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Sample records for opposed jet extinction

  1. Opposed Jet Burner Extinction Limits: Simple Mixed Hydrocarbon Scramjet Fuels vs Air

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Vaden, Sarah N.; Wilson, Lloyd G.

    2007-01-01

    Opposed Jet Burner tools have been used extensively by the authors to measure Flame Strength (FS) of laminar non-premixed H2 air and simple hydrocarbon (HC) air counterflow diffusion flames at 1-atm. FS represents a strain-induced extinction limit based on air jet velocity. This paper follows AIAA-2006-5223, and provides new HC air FSs for global testing of chemical kinetics, and for characterizing idealized flameholding potentials during early scramjet-like combustion. Previous FS data included six HCs, pure and N2-diluted; and three HC-diluted H2 fuels, where FS decayed very nonlinearly as HC was added to H2, due to H-atom scavenging. This study presents FSs on mixtures of (candidate surrogate) HCs, some with very high FS ethylene. Included are four binary gaseous systems at 300 K, and a hot ternary system at approx. 600 K. The binaries are methane + ethylene, ethane + ethylene, methane + ethane, and methane + propylene. The first three also form two ternary systems. The hot ternary includes both 10.8 and 21.3 mole % vaporized n-heptane and full ranges of methane + ethylene. Normalized FS data provide accurate means of (1) validating, globally, chemical kinetics for extinction of non-premixed flames, and (2) estimating (scaling by HC) the loss of incipient flameholding in scramjet combustors. The n-heptane is part of a proposed baseline simulant (10 mole % with 30% methane + 60% ethylene) that mimics the ignition of endothermically cracked JP-7 like kerosene fuel, as suggested by Colket and Spadaccini in 2001 in their shock tube Scramjet Fuels Autoignition Study. Presently, we use FS to gauge idealized flameholding, and define HC surrogates. First, FS was characterized for hot nheptane + methane + ethylene; then a hot 36 mole % methane + 64% ethylene surrogate was defined that mimics FS of the baseline simulant system. A similar hot ethane + ethylene surrogate can also be defined, but it has lower vapor pressure at 300 K, and thus exhibits reduced gaseous

  2. Unsteady Extinction of Opposed Jet Ethylene/Methane HIFiRE Surrogate Fuel Mixtures vs Air

    NASA Technical Reports Server (NTRS)

    Vaden, Sarah N.; Debes, Rachel L.; Lash, E. Lara; Burk, Rachel S.; Boyd, C. Merritt; Wilson, Lloyd G.; Pellett, Gerald L.

    2009-01-01

    A unique idealized study of the subject fuel vs. air systems was conducted using an Oscillatory-input Opposed Jet Burner (OOJB) system and a newly refined analysis. Extensive dynamic-extinction measurements were obtained on unanchored (free-floating) laminar Counter Flow Diffusion Flames (CFDFs) at 1-atm, stabilized by steady input velocities (e.g., U(sub air)) and perturbed by superimposed in-phase sinusoidal velocity inputs at fuel and air nozzle exits. Ethylene (C2H4) and methane (CH4), and intermediate 64/36 and 15/85 molar percent mixtures were studied. The latter gaseous surrogates were chosen earlier to mimic ignition and respective steady Flame Strengths (FS = U(sub air)) of vaporized and cracked, and un-cracked, JP-7 "like" kerosene for a Hypersonic International Flight Research Experimentation (HIFiRE) scramjet. For steady idealized flameholding, the 100% C2H4 flame is respectively approx. 1.3 and approx.2.7 times stronger than a 64/36 mix and CH4; but is still 12.0 times weaker than a 100% H2-air flame. Limited Hot-Wire (HW) measurements of velocity oscillations at convergent-nozzle exits, and more extensive Probe Microphone (PM) measurements of acoustic pressures, were used to normalize Dynamic FSs, which decayed linearly with pk/pk U(sub air) (velocity magnitude, HW), and also pk/pk P (pressure magnitude, PM). Thus Dynamic Flame Weakening (DFW) is defined as % decrease in FS per Pascal of pk/pk P oscillation, namely, DFW = -100 d(U(sub air)/U(sub air),0Hz)/d(pkpk P). Key findings are: (1) Ethylene flames are uniquely strong and resilient to extinction by oscillating inflows below 150 Hz; (2) Methane flames are uniquely weak; (3) Ethylene / methane surrogate flames are disproportionately strong with respect to ethylene content; and (4) Flame weakening is consistent with limited published results on forced unsteady CFDFs. Thus from 0 to approx. 10 Hz and slightly higher, lagging diffusive responses of key species led to progressive phase lags (relative

  3. An Experimental Study of n-Heptane and JP-7 Extinction Limits in an Opposed Jet Burner

    NASA Technical Reports Server (NTRS)

    Convery, Janet L.; Pellett, Gerald L.; O'Brien, Walter F., Jr.; Wilson, Lloyd G.; Williams, John

    2005-01-01

    Propulsion engine combustor design and analysis requires experimentally verified data on the chemical kinetics of fuel. Among the important data is the combustion extinction limit as measured by observed maximum flame strain rate. The extinction limit relates to the ability to maintain a flame in a combustor during operation. Extinction limit data can be obtained for a given fuel by means of a laminar flame experiment using an opposed jet burner (OJB). Laminar extinction limit data can be applied to the turbulent application of a combustor via laminar flamelet modeling. The OJB consists of two axi-symmetric tubes (one for fuel and one for oxidizer), which produce a flat, disk-like counter-flow diffusion flame. This paper presents results of experiments to measure extinction limits for n-heptane and the military specification fuel JP-7, obtained from an OJB. JP-7 is an Air Force-developed fuel that continues to be important in the area of hypersonics. Because of its distinct properties it is currently the hydrocarbon fuel of choice for use in Scramjet engines. This study provides much-desired data for JP-7, for which very little information previously existed. The interest in n-heptane is twofold. First, there has been a significant amount of previous extinction limit study and resulting data with this fuel. Second, n-heptane (C7H16) is a pure substance, and therefore does not vary in composition as does JP-7, which is a mixture of several different hydrocarbons. These two facts allow for a baseline to be established by comparing the new OJB results to those previously taken. Additionally, the data set for n-heptane, which previously existed for mixtures up to 26 mole percent in nitrogen, is completed up to 100% n-heptane. The extinction limit data for the two fuels are compared, and complete experimental results are included.

  4. Gaseous Surrogate Hydrocarbons for a Hifire Scramjet that Mimic Opposed Jet Extinction Limits for Cracked JP Fuels

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Vaden, Sarah N.; Wilson, Lloyd G.

    2008-01-01

    This paper describes, first, the top-down methodology used to define simple gaseous surrogate hydrocarbon (HC) fuel mixtures for a hypersonic scramjet combustion subtask of the HiFIRE program. It then presents new and updated Opposed Jet Burner (OJB) extinction-limit Flame Strength (FS) data obtained from laminar non-premixed HC vs. air counterflow diffusion flames at 1-atm, which follow from earlier investigations. FS represents a strain-induced extinction limit based on cross-section-average air jet velocity, U(sub air), that sustains combustion of a counter jet of gaseous fuel just before extinction. FS uniquely characterizes a kinetically limited fuel combustion rate. More generally, Applied Stress Rates (ASRs) at extinction (U(sub air) normalized by nozzle or tube diameter, D(sub n or t) can directly be compared with extinction limits determined numerically using either a 1-D or (preferably) a 2-D Navier Stokes simulation with detailed transport and finite rate chemistry. The FS results help to characterize and define three candidate surrogate HC fuel mixtures that exhibit a common FS 70% greater than for vaporized JP-7 fuel. These include a binary fuel mixture of 64% ethylene + 36% methane, which is our primary recommendation. It is intended to mimic the critical flameholding limit of a thermally- or catalytically-cracked JP-7 like fuel in HiFIRE scramjet combustion tests. Our supporting experimental results include: (1) An idealized kinetically-limited ASR reactivity scale, which represents maximum strength non-premixed flames for several gaseous and vaporized liquid HCs; (2) FS characterizations of Colket and Spadaccini s suggested ternary surrogate, of 60% ethylene + 30% methane + 10% n-heptane, which matches the ignition delay of a typical cracked JP fuel; (3) Data showing how our recommended binary surrogate, of 64% ethylene + 36% methane, has an identical FS; (4) Data that characterize an alternate surrogate of 44% ethylene + 56% ethane with identical

  5. Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

    SciTech Connect

    Pellett, G.L.; Northam, G.B.; Wilson, L.G.; Jarrett, O. Jr.; Antcliff, R.R.

    1989-01-01

    An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF. 42 refs.

  6. Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Jarrett, Olin, Jr.; Antcliff, R. R.

    1989-01-01

    An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.

  7. Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Jarrett, Olin, Jr.; Antcliff, R. R.

    1989-01-01

    An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.

  8. Drag reduction research in supersonic flow with opposing jet

    NASA Astrophysics Data System (ADS)

    Yisheng, Rong

    2013-10-01

    A CFD study on drag reduction in supersonic flow with opposing jet has been conducted. Flowfield parameters, reattachment point position and surface pressure distributions are obtained and validated with experiments. From the analysis on the physical mechanism of drag reduction, it shows the phenomenon that, when the opposing jet blows, the high pressure region is located between the bow shock wave and the Mach disk, which makes the nose region much lower pressure. As the pressure ratio increases, the high pressure region is gradually pushed away from the surface. Larger the total pressure ratio is, the lower of the drag coefficient is. To study the effect of the intensity of opposing jet more reasonably, a new parameter RPA has been introduced by combining the flux and the total pressure ratio. The study shows that the same shock wave position and drag coefficient can be obtained with the same RPA with different fluxes and the total pressures, which means the new parameter could stand for the intensity of opposing jet and could be used to analyze the influence of opposing jet on flow field and aerodynamic force.

  9. Two opposed lateral jets injected into swirling crossflow

    NASA Technical Reports Server (NTRS)

    Lilley, D. G.; Mcmurry, C. B.; Ong, L. H.

    1987-01-01

    Experiments have been conducted to obtain the time-mean and turbulent quantities of opposed lateral jets in a low speed, nonreacting flowfield. A jet-to-crossflow velocity ratio of R = 4 was used throughout the experiments, with swirl vane angles of 0 (swirler removed), 45 and 70 degrees used with the crossflow. Flow visualization techniques used were neutrally-buoyant helium-filled soap bubbles and multispark photography in order to obtain the gross flowfield characteristics. Measurements of time-mean and turbulent quantities were obtained utilizing a six-orientation single hot-wire technique. For the nonswirling case, the jets were found not to penetrate past the test-section centerline, in contrast to the single lateral jet with the same jet-to-crossflow velocity ratio. In the swirling cases, the crossflow remains in a narrow region near the wall of the test section. The opposed jets are swept from their vertical courses into spiral trajectories close to the confining walls. Extensive results are presented in r-x plane plots.

  10. Two opposed lateral jets injected into swirling crossflow

    NASA Technical Reports Server (NTRS)

    Lilley, D. G.; Mcmurry, C. B.; Ong, L. H.

    1987-01-01

    Experiments have been conducted to obtain the time-mean and turbulent quantities of opposed lateral jets in a low speed, nonreacting flowfield. A jet-to-crossflow velocity ratio of R = 4 was used throughout the experiments, with swirl vane angles of 0 (swirler removed), 45 and 70 degrees used with the crossflow. Flow visualization techniques used were neutrally-buoyant helium-filled soap bubbles and multispark photography in order to obtain the gross flowfield characteristics. Measurements of time-mean and turbulent quantities were obtained utilizing a six-orientation single hot-wire technique. For the nonswirling case, the jets were found not to penetrate past the test-section centerline, in contrast to the single lateral jet with the same jet-to-crossflow velocity ratio. In the swirling cases, the crossflow remains in a narrow region near the wall of the test section. The opposed jets are swept from their vertical courses into spiral trajectories close to the confining walls. Extensive results are presented in r-x plane plots.

  11. Experimental study of planar opposed jets with acoustic excitation

    NASA Astrophysics Data System (ADS)

    Li, Wei-Feng; Huang, Guo-Feng; Tu, Gong-Yi; Liu, Hai-Feng; Wang, Fu-Chen

    2013-01-01

    Oscillation behaviors of planar opposed jets with acoustic excitation were experimentally investigated. The flow regimes of planar opposed jets at various exit air velocities, nozzle separations, excitation frequencies, and excitation amplitudes have been identified by a flow visualization technique combining with a high-speed camera. Results show that planar opposed jets exhibit horizontal instability at L/H ≤ 4 (where L is the nozzle separation and H is the slit height of the planar nozzle) and deflecting oscillation at L/H ≥ 6. The deflecting oscillation is originally started by the antisymmetric structures in the planar jets and is self-sustained by the periodic changes of the velocity field and the pressure field. At L/H ≤ 4, the acoustic excitation results in the horizontal periodic oscillation, whose frequency is equal to the excitation frequency. The acoustic excitation of oscillation amplitude less than 10% has negligible influence on the deflecting oscillation; for synchronous or asynchronous excitation with higher amplitude, the transition from the deflecting oscillation to a steady state or horizontal oscillation occurs.

  12. Re: Penetration Behavior of Opposed Rows of Staggered Secondary Air Jets Depending on Jet Penetration Coefficient and Momentum Flux Ratio

    NASA Technical Reports Server (NTRS)

    Holdeman, James D.

    2016-01-01

    The purpose of this article is to explain why the extension of the previously published C = (S/Ho)sqrt(J) scaling for opposed rows of staggered jets wasn't directly successful in the study by Choi et al. (2016). It is not surprising that staggered jets from opposite sides do not pass each other at the expected C value, because Ho/D and sqrt(J) are much larger than the maximum in previous studies. These, and large x/D's, tend to suggest development of 2-dimensional flow. Although there are distinct optima for opposed rows of in-line jets, single-side injection, and opposed rows of staggered jets based on C, opposed rows of staggered jets provide as good or better mixing performance, at any C value, than opposed rows of in-line jets or jets from single-side injection.

  13. Opposed Jet Burner Approach for Characterizing Flameholding Potentials of Hydrocarbon Scramjet Fuels

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Convery, Janet L.; Wilson, Lloyd G.

    2006-01-01

    Opposed Jet Burner (OJB) tools have been used extensively by the authors to measure Flame Strength (FS) extinction limits of laminar H2/N2 air and (recently) hydrocarbon (HC) air Counterflow Diffusion Flames (CFDFs) at one atm. This paper details normalization of FSs of N2- diluted H2 and HC systems to account for effects of fuel composition, temperature, pressure, jet diameter, inflow Reynolds number, and inflow velocity profile (plug, contoured nozzle; and parabolic, straight tube). Normalized results exemplify a sensitive accurate means of validating, globally, reduced chemical kinetic models at approx. 1 atm and the relatively low temperatures approximating the loss of non-premixed idealized flameholding, e.g., in scramjet combustors. Laminar FS is defined locally as maximum air input velocity, U(sub air), that sustains combustion of a counter-jet of g-fuel at extinction. It uniquely characterizes a fuel. And global axial strain rate at extinction (U(sub air) normalized by nozzle or tube diameter, D(sub n or (sub t)) can be compared directly with computed extinction limits, determined using either a 1-D Navier Stokes stream-function solution, using detailed transport and finite rate chemistry, or (better yet) a detailed 2-D Navier Stokes numerical simulation. The experimental results define an idealized flameholding reactivity scale that shows wide ranging (50 x) normalized FS s for various vaporized-liquid and gaseous HCs, including, in ascending order: JP-10, methane, JP-7, n-heptane, n-butane, propane, ethane, and ethylene. Results from H2 air produce a unique and exceptionally strong flame that agree within approx. 1% of a recent 2-D numerically simulated FS for a 3 mm tube-OJB. Thus we suggest that experimental FS s and/or FS ratios, for various neat and blended HCs w/ and w/o additives, offer accurate global tests of chemical kinetic models at the Ts and Ps of extinction. In conclusion, we argue the FS approach is more direct and fundamental, for

  14. Extinction Criteria for Opposed-Flow Flame Spread in a Microgravity Environment

    NASA Technical Reports Server (NTRS)

    Bhattacharjee, Subrata; Paolini, Chris; Wakai, Kazunori; Takahashi, Shuhei

    2003-01-01

    A simplified analysis is presented to extend a previous work on flame extinction in a quiescent microgravity environment to a more likely situation of a mild opposing flow. The energy balance equation, that includes surface re-radiation, is solved to yield a closed form spread rate expression in terms of its thermal limit, and a radiation number that can be evaluated from the known parameters of the problem. Based on this spread rate expression, extinction criterions for a flame over solid fuels, both thin and thick, have been developed that are qualitatively verified with experiments conducted at the MGLAB in Japan. Flammability maps with oxygen level, opposing flow velocity and fuel thickness as independent variables are extracted from the theory that explains the well-established trends in the existing experimental data.

  15. Analysis of opposed jet hydrogen-air counter flow diffusion flame

    NASA Technical Reports Server (NTRS)

    Ho, Y. H.; Isaac, K. M.

    1989-01-01

    A computational simulation of the opposed-jet diffusion flame is performed to study its structure and extinction limits. The present analysis concentrates on the nitrogen-diluted hydrogen-air diffusion flame, which provides the basic information for many vehicle designs such as the aerospace plane for which hydrogen is a candidate as the fuel. The computer program uses the time-marching technique to solve the energy and species equations coupled with the momentum equation solved by the collocation method. The procedure is implemented in two stages. In the first stage, a one-step forward overal chemical reaction is chosen with the gas phase chemical reaction rate determined by comparison with experimental data. In the second stage, a complete chemical reaction mechanism is introduced with detailed thermodynamic and transport property calculations. Comparison between experimental extinction data and theoretical predictions is discussed. The effects of thermal diffusion as well as Lewis number and Prandtl number variations on the diffusion flame are also presented.

  16. On the Mixing of Single and Opposed Rows of Jets With a Confined Crossflow

    NASA Technical Reports Server (NTRS)

    Holdeman, James D.; Clisset, James R.; Moder, Jeffrey P.; Lear, William E.

    2006-01-01

    The primary objectives of this study were 1) to demonstrate that contour plots could be made using the data interface in the NASA GRC jet-in-crossflow (JIC) spreadsheet, and 2) to investigate the suitability of using superposition for the case of opposed rows of jets with their centerlines in-line. The current report is similar to NASA/TM-2005-213137 but the "basic" effects of a confined JIC that are shown in profile plots there are shown as contour plots in this report, and profile plots for opposed rows of aligned jets are presented here using both symmetry and superposition models. Although superposition was found to be suitable for most cases of opposed rows of jets with jet centerlines in-line, the calculation procedure in the JIC spreadsheet was not changed and it still uses the symmetry method for this case, as did all previous publications of the NASA empirical model.

  17. Effects of water-contaminated air on blowoff limits of opposed jet hydrogen-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Jentzen, Marilyn E.; Wilson, Lloyd G.; Northam, G. Burton

    1988-01-01

    The effects of water-contaminated air on the extinction and flame restoration of the central portion of N2-diluted H2 versus air counterflow diffusion flames are investigated using a coaxial tubular opposed jet burner. The results show that the replacement of N2 contaminant in air by water on a mole for mole basis decreases the maximum sustainable H2 mass flow, just prior to extinction, of the flame. This result contrasts strongly with the analogous substitution of water for N2 in a relatively hot premixed H2-O2-N2 flame, which was shown by Koroll and Mulpuru (1986) to lead to a significant, kinetically controlled increase in laminar burning velocity.

  18. Fluidized Bed Opposed Jet Mill System for Processing Inorganic Materials

    NASA Astrophysics Data System (ADS)

    Al-Nuzal, S. M. D.; Mohammed, M. I.

    2017-08-01

    A jet mill system was built aiming to give values for processing inorganic materials, to be used for different industry. The milling housing of the system is composed of; milling chamber, compressed air nozzles which deliver compressed air in the milling chamber to accelerate sample particles. The classifier wheel is composed of two concentric pieces welded together under argon and coupled to a AC Motor, 0 - 9000 rpm, 2 kW, with AC frequencies convertor. The performances of this jet mill system were tried on five cheap locally available materials, viz. white sand, glass, iron oxide, black carbon and alum. It is possible to get particle sizes of less than 1 μm with narrow distribution of particle sizes.

  19. Combustion rate limits of hydrogen plus hydrocarbon fuel: Air diffusion flames from an opposed jet burner technique

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Guerra, Rosemary; Wilson, Lloyd G.; Reeves, Ronald N.; Northam, G. Burton

    1987-01-01

    Combustion of H2/hydrocarbon (HC) fuel mixtures may be considered in certain volume-limited supersonic airbreathing propulsion applications. Effects of HC addition to H2 were evaluated, using a recent argon-bathed, coaxial, tubular opposed jet burner (OJB) technique to measure the extinction limits of counterflow diffusion flames. The OJB flames were formed by a laminar jet of (N2 and/or HC)-diluted H2 mixture opposed by a similar jet of air at ambient conditions. The OJB data, derived from respective binary mixtures of H2 and methane, ethylene, or propane HCs, were used to characterize BLOWOFF and RESTORE. BLOWOFF is a sudden breaking of the dish-shaped OJB flame to a stable torus or ring shape, and RESTORE marks sudden restoration of the central flame by radial inward flame propagation. BLOWOFF is a measure of kinetically-limited flame reactivity/speed under highly stretched, but relatively ideal impingement flow conditions. RESTORE measures inward radial flame propagation rate, which is sensitive to ignition processes in the cool central core. It is concluded that relatively small molar amounts of added HC greatly reduce the reactivity characteristics of counterflow hydrogen-air diffusion flames, for ambient initial conditions.

  20. Combustion rate limits of hydrogen plus hydrocarbon fuel: Air diffusion flames from an opposed jet burner technique

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Guerra, Rosemary; Wilson, Lloyd G.; Reeves, Ronald N.; Northam, G. Burton

    1987-01-01

    Combustion of H2/hydrocarbon (HC) fuel mixtures may be considered in certain volume-limited supersonic airbreathing propulsion applications. Effects of HC addition to H2 were evaluated, using a recent argon-bathed, coaxial, tubular opposed jet burner (OJB) technique to measure the extinction limits of counterflow diffusion flames. The OJB flames were formed by a laminar jet of (N2 and/or HC)-diluted H2 mixture opposed by a similar jet of air at ambient conditions. The OJB data, derived from respective binary mixtures of H2 and methane, ethylene, or propane HCs, were used to characterize BLOWOFF and RESTORE. BLOWOFF is a sudden breaking of the dish-shaped OJB flame to a stable torus or ring shape, and RESTORE marks sudden restoration of the central flame by radial inward flame propagation. BLOWOFF is a measure of kinetically-limited flame reactivity/speed under highly stretched, but relatively ideal impingement flow conditions. RESTORE measures inward radial flame propagation rate, which is sensitive to ignition processes in the cool central core. It is concluded that relatively small molar amounts of added HC greatly reduce the reactivity characteristics of counterflow hydrogen-air diffusion flames, for ambient initial conditions.

  1. A new method of thermal protection by opposing jet for a hypersonic aeroheating strut

    NASA Astrophysics Data System (ADS)

    Qin, Jiang; Ning, Dongpo; Feng, Yu; Zhang, Junlong; Feng, Shuo; Bao, Wen

    2017-06-01

    This paper presents the numerical investigation of thermal protection of scramjet strut by opposing jet in supersonic stream of Mach number 6 with a hydrogen fueled scramjet strut model using CFD software. Simulation results indicate that when a small amount of fuel is injected from the nose of the strut, the bow shock is pushed away from the strut, and the heat flux is reduced in the strut, especially at the leading edge. Opposing jet forms a recirculation region near the nozzle so that the strut is covered with low temperature fuel and separated from free stream. An appropriate total pressure ratio can be used to reduce not only aerodynamic heating but also the drag of strut. It is therefore concluded that thermal protection of scramjet strut by opposing jet is one of the promising ways to protect scramjet strut in high enthalpy stream.

  2. Extinct Radioactivities and the R-Process Jet

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.

    2001-01-01

    All extinct radioactive species in the solar nebula were injected from a core-collapse supernova. I discuss primarily the products expected from an r-process jet in this supernova, and various supporting astrophysical observations. Additional information is contained in the original extended abstract.

  3. Experiments on opposed lateral jets injected into swirling crossflow. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Mcmurry, C. B.; Lilley, D. G.

    1986-01-01

    Experiments have been conducted to obtain the time-mean and turbulent quantities of opposed lateral jets in a low speed, nonreacting flowfield. A jet-to-crossflow velocity ratio of R = v sub J/u sub 0 = 4 was used throughout the experiments, with swirl vane angles of d = 0 (swirler removed), 45 and 70 deg used with the crossflow. Flow visualization techniques used were neutrally-buoyant helium-filled soap bubbles and multispark photography in order to obtain the gross flowfield characteristics. Measurements of time-mean and turbulent quantities were obtained utilizing a six-orientation single hot-wire technique. For the nonswirling case, the jets were found not to penetrate past the test-section centerline, in contrast to the single lateral jet with the same jet-to-crossflow velocity ratio. In the swirling cases, the crossflow remains in a narrow region near the wall of the test section. The opposed jets are swept from their vertical courses into spiral trajectories close to the confining walls. Extensive results are presented in r-x plane plots.

  4. Numerical investigation on properties of attack angle for an opposing jet thermal protection system

    NASA Astrophysics Data System (ADS)

    Lu, Hai-Bo; Liu, Wei-Qiang

    2012-08-01

    The three-dimensional Navier—Stokes equation and the k-in viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection has failed.

  5. Estradiol and Progesterone have Opposing Roles in the Regulation of Fear Extinction in Female Rats

    PubMed Central

    Graham, Bronwyn M; Daher, Melissa

    2016-01-01

    Fear extinction, the laboratory basis of exposure therapy for anxiety disorders, fluctuates across the female rat estrous cycle, where extinction is enhanced during proestrus (high estradiol and progesterone), and impaired during metestrus (low estradiol and progesterone). During the estrous cycle increasing levels of estradiol precede and then overlap with increased levels of progesterone. We sought to isolate the impact of these hormonal changes on fear extinction by systematically treating ovariectomized female rats with estradiol alone, or in combination with progesterone. We found that estradiol alone facilitated extinction recall, whereas the effects of progesterone on estradiol-treated rats were biphasic and dependent on the time interval between progesterone administration and extinction training. Progesterone potentiated estradiol's facilitation of extinction recall when extinction training occurred 6 h after progesterone administration. However, progesterone abolished estradiol's facilitation of extinction recall when extinction training occurred 24 h after progesterone administration. Furthermore, in naturally cycling rats, blocking progesterone receptor activation during proestrus (when progesterone levels peak) prevented the impairment in extinction recall in rats extinguished during metestrus. These results suggest that in naturally cycling females whereas cyclical increases in estradiol facilitate fear extinction, cyclical increases in progesterone may lead to fear extinction impairments. As extinction training took place after the hormonal treatments had been metabolized, we propose that genomic mechanisms may at least partly mediate the impact of cyclic fluctuations in sex hormones on fear extinction. PMID:26156559

  6. Estradiol and Progesterone have Opposing Roles in the Regulation of Fear Extinction in Female Rats.

    PubMed

    Graham, Bronwyn M; Daher, Melissa

    2016-02-01

    Fear extinction, the laboratory basis of exposure therapy for anxiety disorders, fluctuates across the female rat estrous cycle, where extinction is enhanced during proestrus (high estradiol and progesterone), and impaired during metestrus (low estradiol and progesterone). During the estrous cycle increasing levels of estradiol precede and then overlap with increased levels of progesterone. We sought to isolate the impact of these hormonal changes on fear extinction by systematically treating ovariectomized female rats with estradiol alone, or in combination with progesterone. We found that estradiol alone facilitated extinction recall, whereas the effects of progesterone on estradiol-treated rats were biphasic and dependent on the time interval between progesterone administration and extinction training. Progesterone potentiated estradiol's facilitation of extinction recall when extinction training occurred 6 h after progesterone administration. However, progesterone abolished estradiol's facilitation of extinction recall when extinction training occurred 24 h after progesterone administration. Furthermore, in naturally cycling rats, blocking progesterone receptor activation during proestrus (when progesterone levels peak) prevented the impairment in extinction recall in rats extinguished during metestrus. These results suggest that in naturally cycling females whereas cyclical increases in estradiol facilitate fear extinction, cyclical increases in progesterone may lead to fear extinction impairments. As extinction training took place after the hormonal treatments had been metabolized, we propose that genomic mechanisms may at least partly mediate the impact of cyclic fluctuations in sex hormones on fear extinction.

  7. Numerical Simulation of Aerodynamic Heating Reduction due to Opposing Jet in Supersonic Flow

    NASA Astrophysics Data System (ADS)

    Li, H. Y.; Eri, Q. T.

    In supersonic flight, severe aerodynamic heating takes place at the nose of blunt body and causes ablation. Accurate prediction of aerodynamic heating and construction of proper thermal protection system are required. The numerical study on a reduction of aerodynamic heating by opposing jet has been conducted. Flow field around a hemisphere model is calculated in supersonic free stream of Mach number 3.98 and the coolant gas is injected through the nozzle at the nose the model. CFD method was Finite Volume Method for time integration be used, axisymmetric full Navier-Stokes equations were applied as governing equations and k-ɛturbulence model is used. Numerical simulation demonstrated, compared with no jet, the reduction of aerodynamic heating due to opposing jet was to be proved quite effective at the nose of blunt body. Parameters in this numerical study insofar, as the pressure ratio is increased, caused the wall pressure and heat flux decrease, and recirculation region size largen. effective reduction of the aerodynamic heating remarkably. As the opposing nozzle diameter ratio was decreased, the pressure and heat flux increased, and recirculation region size lessening, the effect of reduction aerodynamic heating was reduced.

  8. Flame Spread and Extinction Over a Thick Solid Fuel in Low-Velocity Opposed and Concurrent Flows

    NASA Astrophysics Data System (ADS)

    Zhu, Feng; Lu, Zhanbin; Wang, Shuangfeng

    2016-05-01

    Flame spread and extinction phenomena over a thick PMMA in purely opposed and concurrent flows are investigated by conducting systematical experiments in a narrow channel apparatus. The present tests focus on low-velocity flow regime and hence complement experimental data previously reported for high and moderate velocity regimes. In the flow velocity range tested, the opposed flame is found to spread much faster than the concurrent flame at a given flow velocity. The measured spread rates for opposed and concurrent flames can be correlated by corresponding theoretical models of flame spread, indicating that existing models capture the main mechanisms controlling the flame spread. In low-velocity gas flows, however, the experimental results are observed to deviate from theoretical predictions. This may be attributed to the neglect of radiative heat loss in the theoretical models, whereas radiation becomes important for low-intensity flame spread. Flammability limits using oxygen concentration and flow velocity as coordinates are presented for both opposed and concurrent flame spread configurations. It is found that concurrent spread has a wider flammable range than opposed case. Beyond the flammability boundary of opposed spread, there is an additional flammable area for concurrent spread, where the spreading flame is sustainable in concurrent mode only. The lowest oxygen concentration allowing concurrent flame spread in forced flow is estimated to be approximately 14 % O2, substantially below that for opposed spread (18.5 % O2).

  9. Spreadsheet Calculations for Jets in Crossflow: Opposed Rows of Inline and Staggered Holes and Single and Opposed Rows with Alternating Hole Sizes

    NASA Technical Reports Server (NTRS)

    Holdeman, James D.; Clisset, James R.; Moder, Jeffrey P.

    2010-01-01

    The primary purpose of this jet-in-crossflow study was to calculate expected results for two configurations for which limited or no experimental results have been published: (1) cases of opposed rows of closely-spaced jets from inline and staggered round holes and (2) rows of jets from alternating large and small round holes. Simulations of these configurations were performed using an Excel (Microsoft Corporation) spreadsheet implementation of a NASA-developed empirical model which had been shown in previous publications to give excellent representations of mean experimental scalar results suggesting that the NASA empirical model for the scalar field could confidently be used to investigate these configurations. The supplemental Excel spreadsheet is posted with the current report on the NASA Glenn Technical Reports Server (http://gltrs.grc.nasa.gov) and can be accessed from the Supplementary Notes section as TM-2010-216100-SUPPL1.xls. Calculations for cases of opposed rows of jets with the orifices on one side shifted show that staggering can improve the mixing, particularly for cases where jets would overpenetrate slightly if the orifices were in an aligned configuration. The jets from the larger holes dominate the mixture fraction for configurations with a row of large holes opposite a row of smaller ones although the jet penetration was about the same. For single and opposed rows with mixed hole sizes, jets from the larger holes penetrated farther. For all cases investigated, the dimensionless variance of the mixture fraction decreased significantly with increasing downstream distance. However, at a given downstream distance, the variation between cases was small.

  10. Heat flux reduction mechanism induced by a combinational opposing jet and cavity concept in supersonic flows

    NASA Astrophysics Data System (ADS)

    Huang, Wei; Jiang, Yan-ping; Yan, Li; Liu, Jun

    2016-04-01

    The thermal protection on the surface of hypersonic vehicles attracts an increasing attention worldwide, especially when the vehicle enters the atmosphere at high speed. In the current study, the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Menter's shear stress transport (SST) model have been employed to investigate the heat flux reduction mechanism induced by the variations of the cavity configuration, the jet pressure ratio and the injectant molecular weight in the combinational opposing jet and cavity concept. The length of the cavity is set to be 6 mm, 8 mm and 10 mm in order to make sure that the cavity configuration is the "open" cavity, and the jet pressure ratio is set to be 0.4, 0.6 and 0.8 in order to make sure that the flow field is steady. The injectant is set to be nitrogen and helium. The obtained results show that the aft angle of the cavity only has a slight impact on the heat flux reduction, and the heat flux peak decreases with the decrease of the length of the cavity. The design of the thermal protection system for the hypersonic blunt body is a multi-objective design exploration problem, and the heat flux distribution depends on the jet pressure ratio, the aft wall of the cavity and the injectant molecular weight. The heat flux peak decreases with the increase of the jet pressure ratio when the aft angle of the cavity is large enough, and this value is 45°.

  11. Spreadsheet Calculation of Jets in Crossflow: Opposed Rows of Slots Slanted at 45 Degrees

    NASA Technical Reports Server (NTRS)

    Holderman, James D.; Clisset, James R.; Moder, Jeffrey P.

    2011-01-01

    The purpose of this study was to extend a baseline empirical model to the case of jets entering the mainstream flow from opposed rows of 45 degrees slanted slots. The results in this report were obtained using a spreadsheet modified from the one posted with NASA/TM--2010-216100. The primary conclusion in this report is that the best mixing configuration for opposed rows of 45 degrees slanted slots at any down stream distance is a parallel staggered configuration where the slots are angled in the same direction on top and bottom walls and one side is shifted by half the orifice spacing. Although distributions from perpendicular slanted slots are similar to those from parallel staggered configurations at some downstream locations, results for perpendicular slots are highly dependent on downstream distance and are no better than parallel staggered slots at locations where they are similar and are worse than parallel ones at other distances.

  12. Opposed jet burner studies of hydrogen combustion with pure and N2, NO-contaminated air

    NASA Technical Reports Server (NTRS)

    Guerra, Rosemary; Pellett, Gerald L.; Northam, G. Burton; Wilson, Lloyd G.

    1987-01-01

    A counterflow diffusion flame formed by an argon-bathed tubular-opposed jet burner (OJB) was used to determine the 'blowoff' and 'restore' combustion characteristics for jets of various H2/N2 mixtures and for jets of air contaminated by NO (which normally occurs in high-enthalpy airflows supplied to hypersonic test facilities for scramjet combustors). Substantial divergence of 'blowoff' and 'restore' limits occurred as H2 mass flux, M(H)2, increased, the H2 jet became richer, and the M(air)/M(H2 + N2) ratio increased from 1 to 3 (molar H2/O2 from 1 to 16). Both OJB limits were sensitive to reactant composition. One to six percent NO in air led to significant N2-corrected decreases in the M(H2) values for 'blowoff' (2-8 percent) and 'restore' (6-12 percent) for mole fractions of H2 ranging from 0.5 to 0.95. However, when H2/O2 was held constant, all N2-corrected changes in M(H2) were negligible.

  13. Structure of Laminar Permanently Blue, Opposed-Jet Ethylene-Fueled Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2000-01-01

    The structure and state relationships of laminar soot-free (permanently blue) ethylene-fueled diffusion flames at various strain rates were studied both experimentally and computationally using an opposed-jet configuration. Measurements of gas velocities, temperatures, and compositions were carried out along the stagnation stream line. Corresponding predictions of flame structure were obtained, based on numerical simulations using several contemporary reaction mechanisms for methane oxidation. Flame conditions studied included ethylene-fueled opposed-jet diffusion flames having stoichiometric mixture fractions of 0.7 with measurements involving strain rates of 60-240/s and predictions involving strain rates of 0-1140/s at normal temperature and pressure. It was found that measured major gas species concentrations and temperature distributions were in reasonably good agreement with predictions using mechanisms due to GRI-Mech and Peters and that effects of preferential diffusion significantly influence flame structure even when reactant mass diffusivities are similar. Oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures were found to exist over a broad range of strain rates, providing potential for significant computational simplifications for modeling purposes in some instances.

  14. Structure of Laminar Permanently Blue, Opposed-Jet Ethylene-Fueled Diffusion Flames. Appendix E

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2000-01-01

    The structure and state relationships of laminar soot-free (permanently blue) ethylene-fueled diffusion flames at various strain rates were studied both experimentally and computationally using an opposed-jet configuration. Measurements of gas velocities, temperatures, and compositions were carried out along the stagnation stream line. Corresponding predictions of flame structure were obtained, based on numerical simulations using several contemporary reaction mechanisms for methane oxidation. Flame conditions studied included ethylene-fueled opposed-jet diffusion flames having stoichiometric mixture fractions of 0.7 with measurements involving strain rates of 60-240/s and predictions involving strain rates of 0-1140/s at normal temperature and pressure. It was found that measured major gas species concentrations and temperature distributions were in reasonably good agreement with predictions using mechanisms due to GRI-Mech and Peters and that effects of preferential diffusion significantly influence flame structure even when reactant mass diffusivities are similar. Oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures were found to exist over a broad range of strain rates, providing potential for significant computational simplifications for modeling purposes in some instances.

  15. Structure of Laminar Permanently Blue, Opposed-Jet Ethylene-Fueled Diffusion Flames. Appendix E

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2000-01-01

    The structure and state relationships of laminar soot-free (permanently blue) ethylene-fueled diffusion flames at various strain rates were studied both experimentally and computationally using an opposed-jet configuration. Measurements of gas velocities, temperatures, and compositions were carried out along the stagnation stream line. Corresponding predictions of flame structure were obtained, based on numerical simulations using several contemporary reaction mechanisms for methane oxidation. Flame conditions studied included ethylene-fueled opposed-jet diffusion flames having stoichiometric mixture fractions of 0.7 with measurements involving strain rates of 60-240/s and predictions involving strain rates of 0-1140/s at normal temperature and pressure. It was found that measured major gas species concentrations and temperature distributions were in reasonably good agreement with predictions using mechanisms due to GRI-Mech and Peters and that effects of preferential diffusion significantly influence flame structure even when reactant mass diffusivities are similar. Oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures were found to exist over a broad range of strain rates, providing potential for significant computational simplifications for modeling purposes in some instances.

  16. Structure of Laminar Permanently Blue, Opposed-Jet Ethylene-Fueled Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2000-01-01

    The structure and state relationships of laminar soot-free (permanently blue) ethylene-fueled diffusion flames at various strain rates were studied both experimentally and computationally using an opposed-jet configuration. Measurements of gas velocities, temperatures, and compositions were carried out along the stagnation stream line. Corresponding predictions of flame structure were obtained, based on numerical simulations using several contemporary reaction mechanisms for methane oxidation. Flame conditions studied included ethylene-fueled opposed-jet diffusion flames having stoichiometric mixture fractions of 0.7 with measurements involving strain rates of 60-240/s and predictions involving strain rates of 0-1140/s at normal temperature and pressure. It was found that measured major gas species concentrations and temperature distributions were in reasonably good agreement with predictions using mechanisms due to GRI-Mech and Peters and that effects of preferential diffusion significantly influence flame structure even when reactant mass diffusivities are similar. Oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures were found to exist over a broad range of strain rates, providing potential for significant computational simplifications for modeling purposes in some instances.

  17. COMPARISON OF EXPERIMENTAL RESULTS TO CFD MODELS FOR BLENDING IN A TANK USING DUAL OPPOSING JETS

    SciTech Connect

    Leishear, R.

    2011-08-07

    Research has been completed in a pilot scale, eight foot diameter tank to investigate blending, using a pump with dual opposing jets. The jets re-circulate fluids in the tank to promote blending when fluids are added to the tank. Different jet diameters and different horizontal and vertical orientations of the jets were investigated. In all, eighty five tests were performed both in a tank without internal obstructions and a tank with vertical obstructions similar to a tube bank in a heat exchanger. These obstructions provided scale models of several miles of two inch diameter, serpentine, vertical cooling coils below the liquid surface for a full scale, 1.3 million gallon, liquid radioactive waste storage tank. Two types of tests were performed. One type of test used a tracer fluid, which was homogeneously blended into solution. Data were statistically evaluated to determine blending times for solutions of different density and viscosity, and the blending times were successfully compared to computational fluid dynamics (CFD) models. The other type of test blended solutions of different viscosity. For example, in one test a half tank of water was added to a half tank of a more viscous, concentrated salt solution. In this case, the fluid mechanics of the blending process was noted to significantly change due to stratification of fluids. CFD models for stratification were not investigated. This paper is the fourth in a series of papers resulting from this research (Leishear, et.al. [1- 4]), and this paper documents final test results, statistical analysis of the data, a comparison of experimental results to CFD models, and scale-up of the results to a full scale tank.

  18. Analysis of opposed-jet hydrogen-air counter flow diffusion flame

    NASA Technical Reports Server (NTRS)

    Ho, Y. H.; Isaac, K. M.; Pellett, G. L.; Northam, G. B.

    1991-01-01

    An opposed-jet counterflow diffusion-flame configuration is considered for the analysis of a nitrogen-diluted hydrogen-air diffusion flame. A boundary-layer similarity solution is employed in order to reduce the governing equations to a set of equations in one independent variable. The equation set is written in the time-dependent form and solved by the finite-volume time-marching technique. This model uses detailed chemistry and accounts for the variations of Prandtl number and Lewis number as well as the effect of thermal diffusion on the flame. It is noted that a one-step model can predict several features of the flame, while the detailed-chemistry model can be used for fine-tuning the results. The present results indicate that thermal diffusion has negligible effect on the characteristics of the flame.

  19. Buoyancy induced extinction of laminar gas jet diffusion flames

    NASA Technical Reports Server (NTRS)

    Altenkirch, R. A.; Eichhorn, R.; Brancic, A. B.

    1977-01-01

    The behavior of laminar gas jet diffusion flames subjected to elevated gravity in order to investigate the role of buoyancy in such flames has been studied experimentally. Higher than earth normal gravity was achieved using a 1.83 m diameter centrifuge. Methane, ethane, propane and hydrogen air flames were stabilized at the exit of small tubular burners ranging in size from .05 to .21 cm in diameter. The experimental arrangement was such that the flames were burnt vertically upward. Following a shortening of the flame and a decrease in luminosity with increasing gravity level, further increases in gravity caused the hydrocarbon flames to separate from the rim and eventually extinguish. The extinction gravity levels appear to correlate with the parameter g alpha (u)/S to the 3rd (u), which should be a constant for buoyancy controlled extinction. This parameter is developed by a rudimentary analysis of the heat loss from the premixed stabilizing flame in the lifted flame base. When the loss is excessive, the flame is extinguished.

  20. Analysis of flowfield characteristics for equal polygon opposing jet on different freeflow conditions

    NASA Astrophysics Data System (ADS)

    Li, Shi-bin; Wang, Zhen-guo; Huang, Wei; Yan, Li

    2017-04-01

    Drag and heat flux reduction efficiency induced by the equal polygon opposing jet could be higher than the one issuing from conventional circular orifice. The two-equation SST k-w turbulence model has been utilized to study the detailed information of flow field, and the numerical method has been validated against the available experimental data in the open literature. At last, the effects of angle of attack (α), angle of sideslip (β) and angle of jet flow (δ) on the aerodynamic characteristics have been investigated numerically in the current study. The obtained results show that the drag force increases with a higher absolute value of α and the Stanton number (St) reaches its maximum when α=-10°. Moreover, the peak St appears when α=5°. The influence of β on drag reduction shows similarity with that of α, and the maximum Cc appears when |β|=10°. More severe aero-heating occurs on the upper surface when |α| or |β| changes from 0° to 15°. The δ can reduce the maximum heat flux (Qmax) in the whole flow field and improve the thermal protection characteristics. The Qmax can reduce 22.5% and 9.3% at most when δ is -5° and 5° respectively.

  1. Experimental Evaluation of Dual-Opposed Jet Mixer Pump Performance for Slurry Mixing

    SciTech Connect

    Bamberger, Judith A.; Enderlin, Carl W.

    2016-07-10

    Million-gallon double-shell tanks at Hanford are used to store transuranic, high-level, and low-level radioactive wastes. These wastes consist of a large volume of salt-laden solution covering a smaller volume of settled sludge primarily containing metal hydroxides. These wastes will be retrieved and processed into immobile waste forms suitable for permanent disposal. Retrieval is an important step in implementing these disposal scenarios. The retrieval concept evaluated is to use submerged dual-nozzle jet mixer pumps with horizontally oriented nozzles located near the tank floor that produce horizontal jets of fluid to mobilize the settled solids. The mixer pumps are oscillated through 180 about a vertical axis so the high velocity fluid jets sweep across the floor of the tank. After the solids are mobilized, the pumps will continue to operate at a reduced flow rate producing lower velocity jets sufficient to maintain the particles in a uniform suspension (concentration uniformity). Several types of waste and tank configurations exist at Hanford. The jet mixer pump systems and operating conditions required to mobilize sludge and maintain slurry uniformity will be a function of the waste type and tank configuration. The focus of this work was to conduct a 1/12-scale experiment to develop an analytical model to relate slurry uniformity to tank and mixer pump configurations, operating conditions, and sludge properties. This experimental study evaluated concentration uniformity in a 1/12-scale experiment varying the Reynolds number (Re), Froude number (Fr), and gravitational settling parameter (Gs) space. Simulant physical properties were chosen to obtain the required Re and Gs where Re and Gs were varied by adjusting the kinematic viscosity and mean particle diameter, respectively. Test conditions were achieved by scaling the jet nozzle exit velocity in a 75-in. diameter tank using a mock-up of a centrally located dual-opposed jet mixer pump located just above the

  2. Pollutant formation in fuel lean recirculating flows. Ph.D. Thesis. Final Report; [in an Opposed Reacting Jet Combustor

    NASA Technical Reports Server (NTRS)

    Schefer, R. W.; Sawyer, R. F.

    1976-01-01

    An opposed reacting jet combustor (ORJ) was tested at a pressure of 1 atmosphere. A premixed propane/air stream was stabilized by a counterflowing jet of the same reactants. The resulting intensely mixed zone of partially reacted combustion products produced stable combustion at equivalence ratios as low as 0.45. Measurements are presented for main stream velocities of 7.74 and 13.6 m/sec with an opposed jet velocity of 96 m/sec, inlet air temperatures from 300 to 600 K, and equivalence ratios from 0.45 to 0.625. Fuel lean premixed combustion was an effective method of achieving low NOx emissions and high combustion efficiencies simultaneously. Under conditions promoting lower flame temperature, NO2 constituted up to 100 percent of the total NOx. At higher temperatures this percentage decreased to a minimum of 50 percent.

  3. Experimental Study on Control of Supersonic Aerodynamic Characteristics of a Vertical Landing Rocket by Using Opposing Jet

    NASA Astrophysics Data System (ADS)

    Akita, Daisuke; Yamada, Kazuhiko; Suzuki, Kojiro

    In order to control a reentry trajectory of a vertical landing rocket, an opposing jet system is experimentally tested at supersonic speeds. Experiments are conducted at Mach number 4.0 in the supersonic wind tunnel of ISAS. Supersonic nozzles of the exit Mach number 2.4 are installed on a blunt nose of a rocket model. The most significant drag reduction due to the jet-spike effect is obtained when the jet is injected from the stagnation point of the body in the opposite direction to the freestream. Various types of the nozzle arrangement are investigated and the method to increase the L/D is discussed. It is found that the off-axis jet is effective both to increase the L/D and to enable a vehicle to be trimmed at an intended attack angle.

  4. Opposing effects of D-cycloserine on fear despite a common extinction duration: interactions between brain regions and behavior.

    PubMed

    Bolkan, Scott S; Lattal, K Matthew

    2014-09-01

    A number of studies have reported that D-cycloserine (DCS), a partial agonist of the N-methyl-D-aspartate glutamate receptor, can facilitate the loss of conditioned fear if it is administered during an extinction trial. Here we examine the effects of DCS injected into the hippocampus or amygdala on extinction of context-evoked freezing after contextual fear conditioning in C57BL/6 mice. We find that DCS administered prior to an extinction session decreased freezing from the outset of the session regardless of which brain region was targeted. Retention tests revealed opposite effects on fear expression despite identical behavioral treatments: intra-hippocampal DCS inhibited fear expression while intra-amygdala DCS potentiated fear expression. Following post-extinction session injections of DCS, we found a similar though less pronounced effect. Closer inspection of the data revealed that the effects of DCS interacted with the behavior of the subjects during extinction. Intra-hippocampal injections of DCS enhanced extinction in those mice that showed the greatest amount of within-session extinction, but had less pronounced effects on mice that showed the least within-session extinction. Intra-amygdala injections of DCS impaired extinction in those mice that showed the least within-session extinction, but there was some evidence that the effect in the amygdala did not depend on behavior during extinction. These findings demonstrate that even with identical extinction trial durations, the effects of DCS administered into the hippocampus and amygdala can heavily depend on the organism's behavior during the extinction session. The broader implication of these findings is that the effects of pharmacological treatments designed to enhance extinction by targeting hippocampal or amygdalar processes may depend on the responsivity of the subject to the behavioral treatment.

  5. Effects of CO addition on the characteristics of laminar premixed CH{sub 4}/air opposed-jet flames

    SciTech Connect

    Wu, C.-Y.; Chao, Y.-C.; Chen, C.-P.; Ho, C.-T.; Cheng, T.S.

    2009-02-15

    The effects of CO addition on the characteristics of premixed CH{sub 4}/air opposed-jet flames are investigated experimentally and numerically. Experimental measurements and numerical simulations of the flame front position, temperature, and velocity are performed in stoichiometric CH{sub 4}/CO/air opposed-jet flames with various CO contents in the fuel. Thermocouple is used for the determination of flame temperature, velocity measurement is made using particle image velocimetry (PIV), and the flame front position is measured by direct photograph as well as with laser-induced predissociative fluorescence (LIPF) of OH imaging techniques. The laminar burning velocity is calculated using the PREMIX code of Chemkin collection 3.5. The flame structures of the premixed stoichiometric CH{sub 4}/CO/air opposed-jet flames are simulated using the OPPDIF package with GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. The measured flame front position, temperature, and velocity of the stoichiometric CH{sub 4}/CO/air flames are closely predicted by the numerical calculations. Detailed analysis of the calculated chemical kinetic structures reveals that as the CO content in the fuel is increased from 0% to 80%, CO oxidation (R99) increases significantly and contributes to a significant level of heat-release rate. It is also shown that the laminar burning velocity reaches a maximum value (57.5 cm/s) at the condition of 80% of CO in the fuel. Based on the results of sensitivity analysis, the chemistry of CO consumption shifts to the dry oxidation kinetics when CO content is further increased over 80%. Comparison between the results of computed laminar burning velocity, flame temperature, CO consumption rate, and sensitivity analysis reveals that the effect of CO addition on the laminar burning velocity of the stoichiometric CH{sub 4}/CO/air flames is due mostly to the transition of the dominant chemical kinetic steps. (author)

  6. Opposing effects of d-cycloserine on fear despite a common extinction duration: Interactions between brain regions and behavior

    PubMed Central

    Bolkan, Scott S.; Lattal, K. Matthew

    2014-01-01

    A number of studies have reported that D-cycloserine (DCS), a partial agonist of the N-methyl-D-aspartate glutamate receptor, can facilitate the loss of conditioned fear if it is administered during an extinction trial. Here we examine the effects of DCS injected into the hippocampus or amygdala on extinction of context-evoked freezing after contextual fear conditioning in C57BL/6 mice. We find that DCS administered prior to an extinction session decreased freezing from the outset of the session regardless of which brain region was targeted. Retention tests revealed opposite effects on fear expression despite identical behavioral treatments: intra-hippocampal DCS inhibited fear expression while intra-amygdala DCS potentiated fear expression. Following post-extinction session injections of DCS, we found a similar though less pronounced effect. Closer inspection of the data revealed that the effects of DCS interacted with the behavior of the subjects during extinction. Intra-hippocampal injections of DCS enhanced extinction in those mice that showed the greatest amount of within-session extinction, but had less pronounced effects on mice that showed the least within-session extinction. Intra-amygdala injections of DCS impaired extinction in those mice that showed the least within-session, but there was some evidence that the effect in the amygdala did not depend on behavior during extinction. These findings demonstrate that even with identical extinction preparations and trial durations, the effects of DCS administered into the hippocampus and amygdala can heavily depend on the organism’s behavior during the extinction session. The broader implication of these findings is that the effects of pharmacological treatments designed to enhance extinction by targeting hippocampal or amygdalar processes may depend greatly on the responsivity of the subject to the behavioral treatment. PMID:24374132

  7. Simultaneous temperature and multi-species measurements in opposed jet flames of nitrogen-diluted hydrogen and air

    NASA Technical Reports Server (NTRS)

    Wehrmeyer, J. A.; Cheng, T. S.; Pitz, R. W.; Nandula, S.; Wilson, L. G.; Pellett, G. L.

    1991-01-01

    A narrowband UV Raman scattering system is used to obtain measurement profiles of major and minor species concentrations, temperature, and mixture fraction in opposed jet diffusion flames. The measurement profiles can be compared to previously obtained temperature and concentration profiles (Pellett et al., 1989), obtained using CARS, and they can also be qualitatively compared to the predicted concentration and temperature profiles in pure hydrogen/air flames (Gutheil and Williams, 1990) and in diluted hydrogen/air flames (Dixon-Lewis and Missaghi, 1988; Ho and Isaac, 1991). The applied stress-rates for the two flame conditions studied are 240/s and 340/s, with respective hydrogen concentrations in the fuel jet of 0.67 and 0.83, on a mole fraction basis (0.13 and 0.26 hydrogen mass fractions, respectively).

  8. Mixing of Multiple Jets With a Confined Subsonic Crossflow. Part 2; Opposed Rows of Orifices in Rectangular Ducts

    NASA Technical Reports Server (NTRS)

    Holdeman, James D.; Liscinsky, David S.; Bain, Daniel B.

    1997-01-01

    This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex 3-D flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the offices investigated were often very large (jet-to-mainstream mass-flow ratio greater than 1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5 respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.

  9. Opposed jet burner studies of silane-methane, silane-hydrogen and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. Presented are: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions: (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  10. Opposed jet burner studies of silane-methane, silane-hydrogen, and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. The paper presents: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions; (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  11. Opposed jet burner studies of silane-methane, silane-hydrogen and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. Presented are: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions: (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  12. Opposed jet burner studies of silane-methane, silane-hydrogen, and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. The paper presents: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions; (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  13. Simulations of localized extinction in turbulent CH 4 jet flames using a Lagrangian model for reactedness

    NASA Astrophysics Data System (ADS)

    Koutmos, P.

    2000-02-01

    2D Large Eddy Simulations of turbulent CH 4 jet flames exhibiting significant finite-rate chemistry effects are presented. A partial equilibrium/two-scalar exponential PDF combustion submodel is applied at the subgrid level. An anisotropic eddy-viscosity and an equation for the SGS energy model the Subgrid motions. Independence of the PDF scalars is avoided and their correlations are obtained from scale-similarity assumptions. Extinction is accounted by comparing the local Damkohler against a "critical" local limit related to the Gibson scale and the reaction zone thickness. The post-extinction and reignition regimes are modeled via a Lagrangian reactedness equation (IEM). Comparisons between simulations and measurements suggested the capability of the method to represent several trends in the partial extinction and reignition behavior observed in the experiments.

  14. State Relationships of Laminar Permanently-Blue Opposed-Jet Hydrocarbon-Fueled Diffusion Flames. Appendix G

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2000-01-01

    The structure and state relationships of laminar soot-free (permanently-blue) diffusion flames at various strain rates were studied experimentally using an opposed-jet configuration, motivated by the importance of soot-free hydrocarbon-fueled diffusion flames for many practical applications. Measurements of gas velocities, temperatures and compositions were carried out along the stagnation stream line. Flame conditions studied included propylene- and 1,3-butadiene-fueled opposed-jet diffusion flames having a stoichiometric mixture fractions of 0.7 and strain rates of 60-240/s at normal temperature and pressure. It was found that oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures for these flames were found to exist over broad ranges of strain rates. In addition, current measurements, as well as previous measurements and predictions of ethylene-fueled permanently-blue diffusion flames, all having a stoichiometric mixture fraction of 0.7, were combined to establish generalized state relationships for permanently-blue diffusion flames for this stoichiometric mixture fraction. The combined measurements and predictions support relatively universal generalized state relationships for N2, CO2, H2O and fuel over a broad range of strain rates and fuel types. State relationships for O2 in the fuel-rich region, and for CO in the fuel-lean region, however, are functions of strain rate and fuel type. State relationships for H2 and temperature exhibit less universality, mainly due to the increased experimental uncertainties for these variables. The existence of state relationships for soot-free hydrocarbon-fueled diffusion

  15. State Relationships of Laminar Permanently-Blue Opposed-Jet Hydrocarbon-Fueled Diffusion Flames. Appendix D

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2000-01-01

    The structure and state relationships of laminar soot-free (permanently-blue) diffusion flames at various strain rates were studied experimentally using an opposed-jet configuration, motivated by the importance of soot-free hydrocarbon-fueled diffusion flames for many practical applications. Measurements of gas velocities, temperatures and compositions were carried out along the stagnation stream line. Flame conditions studied included propylene- and 1,3-butadiene-fueled opposed-jet diffusion flames having a stoichiometric mixture fractions of 0.7 and strain rates of 60-240 s (exp -1) at normal temperature and pressure. It was found that oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures for these flames were found to exist over broad ranges of strain rates. In addition, current measurements, as well as previous measurements and predictions of ethylene-fueled permanently-blue diffusion flames, all having a stoichiometric mixture fraction of 0.7, were combined to establish generalized state relationships for permanently-blue diffusion flames for this stoichiometric mixture fraction. The combined measurements and predictions support relatively universal generalized state relationships for N2, CO2, H2O and fuel over a broad range of strain rates and fuel types. State relationships for O2 in the fuel-rich region, and for CO in the fuel-lean region, however, are functions of strain rate and fuel type. State relationships for H2 and temperature exhibit less universality, mainly due to the increased experimental uncertainties for these variables. The existence of state relationships for soot-free hydrocarbon

  16. Influence of Aerodynamic Strain Rate on Local Extinction in Turbulent Non-premixed Jet Flames

    NASA Astrophysics Data System (ADS)

    Ramachandran, Aravind; Narayanaswamy, Venkateswaran; Lyons, Kevin

    2016-11-01

    2-D velocity field measurements obtained from Particle Image Velocimetry (PIV) are used to obtain aerodynamic strain rate information in regions of local extinction in lifted turbulent non-premixed methane jet flames in coflow. Diluting the coflow to reduce the oxygen molefraction results in increased occurrences of local extinction. Statistical analysis is performed to correlate regions of high local strain rate with local extinctions in both air coflow and diluted coflow cases to study the influence of strain rate against vortical structures in extinguishing the flame front. A comparison is also made with heated and vitiated coflow cases, where autoignition is a flame stabilization mechanism and influenced by local strain rate. At high jet exit velocities (Ux > > Ur), the out-of-plane strain rate component can be neglected but the convection of extinguished pockets into the measurement plane needs to be resolved by stereoscopic (3-D) measurements which will be done in a future work. This work has been supported by the U.S. Army Research Office (Contracts W911NF1210140 and W911NF1610087) Dr. Ralph Anthenien, Technical Monitor, ARO.

  17. Opposed jet burner studies of effects of CO, CO2, and N2 air-contaminants on hydrogen-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Guerra, Rosemary; Pellett, Gerald L.; Northam, G. Burton; Wilson, Lloyd G.

    1987-01-01

    The blowoff/restore characteristics for jets of various H2/N2 mixtures opposed to jets of air contaminated by N2, CO, and CO2 have been determined using a counterflow diffusion flame formed by a tubular opposed jet burner. Both blowoff and restore limits are found to be sensitive to fuel and air composition. Empirically derived variations in the limits of the average mass flux of incoming H2 with percent contaminant, at fixed incoming fuel and H2/O2 inputs, are used to quantify the effects of oxygen dilution, flame augmentation, and flame retardation by N2, CO, and CO2 contaminants. The implications of the results are discussed.

  18. Opposed jet burner studies of effects of CO, CO2, and N2 air-contaminants on hydrogen-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Guerra, Rosemary; Pellett, Gerald L.; Northam, G. Burton; Wilson, Lloyd G.

    1987-01-01

    The blowoff/restore characteristics for jets of various H2/N2 mixtures opposed to jets of air contaminated by N2, CO, and CO2 have been determined using a counterflow diffusion flame formed by a tubular opposed jet burner. Both blowoff and restore limits are found to be sensitive to fuel and air composition. Empirically derived variations in the limits of the average mass flux of incoming H2 with percent contaminant, at fixed incoming fuel and H2/O2 inputs, are used to quantify the effects of oxygen dilution, flame augmentation, and flame retardation by N2, CO, and CO2 contaminants. The implications of the results are discussed.

  19. COMPARISON OF EXPERIMENTS TO CFD MODELS FOR MIXING USING DUAL OPPOSING JETS IN TANKS WITH AND WITHOUT INTERNAL OBSTRUCTIONS

    SciTech Connect

    Leishear, R.; Poirier, M.; Lee, S.; Fowley, M.

    2012-06-26

    This paper documents testing methods, statistical data analysis, and a comparison of experimental results to CFD models for blending of fluids, which were blended using a single pump designed with dual opposing nozzles in an eight foot diameter tank. Overall, this research presents new findings in the field of mixing research. Specifically, blending processes were clearly shown to have random, chaotic effects, where possible causal factors such as turbulence, pump fluctuations, and eddies required future evaluation. CFD models were shown to provide reasonable estimates for the average blending times, but large variations -- or scatter -- occurred for blending times during similar tests. Using this experimental blending time data, the chaotic nature of blending was demonstrated and the variability of blending times with respect to average blending times were shown to increase with system complexity. Prior to this research, the variation in blending times caused discrepancies between CFD models and experiments. This research addressed this discrepancy, and determined statistical correction factors that can be applied to CFD models, and thereby quantified techniques to permit the application of CFD models to complex systems, such as blending. These blending time correction factors for CFD models are comparable to safety factors used in structural design, and compensate variability that cannot be theoretically calculated. To determine these correction factors, research was performed to investigate blending, using a pump with dual opposing jets which re-circulate fluids in the tank to promote blending when fluids are added to the tank. In all, eighty-five tests were performed both in a tank without internal obstructions and a tank with vertical obstructions similar to a tube bank in a heat exchanger. These obstructions provided scale models of vertical cooling coils below the liquid surface for a full scale, liquid radioactive waste storage tank. Also, different jet

  20. Localized flame extinction and re-ignition in turbulent jet ignition assisted combustion

    NASA Astrophysics Data System (ADS)

    Validi, Abdoulahad; Schock, Harold; Jaberi, Farhad; Computational Fluid Dynamics Laboratory Team

    2016-11-01

    Direct numerical simulations (DNS) of turbulent jet ignition (TJI)-assisted combustion of ultra-lean fuel-air is performed in a three-dimensional planar jet configuration. TJI is a novel ignition enhancement method which facilitates the combustion of lean and ultra-lean mixtures by rapidly exposing them to high temperature combustion products. Fully compressible gas dynamics and species equations are solved with high order finite difference methods. The hydrogen-air reaction is simulated with a detailed chemical kinetics mechanism consisting of 9 species and 38 elementary reactions. The interesting phenomena involved in TJI combustion including localized premixed flame extinction/re-ignition and simultaneous premixed/non-premixed flames are investigated by using the flame heat release, temperature, species concentrations, and a newly defined TJI progress variable.

  1. The Relationship of Satellite-Inferred Stratospheric Aerosol Extinction to the Position of the 50-mb North Polar Jet Stream.

    NASA Astrophysics Data System (ADS)

    Livingston, John M.; Endlich, Roy M.

    1988-06-01

    Particulate extinction profiles measured by the satellite-borne SAM II and SAGE I sensors have been used to investigate the relationship between stratospheric aerosols (between 15 and 30 km) and the location of the north polar night stratospheric jet stream during selected periods of the winters of 1979-1982. Mean profiles of aerosol extinction mixing ratio (the ratio of particulate to molecule extinction) and temperature across the jet axis have been constructed by determining the location and the distance of individual SAM II profiles relative to the position of the jet axis on the 50-mb isobaric surface, and averaging all profiles located at similar distances on the same side (cyclonic or anticyclonic) of the jet. Variations in aerosol extinction mixing ratio patterns among winters and during major stratospheric warming events within separate winters have been examined. The analyses show a well-defined positive gradient in extinction mixing ratio and temperature across the jet stream from the cyclonic side to the anticyclonic side at altitudes between 20 and 30 km during each winter period. During major stratospheric warming events, this relationship between the distribution of aerosols and the jet stream axis remained intact, even though the dynamic meteorological structure underwent major changes that typically included the breakdown of an elongated, intense polar vortex into two separate, smaller, and less intense vortices. Time-averaged estimates of extinction mixing ratio profiles measured at locations near the center of the polar vortex suggest that a gradual subsidence took place within the polar vortex during at least three of the four winter periods.

  2. A study of performance parameters on drag and heat flux reduction efficiency of combinational novel cavity and opposing jet concept in hypersonic flows

    NASA Astrophysics Data System (ADS)

    Sun, Xi-wan; Guo, Zhen-yun; Huang, Wei; Li, Shi-bin; Yan, Li

    2017-02-01

    The drag reduction and thermal protection system applied to hypersonic re-entry vehicles have attracted an increasing attention, and several novel concepts have been proposed by researchers. In the current study, the influences of performance parameters on drag and heat reduction efficiency of combinational novel cavity and opposing jet concept has been investigated numerically. The Reynolds-average Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flowfields, and the first-order spatially accurate upwind scheme appears to be more suitable for three-dimensional flowfields after grid independent analysis. Different cases of performance parameters, namely jet operating conditions, freestream angle of attack and physical dimensions, are simulated based on the verification of numerical method, and the effects on shock stand-off distance, drag force coefficient, surface pressure and heat flux distributions have been analyzed. This is the basic study for drag reduction and thermal protection by multi-objective optimization of the combinational novel cavity and opposing jet concept in hypersonic flows in the future.

  3. An experimental study of opposed flow diffusion flame extinction over a thin fuel in microgravity. M.S. Thesis. Final Report

    NASA Technical Reports Server (NTRS)

    Ferkul, Paul V.

    1989-01-01

    The flame spread and flame extinction characteristics of a thin fuel burning in a low-speed forced convective environment in microgravity were examined. The flame spread rate was observed to decrease both with decreasing ambient oxygen concentration as well as decreasing free stream velocity. A new mode of flame extinction was observed, caused by either of two means: keeping the free stream velocity constant and decreasing the oxygen concentration, or keeping the oxygen concentration constant and decreasing the free stream velocity. This extinction is called quenching extinction. By combining this data together with a previous microgravity quiescent flame study and normal-gravity blowoff extinction data, a flammability map was constructed with molar percentage oxygen and characteristic relative velocity as coordinates. The Damkohler number is not sufficient to predict flame spread and extinction in the near quench limit region.

  4. Experimental studies on the extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Wilson, L. G.; Northam, G. B.

    1990-01-01

    The paper presents data on the extinction of hydrogen-air counterflow diffusion flames (CFDFs). In the experiments, five coaxial tubular opposed jet burners were used to form dish-shaped CFDFs, centered by opposing laminar jets of N2-diluted H2 and both clean and contaminated air in the argon-purged chamber at 1 atm. Air jet velocities, U(air), characterized extinction of the air-side flame (blowoff) as functions of input H2/N2 (20-100 mole pct) on the fuel side, and air contaminant (0-20 percent) steam, CO2 and O2 (16-30 percent) on the air side.

  5. Experimental studies on the extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Wilson, L. G.; Northam, G. B.

    1990-01-01

    The paper presents data on the extinction of hydrogen-air counterflow diffusion flames (CFDFs). In the experiments, five coaxial tubular opposed jet burners were used to form dish-shaped CFDFs, centered by opposing laminar jets of N2-diluted H2 and both clean and contaminated air in the argon-purged chamber at 1 atm. Air jet velocities, U(air), characterized extinction of the air-side flame (blowoff) as functions of input H2/N2 (20-100 mole pct) on the fuel side, and air contaminant (0-20 percent) steam, CO2 and O2 (16-30 percent) on the air side.

  6. Search for jet extinction in the inclusive jet-pT spectrum from proton-proton collisions at √s =8 TeV

    NASA Astrophysics Data System (ADS)

    Khachatryan, V.; Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Fabjan, C.; Friedl, M.; Frühwirth, R.; Ghete, V. M.; Hartl, C.; Hörmann, N.; Hrubec, J.; Jeitler, M.; Kiesenhofer, W.; Knünz, V.; Krammer, M.; Krätschmer, I.; Liko, D.; Mikulec, I.; Rabady, D.; Rahbaran, B.; Rohringer, H.; Schöfbeck, R.; Strauss, J.; Taurok, A.; Treberer-Treberspurg, W.; Waltenberger, W.; Wulz, C.-E.; Mossolov, V.; Shumeiko, N.; Suarez Gonzalez, J.; Alderweireldt, S.; Bansal, M.; Bansal, S.; Cornelis, T.; De Wolf, E. A.; Janssen, X.; Knutsson, A.; Luyckx, S.; Ochesanu, S.; Roland, B.; Rougny, R.; Van De Klundert, M.; Van Haevermaet, H.; Van Mechelen, P.; Van Remortel, N.; Van Spilbeeck, A.; Blekman, F.; Blyweert, S.; D'Hondt, J.; Daci, N.; Heracleous, N.; Kalogeropoulos, A.; Keaveney, J.; Kim, T. J.; Lowette, S.; Maes, M.; Olbrechts, A.; Python, Q.; Strom, D.; Tavernier, S.; Van Doninck, W.; Van Mulders, P.; Van Onsem, G. P.; Villella, I.; Caillol, C.; Clerbaux, B.; De Lentdecker, G.; Dobur, D.; Favart, L.; Gay, A. P. R.; Grebenyuk, A.; Léonard, A.; Mohammadi, A.; Perniè, L.; Reis, T.; Seva, T.; Thomas, L.; Vander Velde, C.; Vanlaer, P.; Wang, J.; Adler, V.; Beernaert, K.; Benucci, L.; Cimmino, A.; Costantini, S.; Crucy, S.; Dildick, S.; Fagot, A.; Garcia, G.; Klein, B.; Mccartin, J.; Ocampo Rios, A. A.; Ryckbosch, D.; Salva Diblen, S.; Sigamani, M.; Strobbe, N.; Thyssen, F.; Tytgat, M.; Yazgan, E.; Zaganidis, N.; Basegmez, S.; Beluffi, C.; Bruno, G.; Castello, R.; Caudron, A.; Ceard, L.; Da Silveira, G. G.; Delaere, C.; du Pree, T.; Favart, D.; Forthomme, L.; Giammanco, A.; Hollar, J.; Jez, P.; Komm, M.; Lemaitre, V.; Liao, J.; Nuttens, C.; Pagano, D.; Pin, A.; Piotrzkowski, K.; Popov, A.; Quertenmont, L.; Selvaggi, M.; Vidal Marono, M.; Vizan Garcia, J. M.; Beliy, N.; Caebergs, T.; Daubie, E.; Hammad, G. H.; Alves, G. A.; Correa Martins Junior, M.; Dos Reis Martins, T.; Pol, M. E.; Aldá Júnior, W. L.; Carvalho, W.; Chinellato, J.; Custódio, A.; Da Costa, E. M.; De Jesus Damiao, D.; De Oliveira Martins, C.; Fonseca De Souza, S.; Malbouisson, H.; Malek, M.; Matos Figueiredo, D.; Mundim, L.; Nogima, H.; Prado Da Silva, W. L.; Santaolalla, J.; Santoro, A.; Sznajder, A.; Tonelli Manganote, E. J.; Vilela Pereira, A.; Bernardes, C. A.; Dias, F. A.; Fernandez Perez Tomei, T. R.; Gregores, E. M.; Mercadante, P. G.; Novaes, S. F.; Padula, Sandra S.; Aleksandrov, A.; Genchev, V.; Iaydjiev, P.; Marinov, A.; Piperov, S.; Rodozov, M.; Sultanov, G.; Vutova, M.; Dimitrov, A.; Glushkov, I.; Hadjiiska, R.; Kozhuharov, V.; Litov, L.; Pavlov, B.; Petkov, P.; Bian, J. G.; Chen, G. M.; Chen, H. S.; Chen, M.; Du, R.; Jiang, C. H.; Liang, D.; Liang, S.; Plestina, R.; Tao, J.; Wang, X.; Wang, Z.; Asawatangtrakuldee, C.; Ban, Y.; Guo, Y.; Li, Q.; Li, W.; Liu, S.; Mao, Y.; Qian, S. J.; Wang, D.; Zhang, L.; Zou, W.; Avila, C.; Chaparro Sierra, L. F.; Florez, C.; Gomez, J. P.; Gomez Moreno, B.; Sanabria, J. C.; Godinovic, N.; Lelas, D.; Polic, D.; Puljak, I.; Antunovic, Z.; Kovac, M.; Brigljevic, V.; Kadija, K.; Luetic, J.; Mekterovic, D.; Sudic, L.; Attikis, A.; Mavromanolakis, G.; Mousa, J.; Nicolaou, C.; Ptochos, F.; Razis, P. A.; Bodlak, M.; Finger, M.; Finger, M.; Assran, Y.; Elgammal, S.; Mahmoud, M. A.; Radi, A.; Kadastik, M.; Murumaa, M.; Raidal, M.; Tiko, A.; Eerola, P.; Fedi, G.; Voutilainen, M.; Härkönen, J.; Karimäki, V.; Kinnunen, R.; Kortelainen, M. J.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Peltola, T.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Wendland, L.; Tuuva, T.; Besancon, M.; Couderc, F.; Dejardin, M.; Denegri, D.; Fabbro, B.; Faure, J. L.; Favaro, C.; Ferri, F.; Ganjour, S.; Givernaud, A.; Gras, P.; Hamel de Monchenault, G.; Jarry, P.; Locci, E.; Malcles, J.; Nayak, A.; Rander, J.; Rosowsky, A.; Titov, M.; Baffioni, S.; Beaudette, F.; Busson, P.; Charlot, C.; Dahms, T.; Dalchenko, M.; Dobrzynski, L.; Filipovic, N.; Florent, A.; Granier de Cassagnac, R.; Mastrolorenzo, L.; Miné, P.; Mironov, C.; Naranjo, I. N.; Nguyen, M.; Ochando, C.; Paganini, P.; Salerno, R.; Sauvan, J. B.; Sirois, Y.; Veelken, C.; Yilmaz, Y.; Zabi, A.; Agram, J.-L.; Andrea, J.; Aubin, A.; Bloch, D.; Brom, J.-M.; Chabert, E. C.; Collard, C.; Conte, E.; Fontaine, J.-C.; Gelé, D.; Goerlach, U.; Goetzmann, C.; Le Bihan, A.-C.; Van Hove, P.; Gadrat, S.; Beauceron, S.; Beaupere, N.; Boudoul, G.; Brochet, S.; Carrillo Montoya, C. A.; Chasserat, J.; Chierici, R.; Contardo, D.; Depasse, P.; El Mamouni, H.; Fan, J.; Fay, J.; Gascon, S.; Gouzevitch, M.; Ille, B.; Kurca, T.; Lethuillier, M.; Mirabito, L.; Perries, S.; Ruiz Alvarez, J. D.; Sabes, D.; Sgandurra, L.; Sordini, V.; Vander Donckt, M.; Verdier, P.; Viret, S.; Xiao, H.; Tsamalaidze, Z.; Autermann, C.; Beranek, S.; Bontenackels, M.; Calpas, B.; Edelhoff, M.; Feld, L.; Hindrichs, O.; Klein, K.; Ostapchuk, A.; Perieanu, A.; Raupach, F.; Sammet, J.; Schael, S.; Sprenger, D.; Weber, H.; Wittmer, B.; Zhukov, V.; Ata, M.; Caudron, J.; Dietz-Laursonn, E.; Duchardt, D.; Erdmann, M.; Fischer, R.; Güth, A.; Hebbeker, T.; Heidemann, C.; Hoepfner, K.; Klingebiel, D.; Knutzen, S.; Kreuzer, P.; Merschmeyer, M.; Meyer, A.; Olschewski, M.; Padeken, K.; Papacz, P.; Reithler, H.; Schmitz, S. A.; Sonnenschein, L.; Teyssier, D.; Thüer, S.; Weber, M.; Cherepanov, V.; Erdogan, Y.; Flügge, G.; Geenen, H.; Geisler, M.; Haj Ahmad, W.; Hoehle, F.; Kargoll, B.; Kress, T.; Kuessel, Y.; Lingemann, J.; Nowack, A.; Nugent, I. M.; Perchalla, L.; Pooth, O.; Stahl, A.; Asin, I.; Bartosik, N.; Behr, J.; Behrenhoff, W.; Behrens, U.; Bell, A. J.; Bergholz, M.; Bethani, A.; Borras, K.; Burgmeier, A.; Cakir, A.; Calligaris, L.; Campbell, A.; Choudhury, S.; Costanza, F.; Diez Pardos, C.; Dooling, S.; Dorland, T.; Eckerlin, G.; Eckstein, D.; Eichhorn, T.; Flucke, G.; Garay Garcia, J.; Geiser, A.; Gunnellini, P.; Hauk, J.; Hellwig, G.; Hempel, M.; Horton, D.; Jung, H.; Kasemann, M.; Katsas, P.; Kieseler, J.; Kleinwort, C.; Krücker, D.; Lange, W.; Leonard, J.; Lipka, K.; Lobanov, A.; Lohmann, W.; Lutz, B.; Mankel, R.; Marfin, I.; Melzer-Pellmann, I.-A.; Meyer, A. B.; Mnich, J.; Mussgiller, A.; Naumann-Emme, S.; Novgorodova, O.; Nowak, F.; Ntomari, E.; Perrey, H.; Pitzl, D.; Placakyte, R.; Raspereza, A.; Ribeiro Cipriano, P. M.; Ron, E.; Sahin, M. Ö.; Salfeld-Nebgen, J.; Saxena, P.; Schmidt, R.; Schoerner-Sadenius, T.; Schröder, M.; Spannagel, S.; Vargas Trevino, A. D. R.; Walsh, R.; Wissing, C.; Aldaya Martin, M.; Blobel, V.; Centis Vignali, M.; Erfle, J.; Garutti, E.; Goebel, K.; Görner, M.; Gosselink, M.; Haller, J.; Höing, R. S.; Kirschenmann, H.; Klanner, R.; Kogler, R.; Lange, J.; Lapsien, T.; Lenz, T.; Marchesini, I.; Ott, J.; Peiffer, T.; Pietsch, N.; Rathjens, D.; Sander, C.; Schettler, H.; Schleper, P.; Schlieckau, E.; Schmidt, A.; Seidel, M.; Sibille, J.; Sola, V.; Stadie, H.; Steinbrück, G.; Troendle, D.; Usai, E.; Vanelderen, L.; Barth, C.; Baus, C.; Berger, J.; Böser, C.; Butz, E.; Chwalek, T.; De Boer, W.; Descroix, A.; Dierlamm, A.; Feindt, M.; Hartmann, F.; Hauth, T.; Husemann, U.; Katkov, I.; Kornmayer, A.; Kuznetsova, E.; Lobelle Pardo, P.; Mozer, M. U.; Müller, Th.; Nürnberg, A.; Quast, G.; Rabbertz, K.; Ratnikov, F.; Röcker, S.; Simonis, H. J.; Stober, F. M.; Ulrich, R.; Wagner-Kuhr, J.; Wayand, S.; Weiler, T.; Wolf, R.; Anagnostou, G.; Daskalakis, G.; Geralis, T.; Giakoumopoulou, V. 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M.; Fabbri, F.; Fanfani, A.; Fasanella, D.; Giacomelli, P.; Grandi, C.; Guiducci, L.; Marcellini, S.; Masetti, G.; Montanari, A.; Navarria, F. L.; Perrotta, A.; Primavera, F.; Rossi, A. M.; Rovelli, T.; Siroli, G. P.; Tosi, N.; Travaglini, R.; Albergo, S.; Cappello, G.; Chiorboli, M.; Costa, S.; Giordano, F.; Potenza, R.; Tricomi, A.; Tuve, C.; Barbagli, G.; Ciulli, V.; Civinini, C.; D'Alessandro, R.; Focardi, E.; Gallo, E.; Gonzi, S.; Gori, V.; Lenzi, P.; Meschini, M.; Paoletti, S.; Sguazzoni, G.; Tropiano, A.; Benussi, L.; Bianco, S.; Fabbri, F.; Piccolo, D.; Ferro, F.; Lo Vetere, M.; Robutti, E.; Tosi, S.; Dinardo, M. E.; Fiorendi, S.; Gennai, S.; Gerosa, R.; Ghezzi, A.; Govoni, P.; Lucchini, M. T.; Malvezzi, S.; Manzoni, R. A.; Martelli, A.; Marzocchi, B.; Menasce, D.; Moroni, L.; Paganoni, M.; Pedrini, D.; Ragazzi, S.; Redaelli, N.; Tabarelli de Fatis, T.; Buontempo, S.; Cavallo, N.; Di Guida, S.; Fabozzi, F.; Iorio, A. O. M.; Lista, L.; Meola, S.; Merola, M.; Paolucci, P.; Azzi, P.; Bacchetta, N.; Bisello, D.; Branca, A.; Carlin, R.; Dall'Osso, M.; Dorigo, T.; Galanti, M.; Gasparini, F.; Giubilato, P.; Gozzelino, A.; Kanishchev, K.; Lacaprara, S.; Margoni, M.; Meneguzzo, A. T.; Montecassiano, F.; Passaseo, M.; Pazzini, J.; Pozzobon, N.; Ronchese, P.; Simonetto, F.; Torassa, E.; Tosi, M.; Vanini, S.; Zotto, P.; Zucchetta, A.; Zumerle, G.; Gabusi, M.; Ratti, S. P.; Riccardi, C.; Salvini, P.; Vitulo, P.; Biasini, M.; Bilei, G. M.; Ciangottini, D.; Fanò, L.; Lariccia, P.; Mantovani, G.; Menichelli, M.; Romeo, F.; Saha, A.; Santocchia, A.; Spiezia, A.; Androsov, K.; Azzurri, P.; Bagliesi, G.; Bernardini, J.; Boccali, T.; Broccolo, G.; Castaldi, R.; Ciocci, M. A.; Dell'Orso, R.; Donato, S.; Fiori, F.; Foà, L.; Giassi, A.; Grippo, M. T.; Ligabue, F.; Lomtadze, T.; Martini, L.; Messineo, A.; Moon, C. S.; Palla, F.; Rizzi, A.; Savoy-Navarro, A.; Serban, A. T.; Spagnolo, P.; Squillacioti, P.; Tenchini, R.; Tonelli, G.; Venturi, A.; Verdini, P. G.; Vernieri, C.; Barone, L.; Cavallari, F.; Del Re, D.; Diemoz, M.; Grassi, M.; Jorda, C.; Longo, E.; Margaroli, F.; Meridiani, P.; Micheli, F.; Nourbakhsh, S.; Organtini, G.; Paramatti, R.; Rahatlou, S.; Rovelli, C.; Santanastasio, F.; Soffi, L.; Traczyk, P.; Amapane, N.; Arcidiacono, R.; Argiro, S.; Arneodo, M.; Bellan, R.; Biino, C.; Cartiglia, N.; Casasso, S.; Costa, M.; Degano, A.; Demaria, N.; Finco, L.; Mariotti, C.; Maselli, S.; Migliore, E.; Monaco, V.; Musich, M.; Obertino, M. M.; Ortona, G.; Pacher, L.; Pastrone, N.; Pelliccioni, M.; Pinna Angioni, G. L.; Potenza, A.; Romero, A.; Ruspa, M.; Sacchi, R.; Solano, A.; Staiano, A.; Tamponi, U.; Belforte, S.; Candelise, V.; Casarsa, M.; Cossutti, F.; Della Ricca, G.; Gobbo, B.; La Licata, C.; Marone, M.; Montanino, D.; Schizzi, A.; Umer, T.; Zanetti, A.; Chang, S.; Kropivnitskaya, A.; Nam, S. K.; Kim, D. H.; Kim, G. N.; Kim, M. S.; Kong, D. J.; Lee, S.; Oh, Y. D.; Park, H.; Sakharov, A.; Son, D. C.; Kim, J. Y.; Song, S.; Choi, S.; Gyun, D.; Hong, B.; Jo, M.; Kim, H.; Kim, Y.; Lee, B.; Lee, K. S.; Park, S. K.; Roh, Y.; Choi, M.; Kim, J. H.; Park, I. C.; Park, S.; Ryu, G.; Ryu, M. S.; Choi, Y.; Choi, Y. K.; Goh, J.; Kwon, E.; Lee, J.; Seo, H.; Yu, I.; Juodagalvis, A.; Komaragiri, J. R.; Castilla-Valdez, H.; De La Cruz-Burelo, E.; Heredia-de La Cruz, I.; Lopez-Fernandez, R.; Sanchez-Hernandez, A.; Carrillo Moreno, S.; Vazquez Valencia, F.; Pedraza, I.; Salazar Ibarguen, H. A.; Casimiro Linares, E.; Morelos Pineda, A.; Krofcheck, D.; Butler, P. H.; Reucroft, S.; Ahmad, A.; Ahmad, M.; Hassan, Q.; Hoorani, H. R.; Khalid, S.; Khan, W. A.; Khurshid, T.; Shah, M. A.; Shoaib, M.; Bialkowska, H.; Bluj, M.; Boimska, B.; Frueboes, T.; Górski, M.; Kazana, M.; Nawrocki, K.; Romanowska-Rybinska, K.; Szleper, M.; Zalewski, P.; Brona, G.; Bunkowski, K.; Cwiok, M.; Dominik, W.; Doroba, K.; Kalinowski, A.; Konecki, M.; Krolikowski, J.; Misiura, M.; Olszewski, M.; Wolszczak, W.; Bargassa, P.; Beirão Da Cruz E Silva, C.; Faccioli, P.; Ferreira Parracho, P. 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V.; Vinogradov, A.; Belyaev, A.; Boos, E.; Dubinin, M.; Dudko, L.; Ershov, A.; Gribushin, A.; Klyukhin, V.; Kodolova, O.; Lokhtin, I.; Obraztsov, S.; Petrushanko, S.; Savrin, V.; Snigirev, A.; Azhgirey, I.; Bayshev, I.; Bitioukov, S.; Kachanov, V.; Kalinin, A.; Konstantinov, D.; Krychkine, V.; Petrov, V.; Ryutin, R.; Sobol, A.; Tourtchanovitch, L.; Troshin, S.; Tyurin, N.; Uzunian, A.; Volkov, A.; Adzic, P.; Dordevic, M.; Ekmedzic, M.; Milosevic, J.; Alcaraz Maestre, J.; Battilana, C.; Calvo, E.; Cerrada, M.; Chamizo Llatas, M.; Colino, N.; De La Cruz, B.; Delgado Peris, A.; Domínguez Vázquez, D.; Escalante Del Valle, A.; Fernandez Bedoya, C.; Fernández Ramos, J. P.; Flix, J.; Fouz, M. C.; Garcia-Abia, P.; Gonzalez Lopez, O.; Goy Lopez, S.; Hernandez, J. M.; Josa, M. I.; Merino, G.; Navarro De Martino, E.; Pérez-Calero Yzquierdo, A.; Puerta Pelayo, J.; Quintario Olmeda, A.; Redondo, I.; Romero, L.; Soares, M. S.; Albajar, C.; de Trocóniz, J. 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I.; Vlimant, J. R.; Wardle, N.; Wöhri, H. K.; Zeuner, W. D.; Bertl, W.; Deiters, K.; Erdmann, W.; Horisberger, R.; Ingram, Q.; Kaestli, H. C.; König, S.; Kotlinski, D.; Langenegger, U.; Renker, D.; Rohe, T.; Bachmair, F.; Bäni, L.; Bianchini, L.; Bortignon, P.; Buchmann, M. A.; Casal, B.; Chanon, N.; Deisher, A.; Dissertori, G.; Dittmar, M.; Donegà, M.; Dünser, M.; Eller, P.; Grab, C.; Hits, D.; Lustermann, W.; Mangano, B.; Marini, A. C.; Martinez Ruiz del Arbol, P.; Meister, D.; Mohr, N.; Nägeli, C.; Nef, P.; Nessi-Tedaldi, F.; Pandolfi, F.; Pauss, F.; Peruzzi, M.; Quittnat, M.; Rebane, L.; Ronga, F. J.; Rossini, M.; Starodumov, A.; Takahashi, M.; Theofilatos, K.; Wallny, R.; Weber, H. A.; Amsler, C.; Canelli, M. F.; Chiochia, V.; De Cosa, A.; Hinzmann, A.; Hreus, T.; Ivova Rikova, M.; Kilminster, B.; Millan Mejias, B.; Ngadiuba, J.; Robmann, P.; Snoek, H.; Taroni, S.; Verzetti, M.; Yang, Y.; Cardaci, M.; Chen, K. H.; Ferro, C.; Kuo, C. M.; Lin, W.; Lu, Y. J.; Volpe, R.; Yu, S. S.; Chang, P.; Chang, Y. H.; Chang, Y. W.; Chao, Y.; Chen, K. F.; Chen, P. H.; Dietz, C.; Grundler, U.; Hou, W.-S.; Kao, K. Y.; Lei, Y. J.; Liu, Y. F.; Lu, R.-S.; Majumder, D.; Petrakou, E.; Shi, X.; Tzeng, Y. M.; Wilken, R.; Asavapibhop, B.; Srimanobhas, N.; Suwonjandee, N.; Adiguzel, A.; Bakirci, M. N.; Cerci, S.; Dozen, C.; Dumanoglu, I.; Eskut, E.; Girgis, S.; Gokbulut, G.; Gurpinar, E.; Hos, I.; Kangal, E. E.; Kayis Topaksu, A.; Onengut, G.; Ozdemir, K.; Ozturk, S.; Polatoz, A.; Sogut, K.; Sunar Cerci, D.; Tali, B.; Topakli, H.; Vergili, M.; Akin, I. V.; Bilin, B.; Bilmis, S.; Gamsizkan, H.; Karapinar, G.; Ocalan, K.; Surat, U. E.; Yalvac, M.; Zeyrek, M.; Gülmez, E.; Isildak, B.; Kaya, M.; Kaya, O.; Bahtiyar, H.; Barlas, E.; Cankocak, K.; Vardarlı, F. I.; Yücel, M.; Levchuk, L.; Sorokin, P.; Brooke, J. J.; Clement, E.; Cussans, D.; Flacher, H.; Frazier, R.; Goldstein, J.; Grimes, M.; Heath, G. P.; Heath, H. F.; Jacob, J.; Kreczko, L.; Lucas, C.; Meng, Z.; Newbold, D. 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D.; Symonds, P.; Teodorescu, L.; Turner, M.; Dittmann, J.; Hatakeyama, K.; Kasmi, A.; Liu, H.; Scarborough, T.; Charaf, O.; Cooper, S. I.; Henderson, C.; Rumerio, P.; Avetisyan, A.; Bose, T.; Fantasia, C.; Heister, A.; Lawson, P.; Richardson, C.; Rohlf, J.; Sperka, D.; St. John, J.; Sulak, L.; Alimena, J.; Bhattacharya, S.; Christopher, G.; Cutts, D.; Demiragli, Z.; Ferapontov, A.; Garabedian, A.; Heintz, U.; Jabeen, S.; Kukartsev, G.; Laird, E.; Landsberg, G.; Luk, M.; Narain, M.; Segala, M.; Sinthuprasith, T.; Speer, T.; Swanson, J.; Breedon, R.; Breto, G.; Calderon De La Barca Sanchez, M.; Chauhan, S.; Chertok, M.; Conway, J.; Conway, R.; Cox, P. T.; Erbacher, R.; Gardner, M.; Ko, W.; Lander, R.; Miceli, T.; Mulhearn, M.; Pellett, D.; Pilot, J.; Ricci-Tam, F.; Searle, M.; Shalhout, S.; Smith, J.; Squires, M.; Stolp, D.; Tripathi, M.; Wilbur, S.; Yohay, R.; Cousins, R.; Everaerts, P.; Farrell, C.; Hauser, J.; Ignatenko, M.; Rakness, G.; Takasugi, E.; Valuev, V.; Weber, M.; Babb, J.; Clare, R.; Ellison, J.; Gary, J. W.; Hanson, G.; Heilman, J.; Jandir, P.; Kennedy, E.; Lacroix, F.; Liu, H.; Long, O. R.; Luthra, A.; Malberti, M.; Nguyen, H.; Shrinivas, A.; Sturdy, J.; Sumowidagdo, S.; Wimpenny, S.; Andrews, W.; Branson, J. G.; Cerati, G. B.; Cittolin, S.; D'Agnolo, R. T.; Evans, D.; Holzner, A.; Kelley, R.; Lebourgeois, M.; Letts, J.; Macneill, I.; Olivito, D.; Padhi, S.; Palmer, C.; Pieri, M.; Sani, M.; Sharma, V.; Simon, S.; Sudano, E.; Tadel, M.; Tu, Y.; Vartak, A.; Würthwein, F.; Yagil, A.; Yoo, J.; Barge, D.; Bradmiller-Feld, J.; Campagnari, C.; Danielson, T.; Dishaw, A.; Flowers, K.; Franco Sevilla, M.; Geffert, P.; George, C.; Golf, F.; Incandela, J.; Justus, C.; Mccoll, N.; Richman, J.; Stuart, D.; To, W.; West, C.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Di Marco, E.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Rogan, C.; Spiropulu, M.; Timciuc, V.; Wilkinson, R.; Xie, S.; Zhu, R. Y.; Azzolini, V.; Calamba, A.; Carroll, R.; Ferguson, T.; Iiyama, Y.; Paulini, M.; Russ, J.; Vogel, H.; Vorobiev, I.; Cumalat, J. P.; Drell, B. R.; Ford, W. T.; Gaz, A.; Luiggi Lopez, E.; Nauenberg, U.; Smith, J. G.; Stenson, K.; Ulmer, K. A.; Wagner, S. R.; Alexander, J.; Chatterjee, A.; Chu, J.; Dittmer, S.; Eggert, N.; Hopkins, W.; Kreis, B.; Mirman, N.; Nicolas Kaufman, G.; Patterson, J. R.; Ryd, A.; Salvati, E.; Skinnari, L.; Sun, W.; Teo, W. D.; Thom, J.; Thompson, J.; Tucker, J.; Weng, Y.; Winstrom, L.; Wittich, P.; Winn, D.; Abdullin, S.; Albrow, M.; Anderson, J.; Apollinari, G.; Bauerdick, L. A. T.; Beretvas, A.; Berryhill, J.; Bhat, P. C.; Burkett, K.; Butler, J. N.; Cheung, H. W. K.; Chlebana, F.; Cihangir, S.; Elvira, V. D.; Fisk, I.; Freeman, J.; Gottschalk, E.; Gray, L.; Green, D.; Grünendahl, S.; Gutsche, O.; Hanlon, J.; Hare, D.; Harris, R. M.; Hirschauer, J.; Hooberman, B.; Jindariani, S.; Johnson, M.; Joshi, U.; Kaadze, K.; Klima, B.; Kwan, S.; Linacre, J.; Lincoln, D.; Lipton, R.; Liu, T.; Lykken, J.; Maeshima, K.; Marraffino, J. M.; Martinez Outschoorn, V. I.; Maruyama, S.; Mason, D.; McBride, P.; Mishra, K.; Mrenna, S.; Musienko, Y.; Nahn, S.; Newman-Holmes, C.; O'Dell, V.; Prokofyev, O.; Sexton-Kennedy, E.; Sharma, S.; Soha, A.; Spalding, W. J.; Spiegel, L.; Taylor, L.; Tkaczyk, S.; Tran, N. V.; Uplegger, L.; Vaandering, E. W.; Vidal, R.; Whitbeck, A.; Whitmore, J.; Yang, F.; Acosta, D.; Avery, P.; Bourilkov, D.; Carver, M.; Cheng, T.; Curry, D.; Das, S.; De Gruttola, M.; Di Giovanni, G. P.; Field, R. D.; Fisher, M.; Furic, I. K.; Hugon, J.; Konigsberg, J.; Korytov, A.; Kypreos, T.; Low, J. F.; Matchev, K.; Milenovic, P.; Mitselmakher, G.; Muniz, L.; Rinkevicius, A.; Shchutska, L.; Skhirtladze, N.; Snowball, M.; Yelton, J.; Zakaria, M.; Gaultney, V.; Hewamanage, S.; Linn, S.; Markowitz, P.; Martinez, G.; Rodriguez, J. L.; Adams, T.; Askew, A.; Bochenek, J.; Diamond, B.; Haas, J.; Hagopian, S.; Hagopian, V.; Johnson, K. F.; Prosper, H.; Veeraraghavan, V.; Weinberg, M.; Baarmand, M. M.; Hohlmann, M.; Kalakhety, H.; Yumiceva, F.; Adams, M. R.; Apanasevich, L.; Bazterra, V. E.; Berry, D.; Betts, R. R.; Bucinskaite, I.; Cavanaugh, R.; Evdokimov, O.; Gauthier, L.; Gerber, C. E.; Hofman, D. J.; Khalatyan, S.; Kurt, P.; Moon, D. H.; O'Brien, C.; Silkworth, C.; Turner, P.; Varelas, N.; Albayrak, E. A.; Bilki, B.; Clarida, W.; Dilsiz, K.; Duru, F.; Haytmyradov, M.; Merlo, J.-P.; Mermerkaya, H.; Mestvirishvili, A.; Moeller, A.; Nachtman, J.; Ogul, H.; Onel, Y.; Ozok, F.; Penzo, A.; Rahmat, R.; Sen, S.; Tan, P.; Tiras, E.; Wetzel, J.; Yetkin, T.; Yi, K.; Barnett, B. A.; Blumenfeld, B.; Bolognesi, S.; Fehling, D.; Gritsan, A. V.; Maksimovic, P.; Martin, C.; Swartz, M.; Baringer, P.; Bean, A.; Benelli, G.; Bruner, C.; Gray, J.; Kenny, R. P.; Murray, M.; Noonan, D.; Sanders, S.; Sekaric, J.; Stringer, R.; Wang, Q.; Wood, J. S.; Barfuss, A. F.; Chakaberia, I.; Ivanov, A.; Khalil, S.; Makouski, M.; Maravin, Y.; Saini, L. K.; Shrestha, S.; Svintradze, I.; Gronberg, J.; Lange, D.; Rebassoo, F.; Wright, D.; Baden, A.; Calvert, B.; Eno, S. C.; Gomez, J. A.; Hadley, N. J.; Kellogg, R. G.; Kolberg, T.; Lu, Y.; Marionneau, M.; Mignerey, A. C.; Pedro, K.; Skuja, A.; Tonjes, M. B.; Tonwar, S. C.; Apyan, A.; Barbieri, R.; Bauer, G.; Busza, W.; Cali, I. A.; Chan, M.; Di Matteo, L.; Dutta, V.; Gomez Ceballos, G.; Goncharov, M.; Gulhan, D.; Klute, M.; Lai, Y. S.; Lee, Y.-J.; Levin, A.; Luckey, P. D.; Ma, T.; Paus, C.; Ralph, D.; Roland, C.; Roland, G.; Stephans, G. S. F.; Stöckli, F.; Sumorok, K.; Velicanu, D.; Veverka, J.; Wyslouch, B.; Yang, M.; Zanetti, M.; Zhukova, V.; Dahmes, B.; De Benedetti, A.; Gude, A.; Kao, S. C.; Klapoetke, K.; Kubota, Y.; Mans, J.; Pastika, N.; Rusack, R.; Singovsky, A.; Tambe, N.; Turkewitz, J.; Acosta, J. G.; Oliveros, S.; Avdeeva, E.; Bloom, K.; Bose, S.; Claes, D. R.; Dominguez, A.; Gonzalez Suarez, R.; Keller, J.; Knowlton, D.; Kravchenko, I.; Lazo-Flores, J.; Malik, S.; Meier, F.; Snow, G. R.; Dolen, J.; Godshalk, A.; Iashvili, I.; Kharchilava, A.; Kumar, A.; Rappoccio, S.; Alverson, G.; Barberis, E.; Baumgartel, D.; Chasco, M.; Haley, J.; Massironi, A.; Morse, D. M.; Nash, D.; Orimoto, T.; Trocino, D.; Wood, D.; Zhang, J.; Hahn, K. A.; Kubik, A.; Mucia, N.; Odell, N.; Pollack, B.; Pozdnyakov, A.; Schmitt, M.; Stoynev, S.; Sung, K.; Velasco, M.; Won, S.; Brinkerhoff, A.; Chan, K. M.; Drozdetskiy, A.; Hildreth, M.; Jessop, C.; Karmgard, D. J.; Kellams, N.; Lannon, K.; Luo, W.; Lynch, S.; Marinelli, N.; Pearson, T.; Planer, M.; Ruchti, R.; Valls, N.; Wayne, M.; Wolf, M.; Woodard, A.; Antonelli, L.; Brinson, J.; Bylsma, B.; Durkin, L. S.; Flowers, S.; Hill, C.; Hughes, R.; Kotov, K.; Ling, T. Y.; Puigh, D.; Rodenburg, M.; Smith, G.; Vuosalo, C.; Winer, B. L.; Wolfe, H.; Wulsin, H. W.; Berry, E.; Driga, O.; Elmer, P.; Hebda, P.; Hunt, A.; Koay, S. A.; Lujan, P.; Marlow, D.; Medvedeva, T.; Mooney, M.; Olsen, J.; Piroué, P.; Quan, X.; Saka, H.; Stickland, D.; Tully, C.; Werner, J. S.; Zenz, S. C.; Zuranski, A.; Brownson, E.; Mendez, H.; Ramirez Vargas, J. E.; Alagoz, E.; Barnes, V. E.; Benedetti, D.; Bolla, G.; Bortoletto, D.; De Mattia, M.; Everett, A.; Hu, Z.; Jha, M. K.; Jones, M.; Jung, K.; Kress, M.; Leonardo, N.; Lopes Pegna, D.; Maroussov, V.; Merkel, P.; Miller, D. H.; Neumeister, N.; Radburn-Smith, B. C.; Shipsey, I.; Silvers, D.; Svyatkovskiy, A.; Wang, F.; Xie, W.; Xu, L.; Yoo, H. D.; Zablocki, J.; Zheng, Y.; Parashar, N.; Stupak, J.; Adair, A.; Akgun, B.; Ecklund, K. M.; Geurts, F. J. M.; Li, W.; Michlin, B.; Padley, B. P.; Redjimi, R.; Roberts, J.; Zabel, J.; Betchart, B.; Bodek, A.; Covarelli, R.; de Barbaro, P.; Demina, R.; Eshaq, Y.; Ferbel, T.; Garcia-Bellido, A.; Goldenzweig, P.; Han, J.; Harel, A.; Khukhunaishvili, A.; Miner, D. C.; Petrillo, G.; Vishnevskiy, D.; Ciesielski, R.; Demortier, L.; Goulianos, K.; Lungu, G.; Mesropian, C.; Arora, S.; Barker, A.; Chou, J. P.; Contreras-Campana, C.; Contreras-Campana, E.; Duggan, D.; Ferencek, D.; Gershtein, Y.; Gray, R.; Halkiadakis, E.; Hidas, D.; Lath, A.; Panwalkar, S.; Park, M.; Patel, R.; Rekovic, V.; Salur, S.; Schnetzer, S.; Seitz, C.; Somalwar, S.; Stone, R.; Thomas, S.; Thomassen, P.; Walker, M.; Rose, K.; Spanier, S.; York, A.; Bouhali, O.; Eusebi, R.; Flanagan, W.; Gilmore, J.; Kamon, T.; Khotilovich, V.; Krutelyov, V.; Montalvo, R.; Osipenkov, I.; Pakhotin, Y.; Perloff, A.; Roe, J.; Rose, A.; Safonov, A.; Sakuma, T.; Suarez, I.; Tatarinov, A.; Akchurin, N.; Cowden, C.; Damgov, J.; Dragoiu, C.; Dudero, P. R.; Faulkner, J.; Kovitanggoon, K.; Kunori, S.; Lee, S. W.; Libeiro, T.; Volobouev, I.; Appelt, E.; Delannoy, A. G.; Greene, S.; Gurrola, A.; Johns, W.; Maguire, C.; Mao, Y.; Melo, A.; Sharma, M.; Sheldon, P.; Snook, B.; Tuo, S.; Velkovska, J.; Arenton, M. W.; Boutle, S.; Cox, B.; Francis, B.; Goodell, J.; Hirosky, R.; Ledovskoy, A.; Li, H.; Lin, C.; Neu, C.; Wood, J.; Gollapinni, S.; Harr, R.; Karchin, P. E.; Kottachchi Kankanamge Don, C.; Lamichhane, P.; Belknap, D. A.; Carlsmith, D.; Cepeda, M.; Dasu, S.; Duric, S.; Friis, E.; Hall-Wilton, R.; Herndon, M.; Hervé, A.; Klabbers, P.; Klukas, J.; Lanaro, A.; Lazaridis, C.; Levine, A.; Loveless, R.; Mohapatra, A.; Ojalvo, I.; Perry, T.; Pierro, G. A.; Polese, G.; Ross, I.; Sarangi, T.; Savin, A.; Smith, W. H.; Woods, N.; CMS Collaboration

    2014-08-01

    The first search at the LHC for the extinction of QCD jet production is presented, using data collected with the CMS detector corresponding to an integrated luminosity of 10.7 fb-1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The extinction model studied in this analysis is motivated by the search for signatures of strong gravity at the TeV scale (terascale gravity) and assumes the existence of string couplings in the strong-coupling limit. In this limit, the string model predicts the suppression of all high-transverse-momentum standard model processes, including jet production, beyond a certain energy scale. To test this prediction, the measured transverse-momentum spectrum is compared to the theoretical prediction of the standard model. No significant deficit of events is found at high transverse momentum. A 95% confidence level lower limit of 3.3 TeV is set on the extinction mass scale.

  7. Search for jet extinction in the inclusive jet-pt spectrum from proton-proton collisions at sqrt(s) = 8 TeV

    SciTech Connect

    Khachatryan, Vardan; et al.,

    2014-08-01

    The first search at the LHC for the extinction of QCD jet production is presented, using data collected with the CMS detector corresponding to an integrated luminosity of 10.7 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 8 TeV. The extinction model studied in this analysis is motivated by the search for signatures of strong gravity at the TeV scale (terascale gravity) and assumes the existence of string couplings in the strong-coupling limit. In this limit, the string model predicts the suppression of all high-transverse-momentum standard model processes, including jet production, beyond a certain energy scale. To test this prediction, the measured transverse-momentum spectrum is compared to the theoretical prediction of the standard model. No significant deficit of events is found at high transverse momentum. A 95% confidence level lower limit of 3.3 TeV is set on the extinction mass scale.

  8. Strain-induced extinction of hydrogen-air counterflow diffusion flames - Effects of steam, CO2, N2, and O2 additives to air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.

    1992-01-01

    A fundamental study was performed using axisymmetric nozzle and tubular opposed jet burners to measure the effects of laminar plug flow and parabolic input velocity profiles on the extinction limits of H2-air counterflow diffusion flames. Extinction limits were quantified by 'flame strength', (average axial air jet velocity) at blowoff of the central flame. The effects of key air contaminants, on the extinction limits, are characterized and analyzed relative to utilization of combustion contaminated vitiated air in high enthalpy supersonic test facilities.

  9. Strain-induced extinction of hydrogen-air counterflow diffusion flames - Effects of steam, CO2, N2, and O2 additives to air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.

    1992-01-01

    A fundamental study was performed using axisymmetric nozzle and tubular opposed jet burners to measure the effects of laminar plug flow and parabolic input velocity profiles on the extinction limits of H2-air counterflow diffusion flames. Extinction limits were quantified by 'flame strength', (average axial air jet velocity) at blowoff of the central flame. The effects of key air contaminants, on the extinction limits, are characterized and analyzed relative to utilization of combustion contaminated vitiated air in high enthalpy supersonic test facilities.

  10. The relationship of satellite-inferred stratospheric aerosol extinction to the position of the 50-mb north polar jet stream

    NASA Technical Reports Server (NTRS)

    Livingston, John M.; Endlich, Roy M.

    1988-01-01

    The relationship between stratospheric aerosols and the location of the north polar night stratospheric jet stream was investigated for selected periods of four successive winters (1979-1982), using measurements from SAM II (Stratospheric Aerosol Measurement II) and SAGE I (Stratospheric Aerosol and Gas Experiment I) satellite-borne sun photometers and corresponding meteorological observations. Each period investigated included a polar stratospheric warming during which major dynamic meteorological changes are known to have perturbed the structure of the polar vortex. The analysis of variations in aerosol extinction mixing ratio patterns among winters and during major stratospheric warming events within separate winters showed a well-defined positive gradient in extinction mixing ratio and temperature across the jet stream from the cyclonic side to the anticyclonic side at altitudes between 20 and 30 km during each winter period. Estimates of extinction mixing ratio profiles measured near the center of the polar vortex suggest that a gradual subsidence took place within the polar vortex during at least three of the four winter periods.

  11. Opposed Jet Turbulent Diffusion Flames

    DTIC Science & Technology

    1990-09-05

    40F -2 0 204 to9 FRACTAL PLOTS OF THE FUEL SIDE OF THE REACTION ZONE EoulS. Elm . 9S= 0-2. 18 (b) -1.3- -1. 4 -1.5 -1.6 - -2.5 -2.0 -1.5 -1.0 -. 5 0.0...irregular. This may explain the large size of the recircula- tion zone and may be viewed as a precursor to blow-off. It is of interest to compare the...fluctuations do not strongly affect the flame oscillations and so a measurement technique such as Schlieren, which detects density gradients, would not

  12. Ultrafine grinding using a fluidized bed opposed jet mill: effects of feed load and rotational speed of classifier wheel on particle shape.

    PubMed

    Chan, L W; Lee, C C; Heng, P W S

    2002-09-01

    Circularity, aspect ratio, modelx, and pellips were employed to study the effects of process parameters, namely varying feed loads and rotational speeds of the classifier wheel, of the fluidized bed opposed jet mill on the shape of the micronized particles produced. The Shapiro-Wilk statistical test showed that 80.0% of the shape distributions of the four descriptors were not normal. Therefore, the Kruskal-Wallis test, which is a nonparametric statistical test, was employed to analyze the data. Micronized particles were more spherical and less elongated, as indicated respectively by higher median circularity and lower median modelx values when compared to unmilled lactose. These descriptors were able to indicate that the particles had been micronized. When feed loads of 250 and 350 g were used, increasing the rotational speed of the classifier wheel was found to bring about a decrease in span values of all the shape descriptors, indicating that the micronized particles were more uniform in shape. Micronized particles produced had lower median aspect ratio values than the unmilled lactose, whereas a higher feed load of 450 g resulted in the production of micronized particles that were less uniform in shape and more elliptical in nature, as reflected by the lower median pellips values. A higher feed load of 450 g caused a high level of impingement of particles on to the rotating classifier wheel, causing decreased classifier wheel efficiency, and this resulted in a less well-controlled micronization process. Thus, aspect ratio and pellips were sensitive to the changes in performance of the classifier wheel. The four shape descriptors were proposed to be used collectively as indicators for the monitoring of the micronization process.

  13. A search for jet extinction in the inclusive jet pT spectrum in proton-proton collisions with center-of-mass energy of 7 TeV at the CMS experiment

    NASA Astrophysics Data System (ADS)

    Rose, Keith J.

    The unification of the Standard Model of physics with the theory of general relativity is one of the most salient problems facing theoretical physicists today. A search is presented for strongly-coupled string theory, a possible resolution to this problem. At an accelerator experiment, evidence for this theory could manifest as a shutting off of all Standard Model processes. This phenomenon is referred to as extinction, beyond some energy threshold related to an extinction scale M. The search presented here utilizes 5.0 inverse femtobarns of data taken in proton-proton collisions at sqrt(s) = 7 TeV. These data were taken by the Compact Muon Solenoid (CMS) experiment, situated at the Large Hadron Collider (LHC). The Standard Model predicts the formation of collinear streams of particles known as jets, with one of the highest production cross-sections of any process expected in proton-proton collisions. The transverse momentum distribution of all jets in data is constructed, and compared to that expected by the Standard Model, as well as that expected by extinction physics for various values of M. The standard model and extinction hypotheses are expressed in terms of an explicit calculation of perturbative quantum chromodynamics (pQCD) at next-to-leading order. No significant evidence of an extinction signature is observed, and an upper limit of 3.2 TeV is set on the scale M at 95% C.L.

  14. Jets.

    PubMed

    Rhines, Peter B.

    1994-06-01

    This is a discussion of concentrated large-scale flows in planetary atmospheres and oceans, argued from the viewpoint of basic geophysical fluid dynamics. We give several elementary examples in which these flows form jets on rotating spheres. Jet formation occurs under a variety of circumstances: when flows driven by external stress have a rigid boundary which can balance the Coriolis force, and at which further concentration can be caused by the beta effect; when there are singular lines like the line of vanishing windstress or windstress-curl, or the Equator; when compact sources of momentum, heat or mass radiate jet-like beta plumes along latitude circles; when random external stirring of the fluid becomes organized by the beta effect into jets; when internal instability of the mass field generates zonal flow which then is concentrated into jets; when bottom topographic obstacles radiate jets, and when frontogenesis leads to shallow jet formation. Essential to the process of jet formation in stratified fluids is the baroclinic life cycle described in geostrophic turbulence studies; there, conversion from potential to kinetic energy generates eddy motions, and these convert to quasibarotropic motions which then radiate and induce jet-like large-scale circulation. Ideas of potential vorticity stirring by eddies generalize the notion of Rossby-wave radiation, showing how jets embedded in an ambient potential vorticity gradient (typically due to the spherical geometry of the rotating planet) gain eastward momentum while promoting broader, weaker westward circulation. Homogenization of potential vorticity is an important limit point, which many geophysical circulations achieve. This well-mixed state is found in subdomains of the terrestrial midlatitude oceans, the high-latitude circumpolar ocean, and episodically in the middle atmosphere. Homogenization expels potential vorticity gradients vertically to the top and bottom of the fluid, and sideways to the edges of

  15. The complex, dusty narrow-line region of NGC 4388: gas-jet interactions, outflows and extinction revealed by near-IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Rodríguez-Ardila, A.; Mason, R. E.; Martins, L.; Ramos Almeida, C.; Riffel, R. A.; Riffel, R.; Lira, P.; González Martín, O.; Dametto, N. Z.; Flohic, H.; Ho, L. C.; Ruschel-Dutra, D.; Thanjavur, K.; Colina, L.; McDermid, R. M.; Perlman, E.; Winge, C.

    2017-02-01

    We present Gemini/GNIRS (Gemini Near-Infrared Spectrograph) spectroscopy of the Seyfert 2 galaxy NGC 4388, with simultaneous coverage from 0.85 to 2.5 μm. Several spatially extended emission lines are detected for the first time, both in the obscured and unobscured portion of the optical narrow-line region (NLR), allowing us to assess the combined effects of the central continuum source, outflowing gas and shocks generated by the radio jet on the central 280 pc gas. The H I and [Fe II] lines allow us to map the extinction affecting the NLR. We found that the nuclear region is heavily obscured, with E(B - V) ˜ 1.9 mag. To the NE of the nucleus and up to ˜150 pc, the extinction remains large, ˜1 mag or larger, consistent with the system of dust lanes seen in optical imaging. We derived position-velocity diagrams for the most prominent lines as well as for the stellar component. Only the molecular gas and the stellar component display a well-organized pattern consistent with disc rotation. Other emission lines are kinematically perturbed or show little evidence of rotation. Extended high-ionization emission of sulphur, silicon and calcium is observed to distances of at least 200 pc both NE and SW of the nucleus. We compared flux ratios between these lines with photoionization models and conclude that radiation from the central source alone cannot explain the observed high-ionization spectrum. Shocks between the radio jet and the ambient gas are very likely an additional source of excitation. We conclude that NGC 4388 is a prime laboratory to study the interplay between all these mechanisms.

  16. Nuclear war: Opposing viewpoints

    SciTech Connect

    Szumski, B.

    1985-01-01

    This book presents opposing viewpoints on nuclear war. Topics discussed include: how nuclear would begin; would humanity survive; would civil defense work; will an arms agreement work; and can space weapons reduce the risk of nuclear war.

  17. Effects of H2O, CO2, and N2 air contaminants on critical airside strain rates for extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Guerra, Rosemary

    1989-01-01

    Dish-shaped counterflow diffusion flames centered by opposing laminar jets of H2 and clean and contaminant O2/N2 mixtures in an argon bath at 1 atm were used to study the effects of contaminants on critical airside strain. The jet velocities for both flame extinction and restoration are found for a wide range of contaminant and O2 concentrations in the air jet. The tests are also conducted for a variety of input H2 concentrations. The results are compared with those from several other studies.

  18. Effects of H2O, CO2, and N2 air contaminants on critical airside strain rates for extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Guerra, Rosemary

    1989-01-01

    Dish-shaped counterflow diffusion flames centered by opposing laminar jets of H2 and clean and contaminant O2/N2 mixtures in an argon bath at 1 atm were used to study the effects of contaminants on critical airside strain. The jet velocities for both flame extinction and restoration are found for a wide range of contaminant and O2 concentrations in the air jet. The tests are also conducted for a variety of input H2 concentrations. The results are compared with those from several other studies.

  19. HIGHLY VARIABLE EXTINCTION AND ACCRETION IN THE JET-DRIVING CLASS I-TYPE YOUNG STAR PTF 10nvg (V2492 Cyg, IRAS 20496+4354)

    SciTech Connect

    Hillenbrand, Lynne A.; Carpenter, John M.; Muirhead, Philip S.; Crepp, Justin R.; Miller, Adam A.; Cenko, S. Bradley; Silverman, Jeffrey M.; Bloom, Joshua S.; Filippenko, Alexei V.; Covey, Kevin R.; Fischer, William J.

    2013-03-15

    We report extensive new photometry and spectroscopy of the highly variable young stellar object PTF 10nvg (also known as IRAS 20496+4354 and V2492 Cyg), including optical and near-infrared time-series data as well as mid-infrared and millimeter data. Following the previously reported 2010 rise to R{sub PTF} {approx}<13.{sup m}5 and subsequent fade, during 2011 and 2012 the source underwent additional episodes of brightening, followed by several magnitude dimming events including prolonged faint states at R{sub PTF} {approx}> 20{sup m}. The observed high-amplitude variations are largely consistent with extinction changes ({Delta}A{sub V} up to 30 mag) having a {approx}220 day quasi-periodic signal. However, photometry measured when the source was near maximum brightness in mid-2010 as well as in late-2012 does not phase well to this period. Spectral evolution includes not only changes in the spectral slope but also correlated variation in the prominence of TiO/VO/CO bands and atomic line emission, as well as anti-correlated variation in forbidden line emission which, along with H{sub 2}, dominates optical and infrared spectra at faint epochs. Notably, night-to-night variations in several forbidden doublet strengths and ratios are observed. High-dispersion spectra were obtained in a variety of photometric states and reveal time-variable line profiles. Neutral and singly ionized atomic species are likely formed in an accretion flow and/or impact while the origin of zero-velocity atomic Li I {lambda}6707 in emission is unknown. Forbidden lines, including several rare species, exhibit blueshifted emission profiles and likely arise from an outflow/jet. Several of these lines are also seen spatially offset from the continuum source position, presumably in a shocked region of an extended jet. Blueshifted absorption components of the Na I D doublet, K I {lambda}{lambda}7665, 7669 doublet, and the O I 7774 triplet, as well as blueshifted absorption components seen against

  20. Welfare. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Cozic, Charles P., Ed.; Winters, Paul A., Ed.

    Books in the Opposing Viewpoints Series present debates about current issues that can be used to teach critical reading and thinking skills. The opinions expressed in the selections in each series title examine many different aspects of a single issue. Detractors of the welfare system have long argued that the system promotes dependency. They…

  1. Discrimination. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Williams, Mary E., Ed.

    Books in the Opposing Viewpoints series challenge readers to question their own opinions and assumptions. By reading carefully balanced views, readers confront new ideas on the topic of interest. The Civil Rights Act of 1964, which prohibited job discrimination based on age, race, religion, gender, or national origin, provided the groundwork for…

  2. Poverty. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Leone, Bruno, Ed.

    Books in the Opposing Viewpoints Series present debates about current issues that can be used to teach critical reading and thinking skills. The varied opinions in each collection explore aspects of a social, cultural, or political issue. A great deal of money has been spent in this country to eradicate poverty, but the problem remains. Some…

  3. Gangs. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Cozic, Charles P., Ed.

    Books in the Opposing Viewpoints Series present debates about current issues that can be used to teach critical reading and thinking skills. The variety of opinions expressed in this collection of articles and book excerpts explore many aspects of juvenile gangs. Some youths join gangs of their own free choice, to satisfy ego or greed. Others are…

  4. Are extinction opinions extinct?

    PubMed Central

    2017-01-01

    Extinction models vary in the information they require, the simplest considering the rate of certain sightings only. More complicated methods include uncertain sightings and allow for variation in the reliability of uncertain sightings. Generally extinction models require expert opinion, either as a prior belief that a species is extinct, or to establish the quality of a sighting record, or both. Is this subjectivity necessary? We present two models to explore whether the individual quality of sightings, judged by experts, is strongly informative of the probability of extinction: the ‘quality breakpoint method’ and the ‘quality as variance method’. For the first method we use the Barbary lion as an exemplar. For the second method we use the Barbary lion, Alaotra grebe, Jamaican petrel and Pohnpei starling as exemplars. The ‘quality breakpoint method’ uses certain and uncertain sighting records, and the quality of uncertain records, to establish whether a change point in the rate of sightings can be established using a simultaneous Bayesian optimisation with a non-informative prior. For the Barbary lion, there is a change in subjective quality of sightings around 1930. Unexpectedly sighting quality increases after this date. This suggests that including quality scores from experts can lead to irregular effects and may not offer reliable results. As an alternative, we use quality as a measure of variance around the sightings, not a change in quality. This leads to predictions with larger standard deviations, however the results remain consistent across any prior belief of extinction. Nonetheless, replacing actual quality scores with random quality scores showed little difference, inferring that the quality scores from experts are superfluous. Therefore, we deem the expensive process of obtaining pooled expert estimates as unnecessary, and even when used we recommend that sighting data should have minimal input from experts in terms of assessing the

  5. Opposed-flow virtual cyclone for particle concentration

    DOEpatents

    Rader, Daniel J.; Torczynski, John R.

    2000-12-05

    An opposed-flow virtual cyclone for aerosol collation which can accurately collect, classify, and concentrate (enrich) particles in a specific size range. The opposed-flow virtual cyclone is a variation on the virtual cyclone and has its inherent advantages (no-impact particle separation in a simple geometry), while providing a more robust design for concentrating particles in a flow-through type system. The opposed-flow virtual cyclone consists of two geometrically similar virtual cyclones arranged such that their inlet jets are inwardly directed and symmetrically opposed relative to a plane of symmetry located between the two inlet slits. A top plate bounds both jets on the "top" side of the inlets, while the other or lower wall curves "down" and away from each inlet jet. Each inlet jet will follow the adjacent lower wall as it turns away, and that particles will be transferred away from the wall and towards the symmetry plane by centrifugal action. After turning, the two jets merge smoothly along the symmetry line and flow parallel to it through the throat. Particles are transferred from the main flows, across a dividing streamline, and into a central recirculating region, where particle concentrations become greatly increased relative to the main stream.

  6. Rethinking Extinction

    PubMed Central

    Dunsmoor, Joseph E.; Niv, Yael; Daw, Nathaniel; Phelps, Elizabeth A.

    2015-01-01

    Extinction serves as the leading theoretical framework and experimental model to describe how learned behaviors diminish through absence of anticipated reinforcement. In the past decade, extinction has moved beyond the realm of associative learning theory and behavioral experimentation in animals and has become a topic of considerable interest in the neuroscience of learning, memory, and emotion. Here, we review research and theories of extinction, both as a learning process and as a behavioral technique, and consider whether traditional understandings warrant a re-examination. We discuss the neurobiology, cognitive factors, and major computational theories, and revisit the predominant view that extinction results in new learning that interferes with expression of the original memory. Additionally, we reconsider the limitations of extinction as a technique to prevent the relapse of maladaptive behavior, and discuss novel approaches, informed by contemporary theoretical advances, that augment traditional extinction methods to target and potentially alter maladaptive memories. PMID:26447572

  7. Rethinking Extinction.

    PubMed

    Dunsmoor, Joseph E; Niv, Yael; Daw, Nathaniel; Phelps, Elizabeth A

    2015-10-07

    Extinction serves as the leading theoretical framework and experimental model to describe how learned behaviors diminish through absence of anticipated reinforcement. In the past decade, extinction has moved beyond the realm of associative learning theory and behavioral experimentation in animals and has become a topic of considerable interest in the neuroscience of learning, memory, and emotion. Here, we review research and theories of extinction, both as a learning process and as a behavioral technique, and consider whether traditional understandings warrant a re-examination. We discuss the neurobiology, cognitive factors, and major computational theories, and revisit the predominant view that extinction results in new learning that interferes with expression of the original memory. Additionally, we reconsider the limitations of extinction as a technique to prevent the relapse of maladaptive behavior and discuss novel approaches, informed by contemporary theoretical advances, that augment traditional extinction methods to target and potentially alter maladaptive memories.

  8. Experimental Investigations Of The Influence Of Pressure On Critical Extinction Conditions Of Laminar Nonpremixed Flames Burning Condensed Hydrocarbon Fuels, Jet Fuels, And Surrogates

    DTIC Science & Technology

    2014-10-25

    steady state temperature gradient within the cup and prevents violent surface boiling for a wide range of condensed fuels, ensuring a smooth, consistent...counter?ow, condensed -fuel con?guration is employed. Air diluted with nitrogen at 298 K is injected 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13...burning condensed hydrocarbon fuels, jet fuels, and surrogates The views, opinions and/or findings contained in this report are those of the author(s

  9. Opposed Flow Flame Spread in Normal, Enhanced and Reduced Gravity

    NASA Technical Reports Server (NTRS)

    Altenkirch, Robert A.; Bhattacharjee, Subrata; West, Jeff; Olson, Sandra L.

    1991-01-01

    Experimental and theoretical aspects of opposed-flow flame spread over solid fuels are presented with emphasis on the microgravity environments of spacecraft. For high opposing flow velocities, spread rate decreases with increasing velocity eventually leading to flame blowoff due to kinetic effects. At low opposing flow velocities, where diffusional effects are slowed and radiation becomes important, flame spread rate increases with increasing flow velocity. Extinction at low velocities is due to radiative effects. Modeling efforts that include radiation, both solid surface radiation and gas-phase radiation, predict qualitatively the experimental trends observed. Computationally, gas-phase radiation is conveniently included in solution of the conservation equations by employing a Plank mean absorption coefficient, a fraction of radiation that is fed back to the surface, and a shape function that describes the radiative flux distribution along the surface.

  10. Teens at Risk: Opposing Viewpoints. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Egendorf, Laura K., Ed.; Hurley, Jennifer A., Ed.

    Contributions in this collection present opposing viewpoints about factors that put teens at risk; illustrate how society can deal with teenage crime and violence; show how to prevent teen pregnancy; and present the roles of the media and government in teen substance abuse. The following essays are presented: (1) "A Variety of Factors Put Teens at…

  11. Teens at Risk: Opposing Viewpoints. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Egendorf, Laura K., Ed.; Hurley, Jennifer A., Ed.

    Contributions in this collection present opposing viewpoints about factors that put teens at risk; illustrate how society can deal with teenage crime and violence; show how to prevent teen pregnancy; and present the roles of the media and government in teen substance abuse. The following essays are presented: (1) "A Variety of Factors Put Teens at…

  12. Extinctions of life

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

    1988-01-01

    This meeting presentation examines mass extinctions through earth's history. Extinctions are charted for marine families and marine genera. Timing of marine genera extinctions is discussed. Periodicity in extinctions during the Mesozoic and Cenozoic eras is plotted and compared with Paleozoic extinction peaks. The role of extinction in evolution and mankind's role in present extinctions are examined.

  13. Juvenile Crime. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Sadler, A. E., Ed.

    Books in the Opposing Viewpoints Series present debates about current issues that can be used to teach critical reading and thinking skills. The variety of opinions expressed in this collection of articles and book excerpts explores many aspects of juvenile crime. It is a commonly held view that the number of crimes committed by juveniles is…

  14. The Homeless. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Roleff, Tamara L., Ed.

    Books in the Opposing Viewpoints Series present debates about current issues that can be used to teach critical reading and thinking skills. The variety of opinions expressed in this collection of articles and book excerpts explore many aspects of the problem of homelessness. According to a 1994 report by the U..S. Conference of Mayors, the number…

  15. Illegal Immigration. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Cozic, Charles P., Ed.

    Books in the Opposing Viewpoints Series present debates about current issues that can be used to teach critical reading and thinking skills. The variety of opinions expressed in this collection of articles and book excerpts explore many aspects of illegal immigration. Contrary depictions of the aspirations and attitudes of illegal immigrants fuel…

  16. Interracial America. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Szumski, Bonnie, Ed.

    Books in the Opposing Viewpoints Series present debates about current issues that can be used to teach critical reading and thinking skills. The varied opinions in each book examine different aspects of a single issue. The topics covered in this volume explore the racial and ethnic tensions that concern many Americans today. The racial divide…

  17. Teenage Pregnancy. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Thompson, Stephen P.

    Books in the Opposing Viewpoints series challenge readers to question their own opinions and assumptions. By reading carefully balanced views, readers confront new ideas on the topic of interest. Although some experts believe that the problem of teenage pregnancy has been overstated, other recent studies have led many people to believe that…

  18. Teenage Pregnancy. Opposing Viewpoints Series.

    ERIC Educational Resources Information Center

    Thompson, Stephen P.

    Books in the Opposing Viewpoints series challenge readers to question their own opinions and assumptions. By reading carefully balanced views, readers confront new ideas on the topic of interest. Although some experts believe that the problem of teenage pregnancy has been overstated, other recent studies have led many people to believe that…

  19. Australian Extinctions

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    Massive extinctions of animals and the arrival of the first humans in ancient Australia--which occurred 45,000 to 55,000 years ago--may be linked. Researchers at the Carnegie Institution, University of Colorado, Australian National University, and Bates College believe that massive fires set by the first humans may have altered the ecosystem of…

  20. Australian Extinctions

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    Massive extinctions of animals and the arrival of the first humans in ancient Australia--which occurred 45,000 to 55,000 years ago--may be linked. Researchers at the Carnegie Institution, University of Colorado, Australian National University, and Bates College believe that massive fires set by the first humans may have altered the ecosystem of…

  1. Extinction and near-extinction instability of non-premixed tubular flames

    SciTech Connect

    Hu, Shengteng; Pitz, Robert W.; Yu, Wang

    2009-01-15

    Tubular non-premixed flames are formed by an opposed tubular burner, a new tool to study the effects of curvature on extinction and flame instability of non-premixed flames. Extinction of the opposed tubular flames generated by burning diluted H{sub 2}, CH{sub 4} or C{sub 3}H{sub 8} with air is investigated for both concave and convex curvature. To examine the effects of curvature on extinction, the critical fuel dilution ratios at extinction are measured at various stretch rates, initial mixture strengths and flame curvature for fuels diluted in N{sub 2}, He, Ar or CO{sub 2}. In addition, the onset conditions of the cellular instability are mapped as a function of stretch rates, initial mixture strengths, and flame curvature. For fuel mixtures with Lewis numbers much less than unity, such as H{sub 2}/N{sub 2}, concave flame curvature towards the fuel suppresses cellular instabilities. (author)

  2. Opposed slant tube diabatic sorber

    DOEpatents

    Erickson, Donald C.

    2004-01-20

    A sorber comprised of at least three concentric coils of tubing contained in a shell with a flow path for liquid sorbent in one direction, a flow path for heat transfer fluid which is in counter-current heat exchange relationship with sorbent flow, a sorbate vapor port in communication with at least one of sorbent inlet or exit ports, wherein each coil is coiled in opposite direction to those coils adjoining it, whereby the opposed slant tube configuration is achieved, with structure for flow modification in the core space inside the innermost coil.

  3. Counterflow diffusion flames of hydrogen, and hydrogen plus methane, ethylene, propane, and silane vs. air - Strain rates at extinction

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. Burton; Wilson, L. G.

    1991-01-01

    Five coaxial tubular opposed jet burners (OJBs) with tube diameter D(T) of 1.8-10 mm and 5 mm conical nozzles were used to form dish-shaped counterflow diffusion flames centered by opposing laminar jets of nitrogen and hydrocarbon-diluted H2 versus air in an argon-purged chamber at 1 atm. Area-averaged air jet velocities at blowoff of the central flame, U(air), characterized extinction of the airside flame as functions of input H2 concentration on the fuelside. A master plot of extensive U(air) data at blowoff versus D(T) shows that U(air) varies linearly with D(T). This and other data sets are used to find that nozzle OJB results for U(air)/diameter average 4.24 + or - 0.28 times larger than tubular OJB results for the same fuel compositions. Critical radial velocity gradients consistent with one-dimensional stagnation point boundary theory and with plug flow inputs are estimated. The results compare favorably with published numerical results based only on potential flow.

  4. Counterflow diffusion flames of hydrogen, and hydrogen plus methane, ethylene, propane, and silane vs. air - Strain rates at extinction

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. Burton; Wilson, L. G.

    1991-01-01

    Five coaxial tubular opposed jet burners (OJBs) with tube diameter D(T) of 1.8-10 mm and 5 mm conical nozzles were used to form dish-shaped counterflow diffusion flames centered by opposing laminar jets of nitrogen and hydrocarbon-diluted H2 versus air in an argon-purged chamber at 1 atm. Area-averaged air jet velocities at blowoff of the central flame, U(air), characterized extinction of the airside flame as functions of input H2 concentration on the fuelside. A master plot of extensive U(air) data at blowoff versus D(T) shows that U(air) varies linearly with D(T). This and other data sets are used to find that nozzle OJB results for U(air)/diameter average 4.24 + or - 0.28 times larger than tubular OJB results for the same fuel compositions. Critical radial velocity gradients consistent with one-dimensional stagnation point boundary theory and with plug flow inputs are estimated. The results compare favorably with published numerical results based only on potential flow.

  5. Impossible Extinction

    NASA Astrophysics Data System (ADS)

    Cockell, Charles S.

    2003-03-01

    Every 225 million years the Earth, and all the life on it, completes one revolution around the Milky Way Galaxy. During this remarkable journey, life is influenced by calamitous changes. Comets and asteroids strike the surface of the Earth, stars explode, enormous volcanoes erupt, and, more recently, humans litter the planet with waste. Many animals and plants become extinct during the voyage, but humble microbes, simple creatures made of a single cell, survive this journey. This book takes a tour of the microbial world, from the coldest and deepest places on Earth to the hottest and highest, and witnesses some of the most catastrophic events that life can face. Impossible Extinction tells this remarkable story to the general reader by explaining how microbes have survived on Earth for over three billion years. Charles Cockell received his doctorate from the University of Oxford, and is currently a microbiologist with rhe Search for Extraterrestrial Intelligence Institute (SETI), based at the British Antarctic Survey in Cambridge, UK. His research focusses on astrobiology, life in the extremes and the human exploration of Mars. Cockell has been on expeditions to the Arctic, Antarctic, Mongolia, and in 1993 he piloted a modified insect-collecting ultra-light aircraft over the Indonesian rainforests. He is Chair of the Twenty-one Eleven Foundation for Exploration, a charity that supports expeditions that forge links between space exploration and environmentalism.

  6. Interstellar Extinction

    NASA Astrophysics Data System (ADS)

    Gontcharov, G. A.

    2016-12-01

    This review describes our current understanding of interstellar extinction. This differ substantially from the ideas of the 20th century. With infrared surveys of hundreds of millions of stars over the entire sky, such as 2MASS, SPITZER-IRAC, and WISE, we have looked at the densest and most rarefied regions of the interstellar medium at distances of a few kpc from the Sun. Observations at infrared and microwave wavelengths, where the bulk of the interstellar dust absorbs and radiates, have brought us closer to an understanding of the distribution of the dust particles on scales of the Galaxy and the universe. We are in the midst of a scientific revolution in our understanding of the interstellar medium and dust. Progress in, and the key results of, this revolution are still difficult to predict. Nevertheless, (a) a physically justified model has been developed for the spatial distribution of absorbing material over the nearest few kiloparsecs, including the Gould belt as a dust container, which gives an accurate estimate of the extinction for any object just by its galactic coordinates. It is also clear that (b) the interstellar medium contains roughly half the mass of matter in the galactic vicinity of the solar system (the other half is made up of stars, their remnants, and dark matter) and (c) the interstellar medium and, especially, dust, differ substantially in different regions of space and deep space cannot be understood by only studying near space.

  7. Resistance to extinction and behavioral momentum.

    PubMed

    Nevin, John A

    2012-05-01

    In the metaphor of behavioral momentum, reinforcement is assumed to strengthen discriminated operant behavior in the sense of increasing its resistance to disruption, and extinction is viewed as disruption by contingency termination and reinforcer omission. In multiple schedules of intermittent reinforcement, resistance to extinction is an increasing function of reinforcer rate, consistent with a model based on the momentum metaphor. The partial-reinforcement extinction effect, which opposes the effects of reinforcer rate, can be explained by the large disruptive effect of terminating continuous reinforcement despite its strengthening effect during training. Inclusion of a term for the context of reinforcement during training allows the model to account for a wide range of multiple-schedule extinction data and makes contact with other formulations. The relation between resistance to extinction and reinforcer rate on single schedules of intermittent reinforcement is exactly opposite to that for multiple schedules over the same range of reinforcer rates; however, the momentum model can give an account of resistance to extinction in single as well as multiple schedules. An alternative analysis based on the number of reinforcers omitted to an extinction criterion supports the conclusion that response strength is an increasing function of reinforcer rate during training.

  8. Effects of H2O, CO2, and N2 Air Contaminants on Critical Airside Strain Rates for Extinction of Hydrogen-Air Counterflow Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Wilson, L. G.; Northam, G. B.; Guerra, Rosemary

    1989-01-01

    Coaxial tubular opposed jet burners (OJB) were used to form dish shaped counterflow diffusion flames (CFDF), centered by opposing laminar jets of H2, N2 and both clean and contaminated air (O2/N2 mixtures) in an argon bath at 1 atm. Jet velocities for flame extinction and restoration limits are shown versus wide ranges of contaminant and O2 concentrations in the air jet, and also input H2 concentration. Blowoff, a sudden breaking of CFDF to a stable ring shape, occurs in highly stretched stagnation flows and is generally believed to measure kinetically limited flame reactivity. Restore, a sudden restoration of central flame, is a relatively new phenomenon which exhibits a H2 dependent hysteresis from Blowoff. For 25 percent O2 air mixtures, mole for mole replacement of 25 percent N2 contaminant by steam increased U(air) or flame strength at Blowoff by about 5 percent. This result is consistent with laminar burning velocity results from analogous substitution of steam for N2 in a premixed stoichiometric H2-O2-N2 (or steam) flame, shown by Koroll and Mulpuru to promote a 10 percent increase in experimental and calculated laminar burning velocity, due to enhanced third body efficiency of water in: H + O2 + M yields HO2 + M. When the OJB results were compared with Liu and MacFarlane's experimental laminar burning velocity of premixed stoichiometric H2 + air + steam, a crossover occurred, i.e., steam enhanced OJB flame strength at extinction relative to laminar burning velocity.

  9. Dilution jet mixing program

    NASA Technical Reports Server (NTRS)

    Srinivasan, R.; Coleman, E.; Johnson, K.

    1984-01-01

    Parametric tests were conducted to quantify the mixing of opposed rows of jets (two-sided injection) in a confined cross flow. Results show that jet penetrations for two sided injections are less than that for single-sided injections, but the jet spreading rates are faster for a given momentum ratio and orifice plate. Flow area convergence generally enhances mixing. Mixing characteristics with asymmetric and symmetric convergence are similar. For constant momentum ratio, the optimum S/H(0) with in-line injections is one half the optimum value for single sided injections. For staggered injections, the optimum S/H(0) is twice the optimum value for single-sided injection. The correlations developed predicted the temperature distributions within first order accuracy and provide a useful tool for predicting jet trajectory and temperature profiles in the dilution zone with two-sided injections.

  10. 49 CFR 236.833 - Train, opposing.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 4 2013-10-01 2013-10-01 false Train, opposing. 236.833 Section 236.833..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.833 Train, opposing. A train, the movement of which is in a direction opposite to and toward another train...

  11. 49 CFR 236.833 - Train, opposing.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 4 2014-10-01 2014-10-01 false Train, opposing. 236.833 Section 236.833..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.833 Train, opposing. A train, the movement of which is in a direction opposite to and toward another train...

  12. 49 CFR 236.833 - Train, opposing.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 4 2011-10-01 2011-10-01 false Train, opposing. 236.833 Section 236.833..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.833 Train, opposing. A train, the movement of which is in a direction opposite to and toward another train...

  13. 49 CFR 236.808 - Signals, opposing.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 4 2010-10-01 2010-10-01 false Signals, opposing. 236.808 Section 236.808..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.808 Signals, opposing. Roadway signals which govern movements in opposite directions on the same track. ...

  14. 49 CFR 236.808 - Signals, opposing.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 4 2012-10-01 2012-10-01 false Signals, opposing. 236.808 Section 236.808..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.808 Signals, opposing. Roadway signals which govern movements in opposite directions on the same track. ...

  15. 49 CFR 236.808 - Signals, opposing.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 4 2014-10-01 2014-10-01 false Signals, opposing. 236.808 Section 236.808..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.808 Signals, opposing. Roadway signals which govern movements in opposite directions on the same track. ...

  16. 49 CFR 236.808 - Signals, opposing.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 4 2011-10-01 2011-10-01 false Signals, opposing. 236.808 Section 236.808..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.808 Signals, opposing. Roadway signals which govern movements in opposite directions on the same track. ...

  17. 49 CFR 236.808 - Signals, opposing.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 4 2013-10-01 2013-10-01 false Signals, opposing. 236.808 Section 236.808..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.808 Signals, opposing. Roadway signals which govern movements in opposite directions on the same track. ...

  18. 49 CFR 236.833 - Train, opposing.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 4 2010-10-01 2010-10-01 false Train, opposing. 236.833 Section 236.833..., MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Definitions § 236.833 Train, opposing. A train, the movement of which is in a direction opposite to and toward another...

  19. Perspectives on dilution jet mixing

    NASA Technical Reports Server (NTRS)

    Holdeman, J. D.

    1986-01-01

    A microcomputer code which displays 3-D oblique and 2-D plots of the temperature distribution downstream of jets mixing with a confined crossflow has been used to investigate the effects of varying the several independent flow and geometric parameters on the mixing. Temperature profiles calculated with this empirical model are presented to show the effects of orifice size and spacing, momentum flux ratio, density ratio, variable temperature mainstream, flow area convergence, orifice aspect ratio, and opposed and axially staged rows of jets.

  20. Twin Jet

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda; Bozak, Rick

    2010-01-01

    Many subsonic and supersonic vehicles in the current fleet have multiple engines mounted near one another. Some future vehicle concepts may use innovative propulsion systems such as distributed propulsion which will result in multiple jets mounted in close proximity. Engine configurations with multiple jets have the ability to exploit jet-by-jet shielding which may significantly reduce noise. Jet-by-jet shielding is the ability of one jet to shield noise that is emitted by another jet. The sensitivity of jet-by-jet shielding to jet spacing and simulated flight stream Mach number are not well understood. The current experiment investigates the impact of jet spacing, jet operating condition, and flight stream Mach number on the noise radiated from subsonic and supersonic twin jets.

  1. The nature of extinction.

    PubMed

    Delord, Julien

    2007-09-01

    The phenomenon of species extinction raises more and more concern among ecologists facing the actual crisis of biodiversity. Scientific investigations of the causes and effects of extinction must be completed by a philosophical analysis of the concept of extinction that aims to clarify the meanings of the term 'extinction' and to analyse modalities, criteria and degrees of extinction. We will focus our attention on the apparent paradox of the possible 'resurrection' of species in the near future with the help of genetic biotechnology and cloning techniques. The ontological background of the extinction concept is analysed in relation to the idea of species as classes. We will also show that there is no simple analogy between death and species extinction, and develop a conceptualist and dualistic system of supra-individual entities (species vs. population), supported by an instrumentalist approach to genetic manipulations which transform species into interactive kinds, which can go extinct and be recreated.

  2. Jet shielding of jet noise

    NASA Technical Reports Server (NTRS)

    Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.

    1986-01-01

    An experimental and theoretical study was conducted to develop a validated first principle analysis for predicting the jet noise reduction achieved by shielding one jet exhaust flow with a second, closely spaced, identical jet flow. A generalized fuel jet noise analytical model was formulated in which the acoustic radiation from a source jet propagates through the velocity and temperature discontinuity of the adjacent shielding jet. Input variables to the prediction procedure include jet Mach number, spacing, temperature, diameter, and source frequency. Refraction, diffraction, and reflection effects, which control the dual jet directivity pattern, are incorporated in the theory. The analysis calculates the difference in sound pressure level between the dual jet configuration and the radiation field based on superimposing two independent jet noise directivity patterns. Jet shielding was found experimentally to reduce noise levels in the common plane of the dual jet system relative to the noise generated by two independent jets.

  3. Nitric Oxide and Oxygen Air-Contamination Effects on Extinction Limits of Non-Premixed Hydrocarbon-Air Flames for a HIFiRE Scramjet

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Dawson, Lucy C.; Vaden, Sarah N.; Wilson, Lloyd G.

    2009-01-01

    Unique nitric oxide (NO) and oxygen air-contamination effects on the extinction Flame Strength (FS) of non-premixed hydrocarbon (HC) vs. air flames are characterized for 7 gaseous HCs, using a new idealized 9.3 mm straight-tube Opposed Jet Burner (OJB) at 1 atm. FS represents a laminar strain-induced extinction limit based on cross-section-average air jet velocity, Uair, that sustains combustion of a counter jet of gaseous fuel just before extinction. Besides ethane, propane, butane, and propylene, the HCs include ethylene, methane, and a 64 mole-% ethylene / 36 % methane mixture, the writer s previously recommended gaseous surrogate fuel for HIFiRE scramjet tests. The HC vs. clean air part of the work is an extension of a May 2008 JANNAF paper that characterized surrogates for the HIFiRE project that should mimic the flameholding of reformed (thermally- or catalytically-cracked) endothermic JP-like fuels. The new FS data for 7 HCs vs. clean air are thus consolidated with the previously validated data, normalized to absolute (local) axial-input strain rates, and co-plotted on a dual kinetically dominated reactivity scale. Excellent agreement with the prior data is obtained for all 7 fuels. Detailed comparisons are also made with recently published (Univ. Va) numerical results for ethylene extinction. A 2009-revised ethylene kinetic model (Univ. Southern Cal) led to predicted limits within approx. 5 % (compared to 45 %, earlier) of this writer s 2008 (and present) ethylene FSs, and also with recent independent data (Univ. Va) obtained on a new OJB system. These +/- 5 % agreements, and a hoped-for "near-identically-performing" reduced kinetics model, would greatly enhance the capability for accurate numerical simulations of surrogate HC flameholding in scramjets. The measured air-contamination effects on normalized FS extinction limits are projected to assess ongoing Arc-Heater-induced "facility test effects" of NO production (e.g., 3 mole-%) and resultant oxygen

  4. Is extinction forever?

    PubMed

    Smith-Patten, Brenda D; Bridge, Eli S; Crawford, Priscilla H C; Hough, Daniel J; Kelly, Jeffrey F; Patten, Michael A

    2015-05-01

    Mistrust of science has seeped into public perception of the most fundamental aspect of conservation-extinction. The term ought to be straightforward, and yet, there is a disconnect between scientific discussion and public views. This is not a mere semantic issue, rather one of communication. Within a population dynamics context, we say that a species went locally extinct, later to document its return. Conveying our findings matters, for when we use local extinction, an essentially nonsensical phrase, rather than extirpation, which is what is meant, then we contribute to, if not create outright, a problem for public understanding of conservation, particularly as local extinction is often shortened to extinction in media sources. The public that receives the message of our research void of context and modifiers comes away with the idea that extinction is not forever or, worse for conservation as a whole, that an extinction crisis has been invented. © The Author(s) 2015.

  5. Is extinction forever?

    PubMed Central

    Bridge, Eli S.; Crawford, Priscilla H. C.; Hough, Daniel J.; Kelly, Jeffrey F.; Patten, Michael A.

    2015-01-01

    Mistrust of science has seeped into public perception of the most fundamental aspect of conservation—extinction. The term ought to be straightforward, and yet, there is a disconnect between scientific discussion and public views. This is not a mere semantic issue, rather one of communication. Within a population dynamics context, we say that a species went locally extinct, later to document its return. Conveying our findings matters, for when we use local extinction, an essentially nonsensical phrase, rather than extirpation, which is what is meant, then we contribute to, if not create outright, a problem for public understanding of conservation, particularly as local extinction is often shortened to extinction in media sources. The public that receives the message of our research void of context and modifiers comes away with the idea that extinction is not forever or, worse for conservation as a whole, that an extinction crisis has been invented. PMID:25711479

  6. Experimental investigation of characteristics of a diffusion flame established over liquid ethanol surface under opposed air flow

    SciTech Connect

    Sen, Anirudh; Raghavan, Vasudevan; Shet, U.S.P.

    2009-03-15

    A preliminary study of the shape and the extinction characteristics of a diffusion flame established over a circular liquid fuel surface under the influence of an opposed air flow, is presented. Renewable liquid fuel such as ethanol is employed. A simple heterogeneous combustion setup, which consists of a cylindrical tube containing ethanol located at the bottom, is exposed to an opposed air flow from a coaxial circular pipe of same size located at the top at a fixed separation distance. Axial and radial extents of flame for different air flow rates are qualitatively analyzed. Burning rates of ethanol for different separation distances and air flow rates are recorded. For a fixed separation distance, at a particular air flow rate the flame extinction takes place. Extinction air flow rates and corresponding strain rates for different separation distances are presented. (author)

  7. Enamel wear opposing polished and aged zirconia.

    PubMed

    Burgess, J O; Janyavula, S; Lawson, N C; Lucas, T J; Cakir, D

    2014-01-01

    Aging of dental zirconia roughens its surface through low temperature degradation. We hypothesized that age-related roughening of zirconia crowns may cause detrimental wear to the enamel of an opposing tooth. To test our hypothesis, we subjected artificially aged zirconia and reference specimens to simulated mastication in a wear device and measured the wear of an opposing enamel cusp. Additionally, the roughness of the pretest surfaces was measured. The zirconia specimens, artificially aged by autoclave, showed no significant increase in roughness compared to the nonaged specimens. Furthermore, no significant difference in material or opposing enamel wear between the aged and nonaged zirconia was seen. All zirconia specimens showed less material and opposing enamel wear than the enamel to enamel control or veneering porcelain specimens. Scanning electron micrographs showed relatively smooth surfaces of aged and nonaged zirconia following wear testing. The micrographs of the veneering ceramic showed sharp fractured edges and fragments of wear debris. Zirconia may be considered a wear-friendly material for restorations opposing enamel, even after simulated aging.

  8. Quantitative Studies on the Propagation and Extinction of Near-Limit Premixed Flames under Normal- and Micro-gravity

    NASA Technical Reports Server (NTRS)

    Egolfopoulos, F. N.; Dong, Y.; Spedding, G.; Cuenot, B.; Poinsot, T.

    2001-01-01

    Strained laminar flames have been systematically studied, as the understanding of their structure and dynamic behavior is of relevance to turbulent combustion.. Most of these studies have been conducted in opposed-jet, stagnation-type flow configurations. Studies at high strain rates are important in quantifying and understanding the response of vigorously burning flames and determine extinction states. Studies of weakly strained flames can be of particular interest for all stoichiometries. For example, the laminar flame speeds, S(sup o)(sub u), can be accurately determined by using the counterflow technique only if measurements are obtained at very low strain rates. Furthermore, near-limit flames are stabilized by weak strain rates. Previous studies have shown that near-limit flames are particularly sensitive to chain mechanisms, thermal radiation, and unsteadiness. The stabilization and study of weakly strained flames is complicated by the presence of buoyancy that can render the flames unstable to the point of extinction. Thus, the use of microgravity (mu-g) becomes essential in order to provide meaningful insight into this important combustion regime. In our past studies the laminar flame speeds and extinction strain rates were directly measured at ultra-low strain rates. The laminar flame speeds were measured by having a positively strained planar flame undergoing a transition to a negatively strained Bunsen flame and by measuring the propagation speed during that transition. The extinction strain rates of near-limit flames were measured in mu-g. Results obtained for CH4/air and C3H8/air mixtures are in agreement with those obtained by Maruta et al.

  9. Secondary extinctions of biodiversity.

    PubMed

    Brodie, Jedediah F; Aslan, Clare E; Rogers, Haldre S; Redford, Kent H; Maron, John L; Bronstein, Judith L; Groves, Craig R

    2014-12-01

    Extinctions beget further extinctions when species lose obligate mutualists, predators, prey, or hosts. Here, we develop a conceptual model of species and community attributes affecting secondary extinction likelihood, incorporating mechanisms that buffer organisms against partner loss. Specialized interactors, including 'cryptic specialists' with diverse but nonredundant partner assemblages, incur elevated risk. Risk is also higher for species that cannot either evolve new traits following partner loss or obtain novel partners in communities reorganizing under changing environmental conditions. Partner loss occurs alongside other anthropogenic impacts; multiple stressors can circumvent ecological buffers, enhancing secondary extinction risk. Stressors can also offset each other, reducing secondary extinction risk, a hitherto unappreciated phenomenon. This synthesis suggests improved conservation planning tactics and critical directions for research on secondary extinctions. Copyright © 2014 Elsevier Ltd. All rights reserved.

  10. Jetting tool

    SciTech Connect

    Szarka, D.D.; Schwegman, S.L.

    1991-07-09

    This patent describes an apparatus for hydraulically jetting a well tool disposed in a well, the well tool having a sliding member. It comprises positioner means for operably engaging the sliding member of the well tool; and a jetting means, connected at a rotatable connection to the positioner means so that the jetting means is rotatable relative to the positioner means and the well tool, for hydraulically jetting the well tool as the jetting means is rotated relative thereto.

  11. Mass extinction: a commentary

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1987-01-01

    Four neocatastrophist claims about mass extinction are currently being debated; they are that: 1, the late Cretaceous mass extinction was caused by large body impact; 2, as many as five other major extinctions were caused by impact; 3, the timing of extinction events since the Permian is uniformly periodic; and 4, the ages of impact craters on Earth are also periodic and in phase with the extinctions. Although strongly interconnected the four claims are independent in the sense that none depends on the others. Evidence for a link between impact and extinction is strong but still needs more confirmation through bed-by-bed and laboratory studies. An important area for future research is the question of whether extinction is a continuous process, with the rate increasing at times of mass extinctions, or whether it is episodic at all scales. If the latter is shown to be generally true, then species are at risk of extinction only rarely during their existence and catastrophism, in the sense of isolated events of extreme stress, is indicated. This is line of reasoning can only be considered an hypothesis for testing. In a larger context, paleontologists may benefit from a research strategy that looks to known Solar System and Galactic phenomena for predictions about environmental effects on earth. The recent success in the recognition of Milankovitch Cycles in the late Pleistocene record is an example of the potential of this research area.

  12. Mass extinction: a commentary.

    PubMed

    Raup, D M

    1987-01-01

    Four neocatastrophist claims about mass extinction are currently being debated; they are that: 1, the late Cretaceous mass extinction was caused by large body impact; 2, as many as five other major extinctions were caused by impact; 3, the timing of extinction events since the Permian is uniformly periodic; and 4, the ages of impact craters on Earth are also periodic and in phase with the extinctions. Although strongly interconnected the four claims are independent in the sense that none depends on the others. Evidence for a link between impact and extinction is strong but still needs more confirmation through bed-by-bed and laboratory studies. An important area for future research is the question of whether extinction is a continuous process, with the rate increasing at times of mass extinctions, or whether it is episodic at all scales. If the latter is shown to be generally true, then species are at risk of extinction only rarely during their existence and catastrophism, in the sense of isolated events of extreme stress, is indicated. This is line of reasoning can only be considered an hypothesis for testing. In a larger context, paleontologists may benefit from a research strategy that looks to known Solar System and Galactic phenomena for predictions about environmental effects on earth. The recent success in the recognition of Milankovitch Cycles in the late Pleistocene record is an example of the potential of this research area.

  13. Gradual extinction reduces reinstatement

    PubMed Central

    Shiban, Youssef; Wittmann, Jasmin; Weißinger, Mara; Mühlberger, Andreas

    2015-01-01

    The current study investigated whether gradually reducing the frequency of aversive stimuli during extinction can prevent the return of fear. Thirty-one participants of a three-stage procedure (acquisition, extinction and a reinstatement test on day 2) were randomly assigned to a standard extinction (SE) and gradual extinction (GE) procedure. The two groups differed only in the extinction procedure. While the SE group ran through a regular extinction process without any negative events, the frequency of the aversive stimuli during the extinction phase was gradually reduced for the GE group. The unconditioned stimulus (US) was an air blast (5 bar, 10 ms). A spider and a scorpion were used as conditioned stimuli (CS). The outcome variables were contingency ratings and physiological measures (skin conductance response, SCR and startle response). There were no differences found between the two groups for the acquisition and extinction phases concerning contingency ratings, SCR, or startle response. GE compared to SE significantly reduced the return of fear in the reinstatement test for the startle response but not for SCR or contingency ratings. This study was successful in translating the findings in rodent to humans. The results suggest that the GE process is suitable for increasing the efficacy of fear extinction. PMID:26441581

  14. Opposed Bellows Would Expel Contents Of Tank

    NASA Technical Reports Server (NTRS)

    Whitaker, Willie

    1994-01-01

    Proposed storage tank contains two pairs of opposed bellows used to expel its contents. Storage and expulsion volumes of tank same as those of older version of tank equipped with single bellows. Four bellows offer greater stability. Applications include automobile cooling systems and gasoline-powered tools like chain saws and leaf blowers.

  15. Opposed Bellows Would Expel Contents Of Tank

    NASA Technical Reports Server (NTRS)

    Whitaker, Willie

    1994-01-01

    Proposed storage tank contains two pairs of opposed bellows used to expel its contents. Storage and expulsion volumes of tank same as those of older version of tank equipped with single bellows. Four bellows offer greater stability. Applications include automobile cooling systems and gasoline-powered tools like chain saws and leaf blowers.

  16. The Opposing Forces That Shape Developmental Education

    ERIC Educational Resources Information Center

    Jaggars, Shanna Smith; Hodara, Michelle

    2013-01-01

    Nationwide, community colleges struggle with how to improve the poor outcomes of students referred to developmental education. Based on a case study of an urban community college system, this paper sets forth an "opposing forces framework" to help diagnose the underlying issues that may thwart colleges' efforts to improve developmental outcomes.…

  17. Extinction of chained instrumental behaviors: Effects of procurement extinction on consumption responding.

    PubMed

    Thrailkill, Eric A; Bouton, Mark E

    2015-07-01

    Instrumental behavior often consists of sequences or chains of responses that minimally include procurement behaviors that enable subsequent consumption behaviors. In such chains, behavioral units are linked by access to one another and eventually to a primary reinforcer, such as food or a drug. The present experiments examined the effects of extinguishing procurement responding on consumption responding after training of a discriminated heterogeneous instrumental chain. Rats learned to make a procurement response (e.g., pressing a lever) in the presence of a distinctive discriminative stimulus; making that response led to the presentation of a second discriminative stimulus that set the occasion for a consumption response (e.g., pulling a chain), which then produced a food-pellet reinforcer. Experiment 1 showed that extinction of either the full procurement-consumption chain or procurement alone weakened the consumption response tested in isolation. Experiment 2 replicated the procurement extinction effect and further demonstrated that the opportunity to make the procurement response, as opposed to simple exposure to the procurement stimulus alone, was required. In Experiment 3, rats learned 2 distinct discriminated heterogeneous chains; extinction of 1 procurement response specifically weakened the consumption response that had been associated with it. The results suggest that learning to inhibit the procurement response may produce extinction of consumption responding through mediated extinction. The experiments suggest the importance of an associative analysis of instrumental behavior chains. (PsycINFO Database Record

  18. Extinction of Chained Instrumental Behaviors: Effects of Procurement Extinction on Consumption Responding

    PubMed Central

    Thrailkill, Eric A.; Bouton, Mark E.

    2015-01-01

    Instrumental behavior often consists of sequences or chains of responses that minimally include procurement behaviors that enable subsequent consumption behaviors. In such chains, behavioral units are linked by access to one another and eventually to a primary reinforcer, such as food or a drug. The present experiments examined the effects of extinguishing procurement responding on consumption responding after training of a discriminated heterogeneous instrumental chain. Rats learned to make a procurement response (e.g., pressing a lever) in the presence of a distinctive discriminative stimulus; making that response led to the presentation of a second discriminative stimulus that set the occasion for a consumption response (e.g., pulling a chain), which then produced a food-pellet reinforcer. Experiment 1 showed that extinction of either the full procurement-consumption chain or procurement alone weakened the consumption response tested in isolation. Experiment 2 replicated the procurement extinction effect and further demonstrated that the opportunity to make the procurement response, as opposed to simple exposure to the procurement stimulus alone, was required. In Experiment 3, rats learned 2 distinct discriminated heterogeneous chains; extinction of 1 procurement response specifically weakened the consumption response that had been associated with it. The results suggest that learning to inhibit the procurement response may produce extinction of consumption responding through mediated extinction. The experiments suggest the importance of an associative analysis of instrumental behavior chains. PMID:25915751

  19. Beliefs about Human Extinction

    SciTech Connect

    Tonn, Bruce Edward

    2009-11-01

    This paper presents the results of a web-based survey about futures issues. Among many questions, respondents were asked whether they believe humans will become extinct. Forty-five percent of the almost 600 respondents believe that humans will become extinct. Many of those holding this believe felt that humans could become extinct within 500-1000 years. Others estimated extinction 5000 or more years into the future. A logistic regression model was estimated to explore the bases for this belief. It was found that people who describe themselves a secular are more likely to hold this belief than people who describe themselves as being Protestant. Older respondents and those who believe that humans have little control over their future also hold this belief. In addition, people who are more apt to think about the future and are better able to imagine potential futures tend to also believe that humans will become extinct.

  20. Extinction and climate change.

    PubMed

    Thomas, Chris D; Williamson, Mark

    2012-02-22

    Arising from F. He & S. P. Hubbell 473, 368-371 (2011). Statistical relationships between habitat area and the number of species observed (species-area relationships, SARs) are sometimes used to assess extinction risks following habitat destruction or loss of climatic suitability. He and Hubbell argue that the numbers of species confined to-rather than observed in-different areas (endemics-area relationships, EARs) should be used instead of SARs, and that SAR-based extinction estimates in the literature are too high. We suggest that He and Hubbell's SAR estimates are biased, that the empirical data they use are not appropriate to calculate extinction risks, and that their statements about extinction risks from climate change do not take into account non-SAR-based estimates or recent observations. Species have already responded to climate change in a manner consistent with high future extinction risks.

  1. Jet Engine Exhaust Nozzle Flow Effector

    NASA Technical Reports Server (NTRS)

    Turner, Travis L. (Inventor); Cano, Roberto J. (Inventor); Silcox, Richard J. (Inventor); Buehrle, Ralph D. (Inventor); Cagle, Christopher M. (Inventor); Cabell, Randolph H. (Inventor); Hilton, George C. (Inventor)

    2011-01-01

    A jet engine exhaust nozzle flow effector is a chevron formed with a radius of curvature with surfaces of the flow effector being defined and opposing one another. At least one shape memory alloy (SMA) member is embedded in the chevron closer to one of the chevron's opposing surfaces and substantially spanning from at least a portion of the chevron's root to the chevron's tip.

  2. Jet Engine Exhaust Nozzle Flow Effector

    NASA Technical Reports Server (NTRS)

    Turner, Travis L. (Inventor); Cano, Roberto J. (Inventor); Silox, Richard J. (Inventor); Buehrle, Ralph D. (Inventor); Cagle, Christopher M. (Inventor); Cabell, Randolph H. (Inventor); Hilton, George C. (Inventor)

    2014-01-01

    A jet engine exhaust nozzle flow effector is a chevron formed with a radius of curvature with surfaces of the flow effector being defined and opposing one another. At least one shape memory alloy (SMA) member is embedded in the chevron closer to one of the chevron's opposing surfaces and substantially spanning from at least a portion of the chevron's root to the chevron's tip.

  3. Triggering rogue waves in opposing currents.

    PubMed

    Onorato, Miguel; Proment, Davide; Toffoli, Alessandro

    2011-10-28

    We show that rogue waves can be triggered naturally when a stable wave train enters a region of an opposing current flow. We demonstrate that the maximum amplitude of the rogue wave depends on the ratio between the current velocity U(0) and the wave group velocity c(g). We also reveal that an opposing current can force the development of rogue waves in random wave fields, resulting in a substantial change of the statistical properties of the surface elevation. The present results can be directly adopted in any field of physics in which the focusing nonlinear Schrödinger equation with nonconstant coefficient is applicable. In particular, nonlinear optics laboratory experiments are natural candidates for verifying experimentally our results.

  4. Extinction and the fossil record

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, ,. J. r. (Principal Investigator)

    1994-01-01

    The author examines evidence of mass extinctions in the fossil record and searches for reasons for such large extinctions. Five major mass extinctions eliminated at least 40 percent of animal genera in the oceans and from 65 to 95 percent of ocean species. Questions include the occurrence of gradual or catastrophic extinctions, causes, environment, the capacity of a perturbation to cause extinctions each time it happens, and the possibility and identification of complex events leading to a mass extinction.

  5. Extinction and the fossil record

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, ,. J. r. (Principal Investigator)

    1994-01-01

    The author examines evidence of mass extinctions in the fossil record and searches for reasons for such large extinctions. Five major mass extinctions eliminated at least 40 percent of animal genera in the oceans and from 65 to 95 percent of ocean species. Questions include the occurrence of gradual or catastrophic extinctions, causes, environment, the capacity of a perturbation to cause extinctions each time it happens, and the possibility and identification of complex events leading to a mass extinction.

  6. Fuzzy jets

    NASA Astrophysics Data System (ADS)

    Mackey, Lester; Nachman, Benjamin; Schwartzman, Ariel; Stansbury, Conrad

    2016-06-01

    Collimated streams of particles produced in high energy physics experiments are organized using clustering algorithms to form jets. To construct jets, the experimental collaborations based at the Large Hadron Collider (LHC) primarily use agglomerative hierarchical clustering schemes known as sequential recombination. We propose a new class of algorithms for clustering jets that use infrared and collinear safe mixture models. These new algorithms, known as fuzzy jets, are clustered using maximum likelihood techniques and can dynamically determine various properties of jets like their size. We show that the fuzzy jet size adds additional information to conventional jet tagging variables in boosted topologies. Furthermore, we study the impact of pileup and show that with some slight modifications to the algorithm, fuzzy jets can be stable up to high pileup interaction multiplicities.

  7. Fuzzy jets

    DOE PAGES

    Mackey, Lester; Nachman, Benjamin; Schwartzman, Ariel; ...

    2016-06-01

    Collimated streams of particles produced in high energy physics experiments are organized using clustering algorithms to form jets . To construct jets, the experimental collaborations based at the Large Hadron Collider (LHC) primarily use agglomerative hierarchical clustering schemes known as sequential recombination. We propose a new class of algorithms for clustering jets that use infrared and collinear safe mixture models. These new algorithms, known as fuzzy jets , are clustered using maximum likelihood techniques and can dynamically determine various properties of jets like their size. We show that the fuzzy jet size adds additional information to conventional jet tagging variablesmore » in boosted topologies. Furthermore, we study the impact of pileup and show that with some slight modifications to the algorithm, fuzzy jets can be stable up to high pileup interaction multiplicities.« less

  8. Fuzzy jets

    SciTech Connect

    Mackey, Lester; Nachman, Benjamin; Schwartzman, Ariel; Stansbury, Conrad

    2016-06-01

    Collimated streams of particles produced in high energy physics experiments are organized using clustering algorithms to form jets . To construct jets, the experimental collaborations based at the Large Hadron Collider (LHC) primarily use agglomerative hierarchical clustering schemes known as sequential recombination. We propose a new class of algorithms for clustering jets that use infrared and collinear safe mixture models. These new algorithms, known as fuzzy jets , are clustered using maximum likelihood techniques and can dynamically determine various properties of jets like their size. We show that the fuzzy jet size adds additional information to conventional jet tagging variables in boosted topologies. Furthermore, we study the impact of pileup and show that with some slight modifications to the algorithm, fuzzy jets can be stable up to high pileup interaction multiplicities.

  9. Is extinction age dependent?

    USGS Publications Warehouse

    Doran, N.A.; Arnold, A.J.; Parker, W.C.; Huffer, F.W.

    2006-01-01

    Age-dependent extinction is an observation with important biological implications. Van Valen's Red Queen hypothesis triggered three decades of research testing its primary implication: that age is independent of extinction. In contrast to this, later studies with species-level data have indicated the possible presence of age dependence. Since the formulation of the Red Queen hypothesis, more powerful tests of survivorship models have been developed. This is the first report of the application of the Cox Proportional Hazards model to paleontological data. Planktonic foraminiferal morphospecies allow the taxonomic and precise stratigraphic resolution necessary for the Cox model. As a whole, planktonic foraminiferal morphospecies clearly show age-dependent extinction. In particular, the effect is attributable to the presence of shorter-ranged species (range < 4 myr) following extinction events. These shorter-ranged species also possess tests with unique morphological architecture. The morphological differences are probably epiphenomena of underlying developmental and heterochronic processes of shorter-ranged species that survived various extinction events. Extinction survivors carry developmental and morphological characteristics into postextinction recovery times, and this sets them apart from species populations established independently of extinction events. Copyright ?? 2006, SEPM (Society for Sedimentary Geology).

  10. Two ways to deepen extinction and the difference between them.

    PubMed

    Leung, Hiu Tin; Reeks, Leanne M; Westbrook, R Frederick

    2012-10-01

    A series of experiments used rats to compare and contrast the effects of subjecting an already extinguished target conditioned stimulus (CS) to additional extinction in compound with either another extinguished or a nonextinguished CS. Exposure to either compound restored responding and their extinction deepened the loss of fear responses (freezing) to the target relative to a CS given equivalent extinction in isolation. This deepening was greater to the target extinguished in compound with the nonextinguished than with the extinguished CS. Summation tests showed that the target suppressed responding to an excitor or an excitatory context when it had been extinguished in compound with a nonextinguished but not with an extinguished CS. The results were interpreted to mean that additional extinction in compound with another extinguished CS resulted in the target acquiring the additional inhibition required to more fully oppose its original excitation. In contrast, additional extinction in compound with a nonextinguished CS resulted in the target acquiring not only the additional inhibition required to oppose its original excitation but also that of the nonextinguished CS, thereby converting the target into a net inhibitor.

  11. Protection from extinction.

    PubMed

    Rescorla, Robert A

    2003-05-01

    The effect of the presence of a conditioned inhibitor on extinction of excitatory conditioning was studied in one magazine approach and three autoshaping experiments using rats and pigeons. In each case, the presence of an inhibitor reduced responding to an exciter during extinction but allowed substantial recovery of responding to that exciter when subsequently tested separately. Control stimuli with a history of being irrelevant to reinforcement or being nonreinforced had less of a protective effect. This constitutes a clear demonstration of protection from extinction, a phenomenon of substantial theoretical and applied importance.

  12. Temporal Dynamics of Recovery from Extinction Shortly after Extinction Acquisition

    ERIC Educational Resources Information Center

    Archbold, Georgina E.; Dobbek, Nick; Nader, Karim

    2013-01-01

    Evidence suggests that extinction is new learning. Memory acquisition involves both short-term memory (STM) and long-term memory (LTM) components; however, few studies have examined early phases of extinction retention. Retention of auditory fear extinction was examined at various time points. Shortly (1-4 h) after extinction acquisition…

  13. Temporal Dynamics of Recovery from Extinction Shortly after Extinction Acquisition

    ERIC Educational Resources Information Center

    Archbold, Georgina E.; Dobbek, Nick; Nader, Karim

    2013-01-01

    Evidence suggests that extinction is new learning. Memory acquisition involves both short-term memory (STM) and long-term memory (LTM) components; however, few studies have examined early phases of extinction retention. Retention of auditory fear extinction was examined at various time points. Shortly (1-4 h) after extinction acquisition…

  14. The costly benefits of opposing agricultural biotechnology.

    PubMed

    Apel, Andrew

    2010-11-30

    Rigorous application of a simple definition of what constitutes opposition to agricultural biotechnology readily encompasses a wide array of key players in national and international systems of food production, distribution and governance. Even though the sum of political and financial benefits of opposing agricultural biotechnology appears vastly to outweigh the benefits which accrue to providers of agricultural biotechnology, technology providers actually benefit from this opposition. If these barriers to biotechnology were removed, subsistence farmers still would not represent a lucrative market for improved seed. The sum of all interests involved ensures that subsistence farmers are systematically denied access to agricultural biotechnology. Copyright © 2010 Elsevier B.V. All rights reserved.

  15. Compressive nanomechanics of opposing aggrecan macromolecules.

    PubMed

    Dean, Delphine; Han, Lin; Grodzinsky, Alan J; Ortiz, Christine

    2006-01-01

    In this study, we have measured the nanoscale compressive interactions between opposing aggrecan macromolecules in near-physiological conditions, in order to elucidate the molecular origins of tissue-level cartilage biomechanical behavior. Aggrecan molecules from fetal bovine epiphyseal cartilage were chemically end-grafted to planar substrates, standard nanosized atomic force microscopy (AFM) probe tips (R(tip) approximately 50 nm), and larger colloidal probe tips (R(tip) approximately 2.5 microm). To assess normal nanomechanical interaction forces between opposing aggrecan layers, substrates with microcontact printed aggrecan were imaged using contact mode AFM, and aggrecan layer height (and hence deformation) was measured as a function of solution ionic strength (IS) and applied normal load. Then, using high-resolution force spectroscopy, nanoscale compressive forces between opposing aggrecan on the tip and substrate were measured versus tip-substrate separation distance in 0.001-1M NaCl. Nanosized tips enabled measurement of the molecular stiffness of 2-4 aggrecan while colloidal tips probed the nanomechanical properties of larger assemblies (approximately 10(4) molecules). The compressive stiffness of aggrecan was much higher when using a densely packed colloidal tip than the stiffness measured for using the nanosized tip with a few aggrecan, demonstrating the importance of lateral interactions to the normal nanomechanical properties. The measured stress at 0.1M NaCl (near-physiological ionic strength) increased sharply at aggrecan densities under the tip of approximately 40 mg/ml (physiological densities are approximately 20-80 mg/ml), corresponding to an average inter-GAG spacing of 4-5 Debye lengths (4-5 nm); this characteristic spacing is consistent with the onset of significant electrostatic interactions between GAG chains of opposing aggrecan molecules. Comparison of nanomechanical data to the predictions of Poisson-Boltzmann-based models further

  16. Storm track processes and the opposing influences of climate change

    NASA Astrophysics Data System (ADS)

    Shaw, T. A.; Baldwin, M.; Barnes, E. A.; Caballero, R.; Garfinkel, C. I.; Hwang, Y.-T.; Li, C.; O'Gorman, P. A.; Rivière, G.; Simpson, I. R.; Voigt, A.

    2016-09-01

    Extratropical cyclones are storm systems that are observed to travel preferentially within confined regions known as storm tracks. They contribute to precipitation, wind and temperature extremes in mid-latitudes. Cyclones tend to form where surface temperature gradients are large, and the jet stream influences their speed and direction of travel. Storm tracks shape the global climate through transport of energy and momentum. The intensity and location of storm tracks varies seasonally, and in response to other natural variations, such as changes in tropical sea surface temperature. A hierarchy of numerical models of the atmosphere-ocean system -- from highly idealized to comprehensive -- has been used to study and predict responses of storm tracks to anthropogenic climate change. The future position and intensity of storm tracks depend on processes that alter temperature gradients. However, different processes can have opposing influences on temperature gradients, which leads to a tug of war on storm track responses and makes future projections more difficult. For example, as climate warms, surface shortwave cloud radiative changes increase the Equator-to-pole temperature gradient, but at the same time, longwave cloud radiative changes reduce this gradient. Future progress depends on understanding and accurately quantifying the relative influence of such processes on the storm tracks.

  17. Extinction with multiple excitors.

    PubMed

    McConnell, Bridget L; Miguez, Gonzalo; Miller, Ralph R

    2013-06-01

    Four conditioned suppression experiments with rats, using an ABC renewal design, investigated the effects of compounding the target conditioned excitor with additional, nontarget conditioned excitors during extinction. Experiment 1 showed stronger extinction, as evidenced by less renewal, when the target excitor was extinguished in compound with a second excitor, relative to when it was extinguished with associatively neutral stimuli. Critically, this deepened extinction effect was attenuated (i.e., more renewal occurred) when a third excitor was added during extinction training. This novel demonstration contradicts the predictions of associative learning models based on total error reduction, but it is explicable in terms of a counteraction effect within the framework of the extended comparator hypothesis. The attenuated deepened extinction effect was replicated in Experiments 2a and 3, which also showed that pretraining consisting of weakening the association between the two additional excitors (Experiments 2a and 2b) or weakening the association between one of the additional excitors and the unconditioned stimulus (Experiment 3) attenuated the counteraction effect, thereby resulting in a decrease in responding to the target excitor. These results suggest that more than simple total error reduction determines responding after extinction.

  18. Extinction of oscillating populations

    NASA Astrophysics Data System (ADS)

    Smith, Naftali R.; Meerson, Baruch

    2016-03-01

    Established populations often exhibit oscillations in their sizes that, in the deterministic theory, correspond to a limit cycle in the space of population sizes. If a population is isolated, the intrinsic stochasticity of elemental processes can ultimately bring it to extinction. Here we study extinction of oscillating populations in a stochastic version of the Rosenzweig-MacArthur predator-prey model. To this end we develop a WKB (Wentzel, Kramers and Brillouin) approximation to the master equation, employing the characteristic population size as the large parameter. Similar WKB theories have been developed previously in the context of population extinction from an attracting multipopulation fixed point. We evaluate the extinction rates and find the most probable paths to extinction from the limit cycle by applying Floquet theory to the dynamics of an effective four-dimensional WKB Hamiltonian. We show that the entropic barriers to extinction change in a nonanalytic way as the system passes through the Hopf bifurcation. We also study the subleading pre-exponential factors of the WKB approximation.

  19. Cosmic jets

    NASA Technical Reports Server (NTRS)

    Rees, M. J.

    1986-01-01

    The evidence that active galactic nuclei produce collimated plasma jets is summarised. The strongest radio galaxies are probably energised by relativistic plasma jets generated by spinning black holes interacting with magnetic fields attached to infalling matter. Such objects can produce e(+)-e(-) plasma, and may be relevant to the acceleration of the highest-energy cosmic ray primaries. Small-scale counterparts of the jet phenomenon within our own galaxy are briefly reviewed.

  20. Water Jetting

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Hi-Tech Inc., a company which manufactures water jetting equipment, needed a high pressure rotating swivel, but found that available hardware for the system was unsatisfactory. They were assisted by Marshall, which had developed water jetting technology to clean the Space Shuttles. The result was a completely automatic water jetting system which cuts rock and granite and removes concrete. Labor costs have been reduced; dust is suppressed and production has been increased.

  1. Stress and Fear Extinction

    PubMed Central

    Maren, Stephen; Holmes, Andrew

    2016-01-01

    Stress has a critical role in the development and expression of many psychiatric disorders, and is a defining feature of posttraumatic stress disorder (PTSD). Stress also limits the efficacy of behavioral therapies aimed at limiting pathological fear, such as exposure therapy. Here we examine emerging evidence that stress impairs recovery from trauma by impairing fear extinction, a form of learning thought to underlie the suppression of trauma-related fear memories. We describe the major structural and functional abnormalities in brain regions that are particularly vulnerable to stress, including the amygdala, prefrontal cortex, and hippocampus, which may underlie stress-induced impairments in extinction. We also discuss some of the stress-induced neurochemical and molecular alterations in these brain regions that are associated with extinction deficits, and the potential for targeting these changes to prevent or reverse impaired extinction. A better understanding of the neurobiological basis of stress effects on extinction promises to yield novel approaches to improving therapeutic outcomes for PTSD and other anxiety and trauma-related disorders. PMID:26105142

  2. Biological extinction in earth history

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1986-01-01

    Virtually all plant and animal species that have ever lived on the earth are extinct. For this reason alone, extinction must play an important role in the evolution of life. The five largest mass extinctions of the past 600 million years are of greatest interest, but there is also a spectrum of smaller events, many of which indicate biological systems in profound stress. Extinction may be episodic at all scales, with relatively long periods of stability alternating with short-lived extinction events. Most extinction episodes are biologically selective, and further analysis of the victims and survivors offers the greatest chance of deducing the proximal causes of extinction. A drop in sea level and climatic change are most frequently invoked to explain mass extinctions, but new theories of collisions with extraterrestrial bodies are gaining favor. Extinction may be constructive in a Darwinian sense or it may only perturb the system by eliminating those organisms that happen to be susceptible to geologically rare stresses.

  3. Biological extinction in earth history

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1986-01-01

    Virtually all plant and animal species that have ever lived on the earth are extinct. For this reason alone, extinction must play an important role in the evolution of life. The five largest mass extinctions of the past 600 million years are of greatest interest, but there is also a spectrum of smaller events, many of which indicate biological systems in profound stress. Extinction may be episodic at all scales, with relatively long periods of stability alternating with short-lived extinction events. Most extinction episodes are biologically selective, and further analysis of the victims and survivors offers the greatest chance of deducing the proximal causes of extinction. A drop in sea level and climatic change are most frequently invoked to explain mass extinctions, but new theories of collisions with extraterrestrial bodies are gaining favor. Extinction may be constructive in a Darwinian sense or it may only perturb the system by eliminating those organisms that happen to be susceptible to geologically rare stresses.

  4. Biological extinction in earth history.

    PubMed

    Raup, D M

    1986-03-28

    Virtually all plant and animal species that have ever lived on the earth are extinct. For this reason alone, extinction must play an important role in the evolution of life. The five largest mass extinctions of the past 600 million years are of greatest interest, but there is also a spectrum of smaller events, many of which indicate biological systems in profound stress. Extinction may be episodic at all scales, with relatively long periods of stability alternating with short-lived extinction events. Most extinction episodes are biologically selective, and further analysis of the victims and survivors offers the greatest chance of deducing the proximal causes of extinction. A drop in sea level and climatic change are most frequently invoked to explain mass extinctions, but new theories of collisions with extraterrestrial bodies are gaining favor. Extinction may be constructive in a Darwinian sense or it may only perturb the system by eliminating those organisms that happen to be susceptible to geologically rare stresses.

  5. Species extinction mires ecosystem

    SciTech Connect

    Holzman, D.

    1990-03-26

    Extinction is normal in the evolution of life, but amphibians, insects, birds and mammals are vanishing at an alarming pace. While habitat destruction, overexploitation and pollution are among the main causes, some disappearances cannot be explained. The extinction problem among amphibians mirrors the general, worldwide phenomenon. A synergism of insults may be responsible. Chance events such as a dry year might occasionally clean out a pond. But a larger lake nearby would replenish it. Now acid pollution adds to the ponds' burden while stocking of amphibian-eating sport fish in the lake - which happens even in natural parks - would destroy the source of replenishment. Some fear that extinctions ultimately could destroy nature's fabric.

  6. Extinction learning, reconsolidation and the internal reinforcement hypothesis.

    PubMed

    Eisenhardt, Dorothea; Menzel, Randolf

    2007-02-01

    Retrieving a consolidated memory--by exposing an animal to the learned stimulus but not to the associated reinforcement--leads to two opposing processes: one that weakens the old memory as a result of extinction learning, and another that strengthens the old, already-consolidated memory as a result of some less well-understood form of learning. This latter process of memory strengthening is often referred to as "reconsolidation", since protein synthesis can inhibit this form of memory formation. Although the behavioral phenomena of the two antagonizing forms of learning are well documented, the mechanisms behind the corresponding processes of memory formation are still quite controversial. Referring to results of extinction/reconsolidation experiments in honeybees, we argue that two opposing learning processes--with their respective consolidation phases and memories--are initiated by retrieval trials: extinction learning and reminder learning, the latter leading to the phenomenon of spontaneous recovery from extinction, a process that can be blocked with protein synthesis inhibition.

  7. Supernovae and mass extinctions

    NASA Technical Reports Server (NTRS)

    Vandenbergh, S.

    1994-01-01

    Shklovsky and others have suggested that some of the major extinctions in the geological record might have been triggered by explosions of nearby supernovae. The frequency of such extinction events will depend on the galactic supernova frequency and on the distance up to which a supernova explosion will produce lethal effects upon terrestrial life. In the present note it will be assumed that a killer supernova has to occur so close to Earth that it will be embedded in a young, active, supernova remnant. Such young remnants typically have radii approximately less than 3 pc (1 x 10(exp 19) cm). Larger (more pessimistic?) killer radii have been adopted by Ruderman, Romig, and by Ellis and Schramm. From observations of historical supernovae, van den Bergh finds that core-collapse (types Ib and II) supernovae occur within 4 kpc of the Sun at a rate of 0.2 plus or minus 0.1 per century. Adopting a layer thickness of 0.3 kpc for the galacitc disk, this corresponds to a rate of approximately 1.3 x 10(exp -4) supernovae pc(exp -3) g.y.(exp -1). Including supernovae of type Ia will increase the total supernovae rate to approximately 1.5 x 10(exp -4) supernovae pc(exp -3) g.y.(exp -1). For a lethal radius of R pc the rate of killer events will therefore be 1.7 (R/3)(exp 3) x 10(exp -2) supernovae per g.y. However, a frequency of a few extinctions per g.y. is required to account for the extinctions observed during the phanerozoic. With R (extinction) approximately 3 pc, the galactic supernova frequency is therefore too low by 2 orders of magnitude to account for the major extinctions in the geological record.

  8. Dilution jet mixing program, supplementary report

    NASA Technical Reports Server (NTRS)

    Srinivasan, R.; White, C.

    1986-01-01

    The velocity and temperature distributions predicted by a 3-D numerical model and experimental measurements are compared. Empirical correlations for the jet velocity trajectory developed are presented. The measured velocity distributions for all test cases of phase through phase 3 are presented in the form of contour and oblique plots. quantification of the effects of the following on the jet mixing characteristics with a confined crossflow are: (1) orifice geometry momentum flux ratio and density ratio; (2) nonuniform mainstream temperature and velocity profiles upstream of dilution orifices; (3) cold versus hot jet injection; (4) cross-stream flow are a convergence as encountered in practical dilution zone geometries; (5) 2-D slot versus circular orifices; (6) discrete noncirculcer orifices; (7) single-sided versus opposed jets; (8) single row of jets.

  9. Single nanowire extinction spectroscopy.

    PubMed

    Giblin, Jay; Vietmeyer, Felix; McDonald, Matthew P; Kuno, Masaru

    2011-08-10

    Here we show the first direct extinction spectra of single one-dimensional (1D) semiconductor nanostructures obtained at room temperature utilizing a spatial modulation approach. (1) For these materials, ensemble averaging in conventional extinction spectroscopy has limited our understanding of the interplay between carrier confinement and their electrostatic interactions. (2-4) By probing individual CdSe nanowires (NWs), we have identified and assigned size-dependent exciton transitions occurring across the visible. In turn, we have revealed the existence of room temperature 1D excitons in the narrowest NWs.

  10. Extinction from a paleontological perspective

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1993-01-01

    Extinction of widespread species is common in evolutionary time (millions of years) but rare in ecological time (hundreds or thousands of years). In the fossil record, there appears to be a smooth continuum between background and mass extinction; and the clustering of extinctions at mass extinctions cannot be explained by the chance coincidence of independent events. Although some extinction is selective, much is apparently random in that survivors have no recognizable superiority over victims. Extinction certainly plays an important role in evolution, but whether it is constructive or destructive has not yet been determined.

  11. Extinction from a paleontological perspective

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1993-01-01

    Extinction of widespread species is common in evolutionary time (millions of years) but rare in ecological time (hundreds or thousands of years). In the fossil record, there appears to be a smooth continuum between background and mass extinction; and the clustering of extinctions at mass extinctions cannot be explained by the chance coincidence of independent events. Although some extinction is selective, much is apparently random in that survivors have no recognizable superiority over victims. Extinction certainly plays an important role in evolution, but whether it is constructive or destructive has not yet been determined.

  12. Extinction from a paleontological perspective.

    PubMed

    Raup, D M

    1993-01-01

    Extinction of widespread species is common in evolutionary time (millions of years) but rare in ecological time (hundreds or thousands of years). In the fossil record, there appears to be a smooth continuum between background and mass extinction; and the clustering of extinctions at mass extinctions cannot be explained by the chance coincidence of independent events. Although some extinction is selective, much is apparently random in that survivors have no recognizable superiority over victims. Extinction certainly plays an important role in evolution, but whether it is constructive or destructive has not yet been determined.

  13. Unexpectedly many extinct hominins.

    PubMed

    Bokma, Folmer; van den Brink, Valentijn; Stadler, Tanja

    2012-09-01

    Recent studies indicate that Neanderthal and Denisova hominins may have been separate species, while debate continues on the status of Homo floresiensis. The decade-long debate between "splitters," who recognize over 20 hominin species, and "lumpers," who maintain that all these fossils belong to just a few lineages, illustrates that we do not know how many extinct hominin species to expect. Here, we present probability distributions for the number of speciation events and the number of contemporary species along a branch of a phylogeny. With estimates of hominin speciation and extincton rates, we then show that the expected total number of extinct hominin species is 8, but may be as high as 27. We also show that it is highly unlikely that three very recent species disappeared due to natural, background extinction. This may indicate that human-like remains are too easily considered distinct species. Otherwise, the evidence suggesting that Neanderthal and the Denisova hominin represent distinct species implies a recent wave of extinctions, ostensibly driven by the only survivor, H. sapiens. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

  14. Context, Learning, and Extinction

    ERIC Educational Resources Information Center

    Gershman, Samuel J.; Blei, David M.; Niv, Yael

    2010-01-01

    A. Redish et al. (2007) proposed a reinforcement learning model of context-dependent learning and extinction in conditioning experiments, using the idea of "state classification" to categorize new observations into states. In the current article, the authors propose an interpretation of this idea in terms of normative statistical inference. They…

  15. Extinction in population dynamics

    NASA Astrophysics Data System (ADS)

    Escudero, C.; Buceta, J.; de La Rubia, F. J.; Lindenberg, Katja

    2004-02-01

    We study a generic reaction-diffusion model for single-species population dynamics that includes reproduction, death, and competition. The population is assumed to be confined in a refuge beyond which conditions are so harsh that they lead to certain extinction. Standard continuum mean field models in one dimension yield a critical refuge length Lc such that a population in a refuge larger than this is assured survival. Herein we extend the model to take into account the discreteness and finiteness of the population, which leads us to a stochastic description. We present a particular critical criterion for likely extinction, namely, that the standard deviation of the population be equal to the mean. According to this criterion, we find that while survival can no longer be guaranteed for any refuge size, for sufficiently weak competition one can make the refuge large enough (certainly larger than Lc) to cause extinction to be unlikely. However, beyond a certain value of the competition rate parameter it is no longer possible to escape a likelihood of extinction even in an infinite refuge. These unavoidable fluctuations therefore have a severe impact on refuge design issues.

  16. Biogeography and extinction

    SciTech Connect

    Jablonski, D.

    1985-01-01

    The geographic ranges of species and clades, and the deployment of those clades among biogeographic provinces, are important determinants of rates and patterns of extinction. Studies of Late Cretaceous mollusks of the Gulf and Atlantic Coastal Plain confirm that species duration is closely correlated with geographic range during times of normal, background extinction. When species that originate in the last 2 myr of the Cretaceous, the correlation increases significantly. The fact that even these truncated species frequently attained broad geographic ranges indicates that during background times duration is a function of geographic range and not vice versa. However, during the end-Cretaceous mass extinction, it is clade geographic range and not the within-province ranges of its constituent species that determines survivorship: about 55% of the widespread genera but only 12% of the endemic genera survive, regardless of the ranges of their individual species. Thus, clade geographic range is an irreducible property, with effects decoupled from species-level or organismic traits that determine species' geographic ranges. Clades with tropical distributions suffer disproportionately, again independent of species' geographic range magnitudes. Survivorship of taxa or morphologies during mass extinctions may have little to do with adaptation at the organismic or even species level, but depends at least in part on clade-level traits that are less important during background times.

  17. Context, Learning, and Extinction

    ERIC Educational Resources Information Center

    Gershman, Samuel J.; Blei, David M.; Niv, Yael

    2010-01-01

    A. Redish et al. (2007) proposed a reinforcement learning model of context-dependent learning and extinction in conditioning experiments, using the idea of "state classification" to categorize new observations into states. In the current article, the authors propose an interpretation of this idea in terms of normative statistical inference. They…

  18. Hydrodynamics of submerged turbulent plane offset jets

    NASA Astrophysics Data System (ADS)

    Dey, Subhasish; Ravi Kishore, Galla; Castro-Orgaz, Oscar; Ali, Sk Zeeshan

    2017-06-01

    The results of an experimental study on the turbulent flow characteristics in submerged plane offset jets are presented. The vertical profiles of time-averaged velocity components and Reynolds stresses at different horizontal locations are depicted to illustrate their variations across the pre-attachment, impingement, and wall jet regions. The characteristic lengths and the jet profile of submerged offset jets in the pre-attachment region are determined from the velocity profiles. The regional profiles of velocity and Reynolds stresses are analyzed in the context of the self-similarity, the decay of their representative scales, and the development of the length scales. The self-similarity characteristics in the pre-attachment and wall jet regions are preserved better than those in the impingement region. The turbulent kinetic energy (TKE) fluxes suggest that within the jet layer in the pre-attachment region, an upward advection of low-speed fluid streaks induces a strong retardation to the jet; while in the wall jet region, an inrush of low-speed fluid streaks induces a weak retardation. Analysis of the TKE budget reveals that within the jet layer, the TKE diffusion rate and the pressure energy diffusion rate oppose each other, and the peaks of the dissipation rate lag from those of the corresponding production rate.

  19. Esthetic restorative materials and opposing enamel wear.

    PubMed

    Olivera, Anna Belsuzarri; Marques, Márcia Martins

    2008-01-01

    This in vitro study compared the effects of a gold alloy (Degulor M), four dental ceramics (IPS Empress, IPS Empress 2, Duceram Plus, Duceram LFC) and a laboratory-processed composite (Targis) on the wear of human enamel. The amount of wear of the enamel (dental cusps) and restorative materials (disks) were tested in water at 37 degrees C under standard load (20 N), with a chewing rate of 1.3 Hz and was determined after 150,000 and 300,000 cycles. Before the test, the average surface roughness of the restorative materials was analyzed using the Ra parameter. The results of this study indicate that Targis caused enamel wear similar to Degulor M and resulted in significantly less wear than all the ceramics tested. IPS Empress provoked the greatest amount of enamel wear and Degulor M caused less vertical dimension loss. Targis could be an appropriate alternative material to ceramic, because it is esthetic and produces opposing enamel wear comparable to gold alloy.

  20. Microgravity flame spread over thick solids in low velocity opposed flow

    NASA Astrophysics Data System (ADS)

    Wang, Shuangfeng; Zhu, Feng

    2016-07-01

    Motivated primarily by fire safety of spacecraft, a renewed interest in microgravity flame spread over solid materials has arisen. With few exceptions, however, research on microgravity flame spread has been focused on thermally thin fuels due to the constraint on available test time. In this study, two sets of experiments are conducted to examine the flame spread and extinction behavior over thick PMMA in simulated and actual microgravity environments. The low-gravity flame spread environment is produced by a narrow channel apparatus in normal gravity. Extinction limits using flow velocity and oxygen concentration as coordinates are presented, and flame spread rates are determined as a function of the velocity and oxygen concentration of the gas flow. The microgravity experiments are also performed with varying low-velocity flow and varying ambient oxygen concentration. The important observations include flame behavior and appearance as a function of oxygen concentration and flow velocity, temperature variation in gas and solid phases, and flame spread rate. A comparison between simulated and actual microgravity data is made, and general agreement is found. Based on the experimental observations, mechanisms for flame spread and extinction in low velocity opposed flows are discussed.

  1. Bouncing Jets

    NASA Astrophysics Data System (ADS)

    Wadhwa, Navish; Vlachos, Pavlos; Jung, Sunghwan

    2011-11-01

    Contrary to common intuition, free jets of fluid can ``bounce'' off each other on collision in mid-air, through the effect of a lubricating air film that separates the jets. We have developed a simple experimental setup to stably demonstrate and study the non-coalescence of jets on collision. We present the results of an experimental investigation of oblique collision between two silicone oil jets, supported by a simple analytical explanation. Our focus is on elucidating the role of various physical forces at play such as viscous stresses, capillary force and inertia. A parametric study conducted by varying the nozzle diameter, jet velocity, angle of inclination and fluid viscosity reveals the scaling laws for the quantities involved such as contact time. We observed a transition from bouncing to coalescence with an increase in jet velocity and inclination angle. We propose that a balance between the contact time of jets and the time required for drainage of the trapped air film can provide a criterion for transition from non-coalescence to coalescence.

  2. Mass Extinctions Past and Present.

    ERIC Educational Resources Information Center

    Allmon, Warren Douglas

    1987-01-01

    Discusses some parallels that seem to exist between mass extinction recognizable in the geologic record and the impending extinction of a significant proportion of the earth's species due largely to tropical deforestation. Describes some recent theories of causal factors and periodicities in mass extinction. (Author/TW)

  3. Mass Extinctions Past and Present.

    ERIC Educational Resources Information Center

    Allmon, Warren Douglas

    1987-01-01

    Discusses some parallels that seem to exist between mass extinction recognizable in the geologic record and the impending extinction of a significant proportion of the earth's species due largely to tropical deforestation. Describes some recent theories of causal factors and periodicities in mass extinction. (Author/TW)

  4. Oscillatory Extinction Of Spherical Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Law, C. K.; Yoo, S. W.; Christianson, E. W.

    2003-01-01

    Since extinction has been observed in an oscillatory manner in Le greater than 1 premixed flames, it is not unreasonable to expect that extinction could occur in an unsteady manner for diffusion flames. Indeed, near-limit oscillations have been observed experimentally under microgravity conditions for both candle flames and droplet flames. Furthermore, the analysis of Cheatham and Matalon on the unsteady behavior of diffusion flames with heat loss, identified an oscillatory regime which could be triggered by either a sufficiently large Lewis number (even without heat loss) or an appreciable heat loss (even for Le=1). In light of these recent understanding, the present investigation aims to provide a well-controlled experiment that can unambiguously demonstrate the oscillation of diffusion flames near both the transport- and radiation-induced limits. That is, since candle and jet flames are stabilized through flame segments that are fundamentally premixed in nature, and since premixed flames are prone to oscillate, there is the possibility that the observed oscillation of these bulk diffusion flames could be triggered and sustained by the oscillation of the premixed flame segments. Concerning the observed oscillatory droplet extinction, it is well-known that gas-phase oscillation in heterogeneous burning can be induced by and is thereby coupled with condensed-phase unsteadiness. Consequently, a convincing experiment on diffusion flame oscillation must exclude any ingredients of premixed flames and other sources that may either oscillate themselves or promote the oscillation of the diffusion flame. The present experiment on burner-generated spherical flames with a constant reactant supply endeavored to accomplish this goal. The results are further compared with those from computational simulation for further understanding and quantification of the flame dynamics and extinction.

  5. Extinction of solid rocket motor by liquid injection

    NASA Astrophysics Data System (ADS)

    Yin, Jinqi; Li, Baoxiun; Wang, Kexiu; Wu, Xinping; Zhang, Baoqing; Su, Guangshou

    1992-10-01

    An empirical data-based theoretical model is presented for liquid quenching of a solid rocket motor, taking into account the details of internal-ballistics coupling effects, solid propellant transient burning, liquid drop evaporation, and heat transfer via liquid-jet boiling. The exceeding of a critical injection pressure drop value is found to be required for effective quenching; as the injection pressure drop increases, the volume of the liquid required for reliable extinction decreases. Good agreement with experimental results is obtained.

  6. Business Jet

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The Citation Jet, developed by Cessna Aircraft Company, Wichita, KS, is the first business jet to employ Langley Research Center's natural laminar flow (NLF) technology. NLF reduces drag and therefore saves fuel by using only the shape of the wing to keep the airflow smooth, or laminar. This reduces friction between the air and wing, and therefore, reduces drag. NASA's Central Industrial Applications Center, Rural Enterprises, Inc., Durant, OK, its Kansas affiliate, and Wichita State University assisted in the technology transfer.

  7. Emerging jets

    NASA Astrophysics Data System (ADS)

    Schwaller, Pedro; Stolarski, Daniel; Weiler, Andreas

    2015-05-01

    In this work, we propose a novel search strategy for new physics at the LHC that utilizes calorimeter jets that (i) are composed dominantly of displaced tracks and (ii) have many different vertices within the jet cone. Such emerging jet signatures are smoking guns for models with a composite dark sector where a parton shower in the dark sector is followed by displaced decays of dark pions back to SM jets. No current LHC searches are sensitive to this type of phenomenology. We perform a detailed simulation for a benchmark signal with two regular and two emerging jets, and present and implement strategies to suppress QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this signature can be probed with mediator masses as large as 1.5 TeV for a range of dark pion lifetimes, and the reach is increased further at the high-luminosity LHC. The emerging jet search is also sensitive to a broad class of long-lived phenomena, and we show this for a supersymmetric model with R-parity violation. Possibilities for discovery at LHCb are also discussed.

  8. Direct and indirect effects of biological factors on extinction risk in fossil bivalves.

    PubMed

    Harnik, Paul G

    2011-08-16

    Biological factors, such as abundance and body size, may contribute directly to extinction risk and indirectly through their influence on other biological characteristics, such as geographic range size. Paleontological data can be used to explicitly test many of these hypothesized relationships, and general patterns revealed through analysis of the fossil record can help refine predictive models of extinction risk developed for extant species. Here, I use structural equation modeling to tease apart the contributions of three canonical predictors of extinction--abundance, body size, and geographic range size--to the duration of bivalve species in the early Cenozoic marine fossil record of the eastern United States. I find that geographic range size has a strong direct effect on extinction risk and that an apparent direct effect of abundance can be explained entirely by its covariation with geographic range. The influence of geographic range on extinction risk is manifest across three ecologically disparate bivalve clades. Body size also has strong direct effects on extinction risk but operates in opposing directions in different clades, and thus, it seems to be decoupled from extinction risk in bivalves as a whole. Although abundance does not directly predict extinction risk, I reveal weak indirect effects of both abundance and body size through their positive influence on geographic range size. Multivariate models that account for the pervasive covariation between biological factors and extinction are necessary for assessing causality in evolutionary processes and making informed predictions in applied conservation efforts.

  9. Neuronal circuits of fear extinction.

    PubMed

    Herry, Cyril; Ferraguti, Francesco; Singewald, Nicolas; Letzkus, Johannes J; Ehrlich, Ingrid; Lüthi, Andreas

    2010-02-01

    Fear extinction is a form of inhibitory learning that allows for the adaptive control of conditioned fear responses. Although fear extinction is an active learning process that eventually leads to the formation of a consolidated extinction memory, it is a fragile behavioural state. Fear responses can recover spontaneously or subsequent to environmental influences, such as context changes or stress. Understanding the neuronal substrates of fear extinction is of tremendous clinical relevance, as extinction is the cornerstone of psychological therapy of several anxiety disorders and because the relapse of maladaptative fear and anxiety is a major clinical problem. Recent research has begun to shed light on the molecular and cellular processes underlying fear extinction. In particular, the acquisition, consolidation and expression of extinction memories are thought to be mediated by highly specific neuronal circuits embedded in a large-scale brain network including the amygdala, prefrontal cortex, hippocampus and brain stem. Moreover, recent findings indicate that the neuronal circuitry of extinction is developmentally regulated. Here, we review emerging concepts of the neuronal circuitry of fear extinction, and highlight novel findings suggesting that the fragile phenomenon of extinction can be converted into a permanent erasure of fear memories. Finally, we discuss how research on genetic animal models of impaired extinction can further our understanding of the molecular and genetic bases of human anxiety disorders.

  10. Pulsar extinction. [astrophysics

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Baker, K.; Turk, J. S.

    1975-01-01

    Radio emission from pulsars, attributed to an instability associated with the creation of electron-positron pairs from gamma rays was investigated. The condition for pair creation therefore lead to an extinction condition. The relevant physical processes were analyzed in the context of a mathematical model, according to which radiation originated at the polar caps and magnetic field lines changed from a closed configuration to an open configuration at the force balance or corotation radius.

  11. Extinction in SC galaxies

    NASA Astrophysics Data System (ADS)

    Giovanelli, Riccardo; Haynes, Martha P.; Salzer, John J.; Wegner, Gary; da Costa, Luiz N.; Freudling, Wolfram

    1994-06-01

    We analyze the photometric properties of a sample of Sbc-Sc galaxies with known redshifts, single-dish H I profiles, and Charge Coupled Device (CCD) I band images. We derive laws that relate the measured isophotal radius at muI = 23.5, magnitude, scale length, and H I flux to the face-on aspect. We find spiral galaxies to be substantially less transparent than suggested in most previous determinations, but not as opaque as claimed by Valentijn (1990). Regions in the disk farther than two or three scale lengths from the center are close to completely transparent. In addition to statistically derived relations for the inclination dependence of photometric parameters, we present the results of a modeling exercise that utilizes the 'triplex' model of Disney et al. (1989) to obtain upper limits of the disk opacity. Within the framework of that model, and with qualitative consideration of the effects of scattering on extinction, we estimate late spiral disks at I band to have central optical depths tauI(0) less than 5 and dust absorbing layers with scale heights on the order of half that of the stellar component or less. We discuss our results in light of previous determinations of internal extinction relations and point out the substantial impact of internal extinction on the scatter of the Tully-Fisher relation. We also find that the visual diameters by which large catalogs are constructed (UGC, ESO-Uppsala) are nearly proportional to face-on isophotal diameters.

  12. Multiple Mode Actuation of a Turbulent Jet

    NASA Technical Reports Server (NTRS)

    Pack, LaTunia G.; Seifert, Avi

    2001-01-01

    The effects of multiple mode periodic excitation on the evolution of a circular turbulent jet were studied experimentally. A short, wide-angle diffuser was attached to the jet exit. Streamwise and cross-stream excitations were introduced at the junction between the jet exit and the diffuser inlet on opposing sides of the jet. The introduction of high amplitude, periodic excitation in the streamwise direction enhances the mixing and promotes attachment of the jet shear-layer to the diffuser wall. Cross-stream excitation applied over a fraction of the jet circumference can deflect the jet away from the excitation slot. The two modes of excitation were combined using identical frequencies and varying the relative phase between the two actuators in search of an optimal response. It is shown that, for low and moderate periodic momentum input levels, the jet deflection angles depend strongly on the relative phase between the two actuators. Optimum performance is achieved when the phase difference is pi +/- pi/6. The lower effectiveness of the equal phase excitation is attributed to the generation of an azimuthally symmetric mode that does not produce the required non-axisymmetric vectoring. For high excitation levels, identical phase becomes more effective, while phase sensitivity decreases. An important finding was that with proper phase tuning, two unsteady actuators can be combined to obtain a non-linear response greater than the superposition of the individual effects.

  13. Effects of Inert Dust Clouds on the Extinction of Strained, Laminar Flames at Normal and Micro Gravity

    NASA Technical Reports Server (NTRS)

    Andac, M. Gurhan; Egolfopoulos, Fokion N.; Campbell, Charles S.; Lauvergne, Romain; Wu, Ming-Shin (Technical Monitor)

    2000-01-01

    A combined experimental and detailed numerical study was conducted on the interaction between chemically inert solid particles and strained, atmospheric methane/air and propane/air laminar flames, both premixed and non-premixed. Experimentally, the opposed jet configuration was used with the addition of a particle seeder capable of operating in conditions of varying gravity. The particle seeding system was calibrated under both normal and micro gravity and a noticeable gravitational effect was observed. Flame extinction experiments were conducted at normal gravity by seeding inert particles at various number densities and sizes into the reacting gas phase. Experimental data were taken for 20 and 37 (mu) nickel alloy and 25 and 60 (mu) aluminum oxide particles. The experiments were simulated by solving along the stagnation streamline the conservation equations of mass, momentum, energy, and species conservation for both phases, with detailed descriptions of chemical kinetics, molecular transport, and thermal radiation. The experimental data were compared with numerical simulations, and insight was provided into the effects on extinction of the fuel type, equivalence ratio, flame configuration, strain rate. particle type. particle size. particle mass, delivery rate. the orientation of particle injection with respect to the flame and gravity. It was found that for the same injected solid mass, larger particles can result in more effective flame cooling compared to smaller particles, despite the fact that equivalent masses of the larger particles have smaller total surface area to volume ratio. This counter-intuitive finding resulted from the fact that the heat exchange between the two phases is controlled by the synergistic effect of the total contact area and the temperature difference between the two phases. Results also demonstrate that meaningful scaling of interactions between the two phases may not be possible due to the complexity of the couplings between the

  14. NASA Jet Noise Research

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda

    2016-01-01

    The presentation highlights NASA's jet noise research for 2016. Jet-noise modeling efforts, jet-surface interactions results, acoustic characteristics of multi-stream jets, and N+2 Supersonic Aircraft system studies are presented.

  15. [Jet lag].

    PubMed

    Lagarde, D; Doireau, P

    1997-01-01

    Desynchronization of circadian rhythmicity resulting from rapid travel through at least four time zones leads to symptoms known in everyday English as jet-lag. The most detrimental effect of jet-lag is fatigue with poor alertness and psychomotor performance. Severity is subject to individual variation in susceptibility (morning/evening typology, age,...) and environmental factors (direction of travel, number of time zones crossed, psychosocial environment...). Many measures used to prevent or reduce jet lag are inappropriate or ineffective and some may even be dangerous, such as use of melatonin. One of the most reliable preventive techniques consists of reinforcing social synchronizers by maintaining exposure to sunlight and social activity. Only two drugs currently available on the market can be recommended, i.e. non-benzodiazepinic hypnotics which induce high quality sleep to allow quick recovery and a new time-release caffeine agent which has been shown to prolong psychomotor performance.

  16. MEST- avoid next extinction

    NASA Astrophysics Data System (ADS)

    Cao, Dayong

    2012-11-01

    Asteroid 2011 AG5 will impact on Earth in 2040. (See Donald K. Yoemans, ``Asteroid 2011 AG5 - A Reality Check,'' NASA-JPL, 2012) In 2011, The author say: the dark hole will take the dark comet to impact our solar system in 20 years, and give a systemic model between the sun and its companion-dark hole to explain why were there periodicity mass extinction on earth. (see Dayong Cao, BAPS.2011.CAL.C1.7, BAPS.2011.DFD.LA.24, BAPS.2012.APR.K1.78 and BAPS.2011.APR.K1.17) The dark Asteroid 2011 AG5 (as a dark comet) is made of the dark matter which has a space-time (as frequence-amplitude square) center- a different systemic model from solar systemic model. It can asborb the space-time and wave. So it is ``dark.'' When many dark matters hit on our earth, they can break our atom structure and our genetic code to trigger the Mass Extinction. In our experiments, consciousness can change the systematic model and code by a life-informational technology. So it can change the output signals of the solar cell. (see Dayong Cao, BAPS.2011.MAR.C1.286 and BAPS.2012.MAR.P33.14) So we will develop the genetic code of lives to evolution and sublimation, will use the dark matter to change the systemic model between dark hole and sun and will avoid next extinction.

  17. Extinction events can accelerate evolution.

    PubMed

    Lehman, Joel; Miikkulainen, Risto

    2015-01-01

    Extinction events impact the trajectory of biological evolution significantly. They are often viewed as upheavals to the evolutionary process. In contrast, this paper supports the hypothesis that although they are unpredictably destructive, extinction events may in the long term accelerate evolution by increasing evolvability. In particular, if extinction events extinguish indiscriminately many ways of life, indirectly they may select for the ability to expand rapidly through vacated niches. Lineages with such an ability are more likely to persist through multiple extinctions. Lending computational support for this hypothesis, this paper shows how increased evolvability will result from simulated extinction events in two computational models of evolved behavior. The conclusion is that although they are destructive in the short term, extinction events may make evolution more prolific in the long term.

  18. Extinction Events Can Accelerate Evolution

    PubMed Central

    Lehman, Joel; Miikkulainen, Risto

    2015-01-01

    Extinction events impact the trajectory of biological evolution significantly. They are often viewed as upheavals to the evolutionary process. In contrast, this paper supports the hypothesis that although they are unpredictably destructive, extinction events may in the long term accelerate evolution by increasing evolvability. In particular, if extinction events extinguish indiscriminately many ways of life, indirectly they may select for the ability to expand rapidly through vacated niches. Lineages with such an ability are more likely to persist through multiple extinctions. Lending computational support for this hypothesis, this paper shows how increased evolvability will result from simulated extinction events in two computational models of evolved behavior. The conclusion is that although they are destructive in the short term, extinction events may make evolution more prolific in the long term. PMID:26266804

  19. Middle mississippian blastoid extinction event.

    PubMed

    Ausich, W I; Meyer, D L; Waters, J A

    1988-05-06

    The Middle Mississippian blastoid (Phylum Echinodermata) extinction event (about 340 million years ago) was a rapid, habitat-specific extinction. Blastoids became rare or absent in shallow-water environments after the extinction, and this change was probably synchronous worldwide. Onshore-offshore habitat shifts have been recognized as an important historical trend among marine benthos. Unlike trends exhibited by other groups, blastoids appear to have repopulated shallow-water habitats after a period of diminished diversity and abundance.

  20. The Industrial Base: Facing Extinction

    DTIC Science & Technology

    1992-03-10

    INDUSTRIAL BASE.. FACING EXTINCTION ., TIc LECTE BY UN02 1992 - MR. DAVID L. THOMAS Department of the Army Civilian , 4...Industrial Base: Facing Extinction 12. PERSONAL AUTHOR(S) David L. Thomas, DAC, GM-15 13a. TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (Year, Month...service or government agency. The Industrial Base: Accesioti For Facing Extinction NTIS CRA&IDTIC TAB D] Uanc,ounced 0 Justification AN INDIVIDUAL

  1. Kinetic Effects of Aromatic Molecular Structures on Diffusion Flame Extinction

    SciTech Connect

    Won, Sang Hee; Dooley, S.; Dryer, F. L.; Ju, Yiguang

    2011-01-01

    Kinetic effects of aromatic molecular structures for jet fuel surrogates on the extinction of diffusion flames have been investigated experimentally and numerically in the counterflow configuration for toluene, n-propylbenzene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene. Quantitative measurement of OH concentration for aromatic fuels was conducted by directly measuring the quenching rate from the emission lifetimes of OH planar laser induced fluorescence (LIF). The kinetic models for toluene and 1,2,4-trimethylbenzene were validated against the measurements of extinction strain rates and LIF measurements. A semi-detailed n-propylbenzene kinetic model was developed and tested. The experimental results showed that the extinction limits are ranked from highest to lowest as n-propylbenzene, toluene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene. The present models for toluene and n-propylbenzene agree reasonably well with the measurements, whereas the model for 1,2,4-trimethylbenzene under-estimates extinction limits. Kinetic pathways of OH production and consumption were analyzed to investigate the impact of fuel fragmentation on OH formation. It was found that, for fuels with different molecular structures, the fuel decomposition pathways and their propagation into the formation of radical pool play an important role to determine the extinction limits of diffusion flames. Furthermore, OH concentrations were found to be representative of the entire radical pool concentration, the balance between chain branching and propagation/termination reactions and the balance between heat production from the reaction zone and heat losses to the fuel and oxidizer sides. Finally, a proposed “OH index,” was defined to demonstrate a linear correlation between extinction strain rate and OH index and fuel mole fraction, suggesting that the diffusion flame extinctions for the tested aromatic fuels can be determined by the capability of a fuel to establish a radical pool

  2. The impact of mass extinctions

    NASA Technical Reports Server (NTRS)

    Flessa, Karl W.

    1988-01-01

    In the years since Snowbird an explosive growth of research on the patterns, causes, and consequences of extinction was seen. The fossil record of extinction is better known, stratigraphic sections were scrutinized in great detail, and additional markers of environmental change were discovered in the rock record. However flawed, the fossil record is the only record that exists of natural extinction. Compilations from the primary literature contain a faint periodic signal: the extinctions of the past 250 my may be regulary spaced. The reality of the periodicity remains a subject for debate. The implications of periodicity are so profound that the debate is sure to continue. The greater precision from stratigraphic sections spanning extinction events has yet to resolve controversies concerning the rates at which extinctions occurred. Some sections seem to record sudden terminations, while others suggest gradual or steplike environmental deterioration. Unfortunately, the manner in which the strata record extinctions and compile stratigraphic ranges makes a strictly literal reading of the fossil record inadvisable. Much progress was made in the study of mass extinctions. The issues are more sharply defined but they are not fully resolved. Scenarios should look back to the phenomena they purport to explain - not just an iridium-rich layer, but the complex fabric of a mass extinction.

  3. Periodicity in marine extinction events

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. John, Jr.; Raup, David M.

    1986-01-01

    The periodicity of extinction events is examined in detail. In particular, the temporal distribution of specific, identifiable extinction events is analyzed. The nature and limitations of the data base on the global fossil record is discussed in order to establish limits of resolution in statistical analyses. Peaks in extinction intensity which appear to differ significantly from background levels are considered, and new analyses of the temporal distribution of these peaks are presented. Finally, some possible causes of periodicity and of interdependence among extinction events over the last quarter billion years of earth history are examined.

  4. Periodicity in marine extinction events

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. John, Jr.; Raup, David M.

    1986-01-01

    The periodicity of extinction events is examined in detail. In particular, the temporal distribution of specific, identifiable extinction events is analyzed. The nature and limitations of the data base on the global fossil record is discussed in order to establish limits of resolution in statistical analyses. Peaks in extinction intensity which appear to differ significantly from background levels are considered, and new analyses of the temporal distribution of these peaks are presented. Finally, some possible causes of periodicity and of interdependence among extinction events over the last quarter billion years of earth history are examined.

  5. Direct and indirect effects of biological factors on extinction risk in fossil bivalves

    PubMed Central

    Harnik, Paul G.

    2011-01-01

    Biological factors, such as abundance and body size, may contribute directly to extinction risk and indirectly through their influence on other biological characteristics, such as geographic range size. Paleontological data can be used to explicitly test many of these hypothesized relationships, and general patterns revealed through analysis of the fossil record can help refine predictive models of extinction risk developed for extant species. Here, I use structural equation modeling to tease apart the contributions of three canonical predictors of extinction—abundance, body size, and geographic range size—to the duration of bivalve species in the early Cenozoic marine fossil record of the eastern United States. I find that geographic range size has a strong direct effect on extinction risk and that an apparent direct effect of abundance can be explained entirely by its covariation with geographic range. The influence of geographic range on extinction risk is manifest across three ecologically disparate bivalve clades. Body size also has strong direct effects on extinction risk but operates in opposing directions in different clades, and thus, it seems to be decoupled from extinction risk in bivalves as a whole. Although abundance does not directly predict extinction risk, I reveal weak indirect effects of both abundance and body size through their positive influence on geographic range size. Multivariate models that account for the pervasive covariation between biological factors and extinction are necessary for assessing causality in evolutionary processes and making informed predictions in applied conservation efforts. PMID:21808004

  6. Polyandry prevents extinction.

    PubMed

    Price, Tom A R; Hurst, Greg D D; Wedell, Nina

    2010-03-09

    Females of most animal species are polyandrous, with individual females usually mating with more than one male. However, the ubiquity of polyandry remains enigmatic because of the potentially high costs to females of multiple mating. Current theory to account for the high prevalence of polyandry largely focuses on its benefits to individual females. There are also higher-level explanations for the high incidence of polyandry-polyandrous clades may speciate more rapidly. Here we test the hypothesis that polyandry may also reduce population extinction risk. We demonstrate that mating with multiple males protects populations of the fruit fly Drosophila pseudoobscura against extinction caused by a "selfish" sex-ratio-distorting element. Thus, the frequency of female multiple mating in nature may be associated not only with individual benefits to females of this behavior but also with increased persistence over time of polyandrous species and populations. Furthermore, we show that female remating behavior can determine the frequency of sex-ratio distorters in populations. This may also be true for many other selfish genetic elements in natural populations.

  7. Avoid Earth Extinction

    NASA Astrophysics Data System (ADS)

    Cao, Dayong

    2012-11-01

    In 2011, the author supposes: the dark hole will take the dark comet to impact our solar system in 20 years. (see Dayong Cao, BAPS.2011.DFD.LA.24, BAPS.2012.APR.K1.78 and BAPS.2011.APR.K1.17) Asteroid 2011 AG5 will impact on Earth in 2040. (See Donald K. Yoemans, ``Asteroid 2011 AG5 - A Reality Check,'' NASA-JPL, 2012) The dark Asteroid 2011 AG5 (as a dark comet) is made of the dark matte. Sun and its companion-dark hole are a binary system (Their systemic model- SDS for short there in after). The dark hole has a dark comet belt. The dark hole and dark comet are made of the dark matter which has a space-time (as frequence-amplitude square) center- a different systemic model from solar systemic model. Because it absorb the space-time and wave. So it is ``dark.'' When the dark hole goes near the sun every 25-27 million years, it will take its dark comet belt to go into the solar system to impact our earth. In a other hand, it can change all of our systemic model and code which are controled by the SDS, such as the orbit both of the asteroid belt and planet (such as Jupiter), our atomic structure and our genetic code. It can trigger periodic Mass Extinction. We will use the dark matter to change the SDS to avoid forthcoming extinction.

  8. Gas Jets

    NASA Technical Reports Server (NTRS)

    Chaplygin, S.

    1944-01-01

    A brief summary of the contents of this paper is presented here. In part I the differential equations of the problem of a gas flow in two dimensions is derived and the particular integrals by which the problem on jets is solved are given. Use is made of the same independent variables as Molenbroek used, but it is found to be more suitable to consider other functions. The stream function and velocity potential corresponding to the problem are given in the form of series. The investigation on the convergence of these series in connection with certain properties of the functions entering them forms the subject of part II. In part III the problem of the outflow of a gas from an infinite vessel with plane walls is solved. In part IV the impact of a gas jet on a plate is considered and the limiting case where the jet expands to infinity changing into a gas flow is taken up in more detail. This also solved the equivalent problem of the resistance of a gaseous medium to the motion of a plate. Finally, in part V, an approximate method is presented that permits a simpler solution of the problem of jet flows in the case where the velocities of the gas (velocities of the particles in the gas) are not very large.

  9. Extinction-induced neuroplasticity attenuates stress-induced cocaine seeking: a state-dependent learning hypothesis.

    PubMed

    Self, David W; Choi, Kwang-Ho

    2004-09-01

    Chronic drug use weakens excitatory neocortical input to the nucleus accumbens (NAc). We previously reported that extinction training, a form of inhibitory learning that progressively reduces cocaine-seeking behaviour when reward is withheld, reverses this deficit by up-regulating GluR1 and GluR2/3 subunits of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptors in the NAc. The level of GluR1 up-regulation is positively associated with a reduction in cocaine seeking, suggesting that extinction-induced up-regulation in AMPA receptors in the NAc opposes motivational influences that maintain cocaine seeking. This hypothesis is supported by the finding that over-expression of GluR1 and GluR2 in the NAc facilitates extinction of cocaine self-administration. Furthermore, a single extinction training session conducted during GluR1 and GluR2 over-expression strongly and selectively attenuates the ability of an environmental stressor to trigger relapse to cocaine seeking long after GluR1 and GluR2 over-expression declines. These results could suggest that excitatory input to the NAc promotes extinction learning, but only when memory is recalled under stressful situations. Recent studies indicate that both environmental stress and the frustrative stress of withholding reward during extinction of drug self-administration induce similar neurochemical events in the NAc. These neurochemical events could impose a "state-dependency" on extinction learning such that subsequent exposure to stress acts as a cue to enhance retrieval of extinction memory. Our results suggest that extinction-induced up-regulation in NAc AMPA receptors acts reciprocally to facilitate state-dependent extinction learning, as stressful situations evoke extinction memories that exert powerful inhibitory control over drug-seeking behaviour. These results may have important therapeutic implications for behaviour-based approaches aimed at treating drug addiction.

  10. The dusty silhouette jet HH 1019 in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Kiminki, Megan M.; Smith, Nathan; Bally, John

    2017-06-01

    We report the discovery in Hubble Space Telescope (HST) images of the new Herbig-Haro jet, HH 1019, located near the Tr 14 cluster in the Carina Nebula. Like other HH jets in the region, this bipolar collimated flow emerges from the head of a dark dust pillar. However, HH 1019 is unique because - unlike all other HH jets known to date - it is identified by a linear chain of dark, dusty knots that are seen primarily in silhouette against the background screen of the H II region. Proper motions confirm that these dark condensations move along the jet axis at high speed. [S ii] emission traces a highly collimated jet that is spatially coincident with these dust knots. The high extinction in the body of the jet suggests that this outflow has lifted a large amount of dust directly from the disc, although it is possible that it has entrained dust from its surrounding protostellar envelope before exiting the dust pillar. If dust in HH 1019 originates from the circumstellar disc, this provides further evidence for a jet launched from a range of radii in the disc, including those outside the dust sublimation radius. HH 1019 may be the prototype for a new subclass of dusty HH objects seen primarily in extinction against the background screen of a bright H II region. Such jets may be common, but difficult to observe because they require the special condition of a very bright background in order to be seen in silhouette.

  11. Flammability Aspects of a Cotton-Fiberglass Fabric in Opposed and Concurrent Airflow in Microgravity

    NASA Technical Reports Server (NTRS)

    Ferkul, Paul V.; Olson, Sandra; Johnston, Michael C.; T'ien, James

    2012-01-01

    Microgravity combustion tests burning fabric samples were performed aboard the International Space Station. The cotton-fiberglass blend samples were mounted inside a small wind tunnel which could impose air flow speeds up to 40 cm/s. The wind tunnel was installed in the Microgravity Science Glovebox which supplied power, imaging, and a level of containment. The effects of air flow speed on flame appearance, flame growth, and spread rates were determined in both the opposed and concurrent flow configuration. For the opposed flow configuration, the flame quickly reached steady spread for each flow speed, and the spread rate was fastest at an intermediate value of flow speed. These tests show the enhanced flammability in microgravity for this geometry, since, in normal gravity air, a flame self-extinguishes in the opposed flow geometry (downward flame spread). In the concurrent flow configuration, flame size grew with time during the tests. A limiting length and steady spread rate were obtained only in low flow speeds ( 10 cm/s) for the short-length samples that fit in the small wind tunnel. For these conditions, flame spread rate increased linearly with increasing flow. This is the first time that detailed transient flame growth data was obtained in purely forced flows in microgravity. In addition, by decreasing flow speed to a very low value (around 1 cm/s), quenching extinction was observed. The valuable results from these long-duration experiments validate a number of theoretical predictions and also provide the data for a transient flame growth model under development.

  12. Acoustic integrated extinction

    PubMed Central

    Norris, Andrew N.

    2015-01-01

    The integrated extinction (IE) is defined as the integral of the scattering cross section as a function of wavelength. Sohl et al. (2007 J. Acoust. Soc. Am. 122, 3206–3210. (doi:10.1121/1.2801546)) derived an IE expression for acoustic scattering that is causal, i.e. the scattered wavefront in the forward direction arrives later than the incident plane wave in the background medium. The IE formula was based on electromagnetic results, for which scattering is causal by default. Here, we derive a formula for the acoustic IE that is valid for causal and non-causal scattering. The general result is expressed as an integral of the time-dependent forward scattering function. The IE reduces to a finite integral for scatterers with zero long-wavelength monopole and dipole amplitudes. Implications for acoustic cloaking are discussed and a new metric is proposed for broadband acoustic transparency. PMID:27547100

  13. Originations and Extinctions

    NASA Astrophysics Data System (ADS)

    Ray, Tane; Moseley, Leo; Jan, Naeem

    We analyse the fossil data of Benton1 with and without interpolation schemes. By Fourier transform analysis, we find a frequency dependence of the amplitude of 1/f for the various interpolation schemes used in the past. We illustrate that shuffling the interpolated data changes the spectra only slightly. On the other hand, an identical analysis performed on the raw (uninterpolated) fossil data gives a flat frequency spectrum. We conclude that the 1/f behavior is an artifact of the interpolation schemes. We next introduce a simulation of extinctions driven only by interactions between two trophic levels. Fourier transform analysis of the simulation data shows a frequency dependence of 1/f. When the data are grouped into a form resembling the fossil record the frequency dependence vanishes, giving a flat spectrum. Our simulation produces a frequency spectrum that agrees with the observed fossil record.

  14. Measuring Extinction with ALE

    NASA Astrophysics Data System (ADS)

    Zimmer, Peter C.; McGraw, J. T.; Gimmestad, G. G.; Roberts, D.; Stewart, J.; Smith, J.; Fitch, J.

    2007-12-01

    ALE (Astronomical LIDAR for Extinction) is deployed at the University of New Mexico's (UNM) Campus Observatory in Albuquerque, NM. It has begun a year-long testing phase prior deployment at McDonald Observatory in support of the CCD/Transit Instrument II (CTI-II). ALE is designed to produce a high-precision measurement of atmospheric absorption and scattering above the observatory site every ten minutes of every moderately clear night. LIDAR (LIght Detection And Ranging) is the VIS/UV/IR analog of radar, using a laser, telescope and time-gated photodetector instead of a radio transmitter, dish and receiver. In the case of ALE -- an elastic backscatter LIDAR -- 20ns-long, eye-safe laser pulses are launched 2500 times per second from a 0.32m transmitting telescope co-mounted with a 50mm short-range receiver on an alt-az mounted 0.67m long-range receiver. Photons from the laser pulse are scattered and absorbed as the pulse propagates through the atmosphere, a portion of which are scattered into the field of view of the short- and long-range receiver telescopes and detected by a photomultiplier. The properties of a given volume of atmosphere along the LIDAR path are inferred from both the altitude-resolved backscatter signal as well as the attenuation of backscatter signal from altitudes above it. We present ALE profiles from the commissioning phase and demonstrate some of the astronomically interesting atmospheric information that can be gleaned from these data, including, but not limited to, total line-of-sight extinction. This project is funded by NSF Grant 0421087.

  15. Extinction of Harrington's Mountain Goat

    NASA Astrophysics Data System (ADS)

    Mead, Jim I.; Martin, Paul S.; Euler, Robert C.; Long, Austin; Jull, A. J. T.; Toolin, Laurence J.; Donahue, Douglas J.; Linick, T. W.

    1986-02-01

    Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni, were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 ± 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis, from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters.

  16. Extinction of Harrington's mountain goat

    SciTech Connect

    Mead, J.I.; Martin, P.S.; Euler, R.C.; Long, A.; Jull, A.J.T.; Toolin, L.J.; Donahue, D.J.; Linick, T.W.

    1986-02-01

    Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni, were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 +/- 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis, from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters.

  17. Extinction of Harrington's mountain goat

    PubMed Central

    Mead, Jim I.; Martin, Paul S.; Euler, Robert C.; Long, Austin; Jull, A. J. T.; Toolin, Laurence J.; Donahue, Douglas J.; Linick, T. W.

    1986-01-01

    Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni, were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 ± 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis, from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters. Images PMID:16593655

  18. Interstellar extinction in the ultraviolet

    NASA Technical Reports Server (NTRS)

    Bless, R. C.; Savage, B. D.

    1972-01-01

    Interstellar extinction curves over the region 3600-1100 A for 17 stars are presented. The observations were made by the two Wisconsin spectrometers onboard the OAO-2 with spectral resolutions of 10 A and 20 A. The extinction curves generally show a pronounced maximum at 2175 plus or minus 25 A, a broad minimum in the region 1800-1350 A, and finally a rapid rise to the far ultraviolet. Large extinction variations from star to star are found, especially in the far ultraviolet; however, with only two possible exceptions in this sample, the wavelength at the maximum of the extinction bump is essentially constant. These data are combined with visual and infrared observations to display the extinction behavior over a range in wavelength of about a factor of 20.

  19. Pinpointing and preventing imminent extinctions

    PubMed Central

    Ricketts, Taylor H.; Dinerstein, Eric; Boucher, Tim; Brooks, Thomas M.; Butchart, Stuart H. M.; Hoffmann, Michael; Lamoreux, John F.; Morrison, John; Parr, Mike; Pilgrim, John D.; Rodrigues, Ana S. L.; Sechrest, Wes; Wallace, George E.; Berlin, Ken; Bielby, Jon; Burgess, Neil D.; Church, Don R.; Cox, Neil; Knox, David; Loucks, Colby; Luck, Gary W.; Master, Lawrence L.; Moore, Robin; Naidoo, Robin; Ridgely, Robert; Schatz, George E.; Shire, Gavin; Strand, Holly; Wettengel, Wes; Wikramanayake, Eric

    2005-01-01

    Slowing rates of global biodiversity loss requires preventing species extinctions. Here we pinpoint centers of imminent extinction, where highly threatened species are confined to single sites. Within five globally assessed taxa (i.e., mammals, birds, selected reptiles, amphibians, and conifers), we find 794 such species, three times the number recorded as having gone extinct since 1500. These species occur in 595 sites, concentrated in tropical forests, on islands, and in mountainous areas. Their taxonomic and geographical distribution differs significantly from that of historical extinctions, indicating an expansion of the current extinction episode beyond sensitive species and places toward the planet's most biodiverse mainland regions. Only one-third of the sites are legally protected, and most are surrounded by intense human development. These sites represent clear opportunities for urgent conservation action to prevent species loss. PMID:16344485

  20. Pinpointing and preventing imminent extinctions.

    PubMed

    Ricketts, Taylor H; Dinerstein, Eric; Boucher, Tim; Brooks, Thomas M; Butchart, Stuart H M; Hoffmann, Michael; Lamoreux, John F; Morrison, John; Parr, Mike; Pilgrim, John D; Rodrigues, Ana S L; Sechrest, Wes; Wallace, George E; Berlin, Ken; Bielby, Jon; Burgess, Neil D; Church, Don R; Cox, Neil; Knox, David; Loucks, Colby; Luck, Gary W; Master, Lawrence L; Moore, Robin; Naidoo, Robin; Ridgely, Robert; Schatz, George E; Shire, Gavin; Strand, Holly; Wettengel, Wes; Wikramanayake, Eric

    2005-12-20

    Slowing rates of global biodiversity loss requires preventing species extinctions. Here we pinpoint centers of imminent extinction, where highly threatened species are confined to single sites. Within five globally assessed taxa (i.e., mammals, birds, selected reptiles, amphibians, and conifers), we find 794 such species, three times the number recorded as having gone extinct since 1500. These species occur in 595 sites, concentrated in tropical forests, on islands, and in mountainous areas. Their taxonomic and geographical distribution differs significantly from that of historical extinctions, indicating an expansion of the current extinction episode beyond sensitive species and places toward the planet's most biodiverse mainland regions. Only one-third of the sites are legally protected, and most are surrounded by intense human development. These sites represent clear opportunities for urgent conservation action to prevent species loss.

  1. The end-Permian mass extinction: A complex, multicausal extinction

    NASA Technical Reports Server (NTRS)

    Erwin, D. H.

    1994-01-01

    The end-Permian mass extinction was the most extensive in the history of life and remains one of the most complex. Understanding its causes is particularly important because it anchors the putative 26-m.y. pattern of periodic extinction. However, there is no good evidence for an impact and this extinction appears to be more complex than others, involving at least three phases. The first began with the onset of a marine regression during the Late Permian and resulting elimination of most marine basins, reduction in habitat area, and increased climatic instability; the first pulse of tetrapod extinctions occurred in South Africa at this time. The second phase involved increased regression in many areas (although apparently not in South China) and heightened climatic instability and environmental degradation. Release of gas hydrates, oxidation of marine carbon, and the eruption of the Siberian flood basalts occurred during this phase. The final phase of the extinction episode began with the earliest Triassic marine regression and destruction of nearshore continental habitats. Some evidence suggests oceanic anoxia may have developed during the final phase of the extinction, although it appears to have been insufficient to the sole cause of the extinction.

  2. Jet lag.

    PubMed

    Herxheimer, Andrew

    2008-12-04

    Jet lag affects most air travellers crossing five or more time zones; it tends to be worse on eastward than on westward flights. We conducted a systematic review and aimed to answer the following clinical question: What are the effects of interventions to prevent or minimise jet lag? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2008 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). We found five systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. In this systematic review we present information relating to the effectiveness and safety of the following interventions: hypnotics, melatonin, and lifestyle and environmental adaptations.

  3. Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets

    NASA Astrophysics Data System (ADS)

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A.

    2010-09-01

    By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop Hα macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major coronal mass ejections. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Å snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T ~ 104 - 105 K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  4. DICHOTOMY OF SOLAR CORONAL JETS: STANDARD JETS AND BLOWOUT JETS

    SciTech Connect

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A.

    2010-09-01

    By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H{alpha} macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major coronal mass ejections. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 A snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T {approx} 10{sup 4} - 10{sup 5} K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  5. Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets

    NASA Technical Reports Server (NTRS)

    Moore, R. L.; Cirtain, J. W.; Sterling, A. C.; Falconer, D. A.

    2010-01-01

    By examining many X-ray jets in Hinode/XRT coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H alpha macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major CMEs. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Angstrom snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T 10(exp 4) - 10(exp 5) K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  6. Mass Extinctions in Earth's History

    NASA Astrophysics Data System (ADS)

    Ward, P. D.

    2002-12-01

    Mass extinctions are short intervals of elevated species death. Possible causes of Earth's mass extinctions are both external (astronomical) and internal (tectonic and biotic changes from planetary mechanisms). Paleontologists have identified five "major" mass extinctions (>50 die-off in less than a million years) and more than 20 other minor events over the past 550 million years. Earlier major extinction events undoubtedly also occurred, but we have no fossil record; these were probably associated with, for example, the early heavy bombardment that cleared out the solar system, the advent of oxygen in the atmosphere, and various "snowball Earth" events. Mass extinctions are viewed as both destructive (species death ) and constructive, in that they allow evolutionary innovation in the wake of species disappearances. From an astrobiological perspective, mass extinctions must be considered as able both to reduce biodiversity and even potentially end life on any planet. Of the five major mass extinctions identified on Earth, only one (the Cretaceous/Tertiary event 65 million years ago that famously killed off the dinosaurs ) is unambiguously related to the impact of an asteroid or comet ( 10-km diameter). The Permian/Triassic (250 Myr ago) and Triassic/Jurassic (202 Myr ago) events are now the center of debate between those favoring impact and those suggesting large volume flooding by basaltic lavas. The final two events, Ordovician (440 Myr ago) and Devonian (370 Myr ago) have no accepted causal mechanisms.

  7. Extinction in young massive clusters

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, Nino

    2016-01-01

    Up to ages of ~100 Myr, massive clusters are still swamped in large amounts of gas and dust, causing considerable and uneven levels of extinction. At the same time, large grains (ices?) produced by type II supernovae profoundly alter the interstellar medium (ISM), thus resulting in extinction properties very different from those of the diffuse ISM. To obtain physically meaningful parameters of stars (luminosities, effective temperatures, masses, ages, etc.) we must understand and measure the local extinction law. We have developed a powerful method to unambiguously determine the extinction law everywhere across a cluster field, using multi-band photometry of red giant stars belonging to the red clump (RC) and are applying it to young massive clusters in the Local Group. In the Large Magellanic Cloud, with about 20 RC stars per arcmin2, for each field we can easily derive an accurate extinction curve over the entire wavelength range of the photometry. As an example, we present the extinction law of the Tarantula nebula (30 Dor) based on thousands of stars observed as part of the Hubble Tarantula Treasury Project. We discuss how the incautious adoption of the Milky Way extinction law in the analysis of massive star forming regions may lead to serious underestimates of the fluxes and of the star formation rates by factors of 2 or more.

  8. The learning of fear extinction.

    PubMed

    Furini, Cristiane; Myskiw, Jociane; Izquierdo, Ivan

    2014-11-01

    Recent work on the extinction of fear-motivated learning places emphasis on its putative circuitry and on its modulation. Extinction is the learned inhibition of retrieval of previously acquired responses. Fear extinction is used as a major component of exposure therapy in the treatment of fear memories such as those of the posttraumatic stress disorder (PTSD). It is initiated and maintained by interactions between the hippocampus, basolateral amygdala and ventromedial prefrontal cortex, which involve feedback regulation of the latter by the other two areas. Fear extinction depends on NMDA receptor activation. It is positively modulated by d-serine acting on the glycine site of NMDA receptors and blocked by AP5 (2-amino-5-phosphono propionate) in the three structures. In addition, histamine acting on H2 receptors and endocannabinoids acting on CB1 receptors in the three brain areas mentioned, and muscarinic cholinergic fibers from the medial septum to hippocampal CA1 positively modulate fear extinction. Importantly, fear extinction can be made state-dependent on circulating epinephrine, which may play a role in situations of stress. Exposure to a novel experience can strongly enhance the consolidation of fear extinction through a synaptic tagging and capture mechanism; this may be useful in the therapy of states caused by fear memory like PTSD.

  9. Prefrontal single-unit firing associated with deficient extinction in mice.

    PubMed

    Fitzgerald, Paul J; Whittle, Nigel; Flynn, Shaun M; Graybeal, Carolyn; Pinard, Courtney R; Gunduz-Cinar, Ozge; Kravitz, Alexxai V; Singewald, Nicolas; Holmes, Andrew

    2014-09-01

    The neural circuitry mediating fear extinction has been increasingly well studied and delineated. The rodent infralimbic subregion (IL) of the ventromedial prefrontal cortex (vmPFC) has been found to promote extinction, whereas the prelimbic cortex (PL) demonstrates an opposing, pro-fear, function. Studies employing in vivo electrophysiological recordings have observed that while increased IL single-unit firing and bursting predicts robust extinction retrieval, increased PL firing can correlate with sustained fear and poor extinction. These relationships between single-unit firing and extinction do not hold under all experimental conditions, however. In the current study, we further investigated the relationship between vmPFC and PL single-unit firing and extinction using inbred mouse models of intact (C57BL/6J, B6) and deficient (129S1/SvImJ, S1) extinction strains. Simultaneous single-unit recordings were made in the PL and vmPFC (encompassing IL) as B6 and S1 mice performed extinction training and retrieval. Impaired extinction retrieval in S1 mice was associated with elevated PL single-unit firing, as compared to firing in extinguishing B6 mice, consistent with the hypothesized pro-fear contribution of PL. Analysis of local field potentials also revealed significantly higher gamma power in the PL of S1 than B6 mice during extinction training and retrieval. In the vmPFC, impaired extinction in S1 mice was also associated with exaggerated single-unit firing, relative to B6 mice. This is in apparent contradiction to evidence that IL activity promotes extinction, but could reflect a (failed) compensatory effort by the vmPFC to mitigate fear-promoting activity in other regions, such as the PL or amygdala. In support of this hypothesis, augmenting IL activity via direct infusion of the GABAA receptor antagonist picrotoxin rescued impaired extinction retrieval in S1 mice. Chronic fluoxetine treatment produced modest reductions in fear during extinction retrieval and

  10. Prefrontal single-unit firing associated with deficient extinction in mice

    PubMed Central

    Fitzgerald, Paul J; Whittle, Nigel; Flynn, Shaun M; Graybeal, Carolyn; Pinard, Courtney; Gunduz-Cinar, Ozge; Kravitz, Alexxai; Singewald, Nicolas; Holmes, Andrew

    2014-01-01

    The neural circuitry mediating fear extinction has been increasingly well studied and delineated. The rodent infralimbic subregion (IL) of the ventromedial prefrontal cortex (vmPFC) has been found to promote extinction, whereas the prelimbic cortex (PL) demonstrates an opposing, pro-fear, function. Studies employing in vivo electrophysiological recordings have observed that while increased IL single-unit firing and bursting predicts robust extinction retrieval, increased PL firing can correlate with sustained fear and poor extinction. These relationships between single-unit firing and extinction do not hold under all experimental conditions, however. In the current study, we further investigated the relationship between vmPFC and PL single-unit firing and extinction using inbred mouse models of intact (C57BL/6J, B6) and deficient (129S1/SvImJ, S1) extinction strains. Simultaneous single-unit recordings were made in the PL and vmPFC (encompassing IL) as B6 and S1 mice performed extinction training and retrieval. Impaired extinction retrieval in S1 mice was associated with elevated PL single-unit firing, as compared to firing in extinguishing B6 mice, consistent with the hypothesized pro-fear contribution of PL. Analysis of local field potentials also revealed significantly higher gamma power in the PL of Sthan B6 mice during extinction training and retrieval. In the vmPFC, impaired extinction in S1 mice was also associated with exaggerated single-unit firing, relative to B6 mice. This is in apparent contradiction to evidence that IL activity promotes extinction, but could reflect a (failed) compensatory effort by the vmPFC to mitigate fear-promoting activity in other regions, such as the PL or amygdala. In support of this hypothesis, augmenting IL activity via direct infusion of the GABAA receptor antagonist picrotoxin rescued impaired extinction retrieval in S1 mice. Chronic fluoxetine treatment produced modest reductions in fear during extinction retrieval and

  11. Entorhinal cortex contribution to contextual fear conditioning extinction and reconsolidation in rats.

    PubMed

    Baldi, Elisabetta; Bucherelli, Corrado

    2014-04-01

    During contextual fear conditioning a rat learns a temporal contiguity association between the exposition to a previously neutral context (CS) and an aversive unconditioned stimulus (US) as a footshock. This condition determines in the rat the freezing reaction during the subsequent re-exposition to the context. Potentially the re-exposition without US presentation initiates two opposing and competing processes: reconsolidation and extinction. Reconsolidation process re-stabilizes and strengthens the original memory and it is initiated by a brief re-exposure to context. Instead the extinction process leads to the decrease of the expression of the original memory and it is triggered by prolonged re-exposure to the context. Here we analyzed the entorhinal cortex (ENT) participation in contextual fear conditioning reconsolidation and extinction. The rats were trained in contextual fear conditioning and 24h later they were subjected either to a brief (2 min) reactivation session or to a prolonged (120 min) re-exposition to context to induce extinction of the contextual fear memory. Immediately after the reactivation or the extinction session, the animals were submitted to bilateral ENT TTX inactivation. Memory retention was assessed as conditioned freezing duration measured 72 h after TTX administration. The results showed that ENT inactivation both after reactivation and extinction session was followed by contextual freezing retention impairment. Thus, the present findings point out that ENT is involved in contextual fear memory reconsolidation and extinction. This neural structure might be part of parallel circuits underlying two phases of contextual fear memory processing.

  12. Computational search for hypotheses concerning the endocannabinoid contribution to the extinction of fear conditioning

    PubMed Central

    Anastasio, Thomas J.

    2013-01-01

    Fear conditioning, in which a cue is conditioned to elicit a fear response, and extinction, in which a previously conditioned cue no longer elicits a fear response, depend on neural plasticity occurring within the amygdala. Projection neurons in the basolateral amygdala (BLA) learn to respond to the cue during fear conditioning, and they mediate fear responding by transferring cue signals to the output stage of the amygdala. Some BLA projection neurons retain their cue responses after extinction. Recent work shows that activation of the endocannabinoid system is necessary for extinction, and it leads to long-term depression (LTD) of the GABAergic synapses that inhibitory interneurons make onto BLA projection neurons. Such GABAergic LTD would enhance the responses of the BLA projection neurons that mediate fear responding, so it would seem to oppose, rather than promote, extinction. To address this paradox, a computational analysis of two well-known conceptual models of amygdaloid plasticity was undertaken. The analysis employed exhaustive state-space search conducted within a declarative programming environment. The analysis reveals that GABAergic LTD actually increases the number of synaptic strength configurations that achieve extinction while preserving the cue responses of some BLA projection neurons in both models. The results suggest that GABAergic LTD helps the amygdala retain cue memory during extinction even as the amygdala learns to suppress the previously conditioned response. The analysis also reveals which features of both models are essential for their ability to achieve extinction with some cue memory preservation, and suggests experimental tests of those features. PMID:23761759

  13. New theories about ancient extinctions

    USGS Publications Warehouse

    Spall, H.

    1986-01-01

    But all this may be changing. Mass extinctions have been very much in the news in the last few years, triggered in large part by the proposal that the extinction of the dinosaurs and marine animals was caused by a catastrophic collision between the Earth and an extra-terrestrial body (bolide). Recently an equally contentious suggestion has been made that mass extinctions have swept the Earth every 26 to 31 million years for at least the last 250 million years-caused by encounters with some kind of extra-terrestrial object such as one of the asteroids or the comets. 

  14. Perspectives on the mixing of a row of jets with a confined crossflow

    NASA Technical Reports Server (NTRS)

    Holdeman, J. D.

    1983-01-01

    An interactive computer code, written for a microcomputer, is presented which displays 2-D and 3-D oblique plots of the temperature distribution downstream of jets mixing with a confined crossflow, for either single-side or opposed jet injection. Temperature profiles calculated with this routine are presented to show the effects of flow and geometric variables on the mixing. Examples are shown to illustrate the different perspectives on the mixing available by exercising various view options. In addition, the program is used to calculate profiles for opposed rows of jets with their centerlines in-line, by assuming that the confining effect of an opposite wall is equivalent to that of a plane of symmetry between opposed jets.

  15. Asymmetric interlimb transfer of concurrent adaptation to opposing dynamic forces

    PubMed Central

    Miall, R. C.; Woolley, D. G.

    2007-01-01

    Interlimb transfer of a novel dynamic force has been well documented. It has also been shown that unimanual adaptation to opposing novel environments is possible if they are associated with different workspaces. The main aim of this study was to test if adaptation to opposing velocity dependent viscous forces with one arm could improve the initial performance of the other arm. The study also examined whether this interlimb transfer occurred across an extrinsic, spatial, coordinative system or an intrinsic, joint based, coordinative system. Subjects initially adapted to opposing viscous forces separated by target location. Our measure of performance was the correlation between the speed profiles of each movement within a force condition and an ‘average’ trajectory within null force conditions. Adaptation to the opposing forces was seen during initial acquisition with a significantly improved coefficient in epoch eight compared to epoch one. We then tested interlimb transfer from the dominant to non-dominant arm (D → ND) and vice-versa (ND → D) across either an extrinsic or intrinsic coordinative system. Interlimb transfer was only seen from the dominant to the non-dominant limb across an intrinsic coordinative system. These results support previous studies involving adaptation to a single dynamic force but also indicate that interlimb transfer of multiple opposing states is possible. This suggests that the information available at the level of representation allowing interlimb transfer can be more intricate than a general movement goal or a single perceived directional error. PMID:17703286

  16. De-scenting Extinction: The Promise of De-extinction May Hasten Continuing Extinctions.

    PubMed

    Campagna, Claudio; Guevara, Daniel; Le Boeuf, Bernard

    2017-07-01

    Among the most egregious and discouraging problems of conservation is the rapidly escalating human-caused species extinction rate. "De-extinction" refers to the application of certain cutting-edge techniques for the supposed recovery of lost species and gives the impression that scientists, enlightened and empowered by the miracles of technology, are coming to the rescue. "De-extinction" is the latest example of a long play of language that has given conservation efforts a tragically false sense of accomplishment and has worsened the conservation crisis. De-extinction is the tip of an intellectual iceberg that sits atop of a host of profoundly questionable value systems, expectations, attitudes, and priorities that elude and bewitch critical reflection. It gives the impression that extinction is reversible and, thus, diminishes the gravity of the human annihilation of species. Here, we examine how the language of de-extinction influences attitudes, shapes thoughts and imagination, and creates ethical blindness. The language developing around "de-extinction" reveals what is in fact a profound intellectual crisis at the foundation of conservation. The underlying challenge is to find the language that will articulate and inspire the radical and indispensable change needed to come to grips with the value of nature. © 2017 The Hastings Center.

  17. What Caused the Mass Extinction?

    ERIC Educational Resources Information Center

    Alvarez, Walter; And Others

    1990-01-01

    Presented are the arguments of two different points of view on the mass extinction of the dinosaurs. Evidence of extraterrestrial impact theory and massive volcanic eruption theory are discussed. (CW)

  18. What Caused the Mass Extinction?

    ERIC Educational Resources Information Center

    Alvarez, Walter; And Others

    1990-01-01

    Presented are the arguments of two different points of view on the mass extinction of the dinosaurs. Evidence of extraterrestrial impact theory and massive volcanic eruption theory are discussed. (CW)

  19. Investigation of ultraviolet interstellar extinction

    NASA Technical Reports Server (NTRS)

    Payne, C.; Haramundanis, K. L.

    1973-01-01

    Results concerning interstellar extinction in the ultraviolet are reported. These results were initially obtained by using data from main-sequence stars and were extended to include supergiants and emission stars. The principal finding of the analysis of ultraviolet extinction is not only that it is wavelength dependent, but that if changes with galactic longitude in the U3 passband (lambda sub eff = 1621 A); it does not change significantly in the U2 passband (lambda sub eff = 2308 A). Where data are available in the U4 passband (lambda sub eff = 1537 A), they confirm the rapid rise of extinction in the ultraviolet found by other investigators. However, in all cases, emission stars must be used with great caution. It is important to realize that while extinction continues to rise toward shorter wavelengths in the ultraviolet, including the shortest ultraviolet wavelengths measured (1100 A), it no longer plays an important role in the X-ray region (50 A).

  20. Investigation of ultraviolet interstellar extinction

    NASA Technical Reports Server (NTRS)

    Payne-Gaposchkin, C.; Haramundanis, K. L.

    1973-01-01

    The progress made during the past six months in utilizing Celescope OAO-2 data in a study of extinction is reported along with conclusions drawn from each inquiry. Areas recommended for further investigation are indicated.

  1. Updating Martin's global extinction model

    NASA Astrophysics Data System (ADS)

    Gillespie, Richard

    2008-12-01

    Australia has been cited as a weak link in anthropogenic models of megafauna extinction, but recent work suggests instead that the evidence for rapid extinction shortly after human arrival is robust. The global model is revisited, based on the contention that late Pleistocene megafauna extinctions took place rapidly on islands, and some islands (such as Australia and the Americas) are much larger than others. Modern dating methods are increasingly able to refine chronologies, and careful scrutiny suggests that hundreds of dates should be deleted from archives. An updated summary of results from New Zealand, North America and Australia is presented, with a brief discussion on why temperate refugia offering protection from climate change ultimately did not work, strongly supporting the global extinction hypothesis pioneered by Paul Martin.

  2. Magnetic reversals and mass extinctions

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1985-01-01

    The results of a study of reversals of the earth's magnetic field over the past 165 Myr are presented. A stationary periodicity of 30 Myr emerges which predicts pulses of increased reversal activity centered at 10, 40, 70, . . . Myr before the present. The correlation between the reversal intensity and biological extinctions is examined, and a nontrivial discrepancy is found between the magnetic and extinction periodicity.

  3. Magnetic reversals and mass extinctions

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1985-01-01

    The results of a study of reversals of the earth's magnetic field over the past 165 Myr are presented. A stationary periodicity of 30 Myr emerges which predicts pulses of increased reversal activity centered at 10, 40, 70, . . . Myr before the present. The correlation between the reversal intensity and biological extinctions is examined, and a nontrivial discrepancy is found between the magnetic and extinction periodicity.

  4. The Sixth Great Mass Extinction

    ERIC Educational Resources Information Center

    Wagler, Ron

    2012-01-01

    Five past great mass extinctions have occurred during Earth's history. Humanity is currently in the midst of a sixth, human-induced great mass extinction of plant and animal life (e.g., Alroy 2008; Jackson 2008; Lewis 2006; McDaniel and Borton 2002; Rockstrom et al. 2009; Rohr et al. 2008; Steffen, Crutzen, and McNeill 2007; Thomas et al. 2004;…

  5. Series cell light extinction monitor

    DOEpatents

    Novick, Vincent J.

    1990-01-01

    A method and apparatus for using the light extinction measurements from two or more light cells positioned along a gasflow chamber in which the gas volumetric rate is known to determine particle number concentration and mass concentration of an aerosol independent of extinction coefficient and to determine estimates for particle size and mass concentrations. The invention is independent of particle size. This invention has application to measurements made during a severe nuclear reactor fuel damage test.

  6. The Sixth Great Mass Extinction

    ERIC Educational Resources Information Center

    Wagler, Ron

    2012-01-01

    Five past great mass extinctions have occurred during Earth's history. Humanity is currently in the midst of a sixth, human-induced great mass extinction of plant and animal life (e.g., Alroy 2008; Jackson 2008; Lewis 2006; McDaniel and Borton 2002; Rockstrom et al. 2009; Rohr et al. 2008; Steffen, Crutzen, and McNeill 2007; Thomas et al. 2004;…

  7. Experiments and modeling of dilution jet flow fields

    NASA Technical Reports Server (NTRS)

    Holdeman, James D.

    1986-01-01

    Experimental and analytical results of the mixing of single, double, and opposed rows of jets with an isothermal or variable-temperature main stream in a straight duct are presented. This study was performed to investigate flow and geometric variations typical of the complex, three-dimensional flow field in the dilution zone of gas-turbine-engine combustion chambers. The principal results, shown experimentally and analytically, were the following: (1) variations in orifice size and spacing can have a significant effect on the temperature profiles; (2) similar distributions can be obtained, independent of orifice diameter, if momentum-flux ratio and orifice spacing are coupled; (3) a first-order approximation of the mixing of jets with a variable-temperature main stream can be obtained by superimposing the main-stream and jets-in-an-isothermal-crossflow profiles; (4) the penetration of jets issuing mixing is slower and is asymmetric with respect to the jet centerplanes, which shift laterally with increasing downstream distance; (5) double rows of jets give temperature distributions similar to those from a single row of equally spaced, equal-area circular holes; (6) for opposed rows of jets, with the orifice centerlines in line, the optimum ratio of orifice spacing to duct height is one-half the optimum value for single-side injection at the same momentum-flux ratiol and (7) for opposed rows of jets, with the orifice centerlines staggered, the optimum ratio of orifice spacing to duct height is twice the optimum value for single-side injection at the same momentum-flux ratio.

  8. Measuring Galactic Extinction: A Test

    NASA Astrophysics Data System (ADS)

    Arce, Héctor G.; Goodman, Alyssa A.

    1999-02-01

    We test the recently published all-sky reddening map of Schlegel, Finkbeiner, & Davis (hereafter SFD) using the extinction study of a region in the Taurus dark cloud complex by Arce & Goodman (hereafter AG). In their study, AG use four different techniques to measure the amount and structure of the extinction toward Taurus, and all four techniques agree very well. Thus, we believe that the AG results are a truthful representation of the extinction in the region and can be used to test the reliability of the SFD reddening map. The results of our test show that the SFD all-sky reddening map, which is based on data from COBE/DIRBE and IRAS/ISSA, overestimates the reddening by a factor of 1.3-1.5 in regions of smooth extinction with AV>0.5 mag. In some regions of steep extinction gradients, the SFD map underestimates the reddening value, probably because of its low spatial resolution. We expect that the astronomical community will be using the SFD reddening map extensively. We offer this Letter as a cautionary note about using the SFD map in regions of high extinction (AV>0.5 mag), since it might not be giving accurate reddening values there.

  9. Extinction, relapse, and behavioral momentum.

    PubMed

    Podlesnik, Christopher A; Shahan, Timothy A

    2010-05-01

    Previous experiments on behavioral momentum have shown that relative resistance to extinction of operant behavior in the presence of a discriminative stimulus depends upon the baseline rate or magnitude of reinforcement associated with that stimulus (i.e., the Pavlovian stimulus-reinforcer relation). Recently, we have shown that relapse of operant behavior in reinstatement, resurgence, and context renewal preparations also is a function of baseline stimulus-reinforcer relations. In this paper we present new data examining the role of baseline stimulus-reinforcer relations on resistance to extinction and relapse using a variety of baseline training conditions and relapse operations. Furthermore, we evaluate the adequacy of a behavioral momentum based model in accounting for the results. The model suggests that relapse occurs as a result of a decrease in the disruptive impact of extinction precipitated by a change in circumstances associated with extinction, and that the degree of relapse is a function of the pre-extinction baseline Pavlovian stimulus-reinforcer relation. Across experiments, relative resistance to extinction and relapse were greater in the presence of stimuli associated with more favorable conditions of reinforcement and were positively related to one another. In addition, the model did a good job in accounting for these effects. Thus, behavioral momentum theory may provide a useful quantitative approach for characterizing how differential reinforcement conditions contribute to relapse of operant behavior.

  10. Extinction, Relapse, and Behavioral Momentum

    PubMed Central

    Podlesnik, Christopher A.; Shahan, Timothy A.

    2010-01-01

    Previous experiments on behavioral momentum have shown that relative resistance to extinction of operant behavior in the presence of a discriminative stimulus depends upon the baseline rate or magnitude of reinforcement associated with that stimulus (i.e., the Pavlovian stimulus-reinforcer relation). Recently, we have shown that relapse of operant behavior in reinstatement, resurgence, and context renewal preparations also is a function of baseline stimulus-reinforcer relations. In this paper we present new data examining the role of baseline stimulus-reinforcer relations on resistance to extinction and relapse using a variety of baseline training conditions and relapse operations. Furthermore, we evaluate the adequacy of a behavioral-momentum based model in accounting for the results. The model suggests that relapse occurs as a result of a decrease in the disruptive impact of extinction precipitated by a change in circumstances associated with extinction, and that the degree of relapse is a function of the pre-extinction baseline Pavlovian stimulus-reinforcer relation. Across experiments, relative resistance to extinction and relapse were greater in the presence of stimuli associated with more favorable conditions of reinforcement and were positively related to one another. In addition, the model did a good job in accounting for these effects. Thus, behavioral momentum theory may provide a useful quantitative approach for characterizing how differential reinforcement conditions contribute to relapse of operant behavior. PMID:20152889

  11. Jet lag

    PubMed Central

    2008-01-01

    Introduction Jet lag is a syndrome caused by disruption of the "body clock", and affects most air travellers crossing five or more time zones; it tends to be worse on eastward than on westward flights. Methods and outcomes We conducted a systematic review and aimed to answer the following clinical question: What are the effects of interventions to prevent or minimise jet lag? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2008 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). Results We found five systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. Conclusions In this systematic review we present information relating to the effectiveness and safety of the following interventions: hypnotics, lifestyle and environmental adaptations, and melatonin. PMID:19445780

  12. Species, extinct before we know them?

    PubMed

    Lees, Alexander C; Pimm, Stuart L

    2015-03-02

    Species are going extinct rapidly, while taxonomic catalogues are still incomplete for even the best-known taxa. Intensive fieldwork is finding species so rare and threatened that some become extinct within years of discovery. Recent bird extinctions in Brazil's coastal forests suggest that some species may have gone extinct before we knew of their existence. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Proposal of Pump Using Ultrasonic Transducer and Opposing Surface

    NASA Astrophysics Data System (ADS)

    Shinada, H.; Ishino, Y.; Hara, M.; Yamaguchi, D.; Takasaki, M.; Mizuno, T.

    Conventional pumps include sliding parts and there is a limit of life time due to friction and wear. To solve this problem, a number of pumps using ultrasonic vibration have been proposed. In the present study, we found an occurrence of pump effect when an opposing block faces ultrasonically vibrating surface with small gap. According to the measurement results of gauge pressure, when circumference of the opposing block is tapered, fluid was discharged from the gap of two surfaces. On the other hand, when center of the block is tapered, fluid was sucked in the gap. This paper reports experimental results of the pump effect.

  14. Inclusive Jets in PHP

    NASA Astrophysics Data System (ADS)

    Roloff, P.

    Differential inclusive-jet cross sections have been measured in photoproduction for boson virtualities Q^2 < 1 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 300 pb^-1. Jets were identified in the laboratory frame using the k_T, anti-k_T or SIScone jet algorithms. Cross sections are presented as functions of the jet pseudorapidity, eta(jet), and the jet transverse energy, E_T(jet). Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low E_T(jet) and high eta(jet). The cross sections have the potential to improve the determination of the PDFs in future QCD fits. Values of alpha_s(M_Z) have been extracted from the measurements based on different jet algorithms. In addition, the energy-scale dependence of the strong coupling was determined.

  15. Thermal Transgressions and Phanerozoic Extinctions

    NASA Astrophysics Data System (ADS)

    Worsley, T. R.; Kidder, D. L.

    2007-12-01

    A number of significant Phanerozoic extinctions are associated with marine transgressions that were probably driven by rapid ocean warming. The conditions associated with what we call thermal transgressions are extremely stressful to life on Earth. The Earth system setting associated with end-Permian extinction exemplifies an end-member case of our model. The conditions favoring extreme warmth and sea-level increases driven by thermal expansion are also conducive to changes in ocean circulation that foster widespread anoxia and sulfidic subsurface ocean waters. Equable climates are characterized by reduced wind shear and weak surface ocean circulation. Late Permian and Early Triassic thermohaline circulation differs considerably from today's world, with minimal polar sinking and intensified mid-latitude sinking that delivers sulfate from shallow evaporative areas to deeper water where it is reduced to sulfide. Reduced nutrient input to oceans from land at many of the extinction intervals results from diminished silicate weathering and weakened delivery of iron via eolian dust. The falloff in iron-bearing dust leads to minimal nitrate production, weakening food webs and rendering faunas and floras more susceptible to extinction when stressed. Factors such as heat, anoxia, ocean acidification, hypercapnia, and hydrogen sulfide poisoning would significantly affect these biotas. Intervals of tectonic quiescence set up preconditions favoring extinctions. Reductions in chemical silicate weathering lead to carbon dioxide buildup, oxygen drawdown, nutrient depletion, wind and ocean current abatement, long-term global warming, and ocean acidification. The effects of extinction triggers such as large igneous provinces, bolide impacts, and episodes of sudden methane release are more potent against the backdrop of our proposed preconditions. Extinctions that have characteristics we call for in the thermal transgressions include the Early Cambrian Sinsk event, as well as

  16. The stratigraphy of mass extinction

    NASA Astrophysics Data System (ADS)

    Holland, Steven

    2015-04-01

    The discovery of the end-Cretaceous bolide impact and the recognition of mass extinctions through taxonomic compendia triggered keen interest in the stratigraphic pattern of species extinctions. A principal question has been whether patterns of fossil occurrence indicate gradual, stepwise, pulsed, or instantaneous extinction. Based on principles of sequence stratigraphy, marine ecology, and evolution, numerical models of fossil occurrences in stratigraphic sections indicate that the last occurrence of fossils does not generally indicate the time of extinction but is instead controlled by stratigraphic architecture. These models have been confirmed in multiple field studies from different sedimentary basins of different ages. These models identify several distinct processes controlling the last occurrence of fossils. Anything that lowers the probability of collection of a species, such as peak abundance or environmental tolerance, causes the last occurrence to be shifted backward in time relative to the time of extinction. Sequence-bounding subaerial unconformities generally also force the last occurrence backward in time, except in the case of reworking, which may place fossil remains in rocks younger than the time of extinction. Unconformities also cause last occurrences of multiple species to be clustered as a result of the hiatus. Surfaces of abrupt facies change, such as flooding surfaces and surfaces of forced regression, also cause last occurrences to be clustered, with such clustering reflecting the environmental preferences of species. Stratigraphic condensation can also cause clustering of last occurrences. All of these surfaces - subaerial unconformities, flooding surfaces, surfaces of forced regression, and condensed horizons - have highly predictable positions with depositional sequences. Thus, it is the normal expectation that last occurrences should be clustered in the fossil record, that these clusters should occur in stratigraphically predictable

  17. Global Implications of late Pleistocene Megafaunal Extinctions in the Holarctic

    NASA Astrophysics Data System (ADS)

    Cooper, Alan; Turney, Chris

    2017-04-01

    Improved resolution data from radiocarbon, climate and ancient DNA studies of megafauna and humans is providing the first ability to disentangle the roles of climate change and human impact in the Late Pleistocene megafaunal extinctions. In the Holarctic we find that megafaunal populations underwent repeated local or global extinctions apparently associated with abrupt, centennial to millennial duration warming events (Dansgaard-Oeschger interstadials). Importantly, the extinction events took place both before and after the arrival of modern humans in the landscape. Here we look at the possible role of human activity in Holarctic and suggest it may be through the disruption of metapopulation processes which stabilize ecosystems and may have evolved to provide resilience to rapid and frequent climate shifts in the past. The observed relationship between climate and humans on megafaunal populations may provide a model for global extinction. Fortunately in this regard, the rapid movement of the first Native Americans throughout both American continents during the Last Deglaciation provides a powerful and unique model system for testing the competing roles on extinction because the opposing climate trends in each hemisphere at the time. Here we show that while megafaunal extinctions were associated with warming trends in both cases, the out-of-phase climate patterns caused the sequence and timing of events to be mirrored, providing a unique high-resolution view of the interactions of human colonization and rapid climate change on megafaunal ecosystems, with implications for future warming scenarios. References: Cooper, A., Turney, C., Hughen, K.A., Brook, B.W., McDonald, H.G., Bradshaw, C.J.A., 2015. Abrupt warming events drove Late Pleistocene Holarctic megafaunal turnover. Science 349, 602-606. Metcalf, J.L., Turney, C., Barnett, R., Martin, F., Bray, S.C., Vilstrup, J.T., Orlando, L., Salas-Gismondi, R., Loponte, D., Medina, M., De Nigris, M., Civalero, T., Fern

  18. Diffusion flame extinction in slow convenctive flow under microgravity environment

    NASA Technical Reports Server (NTRS)

    Chen, C. H.

    1986-01-01

    A theoretical analysis is presented to study the extinction characteristics of a diffusion flame near the leading edge of a thin fuel plate in slow, forced convective flows in a microgravity environment. The mathematical model includes two-dimensional Navier-Stokes momentum, energy and species equations with one-step overall chemical reaction using second-order finite rate Arrhenius kinetics. Radiant heat loss on the fuel plate is applied in the model as it is the dominant mechanism for flame extinguishment in the small convective flow regime. A parametric study based on the variation of convective flow velocity, which varies the Damkohler number (Da), and the surface radiant heat loss parameter (S) simultaneously, is given. An extinction limit is found in the regime of slow convective flow when the rate of radiant heat loss from fuel surface outweighs the rate of heat generation due to combustion. The transition from existent envelope flame to extinguishment consists of gradual flame contraction in the opposed flow direction together with flame temperature reduction as the convective flow velocity decreases continuously until the extinction limit is reached. A case of flame structure subjected to surface radiant heat loss is also presented and discussed.

  19. Corporate Jet

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Gulfstream Aerospace Corporation, Savannah, GA, used a version of a NASA program called WIBCO to design a wing for the Gulfstream IV (G-IV) which will help to reduce transonic drag (created by shock waves that develop as an airplane approaches the speed of sound). The G-IV cruises at 88 percent of the speed of sound, and holds the international record in its class for round-the-world flight. They also used the STANS5 and Profile programs in the design. They will use the NASA program GASP to help determine the gross weight, range, speed, payload and optimum wing area of an intercontinental supersonic business jet being developed in cooperation with Sukhoi Design Bureau, a Soviet organization.

  20. Opposing Amygdala and Ventral Striatum Connectivity during Emotion Identification

    ERIC Educational Resources Information Center

    Satterthwaite, Theodore D.; Wolf, Daniel H.; Pinkham, Amy E.; Ruparel, Kosha; Elliott, Mark A.; Valdez, Jeffrey N.; Overton, Eve; Seubert, Janina; Gur, Raquel E.; Gur, Ruben C.; Loughead, James

    2011-01-01

    Lesion and electrophysiological studies in animals provide evidence of opposing functions for subcortical nuclei such as the amygdala and ventral striatum, but the implications of these findings for emotion identification in humans remain poorly described. Here we report a high-resolution fMRI study in a sample of 39 healthy subjects who performed…

  1. 49 CFR 1182.6 - Processing an opposed application.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 8 2010-10-01 2010-10-01 false Processing an opposed application. 1182.6 Section 1182.6 Transportation Other Regulations Relating to Transportation (Continued) SURFACE TRANSPORTATION BOARD, DEPARTMENT OF TRANSPORTATION RULES OF PRACTICE PURCHASE, MERGER, AND CONTROL OF MOTOR PASSENGER...

  2. 49 CFR 1103.28 - Negotiations with opposing party.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 8 2013-10-01 2013-10-01 false Negotiations with opposing party. 1103.28 Section 1103.28 Transportation Other Regulations Relating to Transportation (Continued) SURFACE TRANSPORTATION... Duties and Responsibilities Regarding Witnesses, Other Litigants and the Public § 1103.28 Negotiations...

  3. 49 CFR 1103.28 - Negotiations with opposing party.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 8 2014-10-01 2014-10-01 false Negotiations with opposing party. 1103.28 Section 1103.28 Transportation Other Regulations Relating to Transportation (Continued) SURFACE TRANSPORTATION... Duties and Responsibilities Regarding Witnesses, Other Litigants and the Public § 1103.28 Negotiations...

  4. 49 CFR 1103.28 - Negotiations with opposing party.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 8 2012-10-01 2012-10-01 false Negotiations with opposing party. 1103.28 Section 1103.28 Transportation Other Regulations Relating to Transportation (Continued) SURFACE TRANSPORTATION... Duties and Responsibilities Regarding Witnesses, Other Litigants and the Public § 1103.28 Negotiations...

  5. 49 CFR 1103.28 - Negotiations with opposing party.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 8 2011-10-01 2011-10-01 false Negotiations with opposing party. 1103.28 Section 1103.28 Transportation Other Regulations Relating to Transportation (Continued) SURFACE TRANSPORTATION... Duties and Responsibilities Regarding Witnesses, Other Litigants and the Public § 1103.28 Negotiations...

  6. Opposing Amygdala and Ventral Striatum Connectivity during Emotion Identification

    ERIC Educational Resources Information Center

    Satterthwaite, Theodore D.; Wolf, Daniel H.; Pinkham, Amy E.; Ruparel, Kosha; Elliott, Mark A.; Valdez, Jeffrey N.; Overton, Eve; Seubert, Janina; Gur, Raquel E.; Gur, Ruben C.; Loughead, James

    2011-01-01

    Lesion and electrophysiological studies in animals provide evidence of opposing functions for subcortical nuclei such as the amygdala and ventral striatum, but the implications of these findings for emotion identification in humans remain poorly described. Here we report a high-resolution fMRI study in a sample of 39 healthy subjects who performed…

  7. Low velocity opposed-flow frame spread in a transport-controlled environment DARTFire

    NASA Technical Reports Server (NTRS)

    West, Jeff; Thomas, Pete; Chao, Ruian; Bhattacharjee, Subrata; Tang, TI; Altenkirch, Robert A.; Olson, Sandra L.

    1995-01-01

    The overall objectives of the DARTFire project are to uncover the underlying physics and increase understanding of the mechanisms that cause flames to propagate over solid fuels against a low velocity of oxidizer flow in a low-gravity environment. Specific objectives are (1) to analyze experimentally observed flame shapes, measured gas-phase field variables, spread rates, radiative characteristics, and solid-phase regression rates for comparison with previously developed model prediction capability that will be continually extended, and (2) to investigate the transition from ignition to either flame propagation or extinction in order to determine the characteristics of those environments that lead to flame evolution. To meet the objectives, a series of sounding rocket experiments has been designed to exercise several of the dimensional, controllable variables that affect the flame spread process over PMMA in microgravity, i.e., the opposing flow velocity (1-20 cm/s), the external radiant flux directed to the fuel surface (0-2 W/cm(exp 2)), and the oxygen concentration of the environment (35-70%). Because radiative heat transfer is critical to these microgravity flame spread experiments, radiant heating is imposed, and radiant heat loss will be measured. These are the first attempts at such an experimental control and measurement in microgravity. Other firsts associated with the experiment are (1) the control of the low velocity, opposed flow, which is of the same order as diffusive velocities and Stefan flows; (2) state-of-the-art quantitative flame imaging for species-specific emissions (both infrared and ultraviolet) in addition to novel intensified array imaging to obtain a color image of the very dim, low-gravity flames.

  8. Biostratigraphic case studies of six major extinctions

    NASA Technical Reports Server (NTRS)

    Sloan, R. E.

    1988-01-01

    Biostratigraphic case studies of six major extinctions show all are gradual save one, which is a catastrophic extinction of terrestrial origin. These extinctions show a continuum of environmental insults from major to minor. The major causes of these extinctions are positive and negative eustatic sea level changes, temperature, or ecological competition. Extraterrestrial causes should not be posited without positive association with a stratigraphically sharp extinction. The Cretaceous-Tertiary terrestrial extinction is considerably smaller in percentage of extinction than the marine extinction and is spread over 10 my of the Cretaceous and 1 my of the Tertiary. Sixty percent of the 30 dinosaurs in the northern Great Plains of the U.S. and Canada had become extinct in the 9 my before the late Maastrichtian sea level drop. The best data on the Permo-Triassic terrestrial extinction are from the Karoo basin of South Africa. This is a series of 6 extinctions in some 8 my, recorded in some 2800 meters of sediment. Precision of dating is enhanced by the high rate of accumulation of these sediments. Few data are readily available on the timing of the marine Permo-Triassic extinction, due to the very restricted number of sequences of Tatarian marine rocks. The terminal Ordovician extinction at 438 my is relatively rapid, taking place over about 0.5 my. The most significant aspect of this extinction is a eustatic sea level lowering associated with a major episode of glaciation. New data on this extinction is the reduction from 61 genera of trilobites in North America to 14, for a 77 percent extinction. Another Ordovician extinction present over 10 percent of the North American craton occurs at 454 my in the form of a catastrophic extinction due to a volcanic eruption which blanketed the U.S. east of the Transcontinental Arch. This is the only other sizeable extinction in the Ordovician.

  9. Jet inclusive cross sections

    SciTech Connect

    Del Duca, V.

    1992-11-01

    Minijet production in jet inclusive cross sections at hadron colliders, with large rapidity intervals between the tagged jets, is evaluated by using the BFKL pomeron. We describe the jet inclusive cross section for an arbitrary number of tagged jets, and show that it behaves like a system of coupled pomerons.

  10. A 2-D DNS investigation of extinction and reignition dynamics in nonpremixed flame-vortex interactions

    SciTech Connect

    Venugopal, Rishikesh; Abraham, John

    2008-05-15

    Two-dimensional (2-D) DNS investigations of extinction and reignition dynamics during interactions of laminar nonpremixed flames with counterrotating vortex pairs are performed. The length and velocity scales chosen for the vortices are representative of those in the near fields of high-Reynolds-number jets such as those occurring in Diesel engines. The governing equations are solved with sixth-order spatial discretization and fourth-order time integration. Chemistry is modeled as an irreversible single-step reaction. Local extinction along the symmetry axis, followed by reignition, is observed. The extinction is characterized by strong unsteady effects, which are captured well by 1-D transient diffusion flamelet libraries, provided the time-history of the instantaneous scalar dissipation rate is taken into account. On the other hand, reignition is essentially a 2-D phenomenon involving flame-flame interactions, which are favored for smaller vortices and increasing flame curvature. The effects of unsteadiness and curvature on extinction and reignition are carefully assessed through parametric studies involving a range of vortex and flame characteristics. The interaction outcomes are summarized on Reynolds-Damkoehler number (Re-Da) diagrams, which show the combined effects of unsteadiness and curvature on extinction and reignition. The implications of the observed interaction outcomes for turbulent combustion modeling in the near fields of jet diffusion flames are discussed. (author)

  11. The extinction of the dinosaurs.

    PubMed

    Brusatte, Stephen L; Butler, Richard J; Barrett, Paul M; Carrano, Matthew T; Evans, David C; Lloyd, Graeme T; Mannion, Philip D; Norell, Mark A; Peppe, Daniel J; Upchurch, Paul; Williamson, Thomas E

    2015-05-01

    Non-avian dinosaurs went extinct 66 million years ago, geologically coincident with the impact of a large bolide (comet or asteroid) during an interval of massive volcanic eruptions and changes in temperature and sea level. There has long been fervent debate about how these events affected dinosaurs. We review a wealth of new data accumulated over the past two decades, provide updated and novel analyses of long-term dinosaur diversity trends during the latest Cretaceous, and discuss an emerging consensus on the extinction's tempo and causes. Little support exists for a global, long-term decline across non-avian dinosaur diversity prior to their extinction at the end of the Cretaceous. However, restructuring of latest Cretaceous dinosaur faunas in North America led to reduced diversity of large-bodied herbivores, perhaps making communities more susceptible to cascading extinctions. The abruptness of the dinosaur extinction suggests a key role for the bolide impact, although the coarseness of the fossil record makes testing the effects of Deccan volcanism difficult.

  12. Flood basalts and extinction events

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1993-01-01

    The largest known effusive eruptions during the Cenozoic and Mesozoic Eras, the voluminous flood basalts, have long been suspected as being associated with major extinctions of biotic species. Despite the possible errors attached to the dates in both time series of events, the significance level of the suspected correlation is found here to be 1 percent to 4 percent. Statistically, extinctions lag eruptions by a mean time interval that is indistinguishable from zero, being much less than the average residual derived from the correlation analysis. Oceanic flood basalts, however, must have had a different biological impact, which is still uncertain owing to the small number of known examples and differing physical factors. Although not all continental flood basalts can have produced major extinction events, the noncorrelating eruptions may have led to smaller marine extinction events that terminated at least some of the less catastrophically ending geologic stages. Consequently, the 26 Myr quasi-periodicity seen in major marine extinctions may be only a sampling effect, rather than a manifestation of underlying periodicity.

  13. Flood basalts and mass extinctions

    NASA Technical Reports Server (NTRS)

    Morgan, W. Jason

    1988-01-01

    There appears to be a correlation between the times of flood basalts and mass-extinction events. There is a correlation of flood basalts and hotspot tracks--flood basalts appear to mark the beginning of a new hotspot. Perhaps there is an initial instability in the mantle that bursts forth as a flood basalt but then becomes a steady trickle that persists for many tens of millions of years. Suppose that flood basalts and not impacts cause the environmental changes that lead to mass-extinctions. This is a very testable hypothesis: it predicts that the ages of the flows should agree exactly with the times of extinctions. The Deccan and K-T ages agree with this hypothesis; An iridium anomaly at extinction boundaries apparently can be explained by a scaled-up eruption of the Hawaiian type; the occurrence of shocked-quartz is more of a problem. However if the flood basalts are all well dated and their ages indeed agree with extinction times, then surely some mechanism to appropriately produce shocked-quartz will be found.

  14. Flood basalts and extinction events

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1993-01-01

    The largest known effusive eruptions during the Cenozoic and Mesozoic Eras, the voluminous flood basalts, have long been suspected as being associated with major extinctions of biotic species. Despite the possible errors attached to the dates in both time series of events, the significance level of the suspected correlation is found here to be 1 percent to 4 percent. Statistically, extinctions lag eruptions by a mean time interval that is indistinguishable from zero, being much less than the average residual derived from the correlation analysis. Oceanic flood basalts, however, must have had a different biological impact, which is still uncertain owing to the small number of known examples and differing physical factors. Although not all continental flood basalts can have produced major extinction events, the noncorrelating eruptions may have led to smaller marine extinction events that terminated at least some of the less catastrophically ending geologic stages. Consequently, the 26 Myr quasi-periodicity seen in major marine extinctions may be only a sampling effect, rather than a manifestation of underlying periodicity.

  15. p300/CBP-associated factor selectively regulates the extinction of conditioned fear

    PubMed Central

    Wei, Wei; Coelho, Carlos M.; Li, Xiang; Marek, Roger; Yan, Shanzhi; Anderson, Shawn; Meyers, David; Mukherjee, Chandrani; Sbardella, Gianluca; Castellano, Sabrina; Milite, Ciro; Rotili, Dante; Mai, Antonello; Cole, Philip A.; Sah, Pankaj; Kobor, Michael S.; Bredy, Timothy W.

    2012-01-01

    It is well established that the activity of chromatin-modifying enzymes is crucial for regulating gene expression associated with hippocampal-dependent memories. However, very little is known about how these epigenetic mechanisms influence the formation of cortically-dependent memory, particularly when there is competition between opposing memory traces such as that which occurs during the acquisition and extinction of conditioned fear. Here we demonstrate, in C57/Bl6 mice, that the activity of p300/CBP-associated factor (PCAF) within the infralimbic prefrontal cortex is required for long-term potentiation and is necessary for the formation of memory associated with fear extinction, but not for fear acquisition. Further, systemic administration of the PCAF activator SPV106 enhances memory for fear extinction and prevents fear renewal. The selective influence of PCAF on fear extinction is mediated, in part, by a transient recruitment of the repressive transcription factor ATF4 to the promoter of the immediate early gene zif268, which competitively inhibits its expression. Thus, within the context of fear extinction, PCAF functions as a transcriptional co-activator, which may facilitate the formation of memory for fear extinction by interfering with reconsolidation of the original memory trace. PMID:22933779

  16. A Spreadsheet for the Mixing of Rows of Jets with Confined Crossflow in a Rectangular Duct. Supplement

    NASA Technical Reports Server (NTRS)

    Holderman, James D.; Clisset, James R.; Moder, Jeffrey P.

    2010-01-01

    This is a printout of the supplemental spreadsheet that is a supplement to the document found in NASA/TM-2010-216100. The calculations for cases of opposed rows of jets with the orifices on one side shifted show that staggering can improve the mixing, particularly for cases where jets would overpenetrate slightly if the orifices were in an aligned configuration.

  17. Retrieval and Reconsolidation Accounts of Fear Extinction

    PubMed Central

    Ponnusamy, Ravikumar; Zhuravka, Irina; Poulos, Andrew M.; Shobe, Justin; Merjanian, Michael; Huang, Jeannie; Wolvek, David; O’Neill, Pia-Kelsey; Fanselow, Michael S.

    2016-01-01

    Extinction is the primary mode for the treatment of anxiety disorders. However, extinction memories are prone to relapse. For example, fear is likely to return when a prolonged time period intervenes between extinction and a subsequent encounter with the fear-provoking stimulus (spontaneous recovery). Therefore there is considerable interest in the development of procedures that strengthen extinction and to prevent such recovery of fear. We contrasted two procedures in rats that have been reported to cause such deepened extinction. One where extinction begins before the initial consolidation of fear memory begins (immediate extinction) and another where extinction begins after a brief exposure to the consolidated fear stimulus. The latter is thought to open a period of memory vulnerability similar to that which occurs during initial consolidation (reconsolidation update). We also included a standard extinction treatment and a control procedure that reversed the brief exposure and extinction phases. Spontaneous recovery was only found with the standard extinction treatment. In a separate experiment we tested fear shortly after extinction (i.e., within 6 h). All extinction procedures, except reconsolidation update reduced fear at this short-term test. The findings suggest that strengthened extinction can result from alteration in both retrieval and consolidation processes. PMID:27242459

  18. Infectious Disease, Endangerment, and Extinction

    PubMed Central

    MacPhee, Ross D. E.; Greenwood, Alex D.

    2013-01-01

    Infectious disease, especially virulent infectious disease, is commonly regarded as a cause of fluctuation or decline in biological populations. However, it is not generally considered as a primary factor in causing the actual endangerment or extinction of species. We review here the known historical examples in which disease has, or has been assumed to have had, a major deleterious impact on animal species, including extinction, and highlight some recent cases in which disease is the chief suspect in causing the outright endangerment of particular species. We conclude that the role of disease in historical extinctions at the population or species level may have been underestimated. Recent methodological breakthroughs may lead to a better understanding of the past and present roles of infectious disease in influencing population fitness and other parameters. PMID:23401844

  19. Speeding up spontaneous disease extinction

    NASA Astrophysics Data System (ADS)

    Khasin, Michael

    2012-02-01

    The dynamics of epidemic in a susceptible population is affected both by the random character of interactions between the individuals and by environmental variations. As a consequence, the sizes of the population groups (infected, susceptible, etc.) fluctuate in the course of evolution of the epidemic. In a small community a rare large fluctuation in the number of infected can result in extinction of the disease. We suggest a novel paradigm of controlling the epidemic, where the control field, such as vaccination, is designed to maximize the rate of spontaneous disease extinction. We show that, for a limited-scope vaccination, the optimal vaccination protocol and its impact on the epidemics have universal features: (i) the vaccine must be applied in pulses, (ii) the spontaneous disease extinction is synchronized with the vaccination. We trace this universality to general properties of the response of large fluctuations to external perturbations.

  20. The atmospheric extinction of light

    NASA Astrophysics Data System (ADS)

    Hughes, Stephen W.; Cowley, Michael; Powell, Sean; Carroll, Joshua

    2016-01-01

    An experiment is described that enables students to understand the properties of atmospheric extinction due to Rayleigh scattering. The experiment requires the use of red, green and blue lasers attached to a travelling microscope or similar device. The laser beams are passed through an artificial atmosphere, made from milky water, at varying depths, before impinging on either a light meter or a photodiode integral to a Picotech Dr. DAQ ADC. A plot of measured spectral intensity verses depth reveals the contribution Rayleigh scattering has to the extinction coefficient. For the experiment with the light meter, the extinction coefficients for red, green and blue light in the milky sample of water were 0.27, 0.36 and 0.47 cm-1 respectively and 0.032, 0.037 and 0.092 cm-1 for the Picotech Dr. DAQ ADC.

  1. Infectious disease, endangerment, and extinction.

    PubMed

    Macphee, Ross D E; Greenwood, Alex D

    2013-01-01

    Infectious disease, especially virulent infectious disease, is commonly regarded as a cause of fluctuation or decline in biological populations. However, it is not generally considered as a primary factor in causing the actual endangerment or extinction of species. We review here the known historical examples in which disease has, or has been assumed to have had, a major deleterious impact on animal species, including extinction, and highlight some recent cases in which disease is the chief suspect in causing the outright endangerment of particular species. We conclude that the role of disease in historical extinctions at the population or species level may have been underestimated. Recent methodological breakthroughs may lead to a better understanding of the past and present roles of infectious disease in influencing population fitness and other parameters.

  2. Habituation, latent inhibition, and extinction.

    PubMed

    Jordan, Wesley P; Todd, Travis P; Bucci, David J; Leaton, Robert N

    2015-06-01

    In two conditioned suppression experiments with a latent inhibition (LI) design, we measured the habituation of rats in preexposure, their LI during conditioning, and then extinction over days. In the first experiment, lick suppression, the preexposed group (PE) showed a significant initial unconditioned response (UR) to the target stimulus and significant long-term habituation (LTH) of that response over days. The significant difference between the PE and nonpreexposed (NPE) groups on the first conditioning trial was due solely to the difference in their URs to the conditioned stimulus (CS)-a habituated response (PE) and an unhabituated response (NPE). In the second experiment, bar-press suppression, little UR to the target stimulus was apparent during preexposure, and no detectable LTH. Thus, there was no difference between the PE and NPE groups on the first conditioning trial. Whether the UR to the CS confounds the interpretation of LI (Exp. 1) or not (Exp. 2) can only be known if the UR is measured. In both experiments, LI was observed in acquisition. Also in both experiments, rats that were preexposed and then conditioned to asymptote were significantly more resistant to extinction than were the rats not preexposed. This result contrasts with the consistently reported finding that preexposure either produces less resistance to extinction or has no effect on extinction. The effect of stimulus preexposure survived conditioning to asymptote and was reflected directly in extinction. These two experiments provide a cautionary procedural note for LI experiments and have shown an unexpected extinction effect that may provide new insights into the interpretation of LI.

  3. General relativistic study of astrophysical jets with internal shocks

    NASA Astrophysics Data System (ADS)

    Vyas, Mukesh K.; Chattopadhyay, Indranil

    2017-08-01

    We explore the possibility of the formation of steady internal shocks in jets around black holes. We consider a fluid described by a relativistic equation of state, flowing about the axis of symmetry (θ = 0) in a Schwarzschild metric. We use two models for the jet geometry: (i) a conical geometry and (ii) a geometry with non-conical cross-section. A jet with conical geometry has a smooth flow, while the jet with non-conical cross-section undergoes multiple sonic points and even standing shock. The jet shock becomes stronger, as the shock location is situated farther from the central black hole. Jets with very high energy and very low energy do not harbour shocks, but jets with intermediate energies do harbour shocks. One advantage of these shocks, as opposed to shocks mediated by external medium, is that these shocks have no effect on the jet terminal speed, but may act as possible sites for particle acceleration. Typically, a jet with specific energy 1.8c2 will achieve a terminal speed of v∞ = 0.813c for jet with any geometry, where, c is the speed of light in vacuum. But for a jet of non-conical cross-section for which the length scale of the inner torus of the accretion disc is 40rg, then, in addition, a steady shock will form at rsh ∼ 7.5rg and compression ratio of R ∼ 2.7. Moreover, electron-proton jet seems to harbour the strongest shock. We will discuss possible consequences of such a scenario.

  4. Burning Laminar Jet Diffusion Flame

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence was taken July 15, 1997, MET:14/10:34 (approximate) and shows the ignition and extinction of this flame. LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel -- like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (518KB, 20-second MPEG, screen 160 x 120 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300182.html.

  5. The extinction of starlight revisited

    NASA Astrophysics Data System (ADS)

    Wickramasinghe, N. C.; Jazbi, B.; Hoyle, F.

    1991-12-01

    The rigorous Kerker-Matijevic formulas for light scattering by coaxial double cylinders are used to calculate the extinction properties of hollow organic grains. A size distribution of such particles together with iron whiskers of radii 0.01 micron, silica spheres of radius 0.03 micron and free aromatic molecular clusters comprised of 50-100 atoms yield excellent agreement with data on the extinction of starlight. The mass ratios of silica to organics and of iron to organics are in good accord with cosmic abundance constraints.

  6. Extinction risk of soil biota.

    PubMed

    Veresoglou, Stavros D; Halley, John M; Rillig, Matthias C

    2015-11-23

    No species lives on earth forever. Knowing when and why species go extinct is crucial for a complete understanding of the consequences of anthropogenic activity, and its impact on ecosystem functioning. Even though soil biota play a key role in maintaining the functioning of ecosystems, the vast majority of existing studies focus on aboveground organisms. Many questions about the fate of belowground organisms remain open, so the combined effort of theorists and applied ecologists is needed in the ongoing development of soil extinction ecology.

  7. Star formation and extinct radioactivities

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.

    1984-01-01

    An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.

  8. Extinction risk of soil biota

    PubMed Central

    Veresoglou, Stavros D.; Halley, John M.; Rillig, Matthias C.

    2015-01-01

    No species lives on earth forever. Knowing when and why species go extinct is crucial for a complete understanding of the consequences of anthropogenic activity, and its impact on ecosystem functioning. Even though soil biota play a key role in maintaining the functioning of ecosystems, the vast majority of existing studies focus on aboveground organisms. Many questions about the fate of belowground organisms remain open, so the combined effort of theorists and applied ecologists is needed in the ongoing development of soil extinction ecology. PMID:26593272

  9. Facets of Pavlovian and operant extinction.

    PubMed

    Lattal, K Matthew; Lattal, Kennon A

    2012-05-01

    Research on extinction is of fundamental importance in both Pavlovian and operant approaches to the experimental analysis of learning. Although these approaches are often motivated by different empirical and theoretical questions, extinction has emerged as a research area in which common themes unite the two approaches. In this review, we focus on some common considerations in the analysis of Pavlovian and operant extinction. These include methodological challenges and interpretational issues in analyzing behavior during and after extinction. We consider the different roles that theory has played in the development of research on extinction in these preparations and conclude with some attention to applications of extinction.

  10. Interstellar grains: Effect of inclusions on extinction

    NASA Astrophysics Data System (ADS)

    Katyal, N.; Gupta, R.; Vaidya, D. B.

    2011-10-01

    A composite dust grain model which simultaneously explains the observed interstellar extinction, polarization, IR emission and the abundance constraints, is required. We present a composite grain model, which is made up of a host silicate oblate spheroid and graphite inclusions. The interstellar extinction curve is evaluated in the spectral region 3.4-0.1 μm using the extinction efficiencies of composite spheroidal grains for three axial ratios. Extinction curves are computed using the discrete dipole approximation (DDA). The model curves are subsequently compared with the average observed interstellar extinction curve and with an extinction curve derived from the IUE catalogue data.

  11. Opposing flow in square porous annulus: Influence of Dufour effect

    SciTech Connect

    Athani, Abdulgaphur; Al-Rashed, Abdullah A. A. A.; Khaleed, H. M. T.

    2016-06-21

    Heat and mass transfer in porous medium is very important area of research which is also termed as double diffusive convection or thermo-solutal convection. The buoyancy ratio which is the ratio of thermal to concentration buoyancy can have negative values thus leading to opposing flow. This article is aimed to study the influence of Dufour effect on the opposing flow in a square porous annulus. The partial differential equations that govern the heat and mass transfer behavior inside porous medium are solved using finite element method. A three node triangular element is used to divide the porous domain into smaller elements. Results are presented with respect to geometric and physical parameters such as duct diameter ratio, Rayleigh number, radiation parameter etc. It is found that the heat transfer increase with increase in Rayleigh number and radiation parameter. It is observed that Dufour coefficient has more influence on velocity profile.

  12. Opposing flow in square porous annulus: Influence of Dufour effect

    NASA Astrophysics Data System (ADS)

    Athani, Abdulgaphur; Al-Rashed, Abdullah A. A. A.; Khaleed, H. M. T.

    2016-06-01

    Heat and mass transfer in porous medium is very important area of research which is also termed as double diffusive convection or thermo-solutal convection. The buoyancy ratio which is the ratio of thermal to concentration buoyancy can have negative values thus leading to opposing flow. This article is aimed to study the influence of Dufour effect on the opposing flow in a square porous annulus. The partial differential equations that govern the heat and mass transfer behavior inside porous medium are solved using finite element method. A three node triangular element is used to divide the porous domain into smaller elements. Results are presented with respect to geometric and physical parameters such as duct diameter ratio, Rayleigh number, radiation parameter etc. It is found that the heat transfer increase with increase in Rayleigh number and radiation parameter. It is observed that Dufour coefficient has more influence on velocity profile.

  13. Mindfulness and mind-wandering: finding convergence through opposing constructs.

    PubMed

    Mrazek, Michael D; Smallwood, Jonathan; Schooler, Jonathan W

    2012-06-01

    Research into both mindfulness and mind-wandering has grown rapidly, yet clarification of the relationship between these two seemingly opposing constructs is still absent. A first study addresses the relationship between a dispositional measure of mindfulness (Mindful Attention and Awareness Scale, MAAS) and converging measures of both self-reported and indirect markers of mind-wandering. Negative correlations between dispositional mindfulness and 4 measures of mind-wandering confirm the opposing relationship between the 2 constructs and further validate the use of the MAAS as a dispositional measure of mindfulness. A second study demonstrated that 8 minutes of mindful breathing reduces behavioral indicators of mind-wandering during a Sustained Attention to Response Task compared with both passive relaxation and reading. Together these studies clarify the opposition between the constructs of mindfulness and mind-wandering and so should lead to greater convergence between what have been predominately separate, yet mutually relevant, lines of research.

  14. Endangered and Extinct Radioactivity

    NASA Astrophysics Data System (ADS)

    Leising, M. D.

    1993-07-01

    Gamma ray spectroscopy holds great promise for probing nucleosynthesis in individual nucleosynthesis events, via observations of short-lived radioactivity, and for measuring global galactic nucleosynthesis today with detections of longer-lived radioactivity. Many of the astrophysical issues addressed by these observations are precisely those that must be understood in order to interpret observations of extinct radioactivity in meteorites. It was somewhat surprising that the former case was realized first for a Type II supernova, when both 56Co [1] and 57Co [2] were detected in SN 1987A. These provide unprecedented constraints on models of Type II explosions. Live 26Al in the galaxy might come from Type II supernovae and their progenitors, and if this is eventually shown to be the case, can constrain massive star evolution, supernova nucleosynthesis, the galactic Type II supernova rate, and even models of the chemical evolution of the galaxy [3]. Titanium-44 is produced primarily in the alpha-rich freezeout from nuclear statistical equilibrium, possibly in Type Ia [4] and almost certainly in Type II supernovae [5]. The galactic recurrence time of these events is comparable to the 44Ti lifetime, so we expect to be able to see at most a few otherwise unseen 44Ti remnants at any given time. No such remnants have been detected yet [6]. Very simple arguments lead to the expectation that about 4 x 10^-4 M(sub)solar mass of 44Ca are produced per century. The product of the supernova frequency times the 44Ti yield per event must equal this number. Even assuming that only the latest event would be seen, rates in excess of 2 century^-1 are ruled out at >=99% confidence by the gamma ray limits. Only rates less than 0.3 century^-1 are acceptable at >5% confidence, and this means that the yield per event must be >10^-3 M(sub)solar mass to produce the requisite 44Ca. Rates this low are incompatible with current estimates for Type II supernovae and yields this high are also very

  15. Advanced Opposed-piston Two-stroke Diesel Demonstrator

    DTIC Science & Technology

    2005-12-08

    research engine as a potential alternative to four-stroke diesels and gas turbines for combat vehicle prime power. A liquid-cooled, opposed- piston...stroke diesel research engine as a potential alternative to four-stroke diesels and gas turbines for combat vehicle prime power. A liquid-cooled...Because the Otto cycle has a higher theoretical thermal efficiency than the diesel cycle for the same compression ratio, the OP engine has the

  16. Advanced Opposed-piston Two-stroke Diesel Demonstrator

    DTIC Science & Technology

    2006-08-19

    research engine as a potential alternative to four-stroke diesels and gas turbines for combat vehicle prime power. A liquid-cooled, opposed- piston...to four-stroke diesels and gas turbines for combat vehicle prime power. A liquid-cooled, opposedpiston, two-stroke diesel research engine was developed... diesel cycle for the same compression ratio, the OP engine has the potential of greater thermal efficiency than conventional diesel engines

  17. Stretched Inertial Jets

    NASA Astrophysics Data System (ADS)

    Ghabache, Elisabeth; Antkowiak, Arnaud; Seon, Thomas; Villermaux, Emmanuel

    2015-11-01

    Liquid jets often arise as short-lived bursting liquid flows. Cavitation or impact-driven jets, bursting champagne bubbles, shaped-charge jets, ballistospores or drop-on-demand inkjet printing are a few examples where liquid jets are suddenly released. The trademark of all these discharge jets is the property of being stretched, due to the quenching injection. the present theoretical and experimental investigation, the structure of the jet flow field will be unraveled experimentally for a few emblematic occurrences of discharge jets. Though the injection markedly depends on each flow configuration, the jet velocity field will be shown to be systematically and rapidly attracted to the universal stretching flow z/t. The emergence of this inertial attractor actually only relies on simple kinematic ingredients, and as such is fairly generic. The universality of the jet velocity structure will be discussed.

  18. Opposing influences of affective state valence on visual cortical encoding.

    PubMed

    Schmitz, Taylor W; De Rosa, Eve; Anderson, Adam K

    2009-06-03

    Positive and negative emotional states are thought to have originated from fundamentally opposing approach and avoidance behaviors. Furthermore, affective valence has been hypothesized to exert opposing biases in cognitive control. Here we examined with functional magnetic resonance imaging whether the opposing influences of positive and negative states extend to perceptual encoding in the visual cortices. Based on prior behavioral research, we hypothesized that positive states would broaden and negative states would narrow visual field of view (FOV). Positive, neutral, and negative states were induced on alternating blocks. To index FOV, observers then viewed brief presentations (300 ms) of face/place concentric center/surround stimuli on interleaved blocks. Central faces were attended, rendering the place surrounds unattended. As face and place information was presented at different visual eccentricities, our physiological metric of FOV was a valence-dependent modulation of place processing in the parahippocampal place area (PPA). Consistent with our hypotheses, positive affective states increased and negative states decreased PPA response to novel places as well as adaptation to repeated places. Individual differences in self-reported positive and negative affect correlated inversely with PPA encoding of peripheral places, as well as with activation in the mesocortical prefrontal cortex and amygdala. Psychophysiological interaction analyses further demonstrated that valence-dependent responses in the PPA arose from opponent coupling with extrafoveal regions of the primary visual cortex during positive and negative states. These findings collectively suggest that affective valence differentially biases gating of early visual inputs, fundamentally altering the scope of perceptual encoding.

  19. Transport synthetic acceleration with opposing reflecting boundary conditions

    SciTech Connect

    Zika, M.R.; Adams, M.L.

    2000-02-01

    The transport synthetic acceleration (TSA) scheme is extended to problems with opposing reflecting boundary conditions. This synthetic method employs a simplified transport operator as its low-order approximation. A procedure is developed that allows the use of the conjugate gradient (CG) method to solve the resulting low-order system of equations. Several well-known transport iteration algorithms are cast in a linear algebraic form to show their equivalence to standard iterative techniques. Source iteration in the presence of opposing reflecting boundary conditions is shown to be equivalent to a (poorly) preconditioned stationary Richardson iteration, with the preconditioner defined by the method of iterating on the incident fluxes on the reflecting boundaries. The TSA method (and any synthetic method) amounts to a further preconditioning of the Richardson iteration. The presence of opposing reflecting boundary conditions requires special consideration when developing a procedure to realize the CG method for the proposed system of equations. The CG iteration may be applied only to symmetric positive definite matrices; this condition requires the algebraic elimination of the boundary angular corrections from the low-order equations. As a consequence of this elimination, evaluating the action of the resulting matrix on an arbitrary vector involves two transport sweeps and a transmission iteration. Results of applying the acceleration scheme to a simple test problem are presented.

  20. Extinction of metastable stochastic populations

    NASA Astrophysics Data System (ADS)

    Assaf, Michael; Meerson, Baruch

    2010-02-01

    We investigate the phenomenon of extinction of a long-lived self-regulating stochastic population, caused by intrinsic (demographic) noise. Extinction typically occurs via one of two scenarios depending on whether the absorbing state n=0 is a repelling (scenario A) or attracting (scenario B) point of the deterministic rate equation. In scenario A the metastable stochastic population resides in the vicinity of an attracting fixed point next to the repelling point n=0 . In scenario B there is an intermediate repelling point n=n1 between the attracting point n=0 and another attracting point n=n2 in the vicinity of which the metastable population resides. The crux of the theory is a dissipative variant of WKB (Wentzel-Kramers-Brillouin) approximation which assumes that the typical population size in the metastable state is large. Starting from the master equation, we calculate the quasistationary probability distribution of the population sizes and the (exponentially long) mean time to extinction for each of the two scenarios. When necessary, the WKB approximation is complemented (i) by a recursive solution of the quasistationary master equation at small n and (ii) by the van Kampen system-size expansion, valid near the fixed points of the deterministic rate equation. The theory yields both entropic barriers to extinction and pre-exponential factors, and holds for a general set of multistep processes when detailed balance is broken. The results simplify considerably for single-step processes and near the characteristic bifurcations of scenarios A and B.

  1. Modeling Population Growth and Extinction

    ERIC Educational Resources Information Center

    Gordon, Sheldon P.

    2009-01-01

    The exponential growth model and the logistic model typically introduced in the mathematics curriculum presume that a population grows exclusively. In reality, species can also die out and more sophisticated models that take the possibility of extinction into account are needed. In this article, two extensions of the logistic model are considered,…

  2. Extinction-induced aggression1

    PubMed Central

    Azrin, N. H.; Hutchinson, R. R.; Hake, D. F.

    1966-01-01

    Pigeons were conditioned to peck a response key under a procedure that alternated periods of food reinforcement with periods of extinction. The pigeons attacked a nearby pigeon at the onset of extinction. Some also attacked a stuffed model of a pigeon. The duration of attack was an inverse function of the time since the last food reinforcement and a direct function of the number of reinforcements. The pigeons attacked after the last food delivery whether or not the conditioned pecking response was required and whether or not the extinction period was signaled. The food had to be eaten; the mere sight and sound of food being delivered did not produce attack. Prior satiation reduced attack. The phenomenon was not attributable to a past history of competition between pigeons since socially deprived pigeons also attacked. Superstitious reinforcement of attack was not found to be a factor. The results indicated that the transition from food reinforcement to extinction was an aversive event that produced aggression. PMID:16811286

  3. Modeling Population Growth and Extinction

    ERIC Educational Resources Information Center

    Gordon, Sheldon P.

    2009-01-01

    The exponential growth model and the logistic model typically introduced in the mathematics curriculum presume that a population grows exclusively. In reality, species can also die out and more sophisticated models that take the possibility of extinction into account are needed. In this article, two extensions of the logistic model are considered,…

  4. Control of jet noise

    NASA Technical Reports Server (NTRS)

    Schreck, Stefan

    1992-01-01

    To investigate the possibility of active control of jet noise, knowledge of the noise generation mechanisms in natural jets is essential. Once these mechanisms are determined, active control can be used to manipulate the noise production processes. We investigated the evolution of the flow fields and the acoustic fields of rectangular and circular jets. A predominant flapping mode was found in the supersonic rectangular jets. We hope to increase the spreading of supersonic jets by active control of the flapping mode found in rectangular supersonic jets.

  5. Understanding jet noise.

    PubMed

    Karabasov, S A

    2010-08-13

    Jets are one of the most fascinating topics in fluid mechanics. For aeronautics, turbulent jet-noise modelling is particularly challenging, not only because of the poor understanding of high Reynolds number turbulence, but also because of the extremely low acoustic efficiency of high-speed jets. Turbulent jet-noise models starting from the classical Lighthill acoustic analogy to state-of-the art models were considered. No attempt was made to present any complete overview of jet-noise theories. Instead, the aim was to emphasize the importance of sound generation and mean-flow propagation effects, as well as their interference, for the understanding and prediction of jet noise.

  6. Evaluating Extinction Values using Wire Impactor Data

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The purpose of the study was to compare the extinctions calculated from data obtained with the Ames Wire Impactor to extinctions measured with the SAGE H satellite system. The comparison was intended to serve as a validation of the extinctions obtained using the wire impactor data. It was felt that if the extinctions obtained by the two diverse methods agreed well, it would be an indication that the number densities measured on the wires were correct.

  7. EARTH SCIENCE: Did Volcanoes Drive Ancient Extinctions?

    PubMed

    Kerr, R A

    2000-08-18

    With the publication in recent weeks of two papers on a mass extinction 183 million years ago, researchers can add five suggestive cases to the list of extinctions with known causes. These extinctions coincide with massive outpourings of lava, accompanied by signs that global warming threw the ocean-atmosphere system out of whack. Although no one can yet pin any of these mass extinctions with certainty on the volcanic eruptions, scientists say it's unlikely that they're all coincidences.

  8. The Geochemistry of Mass Extinction

    NASA Astrophysics Data System (ADS)

    Kump, L. R.

    2003-12-01

    The course of biological evolution is inextricably linked to that of the environment through an intricate network of feedbacks that span all scales of space and time. Disruptions to the environment have biological consequences, and vice versa. Fossils provide the prima facie evidence for biotic disruptions: catastrophic losses of global biodiversity at various times in the Phanerozoic. However, the forensic evidence for the causes and environmental consequences of these mass extinctions resides primarily in the geochemical composition of sedimentary rocks deposited during the extinction intervals. Thus, advancement in our understanding of mass extinctions requires detailed knowledge obtained from both paleontological and geochemical records.This chapter reviews the state of knowledge concerning the geochemistry of the "big five" extinctions of the Phanerozoic (e.g., Sepkoski, 1993): the Late Ordovician (Hirnantian; 440 Ma), the Late Devonian (an extended or multiple event with its apex at the Frasnian-Famennian (F-F) boundary; 367 Ma), the Permian-Triassic (P-Tr; 251 Ma), the Triassic-Jurassic (Tr-J; 200 Ma), and the Cretaceous-Tertiary (K-T; 65 Ma). The focus on the big five is a matter of convenience, as there is a continuum in extinction rates from "background" to "mass extinction." Although much of the literature on extinctions centers on the causes and extents of biodiversity loss, in recent years paleontologists have begun to focus on recoveries (see, e.g., Hart, 1996; Kirchner and Weil, 2000; Erwin, 2001 and references therein).To the extent that the duration of the recovery interval may reflect a slow relaxation of the environment from perturbation, analysis of the geochemical record of recovery is an integral part of this effort. In interpreting the geochemical and biological records of recovery, we need to maintain a clear distinction among the characteristics of the global biota: their biodiversity (affected by differences in origination and extinction

  9. Control of jet noise

    NASA Technical Reports Server (NTRS)

    Schreck, Stefan

    1993-01-01

    This reports describes experiments conducted at the High-Speed Jet Facility at the University of Southern California on supersonic jets. The goal of the study was to develop methods for controlling the noise emitted from supersonic jets by passive and/or active means. Work by Seiner et al (1991) indicates that eddy Mach wave radiation is the dominant noise source in a heated high speed jet. Eddy Mach radiation is caused by turbulent eddies traveling at supersonic speed in the shear layer of the jet. The convection velocity of the eddies decays with increasing distance from the nozzle exit due to the mixing of the jet stream with the ambient fluid. Once the convection speed reaches subsonic velocities, eddy Mach wave radiation ceases. To control noise, a rapid decay of the convection velocity is desired. This may be accomplished by enhanced mixing in the jet. In this study, small aspect ratio rectangular jet nozzles were tested. A flapping mode was noticed in the jets. By amplifying screech components of the jets and destabilizing the jet columns with a collar device, the flapping mode was excited. The result was a rapid decay of the jet velocity. A reduction in eddy Mach radiation in rectangular supersonic jets may be achieved with this device.

  10. Further Evidence of Auditory Extinction in Aphasia

    ERIC Educational Resources Information Center

    Marshall, Rebecca Shisler; Basilakos, Alexandra; Love-Myers, Kim

    2013-01-01

    Purpose: Preliminary research ( Shisler, 2005) suggests that auditory extinction in individuals with aphasia (IWA) may be connected to binding and attention. In this study, the authors expanded on previous findings on auditory extinction to determine the source of extinction deficits in IWA. Method: Seventeen IWA (M[subscript age] = 53.19 years)…

  11. Further Evidence of Auditory Extinction in Aphasia

    ERIC Educational Resources Information Center

    Marshall, Rebecca Shisler; Basilakos, Alexandra; Love-Myers, Kim

    2013-01-01

    Purpose: Preliminary research ( Shisler, 2005) suggests that auditory extinction in individuals with aphasia (IWA) may be connected to binding and attention. In this study, the authors expanded on previous findings on auditory extinction to determine the source of extinction deficits in IWA. Method: Seventeen IWA (M[subscript age] = 53.19 years)…

  12. Extinction in multiple contexts: Effects on the rate of extinction and the strength of response recovery.

    PubMed

    Bustamante, Javier; Uengoer, Metin; Thorwart, Anna; Lachnit, Harald

    2016-09-01

    In two human predictive-learning experiments, we investigated the effects of extinction in multiple contexts on the rate of extinction and the strength of response recovery. In each experiment, participants initially received acquisition training with a target cue in one context, followed by extinction either in a different context (extinction in a single context) or in three different contexts (extinction in multiple contexts). The results of both experiments showed that conducting extinction in multiple contexts led to higher levels of responding during extinction than did extinction in a single context. Additionally, Experiment 2 showed that extinction in multiple contexts prevented ABC renewal but had no detectable impact on ABA renewal. Our results are discussed within the framework of contemporary learning theories of contextual control and extinction.

  13. Glottal jet inertance

    NASA Astrophysics Data System (ADS)

    Mphail, Michael; Krane, Michael

    2016-11-01

    Estimates of an inertive contribution of the glottal jet to glottal aerodynamic resistance is presented. Given that inertance of the flow in a constriction can be expressed in terms of the kinetic energy of the flow, and that a jet is a maximum kinetic energy flow pattern, it is argued that the glottal jet possesses its own inertance which is at least as large as that of the vocal tract. These arguments are supported by estimates of inertance obtained from simulations of an unsteady flow through an axisymmetric orifice, and of a compliant constriction with the approximate shape and mechanical properties of the vocal folds. It is further shown that the inertive effect of the glottal jet depends on the jet path and jet mixing, with a slowly diffusing, symmetric jet showing higher inertance than an asymmetric jet which rapidly mixes with supraglottal air. Acknowledge support of NIH Grant 2R01DC005642-10A1.

  14. The AGN Jet Model of the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Guo, Fulai

    2017-01-01

    The nature and origin of the Fermi bubbles detected in the inner Galaxy remain elusive. In this paper, we briefly discuss some recent theoretical and observational developments, with a focus on the AGN jet model. Analogous to radio lobes observed in massive galaxies, the Fermi bubbles could be naturally produced by a pair of opposing jets emanating nearly along the Galaxy's rotation axis from the Galactic center. Our two-fluid hydrodynamic simulations reproduce quite well the bubble location and shape, and interface instabilities at the bubble surface could be effectively suppressed by shear viscosity. We briefly comment on some potential issues related to our model, which may lead to future progress.

  15. Development of Extinction Imagers for the Determination of Atmospheric Optical Extinction

    DTIC Science & Technology

    2014-08-01

    REPORT TYPE Final Report 4. TITLE AND SUBTITLE Development of Extinction Imagers for the Determination of Atmospheric Optical Extinction 6. AUTHOR...further develop Extinction Imagers for use in the ocean environment, and to extend the capabilities into the Short Wave IR (SWIR). Extinction Imaging...is a method for determining the effective extinction coefficient over an extended path using a sensor at one end of the path. It uses calibrated

  16. Fountain-Jet Turbulence.

    DTIC Science & Technology

    1980-09-01

    and 3 times higher than expected from free- jet results. Hill et al., (Reference 6) in work with foun- tain jets impacting fuselage models, detected ...delineate the origins of the turbulent anomalies associated with fountain jets by extending the previous studies. The results are presented herein...jet velocities were detected with a Thermal Systems Inc. Model 1050 dual-channel constant-temperature anemometer equipped with a Thermal Systems Inc

  17. Jets of incipient liquids

    NASA Astrophysics Data System (ADS)

    Reshetnikov, A. V.; Mazheiko, N. A.; Skripov, V. P.

    2000-05-01

    Jets of incipient water escaping into the atmosphere through a short channel are photographed. In some experiments. complete disintegration of the jet is observed. The relationship of this phenomenon with intense volume incipience is considered. The role of the Coanda effect upon complete opening of the jet is revealed. Measurement results of the recoil force R of the jets of incipient liquids are presented. Cases of negative thrust caused by the Coanda effect are noted. Generalization of experimental data is proposed.

  18. NASA Jet Noise Research

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda

    2012-01-01

    The presentation highlights jet-noise research conducted in the Subsonic Fixed Wing, Supersonics, and Environmentally Responsible Aviation Projects in the Fundamental Aeronautics Program at NASA. The research efforts discussed include NASA's updated Aircraft NOise Prediction Program (ANOPP2), acoustic-analogy-based prediction tools, jet-surface-interaction studies, plasma-actuator investigations, N+2 Supersonics Validation studies, rectangular-jet experiments, twin-jet experiments, and Hybrid Wind Body (HWB) activities.

  19. [The formation of the field of psychiatry: two opposing perspectives].

    PubMed

    Gama, Jairo Roberto de Almeida

    2012-03-01

    The article analyzes two opposing views of the formation of the psychiatric field: the Foucauldian perspective, which holds sway in Brazil, and the perspective of Gauchet and Swain. Two works by Foucault (History of Madness and Psychiatric Power) are contrasted with Madness and Democracy, by the latter authors. It is argued that a society's political and assistance strategies about madness are shaped by the conceptual bases defining what constitutes the field of psychiatric theory and how it was formed. The article calls attention to the diverse consequences that these two approaches may have on the reform of Brazilian psychiatry.

  20. OPUS: A Fortran Program for Unsteady Opposed-Flowed Flames

    SciTech Connect

    H. G. Im; L. L. Raja; R. J. Kee; A. E. Lutz; L. R. Petzold

    2000-07-01

    OPUS is a Fortran program for computing unsteady combustion problems in an opposed-flow configuration using one-dimensional similarity coordinate. The code is an extension of the steady counterpart, OPPDIF, to transient problems by modifying the formulation to accommodate gasdynamic compressibility effects, allowing high-accuracy time integration with adaptive time stepping. Time integration of the differential-algebraic system of equations is performed by the DASPK software package, while the Chemkin packages are used to compute chemical reaction rates and thermodynamic/transport properties. This document describes the details of the mathematical formulation and instruction for using the code.

  1. Evaluating Extinction Values Using Wire Impactor Data

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The purpose of the study was to compare the extinctions calculated from data obtained with the Ames Wire Impactor to extinctions measured with the SAGE 11 satellite system. The comparison was intended to serve as a validation of the extinctions obtained using the wire impactor data. It was felt that if the extinctions obtained by the two diverse methods agreed well, it would be an indication that the number densities measured on the wires were correct. Tables and charts are presented to show the extinction values from the two different methods.

  2. The extinction differential induced virulence macroevolution

    NASA Astrophysics Data System (ADS)

    Zhang, Feng; Xu, Liufang; Wang, Jin

    2014-04-01

    We apply the potential-flux landscape theory to deal with the large fluctuation induced extinction phenomena. We quantify the most probable extinction pathway on the landscape and measure the extinction risk by the landscape topography. In this Letter, we investigate the disease extinction through an epidemic model described by a set of chemical reaction. We found the virulence-differential-dependent symbioses between mother and daughter pathogen species: mutualism and parasitism. The symbioses, whether mutualism or parasitism, benefit the higher virulence species. This implies that speciation towards lower virulence is an effective strategy for a pathogen species to reduce its extinction risk.

  3. The peculiar extinction of Herschel 36

    NASA Technical Reports Server (NTRS)

    Donn, B.; Hecht, J. H.; Helfer, H. L.; Wolf, J.; Pipher, J. L.

    1982-01-01

    The extinction of Herschel 36 was measured and found to be peculiar in the same sense as that observed in Orion. Following the treatment of Mathis and Wallenhorst, this can be explained by the presence of large silicate and graphite grains than are normally found in the interstellar medium. Correcting the stellar flux for foreground extinction results in a residual extinction curve for the associated dust cloud, with an unusually small normalized extinction (less than 1.0) at 1500 A. This low UV extinction may be due to the effects of scattering by the dust cloud material.

  4. Darwin and the uses of extinction.

    PubMed

    Beer, Gillian

    2009-01-01

    We currently view extinction with dismay and even horror, but Darwin saw extinction as ordinary and as necessary to evolutionary change. Still, the degree to which extinction is fundamental to his theory is rarely discussed. This essay examines Darwin's linking of the idea of "improvement" with that of natural selection and tracks a cluster of reasons for our changed valuation of extinction now. Those reasons demonstrate how scientific information and ideological preferences have reshaped the concept. The essay challenges the reader to assess some current assumptions about extinction and concludes by considering the shift in Darwin's own understanding from the "Origin" to the late "Autobiography".

  5. Opposing roles of primate areas 25 and 32 and their putative rodent homologs in the regulation of negative emotion.

    PubMed

    Wallis, Chloe U; Cardinal, Rudolf N; Alexander, Laith; Roberts, Angela C; Clarke, Hannah F

    2017-05-16

    Disorders of dysregulated negative emotion such as depression and anxiety also feature increased cardiovascular mortality and decreased heart-rate variability (HRV). These disorders are correlated with dysfunction within areas 25 and 32 of the ventromedial prefrontal cortex (vmPFC), but a causal relationship between dysregulation of these areas and such symptoms has not been demonstrated. Furthermore, cross-species translation is limited by inconsistent findings between rodent fear extinction and human neuroimaging studies of negative emotion. To reconcile these literatures, we applied an investigative approach to the brain-body interactions at the core of negative emotional dysregulation. We show that, in marmoset monkeys (a nonhuman primate that has far greater vmPFC homology to humans than rodents), areas 25 and 32 have causal yet opposing roles in regulating the cardiovascular and behavioral correlates of negative emotion. In novel Pavlovian fear conditioning and extinction paradigms, pharmacological inactivation of area 25 decreased the autonomic and behavioral correlates of negative emotion expectation, whereas inactivation of area 32 increased them via generalization. Area 25 inactivation also increased resting HRV. These findings are inconsistent with current theories of rodent/primate prefrontal functional similarity, and provide insight into the role of these brain regions in affective disorders. They demonstrate that area 32 hypoactivity causes behavioral generalization relevant to anxiety, and that area 25 is a causal node governing the emotional and cardiovascular symptomatology relevant to anxiety and depression.

  6. Neanderthal Extinction by Competitive Exclusion

    PubMed Central

    Banks, William E.; d'Errico, Francesco; Peterson, A. Townsend; Kageyama, Masa; Sima, Adriana; Sánchez-Goñi, Maria-Fernanda

    2008-01-01

    Background Despite a long history of investigation, considerable debate revolves around whether Neanderthals became extinct because of climate change or competition with anatomically modern humans (AMH). Methodology/Principal Findings We apply a new methodology integrating archaeological and chronological data with high-resolution paleoclimatic simulations to define eco-cultural niches associated with Neanderthal and AMH adaptive systems during alternating cold and mild phases of Marine Isotope Stage 3. Our results indicate that Neanderthals and AMH exploited similar niches, and may have continued to do so in the absence of contact. Conclusions/Significance The southerly contraction of Neanderthal range in southwestern Europe during Greenland Interstadial 8 was not due to climate change or a change in adaptation, but rather concurrent AMH geographic expansion appears to have produced competition that led to Neanderthal extinction. PMID:19107186

  7. Testing for periodicity of extinction

    NASA Technical Reports Server (NTRS)

    Raup, David M.; Sepkoski, J. J., Jr.

    1988-01-01

    The statistical techniques used by Raup and Sepkoski (1984 and 1986) to identify a 26-Myr periodicity in the biological extinction record for the past 250 Myr are reexamined, responding in detail to the criticisms of Stigler and Wagner (1987). It is argued that evaluation of a much larger set of extinction data using a time scale with 51 sampling intervals supports the finding of periodicity. In a reply by Sigler and Wagner, the preference for a 26-Myr period is attributed to a numerical quirk in the Harland et al. (1982) time scale, in which the subinterval boundaries are not linear interpolations between the stage boundaries but have 25-Myr periodicity. It is stressed that the results of the stringent statistical tests imposed do not disprove periodicity but rather indicate that the evidence and analyses presented so far are inadequate.

  8. Extinction Risk Escalates in the Tropics

    PubMed Central

    Vamosi, Jana C.; Vamosi, Steven M.

    2008-01-01

    The latitudinal biodiversity gradient remains one of the most widely recognized yet puzzling patterns in nature [1]. Presently, the high level of extinction of tropical species, referred to as the “tropical biodiversity crisis”, has the potential to erode this pattern. While the connection between species richness, extinction, and speciation has long intrigued biologists [2], [3], these interactions have experienced increased poignancy due to their relevancy to where we should concentrate our conservation efforts. Natural extinction is a phenomenon thought to have its own latitudinal gradient, with lower extinction rates in the tropics being reported in beetles, birds, mammals, and bivalves [4]–[7]. Processes that have buffered ecosystems from high extinction rates in the past may also buffer ecosystems against disturbance of anthropogenic origin. While potential parallels between historical and present-day extinction patterns have been acknowledged, they remain only superficially explored and plant extinction patterns have been particularly neglected. Studies on the disappearances of animal species have reached conflicting conclusions, with the rate of extinction appearing either higher [8] or lower [9] in species richness hotspots. Our global study of extinction risk in vascular plants finds disproportionately higher extinction risk in tropical countries, even when indicators of human pressure (GDP, population density, forest cover change) are taken into account. Our results are at odds with the notion that the tropics represent a museum of plant biodiversity (places of historically lowered extinction) and we discuss mechanisms that may reconcile this apparent contradiction. PMID:19066623

  9. Extinction risk escalates in the tropics.

    PubMed

    Vamosi, Jana C; Vamosi, Steven M

    2008-01-01

    The latitudinal biodiversity gradient remains one of the most widely recognized yet puzzling patterns in nature. Presently, the high level of extinction of tropical species, referred to as the "tropical biodiversity crisis", has the potential to erode this pattern. While the connection between species richness, extinction, and speciation has long intrigued biologists, these interactions have experienced increased poignancy due to their relevancy to where we should concentrate our conservation efforts. Natural extinction is a phenomenon thought to have its own latitudinal gradient, with lower extinction rates in the tropics being reported in beetles, birds, mammals, and bivalves. Processes that have buffered ecosystems from high extinction rates in the past may also buffer ecosystems against disturbance of anthropogenic origin. While potential parallels between historical and present-day extinction patterns have been acknowledged, they remain only superficially explored and plant extinction patterns have been particularly neglected. Studies on the disappearances of animal species have reached conflicting conclusions, with the rate of extinction appearing either higher or lower in species richness hotspots. Our global study of extinction risk in vascular plants finds disproportionately higher extinction risk in tropical countries, even when indicators of human pressure (GDP, population density, forest cover change) are taken into account. Our results are at odds with the notion that the tropics represent a museum of plant biodiversity (places of historically lowered extinction) and we discuss mechanisms that may reconcile this apparent contradiction.

  10. Optimising Extinction of Conditioned Disgust

    PubMed Central

    Bosman, Renske C.; Borg, Charmaine; de Jong, Peter J.

    2016-01-01

    Maladaptive disgust responses are tenacious and resistant to exposure-based interventions. In a similar vein, laboratory studies have shown that conditioned disgust is relatively insensitive to Conditioned Stimulus (CS)-only extinction procedures. The relatively strong resistance to extinction might be explained by disgust’s adaptive function to motivate avoidance from contamination threats (pathogens) that cannot be readily detected and are invisible to the naked eye. Therefore, the mere visual presentation of unreinforced disgust eliciting stimuli might not be sufficient to correct a previously acquired threat value of the CS+. Following this, the current study tested whether the efficacy of CS-only exposure can be improved by providing additional safety information about the CS+. For the CSs we included two neutral items a pea soup and a sausage roll, whereas for the Unconditioned Stimulus (US) we used one video clip of a woman vomiting and a neutral one about glass blowing. The additional safety information was conveyed by allowing actual contact with the CS+ or by observing an actress eating the food items representing the CS+. When additional safety information was provided via allowing direct contact with the CS+, there was a relatively strong post-extinction increase in participants’ willingness-to-eat the CS+. This beneficial effect was still evident at one-week follow up. Also self-reported disgust was lower at one-week follow up when additional safety information was provided. The current findings help explain why disgust is relatively insensitive to CS-only extinction procedures, and provide helpful starting points to improve interventions that are aimed to reduce distress in disgust-related psychopathology. PMID:26849211

  11. [Extinction and Reconsolidation of Memory].

    PubMed

    Zuzina, A B; Balaban, P M

    2015-01-01

    Retrieval of memory followed by reconsolidation can strengthen a memory, while retrieval followed by extinction results in a decrease of memory performance due to weakening of existing memory or formation of a competing memory. In our study we analyzed the behavior and responses of identified neurons involved in the network underlying aversive learning in terrestrial snail Helix, and made an attempt to describe the conditions in which the retrieval of memory leads either to extinction or reconsolidation. In the network underlying the withdrawal behavior, sensory neurons, premotor interneurons, motor neurons, and modulatory for this network serotonergic neurons are identified and recordings from representatives of these groups were made before and after aversive learning. In the network underlying feeding behavior, the premotor modulatory serotonergic interneurons and motor neurons involved in motor program of feeding are identified. Analysis of changes in neural activity after aversive learning showed that modulatory neurons of feeding behavior do not demonstrate any changes (sometimes a decrease of responses to food was observed), while responses to food in withdrawal behavior premotor interneurons changed qualitatively, from under threshold EPSPs to spike discharges. Using a specific for serotonergic neurons neurotoxin 5,7-DiHT it was shown previously that the serotonergic system is necessary for the aversive learning, but is not necessary for maintenance and retrieval of this memory. These results suggest that the serotonergic neurons that are necessary as part of a reinforcement for developing the associative changes in the network may be not necessary for the retrieval of memory. The hypothesis presented in this review concerns the activity of the "reinforcement" serotonergic neurons that is suggested to be the gate condition for the choice between extinction/reconsolidation triggered by memory retrieval: if these serotonergic neurons do not respond during the

  12. Were all extinction events caused by impacts?

    NASA Technical Reports Server (NTRS)

    Sheehan, P. M.; Coorough, P. J.

    1994-01-01

    Extraterrestrial impacts are firmly implicated in several of the five major Phanerozoic extinction events. A critical issue now is whether extraterrestrial events have been the only mechanism that produced physical changes of sufficient magnitude to cause major extinction events. While we believe the evidence is overwhelming that the KT extinction event was caused by an impact, we also find that an event of similar or larger size near the end of the Ordovician is best explained by terrestrial causes. The Ordovician extinction event (End-O extinction event) occurred near the end of the Ordovician, but the interval of extinction was completed prior to the newly established Ordovician-Silurian boundary. In spite of extensive field studies, a convincing signature of an associated impact has not been found. However, a prominent glaciation does coincide with the End-O extinction event.

  13. The case for extraterrestrial causes of extinction

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1989-01-01

    The dramatic increase in our knowledge of large-body impacts that have occurred in Earth's history has led to strong arguments for the plausibility of meteorite impact as a cause of extinction. Proof of causation is often hampered, however, by our inability to demonstrate the synchronism of specific impacts and extinctions. A central problem is range truncation: the last reported occurrences of fossil taxa generally underestimate the true times of extinction. Range truncation, because of gaps in sedimentation, lack of preservation, or lack of discovery, can make sudden extinctions appear gradual and gradual extinctions appear sudden. Also, stepwise extinction may appear as an artefact of range truncation. These effects are demonstrated by experiments performed on data from field collections of Cretaceous ammonities from Zumaya (Spain). The challenge for future research is to develop a new calculus for treating biostratigraphic data so that fossils can provide more accurate assessments of the timing of extinctions.

  14. Phylogenetic conservatism of extinctions in marine bivalves.

    PubMed

    Roy, Kaustuv; Hunt, Gene; Jablonski, David

    2009-08-07

    Evolutionary histories of species and lineages can influence their vulnerabilities to extinction, but the importance of this effect remains poorly explored for extinctions in the geologic past. When analyzed using a standardized taxonomy within a phylogenetic framework, extinction rates of marine bivalves estimated from the fossil record for the last approximately 200 million years show conservatism at multiple levels of evolutionary divergence, both within individual families and among related families. The strength of such phylogenetic clustering varies over time and is influenced by earlier extinction history, especially by the demise of volatile taxa in the end-Cretaceous mass extinction. Analyses of the evolutionary roles of ancient extinctions and predictive models of vulnerability of taxa to future natural and anthropogenic stressors should take phylogenetic relationships and extinction history into account.

  15. THE MOLAR EXTINCTION OF RHODOPSIN

    PubMed Central

    Wald, George; Brown, Paul K.

    1953-01-01

    The molar extinction of rhodopsin is 40,600 cm.2 per mole equivalent of retinene; i.e., this is the extinction of a solution of rhodopsin which is produced by, or yields on bleaching, a molar solution of retinene. The molar extinctions of all-trans retinene and all-trans retinene oxime have also been determined in ethyl alcohol and aqueous digitonin solutions. On the assumption that each chromophoric group of rhodopsin is made from a single molecule of retinene, it is concluded that the primary photochemical conversion of rhodopsin to lumi-rhodopsin has a quantum efficiency of 1; though the over-all bleaching of rhodopsin in solution to retinene and opsin may have a quantum efficiency as low as one-half. On bleaching cattle rhodopsin, about two sulfhydryl groups appear for each molecule of retinene liberated. In frog rhodopsin the —SH:retinene ratio appears to be higher, 5:2 or perhaps even 3:1. Some of this sulfhydryl appears to have been engaged in binding retinene to opsin; some may have been exposed as the result of changes in opsin which accompany bleaching, comparable with protein denaturation. PMID:13109155

  16. Perspectives on dilution jet mixing. [in creating temperature patterns at combustor exits in gas turbine engines

    NASA Technical Reports Server (NTRS)

    Holdeman, J. D.; Srinivasan, R.

    1986-01-01

    A microcomputer code which displays 3-D oblique and 2-D plots of the temperature distribution downstream of jets mixing with a confined crossflow has been used to investigate the effects of varying the several independent flow and geometric parameters on the mixing. Temperature profiles calculated with this empirical model are presented to show the effects of orifice size and spacing, momentum flux ratio, density ratio, variable temperature mainstream, flow area convergence, orifice aspect ratio, and opposed and axially staged rows of jets.

  17. The role of medial prefrontal cortex in extinction and reinstatement of alcohol-seeking in rats.

    PubMed

    Willcocks, Andrea L; McNally, Gavan P

    2013-01-01

    The prelimbic (PL) and infralimbic (IL) medial prefrontal cortex (mPFC) are thought to play opposing roles in drug-seeking behaviour. Specifically, the PL promotes drug-seeking whereas the IL is necessary for the inhibition of drug-seeking during extinction. We studied the roles of the PL, IL and dorsal peduncular PFC (DP) in the expression of context-induced reinstatement, reacquisition and extinction of alcoholic beer-seeking. In context-induced reinstatement (renewal), animals were trained to nosepoke for alcoholic beer (context A), extinguished (context B) and then tested in context A and B. In reacquisition, animals received the same instrumental training and extinction without any contextual manipulation. On test, alcoholic beer was again available and responding was compared with naive controls. Just prior to the test, rats received bilateral infusion of baclofen/muscimol into the PL, IL or DP. Reversible inactivation of the PL attenuated ABA renewal but augmented reacquisition. Reversible inactivation of IL had no effect on the reinstatement or reacquisition of alcoholic beer-seeking and had no effect on extinction expression (ABB and AAA). IL inactivation did, however, increase the latencies with which animals responded on test but only when animals were tested in the extinction context. DP inactivation had no effect on reinstatement or reacquisition. These studies are inconsistent with the view that PL and IL exert opposing effects on drug-seeking. Rather, they support the view that PL is important for retrieval of drug-seeking contingency information and that the use of contextual information is enhanced with IL manipulation.

  18. Invasions and Extinctions Reshape Coastal Marine Food Webs

    PubMed Central

    Byrnes, Jarrett E.; Reynolds, Pamela L.; Stachowicz, John J.

    2007-01-01

    The biodiversity of ecosystems worldwide is changing because of species loss due to human-caused extinctions and species gain through intentional and accidental introductions. Here we show that the combined effect of these two processes is altering the trophic structure of food webs in coastal marine systems. This is because most extinctions (∼70%) occur at high trophic levels (top predators and other carnivores), while most invasions are by species from lower trophic levels (70% macroplanktivores, deposit feeders, and detritivores). These opposing changes thus alter the shape of marine food webs from a trophic pyramid capped by a diverse array of predators and consumers to a shorter, squatter configuration dominated by filter feeders and scavengers. The consequences of the simultaneous loss of diversity at top trophic levels and gain at lower trophic levels is largely unknown. However, current research suggests that a better understanding of how such simultaneous changes in diversity can impact ecosystem function will be required to manage coastal ecosystems and forecast future changes. PMID:17356703

  19. Lis1 Has Two Opposing Modes of Regulating Cytoplasmic Dynein.

    PubMed

    DeSantis, Morgan E; Cianfrocco, Michael A; Htet, Zaw Min; Tran, Phuoc Tien; Reck-Peterson, Samara L; Leschziner, Andres E

    2017-09-07

    Regulation is central to the functional versatility of cytoplasmic dynein, a motor involved in intracellular transport, cell division, and neurodevelopment. Previous work established that Lis1, a conserved regulator of dynein, binds to its motor domain and induces a tight microtubule-binding state in dynein. The work we present here-a combination of biochemistry, single-molecule assays, and cryoelectron microscopy-led to the surprising discovery that Lis1 has two opposing modes of regulating dynein, being capable of inducing both low and high affinity for the microtubule. We show that these opposing modes depend on the stoichiometry of Lis1 binding to dynein and that this stoichiometry is regulated by the nucleotide state of dynein's AAA3 domain. The low-affinity state requires Lis1 to also bind to dynein at a novel conserved site, mutation of which disrupts Lis1's function in vivo. We propose a new model for the regulation of dynein by Lis1. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. Anticipatory adjustments to abrupt changes of opposing forces.

    PubMed

    Rapp, Katrin; Heuer, Herbert

    2015-01-01

    Anticipatory adjustments to abrupt load changes are based on task-specific predictive information. The authors asked whether anticipatory adjustments to abrupt offsets of horizontal forces are related to expectancy. In two experiments participants held a position against an opposing force or moved against it. At force offset they had to stop rapidly. Duration of the opposing force or distance moved against it varied between blocks of trials and was constant within each block, or it varied from trial to trial. These two variations resulted in opposite changes of the expectancy of force offset with the passage of time or distance. With constant force durations or distances in each block of trials, anticipatory adjustments tended to be poorest with the longest duration or distance, but with variable force durations or distances they tended to be best with the longest duration or distance. Thus anticipatory adjustments were related to expectancy rather than time or distance per se. Anticipatory adjustments resulted in shorter peak amplitudes of the involuntary movements, accompanied by longer movement times in Experiment 1 and faster movement times in Experiment 2. Thus, for different states of the limb at abrupt dynamic changes anticipatory adjustments involve different mechanisms that modulate different mechanical characteristics.

  1. Large bouncing jets

    NASA Astrophysics Data System (ADS)

    Cardin, Karl; Weislogel, Mark

    2016-11-01

    We experimentally investigate the phenomena of large jet rebound (bounce), a mode of fluid transfer following oblique jet impacts on hydrophobic surfaces. We initially seek to describe the regimes of such jet bounce in tests conducted in the weightless environment of a drop tower. A parametric study reveals the dependence of the rebound mode on the relevant dimensionless groups such as Weber number We⊥ defined on the velocity component perpendicular to the surface. We show that significantly larger diameter jets behave similarly as much smaller jets demonstrated during previous terrestrial investigations when We⊥ 1 . For We⊥ > 1 , large jet impacts create fishbone-like structures. We also explore rebounds from nonplanar substrates. Improving our understanding of such jet rebound opens avenues for unique transport capabilities. NASA Cooperative Agreement NNX12A047A.

  2. Hydroacoustic pulsating jet generator

    NASA Astrophysics Data System (ADS)

    Unrau, A.; Meier, G. E. A.

    1987-04-01

    A high pressure turbulent jet generator connected to a low pressure hydraulic tube is studied to investigate water hammer in tubes with fast flow variations, generating high pressure pulsating water jets. The pulsating jet generator consists of a tube, a hydraulic valve, a spring, and a water container. The jet is the effect of the combination of turbulent pipe flow with a valve for flow nozzle. The jet pressure depends on specific oscillation impedance and flow velocity variations. For inlet pressure of 0.5 to 2 bar the pressure rises to 40 bar. The described pulsating jet generator is more effective than the earlier model. A piezoelectric pressure controller is used to register pressure signals and high speed photos are made of the jet. Test results are consistent with theoretical calculation.

  3. The role of extinction in evolution

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1994-01-01

    The extinction of species is not normally considered an important element of neodarwinian theory, in contrast to the opposite phenomenon, speciation. This is surprising in view of the special importance Darwin attached to extinction, and because the number of species extinctions in the history of life is almost the same as the number of originations; present-day biodiversity is the result of a trivial surplus of originations, cumulated over millions of years. For an evolutionary biologist to ignore extinction is probably as foolhardy as for a demographer to ignore mortality. The past decade has seen a resurgence of interest in extinction, yet research on the topic is still at a reconnaissance level, and our present understanding of its role in evolution is weak. Despite uncertainties, extinction probably contains three important elements. (i) For geographically widespread species, extinction is likely only if the killing stress is one so rare as to be beyond the experience of the species, and thus outside the reach of natural selection. (ii) The largest mass extinctions produce major restructuring of the biosphere wherein some successful groups are eliminated, allowing previously minor groups to expand and diversify. (iii) Except for a few cases, there is little evidence that extinction is selective in the positive sense argued by Darwin. It has generally been impossible to predict, before the fact, which species will be victims of an extinction event.

  4. The role of extinction in evolution

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1994-01-01

    The extinction of species is not normally considered an important element of neodarwinian theory, in contrast to the opposite phenomenon, speciation. This is surprising in view of the special importance Darwin attached to extinction, and because the number of species extinctions in the history of life is almost the same as the number of originations; present-day biodiversity is the result of a trivial surplus of originations, cumulated over millions of years. For an evolutionary biologist to ignore extinction is probably as foolhardy as for a demographer to ignore mortality. The past decade has seen a resurgence of interest in extinction, yet research on the topic is still at a reconnaissance level, and our present understanding of its role in evolution is weak. Despite uncertainties, extinction probably contains three important elements. (i) For geographically widespread species, extinction is likely only if the killing stress is one so rare as to be beyond the experience of the species, and thus outside the reach of natural selection. (ii) The largest mass extinctions produce major restructuring of the biosphere wherein some successful groups are eliminated, allowing previously minor groups to expand and diversify. (iii) Except for a few cases, there is little evidence that extinction is selective in the positive sense argued by Darwin. It has generally been impossible to predict, before the fact, which species will be victims of an extinction event.

  5. Methylphenidate enhances extinction of contextual fear

    PubMed Central

    Abraham, Antony D.; Cunningham, Christopher L.; Lattal, K. Matthew

    2012-01-01

    Methylphenidate (MPH, Ritalin) is a norepinephrine and dopamine transporter blocker that is widely used in humans for treatment of attention deficit disorder and narcolepsy. Although there is some evidence that targeted microinjections of MPH may enhance fear acquisition, little is known about the effect of MPH on fear extinction. Here, we show that MPH, administered before or immediately following extinction of contextual fear, will enhance extinction retention in C57BL/6 mice. Animals that received MPH (2.5–10 mg/kg) before an extinction session showed decreased freezing response during extinction, and the effect of the 10 mg/kg dose on freezing persisted to the next day. When MPH (2.5–40 mg/kg) was administered immediately following an extinction session, mice that received MPH showed dose-dependent decreases in freezing during subsequent tests. MPH administered immediately after a 3-min extinction session or 4 h following the first extinction session did not cause significant differences in freezing. Together, these findings demonstrate that MPH can enhance extinction of fear and that this effect is sensitive to dose, time of injection, and duration of the extinction session. Because MPH is widely used in clinical treatments, these experiments suggest that the drug could be used in combination with behavioral therapies for patients with fear disorders. PMID:22251891

  6. Biological correlates of extinction risk in bats.

    PubMed

    Jones, Kate E; Purvis, Andy; Gittleman, John L

    2003-04-01

    We investigated patterns and processes of extinction and threat in bats using a multivariate phylogenetic comparative approach. Of nearly 1,000 species worldwide, 239 are considered threatened by the International Union for Conservation of Nature and Natural Resources (IUCN) and 12 are extinct. Small geographic ranges and low wing aspect ratios are independently found to predict extinction risk in bats, which explains 48% of the total variance in IUCN assessments of threat. The pattern and correlates of extinction risk in the two bat suborders are significantly different. A higher proportion (4%) of megachiropteran species have gone extinct in the last 500 years than microchiropteran bats (0.3%), and a higher proportion is currently at risk of extinction (Megachiroptera: 34%; Microchiroptera: 22%). While correlates of microchiropteran extinction risk are the same as in the order as a whole, megachiropteran extinction is correlated more with reproductive rate and less with wing morphology. Bat extinction risk is not randomly distributed phylogenetically: closely related species have more similar levels of threat than would be expected if extinction risk were random. Given the unbalanced nature of the evolutionary diversification of bats, it is probable that the amount of phylogenetic diversity lost if currently threatened taxa disappear may be greater than in other clades with numerically more threatened species.

  7. The role of extinction in evolution.

    PubMed Central

    Raup, D M

    1994-01-01

    The extinction of species is not normally considered an important element of neodarwinian theory, in contrast to the opposite phenomenon, speciation. This is surprising in view of the special importance Darwin attached to extinction, and because the number of species extinctions in the history of life is almost the same as the number of originations; present-day biodiversity is the result of a trivial surplus of originations, cumulated over millions of years. For an evolutionary biologist to ignore extinction is probably as foolhardy as for a demographer to ignore mortality. The past decade has seen a resurgence of interest in extinction, yet research on the topic is still at a reconnaissance level, and our present understanding of its role in evolution is weak. Despite uncertainties, extinction probably contains three important elements. (i) For geographically widespread species, extinction is likely only if the killing stress is one so rare as to be beyond the experience of the species, and thus outside the reach of natural selection. (ii) The largest mass extinctions produce major restructuring of the biosphere wherein some successful groups are eliminated, allowing previously minor groups to expand and diversify. (iii) Except for a few cases, there is little evidence that extinction is selective in the positive sense argued by Darwin. It has generally been impossible to predict, before the fact, which species will be victims of an extinction event. PMID:8041694

  8. The ethics of reviving long extinct species.

    PubMed

    Sandler, Ronald

    2014-04-01

    There now appears to be a plausible pathway for reviving species that have been extinct for several decades, centuries, or even millennia. I conducted an ethical analysis of de-extinction of long extinct species. I assessed several possible ethical considerations in favor of pursuing de-extinction: that it is a matter of justice; that it would reestablish lost value; that it would create new value; and that society needs it as a conservation last resort. I also assessed several possible ethical arguments against pursuing de-extinction: that it is unnatural; that it could cause animal suffering; that it could be ecologically problematic or detrimental to human health; and that it is hubristic. There are reasons in favor of reviving long extinct species, and it can be ethically acceptable to do so. However, the reasons in favor of pursuing de-extinction do not have to do with its usefulness in species conservation; rather, they concern the status of revived species as scientific and technological achievements, and it would be ethically problematic to promote de-extinction as a significant conservation strategy, because it does not prevent species extinctions, does not address the causes of extinction, and could be detrimental to some species conservation efforts. Moreover, humanity does not have a responsibility or obligation to pursue de-extinction of long extinct species, and reviving them does not address any urgent problem. Therefore, legitimate ecological, political, animal welfare, legal, or human health concerns associated with a de-extinction (and reintroduction) must be thoroughly addressed for it to be ethically acceptable.

  9. Tobacco industry litigation strategies to oppose tobacco control media campaigns

    PubMed Central

    Ibrahim, J K; Glantz, Stanton A

    2006-01-01

    Objective To document the tobacco industry's litigation strategy to impede tobacco control media campaigns. Methods Data were collected from news and reports, tobacco industry documents, and interviews with health advocates and media campaign staff. Results RJ Reynolds and Lorillard attempted to halt California's Media Campaign alleging that the campaign polluted jury pools and violated First Amendment rights because they were compelled to pay for anti‐industry ads. The American Legacy Foundation was accused of violating the Master Settlement Agreement's vilification clause because its ads attacked the tobacco industry. The tobacco companies lost these legal challenges. Conclusion The tobacco industry has expanded its efforts to oppose tobacco control media campaigns through litigation strategies. While litigation is a part of tobacco industry business, it imposes a financial burden and impediment to media campaigns' productivity. Tobacco control professionals need to anticipate these challenges and be prepared to defend against them. PMID:16436406

  10. Dip coating in the presence of an opposing Marangoni stress.

    PubMed

    Gupta, Sumit; Tiwari, Naveen

    2017-01-01

    Theoretical analysis of the dip coating process of uniformly wetting and selectively wetting substrates with a shear-thinning power-law fluid is presented. The viscosity is modeled by a three-constant Ellis model that allows for Newtonian and power-law fluids at low and high shear, respectively. The effect of an opposing Marangoni stress is studied on the entrained film thickness. Ellis number and Marangoni number are the important parameters in the analysis that control the film thickness. Numerical results show that the film thickness is a monotonically decreasing function of these two parameters. A correlation between the parameters is found for both the surfaces to obtain an apparent "dry" substrate with a microscopically thin film attached to the surfaces.

  11. UXT plays dual opposing roles on SARM-induced apoptosis.

    PubMed

    Sethurathinam, Shalini; Singh, Laishram Pradeepkumar; Panneerselvam, Porkodi; Byrne, Bernadette; Ding, Jeak Ling

    2013-10-11

    Apoptosis is a vital defense mechanism for the clearance of infected cells. Ubiquitously expressed transcript (UXT), which exists in two isoforms (V1 and V2), interact with both apoptotic and cellular proteins. By yeast two-hybrid analysis, we found that UXT interacts with SARM (sterile α and HEAT armadillo motif-containing protein). Since SARM is a TLR adaptor which induces intrinsic apoptosis following immune activation, we were prompted to query whether UXT and SARM might co-regulate apoptosis. We found that the UXT isoforms elicit dual opposing regulatory effects on SARM-induced apoptosis; while UXT V1, co-expressed with SARM, caused a reduction in caspase 8 activity, UXT V2 strongly increased caspase 8 activity and enhanced SARM-induced apoptosis by activating the extrinsic pathway and depolarizing the mitochondria.

  12. Soret effect due to opposing flow in square porous annulus

    NASA Astrophysics Data System (ADS)

    Al-Rashed, Abdullah A. A. A.; Athani, Abdulgaphur; Khaleed, H. M. T.

    2016-06-01

    The present work is undertaken to investigate the behavior of opposing flow in porous medium under the influence of Soret effect in a square porous annulus. The boundary conditions are such that the outer walls of annulus are maintained at higher temperature and concentration as compared to inner walls. This heat and mass transfer phenomenon is governed by three partial differential equations. The differential equations are converted into a matrix form of equations by the application of finite element method and then solved using iterative algorithm. The results are presented in terms of isotherms, iso-concentration and streamlines indicating the thermal energy, concentration and fluid velocity inside the porous medium under applied boundary conditions. It found that the maximum value of stream function in porous medium decreases with decrease in buoyancy ratio.

  13. Dynamic modelling of mechanical systems with opposing restrained preloaded stiffnesses

    NASA Astrophysics Data System (ADS)

    Rogers, R. J.; Garland, P.; Oliver, M.

    2004-07-01

    Preloaded springs are used in many mechanical systems such as suspension systems and linkages, as well as household items such as clothing clasps. Usually, the preload has no effect on small amplitude dynamic responses which occur about the mean preloaded position. However if the system has opposing preloaded elastic elements, where unloading is limited by restraints such as central rods which preserve the preload, then the preload has a dramatic effect on a system's dynamic response. When such a system is set into free oscillation, the period of motion steadily decreases as the amplitude diminishes. Until now the authors have not seen this behavior described elsewhere. The present work is motivated by the modelling of joysticks which are used to actuate hydraulic systems in a wide variety of mobile construction and forestry equipment. Their use for long periods of time may lead to repetitive strain injuries in an operator's upper limbs, neck and back. In order to assess the total force required to move a joystick, the stiffness, damping and inertia characteristics must be determined. A mathematical model for joystick dynamics is presented and the effect of restrained spring preloads on the changing period of free vibration is explained. In addition, procedures to estimate the non-symmetric non-linear damping from experimental data are described. By simulating the dynamic response in MATLAB TM, the damping is fine-tuned by comparing the joystick's simulated free oscillation response with its experimental response. Finally, the torque waveform required to perform a simple joystick motion is estimated. The methods developed in this paper could be applied to any lumped-parameter mechanical system where there are opposing restrained preloaded elastic elements.

  14. Cumulative frequency distribution of past species extinctions

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1991-01-01

    Analysis of Sepkoski's compendium of the time ranges of 30,000+ taxa yields a mean duration of 28.4 ma for genera of fossil invertebrates. This converts to an average extinction rate of 3.5 percent per million years or about one percent every 286,000 years. Using survivorship techniques, these estimates can be converted to the species level, yielding a Phanerozoic average of one percent species extinction every 40,000 years. Variation in extinction rates through time is far greater than the null expectation of a homogeneous birth-death model and this reflects the well-known episodicity of extinction ranging from a few large mass extinctions to so-called background extinction. The observed variation in rates can be used to construct a cumulative frequency distribution of extinction intensity, and this distribution, in the form of a kill curve for species, shows the expected waiting times between extinction events of a given intensity. The kill curve is an average description of the extinction events of a given intensity. The kill curve is an average description of the extinction record and does not imply any cause or causes of extinction. The kill curve shows, among other things, that only about five percent of total species extinctions in the Phanerozoic were involved in the five largest mass extinctions. The other 95 percent were distributed among large and small events not normally called mass extinctions. As an exploration of the possibly absurd proposition that most past extinctions were produced by the effects of large-body impact, the kill curve for species was mapped on the comparable distribution for comet and asteroid impacts. The result is a curve predicting the species kill for a given size of impacting object (expressed as crater size). The results are reasonable in that impacts producing craters less than 30 km (diameter) cause negligible extinction but those producing craters 100-150 km (diameter) cause extinction of species in the range of 45

  15. Reach for Reference. No Opposition Here! Opposing Viewpoints Resource Center Is a Very Good Database

    ERIC Educational Resources Information Center

    Safford, Barbara Ripp

    2004-01-01

    "Opposing Viewpoints" and "Opposing Viewpoints Juniors" have long been standard titles in upper elementary, middle level, and high school collections. "Opposing Viewpoints Juniors" should be required as information literacy/critical thinking curriculum tools as early as fifth grade as they use current controversies to teach students how to…

  16. 32 CFR 776.43 - Fairness to opposing party and counsel.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 5 2010-07-01 2010-07-01 false Fairness to opposing party and counsel. 776.43... ADVOCATE GENERAL Rules of Professional Conduct § 776.43 Fairness to opposing party and counsel. (a) Fairness to opposing party and counsel. A covered attorney shall not: (1) Unlawfully obstruct another party...

  17. Reach for Reference. No Opposition Here! Opposing Viewpoints Resource Center Is a Very Good Database

    ERIC Educational Resources Information Center

    Safford, Barbara Ripp

    2004-01-01

    "Opposing Viewpoints" and "Opposing Viewpoints Juniors" have long been standard titles in upper elementary, middle level, and high school collections. "Opposing Viewpoints Juniors" should be required as information literacy/critical thinking curriculum tools as early as fifth grade as they use current controversies to teach students how to…

  18. Jet Substructure Without Trees

    SciTech Connect

    Jankowiak, Martin; Larkoski, Andrew J.; /SLAC /Stanford U., ITP

    2011-08-19

    We present an alternative approach to identifying and characterizing jet substructure. An angular correlation function is introduced that can be used to extract angular and mass scales within a jet without reference to a clustering algorithm. This procedure gives rise to a number of useful jet observables. As an application, we construct a top quark tagging algorithm that is competitive with existing methods. In preparation for the LHC, the past several years have seen extensive work on various aspects of collider searches. With the excellent resolution of the ATLAS and CMS detectors as a catalyst, one area that has undergone significant development is jet substructure physics. The use of jet substructure techniques, which probe the fine-grained details of how energy is distributed in jets, has two broad goals. First, measuring more than just the bulk properties of jets allows for additional probes of QCD. For example, jet substructure measurements can be compared against precision perturbative QCD calculations or used to tune Monte Carlo event generators. Second, jet substructure allows for additional handles in event discrimination. These handles could play an important role at the LHC in discriminating between signal and background events in a wide variety of particle searches. For example, Monte Carlo studies indicate that jet substructure techniques allow for efficient reconstruction of boosted heavy objects such as the W{sup {+-}} and Z{sup 0} gauge bosons, the top quark, and the Higgs boson.

  19. Light extinction in the atmosphere

    SciTech Connect

    Laulainen, N.

    1992-06-01

    Atmospheric aerosol particles originating from natural sources, such as volcanos and sulfur-bearing gas emissions from the oceans, and from human sources, such as sulfur emissions from fossil fuel combustion and biomass burning, strongly affect visual air quality and are suspected to significantly affect radiative climate forcing of the planet. During the daytime, aerosols obscure scenic vistas, while at night they diminish our ability to observe stellar objects. Scattering of light is the main means by which aerosols attenuate and redistribute light in the atmosphere and by which aerosols can alter and reduce visibility and potentially modify the energy balance of the planet. Trends and seasonal variability of atmospheric aerosol loading, such as column-integrated light extinction or optical depth, and how they may affect potential climate change have been difficult to quantify because there have been few observations made of important aerosol optical parameters, such as optical depth, over the globe and over time and often these are of uneven quality. To address questions related to possible climate change, there is a pressing need to acquire more high-quality aerosol optical depth data. Extensive deployment of improved solar radiometers over the next few years will provide higher-quality extinction data over a wider variety of locations worldwide. An often overlooked source of turbidity data, however, is available from astronomical observations, particularly stellar photoelectric photometry observations. With the exception of the Project ASTRA articles published almost 20 years ago, few of these data ever appear in the published literature. This paper will review the current status of atmospheric extinction observations, as highlighted by the ASTRA work and augmented by more recent solar radiometry measurements.

  20. Sexual selection protects against extinction.

    PubMed

    Lumley, Alyson J; Michalczyk, Łukasz; Kitson, James J N; Spurgin, Lewis G; Morrison, Catriona A; Godwin, Joanne L; Dickinson, Matthew E; Martin, Oliver Y; Emerson, Brent C; Chapman, Tracey; Gage, Matthew J G

    2015-06-25

    Reproduction through sex carries substantial costs, mainly because only half of sexual adults produce offspring. It has been theorized that these costs could be countered if sex allows sexual selection to clear the universal fitness constraint of mutation load. Under sexual selection, competition between (usually) males and mate choice by (usually) females create important intraspecific filters for reproductive success, so that only a subset of males gains paternity. If reproductive success under sexual selection is dependent on individual condition, which is contingent to mutation load, then sexually selected filtering through 'genic capture' could offset the costs of sex because it provides genetic benefits to populations. Here we test this theory experimentally by comparing whether populations with histories of strong versus weak sexual selection purge mutation load and resist extinction differently. After evolving replicate populations of the flour beetle Tribolium castaneum for 6 to 7 years under conditions that differed solely in the strengths of sexual selection, we revealed mutation load using inbreeding. Lineages from populations that had previously experienced strong sexual selection were resilient to extinction and maintained fitness under inbreeding, with some families continuing to survive after 20 generations of sib × sib mating. By contrast, lineages derived from populations that experienced weak or non-existent sexual selection showed rapid fitness declines under inbreeding, and all were extinct after generation 10. Multiple mutations across the genome with individually small effects can be difficult to clear, yet sum to a significant fitness load; our findings reveal that sexual selection reduces this load, improving population viability in the face of genetic stress.

  1. Light extinction in the atmosphere

    SciTech Connect

    Laulainen, N.

    1992-06-01

    Atmospheric aerosol particles originating from natural sources, such as volcanos and sulfur-bearing gas emissions from the oceans, and from human sources, such as sulfur emissions from fossil fuel combustion and biomass burning, strongly affect visual air quality and are suspected to significantly affect radiative climate forcing of the planet. During the daytime, aerosols obscure scenic vistas, while at night they diminish our ability to observe stellar objects. Scattering of light is the main means by which aerosols attenuate and redistribute light in the atmosphere and by which aerosols can alter and reduce visibility and potentially modify the energy balance of the planet. Trends and seasonal variability of atmospheric aerosol loading, such as column-integrated light extinction or optical depth, and how they may affect potential climate change have been difficult to quantify because there have been few observations made of important aerosol optical parameters, such as optical depth, over the globe and over time and often these are of uneven quality. To address questions related to possible climate change, there is a pressing need to acquire more high-quality aerosol optical depth data. Extensive deployment of improved solar radiometers over the next few years will provide higher-quality extinction data over a wider variety of locations worldwide. An often overlooked source of turbidity data, however, is available from astronomical observations, particularly stellar photoelectric photometry observations. With the exception of the Project ASTRA articles published almost 20 years ago, few of these data ever appear in the published literature. This paper will review the current status of atmospheric extinction observations, as highlighted by the ASTRA work and augmented by more recent solar radiometry measurements.

  2. Extinction debt: a challenge for biodiversity conservation.

    PubMed

    Kuussaari, Mikko; Bommarco, Riccardo; Heikkinen, Risto K; Helm, Aveliina; Krauss, Jochen; Lindborg, Regina; Ockinger, Erik; Pärtel, Meelis; Pino, Joan; Rodà, Ferran; Stefanescu, Constantí; Teder, Tiit; Zobel, Martin; Steffan-Dewenter, Ingolf

    2009-10-01

    Local extinction of species can occur with a substantial delay following habitat loss or degradation. Accumulating evidence suggests that such extinction debts pose a significant but often unrecognized challenge for biodiversity conservation across a wide range of taxa and ecosystems. Species with long generation times and populations near their extinction threshold are most likely to have an extinction debt. However, as long as a species that is predicted to become extinct still persists, there is time for conservation measures such as habitat restoration and landscape management. Standardized long-term monitoring, more high-quality empirical studies on different taxa and ecosystems and further development of analytical methods will help to better quantify extinction debt and protect biodiversity.

  3. Contrasting the overexpectation and extinction effects.

    PubMed

    Witnauer, James E; Miller, Ralph R

    2009-06-01

    After many target stimulus (X)-unconditioned stimulus (US) pairings, further conditioning of X in the presence of another well-established signal for the US (A) disrupts X's behavioral control. Some researchers have argued that the mechanism underlying this so-called overexpectation effect is similar to that underlying extinction (a reduction in X's behavioral control due to X-alone presentations). Three conditioned suppression experiments with rats as subjects compared overexpectation and extinction. Experiment 1 replicated the basic overexpectation effect by showing that A disrupts responding to X more than does a previously neutral stimulus. Experiment 2 found that posttraining context exposure disrupts extinction but not overexpectation. Experiment 3 suggested that overexpectation and extinction are differentially sensitive to the effects of overtraining (compound reinforced or nonreinforced, respectively), such that extinction is enhanced by increases in the amount of nonreinforced trials and overexpectation is unaffected. These results are inconsistent with the view that overexpectation and extinction are driven by a common mechanism.

  4. Microwave extinction characteristics of nanoparticle aggregates

    NASA Astrophysics Data System (ADS)

    Wu, Y. P.; Cheng, J. X.; Liu, X. X.; Wang, H. X.; Zhao, F. T.; Wen, W. W.

    2016-07-01

    Structure of nanoparticle aggregates plays an important role in microwave extinction capacity. The diffusion-limited aggregation model (DLA) for fractal growth is utilized to explore the possible structures of nanoparticle aggregates by computer simulation. Based on the discrete dipole approximation (DDA) method, the microwave extinction performance by different nano-carborundum aggregates is numerically analyzed. The effects of the particle quantity, original diameter, fractal structure, as well as orientation on microwave extinction are investigated, and also the extinction characteristics of aggregates are compared with the spherical nanoparticle in the same volume. Numerical results give out that proper aggregation of nanoparticle is beneficial to microwave extinction capacity, and the microwave extinction cross section by aggregated granules is better than that of the spherical solid one in the same volume.

  5. Laboratory-produced MHD plasma jets

    NASA Astrophysics Data System (ADS)

    Bellan, Paul

    2008-04-01

    Because space plasmas are neither confined by vacuum chamber walls nor have magnetic fields produced by physical coils, space plasmas have shapes that are much less determinate than lab plasmas. An experimental program underway at Caltech produces plasmas where the shape is neither fixed by a vacuum chamber wall nor imposed by an external coil set, but rather is allowed to be determined by self-organizing MHD processes subject to the constraint of imposed boundary conditions analogous to the boundary conditions of space plasmas. These self-organizing processes are believed to be fundamental to astrophysical jets, solar coronal loops, and MHD turbulence (e.g. Taylor relaxation). The experimental dynamics are sufficiently reproducible to allow detailed study despite the morphology being complex and dynamic. A surprising result has been the observation that instead of the plasma uniformly filling up the available volume, the plasma is spatially localized in a highly collimated, small diameter magnetic flux tube, the length and axis of which change in time in response to MHD forces. A model shows that the collimation results from stagnation of linked magnetic flux frozen into a MHD-driven jet that accelerates plasma from the wall into the flux tube, filling the flux tube with plasma. Jet flow has been imaged with a high-speed multi-frame camera, diagnosed via Doppler spectroscopy, and most recently (i) the collision between two opposing, color-coded jets flowing from opposite ends of a flux tube has been observed, and (ii) the collision of a jet with a target cloud has been observed.

  6. Comment on the extinct paradox

    NASA Technical Reports Server (NTRS)

    Levine, D. M.

    1983-01-01

    The extinction paradox is a contradiction between geometrical optics results which predict that at high frequencies the scattering cross section of an object should equal its geometrical cross section and rigorous scattering theory which shows that at high frequencies the scattering cross section approaches twice the geometrical cross section of the object. Confusion about the reason for this paradox persists today even though the nature of the paradox was correctly identified many years ago by Brillouin. The resolution of the paradox is restated and illustrated with an example, and then the implications to the interpretation of scattering cross sections are identified.

  7. Mass extinctions and missing matter

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.

    1984-01-01

    The possible influence of 'invisible matter' on the solar system's comet halo, and therefore on quasi-periodic cometary bombardment of the earth and consequent mass extinctions, is briefly addressed. Invisible matter consisting of small or cold interstellar molecular clouds could significantly modulate the comet background flux, while invisible matter consisting of a large population of old, dead stars with a relatively small galactic concentration probably could not. It is also shown that the downward force exerted by the Galaxy will perturb the halo, but will not produce any periodicity.

  8. Mass extinctions and missing matter

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.

    1984-01-01

    The possible influence of 'invisible matter' on the solar system's comet halo, and therefore on quasi-periodic cometary bombardment of the earth and consequent mass extinctions, is briefly addressed. Invisible matter consisting of small or cold interstellar molecular clouds could significantly modulate the comet background flux, while invisible matter consisting of a large population of old, dead stars with a relatively small galactic concentration probably could not. It is also shown that the downward force exerted by the Galaxy will perturb the halo, but will not produce any periodicity.

  9. The astronomical pulse of global extinction events.

    PubMed

    Lewis, David F V; Dorne, Jean-Lou C M

    2006-06-23

    The linkage between astronomical cycles and the periodicity of mass extinctions is reviewed and discussed. In particular, the apparent 26 million year cycle of global extinctions may be related to the motion of the solar system around the galaxy, especially perpendicular to the galactic plane. The potential relevance of Milankovitch cycles is also explored in the light of current evidence for the possible causes of extinction events over a geological timescale.

  10. Mass extinctions, large-body impacts and flood-basalt eruptions: Correlation suggests cataclysms from above or below

    NASA Astrophysics Data System (ADS)

    Rampino, M. R.

    2016-12-01

    Many studies have associated mass extinctions with large-body impacts and flood-basalt eruptions, often as opposing explanations. In comparing the three data sets, we find that at least 8 of a total of 11 extinction events over the last 260 Myr coincide with either a large impact or a continental flood-basalt eruption. The null hypothesis that this could occur by chance can be rejected with very high confidence (>99.99%). The four mass-extinction/flood-basalt correlations involve the four largest eruptions. The null hypothesis that extinction events occur at the same time as either one of the 6 largest impacts or one of the 4 largest flood basalts by chance can also be rejected with a very high degree of confidence (>99.99%). These statistical relationships argue strongly that mass extinctions are tied to both the largest impacts and the largest flood-basalt eruptions. The most severe anoxic events in the oceans of the last 260 Myr are correlated with flood-basalt eruptions, and are coeval with extinction events, suggesting a causal connection.

  11. Mass extinctions vs. uniformitarianism in biological evolution

    SciTech Connect

    Bak, P.; Paczuski, M.

    1995-12-31

    It is usually believed that Darwin`s theory leads to a smooth gradual evolution, so that mass extinctions must be caused by external shocks. However, it has recently been argued that mass extinctions arise from the intrinsic dynamics of Darwinian evolution. Species become extinct when swept by intermittent avalanches propagating through the global ecology. These ideas are made concrete through studies of simple mathematical models of co-evolving species. The models exhibit self-organized criticality and describe some general features of the extinction pattern in the fossil record.

  12. Secondary extinction in Pavlovian fear conditioning.

    PubMed

    Vurbic, Drina; Bouton, Mark E

    2011-09-01

    Pavlov (1927/1960) reported that following the conditioning of several stimuli, extinction of one conditioned stimulus (CS) attenuated responding to others that had not undergone direct extinction. However, this secondary extinction effect has not been widely replicated in the contemporary literature. In three conditioned suppression experiments with rats, we further explored the phenomenon. In Experiment 1, we asked whether secondary extinction is more likely to occur with target CSs that have themselves undergone some prior extinction. A robust secondary extinction effect was obtained with a nonextinguished target CS. Experiment 2 showed that extinction of one CS was sufficient to reduce renewal of a second CS when it was tested in a neutral (nonextinction) context. In Experiment 3, secondary extinction was observed in groups that initially received intermixed conditioning trials with the target and nontarget CSs, but not in groups that received conditioning of the two CSs in separate sessions. The results are consistent with the hypothesis that CSs must be associated with a common temporal context during conditioning for secondary extinction to occur.

  13. Extinction and Autoignition of n-Heptane in Counterflow Configuration

    SciTech Connect

    Seiser, R.; Pitsch, H.; Seshadri, K.; Pitz, W.J.; Curran, H.J.

    2000-01-12

    A study is performed to elucidate the mechanisms of extinction and autoignition of n-heptane in strained laminar flows under nonpremixed conditions. A previously developed detailed mechanism made UP of 2540 reversible elementary reactions among 557 species is the starting point for the study. The detailed mechanism was previously used to calculate ignition delay times in homogeneous reactors, and concentration histories of a number of species in plug-flow and jet-stirred reactors. An intermediate mechanism made up of 1282 reversible elementary reactions among 282 species and a short mechanism made up of 770 reversible elementary reactions among 160 species are assembled from this detailed mechanism. Ignition delay times in an isochoric homogeneous reactor calculated using the intermediate and the short mechanism are found to agree well with those calculated using the detailed mechanism. The intermediate and the short mechanism are used to calculate extinction and autoignition of n-heptane in strained laminar flows. Steady laminar flow of two counter flowing Streams toward a stagnation plane is considered. One stream made up of prevaporized n-heptane and nitrogen is injected from the fuel boundary and the other stream made up of air and nitrogen is injected from the oxidizer boundary. Critical conditions of extinction and autoignition given by the strain rate, temperature and concentrations of the reactants at the boundaries, are calculated. The results are found to agree well with experiments. Sensitivity analysis is carried out to evaluate the influence of various elementary reactions on autoignition. At all values of the strain rate investigated here, high temperature chemical processes are found to control autoignition. In general, the influence of low temperature chemistry is found to increase with decreasing strain. A key finding of the present study is that strain has more influence on low temperature chemistry than the temperature of the reactants.

  14. Lumbar lordosis of extinct hominins.

    PubMed

    Been, Ella; Gómez-Olivencia, Asier; Kramer, Patricia A

    2012-01-01

    The lordotic curvature of the lumbar spine (lumbar lordosis) in humans is a critical component in the ability to achieve upright posture and bipedal gait. Only general estimates of the lordotic angle (LA) of extinct hominins are currently available, most of which are based on the wedging of the vertebral bodies. Recently, a new method for calculating the LA in skeletal material has become available. This method is based on the relationship between the lordotic curvature and the orientation of the inferior articular processes relative to vertebral bodies in the lumbar spines of living primates. Using this relationship, we developed new regression models in order to calculate the LAs in hominins. The new models are based on primate group-means and were used to calculate the LAs in the spines of eight extinct hominins. The results were also compared with the LAs of modern humans and modern nonhuman apes. The lordotic angles of australopithecines (41° ± 4), H. erectus (45°) and fossil H. sapiens (54° ± 14) are similar to those of modern humans (51° ± 11). This analysis confirms the assumption that human-like lordotic curvature was a morphological change that took place during the acquisition of erect posture and bipedalism as the habitual form of locomotion. Neandertals have smaller lordotic angles (LA = 29° ± 4) than modern humans, but higher angles than nonhuman apes (22° ± 3). This suggests possible subtle differences in Neandertal posture and locomotion from that of modern humans.

  15. Extinction-Optimized Volume Illumination.

    PubMed

    Ament, Marco; Zirr, Tobias; Dachsbacher, Carsten

    2016-05-16

    We present a novel method to optimize the attenuation of light for the single scattering model in direct volume rendering. A common problem of single scattering is the high dynamic range between lit and shadowed regions due to the exponential attenuation of light along a ray. Moreover, light is often attenuated too strong between a sample point and the camera, hampering the visibility of important features. Our algorithm employs an importance function to selectively illuminate important structures and make them visible from the camera. With the importance function, more light can be transmitted to the features of interest, while contextual structures cast shadows which provide visual cues for perception of depth. At the same time, more scattered light is transmitted from the sample point to the camera to improve the primary visibility of important features. We formulate a minimization problem that automatically determines the extinction along a view or shadow ray to obtain a good balance between sufficient transmittance and attenuation. In contrast to previous approaches, we do not require a computationally expensive solution of a global optimization, but instead provide a closed-form solution for each sampled extinction value along a view or shadow ray and thus achieve interactive performance.

  16. Phylogenetic Clustering of Origination and Extinction across the Late Ordovician Mass Extinction.

    PubMed

    Krug, Andrew Z; Patzkowsky, Mark E

    2015-01-01

    Mass extinctions can have dramatic effects on the trajectory of life, but in some cases the effects can be relatively small even when extinction rates are high. For example, the Late Ordovician mass extinction is the second most severe in terms of the proportion of genera eliminated, yet is noted for the lack of ecological consequences and shifts in clade dominance. By comparison, the end-Cretaceous mass extinction was less severe but eliminated several major clades while some rare surviving clades diversified in the Paleogene. This disconnect may be better understood by incorporating the phylogenetic relatedness of taxa into studies of mass extinctions, as the factors driving extinction and recovery are thought to be phylogenetically conserved and should therefore promote both origination and extinction of closely related taxa. Here, we test whether there was phylogenetic selectivity in extinction and origination using brachiopod genera from the Middle Ordovician through the Devonian. Using an index of taxonomic clustering (RCL) as a proxy for phylogenetic clustering, we find that A) both extinctions and originations shift from taxonomically random or weakly clustered within families in the Ordovician to strongly clustered in the Silurian and Devonian, beginning with the recovery following the Late Ordovician mass extinction, and B) the Late Ordovician mass extinction was itself only weakly clustered. Both results stand in stark contrast to Cretaceous-Cenozoic bivalves, which showed significant levels of taxonomic clustering of extinctions in the Cretaceous, including strong clustering in the mass extinction, but taxonomically random extinctions in the Cenozoic. The contrasting patterns between the Late Ordovician and end-Cretaceous events suggest a complex relationship between the phylogenetic selectivity of mass extinctions and the long-term phylogenetic signal in origination and extinction patterns.

  17. Phylogenetic Clustering of Origination and Extinction across the Late Ordovician Mass Extinction

    PubMed Central

    Krug, Andrew Z.; Patzkowsky, Mark E.

    2015-01-01

    Mass extinctions can have dramatic effects on the trajectory of life, but in some cases the effects can be relatively small even when extinction rates are high. For example, the Late Ordovician mass extinction is the second most severe in terms of the proportion of genera eliminated, yet is noted for the lack of ecological consequences and shifts in clade dominance. By comparison, the end-Cretaceous mass extinction was less severe but eliminated several major clades while some rare surviving clades diversified in the Paleogene. This disconnect may be better understood by incorporating the phylogenetic relatedness of taxa into studies of mass extinctions, as the factors driving extinction and recovery are thought to be phylogenetically conserved and should therefore promote both origination and extinction of closely related taxa. Here, we test whether there was phylogenetic selectivity in extinction and origination using brachiopod genera from the Middle Ordovician through the Devonian. Using an index of taxonomic clustering (RCL) as a proxy for phylogenetic clustering, we find that A) both extinctions and originations shift from taxonomically random or weakly clustered within families in the Ordovician to strongly clustered in the Silurian and Devonian, beginning with the recovery following the Late Ordovician mass extinction, and B) the Late Ordovician mass extinction was itself only weakly clustered. Both results stand in stark contrast to Cretaceous-Cenozoic bivalves, which showed significant levels of taxonomic clustering of extinctions in the Cretaceous, including strong clustering in the mass extinction, but taxonomically random extinctions in the Cenozoic. The contrasting patterns between the Late Ordovician and end-Cretaceous events suggest a complex relationship between the phylogenetic selectivity of mass extinctions and the long-term phylogenetic signal in origination and extinction patterns. PMID:26658946

  18. Interpretation of extragalactic jets

    SciTech Connect

    Norman, M.L.

    1985-01-01

    The nature of extragalatic radio jets is modeled. The basic hypothesis of these models is that extragalatic jets are outflows of matter which can be described within the framework of fluid dynamics and that the outflows are essentially continuous. The discussion is limited to the interpretation of large-scale (i.e., kiloparsec-scale) jets. The central problem is to infer the physical parameters of the jets from observed distributions of total and polarized intensity and angle of polarization as a function of frequency. 60 refs., 6 figs.

  19. The jet in crossflowa)

    NASA Astrophysics Data System (ADS)

    Karagozian, Ann R.

    2014-10-01

    The jet in crossflow, or transverse jet, is a flowfield that has relevance to a wide range of energy and propulsion systems. Over the years, our group's studies on this canonical flowfield have focused on the dynamics of the vorticity associated with equidensity and variable density jets in crossflow, including the stability characteristics of the jet's upstream shear layer, as a means of explaining jet response to altered types of excitation. The jet's upstream shear layer is demonstrated to exhibit convectively unstable behavior at high jet-to-crossflow momentum flux ratios, transitioning to absolutely unstable behavior at low momentum flux and/or density ratios, with attendant differences in shear layer vorticity evolution and rollup. These differences in stability characteristics are shown to have a significant effect on how one optimally employs external excitation to control jet penetration and spread, depending on the flow regime and specific engineering application. Yet recent unexpected observations on altered transverse jet structure under different flow conditions introduce a host of unanswered questions, primarily but not exclusively associated with the nature of molecular mixing, that make this canonical flowfield one that is of great interest for more extensive exploration.

  20. The remarkable AGN jets

    NASA Astrophysics Data System (ADS)

    Komissarov, Serguei

    The jets from active galactic nuclei exhibit stability which seems to be far superior compared to that of terrestrial and laboratory jets. They manage to propagate over distances up to a billion of initial jet radii. Yet this may not be an indication of some exotic physics but mainly a reflection of the specific environment these jets propagate through. The key property of this environment is a rapid decline of density and pressure along the jet, which promotes its rapid expansion. Such an expansion can suppress global instabilities, which require communication across the jet, and hence ensure its survival over huge distances. At kpc scales, some AGN jets do show signs of strong instabilities and even turn into plumes. This could be a result of the flattening of the external pressure distribution in their host galaxies or inside the radio lobes. In this regard, we discuss the possible connection between the stability issue and the Fanaroff-Riley classification of extragalactic radio sources. The observations of AGN jets on sub-kpc scale do not seem to support their supposed lack of causal connectivity. When interpreted using simple kinematic models, they reveal a rather perplexing picture with more questions than answers on the jets dynamics.

  1. Joint PDF Modelling of Local Extinction and Pollutant Formation in Non-premixed Turbulent Flames

    NASA Astrophysics Data System (ADS)

    Tang, Qing; Xu, Jun; Pope, Stephen B.

    2000-11-01

    A velocity-composition-turbulence frequency joint PDF approach is applied to model piloted methane/air turbulent diffusion flames investigated experimentally by Barlow and Frank. These flames exhibit an increasing amount of local extinction with increasing jet velocity, and are good cases to test the capabilities of turbulence-chemistry and combustion-chemistry models to account for local extinction and pollutant formation. In this study, the chemistry is an augmented reduced mechanism (19 species and 15 reaction steps) derived from the GRI2.11 detailed mechanism for methane oxidation by Sung and co-workers. The mechanism takes account of C2 chemistry, and the formation of oxides of nitrogen is treated by the inclusion of NO, NH3 and HCN. The turbulence models include the simplified Langevin model (SLM) for velocity, a stochastic model of Jayesh and Pope for turbulence frequency, the EMST model of Subramaniam and Pope for molecular mixing. The computational method for the solution of the modeled joint PDF equation features moving particles in a Lagrangian framework. The reaction calculations are performed via the in situ adaptive tabulation (ISAT) algorithm of Pope. The calculation results show good agreement with the experimental data, including the minor species NO and CO. The increase of local extinction (quantitatively characterized by a single variable - burning index) with increasing jet velocity is also accurately predicted by the calculations. It is founded that a small change of the inlet pilot temperature has a significant influence on the calculations and a systematic study has been made to investigate this sensitivity. For the flame with lowest velocity, the large influence is mainly observed close to the nozzle, while for the flame close to extinction, the calculated behavior is exquisitely sensitive to the pilot temperature, i.e., a 10K lower pilot temperature may cause global extinction.

  2. Constraints on Enhanced Extinction Resulting from Extinction Treatment in the Presence of an Added Excitor

    ERIC Educational Resources Information Center

    Urcelay, Gonzalo P.; Lipatova, Olga; Miller, Ralph R.

    2009-01-01

    Three Pavlovian fear conditioning experiments with rats as subjects explored the effect of extinction in the presence of a concurrent excitor. Our aim was to explore this particular treatment, documented in previous studies to deepen extinction, with novel control groups to shed light on the processes involved in extinction. Relative to subjects…

  3. Constraints on Enhanced Extinction Resulting from Extinction Treatment in the Presence of an Added Excitor

    ERIC Educational Resources Information Center

    Urcelay, Gonzalo P.; Lipatova, Olga; Miller, Ralph R.

    2009-01-01

    Three Pavlovian fear conditioning experiments with rats as subjects explored the effect of extinction in the presence of a concurrent excitor. Our aim was to explore this particular treatment, documented in previous studies to deepen extinction, with novel control groups to shed light on the processes involved in extinction. Relative to subjects…

  4. Fear conditioning and extinction: emotional states encoded by distinct signaling pathways

    PubMed Central

    Tronson, Natalie C.; Corcoran, Kevin A.; Jovasevic, Vladimir; Radulovic, Jelena

    2011-01-01

    Conditioning and extinction of fear have traditionally been viewed as two independent learning processes for encoding representations of contexts or cues (conditioned stimuli, CS), aversive events (unconditioned stimuli, US), and their relationship. Based on the analysis of protein kinase signaling patterns in neurons of the fear circuit, we propose that fear and extinction are best conceptualized as emotional states triggered by a single CS representation with two opposing values: aversive and non-aversive. These values are conferred by the presence or absence of the US and encoded by distinct sets of kinase signaling pathways and their downstream targets. Modulating specific protein kinases thus has the potential to modify emotional states, and hence, may emerge as a promising treatment for anxiety disorders. PMID:22118930

  5. Prevalence of the Extinction Burst and Its Attenuation during Treatment.

    ERIC Educational Resources Information Center

    Lerman, Dorothea C.; Iwata, Brian A.

    1995-01-01

    A commonly associated side effect of extinction as a treatment for behavior disorders is an initial increased frequency of the target response, called an "extinction burst." This study analyzed 113 sets of extinction data and found that extinction bursting occurred in only 24% of cases and was less common when extinction was combined…

  6. Extinction and the spatial dynamics of biodiversity

    PubMed Central

    Jablonski, David

    2008-01-01

    The fossil record amply shows that the spatial fabric of extinction has profoundly shaped the biosphere; this spatial dimension provides a powerful context for integration of paleontological and neontological approaches. Mass extinctions evidently alter extinction selectivity, with many factors losing effectiveness except for a positive relation between survivorship and geographic range at the clade level (confirmed in reanalyses of end-Cretaceous extinction data). This relation probably also holds during “normal” times, but changes both slope and intercept with increasing extinction. The strong geographical component to clade dynamics can obscure causation in the extinction of a feature or a clade, owing to hitchhiking effects on geographic range, so that multifactorial analyses are needed. Some extinctions are spatially complex, and regional extinctions might either reset a diversity ceiling or create a diversification debt open to further diversification or invasion. Evolutionary recoveries also exhibit spatial dynamics, including regional differences in invasibilty, and expansion of clades from the tropics fuels at least some recoveries, as well as biodiversity dynamics during normal times. Incumbency effects apparently correlate more closely with extinction intensities than with standing diversities, so that regions with higher local and global extinctions are more subject to invasion; the latest Cenozoic temperate zones evidently received more invaders than the tropics or poles, but this dynamic could shift dramatically if tropical diversity is strongly depleted. The fossil record can provide valuable insights, and their application to present-day issues will be enhanced by partitioning past and present-day extinctions by driving mechanism rather than emphasizing intensity. PMID:18695229

  7. Modulation of the extinction of fear learning.

    PubMed

    Myskiw, Jociane C; Izquierdo, Ivan; Furini, Cristiane R G

    2014-06-01

    We review recent work on extinction learning with emphasis on its modulation. Extinction is the learned inhibition of responding to previously acquired tasks. Like other forms of learning, it can be modulated by a variety of neurotransmitter systems and behavioral procedures. This bears on its use in the treatment of fear memories, particularly in posttraumatic stress disorder (PTSD), for which it is the treatment of choice, often under the name of exposure therapy. There have not been many laboratories interested in the modulation of extinction, but the available data, although not very abundant, are quite conclusive. Most studies on the nature of extinction and on its modulation have been carried out on fear motivated behaviors, possibly because of their applicability to the therapy of PTSD. A role for d-serine and the glycine site of NMDA receptors has been ascertained in two forms of extinction in the ventromedial prefrontal cortex, basolateral amygdala and dorsal hippocampus. The serine analog, d-cycloserine, has received clinical trials as an enhancer of extinction. The brain histaminergic system acting via H2 receptors, and the endocannabinoid system using CB1 receptors in the ventromedial prefrontal cortex, hippocampus and basolateral amygdala enhance extinction. Dopaminergic D1 and ß-noradrenergic receptors also modulate extinction by actions on these three structures. Isolated findings suggest roles for on serotonin-1A, dopaminergic-D2 and a- and ß-noradrenergic receptors in extinction modulation. Importantly, behavioral tagging and capture mechanisms in the hippocampus have been shown to play a major modulatory role in extinction. In addition, extinction of at least one aversive task (inhibitory avoidance) can be made state dependent on peripheral epinephrine.

  8. Sensory cortical population dynamics uniquely track behavior across learning and extinction.

    PubMed

    Moran, Anan; Katz, Donald B

    2014-01-22

    Neural responses in many cortical regions encode information relevant to behavior: information that necessarily changes as that behavior changes with learning. Although such responses are reasonably theorized to be related to behavior causation, the true nature of that relationship cannot be clarified by simple learning studies, which show primarily that responses change with experience. Neural activity that truly tracks behavior (as opposed to simply changing with experience) will not only change with learning but also change back when that learning is extinguished. Here, we directly probed for this pattern, recording the activity of ensembles of gustatory cortical single neurons as rats that normally consumed sucrose avidly were trained first to reject it (i.e., conditioned taste aversion learning) and then to enjoy it again (i.e., extinction), all within 49 h. Both learning and extinction altered cortical responses, consistent with the suggestion (based on indirect evidence) that extinction is a novel form of learning. But despite the fact that, as expected, postextinction single-neuron responses did not resemble "naive responses," ensemble response dynamics changed with learning and reverted with extinction: both the speed of stimulus processing and the relationships among ensemble responses to the different stimuli tracked behavioral relevance. These data suggest that population coding is linked to behavior with a fidelity that single-neuron coding is not.

  9. Affective-associative two-process theory: a neurocomputational account of partial reinforcement extinction effects.

    PubMed

    Lowe, Robert; Almér, Alexander; Billing, Erik; Sandamirskaya, Yulia; Balkenius, Christian

    2017-09-14

    The partial reinforcement extinction effect (PREE) is an experimentally established phenomenon: behavioural response to a given stimulus is more persistent when previously inconsistently rewarded than when consistently rewarded. This phenomenon is, however, controversial in animal/human learning theory. Contradictory findings exist regarding when the PREE occurs. One body of research has found a within-subjects PREE, while another has found a within-subjects reversed PREE (RPREE). These opposing findings constitute what is considered the most important problem of PREE for theoreticians to explain. Here, we provide a neurocomputational account of the PREE, which helps to reconcile these seemingly contradictory findings of within-subjects experimental conditions. The performance of our model demonstrates how omission expectancy, learned according to low probability reward, comes to control response choice following discontinuation of reward presentation (extinction). We find that a PREE will occur when multiple responses become controlled by omission expectation in extinction, but not when only one omission-mediated response is available. Our model exploits the affective states of reward acquisition and reward omission expectancy in order to differentially classify stimuli and differentially mediate response choice. We demonstrate that stimulus-response (retrospective) and stimulus-expectation-response (prospective) routes are required to provide a necessary and sufficient explanation of the PREE versus RPREE data and that Omission representation is key for explaining the nonlinear nature of extinction data.

  10. The Role of the Medial Prefrontal Cortex in the Conditioning and Extinction of Fear

    PubMed Central

    Giustino, Thomas F.; Maren, Stephen

    2015-01-01

    Once acquired, a fearful memory can persist for a lifetime. Although learned fear can be extinguished, extinction memories are fragile. The resilience of fear memories to extinction may contribute to the maintenance of disorders of fear and anxiety, including post-traumatic stress disorder (PTSD). As such, considerable effort has been placed on understanding the neural circuitry underlying the acquisition, expression, and extinction of emotional memories in rodent models as well as in humans. A triad of brain regions, including the prefrontal cortex, hippocampus, and amygdala, form an essential brain circuit involved in fear conditioning and extinction. Within this circuit, the prefrontal cortex is thought to exert top-down control over subcortical structures to regulate appropriate behavioral responses. Importantly, a division of labor has been proposed in which the prelimbic (PL) and infralimbic (IL) subdivisions of the medial prefrontal cortex (mPFC) regulate the expression and suppression of fear in rodents, respectively. Here, we critically review the anatomical and physiological evidence that has led to this proposed dichotomy of function within mPFC. We propose that under some conditions, the PL and IL act in concert, exhibiting similar patterns of neural activity in response to aversive conditioned stimuli and during the expression or inhibition of conditioned fear. This may stem from common synaptic inputs, parallel downstream outputs, or cortico-cortical interactions. Despite this functional covariation, these mPFC subdivisions may still be coding for largely opposing behavioral outcomes, with PL biased towards fear expression and IL towards suppression. PMID:26617500

  11. Laminar Jet Diffusion Flame Burning

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence, using propane fuel, was taken STS-94, July 4 1997, MET:2/05:30 (approximate). LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel-like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (983KB, 9-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300184.html.

  12. Assessing coexisting plant extinction debt and colonization credit in a grassland-forest change gradient.

    PubMed

    Bagaria, Guillem; Helm, Aveliina; Rodà, Ferran; Pino, Joan

    2015-11-01

    Changes in species richness along the ecological succession gradient may be strongly determined by coexisting extinction debts of species from the original habitats and colonization credits of those from the replacing habitats. The magnitude of these processes and their causes remain largely unknown. We explored the extinction debt and colonization credit for grassland and forest specialist plants, respectively, and the local and landscape factors associated to the richness of these species groups in a 50-year process of forest encroachment into semi-natural Mediterranean grasslands. A set of sampling plots of persistent grasslands and forests and their transitional habitat (wooded grasslands) was selected within fixed-area sites distributed across the landscape. Our results confirm the extinction debt and suggest colonization credit (according to observed trends and model predictions) in wooded grasslands when compared to persistent forests, despite wooded grasslands and persistent forests having similar tree cover. Grassland connectivity and solar radiation had opposing effects on the richness of both grassland and forest specialists, and it is possible that the availability of seed sources from old forests may have accelerate the payment of colonization credit in the wooded grasslands. These results suggest that extinction debt and colonization credit have driven species turnover during the 50 years of forest encroachment, but at different rates, and that local and landscape factors have opposing effects on these two phenomena. They also highlight the importance of documenting biodiversity time lags following habitat change when they are still in progress in order to timely and adequately manage habitats of high conservation value such as the grasslands studied here.

  13. Experimental Validation Dataset for CFD Simulations of Buoyancy Opposed Convection

    NASA Astrophysics Data System (ADS)

    Harris, Jeff; Lance, Blake; Smith, Barton

    2013-11-01

    New experiments in the Rotatable Buoyancy Tunnel are described. This unique facility was built specifically for computational fluid dynamics (CFD) validation experiments in natural, forced, and mixed convection in both buoyancy aided or opposed scenarios. The tunnel features clear walls for non-intrusive optical measurements, a heated wall (controlled to isothermal or constant flux conditions), and the capability to invert without changing the inlet or as-built dimensions. The wall temperature and inlet temperature are measured, along with the inlet velocity and turbulence profiles, to define simulation boundary conditions. The experiment includes acquisition of particle image velocimetry data at several streamwise locations in the boundary layer along the heated plate. Heat flux at those locations is also measured. The flow consists of natural convection driving air upwards combined with forced convection (fan driven) drawing air down. A RANS CFD simulation for this scenario is presented, with a comparison of several models' computed boundary layer flow, heat flux, and pressure drop to the measured values of the same. This research is being performed using funding received from the DOE Office of Nuclear Energy's Nuclear Energy University Programs.

  14. Opposing phylogenetic diversity gradients of plant and soil bacterial communities.

    PubMed

    Goberna, Marta; Navarro-Cano, Jose A; Verdú, Miguel

    2016-02-24

    Plants and soil microbes show parallel patterns of species-level diversity. Diverse plant communities release a wider range of organics that are consumed by more microbial species. We speculated, however, that diversity metrics accounting for the evolutionary distance across community members would reveal opposing patterns between plant and soil bacterial phylogenetic diversity. Plant phylogenetic diversity enhances plant productivity and thus expectedly soil fertility. This, in turn, might reduce bacterial phylogenetic diversity by favouring one (or a few) competitive bacterial clade. We collected topsoils in 15 semi-arid plant patches and adjacent low-cover areas configuring a plant phylodiversity gradient, pyrosequenced the 16S rRNA gene to identify bacterial taxa and analysed soil fertility parameters. Structural equation modelling showed positive effects of both plant richness and phylogenetic diversity on soil fertility. Fertility increased bacterial richness but reduced bacterial phylogenetic diversity. This might be attributed to the competitive dominance of a lineage based on its high relative fitness. This suggests biotic interactions as determinants of the soil bacterial community assembly, while emphasizing the need to use phylogeny-informed metrics to tease apart the processes underlying the patterns of diversity.

  15. The opposing roles of laminin-binding integrins in cancer.

    PubMed

    Ramovs, Veronika; Te Molder, Lisa; Sonnenberg, Arnoud

    2017-01-01

    Integrins play an important role in cell adhesion by linking the cytoskeleton of cells to components in the extracellular matrix. In this capacity, integrins cooperate with different cell surface receptors, including growth factor receptors and G-protein coupled receptors, to regulate intracellular signaling pathways that control cell polarization, spreading, migration, survival, and gene expression. A distinct subfamily of molecules in the integrin family of adhesion receptors is formed by receptors that mediate cell adhesion to laminins, major components of the basement membrane that lie under clusters of cells or surround them, separating them from other cells and/or adjacent connective tissue. During the past decades, many studies have provided evidence for a role of laminin-binding integrins in tumorigenesis, and both tumor-promoting and suppressive activities have been identified. In this review we discuss the dual role of the laminin-binding integrins α3β1 and α6β4 in tumor development and progression, and examine the factors and mechanisms involved in these opposing effects.

  16. Opposing plant community responses to warming with and without herbivores.

    PubMed

    Post, Eric; Pedersen, Christian

    2008-08-26

    If controls over primary productivity and plant community composition are mainly environmental, as opposed to biological, then global change may result in large-scale alterations in ecosystem structure and function. This view appears to be favored among investigations of plant biomass and community responses to experimental and observed warming. In far northern and arctic ecosystems, such studies predict increasing dominance of woody shrubs with future warming and emphasize the carbon (C)-sequestration potential and consequent atmospheric feedback potential of such responses. In contrast to previous studies, we incorporated natural herbivory by muskoxen and caribou into a 5-year experimental investigation of arctic plant community response to warming. In accordance with other studies, warming increased total community biomass by promoting growth of deciduous shrubs (dwarf birch and gray willow). However, muskoxen and caribou reduced total community biomass response, and responses of birch and willow, to warming by 19%, 46%, and 11%, respectively. Furthermore, under warming alone, the plant community shifted after 5 years away from graminoid-dominated toward dwarf birch-dominated. In contrast, where herbivores grazed, plant community composition on warmed plots did not differ from that on ambient plots after 5 years. These results highlight the potentially important and overlooked influences of vertebrate herbivores on plant community response to warming and emphasize that conservation and management of large herbivores may be an important component of mitigating ecosystem response to climate change.

  17. Opposing plant community responses to warming with and without herbivores

    PubMed Central

    Post, Eric; Pedersen, Christian

    2008-01-01

    If controls over primary productivity and plant community composition are mainly environmental, as opposed to biological, then global change may result in large-scale alterations in ecosystem structure and function. This view appears to be favored among investigations of plant biomass and community responses to experimental and observed warming. In far northern and arctic ecosystems, such studies predict increasing dominance of woody shrubs with future warming and emphasize the carbon (C)-sequestration potential and consequent atmospheric feedback potential of such responses. In contrast to previous studies, we incorporated natural herbivory by muskoxen and caribou into a 5-year experimental investigation of arctic plant community response to warming. In accordance with other studies, warming increased total community biomass by promoting growth of deciduous shrubs (dwarf birch and gray willow). However, muskoxen and caribou reduced total community biomass response, and responses of birch and willow, to warming by 19%, 46%, and 11%, respectively. Furthermore, under warming alone, the plant community shifted after 5 years away from graminoid-dominated toward dwarf birch-dominated. In contrast, where herbivores grazed, plant community composition on warmed plots did not differ from that on ambient plots after 5 years. These results highlight the potentially important and overlooked influences of vertebrate herbivores on plant community response to warming and emphasize that conservation and management of large herbivores may be an important component of mitigating ecosystem response to climate change. PMID:18719116

  18. Opposing phylogenetic diversity gradients of plant and soil bacterial communities

    PubMed Central

    Goberna, Marta; Navarro-Cano, Jose A.; Verdú, Miguel

    2016-01-01

    Plants and soil microbes show parallel patterns of species-level diversity. Diverse plant communities release a wider range of organics that are consumed by more microbial species. We speculated, however, that diversity metrics accounting for the evolutionary distance across community members would reveal opposing patterns between plant and soil bacterial phylogenetic diversity. Plant phylogenetic diversity enhances plant productivity and thus expectedly soil fertility. This, in turn, might reduce bacterial phylogenetic diversity by favouring one (or a few) competitive bacterial clade. We collected topsoils in 15 semi-arid plant patches and adjacent low-cover areas configuring a plant phylodiversity gradient, pyrosequenced the 16S rRNA gene to identify bacterial taxa and analysed soil fertility parameters. Structural equation modelling showed positive effects of both plant richness and phylogenetic diversity on soil fertility. Fertility increased bacterial richness but reduced bacterial phylogenetic diversity. This might be attributed to the competitive dominance of a lineage based on its high relative fitness. This suggests biotic interactions as determinants of the soil bacterial community assembly, while emphasizing the need to use phylogeny-informed metrics to tease apart the processes underlying the patterns of diversity. PMID:26888037

  19. Opposing effects of reward and punishment on human vigor.

    PubMed

    Griffiths, Benjamin; Beierholm, Ulrik R

    2017-02-13

    The vigor with which humans and animals engage in a task is often a determinant of the likelihood of the task's success. An influential theoretical model suggests that the speed and rate at which responses are made should depend on the availability of rewards and punishments. While vigor facilitates the gathering of rewards in a bountiful environment, there is an incentive to slow down when punishments are forthcoming so as to decrease the rate of punishments, in conflict with the urge to perform fast to escape punishment. Previous experiments confirmed the former, leaving the latter unanswered. We tested the influence of punishment in an experiment involving economic incentives and contrasted this with reward related behavior on the same task. We found that behavior corresponded with the theoretical model; while instantaneous threat of punishment caused subjects to increase the vigor of their response, subjects' response times would slow as the overall rate of punishment increased. We quantitatively show that this is in direct contrast to increases in vigor in the face of increased overall reward rates. These results highlight the opposed effects of rewards and punishments and provide further evidence for their roles in the variety of types of human decisions.

  20. THE ORIENTATION OF ANIMALS BY OPPOSED BEAMS OF LIGHT.

    PubMed

    Crozier, W J

    1927-03-07

    When orientation is attained under the influence of beams of parallel light opposed at 180 degrees the deflection theta from a path at right angles to the beams is given by tan See PDF for Equation, where I(1) and I(2) are the photic intensities and H is the average angle between the photoreceptive surfaces. This expression is independent of the units in which I is measured, and holds whether the primary photosensory effect is proportional to I or to log I. When photokinetic side-to-side motions of the head occur, H decreases with increasing total acting light intensity, but increases if higher total light intensity restricts the amplitude of random movements; in each case, H is very nearly proportional to log I(1)I(2). For beams of light at 90 degrees , See PDF for Equation. The application of these equations to some particular instances is discussed, and it is shown why certain simpler empirical formulae previously found by others yield fair concordance with the experimental data. The result is thus in complete accord with the tropism theory, since the equations are based simply on the assumption that when orientation is attained photic excitation is the same on the two sides.

  1. Vaccine beliefs of parents who oppose compulsory vaccination.

    PubMed Central

    Kennedy, Allison M.; Brown, Cedric J.; Gust, Deborah A.

    2005-01-01

    OBJECTIVES: Our objectives were the following: (1) to describe the sociodemographic factors, vaccine beliefs, and behaviors that are associated with parental opposition to compulsory vaccination, and (2) to determine if the availability of a philosophical exemption in a parent's state of residence is associated with parental opposition to compulsory vaccination. METHODS: Data from the 2002 HealthStyles survey were analyzed. Chi-square analysis was used to identify significant associations between belief and behavior questions and opposition to compulsory vaccination for school entry. Multivariate logistic regression was conducted using significant variables from the bivariate analysis to identify independent predictors of opposition to compulsory vaccination among surveyed parents. RESULTS: Of respondents with at least one child aged < or = 18 years living in the household (n=1,527), 12% were opposed to compulsory vaccination. Survey results indicate that a parent's belief regarding compulsory vaccination for school entry is significantly associated with beliefs in the safety and utility of vaccines, as well as intention to have the youngest child fully vaccinated. Residence in a state that permits philosophical exemption to vaccination also was significantly associated with a parent's opposition to compulsory vaccination for school entry. CONCLUSIONS: Providing basic information to parents regarding vaccines and vaccine-preventable diseases may help reduce opposition to compulsory vaccination by reinforcing the safety and importance of routine childhood vaccinations. PMID:16134564

  2. Vaccine beliefs of parents who oppose compulsory vaccination.

    PubMed

    Kennedy, Allison M; Brown, Cedric J; Gust, Deborah A

    2005-01-01

    Our objectives were the following: (1) to describe the sociodemographic factors, vaccine beliefs, and behaviors that are associated with parental opposition to compulsory vaccination, and (2) to determine if the availability of a philosophical exemption in a parent's state of residence is associated with parental opposition to compulsory vaccination. Data from the 2002 HealthStyles survey were analyzed. Chi-square analysis was used to identify significant associations between belief and behavior questions and opposition to compulsory vaccination for school entry. Multivariate logistic regression was conducted using significant variables from the bivariate analysis to identify independent predictors of opposition to compulsory vaccination among surveyed parents. Of respondents with at least one child aged < or = 18 years living in the household (n=1,527), 12% were opposed to compulsory vaccination. Survey results indicate that a parent's belief regarding compulsory vaccination for school entry is significantly associated with beliefs in the safety and utility of vaccines, as well as intention to have the youngest child fully vaccinated. Residence in a state that permits philosophical exemption to vaccination also was significantly associated with a parent's opposition to compulsory vaccination for school entry. Providing basic information to parents regarding vaccines and vaccine-preventable diseases may help reduce opposition to compulsory vaccination by reinforcing the safety and importance of routine childhood vaccinations.

  3. Opposing effects of reward and punishment on human vigor

    PubMed Central

    Griffiths, Benjamin; Beierholm, Ulrik R.

    2017-01-01

    The vigor with which humans and animals engage in a task is often a determinant of the likelihood of the task’s success. An influential theoretical model suggests that the speed and rate at which responses are made should depend on the availability of rewards and punishments. While vigor facilitates the gathering of rewards in a bountiful environment, there is an incentive to slow down when punishments are forthcoming so as to decrease the rate of punishments, in conflict with the urge to perform fast to escape punishment. Previous experiments confirmed the former, leaving the latter unanswered. We tested the influence of punishment in an experiment involving economic incentives and contrasted this with reward related behavior on the same task. We found that behavior corresponded with the theoretical model; while instantaneous threat of punishment caused subjects to increase the vigor of their response, subjects’ response times would slow as the overall rate of punishment increased. We quantitatively show that this is in direct contrast to increases in vigor in the face of increased overall reward rates. These results highlight the opposed effects of rewards and punishments and provide further evidence for their roles in the variety of types of human decisions. PMID:28205567

  4. Long-Term Maintenance of Immediate or Delayed Extinction Is Determined by the Extinction-Test Interval

    ERIC Educational Resources Information Center

    Johnson, Justin S.; Escobar, Martha; Kimble, Whitney L.

    2010-01-01

    Short acquisition-extinction intervals (immediate extinction) can lead to either more or less spontaneous recovery than long acquisition-extinction intervals (delayed extinction). Using rat subjects, we observed less spontaneous recovery following immediate than delayed extinction (Experiment 1). However, this was the case only if a relatively…

  5. Long-Term Maintenance of Immediate or Delayed Extinction Is Determined by the Extinction-Test Interval

    ERIC Educational Resources Information Center

    Johnson, Justin S.; Escobar, Martha; Kimble, Whitney L.

    2010-01-01

    Short acquisition-extinction intervals (immediate extinction) can lead to either more or less spontaneous recovery than long acquisition-extinction intervals (delayed extinction). Using rat subjects, we observed less spontaneous recovery following immediate than delayed extinction (Experiment 1). However, this was the case only if a relatively…

  6. Glottal jet measurements in synthetic, MRI-based human vocal fold models

    NASA Astrophysics Data System (ADS)

    Thomson, Scott; Pickup, Brian; Gollnick, Paul

    2007-11-01

    Human vocal fold vibration generates a time-varying elliptically-shaped glottal jet that produces sound in speech. Improved understanding of glottal jet dynamics can yield insight into voice production mechanisms and improve the diagnosis and treatment of voice disorders. Experiments using recently developed life-sized synthetic models of the vocal folds are presented. The fabrication process of converting MRI images to synthetic models is described. The process allows for varying the Young's modulus of the models, allowing for asymmetric conditions to be created by casting opposing vocal folds using materials of different stiffness. The models are shown to oscillate at frequencies, pressures, and flow rates typical of human speech. Phase-locked particle image velocimetry (PIV) results are presented which characterize the glottal jet, including jet direction, vortical structures, and turbulence levels. Results are shown for symmetric and asymmetric vocal fold models. The degree of material asymmetry required to cause significant asymmetry in the glottal jet is reported.

  7. Current extinction rates of reptiles and amphibians

    PubMed Central

    Alroy, John

    2015-01-01

    There is broad concern that a mass extinction of amphibians and reptiles is now underway. Here I apply an extremely conservative Bayesian method to estimate the number of recent amphibian and squamate extinctions in nine important tropical and subtropical regions. The data stem from a combination of museum collection databases and published site surveys. The method computes an extinction probability for each species by considering its sighting frequency and last sighting date. It infers hardly any extinction when collection dates are randomized and it provides underestimates when artificial extinction events are imposed. The method also appears to be insensitive to trends in sampling; therefore, the counts it provides are absolute minimums. Extinctions or severe population crashes have accumulated steadily since the 1970s and 1980s, and at least 3.1% of frog species have already disappeared. Based on these data and this conservative method, the best estimate of the global grand total is roughly 200 extinctions. Consistent with previous results, frog losses are heavy in Latin America, which has been greatly affected by the pathogenic chytrid fungus Batrachochytrium dendrobatidis. Extinction rates are now four orders-of-magnitude higher than background, and at least another 6.9% of all frog species may be lost within the next century, even if there is no acceleration in the growth of environmental threats. PMID:26438855

  8. Current extinction rates of reptiles and amphibians.

    PubMed

    Alroy, John

    2015-10-20

    There is broad concern that a mass extinction of amphibians and reptiles is now underway. Here I apply an extremely conservative Bayesian method to estimate the number of recent amphibian and squamate extinctions in nine important tropical and subtropical regions. The data stem from a combination of museum collection databases and published site surveys. The method computes an extinction probability for each species by considering its sighting frequency and last sighting date. It infers hardly any extinction when collection dates are randomized and it provides underestimates when artificial extinction events are imposed. The method also appears to be insensitive to trends in sampling; therefore, the counts it provides are absolute minimums. Extinctions or severe population crashes have accumulated steadily since the 1970s and 1980s, and at least 3.1% of frog species have already disappeared. Based on these data and this conservative method, the best estimate of the global grand total is roughly 200 extinctions. Consistent with previous results, frog losses are heavy in Latin America, which has been greatly affected by the pathogenic chytrid fungus Batrachochytrium dendrobatidis. Extinction rates are now four orders-of-magnitude higher than background, and at least another 6.9% of all frog species may be lost within the next century, even if there is no acceleration in the growth of environmental threats.

  9. Extinction properties of infinitely long graphite cylinders

    NASA Astrophysics Data System (ADS)

    Jazbi, B.; Hoyle, F.; Wickramasinghe, N. C.

    1991-12-01

    The extinction efficiencies of randomly oriented infinite graphite cylinders, including hollow cylinders are calculated, using the rigorous Kerker-Matijevic formulas. The peak in the mid-UV extinction varies in wavelength with particle radius and cavity size in a way that makes such particles of limited interest as models of interstellar grains.

  10. Inferring extinction from a sighting record.

    PubMed

    Solow, Andrew R

    2005-05-01

    The extinctions of plant and animal species are almost never observed directly, but must be inferred from sighting records. This paper reviews some methods for statistical inference about the extinction of a single species based on a record of its sightings.

  11. Periodicity of extinction: A 1988 update

    NASA Technical Reports Server (NTRS)

    Sepkowski, J. John, Jr.

    1988-01-01

    The hypothesis that events of mass extinction recur periodically at approximately 26 my intervals is an empirical claim based on analysis of data from the fossil record. The hypothesis has become closely linked with catastrophism because several events in the periodic series are associated with evidence of extraterrestrial impacts, and terrestrial forcing mechanisms with long, periodic recurrences are not easily conceived. Astronomical mechanisms that have been hypothesized include undetected solar companions and solar oscillation about the galactic plane, which induce comet showers and result in impacts on Earth at regular intervals. Because these mechanisms are speculative, they have been the subject of considerable controversy, as has the hypothesis of periodicity of extinction. In response to criticisms and uncertainties, a data base was developed on times of extinction of marine animal genera. A time series is given and analyzed with 49 sample points for the per-genus extinction rate from the Late Permian to the Recent. An unexpected pattern in the data is the uniformity of magnitude of many of the periodic extinction events. Observations suggest that the sequence of extinction events might be the result of two sets of mechanisms: a periodic forcing that normally induces only moderate amounts of extinction, and independent incidents or catastrophes that, when coincident with the periodic forcing, amplify its signal and produce major-mass extinctions.

  12. Catastrophic extinctions follow deforestation in Singapore.

    PubMed

    Brook, Barry W; Sodhi, Navjot S; Ng, Peter K L

    2003-07-24

    The looming mass extinction of biodiversity in the humid tropics is a major concern for the future, yet most reports of extinctions in these regions are anecdotal or conjectural, with a scarcity of robust, broad-based empirical data. Here we report on local extinctions among a wide range of terrestrial and freshwater taxa from Singapore (540 km2) in relation to habitat loss exceeding 95% over 183 years. Substantial rates of documented and inferred extinctions were found, especially for forest specialists, with the greatest proportion of extinct taxa (34-87%) in butterflies, fish, birds and mammals. Observed extinctions were generally fewer, but inferred losses often higher, in vascular plants, phasmids, decapods, amphibians and reptiles (5-80%). Forest reserves comprising only 0.25% of Singapore's area now harbour over 50% of the residual native biodiversity. Extrapolations of the observed and inferred local extinction data, using a calibrated species-area model, imply that the current unprecedented rate of habitat destruction in Southeast Asia will result in the loss of 13-42% of regional populations over the next century, at least half of which will represent global species extinctions.

  13. Context and Behavioral Processes in Extinction

    ERIC Educational Resources Information Center

    Bouton, Mark E.

    2004-01-01

    This article provides a selective review and integration of the behavioral literature on Pavlovian extinction. The first part reviews evidence that extinction does not destroy the original learning, but instead generates new learning that is especially context-dependent. The second part examines insights provided by research on several related…

  14. Biodiversity conservation: climate change and extinction risk.

    PubMed

    Harte, John; Ostling, Annette; Green, Jessica L; Kinzig, Ann

    2004-07-01

    Thomas et al. have carried out a useful analysis of the extinction risk from climate warming. Their overall conclusion, that a large fraction of extant species could be driven to extinction by expected climate trends over the next 50 years, is compelling: it adds to the many other reasons why new energy policies are needed to reduce the pace of warming.

  15. Lidar extinction measurement in the mid infrared

    NASA Astrophysics Data System (ADS)

    Mitev, Valentin; Babichenko, S.; Borelli, R.; Fiorani, L.; Grigorov, I.; Nuvoli, M.; Palucci, A.; Pistilli, M.; Puiu, Ad.; Rebane, Ott; Santoro, S.

    2014-11-01

    We present a lidar measurement of atmospheric extinction coefficient. The measurement is performed by inversion of the backscatter lidar signal at wavelengths 3'000nm and 3'500nm. The inversion of the backscatter lidar signal was performed with constant extinction-to-backscatter ration values of 104 and exponential factor 0.1.

  16. Reinforcement of competing behavior during extinction.

    PubMed

    Leitenberg, H; Rawson, R A; Bath, K

    1970-07-17

    Conditioned behavior declines in frequency when reinforcement is discontinued. In two experiments this extinction process was facilitated when competing behavior was reinforced as the original response was extinguished. When reinforcement for competing behavior was withdrawn, however, rats resumed their original behavior and there were no overall savings in total responses to extinction.

  17. Survival without recovery after mass extinctions.

    PubMed

    Jablonski, David

    2002-06-11

    Because many survivors of mass extinctions do not participate in postrecovery diversifications, and therefore fall into a pattern that can be termed "Dead Clade Walking" (DCW), the effects of mass extinctions extend beyond the losses observed during the event itself. Analyses at two taxonomic levels provide a first-order test of the prevalence of DCWs by using simple and very conservative operational criteria. For four of the Big Five mass extinctions of the Phanerozoic, the marine genera that survived the extinction suffered approximately 10-20% attrition in the immediately following geologic stage that was significantly greater than the losses sustained in preextinction stages. The stages immediately following the three Paleozoic mass extinctions also account for 17% of all order-level losses in marine invertebrates over that interval, which is, again, significantly greater than that seen for the other stratigraphic stages (no orders are lost immediately after the end-Triassic or end-Cretaceous mass extinctions). DCWs are not evenly distributed among four regional molluscan time-series following the end-Cretaceous extinction, demonstrating the importance of spatial patterns in recovery dynamics. Although biotic interactions have been invoked to explain the differential postextinction success of clades, such hypotheses must be tested against alternatives that include stochastic processes in low-diversity lineages-which is evidently not a general explanation for the ordinal DCW patterns, because postextinction fates are not related to the size of extinction bottlenecks in Paleozoic orders-and ongoing physical environmental changes.

  18. Context and Behavioral Processes in Extinction

    ERIC Educational Resources Information Center

    Bouton, Mark E.

    2004-01-01

    This article provides a selective review and integration of the behavioral literature on Pavlovian extinction. The first part reviews evidence that extinction does not destroy the original learning, but instead generates new learning that is especially context-dependent. The second part examines insights provided by research on several related…

  19. Post-retrieval extinction attenuates cocaine memories.

    PubMed

    Sartor, Gregory C; Aston-Jones, Gary

    2014-04-01

    Recent studies have shown that post-retrieval extinction training attenuates fear and reward-related memories in both humans and rodents. This noninvasive, behavioral approach has the potential to be used in clinical settings to treat maladaptive memories that underlie several psychiatric disorders, including drug addiction. However, few studies to date have used a post-retrieval extinction approach to attenuate addiction-related memories. In the current study, we attempted to disrupt cocaine-related memories by using the post-retrieval extinction paradigm in male Sprague Dawley rats. Results revealed that starting extinction training 1 h after cocaine contextual memory was retrieved significantly attenuated cocaine-primed reinstatement of conditioned place preference (CPP) and relapse of cocaine CPP (drug-free and cocaine-primed) following 30 days of abstinence. However, animals that did not retrieve the contextual cocaine memory before extinction training, or animals that began extinction training 24 h after retrieval (outside of the reconsolidation window), demonstrated normal cocaine CPP. Conversely, animals that received additional CPP conditioning, rather than extinction training, 1 h after reactivation of cocaine memory showed enhanced cocaine CPP compared with animals that did not reactivate the cocaine memory before conditioning. These results reveal that a behavioral manipulation that takes advantage of reconsolidation and extinction of drug memories may be useful in decreasing preference for, and abuse of, cocaine.

  20. Extinction-Induced Variability in Human Behavior

    ERIC Educational Resources Information Center

    Kinloch, Jennifer M.; Foster, T. Mary; McEwan, James S. A.

    2009-01-01

    Participants earned points by pressing a computer space bar (Experiment 1) or forming rectangles on the screen with the mouse (Experiment 2) under differential-reinforcement-of-low-rate schedules, followed by extinction. Variability in interresponse time (the contingent dimension) increased during extinction, as for Morgan and Lee (1996);…

  1. Extinction-Induced Variability in Human Behavior

    ERIC Educational Resources Information Center

    Kinloch, Jennifer M.; Foster, T. Mary; McEwan, James S. A.

    2009-01-01

    Participants earned points by pressing a computer space bar (Experiment 1) or forming rectangles on the screen with the mouse (Experiment 2) under differential-reinforcement-of-low-rate schedules, followed by extinction. Variability in interresponse time (the contingent dimension) increased during extinction, as for Morgan and Lee (1996);…

  2. Mass extinctions and supernova explosions.

    PubMed Central

    Crutzen, P J; Brühl, C

    1996-01-01

    In a recent contribution to this journal Ellis and Schramm [Ellis, J. & Schramm, D. N. (1995) Proc. Natl. Acad. Sci. USA 92, 235-238] claim that supernova explosions can cause massive biological extinctions as a result of strongly enhanced stratospheric NOx (NO + NO2) production by accompanying galactic cosmic rays. They suggested that these NOx productions which would last over several centuries and occur once every few hundred million years would result in ozone depletions of about 95%, leading to vastly increased levels of biologically damaging solar ultraviolet radiation. Our detailed model calculations show, however, substantially smaller ozone depletions ranging from at most 60% at high latitudes to below 20% at the equator. PMID:11607631

  3. Jet lag modification.

    PubMed

    Simmons, Emily; McGrane, Owen; Wedmore, Ian

    2015-01-01

    Athletes often are required to travel for sports participation, both for practice and competition. A number of those crossing multiple time zones will develop jet lag disorder with possible negative consequences on their performance. This review will discuss the etiology of jet lag disorder and the techniques that are available to shorten or minimize its effects. This includes both pharmacological and nonpharmacological approaches.

  4. Jet measurements in ATLAS

    NASA Astrophysics Data System (ADS)

    Loch, Peter; ATLAS Collaboration

    2011-11-01

    The reconstruction of jets generated in the proton-proton collisions at the Large Hadron Collider (LHC) at a center of mass energy of TeV with the ATLAS detector is discussed. Beginning with a brief review of the calorimeter signal definitions relevant for jet finding, and the use of reconstructed charged particle tracks, the jet reconstruction strategy is described in some detail. Emphasis is put on the jet energy scale (JES) calibration strategy applied for first data, which is based on a short sequence of data driven and simulation based calibrations and corrections to restore the measured jet energy to particle level. The level of understanding of the signal patterns entering the JES corrections is shown for selected variables in comparisons to simulations. The present systematic uncertainties on the JES, which can be as low as 2% for central jets, are presented and analyzed with respect to the individual fractional contributions entering their determination. Some characteristic jet reconstruction performance and selected results from the first year of jet physics with ATLAS in a newly accessible kinematic domain are shown in conclusion.

  5. Jet lag prevention

    MedlinePlus

    ... be harder to adjust to because you lose time. Jet lag can make you feel like going to bed ... such as trying to adjust to the new time zone before you arrive. Images Jet lag prevention References Berry RB, Wagner MH. Patients with ...

  6. Mass extinction in poorly known taxa.

    PubMed

    Régnier, Claire; Achaz, Guillaume; Lambert, Amaury; Cowie, Robert H; Bouchet, Philippe; Fontaine, Benoît

    2015-06-23

    Since the 1980s, many have suggested we are in the midst of a massive extinction crisis, yet only 799 (0.04%) of the 1.9 million known recent species are recorded as extinct, questioning the reality of the crisis. This low figure is due to the fact that the status of very few invertebrates, which represent the bulk of biodiversity, have been evaluated. Here we show, based on extrapolation from a random sample of land snail species via two independent approaches, that we may already have lost 7% (130,000 extinctions) of the species on Earth. However, this loss is masked by the emphasis on terrestrial vertebrates, the target of most conservation actions. Projections of species extinction rates are controversial because invertebrates are essentially excluded from these scenarios. Invertebrates can and must be assessed if we are to obtain a more realistic picture of the sixth extinction crisis.

  7. Mass extinction in poorly known taxa

    PubMed Central

    Régnier, Claire; Achaz, Guillaume; Lambert, Amaury; Cowie, Robert H.; Bouchet, Philippe; Fontaine, Benoît

    2015-01-01

    Since the 1980s, many have suggested we are in the midst of a massive extinction crisis, yet only 799 (0.04%) of the 1.9 million known recent species are recorded as extinct, questioning the reality of the crisis. This low figure is due to the fact that the status of very few invertebrates, which represent the bulk of biodiversity, have been evaluated. Here we show, based on extrapolation from a random sample of land snail species via two independent approaches, that we may already have lost 7% (130,000 extinctions) of the species on Earth. However, this loss is masked by the emphasis on terrestrial vertebrates, the target of most conservation actions. Projections of species extinction rates are controversial because invertebrates are essentially excluded from these scenarios. Invertebrates can and must be assessed if we are to obtain a more realistic picture of the sixth extinction crisis. PMID:26056308

  8. Extinctions in ancient and modern seas.

    PubMed

    Harnik, Paul G; Lotze, Heike K; Anderson, Sean C; Finkel, Zoe V; Finnegan, Seth; Lindberg, David R; Liow, Lee Hsiang; Lockwood, Rowan; McClain, Craig R; McGuire, Jenny L; O'Dea, Aaron; Pandolfi, John M; Simpson, Carl; Tittensor, Derek P

    2012-11-01

    In the coming century, life in the ocean will be confronted with a suite of environmental conditions that have no analog in human history. Thus, there is an urgent need to determine which marine species will adapt and which will go extinct. Here, we review the growing literature on marine extinctions and extinction risk in the fossil, historical, and modern records to compare the patterns, drivers, and biological correlates of marine extinctions at different times in the past. Characterized by markedly different environmental states, some past periods share common features with predicted future scenarios. We highlight how the different records can be integrated to better understand and predict the impact of current and projected future environmental changes on extinction risk in the ocean. Copyright © 2012 Elsevier Ltd. All rights reserved.

  9. Retrieval induces reconsolidation of fear extinction memory

    PubMed Central

    Rossato, Janine I.; Bevilaqua, Lia R.; Izquierdo, Iván; Medina, Jorge H.; Cammarota, Martín

    2010-01-01

    The nonreinforced expression of long-tem memory may lead to two opposite protein synthesis-dependent processes: extinction and reconsolidation. Extinction weakens consolidated memories, whereas reconsolidation allows incorporation of additional information into them. Knowledge about these two processes has accumulated in recent years, but their possible interaction has not been evaluated yet. Here, we report that inhibition of protein synthesis in the CA1 region of the dorsal hippocampus after retrieval of fear extinction impedes subsequent reactivation of the extinction memory trace without affecting its storage or that of the initial fear memory. Our results suggest that extinction memory is susceptible to a retrieval-induced process similar to reconsolidation in the hippocampus. PMID:21118982

  10. Retrieval induces reconsolidation of fear extinction memory.

    PubMed

    Rossato, Janine I; Bevilaqua, Lia R; Izquierdo, Iván; Medina, Jorge H; Cammarota, Martín

    2010-12-14

    The nonreinforced expression of long-tem memory may lead to two opposite protein synthesis-dependent processes: extinction and reconsolidation. Extinction weakens consolidated memories, whereas reconsolidation allows incorporation of additional information into them. Knowledge about these two processes has accumulated in recent years, but their possible interaction has not been evaluated yet. Here, we report that inhibition of protein synthesis in the CA1 region of the dorsal hippocampus after retrieval of fear extinction impedes subsequent reactivation of the extinction memory trace without affecting its storage or that of the initial fear memory. Our results suggest that extinction memory is susceptible to a retrieval-induced process similar to reconsolidation in the hippocampus.

  11. Synchronous extinction of North America's Pleistocene mammals.

    PubMed

    Faith, J Tyler; Surovell, Todd A

    2009-12-08

    The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago (approximately 13,800-11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000-10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant.

  12. Species-area relationships underestimate extinction rates

    NASA Astrophysics Data System (ADS)

    Fattorini, Simone; Borges, Paulo A. V.

    2012-04-01

    The species-area relationship (SAR), i.e. the increase in species number with area, has been repeatedly used to predict species extinction, at both local and global scales, with habitat reduction. He and Hubbell (Nature, 2011; 473, 368-371), however, argued that the function that relates species loss with decreasing habitat area cannot be simply obtained reversing the species-area accumulation curve. Using a statistically more appropriate curve based on endemics (EAR), they concluded that the SAR overestimates species extinction. Although we agree that SARs and EARs have different shapes, this does not imply that SARs overestimate species extinction. Empirical evidence suggests that SARs do not overestimate, but underestimate species extinction by habitat loss and fragmentation. We discuss various examples taken from recent literature to show that SARs underestimate species extinction.

  13. Neural Mechanisms of Extinction Learning and Retrieval

    PubMed Central

    Quirk, Gregory J.; Mueller, Devin

    2009-01-01

    Emotional learning is necessary for individuals to survive and prosper. Once acquired, however, emotional associations are not always expressed. Indeed, the regulation of emotional expression under varying environmental conditions is essential for mental health. The simplest form of emotional regulation is extinction, in which conditioned responding to a stimulus decreases when the reinforcer is omitted. Two decades of research on the neural mechanisms of fear conditioning have laid the groundwork for understanding extinction. In this review, we summarize recent work on the neural mechanisms of extinction learning. Like other forms of learning, extinction occurs in three phases: acquisition, consolidation, and retrieval, each of which depends on specific structures (amygdala, prefrontal cortex, hippocampus), and molecular mechanisms (receptors and signaling pathways). Pharmacological methods to facilitate consolidation and retrieval of extinction, for both aversive and appetitive conditioning, are setting the stage for novel treatments for anxiety disorders and addictions. PMID:17882236

  14. Preventing the Next Mass Extinction: Ethical Obligations

    SciTech Connect

    Tonn, Bruce Edward

    2009-11-01

    This paper presents a framework to judge whether we are meeting our ethical responsibilities for preventing massive species extinction. The framework is a generalization from another framework, one that addresses ethical responsibilities related to preventing premature, involuntary human deaths from environmental risks and the extinction of the human race. The resulting ethical risk standards are quite stringent and it is argued that we are nowhere close to meeting any standards, except in the cases of human extinction and extinction of all life on earth, which are met by chance, not by design. Much work is needed to build the 'technology' needed to estimate probabilities associated with massive losses of human life and species extinction over the suggested 1000 year planning horizon.

  15. Synchronous extinction of North America's Pleistocene mammals

    PubMed Central

    Faith, J. Tyler; Surovell, Todd A.

    2009-01-01

    The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago (≈13,800–11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000–10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant. PMID:19934040

  16. An investigation of extinction-induced vocalizations.

    PubMed

    Valentino, Amber L; Shillingsburg, M Alice; Call, Nathan A; Burton, Britney; Bowen, Crystal N

    2011-05-01

    Children with autism have significant communication delays. Although some children develop vocalizations through shaping and differential reinforcement, others rarely exhibit vocalizations, and alternative methods are targeted in intervention. However, vocal language often remains a goal for caregivers and clinicians. Thus, strategies to increase frequency of vocalizations are needed. In the present study, the authors examined the effect of extinction of previously acquired signed mands on vocalizations in three children diagnosed with autism. Experiment 1 examined the effects of differential reinforcement of vocalizations and extinction of signed mands combined. In Experiment 1, it was unknown whether the reinforcement of vocalizations alone could have produced the effects; therefore, Experiment 2 isolated the effects of reinforcement and extinction by reinforcing vocalizations in baseline. An increase in rate of vocalizations occurred following the application of extinction of signed mands and differential reinforcement of vocalizations in Experiment 1 and following extinction of signed mands in Experiment 2.

  17. A new piloted premixed jet burner to study strong finite-rate chemistry effects

    SciTech Connect

    Dunn, Matthew J.; Masri, Assaad R.; Bilger, Robert W.

    2007-10-15

    This paper describes the initial characterization of a piloted premixed jet burner (PPJB) designed to investigate finite-rate chemistry effects in highly turbulent lean premixed combustion. The PPJB consists of a high-velocity lean premixed central jet, piloted by a low-velocity stoichiometric premixed pilot, surrounded by a large-diameter coflow of lean premixed hydrogen-air combustion products. The configuration of a lean central jet supported by a stoichiometric pilot is similar to that of a lean premixed gas turbine combustor, but without additional complications such as swirl, recirculation, and complex boundary conditions. A significant feature of the PPJB is that under certain conditions the central jet combustion process appears to undergo an extinction-reignition process. It is considered likely that intense turbulent mixing after the nozzle drives an initial extinction process that reduces flame luminosity, with reignition occurring downstream where turbulent mixing has decreased, causing an increase in flame luminosity. Four flames are selected for further study, each with an equivalence ratio of 0.5 and with central jet velocities of 50, 100, 150, and 200 m/s. Simultaneous two-dimensional (2D) Rayleigh-OH planar laser-induced fluorescence (PLIF) imaging results are presented for the selected flames, showing that in the ''extinction'' region OH concentrations occur at reduced levels in isolated patchy regions, supporting the idea that extinction is predominantly occurring. Laser Doppler velocimetry (LDV) data are also reported for the flow field turbulence statistics, with the most significant result being that for the reacting cases the pilot delays the occurrence of peak turbulence intensity downstream to near the observed ''extinction'' region. (author)

  18. Effects of memory age and interval of fear extinction sessions on contextual fear extinction.

    PubMed

    Matsuda, Shingo; Matsuzawa, Daisuke; Ishii, Daisuke; Tomizawa, Haruna; Shimizu, Eiji

    2014-08-22

    Fear extinction is a major task in our understanding of the biological mechanisms of exposure therapy, one of the most used treatments for stress-related disorders. It was recently reported that an extinction of 5 consecutive days prevents spontaneous recovery of fear memory. Memory age and the timing of fear extinction influence the effect of fear extinction. In this study, we used contextual fear extinction in adult male mice to examine whether memory age influences an extinction of 5 consecutive days and whether consecutiveness is necessary to prevent spontaneous recovery. Our results showed that, although fear memory was not affected by the passage of time, the old fear memory (28 days after fear conditioning) was more sensitive to fear extinction than the young fear memory (7 days after fear conditioning). Additionally, we demonstrated that consecutiveness of extinction sessions is not necessary to prevent spontaneous recovery. Instead, fear extinction sessions at spaced intervals were found to be more effective than consecutive extinction sessions for young fear memory. Our results suggest that taking memory age and the interval of fear extinction sessions into consideration would help to optimize exposure therapy. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  19. Intrinsic and extrinsic ecological determinants of extinction at the Late Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Dunhill, Alexander

    2017-04-01

    The Late Triassic extinction (c. 201 Ma) is recognised as one of the "Big Five" mass extinction events, resulting in an estimated loss of over 80% of marine species and ranked third, in terms of ecological severity, amongst Phanerozoic extinctions. Here, we assess how intrinsic and extrinsic ecological factors influence extinction intensity. Using the Bambach ecospace model - based on unique combinations of three variables focusing on mobility, feeding, and tiering - we show that extinction was highest in the tropics, and Panthalassan taxa suffered higher extinction rates than taxa residing in the Tethys Ocean. Reef dwelling taxa suffered the highest levels of extinction, whilst those inhabiting inner-shelf environments were the least affected. An erect benthic or pelagic mode of life appears to have been most susceptible to extinction whilst suspension feeders suffered higher extinction rates than taxa displaying other feeding strategies. Non-motile and highly mobile taxa appear to have suffered higher levels of extinction than slow moving and facultative mobile taxa. The results show that both intrinsic and extrinsic ecological factors have a bearing on whether taxa are more or less likely to survive a mass extinction event.

  20. A phantom extinction? New insights into extinction dynamics of the Don-hare Lepus tanaiticus.

    PubMed

    Prost, S; Knapp, M; Flemmig, J; Hufthammer, A K; Kosintsev, P; Stiller, M; Hofreiter, M

    2010-09-01

    The Pleistocene to Holocene transition was accompanied by a worldwide extinction event affecting numerous mammalian species. Several species such as the woolly mammoth and the giant deer survived this extinction wave, only to go extinct a few thousand years later during the Holocene. Another example for such a Holocene extinction is the Don-hare, Lepus tanaiticus, which inhabited the Russian plains during the late glacial. After being slowly replaced by the extant mountain hare (Lepus timidus), it eventually went extinct during the middle Holocene. Here, we report the phylogenetic relationship of L. tanaiticus and L. timidus based on a 339-basepair (bp) fragment of the mitochondrial D-loop. Phylogenetic tree- and network reconstructions do not support L. tanaiticus and L. timidus being different species. Rather, we suggest that the two taxa represent different morphotypes of a single species and the extinction of 'L. tanaiticus' represents the disappearance of a local morphotype rather than the extinction of a species.

  1. Histamine facilitates consolidation of fear extinction.

    PubMed

    Bonini, Juliana Sartori; Da Silva, Weber Cláudio; Da Silveira, Clarice Kras Borges; Köhler, Cristiano André; Izquierdo, Iván; Cammarota, Martín

    2011-10-01

    Non-reinforced retrieval induces memory extinction, a phenomenon characterized by a decrease in the intensity of the learned response. This attribute has been used to develop extinction-based therapies to treat anxiety and post-traumatic stress disorders. Histamine modulates memory and anxiety but its role on fear extinction has not yet been evaluated. Therefore, using male Wistar rats, we determined the effect of the intra-hippocampal administration of different histaminergic agents on the extinction of step-down inhibitory avoidance (IA), a form of aversive learning. We found that intra-CA1 infusion of histamine immediately after non-reinforced retrieval facilitated consolidation of IA extinction in a dose-dependent manner. This facilitation was mimicked by the histamine N-methyltransferase inhibitor SKF91488 and the H2 receptor agonist dimaprit, reversed by the H2 receptor antagonist ranitidine, and unaffected by the H1 antagonist pyrilamine, the H3 antagonist thioperamide and the antagonist at the NMDA receptor (NMDAR) polyamine-binding site ifenprodil. Neither the H1 agonist 2-2-pyridylethylamine nor the NMDAR polyamine-binding site agonist spermidine affected the consolidation of extinction while the H3 receptor agonist imetit hampered it. Extinction induced the phosphorylation of ERK1 in dorsal CA1 while intra-CA1 infusion of the MEK inhibitor U0126 blocked extinction of the avoidance response. The extinction-induced phosphorylation of ERK1 was enhanced by histamine and dimaprit and blocked by ranitidine administered to dorsal CA1 after non-reinforced retrieval. Taken together, our data indicate that the hippocampal histaminergic system modulates the consolidation of fear extinction through a mechanism involving the H2-dependent activation of ERK signalling.

  2. Predicting extinction debt from community patterns.

    PubMed

    Kitzes, Justin; Harte, John

    2015-08-01

    A significant challenge in both measuring and predicting species extinction rates at global and local scales is the possibility of extinction debt, time-delayed extinctions that occur gradually following an initial impact. Here we examine how relative abundance distributions and spatial aggregation combine to influence the likely magnitude of future extinction debt following habitat loss or climate-driven range contraction. Our analysis is based on several fundamental premises regarding abundance distributions, most importantly that species abundances immediately following habitat loss are a sample from an initial relative abundance distribution and that the long-term, steady-state form of the species abundance distribution is a property of the biology of a community and not of area. Under these two hypotheses, the results show that communities following canonical lognormal and broken-stick abundance distributions are prone to exhibit extinction debt, especially when species exhibit low spatial aggregation. Conversely, communities following a logseries distribution with a constant Fisher's α parameter never demonstrate extinction debt and often show an "immigration credit," in which species richness rises in the long term following an initial decrease. An illustration of these findings in 25 biodiversity hotspots suggests a negligible immediate extinction rate for bird communities and eventual extinction debts of 30-50% of initial species richness, whereas plant communities are predicted to immediately lose 5-15% of species without subsequent extinction debt. These results shed light on the basic determinants of extinction debt and provide initial indications of the magnitude of likely debts in landscapes where few empirical data are available.

  3. Multiple jet study

    NASA Technical Reports Server (NTRS)

    Walker, R. E.; Kors, D. L.

    1973-01-01

    Test data is presented which allows determination of jet penetration and mixing of multiple cold air jets into a ducted subsonic heated mainstream flow. Jet-to-mainstream momentum flux ratios ranged from 6 to 60. Temperature profile data is presented at various duct locations up to 24 orifice diameters downstream of the plane of jet injection. Except for two configurations, all geometries investigated had a single row of constant diameter orifices located transverse to the main flow direction. Orifice size and spacing between orifices were varied. Both of these were found to have a significant effect on jet penetration and mixing. The best mixing of the hot and cold streams was achieved with duct height.

  4. Instability of rectangular jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Thies, Andrew T.

    1992-01-01

    The instability of rectangular jets is investigated using a vortex sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

  5. Description of Jet Breakup

    NASA Technical Reports Server (NTRS)

    Papageorgiou, Demetrios T.

    1996-01-01

    In this article we review recent results on the breakup of cylindrical jets of a Newtonian fluid. Capillary forces provide the main driving mechanism and our interest is in the description of the flow as the jet pinches to form drops. The approach is to describe such topological singularities by constructing local (in time and space) similarity solutions from the governing equations. This is described for breakup according to the Euler, Stokes or Navier-Stokes equations. It is found that slender jet theories can be applied when viscosity is present, but for inviscid jets the local shape of the jet at breakup is most likely of a non-slender geometry. Systems of one-dimensional models of the governing equations are solved numerically in order to illustrate these differences.

  6. Relativistic Jets and Collapsars

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Woosley, S. E.

    2001-05-01

    In order to study the relativistic jets from collapsars, we have developed a special relativistic multiple-dimensional hydrodynamics code similar to the GENESIS code (Aloy et al., ApJS, 122, 151). The code is based on the PPM interpolation algorithm and Marquina's Riemann solver. Using this code, we have simulated the propagation of axisymmetric jets along the rotational axis of collapsed rotating stars (collapsars). Using the progenitors of MacFadyen, Woosley, and Heger, a relativistic jet is injected at a given inner boundary radius. This radius, the opening angle of the jet, its Lorentz factor, and its total energy are parameters of the problem. A highly collimated, relativistic outflow is observed at the surface of the star several seconds later. We will discuss the hydrodynamical focusing of the jet, it's break out properties, time evolution, and sensitivity to the adopted parameters.

  7. Jet Lag in Athletes

    PubMed Central

    Lee, Aaron; Galvez, Juan Carlos

    2012-01-01

    Context: Prolonged transmeridian air travel can impart a physical and emotional burden on athletes in jet lag and travel fatigue. Jet lag may negatively affect the performance of athletes. Study Type: Descriptive review. Evidence Acquisition: A Medline search for articles relating to jet lag was performed (1990-present), as was a search relating to jet lag and athletes (1983-January, 2012). The results were reviewed for relevance. Eighty-nine sources were included in this descriptive review. Results: Behavioral strategies are recommended over pharmacological strategies when traveling with athletes; pharmacological aides may be used on an individual basis. Strategic sleeping, timed exposure to bright light, and the use of melatonin are encouraged. Conclusions: There is strong evidence that mood and cognition are adversely affected by jet lag. Some measures of individual and team performance are adversely affected as well. PMID:23016089

  8. Instability of rectangular jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Thies, Andrew T.

    1992-01-01

    The instability of rectangular jets is investigated using a vortex sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

  9. Jet physics at CDF

    SciTech Connect

    Melese, P.

    1997-05-01

    We present high E{sub T} jet measurements from CDF at the Fermilab Tevatron Collider. The incfilusive jet cross section at {radical}s = 1800 GeV with {approximately} 5 times more data is compared to the published CDF results, preliminary D0 results, and next-to-leading order QCD predictions. The {summation}E{sub T} cross section is also compared to QCD predictions and the dijet angular distribution is used to place a limit on quark compositeness. The inclusive jet cross section at {radical}s = 630 GeV is compared with that at 1800 GeV to test the QCD predictions for the scaling of jet cross sections with {radical}s. Finally, we present momentum distributions of charged particles in jets and compare them to Modified Leading Log Approximation predictions.

  10. Numerical Parametric Studies of Laminar Flame Structures in Opposed Jets of Partially Premixed Methane-Air Streams

    NASA Astrophysics Data System (ADS)

    Arun, C. R.; Raghavan, Vasudevan

    2012-09-01

    Interactions of fuel-rich and fuel-lean mixtures and formation of interlinked multiple flame zones are observed in gas turbines and industrial furnaces. For fundamentally understanding such flames, numerical investigation of heat and mass transport, and chemical reaction processes, in laminar, counter flowing partially premixed rich and lean streams of methane and air mixtures, is presented. An axisymmetric numerical reactive flow model, with C2 detailed mechanism for describing methane oxidation in air and an optically thin radiation sub-model, is used in simulations. The numerical results are validated against the experimental results from literature. The equivalence ratios of counter flowing rich and lean reactant streams and the resulting strain rates have been varied. The effect of these parameters on the flame structure is presented. For a given rich and lean side equivalence ratios, by varying the strain rates, triple, double and single flame zones are obtained.

  11. Opposing environmental gradients govern vegetation zonation in an intermountain playa

    USGS Publications Warehouse

    Sanderson, J.S.; Kotliar, N.B.; Steingraeber, D.A.

    2008-01-01

    Vegetation zonation was investigated at an intermountain playa wetland (Mishak Lakes) in the San Luis Valley (SLV) of southern Colorado. Plant composition and abiotic conditions were quantified in six vegetation zones. Reciprocal transplants were performed to test the importance of abiotic factors in governing zonation. Abiotic conditions differed among several vegetation zones. Prolonged inundation led to anaerobic soils in the Eleocharis palustris and the submerged aquatics zones, on the low end of the site's 1.25 m elevation gradient. On the high end of the gradient, soil salinity and sodicity (a measure of exchangeable sodium) were high in the Distichlis spicata zone (electrical conductivity, EC = 5.3 dS/m, sodium absorption ratio, SAR = 44.0) and extreme in the Sarcobatus vermiculatus zone (EC = 21 dS/m, SAR = 274). Transplanted species produced maximum biomass in the zone where they originated, not in any other higher or lower vegetation zone. The greatest overall transplant effect occurred for E. palustris, which experienced a ??? 77% decline in productivity when transplanted to other zones. This study provides evidence that physical factors are a major determinant of vegetation zone composition and distribution across the entire elevation gradient at Mishak Lakes. Patterns at Mishak Lakes arise from counter-directional stress gradients: a gradient from anaerobic to well-oxygenated from basin bottom to upland and a gradient from extremely high salinity to low salinity in the opposing direction. Because abiotic conditions dominate vegetation zonation, restoration of the altered hydrologic regime of this wetland to a natural hydrologic regime may be sufficient to re-establish many of the natural biodiversity functions provided by these wetlands. ?? 2008 The Society of Wetland Scientists.

  12. Drosophila Smad2 Opposes Mad Signaling during Wing Vein Development

    PubMed Central

    Sander, Veronika; Eivers, Edward; Choi, Renee H.; De Robertis, Edward M.

    2010-01-01

    In the vertebrates, the BMP/Smad1 and TGF-β/Smad2 signaling pathways execute antagonistic functions in different contexts of development. The differentiation of specific structures results from the balance between these two pathways. For example, the gastrula organizer/node of the vertebrates requires a region of low Smad1 and high Smad2 signaling. In Drosophila, Mad regulates tissue determination and growth in the wing, but the function of dSmad2 in wing patterning is largely unknown. In this study, we used an RNAi loss-of-function approach to investigate dSmad2 signaling during wing development. RNAi-mediated knockdown of dSmad2 caused formation of extra vein tissue, with phenotypes similar to those seen in Dpp/Mad gain-of-function. Clonal analyses revealed that the normal function of dSmad2 is to inhibit the response of wing intervein cells to the extracellular Dpp morphogen gradient that specifies vein formation, as measured by expression of the activated phospho-Mad protein. The effect of dSmad2 depletion in promoting vein differentiation was dependent on Medea, the co-factor shared by Mad and dSmad2. Furthermore, double RNAi experiments showed that Mad is epistatic to dSmad2. In other words, depletion of Smad2 had no effect in Mad-deficient wings. Our results demonstrate a novel role for dSmad2 in opposing Mad-mediated vein formation in the wing. We propose that the main function of dActivin/dSmad2 in Drosophila wing development is to antagonize Dpp/Mad signaling. Possible molecular mechanisms for the opposition between dSmad2 and Mad signaling are discussed. PMID:20442782

  13. Subcomponents of psychopathy have opposing correlations with punishment judgments.

    PubMed

    Schaich Borg, Jana; Kahn, Rachel E; Sinnott-Armstrong, Walter; Kurzban, Robert; Robinson, Paul H; Kiehl, Kent A

    2013-10-01

    Psychopathy research is plagued by an enigma: Psychopaths reliably act immorally, but they also accurately report whether an action is morally wrong. The current study revealed that cooperative suppressor effects and conflicting subsets of personality traits within the construct of psychopathy might help explain this conundrum. Among a sample of adult male offenders (N = 100) who ranked deserved punishment of crimes, Psychopathy Checklist-Revised (PCL-R) total scores were not linearly correlated with deserved punishment task performance. However, these null results masked significant opposing associations between task performance and factors of psychopathy: the PCL-R Interpersonal/Affective (i.e., manipulative and callous) factor was positively associated with task performance, while the PCL-R Social Deviance (i.e., impulsive and antisocial) factor was simultaneously negatively associated with task performance. These relationships were qualified by a significant interaction where the Interpersonal/Affective traits were positively associated with task performance when Social Deviance traits were high, but Social Deviance traits were negatively associated with task performance when Interpersonal/Affective traits were low. This interaction helped reveal a significant nonlinear relationship between PCL-R total scores and task performance such that individuals with very low or very high PCL-R total scores performed better than those with middle-range PCL-R total scores. These results may explain the enigma of why individuals with very high psychopathic traits, but not other groups of antisocial individuals, usually have normal moral judgment in laboratory settings, but still behave immorally, especially in contexts where social deviance traits have strong influence.

  14. Subcomponents of Psychopathy have Opposing Correlations with Punishment Judgments

    PubMed Central

    Borg, Jana Schaich; Kahn, Rachel E.; Sinnott-Armstrong, Walter; Kurzban, Robert; Robinson, Paul H.; Kiehl, Kent A.

    2013-01-01

    Psychopathy research is plagued by an enigma: Psychopaths reliably act immorally, but they also accurately report whether an action is morally wrong. The current study revealed that cooperative suppressor effects and conflicting subsets of personality traits within the construct of psychopathy might help explain this conundrum. Among a sample of adult male offenders (n = 100) who ranked deserved punishment of crimes, Psychopathy Checklist-Revised (PCL-R) total scores were not linearly correlated with deserved punishment task performance. However, these null results masked significant opposing associations between task performance and factors of psychopathy: the PCL-R Interpersonal/Affective (i.e. manipulative and callous) factor was positively associated with task performance, while the PCL-R Social Deviance (i.e. impulsive and antisocial) factor was simultaneously negatively associated with task performance. Importantly, these relationships were qualified by a significant interaction where the Interpersonal/Affective traits were positively associated with task performance when Social Deviance traits were high, but Social Deviance traits were negatively associated with task performance when Interpersonal/Affective traits were low. This interaction helped reveal a significant non-linear relationship between PCL-R total scores and task performance such that individuals with very low or very high PCL-R total scores performed better than those with middle-range PCL-R total scores. These results may explain the enigma of why individuals with very high psychopathic traits, but not other groups of anti-social individuals, usually have normal moral judgment in laboratory settings, but still behave immorally, especially in contexts where Social Deviance traits have strong influence. PMID:23834639

  15. Optimal Jet Finder

    NASA Astrophysics Data System (ADS)

    Grigoriev, D. Yu.; Jankowski, E.; Tkachov, F. V.

    2003-09-01

    We describe a FORTRAN 77 implementation of the optimal jet definition for identification of jets in hadronic final states of particle collisions. We discuss details of the implementation, explain interface subroutines and provide a usage example. The source code is available from http://www.inr.ac.ru/~ftkachov/projects/jets/. Program summaryTitle of program: Optimal Jet Finder (OJF_014) Catalogue identifier: ADSB Program Summary URL:http://cpc.cs.qub.ac.uk/summaries/ADSB Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: Any computer with the FORTRAN 77 compiler Tested with: g77/Linux on Intel, Alpha and Sparc; Sun f77/Solaris (thwgs.cern.ch); xlf/AIX (rsplus.cern.ch); MS Fortran PowerStation 4.0/Win98 Programming language used: FORTRAN 77 Memory required: ˜1 MB (or more, depending on the settings) Number of bytes in distributed program, including examples and test data: 251 463 Distribution format: tar gzip file Keywords: Hadronic jets, jet finding algorithms Nature of physical problem: Analysis of hadronic final states in high energy particle collision experiments often involves identification of hadronic jets. A large number of hadrons detected in the calorimeter is reduced to a few jets by means of a jet finding algorithm. The jets are used in further analysis which would be difficult or impossible when applied directly to the hadrons. Grigoriev et al. [ hep-ph/0301185] provide a brief introduction to the subject of jet finding algorithms and a general review of the physics of jets can be found in [Rep. Prog. Phys. 36 (1993) 1067]. Method of solution: The software we provide is an implementation of the so-called optimal jet definition ( OJD). The theory of OJD was developed by Tkachov [Phys. Rev. Lett. 73 (1994) 2405; 74 (1995) 2618; Int. J. Mod. Phys. A 12 (1997) 5411; 17 (2002) 2783]. The desired jet configuration is obtained as the one that minimizes Ω R, a certain function of the input particles and jet

  16. Simulations of Solar Jets

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-02-01

    Formation of a coronal jet from twisted field lines that have reconnected with the ambient field. The colors show the radial velocity of the plasma. [Adapted from Szente et al. 2017]How do jets emitted from the Suns surface contribute to its corona and to the solar wind? In a recent study, a team of scientists performed complex three-dimensional simulations of coronal jets to answer these questions.Small ExplosionsCoronal jets are relatively small eruptions from the Suns surface, with heights of roughly 100 to 10,000 km, speeds of 10 to 1,000 km/s, and lifetimes of a few minutes to around ten hours. These jets are constantly present theyre emitted even from the quiet Sun, when activity is otherwise low and weve observed them with a fleet of Sun-watching space telescopes spanning the visible, extreme ultraviolet (EUV), and X-ray wavelength bands.A comparison of simulated observations based on the authors model (left panels) to actual EUV and X-ray observations of jets (right panels). [Szente et al. 2017]Due to their ubiquity, we speculate that these jets might contribute to heating the global solar corona (which is significantly hotter than the surface below it, a curiosity known as the coronal heating problem). We can also wonder what role these jets might play in driving the overall solar wind.Launching a JetLed by Judit Szente (University of Michigan), a team of scientists has explored the impact of coronal jets on the global corona and solar wind with a series of numerical simulations. Szente and collaborators used three-dimensional, magnetohydrodynamic simulations that provide realistic treatment of the solar atmosphere, the solar wind acceleration, and the complexities of heat transfer throughout the corona.In the authors simulations, a jet is initiated as a magnetic dipole rotates at the solar surface, winding up field lines. Magnetic reconnection between the twisted lines and the background field then launches the jet from the dense and hot solar

  17. An Observational and Numerical Study of Marginal Ice Zone Atmospheric Jets

    NASA Astrophysics Data System (ADS)

    Price, D.; Guest, P. S.; Wang, S.; Persson, O. P. G.; Fairall, C. W.

    2016-12-01

    Low level atmospheric jets have been observed to frequently occur in marginal ice zones (MIZs), but little research has been done on the dynamics of these features. During the fall of 2015, during the ONR "Sea State" cruise in the Beaufort Sea, several atmospheric jets were detected in the atmospheric boundary layer or in the capping temperature inversion just above, using radiosondes and shipboard instrumentation. The three strongest jets had maximum wind speeds at elevations near 350 m to 400 m elevation; one of these jets had a secondary maximum wind height at 900 m. Different theories have been suggested as reasons for the existence of MIZ jets including: (1) thermal wind effects where the thermal wind opposes the geostrophic wind due to horizontal temperature changes and/or sloping inversion, (2) inertial effects due to the cut-off of surface friction, similar to nocturnal jets and (3) sea-ice and ice-sea circulations, analogous to land and sea breezes. We present the results of an analysis of the jets based on the in situ measurements, complimented by daily runs of the @COAMPS model by the Naval Research Laboratory. The analysis will consist of reconstructing the 3 dimensional jet scenarios as accurately as possible with emphasis on quantifying the ice edge and location of other surface features compared to the air movement and the vertical location of the jet with respect the atmospheric boundary layer (ABL) and capping inversions. For example, a jet resulting from horizontal temperature differences within an ABL would be expected to result in a wind max within the ABL, while a jet caused by a sloping inversion would be expected to be centered higher up, in the inversion layer. Both these characteristics were observed in different jets. These results will give insights on under what conditions these jets will form, how they can predicted and the resulting impacts on ice cover and sea state.

  18. Dynamic Weakening (Extinction) of Simple Hydrocarbon-air Counterflow Diffusion Flames by Oscillatory Inflows

    NASA Technical Reports Server (NTRS)

    Pellett, G.; Kabaria, A.; Panigrahi, B.; Sammons, K.; Convery, J.; Wilson, L.

    2005-01-01

    This study of laminar non-premixed HC-air flames used an Oscillatory-input Opposed Jet Burner (OOJB) system developed from a previously well-characterized 7.2-mm Pyrex-nozzle OJB system. Over 600 dynamic Flame Strength (FS) measurements were obtained on unanchored (free-floating) laminar Counterflow Diffusion Flames (CFDF's). Flames were stabilized using plug inflows having steady-plus-sinusoidal axial velocities of varied magnitude, frequency, f, up to 1600 Hz, and phase angle from 0 (most data) to 360 degrees. Dynamic FS is defined as the maximum average air input velocity (U(sub air), at nozzle exit) a CFDF can sustain before strain-induced extinction occurs due to prescribed oscillatory peak-to-peak velocity inputs superimposed on steady inputs. Initially, dynamic flame extinction data were obtained at low f, and were supported by 25-120 Hz Hot-Wire cold-flow velocity data at nozzle exits. Later, expanded extinction data were supported by 4-1600 Hz Probe Microphone (PM) pk/pk P data at nozzle exits. The PM data were first obtained without flows, and later with cold stagnating flows, which better represent speaker-diaphragm dynamics during runs. The PM approach enabled characterizations of Dynamic Flame Weakening (DFW) of CFDF's from 8 to 1600 Hz. DFW was defined as % decrease in FS per Pascal of pk/pk P oscillation, namely, DFW = - 100 d(U(sub air) / U(sub air),0Hz) / d(pkpk P). The linear normalization with respect to acoustic pressure magnitude (and steady state (SS) FS) led to a DFW unaffected by strong internal resonances. For the C2H4/N2-air system, from 8 to 20 Hz, DFW is constant at 8.52 plus or minus 0.20 (% weakening)/Pa. This reflects a quasi-steady flame response to an acoustically induced dU(sub air)/dP. Also, it is surprisingly independent of C2H4/N2 mole fraction due to normalization by SS FS. From 20 to approximately 150 Hz, the C2H4/N2 air-flames weakened progressively less, with an inflection at approximately 70 Hz, and became asymptotically

  19. The effect of jet shape on jet injection.

    PubMed

    Park, Geehoon; Modak, Ashin; Hogan, N Catherine; Hunter, Ian W

    2015-01-01

    The effects of the dispersion pattern of a needle-free jet injector are explored. The shape of the jets were compared using a high-speed video camera and jet injections of collimated and dispersed fluid jets with a Lorentz-force actuated jet injector were made into acrylamide gel and post-mortem porcine tissue. A custom-built high-speed X-ray imaging system was used in order to observe the dynamics of the dispersion mechanism for each injection in real time. We show that a collimated jet stream results in greater tissue penetration than a dispersed jet stream.

  20. Directional control of a jet using synthetic jets

    NASA Astrophysics Data System (ADS)

    Frunzulica, Florin; Macovei, Alexandru Cǎtǎlin; Dumitrache, Alexandru; Crunteanu, Daniel

    2017-07-01

    The paper presents an application of synthetic jets in the flow control of a jet. The synthetic jet actuator consists of an oscillating membrane operating at high frequency and separating two cavities with exit slots of different geometries. The synthetic jets work as an alternating push-pull system and the generated vortical structure changes the flow direction of the main jet (jet vectoring). The numerical investigations are performed using a RANS solver with an adequate turbulence model and demonstrates a changing of a jet direction.

  1. Extinction as discrimination: the molar view.

    PubMed

    Baum, William M

    2012-05-01

    The traditional molecular view of behavior explains extinction as the dissipation or inhibition of strength, formerly built up by contiguous reinforcement. In obstinate opposition to this explanation was the partial-reinforcement extinction effect: a partially reinforced response extinguishes more slowly than a continuously reinforced response. It suggests instead that extinction is discrimination. Four pigeons were exposed to daily sessions in which a variable period of food delivery, produced by pecking on a variable-interval schedule, was followed by extinction. The rate of food delivery was varied over a wide range across conditions. Varying the amount of food per delivery inversely with rate of delivery kept response rate from varying excessively. The results confirmed and extended the partial-reinforcement effect; persistence of pecking and time to extinction were inversely related to rate of obtaining food. The results support the molar view of extinction, not as loss of strength of a particular discrete response, but as a transition from one allocation of time among activities to another. Although molecular theories dismiss discrimination due to repeated training and extinction as an impurity or complication, repeated cycles of availability and privation are probably typical of the environment in which most vertebrate species evolved.

  2. Diversity components of impending primate extinctions.

    PubMed

    Jernvall, J; Wright, P C

    1998-09-15

    Many extant species are at risk to go extinct. This impending loss of species is likely to cause changes in future ecosystem functions. Ecological components of diversity, such as dietary or habitat specializations, can be used to estimate the impact of extinctions on ecosystem functions. As an approach to estimate the impact of future extinctions, we tested interdependency between ecological and taxonomic change based on current predictions of extinction rates in primates. We analyzed the ecological characteristics of extant primate faunas having species in various categories of endangerment of extinction and forecasted the future primate faunas as if they were paleontological faunas. Predicting future faunas combines the wealth of ecological information on living primates with large, fossil record-like changes in diversity. Predicted extinction patterns of living primates in Africa, Asia, Madagascar, and South America show that changes in ecology differ among the regions in ways that are not reducible to taxonomic measures. The ecological effects of primate extinctions are initially least severe in South America and larger in Asia and Africa. Disproportionately larger ecological changes are projected for Madagascar. The use of taxonomy as a proxy for ecology can mislead when estimating competence of future primate ecosystems.

  3. Retention of perceptual generalization of fear extinction.

    PubMed

    Pappens, Meike; Schroijen, Mathias; Van den Bergh, Omer; Van Diest, Ilse

    2015-12-01

    Fear reduction obtained during a fear extinction procedure can generalize from the extinction stimulus to other perceptually similar stimuli. Perceptual generalization of fear extinction typically follows a perceptual gradient, with increasing levels of fear reduction the more a stimulus resembles the extinction stimulus. The current study aimed to investigate whether perceptual generalization of fear extinction can be observed also after a retention interval of 24h. Fear was acquired to three geometrical figures of different sizes (CS(+), CS1(+) and CS2(+)) by consistently pairing them with a short-lasting suffocation experience (US). Three other geometrical figures that were never followed by the US served as control stimuli (CS(-), CS1(-), CS2(-)). Next, only the CS(+) was extinguished by presenting it in the absence of the US. One day later, fear responses to all stimuli were assessed without any US-presentation. Outcome measures included startle blink EMG, skin conductance, US expectancy, respiratory rate and tidal volume. On day 2 spontaneous recovery of fear was observed in US expectancy and tidal volume, but not in the other outcomes. Evidence for the retention of fear extinction generalization was present in US expectancy and skin conductance, but a perceptual gradient in the retention of generalized fear extinction could not be observed.

  4. Jet noise suppression

    NASA Astrophysics Data System (ADS)

    Gliebe, P. R.; Brausch, J. F.; Majjigi, R. K.; Lee, R.

    1991-08-01

    The objectives of this chapter are to review and summarize the jet noise suppression technology, to provide a physical and theoretical model to explain the measured jet noise suppression characteristics of different concepts, and to provide a set of guidelines for evolving jet noise suppression designs. The underlying principle for all jet noise suppression devices is to enhance rapid mixing (i.e., diffusion) of the jet plume by geometric and aerothermodynamic means. In the case of supersonic jets, the shock-cell broadband noise reduction is effectively accomplished by the elimination or mitigation of the shock-cell structure. So far, the diffusion concepts have predominantly concentrated on jet momentum and energy (kinetic and thermal) diffusion, in that order, and have yielded better noise reduction than the simple conical nozzles. A critical technology issue that needs resolution is the effect of flight on the noise suppression potential of mechanical suppressor nozzles. A more thorough investigation of this mechanism is necessary for the successful development and design of an acceptable noise suppression device for future high-speed civil transports.

  5. Synthetic Fence Jets

    NASA Astrophysics Data System (ADS)

    Sigurdson, Lorenz; Apps, Christopher

    2000-11-01

    "Synthetic Jets" have previously been produced where an oscillating flow with zero net mass flux acts on the edges of an orifice. The resulting flow is similar to a normal jet. We have proposed and verified that another type of jet called a "Synthetic Fence Jet" (SFJ or "fe-je") can also be created. We introduced a fence perpendicular to both a wall and an oscillating velocity field. Under certain conditions a jet was formed by vortices of alternating sign. The vortices were shed from the fence and they induced each other away from it. This phenomenon could be used as a method of flow control. The objective of this project was to use flow visualization to prove the existence of and characterize this jet. A test rig was used which incorporates smoke-wire flow visualization; independent oscillation level and frequency control; and computer- controlled data acquisition. It has been discovered that the jet direction can be vectored by altering the forcing waveform shape. To explain this a theory was developed that is based on the Biot-Savart law of vortex dynamics.

  6. Jet Noise Suppression

    NASA Technical Reports Server (NTRS)

    Gliebe, P. R.; Brausch, J. F.; Majjigi, R. K.; Lee, R.

    1991-01-01

    The objectives of this chapter are to review and summarize the jet noise suppression technology, to provide a physical and theoretical model to explain the measured jet noise suppression characteristics of different concepts, and to provide a set of guidelines for evolving jet noise suppression designs. The underlying principle for all jet noise suppression devices is to enhance rapid mixing (i.e., diffusion) of the jet plume by geometric and aerothermodynamic means. In the case of supersonic jets, the shock-cell broadband noise reduction is effectively accomplished by the elimination or mitigation of the shock-cell structure. So far, the diffusion concepts have predominantly concentrated on jet momentum and energy (kinetic and thermal) diffusion, in that order, and have yielded better noise reduction than the simple conical nozzles. A critical technology issue that needs resolution is the effect of flight on the noise suppression potential of mechanical suppressor nozzles. A more thorough investigation of this mechanism is necessary for the successful development and design of an acceptable noise suppression device for future high-speed civil transports.

  7. Solar coronal jets

    NASA Astrophysics Data System (ADS)

    Dobrzyck, D.

    The solar jets were first observed by SOHO instruments (EIT, LASCO, UVCS) during the previous solar minimum. They were small, fast ejections originating from flaring UV bright points within large polar coronal holes. The obtained data provided us with estimates of the jet plasma conditions, dynamics, evolution of the electron temperature and heating rate required to reproduce the observed ionization state. To follow the polar jets through the solar cycle a special SOHO Joint Observing Program (JOP 155) was designed. It involves a number of SOHO instruments (EIT, CDS, UVCS, LASCO) as well as TRACE. The coordinated observations have been carried out since April 2002. The data enabled to identify counterparts of the 1996-1998 solar minimum jets. Their frequency of several events per day appear comparable to the frequency from the previous solar minimum. The jets are believed to be triggered by field line reconnection between emerging magnetic dipole and pre-existing unipolar field. Existing models predict that the hot jet is formed together with another jet of a cool material. The particular goal of the coordinated SOHO and TRACE observations was to look for possible association of the hot and cool plasma ejections. Currently there is observational evidence that supports these models.

  8. The effect of geographic range on extinction risk during background and mass extinction.

    PubMed

    Payne, Jonathan L; Finnegan, Seth

    2007-06-19

    Wide geographic range is generally thought to buffer taxa against extinction, but the strength of this effect has not been investigated for the great majority of the fossil record. Although the majority of genus extinctions have occurred between major mass extinctions, little is known about extinction selectivity regimes during these "background" intervals. Consequently, the question of whether selectivity regimes differ between background and mass extinctions is largely unresolved. Using logistic regression, we evaluated the selectivity of genus survivorship with respect to geographic range by using a global database of fossil benthic marine invertebrates spanning the Cambrian through the Neogene periods, an interval of approximately 500 My. Our results show that wide geographic range has been significantly and positively associated with survivorship for the great majority of Phanerozoic time. Moreover, the significant association between geographic range and survivorship remains after controlling for differences in species richness and abundance among genera. However, mass extinctions and several second-order extinction events exhibit less geographic range selectivity than predicted by range alone. Widespread environmental disturbance can explain the reduced association between geographic range and extinction risk by simultaneously affecting genera with similar ecological and physiological characteristics on global scales. Although factors other than geographic range have certainly affected extinction risk during many intervals, geographic range is likely the most consistently significant predictor of extinction risk in the marine fossil record.

  9. The effect of geographic range on extinction risk during background and mass extinction

    PubMed Central

    Payne, Jonathan L.; Finnegan, Seth

    2007-01-01

    Wide geographic range is generally thought to buffer taxa against extinction, but the strength of this effect has not been investigated for the great majority of the fossil record. Although the majority of genus extinctions have occurred between major mass extinctions, little is known about extinction selectivity regimes during these “background” intervals. Consequently, the question of whether selectivity regimes differ between background and mass extinctions is largely unresolved. Using logistic regression, we evaluated the selectivity of genus survivorship with respect to geographic range by using a global database of fossil benthic marine invertebrates spanning the Cambrian through the Neogene periods, an interval of ≈500 My. Our results show that wide geographic range has been significantly and positively associated with survivorship for the great majority of Phanerozoic time. Moreover, the significant association between geographic range and survivorship remains after controlling for differences in species richness and abundance among genera. However, mass extinctions and several second-order extinction events exhibit less geographic range selectivity than predicted by range alone. Widespread environmental disturbance can explain the reduced association between geographic range and extinction risk by simultaneously affecting genera with similar ecological and physiological characteristics on global scales. Although factors other than geographic range have certainly affected extinction risk during many intervals, geographic range is likely the most consistently significant predictor of extinction risk in the marine fossil record. PMID:17563357

  10. Estimating extinction using unsupervised machine learning

    NASA Astrophysics Data System (ADS)

    Meingast, Stefan; Lombardi, Marco; Alves, João

    2017-05-01

    Dust extinction is the most robust tracer of the gas distribution in the interstellar medium, but measuring extinction is limited by the systematic uncertainties involved in estimating the intrinsic colors to background stars. In this paper we present a new technique, Pnicer, that estimates intrinsic colors and extinction for individual stars using unsupervised machine learning algorithms. This new method aims to be free from any priors with respect to the column density and intrinsic color distribution. It is applicable to any combination of parameters and works in arbitrary numbers of dimensions. Furthermore, it is not restricted to color space. Extinction toward single sources is determined by fitting Gaussian mixture models along the extinction vector to (extinction-free) control field observations. In this way it becomes possible to describe the extinction for observed sources with probability densities, rather than a single value. Pnicer effectively eliminates known biases found in similar methods and outperforms them in cases of deep observational data where the number of background galaxies is significant, or when a large number of parameters is used to break degeneracies in the intrinsic color distributions. This new method remains computationally competitive, making it possible to correctly de-redden millions of sources within a matter of seconds. With the ever-increasing number of large-scale high-sensitivity imaging surveys, Pnicer offers a fast and reliable way to efficiently calculate extinction for arbitrary parameter combinations without prior information on source characteristics. The Pnicer software package also offers access to the well-established Nicer technique in a simple unified interface and is capable of building extinction maps including the Nicest correction for cloud substructure. Pnicer is offered to the community as an open-source software solution and is entirely written in Python.

  11. Induction, contrast, and resistance to extinction1

    PubMed Central

    Reynolds, G. S.

    1968-01-01

    The resistance of responding to extinction after variable-interval reinforcement in one of two components of a multiple schedule of reinforcement was (1) greater, when responding in the second component was reinforced on a variable-interval schedule than when responding there was extinguished, (2) not reduced, by a more rapid decrease in the rate of responding than occurs in ordinary extinction in the second component, and, (3) increased, by the occurrence of positive behavioral contrast before the beginning of extinction. PMID:5672253

  12. Jet Physics at CDF

    SciTech Connect

    Sally Seidel

    2004-06-28

    Jets have been studied by the CDF Collaboration [1] as a means of searching for new particles and interactions, testing a variety of perturbative QCD predictions, and providing input for the global parton distribution function (PDF) fits. Unless otherwise indicated below, the jets were reconstructed using a cone algorithm [2] with cone radius R = 0.7 from data taken at the Fermilab Tevatron collider in Run 2, 2001-2003, with {radical}s = 1.96 TeV. Central jets, in the pseudorapidity range relative to fixed detector coordinates 0.1 < |{eta}| < 0.7, are used.

  13. Angular Scaling In Jets

    SciTech Connect

    Jankowiak, Martin; Larkoski, Andrew J.; /SLAC

    2012-02-17

    We introduce a jet shape observable defined for an ensemble of jets in terms of two-particle angular correlations and a resolution parameter R. This quantity is infrared and collinear safe and can be interpreted as a scaling exponent for the angular distribution of mass inside the jet. For small R it is close to the value 2 as a consequence of the approximately scale invariant QCD dynamics. For large R it is sensitive to non-perturbative effects. We describe the use of this correlation function for tests of QCD, for studying underlying event and pile-up effects, and for tuning Monte Carlo event generators.

  14. Extinction from a Rationalist Perspective

    PubMed Central

    Gallistel, C. R.

    2012-01-01

    The merging of the computational theory of mind and evolutionary thinking leads to a kind of rationalism, in which enduring truths about the world have become implicit in the computations that enable the brain to cope with the experienced world. The dead reckoning computation, for example, is implemented within the brains of animals as one of the mechanisms that enables them to learn where they are (Gallistel, 1990, 1995). It integrates a velocity signal with respect to a time signal. Thus, the manner in which position and velocity relate to one another in the world is reflected in the manner in which signals representing those variables are processed in the brain. I use principles of information theory and Bayesian inference to derive from other simple principles explanations for: 1) the failure of partial reinforcement to increase reinforcements to acquisition; 2) the partial reinforcement extinction effect; 3) spontaneous recovery; 4) renewal; 5) reinstatement; 6) resurgence (aka facilitated reacquisition). Like the principle underlying dead-reckoning, these principles are grounded in analytic considerations. They are the kind of enduring truths about the world that are likely to have shaped the brain's computations. PMID:22391153

  15. SP8 Sequencing Extinct Genomes

    PubMed Central

    Poinar, H.

    2007-01-01

    Nucleic acids, which hold clues to the evolution of various animal and hominid taxa, are comparatively weak molecules from other cellular debris, and thus evolutionary biologists are in essence time trapped. Fortunately, DNA and protein fragments do exist in fossil remains beyond what theoretical experimentation would suggest. Sequestering of DNA molecules in humic or Maillard-like complexes likely represents a rich source of DNA molecules from the past, which have yet to be tapped. These molecules were impossible to acquire due to the selective nature of the polymerase chain reaction. Recently, however, rapid parallel pyrosequencing techniques, such as those used in metagenomics-based research, which, in theory, allow for the identification of all short nucleotide sequences in a sample in a non-selective approach, have the potential to allow the identification of all nucleic acids in a sample, and thus represent the way forward for ancient DNA. In theory, this new technology will allow the completion of genomes of extinct animals, plants, and microbes. I will discuss the benefits and pitfalls of this metagenomics approach to ancient DNA, highlighting our recent efforts underway to sequence the wooly mammoth genome as well as other fossil remains.

  16. Extinction from a rationalist perspective.

    PubMed

    Gallistel, C R

    2012-05-01

    The merging of the computational theory of mind and evolutionary thinking leads to a kind of rationalism, in which enduring truths about the world have become implicit in the computations that enable the brain to cope with the experienced world. The dead reckoning computation, for example, is implemented within the brains of animals as one of the mechanisms that enables them to learn where they are (Gallistel, 1990, 1995). It integrates a velocity signal with respect to a time signal. Thus, the manner in which position and velocity relate to one another in the world is reflected in the manner in which signals representing those variables are processed in the brain. I use principles of information theory and Bayesian inference to derive from other simple principles explanations for: (1) the failure of partial reinforcement to increase reinforcements to acquisition; (2) the partial reinforcement extinction effect; (3) spontaneous recovery; (4) renewal; (5) reinstatement; (6) resurgence (aka facilitated reacquisition). Like the principle underlying dead-reckoning, these principles are grounded in analytic considerations. They are the kind of enduring truths about the world that are likely to have shaped the brain's computations.

  17. Hospital autopsy: Endangered or extinct?

    PubMed Central

    Turnbull, Angus; Osborn, Michael; Nicholas, Nick

    2015-01-01

    Aim To determine the hospital autopsy rate for the UK in 2013. Methods A study of data from a ‘Freedom of Information’ request to all (n=186) acute NHS Trusts within England (n=160), NHS Boards in Scotland (n=14) and Wales (n=7) and Social Care Trusts in Northern Ireland (n=5). Hospital autopsy rates were calculated from the number of hospital autopsies performed in 2013 as a percentage of total inpatient deaths in the Trust that year. Results The UK response rate was 99% (n=184), yielding a mean autopsy rate of 0.69%. The mean rates were 0.51% (England), 2.13% (Scotland), 0.65% (Wales) and 0.46% (Northern Ireland). 23% (n=38) of all included respondents had a rate of 0% and 86% (n=143) a rate less than 1%. Conclusions The decline in hospital autopsy has continued relentlessly and, for better or for worse, the practice is on the verge of extinction in the UK. The study highlights to health professionals and policy makers the magnitude of this decline. Further research should investigate the impact of this on patient safety, clinical audit, public health and medical education. PMID:26076965

  18. Hospital autopsy: Endangered or extinct?

    PubMed

    Turnbull, Angus; Osborn, Michael; Nicholas, Nick

    2015-08-01

    To determine the hospital autopsy rate for the UK in 2013. A study of data from a 'Freedom of Information' request to all (n=186) acute NHS Trusts within England (n=160), NHS Boards in Scotland (n=14) and Wales (n=7) and Social Care Trusts in Northern Ireland (n=5). Hospital autopsy rates were calculated from the number of hospital autopsies performed in 2013 as a percentage of total inpatient deaths in the Trust that year. The UK response rate was 99% (n=184), yielding a mean autopsy rate of 0.69%. The mean rates were 0.51% (England), 2.13% (Scotland), 0.65% (Wales) and 0.46% (Northern Ireland). 23% (n=38) of all included respondents had a rate of 0% and 86% (n=143) a rate less than 1%. The decline in hospital autopsy has continued relentlessly and, for better or for worse, the practice is on the verge of extinction in the UK. The study highlights to health professionals and policy makers the magnitude of this decline. Further research should investigate the impact of this on patient safety, clinical audit, public health and medical education. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

  19. Asteroid impact and mass extinction

    NASA Astrophysics Data System (ADS)

    Bell, Peter M.

    Knowledge of the phenomena of impacts of objects from space on planetary surfaces is extensive, resulting from more than a decade of studies of craters on the earth, moon, and the terrestrial planets. Expertise in the geochemical analysis of a trace element assemblage with an extraterrestrial signature, such as iridium, osmium, palladium, nickel, and gold, is also quite well developed, so it was tempting to interpret the finding of such an assemblage in the Cretaceous-Tertiary boundary layer at numerous locations around the globe as being caused by impact of a large asteroid or other body. The evidence was compelling, and the interpretation as applied to certain marine organisms may be correct. What made the discovery newsworthy, however, was the additional interpretation that the impact had caused the known mass extinction of the dinosaurs and certain other flora and fauna 65 million years ago, at the end of the Cretaceous period. Particles of the earth's surface expelled by the impact would have been accelerated into orbit, shielding the earth from sunlight. The example for this was the effect observed after the 1888 explosive volcanic eruption in the sea between Java and Sumatra (now called Rakatu) that virtually propelled fragments of the entire mass of Krakatau into the atmosphere for a period thought to have extended for about 3 years, causing darkening of the sky and unusual and spectacular sunsets.

  20. Warming-induced changes in predation, extinction and invasion in an ectotherm food web.

    PubMed

    Seifert, Linda I; Weithoff, Guntram; Gaedke, Ursula; Vos, Matthijs

    2015-06-01

    Climate change will alter the forces of predation and competition in temperate ectotherm food webs. This may increase local extinction rates, change the fate of invasions and impede species reintroductions into communities. Invasion success could be modulated by traits (e.g., defenses) and adaptations to climate. We studied how different temperatures affect the time until extinction of species, using bitrophic and tritrophic planktonic food webs to evaluate the relative importance of predatory overexploitation and competitive exclusion, at 15 and 25 °C. In addition, we tested how inclusion of a subtropical as opposed to a temperate strain in this model food web affects times until extinction. Further, we studied the invasion success of the temperate rotifer Brachionus calyciflorus into the planktonic food web at 15 and 25 °C on five consecutive introduction dates, during which the relative forces of predation and competition differed. A higher temperature dramatically shortened times until extinction of all herbivore species due to carnivorous overexploitation in tritrophic systems. Surprisingly, warming did not increase rates of competitive exclusion among the tested herbivore species in bitrophic communities. Including a subtropical herbivore strain reduced top-down control by the carnivore at high temperature. Invasion attempts of temperate B. calyciflorus into the food web always succeeded at 15 °C, but consistently failed at 25 °C due to voracious overexploitation by the carnivore. Pre-induction of defenses (spines) in B. calyciflorus before the invasion attempt did not change its invasion success at the high temperature. We conclude that high temperatures may promote local extinctions in temperate ectotherms and reduce their chances of successful recovery.

  1. Blinded by the Jets

    NASA Image and Video Library

    2005-07-04

    This image shows the view from NASA Deep Impact probe 30 minutes before it was pummeled by comet Tempel 1. The picture brightness has been enhanced to show the jets of dust streaming away from the comet.

  2. Counterflowing Jet Subsystem Design

    NASA Technical Reports Server (NTRS)

    Farr, Rebecca; Daso, Endwell; Pritchett, Victor; Wang, Ten-See

    2010-01-01

    A counterflowing jet design (a spacecraft and trans-atmospheric subsystem) employs centrally located, supersonic cold gas jets on the face of the vehicle, ejecting into the oncoming free stream. Depending on the supersonic free-stream conditions and the ejected mass flow rate of the counterflowing jets, the bow shock of the vehicle is moved upstream, further away from the vehicle. This results in an increasing shock standoff distance of the bow shock with a progressively weaker shock. At a critical jet mass flow rate, the bow shock becomes so weak that it is transformed into a series of compression waves spread out in a much wider region, thus significantly modifying the flow that wets the outer surfaces, with an attendant reduction in wave and skin friction drag and aerothermal loads.

  3. Astrophysics: Cosmic jet engines

    NASA Astrophysics Data System (ADS)

    Young, Andy

    2010-02-01

    In some galaxies, matter falling onto a supermassive black hole is ejected in narrow jets moving at close to the speed of light. New observations provide insight into the workings of these cosmic accelerators.

  4. Undercover Jet Exposed

    NASA Image and Video Library

    2011-04-04

    This image layout shows two views of the same baby star from NASA Spitzer Space Telescope. Spitzer view shows that this star has a second, identical jet shooting off in the opposite direction of the first.

  5. Jet propulsion for airplanes

    NASA Technical Reports Server (NTRS)

    Buckingham, Edgar

    1924-01-01

    This report is a description of a method of propelling airplanes by the reaction of jet propulsion. Air is compressed and mixed with fuel in a combustion chamber, where the mixture burns at constant pressure. The combustion products issue through a nozzle, and the reaction of that of the motor-driven air screw. The computations are outlined and the results given by tables and curves. The relative fuel consumption and weight of machinery for the jet, decrease as the flying speed increases; but at 250 miles per hour the jet would still take about four times as much fuel per thrust horsepower-hour as the air screw, and the power plant would be heavier and much more complicated. Propulsion by the reaction of a simple jet can not compete with air screw propulsion at such flying speeds as are now in prospect.

  6. Measurements of railgun generated supersonic plasma jet propagation and two jet oblique merging

    NASA Astrophysics Data System (ADS)

    Merritt, Elizabeth C.

    ne ˜ 10E 16 per cc, Te ≈ 1.4 eV, velocity v ≈ 30 km/s, sonic Mach number M ≈ 14, diameter ≈ 5 cm, and length ≈ 20 cm. Interferometry in conjunction with CCD line-out data showed that the average jet density decreases by a factor of ten after propagating 40 cm, which is at the very low end of the 8--160 times drop predicted by ideal hydrodynamic theory. In oblique merge experiments, interferometry identified a density increase consistent with shock formation as opposed to simple plasma interpenetration, and the consistent formation of a density structure (with scale length ˜ lambdaii') near the merge plane. Imaging showed formation of a multi-peaked emission structure transverse to the jet-merging plane with widths similar to the density structure. Since the merging regime was semi-collisional and the counter-streaming ion collisionality was comparable to the merged-structure size, we interpreted the observations using both hydrodynamic oblique shock and multi-fluid plasma theory and simulations. We find that our observations were consistent with oblique shock theory and a collisional, one-dimensional, multi-fluid plasma simulation.

  7. Colliding jets provide depth control for water jetting in bone tissue.

    PubMed

    den Dunnen, S; Dankelman, J; Kerkhoffs, G M; Tuijthof, G

    2017-08-01

    drilling depth nor the variation in depth. The diameters of the resulting holes in the direction of the jets is significantly larger for CWJ at 90° than for 30° or a single jet. This study shows that CWJ provides accurate depth control when water jet drilling in an inhomogeneous material such as bone. The maximum variance measured by using the 95% confidence interval is 0.6 mm opposed to 5.4 mm for SWJ. This variance is smaller than the accuracy required for bone debridement treatments (2-4 mm deep) or drilling pilot holes. This confirms that the use of CWJ is an inherently safe method that can be used to accurately drill in bones. Copyright © 2017 Elsevier Ltd. All rights reserved.

  8. Estimating human effects on global extinction

    NASA Astrophysics Data System (ADS)

    Wright, D. H.

    1987-12-01

    A quantitative technique for estimating extinctions due to clearing of natural ecosystems is described. Applied on a global scale, the method yields preliminary figures on extinctions of flowering plants, butterflies, land birds and land mammals ranging from 5.4 to 15.3% for the period from the beginning of agriculture until the year 1980. Actual numbers of extinctions of mammals and birds to date are much lower, possibly in part due to a tendency for the technique to overestimate species loss at the global scale. However, delayed extinctions of species whose populations have been reduced but not exterminated by habitat destruction are likely, suggesting that human impacts may be more serious than they currently appear.

  9. Extinction in the Lotka-Volterra model.

    PubMed

    Parker, Matthew; Kamenev, Alex

    2009-08-01

    Birth-death processes often exhibit an oscillatory behavior. We investigate a particular case where the oscillation cycles are marginally stable on the mean-field level. An iconic example of such a system is the Lotka-Volterra model of predator-prey interaction. Fluctuation effects due to discreteness of the populations destroy the mean-field stability and eventually drive the system toward extinction of one or both species. We show that the corresponding extinction time scales as a certain power-law of the population sizes. This behavior should be contrasted with the extinction of models stable in the mean-field approximation. In the latter case the extinction time scales exponentially with size.

  10. Opportunistic exploitation: an overlooked pathway to extinction.

    PubMed

    Branch, Trevor A; Lobo, Aaron S; Purcell, Steven W

    2013-07-01

    How can species be exploited economically to extinction? Past single-species hypotheses examining the economic plausibility of exploiting rare species have argued that the escalating value of rarity allows extinction to be profitable. We describe an alternative pathway toward extinction in multispecies exploitation systems, termed 'opportunistic exploitation'. In this mode, highly valued species that are targeted first by fishing, hunting, and logging become rare, but their populations can decline further through opportunistic exploitation while more common but less desirable species are targeted. Effectively, expanding exploitation to more species subsidizes the eventual extinction of valuable species at low densities. Managers need to recognize conditions that permit opportunistic depletion and pass regulations to protect highly desirable species when exploitation can expand to other species.

  11. Possible involvement of serotonin in extinction.

    PubMed

    Beninger, R J; Phillips, A G

    1979-01-01

    In Experiment 1, rats were trained to leverpress for continuous reinforcement with food; half were then intubated with the serotonin synthesis inhibitor parachlorophenylalanine (PCPA: 400 mg/kg) and half with water. In extinction the PCPA-treated rats responded at a higher rate. In Experiment 2, rats were trained on a random interval schedule and then assigned to two groups, treated as in Experiment 1, and tested in extinction. There was no significant difference in the resistance to extinction of the two groups. In Experiment 3, the responding of rats trained in a punished stepdown response paradigm and then given an intragastric injection of PCPA took longer to recover than the responding of water-injected controls. These observations suggest that serotonergic neurons might play a role in extinction processes.

  12. Electromagnetic wave extinction within a forested canopy

    NASA Technical Reports Server (NTRS)

    Karam, M. A.; Fung, A. K.

    1989-01-01

    A forested canopy is modeled by a collection of randomly oriented finite-length cylinders shaded by randomly oriented and distributed disk- or needle-shaped leaves. For a plane wave exciting the forested canopy, the extinction coefficient is formulated in terms of the extinction cross sections (ECSs) in the local frame of each forest component and the Eulerian angles of orientation (used to describe the orientation of each component). The ECSs in the local frame for the finite-length cylinders used to model the branches are obtained by using the forward-scattering theorem. ECSs in the local frame for the disk- and needle-shaped leaves are obtained by the summation of the absorption and scattering cross-sections. The behavior of the extinction coefficients with the incidence angle is investigated numerically for both deciduous and coniferous forest. The dependencies of the extinction coefficients on the orientation of the leaves are illustrated numerically.

  13. Biomarker Records Associated with Mass Extinction Events

    NASA Astrophysics Data System (ADS)

    Whiteside, Jessica H.; Grice, Kliti

    2016-06-01

    The history of life on Earth is punctuated by a series of mass extinction episodes that vary widely in their magnitude, duration, and cause. Biomarkers are a powerful tool for the reconstruction of historical environmental conditions and can therefore provide insights into the cause and responses to ancient extinction events. In examining the five largest mass extinctions in the geological record, investigators have used biomarkers to elucidate key processes such as eutrophy, euxinia, ocean acidification, changes in hydrological balance, and changes in atmospheric CO2. By using these molecular fossils to understand how Earth and its ecosystems have responded to unusual environmental activity during these extinctions, models can be made to predict how Earth will respond to future changes in its climate.

  14. Electromagnetic wave extinction within a forested canopy

    NASA Technical Reports Server (NTRS)

    Karam, M. A.; Fung, A. K.

    1989-01-01

    A forested canopy is modeled by a collection of randomly oriented finite-length cylinders shaded by randomly oriented and distributed disk- or needle-shaped leaves. For a plane wave exciting the forested canopy, the extinction coefficient is formulated in terms of the extinction cross sections (ECSs) in the local frame of each forest component and the Eulerian angles of orientation (used to describe the orientation of each component). The ECSs in the local frame for the finite-length cylinders used to model the branches are obtained by using the forward-scattering theorem. ECSs in the local frame for the disk- and needle-shaped leaves are obtained by the summation of the absorption and scattering cross-sections. The behavior of the extinction coefficients with the incidence angle is investigated numerically for both deciduous and coniferous forest. The dependencies of the extinction coefficients on the orientation of the leaves are illustrated numerically.

  15. Prehistoric bird extinctions and human hunting.

    PubMed

    Duncan, Richard P; Blackburn, Tim M; Worthy, Trevor H

    2002-03-07

    Holocene fossils document the extinction of hundreds of bird species on Pacific islands during prehistoric human occupation. Human hunting is implicated in these extinctions, but the impact of hunting is difficult to disentangle from the effects of other changes induced by humans, including habitat destruction and the introduction of other mammalian predators. Here, we use data from bones collected at a natural sand dune site and associated archaeological middens in New Zealand to show that, having controlled for differences in body mass and family membership (and hence for variation in life-history traits related to population growth rate), birds that were more intensively hunted by prehistoric humans had a higher probability of extinction. This result cannot be attributed to preservation biases and provides clear evidence that selective hunting contributed significantly to prehistoric bird extinctions at this site.

  16. Context and behavioral processes in extinction.

    PubMed

    Bouton, Mark E

    2004-01-01

    This article provides a selective review and integration of the behavioral literature on Pavlovian extinction. The first part reviews evidence that extinction does not destroy the original learning, but instead generates new learning that is especially context-dependent. The second part examines insights provided by research on several related behavioral phenomena (the interference paradigms, conditioned inhibition, and inhibition despite reinforcement). The final part examines four potential causes of extinction: the discrimination of a new reinforcement rate, generalization decrement, response inhibition, and violation of a reinforcer expectation. The data are consistent with behavioral models that emphasize the role of generalization decrement and expectation violation, but would be more so if those models were expanded to better accommodate the finding that extinction involves a context-modulated form of inhibitory learning.

  17. Calibrating the end-Permian mass extinction.

    PubMed

    Shen, Shu-zhong; Crowley, James L; Wang, Yue; Bowring, Samuel A; Erwin, Douglas H; Sadler, Peter M; Cao, Chang-qun; Rothman, Daniel H; Henderson, Charles M; Ramezani, Jahandar; Zhang, Hua; Shen, Yanan; Wang, Xiang-dong; Wang, Wei; Mu, Lin; Li, Wen-zhong; Tang, Yue-gang; Liu, Xiao-lei; Liu, Lu-jun; Zeng, Yong; Jiang, Yao-fa; Jin, Yu-gan

    2011-12-09

    The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ(13)C over 90,000 years, and coincided with a δ(13)C excursion of -5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

  18. The grey extinction curve in NGC 3603

    NASA Astrophysics Data System (ADS)

    Pang, Xiaoying; Pasquali, Anna; Grebel, Eva K.

    2016-02-01

    We use photometry in the F220W, F250W, F330W, F435W filters from the High Resolution Channel of the Advanced Camera for Surveys and photometry in the F555W, F675W, and F814W filters from the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope to derive individual stellar reddenings and extinctions for member stars in the HD 97950 cluster in the giant H ii region NGC 3603. Within the standard deviation associated with E(λ-F555W)/E(F435W-F555W) in each filter, the cluster extinction curve at ultraviolet wavelengths tends to be greyer than the average Galactic extinction laws from Cardelli et al. (1989) and Fitzpatrick et al. (1999). It is closer to the extinction law derived by Calzetti et al. (2000) for starburst galaxies, where the 0.2175 μm bump is absent.

  19. UV extinction properties of carina nebular dust

    NASA Technical Reports Server (NTRS)

    Massa, Derck

    1993-01-01

    I have performed an analysis of the UV extinction by dust along the line of sight to the young open cluster Tr 16. The observed curves are parameterized in order to extract quantitative information about the structure of the curves. Furthermore, by constructing differential extinction curves, obtained by differencing curves for stars which lie within a few arc seconds of each other on the sky, I was able to obtain a curve which is free of the effects of foreground extinction, and represents the extinction by the dust in the Tr 16 molecular cloud. I then show that this curve is nearly identical to one due to dust in the Orion molecular cloud. This result shows that dust in the Carina arm exhibits the same behavior as that in the local arm.

  20. Vaccine enhanced extinction in stochastic epidemic models

    NASA Astrophysics Data System (ADS)

    Billings, Lora; Mier-Y-Teran, Luis; Schwartz, Ira

    2012-02-01

    We address the problem of developing new and improved stochastic control methods that enhance extinction in disease models. In finite populations, extinction occurs when fluctuations owing to random transitions act as an effective force that drives one or more components or species to vanish. Using large deviation theory, we identify the location of the optimal path to extinction in epidemic models with stochastic vaccine controls. These models not only capture internal noise from random transitions, but also external fluctuations, such as stochastic vaccination scheduling. We quantify the effectiveness of the randomly applied vaccine over all possible distributions by using the location of the optimal path, and we identify the most efficient control algorithms. We also discuss how mean extinction times scale with epidemiological and social parameters.