranges. This report is organized into five sections. The experimental layout and beam parameters have been detailed in previous reports. First the beam initial conditions will be discussed in detail. Since beam injection parameters are ultimately the only variables one can specify in an atmospheric application, the control and documentation of the beam at the entrance to the gas is crucial. Next the beam lead pulse propagation in gas will be reported. Lead pulse results will be compared with past experiments. The density channel production and evolution will be briefly reported; an additional reference is available. Beam propagation in the channel will then be examined. Finally, conclusions will be presented.
The accuracy of dynamic attitude propagation
NASA Technical Reports Server (NTRS)
Harvie, E.; Chu, D.; Woodard, M.
1990-01-01
Propagating attitude by integrating Euler's equation for rigid body motion has long been suggested for the Earth Radiation Budget Satellite (ERBS) but until now has not been implemented. Because of limited Sun visibility, propagation is necessary for yaw determination. With the deterioration of the gyros, dynamic propagation has become more attractive. Angular rates are derived from integrating Euler's equation with a stepsize of 1 second, using torques computed from telemetered control system data. The environmental torque model was quite basic. It included gravity gradient and unshadowed aerodynamic torques. Knowledge of control torques is critical to the accuracy of dynamic modeling. Due to their coarseness and sparsity, control actuator telemetry were smoothed before integration. The dynamic model was incorporated into existing ERBS attitude determination software. Modeled rates were then used for attitude propagation in the standard ERBS fine-attitude algorithm. In spite of the simplicity of the approach, the dynamically propagated attitude matched the attitude propagated with good gyros well for roll and yaw but diverged up to 3 degrees for pitch because of the very low resolution in pitch momentum wheel telemetry. When control anomalies significantly perturb the nominal attitude, the effect of telemetry granularity is reduced and the dynamically propagated attitudes are accurate on all three axes.
Electromagnetic Propagation Prediction Inside Aircraft Cabins
NASA Technical Reports Server (NTRS)
Hankins, Genevieve; Vahala, Linda; Beggs, John H.
2004-01-01
Electromagnetic propagation models for signal strength prediction within aircraft cabins are essential for evaluating and designing a wireless communication system to be implemented onboard aircraft. A model was developed using Wireless Valley's SitePlanner; which is commercial grade software intended for predictions within office buildings. The performance of the model was evaluated through a comparison with test data measurements taken on several aircraft. The comparison concluded that the model can accurately predict power propagation within the cabin. This model can enhance researchers understanding of power propagation within aircraft cabins and will aid in future research.
Propagation considerations in land mobile satellite transmission
NASA Technical Reports Server (NTRS)
Vogel, W. J.; Smith, E. K.
1985-01-01
It appears likely that the Land Mobile Satellite Services (LMSS) will be authorized by the FCC for operation in the 800 to 900 MHz (UHF) and possibly near 1500 MHz (L-band). Propagation problems are clearly an important factor in the effectiveness of this service, but useful measurements are few, and produced contradictory interpretations. A first order overview of existing measurements is presented with particular attention to the first two NASA balloon to mobile vehicle propagation experiments. Some physical insight into the interpretation of propagation effects in LMSS transmissions is provided.
Asymmetric counter propagation of domain walls
NASA Astrophysics Data System (ADS)
Andrade-Silva, I.; Clerc, M. G.; Odent, V.
2016-07-01
Far from equilibrium systems show different states and domain walls between them. These walls, depending on the type of connected equilibria, exhibit a rich spatiotemporal dynamics. Here, we investigate the asymmetrical counter propagation of domain walls in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the shape and speed of the domain walls. Based on the molecular orientation, we infer that the counter propagative walls have different elastic deformations. These deformations are responsible of the asymmetric counter propagating fronts. Theoretically, based on symmetry arguments, we propose a simple bistable model under the influence of a nonlinear gradient, which qualitatively describes the observed dynamics.
Photon propagator in light-shell gauge
NASA Astrophysics Data System (ADS)
Georgi, Howard; Kestin, Greg; Sajjad, Aqil
2016-05-01
We derive the photon propagator in light-shell gauge (LSG) vμAμ=0 , where vμ=(1,r ^ ) μ . This gauge is an important ingredient of the light-shell effective theory—an effective theory for describing high energy jet processes on a 2-dimensional spherical shell expanding at the speed of light around the point of the initial collision producing the jets. Since LSG is a noncovariant gauge, we cannot calculate the LSG propagator by using the standard procedure for covariant gauges. We therefore employ a new technique for computing the propagator, which we hope may be of relevance in other gauges as well.
Propagation of Light Elements in the Galaxy
NASA Technical Reports Server (NTRS)
Moskalenko, I. V.; Strong, A. W.; Mashnik, S. G.; Jones, F. C.
2003-01-01
The origin and evolution of isotopes of the lightest elements d, He-3, Li, Be, and B in the universe is a key problem in such fields as astrophysics of CR, Galactic evolution, non-thermal nucleosynthesis, and cosmological studies. One of the major sources of these species is spallation by CR nuclei in the interstellar medium. On the other hand, it is the Boron/Carbon ratio in CR and Be-10 abundance which are used to fix the propagation parameters and thus spallation rate. We study production and Galactic propagation of these species using the numerical propagation code GALPROP and updated production cross sections.
Propagation of sound through a sheared flow
NASA Technical Reports Server (NTRS)
Woolley, J. P.; Smith, C. A.; Karamcheti, K.
1978-01-01
Sound generated in a moving fluid must propagate through a shear layer in order to be measured by a fixed instrument. These propagation effects were evaluated for noise sources typically associated with single and co-flowing subsonic jets and for subcritical flow over airfoils in such jets. The techniques for describing acoustic propagation fall into two categories: geometric acoustics and wave acoustics. Geometric acoustics is most convenient and accurate for high frequency sound. In the frequency range of interest to the present study (greater than 150 Hz), the geometric acoustics approach was determined to be most useful and practical.
Inward propagating chemical waves in Taylor vortices
NASA Astrophysics Data System (ADS)
Thompson, Barnaby W.; Novak, Jan; Wilson, Mark C. T.; Britton, Melanie M.; Taylor, Annette F.
2010-04-01
Advection-reaction-diffusion (ARD) waves in the Belousov-Zhabotinsky reaction in steady Taylor-Couette vortices have been visualized using magnetic-resonance imaging and simulated using an adapted Oregonator model. We show how propagating wave behavior depends on the ratio of advective, chemical and diffusive time scales. In simulations, inward propagating spiral flamelets are observed at high Damköhler number (Da). At low Da, the reaction distributes itself over several vortices and then propagates inwards as contracting ring pulses—also observed experimentally.
Propagating confined states in phase dynamics
NASA Technical Reports Server (NTRS)
Brand, Helmut R.; Deissler, Robert J.
1992-01-01
Theoretical treatment is given to the possibility of the existence of propagating confined states in the nonlinear phase equation by generalizing stationary confined states. The nonlinear phase equation is set forth for the case of propagating patterns with long wavelengths and low-frequency modulation. A large range of parameter values is shown to exist for propagating confined states which have spatially localized regions which travel on a background with unique wavelengths. The theoretical phenomena are shown to correspond to such physical systems as spirals in Taylor instabilities, traveling waves in convective systems, and slot-convection phenomena for binary fluid mixtures.
Surface acoustic wave propagation in graphene
NASA Astrophysics Data System (ADS)
Thalmeier, Peter; Dóra, Balázs; Ziegler, Klaus
2010-01-01
Surface acoustic wave (SAW) propagation is a powerful method to investigate two-dimensional (2D) electron systems. We show how SAW observables are influenced by coupling to the 2D massless Dirac electrons of graphene and argue that Landau oscillations in SAW propagation can be observed as function of gate voltage for constant field. Contrary to other transport measurements, the zero-field SAW propagation gives the wave-vector dependence of graphene conductivity for small wave numbers. We predict a crossover from Schrödinger to Dirac-like behavior as a function of gate voltage, with no attenuation in the latter for clean samples.
Inward propagating chemical waves in Taylor vortices.
Thompson, Barnaby W; Novak, Jan; Wilson, Mark C T; Britton, Melanie M; Taylor, Annette F
2010-04-01
Advection-reaction-diffusion (ARD) waves in the Belousov-Zhabotinsky reaction in steady Taylor-Couette vortices have been visualized using magnetic-resonance imaging and simulated using an adapted Oregonator model. We show how propagating wave behavior depends on the ratio of advective, chemical and diffusive time scales. In simulations, inward propagating spiral flamelets are observed at high Damköhler number (Da). At low Da, the reaction distributes itself over several vortices and then propagates inwards as contracting ring pulses--also observed experimentally.
Computing Propagation Of Sound In Engine Ducts
NASA Technical Reports Server (NTRS)
Saylor, Silvia
1995-01-01
Frequency Domain Propagation Model (FREDOM) computer program accounts for acoustic loads applied to components of engines. Models propagation of noise through fluids in ducts between components and through passages within components. Used not only to analyze hardware problems, but also for design purposes. Updated version of FREQPL program easier to use. Devised specifically for use in analyzing acoustic loads in rocket engines. Underlying physical and mathematical concepts implemented also applicable to acoustic propagation in other enclosed spaces; analyzing process plumbing and ducts in industrial buildings with view toward reducing noise in work areas.
Debris Flow Distributed Propagation Model
NASA Astrophysics Data System (ADS)
Gregoretti, C.
The debris flow distributed propagation model is a DEM-based model. The fan is dis- cretized by square cells and each cell is assigned an altitude on the sea level. The cells of the catchment are distinguished in two categories: the source cells and the stripe cells. The source cells receive the input hydograph: the cells close to the torrent which are flooded by the debris flow overflowing the torrent embankment are source cells. The stripes cells are the cells flooded by debris flow coming from the surrounding cells. At the first time step only the source cells are flooded by debris flow coming from the torrent. At the second time step a certain number of cells are flooded by de- bris flow coming from the source cells. These cells constitute a stripe of cells and are assigned order two. At the third time step another group of cells are flooded by the debris flow coming from the cells whose order is two. These cells constitute another stripe and are assigned order three. The cell order of a stripe is the time step number corresponding to the transition from dry to flooded state. The mass transfer or mo- mentum exchange between cells is governed by two different mechanisms. The mass transfer is allowed only by a positive or equal to zero flow level difference between the drained cell and the receiving cell. The mass transfer is limited by a not negative final flow level difference between the drained cell and the receiving cells. This limitation excludes the case of possible oscillations in the mass transfer. Another limitation is that the mass drained by a cell should be less than the available mass in that cell. This last condition provides the respect of mass conservation. The first mechanism of mass transfer is the gravity. The mass in a cell is transferred to the neighbouring cells with lower altitude and flow level according to an uniform flow law: The second mecha- nism of mass transfer is the broad crested weir. The mass in a cell is transferred to the
In vitro propagation of Paphiopedilum orchids.
Zeng, Songjun; Huang, Weichang; Wu, Kunlin; Zhang, Jianxia; da Silva, Jaime A Teixeira; Duan, Jun
2016-01-01
Paphiopedilum is one of the most popular and rare orchid genera. Members of the genus are sold and exhibited as pot plants and cut flowers. Wild populations of Paphiopedilum are under the threat of extinction due to over-collection and loss of suitable habitats. A reduction in their commercial value through large-scale propagation in vitro is an option to reduce pressure from illegal collection, to attempt to meet commercial needs and to re-establish threatened species back into the wild. Although they are commercially propagated via asymbiotic seed germination, Paphiopedilum are considered to be difficult to propagate in vitro, especially by plant regeneration from tissue culture. This review aims to cover the most important aspects and to provide an up-to-date research progress on in vitro propagation of Paphiopedilum and to emphasize the importance of further improving tissue culture protocols for ex vitro-derived explants.
Noise propagation in urban and industrial areas
NASA Technical Reports Server (NTRS)
Davies, H. G.
1976-01-01
Noise propagation in streets and the discrepancies between theoretical analyses and field measurements are discussed. A cell-model is used to estimate the general background level of noise due to vehicular sources distributed over the urban area.
The ghost propagator in Coulomb gauge
NASA Astrophysics Data System (ADS)
Watson, P.; Reinhardt, H.
2011-05-01
We present results for a numerical study of the ghost propagator in Coulomb gauge whereby lattice results for the spatial gluon propagator are used as input to solving the ghost Dyson-Schwinger equation. We show that in order to solve completely, the ghost equation must be supplemented by a boundary condition (the value of the inverse ghost propagator dressing function at zero momentum) which determines if the solution is critical (zero value for the boundary condition) or subcritical (finite value). The various solutions exhibit a characteristic behavior where all curves follow the same (critical) solution when going from high to low momenta until `forced' to freeze out in the infrared to the value of the boundary condition. The boundary condition can be interpreted in terms of the Gribov gauge-fixing ambiguity; we also demonstrate that this is not connected to the renormalization. Further, the connection to the temporal gluon propagator and the infrared slavery picture of confinement is discussed.
The ghost propagator in Coulomb gauge
Watson, P.; Reinhardt, H.
2011-05-23
We present results for a numerical study of the ghost propagator in Coulomb gauge whereby lattice results for the spatial gluon propagator are used as input to solving the ghost Dyson-Schwinger equation. We show that in order to solve completely, the ghost equation must be supplemented by a boundary condition (the value of the inverse ghost propagator dressing function at zero momentum) which determines if the solution is critical (zero value for the boundary condition) or subcritical (finite value). The various solutions exhibit a characteristic behavior where all curves follow the same (critical) solution when going from high to low momenta until 'forced' to freeze out in the infrared to the value of the boundary condition. The boundary condition can be interpreted in terms of the Gribov gauge-fixing ambiguity; we also demonstrate that this is not connected to the renormalization. Further, the connection to the temporal gluon propagator and the infrared slavery picture of confinement is discussed.
Promoted Combustion Test Propagation Rate Data
NASA Technical Reports Server (NTRS)
Borstorff, J.; Jones, P.; Lowery, F.
2002-01-01
Combustion propagation rate data were examined for potential use in benchmarking a thermal model of the Promoted Combustion Test (PCT), and also for potential use in measuring the repeatability of PCT results.
Radio wave propagation and acoustic sounding
NASA Astrophysics Data System (ADS)
Singal, S. P.
Radio wave propagation of the decimetric and centimetric waves depends to a large extent on the boundary layer meteorological conditions which give rise to severe fadings, very often due to multipath propagation. Sodar is one of the inexpensive remote sensing techniques which can be employed to probe the boundary layer structure. In the paper a historical perspective has been given of the simultaneously conducted studies on radio waves and sodar at various places. The radio meteorological information needed for propagation studies has been clearly spelt out and conditions of a ray path especially in the presence of a ducting layer have been defined as giving rise to fading or signal enhancement conditions. Finally the potential of the sodar studies to obtain information about the boundary layer phenomena has been stressed, clearly spelling out the use of acoustic sounding in radio wave propagation studies.
Fick's Law Assisted Propagation for Semisupervised Learning.
Gong, Chen; Tao, Dacheng; Fu, Keren; Yang, Jie
2015-09-01
How to propagate the label information from labeled examples to unlabeled examples is a critical problem for graph-based semisupervised learning. Many label propagation algorithms have been developed in recent years and have obtained promising performance on various applications. However, the eigenvalues of iteration matrices in these algorithms are usually distributed irregularly, which slow down the convergence rate and impair the learning performance. This paper proposes a novel label propagation method called Fick's law assisted propagation (FLAP). Unlike the existing algorithms that are directly derived from statistical learning, FLAP is deduced on the basis of the theory of Fick's First Law of Diffusion, which is widely known as the fundamental theory in fluid-spreading. We prove that FLAP will converge with linear rate and show that FLAP makes eigenvalues of the iteration matrix distributed regularly. Comprehensive experimental evaluations on synthetic and practical datasets reveal that FLAP obtains encouraging results in terms of both accuracy and efficiency.
Propagation Regime of Iron Dust Flames
NASA Technical Reports Server (NTRS)
Tang, Francois-David; Goroshin, Samuel; Higgins, Andrew J.
2012-01-01
A flame propagating through an iron-dust mixture can propagate in two asymptotic regimes. When the characteristic time of heat transfer between particles is much smaller than the characteristic time of particle combustion, the flame propagates in the continuum regime where the heat released by reacting particles can be modelled as a space-averaged function. In contrast, when the characteristic time of heat transfer is much larger than the particle reaction time, the flame can no longer be treated as a continuum due to dominating effects associated with the discrete nature of the particle reaction. The discrete regime is characterized by weak dependence of the flame speed on the oxygen concentration compared to the continuum regime. The discrete regime is observed in flames propagating through an iron dust cloud within a gas mixture containing xenon, while the continuum regime is obtained when xenon is substituted with helium.
A solid state lightning propagation speed sensor
NASA Technical Reports Server (NTRS)
Mach, Douglas M.; Rust, W. David
1989-01-01
A device to measure the propagation speeds of cloud-to-ground lightning has been developed. The lightning propagation speed (LPS) device consists of eight solid state silicon photodetectors mounted behind precision horizontal slits in the focal plane of a 50-mm lens on a 35-mm camera. Although the LPS device produces results similar to those obtained from a streaking camera, the LPS device has the advantages of smaller size, lower cost, mobile use, and easier data collection and analysis. The maximum accuracy for the LPS is 0.2 microsec, compared with about 0.8 microsecs for the streaking camera. It is found that the return stroke propagation speed for triggered lightning is different than that for natural lightning if measurements are taken over channel segments less than 500 m. It is suggested that there are no significant differences between the propagation speeds of positive and negative flashes. Also, differences between natural and triggered dart leaders are discussed.
Propagation effects on attosecond pulse generation
NASA Astrophysics Data System (ADS)
Lorin, E.; Chelkowski, S.; Bandrauk, A.
2007-06-01
This paper is devoted to the dynamics of attosecond pulses created during the high order harmonic generation process. In this goal we study Ti:sapphir laser pulses propagating in a H II + gas. The dynamics and propagation of the incident pulse is obtained by solving the macroscopic Maxwell equations. The molecular gas reaction on the electric field, the polarization, is derived from TDSE's following the model presented in [9], [10]. We are especially interested in this work, in the attosecond pulse dynamics and the intensity of the first harmonics dependently of the propagation length inside the gas, on the attosecond pulse generation and propagation and the energy of return graphs in function of the driver phase.
Propagation measurements in Alaska using ACTS beacons
NASA Technical Reports Server (NTRS)
Mayer, Charles E.
1991-01-01
The placement of an ACTS propagation terminal in Alaska has several distinct advantages. First is the inclusion of a new and important climatic zone to the global propagation model. Second is the low elevation look angle from Alaska to ACTS. These two unique opportunities also present problems unique to the location, such as extreme temperatures and lower power levels. These problems are examined and compensatory solutions are presented.
Tropospheric Propagation Modelling with the Parabolic Equation
1990-09-01
raised cosine window to the imaginary part of the square of the refractive index term. From the fust exponential term of (29) it is evident that this...the present implementation of the model, this low pass filtering of spatial frequency is achieved by applying a simple raised cosine window to the...range in thickness from a few metres (these tend to affect propagation above microwave frequencies) up to hundreds of metres (affecting propagation at
POPPY: Physical Optics Propagation in PYthon
NASA Astrophysics Data System (ADS)
Perrin, Marshall; Long, Joseph; Douglas, Ewan; Sivaramakrishnan, Anand; Slocum, Christine
2016-02-01
POPPY (Physical Optics Propagation in PYthon) simulates physical optical propagation including diffraction. It implements a flexible framework for modeling Fraunhofer and Fresnel diffraction and point spread function formation, particularly in the context of astronomical telescopes. POPPY provides the optical modeling framework for WebbPSF (ascl:1504.007) and was developed as part of a simulation package for JWST, but is available separately and is broadly applicable to many kinds of imaging simulations.
A Chebychev propagator for inhomogeneous Schroedinger equations
Ndong, Mamadou; Koch, Christiane P.; Tal-Ezer, Hillel; Kosloff, Ronnie
2009-03-28
A propagation scheme for time-dependent inhomogeneous Schroedinger equations is presented. Such equations occur in time dependent optimal control theory and in reactive scattering. A formal solution based on a polynomial expansion of the inhomogeneous term is derived. It is subjected to an approximation in terms of Chebychev polynomials. Different variants for the inhomogeneous propagator are demonstrated and applied to two examples from optimal control theory. Convergence behavior and numerical efficiency are analyzed.
Managing Mobile/Satellite Propagation Data
NASA Technical Reports Server (NTRS)
Kantak, Anil V.
1990-01-01
"Data Management System for Mobile Satellite Propagation" software package collection of FORTRAN programs and UNIX shell scripts designed to handle huge amounts of data resulting from mobile/satellite radio-propagation experiments. Data from experiments converted into standard and more useful forms. Software package contains program to convert binary format of data into standard ASCII format suitable for use with wide variety of computing-machine architectures. Written in either FORTRAN 77 or UNIX shell scripts.
Error Propagation in a System Model
NASA Technical Reports Server (NTRS)
Schloegel, Kirk (Inventor); Bhatt, Devesh (Inventor); Oglesby, David V. (Inventor); Madl, Gabor (Inventor)
2015-01-01
Embodiments of the present subject matter can enable the analysis of signal value errors for system models. In an example, signal value errors can be propagated through the functional blocks of a system model to analyze possible effects as the signal value errors impact incident functional blocks. This propagation of the errors can be applicable to many models of computation including avionics models, synchronous data flow, and Kahn process networks.
Molecular dynamics simulation of propagating cracks
NASA Technical Reports Server (NTRS)
Mullins, M.
1982-01-01
Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.
Labeling Nodes Using Three Degrees of Propagation
Mostafavi, Sara; Goldenberg, Anna; Morris, Quaid
2012-01-01
The properties (or labels) of nodes in networks can often be predicted based on their proximity and their connections to other labeled nodes. So-called “label propagation algorithms” predict the labels of unlabeled nodes by propagating information about local label density iteratively through the network. These algorithms are fast, simple and scale to large networks but nonetheless regularly perform better than slower and much more complex algorithms on benchmark problems. We show here, however, that these algorithms have an intrinsic limitation that prevents them from adapting to some common patterns of network node labeling; we introduce a new algorithm, 3Prop, that retains all their advantages but is much more adaptive. As we show, 3Prop performs very well on node labeling problems ill-suited to label propagation, including predicting gene function in protein and genetic interaction networks and gender in friendship networks, and also performs slightly better on problems already well-suited to label propagation such as labeling blogs and patents based on their citation networks. 3Prop gains its adaptability by assigning separate weights to label information from different steps of the propagation. Surprisingly, we found that for many networks, the third iteration of label propagation receives a negative weight. Availability The code is available from the authors by request. PMID:23284828
Premixed flame propagation in vertical tubes
NASA Astrophysics Data System (ADS)
Kazakov, Kirill A.
2016-04-01
Analytical treatment of the premixed flame propagation in vertical tubes with smooth walls is given. Using the on-shell flame description, equations for a quasi-steady flame with a small but finite front thickness are obtained and solved numerically. It is found that near the limits of inflammability, solutions describing upward flame propagation come in pairs having close propagation speeds and that the effect of gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a theory of partial flame propagation driven by a strong gravitational field is developed. A complete explanation is given of the intricate observed behavior of limit flames, including dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction. The role of the finite front-thickness effects is discussed in detail. Also, various mechanisms governing flame acceleration in smooth tubes are identified. Acceleration of methane-air flames in open tubes is shown to be a combined effect of the hydrostatic pressure difference produced by the ambient cold air and the difference of dynamic gas pressure at the tube ends. On the other hand, a strong spontaneous acceleration of the fast methane-oxygen flames at the initial stage of their evolution in open-closed tubes is conditioned by metastability of the quasi-steady propagation regimes. An extensive comparison of the obtained results with the experimental data is made.
Making and Propagating Elastic Waves: Overview of the new wave propagation code WPP
McCandless, K P; Petersson, N A; Nilsson, S; Rodgers, A; Sjogreen, B; Blair, S C
2006-05-09
We are developing a new parallel 3D wave propagation code at LLNL called WPP (Wave Propagation Program). WPP is being designed to incorporate the latest developments in embedded boundary and mesh refinement technology for finite difference methods, as well as having an efficient portable implementation to run on the latest supercomputers at LLNL. We are currently exploring seismic wave applications, including a recent effort to compute ground motions for the 1906 Great San Francisco Earthquake. This paper will briefly describe the wave propagation problem, features of our numerical method to model it, implementation of the wave propagation code, and results from the 1906 Great San Francisco Earthquake simulation.
Radiowave propagation measurements in Nigeria (preliminary reports)
NASA Astrophysics Data System (ADS)
Falodun, S. E.; Okeke, P. N.
2013-07-01
International conferences on frequency coordination have, in recent years, required new information on radiowave propagation in tropical regions and, in particular, on propagation in Africa. The International Telecommunications Union (ITU-R) initiated `radio-wave propagation measurement campaign' in some African countries some years back. However, none of the ITU-initiated experiments were mounted in Nigeria, and hence, there is lack of adequate understanding of the propagation mechanisms associated with this region of the tropics. The Centre for Basic Space Science (CBSS) of NASRDA has therefore embarked on propagation data collection from the different climatic zones of Nigeria (namely Coastal, Guinea Savannah, Midland, and Sahelian) with the aim of making propagation data available to the ITU, for design and prediction purposes in order to ensure a qualitative and effective communication system in Nigeria. This paper focuses on the current status of propagation data from Nigeria (collected by CBSS), identifying other parameters that still need to be obtained. The centre has deployed weather stations to different locations in the country for refractivity measurements in clear atmosphere, at the ground surface and at an altitude of 100 m, being the average height of communication mast in Nigeria. Other equipments deployed are Micro Rain Radar and Nigerian Environmental and Climatic Observing Program equipments. Some of the locations of the measurement stations are Nsukka (7.4° E, 6.9° N), Akure (5.12° E, 7.15° N), Minna (6.5° E, 9.6° N), Sokoto (5.25° E, 13.08° N), Jos (8.9° E, 9.86° N), and Lagos (3.35° E, 6.6° N). The results obtained from the data analysis have shown that the refractivity values vary with climatic zones and seasons of the year. Also, the occurrence probability of abnormal propagation events, such as super refraction, sub-refraction, and ducting, depends on the location as well as the local time. We have also attempted to identify
Accurate orbit propagation with planetary close encounters
NASA Astrophysics Data System (ADS)
Baù, Giulio; Milani Comparetti, Andrea; Guerra, Francesca
2015-08-01
We tackle the problem of accurately propagating the motion of those small bodies that undergo close approaches with a planet. The literature is lacking on this topic and the reliability of the numerical results is not sufficiently discussed. The high-frequency components of the perturbation generated by a close encounter makes the propagation particularly challenging both from the point of view of the dynamical stability of the formulation and the numerical stability of the integrator. In our approach a fixed step-size and order multistep integrator is combined with a regularized formulation of the perturbed two-body problem. When the propagated object enters the region of influence of a celestial body, the latter becomes the new primary body of attraction. Moreover, the formulation and the step-size will also be changed if necessary. We present: 1) the restarter procedure applied to the multistep integrator whenever the primary body is changed; 2) new analytical formulae for setting the step-size (given the order of the multistep, formulation and initial osculating orbit) in order to control the accumulation of the local truncation error and guarantee the numerical stability during the propagation; 3) a new definition of the region of influence in the phase space. We test the propagator with some real asteroids subject to the gravitational attraction of the planets, the Yarkovsky and relativistic perturbations. Our goal is to show that the proposed approach improves the performance of both the propagator implemented in the OrbFit software package (which is currently used by the NEODyS service) and of the propagator represented by a variable step-size and order multistep method combined with Cowell's formulation (i.e. direct integration of position and velocity in either the physical or a fictitious time).
NLO error propagation exercise: statistical results
Pack, D.J.; Downing, D.J.
1985-09-01
Error propagation is the extrapolation and cumulation of uncertainty (variance) above total amounts of special nuclear material, for example, uranium or /sup 235/U, that are present in a defined location at a given time. The uncertainty results from the inevitable inexactness of individual measurements of weight, uranium concentration, /sup 235/U enrichment, etc. The extrapolated and cumulated uncertainty leads directly to quantified limits of error on inventory differences (LEIDs) for such material. The NLO error propagation exercise was planned as a field demonstration of the utilization of statistical error propagation methodology at the Feed Materials Production Center in Fernald, Ohio from April 1 to July 1, 1983 in a single material balance area formed specially for the exercise. Major elements of the error propagation methodology were: variance approximation by Taylor Series expansion; variance cumulation by uncorrelated primary error sources as suggested by Jaech; random effects ANOVA model estimation of variance effects (systematic error); provision for inclusion of process variance in addition to measurement variance; and exclusion of static material. The methodology was applied to material balance area transactions from the indicated time period through a FORTRAN computer code developed specifically for this purpose on the NLO HP-3000 computer. This paper contains a complete description of the error propagation methodology and a full summary of the numerical results of applying the methodlogy in the field demonstration. The error propagation LEIDs did encompass the actual uranium and /sup 235/U inventory differences. Further, one can see that error propagation actually provides guidance for reducing inventory differences and LEIDs in future time periods.
Prediction of nonlinear jet noise propagation
NASA Astrophysics Data System (ADS)
Gee, Kent L.
The role of nonlinearity in the propagation of noise radiated from high-performance jet aircraft has not been a well-understood phenomenon in the past. To address the problem of finite-amplitude noise propagation, a hybrid time-frequency domain model has been developed to numerically solve the generalized Mendousse-Burgers equation, which is a parabolic model equation that includes effects of quadratic nonlinearity, atmospheric absorption and dispersion, and geometrical spreading. The algorithm has been compared against analytical theory and numerical issues have been discussed. Three sets of experimental data have been used to evaluate the model: model-scale laboratory jet data, field data using a large loudspeaker, and static engine run-up measurements of the F/A-22 Raptor. Comparison of linearly- and nonlinearly-predicted spectra demonstrates that nonlinearity does, in fact, impact the noise propagation in all three sets of data. Additionally, the extensive comparison with the Raptor data shows that the model is successful in predicting the measured spectrum over multiple angles and engine conditions, demonstrating that the model captures much of the physics of the propagation, despite its current neglect of multipath interference and atmospheric refraction and turbulence effects. Two additional studies have been carried out in order to address fundamental questions relevant to the nonlinear propagation of jet noise: ''What is the impact of nonlinearity on perceived levels?" and ''At what point does the propagation become linear?" An investigation of the perceived impact of nonlinearity shows that there are only minor differences between nonlinear and linear predictions in calculations of power-based, single-number metrics, such as A-weighted overall sound pressure level. On the other hand, the actual perceived differences between nonlinear and linear waveforms are substantially greater and consequently do not correlate well with calculated metrics. This
Effects of fluctuations on propagating fronts
NASA Astrophysics Data System (ADS)
Panja, Debabrata
Propagating fronts are seen in varieties of nonequilibrium pattern forming systems in Physics, Chemistry and Biology. In the last two decades, many researchers have contributed to the understanding of the underlying dynamics of the propagating fronts. Of these, the deterministic and mean-field dynamics of the fronts were mostly understood in late 1980s and 1990s. On the other hand, although the earliest work on the effect of fluctuations on propagating fronts dates back to early 1980s, the subject of fluctuating fronts did not reach its adolescence until the mid 1990s. From there onwards the last few years witnessed a surge in activities in the effect of fluctuations on propagating fronts. Scores of papers have been written on this subject since then, contributing to a significant maturity of our understanding, and only recently a full picture of fluctuating fronts has started to emerge. This review is an attempt to collect all the works on fluctuating (propagating) fronts in a coherent and cogent manner in proper perspective. It is based on the idea of making our knowledge in this field available to a broader audience, and it is also expected to help to collect bits and pieces of loose thread-ends together for possible further investigation.
Propagation in polymer parameterised field theory
NASA Astrophysics Data System (ADS)
Varadarajan, Madhavan
2017-01-01
The Hamiltonian constraint operator in loop quantum gravity acts ultralocally. Smolin has argued that this ultralocality seems incompatible with the existence of a quantum dynamics which propagates perturbations between macroscopically seperated regions of quantum geometry. We present evidence to the contrary within an LQG type ‘polymer’ quantization of two dimensional parameterised field theory (PFT). PFT is a generally covariant reformulation of free field propagation on flat spacetime. We show explicitly that while, as in LQG, the Hamiltonian constraint operator in PFT acts ultralocally, states in the joint kernel of the Hamiltonian and diffeomorphism constraints of PFT necessarily describe propagation effects. The particular structure of the finite triangulation Hamiltonian constraint operator plays a crucial role, as does the necessity of imposing (the continuum limit of) its kinematic adjoint as a constraint. Propagation is seen as a property encoded by physical states in the kernel of the constraints rather than that of repeated actions of the finite triangulation Hamiltonian constraint on kinematic states. The analysis yields robust structural lessons for putative constructions of the Hamiltonian constraint in LQG for which ultralocal action co-exists with a description of propagation effects by physical states.
Slow wave propagation in soft adhesive interfaces.
Viswanathan, Koushik; Sundaram, Narayan K; Chandrasekar, Srinivasan
2016-11-16
Stick-slip in sliding of soft adhesive surfaces has long been associated with the propagation of Schallamach waves, a type of slow surface wave. Recently it was demonstrated using in situ experiments that two other kinds of slow waves-separation pulses and slip pulses-also mediate stick-slip (Viswanathan et al., Soft Matter, 2016, 12, 5265-5275). While separation pulses, like Schallamach waves, involve local interface detachment, slip pulses are moving stress fronts with no detachment. Here, we present a theoretical analysis of the propagation of these three waves in a linear elastodynamics framework. Different boundary conditions apply depending on whether or not local interface detachment occurs. It is shown that the interface dynamics accompanying slow waves is governed by a system of integral equations. Closed-form analytical expressions are obtained for the interfacial pressure, shear stress, displacements and velocities. Separation pulses and Schallamach waves emerge naturally as wave solutions of the integral equations, with oppositely oriented directions of propagation. Wave propagation is found to be stable in the stress regime where linearized elasticity is a physically valid approximation. Interestingly, the analysis reveals that slow traveling wave solutions are not possible in a Coulomb friction framework for slip pulses. The theory provides a unified picture of stick-slip dynamics and slow wave propagation in adhesive contacts, consistent with experimental observations.
Classification of neocortical interneurons using affinity propagation.
Santana, Roberto; McGarry, Laura M; Bielza, Concha; Larrañaga, Pedro; Yuste, Rafael
2013-01-01
In spite of over a century of research on cortical circuits, it is still unknown how many classes of cortical neurons exist. In fact, neuronal classification is a difficult problem because it is unclear how to designate a neuronal cell class and what are the best characteristics to define them. Recently, unsupervised classifications using cluster analysis based on morphological, physiological, or molecular characteristics, have provided quantitative and unbiased identification of distinct neuronal subtypes, when applied to selected datasets. However, better and more robust classification methods are needed for increasingly complex and larger datasets. Here, we explored the use of affinity propagation, a recently developed unsupervised classification algorithm imported from machine learning, which gives a representative example or exemplar for each cluster. As a case study, we applied affinity propagation to a test dataset of 337 interneurons belonging to four subtypes, previously identified based on morphological and physiological characteristics. We found that affinity propagation correctly classified most of the neurons in a blind, non-supervised manner. Affinity propagation outperformed Ward's method, a current standard clustering approach, in classifying the neurons into 4 subtypes. Affinity propagation could therefore be used in future studies to validly classify neurons, as a first step to help reverse engineer neural circuits.
Classification of neocortical interneurons using affinity propagation
Santana, Roberto; McGarry, Laura M.; Bielza, Concha; Larrañaga, Pedro; Yuste, Rafael
2013-01-01
In spite of over a century of research on cortical circuits, it is still unknown how many classes of cortical neurons exist. In fact, neuronal classification is a difficult problem because it is unclear how to designate a neuronal cell class and what are the best characteristics to define them. Recently, unsupervised classifications using cluster analysis based on morphological, physiological, or molecular characteristics, have provided quantitative and unbiased identification of distinct neuronal subtypes, when applied to selected datasets. However, better and more robust classification methods are needed for increasingly complex and larger datasets. Here, we explored the use of affinity propagation, a recently developed unsupervised classification algorithm imported from machine learning, which gives a representative example or exemplar for each cluster. As a case study, we applied affinity propagation to a test dataset of 337 interneurons belonging to four subtypes, previously identified based on morphological and physiological characteristics. We found that affinity propagation correctly classified most of the neurons in a blind, non-supervised manner. Affinity propagation outperformed Ward's method, a current standard clustering approach, in classifying the neurons into 4 subtypes. Affinity propagation could therefore be used in future studies to validly classify neurons, as a first step to help reverse engineer neural circuits. PMID:24348339
Heat pulse propagation studies in TFTR
Fredrickson, E.D.; Callen, J.D.; Colchin, R.J.; Efthimion, P.C.; Hill, K.W.; Izzo, R.; Mikkelsen, D.R.; Monticello, D.A.; McGuire, K.; Bell, J.D.
1986-02-01
The time scales for sawtooth repetition and heat pulse propagation are much longer (10's of msec) in the large tokamak TFTR than in previous, smaller tokamaks. This extended time scale coupled with more detailed diagnostics has led us to revisit the analysis of the heat pulse propagation as a method to determine the electron heat diffusivity, chi/sub e/, in the plasma. A combination of analytic and computer solutions of the electron heat diffusion equation are used to clarify previous work and develop new methods for determining chi/sub e/. Direct comparison of the predicted heat pulses with soft x-ray and ECE data indicates that the space-time evolution is diffusive. However, the chi/sub e/ determined from heat pulse propagation usually exceeds that determined from background plasma power balance considerations by a factor ranging from 2 to 10. Some hypotheses for resolving this discrepancy are discussed. 11 refs., 19 figs., 1 tab.
Coronal Structures Observed by Radio Propagation Measurements
NASA Technical Reports Server (NTRS)
Woo, R.
1995-01-01
This paper summarizes (1) advances in our knowledge of coronal structures inferred from radio propagation measurements, and (2) gains in our understanding of the relationship between radio propagation and white-light coronagraph measurements. Radio propagation measurements confirm that streamers are ray-like structures as depicted in coronagraph pictures, but also reveal a hierarchy of filamentary structures throughout the corona, extending from the size of streamers down to scale sizes as small as about 1 km at the Sun (10(ghe) arcsec). Doppler scintillation measurements, therefore, open a new window on small-scale structure that has long eluded coronagraph measurements. In addition, high precision ranging measurements make it possible to investigate large-scale structures not yet observed in corona graphs, such as plumes in equatorial coronal regions.
Wave propagation into the middle atmosphere
NASA Technical Reports Server (NTRS)
Hirota, I.
1989-01-01
Recent observations of various types of waves propagating into the middle atmosphere are reviewed. Emphasis is made on the excitation processes in the lower atmosphere and their vertical propagation through the background flow as a function of the latitude, height and season. The following subjects are discussed: (1) Vertical propagation of quasi-stationary forced Rossby waves into the winter stratosphere in connection with the sudden warming; (2) Spectral distribution and seasonal characteristics of normal mode (free) Rossby waves and the asymmetry of the Northern and Southern Hemispheres; and (3) Seasonal variation of internal gravity waves in the middle atmosphere. Further discussions are presented for future studies based on accumulated observational data during the MAP period.
Propagation studies using a theoretical ionosphere model
NASA Technical Reports Server (NTRS)
Lee, M.
1973-01-01
The mid-latitude ionospheric and neutral atmospheric models are coupled with an advanced three dimensional ray tracing program to see what success would be obtained in predicting the wave propagation conditions and to study to what extent the use of theoretical ionospheric models is practical. The Penn State MK 1 ionospheric model, the Mitra-Rowe D region model, and the Groves' neutral atmospheric model are used throughout this work to represent the real electron densities and collision frequencies. The Faraday rotation and differential Doppler velocities from satellites, the propagation modes for long distance high frequency propagation, the group delays for each mode, the ionospheric absorption, and the spatial loss are all predicted.
Asymptotic wave propagation in excitable media.
Bernus, Olivier; Vigmond, Edward
2015-07-01
Wave shape and velocity are important issues in reaction-diffusion systems, and are often the result of competition in media with heterogeneous conduction properties. Asymptotic wave front propagation at maximal conduction velocity has been previously reported in the context of anisotropic cardiac tissue, but it is unknown whether this is a universal property of excitable tissues where conduction velocity can be locally modulated by mechanisms other than anisotropy. Here, we investigate the impact of conduction heterogeneities and boundary effects on wave propagation in excitable media. Following a theoretical analysis, we find that wave-front cusps occur where local velocity is reduced and that asymptotic wave fronts propagate at the maximal translational conduction velocity. Simulations performed in different reaction-diffusion systems, including cardiac tissue, confirm our theoretical findings. We conclude that this property can be found in a wide range of reaction-diffusion systems with excitable dynamics and that asymptotic wave-front shapes can be predicted.
Three-Dimensional Gear Crack Propagation Studies
NASA Technical Reports Server (NTRS)
Lewicki, David G.; Sane, Ashok D.; Drago, Raymond J.; Wawrzynek, Paul A.
1998-01-01
Three-dimensional crack growth simulation was performed on a split-tooth gear design using boundary element modeling and linear elastic fracture mechanics. Initial cracks in the fillet of the teeth produced stress intensity factors of greater magnitude (and thus, greater crack growth rates) than those in the root or groove areas of the teeth. Crack growth simulation was performed on a case study to evaluate crack propagation paths. Tooth fracture was predicted from the crack growth simulation for an initial crack in the tooth fillet region. Tooth loads on the uncracked mesh of the split-tooth design were up to five times greater than those on the cracked mesh if equal deflections of the cracked and uncracked teeth were considered. Predicted crack shapes as well as crack propagation life are presented based on calculated stress intensity factors, mixed-mode crack propagation trajectory theories, and fatigue crack growth theories.
Surface Plasmon Propagation in Nanostructured Metallic Waveguides
NASA Astrophysics Data System (ADS)
Calm, Y. M.; Merlo, J. M.; Rose, A. H.; Nesbitt, N. T.; Boyce, A. M.; McMahon, G.; Burns, M. J.; Kempa, K.; Naughton, M. J.
2015-03-01
Visible frequencies of light can be routed on subwavelength scales with nanostructured, metallic waveguides by coupling optical energy to surface plasmon (SP) modes at a metal-insulator interface. Epitaxially-grown Ag nanowires and nanocoaxes provide a low-loss, ``model'' system to characterize the propagation of SP waves. We have studied these structures by electron, focused ion, scanning probe, and optical microscopies, and have observed propagation lengths exceeding 15λvac with confinement on the order of 0 . 07(λvac) 2 . Experimental efforts towards lithographically-fabricated metal-insulator-metal waveguides are discussed. Finally, an architecture for a nanocoax-based optical microscope, which extracts near-field (evanescent) information and propagates it into the far-field, is presented. Supported by the W.M. Keck Foundation.
Shock unsteadiness creation and propagation: experimental analysis
NASA Astrophysics Data System (ADS)
Benay, R.; Alaphilippe, M.; Severac, N.
2012-09-01
The possibility of creating unsteady distortions of the tip shock by waves emitted from an aircraft is assessed experimentally. The model chosen is a cylindrical fore body equipped with a spike. This configuration is known for generating an important level of unsteadiness around the spike in supersonic regime. The wind tunnel Mach number is equal to 2. The experiments show that waves emitted from this source propagate along the tip shock and interact with it. It is then assessed that this interaction produces a periodic distortion of the shock that propagates to the external flow. Unsteady pressure sensors, high speed schlieren films, hot wire probing and laser Doppler velocimetry are used as complementary experimental means. The final result is a coherent representation of the complex mechanism of wave propagation that has been evidenced. The principle of creating unsteady shock deformation by onboard equipments could be examined as a possibly promising method of sonic boom control.
Large scale propagation intermittency in the atmosphere
NASA Astrophysics Data System (ADS)
Mehrabi, Ali
2000-11-01
Long-term (several minutes to hours) amplitude variations observed in outdoor sound propagation experiments at Disneyland, California, in February 1998 are explained in terms of a time varying index of refraction. The experimentally propagated acoustic signals were received and recorded at several locations ranging from 300 meters to 2,800 meters. Meteorological data was taken as a function of altitude simultaneously with the received signal levels. There were many barriers along the path of acoustic propagation that affected the received signal levels, especially at short ranges. In a downward refraction situation, there could be a random change of amplitude in the predicted signals. A computer model based on the Fast Field Program (FFP) was used to compute the signal loss at the different receiving locations and to verify that the variations in the received signal levels can be predicted numerically. The calculations agree with experimental data with the same trend variations in average amplitude.
Displacement of squeezed propagating microwave states
NASA Astrophysics Data System (ADS)
Fedorov, Kirill G.; Zhong, Ling; Pogorzalek, Stefan; Eder, Peter; Fischer, Michael; Goetz, Jan; Wulschner, Friedrich; Xie, Edwar; Menzel, Edwin; Deppe, Frank; Marx, Achim; Gross, Rudolf
Displacement of propagating squeezed states is a fundamental operation for quantum communications. It can be applied to fundamental studies of macroscopic quantum coherence and has an important role in quantum teleportation protocols with propagating microwaves. We generate propagating squeezed states using a Josephson parametric amplifier and implement displacement using a cryogenic directional coupler. We study single- and two-mode displacement regimes. For the single-mode displacement we find that the squeezing level of the displaced squeezed state does not depend on the displacement amplitude. Also, we observe that quantum entanglement between two spatially separated channels stays constant across 4 orders of displacement power. We acknowledge support by the German Research Foundation through SFB 631 and FE 1564/1-1, the EU project PROMISCE, and Elite Network of Bavaria through the program ExQM.
Polarization Shaping for Control of Nonlinear Propagation
NASA Astrophysics Data System (ADS)
Bouchard, Frédéric; Larocque, Hugo; Yao, Alison M.; Travis, Christopher; De Leon, Israel; Rubano, Andrea; Karimi, Ebrahim; Oppo, Gian-Luca; Boyd, Robert W.
2016-12-01
We study the nonlinear optical propagation of two different classes of light beams with space-varying polarization—radially symmetric vector beams and Poincaré beams with lemon and star topologies—in a rubidium vapor cell. Unlike Laguerre-Gauss and other types of beams that quickly experience instabilities, we observe that their propagation is not marked by beam breakup while still exhibiting traits such as nonlinear confinement and self-focusing. Our results suggest that, by tailoring the spatial structure of the polarization, the effects of nonlinear propagation can be effectively controlled. These findings provide a novel approach to transport high-power light beams in nonlinear media with controllable distortions to their spatial structure and polarization properties.
Satellite sound broadcast propagation studies and measurements
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Torrence, Geoffrey W.
1990-01-01
Satellite Sound Broadcasting is an attractive satellite application. Before regulatory decisions can be made in 1992, the propagation effects encountered have to be characterized. The Electrical Engineering Research Laboratory has nearly completed a system which will allow amplitude measurements to be made over 10 MHz bandwidths in the 800 to 1800 MHz frequency range. The system uses transmission from a transportable tower, and reception inside buildings or in the shadow of trees or utility poles. The goal is to derive propagation models for use by systems engineers who are about to design satellite broadcast systems. The advance of fiber-optics technology has helped to focus future development of satellite services into areas where satellites are uniquely competitive. One of these preferred satellite applications is the broadcasting of high-quality sound for stationary or mobile reception by listeners using low-cost, consumer-grade receivers. Before such services can be provided, however, the political hurdles of spectrum allocation have to be surmounted and the technical questions of standardization for world-wide compatibility have to be resolved. In order to arrive at an optimal system design, efficient in the use of our scarce spectral resources, affordable both to the broadcaster and the listener, and providing predictable performance, the propagation effects to which the service is subjected have to be characterized. Consequently, the objective of the research project is to make basic propagation measurements for direct Satellite Sound Broadcasting Service (SSBS). The data obtained should allow the development of propagation models to be used by communications engineers designing the operational systems. Such models shall describe the effects of shadowing and multipath propagation on SSBS receivers operating in a specified environment, such as inside commercial or residential buildings of various construction and also in the shadow of trees or utility poles
Complex singularities in the quark propagator
Roberts, C.D.; Frank, M.R.
1995-08-01
The Dyson-Schwinger equation for the quark propagator is being studied in the rainbow approximation using a gluon propagator that incorporates asymptotic freedom and is an entire function. The gluon propagator has a number of parameters that may be varied in order to obtain a good description of low-energy pion observables; such as f{sub {pi}} and the {pi}-{pi} scattering lengths. This provides a direct means of relating hadronic observables to the form of the quark-quark interaction in the infrared and serves as an adjunct and extension of the separable Ansatz approach discussed above. It also provides a means of examining the pole structure of the quark propagator, which may hold the key to understanding quark confinement. The preliminary results are encouraging. It was demonstrated that it is possible to obtain a good description of pion observables in this approach. Further, when the strength of the quark-quark interaction in the infrared becomes larger than a given critical value, the pole in the quark propagator bifurcates into a pair of complex conjugate poles: m{sub q} = m{sub q}{sup R} {plus_minus} im{sub q}{sup I}, which is a signal of confinement. The interpretation in this case is of 1/m{sub q}{sup I} as the distance over which a quark may propagate before fragmenting. Further, there are indications from these studies that T{sub c}{sup D} < T{sub c}{sup {chi}}, where T{sub c}{sup D} is the critical temperature for deconfinement and T{sub c}{sup {chi}} is the critical temperature for chiral symmetry restoration; i.e., indications that deconfinement occurs at a lower temperature than chiral symmetry restoration. Available results from this work will be presented at the Washington meeting of the APS.
The discrete regime of flame propagation
NASA Astrophysics Data System (ADS)
Tang, Francois-David; Goroshin, Samuel; Higgins, Andrew
The propagation of laminar dust flames in iron dust clouds was studied in a low-gravity envi-ronment on-board a parabolic flight aircraft. The elimination of buoyancy-induced convection and particle settling permitted measurements of fundamental combustion parameters such as the burning velocity and the flame quenching distance over a wide range of particle sizes and in different gaseous mixtures. The discrete regime of flame propagation was observed by substitut-ing nitrogen present in air with xenon, an inert gas with a significantly lower heat conductivity. Flame propagation in the discrete regime is controlled by the heat transfer between neighbor-ing particles, rather than by the particle burning rate used by traditional continuum models of heterogeneous flames. The propagation mechanism of discrete flames depends on the spa-tial distribution of particles, and thus such flames are strongly influenced by local fluctuations in the fuel concentration. Constant pressure laminar dust flames were observed inside 70 cm long, 5 cm diameter Pyrex tubes. Equally-spaced plate assemblies forming rectangular chan-nels were placed inside each tube to determine the quenching distance defined as the minimum channel width through which a flame can successfully propagate. High-speed video cameras were used to measure the flame speed and a fiber optic spectrometer was used to measure the flame temperature. Experimental results were compared with predictions obtained from a numerical model of a three-dimensional flame developed to capture both the discrete nature and the random distribution of particles in the flame. Though good qualitative agreement was obtained between model predictions and experimental observations, residual g-jitters and the short reduced-gravity periods prevented further investigations of propagation limits in the dis-crete regime. The full exploration of the discrete flame phenomenon would require high-quality, long duration reduced gravity environment
Learn Sparse Dictionaries for Edit Propagation.
Xiaowu Chen; Jianwei Li; Dongqing Zou; Qinping Zhao
2016-04-01
With the increasing availability of high-resolution images, videos, and 3D models, the demand for scalable large data processing techniques increases. We introduce a method of sparse dictionary learning for edit propagation of large input data. Previous approaches for edit propagation typically employ a global optimization over the whole set of pixels (or vertexes), incurring a prohibitively high memory and time-consumption for large input data. Rather than propagating an edit pixel by pixel, we follow the principle of sparse representation to obtain a representative and compact dictionary and perform edit propagation on the dictionary instead. The sparse dictionary provides an intrinsic basis for input data, and the coding coefficients capture the linear relationship between all pixels and the dictionary atoms. The learned dictionary is then optimized by a novel scheme, which maximizes the Kullback-Leibler divergence between each atom pair to remove redundant atoms. To enable local edit propagation for images or videos with similar appearance, a dictionary learning strategy is proposed by considering range constraint to better account for the global distribution of pixels in their feature space. We show several applications of the sparsity-based edit propagation, including video recoloring, theme editing, and seamless cloning, operating on both color and texture features. Our approach can also be applied to computer graphics tasks, such as 3D surface deformation. We demonstrate that with an atom-to-pixel ratio in the order of 0.01% signifying a significant reduction on memory consumption, our method still maintains a high degree of visual fidelity.
Proceedings of the Thirteenth NASA Propagation Experimenters Meeting (NAPEX 13)
NASA Technical Reports Server (NTRS)
Davarian, Faramaz (Editor)
1989-01-01
The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. The meeting was organized into three technical sessions: the first focused on mobile satellite propagation; the second examined the propagation effects for frequencies above 10 GHz; and the third addressed studies devoted exclusively to the Olympus/Advanced Communications Technology Satellite (ACTS) Program.
Elementary functions: propagation of partially coherent light.
Burvall, Anna; Smith, Arlene; Dainty, Christopher
2009-07-01
The theory of propagation of partially coherent light is well known, but performing numerical calculations still presents a difficulty because of the dimensionality of the problem. We propose using a recently introduced method based on the use of elementary functions [Wald et al. Proc. SPIE6040, 59621G (2005)] to reduce the integrals to two dimensions. We formalize the method, describe its inherent assumptions and approximations, and introduce a sampling criterion for adequate interpolation. We present an analysis of some special cases, such as the Gaussian Schell-model beam, and briefly discuss generalized numerical propagation of two-dimensional field distributions.
Propagation of transients in a random medium
NASA Technical Reports Server (NTRS)
Wenzel, A. R.
1975-01-01
The propagation of transient scalar waves in a three-dimensional random medium is considered. The analysis is based on the smoothing method. An integro-differential equation for the coherent (or average) wave is derived and solved for the case of a statistically homogeneous and isotropic medium and a delta-function source. This yields the coherent Green's function of the medium. It is found that the waveform of the coherent wave depends generally on the distance from the source measured in terms of a certain dimensionless parameter. Based on the magnitude of this parameter, three propagation zones, called the near zone, the far zone, and the intermediate zone, are defined.
Displacement of Propagating Squeezed Microwave States
NASA Astrophysics Data System (ADS)
Fedorov, Kirill G.; Zhong, L.; Pogorzalek, S.; Eder, P.; Fischer, M.; Goetz, J.; Xie, E.; Wulschner, F.; Inomata, K.; Yamamoto, T.; Nakamura, Y.; Di Candia, R.; Las Heras, U.; Sanz, M.; Solano, E.; Menzel, E. P.; Deppe, F.; Marx, A.; Gross, R.
2016-07-01
Displacement of propagating quantum states of light is a fundamental operation for quantum communication. It enables fundamental studies on macroscopic quantum coherence and plays an important role in quantum teleportation protocols with continuous variables. In our experiments, we have successfully implemented this operation for propagating squeezed microwave states. We demonstrate that, even for strong displacement amplitudes, there is no degradation of the squeezing level in the reconstructed quantum states. Furthermore, we confirm that path entanglement generated by using displaced squeezed states remains constant over a wide range of the displacement power.
Comments on 'Rapid pulsed microwave propagation'
NASA Technical Reports Server (NTRS)
Steffes, Paul G.; Rodrigue, George P.
1992-01-01
Giakos and Ishii (1991) claim conclusive experimental evidence that microwave pulse propagation in waveguides and in air occurs at velocities exceeding the free-space speed of light, and assert that it is possible to transmit both energy and information in a non-TEM waveguiding medium at the lightspeed-exceeding phase velocity. The present analysis of their results reveals several significant potential sources of error in both their laboratory findings and those findings' interpretation. Giakos and Ishii reply that the accuracy of the propagation measurements presented in their study exceeds 0.2 percent.
Mapping mechanical force propagation through biomolecular complexes
Schoeler, Constantin; Bernardi, Rafael C.; Malinowska, Klara H.; Durner, Ellis; Ott, Wolfgang; Bayer, Edward A.; Schulten, Klaus; Nash, Michael A.; Gaub, Hermann E.
2015-08-11
In this paper, we employ single-molecule force spectroscopy with an atomic force microscope (AFM) and steered molecular dynamics (SMD) simulations to reveal force propagation pathways through a mechanically ultrastable multidomain cellulosome protein complex. We demonstrate a new combination of network-based correlation analysis supported by AFM directional pulling experiments, which allowed us to visualize stiff paths through the protein complex along which force is transmitted. Finally, the results implicate specific force-propagation routes nonparallel to the pulling axis that are advantageous for achieving high dissociation forces.
Quantum theory of light propagation - Linear medium
NASA Astrophysics Data System (ADS)
Abram, I.
1987-06-01
A quantum-mechanical formalism has been developed which permits the treatment of light propagation within the conceptual framework of quantum optics. The formalism rests on the calculation of the momentum operator for the radiation field, and yields directly a description for the spatial progression of the electromagnetic waves. In this paper, a quantum-mechanical treatment for refraction and reflection is given by applying the formalism to propagation through a linear dielectric. The fidelity with which this formalism reproduces all results known from classical optics demonstrates its validity.
Propagation of sound in turbulent media
NASA Technical Reports Server (NTRS)
Wenzel, A. R.
1976-01-01
Perturbation methods commonly used to study the propagation of acoustic waves in turbulent media are reviewed. Emphasis is on those techniques which are applicable to problems involving long-range propagation in the atmosphere and ocean. Characteristic features of the various methods are illustrated by applying them to particular problems. It is shown that conventional perturbation techniques, such as the Born approximation, yield solutions which contain secular terms, and which therefore have a relatively limited range of validity. In contrast, it is found that solutions obtained with the aid of the Rytov method or the smoothing method do not contain secular terms, and consequently have a much greater range of validity.
Advances in Geometric Acoustic Propagation Modeling Methods
NASA Astrophysics Data System (ADS)
Blom, P. S.; Arrowsmith, S.
2013-12-01
Geometric acoustics provides an efficient numerical method to model propagation effects. At leading order, one can identify ensonified regions and calculate celerities of the predicted arrivals. Beyond leading order, the solution of the transport equation provides a means to estimate the amplitude of individual acoustic phases. The auxiliary parameters introduced in solving the transport equation have been found to provide a means of identifying ray paths connecting source and receiver, or eigenrays, for non-planar propagation. A detailed explanation of the eigenray method will be presented as well as an application to predicting azimuth deviations for infrasonic data recorded during the Humming Roadrunner experiment of 2012.
Information propagation for interacting-particle systems
Schuch, Norbert; Harrison, Sarah K.; Osborne, Tobias J.; Eisert, Jens
2011-09-15
We study the speed at which information propagates through systems of interacting quantum particles moving on a regular lattice and show that for a certain class of initial conditions there exists a maximum speed of sound at which information can propagate. Our argument applies equally to quantum spins, bosons such as in the Bose-Hubbard model, fermions, anyons, and general mixtures thereof, on arbitrary lattices of any dimension. It also pertains to dissipative dynamics on the lattice, and generalizes to the continuum for quantum fields. Our result can be seen as an analog of the Lieb-Robinson bound for strongly correlated models.
Neutrino propagation in matter with general interactions
Bergmann, S.; Grossman, Y.; Nardi, E.
1999-11-01
We present a general analysis of the effective potential for neutrino propagation in matter, assuming a generic set of Lorentz invariant non-derivative interactions. We find that in addition to the known vector and axial vector terms, in a polarized medium also tensor interactions can play an important role. We compute the effective potential arising from a tensor interaction. We show that the components of the tensor potential transverse to the direction of the neutrino propagation can induce a neutrino spin flip, similar to the one induced by a transverse magnetic field. {copyright} {ital 1999} {ital The American Physical Society}
Surface acoustic wave propagation in graphene film
Roshchupkin, Dmitry Plotitcyna, Olga; Matveev, Viktor; Kononenko, Oleg; Emelin, Evgenii; Irzhak, Dmitry; Ortega, Luc; Zizak, Ivo; Erko, Alexei; Tynyshtykbayev, Kurbangali; Insepov, Zinetula
2015-09-14
Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.
Enhancement of in vitro Guayule propagation
NASA Technical Reports Server (NTRS)
Dastoor, M. N.; Schubert, W. W.; Petersen, G. R. (Inventor)
1982-01-01
A method for stimulating in vitro propagation of Guayule from a nutrient medium containing Guayule tissue by adding a substituted trialkyl amine bioinducing agent to the nutrient medium is described. Selective or differentiated propagation of shoots or callus is obtained by varying the amounts of substituted trialky amine present in the nutrient medium. The luxuriant growth provided may be processed for its poly isoprene content or may be transferred to a rooting medium for production of whole plants as identical clones of the original tissue. The method also provides for the production of large numbers of Guayule plants having identical desirable properties such as high polyisoprene levels.
Surface acoustic wave propagation in graphene film
NASA Astrophysics Data System (ADS)
Roshchupkin, Dmitry; Ortega, Luc; Zizak, Ivo; Plotitcyna, Olga; Matveev, Viktor; Kononenko, Oleg; Emelin, Evgenii; Erko, Alexei; Tynyshtykbayev, Kurbangali; Irzhak, Dmitry; Insepov, Zinetula
2015-09-01
Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.
SQUARE DEAL Explosive Source (SUS) Propagation Measurements
1976-07-19
CI.ASSIPICATION OF THIS PA0l[(30m D41 ktleted) 15a. DD 25 4, 5 Aug 75 CLASSIFIED BY Cont. N0001-75-C-042 9 SUBJECT TO GDS OF EO 11652 AUTOMATICALLY...1) Range Dependence 89 (2) Bottom Effects 89 (3) Source Depth 96 (4) Receiver Depth 96 ()Frequency Dependence 9 b. ACODAC, Site 1C 101 (1) Range...PL 11-8 PROPAGATION LOSS - SITE 2C, EVENT 2a 29 t. 2066 m Receiver Two Source Depths 25, 50, and 158 Hz 11- 9 PROPAGATION LOSS - SITE 2C, EVENT 2a 30
Measurement of low-altitude infrared propagation.
Zeisse, C R; Nener, B D; Dewees, R V
2000-02-20
Infrared propagation at low altitudes is determined by extinction that is due to molecules and aerosol particles and ray bending by refraction, three effects that control the mean value of the signal. Interference causes the signal to fluctuate, or scintillate, about the mean value. We discuss the design, calibration, and limitations of a field instrument for measuring optical propagation inside the midwave and long-wave infrared atmospheric windows. The instrument, which is accurate to ?10%, has been used to investigate aerosol, refractive, and scintillation phenomena in the marine boundary layer.
Propagation of a liquid-liquid explosion
Harlow, F.H.; Ruppel, H.M.
1981-08-01
Direct contact between two liquids, one cold and the other hot, may be precluded by the presence of a vapor film. Bridging of this film by one or both fluids results in rapid local boiling, which may initiate a propagating liquid-liquid explosion. A mechanism is discussed for the propagation that involves implosion of the film, rapid mixing of the fluids, heat exchange to warm the cold fluid above the temperature for spontaneous nucleation, and the explosive generation of vapor, which in turn continues to sustain the film implosion. Plausibility for the model is demonstrated by means of numerical studies by high-speed computer.
Atmospheric Propagation Effects Relevant to Optical Communications
NASA Technical Reports Server (NTRS)
Shaik, K. S.
1988-01-01
A number of atmospheric phenomena affect the propagation of light. This article reviews the effects of clear-air turbulence as well as atmospheric turbidity on optical communications. Among the phenomena considered are astronomical and random refraction, scintillation, beam broadening, spatial coherence, angle of arrival, aperture averaging, absorption and scattering, and the effect of opaque clouds. An extensive reference list is also provided for further study, Useful information on the atmospheric propagation of light in resolution to optical deep-space communications to an earth-based receiving station is available, however, further data must be generated before such a link can be designed with committed performance.
Atmospheric propagation effects relevant to optical communications
NASA Technical Reports Server (NTRS)
Shaik, K. S.
1988-01-01
A number of atmospheric phenomena affect the propagation of light. The effects of clear air turbulence are reviewed as well as atmospheric turbidity on optical communications. Among the phenomena considered are astronomical and random refraction, scintillation, beam broadening, spatial coherence, angle of arrival, aperture averaging, absorption and scattering, and the effect of opaque clouds. An extensive reference list is also provided for further study. Useful information on the atmospheric propagation of light in relation to optical deep space communications to an earth based receiving station is available, however, further data must be generated before such a link can be designed with committed performance.
Underwater Sound Propagation from Marine Pile Driving.
Reyff, James A
2016-01-01
Pile driving occurs in a variety of nearshore environments that typically have very shallow-water depths. The propagation of pile-driving sound in water is complex, where sound is directly radiated from the pile as well as through the ground substrate. Piles driven in the ground near water bodies can produce considerable underwater sound energy. This paper presents examples of sound propagation through shallow-water environments. Some of these examples illustrate the substantial variation in sound amplitude over time that can be critical to understand when computing an acoustic-based safety zone for aquatic species.
Atmospheric propagation issues relevant to optical communications
NASA Technical Reports Server (NTRS)
Churnside, James H.; Shaik, Kamran
1989-01-01
Atmospheric propagation issues relevant to space-to-ground optical communications for near-earth applications are studied. Propagation effects, current optical communication activities, potential applications, and communication techniques are surveyed. It is concluded that a direct-detection space-to-ground link using redundant receiver sites and temporal encoding is likely to be employed to transmit earth-sensing satellite data to the ground some time in the future. Low-level, long-term studies of link availability, fading statistics, and turbulence climatology are recommended to support this type of application.
Future changes in propagating and non-propagating diurnal rainfall over East Asia
NASA Astrophysics Data System (ADS)
Huang, Wan-Ru; Wang, S.-Y. Simon
2016-09-01
The characteristics of diurnal rainfall in the East Asian continent consist of a propagating regime over the Yangtze River and a non-propagating regime in southeast China. Simulations of these two diurnal rainfall regimes by 18 CMIP5 models were evaluated from the historical experiment of 1981-2005. The evaluation led to the identification of one model, the CMCC-CM that replicated the key characteristics of diurnal rainfall regimes including the propagation of moisture convergence. Using the CMCC-CM to assess the future (2076-2100) change of diurnal evolution and propagation projected by the RCP4.5 experiment, it was found that propagating diurnal rainfall will enhance and expand southward into the non-propagating regime in southeast China. This change in diurnal rainfall is attributed to the intensification of diurnal land-sea thermal contrast over eastern China and the southward shift of the upper-level jet stream over 20°-30°N. Similar projected changes in diurnal rainfall and associated large-scale dynamical mechanisms were also depicted by four other models (GFDL-ESM2G, GFDL-ESM2M, MRI-CGCM3, and MRI-ESM1) showing a higher skill in representing the diurnal rainfall regimes over East Asia. If such model projection holds true, southeast China will experience an increase in the eastward propagating diurnal rainfall, which could further impact Taiwan.
Vertical laser beam propagation through the troposphere
NASA Technical Reports Server (NTRS)
Minott, P. O.; Bufton, J. L.; Schaefer, W. H.; Grolemund, D. A.
1974-01-01
The characteristics of the earth's atmosphere and its effects upon laser beams was investigated in a series of balloon borne, optical propagation experiments. These experiments were designed to simulate the space to ground laser link. An experiment to determine the amplitude fluctuation, commonly called scintillation, caused by the atmosphere was described.
Cosmic Ray Origin, Acceleration and Propagation
NASA Technical Reports Server (NTRS)
Baring, Matthew G.
2000-01-01
This paper summarizes highlights of the OG3.1, 3.2 and 3.3 sessions of the 26th International Cosmic Ray Conference in Salt Lake City, which were devoted to issues of origin/composition, acceleration and propagation.
Simulation of action potential propagation in plants.
Sukhov, Vladimir; Nerush, Vladimir; Orlova, Lyubov; Vodeneev, Vladimir
2011-12-21
Action potential is considered to be one of the primary responses of a plant to action of various environmental factors. Understanding plant action potential propagation mechanisms requires experimental investigation and simulation; however, a detailed mathematical model of plant electrical signal transmission is absent. Here, the mathematical model of action potential propagation in plants has been worked out. The model is a two-dimensional system of excitable cells; each of them is electrically coupled with four neighboring ones. Ion diffusion between excitable cell apoplast areas is also taken into account. The action potential generation in a single cell has been described on the basis of our previous model. The model simulates active and passive signal transmission well enough. It has been used to analyze theoretically the influence of cell to cell electrical conductivity and H(+)-ATPase activity on the signal transmission in plants. An increase in cell to cell electrical conductivity has been shown to stimulate an increase in the length constant, the action potential propagation velocity and the temperature threshold, while the membrane potential threshold being weakly changed. The growth of H(+)-ATPase activity has been found to induce the increase of temperature and membrane potential thresholds and the reduction of the length constant and the action potential propagation velocity.
Propagating double layers in electronegative plasmas
Meige, A.; Plihon, N.; Hagelaar, G. J. M.; Boeuf, J.-P.; Chabert, P.; Boswell, R. W.
2007-05-15
Double layers have been observed to propagate from the source region to the diffusion chamber of a helicon-type reactor filled up with a low-pressure mixture of Ar/SF{sub 6} [N. Plihon et al., J. Appl. Phys. 98, 023306 (2005)]. In the present paper the most significant and new experimental results are reported. A fully self-consistent hybrid model in which the electron energy distribution function, the electron temperature, and the various source terms are calculated is developed to investigate these propagating double layers. The spontaneous formation of propagating double layers is only observed in the simulation for system in which the localized inductive heating is combined with small diameter chambers. The conditions of formation and the properties of the propagating double layers observed in the simulation are in good agreement with that of the experiment. By correlating the results of the experiment and the simulation, a formation mechanism compatible with ion two-stream instability is proposed.
Radar propagation in coastal environments: Vampira results
NASA Astrophysics Data System (ADS)
Essen, Helmut; Fuchs, Hans-Hellmuth; Pagels, Anke
2006-09-01
The performance of sensors operating in coastal environments is severely influenced by the actual atmospheric conditions and the sea surface. Propagation models are in existence, which cope with the varying environment and allow a performance prediction for sensors in different bands of the electromagnetic spectrum. Model calculations give evidence for a complementary performance of sensors operating in the IR region and at radar frequencies ranging from X- to W-band. To validate existing radar propagation models like TERPEM and to compare IR with mm-wave propagation over sea under various atmospherically conditions, joint experiments with IR- and radar sensors were conducted over transmission ranges well beyond the horizon. For the measurements a naval vessel was moving on outbound and inbound courses ranging from the sensor site over the horizon, carrying corner reflectors acting as point targets at different heights above sea. This allowed a thorough investigation of duct propagation at different heights above the sea surface. The measurements were accompanied by a detailed environmental characterization of the sea surface and the atmosphere. The paper describes the experimental approach and gives representative results for measurement and simulation. The implications on performance especially for a multispectral (IR/mmW) approach are discussed.
Antenna Construction and Propagation of Radio Waves.
ERIC Educational Resources Information Center
Marine Corps Inst., Washington, DC.
Developed as part of the Marine Corps Institute (MCI) correspondence training program, this course on antenna construction and propagation of radio waves is designed to provide communicators with instructions in the selection and/or construction of the proper antenna(s) for use with current field radio equipment. Introductory materials include…
Propagation handbook, frequencies above 10 GHz
NASA Technical Reports Server (NTRS)
Ippolito, Louis J.
1988-01-01
The progress and accomplishments in the developmet of the Fourth Edition of the NASA Propagation Effects Handbook for Satellite Systems Design, for frequencies 10 to 100 GHz, NASA Reference Publication 1082(04), dated May 1988, prepared by Westighouse Electric Corporation for the Jet Propulsion Laboratory are discussed.
Exact propagators for some degenerate hyperbolic operators
NASA Astrophysics Data System (ADS)
Beals, Richard; Kannai, Yakar
2006-10-01
Exact propagators are obtained for the degenerate second order hyperbolic operators ∂2 t - t 2 l Δ x , l=1,2,..., by analytic continuation from the degenerate elliptic operators ∂2 t + t 2 l Δ x . The partial Fourier transforms are also obtained in closed form, leading to integral transform formulas for certain combinations of Bessel functions and modified Bessel functions.
Space Weather Effects on RF Propagation
2006-03-15
propagation medium that are to be studied depends on the presented at B 1, namely those aspects that will be seen that are related with the Maxwell’s ... equation application, and so with the radiation characteristics of the "virtual antenna". 3- To simulate some point-to-point links using the new procedure
Polymer Dirac field propagator: A model
NASA Astrophysics Data System (ADS)
García-Chung, Angel A.; Morales-Técotl, Hugo A.
2014-03-01
Polymer quantum mechanics, the mechanical analogue of the loop quantization of gravity, has been applied recently to scalar field modes yielding interesting behavior for its corresponding propagator at high, possibly Planck's, energy. Clearly other matter components are worth investigating along these lines, and thus we focus here on the Dirac field. To proceed to the polymer analysis of the Dirac field, a previous canonical analysis of its modes is advantageous. We show that this yields an energy spectrum suggesting a natural Fermi oscillator decomposition and, moreover, that both Fourier modes and Fermi oscillators lead to the corresponding free propagator in flat space-time. Finally, we advance a model entailing the polymer quantization of the Fermi oscillators that make up the Dirac field. It consists of a discrete set that replaces one of the two real anticommutative lines forming the reduced phase space of a Fermi oscillator. This is in analogy to the bosonic harmonic oscillator in which the corresponding polymer quantization involves replacing the real line by a regular lattice. The resulting polymer propagator contains as its body the standard Dirac field propagator plus soul terms involving up to second-order powers in two anticommutative parameters. Some possible physical implications are mentioned in the discussion.
Propagation of shock waves through clouds
NASA Astrophysics Data System (ADS)
Zhou, Xin Xin
1990-10-01
The behavior of a shock wave propagating into a cloud consisting of an inert gas, water vapor and water droplets was investigated. This has particular application to sonic bangs propagating in the atmosphere. The finite different method of MacCormack is extended to solve the one and two dimensional, two phase flow problems in which mass, momentum and energy transfers are included. The FCT (Fluid Corrected Transport) technique developed by Boris and Book was used in the basic numerical scheme as a powerful corrective procedure. The results for the transmitted shock waves propagating in a one dimensional, semi infinite cloud obtained by the finite difference approach are in good agreement with previous results by Kao using the method characteristics. The advantage of the finite difference method is its adaptability to two and three dimensional problems. Shock wave propagation through a finite cloud and into an expansion with a 90 degree corner was investigated. It was found that the transfer processes between the two phases in two dimensional flow are much more complicated than in the one dimensional flow cases. This is mainly due to the vortex and expansion wave generated at the corner. In the case considered, further complications were generated by the reflected shock wave from the floor. Good agreement with experiment was found for one phase flow but experimental data for the two phase case is not yet available to validate the two phase calculations.
Using Least Squares for Error Propagation
ERIC Educational Resources Information Center
Tellinghuisen, Joel
2015-01-01
The method of least-squares (LS) has a built-in procedure for estimating the standard errors (SEs) of the adjustable parameters in the fit model: They are the square roots of the diagonal elements of the covariance matrix. This means that one can use least-squares to obtain numerical values of propagated errors by defining the target quantities as…
Environmental constraints in earth-space propagation
NASA Astrophysics Data System (ADS)
Goodman, J. M.
1980-11-01
The advantages of utilizing space for telecommunications is well known in both the commercial and military arenas. A small complement of satellites at synchronous orbit, for example, may provide nearly global coverage and may be designed to support small disadvantaged customers as well as those characterized by large antenna structures and sophisticated acquisition and processing capabilities. Modern navigational and timing needs can also be satisfied through exploitation of space platforms and NAVSTAR/GPS is a system which exemplifies the utilization of space for those purposes. Applications of space in surveillance and kindred areas also exist and spaceborne instruments for monitoring the exoatmospheric environment and transmissions from the Sun abound. There is an obvious charm in the utilization of space for various purposes, however, most applications require the transmission of intelligence or data between space platforms and other space segments or a ground terminal. Thus the channel or the propagation path clearly becomes a part of the total system as a perturbation source. The nuisance value of the propagation path derives from the extent to which it does not duplicate free space at a specified frequency. This paper reviews the general utilization of space to introduce the importance of Earth-space radio propagation with special emphasis directed toward DoD mission areas. An outline of the basic properties of Earth-space RF propagation follows and finally an assessment of the major effects is given.
Propagation of Innovations in Networked Groups
ERIC Educational Resources Information Center
Mason, Winter A.; Jones, Andy; Goldstone, Robert L.
2008-01-01
A novel paradigm was developed to study the behavior of groups of networked people searching a problem space. The authors examined how different network structures affect the propagation of information in laboratory-created groups. Participants made numerical guesses and received scores that were also made available to their neighbors in the…
Generation and propagation of optical vortices
NASA Astrophysics Data System (ADS)
Rozas, David
Optical vortices are singularities in phase fronts of laser beams. They are characterized by a dark core whose size (relative to the size of the background beam) may dramatically affect their behavior upon propagation. Previously, only large-core vortices have been extensively studied. The object of the research presented in this dissertation was to explore ways of generating small-core optical vortices (also called optical vortex filaments ), and to examine their propagation using analytical, numerical and experimental methods. Computer-generated holography enabled us to create arbitrary distributions of optical vortex filaments for experimental exploration. Hydrodynamic analogies were used to develop an heuristic model which described the dependence of vortex motion on other vortices and the background beam, both qualitatively and quantitatively. We predicted that pair of optical vortex filaments will rotate with angular rates inversely proportional to their separation distance (just like vortices in a fluid). We also reported the first experimental observation of this novel fluid-like effect. It was found, however, that upon propagation in linear media, the fluid-like rotation was not sustained owing to the overlap of diffracting vortex cores. Further numerical studies and experiments showed that rotation angle may be enhanced in nonlinear self-defocusing media. The results presented in this thesis offer us a better understanding of dynamics of propagating vortices which may result in applications in optical switching, optical data storage, manipulation of micro-particles and optical limiting for eye protection.
Detonation propagation in a high loss configuration
Jackson, Scott I; Shepherd, Joseph E
2009-01-01
This work presents an experimental study of detonation wave propagation in tubes with inner diameters (ID) comparable to the mixture cell size. Propane-oxygen mixtures were used in two test section tubes with inner diameters of 1.27 mm and 6.35 mm. For both test sections, the initial pressure of stoichiometric mixtures was varied to determine the effect on detonation propagation. For the 6.35 mm tube, the equivalence ratio {phi} (where the mixture was {phi} C{sub 3}H{sub 8} + 50{sub 2}) was also varied. Detonations were found to propagate in mixtures with cell sizes as large as five times the diameter of the tube. However, under these conditions, significant losses were observed, resulting in wave propagation velocities as slow as 40% of the CJ velocity U{sub CJ}. A review of relevant literature is presented, followed by experimental details and data. Observed velocity deficits are predicted using models that account for boundary layer growth inside detonation waves.
Single cycle terahertz pulse propagation in water
NASA Astrophysics Data System (ADS)
Fox, Colleen J.
Single cycle electromagnetic pulses have been difficult to experimentally generate and to theoretically analyze. With the recent development of terahertz systems based on near infrared femtosecond lasers it has become possible to perform single cycle experiments using picosecond pulses. The work presented in this thesis lays the groundwork for the transition from investigations of ultrafast optical pulse propagation in water to similar work at terahertz frequencies. In this thesis a variety of terahertz generation and detection methods are reviewed. Two commercial terahertz spectroscopy systems are examined in detail, improved upon and put into use. The design of a sample holder for thin, variable thickness samples of water or other highly absorbing liquid is detailed and the constructed holder is utilized in preliminary pulse measurements over a range of paths lengths. How the measured terahertz pulses spectrally and temporally change as they propagate through water is analyzed and used to extract the complex refractive index and attenuation coefficient of the tested water. Current knowledge of the molecular behavior of water in the THz frequency range of 300 GHz to 3 THz is discussed and related to experimental results. This information is also used in the preliminary development of two models. One model examines the molecular energy levels in liquid water, their effect on the propagating pulse, and the potential for the formation of precursors. The other model is based on the double Debye theory and can compare the calculated and measured pulses after propagation in both the time and frequency domains.
Application of Taylor's series to trajectory propagation
NASA Technical Reports Server (NTRS)
Stanford, R. H.; Berryman, K. W.; Breckheimer, P. J.
1986-01-01
This paper describes the propagation of trajectories by the application of the preprocessor ATOMCC which uses Taylor's series to solve initial value problems in ordinary differential equations. Comparison of the results obtained with those from other methods are presented. The current studies indicate that the ATOMCC preprocessor is an easy, yet fast and accurate method for generating trajectories.
Blast noise propagation above a snow cover.
Albert, D G; Hole, L R
2001-06-01
A porous medium model of a snow cover, rather than a viscoelastic treatment, has been used to simulate measured, horizontally traveling acoustic waveform propagation above a dry snow cover 11-20 cm thick. The waveforms were produced by explosions of 1-kg charges at propagation distances of 100 to 1400 m. These waveforms, with a peak frequency around 30 Hz, show pulse broadening effects similar to those previously seen for higher-frequency waves over shorter propagation distances. A rigid-ice-frame porous medium ("rigid-porous") impedance model, which includes the effect of the pores within the snow but ignores any induced motion of the ice particles, is shown to produce much better agreement with the measured waveforms compared with a viscoelastic solid treatment of the snow cover. From the acoustic waveform modeling, the predicted average snow cover depth of 18 cm and effective flow resistivities of 16-31 kPa s m(-2) agree with snow pit observations and with previous acoustic measurements over snow. For propagation in the upwind direction, the pulse broadening caused by the snow cover interaction is lessened, but the overall amplitude decay is greater because of refraction of the blast waves.
NASA Technical Reports Server (NTRS)
Golshan, Nassar (Editor)
1996-01-01
The NASA Propagation Experimenters (NAPEX) Meeting and associated Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop convene yearly to discuss studies supported by the NASA Propagation Program. Representatives from the satellite communications (satcom)industry, academia, and government with an interest in space-ground radio wave propagation have peer discussion of work in progress, disseminate propagation results, and interact with the satcom industry. NAPEX XX, in Fairbanks, Alaska, June 4-5, 1996, had three sessions: (1) "ACTS Propagation Study: Background, Objectives, and Outcomes," covered results from thirteen station-years of Ka-band experiments; (2) "Propagation Studies for Mobile and Personal Satellite Applications," provided the latest developments in measurement, modeling, and dissemination of propagation phenomena of interest to the mobile, personal, and aeronautical satcom industry; and (3)"Propagation Research Topics," covered a range of topics including space/ground optical propagation experiments, propagation databases, the NASA Propagation Web Site, and revision plans for the NASA propagation effects handbooks. The ACTS Miniworkshop, June 6, 1996, covered ACTS status, engineering support for ACTS propagation terminals, and the ACTS Propagation Data Center. A plenary session made specific recommendations for the future direction of the program.
Longitudinal nonlinear wave propagation through soft tissue.
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
NASA Lunar Base Wireless System Propagation Analysis
NASA Technical Reports Server (NTRS)
Hwu, Shian U.; Upanavage, Matthew; Sham, Catherine C.
2007-01-01
There have been many radio wave propagation studies using both experimental and theoretical techniques over the recent years. However, most of studies have been in support of commercial cellular phone wireless applications. The signal frequencies are mostly at the commercial cellular and Personal Communications Service bands. The antenna configurations are mostly one on a high tower and one near the ground to simulate communications between a cellular base station and a mobile unit. There are great interests in wireless communication and sensor systems for NASA lunar missions because of the emerging importance of establishing permanent lunar human exploration bases. Because of the specific lunar terrain geometries and RF frequencies of interest to the NASA missions, much of the published literature for the commercial cellular and PCS bands of 900 and 1800 MHz may not be directly applicable to the lunar base wireless system and environment. There are various communication and sensor configurations required to support all elements of a lunar base. For example, the communications between astronauts, between astronauts and the lunar vehicles, between lunar vehicles and satellites on the lunar orbits. There are also various wireless sensor systems among scientific, experimental sensors and data collection ground stations. This presentation illustrates the propagation analysis of the lunar wireless communication and sensor systems taking into account the three dimensional terrain multipath effects. It is observed that the propagation characteristics are significantly affected by the presence of the lunar terrain. The obtained results indicate the lunar surface material, terrain geometry and antenna location are the important factors affecting the propagation characteristics of the lunar wireless systems. The path loss can be much more severe than the free space propagation and is greatly affected by the antenna height, surface material and operating frequency. The
The Temporal Morphology of Infrasound Propagation
NASA Astrophysics Data System (ADS)
Drob, Douglas P.; Garcés, Milton; Hedlin, Michael; Brachet, Nicolas
2010-05-01
Expert knowledge suggests that the performance of automated infrasound event association and source location algorithms could be greatly improved by the ability to continually update station travel-time curves to properly account for the hourly, daily, and seasonal changes of the atmospheric state. With the goal of reducing false alarm rates and improving network detection capability we endeavor to develop, validate, and integrate this capability into infrasound processing operations at the International Data Centre of the Comprehensive Nuclear Test-Ban Treaty Organization. Numerous studies have demonstrated that incorporation of hybrid ground-to-space (G2S) enviromental specifications in numerical calculations of infrasound signal travel time and azimuth deviation yields significantly improved results over that of climatological atmospheric specifications, specifically for tropospheric and stratospheric modes. A robust infrastructure currently exists to generate hybrid G2S vector spherical harmonic coefficients, based on existing operational and emperical models on a real-time basis (every 3- to 6-hours) (D rob et al., 2003). Thus the next requirement in this endeavor is to refine numerical procedures to calculate infrasound propagation characteristics for robust automatic infrasound arrival identification and network detection, location, and characterization algorithms. We present results from a new code that integrates the local (range-independent) τp ray equations to provide travel time, range, turning point, and azimuth deviation for any location on the globe given a G2S vector spherical harmonic coefficient set. The code employs an accurate numerical technique capable of handling square-root singularities. We investigate the seasonal variability of propagation characteristics over a five-year time series for two different stations within the International Monitoring System with the aim of understanding the capabilities of current working knowledge of the
Three-Dimensional Gear Crack Propagation Studied
NASA Technical Reports Server (NTRS)
Lewicki, David G.
1999-01-01
Gears used in current helicopters and turboprops are designed for light weight, high margins of safety, and high reliability. However, unexpected gear failures may occur even with adequate tooth design. To design an extremely safe system, the designer must ask and address the question, "What happens when a failure occurs?" With gear-tooth bending fatigue, tooth or rim fractures may occur. A crack that propagates through a rim will be catastrophic, leading to disengagement of the rotor or propeller, loss of an aircraft, and possible fatalities. This failure mode should be avoided. A crack that propagates through a tooth may or may not be catastrophic, depending on the design and operating conditions. Also, early warning of this failure mode may be possible because of advances in modern diagnostic systems. One concept proposed to address bending fatigue fracture from a safety aspect is a splittooth gear design. The prime objective of this design would be to control crack propagation in a desired direction such that at least half of the tooth would remain operational should a bending failure occur. A study at the NASA Lewis Research Center analytically validated the crack-propagation failsafe characteristics of a split-tooth gear. It used a specially developed three-dimensional crack analysis program that was based on boundary element modeling and principles of linear elastic fracture mechanics. Crack shapes as well as the crack-propagation life were predicted on the basis of the calculated stress intensity factors, mixed-mode crack-propagation trajectory theories, and fatigue crack-growth theories. The preceding figures show the effect of the location of initial cracks on crack propagation. Initial cracks in the fillet of the teeth produced stress intensity factors of greater magnitude (and thus, greater crack growth rates) than those in the root or groove areas of the teeth. Crack growth was simulated in a case study to evaluate crack-propagation paths. Tooth
Intense femtosecond pulse propagation with applications
NASA Astrophysics Data System (ADS)
Moloney, J. V.
2006-05-01
The fundamental physics of high-field laser-matter interactions has driven ultrashort pulse generation to achieve record power densities of 10 22 Watts per cm2 in focal spot sizes (FWHM) of 0.8 μm1. These enormous fields are generated by compressing longer, high energy pulses to ever shorter lengths using so-called CPA compressors. Great care has to be taken to achieve such record power densities by controlling the spatio-temporal shape during pulse compression. Despite these remarkable experimental achievements, there have been relatively few developments on the theoretical side to derive realistic physical optical material models coupled to sophisticated E.M propagators. Many of the theoretical analysis tools developed in this emerging field of extreme nonlinear optics are restricted to oversimplified 1D models that completely ignore the complex vector spatio-temporal couplings occurring within such small nonlinear interaction volumes. The advent of these high power ultra-short pulsed laser systems has opened up a whole new vista of applications and computational challenges. The applications space spans relatively short propagation lengths of centimeters to meters to a target up to many kilometers in atmospheric propagation studies. The high local field intensities generated within the pulse can potentially lead to electromagnetic carrier wave shocking so it becomes necessary to fully resolve the optical carrier wave within the 3D propagating pulse envelope. High local field intensities also lead to an explosive growth of the white-light supercontinuum spectrum and the intensities of even remote spectral components can be high enough to generate nonlinear coupling to the host material. For this reason, spectrally local models of light-matter coupling are expected to fail. In this paper, we will present a fully carrier-resolved E.M. propagator that allows for few meter long propagation lengths while fully resolving the optical carrier wave. Our applications focus
Efficient Geometric Sound Propagation Using Visibility Culling
NASA Astrophysics Data System (ADS)
Chandak, Anish
2011-07-01
Simulating propagation of sound can improve the sense of realism in interactive applications such as video games and can lead to better designs in engineering applications such as architectural acoustics. In this thesis, we present geometric sound propagation techniques which are faster than prior methods and map well to upcoming parallel multi-core CPUs. We model specular reflections by using the image-source method and model finite-edge diffraction by using the well-known Biot-Tolstoy-Medwin (BTM) model. We accelerate the computation of specular reflections by applying novel visibility algorithms, FastV and AD-Frustum, which compute visibility from a point. We accelerate finite-edge diffraction modeling by applying a novel visibility algorithm which computes visibility from a region. Our visibility algorithms are based on frustum tracing and exploit recent advances in fast ray-hierarchy intersections, data-parallel computations, and scalable, multi-core algorithms. The AD-Frustum algorithm adapts its computation to the scene complexity and allows small errors in computing specular reflection paths for higher computational efficiency. FastV and our visibility algorithm from a region are general, object-space, conservative visibility algorithms that together significantly reduce the number of image sources compared to other techniques while preserving the same accuracy. Our geometric propagation algorithms are an order of magnitude faster than prior approaches for modeling specular reflections and two to ten times faster for modeling finite-edge diffraction. Our algorithms are interactive, scale almost linearly on multi-core CPUs, and can handle large, complex, and dynamic scenes. We also compare the accuracy of our sound propagation algorithms with other methods. Once sound propagation is performed, it is desirable to listen to the propagated sound in interactive and engineering applications. We can generate smooth, artifact-free output audio signals by applying
NASA Technical Reports Server (NTRS)
Davarian, Faramaz (Editor)
1993-01-01
The NASA Propagation Experimenters Meeting (NAPEX) is convened annually to discuss studies made on radio wave propagation by investors from domestic and international organizations. NAPEX 17 was held on 15 June 1993. The meeting was organized into two technical sessions. The first session was dedicated to slant path propagation studies and experiments. The second session focused on propagation studies for mobile and personal communications. Preceding NAPEX 17, the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop was held on 14 June 1993 to review ACTS propagation activities with emphasis on ACTS experiments status and data collection, processing, and exchange.
Temporal coherence of propagating surface plasmons.
Wang, Tao; Comtet, Geneviève; Le Moal, Eric; Dujardin, Gérald; Drezet, Aurélien; Huant, Serge; Boer-Duchemin, Elizabeth
2014-12-01
The temporal coherence of propagating surface plasmons is investigated using a local, broadband plasmon source consisting of a scanning tunneling microscope. A variant of Young's experiment is performed using a sample consisting of a 200-nm-thick gold film perforated by two 1-μm-diameter holes (separated by 4 or 6 μm). The resulting interference fringes are studied as a function of hole separation and source bandwidth. From these experiments, we conclude that apart from plasmon decay in the metal, there is no further loss of plasmon coherence from propagation, scattering at holes, or other dephasing processes. As a result, the plasmon coherence time may be estimated from its spectral bandwidth.
Laser beam shaping profiles and propagation.
Shealy, David L; Hoffnagle, John A
2006-07-20
We consider four families of functions--the super-Gaussian, flattened Gaussian, Fermi-Dirac, and super-Lorentzian--that have been used to describe flattened irradiance profiles. We determine the shape and width parameters of the different distributions, when each flattened profile has the same radius and slope of the irradiance at its half-height point, and then we evaluate the implicit functional relationship between the shape and width parameters for matched profiles, which provides a quantitative way to compare profiles described by different families of functions. We conclude from an analysis of each profile with matched parameters using Kirchhoff-Fresnel diffraction theory and M2 analysis that the diffraction patterns as they propagate differ by small amounts, which may not be distinguished experimentally. Thus, beam shaping optics is designed to produce either of these four flattened output irradiance distributions with matched parameters will yield similar irradiance distributions as the beam propagates.
Method and apparatus for charged particle propagation
Hershcovitch, A.
1996-11-26
A method and apparatus are provided for propagating charged particles from a vacuum to a higher pressure region. A generator includes an evacuated chamber having a gun for discharging a beam of charged particles such as an electron beam or ion beam. The beam is discharged through a beam exit in the chamber into a higher pressure region. A plasma interface is disposed at the beam exit and includes a plasma channel for bounding a plasma maintainable between a cathode and an anode disposed at opposite ends thereof. The plasma channel is coaxially aligned with the beam exit for propagating the beam from the chamber, through the plasma, and into the higher pressure region. The plasma is effective for pumping down the beam exit for preventing pressure increase in the chamber and provides magnetic focusing of the beam discharged into the higher pressure region 24. 7 figs.
Scout trajectory error propagation computer program
NASA Technical Reports Server (NTRS)
Myler, T. R.
1982-01-01
Since 1969, flight experience has been used as the basis for predicting Scout orbital accuracy. The data used for calculating the accuracy consists of errors in the trajectory parameters (altitude, velocity, etc.) at stage burnout as observed on Scout flights. Approximately 50 sets of errors are used in Monte Carlo analysis to generate error statistics in the trajectory parameters. A covariance matrix is formed which may be propagated in time. The mechanization of this process resulted in computer program Scout Trajectory Error Propagation (STEP) and is described herein. Computer program STEP may be used in conjunction with the Statistical Orbital Analysis Routine to generate accuracy in the orbit parameters (apogee, perigee, inclination, etc.) based upon flight experience.
Inferring network topology via the propagation process
NASA Astrophysics Data System (ADS)
Zeng, An
2013-11-01
Inferring the network topology from the dynamics is a fundamental problem, with wide applications in geology, biology, and even counter-terrorism. Based on the propagation process, we present a simple method to uncover the network topology. A numerical simulation on artificial networks shows that our method enjoys a high accuracy in inferring the network topology. We find that the infection rate in the propagation process significantly influences the accuracy, and that each network corresponds to an optimal infection rate. Moreover, the method generally works better in large networks. These finding are confirmed in both real social and nonsocial networks. Finally, the method is extended to directed networks, and a similarity measure specific for directed networks is designed.
Light propagation in periodically modulated complex waveguides
NASA Astrophysics Data System (ADS)
Nixon, Sean; Yang, Jianke
2015-03-01
Light propagation in optical waveguides with periodically modulated index of refraction and alternating gain and loss are investigated for linear and nonlinear systems. Based on a multiscale perturbation analysis, it is shown that for many non-parity-time- (PT -) symmetric waveguides, their linear spectrum is partially complex; thus light exponentially grows or decays upon propagation, and this growth or decay is not altered by nonlinearity. However, several classes of non-PT -symmetric waveguides are also identified to possess all-real linear spectrum. For PT -symmetric waveguides, phase transition is predicted analytically. In the nonlinear regime longitudinally periodic and transversely quasilocalized modes are found for PT -symmetric waveguides both above and below phase transition. These nonlinear modes are stable under evolution and can develop from initially weak initial conditions.
Experiments on the Propagation of Plasma Filaments
Katz, Noam; Egedal, Jan; Fox, Will; Le, Ari; Porkolab, Miklos
2008-07-04
We investigate experimentally the motion and structure of isolated plasma filaments propagating through neutral gas. Plasma filaments, or 'blobs,' arise from turbulent fluctuations in a range of plasmas. Our experimental geometry is toroidally symmetric, and the blobs expand to a larger major radius under the influence of a vertical electric field. The electric field, which is caused by {nabla}B and curvature drifts in a 1/R magnetic field, is limited by collisional damping on the neutral gas. The blob's electrostatic potential structure and the resulting ExB flow field give rise to a vortex pair and a mushroom shape, which are consistent with nonlinear plasma simulations. We observe experimentally this characteristic mushroom shape for the first time. We also find that the blob propagation velocity is inversely proportional to the neutral density and decreases with time as the blob cools.
Human cytomegalovirus: propagation, quantification, and storage.
Britt, William J
2010-08-01
Human cytomegalovirus (HCMV) is the largest and perhaps the most structurally complex member of the family of human herpesviruses. It is the prototypic virus of the beta-herpesvirus subfamily. As with other cytomegaloviruses, HCMV is exquisitely species specific and undergoes lytic replication only in cells of human origin. In addition, its replication is limited almost entirely to primary cells and a limited number of transformed cell lines. Together with its prolonged replicative cycle of approximately 48 hr, the propagation and quantification of HCMV can present technical challenges. In this brief set of protocols, the propagation of laboratory strains of HCMV and their quantitation is described. In a third series of protocols, the concentration and gradient purification of HCMV for more specialized downstream applications is described.
Spacetime and Quantum Propagation From Digital Clocks
NASA Astrophysics Data System (ADS)
Ord, Garnet. N.
2013-09-01
Minkowski spacetime predates quantum mechanics and is frequently regarded as an extension of the classical paradigm of Newtonian physics, rather than a harbinger of quantum mechanics. By inspecting how discrete clocks operate in a relativistic world we show that this view is misleading. Discrete relativistic clocks implicate classical spacetime provided a continuum limit is taken in such a way that successive ticks of the clock yield a smooth worldline. The classical picture emerges but does so by confining unitary propagation into spacetime regions between ticks that have zero area in the continuum limit. Clocks allowed a continuum limit that does not force inter-event intervals to zero, satisfy the Dirac equation. This strongly suggests that the origin of quantum propagation is to be found in the shift from Newton's absolute time to Minkowski's frame dependent time and is ultimately relativistic in origin.
Belief Propagation Algorithm for Portfolio Optimization Problems.
Shinzato, Takashi; Yasuda, Muneki
2015-01-01
The typical behavior of optimal solutions to portfolio optimization problems with absolute deviation and expected shortfall models using replica analysis was pioneeringly estimated by S. Ciliberti et al. [Eur. Phys. B. 57, 175 (2007)]; however, they have not yet developed an approximate derivation method for finding the optimal portfolio with respect to a given return set. In this study, an approximation algorithm based on belief propagation for the portfolio optimization problem is presented using the Bethe free energy formalism, and the consistency of the numerical experimental results of the proposed algorithm with those of replica analysis is confirmed. Furthermore, the conjecture of H. Konno and H. Yamazaki, that the optimal solutions with the absolute deviation model and with the mean-variance model have the same typical behavior, is verified using replica analysis and the belief propagation algorithm.
Terahertz polariton propagation in patterned materials.
Stoyanov, Nikolay S; Ward, David W; Feurer, Thomas; Nelson, Keith A
2002-10-01
Generation and control of pulsed terahertz-frequency radiation have received extensive attention, with applications in terahertz spectroscopy, imaging and ultrahigh-bandwidth electro-optic signal processing. Terahertz 'polaritonics', in which terahertz lattice waves called phonon-polaritons are generated, manipulated and visualized with femtosecond optical pulses, offers prospects for an integrated solid-state platform for terahertz signal generation and guidance. Here, we extend terahertz polaritonics methods to patterned structures. We demonstrate femtosecond laser fabrication of polaritonic waveguide structures in lithium tantalate and lithium niobate crystals, and illustrate polariton focusing into, and propagation within, the fabricated waveguide structures. We also demonstrate a 90 degrees turn within a structure consisting of two waveguides and a reflecting face, as well as a structure consisting of splitting and recombining elements that can be used as a terahertz Mach-Zehnder interferometer. The structures permit integrated terahertz signal generation, propagation through waveguide-based devices, and readout within a single solid-state platform.
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.
Outwardly Propagating Flames at Elevated Pressures
NASA Technical Reports Server (NTRS)
Law, C. K.; Rozenchan, G.; Tse, S. D.; Zhu, D. L.
2001-01-01
Spherical, outwardly-propagating flames of CH4-O2-inert and H2-O2-inert mixtures were experimentally studied in a high pressure apparatus. Stretch-free flame speeds and Markstein lengths were extracted for a wide range of pressures and equivalence ratios for spherically-symmetric, smooth flamefronts and compared to numerical computations with detailed chemistry and transport, as well as existing data in the literature. Wrinkle development was examined for propagating flames that were unstable under our experimental conditions. Hydrodynamic cells developed for most H2-air and CH4-air flames at elevated pressures, while thermal-diffusive instabilities were also observed for lean and near-stoichiometric hydrogen flames at pressures above atmospheric. Strategies in suppressing or delaying the onset of cell formation have been assessed. Buoyancy effects affected sufficiently off-stoichiometric CH4 mixtures at high pressures.
The stratospheric arrival pair in infrasound propagation.
Waxler, Roger; Evers, Läslo G; Assink, Jelle; Blom, Phillip
2015-04-01
The ideal case of a deep and well-formed stratospheric duct for long range infrasound propagation in the absence of tropospheric ducting is considered. A canonical form, that of a pair of arrivals, for ground returns of impulsive signals in a stratospheric duct is determined. The canonical form is derived from the geometrical acoustics approximation, and is validated and extended through full wave modeling. The full caustic structure of the field of ray paths is found and used to determine phase relations between the contributions to the wavetrain from different propagation paths. Finally, comparison with data collected from the 2005 fuel gas depot explosion in Buncefield, England is made. The correspondence between the theoretical results and the observations is shown to be quite good.
Propagation of waves along an impedance boundary
NASA Technical Reports Server (NTRS)
Wenzel, A. R.
1974-01-01
A theoretical analysis of the scalar wave field due to a point source above a plane impedance boundary is presented. A surface wave is found to be an essential component of the total wave field. It is shown that, as a result of ducting of energy by the surface wave, the amplitude of the total wave near the boundary can be greater than it would be if the boundary were perfectly reflecting. Asymptotic results, valid near the boundary, are obtained both for the case of finite impedance (the soft-boundary case) and for the limiting case in which the impedance becomes infinite (the hard-boundary case). In the latter, the wave amplitude in the farfield decreases essentially inversely as the horizontal propagation distance; in the former (if the surface-wave term is neglected), it decreases inversely as the square of the horizontal propagation distance.
Whistler wave propagation in a large magnetoplasma
NASA Technical Reports Server (NTRS)
Stenzel, R. L.
1976-01-01
A large collisionless quiescent plasma source is developed for investigating the phase and amplitude distribution of antenna-launched whistler waves in a specified parameter regime relating wave frequency to electron cyclotron frequency. Wave dispersion is studied both by interferometer techniques with monochromatic waves and by propagation of short phase-coherent wave bursts. The wave damping mechanism is examined by propagating perfectly ducted whistler waves. The dispersion of single frequency waves and wave packets is demonstrated. Trough ducting for wave frequency to electron cyclotron frequency ratio greater than 1/2 is verified, and new eigenmodes in nonuniform plasmas at ratio values less than 1/2 are observed. It is shown that geometric effects due to ray divergence and wave refraction dominate over collisional damping.
Crack Propagation in Bamboo's Hierarchical Cellular Structure
Habibi, Meisam K.; Lu, Yang
2014-01-01
Bamboo, as a natural hierarchical cellular material, exhibits remarkable mechanical properties including excellent flexibility and fracture toughness. As far as bamboo as a functionally graded bio-composite is concerned, the interactions of different constituents (bamboo fibers; parenchyma cells; and vessels.) alongside their corresponding interfacial areas with a developed crack should be of high significance. Here, by using multi-scale mechanical characterizations coupled with advanced environmental electron microscopy (ESEM), we unambiguously show that fibers' interfacial areas along with parenchyma cells' boundaries were preferred routes for crack growth in both radial and longitudinal directions. Irrespective of the honeycomb structure of fibers along with cellular configuration of parenchyma ground, the hollow vessels within bamboo culm affected the crack propagation too, by crack deflection or crack-tip energy dissipation. It is expected that the tortuous crack propagation mode exhibited in the present study could be applicable to other cellular natural materials as well. PMID:24998298
Crack propagation in bamboo's hierarchical cellular structure.
Habibi, Meisam K; Lu, Yang
2014-07-07
Bamboo, as a natural hierarchical cellular material, exhibits remarkable mechanical properties including excellent flexibility and fracture toughness. As far as bamboo as a functionally graded bio-composite is concerned, the interactions of different constituents (bamboo fibers; parenchyma cells; and vessels.) alongside their corresponding interfacial areas with a developed crack should be of high significance. Here, by using multi-scale mechanical characterizations coupled with advanced environmental electron microscopy (ESEM), we unambiguously show that fibers' interfacial areas along with parenchyma cells' boundaries were preferred routes for crack growth in both radial and longitudinal directions. Irrespective of the honeycomb structure of fibers along with cellular configuration of parenchyma ground, the hollow vessels within bamboo culm affected the crack propagation too, by crack deflection or crack-tip energy dissipation. It is expected that the tortuous crack propagation mode exhibited in the present study could be applicable to other cellular natural materials as well.
Hf propagation through actively modified ionospheres
Argo, P.E.; Fitzgerald, T.J.; Wolcott, J.H.; Simons, D.J. ); Warshaw, S.; Carlson, R. )
1990-01-01
We have developed a computer modeling capability to predict the effect of localized electron density perturbations created by chemical releases or high-power radio frequency heating upon oblique, one-hop hf propagation paths. We have included 3-d deterministic descriptions of the depleted or enhanced ionization, including formation, evolution, and drift. We have developed a homing ray trace code to calculate the path of energy propagation through the modified ionosphere in order to predict multipath effects. We also consider the effect of random index of refraction variations using a formalism to calculate the mutual coherence functions for spatial and frequency separations based upon a path integral solution of the parabolic wave equation for a single refracted path through an ionosphere which contains random electron density fluctuations. 5 refs., 8 figs.
Cavitation propagation in water under tension
NASA Astrophysics Data System (ADS)
Noblin, Xavier; Yip Cheung Sang, Yann; Pellegrin, Mathieu; Materials and Complex Fluids Team
2012-11-01
Cavitation appears when pressure decreases below vapor pressure, generating vapor bubbles. It can be obtain in dynamical ways (acoustic, hydraulic) but also in quasi-static conditions. This later case is often observed in nature, in trees, or during the ejection of ferns spores. We study the cavitation bubbles nucleation dynamics and its propagation in a confined microfabricated media. This later is an ordered array of microcavities made in hydrogel filled with water. When the system is put into dry air, it dehydrates, water leaves the cavities and tension (negative pressure) builds in the cavities. This can be sustained up to a critical pressure (of order -20 MPa), then cavitation bubbles appear. We follow the dynamics using ultra high speed imaging. Events with several bubbles cavitating in a few microseconds could be observed along neighboring cells, showing a propagation phenomenon that we discuss. ANR CAVISOFT 2010-JCJC-0407 01.
Atmospheric effects on CO2 laser propagation
NASA Technical Reports Server (NTRS)
Murty, S. S. R.; Bilbro, J. W.
1978-01-01
An investigation was made of the losses encountered in the propagation of CO2 laser radiation through the atmosphere, particularly as it applies to the NASA/Marshall Space Flight Center Pulsed Laser Doppler System. As such it addresses three major areas associated with signal loss: molecular absorption, refractive index changes in a turbulent environment, and aerosol absorption and scattering. In particular, the molecular absorption coefficients of carbon dioxide, water vapor, and nitrous oxide are calculated for various laser lines in the region of 10.6 mu m as a function of various pressures and temperatures. The current status in the physics of low-energy laser propagation through a turbulent atmosphere is presented together with the analysis and evaluation of the associated heterodyne signal power loss. Finally, aerosol backscatter and extinction coefficients are calculated for various aerosol distributions and the results incorporated into the signal-to-noise ratio equation for the Marshall Space Flight Center system.
Propagating Qualitative Values Through Quantitative Equations
NASA Technical Reports Server (NTRS)
Kulkarni, Deepak
1992-01-01
In most practical problems where traditional numeric simulation is not adequate, one need to reason about a system with both qualitative and quantitative equations. In this paper, we address the problem of propagating qualitative values represented as interval values through quantitative equations. Previous research has produced exponential-time algorithms for approximate solution of the problem. These may not meet the stringent requirements of many real time applications. This paper advances the state of art by producing a linear-time algorithm that can propagate a qualitative value through a class of complex quantitative equations exactly and through arbitrary algebraic expressions approximately. The algorithm was found applicable to Space Shuttle Reaction Control System model.
Propagating Resource Constraints Using Mutual Exclusion Reasoning
NASA Technical Reports Server (NTRS)
Frank, Jeremy; Sanchez, Romeo; Do, Minh B.; Clancy, Daniel (Technical Monitor)
2001-01-01
One of the most recent techniques for propagating resource constraints in Constraint Based scheduling is Energy Constraint. This technique focuses in precedence based scheduling, where precedence relations are taken into account rather than the absolute position of activities. Although, this particular technique proved to be efficient on discrete unary resources, it provides only loose bounds for jobs using discrete multi-capacity resources. In this paper we show how mutual exclusion reasoning can be used to propagate time bounds for activities using discrete resources. We show that our technique based on critical path analysis and mutex reasoning is just as effective on unary resources, and also shows that it is more effective on multi-capacity resources, through both examples and empirical study.
Joint Acoustic Propagation Experiment (JAPE-91) Workshop
NASA Technical Reports Server (NTRS)
Willshire, William L., Jr. (Compiler); Chestnutt, David (Compiler)
1993-01-01
The Joint Acoustic Propagation Experiment (JAPE), was conducted at the White Sands Missile Range, New Mexico, USA, during the period 11-28 Jul. 1991. JAPE consisted of various short and long range propagation experiments using various acoustic sources including speakers, propane cannons, helicopters, a 155 mm howitzer, and static high explosives. Of primary importance to the performance of theses tests was the extensive characterization of the atmosphere during these tests. This atmospheric characterization included turbulence measurements. A workshop to disseminate the results of JAPE-91 was held in Hampton, VA, on 28 Apr. 1993. This report is a compilation of the presentations made at the workshop along with a list of attendees and the agenda.
Propagation mechanism of polymer optical fiber fuse
Mizuno, Yosuke; Hayashi, Neisei; Tanaka, Hiroki; Nakamura, Kentaro; Todoroki, Shin-ichi
2014-01-01
A fiber fuse phenomenon in polymer optical fibers (POFs) has recently been observed, and its unique properties such as slow propagation, low threshold power density, and the formation of a black oscillatory damage curve, have been reported. However, its characterization is still insufficient to well understand the mechanism and to avoid the destruction of POFs. Here, we present detailed experimental and theoretical analyses of the POF fuse propagation. First, we clarify that the bright spot is not a plasma but an optical discharge, the temperature of which is ~3600 K. We then elucidate the reasons for the oscillation of the damage curve along with the formation of newly-observed gas bubbles as well as for the low threshold power density. We also present the idea that the POF fuse can potentially be exploited to offer a long photoelectric interaction length. PMID:24762949
Learning representations by back-propagating errors
NASA Astrophysics Data System (ADS)
Rumelhart, David E.; Hinton, Geoffrey E.; Williams, Ronald J.
1986-10-01
We describe a new learning procedure, back-propagation, for networks of neurone-like units. The procedure repeatedly adjusts the weights of the connections in the network so as to minimize a measure of the difference between the actual output vector of the net and the desired output vector. As a result of the weight adjustments, internal `hidden' units which are not part of the input or output come to represent important features of the task domain, and the regularities in the task are captured by the interactions of these units. The ability to create useful new features distinguishes back-propagation from earlier, simpler methods such as the perceptron-convergence procedure1.
Wavepacket propagation using time-sliced semiclassical initial value methods.
Wallace, Brett B; Reimers, Jeffrey R
2004-12-22
A new semiclassical initial value representation (SC-IVR) propagator and a SC-IVR propagator originally introduced by Kay [J. Chem. Phys. 100, 4432 (1994)], are investigated for use in the split-operator method for solving the time-dependent Schrodinger equation. It is shown that the SC-IVR propagators can be derived from a procedure involving modified Filinov filtering of the Van Vleck expression for the semiclassical propagator. The two SC-IVR propagators have been selected for investigation because they avoid the need to perform a coherent state basis set expansion that is necessary in other time-slicing propagation schemes. An efficient scheme for solving the propagators is introduced and can be considered to be a semiclassical form of the effective propagators of Makri [Chem. Phys. Lett. 159, 489 (1989)]. Results from applications to a one-dimensional, two-dimensional, and three-dimensional Hamiltonian for a double-well potential are presented.
Modeling propagation of coherent optical pulses through molecular vapor
Shore, B.W.; Eberly, J.H.
1982-01-01
Results of modeling the mutual coupling of coherent molecular response and coherent optical pulses during propagation are described. The propagation is treated numerically, with particular emphasis on both continuum and discrete behavior associated with the quasicontinuum model.
Ultrashort Laser Pulse Propagation in Water
2009-01-01
coherent Raman spectroscopy. More complex pulse shapes will be particularly important for the studies of nonlinear pulse propagation. In the second...Stokes Raman scattering (CARS) signal (measured in methanol-water solutions) varying in magnitude over many decades15. At a further stage of the...like to next explore the possibility of using the pseudospectral time domain (PSTD) method which we feel will run much faster than the conventional FDTD
Propagation considerations for the Odyssey system design
NASA Technical Reports Server (NTRS)
Ho, Hau H.
1994-01-01
This paper presents an overview of the Odyssey system with special emphasis given to the link availability for both mobile link and feeder link. The Odyssey system design provides high link availability, typically 98 percent in the primary service areas, and better than 95 percent availability in other service areas. Strategies for overcoming Ka-band feeder link rain fades are presented. Mobile link propagation study results and summary link budgets are also presented.
Experimental study of turbulent flame kernel propagation
Mansour, Mohy; Peters, Norbert; Schrader, Lars-Uve
2008-07-15
Flame kernels in spark ignited combustion systems dominate the flame propagation and combustion stability and performance. They are likely controlled by the spark energy, flow field and mixing field. The aim of the present work is to experimentally investigate the structure and propagation of the flame kernel in turbulent premixed methane flow using advanced laser-based techniques. The spark is generated using pulsed Nd:YAG laser with 20 mJ pulse energy in order to avoid the effect of the electrodes on the flame kernel structure and the variation of spark energy from shot-to-shot. Four flames have been investigated at equivalence ratios, {phi}{sub j}, of 0.8 and 1.0 and jet velocities, U{sub j}, of 6 and 12 m/s. A combined two-dimensional Rayleigh and LIPF-OH technique has been applied. The flame kernel structure has been collected at several time intervals from the laser ignition between 10 {mu}s and 2 ms. The data show that the flame kernel structure starts with spherical shape and changes gradually to peanut-like, then to mushroom-like and finally disturbed by the turbulence. The mushroom-like structure lasts longer in the stoichiometric and slower jet velocity. The growth rate of the average flame kernel radius is divided into two linear relations; the first one during the first 100 {mu}s is almost three times faster than that at the later stage between 100 and 2000 {mu}s. The flame propagation is slightly faster in leaner flames. The trends of the flame propagation, flame radius, flame cross-sectional area and mean flame temperature are related to the jet velocity and equivalence ratio. The relations obtained in the present work allow the prediction of any of these parameters at different conditions. (author)
Propagation Limits of High Pressure Cool Flames
NASA Astrophysics Data System (ADS)
Ju, Yiguang
2016-11-01
The flame speeds and propagation limits of premixed cool flames at elevated pressures with radiative heat loss are numerically modelled using dimethyl ether mixtures. The primary focus is paid on the effects of pressure, mixture dilution, flame size, and heat loss on cool flame propagation. The results showed that cool flames exist on both fuel lean and fuel rich sides and thus dramatically extend the lean and rich flammability limits. There exist three different flame regimes, hot flame, cool flame, and double flame. A new flame flammability diagram including both cool flames and hot flames is obtained at elevated pressure. The results show that pressure significantly changes cool flame propagation. It is found that the increases of pressure affects the propagation speeds of lean and rich cool flames differently due to the negative temperature coefficient effect. On the lean side, the increase of pressure accelerates the cool flame chemistry and shifts the transition limit of cool flame to hot flame to lower equivalence ratio. At lower pressure, there is an extinction transition from hot flame to cool flame. However, there exists a critical pressure above which the cool flame to hot flame transition limit merges with the lean flammability limit of the hot flame, resulting in a direct transition from hot flame to cool flame. On the other hand, the increase of dilution reduces the heat release of hot flame and promotes cool flame formation. Moreover, it is shown that a smaller flame size and a higher heat loss also extend the cool flame transition limit and promote cool flame formation.
Crack Propagation in Double-Base Propellants
1976-01-01
propagation tests were conducted on a composite modified double- base ( CMDB ) propellant with the use of center-cracked strip biaxial specimens...double-base ( CMDB ) propellant. He performed a stress analysis of small, precracked, subscale STV motors formulated in terms of stress intensity factors...assumed for Solithane 113. The present program was aimed at evaluating the Schapery theory when it was applied to a CMDB propellant under similar loading
Combustion and Flame Propagation in Heterogeneous Systems
1976-10-29
NACIONAL DE TECNICA AEROESPACIAL MADRID, SPAIN 29 OCTOBER 1976 I A R- R7 6 14 2 j 006223 Grant Number AFOSR 72-2253 fCOMBUSTION AND FLAME PROPAGATION IN...ORGANIZATION NME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASKAREA A WORK UNIT NUMBERS INSTITUO NACIONAL DE TECNICA AEROESPACIAL 681308 DEPARTAMENTO DE CIENCIAS... AEROESPACIALES 9711-01 TORREJ6N DE ARDOZ MADRID, SPAIN 6~110?-. It. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE AIR FORCE OFFICE OF
47 CFR 80.767 - Propagation curve.
Code of Federal Regulations, 2013 CFR
2013-10-01
... propagation graph, § 80.767 Graph 1, must be used in computing the service area contour. The graph provides...: Transmitter output power in watts is converted to dBk by Pt=10 −30. Also see § 80.761 Graph 1 for a conversion graph. G=Antenna gain in dB referred to a standard half-wave dipole, in the direction of each...
47 CFR 80.767 - Propagation curve.
Code of Federal Regulations, 2010 CFR
2010-10-01
... propagation graph, § 80.767 Graph 1, must be used in computing the service area contour. The graph provides...: Transmitter output power in watts is converted to dBk by Pt=10 −30. Also see § 80.761 Graph 1 for a conversion graph. G=Antenna gain in dB referred to a standard half-wave dipole, in the direction of each...
47 CFR 80.767 - Propagation curve.
Code of Federal Regulations, 2014 CFR
2014-10-01
... propagation graph, § 80.767 Graph 1, must be used in computing the service area contour. The graph provides...: Transmitter output power in watts is converted to dBk by Pt=10 −30. Also see § 80.761 Graph 1 for a conversion graph. G=Antenna gain in dB referred to a standard half-wave dipole, in the direction of each...
47 CFR 80.767 - Propagation curve.
Code of Federal Regulations, 2011 CFR
2011-10-01
... propagation graph, § 80.767 Graph 1, must be used in computing the service area contour. The graph provides...: Transmitter output power in watts is converted to dBk by Pt=10 −30. Also see § 80.761 Graph 1 for a conversion graph. G=Antenna gain in dB referred to a standard half-wave dipole, in the direction of each...
47 CFR 80.767 - Propagation curve.
Code of Federal Regulations, 2012 CFR
2012-10-01
... propagation graph, § 80.767 Graph 1, must be used in computing the service area contour. The graph provides...: Transmitter output power in watts is converted to dBk by Pt=10 −30. Also see § 80.761 Graph 1 for a conversion graph. G=Antenna gain in dB referred to a standard half-wave dipole, in the direction of each...
Metamaterial hyperlens demonstration of propagation without diffraction
NASA Astrophysics Data System (ADS)
Fleming, Simon
2017-03-01
Metamaterials are a topic of much research interest because they have such extraordinary properties. Such materials are generally difficult and expensive to make and to characterize, and thus beyond the reach of undergraduate classes. This paper describes a metamaterial hyperlens, fabricated in about an hour from materials costing about one dollar, which permits an experimental demonstration of propagation without diffraction using common undergraduate laboratory microwave equipment.
Light propagation and interaction observed with electrons.
Word, Robert C; Fitzgerald, J P S; Könenkamp, R
2016-01-01
We discuss possibilities for a microscopic optical characterization of thin films and surfaces based on photoemission electron microscopy. We show that propagating light with wavelengths across the visible range can readily be visualized, and linear and non-linear materials properties can be evaluated non-invasively with nanometer spatial resolution. While femtosecond temporal resolution can be achieved in pump-probe-type experiments, the interferometric approach presented here has typical image frame times of ~200 fs.
Semisupervised kernel matrix learning by kernel propagation.
Hu, Enliang; Chen, Songcan; Zhang, Daoqiang; Yin, Xuesong
2010-11-01
The goal of semisupervised kernel matrix learning (SS-KML) is to learn a kernel matrix on all the given samples on which just a little supervised information, such as class label or pairwise constraint, is provided. Despite extensive research, the performance of SS-KML still leaves some space for improvement in terms of effectiveness and efficiency. For example, a recent pairwise constraints propagation (PCP) algorithm has formulated SS-KML into a semidefinite programming (SDP) problem, but its computation is very expensive, which undoubtedly restricts PCPs scalability in practice. In this paper, a novel algorithm, called kernel propagation (KP), is proposed to improve the comprehensive performance in SS-KML. The main idea of KP is first to learn a small-sized sub-kernel matrix (named seed-kernel matrix) and then propagate it into a larger-sized full-kernel matrix. Specifically, the implementation of KP consists of three stages: 1) separate the supervised sample (sub)set X(l) from the full sample set X; 2) learn a seed-kernel matrix on X(l) through solving a small-scale SDP problem; and 3) propagate the learnt seed-kernel matrix into a full-kernel matrix on X . Furthermore, following the idea in KP, we naturally develop two conveniently realizable out-of-sample extensions for KML: one is batch-style extension, and the other is online-style extension. The experiments demonstrate that KP is encouraging in both effectiveness and efficiency compared with three state-of-the-art algorithms and its related out-of-sample extensions are promising too.
FX-25 and FX-100 Propagation Experiments.
1982-07-01
to measure the beam-current distribution in the hose-stable propagation regime. A graphite Rogowski- surface cathode produced a beam that was injected...detector cannot be readily adapted to measurements of net current because of the vastly different sensitivities to beam and plasma currents. The...deposited on the calorimeter from the plasma was not a significant fraction of the beam energy. These calorimetric measurements of beam energy
Enhanced Propagating Surface Plasmon Signal Detection
Gong, Y.; Joly, Alan G.; El-Khoury, Patrick Z.; Hess, Wayne P.
2016-12-21
Overcoming the dissipative nature of propagating surface plasmons (PSPs) is pre-requisite to realizing functional plasmonic circuitry, in which large bandwidth signals can be manipulated over length scales far-below the diffraction limit of light. To this end, we report on a novel PSP enhanced signal detection technique achieved in an all-metallic substrate. We take advantage of two strategically spatio-temporally separated phase-locked femtosecond laser pulses, incident onto lithographically patterned PSP coupling structures. We follow PSP propagation with joint femtosecond temporal and nanometer spatial resolution in a time-resolved non-linear photoemission electron microscopy scheme. Initially, a PSP signal wave packet is launched from a hole etched into the silver surface from where it propagates through an open trench structure and is decoded through the use of a timed probe pulse. FDTD calculations demonstrate that PSP signal waves may traverse open trenches in excess of 10 microns in diameter, thereby allowing remote detection even through vacuum regions. This arrangement results in a 10X enhancement in photoemission relative to readout from the bare metal surface. The enhancement is attributed to an all-optical homodyne detection technique that mixes signal and reference PSP waves in a non-linear scheme. Larger readout trenches achieve higher readout levels, however reduced transmission through the trench limits the trench size to 6 microns for maximum readout levels. However, the use of an array of trenches increases the maximum enhancement to near 30X. The attainable enhancement factor may be harnessed to achieve extended coherent PSP propagation in ultrafast plasmonic circuitry.
Transport Theory for Propagation and Reverberation
2014-09-30
and reverberation modeling is important for many prediction methods that are important for Navy applications and for underwater acoustics systems...development. While acoustic propagation and reverberation modeling has been extensively developed for many years, significant limitations still exist on...the acoustic field in modes, and therefore would most readily apply at mid-frequencies and below, and in relatively shallow water environments such as
Nonlinear quantum beats of propagating polaritons
NASA Astrophysics Data System (ADS)
Pantke, K.-H.; Schillak, P.; Razbirin, B. S.; Lyssenko, V. G.; Hvam, J. M.
1993-01-01
We observe nonequidistant oscillations in the correlation trace of the nonlinear signal in a four-wave mixing experiment when exciting the upper polariton branch between the An=1 and the An=2 excitons in CdSe. The quantum beats are described qualitatively and quantitatively taking into account propagation interference effects on the third-order nonlinear polarization, and the homogeneous dampings of the exciton polaritons are determined.
Propagation and Production of Native Aquatic Plants
2005-09-01
ERDC/TN APCRP-EA-11 September 2005 Propagation and Production of Native Aquatic Plants by Gary Owen Dick , R. Michael Smart, and Joe R. Snow...small, protected plant colonies at strategic locations within unvegetated reservoirs (Smart and Dick 1999). Once successfully established, these...specific treatment of this information is given in Smart and Dick (1999). FACILITIES FOR OFF-SITE PRODUCTION: Production of aquatic plants requires
Engineering Aspects of Fatigue Crack Propagation
1962-01-01
Estimating Notch-Size Effect in Fatigue Tests on Steel. NACA TN 2805, 1952. - 37 - 19. Landers, Charles B., and Hardrath, Herbert F.: Results of Axial- Load... Charles B., and Howell, F. M.: Axial-Load Fatigue Properties of 24S-T and 75S-T Aluminum Alloy as Determined in Several Laboratories. NACA TR 1190, 1954...Hardrath, Herbert F., Leybold, Herbert A., Landers, Charles B., and Hauschild, Louis W.: Fatigue-Crack Propagation in Aluminum- Alloy Box Beams. NACA
Quantum Graphical Models and Belief Propagation
Leifer, M.S. Poulin, D.
2008-08-15
Belief Propagation algorithms acting on Graphical Models of classical probability distributions, such as Markov Networks, Factor Graphs and Bayesian Networks, are amongst the most powerful known methods for deriving probabilistic inferences amongst large numbers of random variables. This paper presents a generalization of these concepts and methods to the quantum case, based on the idea that quantum theory can be thought of as a noncommutative, operator-valued, generalization of classical probability theory. Some novel characterizations of quantum conditional independence are derived, and definitions of Quantum n-Bifactor Networks, Markov Networks, Factor Graphs and Bayesian Networks are proposed. The structure of Quantum Markov Networks is investigated and some partial characterization results are obtained, along the lines of the Hammersley-Clifford theorem. A Quantum Belief Propagation algorithm is presented and is shown to converge on 1-Bifactor Networks and Markov Networks when the underlying graph is a tree. The use of Quantum Belief Propagation as a heuristic algorithm in cases where it is not known to converge is discussed. Applications to decoding quantum error correcting codes and to the simulation of many-body quantum systems are described.
Propagation of seismic waves in tall buildings
Safak, E.
1998-01-01
A discrete-time wave propagation formulation of the seismic response of tall buildings is introduced. The building is modeled as a layered medium, similar to a layered soil medium, and is subjected to vertically propagating seismic shear waves. Soil layers and the bedrock under the foundation are incorporated in the formulation as additional layers. Seismic response is expressed in terms of the wave travel times between the layers, and the wave reflection and transmission coefficients at the layer interfaces. The equations account for the frequency-dependent filtering effects of the foundation and floor masses. The calculation of seismic response is reduced to a pair of simple finite-difference equations for each layer, which can be solved recursively starting from the bedrock. Compared to the commonly used vibration formulation, the wave propagation formulation provides several advantages, including simplified calculations, better representation of damping, ability to account for the effects of the soil layers under the foundation, and better tools for identification and damage detection from seismic records. Examples presented show the versatility of the method. ?? 1998 John Wiley & Sons, Ltd.
Nonlinear propagation of light in Dirac matter.
Eliasson, Bengt; Shukla, P K
2011-09-01
The nonlinear interaction between intense laser light and a quantum plasma is modeled by a collective Dirac equation coupled with the Maxwell equations. The model is used to study the nonlinear propagation of relativistically intense laser light in a quantum plasma including the electron spin-1/2 effect. The relativistic effects due to the high-intensity laser light lead, in general, to a downshift of the laser frequency, similar to a classical plasma where the relativistic mass increase leads to self-induced transparency of laser light and other associated effects. The electron spin-1/2 effects lead to a frequency upshift or downshift of the electromagnetic (EM) wave, depending on the spin state of the plasma and the polarization of the EM wave. For laboratory solid density plasmas, the spin-1/2 effects on the propagation of light are small, but they may be significant in superdense plasma in the core of white dwarf stars. We also discuss extensions of the model to include kinetic effects of a distribution of the electrons on the nonlinear propagation of EM waves in a quantum plasma.
Wave propagation in metamaterial lattice sandwich plates
NASA Astrophysics Data System (ADS)
Fang, Xin; Wen, Jihong; Yin, Jianfei; Yu, Dianlong
2016-04-01
This paper designed a special acoustic metamaterial 3D Kagome lattice sandwich plate. Dispersion properties and vibration responses of both traditional plate and metamaterial plate are investigated based on FEA methods. The traditional plate does not have low-frequency complete bandgaps, but the metamaterial plate has low-frequency complete bandgap (at 620Hz) coming from the symmetrical local cantilever resonators. The bandgap frequency is approximate to the first-order natural frequency of the oscillator. Complex wave modes are analyzed. The dispersion curves of longitudinal waves exist in the flexural bandgap. The dispersion properties demonstrate the metamaterial design is advantageous to suppress the low-frequency flexural wave propagation in lattice sandwich plate. The flexural vibrations near the bandgap are also suppressed efficiently. The longitudinal excitation stimulates mainly longitudinal waves and lots of low-frequency flexural vibration modes are avoided. Furthermore, the free edge effects in metamaterial plate provide new method for damping optimizations. The influences of damping on vibrations of the metamaterial sandwich plate are studied. Damping has global influence on the wave propagation; stronger damping will induce more vibration attenuation. The results enlighten us damping and metamaterial design approaches can be unite in the sandwich plates to suppress the wave propagations.
Wave Propagation in Jointed Geologic Media
Antoun, T
2009-12-17
Predictive modeling capabilities for wave propagation in a jointed geologic media remain a modern day scientific frontier. In part this is due to a lack of comprehensive understanding of the complex physical processes associated with the transient response of geologic material, and in part it is due to numerical challenges that prohibit accurate representation of the heterogeneities that influence the material response. Constitutive models whose properties are determined from laboratory experiments on intact samples have been shown to over-predict the free field environment in large scale field experiments. Current methodologies for deriving in situ properties from laboratory measured properties are based on empirical equations derived for static geomechanical applications involving loads of lower intensity and much longer durations than those encountered in applications of interest involving wave propagation. These methodologies are not validated for dynamic applications, and they do not account for anisotropic behavior stemming from direcitonal effects associated with the orientation of joint sets in realistic geologies. Recent advances in modeling capabilities coupled with modern high performance computing platforms enable physics-based simulations of jointed geologic media with unprecedented details, offering a prospect for significant advances in the state of the art. This report provides a brief overview of these modern computational approaches, discusses their advantages and limitations, and attempts to formulate an integrated framework leading to the development of predictive modeling capabilities for wave propagation in jointed and fractured geologic materials.
RF Wave Propagation and Scattering in Tokamaks
NASA Astrophysics Data System (ADS)
Horton, Wendell; Goniche, Marc; Arefiev, Alex; Peysson, Yves; Ekedahl, Annika; InstituteFusion Studies Collaboration; IRFM CEA Collaboration
2016-10-01
The propagation, scattering and absorption of the lower hybrid and electron cyclotron RF waves used to control fusion plasmas is reviewed. Drift wave turbulence driven by the steep ion and electron temperature gradients in H-mode divertor tokamaks produces strong scattering of the RF waves used for heating and plasma currents drive Both the 3-5GHz lower-hybrid (LH) and the 170GHZ electron cyclotron (EC) waves experience scattering and diffraction as propagating through the statistically complex density of the plasma. Ray equations are used to calculate the spread of the rays and the associated change in the parallel phase, polarization and group velocity of the RF waves in the propagation through the fusion plasma. A Fokker Planck equation for the phase space of the RF plasmons is one method to describe the spread of the RF wave power in the complex geometry of a divertor tokamak using the ray tracing codes. The evolution of the electron distribution function from the resonant electron-wave interactions is summarized for several scenarios. The resulting X-ray spectrum is broaden giving better agreement with the measured X-ray spectrum than that calculated in the absence of the turbulent scattering of the RF waves. M. Goniche et al., and Tore Supra Team, Phys. Plasmas 21, 2014.
Autocatalytic Reaction Front Propagation in Oscillatory Flows
NASA Astrophysics Data System (ADS)
Leconte, Marc; Martin, Jerome; Rakotomalala, Nicole; Salin, Dominique
2003-11-01
Laboratoire Fluides Automatique et Systèmes Thermiques, Universités P. et M. Curie and Paris Sud, C.N.R.S. (UMR 7608) Bâtiment 502, Campus Universitaire, 91405 Orsay Cedex, France. Autocatalytic reaction front between two reacting species is able to propagate as a solitary wave that is at a constant velocity and with a stationary concentration profile resulting from a balance between molecular diffusion and chemical reaction. On the other hand, in laminar flow the association of molecular diffusion and convection leads to an overall diffusion effect, the so-called Taylor dispersion, with a flow dependent enhanced dispersion coefficient. Previous experiments have demonstrated the dissymmetry between supportive and adverse advection flows compared to the reaction front propagation without flow. We analyze experimentally the effect of laminar oscillatory flow on the propagation and on the shape of the fronts in the Iodate-Arsenous Acid autocatalytic reaction in micro Hele-Shaw cells. We observe new solitary waves whose velocity and shape depend on the relative importance of advection, diffusion and reaction. The results are in reasonable with our lattice 3D BGK simulations.
Model-scale sound propagation experiment
NASA Technical Reports Server (NTRS)
Willshire, William L., Jr.
1988-01-01
The results of a scale model propagation experiment to investigate grazing propagation above a finite impedance boundary are reported. In the experiment, a 20 x 25 ft ground plane was installed in an anechoic chamber. Propagation tests were performed over the plywood surface of the ground plane and with the ground plane covered with felt, styrofoam, and fiberboard. Tests were performed with discrete tones in the frequency range of 10 to 15 kHz. The acoustic source and microphones varied in height above the test surface from flush to 6 in. Microphones were located in a linear array up to 18 ft from the source. A preliminary experiment using the same ground plane, but only testing the plywood and felt surfaces was performed. The results of this first experiment were encouraging, but data variability and repeatability were poor, particularly, for the felt surface, making comparisons with theoretical predictions difficult. In the main experiment the sound source, microphones, microphone positioning, data acquisition, quality of the anechoic chamber, and environmental control of the anechoic chamber were improved. High-quality, repeatable acoustic data were measured in the main experiment for all four test surfaces. Comparisons with predictions are good, but limited by uncertainties of the impedance values of the test surfaces.
Current understanding of SEP acceleration and propagation
NASA Astrophysics Data System (ADS)
Klecker, B.
2013-02-01
The solar energetic particle (SEP) populations of electrons and ions are highly variable in space and time, in intensity, energy, and composition. Over the last ~20 years advanced instrumentation onboard many spacecraft (e.g. ACE, Coronas, GOES, Hinode, RHESSI, SAMPEX, SDO, SOHO, STEREO, TRACE, Ulysses, Yokoh, to name a few) extended our ability to explore the characteristics of solar energetic particles by in-situ measurements in interplanetary space and by observing their source characteristics near the Sun by remote-sensing observation of electromagnetic emission over a wide frequency range. These measurements provide crucial information for understanding the sources of the particle populations and the acceleration and propagation processes involved. We are now able to measure intensity-time profiles and anisotropies, energy spectra, elemental and isotopic abundances, and the ionic charge of particles over an extended energy range of 0.01 to several 100 MeV/nuc and for a large dynamic range of particle intensities. Furthermore, multi-spacecraft in-situ observations at different solar longitudes and latitudes provide new insight into the acceleration and propagation processes of SEPs near the Sun and in interplanetary space. In this paper we present an overview of SEP observations, their implications for SEP acceleration and propagation processes, and discuss open questions.
Atmospheric propagation properties of various laser systems
NASA Astrophysics Data System (ADS)
Pitz, Greg A.; Glass, Sara; Kamer, Brian; Klennert, Wade L.; Hostutler, David A.
2012-06-01
Atmospheric propagation properties of various laser systems, including diode pumped alkali lasers (DPALs) and the Chemical Oxygen Iodine Laser (COIL), are of importance. However, there appears to be a lack of highly accurate transmission characteristics of these systems associated with their operating conditions. In this study laser propagation of the rubidium-based DPAL and the COIL has been simulated utilizing integrated cavity output spectroscopy. This technique allowed for the simulation of laser propagation approaching distances of 3 kilometers on a test stand only 35 cm long. The spectral output from these simulations was compared to the HITRAN database with excellent agreement. The spectral prole and proximity of the laser line to the atmospheric absorbers is shown. These low pressure spectral proles were then extrapolated to higher pressures using an in-house hyperne model. These models allowed for the comparison of proposed systems and their output spectral prole. The diode pumped rubidium laser at pressures under an atmosphere has been shown to interact with only one water absorption feature, but at pressures approaching 7 atmospheres the D1 transition may interact with more than 6 water lines depending on resonator considerations. Additionally, a low pressure system may have some slight control of the overlap of the output prole with the water line by changing the buer gases.
Computation of beam propagation in turbulent field
NASA Astrophysics Data System (ADS)
Yang, Yao; Cen, Zhaofeng; Li, Xiaotong
2016-10-01
The split-step Fourier method (SSFM) is introduced to analyze the beam propagation in a relatively large-sized turbulent filed, whose refractive-index profile is already detected. The numerical method is achieved by fast Fourier transform (FFT).To obtain the optimal sampling number, we propose an adaptive spread-spectrum method as an optimization. The SSFM is widely used for solving the nonlinear Schrödinger equation [1].The advantage of the SSFM is apparently its simple formalism and suitability to our situation. The direct numerical solution of the Helmholtz equation, derived from this method, yields detailed information of the spatial and angular properties of the propagation beam. On the other hand, a set of approximations restrict its applicability, the requirements for the accurate application of the method are summarized and a set of formulas is generalized in this paper. The efficiency of the SSFM depends on the sampling number, the adaptive spread-spectrum method yields optimal sampling number to increase the computational efficiency .To testify the accuracy of our algorithm, we use graded-index medium as the turbulent filed, for the reason that the beam propagation in turbulent field with random refractive-index profile is ruleless and has no unified reference. The simulation result testifies our algorithm is tremendously accurate, capable of selecting the optimal N automatically and much more computationally efficient than the original algorithm.
Cosmic ray sources, acceleration and propagation
NASA Technical Reports Server (NTRS)
Ptuskin, V. S.
1986-01-01
A review is given of selected papers on the theory of cosmic ray (CR) propagation and acceleration. The high isotropy and a comparatively large age of galactic CR are explained by the effective interaction of relativistic particles with random and regular electromagnetic fields in interstellar medium. The kinetic theory of CR propagation in the Galaxy is formulated similarly to the elaborate theory of CR propagation in heliosphere. The substantial difference between these theories is explained by the necessity to take into account in some cases the collective effects due to a rather high density of relativisitc particles. In particular, the kinetic CR stream instability and the hydrodynamic Parker instability is studied. The interaction of relativistic particles with an ensemble of given weak random magnetic fields is calculated by perturbation theory. The theory of CR transfer is considered to be basically completed for this case. The main problem consists in poor information about the structure of the regular and the random galactic magnetic fields. An account is given of CR transfer in a turbulent medium.
Premixed Turbulent Flame Propagation in Microgravity
NASA Technical Reports Server (NTRS)
Menon, Suresh
1999-01-01
A combined numerical-experimental study has been carried out to investigate the structure and propagation characteristics of turbulent premixed flames with and without the influence of buoyancy. Experimentally, the premixed flame characteristics are studied in the wrinkled regime using a Couette flow facility and an isotropic flow facility in order to resolve the scale of flame wrinkling. Both facilities were chosen for their ability to achieve sustained turbulence at low Reynolds number. This implies that conventional diagnostics can be employed to resolve the smallest scales of wrinkling. The Couette facility was also built keeping in mind the constraints imposed by the drop tower requirements. Results showed that the flow in this Couette flow facility achieves full-developed turbulence at low Re and all turbulence statistics are in good agreement with past measurements on large-scale facilities. Premixed flame propagation studies were then carried out both using the isotropic box and the Couette facility. Flame imaging showed that fine scales of wrinkling occurs during flame propagation. Both cases in Ig showed significant buoyancy effect. To demonstrate that micro-g can remove this buoyancy effect, a small drop tower was built and drop experiments were conducted using the isotropic box. Results using the Couette facility confirmed the ability to carry out these unique reacting flow experiments at least in 1g. Drop experiments at NASA GRC were planned but were not completed due to termination of this project.
Light propagation in the averaged universe
Bagheri, Samae; Schwarz, Dominik J. E-mail: dschwarz@physik.uni-bielefeld.de
2014-10-01
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 the 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.
VLF/LF long wave propagation study
NASA Astrophysics Data System (ADS)
Verplanck, P.; Kahler, R. C.; Donohoe, J. B.
1981-11-01
A program of ARCAS rocket measurements provided field strength data from 0 to 75 km altitude, in both Transverse Magnetic (TM) and Transverse Electric (TE) polarizations. Sky wave parameters related to survivable ground wave communications were measured at a frequency of 100 kHz, and a method of communicating with short (ground wave) pulses was demonstrated on a 230 km propagation path. Measurements were made in New York state, and in Brazil, to further define the nature of pulse reflections from ionospheric heights below the classical D-region. Instrumentation was developed to detect small changes in 100 kHz ground wave propagation velocity which might correlate with tropospheric conditions. Preliminary mechanical considerations indicate that it might be possible to deploy long center-fed dipole antennas from an Earth satellite. The program of high-resolution ionosounding with TM pulses in Greenland was augmented by transmitting TE pulses from an unused powerline at Thule Air Base. It was demonstrated that the effects of ionospheric disturbances can now be observed simultaneously with both polarizations. Input resistances and reactances of the powerline antenna were measured as functions of frequency in preparation for a follow-on program of long range propagation tests.
Wave propagation in spatially modulated tubes
NASA Astrophysics Data System (ADS)
Ziepke, A.; Martens, S.; Engel, H.
2016-09-01
We investigate wave propagation in rotationally symmetric tubes with a periodic spatial modulation of cross section. Using an asymptotic perturbation analysis, the governing quasi-two-dimensional reaction-diffusion equation can be reduced into a one-dimensional reaction-diffusion-advection equation. Assuming a weak perturbation by the advection term and using projection method, in a second step, an equation of motion for traveling waves within such tubes can be derived. Both methods predict properly the nonlinear dependence of the propagation velocity on the ratio of the modulation period of the geometry to the intrinsic width of the front, or pulse. As a main feature, we observe finite intervals of propagation failure of waves induced by the tube's modulation and derive an analytically tractable condition for their occurrence. For the highly diffusive limit, using the Fick-Jacobs approach, we show that wave velocities within modulated tubes are governed by an effective diffusion coefficient. Furthermore, we discuss the effects of a single bottleneck on the period of pulse trains. We observe period changes by integer fractions dependent on the bottleneck width and the period of the entering pulse train.
Modeling Light Propagation in Luminescent Media
NASA Astrophysics Data System (ADS)
Sahin, Derya
This study presents physical, computational and analytical modeling approaches for light propagation in luminescent random media. Two different approaches are used, namely (i) a statistical approach: Monte-Carlo simulations for photon transport and (ii) a deterministic approach: radiative transport theory. Both approaches account accurately for the multiple absorption and reemission of light at different wavelengths and for anisotropic luminescence. The deterministic approach is a generalization of radiative transport theory for solving inelastic scattering problems in random media. We use the radiative transport theory to study light propagation in luminescent media. Based on this theory, we also study the optically thick medium. Using perturbation methods, a corrected diffusion approximation with asymptotically accurate boundary conditions and a boundary layer solution are derived. The accuracy and the efficacy of this approach is verified for a plane-parallel slab problem. In particular, we apply these two approaches (MC and radiative transport theory) to model light propagation in semiconductor-based luminescent solar concentrators (LSCs). The computational results for both approaches are compared with each other and found to agree. The results of this dissertation present practical and reliable techniques to use for solving forward/inverse inelastic scattering problems arising in various research areas such as optics, biomedical engineering, nuclear engineering, solar science and material science.
Instability and Turbulence of Propagating Particulate Flows
NASA Astrophysics Data System (ADS)
Balachandar, S.
2015-11-01
Propagation of particle-laden fluid into an ambient is a common fluid mechanical process that can be observed in many industrial and environmental applications. Sedimentation fronts, volcanic plumes, dust storms, powder snow avalanches, submarine turbidity currents, explosive powder dispersal and supernovae offer fascinating examples of advancing particulate fronts. The propagating interface can undergo Rayleigh-Taylor, Kelvin-Helmholtz and double-diffusive instabilities and result in the formation of lobes and clefts, spikes and bubbles, and particulate fingers. The interplay between suspended particles and turbulence is often complex due to interaction of competing mechanisms. In problems such as turbidity currents, turbulence controls sediment concentration through resuspension and settling of particles at the bed. Also, turbulent entrainment at the propagating front is observed to be influenced by the sediments. Stable stratification due to suspended sediment concentration can damp and even kill turbulence. This complex turbulence-sediment interaction offers possible explanation for massive sediment deposits observed in nature. The talk will also address challenges and recent advancements in the modeling and simulation of such particle-laden turbulent flows.
Modeling Propagation of Shock Waves in Metals
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. 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 {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.
Large-scale Globally Propagating Coronal Waves.
Warmuth, Alexander
Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the "classical" interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which "pseudo waves" are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.
Cosmic ray propagation with CRPropa 3
NASA Astrophysics Data System (ADS)
Alves Batista, R.; Erdmann, M.; Evoli, C.; Kampert, K.-H.; Kuempel, D.; Mueller, G.; Sigl, G.; Van Vliet, A.; Walz, D.; Winchen, T.
2015-05-01
Solving the question of the origin of ultra-high energy cosmic rays (UHECRs) requires the development of detailed simulation tools in order to interpret the experimental data and draw conclusions on the UHECR universe. CRPropa is a public Monte Carlo code for the galactic and extragalactic propagation of cosmic ray nuclei above ∼ 1017 eV, as well as their photon and neutrino secondaries. In this contribution the new algorithms and features of CRPropa 3, the next major release, are presented. CRPropa 3 introduces time-dependent scenarios to include cosmic evolution in the presence of cosmic ray deflections in magnetic fields. The usage of high resolution magnetic fields is facilitated by shared memory parallelism, modulated fields and fields with heterogeneous resolution. Galactic propagation is enabled through the implementation of galactic magnetic field models, as well as an efficient forward propagation technique through transformation matrices. To make use of the large Python ecosystem in astrophysics CRPropa 3 can be steered and extended in Python.
Fatigue crack layer propagation in silicon-iron
NASA Technical Reports Server (NTRS)
Birol, Y.; Welsch, G.; Chudnovsky, A.
1986-01-01
Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.
Coherence Effects in Light Propagation in Scattering and in Spectroscopy
2005-12-01
Gaussian Schell - model Beams Propagating in Atmospheric Turbulence", Opt. Lett. 28...generated by an electromagnetic Gaussian Schell - model source which propagates through atmospheric turbulence tends to its value at the source plane with...polarization on propagation . We illustrate the results by a numerical example relating to an electromagnetic Gaussian Schell - model beam. 17 51. H.
Elastic Wave Propagation Mechanisms in Underwater Acoustic Environments
2015-09-30
Elastic wave propagation mechanisms in underwater acoustic environments Scott D. Frank Marist College Department of Mathematics Poughkeepsie...conversion from elastic propagation to acoustic propagation, and intense interface waves on underwater acoustic environments with elastic bottoms... acoustic energy in the water column. Elastic material parameters will be varied for analysis of the dissipation of water column acoustic energy
Visual attitude propagation for small satellites
NASA Astrophysics Data System (ADS)
Rawashdeh, Samir A.
As electronics become smaller and more capable, it has become possible to conduct meaningful and sophisticated satellite missions in a small form factor. However, the capability of small satellites and the range of possible applications are limited by the capabilities of several technologies, including attitude determination and control systems. This dissertation evaluates the use of image-based visual attitude propagation as a compliment or alternative to other attitude determination technologies that are suitable for miniature satellites. The concept lies in using miniature cameras to track image features across frames and extracting the underlying rotation. The problem of visual attitude propagation as a small satellite attitude determination system is addressed from several aspects: related work, algorithm design, hardware and performance evaluation, possible applications, and on-orbit experimentation. These areas of consideration reflect the organization of this dissertation. A "stellar gyroscope" is developed, which is a visual star-based attitude propagator that uses relative motion of stars in an imager's field of view to infer the attitude changes. The device generates spacecraft relative attitude estimates in three degrees of freedom. Algorithms to perform the star detection, correspondence, and attitude propagation are presented. The Random Sample Consensus (RANSAC) approach is applied to the correspondence problem to successfully pair stars across frames while mitigating falsepositive and false-negative star detections. This approach provides tolerance to the noise levels expected in using miniature optics and no baffling, and the noise caused by radiation dose on orbit. The hardware design and algorithms are validated using test images of the night sky. The application of the stellar gyroscope as part of a CubeSat attitude determination and control system is described. The stellar gyroscope is used to augment a MEMS gyroscope attitude propagation
Mineral replacement front propagation in deformed rocks
NASA Astrophysics Data System (ADS)
Beaudoin, Nicolas; Koehn, Daniel; Kelka, Ulrich
2015-04-01
Fluid migrations are a major agent of contaminant transport leading to mineral replacement in rocks, impacting their properties as porosity, permeability, and rheology. Understanding the physical and chemical mechanisms that govern mineralogical replacement during and after deformation is required to better understand complex interplays between fluid and rocks that are involved in faulting, seismic cycle, and resource distribution in the upper crust. Dolomitization process related to hydrothermal fluid flow is one of the most studied and debated replacement processes in earth sciences. Dolomitization of limestone is of economic importance as well, as it stands as unconventional oil reservoirs and is systematically observed in Mississippian-Valley Type ore deposit. Despite recent breakthrough about dolomitization processes at large-scale, the small-scale propagation of the reaction front remains unclear. It is poorly documented in the occurrence of stylolites and fractures in the medium while pressure-solution and fracture network development are the most efficient deformation accomodation mechanism in limestone from early compaction to layer-parallel shortening. Thus, the impact of such network on geometry of replaced bodies and on replacement front propagation deserves specific attention. This contribution illustrates the role of fracture and stylolites on the propagation of a reaction front. In a 2 dimensional numerical model we simulate the dolomitization front propagation in a heterogeneous porous medium. The propagation of the reaction front is governed by the competition between advection and diffusion processes, and takes into account reaction rates, disorder in the location of the potential replacement seeds, and permeability heterogeneities. We add stylolites and fractures that can act as barriers or drains to fluid flow according to their orientation and mineralogical content, which can or cannot react with the contaminant. The patterns produced from
Turbulent flame propagation in partially premixed flames
NASA Technical Reports Server (NTRS)
Poinsot, T.; Veynante, D.; Trouve, A.; Ruetsch, G.
1996-01-01
Turbulent premixed flame propagation is essential in many practical devices. In the past, fundamental and modeling studies of propagating flames have generally focused on turbulent flame propagation in mixtures of homogeneous composition, i.e. a mixture where the fuel-oxidizer mass ratio, or equivalence ratio, is uniform. This situation corresponds to the ideal case of perfect premixing between fuel and oxidizer. In practical situations, however, deviations from this ideal case occur frequently. In stratified reciprocating engines, fuel injection and large-scale flow motions are fine-tuned to create a mean gradient of equivalence ratio in the combustion chamber which provides additional control on combustion performance. In aircraft engines, combustion occurs with fuel and secondary air injected at various locations resulting in a nonuniform equivalence ratio. In both examples, mean values of the equivalence ratio can exhibit strong spatial and temporal variations. These variations in mixture composition are particularly significant in engines that use direct fuel injection into the combustion chamber. In this case, the liquid fuel does not always completely vaporize and mix before combustion occurs, resulting in persistent rich and lean pockets into which the turbulent flame propagates. From a practical point of view, there are several basic and important issues regarding partially premixed combustion that need to be resolved. Two such issues are how reactant composition inhomogeneities affect the laminar and turbulent flame speeds, and how the burnt gas temperature varies as a function of these inhomogeneities. Knowledge of the flame speed is critical in optimizing combustion performance, and the minimization of pollutant emissions relies heavily on the temperature in the burnt gases. Another application of partially premixed combustion is found in the field of active control of turbulent combustion. One possible technique of active control consists of pulsating
Jackson, M B; Zhang, S J
1995-01-01
1. A theoretical model was developed to investigate action potential propagation in posterior pituitary nerve terminals. This model was then used to evaluate the efficacy of depolarizing and shunting GABA responses on action potential propagation. 2. Experimental data obtained from the posterior pituitary with patch clamp techniques were used to derive empirical expressions for the voltage and time dependence of the nerve terminal Na+ and K+ channels. The essential structure employed here was based on anatomical and cable data from the posterior pituitary, and consisted of a long cylindrical axon (diameter, 0.5 mm) with a large spherical swelling (diameter, 4-21 mm) in the middle. 3. In the absence of an inhibitory conductance, simulated action potentials propagated with high fidelity through the nerve terminal. Swellings could block propagation, but only when sizes exceeded those observed in the posterior pituitary. Adding axonal branches reduced the critical size only slightly. These results suggested that action potentials invade the entire posterior pituitary nerve terminal in the absence of inhibition or depression. 4. The addition of inhibitory conductance to a swelling caused simulated action potentials to fail at the swelling. Depolarizing inhibitory conductances were 1.6 times more effective than shunting inhibitory conductances in blocking propagation. 5. Inhibitory conductances within the range of experimentally observed magnitudes and localized to swellings in the observed range of sizes were too weak to block simulated action potentials. However, twofold enhancement of GABA responses by neurosteroid resulted in currents strong enough to block propagation in realistic swelling sizes. 6. GABA could block simulated propagation without neurosteroid enhancement provided that GABA was present throughout a region in the order of a few hundred micrometres. For this widespread inhibition depolarizing conductance was 2.2 times more effective than shunting
Hypersonic phonon propagation in one-dimensional surface phononic crystal
NASA Astrophysics Data System (ADS)
Graczykowski, B.; Sledzinska, M.; Kehagias, N.; Alzina, F.; Reparaz, J. S.; Sotomayor Torres, C. M.
2014-03-01
Hypersonic, thermally activated surface acoustic waves propagating in the surface of crystalline silicon patterned with periodic stripes were studied by Brillouin light scattering. Two characteristic directions (normal and parallel to the stripes) of surface acoustic waves propagation were examined exhibiting a distinctive propagation behavior. The measured phononic band structure exhibits diverse features, such as zone folding, band gap opening, and hybridization to local resonance for waves propagating normal to the stripes, and a variety of dispersive modes propagating along the stripes. Experimental results were supported by theoretical calculations performed using finite element method.
Propagation equation for tight-focusing by a parabolic mirror.
Couairon, A; Kosareva, O G; Panov, N A; Shipilo, D E; Andreeva, V A; Jukna, V; Nesa, F
2015-11-30
Part of the chain in petawatt laser systems may involve extreme focusing conditions for which nonparaxial and vectorial effects have high impact on the propagation of radiation. We investigate the possibility of using propagation equations to simulate numerically the focal spot under these conditions. We derive a unidirectional propagation equation for the Hertz vector, describing linear and nonlinear propagation under situations where nonparaxial diffraction and vectorial effects become significant. By comparing our simulations to the results of vector diffraction integrals in the case of linear tight-focusing by a parabolic mirror, we establish a practical criterion for the critical f -number below which initializing a propagation equation with a parabolic input phase becomes inaccurate. We propose a method to find suitable input conditions for propagation equations beyond this limit. Extreme focusing conditions are shown to be modeled accurately by means of numerical simulations of the unidirectional Hertz-vector propagation equation initialized with suitable input conditions.
Synaptic Contacts Enhance Cell-to-Cell Tau Pathology Propagation.
Calafate, Sara; Buist, Arjan; Miskiewicz, Katarzyna; Vijayan, Vinoy; Daneels, Guy; de Strooper, Bart; de Wit, Joris; Verstreken, Patrik; Moechars, Diederik
2015-05-26
Accumulation of insoluble Tau protein aggregates and stereotypical propagation of Tau pathology through the brain are common hallmarks of tauopathies, including Alzheimer's disease (AD). Propagation of Tau pathology appears to occur along connected neurons, but whether synaptic contacts between neurons are facilitating propagation has not been demonstrated. Using quantitative in vitro models, we demonstrate that, in parallel to non-synaptic mechanisms, synapses, but not merely the close distance between the cells, enhance the propagation of Tau pathology between acceptor hippocampal neurons and Tau donor cells. Similarly, in an artificial neuronal network using microfluidic devices, synapses and synaptic activity are promoting neuronal Tau pathology propagation in parallel to the non-synaptic mechanisms. Our work indicates that the physical presence of synaptic contacts between neurons facilitate Tau pathology propagation. These findings can have implications for synaptic repair therapies, which may turn out to have adverse effects by promoting propagation of Tau pathology.
Orbital Propagation of Momentum Exchange Tether Systems
NASA Technical Reports Server (NTRS)
Westerhoff, John
2002-01-01
An advanced concept in in-space transportation currently being studied is the Momentum-Exchange/Electrodynamic Reboost Tether System (MXER). The system acts as a large momentum wheel, imparting a Av to a payload in low earth orbit (LEO) at the expense of its own orbital energy. After throwing a payload, the system reboosts itself using an electrodynamic tether to push against Earth's magnetic field and brings itself back up to an operational orbit to prepare for the next payload. The ability to reboost itself allows for continued reuse of the system without the expenditure of propellants. Considering the cost of lifting propellant from the ,ground to LEO to do the same Av boost at $10000 per pound, the system cuts the launch cost of the payload dramatically, and subsequently, the MXER system pays for itself after a small number of missions.1 One of the technical hurdles to be overcome with the MXER concept is the rendezvous maneuver. The rendezvous window for the capture of the payload is on the order of a few seconds, as opposed to traditional docking maneuvers, which can take as long ets necessary to complete a precise docking. The payload, therefore, must be able to match its orbit to meet up with the capture device on the end of the tether at a specific time and location in the future. In order to be able to determine that location, the MXER system must be numerically propagated forward in time to predict where the capture device will be at that instant. It should be kept in mind that the propagation computation must be done faster than real-time. This study focuses on the efforts to find and/or build the tools necessary to numerically propagate the motion of the MXER system as accurately as possible.
Speeding up tsunami wave propagation modeling
NASA Astrophysics Data System (ADS)
Lavrentyev, Mikhail; Romanenko, Alexey
2014-05-01
Trans-oceanic wave propagation is one of the most time/CPU consuming parts of the tsunami modeling process. The so-called Method Of Splitting Tsunami (MOST) software package, developed at PMEL NOAA USA (Pacific Marine Environmental Laboratory of the National Oceanic and Atmospheric Administration, USA), is widely used to evaluate the tsunami parameters. However, it takes time to simulate trans-ocean wave propagation, that is up to 5 hours CPU time to "drive" the wave from Chili (epicenter) to the coast of Japan (even using a rather coarse computational mesh). Accurate wave height prediction requires fine meshes which leads to dramatic increase in time for simulation. Computation time is among the critical parameter as it takes only about 20 minutes for tsunami wave to approach the coast of Japan after earthquake at Japan trench or Sagami trench (as it was after the Great East Japan Earthquake on March 11, 2011). MOST solves numerically the hyperbolic system for three unknown functions, namely velocity vector and wave height (shallow water approximation). The system could be split into two independent systems by orthogonal directions (splitting method). Each system can be treated independently. This calculation scheme is well suited for SIMD architecture and GPUs as well. We performed adaptation of MOST package to GPU. Several numerical tests showed 40x performance gain for NVIDIA Tesla C2050 GPU vs. single core of Intel i7 processor. Results of numerical experiments were compared with other available simulation data. Calculation results, obtained at GPU, differ from the reference ones by 10^-3 cm of the wave height simulating 24 hours wave propagation. This allows us to speak about possibility to develop real-time system for evaluating tsunami danger.
Calibration of seismic wave propagation in Jordan
Al-Husien, A; Amrat, A; Harris, D; Mayeda, K; Nakanishi, K; Rodgers, A; Ruppert, S; Ryall, F; Skinnell, K; Yazjeen, T
1999-07-23
The Natural Resources Authority of Jordan (NRA), the USGS and LLNL have a collaborative project to improve the calibration of seismic propagation in Jordan and surrounding regions. This project serves common goals of CTBT calibration and earthquake hazard assessment in the region. These objectives include accurate location of local and regional earthquakes, calibration of magnitude scales, and the development of local and regional propagation models. In the CTBT context, better propagation models and more accurately located events in the Dead Sea rift region can serve as (potentially GT5) calibration events for generating IMS location corrections. The detection and collection of mining explosions underpins discrimination research. The principal activity of this project is the deployment of two broadband stations at Hittiyah (south Jordan) and Ruweishid (east Jordan). These stations provide additional paths in the region to constrain structure with surface wave and body wave tomography. The Ruweishid station is favorably placed to provide constraints on Arabian platform structure. Waveform modeling with long-period observations of larger earthquakes will provide constraints on 1-D velocity models of the crust and upper mantle. Data from these stations combined with phase observations from the 26 short-period stations of the Jordan National Seismic Network (JNSN) may allow the construction of a more detailed velocity model of Jordan. The Hittiyah station is an excellent source of ground truth information for the six phosphate mines of southern Jordan and Israel. Observations of mining explosions collected by this station have numerous uses: for definition of templates for screening mining explosions, as ground truth events for calibrating travel-time models, and as explosion populations in development and testing discriminants. Following previously established procedures for identifying explosions, we have identified more than 200 explosions from the first 85 days of
Simulations of Seismic Wave Propagation on Mars
NASA Astrophysics Data System (ADS)
Bozdağ, Ebru; Ruan, Youyi; Metthez, Nathan; Khan, Amir; Leng, Kuangdai; van Driel, Martin; Wieczorek, Mark; Rivoldini, Attilio; Larmat, Carène S.; Giardini, Domenico; Tromp, Jeroen; Lognonné, Philippe; Banerdt, Bruce W.
2017-03-01
We present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust (Sohl and Spohn in J. Geophys. Res., Planets 102(E1):1613-1635, 1997). For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE (Komatitsch and Tromp in Geophys. J. Int. 149(2):390-412, 2002a; 150(1):303-318, 2002b) against the 2D axisymmetric wave propagation solver AxiSEM (Nissen-Meyer et al. in Solid Earth 5(1):425-445, 2014) at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on ray theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars' northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D (Fichtner et al. Geophys. J. Int. 179:1703-1725, 2009) based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. We conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.
Foam front propagation in anisotropic oil reservoirs.
Grassia, P; Torres-Ulloa, C; Berres, S; Mas-Hernández, E; Shokri, N
2016-04-01
The pressure-driven growth model is considered, describing the motion of a foam front through an oil reservoir during foam improved oil recovery, foam being formed as gas advances into an initially liquid-filled reservoir. In the model, the foam front is represented by a set of so-called "material points" that track the advance of gas into the liquid-filled region. According to the model, the shape of the foam front is prone to develop concave sharply curved concavities, where the orientation of the front changes rapidly over a small spatial distance: these are referred to as "concave corners". These concave corners need to be propagated differently from the material points on the foam front itself. Typically the corner must move faster than those material points, otherwise spurious numerical artifacts develop in the computed shape of the front. A propagation rule or "speed up" rule is derived for the concave corners, which is shown to be sensitive to the level of anisotropy in the permeability of the reservoir and also sensitive to the orientation of the corners themselves. In particular if a corner in an anisotropic reservoir were to be propagated according to an isotropic speed up rule, this might not be sufficient to suppress spurious numerical artifacts, at least for certain orientations of the corner. On the other hand, systems that are both heterogeneous and anisotropic tend to be well behaved numerically, regardless of whether one uses the isotropic or anisotropic speed up rule for corners. This comes about because, in the heterogeneous and anisotropic case, the orientation of the corner is such that the "correct" anisotropic speed is just very slightly less than the "incorrect" isotropic one. The anisotropic rule does however manage to keep the corner very slightly sharper than the isotropic rule does.
Laminar flame propagation in a stratified charge
NASA Astrophysics Data System (ADS)
Ra, Youngchul
The propagation of laminar flame from a rich or stoichiometric mixture to a lean mixture in a stratified methane-air charge was investigated experimentally and numerically. Emphasis was on the understanding of the flame behavior in the transition region; in particular, on the mechanism of burning velocity enhancement in this region. In the experimental setup, mixtures of two different equivalence ratios were separated by a soap bubble in a spherical constant volume combustion vessel. The richer mixture inside the bubble was ignited by a focused laser beam. The flame development was observed by Schlieren technique and flame speeds were measured by heat release analysis of the pressure data. An one-dimensional, time- dependant numerical simulation of the flame propagation in a charge with step-stratification was used to interpret the experimental results. Both the experimental and numerical studies showed that the instantaneous flame speed depended on the previous flame history. Thus a `strong' (with mixture equivalence ratio close to stoichiometric) flame can sustain propagation into finite regions of substantially lean equivalence ratio. Both thermal and chemical effects were crucial for explaining the mechanism of the flame speed enhancement in the transition period. Because of the presence of this `back- support' effect, the usual concept of specifying the burning velocity as a function of the end gas state is inadequate for a stratified charge. A simple correlation for instantaneous flame velocity based on the local burned gas temperature is developed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.)
Nonlinear and Dispersive Optical Pulse Propagation
NASA Astrophysics Data System (ADS)
Dijaili, Sol Peter
In this dissertation, there are basically four novel contributions to the field of picosecond pulse propagation and measurement. The first contribution is the temporal ABCD matrix which is an analog of the traditional ABCD ray matrices used in Gaussian beam propagation. The temporal ABCD matrix allows for the easy calculation of the effects of linear chirp or group velocity dispersion in the time domain. As with Gaussian beams in space, there also exists a complete Hermite-Gaussian basis in time whose propagation can be tracked with the temporal ABCD matrices. The second contribution is the timing synchronization between a colliding pulse mode-locked dye laser and a gain-switched Fabry-Perot type AlGaAs laser diode that has achieved less than 40 femtoseconds of relative timing jitter by using a pulsed optical phase lock loop (POPLL). The relative timing jitter was measured using the error voltage of the feedback loop. This method of measurement is accurate since the frequencies of all the timing fluctuations fall within the loop bandwidth. The novel element is a broad band optical cross-correlator that can resolve femtosecond time delay errors between two pulse trains. The third contribution is a novel dispersive technique of determining the nonlinear frequency sweep of a picosecond pulse with relatively good accuracy. All the measurements are made in the time domain and hence there is no time-bandwidth limitation to the accuracy. The fourth contribution is the first demonstration of cross -phase modulation in a semiconductor laser amplifier where a variable chirp was observed. A simple expression for the chirp imparted on a weak signal pulse by the action of a strong pump pulse is derived. A maximum frequency excursion of 16 GHz due to the cross-phase modulation was measured. A value of 5 was found for alpha _{xpm} which is a factor for characterizing the cross-phase modulation in a similar manner to the conventional linewidth enhancement factor, alpha.
Crack propagation modeling using Peridynamic theory
NASA Astrophysics Data System (ADS)
Hafezi, M. H.; Alebrahim, R.; Kundu, T.
2016-04-01
Crack propagation and branching are modeled using nonlocal peridynamic theory. One major advantage of this nonlocal theory based analysis tool is the unifying approach towards material behavior modeling - irrespective of whether the crack is formed in the material or not. No separate damage law is needed for crack initiation and propagation. This theory overcomes the weaknesses of existing continuum mechanics based numerical tools (e.g. FEM, XFEM etc.) for identifying fracture modes and does not require any simplifying assumptions. Cracks grow autonomously and not necessarily along a prescribed path. However, in some special situations such as in case of ductile fracture, the damage evolution and failure depend on parameters characterizing the local stress state instead of peridynamic damage modeling technique developed for brittle fracture. For brittle fracture modeling the bond is simply broken when the failure criterion is satisfied. This simulation helps us to design more reliable modeling tool for crack propagation and branching in both brittle and ductile materials. Peridynamic analysis has been found to be very demanding computationally, particularly for real-world structures (e.g. vehicles, aircrafts, etc.). It also requires a very expensive visualization process. The goal of this paper is to bring awareness to researchers the impact of this cutting-edge simulation tool for a better understanding of the cracked material response. A computer code has been developed to implement the peridynamic theory based modeling tool for two-dimensional analysis. A good agreement between our predictions and previously published results is observed. Some interesting new results that have not been reported earlier by others are also obtained and presented in this paper. The final objective of this investigation is to increase the mechanics knowledge of self-similar and self-affine cracks.
DECIMETRIC TYPE III BURSTS: GENERATION AND PROPAGATION
Li, B.; Cairns, Iver H.; Robinson, P. A.; Yan, Y. H.
2011-09-01
Simulations are presented for decimetric type III radio bursts at 2f{sub p} , where f{sub p} is the local electron plasma frequency. The simulations show that 2f{sub p} radiation can be observed at Earth in two scenarios for the radiation's generation and propagation. In Scenario A, radiation is produced and propagates in warm plasmas in the lower corona that are caused by previous magnetic reconnection outflows and/or chromospheric evaporation. In Scenario B radiation is generated in normal plasmas, then due to its natural directivity pattern and refraction, radiation partly propagates into nearby regions, which are hot because of previous reconnection/evaporation. The profiles of plasma density n{sub e} (r) and electron temperature T{sub e} (r) in the lower corona (r - R{sub sun} {approx}< 100 Mm) are found to be crucial to whether radiation can be produced and escape at observable levels against the effects of free-free absorption, where r is the heliocentric distance. Significantly, the observed wide ranges of radiation properties (e.g., drift rates) require n{sub e} (r) with a large range of scale heights h{sub s} , consistent nonetheless for Scenario B with short observed EUV loops. This is relevant to problems with large h{sub s} inferred from tall EUV loops. The simulations suggest: (1) n{sub e} (r) with small h{sub s} , such as n{sub e} (r){proportional_to}(r - R{sub sun}){sup -2.38} for flaring regions, are unexpectedly common deep in the corona. This result is consistent with recent work on n{sub e} (r) for r {approx} (1.05-2)R{sub sun} extracted from observed metric type IIIs. (2) The dominance of reverse-slope bursts over normal bursts sometimes observed may originate from asymmetric reconnection/acceleration, which favors downgoing beams.
Photon Statistics of Propagating Thermal Microwaves
NASA Astrophysics Data System (ADS)
Goetz, J.; Pogorzalek, S.; Deppe, F.; Fedorov, K. G.; Eder, P.; Fischer, M.; Wulschner, F.; Xie, E.; Marx, A.; Gross, R.
2017-03-01
In experiments with superconducting quantum circuits, characterizing the photon statistics of propagating microwave fields is a fundamental task. We quantify the n2+n photon number variance of thermal microwave photons emitted from a blackbody radiator for mean photon numbers, 0.05 ≲n ≲1.5 . We probe the fields using either correlation measurements or a transmon qubit coupled to a microwave resonator. Our experiments provide a precise quantitative characterization of weak microwave states and information on the noise emitted by a Josephson parametric amplifier.
Parton Propagation and Fragmentation in QCD Matter
Alberto Accardi, Francois Arleo, William Brooks, David D'Enterria, Valeria Muccifora
2009-12-01
We review recent progress in the study of parton propagation, interaction and fragmentation in both cold and hot strongly interacting matter. Experimental highlights on high-energy hadron production in deep inelastic lepton-nucleus scattering, proton-nucleus and heavy-ion collisions, as well as Drell-Yan processes in hadron-nucleus collisions are presented. The existing theoretical frameworks for describing the in-medium interaction of energetic partons and the space-time evolution of their fragmentation into hadrons are discussed and confronted to experimental data. We conclude with a list of theoretical and experimental open issues, and a brief description of future relevant experiments and facilities.
Propagation characteristics of superconducting microstrip lines
Mao, S.G.; Ke, J.Y.; Chen, C.H.
1996-01-01
The modified spectral-domain approach is applied to study the propagation characteristics of high temperature superconducting microstrip lines whose signal strip and ground plane are of arbitrary thickness. In this study, numerical results for effective dielectric constant, attenuation constant, and strip current distribution are presented to discuss the effects due to frequency, temperature, strip thickness, and substrate loss tangent. In particular, the conductor and dielectric attenuation constants of superconducting microstrip line are depicted separately to discuss the mechanism of the line losses. A comparison with published theoretical and experimental results is also included to check the accuracy of the new approach`s results.
Uncertainty propagation within the UNEDF models
NASA Astrophysics Data System (ADS)
Haverinen, T.; Kortelainen, M.
2017-04-01
The parameters of the nuclear energy density have to be adjusted to experimental data. As a result they carry certain uncertainty which then propagates to calculated values of observables. In the present work we quantify the statistical uncertainties of binding energies, proton quadrupole moments and proton matter radius for three UNEDF Skyrme energy density functionals by taking advantage of the knowledge of the model parameter uncertainties. We find that the uncertainty of UNEDF models increases rapidly when going towards proton or neutron rich nuclei. We also investigate the impact of each model parameter on the total error budget.
Propagating torsion in the Einstein frame
NASA Astrophysics Data System (ADS)
Popławski, Nikodem J.
2006-11-01
The Einstein-Cartan-Saa theory of torsion modifies the spacetime volume element so that it is compatible with the connection. The condition of connection compatibility gives constraints on torsion, which are also necessary for the consistence of torsion, minimal coupling, and electromagnetic gauge invariance. To solve the problem of positivity of energy associated with the torsionic scalar, we reformulate this theory in the Einstein conformal frame. In the presence of the electromagnetic field, we obtain the Hojman-Rosenbaum-Ryan-Shepley theory of propagating torsion with a different factor in the torsionic kinetic term.
Elastic Wave Propagation and Generation in Seismology
NASA Astrophysics Data System (ADS)
Lees, Jonathan M.
The majority of mature seismologists of my generation were introduced to theoretical seismology via classic textbooks written in the early 1980s. Since this generation has matured and taken the mantle of teaching seismology to a new generation, several new books have been put forward as replacements, or alternatives, to the original classical texts. The target readers of the new texts range from beginner through intermediate to more advanced, although all have been attempts to improve upon what is now considered standard convention in quantitative seismology. To this plethora of choices we now have a new addition by Jose Pujol, titledElastic Wave Propagation and Generation in Seismology.
Approximate Bruechner orbitals in electron propagator calculations
Ortiz, J.V.
1999-12-01
Orbitals and ground-state correlation amplitudes from the so-called Brueckner doubles approximation of coupled-cluster theory provide a useful reference state for electron propagator calculations. An operator manifold with hold, particle, two-hole-one-particle and two-particle-one-hole components is chosen. The resulting approximation, third-order algebraic diagrammatic construction [2ph-TDA, ADC (3)] and 3+ methods. The enhanced versatility of this approximation is demonstrated through calculations on valence ionization energies, core ionization energies, electron detachment energies of anions, and on a molecule with partial biradical character, ozone.
Dynamic crack propagation in a viscoelastic strip
NASA Astrophysics Data System (ADS)
Popelar, C. H.; Atkinson, C.
1980-04-01
THE DYNAMIC PROPAGATION of a semi-infinite crack in a finite linear viscoelastic strip subjected to Mode I loading is investigated. Through the use of integral transforms the problem is reduced to solving a Wiener-Hopf equation. The asymptotic properties of the transforms are exploited to establish the stress intensity factor. Plane-stress and plane-strain stress intensity factors as a function of crack speed for both fully-clamped and shear-free lateral boundaries are presented for the standard linear viscoelastic solid. Comparisons are made with previously obtained asymptotic stress intensity factors and with stress intensity factors for the equivalent elastic strips.
Nonlinear Gamow vectors in nonlocal optical propagation
NASA Astrophysics Data System (ADS)
Braidotti, M. C.; Gentilini, S.; Marcucci, G.; DelRe, E.; Conti, C.
2016-03-01
Shock waves dominate in a wide variety of fields in physics dealing with nonlinear phenomena, nevertheless the description of their evolution is not resolved for the entire dynamics. Here we propose an analytical method based on Gamow vectors, which belong to irreversible quantum mechanics. We theoretically and experimentally show the appearance of these decaying states during shock evolution allowing to describe the whole wave propagation. These results open new ways to the control of extreme nonlinear regimes such as supercontinuum generation or in the analogies of fundamental physical theories.
Target & Propagation Models for the FINDER Radar
NASA Technical Reports Server (NTRS)
Cable, Vaughn; Lux, James; Haque, Salmon
2013-01-01
Finding persons still alive in piles of rubble following an earthquake, a severe storm, or other disaster is a difficult problem. JPL is currently developing a victim detection radar called FINDER (Finding Individuals in Emergency and Response). The subject of this paper is directed toward development of propagation & target models needed for simulation & testing of such a system. These models are both physical (real rubble piles) and numerical. Early results from the numerical modeling phase show spatial and temporal spreading characteristics when signals are passed through a randomly mixed rubble pile.
Seismotectonics of mid-ocean ridge propagation
NASA Astrophysics Data System (ADS)
Floyd, Jacqueline Suzanne
This dissertation investigates the rifting-spreading transition of two propagating mid-ocean spreading centers within actively rifting lithosphere, Woodlark Basin and Hess Deep. Hess Deep is a 5.4 km-deep oceanic rift basin at the westernmost tip of the Galapagos Spreading Center where it meets the East Pacific Rise at the Galapagos Triple Junction. Hydroacoustic seismicity data recorded over 200 earthquakes in Hess Deep that reveal earthquake and deformation patterns that are similar to those found in the process zone of laboratory-scale propagating tensile cracks. Seismicity and deformation patterns observed in Hess Deep are consistent with those from crack tip process zones Process zone deformation releases large crack tip stresses predicted by theoretical fracture mechanics and allows stable propagation to occur; thus, viscous suction or other forces are not required to balance the crack tip stress as proposed by previous investigators. The western Woodlark Basin of Papua New Guinea is the site of a major low-angle detachment fault immediately ahead of the westward propagating spreading center. We present the results of two studies of this fault: one using reflection seismology to image the fault zone velocity structure and composition, and one using deep crustal refraction seismology to image the large-scale velocity structure of the fault and surrounding crust. Results from genetic algorithm inversion of seismic reflection data show that the fault contains a frictionally weak fault gouge layer and fluids, while results from seismic tomography show that the fault is a major rift boundary between the northern and southern rift margins of the western Woodlark Basin. We conclude that favorable conditions exist for frictional slip at angles of 30° or less and that this will be the last fault to form before the crust completely rifts apart to create new oceanic crust and lithosphere. The morphology of the rifting-spreading transitions in Woodlark Basin and Hess
Shallow water sound propagation with surface waves.
Tindle, Chris T; Deane, Grant B
2005-05-01
The theory of wavefront modeling in underwater acoustics is extended to allow rapid range dependence of the boundaries such as occurs in shallow water with surface waves. The theory allows for multiple reflections at surface and bottom as well as focusing and defocusing due to reflection from surface waves. The phase and amplitude of the field are calculated directly and used to model pulse propagation in the time domain. Pulse waveforms are obtained directly for all wavefront arrivals including both insonified and shadow regions near caustics. Calculated waveforms agree well with a reference solution and data obtained in a near-shore shallow water experiment with surface waves over a sloping bottom.
Reconstructing propagation networks with temporal similarity
Liao, Hao; Zeng, An
2015-01-01
Node similarity significantly contributes to the growth of real networks. In this paper, based on the observed epidemic spreading results we apply the node similarity metrics to reconstruct the underlying networks hosting the propagation. We find that the reconstruction accuracy of the similarity metrics is strongly influenced by the infection rate of the spreading process. Moreover, there is a range of infection rate in which the reconstruction accuracy of some similarity metrics drops nearly to zero. To improve the similarity-based reconstruction method, we propose a temporal similarity metric which takes into account the time information of the spreading. The reconstruction results are remarkably improved with the new method. PMID:26086198
Modelling rock avalanche propagation onto glaciers
NASA Astrophysics Data System (ADS)
Sosio, Rosanna; Crosta, Giovanni B.; Chen, Joanna H.; Hungr, Oldrich
2012-07-01
Ice-rock avalanches which occur in glacial environments are controlled by the presence of snow and ice in the moving material and by possible propagation onto icy basal surfaces. All these factors contribute to enhancing the flow mobility. Mixing with ice and snow hampers block collisions and favours dense flow behaviour. Ice melting reduces granular friction by saturation of the basal material and fluidization effects. Propagating onto glaciers offers a smooth surface with low shear resistance. This work is a review of the best documented ice-rock avalanches and focuses on evaluating their mobility for hazard analysis purposes by providing a set of calibrated cases. The rock avalanches have volumes ranging from 5*106 m3 to 25*106 m3. We replicate these events by using SPH and FEM numerical methods, assuming frictional and Voellmy basal rheologies. The Voellmy rheology best performs at replicating the landslide propagation. Among the back analyzed cases, the frictional coefficient ranges in the interval 0.03-0.1, the turbulent coefficient within 1000 m s-2-2000 m s-2. The bulk basal friction angle ranges within 2.75° and 14° with values inversely related to event volumes. Forward selection of the basal friction angle based on event volume, allows the replication of the Mount Cook ice-rock avalanche predicting a maximum runout which is less than 4% larger than observed. In the perspective of forward modelling, large uncertainty is related to the reconstruction of the post-event topographies, particularly for the sliding surface. Mixing with ice and snow reduces basal friction proportionally to ice and snow content. Pure ice has a basal friction which is reduced by about 75% than basal friction of pure rock. Melting of ice during rock avalanche propagation has been evaluated for the Sherman event. The frictional heat generated at the glacier surface results in the melting of 86.2 ± 5.9 kg m-2, which could have contributed to a minimum 20-35% (±10%) reduction of
Probes of Lorentz violation in neutrino propagation
NASA Astrophysics Data System (ADS)
Ellis, John; Harries, Nicholas; Meregaglia, Anselmo; Rubbia, André; Sakharov, Alexander S.
2008-08-01
It has been suggested that the interactions of energetic particles with the foamy structure of space-time thought to be generated by quantum-gravitational (QG) effects might violate Lorentz invariance, so that they do not propagate at a universal speed of light. We consider the limits that may be set on a linear or quadratic violation of Lorentz invariance in the propagation of energetic neutrinos, v/c=[1±(E/MνQG1)] or [1±(E/MνQG2)2], using data from supernova explosions and the OPERA long-baseline neutrino experiment. Using the SN1987a neutrino data from the Kamioka II, IMB, and Baksan experiments, we set the limits MνQG1>2.7(2.5)×1010GeV for subluminal (superluminal) propagation and MνQG2>4.6(4.1)×104GeV at the 95% confidence level. A future galactic supernova at a distance of 10 kpc would have sensitivity to MνQG1>2(4)×1011GeV for subluminal (superluminal) propagation and MνQG2>2(4)×105GeV. With the current CERN neutrinos to Gran Sasso extraction spill length of 10.5μs and with standard clock synchronization techniques, the sensitivity of the OPERA experiment would reach MνQG1˜7×105GeV (MνQG2˜8×103GeV) after 5 years of nominal running. If the time structure of the super proton synchrotron radio frequency bunches within the extracted CERN neutrinos to Gran Sasso spills could be exploited, these figures would be significantly improved to MνQG1˜5×107GeV (MνQG2˜4×104GeV). These results can be improved further if a similar time resolution can be achieved with neutrino events occurring in the rock upstream of the OPERA detector: we find potential sensitivities to MνQG1˜4×108GeV and MνQG2˜7×105GeV.
Transionospheric HF Propagation Experiments at Auroral Latitudes
NASA Astrophysics Data System (ADS)
James, H. G.; Benson, R. F.
2004-05-01
High-frequency (HF) propagation experiments are planned as part of the Enhanced Polar Outflow Probe (ePOP) satellite mission to be launched for the Canadian Space Agency in 2007. Ground transmitters such as the CADI ionosondes and the SuperDARN radars will be operated collaboratively to emit waves for detection by the Radio Receiver Instrument of ePOP during passes in the vicinity. The scientific goals include improved understanding of F-region morphology and dynamics, wave scattering and microphysical plasma processes. Partly as preparation for ePOP, transionospheric HF propagation data recorded by the receivers of the ISIS-I and ISIS-II spacecraft are being analyzed. The measurements were made in spring-summer 1978. A ground transmitter was built in Ottawa especially for the project. Some of the ISIS data were obtained in digital form from http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html. These digital data are being surveyed in an attempt to establish repeatable propagation characteristics. From these characteristics, the goal is to understand the processes experienced by waves passing through the ionosphere. Several tens of ISIS-II passes recorded at a fixed frequency of 9.303 MHz have been examined. Swept-frequency ionograms interleaved with these fixed-frequency measurements allow two-dimensional electron density distributions to be modeled in altitude and latitude. Computer code has been developed for three-dimensional ray tracing. The computed latitudinal extent of the zone irradiated at the ISIS-II altitude is approximately as observed. Within this "iris" of accessibility, the peak intensity of waves recorded at the spacecraft is within about 10 dB of what is computed with a link calculation. This calculation is based on a model for the 1-kW transmitter, a radiant-transfer calculation that follows the focusing/defocusing of rays using a three-ray pencil between ground and the satellite, and the orientation of the sounder receiving dipole. Poleward
On soliton propagation in biomembranes and nerves.
Heimburg, Thomas; Jackson, Andrew D
2005-07-12
The lipids of biological membranes and intact biomembranes display chain melting transitions close to temperatures of physiological interest. During this transition the heat capacity, volume and area compressibilities, and relaxation times all reach maxima. Compressibilities are thus nonlinear functions of temperature and pressure in the vicinity of the melting transition, and we show that this feature leads to the possibility of soliton propagation in such membranes. In particular, if the membrane state is above the melting transition solitons will involve changes in lipid state. We discuss solitons in the context of several striking properties of nerve membranes under the influence of the action potential, including mechanical dislocations and temperature changes.
Special Course on Acoustic Wave Propagation
1979-08-01
l.Recipient’s Reference 2.Originator’s Reference 3.Further Reference 4.Security Classification of Document AGARD-R-686 ISBN 92-835-0248-5 UNCLASSIFIED 5...3L t’acoustique eat d’Ariatote (384-322 av. .Y.C.) qui a effectud una classification des diffdrentes branches de l’acoustique en cansacrant une part...silence a cotia- tique at balistique. DepuiS la econde guerre mondiale de tres nombreux travaux Sur la propagation acoustique dans les fluides et das
Reconstructing propagation networks with temporal similarity.
Liao, Hao; Zeng, An
2015-06-18
Node similarity significantly contributes to the growth of real networks. In this paper, based on the observed epidemic spreading results we apply the node similarity metrics to reconstruct the underlying networks hosting the propagation. We find that the reconstruction accuracy of the similarity metrics is strongly influenced by the infection rate of the spreading process. Moreover, there is a range of infection rate in which the reconstruction accuracy of some similarity metrics drops nearly to zero. To improve the similarity-based reconstruction method, we propose a temporal similarity metric which takes into account the time information of the spreading. The reconstruction results are remarkably improved with the new method.
Turbulent Transitions in Optical Wave Propagation
NASA Astrophysics Data System (ADS)
Pierangeli, D.; Di Mei, F.; Di Domenico, G.; Agranat, A. J.; Conti, C.; DelRe, E.
2016-10-01
We report the direct observation of the onset of turbulence in propagating one-dimensional optical waves. The transition occurs as the disordered hosting material passes from being linear to one with extreme nonlinearity. As the response grows, increased wave interaction causes a modulational unstable quasihomogeneous flow to be superseded by a chaotic and spatially incoherent one. Statistical analysis of high-resolution wave behavior in the turbulent regime unveils the emergence of concomitant rogue waves. The transition, observed in a photorefractive ferroelectric crystal, introduces a new and rich experimental setting for the study of optical wave turbulence and information transport in conditions dominated by large fluctuations and extreme nonlinearity.
Propagation of cosmic rays in the galaxy
NASA Technical Reports Server (NTRS)
Daniel, R. R.; Stephens, S. A.
1974-01-01
The characteristics of a model for analyzing the propagation of cosmic rays are discussed. The requirements for analyzing the relevant observational data on cosmic rays are defines as: (1) the chemical and isotopic composition of cosmic rays as a function of energy, (2) the flux and energy spectrum of the individual nucleonic components, (3) the flux and energy spectrum of the electronic component, (4) the cosmic ray prehistory, and (5) the degree of isotropy in their arrival directions as a function of energy. It is stated that the model which has been able to bring to pass the greatest measure of success is the galactic confinement model.
Probes of Lorentz violation in neutrino propagation
Ellis, John; Harries, Nicholas; Meregaglia, Anselmo; Sakharov, Alexander S.
2008-08-01
It has been suggested that the interactions of energetic particles with the foamy structure of space-time thought to be generated by quantum-gravitational (QG) effects might violate Lorentz invariance, so that they do not propagate at a universal speed of light. We consider the limits that may be set on a linear or quadratic violation of Lorentz invariance in the propagation of energetic neutrinos, v/c=[1{+-}(E/M{sub {nu}}{sub QG1})] or [1{+-}(E/M{sub {nu}}{sub QG2}){sup 2}], using data from supernova explosions and the OPERA long-baseline neutrino experiment. Using the SN1987a neutrino data from the Kamioka II, IMB, and Baksan experiments, we set the limits M{sub {nu}}{sub QG1}>2.7(2.5)x10{sup 10} GeV for subluminal (superluminal) propagation and M{sub {nu}}{sub QG2}>4.6(4.1)x10{sup 4} GeV at the 95% confidence level. A future galactic supernova at a distance of 10 kpc would have sensitivity to M{sub {nu}}{sub QG1}>2(4)x10{sup 11} GeV for subluminal (superluminal) propagation and M{sub {nu}}{sub QG2}>2(4)x10{sup 5} GeV. With the current CERN neutrinos to Gran Sasso extraction spill length of 10.5 {mu}s and with standard clock synchronization techniques, the sensitivity of the OPERA experiment would reach M{sub {nu}}{sub QG1}{approx}7x10{sup 5} GeV (M{sub {nu}}{sub QG2}{approx}8x10{sup 3} GeV) after 5 years of nominal running. If the time structure of the super proton synchrotron radio frequency bunches within the extracted CERN neutrinos to Gran Sasso spills could be exploited, these figures would be significantly improved to M{sub {nu}}{sub QG1}{approx}5x10{sup 7} GeV (M{sub {nu}}{sub QG2}{approx}4x10{sup 4} GeV). These results can be improved further if a similar time resolution can be achieved with neutrino events occurring in the rock upstream of the OPERA detector: we find potential sensitivities to M{sub {nu}}{sub QG1}{approx}4x10{sup 8} GeV and M{sub {nu}}{sub QG2}{approx}7x10{sup 5} GeV.
Propagation of Evidence Through Fuzzy Rules
1993-09-01
range. Bonissone does not use the MPG used in the TV formulation; instead, the detachment operator is employed to propagate the confidence bounds ...of an S-norm is the maximum function. Thus, the lower bound on the confidence of the conclusion is vL(b) = T(suff, vL(a)) and the upper bound is...method is Piero Bonissone (references 5-7). Bounds on the premise are generated from the data using possibility theory. This interval method also can
Seismic rupture propagation beneath potential landslide wedge
NASA Astrophysics Data System (ADS)
Sakaguchi, A.; Kawamura, K.
2011-12-01
During 2011 Tohoku earthquake (Mw 9.0), much larger slip and tsunami occurred than expectation at outer-wedge (toe of the trench landward slope) of Japan trench (eg. Ide et al., 2011). Similarly, outer-wedge deformation was pointed out in northern segment of 1986 Meiji-Sanriku earthquake (Ms 7.2), and it was discussed that earthquake-related landslide induced large tsunami (eg. Kanamori, 1972; Tanioka and Satake, 1996). Many landslides and normal faults, potential tsunami genesis, are developed at outer-wedge of Japan trench (Henry et al., 1989). Some steep normal-faults turn to horizon at deep portion, and land sliding may be prevented by basal friction. If seismic rupture propagates to basal fault of the outer-wedge, triggered gravity collapse will enlarge deformation of the outer-wedge to cause large tsunamis. It was considered that seismogenic fault locks at deep portion under inner-wedge of the plate subduction zone, and outer-wedge was classified into aseismic zone classically. Seismic rupture propagation to outer-wedge is still uncertain. Seismic slip at the outer-wedge was found from the drilled core during IODP Nankai trough seismogenic zone drilling project (NanTroSEIZE) in Nankai trough, southwest Japan. Samples were obtained from the frontal thrust (438 mbsf), which connects the deep plate boundary to the seafloor at the toe of the accretionary wedge, and from a megasplay fault (271 mbsf) that branches from the plate boundary décollement. Higher vitrinite reflectance of 0.57 % and 0.37 % than the host rock of 0.24 % were found at splay and plate boundary faults zones respectively. These correspond with 300-400 °C and > 20°C of host rock. Local high temperature zone less than several cm thick may be caused by frictional shear heat at fault zone (Sakaguchi, et al., 2011). Shear velocity and durations can be estimated from thermal property of the sediment and distribution of the vitrinite anomaly (Hamada et al., 2011). This result shows that seismic
Cosmic ray propagation in the local superbubble
NASA Technical Reports Server (NTRS)
Steitmatter, R. E.; Balasubrahmanyan, V. K.; Protheroe, R. J.; Ormes, J. F.
1984-01-01
It is suggested that a ring of HI gas lying in the galactic plane is part of a supershell which formed some 3 x to the 7th power years ago. The consequences of a closed magnetic supershell for cosmic ray propagation are examined and it is concluded that there is no evidence which precludes the production and trapping of cosmic rays in such a region. A consequence of superbubble confinement is that the mean age of cosmic rays would be independent of energy. This can be tested by high energy observations of the isotopic composition of Be.
NASA Technical Reports Server (NTRS)
Davarian, Faramaz (Editor)
1994-01-01
The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. Participants included representatives from Canada, the Netherlands, England, and the United States, including researchers from universities, government agencies, and private industry. The meeting was organized into two technical sessions. The first session was dedicated to slant path propagation studies and experiments. The second session focused on propagation studies for mobile, personal, and sound broadcast systems. In total, 14 technical papers and some informal contributions were presented. Preceding NAPEX_17, the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop was held to review ACTS propagation activities.
Propagation of ultrashort laser pulses through water.
Li, Jianchao; Alexander, Dennis R; Zhang, Haifeng; Parali, Ufuk; Doerr, David W; Bruce, John C; Wang, Hao
2007-02-19
In this paper, propagation of ultrashort pulses through a long 3.5 meter water channel was studied. Of particular interest was the attenuation of the beam at various lengths along the variable path length and to find an explanation of why the attenuation deviates from typical Beer Lambert law around 3 meters for ultrashort laser pulse transmission. Laser pulses of 10 fs at 75 MHz, 100 fs at 80 MHz and 300 fs at 1 KHz were employed to investigate the effects of pulse duration, spectrum and repetition rate on the attenuation after propagating through water up to 3 meters. Stretched pulse attenuation measurements produced from 10 fs at a frequency of 75 MHz were compared with the 10 fs attenuation measurements. Results indicate that the broad spectrum of the ultrashort pulse is the dominant reason for the observed decrease in attenuation after 3 meters of travel in a long water channel. The repetition rate is found not to play a significant role at least for the long pulse scenario in this reported attenuation studies.
Line spread instrumentation for propagation measurements
NASA Technical Reports Server (NTRS)
Bailey, W. H., Jr.
1980-01-01
A line spread device capable of yielding direct measure of a laser beam's line spread function (LSF) was developed and employed in propagation tests conducted in a wind tunnel to examine optimal acoustical suppression techniques for laser cavities exposed to simulated aircraft aerodynamic environments. Measurements were made on various aerodynamic fences and cavity air injection techniques that effect the LSF of a propagating laser. Using the quiescent tunnel as a control, the relative effect of each technique on laser beam quality was determined. The optical instrument employed enabled the comparison of relative beam intensity for each fence or mass injection. It was found that fence height had little effect on beam quality but fence porosity had a marked effect, i.e., 58% porosity alleviated cavity resonance and degraded the beam the least. Mass injection had little effect on the beam LSF. The use of a direct LSF measuring device proved to be a viable means of determining aerodynamic seeing qualities of flow fields.
Structure of Propagating and Attached Hydrocarbon Flames
NASA Technical Reports Server (NTRS)
Takahashi, Fumiaki; Katta, Viswanath
2004-01-01
Direct numerical simulations with C3-chemistry and radiative heat-loss models have been performed to reveal the internal structure of propagating and attached flames in an axisymmetric fuel jet of methane, ethane, ethylene, acetylene, or propane in air under normal and zero gravity. Observations of the flames were also made at the NASA Glenn 2.2-Second Drop Tower. In computations, the fuel issued into quasi-quiescent air for a fixed mixing time before it was ignited along the centerline at stoichiometry. The edge of the flame propagated through a flammable layer at the laminar flame speed of the stoichiometric fuel-air mixture independent of gravity. For all cases, a peak reactivity spot, i.e., reaction kernel, was formed in the flame base, thereby holding a trailing diffusion flame. The location of the reaction kernel in the attached flames depended inversely on the reactivity. The reaction-kernel correlations between the reactivity and the velocity were developed further using variables related to local Damkahler and Peclet numbers.
Propagation of olfactory information in Drosophila.
Root, Cory M; Semmelhack, Julia L; Wong, Allan M; Flores, Jorge; Wang, Jing W
2007-07-10
Investigating how information propagates between layers in the olfactory system is an important step toward understanding the olfactory code. Each glomerular output projection neuron (PN) receives two sources of input: the olfactory receptor neurons (ORNs) of the same glomerulus and interneurons that innervate many glomeruli. We therefore asked how these inputs interact to produce PN output. We used receptor gene mutations to silence all of the ORNs innervating a specific glomerulus and recorded PN activity with two-photon calcium imaging and electrophysiology. We found evidence for balanced excitatory and inhibitory synaptic inputs but saw little or no response in the absence of direct ORN input. We next asked whether any transformation of activity occurs at successive layers of the antennal lobe. We found a strong link between PN firing and dendritic calcium elevation, the latter of which is tightly correlated with calcium activity in ORN axons, supporting the idea of glomerular propagation of olfactory information. Finally, we showed that odors are represented by a sparse population of PNs. Together, these results are consistent with the idea that direct receptor input provides the main excitatory drive to PNs, whereas interneurons modulate PN output. Balanced excitatory and inhibitory interneuron input may provide a mechanism to adjust PN sensitivity.
Mechanical Surface Waves Accompany Action Potential Propagation
NASA Astrophysics Data System (ADS)
Machta, Benjamin; El Hady, Ahmed
2015-03-01
The action potential (AP) is the basic mechanism by which information is transmitted along neuronal axons. Although the excitable nature of axons is understood to be primarily electrical, many experimental studies have shown that a mechanical displacement of the axonal membrane co-propagates with the electrical signal. While the experimental evidence for co-propagating mechanical waves is diverse and compelling, there is no consensus for their physical underpinnings. We present a model in which these mechanical displacements arise from the driving of mechanical surface waves, in which potential energy is stored in elastic deformations of the neuronal membrane and cytoskeleton while kinetic energy is stored in the movement of the axoplasmic fluid. In our model these surface waves are driven by the traveling wave of electrical depolarization that characterizes the AP, altering the electrostatic forces across the membrane as it passes. Our model allows us to predict the shape of the displacement that should accompany any traveling wave of voltage, including the well-characterized AP. We expect our model to serve as a framework for understanding the physical origins and possible functional roles of these AWs in neurobiology. See Arxiv/1407.7600
Multi-Frame Imaging of Shock Propagation
NASA Astrophysics Data System (ADS)
Cooper, Leora; Veysset, David; Pein, Brandt; Maznev, Alexei; Kooi, Steven; Nelson, Keith
2015-06-01
We have developed a platform to generate and image shock propagation through quasi-2D materials. A thin material (5-50 μm) is pressed between two glass plates, confining it in one dimension. A sub-nanosecond laser pulses is focused into a ring of 100 μm radius, launching a shock wave that propagates and focuses towards the circle's center. The high pressure of the shock wave causes changes in the refractive index of the material that can be observed with Shlieren imaging using a train of femtosecond pulses. A Fabry-Perot cavity is used to generate a train of imaging pulses spaced 5 ns apart. Using a high-speed multi-frame camera we have been able to take up to sixteen frames with 5 ns intervals of the same shock wave. This single-shot imaging method allows us to investigate irreversible processes in materials including phase transitions, cracking and decomposition in energetic materials, and cavitation and crack formation in water following the shock front.
A Numerical Study of Heat Pulse Propagation
NASA Astrophysics Data System (ADS)
Borse, Garold; Sylvia, Patti; Bateman, Glenn; Kritz, Arnold
1999-11-01
A highly nonlinear transport model in which the effective diffusivity, D, is a step function of the temperature gradient is numerically applied to the phenomena of heat pulse propagation in tokamaks. After obtaining the steady state solution, an instantaneous heat pulse is used as the initial condition for a time-dependent solution. The temperature deviation from steady state is plotted as a function of time at various values of the minor radius, and the time-to-peak of each curve is obtained. Using these results it is found that the solution, while still diffusive, is characterized by two regions of approximately constant, but significantly different diffusivities. The interior region, very close to the pulse edge, is characterized by a slow diffusion and its size is independent of the height of the step in D. The time for the pulse to reach the transition region is inversely proportional to the step height, and the subsequent larger diffusivity is proportional to the step height. Since the results depend strongly on the steepness and step height of D(-fracpartial Tpartial r), it should be possible to determine the value of the diffusivity in the two regions from the characteristics of the heat pulse propagation.
Impulse Propagation in Disordered Hertzian Chains
NASA Astrophysics Data System (ADS)
Manciu, Marian; Sen, Surajit; Hurd, Alan J.
2000-03-01
It was shown by Nesterenko [1] that an impulse initiated at an end of a chain of elastic grains in mutual contact, i.e., interacting via the nonlinear Hertz potential, travels as a soliton-like object. Recent theoretical [2], experimental [3] and numerical studies [4] have validated his findings. In the presentation we shall examine the propagation of an impulse in an imperfect system that is characterized by grains composed of different elastic materials, different sizes, shapes and velocity-dependent friction. Our study shows that even in the presence of considerable disorder, most of the energy still travels as a weakly dispersive bundle of energy. According to our calculations, the amplitude, position and geometry of the leading pulse are related to chain disorder via simple scaling laws. We shall comment upon the inverse problem of determining the material properties by studying the pulse propagation, with many potential applications. [1] V.F. Nesterenko, J Appl Mech Tech Phys 5, 733 (1983) [2] S. Sen and M. Manciu, Physica A 268, 644 (1999); A. Chatterjee, Phys Rev E 59, 5912 (1999) [3] C. Coste, E. Falcon and S. Fauve, Phys Rev E 56, 6104 (1997); E.J. Hinch and S. Saint-Jean, Proc R Soc A 455, 3201 (1999) [4] M. Manciu, V. Tehan and S. Sen, Chaos (in press)
Nonlinear biochemical signal processing via noise propagation
NASA Astrophysics Data System (ADS)
Kim, Kyung Hyuk; Qian, Hong; Sauro, Herbert M.
2013-10-01
Single-cell studies often show significant phenotypic variability due to the stochastic nature of intra-cellular biochemical reactions. When the numbers of molecules, e.g., transcription factors and regulatory enzymes, are in low abundance, fluctuations in biochemical activities become significant and such "noise" can propagate through regulatory cascades in terms of biochemical reaction networks. Here we develop an intuitive, yet fully quantitative method for analyzing how noise affects cellular phenotypes based on identifying a system's nonlinearities and noise propagations. We observe that such noise can simultaneously enhance sensitivities in one behavioral region while reducing sensitivities in another. Employing this novel phenomenon we designed three biochemical signal processing modules: (a) A gene regulatory network that acts as a concentration detector with both enhanced amplitude and sensitivity. (b) A non-cooperative positive feedback system, with a graded dose-response in the deterministic case, that serves as a bistable switch due to noise-induced ultra-sensitivity. (c) A noise-induced linear amplifier for gene regulation that requires no feedback. The methods developed in the present work allow one to understand and engineer nonlinear biochemical signal processors based on fluctuation-induced phenotypes.
Truncation and Accumulated Errors in Wave Propagation
NASA Astrophysics Data System (ADS)
Chiang, Yi-Ling F.
1988-12-01
The approximation of the truncation and accumulated errors in the numerical solution of a linear initial-valued partial differential equation problem can be established by using a semidiscretized scheme. This error approximation is observed as a lower bound to the errors of a finite difference scheme. By introducing a modified von Neumann solution, this error approximation is applicable to problems with variable coefficients. To seek an in-depth understanding of this newly established error approximation, numerical experiments were performed to solve the hyperbolic equation {∂U}/{∂t} = -C 1(x)C 2(t) {∂U}/{∂x}, with both continuous and discontinuous initial conditions. We studied three cases: (1) C1( x)= C0 and C2( t)=1; (2) C1( x)= C0 and C2( t= t; and (3) C 1(x)=1+( {solx}/{a}) 2 and C2( t)= C0. Our results show that the errors are problem dependent and are functions of the propagating wave speed. This suggests a need to derive problem-oriented schemes rather than the equation-oriented schemes as is commonly done. Furthermore, in a wave-propagation problem, measurement of the error by the maximum norm is not particularly informative when the wave speed is incorrect.
Damage Propagation Modeling for Aircraft Engine Prognostics
NASA Technical Reports Server (NTRS)
Saxena, Abhinav; Goebel, Kai; Simon, Don; Eklund, Neil
2008-01-01
This paper describes how damage propagation can be modeled within the modules of aircraft gas turbine engines. To that end, response surfaces of all sensors are generated via a thermo-dynamical simulation model for the engine as a function of variations of flow and efficiency of the modules of interest. An exponential rate of change for flow and efficiency loss was imposed for each data set, starting at a randomly chosen initial deterioration set point. The rate of change of the flow and efficiency denotes an otherwise unspecified fault with increasingly worsening effect. The rates of change of the faults were constrained to an upper threshold but were otherwise chosen randomly. Damage propagation was allowed to continue until a failure criterion was reached. A health index was defined as the minimum of several superimposed operational margins at any given time instant and the failure criterion is reached when health index reaches zero. Output of the model was the time series (cycles) of sensed measurements typically available from aircraft gas turbine engines. The data generated were used as challenge data for the Prognostics and Health Management (PHM) data competition at PHM 08.
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.
Seismic wave propagation in cracked porous media
NASA Astrophysics Data System (ADS)
Pointer, Tim; Liu, Enru; Hudson, John A.
2000-07-01
The movement of interstitial fluids within a cracked solid can have a significant effect on the properties of seismic waves of long wavelength propagating through the solid. We consider three distinct mechanisms of wave-induced fluid flow: flow through connections between cracks in an otherwise non-porous material, fluid movement within partially saturated cracks, and diffusion from the cracks into a porous matrix material. In each case the cracks may be aligned or randomly oriented, leading, respectively, to anisotropic or isotropic wave speeds and attenuation factors. In general, seismic velocities exhibit behaviour that is intermediate between that of empty cracks and that of isolated liquid-filled cracks if fluid flow is significant. In the range of frequencies for which considerable fluid flow occurs there is high attenuation and dispersion of seismic waves. Fluid flow may be on either a wavelength scale or a local scale depending on the model and whether the cracks are aligned or randomly oriented, resulting in completely different effects on seismic wave propagation. A numerical analysis shows that all models can have an effect over the exploration seismic frequency range.
Local constants of motion imply information propagation
NASA Astrophysics Data System (ADS)
Friesdorf, M.; Werner, A. H.; Goihl, M.; Eisert, J.; Brown, W.
2015-11-01
Interacting quantum many-body systems are expected to thermalize, in the sense that the evolution of local expectation values approaches a stationary value resembling a thermal ensemble. This intuition is notably contradicted in systems exhibiting many-body localisation (MBL). In stark contrast to the non-interacting case of Anderson localisation, the entanglement of states grows without limit over time, albeit slowly. In this work, we establish a novel link between quantum information theory and notions of condensed matter physics, capturing this phenomenon in the Heisenberg picture. We show that the mere existence of local constants of motion, often taken as the defining property of MBL, together with a generic spectrum of the Hamiltonian, is already sufficient to rigorously prove information propagation: these systems can be used to send a classical bit over arbitrary distances, in that the impact of a local perturbation can be detected arbitrarily far away. This counterintuitive result is compatible with and further corroborates the intuition of a slow entanglement growth following global quenches in MBL systems. We perform a detailed perturbation analysis of quasi-local constants of motion and also show that they indeed can be used to construct efficient spectral tensor networks, as recently suggested. Our results provide a detailed and at the same time model-independent picture of information propagation in MBL systems.
Wave Propagation in Polymers, Part II
NASA Astrophysics Data System (ADS)
Newlander, David C.; Charest, Jacques A.; Lilly, Martin D.; Eisler, Robert D.
1999-06-01
Work reported in a previous study (Wave Propagations in Polymers, Part I, J.A. Charest, M.D. Lilly, 44th ARA Meeting Munich, Germany Sept. 17-20, 1993) discussed gas gun plane wave impact work and the measurements of stress wave profiles in Polycarbonate at around 2 kbars. The wave profiles were obtained using combined carbon and PVDF thin film stress gauges. The results showed amplitude attenuation and dispersion effects which were neither expected nor predictable from available hydrocode models. The data have been revisited using a modified material model and the PUFF74 computer code. These new wave profile calculations show remarkable agreement with the previous experiments in Polycarbonate. The model treats the material as viscoelastic-plastic using methods developed by Bade (Dynamic Response Model for PMMA, W. L. Bade, AVCO Systems Division, TR K500-74-WLB-204, Oct. 1, 1974). The measured and calculated results are quite different from those exhibited by PMMA at similar impact conditions. This work is expected to further our understanding of the processes that control wave propagation in highly-compressible and viscoelastic/viscoplastic media. It is also expected to provide clues on the effects of high strain rates on properties such as the modulus of elasticity, strength, and material loading behavior.
Noise Propagation in Region Of Interest Measurements
Hansen, Michael S.; Inati, Souheil J.; Kellman, Peter
2014-01-01
Purpose The purpose of this work was to develop and validate a technique for predicting the standard deviation associated with thermal noise propagation in region of interest measurements. Theory and Methods Standard methods for error propagation estimation were used to derive equations for the standard deviations of linear combinations of complex, magnitude, or phase pixel values. The equations were applied to common imaging scenarios where the image pixels were correlated due to anisotropic pixel resolutions and parallel imaging. All standard deviation estimates were evaluated efficiently using only vector-vector multiplications and Fourier transforms. The estimated standard deviations were compared to standard deviations obtained using repeated experiments and pseudo replica reconstructions. Results The proposed method was able to predict region of interest standard deviations in all the tested analysis scenarios. Positive and negative noise correlations caused by different parallel imaging aliasing point spread functions were accurately predicted and the method predicted the confidence intervals of time-intensity curves for in vivo cardiac perfusion measurements. Conclusions An intuitive technique for region of interest confidence intervals was developed and validated using phantom experiments and in vivo data. PMID:24634307
Propagation of electromagnetic radiation in mitochondria?
Thar, Roland; Kühl, Michael
2004-09-21
Mitochondria are the main source of ultra-weak chemiluminescence generated by reactive oxygen species, which are continuously formed during the mitochondrial oxidative metabolism. Vertebrate cells show typically filamentous mitochondria associated with the microtubules of the cytoskeleton, forming together a continuous network (mitochondrial reticulum). The refractive index of both mitochondria and microtubules is higher than the surrounding cytoplasm, which results that the mitochondrial reticulum can act as an optical waveguide, i.e. electromagnetic radiation can propagate within the network. A detailed analysis of the inner structure of mitochondria shows, that they can be optically modelled as a multi-layer system with alternating indices of refraction. The parameters of this multi-layer system are dependent on the physiologic state of the mitochondria. The effect of the multi-layer system on electromagnetic radiation propagating along the mitochondrial reticulum is analysed by the transfer-matrix method. If induced light emission could take place in mitochondria, the multi-layer system could lead to lasing action like it has been realized in technical distributed feedback laser. Based on former reports about the influence of external illumination on the physiology of mitochondria it is speculated whether there exists some kind of long-range interaction between individual mitochondria mediated by electromagnetic radiation.
Mouse Polyomavirus: Propagation, Purification, Quantification, and Storage.
Horníková, Lenka; Žíla, Vojtěch; Španielová, Hana; Forstová, Jitka
2015-08-03
Mouse polyomavirus (MPyV) is a member of the Polyomaviridae family, which comprises non-enveloped tumorigenic viruses infecting various vertebrates including humans and causing different pathogenic responses in the infected organisms. Despite the variations in host tropism and pathogenicity, the structure of the virions of these viruses is similar. The capsid, with icosahedral symmetry (ø, 45 nm, T = 7d), is composed of a shell of 72 capsomeres of structural proteins, arranged around the nucleocore containing approximately 5-kbp-long circular dsDNA in complex with cellular histones. MPyV has been one of the most studied polyomaviruses and serves as a model virus for studies of the mechanisms of cell transformation and virus trafficking, and for use in nanotechnology. It can be propagated in primary mouse cells (e.g., in whole mouse embryo cells) or in mouse epithelial or fibroblast cell lines. In this unit, propagation, purification, quantification, and storage of MPyV virions are presented.
Propagation style controls lava-snow interactions.
Edwards, B R; Belousov, A; Belousova, M
2014-12-16
Understanding interactions between volcanic eruptions and the cryosphere (a.k.a. glaciovolcanism) is important for climate reconstructions as well as for hazard mitigation at ice-clad volcanoes. Here we present unique field observations of interactions between snowpack and advancing basaltic lava flows during the 2012-13 eruption at Tolbachik volcano, Kamchatka, Russia. Our observations show that lava-snow heat transfer is slow, and that styles of lava propagation control snowpack responses. 'A'a and sheet lava flows advance in a rolling caterpillar-track motion on top of the rigid, snowpack substrate with minor lava-snow interaction. In contrast, pahoehoe lava propagates by inflation of lobes beneath/inside the snowpack, producing rigorous lava-snow interaction via meltwater percolation down into the incandescent lava causing production of voluminous steam, rapid surface cooling and thermal shock fragmentation. The textures produced by pahoehoe-snowpack interactions are distinctive and, where observed at other sites, can be used to infer syn-eruption seasonality and climatic conditions.
Method and apparatus for charged particle propagation
Hershcovitch, Ady
1996-11-26
A method and apparatus are provided for propagating charged particles from a vacuum to a higher pressure region. A generator 14,14b includes an evacuated chamber 16a,b having a gun 18,18b for discharging a beam of charged particles such as an electron beam 12 or ion beam 12b. The beam 12,12b is discharged through a beam exit 22 in the chamber 16a,b into a higher pressure region 24. A plasma interface 34 is disposed at the beam exit 22 and includes a plasma channel 38 for bounding a plasma 40 maintainable between a cathode 42 and an anode 44 disposed at opposite ends thereof. The plasma channel 38 is coaxially aligned with the beam exit 22 for propagating the beam 12,12b from the chamber 16a,b, through the plasma 40, and into the higher pressure region 24. The plasma 40 is effective for pumping down the beam exit 22 for preventing pressure increase in the chamber 16a,b, and provides magnetic focusing of the beam 12,12b discharged into the higher pressure region 24.
Deterministic transfer function for transionospheric propagation
NASA Astrophysics Data System (ADS)
Roussel-Dupre, R.; Argo, P.
Recent interest in ground-to-satellite propagation of broadband signals has prompted investigation into the development of a transfer function for the ionosphere that includes effects such as dispersion, refraction, changes in polarization, reflection, absorption, and scattering. Depending on the application (e.g. geolocation), it may be necessary to incorporate all of these processes in order to extract the information of interest from the measured transionospheric signal. A transfer function for midlatitudes at VBF from 25 - 175 MHz is one of the goals of the BLACKBEARD program in characterizing propagation distortion. In support of this program we discuss in this paper an analytic model for the deterministic transfer function of the ionosphere that includes the effects of dispersion, refraction, and changes in polarization to second order in the parameter X = omega(sub pe)(exp 2)/(omega)(exp 2) where X is assumed to be small compared to one, (omega)(sub pe) is the peak plasma frequency of the ionosphere, and omega is the wave frequency. Analytic expressions for the total phase change, group delay, and polarization change in a spherical geometry assuming a radial, electron density profile are presented. A computer code ITF (Ionospheric Transfer Function) that makes use of the ICED (Ionospheric Conductivity and Electron Density) model to, venerate electron density profiles was developed to calculate the ionospheric transfer function along a specified transmitter-to-receiver path. Details of this code will be presented as well as comparisons made between ITF analytic results and ray-tracing calculations.
Calibration of seismic wave propagation in Kuwait
Al-Awadhi, J; Endo, E; Fryall, F; Harris, D; Mayeda, K; Rodgers, A; Ruppert, S; Sweeney, J
1999-07-23
The Kuwait Institute of Scientific Research (KISR), the USGS and LLNL are collaborating to calibrate seismic wave propagation in Kuwait and surrounding regions of the northwest Arabian Gulf using data from the Kuwait National Seismic Network (KNSN). Our goals are to develop local and regional propagation models for locating and characterizing seismic events in Kuwait and portions of the Zagros mountains close to Kuwait. The KNSN consists of 7 short-period stations and one broadband (STS-2) station. Constraints on the local velocity structure may be derived from joint inversions for hypocenters of local events and the local velocity model, receiver functions from three-component observations of teleseisms, and surface wave phase velocity estimated from differential dispersion measurements made across the network aperture. Data are being collected to calibrate travel-time curves for the principal regional phases for events in the Zagros mountains. The available event observations span the distance range from approximately 2.5 degrees to almost 9 degrees. Additional constraints on structure across the deep sediments of the Arabian Gulf will be obtained from long-period waveform modeling.
Propagation container and timing of propagation affects growth and quality of oak seedlings
Technology Transfer Automated Retrieval System (TEKTRAN)
Two experiments were conducted to determine the container effect and the timeline of seed propagation on germination and subsequent shoot and root development for container-grown oaks. Quercus nigra and Q. texana had equal or better growth and better root ratings when acorns were sown in Anderson t...
Pathogen Propagation Model with Superinfection in Vegetatively Propagated Plants on Lattice Space
Sakai, Yuma; Takada, Takenori
2016-01-01
Many clonal plants have two reproductive patterns, seed propagation and vegetative propagation. By vegetative propagation, plants reproduce the genetically identical offspring with a low mortality, because resources are supplied from the other individuals through interconnected ramets at vegetative-propagated offspring. However, the ramets transport not only resources but also systemic pathogen. Pathogens evolve to establish and spread widely within the plant population. The superinfection, which is defined as the ability that an established pathogen spreads widely by infecting to already-infected individuals with other strains of a pathogen, is important to the evolution of pathogens. We examine the dynamics of plant reproduction and pathogen propagation considering spatial structure and the effect of superinfection on genetic diversity of pathogen by analysis of several models, 1-strain and multiple-strain models, on two-dimensional square lattice. In the analysis of 1-strain model, we derive equilibrium value by mean-field approximation and pair approximation, and its local stability by Routh-Hurwitz stability criterion. In the multiple-strain models, we analyze the dynamics by numerical simulation of mean-field approximation, pair approximation and Monte Carlo simulation. Through the analyses, we show the effect of parameter values to dynamics of models, such as transition of dominant strain of pathogen, competition between plants and pathogens and density of individuals. As a result, (i) The strain with intermediate cost becomes dominant when both superinfection rate and growth rate are low. (ii) The competition between plants and pathogens occurs in the phase of coexistence of various strains by pair approximation and Monte Carlo simulation. (iii) Too high growth rate leads to the decrease of plant population in all models. (iv) Pathogens are easy to maintain their genetic diversity with low superinfection rate. However, if they do not superinfect, the
Seismic Wave Propagation on the Tablet Computer
NASA Astrophysics Data System (ADS)
Emoto, K.
2015-12-01
Tablet computers widely used in recent years. The performance of the tablet computer is improving year by year. Some of them have performance comparable to the personal computer of a few years ago with respect to the calculation speed and the memory size. The convenience and the intuitive operation are the advantage of the tablet computer compared to the desktop PC. I developed the iPad application of the numerical simulation of the seismic wave propagation. The numerical simulation is based on the 2D finite difference method with the staggered-grid scheme. The number of the grid points is 512 x 384 = 196,608. The grid space is 200m in both horizontal and vertical directions. That is the calculation area is 102km x 77km. The time step is 0.01s. In order to reduce the user waiting time, the image of the wave field is drawn simultaneously with the calculation rather than playing the movie after the whole calculation. P and S wave energies are plotted on the screen every 20 steps (0.2s). There is the trade-off between the smooth simulation and the resolution of the wave field image. In the current setting, it takes about 30s to calculate the 10s wave propagation (50 times image updates). The seismogram at the receiver is displayed below of the wave field updated in real time. The default medium structure consists of 3 layers. The layer boundary is defined by 10 movable points with linear interpolation. Users can intuitively change to the arbitrary boundary shape by moving the point. Also users can easily change the source and the receiver positions. The favorite structure can be saved and loaded. For the advance simulation, users can introduce the random velocity fluctuation whose spectrum can be changed to the arbitrary shape. By using this application, everyone can simulate the seismic wave propagation without the special knowledge of the elastic wave equation. So far, the Japanese version of the application is released on the App Store. Now I am preparing the
Transionospheric Propagation of VLF Transmitter Signals
NASA Astrophysics Data System (ADS)
Cohen, M.; Inan, U. S.; Lehtinen, N. G.
2012-12-01
Ground based Very Low Frequency (VLF, 3-30 kHz) radio transmitters may play a significant role in precipitation of inner belt (L<2.5) energetic Van Allen electrons. Initial analyses of the total contribution of VLF transmitters utilized models of transionospheric propagation, but some recent studies have suggested that those models may overestimate (by 20-100 dB) the VLF energy reaching the magnetosphere. One possible cause of this discrepancy was suggested to be conversion of wave energy into electrostatic modes in the D, E, and F regions, from ionospheric density irregularities, either natural or generated by the transmitter heating itself. The DEMETER satellite built a six year history of continuous and global survey mode data which, when combined, yields detailed pictures of the radiation pattern from many transmitters into space at 680 km, with 25 km resolution, and clear features like the interference pattern on the ground mapped upwards. With both E and B survey mode data, we can also directly approximate the total power injected into the magnetosphere from each transmitter, separately for day and night, as well as the power arriving at the conjugate region. We find no detectable variation of signal intensity with geomagnetic conditions. We find evidence of transmitter heating affecting the transionospheric propagation of other transmitters. We find that the power reaching the conjugate region is a large fraction of the power injected above the transmitter. We then employ a full wave model to simulate VLF transmitter transionospheric propagation, calculating the electromagnetic fields and power flux injected into the magnetosphere. Although the model does not include ionospheric irregularities, the radiation pattern largely matches the observed one, and the total power calculated is within 6 dB of observations for every transmitter, both day and night, and across a range of low to middle latitudes and transmitter powers. We thus conclude that the effect of
Oscillations above sunspots: Evidence for propagating waves?
NASA Astrophysics Data System (ADS)
O'Shea, E.; Muglach, K.; Fleck, B.
2002-05-01
We present results of an analysis of time series data observed in sunspot umbral regions. The data were obtained in the context of the SOHO Joint Observing Program (JOP) 97 in September 2000. This JOP included the Coronal Diagnostic Spectrometer (CDS) and the Michelson Doppler Imaging (MDI) instrument, both part of SOHO, the TRACE satellite and various ground based observatories. The data was analysed by using both Fourier and wavelet time series analysis techniques. We find that oscillations are present in the umbra at all temperatures investigated, from the temperature minimum as measured by TRACE 1700 Å up to the upper corona as measured by CDS Fe Xvi 335 Å (log T=6.4 K). Oscillations are found to be present with frequencies in the range of 5.4 mHz (185 s) to 8.9 mHz (112 s). Using the techniques of cross-spectral analysis time delays were found between low and high temperature emission suggesting the possibility of both upward and downward wave propagation. It is found that there is typically a good correlation between the oscillations measured at the different emission temperatures, once the time delays are taken into account. We find umbral oscillations both inside and outside of sunspot plume locations which indicates that umbral oscillations can be present irrespective of the presence of these sunspot plumes. We find that a number of oscillation frequencies can exist co-spatially and simultaneously i.e. for one pixel location three different frequencies at 5.40, 7.65 and 8.85 mHz were measured. We investigate the variation of the relative amplitudes of oscillation with temperature and find that there is a tendency for the amplitudes to reach a maximum at the temperature of O Iii (and less typically O V and Mg Ix) and then to decrease to reach a minimum at the temperature of Mg X (log T=6.0 K), before increasing again at the temperature of Fe Xvi. We discuss a number of possible theoretical scenarios that might explain these results. From a measurement of
Adaptive laser link reconfiguration using constraint propagation
NASA Technical Reports Server (NTRS)
Crone, M. S.; Julich, P. M.; Cook, L. M.
1993-01-01
This paper describes Harris AI research performed on the Adaptive Link Reconfiguration (ALR) study for Rome Lab, and focuses on the application of constraint propagation to the problem of link reconfiguration for the proposed space based Strategic Defense System (SDS) Brilliant Pebbles (BP) communications system. According to the concept of operations at the time of the study, laser communications will exist between BP's and to ground entry points. Long-term links typical of RF transmission will not exist. This study addressed an initial implementation of BP's based on the Global Protection Against Limited Strikes (GPALS) SDI mission. The number of satellites and rings studied was representative of this problem. An orbital dynamics program was used to generate line-of-site data for the modeled architecture. This was input into a discrete event simulation implemented in the Harris developed COnstraint Propagation Expert System (COPES) Shell, developed initially on the Rome Lab BM/C3 study. Using a model of the network and several heuristics, the COPES shell was used to develop the Heuristic Adaptive Link Ordering (HALO) Algorithm to rank and order potential laser links according to probability of communication. A reduced set of links based on this ranking would then be used by a routing algorithm to select the next hop. This paper includes an overview of Constraint Propagation as an Artificial Intelligence technique and its embodiment in the COPES shell. It describes the design and implementation of both the simulation of the GPALS BP network and the HALO algorithm in COPES. This is described using a 59 Data Flow Diagram, State Transition Diagrams, and Structured English PDL. It describes a laser communications model and the heuristics involved in rank-ordering the potential communication links. The generation of simulation data is described along with its interface via COPES to the Harris developed View Net graphical tool for visual analysis of communications
A review of uncertainty propagation in orbital mechanics
NASA Astrophysics Data System (ADS)
Luo, Ya-zhong; Yang, Zhen
2017-02-01
Orbital uncertainty propagation plays an important role in space situational awareness related missions such as tracking and data association, conjunction assessment, sensor resource management and anomaly detection. Linear models and Monte Carlo simulation were primarily used to propagate uncertainties. However, due to the nonlinear nature of orbital dynamics, problems such as low precision and intensive computation have greatly hampered the application of these methods. Aiming at solving these problems, many nonlinear uncertainty propagators have been proposed in the past two decades. To motivate this research area and facilitate the development of orbital uncertainty propagation, this paper summarizes the existing linear and nonlinear uncertainty propagators and their associated applications in the field of orbital mechanics. Frameworks of methods for orbital uncertainty propagation, the advantages and drawbacks of different methods, as well as potential directions for future efforts are also discussed.
Simulation of sound propagation over porous barriers of arbitrary shapes.
Ke, Guoyi; Zheng, Z C
2015-01-01
A time-domain solver using an immersed boundary method is investigated for simulating sound propagation over porous and rigid barriers of arbitrary shapes. In this study, acoustic propagation in the air from an impulse source over the ground is considered as a model problem. The linearized Euler equations are solved for sound propagation in the air and the Zwikker-Kosten equations for propagation in barriers as well as in the ground. In comparison to the analytical solutions, the numerical scheme is validated for the cases of a single rigid barrier with different shapes and for two rigid triangular barriers. Sound propagations around barriers with different porous materials are then simulated and discussed. The results show that the simulation is able to capture the sound propagation behaviors accurately around both rigid and porous barriers.
Propagation Characteristics of International Space Station Wireless Local Area Network
NASA Technical Reports Server (NTRS)
Sham, Catherine C.; Hwn, Shian U.; Loh, Yin-Chung
2005-01-01
This paper describes the application of the Uniform Geometrical Theory of Diffraction (UTD) for Space Station Wireless Local Area Networks (WLANs) indoor propagation characteristics analysis. The verification results indicate good correlation between UTD computed and measured signal strength. It is observed that the propagation characteristics are quite different in the Space Station modules as compared with those in the typical indoor WLANs environment, such as an office building. The existing indoor propagation models are not readily applicable to the Space Station module environment. The Space Station modules can be regarded as oversized imperfect waveguides. Two distinct propagation regions separated by a breakpoint exist. The propagation exhibits the guided wave characteristics. The propagation loss in the Space Station, thus, is much smaller than that in the typical office building. The path loss model developed in this paper is applicable for Space Station WLAN RF coverage and link performance analysis.
Fourth International Symposium on Long-Range Sound Propagation
NASA Technical Reports Server (NTRS)
Willshire, William L., Jr. (Compiler)
1990-01-01
Long range sound propagation is an aspect of many acoustical problems ranging from en route aircraft noise to the acoustic detection of aircraft. Over the past decade, the University of Mississippi and the Open University of England, together with a third institution, have held a symposium approx. every 2 years so that experts in the field of long range propagation could exchange information on current research, identify areas needing additional work, and coordinate activities as much as possible. The Fourth International Symposium on Long Range Sound Propagation was jointly sponsored by the University of Mississippi, the Open University of England, and NASA. Papers were given in the following areas: ground effects on propagation; infrasound propagation; and meteorological effects on sound propagation. A compilation of the presentations made at the symposium is presented along with a list of attendees, and the agenda.
Coulomb gauge ghost propagator and the Coulomb form factor
NASA Astrophysics Data System (ADS)
Quandt, M.; Burgio, G.; Chimchinda, S.; Reinhardt, H.
The ghost propagator and the Coulomb potential are evaluated in Coulomb gauge on the lattice, using an improved gauge fixing scheme which includes the residual symmetry. This setting has been shown to be essential in order to explain the scaling violations in the instantaneous gluon propagator. We find that both the ghost propagator and the Coulomb potential are insensitive to the Gribov problem or the details of the residual gauge fixing, even if the Coulomb potential is evaluated from the A0 -propagator instead of the Coulomb kernel. In particular, no signs of scaling violations could be found in either quantity, at least to well below the numerical accuracy where these violations were visible for the gluon propagator. The Coulomb potential from the A0 -propagator is shown to be in qualitative agreement with the (formally equivalent) expression evaluated from the Coulomb kernel.
Safe Laser Beam Propagation for Interplanetary Links
NASA Technical Reports Server (NTRS)
Wilson, Keith E.
2011-01-01
Ground-to-space laser uplinks to Earth–orbiting satellites and deep space probes serve both as a beacon and an uplink command channel for deep space probes and Earth-orbiting satellites. An acquisition and tracking point design to support a high bandwidth downlink from a 20-cm optical terminal on an orbiting Mars spacecraft typically calls for 2.5 kW of 1030-nm uplink optical power in 40 micro-radians divergent beams.2 The NOHD (nominal ocular hazard distance) of the 1030nm uplink is in excess of 2E5 km, approximately half the distance to the moon. Recognizing the possible threat of high power laser uplinks to the flying public and to sensitive Earth-orbiting satellites, JPL developed a three-tiered system at its Optical Communications Telescope Laboratory (OCTL) to ensure safe laser beam propagation through navigational and near-Earth space.
UWB pulse propagation into human tissues
NASA Astrophysics Data System (ADS)
Cavagnaro, Marta; Pittella, Erika; Pisa, Stefano
2013-12-01
In this paper the propagation of a UWB pulse into a layered model of the human body is studied to characterize absorption and reflection of the UWB signal due to the different body tissues. Several time behaviours for the incident UWB pulse are considered and compared with reference to the feasibility of breath and heartbeat activity monitoring. Results show that if the UWB source is placed far from the human body, the reflection coming from the interface between air and skin can be used to detect the respiratory activity. On the contrary, if the UWB source is placed close to the human body, a small reflection due to the interface between the posterior lung wall and the bone, which is well distanced in time from the reflections due to the first layers of the body model, can be used to detect lung and heart changes associated with the cardio-respiratory activity.
Westward propagating predecessors of monsoon depressions
NASA Technical Reports Server (NTRS)
Saha, K.; Sanders, F.; Shukla, J.
1981-01-01
Sea-level pressure data for the period 1969-1978 are used to investigate the relation between Bay of Bengal lows and depressions and disturbances propagating from the east. Of the 52 lows and depressions studied, 45 were associated with such predecessor disturbances. In 12 cases, the predecessor was associated with a typhoon or named tropical storm in the South China Sea, while the remaining 33 were weaker systems originating over a broad region of land and sea. From examination of time sections over the same period from eastern Thailand to the Burmese coast, 50 westward-moving disturbances with considerable vertical extent were identified, 64% of which developed into lows or depressions on reaching the Bay. In 60% of the 50 instances, the disturbance could be traced to the South China Sea (32% typhoons and 28% weaker circulations). The remaining 40% of the 50 disturbances appeared to originate over land.
Impact of Fog on Electromagnetic Wave Propagation
NASA Astrophysics Data System (ADS)
Morris, Jonathon; Fleisch, Daniel
2002-04-01
This experiment was designed to explore the impact of fog on electromagnetic radiation, in particular microwaves and infrared light. For years law enforcement agencies have used microwave radiation (radar guns) to measure the speed of vehicles, and the last ten years has seen increased use of LIDAR, which uses 905-nm infrared radiation rather than microwaves. To evaulate the effect of fog on the operation of these devices, we have constructed a fog chamber with microwave and optical portals to allow light from a HeNe laser and 10.6-GHz microwaves to propagate through various densities of fog. Data is acquired using Vernier Logger Pro and analyzed using MATLAB and Mathematica. Using the attenuation of the laser light to determine fog density, the impact of fog on the signal-to-noise ratio of both microwave and IR devices may be quantified, and the maximum useful range may be calculated.
Skewon field and cosmic wave propagation
NASA Astrophysics Data System (ADS)
Ni, Wei-Tou
2014-03-01
We study the propagation of the Hehl-Obukhov-Rubilar skewon field in weak gravity field/dilute matter or with weak violation of the Einstein Equivalence Principle (EEP), and further classify it into Type I and Type II skewons. From the dispersion relation we show that no dissipation/no amplification condition implies that the additional skewon field must be of Type II. For Type I skewon field, the dissipation/amplification is proportional to the frequency and the CMB spectrum would deviate from Planck spectrum. From the high precision agreement of the CMB spectrum with 2.755 K Planck spectrum, we constrain the Type I cosmic skewon field |χijkl(SkI)| to ⩽ a few ×10-35. The skewon part of constitutive tensor constructed from asymmetric metric is of Type II, hence it is allowed. This study may also be applied to macroscopic electrodynamics in the case of laser pumped medium or dissipative medium.
Wave propagation in a random medium
NASA Technical Reports Server (NTRS)
Lee, R. W.; Harp, J. C.
1969-01-01
A simple technique is used to derive statistical characterizations of the perturbations imposed upon a wave (plane, spherical or beamed) propagating through a random medium. The method is essentially physical rather than mathematical, and is probably equivalent to the Rytov method. The limitations of the method are discussed in some detail; in general they are restrictive only for optical paths longer than a few hundred meters, and for paths at the lower microwave frequencies. Situations treated include arbitrary path geometries, finite transmitting and receiving apertures, and anisotropic media. Results include, in addition to the usual statistical quantities, time-lagged functions, mixed functions involving amplitude and phase fluctuations, angle-of-arrival covariances, frequency covariances, and other higher-order quantities.
Epidemic Propagation In Overlaid Wireless Networks
Yanmaz, Evsen
2008-01-01
Witb tbe emergence of computer worms tbat can spread over air interfaces, wireless ad boc and sensor networks can be vulnerable to node compromises even if the deployed network is not connected to the backbone. Depending on the physical topology of the wireless network, even a single infected node can compromise the whole network. In this work, epidemic (e.g., worm) propagation in a static wireless network is studied, where a number of inCected mobile nodes are injected over the existing network. It is shown that the epidemic spread threshold and size depend on the physical topology of the underlying static wireless network as well as the mobility model employed by the infected mobile nodes. More specifically, results show that in a Cully-connected static wirelessnctwork targeted attacks are more effective, wbereas Cor a random topology random attacks can be sufficient to compromise the whole network.
Signal propagation in stem-cell niches
NASA Astrophysics Data System (ADS)
Zhdanov, Vladimir P.
2009-09-01
Stem cells, maintaining tissue homeostasis, are nurtured in microscopic niches formed of so-called environmental cells. The kinetics of proliferation and differentiation of stem cells in such niches depend on their interaction with the messenger proteins secreted by environmental cells. We propose a generic mean-field kinetic model of the propagation of such signals. To motivate our study, we briefly describe a stem-cell niche in the Drosophila ovary. Our model is however applicable to other niches as well. In particular, it helps one to understand the necessary conditions for the niche function. For example, the model predicts that in the case of the Drosophila ovary each germline stem cell should have in the external membrane at least 700 receptors interacting with the signaling Dpp and Gpp proteins emanating from the cap cells.
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.
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.
Lattice Boltzmann model for wave propagation.
Zhang, Jianying; Yan, Guangwu; Shi, Xiubo
2009-08-01
A lattice Boltzmann model for two-dimensional wave equation is proposed by using the higher-order moment method. The higher-order moment method is based on the solution of a series of partial differential equations obtained by using multiscale technique and Chapman-Enskog expansion. In order to obtain the lattice Boltzmann model for the wave equation with higher-order accuracy of truncation errors, we removed the second-order dissipation term and the third-order dispersion term by employing the moments up to fourth order. The reversibility in time appears owing to the absence of the second-order dissipation term and the third-order dispersion term. As numerical examples, some classical examples, such as interference, diffraction, and wave passing through a convex lens, are simulated. The numerical results show that this model can be used to simulate wave propagation.
Modeling of ultrafast laser pulse propagation
NASA Astrophysics Data System (ADS)
Kolesik, Miroslav; Brown, Jeffrey; Bahl, Anand
2016-05-01
Computer simulations of ultrafast optical pulses face multiple challenges. This requires one to construct a propagation model to reduce the Maxwell system so that it can be efficiently simulated at the temporal and spatial scales relevant to experiments. The second problem concerns the light-matter interactions, demanding novel approaches for gaseous and condensed media alike. As the nonlinear optics pushes into new regimes, the need to honor the first principles is ever greater, and requires striking a balance between computational complexity and physical fidelity of the model. With the emphasis on the dynamics in intense optical pulses, this paper discusses some recent developments and promising directions in the field of ultrashort pulse modeling.
Quantification and Propagation of Nuclear Data Uncertainties
NASA Astrophysics Data System (ADS)
Rising, Michael E.
The use of several uncertainty quantification and propagation methodologies is investigated in the context of the prompt fission neutron spectrum (PFNS) uncertainties and its impact on critical reactor assemblies. First, the first-order, linear Kalman filter is used as a nuclear data evaluation and uncertainty quantification tool combining available PFNS experimental data and a modified version of the Los Alamos (LA) model. The experimental covariance matrices, not generally given in the EXFOR database, are computed using the GMA methodology used by the IAEA to establish more appropriate correlations within each experiment. Then, using systematics relating the LA model parameters across a suite of isotopes, the PFNS for both the uranium and plutonium actinides are evaluated leading to a new evaluation including cross-isotope correlations. Next, an alternative evaluation approach, the unified Monte Carlo (UMC) method, is studied for the evaluation of the PFNS for the n(0.5 MeV)+Pu-239 fission reaction and compared to the Kalman filter. The UMC approach to nuclear data evaluation is implemented in a variety of ways to test convergence toward the Kalman filter results and to determine the nonlinearities present in the LA model. Ultimately, the UMC approach is shown to be comparable to the Kalman filter for a realistic data evaluation of the PFNS and is capable of capturing the nonlinearities present in the LA model. Next, the impact that the PFNS uncertainties have on important critical assemblies is investigated. Using the PFNS covariance matrices in the ENDF/B-VII.1 nuclear data library, the uncertainties of the effective multiplication factor, leakage, and spectral indices of the Lady Godiva and Jezebel critical assemblies are quantified. Using principal component analysis on the PFNS covariance matrices results in needing only 2-3 principal components to retain the PFNS uncertainties. Then, using the polynomial chaos expansion (PCE) on the uncertain output
Digital signal processing for ionospheric propagation diagnostics
NASA Astrophysics Data System (ADS)
Rino, Charles L.; Groves, Keith M.; Carrano, Charles S.; Gunter, Jacob H.; Parris, Richard T.
2015-08-01
For decades, analog beacon satellite receivers have generated multifrequency narrowband complex data streams that could be processed directly to extract total electron content (TEC) and scintillation diagnostics. With the advent of software-defined radio, modern digital receivers generate baseband complex data streams that require intermediate processing to extract the narrowband modulation imparted to the signal by ionospheric structure. This paper develops and demonstrates a processing algorithm for digital beacon satellite data that will extract TEC and scintillation components. For algorithm evaluation, a simulator was developed to generate noise-limited multifrequency complex digital signal realizations with representative orbital dynamics and propagation disturbances. A frequency-tracking procedure is used to capture the slowly changing frequency component. Dynamic demodulation against the low-frequency estimate captures the scintillation. The low-frequency reference can be used directly for dual-frequency TEC estimation.
Expectation propagation for continuous time stochastic processes
NASA Astrophysics Data System (ADS)
Cseke, Botond; Schnoerr, David; Opper, Manfred; Sanguinetti, Guido
2016-12-01
We consider the inverse problem of reconstructing the posterior measure over the trajectories of a diffusion process from discrete time observations and continuous time constraints. We cast the problem in a Bayesian framework and derive approximations to the posterior distributions of single time marginals using variational approximate inference, giving rise to an expectation propagation type algorithm. For non-linear diffusion processes, this is achieved by leveraging moment closure approximations. We then show how the approximation can be extended to a wide class of discrete-state Markov jump processes by making use of the chemical Langevin equation. Our empirical results show that the proposed method is computationally efficient and provides good approximations for these classes of inverse problems.
Roughening of a propagating planar crack front
NASA Astrophysics Data System (ADS)
Åström, J. A.; Alava, M. J.; Timonen, J.
2000-08-01
A numerical model of the front of a planar crack propagating between two connected elastic plates is investigated. The plates are modeled as square lattices of elastic beams. The plates are connected by similar but breakable beams with a randomly varying stiffness. The crack is driven by pulling both plates at one end in Mode I at a constant rate. We find ζ=1/3, z=4/3, and β=1/4 for the roughness, dynamical, and growth exponents, respectively, that describe the front behavior. This is similar to continuum limit analyses based on a perturbative stress-intensity treatment of the front [H. Gao and J. R. Rice, J. Appl. Mech. 56, 828 (1989)]. We discuss the differences to recent experiments.
Corrosion fatigue crack propagation in metals
NASA Technical Reports Server (NTRS)
Gangloff, Richard P.
1990-01-01
This review assesses fracture mechanics data and mechanistic models for corrosion fatigue crack propagation in structural alloys exposed to ambient temperature gases and electrolytes. Extensive stress intensity-crack growth rate data exist for ferrous, aluminum and nickel based alloys in a variety of environments. Interactive variables (viz., stress intensity range, mean stress, alloy composition and microstructure, loading frequency, temperature, gas pressure and electrode potential) strongly affect crack growth kinetics and complicate fatigue control. Mechanistic models to predict crack growth rates were formulated by coupling crack tip mechanics with occluded crack chemistry, and from both the hydrogen embrittlement and anodic dissolution/film rupture perspectives. Research is required to better define: (1) environmental effects near threshold and on crack closure; (2) damage tolerant life prediction codes and the validity of similitude; (3) the behavior of microcrack; (4) probes and improved models of crack tip damage; and (5) the cracking performance of advanced alloys and composites.
New mixed quantum/semiclassical propagation method
NASA Astrophysics Data System (ADS)
Antoniou, Dimitri; Gelman, David; Schwartz, Steven D.
2007-05-01
The authors developed a new method for calculating the quantum evolution of multidimensional systems, for cases in which the system can be assumed to consist of a quantum subsystem and a bath subsystem of heavier atoms. The method combines two ideas: starting from a simple frozen Gaussian description of the bath subsystem, then calculate quantum corrections to the propagation of the quantum subsystem. This follows from recent work by one of them, showing how one can calculate corrections to approximate evolution schemes, even when the Hamiltonian that corresponds to these approximate schemes is unknown. Then, they take the limit in which the width of the frozen Gaussians approaches zero, which makes the corrections to the evolution of the quantum subsystem depend only on classical bath coordinates. The test calculations they present use low-dimensional systems, in which comparison to exact quantum dynamics is feasible.
Feynman propagator for spin foam quantum gravity.
Oriti, Daniele
2005-03-25
We link the notion causality with the orientation of the spin foam 2-complex. We show that all current spin foam models are orientation independent. Using the technology of evolution kernels for quantum fields on Lie groups, we construct a generalized version of spin foam models, introducing an extra proper time variable. We prove that different ranges of integration for this variable lead to different classes of spin foam models: the usual ones, interpreted as the quantum gravity analogue of the Hadamard function of quantum field theory (QFT) or as inner products between quantum gravity states; and a new class of causal models, the quantum gravity analogue of the Feynman propagator in QFT, nontrivial function of the orientation data, and implying a notion of "timeless ordering".
Electrokinetic coupling in hydraulic fracture propagation
NASA Astrophysics Data System (ADS)
Cuevas, Nestor Herman
2009-12-01
Electrokinetic coupling is the most popular mechanism proposed to explain observed electromagnetic signals associated with the hydraulic fracturing of rocks. Measurements in both controlled laboratory and in situ conditions show clear evidence of the phenomenon. However there have been no reports on the description of the source mechanism, its relationship to a propagating crack, nor the electromagnetic field distribution due to such a source advancing through an electrically conductive medium. In this work it is shown that a surface electric current density arising on the walls of a fluid driven propagating crack can explain the measurements of electric streaming potential recorded during hydraulic fracturing experiments. The properties of the streaming current source are studied at the microscopic scale in light of the electrokinetic coupling expected at the outermost grains of the crack's surface. Expressions are derived for the average macroscopic transport equations describing the coupled fluid, and electrical current flow, at the interface between a fluid continuum and a homogeneous porous medium, where a Darcy flow regime (porous medium) competes with a rather Poiseuille type (fracture channels). The properties of the electrokinetic boundary sources are analyzed in light of the average electrical current density arising on the interface, as the fluid electrolyte flows in both the porous media and the adjacent fluid continuum. It is found that two coupling coefficients are required to describe the streaming current density. Indeed the flow is driven by both, a tangential pressure gradient, as well as by forward momentum transfer across the permeable boundary. The coupling coefficients are obtained from the spatial average of the tangential stress exerted on the pore surfaces, and they are found to be position dependent, as the tangential stress transitions from that on the porous conduits, to that on the surface of the outer most grains. Furthermore each
Wave propagation in polymers. Part II
NASA Astrophysics Data System (ADS)
Newlander, C. D.; Cherest, J. A.; Lilly, M. C.; Eisler, R. D.
2000-04-01
Wave profile measurements made in Polycarbonate at around 2.2 kbars were previously reported showing dispersion and amplitude attenuation that were neither expected nor predicted from available models. This data is being re-visited here and analyzed using a modified material model and the PUFF74 computer code. The new computation shows remarkable agreement with the experiments. The modeling treated the material as a visco-elastic/plastic medium using the method developed by Bade. This work is expected to further our understanding of wave propagation in highly compressible and visco-elastic/plastic media. It is also expected to provide insights on the role of strain rate effects on material properties such as elastic moduli, strengths and loading behaviors.
Photon Propagation in Slowly Varying Electromagnetic Fields
NASA Astrophysics Data System (ADS)
Karbstein, F.
2017-03-01
Effective theory of soft photons in slowly varying electromagnetic background fields is studied at one-loop order in QED. This is of relevance for the study of all-optical signatures of quantum vacuum nonlinearity in realistic electromagnetic background fields as provided by high-intensity lasers. The central result derived in this article is a new analytical expression for the photon polarization tensor in two linearly polarized counterpropagating pulsed Gaussian laser beams. Treating the peak field strengths of both laser beams as free parameters, this field configuration can be considered as interpolating between the limiting cases of a purely right- or left-moving laser beam (if one of the peak field strengths is set equal to zero) and the standing-wave type scenario with two counter-propagating beams of equal strength.
Radial propagation of geodesic acoustic modes
Hager, Robert; Hallatschek, Klaus
2009-07-15
The GAM group velocity is estimated from the ratio of the radial free energy flux to the total free energy applying gyrokinetic and two-fluid theory. This method is much more robust than approaches that calculate the group velocity directly and can be generalized to include additional physics, e.g., magnetic geometry. The results are verified with the gyrokinetic code GYRO[J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)], the two-fluid code NLET[K. Hallatschek and A. Zeiler, Phys. Plasmas 7, 2554 (2000)], and analytical calculations. GAM propagation must be kept in mind when discussing the windows of GAM activity observed experimentally and the match between linear theory and experimental GAM frequencies.
Radio propagation for space communications systems
NASA Technical Reports Server (NTRS)
Ippolito, L. J.
1981-01-01
This paper presents a review of the most recent information on the effects of the earth's atmosphere on space communications systems. Models and techniques used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission are discussed. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz are reviewed. Particular emphasis is placed on the effects of precipitation on the earth-space path, including rain attenuation, and rain and ice-particle depolarization. Sky noise, antenna gain degradation, scintillations, and bandwidth coherence are also discussed. The impact of the various propagation factors on communications system design criteria is presented. These criteria include link reliability, power margins, noise contributions, modulation and polarization factors, channel crosstalk, error-rate, and bandwidth limitations.
Acoustic propagation in a rigid torus
NASA Technical Reports Server (NTRS)
El-Raheb, M.; Wagner, P.
1982-01-01
The acoustic propagation in a rigid torus is analyzed using a Green's function method. Three types of surface elements are developed; a flat quadrilateral element used in modeling polygonal cavities, a curved conical element appropriate for surfaces with one curvature, and a toroidal element developed for such doubly curved surfaces as the torus. Curved elements are necessary since the acoustic pressure is sensitive to slope discontinuities between consecutive surface elements especially near cavity resonances. The acoustic characteristics of the torus are compared to those of a bend of square cross section for a frequency range that includes the transverse acoustic resonance. Two equivalences between the different sections are tested; the first conserves curvature and cross-sectional dimension while the second matches transverse resonance and duct volume. The second equivalence accurately matches the acoustic characteristics of the torus up to the cutoff frequency corresponding to a mode with two circumferential waves.
Effect of Microscopic Noise on Front Propagation
NASA Astrophysics Data System (ADS)
Brunet, Éric; Derrida, Bernard
2001-04-01
We study the effect of the noise due to microscopic fluctuations on the position of a one dimensional front propagating from a stable to an unstable region in the "linearly marginal stability case." By simulating a very simple system for which the effective number N of particles can be as large as N=10150, we measure the N dependence of the diffusion constant DN of the front and the shift of its velocity vN. Our results indicate that DN˜(log N)-3. They also confirm our recent claim that the shift of velocity scales like vmin-vN≃K(log N)-2 and indicate that the numerical value of K is very close to the analytical expression Kapprox obtained in our previous work using a simple cut-off approximation.
Pulse propagation in the tapered wiggler
NASA Astrophysics Data System (ADS)
Al-Abawi, H.; McIver, J. K.; Moore, G. T.; Scully, M. O.
Theory and preliminary numerical calculations are presented for coherent optical and electron pulse propagation in a free-electron laser with a tapered wiggler. Since only trapped electrons contribute significantly to the laser radiation, it is possible to define generalized 'slow' space-time coordinates in terms of which the electron pulse envelope may be considered constant. The theory is outlined first for the helical wiggler and then is developed for an arbitrary quasiperiodic wiggler, using a more rigorous 'multiple-scaling' approach. In the latter case a modified definition of the electron phase angle is required, and optical harmonic generation is predicted. The numerical calculations show that substantial energy extraction is achievable, but that the optical pulse rapidly breaks up into a series of spikes in the time domain. Surprisingly, the optical spectrum remains quite smooth in appearance.
Geodesic Acoustic Propagation and Ballooning Mode Formalism
NASA Astrophysics Data System (ADS)
Li, M. B.; Diamond, P. H.; Young, G. G.; Arakawa, M.
2005-10-01
Relevance of ballooning formalism (BMF) in nonlinear interaction of toroidal electromagnetic drift waves in the presence of zonal flows and Geodesic Acoustic Oscillation (GAO) is critically examined from a physical argument of radial propagation of wave packets. To achieve the quasi-translational invariance of poloidal harmonics which is necessary for the BMF, the geodesic curvature induced transfer [1] of fluctuation energy in radial direction should occur faster than the time scale of physical interest. Of course, this does not happen necessarily in drift-Alfven (DALF) turbulence simulations [2]. This observation casts considerable doubts on the applicability of various codes based on the BMF concept to nonlinear electromagnetic problems. [1] B. Scott, Phys. Letters A 320 (2003) 53. [2] B. Scott, New J. Phys 7 (2005) 92.
Quantum propagation in single mode fiber
NASA Technical Reports Server (NTRS)
Joneckis, Lance G.; Shapiro, Jeffrey H.
1994-01-01
This paper presents a theory for quantum light propagation in a single-mode fiber which includes the effects of the Kerr nonlinearity, group-velocity dispersion, and linear loss. The theory reproduces the results of classical self-phase modulation, quantum four-wave mixing, and classical solution physics, within their respective regions of validity. It demonstrates the crucial role played by the Kerr-effect material time constant, in limiting the quantum phase shifts caused by the broadband zero-point fluctuations that accompany any quantized input field. Operator moment equations - approximated, numerically, via a terminated cumulant expansion - are used to obtain results for homodyne-measurement noise spectra when dispersion is negligible. More complicated forms of these equations can be used to incorporate dispersion into the noise calculations.
Propagating wave correlations in complex systems
NASA Astrophysics Data System (ADS)
Creagh, Stephen C.; Gradoni, Gabriele; Hartmann, Timo; Tanner, Gregor
2017-01-01
We describe a novel approach for computing wave correlation functions inside finite spatial domains driven by complex and statistical sources. By exploiting semiclassical approximations, we provide explicit algorithms to calculate the local mean of these correlation functions in terms of the underlying classical dynamics. By defining appropriate ensemble averages, we show that fluctuations about the mean can be characterised in terms of classical correlations. We give in particular an explicit expression relating fluctuations of diagonal contributions to those of the full wave correlation function. The methods have a wide range of applications both in quantum mechanics and for classical wave problems such as in vibro-acoustics and electromagnetism. We apply the methods here to simple quantum systems, so-called quantum maps, which model the behaviour of generic problems on Poincaré sections. Although low-dimensional, these models exhibit a chaotic classical limit and share common characteristics with wave propagation in complex structures.
Dynamic crack propagation through nanoporous media
NASA Astrophysics Data System (ADS)
Nguyen, Thao; Wilkerson, Justin
2015-06-01
The deformation and failure of nanoporous metals may be considerably different than that of more traditional bulk porous metals. The length scales in traditional bulk porous metals are typically large enough for classic plasticity and buckling to be operative. However, the extremely small length scales associated with nanoporous metals may inhibit classic plasticity mechanisms. Here, we motivate an alternative nanovoid growth mechanism mediated by dislocation emission. Following an approach similar to Lubarda and co-workers, we make use of stability arguments applied to the analytic solutions of the elastic interactions of dislocations and voids to derive a simple stress-based criterion for emission activation. We then propose a dynamic nanovoid growth law that is motivated by the kinetics of dislocation emission. The resulting failure model is implemented into a commercial finite element software to simulate dynamic crack growth. The simulations reveal that crack propagation through a nanoporous media proceeds at somewhat faster velocities than through the more traditional bulk porous metal.
[Rapid propagation of Smilax glabra in vitro].
Zeng, Songjun; Wu, Kunlin; Chen, Guohua; Duan, Jun
2005-01-01
In vitro propagation of Smilax glabra Roxb. was studied. The results indicated that sterilized explants cultured on MS + 6-BA 1.0 mg/L + NAA 0.1 mg/L could lead to budding fastly, the medium MS + 6-BA 1.0 mg/L + NAA 0.1 mg/L + 15% CM suitable for the proliferation, 3/2MS + 6-BA 0.05 mg/L + 4% Sugar suitable for buds strong. Treatment on the medium H (modified) + NAA 0.5 mg/L was best for rooting. The survival rate of the test-tube plantlets was 95% in transplanting on media contained turf-sand (1:1).
Propagation degradation for mobile satellite systems
NASA Technical Reports Server (NTRS)
Goldhirsh, Julius; Vogel, Wolfhard J.
1988-01-01
The results of four propagation tests for mobile satellite systems, which used remotely piloted vehicles and helicopters to simulate a transmitter satellite source platform, are presented. The signal degradation by individual trees, attenuation caused by roadside trees when the vehicle was moving, and multipath effects in hilly and mountainous terrain were studied. Three tests were conducted at UHF (870 MHz) and one test was performed at UHF and L band (1500 MHz). It was found that attenuation by roadside trees is the dominant cause of signal fading. The signal degradation may amount to 7 dB or more for 10 percent of the traveling time along tree-lined roads, with attenuations of 15 dB or more 1 percent of the time. The signal degradation caused by multipath effects amounted to only about 2 dB for 10 percent of the time and 9 dB for 1 percent of the time.
Multimodal imaging of spike propagation: a technical case report.
Tanaka, N; Grant, P E; Suzuki, N; Madsen, J R; Bergin, A M; Hämäläinen, M S; Stufflebeam, S M
2012-06-01
We report an 11-year-old boy with intractable epilepsy, who had cortical dysplasia in the right superior frontal gyrus. Spatiotemporal source analysis of MEG and EEG spikes demonstrated a similar time course of spike propagation from the superior to inferior frontal gyri, as observed on intracranial EEG. The tractography reconstructed from DTI showed a fiber connection between these areas. Our multimodal approach demonstrates spike propagation and a white matter tract guiding the propagation.
Multimodal Imaging of Spike Propagation: A Technical Case Report
Tanaka, N.; Grant, P.E.; Suzuki, N.; Madsen, J.R.; Bergin, A.M.; Hämäläinen, M.S; Stufflebeam, S.M.
2012-01-01
SUMMARY We report an 11-year-old boy with intractable epilepsy, who had cortical dysplasia in the right superior frontal gyrus. Spatiotemporal source analysis of MEG and EEG spikes demonstrated a similar time course of spike propagation from the superior to inferior frontal gyri, as observed on intracranial EEG. The tractography reconstructed from DTI showed a fiber connection between these areas. Our multimodal approach demonstrates spike propagation and a white matter tract guiding the propagation. PMID:21960488
Atmospheric Propagation and Combining of High-Power Lasers
2015-09-08
Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6703--15-9646 Atmospheric Propagation and Combining of High - Power Lasers W. NelsoN...ABSTRACT c. THIS PAGE 18. NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Atmospheric Propagation and Combining of High - Power Lasers W. Nelson,* P. Sprangle...Turbulence Beam combining In this paper we analyze the beam combining and atmospheric propagation of high - power lasers for directed-energy (DE
Multilayer Network Modeling of Change Propagation for Engineering Change Management
2010-06-01
communication involves cooperative learning that does not necessarily relate to a specific task. Finally, inspiration-type communication encompasses...ation 411 PNC C ac 2 C PC Not Predicted & Propagated wI Comunication ENot Predicted & Not Propagated w ConPnCcation 04 PPC 5CPredicted & Propagated w...multilayer network turns into a lessons- learned effort. At this stage, an organization can use all the data collected over the course of product
Estimating Failure Propagation in Models of Cascading Blackouts
Dobson, Ian; Carreras, Benjamin A; Lynch, Vickie E; Nkei, Bertrand; Newman, David E
2005-09-01
We compare and test statistical estimates of failure propagation in data from versions of a probabilistic model of loading-dependent cascading failure and a power systems blackout model of cascading transmission line overloads. The comparisons suggest mechanisms affecting failure propagation and are an initial step towards monitoring failure propagation from practical system data. Approximations to the probabilistic model describe the forms of probability distributions of cascade sizes.
An ocean scatter propagation model for aeronautical satellite communication applications
NASA Technical Reports Server (NTRS)
Moreland, K. W.
1990-01-01
In this paper an ocean scattering propagation model, developed for aircraft-to-satellite (aeronautical) applications, is described. The purpose of the propagation model is to characterize the behavior of sea reflected multipath as a function of physical propagation path parameters. An accurate validation against the theoretical far field solution for a perfectly conducting sinusoidal surface is provided. Simulation results for typical L band aeronautical applications with low complexity antennas are presented.
Outdoor propagation analysis of ultrawideband signals
NASA Astrophysics Data System (ADS)
Schiavone, Guy A.; Wahid, Parveen; Palaniappan, Ravi; Tracy, Judd; Van Doorn, Eric; Lonske, Benjamin
2003-08-01
An ultra wide band (UWB) signal is defined as any radiation in which the 3-dB bandwidth is greater than 25% of the center frequency. UWB signals are characterized by extreme low powers and large bandwidths, which can be used for data, voice and video communication. Since UWB waveforms have very short time duration, they are relatively immune to multi-path cancellation effects. In this paper we test the performance of a simulation to model the propagation of an UWB signal in outdoor forested environment. The simulation uses a combination of Finite Difference Time Domain and ray tracing methods to simulate the UWB wave propagation. The model takes into consideration the dielectric constants of the materials of the trees and measures the signal strength for vertical and horizontal polarizations of the UWB antennas placed at various heights and distances from each other. The results of the simulation are compared to measurements obtained from tests conducted at a wooded area in Seneca Creek State Park, Gaithersburg, Maryland. It was observed that upto 150 ft distance between the transmitter and receiver, the horizontally polarized antenna system gave better signal-to-noise ratio, but at greater distances the vertically polarized antenna system gave a better signal-to-noise ration performance. Three dimensional plots of the signal strengths and the signal-to-noise ratio for various transmitter and receiver distances are plotted for the system. These are compared with experimental results and the simulation closely matched the experimental data. The results of the simulation and measurements will be used for further developing an UWB location and tracking system for outdoor environments.
Charge Generation and Propagation in Igneous Rocks
NASA Technical Reports Server (NTRS)
Freund, Friedemann
2000-01-01
Resistivity changes, ground potentials, electromagnetic (EM) and luminous signals prior to or during earthquakes have been reported, in addition to ground uplift and tilt, and to changes in the seismic wave propagation parameters. However, no physical model exists that ties these diverse phenomena together. Through time-resolved impacts experiments it has been observed that, when igneous rocks (gabbro, diorite, granite) are impacted at low velocities (approx. 100 m/sec), highly mobile electronic charge carriers are generated, spreading from a small volume near the impact point, causing electric potentials, EM and light emission. The rock becomes momentarily conductive. When impacted at higher velocities (approx. 1.5 km/sec), the propagation of the P and S waves is registered through the transient piezoelectric response of quartz. At the same time, the rock volume is filled with mobile charge carriers, and a positive surface potential is registered. During the next 1-2 msec the surface potential oscillates, due to electron injection from ground. These observations are consistent with positive holes, e.g. defect electrons in the O(2-) sublattice, that can travel via the O 2p-dominated valence band of the silicate minerals at the speed of a phonon-mediated charge transfer. Before activation, the positive hole charge carriers lay dormant in form of positive hole pairs, PHP, electrically inactive, chemically equivalent to peroxy links in the structures of constituent minerals. PHPs are introduced by way of hydroxyl (O3Si-OH) incorporated into nominally anhydrous minerals when they crystallize in water-laden environments. Given that sound waves of even relatively low intensity appear to cause PHPs dissociation, thus generating mobile positive holes, it is proposed that microfracturing during rock deformation cause PHP dissociation. Depending on where and how much the rock volume is stressed, the positive holes are expected to form fluctuating charge clouds in the
Some Numerical Experiments on Detonation Wave Propagation
NASA Technical Reports Server (NTRS)
Cambier, Jean-Luc; Edwards, Thomas A. (Technical Monitor)
1995-01-01
In this paper we present the results of a series of numerical experiments done on the propagation and initiation of a detonation wave. The calculations are performed in one-dimension, with considerable grid resolution. Of particular interest are the following questions: (1) the nature of periodic and chaotic instabilities generated by the wave; (2) the influence of the grid resolution on these instabilities; (3) the influence of the 'quality' of the numerical scheme; and (4) the influence of 'noise'. In the calculations, we use a second-order Total Variation Diminishing (TVD) scheme as the basic numerical method, with grid spacings as low as a fraction of a micron. Detonations waves are generated at the closed end of a tube, and allowed to propagate for approximately 20 cm. The required energy for successful initiation of the detonation will be measured for different cases of grid resolution and numerical schemes. A modified version of the TVD scheme has also been devised, which allows for much lower numerical diffusion of the radical species in the exponentially growing region behind the shock. The effect of this modification will be demonstrated. Oscillations in peak pressure and induction length are seen to develop in some cases: the oscillations can go through a sequence of modes, from a regular, high frequency mode to a low frequency mode with period doubling. A chaotic regime can also be obtained. General conclusions on the quality of algorithms will be presented. We will also discuss the performance of a version of the code developed on the IBM SP2 parallel computer.
Azimuthal Spoke Propagation in Hall Effect Thrusters
NASA Technical Reports Server (NTRS)
Sekerak, Michael J.; Longmier, Benjamin W.; Gallimore, Alec D.; Brown, Daniel L.; Hofer, Richard R.; Polk, James E.
2013-01-01
Spokes are azimuthally propagating perturbations in the plasma discharge of Hall Effect Thrusters (HETs) that travel in the E x B direction and have been observed in many different systems. The propagation of azimuthal spokes are investigated in a 6 kW HET known as the H6 using ultra-fast imaging and azimuthally spaced probes. A spoke surface is a 2-D plot of azimuthal light intensity evolution over time calculated from 87,500 frames/s videos. The spoke velocity has been determined using three methods with similar results: manual fitting of diagonal lines on the spoke surface, linear cross-correlation between azimuthal locations and an approximated dispersion relation. The spoke velocity for three discharge voltages (300, 400 and 450 V) and three anode mass flow rates (14.7, 19.5 and 25.2 mg/s) yielded spoke velocities between 1500 and 2200 m/s across a range of normalized magnetic field settings. The spoke velocity was inversely dependent on magnetic field strength for low B-field settings and asymptoted at B-field higher values. The velocities and frequencies are compared to standard drifts and plasma waves such as E x B drift, electrostatic ion cyclotron, magnetosonic and various drift waves. The empirically approximated dispersion relation yielded a characteristic velocity that matched the ion acoustic speed for 5 eV electrons that exist in the near-anode and near-field plume regions of the discharge channel based on internal measurements. Thruster performance has been linked to operating mode where thrust-to-power is maximized when azimuthal spokes are present so investigating the underlying mechanism of spokes will benefit thruster operation.
Deterministic transfer function for transionospheric propagation
Roussel-Dupre, R.; Argo, P.
1992-01-01
Recent interest in ground-to-satellite propagation of broadband signals has prompted investigation into the development of a transfer function for the ionosphere that includes effects such as dispersion, refraction, changes in polarization, reflection, absorption, and scattering. Depending on the application (e.g. geolocation), it may be necessary to incorporate all of these processes in order to extract the information of interest from the measured transionospheric signal. A transfer function for midlatitudes at VBF from 25--175 MHz is one of the goals of the BLACKBEARD program in characterizing propagation distortion. In support of this program we discuss in this paper an analytic model for the deterministic transfer function of the ionosphere that includes the effects of dispersion, refraction, and changes in polarization to second order in the parameter X = {omega}{sub pe}{sup 2}/{omega}{sup 2} where X is assumed to be small compared to one, {omega}{sub pe} is the peak plasma frequency of the ionosphere, and {omega} is the wave frequency. Analytic expressions for the total phase change, group delay, and polarization change in a spherical geometry assuming a radial, electron density profile are presented. A computer code ITF (Ionospheric Transfer Function) that makes use of the ICED (Ionospheric Conductivity and Electron Density) model to ,venerate electron density profiles was developed to calculate the ionospheric transfer function along a specified transmitter-to-receiver path. Details of this code will be presented as well as comparisons made between ITF analytic results and ray-tracing calculations.
Deterministic transfer function for transionospheric propagation
Roussel-Dupre, R.; Argo, P.
1992-09-01
Recent interest in ground-to-satellite propagation of broadband signals has prompted investigation into the development of a transfer function for the ionosphere that includes effects such as dispersion, refraction, changes in polarization, reflection, absorption, and scattering. Depending on the application (e.g. geolocation), it may be necessary to incorporate all of these processes in order to extract the information of interest from the measured transionospheric signal. A transfer function for midlatitudes at VBF from 25--175 MHz is one of the goals of the BLACKBEARD program in characterizing propagation distortion. In support of this program we discuss in this paper an analytic model for the deterministic transfer function of the ionosphere that includes the effects of dispersion, refraction, and changes in polarization to second order in the parameter X = {omega}{sub pe}{sup 2}/{omega}{sup 2} where X is assumed to be small compared to one, {omega}{sub pe} is the peak plasma frequency of the ionosphere, and {omega} is the wave frequency. Analytic expressions for the total phase change, group delay, and polarization change in a spherical geometry assuming a radial, electron density profile are presented. A computer code ITF (Ionospheric Transfer Function) that makes use of the ICED (Ionospheric Conductivity and Electron Density) model to ,venerate electron density profiles was developed to calculate the ionospheric transfer function along a specified transmitter-to-receiver path. Details of this code will be presented as well as comparisons made between ITF analytic results and ray-tracing calculations.
Sound wave propagation through glow discharge plasma
NASA Astrophysics Data System (ADS)
Stepaniuk, Vadim P.
This work investigates the use of glow discharge plasma for acoustic wave manipulation. The broader goal is the suppression of aerodynamic noise using atmospheric glow discharge plasma as a sound barrier. Part of the effort was devoted to the development of a system for the generation of a large volume stable DC glow discharge in air both at atmospheric and at reduced pressures. The single tone sound wave propagation through the plasma was systematically studied. Attenuation of the acoustic wave passing through the glow discharge was measured for a range of experimental conditions including different discharge currents, electrode configurations, air pressures and sound frequencies including audible sound and ultrasound. Sound attenuation by glow discharge plasma as high as -28 dB was recorded in the experiments. Two types of possible mechanisms were considered that can potentially cause the observed sound attenuation. One is a global mechanism and the other is a local mechanism. The global mechanism considered is based on the reflection and refraction of acoustic wave due to the gas temperature gradients that form around the plasma. The local mechanism, on the other hand, is essentially the interaction of the acoustic wave with the plasma as it propagates inside the discharge and it can be viewed as a feedback system. Detailed temperature measurements, using laser-induced Rayleigh scattering technique, were carried out in the glow discharge plasma in order to evaluate the role of global mechanism in the observed attenuation. These measurements were made for a range of conditions in the atmospheric glow discharge. Theoretical analysis of the sound attenuation was carried out to identify the physical mechanism for the observed sound attenuation by plasma. It was demonstrated that the global mechanism is the dominant mechanism of sound attenuation. As a result of this study, the potentials and limitations of the plasma noise suppression technology were determined and
Seismic wave propagation in granular media
NASA Astrophysics Data System (ADS)
Tancredi, Gonzalo; López, Francisco; Gallot, Thomas; Ginares, Alejandro; Ortega, Henry; Sanchís, Johnny; Agriela, Adrián; Weatherley, Dion
2016-10-01
Asteroids and small bodies of the Solar System are thought to be agglomerates of irregular boulders, therefore cataloged as granular media. It is a consensus that many asteroids might be considered as rubble or gravel piles.Impacts on their surface could produce seismic waves which propagate in the interior of these bodies, thus causing modifications in the internal distribution of rocks and ejections of particles and dust, resulting in a cometary-type comma.We present experimental and numerical results on the study of propagation of impact-induced seismic waves in granular media, with special focus on behavior changes by increasing compression.For the experiment, we use an acrylic box filled with granular materials such as sand, gravel and glass spheres. Pressure inside the box is controlled by a movable side wall and measured with sensors. Impacts are created on the upper face of the box through a hole, ranging from free-falling spheres to gunshots. We put high-speed cameras outside the box to record the impact as well as piezoelectic sensors and accelerometers placed at several depths in the granular material to detect the seismic wave.Numerical simulations are performed with ESyS-Particle, a software that implements the Discrete Element Method. The experimental setting is reproduced in the numerical simulations using both individual spherical particles and agglomerates of spherical particles shaped as irregular boulders, according to rock models obtained with a 3D scanner. The numerical experiments also reproduces the force loading on one of the wall to vary the pressure inside the box.We are interested in the velocity, attenuation and energy transmission of the waves. These quantities are measured in the experiments and in the simulations. We study the dependance of these three parameters with characteristics like: impact speed, properties of the target material and the pressure in the media.These results are relevant to understand the outcomes of impacts in
Slow crack propagation in composite restorative materials.
Montes-G, G M; Draughn, R A
1987-05-01
The double-torsion test technique was used to study slow crack propagation in a set of dental composite resins including two glass-filled and two microfilled materials. The microstructure within each pair was the same but one of the resins was selfcured and the other photocured. The fracture behavior was dependent on the filler concentration and the presence of absorbed water. Wet materials fractured by slow crack growth in the range of crack velocity studied (10(-7) to 10(-3) m/s), and the microfilled composites, which contain a lower concentration of inorganic filler, had lower stress intensity factors (K1c) than the glass-filled composites tested. Dry specimens of the microfilled materials and the selfcured, glass-filled composite also showed unstable, stick-slip fracture behavior indicative of a crack blunting mechanism which leads to an elevation of the stress intensity factor for crack initiation over K1c for stable crack growth. The plasticizing effect of water increased the viscoelastic response of the materials measured by the slope of curves of slow crack growth. Analysis of fracture surfaces showed that cracks propagated at low velocities (10(-7) to 10(-5) m/s) by the apparent failure of the filler/matrix interfacial bond, and absorbed water affected the strength or fracture resistance of the interface. At high crack velocities the properties of the composite depend on the properties of the polymeric matrix, the filler, and the filler volume fraction, but at low velocities the interface is the controlling factor in the durability of these composites exposed to an aqueous environment.
Flame propagation under partially-premixed conditions
NASA Technical Reports Server (NTRS)
Ruetsch, Gregory R.
1994-01-01
This study concentrates on developing a better understanding of triple flames. We relax the assumption of zero heat release, address the issue of stabilization, and, in order to investigate the role that heat release plays in flame propagation in partially premixed combustion, we return to a simple flow field and investigate the behavior of flames in a laminar environment. We solve the compressible Navier-Stokes equations in a two-dimensional domain. At the boundaries, we use an inflow boundary condition on the left and nearly-perfect reflective boundary conditions, required to avoid pressure drift, at the outflow and sides. After the flow and flame are initialized, the mixture fraction is varied at the inlet from its uniform stoichiometric value to a tanh profile varying from zero to one. As the mixture fraction gradient reaches the flame surface only the centerline is exposed to the stoichionetric mixture fraction and locally maintains the planar flame speed and reaction rate. Above this point the mixture is fuel rich, and below fuel lean. As a result, these regions of non-unity equivalence ratio burn less, the reaction rate drops, and the local flame speed is reduced. The excess fuel and oxidizer then combine behind the premixed flame along the stoichiometric surface and burn in a trailing diffusion flame. Thus the 'triple' flame refers to the fuel-rich premixed flame, the fuel-lean premixed flame, and the trailing diffusion flame. Due to heat release, the normal velocity across the flame is increased, whereas the tangential component remains unchanged. Far-field flame speed, local flame speed, and their differences are shown as a function of the local mixing thickness. It was also determined that the lateral position of the flame affects stabilization, and the distribution of the reaction rate along the premixed wings of triple flames affects flame propagation.
Modeling Passive Propagation of Malwares on the WWW
NASA Astrophysics Data System (ADS)
Chunbo, Liu; Chunfu, Jia
Web-based malwares host in websites fixedly and download onto user's computers automatically while users browse. This passive propagation pattern is different from that of traditional viruses and worms. A propagation model based on reverse web graph is proposed. In this model, propagation of malwares is analyzed by means of random jump matrix which combines orderness and randomness of user browsing behaviors. Explanatory experiments, which has single or multiple propagation sources respectively, prove the validity of the model. Using this model, people can evaluate the hazardness of specified websites and take corresponding countermeasures.
Seismotectonics of mid-ocean ridge propagation in Hess Deep.
Floyd, Jacqueline S; Tolstoy, Maya; Mutter, John C; Scholz, Christopher H
2002-11-29
Hydroacoustic data from the eastern equatorial Pacific reveal low-magnitude seismicity concentrated at the propagating tip of the Galapagos Rise in Hess Deep. The patterns of seismicity and faulting are similar to those observed in the process zone of laboratory-scale propagating tensile cracks. Because the fracture energy required for propagation scales with crack length and process zone size, it follows that ridges can propagate stably in the brittle crust without exceptional resisting forces as proposed by previous models based on linear elastic fracture mechanics.
High Performance Orbital Propagation Using a Generic Software Architecture
NASA Astrophysics Data System (ADS)
Möckel, M.; Bennett, J.; Stoll, E.; Zhang, K.
2016-09-01
Orbital propagation is a key element in many fields of space research. Over the decades, scientists have developed numerous orbit propagation algorithms, often tailored to specific use cases that vary in available input data, desired output as well as demands of execution speed and accuracy. Conjunction assessments, for example, require highly accurate propagations of a relatively small number of objects while statistical analyses of the (untracked) space debris population need a propagator that can process large numbers of objects in a short time with only medium accuracy. Especially in the latter case, a significant increase of computation speed can be achieved by using graphics processors, devices that are designed to process hundreds or thousands of calculations in parallel. In this paper, an analytical propagator is introduced that uses graphics processing to reduce the run time for propagating a large space debris population from several hours to minutes with only a minor loss of accuracy. A second performance analysis is conducted on a parallelised version of the popular SGP4 algorithm. It is discussed how these modifications can be applied to more accurate numerical propagators. Both programs are implemented using a generic, plugin-based software architecture designed for straightforward integration of propagators into other software tools. It is shown how this architecture can be used to easily integrate, compare and combine different orbital propagators, both CPU and GPU-based.
Attenuation characteristic of UWB signals propagation in free space
NASA Astrophysics Data System (ADS)
Li, Meng; Huang, Zhonghua
2016-10-01
Researching attenuation characteristic of UWB signals propagation in free-space is necessary for ultra-wideband (UWB) radio fuze optimized design. Research attenuation characteristic of UWB signals propagation in free space can be achieved by learning attenuation characteristic of radio waves propagation in free-space and UWB signal power spectral density. 50ps, 100ps and 200ps of pulse width UWB fuze transmission narrow pulse signal propagation in free-space are simulated and analyzed. The attenuation of UWB signals at 3m, 6m and 9m are contrasted. The simulation, analysis and contrast is theoretical basis of UWB radio fuze optimized design.
Behavior of ultrasounds crossing perfluorocarbon liquids and random propagation times.
Lacaze, Bernard
2015-12-01
Random propagation times are able to model waves attenuation and velocity. It is true for electromagnetic waves (light, radar, guided propagation) and also for acoustics and ultrasounds (acoustics for high frequencies). About the latter, it can be shown that stable probability laws are well-fitted for frequencies up to dozens of megahertz in numerous cases. Nowadays, medical applications are performed using propagation through perfluorocarbon (PFC). Experiments were done to measure attenuations and phase changes. Using these results, this paper addresses the question to know if stable probability laws can be used to characterize the propagation of ultrasounds through PFC liquids.
NASA Technical Reports Server (NTRS)
Davarian, Faramaz (Editor)
1990-01-01
The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. NAPEX XIV was held on May 11, 1990, at the Balcones Research Centers, University of Texas, Austin, Texas. The meeting was organized into two technical sessions: Satellite (ACTS) and the Olympus Spacecraft, while the second focused on the fixed and mobile satellite propagation studies and experiments. Following NAPEX XIV, the ACTS Miniworkshop was held at the Hotel Driskill, Austin, Texas, on May 12, 1990, to review ACTS propagation activities since the First ACTS Propagation Studies Workshop was held in Santa Monica, California, on November 28 and 29, 1989.
NASA Technical Reports Server (NTRS)
Davarian, Faramaz (Editor)
1991-01-01
The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. The meeting was organized into three technical sessions. The first session was dedicated to Olympus and ACTS studies and experiments, the second session was focused on the propagation studies and measurements, and the third session covered computer-based propagation model development. In total, sixteen technical papers and some informal contributions were presented. Following NAPEX 15, the Advanced Communications Technology Satellite (ACTS) miniworkshop was held on 29 Jun. 1991, to review ACTS propagation activities, with emphasis on ACTS hardware development and experiment planning. Five papers were presented.
Observation and explanation of a 0.3% sunward radial streaming of 1 to 5 GV cosmic radiation
NASA Technical Reports Server (NTRS)
Dyer, C. S.; Engel, A. R.; Quenby, J. J.; Webb, S.
1974-01-01
A high-energy proton telescope on board the HEOS-1 satellite obtained quiet-time anisotropy data between December 1968 and April 1970. Analysis of the data showed an integral radial streaming component towards the sun of 0.3% for particles of rigidity greater than 1 GV. This value is not explicable in terms of any experimental defect, the effect of the earth's magnetosphere or energy loss effects under spherical symmetry in the solar cavity. An explanation in terms of a falling off ecliptic gradient in cosmic ray density most affecting the 1-5 GV range would seem to be the most compelling.
Zhang, Bin; Chu, Xiaoliang; Li, Qiang
2002-07-01
The second-order intensity moments and beam-propagation factor (M2 factor) of partially coherent beams have been generalized to include the case of hard-edged diffraction. A laser beam with amplitude modulation and phase fluctuation and a Gaussian Schell-model beam are taken as two typical examples of partially coherent beams. Analytical expressions for the generalized M2 factor are derived.
NASA Technical Reports Server (NTRS)
Golshan, Nasser (Editor)
1996-01-01
The NASA Propagation Experimenters (NAPEX) Meeting is convened each year to discuss studies supported by the NASA Propagation Program. Representatives from the satellite communications (satcom) industry, academia, and government who have an interest in space-ground radio wave propagation are invited to NAPEX meetings for discussions and exchange of information. The reports delivered at these meetings by program managers and investigators present recent activities and future plans. This forum provides an opportunity for peer discussion of work in progress, timely dissemination of propagation results, and close interaction with the satcom industry.
Propagation of gravity waves across the tropopause
NASA Astrophysics Data System (ADS)
Bense, Vera; Spichtinger, Peter
2015-04-01
The tropopause region is characterised by strong gradients in various atmospheric quantities that exhibit different properties in the troposphere compared to the stratosphere. The temperature lapse rate typically changes from negative to near-zero values resulting in a strong increase in stability. Accordingly, the buoyancy frequency often undergoes a jump at the tropopause. Analysis of radiosounding data also shows the existence of a strong inversion layer (tropopause inversion layer, TIL) characterised by a strong maximum in buoyancy frequency just above the tropopause, see e.g. Birner et al. (2002). Additionally, the magnitude of the vertical wind shear of the horizontal wind maximizes at the tropopause and the region also exhibits characteristical gradients of trace gases. Vertically propagating gravity waves can be excited in the troposphere by several mechanisms, e.g. by flow over topography (e.g. Durran, 1990), by jets and fronts (for a recent review: Plougonven and Zhang, 1990) or by convection (e.g. Clark et al., 1986). When these waves enter the tropopause region, their properties can be changed drastically by the changing stratification and strong wind shear. Within this work, the EULAG (Eulerian/semi-Lagrangian fluid solver, see e.g. Smolarkiewicz and Margolin, 1997) model is used to investigate the impact of the tropopause on vertically propagating gravity waves excited by flows over topography. The choice of topography (sine-shaped mountains, bell-shaped mountain) along with horizontal wind speed and tropospheric value of buoyancy frequency determine the spectrum of waves (horizontal and vertical wavelengths) that is excited in the tropsphere. In order to analyse how these spectra change for several topographies when a tropopause is present, we investigate different idealized cases in a two-dimensional domain. By varying the vertical profiles of buoyancy frequency (step-wise vs. continuos change, including TIL) and wind shear, the tropopause
Acoustic signal propagation characterization of conduit networks
NASA Astrophysics Data System (ADS)
Khan, Muhammad Safeer
Analysis of acoustic signal propagation in conduit networks has been an important area of research in acoustics. One major aspect of analyzing conduit networks as acoustic channels is that a propagating signal suffers frequency dependent attenuation due to thermo-viscous boundary layer effects and the presence of impedance mismatches such as side branches. The signal attenuation due to side branches is strongly influenced by their numbers and dimensions such as diameter and length. Newly developed applications for condition based monitoring of underground conduit networks involve measurement of acoustic signal attenuation through tests in the field. In many cases the exact installation layout of the field measurement location may not be accessible or actual installation may differ from the documented layout. The lack of exact knowledge of numbers and lengths of side branches, therefore, introduces uncertainty in the measurements of attenuation and contributes to the random variable error between measured results and those predicted from theoretical models. There are other random processes in and around conduit networks in the field that also affect the propagation of an acoustic signal. These random processes include but are not limited to the presence of strong temperature and humidity gradients within the conduits, blockages of variable sizes and types, effects of aging such as cracks, bends, sags and holes, ambient noise variations and presence of variable layer of water. It is reasonable to consider that the random processes contributing to the error in the measured attenuation are independent and arbitrarily distributed. The error, contributed by a large number of independent sources of arbitrary probability distributions, is best described by an approximately normal probability distribution in accordance with the central limit theorem. Using an analytical approach to model the attenuating effect of each of the random variable sources can be very complex and
Propagation and excitation of multiple surface waves
NASA Astrophysics Data System (ADS)
Faryad, Muhammad
Surface waves are the solutions of the frequency-domain Maxwell equations at the planar interface of two dissimilar materials. The time-averaged Poynting vector of a surface wave (i) has a significant component parallel to the interface and (ii) decays at sufficiently large distances normal to the interface. If one of the partnering materials is a metal and the other a dielectric, the surface waves are called surface plasmon-polariton (SPP) waves. If both partnering materials are dielectric, with at least one being periodically nonhomogeneous normal to the interface, the surface waves are called Tamm waves; and if that dielectric material is also anisotropic, the surface waves are called Dyakonov--Tamm waves. SPP waves also decays along the direction of propagation, whereas Tamm and Dyakonov--Tamm waves propagate with negligible losses. The propagation and excitation of multiple SPP waves guided by the interface of a metal with a periodically nonhomogeneous sculptured nematic thin film (SNTF), and the interface of a metal with a rugate filter were theoretically investigated. The SNTF is an anisotropic material with a permittivity dyadic that is periodically nonhomogeneous in the thickness direction. A rugate filter is also a periodically nonhomogeneous dielectric material; however, it is an isotropic material. Multiple SPP waves of the same frequency but with different polarization states, phase speeds, attenuation rates, and spatial field profiles were found to be guided by a metal/SNTF interface, a metal/rugate-filter interface, and a metal slab in the SNTF. Multiple Dyakonov--Tamm waves of the same frequency but different polarization states, phase speeds, and spatial field profiles were found to be guided by a structural defect in an SNTF, and by a dielectric slab in an SNTF. The characteristics of multiple SPP and Dyakonov--Tamm waves were established by the investigations on canonical boundary-value problems. The Turbadar-Kretschmann-Raether (TKR) and the
Volcanotectonic earthquakes induced by propagating dikes
NASA Astrophysics Data System (ADS)
Gudmundsson, Agust
2016-04-01
Volcanotectonic earthquakes are of high frequency and mostly generated by slip on faults. During chamber expansion/contraction earthquakes are distribution in the chamber roof. Following magma-chamber rupture and dike injection, however, earthquakes tend to concentrate around the dike and follow its propagation path, resulting in an earthquake swarm characterised by a number of earthquakes of similar magnitudes. I distinguish between two basic processes by which propagating dikes induce earthquakes. One is due to stress concentration in the process zone at the tip of the dike, the other relates to stresses induced in the walls and surrounding rocks on either side of the dike. As to the first process, some earthquakes generated at the dike tip are related to pure extension fracturing as the tip advances and the dike-path forms. Formation of pure extension fractures normally induces non-double couple earthquakes. There is also shear fracturing in the process zone, however, particularly normal faulting, which produces double-couple earthquakes. The second process relates primarily to slip on existing fractures in the host rock induced by the driving pressure of the propagating dike. Such pressures easily reach 5-20 MPa and induce compressive and shear stresses in the adjacent host rock, which already contains numerous fractures (mainly joints) of different attitudes. In piles of lava flows or sedimentary beds the original joints are primarily vertical and horizontal. Similarly, the contacts between the layers/beds are originally horizontal. As the layers/beds become buried, the joints and contacts become gradually tilted so that the joints and contacts become oblique to the horizontal compressive stress induced by a driving pressure of the (vertical) dike. Also, most of the hexagonal (or pentagonal) columnar joints in the lava flows are, from the beginning, oblique to an intrusive sheet of any attitude. Consequently, the joints and contacts function as potential shear
Investigation of Statistical Inference Methodologies Through Scale Model Propagation Experiments
2015-09-30
Investigation of Statistical Inference Methodologies Through Scale Model Propagation Experiments Jason D. Sagers Applied Research Laboratories...statistical inference methodologies for ocean-acoustic problems by investigating and applying statistical methods to data collected from scale -model...experiments over a translationally invariant wedge, (2) to plan and conduct 3D propagation experiments over the Hudson Canyon scale -model bathymetry, and (3
Unified Description of Scattering and Propagation FY15 Annual Report
2015-09-30
random fluctuations in the ocean on both forward and back-propagating acoustic field components. This work is complementary to the continuing investigation...backward propagating average modal intensities. Previously Dozier and Tappert [1] introduced statistical equations for ocean acoustics, but only...and 1736.9 m/s, respectively, consistent with the known properties of the ridge of sand that the ship
Teaching Wave Propagation and the Emergence of Viete's Formula
ERIC Educational Resources Information Center
Cullerne, J. P.; Goekjian, M. C. Dunn
2012-01-01
The well-known result for the frequency of a simple spring-mass system may be combined with elementary concepts like speed = wavelength x frequency to obtain wave propagation speeds for an infinite chain of springs and masses (masses "m" held apart at equilibrium distance "a" by springs of stiffness "gamma"). These propagation speeds are dependent…
Investigation of Propagation in Foliage Using Simulation Techniques
2011-12-01
simulation models provide a rough approximation to radiowave propagation in an actual rainforest environment. Based on the simulated results, the...simulation models provide a rough approximation to radiowave propagation in an actual rainforest environment. Based on the simulated results, the path... Rainforest ...............................2 2. Electrical Properties of a Forest .........................................................3 B. OBJECTIVES OF
Slow light propagation in a ring erbium-doped fiber.
Bencheikh, K; Baldit, E; Briaudeau, S; Monnier, P; Levenson, J A; Mélin, G
2010-12-06
Slow light propagation is demonstrated by implementing Coherent Population Oscillations in a silica fiber doped with erbium ions in a ring surrounding the single mode core. Though only the wings of the mode interact with erbium ions, group velocities around 1360 m/s are obtained without any spatial distortion of the propagating mode.
Light Propagation and Visual Patterns: Preinstruction Learners' Conceptions.
ERIC Educational Resources Information Center
Langley, Dorothy; And Others
1997-01-01
Investigates the conceptions and representations of light propagation, image formation, and sight typical to preinstruction learners (N=139). Findings indicate that preinstructional students display some familiarity with optical systems, light propagation, and illumination patterns and have not developed a consistent descriptive and explanatory…
Effects of nonlinear propagation in ultrasound contrast agent imaging.
Tang, Meng-Xing; Kamiyama, Naohisa; Eckersley, Robert J
2010-03-01
This paper investigates two types of nonlinear propagation and their effects on image intensity and contrast-to-tissue ratio (CTR) in contrast ultrasound images. Previous studies have shown that nonlinear propagation can occur when ultrasound travels through tissue and microbubble clouds, making tissue farther down the acoustic path appear brighter in pulse inversion (PI) images, thus reducing CTR. In this study, the effect of nonlinear propagation through tissue or microbubbles on PI image intensity and CTR are compared at low mechanical index. A combination of simulation and experiment with SonoVue microbubbles were performed using a microbubble dynamics model, a laboratory ultrasound system and a clinical prototype scanner. The results show that, close to the bubble resonance frequency, nonlinear propagation through a bubble cloud of a few centimeter thickness with a modest concentration (1:10000 dilution of SonoVue microbubbles) is much more significant than through tissue-mimicking material. Consequently, CTR in regions distal to the imaging probe is greatly reduced for nonlinear propagation through the bubble cloud, with as much as a 12-dB reduction compared with nonlinear propagation through tissue-mimicking material. Both types of nonlinear propagation cause only a small change in bubble PI signals at the bubble resonance frequency. When the driving frequency increases beyond bubble resonance, nonlinear propagation through bubbles is greatly reduced in absolute values. However because of a greater reduction in nonlinear scattering from bubbles at higher frequencies, the corresponding CTR is much lower than that at bubble resonance frequency.
Graviton propagator from background-independent quantum gravity.
Rovelli, Carlo
2006-10-13
We study the graviton propagator in Euclidean loop quantum gravity. We use spin foam, boundary-amplitude, and group-field-theory techniques. We compute a component of the propagator to first order, under some approximations, obtaining the correct large-distance behavior. This indicates a way for deriving conventional spacetime quantities from a background-independent theory.
Effect of Rim Thickness on Gear Crack Propagation Path.
1996-08-01
Analytical and experimental studies were performed to investigate the effect of rim thickness on gear tooth crack propagation. The goal was to...ANalysis Code) simulated gear tooth crack propagation. The analysis used principles of linear elastic fracture mechanics. Quarter-point, triangular
On the ion acoustic obliquely propagation in magnetized inhomogeneous plasmas
NASA Astrophysics Data System (ADS)
Mowafy, A. E.; El-Shewy, E. K.; Abdelwahed, H. G.
2017-02-01
Inhomogeneous multi-component magnetized plasmas containing inertial ions, nonthermal electrons, and Boltzmannian positrons have been investigated theoretically. Variable coefficients Zakharov Kuznetsov (VZK) equation has been derived in a small amplitude limit. It is found that the propagation directions, positron parameters and magnetic field affected the properties of propagation of positive-negative solitary waves.
Proceedings of the Twelfth NASA Propagation Experimenters Meeting (NAPEX 12)
NASA Technical Reports Server (NTRS)
Davarian, Faramaz (Editor)
1988-01-01
The NASA Propagation Experimenters Meeting was convened on June 9 and 10, 1988. Pilot Field Experiments propagation studies, mobile communication systems, signal fading, communication satellites rain gauge network measurements, atmospheric attenuation studies, optical communication through the atmosphere, and digital beacon receivers were among the topics discussed.
Focality, stochasticity and neuroanatomic propagation in ALS pathogenesis.
Ravits, John
2014-12-01
Amyotrophic lateral sclerosis (ALS) phenotypes such as limb ALS, bulbar ALS, primary lateral sclerosis and primary muscular atrophy are highly heterogeneous and exist on a continuum. These are largely determined by the neuroanatomy of the underlying pathological changes, which can be clinically imputed. Deconstructing these early in disease, before temporal-spatial summation induces complexity, shows that ALS begins focally at a seemingly random location and progresses contiguously. This suggests that focality and anatomic propagation of pathology are significant parts of pathogenesis-disease propagates over space as well as progresses over time. Focality and neuroanatomic propagation can explain how dominant genetic traits manifest with heterogeneous phenotypes, since the anatomic site of outbreak is a prime determinant of phenotype. Focality and neuroanatomic propagation can also explain why frontotemporal dementia (FTD), a neurodegeneration closely related to ALS, has heterogeneous phenotypes, since here too the anatomic site of the outbreak is a prime determinant of phenotype. There are two distinct types of neuroanatomic propagation: contiguous propagation, which occurs side-to-side regionally through the extracellular matrix independent of synaptic connection; and network propagation, which occurs end-to-end dependent on synaptic connections and axonal transmission in connected neuronal networks. The molecular basis of neuroanatomic propagation is unknown, although prion-like misfolding and templating of pathogenic proteins is a compelling unifying hypothesis.
Error Propagation Made Easy--Or at Least Easier
ERIC Educational Resources Information Center
Gardenier, George H.; Gui, Feng; Demas, James N.
2011-01-01
Complex error propagation is reduced to formula and data entry into a Mathcad worksheet or an Excel spreadsheet. The Mathcad routine uses both symbolic calculus analysis and Monte Carlo methods to propagate errors in a formula of up to four variables. Graphical output is used to clarify the contributions to the final error of each of the…
Yield performance of cacao propagated by somatic embryogenesis and grafting
Technology Transfer Automated Retrieval System (TEKTRAN)
Twelve cacao (Theobroma cacao) clones propagated by grafting and somatic embryogenesis and grown on an Ultisol soil were evaluated for five years under intensive management at Corozal, Puerto Rico. Preliminary data showed no significant differences between propagation methods for yield of dry beans ...
Lunar Surface Propagation Modeling and Effects on Communications
NASA Technical Reports Server (NTRS)
Hwu, Shian U.; Upanavage, Matthew; Sham, Catherine C.
2008-01-01
This paper analyzes the lunar terrain effects on the signal propagation of the planned NASA lunar wireless communication and sensor systems. It is observed that the propagation characteristics are significantly affected by the presence of the lunar terrain. The obtained results indicate that the terrain geometry, antenna location, and lunar surface material are important factors determining the propagation characteristics of the lunar wireless communication systems. The path loss can be much more severe than the free space propagation and is greatly affected by the antenna height, operating frequency, and surface material. The analysis results from this paper are important for the lunar communication link margin analysis in determining the limits on the reliable communication range and radio frequency coverage performance at planned lunar base worksites. Key Words lunar, multipath, path loss, propagation, wireless.
Radio propagation through solar and other extraterrestrial ionized media
NASA Technical Reports Server (NTRS)
Smith, E. K.; Edelson, R. E.
1980-01-01
The present S- and X-band communications needs in deep space are addressed to illustrate the aspects which are affected by propagation through extraterrestrial plasmas. The magnitude, critical threshold, and frequency dependence of some eight propagation effects for an S-band propagation path passing within 4 solar radii of the Sun are described. The theory and observation of propagation in extraterrestrial plasmas are discussed and the various plasma states along a near solar propagation path are illustrated. Classical magnetoionic theory (cold anisotropic plasma) is examined for its applicability to the path in question. The characteristics of the plasma states found along the path are summarized and the errors in some of the standard approximations are indicated. Models of extraterrestrial plasmas are included. Modeling the electron density in the solar corona and solar wind, is emphasized but some cursory information on the terrestrial planets plus Jupiters is included.
Numerical simulation of wave propagation in cancellous bone.
Padilla, F; Bossy, E; Haiat, G; Jenson, F; Laugier, P
2006-12-22
Numerical simulation of wave propagation is performed through 31 3D volumes of trabecular bone. These volumes were reconstructed from high synchrotron microtomography experiments and are used as the input geometry in a simulation software developed in our laboratory. The simulation algorithm accounts for propagation into both the saturating fluid and bone but absorption is not taken into account. We show that 3D simulation predicts phenomena observed experimentally in trabecular bones : linear frequency dependence of attenuation, increase of attenuation and speed of sound with the bone volume fraction, negative phase velocity dispersion in most of the specimens, propagation of fast and slow wave depending on the orientation of the trabecular network compared to the direction of propagation of the ultrasound. Moreover, the predicted attenuation is in very close agreement with the experimental one measured on the same specimens. Coupling numerical simulation with real bone architecture therefore provides a powerful tool to investigate the physics of ultrasound propagation in trabecular structures.
Acoustoelastic lamb wave propagation in a homogeneous, isotropic aluminum plate
Gandhi, Navneet; Michaels, Jennifer E.; Lee, Sang Jun
2011-06-23
The effect of stress on Lamb wave propagation is relevant to both nondestructive evaluation and structural health monitoring because of changes in received signals due to both the associated strain and the acoustoelastic effect. A homogeneous plate that is initially isotropic becomes anisotropic under uniaxial stress, and dispersion of propagating waves becomes directionally dependent. The problem is similar to Lamb wave propagation in an anisotropic plate, except the fourth order tensor in the resulting wave equation does not have the same symmetry as that for the unstressed anisotropic plate, and the constitutive equation relating incremental stress to incremental strain is more complicated. Here we consider the theory of acoustoelastic Lamb wave propagation and show how dispersion curves shift anisotropically for an aluminum plate under uniaxial tension. Theoretical predictions of changes in phase velocity as a function of propagation direction are compared to experimental results for a single wave mode.
Laser beam propagation in atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murty, S. S. R.
1979-01-01
The optical effects of atmospheric turbulence on the propagation of low power laser beams are reviewed in this paper. The optical effects are produced by the temperature fluctuations which result in fluctuations of the refractive index of air. The commonly-used models of index-of-refraction fluctuations are presented. Laser beams experience fluctuations of beam size, beam position, and intensity distribution within the beam due to refractive turbulence. Some of the observed effects are qualitatively explained by treating the turbulent atmosphere as a collection of moving gaseous lenses of various sizes. Analytical results and experimental verifications of the variance, covariance and probability distribution of intensity fluctuations in weak turbulence are presented. For stronger turbulence, a saturation of the optical scintillations is observed. The saturation of scintillations involves a progressive break-up of the beam into multiple patches; the beam loses some of its lateral coherence. Heterodyne systems operating in a turbulent atmosphere experience a loss of heterodyne signal due to the destruction of coherence.
Numerical Investigation of Fracture Propagation in Geomaterials
NASA Astrophysics Data System (ADS)
Newell, P.; Borowski, E.; Major, J. R.; Eichhubl, P.
2015-12-01
Fracture in geomaterials is a critical behavior that affects the long-term structural response of geosystems. The processes involving fracture initiation and growth in rocks often span broad time scales and size scales, contributing to the complexity of these problems. To better understand fracture behavior, the authors propose an initial investigation comparing the fracture testing techniques of notched three-point bending (N3PB), short rod (SR), and double torsion (DT) on geomaterials using computational analysis. Linear softening cohesive fracture modeling (LCFM) was applied using ABAQUS to computationally simulate the three experimental set-ups. By applying material properties obtained experimentally, these simulations are intended to predict single-trace fracture growth. The advantages and limitations of the three testing techniques were considered for application to subcritical fracture propagation taking into account the accuracy of constraints, load applications, and modes of fracture. This work is supported as part of the Geomechanics of CO2 Reservoir Seals, a DOE-NETL funded under Award Number DE-FOA-0001037. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Specificity, propagation, and memory of pericentric heterochromatin
Müller-Ott, Katharina; Erdel, Fabian; Matveeva, Anna; Mallm, Jan-Philipp; Rademacher, Anne; Hahn, Matthias; Bauer, Caroline; Zhang, Qin; Kaltofen, Sabine; Schotta, Gunnar; Höfer, Thomas; Rippe, Karsten
2014-01-01
The cell establishes heritable patterns of active and silenced chromatin via interacting factors that set, remove, and read epigenetic marks. To understand how the underlying networks operate, we have dissected transcriptional silencing in pericentric heterochromatin (PCH) of mouse fibroblasts. We assembled a quantitative map for the abundance and interactions of 16 factors related to PCH in living cells and found that stably bound complexes of the histone methyltransferase SUV39H1/2 demarcate the PCH state. From the experimental data, we developed a predictive mathematical model that explains how chromatin-bound SUV39H1/2 complexes act as nucleation sites and propagate a spatially confined PCH domain with elevated histone H3 lysine 9 trimethylation levels via chromatin dynamics. This “nucleation and looping” mechanism is particularly robust toward transient perturbations and stably maintains the PCH state. These features make it an attractive model for establishing functional epigenetic domains throughout the genome based on the localized immobilization of chromatin-modifying enzymes. PMID:25134515
Acoustic propagation under tidally driven, stratified flow.
Finette, Steven; Oba, Roger; Shen, Colin; Evans, Thomas
2007-05-01
Amplitude and phase variability in acoustic fields are simulated within a canonical shelf-break ocean environment using sound speed distributions computed from hydrodynamics. The submesoscale description of the space and time varying environment is physically consistent with tidal forcing of stratified flows over variable bathymetry and includes the generation, evolution and propagation of internal tides and solibores. For selected time periods, two-dimensional acoustic transmission examples are presented for which signal gain degradation is computed between 200 and 500 Hz on vertical arrays positioned both on the shelf and beyond the shelf break. Decorrelation of the field is dominated by the phase contribution and occurs over 2-3 min, with significant recorrelation often noted for selected frequency subbands. Detection range is also determined in this frequency band. Azimuth-time variations in the acoustic field are illustrated for 100 Hz sources by extending the acoustic simulations to three spatial dimensions. The azimuthal and temporal structure of both the depth-averaged transmission loss and temporal correlation of the acoustic fields under different environmental conditions are considered. Depth-averaged transmission loss varies up to 4 dB, depending on a combination of source depth, location relative to the slope and tidally induced volumetric changes in the sound speed distribution.
Mechanisms of large rock avalanche propagation
NASA Astrophysics Data System (ADS)
Bowman, Elisabeth
2014-05-01
Large rock avalanches present a serious mountain hazard to lifelines, infrastructure and lives. They are one of a class of low frequency, high impact events for which there is a still considerable debate over the transport mechanism. The behaviour of large rock avalanches, sometimes referred to as sturzstrom or "stream flow" after Heim, is characterised by a volumetric dependence, so that very large rock avalanches tend to travel with a greater spreading "efficiency" than smaller ones. In this work we propose a mechanism for the volumetric dependence of rock avalanche spread (or runout) in light of the ubiquitous dynamic fragmentation behaviour of brittle solids, Terzaghi's principle of effective stress as used most commonly in soil mechanics, and concepts of momentum transfer. The proposed conceptual model is based on both observations of field scale events, such as made at Elm in Switzerland, Huascaran in Peru and Falling Mountain in New Zealand, and small scale physical model experiments using analogue rock materials which have been conducted at elevated g-level so as to increase stress levels within the experiments. In particular the model aims to explain how momentum transfer between elements within a fragmenting rock avalanche mass may lead to the greater mobility or spreading efficiency that is observed at large scale and may provide insight as to the conditions needed for rock avalanche propagation and arrest.
Formation and Propagation of Tau Oligomeric Seeds
Gerson, Julia E.; Kayed, Rakez
2013-01-01
Tau misfolding and aggregation leads to the formation of neurofibrillary tangles (NFTs), which have long been considered one of the main pathological hallmarks for numerous neurodegenerative diseases known as tauopathies, including Alzheimer’s Disease (AD) and Parkinson’s Disease (PD). However, recent studies completed both in vitro and in vivo suggest that intermediate forms of tau, known as tau oligomers, between the monomeric form and NFTs are the true toxic species in disease and the best targets for anti-tau therapies. However, the exact mechanism by which the spread of pathology occurs is unknown. Evidence suggests that tau oligomers may act as templates for the misfolding of native tau, thereby seeding the spread of the toxic forms of the protein. Recently, researchers have reported the ability of tau oligomers to enter and exit cells, propagating from disease-affected regions to unaffected areas. While the mechanism by which the spreading of misfolded tau occurs has yet to be elucidated, there are a few different models which have been proposed, including cell membrane stress and pore-formation, endocytosis and exocytosis, and non-traditional secretion of protein not enclosed by a membrane. Coming to an understanding of how toxic tau species seed and spread through the brain will be crucial to finding effective treatments for neurodegenerative tauopathies. PMID:23882255
Pressure wave propagation studies for oscillating cascades
NASA Technical Reports Server (NTRS)
Huff, Dennis L.
1992-01-01
The unsteady flowfield around an oscillating cascade of flat plates is studied using a time marching Euler code. Exact solutions based on linear theory serve as model problems to study pressure wave propagation in the numerical solution. The importance of using proper unsteady boundary conditions, grid resolution, and time step is demonstrated. Results show that an approximate non-reflecting boundary condition based on linear theory does a good job of minimizing reflections from the inflow and outflow boundaries and allows the placement of the boundaries to be closer than cases using reflective boundary conditions. Stretching the boundary to dampen the unsteady waves is another way to minimize reflections. Grid clustering near the plates does a better job of capturing the unsteady flowfield than cases using uniform grids as long as the CFL number is less than one for a sufficient portion of the grid. Results for various stagger angles and oscillation frequencies show good agreement with linear theory as long as the grid is properly resolved.
Pressure wave propagation studies for oscillating cascades
NASA Technical Reports Server (NTRS)
Huff, Dennis L.
1992-01-01
The unsteady flow field around an oscillating cascade of flat plates is studied using a time marching Euler code. Exact solutions based on linear theory serve as model problems to study pressure wave propagation in the numerical solution. The importance of using proper unsteady boundary conditions, grid resolution, and time step is demonstrated. Results show that an approximate non-reflecting boundary condition based on linear theory does a good job of minimizing reflections from the inflow and outflow boundaries and allows the placement of the boundaries to be closer than cases using reflective boundary conditions. Stretching the boundary to dampen the unsteady waves is another way to minimize reflections. Grid clustering near the plates does a better job of capturing the unsteady flow field than cases using uniform grids as long as the CFL number is less than one for a sufficient portion of the grid. Results for various stagger angles and oscillation frequencies show good agreement with linear theory as long as the grid is properly resolved.
Effect of Resolution on Propagating Detonation Wave
Menikoff, Ralph
2014-07-10
Simulations of the cylinder test are used to illustrate the effect of mesh resolution on a propagating detonation wave. For this study we use the xRage code with the SURF burn model for PBX 9501. The adaptive mesh capability of xRage is used to vary the resolution of the reaction zone. We focus on two key properties: the detonation speed and the cylinder wall velocity. The latter is related to the release isentrope behind the detonation wave. As the reaction zone is refined (2 to 15 cells for cell size of 62 to 8μm), both the detonation speed and final wall velocity change by a small amount; less than 1 per cent. The detonation speed decreases with coarser resolution. Even when the reaction zone is grossly under-resolved (cell size twice the reaction-zone width of the burn model) the wall velocity is within a per cent and the detonation speed is low by only 2 per cent.
Synchronization and Propagation of Global Sleep Spindles
de Souza, Rafael Toledo Fernandes; Gerhardt, Günther Johannes Lewczuk; Schönwald, Suzana Veiga; Rybarczyk-Filho, José Luiz; Lemke, Ney
2016-01-01
Sleep spindles occur thousands of times during normal sleep and can be easily detected by visual inspection of EEG signals. These characteristics make spindles one of the most studied EEG structures in mammalian sleep. In this work we considered global spindles, which are spindles that are observed simultaneously in all EEG channels. We propose a methodology that investigates both the signal envelope and phase/frequency of each global spindle. By analysing the global spindle phase we showed that 90% of spindles synchronize with an average latency time of 0.1 s. We also measured the frequency modulation (chirp) of global spindles and found that global spindle chirp and synchronization are not correlated. By investigating the signal envelopes and implementing a homogeneous and isotropic propagation model, we could estimate both the signal origin and velocity in global spindles. Our results indicate that this simple and non-invasive approach could determine with reasonable precision the spindle origin, and allowed us to estimate a signal speed of 0.12 m/s. Finally, we consider whether synchronization might be useful as a non-invasive diagnostic tool. PMID:26963102
Simulation of MAD Cow Disease Propagation
NASA Astrophysics Data System (ADS)
Magdoń-Maksymowicz, M. S.; Maksymowicz, A. Z.; Gołdasz, J.
Computer simulation of dynamic of BSE disease is presented. Both vertical (to baby) and horizontal (to neighbor) mechanisms of the disease spread are considered. The game takes place on a two-dimensional square lattice Nx×Ny = 1000×1000 with initial population randomly distributed on the net. The disease may be introduced either with the initial population or by a spontaneous development of BSE in an item, at a small frequency. Main results show a critical probability of the BSE transmission above which the disease is present in the population. This value is vulnerable to possible spatial clustering of the population and it also depends on the mechanism responsible for the disease onset, evolution and propagation. A threshold birth rate below which the population is extinct is seen. Above this threshold the population is disease free at equilibrium until another birth rate value is reached when the disease is present in population. For typical model parameters used for the simulation, which may correspond to the mad cow disease, we are close to the BSE-free case.
Propagation phasor approach for holographic image reconstruction
Luo, Wei; Zhang, Yibo; Göröcs, Zoltán; Feizi, Alborz; Ozcan, Aydogan
2016-01-01
To achieve high-resolution and wide field-of-view, digital holographic imaging techniques need to tackle two major challenges: phase recovery and spatial undersampling. Previously, these challenges were separately addressed using phase retrieval and pixel super-resolution algorithms, which utilize the diversity of different imaging parameters. Although existing holographic imaging methods can achieve large space-bandwidth-products by performing pixel super-resolution and phase retrieval sequentially, they require large amounts of data, which might be a limitation in high-speed or cost-effective imaging applications. Here we report a propagation phasor approach, which for the first time combines phase retrieval and pixel super-resolution into a unified mathematical framework and enables the synthesis of new holographic image reconstruction methods with significantly improved data efficiency. In this approach, twin image and spatial aliasing signals, along with other digital artifacts, are interpreted as noise terms that are modulated by phasors that analytically depend on the lateral displacement between hologram and sensor planes, sample-to-sensor distance, wavelength, and the illumination angle. Compared to previous holographic reconstruction techniques, this new framework results in five- to seven-fold reduced number of raw measurements, while still achieving a competitive resolution and space-bandwidth-product. We also demonstrated the success of this approach by imaging biological specimens including Papanicolaou and blood smears. PMID:26964671
Back propagation parameter analysis on multiprocessors
Cerf, G.; Mokry, R.; Weintraub, J.
1988-09-01
In order to develop systems of artificial neural networks which can be scaled up to perform practical tasks such as pattern recognition or speech processing, the use of powerful computing tools is essential. Multiprocessors are becoming increasingly popular in the simulation and study of large networks, as the inherent parallelism of many neural architectures and learning algorithms lends itself quite naturally to implementation on concurrent processors. In this study, a multiprocessor system based on the Inmos transputer has been used to examine the stability and convergence rates of the back propagation algorithm as a function of changes in parameters such as activation values, number of hidden units, learning rate, momentum, and initial weight and bias configurations. The Victor V32 is a prototype low-cost message-passing multiprocessor system, designed and implemented by the Victor project in the Microsystems and VLSI group at the IBM T.J. Watson Research Center. A sample topology for the system is 32 nodes in a fixed 4 x 8 mesh. A host processor interfaced to a PC AT and connected to one of the corners of the mesh provides screen and disc I/O. Each of the 32 nodes consists of an INMOS T414 transputer and 4 Megabytes of local memory. Four high-speed (20 Mbits/sec) serial links provide communication among the nodes.
Premixed turbulent flame propagation in microgravity
NASA Technical Reports Server (NTRS)
Menon, S.; Jagoda, J.; Sujith, R.
1995-01-01
To reduce pollutant formation there is, at present, an increased interest in employing premixed fuel/air mixture in combustion devices. It is well known that greater control over local temperature can be achieved with premixed flames and with lean premixed mixtures, significant reduction of pollutants such as NO(x) can be achieved. However, an issue that is still unresolved is the predictability of the flame propagation speed in turbulent premixed mixtures, especially in lean mixtures. Although substantial progress has been made in recent years, there is still no direct verification that flame speeds in turbulent premixed flows are highly predictable in complex flow fields found in realistic combustors. One of the problems associated with experimental verification is the difficulty in obtaining access to all scales of motion in typical high Reynolds number flows, since, such flows contain scales of motion that range from the size of the device to the smallest Kolmogorov scale. The overall objective of this study is to characterize the behavior of turbulent premixed flames at reasonable high Reynolds number, Re(sub L). Of particular interest here is the thin flame limit where the laminar flame thickness is much smaller than the Kolmogorov scale. Thin flames occur in many practical combustion devices and will be numerically studied using a recently developed new formulation that is briefly described.
Uncertainty Propagation for Terrestrial Mobile Laser Scanner
NASA Astrophysics Data System (ADS)
Mezian, c.; Vallet, Bruno; Soheilian, Bahman; Paparoditis, Nicolas
2016-06-01
Laser scanners are used more and more in mobile mapping systems. They provide 3D point clouds that are used for object reconstruction and registration of the system. For both of those applications, uncertainty analysis of 3D points is of great interest but rarely investigated in the literature. In this paper we present a complete pipeline that takes into account all the sources of uncertainties and allows to compute a covariance matrix per 3D point. The sources of uncertainties are laser scanner, calibration of the scanner in relation to the vehicle and direct georeferencing system. We suppose that all the uncertainties follow the Gaussian law. The variances of the laser scanner measurements (two angles and one distance) are usually evaluated by the constructors. This is also the case for integrated direct georeferencing devices. Residuals of the calibration process were used to estimate the covariance matrix of the 6D transformation between scanner laser and the vehicle system. Knowing the variances of all sources of uncertainties, we applied uncertainty propagation technique to compute the variance-covariance matrix of every obtained 3D point. Such an uncertainty analysis enables to estimate the impact of different laser scanners and georeferencing devices on the quality of obtained 3D points. The obtained uncertainty values were illustrated using error ellipsoids on different datasets.
Light propagation through black-hole lattices
NASA Astrophysics Data System (ADS)
Bentivegna, Eloisa; Korzyński, Mikołaj; Hinder, Ian; Gerlicher, Daniel
2017-03-01
The apparent properties of distant objects encode information about the way the light they emit propagates to an observer, and therefore about the curvature of the underlying spacetime. Measuring the relationship between the redshift z and the luminosity distance DL of a standard candle, for example, yields information on the Universe's matter content. In practice, however, in order to decode this information the observer needs to make an assumption about the functional form of the DL(z) relation; in other words, a cosmological model needs to be assumed. In this work, we use numerical-relativity simulations, equipped with a new ray-tracing module, to numerically obtain this relation for a few black-hole-lattice cosmologies and compare it to the well-known Friedmann-Lema{ȋtre-Robertson-Walker case, as well as to other relevant cosmologies and to the Empty-Beam Approximation. We find that the latter provides the best estimate of the luminosity distance and formulate a simple argument to account for this agreement. We also find that a Friedmann-Lema{ȋtre-Robertson-Walker model can reproduce this observable exactly, as long as a time-dependent cosmological constant is included in the fit. Finally, the dependence of these results on the lattice mass-to-spacing ratio μ is discussed: we discover that, unlike the expansion rate, the DL(z) relation in a black-hole lattice does not tend to that measured in the corresponding continuum spacetime as 0μ → .
Transionospheric VLF Propagation as an Ionospheric Diagnostic
NASA Astrophysics Data System (ADS)
Worthington, E. R.; Cohen, M.
2015-12-01
Very Low Frequency (VLF, 3-30 kHz) radio waves emitted from ground-based sources, such as VLF transmitters or lightning strokes, are attenuated as they travel through the D-region of the ionosphere, making measurements taken of the VLF energy that has escaped this region useful in estimating the electron density. It has been also been suggested that F-region irregularities may contribute additional attenuation to the VLF signal. Additionally, energy at these frequencies that escapes the ionosphere altogether strongly impacts the radiation belts, driving electron precipitation via whistler-electron gyroresonance, and contributes to the formation of the slot region. We present an analysis of measurements captured by the DEMETER satellite over VLF transmitters. During its six-year mission, DEMETER completed hundreds of passes above well-characterized VLF transmitters while recording electric and magnetic field strengths. Statistically significant (daytime and nighttime) seasonal variations were observed in this data set. We compare observations with estimates obtained using a sophisticated full wave model of trans-ionospheric propagation, and discuss the viability of the International Reference Ionosphere in correctly predicting transionospheric VLF energy.
Features of light propagation in chiral media
Aksenova, E. V. Kryukov, E. V. Romanov, V. P.
2007-12-15
Light propagation in uniaxial chiral liquid crystals with large pitch was studied. Vicinities of turning points were analyzed, and the effect of extraordinary wave transmission through bandgap layers was considered. It was shown that the description of wave transmission through the forbidden zone in the general case requires taking into account the existence of four singular points, two of which are responsible for the interaction of extraordinary rays and two points are responsible for the interaction of ordinary and extraordinary rays. Ray transmission in the case of wide bandgap layers was analyzed, when regions of applicability of the Wentzel-Kramers-Brillouin (WKB) approximation take place between singular points. The case of narrow bandgap layers, where singular points merge, was studied in detail. It was shown that the effect of ray transmission through such a zone and the above-barrier reflection effect is equivalent to the tunneling effect for the parabolic potential barrier. Angular dependences of the intensity of rays subject to internal refraction and transmitted through the bandgap layer were calculated. It was shown that the tunneling effect can be experimentally observed.
Solar Cosmic Ray Acceleration and Propagation
NASA Astrophysics Data System (ADS)
Podgorny, I. M.; Podgorny, A. I.
2016-05-01
The GOES data for emission of flare protons with the energies of 10 - 100 MeV are analyzed. Proton fluxes of ~1032 accelerated particles take place at the current sheet decay. Proton acceleration in a flare occurs along a singular line of the current sheet by the Lorentz electric field, as in the pinch gas discharge. The duration of proton flux measured on the Earth orbit is by 2 - 3 orders of magnitude longer than the duration of flares. The high energy proton flux from the flares that appear on the western part of the solar disk arrives to Earth with the time of flight. These particles propagate along magnetic lines of the Archimedes spiral connecting the flare with the Earth. Protons from the flare on the eastern part of the solar disk begin to register with a delay of several hours. Such particles cannot get on the magnetic field line connecting the flare with the Earth. These protons reach the Earth, moving across the interplanetary magnetic field. The particles captured by the magnetic field in the solar wind are transported with solar wind and due to diffusion across the magnetic field. The patterns of solar cosmic rays generation demonstrated in this paper are not always observed in the small ('1 cm-2 s-1 ster-1) proton events.
Myxoma virus: propagation, purification, quantification, and storage.
Smallwood, Sherin E; Rahman, Masmudur M; Smith, Dorothy W; McFadden, Grant
2010-05-01
Myxoma virus (MYXV) is a member of the Poxviridae family and prototype for the genus Leporipoxvirus. It is pathogenic only for European rabbits, in which it causes the lethal disease myxomatosis, and two North American species, in which it causes a less severe disease. MYXV replicates exclusively in the cytoplasm of the host cell. Although not infectious in humans, its genome encodes proteins that can interfere with or modulate host defense mechanisms; it is able to productively infect a number of human cancer cell lines, but not normal human cells, and has also been shown to increase survival time in mouse models of human glioma. These characteristics suggest that MYXV could be a viable therapeutic agent, e.g., in anti-inflammatory or anti-immune therapy, or as an oncolytic agent. MYXV is also an excellent model for poxvirus biology, pathogenesis, and host tropism studies. It is easily propagated in a number of cell lines, including adherent cells and suspension cultures, and minimal purification is required to provide a stock for in vivo and in vitro studies.
Fatigue crack propagation analysis of plaque rupture.
Pei, Xuan; Wu, Baijian; Li, Zhi-Yong
2013-10-01
Rupture of atheromatous plaque is the major cause of stroke or heart attack. Considering that the cardiovascular system is a classic fatigue environment, plaque rupture was treated as a chronic fatigue crack growth process in this study. Fracture mechanics theory was introduced to describe the stress status at the crack tip and Paris' law was used to calculate the crack growth rate. The effect of anatomical variation of an idealized plaque cross-section model was investigated. The crack initiation was considered to be either at the maximum circumferential stress location or at any other possible locations around the lumen. Although the crack automatically initialized at the maximum circumferential stress location usually propagated faster than others, it was not necessarily the most critical location where the fatigue life reached its minimum. We found that the fatigue life was minimum for cracks initialized in the following three regions: the midcap zone, the shoulder zone, and the backside zone. The anatomical variation has a significant influence on the fatigue life. Either a decrease in cap thickness or an increase in lipid pool size resulted in a significant decrease in fatigue life. Comparing to the previously used stress analysis, this fatigue model provides some possible explanations of plaque rupture at a low stress level in a pulsatile cardiovascular environment, and the method proposed here may be useful for further investigation of the mechanism of plaque rupture based on in vivo patient data.
Back propagation neural networks for facial verification
Garnett, A.E.; Solheim, I.; Payne, T.; Castain, R.H.
1992-10-01
We conducted a test to determine the aptitude of neural networks to recognize human faces. The pictures we collected of 511 subjects captured both profiles and many natural expressions. Some of the subjects were wearing glasses, sunglasses, or hats in some of the pictures. The images were compressed by a factor of 100 and converted into image vectors of 1400 pixels. The image vectors were fed into a back propagation neural network with one hidden layer and one output node. The networks were trained to recognize one target person and to reject all other persons. Neural networks for 37 target subjects were trained with 8 different training sets that consisted of different subsets of the data. The networks were then tested on the rest of the data, which consisted of 7000 or more unseen pictures. Results indicate that a false acceptance rate of less than 1 percent can be obtained, and a false rejection rate of 2 percent can be obtained when certain restrictions are followed.
Cosmic ray propagation in interplanetary space
NASA Technical Reports Server (NTRS)
Voelk, H. J.
1975-01-01
The validity of the test-particle picture, the approximation of static fields, and the spatial-diffusion approximation are discussed in a general way before specific technical assumptions are introduced. It is argued that the spatial-diffusion equation for the intensity per unit energy has a much wider range of applicability than the kinetic (Fokker-Planck) equation it is derived from. This gives strong weight to the phenomenological propagation theory. The general success (and possible failure at small energies) of the phenomenological theory for the modulation of galactic cosmic rays and solar events is described. Apparent effects such as the 'free boundary' are given disproportionate weight since they establish the connection with the detailed plasma physics of the solar wind. Greatest attention is paid to the pitch-angle diffusion theory. A general theory is presented which removes the well-known secularities of the quasi-linear approximation. The possible breakdown of any pitch-angle diffusion theory at very small energies is perhaps connected with the observed 'turn up' of the spectrum at low energies. A first attempt to derive the spatial dependence of the diffusion coefficient in the solar cavity, using such a divergence free scattering theory, is described and compared with recent observations out to 5 AU.
Propagation of Axially Symmetric Detonation Waves
Druce, R L; Roeske, F; Souers, P C; Tarver, C M; Chow, C T S; Lee, R S; McGuire, E M; Overturf, G E; Vitello, P A
2002-06-26
We have studied the non-ideal propagation of detonation waves in LX-10 and in the insensitive explosive TATB. Explosively-driven, 5.8-mm-diameter, 0.125-mm-thick aluminum flyer plates were used to initiate 38-mm-diameter, hemispherical samples of LX-10 pressed to a density of 1.86 g/cm{sup 3} and of TATB at a density of 1.80 g/cm{sup 3}. The TATB powder was a grade called ultrafine (UFTATB), having an arithmetic mean particle diameter of about 8-10 {micro}m and a specific surface area of about 4.5 m{sup 2}/g. Using PMMA as a transducer, output pressure was measured at 5 discrete points on the booster using a Fabry-Perot velocimeter. Breakout time was measured on a line across the booster with a streak camera. Each of the experimental geometries was calculated using the Ignition and Growth Reactive Flow Model, the JWL++ Model and the Programmed Burn Model. Boosters at both ambient and cold (-20 C and -54 C) temperatures have been experimentally and computationally studied. A comparison of experimental and modeling results is presented.
Synchronization with propagation - The functional differential equations
NASA Astrophysics Data System (ADS)
Rǎsvan, Vladimir
2016-06-01
The structure represented by one or several oscillators couple to a one-dimensional transmission environment (e.g. a vibrating string in the mechanical case or a lossless transmission line in the electrical case) turned to be attractive for the research in the field of complex structures and/or complex behavior. This is due to the fact that such a structure represents some generalization of various interconnection modes with lumped parameters for the oscillators. On the other hand the lossless and distortionless propagation along transmission lines has generated several research in electrical, thermal, hydro and control engineering leading to the association of some functional differential equations to the basic initial boundary value problems. The present research is performed at the crossroad of the aforementioned directions. We shall associate to the starting models some functional differential equations - in most cases of neutral type - and make use of the general theorems for existence and stability of forced oscillations for functional differential equations. The challenges introduced by the analyzed problems for the general theory are emphasized, together with the implication of the results for various applications.
Error propagation in energetic carrying capacity models
Pearse, Aaron T.; Stafford, Joshua D.
2014-01-01
Conservation objectives derived from carrying capacity models have been used to inform management of landscapes for wildlife populations. Energetic carrying capacity models are particularly useful in conservation planning for wildlife; these models use estimates of food abundance and energetic requirements of wildlife to target conservation actions. We provide a general method for incorporating a foraging threshold (i.e., density of food at which foraging becomes unprofitable) when estimating food availability with energetic carrying capacity models. We use a hypothetical example to describe how past methods for adjustment of foraging thresholds biased results of energetic carrying capacity models in certain instances. Adjusting foraging thresholds at the patch level of the species of interest provides results consistent with ecological foraging theory. Presentation of two case studies suggest variation in bias which, in certain instances, created large errors in conservation objectives and may have led to inefficient allocation of limited resources. Our results also illustrate how small errors or biases in application of input parameters, when extrapolated to large spatial extents, propagate errors in conservation planning and can have negative implications for target populations.
Wave propagation in axially moving periodic strings
NASA Astrophysics Data System (ADS)
Sorokin, Vladislav S.; Thomsen, Jon Juel
2017-04-01
The paper deals with analytically studying transverse waves propagation in an axially moving string with periodically modulated cross section. The structure effectively models various relevant technological systems, e.g. belts, thread lines, band saws, etc., and, in particular, roller chain drives for diesel engines by capturing both their spatial periodicity and axial motion. The Method of Varying Amplitudes is employed in the analysis. It is shown that the compound wave traveling in the axially moving periodic string comprises many components with different frequencies and wavenumbers. This is in contrast to non-moving periodic structures, for which all components of the corresponding compound wave feature the same frequency. Due to this "multi-frequency" character of the wave motion, the conventional notion of frequency band-gaps appears to be not applicable for the moving periodic strings. Thus, for such structures, by frequency band-gaps it is proposed to understand frequency ranges in which the primary component of the compound wave attenuates. Such frequency band-gaps can be present for a moving periodic string, but only if its axial velocity is lower than the transverse wave speed, and, the higher the axial velocity, the narrower the frequency band-gaps. The revealed effects could be of potential importance for applications, e.g. they indicate that due to spatial inhomogeneity, oscillations of axially moving periodic chains always involve a multitude of frequencies.
NASA Technical Reports Server (NTRS)
Wu, S. T.
1974-01-01
The responses of the solar atmosphere due to an outward propagation shock are examined by employing the Lax-Wendroff method to solve the set of nonlinear partial differential equations in the model of the solar atmosphere. It is found that this theoretical model can be used to explain the solar phenomena of surge and spray. A criterion to discriminate the surge and spray is established and detailed information concerning the density, velocity, and temperature distribution with respect to the height and time is presented. The complete computer program is also included.
Tilt anisoplanatism in extended turbulence propagation
NASA Astrophysics Data System (ADS)
Magee, Eric P.; Whiteley, Matthew R.; Das, Shashikala T.; Welsh, Byron M.
2003-04-01
The use of high-energy laser (HEL) weapon systems in tactical air-to-ground target engagements offers great promise for revolutionizing the USAF's war-fighting capabilities. Laser directed-energy systems will enable ultra-precision strike with minimal collateral damage and significant stand-off range for the aerial platform. The tactical directed energy application differs in many crucial ways from the conventional approach used in missile defense. Tactical missions occur at much lower altitudes and involve look-down to low-contrast ground targets instead of a high-contrast boosting missile. At these lower altitudes, the strength of atmospheric turbulence is greatly enhanced. Although the target slant ranges are much shorter, tactical missions may still involve moderate values of the Rytov number (0.1-0.5), and small isoplanatic angles compared to the diffraction angle. With increased density of air in the propagation path, and the potential for slow-moving or stationary ground targets, HEL-induced thermal blooming will certainly be a concern. In order to minimize the errors induced by tracking through thermal blooming, offset aimpoint tracking can be used. However, this will result in significant tilt anisoplanatism, thus degrading beam stabilization on target. In this paper we investigate the effects of extended turbulence on tracking (or tilt) anisoplanatism using theory and wave optics simulations. The simulations show good agreement with geometric optics predictions at angles larger than about 5 micro-radians (asymptotic regime) while at smaller angles the agreement is poor. We present a theoretical basis for this observation.
Sythesis of MCMC and Belief Propagation
Ahn, Sungsoo; Chertkov, Michael; Shin, Jinwoo
2016-05-27
Markov Chain Monte Carlo (MCMC) and Belief Propagation (BP) are the most popular algorithms for computational inference in Graphical Models (GM). In principle, MCMC is an exact probabilistic method which, however, often suffers from exponentially slow mixing. In contrast, BP is a deterministic method, which is typically fast, empirically very successful, however in general lacking control of accuracy over loopy graphs. In this paper, we introduce MCMC algorithms correcting the approximation error of BP, i.e., we provide a way to compensate for BP errors via a consecutive BP-aware MCMC. Our framework is based on the Loop Calculus (LC) approach which allows to express the BP error as a sum of weighted generalized loops. Although the full series is computationally intractable, it is known that a truncated series, summing up all 2-regular loops, is computable in polynomial-time for planar pair-wise binary GMs and it also provides a highly accurate approximation empirically. Motivated by this, we first propose a polynomial-time approximation MCMC scheme for the truncated series of general (non-planar) pair-wise binary models. Our main idea here is to use the Worm algorithm, known to provide fast mixing in other (related) problems, and then design an appropriate rejection scheme to sample 2-regular loops. Furthermore, we also design an efficient rejection-free MCMC scheme for approximating the full series. The main novelty underlying our design is in utilizing the concept of cycle basis, which provides an efficient decomposition of the generalized loops. In essence, the proposed MCMC schemes run on transformed GM built upon the non-trivial BP solution, and our experiments show that this synthesis of BP and MCMC outperforms both direct MCMC and bare BP schemes.
Algorithms for propagating uncertainty across heterogeneous domains
Cho, Heyrim; Yang, Xiu; Venturi, D.; Karniadakis, George E.
2015-12-30
We address an important research area in stochastic multi-scale modeling, namely the propagation of uncertainty across heterogeneous domains characterized by partially correlated processes with vastly different correlation lengths. This class of problems arise very often when computing stochastic PDEs and particle models with stochastic/stochastic domain interaction but also with stochastic/deterministic coupling. The domains may be fully embedded, adjacent or partially overlapping. The fundamental open question we address is the construction of proper transmission boundary conditions that preserve global statistical properties of the solution across different subdomains. Often, the codes that model different parts of the domains are black-box and hence a domain decomposition technique is required. No rigorous theory or even effective empirical algorithms have yet been developed for this purpose, although interfaces defined in terms of functionals of random fields (e.g., multi-point cumulants) can overcome the computationally prohibitive problem of preserving sample-path continuity across domains. The key idea of the different methods we propose relies on combining local reduced-order representations of random fields with multi-level domain decomposition. Specifically, we propose two new algorithms: The first one enforces the continuity of the conditional mean and variance of the solution across adjacent subdomains by using Schwarz iterations. The second algorithm is based on PDE-constrained multi-objective optimization, and it allows us to set more general interface conditions. The effectiveness of these new algorithms is demonstrated in numerical examples involving elliptic problems with random diffusion coefficients, stochastically advected scalar fields, and nonlinear advection-reaction problems with random reaction rates.
Wave propagation in predator-prey systems
NASA Astrophysics Data System (ADS)
Fu, Sheng-Chen; Tsai, Je-Chiang
2015-12-01
In this paper, we study a class of predator-prey systems of reaction-diffusion type. Specifically, we are interested in the dynamical behaviour for the solution with the initial distribution where the prey species is at the level of the carrying capacity, and the density of the predator species has compact support, or exponentially small tails near x=+/- ∞ . Numerical evidence suggests that this will lead to the formation of a pair of diverging waves propagating outwards from the initial zone. Motivated by this phenomenon, we establish the existence of a family of travelling waves with the minimum speed. Unlike the previous studies, we do not use the shooting argument to show this. Instead, we apply an iteration process based on Berestycki et al 2005 (Math Comput. Modelling 50 1385-93) to construct a set of super/sub-solutions. Since the underlying system does not enjoy the comparison principle, such a set of super/sub-solutions is not based on travelling waves, and in fact the super/sub-solutions depend on each other. With the aid of the set of super/sub-solutions, we can construct the solution of the truncated problem on the finite interval, which, via the limiting argument, can in turn generate the wave solution. There are several advantages to this approach. First, it can remove the technical assumptions on the diffusivities of the species in the existing literature. Second, this approach is of PDE type, and hence it can shed some light on the spreading phenomenon indicated by numerical simulation. In fact, we can compute the spreading speed of the predator species for a class of biologically acceptable initial distributions. Third, this approach might be applied to the study of waves in non-cooperative systems (i.e. a system without a comparison principle).
Torsional wave propagation in solar tornadoes
NASA Astrophysics Data System (ADS)
Vasheghani Farahani, S.; Ghanbari, E.; Ghaffari, G.; Safari, H.
2017-02-01
Aims: We investigate the propagation of torsional waves in coronal structures together with their collimation effects in the context of magnetohydrodynamic (MHD) theory. The interplay of the equilibrium twist and rotation of the structure, e.g. jet or tornado, together with the density contrast of its internal and external media is studied to shed light on the nature of torsional waves. Methods: We consider a rotating magnetic cylinder embedded in a plasma with a straight magnetic field. This resembles a solar tornado. In order to express the dispersion relations and phase speeds of the axisymmetric magnetohydrodynamic waves, the second-order thin flux tube approximation is implemented for the internal medium and the ideal MHD equations are implemented for the external medium. Results: The explicit expressions for the phase speed of the torsional wave show the modification of the torsional wave speed due to the equilibrium twist, rotation, and density contrast of the tornado. The speeds could be either sub-Alfvénic or ultra-Alfvénic depending on whether the equilibrium twist or rotation is dominant. The equilibrium twist increases the phase speed while the equilibrium rotation decreases it. The good agreement between the explicit versions for the phase speed and that obtained numerically proves adequate for the robustness of the model and method. The density ratio of the internal and external media also play a significant role in the speed and dispersion. Conclusions: The dispersion of the torsional wave is an indication of the compressibility of the oscillations. When the cylinder is rotating or twisted, in contrast to when it only possesses a straight magnetic field, the torsional wave is a collective mode. In this case its phase speed is determined by the Alfvén waves inside and outside the tornado.
Regional Wave Propagation in Southeastern United States
NASA Astrophysics Data System (ADS)
Jemberie, A. L.; Langston, C. A.
2003-12-01
Broad band seismograms from the April 29, 2003, M4.6 Fort Payne, Alabama earthquake are analyzed to infer mechanisms of crustal wave propagation, crust and upper mantle velocity structure in southeastern United States, and source parameters of the event. In particular, we are interested in producing deterministic models of the distance attenuation of earthquake ground motions through computation of synthetic seismograms. The method first requires constraining the source parameters of an earthquake and then modeling the amplitude and times of broadband arrivals within the waveforms to infer appropriate layered earth models. A first look at seismograms recorded by stations outside the Mississippi Embayment (ME) show clear body phases such P, sP, Pnl, Sn and Lg. The ME signals are qualitatively different from others because they have longer durations and large surface waves. A straightforward interpretation of P wave arrival times shows a typical upper mantle velocity of 8.18 km/s. However, there is evidence of significantly higher P phase velocities at epicentral distances between 400 and 600km, that may be caused by a high velocity upper mantle anomaly; triplication of P-waves is seen in these seismograms. The arrival time differences between regional P and the depth phase sP at different stations are used to constrain the depth of the earthquake. The source depth lies between 9.5 km and 13km which is somewhat more shallow than the network location that was constrained to 15km depth. The Fort Payne earthquake is the largest earthquake to have occurred within the Eastern Tennessee Seismic Zone.