The stationary non-equilibrium plasma of cosmic-ray electrons and positrons

NASA Astrophysics Data System (ADS)

Tomaschitz, Roman

2016-06-01

The statistical properties of the two-component plasma of cosmic-ray electrons and positrons measured by the AMS-02 experiment on the International Space Station and the HESS array of imaging atmospheric Cherenkov telescopes are analyzed. Stationary non-equilibrium distributions defining the relativistic electron-positron plasma are derived semi-empirically by performing spectral fits to the flux data and reconstructing the spectral number densities of the electronic and positronic components in phase space. These distributions are relativistic power-law densities with exponential cutoff, admitting an extensive entropy variable and converging to the Maxwell-Boltzmann or Fermi-Dirac distributions in the non-relativistic limit. Cosmic-ray electrons and positrons constitute a classical (low-density high-temperature) plasma due to the low fugacity in the quantized partition function. The positron fraction is assembled from the flux densities inferred from least-squares fits to the electron and positron spectra and is subjected to test by comparing with the AMS-02 flux ratio measured in the GeV interval. The calculated positron fraction extends to TeV energies, predicting a broad spectral peak at about 1 TeV followed by exponential decay.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring

NASA Astrophysics Data System (ADS)

Gong, Chao; Tochitsky, Sergei Ya.; Fiuza, Frederico; Pigeon, Jeremy J.; Joshi, Chan

2016-06-01

We have used multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, vHB, of the density cavity pushed forward by a train of C O2 laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the vHB falls rapidly as the laser pulse intensity falls at the back of the laser pulse train. A heuristic theory is presented that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. The measured values of vHB, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring

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

Gong, Chao; Tochitsky, Sergei Ya.; Fiuza, Frederico

Here, we use multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, vHB, of the density cavity pushed forward by a train of CO 2 laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the vHB falls rapidly as the laser pulse intensity falls at the back of the laser pulsemore » train. We present a heuristic theory that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. Furthermore, the measured values of v HB, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.« less

Plasma dynamics near critical density inferred from direct measurements of laser hole boring.

PubMed

Gong, Chao; Tochitsky, Sergei Ya; Fiuza, Frederico; Pigeon, Jeremy J; Joshi, Chan

2016-06-01

We have used multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, v_{HB}, of the density cavity pushed forward by a train of CO_{2} laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the v_{HB} falls rapidly as the laser pulse intensity falls at the back of the laser pulse train. A heuristic theory is presented that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. The measured values of v_{HB}, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring

DOE PAGES

Gong, Chao; Tochitsky, Sergei Ya.; Fiuza, Frederico; ...

2017-06-24

Here, we use multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, vHB, of the density cavity pushed forward by a train of CO 2 laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the vHB falls rapidly as the laser pulse intensity falls at the back of the laser pulsemore » train. We present a heuristic theory that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. Furthermore, the measured values of v HB, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.« less

Coincident observations of ionospheric troughs and the equatorial plasmapause

NASA Technical Reports Server (NTRS)

Grebowsky, J. M.; Maynard, N. C.; Tulunay, Y. K.; Lanzerotti, L. J.

1976-01-01

Electron-density observations made in the topside ionosphere by the Ariel 4 and Isis 2 satellites are examined in conjunction with results obtained by Explorer 45 when it traversed the near-equatorial plasmapause with one hour (both UT and MLT) of the Ariel and Isis traversals of the same L coordinate. Both dusk and night observations are analyzed, and an attempt is made to show that depressions in ionospheric electron density occur in the vicinity of the plasmapause field line. It is concluded that the electron distributions observed in the electron-density troughs at 550 km near dusk by Ariel and at 1400 km near midnight by Isis do not always parallel variations in the light-ion distribution inferred from the Explorer plasmapause traversals and that there appears to be no specific feature of the main ionospheric trough which can be used to identify the plasmapause field line except in a statistical sense.

Heat budget of ionospheric electrons

NASA Technical Reports Server (NTRS)

Prasad, S. S.; Schneck, L. J.

1976-01-01

Heat input calculations were detached from solar extreme UV data and monatomic oxygen densities were derived from simultaneously measured data sets (ion composition 146-191 km) in a study of the heat budget of ionosphere electrons. Earlier inferences that cooling predominates over heating are supported. A search for additional heat sources or a revision of the cooling rates is recommended, by way of balancing the heat budget. Importance is attached to electron cooling by fine structure excitation of monatomic oxygen.

Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Benz, Arnold O.

1996-01-01

We compare electron densities measured at three different locations in solar flares: (1) in Soft X-Ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps (n(sub e, sup SXR) = (0.2-2.5) x 10(exp 11)/ cu cm); (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zuerich (n(sub e, sup upflow) = (0.3-11) x 10(exp 10)/cu cm; and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [n(sub e, sup acc) = (0.6-10) x 10(exp 9)/cu cm]. The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range n(sub e, sup upflow)/n(sub e, sup SXR) = 0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., n(sub e, sup acc)/n(sub e, sup SXR) = 0.005- 0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models).

Using Secondary Nuclear Reaction Products to Infer the Fuel Areal Density, Convergence, and Electron Temperatures of Imploding D2 and D3 He Filled Capsules on the NIF

NASA Astrophysics Data System (ADS)

Lahmann, B.; Frenje, J. A.; Gatu Johnson, M.; Seguin, F. H.; Li, C. K.; Petrasso, R. D.; Hartouni, E. P.; Yeamans, C. B.; Rinderknecht, H. G.; Sayre, D. B.; Grim, G.; Baker, K.; Casey, D. T.; Dewald, E.; Goyon, C.; Jarrott, L. C.; Khan, S.; Lepape, S.; Ma, T.; Pickworth, L.; Shah, R.; Kline, J. L.; Perry, T.; Zylstra, A.; Yi, S. A.

2017-10-01

In deuterium-filled inertial confinement fusion implosions, 0.82 MeV 3He and 1.01 MeV T (generated by the primary DD reaction branches) can undergo fusion reactions with the thermal deuterium plasma to create secondary D3He protons and DT neutrons, respectively. In regimes of moderate fuel areal density (ρR 5 - 100 mg/cm2) the ratio of both of these secondary yields to the primary yield can be used to infer the fuel ρR, convergence ratio (CR), and an electron temperature (Te) . This technique has been used on a myriad of deuterium filled capsule implosion experiments on the NIF using the neutron time of flight (nTOF) diagnostics to measure the yield of secondary DT neutrons and CR-39 based wedge range filters (WRFs) to measure the yield of secondary D3He protons. This work is supported in part by the U.S. DoE and LLNL.

Temperature-dependent band structure of SrTiO3 interfaces

NASA Astrophysics Data System (ADS)

Raslan, Amany; Lafleur, Patrick; Atkinson, W. A.

2017-02-01

We build a theoretical model for the electronic properties of the two-dimensional (2D) electron gas that forms at the interface between insulating SrTiO3 and a number of polar cap layers, including LaTiO3, LaAlO3, and GdTiO3. The model treats conduction electrons within a tight-binding approximation and the dielectric polarization via a Landau-Devonshire free energy that incorporates strontium titanate's strongly nonlinear, nonlocal, and temperature-dependent dielectric response. The self-consistent band structure comprises a mix of quantum 2D states that are tightly bound to the interface and quasi-three-dimensional (3D) states that extend hundreds of unit cells into the SrTiO3 substrate. We find that there is a substantial shift of electrons away from the interface into the 3D tails as temperature is lowered from 300 K to 10 K. This shift is least important at high electron densities (˜1014cm-2 ) but becomes substantial at low densities; for example, the total electron density within 4 nm of the interface changes by a factor of two for 2D electron densities ˜1013cm-2 . We speculate that the quasi-3D tails form the low-density high-mobility component of the interfacial electron gas that is widely inferred from magnetoresistance measurements.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes.

PubMed

Kumar, Niraj; Pal, Dharmendra Kumar; Jadon, Arvind Singh; Pal, Udit Narayan; Rahaman, Hasibur; Prakash, Ram

2016-03-01

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

Two-resonance probe for measuring electron density in low-pressure plasmas

NASA Astrophysics Data System (ADS)

Kim, D. W.; You, S. J.; Kim, S. J.; Kim, J. H.; Oh, W. Y.

2017-04-01

A technique for measuring double-checked electron density using two types of microwave resonance is presented. Simultaneous measurement of the resonances (plasma and quarter-wavelength resonator resonances), which were used for the cutoff probe (CP) and hairpin probe (HP), was achieved by the proposed microwave resonance probe. The developed two-resonance probe (TRP) consists of parallel separated coaxial cables exposing the radiation and detection tips. The structure resembles that of the CP, except the gapped coaxial cables operate not only as a microwave feeder for the CP but also as a U- shaped quarter-wavelength resonator for the HP. By virtue of this structure, the microwave resonances that have typically been used for measuring the electron density for the CP and HP were clearly identified on the microwave transmission spectrum of the TRP. The two types of resonances were measured experimentally under various power and pressure conditions for the plasma. A three-dimensional full-wave simulation model for the TRP is also presented and used to investigate and reproduce the resonances. The electron densities inferred from the resonances were compared and showed good agreement. Quantitative differences between the densities were attributed to the effects of the sheath width and spatial density gradient on the resonances. This accessible technique of using the TRP to obtain double-checked electron densities may be useful for comparative study and provides complementary uses for the CP and HP.

In-flight calibration of mesospheric rocket plasma probes

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

Havnes, Ove; University Studies Svalbard; Hartquist, Thomas W.

Many effects and factors can influence the efficiency of a rocket plasma probe. These include payload charging, solar illumination, rocket payload orientation and rotation, and dust impact induced secondary charge production. As a consequence, considerable uncertainties can arise in the determination of the effective cross sections of plasma probes and measured electron and ion densities. We present a new method for calibrating mesospheric rocket plasma probes and obtaining reliable measurements of plasma densities. This method can be used if a payload also carries a probe for measuring the dust charge density. It is based on that a dust probe's effectivemore » cross section for measuring the charged component of dust normally is nearly equal to its geometric cross section, and it involves the comparison of variations in the dust charge density measured with the dust detector to the corresponding current variations measured with the electron and/or ion probes. In cases in which the dust charge density is significantly smaller than the electron density, the relation between plasma and dust charge density variations can be simplified and used to infer the effective cross sections of the plasma probes. We illustrate the utility of the method by analysing the data from a specific rocket flight of a payload containing both dust and electron probes.« less

In-flight calibration of mesospheric rocket plasma probes.

PubMed

Havnes, Ove; Hartquist, Thomas W; Kassa, Meseret; Morfill, Gregor E

2011-07-01

Many effects and factors can influence the efficiency of a rocket plasma probe. These include payload charging, solar illumination, rocket payload orientation and rotation, and dust impact induced secondary charge production. As a consequence, considerable uncertainties can arise in the determination of the effective cross sections of plasma probes and measured electron and ion densities. We present a new method for calibrating mesospheric rocket plasma probes and obtaining reliable measurements of plasma densities. This method can be used if a payload also carries a probe for measuring the dust charge density. It is based on that a dust probe's effective cross section for measuring the charged component of dust normally is nearly equal to its geometric cross section, and it involves the comparison of variations in the dust charge density measured with the dust detector to the corresponding current variations measured with the electron and/or ion probes. In cases in which the dust charge density is significantly smaller than the electron density, the relation between plasma and dust charge density variations can be simplified and used to infer the effective cross sections of the plasma probes. We illustrate the utility of the method by analysing the data from a specific rocket flight of a payload containing both dust and electron probes.

Model uncertainties of local-thermodynamic-equilibrium K-shell spectroscopy

NASA Astrophysics Data System (ADS)

Nagayama, T.; Bailey, J. E.; Mancini, R. C.; Iglesias, C. A.; Hansen, S. B.; Blancard, C.; Chung, H. K.; Colgan, J.; Cosse, Ph.; Faussurier, G.; Florido, R.; Fontes, C. J.; Gilleron, F.; Golovkin, I. E.; Kilcrease, D. P.; Loisel, G.; MacFarlane, J. J.; Pain, J.-C.; Rochau, G. A.; Sherrill, M. E.; Lee, R. W.

2016-09-01

Local-thermodynamic-equilibrium (LTE) K-shell spectroscopy is a common tool to diagnose electron density, ne, and electron temperature, Te, of high-energy-density (HED) plasmas. Knowing the accuracy of such diagnostics is important to provide quantitative conclusions of many HED-plasma research efforts. For example, Fe opacities were recently measured at multiple conditions at the Sandia National Laboratories Z machine (Bailey et al., 2015), showing significant disagreement with modeled opacities. Since the plasma conditions were measured using K-shell spectroscopy of tracer Mg (Nagayama et al., 2014), one concern is the accuracy of the inferred Fe conditions. In this article, we investigate the K-shell spectroscopy model uncertainties by analyzing the Mg spectra computed with 11 different models at the same conditions. We find that the inferred conditions differ by ±20-30% in ne and ±2-4% in Te depending on the choice of spectral model. Also, we find that half of the Te uncertainty comes from ne uncertainty. To refine the accuracy of the K-shell spectroscopy, it is important to scrutinize and experimentally validate line-shape theory. We investigate the impact of the inferred ne and Te model uncertainty on the Fe opacity measurements. Its impact is small and does not explain the reported discrepancies.

Using multiple secondary fusion products to evaluate fuel ρR, electron temperature, and mix in deuterium-filled implosions at the NIF

DOE PAGES

Rinderknecht, H. G.; Rosenberg, M. J.; Zylstra, A. B.; ...

2015-08-25

In deuterium-filled inertial confinement fusion implosions, the secondary fusion processes D( 3He,p) 4He and D(T,n) 4He occur, as the primary fusion products 3He and T react in flight with thermal deuterons. In implosions with moderate fuel areal density (~ 5–100 mg/cm 2), the secondary D- 3He reaction saturates, while the D-T reaction does not, and the combined information from these secondary products is used to constrain both the areal density and either the plasma electron temperature or changes in the composition due to mix of shell material into the fuel. The underlying theory of this technique is developed and appliedmore » to three classes of implosions on the National Ignition Facility: direct-drive exploding pushers, indirect-drive 1-shock and 2-shock implosions,and polar direct-drive implosions. In the 1- and 2-shock implosions, the electron temperature is inferred to be 0.65 x and 0.33 x the burn-averaged ion temperature, respectively. The inferred mixed mass in the polar direct-drive implosions is in agreement with measurements using alternative techniques.« less

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes

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

Kumar, Niraj; Pal, Udit Narayan; Prakash, Ram

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electronmore » beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.« less

The auroral current circuit and field-aligned currents observed by FAST

NASA Astrophysics Data System (ADS)

Elphic, R. C.; Bonnell, J. W.; Strangeway, R. J.; Kepko, L.; Ergun, R. E.; McFadden, J. P.; Carlson, C. W.; Peria, W.; Cattell, C. A.; Klumpar, D.; Shelley, E.; Peterson, W.; Moebius, E.; Kistler, L.; Pfaff, R.

FAST observes signatures of small-scale downward-going current at the edges of the inverted-V regions where the primary (auroral) electrons are found. In the winter pre-midnight auroral zone these downward currents are carried by upward flowing low- and medium-energy (up to several keV) electron beams. FAST instrumentation shows agreement between the current densities inferred from both the electron distributions and gradients in the magnetic field. FAST data taken near apogee (˜4000-km altitude) commonly show downward current magnetic field deflections consistent with the observed upward flux of ˜109 electrons cm-2 s-1, or current densities of several µA m-2. The electron, field-aligned current and electric field signatures indicate the downward currents may be associated with “black aurora” and auroral ionospheric cavities. The field-aligned voltage-current relationship in the downward current region is nonlinear.

Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Benz, Arnold O.

1995-01-01

We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca xix soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T-(exp -3/2) dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyzed 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Phoenix, hard X-ray data from BATSE/CGRO, and soft X-ray data from GOES were available. We detected slowly drifting high-frequency cutoffs between 1.1 and 3.0 GHz, with drift rates of -41 +/- 32 MHz/s, extending over time intervals of 24 +/- 23 s. Developing a density model for type III-emitting flare loops based on the statistically observed drift rate of type III bursts by Alvarez & Haddock, we infer velocities of up to 360 km/s for the upflowing plasma, with an average of v(sub CE) = 236 +/- 130 km /s for episodes with 5-15 s duration. The mean electron density of the upflowing plasma is n(sub e) = 5.2(+/-3.1) x 10(exp 10) /cu cm when it is first detected in radio, at coronal altitudes of h(sub 0) = 9.2 +/- 2.3 Mm.

Density of Trap States and Auger-mediated Electron Trapping in CdTe Quantum-Dot Solids.

PubMed

Boehme, Simon C; Azpiroz, Jon Mikel; Aulin, Yaroslav V; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Infante, Ivan; Houtepen, Arjan J

2015-05-13

Charge trapping is an ubiquitous process in colloidal quantum-dot solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermoelectrics. Although empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact chemical nature of the trapping mechanism remains largely unidentified. In this study, we determine the density of trap states in CdTe quantum-dot solids both experimentally, using a combination of electrochemical control of the Fermi level with ultrafast transient absorption and time-resolved photoluminescence spectroscopy, and theoretically, via density functional theory calculations. We find a high density of very efficient electron traps centered ∼0.42 eV above the valence band. Electrochemical filling of these traps increases the electron lifetime and the photoluminescence quantum yield by more than an order of magnitude. The trapping rate constant for holes is an order of magnitude lower that for electrons. These observations can be explained by Auger-mediated electron trapping. From density functional theory calculations we infer that the traps are formed by dicoordinated Te atoms at the quantum dot surface. The combination of our unique experimental determination of the density of trap states with the theoretical modeling of the quantum dot surface allows us to identify the trapping mechanism and chemical reaction at play during charge trapping in these quantum dots.

Refraction-enhanced backlit imaging of axially symmetric inertial confinement fusion plasmas.

PubMed

Koch, Jeffrey A; Landen, Otto L; Suter, Laurence J; Masse, Laurent P; Clark, Daniel S; Ross, James S; Mackinnon, Andrew J; Meezan, Nathan B; Thomas, Cliff A; Ping, Yuan

2013-05-20

X-ray backlit radiographs of dense plasma shells can be significantly altered by refraction of x rays that would otherwise travel straight-ray paths, and this effect can be a powerful tool for diagnosing the spatial structure of the plasma being radiographed. We explore the conditions under which refraction effects may be observed, and we use analytical and numerical approaches to quantify these effects for one-dimensional radial opacity and density profiles characteristic of inertial-confinement fusion (ICF) implosions. We also show how analytical and numerical approaches allow approximate radial plasma opacity and density profiles to be inferred from point-projection refraction-enhanced radiography data. This imaging technique can provide unique data on electron density profiles in ICF plasmas that cannot be obtained using other techniques, and the uniform illumination provided by point-like x-ray backlighters eliminates a significant source of uncertainty in inferences of plasma opacity profiles from area-backlit pinhole imaging data when the backlight spatial profile cannot be independently characterized. The technique is particularly suited to in-flight radiography of imploding low-opacity shells surrounding hydrogen ice, because refraction is sensitive to the electron density of the hydrogen plasma even when it is invisible to absorption radiography. It may also provide an alternative approach to timing shockwaves created by the implosion drive, that are currently invisible to absorption radiography.

Heater-induced ionization inferred from spectrometric airglow measurements

NASA Astrophysics Data System (ADS)

Hysell, D. L.; Miceli, R. J.; Varney, R. H.; Schlatter, N.; Huba, J. D.

2013-12-01

Spectrographic airglow measurements were made during an ionospheric modification experiment at HAARP on March 12, 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert [1968, 1970], we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with significant induced ionization in view of the spatial intermittency of the airglow.

Origins of the Thermosphere-Ionosphere Semiannual Oscillation: Reformulating the "Thermospheric Spoon" Mechanism

NASA Astrophysics Data System (ADS)

Jones, M.; Emmert, J. T.; Drob, D. P.; Picone, J. M.; Meier, R. R.

2018-01-01

We demonstrate how Earth's obliquity generates the global thermosphere-ionosphere (T-I) semiannual oscillation (SAO) in mass density and electron density primarily through seasonally varying large-scale advection of neutral thermospheric constituents, sometimes referred to as the "thermospheric spoon" mechanism (TSM). The National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) is used to isolate the TSM forcing of this prominent intraannual variation (IAV) and to elucidate the contributions of other processes to the T-I SAO. An ˜30% SAO in globally averaged mass density (relative to its global annual average) at 400 km is reproduced in the TIME-GCM in the absence of seasonally varying eddy diffusion, tropospheric tidal forcing, and gravity wave breaking. Artificially, decreasing the tilt of Earth's rotation axis with respect to the ecliptic plane to 11.75° reduces seasonal variations in insolation and weakens interhemispheric pressure differences at the solstices, thereby damping the global-scale, interhemispheric transport of atomic oxygen (O) and molecular nitrogen in the thermosphere and reducing the simulated global mass density SAO amplitude to ˜10%. Simulated T-I IAVs in mass density and electron density have equinoctial maxima at all latitudes near the F2 region peak; this phasing and its latitude dependence agree well with empirically inferred climatologies. When tropospheric tides and gravity waves are included, simulated IAV amplitudes and their latitudinal dependence also agree well with empirically inferred climatologies. Simulated meridional and vertical transport of O due to the TSM couples to the upper mesospheric circulation, which also contributes to the T-I SAO through O chemistry.

Properties of the Io plasma torus inferred from Voyager EUV data

NASA Technical Reports Server (NTRS)

Strobel, D. F.; Davis, J.

1980-01-01

A physical model for the Io plasma torus is constructed to explain the EUV radiative emission observed by the Voyager UV spectrometer. Electron impact excitation rate coefficients for electronic transitions of S III, S IV, O II and O III are calculated by the method of distorted waves (Davis, Kepple, and Blaha, 1976); these coefficients account for the asymmetric shape of the 686 A feature. It is concluded that the electron gas must have a distribution function with a non-Maxwellian tail. An approximate representation of the distribution function as two temperature components requires a cold component of 3.5-4 eV and density of 2000 per cu cm and a hot component of about 100 eV and density of 50-100 per cu cm to satisfy observational constraints.

Space weather effects on lower ionosphere: First investigation from Bharati station during 34th Indian scientific expedition to Antarctica

NASA Astrophysics Data System (ADS)

Guha, Anirban; Saha, Kumarjit; De, Barin Kumar; Subrahmanyam, Kandula Venkata; Shreedevi, P. R.

2017-04-01

We investigate the solar flare effects on the D-region of the ionosphere with the help of VLF (Very Low Frequency) radio waves using a portable E-field system from Antarctica during the summer period of 34th Indian scientific expedition. Two GPS time synchronized VLF receivers, one located at Bharati, Antarctica (geographical latitude 69.40°S, longitude 76.18°E) and another located at Tripura, India (geographical latitude 23.84°N, longitude 91.28°E) were operated simultaneously to infer common mode changes in the lower ionosphere for a number of solar flares events. The two systems constantly monitored the carrier amplitude and phase of the MSK (Minimum Shift Keying) modulated navy transmitter located in Australia (Callsign: NWC, 19.8 kHz, geographical latitude 21.88°S, longitude 114.13°E), around 5.6 Mm great circle distance from the two receivers. The results are interpreted in terms of Earth-ionosphere wave-guide characteristics. A Long Wave Propagation Capability (LWPC) model study is also performed to infer the changes in the daytime electron density in polar D-region ionosphere during the solar flares. The exponential fit of the modeled electron density change with average X-ray flux change shows an excellent correlation (R2 value 0.95). The exponential fit is utilized to infer the daytime electron density change in the polar ionosphere during solar flare events. The analyses indicate that small solar flares of class 'C' can be very effectively detected with the portable antenna system even if the receiver is located in polar coastal region compared to equatorial region. The expedition results also demonstrate the feasibility of using portable VLF receivers from the coastal stations for monitoring the polar lower ionosphere from Antarctica and open up new opportunities for long term exploration.

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

Beiersdorfer, P.; Hell, N.; Lepson, J. K.

We identified a previously unassigned pair of lines between 169 and 170 Å in the coronae of cool stars. Here, we attribute these lines to Fe xiv and show that their intensity ratio is sensitive to the electron density. Using observations taken with the Low Energy Transmission Grating Spectrometer of the Chandra X-ray Observatory we infer a density of log (n e/cm -3) = 10.2 ± 0.7 and 10.3 ± 0.8 from the newly identified line pair in the coronae of Procyon and α Cen A, respectively.

Observations of the Ca/+/ twilight airglow from intermediate layers of ionization

NASA Technical Reports Server (NTRS)

Tepley, C. A.; Meriwether, J. W., Jr.; Walker, J. C. G.; Mathews, J. D.

1981-01-01

Optical and incoherent scatter radar techniques are applied to detect the presence of Ca(+) in lower thermospheric intermediate layers over Arecibo. The Arecibo 430 MHz radar is used to measure electron densities, and the altitude distribution and density of the calcium ion is inferred from the variation of twilight resonant scattering with solar depression angle. Ca(+) and electron column densities are compared, and results indicate that the composition of low-altitude intermediate layers is 2% Ca(+), which is consistent with rocket mass spectrometer measurements. Fe(+) and Mg(+) ultraviolet resonance lines are not detected from the ground due to ozone absorbing all radiation short of 3000 A, and measurements of the neutral iron resonance line at 3860 A show that an atmospheric continuum may result in overestimations of emission rates at high solar depression angles.

A Concept for Ionospheric Tomography from a CubeSat Platform at Low Earth Orbit

NASA Astrophysics Data System (ADS)

Chakrabarti, S.; Cook, T.; Finn, S. C.; Mendillo, C.; Martel, J.; Geddes, G.

2015-12-01

Remote sensing of the neutral atmosphere and ionosphere using extreme and far ultraviolet airglow has now been well established. It has been shown that the OI 135.6 nm nightglow can be used to infer the density of singly ionized atomic oxygen ions, the dominant ion in the F2 region. It has also been shown that zenith angle profiles of OII 83.4 nm emissions in the dayglow are sensitive to the electron density profiles as measured by incoherent scatter radar. Finally, simultaneous measurements of OII 61.7 nm and OII 83.4 nm emissions have been shown to yield daytime electron densities. We describe several key technological advances that have made it possible to consider self-consistent characterization of the thermosphere and ionosphere from a CubeSat platform.

Multi-hop Whistler-Mode ELF/VLF Signals and Triggered Emissions Excited by the HAARP HF Heater

DTIC Science & Technology

2004-12-28

distribution along the field line [ Angerami and Thomas, 1964] to infer the equatorial electron density Neq. This analysis revealed values of L ’ 4.9 and...the ELF/VLF receiver used on RV Tangaroa. References Angerami , J. J., and J. O. Thomas (1964), Studies of planetary atmospheres: 1. The distribution of

LLE Review Quarterly Report (October - December 2007). Volume 113

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

Zuegel, Jonathan D.

2007-12-01

This volume of the LLE Review, covering October–December 2007, features “High-Intensity Laser–Plasma Interactions in the Refluxing Limit,” by P. M. Nilson, W. Theobald, J. Myatt, C. Stoeckl, M. Storm, O. V. Gotchev, J. D. Zuegel, R. Betti, D. D. Meyerhofer, and T. C. Sangster. In this article (p. 1), the authors report on target experiments using the Multi-Terawatt (MTW) Laser Facility to study isochoric heating of solid-density targets by fast electrons produced from intense, short-pulse laser irradiation. Electron refluxing occurs due to target-sheath field effects and contains most of the fast electrons within the target volume. This efficiently heats themore » solid-density plasma through collisions. X-ray spectroscopic measurements of absolute K α (x-radiation) photon yields and variations of the K β/K α b emission ratio both indicate that laser energy couples to fast electrons with a conversion efficiency of approximately 20%. Bulk electron temperatures of at least 200 eV are inferred for the smallest mass targets.« less

Heater-induced ionization inferred from spectrometric airglow measurements

NASA Astrophysics Data System (ADS)

Hysell, D. L.; Miceli, R. J.; Kendall, E. A.; Schlatter, N. M.; Varney, R. H.; Watkins, B. J.; Pedersen, T. R.; Bernhardt, P. A.; Huba, J. D.

2014-03-01

Spectrographic airglow measurements were made during an ionospheric modification experiment at High Frequency Active Auroral Research Program on 12 March 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert (1968, 1970), we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with heater-induced ionization in view of the spatial intermittency of the airglow.

Electronic structure and static dipole polarizability of C60@C240

NASA Astrophysics Data System (ADS)

Zope, Rajendra R.

2008-04-01

The electronic structure of C60@C240 and its first-order response to a static electric field is studied by an all-electron density functional theory calculation using large polarized Gaussian basis sets. Our results show that the outer C240 shell almost completely shields the inner C60 as inferred from the practically identical values of dipole polarizability of the C60@C240 onion (449 Å3) and that of the isolated C240 fullerene (441 Å3). The C60@C240 is thus a near-perfect Faraday cage.

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

Migunov, V., E-mail: v.migunov@fz-juelich.de; Dunin-Borkowski, R. E.; London, A.

The one-dimensional charge density distribution along an electrically biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holography in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge density distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional electricmore » field and electrostatic potential around the needle with ∼10 nm spatial resolution, without needing to consider either the influence of the perturbed reference wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge density in a material using electron holography in the presence of additional contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness.« less

Comparative analyses of plasma probe diagnostics techniques

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

Godyak, V. A.; Alexandrovich, B. M.

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much asmore » an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.« less

Comparative analyses of plasma probe diagnostics techniques

NASA Astrophysics Data System (ADS)

Godyak, V. A.; Alexandrovich, B. M.

2015-12-01

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much as an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.

An integrated charge exchange recombination spectroscopy/beam emission spectroscopy diagnostic for Alcator C-Mod tokamak.

PubMed

Bespamyatnov, I O; Rowan, W L; Liao, K T; Granetz, R S

2010-10-01

A novel integrated charge exchange recombination spectroscopy (CXRS)/beam emission spectroscopy (BES) system is proposed for C-Mod, in which both measurements are taken from a shared viewing geometry. The supplementary BES system serves to quantify local beam densities and supplants the common calculation of beam attenuation. The new system employs two optical viewing arrays, 20 poloidal and 22 toroidal channels. A dichroic filter splits the light between two spectrometers operating at different wavelengths for impurity ion and beam neutrals emission. In this arrangement, the impurity density is inferred from the electron density, measured BES and CXRS spectral radiances, and atomic emission rates.

THE THOMSON SURFACE. I. REALITY AND MYTH

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

Howard, T. A.; DeForest, C. E., E-mail: howard@boulder.swri.edu

2012-06-20

The solar corona and heliosphere are visible via sunlight that is Thomson-scattered off free electrons and detected by coronagraphs and heliospheric imagers. It is well known that these instruments are most responsive to material at the 'Thomson surface', the sphere with a diameter passing through both the observer and the Sun. It is less well known that in fact the Thomson scattering efficiency is minimized on the Thomson surface. Unpolarized heliospheric imagers such as STEREO/HI are thus approximately equally responsive to material over more than a 90 Degree-Sign range of solar exit angles at each given position in the imagemore » plane. We call this range of angles the 'Thomson plateau'. We observe that heliospheric imagers are actually more sensitive to material far from the Thomson surface than close to it, at a fixed radius from the Sun. We review the theory of Thomson scattering as applied to heliospheric imaging, feature detection in the presence of background noise, geometry inference, and feature mass measurement. We show that feature detection is primarily limited by observing geometry and field of view, that the highest sensitivity for detection of density features is to objects close to the observer, that electron surface density inference is independent of geometry across the Thomson plateau, and that mass inference varies with observer distance in all geometries. We demonstrate the sensitivity results with a few examples of features detected by STEREO, far from the Thomson surface.« less

Geometry dependence of electron donating or accepting abilities of amine groups in 4,4‧-disulfanediylbis(methylene)dithiazol-2-amine: Pyramidal versus planar

NASA Astrophysics Data System (ADS)

Karabıyık, Hasan; Kırılmış, Cumhur; Karabıyık, Hande

2017-08-01

The molecular and crystal structure of the title compound in which two thiazole-2-amine rings are linked to each other by disulfide bridge (sbnd Csbnd Ssbnd Ssbnd Csbnd) were studied by single-crystal X-ray diffraction, FT-IR, NMR spectroscopy, quantum chemical calculations and topological analyses on the electron density. A novel synthesis route for the compounds having symmetrical disulfide bridge is reported. The most important result regarding the compound is about electron donating or accepting properties of the terminal amine groups. Planar amine group acts as an electron-donating group, while pyramidal amine behaves as electron-accepting group. This inference was confirmed by scrutiny of crystallographic geometry and quantum chemical studies. To ascertain underlying reasons for this fact, intermolecular interactions (Nsbnd H⋯N type H-bonds and Csbnd H···π interactions) were studied. These interactions involving aromatic thiazole rings are verified by topological electron density and Hirshfeld surface analyses. Intermolecular interactions do not have an effect on the differentiation in electron donating or accepting ability of amine groups, because both amine groups are involved in Nsbnd H⋯N type H-bonds. In methodological sense, it has been understood that Ehrenfest forces acting on electron density are useful theoretical probe to analyze intra-molecular charge transfer processes.

Nature of electron trap states under inversion at In0.53Ga0.47As/Al2O3 interfaces

NASA Astrophysics Data System (ADS)

Colleoni, Davide; Pourtois, Geoffrey; Pasquarello, Alfredo

2017-03-01

In and Ga impurities substitutional to Al in the oxide layer resulting from diffusion out of the substrate are identified as candidates for electron traps under inversion at In0.53Ga0.47As/Al2O3 interfaces. Through density-functional calculations, these defects are found to be thermodynamically stable in amorphous Al2O3 and to be able to capture two electrons in a dangling bond upon breaking bonds with neighboring O atoms. Through a band alignment based on hybrid functional calculations, it is inferred that the corresponding defect levels lie at ˜1 eV above the conduction band minimum of In0.53Ga0.47As, in agreement with measured defect densities. These results support the technological importance of avoiding cation diffusion into the oxide layer.

Aspects of electron transport in zigzag graphene nanoribbons

NASA Astrophysics Data System (ADS)

Bhalla, Pankaj; Pratap, Surender

2018-05-01

In this paper, we investigate the aspects of electron transport in the zigzag graphene nanoribbons (ZGNRs) using the nonequilibrium Green’s function (NEGF) formalism. The latter is an esoteric tool in mesoscopic physics. It is used to perform an analysis of ZGNRs by considering potential well. Within this potential, the dependence of transmission coefficient, local density of states (LDOS) and electron transport properties on number of atoms per unit cell is discussed. It is observed that there is an increment in electron and thermal conductance with increasing number of atoms. In addition to these properties, the dependence of same is also studied in figure of merit. The results infer that the contribution of electrons to enhance the figure of merit is important above the crossover temperature.

Characterization of swift heavy ion irradiation damage in ceria

DOE PAGES

Yablinsky, Clarissa A.; Devanathan, Ram; Pakarinen, Janne; ...

2015-03-04

Swift heavy ion induced radiation damage is investigated for ceria (CeO 2), which serves as a UO 2 fuel surrogate. Microstructural changes resulting from an irradiation with 940 MeV gold ions of 42 keV/nm electronic energy loss are investigated by means of electron microscopy accompanied by electron energy loss spectroscopy showing that there exists a small density reduction in the ion track core. While chemical changes in the ion track are not precluded, evidence of them was not observed. Classical molecular dynamics simulations of thermal spikes in CeO 2 with an energy deposition of 12 and 36 keV/nm show damagemore » consisting of isolated point defects at 12 keV/nm, and defect clusters at 36 keV/nm, with no amorphization at either energy. Furthermore, inferences are drawn from modeling about density changes in the ion track and the formation of interstitial loops that shed light on features observed by electron microscopy of swift heavy ion irradiated ceria.« less

Ambipolar nature of dimethyl benzo difuran (DMBDF) molecule: A charge transport study

NASA Astrophysics Data System (ADS)

Sahoo, Smruti Ranjan; Sahu, Sridhar

2017-05-01

We describe a theoretical study of the charge transport properties of the organic dimethyl benzo difuran (DMBDF) molecule based on density functional theory (DFT). Reorganization energy, ionization potential (IP), electron affinity (EA), energy gaps, transfer integral (t) and charge mobility (μ) has been studied to depict the transport properties in the conjugated organic molecules. We computed, large homo transfer integral and IP value leading to high hole mobility (4.46 cm2/V sec). However, the electron reorganization energy (0.34 eV) and the electron mobility of 1.62 cm2/V sec, infers that the DMBDF organic molecule bears an ambipolar character.

On the role of electron-driven processes in planetary atmospheres and comets

NASA Astrophysics Data System (ADS)

Campbell, L.; Brunger, M. J.

2009-11-01

After the presence of ionized layers in the Earth's atmosphere was inferred, it took 50 years to quantitatively understand them. The electron density could not be accounted for until Sir David Bates first suggested (along with Sir Harrie Massey) that the main electron-loss process was dissociative recombination with molecular ions, and he and colleagues then developed a theory to predict those rates of dissociative recombination. However, electron impact processes, particularly excitation, have been considered insignificant in most situations, in both planetary and cometary atmospheres. Here we describe cases where recent calculations have shown that electron impact excitation of molecules is important, suggesting that, just as in the time of Sir David Bates, electron-driven processes remain fundamental to our quantitative understanding of atmospheric and cometary phenomena.

Impedance of an intense plasma-cathode electron source for tokamak startup

NASA Astrophysics Data System (ADS)

Hinson, E. T.; Barr, J. L.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Perry, J. M.

2016-05-01

An impedance model is formulated and tested for the ˜1 kV , 1 kA/cm2 , arc-plasma cathode electron source used for local helicity injection tokamak startup. A double layer sheath is established between the high-density arc plasma ( narc≈1021 m-3 ) within the electron source, and the less dense external tokamak edge plasma ( nedge≈1018 m-3 ) into which current is injected at the applied injector voltage, Vinj . Experiments on the Pegasus spherical tokamak show that the injected current, Iinj , increases with Vinj according to the standard double layer scaling Iinj˜Vinj3 /2 at low current and transitions to Iinj˜Vinj1 /2 at high currents. In this high current regime, sheath expansion and/or space charge neutralization impose limits on the beam density nb˜Iinj/Vinj1 /2 . For low tokamak edge density nedge and high Iinj , the inferred beam density nb is consistent with the requirement nb≤nedge imposed by space-charge neutralization of the beam in the tokamak edge plasma. At sufficient edge density, nb˜narc is observed, consistent with a limit to nb imposed by expansion of the double layer sheath. These results suggest that narc is a viable control actuator for the source impedance.

Dynamical Bayesian inference of time-evolving interactions: from a pair of coupled oscillators to networks of oscillators.

PubMed

Duggento, Andrea; Stankovski, Tomislav; McClintock, Peter V E; Stefanovska, Aneta

2012-12-01

Living systems have time-evolving interactions that, until recently, could not be identified accurately from recorded time series in the presence of noise. Stankovski et al. [Phys. Rev. Lett. 109, 024101 (2012)] introduced a method based on dynamical Bayesian inference that facilitates the simultaneous detection of time-varying synchronization, directionality of influence, and coupling functions. It can distinguish unsynchronized dynamics from noise-induced phase slips. The method is based on phase dynamics, with Bayesian inference of the time-evolving parameters being achieved by shaping the prior densities to incorporate knowledge of previous samples. We now present the method in detail using numerically generated data, data from an analog electronic circuit, and cardiorespiratory data. We also generalize the method to encompass networks of interacting oscillators and thus demonstrate its applicability to small-scale networks.

Ideal laser-beam propagation through high-temperature ignition Hohlraum plasmas.

PubMed

Froula, D H; Divol, L; Meezan, N B; Dixit, S; Moody, J D; Neumayer, P; Pollock, B B; Ross, J S; Glenzer, S H

2007-02-23

We demonstrate that a blue (3omega, 351 nm) laser beam with an intensity of 2 x 10(15) W cm(-2) propagates nearly within the original beam cone through a millimeter scale, T(e)=3.5 keV high density (n(e)=5 x 10(20) cm(-3)) plasma. The beam produced less than 1% total backscatter at these high temperatures and densities; the resulting transmission is greater than 90%. Scaling of the electron temperature in the plasma shows that the plasma becomes transparent for uniform electron temperatures above 3 keV. These results are consistent with linear theory thresholds for both filamentation and backscatter instabilities inferred from detailed hydrodynamic simulations. This provides a strong justification for current inertial confinement fusion designs to remain below these thresholds.

Use of multiwavelength emission from hollow cathode lamp for measurement of state resolved atom density of metal vapor produced by electron beam evaporation

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

Majumder, A.; Dikshit, B.; Bhatia, M. S.

2008-09-15

State resolved atom population of metal vapor having low-lying metastable states departs from equilibrium value. It needs to be experimentally investigated. This paper reports the use of hollow cathode lamp based atomic absorption spectroscopy technique to measure online the state resolved atom density (ground and metastable) of metal vapor in an atomic beam produced by a high power electron gun. In particular, the advantage of availability of multiwavelength emission in hollow cathode lamp is used to determine the atom density in different states. Here, several transitions pertaining to a given state have also been invoked to obtain the mean valuemore » of atom density thereby providing an opportunity for in situ averaging. It is observed that at higher source temperatures the atoms from metastable state relax to the ground state. This is ascribed to competing processes of atom-atom and electron-atom collisions. The formation of collision induced virtual source is inferred from measurement of atom density distribution profile along the width of the atomic beam. The total line-of-sight average atom density measured by absorption technique using hollow cathode lamp is compared to that measured by atomic vapor deposition method. The presence of collisions is further supported by determination of beaming exponent by numerically fitting the data.« less

Study of Plasma Waves Observed onboard Rosetta in the 67P/ChuryumovGerasimenko Comet Environment Using High Time Resolution Density Data Inferred from RPC-MIP and RPC-LAP Cross-calibration

NASA Astrophysics Data System (ADS)

Breuillard, H.; Henri, P.; Vallières, X.; Eriksson, A. I.; Odelstad, E.; Johansson, F. L.; Richter, I.; Goetz, C.; Wattieaux, G.; Tsurutani, B.; Hajra, R.; Le Contel, O.

2017-12-01

During two years, the groundbreaking ESA/Rosetta mission was able to escort comet 67P where previous cometary missions were only limited to flybys. This enabled for the first time to make in-situ measurements of the evolution of a comet's plasma environment. The density and temperature measured by Rosetta are derived from RPC-Mutual Impedance Probe (MIP) and RPC-Langmuir Probe (LAP). On one hand, low time resolution electron density are calculated using the plasma frequency extracted from the MIP mutual impedance spectra. On the other hand, high time resolution density fluctuations are estimated from the spacecraft potential measured by LAP. In this study, using a simple spacecraft charging model, we perform a cross-calibration of MIP plasma density and LAP spacecraft potential variations to obtain high time resolution measurements of the electron density. These results are also used to constrain the electron temperature. Then we make use of these new dataset, together with RPC-MAG magnetic field measurements, to investigate for the first time the compressibility and the correlations between plasma and magnetic field variations, for both singing comet waves and steepened waves observed, respectively during low and high cometary outgassing activity, in the plasma environment of comet 67P.

Measuring the ionization balance of gold in a low-density plasma of importance to ICF

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

May, M; Beiersdorfer, P; Schneider, M

Charge state distributions (CSDs) have been determined in low density ({approx}10 {sup 12} cm{sup -3}) gold plasmas having either a monoenergetic beam (E{sub Beam} = 2.66, 3.53 and 4.54 keV) or experimentally simulated thermal electron distributions (T{sub e} = 2.0, 2.5 and 3.0 keV). These plasmas were created in the Livermore electron beam ion traps EBIT-I and EBIT-II. Line emission and radiative recombination features of Ni to Kr-like gold ions were recorded in the x-ray region with a crystal spectrometer and a photometrically calibrated microcalorimeter. The CSDs in the experimentally simulated thermal plasmas were inferred by fitting the observed 4f{yields}3dmore » and 5f{yields}3d lines with synthetic spectra from the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Additionally, the CSDs in the beam plasmas were inferred both from fitting the line emission and fitting the radiative recombination emission to calculations from the General Relativistic Atomic Structure Program (GRASP). Despite the relatively simple atomic physics in the low density plasma, differences existed between the experimental CSDs and the simulations from several available codes (e.g. RIGEL). Our experimental CSD relied upon accurate electron impact cross sections provided by HULLAC. To determine their reliability, we have experimentally determined the cross sections for several of the n=3{yields}4 and n=3{yields}5 excitations in Ni to Ga-like Au and compared them to distorted wave calculations. Recent Au spectra recorded during experiments at the HELEN laser facility are presented and compared with those from EBIT-I and EBIT-II.« less

Measuring the Ionization Balance of Gold in a Low-Density Plasma of Importance to ICF

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

May, M.J.; Beiersdorfer, P.; Schneider, M.

Charge state distributions (CSDs) have been determined in low density ({approx_equal}1012 cm-3) gold plasmas having either a monoenergetic beam (EBeam = 2.66, 3.53 and 4.54 keV) or experimentally simulated thermal electron distributions (Te = 2.0, 2.5 and 3.0 keV). These plasmas were created in the Livermore electron beam ion traps EBIT-I and EBIT-II. Line emission and radiative recombination features of Ni to Kr-like gold ions were recorded in the x-ray region with a crystal spectrometer and a photometrically calibrated microcalorimeter. The CSDs in the experimentally simulated thermal plasmas were inferred by fitting the observed 4f{yields}3d and 5f{yields}3d lines with syntheticmore » spectra from the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Additionally, the CSDs in the beam plasmas were inferred both from fitting the line emission and fitting the radiative recombination emission to calculations from the General Relativistic Atomic Structure Program (GRASP). Despite the relatively simple atomic physics in the low density plasma, differences existed between the experimental CSDs and the simulations from several available codes (e.g. RIGEL). Our experimental CSD relied upon accurate electron impact cross sections provided by HULLAC. To determine their reliability, we have experimentally determined the cross sections for several of the n=3{yields}4 and n=3{yields}5 excitations in Ni to Ga-like Au and compared them to distorted wave calculations. Recent Au spectra recorded during experiments at the HELEN laser facility are presented and compared with those from EBIT-I and EB0011IT-.« less

Staging of laser-plasma accelerators

DOE PAGES

Steinke, S.; van Tilborg, J.; Benedetti, C.; ...

2016-05-02

We present results of an experiment where two laser-plasma-accelerator stages are coupled at a short distance by a plasma mirror. Stable electron beams from the first stage were used to longitudinally probe the dark-current-free, quasi-linear wakefield excited by the laser of the second stage. Changing the arrival time of the electron beam with respect to the second stage laser pulse allowed reconstruction of the temporal wakefield structure, determination of the plasma density, and inference of the length of the electron beam. The first stage electron beam could be focused by an active plasma lens to a spot size smaller thanmore » the transverse wake size at the entrance of the second stage. Furthermore, this permitted electron beam trapping, verified by a 100 MeV energy gain.« less

Measuring Mars' Atmospheric Neutral Density from 160 to 220km with the MGS Electron Reflectometer

NASA Astrophysics Data System (ADS)

Lillis, R.; Engel, J.; Mitchell, D.; Brain, D.; Lin, R.; Bougher, S.; Acuna, M.

2005-08-01

The Magnetometer/Electron Reflectometer (MAG/ER) experiment aboard Mars Global Surveyor (MGS) samples the local electron population's distribution in energy and pitch angle (angle between electron velocity and local magnetic field direction) at the mapping orbit altitude of ˜400km. We develop a single-particle model of the electrons' interaction with the neutral atmosphere and motion along open field-lines connecting the solar wind to remnant crustal magnetization. Electron reflection from magnetic gradients and absorption due to inelastic collisons with atmospheric neutrals results in characteristic pitch angle (PA) distributions for open field lines. By assuming the validity of spherical harmonic expansions (Cain et al, 2003) in the strongest field regions of Mars (such as Terra Sirenum), we trace the electron paths and fit these PA distributions to our model to constrain the scale height and density of the neutral atmosphere in the region of greatest absorption, 160-220km. We analyse almost 3 martian years of MGS mapping Orbit Data and present the first measurements of Mars' neutral density above 180km. Although the uncertainties in single measurements are quite large, averaging over many measurements over a period of weeks allows us to see long-term trends. Major results are: 1) a mean density of 0.03 kg/km3 at 160km with a month-averaged variation of ˜40%, 2) a very strong annual seasonal variation, confirmed by periodogram and least-squares fit and 3) increasing seasonal density variability with distance from the equator. We see broad general agreement with predictions from Mars Thermosphere Global Circulation Model (MTGCM) simulations [Bougher et al, 2004] and with inferred densities from MGS Doppler tracking data [Tracadas et al, 2001]. Our results will help to constrain the upper boundaries of GCMs and assist orbital decay calculations for low-orbiting spacecraft, such as the 2005 Mars Reconnaissance Orbiter. We thank the NASA Jet Propulsion Laboratory for funding assistance for this research.

Neutral depletion and the helicon density limit

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

Magee, R. M.; Galante, M. E.; Carr, J. Jr.

2013-12-15

It is straightforward to create fully ionized plasmas with modest rf power in a helicon. It is difficult, however, to create plasmas with density >10{sup 20} m{sup −3}, because neutral depletion leads to a lack of fuel. In order to address this density limit, we present fast (1 MHz), time-resolved measurements of the neutral density at and downstream from the rf antenna in krypton helicon plasmas. At the start of the discharge, the neutral density underneath the antenna is reduced to 1% of its initial value in 15 μs. The ionization rate inferred from these data implies that the electronmore » temperature near the antenna is much higher than the electron temperature measured downstream. Neutral density measurements made downstream from the antenna show much slower depletion, requiring 14 ms to decrease by a factor of 1/e. Furthermore, the downstream depletion appears to be due to neutral pumping rather than ionization.« less

Dynamical Bayesian inference of time-evolving interactions: From a pair of coupled oscillators to networks of oscillators

NASA Astrophysics Data System (ADS)

Duggento, Andrea; Stankovski, Tomislav; McClintock, Peter V. E.; Stefanovska, Aneta

2012-12-01

Living systems have time-evolving interactions that, until recently, could not be identified accurately from recorded time series in the presence of noise. Stankovski [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.109.024101 109, 024101 (2012)] introduced a method based on dynamical Bayesian inference that facilitates the simultaneous detection of time-varying synchronization, directionality of influence, and coupling functions. It can distinguish unsynchronized dynamics from noise-induced phase slips. The method is based on phase dynamics, with Bayesian inference of the time-evolving parameters being achieved by shaping the prior densities to incorporate knowledge of previous samples. We now present the method in detail using numerically generated data, data from an analog electronic circuit, and cardiorespiratory data. We also generalize the method to encompass networks of interacting oscillators and thus demonstrate its applicability to small-scale networks.

Laboratory measurements of white dwarf photospheric spectral lines: Hβ

DOE PAGES

Falcon, Ross Edward; Rochau, Gregory A.; Bailey, James E.; ...

2015-06-18

We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. We also present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, n e, and n = 2 level population, n 2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, wemore » infer a continuous range of electron densities increasing from n e ~ 4 to ~30 × 10 16 cm -3 throughout a 120-ns evolution of our plasma. Also, we observe n 2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ~55 ns to become consistent with LTE. This also supports our electron-temperature determination of T e ~ 1.3 eV (~15,000 K) after this time. At n e≲ 10 17 cm -3, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ 2) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. Lastly, this work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.« less

Probing matter at extreme Gbar pressures at the NIF

DOE PAGES

Kritcher, A. L.; Doeppner, T.; Swift, D.; ...

2013-12-04

Here we describe a platform to measure the material properties, specifically the equation of state and electron temperature, at pressures of 100 Mbar to a Gbar at the National Ignition Facility (NIF). In our experiments we launch spherically convergent shock waves into solid CH, CD, or diamond samples using a hohlraum radiation drive, in an indirect drive laser geometry. X-ray radiography is applied to measure the shock speed and infer the mass density profile, enabling determination of the material pressure and Hugoniot equation of state. X-ray scattering is applied to measure the electron temperature through probing of the electron velocitymore » distribution via Doppler broadening.« less

Electron Transfer Mechanism in Gold Surface Modified with Self-Assembly Monolayers from First Principles

NASA Astrophysics Data System (ADS)

Lima, Filipe C. D. A.; Iost, Rodrigo M.; Crespilho, Frank N.; Caldas, Marília J.; Calzolari, Arrigo; Petrilli, Helena M.

2013-03-01

We report the investigation of electron tunneling mechanism of peptide ferrocenyl-glycylcystamine self-assembled monolayers (SAMs) onto Au (111) electrode surfaces. Recent experimental investigations showed that electron transfer in peptides can occur across long distances by separating the donor from the acceptor. This mechanism can be further fostered by the presence of electron donor terminations of Fc terminal units on SAMs but the charge transfer mechanism is still not clear. We study the interaction of the peptide ferrocenyl-glycylcystamine on the Au (111) from first principles calculations to evaluate the electron transfer mechanism. For this purpose, we used the Kohn Sham (KS) scheme for the Density Functional Theory (DFT) as implemented in the Quantum-ESPRESSO suit of codes, using Vandebilt ultrasoft pseudopotentials and GGA-PBE exchange correlation functional to evaluate the ground-state atomic and electronic structure of the system. The analysis of KS orbital at the Fermi Energy showed high electronic density localized in Fc molecules and the observation of a minor contribution from the solvent and counter ion. Based on the results, we infer evidences of electron tunneling mechanism from the molecule to the Au(111). We acknowledge FAPESP for grant support. Also, LCCA/USP, RICE and CENAPAD for computational resources.

Thermal Conductivity and Thermopower near the 2D Metal-Insulator transition, Final Technical Report

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

Sarachik, Myriam P.

2015-02-20

STUDIES OF STRONGLY-INTERACTING 2D ELECTRON SYSTEMS – There is a great deal of current interest in the properties of systems in which the interaction between electrons (their potential energy) is large compared to their kinetic energy. We have investigated an apparent, unexpected metal-insulator transition inferred from the behavior of the temperature-dependence of the resistivity; moreover, detailed analysis of the behavior of the magnetoresistance suggests that the electrons’ effective mass diverges, supporting this scenario. Whether this is a true phase transition or crossover behavior has been strenuously debated over the past 20 years. Our measurements have now shown that the thermoelectricmore » power of these 2D materials diverges at a finite density, providing clear evidence that this is, in fact, a phase transition to a new low-density phase which may be a precursor or a direct transition to the long sought-after electronic crystal predicted by Eugene Wigner in 1934.« less

Ionospheric Profiling Through Nonlinear Dielectric Response to Electron Density*

NASA Astrophysics Data System (ADS)

Moses, R. W.; Jacobson, A. R.

2002-12-01

It is well known that the total electron content (TEC) along a line of sight in the ionosphere can be extracted from the frequency-dependent time lag measured in transionospheric RF signals [1]. For five years the FORTE satellite has been used to develop a substantial data base of transionospheric signals originating in both lightning and man-made sources. Here, we use signals generated by the Los Alamos Portable Pulser (LAPP) [2] and recorded by FORTE as input to a multi-layer computer model of RF wave propagation in the ionosphere, including Faraday rotation in the Earth's magnetic field. Nonlinearities in both the frequency dependence of the group velocity and the optical pathlength are modeled and matched to FORTE data to infer details of the vertical profile of electron density. Using the International Reference Ionosphere [3] as a profile model, we show how the vertical TEC, peak electron density, and ionospheric thickness can be extracted even at large transmitter-to-satellite separations. [1] Roussel-Dupre, R. A., A. R. Jacobson, and L. A. Triplett, Radio Sci., 36, 1615 (2001). [2] Massey, R.S., S.O. Knox, R.C. Franz, D.N. Holden, and C.T. Rhodes, Radio Sci., 33, 1739 (1998). [3] Bilitza, D., "International Reference Ionosphere 1990," NSSDC/WDC-A-R&S 90-92. *Work supported by USDOE

An automated design process for short pulse laser driven opacity experiments

DOE PAGES

Martin, M. E.; London, R. A.; Goluoglu, S.; ...

2017-12-21

Stellar-relevant conditions can be reached by heating a buried layer target with a short pulse laser. Previous design studies of iron buried layer targets found that plasma conditions are dominantly controlled by the laser energy while the accuracy of the inferred opacity is limited by tamper emission and optical depth effects. In this paper, we developed a process to simultaneously optimize laser and target parameters to meet a variety of design goals. We explored two sets of design cases: a set focused on conditions relevant to the upper radiative zone of the sun (electron temperatures of 200 to 400 eVmore » and densities greater than 1/10 of solid density) and a set focused on reaching temperatures consistent with deep within the radiative zone of the sun (500 to 1000 eV) at a fixed density. We found optimized designs for iron targets and determined that the appropriate dopant, for inferring plasma conditions, depends on the goal temperature: magnesium for up to 300 eV, aluminum for 300 to 500 eV, and sulfur for 500 to 1000 eV. The optimal laser energy and buried layer thickness increase with goal temperature. The accuracy of the inferred opacity is limited to between 11% and 31%, depending on the design. Finally, overall, short pulse laser heated iron experiments reaching stellar-relevant conditions have been designed with consideration of minimizing tamper emission and optical depth effects while meeting plasma condition and x-ray emission goals.« less

An automated design process for short pulse laser driven opacity experiments

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

Martin, M. E.; London, R. A.; Goluoglu, S.

Stellar-relevant conditions can be reached by heating a buried layer target with a short pulse laser. Previous design studies of iron buried layer targets found that plasma conditions are dominantly controlled by the laser energy while the accuracy of the inferred opacity is limited by tamper emission and optical depth effects. In this paper, we developed a process to simultaneously optimize laser and target parameters to meet a variety of design goals. We explored two sets of design cases: a set focused on conditions relevant to the upper radiative zone of the sun (electron temperatures of 200 to 400 eVmore » and densities greater than 1/10 of solid density) and a set focused on reaching temperatures consistent with deep within the radiative zone of the sun (500 to 1000 eV) at a fixed density. We found optimized designs for iron targets and determined that the appropriate dopant, for inferring plasma conditions, depends on the goal temperature: magnesium for up to 300 eV, aluminum for 300 to 500 eV, and sulfur for 500 to 1000 eV. The optimal laser energy and buried layer thickness increase with goal temperature. The accuracy of the inferred opacity is limited to between 11% and 31%, depending on the design. Finally, overall, short pulse laser heated iron experiments reaching stellar-relevant conditions have been designed with consideration of minimizing tamper emission and optical depth effects while meeting plasma condition and x-ray emission goals.« less

Imaging spectroscopy of type U and J solar radio bursts with LOFAR

NASA Astrophysics Data System (ADS)

Reid, Hamish A. S.; Kontar, Eduard P.

2017-10-01

Context. Radio U-bursts and J-bursts are signatures of electron beams propagating along magnetic loops confined to the corona. The more commonly observed type III radio bursts are signatures of electron beams propagating along magnetic loops that extend into interplanetary space. Given the prevalence of solar magnetic flux to be closed in the corona, why type III bursts are more frequently observed than U-bursts or J-bursts is an outstanding question. Aims: We use Low-Frequency Array (LOFAR) imaging spectroscopy between 30-80 MHz of low-frequency U-bursts and J-bursts, for the first time, to understand why electron beams travelling along coronal loops produce radio emission less often. Radio burst observations provide information not only about the exciting electron beams but also about the structure of large coronal loops with densities that are too low for standard extreme ultraviolet (EUV) or X-ray analysis. Methods: We analysed LOFAR images of a sequence of two J-bursts and one U-burst. The different radio source positions were used to model the spatial structure of the guiding magnetic flux tube and then deduce the energy range of the exciting electron beams without the assumption of a standard density model. We also estimated the electron density along the magnetic flux rope and compared it to coronal models. Results: The radio sources infer a magnetic loop that is 1 solar radius in altitude with the highest frequency sources starting around 0.6 solar radii. Electron velocities were found between 0.13 c and 0.24 c with the front of the electron beam travelling faster than the back of the electron beam. The velocities correspond to energy ranges within the beam from 0.7-11 keV to 0.7-43 keV. The density along the loop is higher than typical coronal density models and the density gradient is smaller. Conclusions: We found that a more restrictive range of accelerated beam and background plasma parameters can result in U-bursts or J-bursts, causing type III bursts to be more frequently observed. The large instability distances required before Langmuir waves are produced by some electron beams, and the small magnitude of the background density gradients makes closed loops less facilitative for radio emission than loops that extend into interplanetary space.

Confinement time exceeding one second for a toroidal electron plasma.

PubMed

Marler, J P; Stoneking, M R

2008-04-18

Nearly steady-state electron plasmas are trapped in a toroidal magnetic field for the first time. We report the first results from a new toroidal electron plasma experiment, the Lawrence Non-neutral Torus II, in which electron densities on the order of 10(7) cm(-3) are trapped in a 270-degree toroidal arc (670 G toroidal magnetic field) by application of trapping potentials to segments of a conducting shell. The total charge inferred from measurements of the frequency of the m=1 diocotron mode is observed to decay on a 3 s time scale, a time scale that approaches the predicted limit due to magnetic pumping transport. Three seconds represents approximately equal to 10(5) periods of the lowest frequency plasma mode, indicating that nearly steady-state conditions are achieved.

Specular reflectivity and hot-electron generation in high-contrast relativistic laser-plasma interactions

NASA Astrophysics Data System (ADS)

Kemp, Gregory Elijah

Ultra-intense laser (> 1018 W/cm2) interactions with matter are capable of producing relativistic electrons which have a variety of applications in state-of-the-art scientific and medical research conducted at universities and national laboratories across the world. Control of various aspects of these hot-electron distributions is highly desired to optimize a particular outcome. Hot-electron generation in low-contrast interactions, where significant amounts of under-dense pre-plasma are present, can be plagued by highly non-linear relativistic laser-plasma instabilities and quasi-static magnetic field generation, often resulting in less than desirable and predictable electron source characteristics. High-contrast interactions offer more controlled interactions but often at the cost of overall lower coupling and increased sensitivity to initial target conditions. An experiment studying the differences in hot-electron generation between high and low-contrast pulse interactions with solid density targets was performed on the Titan laser platform at the Jupiter Laser Facility at Lawrence Livermore National Laboratory in Livermore, CA. To date, these hot-electrons generated in the laboratory are not directly observable at the source of the interaction. Instead, indirect studies are performed using state-of-the-art simulations, constrained by the various experimental measurements. These measurements, more-often-than-not, rely on secondary processes generated by the transport of these electrons through the solid density materials which can susceptible to a variety instabilities and target material/geometry effects. Although often neglected in these types of studies, the specularly reflected light can provide invaluable insight as it is directly influenced by the interaction. In this thesis, I address the use of (personally obtained) experimental specular reflectivity measurements to indirectly study hot-electron generation in the context of high-contrast, relativistic laser-plasma interactions. Spatial, temporal and spectral properties of the incident and specular pulses, both near and far away from the interaction region where experimental measurements are obtained, are used to benchmark simulations designed to infer dominant hot-electron acceleration mechanisms and their corresponding energy/angular distributions. To handle this highly coupled interaction, I employed particle-in-cell modeling using a wide variety of algorithms (verified to be numerically stable and consistent with analytic expressions) and physical models (validated by experimental results) to reasonably model the interaction's sweeping range of plasma densities, temporal and spatial scales, electromagnetic wave propagation and its interaction with solid density matter. Due to the fluctuations in the experimental conditions and limited computational resources, only a limited number of full-scale simulations were performed under typical experimental conditions to infer the relevant physical phenomena in the interactions. I show the usefulness of the often overlooked specular reflectivity measurements in constraining both high and low-contrast simulations, as well as limitations of their experimental interpretations. Using these experimental measurements to reasonably constrain the simulation results, I discuss the sensitivity of relativistic electron generation in ultra-intense laser plasma interactions to initial target conditions and the dynamic evolution of the interaction region.

Picosecond time-resolved measurements of dense plasma line shifts

DOE PAGES

Stillman, C. R.; Nilson, P. M.; Ivancic, S. T.; ...

2017-06-13

Picosecond time-resolved x-ray spectroscopy is used to measure the spectral line shift of the 1s2p–1s 2 transition in He-like Al ions as a function of the instantaneous plasma conditions. The plasma temperature and density are inferred from the Al He α complex using a nonlocal-thermodynamic-equilibrium atomic physics model. The experimental spectra show a linearly increasing red shift for electron densities of 1 to 5 × 10 23 cm –3. Furthermore, the measured line shifts are broadly consistent with a generalized analytic line-shift model based on calculations of a self-consistent field ion sphere model.

Picosecond time-resolved measurements of dense plasma line shifts

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

Stillman, C. R.; Nilson, P. M.; Ivancic, S. T.

Picosecond time-resolved x-ray spectroscopy is used to measure the spectral line shift of the 1s2p–1s 2 transition in He-like Al ions as a function of the instantaneous plasma conditions. The plasma temperature and density are inferred from the Al He α complex using a nonlocal-thermodynamic-equilibrium atomic physics model. The experimental spectra show a linearly increasing red shift for electron densities of 1 to 5 × 10 23 cm –3. Furthermore, the measured line shifts are broadly consistent with a generalized analytic line-shift model based on calculations of a self-consistent field ion sphere model.

Full PIC simulations of solar radio emission

NASA Astrophysics Data System (ADS)

Sgattoni, A.; Henri, P.; Briand, C.; Amiranoff, F.; Riconda, C.

2017-12-01

Solar radio emissions are electromagnetic (EM) waves emitted in the solar wind plasma as a consequence of electron beams accelerated during solar flares or interplanetary shocks such as ICMEs. To describe their origin, a multi-stage model has been proposed in the 60s which considers a succession of non-linear three-wave interaction processes. A good understanding of the process would allow to infer the kinetic energy transfered from the electron beam to EM waves, so that the radio waves recorded by spacecraft can be used as a diagnostic for the electron beam.Even if the electrostatic problem has been extensively studied, full electromagnetic simulations were attempted only recently. Our large scale 2D-3V electromagnetic PIC simulations allow to identify the generation of both electrostatic and EM waves originated by the succession of plasma instabilities. We tested several configurations varying the electron beam density and velocity considering a background plasma of uniform density. For all the tested configurations approximately 105 of the electron-beam kinetic energy is transfered into EM waves emitted in all direction nearly isotropically. With this work we aim to design experiments of laboratory astrophysics to reproduce the electromagnetic emission process and test its efficiency.

Chromospheric evaporation and decimetric radio emission in solar flares

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Benz, Arnold O.

1995-01-01

We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca XIX soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T(exp -3/2) dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyze 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Pheonix, hard X-ray data from (BATSE/CGRO) and soft X-ray data from Burst and Transient Source Experiment/Compton Gamma Ray Observatory (GOES) were available.

Density Determinations of the Coronae of Cool Stars Using a Newly Assigned Pair of Fe Xiv Lines in the Spectra of α Canis Minor, α Centauri, and the Sun [Density determinations of the coronae of cool stars using a newly assigned pair of Fe XIV lines in the spectra of alpha Canis Minor, alpha Centauri, and the Sun.

DOE PAGES

Beiersdorfer, P.; Hell, N.; Lepson, J. K.; ...

2015-12-02

We identified a previously unassigned pair of lines between 169 and 170 Å in the coronae of cool stars. Here, we attribute these lines to Fe xiv and show that their intensity ratio is sensitive to the electron density. Using observations taken with the Low Energy Transmission Grating Spectrometer of the Chandra X-ray Observatory we infer a density of log (n e/cm -3) = 10.2 ± 0.7 and 10.3 ± 0.8 from the newly identified line pair in the coronae of Procyon and α Cen A, respectively.

UHF Radar observations at HAARP with HF pump frequencies near electron gyro-harmonics and associated ionospheric effects

NASA Astrophysics Data System (ADS)

Watkins, Brenton; Fallen, Christopher; Secan, James

Results for HF modification experiments at the HAARP facility in Alaska are presented for experiments with the HF pump frequency near third and fourth electron gyro-harmonics. A UHF diagnostic radar with range resolution of 600 m was used to determine time-dependent altitudes of scattering from plasma turbulence during heating experiments. Experiments were conducted with multiple HF frequencies stepped by 20 kHz above and below the gyro-harmonic values. During times of HF heating the HAARP facility has sufficient power to enhance large-scale ionospheric densities in the lower ionosphere (about 150-200 km altitude) and also in the topside ionosphere (above about 350 km). In the lower ionosphere, time-dependent decreases of the altitude of radar scatter result from electron density enhancements. The effects are substantially different even for relatively small frequency steps of 20 kHz. In all cases the time-varying altitude decrease of radar scatter stops about 5-10 km below the gyro-harmonic altitude that is frequency dependent; we infer that electron density enhancements stop at this altitude where the radar signals stop decreasing with altitude. Experiments with corresponding total electron content (TEC) data show that for HF interaction altitudes above about 170 km there is substantial topside electron density increases due to upward electron thermal conduction. For lower altitudes of HF interaction the majority of the thermal energy is transferred to the neutral gas and no significant topside density increases are observed. By selecting an appropriate HF frequency a little greater than the gyro-harmonic value we have demonstrated that the ionospheric response to HF heating is a self-oscillating mode where the HF interaction altitude moves up and down with a period of several minutes. If the interaction region is above about 170 km this also produces a continuously enhanced topside electron density and upward plasma flux. Experiments using an FM scan with the HF frequency increasing near the gyro-harmonic value were conducted. The FM scan rate was sufficiently slow that the electron density was approximately in an equilibrium state. For these experiments the altitude of the HF interaction follows a near straight line downward parallel to the altitude-dependent gyro-harmonic level.

A Two-Fluid, MHD Coronal Model

NASA Technical Reports Server (NTRS)

Suess, Steven T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

1998-01-01

We describe first results from a numerical two-fluid MHD model of the global structure of the solar corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and momentum sources are required to produce high speed wind from coronal holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature in the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UVCS, and with the Ulysses/SWOOPS proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 solar radii and 5 solar radii (2RS and 5RS) is similar to the density reported from SPARTAN 201-01 measurements by Fisher and Guhathakurta. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer, the temperature and density are similar to those reported empirically by Li et al and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub s), as it is in all other MHD coronal streamer models.

Proton deflectometry of laser-driven relativistic electron jet from thin foil target

NASA Astrophysics Data System (ADS)

Huang, Chengkun; Palaniyappan, S.; Gautier, D. C.; Johnson, R. P.; Shimada, T.; Fernandez, J. C.; Tsung, F. S.; Mori, W. B.

2017-10-01

Near critical density relativistic electron jets from laser solid interaction carry currents approaching the Alfvén-limit and tens of kilo-Tesla magnetic fields. Such jets are often found in kinetic simulations with low areal density targets, but have not been confirmed experimentally. They may be used for X/gamma-ray generation and is also important for the understanding of post-transparency plasma dynamics. With a short-pulse probe beam at the Trident laser facility, we employed proton deflectometry to infer the jet's properties, structure and the long-time dynamics. We develop corresponding GEANT4 simulation model of the proton deflectometry, with input from the kinetic PIC simulations in 2D and quasi-3D geometry, to compare with the experimental radiography images. Detail comparison of the experimental and simulation features in the deflectometry will be discussed. Work supported by the LDRD program at LANL.

Reflectometry diagnostics on TCV

NASA Astrophysics Data System (ADS)

Molina Cabrera, Pedro; Coda, Stefano; Porte, Laurie; Offeddu, Nicola; Tcv Team

2017-10-01

Both profile reflectometer and Doppler back-scattering (DBS) diagnostics are being developed for the TCV Tokamak using a steerable quasi-optical launcher and universal polarizers. First results will be presented. A pulse reflectometer is being developed to complement Thomson Scattering measurements of electron density, greatly increasing temporal resolution and also effectively enabling fluctuation measurements. Pulse reflectometry consists of sending short pulses of varying frequency and measuring the roundtrip group-delay with precise chronometers. A fast arbitrary waveform generator is used as a pulse source feeding frequency multipliers that bring the pulses to V-band. A DBS diagnostic is currently operational in TCV. DBS may be used to infer the perpendicular velocity and wave number spectrum of electron density fluctuations in the 3-15 cm-1 wave-number range. Off-the-shelf transceiver modules, originally used for VNA measurements, are being used in a Doppler radar configuration. See author list of S. Coda et al., 2017 Nucl. Fusion 57 102011.

Measurements of shock-front structure in multi-species plasmas on OMEGA

NASA Astrophysics Data System (ADS)

Rinderknecht, Hans G.; Park, H.-S.; Ross, J. S.; Wilks, S. C.; Amendt, P. A.; Heeter, R. F.; Katz, J.; Hoffman, N. M.; Vold, E.; Taitano, W.; Simakov, A.; Chacon, L.

2016-10-01

The structure of a shock front in a plasma with multiple ion species is measured for the first time in experiments on the OMEGA laser. Thomson scattering of a 263.25 nm probe beam is used to diagnose electron density, electron and ion temperature, ion species concentration, and flow velocity in strong shocks (M 5) propagating through low-density (ρ 0.1 mg/cc) plasmas composed of H(98%)+Ne(2%) and H(98%)+C(2%). Separation of the ion species within the shock front is inferred. Although shocks play an important role in ICF and astrophysical plasmas, the intrinsically kinetic nature of the shock front indicates the need for experiments to benchmark hydrodynamic models. Comparison with PIC, Vlasov-Fokker-Planck, and multi-component hydrodynamic simulations will be presented. This work performed under auspices of U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Non-Gaussianity in a quasiclassical electronic circuit

NASA Astrophysics Data System (ADS)

Suzuki, Takafumi J.; Hayakawa, Hisao

2017-05-01

We study the non-Gaussian dynamics of a quasiclassical electronic circuit coupled to a mesoscopic conductor. Non-Gaussian noise accompanying the nonequilibrium transport through the conductor significantly modifies the stationary probability density function (PDF) of the flux in the dissipative circuit. We incorporate weak quantum fluctuation of the dissipative LC circuit with a stochastic method and evaluate the quantum correction of the stationary PDF. Furthermore, an inverse formula to infer the statistical properties of the non-Gaussian noise from the stationary PDF is derived in the classical-quantum crossover regime. The quantum correction is indispensable to correctly estimate the microscopic transfer events in the QPC with the quasiclassical inverse formula.

LABORATORY MEASUREMENTS OF WHITE DWARF PHOTOSPHERIC SPECTRAL LINES: Hβ

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

Falcon, Ross E.; Gomez, T. A.; Montgomery, M. H.

2015-06-20

We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. Here we present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, n{sub e}, and n = 2 level population, n{sub 2}. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, wemore » infer a continuous range of electron densities increasing from n{sub e} ∼ 4 to ∼30 × 10{sup 16} cm{sup −3} throughout a 120-ns evolution of our plasma. Also, we observe n{sub 2} to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ∼55 ns to become consistent with LTE. This supports our electron-temperature determination of T{sub e} ∼ 1.3 eV (∼15,000 K) after this time. At n{sub e} ≳ 10{sup 17} cm{sup −3}, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ{sup 2}) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. This work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.« less

Impedance of an intense plasma-cathode electron source for tokamak startup

DOE PAGES

Hinson, Edward Thomas; Barr, Jayson L.; Bongard, Michael W.; ...

2016-05-31

In this study, an impedance model is formulated and tested for the ~1kV, ~1kA/cm 2, arc-plasma cathode electron source used for local helicity injection tokamak startup. A double layer sheath is established between the high-density arc plasma (n arc ≈ 10 21 m -3) within the electron source, and the less dense external tokamak edge plasma (n edge ≈ 10 18 m -3) into which current is injected at the applied injector voltage, V inj. Experiments on the Pegasus spherical tokamak show the injected current, I inj, increases with V inj according to the standard double layer scaling I injmore » ~ V inj 3/2 at low current and transitions to I inj ~ V inj 1/2 at high currents. In this high current regime, sheath expansion and/or space charge neutralization impose limits on the beam density n b ~ I inj/V inj 1/2. For low tokamak edge density n edge and high I inj, the inferred beam density n b is consistent with the requirement n b ≤ n edge imposed by space-charge neutralization of the beam in the tokamak edge plasma. At sufficient edge density, n b ~ n arc is observed, consistent with a limit to n b imposed by expansion of the double layer sheath. These results suggest that n arc is a viable control actuator for the source impedance.« less

Multibit Polycristalline Silicon-Oxide-Silicon Nitride-Oxide-Silicon Memory Cells with High Density Designed Utilizing a Separated Control Gate

NASA Astrophysics Data System (ADS)

Rok Kim, Kyeong; You, Joo Hyung; Dal Kwack, Kae; Kim, Tae Whan

2010-10-01

Unique multibit NAND polycrystalline silicon-oxide-silicon nitride-oxide-silicon (SONOS) memory cells utilizing a separated control gate (SCG) were designed to increase memory density. The proposed NAND SONOS memory device based on a SCG structure was operated as two bits, resulting in an increase in the storage density of the NVM devices in comparison with conventional single-bit memories. The electrical properties of the SONOS memory cells with a SCG were investigated to clarify the charging effects in the SONOS memory cells. When the program voltage was supplied to each gate of the NAND SONOS flash memory cells, the electrons were trapped in the nitride region of the oxide-nitride-oxide layer under the gate to supply the program voltage. The electrons were accumulated without affecting the other gate during the programming operation, indicating the absence of cross-talk between two trap charge regions. It is expected that the inference effect will be suppressed by the lower program voltage than the program voltage of the conventional NAND flash memory. The simulation results indicate that the proposed unique NAND SONOS memory cells with a SCG can be used to increase memory density.

The Comet Giacobini-Zinner magnetotail: Axial stresses and inferred near-nucleus properties

NASA Technical Reports Server (NTRS)

Mccomas, D. J.; Gosling, J. T.; Bame, S. J.; Slavin, J. A.; Smith, E. J.; Steinberg, J. L.

1986-01-01

Utilizing the electron and magnetic field data from the ICE tail traversal of comet Giacobini-Zinner along with the MHD equations, a steady state, stress balance model of the cometary magnetotail was developed, and used to infer important but unmeasured ion properties within the magnetotail at ICE and upstream at the average point along each streamline where cometary ions are picked-up. The derived tailward ion flow speed at ICE is quite constant at approx. -20 to -30 km/sec across the entire tail. The flow velocity, ion temperature, density, and ion source rates upstream from the lobes (current sheet) at the average pick-up locations are approx. -75 km/sec (approx. -12), approx. 4 million K (approx. 100,000), approx. 20 cc (approx. 400), and approx. 15 cu cm/sec. Gradients in the plasma properties between the two regions are quite strong. Implications of inferred plasma properties for the near-nucleus region and for cometary magnetotail formation are examined.

Correlating Metastable-Atom Density, Reduced Electric Field, and Electron Energy Distribution in the Initiation, Transient, and Post-Transient Stages of a Pulsed Argon Discharge

NASA Astrophysics Data System (ADS)

Franek, James B.

Argon emission lines, particularly those in the near-infrared region (700-900nm), are used to determine plasma properties in low-temperature, partially ionized plasmas to determine effective electron temperature [Boffard et al., 2012], and argon excited state density [Boffard et al., 2009] using appropriately assumed electron energy distributions. While the effect of radiation trapping influences the interpretation of plasma properties from emission-line ratio analysis, eliminating the need to account for these effects by directly observing the 3px-to-1sy transitions [ Boffard et al., 2012] is preferable in most cases as this simplifies the analysis. In this dissertation, a 1-Torr argon, pulsed positive column in a hollow-cathode discharge is used to study the correlation between four quantities: 420.1-419.8nm emission-line ratio, metastable-atom density, reduced electric field, and electron energy distribution. The extended coronal model is used to acquire an expression for 420.1-419.8nm emission-line ratio, which is sensitive to direct electron-impact excitation of argon excited states as well as stepwise electron-impact excitation of argon excited states for the purpose of inferring plasma quantities from experimental measurements. Initial inspection of the 420.1-419.8nm emission-line ratio suggests the pulse may be empirically divided into three distinct stages labelled the Initiation Stage, Transient Stage, and Post-Transient stage. Using equilibrium electron energy distributions from simulation to deduce excitation rates [Adams et al., 2012] in the extended coronal model affords agreement between predicted and observed metastable density in the Post-Transient stage of the discharge [Franek et al., 2015]. Applying this model-assisted diagnostic technique to the characterization of plasma systems utilizing lower-resolution spectroscopic systems is not straightforward, however, as the 419.8nm and 420.1nm emission-line profiles are convolved and become insufficiently resolved for treating the convolution as two separate emission-lines. To remedy this, the argon 425.9nm emission-line is evaluated as a proxy for the 419.8 nm emission-line. Both emission-lines (419.8nm and 425.9nm) are attributed to direct excitation from the argon ground state. The intensity of the 425.9nm emission-line is compared to the intensity of the 419.8nm emission-line over a range of plasma conditions to infer the same plasma quantities from similar experimental measurements. Discrepancies between the observed intensities of the emission-lines (419.8nm, 425.9nm) are explained by electron-impact cross-sections of their parent states. It is shown that the intensity of the argon 425.9nm emission-line is similar to that of the 419.8nm emission-line. The difference between the observed emission lines (425.9nm, 419.8nm) is attributed to the electron energy distribution in the plasma.

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

NASA Astrophysics Data System (ADS)

Weilacher, F.; Radha, P. B.; Forrest, C.

2018-04-01

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium-tritium (D-T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. It is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D-D and D-T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D-D reaction, whereas they insignificantly influence the inferred D-T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. This code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.

Thermionic emission from monolayer graphene, sheath formation and its feasibility towards thermionic converters

NASA Astrophysics Data System (ADS)

Misra, Shikha; Upadhyay Kahaly, M.; Mishra, S. K.

2017-02-01

A formalism describing the thermionic emission from a single layer graphene sheet operating at a finite temperature and the consequent formation of the thermionic sheath in its proximity has been established. The formulation takes account of two dimensional densities of state configuration, Fermi-Dirac (f-d) statistics of the electron energy distribution, Fowler's treatment of electron emission, and Poisson's equation. The thermionic current estimates based on the present analysis is found to be in reasonably good agreement with experimental observations (Zhu et al., Nano Res. 07, 1 (2014)). The analysis has further been simplified for the case where f-d statistics of an electron energy distribution converges to Maxwellian distribution. By using this formulation, the steady state sheath features, viz., spatial dependence of the surface potential and electron density structure in the thermionic sheath are derived and illustrated graphically for graphene parameters; the electron density in the sheath is seen to diminish within ˜10 s of Debye lengths. By utilizing the graphene based cathode in configuring a thermionic converter (TC), an appropriate operating regime in achieving the efficient energy conversion has been identified. A TC configured with the graphene based cathode (operating at ˜1200 K/work function 4.74 V) along with the metallic anode (operating at ˜400 K/ work function 2.0 V) is predicted to display ˜56% of the input thermal flux into the electrical energy, which infers approximately ˜84% of the Carnot efficiency.

X-ray Spectroscopic Characterization of Plasma for a Charged-Particle Energy-Loss Experiment

NASA Astrophysics Data System (ADS)

Hoffman, Nm; Lee, Cl; Wilson, Dc; Barnes, Cris W.; Petrasso, Rd; Li, C.; Hicks, D.

2000-10-01

We are pursuing an approach to a charged-particle energy-loss experiment in which charged fusion products from an imploded ICF capsule travel through a well characterized, spatially separate plasma. For this purpose, a fully ionized, uniform, nearly steady-state carbon-hydrogen plasma will be created by laser irradiation of a plastic foil. The temperature and density structure of this plasma must be determined accurately in order to relate observed energy losses to predictions of theory. Various methods for diagnosing the plasma are possible, including Thomson scattering. Alternatively, if a small admixture of higher-Z material such as chlorine is included in the plastic, x-ray spectroscopic techniques will allow the plasma's temperature and density to be determined. Electron temperature is inferred from the ratios of line strengths of various chlorine ion stages, while electron density is determined from the spectra of lithium-like satellite lines near the He beta line of helium-like chlorine. We present results from detailed-configuration accounting (DCA) models of line emission from C+H+Cl plasmas, and estimate the accuracy with which such plasmas can be characterized.

X-ray line emission from the Puppis A supernova remnant - Oxygen lines

NASA Technical Reports Server (NTRS)

Winkler, P. F.; Clark, G. W.; Markert, T. H.; Petre, R.; Canizares, C. R.

1981-01-01

Six prominent X-ray emission lines of O VII and O VIII have been detected from a portion of the Puppis A supernova remnant in observations with the Einstein Observatory Focal Plane Crystal Spectrometer. The lines are sufficiently well resolved to serve as diagnostics of the emitting plasma. From the relative intensities of the lines, it is inferred that the population of O VIII is about 1.5 times that of O VII, and that electron collisions are the dominant excitation mechanism in the plasma. A locus of allowed electron temperatures and interstellar-absorption column densities is derived: 1.5 x 10 to the 6th K, and (2-6) x 10 to the 21st per sq cm. The data are consistent with either a thin plasma source in equilibrium at a temperature of 2.2 x 10 to the 6th K with a column density of 4 x 10 to the 21st per sq cm, or with a nonequilibrium source in which the electrons have been shock-heated to a higher temperature and oxygen is underionized.

White dwarf stars exceeding the Chandrasekhar mass limit

NASA Astrophysics Data System (ADS)

Tomaschitz, Roman

2018-01-01

The effect of nonlinear ultra-relativistic electron dispersion on the mass-radius relation of high-mass white dwarfs is studied. The dispersion is described by a permeability tensor in the Dirac equation, generated by the ionized high-density stellar matter, which constitutes the neutralizing background of the nearly degenerate electron plasma. The electron dispersion results in a stable mass-radius relation for high-mass white dwarfs, in contrast to a mass limit in the case of vacuum permeabilities. In the ultra-relativistic regime, the dispersion relation is a power law whose amplitude and scaling exponent is inferred from mass and radius estimates of two high-mass white dwarfs, Sirius B and LHS 4033. Evidence for the existence of super-Chandrasekhar mass white dwarfs is provided by several Type Ia supernovae (e.g., SN 2013cv, SN 2003fg, SN 2007if and SN 2009dc), whose mass ejecta exceed the Chandrasekhar limit by up to a factor of two. The dispersive mass-radius relation is used to estimate the radii, central densities, Fermi temperatures, bulk and compression moduli and sound velocities of their white dwarf progenitors.

Langmuir Probe Measurements in a Grid-Assisted Magnetron Sputtering System

NASA Astrophysics Data System (ADS)

Sagás, Julio César; Pessoa, Rodrigo Sávio; Maciel, Homero Santiago

2018-02-01

The grid-assisted magnetron sputtering is a variation of the magnetron sputtering commonly used for thin film deposition. In this work, Langmuir probe measurements were performed in such a system by using the grid under two basic and practical electrical conditions, i.e., floating and grounded. The results show that grounding the grid leads to an enhancement of the plasma confinement and to increases in both floating and plasma potential, as inferred from the probe characteristics. The grounded grid drains electrons from the plasma, acting as an auxiliary anode and reducing the plasma diffusion toward the chamber walls. For the same discharge current, the improved confinement results in a lower electron temperature when compared to floating condition, although the electron densities are comparable in both cases.

Altitude Variation of the Plasmapause Signature in the Main Ionospheric Trough

NASA Technical Reports Server (NTRS)

Grebowsky, Joseph M.; Benson, Robert F.; Webb, Phillip A.; Truhlik, Vladimir; Bilitza, Dieter

2009-01-01

The projection of the plasmapause magnetic-field lines to low altitudes, where the light-ion chemistry is dominated by O(+), tends to occur near the minimum electron density in the main (midlatitude) electron density trough at night. With increasing attitude in the trough, where H(+) emerges as the dominant iota on the low-latitude boundary, we have found cases where the plasmapause field lines are located on the sharp low-Latitude side of the trough as expected if this topside ionosphere H(+) distribution varies in step with the plasmapause gradient in the distant plasmasphere. These conclusions are based on near-equatorial crossings of the plasmapause (corresponding to the steep gradient in the dominant species H(+) by the Explorer-45 satellite as determined from electric-field measurements by Maynard and Cauffman in the early 1970s and ISIS-2 ionospheric topside-sounder measurements. The former data have now been converted to digital form and made available at http://nssdcftp.gsfc.nasa.gov. The latter provide samples of nearly coincident observations of ionospheric main trough crossings near the same magnetic-field lines of the Explorer 45-determined equatorial plasmapause. The ISIS-2 vertical electron density profiles are used to infer where the F-region transitions from an O(+) to a H(+) dominated plasma through the main trough boundaries.

Plasma flow measurements in the Prototype-Material Plasma Exposure eXperiment (Proto-MPEX) and comparison with B2.5-Eirene modeling

NASA Astrophysics Data System (ADS)

Kafle, N.; Owen, L. W.; Caneses, J. F.; Biewer, T. M.; Caughman, J. B. O.; Donovan, D. C.; Goulding, R. H.; Rapp, J.

2018-05-01

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory is a linear plasma device that combines a helicon plasma source with additional microwave and radio frequency heating to deliver high plasma heat and particle fluxes to a target. Double Langmuir probes and Thomson scattering are being used to measure local electron temperature and density at various radial and axial locations. A recently constructed Mach-double probe provides the added capability of simultaneously measuring electron temperatures ( T e), electron densities ( n e), and Mach numbers (M). With this diagnostic, it is possible to infer the plasma flow, particle flux, and heat flux at different locations along the plasma column in Proto-MPEX. Preliminary results show Mach numbers of 0.5 (towards the dump plate) and 1.0 (towards the target plate) downstream from the helicon source, and a stagnation point (no flow) near the source for the case where the peak magnetic field was 1.3 T. Measurements of particle flow and ne and Te profiles are discussed. The extensive coverage provided by these diagnostics permits data-constrained B2.5-Eirene modeling of the entire plasma column, and comparison with results of modeling in the high-density helicon plasmas will be presented.

Mechanical and magneto-opto-electronic investigation of transition metal based fluoro-perovskites: An ab-initio DFT study

NASA Astrophysics Data System (ADS)

Erum, Nazia; Azhar Iqbal, Muhammad

2017-09-01

Detailed ab-initio calculations are performed to investigate structural, elastic, mechanical, magneto-electronic and optical properties of the KXF3 (X = V, Fe, Co, Ni) fluoro-perovskites using Full Potential Linearized Augmented Plane Wave (FP-LAPW) method within the framework of density functional theory (DFT). The calculated structural parameters by DFT and analytical methods are found consistent with the experimental results. From the elastic and mechanical properties, it can be inferred that these compounds are elastically stable and anisotropic while KCoF3 is harder than rest of the compounds. Furthermore, thermal behavior of these compounds is analyzed by calculating Debye temperature (θD). The calculated spin dependent magneto-electronic properties in these compounds reveal that exchange splitting is dominated by N-3d orbital. The stable magnetic phase optimizations verify the experimental observations at low temperature. Type of chemical bonding is analyzed with the help of variations in electron density difference distribution that is induced due to changes of the second cation. The linear optical properties are also discussed in terms of optical spectra. The present methodology represents an influential approach to calculate the whole set of mechanical and magneto-opto-electronic parameters, which would support to understand various physical phenomena and empower device engineers for implementing these materials in spintronic applications.

Heat-Flux Measurements from Collective Thomson-Scattering Spectra

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Hu, S. X.; Katz, J.; Froula, D. H.; Rozmus, W.

2015-11-01

Collective Thomson scattering was used to measure heat flux in coronal plasmas. The relative amplitude of the Thomson-scattered power into the up- and downshifted electron plasma wave features was used to determine the flux of electrons moving along the temperature gradient at three to four times the electron thermal velocity. Simultaneously, the ion-acoustic wave features were measured. Their relative amplitude is used to measure the flux of the return-current electrons. The frequencies of these ion-acoustic and electron plasma wave features provide local measurements of the electron temperature and density. These spectra were obtained at five locations along the temperature gradient in a laser-produced blowoff plasma. These measurements of plasma parameters are used to infer the Spitzer -Härm flux qSH = - κ∇Te and are in good agreement with the values of the heat flux measured from the scattering-feature asymmetries. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Modeling the behavior of ionosphere above Millstone Hill during the September 21-27, 1998 storm

NASA Astrophysics Data System (ADS)

Lei, Jiuhou; Liu, Libo; Wan, Weixing; Zhang, Shun-Rong

2004-08-01

A theoretical ionospheric model is employed to investigate the ionospheric behavior as observed by the incoherent-scatter radar (ISR) at Millstone Hill during the September 21-27, 1998 storm. The observed NmF2 presented a significant negative phase on September 25, and a G condition (hmF2<200km) was also observed. The model results based on the standard input parameters (climatological model values) are in good agreement with the observed electron densities under quiet conditions, but there are large discrepancies during disturbed periods. The exospheric temperature Tex, neutral winds, atomic oxygen density [O] and molecular nitrogen density [N2], and solar flux are inferred from the ISR ion temperature profiles and from the electron density profiles. Our calculated results show that the maximum Tex is higher than 1700K, and an averaged decrease in [O] is a factor of 2.2 and an increase in [N2] at 300km is about 1.8 times for the disturbed day, September 25, relative to the quiet day level. Therefore, the large change of [N2]/[O] ratio gives a good explanation for the negative phase at Millstone Hill during this storm. Furthermore, at the disturbed nighttime the observations show a strong NmF2 decrease, accompanied by a significant hmF2 increase after the sudden storm commencement (SSC). Simulations are carried out based on the inferred Tex. It is found that the uplift of F2 layer during the period from sunset to post-midnight is mainly associated with the large equatorward winds, and a second rise in hmF2 after midnight results from the depleted Ne in the bottom-side of F2 layer due to the increased recombination, while the ``midnight collapse'' of hmF2 is attributed to the large-scale traveling atmospheric disturbances.

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

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

Weilacher, F.; Radha, P. B.; Forrest, C.

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium–tritium (D–T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. Here, it is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [T. R.more » Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D–D and D–T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D–D reaction, whereas they insignificantly influence the inferred D–T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. Finally, this code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.« less

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

DOE PAGES

Weilacher, F.; Radha, P. B.; Forrest, C.

2018-04-26

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium–tritium (D–T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. Here, it is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [T. R.more » Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D–D and D–T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D–D reaction, whereas they insignificantly influence the inferred D–T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. Finally, this code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.« less

Latitudinal variation of speed and mass flux in the acceleration region of the solar wind inferred from spectral broadening measurements

NASA Technical Reports Server (NTRS)

Woo, Richard; Goldstein, Richard M.

1994-01-01

Spectral broadening measurements conducted at S-band (13-cm wavelength) during solar minimum conditions in the heliocentric distance range of 3-8 R(sub O) by Mariner 4, Pioneer 10, Mariner 10, Helios 1, Helios 2, and Viking have been combined to reveal a factor of 2.6 reduction in bandwidth from equator to pole. Since spectral broadening bandwidth depends on electron density fluctuation and solar wind speed, and latitudinal variation of the former is available from coherence bandwidth measurements, the remote sensing spectral broadening measurements provide the first determination of the latitudinal variation of solar wind speed in the acceleration region. When combined with electron density measurements deduced from white-light coronagraphs, this result also leads to the first determination of the latitudinal variation of mass flux in the acceleration region. From equator to pole, solar wind speed increases by a factor of 2.2, while mass flux decreases by a factor of 2.3. These results are consistent with measurements of solar wind speed by multi-station intensity scintillation measurements, as well as measurements of mass flux inferred from Lyman alpha observations, both of which pertain to the solar wind beyond 0.5 AU. The spectral broadening observations, therefore, strengthen earlier conclusions about the latitudinal variation of solar wind speed and mass flux, and reinforce current solar coronal models and their implications for solar wind acceleration and solar wind modeling.

Dislocation substructure of mantle-derived olivine as revealed by selective chemical etching and transmission electron microscopy

USGS Publications Warehouse

Kirby, S.H.; Wegner, M.W.

1978-01-01

Cleaved and mechanically polished surfaces of olivine from peridotite xenoliths from San Carlos, Arizona, were chemically etched using the techniques of Wegner and Christie (1974). Dislocation etch pits are produced on all surface orientations and they tend to be preferentially aligned along the traces of subgrain boundaries, which are approximately parallel to (100), (010), and (001). Shallow channels were also produced on (010) surfaces and represent dislocations near the surface that are etched out along their lengths. The dislocation etch channel loops are often concentric, and emanate from (100) subgrain boundaries, which suggests that dislocation sources are in the boundaries. Data on subgrain misorientation and dislocation line orientation and arguments based on subgrain boundary energy minimization are used to characterize the dislocation structures of the subgrain boundaries. (010) subgrain boundaries are of the twist type, composed of networks of [100] and [001] screw dislocations. Both (100) and (001) subgrain boundaries are tilt walls composed of arrays of edge dislocation with Burgers vectors b=[100] and [001], respectively. The inferred slip systems are {001} ???100???, {100} ???001???, and {010} ???100??? in order of diminishing importance. Exploratory transmission electron microscopy is in accord with these identifications. The flow stresses associated with the development of the subgrain structure are estimated from the densities of free dislocations and from the subgrain dimensions. Inferred stresses range from 35 to 75 bars using the free dislocation densities and 20 to 100 bars using the subgrain sizes. ?? 1978 Springer-Verlag.

Development and Testing of a Decision Making Based Method to Adjust Automatically the Harrowing Intensity

PubMed Central

Rueda-Ayala, Victor; Weis, Martin; Keller, Martina; Andújar, Dionisio; Gerhards, Roland

2013-01-01

Harrowing is often used to reduce weed competition, generally using a constant intensity across a whole field. The efficacy of weed harrowing in wheat and barley can be optimized, if site-specific conditions of soil, weed infestation and crop growth stage are taken into account. This study aimed to develop and test an algorithm to automatically adjust the harrowing intensity by varying the tine angle and number of passes. The field variability of crop leaf cover, weed density and soil density was acquired with geo-referenced sensors to investigate the harrowing selectivity and crop recovery. Crop leaf cover and weed density were assessed using bispectral cameras through differential images analysis. The draught force of the soil opposite to the direction of travel was measured with electronic load cell sensor connected to a rigid tine mounted in front of the harrow. Optimal harrowing intensity levels were derived in previously implemented experiments, based on the weed control efficacy and yield gain. The assessments of crop leaf cover, weed density and soil density were combined via rules with the aforementioned optimal intensities, in a linguistic fuzzy inference system (LFIS). The system was evaluated in two field experiments that compared constant intensities with variable intensities inferred by the system. A higher weed density reduction could be achieved when the harrowing intensity was not kept constant along the cultivated plot. Varying the intensity tended to reduce the crop leaf cover, though slightly improving crop yield. A real-time intensity adjustment with this system is achievable, if the cameras are attached in the front and at the rear or sides of the harrow. PMID:23669712

Mercury: results on mass, radius, ionosphere, and atmosphere from mariner 10 dual-frequency radio signals.

PubMed

Howard, H T; Tyler, G L; Esposito, P B; Anderson, J D; Reasenberg, R D; Shapiro, I I; Fjeldbo, G; Kliore, A J; Levy, G S; Brunn, D L; Dickinson, R; Edelson, R E; Martin, W L; Postal, R B; Seidel, B; Sesplaukis, T T; Shirley, D L; Stelzried, C T; Sweetnam, D N; Wood, G E; Zygielbaum, A I

1974-07-12

Analysis of the radio-tracking data from Mariner 10 yields 6,023,600 +/- 600 for the ratio of the mass of the sun to that of Mercury, in very good agreement with values determined earlier from radar data alone. Occultation measurements yielded values for the radius of Mercury of 2440 +/- 2 and 2438 +/- 2 kilometers at laditudes of 2 degrees N and 68 degrees N, respectively, again in close agreement with the average equatorial radius of 2439 +/- 1 kilometers determined from radar data. The mean density of 5.44 grams per cubic centimeter deduced for Mercury from Mariner 10 data thus virtually coincides with the prior determination. No evidence of either an ionosphere or an atmosphere was found, with the data yielding upper bounds on the electron density of about 1500 and 4000 electrons per cubic centimeter on the dayside and nightside, respectively, and an inferred upper bound on the surface pressure of 10(-8) millibar.

Electrostatic-probe measurements of plasma parameters for two reentry flight experiments at 25000 feet per second

NASA Technical Reports Server (NTRS)

Jones, W. L., Jr.; Cross, A. E.

1972-01-01

Unique plasma diagnostic measurements at high altitudes from two geometrically similar blunt body reentry spacecraft using electrostatic probe rakes are presented. The probes measured the positive ion density profiles (shape and magnitude) during the two flights. The probe measurements were made at eight discrete points (1 cm to 7 cm) from the vehicle surface in the aft flow field of the spacecraft over the altitude range of 85.3 to 53.3 km (280,000 to 175,000 ft) with measured densities of 10 to the 8th power to 10 to the 12th power electrons/cu cm, respectively. Maximum reentry velocity for each spacecraft was approximately 7620 meters/second (25,000 ft/sec). In the first flight experiment, water was periodically injected into a flow field which was contaminated by ablation products from the spacecraft nose region. The nonablative nose of the second spacecraft thereby minimized flow field contamination. Comparisons of the probe measured density profiles with theoretical calculations are presented with discussion as to the probable cause of significant disagreement. Also discussed are the correlation of probe measurements with vehicle angle of attack motions and the good high altitude agreement between electron densities inferred from the probe measurements, VHF antenna measurements, and microwave reflectometer diagnostic measurements.

The ancient oxygen exosphere of Mars - Implications for atmosphere evolution

NASA Technical Reports Server (NTRS)

Zhang, M. H. G.; Luhmann, J. G.; Bougher, S. W.; Nagy, A. F.

1993-01-01

The paper considers absorption of oxygen (atoms and ions) by the surface as a mechanism for the early Martian atmosphere escape, due to the effect of high EUV flux of the ancient sun. Hot oxygen exosphere densities in ancient atmosphere and ionosphere are calculated for different EUV fluxes and the escape fluxes associated with these exposures. Using these densities, the ion production rate above the ionopause is calculated for different epochs including photoionization, charge exchange, and solar wind electron impact. It is found that, when the inferred high solar EUV fluxes of the past are taken into account, oxygen equivalent to that in several tens of meters of water, planet-wide, should have escaped Martian atmosphere to space over the last 3 Gyr.

The ancient oxygen exosphere of Mars - Implications for atmosphere evolution

NASA Astrophysics Data System (ADS)

Zhang, M. H. G.; Luhmann, J. G.; Bougher, S. W.; Nagy, A. F.

1993-06-01

The paper considers absorption of oxygen (atoms and ions) by the surface as a mechanism for the early Martian atmosphere escape, due to the effect of high EUV flux of the ancient sun. Hot oxygen exosphere densities in ancient atmosphere and ionosphere are calculated for different EUV fluxes and the escape fluxes associated with these exposures. Using these densities, the ion production rate above the ionopause is calculated for different epochs including photoionization, charge exchange, and solar wind electron impact. It is found that, when the inferred high solar EUV fluxes of the past are taken into account, oxygen equivalent to that in several tens of meters of water, planet-wide, should have escaped Martian atmosphere to space over the last 3 Gyr.

A MODEL FOR THE ORIGIN OF HIGH DENSITY IN LOOPTOP X-RAY SOURCES

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

Longcope, D. W.; Guidoni, S. E.

Super-hot (SH) looptop sources, detected in some large solar flares, are compact sources of HXR emission with spectra matching thermal electron populations exceeding 30 MK. High observed emission measure (EM) and inference of electron thermalization within the small source region both provide evidence of high densities at the looptop, typically more than an order of magnitude above ambient. Where some investigators have suggested such density enhancement results from a rapid enhancement in the magnetic field strength, we propose an alternative model, based on Petschek reconnection, whereby looptop plasma is heated and compressed by slow magnetosonic shocks generated self-consistently through fluxmore » retraction following reconnection. Under steady conditions such shocks can enhance density by no more than a factor of four. These steady shock relations (Rankine-Hugoniot relations) turn out to be inapplicable to Petschek's model owing to transient effects of thermal conduction. The actual density enhancement can in fact exceed a factor of 10 over the entire reconnection outflow. An ensemble of flux tubes retracting following reconnection at an ensemble of distinct sites will have a collective EM proportional to the rate of flux tube production. This rate, distinct from the local reconnection rate within a single tube, can be measured separately through flare ribbon motion. Typical flux transfer rates and loop parameters yield EMs comparable to those observed in SH sources.« less

Observations Of Planetary Nebula NGC 3242 Using STIS From HST19 GO 12600

NASA Astrophysics Data System (ADS)

Miller, Timothy R.; Dufour, Reginald J.; Henry, Richard B. C.; Kwitter, Karen B.; Shaw, Richard A.; Balick, Bruce; Corradi, Romano

2014-06-01

During HST Cycle 19, we obtained long-slit spectra using STIS of the planetary nebula NGC 3242 with higher spatial resolution than previously published. The full wavelength range is around 1100-10200Å, covering many nebular lines for determining numerous ionic abundances and electron densities and temperatures. In this work, we first analyze the low- and moderate-resolution UV emission lines of carbon, nitrogen and oxygen. In particular, the resolved lines of C_III] 1907 and C_III] 1909 have yielded a direct measurement of one of the dominant ionic species for carbon and a determination of the density occupied by doubly-ionized carbon and other similar ions. Next, the spatial emission profile of these lines reveals variations in the inferred density along the line of sight from about 2800-11500 cm-3, compared with a value ~3800 cm-3, when averaged over the entire slit. Similarly, the electron temperature is around 12000K for the entire slit and ranges from about 11400-14000K when the slit is divided into smaller sub-regions. Lastly, these sub-regions of the nebula have been modeled in detail with the photoionization code CLOUDY. This modeling will assess the density profile that produces the observed density variation, reproduce the temperature fluctuations, and constrain the central star temperature. We acknowledge the gracious support from HST and the University of Oklahoma.

A Two-Fluid, MHD Coronal Model

NASA Technical Reports Server (NTRS)

Suess, S. T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

1999-01-01

We describe first results from a numerical two-fluid MHD model of the global structure of the solar Corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and Momentum sources are required to produce high speed wind from Corona] holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature above the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UltraViolet Coronagraph Spectrometer instrument (UVCS), and with the Ulysses/Solar Wind Observations Over the Poles of the Sun instrument (SWOOPS) proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 and 5 solar radii (2 and 5 R(sub S)) is similar to the density reported from SPARTAN 201.-01 measurements by Fisher and Guhathakurta [19941. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer the temperature and density are similar to those reported empirically by Li et al. [1998], and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub S), as it is in all other MHD coronal streamer models [e.g., Steinolfson et al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal magnetic field, submitted to Solar Physics, 1998].

Non-Born-Oppenheimer electronic and nuclear densities for a Hooke-Calogero three-particle model: non-uniqueness of density-derived molecular structure.

PubMed

Ludeña, E V; Echevarría, L; Lopez, X; Ugalde, J M

2012-02-28

We consider the calculation of non-Born-Oppenheimer, nBO, one-particle densities for both electrons and nuclei. We show that the nBO one-particle densities evaluated in terms of translationally invariant coordinates are independent of the wavefunction describing the motion of center of mass of the whole system. We show that they depend, however, on an arbitrary reference point from which the positions of the vectors labeling the particles are determined. We examine the effect that this arbitrary choice has on the topology of the one-particle density by selecting the Hooke-Calogero model of a three-body system for which expressions for the one-particle densities can be readily obtained in analytic form. We extend this analysis to the one-particle densities obtained from full Coulomb interaction wavefunctions for three-body systems. We conclude, in view of the fact that there is a close link between the choice of the reference point and the topology of one-particle densities that the molecular structure inferred from the topology of these densities is not unique. We analyze the behavior of one-particle densities for the Hooke-Calogero Born-Oppenheimer, BO, wavefunction and show that topological transitions are also present in this case for a particular mass value of the light particles even though in the BO regime the nuclear masses are infinite. In this vein, we argue that the change in topology caused by variation of the mass ratio between light and heavy particles does not constitute a true indication in the nBO regime of the emergence of molecular structure.

Non-Born-Oppenheimer electronic and nuclear densities for a Hooke-Calogero three-particle model: Non-uniqueness of density-derived molecular structure

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

Ludena, E. V.; Echevarria, L.; Lopez, X.

2012-02-28

We consider the calculation of non-Born-Oppenheimer, nBO, one-particle densities for both electrons and nuclei. We show that the nBO one-particle densities evaluated in terms of translationally invariant coordinates are independent of the wavefunction describing the motion of center of mass of the whole system. We show that they depend, however, on an arbitrary reference point from which the positions of the vectors labeling the particles are determined. We examine the effect that this arbitrary choice has on the topology of the one-particle density by selecting the Hooke-Calogero model of a three-body system for which expressions for the one-particle densities canmore » be readily obtained in analytic form. We extend this analysis to the one-particle densities obtained from full Coulomb interaction wavefunctions for three-body systems. We conclude, in view of the fact that there is a close link between the choice of the reference point and the topology of one-particle densities that the molecular structure inferred from the topology of these densities is not unique. We analyze the behavior of one-particle densities for the Hooke-Calogero Born-Oppenheimer, BO, wavefunction and show that topological transitions are also present in this case for a particular mass value of the light particles even though in the BO regime the nuclear masses are infinite. In this vein, we argue that the change in topology caused by variation of the mass ratio between light and heavy particles does not constitute a true indication in the nBO regime of the emergence of molecular structure.« less

Application and Analysis of the Isoelectronic Line Ratio Temperature Diagnostic in a Planar Ablating-Plasma Experiment at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Epstein, R.; Rosenberg, M. J.; Solodov, A. A.; Myatt, J. F.; Regan, S. P.; Seka, W.; Hohenberger, M.; Barrios, M. A.; Moody, J. D.

2015-11-01

The Mn/Co isoelectronic emission-line ratio from a microdot source in planar CH foil targets was measured to infer the electron temperature (Te) in the ablating plasma during two-plasmon-decay experiments at the National Ignition Facility (NIF). We examine the systematic uncertainty in the Te estimate based on the temperature and density sensitivities of the line ratio in conjunction with plausible density constraints, and its contribution to the total Te estimate uncertainty. The potential advantages of alternative microdot elements (e.g., Ti/Cr and Sc/V) are considered. The microdot mass was selected to provide ample line strength while minimizing the effect of self-absorption on the line emission, which is of particular concern, given the narrow linewidths of mid- Z emitters at subcritical electron densities. Atomic line-formation theory and detailed atomic-radiative simulations show that the straight forward interpretation of the isoelectronic ratio solely in terms of its temperature independence remains valid with lines of moderate optical thickness (up to ~ 10) at line center. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Laser experiments to simulate coronal mass ejection driven magnetospheres and astrophysical plasma winds on compact magnetized stars

NASA Astrophysics Data System (ADS)

Horton, W.; Ditmire, T.; Zakharov, Yu. P.

2010-06-01

Laboratory experiments using a plasma wind generated by laser-target interaction are proposed to investigate the creation of a shock in front of the magnetosphere and the dynamo mechanism for creating plasma currents and voltages. Preliminary experiments are shown where measurements of the electron density gradients surrounding the obstacles are recorded to infer the plasma winds. The proposed experiments are relevant to understanding the electron acceleration mechanisms taking place in shock-driven magnetic dipole confined plasmas surrounding compact magnetized stars and planets. Exploratory experiments have been published [P. Brady, T. Ditmire, W. Horton, et al., Phys. Plasmas 16, 043112 (2009)] with the one Joule Yoga laser and centimeter sized permanent magnets.

The Electronics and Data Acquisition System of the DarkSide Dark Matter Search

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

Agnes, P.; et al.

2014-12-09

It is generally inferred from astronomical measurements that Dark Matter (DM) comprises approximately 27\\% of the energy-density of the universe. If DM is a subatomic particle, a possible candidate is a Weakly Interacting Massive Particle (WIMP), and the DarkSide-50 (DS) experiment is a direct search for evidence of WIMP-nuclear collisions. DS is located underground at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, and consists of three active, embedded components; an outer water veto (CTF), a liquid scintillator veto (LSV), and a liquid argon (LAr) time projection chamber (TPC). This paper describes the data acquisition and electronic systems ofmore » the DS detectors, designed to detect the residual ionization from such collisions.« less

Inelastic X-ray Scattering from Shocked Liquid Deuterium

DOE PAGES

Regan, S. P.; Falk, K.; Gregori, G.; ...

2012-12-28

The Fermi-degenerate plasma conditions created in liquid deuterium by a laser-ablation—driven shock wave were probed with noncollective, spectrally resolved, inelastic x-ray Thomson scattering employing Cl Ly α line emission at 2.96 keV. Thus, these first x-ray Thomson scattering measurements of the microscopic properties of shocked deuterium show an inferred spatially averaged electron temperature of 8±5 eV, an electron density of 2.2(±0.5)×10 23 cm -3, and an ionization of 0.8 (-0.25, +0.15). Our two-dimensional hydrodynamic simulations using equation-of-state models suited for the extreme parameters occurring in inertial confinement fusion research and planetary interiors are consistent with the experimental results.

Full-wave reflection of lightning long-wave radio pulses from the ionospheric D region: Comparison with midday observations of broadband lightning signals

NASA Astrophysics Data System (ADS)

Jacobson, Abram R.; Shao, Xuan-Min; Holzworth, Robert

2010-05-01

We are developing and testing a steep-incidence D region sounding method for inferring profile information, principally regarding electron density. The method uses lightning emissions (in the band 5-500 kHz) as the probe signal. The data are interpreted by comparison against a newly developed single-reflection model of the radio wave's encounter with the lower ionosphere. The ultimate application of the method will be to study transient, localized disturbances of the nocturnal D region, including those instigated by lightning itself. Prior to applying the method to study lightning-induced perturbations of the nighttime D region, we have performed a validation test against more stable and predictable daytime observations, where the profile of electron density is largely determined by direct solar X-ray illumination. This article reports on the validation test. Predictions from our recently developed full-wave ionospheric-reflection model are compared to statistical summaries of daytime lightning radiated waveforms, recorded by the Los Alamos Sferic Array. The comparison is used to retrieve best fit parameters for an exponential profile of electron density in the ionospheric D region. The optimum parameter values are compared to those found elsewhere using a narrowband beacon technique, which used totally different measurements, ranges, and modeling approaches from those of the work reported here.

Coordinated Radio, Electron, and Waves Experiment (CREWE) for the NASA Comet Rendezvous and Asteroid Flyby (CRAF) instrument

NASA Technical Reports Server (NTRS)

Scudder, Jack D.

1992-01-01

The Coordinated Radio, Electron, and Waves Experiment (CREWE) was designed to determine density, bulk velocity and temperature of the electrons for the NASA Comet Rendezvous and Asteroid Flyby Spacecraft, to define the MHD-SW IMF flow configuration; to clarify the role of impact ionization processes, to comment on the importance of anomalous ionization phenomena (via wave particle processes), to quantify the importance of wave turbulence in the cometary interaction, to establish the importance of photoionization via the presence of characteristic lines in a structured energy spectrum, to infer the presence and grain size of significant ambient dust column density, to search for the theoretically suggested 'impenetrable' contact surface, and to quantify the flow of heat (in the likelihood that no surface exists) that will penetrate very deep into the atmosphere supplying a good deal of heat via impact and charge exchange ionization. This final report provides an instrument description, instrument test plans, list of deliverables/schedule, flight and support equipment and software schedule, CREWE accommodation issues, resource requirements, status of major contracts, an explanation of the non-NASA funded efforts, status of EIP and IM plan, descope options, and Brinton questions.

IR-UV double resonance spectroscopic investigation of phenylacetylene-alcohol complexes. Alkyl group induced hydrogen bond switching.

PubMed

Singh, Prashant Chandra; Patwari, G Naresh

2008-06-12

The electronic transitions of phenylacetylene complexes with water and trifluoroethanol are shifted to the blue, while the corresponding transitions for methanol and ethanol complexes are shifted to the red relative to the phenylacetylene monomer. Fluorescence dip infrared (FDIR) spectra in the O-H stretching region indicate that, in all the cases, phenylacetylene is acting as a hydrogen bond acceptor to the alcohols. The FDIR spectrum in the acetylenic C-H stretching region shows Fermi resonance bands for the bare phenylacetylene, which act as a sensitive tool to probe the intermolecular structures. The FDIR spectra reveal that water and trifluoroethanol interact with the pi electron density of the acetylene C-C triple bond, while methanol and ethanol interact with the pi electron density of the benzene ring. It can be inferred that the hydrogen bonding acceptor site on phenylacetylene switches from the acetylene pi to the benzene pi with lowering in the partial charge on the hydrogen atom of the OH group. The most significant finding is that the intermolecular structures of water and methanol complexes are notably distinct, which, to the best of our knowledge, this is first such observation in the case of complexes of substituted benzenes.

Ionospheric Electron Density Measurements Using COSMIC

NASA Astrophysics Data System (ADS)

Dymond, K. F.; Budzien, S. A.; Bernhardt, P. A.; Rocken, C.; Syndergaard, S.

2007-12-01

At 0140 UTC on April 15, 2006, the joint Taiwan-U.S. COSMIC/FORMOSAT-3 (Constellation Observing System for Meteorology, Ionosphere, and Climate and Formosa Satellite mission #3; hereafter COSMIC) mission, a constellation of six micro-satellites, was launched into a 512-km orbit from Vandenberg Air Force Base in California. Using on-board propulsion these satellites have been deployed to their final orbits at 800 km with 30 degrees of separation. This process has taken about 17 months following the launch. There are three instruments aboard each COSMIC satellite: the GPS Occultation Experiment (GOX), the Tri-Band Beacon (TBB), and the Tiny Ionospheric Photometer (TIP). These three instruments constitute a unique suite of instruments for studying the Earth's ionosphere. The GOX instrument operates by inferring the slant total electron content (the integral of the electron density along the line-of-sight) between the COSMIC satellites and the GPS satellites as a function of tangent height above the Earth's limb. These data can be inverted to produce electron density profiles in the E and F regions of the ionosphere. The TBB is a three frequency radio beacon that radiates coherently at 150, 400, and 1067 MHz. When the relative phases of the signals are measured between the COSMIC satellites and ground-based or space-based receivers, the total electron content along the line-of-sight can be determined. By making the measurements from a set of receivers, the two-dimensional distribution of electrons beneath the satellite can be determined using tomographic techniques. The TIP instrument measures the optical signature of the natural decay of the ionosphere produced via ecombination of the O+ ions and electrons. The TIP measurements can be used to characterize the morphology and dynamics of the global ionosphere. Additionally, the TIP measurements can be inverted in conjunction with the GPS occultation measurements, using tomographic techniques, to produce the two- dimensional distribution of electrons beneath the satellite. We present an overview of the COSMIC mission, the instruments, and their application to ionospheric sensing.

Growth mechanism of surface roughed platinum nanowires through electrodeposition current control and their electrochemical applications

NASA Astrophysics Data System (ADS)

Ruan, Dajiang

The aim of this work is to investigate the effect of current density on the grain size and surface morphology of electrodeposited platinum nanowires and their applications. Platinum (Pt) nanowires were fabricated by a galvanostatic electrodeposition method in a porous anodic alumina oxide (AAO) template with different current densities. Both direct current and pulse current electrodeposition were used to synthesize the Pt nanowires. The grain size and surface morphology of the Pt nanowires were studied by field emission scanning electron microscopy (FE-SEM), transmission electron microcopy (TEM) and X-ray diffraction (XRD). The experimental results showed that the current density was the key factor to control the surface roughness. The surface of the Pt nanowires became rougher and the grain sizes were increased by increasing the current densities. From the experimental results, a growth mechanism of Pt nanowires based on progressive nucleation and crystallization was proposed in order to find out the relationship between the surface morphology and current density. The electrochemical properties and catalytic activities of these surface roughed Pt nanowires were investigated in the detection of H20 2 and for the methanol oxidation. Cyclic voltammograms of Pt nanowire modified electrodes were obtained using a potentiostat, which showed that rougher Pt nanowires have higher response and better activity than that of smooth nanowires. For H202 detection, the effect of scan rate and H202 concentration were studied and it was found that the peak current for hydrogen peroxide reduction became larger with the increasing of either scan rate or H202 concentration. It can be inferred that the process of electrocatalytic hydrogen peroxide reduction may be controlled by diffusion of hydrogen peroxide and the Pt nanowire modified glassy carbon electrode (GCE) is well suited for the detection of H202. From the relationship between the peak current and square root of scan rates for methanol oxidation, it can be inferred that the process of electrocatalytic methanol oxidation was controlled by diffusion of methanol. To understand the effect of the morphological feature on the electrocatalytic activity of the Pt nanowire catalysts, the electrochemically active surface area (ECSA) as a function of deposited current density was investigated, which suggests that Pt nanowire catalysts deposited at highest current density had the most ECSA surface morphology of the Pt nanowires. The chronoamperometric curves and electrochemical impedance spectroscopy (EIS) results confirmed that the Pt nanowire catalyst synthesized at higher current density possessed longer durability and gave more efficient electrochemical performance.

DE 1 observations of theta aurora plasma source regions and Birkeland current charge carriers

NASA Technical Reports Server (NTRS)

Menietti, J. D.; Burch, J. L.

1987-01-01

Detailed analyses of the DE 1 high-altitude plasma instrument electron and ion data have been performed for four passes during which theta auroras were observed. The data indicate that the theta auroras occur on what appear to be closed field lines with particle signatures and plasma parameters that are quite similar to those of the magnetospheric boundary plasma sheet. The field-aligned currents computed from particle fluxes in the energy range 18-13 keV above the theta auroras are observed to be generally downward on the dawnside of the arcs with a narrower region of larger (higher density) upward currents on the duskside of the arcs. These currents are carried predominantly by field-aligned beams of accelerated cold electrons. Of particualr interest in regions of upward field-aligned current are downward electron beams at energies less than the inferred potential drop above the spacecraft.

New insights into sub-ion scale turbulence in Earth's magnetosheath using MMS data

NASA Astrophysics Data System (ADS)

Breuillard, Hugo; Andriopoulou, Maria; Graham, Daniel; Le Contel, Olivier; Huang, Shiyong; Hadid, Lina; Sahraoui, Fouad; Alexandrova, Olga; Berthomier, Matthieu; Retino, Alessandro; Nakamura, Rumi; Baumjohann, Wolfgang

2017-04-01

On January 22nd 2016, MMS was located in Earth's magnetosheath and detected intense lion roars showing a secondary bandwidth. Detailed polarization analysis, using burst data from SCM and EDP instruments, and numerical simulation, using WHAMP, are performed in this study. They show that these mainly perpendicular fluctuations are highly nonlinear whistler wave packets, and that a high sampling rate is needed to pick up the peaks of the signal. As a result, their amplitude might have been underestimated in previous missions such as Cluster, which can have a significant impact on electron dynamics. Using FPI burst data, we show that electron velocity distribution functions exhibit a gyrophase-bunched signature in the presence of these lion roars. The analysis of magnetic and density fluctuations, inferred from spacecraft potential, also show the highly-compressible nature of turbulence up to electron scales.

A study of solar preflare activity using two-dimensional radio and SMM-XRP observations

NASA Technical Reports Server (NTRS)

Kundu, M. R.; Gopalswamy, N.; Saba, J. L. R.; Schmelz, J. T. S.; Strong, K. T.

1987-01-01

A study of type III activity at meter-decameter wavelengths in the preflare phase of the February 3, 1986 flare is presented, using data obtained with the Clark Lake Multifrequency Radioheliograph. This activity is compared with similar type III burst activity during the impulsive phase, and it is found that there is a displacement of burst sources between the onset and end times of the activity. A comparison of this displacement at three frequencies suggests that the type III emitting electrons gain access progressively to diverging and different field lines relative to the initial field lines. The energetics of the type III emitting electrons are inferred from observations and compared with those of the associated hard X-ray emitting electrons. The soft X-ray data from SMM-XRP show enhanced emission measure, density, and temperature in the region associated with the preflare type III activity.

A study of solar preflare activity using two-dimensional radio and SMM-XRP observations

NASA Astrophysics Data System (ADS)

Kundu, M. R.; Gopalswamy, N.; Saba, J. L. R.; Schmelz, J. T. S.; Strong, K. T.

1987-09-01

The authors present a study of type III activity at meter-decameter wavelengths in the preflare phase of the 1986 February 3 flare using data obtained with the Clark Lake Multifrequency Radioheliograph. They compare this activity with similar type III burst activity during the impulsive phase and find that there is a displacement of burst sources between the onset and end times of the activity. A comparison of this displacement at three frequencies suggests that the type III emitting electrons gain access progressively to diverging and different field lines relative to the initial field lines. The energetics of the type III emitting electrons are inferred from observations and compared with those of the associated hard X-ray emitting electrons. The soft X-ray data from SMM-XRP shows enhanced emission measure, density and temperature in the region associated with the preflare type III activity.

Cluster Analysis of Time-Dependent Crystallographic Data: Direct Identification of Time-Independent Structural Intermediates

PubMed Central

Kostov, Konstantin S.; Moffat, Keith

2011-01-01

The initial output of a time-resolved macromolecular crystallography experiment is a time-dependent series of difference electron density maps that displays the time-dependent changes in underlying structure as a reaction progresses. The goal is to interpret such data in terms of a small number of crystallographically refinable, time-independent structures, each associated with a reaction intermediate; to establish the pathways and rate coefficients by which these intermediates interconvert; and thereby to elucidate a chemical kinetic mechanism. One strategy toward achieving this goal is to use cluster analysis, a statistical method that groups objects based on their similarity. If the difference electron density at a particular voxel in the time-dependent difference electron density (TDED) maps is sensitive to the presence of one and only one intermediate, then its temporal evolution will exactly parallel the concentration profile of that intermediate with time. The rationale is therefore to cluster voxels with respect to the shapes of their TDEDs, so that each group or cluster of voxels corresponds to one structural intermediate. Clusters of voxels whose TDEDs reflect the presence of two or more specific intermediates can also be identified. From such groupings one can then infer the number of intermediates, obtain their time-independent difference density characteristics, and refine the structure of each intermediate. We review the principles of cluster analysis and clustering algorithms in a crystallographic context, and describe the application of the method to simulated and experimental time-resolved crystallographic data for the photocycle of photoactive yellow protein. PMID:21244840

Interplanetary Coronal Mass Ejection effects on thermospheric density as inferred from International Space Station orbital data

NASA Astrophysics Data System (ADS)

Mendaza, T.; Blanco-Ávalos, J. J.; Martín-Torres, J.

2017-11-01

The solar activity induces long term and short term periodical variations in the dynamics and composition of Earth's atmosphere. The Sun also shows non periodical (i.e., impulsive) activity that reaches the planets orbiting around it. In particular, Interplanetary Coronal Mass Ejections (ICMEs) reach Earth and interact with its magnetosphere and upper neutral atmosphere. Nevertheless, the interaction with the upper atmosphere is not well characterized because of the absence of regular and dedicated in situ measurements at high altitudes; thus, current descriptions of the thermosphere are based on semi empirical models. In this paper, we present the total neutral mass densities of the thermosphere retrieved from the orbital data of the International Space Station (ISS) using the General Perturbation Method, and we applied these densities to routinely compiled trajectories of the ISS in low Earth orbit (LEO). These data are explicitly independent of any atmospheric model. Our density values are consistent with atmospheric models, which demonstrates that our method is reliable for the inference of thermospheric density. We have inferred the thermospheric total neutral density response to impulsive solar activity forcing from 2001 to the end of 2006 and determined how solar events affect this response. Our results reveal that the ISS orbital parameters can be used to infer the thermospheric density and analyze solar effects on the thermosphere.

Average-atom treatment of relaxation time in x-ray Thomson scattering from warm dense matter.

PubMed

Johnson, W R; Nilsen, J

2016-03-01

The influence of finite relaxation times on Thomson scattering from warm dense plasmas is examined within the framework of the average-atom approximation. Presently most calculations use the collision-free Lindhard dielectric function to evaluate the free-electron contribution to the Thomson cross section. In this work, we use the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time is evaluated by treating the average atom as an impurity in a uniform electron gas and depends critically on the transport cross section. The calculated relaxation rates agree well with values inferred from the Ziman formula for the static conductivity and also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis in the average-atom potential are compared with those evaluated in the commonly used Born approximation. The Born approximation converges to the exact cross sections at high energies; however, differences that occur at low energies lead to corresponding differences in relaxation rates. The relative importance of including relaxation time when modeling x-ray Thomson scattering spectra is examined by comparing calculations of the free-electron dynamic structure function for Thomson scattering using Lindhard and Mermin dielectric functions. Applications are given to warm dense Be plasmas, with temperatures ranging from 2 to 32 eV and densities ranging from 2 to 64 g/cc.

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

Johnson, W. R.; Nilsen, J.

Here, the influence of finite relaxation times on Thomson scattering from warm dense plasmas is examined within the framework of the average-atom approximation. Presently most calculations use the collision-free Lindhard dielectric function to evaluate the free-electron contribution to the Thomson cross section. In this work, we use the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time is evaluated by treating the average atom as an impurity in a uniform electron gas and depends critically on the transport cross section. The calculated relaxation rates agree well with values inferred from the Ziman formula for the static conductivity andmore » also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis in the average-atom potential are compared with those evaluated in the commonly used Born approximation. The Born approximation converges to the exact cross sections at high energies; however, differences that occur at low energies lead to corresponding differences in relaxation rates. The relative importance of including relaxation time when modeling x-ray Thomson scattering spectra is examined by comparing calculations of the free-electron dynamic structure function for Thomson scattering using Lindhard and Mermin dielectric functions. Applications are given to warm dense Be plasmas, with temperatures ranging from 2 to 32 eV and densities ranging from 2 to 64 g/cc.« less

Average-atom treatment of relaxation time in x-ray Thomson scattering from warm dense matter

DOE PAGES

Johnson, W. R.; Nilsen, J.

2016-03-14

Here, the influence of finite relaxation times on Thomson scattering from warm dense plasmas is examined within the framework of the average-atom approximation. Presently most calculations use the collision-free Lindhard dielectric function to evaluate the free-electron contribution to the Thomson cross section. In this work, we use the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time is evaluated by treating the average atom as an impurity in a uniform electron gas and depends critically on the transport cross section. The calculated relaxation rates agree well with values inferred from the Ziman formula for the static conductivity andmore » also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis in the average-atom potential are compared with those evaluated in the commonly used Born approximation. The Born approximation converges to the exact cross sections at high energies; however, differences that occur at low energies lead to corresponding differences in relaxation rates. The relative importance of including relaxation time when modeling x-ray Thomson scattering spectra is examined by comparing calculations of the free-electron dynamic structure function for Thomson scattering using Lindhard and Mermin dielectric functions. Applications are given to warm dense Be plasmas, with temperatures ranging from 2 to 32 eV and densities ranging from 2 to 64 g/cc.« less

Information theory lateral density distribution for Earth inferred from global gravity field

NASA Technical Reports Server (NTRS)

Rubincam, D. P.

1981-01-01

Information Theory Inference, better known as the Maximum Entropy Method, was used to infer the lateral density distribution inside the Earth. The approach assumed that the Earth consists of indistinguishable Maxwell-Boltzmann particles populating infinitesimal volume elements, and followed the standard methods of statistical mechanics (maximizing the entropy function). The GEM 10B spherical harmonic gravity field coefficients, complete to degree and order 36, were used as constraints on the lateral density distribution. The spherically symmetric part of the density distribution was assumed to be known. The lateral density variation was assumed to be small compared to the spherically symmetric part. The resulting information theory density distribution for the cases of no crust removed, 30 km of compensated crust removed, and 30 km of uncompensated crust removed all gave broad density anomalies extending deep into the mantle, but with the density contrasts being the greatest towards the surface (typically + or 0.004 g cm 3 in the first two cases and + or - 0.04 g cm 3 in the third). None of the density distributions resemble classical organized convection cells. The information theory approach may have use in choosing Standard Earth Models, but, the inclusion of seismic data into the approach appears difficult.

Determination of n-Type Doping Level in Single GaAs Nanowires by Cathodoluminescence.

PubMed

Chen, Hung-Ling; Himwas, Chalermchai; Scaccabarozzi, Andrea; Rale, Pierre; Oehler, Fabrice; Lemaître, Aristide; Lombez, Laurent; Guillemoles, Jean-François; Tchernycheva, Maria; Harmand, Jean-Christophe; Cattoni, Andrea; Collin, Stéphane

2017-11-08

We present an effective method of determining the doping level in n-type III-V semiconductors at the nanoscale. Low-temperature and room-temperature cathodoluminescence (CL) measurements are carried out on single Si-doped GaAs nanowires. The spectral shift to higher energy (Burstein-Moss shift) and the broadening of luminescence spectra are signatures of increased electron densities. They are compared to the CL spectra of calibrated Si-doped GaAs layers, whose doping levels are determined by Hall measurements. We apply the generalized Planck's law to fit the whole spectra, taking into account the electron occupation in the conduction band, the bandgap narrowing, and band tails. The electron Fermi levels are used to determine the free electron concentrations, and we infer nanowire doping of 6 × 10 17 to 1 × 10 18  cm -3 . These results show that cathodoluminescence provides a robust way to probe carrier concentrations in semiconductors with the possibility of mapping spatial inhomogeneities at the nanoscale.

Quality of Computationally Inferred Gene Ontology Annotations

PubMed Central

Škunca, Nives; Altenhoff, Adrian; Dessimoz, Christophe

2012-01-01

Gene Ontology (GO) has established itself as the undisputed standard for protein function annotation. Most annotations are inferred electronically, i.e. without individual curator supervision, but they are widely considered unreliable. At the same time, we crucially depend on those automated annotations, as most newly sequenced genomes are non-model organisms. Here, we introduce a methodology to systematically and quantitatively evaluate electronic annotations. By exploiting changes in successive releases of the UniProt Gene Ontology Annotation database, we assessed the quality of electronic annotations in terms of specificity, reliability, and coverage. Overall, we not only found that electronic annotations have significantly improved in recent years, but also that their reliability now rivals that of annotations inferred by curators when they use evidence other than experiments from primary literature. This work provides the means to identify the subset of electronic annotations that can be relied upon—an important outcome given that >98% of all annotations are inferred without direct curation. PMID:22693439

Study of high resolution x-ray spectrometer concepts for NIF experiments

NASA Astrophysics Data System (ADS)

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; Efthimion, P.; Gao, L.; Maddox, J.; Pablant, N. A.; Beiersdorfer, P.; Chen, H.; Coppari, F.; Ma, T.; Nora, R.; Scott, H.; Schneider, M.; Mancini, R.

2015-11-01

Options have been investigated for DIM-insertable (Diagnostic Instrument Manipulator) high resolution (E/ ΔE ~ 3000 - 5000) Bragg crystal x-ray spectrometers for experiments on the NIF. Of interest are time integrated Cu K- and Ta L-edge absorption spectra and time resolved Kr He- β emission from compressed symcaps for inference of electron temperature from dielectronic satellites and electron density from Stark broadening. Cylindrical and conical von Hamos, Johann, and advanced high throughput designs have been studied. Predicted x-ray intensities, spectrometer throughputs, spectral resolution, and spatial focusing properties, as well as lab evaluations of some spectrometer candidates will be presented. Performed under the auspices of the US DOE by PPPL under contract DE-AC02-09CH11466 and by LLNL under contract DE-AC52-07NA27344.

Core Radial Electric Field and Transport in Wendelstein 7-X Plasmas

NASA Astrophysics Data System (ADS)

Pablant, Novimir

2016-10-01

Results from the investigation of core transport and the role of the radial electric field profile (Er) in the first operational phase of the Wendelstein 7-X (W7-X) stellarator are presented. In stellarator plasmas, the details of the Er profile are expected to have a strong effect on both the particle and heat fluxes. Neoclassical particle fluxes are not intrinsically ambipolar, which leads to the formation of a radial electric field that enforces ambipolarity. The radial electric field is closely related to the perpendicular plasma flow (u⊥) through the force balance equation. This allows the radial electric field to be inferred from measurements of the perpendicular flow velocity from the x-ray imaging crystal spectrometer (XICS) and correlation reflectometry diagnostics. Large changes in the perpendicular rotation, on the order of Δu⊥ 5km /s (ΔEr 12kV / m), have been observed within a set of experiments where the heating power was stepped down from 2 MW to 0.6 MW . These experiments are examined in detail to explore the relationship between, heating power, response of the temperature and density profiles and the response of the radial electric field. Estimations of the core transport are based on power balance and utilize electron temperature (Te) profiles from the ECE and Thomson scattering, electron density profiles (ne) from interferometry and Thomson scattering, ion temperature (Ti) profiles from XICS, along with measurements of the total stored energy and radiated power. Also described are a set core impurity confinement experiments and results. Impurity confinement has been investigated through the injection of trace amount of argon impurity gas at the plasma edge in conjunction with measurements of the density of various ionization states of argon from the XICS and High Efficiency eXtreme-UV Overview Spectrometer (HEXOS) diagnostics. Finally the inferred Er and heat flux profiles are compared to initial neoclassical calculations using measured plasma profiles. On behalf of the W7-X Team.

Effects of magnetic field on the interaction between terahertz wave and non-uniform plasma slab

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

Tian, Yuan; Han, YiPing; Guo, LiXin

2015-10-15

In this paper, the interaction between terahertz electromagnetic wave and a non-uniform magnetized plasma slab is investigated. Different from most of the published literatures, the plasma employed in this work is inhomogeneous in both collision frequency and electron density. Profiles are introduced to describe the non-uniformity of the plasma slab. At the same time, magnetic field is applied to the background of the plasma slab. It came out with an interesting phenomenon that there would be a valley in the absorption band as the plasma's electromagnetic characteristic is affected by the magnetic field. In addition, the valley located just nearmore » the middle of the absorption peak. The cause of the valley's appearance is inferred in this paper. And the influences of the variables, such as magnetic field strength, electron density, and collision frequency, are discussed in detail. The objective of this work is also pointed out, such as the applications in flight communication, stealth, emissivity, plasma diagnose, and other areas of plasma.« less

On the Determination of Ejecta Structure and Explosion Asymmetry from the X-ray Knots of Cassiopeia A

NASA Technical Reports Server (NTRS)

Laming, J. Martin; Hwang, Una

2003-01-01

We present a detailed analysis of Chandra X-ray spectra from individual ejecta knots in the supernova remnant Cassiopeia A. The spectra are fitted to give the electron temperature T(sub e), and (single) ionization age n(sub e)t. These quantities are compared with the predictions of self similar hydrodynamic models incorporating time dependent ionization and radiation losses, and Coulomb electron-ion equilibration behind the reverse shock, for a variety of different ejecta density profiles described by a uniform density core and a power law envelope. We find that the ejecta close to the 'jet' region in the NE, but not actually in the jet itself, have a systematically shallower outer envelope than ejecta elsewhere in the remnant, and we interpret this as being due to more energy of the initial explosion being directed in this polar direction as opposed to equatorially. The degree of asymmetry we infer is at the low end of that generally modelled in asymmetric core-collapse simulations, and may be used to rule out highly asymmetric explosion models.

Field emission energy distributions of hydrogen and deuterium on the /100/ and /110/ planes of tungsten.

NASA Technical Reports Server (NTRS)

Plummer, E. W.; Bell, A. E.

1972-01-01

Total energy distributions of field emitted electrons from the tungsten (110) and (100) planes as a function of coverage by hydrogen and deuterium have been recorded utilizing a spherical deflection energy analyzer. The elastic tunneling resonance spectrum gives a plot of the 'local density of states' in the adsorbate. The inelastic tunneling spectrum reveals those discrete excitation energies available in the adsorbate-substrate complex. These spectroscopic data have been used to infer the chemical nature of the binding states which have been observed in the flash desorption spectrum of hydrogen from tungsten.

Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

NASA Astrophysics Data System (ADS)

Zhang, M. H. G.; Luhmann, J. G.; Nagy, A. F.; Spreiter, J. R.; Stahara, S. S.

1993-02-01

Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

Detection of Ionospheric Alfven Resonator Signatures Onboard C/NOFS: Implications for IRI Modeling

NASA Technical Reports Server (NTRS)

Simoes, F.; Klenzing, J.; Ivanov, S.; Pfaff, R.; Rowland, D.; Bilitza, D.

2011-01-01

The 2008-2009 long-lasting solar minimum activity has been the one of its kind since the dawn of space age, offering exceptional conditions for investigating space weather in the near-Earth environment. First ever detection of Ionospheric Alfven Resonator (IAR) signatures in orbit offers new means for investigating ionospheric electrodynamics, namely MHD (MagnetoHydroDynamics) wave propagation, aeronomy processes, ionospheric dynamics, and Sun-Earth connection mechanisms at a local scale. Local and global plasma density heterogeneities in the ionosphere and magnetosphere allow for formation of waveguides and resonators where magnetosonic and shear Alfven waves propagate. The ionospheric magnetosonic waveguide results from complete magnetosonic wave reflection about the ionospheric F-region peak, where the Alfven index of refraction presents a maximum. MHD waves can also be partially trapped in the vertical direction between the lower boundary of the ionosphere and the magnetosphere, a resonance mechanism known as IAR. In this work we present C/NOFS (Communications/Navigation Outage Forecasting System) Extremely Low Frequency (ELF) electric field measurements related to IAR signatures, discuss the resonance and wave propagation mechanisms in the ionosphere, and address the electromagnetic inverse problem from which electron/ion distributions can be derived. These peculiar IAR electric field measurements provide new, complementary methodologies for inferring ionospheric electron and ion density profiles, and also contribute for the investigation of ionosphere dynamics and space weather monitoring. Specifically, IAR spectral signatures measured by C/NOFS contribute for improving the International Reference Ionosphere (IRI) model, namely electron density and ion composition.

Cassini RPWS Measurement of Dust Particles in Saturn's Magnetosphere

NASA Astrophysics Data System (ADS)

Ye, S.; Gurnett, D. A.; Kurth, W. S.; Averkamp, T. F.; Kempf, S.; Hsu, S.; Sakai, S.; Morooka, M.; Wahlund, J.

2013-12-01

The Cassini Radio and Plasma Wave Science (RPWS) instrument can detect dust impacts when voltage pulses induced by the impact charges are observed in the wideband receiver. The size of the voltage pulse is proportional to the mass of the impacting dust particle. Based on the data collected during the E-ring crossings and Enceladus flybys, we show that the size distribution of the dust particles can be characterized as dn/dr ∝ rμ, where μ~-4. We compare the density of dust particles above a certain size threshold calculated from the impact rate with the Cosmic Dust Analyzer (CDA) High Rate Detector (HRD) data. When the monopole antenna is connected to the wideband receiver, the polarity of the dust impact signal is determined by the spacecraft potential and the location of the impact (on the spacecraft body or the antenna). Because the effective area of the antenna is relatively easy to estimate, we use the polarity ratio of the dust impacts to infer the effective area of the spacecraft body. RPWS onboard dust detection data is analyzed, from which we infer the sign of the spacecraft potential and the dust density within Saturn's magnetosphere. A new phenomenon called dust ringing has been found to reveal the electron density inside the Enceladus plume. The ringing frequencies, interpreted as the local plasma frequencies, are consistent with the values measured by other methods, i.e., Langmuir probe and upper hybrid resonance.

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

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

Thomsen, M. F.; Coates, A. J.; Jackman, C. M.

A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416-s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties ofmore » various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z-component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach-number bow shock is ~4% of the dissipated flow energy. The data set is available as an electronic supplement to this paper.« less

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

DOE PAGES

Thomsen, M. F.; Coates, A. J.; Jackman, C. M.; ...

2018-03-01

A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416-s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties ofmore » various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z-component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach-number bow shock is ~4% of the dissipated flow energy. The data set is available as an electronic supplement to this paper.« less

The equatorial airglow and the ionospheric geomagnetic anomaly

NASA Technical Reports Server (NTRS)

Chandra, S.; Reed, E. I.; Troy, B. E., Jr.; Blamont, J. E.

1972-01-01

OGO D observations of OI (6300A) emissions reveal a global pattern in the equatorial airglow undetected from the ground-based observations. The post sunset emission rate of OI is generally asymmetrical with respect to the geomagnetic equator and shows no apparent correlation with the ultraviolet airglow (OI 1304 and 1356A) and F region electron density measured simultaneously from the same spacecraft. Both the ultraviolet airglow and the ion density measured in the altitude region of 450 km follow similar latitudinal variations and exhibit properties of the equatorial ionospheric anomaly. The asymmetry in OI emission can be attributed to the asymmetry in the height of the F 2 maximum inferred from the height of the maximum emission. From correlative studies of the airglow and the ionospheric measurements, the mechanisms for the ultraviolet and the 6300A emission are discussed in terms of the processes involving radiative and dissociative recombinations. A relationship between molecular oxygen density and the integrated OI emission rate is derived and the feasibility of using this relationship for estimating O2 density is discussed.

Inelastic X-ray Scattering Measurements of Ionization in Warm, Dense Matter

NASA Astrophysics Data System (ADS)

Davis, Paul F.

In this work we demonstrate spectrally resolved x-ray scattering from electron-plasma waves in shock-compressed deuterium and proton-heated matter. Because the spectral signature of inelastic x-ray scattering is strongly dependent on the free electron density of the system, it is used to infer ionization in dynamically heated samples. Using 2-6 ns, 500 J laser pulses from LLNL's Janus laser, we shocked liquid deuterium to pressures approaching 50 GPa, reaching compressions of 4 times liquid density. A second laser produced intense 2 keV x-rays. By collecting and spectrally dispersing forward scattered photons at 45°, the onset of ionization was detected at compressions of about 3 times in the form of plasmon oscillations. Backscattered x-rays bolstered this observation by measuring the free electron distribution through Compton scattering. Comparison with simulations shows very close agreement between the pressure dependence of ionization and molecular dissociation in dynamically compressed deuterium. In a second set of experiments, a 10 ps, 200 J Titan laser pulse was split into two beams. One created a stream of MeV protons to heat samples of boron and boron-nitride and the other pumped 4.5 keV K-alpha radiation in a titanium foil to probe the hot target. We observed scattered x-rays 300 ps after heating, noting a strong difference in average ionization between the two target materials at temperatures of 16 eV and very similar mass densities. Comparison with electron structure calculations suggests that this difference is due to a persistence of long-range ion structure in BN resulting in high-temperature band structure. These results underscore the importance of understanding the complex electron structure of materials even at electron-volt temperatures and gigapascal pressures. Our results provide new data to guide the theoretical modeling of warm, dense matter important to understanding giant planets and inertial fusion targets.

Structural Information Inference from Lanthanoid Complexing Systems: Photoluminescence Studies on Isolated Ions

NASA Astrophysics Data System (ADS)

Greisch, Jean Francois; Harding, Michael E.; Chmela, Jiri; Klopper, Willem M.; Schooss, Detlef; Kappes, Manfred M.

2016-06-01

The application of lanthanoid complexes ranges from photovoltaics and light-emitting diodes to quantum memories and biological assays. Rationalization of their design requires a thorough understanding of intramolecular processes such as energy transfer, charge transfer, and non-radiative decay involving their subunits. Characterization of the excited states of such complexes considerably benefits from mass spectrometric methods since the associated optical transitions and processes are strongly affected by stoichiometry, symmetry, and overall charge state. We report herein spectroscopic measurements on ensembles of ions trapped in the gas phase and soft-landed in neon matrices. Their interpretation is considerably facilitated by direct comparison with computations. The combination of energy- and time-resolved measurements on isolated species with density functional as well as ligand-field and Franck-Condon computations enables us to infer structural as well as dynamical information about the species studied. The approach is first illustrated for sets of model lanthanoid complexes whose structure and electronic properties are systematically varied via the substitution of one component (lanthanoid or alkali,alkali-earth ion): (i) systematic dependence of ligand-centered phosphorescence on the lanthanoid(III) promotion energy and its impact on sensitization, and (ii) structural changes induced by the substitution of alkali or alkali-earth ions in relation with structures inferred using ion mobility spectroscopy. The temperature dependence of sensitization is briefly discussed. The focus is then shifted to measurements involving europium complexes with doxycycline an antibiotic of the tetracycline family. Besides discussing the complexes' structural and electronic features, we report on their use to monitor enzymatic processes involving hydrogen peroxide or biologically relevant molecules such as adenosine triphosphate (ATP).

Spin-dependent electrical conduction in a pentacene Schottky diode explored by electrically detected magnetic resonance

NASA Astrophysics Data System (ADS)

Fukuda, Kunito; Asakawa, Naoki

2017-02-01

Reported is the observation of dark spin-dependent electrical conduction in a Schottky barrier diode with pentacene (PSBD) using electrically detected magnetic resonance at room temperature. It is suggested that spin-dependent conduction exists in pentacene thin films, which is explored by examining the anisotropic linewidth of the EDMR signal and current density-voltage (J-V) measurements. The EDMR spectrum can be decomposed to Gaussian and Lorentzian components. The dependency of the two signals on the applied voltage was consistent with the current density-voltage (J-V) of the PSBD rather than that of the electron-only device of Al/pentacene/Al, indicating that the spin-dependent conduction is due to bipolaron formation associated with hole polaronic hopping processes. The applied-voltage dependence of the ratio of intensity of the Gaussian line to the Lorentzian may infer that increasing current density should make conducting paths more dispersive, thereby resulting in an increased fraction of the Gaussian line due to the higher dispersive g-factor.

An overview of Laser-Produced Relativistic Positrons in the Laboratory

NASA Astrophysics Data System (ADS)

Edghill, Brandon; Williams, Gerald; Chen, Hui; Beg, Farhat

2017-10-01

The production of relativistic positrons using ultraintense lasers can facilitate studies of fundamental pair plasma science in the relativistic regime and laboratory studies of scaled energetic astrophysical mechanisms such as gamma ray bursts. The positron densities and spatial scales required for these applications, however, are larger than current capabilities. Here, we present an overview of the experimental laser-produced positron results and their respective modeling for both the direct laser-irradiated process and the indirect process (laser wakefield accelerated electrons irradiating a high-Z converter). Conversion efficiency into positrons and positron beam characteristics are compared, including total pair yield, mean energy, angular divergence, and inferred pair density for various laser and target conditions. Prospects towards increasing positron densities and beam repetition rates will also be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and funded by LDRD (#17-ERD-010).

Relationship between field-aligned currents and inverted-V parallel potential drops observed at midaltitudes

NASA Astrophysics Data System (ADS)

Sakanoi, T.; Fukunishi, H.; Mukai, T.

1995-10-01

The inverted-V field-aligned acceleration region existing in the altitude range of several thousand kilometers plays an essential role for the magnetosphere-ionosphere coupling system. The adiabatic plasma theory predicts a linear relationship between field-aligned current density (J∥) and parallel potential drop (Φ∥), that is, J∥=KΦ∥, where K is the field-aligned conductance. We examined this relationship using the charged particle and magnetic field data obtained from the Akebono (Exos D) satellite. The potential drop above the satellite was derived from the peak energy of downward electrons, while the potential drop below the satellite was derived from two different methods: the peak energy of upward ions and the energy-dependent widening of electron loss cone. On the other hand, field-aligned current densities in the inverted-V region were estimated from the Akebono magnetometer data. Using these potential drops and field-aligned current densities, we estimated the linear field-aligned conductance KJΦ. Further, we obtained the corrected field-aligned conductance KCJΦ by applying the full Knight's formula to the current-voltage relationship. We also independently estimated the field-aligned conductance KTN from the number density and the thermal temperature of magnetospheric source electrons which were obtained by fitting accelerated Maxwellian functions for precipitating electrons. The results are summarized as follows: (1) The latitudinal dependence of parallel potential drops is characterized by a narrow V-shaped structure with a width of 0.4°-1.0°. (2) Although the inverted-V potential region exactly corresponds to the upward field aligned current region, the latitudinal dependence of upward current intensity is an inverted-U shape rather than an inverted-V shape. Thus it is suggested that the field-aligned conductance KCJΦ changes with a V-shaped latitudinal dependence. In many cases, KCJΦ values at the edge of the inverted-V region are about 5-10 times larger than those at the center. (3) By comparing KCJΦ with KTN, KCJΦ is found to be about 2-20 times larger than KTN. These results suggest that low-energy electrons such as trapped electrons, secondary and back-scattered electrons, and ionospheric electrons significantly contribute to upward field-aligned currents in the inverted-V region. It is therefore inferred that non adiabatic pitch angle scattering processes play an important role in the inverted-V region. .

An X-ray/SDSS sample. II. AGN-driven outflowing gas plasma properties

NASA Astrophysics Data System (ADS)

Perna, M.; Lanzuisi, G.; Brusa, M.; Cresci, G.; Mignoli, M.

2017-10-01

Aims: Galaxy-scale outflows are currently observed in many active galactic nuclei (AGNs); however, characterisation of them in terms of their (multi-) phase nature, amount of flowing material, and effects on their host galaxy is still unresolved. In particular, ionised gas mass outflow rate and related energetics are still affected by many sources of uncertainty. In this respect, outflowing gas plasma conditions, being largely unknown, play a crucial role. Methods: We have analysed stacked spectra and sub-samples of sources with high signal-to-noise temperature- and density-sensitive emission lines to derive the plasma properties of the outflowing ionised gas component. We did this by taking advantage of the spectroscopic analysis results we obtained while studying the X-ray/SDSS sample of 563 AGNs at z < 0.8 presented in our companion paper. For these sources, we also studied in detail various diagnostic diagrams to infer information about outflowing gas ionisation mechanisms. Results: We derive, for the first time, median values for electron temperature and density of outflowing gas from medium-size samples ( 30 targets) and stacked spectra of AGNs. Evidence of shock excitation are found for outflowing gas. Conclusions: We measure electron temperatures of the order of 1.7 × 104 K and densities of 1200 cm-3 for faint and moderately luminous AGNs (intrinsic X-ray luminosity 40.5 < log (LX) < 44 in the 2-10 keV band). We note that the electron density that is usually assumed (Ne = 100 cm-3) in ejected material might result in relevant overestimates of flow mass rates and energetics and, as a consequence, of the effects of AGN-driven outflows on the host galaxy.

Analysis of Co-spatial UV-Optical STIS Spectra of Seven Planetary Nebulae From HST Cycle 19 GO 12600

NASA Astrophysics Data System (ADS)

Miller, Timothy R.; Henry, Richard B. C.; Dufour, Reginald J.; Kwitter, Karen B.; Shaw, Richard A.; Balick, Bruce; Corradi, Romano

2016-01-01

We present an analysis of seven spatially resolved planetary nebulae (PNe), NGC 2440, NGC 3242, NGC 5315, NGC 5882, NGC 7662, IC 2165, and IC 3568, from observations in the Cycle 19 program GO 12600 using HST STIS. These seven observations cover the wavelength range 1150-10,270 Å with 0.2 and 0.5 arcsec wide slits, and are co-spatial to within 0.1 arcsec along a 25 arcsec length across each nebula. The wavelength and spatial coverage enabled a detailed study of physical conditions and abundances from UV and optical line emissions (compared to only optical lines) for these seven PNe. The first UV lines of interest are those of carbon. The resolved lines of C III] 1906.68 and 1908.73 yielded a direct measurement of the density within the volume occupied by doubly-ionized carbon and other similar co-spatial ions as well as contributed to an accurate measurement of the carbon abundance. Each PN spectrum was divided into smaller spatial regions or segments in order to assess inferred density variations among the regions along the entire slit. There is a clear difference in the inferred density for several regions of each PNe. Variations in electron temperature and chemical abundances were also probed and shown to be completely homogeneous within the errors. Lastly, these nebulae were modeled in detail with the photoionization code CLOUDY. This modeling constrained the central star parameters of temperature and luminosity and tested the effects different density profiles have on these parameters. We gratefully acknowledge generous support from NASA through grants related to the Cycle 19 program GO 12600, as well as from the University of Oklahoma.

Classical Heat-Flux Measurements in Coronal Plasmas from Collective Thomson-Scattering Spectra

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Hu, S. X.; Katz, J.; Froula, D. H.; Rozmus, W.

2016-10-01

Collective Thomson scattering was used to measure heat flux in coronal plasmas. The relative amplitude of the Thomson-scattered power into the up- and downshifted electron plasma wave features was used to determine the flux of electrons moving along the temperature gradient at three to four times the electron thermal velocity. Simultaneously, the ion-acoustic wave features were measured. Their relative amplitude was used to measure the flux of the return-current electrons. The frequencies of these ion-acoustic and electron plasma wave features provide local measurements of the electron temperature and density. These spectra were obtained at five locations along the temperature gradient in a laser-produced blowoff plasma. These measurements of plasma parameters are used to infer the Spitzer-Härm flux (qSH = - κ∇Te ) and are in good agreement with the values of the heat flux measured from the scattering-feature asymmetries. Additional experiments probed plasma waves perpendicular to the temperature gradient. The data show small effects resulting from heat flux compared to probing waves along the temperature gradient. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Direct evidence for EMIC wave scattering of relativistic electrons in space

NASA Astrophysics Data System (ADS)

Zhang, X.-J.; Li, W.; Ma, Q.; Thorne, R. M.; Angelopoulos, V.; Bortnik, J.; Chen, L.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Baker, D. N.; Reeves, G. D.; Spence, H. E.; Blake, J. B.; Fennell, J. F.

2016-07-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) are also used to infer their magnetic local time (MLT) coverage. From the observed EMIC wave spectra and local plasma parameters, we compute wave diffusion rates and model the evolution of electron pitch angle distributions. By comparing model results with local observations of pitch angle distributions, we show direct, quantitative evidence of EMIC wave-driven relativistic electron losses in the Earth's outer radiation belt.

Physical Conditions of a Lensed Star-Forming Galaxy at Z=1.7

NASA Technical Reports Server (NTRS)

Rigby, Jane; Wuyts, E.; Gladders, M.; Sharon, K.; Becker, G. D.

2010-01-01

We report rest-frame optical Keck/NIRSPEC spectroscopy of the brightest lensed galaxy yet discovered, RCSGA 032727-132609 at z=1.7037. From precise measurements of the nebular lines, we infer a number of physical properties: redshift, extinction, star formation rate, ionization parameter, electron density, electron temperature, oxygen abundance, and N/O, Ne/O, and Ar/O abundance ratios. The limit on [O III] 4363 A tightly constrains the oxygen abundance via the "direct" or Tc method, for the first time in all metallicity galaxy at z approx.2. We compare this result to several standard "bright-line" O abundance diagnostics, thereby testing these empirically calibrated diagnostics in situ. Finally, we explore the positions of lensed and unlensed galaxies in standard diagnostic diagrams, and explore the diversity of ionization conditions and mass-metallicity ratios at z=2.

The Physical Conditions of a Lensed Star-Forming Galaxy at Z=1.7

NASA Technical Reports Server (NTRS)

Rigby, Jane; Wuyts, E.; Gladders, M.; Sharon, K.; Becker, G.

2011-01-01

We report rest-frame optical Keck/NIRSPEC spectroscopy of the brightest lensed galaxy yet discovered, RCSGA 032727-132609 at z=1.7037. From precise measurements of the nebular lines, we infer a number of physical properties: redshift ' extinction, star formation rate ' ionization parameter, electron density, electron temperature, oxygen abundance, and N/O, Ne/O, and Ar/O abundance ratios, The limit on [O III] 4363 A tightly constrains the oxygen abundance via the "direct" or Te method, for the first time in an average-metallicity galaxy at z approx.2. We compare this result to several standard "bright-line" O abundance diagnostics, thereby testing these empirically-calibrated diagnostics in situ. Finally, we explore the positions of lensed and unlensed galaxies in standard diagnostic diagrams, to explore the diversity of ionization conditions and mass-metallicity ratios at z=2.

Faraday rotation in the M87 radio/X-ray halo

NASA Technical Reports Server (NTRS)

Dennison, B.

1980-01-01

Comparison of polarization maps at various wavelengths demonstrates the existence of a large Faraday rotation uniform over the radio core of M87. Much of this rotation must be external to the core, lest it appear completely depolarized when the rotation is about 90 degrees. The Faraday rotation is shown to occur primarily in the surrounding radio/X-ray halo. Using the electron density inferred from X-ray observations, the magnetic field in the halo is found to be 2.5 microgauss. The deduced magnetic field strength permits an evaluation of the importance of Compton scattering of 3 K background photons by relativistic electrons in the radio halo. The emergent Compton-scattered spectrum is calculated, and its contribution to the observed X-ray flux is small, probably about a percent or so, while the rest is due to thermal bremsstrahlung.

A long-lived refilling event of the slot region between the Van Allen radiation belts from Nov 2004 to Jan 2005

NASA Astrophysics Data System (ADS)

Yang, X.

2015-12-01

A powerful relativistic electron enhancement in the slot region between the inner and outer radiation belts is investigated by multi-satellites measurements. The measurement from Space Particle Component Detectors (SPCDs) aboard Fengyun-1 indicates that the relativistic electron (>1.6MeV) flux began to enhance obviously on early 10 November with the flux peak fixed at L~3.0. In the next day, the relativistic electron populations increased dramatically. Subsequently, the flux had been enhancing slowly, but unceasingly, until 17 November, and the maximum flux reached up to 7.8×104 cm-2·sr-1·s-1 at last. The flux peak fixed at L~3.0 and the very slow decay rate in this event make it to be an unusual long-lived slot region refilling event. We trace the cause of the event back to the interplanetary environment and find that there were two evident magnetic cloud constructions: dramatically enhanced magnetic field strength and long and smooth rotation of field vector from late 7 to 8 November and from late 9 to 10 November, respectively; solar wind speed increased in 'step-like' fashion on late 7 November and persisted the level of high speed >560 km·s-1 for about 124 hours. Owed to the interplanetary disturbances, very strong magnetic storms and substorms occurred in the magnetosphere. Responding to the extraordinarily magnetic perturbations, the plasmasphere shrank sharply. The location of plasmapause inferred from Dst indicates that the plasmapause shrank inward to as low as L~2.5. On account of these magnetospheric conditions, strong chorus emissions are expected near the earth. In fact, the STAFF on Cluster mission measured intensive whistler mode chorus emissions on 10 and 12 November, corresponding to the period of the remarkable enhancement of relativistic electron. Furthermore, we investigate the radial profile of phase space density (PSD) by electron flux from multi-satellites, and the evolution of the phase space density profile reveals that the local acceleration by whistler mode chorus could be the important mechanism in this event. The movement of the inferred plasmapause location indicates that the enhanced outer zone is divided into two portions by the plasmapause and the slow loss rate in the plasmasphere due to hiss primarily contributed to the long-lived characteristic of this event.

Inferring Nighttime Ionospheric Parameters with the Far Ultraviolet Imager Onboard the Ionospheric Connection Explorer

NASA Astrophysics Data System (ADS)

Kamalabadi, Farzad; Qin, Jianqi; Harding, Brian J.; Iliou, Dimitrios; Makela, Jonathan J.; Meier, R. R.; England, Scott L.; Frey, Harald U.; Mende, Stephen B.; Immel, Thomas J.

2018-06-01

The Ionospheric Connection Explorer (ICON) Far Ultraviolet (FUV) imager, ICON FUV, will measure altitude profiles of OI 135.6 nm emissions to infer nighttime ionospheric parameters. Accurate estimation of the ionospheric state requires the development of a comprehensive radiative transfer model from first principles to quantify the effects of physical processes on the production and transport of the 135.6 nm photons in the ionosphere including the mutual neutralization contribution as well as the effect of resonant scattering by atomic oxygen and pure absorption by oxygen molecules. This forward model is then used in conjunction with a constrained optimization algorithm to invert the anticipated ICON FUV line-of-sight integrated measurements. In this paper, we describe the connection between ICON FUV measurements and the nighttime ionosphere, along with the approach to inverting the measured emission profiles to derive the associated O+ profiles from 150-450 km in the nighttime ionosphere that directly reflect the electron density in the F-region of the ionosphere.

Inferring Recent Demography from Isolation by Distance of Long Shared Sequence Blocks

PubMed Central

Ringbauer, Harald; Coop, Graham

2017-01-01

Recently it has become feasible to detect long blocks of nearly identical sequence shared between pairs of genomes. These identity-by-descent (IBD) blocks are direct traces of recent coalescence events and, as such, contain ample signal to infer recent demography. Here, we examine sharing of such blocks in two-dimensional populations with local migration. Using a diffusion approximation to trace genetic ancestry, we derive analytical formulas for patterns of isolation by distance of IBD blocks, which can also incorporate recent population density changes. We introduce an inference scheme that uses a composite-likelihood approach to fit these formulas. We then extensively evaluate our theory and inference method on a range of scenarios using simulated data. We first validate the diffusion approximation by showing that the theoretical results closely match the simulated block-sharing patterns. We then demonstrate that our inference scheme can accurately and robustly infer dispersal rate and effective density, as well as bounds on recent dynamics of population density. To demonstrate an application, we use our estimation scheme to explore the fit of a diffusion model to Eastern European samples in the Population Reference Sample data set. We show that ancestry diffusing with a rate of σ≈50−−100 km/gen during the last centuries, combined with accelerating population growth, can explain the observed exponential decay of block sharing with increasing pairwise sample distance. PMID:28108588

Semiclassical transport properties of IrGa₃: a promising thermoelectric material.

PubMed

Alvarez Quiceno, Juan Camilo; Dalpian, Gustavo; Fazzio, Adalberto; Osorio-Guillén, Jorge M

2018-01-09

IrGa3 is an intermetallic compound which is expected to be a metal, but a study on the electronic properties of this material to confirm its metallic character is not available in the literature. In this work, we report for the first time a first-principles Density Functional Theory and semiclassical Boltzmann theory study of the structural, electronic and transport properties of this material. The inclusion of the spin-orbit coupling term is crucial to calculate accurately the electronic properties of this compound. We have established that IrGa3 is an indirect semiconductor with a narrow gap of 0.07 eV. From semiclassical Boltzmann transport theory, it is inferred that this material, with the appropriate hole concentration, could have a thermoelectric figure of merit at room temperature comparable to other intermetallic compounds such as FeGa3, though the transport properties of IrGa3 are highly anisotropic. . © 2018 IOP Publishing Ltd.

Towards quantitative off-axis electron holographic mapping of the electric field around the tip of a sharp biased metallic needle

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

Beleggia, M.; Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin; Kasama, T.

We apply off-axis electron holography and Lorentz microscopy in the transmission electron microscope to map the electric field generated by a sharp biased metallic tip. A combination of experimental data and modelling provides quantitative information about the potential and the field around the tip. Close to the tip apex, we measure a maximum field intensity of 82 MV/m, corresponding to a field k factor of 2.5, in excellent agreement with theory. In order to verify the validity of the measurements, we use the inferred charge density distribution in the tip region to generate simulated phase maps and Fresnel (out-of-focus) imagesmore » for comparison with experimental measurements. While the overall agreement is excellent, the simulations also highlight the presence of an unexpected astigmatic contribution to the intensity in a highly defocused Fresnel image, which is thought to result from the geometry of the applied field.« less

Use of a wave reverberation technique to infer the density compression of shocked liquid deuterium to 75 GPa.

PubMed

Knudson, M D; Hanson, D L; Bailey, J E; Hall, C A; Asay, J R

2003-01-24

A novel approach was developed to probe density compression of liquid deuterium (L-D2) along the principal Hugoniot. Relative transit times of shock waves reverberating within the sample are shown to be sensitive to the compression due to the first shock. This technique has proven to be more sensitive than the conventional method of inferring density from the shock and mass velocity, at least in this high-pressure regime. Results in the range of 22-75 GPa indicate an approximately fourfold density compression, and provide data to differentiate between proposed theories for hydrogen and its isotopes.

Ionospheric and Birkeland current distributions inferred from the MAGSAT magnetometer data

NASA Technical Reports Server (NTRS)

Zanetti, L. J.; Potemra, T. A.; Baumjohann, W.

1983-01-01

Ionospheric and field-aligned sheet current density distributions are presently inferred by means of MAGSAT vector magnetometer data, together with an accurate magnetic field model. By comparing Hall current densities inferred from the MAGSAT data and those inferred from simultaneously recorded ground based data acquired by the Scandinavian magnetometer array, it is determined that the former have previously been underestimated due to high damping of magnetic variations with high spatial wave numbers between the ionosphere and the MAGSAT orbit. Among important results of this study is noted the fact that the Birkeland and electrojet current systems are colocated. The analyses have shown a tendency for triangular rather than constant electrojet current distributions as a function of latitude, consistent with the statistical, uniform regions 1 and 2 Birkeland current patterns.

Multimodel inference to quantify the relative importance of abiotic factors in the population dynamics of marine zooplankton

NASA Astrophysics Data System (ADS)

Everaert, Gert; Deschutter, Yana; De Troch, Marleen; Janssen, Colin R.; De Schamphelaere, Karel

2018-05-01

The effect of multiple stressors on marine ecosystems remains poorly understood and most of the knowledge available is related to phytoplankton. To partly address this knowledge gap, we tested if combining multimodel inference with generalized additive modelling could quantify the relative contribution of environmental variables on the population dynamics of a zooplankton species in the Belgian part of the North Sea. Hence, we have quantified the relative contribution of oceanographic variables (e.g. water temperature, salinity, nutrient concentrations, and chlorophyll a concentrations) and anthropogenic chemicals (i.e. polychlorinated biphenyls) to the density of Acartia clausi. We found that models with water temperature and chlorophyll a concentration explained ca. 73% of the population density of the marine copepod. Multimodel inference in combination with regression-based models are a generic way to disentangle and quantify multiple stressor-induced changes in marine ecosystems. Future-oriented simulations of copepod densities suggested increased copepod densities under predicted environmental changes.

On the use of the double floating probe method to infer the difference between the electron and the heavy particles temperatures in an atmospheric pressure, vortex-stabilized nitrogen plasma jet

NASA Astrophysics Data System (ADS)

Prevosto, L.; Kelly, H.; Mancinelli, B. R.

2014-05-01

Sweeping double probe measurements in an atmospheric pressure direct current vortex-stabilized plasma jet are reported (plasma conditions: 100 A discharge current, N2 gas flow rate of 25 Nl/min, thoriated tungsten rod-type cathode, copper anode with 5 mm inner diameter). The interpretation of the double probe characteristic was based on a generalization of the standard double floating probe formulae for non-uniform plasmas coupled to a non-equilibrium plasma composition model. Perturbations caused by the current to the probe together with collisional and thermal processes inside the probe perturbed region were taken into account. Radial values of the average electron and heavy particle temperatures as well as the electron density were obtained. The calculation of the temperature values did not require any specific assumption about a temperature relationship between different particle species. An electron temperature of 10 900 ± 900 K, a heavy particle temperature of 9300 ± 900 K, and an electron density of about 3.5 × 1022 m-3 were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found toward the outer border of the plasma jet. These results showed good agreement with those previously reported by the authors by using a single probe technique. The calculations have shown that this method is particularly useful for studying spraying-type plasma torches operated at power levels of about 15 kW.

On the use of the double floating probe method to infer the difference between the electron and the heavy particles temperatures in an atmospheric pressure, vortex-stabilized nitrogen plasma jet.

PubMed

Prevosto, L; Kelly, H; Mancinelli, B R

2014-05-01

Sweeping double probe measurements in an atmospheric pressure direct current vortex-stabilized plasma jet are reported (plasma conditions: 100 A discharge current, N2 gas flow rate of 25 Nl/min, thoriated tungsten rod-type cathode, copper anode with 5 mm inner diameter). The interpretation of the double probe characteristic was based on a generalization of the standard double floating probe formulae for non-uniform plasmas coupled to a non-equilibrium plasma composition model. Perturbations caused by the current to the probe together with collisional and thermal processes inside the probe perturbed region were taken into account. Radial values of the average electron and heavy particle temperatures as well as the electron density were obtained. The calculation of the temperature values did not require any specific assumption about a temperature relationship between different particle species. An electron temperature of 10,900 ± 900 K, a heavy particle temperature of 9300 ± 900 K, and an electron density of about 3.5 × 10(22) m(-3) were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found toward the outer border of the plasma jet. These results showed good agreement with those previously reported by the authors by using a single probe technique. The calculations have shown that this method is particularly useful for studying spraying-type plasma torches operated at power levels of about 15 kW.

Taking the Universe's Temperature with Spectral Distortions of the Cosmic Microwave Background.

PubMed

Hill, J Colin; Battaglia, Nick; Chluba, Jens; Ferraro, Simone; Schaan, Emmanuel; Spergel, David N

2015-12-31

The cosmic microwave background (CMB) energy spectrum is a near-perfect blackbody. The standard model of cosmology predicts small spectral distortions to this form, but no such distortion of the sky-averaged CMB spectrum has yet been measured. We calculate the largest expected distortion, which arises from the inverse Compton scattering of CMB photons off hot, free electrons, known as the thermal Sunyaev-Zel'dovich (TSZ) effect. We show that the predicted signal is roughly one order of magnitude below the current bound from the COBE-FIRAS experiment, but it can be detected at enormous significance (≳1000σ) by the proposed Primordial Inflation Explorer (PIXIE). Although cosmic variance reduces the effective signal-to-noise ratio to 230σ, this measurement will still yield a subpercent constraint on the total thermal energy of electrons in the observable Universe. Furthermore, we show that PIXIE can detect subtle relativistic effects in the sky-averaged TSZ signal at 30σ, which directly probe moments of the optical depth-weighted intracluster medium electron temperature distribution. These effects break the degeneracy between the electron density and the temperature in the mean TSZ signal, allowing a direct inference of the mean baryon density at low redshift. Future spectral distortion probes will thus determine the global thermodynamic properties of ionized gas in the Universe with unprecedented precision. These measurements will impose a fundamental "integral constraint" on models of galaxy formation and the injection of feedback energy over cosmic time.

Cryogenic Target-Implosion Experiments on OMEGA

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

Harding, D.R.; Meyerhofer, D.D.; Sangster, T.C.

The University of Rochester’s Laboratory for Laser Energetics has been imploding thick cryogenic targets for six years. Improvements in the Cryogenic Target Handling System and the ability to accurately design laser pulse shapes that properly time shocks and minimize electron preheat, produced high fuel areal densities in deuterium cryogenic targets (202+/-7 mg/cm^2). The areal density was inferred from the energy loss of secondary protons in the fuel (D2) shell. Targets were driven on a low final adiabat (alpha = 2) employing techniques to radially grade the adiabat (the highest adiabat at the ablation surface). The ice layer meets the target-designmore » toughness specification for DT ice of 1-um rms (all modes), while D2 ice layers average 3.0-um-rms roughness. The implosion experiments and the improvements in the quality and understanding of cryogenic targets are presented.« less

Three-dimensional charge density wave order in YBa 2Cu 3O 6.67 at high magnetic fields

DOE PAGES

Gerber, S.; Jang, H.; Nojiri, H.; ...

2015-11-20

In this study, charge density wave (CDW) correlations have recently been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa 2Cu 3O 6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. Themore » field-induced CDW onsets around the zero-field superconducting transition temperature, yet the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.« less

Direct evidence for EMIC wave scattering of relativistic electrons in space: EMIC-Driven Electron Losses in Space

DOE PAGES

Zhang, X. -J.; Li, W.; Ma, Q.; ...

2016-07-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes.more » EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) are also used to infer their magnetic local time (MLT) coverage. From the observed EMIC wave spectra and local plasma parameters, we compute wave diffusion rates and model the evolution of electron pitch angle distributions. In conclusion, by comparing model results with local observations of pitch angle distributions, we show direct, quantitative evidence of EMIC wave-driven relativistic electron losses in the Earth’s outer radiation belt.« less

Corotation of an intermittent solar wind source

NASA Technical Reports Server (NTRS)

Croft, T. A.

1972-01-01

The measured electron content of the solar wind in mid-1970 exhibited a region of relatively high electron density that reappeared at intervals of about 27.8 days. It is shown that the repeating event cannot be reconciled with the concept of a long-enduring steady flow, even though the recurrence period is close to the rotation period of the sun. This evidence of transients is inferred from the short duration of each appearance of the interval of higher density; each should last for roughly one corotation interval if it is caused by a steady stream. The radio path was approximately 0.8 AU long, and the corotation interval exceeded 3 days. Other aspects of the content data patterns support the view that such transient events are common in the solar wind. The mid-1970 repeating event is an unusually good example of the intermittent character of flow regions in the solar wind that fluctuate on a time scale of days but endure as identifiable regions for many months. A sputtering corotating source of thin solar plasma streams could explain this series of events; it could also be explained in terms of a stream that is steady in density and speed but undulating north-south so that it passes into and out of the 0.8 AU radio path in a matter of a day or less.

Determination of ionospheric electron density profiles from satellite UV (Ultraviolet) emission measurements, fiscal year 1984

NASA Astrophysics Data System (ADS)

Daniell, R. E.; Strickland, D. J.; Decker, D. T.; Jasperse, J. R.; Carlson, H. C., Jr.

1985-04-01

The possible use of satellite ultraviolet measurements to deduce the ionospheric electron density profile (EDP) on a global basis is discussed. During 1984 comparisons were continued between the hybrid daytime ionospheric model and the experimental observations. These comparison studies indicate that: (1) the essential features of the EDP and certain UV emissions can be modelled; (2) the models are sufficiently sensitive to input parameters to yield poor agreement with observations when typical input values are used; (3) reasonable adjustments of the parameters can produce excellent agreement between theory and data for either EDP or airglow but not both; and (4) the qualitative understanding of the relationship between two input parameters (solar flux and neutral densities) and the model EDP and airglow features has been verified. The development of a hybrid dynamic model for the nighttime midlatitude ionosphere has been initiated. This model is similar to the daytime hybrid model, but uses the sunset EDP as an initial value and calculates the EDP as a function of time through the night. In addition, a semiempirical model has been developed, based on the assumption that the nighttime EDP is always well described by a modified Chapman function. This model has great simplicity and allows the EDP to be inferred in a straightforward manner from optical observations. Comparisons with data are difficult, however, because of the low intensity of the nightglow.

Investigation of the Fe{sup 3+} centers in perovskite KMgF{sub 3} through a combination of ab initio (density functional theory) and semi-empirical (superposition model) calculations

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

Emül, Y.; Department of Software Engineering, Cumhuriyet University, 58140 Sivas; Erbahar, D.

2015-08-14

Analyses of the local crystal and electronic structure in the vicinity of Fe{sup 3+} centers in perovskite KMgF{sub 3} crystal have been carried out in a comprehensive manner. A combination of density functional theory (DFT) and a semi-empirical superposition model (SPM) is used for a complete analysis of all Fe{sup 3+} centers in this study for the first time. Some quantitative information has been derived from the DFT calculations on both the electronic structure and the local geometry around Fe{sup 3+} centers. All of the trigonal (K-vacancy case, K-Li substitution case, and normal trigonal Fe{sup 3+} center case), FeF{sub 5}Omore » cluster, and tetragonal (Mg-vacancy and Mg-Li substitution cases) centers have been taken into account based on the previously suggested experimental and theoretical inferences. The collaboration between the experimental data and the results of both DFT and SPM calculations provides us to understand most probable structural model for Fe{sup 3+} centers in KMgF{sub 3}.« less

Response of the Earth’s lower ionosphere to the Ground Level Enhancement event of December 13, 2006

NASA Astrophysics Data System (ADS)

Žigman, Vida; Kudela, Karel; Grubor, Davorka

2014-03-01

In this study we analyze the Ground Level Enhancement Event No 70 observed on December 13, 2006, by correlating the observations from two research topics: Cosmic rays and Very Low Frequency (VLF < 30 kHz) wave propagation, as two ground based techniques for the detection of solar proton events, and their impact on the lower ionosphere. The observations have been endorsed from recordings of worldwide network ground based Neutron Monitors as well as by satellite data from the satellites GOES 12 (www.swpc.noaa.gov) and Pamela (www.pamela.roma2infn.it). We have evaluated the ionization rate for protons in the altitude range relevant to VLF propagation, and for galactic cosmic ray (GCR) background, finding that at energies up to ˜2 GeV the ionization rate of solar protons exceeded the GCR ionization by 1.5 orders of magnitude. We have applied the Long Wave Propagation Capability (LWPC) code to evaluate the enhancement of the electron density from VLF signal perturbation and have inferred corresponding electron densities from the evaluated ionization rates and effective recombination coefficients from literature, to find the two independent sets in good agreement.

Investigations of Particle Transport in the Texas Helimak

NASA Astrophysics Data System (ADS)

Taylor, E. I.; Rowan, W. L.; Gentle, K. W.; Huang, H.; Williams, C. B.

2016-10-01

The correlation between electrostatic turbulence and particle flux is investigated in a simple magnetic torus, the Helimak. The Helimak is an experimental realization of a sheared cylindrical slab that generates and heats a plasma with microwaves at 2.45 GHz and confines it in a helical magnetic field. Although it is MHD stable, the plasma is always in a nonlinearly saturated state of microturbulence. The causes of this turbulence are diverse and it is thought that it is either due to drift wave instabilities or interchange instabilites. The local particle flux is estimated over most of the plasma cross section by measuring the particle source using filtered cameras. Plasma flow along the field lines is physically similar to SOL flows in tokamaks. It is significant and can be measured directly as well as inferred from asymmetries in the electron density. The cross field transport due to electrostatic turbulence is measured as the cross correlation of radial electric field fluctuations with electron density fluctuations with the data acquired using Langmuir probes. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences under Award Number DE-FG02-04ER54766.

Modeling Laser-Plasma Interactions at Direct-Drive Ignition-Relevant Plasma Conditions at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Solodov, A. A.; Rosenberg, M. J.; Myatt, J. F.; Epstein, R.; Seka, W.; Hohenberger, M.; Short, R. W.; Shaw, J. G.; Regan, S. P.; Froula, D. H.; Radha, P. B.; Bates, J. W.; Schmitt, A. J.; Michel, P.; Moody, J. D.; Ralph, J. E.; Turnbull, D. P.; Barrios, M. A.

2016-10-01

Laser-plasma interaction instabilities, such as two-plasmon decay (TPD) and stimulated Raman scattering (SRS), can be detrimental for direct-drive inertial confinement fusion because of target preheat by generated high-energy electrons. The radiation-hydrodynamics code DRACO has been used to design planar-target experiments that generate plasma and interaction conditions relevant to direct-drive-ignition designs (IL 1015 W / cm 2 , Te > 3 KeV density gradient scale lengths of Ln 600 μm) . The hot-electron temperature of 40to50keV and the fraction of laser energy converted to hot electrons of 0.5to were inferred based on comparing the simulated and experimentally observed x-ray emission when the laser intensity at the quarter-critical surface increased from 6 to 15 ×1014 W / cm 2 . The measured SRS energy was sufficient to explain the observed total energy in hot electrons. Implications for ignition-scale direct-drive experiments and hot-electron preheat mitigation using mid- Z ablators will be discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Dynamic evolution of the source volumes of gradual and impulsive solar flare emissions

NASA Technical Reports Server (NTRS)

Bruner, M. E.; Crannell, C. J.; Goetz, F.; Magun, A.; Mckenzie, D. L.

1987-01-01

This study compares flare source volumes inferred from impulsive hard X-rays and microwaves with those derived from density sensitive soft X-ray line ratios in the O VII spectrum. The data for this study were obtained with the SMM Hard X-Ray Burst Spectrometer, Earth-based radio observatories, and the SOLEX-B spectrometer on the P78-1 satellite. Data were available for the flares of 1980 April 8, 1980 May 9, and 1981 February 26. The hard X-ray/microwave source volume is determined under the assumption that the same electron temperature or power law index characterizes both the source of hard X-rays and the source of microwaves. The O VII line ratios yield the density and volume of the 2 X 10 to the 6th K plasma. For all three flares, the O VII source volume is found to be smallest at the beginning of the flare, near the time when the impulsive hard X-ray/microwave volume reaches its first maximum. At this time, the O VII volume is three to four orders of magnitude smaller than that inferred from the hard X-ray/microwave analysis. Subsequently, the O VII source volume increases by one or two orders of magnitude then remains almost constant until the end of the flare when it apparently increases again.

RF wave observations in beam-plasma discharge

NASA Technical Reports Server (NTRS)

Bernstein, W.

1986-01-01

The Beam Plasma Discharge (BPD) was produced in the large vacuum chamber at Johnson Space Center (20 x 30 m) using an energetic electron beam of moderately high perveance. A more complete expression of the threshold current I sub c taking into account the pitch angle injection dependence is given. Ambient plasma density inferred from wave measurements under various beam conditions are reported. Maximum frequency of the excited RF band behaves differently than the frequency of the peak amplitude. The latter shows signs of parabolic saturation consistent with the light data. Beam plasma state (pre-BPD or BPD) does not affect the pitch angle dependence. Unexpected strong modulation of the RF spectrum at half odd integer of the electron cyclotron frequency (n + 1/2)f sub ce is reported (5 n 10). Another new feature, the presence of wave emission around 3/2 f sub ce for I sub b is approximate I sub c is reported.

Theoretical prediction of the electronic transport properties of the Al-Cu alloys based on the first-principle calculation and Boltzmann transport equation

NASA Astrophysics Data System (ADS)

Choi, Garam; Lee, Won Bo

Metal alloys, especially Al-based, are commonly-used materials for various industrial applications. In this paper, the Al-Cu alloys with varying the Al-Cu ratio were investigated based on the first-principle calculation using density functional theory. And the electronic transport properties of the Al-Cu alloys were carried out using Boltzmann transport theory. From the results, the transport properties decrease with Cu-containing ratio at the temperature from moderate to high, but with non-linearity. It is inferred by various scattering effects from the calculation results with relaxation time approximation. For the Al-Cu alloy system, where it is hard to find the reliable experimental data for various alloys, it supports understanding and expectation for the thermal electrical properties from the theoretical prediction. Theoretical and computational soft matters laboratory.

First principles view on chemical compound space: Gaining rigorous atomistic control of molecular properties

DOE PAGES

von Lilienfeld, O. Anatole

2013-02-26

A well-defined notion of chemical compound space (CCS) is essential for gaining rigorous control of properties through variation of elemental composition and atomic configurations. Here, we give an introduction to an atomistic first principles perspective on CCS. First, CCS is discussed in terms of variational nuclear charges in the context of conceptual density functional and molecular grand-canonical ensemble theory. Thereafter, we revisit the notion of compound pairs, related to each other via “alchemical” interpolations involving fractional nuclear charges in the electronic Hamiltonian. We address Taylor expansions in CCS, property nonlinearity, improved predictions using reference compound pairs, and the ounce-of-gold prizemore » challenge to linearize CCS. Finally, we turn to machine learning of analytical structure property relationships in CCS. Here, these relationships correspond to inferred, rather than derived through variational principle, solutions of the electronic Schrödinger equation.« less

Vertical structure of medium-scale traveling ionospheric disturbances

NASA Astrophysics Data System (ADS)

Ssessanga, Nicholas; Kim, Yong Ha; Kim, Eunsol

2015-11-01

We develop an algorithm of computerized ionospheric tomography (CIT) to infer information on the vertical and horizontal structuring of electron density during nighttime medium-scale traveling ionospheric disturbances (MSTIDs). To facilitate digital CIT we have adopted total electron contents (TEC) from a dense Global Positioning System (GPS) receiver network, GEONET, which contains more than 1000 receivers. A multiplicative algebraic reconstruction technique was utilized with a calibrated IRI-2012 model as an initial solution. The reconstructed F2 peak layer varied in altitude with average peak-to-peak amplitude of ~52 km. In addition, the F2 peak layer anticorrelated with TEC variations. This feature supports a theory in which nighttime MSTID is composed of oscillating electric fields due to conductivity variations. Moreover, reconstructed TEC variations over two stations were reasonably close to variations directly derived from the measured TEC data set. Our tomographic analysis may thus help understand three-dimensional structure of MSTIDs in a quantitative way.

Structural differences existing in bulk and nanoparticles of Y{sub 2}Sn{sub 2}O{sub 7}: Investigated by experimental and theoretical methods

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

Nigam, Sandeep, E-mail: snigam@barc.gov.in; Sudarsan, V., E-mail: vsudar@barc.gov.in; Majumder, C.

Present manuscript deals with the structural changes associated with transformation of bulk Y{sub 2}Sn{sub 2}O{sub 7} into nanoparticles of Y{sub 2}Sn{sub 2}O{sub 7}. Nanoparticles of Y{sub 2}Sn{sub 2}O{sub 7} both undoped and Eu{sup 3+} doped, were prepared at a relatively low temperature (700 °C) and investigated for their structural and luminescence properties and compared them with that of bulk Y{sub 2}Sn{sub 2}O{sub 7} sample prepared by the solid-state method at 1300 °C. Significant distortion in geometry and electron density distribution around Y{sup 3+}/Eu{sup 3+} ions in nanoparticles are confirmed from the Rietveld refinement of the powder X-ray diffraction patterns andmore » theoretical calculations based on the density functional theory (DFT). The SnO{sub 6} octahedron in Y{sub 2}Sn{sub 2}O{sub 7} is more expanded in nanoparticles compared to bulk. Iso-surface density distribution reveals that while bulk sample shows typical ionic feature in Y/Eu--O bonds, nanoparticle sample shows sharing of electron density along bond axis pertaining to covalent character. These inferences are further supported by the doped Eu{sup 3+} luminescence and calculated Ω{sub 2} and Ω{sub 4} parameters. - Graphical abstract: YO{sub 8} scalenohedron present in bulk and nanoparticles of Y{sub 2}Sn{sub 2}O{sub 7}.Variation of the electron density around Y{sup 3+} ions in YO{sub 8} polyhedron is also shown in bulk and nanoparticles of Y{sub 2}Sn{sub 2}O{sub 7}. The difference in the extent of ionic/covalent nature of the Y--O bond is clearly seen the contour plot of electron density. Highlights: ► YO{sub 8} scalenohedron is axially and equatorially distorted in Y{sub 2}Sn{sub 2}O{sub 7} nanoparticles. ► Enlargement of SnO{sub 6} octahedron in nanoparticles of Y{sub 2}Sn{sub 2}O{sub 7} compared to bulk. ► Less symmetric charge distribution around Y{sup 3+} ions in Y{sub 2}Sn{sub 2}O{sub 7} nanoparticles.« less

Effect of magnetic and density fluctuations on the propagation of lower hybrid waves in tokamaks

NASA Astrophysics Data System (ADS)

Vahala, George; Vahala, Linda; Bonoli, Paul T.

1992-12-01

Lower hybrid waves have been used extensively for plasma heating, current drive, and ramp-up as well as sawteeth stabilization. The wave kinetic equation for lower hybrid wave propagation is extended to include the effects of both magnetic and density fluctuations. This integral equation is then solved by Monte Carlo procedures for a toroidal plasma. It is shown that even for magnetic/density fluctuation levels on the order of 10-4, there are significant magnetic fluctuation effects on the wave power deposition into the plasma. This effect is quite pronounced if the magnetic fluctuation spectrum is peaked within the plasma. For Alcator-C-Mod [I. H. Hutchinson and the Alcator Group, Proceedings of the IEEE 13th Symposium on Fusion Engineering (IEEE, New York, 1990), Cat. No. 89CH 2820-9, p. 13] parameters, it seems possible to be able to infer information on internal magnetic fluctuations from hard x-ray data—especially since the effects of fluctuations on electron power density can explain the hard x-ray data from the JT-60 tokamak [H. Kishimoto and JT-60 Team, in Plasma Physics and Controlled Fusion (International Atomic Energy Agency, Vienna, 1989), Vol. I, p. 67].

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

Popovich, P.; Carter, T. A.; Friedman, B.

Numerical simulation of plasma turbulence in the Large Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991)] is presented. The model, implemented in the BOUndary Turbulence code [M. Umansky, X. Xu, B. Dudson et al., Contrib. Plasma Phys. 180, 887 (2009)], includes three-dimensional (3D) collisional fluid equations for plasma density, electron parallel momentum, and current continuity, and also includes the effects of ion-neutral collisions. In nonlinear simulations using measured LAPD density profiles but assuming constant temperature profile for simplicity, self-consistent evolution of instabilities and nonlinearly generated zonal flows results in a saturatedmore » turbulent state. Comparisons of these simulations with measurements in LAPD plasmas reveal good qualitative and reasonable quantitative agreement, in particular in frequency spectrum, spatial correlation, and amplitude probability distribution function of density fluctuations. For comparison with LAPD measurements, the plasma density profile in simulations is maintained either by direct azimuthal averaging on each time step, or by adding particle source/sink function. The inferred source/sink values are consistent with the estimated ionization source and parallel losses in LAPD. These simulations lay the groundwork for more a comprehensive effort to test fluid turbulence simulation against LAPD data.« less

Surface radiant flux densities inferred from LAC and GAC AVHRR data

NASA Astrophysics Data System (ADS)

Berger, F.; Klaes, D.

To infer surface radiant flux densities from current (NOAA-AVHRR, ERS-1/2 ATSR) and future meteorological (Envisat AATSR, MSG, METOP) satellite data, the complex, modular analysis scheme SESAT (Strahlungs- und Energieflüsse aus Satellitendaten) could be developed (Berger, 2001). This scheme allows the determination of cloud types, optical and microphysical cloud properties as well as surface and TOA radiant flux densities. After testing of SESAT in Central Europe and the Baltic Sea catchment (more than 400scenes U including a detailed validation with various surface measurements) it could be applied to a large number of NOAA-16 AVHRR overpasses covering the globe.For the analysis, two different spatial resolutions U local area coverage (LAC) andwere considered. Therefore, all inferred results, like global area coverage (GAC) U cloud cover, cloud properties and radiant properties, could be intercompared. Specific emphasis could be made to the surface radiant flux densities (all radiative balance compoments), where results for different regions, like Southern America, Southern Africa, Northern America, Europe, and Indonesia, will be presented. Applying SESAT, energy flux densities, like latent and sensible heat flux densities could also be determined additionally. A statistical analysis of all results including a detailed discussion for the two spatial resolutions will close this study.

Bayesian Nonparametric Inference – Why and How

PubMed Central

Müller, Peter; Mitra, Riten

2013-01-01

We review inference under models with nonparametric Bayesian (BNP) priors. The discussion follows a set of examples for some common inference problems. The examples are chosen to highlight problems that are challenging for standard parametric inference. We discuss inference for density estimation, clustering, regression and for mixed effects models with random effects distributions. While we focus on arguing for the need for the flexibility of BNP models, we also review some of the more commonly used BNP models, thus hopefully answering a bit of both questions, why and how to use BNP. PMID:24368932

Inferring animal densities from tracking data using Markov chains.

PubMed

Whitehead, Hal; Jonsen, Ian D

2013-01-01

The distributions and relative densities of species are keys to ecology. Large amounts of tracking data are being collected on a wide variety of animal species using several methods, especially electronic tags that record location. These tracking data are effectively used for many purposes, but generally provide biased measures of distribution, because the starts of the tracks are not randomly distributed among the locations used by the animals. We introduce a simple Markov-chain method that produces unbiased measures of relative density from tracking data. The density estimates can be over a geographical grid, and/or relative to environmental measures. The method assumes that the tracked animals are a random subset of the population in respect to how they move through the habitat cells, and that the movements of the animals among the habitat cells form a time-homogenous Markov chain. We illustrate the method using simulated data as well as real data on the movements of sperm whales. The simulations illustrate the bias introduced when the initial tracking locations are not randomly distributed, as well as the lack of bias when the Markov method is used. We believe that this method will be important in giving unbiased estimates of density from the growing corpus of animal tracking data.

Photoionization and heating of a supernova-driven turbulent interstellar medium

NASA Astrophysics Data System (ADS)

Barnes, J. E.; Wood, Kenneth; Hill, Alex S.; Haffner, L. M.

2014-06-01

The diffuse ionized gas (DIG) in galaxies traces photoionization feedback from massive stars. Through three-dimensional photoionization simulations, we study the propagation of ionizing photons, photoionization heating and the resulting distribution of ionized and neutral gas within snapshots of magnetohydrodynamic simulations of a supernova-driven turbulent interstellar medium. We also investigate the impact of non-photoionization heating on observed optical emission line ratios. Inclusion of a heating term which scales less steeply with electron density than photoionization is required to produce diagnostic emission line ratios similar to those observed with the Wisconsin Hα Mapper. Once such heating terms have been included, we are also able to produce temperatures similar to those inferred from observations of the DIG, with temperatures increasing to above 15 000 K at heights |z| ≳ 1 kpc. We find that ionizing photons travel through low-density regions close to the mid-plane of the simulations, while travelling through diffuse low-density regions at large heights. The majority of photons travel small distances (≲100 pc); however some travel kiloparsecs and ionize the DIG.

Physics-based Tests to Identify the Accuracy of Solar Wind Ion Measurements: A Case Study with the Wind Faraday Cups

NASA Technical Reports Server (NTRS)

Kasper, J. C.; Lazarus, A. J.; Steinberg, J. T.; Ogilvie, K. W.; Szabo, A.

2006-01-01

We present techniques for comparing measurements of velocity, temperature, and density with constraints imposed by the plasma physics of magnetized bi-Maxwellian ions. Deviations from these physics-based constraints are interpreted as arising from measurement errors. Two million ion spectra from the Solar Wind Experiment Faraday Cup instruments on the Wind spacecraft are used as a case study. The accuracy of velocity measurements is determined by the fact that differential flow between hydrogen and helium should be aligned with the ambient magnetic field. Modeling the breakdown of field alignment suggests velocity uncertainties are less than 0.16% in magnitude and 3deg in direction. Temperature uncertainty is found by examining the distribution of observed temperature anisotropies in high-beta solar wind intervals where the firehose, mirror, and cyclotron microinstabilities should drive the distribution to isotropy. The presence of a finite anisotropy at high beta suggests overall temperature uncertainties of 8%. Hydrogen and helium number densities are compared with the electron density inferred from observations of the local electron plasma frequency as a function of solar wind speed and year. We find that after accounting for the contribution of minor ions, the results are consistent with a systematic offset between the two instruments of 34%. The temperature and density methods are sensitive to non-Maxwellian features such as heat flux and proton beams and as a result are more suited to slow solar wind where these features are rare. These procedures are of general use in identifying the accuracy of observations from any solar wind ion instrument.

Direct Evidence of EMIC-Driven Electron Loss in Space: Evaluation of an Electron Dropout Event

NASA Astrophysics Data System (ADS)

Zhang, X.; Li, W.; Ma, Q.; Thorne, R. M.; Angelopoulos, V.

2015-12-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed as a mechanism to cause efficient losses of highly relativistic (>MeV) electrons via gyroresonant interactions. However, simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited. In the present study, we evaluate the effect of EMIC waves on the pitch angle scattering of relativistic and ultrarelativistic (0.5-5 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both the Van Allen Probes and one of the THEMIS probes. EMIC waves captured on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) and enhanced precipitation of >~0.7 MeV electrons captured by POES are used to infer the MLT coverage of EMIC waves. Based on the observed EMIC wave spectra, local fpe and fce, we estimate the wave diffusion rates and model the evolution of electron pitch angle distributions. By comparing the modeled results with local observations of pitch angle distributions, for the first time, we are able to show direct, quantitative evidence of EMIC wave-driven relativistic electron loss in the Earth's outer radiation belt.

Massive optimal data compression and density estimation for scalable, likelihood-free inference in cosmology

NASA Astrophysics Data System (ADS)

Alsing, Justin; Wandelt, Benjamin; Feeney, Stephen

2018-07-01

Many statistical models in cosmology can be simulated forwards but have intractable likelihood functions. Likelihood-free inference methods allow us to perform Bayesian inference from these models using only forward simulations, free from any likelihood assumptions or approximations. Likelihood-free inference generically involves simulating mock data and comparing to the observed data; this comparison in data space suffers from the curse of dimensionality and requires compression of the data to a small number of summary statistics to be tractable. In this paper, we use massive asymptotically optimal data compression to reduce the dimensionality of the data space to just one number per parameter, providing a natural and optimal framework for summary statistic choice for likelihood-free inference. Secondly, we present the first cosmological application of Density Estimation Likelihood-Free Inference (DELFI), which learns a parametrized model for joint distribution of data and parameters, yielding both the parameter posterior and the model evidence. This approach is conceptually simple, requires less tuning than traditional Approximate Bayesian Computation approaches to likelihood-free inference and can give high-fidelity posteriors from orders of magnitude fewer forward simulations. As an additional bonus, it enables parameter inference and Bayesian model comparison simultaneously. We demonstrate DELFI with massive data compression on an analysis of the joint light-curve analysis supernova data, as a simple validation case study. We show that high-fidelity posterior inference is possible for full-scale cosmological data analyses with as few as ˜104 simulations, with substantial scope for further improvement, demonstrating the scalability of likelihood-free inference to large and complex cosmological data sets.

From Neutron Star Observables to the Equation of State. II. Bayesian Inference of Equation of State Pressures

NASA Astrophysics Data System (ADS)

Raithel, Carolyn A.; Özel, Feryal; Psaltis, Dimitrios

2017-08-01

One of the key goals of observing neutron stars is to infer the equation of state (EoS) of the cold, ultradense matter in their interiors. Here, we present a Bayesian statistical method of inferring the pressures at five fixed densities, from a sample of mock neutron star masses and radii. We show that while five polytropic segments are needed for maximum flexibility in the absence of any prior knowledge of the EoS, regularizers are also necessary to ensure that simple underlying EoS are not over-parameterized. For ideal data with small measurement uncertainties, we show that the pressure at roughly twice the nuclear saturation density, {ρ }{sat}, can be inferred to within 0.3 dex for many realizations of potential sources of uncertainties. The pressures of more complicated EoS with significant phase transitions can also be inferred to within ˜30%. We also find that marginalizing the multi-dimensional parameter space of pressure to infer a mass-radius relation can lead to biases of nearly 1 km in radius, toward larger radii. Using the full, five-dimensional posterior likelihoods avoids this bias.

Bayesian power spectrum inference with foreground and target contamination treatment

NASA Astrophysics Data System (ADS)

Jasche, J.; Lavaux, G.

2017-10-01

This work presents a joint and self-consistent Bayesian treatment of various foreground and target contaminations when inferring cosmological power spectra and three-dimensional density fields from galaxy redshift surveys. This is achieved by introducing additional block-sampling procedures for unknown coefficients of foreground and target contamination templates to the previously presented ARES framework for Bayesian large-scale structure analyses. As a result, the method infers jointly and fully self-consistently three-dimensional density fields, cosmological power spectra, luminosity-dependent galaxy biases, noise levels of the respective galaxy distributions, and coefficients for a set of a priori specified foreground templates. In addition, this fully Bayesian approach permits detailed quantification of correlated uncertainties amongst all inferred quantities and correctly marginalizes over observational systematic effects. We demonstrate the validity and efficiency of our approach in obtaining unbiased estimates of power spectra via applications to realistic mock galaxy observations that are subject to stellar contamination and dust extinction. While simultaneously accounting for galaxy biases and unknown noise levels, our method reliably and robustly infers three-dimensional density fields and corresponding cosmological power spectra from deep galaxy surveys. Furthermore, our approach correctly accounts for joint and correlated uncertainties between unknown coefficients of foreground templates and the amplitudes of the power spectrum. This effect amounts to correlations and anti-correlations of up to 10 per cent across wide ranges in Fourier space.

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

Klem, Michael

The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory seeks to achieve thermonuclear ignition through inertial confinement fusion. The accurate assessment of the performance of each implosion experiment is a crucial step. Here we report on work to derive a reliable electron temperature for the cryogenic deuteriumtritium implosions completed on the NIF using the xray signal from the Ross filter diagnostic. These Xrays are dominated by bremsstrahlung emission. By fitting the xray signal measured through each of the individual Ross filters, the source bremsstrahlung spectrum can be inferred, and an electron temperature of the implosion hot spot inferred.more » Currently, each filter is weighted equally in this analysis. We present work quantifying the errors with such a technique and the results from investigating the contribution of each filter to the overall accuracy of the temperature inference. Using this research, we also compare the inferred electron temperature against other measured implosion quantities to develop a more complete understanding of the hotspot physics.« less

Electron Scattering by High-Frequency Whistler Waves at Earth's Bow Shock

NASA Technical Reports Server (NTRS)

Oka, M.; Wilson, L. B., III; Phan, T. D.; Hull, A. J.; Amano, T.; Hoshino, M.; Argall, M. R.; Le Contel, O.; Agapitov, O.; Gersham, D. J.;

Electron Scattering by High-frequency Whistler Waves at Earth’s Bow Shock

NASA Astrophysics Data System (ADS)

Oka, M.; Wilson, L. B., III; Phan, T. D.; Hull, A. J.; Amano, T.; Hoshino, M.; Argall, M. R.; Le Contel, O.; Agapitov, O.; Gershman, D. J.; Khotyaintsev, Y. V.; Burch, J. L.; Torbert, R. B.; Pollock, C.; Dorelli, J. C.; Giles, B. L.; Moore, T. E.; Saito, Y.; Avanov, L. A.; Paterson, W.; Ergun, R. E.; Strangeway, R. J.; Russell, C. T.; Lindqvist, P. A.

2017-06-01

Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earth’s bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ˜11 and a shock angle ˜84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5-2 keV) electron flux, correlated with high-frequency (0.2-0.4 {{{Ω }}}{ce}, where {{{Ω }}}{ce} is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

Feasibility study of direct spectra measurements for Thomson scattered signals for KSTAR fusion-grade plasmas

NASA Astrophysics Data System (ADS)

Park, K.-R.; Kim, K.-h.; Kwak, S.; Svensson, J.; Lee, J.; Ghim, Y.-c.

2017-11-01

Feasibility study of direct spectra measurements of Thomson scattered photons for fusion-grade plasmas is performed based on a forward model of the KSTAR Thomson scattering system. Expected spectra in the forward model are calculated based on Selden function including the relativistic polarization correction. Noise in the signal is modeled with photon noise and Gaussian electrical noise. Electron temperature and density are inferred using Bayesian probability theory. Based on bias error, full width at half maximum and entropy of posterior distributions, spectral measurements are found to be feasible. Comparisons between spectrometer-based and polychromator-based Thomson scattering systems are performed with varying quantum efficiency and electrical noise levels.

Freja Studies of the Current-Voltage Relation in Substorm-Related Events

NASA Technical Reports Server (NTRS)

Olsson, A.; Andersson, Laila; Eriksson, A. I.; Clemmons, J.; Erlandsson, R. E.; Reeves, G.; Hughes, T.; Murphee, J. S.

2000-01-01

Field-aligned currents and electrostatic potentials play important roles in the coupling between the magnetosphere and the ionosphere. If one assumes that the ionosphere-magnetosphere potential difference is mainly due to the mirror force, one can use the single particle adiabatic kinetic theory to describe the system. From this theory, a linear relationship j(sub II) = KV between field-aligned current density j(sub II) and potential drop V along the same field line can be derived, provided that the potential drop is not too large and not too small. With rare exceptions, observational tests of this relation have mainly concentrated on quiet magnetospheric situations, with acceleration voltages V approx. less than 5 kV. Here we use observations from the Freja satellite of precipitating auroral electrons at 1.700 km altitude to study substorm related events, with acceleration voltages up to 20 keV. The observations are found to be consistent with a linear current-voltage relation even i n these conditions, although with values of the field aligned K lower than previously reported (1-5 x 10(exp 11 S/sq m). This can be explained by lower densities and higher characteristic electron energies in the magnetospheric source region of the precipitating electrons. We analyze the data by three different methods, which are all found to be in general agreement. The results are in agreement with a previous study, where the spectra of precipitating electrons --were indirectly inferred by inversion of data from the EISCAT incoherent scatter radar, thereby validating the use of radar data for studies of auroral electrons. Comparisons with previous studies are made, emphasizing the dependence of the results on the type of auroral structure and magnetospheric conditions.

Freja studies of the current-voltage relation in substorm-related events

NASA Astrophysics Data System (ADS)

Olsson, A.; Andersson, L.; Eriksson, A. I.; Clemmons, J.; Erlandsson, R. E.; Reeves, G.; Huges, T.; Murphee, J. S.

1998-03-01

Field-aligned currents and electrostatic potentials play important roles in the coupling between the magnetosphere and the ionosphere. If one assumes that the ionosphere-magnetosphere potential difference is mainly due to the mirror force, one can use the single particle adiabatic kinetic theory to describe the system. From this theory, a linear relationship j∥=KV between field-aligned current density j∥ and potential drop V along the same field line can be derived, provided that the potential drop is not too large and not too small. With rare exceptions, observational tests of this relation have mainly concentrated on quiet magnetospheric situations, with acceleration voltages V<~5kV. Here we use observations from the Freja satellite of precipitating auroral electrons at 1.700 km altitude to study substorm related events, with acceleration voltages up to 20 keV. The observations are found to be consistent with a linear current-voltage relation even in these conditions, although with values of the field aligned K lower than previously reported (1-5×10-11S/m2). This can be explained by lower densities and higher characteristic electron energies in the magnetospheric source region of the precipitating electrons. We analyze the data by three different methods, which are all found to be in general agreement. The results are in agreement with a previous study [Olsson et al., 1996 b], where the spectra of precipitating electrons were indirectly infered by inversion of data from the EISCAT incoherent scatter radar, thereby validating the use of radar data for studies of auroral electrons. Comparisons with previous studies are made, emphasizing the dependence of the results on the type of auroral structure and magnetospheric conditions.

Heat-Flux Measurements in Laser-Produced Plasmas Using Thomson Scattering from Electron Plasma Waves

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Goncharov, V. N.; Cao, D.; Katz, J.; Froula, D. H.; Rozmus, W.

2017-10-01

An experiment was designed to measure heat flux in coronal plasmas using collective Thomson scattering. Adjustments to the electron distribution function resulting from heat flux affect the shape of the collective Thomson scattering features through wave-particle resonance. The amplitude of the Spitzer-Härm electron distribution function correction term (f1) was varied to match the data and determines the value of the heat flux. Independent measurements of temperature and density obtained from Thomson scattering were used to infer the classical heat flux (q = - κ∇Te) . Time-resolved Thomson-scattering data were obtained at five locations in the corona along the target normal in a blowoff plasma formed from a planar Al target with 1.5 kJ of 351-nm laser light in a 2-ns square pulse. The flux measured through the Thomson-scattering spectra is a factor of 5 less than the κ∇Te measurements. The lack of collisions of heat-carrying electrons suggests a nonlocal model is needed to accurately describe the heat flux. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Electron acceleration by laser produced wake field: Pulse shape effect

NASA Astrophysics Data System (ADS)

Malik, Hitendra K.; Kumar, Sandeep; Nishida, Yasushi

2007-12-01

Analytical expressions are obtained for the longitudinal field (wake field: Ex), density perturbations ( ne') and the potential ( ϕ) behind a laser pulse propagating in a plasma with the pulse duration of the electron plasma period. A feasibility study on the wake field is carried out with Gaussian-like (GL) pulse, rectangular-triangular (RT) pulse and rectangular-Gaussian (RG) pulse considering one-dimensional weakly nonlinear theory ( ne'/n0≪1), and the maximum energy gain acquired by an electron is calculated for all these three types of the laser pulse shapes. A comparative study infers that the RT pulse yields the best results: In its case maximum electron energy gain is 33.5 MeV for a 30 fs pulse duration whereas in case of GL (RG) pulse of the same duration the gain is 28.6 (28.8)MeV at the laser frequency of 1.6 PHz and the intensity of 3.0 × 10 18 W/m 2. The field of the wake and hence the energy gain get enhanced for the higher laser frequency, larger pulse duration and higher laser intensity for all types of the pulses.

Cosmic dust particle densities - Evidence for two populations of stony micrometeorites

NASA Technical Reports Server (NTRS)

Flynn, G. J.; Sutton, S. R.

1991-01-01

The existence of two populations of stony micrometeorites of distinctly different densities would result in significantly different orbital evolution properties for particles from each group. The densities inferred from deceleration of meteors in the earth's atmosphere suggest a substantial amount of the meteoric material has densities of 1 g/cu cm or less (Verniani, 1973). However, measurements of microcraters on lunar rock surfaces led Brownlee et al. (1973) to the conclusion that most micrometeoroids impacting the moon had densities in the 2-4 g/cu cm range, and low-density micrometeoroids were rare. The recovery of stony micrometeorites from the earth's stratosphere after atmospheric deceleration provides the opportunity to resolve the discrepancies. Here, the densities of 12 stony micrometeorites are determined, using synchrotron X-ray fluorescence to infer the particle mass and optical microscope measurements of the volumes. The particles fall into two distinct density groups, with mean values of 0.6 and 1.9 g/cu cm. The factor of 3 difference in the mean densities between the two populations implies differences in the orbital evolution time scales.

Mechanisms of Ionospheric Mass Escape

NASA Technical Reports Server (NTRS)

Moore, T. E.; Khazanov, G. V.

2010-01-01

The dependence of ionospheric O+ escape flux on electromagnetic energy flux and electron precipitation into the ionosphere is derived for a hypothetical ambipolar pick-up process, powered the relative motion of plasmas and neutral upper atmosphere, and by electron precipitation, at heights where the ions are magnetized but influenced by photo-ionization, collisions with gas atoms, ambipolar and centrifugal acceleration. Ion pick-up by the convection electric field produces "ring-beam" or toroidal velocity distributions, as inferred from direct plasma measurements, from observations of the associated waves, and from the spectra of incoherent radar echoes. Ring-beams are unstable to plasma wave growth, resulting in rapid relaxation via transverse velocity diffusion, into transversely accelerated ion populations. Ion escape is substantially facilitated by the ambipolar potential, but is only weakly affected by centrifugal acceleration. If, as cited simulations suggest, ion ring beams relax into non-thermal velocity distributions with characteristic speed equal to the local ion-neutral flow speed, a generalized "Jeans escape" calculation shows that the escape flux of ionospheric O+ increases with Poynting flux and with precipitating electron density in rough agreement with observations.

High-resolution multi-MeV x-ray radiography using relativistic laser-solid interaction

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

Courtois, C.; Compant La Fontaine, A.; Barbotin, M.

2011-02-15

When high intensity ({>=}10{sup 19} W cm{sup -2}) laser light interacts with matter, multi-MeV electrons are produced. These electrons can be utilized to generate a MeV bremsstrahlung x-ray emission spectrum as they propagate into a high-Z solid target positioned behind the interaction area. The short duration (<10 ps) and the small diameter (<500 {mu}m) of the x-ray pulse combined with the MeV x-ray spectrum offers an interesting alternative to conventional bremsstrahlung x-ray sources based on an electron accelerator used to radiograph dense, rapidly moving objects. In experiments at the Omega EP laser, a multi-MeV x-ray source is characterized consistently withmore » number of independent diagnostics. An unfiltered x-ray dose of approximately 2 rad in air at 1 m and a source diameter of less than 350 {mu}m are inferred. Radiography of a complex and high area density (up to 61 g/cm{sup 2}) object is then performed with few hundred microns spatial resolution.« less

Spectral likelihood expansions for Bayesian inference

NASA Astrophysics Data System (ADS)

Nagel, Joseph B.; Sudret, Bruno

2016-03-01

A spectral approach to Bayesian inference is presented. It pursues the emulation of the posterior probability density. The starting point is a series expansion of the likelihood function in terms of orthogonal polynomials. From this spectral likelihood expansion all statistical quantities of interest can be calculated semi-analytically. The posterior is formally represented as the product of a reference density and a linear combination of polynomial basis functions. Both the model evidence and the posterior moments are related to the expansion coefficients. This formulation avoids Markov chain Monte Carlo simulation and allows one to make use of linear least squares instead. The pros and cons of spectral Bayesian inference are discussed and demonstrated on the basis of simple applications from classical statistics and inverse modeling.

Investigation of a possible electronic phase separation in the magnetic semiconductors Ga1 -xMnxAs and Ga1 -xMnxP by means of fluctuation spectroscopy

NASA Astrophysics Data System (ADS)

Lonsky, Martin; Teschabai-Oglu, Jan; Pierz, Klaus; Sievers, Sibylle; Schumacher, Hans Werner; Yuan, Ye; Böttger, Roman; Zhou, Shengqiang; Müller, Jens

2018-02-01

We present systematic temperature-dependent resistance noise measurements on a series of ferromagnetic Ga1 -xMnxAs epitaxial thin films covering a large parameter space in terms of the Mn content x and other variations regarding sample fabrication. We infer that the electronic noise is dominated by switching processes related to impurities in the entire temperature range. While metallic compounds with x >2 % do not exhibit any significant change in the low-frequency resistance noise around the Curie temperature TC, we find indications for an electronic phase separation in films with x <2 % in the vicinity of TC, manifesting itself in a maximum in the noise power spectral density. These results are compared with noise measurements on an insulating Ga1 -xMnxP reference sample, for which the evidence for an electronic phase separation is even stronger and a possible percolation of bound magnetic polarons is discussed. Another aspect addressed in this work is the effect of ion-irradiation-induced disorder on the electronic properties of Ga1 -xMnxAs films and, in particular, whether any electronic inhomogeneities can be observed in this case. Finally, we put our findings into the context of the ongoing debate on the electronic structure and the development of spontaneous magnetization in these materials.

Planar Two-Plasmon-Decay Experiments at Polar-Direct-Drive Ignition-Relevant Scale Lengths at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Rosenberg, M. J.; Solodov, A. A.; Seka, W.; Myatt, J. F.; Regan, S. P.; Hohenberger, M.; Epstein, R.; Collins, T. J. B.; Turnbull, D. P.; Ralph, J. E.; Barrios, M. A.; Moody, J. D.

2015-11-01

Results from the first experiments at the National Ignition Facility (NIF) to probe two-plasmon -decay (TPD) hot-electron production at scale lengths relevant to polar-direct-drive (PDD) ignition are reported. The irradiation on one side of a planar CH foil generated a plasma at the quarter-critical surface with a predicted density gradient scale length of Ln ~ 600 μm , a measured electron temperature of Te ~ 3 . 5 to 4.0 keV, an overlapped laser intensity of I ~ 6 ×1014 W/cm2, and a predicted TPD threshold parameter of η ~ 4 . The hard x-ray spectrum and the Kα emission from a buried Mo layer were measured to infer the hot-electron temperature and the fraction of total laser energy converted to TPD hot electrons. Optical emission at ω/2 correlated with the time-dependent hard x-ray signal confirms that TPD is responsible for the hot-electron generation. The effect of laser beam angle of incidence on TPD hot-electron generation was assessed, and the data show that the beam angle of incidence did not have a strong effect. These results will be used to benchmark simulations of TPD hot-electron production at conditions relevant to PDD ignition-scale implosions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Energy Estimates of Lightning-Generated Whistler-Mode Waves in the Venus Ionosphere

NASA Astrophysics Data System (ADS)

Hart, Richard; Russell, Christopher T.; Zhang, Tielong

2016-10-01

The dual fluxgate magnetometer on the Venus Express Mission sampled at 128 Hz allowing for signals up to 64 Hz to be detected. These signals are found at all local times and at altitudes up to 600 km while near periapsis. The spacecraft had a periapsis within 15 degrees of the north pole for nearly the entire mission, concentrating observations at high latitudes. At solar minimum, when the ionosphere can become strongly magnetized, the waves were more readily guided along the field up to the spacecraft. During this time, whistlers were observed 3% of the time while VEX was at 250 km altitude. Detection rates reached 5% at this altitude while near the dawn terminator due to a low altitude magnetic belt that provides a radial component enabling better access of the signals to the spacecraft.Since the majority of these observations were made at relatively low altitudes, reasonable assumptions can be made about the ionospheric conditions along the wave's path from the base of the ionosphere to the spacecraft. The electron density can be inferred by utilizing the VERA model and scaling it to match the solar cycle conditions during the Venus Express campaign. With the electron density and the three components of the magnetic field measurement, we then calculate the Poynting flux to determine the energy density of the wave. This enables us to determine the strength of the source lightning and compares this strength to that on Earth.

Energy Estimates of Lightning-Generated Whistler-Mode Waves in the Ionosphere of Venus

NASA Astrophysics Data System (ADS)

Hart, R. A.; Russell, C. T.; Zhang, T.

2016-12-01

The dual fluxgate magnetometer on the Venus Express Mission sampled at 128 Hz allowing for signals up to 64 Hz to be detected. These signals are found at all local times and at altitudes up to 600 km while near periapsis. The spacecraft had a periapsis within 15º of the north pole for nearly the entire mission, concentrating observations at high latitudes. At solar minimum, when the ionosphere can become strongly magnetized, the waves were more readily guided along the field up to the spacecraft. During this time, whistlers were observed 3% of the time while VEX was at 250 km altitude. Detection rates reached 5% at this altitude while near the dawn terminator due to a low altitude magnetic belt that provides a radial component enabling better access of the signals to the spacecraft. Since the majority of these observations were made at relatively low altitudes, reasonable assumptions can be made about the ionospheric conditions along the wave's path from the base of the ionosphere to the spacecraft. The electron density can be inferred by utilizing the VERA model and scaling it to match the solar cycle conditions during the Venus Express campaign. With the electron density and the three components of the magnetic field measurement, we then calculate the Poynting flux to determine the energy density of the wave. This enables us to determine the strength of the source lightning and compare it to that on Earth.

On the Connection Between Microbursts and Nonlinear Electronic Structures in Planetary Radiation Belts

NASA Technical Reports Server (NTRS)

Osmane, Adnane; Wilson, Lynn B., III; Blum, Lauren; Pulkkinen, Tuija I.

2016-01-01

Using a dynamical-system approach, we have investigated the efficiency of large-amplitude whistler waves for causing microburst precipitation in planetary radiation belts by modeling the microburst energy and particle fluxes produced as a result of nonlinear wave-particle interactions. We show that wave parameters, consistent with large amplitude oblique whistlers, can commonly generate microbursts of electrons with hundreds of keV-energies as a result of Landau trapping. Relativistic microbursts (greater than 1 MeV) can also be generated by a similar mechanism, but require waves with large propagation angles Theta (sub k)B greater than 50 degrees and phase-speeds v(sub phi) greater than or equal to c/9. Using our result for precipitating density and energy fluxes, we argue that holes in the distribution function of electrons near the magnetic mirror point can result in the generation of double layers and electron solitary holes consistent in scales (of the order of Debye lengths) to nonlinear structures observed in the radiation belts by the Van Allen Probes. Our results indicate a relationship between nonlinear electrostatic and electromagnetic structures in the dynamics of planetary radiation belts and their role in the cyclical production of energetic electrons (E greater than or equal to 100 keV) on kinetic timescales, which is much faster than previously inferred.

A multi-epoch spectroscopic study of the BAL quasar APM 08279+5255. II. Emission- and absorption-line variability time lags

NASA Astrophysics Data System (ADS)

Saturni, F. G.; Trevese, D.; Vagnetti, F.; Perna, M.; Dadina, M.

2016-03-01

Context. The study of high-redshift bright quasars is crucial to gather information about the history of galaxy assembly and evolution. Variability analyses can provide useful data on the physics of quasar processes and their relation with the host galaxy. Aims: In this study, we aim to measure the black hole mass of the bright lensed BAL QSO APM 08279+5255 at z = 3.911 through reverberation mapping, and to update and extend the monitoring of its C IV absorption line variability. Methods: We perform the first reverberation mapping of the Si IV and C IV emission lines for a high-luminosity quasar at high redshift with the use of 138 R-band photometric data and 30 spectra available over 16 years of observations. We also cross-correlate the C IV absorption equivalent width variations with the continuum light curve to estimate the recombination time lags of the various absorbers and infer the physical conditions of the ionised gas. Results: We find a reverberation-mapping time lag of ~900 rest-frame days for both Si IV and C IV emission lines. This is consistent with an extension of the BLR size-to-luminosity relation for active galactic nuclei up to a luminosity of ~1048 erg s-1, and implies a black hole mass of 1010 M⊙. Additionally, we measure a recombination time lag of ~160 days in the rest frame for the C IV narrow absorption system, which implies an electron density of the absorbing gas of ~2.5 × 104 cm-3. Conclusions: The measured black hole mass of APM 08279+5255 indicates that the quasar resides in an under-massive host-galaxy bulge with Mbulge ~ 7.5MBH, and that the lens magnification is lower than ~8. Finally, the inferred electron density of the narrow-line absorber implies a distance of the order of 10 kpc of the absorbing gas from the quasar, placing it within the host galaxy.

Measurement of Two-Plasmon-Decay Dependence on Plasma Density Scale Length

NASA Astrophysics Data System (ADS)

Haberberger, D.

2013-10-01

An accurate understanding of the plasma scale-length (Lq) conditions near quarter-critical density is important in quantifying the hot electrons generated by the two-plasmon-decay (TPD) instability in long-scale-length plasmas. A novel target platform was developed to vary the density scale length and an innovative diagnostic was implemented to measure the density profiles above 1021 cm-3 where TPD is expected to have the largest growth. A series of experiments was performed using the four UV (351-nm) beams on OMEGA EP that varied the Lq by changing the radius of curvature of the target while maintaining a constant Iq/Tq. The fraction of laser energy converted to hot electrons (fhot) was observed to increase rapidly from 0.005% to 1% by increasing the plasma scale length from 130 μm to 300 μm, corresponding to target diameters of 0.4 mm to 8 mm. A new diagnostic was developed based on refractometry using angular spectral filters to overcome the large phase accumulation in standard interferometric techniques. The angular filter refractometer measures the refraction angles of a 10-ps, 263-nm probe laser after propagating through the plasma. An angular spectral filter is used in the Fourier plane of the probe beam, where the refractive angles of the rays are mapped to space. The edges of the filter are present in the image plane and represent contours of constant refraction angle. These contours are used to infer the phase of the probe beam, which are used to calculate the plasma density profile. In long-scale-length plasmas, the diagnostic currently measures plasma densities from ~1019 cm-3 to ~2 × 1021 cm-3. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. In collaboration with D. H. Edgell, S. X. Hu, S. Ivancic, R. Boni, C. Dorrer, and D. H. Froula (Laboratory for Laser Energetics, U. of Rochester).

High-Resolution Gravity Field Modeling for Mercury to Estimate Crust and Lithospheric Properties

NASA Astrophysics Data System (ADS)

Goossens, S.; Mazarico, E.; Genova, A.; James, P. B.

2018-05-01

We estimate a gravity field model for Mercury using line-of-sight data to improve the gravity field model at short wavelengths. This can be used to infer crustal density and infer the support mechanism of the lithosphere.

Plasma observations near jupiter: initial results from voyager 2.

PubMed

Bridge, H S; Belcher, J W; Lazarus, A J; Sullivan, J D; Bagenal, F; McNutt, R L; Ogilvie, K W; Scudder, J D; Sittler, E C; Vasyliunas, V M; Goertz, C K

1979-11-23

The first of at least nine bow shock crossings observed on the inbound pass of Voyager 2 occurred at 98.8 Jupiter radii (R(J)) with final entry into the magnetosphere at 62 R(J). On both the inbound and outbound passes the plasma showed a tendency to move in the direction of corotation, as was observed on the inbound pass of Voyager 1. Positive ion densities and electron intensities observed by Voyager 2 are comparable within a factor of 2 to those seen by Voyager 1 at the same radial distance from Jupiter; the composition of the magnetospheric plasma is again dominated by heavy ions with a ratio of mass density relative to hydrogen of about 100/1. A series of dropouts of plasma intensity near Ganymede may be related to a complex interaction between Ganymede and the magnetospheric plasma. From the planetary spin modulation of the intensity of plasma electrons it is inferred that the plasma sheet is centered at the dipole magnetic equator out to a distance of 40 to 50 R(J) and deviates from it toward the rotational equator at larger distances. The longitudinal excursion of the plasma sheet lags behind the rotating dipole by a phase angle that increases with increasing radial distance.

Characterization of microwave plasma in a multicusp using 2D emission based tomography: Bessel modes and wave absorption

NASA Astrophysics Data System (ADS)

Rathore, Kavita; Bhattacharjee, Sudeep; Munshi, Prabhat

2017-06-01

A tomographic method based on the Fourier transform is used for characterizing a microwave plasma in a multicusp (MC), in order to obtain 2D distribution of plasma emissions, plasma (electron) density (Ne) and temperature (Te). The microwave plasma in the MC is characterized as a function of microwave power, gas pressure, and axial distance. The experimentally obtained 2D emission profiles show that the plasma emissions are generated in a circular ring shape. There are usually two bright rings, one at the plasma core and another near the boundary. The experimental results are validated using a numerical code that solves Maxwell's equations inside a waveguide filled with a plasma in a magnetic field, with collisions included. It is inferred that the dark and bright circular ring patterns are a result of superposition of Bessel modes (TE11 and TE21) of the wave electric field inside the plasma filled MC, which are in reasonable agreement with the plasma emission profiles. The tomographically obtained Ne and Te profiles indicate higher densities in the plasma core (˜1010 cm-3) and enhanced electron temperature in the ECR region (˜13 eV), which are in agreement with earlier results using a Langmuir probe and optical emission spectroscopy (OES) diagnostics.

Development of large volume double ring penning plasma discharge source for efficient light emissions

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

Prakash, Ram; Vyas, Gheesa Lal; Jain, Jalaj

In this paper, the development of large volume double ring Penning plasma discharge source for efficient light emissions is reported. The developed Penning discharge source consists of two cylindrical end cathodes of stainless steel having radius 6 cm and a gap 5.5 cm between them, which are fitted in the top and bottom flanges of the vacuum chamber. Two stainless steel anode rings with thickness 0.4 cm and inner diameters 6.45 cm having separation 2 cm are kept at the discharge centre. Neodymium (Nd{sub 2}Fe{sub 14}B) permanent magnets are physically inserted behind the cathodes for producing nearly uniform magnetic fieldmore » of {approx}0.1 T at the center. Experiments and simulations have been performed for single and double anode ring configurations using helium gas discharge, which infer that double ring configuration gives better light emissions in the large volume Penning plasma discharge arrangement. The optical emission spectroscopy measurements are used to complement the observations. The spectral line-ratio technique is utilized to determine the electron plasma density. The estimated electron plasma density in double ring plasma configuration is {approx}2 Multiplication-Sign 10{sup 11} cm{sup -3}, which is around one order of magnitude larger than that of single ring arrangement.« less

Development of large volume double ring penning plasma discharge source for efficient light emissions.

PubMed

Prakash, Ram; Vyas, Gheesa Lal; Jain, Jalaj; Prajapati, Jitendra; Pal, Udit Narayan; Chowdhuri, Malay Bikas; Manchanda, Ranjana

2012-12-01

In this paper, the development of large volume double ring Penning plasma discharge source for efficient light emissions is reported. The developed Penning discharge source consists of two cylindrical end cathodes of stainless steel having radius 6 cm and a gap 5.5 cm between them, which are fitted in the top and bottom flanges of the vacuum chamber. Two stainless steel anode rings with thickness 0.4 cm and inner diameters 6.45 cm having separation 2 cm are kept at the discharge centre. Neodymium (Nd(2)Fe(14)B) permanent magnets are physically inserted behind the cathodes for producing nearly uniform magnetic field of ~0.1 T at the center. Experiments and simulations have been performed for single and double anode ring configurations using helium gas discharge, which infer that double ring configuration gives better light emissions in the large volume Penning plasma discharge arrangement. The optical emission spectroscopy measurements are used to complement the observations. The spectral line-ratio technique is utilized to determine the electron plasma density. The estimated electron plasma density in double ring plasma configuration is ~2 × 10(11) cm(-3), which is around one order of magnitude larger than that of single ring arrangement.

Optical diagnostics of laser-produced aluminium plasmas under water

NASA Astrophysics Data System (ADS)

Walsh, N.; Costello, J. T.; Kelly, T. J.

2017-06-01

We report on the findings of double-pulse studies performed on an aluminium target submerged in water using Nd:YAG laser pulses. Shadowgraphy measurements were performed to examine the dynamic behaviour of the cavitation bubble that eventually forms some considerable time post-plasma ignition. These measurements were used to inform subsequent investigations designed to probe the bubble environment. The results of time-resolved imaging from within the cavitation bubble following irradiation by a second laser pulse reveal the full dynamic evolution of a plasma formed in such an environment. Rapid displacement of the plasma plume in a direction normal to the target surface followed by a diffusive outwards expansion is observed and a qualitative model is proposed to explain the observed behaviour. Line profiles of several ionic and atomic species were observed within the irradiated cavitation bubble. Electron densities were determined using the Stark broadening of the Al II line at 466.3 nm and electron temperatures inferred using the ratio of the Al II (466.3 nm) and Al I (396.15 nm) lines. Evidence of self-reversal of neutral emission lines was observed at times corresponding to growth and collapse phases of the cavitation bubble suggesting high population density for ground state atoms during these times.

A Detailed History of Intron-rich Eukaryotic Ancestors Inferred from a Global Survey of 100 Complete Genomes

PubMed Central

Csuros, Miklos; Rogozin, Igor B.; Koonin, Eugene V.

2011-01-01

Protein-coding genes in eukaryotes are interrupted by introns, but intron densities widely differ between eukaryotic lineages. Vertebrates, some invertebrates and green plants have intron-rich genes, with 6–7 introns per kilobase of coding sequence, whereas most of the other eukaryotes have intron-poor genes. We reconstructed the history of intron gain and loss using a probabilistic Markov model (Markov Chain Monte Carlo, MCMC) on 245 orthologous genes from 99 genomes representing the three of the five supergroups of eukaryotes for which multiple genome sequences are available. Intron-rich ancestors are confidently reconstructed for each major group, with 53 to 74% of the human intron density inferred with 95% confidence for the Last Eukaryotic Common Ancestor (LECA). The results of the MCMC reconstruction are compared with the reconstructions obtained using Maximum Likelihood (ML) and Dollo parsimony methods. An excellent agreement between the MCMC and ML inferences is demonstrated whereas Dollo parsimony introduces a noticeable bias in the estimations, typically yielding lower ancestral intron densities than MCMC and ML. Evolution of eukaryotic genes was dominated by intron loss, with substantial gain only at the bases of several major branches including plants and animals. The highest intron density, 120 to 130% of the human value, is inferred for the last common ancestor of animals. The reconstruction shows that the entire line of descent from LECA to mammals was intron-rich, a state conducive to the evolution of alternative splicing. PMID:21935348

Magnetospheric electron density long-term (>1 day) refilling rates inferred from passive radio emissions measured by IMAGE RPI during geomagnetically quiet times

NASA Astrophysics Data System (ADS)

Denton, R. E.; Wang, Y.; Webb, P. A.; Tengdin, P. M.; Goldstein, J.; Redfern, J. A.; Reinisch, B. W.

2012-03-01

Using measurements of the electron density ne found from passive radio wave observations by the IMAGE spacecraft RPI instrument on consecutive passes through the magnetosphere, we calculate the long-term (>1 day) refilling rate of equatorial electron density dne,eq/dt from L = 2 to 9. Our events did not exhibit saturation, probably because our data set did not include a deep solar minimum and because saturation is an unusual occurrence, especially outside of solar minimum. The median rate in cm-3/day can be modeled with log10(dne,eq/dt) = 2.22 - 0.006L - 0.0347L2, while the third quartile rate can be modeled with log10(dne,eq/dt) = 3.39 - 0.353L, and the mean rate can be modeled as log10(dne,eq/dt) = 2.74 - 0.269L. These statistical values are found from the ensemble of all observed rates at each L value, including negative rates (decreases in density due to azimuthal structure or radial motion or for other reasons), in order to characterize the typical behavior. The first quartile rates are usually negative for L < 4.7 and close to zero for larger L values. Our rates are roughly consistent with previous observations of ion refilling at geostationary orbit. Most previous studies of refilling found larger refilling rates, but many of these examined a single event which may have exhibited unusually rapid refilling. Comparing refilling rates at solar maximum to those at solar minimum, we found that the refilling rate is larger at solar maximum for small L < 4, about the same at solar maximum and solar minimum for L = 4.2 to 5.8, and is larger at solar minimum for large L > 5.8 such as at geostationary orbit (L ˜ 6.8) (at least to L of about 8). These results agree with previous results for ion refilling at geostationary orbit, may agree with previous results at lower L, and are consistent with some trends for ionospheric density.

Inferring probabilistic stellar rotation periods using Gaussian processes

NASA Astrophysics Data System (ADS)

Angus, Ruth; Morton, Timothy; Aigrain, Suzanne; Foreman-Mackey, Daniel; Rajpaul, Vinesh

2018-02-01

Variability in the light curves of spotted, rotating stars is often non-sinusoidal and quasi-periodic - spots move on the stellar surface and have finite lifetimes, causing stellar flux variations to slowly shift in phase. A strictly periodic sinusoid therefore cannot accurately model a rotationally modulated stellar light curve. Physical models of stellar surfaces have many drawbacks preventing effective inference, such as highly degenerate or high-dimensional parameter spaces. In this work, we test an appropriate effective model: a Gaussian Process with a quasi-periodic covariance kernel function. This highly flexible model allows sampling of the posterior probability density function of the periodic parameter, marginalizing over the other kernel hyperparameters using a Markov Chain Monte Carlo approach. To test the effectiveness of this method, we infer rotation periods from 333 simulated stellar light curves, demonstrating that the Gaussian process method produces periods that are more accurate than both a sine-fitting periodogram and an autocorrelation function method. We also demonstrate that it works well on real data, by inferring rotation periods for 275 Kepler stars with previously measured periods. We provide a table of rotation periods for these and many more, altogether 1102 Kepler objects of interest, and their posterior probability density function samples. Because this method delivers posterior probability density functions, it will enable hierarchical studies involving stellar rotation, particularly those involving population modelling, such as inferring stellar ages, obliquities in exoplanet systems, or characterizing star-planet interactions. The code used to implement this method is available online.

Inferring the three-dimensional distribution of dust in the Galaxy with a non-parametric method . Preparing for Gaia

NASA Astrophysics Data System (ADS)

Rezaei Kh., S.; Bailer-Jones, C. A. L.; Hanson, R. J.; Fouesneau, M.

2017-02-01

We present a non-parametric model for inferring the three-dimensional (3D) distribution of dust density in the Milky Way. Our approach uses the extinction measured towards stars at different locations in the Galaxy at approximately known distances. Each extinction measurement is proportional to the integrated dust density along its line of sight (LoS). Making simple assumptions about the spatial correlation of the dust density, we can infer the most probable 3D distribution of dust across the entire observed region, including along sight lines which were not observed. This is possible because our model employs a Gaussian process to connect all LoS. We demonstrate the capability of our model to capture detailed dust density variations using mock data and simulated data from the Gaia Universe Model Snapshot. We then apply our method to a sample of giant stars observed by APOGEE and Kepler to construct a 3D dust map over a small region of the Galaxy. Owing to our smoothness constraint and its isotropy, we provide one of the first maps which does not show the "fingers of God" effect.

Statistical density modification using local pattern matching

DOEpatents

Terwilliger, Thomas C.

2007-01-23

A computer implemented method modifies an experimental electron density map. A set of selected known experimental and model electron density maps is provided and standard templates of electron density are created from the selected experimental and model electron density maps by clustering and averaging values of electron density in a spherical region about each point in a grid that defines each selected known experimental and model electron density maps. Histograms are also created from the selected experimental and model electron density maps that relate the value of electron density at the center of each of the spherical regions to a correlation coefficient of a density surrounding each corresponding grid point in each one of the standard templates. The standard templates and the histograms are applied to grid points on the experimental electron density map to form new estimates of electron density at each grid point in the experimental electron density map.

INFERRING THE CORONAL DENSITY IRREGULARITY FROM EUV SPECTRA

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

Hahn, M.; Savin, D. W., E-mail: mhahn@astro.columbia.edu

2016-09-20

Understanding the density structure of the solar corona is important for modeling both coronal heating and the solar wind. Direct measurements are difficult because of line-of-sight integration and possible unresolved structures. We present a new method for quantifying such structures using density-sensitive extreme ultraviolet line intensities to derive a density irregularity parameter, a relative measure of the amount of structure along the line of sight. We also present a simple model to relate the inferred irregularities to physical quantities, such as the filling factor and density contrast. For quiet-Sun regions and interplume regions of coronal holes, we find a densitymore » contrast of at least a factor of 3–10 and corresponding filling factors of about 10%–20%. Our results are in rough agreement with other estimates of the density structures in these regions. The irregularity diagnostic provides a useful relative measure of unresolved structure in various regions of the corona.« less

Deducing Electron Properties from Hard X-Ray Observations

NASA Technical Reports Server (NTRS)

Kontar, E. P.; Brown, J. C.; Emslie, A. G.; Hajdas, W.; Holman, G. D.; Hurford, G. J.; Kasparova, J.; Mallik, P. C. V.; Massone, A. M.; McConnell, M. L.;

Direct observation of the lowest indirect exciton state in the bulk of hexagonal boron nitride

NASA Astrophysics Data System (ADS)

Schuster, R.; Habenicht, C.; Ahmad, M.; Knupfer, M.; Büchner, B.

2018-01-01

We combine electron energy-loss spectroscopy and first-principles calculations based on density-functional theory (DFT) to identify the lowest indirect exciton state in the in-plane charge response of hexagonal boron nitride (h-BN) single crystals. This remarkably sharp mode forms a narrow pocket with a dispersion bandwidth of ˜100 meV and, as we argue based on a comparison to our DFT calculations, is predominantly polarized along the Γ K direction of the hexagonal Brillouin zone. Our data support the recent report by Cassabois et al. [Nat. Photonics 10, 262 (2016), 10.1038/nphoton.2015.277] who indirectly inferred the existence of this mode from the photoluminescence signal, thereby establishing h-BN as an indirect semiconductor.

Optical Emission Spectroscopy in an Unmagnetized Plasma

NASA Astrophysics Data System (ADS)

Milhone, Jason; Cooper, Christopher; Desangles, Victor; Nornberg, Mark; Seidlitz, Blair; Forest, Cary; WiPAL Team

2015-11-01

An optical emission spectroscopic analysis has been developed to measure electron temperature, neutral burnout, and Zeff in Ar and He plasmas in the Wisconsin plasma astrophysics laboratory (WiPAL). The WiPAL vacuum chamber is a 3 meter diameter spherical vessel lined with 3000 SmCo permanent magnets (B > 3 kG) that create an axisymmetric multi-cusp ring for confining the plasma. WiPAL is designed to study unmagnetized plasmas that are hot (Te > 10 eV), dense (ne >1018), and with high ionization fraction. Electron temperature and density can be measured via Langmuir probes. However, probes can disturb the plasma, be difficult to interpret, and become damaged by large heat loads from the plasma. A low cost non-invasive spectroscopy system capable of scanning the plasma via a linear stage has been installed to study plasma properties. From the neutral particle emission, the neutral burnout and estimated neutral temperature can be inferred. A modified coronal model with metastable states is being implemented to determine Te for Ar plasmas.

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

Nagayama, T.; Bailey, J. E.; Loisel, G. P.

Iron opacity calculations presently disagree with measurements at an electron temperature of ~180–195 eV and an electron density of (2–4)×10 22cm –3, conditions similar to those at the base of the solar convection zone. The measurements use x rays to volumetrically heat a thin iron sample that is tamped with low-Z materials. The opacity is inferred from spectrally resolved x-ray transmission measurements. Plasma self-emission, tamper attenuation, and temporal and spatial gradients can all potentially cause systematic errors in the measured opacity spectra. In this article we quantitatively evaluate these potential errors with numerical investigations. The analysis exploits computer simulations thatmore » were previously found to reproduce the experimentally measured plasma conditions. The simulations, combined with a spectral synthesis model, enable evaluations of individual and combined potential errors in order to estimate their potential effects on the opacity measurement. Lastly, the results show that the errors considered here do not account for the previously observed model-data discrepancies.« less

STM-electroluminescence from clustered C3N4 nanodomains synthesized via green chemistry process.

PubMed

Andrade, E P; Costa, B B A; Chaves, C R; de Paula, A M; Cury, L A; Malachias, A; Safar, G A M

2018-01-01

A Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and synchrotron X-ray diffraction study on clustered C 3 N 4 nanoparticles (nanoflakes) is conducted on green-chemistry synthesized samples obtained from chitosan through high power sonication. Morphological aspects and the electronic characteristics are investigated. The observed bandgap of the nanoflakes reveals the presence of different phases in the material. Combining STM morphology, STS spectra and X-ray diffraction (XRD) results one finds that the most abundant phase is graphitic C 3 N 4 . A high density of defects is inferred from the XRD measurements. Additionally, STM-electroluminescence (STMEL) is detected in C 3 N 4 nanoflakes deposited on a gold substrate. The tunneling current creates photons that are three times more energetic than the tunneling electrons of the STM sample. We ponder about the two most probable models to explain the observed photon emission energy: either a nonlinear optical phenomenon or a localized state emission. Copyright © 2017 Elsevier B.V. All rights reserved.

Development of a High Resolution X-Ray Spectrometer for the National Ignition Facility (NIF)

NASA Astrophysics Data System (ADS)

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; Efthimion, P. C.; Ellis, R.; Gao, L.; Maddox, J.; Pablant, N. A.; Schneider, M. B.; Chen, H.; Ayers, S.; Kauffman, R. L.; Macphee, A. G.; Beiersdorfer, P.; Ma, T.; Nora, R. C.; Scott, H. A.; Thorn, D. B.; Kilkenny, J. D.; Nelson, D.; Shoup, M., III; Maron, Y.

2016-10-01

A high resolution (E/ ΔE 2000) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in NIF experiments. The instrument will be a positioner insertable cassette designed to infer electron density in compressed capsules from Stark broadening of the helium- β (1s2-1s3p) lines of krypton, and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and sagittally focus (1) the Kr He β complex and (2) the He α and Ly α complexes onto a streak camera photocathode for time resolved measurement. A third cylindrical crystal will focus the full He α to He β spectrum onto an image plate for a time integrated calibration spectrum. Performance estimates and design status will be presented. Performed under the auspices of the US DOE by PPPL under contract DE-AC02-09CH11466 and by LLNL under contract DE-AC52-07NA27344.

Net field-aligned currents observed by Triad

NASA Technical Reports Server (NTRS)

Sugiura, M.; Potemra, T. A.

1975-01-01

From the Triad magnetometer observation of a step-like level shift in the east-west component of the magnetic field at 800 km altitude, the existence of a net current flowing into or away from the ionosphere in a current layer was inferred. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The field aligned currents observed by Triad are considered as being an important element in the electro-dynamical coupling between the distant magnetosphere and the ionosphere. The current density integrated over the thickness of the layer increases with increasing magnetic activity, but the relation between the current density and Kp in individual cases is not a simple linear relation. An extrapolation of the statistical relation to Kp = 0 indicates existence of a sheet current of order 0.1 amp/m even at extremely quiet times. During periods of higher magnetic activity an integrated current of approximately 1 amp/m and average current density of order 0.000001 amp/sq m are observed. The location and the latitudinal width of the field aligned current layer carrying the net current very roughly agree with those of the region of high electron intensities in the trapping boundary.

The study of variability of TEC over mid-latitude American regions during the ascending phase of solar cycle 24 (2009-2011)

NASA Astrophysics Data System (ADS)

Asmare Tariku, Yekoye

2016-08-01

This paper deals with the pattern of the variability of the Global Positioning System vertical total electron content (GPS VTEC) and the modeled vertical total electron content (IRI 2012 TEC) over American mid-latitude regions during the rising phase of solar cycle 24 (2009-2011). This has been conducted employing ground-based dual frequency GPS receiver installed at Mississippi County Airport (geographic lat. 36.85°N and long. 270.64°E). In this work, the monthly and seasonal variations in the measured VTEC have been analyzed and compared with the VTEC inferred from IRI-2012 model. It has been shown that the monthly and seasonal mean VTEC values get decreased mostly between 05:00 and 10:00 UT and reach their minimal nearly at around 10:00 UT for both the experimental and the model. The VTEC values then get increased and reach the peak values at around 20:00 UT and decrease again. Moreover, it is depicted that the model better estimates both the monthly and seasonal mean hourly VTEC values mostly between 15:00 and 20:00 UT. The modeled monthly and seasonal VTEC values are smaller than the corresponding measured values as the solar activity decreases when all options for the topside electron density are used. However, as the Sun goes from a very low to a high solar activity, the overestimation performance of the VTEC values derived from the model increases. The overall results show that it is generally better to use the model with IRI-2000 option for the topside electron density in estimating the monthly and seasonal VTEC variations, especially when the activity of the Sun decreases.

Intermediate scale plasma density irregularities in the polar ionosphere inferred from radio occultation

NASA Astrophysics Data System (ADS)

Shume, E. B.; Komjathy, A.; Langley, R. B.; Verkhoglyadova, O. P.; Butala, M.; Mannucci, A. J.

2014-12-01

In this research, we report intermediate scale plasma density irregularities in the high-latitude ionosphere inferred from high-resolution radio occultation (RO) measurements in the CASSIOPE (CAScade Smallsat and IOnospheric Polar Explorer) - GPS (Global Positioning System) satellites radio link. The high inclination of the CASSIOPE satellite and high rate of signal receptionby the occultation antenna of the GPS Attitude, Positioning and Profiling (GAP) instrument on the Enhanced Polar Outflow Probe platform on CASSIOPE enable a high temporal and spatial resolution investigation of the dynamics of the polar ionosphere, magnetosphere-ionospherecoupling, solar wind effects, etc. with unprecedented details compared to that possible in the past. We have carried out high spatial resolution analysis in altitude and geomagnetic latitude of scintillation-producing plasma density irregularities in the polar ionosphere. Intermediate scale, scintillation-producing plasma density irregularities, which corresponds to 2 to 40 km spatial scales were inferred by applying multi-scale spectral analysis on the RO phase delay measurements. Using our multi-scale spectral analysis approach and Polar Operational Environmental Satellites (POES) and Defense Meteorological Satellite Program (DMSP) observations, we infer that the irregularity scales and phase scintillations have distinct features in the auroral oval and polar cap regions. In specific terms, we found that large length scales and and more intense phase scintillations are prevalent in the auroral oval compared to the polar cap region. Hence, the irregularity scales and phase scintillation characteristics are a function of the solar wind and the magnetospheric forcing. Multi-scale analysis may become a powerful diagnostic tool for characterizing how the ionosphere is dynamically driven by these factors.

The relation between the column density structures and the magnetic field orientation in the Vela C molecular complex

NASA Astrophysics Data System (ADS)

Soler, J. D.; Ade, P. A. R.; Angilè, F. E.; Ashton, P.; Benton, S. J.; Devlin, M. J.; Dober, B.; Fissel, L. M.; Fukui, Y.; Galitzki, N.; Gandilo, N. N.; Hennebelle, P.; Klein, J.; Li, Z.-Y.; Korotkov, A. L.; Martin, P. G.; Matthews, T. G.; Moncelsi, L.; Netterfield, C. B.; Novak, G.; Pascale, E.; Poidevin, F.; Santos, F. P.; Savini, G.; Scott, D.; Shariff, J. A.; Thomas, N. E.; Tucker, C. E.; Tucker, G. S.; Ward-Thompson, D.

2017-07-01

We statistically evaluated the relative orientation between gas column density structures, inferred from Herschel submillimetre observations, and the magnetic field projected on the plane of sky, inferred from polarized thermal emission of Galactic dust observed by the Balloon-borne Large-Aperture Submillimetre Telescope for Polarimetry (BLASTPol) at 250, 350, and 500 μm, towards the Vela C molecular complex. First, we find very good agreement between the polarization orientations in the three wavelength-bands, suggesting that, at the considered common angular resolution of 3.´0 that corresponds to a physical scale of approximately 0.61 pc, the inferred magnetic field orientation is not significantly affected by temperature or dust grain alignment effects. Second, we find that the relative orientation between gas column density structures and the magnetic field changes progressively with increasing gas column density, from mostly parallel or having no preferred orientation at low column densities to mostly perpendicular at the highest column densities. This observation is in agreement with previous studies by the Planck collaboration towards more nearby molecular clouds. Finally, we find a correspondencebetween (a) the trends in relative orientation between the column density structures and the projected magnetic field; and (b) the shape of the column density probability distribution functions (PDFs). In the sub-regions of Vela C dominated by one clear filamentary structure, or "ridges", where the high-column density tails of the PDFs are flatter, we find a sharp transition from preferentially parallel or having no preferred relative orientation at low column densities to preferentially perpendicular at highest column densities. In the sub-regions of Vela C dominated by several filamentary structures with multiple orientations, or "nests", where the maximum values of the column density are smaller than in the ridge-like sub-regions and the high-column density tails of the PDFs are steeper, such a transition is also present, but it is clearly less sharp than in the ridge-like sub-regions. Both of these results suggest that the magnetic field is dynamically important for the formation of density structures in this region.

I. Excitonic Phase Diagram in Silicon: Evidence for Two Condensed Phases. I. Motion of Photoexcited Carriers in GALLIUM-ARSENIDE/ALUMINUM(X)GALLIUM(1-X)ARSENIDE Multiple Quantum Wells-Anomalous Confinement at High Densities.

NASA Astrophysics Data System (ADS)

Smith, Leigh Morris

This thesis describes work on the thermodynamics and transport properties of photoexcited carriers in bulk and two-dimensional semiconductors. Two major topics are addressed. I. Photoluminescence experiments of excitons in unstressed silicon are presented which indicate the existence of a new non-degenerate condensed phase of plasma. This new liquid has a density one-tenth that of the ground state electron-hole liquid and is observed both above and below the liquid-gas critical point (~24.5K). A new phase diagram of excitons in silicon is presented which includes these two condensed plasmas. Consistent with the Gibbs phase rule, a triple point at 18.5 K is inferred from the luminescence data as the only temperature where the exciton gas, condensed plasma (CP) and electron-hole liquid (EHL) coexist. The low density condensed plasma persists up to a second critical point at 45 +/- 5K, above which the photoexcited carriers are observed to continuously decay into a partially ionized excitonic gas. II. We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 μm spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n = 2 times 10^{11}cm ^{-2} is found to depend upon excitation level, possibly indicating defect-limited diffusion or phonon-wind effects. Above this density the spatial profiles exhibit two distinct components with widely differing diffusivities. This remarkable behavior may be understood with consideration of the interactions of non-equilibrium phonons with the photoexcited carriers. We postulate that the slowly diffusing component represents carriers which are "thermally confined" to a phonon hot spot, while the rapidly moving component is driven by the flux of non-equilibrium phonons away from the excitation region.

Galactoseismology and the local density of dark matter

DOE PAGES

Banik, Nilanjan; Widrow, Lawrence M.; Dodelson, Scott

2016-10-08

Here, we model vertical breathing mode perturbations in the Milky Way's stellar disc and study their effects on estimates of the local dark matter density, surface density, and vertical force. Evidence for these perturbations, which involve compression and expansion of the Galactic disc perpendicular to its midplane, come from the SEGUE, RAVE, and LAMOST surveys. We show that their existence may lead to systematic errors ofmore » $$10\\%$$ or greater in the vertical force $$K_z(z)$$ at $$|z|=1.1\\,{\\rm kpc}$$. These errors translate to $$\\gtrsim 25\\%$$ errors in estimates of the local dark matter density. Using different mono-abundant subpopulations as tracers offers a way out: if the inferences from all tracers in the Gaia era agree, then the dark matter determination will be robust. Disagreement in the inferences from different tracers will signal the breakdown of the unperturbed model and perhaps provide the means for determining the nature of the perturbation.« less

On the roles of close shell interactions in the structure of acyl-substituted hydrazones: An experimental and theoretical approach

NASA Astrophysics Data System (ADS)

Saeed, Aamer; Ifzan Arshad, M.; Bolte, Michael; Fantoni, Adolfo C.; Delgado Espinoza, Zuly Y.; Erben, Mauricio F.

2016-03-01

The 2-(phenyl-hydrazono)-succinic acid dimethyl ester compound was synthesized by reacting phenylhydrazine with dimethylacetylene dicarboxylate at room temperature and characterized by elemental analysis, infrared, Raman, 1H and 13C NMR spectroscopies and mass spectrometry. Its solid state structure was determined by X-ray diffraction methods. The X-ray structure determination corroborates that the molecule is present in the crystal as the hydrazone tautomer, probably favored by a strong intramolecular N-H···Odbnd C hydrogen bond occurring between the carbonyl (-Cdbnd O) and the hydrazone -Cdbnd N-NH- groups. A substantial fragment of the molecular skeleton is planar due to an extended π-bonding delocalization. The topological analysis of the electron densities (Atom in Molecule, AIM) allows characterization of intramolecular N-H···O interaction, that can be classified as a resonant assisted hydrogen bond (RAHB). Moreover, the Natural Bond Orbital population analysis confirms that a strong hyperconjugative lpO1 → σ*(N2-H) remote interaction between the C2dbnd O1 and N2-H groups takes place. Periodic system electron density and topological analysis have been applied to characterize the intermolecular interactions in the crystal. Weak intermolecular interactions determine the crystal packing, and the prevalence of non-directional dispersive contributions are inferred on topological grounds. The IR spectrum of the crystalline compound was investigated by means of density functional theory calculations carried out with periodic boundary conditions on the crystal, showing excellent agreement between theory and the experiments. The vibrational assignment is complemented with the analysis of the Raman spectrum.

3D-Stereoscopic Analysis of Solar Active Region Loops: I: SoHo/EIT Observations at Temperatures of 1.0-1.5 MK

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Newmark, Jeff; Delaboudiniere, Jean-Pierre; Neupert, Werner M.; Portier-Fozzani, Fabrice; Gary, G. Allen; Zucker, Arik

1998-01-01

The three-dimensional (3D) structure of solar active region NOAA 7986 observed on 1996 August 30 with the Extrem-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SoHO) is analyzed. We develop a new method of Dynamic Stereoscopy to reconstruct the 3D geometry of dynamically changing loops, which allows us to determine the orientation of the loop plane with respect to the line-of-sight, a prerequisite to correct properly for projection effects in 3D loop models. With this method and the filter-ratio technique applied to EIT 171 A and 195 A images we determine the 3D coordinates (x(s), y(s), z(s)), the loop width) w(s), the electron density n(sub e)(s), and the electron temperature T(sub e)(s) as function of the loop length s for 30 loop segments. Fitting the loop densities with an exponential density model n(sub e)(h) we find that the so inferred scale height temperatures, T(sub e)(sup lambda) = 1.22 +/- 0.23 MK, match closely the EIT filter-ratio temperatures, T(sub e)(sup FIT) = 1.21 +/- 0.06 MK. We conclude that these rather large-scale loops (with heights of h approx. equals 50 - 200 Mm) that dominate EIT 171 A images are close to thermal equilibrium. Most of the loops show no significant thickness variation w(s), but many exhibit a trend of increasing temperature (dT/ds greater than 0) above the footpoint.

Electron spectroscopy imaging and surface defect configuration of zinc oxide nanostructures under different annealing ambient

NASA Astrophysics Data System (ADS)

Ann, Ling Chuo; Mahmud, Shahrom; Bakhori, Siti Khadijah Mohd

2013-01-01

In this study, electron spectroscopy imaging was used to visualize the elemental distribution of zinc oxide nanopowder. Surface modification in zinc oxide was done through annealing treatment and type of surface defect was also inferred from the electron spectroscopy imaging investigation. The micrographs revealed the non-stoichiometric distribution of the elements in the unannealed samples. Annealing the samples in nitrogen and oxygen ambient at 700 °C would alter the density of the elements in the samples as a result of removal or absorption of oxygen. The electrical measurement showed that nitrogen annealing treatment improved surface electrical conductivity, whereas oxygen treatment showed an adverse effect. Observed change in the photoluminescence green emission suggested that oxygen vacancies play a significant role as surface defects. Structural investigation carried out through X-ray diffraction revealed the polycrystalline nature of both zinc oxide samples with hexagonal phase whereby annealing process increased the crystallinity of both zinc oxide specimens. Due to the different morphologies of the two types of zinc oxide nanopowders, X-ray diffraction results showed different stress levels in their structures and the annealing treatment give significant effect to the structural stress. Electron spectroscopy imaging was a useful technique to identify the elemental distribution as well as oxygen defect in zinc oxide nanopowder.

Design-based and model-based inference in surveys of freshwater mollusks

USGS Publications Warehouse

Dorazio, R.M.

1999-01-01

Well-known concepts in statistical inference and sampling theory are used to develop recommendations for planning and analyzing the results of quantitative surveys of freshwater mollusks. Two methods of inference commonly used in survey sampling (design-based and model-based) are described and illustrated using examples relevant in surveys of freshwater mollusks. The particular objectives of a survey and the type of information observed in each unit of sampling can be used to help select the sampling design and the method of inference. For example, the mean density of a sparsely distributed population of mollusks can be estimated with higher precision by using model-based inference or by using design-based inference with adaptive cluster sampling than by using design-based inference with conventional sampling. More experience with quantitative surveys of natural assemblages of freshwater mollusks is needed to determine the actual benefits of different sampling designs and inferential procedures.

Interstellar abundances and depletions inferred from observations of neutral atoms

NASA Technical Reports Server (NTRS)

Snow, T. P.

1984-01-01

Data on neutral atomic species are analyzed for the purpose of inferring relative elemental abundances and depletions in diffuse cloud cores, where it is assumed that densities are enhanced in comparison with mean densities over integrated lines of sight. Column densities of neutral atoms are compared to yield relative column densities of singly ionized species, which are assumed dominant in cloud cores. This paper incorporates a survey of literature data on neutral atomic abundances with the result that no systematic enhancement in the depletions of calcium or iron in cloud cores is found, except for zeta Ophiuchi. This may imply that depletions are not influenced by density, but other data argue against this interpretation. It is concluded either that in general all elements are depleted together in dense regions so that their relative abundances remain constant, or that typical diffuse clouds do not have significant cores, but instead are reasonably homogeneous. The data show a probable correlation between cloud-core depletion and hydrogen-molecular fraction, supporting the assumption that overall depletions are a function of density.

Broadband Observations and Modeling of the Shell-Type Supernova Remnant G347.3-0.5

NASA Technical Reports Server (NTRS)

Ellison, Donald C.; Slane, Patrick O.; Gaensler, Bryan M.

2002-01-01

The supernova remnant G347.3-0.5 emits a featureless power law in X-rays, thought to indicate shock acceleration of electrons to high energies. We here produce a broadband spectrum of the bright northwest limb of this source by combining radio observations from the Australia Telescope Compact Array (ATCA), X-ray observations from the Advanced Satellite for Cosmology and Astrophysics (ASCA), and TeV gamma-ray observations from the CANGAROO imaging Cerenkov telescope. We assume that this emission is produced by an electron population generated by diffusive shock acceleration at the remnant forward shock. The nonlinear aspects of the particle acceleration force a connection between the widely different wavelength bands and between the electrons and the unseen ions, presumably accelerated simultaneously with the electrons. This allows us to infer the relativistic proton spectrum and estimate ambient parameters such as the supernova explosion energy, magnetic field, matter density in the emission region, and efficiency of the shock acceleration process. We find convincing evidence that the shock acceleration is efficient, placing greater than 25% of the shock kinetic energy flux into relativistic ions. Despite this high efficiency, the maximum electron and proton energies, while depending somewhat on assumptions for the compression of the magnetic field in the shock, are well below the observed 'knee' at 10(exp 15) eV in the Galactic cosmic-ray spectrum.

Detection and Analysis of X Ray Emission from the Princeton-Field-Reversed Configuration (PFRC-2)

NASA Astrophysics Data System (ADS)

Bosh, Alexandra; Swanson, Charles; Jandovitz, Peter; Cohen, Samuel

2016-10-01

The PFRC is an odd-parity rotating-magnetic-field-driven field-reversed-configuration magnetic confinement experiment. Studying X rays produced via electron Bremsstrahlung with neutral particles is crucial to the further understanding of the energy and particle confinement of the PFRC. The data on the x rays are collected using a detector system comprised of two, spatially scannable Amptek XR-100 CR detectors and a Amptek XR-100 SDD detector that view the plasma column at two axial locations, one in the divertor and one near the axial midplane. These provide X-ray energy and arrival-time information. (Data analysis requires measurement of each detector's efficiency, a parameter that is modified by window transmission. Detector calibrations were performed with a custom-made X-ray tube that impinged 1-microamp 1-5 kV electron beams onto a carbon target.) From the analyzed data, the average electron energy, effective temperature, and electron density can be extracted. Spatial scans then allow the FRC's internal energy to be measured. We present recent measurements of the Bremsstrahlung spectrum from 0.8 to 6 keV and the inferred electron temperature in the PFRC device as functions of heating power, magnetic field and fill gas pressure. This work was supported, in part, by DOE Contract Number DE-AC02-09CH11466.

Ultrafast Photoinduced Electron Transfer in a π-Conjugated Oligomer/Porphyrin Complex.

PubMed

Aly, Shawkat M; Goswami, Subhadip; Alsulami, Qana A; Schanze, Kirk S; Mohammed, Omar F

2014-10-02

Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor-acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR are desirable for optimal device performance. In this Letter, the ultrafast excited-state CT between platinum oligomer (DPP-Pt(acac)) as a new electron donor and porphyrin as an electron acceptor is monitored for the first time using femtosecond (fs) transient absorption (TA) spectroscopy with broad-band capability and 120 fs temporal resolution. Turning the CT on/off has been shown to be possible either by switching from an organometallic oligomer to a metal-free oligomer or by controlling the charge density on the nitrogen atom of the porphyrin meso unit. Our time-resolved data show that the CT and CS between DPP-Pt(acac) and cationic porphyrin are ultrafast (approximately 1.5 ps), and the CR is slow (ns time scale), as inferred from the formation and the decay of the cationic and anionic species. We also found that the metallic center in the DPP-Pt(acac) oligomer and the positive charge on the porphyrin are the keys to switching on/off the ultrafast CT process.

Strong plasma turbulence in the earth's electron foreshock

NASA Technical Reports Server (NTRS)

Robinson, P. A.; Newman, D. L.

1991-01-01

A quantitative model is developed to account for the distribution in magnitude and location of the intense plasma waves observed in the earth's electron foreshock given the observed rms levels of waves. In this model, nonlinear strong-turbulence effects cause solitonlike coherent wave packets to form and decouple from incoherent background beam-excited weak turbulence, after which they convect downstream with the solar wind while collapsing to scales as short as 100 m and fields as high as 2 V/m. The existence of waves with energy densities above the strong-turbulence wave-collapse threshold is inferred from observations from IMP 6 and ISEE 1 and quantitative agreement is found between the predicted distribution of fields in an ensemble of such wave packets and the actual field distribution observed in situ by IMP 6. Predictions for the polarization of plasma waves and the bandwidth of ion-sound waves are also consistent with the observations. It is shown that strong-turbulence effects must be incorporated in any comprehensive theory of the propagation and evolution of electron beams in the foreshock. Previous arguments against the existence of strong turbulence in the foreshock are refuted.

Inferences about landbird abundance from count data: recent advances and future directions

USGS Publications Warehouse

Nichols, J.D.; Thomas, L.; Conn, P.B.; Thomson, David L.; Cooch, Evan G.; Conroy, Michael J.

2009-01-01

We summarize results of a November 2006 workshop dealing with recent research on the estimation of landbird abundance from count data. Our conceptual framework includes a decomposition of the probability of detecting a bird potentially exposed to sampling efforts into four separate probabilities. Primary inference methods are described and include distance sampling, multiple observers, time of detection, and repeated counts. The detection parameters estimated by these different approaches differ, leading to different interpretations of resulting estimates of density and abundance. Simultaneous use of combinations of these different inference approaches can not only lead to increased precision but also provides the ability to decompose components of the detection process. Recent efforts to test the efficacy of these different approaches using natural systems and a new bird radio test system provide sobering conclusions about the ability of observers to detect and localize birds in auditory surveys. Recent research is reported on efforts to deal with such potential sources of error as bird misclassification, measurement error, and density gradients. Methods for inference about spatial and temporal variation in avian abundance are outlined. Discussion topics include opinions about the need to estimate detection probability when drawing inference about avian abundance, methodological recommendations based on the current state of knowledge and suggestions for future research.

Use of the Richtmyer-Meshkov Instability to Infer Yield Stress at High-Energy Densities

NASA Astrophysics Data System (ADS)

Dimonte, Guy; Terrones, G.; Cherne, F. J.; Germann, T. C.; Dupont, V.; Kadau, K.; Buttler, W. T.; Oro, D. M.; Morris, C.; Preston, D. L.

2011-12-01

We use the Richtmyer-Meshkov instability (RMI) at a metal-gas interface to infer the metal’s yield stress (Y) under shock loading and release. We first model how Y stabilizes the RMI using hydrodynamics simulations with a perfectly plastic constitutive relation for copper (Cu). The model is then tested with molecular dynamics (MD) of crystalline Cu by comparing the inferred Y from RMI simulations with direct stress-strain calculations, both with MD at the same conditions. Finally, new RMI experiments with solid Cu validate our simulation-based model and infer Y˜0.47GPa for a 36 GPa shock.

Sequential Monte Carlo for inference of latent ARMA time-series with innovations correlated in time

NASA Astrophysics Data System (ADS)

Urteaga, Iñigo; Bugallo, Mónica F.; Djurić, Petar M.

2017-12-01

We consider the problem of sequential inference of latent time-series with innovations correlated in time and observed via nonlinear functions. We accommodate time-varying phenomena with diverse properties by means of a flexible mathematical representation of the data. We characterize statistically such time-series by a Bayesian analysis of their densities. The density that describes the transition of the state from time t to the next time instant t+1 is used for implementation of novel sequential Monte Carlo (SMC) methods. We present a set of SMC methods for inference of latent ARMA time-series with innovations correlated in time for different assumptions in knowledge of parameters. The methods operate in a unified and consistent manner for data with diverse memory properties. We show the validity of the proposed approach by comprehensive simulations of the challenging stochastic volatility model.

Inference of missing data and chemical model parameters using experimental statistics

NASA Astrophysics Data System (ADS)

Casey, Tiernan; Najm, Habib

2017-11-01

A method for determining the joint parameter density of Arrhenius rate expressions through the inference of missing experimental data is presented. This approach proposes noisy hypothetical data sets from target experiments and accepts those which agree with the reported statistics, in the form of nominal parameter values and their associated uncertainties. The data exploration procedure is formalized using Bayesian inference, employing maximum entropy and approximate Bayesian computation methods to arrive at a joint density on data and parameters. The method is demonstrated in the context of reactions in the H2-O2 system for predictive modeling of combustion systems of interest. Work supported by the US DOE BES CSGB. Sandia National Labs is a multimission lab managed and operated by Nat. Technology and Eng'g Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell Intl, for the US DOE NCSA under contract DE-NA-0003525.

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

Gerber, S.; Jang, H.; Nojiri, H.

Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW onsets around the zero-field superconductingmore » transition temperature, yet the incommensurate inplane ordering vector is field-independent. This implies that the two forms of CDW and hightemperature superconductivity are intimately linked.« less

Searching for chameleon-like scalar fields with the ammonia method

NASA Astrophysics Data System (ADS)

Levshakov, S. A.; Molaro, P.; Lapinov, A. V.; Reimers, D.; Henkel, C.; Sakai, T.

2010-03-01

Aims: We probe the dependence of the electron-to-proton mass ratio, μ = me/mp, on the ambient matter density by means of radio astronomical observations. Methods: The ammonia method, which has been proposed to explore the electron-to-proton mass ratio, is applied to nearby dark clouds in the Milky Way. This ratio, which is measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter is supposed to vary in chameleon-like scalar field models, which predict strong dependences of both masses and coupling constant on the local matter density. High resolution spectral observations of molecular cores in lines of NH3 (J,K) = (1,1), HC_3N J = 2-1, and N_2H^+ J = 1-0 were performed at three radio telescopes to measure the radial velocity offsets, Δ V ≡ Vrot - Vinv, between the inversion transition of NH_3 (1,1) and the rotational transitions of other molecules with different sensitivities to the parameter Δμ/μ ≡ (μ_obs - μ_lab)/μ_lab. Results: The measured values of Δ V exhibit a statistically significant velocity offset of 23±4_stat ± 3_sys m s-1 . When interpreted in terms of the electron-to-proton mass ratio variation, this infers that Δμ/μ = (2.2±0.4_stat ± 0.3_sys) × 10-8. If only a conservative upper bound is considered, then the maximum offset between ammonia and the other molecules is |Δ V| ≤ 30 m s-1 . This provides the most accurate reference point at z = 0 for Δμ/μ of |Δ μ/μ| ≤ 3×10-8. Based on observations obtained with the Medicina 32-m telescope operated by INAF - Istituto di Radioastronomia, the 100-m telescope of the Max-Planck Institut für Radioastronomie at Effelsberg, and the Nobeyama Radio Observatory 45-m telescope of the National Astronomical Observatory of Japan.

Multicomponent density functional theory embedding formulation.

PubMed

Culpitt, Tanner; Brorsen, Kurt R; Pak, Michael V; Hammes-Schiffer, Sharon

2016-07-28

Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density is separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF(-) molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.

Multicomponent density functional theory embedding formulation

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

Culpitt, Tanner; Brorsen, Kurt R.; Pak, Michael V.

Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density ismore » separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF{sup −} molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.« less

On the derivation of empirical limits on the helium abundance in coronal holes below 1.5 solar radius

NASA Technical Reports Server (NTRS)

Habbal, Shadia Rifai; Esser, Ruth

1994-01-01

We present a simple technique describing how limits on the helium abundance, alpha, defined as the ratio of helium to proton number density, can be inferred from measurements of the electron density and temperature below 1.5 solar radius. As an illustration, we apply this technique to two different data sets: emission-line intensities in the extreme ultraviolet (EUV) and white-light observations, both measured in polar coronal holes. For the EUV data, the temperature gradient is derived from line intensity ratios, and the density gradient is replaced by the gradient of the line intensity. The lower limit on alpha derived from these data is 0.2-0.3 at 1 solar radius and drops very sharply to interplanetary values of a few percent below 1.06 solar radius. The white-light observations yield density gradients in the inner corona beyond 1.25 solar radius but do not have corresponding temperature gradients. In this case we consider an isothermal atmosphere, and derive an upper limit of 0.2 for alpha. These examples are used to illustrate how this technique could be applicable to the more extensive data to be obtained with the upcoming SOHO mission. Although only ranges on alpha can be derived, the application of the technique to data currently available merely points to the fact that alpha can be significantly large in the inner corona.

Normal and abnormal evolution of argon metastable density in high-density plasmas

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

Seo, B. H.; Kim, J. H., E-mail: jhkim86@kriss.re.kr; You, S. J., E-mail: sjyou@cnu.ac.kr

2015-05-15

A controversial problem on the evolution of Ar metastable density as a function of electron density (increasing trend versus decreasing trend) was resolved by discovering the anomalous evolution of the argon metastable density with increasing electron density (discharge power), including both trends of the metastable density [Daltrini et al., Appl. Phys. Lett. 92, 061504 (2008)]. Later, by virtue of an adequate physical explanation based on a simple global model, both evolutions of the metastable density were comprehensively understood as part of the abnormal evolution occurring at low- and high-density regimes, respectively, and thus the physics behind the metastable evolution hasmore » seemed to be clearly disclosed. In this study, however, a remarkable result for the metastable density behavior with increasing electron density was observed: even in the same electron density regime, there are both normal and abnormal evolutions of metastable-state density with electron density depending on the measurement position: The metastable density increases with increasing electron density at a position far from the inductively coupled plasma antenna but decreases at a position close to the antenna. The effect of electron temperature, which is spatially nonuniform in the plasma, on the electron population and depopulation processes of Argon metastable atoms with increasing electron density is a clue to understanding the results. The calculated results of the global model, including multistep ionization for the argon metastable state and measured electron temperature, are in a good agreement with the experimental results.« less

Possible impact of multi-electron loss events on the average beam charge state in an HIF target chamber and a neutral beam approach

NASA Astrophysics Data System (ADS)

Grisham, L. R.

2001-05-01

Experiments were carried out during the early 1980s to assess the obtainable atomic neutralization of energetic beams of negative ions ranging from lithium to silicon. The experiments found (Grisham et al. Rev. Sci. Instrum. 53 (1982) 281; Princeton Plasma Physics Laboratory Report PPPL-1857, 1981) that, for higher atomic number elements than lithium, it appeared that a substantial fraction of the time more than one electron was being lost in a single collision. This result was inferred from the existence of more than one ionization state in the product beam for even the thinnest line densities at which any electron removal took place. Because of accelerator limitations, these experiments were limited to maximum energies of 7 MeV. However, based upon these results, it is possible that multi-electron loss events may also play a significant role in determining the average ion charge state of the much higher Z and more energetic beams traversing the medium in an heavy ion fusion chamber. This could result in the beam charge state being considerably higher than previously anticipated, and might require designers to consider harder vacuum ballistic focusing approaches, or the development of additional space charge neutralization schemes. This paper discusses the measurements that gave rise for these concerns, as well as a description of further measurements that are proposed to be carried out for atomic numbers and energies per amu which would be closer to those required for heavy ion fusion drivers. With a very low current beam of a massive, but low charge state energetic ion, the charge state distribution emerging from a target gas cell could be measured as a function of line density and medium composition. Varying the line density would allow one to simulate the charge state evolution of the beam as a function of distance into the target chamber. This paper also briefly discusses a possible alternative driver approach using photodetachment-neutralized atomic beams, which could reduce plasma complications far from the target, but which would impose more stringent limitations upon chamber pressure and repetition rate.

Influence of the electrode gap separation on the pseudospark-sourced electron beam generation

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

Zhao, J., E-mail: junping.zhao@qq.com; State Key Laboratory of Electrical Insulation and Power Equipment, West Xianning Road, Xi'an 710049; Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG Scotland

Pseudospark-sourced electron beam is a self-focused intense electron beam which can propagate without any external focusing magnetic field. This electron beam can drive a beam-wave interaction directly or after being post-accelerated. It is especially suitable for terahertz radiation generation due to the ability of a pseudospark discharge to produce small size in the micron range and very high current density and bright electron beams. In this paper, a single-gap pseudospark discharge chamber has been built and tested with several electrode gap separations to explore the dependence of the pseudospark-sourced electron beam current on the discharge voltage and the electrode gapmore » separation. Experimental results show that the beam pulses have similar pulse width and delay time from the distinct drop of the applied voltage for smaller electrode gap separations but longer delay time for the largest gap separation used in the experiment. It has been found that the electron beam only starts to occur when the charging voltage is above a certain value, which is defined as the starting voltage of the electron beam. The starting voltage is different for different electrode gap separations and decreases with increasing electrode gap separation in our pseudospark discharge configuration. The electron beam current increases with the increasing discharge voltage following two tendencies. Under the same discharge voltage, the configuration with the larger electrode gap separation will generate higher electron beam current. When the discharge voltage is higher than 10 kV, the beam current generated at the electrode gap separation of 17.0 mm, is much higher than that generated at smaller gap separations. The ionization of the neutral gas in the main gap is inferred to contribute more to the current increase with increasing electrode gap separation.« less

Mitigation of Hot Electrons from Laser-Plasma Instabilities in Laser-Generated X-Ray Sources

NASA Astrophysics Data System (ADS)

Fein, Jeffrey R.

This thesis describes experiments to understand and mitigate energetic or "hot" electrons from laser-plasma instabilities (LPIs) in an effort to improve radiographic techniques using laser-generated x-ray sources. Initial experiments on the OMEGA-60 laser show evidence of an underlying background generated by x-rays with energies over 10 keV on radiographs using backlit pinhole radiography, whose source is consistent with hard x-rays from LPI-generated hot electrons. Mitigating this background can dramatically reduce uncertainties in measured object densities from radiographs and may be achieved by eliminating the target components in which LPIs are most likely to grow. Experiments were performed on the OMEGA-EP laser to study hot electron production from laser-plasma instabilities in high-Z plasmas relevant to laser-generated x-ray sources. Measurements of hard x-rays show a dramatic reduction in hot-electron energy going from low-Z CH to high-Z Au targets, in a manner that is consistent with steepening electron density profiles that were also measured. The profile-steepening, we infer, increased thresholds of LPIs and contributed to the reduced hot-electron production at higher Z. Possible mechanisms for generating hot electrons include the two-plasmon decay and stimulated Raman scattering instabilities driven by multiple laser beams. Radiation hydrodynamic simulations using the CRASH code predict that both of these instabilities were above threshold with linear threshold parameters that decreased with increasing Z due to steepening length-scales, as well as enhanced laser absorption and increased collisional and Landau damping of electron plasma waves. Another set of experiments were performed on the OMEGA-60 laser to test whether hard x-ray background could be mitigated in backlit pinhole imagers by controlling laser-plasma instabilities. Based on the results above, we hypothesized that LPIs and hot electrons that lead to hard x-ray background would be reduced by increasing the atomic number of the irradiated components in the pinhole imagers. Using higher-Z materials we demonstrate significant reduction in x-rays between 30-70 keV and 70% increase in the signal-to-background ratio. Based on this, a proposed backlighter and detector setup predicts a signal-to-background ratio of up to 4.5:1.

Diagnostics of laser-produced plasmas based on the analysis of intensity ratios of He-like ions X-ray emission

DOE PAGES

Ryazantsev, S. N.; Skobelev, I. Yu.; Faenov, A. Ya.; ...

2016-12-08

Here, in this paper, we detail the diagnostic technique used to infer the spatially resolved electron temperatures and densities in experiments dedicated to investigate the generation of magnetically collimated plasma jets. It is shown that the relative intensities of the resonance transitions in emitting He-like ions can be used to measure the temperature in such recombining plasmas. The intensities of these transitions are sensitive to the plasma density in the range of 10 16–10 20 cm -3 and to plasma temperature ranges from 10 to 100 eV for ions with a nuclear charge Z n ~10. We show how detailedmore » calculations of the emissivity of F VIII ions allow to determine the parameters of the plasma jets that were created using ELFIE ns laser facility (Ecole Polytechnique, France). Lastly, the diagnostic and analysis technique detailed here can be applied in a broader context than the one of this study, i.e., to diagnose any recombining plasma containing He-like fluorine ions.« less

Quantifying uncertainty in soot volume fraction estimates using Bayesian inference of auto-correlated laser-induced incandescence measurements

NASA Astrophysics Data System (ADS)

Hadwin, Paul J.; Sipkens, T. A.; Thomson, K. A.; Liu, F.; Daun, K. J.

2016-01-01

Auto-correlated laser-induced incandescence (AC-LII) infers the soot volume fraction (SVF) of soot particles by comparing the spectral incandescence from laser-energized particles to the pyrometrically inferred peak soot temperature. This calculation requires detailed knowledge of model parameters such as the absorption function of soot, which may vary with combustion chemistry, soot age, and the internal structure of the soot. This work presents a Bayesian methodology to quantify such uncertainties. This technique treats the additional "nuisance" model parameters, including the soot absorption function, as stochastic variables and incorporates the current state of knowledge of these parameters into the inference process through maximum entropy priors. While standard AC-LII analysis provides a point estimate of the SVF, Bayesian techniques infer the posterior probability density, which will allow scientists and engineers to better assess the reliability of AC-LII inferred SVFs in the context of environmental regulations and competing diagnostics.

A Robust Mass Estimator for Dark Matter Subhalo Perturbations in Strong Gravitational Lenses

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

Minor, Quinn E.; Kaplinghat, Manoj; Li, Nan

A few dark matter substructures have recently been detected in strong gravitational lenses through their perturbations of highly magnified images. We derive a characteristic scale for lensing perturbations and show that they are significantly larger than the perturber’s Einstein radius. We show that the perturber’s projected mass enclosed within this radius, scaled by the log-slope of the host galaxy’s density profile, can be robustly inferred even if the inferred density profile and tidal radius of the perturber are biased. We demonstrate the validity of our analytic derivation using several gravitational lens simulations where the tidal radii and the inner log-slopesmore » of the density profile of the perturbing subhalo are allowed to vary. By modeling these simulated data, we find that our mass estimator, which we call the effective subhalo lensing mass, is accurate to within about 10% or smaller in each case, whereas the inferred total subhalo mass can potentially be biased by nearly an order of magnitude. We therefore recommend that the effective subhalo lensing mass be reported in future lensing reconstructions, as this will allow for a more accurate comparison with the results of dark matter simulations.« less

Calibrated birth-death phylogenetic time-tree priors for bayesian inference.

PubMed

Heled, Joseph; Drummond, Alexei J

2015-05-01

Here we introduce a general class of multiple calibration birth-death tree priors for use in Bayesian phylogenetic inference. All tree priors in this class separate ancestral node heights into a set of "calibrated nodes" and "uncalibrated nodes" such that the marginal distribution of the calibrated nodes is user-specified whereas the density ratio of the birth-death prior is retained for trees with equal values for the calibrated nodes. We describe two formulations, one in which the calibration information informs the prior on ranked tree topologies, through the (conditional) prior, and the other which factorizes the prior on divergence times and ranked topologies, thus allowing uniform, or any arbitrary prior distribution on ranked topologies. Although the first of these formulations has some attractive properties, the algorithm we present for computing its prior density is computationally intensive. However, the second formulation is always faster and computationally efficient for up to six calibrations. We demonstrate the utility of the new class of multiple-calibration tree priors using both small simulations and a real-world analysis and compare the results to existing schemes. The two new calibrated tree priors described in this article offer greater flexibility and control of prior specification in calibrated time-tree inference and divergence time dating, and will remove the need for indirect approaches to the assessment of the combined effect of calibration densities and tree priors in Bayesian phylogenetic inference. © The Author(s) 2014. Published by Oxford University Press, on behalf of the Society of Systematic Biologists.

Porosity and the ecology of icy satellites

NASA Technical Reports Server (NTRS)

Croft, Steven K.

1993-01-01

The case for a significant role for porosity in the structure and evolution of icy bodies in the Solar System has been difficult to establish. We present a relevant new data set and a series of structure models including a mechanical compression, not thermal creep, model for porosity that accounts satisfactorily for observed densities, moments of inertia, geologic activity, and sizes of tectonic features on icy satellites. Several types of observational data sets have been used to infer significant porosity, but until recently, alternative explanations have been preferred. Our first area of concern is the occurrence of cryovolcanism as a function of satellite radius; simple radiogenic heating models of icy satellites suggest minimum radii for melting and surface cryovolcanism to be 400 to 500 km, yet inferred melt deposits are seen on satellites half that size. One possible explanation is a deep, low conductivity regolith which lowers conductivity and raises internal temperatures, but other possibilities include tidal heating or crustal compositions of low conductivity. Our second area of concern is the occurrence and magnitude of tectonic strain; tectonic structures have been seen on icy satellites as small as Mimas and Proteus. The structures are almost exclusively extensional, with only a few possible compression Al features, and inferred global strains are on the order of 1 percent expansion. Expansions of this order in small bodies like Mimas and prevention of late compressional tectonics due to formation of ice mantles in larger bodies like Rhea are attained only in structure models including low-conductivity, and thus possibly high porosity, crusts. Thirdly, inferred moments of inertia less than 0.4 in Mimas and Tethys can be explained by high-porosity crusts, but also by differentiation of a high density core. Finally, the relatively low densities of smaller satellites like Mimas and Miranda relative to larger neighbors can be explained by deep porosity, but also by bulk compositional differences. Recent work has strengthened the case for significant porosity. Halley's nucleus was found to have a density near 0.6 g/cu cm, Janus and Epimethus were proposed to have densities near 0.7 g/cu cm, densities almost certainly due to high porosity. The irregular-spherical shape transition of icy satellites was quantitatively explained by low conductivity regoliths. A creative structure/thermal history model for Mimas simultaneously accounts quantitatively for Mimas' low density and moment of inertia by invoking initial high-porosity and subsequent compaction in the deep interior by thermal creep. The main problem with this promising model is that approximately 7 percent predicts a reduction in Mimas' radius, implying significant compressional failure and prevention of extensional tectonics, in contradiction to the observed extensional features and inferred 1 percent expansion in radius.

Secure Mass Measurements from Transit Timing: 10 Kepler Exoplanets between 3 and 8 M⊕ with Diverse Densities and Incident Fluxes

NASA Astrophysics Data System (ADS)

Jontof-Hutter, Daniel; Ford, Eric B.; Rowe, Jason F.; Lissauer, Jack J.; Fabrycky, Daniel C.; Van Laerhoven, Christa; Agol, Eric; Deck, Katherine M.; Holczer, Tomer; Mazeh, Tsevi

2016-03-01

We infer dynamical masses in eight multiplanet systems using transit times measured from Kepler's complete data set, including short-cadence data where available. Of the 18 dynamical masses that we infer, 10 pass multiple tests for robustness. These are in systems Kepler-26 (KOI-250), Kepler-29 (KOI-738), Kepler-60 (KOI-2086), Kepler-105 (KOI-115), and Kepler-307 (KOI-1576). Kepler-105 c has a radius of 1.3 R⊕ and a density consistent with an Earth-like composition. Strong transit timing variation (TTV) signals were detected from additional planets, but their inferred masses were sensitive to outliers or consistent solutions could not be found with independently measured transit times, including planets orbiting Kepler-49 (KOI-248), Kepler-57 (KOI-1270), Kepler-105 (KOI-115), and Kepler-177 (KOI-523). Nonetheless, strong upper limits on the mass of Kepler-177 c imply an extremely low density of ˜0.1 g cm-3. In most cases, individual orbital eccentricities were poorly constrained owing to degeneracies in TTV inversion. For five planet pairs in our sample, strong secular interactions imply a moderate to high likelihood of apsidal alignment over a wide range of possible eccentricities. We also find solutions for the three planets known to orbit Kepler-60 in a Laplace-like resonance chain. However, nonlibrating solutions also match the transit timing data. For six systems, we calculate more precise stellar parameters than previously known, enabling useful constraints on planetary densities where we have secure mass measurements. Placing these exoplanets on the mass-radius diagram, we find that a wide range of densities is observed among sub-Neptune-mass planets and that the range in observed densities is anticorrelated with incident flux.

Inferring physical properties of galaxies from their emission-line spectra

NASA Astrophysics Data System (ADS)

Ucci, G.; Ferrara, A.; Gallerani, S.; Pallottini, A.

2017-02-01

We present a new approach based on Supervised Machine Learning algorithms to infer key physical properties of galaxies (density, metallicity, column density and ionization parameter) from their emission-line spectra. We introduce a numerical code (called GAME, GAlaxy Machine learning for Emission lines) implementing this method and test it extensively. GAME delivers excellent predictive performances, especially for estimates of metallicity and column densities. We compare GAME with the most widely used diagnostics (e.g. R23, [N II] λ6584/Hα indicators) showing that it provides much better accuracy and wider applicability range. GAME is particularly suitable for use in combination with Integral Field Unit spectroscopy, both for rest-frame optical/UV nebular lines and far-infrared/sub-millimeter lines arising from photodissociation regions. Finally, GAME can also be applied to the analysis of synthetic galaxy maps built from numerical simulations.

Dust Plasma Environment between Saturn's Rings and Mimas' L Shell

NASA Astrophysics Data System (ADS)

Sittler, E. C., Jr.; Johnson, R. E.

2015-12-01

We will present a new analysis of the available data on the extension of Saturn's ring atmosphere into the magnetosphere beyond the A-ring outer edge (Johnson et al. 2006) out to the orbit of Mimas. This is an interesting region in Saturn's magnetosphere containing the F and G rings and penetrated by the E-ring and the Enceladus neutral torus. This analysis will include a comparison of the Cassini Plasma Spectrometer (CAPS) plasma data, Radio and Plasma Wave Spectrometer (RPWS) plasma wave observations, RPWS Langmuir Probe (LP) observations and Cassini Dust Analyzer (CDA). The central focus will be on the dust plasma interactions. Specific attention will be paid to the SOI data for which there are considerable differences between the ion and electron densities (Elrod et al., 2012) while for other close flybys inside Mimas' L shell such differences are less obvious but the electron data appear to be highly variable. Using previous identifications of nm particles (Jones et al., 2010) inferred from CAPS data and micron sized particles that can be detected by CDA (Kempf et al., 2006) and the RPWS plasma wave dust impact signatures (Kurth et al., 2006) we will attempt to infer the full particle size distribution between the A-ring and Mimas. These nm to micron sized particles can accumulate considerable charge and under certain circumstances could account for the radial trend in the ion density described in Elrod et al. (2014) a critical issue in preparation for the Cassini proximal orbits. References: Elrod, M.K., W.-L. Tseng, R.J. Wilson, R.E. Johnson, J. Geophys. Res., 117, A03207, 2012. Elrod, M.K., W-L Tseng, A.K. Woodson, R.E. Johnson, Icarus, 242, 130-137,2014. Johnson, R. E., et al., Icarus, 180, 393-402, 2006. Jones, G. H., et al., Geophys. Res. Lett., 36, L16204, 2009. Kempf, S., U. Beckmann, R. Srama, M. Horanyi, S. Auerd, E. Grun, Planet. Space Sci., 54, 999-1006, 2006. Kurth, W. S., T.F. Averkamp, D.A. Gurnett, Z. Wang, Planet. Space Sci., 54, 988-998, 2006.

D-region Ionospheric Imaging Using VLF/LF Broadband Sferics, Forward Modeling, and Tomography

NASA Astrophysics Data System (ADS)

McCormick, J.; Cohen, M.

2017-12-01

The D-region of the ionosphere (60-90 km altitude) is highly variable on timescales from fractions of a second to many hours, and on spatial scales from 10 km to many hundreds of km. VLF and LF (3-30kHz, 30-300kHz) radio waves are guided to global distances by reflecting off of the ground and the D-region, making the Earth-ionosphere waveguide (EIWG). Therefore, information about the current state of the ionosphere is encoded in received VLF/LF radio waves since they act like probes of the D-region. The return stroke of lightning is an impulsive event that radiates powerful broadband radio emissions in VLF/LF bands known as `radio atmospherics' or `sferics'. Lightning flashes occur about 40-50 times per second throughout the Earth. An average of 2000 lightning storms occur each day with a mean duration of 30 minutes creating a broad spatial and temporal distribution of lightning VLF/LF sources. With careful processing, we can recover high fidelity measurements of amplitude and phase of both the radial and azimuthal magnetic field sferic components. By comparison to a theoretical EIWG propagation model such as the Long Wave Propagation Capability (LWPC) developed by the US Navy, with a standard forward modeling approach, we can infer information about the current state of the D-region. Typically, the ionosphere is parametrized to reduce the dimensionality of the problem which usually results in an electron density vs altitude profile. For large distances (Greater than 1000 km), these results can be interpreted as path-averaged information. In contrast to studies using navy transmitters to study the D-region, the full spectral information allows for more complete information and less ambiguous inferred ionospheric parameters. With the spatial breadth of lightning sources taken together with a broadly distributed VLF/LF receiver network, a dense set of measurements are acquired in a tomographic sense. Using the wealth of linear algebra and imaging techniques it is possible to produce a 2D image of the D-region electron density profile.

Alternative Explanations for Extreme Supersolar Iron Abundances Inferred from the Energy Spectrum of Cygnus X-1

NASA Astrophysics Data System (ADS)

Tomsick, John A.; Parker, Michael L.; García, Javier A.; Yamaoka, Kazutaka; Barret, Didier; Chiu, Jeng-Lun; Clavel, Maïca; Fabian, Andrew; Fürst, Felix; Gandhi, Poshak; Grinberg, Victoria; Miller, Jon M.; Pottschmidt, Katja; Walton, Dominic J.

2018-03-01

Here we study a 1–200 keV energy spectrum of the black hole binary Cygnus X-1 taken with NuSTAR and Suzaku. This is the first report of a NuSTAR observation of Cyg X-1 in the intermediate state, and the observation was taken during the part of the binary orbit where absorption due to the companion’s stellar wind is minimal. The spectrum includes a multi-temperature thermal disk component, a cutoff power-law component, and relativistic and nonrelativistic reflection components. Our initial fits with publicly available constant density reflection models (relxill and reflionx) lead to extremely high iron abundances (>9.96 and {10.6}-0.9+1.6 times solar, respectively). Although supersolar iron abundances have been reported previously for Cyg X-1, our measurements are much higher and such variability is almost certainly unphysical. Using a new version of reflionx that we modified to make the electron density a free parameter, we obtain better fits to the spectrum even with solar iron abundances. We report on how the higher density ({n}e=({3.98}-0.25+0.12)× {10}20 cm‑3) impacts other parameters such as the inner radius and inclination of the disk.

A framework for inference about carnivore density from unstructured spatial sampling of scat using detector dogs

Treesearch

Craig M. Thompson; J. Andrew Royle; James D. Garner

2012-01-01

Wildlife management often hinges upon an accurate assessment of population density. Although undeniably useful, many of the traditional approaches to density estimation such as visual counts, livetrapping, or mark–recapture suffer from a suite of methodological and analytical weaknesses. Rare, secretive, or highly mobile species exacerbate these problems through the...

Social networks and inference about unknown events: A case of the match between Google's AlphaGo and Sedol Lee.

PubMed

Bae, Jonghoon; Cha, Young-Jae; Lee, Hyungsuk; Lee, Boyun; Baek, Sojung; Choi, Semin; Jang, Dayk

2017-01-01

This study examines whether the way that a person makes inferences about unknown events is associated with his or her social relations, more precisely, those characterized by ego network density that reflects the structure of a person's immediate social relation. From the analysis of individual predictions over the Go match between AlphaGo and Sedol Lee in March 2016 in Seoul, Korea, this study shows that the low-density group scored higher than the high-density group in the accuracy of the prediction over a future state of a social event, i.e., the outcome of the first game. We corroborated this finding with three replication tests that asked the participants to predict the following: film awards, President Park's impeachment in Korea, and the counterfactual assessment of the US presidential election. Taken together, this study suggests that network density is negatively associated with vision advantage, i.e., the ability to discover and forecast an unknown aspect of a social event.

Electron temperatures within magnetic clouds between 2 and 4 AU: Voyager 2 observations

NASA Astrophysics Data System (ADS)

Sittler, E. C.; Burlaga, L. F.

1998-08-01

We have performed an analysis of Voyager 2 plasma electron observations within magnetic clouds between 2 and 4 AU identified by Burlaga and Behannon [1982]. The analysis has been confined to three of the magnetic clouds identified by Burlaga and Behannon that had high-quality data. The general properties of the plasma electrons within a magnetic cloud are that (1) the moment electron temperature anticorrelates with the electron density within the cloud, (2) the ratio Te/Tp tends to be >1, and (3) on average, Te/Tp~7.0. All three results are consistent with previous electron observations within magnetic clouds. Detailed analyses of the core and halo populations within the magnetic clouds show no evidence of either an anticorrelation between the core temperature TC and the electron density Ne or an anticorrelation between the halo temperature TH and the electron density. Within the magnetic clouds the halo component can contribute more than 50% of the electron pressure. The anticorrelation of Te relative to Ne can be traced to the density of the halo component relative to the density of the core component. The core electrons dominate the electron density. When the density goes up, the halo electrons contribute less to the electron pressure, so we get a lower Te. When the electron density goes down, the halo electrons contribute more to the electron pressure, and Te goes up. We find a relation between the electron pressure and density of the form Pe=αNeγ with γ~0.5.

The prevalence of terraced treescapes in analyses of phylogenetic data sets.

PubMed

Dobrin, Barbara H; Zwickl, Derrick J; Sanderson, Michael J

2018-04-04

The pattern of data availability in a phylogenetic data set may lead to the formation of terraces, collections of equally optimal trees. Terraces can arise in tree space if trees are scored with parsimony or with partitioned, edge-unlinked maximum likelihood. Theory predicts that terraces can be large, but their prevalence in contemporary data sets has never been surveyed. We selected 26 data sets and phylogenetic trees reported in recent literature and investigated the terraces to which the trees would belong, under a common set of inference assumptions. We examined terrace size as a function of the sampling properties of the data sets, including taxon coverage density (the proportion of taxon-by-gene positions with any data present) and a measure of gene sampling "sufficiency". We evaluated each data set in relation to the theoretical minimum gene sampling depth needed to reduce terrace size to a single tree, and explored the impact of the terraces found in replicate trees in bootstrap methods. Terraces were identified in nearly all data sets with taxon coverage densities < 0.90. They were not found, however, in high-coverage-density (i.e., ≥ 0.94) transcriptomic and genomic data sets. The terraces could be very large, and size varied inversely with taxon coverage density and with gene sampling sufficiency. Few data sets achieved a theoretical minimum gene sampling depth needed to reduce terrace size to a single tree. Terraces found during bootstrap resampling reduced overall support. If certain inference assumptions apply, trees estimated from empirical data sets often belong to large terraces of equally optimal trees. Terrace size correlates to data set sampling properties. Data sets seldom include enough genes to reduce terrace size to one tree. When bootstrap replicate trees lie on a terrace, statistical support for phylogenetic hypotheses may be reduced. Although some of the published analyses surveyed were conducted with edge-linked inference models (which do not induce terraces), unlinked models have been used and advocated. The present study describes the potential impact of that inference assumption on phylogenetic inference in the context of the kinds of multigene data sets now widely assembled for large-scale tree construction.

Inference for Continuous-Time Probabilistic Programming

DTIC Science & Technology

2017-12-01

Parzen window density estimator to jointly model the inter-camera travel time intervals, locations of exit/entrances, and velocities of ob- jects...asked to travel across the scene multiple times . Even in such a scenario they formed groups and made social interactions, which Fig. 7: Topology of...INFERENCE FOR CONTINUOUS- TIME PROBABILISTIC PROGRAMMING UNIVERSITY OF CALIFORNIA AT RIVERSIDE DECEMBER 2017 FINAL TECHNICAL REPORT APPROVED FOR

Observation of ionization fronts in low density foam targets

NASA Astrophysics Data System (ADS)

Hoarty, D.; Willi, O.; Barringer, L.; Vickers, C.; Watt, R.; Nazarov, W.

1999-05-01

Ionization fronts have been observed in low density chlorinated foam targets and low density foams confined in gold tubes using time resolved K-shell absorption spectroscopy. The front was driven by an intense pulse of soft x-rays produced by high power laser irradiation. The density and temperature profiles inferred from the radiographs provided detailed measurement of the conditions. The experimental data were compared to radiation hydrodynamics simulations and reasonable agreement was obtained.

Development of a high resolution x-ray spectrometer for the National Ignition Facility (NIF)

DOE PAGES

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; ...

2016-09-28

A high resolution (E/ΔE = 1200-1800) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in National Ignition Facility experiments. The instrument will be a diagnostic instrument manipulator positioned cassette designed mainly to infer electron density in compressed capsules from Stark broadening of the helium-β (1s 2-1s3p) lines of krypton and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and focus (1) the Kr Heβ complex and (2) the Heα (1s 2-1s2p) and Lyα (1s-2p) complexes onto a streak camera photocathode for time resolved measurement, and a third cylindrical or conicalmore » crystal will focus the full Heα to Heβ spectral range onto an image plate to provide a time integrated calibration spectrum. Calculations of source x-ray intensity, spectrometer throughput, and spectral resolution are presented. Furthermore, details of the conical-crystal focusing properties as well as the status of the instrumental design are also presented.« less

Bricks in historical buildings of Toledo City: characterisation and restoration

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

Lopez-Arce, Paula; Garcia-Guinea, Javier; Gracia, Mercedes

2003-01-15

Two different types of ancient bricks (12th to 14th centuries) collected from historical buildings of Toledo (Spain) were characterised by optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectrometers (SEM/EDS), electron probe microanalysis (EM), X-ray diffraction (XRD), differential thermal analysis (DTA) and {sup 57}Fe-Moessbauer spectroscopy. Physical properties such as water absorption and suction, porosity, density and compression strength were also determined. Several minerals found in the brick matrix, such as garnet, let us infer raw material sources; calcite, dolomite, illite and neoformed gehlenite and diopside phases, on temperature reached in firing; secondary calcite, on first cooling scenarios; and manganese micronodules, on latemore » pollution environments. XRD and DTA of original and refired samples supply information about firing temperatures. Additional data on firing conditions and type of the original clay are provided by the Moessbauer study. Physical properties of both types of bricks were compared and correlated with raw materials and fabric and firing technology employed. The physicochemical characterisation of these bricks provides valuable data for restoration purposes to formulate new specific bricks using neighbouring raw materials.« less

Development of a high resolution x-ray spectrometer for the National Ignition Facility (NIF).

PubMed

Hill, K W; Bitter, M; Delgado-Aparicio, L; Efthimion, P C; Ellis, R; Gao, L; Maddox, J; Pablant, N A; Schneider, M B; Chen, H; Ayers, S; Kauffman, R L; MacPhee, A G; Beiersdorfer, P; Bettencourt, R; Ma, T; Nora, R C; Scott, H A; Thorn, D B; Kilkenny, J D; Nelson, D; Shoup, M; Maron, Y

2016-11-01

A high resolution (E/ΔE = 1200-1800) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in National Ignition Facility experiments. The instrument will be a diagnostic instrument manipulator positioned cassette designed mainly to infer electron density in compressed capsules from Stark broadening of the helium-β (1s 2 -1s3p) lines of krypton and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and focus (1) the Kr Heβ complex and (2) the Heα (1s 2 -1s2p) and Lyα (1s-2p) complexes onto a streak camera photocathode for time resolved measurement, and a third cylindrical or conical crystal will focus the full Heα to Heβ spectral range onto an image plate to provide a time integrated calibration spectrum. Calculations of source x-ray intensity, spectrometer throughput, and spectral resolution are presented. Details of the conical-crystal focusing properties as well as the status of the instrumental design are also presented.

Numerical investigations of potential systematic uncertainties in iron opacity measurements at solar interior temperatures

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

Nagayama, T.; Bailey, J. E.; Loisel, G. P.

Iron opacity calculations presently disagree with measurements at an electron temperature of ~180–195 eV and an electron density of (2–4)×10 22cm –3, conditions similar to those at the base of the solar convection zone. The measurements use x rays to volumetrically heat a thin iron sample that is tamped with low-Z materials. The opacity is inferred from spectrally resolved x-ray transmission measurements. Plasma self-emission, tamper attenuation, and temporal and spatial gradients can all potentially cause systematic errors in the measured opacity spectra. In this article we quantitatively evaluate these potential errors with numerical investigations. The analysis exploits computer simulations thatmore » were previously found to reproduce the experimentally measured plasma conditions. The simulations, combined with a spectral synthesis model, enable evaluations of individual and combined potential errors in order to estimate their potential effects on the opacity measurement. Lastly, the results show that the errors considered here do not account for the previously observed model-data discrepancies.« less

A High Stability Optical Shadow Sensor With Applications for Precision Accelerometers

NASA Astrophysics Data System (ADS)

Bramsiepe, Steven G.; Loomes, David; Middlemiss, Richard P.; Paul, Douglas J.; Hammond, Giles D.

2018-05-01

Gravimeters are devices which measure changes in the value of the gravitational acceleration, \\textit{g}. This information is used to infer changes in density under the ground allowing the detection of subsurface voids; mineral, oil and gas reserves; and even the detection of the precursors of volcanic eruptions. A micro-electro mechanical system (MEMS) gravimeter has been fabricated completely in silicon allowing the possibility of cost e-effective, lightweight and small gravimeters. To obtain a measurement of gravity, a highly stable displacement measurement of the MEMS is required. This requires the development of a portable electronics system that has a displacement sensitivity of $\\leq 2.5$ nm over a period of a day or more. The portable electronics system presented here has a displacement sensitivity $\\leq 10$ nm$/\\sqrt{\\textrm{Hz}}$ ($\\leq 0.6$ nm at $1000$ s). The battery power system used a modulated LED for measurements and required temperature control of the system to $\\pm$ 2 mK, monitoring of the tilt to $\\pm$ 2 $\\mu$radians, the storage of measured data and the transmission of the data to an external server.

Spin transport properties of n-polyacene molecules (n = 1–15) connected to Ni surface electrodes: Theoretical analysis

PubMed Central

Caliskan, S.; Laref, A.

2014-01-01

Using non-equilibrium Green function formalism in conjunction with density functional theory, we explore the spin-polarized transport characteristics of several planar n-acene molecules suspended between two semi-infinite Ni electrodes via the thiol group. We examine the spin-dependence transport on Ni-n-acenes-Ni junctions, while the number of fused benzene rings varies between 1 and 15. Intriguingly, the induced magnetic moments of small acene molecules are higher than that of longer acene rings. The augmentation of fused benzene rings affects both the magnetic and transport features, such as the transmission function and conductance owing to their coupling to the Ni surface contacts via the anchoring group. The interplay between the spin-polarized transport properties, structural configuration and molecular electronic is a fortiori essential in these attractive molecular devices. Thus, this can conduct to the engineering of the electron spin transport in atomistic and molecular junctions. These prominent molecules convincingly infer that the molecular spin valves can conduct to thriving molecular devices. PMID:25482076

Numerical investigations of potential systematic uncertainties in iron opacity measurements at solar interior temperatures

DOE PAGES

Nagayama, T.; Bailey, J. E.; Loisel, G. P.; ...

2017-06-26

Iron opacity calculations presently disagree with measurements at an electron temperature of ~180–195 eV and an electron density of (2–4)×10 22cm –3, conditions similar to those at the base of the solar convection zone. The measurements use x rays to volumetrically heat a thin iron sample that is tamped with low-Z materials. The opacity is inferred from spectrally resolved x-ray transmission measurements. Plasma self-emission, tamper attenuation, and temporal and spatial gradients can all potentially cause systematic errors in the measured opacity spectra. In this article we quantitatively evaluate these potential errors with numerical investigations. The analysis exploits computer simulations thatmore » were previously found to reproduce the experimentally measured plasma conditions. The simulations, combined with a spectral synthesis model, enable evaluations of individual and combined potential errors in order to estimate their potential effects on the opacity measurement. Lastly, the results show that the errors considered here do not account for the previously observed model-data discrepancies.« less

Simultaneous SMM flat crystal spectrometer and Very Large Array observations of solar active regions

NASA Technical Reports Server (NTRS)

Lang, Kenneth R.; Willson, Robert F.; Smith, Kermit L.; Strong, Keith T.

1987-01-01

High-resolution images of the quiescent emission from two solar active regions at 20 cm (VLA) and soft X-ray (SMM FCS) wavelengths are compared. There are regions where the X-ray coronal loops have been completely imaged at 20 cm wavelength. In other regions, the X-ray radiation was detected without detectable 20 cm radiation, and vice versa. The X-ray data were used to infer average electron temperatures of about 3-million K and average electron densities of about 2.5 x 10 to the 9th/cu cm for the X-ray emitting plasma in the two active regions. The thermal bremsstrahlung of the X-ray emitting plasma is optically thin at 20 cm wavelength. The 20 cm brightness temperatures were always less than T(e), which is consistent with optically thin bremsstrahlung. The low T(B) can be explained if a higher, cooler plasma covers the hotter X-ray emitting plasma. Thermal gyroresonance radiation must account for the intense 20 cm radiation near and above sunspots where no X-ray radiation is detected.

Extracting a mix parameter from 2D radiography of variable density flow

NASA Astrophysics Data System (ADS)

Kurien, Susan; Doss, Forrest; Livescu, Daniel

2017-11-01

A methodology is presented for extracting quantities related to the statistical description of the mixing state from the 2D radiographic image of a flow. X-ray attenuation through a target flow is given by the Beer-Lambert law which exponentially damps the incident beam intensity by a factor proportional to the density, opacity and thickness of the target. By making reasonable assumptions for the mean density, opacity and effective thickness of the target flow, we estimate the contribution of density fluctuations to the attenuation. The fluctuations thus inferred may be used to form the correlation of density and specific-volume, averaged across the thickness of the flow in the direction of the beam. This correlation function, denoted by b in RANS modeling, quantifies turbulent mixing in variable density flows. The scheme is tested using DNS data computed for variable-density buoyancy-driven mixing. We quantify the deficits in the extracted value of b due to target thickness, Atwood number, and modeled noise in the incident beam. This analysis corroborates the proposed scheme to infer the mix parameter from thin targets at moderate to low Atwood numbers. The scheme is then applied to an image of counter-shear flow obtained from experiments at the National Ignition Facility. US Department of Energy.

Fingerprint-Based Structure Retrieval Using Electron Density

PubMed Central

Yin, Shuangye; Dokholyan, Nikolay V.

2010-01-01

We present a computational approach that can quickly search a large protein structural database to identify structures that fit a given electron density, such as determined by cryo-electron microscopy. We use geometric invariants (fingerprints) constructed using 3D Zernike moments to describe the electron density, and reduce the problem of fitting of the structure to the electron density to simple fingerprint comparison. Using this approach, we are able to screen the entire Protein Data Bank and identify structures that fit two experimental electron densities determined by cryo-electron microscopy. PMID:21287628

Fingerprint-based structure retrieval using electron density.

PubMed

Yin, Shuangye; Dokholyan, Nikolay V

2011-03-01

We present a computational approach that can quickly search a large protein structural database to identify structures that fit a given electron density, such as determined by cryo-electron microscopy. We use geometric invariants (fingerprints) constructed using 3D Zernike moments to describe the electron density, and reduce the problem of fitting of the structure to the electron density to simple fingerprint comparison. Using this approach, we are able to screen the entire Protein Data Bank and identify structures that fit two experimental electron densities determined by cryo-electron microscopy. Copyright © 2010 Wiley-Liss, Inc.

Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

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

Ruiz Ruiz, J.; White, A. E.; Ren, Y.

2015-12-15

Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, k{sub ⊥}ρ{sub e} ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which ismore » shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.« less

RANGE AND DENSITY OF ALIEN FISH IN WESTERN STREAMS AND RIVERS, US

EPA Science Inventory

Alien fish have become increasingly prevalent in Western U.S. waters. The EPA Environmental Monitoring and Assessment Program's Western Pilot (12 western states), which is based upon a probabilistic design, provides an opportunity to make inferences about the range and density of...

Characterization of polyploid wheat genomic diversity using a high-density 90 000 single nucleotide polymorphism array

USDA-ARS?s Scientific Manuscript database

High-density single nucleotide polymorphism (SNP) genotyping chips are a powerful tool for studying genomic patterns of diversity, inferring ancestral relationships among individuals in populations and studying marker-trait associations in mapping experiments. We developed a genotyping array includ...

Influence of uncertainties of the empirical models for inferring the E-region electric fields at the dip equator

NASA Astrophysics Data System (ADS)

Moro, Juliano; Denardini, Clezio Marcos; Resende, Laysa Cristina Araújo; Chen, Sony Su; Schuch, Nelson Jorge

2016-06-01

Daytime E-region electric fields play a crucial role in the ionospheric dynamics at the geomagnetic dip latitudes. Due to their importance, there is an interest in accurately measuring and modeling the electric fields for both climatological and near real-time studies. In this work, we present the daytime vertical ( Ez) and eastward ( Ey) electric fields for a reference quiet day (February 7, 2001) at the São Luís Space Observatory, Brazil (SLZ, 2.31°S, 44.16°W). The component Ez is inferred from Doppler shifts of type II echoes (gradient drift instability) and the anisotropic factor, which is computed from ion and electron gyro frequencies as well as ion and electron collision frequencies with neutral molecules. The component Ey depends on the ratio of Hall and Pedersen conductivities and Ez. A magnetic field-line-integrated conductivity model is used to obtain the anisotropic factor for calculating Ez and the ionospheric conductivities for calculating Ey. This model uses the NRLMSISE-00, IRI-2007, and IGRF-11 empirical models as input parameters for neutral atmosphere, ionosphere, and geomagnetic field, respectively. Consequently, it is worth determining the uncertainties (or errors) in Ey and Ez associated with these empirical model outputs in order to precisely define the confidence limit for the estimated electric field components. For this purpose, errors of ±10 % were artificially introduced in the magnitude of each empirical model output before estimating Ey and Ez. The corresponding uncertainties in the ionospheric conductivity and electric field are evaluated considering the individual and cumulative contribution of the artificial errors. The results show that the neutral densities and temperature may be responsible for the largest changes in Ey and Ez, followed by changes in the geomagnetic field intensity and electron and ions compositions.

Calibrated simulations of Z opacity experiments that reproduce the experimentally measured plasma conditions

DOE PAGES

Nagayama, T.; Bailey, J. E.; Loisel, G.; ...

2016-02-05

Recently, frequency-resolved iron opacity measurements at electron temperatures of 170–200 eV and electron densities of (0.7 – 4.0) × 10 22 cm –3 revealed a 30–400% disagreement with the calculated opacities [J. E. Bailey et al., Nature (London) 517, 56 (2015)]. The discrepancies have a high impact on astrophysics, atomic physics, and high-energy density physics, and it is important to verify our understanding of the experimental platform with simulations. Reliable simulations are challenging because the temporal and spatial evolution of the source radiation and of the sample plasma are both complex and incompletely diagnosed. In this article, we describe simulationsmore » that reproduce the measured temperature and density in recent iron opacity experiments performed at the Sandia National Laboratories Z facility. The time-dependent spectral irradiance at the sample is estimated using the measured time- and space-dependent source radiation distribution, in situ source-to-sample distance measurements, and a three-dimensional (3D) view-factor code. The inferred spectral irradiance is used to drive 1D sample radiation hydrodynamics simulations. The images recorded by slit-imaged space-resolved spectrometers are modeled by solving radiation transport of the source radiation through the sample. We find that the same drive radiation time history successfully reproduces the measured plasma conditions for eight different opacity experiments. These results provide a quantitative physical explanation for the observed dependence of both temperature and density on the sample configuration. Simulated spectral images for the experiments without the FeMg sample show quantitative agreement with the measured spectral images. The agreement in spectral profile, spatial profile, and brightness provides further confidence in our understanding of the backlight-radiation time history and image formation. Furthermore, these simulations bridge the static-uniform picture of the data interpretation and the dynamic-gradient reality of the experiments, and they will allow us to quantitatively assess the impact of effects neglected in the data interpretation.« less

Observation of quasi-periodic solar radio bursts associated with propagating fast-mode waves

NASA Astrophysics Data System (ADS)

Goddard, C. R.; Nisticò, G.; Nakariakov, V. M.; Zimovets, I. V.; White, S. M.

2016-10-01

Aims: Radio emission observations from the Learmonth and Bruny Island radio spectrographs are analysed to determine the nature of a train of discrete, periodic radio "sparks" (finite-bandwidth, short-duration isolated radio features) which precede a type II burst. We analyse extreme ultraviolet (EUV) imaging from SDO/AIA at multiple wavelengths and identify a series of quasi-periodic rapidly-propagating enhancements, which we interpret as a fast wave train, and link these to the detected radio features. Methods: The speeds and positions of the periodic rapidly propagating fast waves and the coronal mass ejection (CME) were recorded using running-difference images and time-distance analysis. From the frequency of the radio sparks the local electron density at the emission location was estimated for each. Using an empirical model for the scaling of density in the corona, the calculated electron density was used to obtain the height above the surface at which the emission occurs, and the propagation velocity of the emission location. Results: The period of the radio sparks, δtr = 1.78 ± 0.04 min, matches the period of the fast wave train observed at 171 Å, δtEUV = 1.7 ± 0.2 min. The inferred speed of the emission location of the radio sparks, 630 km s-1, is comparable to the measured speed of the CME leading edge, 500 km s-1, and the speeds derived from the drifting of the type II lanes. The calculated height of the radio emission (obtained from the density) matches the observed location of the CME leading edge. From the above evidence we propose that the radio sparks are caused by the quasi-periodic fast waves, and the emission is generated as they catch up and interact with the leading edge of the CME. The movie associated to Fig. 2 is available at http://www.aanda.org

Solar Flare Track Exposure Ages in Regolith Particles: A Calibration for Transmission Electron Microscope Measurements

NASA Technical Reports Server (NTRS)

Berger, Eve L.; Keller, Lindsay P.

2015-01-01

Mineral grains in lunar and asteroidal regolith samples provide a unique record of their interaction with the space environment. Space weathering effects result from multiple processes including: exposure to the solar wind, which results in ion damage and implantation effects that are preserved in the rims of grains (typically the outermost 100 nm); cosmic ray and solar flare activity, which result in track formation; and impact processes that result in the accumulation of vapor-deposited elements, impact melts and adhering grains on particle surfaces. Determining the rate at which these effects accumulate in the grains during their space exposure is critical to studies of the surface evolution of airless bodies. Solar flare energetic particles (mainly Fe-group nuclei) have a penetration depth of a few millimeters and leave a trail of ionization damage in insulating materials that is readily observable by transmission electron microscope (TEM) imaging. The density of solar flare particle tracks is used to infer the length of time an object was at or near the regolith surface (i.e., its exposure age). Track measurements by TEM methods are routine, yet track production rate calibrations have only been determined using chemical etching techniques [e.g., 1, and references therein]. We used focused ion beam-scanning electron microscope (FIB-SEM) sample preparation techniques combined with TEM imaging to determine the track density/exposure age relations for lunar rock 64455. The 64455 sample was used earlier by [2] to determine a track production rate by chemical etching of tracks in anorthite. Here, we show that combined FIB/TEM techniques provide a more accurate determination of a track production rate and also allow us to extend the calibration to solar flare tracks in olivine.

Novel high volumetric energy density nanostructured electrode materials for biomedical applications

NASA Astrophysics Data System (ADS)

Tong, Wei

A definitive focus is being made to develop cathode materials of higher energy and good power for primary and rechargeable lithium batteries upon the development of implantable biomedical devices (cardiac defibrillators). In this thesis, novel electroactive nanostructured silver metal oxyfluoride perovskites, Ag1+3Mo6+(O3F 3) and Ag1+3Nb5+(O2F 4) have been successfully synthesized by a mechanochemical reaction. The formation of these perovskites was investigated throughout the Ag-Mo / Nb composition range with the use of either Ag1+ or Ag 2+ in the form of AgF and AgF2 as the reactant, respectively. The compositional study combined with XRD and extensive Raman investigation was utilized to determine structure and cation distribution and infer oxidation state. An electrochemical characterization of these silver metal oxyfluoride perovskite positive electrodes for Li batteries was investigated for the first time as a function of synthesis condition, stoichiometry and effect of Mo and Ag derived second phases. A detailed in-situ electrochemical study by XAS, Raman and XRD was performed, revealing a 3 electron silver displacement or conversion reaction at > 3 V and a 2 electron reduction of Mo6+ to Mo4+ in the region < 3 V. To further improve the rate capability of silver metal oxyfluorides, metallic Ag2F phase has been successfully synthesized through the mechanochemical reaction of Ag and AgF. Its unique metallic character within Ag layers lead to a very good electronic conductivity (7.89x10 -2 S/cm). The efficacy of SMOF composites consisting of conducting matrix (carbon black, Ag2F and Ag phase) for lithium battery was investigated through discharge rate studies. Results indicated that Ag 2F phase could be utilized as an alternative conductive additive with exceptional density.

Discrete and broadband electron acceleration in Jupiter's powerful aurora.

PubMed

Mauk, B H; Haggerty, D K; Paranicas, C; Clark, G; Kollmann, P; Rymer, A M; Bolton, S J; Levin, S M; Adriani, A; Allegrini, F; Bagenal, F; Bonfond, B; Connerney, J E P; Gladstone, G R; Kurth, W S; McComas, D J; Valek, P

2017-09-06

The most intense auroral emissions from Earth's polar regions, called discrete for their sharply defined spatial configurations, are generated by a process involving coherent acceleration of electrons by slowly evolving, powerful electric fields directed along the magnetic field lines that connect Earth's space environment to its polar regions. In contrast, Earth's less intense auroras are generally caused by wave scattering of magnetically trapped populations of hot electrons (in the case of diffuse aurora) or by the turbulent or stochastic downward acceleration of electrons along magnetic field lines by waves during transitory periods (in the case of broadband or Alfvénic aurora). Jupiter's relatively steady main aurora has a power density that is so much larger than Earth's that it has been taken for granted that it must be generated primarily by the discrete auroral process. However, preliminary in situ measurements of Jupiter's auroral regions yielded no evidence of such a process. Here we report observations of distinct, high-energy, downward, discrete electron acceleration in Jupiter's auroral polar regions. We also infer upward magnetic-field-aligned electric potentials of up to 400 kiloelectronvolts, an order of magnitude larger than the largest potentials observed at Earth. Despite the magnitude of these upward electric potentials and the expectations from observations at Earth, the downward energy flux from discrete acceleration is less at Jupiter than that caused by broadband or stochastic processes, with broadband and stochastic characteristics that are substantially different from those at Earth.

Constraining Mass Anomalies Using Trans-dimensional Gravity Inversions

NASA Astrophysics Data System (ADS)

Izquierdo, K.; Montesi, L.; Lekic, V.

2016-12-01

The density structure of planetary interiors constitutes a key constraint on their composition, temperature, and dynamics. This has motivated the development of non-invasive methods to infer 3D distribution of density anomalies within a planet's interior using gravity observations made from the surface or orbit. On Earth, this information can be supplemented by seismic and electromagnetic observations, but such data are generally not available on other planets and inferences must be made from gravity observations alone. Unfortunately, inferences of density anomalies from gravity are non-unique and even the dimensionality of the problem - i.e., the number of density anomalies detectable in the planetary interior - is unknown. In this project, we use the Reversible Jump Markov chain Monte Carlo (RJMCMC) algorithm to approach gravity inversions in a trans-dimensional way, that is, considering the magnitude of the mass, the latitude, longitude, depth and number of anomalies itself as unknowns to be constrained by the observed gravity field at the surface of a planet. Our approach builds upon previous work using trans-dimensional gravity inversions in which the density contrast between the anomaly and the surrounding material is known. We validate the algorithm by analyzing a synthetic gravity field produced by a known density structure and comparing the retrieved and input density structures. We find excellent agreement between the input and retrieved structure when working in 1D and 2D domains. However, in 3D domains, comprehensive exploration of the much larger space of possible models makes search efficiency a key ingredient in successful gravity inversion. We find that upon a sufficiently long RJMCMC run, it is possible to use statistical information to recover a predicted model that matches the real model. We argue that even more complex problems, such as those involving real gravity acceleration data of a planet as the constraint, our trans-dimensional gravity inversion algorithm provides a good option to overcome the problem of non-uniqueness while achieving parsimony in gravity inversions.

Model of electron pairs in electron-doped cuprates

NASA Astrophysics Data System (ADS)

Singh, R. J.; Khan, Shakeel

2016-07-01

In the order parameter of hole-doped cuprate superconductors in the pseudogap phase, two holes enter the order parameter from opposite sides and pass through various CuO2 cells jumping from one O2- to the other under the influence of magnetic field offered by the Cu2+ ions in that CuO2 cell and thus forming hole pairs. In the pseudogap phase of electron-doped cuprates, two electrons enter the order parameter at Cu2+ sites from opposite ends and pass from one Cu2+ site to the diagonally opposite Cu2+ site. Following this type of path, they are subjected to high magnetic fields from various Cu2+ ions in that cell. They do not travel from one Cu2+ site to the other along straight path but by helical path. As they pass through the diagonal, they face high to low to very high magnetic field. Therefore, frequency of helical motion and pitch goes on changing with the magnetic field. Just before reaching the Cu2+ ions at the exit points of all the cells, the pitch of the helical motion is enormously decreased and thus charge density at these sites is increased. So the velocity of electrons along the diagonal path is decreased. Consequently, transition temperature of electron-doped cuprates becomes less than that of hole-doped cuprates. Symmetry of the order parameter of the electron-doped cuprates has been found to be of 3dx2-y2 + iS type. It has been inferred that internal magnetic field inside the order parameter reconstructs the Fermi surface, which is requisite for superconductivity to take place. Electron pairs formed in the pseudogap phase are the precursors of superconducting order parameter when cooled below Tc.

Electronic energy density in chemical reaction systems

NASA Astrophysics Data System (ADS)

Tachibana, Akitomo

2001-08-01

The energy of chemical reaction is visualized in real space using the electronic energy density nE(r⃗) associated with the electron density n(r⃗). The electronic energy density nE(r⃗) is decomposed into the kinetic energy density nT(r⃗), the external potential energy density nV(r⃗), and the interelectron potential energy density nW(r⃗). Using the electronic energy density nE(r⃗) we can pick up any point in a chemical reaction system and find how the electronic energy E is assigned to the selected point. We can then integrate the electronic energy density nE(r⃗) in any region R surrounding the point and find out the regional electronic energy ER to the global E. The kinetic energy density nT(r⃗) is used to identify the intrinsic shape of the reactants, the electronic transition state, and the reaction products along the course of the chemical reaction coordinate. The intrinsic shape is identified with the electronic interface S that discriminates the region RD of the electronic drop from the region RA of the electronic atmosphere in the density distribution of the electron gas. If the R spans the whole space, then the integral gives the total E. The regional electronic energy ER in thermodynamic ensemble is realized in electrochemistry as the intrinsic Volta electric potential φR and the intrinsic Herring-Nichols work function ΦR. We have picked up first a hydrogen-like atom for which we have analytical exact expressions of the relativistic kinetic energy density nTM(r⃗) and its nonrelativistic version nT(r⃗). These expressions are valid for any excited bound states as well as the ground state. Second, we have selected the following five reaction systems and show the figures of the nT(r⃗) as well as the other energy densities along the intrinsic reaction coordinates: a protonation reaction to He, addition reactions of HF to C2H4 and C2H2, hydrogen abstraction reactions of NH3+ from HF and NH3. Valence electrons possess their unique delocalized drop region remote from those heavily localized drop regions adhered to core electrons. The kinetic energy density nT(r⃗) and the tension density τ⃗S(r⃗) can vividly demonstrate the formation of the chemical bond. Various basic chemical concepts in these chemical reaction systems have been clearly visualized in real three-dimensional space.

PHYSICAL CONDITIONS OF CORONAL PLASMA AT THE TRANSIT OF A SHOCK DRIVEN BY A CORONAL MASS EJECTION

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

Susino, R.; Bemporad, A.; Mancuso, S., E-mail: susino@oato.inaf.it

2015-10-20

We report here on the determination of plasma physical parameters across a shock driven by a coronal mass ejection using white light (WL) coronagraphic images and radio dynamic spectra (RDS). The event analyzed here is the spectacular eruption that occurred on 2011 June 7, a fast CME followed by the ejection of columns of chromospheric plasma, part of them falling back to the solar surface, associated with a M2.5 flare and a type-II radio burst. Images acquired by the Solar and Heliospheric Observatory/LASCO coronagraphs (C2 and C3) were employed to track the CME-driven shock in the corona between 2–12 R{submore » ⊙} in an angular interval of about 110°. In this interval we derived two-dimensional (2D) maps of electron density, shock velocity, and shock compression ratio, and we measured the shock inclination angle with respect to the radial direction. Under plausible assumptions, these quantities were used to infer 2D maps of shock Mach number M{sub A} and strength of coronal magnetic fields at the shock's heights. We found that in the early phases (2–4 R{sub ⊙}) the whole shock surface is super-Alfvénic, while later on (i.e., higher up) it becomes super-Alfvénic only at the nose. This is in agreement with the location for the source of the observed type-II burst, as inferred from RDS combined with the shock kinematic and coronal densities derived from WL. For the first time, a coronal shock is used to derive a 2D map of the coronal magnetic field strength over intervals of 10 R{sub ⊙} altitude and ∼110° latitude.« less

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

Gerber, S.; Jang, H.; Nojiri, H.

In this study, charge density wave (CDW) correlations have recently been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa 2Cu 3O 6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. Themore » field-induced CDW onsets around the zero-field superconducting transition temperature, yet the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.« less

Determining the nature of excitonic dephasing in high-quality GaN/AlGaN quantum wells through time-resolved and spectrally resolved four-wave mixing spectroscopy

NASA Astrophysics Data System (ADS)

Gallart, M.; Ziegler, M.; Crégut, O.; Feltin, E.; Carlin, J.-F.; Butté, R.; Grandjean, N.; Hönerlage, B.; Gilliot, P.

2017-07-01

Applying four-wave mixing spectroscopy to a high-quality GaN/AlGaN single quantum well, we report on the experimental determination of excitonic dephasing times at different temperatures and exciton densities in III-nitride heterostructures. By comparing the evolution with the temperature of the dephasing and the spin-relaxation rate, we conclude that both processes are related to the rate of excitonic collisions. When spin relaxation occurs in the motional-narrowing regime, it remains constant over a large temperature range as the spin-precession frequency increases linearly with temperature, hence compensating for the observed decrease in the dephasing time. From those measurements, a value of the electron-hole exchange interaction strength of 0.45 meV at T =10 K is inferred.

Ultra-Intense Short-Pulse Pair Creation Using the Texas Petawatt Laser

NASA Astrophysics Data System (ADS)

Liang, Edison; Henderson, Alexander; Clarke, Taylor; Taylor, Devin; Chaguine, Petr; Serratto, Kristina; Riley, Nathan; Dyer, Gilliss; Donovan, Michael; Ditmire, Todd

2013-10-01

We report results from the 2012 pair creation experiment using the Texas Petawatt Laser. Up to 1011 positrons per steradian were detected using 100 Joule pulses from the Texas Petawatt Laser to irradiate gold targets, with peak laser intensities up to 1.9 × 1021W/cm2 and pulse durations as short as 130 fs. Positron-to-electron ratios exceeding 20% were measured on some shots. The positron energy, positron yield per unit laser energy, and inferred positron density are significantly higher than those reported in previous experiments. This confirms that, for a given laser energy, higher intensity and shorter pulses irradiating thicker targets are more favorable for pair creation. Narrow-band high-energy positrons up to 23 MeV were observed from thin targets. Supported by DOE Grant DE-SC-0001481 and Rice FIF.

Measurement of the hot spot electron temperature in NIF ICF implosions using Krypton x-ray emission spectroscopy

NASA Astrophysics Data System (ADS)

Ma, T.; Chen, H.; Patel, P. K.; Schneider, M.; Barrios, M.; Berzak Hopkins, L.; Casey, D.; Chung, H.-K.; Hammel, B.; Jarrott, C.; Nora, R.; Pak, A.; Scott, H.; Spears, B.; Weber, C.

2015-11-01

The inference of ion temperature from neutron spectral measurements in indirect-drive ICF implosions is known to be sensitive to non-thermal velocity distributions in the fuel. The electron temperature (Te) inferred from dopant line ratios should not be sensitive to these bulk motions and hence may be a better measure of the thermal temperature of the hot spot. Here we describe a series of experiments to be conducted on the NIF where a small concentration of a mid-Z dopant (Krypton) is added to the fuel gas. The x-ray spectra is measured and the electron temperature is inferred from Kr line ratios. We also quantify the level of radiative cooling in the hot spot due to this mid-Z dopant. These experiments represent the first direct measurement of hot spot Te using spectroscopy, and we will describe the considerations for applying x-ray spectroscopy in such dense and non-uniform hot spots. This work performed under the auspices of U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Field dynamics inference via spectral density estimation

NASA Astrophysics Data System (ADS)

Frank, Philipp; Steininger, Theo; Enßlin, Torsten A.

2017-11-01

Stochastic differential equations are of utmost importance in various scientific and industrial areas. They are the natural description of dynamical processes whose precise equations of motion are either not known or too expensive to solve, e.g., when modeling Brownian motion. In some cases, the equations governing the dynamics of a physical system on macroscopic scales occur to be unknown since they typically cannot be deduced from general principles. In this work, we describe how the underlying laws of a stochastic process can be approximated by the spectral density of the corresponding process. Furthermore, we show how the density can be inferred from possibly very noisy and incomplete measurements of the dynamical field. Generally, inverse problems like these can be tackled with the help of Information Field Theory. For now, we restrict to linear and autonomous processes. To demonstrate its applicability, we employ our reconstruction algorithm on a time-series and spatiotemporal processes.

Field dynamics inference via spectral density estimation.

PubMed

Frank, Philipp; Steininger, Theo; Enßlin, Torsten A

2017-11-01

Stochastic differential equations are of utmost importance in various scientific and industrial areas. They are the natural description of dynamical processes whose precise equations of motion are either not known or too expensive to solve, e.g., when modeling Brownian motion. In some cases, the equations governing the dynamics of a physical system on macroscopic scales occur to be unknown since they typically cannot be deduced from general principles. In this work, we describe how the underlying laws of a stochastic process can be approximated by the spectral density of the corresponding process. Furthermore, we show how the density can be inferred from possibly very noisy and incomplete measurements of the dynamical field. Generally, inverse problems like these can be tackled with the help of Information Field Theory. For now, we restrict to linear and autonomous processes. To demonstrate its applicability, we employ our reconstruction algorithm on a time-series and spatiotemporal processes.

Measurements of plasma sheath heat flux in the Alcator C-Mod divertor

NASA Astrophysics Data System (ADS)

Brunner, Dan; Labombard, Brian; Terry, Jim; Reinke, Matt

2010-11-01

Heat flux is one of the most important parameters controlling the lifetime of first-wall components in fusion experiments and reactors. The sheath heat flux coefficient (γ) is a parameter relating heat flux (from a plasma to a material surface) to the electron temperature and ion saturation current. Being such a simple expression for a kinetic process, it is of great interest to plasma edge fluid modelers. Under the assumptions of equal ion and electron temperatures, no secondary electron emission, and no net current to the surface the value of γ is approximately 7 [1]. Alcator C-Mod provides a unique opportunity among today's experiments to measure reactor-relevant heat fluxes (100's of MW/m^2 parallel to the magnetic field) in reactor-like divertor geometry. Motivated by the DoE 2010 joint milestone to measure heat flux footprints, the lower outer divertor of Alcator has been instrumented with a suite of Langmuir probes, novel surface thermocouples, and calorimeters in tiles purposefully ramped to eliminate shadowing; all within view of an IR camera. Initial results indicate that the experimentally inferred values of γ are found to agree with simple theory in the sheath limited regime and diverges to lower values as the density increases.

Shack-Hartmann Electron Densitometer (SHED): An Optical System for Diagnosing Free Electron Density in Laser-Produced Plasmas

DTIC Science & Technology

2016-11-01

a few nanoseconds. The challenge remains to diagnose plasmas via the free electron density in this short window of time and often in a small volume ...Free Electron Density in Laser-Produced Plasmas by Anthony R Valenzuela Approved for public release; distribution is...US Army Research Laboratory Shack-Hartmann Electron Densitometer (SHED): An Optical System for Diagnosing Free Electron Density in Laser

Pragmatic Inference Abilities in Individuals with Asperger Syndrome or High-Functioning Autism. A Review

ERIC Educational Resources Information Center

Loukusa, Soile; Moilanen, Irma

2009-01-01

This review summarizes studies involving pragmatic language comprehension and inference abilities in individuals with Asperger syndrome or high-functioning autism. Systematic searches of three electronic databases, selected journals, and reference lists identified 20 studies meeting the inclusion criteria. These studies were evaluated in terms of:…

ON THE ORIGIN OF THE {gamma}-RAY/OPTICAL LAGS IN LUMINOUS BLAZARS

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

Janiak, Mateusz; Sikora, Marek; Moderski, Rafal

2012-12-01

Blazars are strongly variable sources that occasionally show spectacular flares visible in various energy bands. These flares are often, but not always, correlated. In a number of cases, the peaks of optical flares are found to be somewhat delayed with respect to the {gamma}-ray peaks. One notable example of such a delay was found in 3C 279 by Hayashida et al. and interpreted as a result of steeper drop with a distance of the energy density of an external radiation field than of the magnetic energy density. In this paper, we demonstrate that, in general, depending on the respective energymore » density profile along the jet, such lags can have both signs and that they can take place for any ratio of these energy densities. We study the dependence of such lags on the ratio of these energy densities at a distance of a maximal energy dissipation in a jet, on their gradients, as well as on the time profile of the relativistic electron injection within the moving source. We show how prominent such lags can be, and their expected timescales. We suggest that studies of such lags can provide a powerful tool to resolve the structure of relativistic jets and their radiative environment. As an example we model the lag observed in 3C 279, showing that in this object the flare is produced at a distance of a few parsecs from the central black hole, consistent with our previous inferences based on the spectra and optical polarization properties.« less

Non-thermal pressure in the outskirts of Abell 2142

NASA Astrophysics Data System (ADS)

Fusco-Femiano, Roberto; Lapi, Andrea

2018-03-01

Clumping and turbulence are expected to affect the matter accreted on to the outskirts of galaxy clusters. To determine their impact on the thermodynamic properties of Abell 2142, we perform an analysis of the X-ray temperature data from XMM-Newton via our SuperModel, a state-of-the-art tool for investigating the astrophysics of the intracluster medium already tested on many individual clusters (since Cavaliere, Lapi & Fusco-Femiano 2009). Using the gas density profile corrected for clumpiness derived by Tchernin et al. (2016), we find evidence for the presence of a non-thermal pressure component required to sustain gravity in the cluster outskirts of Abell 2142, that amounts to about 30 per cent of the total pressure at the virial radius. The presence of the non-thermal component implies the gas fraction to be consistent with the universal value at the virial radius and the electron thermal pressure profile to be in good agreement with that inferred from the SZ data. Our results indicate that the presence of gas clumping and of a non-thermal pressure component are both necessary to recover the observed physical properties in the cluster outskirts. Moreover, we stress that an alternative method often exploited in the literature (included Abell 2142) to determine the temperature profile kBT = Pe/ne basing on a combination of the Sunyaev-Zel'dovich (SZ) pressure Pe and of the X-ray electron density ne does not allow us to highlight the presence of non-thermal pressure support in the cluster outskirts.

Electron dynamics in high energy density plasma bunch generation driven by intense picosecond laser pulse

NASA Astrophysics Data System (ADS)

Li, M.; Yuan, T.; Xu, Y. X.; Luo, S. N.

2018-05-01

When an intense picosecond laser pulse is loaded upon a dense plasma, a high energy density plasma bunch, including electron bunch and ion bunch, can be generated in the target. We simulate this process through one-dimensional particle-in-cell simulation and find that the electron bunch generation is mainly due to a local high energy density electron sphere originated in the plasma skin layer. Once generated the sphere rapidly expands to compress the surrounding electrons and induce high density electron layer, coupled with that, hot electrons are efficiently triggered in the local sphere and traveling in the whole target. Under the compressions of light pressure, forward-running and backward-running hot electrons, a high energy density electron bunch generates. The bunch energy density is as high as TJ/m3 order of magnitude in our conditions, which is significant in laser driven dynamic high pressure generation and may find applications in high energy density physics.

Thermally Driven One-Fluid Electron-Proton Solar Wind: Eight-Moment Approximation

NASA Astrophysics Data System (ADS)

Olsen, Espen Lyngdal; Leer, Egil

1996-05-01

In an effort to improve the "classical" solar wind model, we study an eight-moment approximation hydrodynamic solar wind model, in which the full conservation equation for the heat conductive flux is solved together with the conservation equations for mass, momentum, and energy. We consider two different cases: In one model the energy flux needed to drive the solar wind is supplied as heat flux from a hot coronal base, where both the density and temperature are specified. In the other model, the corona is heated. In that model, the coronal base density and temperature are also specified, but the temperature increases outward from the coronal base due to a specified energy flux that is dissipated in the corona. The eight-moment approximation solutions are compared with the results from a "classical" solar wind model in which the collision-dominated gas expression for the heat conductive flux is used. It is shown that the "classical" expression for the heat conductive flux is generally not valid in the solar wind. In collisionless regions of the flow, the eight-moment approximation gives a larger thermalization of the heat conductive flux than the models using the collision-dominated gas approximation for the heat flux, but the heat flux is still larger than the "saturation heat flux." This leads to a breakdown of the electron distribution function, which turns negative in the collisionless region of the flow. By increasing the interaction between the electrons, the heat flux is reduced, and a reasonable shape is obtained on the distribution function. By solving the full set of equations consistent with the eight-moment distribution function for the electrons, we are thus able to draw inferences about the validity of the eight-moment description of the solar wind as well as the validity of the very commonly used collision-dominated gas approximation for the heat conductive flux in the solar wind.

Adsorption of alanine with heteroatom substituted fullerene for solar cell application: A DFT study.

PubMed

Dheivamalar, S; Sugi, L; Ravichandran, K; Sriram, S

2018-09-05

C 20 is the most important fullerene cage and alanine is the simplest representation of a backbone unit of the protein. The absorption feasibility of alanine molecule in the Si-doped C 20 and B-doped C 20 fullerenes has been studied based on calculated electronic properties of fullerenes using density functional theory (DFT). In this work, we explore the ability of Si-doped C 20 , B-doped C 20 fullerene to interact with alanine at the DFT-B3LYP/6-31G, RHF level of theory. We find that noticeable structural change takes place in C 20 when one of its carbon is substituted with Si or B. The molecular geometry, electronic properties and vibrational analysis have also been performed on the title compounds. The NMR study reveals the aromaticity of the pure and doped fullerene compounds. Stability of the doped fullerene - alanine compound arises from hyper conjugative interactions. It leads to one of the major property of bioactivity, charge transfer and delocalization of charge and this properties has been analyzed using Natural Bond Orbital (NBO) analysis. The energy gap of the doped fullerene reveals that there is a decrease in the size of energy gap significantly, making them more reactive as compared to C 20 fullerene. Theoretical studies of the electronic spectra by using time - dependent density functional theory (TD-DFT) method were helpful to interpret the observed electronic transition state. We aim to optimize the performance of the solar cells by altering the frontier orbital energy gaps. Considering all studied properties, it may be inferred that the applicability of C 20 fullerene as the non-linear optical (NLO) material and its NLO property would increase on doping fullerene with Si and B atom. Specifically C 19 Si would be better among them. Copyright © 2018. Published by Elsevier B.V.

Teaching machines to find mantle composition

NASA Astrophysics Data System (ADS)

Atkins, Suzanne; Tackley, Paul; Trampert, Jeannot; Valentine, Andrew

2017-04-01

The composition of the mantle affects many geodynamical processes by altering factors such as the density, the location of phase changes, and melting temperature. The inferences we make about mantle composition also determine how we interpret the changes in velocity, reflections, attenuation and scattering seen by seismologists. However, the bulk composition of the mantle is very poorly constrained. Inferences are made from meteorite samples, rock samples from the Earth and inferences made from geophysical data. All of these approaches require significant assumptions and the inferences made are subject to large uncertainties. Here we present a new method for inferring mantle composition, based on pattern recognition machine learning, which uses large scale in situ observations of the mantle to make fully probabilistic inferences of composition for convection simulations. Our method has an advantage over other petrological approaches because we use large scale geophysical observations. This means that we average over much greater length scales and do not need to rely on extrapolating from localised samples of the mantle or planetary disk. Another major advantage of our method is that it is fully probabilistic. This allows us to include all of the uncertainties inherent in the inference process, giving us far more information about the reliability of the result than other methods. Finally our method includes the impact of composition on mantle convection. This allows us to make much more precise inferences from geophysical data than other geophysical approaches, which attempt to invert one observation with no consideration of the relationship between convection and composition. We use a sampling based inversion method, using hundreds of convection simulations run using StagYY with self consistent mineral physics properties calculated using the PerpleX package. The observations from these simulations are used to train a neural network to make a probabilistic inference for major element oxide composition of the mantle. We find we can constrain bulk mantle FeO molar percent, FeO/MgO and FeO/SiO2 using observations of the temperature and density structure of the mantle in convection simulations.

Effective Online Bayesian Phylogenetics via Sequential Monte Carlo with Guided Proposals

PubMed Central

Fourment, Mathieu; Claywell, Brian C; Dinh, Vu; McCoy, Connor; Matsen IV, Frederick A; Darling, Aaron E

2018-01-01

Abstract Modern infectious disease outbreak surveillance produces continuous streams of sequence data which require phylogenetic analysis as data arrives. Current software packages for Bayesian phylogenetic inference are unable to quickly incorporate new sequences as they become available, making them less useful for dynamically unfolding evolutionary stories. This limitation can be addressed by applying a class of Bayesian statistical inference algorithms called sequential Monte Carlo (SMC) to conduct online inference, wherein new data can be continuously incorporated to update the estimate of the posterior probability distribution. In this article, we describe and evaluate several different online phylogenetic sequential Monte Carlo (OPSMC) algorithms. We show that proposing new phylogenies with a density similar to the Bayesian prior suffers from poor performance, and we develop “guided” proposals that better match the proposal density to the posterior. Furthermore, we show that the simplest guided proposals can exhibit pathological behavior in some situations, leading to poor results, and that the situation can be resolved by heating the proposal density. The results demonstrate that relative to the widely used MCMC-based algorithm implemented in MrBayes, the total time required to compute a series of phylogenetic posteriors as sequences arrive can be significantly reduced by the use of OPSMC, without incurring a significant loss in accuracy. PMID:29186587

The interior structure of Ceres as revealed by surface topography

NASA Astrophysics Data System (ADS)

Fu, Roger R.; Ermakov, Anton I.; Marchi, Simone; Castillo-Rogez, Julie C.; Raymond, Carol A.; Hager, Bradford H.; Zuber, Maria T.; King, Scott D.; Bland, Michael T.; Cristina De Sanctis, Maria; Preusker, Frank; Park, Ryan S.; Russell, Christopher T.

2017-10-01

Ceres, the largest body in the asteroid belt (940 km diameter), provides a unique opportunity to study the interior structure of a volatile-rich dwarf planet. Variations in a planetary body's subsurface rheology and density affect the rate of topographic relaxation. Preferential attenuation of long wavelength topography (≥150 km) on Ceres suggests that the viscosity of its crust decreases with increasing depth. We present finite element (FE) geodynamical simulations of Ceres to identify the internal structures and compositions that best reproduce its topography as observed by the NASA Dawn mission. We infer that Ceres has a mechanically strong crust with maximum effective viscosity ∼1025 Pa s. Combined with density constraints, this rheology suggests a crustal composition of carbonates or phyllosilicates, water ice, and at least 30 volume percent (vol.%) low-density, high-strength phases most consistent with salt and/or clathrate hydrates. The inference of these crustal materials supports the past existence of a global ocean, consistent with the observed surface composition. Meanwhile, we infer that the uppermost ≥60 km of the silicate-rich mantle is mechanically weak with viscosity <1021 Pa s, suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes.

Bayesian inference based on stationary Fokker-Planck sampling.

PubMed

Berrones, Arturo

2010-06-01

A novel formalism for bayesian learning in the context of complex inference models is proposed. The method is based on the use of the stationary Fokker-Planck (SFP) approach to sample from the posterior density. Stationary Fokker-Planck sampling generalizes the Gibbs sampler algorithm for arbitrary and unknown conditional densities. By the SFP procedure, approximate analytical expressions for the conditionals and marginals of the posterior can be constructed. At each stage of SFP, the approximate conditionals are used to define a Gibbs sampling process, which is convergent to the full joint posterior. By the analytical marginals efficient learning methods in the context of artificial neural networks are outlined. Offline and incremental bayesian inference and maximum likelihood estimation from the posterior are performed in classification and regression examples. A comparison of SFP with other Monte Carlo strategies in the general problem of sampling from arbitrary densities is also presented. It is shown that SFP is able to jump large low-probability regions without the need of a careful tuning of any step-size parameter. In fact, the SFP method requires only a small set of meaningful parameters that can be selected following clear, problem-independent guidelines. The computation cost of SFP, measured in terms of loss function evaluations, grows linearly with the given model's dimension.

The interior structure of Ceres as revealed by surface topography

USGS Publications Warehouse

Fu, Roger R.; Ermakov, Anton; Marchi, Simone; Castillo-Rogez, Julie C.; Raymond, Carol A.; Hager, Bradford; Zuber, Maria; King, Scott D.; Bland, Michael T.; De Sanctis, Maria Cristina; Preusker, Frank; Park, Ryan S.; Russell, Christopher T.

2017-01-01

Ceres, the largest body in the asteroid belt (940 km diameter), provides a unique opportunity to study the interior structure of a volatile-rich dwarf planet. Variations in a planetary body's subsurface rheology and density affect the rate of topographic relaxation. Preferential attenuation of long wavelength topography (≥150 km) on Ceres suggests that the viscosity of its crust decreases with increasing depth. We present finite element (FE) geodynamical simulations of Ceres to identify the internal structures and compositions that best reproduce its topography as observed by the NASA Dawn mission. We infer that Ceres has a mechanically strong crust with maximum effective viscosity ∼1025 Pa s. Combined with density constraints, this rheology suggests a crustal composition of carbonates or phyllosilicates, water ice, and at least 30 volume percent (vol.%) low-density, high-strength phases most consistent with salt and/or clathrate hydrates. The inference of these crustal materials supports the past existence of a global ocean, consistent with the observed surface composition. Meanwhile, we infer that the uppermost ≥60 km of the silicate-rich mantle is mechanically weak with viscosity <1021 Pa s, suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes.

Advanced density profile reflectometry; the state-of-the-art and measurement prospects for ITER

NASA Astrophysics Data System (ADS)

Doyle, E. J.

2006-10-01

Dramatic progress in millimeter-wave technology has allowed the realization of a key goal for ITER diagnostics, the routine measurement of the plasma density profile from millimeter-wave radar (reflectometry) measurements. In reflectometry, the measured round-trip group delay of a probe beam reflected from a plasma cutoff is used to infer the density distribution in the plasma. Reflectometer systems implemented by UCLA on a number of devices employ frequency-modulated continuous-wave (FM-CW), ultrawide-bandwidth, high-resolution radar systems. One such system on DIII-D has routinely demonstrated measurements of the density profile over a range of electron density of 0-6.4x10^19,m-3, with ˜25 μs time and ˜4 mm radial resolution, meeting key ITER requirements. This progress in performance was made possible by multiple advances in the areas of millimeter-wave technology, novel measurement techniques, and improved understanding, including: (i) fast sweep, solid-state, wide bandwidth sources and power amplifiers, (ii) dual polarization measurements to expand the density range, (iii) adaptive radar-based data analysis with parallel processing on a Unix cluster, (iv) high memory depth data acquisition, and (v) advances in full wave code modeling. The benefits of advanced system performance will be illustrated using measurements from a wide range of phenomena, including ELM and fast-ion driven mode dynamics, L-H transition studies and plasma-wall interaction. The measurement capabilities demonstrated by these systems provide a design basis for the development of the main ITER profile reflectometer system. This talk will explore the extent to which these reflectometer system designs, results and experience can be translated to ITER, and will identify what new studies and experimental tests are essential.

Density of the lunar interior.

NASA Technical Reports Server (NTRS)

Gast, P. W.; Giuli, R. T.

1972-01-01

It is attempted to derive the constraints that can be placed on the density of the lunar interior. The moment of inertia of the moon and its mean density are being considered in the investigation together with the mass and density of the lunar crust that have been inferred from the seismic refraction data recorded by the passive seismometer. The calculations presented show that the density of the lunar interior can easily approach values as high as 3.5 for a fraction of the lunar mass which lies in the range from 1/2 to 2/3.

Where the wild things are: informal experience and ecological reasoning.

PubMed

Coley, John D

2012-01-01

Category-based induction requires selective use of different relations to guide inferences; this article examines the development of inferences based on ecological relations among living things. Three hundred and forty-six 6-, 8-, and 10-year-old children from rural, suburban, and urban communities projected novel diseases or insides from one species to an ecologically or taxonomically related species; they were also surveyed about hobbies and activities. Frequency of ecological inferences increased with age and with reports of informal exploration of nature, and decreased with population density. By age 10, children preferred taxonomic inferences for insides and ecological inferences for disease, but this pattern emerged earlier among rural children. These results underscore the importance of context by demonstrating effects of both domain-relevant experience and environment on biological reasoning. © 2012 The Authors. Child Development © 2012 Society for Research in Child Development, Inc.

Unbiased Inference of the Masses of Transiting Planets from Radial Velocity Follow-up

NASA Astrophysics Data System (ADS)

Montet, Benjamin T.

2018-05-01

Data from the TESS mission will be used to discover hundreds of small planets amenable to radial velocity (RV) followup. Often, RV observations are obtained until a particular fractional precision on the inferred mass is achieved. I show that when the decision to stop collecting RV observations depends on the mass inferred from already-collected data, this will bias mass measurements upward, particularly when the fixed length of RV observing campaigns is considered. I suggest that observing teams should determine their observing strategy for each star before any data are collected, and all stopping criteria should not directly depend on the inferred mass. Observing teams should explicitly publish both their criteria for observing targets and deciding to end their observations, as well as their mass non-detections to avoid introducing biases into the masses---and thus inferences on the densities, compositions, and atmospheres---of transiting planets.

Measurement of electron-ion relaxation in warm dense copper

DOE PAGES

Cho, B. I.; Ogitsu, T.; Engelhorn, K.; ...

2016-01-06

Experimental investigation of electron-ion coupling and electron heat capacity of copper in warm and dense states are presented. From time-resolved x-ray absorption spectroscopy, the temporal evolution of electron temperature is obtained for non-equilibrium warm dense copper heated by an intense femtosecond laser pulse. Electron heat capacity and electron-ion coupling are inferred from the initial electron temperature and its decrease over 10 ps. As a result, data are compared with various theoretical models.

The topology of the Coulomb potential density. A comparison with the electron density, the virial energy density, and the Ehrenfest force density.

PubMed

Ferreira, Lizé-Mari; Eaby, Alan; Dillen, Jan

2017-12-15

The topology of the Coulomb potential density has been studied within the context of the theory of Atoms in Molecules and has been compared with the topologies of the electron density, the virial energy density and the Ehrenfest force density. The Coulomb potential density is found to be mainly structurally homeomorphic with the electron density. The Coulomb potential density reproduces the non-nuclear attractor which is observed experimentally in the molecular graph of the electron density of a Mg dimer, thus, for the first time ever providing an alternative and energetic foundation for the existence of this critical point. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Method for removing atomic-model bias in macromolecular crystallography

DOEpatents

Terwilliger, Thomas C [Santa Fe, NM

2006-08-01

Structure factor bias in an electron density map for an unknown crystallographic structure is minimized by using information in a first electron density map to elicit expected structure factor information. Observed structure factor amplitudes are combined with a starting set of crystallographic phases to form a first set of structure factors. A first electron density map is then derived and features of the first electron density map are identified to obtain expected distributions of electron density. Crystallographic phase probability distributions are established for possible crystallographic phases of reflection k, and the process is repeated as k is indexed through all of the plurality of reflections. An updated electron density map is derived from the crystallographic phase probability distributions for each one of the reflections. The entire process is then iterated to obtain a final set of crystallographic phases with minimum bias from known electron density maps.

Device and method for electron beam heating of a high density plasma

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high density plasma in a small localized region. A relativistic electron beam generator produces a high voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target plasma is ionized prior to application of the electron beam by means of a laser or other preionization source. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high density target plasma causing the relativistic electron beam to efficiently deposit its energy into a small localized region within the high density plasma target.

A review of causal inference for biomedical informatics

PubMed Central

Kleinberg, Samantha; Hripcsak, George

2011-01-01

Causality is an important concept throughout the health sciences and is particularly vital for informatics work such as finding adverse drug events or risk factors for disease using electronic health records. While philosophers and scientists working for centuries on formalizing what makes something a cause have not reached a consensus, new methods for inference show that we can make progress in this area in many practical cases. This article reviews core concepts in understanding and identifying causality and then reviews current computational methods for inference and explanation, focusing on inference from large-scale observational data. While the problem is not fully solved, we show that graphical models and Granger causality provide useful frameworks for inference and that a more recent approach based on temporal logic addresses some of the limitations of these methods. PMID:21782035

The gamma-ray emitting region of the jet in Cyg X-3

NASA Astrophysics Data System (ADS)

Zdziarski, Andrzej A.; Sikora, Marek; Dubus, Guillaume; Yuan, Feng; Cerutti, Benoit; Ogorzałek, Anna

2012-04-01

We study models of the γ-ray emission of Cyg X-3 observed by Fermi. We calculate the average X-ray spectrum during the γ-ray active periods. Then, we calculate spectra from Compton scattering of a photon beam into a given direction by isotropic relativistic electrons with a power-law distribution, both based on the Klein-Nishina cross-section and in the Thomson limit. Applying the results to scattering of stellar blackbody radiation in the inner jet of Cyg X-3, we find that a low-energy break in the electron distribution at a Lorentz factor of ˜300-103 is required by the shape of the observed X-ray/γ-ray spectrum in order to avoid overproducing the observed X-ray flux. The electrons giving rise to the observed γ-rays are efficiently cooled by Compton scattering, and the power-law index of the acceleration process is ≃2.5-3. The bulk Lorentz factor of the jet and the kinetic power before the dissipation region depend on the fraction of the dissipation power supplied to the electrons; if it is ≃1/2, the Lorentz factor is ˜2.5, and the kinetic power is ˜1038 erg s-1, which represents a firm lower limit on the jet power, and is comparable to the bolometric luminosity of Cyg X-3. Most of the power supplied to the electrons is radiated. The broad-band spectrum constrains the synchrotron and self-Compton emission from the γ-ray emitting electrons, which requires the magnetic field to be relatively weak, with the magnetic energy density ≲ a few times 10-3 of that in the electrons. The actual value of the magnetic field strength can be inferred from a future simultaneous measurement of the infrared and γ-ray fluxes.

Spatially explicit inference for open populations: estimating demographic parameters from camera-trap studies

USGS Publications Warehouse

Gardner, Beth; Reppucci, Juan; Lucherini, Mauro; Royle, J. Andrew

2010-01-01

We develop a hierarchical capture–recapture model for demographically open populations when auxiliary spatial information about location of capture is obtained. Such spatial capture–recapture data arise from studies based on camera trapping, DNA sampling, and other situations in which a spatial array of devices records encounters of unique individuals. We integrate an individual-based formulation of a Jolly-Seber type model with recently developed spatially explicit capture–recapture models to estimate density and demographic parameters for survival and recruitment. We adopt a Bayesian framework for inference under this model using the method of data augmentation which is implemented in the software program WinBUGS. The model was motivated by a camera trapping study of Pampas cats Leopardus colocolo from Argentina, which we present as an illustration of the model in this paper. We provide estimates of density and the first quantitative assessment of vital rates for the Pampas cat in the High Andes. The precision of these estimates is poor due likely to the sparse data set. Unlike conventional inference methods which usually rely on asymptotic arguments, Bayesian inferences are valid in arbitrary sample sizes, and thus the method is ideal for the study of rare or endangered species for which small data sets are typical.

Spatially explicit inference for open populations: estimating demographic parameters from camera-trap studies.

PubMed

Gardner, Beth; Reppucci, Juan; Lucherini, Mauro; Royle, J Andrew

2010-11-01

We develop a hierarchical capture-recapture model for demographically open populations when auxiliary spatial information about location of capture is obtained. Such spatial capture-recapture data arise from studies based on camera trapping, DNA sampling, and other situations in which a spatial array of devices records encounters of unique individuals. We integrate an individual-based formulation of a Jolly-Seber type model with recently developed spatially explicit capture-recapture models to estimate density and demographic parameters for survival and recruitment. We adopt a Bayesian framework for inference under this model using the method of data augmentation which is implemented in the software program WinBUGS. The model was motivated by a camera trapping study of Pampas cats Leopardus colocolo from Argentina, which we present as an illustration of the model in this paper. We provide estimates of density and the first quantitative assessment of vital rates for the Pampas cat in the High Andes. The precision of these estimates is poor due likely to the sparse data set. Unlike conventional inference methods which usually rely on asymptotic arguments, Bayesian inferences are valid in arbitrary sample sizes, and thus the method is ideal for the study of rare or endangered species for which small data sets are typical.

Handling Density Conversion in TPS.

PubMed

Isobe, Tomonori; Mori, Yutaro; Takei, Hideyuki; Sato, Eisuke; Tadano, Kiichi; Kobayashi, Daisuke; Tomita, Tetsuya; Sakae, Takeji

2016-01-01

Conversion from CT value to density is essential to a radiation treatment planning system. Generally CT value is converted to the electron density in photon therapy. In the energy range of therapeutic photon, interactions between photons and materials are dominated with Compton scattering which the cross-section depends on the electron density. The dose distribution is obtained by calculating TERMA and kernel using electron density where TERMA is the energy transferred from primary photons and kernel is a volume considering spread electrons. Recently, a new method was introduced which uses the physical density. This method is expected to be faster and more accurate than that using the electron density. As for particle therapy, dose can be calculated with CT-to-stopping power conversion since the stopping power depends on the electron density. CT-to-stopping power conversion table is also called as CT-to-water-equivalent range and is an essential concept for the particle therapy.

Performance in wild ungulates: measuring population density and condition of individuals

Treesearch

John G. Kie

1988-01-01

Measures of performance in wild ungulates can include characteristics indicative of condition and health such as body weights, fat reserves, blood values, reproductive rates, and parasite loads. Performance may also be inferred from habitat-related factors, such as diet and nutritional intake. However, these parameters interact with population density to form a...

Social networks and inference about unknown events: A case of the match between Google’s AlphaGo and Sedol Lee

PubMed Central

Bae, Jonghoon; Cha, Young-Jae; Lee, Hyungsuk; Lee, Boyun; Baek, Sojung; Choi, Semin

2017-01-01

This study examines whether the way that a person makes inferences about unknown events is associated with his or her social relations, more precisely, those characterized by ego network density that reflects the structure of a person’s immediate social relation. From the analysis of individual predictions over the Go match between AlphaGo and Sedol Lee in March 2016 in Seoul, Korea, this study shows that the low-density group scored higher than the high-density group in the accuracy of the prediction over a future state of a social event, i.e., the outcome of the first game. We corroborated this finding with three replication tests that asked the participants to predict the following: film awards, President Park’s impeachment in Korea, and the counterfactual assessment of the US presidential election. Taken together, this study suggests that network density is negatively associated with vision advantage, i.e., the ability to discover and forecast an unknown aspect of a social event. PMID:28222114

Verification of Loop Diagnostics

NASA Technical Reports Server (NTRS)

Winebarger, A.; Lionello, R.; Mok, Y.; Linker, J.; Mikic, Z.

2014-01-01

Many different techniques have been used to characterize the plasma in the solar corona: density-sensitive spectral line ratios are used to infer the density, the evolution of coronal structures in different passbands is used to infer the temperature evolution, and the simultaneous intensities measured in multiple passbands are used to determine the emission measure. All these analysis techniques assume that the intensity of the structures can be isolated through background subtraction. In this paper, we use simulated observations from a 3D hydrodynamic simulation of a coronal active region to verify these diagnostics. The density and temperature from the simulation are used to generate images in several passbands and spectral lines. We identify loop structures in the simulated images and calculate the loop background. We then determine the density, temperature and emission measure distribution as a function of time from the observations and compare with the true temperature and density of the loop. We find that the overall characteristics of the temperature, density, and emission measure are recovered by the analysis methods, but the details of the true temperature and density are not. For instance, the emission measure curves calculated from the simulated observations are much broader than the true emission measure distribution, though the average temperature evolution is similar. These differences are due, in part, to inadequate background subtraction, but also indicate a limitation of the analysis methods.

X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics

NASA Astrophysics Data System (ADS)

Rouxel, Jérémy R.; Kowalewski, Markus; Bennett, Kochise; Mukamel, Shaul

2018-06-01

X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved x-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear x-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband x-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor or acceptor substituted stilbene.

Anomalous evolution of Ar metastable density with electron density in high density Ar discharge

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

Park, Min; Chang, Hong-Young; You, Shin-Jae

2011-10-15

Recently, an anomalous evolution of argon metastable density with plasma discharge power (electron density) was reported [A. M. Daltrini, S. A. Moshkalev, T. J. Morgan, R. B. Piejak, and W. G. Graham, Appl. Phys. Lett. 92, 061504 (2008)]. Although the importance of the metastable atom and its density has been reported in a lot of literature, however, a basic physics behind the anomalous evolution of metastable density has not been clearly understood yet. In this study, we investigated a simple global model to elucidate the underlying physics of the anomalous evolution of argon metastable density with the electron density. Onmore » the basis of the proposed simple model, we reproduced the anomalous evolution of the metastable density and disclosed the detailed physics for the anomalous result. Drastic changes of dominant mechanisms for the population and depopulation processes of Ar metastable atoms with electron density, which take place even in relatively low electron density regime, is the clue to understand the result.« less

MAVEN observations of dayside peak electron densities in the ionosphere of Mars

NASA Astrophysics Data System (ADS)

Vogt, Marissa F.; Withers, Paul; Fallows, Kathryn; Andersson, Laila; Girazian, Zachary; Mahaffy, Paul R.; Benna, Mehdi; Elrod, Meredith K.; Connerney, John E. P.; Espley, Jared R.; Eparvier, Frank G.; Jakosky, Bruce M.

2017-01-01

The peak electron density in the dayside Martian ionosphere is a valuable diagnostic of the state of the ionosphere. Its dependence on factors like the solar zenith angle, ionizing solar irradiance, neutral scale height, and electron temperature has been well studied. The Mars Atmosphere and Volatile EvolutioN spacecraft's September 2015 "deep dip" orbits, in which the orbital periapsis was lowered to 125 km, provided the first opportunity since Viking to sample in situ a complete dayside electron density profile including the main peak. Here we present peak electron density measurements from 37 deep dip orbits and describe conditions at the altitude of the main peak, including the electron temperature and composition of the ionosphere and neutral atmosphere. We find that the dependence of the peak electron density and the altitude of the main peak on solar zenith angle are well described by analytical photochemical theory. Additionally, we find that the electron temperatures at the main peak display a dependence on solar zenith angle that is consistent with the observed variability in the peak electron density. Several peak density measurements were made in regions of large crustal magnetic field, but there is no clear evidence that the crustal magnetic field strength influences the peak electron density, peak altitude, or electron temperature. Finally, we find that the fractional abundance of O2+ and CO2+ at the peak altitude is variable but that the two species together consistently represent 95% of the total ion density.

A comparison of measured and predicted test flow in an expansion tube with air and oxygen test gases

NASA Technical Reports Server (NTRS)

Aaggard, K. V.; Goad, W. K.

1975-01-01

Simultaneous time-resolved measurements of temperature, density, pitot pressure, and wall pressure in both air and O2 test gases were obtained in the Langley pilot model expansion tube. These tests show nonequilibrium chemical and vibrational relaxation significantly affect the test-flow condition. The use of an electromagnetic device to preopen the secondary diaphragm before the arrival of the primary shock wave resulted in an improvement in the agreement between the measured pitot pressure and the value inferred from measured density and interface velocity. Boundary-layer splitter plates used to reduce the wall boundary layer show that this disagreement in the measured and inferred pitot pressures is not a result of boundary-layer effects.

Correlation between Na/K ratio and electron densities in blood samples of breast cancer patients.

PubMed

Topdağı, Ömer; Toker, Ozan; Bakırdere, Sezgin; Bursalıoğlu, Ertuğrul Osman; Öz, Ersoy; Eyecioğlu, Önder; Demir, Mustafa; İçelli, Orhan

2018-05-31

The main purpose of this study was to investigate the relationship between the electron densities and Na/K ratio which has important role in breast cancer disease. Determinations of sodium and potassium concentrations in blood samples performed with inductive coupled plasma-atomic emission spectrometry. Electron density values of blood samples were determined via ZXCOM. Statistical analyses were performed for electron densities and Na/K ratio including Kolmogorov-Smirnov normality tests, Spearman's rank correlation test and Mann-Whitney U test. It was found that the electron densities significantly differ between control and breast cancer groups. In addition, statistically significant positive correlation was found between the electron density and Na/K ratios in breast cancer group.

Device and method for electron beam heating of a high density plasma

DOEpatents

Thode, L.E.

A device and method for relativistic electron beam heating of a high density plasma in a small localized region are described. A relativistic electron beam generator produces a high voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10/sup 17/ to 10/sup 20/.

Longitudinal Ionospheric Variability Observed by LITES on the ISS

NASA Astrophysics Data System (ADS)

Stephan, A. W.; Finn, S. C.; Cook, T.; Geddes, G.; Chakrabarti, S.; Budzien, S. A.

2017-12-01

The Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrograph (LITES) is an imaging spectrograph designed to measure altitude profiles (150-350 km) of extreme- and far-ultraviolet airglow emissions that originate from photochemical processes in the ionosphere and thermosphere. During the daytime, LITES observes the bright O+ 83.4 nm emission from which the ionospheric profile can be inferred. At night, recombination emissions at 91.1 and 135.6 nm provide a direct measure of the electron content along the line of sight. LITES was launched and installed on the International Space Station (ISS) in late February 2017 where it has been operating along with the highly complementary GPS Radio Occultation and Ultraviolet Photometry - Colocated (GROUP-C) experiment. We will present some of the first observations from LITES in April 2017 that show longitudinal patterns in ionospheric density and the daily variability in those patterns. LITES vertical imaging from a vantage point near 410 km enables a particularly unique perspective on the altitude of the ionospheric peak density at night that can complement and inform other ground- and space-based measurements, and track the longitude-altitude variability that is reflective of changes in equatorial electrodynamics.

Picosecond Streaked K-Shell Spectroscopy of Near Solid-Density Aluminum Plasmas

NASA Astrophysics Data System (ADS)

Stillman, C. R.; Nilson, P. M.; Ivancic, S. T.; Mileham, C.; Froula, D. H.; Golovkin, I. E.

2016-10-01

The thermal x-ray emission from rapidly heated solid targets containing a buried-aluminum layer was measured. The targets were driven by high-contrast 1 ω or 2 ω laser pulses at focused intensities up to 1 ×1019W/Wcm2 cm2 . A streaked x-ray spectrometer recorded the Al Heα and lithium-like satellite lines with 2-ps temporal resolution and moderate resolving power (E/E ΔE 700). Time-integrated measurements over the same spectral range were used to correct the streaked data for variations in photocathode sensitivity. Line widths and intensity ratios from the streaked data were interpreted using a collisional radiative atomic model to provide the average plasma conditions in the buried layer as a function of time. It was observed that the resonance line tends toward lower photon energies at high electron densities. The measured shifts will be compared to predicted shifts from Stark-operator calculations at the inferred plasma conditions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944, the office of Fusion Energy Sciences Award Number DE-SC0012317, and the Stewardship Science Graduate Fellowship Grant Number DE-NA0002135.

Constraints on Exposure Ages of Lunar and Asteroidal Regolith Particles

NASA Technical Reports Server (NTRS)

Berger, Eve L.; Keller, Lindsay P

2014-01-01

Mineral grains in lunar and asteroidal regolith samples provide a unique record of their interaction with the space environment. Exposure to the solar wind results in implantation effects that are preserved in the rims of grains (typically the outermost 100 nm), while impact processes result in the accumulation of vapor-deposited elements, impact melts and adhering grains on particle surfaces. These processes are collectively referred to as space weathering. A critical element in the study of these processes is to determine the rate at which these effects accumulate in the grains during their space exposure. For small particulate samples, one can use the density of solar flare particle tracks to infer the length of time the particle was at the regolith surface (i.e., its exposure age). We have developed a new technique that enables more accurate determination of solar flare particle track densities in mineral grains <50 micron in size that utilizes focused ion beam (FIB) sample preparation combined with transmission electron microscopy (TEM) imaging. We have applied this technique to lunar soil grains from the Apollo 16 site (soil 64501) and most recently to samples from asteroid 25143 Itokawa returned by the Hayabusa mission. Our preliminary results show that the Hayabusa grains have shorter exposure ages compared to typical lunar soil grains. We will use these techniques to re-examine the track density-exposure age calibration from lunar samples reported by Blanford et al. (1975).

Inference of the electron temperature in ICF implosions from the hard X-ray spectral continuum

NASA Astrophysics Data System (ADS)

Kagan, Grigory; Landen, O. L.; Svyatsky, D.; Sio, H.; Kabadi, N. V.; Simpson, R. A.; Gatu Johnson, M.; Frenje, J. A.; Petrasso, R. D.; Shah, R. C.; Joshi, T. R.; Hakel, P.; Weber, T. E.; Rinderknecht, H. G.; Thorn, D.; Schneider, M.; Bradley, D.; Kilkenny, J.

2017-10-01

The NIF Continuum Spectrometer, scheduled to be first deployed in Fall of 2017, will infer the imploded core electron temperature from the free-free continuum self-emission spectra of photons with energies of 20 to 30 keV. However, this hard X-ray radiation is emitted by the tail of the electron distribution, which likely deviates from Maxwellian and thus obscures interpretation of the data. We investigate resulting modifications to the X-ray spectra. The logarithmic slope of the spectrum from the more realistic, non-thermal tail of the electron distribution is found to decrease more rapidly at higher photon energies, as compared to the perfectly Maxwellian case. Interpreting the spectrum with assumption of Maxwellian electrons enforced is shown to give an electron temperature that is lower than the actual one. Conversely, due to its connection with the non-thermal features in the electron distribution, hard X-ray emission can provide unprecedented information about kinetic processes in the hot DT core. This work was performed under the auspices of the U.S. Dept. of Energy by the Los Alamos National Security, LLC, Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396.

Distribution of E/N and N/e/ in a cross-flow electric discharge laser. [electric field to neutral gas density and electron number density

NASA Technical Reports Server (NTRS)

Dunning, J. W., Jr.; Lancashire, R. B.; Manista, E. J.

1976-01-01

Measurements have been conducted of the effect of the convection of ions and electrons on the discharge characteristics in a large scale laser. The results are presented for one particular distribution of ballast resistance. Values of electric field, current density, input power density, ratio of electric field to neutral gas density (E/N), and electron number density were calculated on the basis of measurements of the discharge properties. In a number of graphs, the E/N ratio, current density, power density, and electron density are plotted as a function of row number (downstream position) with total discharge current and gas velocity as parameters. From the dependence of the current distribution on the total current, it appears that the electron production in the first two rows significantly affects the current flowing in the succeeding rows.

THE KINEMATICS AND IONIZATION OF NUCLEAR GAS CLOUDS IN CENTAURUS A

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

Bicknell, Geoffrey V.; Sutherland, Ralph S.; Neumayer, Nadine, E-mail: Geoff.Bicknell@anu.edu.au, E-mail: Ralph.Sutherland@anu.edu.au, E-mail: nadine.neumayer@universe-cluster.de

2013-03-20

Neumayer et al. established the existence of a blueshifted cloud in the core of Centaurus A, within a few parsecs of the nucleus and close to the radio jet. We propose that the cloud has been impacted by the jet, and that it is in the foreground of the jet, accounting for its blueshifted emission on the southern side of the nucleus. We consider both shock excitation and photoionization models for the excitation of the cloud. Shock models do not account for the [Si VI] and [Ca VIII] emission line fluxes. However, X-ray observations indicate a source of ionizing photonsmore » in the core of Centaurus A; photoionization by the inferred flux incident on the cloud can account for the fluxes in these lines relative to Brackett-{gamma}. The power-law slope of the ionizing continuum matches that inferred from synchrotron models of the X-rays. The logarithm of the ionization parameter is -1.9, typical of that in Seyfert galaxies and consistent with the value proposed for dusty ionized plasmas. The model cloud density depends upon the Lorentz factor of the blazar and the inclination of our line of sight to the jet axis. For acute inclinations, the inferred density is consistent with expected cloud densities. However, for moderate inclinations of the jet to the line of sight, high Lorentz factors imply cloud densities in excess of 10{sup 5} cm{sup -3} and very low filling factors, suggesting that models of the gamma-ray emission should incorporate jet Lorentz factors {approx}< 5.« less

Radiation source

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the relativistic electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy into a small localized region of the high-density plasma target.

Transition-zone observations of rapid flare events as observed by OSO-8

NASA Technical Reports Server (NTRS)

Lites, B. W.

1981-01-01

The rapid dissipation of flare energy has been observed in the transition-zone line of C IV at 1548.2 A using the University of Colorado spectrometer aboard OSO-8. Impulsive brightenings have been resolved with characteristic rise times as low as 3.5s. One event is analyzed in detail, and it is inferred that the electron density is greater than 2 x 10 to the 11th/cu cm at a temperature of 60,000 K, and that the flare energy is deposited at a rate of 2 ergs/cu cm per sec or greater. The temporal behavior of the intensity at the center of the C IV line is consistent with a nonequilibrium ionization of C III through C V. If this event is a result of the multiple tearing mode instability as the primary energy release mechanism, then the observations indicate a preflare magnetic field of about 175 G.

Inference of Heating Properties from "Hot" Non-flaring Plasmas in Active Region Cores. I. Single Nanoflares

NASA Astrophysics Data System (ADS)

Barnes, W. T.; Cargill, P. J.; Bradshaw, S. J.

2016-09-01

The properties that are expected of “hot” non-flaring plasmas due to nanoflare heating in active regions are investigated using hydrodynamic modeling tools, including a two-fluid development of the Enthalpy Based Thermal Evolution of Loops code. Here we study a single nanoflare and show that while simple models predict an emission measure distribution extending well above 10 MK, which is consistent with cooling by thermal conduction, many other effects are likely to limit the existence and detectability of such plasmas. These include: differential heating between electrons and ions, ionization non-equilibrium, and for short nanoflares, the time taken for the coronal density to increase. The most useful temperature range to look for this plasma, often called the “smoking gun” of nanoflare heating, lies between 106.6 and 107 K. Signatures of the actual heating may be detectable in some instances.

Temperature-dependent ac conductivity and dielectric response of vanadium doped CaCu3Ti4O12 ceramic

NASA Astrophysics Data System (ADS)

Sen, A.; Maiti, U. N.; Thapa, R.; Chattopadhyay, K. K.

2011-09-01

Successful incorporation of vanadium dopant within the giant dielectric material CaCu 3Ti 4O12 (CCTO) through a conventional solid-state sintering process is achieved and its influence on the dielectric as well as electrical properties as a function of temperature and frequency is reported here. Proper crystalline phase formation together with dopant induced lattice constant shrinkage was confirmed through X-ray diffraction. The temperature dependence of the dielectric constant at different constant frequencies was investigated. We infer that the correlated barrier hopping (CBH) model is dominant in the conduction mechanism of the ceramic as per the temperature-dependent ac conductivity measurements. The electronic parameters such as density of the states at the Fermi level, N( E f) and hopping distance, R ω of the ceramic were also calculated using this model.

Thermo-structural analysis and electrical conductivity behavior of epoxy/metals composites

NASA Astrophysics Data System (ADS)

Boumedienne, N.; Faska, Y.; Maaroufi, A.; Pinto, G.; Vicente, L.; Benavente, R.

2017-05-01

This paper reports on the elaboration and characterization of epoxy resin filled with metallic particles powder (aluminum, tin and zinc) composites. The scanning electron microscopy (SEM) pictures, density measurements and x-ray diffraction analysis (DRX) showed a homogeneous phase of obtained composites. The differential scanning calorimetry revealed a good adherence at matrix-filler interfaces, confirming the SEM observations. The measured glass transition temperatures depend on composites fillers' nature. Afterwards, the electrical conductivity of composites versus their fillers' contents has been investigated. The obtained results depict a nonlinear behavior, indicating an insulator to conductor phase transition at a conduction threshold; with high contrast of ten decades. Hence, the elaborated materials give a possibility to obtain dielectric or electrically conducting phases, which can to be interesting in the choice of desired applications. Finally, the obtained results have been successfully simulated on the basis of different percolation models approach combined with structural characterization inferences.

F layer positive response to a geomagnetic storm - June 1972

NASA Technical Reports Server (NTRS)

Miller, N. J.; Grebowsky, J. M.; Mayr, H. G.; Harris, I.; Tulunay, Y. K.

1979-01-01

A circulation model of neutral thermosphere-ionosphere coupling is used to interpret in situ spacecraft measurements taken during a topside midlatitude ionospheric storm. The data are measurements of electron density taken along the circular polar orbit of Ariel 4 at 550 km during the geomagnetically disturbed period June 17-18, 1972. It is inferred that collisional momentum transfer from the disturbed neutral thermosphere to the ionosphere was the dominant midday process generating the positive F-layer storm phase in the summer hemisphere. In the winter hemisphere the positive storm phase drifted poleward in the apparent response to magnetospheric E x B drifts. A summer F-layer positive phase developed at the sudden commencement and again during the geomagnetic main phase; a winter F-layer positive phase developed only during the geomagnetic main phase. The observed seasonal differences in both the onsets and the magnitudes of the positive phases are attributed to the interhemispheric asymmetry in thermospheric dynamics.

Changes in atmospheric composition inferred from ionospheric production rates

NASA Technical Reports Server (NTRS)

Titheridge, J. E.

1974-01-01

Changes in the total electron content of the ionosphere near sunrise are used to determine the integrated production rate in the ionosphere (Q) from 1965 to 1971 at latitudes of 34S, 20N, and 34N. The observed regular semiannual variation in Q through a range of 1:3:1 is interpreted as an increase in the ratio O/N2 (relative densities) near the equinoxes. It follows that there is a worldwide semiannual variation in atmospheric composition, with the above ratio maximum just after the equinoxes. There is a large seasonal variation in the Northern hemisphere with a maximum in mid-summer. This effect is absent in the Southern hemisphere. At all times except solar maximum in the Northern hemisphere there is a global asymmetry. The ratio O/N2 is about three times as large in the Northern hemisphere. The overall mechanism appears to be N2 absorption.

Degradation mechanism of Direct Pink 12B treated by iron-carbon micro-electrolysis and Fenton reaction.

PubMed

Wang, Xiquan; Gong, Xiaokang; Zhang, Qiuxia; Du, Haijuan

2013-12-01

The Direct Pink 12B dye was treated by iron-carbon micro-electrolysis (ICME) and Fenton oxidation. The degradation pathway of Direct Pink 12B dye was inferred by ultraviolet visible (UV-Vis), infrared absorption spectrum (IR) and high performance liquid chromatography-mass spectrometry (HPLC-MS). The major reason of decolorization was that the conjugate structure was disrupted in the iron-carbon micro-electrolysis (ICME) process. However, the dye was not degraded completely because benzene rings and naphthalene rings were not broken. In the Fenton oxidation process, the azo bond groups surrounded by higher electron cloud density were first attacked by hydroxyl radicals to decolorize the dye molecule. Finally benzene rings and naphthalene rings were mineralized to H2O and CO2 under the oxidation of hydroxyl radicals. Copyright © 2013 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Spallation processes and nuclear interaction products of cosmic rays.

PubMed

Silberberg, R; Tsao, C H

1990-08-01

Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.

Electron (charge) density studies of cellulose models

USDA-ARS?s Scientific Manuscript database

Introductory material first describes electron density approaches and demonstrates visualization of electron lone pairs and bonding as concentrations of electron density. Then it focuses on the application of Bader’s Quantum Theory of Atoms-in-Molecules (AIM) to cellulose models. The purpose of the ...

Electron densities in the ionosphere of Mars: A comparison of MARSIS and radio occultation measurements

NASA Astrophysics Data System (ADS)

Vogt, Marissa F.; Withers, Paul; Fallows, Kathryn; Flynn, Casey L.; Andrews, David J.; Duru, Firdevs; Morgan, David D.

2016-10-01

Radio occultation electron densities measurements from the Mariner 9 and Viking spacecraft, which orbited Mars in the 1970s, have recently become available in a digital format. These data are highly complementary to the radio occultation electron density profiles from Mars Global Surveyor, which were restricted in solar zenith angle and altitude. We have compiled data from the Mariner 9, Viking, and Mars Global Surveyor radio occultation experiments for comparison to electron density measurements made by Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), the topside radar sounder on Mars Express, and MARSIS-based empirical density models. We find that the electron densities measured by radio occultation are in generally good agreement with the MARSIS data and model, especially near the altitude of the peak electron density but that the MARSIS data and model display a larger plasma scale height than the radio occultation profiles at altitudes between the peak density and 200 km. Consequently, the MARSIS-measured and model electron densities are consistently larger than radio occultation densities at altitudes 200-300 km. Finally, we have analyzed transitions in the topside ionosphere, at the boundary between the photochemically controlled and transport-controlled regions, and identified the average transition altitude, or altitude at which a change in scale height occurs. The average transition altitude is 200 km in the Mariner 9 and Viking radio occultation profiles and in profiles of the median MARSIS radar sounding electron densities.

Solar X-Ray Processes

NASA Astrophysics Data System (ADS)

Mallik, P. C. V.; Brown, J. C.; MacKinnon, A. L.

Past analyses of solar flares have ignored nonthermal recombination (NTR) emission as a means of producing Hard X-rays (HXRs) in the corona and chromosphere. However, Brown and Mallik (2008, A&A, 481, 507) have shown that NTR can be significant and even exceed nonthermal bremsstrahlung (NTB) emission for certain flare conditions that are quite common. For hot enough plasma (T > 10 MK), HXR emission of a few deka-keV has a large contribution from NTR onto highly ionized heavy elements, especially Fe. Consequently, including NTR has implications for the magnitude and the form of the inferred electron spectrum, F(E), and hence for fast-electron density and energy budgets and for the acceleration mechanisms. We show under what circumstances NTR dominates in deka-keV HXR emission. It is important to note that at high temperatures, HXR emission from thermal electrons (recombination and bremsstrahlung) becomes important. However, NTR dominates over NTB without being swamped by thermal emission in the photon energy (ɛ) regime of 20-30 keV and temperature range of 10-25MK (Fig. 1, left). By integrating the flux for all ɛ > 20keV, i.e., looking at the source luminosity function above 20 keV, we were able to show that by including NTR, the acceleration requirements are less demanding for every event, but to varying degrees based on temperature (T), spectral index (δ) and electron low-energy cut-off (Ec). Our key result is that, for T > 10MK and δ ≈ 5, including NTR reduces the demand for nonthermal electrons by up to 85%. Our paper with these results will be submitted to ApJ Letters.

Density Estimation with Mercer Kernels

NASA Technical Reports Server (NTRS)

Macready, William G.

2003-01-01

We present a new method for density estimation based on Mercer kernels. The density estimate can be understood as the density induced on a data manifold by a mixture of Gaussians fit in a feature space. As is usual, the feature space and data manifold are defined with any suitable positive-definite kernel function. We modify the standard EM algorithm for mixtures of Gaussians to infer the parameters of the density. One benefit of the approach is it's conceptual simplicity, and uniform applicability over many different types of data. Preliminary results are presented for a number of simple problems.

Observation of a metric type N solar radio burst

DOE PAGES

Kong, Xiangliang; Chen, Yao; Feng, Shiwei; ...

2016-10-10

Type III and type-III-like radio bursts are produced by energetic electron beams guided along coronal magnetic fields. As a variant of type III bursts, Type N bursts appear as the letter "N" in the radio dynamic spectrum and reveal a magnetic mirror effect in coronal loops. Here, we report a well-observed N-shaped burst consisting of three successive branches at metric wavelength with both fundamental and harmonic components and a high brightness temperature (>10 9 K). We verify the burst as a true type N burst generated by the same electron beam from three aspects of the data. First, durations ofmore » the three branches at a given frequency increase gradually and may be due to the dispersion of the beam along its path. Second, the flare site, as the only possible source of non-thermal electrons, is near the western feet of large-scale closed loops. Third, the first branch and the following two branches are localized at different legs of the loops with opposite senses of polarization. We also find that the sense of polarization of the radio burst is in contradiction to the O-mode and there exists a fairly large time delay (~3–5 s) between the fundamental and harmonic components. Possible explanations accounting for these observations are presented. Finally, assuming the classical plasma emission mechanism, we can infer coronal parameters such as electron density and magnetic field near the radio source and make diagnostics on the magnetic mirror process.« less

The electrons and ion characteristics of Saturn's plasma disk inside the Enceladus orbit

NASA Astrophysics Data System (ADS)

Morooka, Michiko; Wahlund, Jan-Erik; Ye, Sheng-Yi; Kurth, William; Persoon, Ann; Holmberg, Mika

2017-04-01

Cassini observations revealed that Saturn's icy moon Enceladus and surrounding E ring are the significant plasma source of the magnetosphere. However, the observations sometimes show the electron density enhancement even inside the Enceladus orbiting distance, 4RS. Further plasma contribution from the inner rings, the G and the F rings and main A ring are the natural candidate as an additional plasma source. The Cassini/RPWS Langmuir Probe (LP) measurement provides the characteristics of the electrons and ions independently in a cold dense plasma. The observations near the center of the E ring showed that the ion density being larger than the electron density, indicating that there is additional particle as a negative charge carrier. Those are the small nm and μm sized dust grains that are negatively charged by the electron attachments. The faint F and G rings, located at R=2RS and 3RS, consist of small grains and similar electron/ion density discrepancies can be expected. We will show different types of the LP observations when Cassini traveled the equator region of the plasma disk down to 3RS. One with the electron density increasing inside 4RS, and another with the electron density decreasing inside 4RS. During the orbit 016 (2005 doy-284/285), the electron density continued to increase toward the planet. On the other hand, the ion currents, the LP measured currents from the negative bias voltage, turn to decreasing inside 4RS, implying the density decrease of the ions. By comparing the observed LP ion current characteristics and the modeled values using the obtained electron density, we found that the characteristic ion mass can be several times larger than the water ions (AMU=18) that we expected in this region. During the orbit 015 (2005 doy-266/267), on the other hand, the LP observed sharp electron density drop near 3RS. The dust signals from the RPWS antenna showed the density enhancement of the μm sized grains coincide the electron density drop and we have estimated that the characteristic ion mass can exceed AMU=100. Throughout the whole Cassini observation near the equator inside 4RS, we didn't find the case with the ion densities larger than the electron densities as were found near the E ring and the Enceladus plume. We suggest that Saturn's plasmadisk inside the Enceladus orbit is dynamic in ion characteristics where the water molecules coagulate and grow into a small icy dust grains. In the presentation we discuss the relationship between the electron/ion density and the density of the nm and μm sized grains.

Electron density profile measurements at a self-focusing ion beam with high current density and low energy extracted through concave electrodes.

PubMed

Fujiwara, Y; Hirano, Y; Kiyama, S; Nakamiya, A; Koguchi, H; Sakakita, H

2014-02-01

The self-focusing phenomenon has been observed in a high current density and low energy ion beam. In order to study the mechanism of this phenomenon, a special designed double probe to measure the electron density and temperature is installed into the chamber where the high current density ion beam is injected. Electron density profile is successfully measured without the influence of the ion beam components. Estimated electron temperature and density are ∼0.9 eV and ∼8 × 10(8) cm(-3) at the center of ion beam cross section, respectively. It was found that a large amount of electrons are spontaneously accumulated in the ion beam line in the case of self-forcing state.

Scex 3 and Electron Echo 7, a Comparison of Data from Two Rocket Experiments.

NASA Astrophysics Data System (ADS)

Bale, Stuart Douglas

Results from two separate active sounding rocket experiments are presented and discussed. The SCEX III sounding rocket (NASA 39.002 UE) and Electron Echo 7 (NASA 36.015) were both launched from the Poker Flat Research Range (65.1^circ N, 147.5^circ W) near Fairbanks, Alaska, on 1 February, 1990 and 9 February, 1988, respectively. Each payload was equipped with an electron accelerator to study both natural and beam-related plasma phenomena. Data from the SCEX III retarding potential analyzer (RPA) and 3805 A and 3914 A photometers show evidence of a plasma discharge process occurring concomitant with operation of the electron gun. This appears as an enhanced electron current, nonlinear with gun injection current, in the RPA. The photometers register a sharp increase in luminosity during full current electron injection. This luminosity is an indicator of the ionizing electron-neutral collisions which liberate electrons and lead to the cascade-type discharge process. These observations are used to attempt to infer the mechanism of electron acceleration which leads to the discharge process. Before the electron gun was activated, the SCEX III payload flew through a region of auroral activity as evidenced by ground-based all-sky TV and energetic particle flux in the forward payload RPA. During this time, low frequency (10 Hz) electrostatic waves were observed in the DC receivers and Langmuir probe instrument. This data is analyzed, with a cross-spectral technique, and an approximate wave number is inferred. Comparison with theory suggests that the observed wave is the electrostatic ion cyclotron mode (EIC) operating on a heavy ion species (NO or O _2). The Echo 7 nose payload, carrying a plasma wave receiver, was ejected upfield of the main electron gun -equipped payload. Data from the swept frequency analyzer experiment provide wave amplitudes, at frequencies up to 15 MHz, as a function of separation of the main and nose payloads. These observations, and the wave modes inferred, shed light on the wave generation region upfield from a beam-emitting ionospheric payload.

Spectral decompositions of multiple time series: a Bayesian non-parametric approach.

PubMed

Macaro, Christian; Prado, Raquel

2014-01-01

We consider spectral decompositions of multiple time series that arise in studies where the interest lies in assessing the influence of two or more factors. We write the spectral density of each time series as a sum of the spectral densities associated to the different levels of the factors. We then use Whittle's approximation to the likelihood function and follow a Bayesian non-parametric approach to obtain posterior inference on the spectral densities based on Bernstein-Dirichlet prior distributions. The prior is strategically important as it carries identifiability conditions for the models and allows us to quantify our degree of confidence in such conditions. A Markov chain Monte Carlo (MCMC) algorithm for posterior inference within this class of frequency-domain models is presented.We illustrate the approach by analyzing simulated and real data via spectral one-way and two-way models. In particular, we present an analysis of functional magnetic resonance imaging (fMRI) brain responses measured in individuals who participated in a designed experiment to study pain perception in humans.

The polar thermosphere of Venus

NASA Astrophysics Data System (ADS)

Mueller-Wodarg, Ingo; Rosenblatt, Pascal; Bruinsma, Sean; Yelle, Roger; Svedhem, Håkan; Forbes, Jeffrey M.; Withers, Paul; Keating Sci. Gerald, Sr.; Lopez-Valverde, Miguel Angel

The thermosphere of Venus has been extensively observed in-situ primarily by the Pioneer Venus Orbiter, but those measurements concentrated on the low latitude regions. Until recently, no in-situ observations were made of the polar thermosphere of Venus, and reference atmospheres such as the VTS3 and VIRA models relied on solar zenith angle trends inferred at low latitudes in order to extrapolate to polar latitudes. The Venus Express Atmospheric Drag Experiment (VExADE) carries out accurate orbital tracking in order to infer for the first time ever the densities in Venus' polar thermosphere near 180 km altitude at solar minimum. During 3 recent tracking campaigns we obtained density measurements that allow us to compare actual densities in those regions with those predicted by the reference atmosphere models. We constructed a hydrostatic diffusive equilibrium at-mosphere model that interpolates between the Venus Express remote sensing measurements in the upper mesosphere and lower thermosphere region and the in-situ drag measurements by VExADE. This paper will present and discuss our latest findings.

Inference of relativistic electron spectra from measurements of inverse Compton radiation

NASA Astrophysics Data System (ADS)

Craig, I. J. D.; Brown, J. C.

1980-07-01

The inference of relativistic electron spectra from spectral measurement of inverse Compton radiation is discussed for the case where the background photon spectrum is a Planck function. The problem is formulated in terms of an integral transform that relates the measured spectrum to the unknown electron distribution. A general inversion formula is used to provide a quantitative assessment of the information content of the spectral data. It is shown that the observations must generally be augmented by additional information if anything other than a rudimentary two or three parameter model of the source function is to be derived. It is also pointed out that since a similar equation governs the continuum spectra emitted by a distribution of black-body radiators, the analysis is relevant to the problem of stellar population synthesis from galactic spectra.

Device and method for relativistic electron beam heating of a high-density plasma to drive fast liners

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner which is generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner.

IV INTERNATIONAL CONFERENCE ON ATOM AND MOLECULAR PULSED LASERS (AMPL'99): Critical electron density in a self-contained copper vapour laser in the restricted pulse repetition rate

NASA Astrophysics Data System (ADS)

Yakovlenko, Sergei I.

2000-06-01

One of the mechanisms of the inversion breaking in copper vapour lasers caused by a high prepulse electron density is considered. Inversion breaking occurs at a critical electron density Ne cr. If the prepulse electron density exceeds Ne cr, the electron temperature Te cr cannot reach, during a plasma heating pulse, the temperature of ~2eV required for lasing. A simple estimate of Ne cr is made.

Temperatures and Altitudes of Jupiter's Ultraviolet Aurora Inferred from GHRS Observations with the Hubble Space Telescope

NASA Astrophysics Data System (ADS)

Kim, Y. H.; Fox, J. L.; Caldwell, John J.

1997-07-01

We observed the jovian UV auroral regions with the Goddard high resolution spectrograph (GHRS) on board the Hubble Space Telescope (HST) on Apr. 29, May 2, and June 10, 1995. Observations of target areas were made in pairs in the two wavelength ranges 1257-1293 Å and 1587-1621 Å. Spectra in the long wavelength range are dominated by emissions of the H2Lyman band system and show well separated rotational features, which we have used to determine the temperatures of the auroral emission regions. Spectra in the short wavelength range are mostly due to emission in the H2Lyman and Werner band systems, but their intensities are reduced by hydrocarbon absorption. The brightest spectral pair was observed toward an area with longitude 155° and jovicentric latitude 58° when the central meridian longitudes (CMLs) were 191° and 203°. This area was found to be bright in our previous HST observations in 1993 and in HST faint object camera images. Assuming that electron impact excitation is the major source of the jovian aurora, we estimate total emission rates in the Lyman band system of about 270 and 46 kR for the long and short wavelength spectra of the pair, respectively. The attenuation of emission rate in the short wavelength spectrum implies a methane column density of about 3 × 1016cm-2, and a temperature of about 450 K is inferred from the long wavelength spectrum of the brightest pair. For all six pairs of observed spectra, we estimate methane column densities in the range (1-7) × 1016cm-2, which, when compared to a standard mid-latitude model, corresponds to a pressure range from a few μbar to a few tens of μbar. The temperatures derived are in the range 400-850 K with a possible tendency toward lower temperatures for higher methane column densities. This tendency and the uncertainty in the temperatures derived may indicate that the temperatures increases rapidly with altitude around the methane homopause in the auroral regions.

Semiannual Status Report. [excitation of electromagnetic waves in the whistler frequency range

NASA Technical Reports Server (NTRS)

1994-01-01

During the last six months, we have continued our study of the excitation of electromagnetic waves in the whistler frequency range and the role that these waves will play in the acceleration of electrons and ions in the auroral region. A paper entitled 'Electron Beam Excitation of Upstream Waves in the Whistler Mode Frequency Range' was listed in the Journal of Geophysical Research. In this paper, we have shown that an anisotropic electron beam (or gyrating electron beam) is capable of generating both left-hand and right-hand polarized electromagnetic waves in the whistler frequency range. Since right-hand polarized electromagnetic waves can interact with background electrons and left-hand polarized waves can interact with background ions through cyclotron resonance, it is possible that these beam generated left-hand and right-hand polarized electromagnetic waves can accelerate either ions or electrons (or both), depending on the physical parameters under consideration. We are currently carrying out a comprehensive study of the electromagnetic whistler and lower hybrid like waves observed in the auroral zone using both wave and particle data. Our first task is to identify these wave modes and compare it with particle observations. Using both the DE-1 particle and wave measurements, we can positively identify those electromagnetics lower hybrid like waves as fast magnetosonic waves and the upper cutoff of these waves is the local lower hybrid frequency. From the upper cutoff of the frequency spectrum, one can infer the particle density and the result is in very good agreement with the particle data. Since these electromagnetic lower hybrid like waves can have frequencies extended down to the local ion cyclotron frequency, it practically confirms that they are not whistler waves.

Electrophysiological time course and brain areas of spontaneous and intentional trait inferences

PubMed Central

Van Duynslaeger, Marijke; Verstraeten, Edwin

2007-01-01

This study measured event-related potentials during spontaneous and intentional trait inferences. Participants read sentences describing the behavior of a target person from which a strong moral trait could be inferred. The last word of each sentence determined the consistency with the trait induced during an introductory paragraph. In comparison with behaviors that were consistent with the implied trait, a P300 waveform was obtained when the behaviors were evaluative inconsistent with that trait. This dependency on behavioral consistency indicates that trait inferences were made previously while reading the preceding behaviors, irrespective of the participants’ spontaneous or intentional goals. Overall, the P300 shows considerable parallels between spontaneous and intentional inferences, indicating that the type and timing of the inconsistency process is very similar. In contrast, source localization (LORETA) of the event-related potentials suggest that spontaneous inferences show greater activation in the temporo-parietal junction compared to intentional inferences following an inconsistency. Memory measures taken after the presentation of the stimulus material involved sentence completion and trait-cued recall, and supported the occurrence of trait inferences associated with the actor. They also showed significant correlations with the neural components (i.e. P300 and its current density at the temporo-parietal junction) predominantly following spontaneous instructions, indicating that these components are valid neural indices of spontaneous inferences. PMID:18985139

Vertical and Lateral Electron Content in the Martian Ionosphere

NASA Astrophysics Data System (ADS)

Paetzold, M. P.; Peter, K.; Bird, M. K.; Häusler, B.; Tellmann, S.

2016-12-01

The radio-science experiment MaRS (Mars Express Radio Science) on the Mars Express spacecraft sounds the neutral atmosphere and ionosphere of Mars since 2004. Approximately 800 vertical profiles of the ionospheric electron density have been acquired until today. The vertical electron content (TEC) is easily computed from the vertical electron density profile by integrating along the altitude. The TEC is typically a fraction of a TEC unit (1E16 m^-2) and depends on the solar zenith angle. The magnitude of the TEC is however fully dominated by the electron density contained in the main layer M2. The contributions by the M1 layer below M2 or the topside is marginal. MaRS is using two radio frequencies for the sounding of the ionosphere. The directly observed differential Doppler from the two received frequencies is a measure of the lateral electron content that means along the ray path and perpendicular to the vertical electron density profile. Combining both the vertical electron density profile, the vertical TEC and the directly observed lateral TEC describes the lateral electron density distribution in the ionosphere.

Investigation of mid-latitude electron density enhancement using total electron content measurements and FORMOSAT-3/COSMIC electron density profiles

NASA Astrophysics Data System (ADS)

Rajesh, P. K.; Nanan, Balan; Liu, Jann-Yenq; Lin, Charles C. H.; Chang, S. Y.; Chen, Chia-Hung

This study investigates the mid-latitude electron density enhancement (MEDE) using global ionospheric map (GIM) total electron content (TEC) measurements and FORMOSAT-3/COSMIC (F3/C) electron density profiles. Diurnal, seasonal, latitudinal, and solar activity variations in the occurrence and strength of MEDE are examined using global GIM TEC data in the years 2002 and 2009. The results show that MEDE occurrence is pronounced during 2200-0400 LT, the feature also appears during day. The strength of MEDE maximizes around 0400 LT, and is very weak during daytime. The occurrence and strength show significant longitude dependence, and vary with season and solar activity. Concurrent F3/C electron density profiles also reveal enhancement of the peak electron density and total electron content. Further studies are carried out by examining the role of neutral wind in re-organizing the plasma using SAMI2 and HWM93 models. The results indicate that meridional neutral wind could cause the plasma to converge over mid-latitudes, and thus support in maintaining the enhancement.

Laser-Plasma Interaction Experiments at Direct-Drive Ignition-Relevant Plasma Conditions at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Solodov, A. A.; Rosenberg, M. J.; Myatt, J. F.; Shaw, J. G.; Seka, W.; Epstein, R.; Short, R. W.; Follett, R. K.; Regan, S. P.; Froula, D. H.; Radha, P. B.; Michel, P.; Chapman, T.; Hohenberger, M.

2017-10-01

Laser-plasma interaction (LPI) instabilities, such as stimulated Raman scattering (SRS) and two-plasmon decay, can be detrimental for direct-drive inertial confinement fusion because of target preheat by the high-energy electrons they generate. The radiation-hydrodynamic code DRACO was used to design planar-target experiments at the National Ignition Facility that generated plasma and interaction conditions relevant to ignition direct-drive designs (IL 1015W/cm2 , Te > 3 keV, density gradient scale lengths of Ln 600 μm). Laser-energy conversion efficiency to hot electrons of 0.5% to 2.5% with temperature of 45 to 60 keV was inferred from the experiment when the laser intensity at the quarter-critical surface increased from 6 to 15 ×1014W/cm2 . LPI was dominated by SRS, as indicated by the measured scattered-light spectra. Simulations of SRS using the LPI code LPSE have been performed and compared with predictions of theoretical models. Implications for ignition-scale direct-drive experiments will be discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Modelling Hard Gamma-Ray Emission from Supernova Remnants

NASA Technical Reports Server (NTRS)

Baring, Matthew

2000-01-01

The observation by the CANGAROO experiment of TeV emission from SN 1006, in conjunction with several instances of non-thermal X-ray emission from supernova remnants, has led to inferences of super-TeV electrons in these extended sources. While this is sufficient to propel the theoretical community in their modelling of particle acceleration and associated radiation, the anticipated emergence in the next decade of a number of new experiments probing the TeV and sub-TeV bands provides further substantial motivation for modellers. In particular, the quest for obtaining unambiguous gamma-ray signatures of cosmic ray ion acceleration defines a "Holy Grail" for observers and theorists alike. This review summarizes theoretical developments in the prediction of MeV-TeV gamma-rays from supernova remnants over the last five years, focusing on how global properties of models can impact, and be impacted by, hard gamma-ray observational programs, thereby probing the supernova remnant environment. Properties of central consideration include the maximum energy of accelerated particles, the density of the unshocked interstellar medium, the ambient magnetic field, and the relativistic electron-to-proton ratio. Criteria for determining good candidate remnants for observability in the TeV band are identified.

A Multi-spacecraft Study of the Magnetospheric Influence on Ionospheric Chemistry - a Detailed Examination of Recent Geomagnetically Active Periods

NASA Astrophysics Data System (ADS)

Petrinec, S. M.; Chenette, D. L.; Imhof, W. L.; Baker, D. N.; Barth, C. A.; Mankoff, K. D.; Luhmann, J. G.; Mason, G. M.; Mazur, J. E.; Evans, D. S.

2001-12-01

A detailed analysis of the particle precipitation into the auroral regions during specific storm intervals is performed. The global energetic particle input to the ionosphere and lower thermosphere is provided by several monitors; namely the Polar Ionospheric X-ray Experiment (PIXIE) on board the NASA/GGS Polar satellite (for inferred electron energies greater than about 3 keV); the TED sensor system on board the NOAA/Polar Orbiting Environmental Satellite (POES) (particle energies between about 50 eV and 20 keV), and the sensor system (LICA) on board the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) spacecraft (for electron energies greater then 25 keV). Changes in nitric oxide (NO) densities at altitudes between 97 and 150 km during these storm intervals are studied using observations from the Student Nitric Oxide Explorer (SNOE). Solar wind observations are also used to provide important information regarding the external drivers for the magnetospheric input to the upper atmosphere. Specific intervals of examination include the recent large geomagnetic event of March 31-April 1, 2001, and other events from the most recent solar maximum.

Photoelectron spectroscopy study of the electronic structures at CoPc/Bi(111) interface

NASA Astrophysics Data System (ADS)

Sun, Haoliang; Liang, Zhaofeng; Shen, Kongchao; Hu, Jinbang; Ji, Gengwu; Li, Zheshen; Li, Haiyang; Zhu, Zhiyuan; Li, Jiong; Gao, Xingyu; Han, Huang; Jiang, Zheng; Song, Fei

2017-07-01

Self-assembly of functional molecules on solid substrate has been recognized as an appealing approach for the fabrication of diverse nanostructures for nanoelectronics. Herein, we investigate the growth of cobalt phthalocyanine (CoPc) on a Bi(111) surface with focus on the interface electronic structures utilizing photoelectron spectroscopy. While charge transfer from bismuth substrate to the molecule results in the emergence of an interface component in the Co 3p core level at lower binding energy, core-levels associated to the molecular ligand (C 1s and N 1s) are less influenced by the adsorption. In addition, density functional theory (DFT) calculations also support the empirical inference that the molecule-substrate interaction mainly involves the out-of-plane empty Co 3d orbital and bismuth states. Finally, valence band spectra demonstrate the molecule-substrate interaction is induced by interface charge transfer, agreeing well with core level measurements. Charge transfer is shown to be mainly from the underlying bismuth substrate to the empty states located at the central Co atom in the CoPc molecules. This report may provide a fundamental basis to the on-surface engineering of interfaces for molecular devices and spintronics.

Observation of Transonic Ionization Fronts in Low-Density Foam Targets

NASA Astrophysics Data System (ADS)

Hoarty, D.; Barringer, L.; Vickers, C.; Willi, O.; Nazarov, W.

1999-04-01

Transonic ionization fronts have been observed in low-density chlorinated foam targets using time-resolved K-shell absorption spectroscopy. The front was driven by an intense pulse of soft x rays produced by high-power laser irradiation of a thin foil. The density and temperature profiles inferred from the radiographs provided detailed measurement of the conditions at a number of times. The experimental data were compared to radiation hydrodynamics simulations and reasonable agreement was obtained.

Information Theory and the Earth's Density Distribution

NASA Technical Reports Server (NTRS)

Rubincam, D. P.

1979-01-01

An argument for using the information theory approach as an inference technique in solid earth geophysics. A spherically symmetric density distribution is derived as an example of the method. A simple model of the earth plus knowledge of its mass and moment of inertia lead to a density distribution which was surprisingly close to the optimum distribution. Future directions for the information theory approach in solid earth geophysics as well as its strengths and weaknesses are discussed.

Using color as a proxy for symbiont density to assess health in the facultatively symbiotic northern coral, Astrangia poculata

NASA Astrophysics Data System (ADS)

Seballos, R.; Burmester, E. M.; Rotjan, R. D.

2016-02-01

Unlike most tropical corals, the northern star coral, Astrangia poculata, can survive and thrive with and without its photosynthetic endosymbionts, Symbiodinium psygmophilum. The degree of symbiosis is dependent on symbiont cell density, but the measurement of cell density is de facto destructive. We therefore explored the use of color (RGB) as a non-destructive proxy for symbiont state, building on the methods of Dimond and Carrington (2008). RGB color values, derived from a custom image analysis tool built in Matlab, were used to determine the inferred chlorophyll density of corals throughout an 8 week period. We found that non-destructive color analysis was a good metric to describe symbiotic state. To explore this method in an experimental context, we manipulated the impact of host condition (fed vs. starved) on the likelihood of wound healing in both symbiotic and aposymbiotic states. No difference was observed between either wounding or nutrition treatments, indicating that symbiotic state is likely controlled by other factors. In tropical corals, assessing the breakdown of symbiosis is an important predictor of holobiont stress, and colorimetric methods have been used to assess the extent of bleaching. Our method instead explores the spectral quality and extent of pigmentation to infer chlorophyll densities and symbiont cell densities, thereby extending the use of nondestructive methods to explore the strength of symbiosis.

Analysis of Total Electron Content and Electron Density Profile during Different Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Chapagain, N. P.; Rana, B.; Adhikari, B.

2017-12-01

Total Electron content (TEC) and electron density are the key parameters in the mitigation of ionospheric effects on radio communication system. Detail study of the TEC and electron density variations has been carried out during geomagnetic storms, with longitude and latitude, for four different locations: (13˚N -17˚N, 88˚E -98˚E), (30˚N-50˚N, 120˚W -95˚W), (29˚S-26˚S, 167˚W-163˚W,) and (60˚S-45˚S, 120˚W-105˚W) using the Gravity Recovery and Climate Experiment (GRACE) satellite observations. In order to find the geomagnetic activity, the solar wind parameters such as north-south component of inter planetary magnetic field (Bz), plasma drift velocity (Vsw), flow pressure (nPa), AE, Dst and Kp indices were obtained from Operating Mission as Nodes on the Internet (OMNI) web system. The data for geomagnetic indices have been correlated with the TEC and electron density for four different events of geomagnetic storms on 6 April 2008, 27 March 2008, 4 September 2008, and 11 October 2008. The result illustrates that the observed TEC and electron density profile significantly vary with longitudes and latitudes. This study illustrates that the values of TEC and the vertical electron density profile are influenced by the solar wind parameters associated with solar activities. The peak values of electron density and TEC increase as the geomagnetic storms become stronger. Similarly, the electron density profile varies with altitudes, which peaks around the altitude range of about 250- 350 km, depending on the strength of geomagnetic storms. The results clearly show that the peak electron density shifted to higher altitude (from about 250 km to 350 km) as the geomagnetic disturbances becomes stronger.

Profiles of Ionospheric Storm-enhanced Density during the 17 March 2015 Great Storm

NASA Astrophysics Data System (ADS)

Liu, J.; Wang, W.; Burns, A. G.; Yue, X.; Zhang, S.; Zhang, Y.

2015-12-01

Ionospheric F2 region peak densities (NmF2) are expected to show a positive phase correlation with total electron content (TEC), and electron density is expected to have an anti-correlation with electron temperature near the ionospheric F2 peak. However, we show that, during the 17 March 2015 great storm, TEC and F2 region electron density peak height (hmF2) over Millstone Hill increased, but the F2 region electron density peak (NmF2) decreased significantly during the storm-enhanced density (SED) phase of the storm compared with the quiet-time ionosphere. This SED occurred where there was a negative ionospheric storm near the F2 peak and below it. The weak ionosphere below the F2 peak resulted in much reduced downward heat conduction for the electrons, trapping the heat in the topside. This, in turn, increased the topside scale height, so that, even though electron densities at the F2 peak were depleted, TEC increased in the SED. The depletion in NmF2 was probably caused by an increase in the density of the molecular neutrals, resulting in enhanced recombination. In addition, the storm-time topside ionospheric electron density profile was much closer to diffusive equilibrium than non-storm time profile because of less daytime plasma flow from the ionosphere to the plasmasphere.

Local ion direction of motion and electron flow in a magnetically insulated diode

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

Maron, Y.; Litwin, C.

Ion motion in the acceleration region of a magnetically insulated ion diode and electron flux to the anode are studied locally. Two classes of slowly growing ion deflections are observed, indicating the presence of transverse electric fields in the diode gap. A simple model, which treates the diode as an emitting surface perturbed away from planarity, is offered to infer profiles of the electric field. These profiles are consistent with the observation that one of the ion-deflection classes is associated with a significant fraction of the increases of the electron flux to the anode. The inferred growth rates of themore » perturbations suggest that the observed ion deflections are caused by a nonuniform expansion of the anode plasma. The transverse electric fields associated with the perturbations constitute a significant (as much as 20%) fraction of the diode accelerating field. Short duration ion deflections accompanied by intense electron bursts to the anode are also observed. The data suggest that these deflections and the electron bursts originate at processes in the cathode plasma.« less

SU-G-JeP2-02: A Unifying Multi-Atlas Approach to Electron Density Mapping Using Multi-Parametric MRI for Radiation Treatment Planning

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

Ren, S; Tianjin University, Tianjin; Hara, W

Purpose: MRI has a number of advantages over CT as a primary modality for radiation treatment planning (RTP). However, one key bottleneck problem still remains, which is the lack of electron density information in MRI. In the work, a reliable method to map electron density is developed by leveraging the differential contrast of multi-parametric MRI. Methods: We propose a probabilistic Bayesian approach for electron density mapping based on T1 and T2-weighted MRI, using multiple patients as atlases. For each voxel, we compute two conditional probabilities: (1) electron density given its image intensity on T1 and T2-weighted MR images, and (2)more » electron density given its geometric location in a reference anatomy. The two sources of information (image intensity and spatial location) are combined into a unifying posterior probability density function using the Bayesian formalism. The mean value of the posterior probability density function provides the estimated electron density. Results: We evaluated the method on 10 head and neck patients and performed leave-one-out cross validation (9 patients as atlases and remaining 1 as test). The proposed method significantly reduced the errors in electron density estimation, with a mean absolute HU error of 138, compared with 193 for the T1-weighted intensity approach and 261 without density correction. For bone detection (HU>200), the proposed method had an accuracy of 84% and a sensitivity of 73% at specificity of 90% (AUC = 87%). In comparison, the AUC for bone detection is 73% and 50% using the intensity approach and without density correction, respectively. Conclusion: The proposed unifying method provides accurate electron density estimation and bone detection based on multi-parametric MRI of the head with highly heterogeneous anatomy. This could allow for accurate dose calculation and reference image generation for patient setup in MRI-based radiation treatment planning.« less

Natural language processing and inference rules as strategies for updating problem list in an electronic health record.

PubMed

Plazzotta, Fernando; Otero, Carlos; Luna, Daniel; de Quiros, Fernan Gonzalez Bernaldo

2013-01-01

Physicians do not always keep the problem list accurate, complete and updated. To analyze natural language processing (NLP) techniques and inference rules as strategies to maintain completeness and accuracy of the problem list in EHRs. Non systematic literature review in PubMed, in the last 10 years. Strategies to maintain the EHRs problem list were analyzed in two ways: inputting and removing problems from the problem list. NLP and inference rules have acceptable performance for inputting problems into the problem list. No studies using these techniques for removing problems were published Conclusion: Both tools, NLP and inference rules have had acceptable results as tools for maintain the completeness and accuracy of the problem list.

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

Finzel, Kati, E-mail: kati.finzel@liu.se

The local conditions for the Pauli potential that are necessary in order to yield self-consistent electron densities from orbital-free calculations are investigated for approximations that are expressed with the help of a local position variable. It is shown that those local conditions also apply when the Pauli potential is given in terms of the electron density. An explicit formula for the Ne atom is given, preserving the local conditions during the iterative procedure. The resulting orbital-free electron density exhibits proper shell structure behavior and is in close agreement with the Kohn-Sham electron density. This study demonstrates that it is possiblemore » to obtain self-consistent orbital-free electron densities with proper atomic shell structure from simple one-point approximations for the Pauli potential at local density level.« less

Relationship between the Geotail spacecraft potential and the magnetospheric electron number density including the distant tail regions

NASA Astrophysics Data System (ADS)

Ishisaka, K.; Okada, T.; Tsuruda, K.; Hayakawa, H.; Mukai, T.; Matsumoto, H.

2001-04-01

The spacecraft potential has been used to derive the electron number density surrounding the spacecraft in the magnetosphere and solar wind. We have investigated the correlation between the spacecraft potential of the Geotail spacecraft and the electron number density derived from the plasma waves in the solar wind and almost all the regions of the magnetosphere, except for the high-density plasmasphere, and obtained an empirical formula to show their relation. The new formula is effective in the range of spacecraft potential from a few volts up to 90 V, corresponding to the electron number density from 0.001 to 50 cm-3. We compared the electron number density obtained by the empirical formula with the density obtained by the plasma wave and plasma particle measurements. On occasions the density determined by plasma wave measurements in the lobe region is different from that calculated by the empirical formula. Using the difference in the densities measured by two methods, we discuss whether or not the lower cutoff frequency of the plasma waves, such as continuum radiation, indicates the local electron density near the spacecraft. Then we applied the new relation to the spacecraft potential measured by the Geotail spacecraft during the period from October 1993 to December 1995, and obtained the electron spatial distribution in the solar wind and magnetosphere, including the distant tail region. Higher electron number density is clearly observed on the dawnside than on the duskside of the magnetosphere in the distant tail beyond 100RE.

[Study on the distribution of plasma parameters in electrodeless lamp using emission spectrometry].

PubMed

Wang, Chang-Quan; Zhang, Gui-Xin; Wang, Xin-Xin; Shao, Ming-Song; Dong, Jin-Yang; Wang, Zan-Ji

2011-09-01

Electrodeless lamp in pear shape was ignited using inductively coupled discharge setup and Ar-Hg mixtures as working gas. The changes in electronic temperature and density with axial and radial positions at 5 s of igniting were studied by means of emission spectrometry. The changes in electronic temperature were obtained according to the Ar line intensity ratio of 425.9 nm/ 750.4 nm. And the variations in electronic density were analyzed using 750.4 nm line intensity. It was found that plasma electronic temperature and density is various at different axial or radial positions. The electronic temperatures first increase, then decrease, and then increase quickly, and finally decline. While the electronic density firstly increase quickly, the decrease, and then rise slowly and finally decline again with axial distance increasing. With radial distance increasing, electronic temperature increases to a stable area, then continues to rise, while electronic density decreases.

Density contrast across the Moho beneath the Indian shield: Implications for isostasy

NASA Astrophysics Data System (ADS)

Paul, Himangshu; Mangalampally, Ravi Kumar; Tiwari, Virendra Mani; Singh, Arun; Chadha, Rajender Kumar; Davuluri, Srinagesh

2018-04-01

Knowledge of isostasy provides insights into how excess (or deficit) of mass on and within the lithosphere is maintained over different time scales, and also helps decipher the vertical dynamics. In continental regions, isostasy is primarily manifested as a crustal root, the extent of which is defined by the lithospheric strength and the density contrast at the Moho. In this study, we briefly review the methodology for extracting the density contrast across the Moho using the amplitudes of the P-to-s converted and free-surface reverberating phases in a receiver function (RF). We test the efficacy of this technique by applying it on synthetic and real data from 10 broadband seismic stations sited on diverse tectonic provinces in the Indian shield. We determine the density contrast after parameterizing the shear-wave velocity structure beneath the stations using the nearest neighbourhood algorithm. We find considerable variation in the density contrast across the Moho beneath the stations (0.4-0.65 gm/cc). This is explained in terms of isostatic compensation, incorporating the existing estimates of lithospheric strength (Te). Crustal roots computed using the estimated Te and the deduced density contrast substantiate the crustal thickness values inferred through RF analysis, and vice versa. This illustrates isostasy as a combination of variation in density contrast and Te. The density contrasts and crustal thicknesses inferred from RF analysis explain well the isostatic compensation mechanism in different regions. However, unusually large density contrasts (∼0.6 gm/cc) corresponding to elevated regions are intriguing and warrant further investigations. Our observation of varied density contrasts at the Moho in a Precambrian continental setting is interesting and raises a question about the existence of such situations in other parts of the world.

Petrophysical Properties of Twenty Drill Cores from the Los Azufres, Mexico, Geothermal Field

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

Iglesias, E.R.; Contreras L., E.; Garcia G., A.

1987-01-20

For this study we selected 20 drill cores covering a wide range of depths (400-3000 m), from 15 wells, that provide a reasonable coverage of the field. Only andesite, the largely predominant rock type in the field, was included in this sample. We measured bulk density, grain (solids) density, effective porosity and (matrix) permeability on a considerable number of specimens taken from the cores; and inferred the corresponding total porosity and fraction of interconnected total porosity. We characterized the statistical distributions of the measured and inferred variables. The distributions of bulk density and grain density resulted approximately normal; the distributionsmore » of effective porosity, total porosity and fraction of total porosity turned out to be bimodal; the permeability distribution resulted highly skewed towards very small (1 mdarcy) values, though values as high as 400 mdarcies were measured. We also characterized the internal inhomogeneity of the cores by means of the ratio (standard deviation/mean) corresponding to the bulk density in each core (in average there are 9 specimens per core). The cores were found to present clearly discernible inhomogeneity; this quantitative characterization will help design new experimental work and interpret currently available and forthcoming results. We also found statistically significant linear correlations between total density and density of solids, effective porosity and total density, total porosity and total density, fraction of interconnected total porosity and the inverse of the effective porosity, total porosity and effective porosity; bulk density and total porosity also correlate with elevation. These results provide the first sizable and statistically detailed database available on petrophysical properties of the Los Azufres andesites. 1 tab., 16 figs., 4 refs.« less

The Holographic Electron Density Theorem, de-quantization, re-quantization, and nuclear charge space extrapolations of the Universal Molecule Model

NASA Astrophysics Data System (ADS)

Mezey, Paul G.

2017-11-01

Two strongly related theorems on non-degenerate ground state electron densities serve as the basis of "Molecular Informatics". The Hohenberg-Kohn theorem is a statement on global molecular information, ensuring that the complete electron density contains the complete molecular information. However, the Holographic Electron Density Theorem states more: the local information present in each and every positive volume density fragment is already complete: the information in the fragment is equivalent to the complete molecular information. In other words, the complete molecular information provided by the Hohenberg-Kohn Theorem is already provided, in full, by any positive volume, otherwise arbitrarily small electron density fragment. In this contribution some of the consequences of the Holographic Electron Density Theorem are discussed within the framework of the "Nuclear Charge Space" and the Universal Molecule Model. In the Nuclear Charge Space" the nuclear charges are regarded as continuous variables, and in the more general Universal Molecule Model some other quantized parameteres are also allowed to become "de-quantized and then re-quantized, leading to interrelations among real molecules through abstract molecules. Here the specific role of the Holographic Electron Density Theorem is discussed within the above context.

Analysis of rapid increase in the plasma density during the ramp-up phase in a radio frequency negative ion source by large-scale particle simulation

NASA Astrophysics Data System (ADS)

Yasumoto, M.; Ohta, M.; Kawamura, Y.; Hatayama, A.

2014-02-01

Numerical simulations become useful for the developing RF-ICP (Radio Frequency Inductively Coupled Plasma) negative ion sources. We are developing and parallelizing a two-dimensional three velocity electromagnetic Particle-In-Cell code. The result shows rapid increase in the electron density during the density ramp-up phase. A radial electric field due to the space charge is produced with increase in the electron density and the electron transport in the radial direction is suppressed. As a result, electrons stay for a long period in the region where the inductive electric field is strong, and this leads efficient electron acceleration and a rapid increasing of the electron density.

A steady-state supersonic downflow in the transition region above a sunspot umbra

NASA Astrophysics Data System (ADS)

Straus, Thomas; Fleck, Bernhard; Andretta, Vincenzo

2015-10-01

We investigate a small-scale (~1.5 Mm along the slit), supersonic downflow of about 90 km s-1 in the transition region above the lightbridged sunspot umbra in AR 11836. The observations were obtained with the Interface Region Spectrograph (IRIS) on 2013 September 2 from 16:40 to 17:59 UT. The downflow shows up as redshifted "satellite" lines of the Si iv and O iv transition region lines and is remarkably steady over the observing period of nearly 80 min. The downflow is not visible in the chromospheric lines, which only show an intensity enhancement at the location of the downflow. The density inferred from the line ratio of the redshifted satellites of the O iv lines (Ne = 1010.6 ± 0.25 cm-3) is only a factor 2 smaller than the one inferred from the main components (Ne = 1010.95 ± 0.20 cm-3). Consequently, this implies a substantial mass flux (~5 × 10-7 g cm-2 s-1), which would evacuate the overlying corona on timescales close to 10 s. We interpret these findings as evidence of a stationary termination shock of a supersonic siphon flow in a cool loop that is rooted in the central umbra of the spot. The movie is available in electronic form at http://www.aanda.org

Analysis of Co-spatial UV-Optical STIS Spectra of Planetary Nebulae From HST Cycle 19 GO 12600

NASA Astrophysics Data System (ADS)

Miller, Timothy R.; Henry, Richard B. C.; Dufour, Reginald J.; Kwitter, Karen B.; Shaw, Richard A.; Balick, Bruce; Corradi, Romano

2015-01-01

We present an analysis of five spatially resolved planetary nebulae (PNe), NGC 5315, NGC 5882, NGC 7662, IC 2165, and IC 3568, from observations in the Cycle 19 program GO 12600 using HST STIS. Details of the observations and data are presented in the poster by Dufour et al. in this session. These five observations cover the wavelength range 1150-10,270 Å with 0.2 and 0.5 arcsec wide slits, and are co-spatial to 0.1 arcsec along a 25 arcsec length across each nebula. This unprecedented resolution in both wavelength and spatial coverage enabled detailed studies of physical conditions and abundances from UV line ion emissions (compared to optical lines). We first analyzed the low- and moderate-resolution UV emission lines of carbon using the resolved lines of C III] 1906.68 and 1908.73, which yielded a direct measurement of the density within the volume occupied by doubly-ionized carbon and other similar co-spatial ions. Next, each PN spectrum was divided into spatial sub-regions in order to assess inferred density variations among the sub-regions along the entire slit. Variations in electron temperature and chemical abundances were also probed. Lastly, these nebulae were modeled in detail with the photoionization code CLOUDY. This modeling tested different density profiles in order to reproduce the observed density variations and temperature fluctuations, and constrain central star parameters. We gratefully acknowledge generous support from NASA through grants related to the Cycle 19 program GO 12600, as well as from the University of Oklahoma.

Inner Plasma Structure of the Low-Latitude Reconnection Layer

NASA Technical Reports Server (NTRS)

Zhang, Q.-H.; Dunlop, M. W.; Lockwood, M.; Lavraud, B.; Bogdanova, Y. V.; Hasegawa, H.; Yang, H. -G.; Liu, R. -Y.; Hu, H. -Q.; Zhang, B. -C.;

Optical determination of the electronic coupling and intercalation geometry of thiazole orange homodimer in DNA

NASA Astrophysics Data System (ADS)

Cunningham, Paul D.; Bricker, William P.; Díaz, Sebastián A.; Medintz, Igor L.; Bathe, Mark; Melinger, Joseph S.

2017-08-01

Sequence-selective bis-intercalating dyes exhibit large increases in fluorescence in the presence of specific DNA sequences. This property makes this class of fluorophore of particular importance to biosensing and super-resolution imaging. Here we report ultrafast transient anisotropy measurements of resonance energy transfer (RET) between thiazole orange (TO) molecules in a complex formed between the homodimer TOTO and double-stranded (ds) DNA. Biexponential homo-RET dynamics suggest two subpopulations within the ensemble: 80% intercalated and 20% non-intercalated. Based on the application of the transition density cube method to describe the electronic coupling and Monte Carlo simulations of the TOTO/dsDNA geometry, the dihedral angle between intercalated TO molecules is estimated to be 81° ± 5°, corresponding to a coupling strength of 45 ± 22 cm-1. Dye intercalation with this geometry is found to occur independently of the underlying DNA sequence, despite the known preference of TOTO for the nucleobase sequence CTAG. The non-intercalated subpopulation is inferred to have a mean inter-dye separation distance of 19 Å, corresponding to coupling strengths between 0 and 25 cm-1. This information is important to enable the rational design of energy transfer systems that utilize TOTO as a relay dye. The approach used here is generally applicable to determining the electronic coupling strength and intercalation configuration of other dimeric bis-intercalators.

Gedanken densities and exact constraints in density functional theory.

PubMed

Perdew, John P; Ruzsinszky, Adrienn; Sun, Jianwei; Burke, Kieron

2014-05-14

Approximations to the exact density functional for the exchange-correlation energy of a many-electron ground state can be constructed by satisfying constraints that are universal, i.e., valid for all electron densities. Gedanken densities are designed for the purpose of this construction, but need not be realistic. The uniform electron gas is an old gedanken density. Here, we propose a spherical two-electron gedanken density in which the dimensionless density gradient can be an arbitrary positive constant wherever the density is non-zero. The Lieb-Oxford lower bound on the exchange energy can be satisfied within a generalized gradient approximation (GGA) by bounding its enhancement factor or simplest GGA exchange-energy density. This enhancement-factor bound is well known to be sufficient, but our gedanken density shows that it is also necessary. The conventional exact exchange-energy density satisfies no such local bound, but energy densities are not unique, and the simplest GGA exchange-energy density is not an approximation to it. We further derive a strongly and optimally tightened bound on the exchange enhancement factor of a two-electron density, which is satisfied by the local density approximation but is violated by all published GGA's or meta-GGA's. Finally, some consequences of the non-uniform density-scaling behavior for the asymptotics of the exchange enhancement factor of a GGA or meta-GGA are given.

Quantitative electron density characterization of soft tissue substitute plastic materials using grating-based x-ray phase-contrast imaging

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

Sarapata, A.; Chabior, M.; Zanette, I.

2014-10-15

Many scientific research areas rely on accurate electron density characterization of various materials. For instance in X-ray optics and radiation therapy, there is a need for a fast and reliable technique to quantitatively characterize samples for electron density. We present how a precise measurement of electron density can be performed using an X-ray phase-contrast grating interferometer in a radiographic mode of a homogenous sample in a controlled geometry. A batch of various plastic materials was characterized quantitatively and compared with calculated results. We found that the measured electron densities closely match theoretical values. The technique yields comparable results between amore » monochromatic and a polychromatic X-ray source. Measured electron densities can be further used to design dedicated X-ray phase contrast phantoms and the additional information on small angle scattering should be taken into account in order to exclude unsuitable materials.« less

Anomalously-dense firn in an ice-shelf channel revealed by wide-angle radar

NASA Astrophysics Data System (ADS)

Drews, R.; Brown, J.; Matsuoka, K.; Witrant, E.; Philippe, M.; Hubbard, B.; Pattyn, F.

2015-10-01

The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium for which knowledge of the depth-averaged density is essential. The densification from snow to ice depends on a number of local factors (e.g. temperature and surface mass balance) causing spatial and temporal variations in density-depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar datasets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. Using a novel algorithm including traveltime inversion and raytracing with a prescribed shape of the depth-density relationship, we show that the depth to internal reflectors, the local ice thickness and depth-averaged densities can reliably be reconstructed. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggests that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals 10 % denser firn inside compared to outside the channel. The denser firn in the ice-shelf channel should be accounted for when using the hydrostatic ice thickness for determining basal melt rates. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

Constraining variable density of ice shelves using wide-angle radar measurements

NASA Astrophysics Data System (ADS)

Drews, Reinhard; Brown, Joel; Matsuoka, Kenichi; Witrant, Emmanuel; Philippe, Morgane; Hubbard, Bryn; Pattyn, Frank

2016-04-01

The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium, for which knowledge of the depth-averaged density is essential. The densification from snow to ice depends on a number of local factors (e.g., temperature and surface mass balance) causing spatial and temporal variations in density-depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar data sets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. We reconstruct depth to internal reflectors, local ice thickness, and firn-air content using a novel algorithm that includes traveltime inversion and ray tracing with a prescribed shape of the depth-density relationship. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggest that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals that the firn inside the channel is 4.7 % denser than that outside the channel. Hydrostatic ice thickness calculations used for determining basal melt rates should account for the denser firn in ice-shelf channels. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

Unscreening Modified Gravity in the Matter Power Spectrum.

PubMed

Lombriser, Lucas; Simpson, Fergus; Mead, Alexander

2015-06-26

Viable modifications of gravity that may produce cosmic acceleration need to be screened in high-density regions such as the Solar System, where general relativity is well tested. Screening mechanisms also prevent strong anomalies in the large-scale structure and limit the constraints that can be inferred on these gravity models from cosmology. We find that by suppressing the contribution of the screened high-density regions in the matter power spectrum, allowing a greater contribution of unscreened low densities, modified gravity models can be more readily discriminated from the concordance cosmology. Moreover, by variation of density thresholds, degeneracies with other effects may be dealt with more adequately. Specializing to chameleon gravity as a worked example for screening in modified gravity, employing N-body simulations of f(R) models and the halo model of chameleon theories, we demonstrate the effectiveness of this method. We find that a percent-level measurement of the clipped power at k<0.3h/Mpc can yield constraints on chameleon models that are more stringent than what is inferred from Solar System tests or distance indicators in unscreened dwarf galaxies. Finally, we verify that our method is also applicable to the Vainshtein mechanism.

Inference about density and temporary emigration in unmarked populations

USGS Publications Warehouse

Chandler, Richard B.; Royle, J. Andrew; King, David I.

2011-01-01

Few species are distributed uniformly in space, and populations of mobile organisms are rarely closed with respect to movement, yet many models of density rely upon these assumptions. We present a hierarchical model allowing inference about the density of unmarked populations subject to temporary emigration and imperfect detection. The model can be fit to data collected using a variety of standard survey methods such as repeated point counts in which removal sampling, double-observer sampling, or distance sampling is used during each count. Simulation studies demonstrated that parameter estimators are unbiased when temporary emigration is either "completely random" or is determined by the size and location of home ranges relative to survey points. We also applied the model to repeated removal sampling data collected on Chestnut-sided Warblers (Dendroica pensylvancia) in the White Mountain National Forest, USA. The density estimate from our model, 1.09 birds/ha, was similar to an estimate of 1.11 birds/ha produced by an intensive spot-mapping effort. Our model is also applicable when processes other than temporary emigration affect the probability of being available for detection, such as in studies using cue counts. Functions to implement the model have been added to the R package unmarked.

Ion Densities in the Nightside Ionosphere of Mars: Effects of Electron Impact Ionization

NASA Astrophysics Data System (ADS)

Girazian, Z.; Mahaffy, P.; Lillis, R. J.; Benna, M.; Elrod, M.; Fowler, C. M.; Mitchell, D. L.

2017-11-01

We use observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to show how superthermal electron fluxes and crustal magnetic fields affect ion densities in the nightside ionosphere of Mars. We find that due to electron impact ionization, high electron fluxes significantly increase the CO2+, O+, and O2+ densities below 200 km but only modestly increase the NO+ density. High electron fluxes also produce distinct peaks in the CO2+, O+, and O2+ altitude profiles. We also find that superthermal electron fluxes are smaller near strong crustal magnetic fields. Consequently, nightside ion densities are also smaller near strong crustal fields because they decay without being replenished by electron impact ionization. Furthermore, the NO+/O2+ ratio is enhanced near strong crustal fields because, in the absence of electron impact ionization, O2+ is converted into NO+ and not replenished. Our results show that electron impact ionization is a significant source of CO2+, O+, and O2+ in the nightside ionosphere of Mars.

Temporal-spatial measurement of electron relaxation time in femtosecond laser induced plasma using two-color pump-probe imaging technique

NASA Astrophysics Data System (ADS)

Pan, Changji; Jiang, Lan; Wang, Qingsong; Sun, Jingya; Wang, Guoyan; Lu, Yongfeng

2018-05-01

The femtosecond (fs) laser is a powerful tool to study ultrafast plasma dynamics, especially electron relaxation in strong ionization of dielectrics. Herein, temporal-spatial evolution of femtosecond laser induced plasma in fused silica was investigated using a two-color pump-probe technique (i.e., 400 nm and 800 nm, respectively). We demonstrated that when ionized electron density is lower than the critical density, free electron relaxation time is inversely proportional to electron density, which can be explained by the electron-ion scattering regime. In addition, electron density evolution within plasma was analyzed in an early stage (first 800 fs) of the laser-material interaction.

Ionospheric E-region electron density and neutral atmosphere variations

NASA Technical Reports Server (NTRS)

Stick, T. L.

1976-01-01

Electron density deviations from a basic variation with the solar zenith angle were investigated. A model study was conducted in which the effects of changes in neutral and relative densities of atomic and molecular oxygen on calculated electron densities were compared with incoherent scatter measurements in the height range 100-117 km at Arecibo, Puerto Rico. The feasibility of determining tides in the neutral atmosphere from electron density profiles was studied. It was determined that variations in phase between the density and temperature variation and the comparable magnitudes of their components make it appear improbable that the useful information on tidal modes can be obtained in this way.

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas with linear density and temperature ramps

NASA Astrophysics Data System (ADS)

Hashemzadeh, M.

2018-01-01

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas are investigated in the presence of various laser intensities and linear density and temperature ramps. Considering the ponderomotive force and using the momentum transfer and energy equations, the nonlinear electron density is derived. Taking into account the paraxial approximation and nonlinear electron density, a nonlinear differential equation, governing the focusing and defocusing of the laser beam, is obtained. Results show that in the absence of ramps the laser beam is focused between a minimum and a maximum value of laser intensity. For a certain value of laser intensity and initial electron density, the self-focusing process occurs in a temperature range which reaches its maximum at turning point temperature. However, the laser beam is converged in a narrow range for various amounts of initial electron density. It is indicated that the σ2 parameter and its sign can affect the self-focusing process for different values of laser intensity, initial temperature, and initial density. Finally, it is found that although the electron density ramp-down diverges the laser beam, electron density ramp-up improves the self-focusing process.

Molecular Electron Density Theory: A Modern View of Reactivity in Organic Chemistry.

PubMed

Domingo, Luis R

2016-09-30

A new theory for the study of the reactivity in Organic Chemistry, named Molecular Electron Density Theory (MEDT), is proposed herein. MEDT is based on the idea that while the electron density distribution at the ground state is responsible for physical and chemical molecular properties, as proposed by the Density Functional Theory (DFT), the capability for changes in electron density is responsible for molecular reactivity. Within MEDT, the reactivity in Organic Chemistry is studied through a rigorous quantum chemical analysis of the changes of the electron density as well as the energies associated with these changes along the reaction path in order to understand experimental outcomes. Studies performed using MEDT allow establishing a modern rationalisation and to gain insight into molecular mechanisms and reactivity in Organic Chemistry.

Communication: Near-locality of exchange and correlation density functionals for 1- and 2-electron systems

NASA Astrophysics Data System (ADS)

Sun, Jianwei; Perdew, John P.; Yang, Zenghui; Peng, Haowei

2016-05-01

The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin density approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound.

Two-dimensional electron density characterisation of arc interruption phenomenon in current-zero phase

NASA Astrophysics Data System (ADS)

Inada, Yuki; Kamiya, Tomoki; Matsuoka, Shigeyasu; Kumada, Akiko; Ikeda, Hisatoshi; Hidaka, Kunihiko

2018-01-01

Two-dimensional electron density imaging over free burning SF6 arcs and SF6 gas-blast arcs was conducted at current zero using highly sensitive Shack-Hartmann type laser wavefront sensors in order to experimentally characterise electron density distributions for the success and failure of arc interruption in the thermal reignition phase. The experimental results under an interruption probability of 50% showed that free burning SF6 arcs with axially asymmetric electron density profiles were interrupted with a success rate of 88%. On the other hand, the current interruption of SF6 gas-blast arcs was reproducibly achieved under locally reduced electron densities and the interruption success rate was 100%.

Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer

NASA Astrophysics Data System (ADS)

Kube, R.; Garcia, O. E.; Theodorsen, A.; Brunner, D.; Kuang, A. Q.; LaBombard, B.; Terry, J. L.

2018-06-01

The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma conditions in an ohmically heated, lower single null diverted discharge. The electron density and temperature are strongly correlated and feature fluctuation statistics similar to the ion saturation current. Both electron density and temperature time series are dominated by intermittent, large-amplitude burst with an exponential distribution of both burst amplitudes and waiting times between them. The characteristic time scale of the large-amplitude bursts is approximately 15 μ {{s}}. Large-amplitude velocity fluctuations feature a slightly faster characteristic time scale and appear at a faster rate than electron density and temperature fluctuations. Describing these time series as a superposition of uncorrelated exponential pulses, we find that probability distribution functions, power spectral densities as well as auto-correlation functions of the data time series agree well with predictions from the stochastic model. The electron particle and heat fluxes present large-amplitude fluctuations. For this low-density plasma, the radial electron heat flux is dominated by convection, that is, correlations of fluctuations in the electron density and radial velocity. Hot and dense blobs contribute only a minute fraction of the total fluctuation driven heat flux.

MAVEN Observations of Dayside Peak Electron Densities in the Ionosphere of Mars

NASA Astrophysics Data System (ADS)

Vogt, M. F.; Withers, P.; Andersson, L.; Mahaffy, P. R.; Benna, M.; Elrod, M. K.; Connerney, J. E. P.; Espley, J. R.; Eparvier, F. G.; Jakosky, B. M.

2016-12-01

The peak electron density in the dayside Martian ionosphere is a valuable diagnostic of the state of the ionosphere. Its dependence on factors like the solar zenith angle, ionizing solar irradiance, neutral scale height, and electron temperature has been well studied. The MAVEN spacecraft's September 2015 "deep dip" orbits, in which the orbital periapsis is lowered to 120 km, provided our first opportunity since Viking to sample in situ a complete dayside electron density profiles including the main peak, and the first observations with contemporaneous comprehensive measurements of the local plasma and magnetic field properties. We have analyzed the peak electron density measurements from the MAVEN deep dip orbits and will discuss their variability with various ionospheric properties, including the proximity to regions of large crustal magnetic fields, and external drivers. We will also present observations of the electron temperature and atmospheric neutral and ion composition at the altitude of the peak electron density.

Use of Total Electron Content data to analyze ionosphere electron density gradients

NASA Astrophysics Data System (ADS)

Nava, B.; Radicella, S. M.; Leitinger, R.; Coisson, P.

In presence of electron density gradients the thin shell approximation for the ionosphere used together with a simple mapping function to convert slant Total Electron Content TEC to vertical TEC could lead to TEC conversion errors Therefore these mapping function errors can be used to identify the effects of the electron density gradients in the ionosphere In the present work high precision GPS derived slant TEC data have been used to investigate the effects of the electron density gradients in the middle and low latitude ionosphere under geomagnetic quiet and disturbed conditions In particular the data corresponding to the geographic area of the American sector for the days 5-7 April 2000 have been used to perform a complete analysis of mapping function errors based on the coinciding pierce point technique The results clearly illustrate the electron density gradient effects according to the locations considered and to the actual levels of disturbance of the ionosphere

Inference of reaction rate parameters based on summary statistics from experiments

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

Khalil, Mohammad; Chowdhary, Kamaljit Singh; Safta, Cosmin

Here, we present the results of an application of Bayesian inference and maximum entropy methods for the estimation of the joint probability density for the Arrhenius rate para meters of the rate coefficient of the H 2/O 2-mechanism chain branching reaction H + O 2 → OH + O. Available published data is in the form of summary statistics in terms of nominal values and error bars of the rate coefficient of this reaction at a number of temperature values obtained from shock-tube experiments. Our approach relies on generating data, in this case OH concentration profiles, consistent with the givenmore » summary statistics, using Approximate Bayesian Computation methods and a Markov Chain Monte Carlo procedure. The approach permits the forward propagation of parametric uncertainty through the computational model in a manner that is consistent with the published statistics. A consensus joint posterior on the parameters is obtained by pooling the posterior parameter densities given each consistent data set. To expedite this process, we construct efficient surrogates for the OH concentration using a combination of Pad'e and polynomial approximants. These surrogate models adequately represent forward model observables and their dependence on input parameters and are computationally efficient to allow their use in the Bayesian inference procedure. We also utilize Gauss-Hermite quadrature with Gaussian proposal probability density functions for moment computation resulting in orders of magnitude speedup in data likelihood evaluation. Despite the strong non-linearity in the model, the consistent data sets all res ult in nearly Gaussian conditional parameter probability density functions. The technique also accounts for nuisance parameters in the form of Arrhenius parameters of other rate coefficients with prescribed uncertainty. The resulting pooled parameter probability density function is propagated through stoichiometric hydrogen-air auto-ignition computations to illustrate the need to account for correlation among the Arrhenius rate parameters of one reaction and across rate parameters of different reactions.« less

Inference of reaction rate parameters based on summary statistics from experiments

DOE PAGES

Khalil, Mohammad; Chowdhary, Kamaljit Singh; Safta, Cosmin; ...

2016-10-15

Here, we present the results of an application of Bayesian inference and maximum entropy methods for the estimation of the joint probability density for the Arrhenius rate para meters of the rate coefficient of the H 2/O 2-mechanism chain branching reaction H + O 2 → OH + O. Available published data is in the form of summary statistics in terms of nominal values and error bars of the rate coefficient of this reaction at a number of temperature values obtained from shock-tube experiments. Our approach relies on generating data, in this case OH concentration profiles, consistent with the givenmore » summary statistics, using Approximate Bayesian Computation methods and a Markov Chain Monte Carlo procedure. The approach permits the forward propagation of parametric uncertainty through the computational model in a manner that is consistent with the published statistics. A consensus joint posterior on the parameters is obtained by pooling the posterior parameter densities given each consistent data set. To expedite this process, we construct efficient surrogates for the OH concentration using a combination of Pad'e and polynomial approximants. These surrogate models adequately represent forward model observables and their dependence on input parameters and are computationally efficient to allow their use in the Bayesian inference procedure. We also utilize Gauss-Hermite quadrature with Gaussian proposal probability density functions for moment computation resulting in orders of magnitude speedup in data likelihood evaluation. Despite the strong non-linearity in the model, the consistent data sets all res ult in nearly Gaussian conditional parameter probability density functions. The technique also accounts for nuisance parameters in the form of Arrhenius parameters of other rate coefficients with prescribed uncertainty. The resulting pooled parameter probability density function is propagated through stoichiometric hydrogen-air auto-ignition computations to illustrate the need to account for correlation among the Arrhenius rate parameters of one reaction and across rate parameters of different reactions.« less

Detection of the Small Magellanic Cloud in gamma-rays with  Fermi /LAT

DOE PAGES

Abdo, A. A.

2010-11-01

Context. The flux of gamma rays with energies greater than 100 MeV is dominated by diffuse emission coming from cosmic-rays (CRs) illuminating the interstellar medium (ISM) of our Galaxy through the processes of Bremsstrahlung, pion production and decay, and inverse-Compton scattering. The study of this diffuse emission provides insight into the origin and transport of cosmic rays. Aims. We searched for gamma-ray emission from the Small Magellanic Cloud (SMC) in order to derive constraints on the cosmic-ray population and transport in an external system with properties different from the Milky Way. Methods. We analysed the first 17 months of continuousmore » all-sky observations by the Large Area Telescope (LAT) of the Fermi mission to determine the spatial distribution, flux and spectrum of the gamma-ray emission from the SMC. We also used past radio synchrotron observations of the SMC to study the population of CR electrons specifically. Results. We obtained the first detection of the SMC in high-energy gamma rays, with an integrated >100 MeV flux of (3.7 ± 0.7) × 10 -8 ph cm -2 s -1, with additional systematic uncertainty of ≤16%. The emission is steady and from an extended source ~3° in size. It is not clearly correlated with the distribution of massive stars or neutral gas, nor with known pulsars or supernova remnants, but a certain correlation with supergiant shells is observed. Conclusions. The observed flux implies an upper limit on the average CR nuclei density in the SMC of ~15% of the value measured locally in the Milky Way. The population of high-energy pulsars of the SMC may account for a substantial fraction of the gamma-ray flux, which would make the inferred CR nuclei density even lower. The average density of CR electrons derived from radio synchrotron observations is consistent with the same reduction factor but the uncertainties are large. From our current knowledge of the SMC, such a low CR density does not seem to be due to a lower rate of CR injection and rather indicates a smaller CR confinement volume characteristic size.« less

Detection of the Small Magellanic Cloud in gamma-rays with Fermi/LAT

NASA Astrophysics Data System (ADS)

Abdo, A. A.; Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Dermer, C. D.; de Palma, F.; Digel, S. W.; Silva, E. Do Couto E.; Drell, P. S.; Dubois, R.; Dumora, D.; Favuzzi, C.; Fegan, S. J.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Harding, A. K.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jean, P.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kerr, M.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Makeev, A.; Martin, P.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann-Godo, M.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Reposeur, T.; Ripken, J.; Ritz, S.; Romani, R. W.; Sadrozinski, H. F.-W.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Sgrò, C.; Siskind, E. J.; Smith, D. A.; Smith, P. D.; Spandre, G.; Spinelli, P.; Strickman, M. S.; Strong, A. W.; Suson, D. J.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Yang, Z.; Ylinen, T.; Ziegler, M.

2010-11-01

Context. The flux of gamma rays with energies greater than 100 MeV is dominated by diffuse emission coming from cosmic-rays (CRs) illuminating the interstellar medium (ISM) of our Galaxy through the processes of Bremsstrahlung, pion production and decay, and inverse-Compton scattering. The study of this diffuse emission provides insight into the origin and transport of cosmic rays. Aims: We searched for gamma-ray emission from the Small Magellanic Cloud (SMC) in order to derive constraints on the cosmic-ray population and transport in an external system with properties different from the Milky Way. Methods: We analysed the first 17 months of continuous all-sky observations by the Large Area Telescope (LAT) of the Fermi mission to determine the spatial distribution, flux and spectrum of the gamma-ray emission from the SMC. We also used past radio synchrotron observations of the SMC to study the population of CR electrons specifically. Results: We obtained the first detection of the SMC in high-energy gamma rays, with an integrated >100 MeV flux of (3.7±0.7) × 10-8 ph cm-2 s-1, with additional systematic uncertainty of ≤16%. The emission is steady and from an extended source ~3° in size. It is not clearly correlated with the distribution of massive stars or neutral gas, nor with known pulsars or supernova remnants, but a certain correlation with supergiant shells is observed. Conclusions: The observed flux implies an upper limit on the average CR nuclei density in the SMC of ~15% of the value measured locally in the Milky Way. The population of high-energy pulsars of the SMC may account for a substantial fraction of the gamma-ray flux, which would make the inferred CR nuclei density even lower. The average density of CR electrons derived from radio synchrotron observations is consistent with the same reduction factor but the uncertainties are large. From our current knowledge of the SMC, such a low CR density does not seem to be due to a lower rate of CR injection and rather indicates a smaller CR confinement volume characteristic size.

Estimating Parameters for the Earth-Ionosphere Waveguide Using VLF Narrowband Transmitters

NASA Astrophysics Data System (ADS)

Gross, N. C.; Cohen, M.

2017-12-01

Estimating the D-region (60 to 90 km altitude) ionospheric electron density profile has always been a challenge. The D-region's altitude is too high for aircraft and balloons to reach but is too low for satellites to orbit at. Sounding rocket measurements have been a useful tool for directly measuring the ionosphere, however, these types of measurements are infrequent and costly. A more sustainable type of measurement, for characterizing the D-region, is remote sensing with very low frequency (VLF) waves. Both the lower ionosphere and Earth's ground strongly reflect VLF waves. These two spherical reflectors form what is known as the Earth-ionosphere waveguide. As VLF waves propagate within the waveguide, they interact with the D-region ionosphere, causing amplitude and phase changes that are polarization dependent. These changes can be monitored with a spatially distributed array of receivers and D-region properties can be inferred from these measurements. Researchers have previously used VLF remote sensing techniques, from either narrowband transmitters or sferics, to estimate the density profile, but these estimations are typically during a short time frame and over a narrow propagation region. We report on an effort to improve the understanding of VLF wave propagation by estimating the commonly known h' and beta two parameter exponential electron density profile. Measurements from multiple narrowband transmitters at multiple receivers are taken, concurrently, and input into an algorithm. The cornerstone of the algorithm is an artificial neural network (ANN), where input values are the received narrowband amplitude and phase and the outputs are the estimated h' and beta parameters. Training data for the ANN is generated using the Navy's Long-Wavelength Propagation Capability (LWPC) model. Emphasis is placed on profiling the daytime ionosphere, which has a more stable and predictable profile than the nighttime. Daytime ionospheric disturbances, from high solar activity, are also analyzed.

Facile hydrothermal synthesis of carbon-coated cobalt ferrite spherical nanoparticles as a potential negative electrode for flexible supercapattery.

PubMed

Sankar, Kalimuthu Vijaya; Shanmugapriya, Sathyanarayanan; Surendran, Subramani; Jun, Seong Chan; Selvan, Ramakrishnan Kalai

2018-03-01

Battery type electrodes would replace the currently available pseudocapacitive electrodes by the cause of high energy density and long discharge time. In this regard, battery type carbon coated CoFe 2 O 4 spherical nanoparticles is prepared by the facile hydrothermal method and tested as the possible negative electrode for supercapattery applications. The phase purity, electronic states of elements, and the presence of carbon is inferred through various sophisticated techniques. The calculated surface area of CoFe 2 O 4 and carbon coated CoFe 2 O 4 are found to be 9 and 26 m 2  g -1 , respectively. The morphological analysis confirms the formation of uniform CoFe 2 O 4 nanospheres (∼25 nm) with a thin layer of carbon coating (∼2 nm). The amorphous carbon coating over CoFe 2 O 4 nanosphere is identified via high-resolution transmission electron microscope. The observed peak and plateau regions in the cyclic voltammogram and galvanostatic charge/discharge curves reveals the battery-type charge storage behaviour of the material. The carbon coated CoFe 2 O 4 delivers the maximum length capacitance of 9.9 F m -1 at 1 mV s -1 with a useful lifespan over 5000 cycles. The electrochemical impedance spectroscopy reveals that the carbon-coated CoFe 2 O 4 delivers the low charge transfer resistance than CoFe 2 O 4 . Further, the fabricated supercapattery provides the energy density of 160 × 10 -8  Wh cm -1 at a power density of 67.2 μW cm -1 . As well as, the device shows 93% of coulombic efficiency and 75% of the specific capacitance retention over 11,000 cycles. Overall, it is believed that the carbon-coated CoFe 2 O 4 can serve as a good candidate for flexible supercapatteries. Copyright © 2017 Elsevier Inc. All rights reserved.

First Retrieval of Thermospheric Carbon Monoxide From Mars Dayglow Observations

NASA Astrophysics Data System (ADS)

Evans, J. Scott; Stevens, Michael H.; Jain, Sonal; Deighan, Justin; Lumpe, Jerry; Schneider, Nicholas M.; Stewart, A. Ian; Crismani, Matteo; Stiepen, Arnaud; Chaffin, Michael S.; Mayyasi-Matta, Majd A.; McClintock, William E.; Holsclaw, Greg; Lefevre, Franck; Lo, Daniel; Clarke, John T.; Montmessin, Franck; Bougher, Stephen W.; Bell, Jared M.; Eparvier, Frank; Thiemann, Ed; Mahaffy, Paul R.; Benna, Mehdi; Elrod, Meredith K.; Jakosky, Bruce

2017-10-01

As a minor species in the Martian thermosphere, Carbon Monoxide (CO) is a tracer that can be used to constrain changing circulation patterns between the lower thermosphere and upper mesosphere of Mars. By linking CO density distributions to dynamical wind patterns, the structure and variability of the atmosphere will be better understood. Direct measurements of CO can therefore provide insight into the magnitude and pattern of winds and provide a metric for studying the response of the atmosphere to solar forcing. In addition, CO measurements can help solve outstanding photochemical modeling problems in explaining the abundance of CO at Mars. CO is directly observable by electron impact excitation and solar resonance fluorescence emissions in the far-ultraviolet (FUV). The retrieval of CO from solar fluorescence was first proposed over 40 years ago, but has been elusive at Mars due to significant spectral blending. However, by simulating the spectral shape of each contributing emission feature, electron impact excitation and solar fluorescence brightnesses can be extracted from the composite spectrum using a multiple linear regression approach. We use CO Fourth Positive Group (4PG) molecular band emission observed on the limb (130 - 200 km) by the Imaging Ultraviolet Spectrograph (IUVS) on NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft over both northern and southern hemispheres from October 2014 to December 2016. We present the first direct retrieval of CO densities by FUV remote sensing in the upper atmosphere of Mars. Atmospheric composition is inferred using the terrestrial Atmospheric Ultraviolet Radiance Integrated Code adapted to the Martian atmosphere. We investigate the sensitivity of CO density retrievals to variability in solar irradiance, solar longitude, and local time. We compare our results to predictions from the Mars Global Ionosphere-Thermosphere Model as well as in situ measurements by the Neutral Gas and Ion Mass Spectrometer on MAVEN and quantify any differences.

Preliminary Observations of Ionospheric Response to an Auroral Driver from the MICA (Magnetosphere-Ionosphere Coupling in the Alfvén Resonator) Sounding Rocket Campaign

NASA Astrophysics Data System (ADS)

Fernandes, P. A.; Lynch, K. A.; Hysell, D. L.; Powell, S.; Miceli, R.; Hampton, D. L.; Ahrns, J.; Lessard, M.; Cohen, I. J.; Moen, J. I.; Bekkeng, T.

2012-12-01

The nightside sounding rocket MICA (Magnetosphere-Ionosphere Coupling in the Alfvén Resonator) launched from Poker Flat, AK, on February 19, 2012, and reached an apogee of 325km. MICA was launched into several discrete, localized arcs in the wake of a westward traveling surge. The MICA instrumentation included both in situ and ground based instruments, and was designed to measure the response of the ionosphere to an auroral driver. More specifically, the science goal was to measure response of the ionosphere to a feedback instability in the ionospheric Alfvén resonator. The MICA payload included in situ particle, electric and magnetic field, and GPS instruments. The ground-based array consisted of a multitude of imagers, coherent and incoherent scatter radars, and a Fabry-Perot interferometer. We present observational characteristics of the response of the ionospheric plasma to the auroral drivers inferred from inverting camera data. We compare the measured precipitating electron population to inversions of camera images, which use a transport model to infer a 2D map of the precipitation. Comparisons show that as the payload passes through what appears to be an Alfvénic auroral arc, the in situ electron instrument shows dispersions indicative of Alfvénic activity. We then introduce measurements of the thermal ion distribution, to examine how the auroral arcs drive a response in the ionosphere. The thermal ion data show that the payload potential strengthens as the payload passes through the arc. When including electron density, temperature, and electric field data, we observe times in which the ionospheric environment changes as the precipitation changes, and times during which there is no measured response by the ionosphere. Future work will compare how the ion bulk flow as measured by the thermal ion instrument compares to the ExB drift as measured by the electric field instrument and to the neutral wind measurements from the Fabry-Perot interferometer. Further analysis of the particle data will yield the ion temperature, whose validity we will quantify by comparison to sheath models.

[Study of the effect of heat source separation distance on plasma physical properties in laser-pulsed GMAW hybrid welding based on spectral diagnosis technique].

PubMed

Liao, Wei; Hua, Xue-Ming; Zhang, Wang; Li, Fang

2014-05-01

In the present paper, the authors calculated the plasma's peak electron temperatures under different heat source separation distance in laser- pulse GMAW hybrid welding based on Boltzmann spectrometry. Plasma's peak electron densities under the corresponding conditions were also calculated by using the Stark width of the plasma spectrum. Combined with high-speed photography, the effect of heat source separation distance on electron temperature and electron density was studied. The results show that with the increase in heat source separation distance, the electron temperatures and electron densities of laser plasma did not changed significantly. However, the electron temperatures of are plasma decreased, and the electron densities of are plasma first increased and then decreased.

Bayesian Inference in Satellite Gravity Inversion

NASA Technical Reports Server (NTRS)

Kis, K. I.; Taylor, Patrick T.; Wittmann, G.; Kim, Hyung Rae; Torony, B.; Mayer-Guerr, T.

2005-01-01

To solve a geophysical inverse problem means applying measurements to determine the parameters of the selected model. The inverse problem is formulated as the Bayesian inference. The Gaussian probability density functions are applied in the Bayes's equation. The CHAMP satellite gravity data are determined at the altitude of 400 kilometer altitude over the South part of the Pannonian basin. The model of interpretation is the right vertical cylinder. The parameters of the model are obtained from the minimum problem solved by the Simplex method.

The Effects of Concordance-Based Electronic Glosses on L2 Vocabulary Learning

ERIC Educational Resources Information Center

Lee, Hansol; Warschauer, Mark; Lee, Jang Ho

2017-01-01

The present study investigates the effects of two different vocabulary learning conditions in digital reading environments equipped with electronic textual glossing. The first condition presents the concordance lines of a target lexical item, thereby making learners infer its meaning by reading the referenced sentences. The second condition…

TH-CD-201-06: Experimental Characterization of Acoustic Signals Generated in Water Following Clinical Photon and Electron Beam Irradiation

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

Hickling, S; El Naqa, I

Purpose: Previous work has demonstrated the detectability of acoustic waves induced following the irradiation of high density metals with radiotherapy linac photon beams. This work demonstrates the ability to experimentally detect such acoustic signals following both photon and electron irradiation in a more radiotherapy relevant material. The relationship between induced acoustic signal properties in water and the deposited dose distribution is explored, and the feasibility of exploiting such signals for radiotherapy dosimetry is demonstrated. Methods: Acoustic waves were experimentally induced in a water tank via the thermoacoustic effect following a single pulse of photon or electron irradiation produced by amore » clinical linac. An immersion ultrasound transducer was used to detect these acoustic waves in water and signals were read out on an oscilloscope. Results: Peaks and troughs in the detected acoustic signals were found to correspond to the location of gradients in the deposited dose distribution following both photon and electron irradiation. Signal amplitude was linearly related to the dose per pulse deposited by photon or electron beams at the depth of detection. Flattening filter free beams induced large acoustic signals, and signal amplitude decreased with depth after the depth of maximum dose. Varying the field size resulted in a temporal shift of the acoustic signal peaks and a change in the detected signal frequency. Conclusion: Acoustic waves can be detected in a water tank following irradiation by linac photon and electron beams with basic electronics, and have characteristics related to the deposited dose distribution. The physical location of dose gradients and the amount of dose deposited can be inferred from the location and magnitude of acoustic signal peaks. Thus, the detection of induced acoustic waves could be applied to photon and electron water tank and in vivo dosimetry. This work was supported in part by CIHR grants MOP-114910 and MOP-136774. S.H. acknowledges support by the NSERC CREATE Medical Physics Research Training Network grant 432290.« less

An ANFIS-based on B2C electronic commerce transaction

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

Lin, Juan, E-mail: linjuanliucaihong@qq.com; Liu, Chenlian, E-mail: chenglian.liu@gmail.com; Guo, Yongning, E-mail: guoyn@163.com

2014-10-06

The purpose of this study is to use an adaptive-network-based fuzzy inference system to model a fuzzy logic-based system (FIS) for supporting decision-making process in B2C electronic commerce transaction. Firstly we introduce FIS in B2C electronic commerce transaction and ANFIS. Then we use ANFIS to model FIS with different membership functions(MF). Lastly we give a conclusion.

An ANFIS-based on B2C electronic commerce transaction

NASA Astrophysics Data System (ADS)

Lin, Juan; Liu, Chenlian; Guo, Yongning

2014-10-01

The purpose of this study is to use an adaptive-network-based fuzzy inference system to model a fuzzy logic-based system (FIS) for supporting decision-making process in B2C electronic commerce transaction. Firstly we introduce FIS in B2C electronic commerce transaction and ANFIS. Then we use ANFIS to model FIS with different membership functions(MF). Lastly we give a conclusion.

Lumped Parameter Modeling for Rapid Vibration Response Prototyping and Test Correlation for Electronic Units

NASA Technical Reports Server (NTRS)

Van Dyke, Michael B.

2013-01-01

Present preliminary work using lumped parameter models to approximate dynamic response of electronic units to random vibration; Derive a general N-DOF model for application to electronic units; Illustrate parametric influence of model parameters; Implication of coupled dynamics for unit/board design; Demonstrate use of model to infer printed wiring board (PWB) dynamics from external chassis test measurement.

Correcting magnetic probe perturbations on current density measurements of current carrying plasmas.

PubMed

Knoblauch, P; Raspa, V; Di Lorenzo, F; Lazarte, A; Clausse, A; Moreno, C

2010-09-01

A method to infer the current density distribution in the current sheath of a plasma focus discharge from a magnetic probe is formulated and then applied to experimental data obtained in a 1.1 kJ device. Distortions on the magnetic probe signal caused by current redistribution and by a time-dependent total discharge current are considered simultaneously, leading to an integral equation for the current density. Two distinct, easy to implement, numerical procedures are given to solve such equation. Experimental results show the coexistence of at least two maxima in the current density structure of a nitrogen sheath.

Observations of the electron density perturbation in the cusp irregularities during the ICI-2 campaign

NASA Astrophysics Data System (ADS)

Abe, Takumi; Moen, J. I.

The ICI-2 (Investigation of Cusp Irregularities-2) sounding rocket campaign was conducted in Svalbard, Norway on December 2008. The scientific objective of ICI-2 is to investigate genera-tion mechanism(s) of coherent HF radar backscatter targets. Strong coherent HF backscatter echoes are well-known phenomena in the polar ionospheric cusp, and are thought to result from field-aligned plasma irregularities with decameter scale length. However, the generation mech-anism of backscatter targets has not yet been understood, and even the altitude profile of HF cusp backscatter is unknown. The ICI-2 rocket was launched at 10:35:10 UT at Ny-˚lesund, A and reached an apogee of 330 km at about 5 minutes after the launch. All onboard systems functioned flawlessly. A comprehensive measurement of the electron density, low energy elec-tron flux, medium energy particle flux, AC and DC electric fields was conducted to exploit the potential role of the gradient drift instability versus the other suggested mechanisms. We present a result obtained from a Fixed-Biased Probe (FBP) which was aimed at measuring fine-scale (< 1 m) electron density perturbation. Our analysis of the FBP data during the rocket's flight indicates that the rocket traversed HF backscatter regions where the electron density perturbation is relatively large. The power spectrum analysis of the electron density shows that the amplitude increases not only in the decameter wavelength but also in the broad range of frequency. Characteristic features of the electron density perturbation are summarized as follows: 1) A strong perturbation of the electron density was observed by the FBP when the ICI-2 rocket passed through a front side of the poleward moving 630 nm emission region which was identified by the all-sky imager. This means that the electron density perturbation and the 630 nm emission are observed to coexist in the same region. 2) The absolute value of the electron density becomes larger in the disturbed region than in the surrounding region. The electron density gradient in the boundary with the outer region is larger in the equatorward side than in the poleward side. 3) The amplitude of the electron density perturbation is remarkably large in the equatorward edge rather than the poleward boundaries. 4) The FBP identified the electron density perturbation at three different altitudes during the rocket flight. This indicates that the perturbation likely exists not only within the narrow limits but in a larger extent in the vertical direction.

Past and present cosmic structure in the SDSS DR7 main sample

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

Jasche, J.; Leclercq, F.; Wandelt, B.D., E-mail: jasche@iap.fr, E-mail: florent.leclercq@polytechnique.org, E-mail: wandelt@iap.fr

2015-01-01

We present a chrono-cosmography project, aiming at the inference of the four dimensional formation history of the observed large scale structure from its origin to the present epoch. To do so, we perform a full-scale Bayesian analysis of the northern galactic cap of the Sloan Digital Sky Survey (SDSS) Data Release 7 main galaxy sample, relying on a fully probabilistic, physical model of the non-linearly evolved density field. Besides inferring initial conditions from observations, our methodology naturally and accurately reconstructs non-linear features at the present epoch, such as walls and filaments, corresponding to high-order correlation functions generated by late-time structuremore » formation. Our inference framework self-consistently accounts for typical observational systematic and statistical uncertainties such as noise, survey geometry and selection effects. We further account for luminosity dependent galaxy biases and automatic noise calibration within a fully Bayesian approach. As a result, this analysis provides highly-detailed and accurate reconstructions of the present density field on scales larger than ∼ 3 Mpc/h, constrained by SDSS observations. This approach also leads to the first quantitative inference of plausible formation histories of the dynamic large scale structure underlying the observed galaxy distribution. The results described in this work constitute the first full Bayesian non-linear analysis of the cosmic large scale structure with the demonstrated capability of uncertainty quantification. Some of these results will be made publicly available along with this work. The level of detail of inferred results and the high degree of control on observational uncertainties pave the path towards high precision chrono-cosmography, the subject of simultaneously studying the dynamics and the morphology of the inhomogeneous Universe.« less

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

DOE PAGES

Tao, Jianmin; Ye, Lin -Hui; Duan, Yuhua

2017-11-20

The primary goal of Kohn–Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao–Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew–Burke–Ernzerhof (PBE), Tao–Perdew–Staroverov–Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree–Fock density yields the exchange and correlation energies in good agreement with the Optimizedmore » Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Lastly, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.« less

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

NASA Astrophysics Data System (ADS)

Tao, Jianmin; Ye, Lin-Hui; Duan, Yuhua

2017-12-01

The primary goal of Kohn-Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao-Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew-Burke-Ernzerhof (PBE), Tao-Perdew-Staroverov-Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree-Fock density yields the exchange and correlation energies in good agreement with the Optimized Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Finally, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

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

Tao, Jianmin; Ye, Lin -Hui; Duan, Yuhua

The primary goal of Kohn–Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao–Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew–Burke–Ernzerhof (PBE), Tao–Perdew–Staroverov–Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree–Fock density yields the exchange and correlation energies in good agreement with the Optimizedmore » Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Lastly, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.« less

Electron energy distribution function in the divertor region of the COMPASS tokamak during neutral beam injection heating

NASA Astrophysics Data System (ADS)

Hasan, E.; Dimitrova, M.; Havlicek, J.; Mitošinková, K.; Stöckel, J.; Varju, J.; Popov, Tsv K.; Komm, M.; Dejarnac, R.; Hacek, P.; Panek, R.; the COMPASS Team

2018-02-01

This paper presents the results from swept probe measurements in the divertor region of the COMPASS tokamak in D-shaped, L-mode discharges, with toroidal magnetic field BT = 1.15 T, plasma current Ip = 180 kA and line-average electron densities varying from 2 to 8×1019 m-3. Using neutral beam injection heating, the electron energy distribution function is studied before and during the application of the beam. The current-voltage characteristics data are processed using the first-derivative probe technique. This technique allows one to evaluate the plasma potential and the real electron energy distribution function (respectively, the electron temperatures and densities). At the low average electron density of 2×1019 m-3, the electron energy distribution function is bi-Maxwellian with a low-energy electron population with temperatures 4-6 eV and a high-energy electron group 12-25 eV. As the line-average electron density is increased, the electron temperatures decrease. At line-average electron densities above 7×1019 m-3, the electron energy distribution function is found to be Maxwellian with a temperature of 6-8.5 eV. The effect of the neutral beam injection heating power in the divertor region is also studied.

A VLT VIMOS study of the anomalous BCD Mrk996: mapping the ionized gas kinematics and abundances

NASA Astrophysics Data System (ADS)

James, B. L.; Tsamis, Y. G.; Barlow, M. J.; Westmoquette, M. S.; Walsh, J. R.; Cuisinier, F.; Exter, K. M.

2009-09-01

A study of the blue compact dwarf (BCD) galaxy Mrk996 based on high-resolution optical Very Large Telescope Visible Multi-Object Spectrograph integral field unit spectroscopy is presented. Mrk996 displays multicomponent line emission, with most line profiles consisting of a narrow, central Gaussian [full width at half-maximum (FWHM) ~ 110kms-1] with an underlying broad component (FWHM ~ 400kms-1). The broad HI Balmer component splits into two separate broad components inside a 1.5-arcsec radius from the nucleus; these are attributed to a two-armed minispiral. This spiral-like nucleus rotates in the same sense as the extended narrow line ionized gas but is offset by ~50kms-1 from the systemic velocity of the galaxy. The rotation curve of Mrk996 derived from the Hα narrow component yields a total mass of 5 × 108Msolar within a radius of 3kpc. From the Hα luminosity we infer a global star formation rate of ~2Msolaryr-1. The high excitation energy, high critical density [OIII] λ4363 and [NII] λ5755 lines are only detected from the inner region and exist purely in broad component form, implying unusual excitation conditions. Surface brightness, radial velocity and FWHM maps for several emission components are presented. A separate physical analysis of the broad and narrow emission line regions is undertaken. We derive an upper limit of 10000K for the electron temperature of the narrow line gas, together with an electron density of 170cm-3, typical of normal HII regions. For the broad line component, measured [OIII] and [FeIII] diagnostic line ratios are consistent with a temperature of 11000K and an electron density of 107cm-3. The broad line emission regions show N/H and N/O enrichment factors of ~20 relative to the narrow line regions, but no He/H, O/H, S/H or Ar/H enrichment is inferred. Previous studies indicated that Mrk996 showed anomalously high N/O ratios compared with BCDs of a similar metallicity. Our multicomponent analysis yields a revised metallicity of >=0.5Zsolar (12 + logO/H = 8.37) for both the narrow and broad gas components, significantly higher than previous studies. As a result the narrow line region's N/O ratio is now typical for the galaxy's metallicity. The narrow line component's N/O ratio peaks outside the core region, spatially correlating with ~3-Myr-old stellar populations. The dominant line excitation mechanism is photoionization by the ~3000 Wolf-Rayet stars and ~150000 O-type stars estimated to be present in the core. This is indeed a peculiar BCD, with extremely dense zones of gas in the core, through which stellar outflows and possible shock fronts permeate contributing to the excitation of the broad line emission. Based on observations made with ESO telescopes at the Paranal Observatory under programme ID 078.B-0353(A). E-mail: bj@star.ucl.ac.uk (BLJ); tsamis@iaa.es (YGT)

Device and method for imploding a microsphere with a fast liner

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner to drive the fast liner to implode a microsphere.

Quantitative contribution of molecular orbitals to hydrogen bonding in a water dimer: Electron density projected integral (EDPI) analysis

NASA Astrophysics Data System (ADS)

Zhang, Zhiyuan; Jiang, Wanrun; Wang, Bo; Wang, Zhigang

2017-06-01

We introduce the orbital-resolved electron density projected integral (EDPI) along the H-bond in the real space to quantitatively investigate the specific contribution from the molecular orbitals (MOs) aspect in (H2O)2. Calculation results show that, the electronic occupied orbital (HOMO-4) of (H2O)2 accounts for about surprisingly 40% of the electron density at the bond critical point. Moreover, the electronic density difference analysis visualizes the electron accumulating effect of the orbital interaction within the H-bond between water molecules, supporting its covalent-like character. Our work expands the understanding of H-bond with specific contributions from certain MOs.

2D microwave imaging reflectometer electronics.

PubMed

Spear, A G; Domier, C W; Hu, X; Muscatello, C M; Ren, X; Tobias, B J; Luhmann, N C

2014-11-01

A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.

A tunable electron beam source using trapping of electrons in a density down-ramp in laser wakefield acceleration.

PubMed

Ekerfelt, Henrik; Hansson, Martin; Gallardo González, Isabel; Davoine, Xavier; Lundh, Olle

2017-09-25

One challenge in the development of laser wakefield accelerators is to demonstrate sufficient control and reproducibility of the parameters of the generated bunches of accelerated electrons. Here we report on a numerical study, where we demonstrate that trapping using density down-ramps allows for tuning of several electron bunch parameters by varying the properties of the density down-ramp. We show that the electron bunch length is determined by the difference in density before and after the ramp. Furthermore, the transverse emittance of the bunch is controlled by the steepness of the ramp. Finally, the amount of trapped charge depends both on the density difference and on the steepness of the ramp. We emphasize that both parameters of the density ramp are feasible to vary experimentally. We therefore conclude that this tunable electron accelerator makes it suitable for a wide range of applications, from those requiring short pulse length and low emittance, such as the free-electron lasers, to those requiring high-charge, large-emittance bunches to maximize betatron X-ray generation.

On the interpretation of continuous wave electron spin resonance spectra of tempo-palmitate in 5-cyanobiphenyl.

PubMed

Zerbetto, Mirco; Polimeno, Antonino; Cimino, Paola; Barone, Vincenzo

2008-01-14

Electron spin resonance (ESR) measurements are highly informative on the dynamic behavior of molecules, which is of fundamental importance to understand their stability, biological functions and activities, and catalytic action. The wealth of dynamic information which can be extracted from a continuous wave electron spin resonance (cw-ESR) spectrum can be inferred by a basic theoretical approach defined within the stochastic Liouville equation formalism, i.e., the direct inclusion of motional dynamics in the form of stochastic (Fokker-Planck/diffusive) operators in the super Hamiltonian H governing the time evolution of the system. Modeling requires the characterization of magnetic parameters (e.g., hyperfine and Zeeman tensors) and the calculation of ESR observables in terms of spectral densities. The magnetic observables can be pursued by the employment of density functional theory which is apt, provided that hybrid functionals are employed, for the accurate computation of structural properties of molecular systems. Recently, an ab initio integrated computational approach to the in silico interpretation of cw-ESR spectra of multilabeled systems in isotropic fluids has been discussed. In this work we present the extension to the case of nematic liquid crystalline environments by performing simulations of the ESR spectra of the prototypical nitroxide probe 4-(hexadecanoyloxy)-2,2,6,6-tetramethylpiperidine-1-oxy in isotropic and nematic phases of 5-cyanobiphenyl. We first discuss the basic ingredients of the integrated approach, i.e., (1) determination of geometric and local magnetic parameters by quantum-mechanical calculations, taking into account the solvent and, when needed, the vibrational averaging contributions; (2) numerical solution of a stochastic Liouville equation in the presence of diffusive rotational dynamics, based on (3) parameterization of diffusion rotational tensor provided by a hydrodynamic model. Next we present simulated spectra with minimal resorting to fitting procedures, proving that the combination of sensitive ESR spectroscopy and sophisticated modeling can be highly helpful in providing three-dimensional structural and dynamic information on molecular systems in anisotropic environments.

Electron density studies of methyl cellobioside

USDA-ARS?s Scientific Manuscript database

Experimental X-ray diffraction crystallography determines the variations in electron density that result from the periodic array of atoms in a crystal. Normally, the positions and type of atom are determined from the electron density based on an approximation that the atoms are spherical. However, t...

Stan : A Probabilistic Programming Language

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

Carpenter, Bob; Gelman, Andrew; Hoffman, Matthew D.

Stan is a probabilistic programming language for specifying statistical models. A Stan program imperatively defines a log probability function over parameters conditioned on specified data and constants. As of version 2.14.0, Stan provides full Bayesian inference for continuous-variable models through Markov chain Monte Carlo methods such as the No-U-Turn sampler, an adaptive form of Hamiltonian Monte Carlo sampling. Penalized maximum likelihood estimates are calculated using optimization methods such as the limited memory Broyden-Fletcher-Goldfarb-Shanno algorithm. Stan is also a platform for computing log densities and their gradients and Hessians, which can be used in alternative algorithms such as variational Bayes, expectationmore » propagation, and marginal inference using approximate integration. To this end, Stan is set up so that the densities, gradients, and Hessians, along with intermediate quantities of the algorithm such as acceptance probabilities, are easily accessible. Stan can also be called from the command line using the cmdstan package, through R using the rstan package, and through Python using the pystan package. All three interfaces support sampling and optimization-based inference with diagnostics and posterior analysis. rstan and pystan also provide access to log probabilities, gradients, Hessians, parameter transforms, and specialized plotting.« less

Stan : A Probabilistic Programming Language

DOE PAGES

Carpenter, Bob; Gelman, Andrew; Hoffman, Matthew D.; ...

2017-01-01

Stan is a probabilistic programming language for specifying statistical models. A Stan program imperatively defines a log probability function over parameters conditioned on specified data and constants. As of version 2.14.0, Stan provides full Bayesian inference for continuous-variable models through Markov chain Monte Carlo methods such as the No-U-Turn sampler, an adaptive form of Hamiltonian Monte Carlo sampling. Penalized maximum likelihood estimates are calculated using optimization methods such as the limited memory Broyden-Fletcher-Goldfarb-Shanno algorithm. Stan is also a platform for computing log densities and their gradients and Hessians, which can be used in alternative algorithms such as variational Bayes, expectationmore » propagation, and marginal inference using approximate integration. To this end, Stan is set up so that the densities, gradients, and Hessians, along with intermediate quantities of the algorithm such as acceptance probabilities, are easily accessible. Stan can also be called from the command line using the cmdstan package, through R using the rstan package, and through Python using the pystan package. All three interfaces support sampling and optimization-based inference with diagnostics and posterior analysis. rstan and pystan also provide access to log probabilities, gradients, Hessians, parameter transforms, and specialized plotting.« less

Artificial Ionization and UHF Radar Response Associated with HF Frequencies near Electron Gyro-Harmonics (Invited)

NASA Astrophysics Data System (ADS)

Watkins, B. J.; Fallen, C. T.; Secan, J. A.

2013-12-01

We present new results from O-mode ionospheric heating experiments at the HAARP facility in Alaska to demonstrate that the magnitude of artificial ionization production is critically dependent on the choice of HF frequency near gyro-harmonics. For O-mode heating in the lower F-region ionosphere, typically about 200 km altitude, artificial ionization enhancements are observed in the lower ionosphere (about 150 - 220 km) and also in the topside ionosphere above about 500 km. Lower ionosphere density enhancements are inferred from HF-enhanced ion and plasma-line signals observed with UHF radar. Upper ionospheric density enhancements have been observed with TEC (total electron content) experiments by monitoring satellite radio beacons where signal paths traverse the HF-modified ionosphere. Both density enhancements and corresponding upward plasma fluxes have also been observed in the upper ionosphere via in-situ satellite observations. The data presented focus mainly on observations near the third and fourth gyro-harmonics. The specific values of the height-dependent gyro-harmonics have been computed from a magnetic model of the field line through the HF heated volume. Experiments with several closely spaced HF frequencies around the gyro-harmonic frequency region show that the magnitude of the lower-ionosphere artificial ionization production maximizes for HF frequencies about 1.0 - 1.5 MHz above the gyro-harmonic frequency. The response is progressively larger as the HF frequency is increased in the frequency region near the gyro-harmonics. For HF frequencies that are initially greater than the gyro-harmonic value the UHF radar scattering cross-section is relatively small, and non-existent or very weak signals are observed; as the signal returns drop in altitude due to density enhancements the HF interaction region passes through lower altitudes where the HF frequency is less than the gyro-harmonic value, for these conditions the radar scattering cross-section is significantly increased and strong signals persist while the high-power HF is present . Simultaneous observations of topside TEC measurements and lower-ionosphere UHF radar observations suggest there is an optimum altitude region to heat the lower F-region in order to produce topside ionosphere density enhancements. The observations are dependent on HF power levels and we show several examples where heating results are only observed for the high-power levels attainable with the HAARP facility.

Probing the intrinsic electronic structure of the bis(dithiolene) anions [M(mnt)2]2- and [M(mnt)2]1- (M = Ni, Pd, Pt; mnt = 1,2-S2C2(CN)2) in the gas phase by photoelectron spectroscopy.

PubMed

Waters, Tom; Woo, Hin-Koon; Wang, Xue-Bin; Wang, Lai-Sheng

2006-04-05

A detailed understanding of the electronic structure of transition metal bis(dithiolene) complexes is important because of their interesting redox, magnetic, optical, and conducting properties and their relevance to enzymes containing molybdenum and tungsten bis(dithiolene) centers. The electronic structures of the bis(dithiolene) anions [M(mnt)(2)](n-) (M = Ni, Pd, Pt; mnt = 1,2-S(2)C(2)(CN)(2); n = 0-2) were examined by a combination of photodetachment photoelectron spectroscopy (PES) and density functional theory calculations. The combined experimental and theoretical data provide insight into the molecular orbital energy levels of [M(mnt)(2)](2-) and the ground and excited states of [M(mnt)(2)](1-) and [M(mnt)(2)]. Detachment features from ligand-based orbitals of [M(mnt)(2)](2-) occur at similar energies for each species, independent of the metal center, while those arising from metal-based orbitals occur at higher energies for the heavier congeners. Electronic excitation energies inferred for [M(mnt)(2)](1-) from the PES experiments agree well with those obtained in optical absorption experiments in solution, with the PES experiments providing additional insight into the changes in energy of these transitions as a function of metal. The singly charged anions [M(mnt)(2)](1-) were also prepared and studied independently. Electron detachment from the ground states of these doublet anions accessed the lowest singlet and triplet states of neutral [M(mnt)(2)], thereby providing a direct experimental measure of their singlet-triplet splitting.

Spectroscopy of PAHs with carbon side chains

NASA Astrophysics Data System (ADS)

Rouille, G.; Steglich, M.; Carpentier, Y.; Huisken, F.; Henning, T.

2011-05-01

The presence of polycyclic aromatic hydrocarbons (PAHs) in space has been inferred ever since sp ecific infrared emission bands were interpreted as their collective fingerprint. In parallel, it has been admitted that the famous diffuse interstellar bands (DIBs), which are absorption features observed in the visible wavelength range, are bands belonging to the electronic spectra of free-flying interstellar molecules yet to be identified. As neutral PAHs of medium and large sizes exhibit absorption bands in the range where the DIBs are found, these molecules, which also fulfill other criteria, have been proposed as potential carriers. Studies of small PAHs in solutions have shown that adding an ethynyl side chain (--CCH) to their structure causes their electronic transitions to shift toward longer wavelengths. This fact, added to the observations of interstellar polyynyl radicals, motivated our current research project on PAHs carrying polyynyl side chains. In a first stage, we are measuring the electronic spectra of small PAHs and of their ethynyl and butadiynyl (--CCCCH) derivatives at cryogenic temperatures in rare gas matrices. Then, measurements will be carried out in supersonic jets, providing us with spectra obtained under conditions relevant to the study of free-flying interstellar molecules. The results of IR absorption measurements will be included in our set of new data. As a complement to our laboratory study on the substituted PAHs, quantum chemical calculations are carried out to interprete and simulate their IR and vibronic spectra. We use the density functional theory approach and its time-dependent extension for calculating the electronic ground states and the electronically excited states, respectively. Through the analysis of the new data, it will be determined whether PAHs carrying polyynyl side chains can play a role in interstellar phenomena. The latest results of this on-going project will be presented.

Thermal imaging diagnostics of high-current electron beams.

PubMed

Pushkarev, A; Kholodnaya, G; Sazonov, R; Ponomarev, D

2012-10-01

The thermal imaging diagnostics of measuring pulsed electron beam energy density is presented. It provides control of the electron energy spectrum and a measure of the density distribution of the electron beam cross section, the spatial distribution of electrons with energies in the selected range, and the total energy of the electron beam. The diagnostics is based on the thermal imager registration of the imaging electron beam thermal print in a material with low bulk density and low thermal conductivity. Testing of the thermal imaging diagnostics has been conducted on a pulsed electron accelerator TEU-500. The energy of the electrons was 300-500 keV, the density of the electron current was 0.1-0.4 kA/cm(2), the duration of the pulse (at half-height) was 60 ns, and the energy in the pulse was up to 100 J. To register the thermal print, a thermal imager Fluke-Ti10 was used. Testing showed that the sensitivity of a typical thermal imager provides the registration of a pulsed electron beam heat pattern within one pulse with energy density over 0.1 J/cm(2) (or with current density over 10 A/cm(2), pulse duration of 60 ns and electron energy of 400 keV) with the spatial resolution of 0.9-1 mm. In contrast to the method of using radiosensitive (dosimetric) materials, thermal imaging diagnostics does not require either expensive consumables, or plenty of processing time.

Improving statistical inference on pathogen densities estimated by quantitative molecular methods: malaria gametocytaemia as a case study.

PubMed

Walker, Martin; Basáñez, María-Gloria; Ouédraogo, André Lin; Hermsen, Cornelus; Bousema, Teun; Churcher, Thomas S

2015-01-16

Quantitative molecular methods (QMMs) such as quantitative real-time polymerase chain reaction (q-PCR), reverse-transcriptase PCR (qRT-PCR) and quantitative nucleic acid sequence-based amplification (QT-NASBA) are increasingly used to estimate pathogen density in a variety of clinical and epidemiological contexts. These methods are often classified as semi-quantitative, yet estimates of reliability or sensitivity are seldom reported. Here, a statistical framework is developed for assessing the reliability (uncertainty) of pathogen densities estimated using QMMs and the associated diagnostic sensitivity. The method is illustrated with quantification of Plasmodium falciparum gametocytaemia by QT-NASBA. The reliability of pathogen (e.g. gametocyte) densities, and the accompanying diagnostic sensitivity, estimated by two contrasting statistical calibration techniques, are compared; a traditional method and a mixed model Bayesian approach. The latter accounts for statistical dependence of QMM assays run under identical laboratory protocols and permits structural modelling of experimental measurements, allowing precision to vary with pathogen density. Traditional calibration cannot account for inter-assay variability arising from imperfect QMMs and generates estimates of pathogen density that have poor reliability, are variable among assays and inaccurately reflect diagnostic sensitivity. The Bayesian mixed model approach assimilates information from replica QMM assays, improving reliability and inter-assay homogeneity, providing an accurate appraisal of quantitative and diagnostic performance. Bayesian mixed model statistical calibration supersedes traditional techniques in the context of QMM-derived estimates of pathogen density, offering the potential to improve substantially the depth and quality of clinical and epidemiological inference for a wide variety of pathogens.

Effect of Sintering Atmosphere and Solution Treatment on Density, Microstructure and Tensile Properties of Duplex Stainless Steels Developed from Pre-alloyed Powders

NASA Astrophysics Data System (ADS)

Murali, Arun Prasad; Mahendran, Sudhahar; Ramajayam, Mariappan; Ganesan, Dharmalingam; Chinnaraj, Raj Kumar

2017-10-01

In this research, Powder Metallurgy (P/M) of Duplex Stainless Steels (DSS) of different compositions were prepared through pre-alloyed powders and elemental powders with and without addition of copper. The powder mix was developed by pot mill for 12 h to obtain the homogeneous mixture of pre-alloyed powder with elemental compositions. Cylindrical green compacts with the dimensions of 30 mm diameter and 12 mm height were compacted through universal testing machine at a pressure level of 560 ± 10 MPa. These green compacts were sintered at 1350 °C for 2 h in hydrogen and argon atmospheres. Some of the sintered stainless steel preforms were solution treated at 1050 °C followed by water quenching. The sintered as well as solution treated samples were analysed by metallography examination, Scanning Electron Microscopy and evaluation of mechanical properties. Ferrite content of sintered and solution treated DSS were measured by Fischer Ferritoscope. It is inferred that the hydrogen sintered DSS depicted better density (94% theoretical density) and tensile strength (695 MPa) than the argon sintered steels. Similarly the microstructure of solution treated DSS revealed existence of more volume of ferrite grains than its sintered condition. Solution treated hydrogen sintered DSS A (50 wt% 316L + 50 wt% 430L) exhibited higher tensile strength of 716 MPa and elongation of 17%, which are 10-13% increment than the sintered stainless steels.

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

Raymund, T.D.

Recently, several tomographic techniques for ionospheric electron density imaging have been proposed. These techniques reconstruct a vertical slice image of electron density using total electron content data. The data are measured between a low orbit beacon satellite and fixed receivers located along the projected orbital path of the satellite. By using such tomographic techniques, it may be possible to inexpensively (relative to incoherent scatter techniques) image the ionospheric electron density in a vertical plane several times per day. The satellite and receiver geometry used to measure the total electron content data causes the data to be incomplete; that is, themore » measured data do not contain enough information to completely specify the ionospheric electron density distribution in the region between the satellite and the receivers. A new algorithm is proposed which allows the incorporation of other complementary measurements, such as those from ionosondes, and also includes ways to include a priori information about the unknown electron density distribution in the reconstruction process. The algorithm makes use of two-dimensional basis functions. Illustrative application of this algorithm is made to simulated cases with good results. The technique is also applied to real total electron content (TEC) records collected in Scandinavia in conjunction with the EISCAT incoherent scatter radar. The tomographic reconstructions are compared with the incoherent scatter electron density images of the same region of the ionosphere.« less

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

Verheest, Frank, E-mail: frank.verheest@ugent.be; School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000; Hellberg, Manfred A., E-mail: hellberg@ukzn.ac.za

The propagation of arbitrary amplitude electron-acoustic solitons and double layers is investigated in a plasma containing cold positive ions, cool adiabatic and hot isothermal electrons, with the retention of full inertial effects for all species. For analytical tractability, the resulting Sagdeev pseudopotential is expressed in terms of the hot electron density, rather than the electrostatic potential. The existence domains for Mach numbers and hot electron densities clearly show that both rarefactive and compressive solitons can exist. Soliton limitations come from the cool electron sonic point, followed by the hot electron sonic point, until a range of rarefactive double layers occurs.more » Increasing the relative cool electron density further yields a switch to compressive double layers, which ends when the model assumptions break down. These qualitative results are but little influenced by variations in compositional parameters. A comparison with a Boltzmann distribution for the hot electrons shows that only the cool electron sonic point limit remains, giving higher maximum Mach numbers but similar densities, and a restricted range in relative hot electron density before the model assumptions are exceeded. The Boltzmann distribution can reproduce neither the double layer solutions nor the switch in rarefactive/compressive character or negative/positive polarity.« less

Talbot-Lau x-ray deflectometer electron density diagnostic for laser and pulsed power high energy density plasma experiments (invited).

PubMed

Valdivia, M P; Stutman, D; Stoeckl, C; Mileham, C; Begishev, I A; Theobald, W; Bromage, J; Regan, S P; Klein, S R; Muñoz-Cordovez, G; Vescovi, M; Valenzuela-Villaseca, V; Veloso, F

2016-11-01

Talbot-Lau X-ray deflectometry (TXD) has been developed as an electron density diagnostic for High Energy Density (HED) plasmas. The technique can deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single Moiré image. An 8 keV Talbot-Lau interferometer was deployed using laser and x-pinch backlighters. Grating survival and electron density mapping were demonstrated for 25-29 J, 8-30 ps laser pulses using copper foil targets. Moiré pattern formation and grating survival were also observed using a copper x-pinch driven at 400 kA, ∼1 kA/ns. These results demonstrate the potential of TXD as an electron density diagnostic for HED plasmas.

Talbot-Lau X-ray Deflectometer electron density diagnostic for laser and pulsed power high energy density plasma experiments

DOE PAGES

Valdivia, M. P.; Stutman, D.; Stoeckl, C.; ...

2016-04-21

Talbot-Lau X-ray Deflectometry has been developed as an electron density diagnostic for High Energy Density plasmas. The technique can deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single Moiré image. An 8 keV Talbot-Lau interferometer was deployed using laser and x-pinch backlighters. Grating survival and electron density mapping was demonstrated for 25-29 J, 8-30 ps laser pulses using copper foil targets. Moire pattern formation and grating survival was also observed using a copper x-pinch driven at 400 kA, ~1 kA/ns. Lastly, these results demonstrate the potential of TXD as an electron density diagnostic for HED plasmas.

Pilot model expansion tunnel test flow properties obtained from velocity, pressure, and probe measurements

NASA Technical Reports Server (NTRS)

Friesen, W. J.; Moore, J. A.

1973-01-01

Velocity-profile, pitot-pressure, and supplemental probe measurements were made at the nozzle exist of an expansion tunnel (a modification to the Langley pilot model expansion tube) for a nozzle net condition of a nitrogen test sample with a velocity of 4.5 km/sec and a density 0.005 times the density of nitrogen at standard conditions, both with the nozzle initially immersed in a helium atmosphere and with the nozzle initially evacuated. The purpose of the report is to present the results of these measurements and some of the physical properties of the nitrogen test sample which can be inferred from the measured results. The main conclusions reached are that: the velocity profiles differ for two nozzle conditions; regions of the flow field can be found where the velocity is uniform to within 5 percent and constant for several hundred microseconds; the velocity of the nitrogen test sample is reduced due to passage through the nozzle; and the velocity profiles do not significantly reflect the large variations which occur in the inferred density profiles.

A Topological Criterion for Filtering Information in Complex Brain Networks

PubMed Central

Latora, Vito; Chavez, Mario

2017-01-01

In many biological systems, the network of interactions between the elements can only be inferred from experimental measurements. In neuroscience, non-invasive imaging tools are extensively used to derive either structural or functional brain networks in-vivo. As a result of the inference process, we obtain a matrix of values corresponding to a fully connected and weighted network. To turn this into a useful sparse network, thresholding is typically adopted to cancel a percentage of the weakest connections. The structural properties of the resulting network depend on how much of the inferred connectivity is eventually retained. However, how to objectively fix this threshold is still an open issue. We introduce a criterion, the efficiency cost optimization (ECO), to select a threshold based on the optimization of the trade-off between the efficiency of a network and its wiring cost. We prove analytically and we confirm through numerical simulations that the connection density maximizing this trade-off emphasizes the intrinsic properties of a given network, while preserving its sparsity. Moreover, this density threshold can be determined a-priori, since the number of connections to filter only depends on the network size according to a power-law. We validate this result on several brain networks, from micro- to macro-scales, obtained with different imaging modalities. Finally, we test the potential of ECO in discriminating brain states with respect to alternative filtering methods. ECO advances our ability to analyze and compare biological networks, inferred from experimental data, in a fast and principled way. PMID:28076353

Tracing the Fingerprint of Chemical Bonds within the Electron Densities of Hydrocarbons: A Comparative Analysis of the Optimized and the Promolecule Densities.

PubMed

Keyvani, Zahra Alimohammadi; Shahbazian, Shant; Zahedi, Mansour

2016-10-18

The equivalence of the molecular graphs emerging from the comparative analysis of the optimized and the promolecule electron densities in two hundred and twenty five unsubstituted hydrocarbons was recently demonstrated [Keyvani et al. Chem. Eur. J. 2016, 22, 5003]. Thus, the molecular graph of an optimized molecular electron density is not shaped by the formation of the C-H and C-C bonds. In the present study, to trace the fingerprint of the C-H and C-C bonds in the electron densities of the same set of hydrocarbons, the amount of electron density and its Laplacian at the (3, -1) critical points associated with these bonds are derived from both optimized and promolecule densities, and compared in a newly proposed comparative analysis. The analysis not only conforms to the qualitative picture of the electron density build up between two atoms upon formation of a bond in between, but also quantifies the resulting accumulation of the electron density at the (3, -1) critical points. The comparative analysis also reveals a unified mode of density accumulation in the case of 2318 studied C-H bonds, but various modes of density accumulation are observed in the case of 1509 studied C-C bonds and they are classified into four groups. The four emerging groups do not always conform to the traditional classification based on the bond orders. Furthermore, four C-C bonds described as exotic bonds in previous studies, for example the inverted C-C bond in 1,1,1-propellane, are naturally distinguished from the analysis. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modern Possibilities for Calculating Some Properties of Molecules and Crystals from the Experimental Electron Density

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

Stash, A.I.; Tsirelson, V.G.

2005-03-01

Methods for calculating some properties of molecules and crystals from the electron density reconstructed from a precise X-ray diffraction experiment using the multipole model are considered. These properties include, on the one hand, the characteristics of the electron density and the inner-crystal electrostatic field and, on the other hand, the local electronic energies (kinetic, potential, total), the exchange energy density, the electron-pair localization function, the localized-orbital locator, the effective crystal potential, and others. It is shown that the integration of these characteristics over pseudoatomic volumes bounded by the surfaces of the zero flux of the electron density gradient makes itmore » possible to characterize directly from an experiment the properties of molecules and crystals in terms of the atomic contributions. The computer program WinXPRO2004, realizing these possibilities, is briefly described.« less

Topology of the electron density of d0 transition metal compounds at subatomic resolution.

PubMed

Batke, Kilian; Eickerling, Georg

2013-11-14

Accurate X-ray diffraction experiments allow for a reconstruction of the electron density distribution of solids and molecules in a crystal. The basis for the reconstruction of the electron density is in many cases a multipolar expansion of the X-ray scattering factors in terms of spherical harmonics, a so-called multipolar model. This commonly used ansatz splits the total electron density of each pseudoatom in the crystal into (i) a spherical core, (ii) a spherical valence, and (iii) a nonspherical valence contribution. Previous studies, for example, on diamond and α-silicon have already shown that this approximation is no longer valid when ultrahigh-resolution diffraction data is taken into account. We report here the results of an analysis of the calculated electron density distribution in the d(0) transition metal compounds [TMCH3](2+) (TM = Sc, Y, and La) at subatomic resolution. By a detailed molecular orbital analysis, it is demonstrated that due to the radial nodal structure of the 3d, 4d, and 5d orbitals involved in the TM-C bond formation a significant polarization of the electron density in the inner electronic shells of the TM atoms is observed. We further show that these polarizations have to be taken into account by an extended multipolar model in order to recover accurate electron density distributions from high-resolution structure factors calculated for the title compounds.

Degree of Ice Particle Surface Roughness Inferred from Polarimetric Observations

NASA Technical Reports Server (NTRS)

Hioki, Souichiro; Yang, Ping; Baum, Bryan A.; Platnick, Steven; Meyer, Kerry G.; King, Michael D.; Riedi, Jerome

2016-01-01

The degree of surface roughness of ice particles within thick, cold ice clouds is inferred from multidirectional, multi-spectral satellite polarimetric observations over oceans, assuming a column-aggregate particle habit. An improved roughness inference scheme is employed that provides a more noise-resilient roughness estimate than the conventional best-fit approach. The improvements include the introduction of a quantitative roughness parameter based on empirical orthogonal function analysis and proper treatment of polarization due to atmospheric scattering above clouds. A global 1-month data sample supports the use of a severely roughened ice habit to simulate the polarized reflectivity associated with ice clouds over ocean. The density distribution of the roughness parameter inferred from the global 1- month data sample and further analyses of a few case studies demonstrate the significant variability of ice cloud single-scattering properties. However, the present theoretical results do not agree with observations in the tropics. In the extra-tropics, the roughness parameter is inferred but 74% of the sample is out of the expected parameter range. Potential improvements are discussed to enhance the depiction of the natural variability on a global scale.

ERTS/Nimbus radiation environment information

NASA Technical Reports Server (NTRS)

Stassinopoulos, E. G.

1973-01-01

The results of the ERTS/Nimbus satellite investigation of electron flux levels are presented. Flux calculations were made with the use of two electron environment models, both of which are static and describe the environment during the solar maximum conditions of October 1967. It is concluded that the construction of these models makes it possible to infer a change of the average quiet time electron flux levels as a function of the solar cycle.

Use of total electron content data to analyze ionosphere electron density gradients

NASA Astrophysics Data System (ADS)

Nava, B.; Radicella, S. M.; Leitinger, R.; Coïsson, P.

In the presence of electron density gradients the thin shell approximation for the ionosphere, used together with a simple mapping function to convert slant total electron content (TEC) to vertical TEC, could lead to TEC conversion errors. These "mapping function errors" can therefore be used to detect the electron density gradients in the ionosphere. In the present work GPS derived slant TEC data have been used to investigate the effects of the electron density gradients in the middle and low latitude ionosphere under geomagnetic quiet and disturbed conditions. In particular the data corresponding to the geographic area of the American Sector for the days 5-7 April 2000 have been used to perform a complete analysis of mapping function errors based on the "coinciding pierce point technique". The results clearly illustrate the electron density gradient effects according to the locations considered and to the actual levels of disturbance of the ionosphere. In addition, the possibility to assess an ionospheric shell height able to minimize the mapping function errors has been verified.

Experimental investigation of mode transitions in asymmetric capacitively coupled radio-frequency Ne and CF4 plasmas

NASA Astrophysics Data System (ADS)

Liu, Gang-Hu; Liu, Yong-Xin; Bai, Li-Shui; Zhao, Kai; Wang, You-Nian

2018-02-01

The dependence of the electron density and the emission intensity on external parameters during the transitions of the electron power absorption mode is experimentally studied in asymmetric electropositive (neon) and electronegative (CF4) capacitively coupled radio-frequency plasmas. The spatio-temporal distribution of the emission intensity is measured with phase resolved optical emission spectroscopy and the electron density at the discharge center is measured by utilizing a floating hairpin probe. In neon discharge, the emission intensity increases almost linearly with the rf voltage at all driving frequencies covered here, while the variation of the electron density with the rf voltage behaves differently at different driving frequencies. In particular, the electron density increases linearly with the rf voltage at high driving frequencies, while at low driving frequencies the electron density increases slowly at the low-voltage side and, however, grows rapidly, when the rf voltage is higher than a certain value, indicating a transition from α to γ mode. The rf voltage, at which the mode transition occurs, increases with the decrease of the driving frequency/the working pressure. By contrast, in CF4 discharge, three different electron power absorption modes can be observed and the electron density and emission intensity do not exhibit a simple dependence on the rf voltage. In particular, the electron density exhibits a minimum at a certain rf voltage when the electron power absorption mode is switching from drift-ambipolar to the α/γ mode. A minimum can also be found in the emission intensity at a higher rf voltage when a discharge is switching into the γ mode.

Marshall N. Rosenbluth Outstanding Doctoral Thesis Award Talk: Simultaneous Measurement of Electron Temperature and Density Fluctuations in the Core of DIII-D Plasmas

NASA Astrophysics Data System (ADS)

White, A. E.

2009-11-01

Multi-field fluctuation measurements provide opportunities for rigorous comparison between experiment and nonlinear gyrokinetic turbulence simulations. A unique set of diagnostics on DIII-D allows for simultaneous study of local, long-wavelength (0 < kθρs< 0.5) electron temperature and density fluctuations in the core plasma (0.4 < ρ< 0.8). Previous experiments in L-mode indicate that normalized electron temperature fluctuation levels (40 < f < 400,kHz) increase with radius from ˜0.4% at ρ= 0.5 to ˜2% at ρ=0.8, similar to simultaneously measured density fluctuations. Electron cyclotron heating (ECH) is used to increase Te, which increases electron temperature fluctuation levels and electron heat transport in the experiments. In contrast, long wavelength density fluctuation levels change very little. The different responses are consistent with increased TEM drive relative to ITG-mode drive. A new capability at DIII-D is the measurement of phase angle between electron temperature and density fluctuations using coupled correlation electron cyclotron emission radiometer and reflectometer diagnostics. Linear and nonlinear GYRO runs have been used to design validation experiments that focus on measurements of the phase angle. GYRO shows that if Te and ∇Te increase 50% in a beam-heated L-mode plasma (ρ=0.5), then the phase angle between electron temperature and density fluctuations decreases 30%-50% and electron temperature fluctuation levels increase a factor of two more than density fluctuations. Comparisons between these predictions and experimental results will be presented.

Phosphorus and carrier density of heavily n-type doped germanium

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

Takinai, K.; Wada, K.

2016-05-14

The threshold current density of n-type, tensile-strained Ge lasers strongly depends on the electron density. Although optical net gain analyses indicate that the optimum electron density should be on the order of 1 × 10{sup 20} cm{sup −3} to get the lowest threshold, it is not a simple task to increase the electron density beyond the mid range of 10{sup 19} cm{sup −3}. The present paper analyzes the phenomenon where electron density is not proportional to phosphorus donor density, i.e., “saturation” phenomenon, by applying the so-called amphoteric defect model. The analyses indicate that the saturation phenomenon can be well explained by the charge compensationmore » between the phosphorus donors (P{sup +}) and doubly negative charged Ge vacancies (V{sup 2−}).« less

The inter-ELM tungsten erosion profile in DIII-D H-mode discharges and benchmarking with ERO+OEDGE modeling

NASA Astrophysics Data System (ADS)

Abrams, T.; Ding, R.; Guo, H. Y.; Thomas, D. M.; Chrobak, C. P.; Rudakov, D. L.; McLean, A. G.; Unterberg, E. A.; Briesemeister, A. R.; Stangeby, P. C.; Elder, J. D.; Wampler, W. R.; Watkins, J. G.

2017-05-01

It is important to develop a predictive capability for the tungsten source rate near the strike points during H-mode operation in ITER and beyond. H-mode deuterium plasma exposures were performed on W-coated graphite and molybdenum substrates in the DIII-D divertor using DiMES. The W-I 400.9 nm spectral line was monitored by fast filtered diagnostics cross calibrated via a high-resolution spectrometer to resolve inter-ELM W erosion. The effective ionization/photon (S/XB) was calibrated using a unique method developed on DIII-D based on surface analysis. Inferred S/XB values agree with an existing empirical scaling at low electron density (n e) but diverge at higher densities, consistent with recent ADAS atomic physics modeling results. Edge modeling of the inter-ELM phase is conducted via OEDGE utilizing the new capability for charge-state resolved carbon impurity fluxes. ERO modeling is performed with the calculated main ion and impurity plasma background from OEDGE. ERO results demonstrate the importance a mixed-material surface model in the interpretation of W sourcing measurements. It is demonstrated that measured inter-ELM W erosion rates can be well explained by C→W sputtering only if a realistic mixed material model is incorporated.

Experimental study on structural, optoelectronic and room temperature sensing performance of Nickel doped ZnO based ethanol sensors

NASA Astrophysics Data System (ADS)

Sudha, M.; Radha, S.; Kirubaveni, S.; Kiruthika, R.; Govindaraj, R.; Santhosh, N.

2018-04-01

Nano crystalline undoped (1Z) Zinc Oxide (ZnO) and 5, 10 and 15 Wt. % (1ZN, 2ZN and 3ZN) of Nickel doped ZnO based sensors were fabricated using the hydrothermal approach on Fluorine doped Tin Oxide (FTO) glass substrates. X-ray diffraction (XRD) analysis proved the hexagonal Wurtzite structure of ZnO. Parametric variations in terms of dislocation density, bond length, lattice parameters and micro strain with respect to dopant concentration were analysed. The prominent variations in the crystallite size, optical band gap and Photoluminescence peak ratio of devices fabricated was observed. The Field Emission Scanning Electron Microscope (FESEM) images showed a change in diameter and density of the nanorods. The effect of the operating temperature, concentration of ethanol and the different doping levels of sensitivity, response and recovery time were investigated. It was inferred that 376% of sensitivity with a very quick response and recovery time of <5 s and 10 s respectively at 150 °C of 3ZN sensor has better performance compared to other three sensors. Also 3ZN sensor showed improved sensitivity of 114%, even at room temperature with response and recovery time of 35 s and 45 s respectively.

Viking Doppler noise used to determine the radial dependence of electron density in the extended corona

NASA Technical Reports Server (NTRS)

Berman, A. L.; Wackley, J. A.; Rockwell, S. T.; Kwan, M.

1977-01-01

The common form for radial dependence of electron density in the extended corona is given. By assuming proportionality between Doppler noise and integrated signal path electron density, Viking Doppler noise can be used to solve for a numerical value of X.

Density matrix renormalization group with efficient dynamical electron correlation through range separation

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

Hedegård, Erik Donovan, E-mail: erik.hedegard@phys.chem.ethz.ch; Knecht, Stefan; Reiher, Markus, E-mail: markus.reiher@phys.chem.ethz.ch

2015-06-14

We present a new hybrid multiconfigurational method based on the concept of range-separation that combines the density matrix renormalization group approach with density functional theory. This new method is designed for the simultaneous description of dynamical and static electron-correlation effects in multiconfigurational electronic structure problems.

Brain Tissue Compartment Density Estimated Using Diffusion-Weighted MRI Yields Tissue Parameters Consistent With Histology

PubMed Central

Sepehrband, Farshid; Clark, Kristi A.; Ullmann, Jeremy F.P.; Kurniawan, Nyoman D.; Leanage, Gayeshika; Reutens, David C.; Yang, Zhengyi

2015-01-01

We examined whether quantitative density measures of cerebral tissue consistent with histology can be obtained from diffusion magnetic resonance imaging (MRI). By incorporating prior knowledge of myelin and cell membrane densities, absolute tissue density values were estimated from relative intra-cellular and intra-neurite density values obtained from diffusion MRI. The NODDI (neurite orientation distribution and density imaging) technique, which can be applied clinically, was used. Myelin density estimates were compared with the results of electron and light microscopy in ex vivo mouse brain and with published density estimates in a healthy human brain. In ex vivo mouse brain, estimated myelin densities in different sub-regions of the mouse corpus callosum were almost identical to values obtained from electron microscopy (Diffusion MRI: 42±6%, 36±4% and 43±5%; electron microscopy: 41±10%, 36±8% and 44±12% in genu, body and splenium, respectively). In the human brain, good agreement was observed between estimated fiber density measurements and previously reported values based on electron microscopy. Estimated density values were unaffected by crossing fibers. PMID:26096639

Characterization of the fast electrons distribution produced in a high intensity laser target interaction

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

Westover, B.; Lawrence Livermore National Laboratory, Livermore, California 94550; Chen, C. D.

2014-03-15

Experiments on the Titan laser (∼150 J, 0.7 ps, 2 × 10{sup 20} W cm{sup −2}) at the Lawrence Livermore National Laboratory were carried out in order to study the properties of fast electrons produced by high-intensity, short pulse laser interacting with matter under conditions relevant to Fast Ignition. Bremsstrahlung x-rays produced by these fast electrons were measured by a set of compact filter-stack based x-ray detectors placed at three angles with respect to the target. The measured bremsstrahlung signal allows a characterization of the fast electron beam spectrum, conversion efficiency of laser energy into fast electron kinetic energy and angular distribution. A Monte Carlo codemore » Integrated Tiger Series was used to model the bremsstrahlung signal and infer a laser to fast electron conversion efficiency of 30%, an electron slope temperature of about 2.2 MeV, and a mean divergence angle of 39°. Simulations were also performed with the hybrid transport code ZUMA which includes fields in the target. In this case, a conversion efficiency of laser energy to fast electron energy of 34% and a slope temperature between 1.5 MeV and 4 MeV depending on the angle between the target normal direction and the measuring spectrometer are found. The observed temperature of the bremsstrahlung spectrum, and therefore the inferred electron spectrum are found to be angle dependent.« less

Self-injection of electrons in a laser-wakefield accelerator by using longitudinal density ripple

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

Dahiya, Deepak; Sharma, A. K.; Sajal, Vivek

By introducing a longitudinal density ripple (periodic modulation in background plasma density), we demonstrate self-injection of electrons in a laser-wakefield accelerator. The wakefield driven plasma wave, in presence of density ripple excites two side band waves of same frequency but different wave numbers. One of these side bands, having smaller phase velocity compared to wakefield driven plasma wave, preaccelerates the background plasma electrons. Significant number of these preaccelerated electrons get trapped in the laser-wakefield and further accelerated to higher energies.

Density functional theory and an experimentally-designed energy functional of electron density.

PubMed

Miranda, David A; Bueno, Paulo R

2016-09-21

We herein demonstrate that capacitance spectroscopy (CS) experimentally allows access to the energy associated with the quantum mechanical ground state of many-electron systems. Priorly, electrochemical capacitance, C [small mu, Greek, macron] [ρ], was previously understood from conceptual and computational density functional theory (DFT) calculations. Thus, we herein propose a quantum mechanical experiment-based variational method for electron charging processes based on an experimentally-designed functional of the ground state electron density. In this methodology, the electron state density, ρ, and an energy functional of the electron density, E [small mu, Greek, macron] [ρ], can be obtained from CS data. CS allows the derivative of the electrochemical potential with respect to the electron density, (δ[small mu, Greek, macron][ρ]/δρ), to be obtained as a unique functional of the energetically minimised system, i.e., β/C [small mu, Greek, macron] [ρ], where β is a constant (associated with the size of the system) and C [small mu, Greek, macron] [ρ] is an experimentally observable quantity. Thus the ground state energy (at a given fixed external potential) can be obtained simply as E [small mu, Greek, macron] [ρ], from the experimental measurement of C [small mu, Greek, macron] [ρ]. An experimental data-set was interpreted to demonstrate the potential of this quantum mechanical experiment-based variational principle.

Influence of Ce Doping on Structural and Transport Properties of Ca1- x Ce x MnO3 ( x=0.2) Manganite

NASA Astrophysics Data System (ADS)

Varshney, Dinesh; Mansuri, Irfan

2011-01-01

We have investigated structural, electric, magnetic and thermal transport properties of electron doped Ca1- x Ce x MnO3 ( x=0.2) manganites. The Cerium substitution for Ca2+causes electron doping into insulating CaMnO3 without e g electron. At room temperature the polycrystalline Ca0.8Ce0.2MnO3 is in the crystallographic orthorhombic structure, with Pnma space group symmetry from the refinement of x-ray powder diffraction patterns. The electrical resistivity data infers that Ca0.8Ce0.2MnO3 manganite is in the semiconducting phase. A smooth linear behavior of log plot values is obtained and is well fitted with adiabatic small polaron conduction model. Nearest-neighbor hopping of a small polaron leads to a mobility with a thermally activated form. The negative values of thermopower infer electron as carriers in Ca0.8Ce0.2MnO3. From susceptibility measurements the Ce doped CaMnO3 shows a transition from antiferromagnetic (AFM) to paramagnetic (PM) phase.

Evolution of Field-Aligned Electron and Ion Densities From Whistler Mode Radio Soundings During Quiet to Moderately Active Period and Comparisons With SAMI2 Simulations

NASA Astrophysics Data System (ADS)

Reddy, A.; Sonwalkar, V. S.; Huba, J. D.

2018-02-01

Knowledge of field-aligned electron and ion distributions is necessary for understanding the physical processes causing variations in field-aligned electron and ion densities. Using whistler mode sounding by Radio Plasma Imager/Imager for Magnetopause-to-Aurora Global Exploration (RPI/IMAGE), we determined the evolution of dayside electron and ion densities along L ˜ 2 and L ˜ 3 (90-4,000 km) during a 7 day (21-27 November 2005) geomagnetically quiet to moderately active period. Over this period the O+/H+ transition height was ˜880 ± 60 km and ˜1000 ± 100 km, respectively, at L ˜ 2 and L ˜ 3. The electron density varied in a complex manner; it was different at L ˜ 2 and L ˜ 3 and below and above the O+/H+ transition height. The measured electron and ion densities are consistent with those from Challenging Minisatellite Payload (CHAMP) and Defense Meteorological Satellite Program (DMSP) and other past measurements, but they deviated from bottomside sounding and International Reference Ionosphere (IRI) 2012 empirical model results. Using SAMI2 (Naval Research Laboratory (NRL) ionosphere model) with reasonably adjusted values of inputs (neutral densities, winds, electric fields, and photoelectron heating), we simulated the evolution of O+/H+ transition height and field-aligned electron and ion densities so that a fair agreement was obtained between the simulation results and observations. Simulation studies indicated that reduced neutral densities (H and/or O) with time limited O+-H charge exchange process. This reduction in neutral densities combined with changes in neutral winds and plasma temperature led to the observed variations in the electron and ion densities. The observation/simulation method presented here can be extended to investigate the role of neutral densities and composition, disturbed winds, and prompt penetration electric fields in the storm time ionosphere/plasmasphere dynamics.

Characterization of an F-center in an alkali halide cluster

NASA Astrophysics Data System (ADS)

Bader, R. F. W.; Platts, J. A.

1997-11-01

The removal of a fluorine atom from its central position in a cubiclike Li14F13+ cluster creates an F-center vacancy that may or may not be occupied by the remaining odd electron. The topology exhibited by the electron density in Li14F12+, the F-center cluster, enables one to make a clear distinction between the two possible forms that the odd electron can assume. If it possesses a separate identity, then a local maximum in the electron density will be found within the vacancy and the F-center will behave quantum mechanically as an open system, bounded by a surface of local zero flux in the gradient vector field of the electron density. If, however, the density of the odd electron is primarily delocalized onto the neighboring ions, then a cage critical point, a local minimum in the density, will be found at the center of the vacancy. Without an associated local maximum, the vacancy has no boundary and is undefined. Self-consistent field (SCF) calculations with geometry optimization of the Li14F13+ cluster and of the doublet state of Li14F12+ show that the creation of the central vacancy has only a minor effect upon the geometry of the cluster, the result of a local maximum in the electron density being formed within the vacancy. Thus the F-center is the physical manifestation of a non-nuclear attractor in the electron density. It is consequently a proper open system with a definable set of properties, the most characteristic being its low kinetic energy per electron. In addition to determining the properties of the F-center, the effect of its formation on the energies, volumes, populations, both electron and spin, and electron localizations of the ions in the cluster are determined.

Cyclic evolution of the electron temperature and density in dusty low-pressure radio frequency plasmas with pulsed injection of hexamethyldisiloxane

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

Garofano, V.; Stafford, L., E-mail: luc.stafford@umontreal.ca, E-mail: kremena.makasheva@laplace.univ-tlse.fr; Despax, B.

2015-11-02

Optical emission spectroscopy was used to analyze the very-low-frequency cyclic evolution of the electron energy and density caused by repetitive formation and loss of dust nanoparticles in argon plasmas with pulsed injection of hexamethyldisiloxane (HMDSO, [CH{sub 3}]{sub 6}Si{sub 2}O). After elaborating a Boltzmann diagram for Ar high-lying levels and a collisional-radiative model for Ar 2p (Paschen notation) states, temperatures characterizing the low- and high-energy parts of the electron population were calculated. Relative electron densities were also estimated from relative line emission intensities. Both temperatures increase when the dust occupation increases, and then decrease when dust is lost. The opposite trendmore » was observed for the electron density. Such cyclic behaviors of the electron energy and electron density in the HMDSO-containing plasmas are in good agreement with the evolution processes in dusty plasmas, in which the formation of negative ions followed by an electron attachment on the surfaces of the nanoparticles is a critical phenomenon driving dust growth.« less

Effective mass in bilayer graphene at low carrier densities: The role of potential disorder and electron-electron interaction

NASA Astrophysics Data System (ADS)

Li, J.; Tan, L. Z.; Zou, K.; Stabile, A. A.; Seiwell, D. J.; Watanabe, K.; Taniguchi, T.; Louie, Steven G.; Zhu, J.

2016-10-01

In a two-dimensional electron gas, the electron-electron interaction generally becomes stronger at lower carrier densities and renormalizes the Fermi-liquid parameters, such as the effective mass of carriers. We combine experiment and theory to study the effective masses of electrons and holes me* and mh* in bilayer graphene in the low carrier density regime on the order of 1 ×1011c m-2 . Measurements use temperature-dependent low-field Shubnikov-de Haas oscillations observed in high-mobility hexagonal boron nitride supported samples. We find that while me* follows a tight-binding description in the whole density range, mh* starts to drop rapidly below the tight-binding description at a carrier density of n =6 ×1011c m-2 and exhibits a strong suppression of 30% when n reaches 2 ×1011c m-2 . Contributions from the electron-electron interaction alone, evaluated using several different approximations, cannot explain the experimental trend. Instead, the effect of the potential fluctuation and the resulting electron-hole puddles play a crucial role. Calculations including both the electron-electron interaction and disorder effects explain the experimental data qualitatively and quantitatively. This Rapid Communication reveals an unusual disorder effect unique to two-dimensional semimetallic systems.

Generalization of the Kohn-Sham system that can represent arbitrary one-electron density matrices

DOE PAGES

Hubertus J. J. van Dam

2016-04-27

Density functional theory is currently the most widely applied method in electronic structure theory. The Kohn-Sham method, based on a fictitious system of noninteracting particles, is the workhorse of the theory. The particular form of the Kohn-Sham wave function admits only idempotent one-electron density matrices whereas wave functions of correlated electrons in post-Hartree-Fock methods invariably have fractional occupation numbers. Here we show that by generalizing the orbital concept and introducing a suitable dot product as well as a probability density, a noninteracting system can be chosen that can represent the one-electron density matrix of any system, even one with fractionalmore » occupation numbers. This fictitious system ensures that the exact electron density is accessible within density functional theory. It can also serve as the basis for reduced density matrix functional theory. Moreover, to aid the analysis of the results the orbitals may be assigned energies from a mean-field Hamiltonian. This produces energy levels that are akin to Hartree-Fock orbital energies such that conventional analyses based on Koopmans' theorem are available. Lastly, this system is convenient in formalisms that depend on creation and annihilation operators as they are trivially applied to single-determinant wave functions.« less

Robust Estimation of Electron Density From Anatomic Magnetic Resonance Imaging of the Brain Using a Unifying Multi-Atlas Approach

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

Ren, Shangjie; Department of Radiation Oncology, Stanford University School of Medicine, Palo Alto, California; Hara, Wendy

Purpose: To develop a reliable method to estimate electron density based on anatomic magnetic resonance imaging (MRI) of the brain. Methods and Materials: We proposed a unifying multi-atlas approach for electron density estimation based on standard T1- and T2-weighted MRI. First, a composite atlas was constructed through a voxelwise matching process using multiple atlases, with the goal of mitigating effects of inherent anatomic variations between patients. Next we computed for each voxel 2 kinds of conditional probabilities: (1) electron density given its image intensity on T1- and T2-weighted MR images; and (2) electron density given its spatial location in a referencemore » anatomy, obtained by deformable image registration. These were combined into a unifying posterior probability density function using the Bayesian formalism, which provided the optimal estimates for electron density. We evaluated the method on 10 patients using leave-one-patient-out cross-validation. Receiver operating characteristic analyses for detecting different tissue types were performed. Results: The proposed method significantly reduced the errors in electron density estimation, with a mean absolute Hounsfield unit error of 119, compared with 140 and 144 (P<.0001) using conventional T1-weighted intensity and geometry-based approaches, respectively. For detection of bony anatomy, the proposed method achieved an 89% area under the curve, 86% sensitivity, 88% specificity, and 90% accuracy, which improved upon intensity and geometry-based approaches (area under the curve: 79% and 80%, respectively). Conclusion: The proposed multi-atlas approach provides robust electron density estimation and bone detection based on anatomic MRI. If validated on a larger population, our work could enable the use of MRI as a primary modality for radiation treatment planning.« less

Experimental charge density analysis of a gallium(I) N-heterocyclic carbene analogue.

PubMed

Overgaard, Jacob; Jones, Cameron; Dange, Deepak; Platts, James A

2011-09-05

The experimental electron density of the only known example of a four-membered Ga(I) N-heterocyclic carbene analogue has been determined by multipole modeling of 90 K X-ray diffraction data and compared to theoretical data. In order to obtain a satisfactory model, it is necessary to modify the radial dependency of the core electrons of Ga using two separate scaling parameters for s,p- and d-electrons. Evidence for significant lone-pair density on Ga is found in the electron density and derived properties despite the partial positive charge of this atom. Static deformation density and molecular electrostatic potential clearly show a directional lone pair on Ga, whereas the Laplacian of the total electron density does not; this feature is, however, present in the Laplacian of the valence-only density. The Ga center also acts as an acceptor in four intramolecular C-H···Ga contacts, whose nature is probed by density properties. Substantial covalent character is apparent in the Ga-N bonds, but no sign of donation from filled N p-orbitals to empty Ga p-orbitals is found, whereas π-delocalization over the organic ligand is evident. This study highlights the utility of experimental charge density analysis as a technique to investigate the unusual bonding and electronic characteristics of low oxidation state/low coordinate p-block complexes.

Teaching Chemistry with Electron Density Models.

ERIC Educational Resources Information Center

Shusterman, Gwendolyn P.; Shusterman, Alan J.

1997-01-01

Describes a method for teaching electronic structure and its relevance to chemical phenomena that relies on computer-generated three-dimensional models of electron density distributions. Discusses the quantum mechanical background needed and presents ways of using models of electronic ground states to teach electronic structure, bonding concepts,…

Molybdenum emission from impurity-induced m= 1 snake-modes on the Alcator C-Mod tokamak

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

Delgado-Aparicio, L.; MIT - Plasma Science and Fusion Center, Cambridge, Massachusetts 02139; Bitter, M.

2012-10-15

A suite of novel high-resolution spectroscopic imaging diagnostics has facilitated the identification and localization of molybdenum impurities as the main species during the formation and lifetime of m= 1 impurity-induced snake-modes on Alcator C-Mod. Such measurements made it possible to infer, for the first time, the perturbed radiated power density profiles from which the impurity density can be deduced.

The Evolution of Quorum Sensing as a Mechanism to Infer Kinship

PubMed Central

Schluter, Jonas; Schoech, Armin P.; Foster, Kevin R.; Mitri, Sara

2016-01-01

Bacteria regulate many phenotypes via quorum sensing systems. Quorum sensing is typically thought to evolve because the regulated cooperative phenotypes are only beneficial at certain cell densities. However, quorum sensing systems are also threatened by non-cooperative “cheaters” that may exploit quorum-sensing regulated cooperation, which begs the question of how quorum sensing systems are maintained in nature. Here we study the evolution of quorum sensing using an individual-based model that captures the natural ecology and population structuring of microbial communities. We first recapitulate the two existing observations on quorum sensing evolution: density-dependent benefits favor quorum sensing but competition and cheating will destabilize it. We then model quorum sensing in a dense community like a biofilm, which reveals a novel benefit to quorum sensing that is intrinsically evolutionarily stable. In these communities, competing microbial genotypes gradually segregate over time leading to positive correlation between density and genetic similarity between neighboring cells (relatedness). This enables quorum sensing to track genetic relatedness and ensures that costly cooperative traits are only activated once a cell is safely surrounded by clonemates. We hypothesize that under similar natural conditions, the benefits of quorum sensing will not result from an assessment of density but from the ability to infer kinship. PMID:27120081

Peculiarities of electron density distribution in bismuth chalcogenides, iron pnictides, cuprates and related unconventional superconductors

NASA Astrophysics Data System (ADS)

Orlov, V. G.; Sergeev, G. S.

2018-05-01

With the aim to reveal the origin of instabilities in the electron subsystem of unconventional superconductors, such as stripes or nematic symmetry breaking, electron band structure calculations were performed for a number of bismuth chalcogenides, bismuth oxide, iron pnictides, as well as for Bi2Sr2CaCu2O8, YBa2Cu3O7 and La2CuO4. It was found that bond critical points in the electron density distribution ρ(r) of all the studied compounds were characterized by positive sign of electron density Laplacian evidencing on depletion of electron charge from the area of bond critical points. A correlation was found between the Tc and the value of electron density Laplacian in the strongest bond critical points of superconductors and related substances.

Uncovering the nonadiabatic response of geosynchronous electrons to geomagnetic disturbance

USGS Publications Warehouse

Gannon, Jennifer; Elkington, Scot R.; Onsager, Terrance G.

2012-01-01

We describe an energy spectrum method for scaling electron integral flux, which is measured at a constant energy, to phase space density at a constant value of the first adiabatic invariant which removes much of the variation due to reversible adiabatic effects. Applying this method to nearly a solar cycle (1995 - 2006) of geosynchronous electron integral flux (E>2.0MeV) from the GOES satellites, we see that much of the diurnal variation in electron phase space density at constant energy can be removed by the transformation to phase space density at constant μ (4000 MeV/G). This allows us a clearer picture of underlying non-adiabatic electron population changes due to geomagnetic activity. Using scaled phase space density, we calculate the percentage of geomagnetic storms resulting in an increase, decrease or no change in geosynchronous electrons as 38%, 7%, and 55%, respectively. We also show examples of changes in the electron population that may be different than the unscaled fluxes alone suggest. These examples include sudden electron enhancements during storms which appear during the peak of negative Dst for μ-scaled phase space density, contrary to the slow increase seen during the recovery phase for unscaled phase space density for the same event.

Experimental investigations of driving frequency effect in low-pressure capacitively coupled oxygen discharges

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

Liu, Jia; Liu, Yong-Xin; Liu, Gang-Hu

2015-04-14

The effect of driving frequency on the electron density is investigated in low-pressure capacitively coupled oxygen plasmas by utilizing a floating hairpin probe. The power absorbed by the plasma is investigated and it is found that the power lost in the matching network can reach 50% or higher under certain conditions. The effect of driving frequency on the electron density is studied from two aspects, i.e., constant absorbed power and electrode voltage. In the former case, the electron density increases with the driving frequency increasing from 13.56 to 40.68 MHz and slightly changes depending on the gas pressures with the frequencymore » further increasing to 100 MHz. In the latter case, the electron density rapidly increases when the driving frequency increases from 13.56 to 40.68 MHz, and then decreases with the frequency further increasing to 100 MHz. The electron series resonance is observed at 40.68 MHz and can be attributed to the higher electron density. And the standing wave effect also plays an important role in increasing electron density at 100 MHz and 2.6 Pa.« less

The impact of spherical symmetry assumption on radio occultation data inversion in the ionosphere: An assessment study

NASA Astrophysics Data System (ADS)

Shaikh, M. M.; Notarpietro, R.; Nava, B.

2014-02-01

'Onion-peeling' is a very common technique used to invert Radio Occultation (RO) data in the ionosphere. Because of the implicit assumption of spherical symmetry for the electron density (N(e)) distribution in the ionosphere, the standard Onion-peeling algorithm could give erroneous concentration values in the retrieved electron density profile. In particular, this happens when strong horizontal ionospheric electron density gradients are present, like for example in the Equatorial Ionization Anomaly (EIA) region during high solar activity periods. In this work, using simulated RO Total Electron Content (TEC) data computed by means of the NeQuick2 ionospheric electron density model and ideal RO geometries, we tried to formulate and evaluate an asymmetry level index for quasi-horizontal TEC observations. The asymmetry index is based on the electron density variation that a signal may experience along its path (satellite to satellite link) in a RO event and is strictly dependent on the occultation geometry (e.g. azimuth of the occultation plane). A very good correlation has been found between the asymmetry index and errors related to the inversion products, in particular those concerning the peak electron density NmF2 estimate and the Vertical TEC (VTEC) evaluation.

Orbital order and effective mass enhancement in t2 g two-dimensional electron gases

NASA Astrophysics Data System (ADS)

Tolsma, John; Principi, Alessandro; Polini, Marco; MacDonald, Allan

2015-03-01

It is now possible to prepare d-electron two-dimensional electron gas systems that are confined near oxide heterojunctions and contain t2 g electrons with a density much smaller than one electron per metal atom. I will discuss a generic model that captures all qualitative features of electron-electron interaction physics in t2 g two-dimensional electron gas systems, and the use of a GW approximation to explore t2 g quasiparticle properties in this new context. t2 g electron gases contain a high density isotropic light mass xy component and low-density xz and yz anisotropic components with light and heavy masses in orthogonal directions. The high density light mass band screens interactions within the heavy bands. As a result the wave vector dependence of the self-energy is reduced and the effective mass is increased. When the density in the heavy bands is low, the difference in anisotropy between the two heavy bands favors orbital order. When orbital order does not occur, interactions still reshape the heavy-band Fermi surfaces. I will discuss these results in the context of recently reported magnetotransport experiments.