Science.gov

Sample records for field aligned scattering

  1. Theory of VHF Scattering by Field-Aligned Irregularities in the Ionosphere.

    DTIC Science & Technology

    1986-09-01

    A. (1981), "A Global Model for Wideband *HF Skywave Propagation ", in Effect of the Ionosphere on Radiowave Systems, J.M. Goodman Ed., U.S. Government... SCHELL Chief " ’ Electromagnetic Sciences Division FOR THE COMMANDER: LOHN A. RSTZ Plans & Programs Division If your address has changed or if you wish to...SUB-GROUP Field Aligned Scatter Anisotropic Scatter 17 02 1 Auroral Scatter VHF Propagatione -4 20 14 ’." . ~lg. ABSTRACT (Cantino n on reverse if

  2. Construction of theoretical F-spread ionogams from scattering in the HF band from field-aligned irregularities

    SciTech Connect

    Powers, W.J.

    1985-01-01

    The scattering and propagation of electromagnetic fields in the ionosphere for the HF band is considered. Particular attention is given to scattering at the geomagnetic equator from irregularities of ionization density that are aligned along the earth's magnetic field and that have lengths that are much greater than a Fresnel scale. Perpendicular to the earth's magnetic field the irregularities are assumed to be isotropic with scale lengths (wavelengths /(2..pi..)) extending from an inner scale equal to the ionic gyroradius to an outer scale on the order of the scale height of the ionosphere. Primary emphasis is placed on the weak scattering of pulses from field-aligned irregularities embedded in the night time F-layer, with application to explaining F-spread ionograms. The average ionization density of the night time F-layer is assumed to be well modeled by a parabolic layer. Assuming that the effects of the earth's magnetic field and collisions can be neglected, an approximate dyadic Green's function is derived and utilized in the determination of the incident and singly scattered fields.

  3. SPEAR-induced field-aligned irregularities observed from bi-static HF radio scattering in the polar ionosphere

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Kornienko, V. A.; Kalishin, A. S.; Robinson, T. R.; Yeoman, T. K.; Wright, D. M.; Baddeley, L. J.

    2009-01-01

    Experimental results from SPEAR HF heating experiments in the polar ionosphere are examined. Bi-static scatter measurements of HF diagnostic signals were carried out on the Pori (Finland)-SPEAR-St. Petersburg path at operational frequencies of 11,755 and 15,400 kHz and the London-SPEAR-St. Petersburg path at frequencies of 12,095 and 17,700 kHz, using a Doppler spectral method. The SPEAR HF heating facility generates heater-induced artificial field-aligned small-scale irregularities (AFAIs), which can be detected by HF diagnostic bi-static radio scatter techniques at St. Petersburg at a distance of about 2000 km. In accordance with the Bragg condition, HF bi-static backscatters were sensitive to small-scale irregularities having spatial sizes of the order of 9-13 m across the geomagnetic field line. The properties and behaviour of AFAIs have been considered in the winter and summer seasons under quiet magnetic conditions and under various status of the polar ionosphere (the presence of "thick" and "thin" sporadic Es layers, different structures of the F2 layer). The experimental results obtained have shown that AFAIs can be excited in the F as well as in the E regions of the polar ionosphere. The excitation of a very intense wide-band spectral component with an abrupt increase in the spectral width up to 16-20 Hz has been found in the signals scattered from striations. Along with a wide-band component, a narrow-band spectral component can be also seen in the Doppler sonograms and in the average spectra of the signals scattered from the SPEAR-induced striations. AFAIs were excited even when the HF heater frequency was up to 0.5 MHz larger than the critical frequency. A simulation of the ray geometry for the diagnostic HF radio waves scattered from AFAIs in the polar ionosphere has been made for the geophysical conditions prevailing during experiments carried out in both the winter and summer seasons.

  4. VHF coherent scatter radar observations of mid-latitude F-region field-aligned irregularities over South Korea

    NASA Astrophysics Data System (ADS)

    Kwak, Y.; Yang, T.; Lee, J.; Hwang, J.; Kil, H.; Park, Y.

    2011-12-01

    We examine the mid-latitude F-region field-aligned irregularity (FAI) activity during 2010-2011 by using the VHF coherent scatter radar data in Daejeon (36.2°N, 127.1°E; dip latitude 26.7°N), South Korea. The VHF radar has been operated since December 2009 and provides a unique opportunity to investigate the variability of the FAI activity with local time, season, solar flux, and magnetic activity. Our preliminary results during the solar minimum show that FAIs preferentially occur at post-sunset and pre-sunrise and during the June solstice. The seasonal variation of the FAI occurrence frequency is similar to that of the electron density irregularities observed by the C/NOFS satellite. For one event, we observed the association of the FAIs with a medium-scale traveling ionospheric disturbance (MSTID). Our study extends to the investigation of the correlations between the irregularities in the equatorial region and middle latitudes and between the conjugate F regions, and the causal linkage of the FAIs with the E-region perturbations. For this purpose, we analyze the VHF radar and C/NOFS data during 2010-2011.

  5. Measurements of magnetic field alignment

    SciTech Connect

    Kuchnir, M.; Schmidt, E.E.

    1987-11-06

    The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs.

  6. Occurrence climatology of F region field-aligned irregularities in middle latitudes as observed by a 40.8 MHz coherent scatter radar in Daejeon, South Korea

    NASA Astrophysics Data System (ADS)

    Yang, Tae-Yong; Kwak, Young-Sil; Kil, Hyosub; Lee, Young-Sook; Lee, Woo Kyoung; Lee, Jae-jin

    2015-11-01

    A new 40.8 MHz coherent scatter radar was built in Daejeon, South Korea (36.18°N, 127.14°E, dip latitude: 26.7°N) on 29 December 2009 and has since been monitoring the occurrence of field-aligned irregularities (FAIs) in the northern middle latitudes. We report on the occurrence climatology of the F region FAIs as observed by the Daejeon radar between 2010 and 2014. The F region FAIs preferentially occur around 250-350 km at 18:00-21:00 local time (postsunset FAI), around 350-450 km near midnight (nighttime FAI), around 250-350 km before sunrise (presunrise FAI), and around 160-300 km after 05:00 local time (postsunrise FAI). The occurrence rates of nighttime and presunrise FAIs are maximal during summer, though the occurrence rates of postsunset and postsunrise FAIs are maximal during the equinoxes. FAIs rarely occur during local winter. The occurrence rate of F region FAIs increases in concert with increases in solar activity. Medium-scale traveling ionospheric disturbances (MSTIDs) are known as an important source of the F region FAIs in middle latitudes. The high occurrence rate of the nighttime FAIs in local summer is consistent with the high occurrence rate of MSTIDs in that season. However, the dependence of the FAI activity on the solar cycle is inconsistent with the MSTID activity. The source of the F region FAIs in middle latitudes is an open question. Our report of different types of FAIs and their occurrence climatology may provide a useful reference for the identification of the source of the middle latitude FAIs.

  7. Molecular alignment and orientation with a hybrid Raman scattering technique

    NASA Astrophysics Data System (ADS)

    Bustard, Philip J.; Lausten, R.; Sussman, Benjamin J.

    2012-11-01

    We demonstrate a scheme for the preparation of molecular alignment and angular momentum orientation using a hybrid combination of two limits of Raman scattering. First a weak, impulsive pump pulse initializes the system via the nonresonant dynamic Stark effect. Then, having overcome the influence of the vacuum fluctuations, an amplification pulse selectively enhances the initial coherences by transient stimulated Raman scattering, generating alignment and angular momentum orientation of molecular hydrogen. The amplitude and phase of the resulting coherent dynamics are experimentally probed, indicating an amplification factor of 4.5. An analytic theory is developed to model the dynamics.

  8. Block Copolymer Nanocomposites in Electric Fields: Kinetics of Alignment

    SciTech Connect

    Liedel, Clemens; Pester, Christian; Ruppel, Markus A; Lewin, Christian; Pavan, Mariela J.; Urban, Volker S; Shenhar, Roy; Bosecke, Peter; Boker, Alexander

    2013-01-01

    We investigate the kinetics of block copolymer/nanoparticle composite alignment in an electric field using in situ transmission small-angle X-ray scattering. As a model system, we employ a lamellae forming polystyrene-block-poly(2-vinyl pyridine) block copolymer with different contents of gold nanoparticles in thick films under solvent vapor annealing. While the alignment improves with increasing nanoparticle fraction, the kinetics slows down. This is explained by changes in the degree of phase separation and viscosity. Our findings provide extended insights into the basics of nanocomposite alignment.

  9. Statistical characteristics of nighttime mid-latitude F-region field-aligned irregularities observed by Daejeon VHF coherent scattering radar in South Korea

    NASA Astrophysics Data System (ADS)

    Yang, T. Y.; Kwak, Y. S.; Kil, H.; Lee, Y.; Lee, W. K.; Park, Y. D.

    2014-12-01

    We report statistical characteristics of mid-latitude nighttime F-region field-aligned irregularities (FAIs) based on more than three-year observations by Daejeon VHF coherent backscatter radar. This radar has built at Daejeon (36.18°N, 127.14°E, dip lat. 26.7°N) in 2009 with 40.8 MHz operating frequency for continuous monitoring of the behavior of electron density irregularities in the middle latitude. By using long-term observations from January 2010 to December 2013, we obtained the annual, diurnal and seasonal characteristics of a variety of a percentage occurrence, signal-to-noise ratio, and Doppler velocities from the nighttime F-region irregularities over Korea peninsular. From almost four-year observations, the F-region nighttime irregularities occurred most frequently during post-sunset period. These nighttime irregularities usually appeared with occupying different height levels according to local time. This height variation of F-region FAIs was correlated with hmf2 of ionosonde in Icheon, South Korea. The irregularities were least active near the winter solstice and most active near summer solstice. From the annual occurrence variations, F-region nighttime irregularities seem to have tendency with solar activity.

  10. Artificial field-aligned irregularities in the nightside auroral ionosphere

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N.; Borisova, T.; Kornienko, V.; Leyser, T.; Rietveld, M.; Thide', B.

    The properties and behaviors of the artificial field-aligned small-scale irregularities (striations) in the nightside high latitudinal F-region in course of the Tromso ionospheric modification experiments are examined. Bistatic scatter measurements of HF diagnostic signals were carried out on the London-Tromso-St.Petersburg and Pori-Tromso-St.Petersburg paths using a Doppler spectral method. Striations act as an artificially produced target for the diagnostic HF radio waves and they are responsible for back-scattered signals. The main attention was paid to the aspect angle dependence of striations. It was found that the spectral features of the scattered signals are strongly dependent on the elevation angles of the HF heater antenna beam. The spectral power, broadening of the Doppler spectra, and median values of Doppler shift were maximal during the field-aligned direction of the HF heater antenna beam, whereas they were minimal during the vertical pointing of the HF beam. Simultaneous measurements from the EISCAT UHF incoherent scatter radar showed also the strongest heating effects in the field-aligned position. Electron temperature increases of up to 3000K (300%) induced by powerful HF pumping waves have been measured. Associated with them are the field-aligned ion outflows. Further observations of striations have been made using a narrower HF heater beam (sometimes termed "superheater"). The comparison between two HF heating experiments in a superheater mode, performed under the same geophysical conditions, also shows the strongest striations in the field-aligned position of the HF heater beam. The possible mechanisms for the directional dependence of striations are discussed.

  11. Molecular focusing and alignment with plasmon fields.

    PubMed

    Artamonov, Maxim; Seideman, Tamar

    2010-12-08

    We show the possibility of simultaneously aligning molecules and focusing their center-of-mass motion near a metal nanoparticle in the field intensity gradient created by the surface plasmon enhancement of incident light. The rotational motion is described quantum mechanically while the translation is treated classically. The effects of the nanoparticle shape on the alignment and focusing are explored. Our results carry interesting implications to the field of molecular nanoplasmonics and suggest several potential applications in nanochemistry.

  12. Laboratory simulation of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Wessel, Frank J.; Rostoker, Norman

    1993-01-01

    A summary of progress during the period Apr. 1992 to Mar. 1993 is provided. Objectives of the research are (1) to simulate, via laboratory experiments, the three terms of the field-aligned current equation; (2) to simulate auroral-arc formation processes by configuring the boundary conditions of the experimental chamber and plasma parameters to produce highly localized return currents at the end of a field-aligned current system; and (3) to extrapolate these results, using theoretical and computational techniques, to the problem of magnetospheric-ionospheric coupling and to compare them with published literature signatures of auroral-arc phenomena.

  13. Scattering matrix theory for stochastic scalar fields.

    PubMed

    Korotkova, Olga; Wolf, Emil

    2007-05-01

    We consider scattering of stochastic scalar fields on deterministic as well as on random media, occupying a finite domain. The scattering is characterized by a generalized scattering matrix which transforms the angular correlation function of the incident field into the angular correlation function of the scattered field. Within the accuracy of the first Born approximation this matrix can be expressed in a simple manner in terms of the scattering potential of the scatterer. Apart from determining the angular distribution of the spectral intensity of the scattered field, the scattering matrix makes it possible also to determine the changes in the state of coherence of the field produced on scattering.

  14. Field-aligned currents and large scale magnetospheric electric fields

    NASA Technical Reports Server (NTRS)

    Dangelo, N.

    1980-01-01

    D'Angelo's model of polar cap electric fields (1977) was used to visualize how high-latitude field-aligned currents are driven by the solar wind generator. The region 1 and region 2 currents of Iijima and Potemra (1976) and the cusp field-aligned currents of Wilhjelm et al. (1978) and McDiarmid et al. (1978) are apparently driven by different generators, although in both cases the solar wind is their ultimate source.

  15. FDTD scattered field formulation for scatterers in stratified dispersive media.

    PubMed

    Olkkonen, Juuso

    2010-03-01

    We introduce a simple scattered field (SF) technique that enables finite difference time domain (FDTD) modeling of light scattering from dispersive objects residing in stratified dispersive media. The introduced SF technique is verified against the total field scattered field (TFSF) technique. As an application example, we study surface plasmon polariton enhanced light transmission through a 100 nm wide slit in a silver film.

  16. Uniformly spaced field-aligned ionization ducts

    NASA Technical Reports Server (NTRS)

    Gross, S. H.; Muldrew, D. B.

    1984-01-01

    A number of interesting cases of combination mode ducted echoes for mid- and low-latitude regions are presented that show nearly uniformly spaced multiple combination mode traces on the ionograms in the frequency range above 1 MHz. These traces suggest that a parallel system of field-aligned ducts is present. Ray tracing studies are made to determine the structure that would explain the observations using the electron density profile derivable from the vertical trace and assuming field-aligned ducts. Spacing perpendicular to the ducts is found to be as much as 70 km. Some of these parallel duct structures are found to extend to the conjugate hemisphere, possibly to the F peak.

  17. Simultaneous particle and field observations of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Berko, F. W.; Hoffman, R. A.; Burton, R. K.; Holzer, R. E.

    1973-01-01

    Simultaneous measurements of low energy precipitating electrons and magnetic fluctuations from the low altitude polar orbiting satellite OGO-4 have been compared. Analysis of the two sets of experimental data for isolated events led to the classification of high latitude field-aligned currents as purely temporal or purely spatial variations. Magnetic field disturbances calculated using these simple current models and the measured particle fluxes were in good agreement with measured field values. While fluxes of greater than 1 keV electrons are detected primarily on the nightside, magnetometer disturbances indicative of field-aligned currents were seen at all local times, both in the visual auroral regions and dayside polar cusp. Thus electrons with energies less than approximately 1 keV are the prime charge carriers in high latitude dayside field-aligned currents. The satellite measurements are in good agreement with previously measured field-aligned current values and with values predicted from several models involving magnetospheric field-aligned currents.

  18. Field emission and scattering from conducting nanofibers

    NASA Astrophysics Data System (ADS)

    Marinov, Toma M.

    Field emission from conducting nanofibers has a significant importance due to its possible application in electronics like flat panel displays, x-ray machines, sensors, etc. The standard theoretical model describing field emission is the Fowler-Nordheim model, which is valid for bulk material, constant applied electric field and O°K. A more general theoretical model is required in the realistic cases of arbitrary electromagnetic fields and arbitrary but finite temperature. This work presents an asymptotic procedure for calculating field emission from nanofibers of finite length for static and dynamic fields at arbitrary finite temperature. It investigates the behavior of a nanofiber in the presence of electrostatic and EM fields. The resultant field potentials outside the system are obtained by employing the slender-body approximation ([1], [2], [3]). The total external potential is used in conjunction with the the Wentzel-Krammers-Brillouin approximation [4] to estimate the tunneling probability of the electrons in the fiber due the total external field. Unlike the standard Fowler-Nordheim method [5], the current density of the field emission is obtained by using quantum wire density of states. In addition, this work investigates radiative and scattering properties of conducting nanofibers for the purpose of nanoantenna applications. The results for the distributions of the induced currents are compared to the results from the solution of Hallen's integral equation [6] and the corresponding radiation patterns are compared. The results are extended for the case of a broadside uniform array of N aligned fibers.

  19. Field-aligned currents and ionospheric electric fields

    NASA Technical Reports Server (NTRS)

    Yasuhara, F.; Akasofu, S.-I.

    1977-01-01

    It is shown that the observed distribution of the ionospheric electric field can be deduced from an equation combining Ohm's law with the current continuity equation by using the 'observed' distribution of field-aligned currents as the boundary condition for two models of the ionosphere. The first model has one conductive annular ring representing the quiet-time auroral precipitation belt; the second has two conductive annular rings that simulate the discrete and diffuse auroral regions. An analysis is performed to determine how well the electric-field distribution can be reproduced. The results indicate that the first model reproduces the Sq(p)-type distribution, the second model reproduces reasonably well a substorm-type potential and ionospheric current patterns together with the Harang discontinuity, and that the distribution of field-aligned currents is the same for both models.

  20. Dynamics of field-aligned currents reconstructed by the ground-based and satellite data

    NASA Astrophysics Data System (ADS)

    Nikolaeva, V. D.; Kotikov, A. L.; Sergienko, T. I.

    2014-09-01

    Parameters of field-aligned currents reconstructed by ground-based measurements of magnetic field in the Scandinavian countries (IMAGE) and ionospheric conductivity for specific events of the 6 and 8 December 2004 are represented here. Ionospheric conductivity was calculated from precipitating electron flux measured at DMSP-13 satellite and electron density EISCAT incoherent scattering radar direct measurements. There is a high correlation between field-aligned currents, calculated from DMSP-13 satellite data and field-aligned currents calculated from radar measurements for the December 6, 2004 in the presence of developed ionospheric current system. The comparison of field-aligned currents, reconstructed by the proposed method, with the currents calculated by the variation of magnetic field on the DMSP satellites, confirms correctness of the offered algorithm.

  1. Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field

    SciTech Connect

    De France, Kevin J.; Yager, Kevin G.; Hoare, Todd; Cranston, Emily D.

    2016-07-13

    Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strength following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = –0.499 where S = –0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = –0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.

  2. Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field

    DOE PAGES

    De France, Kevin J.; Yager, Kevin G.; Hoare, Todd; ...

    2016-07-13

    Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strengthmore » following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = –0.499 where S = –0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = –0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.« less

  3. Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field

    SciTech Connect

    De France, Kevin J.; Yager, Kevin G.; Hoare, Todd; Cranston, Emily D.

    2016-07-13

    Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strength following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = –0.499 where S = –0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = –0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.

  4. Scatter integration with right triangular fields.

    PubMed

    Siddon, R L; Dewyngaert, J K; Bjärngard, B E

    1985-01-01

    The concept of the equivalent field is used extensively in radiotherapy dose calculation algorithms. The rationale for using equivalent fields is to allow dose calculations for a wide variety of field shapes, while maintaining dose calculational data for only a few, very regularly shaped fields. A common example is the table of equivalent squares of rectangular fields presented by Day in the British Journal of Radiology. Recently, in searching for fast dose calculation algorithms for irregular fields, we introduced the concept of the equivalent square of a right triangular field. It is shown that an arbitrary irregular field of N vertices may be decomposed into 2N right triangular fields, each with a precalculated equivalent square. The scatter at the point of calculation due to the irregular field is then obtained as a sum of the scatter contributions from the equivalent squares. The scatter integration with right triangles is compared with scatter integration using program IRREG.

  5. Scattering in a magnetic field

    SciTech Connect

    David C. Carey

    2002-08-19

    The fixed target program at Fermilab has come to an end. New projects are in the planning stage. Among them is a muon storage ring. Up to the present, all storage rings in high-energy physics have carried stable particles, namely the electron and proton and their antiparticles. The muon is unstable and decays with a mean lifetime of 2.0 x 10{sup -6} sec. Two types of cooling have been used in the past. One is stochastic cooling where an electrode is used to detect the positions of the particles and send a signal to another position across the ring. Through successive applications of this technique, the phase space is ultimately greatly reduced and beams can be made to collide with a useful event rate. The second type of cooling is electron cooling. Here protons and electrons are made to travel together for a short distance. Equipartition causes transfer of transverse energy of the protons to that of the electrons. Neither of these methods is fast enough to allow acceleration of a sufficient number of muons up to maximum energy before they decay. A new method known as ionization cooling has been proposed.[1] The muons are cooled by passing them through a container of liquid hydrogen. The energy loss reduces both transverse and longitudinal momentum. The longitudinal momentum is restored with RF cavities. The net result is to maintain the longitudinal momentum while cooling the transverse momentum. To minimize the total travel distance of the muons the liquid hydrogen is placed inside the focusing solenoids. The question arises as to whether the presence of the solenoids influences the phase space occupied by the muons. After the muon scatters it has transverse momentum. In a constant longitudinal magnetic field the trajectory wraps around the field lines and coincides in momentum and position with a particle which scatters one cycle later. Here we calculate the change in emittance for both a drift space and a solenoid. We find that the presence of the solenoid does

  6. Field-Aligned Current Systems at Mercury

    NASA Astrophysics Data System (ADS)

    Heyner, Daniel; Exner, Willi

    2017-04-01

    Mercury exhibits a very dynamic magnetosphere, which is partially due to strong dayside reconnection and fast magnetospheric convection. It has been shown that dayside reconnection occurs even on low magnetic shear angles across the magnetopause. This drives quasi-steady region 1 field-aligned currents (FAC) that are observable in in-situ MESSENGER data. Here, the structure of the Hermean FAC-system is discussed and compared to the terrestrial counterpart. Due to the lack of a significant ionosphere at Mercury, it has to be examined how much of the poloidal FAC is reflected back to the magnetosphere, closed via toroidal currents in the planetary interior or via Pedersen currents in the tenuous exosphere. This investigation gives insights into the planetary conductivity structure as well as the exospheric plasma densities. Furthermore, it will be examined how much the only partially developed ring current at Mercury produces possible region 2 FAC signatures. We conclude with requirements to simulations that are needed to forecast the FAC structure on the southern hemisphere that will be closely studied with the upcoming BepiColombo mission.

  7. Alignment creaction by elastic electron scattering by ions in a plasma

    SciTech Connect

    Csanak, G. Y.; Kilcrease, D. P.; Bray, I; Fursa, D. V.

    2004-01-01

    Alignment creation by elastic hcavy particle scattering has been studied for many years by Oniont, by Dyakonov and Perel, and by Petrashen, Rebane, and Rebane. The technique has been adapted for arbitrary perturbers (including electrons) by Fujimoto et al. and by Fujimoto and Kazantsev. In the case of heavy particle perturbers (e.g. ions) there was an argument by Petrashen, Rebane, and Rebane that under certain conditions (namely only elastic scattering is possible and the semi-classical straight-line trajectory assumption holds) in the case of an isolated level, alignment can not be created by elastic scattering. This contention has been questioned by Dashevskaya and Nikitin who argued that the above conclusion of Petrashen et al. is due to an extra symmetry introduced into the problem by the straight-line trajectory approximation (which introduces detailed balance for magnetic sublevel to magnetic sublevel transitions) and if a more accurate approximation is made alignment creation can be obtained by elastic scattering. See the discussion in Fujimoto et al. In the case of inelastic scattering Kazantsev et al. gave a quantum-mechanical definition of the alignment creation cross section. In carlier works, Trdjrnaf et al. and Csanak et al. adopted the inelastic alignment creation cross section definition of Kazantsev et al. for elastic electron scattering and reported results for Ba and O V ions based on that formula. (Apparently Dashevskaya and Nikitin used the same formula.) However, a closer inspection of the semi-classical formula of Fujimoto et al. and Fujimoto and Kazantsev 1141 as well as the quantum-mechanical rate equations of Ben-Reuven and Nienhuis and Bommier and Sahal-Brechot also indicated that the inelastic scattering fomiula might not hold for elastic scattering. The present work reinvestigates this problem, and shows that indeed the alignment creation cross section formula is different for elastic scattering, as compared to the inelastic Scattering

  8. Scatter factor corrections for elongated fields.

    PubMed

    Higgins, P D; Sohn, W H; Sibata, C H; McCarthy, W A

    1989-01-01

    Measurements have been made to determine scatter factor corrections for elongated fields of Cobalt-60 and for nominal linear accelerator energies of 6 MV (Siemens Mevatron 67) and 18 MV (AECL Therac 20). It was found that for every energy the collimator scatter factor varies by 2% or more as the field length-to-width ratio increases beyond 3:1. The phantom scatter factor is independent of which collimator pair is elongated at these energies. For 18 MV photons it was found that the collimator scatter factor is complicated by field-size-dependent backscatter into the beam monitor.

  9. Scatter factor corrections for elongated fields

    SciTech Connect

    Higgins, P.D.; Sohn, W.H.; Sibata, C.H.; McCarthy, W.A. )

    1989-09-01

    Measurements have been made to determine scatter factor corrections for elongated fields of Cobalt-60 and for nominal linear accelerator energies of 6 MV (Siemens Mevatron 67) and 18 MV (AECL Therac 20). It was found that for every energy the collimator scatter factor varies by 2% or more as the field length-to-width ratio increases beyond 3:1. The phantom scatter factor is independent of which collimator pair is elongated at these energies. For 18 MV photons it was found that the collimator scatter factor is complicated by field-size-dependent backscatter into the beam monitor.

  10. Scattering theorems for dyadic chiral fields

    NASA Astrophysics Data System (ADS)

    Athanasiadis, Christodoulos; Gotopoulos, Stavros

    2004-06-01

    A time-harmonic plane dyadic electromagnetic field is scattered by a chiral body in a chiral environment. The body is either a perfect conductor or a dielectric. The incident field is a linear combination of left-circularly polarized and right-circularly polarized dyadic electromagnetic fields, each of which has a different wave number. We prove reciprocity and scattering theorems in dyadic form, which incorporate as special cases the corresponding known theorems for vector electromagnetic waves. Specializing to the same direction of incidence and observation in the general scattering theorems we obtain forward scattering theorems.

  11. Field aligned current observations in the polar cusp ionosphere

    NASA Technical Reports Server (NTRS)

    Ledley, B. G.; Farthing, W. H.

    1973-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F-region which are interpreted as being caused by the payload's passage through a structured field aligned current system. The field aligned currents have a characteristic horizontal scale size of one kilometer. Analysis of one large field fluctuation gives a current density of 0.0001 amp/m sq.

  12. Mid-latitude field-aligned ionospheric irregularities and its impact on GPS

    NASA Astrophysics Data System (ADS)

    Yasyukevich, Yury; Afraimovich, Edward; Ishin, Artem; Tinin, Mikhail

    2010-05-01

    Strong scintillations of amplitude and phase of transionospheric radio signals occur due to signal scattering on intensive small scale irregularities. Scintillation can have an adverse effect on GPS signals and cause a GPS receiver to lose lock on the signal in some extreme cases. Although the plasma bubble is a common phenomenon and it has been studied for years, precise observed data of ionospheric scintillations and loss of lock to GPS receivers due to plasma bubble at mid-latitude are still limited. In most papers there are no data regarding the space geometry of field-aligned irregularities. For the first time, we propose a GPS method to detect mid-latitude field-aligned irregularities (FAIs) by line-of-sight angular scanning regarding the local magnetic field vector. We show that total GPS L2 phase slips over Japan during the recovery phase of the 12 February, 2000 geomagnetic storm (Ma and Maruyama, 2006, doi:10.1029/2006GL027512) were caused by GPS signal scattering on FAIs for the line-of-sight of both aligned to magnetic field line (the field of aligned scattering, FALS), and across it or at large angles to magnetic field line (the field of across scattering, FACS). Our FALS results confirm well with data of investigation of magnetic field orientation control of GPS occultation observations of equatorial scintillation during detailed LEO CHAMP, SAC-C and PICOSat measurements, realized by Anderson and Strauss (2005, doi:10.1029/2005GL023781). The role of large-angle scattering almost along the normal to the magnetic field line in GPS scintillation is determined by attenuation of the irregularity anisotropy factor as compared with the other factors. The work was supported by the Fundamental Research Program of RAS Physical Science Department (Project IV.12 "Modern problems of radiophysics").

  13. A neutron imaging device for sample alignment in a pulsed neutron scattering instrument

    SciTech Connect

    Grazzi, F.; Scherillo, A.; Zoppi, M.

    2009-09-15

    A neutron-imaging device for alignment purposes has been tested on the INES beamline at ISIS, the pulsed neutron source of Rutherford Appleton Laboratory (U.K.). Its use, in conjunction with a set of movable jaws, turns out extremely useful for scattering application to complex samples where a precise and well-defined determination of the scattering volume is needed.

  14. A neutron imaging device for sample alignment in a pulsed neutron scattering instrument

    NASA Astrophysics Data System (ADS)

    Grazzi, F.; Scherillo, A.; Zoppi, M.

    2009-09-01

    A neutron-imaging device for alignment purposes has been tested on the INES beamline at ISIS, the pulsed neutron source of Rutherford Appleton Laboratory (U.K.). Its use, in conjunction with a set of movable jaws, turns out extremely useful for scattering application to complex samples where a precise and well-defined determination of the scattering volume is needed.

  15. Sources of field-aligned currents in the auroral plasma

    SciTech Connect

    Marshall, J.A.; Burch, J.L. ); Kan, J.R. ); Reiff, P.H. ); Slavin, J.A. )

    1991-01-01

    Data from the Dynamics Explorer 1 High Altitude Plasma Instrument (HAPI) and magnetometer are used to investigate the sources of field-aligned currents in the nightside auroral zone. It is found that the formula developed by S. Knight predicts the field-aligned current density fairly accurately in regions where a significant potential drop can be inferred from the HAPI data; there are, however, regions in which the proportionality between potential drop and field-aligned current does not hold. In particular, the authors note occurrences of strong upward field-aligned current associated not with inverted-V events but instead with suprathermal bursts. In addition, upward field-aligned currents are often observed to peak near the edges of inverted-V events, rather than in the center as would be predicted by Knight.

  16. Sources of field-aligned currents in the auroral plasma

    NASA Astrophysics Data System (ADS)

    Marshall, J. A.; Burch, J. L.; Kan, J. R.; Reiff, P. H.; Slavin, J. A.

    1991-01-01

    Data from the Dynamics Explorer 1 High Altitude Plasma Instrument (HAPI) and magnetometer are used to investigate the sources of field-aligned currents in the nightside auroral zone. It is found that the formula developed by S. Knight predicts the field-aligned current density fairly accurately in regions where a significant potential drop can be inferred from the HAPI data; there are, however, regions in which the proportionality between potential drop and field-aligned current does not hold. In particular, occurrences of strong upward field-aligned current associated not with inverted-V events but instead with suprathermal bursts are noted. In addition, upward field-aligned currents are often observed to peak near the edges of inverted-V events, rather than in the center as would be predicted by Knight.

  17. Modeling of Field-Aligned Guided Echoes in the Plasmasphere

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.; Green, James L.

    2004-01-01

    The conditions under which high frequency (f>>f(sub uh)) long-range extraordinary-mode discrete field-aligned echoes observed by the Radio Plasma Imager (RPI) on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite in the plasmasphere are investigated by ray tracing modeling. Field-aligned discrete echoes are most commonly observed by RPI in the plasmasphere although they are also observed over the polar cap region. The plasmasphere field-aligned echoes appearing as multiple echo traces at different virtual ranges are attributed to signals reflected successively between conjugate hemispheres that propagate along or nearly along closed geomagnetic field lines. The ray tracing simulations show that field-aligned ducts with as little as 1% density perturbations (depletions) and less than 10 wavelengths wide can guide nearly field-aligned propagating high frequency X mode waves. Effective guidance of wave at a given frequency and wave normal angle (Psi) depends on the cross-field density scale of the duct, such that ducts with stronger density depletions need to be wider in order to maintain the same gradient of refractive index across the magnetic field. While signal guidance by field aligned density gradient without ducting is possible only over the polar region, conjugate field-aligned echoes that have traversed through the equatorial region are most likely guided by ducting.

  18. Direct inelastic scattering of N/sub 2/ from Ag(111). I. Rotational populations and alignment

    SciTech Connect

    Sitz, G.O.; Kummel, A.C.; Zare, R.N.

    1988-08-15

    The rotational state populations and the quadrupole and hexadecapole alignment moments of N/sub 2/ scattered off clean Ag(111) are determined by resonance enhanced multiphoton ionization (REMPI). The scattered N/sub 2/ is found to be highly aligned with its rotational angular momentum vector J parallel to the surface. The degree of alignment is found to increase with increasing rotational excitation. We see less than perfect alignment at intermediate J values indicating that the surface is not completely flat. The alignment is relatively insensitive to incident energy, incident angle, or surface temperature T/sub s/. However, the rotational state population distributions show pronounced rainbows for higher incident energy and/or more grazing exit angle. The rotational state distributions are found to depend strongly on the final scattering angle at low T/sub s/; this effect is markedly reduced at higher T/sub s/. Time-of-flight measurements are used to determine the average velocity of the scattered N/sub 2/ as a function of rotational level. It is found that higher rotational excitation correlates with lower average velocity and that the incident molecules lose 20%--30% of their translational energy to the solid. No correlation is found between velocity and alignment. A comparison is made with published results for the NO/Ag(111) system and a variety of theoretical models found in the literature.

  19. The electric field alignment of ice particles in thunderstorms

    NASA Technical Reports Server (NTRS)

    Weinheimer, Andrew J.; Few, Arthur A.

    1987-01-01

    Electrical and aerodynamic torques on atmospheric ice particles are calculaed in order to assess the degree of alignment of these particles with the electric fields in thunderstorms. In such clouds fields of many tens of kilovolts per meter are commonly measured, and values of 100 to 200 kV/m are not rare. For E = 100 kV/m the calculations indicate that electric field alignment occurs for crystals with major dimensions up to maximum values in the range from 200 microns to 1 mm, depending upon crystal type. Columns are aligned more easily than platelike crystals, except for dendrites which, by virtue of their smaller assumed density, have smaller fall velocities thereby experiencing weaker aerodynamic torques. Thus a substantial degree of alignment is expected for E = 100 kV/m. For E = 10 kV/m only much smaller crystals will be aligned, probably only ones with major dimensions of less than 50 microns or so.

  20. The electric field alignment of ice particles in thunderstorms

    NASA Technical Reports Server (NTRS)

    Weinheimer, Andrew J.; Few, Arthur A.

    1987-01-01

    Electrical and aerodynamic torques on atmospheric ice particles are calculaed in order to assess the degree of alignment of these particles with the electric fields in thunderstorms. In such clouds fields of many tens of kilovolts per meter are commonly measured, and values of 100 to 200 kV/m are not rare. For E = 100 kV/m the calculations indicate that electric field alignment occurs for crystals with major dimensions up to maximum values in the range from 200 microns to 1 mm, depending upon crystal type. Columns are aligned more easily than platelike crystals, except for dendrites which, by virtue of their smaller assumed density, have smaller fall velocities thereby experiencing weaker aerodynamic torques. Thus a substantial degree of alignment is expected for E = 100 kV/m. For E = 10 kV/m only much smaller crystals will be aligned, probably only ones with major dimensions of less than 50 microns or so.

  1. X-ray scattering from a highly aligned Bacteriorhodopsin multilayer

    NASA Astrophysics Data System (ADS)

    Salditt, T.; Koltover, I.; Safinya, C. R.

    1997-03-01

    The purple membrane of the achebacteria Halobacterium salinarium with its native photoactive protein bacteriorhodopsin (bR) was investigated by x-ray reflectivity, nonspecular scattering, and truncation rod scattering. The application of these scattering techniques has become possible after the preparation of giant fused-patch single crystal domains (~= 50 μm). These patches orient on Si-substrates with a mosaicity of less than 4/100 ^o. Experiments have been carried out on multilayer samples of about 10 periods at different hydration levels. The nonspecular (diffuse scattering) indicates a membrane corrugation on lateral length scale of 400Å that is conformaly replicated through the stack. The results of this first investigation and future prospects of this novel technique for the study of membrane proteins are discussed. Work supported in part by NSF grant DMR-9624091, the Petroleum research Fund (No.31352-AC7), a Los Alamos CULAR grant No.STB/UC:95-146, and a DAAD fellowship to T.S.

  2. Generation and Suppression of E Region Artificial Field Aligned Irregularities

    NASA Astrophysics Data System (ADS)

    Miceli, R. J.; Hysell, D. L.; Munk, J.; Han, S.

    2012-12-01

    Artificial field-aligned plasma density irregularities (FAIs) were generated in the E region of the ionosphere above the High Frequency Active Auroral Research Program (HAARP) facility during campaigns in May and August of 2012 and were quantified using a 30 MHz coherent scatter radar in Homer, Alaska. The purpose of the experiment was to analyze the X-mode suppression of FAIs generated from O-mode heating and to measure the threshold required to excite thermal parametric instabilities. The irregularities were excited by gradually increasing the power of a zenith pointing O-mode emission transmitted at a frequency of 2.75 MHz. To suppress the irregularities, a second X-mode emission at a higher frequency was added on alternating power cycles. The Homer radar measured the signal-to-noise ratio, Doppler shift, and spectral width of echoes reflected from the irregularities. We will calculate the threshold electric field required to excite the irregularities and compare with similar experiments in order to better understand the thermal parametric instability.

  3. Detecting Field-Aligned Current Signatures Using MAVEN Observations

    NASA Astrophysics Data System (ADS)

    Hanley, K.; Brain, D.; Weber, T. D.

    2016-12-01

    Currents aligned with magnetic field lines have been observed on multiple planets, including Mars, Mercury, Earth, Saturn, and Jupiter. As documented by Mars Global Surveyor, field-aligned currents occur at Mars near regions of moderate or strong crustal magnetic fields. These currents, identified by the magnetic field perturbations they cause, indicate the acceleration of charged particles toward the Martian atmosphere, which may result in atmospheric heating, ionization, and discrete aurora observed at ultraviolet wavelengths. It is likely that charged particles are removed from the atmosphere via these currents in magnetic cusp regions. At present, the locations and conditions for which field-aligned current systems can occur at Mars are not well understood. We use magnetic field measurements collected by MAVEN between December 2014 and September 2015 to investigate the incidence of low-altitude field-aligned currents on the nightside of the planet in regions of strong crustal fields. These currents have been found to cause perturbations in the magnetic field at magnitudes of 5 nT. We have automated the detection process in order to facilitate future study of field-aligned currents using MAVEN data. First, low-frequency signals caused by spacecraft motion are removed from the data, revealing short-term (1-5 seconds) perturbations. The disturbances due to field-aligned currents are recorded by finding areas where the filtered data exceeds a threshold value for multiple seconds. Current events are then mapped to the planet's surface. We report on the geographic distribution of field-aligned current signatures, as well as their distributions with respect to local time.

  4. A Statistical Model of the Electric Field and Field-aligned Ion Drift over Millstone Hill

    NASA Astrophysics Data System (ADS)

    Holt, J. M.; Zhang, S.

    2001-12-01

    All Millstone Hill incoherent scatter radar data collected since 1978 are available through the Madrigal Database at MIT Haystack Observatory. A set of empirical models for basic and derived incoherent scatter parameters, including electron density Ne, electron and ion temperatures Te and Ti, electric field and parallel ion drift is being developed from this extensive dataset. Such models of the average behavior of key ionosphere-thermosphere (IT) parameters, based on long term accumulated data, are important for space weather studies not only in terms of quantitative descriptions of the IT system but also in terms of clarifying several outstanding scientific problems. This paper presents statistical models of the local electric field and geomagnetic-field-aligned ion drift in the ionospheric F-layer. All local (radar elevation > 45 degrees) ion line-of sight measurements are sorted into bins. The binning parameters are local time (0000-2400 LT), and day of year (season). Each data point has a corresponding solar flux index F10.7 and geomagnetic activity index Ap. A least-squares fit to all the data in each bin is computed to determine the electric field as a function of Ap and the field-aligned drift as a function of F107 and Ap. Unlike previous Millstone Hill local electric field models, the components of the drift are determined in a statistical sense rather than by first computing the parallel and perpendicular drift components from triplets of line-of-sight measurements. We will present the data distribution in each bin and discuss the main features of the results.

  5. First evidence of anisotropy of GPS phase slips caused by the mid-latitude field-aligned ionospheric irregularities

    NASA Astrophysics Data System (ADS)

    Afraimovich, E. L.; Ishin, A. B.; Tinin, M. V.; Yasyukevich, Yu. V.; Jin, S. G.

    2011-05-01

    The mid-latitude field-aligned irregularity (FAI) along the magnetic field line is a common phenomenon in the ionosphere. However, few data reveal the field-aligned ionospheric irregularities. They are insufficient to identify FAIs effects so far, particularly effect on global positioning system (GPS) signals. In this paper, the mid-latitude FAIs by line-of-sight angular scanning relative to the local magnetic field vector are investigated using the denser GPS network observations in Japan. It has been the first found that total GPS L2 phase slips over Japan, during the recovery phase of the 12 Feb 2000 geomagnetic storm were caused by GPS signal scattering on FAIs both for the lines-of-sight aligned to the magnetic field line (the field of aligned scattering, FALS) and across the magnetic field line (the field of across scattering, FACS). The FALS results are also in a good agreement with the data of the magnetic field orientation control of GPS occultation observations of equatorial scintillation during thorough low earth orbit (LEO) satellites measurements, e.g. Challenging Minisatellite Payload (CHAMP) and Satellite de Aplicaciones Cientificas-C (SAC-C). The role of large-angle scattering almost along the normal to the magnetic field line in GPS scintillation is determined by attenuation of the irregularity anisotropy factor as compared with the other factors.

  6. Field-free alignment in repetitively kicked nitrogen gas

    SciTech Connect

    Cryan, James P.; Bucksbaum, Philip H.; Coffee, Ryan N.

    2009-12-15

    We demonstrate a high level of laser-induced transient alignment in room temperature and density N{sub 2} with a technique that avoids laser field ionization. Our measured alignment shows an improvement over previous one-pulse or two-pulse experimental alignment results and approaches the theoretical maximum value. We employ eight equally spaced ultrafast laser pulses with a separation that takes advantage of the periodic revivals for the ensemble of quantum rotors. Each successive pulse increases the transient alignment [(t)] and also moves the rotational population away from thermal equilibrium. These measurements are combined with simulations to determine the value of , the J-state distributions, and the functional dependencies of the alignment features.

  7. Disc polarization from both emission and scattering of magnetically aligned grains: the case of NGC 1333 IRAS 4A1

    NASA Astrophysics Data System (ADS)

    Yang, Haifeng; Li, Zhi-Yun; Looney, Leslie W.; Cox, Erin G.; Tobin, John; Stephens, Ian W.; Segura-Cox, Dominque M.; Harris, Robert J.

    2016-08-01

    Dust polarization in millimetre (and centimetre) has been mapped in discs around an increasing number of young stellar objects. It is usually thought to come from emission by magnetically aligned (non-spherical) grains, but can also be produced by dust scattering. We present a semi-analytic theory of disc polarization that includes both the direction emission and scattering, with an emphasis on their relative importance and how they are affected by the disc inclination. For face-on discs, both emission and scattering tend to produce polarization in the radial direction, making them difficult to distinguish, although the scattering-induced polarization can switch to the azimuthal direction if the incident radiation is beamed strongly enough in the radial direction in the disc plane. Disc inclination affects the polarizations from emission and scattering differently, especially on the major axis where, in the edge-on limit, the former vanishes while the latter reaches a polarization fraction as large as 1/3. The polarizations from the two competing mechanisms tend to cancel each other on the major axis, producing two low polarization `holes' (one on each side of the centre) under certain conditions. We find tantalizing evidence for at least one such `hole' in NGC 1333 IRAS 4A1, whose polarization observed at 8 mm on the 100 au scale is indicative of a pattern dominated by scattering close to the centre and by direction emission in the outer region. If true, it would imply not only that a magnetic field exists on the disc scale, but that it is strong enough to align large, possibly mm-sized, grains.

  8. Compton scattering in strong magnetic fields

    NASA Technical Reports Server (NTRS)

    Daugherty, Joseph K.; Harding, Alice K.

    1986-01-01

    The relativistic cross section for Compton scattering by electrons in strong magnetic fields is derived. The results confirm and extend earlier work which has treated only transitions to the lowest or first excited Landau levels. For the teragauss field strengths expected in neutron star magnetospheres, the relative rates for excited state transitions are found to be significant, especially for incident photon energies several times the cyclotron frequency. Since these transitions must result in the rapid emission of one or more cyclotron photons as well as the Compton-scattered photon, the scattering process actually becomes a photon 'splitting' mechanism which acts to soften hard photon spectra, and also provides a specific mechanism for populating higher Landau levels in the electron distribution function. The results should be significant for models of gamma-ray bursters and pulsating X-ray sources.

  9. Generation of large scale field-aligned density irregularities in ionospheric heating experiments. [electromagnetic wave decay

    NASA Technical Reports Server (NTRS)

    Fejer, J. A.

    1974-01-01

    Threshold and growth rate for stimulated Brillouin scattering are calculated for a uniform magnetoplasma. These are then compared with the threshold and growth rate of a new thermal instability in which the nonlinear Lorentz force felt by the electrons at the beat frequency of the two electromagnetic waves is replaced by a pressure force due to differential heating in the interference pattern of the pump wave and the generated electromagnetic wave. This thermal instability, which is still essentially stimulated Brillouin scattering, has a threshold which is especially low when the propagation vector of the beat wave is almost normal to the magnetic field. The threshold is then considerably lower than the threshold for normal stimulated Brillouin scattering and therefore this new instability is probably responsible for the generation of large scale field aligned irregularities and ionospheric spread F.

  10. Ro-vibrational excitation, alignment and orientation distributions of fast non-dissociatively scattered molecules

    NASA Astrophysics Data System (ADS)

    Harder, R.; Snowdon, K. J.

    1997-12-01

    The ro-vibrational distribution of fast diatomic molecules scattered from an uncorrugated surface under strongly dissipative glancing incidence conditions is calculated. The classical trajectory simulation includes potential surface switching associated with hot-electron scattering processes. Both ro-vibrational excitation and strong alignment of the classical angular momentum vector in the surface plane ("cartwheel motion") are observed, independent of the occurrence of potential surface switching. Ro-vibrational excitation is enhanced strongly by transitions between potential surfaces. The resultant larger proportion of molecules in highly rotationally excited states leads to a higher fraction of cartwheel-aligned molecules in the scattered molecule ensemble. The molecules which dissociate in the simulation are characterised by surface normal peaked internuclear axis orientation distributions. This is in agreement with the results of recent experiments [A. Nesbitt et al., Surf. Sci. 331-333 (1995) 321]. We observe, in addition, an enhanced rotational population of "topspin" oriented molecules, which arises from differences in the surface parallel oriented friction forces acting on each atom of the molecule. Glancing incidence scattering from well-prepared close-packed metal surfaces would appear to provide an efficient, general method to obtain a beam of preferentially aligned fast neutral diatomic molecules.

  11. Alignment induced aberration fields of next generation telescopes

    NASA Astrophysics Data System (ADS)

    Schmid, Tobias; Thompson, Kevin; Rolland, Jannick

    2008-08-01

    There is a long list of new ground-based optical telescopes being considered around the world. While many are conventional Cassegrain and Ritchey-Chretien designs, some are from a family of three mirror anastigmatic (TMA) telescopes that are configured with an offset field (but still obscured) that trace back to designs developed in the 1970s for military applications. The nodal theory of aberrations, developed in the late 1970s, provides valuable insights into the response of TMA telescopes to alignment errors. Here it is shown for the first time that the alignment limiting aberration in any TMA telescope is a 3rd order astigmatism term with a new field dependence, termed field-asymmetric, field-linear 3rd order astigmatism. It is also shown that a TMA telescope under assembly that is only measured to have excellent/perfect performance onaxis is not aligned in any significant way. This is because the new astigmatic term is always zero on-axis, even though it is large over the field of view. Knowledge of this intrinsic misalignment aberration field for any TMA telescope aids greatly in ensuring it can be aligned successfully. The James Webb Space Telescope (JWST), is used an example of a relevant TMA system.

  12. Dark Field Technology - A Practical Approach To Local Alignment

    NASA Astrophysics Data System (ADS)

    Beaulieu, David R.; Hellebrekers, Paul P.

    1987-01-01

    A fully automated direct reticle reference alignment system for use in step and repeat camera systems is described. The technique, first outlined by Janus S. Wilczynski, ("Optical Step and Repeat Camera with Dark Field Alignment", J. Vac. Technol., 16(6), Nov./Dec. 1979), has been implemented on GCA Corporation's DSW Wafer Stepper. Results from various process levels covering the typical CMOS process have shown that better than ±0.2μm alignment accuracy can be obtained with minimal process sensitivity. The technique employs fixed illumination and microscope optics to achieve excellent registration stability and maintenance-free operation. Latent image techniques can be exploited for intra-field, grid and focus characterization.

  13. Thermal electron acceleration by electric field spikes in the outer radiation belt: generation of field-aligned pitch angle distributions

    NASA Astrophysics Data System (ADS)

    Vasko, I.; Agapitov, O. V.; Mozer, F.; Artemyev, A.

    2015-12-01

    Van Allen Probes observations in the outer radiation belt have demonstrated an abundance non-linear electrostatic stucture called Time Domain Structures (TDS). One of the type of TDS is electrostatic electron-acoustic double layers (DL). Observed DLs are frequently accompanied by field-aligned (bi-directional) pitch angle distributions (PAD) of electrons with energies from hundred eVs up to several keV (rarely up to tens of keV). We perform numerical simulations of the DL interaction with thermal electrons making use of the test particle approach. DL parameters assumed in the simulations are adopted from observations. We show that DLs accelerate thermal electrons parallel to the magnetic field via the electrostatic Fermi mechanism, i.e. due to reflections from DL potential humps. Due to this interaction some fraction of electrons is scattered into the loss cone. The electron energy gain is larger for larger DL scalar potential amplitudes and higher propagation velocities. In addition to the Fermi mechanism electrons can be trapped by DLs in their generation region and accelerated due to transport to higher latitudes. Both mechanisms result in formation of field-aligned PADs for electrons with energies comparable to those found in observations. The Fermi mechanism provides field-aligned PADs for <1 keV electrons, while the trapping mechanism extends field-aligned PADs to higher energy electrons.

  14. Thermal electron acceleration by electric field spikes in the outer radiation belt: Generation of field-aligned pitch angle distributions

    NASA Astrophysics Data System (ADS)

    Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; Artemyev, A. V.

    2015-10-01

    Van Allen Probes observations in the outer radiation belt have demonstrated an abundance of electrostatic electron-acoustic double layers (DL). DLs are frequently accompanied by field-aligned (bidirectional) pitch angle distributions (PAD) of electrons with energies from hundred eVs up to several keV. We perform numerical simulations of the DL interaction with thermal electrons making use of the test particle approach. DL parameters assumed in the simulations are adopted from observations. We show that DLs accelerate thermal electrons parallel to the magnetic field via the electrostatic Fermi mechanism, i.e., due to reflections from DL potential humps. The electron energy gain is larger for larger DL scalar potential amplitudes and higher propagation velocities. In addition to the Fermi mechanism, electrons can be trapped by DLs in their generation region and accelerated due to transport to higher latitudes. Both mechanisms result in formation of field-aligned PADs for electrons with energies comparable to those found in observations. The Fermi mechanism provides field-aligned PADs for <1 keV electrons, while the trapping mechanism extends field-aligned PADs to higher-energy electrons. It is shown that the Fermi mechanism can result in scattering into the loss cone of up to several tenths of percent of electrons with flux peaking at energies up to several hundred eVs.

  15. Equivalent fields and scatter integration for photon fields.

    PubMed

    Xiao, Y; Bjärngard, B E; Reiff, J

    1999-04-01

    Equivalent fields are often used in radiation oncology for calculation of dose. This avoids the need to make a scatter integration but has limited applicability and some inaccuracy. We have evaluated the alternative of explicit integration of phantom-scatter dose using a functional representation, sigma, of the ratio between the scatter dose and the primary dose. The independent parameters are depth and the side of the square field. The function chosen has the advantage that the integral for a right triangle is available in closed form, which simplifies the determination of the dose from phantom-scattered photons for irregular fields by summation over such triangles. This approach accounts for the influence of depth and beam quality, which the commonly used equivalent-field tables and the area-over-perimeter relation ignore. The accuracy of this procedure is determined by the accuracy of the function sigma. This has about a 1% error of total dose for high-energy x-rays. We conclude that the tables and rules can be replaced by a computer-implemented integration of the phantom-scatter dose represented by this function sigma and using sectors or right triangles. Summing the closed-form contributions from component right triangles reduces the calculation time, which is particularly desirable when many fields are employed, as for intensity-modulated techniques and inverse planning. Measurements performed on irregular MLC-shaped fields compared well with the result from calculations.

  16. Orbital alignment in photodissociation probed using strong field ionization

    SciTech Connect

    Lin Yunfei; Yan Lu; Lee, Suk Kyoung; Herath, Thushani; Li Wen

    2011-12-21

    The photodissociation of molecules often produces atomic fragments with polarized electronic angular momentum, and the atomic alignment, for example, can provide valuable information on the dynamical pathways of chemical reactions unavailable by other means. In this work, we demonstrate for the first time that orbital polarization in chemical reactions can be measured with great sensitivity using strong field ionization by exploiting its extreme nonlinearity.

  17. Elevation angle alignment of quasi optical receiver mirrors of collective Thomson scattering diagnostic by sawtooth measurements

    SciTech Connect

    Moseev, D.; Meo, F.; Korsholm, S. B.; Leipold, F.; Michelsen, P. K.; Nielsen, S. K.; Salewski, M.; Stejner, M.; Bindslev, H.; Furtula, V.; Kantor, M.

    2012-10-15

    Localized measurements of the fast ion velocity distribution function and the plasma composition measurements are of significant interest for the fusion community. Collective Thomson scattering (CTS) diagnostics allow such measurements with spatial and temporal resolution. Localized measurements require a good alignment of the optical path in the transmission line. Monitoring the alignment during the experiment greatly benefits the confidence in the CTS measurements. An in situ technique for the assessment of the elevation angle alignment of the receiver is developed. Using the CTS diagnostic on TEXTOR without a source of probing radiation in discharges with sawtooth oscillations, an elevation angle misalignment of 0.9 Degree-Sign was found with an accuracy of 0.25 Degree-Sign .

  18. Elevation angle alignment of quasi optical receiver mirrors of collective Thomson scattering diagnostic by sawtooth measurementsa)

    NASA Astrophysics Data System (ADS)

    Moseev, D.; Meo, F.; Korsholm, S. B.; Bindslev, H.; Furtula, V.; Kantor, M.; Leipold, F.; Michelsen, P. K.; Nielsen, S. K.; Salewski, M.; Stejner, M.

    2012-10-01

    Localized measurements of the fast ion velocity distribution function and the plasma composition measurements are of significant interest for the fusion community. Collective Thomson scattering (CTS) diagnostics allow such measurements with spatial and temporal resolution. Localized measurements require a good alignment of the optical path in the transmission line. Monitoring the alignment during the experiment greatly benefits the confidence in the CTS measurements. An in situ technique for the assessment of the elevation angle alignment of the receiver is developed. Using the CTS diagnostic on TEXTOR without a source of probing radiation in discharges with sawtooth oscillations, an elevation angle misalignment of 0.9° was found with an accuracy of 0.25°.

  19. Retardance of bilayer anisotropic samples consisting of well-aligned cylindrical scatterers and birefringent media

    NASA Astrophysics Data System (ADS)

    Guo, Yihong; Zeng, Nan; He, Honghui; Liu, Celong; Du, E.; He, Yonghong; Ma, Hui

    2016-05-01

    Both cylindrical scatterers and birefringent media may contribute to the anisotropy of tissue, where anisotropy can be characterized using polarization techniques. Our previous studies have shown that a layer of well-aligned cylindrical scatterers displays anisotropic properties similar to those of a piece of birefringent media, whose equivalent extraordinary axis is along the axial direction of the cylinders. We focused on a sample consisting of two layers of anisotropic media, with each layer having a different orientation; the characteristics of this sample were representative of the properties of multilayer fibrous tissues. Using a Mueller matrix decomposition method, we examined in detail how the total retardance and the equivalent extraordinary axis of the bilayered sample varied with changes in the retardance of the two layers and the direction of the extraordinary axis. The results of this study showed that, in such bilayer samples, a layer of well-aligned cylindrical scatterers generated a retardance that behaved exactly like the retardance generated by a piece of birefringent media. The simulated results were also confirmed by the results of experiments using aligned glass fibers.

  20. Magnetic field alignment studies for the URAGAN-3 torsatron

    SciTech Connect

    Colchin, R.J.; Fedotov, S.I.; Harris, J.H.; Lee, D.K.; Ozherel'ev, F.I.; Pavlichenko, O.S.; Pogozhev, D.P.; Rome, J.A.; Treffert, J.D.; Zalkind, V.M.

    1986-02-01

    If the major axes of the helical and vertical field coils of a torsatron plasma confinement device are not aligned to within approx.1% of their major radii, the resulting error field can break up closed magnetic flux surfaces and reduce the effective plasma confinement volume. A novel technique for accurately locating the magnetic symmetry axes of torsatron helical and vertical coil sets to within approx.1 mm using magnetic field measurements near the device major axis (i.e., away from the confinement volume) is described and applied to the URAGAN-3 torsatron. The axis of the vertical field coil set was found to be shifted by approx.1 cm relative to the axis of the helical coil set; this shift could account for the reduced confinement volume observed in previous experiments. The magnetic measurements were repeated after coil repositioning to verify correct alignment. 10 refs., 13 figs.

  1. Swarm Observations of Field Aligned Currents during Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Le, G.; Luhr, H.; Anderson, B. J.; Strangeway, R. J.; Russell, C. T.; Slavin, J. A.; Bromund, K. R.; Plaschke, F.; Magnes, W.; Fischer, D.; Nakamura, R.; Leinweber, H. K.; Torbert, R. B.; Le Contel, O.; Oliveira, D. M.; Raeder, J.; Kepko, L.

    2015-12-01

    Field-aligned currents connect the Earth's magnetosphere to the high latitude ionosphere, and provide a main channel for energy transfer from the magnetosphere to the ionosphere. They are driven by solar wind-magnetosphere interactions and respond dynamically to changes in the solar wind and interplanetary magnetic field. Enhanced interaction during geomagnetic storms significantly intensifies their strength and variability. In this paper, we review our recent observations of field-aligned currents (FACs) during geomagnetic storms using observations from polar orbiting Swarm constellation as well as the Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE). Both temporal resolutions and spatial coverage of these observations provide new insights in understanding the FACs and the magnetosphere-ionosphere coupling. We will discuss their spatial and temporal evolutions, ionospheric closure currents, and hemispheric asymmetry during storms.

  2. Generation of field-aligned current in the auroral zone

    NASA Technical Reports Server (NTRS)

    Okuda, Hideo

    1991-01-01

    Generation of a magnetic field-aligned current in the auroral zone connecting the magnetospheric and ionospheric plasmas has been studied by means of a three dimensional particle simulation model. The model is of a magnetostatic variety appropriate for a low beta plasma in which the high frequency transverse displacement current has been eliminated. The simulation model is highly elongated along the magnetic field lines in order to model a highly elongated flux tube in the auroral zone. An enhanced field-aligned current was generated by injection of a magnetospheric plasma across the auroral zone magnetic field at the center of the model. Such a plasma injection may correspond to a plasmoid injection at the geomagnetic tail associated with magnetic reconnection during a substorm or a transverse plasma flow along the low latitude magnetopause boundary layer. The results of the simulations show that the field-aligned current can be enhanced over the thermal current by a factor of 5 - 10 via such injection. Associated with the enhanced current are the electrostatic ion cyclotron waves and shear Alfven waves excited in the auroral zone.

  3. Thomson scattering in a magnetic field. II - Arbitrary field orientation

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara A.

    1991-01-01

    This paper presents solutions to the equation of transfer for Thomson scattering in a constant magnetic field of arbitrary orientation. Results from several atmospheres are combined to give the flux from a dipole star. The results are compared to the polarization data of the magnetic white dwarf Grw + 70 deg 8247. The fit is good, though it implies a very large polarization in the ultraviolet. Thomson scattering is not thought to be an important opacity source in white dwarfs, so the good fit is either fortuitous or is perhaps explained by assuming the magnetic field affects the polarization processes in all opacities similarly.

  4. Ground Observations of Artificial E Region Field-Aligned Irregularities Over HAARP

    NASA Astrophysics Data System (ADS)

    Nossa, E.; Hysell, D. L.

    2008-12-01

    Heating experiments were performed at HAARP intended to create E region field aligned plasma irregularities (FAIs) at midday in July of 2008 when the critical frequency of the E layer is a maximum. Field-aligned backscatter was observed using a 30 MHz imaging coherent scatter radar located close to Homer, Alaska. Three experiment modes were used, involving 1) heating alternately at zenith and magnetic zenith, 2) heating using triangular power modulation, and 3) heating slightly above and below the second electron gyroharmonic. Strong echoes were observed in all cases. Radar imaging and other diagnostic methods are used to examine the degree to which irregularities can be observed outside the Spitze angle, the possible effects of predonditioning on thermal parametric instability, and the effects of the double resonance on backscatter intensity and irregularity formation.

  5. Phase-dependent field-free molecular alignment and orientation

    NASA Astrophysics Data System (ADS)

    Qin, Chaochao; Liu, Yuzhu; Zhang, Xianzhou; Gerber, Thomas

    2014-11-01

    We investigated the temporal behavior of alignment and orientation of LiH following a femtosecond laser pulse excitation comprising two fields at center frequencies ω and 2 ω (e.g., E (t )=E [cos(ω t )+cos(2 ω t +Φ ) ] ) shifted by a phase Φ . The effects of repopulations and rephasing of rotational states on the resulting alignment and orientation were evaluated. The population distribution of rotational states is only changed during the exciting pulse. Afterwards the established rotational state distribution is maintained in the absence of collisions. The phases of rotational states play the most crucial role in determining the time evolution of molecular alignment and orientation. Equal alignment and rotational populations are obtained when the phases are chosen Φ =0 and Φ =π . However, orientation is different due to the fact that in the case Φ =π the mutual phases of even rotation states are not changed but the phases of odd rotational states are shifted by π , comparing with that of Φ =0 . The effect of temperature on molecular orientation was also addressed. It was shown that an efficient field-free molecular orientation can be observed even at room temperature.

  6. Thomson scattering in a magnetic field. I - Field along z

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara A.

    1991-01-01

    The Monte Carlo method is used here to solve the radiative transfer equation for Thomson scattering in a constant magnetic field perpendicular to the atmosphere. Emergent radiation and polarization are presented for various atmospheric thicknesses. The circular polarization peaks at frequencies near the cyclotron, omega(c), and for propagation direction along the field. At low field strengths, the circular polarization is roughly proportional to omega(c)/omega; the linear polarization is proportional to the square of omega(c)/omega and the amount of circular polarization present at each scatter and is therefore much smaller than the circular polarization. The linear polarization is large for propagation direction perpendicular to the magnetic field and at frequencies near the cyclotron and in the strong-field limit. The position angle of the linear polarization undergoes a rotation of 90 deg at a value of omega(c)/omega near the square root of three.

  7. In-situ temperature-controllable shear flow device for neutron scattering measurement—An example of aligned bicellar mixtures

    NASA Astrophysics Data System (ADS)

    Xia, Yan; Li, Ming; Kučerka, Norbert; Li, Shutao; Nieh, Mu-Ping

    2015-02-01

    We have designed and constructed a temperature-controllable shear flow cell for in-situ study on flow alignable systems. The device has been tested in the neutron diffraction and has the potential to be applied in the small angle neutron scattering configuration to characterize the nanostructures of the materials under flow. The required sample amount is as small as 1 ml. The shear rate on the sample is controlled by the flow rate produced by an external pump and can potentially vary from 0.11 to 3.8 × 105 s-1. Both unidirectional and oscillational flows are achievable by the setting of the pump. The instrument is validated by using a lipid bicellar mixture, which yields non-alignable nanodisc-like bicelles at low T and shear-alignable membranes at high T. Using the shear cell, the bicellar membranes can be aligned at 31 °C under the flow with a shear rate of 11.11 s-1. Multiple high-order Bragg peaks are observed and the full width at half maximum of the "rocking curve" around the Bragg's condition is found to be 3.5°-4.1°. It is noteworthy that a portion of the membranes remains aligned even after the flow stops. Detailed and comprehensive intensity correction for the rocking curve has been derived based on the finite rectangular sample geometry and the absorption of the neutrons as a function of sample angle [See supplementary material at http://dx.doi.org/10.1063/1.4908165 for the detailed derivation of the absorption correction]. The device offers a new capability to study the conformational or orientational anisotropy of the solvated macromolecules or aggregates induced by the hydrodynamic interaction in a flow field.

  8. In-situ temperature-controllable shear flow device for neutron scattering measurement—An example of aligned bicellar mixtures

    SciTech Connect

    Xia, Yan; Li, Ming; Kučerka, Norbert; Li, Shutao; Nieh, Mu-Ping

    2015-02-15

    We have designed and constructed a temperature-controllable shear flow cell for in-situ study on flow alignable systems. The device has been tested in the neutron diffraction and has the potential to be applied in the small angle neutron scattering configuration to characterize the nanostructures of the materials under flow. The required sample amount is as small as 1 ml. The shear rate on the sample is controlled by the flow rate produced by an external pump and can potentially vary from 0.11 to 3.8 × 10{sup 5} s{sup −1}. Both unidirectional and oscillational flows are achievable by the setting of the pump. The instrument is validated by using a lipid bicellar mixture, which yields non-alignable nanodisc-like bicelles at low T and shear-alignable membranes at high T. Using the shear cell, the bicellar membranes can be aligned at 31 °C under the flow with a shear rate of 11.11 s{sup −1}. Multiple high-order Bragg peaks are observed and the full width at half maximum of the “rocking curve” around the Bragg’s condition is found to be 3.5°–4.1°. It is noteworthy that a portion of the membranes remains aligned even after the flow stops. Detailed and comprehensive intensity correction for the rocking curve has been derived based on the finite rectangular sample geometry and the absorption of the neutrons as a function of sample angle [See supplementary material at http://dx.doi.org/10.1063/1.4908165 for the detailed derivation of the absorption correction]. The device offers a new capability to study the conformational or orientational anisotropy of the solvated macromolecules or aggregates induced by the hydrodynamic interaction in a flow field.

  9. Generation of macroscopic magnetic-field-aligned electric fields by the convection surge ion acceleration mechanism

    NASA Technical Reports Server (NTRS)

    Mauk, B. H.

    1989-01-01

    The 'convection surge' model for ion acceleration, designed by Mauk (1986) to explain the observed ion distributions and the field-aligned character of middle magnetospheric ion distributions during the expansion phase of a substorm, was extended to include the self-consistent generation of magnetic-field-aligned electric fields. Results from the modified model show that the convection surge mechanism leads to the generation of dynamical macroscopic magnetic field-aligned electric fields that begin their strongest developments very near the magnetic equator and then propagate to higher latitudes. Potential drops as high as 1 to 10 kV might be expected, depending on the mass species of the ions and on the electron temperatures. It is speculated that the convection surge mechanism could be a key player in the transient field-aligned electromagnetic processes observed to operate within the middle magnetosphere.

  10. Mapping local orientation of aligned fibrous scatterers for cancerous tissues using backscattering Mueller matrix imaging

    NASA Astrophysics Data System (ADS)

    He, Honghui; Sun, Minghao; Zeng, Nan; Du, E.; Liu, Shaoxiong; Guo, Yihong; Wu, Jian; He, Yonghong; Ma, Hui

    2014-10-01

    Polarization measurements are sensitive to the microstructure of tissues and can be used to detect pathological changes. Many tissues contain anisotropic fibrous structures. We obtain the local orientation of aligned fibrous scatterers using different groups of the backscattering Mueller matrix elements. Experiments on concentrically well-aligned silk fibers and unstained human papillary thyroid carcinoma tissues show that the m22, m33, m23, and m32 elements have better contrast but higher degeneracy for the extraction of orientation angles. The m12 and m13 elements show lower contrast, but allow us to determine the orientation angle for the fibrous scatterers along all directions. Moreover, Monte Carlo simulations based on the sphere-cylinder scattering model indicate that the oblique incidence of the illumination beam introduces some errors in the orientation angles obtained by both methods. Mapping the local orientation of anisotropic tissues may not only provide information on pathological changes, but can also give new leads to reduce the orientation dependence of polarization measurements.

  11. Relationships between Geomagnetic Induced Currents and Field Aligned Currents

    NASA Astrophysics Data System (ADS)

    Waters, C. L.; Barnett, R.; Anderson, B. J.; Gjerloev, J. W.; Korth, H.; Barnes, R. J.

    2015-12-01

    Geomagnetic Induced Currents (GICs) appear in the ground due to time varying magnetic fields that occur during periods of enhanced geomagnetic activity. The resultant time varying electric fields at Earth's surface drive very low frequency, currents through electricity supply transformers which reduces transforming capacity. In extreme cases, electricity supply grids can collapse as multiple transformers are affected. GICs have larger magnitudes at auroral latitudes and should be related to the field aligned current (FAC) and auroral ionosphere currents systems. At ground locations under the regions between upward and downward FACs, the GIC related fields show a direct relationship with the time derivative of the FACs. This allows a conversion factor between FAC and GIC magnitudes. Examples of the relationship between FAC and GIC related fields are presented using data derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) and SuperMAG.

  12. Observed molecular alignment in gaseous streams and possible chiral effects in vortices and in surface scattering.

    PubMed

    Aquilanti, V; Maciel, G S

    2006-12-01

    Extensive work in this laboratory has been devoted to the study of intermolecular interactions from scattering experiments, in order to provide ingredients for modelling forces acting in systems involving hydrocarbons, the components of atmospheres, and water. Our detection of aligned oxygen in gaseous streams and further evidence on simple molecules has been extended to benzene and various hydrocarbons. Chiral effects can be seen in the differential scattering of oriented molecules, in particular from surfaces. It is pointed out that it may be of pre-biotical interest that we focus on possible mechanisms for chiral bio-stereochemistry of oriented reactants, for example when flowing in atmospheres of rotating bodies, specifically the planet earth, as well as in vortex motions of celestial objects. Molecular dynamics simulations and experimental verifications are in progress.

  13. Polar Rain Gradients and Field-Aligned Polar Cap Potentials

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.; Wing, S.; Newell, P. T.; Ruohoniemi, J. M.; Gosling, J. T.; Skoug, R. M.

    2008-01-01

    ACE SWEPAM measurements of solar wind field-aligned electrons have been compared with simultaneous measurements of polar rain electrons precipitating over the polar cap and detected by DMSP spacecraft. Such comparisons allow investigation of cross-polarcap gradients in the intensity of otherwise-steady polar rain. The generally good agreement of the distribution functions, f, from the two data sources confirms that direct entry of solar electrons along open field lines is indeed the cause of polar rain. The agreement between the data sets is typically best on the side of the polar cap with most intense polar rain but the DMSP f's in less intense regions can be brought into agreement with ACE measurements by shifting all energies by a fixed amounts that range from tens to several hundred eV. In most cases these shifts are positive which implies that field-aligned potentials of these amounts exist on polar cap field lines which tend to retard the entry of electrons and produce the observed gradients. These retarding potentials undoubtedly appear in order to prevent the entry of low-energy electrons and maintain charge quasi-neutrality that would otherwise be violated since most tailward flowing magnetosheath ions are unable to follow polar rain electrons down to the polar cap. In more limited regions near the boundary of the polar cap there is sometimes evidence for field-aligned potentials of the opposite sign that accelerate polar rain electrons. A solar electron burst is also studied and it is concluded that electrons from such bursts can enter the magnetotail and precipitate in the same manner as polar rain.

  14. Statistical relationship between large-scale upward field-aligned currents and electron precipitation

    NASA Astrophysics Data System (ADS)

    Korth, Haje; Zhang, Yongliang; Anderson, Brian J.; Sotirelis, Thomas; Waters, Colin L.

    2014-08-01

    Simultaneous observations of Birkeland currents by the constellation of Iridium satellites and N2 Lyman-Birge-Hopfield (LBH) auroral emissions measured by the Global Ultraviolet Imager (GUVI) onboard the Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) satellite are used to establish relationships between large-scale upward field-aligned currents and electron precipitation during stable current configurations. The electron precipitation was inferred from GUVI data using a statistical relationship between LBH intensity and electron energy flux. LBH emissions with >5% contribution from protons, identified by Lyman-alpha intensity, were excluded from the analysis. The Birkeland currents were derived with a spatial resolution of 3° in latitude and 2 h in local time. For southward interplanetary magnetic field (IMF), the electron precipitation occurred primarily within and near large-scale upward currents. The correspondence was less evident for northward IMF, presumably because the spatial variability is large compared to the areas of interest so that the number of events identified is smaller and the derived statistical distributions are less reliable. At dusk, the correlation between upward current and precipitation was especially high, where a larger fraction of the electron precipitation is accelerated downward by a field-aligned potential difference. Unaccelerated electron precipitation dominated in the morning sector, presumably induced by scattering of eastward-drifting energetic electrons into the loss cone through interaction with whistler-mode waves (diffuse precipitation) rather than by field-aligned acceleration. In the upward Region 1 on the dayside, where the electron precipitation is almost exclusively due to field-aligned acceleration, a quadratic relationship between current density and electron energy flux was observed, implying a linear current-voltage relationship in this region. Current density and electron energy flux in

  15. Field-aligned current response to solar indices

    NASA Astrophysics Data System (ADS)

    Edwards, Thom R.; Weimer, D. R.; Tobiska, W. K.; Olsen, Nils

    2017-05-01

    Magnetometer data from three satellite missions have been used to analyze and identify the effects of varying solar radiation on the magnitudes and locations of field-aligned currents in the Earth's upper atmosphere. Data from the CHAMP, Ørsted, and Swarm satellite missions have been brought together to provide a database spanning a 15 year period. The extensive time frame has been augmented by data from the ACE satellite, as well as a number of indices of solar radiation. This data set has been sorted by a number of solar wind, interplanetary magnetic field, and solar radiation indices to provide measurements for the field-aligned current structures in both hemispheres for arbitrary seasonal tilts. In addition, routines have been developed to extract the total current for different regions of the current structures, including regions 0, 1, and 2. Results from this study have been used to evaluate the effects of variations in four different solar indices on the total current in different regions of the polar cap. While the solar indices do not have major influence on the total current of the polar cap when compared to solar wind and interplanetary magnetic field parameters, it does appear that there is a nonlinear response to increasing F10.7, M10.7, and S10.7 solar indices. Surprisingly, there appears to be a very linear response as Y10.7 solar index increases.

  16. He I VECTOR MAGNETOMETRY OF FIELD-ALIGNED SUPERPENUMBRAL FIBRILS

    SciTech Connect

    Schad, T. A.; Penn, M. J.; Lin, H.

    2013-05-10

    Atomic-level polarization and Zeeman effect diagnostics in the neutral helium triplet at 10830 A in principle allow full vector magnetometry of fine-scaled chromospheric fibrils. We present high-resolution spectropolarimetric observations of superpenumbral fibrils in the He I triplet with sufficient polarimetric sensitivity to infer their full magnetic field geometry. He I observations from the Facility Infrared Spectropolarimeter are paired with high-resolution observations of the H{alpha} 6563 A and Ca II 8542 A spectral lines from the Interferometric Bidimensional Spectrometer from the Dunn Solar Telescope in New Mexico. Linear and circular polarization signatures in the He I triplet are measured and described, as well as analyzed with the advanced inversion capability of the ''Hanle and Zeeman Light'' modeling code. Our analysis provides direct evidence for the often assumed field alignment of fibril structures. The projected angle of the fibrils and the inferred magnetic field geometry align within an error of {+-}10 Degree-Sign . We describe changes in the inclination angle of these features that reflect their connectivity with the photospheric magnetic field. Evidence for an accelerated flow ({approx}40 m s{sup -2}) along an individual fibril anchored at its endpoints in the strong sunspot and weaker plage in part supports the magnetic siphon flow mechanism's role in the inverse Evershed effect. However, the connectivity of the outer endpoint of many of the fibrils cannot be established.

  17. Enhanced Alignment Techniques for the Thomson Scattering Diagnostic on the Lithium Tokamak eXperiment (LTX)

    NASA Astrophysics Data System (ADS)

    Merino, Enrique; Kozub, Tom; Boyle, Dennis; Lucia, Matthew; Majeski, Richard; Kaita, Robert; Schmitt, John C.; Leblanc, Benoit; Diallo, Ahmed; Jacobson, C. M.

    2014-10-01

    The Thomson Scattering (TS) System in LTX is used to measure electron temperature and density profiles of core and edge plasmas. In view of TS measurements showing low signal-to-noise and high stray light, numerous improvements were performed in recent months. These will allow for better measurements. Due to the nature of LTX's lithium coated walls, a particular challenge was presented by alignment procedures which required insertion and precise positioning of equipment in the vacuum vessel without breaking vacuum. To overcome these difficulties, the laser flight tubes were removed and an alignment probe setup placed along the beam line on a differentially pumped assembly. The probe was then driven into the vacuum vessel and back-illumination of the viewing optics on it allowed for alignment and spatial calibration. Other upgrades included better bracing of flight tubes and viewing optics as well as a redesigned beam dump. An overview of these improvements will be presented. Supported by US DOE Contracts DE-AC02-09CH11466 and DE-AC52-07NA27344.

  18. Aligned Single Wall Carbon Nanotube Polymer Composites Using an Electric Field

    NASA Technical Reports Server (NTRS)

    Park, Cheol; Wiklinson, John; Banda, Sumanth; Ounaies, Zoubeida; Wise, Kristopher E.; Sauti, Godfrey; Lillehei, Peter T.; Harrison, Joycelyn S.

    2005-01-01

    While high shear alignment has been shown to improve the mechanical properties of single wall carbon nanotubes (SWNT)-polymer composites, it is difficult to control and often results in degradation of the electrical and dielectric properties of the composite. Here, we report a novel method to actively align SWNTs in a polymer matrix, which allows for control over the degree of alignment of SWNTs without the side effects of shear alignment. In this process, SWNTs are aligned via field-induced dipolar interactions among the nanotubes under an AC electric field in a liquid matrix followed by immobilization by photopolymerization while maintaining the electric field. Alignment of SWNTs was controlled as a function of magnitude, frequency, and application time of the applied electric field. The degree of SWNT alignment was assessed using optical microscopy and polarized Raman spectroscopy and the morphology of the aligned nanocomposites was investigated by high resolution scanning electron microscopy. The structure of the field induced aligned SWNTs is intrinsically different from that of shear aligned SWNTs. In the present work, SWNTs are not only aligned along the field, but also migrate laterally to form thick, aligned SWNT percolative columns between the electrodes. The actively aligned SWNTs amplify the electrical and dielectric properties in addition to improving the mechanical properties of the composite. All of these properties of the aligned nanocomposites exhibited anisotropic characteristics, which were controllable by tuning the applied field conditions.

  19. 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.

  20. Terrestrial ionospheric signatures of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Friis-Christensen, E.

    1990-01-01

    The occurrence of traveling field-aligned current filaments and twin-vortex patterns is suggested to be related to sudden changes in solar wind dynamic pressure and/or the IMF. Greenland magnetometer observations of the cleft region magnetic perturbations associated with small-scale twin-vortex patterns show that these events occur on both sides of the magnetic local noon, contradicting Glassmeier at al.'s (1989) statistical analysis of 82 twin-vortex subauroral-latitude events obtained by the Scandinavian Magnetometer Array; the stations are closer to the ionospheric projection of the cleft earlier in magnetic local time, relative to the across-the-cleft-located Greenland stations.

  1. Study on the scale distribution of the field-aligned irregularities in E-region

    NASA Astrophysics Data System (ADS)

    Gong, Wanlin; Qi, Hao

    2016-12-01

    The field-aligned backscattering region in the ionospheric E-region is considered to contain many small irregularities, which are arrayed along the magnetic lines. The scale and number of these irregularities in the backscattering region are different. The irregularities of a certain scale can reflect the radio wave of the corresponding wavelength on the basis of the Bragg scattering theory. The more the irregularities of a scale, the stronger is the backscattered power. Thus, the scale distribution can be estimated by the function relationship between the scale and the echo amplitude, while the incidence direction of the wave path is perpendicular to the geomagnetic field. Moreover, the echoes with oblique incidence direction can also be used to estimate the scale distribution, considering the factor of the angle between the wave path and the perpendicular field direction.

  2. Electric Field Light Scattering by Rod-Like Polyelectrolytes in Aqueous Suspensions

    NASA Astrophysics Data System (ADS)

    Martin, C.; Weyerich, B.; Biegel, J.; Deike, R.; Johner, C.; Klein, R.; Weber, R.

    1995-05-01

    Static light scattering measurements are presented for rod-like fd-virus particles (L=880 nm, D= 9 nm) subjected to a pulsed alternating electric field in aqueous suspensions at very low ionic strength. In aqueous suspensions the dispersed fd-particles are negatively charged and surrounded by a diffuse Debye counterion cloud. In an external electric field an induced dipole originating from a deformation of the diffuse counterion cloud causes the alignment of the macromolecules. The anisotropic orientation distribution of the particles in the presence of the electric field results in a change of the angular distribution of the scattered light intensity with regard to the isotropic case. The steady-state electric field light scattering effect Δ I/I_0 is measured as a function of the electric field strength and its frequency at a fixed scattering angle. The determination of the anisotropy of the electric polarizability Δα_el of a fd-virus particle at higher electric field strengths, above the Kerr regime, shows a decrease of Δα_el with increasing field. This is interpreted as a destruction of the diffuse Debye cloud in high electric fields. The orientational order parameter has been found to be as large as 0.93 indicating an almost complete particle orientation along the external field at the highest fields. It is also shown that in the frequency regime below 1 kHz electrostatically interacting rods can align perpendicular to the external electric field, whereas at higher frequencies this anomalous behaviour disappears. From the scattered intensity the form-factor and the static structure factor of interacting fd-virus particles have been determined. With increasing fields a substantial increase in the peak height of the static structure factor is found. The data is in good agreement with Monte Carlo simulations using a simple interaction model for the system. The orientation of the macromolecules in the presence of an electric field is affected by the

  3. Space Technology 5 observations of auroral field-aligned currents

    NASA Astrophysics Data System (ADS)

    Slavin, James

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.6o) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness, and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the "standard method," based upon s/c velocity, but corrected for FAC current sheet motion, and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data set and expand to include horizontal ionospheric currents, ULF waves and geomagnetic field gradient analyses.

  4. Space Technology 5 Observations of Auroral Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Slavin, James

    2008-01-01

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.60) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness. and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the -standard method." based upon s/c velocity, but corrected for FAC current sheet motion. and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data sct and expand to include horizontal ionospheric currents. ULF waves and geomagnetic field gradient analyses.

  5. On the Field-Aligned Beam Thermal Energy

    NASA Astrophysics Data System (ADS)

    Meziane, K.; Hamza, A. M.; Wilber, M.; Mazelle, C.; Lee, M. A.

    2013-11-01

    The parallel and perpendicular reduced distribution functions of field-aligned beams (FABs) observed upstream of the Earth's bow shock using the Cluster spacecrafts are examined. A previous study revealed that FABs, observed in oblique shock geometries, exhibit reduced distribution functions with high-energy tails. A selection of FABs with weak-energy tails are considered, and the associated reduced distributions are fit with Maxwellians. First, we have found that the FABs full width at half maximum (FWHM), σ∥ and σ⊥ derived from the fit, are linearly correlated with the solar wind speed (or equivalently to solar wind temperature). Moreover, the parallel beam σ∥ has a very weak dependence upon the beam parallel speed which reflects the shock geometry; we have found that σ∥˜0.23Vsw. In contrast, we have found that the perpendicular beam σ⊥, in the range of beam speeds investigated, depends on the shock geometry. These new results indicate that the parallel σ∥ is essentially controlled by the solar wind while the shock geometry plays, along with the solar wind, a role in the perpendicular σ⊥. These results also put some strong constraints on theoretical models as far as field-aligned beam production mechanisms are concerned. One potential explanation for the significant perpendicular broadening of the FAB distribution reported in this study could be the presence of kinetic Alfvèn (or/and whistler) turbulence at the shock.

  6. Assessment of a field-aligned ICRF antenna

    NASA Astrophysics Data System (ADS)

    Wukitch, S. J.; Brunner, D.; Ennever, P.; Garrett, M. L.; Hubbard, A.; Labombard, B.; Lau, C.; Lin, Y.; Lipschultz, B.; Miller, D.; Ochoukov, R.; Porkolab, M.; Reinke, M. L.; Terry, J. L.

    2014-02-01

    Impurity contamination and localized heat loads associated with ion cyclotron range of frequency (ICRF) antenna operation are among the most challenging issues for ICRF utilization.. Another challenge is maintaining maximum coupled power through plasma variations including edge localized modes (ELMs) and confinement transitions. Here, we report on an experimental assessment of a field aligned (FA) antenna with respect to impurity contamination, impurity sources, RF enhanced heat flux and load tolerance. In addition, we compare the modification of the scrape of layer (SOL) plasma potential of the FA antenna to a conventional, toroidally aligned (TA) antenna, in order to explore the underlying physics governing impurity contamination linked to ICRF heating. The FA antenna is a 4-strap ICRF antenna where the current straps and antenna enclosure sides are perpendicular to and the Faraday screen rods are parallel to the total magnetic field. In principle, alignment with respect to the total magnetic field minimizes integrated E∥ (electric field along a magnetic field line) via symmetry. Consistent with expectations, we observed that the impurity contamination and impurity source at the FA antenna are reduced compared to the TA antenna. In both L and H-mode discharges, the radiated power is 20-30% lower for a FA-antenna heated discharge than a discharge heated with the TA-antennas. Further we observe that the fraction of RF energy deposited upon the antenna is less than 0.4 % of the total injected RF energy in dipole phasing. The total deposited energy increases significantly when the FA antenna is operated in monopole phasing. The FA antenna also exhibits an unexpected load tolerance for ELMs and confinement transitions compared to the TA antennas. However, inconsistent with expectations, we observe RF induced plasma potentials to be nearly identical for FA and TA antennas when operated in dipole phasing. In monopole phasing, the FA antenna has the highest plasma

  7. Assessment of a field-aligned ICRF antenna

    SciTech Connect

    Wukitch, S. J.; Brunner, D.; Ennever, P.; Garrett, M. L.; Hubbard, A.; Labombard, B.; Lau, C.; Lin, Y.; Lipschultz, B.; Miller, D.; Ochoukov, R.; Porkolab, M.; Reinke, M. L.; Terry, J. L.

    2014-02-12

    Impurity contamination and localized heat loads associated with ion cyclotron range of frequency (ICRF) antenna operation are among the most challenging issues for ICRF utilization.. Another challenge is maintaining maximum coupled power through plasma variations including edge localized modes (ELMs) and confinement transitions. Here, we report on an experimental assessment of a field aligned (FA) antenna with respect to impurity contamination, impurity sources, RF enhanced heat flux and load tolerance. In addition, we compare the modification of the scrape of layer (SOL) plasma potential of the FA antenna to a conventional, toroidally aligned (TA) antenna, in order to explore the underlying physics governing impurity contamination linked to ICRF heating. The FA antenna is a 4-strap ICRF antenna where the current straps and antenna enclosure sides are perpendicular to and the Faraday screen rods are parallel to the total magnetic field. In principle, alignment with respect to the total magnetic field minimizes integrated E∥ (electric field along a magnetic field line) via symmetry. Consistent with expectations, we observed that the impurity contamination and impurity source at the FA antenna are reduced compared to the TA antenna. In both L and H-mode discharges, the radiated power is 20–30% lower for a FA-antenna heated discharge than a discharge heated with the TA-antennas. Further we observe that the fraction of RF energy deposited upon the antenna is less than 0.4 % of the total injected RF energy in dipole phasing. The total deposited energy increases significantly when the FA antenna is operated in monopole phasing. The FA antenna also exhibits an unexpected load tolerance for ELMs and confinement transitions compared to the TA antennas. However, inconsistent with expectations, we observe RF induced plasma potentials to be nearly identical for FA and TA antennas when operated in dipole phasing. In monopole phasing, the FA antenna has the highest plasma

  8. Connecting the Sun and Earth: Field ALigned Connections Constellation

    NASA Astrophysics Data System (ADS)

    Stoneback, R.

    2016-12-01

    As the solar wind flows past the Earth power flows along geomagnetic field lines into the Earth's ionosphere, driving high latitude convection and plasma motions throughout the magnetosphere. Complete understanding of this energy flux has been limited by the availability of measurements. The presented Field ALigned CONnections constellation concept is designed to measure the energy flux as well as the energy deposited into the polar ionosphere. In collaboration with the ground based SuperDARN, measurements from both platforms may be assimilated into a cohesive system to better understand energy flow. The assimilation of DMSP and SuperDARN high-latitude convection measurements using Data Interpolating Empirical Orthogonal Functions (DINEOFs) will be shown.

  9. Swarm Observations of Field-Aligned Currents: Case Studies

    NASA Astrophysics Data System (ADS)

    Le, G.; Chi, P. J.; Gjerloev, J. W.; Stolle, C.; Luhr, H.; Park, J.; Rauberg, J.

    2014-12-01

    In this paper, we report the results of a few case studies of multi-point magnetic field measurements of field-aligned currents (FACs) from Swarm constellation mission to understand their temporal and spatial characteristics. During the commissioning phase, the three Swarm spacecraft were in an identical polar orbit with a string-of-pearl configuration with small separations. During the science operational phase (since April, 2014), the three spacecraft were placed in slightly different polar orbits: one spacecraft in a higher altitude orbit (507km x 512km) and two side-by-side in lower altitude orbits (459km x 462km). We analyze a few FAC events in both orbital phases and during periods of active geomagnetic conditions. The multi-point observations enable us to examine the FACs' temporal evolution and separate their temporal and spatial variations.

  10. Field-aligned ICRF antenna design for EAST

    NASA Astrophysics Data System (ADS)

    Wukitch, S. J.; Lin, Y.; Qin, C.; Zhang, X.; Beck, W.; Koert, P.; Zhou, L.

    2015-12-01

    For ion cyclotron range of frequency (ICRF), a number of physics and technological challenges remain for steady state, toroidal devices. Among the most critical is maintaining good coupling and maximizing the coupled power through plasma variations including edge localized modes (ELMs) and confinement transitions. As pulse length increases, enhanced localized heat loads associated with antenna operation can challenge antenna integrity. In addition, ICRF impurity sources and contamination need to be minimized to enable effective plasma heating. Here, we report on a four strap field aligned (FA) antenna design for the EAST tokamak. A FA antenna is an antenna where the current straps and antenna side enclosure are perpendicular to the total magnetic field while the Faraday screen rods are parallel to the total magnetic field. In C-Mod, a FA antenna has been shown to be inherently load tolerant which allows for robust power delivery to the plasma. Furthermore, the RF enhanced heat flux and antenna impurity source were nearly eliminated. For both L and H-mode discharges, the core impurity contamination is 20-30% lower but not eliminated. The emerging physics understanding is that the local RF impurity sources and RF enhanced heat flux is reduced due to the geometric alignment of the FA antenna while impurity contamination is a result of far field sheaths. An important aspect of antenna design is to identify a core absorption scenario that is characterized by strong single pass absorption for a broad range of target discharges. To maximize power coupling, the antenna spectrum needs to balance the k|| needed for strong single pass absorption and high coupling efficiency through evanescent layer. The latest design for a FA four strap adapted to EAST device is balance between geometrical constraints and physics requirements.

  11. MRFalign: protein homology detection through alignment of Markov random fields.

    PubMed

    Ma, Jianzhu; Wang, Sheng; Wang, Zhiyong; Xu, Jinbo

    2014-03-01

    Sequence-based protein homology detection has been extensively studied and so far the most sensitive method is based upon comparison of protein sequence profiles, which are derived from multiple sequence alignment (MSA) of sequence homologs in a protein family. A sequence profile is usually represented as a position-specific scoring matrix (PSSM) or an HMM (Hidden Markov Model) and accordingly PSSM-PSSM or HMM-HMM comparison is used for homolog detection. This paper presents a new homology detection method MRFalign, consisting of three key components: 1) a Markov Random Fields (MRF) representation of a protein family; 2) a scoring function measuring similarity of two MRFs; and 3) an efficient ADMM (Alternating Direction Method of Multipliers) algorithm aligning two MRFs. Compared to HMM that can only model very short-range residue correlation, MRFs can model long-range residue interaction pattern and thus, encode information for the global 3D structure of a protein family. Consequently, MRF-MRF comparison for remote homology detection shall be much more sensitive than HMM-HMM or PSSM-PSSM comparison. Experiments confirm that MRFalign outperforms several popular HMM or PSSM-based methods in terms of both alignment accuracy and remote homology detection and that MRFalign works particularly well for mainly beta proteins. For example, tested on the benchmark SCOP40 (8353 proteins) for homology detection, PSSM-PSSM and HMM-HMM succeed on 48% and 52% of proteins, respectively, at superfamily level, and on 15% and 27% of proteins, respectively, at fold level. In contrast, MRFalign succeeds on 57.3% and 42.5% of proteins at superfamily and fold level, respectively. This study implies that long-range residue interaction patterns are very helpful for sequence-based homology detection. The software is available for download at http://raptorx.uchicago.edu/download/. A summary of this paper appears in the proceedings of the RECOMB 2014 conference, April 2-5.

  12. MRFalign: Protein Homology Detection through Alignment of Markov Random Fields

    PubMed Central

    Ma, Jianzhu; Wang, Sheng; Wang, Zhiyong; Xu, Jinbo

    2014-01-01

    Sequence-based protein homology detection has been extensively studied and so far the most sensitive method is based upon comparison of protein sequence profiles, which are derived from multiple sequence alignment (MSA) of sequence homologs in a protein family. A sequence profile is usually represented as a position-specific scoring matrix (PSSM) or an HMM (Hidden Markov Model) and accordingly PSSM-PSSM or HMM-HMM comparison is used for homolog detection. This paper presents a new homology detection method MRFalign, consisting of three key components: 1) a Markov Random Fields (MRF) representation of a protein family; 2) a scoring function measuring similarity of two MRFs; and 3) an efficient ADMM (Alternating Direction Method of Multipliers) algorithm aligning two MRFs. Compared to HMM that can only model very short-range residue correlation, MRFs can model long-range residue interaction pattern and thus, encode information for the global 3D structure of a protein family. Consequently, MRF-MRF comparison for remote homology detection shall be much more sensitive than HMM-HMM or PSSM-PSSM comparison. Experiments confirm that MRFalign outperforms several popular HMM or PSSM-based methods in terms of both alignment accuracy and remote homology detection and that MRFalign works particularly well for mainly beta proteins. For example, tested on the benchmark SCOP40 (8353 proteins) for homology detection, PSSM-PSSM and HMM-HMM succeed on 48% and 52% of proteins, respectively, at superfamily level, and on 15% and 27% of proteins, respectively, at fold level. In contrast, MRFalign succeeds on 57.3% and 42.5% of proteins at superfamily and fold level, respectively. This study implies that long-range residue interaction patterns are very helpful for sequence-based homology detection. The software is available for download at http://raptorx.uchicago.edu/download/. A summary of this paper appears in the proceedings of the RECOMB 2014 conference, April 2–5. PMID:24675572

  13. Modeling magnetic perturbation fields associated with ionospheric and geomagnetic-field-aligned currents

    NASA Astrophysics Data System (ADS)

    Richmond, A. D.; Maute, A.

    2003-04-01

    The National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model calculates ionospheric and geomagnetic-field-aligned electric currents produced by ionospheric wind dynamo action, taking into account magnetospheric sources at high latitudes. The associated magnetic perturbations at the ground and at low-Earth-orbit (LEO) satellite altitudes are calculated by representing the height-integrated horizontal ionospheric current as a current sheet at 110 km, connected to geomagnetic-field-aligned currents flowing into and out of the top. The horizontal sheet current can be divided into two components: a divergence-free equivalent current which, together with the associated induced Earth currents, is responsible for all of the magnetic perturbations below the current sheet, and a divergent (but not irrotational) current that closes the field-aligned currents above. We call the combination of the field-aligned currents and their closing ionospheric currents the ``nonequivalent'' currents. By definition, these produce no magnetic effect at the ground, but they do produce important magnetic effects at LEO altitudes, generally dominating the component of LEO magnetic perturbations perpendicular to the main geomagnetic field. At high magnetic latitudes the nonequivalent LEO magnetic perturbations are largely toroidal, and are associated with the strong field-aligned currents that couple the ionosphere with the outer magnetosphere. At middle and low magnetic latitudes the nonequivalent LEO magnetic perturbations are largely associated with field-aligned currents that flow between the northern and southern hemispheres, and that can produce east-west perturbations of tens of nanoteslas.

  14. Computational studies of x-ray scattering from three-dimensionally-aligned asymmetric-top molecules.

    SciTech Connect

    Pabst, S.; Ho, P.; Santra, R.

    2010-01-01

    We theoretically and numerically analyze x-ray scattering from asymmetric-top molecules three-dimensionally aligned using elliptically polarized laser light. A rigid-rotor model is assumed. The principal axes of the polarizability tensor are assumed to coincide with the principal axes of the moment of inertia tensor. Several symmetries in the Hamiltonian are identified and exploited to enhance the efficiency of solving the time-dependent Schroedinger equation for each rotational state initially populated in a thermal ensemble. Using a phase-retrieval algorithm, the feasibility of structure reconstruction from a quasiadiabatically aligned sample is illustrated for the organic molecule naphthalene. The spatial resolution achievable strongly depends on the laser parameters, the initial rotational temperature, and the x-ray pulse duration. We demonstrate that for a laser peak intensity of 5 TW/cm{sup 2}, a laser pulse duration of 100 ps, a rotational temperature of 10 mK, and an x-ray pulse duration of 1 ps, the molecular structure may be probed at a resolution of 1 {angstrom}.

  15. Computational studies of x-ray scattering from three-dimensionally-aligned asymmetric-top molecules

    SciTech Connect

    Pabst, Stefan; Ho, Phay J.; Santra, Robin

    2010-04-15

    We theoretically and numerically analyze x-ray scattering from asymmetric-top molecules three-dimensionally aligned using elliptically polarized laser light. A rigid-rotor model is assumed. The principal axes of the polarizability tensor are assumed to coincide with the principal axes of the moment of inertia tensor. Several symmetries in the Hamiltonian are identified and exploited to enhance the efficiency of solving the time-dependent Schroedinger equation for each rotational state initially populated in a thermal ensemble. Using a phase-retrieval algorithm, the feasibility of structure reconstruction from a quasiadiabatically aligned sample is illustrated for the organic molecule naphthalene. The spatial resolution achievable strongly depends on the laser parameters, the initial rotational temperature, and the x-ray pulse duration. We demonstrate that for a laser peak intensity of 5 TW/cm{sup 2}, a laser pulse duration of 100 ps, a rotational temperature of 10 mK, and an x-ray pulse duration of 1 ps, the molecular structure may be probed at a resolution of 1 A ring .

  16. Computational studies of x-ray scattering from three-dimensionally-aligned asymmetric-top molecules

    NASA Astrophysics Data System (ADS)

    Pabst, Stefan; Ho, Phay; Santra, Robin

    2009-11-01

    We theoretically and numerically analyze x-ray scattering from asymmetric-top molecules three-dimensionally aligned using elliptically polarized laser light. A rigid-rotor model is assumed. The principal axes of the polarizability tensor are assumed to coincide with the principal axes of the moment of inertia tensor. Several symmetries in the Hamiltonian are identified and employed to enhance the efficiency of solving the time-dependent Schr"odinger equation for each rotational state initially populated in a thermal ensemble. Using a phase-retrieval algorithm, the feasibility of structure reconstruction from a quasi-adiabatically-aligned sample is illustrated for the organic molecule naphthalene. The spatial resolution achievable strongly depends on the laser parameters, the initial rotational temperature, and the x-ray pulse duration. We demonstrate that for a laser peak intensity of 5 TW/cm^2, a laser pulse duration of 100 ps, a rotational temperature of 10 mK, and an x-ray pulse duration of 1 ps, the molecular structure may be probed at a resolution of 1 å.

  17. Alignment of Iron Nanoparticles in a Magnetic Field Due to Shape Anisotropy

    DOE PAGES

    Radhakrishnan, Balasubramaniam; Nicholson, Don M; Eisenbach, Markus; ...

    2015-07-09

    During high magnetic field processing there is evidence for alignment of non-spherical metallic particles above the Curie temperature in alloys with negligible magneto-crystalline anisotropy. The main driving force for alignment is the magnetic shape anisotropy. Current understanding of the phenomenon is not adequate to quantify the effect of particle size, aspect ratio, temperature and the magnetic field on particle alignment. We demonstrate a Monte Carlo approach coupled with size scaling to show the conditions under which alignment is possible.

  18. Alignment of Iron Nanoparticles in a Magnetic Field Due to Shape Anisotropy

    SciTech Connect

    Radhakrishnan, Balasubramaniam; Nicholson, Don M; Eisenbach, Markus; Ludtka, Gerard Michael; Rios, Orlando; Parish, Chad M

    2015-07-09

    During high magnetic field processing there is evidence for alignment of non-spherical metallic particles above the Curie temperature in alloys with negligible magneto-crystalline anisotropy. The main driving force for alignment is the magnetic shape anisotropy. Current understanding of the phenomenon is not adequate to quantify the effect of particle size, aspect ratio, temperature and the magnetic field on particle alignment. We demonstrate a Monte Carlo approach coupled with size scaling to show the conditions under which alignment is possible.

  19. Investigation of moderately turbid suspensions by heterodyne near field scattering.

    PubMed

    Escobedo-Sánchez, M A; Rojas-Ochoa, L F; Laurati, M; Egelhaaf, S U

    2017-08-03

    Light scattering has proven to be a very powerful technique to characterize soft matter systems. However, many samples are turbid and hence suffer from multiple scattering which can affect the signal considerably. Multiple scattering can be reduced by diluting the sample or changing the solvent, but often this alters the sample and hence is precluded. Here we study the dynamics of a model system. In particular, we investigate the effects of moderate multiple scattering on small-angle heterodyne near field scattering (HNFS). Varying the particle concentration and size we change the degree of multiple scattering, which is quantified by the transmission of light. In dependence of the degree of multiple scattering, we analyze the statistical properties of the HNFS signal, which is the difference between two intensity patterns separated by a delay time. The distribution of intensity differences follows a Gaussian distribution if single scattering dominates and a Laplace distribution in the presence of extreme multiple scattering. We also investigate the effects of multiple scattering on the measured intermediate scattering function and the hydrodynamic radius of the particles. Reliable data are obtained for sample transmissions down to about 0.7. This is confirmed by a comparison with results from a far field cross-correlation instrument that suppresses multiple scattering contributions. Therefore, HNFS represents a technically simple but powerful method to investigate samples that are moderately multiple scattering.

  20. Weak scattering of scalar and electromagnetic random fields

    NASA Astrophysics Data System (ADS)

    Tong, Zhisong

    This dissertation encompasses several studies relating to the theory of weak potential scattering of scalar and electromagnetic random, wide-sense statistically stationary fields from various types of deterministic or random linear media. The proposed theory is largely based on the first Born approximation for potential scattering and on the angular spectrum representation of fields. The main focus of the scalar counterpart of the theory is made on calculation of the second-order statistics of scattered light fields in cases when the scattering medium consists of several types of discrete particles with deterministic or random potentials. It is shown that the knowledge of the correlation properties for the particles of the same and different types, described with the newly introduced pair-scattering matrix, is crucial for determining the spectral and coherence states of the scattered radiation. The approach based on the pair-scattering matrix is then used for solving an inverse problem of determining the location of an "alien" particle within the scattering collection of "normal" particles, from several measurements of the spectral density of scattered light. Weak scalar scattering of light from a particulate medium in the presence of optical turbulence existing between the scattering centers is then approached using the combination of the Born's theory for treating the light interaction with discrete particles and the Rytov's theory for light propagation in extended turbulent medium. It is demonstrated how the statistics of scattered radiation depend on scattering potentials of particles and the power spectra of the refractive index fluctuations of turbulence. This theory is of utmost importance for applications involving atmospheric and oceanic light transmission. The second part of the dissertation includes the theoretical procedure developed for predicting the second-order statistics of the electromagnetic random fields, such as polarization and linear momentum

  1. Large aperture laser beam alignment system based on far field sampling technique

    NASA Astrophysics Data System (ADS)

    Zhang, J. C.; Liu, D. Z.; Ouyang, X. P.; Kang, J.; Xie, X. L.; Zhou, J.; Gong, L.; Zhu, B. Q.

    2016-11-01

    Laser beam alignment is very important for high-power laser facility. Long laser path and large-aperture lens for alignment are generally used, while the proposed alignment system with a wedge by far-field sampling technique reduces both space and cost requirements. General alignment system for large-aperture laser beam is long in distance and large in volum because of taking near-field sampling technique. With the development of laser fusion facilities, the space for alignment system is limited. A new alignment system for large-aperture laser beam is designed to save space and reduce operating costs. The new alignment for large-aperture laser beam with a wedge is based on far-field sampling technique. The wedge is placed behind the spatial filter to reflect some laser beam as signal light for alignment. Therefore, laser beam diameter in alignment system is small, which can save space for the laser facility. Comparing to general alignment system for large-aperture laser beam, large-aperture lenses for near-field and far-field sampling, long distance laser path are unnecessary for proposed alignment system, which saves cost and space greatly. This alignment system for large-aperture laser beam has been demonstrated well on the Muliti-PW Facility which uses the 7th beam of the SG-Ⅱ Facility as pump source. The experimental results indicate that the average near-field alignment error is less than 1% of reference, and the average far-filed alignment error is less than 5% of spatial filter pinhole diameter, which meet the alignment system requirements for laser beam of Multi-PW Facility.

  2. Final Technical Report: Global Field Aligned Mesh and Gyrokinetic Field Solver in a Tokamak Edge Geometry

    SciTech Connect

    Cummings, Julian C.

    2013-05-15

    This project was a collaboration between researchers at the California Institute of Technology and the University of California, Irvine to investigate the utility of a global field-aligned mesh and gyrokinetic field solver for simulations of the tokamak plasma edge region. Mesh generation software from UC Irvine was tested with specific tokamak edge magnetic geometry scenarios and the quality of the meshes and the solutions to the gyrokinetic Poisson equation were evaluated.

  3. Anomalous foreshock field-aligned beams observed by Cluster

    NASA Astrophysics Data System (ADS)

    Meziane, K.; Hamza, A. M.; Wilber, M.; Mazelle, C.; Lee, M. A.

    2011-10-01

    We report occasional observations of two simultaneously distinct ion foreshock components recorded by the Cluster spacecraft upstream of the Earth's bow shock. In most occurrences, the lower-energy population originates as a field-aligned beam (FAB) associated with quasi-perpendicular regions, which loses energy as the IMF rotates into oblique geometries. A second beam, with energies in excess of ~10 keV, appears sometimes in association with the onset of ultra-low frequency (ULF) waves, and sometimes ahead of the appearance of the latter. Measurements from the mass spectrometer indicate that both beams consist of protons. While the lower-speed beam is well-accounted for by a known reflection mechanism, the non-radial IMF orientations as well as other arguments seem to rule out magnetosheath or magnetospheric sources for the higher energy component. The wave characteristics are typical of the oblique foreshock and we have found that they are in cyclotron-resonance with the low speed beam (FAB). These observations constitute a theoretical challenge since conventional mechanisms described in the literature cannot account for the production of beams at two different energies.

  4. Magnetic field-aligned electric field acceleration and the characteristics of the optical aurora

    NASA Technical Reports Server (NTRS)

    Christensen, A. B.; Lyons, L. R.; Hecht, J. H.; Sivjee, G. G.; Meier, R. R.

    1987-01-01

    The long-recognized association of brighter aurora with more deeply penetrating, and hence more energetic, electrons is examined. Using the Knight (1973) relation between the magnetic-field-aligned current density and potential drop (derived from the theory of single-particle motion in the presence of a magnetic-field-aligned electric field), an approximate expression relating the energy flux of the precipitating electrons over discrete aurora and the mean particle energy is derived. This expression is used in conjunction with an auroral optical excitation and emission model to specify the dependence of the red/blue ratio of auroral optical emissions on the brightness of the aurora. It is shown that the quantitative predictions of the discrete auroral theory are in accord with observations of the aurora.

  5. Magnetic field-aligned electric field acceleration and the characteristics of the optical aurora

    NASA Technical Reports Server (NTRS)

    Christensen, A. B.; Lyons, L. R.; Hecht, J. H.; Sivjee, G. G.; Meier, R. R.

    1987-01-01

    The long-recognized association of brighter aurora with more deeply penetrating, and hence more energetic, electrons is examined. Using the Knight (1973) relation between the magnetic-field-aligned current density and potential drop (derived from the theory of single-particle motion in the presence of a magnetic-field-aligned electric field), an approximate expression relating the energy flux of the precipitating electrons over discrete aurora and the mean particle energy is derived. This expression is used in conjunction with an auroral optical excitation and emission model to specify the dependence of the red/blue ratio of auroral optical emissions on the brightness of the aurora. It is shown that the quantitative predictions of the discrete auroral theory are in accord with observations of the aurora.

  6. High Latitude Precipitating Energy Flux and Joule Heating During Geomagnetic Storms Determined from AMPERE Field-aligned Currents

    NASA Astrophysics Data System (ADS)

    Robinson, R. M.; Zanetti, L. J.; Anderson, B. J.; Korth, H.; Samara, M.; Michell, R.; Grubbs, G. A., II; Hampton, D. L.; Dropulic, A.

    2016-12-01

    A high latitude conductivity model based on field-aligned currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) provides the means for complete specification of electric fields and currents at high latitudes. Based on coordinated measurements made by AMPERE and the Poker Flat Incoherent Scatter Radar, the model determines the most likely value of the ionospheric conductance from the direction, magnitude, and magnetic local time of the field-aligned current. A conductance model driven by field-aligned currents ensures spatial and temporal consistency between the calculated electrodynamic parameters. To validate the results, the Pedersen and Hall conductances were used to calculate the energy flux associated with the energetic particle precipitation. When integrated over the entire hemisphere, the total energy flux compares well with the Hemispheric Power Index derived from the OVATION-PRIME model. The conductances were also combined with the field-aligned currents to calculate the self-consistent electric field, which was then used to compute horizontal currents and Joule heating. The magnetic perturbations derived from the currents replicate most of the variations observed in ground-based magnetograms. The model was used to study high latitude particle precipitation, currents, and Joule heating for 24 magnetic storms. In most cases, the total energy input from precipitating particles and Joule heating exhibits a sharply-peaked maximum at the times of local minima in Dst, suggesting a close coupling between the ring current and the high latitude currents driven by the Region 2 field-aligned currents. The rapid increase and decrease of the high latitude energy deposition suggests an explosive transfer of energy from the magnetosphere to the ionosphere just prior to storm recovery.

  7. Magnetic field alignment of randomly oriented, high aspect ratio silicon microwires into vertically oriented arrays.

    PubMed

    Beardslee, Joseph A; Sadtler, Bryce; Lewis, Nathan S

    2012-11-27

    External magnetic fields have been used to vertically align ensembles of silicon microwires coated with ferromagnetic nickel films. X-ray diffraction and image analysis techniques were used to quantify the degree of vertical orientation of the microwires. The degree of vertical alignment and the minimum field strength required for alignment were evaluated as a function of the wire length, coating thickness, magnetic history, and substrate surface properties. Nearly 100% of 100 μm long, 2 μm diameter, Si microwires that had been coated with 300 nm of Ni could be vertically aligned by a 300 G magnetic field. For wires ranging from 40 to 60 μm in length, as the length of the wire increased, a higher degree of alignment was observed at lower field strengths, consistent with an increase in the available magnetic torque. Microwires that had been exposed to a magnetic sweep up to 300 G remained magnetized and, therefore, aligned more readily during subsequent magnetic field alignment sweeps. Alignment of the Ni-coated Si microwires occurred at lower field strengths on hydrophilic Si substrates than on hydrophobic Si substrates. The magnetic field alignment approach provides a pathway for the directed assembly of solution-grown semiconductor wires into vertical arrays, with potential applications in solar cells as well as in other electronic devices that utilize nano- and microscale components as active elements.

  8. Plate Scattering Visualization: Images, Near Fields, Currents, and Far Field Patterns

    NASA Technical Reports Server (NTRS)

    Shaeffer, John; Hom, Kam

    2004-01-01

    This paper presents a case study of a simple yet robust target for demonstration of the EM visualization process. A five lambda square plate exhibits many scattering mechanisms depending on excitation angle and polarization: specular scattering, leading and trailing edge diffraction, traveling wave, and edge wave scattering. Bistatic k space radiation images, currents maps, and near scattered / total fields are examined for each of these scattering mechanisms.

  9. Electric-Field-Induced Alignment of Block Copolymer/Nanoparticle Blends

    SciTech Connect

    Liedel, Clemens; Schindler, Kerstin; Pavan, Mariela J.; Lewin, Christian; Pester, Christian W; Ruppel, Markus A; Urban, Volker S; Shenhar, Roy; Boker, Alexander

    2013-01-01

    External electric fi elds readily align birefringent block-copolymer mesophases. In this study the effect of gold nanoparticles on the electric-fi eld-induced alignment of a lamellae-forming polystyrene- block -poly(2-vinylpyridine) copolymer is assessed. Nanoparticles are homogeneously dispersed in the styrenic phase and promote the quantitative alignment of lamellar domains by substantially lowering the critical field strength above which alignment proceeds. The results suggest that the electric-fi eldassisted alignment of nanostructured block copolymer/nanoparticle composites may offer a simple way to greatly mitigate structural and orientational defects of such fi lms under benign experimental conditions.

  10. Electric field autocorrelation functions for beginning multiple rayleigh scattering.

    PubMed

    Lock, J A

    2001-08-20

    The polarization-resolved electric field autocorrelation function for p-order scattering was derived from the order-of-scattering solution of the exact equations for electromagnetic multiple Rayleigh scattering and was calculated for 2 scattering-angle dependence of the p-order autocorrelation function approximately decoupled from the delay-time dependence for p ? 3. The polarization-channel and the scattering-angle dependence were analytically calculated, and the delay-time dependence was analytically approximated. The resulting analytical model for the polarization-resolved autocorrelation function for beginning multiple Rayleigh scattering was then tested against experimental autocorrelation data. The data were found to be well fitted by the model.

  11. Electric Field Autocorrelation Functions for Beginning Multiple Rayleigh Scattering

    NASA Astrophysics Data System (ADS)

    Lock, James A.

    2001-08-01

    The polarization-resolved electric field autocorrelation function for p -order scattering was derived from the order-of-scattering solution of the exact equations for electromagnetic multiple Rayleigh scattering and was calculated for 2 p 6 for particles undergoing diffusive motion in an idealized sample cell. It was found that the polarization-channel and the scattering-angle dependence of the p -order autocorrelation function approximately decoupled from the delay-time dependence for p ~ 3 . The polarization-channel and the scattering-angle dependence were analytically calculated, and the delay-time dependence was analytically approximated. The resulting analytical model for the polarization-resolved autocorrelation function for beginning multiple Rayleigh scattering was then tested against experimental autocorrelation data. The data were found to be well fitted by the model.

  12. Aligned nanostructured polymers by magnetic-field-directed self-assembly of a polymerizable lyotropic mesophase.

    PubMed

    Tousley, Marissa E; Feng, Xunda; Elimelech, Menachem; Osuji, Chinedum O

    2014-11-26

    Magnetic-field-directed assembly of lyotropic surfactant mesophases provides a scalable approach for the fabrication of aligned nanoporous polymers by templated polymerization. We develop and characterize a lyotropic liquid crystalline system containing hexagonally packed cylindrical micelles of a polymerizable surfactant in a polymerizable solvent. The system exhibits negative magnetic anisotropy, resulting in the degenerate alignment of cylindrical micelles perpendicular to the magnetic field. Sample rotation during field alignment is used to effectively break this degeneracy and enable the production of uniformly well-aligned mesophases. High-fidelity retentions of the hexagonal structure and alignment were successfully achieved in polymer films produced upon UV exposure of the reactive system. The success of this effort provides a route for the fabrication of aligned nanoporous membranes suitable for highly selective separations, sensing, and templated nanomaterial synthesis.

  13. Asymmetric field-aligned currents in the conjugate hemispheres

    NASA Astrophysics Data System (ADS)

    Reistad, J. P.; Ostgaard, N.; Oksavik, K.; Laundal, K. M.

    2012-12-01

    Earlier studies using simultaneous imaging from space of the Aurora Borealis (Northern Hemisphere) and Aurora Australis (Southern Hemisphere) have revealed that the aurora can experience a high degree of asymmetry between the two hemispheres. Using 19 hours of simultaneous global imaging from both hemispheres (IMAGE satellite in north and Polar satellite in south) in conjunction with the entire IMAGE WIC database, we investigate the importance of various mechanisms thought to generate the asymmetries seen in global imaging. In terms of asymmetric or interhemispheric field-aligned currents, three candidate mechanisms have been suggested: 1) Hemispheric differences in solar wind dynamo efficiency mainly controlled by IMF Bx leading to asymmetric region 1 currents; 2) conductivity differences in conjugate areas; and 3) penetration of IMF By into the closed magnetosphere possibly generating a pair of oppositely directed interhemispheric currents. From the 19 hour conjugate dataset we find that the solar wind dynamo is likely to be the most important controlling mechanism for asymmetric bright aurora in the polar part of the nightside oval. Here we present statistical analyses of candidates 1) and 3). Using the entire IMAGE WIC database, a statistical analysis of the auroral brightness distribution along and across the Northern Hemisphere oval is carried out. For each candidate, two extreme cases (+/- IMF Bx for 1) and +/- IMF By for 3)) are compared during times non-favorable for the other two mechanisms. Our results indicate that solar wind dynamo induced currents play an important role for the nightside auroral brightness in an average sense. Also, signatures of interhemispheric currents due to IMF By penetration are seen in our statistics, although this effect is somehow weaker.

  14. Microwave scattering properties of snow fields

    NASA Technical Reports Server (NTRS)

    Angelakos, D. J.

    1977-01-01

    Experimental results were presented showing backscatter dependence on frequency, angle of incidence, snow wetness, and frequency modulation. Theoretical studies were made of the inverse scattering problem yielding some preliminary results concerning the determination of the dielectric constant of the snow layer. The experimental results lead to the following conclusions: (1) snow layering affects backscatter; (2) layer response was significant up to 45 degrees of incidence; (3) wetness modifies snow layer effects; and (4) frequency modulation masks the layer response.

  15. Matched-field evaluation of acoustic scattering from Arctic ice

    SciTech Connect

    Kapoor, T.K.; Schmidt, H.

    1997-08-01

    This paper investigates the three-dimensional acoustic scatter from large-scale features under the Arctic ice cover using field data collected during the CEAREX experiments in April 1989. The analysis involves the identification and isolation of the features under the ice canopy, and the simultaneous evaluation of their spatial scattering characteristics. A two-step matched-field processing (MFP) algorithm is used to solve this complex multiparameter estimation problem. Using one large ({approximately}1200m) and four short ({approximately}300m) vertical line arrays, and a crossed horizontal hydrophone array in a matched-field processing scheme, beamforming under the ice sheet was performed to obtain an approximate map of the rough interface between ice and water. This analysis yields estimates for scattering strengths for frequencies ranging between 25 and 105 Hz. It is shown that scatter from the elastic ice surface is a frequency selective phenomenon. This beamformed map is then used to isolate a single discrete scatterer, and subsequently, its scattering characteristics are evaluated. Simultaneously, an idealized environmental model is developed to compute scatter from a canonical protuberance. Matching the theoretical results from the analytical model with the experimental data, which consists of contributions from multiple scatterers, yields the statistics of the distribution of ice protuberances. {copyright} {ital 1997 Acoustical Society of America.}

  16. Universal dimer–dimer scattering in lattice effective field theory

    DOE PAGES

    Elhatisari, Serdar; Katterjohn, Kris; Lee, Dean; ...

    2017-03-14

    We consider two-component fermions with short-range interactions and large scattering length. This system has universal properties that are realized in several different fields of physics. In the limit of large fermion–fermion scattering length aff and zero-range interaction, all properties of the system scale proportionally with aff. For the case with shallow bound dimers, we calculate the dimer–dimer scattering phase shifts using lattice effective field theory. We extract the universal dimer–dimer scattering length add/aff=0.618(30) and effective range rdd/aff=-0.431(48). This result for the effective range is the first calculation with quantified and controlled systematic errors. We also benchmark our methods by computingmore » the fermion–dimer scattering parameters and testing some predictions of conformal scaling of irrelevant operators near the unitarity limit.« less

  17. ADE-FDTD Scattered-Field Formulation for Dispersive Materials.

    PubMed

    Kong, Soon-Cheol; Simpson, Jamesina J; Backman, Vadim

    2008-01-01

    This Letter presents a scattered-field formulation for modeling dispersive media using the finite-difference time-domain (FDTD) method. Specifically, the auxiliary differential equation method is applied to Drude and Lorentz media for a scattered field FDTD model. The present technique can also be applied in a straightforward manner to Debye media. Excellent agreement is achieved between the FDTD-calculated and exact theoretical results for the reflection coefficient in half-space problems.

  18. Filtered Rayleigh Scattering Measurements in a Buoyant Flow Field

    DTIC Science & Technology

    2008-03-01

    John William Strutt , the third Baron of Rayleigh , or more commonly known as Lord Rayleigh , was the first to offer a correct explanation of the...FILTERED RAYLEIGH SCATTERING MEASUREMENTS IN A BUOYANT FLOW FIELD         THESIS       Steven Michael Meents, Captain, USAF...AFIT/GAE/ENY/08-M22 FILTERED RAYLEIGH SCATTERING MEASUREMENTS IN A BUOYANT FLOW FIELD THESIS Presented to the Faculty Department of Aeronautics

  19. Observations of field-aligned currents, waves, and electric fields at substorm onset

    NASA Technical Reports Server (NTRS)

    Smits, D. P.; Hughes, W. J.; Cattell, C. A.; Russell, C. T.

    1986-01-01

    Substorm onsets, identified Pi 2 pulsations observed on the Air Force Geophysics Laboratory Magnetometer Network, are studied using magnetometer and electric field data from ISEE 1 as well as magnetometer data from the geosynchronous satellites GOES 2 and 3. The mid-latitude magnetometer data provides the means of both timing and locating the substorm onset so that the spacecraft locations with respect to the substorm current systems are known. During two intervals, each containing several onsets or intensifications, ISEE 1 observed field-aligned current signatures beginning simultaneously with the mid-latitude Pi 2 pulsation. Close to the earth broadband bursts of wave noise were observed in the electric field data whenever field-aligned currents were detected. One onset occurred when ISEE 1 and GOES 2 were on the same field line but in opposite hemispheres. During this onset ISEE 1 and GOES 2 saw magnetic signatures which appear to be due to conjugate field-aligned currents flowing out of the western end of the westward auroral electrojets. The ISEE 1 signature is of a line current moving westward past the spacecraft. During the other interval, ISEE 1 was in the near-tail region near the midnight meridian. Plasma data confirms that the plasma sheet thinned and subsequently expanded at onset. Electric field data shows that the plasma moved in the opposite direction to the plasma sheet boundary as the boundary expanded which implies that there must have been an abundant source of hot plasma present. The plasma motion was towards the center of the plasma sheet and earthwards and consisted of a series of pulses rather than a steady flow.

  20. The optical wing aligning device of the Langley Field tunnel

    NASA Technical Reports Server (NTRS)

    Norton, F H; Bacon, D L

    1921-01-01

    Described here is a convenient and accurate method of aligning the wing chord with the airflow. The device was developed to permit rapid and accurate alignment of airfoils and models with the airstream passing through the tunnel. It consists of three main parts: a projector, a reflector, and a target. The arrangement, which is shown in a figure, has proven satisfactory in operation. It is far better than the old method of sighting across a long batten, as the operator of a balance may see the target and correctly judge the accuracy of his alignment. Whereas the old method required two operators and several minutes time to align to within 1/10 degree, this method enables one operator to align a wing to within 1/100 of a degree in a few seconds. This method also has the advantage of being able to measure the angle of the wing while the tunnel is running. Thus, the true angle of incidence is shown.

  1. Relationships between field-aligned currents, electric fields and particle precipitation as observed by dynamics Explorer-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Iyemori, T.; Hoffman, R. A.; Maynard, N. C.; Burch, J. L.; Winningham, J. D.

    1983-01-01

    The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

  2. Relationships between field-aligned currents, electric fields, and particle precipitation as observed by Dynamics Explorer-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Iyemori, T.; Hoffman, R. A.; Maynard, N. C.; Burch, J. L.; Winningham, J. D.

    1984-01-01

    The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

  3. Light fields in complex media: Mesoscopic scattering meets wave control

    NASA Astrophysics Data System (ADS)

    Rotter, Stefan; Gigan, Sylvain

    2017-01-01

    The newly emerging field of wave front shaping in complex media has recently seen enormous progress. The driving force behind these advances has been the experimental accessibility of the information stored in the scattering matrix of a disordered medium, which can nowadays routinely be exploited to focus light as well as to image or to transmit information even across highly turbid scattering samples. An overview of these new techniques, their experimental implementations, and the underlying theoretical concepts following from mesoscopic scattering theory is provided. In particular, the intimate connections between quantum transport phenomena and the scattering of light fields in disordered media, which can both be described by the same theoretical concepts, are highlighted. Particular emphasis is put on how these topics relate to application-oriented research fields such as optical imaging, sensing, and communication.

  4. Potential scattering of electrons in a quantized radiation field

    NASA Astrophysics Data System (ADS)

    Bergou, J.; Ehlotzky, F.

    1986-05-01

    Potential scattering of electrons in a strong laser field is reconsidered. The laser beam is described by a quantized single-mode plane-wave field with a finite number of quanta in the mode. The scattering amplitude is expanded in powers of the potential, and the first two Born terms are considered. It is shown that in the limit of an infinite number of field quanta, the Kroll-Watson approximation is recovered. Additional insight is gained into the validity of this low-frequency theorem. The approach rests on the introduction of electron-dressed quantized-field states. Relations to earlier work are indicated.

  5. Chaotic inflation with kinetic alignment of axion fields

    NASA Astrophysics Data System (ADS)

    Bachlechner, Thomas C.; Dias, Mafalda; Frazer, Jonathan; McAllister, Liam

    2015-01-01

    N-flation is a radiatively stable scenario for chaotic inflation in which the displacements of N ≫1 axions with decay constants f1≤…≤fNalignment, allowing for effective displacements as large as √{N }fN≥fPy, even if f1,…,fN -1 are arbitrarily small. At the level of kinematics, the necessary alignment occurs with very high probability, because of eigenvector delocalization. We present conditions under which inflation can take place along an aligned direction. Our construction sharply reduces the challenge of realizing N-flation in string theory.

  6. Cutoff frequencies and excitation threshold of artificial E region field aligned irregularities

    NASA Astrophysics Data System (ADS)

    Hysell, D. L.; Nossa, E.

    2009-12-01

    Artificial E region field aligned irregularities generated by HAARP have been observed using a coherent scatter radar imager in Homer, Alaska, in August of 2009. As in previous experiments, irregularities could be generated using O-mode pump frequencies both above and below the second electron gyroharmonic frequency, with no obvious differences in the irregularity properties in either case. However, echo suppression was observed when the pump frequency was swept across the second electron gyroharmonic frequency in small steps. This finding is consistent with the theory of thermal oscillating two-stream instability and the role of upper-hybrid waves, which are damped near gyroharmonic frequencies. The small frequency steps permit us to identify the width of the suppressed frequency band. Suppression was not complete, most likely because the double resonance matching condition cannot be met everywhere in the modified ionospheric volume. In separate experiments, the pump wave power was also varied in gradual, quadratic steps in order to identify the threshold in situ electric field amplitude for irregularity generation. The threshold field found this way, which was of the order of 100 mV/m, was smaller than previous experimental estimates and also approximately consistent with theory, although a great deal of uncertainty remains in both the contemporary theoretical formulation of the problem and the experimental conditions in the ionosphere.

  7. Excitation threshold and gyroharmonic suppression of artificial E region field-aligned plasma density irregularities

    NASA Astrophysics Data System (ADS)

    Hysell, D. L.; Nossa, E.; McCarrick, M.

    2010-12-01

    Ionospheric modification experiments have been carried out using the HAARP facility along with a 30 MHz coherent scatter radar imager in Alaska to examine properties of artificial E region field-aligned plasma density irregularities (FAIs). In one set of experiments, the RF emission power was varied gradually in order to determine the threshold electric field for irregularity generation. A threshold O mode peak electric field amplitude of 170-195 mV/m at an altitude of 99 km and a heating frequency of 2.7 MHz was identified based on the full-wave formalism of Thidé and Lundborg (1986). In another, the pump frequency was varied gradually to investigate the suppression of the FAIs at frequencies near the second electron gyroharmonic frequency (2Ωe). Coherent echoes were found to be suppressed for pump frequencies in an asymmetric band 40-50 kHz wide around 2Ωe but only for irregularities driven marginally above threshold. Theoretical context for these results is provided.

  8. Magnetic and electric field alignments of cellulose chains for electro-active paper actuator

    NASA Astrophysics Data System (ADS)

    Yun, Sungryul; Chen, Yi; Lee, Sang Woo; Kim, Jaehwan; Kim, Heung Soo

    2008-03-01

    To improve the piezoelectricity of cellulose electro-active paper (EAPap), electrical field and magnetic field alignments were investigated. EAPap is made with cellulose by dissolving cotton pulp and regenerating cellulose with aligned cellulose fibers. EAPap made with cellulose has piezoelectric property due to its structural crystallinity. Noncentro-symmetric crystal structure of EAPap, which is mostly cellulose II, can exhibit piezoelectricity. However, EAPap has ordered crystal parts as well as disordered parts of cellulose. Thus, well alignment of cellulose chains in EAPap is important to improve its piezoelectricity. In this paper, uniaxial alignments of cellulose chains were investigated by applying electric field and magnetic field. As exposing different fields to EAPap samples, the changed characteristics were analyzed by X-Ray diffractometer (XRD) and Scanning electron microscopy (SEM). Finally, the piezoelectricity of EAPap samples was evaluated by comparing their piezoelectric charge constant [d 31]. As increasing applied electric field up to 40V/mm, d 31 value was gradually improved due to increased cellulose crystallinity as well as alignment of cellulose chains. Also the alignment of cellulose chains was improved with increasing the exposing time to magnetic field (5.3T) and well alignment was achieved by exposing EAPap sample on the magnetic field for 180min.

  9. Electromagnetic Scattered Field Evaluation and Data Compression Using Imaging Techniques

    NASA Technical Reports Server (NTRS)

    Gupta, I. J.; Burnside, W. D.

    1996-01-01

    This is the final report on Project #727625 between The Ohio State University and NASA, Lewis Research Center, Cleveland, Ohio. Under this project, a data compression technique for scattered field data of electrically large targets is developed. The technique was applied to the scattered fields of two targets of interest. The backscattered fields of the scale models of these targets were measured in a ra compact range. For one of the targets, the backscattered fields were also calculated using XPATCH computer code. Using the technique all scattered field data sets were compressed successfully. A compression ratio of the order 40 was achieved. In this report, the technique is described briefly and some sample results are included.

  10. Comparative study of cross-field and field-aligned electron beams in active experiments. [in upper atmosphere

    NASA Technical Reports Server (NTRS)

    Winglee, R. M.; Pritchett, P. L.

    1988-01-01

    Beam-plasma interactions associated with the cross-field and field-aligned injection of electron beams from spacecraft were investigated using a two-dimensional (three velocity component) electrostatic particle simulations. It is shown that the beam properties and plasma response can be characterized well by the ratio between the stagnation time and the plasma response time, which depends on the ratio of the ambient plasma density to the beam density, the beam width, the beam energy, and the spacecraft length. It was found that the beams injected across the field lines tend to lose their coherence after about one or two gyrations due to space-charge oscillations induced by the beam, irrespective of the spacecraft charging. These oscillations scatter the beam electrons into a hollow cylinder of a radius equal to a beam electron gyroradius and thickness of the order of two beam Debye lengths. Parallel injected beams are subjected to similar oscillations, which cause the beam to expand to fill a solid cylinder of a comparable thickness.

  11. Field-aligned current and the auroral electrojets in the post-noon quadrant

    NASA Astrophysics Data System (ADS)

    Rostoker, G.; Mareschal, M.

    1982-11-01

    It is shown that in the post-noon quadrant, the combination of field-aligned currents associated with the eastward auroral electrojet and polar cap currents produces a magnetic field perturbation pattern on the ground and at TRIAD altitude (800 km) in good agreement with observations. This model permits downward net field-aligned current flow across the post-noon sector auroral oval while at the same time replicating the observation of a sharp level shift in the east-west component of the magnetic perturbation field at 800-km altitude attributed, until now, to net upward field-aligned current. These results reconcile the contentions of Hughes and Rostoker (1977, 1979) that there is net downward field-aligned current across the post-noon auroral oval and of Sugiura and Potemra (1976) that the net current flow in the post-noon quadrant is upward.

  12. Alignments of Dark Matter Halos with Large-scale Tidal Fields: Mass and Redshift Dependence

    NASA Astrophysics Data System (ADS)

    Chen, Sijie; Wang, Huiyuan; Mo, H. J.; Shi, Jingjing

    2016-07-01

    Large-scale tidal fields estimated directly from the distribution of dark matter halos are used to investigate how halo shapes and spin vectors are aligned with the cosmic web. The major, intermediate, and minor axes of halos are aligned with the corresponding tidal axes, and halo spin axes tend to be parallel with the intermediate axes and perpendicular to the major axes of the tidal field. The strengths of these alignments generally increase with halo mass and redshift, but the dependence is only on the peak height, ν \\equiv {δ }{{c}}/σ ({M}{{h}},z). The scaling relations of the alignment strengths with the value of ν indicate that the alignment strengths remain roughly constant when the structures within which the halos reside are still in a quasi-linear regime, but decreases as nonlinear evolution becomes more important. We also calculate the alignments in projection so that our results can be compared directly with observations. Finally, we investigate the alignments of tidal tensors on large scales, and use the results to understand alignments of halo pairs separated at various distances. Our results suggest that the coherent structure of the tidal field is the underlying reason for the alignments of halos and galaxies seen in numerical simulations and in observations.

  13. Field line twist and field-aligned currents in an axially symmetric equilibrium magnetosphere. [of Uranus

    NASA Technical Reports Server (NTRS)

    Voigt, Gerd-Hannes

    1986-01-01

    Field-aligned Birkeland currents and the angle of the magnetic line twist were calculated for an axially symmetric pole-on magnetosphere (assumed to be in MHD equilibrium). The angle of the field line twist was shown to have a strong radial dependence on the axisymmetric magnetotail as well as on the ionospheric conductivity and the amount of thermal plasma contained in closed magnetotail flux tubes. The field line twist results from the planetary rotation, which leads to the development of a toroidal magnetic B-sub-phi component and to differentially rotating magnetic field lines. It was shown that the time development of the toroidal magnetic B-sub-phi component and the rotation frequency are related through an induction equation.

  14. Dependence of field-aligned electron precipitation on season, altitude and pitch angle

    NASA Technical Reports Server (NTRS)

    Berko, F. W.; Hoffman, R. A.

    1973-01-01

    The occurrence of field-aligned 2.3 keV electron precipitation was examined by using data from more than 7500 orbits of the polar-orbiting satellite, OGO-4. The frequency of occurrence of field aligned precipitation was highest at actual pitch angles between 7 and 10 deg, being highest in the winter months, at highest satellite altitudes. Acceleration by a localized parallel electric field established by electrostatic charge layers is proposed to explain particle observations.

  15. Influence of the electron source distribution on field-aligned currents

    NASA Astrophysics Data System (ADS)

    Bruening, K.; Goertz, C. K.

    1985-01-01

    The field-aligned current density above a discrete auroral arc has been deduced from the downward electron flux and magnetic field measurements onboard the rocket Porcupine flight 4. Both measurements show that the field-aligned current density is, in spite of decreasing peak energies towards the edge of the arc, about 4 times higher there than in the center of the arc. This can be explained by using the single particle description for an anisotropic electron source distribution.

  16. Plasmonic and photonic scattering and near fields of nanoparticles.

    PubMed

    Schmid, Martina; Andrae, Patrick; Manley, Phillip

    2014-01-29

    We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell's equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results.

  17. Plasmonic and photonic scattering and near fields of nanoparticles

    PubMed Central

    2014-01-01

    We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell’s equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results. PMID:24475923

  18. Plasmonic and photonic scattering and near fields of nanoparticles

    NASA Astrophysics Data System (ADS)

    Schmid, Martina; Andrae, Patrick; Manley, Phillip

    2014-01-01

    We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell's equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results.

  19. Electric fields and neutral winds from monostatic incoherent scatter measurements by means of stochastic inversion

    NASA Astrophysics Data System (ADS)

    Nygrén, T.; Aikio, A. T.; Kuula, R.; Voiculescu, M.

    2011-05-01

    A new method utilizing stochastic inversion in determining the electric field and neutral wind from monostatic beam swing incoherent scatter measurements is described. The method consists of two stages. In the first stage, beam-aligned ion velocities from a chosen F region height interval and a set of subsequent beam directions are taken as measurements. The unknowns are the two electric field components and the field-aligned ion velocity profile. The solution gives the most probable values of the unknowns with error estimates. In the second stage, the measurements consist of beam-aligned ion velocities from the E region, and the electric fields given by the first inversion problem are also used as measurements. The number of applied beam directions may be greater than in the first inversion problem. This is a feasible approach since the neutral wind usually changes more slowly than the electric field. The solution of the second inversion problem gives the most probable values of the three neutral wind components. Results of the method are shown for 11 September 2005, when the European Incoherent Scatter (EISCAT) UHF radar was running in the CP2 experiment mode, which is a four-position 6 min monostatic cycle. In addition, from each beam direction a tristatic measurement at one F region range gate was made using two additional receivers. That allowed comparison between the monostatic and tristatic electric field results, which were in excellent agreement. The calculated neutral wind components were in good accordance with previous measurements during disturbed conditions from the same site.

  20. The aligned magnetic field with convective boundary conditions over a stretching sheet in a viscous fluid

    NASA Astrophysics Data System (ADS)

    Arifin, N. S.; Zokri, S. M.; Aziz, L. A.; Kasim, A. R. M.; Salleh, M. Z.; Mohammad, N. F.

    2017-05-01

    In this study, the aligned magnetic field on the flow of a viscous fluid over a stretching sheet with convective boundary conditions is analyzed. The governing nonlinear boundary layer equations is transformed into ordinary differential equations and then solved numerically by Keller-box method. The numerical solutions with different values of aligned angle, Prandtl number and magnetic field are presented graphically and tabular form. It is found that the velocity profile, skin friction coefficient and Nusselt number decreases with the increasing of aligned angle and magnetic field. Similarly, increment in Prandtl number decreases the temperature profile.

  1. Adiabatic Field-Free Alignment of Asymmetric Top Molecules with an Optical Centrifuge

    NASA Astrophysics Data System (ADS)

    Korobenko, A.; Milner, V.

    2016-05-01

    We use an optical centrifuge to align asymmetric top SO2 molecules by adiabatically spinning their most polarizable O-O axis. The effective centrifugal potential in the rotating frame confines the sulfur atoms to the plane of the laser-induced rotation, leading to the planar molecular alignment that persists after the molecules are released from the centrifuge. The periodic appearance of the full three-dimensional alignment, typically observed only with linear and symmetric top molecules, is also detected. Together with strong in-plane centrifugal forces, which bend the molecules by up to 10 deg, permanent field-free alignment offers new ways of controlling molecules with laser light.

  2. Adiabatic field-free alignment of asymmetric top molecules with an optical centrifuge

    NASA Astrophysics Data System (ADS)

    Korobenko, Aleksey; Milner, Valery

    2016-05-01

    We use an optical centrifuge to align asymmetric top SO2 molecules by adiabatically spinning their most polarizable O-O axis. The effective centrifugal potential in the rotating frame confines sulfur atoms to the plane of the laser-induced rotation, leading to the planar molecular alignment which persists after the molecules are released from the centrifuge. Periodic appearance of the full three-dimensional alignment, typically observed only with linear and symmetric top molecules, is also detected. Together with strong in-plane centrifugal forces, which bend the molecules by up to 10 degrees, permanent field-free alignment offers new ways of controlling molecules with laser light.

  3. Localized field-aligned currents in the polar cap associated with airglow patches

    NASA Astrophysics Data System (ADS)

    Zou, Ying; Nishimura, Yukitoshi; Burchill, Johnathan K.; Knudsen, David J.; Lyons, Larry R.; Shiokawa, Kazuo; Buchert, Stephan; Chen, Steve; Nicolls, Michael J.; Ruohoniemi, J. Michael; McWilliams, Kathryn A.; Nishitani, Nozomu

    2016-10-01

    Airglow patches have been recently associated with channels of enhanced antisunward ionospheric flows propagating across the polar cap from the dayside to nightside auroral ovals. However, how these flows maintain their localized nature without diffusing away remains unsolved. We examine whether patches and collocated flows are associated with localized field-aligned currents (FACs) in the polar cap by using coordinated observations of the Swarm spacecraft, a polar cap all-sky imager, and Super Dual Auroral Radar Network (SuperDARN) radars. We commonly (66% of cases) identify substantial FAC enhancements around patches, particularly near the patches' leading edge and center, in contrast to what is seen in the otherwise quiet polar cap. These FACs have densities of 0.1-0.2 μA/m-2 and have a distribution of width peaking at 75 km. They can be approximated as infinite current sheets that are orientated roughly parallel to patches. They usually exhibit a Region 1 sense, i.e., a downward FAC lying eastward of an upward FAC. With the addition of Resolute Bay Incoherent Scatter radar data, we find that the FACs can close through Pedersen currents in the ionosphere, consistent with the locally enhanced dawn-dusk electric field across the patch. Our results suggest that ionospheric polar cap flow channels are imposed by structures in the magnetospheric lobe via FACs, and thus manifest mesoscale magnetosphere-ionosphere coupling embedded in large-scale convection.

  4. Origins of enhanced field-aligned current at the edge of an auroral arc

    NASA Astrophysics Data System (ADS)

    Greenspan, M. E.

    1989-09-01

    Consideration is given to observations showing that the upward field-aligned currents associated with auroral arcs are larger at their edges than within the arcs, focusing on the observations made with the Porcupine F4 rocket (Bruning and Geortz, 1985). It is found that an increase in the altitude of the top of the parallel electric field region does not sufficiently explain the increase in the upward field-aligned current at the edge of the arc crossed by the Porcupine F4. Other explanations are discussed, including the adiabatic acceleration of magnetospheric electrons through a field-aligned electrostatic potential. It is suggested that an increase in the density and/or a decrease in the perpendicular temperature of the magnetospheric electron population at the edge of the arc may explain the observed increase in upward field-aligned current.

  5. Field-aligned currents and large-scale magnetospheric electric fields

    NASA Technical Reports Server (NTRS)

    Dangelo, N.

    1979-01-01

    The existence of field-aligned currents (FAC) at northern and southern high latitudes was confirmed by a number of observations, most clearly by experiments on the TRIAD and ISIS 2 satellites. The high-latitude FAC system is used to relate what is presently known about the large-scale pattern of high-latitude ionospheric electric fields and their relation to solar wind parameters. Recently a simplified model was presented for polar cap electric fields. The model is of considerable help in visualizing the large-scale features of FAC systems. A summary of the FAC observations is given. The simplified model is used to visualize how the FAC systems are driven by their generators.

  6. Investigation of the Influence of Magnetospheric Sources of Field-Aligned Currents on the Equatorial Electric Fields

    NASA Astrophysics Data System (ADS)

    Beloushko, Konstantin; Knyazeva, Mariya

    The urgency of studying electrodynamic processes related to the influence of spatial and temporal heterogeneities of the electromagnetic field in the Earth's upper atmosphere to the functioning of modern technological systems , satellite navigation systems , radio propagation Fundamentally new is the use of various third-party electrodynamic models in the total open loop model of the atmosphere based on the Upper Atmosphere Model (UAM) [1,2]. Performing calculations on model UAM using different spatial and temporal distributions of field-aligned currents and brands Lukianova and Papitashvili. A comparison of model results with data Jicamarca Incoherent Scatter Radar (Peru). References begin{enumerate} Namgaladze A.A., Korenkov Yu.N., Klimenko V.V., Karpov I.V., Bessarab F.S., Surotkin V.A., Gluschenko T.A., Naumova N.M. Global model of the thermosphere-ionosphere-protonosphere system. Pure and Applied Geophysics. № 2/3, 127, 219-254, 1988. Namgaladze A.A., Martynenko O.V., Namgaladze A.N. Global model of the upper atmosphere with variable latitudinal steps of numerical integration, IUGG XXI General Assembly, Boulder, 1995, Abstracts, GAB41F-6, B150, 1995, and (in Russian) Geamagn. Aeron., 36, 89-95, 1996a.

  7. Polar cap field-aligned currents for southward interplanetary magnetic fields

    SciTech Connect

    Xu, D.; Kivelson, M.G.

    1994-04-01

    It has been common to suppose that polar region field-aligned currents for southward interplanetary magnetic fields (IMF) consist of two parts: region 1 and region 2 currents. It is often suggested that both of these current systems flow on closed field lines. In this pilot study the limited data available from the ISIS 2 satellite are used to examine region 1 currents with the objective of establishing whether or not they can exist partially on open field lines (i.e., inside the polar caps) for southward IMF. Magnetic field perturbations were used to identify the field-aligned currents (FACs). The absence of {ge}keV electrons but the presence of {le}200 eV electrons in the polar cap or background polar rain is considered as the signature of open field lines. On some passes, region 1 sense FACs appear to be composed of two parts. The poleward part of the current signature is accompanied by electron fluxes at energies {le}200 eV or occasionally by fluxes at background levels while the equatorward part of the interval is accompanied by electron fluxes at energies both {le}200 eV and {ge}keV. On other passes, region 1 sense currents are accompanied by both {le}200 eV and {ge}keV electron fluxes during the entire pass. The authors propose that region 1 sense FACs flow on both closed and open field lines for the first situation and on closed field lines for the second situation. In seeking to understand why region 1 currents sometimes flow only on closed field lines and sometimes flow on open as well as closed field lines, the authors suggest a control by the IMF B{sub y}. The IMF B{sub y} may also shift the region 1 currents on open field lines to one side (dawn or dusk) of the polar cap like the convection cells. Such a shift provides a consistent model of the data taken on the dayside and the authors discuss why night side observations may be different. 47 refs., 6 figs., 1 tab.

  8. Field-aligned current associated with a distorted two-cell convection pattern during northward interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Zhu, L.; Schunk, R. W.; Sojka, J. J.

    1991-01-01

    The influence of the ionospheric conductance on the field-aligned current associated with a distorted two-cell convection pattern during northward IMF was investigated using the Heppner-Maynard (1987) convection model and the Utah State University conductivity model described by Rasmussen and Schunk (1987). Results show that the variation of the ionospheric conductivity distribution can significantly affect the features of the field-aligned current for northward IMF, where matching or mismatching between the conductance gradient and the convection electric field plays a key role. It was found that the increase of the field-aligned current in the polar cap observed during summer is mainly due to the increasing contribution from the Pedersen current, and that the increase of the field-aligned current in both the oval region and the evening-midnight sector during the active aurora period is mainly due to the increasing contribution from the Hall current.

  9. Mott scattering in an elliptically polarized laser field

    SciTech Connect

    Attaourti, Y.; Manaut, B.; Taj, S.

    2004-08-01

    We study Mott scattering in the presence of a strong elliptically polarized field. Using the first Born approximation and the Dirac-Volkov states for the electron, we obtain an analytic formula for the unpolarized differential cross section. This generalizes the results found for the linearly polarized field by Li et al. [ 67, 063409 (2003)] and for the circularly polarized field by Attaourti and Manaut [ 68, 067401 (2003)].

  10. Fabrication of aligned nanofibers by electric-field-controlled electrospinning: insulating-block method

    NASA Astrophysics Data System (ADS)

    Hwang, Wontae; Pang, Changhyun; Chae, Heeyeop

    2016-10-01

    Aligned nanofiber arrays and mats were fabricated with an electrospinning process by manipulating the electric field. The electric field was modified by insulating blocks (IBs) that were installed between the nozzle and the substrate as guiding elements to control the trajectory of the electrospinning jet flow. Simulation results showed that the electric field was deformed near the IBs, resulting in confinement of the electrospinning jet between the blocks. The balance of the electric field in the vertical direction and the repulsive force by space charges in the confined electrified jet stream was attributed to the aligned motion of the jet. Aligned arrays of 200 nm thick polyethylene oxide nanofibers were obtained, exhibiting wave-shaped and cross patterns as well as rectilinear patterns. In addition, 40 μm thick quasi-aligned carbon-nanofiber mats with anisotropic electrical property were also attained by this method.

  11. Wide-Viewing-Angle Hybrid Aligned Nematic Liquid Crystal Cell Controlled by Complex Electric Field

    NASA Astrophysics Data System (ADS)

    Hong, Seung Ho; Kim, Hyang Yul; Kim, Jae-Hyung; Nam, Sang-Hee; Lee, Myong-Hoon; Lee, Seung Hee

    2002-07-01

    We have developed a hybrid aligned nematic liquid crystal (LC) cell driven by a complex electric field. In the device, the pixel electrode exists on the bottom substrate and the counter electrodes exist on the top and bottom substrates such that with a bias voltage both vertical and horizontal fields are generated. The LC molecules are hybrid aligned with homogeneous alignment on the bottom substrate where the alignment direction is coincident with one of the transmission axes of the crossed polarizers. Therefore, the cell appears to be black in the absence of an electric field. When a voltage is applied to obtain a white state, both vertical and horizontal fields enable the LC molecules to rotate with lowered tilt angles than those in the dark state. The device shows a much wider viewing angle than that of the twisted nematic mode, high light efficiency and low driving voltage in electro-optic characteristics.

  12. Fabrication of aligned nanofibers by electric-field-controlled electrospinning: insulating-block method.

    PubMed

    Hwang, Wontae; Pang, Changhyun; Chae, Heeyeop

    2016-10-28

    Aligned nanofiber arrays and mats were fabricated with an electrospinning process by manipulating the electric field. The electric field was modified by insulating blocks (IBs) that were installed between the nozzle and the substrate as guiding elements to control the trajectory of the electrospinning jet flow. Simulation results showed that the electric field was deformed near the IBs, resulting in confinement of the electrospinning jet between the blocks. The balance of the electric field in the vertical direction and the repulsive force by space charges in the confined electrified jet stream was attributed to the aligned motion of the jet. Aligned arrays of 200 nm thick polyethylene oxide nanofibers were obtained, exhibiting wave-shaped and cross patterns as well as rectilinear patterns. In addition, 40 μm thick quasi-aligned carbon-nanofiber mats with anisotropic electrical property were also attained by this method.

  13. Mott scattering of polarized electrons in a strong laser field

    SciTech Connect

    Manaut, B.; Taj, S.; Attaourti, Y.

    2005-04-01

    We present analytical and numerical results of the relativistic calculation of the transition matrix element S{sub fi} and differential cross sections for Mott scattering of initially polarized Dirac particles (electrons) in the presence of a strong laser field with linear polarization. We use exact Dirac-Volkov wave functions to describe the dressed electrons and the collision process is treated in the first Born approximation. The influence of the laser field on the degree of polarization of the scattered electron is reported.

  14. Rainbow scattering in the gravitational field of a compact object

    NASA Astrophysics Data System (ADS)

    Dolan, Sam R.; Stratton, Tom

    2017-06-01

    We study the elastic scattering of a planar wave in the curved spacetime of a compact object such as a neutron star, via a heuristic model: a scalar field impinging upon a spherically symmetric uniform density star of radius R and mass M . For R scattering (orbiting) and a backward glory; whereas for R >rc, there instead arises a stationary point in the deflection function which creates a caustic and rainbow scattering. As in nuclear rainbow scattering, there is an Airy-type oscillation on a Rutherford-like cross section, followed by a shadow zone. We show that, for R ˜3.5 G M /c2, the rainbow angle lies close to 180°, and thus there arises enhanced backscattering and glory. We explore possible implications for gravitational wave astronomy and dark matter models.

  15. The acoustic field scattered from some approximate pressure release materials

    NASA Astrophysics Data System (ADS)

    Caille, Gary W.

    1988-03-01

    The objective was to determine if a pressure release boundary condition can be achieved by coating an elastic shell with a visco-elastic material. One necessary condition is that the coating must acoustically decouple the shell from the scattering problem. Two closed cell rubbers and two cork-rubber composites (nitrile and neoprene based) were investigated. The dynamic viscoelastic constants of the materials were determined by wave propagation techniques. The far field scattering form functions for an infinite cylindrical shell coated with the viscoelastic material were calculated using the complete elastic equations of motion. The form functions were experimentally measured for the different materials at different thicknesses as verification of the theory. A thick finite right cylindrical shell was coated with .25 inches of closed cell neoprene and the normalized scattered pressure measured. The pressure release normalized scattered pressure was determined for the end on incident plane wave case using the acoustic radiation Simplified Helmholtz Integral Program (SHIP).

  16. Analytic expression for in-field scattered light distribution

    NASA Astrophysics Data System (ADS)

    Peterson, Gary L.

    2004-01-01

    Light that is scattered from lenses and mirrors in an optical system produces a halo of stray light around bright objects within the field of view. The angular distribution of scattered light from any one component is usually described by the Harvey model. This paper presents analytic expressions for the scattered irradiance at a focal plane from optical components that scatter light in accordance with the Harvey model. It is found that the irradiance is independent of the location of an optical element within the system, provided the element is not located at or near an intermediate image plane. It is also found that the irradiance has little or no dependence on the size of the element.

  17. Magnetic field contribution to the last electron-photon scattering

    NASA Astrophysics Data System (ADS)

    Giovannini, Massimo

    2010-11-01

    When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron-photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tensor modes of the geometry. The propagation of relic vectors and relic gravitons is discussed for a varying magnetic field orientation and for different photon directions. The source terms of the transport equations in the presence of the relativistic fluctuations of the geometry are also explicitly averaged over the magnetic field orientations and the problem of a consistent account of the small-scale and large-scale magnetic field is briefly outlined.

  18. Alignment of the hydrogen molecule under intense laser fields

    NASA Astrophysics Data System (ADS)

    Lopez, Gary V.; Fournier, Martin; Jankunas, Justin; Spiliotis, Alexandros K.; Rakitzis, T. Peter; Chandler, David W.

    2017-07-01

    Alignment of the electronically excited E,F state of the H2 molecule is studied using the velocity mapping imaging technique. Photofragment images of H+ due to the dissociation mechanism that follows the 2-photon excitation into the (E,F; ν = 0, J = 0) electronic state show a strong dependence on laser intensity, which is attributed to the high polarizability anisotropy of the H2 (E,F) state. We observe a marked structure in the angular distribution, which we explain as the interference between the prepared J = 0 and Stark-mixed J = 2 rovibrational states of H2, as the laser intensity increases. Quantification of these effects allows us to extract the polarizability anisotropy of the H2 (E,F J = 0) state yielding a value of 312 ± 82 a.u. (46 Å3). By comparison, CS2 has 10 Å3, I2 has 7 Å3, and hydrochlorothiazide (C7H8ClN3O4S2) has about 25 Å3 meaning that we have created the most easily aligned molecule ever measured, by creating a mixed superposition state that is highly anisotropic in its polarizability.

  19. Effects of magnetic field on electron-electron intersubband scattering rates in quantum wells.

    NASA Astrophysics Data System (ADS)

    Kempa, K.; Zhou, Y.; Engelbrecht, J.; Bakshi, P.

    2001-03-01

    Electron-electron scattering dominates the physics of carrier relaxation in quantum nano-structures used as active regions of THz radiation sources. This is the limiting mechanism in achieving population inversion, and reducing its deleterious effects could clear the way to a THz laser. We study here the inter-subband relaxation processes due to the electron-electron scattering in quantum well structures, in a magnetic field. We obtain the scattering rate from the imaginary part of the electron self-energy in the random phase approximation, extending our earlier studies [1] to nonzero magnetic fields. We find that the scattering rate is peaked at two possible sets of arrangements of the Landau levels (LL) of the two subbands of interest. The first set occurs when the LL of both subbands align, and the other when the LL misalign, so that the LL of one subband lie exactly in the middle between those of the other subband. Experiments on various quantum cascade structures show that the misaligned set of transitions is completely suppressed. >From our calculations this implies that there is no population inversion in those structures. Work supported by US Army Research Office. [1] K. Kempa, P. Bakshi, J. R. Engelbrecht, and Y. Zhou, Phys. Rev. B61, 11083 (2000).

  20. Studies of Westward Electrojets and Field-Aligned Currents in the Magnetotail during Substorms: Implications for Magnetic Field Models

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Our studies elucidated the relationship between the auroral arcs and magnetotail phenomena. One paper examined particle energization in the source region of the field-aligned currents that intensify at substorm onset when the arc brightens to form the westward electrojet. A second paper examined the relationship between the precipitating particles in the arcs, the location of the westward electrojet, and magnetospheric source regions. Two earlier papers also investigated the roles that field aligned currents and particle acceleration have during substorms.

  1. Transient scattering from dielectric cylinders - E-field, H-field, and combined field solutions

    NASA Technical Reports Server (NTRS)

    Vechinski, Douglas A.; Rao, Sadasiva M.

    1992-01-01

    In this work, the problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the equivalence principle. Three different formulations, namely, the electric field integral equation formulation, the magnetic field integral equation formulation, and the combined field integral equation formulation are considered. Numerical results are presented for two cross sections, namely, a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution.

  2. X-mode suppression of artificial E region field-aligned plasma density irregularities

    NASA Astrophysics Data System (ADS)

    Hysell, D. L.; Nossa, E.; McCarrick, M.

    2011-04-01

    Ionospheric modification experiments have been performed at the High frequency Active Auroral Research Program involving the creation and suppression of artificial field-aligned density irregularities (AFAIs) using O-mode and X-mode continuous wave emissions, respectively. The emission frequencies were offset so that the O-mode upper hybrid interaction height nearly matched the X-mode reflection height in the ionospheric E region. AFAIs created by O-mode heating were observed using a 30 MHz coherent scatter radar imager. Simultaneous X-mode heating was found to suppress the AFAI intensity and increase the threshold power for excitation by approximately a factor of 5 in our experiments. The effects are attributed in part to the broadening of the upper hybrid interaction region and in part to increased O-mode absorption, which reduces the amplitude of the standing wave pattern in that region. Preliminary estimates based on local calculations suggest that the electron temperature in the E region was increased by a factor of about 1.6 in these experiments.

  3. Feasibility study of cellulose nanofiber alignment by high DC magnetic field

    NASA Astrophysics Data System (ADS)

    Kim, Hyun Chan; Kang, Jinmo; Park, Jung Ho; Akther, Asma; Kim, Jaehwan

    2017-04-01

    Cellulose nanofiber (CNF) has taken center stage as a future material with high specific strength, specific modulus and environmentally friendly behavior. However, natural CNFs are so randomly oriented that once CNFs are used in composites, their mechanical properties are not the same as expected from the CNFs. Thus, CNF alignment is important in fabricating composites and fibers. Interestingly, CNFs have negative diamagnetic anisotropy. In the presence of high magnetic field, the fiber axis of CNF can be aligned perpendicular to the applied field. This paper reports a preliminary study of CNF alignment by high dc magnetic field. The CNF emulsion is prepared by aqueous counter collision method and centrifugation. The CNF emulsion is placed in the high dc magnet and cured for a certain time. The alignment of CNF is investigated by scanning electron microscopy, mechanical tensile test.

  4. Dust Particle Alignment in the Solar Magnetic Field: a Possible Cause of the Cometary Circular Polarization

    NASA Astrophysics Data System (ADS)

    Kolokolova, L.; Koenders, C.; Rosenbush, V.; Kiselev, N.; Ivanova, A.; Afanasiev, V.

    2015-12-01

    Circular polarization (CP) produced by scattering of sunlight on cometary dust has been observed in 11 comets, and showed the values from 0.01% to 0.8%. CP of both signs was observed, although negative (left-handed) CP dominates. Recent observations of several comets using SCORPIO-2 focal reducer at the 6-m BTA telescope of the Special Astrophysical Observatory (Russia) allowed producing maps of CP in the comet continuum filter at 684 nm and red wide-band filter. A gradual increase of the CP with the nucleocentric distance was usually observed. The most plausible reason why the light scattered by cometary dust becomes circularly polarized is alignment of the dust particles in the solar magnetic field. However, in-situ data for comet Halley, indicated that the solar magnetic field could not penetrate deep into the coma, limited by the diamagnetic cavity, and, thus, could not be responsible for the CP observed closer than ~4000 km from the nucleus. Advanced theoretical studies of interaction of the solar magnetic field with cometary ions led to reconsidering the diamagnetic cavity boundary - it is defined by the cometary ionopause, at which a balance is achieved between the magnetic pressure in the magnetic pile up region and the neutral friction force. The nucleocentric distance where this balance is achieved depends on the comet characteristics, increasing with the increase of the gas production rate, and local solar wind conditions, approximatively given by the comet location, specifically, its heliocentric distance. The size of diamagnetic cavity was calculated for the conditions of our CP observations. We found that it could be as small as dozens (comets 73P, 8P, 290P) or hundreds (comets Q4 NEAT, K1 PanSTARRS, Tago-Sato-Kosaka) kilometers. Thus, non-zero CP close to the nucleus can be easily explained by the interaction of the dust particles with the solar magnetic field. This mechanism also explains the observed increase in CP with the distance from the

  5. Momentum transfer using chirped standing-wave fields: Bragg scattering

    SciTech Connect

    Malinovsky, Vladimir S.; Berman, Paul R.

    2003-08-01

    We consider momentum transfer using frequency-chirped standing-wave fields. Atom-beam splitter and mirror schemes based on Bragg scattering are presented. It is shown that a predetermined number of photon momenta can be transferred to the atoms in a single interaction zone.

  6. Nonadiabatic molecular alignment of linear molecules probed by strong-field ionization yields of photoelectrons

    NASA Astrophysics Data System (ADS)

    Kaya, G.; Kaya, N.; Strohaber, J.; Hart, N. A.; Kolomenskii, A. A.; Schuessler, H. A.

    2016-12-01

    The dynamics of rotational wave packets of laser-aligned linear molecules were studied with femtosecond laser-driven strong-field ionization (SFI). The dynamics were observed as a function of the delay between a femtosecond probe pulse and a linearly polarized aligning pump pulse. The induced nonadiabatic molecular alignment was directly monitored by the total SFI yield. The measured revival signatures were compared to the calculated degree of molecular alignment taking into account the effects of electronic structure and symmetry of the molecules. By fitting the calculated alignment parameter to the measured experimental data, we also determined the molecular rotational constants of N2, CO, O2, and C2H2 gas molecules.

  7. ALIGNMENT OF THE SCALAR GRADIENT IN EVOLVING MAGNETIC FIELDS

    SciTech Connect

    Sur, Sharanya; Scannapieco, Evan; Pan, Liubin E-mail: evan.scannapieco@asu.edu

    2014-07-20

    We conduct simulations of turbulent mixing in the presence of a magnetic field, grown by the small-scale dynamo. We show that the scalar gradient field, ∇C, which must be large for diffusion to operate, is strongly biased perpendicular to the magnetic field, B. This is true both early on, when the magnetic field is negligible, and at late times, when the field is strong enough to back react on the flow. This occurs because ∇C increases within the plane of a compressive motion, but B increases perpendicular to it. At late times, the magnetic field resists compression, making it harder for scalar gradients to grow and likely slowing mixing.

  8. Fundamental Studies of Electric-Field-Induced Coherent Raman Scattering

    DTIC Science & Technology

    2011-06-07

    mechanisms of nanosecond- pulsed dielectric barrier discharges generated in open air. Our experimental observations have revealed that, in the pre...dynamics in nanosecond- pulsed discharges . a) Electric-field-induced coherent Raman scattering (E-CRS) In this section, I describe the...the electric field in hydrogen. With E-CRS method, our group has revealed very fast discharge dynamics in repetitively pulsed nanosecond discharges [4

  9. Alignment Behavior of Crystal with Magnetic Anisotropy of χc < χa under Rotating Magnetic Field

    NASA Astrophysics Data System (ADS)

    Iwai, Kazuhiko; Niimi, Masahiro; Kohama, Takenori

    2009-10-01

    The alignment behavior of a crystal has been investigated by numerical calculation and an in situ observation experiment with a process combining magnetic field imposition and sample rotation to form unidirectionally aligned crystals with a magnetic anisotropy of χc < χa. The experimentally observed alignment behavior of a polymeric fiber and its alignment time agreed with the numerically calculated ones. Crystal alignment under the out-of-step condition alternately repeats the alignment duration and the keeping of a constant duration, and finally the crystal aligns in a specific direction. The alignment time under the synchronous condition is longer than that under the out-of-step condition if the magnetic field intensity is constant. To reduce the alignment time, a strong magnetic field under the out-of-step condition is desirable in this process.

  10. A numerical model of ionospheric convection derived from field-alignment currents and the corresponding conductivity

    NASA Astrophysics Data System (ADS)

    Blomberg, L. G.; Marklund, G. T.

    1991-08-01

    A numerical model for the calculation of ionospheric convection patterns from given distributions of field aligned current and ionospheric conductivity is described. The model includes a coupling between the conductivity and the field aligned current. The input contributions, the field aligned current and the conductivity, are parametrized. From the primary model output a number of other quantities can be computed: the potential in the inertial frame, the potential in the magnetospheric equatorial plane, the distribution of ionosheric current, and the Joule heating in the ionosphere. This model was used together with a technique to caculate the high latitude potential distribution prevailing during a particular event by combining information from global auroral images and local measurements of fields and particles. The model potential variation along the satellite orbit was found to be in agreement with that calculated from the measured electric field. The model was also used to study some fundamental properties of the electrodynamics of the high latitude ionosphere.

  11. Field-Aligned Current Reconfiguration and Magnetospheric Response to an Impulse in the Interplanetary Magnetic Field BY Component

    NASA Astrophysics Data System (ADS)

    Wilder, F. D.; Eriksson, S.; Korth, H.; Hairston, M. R.; Baker, J. B.; Heinselman, C. J.

    2013-12-01

    When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the DMSP spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawn-side FAC pair. We find there is a delay of approximately 1.25 hours between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvénic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

  12. Field-aligned current reconfiguration and magnetospheric response to an impulse in the interplanetary magnetic field BY component

    NASA Astrophysics Data System (ADS)

    Wilder, F. D.; Eriksson, S.; Korth, H.; Baker, J. B. H.; Hairston, M. R.; Heinselman, C.; Anderson, B. J.

    2013-06-01

    the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the Defense Meteorological Satellite Program spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawnside FAC pair. We find there is a delay of approximately 1.25 h between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvénic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

  13. Inertial range spectrum of field-aligned whistler turbulence

    NASA Astrophysics Data System (ADS)

    Dwivedi, Navin Kumar; Singh, Shobhana

    2017-03-01

    An analytical model to study the whistler turbulence spectrum and inertial range spectral scalings related with the electric and magnetic field spectra in a weakly non-collisional magnetized plasma is developed. In the present model, the dispersion relation of whistler wave propagating along the background magnetic field is exploited to derive the inertial range scaling laws corresponding to the electric field and magnetic field fluctuations. The model is based on the concept of Iroshnikov–Kraichnan inertial range magnetohydrodynamic turbulence. The present phenomenological turbulence scaling model suggests the energy spectra associated with the whistler wave electric field fluctuations and magnetic field fluctuations pursue ‑1 and ‑3 power-laws, respectively. Moreover, the results obtained by the present analytical model reasonably able to explain and compare the observational energy spectra in the wave number domain. The observational and analytical results support the whistler dominated turbulence with the similar spectral index ‑1 of the electric field spectra, whereas, the magnetic field spectral indices in the wave number domain are found -13/3 and ‑3 for the observational and analytical approach, respectively.

  14. Mineral crystal alignment in mineralized fracture callus determined by 3D small-angle X-ray scattering

    NASA Astrophysics Data System (ADS)

    Liu, Yifei; Manjubala, Inderchand; Roschger, Paul; Schell, Hanna; Duda, Georg N.; Fratzl, Peter

    2010-10-01

    Callus tissue formed during bone fracture healing is a mixture of different tissue types as revealed by histological analysis. But the structural characteristics of mineral crystals within the healing callus are not well known. Since two-dimensional (2D) scanning small-angle X-ray scattering (sSAXS) patterns showed that the size and orientation of callus crystals vary both spatially and temporally [1] and 2D electron microscopic analysis implies an anisotropic property of the callus morphology, the mineral crystals within the callus are also expected to vary in size and orientation in 3D. Three-dimensional small-angle X-ray scattering (3D SAXS), which combines 2D SAXS patterns collected at different angles of sample tilting, has been previously applied to investigate bone minerals in horse radius [2] and oim/oim mouse femur/tibia [3]. We implement a similar 3D SAXS method but with a different way of data analysis to gather information on the mineral alignment in fracture callus. With the proposed accurate yet fast assessment of 3D SAXS information, it was shown that the plate shaped mineral particles in the healing callus were aligned in groups with their predominant orientations occurring as a fiber texture.

  15. FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

    NASA Technical Reports Server (NTRS)

    Schriver, D.; Ashour-Abdalla, M.; Strangeway, R. J.; Richard, R. L.; Klezting, C.; Dotan, Y.; Wygant, J.

    2003-01-01

    The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identi@ the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral Snapshot (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data were used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and/or a long-system particle in cell simulation to model the magnetically connected region between the two satellites. Results from the study indicate that there are three main drivers of auroral acceleration: (1) field-aligned currents that lead to quasistatic parallel potential drops (parallel electric fields), (2) earthward flow of high-energy plasma beams from the magnetotail into the auroral zone that lead to quasistatic parallel potential drops, and (3) large-amplitude Alfven waves that propagate into the auroral region from the magnetotail. The events examined thus far confm the previously established invariant latitudinal dependence of the drivers and show a strong dependence on magnetic activity. Alfven waves tend to occur primarily at the poleward edge of the auroral region during more magnetically active times and are correlated with intense electron precipitation. At lower latitudes away

  16. FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

    NASA Technical Reports Server (NTRS)

    Schriver, D.; Ashour-Abdalla, M.; Strangeway, R. J.; Richard, R. L.; Klezting, C.; Dotan, Y.; Wygant, J.

    2003-01-01

    The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identi@ the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral Snapshot (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data were used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and/or a long-system particle in cell simulation to model the magnetically connected region between the two satellites. Results from the study indicate that there are three main drivers of auroral acceleration: (1) field-aligned currents that lead to quasistatic parallel potential drops (parallel electric fields), (2) earthward flow of high-energy plasma beams from the magnetotail into the auroral zone that lead to quasistatic parallel potential drops, and (3) large-amplitude Alfven waves that propagate into the auroral region from the magnetotail. The events examined thus far confm the previously established invariant latitudinal dependence of the drivers and show a strong dependence on magnetic activity. Alfven waves tend to occur primarily at the poleward edge of the auroral region during more magnetically active times and are correlated with intense electron precipitation. At lower latitudes away

  17. The aligned magnetic field of a dusty fluid flow over a stretching sheet

    NASA Astrophysics Data System (ADS)

    Arifin, N. S.; Zokri, S. M.; Kasim, A. R. M.; Salleh, M. Z.; Mohammad, N. F.

    2017-08-01

    In this study, the aligned magnetic field on the flow of a dusty fluid over a stretching sheet is analyzed. The governing nonlinear boundary layer equations is transformed into ordinary differential equations and then solved numerically by the Runge-Kutta Fehlberg fourth-fifth method (RKF45). The numerical solutions with different values of aligned angle, fluid particle interaction parameter and Prandtl number are presented in graphical form. It is found that, increasing aligned angle lead to the decreasing velocity profile while increasing the temperature profile for both fluid and dust phases respectively.

  18. Fully quantum state-resolved inelastic scattering of NO(X) + Kr: Differential cross sections and product rotational alignment

    SciTech Connect

    Brouard, M. Chadwick, H.; Gordon, S. D. S.; Hornung, B.; Nichols, B.; Kłos, J.; Aoiz, F. J.; Stolte, S.

    2014-10-28

    Fully quantum state selected and resolved inelastic scattering of NO(X) by krypton has been investigated. Initial Λ-doublet state selection is achieved using an inhomogeneous hexapole electric field. Differential cross sections and even-moment polarization dependent differential cross sections have been obtained at a collision energy of 514 cm{sup −1} for both spin-orbit and parity conserving and changing collisions. Experimental results are compared with those obtained from quantum scattering calculations and are shown to be in very good agreement. Hard shell quantum scattering calculations are also performed to determine the effects of the different parts of the potential on the scattering dynamics. Comparisons are also made with the NO(X) + Ar system.

  19. Fully quantum state-resolved inelastic scattering of NO(X) + Kr: differential cross sections and product rotational alignment.

    PubMed

    Brouard, M; Chadwick, H; Gordon, S D S; Hornung, B; Nichols, B; Kłos, J; Aoiz, F J; Stolte, S

    2014-10-28

    Fully quantum state selected and resolved inelastic scattering of NO(X) by krypton has been investigated. Initial Λ-doublet state selection is achieved using an inhomogeneous hexapole electric field. Differential cross sections and even-moment polarization dependent differential cross sections have been obtained at a collision energy of 514 cm(-1) for both spin-orbit and parity conserving and changing collisions. Experimental results are compared with those obtained from quantum scattering calculations and are shown to be in very good agreement. Hard shell quantum scattering calculations are also performed to determine the effects of the different parts of the potential on the scattering dynamics. Comparisons are also made with the NO(X) + Ar system.

  20. The evolution of arguments regarding the existence of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Dessler, A. J.

    1984-01-01

    The present understanding of Birkeland (magnetically-field-aligned) currents was not obtained by a direct, logical course. The story is rather more complex. Starting at the end of the 19th century, the Norwegian scientist Kristian Birkeland laid out a compelling case, supported by both theory and experiment, for the existence of field-aligned currents that cause both the aurora and polar geomagnetic disturbances. Sydney Chapman, the British geophysicist, became the acknowledged leader and opinion maker in the field in the decades following Birkeland's death. Chapman proposed, in contradistinction to Birkeland's ideas, equivalent currents that were restricted to flow in the ionosphere with no vertical or field-aligned components. Birkeland's ideas may have faded completely if it had not been for Hannes Alfven, who became involved well after Chapman's ideas gained predominance. Alfven kept insisting that Birkeland's current system made more sense because field-aligned currents were required to drive most of the ionospheric currents. The author became personally involved when Zmuda et al. (1966) submitted to the Journal of Geophysical Research a paper reporting satellite data showing magnetic disturbances above the ionosphere that were consistent with field-aligned Birkeland currents, but which they did not interpret as being due to such currents.

  1. The phase speed of artificial field-aligned irregularities observed by CUTLASS during HF modification of the auroral ionosphere

    NASA Astrophysics Data System (ADS)

    Eglitis, P.; Robinson, T. R.; Rietveld, M. T.; Wright, D. M.; Bond, G. E.

    1998-02-01

    The RF heater facility at Ramfjordmoen, Tromsø can generate field-aligned plasma irregularities in the field of view of the Cooperative UK Twin-Located Auroral Sounding System (CUTLASS) coherent backscatter radar at Hankasalmi, Finland. In a recent set of experiments conducted in April 1996, the phase speed of the generated plasma irregularities has been compared with independent measurements of the plasma drift velocity observed by the European Incoherent Scatter radar facility. The phase speed of the plasma irregularities is found to be equal to the component of the plasma drift velocity in the direction of propagation of the plasma wave. This result is a further verification of the high performance of the CUTLASS radar and also demonstrates how artificially generated plasma irregularities can be employed to detect small plasma drift velocities and contribute to geophysical research. The characteristics of the Doppler spectrum of the artificial plasma waves are also described and discussed.

  2. Field-aligned currents, convection electric fields, and ULF-ELF waves in the cusp

    NASA Technical Reports Server (NTRS)

    Saflekos, N. A.; Potemra, T. A.; Kintner, P. M., Jr.; Green, J. L.

    1979-01-01

    Nearly simultaneous observations from the Triad and Hawkeye satellites over the Southern Hemisphere, at low altitudes near the noon meridian and close to the usual polar cusp latitudes, show that in and near the polar cusp there exist several relationships between field-aligned currents (FACs), convection electric fields, ULF-ELF magnetic noise, broadband electrostatic noise and interplanetary magnetic fields. The most important findings are (1) the FACs directed into the ionosphere in the noon-to-dusk local time sector and directed away from the ionosphere in the noon-to-dawn local time sector and identified as region-1 permanent FACs (Iijima and Potemra, 1976a) and are located equatorward of the regions of antisunward (westward) convection; (2) the observations are consistent with a two-cell convection pattern symmetric in one case (throat positioned at noon) and asymmetric in another (throat located in a sector on the forenoon side in juxtaposition to the region of strong convection on the afternoon side); and (3) fine-structure FACs are responsible for the generation of ULF-ELF noise in the polar cusp.

  3. Freestanding vertically aligned arrays of individual carbon nanotubes on metallic substrates for field emission cathodes

    NASA Astrophysics Data System (ADS)

    Mauger, M.; Binh, Vu Thien; Levesque, A.; Guillot, D.

    2004-07-01

    Direct growth of individual and vertically aligned carbon nanotubes (CNTs) onto a metallic tip apex using a two-chamber radio-frequency plasma-enhanced chemical vapor deposition is reported. Individual Ni nanocatalysts, obtained by a sol-gel combustion technique, were dots for the nucleation of individual CNTs that were freestanding, clean, and vertically aligned by the presence of a controlled applied field. The arrays of CNTs obtained, having a low-density spatial distribution to avoid mutual electrostatic field screening, gave uniform stable overall field emission patterns after a conditioning process. Effective total current densities up to 1A /cm2 can be extracted.

  4. Secondary nanotube growth on aligned carbon nanofibre arrays for superior field emission.

    PubMed

    Watts, Paul C P; Lyth, Stephen M; Henley, Simon J; Silva, S Ravi P

    2008-04-01

    We report substantial improvement of the field emission properties from aligned carbon nanotubes grown on aligned carbon nanofibres by a two-stage plasma enhanced chemical vapour deposition (PECVD) process. The threshold field decreased from 15.0 to 3.6 V/microm after the secondary growth. The field enhancement factor increased from 240 to 1480. This technique allows for superior emission of electrons for carbon nanotube/nanofibre arrays grown directly on highly doped silicon for direct integration in large area displays.

  5. Transition of vertically aligned liquid crystal driven by fan-shaped electric field

    NASA Astrophysics Data System (ADS)

    Tsung, J. W.; Ting, T. L.; Chen, C. Y.; Liang, W. L.; Lai, C. W.; Lin, T. H.; Hsu, W. H.

    2017-09-01

    Interdigital electrodes are implemented in many commercial and novel liquid crystal devices to align molecules. Although many empirical principles and patents apply to electrode design, only a few numerical simulations of alignment have been conducted. Why and how the molecules align in an ordered manner has never been adequately explained. Hence, this investigation addresses the Fréedericksz transition of vertically aligned liquid crystal that is driven by fishbone electrodes, and thereafter identifies the mechanism of liquid crystal alignment. Theoretical calculations suggest that the periodic deformation that is caused by the fan-shaped fringe field minimizes the free energy in the liquid crystal cell, and the optimal alignment can be obtained when the cell parameters satisfy the relation p /2 d =√{k11/k33 } , where p is the spatial period of the strips of the electrode; d denotes the cell gap; and k11 and k33 are the splay and bend elastic constants of the liquid crystal, respectively. Polymer-stabilized vertical alignment test cells with various p values and spacings between the electrodes were fabricated, and the process of liquid crystal alignment was observed under an optical microscope. The degree of alignment was evaluated by measuring the transmittance of the test cell. The experimental results were consistent with the theoretical predictions. The principle of design, p /2 d =√{k11/k33 } , greatly improves the uniformity and stability of the aligned liquid crystal. The methods that are presented here can be further applied to cholesteric liquid crystal and other self-assembled soft materials.

  6. On the alignment of diamagnetic molecules in interstellar magnetic fields

    NASA Astrophysics Data System (ADS)

    Papoular, R.

    2017-01-01

    This paper reports the results of new chemical modeling measurements of the Faraday rotation braking mechanism operating on a diamagnetic molecule in a magnetic field (see Papoular 2016). The time length of the experiment is extended, more relevant variables are measured (rotation, vibration, drift energies; molecule orientation), and more accurately, as a function of time. The polarization of light by the moving molecule is computed. The observed behavior of the molecule may be understood, and the rotation damping time more accurately deduced by fitting a mathematical model built upon the classical equations of motion in a field. This model, meant to include the essential physics involved in the experiment, with the minimum number of parameters, also allows the chemical modeling experimental results to be extrapolated to other molecular structures, shapes and sizes, and other magnetic fields. For a given particle, the rotation damping time scales like 1/H and is independent on rotation frequency. As an example, we follow the motion of a rod of homogeneous material, 10-5 cm in length, moving in a field 5 10-6 G in intensity. Its angular rotation is found to decrease to 0, while its axis settles perpendicularly to the field within a few years. Molecular vibrations appear as an illustration of the fluctuation-dissipation theorem: they absorb friction heat and, at the same time, are the very cause of this friction.

  7. Re-grown aligned carbon nanotubes with improved field emission.

    PubMed

    Lim, Xiaodai; Zhu, Yanwu; Varghese, Binni; Gao, Xingyu; Wee, Andrew Thye Shen; Sow, Chorng-Haur

    2012-01-01

    In this work, a simple technique to improve the field emission property of multi-walled carbon nanotubes is presented. Re-grown multi-walled carbon nanotubes are grown on the same substrates after the as-grown multi-walled carbon nanotubes are transferred to other substrates using polydimethylsiloxane as intermediation. For the duration of the synthesis of the re-grown multi-walled carbon nanotubes, similar synthesis parameters used in growing the as-grown multi-walled carbon nanotubes are utilized. As a form of possible application, field emission studies show -2.6 times improvement in field enhancement factor and more uniform emission for the re-grown multi-walled carbon nanotubes. In addition, the turn-on field is reduced from 2.85 V/microm to 1.40 V/microm. Such significant improvements are attributed to new emission sites comprising of sharp carbonaceous impurities encompassing both tip and upper portion of the multi-walled carbon nanotubes. As such, this technique presents a viable route for the production of multi-walled carbon nanotubes with better field emission quality.

  8. Reduction of the field-aligned potential drop in the polar cap during large geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Kitamura, N.; Seki, K.; Nishimura, Y.; Hori, T.; Terada, N.; Ono, T.; Strangeway, R. J.

    2013-12-01

    We have studied photoelectron flows and the inferred field-aligned potential drop in the polar cap during 5 large geomagnetic storms that occurred in the periods when the photoelectron observations in the polar cap were available near the apogee of the FAST satellite (~4000 km) at solar maximum, and the footprint of the satellite paths in the polar cap was under sunlit conditions most of the time. In contrast to the ~20 V potential drop during geomagnetically quiet periods at solar maximum identified by Kitamura et al. [JGR, 2012], the field-aligned potential drop frequently became smaller than ~5 V during the main and early recovery phases of the large geomagnetic storms. Because the potential acts to inhibit photoelectron escape, this result indicates that the corresponding acceleration of ions by the field-aligned potential drop in the polar cap and the lobe region is smaller during the main and early recovery phases of large geomagnetic storms compared to during geomagnetically quiet periods. Under small field-aligned current conditions, the number flux of outflowing ions should be nearly equal to the net escaping electron number flux. Since ions with large flux originating from the cusp/cleft ionosphere convect into the polar cap during geomagnetic storms [e.g., Kitamura et al., JGR, 2010], the net escaping electron number flux should increase to balance the enhanced ion outflows. The magnitude of the field-aligned potential drop would be reduced to let a larger fraction of photoelectrons escape.

  9. Thomson scattering in magnetic fields. [of white dwarf stars

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara

    1989-01-01

    The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.

  10. Linac head scatter factor for asymmetric radiation field

    NASA Astrophysics Data System (ADS)

    Soubra, Mazen Ahmed

    1997-11-01

    The head scatter factor, Sh is an important dosimetric quantity used in radiation therapy dose calculation. It is empirically determined and its field size dependence reflects changes in photon scatter from components in the linac treatment head. In this work a detailed study of the physical factors influencing the determination of Sh was performed with particular attention given to asymmetric field geometries. Ionization measurements for 6 and 18 MV photon beams were made to examine the factors which determine Sh. These include: phantom size and material, collimator backscatter, non-lateral electronic equilibrium (LEE) conditions, electron contamination, collimator-exchange, photon energy, flattening filter and off-axis distance (OAD). Results indicated that LEE is not required for Sh measurements if electron contamination is minimized. Brass caps or polystyrene miniphantoms can both be used in Sh measurements provided the phantom thickness is large enough to stop contaminant electrons. Backscatter radiation effects into the monitor chamber were found to be negligible for the Siemens linac. It was found that the presence and shape of the flattening filter had a significant effect on the empirically determined value of Sh was also shown to be a function of OAD, particularly for small fields. For fields larger than 12×12 cm2/ Sh was independent of OAD. A flattening filter mass model was introduced to explain qualitatively the above results. A detailed Monte Carlo simulation of the Siemens KD2 linac head in 6 MV mode was performed to investigate the sources of head scatter which contribute to the measured Sh. The simulated head components include the flattening filter, the electron beam stopper, the primary collimator, the photon monitor chamber and the secondary collimators. The simulations showed that the scatter from the head of the Siemens linac is a complex function of the head components. On the central axis the flattening filter played the dominant role in

  11. Field-aligned fluxes in the geomagnetic equator

    NASA Technical Reports Server (NTRS)

    Semar, C. L.; Konradi, A.

    1976-01-01

    During 12 electron injection events observed by Explorer 45 during the December, 1971, and February, 1972, in magnetic storms it was found that the lowest observable pitch angle particles (down to 7 degrees in one case) arrived first. Pitch angle dispersion and shell-splitting effects are shown to be inadequate explanations for most of these pitch angle distributions. It is suggested that parallel electric fields may be supplying 1- to 5-keV electrons to the magnetosphere from the ionosphere. Various models of parallel electric fields are discussed.

  12. Scatter dose summation for irregular fields: speed and accuracy study.

    PubMed

    DeWyngaert, J K; Siddon, R L; Bjarngard, B E

    1986-05-01

    Using program IRREG as a standard, we have compared speed and accuracy of several algorithms that calculate the scatter dose in an irregular field. All the algorithms, in some manner, decompose the irregular field into component triangles and obtain the scatter dose as the sum of the contributions from those triangles. Two of the algorithms replace each such component triangle with a sector of a certain "effective radius": in one case the average radius of the triangle, in the other the radius of the sector having the same area as the component triangle. A third algorithm decomposes each triangle further into two right triangles and utilizes the precalculated "equivalent radius" of each, to find the scatter contribution. For points near the center of a square field, all the methods compare favorably in accuracy to program IRREG, with less than a 1% error in total dose and with approximately a factor of 3-5 savings in computation time. Even for extreme rectangular fields (2 cm X 30 cm), the methods using the average radius and the equivalent right triangles agree to within 2% in total dose and approximately a factor of 3-4 savings in computation time.

  13. An effective field theory for forward scattering and factorization violation

    DOE PAGES

    Rothstein, Ira Z.; Stewart, Iain W.

    2016-08-03

    Starting with QCD, we derive an effective field theory description for forward scattering and factorization violation as part of the soft-collinear effective field theory (SCET) for high energy scattering. These phenomena are mediated by long distance Glauber gluon exchanges, which are static in time, localized in the longitudinal distance, and act as a kernel for forward scattering where |t| << s. In hard scattering, Glauber gluons can induce corrections which invalidate factorization. With SCET, Glauber exchange graphs can be calculated explicitly, and are distinct from graphs involving soft, collinear, or ultrasoft gluons. We derive a complete basis of operators whichmore » describe the leading power effects of Glauber exchange. Key ingredients include regulating light-cone rapidity singularities and subtractions which prevent double counting. Our results include a novel all orders gauge invariant pure glue soft operator which appears between two collinear rapidity sectors. The 1-gluon Feynman rule for the soft operator coincides with the Lipatov vertex, but it also contributes to emissions with ≥ 2 soft gluons. Our Glauber operator basis is derived using tree level and one-loop matching calculations from full QCD to both SCETII and SCETI. The one-loop amplitude’s rapidity renormalization involves mixing of color octet operators and yields gluon Reggeization at the amplitude level. The rapidity renormalization group equation for the leading soft and collinear functions in the forward scattering cross section are each given by the BFKL equation. Various properties of Glauber gluon exchange in the context of both forward scattering and hard scattering factorization are described. For example, we derive an explicit rule for when eikonalization is valid, and provide a direct connection to the picture of multiple Wilson lines crossing a shockwave. In hard scattering operators Glauber subtractions for soft and collinear loop diagrams ensure that we are not

  14. An effective field theory for forward scattering and factorization violation

    SciTech Connect

    Rothstein, Ira Z.; Stewart, Iain W.

    2016-08-03

    Starting with QCD, we derive an effective field theory description for forward scattering and factorization violation as part of the soft-collinear effective field theory (SCET) for high energy scattering. These phenomena are mediated by long distance Glauber gluon exchanges, which are static in time, localized in the longitudinal distance, and act as a kernel for forward scattering where |t| << s. In hard scattering, Glauber gluons can induce corrections which invalidate factorization. With SCET, Glauber exchange graphs can be calculated explicitly, and are distinct from graphs involving soft, collinear, or ultrasoft gluons. We derive a complete basis of operators which describe the leading power effects of Glauber exchange. Key ingredients include regulating light-cone rapidity singularities and subtractions which prevent double counting. Our results include a novel all orders gauge invariant pure glue soft operator which appears between two collinear rapidity sectors. The 1-gluon Feynman rule for the soft operator coincides with the Lipatov vertex, but it also contributes to emissions with ≥ 2 soft gluons. Our Glauber operator basis is derived using tree level and one-loop matching calculations from full QCD to both SCETII and SCETI. The one-loop amplitude’s rapidity renormalization involves mixing of color octet operators and yields gluon Reggeization at the amplitude level. The rapidity renormalization group equation for the leading soft and collinear functions in the forward scattering cross section are each given by the BFKL equation. Various properties of Glauber gluon exchange in the context of both forward scattering and hard scattering factorization are described. For example, we derive an explicit rule for when eikonalization is valid, and provide a direct connection to the picture of multiple Wilson lines crossing a shockwave. In hard scattering operators Glauber subtractions for soft and collinear loop diagrams ensure that we

  15. An effective field theory for forward scattering and factorization violation

    NASA Astrophysics Data System (ADS)

    Rothstein, Ira Z.; Stewart, Iain W.

    2016-08-01

    Starting with QCD, we derive an effective field theory description for forward scattering and factorization violation as part of the soft-collinear effective field theory (SCET) for high energy scattering. These phenomena are mediated by long distance Glauber gluon exchanges, which are static in time, localized in the longitudinal distance, and act as a kernel for forward scattering where | t| ≪ s. In hard scattering, Glauber gluons can induce corrections which invalidate factorization. With SCET, Glauber exchange graphs can be calculated explicitly, and are distinct from graphs involving soft, collinear, or ultrasoft gluons. We derive a complete basis of operators which describe the leading power effects of Glauber exchange. Key ingredients include regulating light-cone rapidity singularities and subtractions which prevent double counting. Our results include a novel all orders gauge invariant pure glue soft operator which appears between two collinear rapidity sectors. The 1-gluon Feynman rule for the soft operator coincides with the Lipatov vertex, but it also contributes to emissions with ≥ 2 soft gluons. Our Glauber operator basis is derived using tree level and one-loop matching calculations from full QCD to both SCETII and SCETI. The one-loop amplitude's rapidity renormalization involves mixing of color octet operators and yields gluon Reggeization at the amplitude level. The rapidity renormalization group equation for the leading soft and collinear functions in the forward scattering cross section are each given by the BFKL equation. Various properties of Glauber gluon exchange in the context of both forward scattering and hard scattering factorization are described. For example, we derive an explicit rule for when eikonalization is valid, and provide a direct connection to the picture of multiple Wilson lines crossing a shockwave. In hard scattering operators Glauber subtractions for soft and collinear loop diagrams ensure that we are not sensitive to

  16. Electrokinetics of scalable, electric-field-assisted fabrication of vertically aligned carbon-nanotube/polymer composites

    NASA Astrophysics Data System (ADS)

    Castellano, Richard J.; Akin, Cevat; Giraldo, Gabriel; Kim, Sangil; Fornasiero, Francesco; Shan, Jerry W.

    2015-06-01

    Composite thin films incorporating vertically aligned carbon nanotubes (VACNTs) offer promise for a variety of applications where the vertical alignment of the CNTs is critical to meet performance requirements, e.g., highly permeable membranes, thermal interfaces, dry adhesives, and films with anisotropic electrical conductivity. However, current VACNT fabrication techniques are complex and difficult to scale up. Here, we describe a solution-based, electric-field-assisted approach as a cost-effective and scalable method to produce large-area VACNT composites. Multiwall-carbon nanotubes are dispersed in a polymeric matrix, aligned with an alternating-current (AC) electric field, and electrophoretically concentrated to one side of the thin film with a direct-current (DC) component to the electric field. This approach enables the fabrication of highly concentrated, individually aligned nanotube composites from suspensions of very dilute ( ϕ = 4 × 10 - 4 ) volume fraction. We experimentally investigate the basic electrokinetics of nanotube alignment under AC electric fields, and show that simple models can adequately predict the rate and degree of nanotube alignment using classical expressions for the induced dipole moment, hydrodynamic drag, and the effects of Brownian motion. The composite AC + DC field also introduces complex fluid motion associated with AC electro-osmosis and the electrochemistry of the fluid/electrode interface. We experimentally probe the electric-field parameters behind these electrokinetic phenomena, and demonstrate, with suitable choices of processing parameters, the ability to scalably produce large-area composites containing VACNTs at number densities up to 1010 nanotubes/cm2. This VACNT number density exceeds that of previous electric-field-fabricated composites by an order of magnitude, and the surface-area coverage of the 40 nm VACNTs is comparable to that of chemical-vapor-deposition-grown arrays of smaller-diameter nanotubes.

  17. Field-aligned Transport and Acceleration of Solar Energetic Particles

    NASA Astrophysics Data System (ADS)

    Borovikov, D.; Sokolov, I.; Tenishev, V.; Gombosi, T. I.

    2015-12-01

    Solar Energetic Particle (SEP) phenomena represent one of the major components of space weather. Often, but not exclusively associated with Coronal Mass Ejections (CMEs), they pose a significant scientific as well as practical interest. As these particles originate at such explosive events, they have energies up to several GeV. SEP may cause disruptions in operations of space instruments and spacecrafts and are dangerous to astronauts. For this reason, studies of SEP events and predictions of their impact are of great importance. The motion and acceleration of SEP, though kinetic in nature, is governed by Interplanetary Magnetic Field (IMF) and its disturbances. Therefore, a consistent and accurate simulation and predictive tool must include a realistic MHD model of IMF. At the same time, transport of SEP is essentially one-dimensional as at high energies particles are tied to magnetic field lines. This allows building a model that can effectively map active regions on the solar surface onto various regions of the Solar System thus predicting the affected regions of the at any distance from the Sun. We present the first attempt to construct a model that employs coupling of MHD and kinetic models. The former describes the evolution of IMF disturbed by CME, while the latter simulates particles moving along the field lines extracted from MHD model. The first results are provided.

  18. Implications of grain size variation in magnetic field alignment of block copolymer blends

    DOE PAGES

    Rokhlenko, Yekaterina; Majewski, Pawel W.; Larson, Steven R.; ...

    2017-03-28

    Recent experiments have highlighted the intrinsic magnetic anisotropy in coil–coil diblock copolymers, specifically in poly(styrene-block-4-vinylpyridine) (PS-b-P4VP), that enables magnetic field alignment at field strengths of a few tesla. We consider here the alignment response of two low molecular weight (MW) lamallae-forming PS-b-P4VP systems. Cooling across the disorder–order transition temperature (Todt) results in strong alignment for the higher MW sample (5.5K), whereas little alignment is discernible for the lower MW system (3.6K). This disparity under otherwise identical conditions of field strength and cooling rate suggests that different average grain sizes are produced during slow cooling of these materials, with larger grainsmore » formed in the higher MW material. Blending the block copolymers results in homogeneous samples which display Todt, d-spacings, and grain sizes that are intermediate between the two neat diblocks. Similarly, the alignment quality displays a smooth variation with the concentration of the higher MW diblock in the blends, and the size of grains likewise interpolates between limits set by the neat diblocks, with a factor of 3.5× difference in the grain size observed in high vs low MW neat diblocks. Finally, these results highlight the importance of grain growth kinetics in dictating the field response in block copolymers and suggests an unconventional route for the manipulation of such kinetics.« less

  19. Far-field superresolution by imaging of resonance scattering

    NASA Astrophysics Data System (ADS)

    Schuster, Gerard T.; Huang, Yunsong

    2014-12-01

    We show that superresolution imaging in the far-field region of the sources and receivers is theoretically and practically possible if migration of resonant multiples is employed. A resonant multiple is one that bounces back and forth between two scattering points; it can also be the multiple between two smoothly varying interfaces as long as the reflection wave paths partially overlap and reflect from the same Fresnel zone. For a source with frequency f, compared to a one-way trip, N round trips in propagating between two scatterers increase the effective frequency by 2N × f and decrease the effective wavelength by λ/(2N). Thus, multiples can, in principle, be used as high-frequency probes to estimate detailed properties of layers. Tests with both synthetic and field data validate this claim. Improved resolution by multiple imaging is not only feasible for crustal reflections, but might be applicable to mantle and core reverberations recorded by earthquake seismologists.

  20. Back Compton Scattering in Strong Uniform Magnetic Field

    SciTech Connect

    Xu, W.; Huang Wei; Yan Mulin

    2006-11-02

    In this paper, we show that there is a Non-Commutative Plane (NCP) in the perpendicular magnetic fields in the accelerator, and the QED with NCP (QED-NCP) has been formulated. Being similar to the theory of quantum Hall effects, an effective filling factor f(B) is introduced, which characters the possibility occupied the LLL state by the electrons living on NCP. The back Compton scattering amplitudes of QED-NCP are derived, and the differential cross sections for the process with fixed initial polarizing electrons and photons are calculated. We propose to precisely measure the polarization dependent differential cross sections of the back Compton scattering in the perpendicular magnetic fields experimentally, which may lead to reveal the effects of QED with NCP. This should be interesting and remarkable. The existing Spring-8's data have been analyzed primitively, and some hints for QED-NCP effects are seen.

  1. Scattering detection of a solenoidal Poynting vector field.

    PubMed

    Fardad, Shima; Salandrino, Alessandro; Samadi, Akbar; Heinrich, Matthias; Chen, Zhigang; Christodoulides, Demetrios N

    2016-08-01

    The Poynting vector S plays a central role in electrodynamics as it is directly related to the power and the momentum carried by an electromagnetic wave. In the presence of multiple electromagnetic waves with different polarizations and propagation directions, the Poynting vector may exhibit solenoidal components which are not associated to any power flow. Here, we demonstrate theoretically and experimentally that the presence of such solenoidal components has physical consequences, and it is not a mere artifact of the gauge invariance of S. In particular, we identify a simple field configuration displaying solenoidal components of S and theoretically show that a judiciously designed scatterer can act as a "Poynting vector detector" which when immersed in such field distribution would experience a transverse optical force orthogonal to the incidence plane. We experimentally validate our theoretical predictions by observing a pronounced asymmetry in the scattering pattern of a spherical nanoparticle.

  2. Multi-point Magnetic Field Observations of Field-Aligned Currents from Swarm Constellation Mission

    NASA Astrophysics Data System (ADS)

    Le, Guan; Chi, Peter; Lühr, Hermann; Gjerloev, Jesper; Stolle, Claudia; Park, Jaeheung; Rauberg, Jan

    2015-04-01

    In this paper, we report the results of case studies of multi-point magnetic field measurements of field-aligned currents (FACs) from Swarm constellation mission to understand their temporal characteristics and hemispheric asymmetry. For science operations (since April, 2014), the three spacecraft were placed in slightly different polar orbits: Swarm B spacecraft in a higher altitude orbit (507km x 512km) and Swarm A and C side-by-side in lower altitude orbits (459km x 462km). In the beginning of the science operational phase, the longitudinal separations of the orbital planes were small, and Swarm A/C pair and Swarm B were nearly out of phase in the orbit. This unique orbit configuration provides opportunities to study some new features of FACs. Specifically, the Swarm satellites make multiple crossings of a FAC region within a few hours. Such data enable us to study temporal variations in several time scales, from 1 minute up to about 3 hours. Furthermore, the three satellites make nearly simultaneous observations of FACs in northern and southern hemispheres, which provide us an opportunity to study the hemispheric asymmetry.

  3. Dynamics of electric field induced particle alignment in nonpolar polymer matrix

    NASA Astrophysics Data System (ADS)

    Tai, Xiangyang; Wu, Guozhang; Yui, Hiroshi; Asai, Shigeo; Sumita, Masao

    2003-11-01

    The dynamics of electric field induced particle alignment in nonpolar polymer matrix to build one-dimensional conductive materials was investigated. The influence of electric field on particle alignment was real-time traced by dynamic percolation measurement using carbon black (CB) filled polyethylene as a model system. The activation energy of the continuous CB path formation was calculated and found to be unchanged with CB alignment. The critical percolation concentration at thermodynamic equilibrium state φc* was deduced to characterize the anisotropism of network structure, by which the thermodynamic prerequisite electric field E* for the transition from three-dimensional isotropic network to one-dimensional chain could be easily found out.

  4. Dust Grain Alignment and Magnetic Field Strength in the Wall of the Local Bubble

    NASA Astrophysics Data System (ADS)

    Andersson, B.-G.; Medan, Ilija

    2017-01-01

    We use archival data on polarization (Berdyugin 2014) and extinction in the wall of the Local Bubble to study the grain alignment efficiency and the magnetic field strength. We find that the grain alignment efficiency variations can be directly tied to the location of the known OB-associations within 200pc from the Sun, strongly supporting modern, radiation-driven dust grain alignment. Based on the Davis-Chandrasekhar-Fermi method, we find a bimodal magnetic field-strength distribution, where the locations of the strongest fields correlate with the directions towards the near-by OB associations. We hypothesize that this strengthening is due to compression of the bubble wall by the opposing outflows in the Local Bubble and from the surrounding OB associations.

  5. ITG modes in the presence of inhomogeneous field-aligned flow

    NASA Astrophysics Data System (ADS)

    Sen, S.; McCarthy, D. R.; Lontano, M.; Lazzaro, E.; Honary, F.

    2010-02-01

    In a recent paper, Varischetti et al. (Plasma Phys. Contr. F. 2008, 50, 105008-1-15) have found that in a slab geometry the effect of the flow shear in the field-aligned parallel flow on the linear mode stability of the ion temperature gradient (ITG)-driven modes is not very prominent. They found that the flow shear also has a negligible effect on the mode characteristics. The work in this paper shows that the inclusion of flow curvature in the field-aligned flow can have a considerable effect on the mode stability; it can also change the mode structure so as to effect the mixing length transport in the core region of a fusion device. Flow shear, on the other hand, has indeed an insignificant role in the mode stability and mode structure. Inhomogeneous field-aligned flow should therefore still be considered for a viable candidate in controlling the ITG mode stability and mode structure.

  6. Analysis on near field scattering spectra around nanoparticles by using parametric indirect microscopic imaging

    NASA Astrophysics Data System (ADS)

    Guoyan, Liu; Kun, Gao; Xuefeng, Liu; Guoqiang, Ni

    2016-10-01

    We report the simulation and measurement results of near field spatial scattering spectra around nanoparticles. Our measurement and simulations results have indicated that Parametric Indirect Microscopic Imaging can image the near field spatial scattering to a much larger distance from the scattering source of the particle under measurement whereas this part of spatial scattering was lost in the conventional microscopy. Both FDTD modeling and measurement provided evidence that parameters of indirect optical wave vector have higher sensitivity to near field scattering.

  7. Adiabatic Field-Free Alignment of Asymmetric Top Molecules with an Optical Centrifuge.

    PubMed

    Korobenko, A; Milner, V

    2016-05-06

    We use an optical centrifuge to align asymmetric top SO_{2} molecules by adiabatically spinning their most polarizable O-O axis. The effective centrifugal potential in the rotating frame confines the sulfur atoms to the plane of the laser-induced rotation, leading to the planar molecular alignment that persists after the molecules are released from the centrifuge. The periodic appearance of the full three-dimensional alignment, typically observed only with linear and symmetric top molecules, is also detected. Together with strong in-plane centrifugal forces, which bend the molecules by up to 10 deg, permanent field-free alignment offers new ways of controlling molecules with laser light.

  8. Longwave scattering effects on fluxes in broken cloud fields

    SciTech Connect

    Takara, E.E.; Ellingson, R.G.

    1996-04-01

    The optical properties of clouds in the radiative energy balance are important. Most works on the effects of scattering have been in the shortwave; but longwave effects can be significant. In this work, the fluxes above and below a single cloud layer are presented, along with the errors in assuming flat black plate clouds or black clouds. The predicted fluxes are the averaged results of analysis of several fields with the same cloud amount.

  9. Gamma-Deuteron Compton Scattering in Effective Field Theory

    SciTech Connect

    Jiunn-Wei Chen; Harald W. Griesshammer; Martin J. Savage; Roxanne P. Springer

    1998-12-01

    The differential cross section for {gamma}-deuteron Compton scattering is computed to next-to-leading order (NLO) in an effective field theory that describes nucleon-nucleon interactions below the pion production threshold. Contributions at NLO include the nucleon isoscalar electric polarizability from its 1/m{sub {pi}} behavior in the chiral limit. The parameter free prediction of the {gamma}-deuteron differential cross section at NLO is in good agreement with data.

  10. Light scattering in colloidal solution of magnetite in electric and magnetic fields.

    PubMed

    Yerin, Constantine V

    2007-04-15

    Light scattering by magnetite particles in kerosene under the simultaneous action of crossed electric and magnetic fields was studied. Decreasing of variation of light scattering intensity at some values of electric and magnetic fields have been found. Values of fields at which a minimum of light scattering intensity occur depend on the angle between laser beam and the plane of crossed fields.

  11. Nonlinear Compton scattering in a strong rotating electric field

    NASA Astrophysics Data System (ADS)

    Raicher, Erez; Eliezer, Shalom; Zigler, Arie

    2016-12-01

    The nonlinear Compton scattering rate in a rotating electric field is explicitly calculated. For this purpose, an approximate solution to the Klein-Gordon equation in the presence of a rotating electric field is applied. An analytical expression for the emission rate is obtained, as well as a simplified approximation adequate for implementation in kinetic codes. The spectrum is numerically calculated for present-day optical and x-ray laser parameters. The results are compared to the standard Volkov-Ritus rate for a particle in a plane wave, which is commonly assumed to be valid for a rotating electric field under certain conditions. Substantial deviations between the two models, in both the radiated power and the spectral shape, are demonstrated. First, the typical number of photons participating in the scattering process is much smaller compared to the Volkov-Ritus rate, resulting in up to an order of magnitude lower emitted power. Furthermore, our model predicts a discrete harmonic spectrum for electrons with low asymptotic momentum compared to the field amplitude. This discrete structure is a clear imprint of the electric field frequency, as opposed to the Volkov-Ritus rate, which reduces to the constant crossed field rate for the physical conditions under consideration. Our model predictions can be tested with present-day laser facilities.

  12. Alfven Wave - DC Dualism in Description of Stationary Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.

    2009-01-01

    In many cases, the field-aligned currents (FACs) in the Earth's magnetosphere and heliosphere may be described in terms of both DC currents and the currents of a propagating Alfven wave. The simplest example is when a propagating Alfven wave transports a potential hop along the magnetic fieid: between the source of the wave and its front, the problem is well stationary and includes the stationary field-aligned currents, transporting the electric charges along the magnetic field, which may be described as a DC problem, and only at the front of the wave there are the polarization (inertial) currents, closing across the magnetic field. In some cases, the Alfven wave approach brings better understanding to many problems. We will consider here the results of the applications of this approach to two long-staying problems: the effect of saturation of the transpolar voltage in the Earth's magnetosphere, and the experimentally-observed existence of the strong field-aligned currents in the subtle Mercury's magnetosphere which is not able tc close the measured field-aligned currents.

  13. Alfven Wave - DC Dualism in Description of Stationary Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.

    2009-01-01

    In many cases, the field-aligned currents (FACs) in the Earth's magnetosphere and heliosphere may be described in terms of both DC currents and the currents of a propagating Alfven wave. The simplest example is when a propagating Alfven wave transports a potential hop along the magnetic fieid: between the source of the wave and its front, the problem is well stationary and includes the stationary field-aligned currents, transporting the electric charges along the magnetic field, which may be described as a DC problem, and only at the front of the wave there are the polarization (inertial) currents, closing across the magnetic field. In some cases, the Alfven wave approach brings better understanding to many problems. We will consider here the results of the applications of this approach to two long-staying problems: the effect of saturation of the transpolar voltage in the Earth's magnetosphere, and the experimentally-observed existence of the strong field-aligned currents in the subtle Mercury's magnetosphere which is not able tc close the measured field-aligned currents.

  14. Direct determination of large-scale magnetospheric field-aligned currents with superDARN

    SciTech Connect

    Solfo, G.J.; Greenwald, R.; Bristow, W.

    1995-08-01

    The authors present 2D images of plasma convection velocities in the high latitude F region, measured using a dual radar pair. These maps allow them to calculate the vorticity of the plasma flow. The authors argue that this provides a measure of the field aligned currents in the F regions, in that velocity is equivalent to J{sub m}/{Sigma}{sub p}, where J{sub m} is the magnetospheric component of the field aligned current, and {Sigma}{sub p} is the integrated Pederson conductivity.

  15. Ultraviolet refractometry using field-based light scattering spectroscopy

    PubMed Central

    Fu, Dan; Choi, Wonshik; Sung, Yongjin; Oh, Seungeun; Yaqoob, Zahid; Park, YongKeun; Dasari, Ramachandra R.; Feld, Michael S.

    2010-01-01

    Accurate refractive index measurement in the deep ultraviolet (UV) range is important for the separate quantification of biomolecules such as proteins and DNA in biology. This task is demanding and has not been fully exploited so far. Here we report a new method of measuring refractive index using field-based light scattering spectroscopy, which is applicable to any wavelength range and suitable for both solutions and homogenous objects with well-defined shape such as microspheres. The angular scattering distribution of single microspheres immersed in homogeneous media is measured over the wavelength range 260 to 315 nm using quantitative phase microscopy. By least square fitting the observed scattering distribution with Mie scattering theory, the refractive index of either the sphere or the immersion medium can be determined provided that one is known a priori. Using this method, we have measured the refractive index dispersion of SiO2 spheres and bovine serum albumin (BSA) solutions in the deep UV region. Specific refractive index increments of BSA are also extracted. Typical accuracy of the present refractive index technique is ≤0.003. The precision of refractive index measurements is ≤0.002 and that of specific refractive index increment determination is ≤0.01 mL/g. PMID:20372622

  16. Diffusive alignment of the magnetic field in active regions of plasmas

    PubMed

    Nunez

    2000-11-01

    Regions of high magnetic field within plasmas tend to keep this field aligned in a dominant direction. This occurs both in observed phenomena and in simulations of kinematic and nonlinear dynamos. Although most of this effect is due to the particular dynamics of each case, magnetic diffusion also plays an important role. It is shown here that the unitary magnetic field vector satisfies a certain estimate that bounds its possible variations. The dependence of the bound on the plasma parameters is analyzed.

  17. Field-aligned currents calculated based on the upgraded Prairie View Magnetosphere- ionosphere Coupling Model

    NASA Astrophysics Data System (ADS)

    Romashets, E.; Huang, T.

    2006-12-01

    Using the experimental magnetic field and the newly defined Eular Potentials, we upgraded Prairie View Magnetosphere-ionosphere Coupling Model that was originally created in the frame of IGRF. The electric fields in the ionosphere and the field-aligned currents in the magnetosphere are calculated with the upgraded magnetosphere-ionosphere coupling model, and a preliminary comparison of the calculations with the measurements from ST5 will be presented.

  18. Quasi-steady current sheet structures with field-aligned flow

    NASA Technical Reports Server (NTRS)

    Birn, J.

    1992-01-01

    The paper discusses the characteristics of quasi-steady plasma and field structures with field-aligned flow. Explicit solutions are developed for modeling the compressible flow around a plasmoid in the distant magnetotail. The expected and observed plasmoid signatures are found. Field signatures outside the plasmoid are typically those of encounters of traveling compression region: a north-south signature of Bz accompanied by an enhancement of Bx.

  19. Wide-field imaging through scattering media by scattered light fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Zhou, Yulan; Li, Xun

    2017-08-01

    To obtain images through scattering media, scattered light fluorescence (SLF) microscopy that utilizes the optical memory effect has been developed. However, the small field of view (FOV) of SLF microscopy limits its application. In this paper, we have introduced a re-modulation method to achieve wide-field imaging through scattering media by SLF microscopy. In the re-modulation method, to raster scan the focus across the object plane, the incident wavefront is re-modulated via a spatial light modulator (SLM) in the updated phase compensation calculated using the optimized iterative algorithm. Compared with the conventional optical memory effect method, the re-modulation method can greatly increase the FOV of a SLF microscope. With the phase compensation theoretically calculated, the process of updating the phase compensation of a high speed SLM is fast. The re-modulation method does not increase the imaging time. The re-modulation method is, therefore, expected to make SLF microscopy have much wider applications in biology, medicine and physiology.

  20. Solution-based electric-field-assisted assembly of vertically aligned CNT membranes

    NASA Astrophysics Data System (ADS)

    Castellano, Richard; Akin, Cevat; Shan, Jerry

    2014-11-01

    Carbon-nanotube (CNT) membranes are of interest due to experiments and simulations showing flow through nanotubes to be 3 to 5 orders of magnitude faster than predicted by viscous flow theory. Thus, membranes incorporating vertically aligned CNTs (VACNTs) as through-pores offer promise as highly efficient and permeable membranes for a variety of filter and separation processes. However, current membrane-fabrication techniques utilizing CVD-grown VACNT arrays are costly and difficult to scale up. We are developing a solution-based, electric-field-assisted approach as a cost-effective and scalable method to producing large-area VACNT membranes and composites. Post-growth nanotubes are first dispersed in a polymeric matrix and then aligned with an AC electric field. A DC component induces electrophoresis to the CNTs to significantly increase the VACNT number density. This composite field also introduces complex fluid motion caused by induced-charge electro-osmosis and the electrochemistry of the fluid/electrode interface. We experimentally probe all of these effects and consider factors affecting the number density and spatial uniformity of VACNT membranes. We also consider the basic electrokinetics of nanotube alignment under spatially uniform AC electric fields, making quantitative comparison with classical models of the dynamics of polarizable, 1D particles under the combined effects of electric fields, hydrodynamic drag, and Brownian motion. We conclude by discussing the implications of these fundamental electrohydrodynamic studies for producing large-area membranes containing aligned CNTs.

  1. Structural and magnetic properties of L10 -FePt nanoparticles aligned by external magnetic field

    NASA Astrophysics Data System (ADS)

    Tamada, Yoshinori; Yamamoto, Shinpei; Nasu, Saburo; Ono, Teruo

    2008-12-01

    We investigated structural and magnetic properties of the easy-axis aligned L10 -FePt nanoparticles by the combined use of x-ray diffraction (XRD), magnetization, and F57e Mössbauer measurements. The L10 -FePt nanoparticles were fixed in a polystyrene matrix by performing free radical polymerization of styrene under an aligning external magnetic field. Mössbauer spectrum of the L10 -FePt nanoparticles/polystyrene composite showed tremendous decrease in the second and fifth absorption lines under the condition that the incident γ ray was parallel to the aligning field. This result indicates that the easy axes of the L10 -FePt nanoparticles in the composite have a strong preferred orientation with a finite distribution. We estimated the distribution of easy-axis orientation by using the Mössbauer hyperfine parameters, which is in good agreement with that determined by the XRD rocking curve.

  2. Alignment effect in nonsequential double ionization of diatomic molecules in strong laser fields

    SciTech Connect

    Li, Y.; Yang, S. P.; Chen, J.; Liu, J.

    2007-08-15

    Using a semiclassical rescattering model, we investigate the nonsequential double ionization (NSDI) process of diatomic molecules aligned parallel and perpendicular to the intense linearly polarized field. It is shown that a simple hydrogen-molecule-like model can simulate a nitrogen molecule effectively by giving the alignment dependence of the ratio of double to single ionization and the momentum distribution qualitatively consistent with the experimental result of N{sub 2}. However, the alignment dependence of the momentum correlation of two ejected electrons does not agree with the experimental result, which indicates that the quantum effect needs to be included in the rescattering and the field-ionization process to explain the experimental observation.

  3. Field induced UV-alignment method for a zero pre-tilt liquid crystal cell

    NASA Astrophysics Data System (ADS)

    Oh, Seung-Won; Park, Jun-Hee; Yoon, Tae-Hoon

    2016-09-01

    Recently, photo-alignment technology has been the focus of research efforts because lowering the pre-tilt angle is essential for complete elimination of the off-axis light leakage. However, even though photo-alignment can provide zero pre-tilt angle, it has not yet been widely applied in mass production because of its weak surface anchoring, high curing energy, and strong image sticking. In this paper, we demonstrate that the zero pre-tilt angle can be obtained by employing the field-induced UV-alignment method. We have shown electro-optical characteristics and parameters related to the image quality of a fringe-field switching cell fabricated using the proposed method as functions of the monomer concentration and the UV irradiation time.

  4. Dependence of field-aligned electron precipitation occurrence on season and altitude

    NASA Technical Reports Server (NTRS)

    Berko, F. W.; Hoffman, R. A.

    1974-01-01

    An examination of factors affecting the occurrence of field-aligned 2.3-keV electron precipitation has been performed by using data from more than 7500 orbits of the polar-orbiting satellite Ogo 4. Both season and altitude were found to be parameters that are directly related to the probability of occurrence. The highest probabilities occurred when the measurements were made at altitudes from 800 km to apogee (914 km), except during summer. In this altitude interval, the electron precipitation was more likely to be field-aligned during winter than during any other season. The analysis suggests the establishment by electrostatic charge layers of localized electric fields parallel to the magnetic field. The resulting potential distribution focuses the electron beam along the field lines in the region between the charge layers but destroys the focused beam below the lower layer, and thus an altitude dependence is created.

  5. Imaging of Vector Electric Fields Surrounding Auroral Arcs from Multibeam Incoherent Scatter Radar Measurements.

    NASA Astrophysics Data System (ADS)

    Maksimova, N.; Varney, R. H.; Cosgrove, R. B.; Kaeppler, S. R.; Nicolls, M. J.

    2015-12-01

    Evaluating the ionospheric electric fields and current systems surrounding auroral arcs aids in distinguishing physical mechanisms that drive arc generation and current closure. Auroral forms involve spatial scales that are small in comparison with the magnetosphere-ionosphere-thermosphere (MIT) system, and yet these forms are thought to be closely tied to the overall system response. Spatially resolved measurements of the horizontal ionospheric current can, in principle, be used to determine the field-aligned currents (FAC) that are responsible for energy transfer between the magnetosphere and the ionosphere/thermosphere, leading to heating and upwelling of the neutral gas and acceleration of ion upflows and outflows. Furthermore, the closure of FACs in the ionosphere regulates modes of magnetospheric convection and substorms. An algorithm has been developed to image the local structure in the convection electric field using multibeam incoherent scatter radar (ISR) measurements. Given the inherent difficulty of reconstructing vector quantities from line of sight (LOS) velocity measurements, the algorithm's aim is to select from the solution space for the possible field configurations a unique solution for the electric field distribution by constraining the reconstructed electric field to reproduce the LOS measurements within measurement errors while simultaneously minimizing a measure of the field's curvature and absolute gradient. Using the method of Lagrange multipliers, the algorithm regularizes the underdetermined problem defined by the LOS radar velocity measurements and guarantees a unique solution when the average measurement error is smaller than the average measurement amplitude. The algorithm is tested on a variety of simulated fields in a sensitivity study to determine the extent to which the solution depends on the a priori assumptions and the observation geometry. In addition, a case study of a quiescent auroral arc observed by the Poker Flat

  6. A compact neutron scatter camera for field deployment

    DOE PAGES

    Goldsmith, John E. M.; Gerling, Mark D.; Brennan, James S.

    2016-08-23

    Here, we describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metalmore » from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.« less

  7. Research of microwave scattering properties of snow fields

    NASA Technical Reports Server (NTRS)

    Angelakos, D. J.

    1978-01-01

    The results obtained in the research program of microwave scattering properties of snow fields are presented. Experimental results are presented showing backscatter dependence on frequency (5.8-8.0 GHz), angle of incidence (0-60 degrees), snow wetness (time of day), and frequency modulation (0-500 MHz). Theoretical studies are being made of the inverse scattering problem yielding some preliminary results concerning the determination of the dielectric constant of the snow layer. The experimental results lead to the following conclusions: snow layering affects backscatter, layer response is significant up to 45 degrees of incidence, wetness modifies snow layer effects, frequency modulation masks the layer response, and for the proper choice of probing frequency and for nominal snow depths, it appears to be possible to measure the effective dielectric constant and the corresponding water content of a snow pack.

  8. A compact neutron scatter camera for field deployment

    SciTech Connect

    Goldsmith, John E. M.; Gerling, Mark D.; Brennan, James S.

    2016-08-23

    Here, we describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.

  9. A compact neutron scatter camera for field deployment

    SciTech Connect

    Goldsmith, John E. M.; Gerling, Mark D.; Brennan, James S.

    2016-08-23

    Here, we describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.

  10. A compact neutron scatter camera for field deployment

    NASA Astrophysics Data System (ADS)

    Goldsmith, John E. M.; Gerling, Mark D.; Brennan, James S.

    2016-08-01

    We describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.

  11. Radiography by selective detection of scatter field velocity components

    NASA Technical Reports Server (NTRS)

    Jacobs, Alan M. (Inventor); Dugan, Edward T. (Inventor); Shedlock, Daniel (Inventor)

    2007-01-01

    A reconfigurable collimated radiation detector, system and related method includes at least one collimated radiation detector. The detector has an adjustable collimator assembly including at least one feature, such as a fin, optically coupled thereto. Adjustments to the adjustable collimator selects particular directions of travel of scattered radiation emitted from an irradiated object which reach the detector. The collimated detector is preferably a collimated detector array, where the collimators are independently adjustable. The independent motion capability provides the capability to focus the image by selection of the desired scatter field components. When an array of reconfigurable collimated detectors is provided, separate image data can be obtained from each of the detectors and the respective images cross-correlated and combined to form an enhanced image.

  12. Sound field reproduction as an equivalent acoustical scattering problem.

    PubMed

    Fazi, Filippo Maria; Nelson, Philip A

    2013-11-01

    Given a continuous distribution of acoustic sources, the determination of the source strength that ensures the synthesis of a desired sound field is shown to be identical to the solution of an equivalent acoustic scattering problem. The paper begins with the presentation of the general theory that underpins sound field reproduction with secondary sources continuously arranged on the boundary of the reproduction region. The process of reproduction by a continuous source distribution is modeled by means of an integral operator (the single layer potential). It is then shown how the solution of the sound reproduction problem corresponds to that of an equivalent scattering problem. Analytical solutions are computed for two specific instances of this problem, involving, respectively, the use of a secondary source distribution in spherical and planar geometries. The results are shown to be the same as those obtained with analyses based on High Order Ambisonics and Wave Field Synthesis, respectively, thus bringing to light a fundamental analogy between these two methods of sound reproduction. Finally, it is shown how the physical optics (Kirchhoff) approximation enables the derivation of a high-frequency simplification for the problem under consideration, this in turn being related to the secondary source selection criterion reported in the literature on Wave Field Synthesis.

  13. An X-ray scattering study of flow-aligned samples of a lyotropic liquid-crystalline hexagonal phase

    NASA Astrophysics Data System (ADS)

    Impéror-Clerc, M.; Davidson, P.

    Large flow-aligned samples of the hexagonal mesophase of the (sodium dodecylsulfate, pentanol, water) ternary system were produced by merely sucking the material into flat glass capillaries. These samples were examined by polarized light microscopy and X-ray scattering. In the plane of the hexagonal lattice, the `` -mosaic'' is only because the dense (10) hexagonal planes lie parallel to the flat glass plates of the capillaries. In contrast, the `` -mosaic'' of the C6 axis reaches 5-10 because the samples undergo a thermomechanical instability of the columns already investigated by Oswald et al. in detail on the (C12EO6, H2O) system. Anisotropic thermal diffuse scattering is observed around the Bragg peaks and its description in the frame of an elastic continuum model provides estimates of the elastic constants. On heating the samples, we observed a clear splitting of four of the (10) hexagonal lattice reflections. This splitting is the defining signature of the thermomechanical instability by which the columns form zig-zags. The fact that two of the (10) reflections are not affected by the instability demonstrates that it is confined to the plane of the capillary. The influence of temperature on the thermomechanical instability was also studied in detail.

  14. Theory of weak scattering of stochastic electromagnetic fields from deterministic and random media

    SciTech Connect

    Tong Zhisong; Korotkova, Olga

    2010-09-15

    The theory of scattering of scalar stochastic fields from deterministic and random media is generalized to the electromagnetic domain under the first-order Born approximation. The analysis allows for determining the changes in spectrum, coherence, and polarization of electromagnetic fields produced on their propagation from the source to the scattering volume, interaction with the scatterer, and propagation from the scatterer to the far field. An example of scattering of a field produced by a {delta}-correlated partially polarized source and scattered from a {delta}-correlated medium is provided.

  15. Electric Field Effects on Fiber Alignment Using an Auxiliary Electrode During Electrospinning

    NASA Technical Reports Server (NTRS)

    Carnell, Lisa S.; Siochi, Emilie J.; Wincheski, Russell A.; Holloway, Nancy M.; Clark, Robert L.

    2009-01-01

    Control of electrospun fiber placement and distribution was investigated by examining the effect of electric field parameters on the electrospinning of fibers. The experimental set-up used in this study eliminated the bending instability and whipping, allowing the jet to be modeled as a stable trajectory. Coupling of experimental and computational results suggests the potential for predicting aligned fiber distribution in electrospun mats.

  16. Modified ion-acoustic solitary waves in plasmas with field-aligned shear flows

    SciTech Connect

    Saleem, H.; Haque, Q.

    2015-08-15

    The nonlinear dynamics of ion-acoustic waves is investigated in a plasma having field-aligned shear flow. A Korteweg-deVries-type nonlinear equation for a modified ion-acoustic wave is obtained which admits a single pulse soliton solution. The theoretical result has been applied to solar wind plasma at 1 AU for illustration.

  17. Electrical Properties of Composite Materials with Electric Field-Assisted Alignment of Nanocarbon Fillers

    NASA Astrophysics Data System (ADS)

    Yakovenko, Olena; Matzui, Ludmila; Danylova, Ganna; Zadorozhnii, Victor; Vovchenko, Ludmila; Perets, Yulia; Lazarenko, Oleksandra

    2017-07-01

    The article reports about electric field-induced alignment of the carbon nanoparticles embedded in epoxy matrix. Optical microscopy was performed to consider the effect of the electric field magnitude and configuration, filler morphology, and aspect ratio on alignment process. Characteristic time of aligned network formation was compared with modeling predictions. Carbon nanotube and graphite nanoplatelet rotation time was estimated using an analytical model based on effective medium approach. Different depolarization factor was applied according to the geometries of the particle and electric field. Solid nanocomposites were fabricated by using AC electric field. We have investigated concentration dependence of electrical conductivity of graphite nanoplatelets/epoxy composites using two-probe technique. It was established that the electrical properties of composites with random and aligned filler distribution are differ by conductivity value at certain filler content and distinguish by a form of concentration dependence of conductivity for fillers with different morphology. These differences were explained in terms of the dynamic percolation and formation of various conductive networks: chained in case of graphite nanoplatelets and crossed framework in case of carbon nanotubes filler.

  18. Alfven Wave Reflection Model of Field-Aligned Currents at Mercury

    NASA Technical Reports Server (NTRS)

    Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James

    2010-01-01

    An Alfven Wave Reflection (AWR) model is proposed that provides closure for strong field-aligned currents (FACs) driven by the magnetopause reconnection in the magnetospheres of planets having no significant ionospheric and surface electrical conductance. The model is based on properties of the Alfven waves, generated at high altitudes and reflected from the low-conductivity surface of the planet. When magnetospheric convection is very slow, the incident and reflected Alfven waves propagate along approximately the same path. In this case, the net field-aligned currents will be small. However, as the convection speed increases. the reflected wave is displaced relatively to the incident wave so that the incident and reflected waves no longer compensate each other. In this case, the net field-aligned current may be large despite the lack of significant ionospheric and surface conductivity. Our estimate shows that for typical solar wind conditions at Mercury, the magnitude of Region 1-type FACs in Mercury's magnetosphere may reach hundreds of kilo-Amperes. This AWR model of field-aligned currents may provide a solution to the long-standing problem of the closure of FACs in the Mercury's magnetosphere. c2009 Elsevier Inc. All rights reserved.

  19. Alfven Wave Reflection Model of Field-Aligned Currents at Mercury

    NASA Technical Reports Server (NTRS)

    Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James

    2010-01-01

    An Alfven Wave Reflection (AWR) model is proposed that provides closure for strong field-aligned currents (FACs) driven by the magnetopause reconnection in the magnetospheres of planets having no significant ionospheric and surface electrical conductance. The model is based on properties of the Alfven waves, generated at high altitudes and reflected from the low-conductivity surface of the planet. When magnetospheric convection is very slow, the incident and reflected Alfven waves propagate along approximately the same path. In this case, the net field-aligned currents will be small. However, as the convection speed increases. the reflected wave is displaced relatively to the incident wave so that the incident and reflected waves no longer compensate each other. In this case, the net field-aligned current may be large despite the lack of significant ionospheric and surface conductivity. Our estimate shows that for typical solar wind conditions at Mercury, the magnitude of Region 1-type FACs in Mercury's magnetosphere may reach hundreds of kilo-Amperes. This AWR model of field-aligned currents may provide a solution to the long-standing problem of the closure of FACs in the Mercury's magnetosphere. c2009 Elsevier Inc. All rights reserved.

  20. Electric Field Effects on Fiber Alignment Using an Auxiliary Electrode During Electrospinning

    NASA Technical Reports Server (NTRS)

    Carnell, Lisa S.; Siochi, Emilie J.; Wincheski, Russell A.; Holloway, Nancy M.; Clark, Robert L.

    2009-01-01

    Control of electrospun fiber placement and distribution was investigated by examining the effect of electric field parameters on the electrospinning of fibers. The experimental set-up used in this study eliminated the bending instability and whipping, allowing the jet to be modeled as a stable trajectory. Coupling of experimental and computational results suggests the potential for predicting aligned fiber distribution in electrospun mats.

  1. Field-aligned electric currents and their measurement by the incoherent backscatter technique

    NASA Technical Reports Server (NTRS)

    Bauer, P.; Cole, K. D.; Lejeume, G.

    1975-01-01

    Field aligned electric currents flow in the magnetosphere in many situations of fundamental geophysical interest. It is shown here that the incoherent backscatter technique can be used to measure these currents when the plasma line can be observed. The technique provides a ground based means of measuring these currents which complements the rocket and satellite ones.

  2. Robust multiscale field-only formulation of electromagnetic scattering

    NASA Astrophysics Data System (ADS)

    Sun, Qiang; Klaseboer, Evert; Chan, Derek Y. C.

    2017-01-01

    We present a boundary integral formulation of electromagnetic scattering by homogeneous bodies that are characterized by linear constitutive equations in the frequency domain. By working with the Cartesian components of the electric E and magnetic H fields and with the scalar functions (r .E ) and (r .H ) where r is a position vector, the problem can be cast as having to solve a set of scalar Helmholtz equations for the field components that are coupled by the usual electromagnetic boundary conditions at material boundaries. This facilitates a direct solution for the surface values of E and H rather than having to work with surface currents or surface charge densities as intermediate quantities in existing methods. Consequently, our formulation is free of the well-known numerical instability that occurs in the zero-frequency or long-wavelength limit in traditional surface integral solutions of Maxwell's equations and our numerical results converge uniformly to the static results in the long-wavelength limit. Furthermore, we use a formulation of the scalar Helmholtz equation that is expressed as classically convergent integrals and does not require the evaluation of principal value integrals or any knowledge of the solid angle. Therefore, standard quadrature and higher order surface elements can readily be used to improve numerical precision for the same number of degrees of freedom. In addition, near and far field values can be calculated with equal precision, and multiscale problems in which the scatterers possess characteristic length scales that are both large and small relative to the wavelength can be easily accommodated. From this we obtain results for the scattering and transmission of electromagnetic waves at dielectric boundaries that are valid for any ratio of the local surface curvature to the wave number. This is a generalization of the familiar Fresnel formula and Snell's law, valid at planar dielectric boundaries, for the scattering and transmission

  3. Space Technology 5 Multipoint Observations of Temporal and Spatial Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, G.; Wang, Y.; Slavin, J. A.; Strangeway, R. L.

    2009-01-01

    Space Technology 5 (ST5) is a constellation mission consisting of three microsatellites. It provides the first multipoint magnetic field measurements in low Earth orbit, which enables us to separate spatial and temporal variations. In this paper, we present a study of the temporal variability of field-aligned currents using the ST5 data. We examine the field-aligned current observations during and after a geomagnetic storm and compare the magnetic field profiles at the three spacecraft. The multipoint data demonstrate that mesoscale current structures, commonly embedded within large-scale current sheets, are very dynamic with highly variable current density and/or polarity in approx.10 min time scales. On the other hand, the data also show that the time scales for the currents to be relatively stable are approx.1 min for mesoscale currents and approx.10 min for large-scale currents. These temporal features are very likely associated with dynamic variations of their charge carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of mesoscale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  4. High current density and low turn-on field from aligned Cd(OH)2 nanosheets

    NASA Astrophysics Data System (ADS)

    Bagal, Vivekanand S.; Patil, Girish P.; Deore, Amol B.; Baviskar, Prashant K.; Suryawanshi, Sachin R.; More, Mahendra A.; Chavan, Padmakar G.

    2016-04-01

    High current density of 9.8 mA/cm2 was drawn at an applied field of 4.1 V/μm from aligned Cd(OH)2 nanosheets and low turn-on field of 1.4 V/μm was found for the emission current density of 10 μA/cm2. The aligned Cd(OH)2 nanosheets were synthesized by CBD technique on Cadmium foil. To the best of our knowledge this is the first report on the field emission studies of Cd(OH)2 nanosheets. Simple synthesis route coupled with superior field emission properties indicate the possible use of Cd(OH)2 nanosheets for micro/nanoelectronic devices.

  5. Simulations of the equatorial thermosphere anomaly: Field-aligned ion drag effect

    NASA Astrophysics Data System (ADS)

    Lei, Jiuhou; Thayer, Jeffrey P.; Wang, Wenbin; Richmond, Arthur D.; Roble, Raymond; Luan, Xiaoli; Dou, Xiankang; Xue, Xianghui; Li, Tao

    2012-01-01

    In this paper the impact of the field-aligned ion drag on equatorial thermosphere temperature and density is quantitatively investigated on the basis of the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (NCAR TIEGCM) simulations under high solar activity (F107 = 180). The increase of upward vertical winds over the magnetic equator associated with the additional divergence of meridional winds, caused by the inclusion of field-aligned ion drag, leads to a reduction in thermosphere temperature and density at the magnetic equator through enhanced adiabatic cooling. We found that the field-aligned ion drag has an obvious impact on the thermosphere only over the magnetic equatorial region in the daytime and evening sectors, whereas it has less effect on the equatorial thermosphere anomaly (ETA) crests. The daytime neutral temperature over the magnetic equator is reduced by about 30 K, for altitudes above 250 km without significant altitudinal variations, when field-aligned ion drag is included in the simulation. The thermosphere density in the magnetic equatorial region starts to change slightly at 300 km and depletes by about 5% at 400 km, while experiencing a greater decrease with altitude. Furthermore, the trough produced in the neutral temperature and density corresponds well with the magnetic dip equator. The ETA features during 12:00-18:00 LT become obvious as a result of the inclusion of the field-aligned ion drag. Specifically, our results show that at 400 km the crest-trough differences in neutral temperature are about 30-60 K, and the crest-trough ratios in thermosphere density are 1.03-1.06, comparable with observations.

  6. Measuring the complex field scattered by single submicron particles

    SciTech Connect

    Potenza, Marco A. C. Sanvito, Tiziano

    2015-11-15

    We describe a method for simultaneous measurements of the real and imaginary parts of the field scattered by single nanoparticles illuminated by a laser beam, exploiting a self-reference interferometric scheme relying on the fundamentals of the Optical Theorem. Results obtained with calibrated spheres of different materials are compared to the expected values obtained through a simplified analytical model without any free parameters, and the method is applied to a highly polydisperse water suspension of Poly(D,L-lactide-co-glycolide) nanoparticles. Advantages with respect to existing methods and possible applications are discussed.

  7. Angle-dependent radiative grain alignment. Confirmation of a magnetic field - radiation anisotropy angle dependence on the efficiency of interstellar grain alignment

    NASA Astrophysics Data System (ADS)

    Andersson, B.-G.; Pintado, O.; Potter, S. B.; Straižys, V.; Charcos-Llorens, M.

    2011-10-01

    Context. Interstellar grain alignment studies are currently experiencing a renaissance due to the development of a new quantitative theory based on radiative alignment torques (RAT). One of the distinguishing predictions of this theory is a dependence of the grain alignment efficiency on the relative angle (Ψ) between the magnetic field and the anisotropy direction of the radiation field. In an earlier study we found observational evidence for such an effect from observations of the polarization around the star HD 97300 in the Chamaeleon I cloud. However, due to the large uncertainties in the measured visual extinctions, the result was uncertain. Aims: By acquiring explicit spectral classification of the polarization targets, we have sought to perform a more precise reanalysis of the existing polarimetry data. Methods: We have obtained new spectral types for the stars in our for our polarization sample, which we combine with photometric data from the literature to derive accurate visual extinctions for our sample of background field stars. This allows a high accuracy test of the grain alignment efficiency as a function of Ψ. Results: We confirm and improve the measured accuracy of the variability of the grain alignment efficiency with Ψ, seen in the earlier study. We note that the grain temperature (heating) also shows a dependence on Ψ which we interpret as a natural effect of the projection of the grain surface to the illuminating radiation source. This dependence also allows us to derive an estimate of the fraction of aligned grains in the cloud.

  8. A numerical model of ionospheric convection derived from field-aligned currents and the corresponding conductivity

    NASA Astrophysics Data System (ADS)

    Blomberg, L. G.; Marklund, G. T.

    1988-03-01

    A numerical model for the calculation of ionospheric convection patterns from given distributions of field-aligned current and ionospheric conductivity is described. The model includes a coupling between the conductivity and the field-aligned current, so that the conductivity peaks in regions of upward current, as usually observed by measurements. The model is very flexible in that the input distributions, the field-aligned current, and the conductivity are parameterized in a convenient way. From the primary model output, namely the ionospheric electrostatic potential (or convection) in the corotating frame, a number of other quantities can be computed. These include: the potential in a Sun-fixed frame (the transformation takes into account the nonalignment of the Earth's magnetic and geographic axes); the potential in the magnetospheric equatorial plane (projected using either a dipole magnetic field model or the Tsyganenko-Usmanov model, and the assumption of vanishing parallel electric field); the distribution of ionospheric (horizontal) current; and Joule heating in the ionosphere. The model was used with input data inferred from satellite measurements to calculate the high-latitude potential distribution prevailing during a particular event. The model potential variation along the satellite orbit is found to be in excellent agreement with the measured electric field.

  9. FLASHFLOOD: A 3D Field-based similarity search and alignment method for flexible molecules

    NASA Astrophysics Data System (ADS)

    Pitman, Michael C.; Huber, Wolfgang K.; Horn, Hans; Krämer, Andreas; Rice, Julia E.; Swope, William C.

    2001-07-01

    A three-dimensional field-based similarity search and alignment method for flexible molecules is introduced. The conformational space of a flexible molecule is represented in terms of fragments and torsional angles of allowed conformations. A user-definable property field is used to compute features of fragment pairs. Features are generalizations of CoMMA descriptors (Silverman, B.D. and Platt, D.E., J. Med. Chem., 39 (1996) 2129.) that characterize local regions of the property field by its local moments. The features are invariant under coordinate system transformations. Features taken from a query molecule are used to form alignments with fragment pairs in the database. An assembly algorithm is then used to merge the fragment pairs into full structures, aligned to the query. Key to the method is the use of a context adaptive descriptor scaling procedure as the basis for similarity. This allows the user to tune the weights of the various feature components based on examples relevant to the particular context under investigation. The property fields may range from simple, phenomenological fields, to fields derived from quantum mechanical calculations. We apply the method to the dihydrofolate/methotrexate benchmark system, and show that when one injects relevant contextual information into the descriptor scaling procedure, better results are obtained more efficiently. We also show how the method works and include computer times for a query from a database that represents approximately 23 million conformers of seventeen flexible molecules.

  10. Collective migration exhibits greater sensitivity but slower dynamics of alignment to applied electric fields

    PubMed Central

    Lalli, Mark L.; Asthagiri, Anand R.

    2015-01-01

    During development and disease, cells migrate collectively in response to gradients in physical, chemical and electrical cues. Despite its physiological significance and potential therapeutic applications, electrotactic collective cell movement is relatively less well understood. Here, we analyze the combined effect of intercellular interactions and electric fields on the directional migration of non-transformed mammary epithelial cells, MCF-10A. Our data show that clustered cells exhibit greater sensitivity to applied electric fields but align more slowly than isolated cells. Clustered cells achieve half-maximal directedness with an electric field that is 50% weaker than that required by isolated cells; however, clustered cells take ∼2-4 fold longer to align. This trade-off in greater sensitivity and slower dynamics correlates with the slower speed and intrinsic directedness of collective movement even in the absence of an electric field. Whereas isolated cells exhibit a persistent random walk, the trajectories of clustered cells are more ballistic as evidenced by the superlinear dependence of their mean square displacement on time. Thus, intrinsically-directed, slower clustered cells take longer to redirect and align with an electric field. These findings help to define the operating space and the engineering trade-offs for using electric fields to affect cell movement in biomedical applications. PMID:26692908

  11. Space Technology 5 Multi-Point Observations of Temporal Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, Guan; Wang, Yongli; Slavin, James A.; Strangeway, Robert J.

    2008-01-01

    Space Technology 5 (ST5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from ST5. The data demonstrate that meso-scale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of approximately 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are approximately 1 min for meso-scale currents and approximately 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  12. Space Technology 5 (ST-5) Observations of Field-Aligned Currents: Temporal Variability

    NASA Technical Reports Server (NTRS)

    Le, Guan

    2010-01-01

    Space Technology 5 (ST-5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from STS. The data demonstrate that masoscale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of about 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are about I min for meso-scale currents and about 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  13. Space Technology 5 Multi-Point Observations of Temporal Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, Guan; Wang, Yongli; Slavin, James A.; Strangeway, Robert J.

    2008-01-01

    Space Technology 5 (ST5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from ST5. The data demonstrate that meso-scale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of approximately 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are approximately 1 min for meso-scale currents and approximately 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  14. Collective migration exhibits greater sensitivity but slower dynamics of alignment to applied electric fields.

    PubMed

    Lalli, Mark L; Asthagiri, Anand R

    2015-06-01

    During development and disease, cells migrate collectively in response to gradients in physical, chemical and electrical cues. Despite its physiological significance and potential therapeutic applications, electrotactic collective cell movement is relatively less well understood. Here, we analyze the combined effect of intercellular interactions and electric fields on the directional migration of non-transformed mammary epithelial cells, MCF-10A. Our data show that clustered cells exhibit greater sensitivity to applied electric fields but align more slowly than isolated cells. Clustered cells achieve half-maximal directedness with an electric field that is 50% weaker than that required by isolated cells; however, clustered cells take ∼2-4 fold longer to align. This trade-off in greater sensitivity and slower dynamics correlates with the slower speed and intrinsic directedness of collective movement even in the absence of an electric field. Whereas isolated cells exhibit a persistent random walk, the trajectories of clustered cells are more ballistic as evidenced by the superlinear dependence of their mean square displacement on time. Thus, intrinsically-directed, slower clustered cells take longer to redirect and align with an electric field. These findings help to define the operating space and the engineering trade-offs for using electric fields to affect cell movement in biomedical applications.

  15. Characteristics of ionospheric convection and field-aligned current in the dayside cusp region

    NASA Technical Reports Server (NTRS)

    Lu, G.; Lyons, L. R.; Reiff, P. H.; Denig, W. F.; Beaujardiere, O. De LA; Kroehl, H. W.; Newell, P. T.; Rich, F. J.; Opgenoorth, H.; Persson, M. A. L.

    1995-01-01

    The assimilative mapping of ionospheric electrodynamics (AMIE) technique has been used to estimate global distributions of high-latitude ionospheric convection and field-aligned current by combining data obtained nearly simultaneously both from ground and from space. Therefore, unlike the statistical patterns, the 'snapshot' distributions derived by AMIE allow us to examine in more detail the distinctions between field-aligned current systems associated with separate magnetospheric processes, especially in the dayside cusp region. By comparing the field-aligned current and ionospheric convection patterns with the corresponding spectrograms of precipitating particles, the following signatures have been identified: (1) For the three cases studied, which all had an IMF with negative y and z components, the cusp precipitation was encountered by the DMSP satellites in the postnoon sector in the northern hemisphere and in the prenoon sector in the southern hemisphere. The equatorward part of the cusp in both hemispheres is in the sunward flow region and marks the beginning of the flow rotation from sunward to antisunward. (2) The pair of field-aligned currents near local noon, i.e., the cusp/mantle currents, are coincident with the cusp or mantle particle precipitation. In distinction, the field-aligned currents on the dawnside and duskside, i.e., the normal region 1 currents, are usually associated with the plasma sheet particle precipitation. Thus the cusp/mantle currents are generated on open field lines and the region 1 currents mainly on closed field lines. (3) Topologically, the cusp/mantle currents appear as an expansion of the region 1 currents from the dawnside and duskside and they overlap near local noon. When B(sub y) is negative, in the northern hemisphere the downward field-aligned current is located poleward of the upward current; whereas in the southern hemisphere the upward current is located poleward of the downward current. (4) Under the assumption of

  16. Liquid Crystalline Block Copolymers with Brush Type Architecture: Toward Functional Membranes by Magnetic Field Alignment

    NASA Astrophysics Data System (ADS)

    Choo, Youngwoo; Gopinadhan, Manesh; Mahajan, Lalit; Kasi, Rajeswari; Osuji, Chinedum

    2015-03-01

    We introduce a novel liquid crystalline block copolymer with brush type architecture for membrane applications by magnetic field directed self-assembly. Ring-opening metathesis of n-alkyloxy cyanobiphenyl and polylactide (PLA) functionalized norbornene monomers provides efficient polymerization yielding low polydispersity block copolymers. The molecular weight of the PLA side chains, spacer length of the cyanobiphenyl mesogens are systematically varied to form well-ordered BCP morphologies at varying volume fractions. Interestingly, the system features morphology dependent anchoring condition where mesogens adopt planar anchoring on cylindrical interface while homeotropic anchoring was preferred on a planar block interface. The minority PLA domains from highly aligned materials can be readily degraded by hydrolysis to produce vertically aligned nanoporous polymer films which exhibit reversible thermal switching behavior. The polymers introduced here provide a versatile platform for scalable fabrication of aligned membranes and further functional materials based on such templates. This work was supported by NSF(CCMI-1246804).

  17. Design of practical alignment device in KSTAR Thomson diagnostic

    NASA Astrophysics Data System (ADS)

    Lee, J. H.; Lee, S. H.; Yamada, I.

    2016-11-01

    The precise alignment of the laser path and collection optics in Thomson scattering measurements is essential for accurately determining electron temperature and density in tokamak experiments. For the last five years, during the development stage, the KSTAR tokamak's Thomson diagnostic system has had alignment fibers installed in its optical collection modules, but these lacked a proper alignment detection system. In order to address these difficulties, an alignment verifying detection device between lasers and an object field of collection optics is developed. The alignment detection device utilizes two types of filters: a narrow laser band wavelength for laser, and a broad wavelength filter for Thomson scattering signal. Four such alignment detection devices have been successfully developed for the KSTAR Thomson scattering system in this year, and these will be tested in KSTAR experiments in 2016. In this paper, we present the newly developed alignment detection device for KSTAR's Thomson scattering diagnostics.

  18. Design of practical alignment device in KSTAR Thomson diagnostic

    SciTech Connect

    Lee, J. H.; Lee, S. H.; Yamada, I.

    2016-11-15

    The precise alignment of the laser path and collection optics in Thomson scattering measurements is essential for accurately determining electron temperature and density in tokamak experiments. For the last five years, during the development stage, the KSTAR tokamak’s Thomson diagnostic system has had alignment fibers installed in its optical collection modules, but these lacked a proper alignment detection system. In order to address these difficulties, an alignment verifying detection device between lasers and an object field of collection optics is developed. The alignment detection device utilizes two types of filters: a narrow laser band wavelength for laser, and a broad wavelength filter for Thomson scattering signal. Four such alignment detection devices have been successfully developed for the KSTAR Thomson scattering system in this year, and these will be tested in KSTAR experiments in 2016. In this paper, we present the newly developed alignment detection device for KSTAR’s Thomson scattering diagnostics.

  19. Vertically aligned diamond-graphite hybrid nanorod arrays with superior field electron emission properties

    NASA Astrophysics Data System (ADS)

    Ramaneti, R.; Sankaran, K. J.; Korneychuk, S.; Yeh, C. J.; Degutis, G.; Leou, K. C.; Verbeeck, J.; Van Bael, M. K.; Lin, I. N.; Haenen, K.

    2017-06-01

    A "patterned-seeding technique" in combination with a "nanodiamond masked reactive ion etching process" is demonstrated for fabricating vertically aligned diamond-graphite hybrid (DGH) nanorod arrays. The DGH nanorod arrays possess superior field electron emission (FEE) behavior with a low turn-on field, long lifetime stability, and large field enhancement factor. Such an enhanced FEE is attributed to the nanocomposite nature of the DGH nanorods, which contain sp2-graphitic phases in the boundaries of nano-sized diamond grains. The simplicity in the nanorod fabrication process renders the DGH nanorods of greater potential for the applications as cathodes in field emission displays and microplasma display devices.

  20. Field-aligned currents observed in the vicinity of a moving auroral arc

    NASA Astrophysics Data System (ADS)

    Goertz, C. K.; Bruening, K.

    1984-09-01

    The sounding rocket Porcupine F4 was launched into an auroral arc and the field aligned currents were independently deduced from magnetic field measurements; the horizontal current deduced from the electric field measurements and height integrated conductivity calculations; and measurements of electron fluxes. Above the arc the different methods agree. The magnetosphere acts as generator and the ionosphere as load. North of the arc, the first two methods disagree, possibly due to an Alfven wave carrying the observed magnetic field perturbation. The energy flow is out of the ionosphere. Here the ionosphere acts as generator and the magnetosphere as load.

  1. Field-aligned currents observed in the vicinity of a moving auroral arc

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.; Bruening, K.

    1984-01-01

    The sounding rocket Porcupine F4 was launched into an auroral arc and the field aligned currents were independently deduced from magnetic field measurements; the horizontal current deduced from the electric field measurements and height integrated conductivity calculations; and measurements of electron fluxes. Above the arc the different methods agree. The magnetosphere acts as generator and the ionosphere as load. North of the arc, the first two methods disagree, possibly due to an Alfven wave carrying the observed magnetic field perturbation. The energy flow is out of the ionosphere. Here the ionosphere acts as generator and the magnetosphere as load.

  2. Hydration dependent studies of highly aligned multilayer lipid membranes by neutron scattering

    NASA Astrophysics Data System (ADS)

    Trapp, Marcus; Gutberlet, Thomas; Juranyi, Fanni; Unruh, Tobias; Demé, Bruno; Tehei, Moeava; Peters, Judith

    2010-10-01

    We investigated molecular motions on a picosecond timescale of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) model membranes as a function of hydration by using elastic and quasielastic neutron scattering. Two different hydrations corresponding to approximately nine and twelve water molecules per lipid were studied, the latter being the fully hydrated state. In our study, we focused on head group motions by using chain deuterated lipids. Information on in-plane and out-of-plane motions could be extracted by using solid supported DMPC multilayers. Our studies confirm and complete former investigations by König et al. [J. Phys. II (France) 2, 1589 (1992)] and Rheinstädter et al. [Phys. Rev. Lett. 101, 248106 (2008)] who described the dynamics of lipid membranes, but did not explore the influence of hydration on the head group dynamics as presented here. From the elastic data, a clear shift of the main phase transition from the Pβ ripple phase to the Lα liquid phase was observed. Decreasing water content moves the transition temperature to higher temperatures. The quasielastic data permit a closer investigation of the different types of head group motion of the two samples. Two different models are needed to fit the elastic incoherent structure factor and corresponding radii were calculated. The presented data show the strong influence hydration has on the head group mobility of DMPC.

  3. Hydration dependent studies of highly aligned multilayer lipid membranes by neutron scattering.

    PubMed

    Trapp, Marcus; Gutberlet, Thomas; Juranyi, Fanni; Unruh, Tobias; Demé, Bruno; Tehei, Moeava; Peters, Judith

    2010-10-28

    We investigated molecular motions on a picosecond timescale of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) model membranes as a function of hydration by using elastic and quasielastic neutron scattering. Two different hydrations corresponding to approximately nine and twelve water molecules per lipid were studied, the latter being the fully hydrated state. In our study, we focused on head group motions by using chain deuterated lipids. Information on in-plane and out-of-plane motions could be extracted by using solid supported DMPC multilayers. Our studies confirm and complete former investigations by König et al. [J. Phys. II (France) 2, 1589 (1992)] and Rheinstädter et al. [Phys. Rev. Lett. 101, 248106 (2008)] who described the dynamics of lipid membranes, but did not explore the influence of hydration on the head group dynamics as presented here. From the elastic data, a clear shift of the main phase transition from the P(β) ripple phase to the L(α) liquid phase was observed. Decreasing water content moves the transition temperature to higher temperatures. The quasielastic data permit a closer investigation of the different types of head group motion of the two samples. Two different models are needed to fit the elastic incoherent structure factor and corresponding radii were calculated. The presented data show the strong influence hydration has on the head group mobility of DMPC.

  4. Three-dimensional structure of ionospheric currents produced by field-aligned currents

    NASA Astrophysics Data System (ADS)

    Takeda, M.

    1982-08-01

    Ionospheric currents caused by field-aligned currents are calculated three-dimensionally under quiet conditions at the equinox, using a magnetic field line coordinate system and with the assumption of infinite parallel conductivity. Input field-aligned currents are assumed to be distributed only in the daytime and the whole system is assumed to be symmetric about the equator. Calculated currents are comparable with those of the ionospheric dynamo in higher latitudes, but much weaker in lower latitudes including the equatorial electrojet region. Hence, if the model is valid these currents may have a considerable effect on the day-to-day variation of Sq currents in higher latitudes, but little effect on those in lower latitudes such as the counter-electrojet.

  5. Improving nanowire sensing capability by electrical field alignment of surface probing molecules.

    PubMed

    Chu, Chia-Jung; Yeh, Chia-Sen; Liao, Chun-Kai; Tsai, Li-Chu; Huang, Chun-Ming; Lin, Hung-Yi; Shyue, Jing-Jong; Chen, Yit-Tsong; Chen, Chii-Dong

    2013-06-12

    We argue that the structure ordering of self-assembled probing molecular monolayers is essential for the reliability and sensitivity of nanowire-based field-effect sensors because it can promote the efficiency for molecular interactions as well as strengthen the molecular dipole field experienced by the nanowires. In the case of monolayers, we showed that structure ordering could be improved by means of electrical field alignment. This technique was then employed to align multilayer complexes for nanowire sensing applications. The sensitivity we achieved for detection of hybridization between 15-base single-strand DNA molecules is 0.1 fM and for alcohol sensors is 0.5 ppm. The reliability was confirmed by repeated tests on chips that contain multiple nanowire sensors.

  6. Alignment and measurement of the magnetic field for the BESIII muon counter

    NASA Astrophysics Data System (ADS)

    Gao, Qing; Zhang, Jing-Zhi; Li, Chun-Hua; Yin, Jun-Hao

    2016-11-01

    Based on cosmic ray events without a magnetic field taken with the BESIII detector during the summer shutdown of BEPCII in 2012 and di-muon events from a data sample taken at center-of-mass energy of 3.686 GeV in 2009, we compare the coordinates of hits registered in the BESIII muon counter with the expected interaction point extrapolated from reconstructed tracks from the inner tracking system in the absence of a magnetic field. By minimizing the difference, we align the muon counter with the inner tracking system. Moreover, the strength of the magnetic field in the muon counter is measured for the first time with di-muon events from data taken at a center-of-mass energy of 3.686 GeV. After the alignment and the magnetic field strength measurement, the offsets in the reconstructed hit positions for muon tracks are reduced, which improves the muon identification. The alignment and magnetic field strength measurement have been adopted in the latest version of the BESIII offline software system. This addition to the software reduces the systematic uncertainty for the physics analysis in cases where the muon counter information is used. Supported by National Key Basic Research Program of China (2015CB856701), National Natural Science Foundation of China (NSFC) (11475187, 11575198, 11521505), 100 Talents Program of CAS (U-25)

  7. Magnetospheric Multiscale Observations of Field-aligned Currents at the Magnetopause

    NASA Astrophysics Data System (ADS)

    Strangeway, R. J.; Russell, C. T.; Zhao, C.; Magnes, W.; Bromund, K. R.; Plaschke, F.; Fischer, D.; Anderson, B. J.; Le, G.; Chutter, M.; Slavin, J. A.; Nakamura, R.; Baumjohann, W.; Paterson, W. R.; Torbert, R. B.; Burch, J. L.

    2016-12-01

    Magnetospheric Multiscale (MMS) has demonstrated that the dayside magnetopause is usually highly structured, with multiple layers. Within these layers currents are observed to be flowing both parallel and perpendicular to the magnetic field. The parallel currents primarily act to bend or shear the magnetic field, while the perpendicular currents mainly change the field strength. We note that within the magnetopause MMS observes current densities that can be of the order of 100s of nAm-2. If these currents were to map to the ionosphere, then they would correspond to field-aligned current densities of the order of 100s of μAm-2, orders of magnitude larger than the observed low altitude field-aligned currents. A survey of several magnetopause crossings shows that the field-aligned currents on the magnetosphere side of the current layers can be flowing either parallel or anti-parallel to the magnetic field. On the magnetospheric side of the magnetopause current layers the plasma flows are generally in the -z direction (in GSM coordinates) for the events studied, suggesting that the observations are to the south of the reconnection site. If the currents were to correspond to Region-1 sense currents flowing into and out of the southern ionosphere, then the polarity of the currents would be ordered by local time, flowing parallel to the local magnetic field on the dusk-side of noon, and anti-parallel on the dawn-side of noon. But the current signatures are mixed, and sometimes the field-aligned currents reverse polarity within one crossing of the magnetopause. The issue is therefore how do we reconcile the local magnetopause field-aligned current signatures with what would be expected for the large-scale Region-1 currents that are typically associated with flow shears introduced through reconnection? Given the strength of the currents and their structure much of the current may be closed locally, with only a residual contributing to the large-scale currents.

  8. Correlation between magnetic and electric field perturbations in the field-aligned current regions deduced from DE 2 observations

    NASA Technical Reports Server (NTRS)

    Ishii, M.; Sugiura, M.; Iyemori, T.; Slavin, J. A.

    1992-01-01

    The satellite-observed high correlations between magnetic and electric field perturbations in the high-latitude field-aligned current regions are investigated by examining the dependence of the relationship between Delta-B and E on spatial scale, using the electric and magnetic field data obtained by DE 2 in the polar regions. The results are compared with the Pedersen conductivity inferred from the international reference ionosphere model and the Alfven wave velocity calculated from the in situ ion density and magnetic field measurements.

  9. Application of relativistic mean field and effective field theory densities to scattering observables for Ca isotopes

    SciTech Connect

    Bhuyan, M.; Panda, R. N.; Routray, T. R.; Patra, S. K.

    2010-12-15

    In the framework of relativistic mean field (RMF) theory, we have calculated the density distribution of protons and neutrons for {sup 40,42,44,48}Ca with NL3 and G2 parameter sets. The microscopic proton-nucleus optical potentials for p+{sup 40,42,44,48}Ca systems are evaluated from the Dirac nucleon-nucleon scattering amplitude and the density of the target nucleus using relativistic-Love-Franey and McNeil-Ray-Wallace parametrizations. We have estimated the scattering observables, such as the elastic differential scattering cross section, analyzing power and the spin observables with the relativistic impulse approximation (RIA). The results have been compared with the experimental data for a few selective cases and we find that the use of density as well as the scattering matrix parametrizations are crucial for the theoretical prediction.

  10. Microphase Separation and Shear Alignment of Gradient Copolymers: Melt Rheology and Small-Angle X-Ray Scattering Analysis

    SciTech Connect

    Mok, Michelle M.; Pujari, Saswati; Burghardt, Wesley R.; Dettmer, Christine M.; Nguyen, SonBinh T.; Ellison, Christopher J.; Torkelson, John M.

    2008-10-24

    The degree of microphase or nanophase segregation in gradient copolymers with compositions varying across the whole copolymer backbone is studied via low-amplitude oscillatory shear (LAOS) measurements and small-angle X-ray scattering (SAXS). Studies are done as a function of comonomer segregation strength, molecular weight (MW), gradient architecture and temperature. Controlled radical polymerization is used to synthesize strongly segregating styrene/4-acetoxystyrene (S/AS) and the more weakly segregating S/n-butyl acrylate (S/nBA) gradient copolymers. Results are compared to those from S/AS and S/nBA random and block copolymers. The higher MW S/AS gradient copolymer exhibits LAOS behavior similar to the highly microphase segregated S/AS block copolymer, while the lower MW S/AS gradient copolymer exhibits complex, nonterminal behavior indicative of a lower degree of microphase segregation. The S/nBA gradient copolymers demonstrate more liquidlike behavior, with the lower MW sample exhibiting near-Newtonian behavior, indicative of a weakly segregating structure, while the higher MW, steeper gradient sample shows behavior ranging from solidlike to more liquidlike with increasing temperature. With the exception of the lower MW S/nBA case, the gradient copolymers exhibit temperature-dependent LAOS behavior over a wide temperature range, reflecting their temperature-dependent nanodomain composition amplitudes. The S/AS samples have SAXS results consistent with the degree of microphase segregation observed via rheology. Shear alignment studies are done on the higher MW S/AS gradient copolymer, which is the most highly microphase segregated gradient copolymer. Rheology and SAXS provide evidence of shear alignment, despite the gradual variation in composition profile across the nanodomains of such gradient copolymers. A short review of the nomenclature and behavior of linear copolymer architectures is also provided.

  11. Effective Field Theories from Soft Limits of Scattering Amplitudes.

    PubMed

    Cheung, Clifford; Kampf, Karol; Novotny, Jiri; Trnka, Jaroslav

    2015-06-05

    We derive scalar effective field theories-Lagrangians, symmetries, and all-from on-shell scattering amplitudes constructed purely from Lorentz invariance, factorization, a fixed power counting order in derivatives, and a fixed order at which amplitudes vanish in the soft limit. These constraints leave free parameters in the amplitude which are the coupling constants of well-known theories: Nambu-Goldstone bosons, Dirac-Born-Infeld scalars, and Galilean internal shift symmetries. Moreover, soft limits imply conditions on the Noether current which can then be inverted to derive Lagrangians for each theory. We propose a natural classification of all scalar effective field theories according to two numbers which encode the derivative power counting and soft behavior of the corresponding amplitudes. In those cases where there is no consistent amplitude, the corresponding theory does not exist.

  12. Magnetic field aligned assembly of nonmagnetic composite dumbbells in nanoparticle-based aqueous ferrofluid.

    PubMed

    Takahashi, Hayato; Nagao, Daisuke; Watanabe, Kanako; Ishii, Haruyuki; Konno, Mikio

    2015-05-26

    Monodisperse, nonmagnetic, asymmetrical composite dumbbells in a suspension of magnetic nanoparticles (ferrofluid) were aligned by application of an external magnetic field to the ferrofluid. The asymmetrical composite dumbbells were prepared by two-step soap-free emulsion polymerization consisting of the first polymerization to coat spherical silica cores with cross-linked poly(methyl methacrylate) (PMMA) shell and the second polymerization to protrude a polystyrene (PSt) lobe from the core-shell particles. A chain structure of nonmagnetic dumbbells oriented to the applied magnetic field was observed at nanoparticle content of 2.0 vol % and field strengths higher than 1.0 mT. A similar chain structure of the dumbbells was observed under application of alternating electric field at strengths higher than 50 V/mm. Parallel and orthogonally combined applications of the electric and magnetic fields were also conducted to examine independence of the electric and magnetic applications as operational factors in the dumbbell assembling. Dumbbell chains stiffer than those in a single application of external field were formed in the parallel combined application of electric and magnetic fields. The orthogonal combination of the different applied fields could form a magnetically aligned chain structure of the nonmagnetic dumbbells oriented to the electric field. The present work experimentally indicated that the employment of inverse magnetorheological effect for nonmagnetic, anisotropic particles can be a useful method for the simultaneous controls over the orientation and the positon of anisotropic particles in their assembling.

  13. Positioning and aligning CNTs by external magnetic field to assist localised epoxy cure

    NASA Astrophysics Data System (ADS)

    Ariu, G.; Hamerton, I.; Ivanov, D.

    2016-01-01

    This work focuses on the generation of conductive networks through the localised alignment of nano fillers, such as multi-walled carbon nanotubes (MWCNTs). The feasibility of alignment and positioning of functionalised MWCNTs by external DC magnetic fields was investigated. The aim of this manipulation is to enhance resin curing through AC induction heating due to hysteresis losses from the nanotubes. Experimental analyses focused on in-depth assessment of the nanotube functionalisation, processing and characterisation of magnetic, rheological and cure kinetics properties of the MWCNT solution. The study has shown that an external magnetic field has great potential for positioning and alignment of CNTs. The study demonstrated potential for creating well-ordered architectures with an unprecedented level of control of network geometry. Magnetic characterisation indicated cobalt-plated nanotubes to be the most suitable candidate for magnetic alignment due to their high magnetic sensitivity. Epoxy/metal-plated CNT nanocomposite systems were validated by thermal analysis as induction heating mediums. The curing process could therefore be optimised by the use of dielectric resins. This study offers a first step towards the proof of concept of this technique as a novel repair technology.

  14. Renormalized theory of ion temperature gradient instability of the magnetic-field-aligned plasma shear flow with hot ions

    SciTech Connect

    Mikhailenko, V. V. Mikhailenko, V. S.; Lee, Hae June

    2015-10-15

    The developed kinetic theory for the stability of a magnetic-field-aligned (parallel) shear flow with inhomogeneous ion temperature [Mikhailenko et al., Phys. Plasmas 21, 072117 (2014)] predicted that a kinetic instability arises from the coupled reinforcing action of the flow velocity shear and ion temperature gradient in the cases where comparable ion and electron temperatures exist. In the present paper, the nonlinear theory was developed for the instability caused by the combined effects of ion-temperature-gradient and shear-flow (ITG–SF). The level of the electrostatic turbulence is determined for the saturation state of the instability on the basis of the nonlinear dispersion equation, which accounts for a nonlinear scattering of ions by the developed turbulence in a sheared flow. The renormalized quasilinear equation for the ion distribution function, which accounts for the turbulent scattering of ions by ITG–SF driven turbulence, was derived and employed for the estimation of the turbulent ion viscosity, the anomalous ion thermal conductivity, and anomalous ion heating rate at the saturation state of the instability.

  15. Alignment method for fabricating a parallel flat-field grating used in soft x-ray region.

    PubMed

    Wang, Qingbo; Liu, Zhengkun; Zheng, Yanchang; Chen, Huoyao; Wang, Yu; Liu, Ying; Hong, Yilin

    2015-06-20

    Parallel flat-field gratings consist of two flat-field gratings lying on one substrate, one for 5-20 nm and the other for 2-5 nm spectral regions, and thus can be widely used in various fields to record broader spectra in the soft x-ray region. The alignment of two subgratings directly determines the resolving power of parallel flat-field gratings. The theoretical resolving power is evaluated by means of the ray-tracing method and the maximal allowable alignment error is 0.366°. Alignment is based on diffraction patterns and moiré fringes and the total alignment error in our experiment is within 0.234°. The results demonstrate that this alignment method is an effective way for fabricating parallel flat-field gratings.

  16. The inhomogeneous ion temperature anisotropy instabilities of magnetic-field-aligned plasma sheared flow

    NASA Astrophysics Data System (ADS)

    Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June

    2016-11-01

    The stability of the magnetic field aligned sheared flow with anisotropic ion temperatures, which have the anisotropic spatial inhomogeneities across the magnetic field and are comparable with or are above the electron temperature, is investigated numerically and analytically. The ion temperatures gradients across the magnetic field affect the instability development only when the inhomogeneous is the ion temperature along the magnetic field irrespective the inhomogeneity of the ion temperature across the magnetic field. In this case, the instability is developed due to the combined effect of the ion Landau damping, velocity shear, ion temperature anisotropy, and anisotropy of the ion temperature gradients. In the case when the ion temperature along the magnetic field is homogeneous, but the ion temperature across the magnetic field is inhomogeneous, the short wavelength instability develops with the wave length less than the thermal ion Larmor radius. This instability excites due to the coupled effect of the ion Landau damping, velocity shear and ion temperature anisotropy.

  17. New 0.54 aperture i-line wafer stepper with field-by-field leveling combined with global alignment

    NASA Astrophysics Data System (ADS)

    van den Brink, Martin A.; Katz, Barton A.; Wittekoek, Stefan

    1991-07-01

    i-line wafer steppers are evolving as established production tools, and it is evident that they will be used to realize features in the sub-half-micron region. Consequently, i-line steppers can be expected to be the equipment of choice for volume production of 16 MBit DRAMs and possibly the first generation of 64 Mbit devices, before the introduction of DUV lithography. However, for this sub-half-micron resolution, lenses with higher apertures and large field sizes will be required. In this paper a new family of wafer steppers is introduced, with a new mechanical frame design and modular architecture which can accommodate a family of large field i-line and deep UV lenses. Results from the first lens type with NAequals0.54 and a field diameter of 25.5 mm are described. To overcome the anticipated depth of focus problems on production wafers, a field-by-field leveling system is introduced, ensuring optimum focus over the whole image field. A challenging problem of wafer steppers using this option is the alignment accuracy during stepping of stage and active leveling of the wafer chuck. The stepper concept introduced here is able to realize the field-by-field leveling without the need for the throughput consuming field-by-field alignment. For that purpose a wafer stage with a new metrology system and improved accuracy has been designed, resulting in an overlay accuracy better than 85 nm in the global alignment mode. Simultaneously a throughput of more than 80 150 mm wafers per hour is realized. Along with the new lens and metrology concept, the stepper contains local environmental control systems performing better than class 1, to ensure clean handling of 8-inch wafers without the need for space consuming environmental enclosures. This paper reports practical results from the new stepper, including resist features below 0.4 micrometers , overlay measurements, particle control, as well as a general description of the new stepper architecture.

  18. Field-aligned currents observed by the OGO 5 and Triad satellites

    NASA Technical Reports Server (NTRS)

    Sugiura, M.

    1975-01-01

    The existence of field-aligned currents in the polar cap boundary layer as a permanent feature of the magnetosphere is investigated. Magnetic field observations from Triad at 800 km altitude and from OGO 5 in the high-altitude magnetosphere are examined. Results indicate that in the morning half of the boundary layer, currents flow into the ionosphere, and that the current direction is reversed in the afternoon half of the layer. The Triad data further indicate that the net current is a maximum near 1500 MLT and that there may be a secondary maximum during early morning hours. According to the Isis 2 electron observations, the locations of these maximums of field-aligned net current roughly match those of two maximums in the isointensity contours for 150 ev electrons. It is proposed that the polar cap boundary current is driven by a current generator in the magnetotail, or ultimately in the solar wind. It is suggested that the large scale field-aligned currents in the polar cap boundary layer are associated with the dominance of protons on the morning side and of electrons on the afternoon side near the poleward edge of the precipitation zone along the auroral oval.

  19. Short-term magnetic field alignment variations of equatorial ionospheric irregularities

    SciTech Connect

    Johnson, A.L.

    1988-06-01

    The ionospheric irregularities that cause equatorial scintillation are elongated along the north-south magnetic field lines. During a 1981 field campaign at Ascension Island, 250-MHz receivers were spaced from 300 m to 1.6 km along the field lines, and the signals received from the Marisat satellite were cross correlated. Data collected during eight nights of fading showed a linear relationship between fading rate and cross correlation. The alignment of the antennas was adjusted to give a zero time lag between the widely spaced receivers with a measurement accuracy of 0.03 s. Since the average irregularity velocity was 125 m/s, this time accuracy translated to an angular measurement accuracy of 0.1 deg. During a 4-hour period of nightly fading, occasional differences in time of arrival were noted that corresponded to a tilt in the north-south alignment of + or - 1 deg. Data from several nights of fading were analyzed, and each night exhibited the same variance in the north-south irregularity alignment. It is postulated that the shift in the measured peak correlation may have been caused by patches of irregularities at different altitudes where the magnetic field lines have a slightly different direction. 13 references.

  20. High-latitude convection patterns for various large-scale field-aligned current configurations

    SciTech Connect

    Blomberg, L.G.; Marklund, G.T. )

    1991-04-01

    The large-scale field-aligned current system for persistent northward interplanetary magnetic field (IMF) is typically different from that for persistent southward IMF. One characteristic difference is that for northward IMF there is often a large-scale field-aligned current system poleward of the main auroral oval. This current system (the NBZ current) typically occupies a large function of the region poleward of the region 1 and 2 currents. The present paper models the high-latitude convection as a function of the large-scale field-aligned currents. In particular, a possible evolution of the convection pattern as the current system changes from a typical configuration for southward IMF to a configuration representing northward IMF (or vice versa) is presented. Depending on additional assumptions, for example about the y-component of the IMF, the convection pattern could either turn directly from a two-cell type to a four-cell type, or a three-cell type pattern could show up as an intermediate state. An interesting although rather surprising result of this study is that different ways of balancing the NBZ currents has a minor influence on the large-scale convection pattern.

  1. Electric Field Effects on Fiber Alignment Using an Auxiliary Electrode during Electrospinning

    NASA Technical Reports Server (NTRS)

    Carnell, Lisa S.; Wincheski, Russell A.; Siochi, Emilie, J.; Holloway, Nancy M.; Clark, Robert L.

    2007-01-01

    This viewgraph presentation reviews auxiliary and electric field effects on fiber alignment during the process of electrospinning. The contents include: 1) Electrospinning Overview; 2) Experimental Set-up; 3) Jet Exit; 4) Auxiliary Electrode Effects; 5) Electrospinning High Speed Video; 6) Effect of Auxiliary Electrode Position; 7) Micro & Nano Fibers Produced; 8) Micro and Nano Fibrous Mats; 9) Field Effect on Fiber Distribution; 10) Modeling; 11) Calculated trajectories: 5, 10, 15 & 20cm electrode spacing; 12) Off Axis Auxiliary Electrode; 13) Field Strength Effects; and 14) Potential Applications.

  2. Effect of Interhemispheric Field-Aligned Currents on Region-1 Currents

    NASA Technical Reports Server (NTRS)

    Lyatsky, Sonya; Lyatsky, Wladislaw; Khazanov, George V.

    2015-01-01

    An asymmetry in ionospheric conductivity between two hemispheres results in the formation of additional, interhemispheric field-aligned currents flowing between conjugate ionospheres within two auroral zones. These interhemispheric currents are especially significant during summer-winter conditions when there is a significant asymmetry in ionospheric conductivity in two hemispheres. In such conditions, these currents may be comparable in magnitude with the Region 1 field-aligned currents. In this case, the R1 current is the sum of two FACs: one is going from to the solar wind, and another is flowing between conjugate ionospheres. These interhemispheric currents can also cause the formation of auroras extended along the nightside polar cap boundary, which may be related to the so-called double auroral oval. In this study, we present the results of analytical and numerical solutions for the interhemispheric currents and their effect on the Region 1 currents.

  3. Coherent anti-Stokes Raman scattering under electric field stimulation

    NASA Astrophysics Data System (ADS)

    Capitaine, Erwan; Ould Moussa, Nawel; Louot, Christophe; Lefort, Claire; Pagnoux, Dominique; Duclère, Jean-René; Kaneyasu, Junya F.; Kano, Hideaki; Duponchel, Ludovic; Couderc, Vincent; Leproux, Philippe

    2016-12-01

    We introduce an experiment using electro-CARS, an electro-optical method based on the combination of ultrabroadband multiplex coherent anti-Stokes Raman scattering (M-CARS) spectroscopy and electric field stimulation. We demonstrate that this method can effectively discriminate the resonant CARS signal from the nonresonant background owing to a phenomenon of molecular orientation in the sample medium. Such molecular orientation is intrinsically related to the induction of an electric dipole moment by the applied static electric field. Evidence of the electro-CARS effect is obtained with a solution of n -alkanes (CnH2 n +2 , 15 ≤n ≤40 ), for which an enhancement of the CARS signal-to-noise ratio is achieved in the case of CH2 and CH3 symmetric/asymmetric stretching vibrations. Additionally, an electric-field-induced second-harmonic generation experiment is performed in order to corroborate the orientational organization of molecules due to the electric field excitation. Finally, we use a simple mathematical approach to compare the vibrational information extracted from electro-CARS measurements with spontaneous Raman data and to highlight the impact of electric stimulation on the vibrational signal.

  4. Stimulated Brillouin scattering in the field of a two-dimensionally localized pumping wave

    SciTech Connect

    Solikhov, D. K.; Dvinin, S. A.

    2016-06-15

    Stimulated Brillouin scattering of electromagnetic waves in the field of a two-dimensionally localized pump wave at arbitrary scattering angles in the regime of forward scattering is analyzed. Spatial variations in the amplitudes of interacting waves are studied for different values of the pump field and different dimensions of the pump wave localization region. The intensity of scattered radiation is determined as a function of the scattering angle and the dimensions of the pump wave localization region. It is shown that the intensity increases with increasing scattering angle.

  5. Stimulated Brillouin scattering in the field of a two-dimensionally localized pumping wave

    NASA Astrophysics Data System (ADS)

    Solikhov, D. K.; Dvinin, S. A.

    2016-06-01

    Stimulated Brillouin scattering of electromagnetic waves in the field of a two-dimensionally localized pump wave at arbitrary scattering angles in the regime of forward scattering is analyzed. Spatial variations in the amplitudes of interacting waves are studied for different values of the pump field and different dimensions of the pump wave localization region. The intensity of scattered radiation is determined as a function of the scattering angle and the dimensions of the pump wave localization region. It is shown that the intensity increases with increasing scattering angle.

  6. Filamentary field-aligned currents at the polar cap region during northward interplanetary magnetic field derived with the Swarm constellation

    NASA Astrophysics Data System (ADS)

    Lühr, Hermann; Huang, Tao; Wing, Simon; Kervalishvili, Guram; Rauberg, Jan; Korth, Haje

    2016-10-01

    ESA's Swarm constellation mission makes it possible for the first time to determine field-aligned currents (FACs) in the ionosphere uniquely. In particular at high latitudes, the dual-satellite approach can reliably detect some FAC structures which are missed by the traditional single-satellite technique. These FAC events occur preferentially poleward of the auroral oval and during times of northward interplanetary magnetic field (IMF) orientation. Most events appear on the nightside. They are not related to the typical FAC structures poleward of the cusp, commonly termed NBZ. Simultaneously observed precipitating particle spectrograms and auroral images from Defense Meteorological Satellite Program (DMSP) satellites are consistent with the detected FACs and indicate that they occur on closed field lines mostly adjacent to the auroral oval. We suggest that the FACs are associated with Sun-aligned filamentary auroral arcs. Here we introduce in an initial study features of the high-latitude FAC structures which have been observed during the early phase of the Swarm mission. A more systematic survey over longer times is required to fully characterize the so far undetected field aligned currents.

  7. Design and fabrication of advanced fiber alignment structures for field-installable fiber connectors

    NASA Astrophysics Data System (ADS)

    Van Erps, Jürgen; Vervaeke, Michael; Sánchez Martínez, Alberto; Beri, Stefano; Debaes, Christof; Watté, Jan; Thienpont, Hugo

    2012-06-01

    Fiber-To-The-Home (FTTH) networks have been adopted as a potential replacement of traditional electrical connections for the 'last mile' transmission of information at bandwidths over 1Gb/s. However, the success and adoption of optical access networks critically depend on the quality and reliability of connections between optical fibers. In particular a further reduction of insertion loss of field-installable connectors must be achieved without a significant increase in component cost. This requires precise alignment of fibers that can differ in terms of ellipticity, eccentricity or diameter and seems hardly achievable using today's widespread ferrule-based alignment systems. Novel low-cost structures for bare fiber alignment with outstanding positioning accuracies are strongly desired as they would allow reducing loss beyond the level achievable with ferrule-bore systems. However, the realization of such alignment system is challenging as it should provide sufficient force to position the fiber with sub-micron accuracy required in positioning the fiber. In this contribution we propose, design and prototype a bare-fiber alignment system which makes use of deflectable/compressible micro-cantilevers. Such cantilevers behave as springs and provide self-centering functionality to the structure. Simulations of the mechanical properties of the cantilevers are carried out in order to get an analytical approximation and a mathematical model of the spring constant and stress in the structure. Elastic constants of the order of 104 to 105N/m are found out to be compatible with a proof stress of 70 MPa. Finally a first self-centering structure is prototyped in PMMA using our Deep Proton Writing technology. The spring constants of the fabricated cantilevers are in the range of 4 to 6 × 104N/m and the stress is in the range 10 to 20 MPa. These self-centering structures have the potential to become the basic building blocks for a new generation of field-installable connectors.

  8. A novel flexible field-aligned coordinate system for tokamak edge plasma simulation

    NASA Astrophysics Data System (ADS)

    Leddy, J.; Dudson, B.; Romanelli, M.; Shanahan, B.; Walkden, N.

    2017-03-01

    Tokamak plasmas are confined by a magnetic field that limits the particle and heat transport perpendicular to the field. Parallel to the field the ionised particles can move freely, so to obtain confinement the field lines are ;closed; (i.e. form closed surfaces of constant poloidal flux) in the core of a tokamak. Towards, the edge, however, the field lines intersect physical surfaces, leading to interaction between neutral and ionised particles, and the potential melting of the material surface. Simulation of this interaction is important for predicting the performance and lifetime of future tokamak devices such as ITER. Field-aligned coordinates are commonly used in the simulation of tokamak plasmas due to the geometry and magnetic topology of the system. However, these coordinates are limited in the geometry they allow in the poloidal plane due to orthogonality requirements. A novel 3D coordinate system is proposed herein that relaxes this constraint so that any arbitrary, smoothly varying geometry can be matched in the poloidal plane while maintaining a field-aligned coordinate. This system is implemented in BOUT++ and tested for accuracy using the method of manufactured solutions. A MAST edge cross-section is simulated using a fluid plasma model and the results show expected behaviour for density, temperature, and velocity. Finally, simulations of an isolated divertor leg are conducted with and without neutrals to demonstrate the ion-neutral interaction near the divertor plate and the corresponding beneficial decrease in plasma temperature.

  9. Preparation and properties of alumina composites modified by electric field-induced alignment of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zhu, Yue-Feng; Shi, Lei; Zhang, Chan; Yang, Xi-Zhi; Liang, Ji

    2007-11-01

    Catalytic chemical vapor deposition (CVD) grown multi-walled carbon nanotubes (MWNTs) are treated with HF and deionized water and are then placed into alumina ceramics for improvement of both electrical conductivity and mechanical properties. In particular, an alternating current (ac) electric field is applied during the coagulation of the alumina slurries to induce the formation of aligned MWNT networks in the alumina matrix. The coagulated alumina matrix composite bases filled with 2 wt. % ac electric field-induced aligned MWNTs, are then sintered by hot pressing. The electrical conductivities of the prepared composites in directions both parallel and perpendicular to the MWNTs alignment, reach values of 6.2×10-2 S m-1 and 6.8×10-9 S m-1, respectively, compared with that of 4.5×10-15 S m-1 for pristine alumina ceramics. The fracture toughness and flexing strengths of the prepared composites in the two directions are 4.66±0.66 MPa m0.5, 390±70 MPa, and 3.65±0.46 MPa m0.5, 191±5 MPa, respectively, compared with 3.78±0.66 MPa m0.5 and 302±50 MPa for pristine alumina, 4.09±0.15 MPa m0.5 and 334±60 MPa for alumina filled with 2 wt. % MWNTs prepared without the effect of an electric field, respectively. The results indicate that the electric field leads to anisotropic behaviour. The properties of the composites along the direction of the MWNTs alignment are much improved with the addition of a small amount of CVD grown MWNTs.

  10. Reciprocity principle for scattered fields from discontinuities in waveguides.

    PubMed

    Pau, Annamaria; Capecchi, Danilo; Vestroni, Fabrizio

    2015-01-01

    This study investigates the scattering of guided waves from a discontinuity exploiting the principle of reciprocity in elastodynamics, written in a form that applies to waveguides. The coefficients of reflection and transmission for an arbitrary mode can be derived as long as the principle of reciprocity is satisfied at the discontinuity. Two elastodynamic states are related by the reciprocity. One is the response of the waveguide in the presence of the discontinuity, with the scattered fields expressed as a superposition of wave modes. The other state is the response of the waveguide in the absence of the discontinuity oscillating according to an arbitrary mode. The semi-analytical finite element method is applied to derive the needed dispersion relation and wave mode shapes. An application to a solid cylinder with a symmetric double change of cross-section is presented. This model is assumed to be representative of a damaged rod. The coefficients of reflection and transmission of longitudinal waves are investigated for selected values of notch length and varying depth. Copyright © 2014 Elsevier B.V. All rights reserved.

  11. An MHD simulation of By-dependent magnetospheric convection and field-aligned currents during northward IMF

    NASA Technical Reports Server (NTRS)

    Ogino, T.; Walker, R. J.; Ashour-Abdalla, M.; Dawson, J. M.

    1985-01-01

    A three-dimensional MHD simulation code is used to model the magnetospheric configuration when the IMF has both a northward B(z) component and a B(y) component in the east-west direction. Projections of the plasma pressure, the field-aligned velocity, the field-aligned vorticity, and the field-aligned current along the magnetic field lines into the northern ionosphere are shown and discussed. Cross-sectional patterns of these parameters are shown. The results demonstrate that the B(y) component of the IMF strongly influences the plasma sheet configuration and the magnetospheric convection pattern.

  12. Field-aligned electron density irregularities near 500 km Equator to polar cap topside sounder observations

    SciTech Connect

    Benson, R.F.

    1985-06-01

    In addition to spread F, evidence for field-aligned electron density irregularities is commonly observed on Alouette 2 topside sounder ionograms recorded near perigee (500 km). This evidence is provided by distinctive signal returns from sounder-generated Z mode waves. At low latitudes these waves become guided in wave ducts caused by field-aligned electron density irregularities and give rise to strong long-duration echoes. At high latitudes, extending well into the polar cap, these Z mode waves (and stimulated electrostatic waves at the plasma frequency) produce a series of vertical bars on the ionogram display as the satellite traverses discrete field-aligned density structures. The radio frequency (RF) noise environment to be expected in the 400 to 500 km altitude region from low to high latitudes was examined by analyzing perigee Alouette 2 topside sounder data. All observed noise bands were scaled on nearly 200 topside sounder ionograms recorded near perigee at low, mid, and high latitude telemetry stations. The minimum and maximum frequencies of each noise band were entered into a data base or computer analysis. The signals of primary interest in the perigee study were found to be sounder-generated. 15 references.

  13. Local and nonlocal strain rate fields and vorticity alignment in turbulent flows.

    PubMed

    Hamlington, Peter E; Schumacher, Jörg; Dahm, Werner J A

    2008-02-01

    Local and nonlocal contributions to the total strain rate tensor S(ij) at any point x in a flow are formulated from an expansion of the vorticity field in a local spherical neighborhood of radius R centered on x. The resulting exact expression allows the nonlocal (background) strain rate tensor S(ij)(B)(x) to be obtained from S(ij)(x). In turbulent flows, where the vorticity naturally concentrates into relatively compact structures, this allows the local alignment of vorticity with the most extensional principal axis of the background strain rate tensor to be evaluated. In the vicinity of any vortical structure, the required radius R and corresponding order n to which the expansion must be carried are determined by the viscous length scale lambda(nu). We demonstrate the convergence to the background strain rate field with increasing R and n for an equilibrium Burgers vortex, and show that this resolves the anomalous alignment of vorticity with the intermediate eigenvector of the total strain rate tensor. We then evaluate the background strain field S(ij)(B)(x) in direct numerical simulations of homogeneous isotropic turbulence where, even for the limited R and n corresponding to the truncated series expansion, the results show an increase in the expected equilibrium alignment of vorticity with the most extensional principal axis of the background strain rate tensor.

  14. FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

    NASA Technical Reports Server (NTRS)

    Schriver, D.; Ashour-Abdalla, M.; Strangeway, R. J.; Richard, R. L.; Klezting, C.; Dotan, Y.; Wygant, J.

    2002-01-01

    The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identity the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral SnapshoT (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data was used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and a long-system particle-in-cell simulation to model the magnetically connected region between the two satellites.

  15. Field-aligned electron density irregularities near 500 km Equator to polar cap topside sounder observations

    NASA Astrophysics Data System (ADS)

    Benson, R. F.

    1985-06-01

    In addition to spread F, evidence for field-aligned electron density irregularities is commonly observed on Alouette 2 topside sounder ionograms recorded near perigee (500 km). This evidence is provided by distinctive signal returns from sounder-generated Z mode waves. At low latitudes these waves become guided in wave ducts caused by field-aligned electron density irregularities and give rise to strong long-duration echoes. At high latitudes, extending well into the polar cap, these Z mode waves (and stimulated electrostatic waves at the plasma frequency) produce a series of vertical bars on the ionogram display as the satellite traverses discrete field-aligned density structures. The radio frequency (RF) noise environment to be expected in the 400 to 500 km altitude region from low to high latitudes was examined by analyzing perigee Alouette 2 topside sounder data. All observed noise bands were scaled on nearly 200 topside sounder ionograms recorded near perigee at low, mid, and high latitude telemetry stations. The minimum and maximum frequencies of each noise band were entered into a data base or computer analysis. The signals of primary interest in the perigee study were found to be sounder-generated.

  16. Study on field-aligned electrons with Cluster observation in the Earth's cusp

    NASA Astrophysics Data System (ADS)

    Shi, Jiankui; Torkar, Klaus; Cheng, Zhengwei

    2017-04-01

    Cusp region is very important to the solar wind-magnetosphere coupling. The solar wind particles, through the cusp, can directly entry into the magnetosphere and ionosphere, and transport the mass, momentum and energy. The gyrating charged particles with field-aligned velocity are significant to perform the transportation. In this study, data from Cluster observation are used to study the characteristics of field-aligned electrons (FAE's) including the downward and the upward FAEs in the cusp. We select FAE event to do analysis. The durations of the FAE event covered a wide range from 6 to 475 seconds. The FAE's were found to occur very commonly in a circumpolar zone in the polar region and the MLT and ILAT distributions showed that most of the FAE events were observed around the cusp (70-80°ILAT, 0900-1500MLT). With the FAE flux the contribution of the electrons to the Field-Aligned Current (FAC) is estimated and the result shows that the FAE was the main carrier to the FAC in the cusp. The physical mechanisms of the FAE are analyzed, namely that the downward electrons were mainly from the solar wind and the upward electrons may originated from accelerated ionospheric up-flowing electrons or mirrored solar wind electrons. The energy transportation into the magnetosphere by the solar wind electrons through the cusp is also investigated.

  17. Morphologically Aligned Cation-Exchange Membranes by a Pulsed Electric Field for Reverse Electrodialysis.

    PubMed

    Lee, Ju-Young; Kim, Jae-Hun; Lee, Ju-Hyuk; Kim, Seok; Moon, Seung-Hyeon

    2015-07-21

    A low-resistance ion-exchange membrane is essential to achieve the high-performance energy conversion or storage systems. The formation methods for low-resistance membranes are various; one of the methods is the ion channel alignment of an ion-exchange membrane under a direct current (DC) electric field. In this study, we suggest a more effective alignment method than the process with the DC electric field. First, an ion-exchange membrane was prepared under a pulsed electric field [alternating current (AC) mode] to enhance the effectiveness of the alignment. The membrane properties and the performance in reverse electrodialysis (RED) were then examined to assess the membrane resistance and ion selectivity. The results show that the membrane electrical resistance (MER) had a lower value of 0.86 Ω cm(2) for the AC membrane than 2.13 Ω cm(2) observed for the DC membrane and 4.30 Ω cm(2) observed for the pristine membrane. Furthermore, RED achieved 1.34 W/m(2) of maximum power density for the AC membrane, whereas that for the DC membrane was found to be 1.14 W/m(2) [a RED stack assembled with CMX, used as a commercial cation-exchange membrane (CEM), showed 1.07 W/m(2)]. Thereby, the novel preparation process for a remarkable low-resistance membrane with high ion selectivity was demonstrated.

  18. Field-aligned electron density irregularities near 500 km Equator to polar cap topside sounder observations

    NASA Technical Reports Server (NTRS)

    Benson, R. F.

    1985-01-01

    In addition to spread F, evidence for field-aligned electron density irregularities is commonly observed on Alouette 2 topside sounder ionograms recorded near perigee (500 km). This evidence is provided by distinctive signal returns from sounder-generated Z mode waves. At low latitudes these waves become guided in wave ducts caused by field-aligned electron density irregularities and give rise to strong long-duration echoes. At high latitudes, extending well into the polar cap, these Z mode waves (and stimulated electrostatic waves at the plasma frequency) produce a series of vertical bars on the ionogram display as the satellite traverses discrete field-aligned density structures. The radio frequency (RF) noise environment to be expected in the 400 to 500 km altitude region from low to high latitudes was examined by analyzing perigee Alouette 2 topside sounder data. All observed noise bands were scaled on nearly 200 topside sounder ionograms recorded near perigee at low, mid, and high latitude telemetry stations. The minimum and maximum frequencies of each noise band were entered into a data base or computer analysis. The signals of primary interest in the perigee study were found to be sounder-generated.

  19. Dark matter effective field theory scattering in direct detection experiments

    SciTech Connect

    Schneck, K.; Cabrera, B.; Cerdeño, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, P.; Daal, M.; Di Stefano, P. C. F.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, J.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, P.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.

    2015-05-18

    We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.

  20. Dark matter effective field theory scattering in direct detection experiments

    DOE PAGES

    Schneck, K.

    2015-05-01

    We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implicationsmore » of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.« less

  1. Quantifying truncation errors in chiral effective field theory: NN scattering

    NASA Astrophysics Data System (ADS)

    Phillips, Daniel; Melendez, Jordan; Wesolowski, Sarah; Furnstahl, Richard; Klco, Natalie; Buqeye Collaboration

    2017-01-01

    Bayesian procedures designed to quantify truncation errors in perturbative calculations were recently adapted to expansions in effective field theory (EFT). By encoding expectations about the naturalness of EFT coefficients in Bayesian priors, this framework provides a statistical interpretation of the standard EFT procedure where truncation errors are estimated using the order-by-order convergence of the expansion. It also permits exploration of the ways in which such error bars are, and are not, sensitive to assumptions about EFT-coefficient naturalness. The procedure has been applied to chiral EFT calculations of neutron-proton scattering that use the semi-local potentials of Epelbaum, Krebs, and Meißner. This talk describes the Bayesian assignment of truncation errors for the total np cross section at a discrete set of energies, and then considers the extension to a full set of observables and arbitrary energy. This research was supported by the US Department of Energy and the National Science Foundation.

  2. An effective field theory for coupled-channel scattering

    NASA Astrophysics Data System (ADS)

    Cohen, Thomas D.; Gelman, Boris A.; van Kolck, U.

    2004-05-01

    The problem of describing low-energy two-body scattering for systems with two open channels with different thresholds is addressed in the context of an effective field theory. In particular, the problem where the threshold is unnaturally small and the cross section at low energy is unnaturally large is considered. It is shown that the lowest-order point coupling associated with the mixing of the channels scales as Λ-2 rather than Λ-1 (the scaling of the same-channel coupling and the scaling in a single-channel case) where Λ is the ultraviolet cutoff. The renormalization of the theory at lowest order is given explicitly. The treatment of higher orders is straightforward. The potential implications for systems with deep open channels are discussed.

  3. Dark matter effective field theory scattering in direct detection experiments

    SciTech Connect

    Schneck, K.; Cabrera, B.; Cerdeño, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, P.; Daal, M.; Di Stefano, P. C. F.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, J.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, P.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.

    2015-05-18

    We examine the consequences of the effective field theory (EFT) of dark matter-nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. Here. we demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. In conclusion, we discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.

  4. Dark matter effective field theory scattering in direct detection experiments

    SciTech Connect

    Schneck, K.

    2015-05-01

    We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.

  5. Electric field alignment of nanofibrillated cellulose (NFC) in silicone oil: impact on electrical properties.

    PubMed

    Kadimi, Amal; Benhamou, Karima; Ounaies, Zoubeida; Magnin, Albert; Dufresne, Alain; Kaddami, Hamid; Raihane, Mustapha

    2014-06-25

    This work aims to study how the magnitude, frequency, and duration of an AC electric field affect the orientation of two kinds of nanofibrillated cellulose (NFC) dispersed in silicone oil that differ by their surface charge density and aspect ratio. In both cases, the electric field alignment occurs in two steps: first, the NFC makes a gyratory motion oriented by the electric field; second, NFC interacts with itself to form chains parallel to the electric field lines. It was also observed that NFC chains become thicker and longer when the duration of application of the electric field is increased. In-situ dielectric properties have shown that the dielectric constant of the medium increases in comparison to the randomly dispersed NFC (when no electric field is applied). The optimal parameters of alignment were found to be 5000 Vpp/mm and 10 kHz for a duration of 20 min for both kinds of NFC. The highest increase in dielectric constant was achieved with NFC oxidized for 5 min (NFC-O-5 min) at the optimum conditions mentioned above.

  6. Saturn's auroral morphology and field-aligned currents during a solar wind compression

    NASA Astrophysics Data System (ADS)

    Badman, S. V.; Provan, G.; Bunce, E. J.; Mitchell, D. G.; Melin, H.; Nichols, J. D.; Jinks, S. L.; Cowley, S. W. H.; Stallard, T.; Radioti, A.; Pryor, W. R.; Kurth, W. S.; Brown, R. H.; Baines, K. H.; Dougherty, M. K.

    2014-04-01

    During the 2013 auroral observing campaign, instruments onboard Cassini and the Hubble Space Telescope observed Saturn's aurora while Cassini traversed the high latitude auroral field lines. Signatures of upward and downward field-aligned currents were detected on the nightside in the magnetic field and plasma measurements. The location of the upward current corresponded to the bright auroral arc seen in the auroral images, and the downward current region was located poleward of the upward current in an aurorally dark region. A solar wind compression region impacted Saturn's magnetosphere at the start of 2013-112 with the following sequence of effects: (1) intensification and extension to lower frequencies of the Saturn Kilometric Radiation; (2) intensification and spatial expansion of the auroral field-aligned current regions; (3) appearance of a localised, intense bulge in the dawnside aurora while the nightside aurora remained fainter and narrow; (4) latitudinal broadening and poleward contraction of the nightside aurora, where the poleward motion in this sector is opposite to that expected from a model of the auroral oval's usual oscillation. These observations are interpreted as the response to tail reconnection events, initially involving Vasyliunas-type reconnection of closed, mass-loaded magnetotail field lines, and then proceeding onto open lobe field lines, causing the contraction of the polar cap region.

  7. Scattering amplitudes over finite fields and multivariate functional reconstruction

    NASA Astrophysics Data System (ADS)

    Peraro, Tiziano

    2016-12-01

    Several problems in computer algebra can be efficiently solved by reducing them to calculations over finite fields. In this paper, we describe an algorithm for the reconstruction of multivariate polynomials and rational functions from their evaluation over finite fields. Calculations over finite fields can in turn be efficiently performed using machine-size integers in statically-typed languages. We then discuss the application of the algorithm to several techniques related to the computation of scattering amplitudes, such as the four- and six-dimensional spinor-helicity formalism, tree-level recursion relations, and multi-loop integrand reduction via generalized unitarity. The method has good efficiency and scales well with the number of variables and the complexity of the problem. As an example combining these techniques, we present the calculation of full analytic expressions for the two-loop five-point on-shell integrands of the maximal cuts of the planar penta-box and the non-planar double-pentagon topologies in Yang-Mills theory, for a complete set of independent helicity configurations.

  8. Comparison of auroral ionospheric and field-aligned currents derived from Swarm and ground magnetic field measurements

    NASA Astrophysics Data System (ADS)

    Juusola, L.; Kauristie, K.; Vanhamäki, H.; Aikio, A.; Kamp, M.

    2016-09-01

    Derivation of the auroral ionospheric currents from magnetic field measurements can produce drastically different results depending on the data and method used. We have cross tested several methods for obtaining instantaneous field-aligned and horizontal currents from Swarm satellite and International Monitor for Auroral Geomagnetic Effects (IMAGE) ground magnetic field measurements. We found that Swarm can yield latitude profiles of the east-west component of the divergence-free current density at most at ˜200 km resolution, typically resolving the electrojets. The north-south divergence-free component, on the other hand, is not always well reproduced due to the small longitudinal distance between the side-by-side flying satellite pair. Swarm can yield the field-aligned and curl-free current density at a wider range of latitude resolutions (˜7.5-200 km) than the divergence-free current density. While 7.5 km is suitable for comparison with auroras, 200 km typically resolves the Regions 1 and 2 field-aligned currents. IMAGE can yield maps of the divergence-free current density at ˜50 km resolution. Induced telluric currents should be accounted for in the derivation. Not accounting for them in the Swarm analysis, however, does not appear to introduce significant errors. Ionospheric conductances can be estimated by combining the total horizontal current density, consisting of the curl-free and divergence-free components, with the electric field measurements. Our results indicate that Swarm can only yield these at ˜200 km scale size when there is no significant dependence on longitude. However, combining the divergence-free current from IMAGE with the curl-free current and electric field from Swarm could yield conductance maps at ˜50 km resolution.

  9. Field-Aligned ICRF Antenna Characterization and Performance in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Wukitch, Stephen

    2012-10-01

    Impurity contamination associated with ion cyclotron range of frequency (ICRF) heating remains a major challenge to ICRF utilization in magnetic confinement devices, particularly with metallic plasma facing components. Here, we report results on an experimental investigation of a high power, magnetic field-aligned (FA) antenna, designed to reduce parallel electric (E||) field through symmetry and thereby reduce RF related impurity contamination. Using the standard non-field aligned antennas (ST) as a reference, the impurity contamination and sources on the antenna are significantly lower for the FA-antenna than the ST antennas. In addition, the radiated power is reduced for given injected power for the FA-antenna compared to the ST-antennas in L and H-mode discharges. The improved performance is consistent with simulations indicating that the FA-antenna has reduced integrated E|| relative to the non-aligned antennas. However, the simulation also predicts that so-called monopole phasing, where antenna strap current has [0,0,0,0] phase, should have the lowest integrated E||. The initial results suggest that monopole phasing has a stronger impact on the plasma potential and higher core impurity contamination and sources at the antenna. Utilizing gas puff imaging, the radial electric field profile in the scrape-off-layer (SOL) is readily measured. For the ST and FA-antennas, fine structure (variations of order ˜0.5 cm) in the radial electric field is observed and radial penetration of the rectified potential structures is ˜10 times greater than the skin depth. This anomalous penetration appears to be consistent with including cross-field RF polarization currents in the sheath model. Further comparisons of the FA- and ST-antennas are being carried out with an extensive array of boundary plasma diagnostics to characterize the impurity behavior and impact on the SOL transport and SOL density profiles; the latest results will be presented.

  10. Field Emission Characteristics of the Structure of Vertically Aligned Carbon Nanotube Bundles.

    PubMed

    Lin, Pao-Hung; Sie, Cong-Lin; Chen, Ching-An; Chang, Hsuan-Chen; Shih, Yi-Ting; Chang, Hsin-Yueh; Su, Wei-Jhih; Lee, Kuei-Yi

    2015-12-01

    In this study, we performed thermal chemical vapor deposition for growing vertically aligned carbon nanotube (VACNT) bundles for a field emitter and applied photolithography for defining the arrangement pattern to simultaneously compare square and hexagonal arrangements by using two ratios of the interbundle distance to the bundle height (R) of field emitters. The hexagon arrangement with R = 2 had the lowest turn-on electric field (E to) and highest enhancement factor, whereas the square arrangement with R = 3 had the most stable field emission (FE) characteristic. The number density can reveal the correlation to the lowest E to and highest enhancement factor more effectively than can the R or L. The fluorescent images of the synthesized VACNT bundles manifested the uniformity of FE currents. The results of our study indicate the feasibility of applying the VACNT field emitter arrangement to achieve optimal FE performance.

  11. Field Emission Characteristics of the Structure of Vertically Aligned Carbon Nanotube Bundles

    NASA Astrophysics Data System (ADS)

    Lin, Pao-Hung; Sie, Cong-Lin; Chen, Ching-An; Chang, Hsuan-Chen; Shih, Yi-Ting; Chang, Hsin-Yueh; Su, Wei-Jhih; Lee, Kuei-Yi

    2015-07-01

    In this study, we performed thermal chemical vapor deposition for growing vertically aligned carbon nanotube (VACNT) bundles for a field emitter and applied photolithography for defining the arrangement pattern to simultaneously compare square and hexagonal arrangements by using two ratios of the interbundle distance to the bundle height ( R) of field emitters. The hexagon arrangement with R = 2 had the lowest turn-on electric field ( E to) and highest enhancement factor, whereas the square arrangement with R = 3 had the most stable field emission (FE) characteristic. The number density can reveal the correlation to the lowest E to and highest enhancement factor more effectively than can the R or L. The fluorescent images of the synthesized VACNT bundles manifested the uniformity of FE currents. The results of our study indicate the feasibility of applying the VACNT field emitter arrangement to achieve optimal FE performance.

  12. Observations of Field-Aligned Current Spatial and Temporal Variations by Space Technology 5

    NASA Astrophysics Data System (ADS)

    Le, G.; Slavin, J. A.; Strangeway, R. J.; Wang, Y.

    2013-12-01

    In this paper, we report the results of magnetic field measurements of field-aligned currents (FACs) using multi-point magnetic field data from Space Technology 5 (ST-5) mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun synchronous polar orbit. The spacecraft were maintained in a 'pearls on a sting' constellation with controlled spacings ranging from just over 5000 km down to under 50 km. During the three-month mission duration, the constellation mission returned high quality multi-point measurements of the magnetic field through Earth's dynamic ionospheric current systems over a range of inter-satellite spacing. In this study, we use the ST-5 magnetic field measurements to separate spatial and temporal variations of FACs and to quantify the imbalance between the region 1 (R1) and the region 2 (R2) currents.

  13. Field emission from in situ-grown vertically aligned SnO2 nanowire arrays

    PubMed Central

    2012-01-01

    Vertically aligned SnO2 nanowire arrays have been in situ fabricated on a silicon substrate via thermal evaporation method in the presence of a Pt catalyst. The field emission properties of the SnO2 nanowire arrays have been investigated. Low turn-on fields of 1.6 to 2.8 V/μm were obtained at anode-cathode separations of 100 to 200 μm. The current density fluctuation was lower than 5% during a 120-min stability test measured at a fixed applied electric field of 5 V/μm. The favorable field-emission performance indicates that the fabricated SnO2 nanowire arrays are promising candidates as field emitters. PMID:22330800

  14. Field-aligned currents and magnetospheric convection - A comparison between MHD simulations and observations

    NASA Technical Reports Server (NTRS)

    Walker, Raymond J.; Ogino, Tatsuki

    1988-01-01

    A time-dependent three-dimensional MHD model was used to investigate the magnetospheric configuration as a function of the interplanetary magnetic field direction when it was in the y-z plane in geocentric solar magnetospheric coordinates. The model results show large global convection cells, tail lobe cells, high-latitude polarcap cells, and low latitude cells. The field-aligned currents generated in the model magnetosphere and the model convection system are compared with observations from low-altitude polar orbiting satellites.

  15. Field-dependent magnetic domain structure in antiferromagnetically coupled multilayers by polarized neutron scattering

    SciTech Connect

    Paul, Amitesh; Kentzinger, Emmanuel; Ruecker, Ulrich; Buergler, Daniel E.; Brueckel, Thomas

    2006-03-01

    We study the magnetic structure of antiferromagnetically (AF) coupled Co/Cu multilayers (MLs) with 10 or 40 bilayers under the influence of an external field by polarized neutron scattering in specular and off-specular geometry. We observe in the spin-flip channels off-specular intensities around the (1/2)-order Bragg position. Based on simulations of the measured data within the distorted-wave Born approximation we find vertically correlated domains, and their domain size evolves for a sufficiently large number of bilayers along the ML stack. Small domains most likely at the top and large domains presumably at the bottom coexist within a single ML. The small domains gradually get aligned with the applied field direction around 0.5 kOe, whereas the bigger domains remain AF coupled up to 3.0 kOe, which is well above the apparent saturation field measured by conventional magnetometry methods. Moreover, we observe a double-peak structure at the (1/2)-order position for the MLs with ten as well as 40 bilayers.

  16. Alignments of Radio Sources in the GMRT ELAIS N1 Deep Field

    NASA Astrophysics Data System (ADS)

    Jagannathan, Preshanth; Taylor, R.

    2014-01-01

    Results of the active galactic jet position angle alignments in the ELAIS N1 Deep radio survey are presented here. The ELAIS N1 deep radio survey was carried out with the Giant Meter-wave Radio Telescope at 615 MHz. The deep field is a seven pointing mosaic that covers 1.0 square degrees of the ELAIS N1 field with an average angular resolution of 5 arcsec by 5 arcsec, across the mosaic. The average sensitivity of the mosaicked image is 10 microJy/beam in Stokes I. There were 65 extended radio galaxy jets extracted from the mosaic of which 33 galaxies have redshift information available. The position angles of radio galaxy jets are expected to be uniform, but the radio galaxy jets in our sample were found to deviate from uniform distribution of positions angles to 99 percent significance level. Further testing with angular covariance reveals alignments in radio position angles, across angular scales of up to 1.8 degrees. Position angle correlations at scales of 1.8 degrees translates to a co-moving scale of 53 Mpc at a redshift of 1. These results corroborate prior evidence for large scale alignments in quasar optical polarization studies. The absence of interfering propagation effects that introduce uncertainty in optical polarization studies makes the study of radio galaxy jet position angles an attractive alternative methodology.

  17. Study of Field Aligned Plasma Acceleration during a H.A.N.E.(High Altitude Nuclear Explosion).

    DTIC Science & Technology

    1983-03-01

    I!7AD-A141 340 STUDY OF FIELD ALIGNED PLASMA ACCELERATION DURING A I/1 HANE(HIGH ALTITUDE NU.. (U) BERKELEY RESEARCH ASSOCIATES NC CA S H RECHT ET AL...CHART NATIONAL BIUREAU OF STANDARDS-1963-A AD-A141 340 DNA-TR-82-96 STUDY OF FIELD ALIGNED PLASMA ACCELERATION DURING A H.A.N.E. Stephen H. Brecht...TR-82-96 1ADA 1q1 z3__ 4. TITLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVERED STUDY OF FIELD ALIGNED PLASMA ACCELERATION Technical Report DURING

  18. Alignment-assisted field-free orientation of rotationally cold CO molecules

    NASA Astrophysics Data System (ADS)

    Ren, Xiaoming; Makhija, Varun; Li, Hui; Kling, Matthias F.; Kumarappan, Vinod

    2014-07-01

    We follow the alignment-assisted orientation technique proposed by Zhang et al. [Phys. Rev. A 83, 043410 (2011), 10.1103/PhysRevA.83.043410] to experimentally demonstrate a substantial enhancement of the field-free orientation by using a combination of single- and two-color laser pulses. When a two-color orienting pulse is preceded by a single-color aligning pulse by a suitable time, the resulting orientation is thrice as large as that obtained with the two-color pulse alone. We ensure that the orientation is the result of the hyperpolarizability interaction rather than ionization depletion by keeping the ionization due to the pump pulses small and demonstrate a useful level of orientation without the complications of a partially ionized target.

  19. Large magnetostrain in magnetic-field-aligned Mn0.965CoGe compound

    NASA Astrophysics Data System (ADS)

    Hu, Qiu-Bo; Hu, Yong; Fang, Yong; Wang, Dun-Hui; Cao, Qing-Qi; Yang, Yan-Ting; Li, Jing; Du, You-Wei

    2017-05-01

    By applying external stimulus (temperature or magnetic field), MnCoGe-based compounds undergo a martensitic transformation from hexagonal Ni2In-type to orthorhombic TiNiSi-type structure accompanied with a giant negative thermal expansion, which suggests a large magnetic-field-induced strain. However, these compounds naturally collapse into powders and are difficult to be oriented, which hinder their applications for magnetostrain. In this paper, a magnetic-field-aligned Mn0.965CoGe compound was prepared by bonding with epoxy resin and orientating in a magnetic field. The XRD patterns revealed the texture in this sample. By introducing vacancies of Mn element, the magnetostructural transformation temperature of Mn0.965CoGe compound was shifted down to 278 K. The magnetostrain was measured at some selected temperatures and the maximal strain could reach up to 925 ppm at 270 K.

  20. Patterned growth of carbon nanotubes over vertically aligned silicon nanowire bundles for achieving uniform field emission.

    PubMed

    Hung, Yung-Jr; Huang, Yung-Jui; Chang, Hsuan-Chen; Lee, Kuei-Yi; Lee, San-Liang

    2014-01-01

    A fabrication strategy is proposed to enable precise coverage of as-grown carbon nanotube (CNT) mats atop vertically aligned silicon nanowire (VA-SiNW) bundles in order to realize a uniform bundle array of CNT-SiNW heterojunctions over a large sample area. No obvious electrical degradation of as-fabricated SiNWs is observed according to the measured current-voltage characteristic of a two-terminal single-nanowire device. Bundle arrangement of CNT-SiNW heterojunctions is optimized to relax the electrostatic screening effect and to maximize the field enhancement factor. As a result, superior field emission performance and relatively stable emission current over 12 h is obtained. A bright and uniform fluorescent radiation is observed from CNT-SiNW-based field emitters regardless of its bundle periodicity, verifying the existence of high-density and efficient field emitters on the proposed CNT-SiNW bundle arrays.

  1. Magnetospheric Multiscale analysis of intense field-aligned Poynting flux near the Earth's plasma sheet boundary

    NASA Astrophysics Data System (ADS)

    Stawarz, J. E.; Eastwood, J. P.; Varsani, A.; Ergun, R. E.; Shay, M. A.; Nakamura, R.; Phan, T. D.; Burch, J. L.; Gershman, D. J.; Giles, B. L.; Goodrich, K. A.; Khotyaintsev, Y. V.; Lindqvist, P.-A.; Russell, C. T.; Strangeway, R. J.; Torbert, R. B.

    2017-07-01

    The Magnetospheric Multiscale mission is employed to examine intense Poynting flux directed along the background magnetic field toward Earth, which reaches amplitudes of nearly 2 mW/m2. The event is located within the plasma sheet but likely near the boundary at a geocentric distance of 9 RE in association with bulk flow signatures. The fluctuations have wavelengths perpendicular to the magnetic field of 124-264 km (compared to an ion gyroradius of 280 km), consistent with highly kinetic Alfvén waves. While the wave vector remains highly perpendicular to the magnetic field, there is substantial variation of the direction in the perpendicular plane. The field-aligned Poynting flux may be associated with kinetic Alfvén waves released along the separatrix by magnetotail reconnection and/or the radiation of waves excited by bursty bulk flow braking and may provide a means through which energy released by magnetic reconnection is transferred to the auroral region.

  2. Joule heating and field-aligned currents: Preliminary results from DE-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.

    1986-01-01

    There are three main processes by which energy is transferred from the magnetosphere to the thermosphere: (1) charge exchange of the ring current particles; (2) precipitation of charged particles; and (3) joule dissipation by the magnetosphere-ionosphere current systems. The importance of this last process has been recognized and the rate of joule heating has been estimated by many workers. Observations of the electric (E) and magnetic (B) fields from Dynamics Explorer Satellite 2 are providing a new set of data on field-aligned currents. One of the remarkable features found in these observations is the high correlation between an orthogonal pair of the E and B field components. In recent years, observational data have accrued concerning the relationship between the interplanetary magnetic field and the size of the polar cap and also about the evolution of a substorm or a magnetic storm. It is suggested that these findings be incorporated in future model calculations.

  3. Shock aurora: Field-aligned discrete structures moving along the dawnside oval

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaoyan; Haerendel, Gerhard; Moen, Jøran I.; Trondsen, Espen; Clausen, Lasse; Strangeway, Robert J.; Lybekk, Bjørn; Lorentzen, Dag A.

    2017-03-01

    Generated by interplanetary shocks or solar wind pressure pulses, shock aurora has transient, global, and dynamic significances and provides a direct manifestation of the solar wind-magnetosphere-ionosphere interaction. As a part of a series of studies of the shock aurora, this paper focuses on the interaction at the morning magnetopause and its auroral manifestation at 06 magnetic local time, where the velocity and magnetic field shears dominate the interaction. Flow shears can generate wave-like structures inside a viscous boundary layer or even larger-scale vortices. These structures couple to the ionosphere via quasi-static field-aligned currents or via kinetic Alfvén waves. Potential drops along field-aligned filaments may be generated accelerating electrons to form auroral manifestations of the structures. A shock aurora event at dawnside is used to test this scenario. The findings include moving auroral streaks/rays that have a vertical profile from red (at 250 km altitude) to purple (at 100 km). The streaks moved antisunward along the poleward boundary of the oval at an ionospheric speed of 3 km s-1. It was mapped to the magnetopause flank at 133 km s-1, which was consistent with the observed speed of the magnetopause surface waves generated by the Kelvin-Helmholtz instability. The calculated field-aligned potential drop using Haerendel's analytic model was 5 kV that reasonably explained the observations. The results support the above scenario and reveal that magnetic and velocity shears at the flanks of the magnetospause may be the main cause of the fast moving shock aurora streaks.

  4. Director alignment by crossed electric and magnetic fields: a deuterium NMR study.

    PubMed

    Hamasuna, D; Luckhurst, G R; Sugimura, A; Timimi, B A; Zimmermann, H

    2011-07-01

    The static director distribution in thin nematic liquid crystal cells, subject to both electric and magnetic fields, has been investigated using a combination of deuterium nuclear magnetic resonance (NMR) spectroscopy and continuum theory in terms of the director distribution function, which gives the probability density for finding the director at a given orientation. A series of deuterium NMR spectra for the nematic liquid crystal, 4-pentyl-d(2)-4'-cyanobiphenyl deuteriated in the α position of the pentyl chain were acquired as a function of the applied electric field. This powerful experimental technique allowed us to observe uniform and nonuniform director alignment depending on the angle between the two fields and their relative strength. On the basis of the detailed experimental results, we have explored the factors that influence the nature of both the uniform and the nonuniform director distributions. We have discussed the questions that are raised by our attempt to understand the static director distribution as a function of the angle between the two fields. We have discovered that the alignment of the director at the surface of the Teflon spacers is essential in addition to the random variation in the cell thickness in order to account for the static director distribution determined from the NMR spectra.

  5. A new angle for probing field-aligned irregularities with the Murchison Widefield Array

    NASA Astrophysics Data System (ADS)

    Loi, Shyeh Tjing; Murphy, Tara; Cairns, Iver H.; Trott, Cathryn M.; Hurley-Walker, Natasha; Feng, Lu; Hancock, Paul J.; Kaplan, David L.

    2016-06-01

    Electron density irregularities in the ionosphere are known to be magnetically anisotropic, preferentially elongated along the lines of force. While many studies of their morphology have been undertaken by topside sounding and whistler measurements, it is only recently that detailed regional-scale reconstructions have become possible, enabled by the advent of widefield radio telescopes. Here we present a new approach for visualizing and studying field-aligned irregularities (FAIs), which involves transforming interferometric measurements of total electron content gradients onto a magnetic shell tangent plane. This removes the perspective distortion associated with the oblique viewing angle of the irregularities from the ground, facilitating the decomposition of dynamics along and across magnetic field lines. We apply this transformation to the data set of Loi et al. (2015a), obtained on 15 October 2013 by the Murchison Widefield Array (MWA) radio telescope and displaying prominent FAIs. We study these FAIs in the new reference frame, quantifying field-aligned and field-transverse behavior, examining time and altitude dependencies, and extending the analysis to FAIs on subarray scales. We show that the inclination of the plane can be derived solely from the data and verify that the best fit value is consistent with the known magnetic inclination. The ability of the model to concentrate the fluctuations along a single spatial direction may find practical application to future calibration strategies for widefield interferometry, by providing a compact representation of FAI-induced distortions.

  6. Label-free hyperspectral dark-field microscopy for quantitative scatter imaging

    NASA Astrophysics Data System (ADS)

    Cheney, Philip; McClatchy, David; Kanick, Stephen; Lemaillet, Paul; Allen, David; Samarov, Daniel; Pogue, Brian; Hwang, Jeeseong

    2017-03-01

    A hyperspectral dark-field microscope has been developed for imaging spatially distributed diffuse reflectance spectra from light-scattering samples. In this report, quantitative scatter spectroscopy is demonstrated with a uniform scattering phantom, namely a solution of polystyrene microspheres. A Monte Carlo-based inverse model was used to calculate the reduced scattering coefficients of samples of different microsphere concentrations from wavelength-dependent backscattered signal measured by the dark-field microscope. The results are compared to the measurement results from a NIST double-integrating sphere system for validation. Ongoing efforts involve quantitative mapping of scattering and absorption coefficients in samples with spatially heterogeneous optical properties.

  7. Short-range order and near-field effects on optical scattering and structural coloration

    SciTech Connect

    Liew, S.F.; Forster, J.; Noh, H.; Schreck, C.F.; Saranathan, V.; Lu, X.; Yang, L.; Prum, Richard O.; O’Hern, C.S.; Dufresne, E.R.; Cao, H.

    2012-03-26

    We have investigated wavelength-dependent light scattering in biomimetic structures with short-range order. Coherent backscattering experiments are performed to measure the transport mean free path over a wide wavelength range. Overall scattering strength is reduced significantly due to short-range order and near-field effects. Our analysis explains why single scattering of light is dominant over multiple scattering in similar biological structures and is responsible for color generation.

  8. Effect of circularly polarized femtosecond laser pulses on alignment dynamics of linear molecules observed by strong-field photoelectron yields

    NASA Astrophysics Data System (ADS)

    Kaya, Necati; Kaya, Gamze; Strohaber, James; Kolomenskii, Alexandre A.; Schuessler, Hans A.

    2016-10-01

    By measuring femtosecond laser driven strong-field electron yields for linear molecules aligned by circularly polarized femtosecond laser pulses, we study the rotational wavepacket evolution of N2, CO, and C2H2 gas molecules. We show that circular polarization produces a net alignment along the laser pulse propagation axis at certain phases of the evolution. This gives the possibility to control alignment of linear molecules outside the plane of polarization, which can provide new capabilities for molecular imaging. The experimental results were compared to the calculated field-free molecular alignment parameter taking into account the effects of electronic structure and symmetry of the molecules. By fitting the calculated impulsive alignment parameter to the measured experimental data we determined the molecular rotational constants of the linear gas molecules.

  9. Saturn's auroral morphology and field-aligned currents during a solar wind compression

    NASA Astrophysics Data System (ADS)

    Badman, S. V.; Provan, G.; Bunce, E. J.; Mitchell, D. G.; Melin, H.; Cowley, S. W. H.; Radioti, A.; Kurth, W. S.; Pryor, W. R.; Nichols, J. D.; Jinks, S. L.; Stallard, T. S.; Brown, R. H.; Baines, K. H.; Dougherty, M. K.

    2016-01-01

    On 21-22 April 2013, during a coordinated auroral observing campaign, instruments onboard Cassini and the Hubble Space Telescope observed Saturn's aurora while Cassini traversed Saturn's high latitude auroral field lines. Signatures of upward and downward field-aligned currents were detected in the nightside magnetosphere in the magnetic field and plasma measurements. The location of the upward current corresponded to the bright ultraviolet auroral arc seen in the auroral images, and the downward current region was located poleward of the upward current in an aurorally dark region. Within the polar cap magnetic field and plasma fluctuations were identified with periods of ∼20 and ∼60 min. The northern and southern auroral ovals were observed to rock in latitude in phase with the respective northern and southern planetary period oscillations. A solar wind compression impacted Saturn's magnetosphere at the start of 22 April 2013, identified by an intensification and extension to lower frequencies of the Saturn kilometric radiation, with the following sequence of effects: (1) intensification of the auroral field-aligned currents; (2) appearance of a localised, intense bulge in the dawnside (04-06 LT) aurora while the midnight sector aurora remained fainter and narrow; and (3) latitudinal broadening and poleward contraction of the nightside aurora, where the poleward motion in this sector is opposite to that expected from a model of the auroral oval's usual oscillation. These observations are interpreted as the response to tail reconnection events, initially involving Vasyliunas-type reconnection of closed mass-loaded magnetotail field lines, and then proceeding onto open lobe field lines, causing the contraction of the polar cap region on the night side.

  10. Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms

    NASA Astrophysics Data System (ADS)

    Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Plaschke, F.; Magnes, W.; Fischer, D.; Varsani, A.; Schmid, D.; Nakamura, T. K. M.; Russell, C. T.; Strangeway, R. J.; Leinweber, H. K.; Le, G.; Bromund, K. R.; Pollock, C. J.; Giles, B. L.; Dorelli, J. C.; Gershman, D. J.; Paterson, W.; Avanov, L. A.; Fuselier, S. A.; Genestreti, K.; Burch, J. L.; Torbert, R. B.; Chutter, M.; Argall, M. R.; Anderson, B. J.; Lindqvist, P.-A.; Marklund, G. T.; Khotyaintsev, Y. V.; Mauk, B. H.; Cohen, I. J.; Baker, D. N.; Jaynes, A. N.; Ergun, R. E.; Singer, H. J.; Slavin, J. A.; Kepko, E. L.; Moore, T. E.; Lavraud, B.; Coffey, V.; Saito, Y.

    2016-05-01

    We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

  11. Transient, Small-Scale Field-Aligned Currents in the Plasma Sheet Boundary Layer During Storm Time Substorms

    NASA Technical Reports Server (NTRS)

    Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Plaschke, F.; Magnes, W.; Fischer, D.; Varsani, A.; Schmid, D.; Nakamura, T. K. M.; Russell, C. T.; hide

    2016-01-01

    We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the Separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward earth ward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

  12. Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms.

    PubMed

    Nakamura, R; Sergeev, V A; Baumjohann, W; Plaschke, F; Magnes, W; Fischer, D; Varsani, A; Schmid, D; Nakamura, T K M; Russell, C T; Strangeway, R J; Leinweber, H K; Le, G; Bromund, K R; Pollock, C J; Giles, B L; Dorelli, J C; Gershman, D J; Paterson, W; Avanov, L A; Fuselier, S A; Genestreti, K; Burch, J L; Torbert, R B; Chutter, M; Argall, M R; Anderson, B J; Lindqvist, P-A; Marklund, G T; Khotyaintsev, Y V; Mauk, B H; Cohen, I J; Baker, D N; Jaynes, A N; Ergun, R E; Singer, H J; Slavin, J A; Kepko, E L; Moore, T E; Lavraud, B; Coffey, V; Saito, Y

    2016-05-28

    We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

  13. Alignment of SWNTs by protein-ligand interaction of functionalized magnetic particles under low magnetic fields.

    PubMed

    Park, Tae Jung; Park, Jong Pil; Lee, Seok Jae; Jung, Dae-Hwan; Ko, Young Koan; Jung, Hee-Tae; Lee, Sang Yup

    2011-05-01

    Carbon nanotubes (CNTs) have attracted considerable attention for applications using their superior mechanical, thermal and electrical properties. A simple method to controllably align single-walled CNTs (SWNTs) by using magnetic particles embedded with superparamagnetic iron oxide as an accelerator under the magnetic field was developed. The functionalization of SWNTs using biotin, interacted with streptavidin-coupled magnetic particles (micro-to-nano in diameter), and layer-by-layer assembly were performed for the alignment of a particular direction onto the clean silicon and the gold substrate at very low magnetic forces (0.02-0.89 T) at room temperature. The successful alignment of the SWNTs with multi-layer film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By changing the orientation and location of the substrates, crossed-networks of SWNTs-magnetic particle complex could easily be fabricated. We suggest that this approach, which consists of a combination of biological interaction among streptavidin-biotin and magnetite particles, should be useful for lateral orientation of individual SWNTs with controllable direction.

  14. The Extent to Which Dayside Reconnection Drives Field-Aligned Currents During Substorms

    NASA Astrophysics Data System (ADS)

    Forsyth, C.; Shortt, M. W.; Coxon, J.; Rae, J.; Freeman, M. P.; Kalmoni, N. M. E.; Jackman, C. M.; Anderson, B. J.

    2016-12-01

    Field-aligned currents, also known as Birkeland currents, are the agents by which energy and momentum is transferred to the ionosphere from the magnetosphere and solar wind. In order to understand this coupling, it is necessary to analyze the variations in these current systems with respect to the main energy sources of the solar wind and substorms. In this study, we perform a superposed epoch analysis of field-aligned currents determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) project with respect to substorm expansion phase onsets identified using the Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE) technique. We examine the total upward and downward currents separately in the noon, dusk, dawn and midnight sectors. Our results show that the dusk and dawn currents have up to a 66% linear correlated with the dayside reconnection rate estimated from solar wind measurements, whereas the noon and midnight currents are not. The noon currents show little or no variation throughout the substorm cycle. The midnight currents follows the dusk currents up to 20 min before onset, after which the midnight current increases more rapidly and exponentially. At substorm onset, the exponential growth rate increases. While the midnight field-aligned currents grow exponentially after substorm onset, the auroral indices vary with a 1/6th power law. Overall, our results show that the growth and decay rates of the Region 1 and 2 current systems, which are strongest at dawn and dusk, are directly driven by the solar wind, whereas the growth and decay rates of the substorm current system, which are dominant at midnight, act independently of the upstream driver.

  15. Evaluating the diffusive equilibrium models: Comparison with the IMAGE RPI field-aligned electron density measurements

    NASA Astrophysics Data System (ADS)

    Ozhogin, P.; Song, P.; Tu, J.; Reinisch, B. W.

    2014-06-01

    The diffusive equilibrium models that are widely used by the space physics community to describe the plasma densities in the plasmasphere are evaluated with field-aligned electron density measurements from the radio plasma imager (RPI) instrument onboard the IMAGE satellite. The original mathematical form of the diffusive equilibrium model was based on the hydrostatic equilibrium along the magnetic field line with the centrifugal force and the field-aligned electrostatic force as well as a large number of simplifying approximations. Six free parameters in the mathematical form have been conventionally determined from observations. We evaluate four sets of the parameters that have been reported in the literature. The evaluation is made according to the equatorial radial distance dependence, latitudinal dependence at a given radial distance, and the combined radial and latitudinal dependences. We find that the mathematical form given in the diffusive equilibrium model is intrinsically incompatible with the measurements unless another large number of free parameters are artificially introduced, which essentially changes the nature of a theoretical model to an empirical model.

  16. Space Technology 5 Multi-Point Field-Aligned Current Measurements (Invited)

    NASA Astrophysics Data System (ADS)

    Slavin, J. A.; Le, G.; Gjerloev, J. W.

    2013-12-01

    NASA's Space Technology 5 (ST 5) microsatellite constellation technology mission was launched by a Pegasus launch vehicle on March 22, 2006. The three small (48 cm tall, 50 cm diameter, 25 kg mass, spin stabilized at 20 rpm) satellites were placid in a 300 x 4500 km, dawn to dusk, sun synchronous orbit (inclination = 105.6 deg) orbit with a period of 138 min. They were maintained in this 'pearls on a sting' formation with inter-satellite spacings ranging from over 5000 km to under 50 km. Each satellite carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles. Field aligned currents (FACs) form in response to the stress exerted on the magnetosphere by the solar wind and act as the primary mechanism for dissipating solar wind energy into the ionosphere and upper atmosphere during the solar wind magnetosphere ionosphere coupling process. ST 5 returned the first direct, simultaneous, multipoint measurements of FAC motion, thickness, and temporal variability. Current density was measured using both 1) the 'standard method' based upon s/c velocity, but corrected for FAC current sheet motion, with the assumption of a time-stationary current density profile, and 2) for the first time at low altitudes, the 'gradiometer method' which uses simultaneous magnetic field measurements at two points with known separation. Here we review the ST 5 scientific results concerning FACs and discuss their implications for future investigations of field aligned currents systems using distributed systems of spaceborne magnetometers.

  17. Validation of a new plasmapause model derived from CHAMP field-aligned current signatures

    NASA Astrophysics Data System (ADS)

    Heilig, Balázs; Darrouzet, Fabien; Vellante, Massimo; Lichtenberger, János; Lühr, Hermann

    2014-05-01

    Recently a new model for the plasmapause location in the equatorial plane was introduced based on magnetic field observations made by the CHAMP satellite in the topside ionosphere (Heilig and Lühr, 2013). Related signals are medium-scale field-aligned currents (MSFAC) (some 10km scale size). An empirical model for the MSFAC boundary was developed as a function of Kp and MLT. The MSFAC model then was compared to in situ plasmapause observations of IMAGE RPI. By considering this systematic displacement resulting from this comparison and by taking into account the diurnal variation and Kp-dependence of the residuals an empirical model of the plasmapause location that is based on MSFAC measurements from CHAMP was constructed. As a first step toward validation of the new plasmapause model we used in-situ (Van Allen Probes/EMFISIS, Cluster/WHISPER) and ground based (EMMA) plasma density observations. Preliminary results show a good agreement in general between the model and observations. Some observed differences stem from the different definitions of the plasmapause. A more detailed validation of the method can take place as soon as SWARM and VAP data become available. Heilig, B., and H. Lühr (2013) New plasmapause model derived from CHAMP field-aligned current signatures, Ann. Geophys., 31, 529-539, doi:10.5194/angeo-31-529-2013

  18. Driven magnetic reconnection in three dimensions - Energy conversion and field-aligned current generation

    NASA Technical Reports Server (NTRS)

    Sato, T.; Walker, R. J.; Ashour-Abdalla, M.

    1984-01-01

    The energy conversion processes occurring in three-dimensional driven reconnection is analyzed. In particular, the energy conversion processes during localized reconnection in a taillike magnetic configuration are studied. It is found that three-dimensional driven reconnection is a powerful energy converter which transforms magnetic energy into plasma bulk flow and thermal energy. Three-dimensional driven reconnection is an even more powerful energy converter than two-dimensional reconnection, because in the three-dimensional case, plasmas were drawn into the reconnection region from the sides as well as from the top and bottom. Field-aligned currents are generated by three-dimensional driven reconnection. The physical mechanism responsible for these currents which flow from the tail toward the ionosphere on the dawnside of the reconnection region and from the ionosphere toward the tail on the duskside is identified. The field-aligned currents form as the neutral sheet current is diverted through the slow shocks which form on the outer edge of the reconnected field lines (outer edge of the plasma sheet).

  19. Non-adiabatic effects in near-adiabatic mixed-field orientation and alignment

    NASA Astrophysics Data System (ADS)

    Maan, Anjali; Ahlawat, Dharamvir Singh; Prasad, Vinod

    2016-11-01

    We present a theoretical study of the impact of a pair of moderate electric fields tilted an angle with respect to one another on a molecule. As a prototype, we consider a molecule with large rotational constant (with corresponding small rotational period) and moderate dipole moment. Within rigid-rotor approximation, the time-dependent Schrodinger equation is solved using fourth-order Runge-Kutta method. We have analysed that lower rotational states are significantly influenced by variation in pulse durations, the tilt angle between the fields and also on the electric field strengths. We also suggest a control scheme of how the rotational dynamics, orientation and alignment of a molecule can be enhanced by a combination of near-adiabatic pulses in comparision to non-adiabatic or adiabatic pulses.

  20. A High-resolution Model of Field-aligned Currents Through Empirical Orthogonal Functions Analysis (MFACE)

    NASA Technical Reports Server (NTRS)

    He, Maosheng; Vogt, Joachim; Luehr, Hermann; Sorbalo, Eugen; Blagau, Adrian; Le, Guan; Lu, Gang

    2012-01-01

    Ten years of CHAMP magnetic field measurements are integrated into MFACE, a model of field-aligned currents (FACs) using empirical orthogonal functions (EOFs). EOF1 gives the basic Region-1/Region-2 pattern varying mainly with the interplanetary magnetic field Bz component. EOF2 captures separately the cusp current signature and By-related variability. Compared to existing models, MFACE yields significantly better spatial resolution, reproduces typically observed FAC thickness and intensity, improves on the magnetic local time (MLT) distribution, and gives the seasonal dependence of FAC latitudes and the NBZ current signature. MFACE further reveals systematic dependences on By, including 1) Region-1/Region-2 topology modifications around noon; 2) imbalance between upward and downward maximum current density; 3) MLT location of the Harang discontinuity. Furthermore, our procedure allows quantifying response times of FACs to solar wind driving at the bow shock nose: we obtain 20 minutes and 35-40 minutes lags for the FAC density and latitude, respectively.

  1. Radar observations of field-aligned plasma propagations associated with NASA's PMG experiment

    NASA Astrophysics Data System (ADS)

    Olson, Darren M.

    1994-09-01

    NASA's Plasma Motor Generator (PMG) tethered satellite mission was launched in June 1993 to verify the ability of hollow cathode plasma sources to couple electric currents from an electrodynamic tether into the ambient ionospheric plasma. This large-scale coupling process resulted in turbulent plasma signatures associated with the orbiting plasma generator, which propagated over great distances along the earth's geomagnetic field lines. VHF radars in Hilo, Hawaii and Jicamarca, Peru recorded observations of these field-aligned disturbances as part of the experiment. Based on analysis of these radar observations and tracking data of PMG's orbit, the effective propagation velocity of these traveling plasma waveforms was calculated to be of the order of 1000 meters per second. Detection of these disturbances, associated with PMG's passage overhead, supports the existence of a phantom current loop allowing current flow along the magnetic field lines of the earth and into the lower ionosphere from either end of an electrodynamic tether.

  2. On the relationship between morning sector irregular magnetic pulsations and field aligned currents

    NASA Technical Reports Server (NTRS)

    Engebretson, M. J.; Cahill, L. J., Jr.; Potemra, T. A.; Zanetti, L. J.; Arnoldy, R. L.; Mende, S. B.; Rosenberg, T. J.

    1984-01-01

    For three magnetically disturbed days in early 1980, data from south polar masses of the Magsat satellite are compared with data from search coil magnetometer, riometer, and photometer instrumentation at Siple, Antarctica. It is found that during each Magsat polar pass in the morning sector, the level of Pi 1 activity correlates well with the intensities of three-dimensional current systems. Fine structure is often observed in the field-aligned currents during periods of intense Pi activity. Among the Birkeland currents are 2-s to 10-s (16-80 km) structured perturbations; these are evident in the transverse components of the field and are thought to indicate filamentary currents. Pi 1 amplitudes are found to be considerably larger when region 2 Birkeland currents are overhead than when they are not. In one case, detailed features are identified in the high-resolution Magsat magnetic field data that may be current fluctuations related to asymmetric Pi 1.

  3. Complexities of determining the Field-Aligned current density from LEO satellites.

    NASA Astrophysics Data System (ADS)

    Gjerloev, J. W.; Friel, M. M.; Ohtani, S.; Muhleisen, M.; Gjerloev, A. W.; Martin, P.; Barnes, R. J.

    2015-12-01

    We show results from a study of the field-aligned currents (FAC) as derived from SWARM magnetic field perturbations. We calculate the FAC density using four different techniques and explain why they provide different results. Theoretical work, simulations and data are used to show that widely used techniques can provide current density estimates with errors of 1000%. These errors can be explained by spatial gradients in the currents and temporal variability of the currents as well as a breakdown of other fundamental assumptions. We apply the techniques to auroral crossings with THEMIS ASI coverage and use the SWARM magnetic field observations to calculate the current density. Finally, we show how to estimate the errors in the current density calculations.

  4. Radar observations of field-aligned plasma propagations associated with nasa's PMG experiment. Master's thesis

    SciTech Connect

    Olson, D.M.

    1994-09-01

    NASA's Plasma Motor Generator (PMG) tethered satellite mission was launched in June 1993 to verify the ability of hollow cathode plasma sources to couple electric currents from an electrodynamic tether into the ambient ionospheric plasma. This large-scale coupling process resulted in turbulent plasma signatures associated with the orbiting plasma generator, which propagated over great distances along the earth's geomagnetic field lines. VHF radars in Hilo, Hawaii and Jicamarca, Peru recorded observations of these field-aligned disturbances as part of the experiment. Based on analysis of these radar observations and tracking data of PMG's orbit, the effective propagation velocity of these traveling plasma waveforms was calculated to be of the order of 1000 meters per second. Detection of these disturbances, associated with PMG's passage overhead, supports the existence of a phantom current loop allowing current flow along the magnetic field lines of the earth and into the lower ionosphere from either end of an electrodynamic tether.

  5. Can the high latitude ionosphere support large field-aligned ion drifts?

    NASA Technical Reports Server (NTRS)

    Sica, R. J.; Schunk, R. W.; Rasmussen, C. E.

    1988-01-01

    A three-dimensional time-dependent model of the ionosphere is used to examine recent results on vertical drift velocities and electron densities in the high latitude ionosphere. Upper limits for the downward ion velocity were found to be smaller than those obtained from previous measurements. The downward force in the model was arbitrarily increased to try to account for the narrow electron density profiles. It is noted that if the common volume measurement is made in a region of O(+) precipitation then the line profile would not be Doppler shifted when viewed off-zenith, and small field-aligned velocities and narrow profile widths would result.

  6. Numerical study of anomalous absorption of O mode waves on magnetic field-aligned striations

    NASA Astrophysics Data System (ADS)

    Eliasson, B.; Papadopoulos, K.

    2015-04-01

    Simple expressions that describe mode conversion and anomalous absorption of ordinary (O) mode waves injected at angles between the vertical and magnetic zenith to upper hybrid (UH) oscillations in the presence of field-aligned density striations are presented. The absorption takes place in a region above the UH resonance layer where the striations allow trapped eigenmodes, leading to excitation of large-amplitude UH waves. The derivation of the expressions is guided by dimensional analysis and numerical simulations. The results are relevant in interpreting high-latitude heating experiments where anomalous absorption due to striations plays a crucial role.

  7. Self-Aligned Integrally Gated Nanofilament Field Emitter Cell and Array

    DTIC Science & Technology

    2001-03-09

    composed of carbon nanotubes , alternate nanofilaments may be nanowires composed of Si, Ge, SiC, GaAs, GaP, InAs, InP, ZnS, ZnSe, CdS, CdSe, MoS2 , WS2...integrally gated, self-aligned field emitter cell and array whose cathode is formed of a recently discovered class of materials of nanotubes and...nanotechnology have resulted in the creation of nanofilaments including nanotubes . One such example is carbon nanotubes . These nanotubes behave like

  8. Angular distribution of field emitted electrons from vertically aligned carbon nanotube arrays

    NASA Astrophysics Data System (ADS)

    Iacobucci, S.; Fratini, M.; Rizzo, A.; Scarinci, F.; Zhang, Y.; Mann, M.; Li, C.; Milne, W. I.; El Gomati, M. M.; Lagomarsino, S.; Stefani, G.

    2012-01-01

    Angular field emission (FE) properties of vertically aligned carbon nanotube arrays have been measured on samples grown by plasma enhanced chemical vapor deposition and characterized by scanning electron microscope and I-V measurements. These properties determine the angular divergence of electron beams, a crucial parameter in order to obtain high brilliance FE based cathodes. From angular distributions of the electron beam transmitted through extraction grids of different mesh size and by using ray-tracing simulations, the maximum emission angle from carbon nanotube tips has been determined to be about ± 30° around the tube main axis.

  9. Can the high latitude ionosphere support large field-aligned ion drifts?

    NASA Technical Reports Server (NTRS)

    Sica, R. J.; Schunk, R. W.; Rasmussen, C. E.

    1988-01-01

    A three-dimensional time-dependent model of the ionosphere is used to examine recent results on vertical drift velocities and electron densities in the high latitude ionosphere. Upper limits for the downward ion velocity were found to be smaller than those obtained from previous measurements. The downward force in the model was arbitrarily increased to try to account for the narrow electron density profiles. It is noted that if the common volume measurement is made in a region of O(+) precipitation then the line profile would not be Doppler shifted when viewed off-zenith, and small field-aligned velocities and narrow profile widths would result.

  10. Can primordial magnetic fields seeded by electroweak strings cause an alignment of quasar axes on cosmological scales?

    PubMed

    Poltis, Robert; Stojkovic, Dejan

    2010-10-15

    The decay of nontopological electroweak strings may leave an observable imprint in the Universe today in the form of primordial magnetic fields. Protogalaxies preferentially tend to form with their axis of rotation parallel to an external magnetic field, and, moreover, an external magnetic field produces torque which tends to align the galaxy axis with the magnetic field. We demonstrate that the shape of a magnetic field left over from two looped electroweak strings can explain the observed nontrivial alignment of quasar polarization vectors and make predictions for future observations.

  11. Influence of magnetic field alignment of cellulose whiskers on the mechanics of all-cellulose nanocomposites.

    PubMed

    Pullawan, Tanittha; Wilkinson, Arthur N; Eichhorn, Stephen J

    2012-08-13

    Orientation of cellulose nanowhiskers (CNWs) derived from tunicates, in an all-cellulose nanocomposite, is achieved through the application of a magnetic field. CNWs are incorporated into a dissolved cellulose matrix system and during solvent casting of the nanocomposite a magnetic field is applied to induce their alignment. Unoriented CNW samples, without the presence of a magnetic field, are also produced. The CNWs are found to orient under the action of the magnetic field, leading to enhanced stiffness and strength of the composites, but not to the level that is theoretically predicted for a fully aligned system. Lowering the volume fraction of the CNWs is shown to allow them to orient more readily in the magnetic field, leading to larger relative increases in the mechanical properties. It is shown, using polarized light microscopy, that the all-cellulose composites have a domain structure, with some domains showing pronounced orientation of CNWs and others where no preferred orientation occurs. Raman spectroscopy is used to both follow the position of bands located at ~1095 and ~895 cm(-1) with deformation and also their intensity as a function rotation angle of the specimens. It is shown that these approaches give valuable independent information on the respective molecular deformation and orientation of the CNWs, and the molecules in the matrix phase, in oriented and nonoriented domains of all-cellulose composites. These data are then related to an increase in the level of molecular deformation in the axial direction, as revealed by the Raman technique. Little orientation of the matrix phase is observed under the action of the magnetic field indicating the dominance of the stiff CNWs in governing mechanical properties.

  12. Numerically investigating near-field scattering for spatial enhancement of single irregular nano plasma particle.

    PubMed

    Chen, Sheng Chung; Tsai, Din Ping

    2004-01-01

    Near-field scattering from a nano silver particle has been studied with an optical wave passing through it. The scattered field was found to be enhanced around the semisphere on which the incident wave impinges. Comparing it with the spherical particle, the irregular shape of a nanoparticle only changes the distribution of the scattered field. In this investigation, approached by finite difference time domain (FDTD), it was revealed that the peak value of the scattered field is proportional to the particle radius; this might be due to the fact that more plasmons could be excited. Furthermore, the highest enhancement occurred at the incident frequency close to plasma frequency of silver (approximately 2000 THz). Thus, the numerical results could give a guide for optimizing AgOx type super resolution near-field structure (RENS) applications. When the red light source can be replaced with shorter wavelength ones, or larger silver particles can be segregated, the near-field scattered enhancement might result.

  13. Plasma Sheet Response to the Ionosphere's Demand for Field-Aligned Current

    NASA Astrophysics Data System (ADS)

    Coroniti, F. V.; Pritchett, P. L.

    2007-12-01

    Magnetospheric convection electric fields and plasma stresses are transmitted to the ionosphere by Alfvén wave electric fields and field-aligned currents (FACs). The closure of the FACs by ionospheric Hall and Pedersen currents drives the ionospheric convection system. However, the ionospheric system does not necessarily mesh smoothly with the magnetospheric drivers, and the magnetosphere must respond by altering its convection and plasma stress configuration, thereby creating self-consistent closure paths for the complete coupled system of currents and electric potentials. Three-dimensional particle-in-cell plasma kinetic simulations are used to determine the plasma sheet response to various current systems imposed as boundary conditions at the near-Earth boundary. These systems consist of separate downward and upward tubes of FAC and a substorm current wedge configuration. The results demonstrate that the creation of closure paths for ionospheric FACs can result in large configuration changes within the near-Earth plasma sheet. The plasma sheet is forced to establish polarization electric fields that locally increase the cross-tail current by producing a duskward Hall electron current; this results in the formation of thin (in z), spatially localized (in y) electron-dominated Hall current sheets. The observed complex magnetic field configuration with opposite polarity Bz fields in close proximity separated by electron scale thin current sheets is reminiscent of the turbulent magnetic fields that are observed within the near-Earth current disruption region at substorm breakup [ Lui et al., 1988, 1992].

  14. Reexamining X-mode suppression and fine structure in artificial E region field-aligned plasma density irregularities

    NASA Astrophysics Data System (ADS)

    Miceli, R. J.; Hysell, D. L.; Munk, J.; McCarrick, M.; Huba, J. D.

    2013-09-01

    Artificial field-aligned plasma density irregularities (FAIs) were generated in the E region of the ionosphere above the High Frequency Active Auroral Research Program facility during campaigns in May and August of 2012 and observed using a 30 MHz coherent scatter radar imager in Homer, Alaska. The purpose of this ionospheric modification experiment was to measure the threshold pump power required to excite thermal parametric instabilities by O-mode heating and to investigate the suppression of the FAIs by simultaneous X-mode heating. We find that the threshold pump power for irregularity excitation was consistent with theoretical predictions and increased by approximately a factor of 2 when X-mode heating was present. A modified version of the Another Model of the Ionosphere (SAMI2) ionospheric model was used to simulate the threshold experiments and suggested that the increase was entirely due to enhanced D region absorption associated with X-mode heating. Additionally, a remarkable degree of fine structure possibly caused by natural gradient drift instability in the heater-modified volume was observed in experiments performed during geomagnetically active conditions.

  15. Artificial E-region field-aligned plasma irregularities generated at pump frequencies near the second electron gyroharmonic

    NASA Astrophysics Data System (ADS)

    Hysell, D. L.; Nossa, E.

    2009-07-01

    E region ionospheric modification experiments have been performed at HAARP using pump frequencies about 50 kHz above and below the second electron gyroharmonic frequency. Artificial E region field-aligned plasma density irregularities (FAIs) were created and observed using the imaging coherent scatter radar near Homer, Alaska. Echoes from FAIs generated with pump frequencies above and below 2Ωe did not appear to differ significantly in experiments conducted on summer afternoons in 2008, and the resonance instability seemed to be at work in either case. We argue that upper hybrid wave trapping and resonance instability at pump frequencies below the second electron gyroharmonic frequency are permitted theoretically when the effects of finite parallel wavenumbers are considered. Echoes from a sporadic E layer were observed to be somewhat weaker when the pump frequency was 50 kHz below the second electron gyroharmonic frequency. This may indicate that finite parallel wavenumbers are inconsistent with wave trapping in thin sporadic E ionization layers.

  16. Periodicity property of relativistic Thomson scattering with application to exact calculations of angular and spectral distributions of the scattered field

    SciTech Connect

    Popa, Alexandru

    2011-08-15

    We prove that the analytical expression of the intensity of the relativistic Thomson scattered field for a system composed of an electron interacting with a plane electromagnetic field can be written in the form of a composite periodic function of only one variable, that is, the phase of the incident field. This property is proved without using any approximation in the most general case in which the field is elliptically polarized, the initial phase of the incident field and the initial velocity of the electron are taken into consideration, and the direction in which the radiation is scattered is arbitrary. This property leads to an exact method for calculating the angular and spectral distributions of the scattered field, which reveals a series of physical details of these distributions, such as their dependence on the components of the initial electron velocity. Since the phase of the field is a relativistic invariant, it follows that the periodicity property is also valid when the analysis is made in the inertial system in which the initial velocity of the electron is zero in the case of interactions between very intense electromagnetic fields and relativistic electrons. Consequently, the calculation method can be used for the evaluation of properties of backscattered hard radiations generated by this type of interaction. The theoretical evaluations presented in this paper are in good agreement with the experimental data from literature.

  17. The Effects of GPS Signal Propagation Paths Alignment with Low-Latitude Ionospheric Field-Aligned Plasma Bubble Structures on Scintillation

    NASA Astrophysics Data System (ADS)

    Paula, E. R.; Moraes, A. D. O.; Costa, E.; Vani, B. C.; Abdu, M. A.; Galera Monico, J. F.

    2016-12-01

    This work analyzes GPS scintillation data recorded during five months (Nov/2014 to Mar/2015) at São José dos Campos, Brazil, located near the southern crest of the equatorial ionization anomaly. Analysis has been performed aiming at relating amplitude and phase scintillation indices with the orientation of the propagation path through the ionospheric irregularities and then evaluating its effects on receiver positioning and GPS availability. Based on the analysis of an extensive set with 311,369 samples, it was noted that there is a dominance of intense scintillation events around the azimuth angle of 345º (geographic northwest but nearly aligned with geomagnetic field lines). In view of the large westward magnetic declination (21.4ºW) of this region and of the nature of the plasma bubble irregularity distribution with respect to the geomagnetic field configuration, this result strongly suggests that such GPS signal propagation paths were close to being end-on through magnetic field aligned plasma bubbles. This work will show that during this alignment, the extensive propagation path length through the bubbles can result in larger scintillation intensity cases. Further analysis based on calculation of the propagation angles with respect to the magnetic field line (in elevation and azimuth) clearly support the interpretation that cases of loss of phase lock are most likely to occur for small values of these angles and that those cases are distributed around the value of the scintillation index S4 = 1. Thus, the present work provides for the first time a quantitative verification and confirmation of such effect of scintillation enhancement due to nearly magnetic longitudinal satellite-to-receiver propagation paths. Additionally, this work will show the consequences of such alignment on precise pointing positioning, highlighting the threat that this type of scenario could represent to users of such application.

  18. Field-aligned currents onboard the Intercosmos Bulgaria-1300 satellite in comparison with modeled FAC

    NASA Astrophysics Data System (ADS)

    Danov, Dimitar

    2008-02-01

    The statistical field-aligned current (FAC) distribution has been demonstrated by [Iijima, T., Potemra, T.A., 1976. The amplitude distribution of field-aligned currents at northern high latitudes observed by Triad. Journal of Geophysical Research 81(13), 2165-2174] and many other authors. The large-scale (LS) FACs have been described by different empirical/statistical models [Feldstein, Ya. I., Levitin, A.E., 1986. Solar wind control of electric fields and currents in the ionosphere. Journal of Geomagnetism and Geoelectricity 38, 1143; Papitashvili, V.O., Rich, F.J., Heinemann, M.A., Hairston, M.R., 1999. Parameterization of the Defense Meteorological Satellite Program ionospheric electrostatic potentials by the interplanetary magnetic field strength and direction. Journal of Geophysical Research 104, 177-184; Papitashvili, V.O., Christiansen, F., Neubert, T., 2002. A new model of field-aligned currents derived from high-precision satellite magnetic field data. Geophysical Research Letters, 29(14), 1683, doi:10.1029/2001GL014207; Tsyganenko, N.A., 2001. A model of the near magnetosphere with a dawn-dusk asymetry (I. Mathematical structure). Journal of Geophysical Research 107(A8), doi:10.1029/2001JA000219; Weimer, D.R., 1996a. A new model for prediction of ionospheric electric potentials as a function of the IMF. In: Snowmass'96 Online Poster Session; Weimer, D.R., 1996b. Substorm influence on the ionospheric convection patterns. In: Snowmass'96 Online Poster Session; Weimer, D.R., 2001. Maps of ionospheric field-aligned currents as a function of the interplanetary magnetic field derived from Dynamic Explorer 2 data. Journal of Geophysical Research 106, 12,889-12,902; Weimer, D.R., 2005. Improved ionospheric electrodynamic models and application to calculating Joule heating rates. Journal of Geophysical Research 110, A05306, doi:10.1029/2004JA010884]. In the present work, we compare two cases of LS FAC obtained from magnetic field measurements onboard the

  19. Magnetic-field-dependent small-angle neutron scattering on random anisotropy ferromagnets

    NASA Astrophysics Data System (ADS)

    Michels, Andreas; Weissmüller, Jörg

    2008-06-01

    We report on the recently developed technique of magnetic-field-dependent small-angle neutron scattering (SANS), with attention to bulk ferromagnets exhibiting random magnetic anisotropy. In these materials, the various magnetic anisotropy fields (magnetocrystalline, magnetoelastic, and/or magnetostatic in origin) perturb the perfectly parallel spin alignment of the idealized ferromagnetic state. By varying the applied magnetic field, one can control one of the ordering terms which competes with the above-mentioned perturbing fields. Experiments which explore the ensuing reaction of the magnetization will therefore provide information not only on the field-dependent spin structure but, importantly, on the underlying magnetic interaction terms. This strategy, which underlies conventional studies of hysteresis loops in magnetometry, is here combined with magnetic SANS. While magnetometry generally records only a single scalar quantity, the integral magnetization, SANS provides access to a vastly richer data set, the Fourier spectrum of the response of the spin system as a function of the magnitude and orientation of the wave vector. The required data-analysis procedures have recently been established, and experiments on a number of magnetic materials, mostly nanocrystalline or nanocomposite metals, have been reported. Here, we summarize the theory of magnetic-field-dependent SANS along with the underlying description of random anisotropy magnets by micromagnetic theory. We review experiments which have explored the magnetic interaction parameters, the value of the exchange-stiffness constant as well as the Fourier components of the magnetic anisotropy field and of the magnetostatic stray field. A model-independent approach, based on the experimental autocorrelation function of the spin misalignment, provides access to the characteristic length of the spin misalignment. The field dependence of this quantity is in quantitative agreement with the predictions of

  20. Topography, Astronomy And Dynastic History In The Alignments Of The Pyramid Fields Of The Old Kingdom

    NASA Astrophysics Data System (ADS)

    Magli, G.

    It is known since the 19 century that in the layout of the pyramid field of the pharaohs of the 4th Egyptian dynasty at Giza, a "main axis" exists. Indeed, the south-east corners of these monuments align towards the site of the temple of Heliopolis, which was plainly visible in ancient times. It was later discovered that a similar situation occurs in the main pyramid field of the subsequent dynasty at Abu Sir. Here, the north-west corners of three chronologically successive pyramids again voluntarily align towards Heliopolis. However, the temple was in this case not visible, due to the rock outcrop- today occupied by the Cairo citadel - which blocks the view. In the present paper, a interdisciplinary approach based on historical, topographical and archaeoastronomical analysis is developed in an attempt at understanding such peculiar features, which governed from the very beginning the planning of these wonderful monuments. A general pattern actually arises, which appears to have inspired the choice of the sites and the disposition on the ground of almost all the funerary complexes of the kings during the Old Kingdom. In particular, this pattern helps to explain the choices in the location of the funerary complexes of Niuserre in Abusir, of Unas in Saqqara and of the kings of the 6th dynasty at south Saqqara.

  1. Polar Observations of Topside Field-Aligned O+ Flows and Auroral Forms

    NASA Technical Reports Server (NTRS)

    Stevenson, B. A.; Horwitz, J. L.; Germany, G.; Moore, T. E.; Giles, B. L.; Craven, P. D.; Chandler, M. O.; Su, Y.-J.; Parks, G. K.

    2001-01-01

    Measurements of thermal O+ ion densities, field-aligned velocities, and fluxes from the Thermal Ion Dynamics Experiment (TIDE) on Polar obtained near 5000 km altitude over the Southern Hemisphere are compared with auroral images from the Ultraviolet Imager (UVI). Three passes were selected for analysis in this paper based on data availability from the TIDE and UVI instruments. Results indicate upward O+ flows in the cleft region but downward O+ flows in the polar cap region. Also, the O+ ion density follows a decreasing trend from the poleward side of the cusp region into the nightside aurora region. The magnitude of the downward O+ parallel velocities increases from dayside to nightside across the polar cap boundary. The upflows tend to occur over or near auroral forms, while the downflows are seen in relatively dark regions, such as the polar cap. These results are consistent with a cleft ion fountain source for the polar cap O+ ions. In the nightside polar cap, the results indicate a transition from downward to upflowing field-aligned O+ ions near boundaries of bright auroral arcs.

  2. POLAR Observations of Topside Field-Aligned O+ Flows and Auroral Forms

    NASA Technical Reports Server (NTRS)

    Stevenson, B. A.; Horwitz, J. L.; Germany, G.; Moore, T. E.; Giles, B. L.; Craven, P. D.; Chandler, M. O.; Su, Y. J.; Parks, G. K.

    2000-01-01

    Measurements of thermal O (sup +) ion densities, field-aligned velocities, and fluxes from the Thermal Ion Dynamics Experiment (TIDE) on POLAR obtained near 5000 km altitude over the Southern hemisphere are compared with auroral images from the Ultra Violet Imager (UVI). We find upward O (sup +) flows in the cleft region, but subsonic O (sup +) downflows in the polar cap region. Also, the O (sup +) ion density follows a decreasing trend from the poleward side of the cusp region into the nightside aurora region. The magnitude of the downward O (sup +) parallel velocities increases from dayside to nightside across the polar cap boundary. The upflows tend to occur over or near auroral forms, while the downflows are seen in relatively dark regions, such as the polar cap. These results are consistent with a cleft ion fountain source for the polar cap O (sup +) ions. In the nightside polar cap, the results indicate a transition from downward to upflowing field-aligned O (sup +) ions near boundaries of bright auroral arcs.

  3. Dynamics of the field-aligned current distribution during a magnetic storm: AMPERE

    NASA Astrophysics Data System (ADS)

    Vassiliadis, D.; Tepke, B. P.

    2015-12-01

    Field-aligned current density in the ionosphere can be used to identify the location and intensity of solar wind-magnetosphere-ionosphere coupling, and help identify the large-scale processes that contribute to this coupling. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) mission effectively provides high-resolution spatial and temporal measurements of the radial current during magnetic storms. These in situ measurements are complementary to magnetic remote sensing from the ground using magnetometer arrays. Here we examine two storms, on May 29, 2010 and August 5, 2011, using AMPERE and solar wind data. We identify the regions whose radial current density has the greatest correlation with solar wind coupling functions and individual magnetic and plasma variables. We develop a statistical model of the radial current density from the magnetospheric and solar wind data which is then used to represent regions of outflowing and inflowing current in the two hemispheres. While the model is limited in representing high spatial resolution, time series of regional and global field-aligned current are reproduced with relatively large correlation coefficients (0.70-0.90) in each event.

  4. Suppression of drift wave instability due to sheared field-aligned flow and negative ions

    NASA Astrophysics Data System (ADS)

    Ichiki, Ryuta; Hayashi, Kenichiro; Kaneko, Toshiro; Hatakeyama, Rikizo

    2006-10-01

    Sheared field-aligned plasma flow is a significant topic in space/circumterrestrial plasmas. Taking into account negative ions or dust grains will make the space plasma physics more general and accurate. Using the QT-Upgrade Machine, we have conducted laboratory experiments to examine negative ion effects on shear-modified drift waves. Field-aligned K^+ ion flow and its shear strength are controlled with a concentrically segmented W hot plate. Negative ions SF6^- are produced by introducing SF6 gas in the plasma. The drift wave shows a gradual monotonic decrease in amplitude as the shear strength is increased from zero. However, as the shear strength is decreased from zero to negative values, the amplitude increases up to a certain shear strength and rapidly decreases after the peaking. The negative ion introduction, in general, suppresses this instability while retaining the dependence of the amplitude on the shear. These wave characteristics are interpreted using the theories of current-driven (kinetic) and of D’Angelo (fluid) instabilities.

  5. On the far field patterns for electromagnetic scattering by a chiral obstacle in a chiral environment

    NASA Astrophysics Data System (ADS)

    Athanasiadis, Christodoulos

    2005-09-01

    A time-harmonic plane electromagnetic wave is scattered by a chiral body in a chiral environment. The body is either a perfect conductor, or a dielectric, or a scatterer with an impedance surface. Using the Huygens's principle, we construct in closed forms both the left-circularly polarized and right-circularly polarized electric far field patterns for such chiral mediaE We prove reciprocity relations and general scattering theorems for chiral materials which are a generalization of those obtained by Twersky for achiral electromagnetic scattering. In the special case when the directions of incidence and observation are the same we prove the associated forward scattering theorems.

  6. Single and multiple light scattering studies of PDLC films in the presence of electric fields

    NASA Astrophysics Data System (ADS)

    Wu, Wei

    Light scattering from Polymer Dispersed Liquid Crystal (PDLC) films is studied in four major respects: the differential scattering cross-section of a single liquid crystal droplet; the total scattering cross-section and film transmittance; multiple scattering effects; and scattering by absorbing droplets (PDLC doped with dichroic dye). The effects of applied electric field, light wavelength and the liquid crystal droplet size on the scattering behavior are examined. PDLC scattering properties under electric field are described by combining the Anomalous Diffraction Approach (ADA) with PDLC electro-optical response theory. Numerical computation results directly demonstrate how the total scattering cross section relates to the incident light wavelength, the droplet size and the applied electric field. Transmittance measurements are used to study the total scattering cross-section. Analyses of the transmittance characteristics show good agreement with the theoretical predictions. PDLC samples with a practical contrast ratio exhibit strong multiple scattering effects. Studies of the single scattering differential cross section provide a foundation for the modeling and experimental work on the multiple scattering effects. Single scattering characteristics of a bipolar droplet director configuration are derived for a highly symmetric situation. The results offer qualitative explanations for some experimental observations, such as the presence of off-normal maxima and breakdown of rotational symmetry in the scattering pattern. As a novel approach, we propose a multiple scattering model for PDLC based on successive order and Monte Carlo methods. This model, along with ADA and electro-optical response theories, was used to calculate the angular distribution of scattered light and electric field switching response. The predictions demonstrate close quantitative agreement with experimental results. Incorporating complex refractive indices to treat dye- doped PDLC

  7. Comparison of field-aligned currents at ionospheric and magnetospheric altitudes

    NASA Technical Reports Server (NTRS)

    Spence, H. E.; Kivelson, M. G.; Walker, R. J.

    1988-01-01

    Using the empirical terrestrial magnetospheric magnetic field models of Tsyganenko and Usmanov (1982) and Tsyganenko (1987) the average field-aligned currents (FACs) in the magnetosphere were determined as a function of the Kp index. Three major model FAC systems were identified, namely, the dayside region 1, the nightside region 1, and the nightside polar cap. The models provide information about the sources of the current systems. Mapped ionospheric model FACs are compared with low-altitude measurements obtained by the spacecraft. It is found that low-altitude data can reveal either classic region 1/2 or more highly structured FAC patterns. Therefore, statistical results either obtained from observations or inferred from models are expected to be averages over temporally and spatially shifting patterns.

  8. Depth-reversal-free three-dimensional display by adjusting the light field alignment

    NASA Astrophysics Data System (ADS)

    Xie, Songlin; Sang, Xinzhu; Wang, Peng; Guo, Nan; Chen, Zhidong; Yu, Xunbo; Yan, Binbin; Wang, Kuiru; Yu, Chongxiu

    2017-03-01

    A multi-view content generation method for three-dimensional (3D) display without depth-reversed area is demonstrated. The viewing zone periodicity of an autostereoscopic display is utilized to eliminate the depth-reversal by adjusting the light field alignment in the 3D light field. The conditions that a multi-view sequence should satisfies to form a depth-reversal-free sequence are given and detailed processes for converting the multi-view sequence into a depth-reversal-free sequence are presented. Experimental results show that the depth-reversed area is well eliminated, and the smooth motion parallax can be achieved when the viewer moves in front of the display within a 60°viewing angle. The number of presented perspectives can be 8 times more than the viewpoint number of the autostereoscopic display with the help of viewing zones integration.

  9. A seasonal change in the effect of field-aligned currents at synchronous orbit

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.; Barfield, J. N.

    1980-01-01

    The expected signature of substorm field-aligned currents is described for synchronous satellites near 10 deg magnetic latitude. The main effect is a positive D perturbation premidnight and a negative D perturbation postmidnight. This behavior is illustrated for two substorms near the fall equinox. A second pair of substorms taken from winter solstice do not show the expected behavior. The absence of this effect in winter observations is verified statistically by superposed epoch analysis. A simple explanation of this behavior based on the geometry of the plane of magnetic symmetry is presented. During disturbed times at winter solstice a synchronous satellite nominally at 10 deg magnetic latitude is effectively at the magnetic equator. This distortion of the magnetic equator must be considered in future models of the disturbed magnetospheric magnetic field.

  10. DMSP F7 observations of a substorm field-aligned current

    NASA Technical Reports Server (NTRS)

    Lopez, R. E.; Spence, H. E.; Meng, C.-I.

    1991-01-01

    Observations are described of a substorm field-aligned current (FAC) system traversed by the DMSP F7 spacecraft just after 0300 UT on April 25, 1985. It is shown that the substorm FAC portion of the current system was located equatorward of the boundary between open and closed field lines. The equatorward boundary of the substorm FAC into the magnetotail was mapped using the Tsyganenko (1987) model, showing that the boundary corresponds to 6.9 earth radii. The result is consistent with the suggestion of Akasofu (1972) and Lopez and Lui (1990) that the region of substorm initiation lies relatively close to the earth and the concept that an essential feature of substorms is the disruption and diversion of the near-earth current sheet.

  11. A New Feature of Field-Aligned Auroral Ion Beams Observed by Cluster

    NASA Astrophysics Data System (ADS)

    Parks, George; lee, Ensang; Suiyan, Fu; Fillingim, Matt; Cui, Yanbon; Hong, Jinhy; Dandouras, Iaonnis; reme, henri; Canu, Patrick; Lin, Naiguo

    2015-04-01

    Cluster measures 3D distributions in one spin of the spacecraft (4s). Field-aligned ion beams (H+, He+ and O+) are often observed accelerated out of the ionosphere. The escaping beams can be narrow in velocity space or more extended with a continuous range of velocities. Narrow velocity beams indicate the particles have been accelerated by a potential structure localized in space and beams with a wider velocity range indicate the potential structure is extended and distributed along the magnetic field. The Cluster ion composition experiment has now revealed a new feature showing some H+, He+ and O+ field-aligned beams are broken into many discrete beams each with its own velocity covering a wide velocity range. To interpret the discrete beams, the potential model requires existence of many narrow isolated potential structures along a magnetic field but there are currently no U-shaped theories or models that can explain how the discrete potential structures are formed or maintained. Our interpretation is that Cluster SC have actually crossed an auroral arc structure at a height of 3.5 RE and the discrete beams represent particles accelerated on different equi-potential contours of an aurora. While similar beams are observed in three of the four SC, the detailed features are not identical, indicating the beams have limited spatial scales and/or the dynamics include temporal variations. The distance between two discrete beams is estimated to be as small as ~145-290 meters at the SC position. This dimension mapped to the ionosphere is ~72-145 meters, which is a typical thickness of an auroral arc (Maggs and Davis, PSS 16, 205, 1968). The velocity of the beam increases as the SC moves toward the equator indicating that the auroral potential is higher at lower latitudes. This talk will discuss the new discrete beams and their interesting properties.

  12. Terminator field-aligned current system: A new finding from model-assimilated data set (MADS)

    NASA Astrophysics Data System (ADS)

    Zhu, L.; Schunk, R. W.; Scherliess, L.; Sojka, J. J.; Gardner, L. C.; Eccles, J. V.; Rice, D.

    2013-12-01

    Physics-based data assimilation models have been recognized by the space science community as the most accurate approach to specify and forecast the space weather of the solar-terrestrial environment. The model-assimilated data sets (MADS) produced by these models constitute an internally consistent time series of global three-dimensional fields whose accuracy can be estimated. Because of its internal consistency of physics and completeness of descriptions on the status of global systems, the MADS has also been a powerful tool to identify the systematic errors in measurements, reveal the missing physics in physical models, and discover the important dynamical physical processes that are inadequately observed or missed by measurements due to observational limitations. In the past years, we developed a data assimilation model for the high-latitude ionospheric plasma dynamics and electrodynamics. With a set of physical models, an ensemble Kalman filter, and the ingestion of data from multiple observations, the data assimilation model can produce a self-consistent time-series of the complete descriptions of the global high-latitude ionosphere, which includes the convection electric field, horizontal and field-aligned currents, conductivity, as well as 3-D plasma densities and temperatures, In this presentation, we will show a new field-aligned current system discovered from the analysis of the MADS produced by our data assimilation model. This new current system appears and develops near the ionospheric terminator. The dynamical features of this current system will be described and its connection to the active role of the ionosphere in the M-I coupling will be discussed.

  13. Quantitative patterns of large-scale field-aligned currents in the auroral ionosphere

    SciTech Connect

    Foster, J.C.; Fuller-Rowell, T.; Evans, D.S.

    1989-03-01

    Quantitative patterns of the distribution of field-aligned current (FAC) density have been derived from gradients of the average patterns of the Hall and Pedersen currents at high latitudes under the assumption that the total current is divergence-free. The horizontal currents were calculated from empirical convection electric field models, derived from Millstone Hill radar observations, and the ionospheric Hall and Pedersen conductances, based on satellite observations of the precipitating particle energy flux and spectrum and including an average (equinox) solar contribution. These independent empirical models, and the resultant patterns of the field-aligned currents, are keyed to an auroral precipitation index which quantifies the intensity and spatial extent of high-latitude particle precipitation and which is determined from a single satellite crossing of the auroral precipitation pattern. The patterns detail the spatial distribution of the currents as a function of increasing disturbance level. The magnitudes of the total single-hemisphere currents into or out of the ionosphere are closely balanced at each activity level and increase exponentially between 0.1 and 6 MA with increasing values of the precipitation index. The interplanetary magnetic field (IMF) sector dependence of the FAC patterns is investigated for disturbed conditions. A large portion of the FAC pattern is closed by local Pedersen currents (current into the ionosphere is balanced by an equal current out of the ionosphere at that local time). This locally balanced portion of the FAC system is enhanced in the prenoon (postnoon) sector for IMF B/sub v/>+1 nT (B/sub y/<-1 nT). In addition, there are net currents into the ionosphere postnoon and out of the ionosphere in the premidnight sector.

  14. Field application of moment-based wavefront sensing to in-situ alignment and image quality assessment of astronomical spectrographs: results and analysis of aligning VIRUS unit spectrographs

    NASA Astrophysics Data System (ADS)

    Lee, Hanshin; Hill, Gary J.; Tuttle, Sarah E.; Noyola, Eva; Peterson, Trent; Vattiat, Brian L.

    2014-07-01

    Teague introduced a phase retrieval method that uses the image shape moments. More recently, an independent study arrived at a similar technique, which was then applied to in-situ full-field image-quality evaluation of spectroscopic systems. This moment-based wavefront sensing (MWFS) method relies on the geometric relation between the image shape moments and the geometric wavefront modal coefficients. The MWFS method allows a non-iterative determination of the modal coefficients from focus-modulated images at arbitrary spatial resolutions. The determination of image moments is a direct extension of routine centroid and image size calculation, making its implementation easy. Previous studies showed that the MWFS works well in capturing large low-order modes, and is quite suitable for in-situ alignment diagnostics. At the Astronomical Instrumentation conference in 2012, we presented initial results of the application of the moment-based wavefront sensing to a fiber-fed astronomical spectrograph, called VIRUS (a set of replicated 150 identical integral-field unit spectrographs contained in 75 unit pairs). This initial result shows that the MWFS can provide accurate full-field image-quality assessment for efficiently aligning these 150 spectrographs. Since then, we have assembled more than 24 unit pairs using this technique. In this paper, we detail the technical update/progress made so far for the moment-based wavefront sensing method and the statistical estimates of the before/after alignment aberrations, image-quality, and various efficiency indicators of the unit spectrograph alignment process.

  15. Electromagnetic scattering of a polarized plane wave from an ellipsoidal particle in the near field

    NASA Astrophysics Data System (ADS)

    Chen, Feinan; Li, Jia

    2017-06-01

    Within the validity of the first-order Born approximation, we study the near-zone evanescent wave properties for a polarized plane wave scattering upon an ellipsoidal particle. Integral expressions are obtained for the three-dimensional electromagnetic field of the near-zone scattered evanescent wave, and the dependences of the scattered intensity distributions on the degree of polarization of the incident wave and the scattering potential profile of the particle are presented. The scattered intensity from the particle can exhibit a focused pattern concentrated around the central scattering region, but the scattered intensity generated from a circularly polarized wave shows a smooth distribution for different scattering angles. Moreover, the scattered intensity also enhances when either the summation index or the effective radius of the particle increases. Our results can be utilized to generate near-field focused scattered patterns that can be tuned flexibly by controlling the degree of the polarization of the plane wave and the scattering potential parameters of the ellipsoidal particle.

  16. Electric fields and field-aligned currents in polar regions of the solar corona: 3-D MHD consideration

    NASA Technical Reports Server (NTRS)

    Pisanko, Yu. V.

    1995-01-01

    The calculation of the solar rotation electro-dynamical effects in the near-the-Sun solar wind seems more convenient from the non-inertial corotating reference frame. This implies some modification of the 3-D MHD equations generally on the base of the General Theory of Relativity. The paper deals with the search of stationary (in corotating non-inertial reference frame) solutions of the modified 3-D MHD equations for the in near-the-Sun high latitude sub-alfvenic solar wind. The solution is obtained requiring electric fields and field-aligned electric currents in the high latitude near-the-Sun solar wind. Various scenario are explored self-consistently via a number of numerical experiments. The analogy with the high latitude Earth's magnetosphere is used for the interpretation of the results. Possible observational manifestations are discussed.

  17. Electron Weibel instability in relativistic counterstreaming plasmas with flow-aligned external magnetic fields.

    PubMed

    Grassi, A; Grech, M; Amiranoff, F; Pegoraro, F; Macchi, A; Riconda, C

    2017-02-01

    The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.

  18. Electron Weibel instability in relativistic counterstreaming plasmas with flow-aligned external magnetic fields

    NASA Astrophysics Data System (ADS)

    Grassi, A.; Grech, M.; Amiranoff, F.; Pegoraro, F.; Macchi, A.; Riconda, C.

    2017-02-01

    The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.

  19. Calculation of electromagnetic fields in the near-field region of a moving scattering object

    NASA Astrophysics Data System (ADS)

    Vogel, M. H.

    1990-07-01

    The problem of scattering of electromagnetic fields by perfectly conducting, moving objects is solved with the Lorentz transformation and the plane wave formulation. Apart from the physical optics approximation, the solution is exact. The result is subsequently applied to the special case of monostatic reflection by an object that moves slowly with respect to the velocity of light. The result can be used to predict the time dependent reflection from an aircraft that passes the antenna of a proximity fuze, and the optimum fuze algorithm can be selected.

  20. Dependence of premidnight field-aligned currents and particle precipitation on solar illumination

    NASA Astrophysics Data System (ADS)

    Ohtani, S.; Wing, S.; Ueno, G.; Higuchi, T.

    2009-12-01

    The present study statistically addresses the dependence of large-scale field-aligned currents (R1/R2) and particle precipitation in the premidnight sector on solar illumination at the ionosphere. The energy flux and average energy of precipitating electrons and ions are examined for downward R2 and upward R1 currents. Results are summarized as follows: (1) The R1 current density is larger in the dark hemisphere, whereas the dependence of R2 density on solar illumination is unclear. (2) For R1 currents the electron energy flux is larger and the average electron energy is higher in the dark hemisphere. (3) For R2 currents, a similar preference for the dark hemisphere is found for the electron energy flux, which, however, is significantly lower than for R1 currents. The average electron energy is similar between the two hemispheres. (4) For both R1 and R2 currents, ion precipitation is more intense and energetic in the dark hemisphere. (5) For a given field-aligned current density, whether R1 or R2 currents, both electron and ion precipitation is more intense and energetic in the dark hemisphere. The Pedersen conductivity is estimated from electron precipitation and solar illumination. The result suggests that in the dark hemisphere the absence of solar illumination is often overcompensated by more intense and energetic electron precipitation. The interhemispheric difference in electron acceleration may be interpreted in terms of plasma density in the acceleration region, which is known to be significantly lower in the dark hemisphere, and therefore electrons need to be more accelerated along the field line to carry imposed currents.

  1. Climatology of the inter-hemispheric field-aligned currents system over the Nigeria ionosphere

    NASA Astrophysics Data System (ADS)

    Bolaji, O. S.; Rabiu, A. B.; Oyeyemi, E. O.; Yumoto, K.

    2012-11-01

    Records of the declination (D) magnetic field data for the year 2009 from the Magnetic Data Acquisition System (MAGDAS) facilities at University of Ilorin were employed for this work. From the minutes value of the D-component, the deduced hourly values of the D-component (Sq(QD)) were used to estimate its diurnal (Sq(D)) values with the most five quietest days identified. The monthly mean (MSq(D)) of the most five quietest days and their seasonal (SSq(D)) variabilities were investigated. The inter-hemispheric field aligned currents (IHFACs) exhibit downward and upward inter-hemispheric field-aligned sheet current that appears as a pair at all local times of the Sq(D), MSq(D), and SSq(D) variations. From these variabilities, the IHFACs were observed to flow from the winter to summer hemisphere during noon and dusk sector and flowing in opposite direction during the dawn sector. The Sq(D) variability patterns that were observed in May, June, August September are gentle compared to the disturbed variabilities in January, February, March and November. The highest positive (˜1.7 arc-min) and negative (˜-2.7 arc min) MSq(D) maxima values were observed in August during the dawn and noon sectors respectively. These values indicated that the IHFACs flow in August is strongly southbound (positive) and northbound (negative) in the dawn and noon sectors respectively. Dusk-side IHFACs as can be observed by MAGDAS are weakly northbound in all the seasons. The direction of IHFACs does not flip at the equinoxes but in June and November and does not become largest at solstices but in August. The IHFACs was observed to exhibit longitudinal variability, which indicated that larger amplitude of winter-to-summer IHFACs is observed to be greater in June solstice (northbound/negative IHFACs) than in the December solstice (southbound/positive IHFACs) during the noon sector.

  2. Application of The Alfvén-Assisted Precipitation Model to Field-Aligned Electron Bursts

    NASA Astrophysics Data System (ADS)

    Lee, J. H.; Clemmons, J. H.; Angelopoulos, V.; Pfaff, R. F.; Wallis, D. D.; Knudsen, D. J.

    2009-12-01

    A close relationship between field-aligned electron bursts and Alfvén waves has been identified by numerous sounding rocket and satellite missions. While previous work has demonstrated the ability of inertial Alfvén waves to accelerate electrons along the geomagnetic field lines in the dayside cusp, the nightside signatures of Alfvén wave interactions with cold electrons in the auroral ionosphere have yet to be explained in a reasonable manner. The Alfvén-assisted precipitation model and new analyses of observations supporting its validity are presented. High time resolution electron flux data from the GEODESIC sounding rocket flight of 2000, taken during an active auroral breakup, show dozens of field-aligned electron bursts; the bursts display energy-time dispersion with higher energy electrons appearing earlier in time and have peak energies with a range up to—but not exceeding—the energy of a nearby inverted-V peak, up to about 20 keV. Several of these bursts occur separately from inverted-V electron distributions and an instance of a burst occurring near the edge of an auroral arc with fluxes higher than the accompanying inverted-V electron distribution is also present. The observations not only suggest separate source locations for the burst electrons and the quasistatic, isotropic inverted-V electrons, but also support the existence of a quasistatic potential structure without simultaneous inverted-V electron precipitation. The model incorporates the aforementioned attributes displayed by the observations and provides a set of physical parameters which help characterize individual phenomena. Energy-time dispersion signatures are derived and shown for each of the individual bursts; model fits to these signatures demonstrate agreement with the model. Examples from Freja and FAST satellite data are also discussed.

  3. Static magnetic fields enhance skeletal muscle differentiation in vitro by improving myoblast alignment.

    PubMed

    Coletti, Dario; Teodori, Laura; Albertini, Maria C; Rocchi, Marco; Pristerà, Alessandro; Fini, Massimo; Molinaro, Mario; Adamo, Sergio

    2007-10-01

    Static magnetic field (SMF) interacts with mammal skeletal muscle; however, SMF effects on skeletal muscle cells are poorly investigated. The myogenic cell line L6, an in vitro model of muscle development, was used to investigate the effect of a 80 +/- mT SMF generated by a custom-made magnet. SMF promoted myogenic cell differentiation and hypertrophy, i.e., increased accumulation of actin and myosin and formation of large multinucleated myotubes. The elevated number of nuclei per myotube was derived from increased cell fusion efficiency, with no changes in cell proliferation upon SMF exposure. No alterations in myogenin expression, a modulator of myogenesis, occurred upon SMF exposure. SMF induced cells to align in parallel bundles, an orientation conserved throughout differentiation. SMF stimulated formation of actin stress-fiber like structures. SMF rescued muscle differentiation in the presence of TNF, a muscle differentiation inhibitor. We believe this is the first report showing that SMF promotes myogenic differentiation and cell alignment, in the absence of any invasive manipulation. SMF-enhanced parallel orientation of myotubes is relevant to tissue engineering of a highly organized tissue such as skeletal muscle. SMF rescue of muscle differentiation in the presence of TNF may have important therapeutic implications.

  4. High-energy scatterings in infinite-derivative field theory and ghost-free gravity

    NASA Astrophysics Data System (ADS)

    Talaganis, Spyridon; Mazumdar, Anupam

    2016-07-01

    In this paper, we will consider scattering diagrams in the context of infinite-derivative theories. First, we examine a finite-order, higher-derivative scalar field theory and find that we cannot eliminate the growth of scattering diagrams for large external momenta. Then, we employ an infinite-derivative scalar toy model and obtain that the external momentum dependence of scattering diagrams is convergent as the external momenta become very large. In order to eliminate the external momentum growth, one has to dress the bare vertices of the scattering diagrams by considering renormalised propagator and vertex loop corrections to the bare vertices. Finally, we investigate scattering diagrams in the context of a scalar toy model which is inspired by a ghost-free and singularity-free infinite-derivative theory of gravity, where we conclude that infinite derivatives can eliminate the external momentum growth of scattering diagrams and make the scattering diagrams convergent in the ultraviolet.

  5. Interplanetary magnetic field control of mantle precipitation and associated field-aligned currents

    NASA Technical Reports Server (NTRS)

    Xu, Dingan; Kivelson, Margaret G.; Walker, Ray J.; Newell, Patrick T.; Meng, C.-I.

    1995-01-01

    Dayside reconnection, which is particularly effective for a southward interplanetary magnetic field (IMF), allows magnetosheath particles to enter the magnetosphere where they form the plasma mantle. The motions of the reconnected flux tube produce convective flows in the ionosphere. It is known that the convection patterns in the polar cap are skewed to the dawnside for a positive IMF B(sub y) (or duskside for a negative IMF B(sub y)) in the northern polar cap. Correspondingly, one would expect to find asymmetric distributions of mantle particle precipitation, but previous results have been unclear. In this paper the correlation between B(sub y) and the distribution of mantle particle precipitation is studied for steady IMF conditions with southward IMF. Ion and electron data from the Defense Meteorological Satellite Program (DMSP) F6 and F7 satellites are used to identify the mantle region and IMP 8 is used as a solar wind monitor to characterize the IMF. We study the local time extension of mantle precipitation in the prenoon and postnoon regions. We find that, in accordance with theoretical expectations for a positive (negative) IMF B(sub y), mantle particle precipitation mainly appears in the prenoon region of the northern (southern) hemisphere. The mantle particle precipitation can extend to as early as 0600 magnetic local time (MLT) in the prenoon region but extends over a smaller local time region in the postnoon sector (we did not find mantle plasma beyond 1600 MLT in our data set although coverage is scant in this area). Magnetometer data from F7 are used to determine whether part of the region 1 current flows on open field lines. We find that at times part of the region 1 sense current extends into the region of mantle particle precipitation, and is therefore on open field lines. In other cases, region 1 currents are absent on open field lines. Most of the observed features can be readily interpreted in terms of the open magnetosphere model.

  6. Interplanetary magnetic field control of mantle precipitation and associated field-aligned currents

    NASA Technical Reports Server (NTRS)

    Xu, Dingan; Kivelson, Margaret G.; Walker, Ray J.; Newell, Patrick T.; Meng, C.-I.

    1995-01-01

    Dayside reconnection, which is particularly effective for a southward interplanetary magnetic field (IMF), allows magnetosheath particles to enter the magnetosphere where they form the plasma mantle. The motions of the reconnected flux tube produce convective flows in the ionosphere. It is known that the convection patterns in the polar cap are skewed to the dawnside for a positive IMF B(sub y) (or duskside for a negative IMF B(sub y)) in the northern polar cap. Correspondingly, one would expect to find asymmetric distributions of mantle particle precipitation, but previous results have been unclear. In this paper the correlation between B(sub y) and the distribution of mantle particle precipitation is studied for steady IMF conditions with southward IMF. Ion and electron data from the Defense Meteorological Satellite Program (DMSP) F6 and F7 satellites are used to identify the mantle region and IMP 8 is used as a solar wind monitor to characterize the IMF. We study the local time extension of mantle precipitation in the prenoon and postnoon regions. We find that, in accordance with theoretical expectations for a positive (negative) IMF B(sub y), mantle particle precipitation mainly appears in the prenoon region of the northern (southern) hemisphere. The mantle particle precipitation can extend to as early as 0600 magnetic local time (MLT) in the prenoon region but extends over a smaller local time region in the postnoon sector (we did not find mantle plasma beyond 1600 MLT in our data set although coverage is scant in this area). Magnetometer data from F7 are used to determine whether part of the region 1 current flows on open field lines. We find that at times part of the region 1 sense current extends into the region of mantle particle precipitation, and is therefore on open field lines. In other cases, region 1 currents are absent on open field lines. Most of the observed features can be readily interpreted in terms of the open magnetosphere model.

  7. Alignment- and orientation-dependent strong-field ionization of molecules: Field-induced orbital distortion effects

    NASA Astrophysics Data System (ADS)

    Spiewanowski, Maciej Dominik; Madsen, Lars Bojer

    2015-05-01

    Strong-field ionization (SFI) is a starting point for many strong-field phenomena, e.g., high-order harmonic generation, as well as a source of fundamental information about the ionized target. Therefore, investigation of SFI of atoms and molecules has been the aim for research since the first strong laser pulses became available. We present a recently developed method, adiabatic strong-field approximation, to study ionization yields as a function of alignment angle for CO2, CO, and OCS molecules. We show that orbital distortion plays an important role in explaining the position and relative strength of maxima in the yields for both polar and nonpolar molecules, even for targets with low polarizabilities at low laser intensities. In particular, we report that for ionization of CO2 the maximum in ionization yield shifts towards the experimentally-measured maximum with respect to the strong-field approximation. For ionization of the CO molecule, not only does the theory predict the preferred direction of ionization correctly, but also the ratio between yields for the two molecular orientations where the electric field points either towards the C or towards the O end. Finally, we find that ionization of OCS is more probable for the laser pointing from the O end towards the S end. Work supported by the Natural Sciences and Engineering Research Council of Canada, the ERC-StG (Project No. 277767-TDMET), and the VKR center of excellence, QUS- COPE.

  8. Acoustic radiation torque on an irregularly shaped scatterer in an arbitrary sound field.

    PubMed

    Fan, Zongwei; Mei, Deqing; Yang, Keji; Chen, Zichen

    2008-11-01

    To eliminate the limitation of the conventional acoustic radiation torque theory, which is only applicable to a disklike scatterer in a plane sound field, a new theory is established to calculate the radiation torque on any irregularly shaped scatterer in any arbitrary sound field. First, with the aid of the conservation law of angular momentum, the acoustic radiation torque is expressed as the angular momentum flux through a spherical surface with the center at the scatterer's centroid. Second, the velocity potential of the scattered field is derived, taking into account the influences of the translational and rotational movements of the scatterer induced by the first order stress of the incident sound field. Finally, a general calculating formula of the acoustic radiation torque is achieved. For a disklike scatterer in a plane sound filed, results from the above formula are well identical with those conventional formulas. By studying the case of a semicircular cylinder scatterer in a standing-wave sound field, it is found that for an irregularly shaped scatterer its rotation velocity is normally nonzero and the radiation torque changes with the spatial attitude.

  9. Field emission luminescence of nanodiamonds deposited on the aligned carbon nanotube array

    PubMed Central

    Fedoseeva, Yu. V.; Bulusheva, L. G.; Okotrub, A. V.; Kanygin, M. A.; Gorodetskiy, D. V.; Asanov, I. P.; Vyalikh, D. V.; Puzyr, A. P.; Bondar, V. S.

    2015-01-01

    Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT–ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT–ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT–ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis. PMID:25797710

  10. Field emission luminescence of nanodiamonds deposited on the aligned carbon nanotube array

    NASA Astrophysics Data System (ADS)

    Fedoseeva, Yu. V.; Bulusheva, L. G.; Okotrub, A. V.; Kanygin, M. A.; Gorodetskiy, D. V.; Asanov, I. P.; Vyalikh, D. V.; Puzyr, A. P.; Bondar, V. S.

    2015-03-01

    Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT-ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT-ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT-ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis.

  11. Field emission behavior of vertically aligned ZnO nanowire planar cathodes

    SciTech Connect

    Semet, V.; Binh, Vu Thien; Pauporte, Th.; Joulaud, L.; Vermersch, F. J.

    2011-03-01

    A field emission (FE) study by scanning anode field emission microscopy was performed to evaluate the FE properties of vertically aligned zinc oxide (ZnO) nanowire arrays electrodeposited on a plane conductive surface. The specific FE behaviors of the cathode observed experimentally are (1) a turn-on macroscopic field of about 6 V/{mu}m for a FE current density J{sub FE} 5 x 10{sup -4} A/cm{sup 2}, (2) a stable FE characteristics for 5 x 10{sup -4} < J{sub FE} < 5 x 10{sup -2} A/cm{sup 2}, and (3) a brutal shut down of FE when J{sub FE} crossed a limiting value of {approx}0.05 A/cm{sup 2} due to a rapid evolution of the nanowires toward a bulbous tip geometry or a complete melting. A physical process of FE from ZnO nanostructures is proposed from the experimental data analyses. An effective surface barrier of about 1 eV was determined from the experimental Fowler-Nordheim plot and the presence of a Zn enriched surface was assumed in considering the possibility of important modifications of the crystallography and charge transfers at the surface of ZnO nanowires during the application of the strong electric field required for FE.

  12. Field emission luminescence of nanodiamonds deposited on the aligned carbon nanotube array.

    PubMed

    Fedoseeva, Yu V; Bulusheva, L G; Okotrub, A V; Kanygin, M A; Gorodetskiy, D V; Asanov, I P; Vyalikh, D V; Puzyr, A P; Bondar, V S

    2015-03-23

    Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT-ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT-ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT-ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis.

  13. Time-of-Flight Bragg Scattering from Aligned Stacks of Lipid Bilayers using the Liquids Reflectometer at the Spallation Neutron Source

    SciTech Connect

    Pan, Jianjun; Heberle, Frederick A; Carmichael, Justin R; Ankner, John Francis; Katsaras, John

    2012-01-01

    Time-of-flight (TOF) neutron diffraction experiments on aligned stacks of lipid bilayers using the horizontal Liquids Reflectometer at the Spallation Neutron Source are reported. Specific details are given regarding the instrumental setup, data collection and reduction, phase determination of the structure factors, and reconstruction of the one-dimensional neutron scattering length density (NSLD) profile. The validity of using TOF measurements to determine the one-dimensional NSLD profile is demonstrated by reproducing the results of two well known lipid bilayer structures. The method is then applied to show how an antimicrobial peptide affects membranes with and without cholesterol.

  14. Direct fabrication of aligned metal composite carbon nanofibers on copper substrate at room temperature and their field emission property.

    PubMed

    Ghosh, Pradip; Yusop, M Zamri; Ghosh, Debasish; Hayashi, Akari; Hayashi, Yasuhiko; Tanemura, Masaki

    2011-04-28

    Direct growth of aligned metal composite carbon nanofibers (MCNFs) was achieved by a highly reproducible room temperature growth process on cost effective electrically conductive copper (Cu) substrate without any catalyst. The direct fabrication of MCNFs on electrically conductive substrate might offer new perspectives in the field of field emission displays (FEDs).

  15. Self-aligned, full solution process polymer field-effect transistor on flexible substrates

    PubMed Central

    Yan, Yan; Huang, Long-Biao; Zhou, Ye; Han, Su-Ting; Zhou, Li; Zhuang, Jiaqing; Xu, Zong-Xiang; Roy, V. A. L.

    2015-01-01

    Conventional techniques to form selective surface energy regions on rigid inorganic substrates are not suitable for polymer interfaces due to sensitive and soft limitation of intrinsic polymer properties. Therefore, there is a strong demand for finding a novel and compatible method for polymeric surface energy modification. Here, by employing the confined photo-catalytic oxidation method, we successfully demonstrate full polymer filed-effect transistors fabricated through four-step spin-coating process on a flexible polymer substrate. The approach shows negligible etching effect on polymeric film. Even more, the insulating property of polymeric dielectric is not affected by the method, which is vital for polymer electronics. Finally, the self-aligned full polymer field-effect transistors on the flexible polymeric substrate are fabricated, showing good electrical properties and mechanical flexibility under bending tests. PMID:26497412

  16. Variations of thermal electron energy distribution associated with field-aligned currents

    SciTech Connect

    Oyama, Kohichiro ); Fukunishi, Hiroshi ); Abe, Takumi; Okuzawa, Takashi; Fujii, Ryoichi

    1991-02-01

    Relationships between thermal electrons and field aligned currents (FACs) in the auroral region have been investigated using data simultaneously obtained from the Thermal Electron Detector (TED) and the fluxgate magnetometer both onboard the EXOS-D satellite. Several features resulted from the observations are summarized as; (1) At altitudes from 300 to 1,800km, electron temperature in the upward FAC region is higher than that of the neighboring no FAC region by the increment {Delta}T=1,100-9,500K, while the temperature is lower in the downward FAC region by the decrement {minus}{Delta}T=500-1,500K. (2) The electron temperature increase in the upward-current region grows with an increase of the FAC density. (3) The thermal electrons do not have Maxwell distribution in the upward-current region at altitudes higher than about 2,000km.

  17. Atomic barium and cesium alignment-to-orientation conversion in external electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Hilborn, Robert C.; Hunter, Larry R.; Johnson, Kent; Peck, Stephen K.; Spencer, Alison; Watson, John

    1994-09-01

    We present an alternative method for changing atomic alignment to orientation through interactions with orthogonal static electric and magnetic fields. Experimental results demonstrating this effect in the 5d6p 1P state of atomic barium and the F=4 hyperfine level of the ground state of atomic cesium are presented. The theory of this effect for a j=0 to j=1 electric dipole transition is discussed in detail. The tensor polarizability of the 5d6p 1P state of Ba is determined to be 1.31(15) MHz/(kV/cm)2, in good agreement with the results of van Leeuwen and Hogervorst [Z. Phys. A 310, 37 (1983)].

  18. A finite element Poisson solver for gyrokinetic particle simulations in a global field aligned mesh

    SciTech Connect

    Nishimura, Y. . E-mail: nishimuy@uci.edu; Lin, Z.; Lewandowski, J.L.V.; Ethier, S.

    2006-05-20

    A new finite element Poisson solver is developed and applied to a global gyrokinetic toroidal code (GTC) which employs the field aligned mesh and thus a logically non-rectangular grid in a general geometry. Employing test cases where the analytical solutions are known, the finite element solver has been verified. The CPU time scaling versus the matrix size employing portable, extensible toolkit for scientific computation (PETSc) to solve the sparse matrix is promising. Taking the ion temperature gradient modes (ITG) as an example, the solution from the new finite element solver has been compared to the solution from the original GTC's iterative solver which is only efficient for adiabatic electrons. Linear and nonlinear simulation results from the two different forms of the gyrokinetic Poisson equation (integral form and the differential form) coincide each other. The new finite element solver enables the implementation of advanced kinetic electron models for global electromagnetic simulations.

  19. Controllable deposition distance of aligned pattern via dual-nozzle near-field electrospinning

    NASA Astrophysics Data System (ADS)

    Wang, Zhifeng; Chen, Xindu; Zeng, Jun; Liang, Feng; Wu, Peixuan; Wang, Han

    2017-03-01

    For large area micro/nano pattern printing, multi-nozzle electrohydrodynamic (EHD) printing setup is an efficient method to boost productivity in near-field electrospinning (NFES) process. And controlling EHD multi-jet accurate deposition under the interaction of nozzles and other parameters are crucial concerns during the process. The influence and sensitivity of various parameters such as the needle length, needle spacing, electrode-to-collector distance, voltage etc. on the direct-write patterning performance was investigated by orthogonal experiments with dual-nozzle NFES setup, and then the deposition distance estimated based on a novel model was compared with measurement results and proven. More controllable deposition distance and much denser of aligned naofiber can be achieved by rotating the dual-nozzle setup. This study can be greatly contributed to estimate the deposition distance and helpful to guide the multi-nozzle NFES process to accurate direct-write pattern in manufacturing process in future.

  20. Self-aligned multi-channel silicon nanowire field-effect transistors

    NASA Astrophysics Data System (ADS)

    Zhu, Hao; Li, Qiliang; Yuan, Hui; Baumgart, Helmut; Ioannou, Dimitris E.; Richter, Curt A.

    2012-12-01

    Si nanowire field effect transistors (SiNW FETs) with multiple nanowire channels and different gate lengths have been fabricated by using a directed assembly approach combined with a standard photolithographic process. The electrical characteristics of SiNW FETs containing different numbers of nanowire channels were measured and compared. The multi-channel SiNW FETs show excellent performance: small subthreshold slope (≈75 mV/dec), large ON/OFF ratio (≈108), good break-down voltage (>30 V) and good carrier mobility (μp ≈ 100 cm2 V-1s-1). These excellent device properties were achieved by using a clean self-alignment process and an improved device structure with Schottky barriers at the source and drain contacts. Such high-performance multi-nanowire FETs are attractive for logic, memory, and sensor applications.

  1. Field-induced alignment of a smectic-A phase: a time-resolved x-ray diffraction investigation.

    PubMed

    Bras, W; Emsley, J W; Levine, Y K; Luckhurst, G R; Seddon, J M; Timimi, B A

    2004-09-01

    The field-induced alignment of a smectic-A phase is, in principle, a complicated process involving the director rotation via the interaction with the field and the layer rotation via the molecular interactions. Time-resolved nuclear magnetic resonance spectroscopy has revealed this complexity in the case of the director alignment, but provides no direct information on the motion of the layers. Here we describe a time-resolved x-ray diffraction experiment using synchrotron radiation to solve the challenging problem of capturing the diffraction pattern on a time scale which is fast in comparison with that for the alignment of the smectic layers. We have investigated the alignment of the smectic-A phase of 4-octyl-4(')-cyanobiphenyl by a magnetic field. The experiment consists of creating a monodomain sample of the smectic-A phase by slow cooling from the nematic phase in a magnetic field with a flux density of 7 T. The sample is then turned quickly through an angle phi(0) about an axis parallel to the x-ray beam direction but orthogonal to the field. A sequence of two-dimensional small angle x-ray diffraction patterns are then collected at short time intervals. Experiments were carried out for different values of phi(0), and at different temperatures. The results show that the alignment behavior changes fundamentally when phi(0) exceeds 45 degrees, and that there is a sharp change in the alignment process when the temperature is less than 3 degrees C below the smectic-A-nematic transition. The results of the x-ray experiments are in broad agreement with the NMR results, but reveal major phenomena concerning the maintenance of the integrity of the smectic-A layer structure during the alignment process. (c) 2004 American Institute of Physics

  2. Relation of field-aligned currents measured by AMPERE project to solar wind and substorms

    NASA Astrophysics Data System (ADS)

    McPherron, R. L.; Anderson, B. J.; Chu, X.

    2016-12-01

    Magnetic perturbations measured in the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) by the Iridium constellation of spacecraft have been processed to obtain the time history of field-aligned currents (FAC) connecting the magnetosphere to the ionosphere. We find that the strength of these currents is closely related to the strength of the solar wind driver defined as a running average of the previous three hours of the optimum AL (auroral lower) coupling function. The relation is well represented by a saturation model I = A*S*Ss/(S+Ss) with I the current strength in mega Amps, S the driver strength in mV/m, Ss the saturation value of 7.78 mV/m, and A = 2.55 scales the relation to units of current. We also find that in general the upward current on the nightside increases with each substorm expansion onset defined by a combination of the SuperMag SML (SuperMag AL) and midlatitude positive bay (MPB) onset lists. A superposed epoch analysis using 700 onsets in 2010 shows the following: solar wind coupling peaks at expansion onset; dayside outward current starts to increase one hour before onset while nightside outward current starts suddenly at onset; nightside outward current reaches a peak at 28 minutes as do SML and MPB indices; FAC, SML, and MPB respectively take 1, 2, and 3 hours to decay to background. The data indicate that the substorm current wedge is superposed on a pre-existing field-aligned current system and that the location and properties of the current wedge can be studied with the AMPERE data.

  3. Simultaneous measurements of HF-enhanced plasma waves and artificial field-aligned irregularities at Arecibo

    SciTech Connect

    Noble, S.T. ); Djuth, F.T. )

    1990-09-01

    Two radar systems with beams intersecting in the HF-modified F region were used to simultaneously measure HF-enhanced plasma lines (HFPLs) and artificial geomagnetic field-aligned irregularities (AFAIs). The Arecibo 430-MHz radar was used for the HFPL observations, and a portable 49.92-MHz backscatter radar was deployed on the island of Guadeloupe to monitor the AFAIs. The experiment was desgined to examine the degree to which HF-induced plasma turbulence influences the development of AFAIs. When the HF beam is stepped up in power, sustained HFPLs and AFAIs are first observed at the same HF power level, indicating that ponderomotively driven instabilities may be involved in the early time development of AFAIs. As the HF power is increased, the HFPL backscatter power begins to saturate at {approximately}70 MW effective radiated power (ERP). However, the backscatter from AFAIs is linearly dependent on HF power, even at the highest (120 MW ERP) HF power levels available at Arecibo. This suggests that additional processes may contribute to the development of AFAIs. For example, ponderomotively driven instabilities may give rise to weak geomagnetic field-aligned irregularities that are subsequently driven unstable by processes excited near the upper hybrid resonance. It is also likely that AFAIs greatly impact the development of HF-induced plasma turbulence at late times (>1 s) following HF turn-on. Once the ionosphere is preconditioned by high-power HF modifications, AFAIs and HFPLs can be simultaneously sustained at a much lower HF power level than that needed to originally excite them. The nature of the preconditioning process is currently not well understood. New theoretical initiatives are clearly needed to guide future experimental activity in this area.

  4. Intermediate regime of charged particle scattering in the field-reversal configuration.

    PubMed

    Shustov, P I; Artemyev, A V; Yushkov, E V

    2015-12-01

    In this paper, we investigate the charged particle scattering in the magnetic field configuration with stretched magnetic field lines. This scattering results from the violation of the adiabaticity of charged particle motion in the region with the strong gradient of the magnetic field. We consider the intermediate regime of charged particle dynamics, when the violation of the adiabaticity is significant enough, but particle motion is not chaotic. We demonstrate and describe the significant scattering of particles with large adiabatic invariants (magnetic moment). We discuss a possible application of obtained results for description of the peculiarities of pitch-angle diffusion of relativistic electrons in the Earth radiation belts.

  5. Intermediate regime of charged particle scattering in the field-reversal configuration

    SciTech Connect

    Shustov, P. I. Yushkov, E. V.; Artemyev, A. V.

    2015-12-15

    In this paper, we investigate the charged particle scattering in the magnetic field configuration with stretched magnetic field lines. This scattering results from the violation of the adiabaticity of charged particle motion in the region with the strong gradient of the magnetic field. We consider the intermediate regime of charged particle dynamics, when the violation of the adiabaticity is significant enough, but particle motion is not chaotic. We demonstrate and describe the significant scattering of particles with large adiabatic invariants (magnetic moment). We discuss a possible application of obtained results for description of the peculiarities of pitch-angle diffusion of relativistic electrons in the Earth radiation belts.

  6. By-controlled convection and field-aligned currents near midnight auroral oval for northward interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Taguchi, S.; Sugiura, M.; Iyemori, T.; Winningham, J. D.; Slavin, J. A.

    1994-01-01

    Using the Dynamics Explorer (DE) 2 magnetic and electric field and plasma data, B(sub y)- controlled convection and field-aligned currents in the midnight sector for northward interplanetary magnetic field (IMF) are examined. The results of an analysis of the electric field data show that when IMF is stable and when its magnitude is large, a coherent B(sub y)-controlled convection exists near the midnight auroral oval in the ionosphere having adequate conductivities. When B(sub y) is negative, the convection consists of a westward (eastward) plasma flow at the lower latitudes and an eastward (westward) plasma flow at the higher latitudes in the midnight sector in the northern (southern) ionosphere. When B(sub y) is positive, the flow directions are reversed. The distribution of the field-aligned currents associated with the B(sub y)-controlled convection, in most cases, shows a three-sheet structure. In accordance with the convection the directions of the three sheets are dependent on the sign of B(sub y). The location of disappearance of the precipitating intense electrons having energies of a few keV is close to the convection reversal surface. However, the more detailed relationship between the electron precipitation boundary and the convection reversal surface depends on the case. In some cases the precipitating electrons extend beyond the convection reversal surface, and in others the poleward boundary terminates at a latitude lower than the reversal surface. Previous studies suggest that the poleward boundary of the electrons having energies of a few keV is not necessarily coincident with an open/closed bounary. Thus the open/closed boundary may be at a latitude higher than the poleward boundary of the electron precipitation, or it may be at a latitude lower than the poleward boundary of the electron precipitation. We discuss relationships between the open/closed boundary and the convection reversal surface. When as a possible choice we adopt a view that the

  7. Predicting Field-Aligned Transport and Acceleration of Solar Energetic Particles During Extreme Space Weather Events

    NASA Astrophysics Data System (ADS)

    Borovikov, D.; Sokolov, I.; Gombosi, T. I.

    2016-12-01

    Solar Energetic Particle (SEP) phenomena represent one of the major components of space weather. Often, but not exclusively associated with Coronal Mass Ejections (CMEs), they pose a significant scientific as well as practical interest. As these particles originate at such explosive events, they have energies up to several GeV. SEP may cause disruptions in operations of space instruments and spacecrafts and are dangerous to astronauts. For this reason, studies of SEP events and predictions of their impact are of great importance. The motion and acceleration of SEP, though kinetic in nature, is governed by Interplanetary Magnetic Field (IMF) and its disturbances. Therefore, a consistent and accurate simulation and predictive tool must include a realistic MHD model of IMF. At the same time, transport of SEP is essentially one-dimensional as at high energies particles are tied to magnetic field lines. This allows building a model that can effectively map active regions on the solar surface onto various regions of the Solar System thus predicting the affected regions of the at any distance from the Sun. We present an attempt to construct a model for field-aligned transport and acceleration of SEP. The first results are provided.

  8. Field-aligned electrostatic potential differences on the Martian night side

    NASA Astrophysics Data System (ADS)

    Lillis, Rob; Collinson, Glyn; Mitchell, David

    2017-04-01

    Field-aligned electrostatic potential differences on the Martian night side above 170 km can be inferred with the aid of a kinetic electron transport model and in a statistical sense, by energy-dependent angular shifts in electron loss cones measured in Mars orbit. Potentials between 170 km and 400 km derived from pitch angle distributions measured by the Mars Global Surveyor (MGS) Magnetometer/ Electron Reflectometer experiment (MAG/ER) at 2 a.m. local time are typically small (-10 V to 10 V) but can reach magnitudes of >100 V. Geographically, the strongest negative potential differences (with mean values up to -50 V) are preferentially observed at the boundaries between open and closed strong magnetic field regions, while positive potential differences are preferentially observed further from open field lines. These characteristics may reflect current systems closing at high altitude through cross-tail currents and at low altitude in the conducting night side ionosphere. We will present a synthesis of potentials derived from pitch angle distributions measured by both MGS MAG/ER as mentioned above, and by the MAVEN Solar Wind Electron Analyzer (SWEA) collected at a range of local times and altitudes.

  9. Field-aligned currents distribution as derived from the Swarm satellite constellation

    NASA Astrophysics Data System (ADS)

    Luhr, H.; Kervalishvili, G.; Rauberg, J.; Michaelis, I.

    2015-12-01

    The seminal studies of Iijima and Potemra have outlined the major distribution features of field-aligned currents (FACs) in a local time versus magnetic latitude frame. The related plot showing the Region 1 and 2 FAC belts has been the reference in many studies as the baseline configuration during the past decades. What did we learn more since then? ESA's constellation mission Swarm provides the opportunity to derive more reliable FAC estimates from multi-satellite magnetic field measurements. We make use of the Swarm A/C satellite pair, which flies side-by-side at a separation of 1.4° in longitude. By considering along-track differences over 5 s the four readings at the corners of an almost symmetrical quad are used for calculating the mean vertical current density flowing through the encircled area. FACs are estimated by mapping the vertical current component onto the field direction. Within the auroral oval current estimates from single and dual-satellite solutions agree generally well. Significant differences are frequently observed in the polar cap. Here underlying assumptions for single-satellite solutions are obviously not well satisfied. Another characteristic derived from the multi-satellite observations: FACs can be divided into two classes. For scale sizes up to some ten kilometers rapid temporal variations are observed. These FACs are related to kinetic Alfvén waves. The other class with scale lengths of more than 150 km can be regarded as stationary current systems lasting for more than a minute.

  10. Room temperature-synthesized vertically aligned InSb nanowires: electrical transport and field emission characteristics

    PubMed Central

    2013-01-01

    Vertically aligned single-crystal InSb nanowires were synthesized via the electrochemical method at room temperature. The characteristics of Fourier transform infrared spectrum revealed that in the syntheses of InSb nanowires, energy bandgap shifts towards the short wavelength with the occurrence of an electron accumulation layer. The current–voltage curve, based on the metal–semiconductor–metal model, showed a high electron carrier concentration of 2.0 × 1017 cm−3 and a high electron mobility of 446.42 cm2 V−1 s−1. Additionally, the high carrier concentration of the InSb semiconductor with the surface accumulation layer induced a downward band bending effect that reduces the electron tunneling barrier. Consequently, the InSb nanowires exhibit significant field emission properties with an extremely low turn-on field of 1.84 V μm−1 and an estimative threshold field of 3.36 V μm−1. PMID:23399075

  11. Detection of invisible phonon modes in individual defect-free carbon nanotubes by gradient-field Raman scattering

    NASA Astrophysics Data System (ADS)

    Yang, Feng; Ji, Yinglu; Zhang, Xiao; Fan, Qingxia; Zhang, Nan; Gu, Xiaogang; Xiao, Zhuojian; Zhang, Qiang; Wang, Yanchun; Wu, Xiaochun; Li, Junjie; Zhou, Weiya

    2017-06-01

    We provide an effective method to investigate the field gradient effect in nanoconfined plasmon-matter interaction. Aligned ultralong SWNTs without defects were grown on marked substrates, followed by assembling gold nanoparticle clusters around individual nanotubes. The Raman scattering behavior of a nanotube placed in an atomic scale nanogap between adjacent nanoparticles was studied. In addition to the expected plasmon-induced Raman enhancement up to 103, the defect-free D-mode of an individual SWNT induced by gradient field is found for the first time. When the light is confined at atomic scale, gradient field Raman scattering becomes significant and dipole-forbidden phonon modes can be activated by quadrupole Raman tensor variation, indicating breakdown of the Raman selection rules. Project supported by the National Basic Research Program of China (Grant No. 2012CB932302), the National Natural Science Foundation of China (Grant Nos. 11634014, 51172271, and 51372269), and the “Strategic Priority Research Program” of the Chinese Academy of Sciences (Grant Nos. XDA09040202 and XDA09040400).

  12. Highly aligned conjugated polymer films prepared by rotation coating for high-performance organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Van Tho, Luu; Park, Won-Tae; Choi, Eun-Young; Noh, Yong-Young

    2017-04-01

    Recently, exceptionally high field-effect mobility in organic field-effect transistors (OFETs) has been fabricated using semiconducting films with one-dimensionally aligned, highly planar electron donor-acceptor copolymers, within the channel of transistors. Here, we propose an extremely simple coating method, called rotation coating, for preparing highly aligned, conjugated polymer thin films for applications in various organic electronic devices. We realize highly aligned polymer films using various conjugated polymers and applied the films as active layers for high-performance OFETs. Significantly high field-effect mobility values of 1.45 ± 0.46 cm2/Vs have been achieved for rotation coated diketopyrrolopyrrole-thieno[3,2-b]thiophene copolymer films.

  13. Magneto-plasmonic study of aligned Ni, Co and Ni/Co multilayer in polydimethylsiloxane as magnetic field sensor

    NASA Astrophysics Data System (ADS)

    Hamidi, Seyedeh Mehri; Mosaeii, Babak; Afsharnia, Mina; Aftabi, Ali; Najafi, Mojgan

    2016-11-01

    We report the magneto-optical properties of aligned cobalt, Nickel and nickel/ Cobalt multilayer nanowires embedded in polydimethylsiloxane matrix. The NWs prepared by electrodeposition method in anodic alumina template and then dispersed in ethanol and placed in a heater to evaporate the ethanol and finally dispersed in polydimethylsiloxane matrix to reach to the composite. The used external magnetic field arranges the nanowires and our aligned nanowires were investigated by magneto-optical surface plasmon resonance techniques in two easy and hard axis configurations. Our results show the sufficient sensitivity in magneto-optical surface plasmon resonance of Nickel and cobalt arrays nanowires and because the different modulation mechanism in Ni and Co nanodisks, in Ni/Co multilayer we see the magnetization modulation of the excitation angle in accordance with magnetic field modulation of the SPP wave vector in each nanodisk. Finally, we show that the Ni/Co multilayer aligned nanowires can be used as efficient magnetic field sensor.

  14. Time-dependent modeling of field-aligned current-generated ion transients in the polar wind

    NASA Technical Reports Server (NTRS)

    Gombosi, T. I.; Nagy, A. F.

    1989-01-01

    The time evolution of field-aligned current-generated transient features in the high-latitude ionosphere is investigated. Ionospheric return currents generate significant downward heavy ion flows in the topside ionosphere with peak values well exceeding 10 to the 8th sq cm/s. When the return current ceases, the polar ionosphere rapidly returns to its previous equilibrium state. During the recovery phase of the return current event, an upward propagating heavy ion transient is formed, which is mainly characterized by a relatively short O(+) upwelling event. On the other hand, the H(+) escape flux remains relatively constant (within 10-20 percent) during field-aligned current events. It is also found that upward currents generate a transient heavy ion outflow, which exceeds the ambient H(+) escape flux by a factor of 3 to 5, depending on the duration and strength of the field-aligned current event.

  15. Galactic cosmic ray gradients, field-aligned and latitudinal, among Voyagers 1/2 and IMP-8

    NASA Technical Reports Server (NTRS)

    Roelof, E. C.; Decker, R. B.; Krimigis, S. M.; Venkatesan, D.; Lazarus, A. J.

    1982-01-01

    The present investigation represents a summary of a comprehensive analysis of the same subject conducted by Roelof et al. (1981). It is pointed out that the tandem earth-Jupiter trajectories of the Voyager 1/2 spacecraft, combined with baseline measurements from the earth-orbiting IMP 7/8 spacecraft, provide the first opportunity for unambiguously separating latitude from radial or field-aligned effects in galactic cosmic ray gradients. Attention is given to the method of data analysis, and the separation of field-aligned and latitudinal gradients. It is found that latitudinal gradients approximately equal to or greater than 1 percent per deg in the cosmic ray intensity were a common feature of the interplanetary medium between 1 and 5 AU in 1977-78. Except in the most disturbed periods, cosmic ray intensities are well-ordered in field-aligned structures.

  16. Method to determine and adjust the alignment of the transmitter and receiver fields of view of a LIDAR system

    DOEpatents

    Schmitt, Randal L.; Henson, Tammy D.; Krumel, Leslie J.; Hargis, Jr., Philip J.

    2006-06-20

    A method to determine the alignment of the transmitter and receiver fields of view of a light detection and ranging (LIDAR) system. This method can be employed to determine the far-field intensity distribution of the transmitter beam, as well as the variations in transmitted laser beam pointing as a function of time, temperature, or other environmental variables that may affect the co-alignment of the LIDAR system components. In order to achieve proper alignment of the transmitter and receiver optical systems when a LIDAR system is being used in the field, this method employs a laser-beam-position-sensing detector as an integral part of the receiver optics of the LIDAR system.

  17. Dynamic Scattering Mode LCDs

    NASA Astrophysics Data System (ADS)

    Bahadur, Birendra

    The following sections are included: * INTRODUCTION * CELL DESIGNING * EXPERIMENTAL OBSERVATIONS IN NEMATICS RELATED WITH DYNAMIC SCATTERING * Experimental Observations at D.C. Field and Electrode Effects * Experimental Observation at Low Frequency A.C. Fields * Homogeneously Aligned Nematic Regime * Williams Domains * Dynamic Scattering * Experimental Observation at High Frequency A.C. Field * Other Experimental Observations * THEORETICAL INTERPRETATIONS * Felici Model * Carr-Helfrich Model * D.C. Excitation * Dubois-Violette, de Gennes and Parodi Model * Low Freqency or Conductive Regime * High Frequency or Dielectric Regime * DYNAMIC SCATTERING IN SMECRIC A PHASE * ELECTRO-OPTICAL CHARACTERISTICS AND LIMITATIONS * Contrast Ratio vs. Voltage, Viewing Angle, Cell Gap, Wavelength and Temperature * Display Current vs. Voltage, Cell Gap and Temperature * Switching Time * Effect of Alignment * Effect of Conductivity, Temperature and Frequency * Addressing of DSM LCDs * Limitations of DSM LCDs * ACKNOWLEDGEMENTS * REFERENCES

  18. Image stack alignment in full-field X-ray absorption spectroscopy using SIFT_PyOCL.

    PubMed

    Paleo, Pierre; Pouyet, Emeline; Kieffer, Jérôme

    2014-03-01

    Full-field X-ray absorption spectroscopy experiments allow the acquisition of millions of spectra within minutes. However, the construction of the hyperspectral image requires an image alignment procedure with sub-pixel precision. While the image correlation algorithm has originally been used for image re-alignment using translations, the Scale Invariant Feature Transform (SIFT) algorithm (which is by design robust versus rotation, illumination change, translation and scaling) presents an additional advantage: the alignment can be limited to a region of interest of any arbitrary shape. In this context, a Python module, named SIFT_PyOCL, has been developed. It implements a parallel version of the SIFT algorithm in OpenCL, providing high-speed image registration and alignment both on processors and graphics cards. The performance of the algorithm allows online processing of large datasets.

  19. Transport in a field aligned magnetized plasma/neutral gas boundary: the end of the plasma

    NASA Astrophysics Data System (ADS)

    Cooper, Christopher Michael

    The objective of this dissertation is to characterize the physics of a boundary layer between a magnetized plasma and a neutral gas along the direction of a confining magnetic field. A series of experiments are performed at the Enormous Toroidal Plasma Device (ETPD) at UCLA to study this field aligned Neutral Boundary Layer (NBL) at the end of the plasma. A Lanthanum Hexaboride (LaB6) cathode and semi-transparent anode creates a magnetized, current-free helium plasma which terminates on a neutral helium gas without touching any walls. Probes are inserted into the plasma to measure the basic plasma parameters and study the transport in the NBL. The experiment is performed in the weakly ionized limit where the plasma density (ne) is much less than the neutral density (nn) such that ne/nn < 5%. The NBL is characterized by a field-aligned electric field which begins at the point where the plasma pressure equilibrates with the neutral gas pressure. Beyond the pressure equilibration point the electrons and ions lose their momentum by collisions with the neutral gas and come to rest. An electric field is established self consistently to maintain a current-free termination through equilibration of the different species' stopping rates in the neutral gas. The electric field resembles a collisional quasineutral sheath with a length 10 times the electron-ion collision length, 100 times the neutral collision length, and 10,000 times the Debye length. Collisions with the neutral gas dominate the losses in the system. The measured plasma density loss rates are above the classical cross-field current-free ambipolar rate, but below the anomalous Bohm diffusion rate. The electron temperature is below the ionization threshold of the gas, 2.2 eV in helium. The ions are in thermal equilibrium with the neutral gas. A generalized theory of plasma termination in a Neutral Boundary Layer is applied to this case using a two-fluid, current-free, weakly ionized transport model. The electron

  20. 3D model of small-scale density cavities in the auroral magnetosphere with field-aligned current

    NASA Astrophysics Data System (ADS)

    Bespalov, P. A.; Misonova, V. G.; Savina, O. N.

    2016-09-01

    We propose a 3D model of small-scale density cavities stimulated by an auroral field-aligned current and an oscillating field-aligned current of kinetic Alfvén waves. It is shown that when the field-aligned current increases so that the electron drift velocity exceeds a value of the order of the electron thermal velocity, the plasma becomes unstable to the formation of cavities with low density and strong electric field. The condition of instability is associated with the value of the background magnetic field. In the case of a relatively weak magnetic field (where the electron gyro-radius is greater than the ion acoustic wavelength), the current instability can lead to the formation of one-dimensional cavities along the magnetic field. In the case of a stronger magnetic field (where the ion acoustic wavelength is greater than the electron gyro-radius, but still is less than the ion gyro-radius), the instability can lead to the formation of 3D density cavities. In this case, the spatial scales of the cavity, both along and across the background magnetic field, can be comparable, and at the earlier stage of the cavity formation they are of the order of the ion acoustic wavelength. Rarefactions of the cavity density are accompanied by an increase in the electric field and are limited by the pressure of bipolar electric fields that occur within them. The estimates of typical density cavity characteristics and the results of numerical solutions agree with known experimental data: small-scale structures with a sufficiently strong electric field are observed in the auroral regions with strong field-aligned current.

  1. Aftershocks are well aligned with the background stress field, contradicting the hypothesis of highly-heterogeneous crustal stress

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2010-01-01

    It has been proposed that the crustal stress field contains small-length-scale heterogeneity of much larger amplitude than the uniform background stress. This model predicts that earthquake focal mechanisms should reflect the loading stress rather than the uniform background stress. So, if the heterogeneous stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same stress field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers stress field and then loaded by the Landers-induced static stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential stress change align with the modeled Landers-induced static stress change, implying that they were triggered by the stress perturbation. Contrary to the heterogeneous stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers stress field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers stress must represent the persistent background stress field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background stress field, which is large relative to any small-scale stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous stress model is not widely applicable.

  2. Nuclear forward scattering of synchrotron radiation in pulsed high magnetic fields.

    PubMed

    Strohm, C; Van der Linden, P; Rüffer, R

    2010-02-26

    We report the demonstration of nuclear forward scattering of synchrotron radiation from 57Fe in ferromagnetic alpha iron in pulsed high magnetic fields up to 30 T. The observed magnetic hyperfine field follows the calculated high field bulk magnetization within 1%, establishing the technique as a precise tool for the study of magnetic solids in very high magnetic fields. To perform these experiments in pulsed fields, we have developed a detection scheme for fully time resolved nuclear forward scattering applicable to other pump probe experiments.

  3. Resonant scattering of ultrarelativistic electrons in the strong field of a pulsed laser wave

    NASA Astrophysics Data System (ADS)

    Lebed', A. A.; Padusenko, E. A.; Roshchupkin, S. P.

    2016-02-01

    Electron-electron scattering in a strong field of a pulsed laser wave is studied theoretically. Resonant scattering kinematics at the small polar angles for electron ultrarelativistic energy is studied in detail. Compact analytical expressions for the amplitude and the differential cross section for wave elliptical polarization are obtained under resonant conditions. The resonant cross section of electron-electron scattering is shown to decrease sharply with increasing the electron ultrarelativistic energies for weak and moderately strong fields. It was demonstrated that the resonant cross section of electron-electron scattering at wave circular polarization is four times greater than the corresponding cross section at linear polarization. The resonant cross section may exceed the corresponding cross section of a field-free process: by 5-6 orders of magnitude for electron MeV-energy and petawatt optical lasers (PHELIX, Vulcan); and 8-9 orders for multipetawatt laser fields within the femtosecond range (Vulcan10, ELI).

  4. Coordinated observations of F region 3 m field-aligned plasma irregularities associated with medium-scale traveling ionospheric disturbances

    NASA Astrophysics Data System (ADS)

    Lin, F. F.; Wang, C. Y.; Su, C. L.; Shiokawa, K.; Saito, S.; Chu, Y. H.

    2016-04-01

    Three meter field-aligned irregularities (3 m FAIs) associated with medium-scale traveling ionospheric disturbances (MSTIDs) that occurred on 5 February 2008 were observed by using the Chung-Li 52 MHz coherent scatter radar. Interferometry measurements show that the plasma structures responsible for the 3 m FAI echoes are in a clumpy shape with a horizontal dimension of about 10-78 km in a height range of 220-300 km. In order to investigate the dynamic behaviors of the plasma irregularities at different scales in the bottomside of F region, the VHF radar echo structures from the 3 m FAIs combined with the 630 nm airglow images provided by the Yonaguni all-sky imager are compared and analyzed. The results show that the radar echoes were located at the west edge of the depletion zones of the 630 nm airglow image of the MSTIDs. The bulk echo structures of the 3 m FAIs drifted eastward at a mean trace velocity of about 30 m/s that is in general agreement with the zonal trace velocity of the MSTIDs shown in the 630 nm airglow images. These results suggest that the observed F region 3 m FAIs for the present case can be regarded as the targets that are frozen in the local region of the MSTIDs. In addition, the radar-observed 3 m FAI echo intensity and spectral width bear high correlations to the percentage variations of the 630 nm emission intensity. These results seem to suggest that through the nonlinear turbulence cascade process, the MSTID-associated 3 m FAIs are very likely generated from the kilometer-scale plasma irregularities with large amplitude excited by the gradient drift instability.

  5. Improved Efficiency of Marine EM Subsurface Modeling Using the Total-Field Scattered-Field FDTD Formulation

    NASA Astrophysics Data System (ADS)

    Dukeshire, Andrea

    To efficiently model the effect of the airwave in the controlled-source electromagnetics (CSEM) method has historically been a problem of major interest. The methods proposed in this thesis provide a new method of simulating CSEM interactions in the finite-difference time-domain (FDTD) by using the total-field scattered-field (TFSF) formulation. TFSF provides an inherent separation of the total and scattered fields, which allows the proposed method to decompose the CSEM domain into separate simulation runs. By simulating the problem in stages, the process of extracting the response of the scatterer is streamlined. If the increased efficiency options within the proposed method are utilized, the efficiency of single forward simulations can be improved. This method shows potential for computational cost savings, especially in typical CSEM data analysis and reconstruction situations where numerous iterations of various scatterers are required.

  6. SuperDARN-derived plasma convection: Comparison with other data and application to field-aligned current measurements

    NASA Astrophysics Data System (ADS)

    Xu, Liang

    In this thesis, several aspects of the SuperDARN HF radar observations at high latitudes are investigated in cooperation with measurements performed by three other instruments, the Sondrestrom incoherent scatter radar, the ion drift meter onboard of the DMSP satellite and the CADI ionosonde. The first issue under investigation was consistency of plasma convection data provided by these instruments. First, routine measurements by the Goose Bay and Stokkseyri SuperDARN radar pair ("merge" velocity estimates) were compared with the Sondrestrom incoherent scatter radar data. Three different levels of assessment were used; by looking at the line-of-sight velocities, by comparing the SuperDARN vectors and corresponding Sondrestrom line-of-sight velocities and by comparing the end products of the instruments, the convection maps. All three comparisons showed overall reasonable agreement of the convection measurements though the data spread was significant and for some points a strong disagreement was obvious. Importantly, the convection map comparison showed a tendency for the SuperDARN velocities to be often less than the Sondrestrom drifts for strong flows (velocities > 1000 m/s) and larger for weak flows (velocities < 500 m/s). The second issue under investigation was the configuration of the ionospheric plasma convection and field-aligned currents (FACs) in the dayside ionosphere at small IMF B2 and By. By merging SuperDARN convection data for a number of events, it was found that convection tends to be compressed to the poleward edge of the polar cap with a noticeable decrease of the flow velociity inside the central polar cap for this condition. Also, for individual events, existence of three sheets of FACs was illustrated. FACs had similar appearance as region 1, region 2, and region 0 currents known from satellite magnetometer observations for the disturbed magnetosphere. Spatially, sheets of region 1 FACs were co-located with a line separating the plasma flow of

  7. The Evidence of Radio Polarization Induced by the Radiative Grain Alignment and Self-scattering of Dust Grains in a Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Kataoka, Akimasa; Tsukagoshi, Takashi; Pohl, Adriana; Muto, Takayuki; Nagai, Hiroshi; Stephens, Ian W.; Tomisaka, Kohji; Momose, Munetake

    2017-07-01

    The mechanisms causing millimeter-wave polarization in protoplanetary disks are under debate. To disentangle the polarization mechanisms, we observe the protoplanetary disk around HL Tau at 3.1 mm with the Atacama Large Millimeter/submillimeter Array (ALMA), which had the polarization detected with CARMA at 1.3 mm. We successfully detect the ring-like azimuthal polarized emission at 3.1 mm. This indicates that dust grains are aligned with the major axis being in the azimuthal direction, which is consistent with the theory of radiative alignment of elongated dust grains, where the major axis of dust grains is perpendicular to the radiation flux. Furthermore, the morphology of the polarization vectors at 3.1 mm is completely different from those at 1.3 mm. We interpret the polarization at 3.1 mm to be dominated by the grain alignment with the radiative flux producing azimuthal polarization vectors, while the self-scattering dominates at 1.3 mm and produces the polarization vectors parallel to the minor axis of the disk. By modeling the total polarization fraction with a single grain population model, the maximum grain size is constrained to be 100 μ {{m}}, which is smaller than the previous predictions based on the spectral index between ALMA at 3 mm and the Very Large Array at 7 mm.

  8. Four large-scale field-aligned current systems in the dayside high-latitude region

    SciTech Connect

    Ohtani, S.; Potemra, T.A.; Newell, P.T.

    1995-01-01

    A system of four current sheets of large-scale field-aligned currents (FACs) was discovered in the data set of simultaneous Viking and DMSP-F7 crossings of the dayside high-latitude region. This paper reports four examples of this system that were observed in the prenoon sector. The flow polarities of FACs are upward, downward, upward, and downward, from equatorward to poleward. The lowest-latitude upward current is flowing mostly in the CPS precipitation region, often overlapping with the BPS at its poleward edge, and is interpreted as a region 2 current. The pair of downward and upward FACs in the middle of the structure are collocated with structured electron precipitation. The precipitation of high-energy (>1 keV) electrons is more intense in the lower-latitude downward current sheet. The highest-latitude downward flowing current sheet is located in a weak, low-energy particle precipitation region, suggesting that this current is flowing on open field lines. Simultaneous observations in the postnoon local time sector reveal the standard three-sheet structure of FACs, sometimes described as region 2, region 1, and mantle (referred to the midday region 0) currents. A high correlation was found between the occurrence of the four FAC sheet structure and negative interplanetary magnetic field (IMF) B{sub Y}. The authors discuss the FAC structure in terms of three types of convection cells: the merging, viscous, and lobe cells. During strongly negative IMF B{sub Y}, two convection reversals exist in the prenoon sector; one is inside the viscous cell, and the other is between the viscous cell and the lobe cell. This structure of convection flow is supported by the Viking electric field and auroral UV image data. Based on the convection pattern, the four FAC sheet structure is interpreted as the latitudinal overlap of midday and morning FAC systems. 47 refs., 12 figs., 1 tab.

  9. The optical manifestation of dispersive field-aligned bursts in auroral breakup arcs

    NASA Astrophysics Data System (ADS)

    Dahlgren, H.; Semeter, J. L.; Marshall, R. A.; Zettergren, M.

    2013-07-01

    High-resolution optical observations of a substorm expansion show dynamic auroral rays with surges of luminosity traveling up the magnetic field lines. Observed in ground-based imagers, this phenomenon has been termed auroral flames, whereas the rocket signatures of the corresponding energy dispersions are more commonly known as field-aligned bursts. In this paper, observations of auroral flames obtained at 50 frames/s with a scientific-grade Complementary Metal Oxide Semiconductor (CMOS) sensor (30° × 30° field of view, 30 m resolution at 120 km) are used to provide insight into the nature of the precipitating electrons similar to high-resolution particle detectors. Thanks to the large field of view and high spatial resolution of this system, it is possible to obtain a first-order estimate of the temporal evolution in altitude of the volume emission rate from a single sensor. The measured volume emission rates are compared with the sum of modeled eigenprofiles obtained for a finite set of electron beams with varying energy provided by the TRANSCAR auroral flux tube model. The energy dispersion signatures within each auroral ray can be analyzed in detail during a fraction of a second. The evolution of energy and flux of the precipitation shows precipitation spanning over a large range of energies, with the characteristic energy dropping from 2.1 keV to 0.87 keV over 0.2 s. Oscillations at 2.4 Hz in the magnetic zenith correspond to the period of the auroral flames, and the acceleration is believed to be due to Alfvenic wave interaction with electrons above the ionosphere.

  10. Some properties of field-aligned electron events in high-altitude polar regions

    NASA Astrophysics Data System (ADS)

    Zhang, ZiYing; Shi, JianKui; Zhou, MingQuan; Cheng, ZhengWei; Zhou, Hua

    2016-02-01

    Using data from the Cluster spacecraft from January 2003 to December 2004, we perform a statistical study on some properties of the field-aligned electron (FAE) events and interplanetary magnetic field (IMF) By dependence of FAE events with different durations in high-altitude polar regions. A total of 1335 FAE events were observed by the C3 spacecraft. More down-flowing events were observed in the Southern Hemisphere, and more up-flowing events were observed in the Northern Hemisphere. It proves that down-flowing events mainly originate from magnetosphere or solar wind and up-flowing events are mainly derived from ionosphere. Short-lifetime events showed a morning concentration in the magnetic local time distribution, and long-lifetime events were concentrated both before and after noon. For the IMF By dependence of the FAE events, short-lifetime events were much affected by IMF By and resulted in a morning concentration, while the long-lifetime events were almost unaffected by IMF By. With further analysis, we determined that the short-lifetime and long-lifetime events had different sources.

  11. Spatial and Alignment Analyses for a field of Small Volcanic Vents South of Pavonis Mons Mars

    NASA Technical Reports Server (NTRS)

    Bleacher, J. E.; Glaze, L. S.; Greeley, R.; Hauber, E.; Baloga, S. M.; Sakimoto, S. E. H.; Williams, D. A.; Glotch, T. D.

    2008-01-01

    The Tharsis province of Mars displays a variety of small volcanic vent (10s krn in diameter) morphologies. These features were identified in Mariner and Viking images [1-4], and Mars Orbiter Laser Altimeter (MOLA) data show them to be more abundant than originally observed [5,6]. Recent studies are classifying their diverse morphologies [7-9]. Building on this work, we are mapping the location of small volcanic vents (small-vents) in the Tharsis province using MOLA, Thermal Emission Imaging System, and High Resolution Stereo Camera data [10]. Here we report on a preliminary study of the spatial and alignment relationships between small-vents south of Pavonis Mons, as determined by nearest neighbor and two-point azimuth statistical analyses. Terrestrial monogenetic volcanic fields display four fundamental characteristics: 1) recurrence rates of eruptions,2 ) vent abundance, 3) vent distribution, and 4) tectonic relationships [11]. While understanding recurrence rates typically requires field measurements, insight into vent abundance, distribution, and tectonic relationships can be established by mapping of remotely sensed data, and subsequent application of spatial statistical studies [11,12], the goal of which is to link the distribution of vents to causal processes.

  12. The particle carriers of field-aligned currents in the Earth's magnetotail during a substorm

    NASA Astrophysics Data System (ADS)

    Cheng, Z. W.; Zhang, J. C.; Shi, J. K.; Kistler, L. M.; Dunlop, M.; Dandouras, I.; Fazakerley, A.

    2016-04-01

    Although the particle carriers of field-aligned currents (FACs) in the Earth's magnetotail play an important role in the transfer of momentum and energy between the solar wind, magnetosphere, and ionosphere, the characteristics of the FAC carriers have been poorly understood. Taking advantage of multiinstrument magnetic field and plasma data collected by the four spacecraft of the Cluster constellation as they traversed the northern plasma sheet boundary layer in the magnetotail on 14 September 2004, we identified the species type and energy range of the FAC carriers for the first time. The results indicate that part of tailward FACs is carried by energetic keV ions, which are probably originated from the ionosphere through outflow, and they are not too small (~2 nA/m2) to be ignored. The earthward (tailward) FACs are mainly carried by the dominant tailward (earthward) motion of electrons, and higher-energy electrons (from ~0.5 to 26 keV) are the main carriers.

  13. Field-Aligned Current at Plasma Sheet Boundary Layers During Storm Time: Cluster Observation

    NASA Astrophysics Data System (ADS)

    Shi, J.; Cheng, Z.; Zhang, T.; Dunlop, M.; Liu, Z.

    2007-05-01

    The magnetic field data from the FGM instruments on board the four Cluster spacecrafts were used to study Field Aligned Current (FAC) at the Plasma Sheet Boundary Layers (PSBLs) with the so called "curlometer technique". We analyzed the date obtained in 2001 in the magnetotail and only two cases were found in the storm time. One (August 17, 2001) occurred from sudden commencement to main phase, and the other (October 1, 2001) lay in the main phase and recovery phase. The relationship between the FAC density and the AE index was studied and the results are shown as follows. (1) In the sudden commencement and the main phase the density of the FAC increases obviously, in the recovery phase the density of the FAC increases slightly. (2) From the sudden commencement to the initial stage of the main phase the FAC increases with decreasing AE index and decreases with increasing AE index. From the late stage of the main phase to initial stage of the recovery phase, the FAC increases with increasing AE index and decreases with decreasing AE index. In the late stage of the recovery phase the disturbance of the FAC is not so violent, so that the FAC varying with the AE index is not very obvious.

  14. Field-Aligned and Ionospheric Current Contributions to Ground Magnetic Perturbations

    NASA Astrophysics Data System (ADS)

    Connors, M. G.; McPherron, R. L.; Anderson, B. J.; Korth, H.; Russell, C. T.; Chu, X.

    2014-12-01

    AMPERE data provides global space-derived radial electric currents on temporal and spatial scales suited to studying magnetic fields at ULF frequencies. It responds little to ionspheric currents, which dominate ground-based measurements, so that AMPERE and ground datasets complement each other to give a comprehensive view of near-Earth electric currents. Connors et al. (GRL, 2014) found that a three-dimensional current system slightly modified from the original substorm current wedge (SCW) concept of McPherron et al. (JGR, 1973) represented substorm midnight sector perturbations well both in the auroral and subauroral regions, if a current equivalent to that found by integrating AMPERE downward current was used, located where clear SCW signatures were indicated by AMPERE, and featuring an ionospheric electrojet. The AMPERE upward current was found to exceed that in the SCW, at least in part since the evening sector electrojet fed into it. We extend these results with a more detailed accounting of field-aligned and ionospheric currents throughout the active period (including growth phase). Ionospheric currents for the study are obtained from ground perturbations through optimization of a simple forward model over regions or on a meridian chain. We also investigate the degree to which subauroral perturbations may be directly calculated from AMPERE results. We further find that auroral zone currents may be very localized, to the extent that the entire SCW ionospheric current flows in a very restricted latitudinal range near onset, possibly corresponding to a single auroral arc.

  15. Light scattering, field localization and local density of states in co-axial plasmonic nanowires.

    PubMed

    Lawrence, Nate; Dal Negro, Luca

    2010-07-19

    Based on analytical scattering theory, we develop a multipolar expansion method to investigate systematically the near-field enhancement, far-field scattering and Local Density of States (LDOS) spectra in concentric metal-insulator-metal (MIM) cylindrical nanostructures, or coaxial plasmonic nanowires (CPNs). We demonstrate that these structures support distinctive plasmonic resonances with strongly reduced scattering in the far-field zone and significant electric field enhancement in deep sub-wavelength dielectric regions. Additionally, we study systematically the effects of geometrical parameters and dielectric index on the near-field and far-field plasmonic response of CPNs in the visible and near infrared spectral range. Finally, we demonstrate that CPNs provide a convenient approach for engineering strong (almost three orders of magnitude) LDOS enhancement in sub-wavelength dielectric gaps at multiple frequencies. These results enable the engineering of multiband optical detectors and CPNs-based light emitters with simultaneously enhanced excitation and emission rates for nanoplasmonics.

  16. Magnetopause Erosion During the 17 March 2015 Magnetic Storm: Combined Field-Aligned Currents, Auroral Oval, and Magnetopause Observations

    NASA Technical Reports Server (NTRS)

    Le, G.; Luehr, H.; Anderson, B. J.; Strangeway, R. J.; Russell, C. T.; Singer, H.; Slavin, J. A.; Zhang, Y.; Huang, T.; Bromund, K.; hide

    2016-01-01

    We present multimission observations of field-aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field-aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field-aligned currents .The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field-aligned currents and the auroral arc move equatorward reaching as low as approx. 60 deg. magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.

  17. Magnetopause erosion during the 17 March 2015 magnetic storm: Combined field-aligned currents, auroral oval, and magnetopause observations

    NASA Astrophysics Data System (ADS)

    Le, G.; Lühr, H.; Anderson, B. J.; Strangeway, R. J.; Russell, C. T.; Singer, H.; Slavin, J. A.; Zhang, Y.; Huang, T.; Bromund, K.; Chi, P. J.; Lu, G.; Fischer, D.; Kepko, E. L.; Leinweber, H. K.; Magnes, W.; Nakamura, R.; Plaschke, F.; Park, J.; Rauberg, J.; Stolle, C.; Torbert, R. B.

    2016-03-01

    We present multimission observations of field-aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field-aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field-aligned currents. The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field-aligned currents and the auroral arc move equatorward reaching as low as ~60° magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.

  18. Field-Aligned Electron Events Observed in the Radiation Belts by the HOPE Instruments aboard the Van Allen Probes

    NASA Astrophysics Data System (ADS)

    Lejosne, S.; Agapitov, O. V.; Mozer, F.

    2015-12-01

    Field-aligned electron events (FAEs) are defined as events having the ratio of field-aligned to perpendicular flux greater than three. Time Domain Structures (TDS) are known to produce FAEs. Whistler and ECH waves are other possible candidates. Our objective is to derive the general features of the FAEs, to identify their driving mechanisms and to evaluate the importance of the different mechanisms. More than two years of measurements by the Helium Oxygen Proton Electron mass spectrometer and the Electric Field and Waves experiment are analyzed to identify low-energy (100eV-50keV) FAEs and to quantify the concurrent electric and magnetic wave components. We also peek at the observable waveforms with bursts of high-time resolution measurements. From statistical analysis and case studies, we suggest in particular that TDS cause field-alignment of ~300eV electrons in the pre-midnight sector while chorus waves cause field-alignment of electrons of ~10keV in the morning sector of the outer belt.

  19. Roll to Roll Electric Field "Z" Alignment of Nanoparticles from Polymer Solutions for Manufacturing Multifunctional Capacitor Films.

    PubMed

    Guo, Yuanhao; Batra, Saurabh; Chen, Yuwei; Wang, Enmin; Cakmak, Miko

    2016-07-20

    A roll to roll continuous processing method is developed for vertical alignment ("Z" alignment) of barium titanate (BaTiO3) nanoparticle columns in polystyrene (PS)/toluene solutions. This is accomplished by applying an electric field to a two-layer solution film cast on a carrier: one is the top sacrificial layer contacting the electrode and the second is the polymer solution dispersed with BaTiO3 particles. Flexible Teflon coated mesh is utilized as the top electrode that allows the evaporation of solvent through the openings. The kinetics of particle alignment and chain buckling is studied by the custom-built instrument measuring the real time optical light transmission during electric field application and drying steps. The nanoparticles dispersed in the composite bottom layer form chains due to dipole-dipole interaction under an applied electric field. In relatively weak electric fields, the particle chain axis tilts away from electric field direction due to bending caused by the shrinkage of the film during drying. The use of strong electric fields leads to maintenance of alignment of particle chains parallel to the electric field direction overcoming the compression effect. At the end of the process, the surface features of the top porous electrodes are imprinted at the top of the top sacrificial layer. By removing this layer a smooth surface film is obtained. The nanocomposite films with "Z" direction alignment of BaTiO3 particles show substantially increased dielectric permittivity in the thickness direction for enhancing the performance of capacitors.

  20. Inverse scattering from phaseless measurements of the total field on open lines

    NASA Astrophysics Data System (ADS)

    Bucci, Ovidio Mario; Crocco, Lorenzo; D'Urso, Michele; Isernia, Tommaso

    2006-10-01

    A new solution approach to inverse scattering from aspect-limited phaseless measurements of the total field is introduced and discussed. In analogy with the case of measurements on closed curves [J. Opt. Soc. Am. A21, 622 (2004)], the procedure splits the problem into two different steps. In the first step, amplitude and phase of the scattered field are estimated from only amplitude information of the total field. By properly extending the concept of reduced radiated field to the case of scattered fields (as a function of both illumination and measurement variables) and taking advantage of the properties of the square amplitude distribution of the total field, criteria are given for an optimal choice of the measurement setup and a successful retrieval. Then the complex permittivity profile is reconstructed in the second step, starting from the scattered fields estimated in the previous step. Numerical examples are provided to assess the effectiveness of the whole chain in the presence of noise-corrupted data and the relevance of the representation introduced for the scattered fields.

  1. Influences of the interplanetary magnetic field clock angle and cone angle on the field-aligned currents in the magnetotail

    NASA Astrophysics Data System (ADS)

    Cheng, Z. W.; Shi, J. K.; Dunlop, M.; Liu, Z. X.

    2013-10-01

    The influences of the interplanetary magnetic field (IMF) cone angle θ and clock angle ϕ on the field-aligned currents (FACs) at the plasma sheet boundary layers (PSBLs) have been investigated using Cluster Data. The FAC occurrence increases monotonically with IMF cone angle and has two peaks at -90° and +110° clock angle, respectively. The peak at +110° is distinctly larger than that at -90°. Overall, there are more FACs between 0° < ϕ < 180°, indicating that FACs occurrence is closely associated with duskward IMF. More FACs occur when 90° < |ϕ| < 180°, implying that FAC is closely associated with southward IMF. The large FAC densities occur when 60° < |ϕ| < 120°. The density also has two peaks and the peak at +90° clock angle (duskward IMF) is larger than that at -90° (dawnward IMF). These results indicate that the IMF influence on the FACs is from all IMF components and not only from a single component.

  2. How to measure a complete set of polarization-dependent differential cross sections in a scattering experiment with aligned reagents?

    PubMed

    Wang, Fengyan; Lin, Jui-San; Liu, Kopin

    2014-02-28

    Polarization-dependent differential cross section (PDDCS) is one of the three-vector correlations (k, k('), j) in molecular collisions, which provides the most detailed insights into the steric requirements of chemical reactions, i.e., how the reactivity depends on the polarization of reagents. Only quite recently has such quantity been fully realized experimentally in the study of the reaction of the aligned CHD3(v1 = 1, |jK⟩ = |10⟩) molecules with Cl((2)P3/2) atoms. Theoretically, PDDCS is a relatively new concept; experimental realization of the theoretical construct requires some careful considerations that are not readily available in the literature. Here, we present the "know-how" behind the full PDDCS measurements to fill the gaps and to provide a clear roadmap for future applications. To make the connection apparent between the methodology presented here and the stereodynamics revealed in previous reports, the same Cl + aligned CHD3 reaction is used for illustration.

  3. Molecular structure determination from x-ray scattering patterns of laser-aligned symmetric-top molecules.

    PubMed

    Ho, P J; Starodub, D; Saldin, D K; Shneerson, V L; Ourmazd, A; Santra, R

    2009-10-07

    We investigate the molecular structure information contained in the x-ray diffraction patterns of an ensemble of rigid CF(3)Br molecules aligned by an intense laser pulse at finite rotational temperature. The diffraction patterns are calculated at an x-ray photon energy of 20 keV to probe molecular structure at angstrom-scale resolution. We find that a structural reconstruction algorithm based on iterative phase retrieval fails to extract a reliable structure. However, the high atomic number of Br compared with C or F allows each diffraction pattern to be treated as a hologram. Using this approach, the azimuthal projection of the molecular electron density about the alignment axis may be retrieved.

  4. Diffusion of electrons scattered by short-range impurities in a quantizing magnetic field

    SciTech Connect

    Andreev, S. P. Pavlova, T. V.

    2008-04-15

    Formulas for transverse diffusion and conductivity in a semiconductor are obtained for electrons scattered by neutral impurities in a quantizing magnetic field. The formulas are valid for an impurity potential of arbitrary depth. Based on Kubo's theory, calculations are performed using electron wavefunctions of the problem of single-impurity scattering in a magnetic field. The poles of the scattering amplitude correctly determine electron eigenstates and magnetic impurity states. As a result, an exact expression is found for the dependence of transverse diffusion coefficient D{sub perpendicular} on longitudinal electron energy {epsilon} due to scattering by short-range (neutral) impurities. The behavior of D{sub perpendicular} ({epsilon}) is examined over an interval of magnetic field strength for several values of impurity potential depth. The experimental observability of diffusion and conductivity using IR lasers is discussed.

  5. Mitigating stimulated scattering processes in gas-filled Hohlraums via external magnetic fields

    SciTech Connect

    Gong, Tao; Zheng, Jian; Li, Zhichao; Ding, Yongkun; Yang, Dong; Hu, Guangyue; Zhao, Bin

    2015-09-15

    A simple model, based on energy and pressure equilibrium, is proposed to deal with the effect of external magnetic fields on the plasma parameters inside the laser path, which shows that the electron temperature can be significantly enhanced as the intensity of the external magnetic fields increases. With the combination of this model and a 1D three-wave coupling code, the effect of external magnetic fields on the reflectivities of stimulated scattering processes is studied. The results indicate that a magnetic field with an intensity of tens of Tesla can decrease the reflectivities of stimulated scattering processes by several orders of magnitude.

  6. Kinetic Alfven Waves Carrying Intense Field Aligned Currents: Particle Trapping and Electron Acceleration

    NASA Astrophysics Data System (ADS)

    Rankin, R.; Artemyev, A.

    2015-12-01

    It is now common knowledge that dispersive scale Alfvén waves can drive parallel electron acceleration [Lotko et al., JGR, 1998; Samson et al., Ann. Geophys., 2003; Wygant et al., JGR, 2002] and transverse ion energization in the auroral zone and inner magnetosphere [Johnson and Cheng, JGR, 2001; Chaston et al., 2004]. In this paper we show that relatively low energy electrons (plasma sheet electrons with energies ranging up to ˜100 eV) can be accelerated very efficiently as they interact nonlinearly with kinetic Alfvén waves (KAWs) that carry intense field aligned currents from the equatorial plane toward the ionosphere in the inner magnetosphere. We propose a theoretical model describing electron trapping into an effective wave potential generated by parallel wave electric fields (with perpendicular wavelengths on the order of the ion gyro-radius) and the mirror force acting on electrons as they propagate along geomagnetic field lines. We demonstrate that waves with an electric potential amplitude between ~100 - 400 V can trap and accelerate electrons to energies approaching several keVs. Trapping acceleration corresponds to conservation of the electron magnetic moment and, thus, results in a significant decrease of the electron equatorial pitch-angle with time. Analytical and numerical estimates of the maximum energy and probability of trapping are presented. We discuss the application of the proposed model in light of recent observations of electromagnetic fluctuations in the inner magnetosphere that are present during periods of strong geomagnetic activity [Chaston et al., GRL, 2014; Califf et al., JGR, 2015].

  7. Numerical simulations of Hall-effect plasma accelerators on a magnetic-field-aligned mesh.

    PubMed

    Mikellides, Ioannis G; Katz, Ira

    2012-10-01

    The ionized gas in Hall-effect plasma accelerators spans a wide range of spatial and temporal scales, and exhibits diverse physics some of which remain elusive even after decades of research. Inside the acceleration channel a quasiradial applied magnetic field impedes the current of electrons perpendicular to it in favor of a significant component in the E×B direction. Ions are unmagnetized and, arguably, of wide collisional mean free paths. Collisions between the atomic species are rare. This paper reports on a computational approach that solves numerically the 2D axisymmetric vector form of Ohm's law with no assumptions regarding the resistance to classical electron transport in the parallel relative to the perpendicular direction. The numerical challenges related to the large disparity of the transport coefficients in the two directions are met by solving the equations on a computational mesh that is aligned with the applied magnetic field. This approach allows for a large physical domain that extends more than five times the thruster channel length in the axial direction and encompasses the cathode boundary where the lines of force can become nonisothermal. It also allows for the self-consistent solution of the plasma conservation laws near the anode boundary, and for simulations in accelerators with complex magnetic field topologies. Ions are treated as an isothermal, cold (relative to the electrons) fluid, accounting for the ion drag in the momentum equation due to ion-neutral (charge-exchange) and ion-ion collisions. The density of the atomic species is determined using an algorithm that eliminates the statistical noise associated with discrete-particle methods. Numerical simulations are presented that illustrate the impact of the above-mentioned features on our understanding of the plasma in these accelerators.

  8. Ion gyroradius effects on Alfvenic field aligned currents and electron energization in planetary magnetospheres.

    NASA Astrophysics Data System (ADS)

    Damiano, P. A.; Johnson, J.; Chaston, C. C.; Fox, W. R., II; Delamere, P. A.; Stauffer, B. H.

    2015-12-01

    Alfvenic current systems are a ubiquitous feature of planetary magnetospheres that can be generated by several mechanisms including the braking of flows (e.g. associated with reconnection at substorm onset) and via moon-planet interactions. The energetic electrons needed to carry the field-aligned currents are generally thought to be accelerated on either electron inertial or ion acoustic gyroradius scale lengths in the limit of inertial and kinetic Alfven waves respectively. Recent 2D dipolar hybrid gyrofluid-kinetic electron simulations of kinetic Alfven waves (Damiano et al., JGR, 2015), associated with the braking of fast flows in the terrestrial magnetotail, have illustrated that hot ion effects can act to limit the extent of the parallel current (all along the field line) from what would be expected in the cold ion limit. This correspondingly affects the characteristics of the electron energization, reducing both the parallel elongation in the electron distribution function associated with electron trapping in the kinetic Alfven wave regime and the extent of high energy tails evident in the inertial Alfven wave region above the ionosphere. In this presentation, we build on these initial simulation results analyzing the characteristics of the parallel current system and electron acceleration (associated with both inertial and kinetic Alfven waves) for a range of wave amplitudes and ratios of the electron to ion temperature. One finding is that for a given ion temperature, increasing wave amplitude recovers some of the features of the electron energization evident in the cold ion limit, but this is modulated by the effect of wave energy dispersion perpendicular to the ambient magnetic field. These results will be summarized and the relevance and extension of this work to consider Alfvenic aurora in the Jupiter magnetosphere (e.g. via either interchange motion or the Io-Jupiter interaction) will also be discussed.

  9. Relating field-aligned beams to inverted-V structures and visible auroras

    NASA Astrophysics Data System (ADS)

    Lee, E.; Parks, G. K.; Fu, S. Y.; Fillingim, M.; Cui, Y. B.; Hong, J.; Dandouras, I.; Rème, H.

    2015-10-01

    The ion composition experiment on Cluster measures 3-D distributions in one spin of the spacecraft (4 s). These distributions often measure field-aligned ion beams (H+, He+ and O+) accelerated out of the ionosphere. The standard model of these beams relies on a quasi-static U-shaped potential model. The beams contain important information about the structure and distribution of the U-shaped potential structures. For example, a simple beam with a narrow velocity range tells us that the particles are accelerated going through a quasi-static U-shaped potential structure localized in space. A more complex beam with a large range of velocities varying smoothly (a few tens of kilometers per second to > 100 km s-1) tells us that the potential structure is extended and distributed along the magnetic field. The Cluster experiment has now revealed new features about the beams. Some beams are broken into many individual structures each with their own velocity. The U-shaped potential model would interpret the new features in terms of particles accelerated by narrow isolated potential structures maintained over an extended region of the magnetic field. Another interpretation is that these features arise as Cluster traverses toward the center of a small-scale U-shaped potential region detecting particles accelerated on different equipotential contours. The estimate of the distance of the adjacent contours is ~ 590-610 m at a Cluster height of ~ 3.5 RE. The observed dimensions map to ~ 295-305 m in the ionosphere, suggesting Cluster has measured the potential structure of an auroral arc.

  10. Flat Fielding and Image Alignments for AIA/SDO Data Images

    NASA Astrophysics Data System (ADS)

    Shine, R. A.; Nightingale, R. W.; Boerner, P.; Tarbell, T. D.; Wolfson, C. J.

    2010-12-01

    The Atmospheric Imaging Assembly (AIA) on the NASA Solar Dynamics Observatory (SDO) takes 4096 by 4096 CCD images of the sun in 10 wavelengths utilizing 4 telescopes and each wavelength channel requires a flat field that is applied shortly after receipt of the data on the ground. Although some useful information about the CCD's was obtained pre-launch, most of the flat field computation must be done with solar images taken in orbit. Raw flat field images are collected as out of focus images at 14 offsets using PZT adjustments on each telescope and then each wavelength group is processed together using the Kuhn, Lin, and Loranz (1991) flat field algorithm. However, the PZT motions are restricted to about 14 arc sec limiting the measurement of large scale variations. Hence larger offsets are also used by adjusting the space craft pointing. All of these suffer from changes in the solar image between exposures (especially the larger offsets), low counts in some channels, and reflections in the UV channels. These make direct use of the flats unfeasible and instead we process them to compute 6 separable effects: 1) differences in the CCD quad gains and inner row/column effects, 2) a repeating pattern across the CCD from the manufacturing process (dubbed "tire tracks"), 3) a grid pattern in the extreme ultraviolet wavelengths from the back filter, 4) blemishes (some are translucent and some are treated as bad pixels), 5) large scale vignetting, and 6) all other variations. The last category includes all remaining flat field effects after the others are removed. This has not been done well for any of the wavelengths yet. These effects will be described and illustrated, as will the before and after images resulting from applying the processed flat fields. We also describe techniques for fitting the solar limb to accurately determine image centers and radii. This is not a trivial problem for the extreme ultraviolet images but is required to align images, determine relative

  11. Solving outside-axial-field-of-view scatter correction problem in PET via digital experimentation

    NASA Astrophysics Data System (ADS)

    Andreyev, Andriy; Zhu, Yang-Ming; Ye, Jinghan; Song, Xiyun; Hu, Zhiqiang

    2016-03-01

    Unaccounted scatter impact from unknown outside-axial-field-of-view (outside-AFOV) activity in PET is an important degrading factor for image quality and quantitation. Resource consuming and unpopular way to account for the outside- AFOV activity is to perform an additional PET/CT scan of adjacent regions. In this work we investigate a solution to the outside-AFOV scatter problem without performing a PET/CT scan of the adjacent regions. The main motivation for the proposed method is that the measured random corrected prompt (RCP) sinogram in the background region surrounding the measured object contains only scattered events, originating from both inside- and outside-AFOV activity. In this method, the scatter correction simulation searches through many randomly-chosen outside-AFOV activity estimates along with known inside-AFOV activity, generating a plethora of scatter distribution sinograms. This digital experimentation iterates until a decent match is found between a simulated scatter sinogram (that include supposed outside-AFOV activity) and the measured RCP sinogram in the background region. The combined scatter impact from inside- and outside-AFOV activity can then be used for scatter correction during final image reconstruction phase. Preliminary results using measured phantom data indicate successful phantom length estimate with the method, and, therefore, accurate outside-AFOV scatter estimate.

  12. Images of transequatorial bubbles based on field-aligned airglow observations from Haleakala in 1984-1986

    SciTech Connect

    Rohrbaugh, R.P.; Hanson, W.B.; Tinsley, B.A.; Cragin, B.L.; McClure, J.P. ); Broadfoot, A.L. )

    1989-06-01

    Images in the 6300-{angstrom} and 7774-{angstrom} plasma recombination emissions have been made that show the development and dynamics of field-aligned bubbles of low density plasma in the tropical nighttime F region. An intensified charge coupled device detector was used with an eight-filter camera to view a field-aligned section of the F region that mapped to magnetic apex heights from 400 to 900 km above the dip equator and up to 700 km in east-west extent from a ground-based observation site on Mount Haleakala, Hawaii. Field-aligned bubbles were observed to grow from near-stationary wavelike perturbations with horizontal scale sizes of about 100 km at the lower apex altitude regions during the evening hours. The bubbles were seen to elongate toward higher apex levels as they accelerated eastward, sometimes reaching eastward velocities of over 100 m/s. In general, field-aligned depletions were observed to occur over all portions of the night. A characteristic shape was often observed with a rather sharp vertical wall bounding the depletion on the eastward side and with several tilted branches on the westward side. The structures were often observed to develop westward tilts as shear motions yielded eastward drifts that decreased with increasing apex altitude. During periods of extreme levels of shear, isolated depletions were seen to drift separately from neighboring depletion structures.

  13. Is the flow-aligned component of IMF really able to impact the magnetic field structure of Venusian magnetotail?

    NASA Astrophysics Data System (ADS)

    Rong, Z. J.; Stenberg, G.; Wei, Y.; Chai, L. H.; Futaana, Y.; Barabash, S.; Wan, W. X.; Shen, C.

    2016-11-01

    An earlier statistical survey suggested that the flow-aligned component of upstream interplanetary magnetic field (IMF) may play an important role in controlling the lobe asymmetries of the Venusian magnetotail. The tail current sheet would be displaced and the magnetic field configuration would show asymmetries with respect to the current sheet. The asymmetries are expected to be more evident when the flow-aligned component becomes dominant. Here with carefully selected cases as well as a statistical study based on Venus Express observations in the near-Venus tail, we show that the lobe asymmetries of the magnetic field as well as the displacement of the current sheet are common characteristics of the Venusian magnetotail. However, the asymmetries and the displacement of the current sheet do not show a significant dependence on the flow-aligned component of the IMF. Our results suggest that the flow-aligned component of IMF cannot penetrate into the near magnetotail to impact the magnetic field structure.

  14. Inverse scattering for frequency-scanned full-field optical coherence tomography.

    PubMed

    Marks, Daniel L; Ralston, Tyler S; Boppart, Stephen A; Carney, P Scott

    2007-04-01

    Full-field optical coherence tomography (OCT) is able to image an entire en face plane of scatterers simultaneously, but typically the focus is scanned through the volume to acquire three-dimensional structure. By solving the inverse scattering problem for full-field OCT, we show it is possible to computationally reconstruct a three-dimensional volume while the focus is fixed at one plane inside the sample. While a low-numerical-aperture (NA) OCT system can tolerate defocus because the depth of field is large, for high NA it is critical to correct for defocus. By deriving a solution to the inverse scattering problem for full-field OCT, we propose and simulate an algorithm that recovers object structure both inside and outside the depth of field, so that even for high NA the focus can be fixed at a particular plane within the sample without compromising resolution away from the focal plane.

  15. Coherence vortices in Mie scattering of statistically stationary partially coherent fields.

    PubMed

    Marasinghe, Madara L; Premaratne, Malin; Paganin, David M

    2010-03-29

    Points within a fully coherent complex scalar optical field, where the amplitude is identically zero but the optical phase has a jump discontinuity, have been widely investigated by the singular-optics community. More recent researches have extended the domain of singular optics to include partially coherent fields. For example, in coherence vortices the phase of the two-point spectral degree of coherence of a partially coherent field exhibits vortex structure around a point where the magnitude of the spectral degree of coherence vanishes. We show that the spectral degree of coherence of Mie scattered partially coherent statistically stationary electromagnetic fields exhibits a rich set of coherence vortices in both the internal and external fields. Specifically, we look at Mie scattering of a stationary beam from a dielectric sphere and study the formation of coherence vortices and their evolution with both the properties of the scattering sphere, and of the incident partially coherent beam.

  16. Examining the Electric Fields of the Evening Equatorial Ionosphere When the Solar Terminator is Aligned and Not Aligned with the Magnetic Meridian

    NASA Astrophysics Data System (ADS)

    Eccles, J. V.

    2014-12-01

    The electric field structure of the equatorial ionosphere near sunset has implications on the development of plasma irregularities. The details of the development of the electric fields are examined using a global ionosphere-electrodynamics model. The results of simulations of simplified conditions show the influence of the arrangement of the solar terminator with the magnetic meridian. The relationships of the Curl-Free mechanism, the Hall Current Divergence mechanism, and the role of the Equatorial Electorjet region control the magnitude and timing of the Prereversal Enhancement of the zonal electric field as well as its altitude profile above the F region bottomside. Realistic conditions for 'equinox' and 'solstice' solar terminator arrangments are presented. The stability of the low-latitude ionosphere has a demonstrated relationship with the solar terminator alignment [Tsunoda, JGR, 1981]. The profile of the vertical and zonal electric field below the bottomside is then examined using the global model to explore the controlling elements of the electric field structure and the growth rates of the Rayleigh-Taylor instability and Collisional Shear instability.Tsunoda, R. T. (1985), Control of the seasonal and longitudinal occurrence of equatorial scintillations by the longitudinal gradient in integrated E region Pedersen conductivity, J. Geophys. Res., 90(A1),447-456, doi:10.1029/JA090iA01p00447.

  17. Field-free long-lived alignment of molecules with a two-dimensional optical centrifuge

    NASA Astrophysics Data System (ADS)

    Milner, A. A.; Korobenko, A.; Milner, V.

    2016-05-01

    We introduce an optical tool—a "two-dimensional optical centrifuge"—capable of aligning molecules in extreme rotational states. The alignment is studied in oxygen under ambient conditions, and in a cold jet of nitrogen. Unlike the conventional centrifuge, which confines the molecules in the plane of their rotation, its two-dimensional version aligns the molecules along a well-defined axis, similar to the effect of a single linearly polarized laser pulse, but at a much higher level of rotational excitation. We observe long lifetimes of the created alignment due to the increased robustness of ultrahigh rotational states with respect to collisions. The adiabatic nature of the centrifuge excitation provides a means of generating stationary aligned states.

  18. Mesoscale Magnetosphere-Ionosphere Coupling along Open Magnetic Field Lines Associated with Airglow Patches: Field-aligned Currents and Precipitation

    NASA Astrophysics Data System (ADS)

    Zou, Y.; Nishimura, Y.; Lyons, L. R.; Shiokawa, K.; Burchill, J. K.; Knudsen, D. J.; Buchert, S. C.; Chen, S.; Nicolls, M. J.; Ruohoniemi, J. M.; McWilliams, K. A.; Nishitani, N.

    2016-12-01

    Although airglow patches are traditionally regarded as high-density plasma unrelated to local field-aligned currents (FACs) and precipitation, past observations were limited to storm-time conditions. Recent non-storm time observations show patches to be associated with azimuthally narrow ionospheric fast flow channels that substantially contribute to plasma transportation across the polar cap and connect dayside and nightside explosive disturbances. We examine whether non-storm time patches are related also to localized polar cap FACs and precipitation using Swarm- and FAST-imager-radar conjunctions. In Swarm data, we commonly (66%) identify substantial magnetic perturbations indicating FAC enhancements around patches. These FACs have substantial densities (0.1-0.2 μA/m-2) and can be approximated as infinite current sheets (typically 75 km wide) orientated roughly parallel to patches. They usually exhibit a Region-1 sense, i.e. a downward FAC lying eastward of an upward FAC, and can close through Pedersen currents in the ionosphere, implying that the locally enhanced dawn-dusk electric field across the patch is imposed by processes in the magnetosphere. In FAST data, we identify localized precipitation that is enhanced within patches in comparison to weak polar rain outside patches. The precipitation consists of structured or diffuse soft electron fluxes. While the latter resembles polar rain only with higher fluxes, the former consists of discrete fluxes enhanced by 1-2 orders of magnitude from several to several hundred eV. Although the precipitation is not a major contributor to patch ionization, it implies that newly reconnected flux tubes that retain electrons of magnetosheath origin can rapidly traverse the polar cap from the dayside. Therefore non-storm time patches should be regarded as part of a localized magnetosphere-ionosphere coupling system along open magnetic field lines, and their transpolar evolution as a reflection of reconnected flux tubes

  19. The Four-Part Field-Aligned Current System in the Ionosphere at Substorm Onset

    NASA Astrophysics Data System (ADS)

    McWilliams, K. A.; Sofko, G. J.; Bristow, W. A.; Hussey, G. C.

    2015-12-01

    Whereas the plasma circulation in the ionosphere is driven by convective drift which is the same for ions and electrons, the magnetospheric plasma circulation includes curvature and gradient drifts, which are charge-dependent. There is even a region of the Neutral Sheet in which the ions, but not the electrons, are "unmagnetized" and where charge separation can occur even for convective drift, which the electrons execute but the ions do not. Due to the charge separations in the magnetosphere, field-aligned currents are generated. The FACs and the associated electric fields play an important role in producing the convection pattern in the ionosphere. Here we argue that there are two pairs of FACs near substorm onset. One pair involves the auroral zone portion of the convection. There, a downward D FAC occurs in the poleward part of the auroral zone and an upward U FAC occurs in the equatorward part. We show that the D-U auroral FAC pair results from the odd situation in the INSh, where the electrons can convect earthward while the unmagnetized ions do not and so remain further tailward of the electrons. The equatorward edge of the auroral zone is marked by a convection reversal, because the auroral zone flows have an eastward velocity component, whereas subauroral flows have a westward component. At the convection reversal, the flow is strictly southward and the electric field strictly westward. The subauroral zone maps out to the outer radiation belt, where the high-energy electrons precipitate tailward of the energetic electron trapping boundary,and high-energy ions precipitate tailward of the energetic ion trapping boundary, the latter being earthward of the former. As a result, another FAC pair forms on field lines in the ORB/subauroral regions. The U FAC of the latter region is adjacent but earthward of the U FAC of the auroral zone pair. The D-U auroral zone pair is poleward of the U-D subauroral (Radiation Belt) pair. Finally, we note that the electric field

  20. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields.

    PubMed

    Armas-Pérez, Julio C; Londono-Hurtado, Alejandro; Guzmán, Orlando; Hernández-Ortiz, Juan P; de Pablo, Juan J

    2015-07-28

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

  1. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

    SciTech Connect

    Armas-Pérez, Julio C.; Londono-Hurtado, Alejandro; Guzmán, Orlando; Hernández-Ortiz, Juan P.; Pablo, Juan J. de

    2015-07-28

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

  2. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields.

    SciTech Connect

    Armas-Perez, Julio C.; Londono-Hurtado, Alejandro; Guzman, Orlando; Hernandez-Ortiz, Juan P.; de Pablo, Juan J.

    2015-07-27

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

  3. Shocklets, SLAMS, and Field-Aligned Ion Beams in the Terrestrial Foreshock

    NASA Technical Reports Server (NTRS)

    Wilson, L. B.; Koval, A.; Sibeck, D. G.; Szabo, A.; Cattell, C. A.; Kasper, J. C.; Maruca, B. A.; Pulupa, M.; Salem, C. S.; Wilber, M.

    2012-01-01

    We present Wind spacecraft observations of ion distributions showing field- aligned beams (FABs) and large-amplitude magnetic fluctuations composed of a series of shocklets and short large-amplitude magnetic structures (SLAMS). The FABs are found to have T(sub k) approx 80-850 eV, V(sub b)/V(sub sw) approx 1.3-2.4, T(sub perpendicular,b)/T(sub paralell,b) approx 1-8, and n(sub b)/n(sub o) approx 0.2-11%. Saturation amplitudes for ion/ion resonant and non-resonant instabilities are too small to explain the observed SLAMS amplitudes. We show two examples where groups of SLAMS can act like a local quasi-perpendicular shock reflecting ions to produce the FABs, a scenario distinct from the more-common production at the quasi-perpendicular bow shock. The SLAMS exhibit a foot-like magnetic enhancement with a leading magnetosonic whistler train, consistent with previous observations. Strong ion and electron heating are observed within the series of shocklets and SLAMS with temperatures increasing by factors approx > 5 and approx >3, respectively. Both the core and halo electron components show strong perpendicular heating inside the feature.

  4. Shocklets, SLAMS, and field-aligned ion beams in the terrestrial foreshock

    NASA Astrophysics Data System (ADS)

    Wilson, L. B., III; Koval, A.; Sibeck, D. G.; Szabo, A.; Cattell, C. A.; Kasper, J. C.; Maruca, B. A.; Pulupa, M.; Salem, C. S.; Wilber, M.

    2012-12-01

    We present Wind spacecraft observations of ion distributions showing field-aligned beams (FABs) and large-amplitude magnetic fluctuations composed of a series of shocklets and short large-amplitude magnetic structures (SLAMS). We show that the SLAMS are acting like a local quasi-perpendicular shock reflecting ions to produce the FABs. Previous FAB observations reported the source as the quasi-perpendicular bow shock. The SLAMS exhibit a foot-like magnetic enhancement with a leading magnetosonic whistler train, consistent with previous observations. The FABs are found to have T_b ~ 80-850 eV, V_b/V_sw ~ 1-2, T_perp/T_para ~ 1-10, and n_b/n_i ~ 0.2-14%. Strong ion and electron heating are observed within the series of shocklets and SLAMS increasing by factors ≥ 5 and ≥ 3, respectively. Both the core and halo electron components show strong perpendicular heating inside the feature.

  5. Statistics of field-aligned intermittent electron flux in a linear ECR plasma

    NASA Astrophysics Data System (ADS)

    Yoshimura, Shinji; Terasaka, Kenichiro; Aramaki, Mitsutoshi; Tanaka, Masayoshi Y.

    2012-10-01

    Spontaneous emission of field-aligned intermittent high-energy electron flux has been observed in a linear electron-cyclotron-resonance (ECR) plasma produced in the HYPER-I device (NIFS, Japan). We utilized the temporal variation of probe's floating potential due to electron influx as an index of the intermittent events. Time series of the floating potential fluctuation have been analyzed statistically. The probability density function (PDF) exhibits a non-Gaussian distribution with a long tail in the negative amplitude side, indicating that the signal is dominated by large amplitude negative spikes. The frequency distribution of waiting time, which is defined by the time interval between two consecutive spikes, is well fitted by an exponential distribution, implying a probable connection to the stationary Poisson process. Although a power-law dependence is found in the duration distribution, its relation to the self-organized criticality has not been clear. The effect of ion species on the statistics above will also be discussed.

  6. Does the Earth's Magnetic Field Serve as a Reference for Alignment of the Honeybee Waggle Dance?

    PubMed Central

    Lambinet, Veronika; Hayden, Michael E.; Bieri, Marco; Gries, Gerhard

    2014-01-01

    The honeybee (Apis mellifera) waggle dance, which is performed inside the hive by forager bees, informs hive mates about a potent food source, and recruits them to its location. It consists of a repeated figure-8 pattern: two oppositely directed turns interspersed by a short straight segment, the “waggle run”. The waggle run consists of a single stride emphasized by lateral waggling motions of the abdomen. Directional information pointing to a food source relative to the sun's azimuth is encoded in the angle between the waggle run line and a reference line, which is generally thought to be established by gravity. Yet, there is tantalizing evidence that the local (ambient) geomagnetic field (LGMF) could play a role. We tested the effect of the LGMF on the recruitment success of forager bees by placing observation hives inside large Helmholtz coils, and then either reducing the LGMF to 2% or shifting its apparent declination. Neither of these treatments reduced the number of nest mates that waggle dancing forager bees recruited to a feeding station located 200 m north of the hive. These results indicate that the LGMF does not act as the reference for the alignment of waggle-dancing bees. PMID:25541731

  7. Does the Earth's magnetic field serve as a reference for alignment of the honeybee Waggle dance?

    PubMed

    Lambinet, Veronika; Hayden, Michael E; Bieri, Marco; Gries, Gerhard

    2014-01-01

    The honeybee (Apis mellifera) waggle dance, which is performed inside the hive by forager bees, informs hive mates about a potent food source, and recruits them to its location. It consists of a repeated figure-8 pattern: two oppositely directed turns interspersed by a short straight segment, the "waggle run". The waggle run consists of a single stride emphasized by lateral waggling motions of the abdomen. Directional information pointing to a food source relative to the sun's azimuth is encoded in the angle between the waggle run line and a reference line, which is generally thought to be established by gravity. Yet, there is tantalizing evidence that the local (ambient) geomagnetic field (LGMF) could play a role. We tested the effect of the LGMF on the recruitment success of forager bees by placing observation hives inside large Helmholtz coils, and then either reducing the LGMF to 2% or shifting its apparent declination. Neither of these treatments reduced the number of nest mates that waggle dancing forager bees recruited to a feeding station located 200 m north of the hive. These results indicate that the LGMF does not act as the reference for the alignment of waggle-dancing bees.

  8. Observations of field-aligned currents, particles, and plasma drift in the polar cusps near solstice

    NASA Technical Reports Server (NTRS)

    Bythrow, P. F.; Potemra, T. A.; Hoffman, R. A.

    1982-01-01

    Magnetic perturbations observed by the TRIAD magnetometer within two hours of an AE-C spacecraft pass provide field-aligned current data, from the same local time in the northern hemisphere, for a study of the polar cusp. The AE-C spinning mode has allowed the use of the Z-axis magnetometer for Birkeland current observations, in conjunction with particle and drift measurements. The average B(z) were found to be 1.9 nT and -1.1 nT during the first two hourly intervals on January 15, 1977. Measurements from the low energy electron experiment revealed intense fluxes of soft, cusp-like 100 eV Maxwellian electrons throughout the prenoon polar cap. The upward directed current can be identified as the dominant cusp current appropriate for B(y) values lower than zero, while the downward directed current, which has the appropriate sign of a dayside region 1 current, is observed to lie entirely within a westerly, antisunward-convecting plasma.

  9. Dark matter effective field theory scattering in direct detection experiments

    SciTech Connect

    Schneck, K.; Cabrera, B.; Cerdeno, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, Priscilla B.; Daal, M.; Di Stefano, P. C.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, Jeter C.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, W.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.

    2015-05-01

    We examine the consequences of the effective eld theory (EFT) of dark matter-nucleon scattering or current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral di*erences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.

  10. Imaging of Passive Scalar Fields by Filtered Rayleigh Scattering

    NASA Astrophysics Data System (ADS)

    Kearney, Sean; Grasser, Thomas; Beresh, Steven; Schefer, Robert

    2002-11-01

    Filtered Rayleigh Scattering (FRS) is a molecular-filter-based, laser-diagnostic approach for multiparameter flowfield imaging that has been gaining popularity over the past 5-10 years [1]. Advantages of FRS for noninvasive gas-phase imaging include: (1) elimination of particle or chemical seeding requirements, (2) increased optical noise rejection allowing imaging close to walls and in "dirty" laboratory environments, (3) imaging of multiple flowfield parameters with a single diagnostic. In this work, the construction and performance of a FRS optical system for passive scalar imaging at Sandia National Laboratories is presented. Data were obtained in an open lab where no special precautions for the elimination of room particulate were made. Results from nonreacting jets and from a premixed flame are shown. Temperature imaging in a nonreacting, steady calibration jet reveals the precision of the time-averaged FRS thermometry results to be ±20 K, or 4of the characteristic temperature difference, while the single-laser-pulse precision is degraded to approximately ±40-50 K. These results are adequate for combustion thermometry purposes. Relative to the jet temperature measurements, species concentration imaging of a buoyant helium jet displays increased signal dynamic range and further improved precision. Reacting flow measurements from the combustion-product region of a methane-air Hencken-type premixed flame are also presented and a comparison of FRS and coherent anti-Stokes Raman scattering (CARS) experiments to calculated adiabatic-equilibrium product temperatures is made which validates the suitability of our FRS instrument for combustion temperature imaging. [1]G.S. Elliott, N. Glumac, and C.D. Carter, Meas. Sci. Tech., 12, 452, 2001.

  11. Fine optical alignment correction of astronomical spectrographs via in-situ full-field moment-based wavefront sensing

    NASA Astrophysics Data System (ADS)

    Lee, Hanshin; Hill, Gary J.; Tuttle, Sarah E.; Vattiat, Brian L.

    2012-09-01

    The image moment-based wavefront sensing (IWFS) utilizes moments of focus-modulated focal plane images to determine modal wavefront aberrations. This permits fast, easy, and accurate measurement of wavefront error (WFE) on any available finite-sized isolated targets across the entire focal plane (FP) of an imaging system, thereby allowing not only in-situ full-field image quality assessment, but also deterministic fine alignment correction of the imaging system. We present an experimental demonstration where fine alignment correction of a fast camera system in a fiber-fed astronomical spectrograph, called VIRUS, is accomplished by using IWFS.

  12. Evaluation of sound fields in a concert hall involving scattered reflections applying the subjective preference theory

    NASA Astrophysics Data System (ADS)

    Suzumura, Yukio

    2003-08-01

    Convex tilted rear walls in a stage enclosure, an array of circular columns installed in front of walls, and triangular reflectors above the stage were newly adopted as scattering obstacles in an acoustic design of Tsuyama Music Cultural Hall, called ``Bell Fole‸t Tsuyama.'' The fundamental shape of the hall was designed using the theory of subjective preference. To calculate the effects of scattered reflections on a sound field in a real concert hall is extremely laborious. For this reason, the evaluation of effects of scattered reflections on the sound field in the hall was made experimentally by use of a 110 acoustical scale. After construction of the hall, therefore, sound fields of the hall, which involves scattered reflections caused by the tilted convex rear, by the array of circular columns, and by the triangular reflectors, were measured using four orthogonal physical factors (LL, Δt1, Tsub, IACC) described in the theory and the acoustical character of these scattering obstacles was clarified. Results clearly showed that these new attempts on scattered reflections substantially improved the quality of the sound field in the hall. Thesis advisor: Yoichi Ando Copies of this thesis written in English can be obtained from Yukio Suzumura. E-mail address: ysuzu11@lapis.plala.or.jp

  13. Sound field separating on arbitrary surfaces enclosing a sound scatterer based on combined integral equations.

    PubMed

    Fan, Zongwei; Mei, Deqing; Yang, Keji; Chen, Zichen

    2014-12-01

    To eliminate the limitations of the conventional sound field separation methods which are only applicable to regular surfaces, a sound field separation method based on combined integral equations is proposed to separate sound fields directly in the spatial domain. In virtue of the Helmholtz integral equations for the incident and scattering fields outside a sound scatterer, combined integral equations are derived for sound field separation, which build the quantitative relationship between the sound fields on two arbitrary separation surfaces enclosing the sound scatterer. Through boundary element discretization of the two surfaces, corresponding systems of linear equations are obtained for practical application. Numerical simulations are performed for sound field separation on different shaped surfaces. The influences induced by the aspect ratio of the separation surfaces and the signal noise in the measurement data are also investigated. The separated incident and scattering sound fields agree well with the original corresponding fields described by analytical expressions, which validates the effectiveness and accuracy of the combined integral equations based separation method. Copyright © 2014 Elsevier B.V. All rights reserved.

  14. Communications through EM-wave scattering

    NASA Astrophysics Data System (ADS)

    Ince, A. N.

    1982-05-01

    Various scatter systems are examined with reference to the underlying physical processes and communications capabilities. The systems reviewed include ionoscatter, meteor burst, field-aligned scatter, chaff and needles, troposcatter, and optical scattering by aerosols. The scatter channel characteristics discussed include transmission loss, long- and short-term fading, signal distortion, and antenna gain degradation. Although the capacities of the scatter systems are restricted, the ranges they cover put them in the same group as the conventional HF radio and modern satellite communications. Scatter systems can be designed to be more robust than HF and more economical than satellite communication systems.

  15. Extremely field-aligned cool electrons in the dayside outer magnetosphere

    NASA Astrophysics Data System (ADS)

    Mozer, F. S.; Agapitov, O. A.; Angelopoulos, V.; Hull, A.; Larson, D.; Lejosne, S.; McFadden, J. P.

    2017-01-01

    For 200 days in 2016 while Time History of Events and Macroscale Interactions during Substorms D (THEMIS-D) was in the dayside, equatorial magnetosphere, its electron energy coverage was modified such that the first 15 energy steps covered the range of 1-30 eV and 16 steps covered energies to 30 keV. These measurements were free of backgrounds from photoelectrons, secondaries, or ionospheric plasma plumes. Three energy bands of electrons were observed: cold electrons having energies below 1 eV (plasmaspheric plumes measured by the spacecraft potential); cool electrons, defined as electrons having energies of 1-25 eV; and hot electrons having energies of 25 eV to 30 keV. The cool electron fluxes at fixed radial distances varied by an order of magnitude from one orbit to the next. These fluxes often increased with increasing radial distance, suggesting an external source. They were extremely field aligned, having pitch angle ratios (flux at 0-20° and 160-180° divided by the flux at 80-100°) greater than 100. Evidence is presented that they resulted from cusp electrons moving from open to closed magnetospheric field lines due to their E × B/B2 drift. They constituted the majority of the electron energy density at such times and places. They were not associated with magnetopause reconnection because they were not observed at the magnetopause, but they were observed as far as 3 RE inside of it. Their occurrence probability in the outer magnetosphere was 50% in June and 10% in September, suggesting a dayside source attributed to the tilt of the northern cusp toward the Sun during the summer.

  16. Field-aligned current signatures during the March 13-14, 1989, great magnetic storm

    SciTech Connect

    Fujii, R. ); Fukunishi, H. ); Kokubun, S. ); Sugiura, M. ); Tohyama, F. ); Hayakawa, H.; Tsuruda, K. ); Okada, T. )

    1992-07-01

    Characteristics of field-aligned currents (FACs) in the evening and morning regions during the March 13-14, 1989, great magnetic storm have been determined using magnetic and electric field data obtained from the EXOS D spacecraft. This storm began with an SSC at 0128 UT on March 13, and the second SSC occurred at 0747 UT on the same day. The storm continued until March 14. The equatorward boundary of the FAC region began to move equatorward right after the first SSC in both the evening and morning sectors, but the poleward boundary did not immediately respond to the SSC. The equatorward boundary of the FAC system reached as low as below 48{degree} invariant latitude, which corresponds to L = 2.2, and the latitudinal width of the FAC region increased greatly, particularly in the morning sector ({approximately}33{degree} in invariant latitude). In the evening sector the conventional current system characterized by a pair of upward region 1 and downward region 2 FACs changed into complicated patterns consisting of many pairs of upward and downward FACs with the development of the storm, particularly around 22 UT on March 13 when an intense eastward electrojet was observed as low as 50{degree} invariant latitude on the ground. In the morning sector an additional large-scale upward FAC was observed poleward of the conventional downward region 1 and upward region 2 FAC system throughout the storm. In addition, a pair of FACs with a narrow latitudinal width ({approximately}1.5{degree}) was observed at the poleward boundary of the extra upward FAC.

  17. Quasiperiodic field-aligned current dynamics associated with auroral undulations during a substorm recovery

    NASA Astrophysics Data System (ADS)

    Bunescu, C.; Marghitu, O.; Vogt, J.; Constantinescu, D.; Partamies, N.

    2017-03-01

    A substorm recovery event in the early morning sector is explored by means of ground and spacecraft data. The ground data are provided by stations of the MIRACLE network, in northern Scandinavia and Svalbard, while spacecraft data are observed by the Cluster satellites, toward the end of the recovery phase. Additional information is provided by the Fast Auroral SnapshoT (FAST) satellite, conjugate to Cluster 3 (C3). A prominent signature in the Cluster data is the low-frequency oscillations of the perturbation magnetic field, in the Pc5 range, interpreted in terms of a motion of quasi-stationary mesoscale field-aligned currents (FACs). Ground magnetic pulsations in the Ps6 range suggest that the Cluster observations are the high-altitude counterpart of the drifting auroral undulations, whose features thus can be explored closely. While multiscale minimum variance analysis provides information on the planarity, orientation, and scale of the FAC structures, the conjugate data from FAST and from the ground stations can be used to resolve also the azimuthal motion. A noteworthy feature of this event, revealed by the Cluster observations, is the apparent relaxation of the twisted magnetic flux tubes, from a sequence of 2-D current filaments to an undulated current sheet, on a timescale of about 10 min. This timescale appears to be consistent with the drift mirror instability in the inner magnetosphere, mapping to the equatorward side of the oval, or the Kelvin-Helmholtz instability related to bursty bulk flows farther downtail, mapping to the poleward side of the oval. However, more work is needed and a better event statistics, to confirm these tentative mechanisms as sources of Ω-like auroral undulations during late substorm recovery.

  18. Field-aligned currents in Saturn's southern nightside magnetosphere: Subcorotation and planetary period oscillation components

    NASA Astrophysics Data System (ADS)

    Hunt, G. J.; Cowley, S. W. H.; Provan, G.; Bunce, E. J.; Alexeev, I. I.; Belenkaya, E. S.; Kalegaev, V. V.; Dougherty, M. K.; Coates, A. J.

    2014-12-01

    We investigate magnetic data showing the presence of field-aligned magnetosphere-ionosphere coupling currents on 31 Cassini passes across Saturn's southern postmidnight auroral region. The currents are strongly modulated in magnitude, form, and position by the phase of the southern planetary period oscillations (PPOs). PPO-independent currents are separated from PPO-related currents using the antisymmetry of the latter with respect to PPO phase. PPO-independent downward currents ~1.1 MA per radian of azimuth flow over the polar open field region indicative of significant plasma subcorotation are enhanced in an outer plasma sheet layer of elevated ionospheric conductivity carrying ~0.8 MA rad-1 and close principally in an upward directed current sheet at ~17°-19° ionospheric colatitude carrying ~2.3 MA rad-1 that maps to the outer hot plasma region in Saturn's magnetosphere (equatorial range ~11-16 Saturn radii (RS)) colocated with the UV oval. Subsidiary downward and upward currents ~0.5 MA rad-1 lie at ~19°-20.5° colatitude mapping to the inner hot plasma region, but no comparable currents are detected at larger colatitudes mapping to the cool plasma regime inside ~8 RS. PPO-related currents at ~17.5°-20° colatitude overlap the main upward and subsidiary downward currents and carry comparable rotating upward and downward currents peaking at ~1.7 MA rad-1. The overall current layer colatitude is also modulated with 1° amplitude in the PPO cycle, maximum equatorward adjacent to the peak upward PPO current and maximum poleward adjacent to peak downward PPO current. This phasing requires the current system to be driven from the planetary atmosphere rather than directly from the magnetosphere.

  19. KINETIC ALFVEN WAVE INSTABILITY DRIVEN BY FIELD-ALIGNED CURRENTS IN SOLAR CORONAL LOOPS

    SciTech Connect

    Chen, L.; Wu, D. J. E-mail: djwu@pmo.ac.cn

    2012-08-01

    Magneto-plasma loops, which trace closed solar magnetic field lines, are the primary structural elements of the solar corona. Kinetic Alfven wave (KAW) can play an important role in inhomogeneous heating of these magneto-plasma structures in the corona. By the use of a low-frequency kinetic dispersion equation, which is presented in this paper and is valid in a finite-{beta} plasma with Q < {beta} < 1 plasma (where {beta} is the kinetic to magnetic pressure ratio and Q = m{sub e} /m{sub i} is the mass ratio of electrons to ions), KAW instability driven by a field-aligned current in the current-carrying loops in the solar corona is investigated. The results show that the KAW instability can occur in wave number regimes 0 < k{sub z} < k{sup c}{sub z} and 0 < k < k{sup c} , and that the critical wave numbers k{sup c}{sub z} and k{sup c} and the growth rate both considerably increase as the drift velocity V{sub D} of the current-carrying electrons increases in the loops. In particular, for typical parameters of the current-carrying loops in the solar corona this instability mechanism results in a high growth rate of KAWs, {omega}{sub i} {approx} 0.01-0.1{omega}{sub ci} {approx} 10{sup 3}-10{sup 4} s{sup -1}. The results are of importance in understanding the physics of the electric current dissipation and plasma heating of the current-carrying loops in the solar corona.

  20. Molecular collisions and reactive scattering in external fields: Are field-induced couplings important at short range?

    NASA Astrophysics Data System (ADS)

    Vieira, D.; Krems, R. V.; Tscherbul, T. V.

    2017-01-01

    We use accurate quantum scattering calculations to elucidate the role of short-range molecule-field interactions in atom-molecule inelastic collisions and abstraction chemical reactions at low temperatures. We consider two examples: elastic and inelastic scattering of NH(3Σ) molecules with Mg(1S) atoms in a magnetic field; reactive scattering LiF + H → Li + HF in an electric field. Our calculations suggest that, for non-reactive collision systems and abstraction chemical reactions, the molecule-field interactions cannot generally be neglected at short range because the atom-molecule potential passes through zero at short range. An important exception occurs for Zeeman transitions in atom-molecule collisions at magnetic fields ≲1000 G, for which the molecule-field couplings need only be included at large ρ outside the range of the atom-molecule interaction. Our results highlight the importance of an accurate description of ρ-dependent molecule-field interactions in quantum scattering calculations on molecular collisions and chemical reactions at low temperatures.

  1. Space Technology 5 (ST-5) Multipoint Observations of Temporal and Spatial Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, Guan

    2010-01-01

    Space Technology 5 (ST-5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from ST5. The data demonstrate that mesoscale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of about 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are about 1 min for meso-scale currents and about 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  2. Space Technology 5 Multi-point Observations of Field-aligned Currents: Temporal Variability of Meso-Scale Structures

    NASA Technical Reports Server (NTRS)

    Le, Guan; Wang, Yongli; Slavin, James A.; Strangeway, Robert J.

    2007-01-01

    Space Technology 5 (ST5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from ST5. The data demonstrate that meso-scale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of - 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are approx. 1 min for meso-scale currents and approx. 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  3. Space Technology 5 Multi-point Observations of Field-aligned Currents: Temporal Variability of Meso-Scale Structures

    NASA Technical Reports Server (NTRS)

    Le, Guan; Wang, Yongli; Slavin, James A.; Strangeway, Robert J.

    2007-01-01

    Space Technology 5 (ST5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from ST5. The data demonstrate that meso-scale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of - 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are approx. 1 min for meso-scale currents and approx. 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  4. Four large-scale field-aligned current systmes in the dayside high-latitude region

    NASA Technical Reports Server (NTRS)

    Ohtani, S.; Potemra, T. A.; Newell, P.T.; Zanetti, L. J.; Iijima, T.; Watanabe, M.; Blomberg, L. G.; Elphinstone, R. D.; Murphree, J. S.; Yamauchi, M.

    1995-01-01

    A system of four current sheets of large-scale field-aligned currents (FACs) was discovered in the data set of simultaneous Viking and Defense Meteorological Satellire Program-F7 (DMSP-F7) crossing of the dayside high-latitude region. This paper reports four examples of this system that were observed in the prenoon sector. The flow polarities of FACs are upward, downward, upward, and downward, from equatorward to poleward. The lowest-latitude upward current is flowing mostly in the central plasma sheet (CPS) precipitation region, often overlapping with the boundary plasma sheet (BPS) at its poleward edge, andis interpreted as a region 2 current. The pair of downward and upward FACs in the middle of te structure are collocated with structured electron precipitation. The precipitation of high-energy (greater than 1 keV) electrons is more intense in the lower-latitude downward current sheet. The highest-latitude downward flowing current sheet is located in a weak, low-energy particle precipitation region, suggesting that this current is flowing on open field lines. Simulaneous observations in the postnoon local time sector reveal the standard three-sheet structure of FACs, sometimes described as region 2, region 1, and mantle (referred to the midday region O) currents. A high correlation was found between the occurrence of the four FAC sheet structure and negative interplanetary magnetic field (IMF) B(sub Y). We discuss the FAC structurein terms of three types of convection cells: the merging, viscous, andlobe cells. During strongly negative IMF B(sub Y), two convection reversals exist in the prenoon sector; one is inside the viscous cell, and the other is between the viscous cell and the lobe cell. This structure of convection flow is supported by the Viking electric field and auroral UV image data. Based on the convection pattern, the four FAC sheet structure is interpreted as the latitude overlap of midday and morning FAC systems. We suggest that the for

  5. Four large-scale field-aligned current systmes in the dayside high-latitude region

    NASA Technical Reports Server (NTRS)

    Ohtani, S.; Potemra, T. A.; Newell, P.T.; Zanetti, L. J.; Iijima, T.; Watanabe, M.; Blomberg, L. G.; Elphinstone, R. D.; Murphree, J. S.; Yamauchi, M.

    1995-01-01

    A system of four current sheets of large-scale field-aligned currents (FACs) was discovered in the data set of simultaneous Viking and Defense Meteorological Satellire Program-F7 (DMSP-F7) crossing of the dayside high-latitude region. This paper reports four examples of this system that were observed in the prenoon sector. The flow polarities of FACs are upward, downward, upward, and downward, from equatorward to poleward. The lowest-latitude upward current is flowing mostly in the central plasma sheet (CPS) precipitation region, often overlapping with the boundary plasma sheet (BPS) at its poleward edge, andis interpreted as a region 2 current. The pair of downward and upward FACs in the middle of te structure are collocated with structured electron precipitation. The precipitation of high-energy (greater than 1 keV) electrons is more intense in the lower-latitude downward current sheet. The highest-latitude downward flowing current sheet is located in a weak, low-energy particle precipitation region, suggesting that this current is flowing on open field lines. Simulaneous observations in the postnoon local time sector reveal the standard three-sheet structure of FACs, sometimes described as region 2, region 1, and mantle (referred to the midday region O) currents. A high correlation was found between the occurrence of the four FAC sheet structure and negative interplanetary magnetic field (IMF) B(sub Y). We discuss the FAC structurein terms of three types of convection cells: the merging, viscous, andlobe cells. During strongly negative IMF B(sub Y), two convection reversals exist in the prenoon sector; one is inside the viscous cell, and the other is between the viscous cell and the lobe cell. This structure of convection flow is supported by the Viking electric field and auroral UV image data. Based on the convection pattern, the four FAC sheet structure is interpreted as the latitude overlap of midday and morning FAC systems. We suggest that the for

  6. Towards identifying the mechanisms underlying field-aligned edge-loss of HHFW power on NSTX

    SciTech Connect

    Perkins, R. J.; Ahn, Joonwook; Bell, R. E.; Bertelli, Nicola; Diallo, A.; Gerhardt, S.; Gray, T. K.; Green, David L; Jaeger, E. F.; Hosea, J.; Jaworski, M. A.; LeBlanc, B; Kramer, G.; McLean, Adam G; Maingi, Rajesh; Phillips, C. K.; Podesta, M.; Ryan, Philip Michael; Sabbagh, S. A.; Scotti, F.; Taylor, G.; Wilson, J. R.

    2013-01-01

    Fast-wave heating will be a major heating scheme on ITER, as it can heat ions directly and is relatively unaffected by the large machine size unlike neutral beams. However, fast-wave interactions with the plasma edge can lead to deleterious effects such as, in the case of the high-harmonic fast-wave (HHFW) system on NSTX, large losses of fast-wave power in the scrape off layer (SOL) under certain conditions. In such scenarios, a large fraction of the lost HHFW power is deposited on the upper and lower divertors in bright spiral shapes. The responsible mechanism(s) has not yet been identified but may include fast-wave propagation in the scrape off layer, parametric decay instability, and RF currents driven by the antenna reactive fields. Understanding and mitigating these losses is important not only for improving the heating and current-drive on NSTX-Upgrade but also for understanding fast-wave propagation across the SOL in any fast-wave system. This talk summarizes experimental results demonstrating that the flow of lost HHFW power to the divertor regions largely follows the open SOL magnetic field lines. This lost power flux is relatively large close to both the antenna and the last closed flux surface with a reduced level in between, so the loss mechanism cannot be localized to the antenna. At the same time, significant losses also occur along field lines connected to the inboard edge of the bottom antenna plate. The power lost within the spirals is roughly estimated, showing that these field-aligned losses to the divertor are significant but may not account for the total HHFW loss. To elucidate the role of the onset layer for perpendicular fast-wave propagation with regards to fast-wave propagation in the SOL, a cylindrical cold-plasma model is being developed. This model, in addition to advanced RF codes such as TORIC and AORSA, is aimed at identifying the underlying mechanism(s) behind these SOL losses, to minimize their effects in NSTX-U, and to predict

  7. Towards identifying the mechanisms underlying field-aligned edge-loss of HHFW power on NSTX

    SciTech Connect

    Perkins, R. J.; Bell, R. E.; Bertelli, N.; Diallo, A.; Gerhardt, S.; Hosea, J. C.; Jaworski, M. A.; LeBlanc, B. P.; Kramer, G. J.; Maingi, R.; Phillips, C. K.; Podestà, M.; Roquemore, L.; Scotti, F.; Taylor, G.; Wilson, J. R.; Ahn, J-W.; Gray, T. K.; Green, D. L.; McLean, A.; and others

    2014-02-12

    Fast-wave heating will be a major heating scheme on ITER, as it can heat ions directly and is relatively unaffected by the large machine size unlike neutral beams. However, fast-wave interactions with the plasma edge can lead to deleterious effects such as, in the case of the high-harmonic fast-wave (HHFW) system on NSTX, large losses of fast-wave power in the scrape off layer (SOL) under certain conditions. In such scenarios, a large fraction of the lost HHFW power is deposited on the upper and lower divertors in bright spiral shapes. The responsible mechanism(s) has not yet been identified but may include fast-wave propagation in the scrape off layer, parametric decay instability, and RF currents driven by the antenna reactive fields. Understanding and mitigating these losses is important not only for improving the heating and current-drive on NSTX-Upgrade but also for understanding fast-wave propagation across the SOL in any fast-wave system. This talk summarizes experimental results demonstrating that the flow of lost HHFW power to the divertor regions largely follows the open SOL magnetic field lines. This lost power flux is relatively large close to both the antenna and the last closed flux surface with a reduced level in between, so the loss mechanism cannot be localized to the antenna. At the same time, significant losses also occur along field lines connected to the inboard edge of the bottom antenna plate. The power lost within the spirals is roughly estimated, showing that these field-aligned losses to the divertor are significant but may not account for the total HHFW loss. To elucidate the role of the onset layer for perpendicular fast-wave propagation with regards to fast-wave propagation in the SOL, a cylindrical cold-plasma model is being developed. This model, in addition to advanced RF codes such as TORIC and AORSA, is aimed at identifying the underlying mechanism(s) behind these SOL losses, to minimize their effects in NSTX-U, and to predict

  8. Numerical modeling of scattering type scanning near-field optical microscopy

    NASA Astrophysics Data System (ADS)

    Ravichandran, Arvindvivek; Kinzel, Edward C.; Ginn, James C.; D'Archangel, Jeffery A.; Tucker, Eric Z.; Lail, Brian A.; Raschke, Markus B.; Boreman, Glenn D.

    2013-09-01

    Apertureless scattering-type Scanning Near-field Optical Microscopy (s-SNOM) has been used to study the electromagnetic response of infrared antennas below the diffraction limit. The ability to simultaneously resolve the phase and amplitude of the evanescent field relies on the implementation of several experimentally established background suppression techniques. We model the interaction of the probe with a patch antenna using the Finite Element Method (FEM). Green's theorem is used to predict the far-field, cross-polarized scattering and to construct the homodyne amplified signal. This approach allows study of important experimental phenomena, specifically the effects of the reference strength, demodulation harmonic, and detector location.

  9. Development of scattering near-field optical microspectroscopy apparatus using an infrared synchrotron radiation source

    NASA Astrophysics Data System (ADS)

    Ikemoto, Yuka; Ishikawa, Michio; Nakashima, Satoru; Okamura, Hidekazu; Haruyama, Yuichi; Matsui, Shinji; Moriwaki, Taro; Kinoshita, Toyohiko

    2012-04-01

    We report the status of a scattering near-field microspectroscopy apparatus developed at SPring-8 using an infrared synchrotron radiation (IR-SR) source. It consists of a scattering type scanning near-field optical microscope and a Fourier transform infrared spectrometer. The IR-SR is used as a highly brilliant and broad-band IR source. This apparatus has potential for application in near-field spectroscopy with high spatial resolution beyond the diffraction limit. In order to eliminate background scatterings from the probe shaft and/or sample surface, we used higher harmonic demodulation method. The near-field spectra were observed by 2nd harmonic components using the lock-in detection. The spatial resolution of about 300 nm was achieved at around 1000 cm- 1 (10 μm wavelength).

  10. How to measure a complete set of polarization-dependent differential cross sections in a scattering experiment with aligned reagents?

    SciTech Connect

    Wang, Fengyan E-mail: kliu@po.iams.sinica.edu.tw; Lin, Jui-San; Liu, Kopin E-mail: kliu@po.iams.sinica.edu.tw

    2014-02-28

    Polarization-dependent differential cross section (PDDCS) is one of the three-vector correlations (k, k{sup ′}, j) in molecular collisions, which provides the most detailed insights into the steric requirements of chemical reactions, i.e., how the reactivity depends on the polarization of reagents. Only quite recently has such quantity been fully realized experimentally in the study of the reaction of the aligned CHD{sub 3}(v{sub 1} = 1, |jK〉 = |10〉) molecules with Cl({sup 2}P{sub 3/2}) atoms. Theoretically, PDDCS is a relatively new concept; experimental realization of the theoretical construct requires some careful considerations that are not readily available in the literature. Here, we present the “know-how” behind the full PDDCS measurements to fill the gaps and to provide a clear roadmap for future applications. To make the connection apparent between the methodology presented here and the stereodynamics revealed in previous reports, the same Cl + aligned CHD{sub 3} reaction is used for illustration.

  11. Strong IMF By-Related Plasma Convection in the Ionosphere and Cusp Field-Aligned Currents Under Northward IMF Conditions

    NASA Technical Reports Server (NTRS)

    Le, G.; Lu, G.; Strangeway, R. J.; Pfaff, R. F., Jr.; Vondrak, Richard R. (Technical Monitor)

    2001-01-01

    We present in this paper an investigation of IMF-By related plasma convection and cusp field-aligned currents using FAST data and AMIE model during a prolonged interval with large positive IMF By and northward Bz conditions (By/Bz much greater than 1). Using the FAST single trajectory observations to validate the global convection patterns at key times and key locations, we have demonstrated that the AMIE procedure provides a reasonably good description of plasma circulations in the ionosphere during this interval. Our results show that the plasma convection in the ionosphere is consistent with the anti-parallel merging model. When the IMF has a strongly positive By component under northward conditions, we find that the global plasma convection forms two cells oriented nearly along the Sun-earth line in the ionosphere. In the northern hemisphere, the dayside cell has clockwise convection mainly circulating within the polar cap on open field lines. A second cell with counterclockwise convection is located in the nightside circulating across the polar cap boundary, The observed two-cell convection pattern appears to be driven by the reconnection along the anti-parallel merging lines poleward of the cusp extending toward the dusk side when IMF By/Bz much greater than 1. The magnetic tension force on the newly reconnected field lines drives the plasma to move from dusk to dawn in the polar cusp region near the polar cap boundary. The field-aligned currents in the cusp region flow downward into the ionosphere. The return field-aligned currents extend into the polar cap in the center of the dayside convection cell. The field-aligned currents are closed through the Peterson currents in the ionosphere, which flow poleward from the polar cap boundary along the electric field direction.

  12. Bragg scattering of light in vacuum structured by strong periodic fields.

    PubMed

    Kryuchkyan, Gagik Yu; Hatsagortsyan, Karen Z

    2011-07-29

    Elastic scattering of laser radiation due to vacuum polarization by spatially modulated strong electromagnetic fields is considered. The Bragg interference arising at a specific impinging direction of the probe wave concentrates the scattered light in specular directions. The interference maxima are enhanced with respect to the usual vacuum polarization effect proportional to the square of the number of modulation periods within the interaction region. The Bragg scattering can be employed to detect the vacuum polarization effect in a setup of multiple crossed superstrong laser beams with parameters envisaged in the future Extreme Light Infrastructure.

  13. Effective field theory for large logarithms in radiative corrections to electron proton scattering

    NASA Astrophysics Data System (ADS)

    Hill, Richard J.

    2017-01-01

    Radiative corrections to elastic electron proton scattering are analyzed in effective field theory. A new factorization formula identifies all sources of large logarithms in the limit of large momentum transfer, Q2≫me2. Explicit matching calculations are performed through two-loop order. A renormalization analysis in soft-collinear effective theory is performed to systematically compute and resum large logarithms. Implications for the extraction of charge radii and other observables from scattering data are discussed. The formalism may be applied to other lepton-nucleon scattering and e+e- annihilation processes.

  14. On the concept of random orientation in far-field electromagnetic scattering by nonspherical particles.

    PubMed

    Mishchenko, Michael I; Yurkin, Maxim A

    2017-02-01

    Although the model of randomly oriented nonspherical particles has been used in a great variety of applications of far-field electromagnetic scattering, it has never been defined in strict mathematical terms. In this Letter, we use the formalism of Euler rigid-body rotations to clarify the concept of statistically random particle orientations and derive its immediate corollaries in the form of the most general mathematical properties of the orientation-averaged extinction and scattering matrices. Our results serve to provide a rigorous mathematical foundation for numerous publications in which the notion of randomly oriented particles and its light-scattering implications have been considered intuitively obvious.

  15. Enhancing Photoresponsivity of Self-Aligned MoS2 Field-Effect Transistors by Piezo-Phototronic Effect from GaN Nanowires.

    PubMed

    Liu, Xingqiang; Yang, Xiaonian; Gao, Guoyun; Yang, Zhenyu; Liu, Haitao; Li, Qiang; Lou, Zheng; Shen, Guozhen; Liao, Lei; Pan, Caofeng; Lin Wang, Zhong

    2016-08-23

    We report high-performance self-aligned MoS2 field-effect transistors (FETs) with enhanced photoresponsivity by the piezo-phototronic effect. The FETs are fabricated based on monolayer MoS2 with a piezoelectric GaN nanowire (NW) as the local gate, and a self-aligned process is employed to define the source/drain electrodes. The fabrication method allows the preservation of the intrinsic property of MoS2 and suppresses the scattering center density in the MoS2/GaN interface, which results in high electrical and photoelectric performances. MoS2 FETs with channel lengths of ∼200 nm have been fabricated with a small subthreshold slope of 64 mV/dec. The photoresponsivity is 443.3 A·W(-1), with a fast response and recovery time of ∼5 ms under 550 nm light illumination. When strain is introduced into the GaN NW, the photoresponsivity is further enhanced to 734.5 A·W(-1) and maintains consistent response and recovery time, which is comparable with that of the mechanical exfoliation of MoS2 transistors. The approach presented here opens an avenue to high-performance top-gated piezo-enhanced MoS2 photodetectors.

  16. The interplanetary magnetic field B sub y -dependent field-aligned current in the dayside polar cap under quiet conditions

    SciTech Connect

    Yamauchi, M. Kyoto Univ. ); Araki, T. )

    1989-03-01

    Spatial distribution and temporal variation of the interplanetary magnetic field (IMF) B{sub y}-dependent cusp region field-aligned currents (FACs) during quiet periods were studied by use of magnetic data observed by Magsat. The analysis was made for 11 events (each event lasts more than one and a half days) when the IMF B{sub y} component was steadily large and B{sub x} was relatively small ({vert bar}B{sub z}{vert bar} < {vert bar}B{sub y}{vert bar}). Results of the analysis of total 62 half-day periods for the IMF B{sub y}-dependent cusp region FAC are summarized as follows: (1) the IMF B{sub y}-dependent cusp region FAC is located at around 86{degree}-87{degree} invariant latitude local noon, which is more poleward than the location of the IMF B{sub z}-dependent cusp region FAC; (2) the current density of this FAC is greater than previous studies ({ge} 4 {mu}A/m{sup 2} for IMF B{sub y} = 6 nT); (3) there are two time scales for the IMF B{sub y}-dependent cusp region FAC to appear: the initial rise of the current is on a short time scale, {approximately} 10 min, and it is followed by a gradual increase on a time scale of several hours to a half day; (4) the seasonal change of this FAC is greater than that of the nightside region 1 or region 2 FACs; (5) the IMF B{sub z}-dependent cusp region FAC is not well observed around the cusp when the IMF B{sub y}-dependent cusp region FAC is intense.

  17. Dual-Scattering Near-Field Microscope for Correlative Nanoimaging of SERS and Electromagnetic Hotspots.

    PubMed

    Kusch, Patryk; Mastel, Stefan; Mueller, Niclas S; Morquillas Azpiazu, Nieves; Heeg, Sebastian; Gorbachev, Roman; Schedin, Fredrik; Hübner, Uwe; Pascual, Jose I; Reich, Stephanie; Hillenbrand, Rainer

    2017-04-12

    Surface-enhanced Raman spectroscopy (SERS) enables sensitive chemical studies and materials identification, relying on electromagnetic (EM) and chemical-enhancement mechanisms. Here we introduce a tool for the correlative nanoimaging of EM and SERS hotspots, areas of strongly enhanced EM fields and Raman scattering, respectively. To that end, we implemented a grating spectrometer into a scattering-type scanning near-field optical microscope (s-SNOM) for mapping of both the elastically and inelastically (Raman) scattered light from the near-field probe, that is, a sharp silicon tip. With plasmon-resonant gold dimers (canonical SERS substrates) we demonstrate with nanoscale spatial resolution that the enhanced Raman scattering from the tip is strongly correlated with its enhanced elastic scattering, the latter providing access to the EM-field enhancement at the illumination frequency. Our technique has wide application potential in the correlative nanoimaging of local-field enhancement and SERS efficiency as well as in the investigation and quality control of novel SERS substrates.

  18. Nonspecular meteor trails from non-field-aligned irregularities: Can they be explained by presence of charged meteor dust?

    NASA Astrophysics Data System (ADS)

    Chau, J. L.; Strelnikova, I.; Schult, C.; Oppenheim, M. M.; Kelley, M. C.; Stober, G.; Singer, W.

    2014-05-01

    Nonspecular meteor echoes have been associated with field-aligned irregularities and have been observed at low-latitude and midlatitude sites. We present observations obtained at high latitudes with range-time features that resemble those at lower latitudes. However, these echoes cannot come from field-aligned irregularities, since the radar-pointing angles are almost parallel to the magnetic field. Using interferometry, we have been able to discriminate space and time features. Our echoes could be qualitatively explained by the presence of charged dust forming from the meteoric material immersed in a turbulent flow. This can lead to a high Schmidt number plasma that can sustain meter-scale turbulence just as it does for the polar mesospheric summer echoes. These rare events require relatively large meteoroids. The result emphasizes the importance of charged dust in understanding all long-duration nonspecular meteor echoes. This dust will extend their diffusion times and will affect temperature estimations from specular echoes.

  19. Latitudinal and field-aligned cosmic ray gradients 2 to 5 AU Voyagers 1 and 2 and IMP 8

    NASA Technical Reports Server (NTRS)

    Roelof, E. C.; Decker, R. B.; Krimigis, S. M.

    1983-01-01

    Results are presented showing that the contemporary picture of a relatively small heliocentric radial gradient is generally correct. They emphasize that such a gradient should really be thought of in terms of field-aligned structures since the cosmic ray populations tend to 'corotate' locally with the interplanetary field structure. Nonuniform latitudinal gradients of approximately 2 to 5 percent/deg in structures lasting 10 to 30 days are identified unambiguously. Additional evidence is seen for somewhat smaller latitudinal gradients often north to south and probably mixed with small field-aligned gradients of less than 1 percent/AU that persist for several solar rotations. It is suggested that these smallest ephemeral latitudinal gradients manifest themselves by affecting the degree of irregularity in diurnal variations of high latitude neutron monitors.

  20. Dynamics of debye-scale nonstationary plasma structures in the region of auroral field-aligned currents

    NASA Astrophysics Data System (ADS)

    Bespalov, P. A.; Mizonova, V. G.

    2017-01-01

    We consider the formation of small-scale nonstationary plasma structures in the region of relatively strong field-aligned electric currents. The formation of these structures has been shown to be associated with the density instability developed when the current velocity exceeds a critical value. The conditions for the development of this instability can be most favorable in the region of low-density plasma. Numerical calculations have been performed for the initial nonlinear stage of the structure development. The main parameters of the structure, i.e., the times of its formation and destruction, spatial scales, and electric field, have been estimated. The features of the structures are consistent with the existing data from space experiments in the region of auroral field-aligned currents of the Earth.