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Sample records for field aligned scattering

  1. Electrostatic lower hybrid waves excited by electromagnetic whistler mode waves scattering from planar magnetic-field-aligned plasma density irregularities

    NASA Technical Reports Server (NTRS)

    Bell, T. F.; Ngo, H. D.

    1990-01-01

    This paper presents a theoretical model for electrostatic lower hybrid waves excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and the topside ionosphere, where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. In this model, the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. Results indicate that high-amplitude short-wavelength (5 to 100 m) quasi-electrostatic whistler mode waves can be excited when electromagnetic whistler mode waves scatter from small-scale planar magnetic-field-aligned plasma density irregularities in the topside ionosphere and magnetosphere.

  2. HF scattering induced by field-aligned irregularities in the equatorial E-region during total solar eclipses

    NASA Astrophysics Data System (ADS)

    Zhang, X. J.; Xiong, N. L.

    1985-10-01

    Results and analyses of solar eclipse effects on the lower ionosphere are presented. After the first contact of the total eclipse on February 16, 1980, an absorption increment of 12 dB was observed. At the same time, the frequency of amplitude fading increased and Doppler frequency shift disturbances appeared. The calculation of signal strength is carried out by means of Booker's (1978, 1980) scattering theory, supposing an outer scale equal to 1000 m and an inner scale equal to 5 m, of space scale spectrum of field-aligned irregularities in the equatorial E-region. The calculated results agree fairly well with observations. Results showed that, because of the formation of lower ionospheric field-aligned irregularities in the course of the obscuration of solar local ionization source, radio wave scattering was strengthened.

  3. Theory of vhf (very high frequency) scattering by field-aligned irregularities in the ionosphere. Interim report, June 1984-August 1985

    SciTech Connect

    Malaga

    1986-09-01

    The theory describing the scattering of vhf radiowaves by anisotropic irregularities aligned along the earth's magnetic field is presented and applied to treat auroral scatter. Results showing the aspect sensitivity, polarization effects, antenna bandwidth effects and frequency dependence of auroral are presented.

  4. 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.

  5. 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.

  6. MAST YAG Thomson scattering upgrade alignment system

    SciTech Connect

    Figueiredo, J.; Serra, F.; Naylor, G.; Walsh, M.; Dunstan, M.; Scannell, R.

    2010-10-15

    The recent upgrade to the MAST YAG Thomson scattering while enhancing the diagnostic capabilities increased the complexity of the system. There are eight YAG lasers now operational, doubling the number from the previous setup. This means alignment between each laser individually and reference points is essential to guarantee data quality and diagnostic reliability. To address this issue an alignment system was recently installed. It mimics the beams alignment in MAST by sampling 1% of the laser beam that is sent into a telescope which demagnifies by a factor of 8. The demagnified beam is viewed with a CCD camera. By scanning the camera the profile and position of the beams in the scattering zone and in a range of several meters inside MAST can be determined. Therefore alignment is checked along the beam path without having to sample it inside the vessel. The experimental apparatus and test procedures are described.

  7. 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.

  8. Statistical characteristics and occurrences of the F-region field-aligned irregularities in middle latitudes observed with Korea VHF coherent scattering radar

    NASA Astrophysics Data System (ADS)

    Yang, T.; Kwak, Y.; Kil, H.; Park, Y.

    2013-12-01

    We report for the first time of the long term characteristics and percentage occurrences of F-region field-aligned irregularities (FAIs) in the middle latitude observed with Korea VHF coherent scattering radar. This radar was built at Daejeon(36.18°N, 127.14°E, dip latitude 26.7°N) with 40.8 MHz operating frequency for continuous monitoring of the behavior of electron density irregularities in the middle latitude. From more than three-year of continuous observations since 2010, we have obtained the diurnal and seasonal characteristics of a signal-to-noise ratio and percentage occurrence variations from F-region FAIs over Korea peninsular. F-region FAIs appeared frequently at right after the sunset in both equinoxes, but pre- and post-midnight in summer season. F-region irregularities are intensified after sunset to before sunrise, and then the occurrence of F-region FAIs is rapidly decreased after sunrise. Peak height of F-region irregularities have seen around 300 km altitudes in the evening, then at higher altitude up to 400 km near local midnight and then lower altitudes around 300 km again in the early morning. And also we found that the obtained F-region echoes can be classified as E-region's continuous and quasi-periodic echoes, even though, the duration, occur time and locations are different from Kwak et al. (this issue).

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Studies of Interstellar and Circumstellar Magnetic Field with Aligned Atoms

    NASA Astrophysics Data System (ADS)

    Lazarian, A.; Yan, H.

    2004-12-01

    Population of levels of the hyperfine and fine split ground state of an atom is affected by radiative transitions induced by anisotropic radiation flux. Such aligned atoms precess in the external magnetic field and this affects properties of polarized radiation arising from both scattering and absorption by atoms. As the result the degree of light polarization depends on the direction of the magnetic field. This provides a new tool for studies of astrophysical magnetic fields using optical and UV polarimetry. We provide calculations for several atoms and ions that can be used to study magnetic fields in interplanetary medium, interstellar medius, circumstellar regions and quasars.

  14. 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.

  15. Nonspecular neutron scattering from highly aligned phospholipid membranes

    NASA Astrophysics Data System (ADS)

    Münster, C.; Salditt, T.; Vogel, M.; Siebrecht, R.; Peisl, J.

    1999-05-01

    We report a neutron scattering study of multilamellar membranes supported on solid substrates. In contrast to previous work, the high degree of orientational alignment allows for a clear distinction between specular and nonspecular reflectivity contributions. In particular, we demonstrate that by using the specific advantages of neutron optics the nonspecular scattering can be mapped over a wide range of reciprocal space. Several orders of magnitude in scattering signal and parallel momentum transfer can easily be recorded in multilamellar stacks of lipid membranes. This opens up the possibility to study fluctuations, and more generally lateral structure parameters of membrane on length scales between a few Å up to several μm. The first results obtained for a system of partially hydrated 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) indicate strong deviations from the predictions of the standard Caillé model.

  16. 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.

  17. Conditional alignment random fields for multiple motion sequence alignment.

    PubMed

    Kim, Minyoung

    2013-11-01

    We consider the multiple time-series alignment problem, typically focusing on the task of synchronizing multiple motion videos of the same kind of human activity. Finding an optimal global alignment of multiple sequences is infeasible, while there have been several approximate solutions, including iterative pairwise warping algorithms and variants of hidden Markov models. In this paper, we propose a novel probabilistic model that represents the conditional densities of the latent target sequences which are aligned with the given observed sequences through the hidden alignment variables. By imposing certain constraints on the target sequences at the learning stage, we have a sensible model for multiple alignments that can be learned very efficiently by the EM algorithm. Compared to existing methods, our approach yields more accurate alignment while being more robust to local optima and initial configurations. We demonstrate its efficacy on both synthetic and real-world motion videos including facial emotions and human activities. PMID:24051737

  18. Aligning Paramecium caudatum with static magnetic fields.

    PubMed

    Guevorkian, Karine; Valles, James M

    2006-04-15

    As they negotiate their environs, unicellular organisms adjust their swimming in response to various physical fields such as temperature, chemical gradients, and electric fields. Because of the weak magnetic properties of most biological materials, however, they do not respond to the earth's magnetic field (5 x 10(-5) Tesla) except in rare cases. Here, we show that the trajectories of Paramecium caudatum align with intense static magnetic fields >3 Tesla. Otherwise straight trajectories curve in magnetic fields and eventually orient parallel or antiparallel to the applied field direction. Neutrally buoyant immobilized paramecia also align with their long axis in the direction of the field. We model this magneto-orientation as a strictly passive, nonphysiological response to a magnetic torque exerted on the diamagnetically anisotropic components of the paramecia. We have determined the average net anisotropy of the diamagnetic susceptibility, Deltachi(p), of a whole Paramecium: Deltachi(p) = (6.7+/- 0.7) x 10(-23) m(3). We show how the measured Deltachi(p) compares to the anisotropy of the diamagnetic susceptibilities of the components in the cell. We suggest that magnetic fields can be exploited as a novel, noninvasive, quantitative means to manipulate swimming populations of unicellular organisms. PMID:16461406

  19. Multiscale field-aligned current analyzer

    NASA Astrophysics Data System (ADS)

    Bunescu, C.; Marghitu, O.; Constantinescu, D.; Narita, Y.; Vogt, J.; Blǎgǎu, A.

    2015-11-01

    The magnetosphere-ionosphere coupling is achieved, essentially, by a superposition of quasi-stationary and time-dependent field-aligned currents (FACs), over a broad range of spatial and temporal scales. The planarity of the FAC structures observed by satellite data and the orientation of the planar FAC sheets can be investigated by the well-established minimum variance analysis (MVA) of the magnetic perturbation. However, such investigations are often constrained to a predefined time window, i.e., to a specific scale of the FAC. The multiscale field-aligned current analyzer, introduced here, relies on performing MVA continuously and over a range of scales by varying the width of the analyzing window, appropriate for the complexity of the magnetic field signatures above the auroral oval. The proposed technique provides multiscale information on the planarity and orientation of the observed FACs. A new approach, based on the derivative of the largest eigenvalue of the magnetic variance matrix with respect to the length of the analysis window, makes possible the inference of the current structures' location (center) and scale (thickness). The capabilities of the FAC analyzer are explored analytically for the magnetic field profile of the Harris sheet and tested on synthetic FAC structures with uniform current density and infinite or finite geometry in the cross-section plane of the FAC. The method is illustrated with data observed by the Cluster spacecraft on crossing the nightside auroral region, and the results are cross checked with the optical observations from the Time History of Events and Macroscale Interactions during Substorms ground network.

  20. 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.

  1. Leveraging intrinsic chain anisotropy to align coil-coil block copolymers with magnetic fields

    NASA Astrophysics Data System (ADS)

    Rokhlenko, Yekaterina; Zhang, Kai; Gopinadhan, Manesh; Larson, Steve; Majewski, Pawel; Yager, Kevin; Gopalan, Padma; O'Hern, Corey; Osuji, Chinedum

    Magnetic field alignment of block copolymers (BCPs) has typically relied on the presence of liquid crystalline or crystalline assemblies to provide sufficient magnetic anisotropy to drive alignment. Recent experiments however show that alignment is also possible in simple coil-coil BCPs. In particular, alignment of lamellae was observed in poly(styrene-b-4-vinylpyridine) (PS-P4VP) on cooling across the order-disorder transition at field strengths as low as 1 T, with alignment improving markedly with increasing field strength and decreasing cooling rate. Here we discuss the intrinsic chain anisotropy which drives the observed alignment, and its display as a net microdomain anisotropy due to chain tethering at the block interface. We use in-situ X-ray scattering to study the phase behavior and temperature-, time-, and field- dependent dynamics of magnetic alignment in coil-coil BCPs, highlighting the important roles of chain anisotropy and grain size in alignment. For the right combination of field strength and grain size, we can leverage intrinsic chain anisotropy to magnetically direct self-assembly in other coil-coil systems, including cylinder-forming poly(styrene-b-dimethylsiloxane). Field alignment of PS-P4VP with PEO and other blends provides a route to form functional materials such as nanoporous films and ion conducting polymers.

  2. Cooperative Ordering and Kinetics of Cellulose Nanocrystal Alignment in a Magnetic Field.

    PubMed

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

    2016-08-01

    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. PMID:27407001

  3. Interhemispheric Field-Aligned Currents: Simulation Results

    NASA Astrophysics Data System (ADS)

    Lyatsky, Sonya

    2016-04-01

    We present simulation results of the 3-D magnetosphere-ionosphere current system including the Region 1, Region 2, and interhemispheric (IHC) field-aligned currents flowing between the Northern and Southern conjugate ionospheres in the case of asymmetry in ionospheric conductivities in two hemispheres (observed, for instance, during the summer-winter seasons). We also computed the maps of ionospheric and equivalent ionospheric currents in two hemispheres. The IHCs are an important part of the global 3-D current system in high-latitude ionospheres. These currents are especially significant during summer and winter months. In the winter ionosphere, they may be comparable and even exceed both Region 1 and Region 2 field-aligned currents. An important feature of these interhemispheric currents is that they link together processes in two hemispheres, so that the currents observed in one hemisphere can provide us with information about the currents in the opposite hemisphere. Despite the significant role of these IHCs in the global 3-D current system, they have not been sufficiently studied yet. The main results of our research may be summarized as follows: 1) In winter hemisphere, the IHCs may significantly exceed and be a substitute for the local Region 1 and Region 2 currents; 2) The IHCs may strongly affect the magnitude, location, and direction of the ionospheric and equivalent ionospheric currents (especially in the nightside winter auroral ionosphere). 3) The IHCs in winter hemisphere may be, in fact, an important (and sometimes even major) source of the Westward Auroral Electrojet, observed in both hemispheres during substorm activity. The study of the contribution from the IHCs into the total global 3-D current system allows us to improve the understanding and forecasting of geomagnetic, auroral, and ionospheric disturbances in two hemispheres. The results of our studies of the Interhemispheric currents are presented in papers: (note: for publications my last

  4. Observations of field-aligned density microstructure near the Sun

    NASA Astrophysics Data System (ADS)

    Grall, R. R.; Coles, W. A.; Spangler, S. R.; Sakurai, T.; Harmon, J. K.

    1997-01-01

    Radio scattering observations made with multiple antennas provide a direct measure of the two-dimensional microstructure of the solar wind. Previous multiple antenna observations have shown that the microstructure at scales of the order of 10 km becomes highly field-aligned inside of 6 RS [e.g., Armstrong et al., 1990]. Single antenna observations, which can measure only a radial cut through the microstructure, have shown that scales larger than 1000 km have a Kolmogorov spectrum, whereas the smaller-scale structure has a flatter spectrum and is considerably enhanced above the Kolmogorov ``background'' [e.g., Coles et al., 1991]. Here we present new multiple antenna ``angular broadening'' observations made in 1990 and 1992. These confirm that the microstructure is highly field-aligned near the Sun, they show that it has elliptical symmetry, and they show that the axial ratio changes quite abruptly near 6 RS. We also present simultaneous measurements at 9 RS of the anisotropy on scales of 1 to 30 km and on scales of 200 to 3000 km. Significant anisotropy was seen on the smaller scales but not on the larger scales. This suggests that the process responsible for the anisotropic microstructure is distinct from the larger-scale, more isotropic structure.

  5. Computational studies of the x-ray scattering properties of laser aligned stilbene

    SciTech Connect

    Debnarova, Andrea; Techert, Simone; Schmatz, Stefan

    2011-02-07

    The enhancement of the x-ray scattering signal from partially aligned molecular samples is investigated. The alignment properties of the studied molecular system are modeled based on the method of laser alignment. With the advances in the area of laser alignment of molecules, the application of this sample manipulation technique promises a great potential for x-ray scattering measurements. Preferential alignment of molecules in an otherwise amorphous sample leads to constructive interference and thus increases the scattering intensity. This enhances the structural information encoded in the scattering images and enables improved resolution in studies of reaction dynamics, as in this work is shown for the example of the photo-isomerization of stilbene. We demonstrate that the scattering signal is strongly influenced by the alignment axis. Even the most basic one-dimensional alignment offers significant improvement compared to the structural information provided by a randomly oriented sample. Although the signal is sensitive to the uncertainty in the alignment angle, it offers encouraging results even at realistic alignment uncertainties.

  6. The Challenge of Photometric Alignment: Proper Flat Fielding

    NASA Astrophysics Data System (ADS)

    Riffeser, A.; Gössl, C. A.; Koppenhöfer, J.

    2007-10-01

    Photometric alignment is crucial for a precise comparison of imaging data obtained under varying conditions; there are several effects that make these data differ by multiplicative and additive terms: moon and sky light, atmospheric extinction, optics (e.g. filter, focus, field distortion), dust, reflections (concentration) and scattered light (telescope baffle). For the flat-field correction, twilight images and dome flats are used to correct for pixel-to-pixel variations and for the absorption of the instrument including all multiplicative effects. We present an algorithm to combine all flat-field calibration frames very efficiently. An inhomogeneous illumination for those flat-field calibration frames may lead to systematic zero-point offsets depending on the position on the CCD. We present a solution to correct science frames with an optimal flat-field calibration frame using a simple observational method to measure the true illumination. We also discuss the importance of distinguishing between spatially varying absorption in the instrument and field distortion resulting from a non-flat optical plane. We present our theoretical description and the practical implementation to correct for the additive sky and multiplicative photometric terms.

  7. Rapid alignment of velocity and magnetic field in magnetohydrodynamic turbulence.

    PubMed

    Matthaeus, W H; Pouquet, A; Mininni, P D; Dmitruk, P; Breech, B

    2008-02-29

    We show that local directional alignment of the velocity and magnetic field fluctuations occurs rapidly in magnetohydrodynamics for a variety of parameters and is seen both in direct numerical simulations and in solar wind data. The phenomenon is due to an alignment between magnetic field and gradients of either pressure or kinetic energy, and is similar to alignment of velocity and vorticity in Navier-Stokes turbulence. This rapid and robust relaxation process leads to a local weakening of nonlinear terms. PMID:18352632

  8. 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.

  9. 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.

  10. 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").

  11. Optically Probed Laser-Induced Field-Free Molecular Alignment

    NASA Astrophysics Data System (ADS)

    Faucher, O.; Lavorel, B.; Hertz, E.; Chaussard, F.

    Molecular alignment induced by laser fields has been investigated in research laboratories for over two decades. It led to a better understanding of the fundamental processes at play in the interaction of strong laser fields with molecules, and also provided significant contributions to the fields of high harmonic generation, laser spectroscopy, and laser filamentation. In this chapter, we discuss molecular alignment produced under field-free conditions, as resulting from the interaction of a laser pulse of duration shorter than the rotational period of the molecule. The experimental results presented will be confined to the optically probed alignment of linear as well as asymmetric top molecules. Special care will be taken to describe and compare various optical methods that can be employed to characterize laser-induced molecular alignment. Promising applications of optically probed molecular alignment will be also demonstrated.

  12. Alignment of atmospheric mineral dust due to electric field

    NASA Astrophysics Data System (ADS)

    Ulanowski, Z.; Bailey, J.; Lucas, P. W.; Hough, J. H.; Hirst, E.

    2007-12-01

    Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction indicating the presence of vertically aligned particles in the atmosphere. Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here. It is also possible that the alignment and the electric field modify dust transport.

  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. 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.

  15. Optical Polarization From Aligned Atoms As A Diagnostic Of Interstellar And Circumstellar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Yan, H.; Lazarian, A.

    2005-12-01

    Population among sublevels of the ground state of an atom is affected by radiative transitions induced by anisotropic radiation flux. Such aligned atoms precess in the external magnetic field and this affects properties of polarized radiation arising from both scattering and absorption by atoms. As the result the degree of light polarization depends on the direction of the magnetic field. This provides a perspective tool for studies of astrophysical magnetic fields using optical and UV polarimetry. We discuss the process of alignment that can be used to study magnetic fields in interplanetary medium, interstellar medium, circumstellar regions and quasars. To exemplify what atomic alignment can provide to the observers we consider synthetic data obtained with MHD simulations of comet wake.

  16. Aligned Immobilization of Proteins Using AC Electric Fields.

    PubMed

    Laux, Eva-Maria; Knigge, Xenia; Bier, Frank F; Wenger, Christian; Hölzel, Ralph

    2016-03-01

    Protein molecules are aligned and immobilized from solution by AC electric fields. In a single-step experiment, the enhanced green fluorescent proteins are immobilized on the surface as well as at the edges of planar nanoelectrodes. Alignment is found to follow the molecules' geometrical shape with their longitudinal axes parallel to the electric field. Simultaneous dielectrophoretic attraction and AC electroosmotic flow are identified as the dominant forces causing protein movement and alignment. Molecular orientation is determined by fluorescence microscopy based on polarized excitation of the proteins' chromophores. The chromophores' orientation with respect to the whole molecule supports X-ray crystal data. PMID:26779699

  17. Depolarization of subalfvenic plasma jet generating field-aligned currents

    NASA Astrophysics Data System (ADS)

    Sobyanin, D. B.; Gavrilov, B. G.; Podgorny, I. M.

    2004-01-01

    The subalfvenic magnetized plasma jet propagating across the geomagnetic field generates the field-aligned currents in ionospheric plasma. The transverse polarization electric field Ep = - V × B in the jet is reduced due to a leakage of polarization charges through the field-aligned currents (plasma jet depolarization). These phenomena are investigated in the laboratory experiment. It was revealed that the depolarization is accompanied by appearing of the electric field Ea along the plasma velocity vector and creation of an additional pair of the field-aligned currents being generated at the leading and trailing edge of the moving plasma. The value of Ea is comparable with the transverse electric field Ep. The depolarization results in the plasma jet deflection. The possibility of a manifestation of these effects in the NORTH STAR Russian-American active rocket experiment is discussed.

  18. Real-time detection of airborne asbestos by light scattering from magnetically re-aligned fibers.

    PubMed

    Stopford, Christopher; Kaye, Paul H; Greenaway, Richard S; Hirst, Edwin; Ulanowski, Zbigniew; Stanley, Warren R

    2013-05-01

    Inadvertent inhalation of asbestos fibers and the subsequent development of incurable cancers is a leading cause of work-related deaths worldwide. Currently, there is no real-time in situ method for detecting airborne asbestos. We describe an optical method that seeks to address this deficiency. It is based on the use of laser light scattering patterns to determine the change in angular alignment of individual airborne fibers under the influence of an applied magnetic field. Detection sensitivity estimates are given for both crocidolite (blue) and chrysotile (white) asbestos. The method has been developed with the aim of providing a low-cost warning device to trades people and others at risk from inadvertent exposure to airborne asbestos. PMID:23669992

  19. 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.

  20. Far-field detection system for laser beams alignment and crystals alignment

    NASA Astrophysics Data System (ADS)

    Liu, D.; Qin, H.; Zhu, B.

    2015-08-01

    Laser beams far-field alignment is very important for the high power laser facility as well as the frequency doubling crystals adjustment. Traditional beams alignment system and crystals alignment system are separated. That means, they use different optical image systems and CCD cameras, which will occupy larger space and use more money. A new farfield detection system of laser beams is presented with a big diffraction grating (37mm*37mm), a set of optical imaging components and a high resolution CCD camera. This detection system, which is fully demonstrated on the National Laser Facility of Israel, can align high power laser facility beams' direction as well as the frequency doubling crystals. The new system occupies small space in the spatial filter through off-axial grating sampling. The experimental results indicate that the average far-field alignment error is less than 5% of spatial filter pinhole diameter, and the average crystals' matching angle error is less than 10urad, which meet the alignment system requirements for beams and crystals.

  1. 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.

  2. 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.

  3. Dynamics of Magnetic Field Alignment of Block Copolymers by In-Situ SAXS

    NASA Astrophysics Data System (ADS)

    Osuji, Chinedum; Gopinadhan, Manesh; Majewski, Pawel

    2013-03-01

    The use of external fields to direct block copolymer self-assembly is well documented. Magnetic fields offer particular promise due to their space-pervasive nature and the ability to produce arbitrary alignments over truly macroscopic length scales in appropriate systems. We present here the results of in-situ SAXS studies performed using a custom superconducting magnet integrated with lab-scale x-ray scattering instruments. We consider the case of side-chain liquid crystalline diblock copolymers ordering under high magnetic fields. Despite the coincidence of the block copolymer order-disorder transition (ODT) and the LC clearing temperature in these weakly segregated materials, there is no measurable effect of the field on the ODT of the system, up to 6 T. This is in line with estimates based simply on the magnitudes of the relevant energy scales - the free energy of field interaction and the enthalpy of the isotropic-LC transition. We show that the alignment of the system is critically limited by the viscosity of the mesophase such that alignment can only be advanced by residence in a small temperature window near the ODT. This residence produces a weakly aligned system which thereafter transitions to a strongly aligned state on cooling even in the absence of the field. This work was conducted with support from NSF under DMR-0847534

  4. Studies of relativistic electron scattering at planar alignment in a thin Si crystal

    NASA Astrophysics Data System (ADS)

    Takabayashi, Y.; Pivovarov, Yu. L.; Tukhfatullin, T. A.

    2014-04-01

    Experiments on 255-MeV electron scattering under (220) planar channeling conditions in a Si crystal were carried out at the linac of the SAGA Light Source. The spatial and angular distributions of electrons penetrating through a 20-μm thick Si crystal at different incident angles with respect to the (220) plane were measured, and features characteristic of the planar alignment were identified. The experimental results were compared with computer simulations, and showed a reasonable agreement. A comparison with doughnut scattering at axial channeling in the same crystal was also performed. It was confirmed that the planar alignment effect is weaker than the axial alignment effect. These studies are important for understanding the basic mechanism of electron scattering and radiation processes in a crystal.

  5. Alignment of atmospheric mineral dust due to electric field

    NASA Astrophysics Data System (ADS)

    Ulanowski, Z.; Bailey, J.; Lucas, P. W.; Hough, J. H.; Hirst, E.

    2007-09-01

    Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction consistent with the presence of vertically aligned particles in the atmosphere. Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling also indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here.

  6. Ground state alignment as a tracer of interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Yan, H.

    2012-12-01

    We demonstrate a new way of studying interplanetary magnetic field -- spectropolarimetry based on ground state alignment. Ground state alignment is a new promising way of sub-gausian magnetic fields in radiation-dominated environment. The polarization of spectral lines that are pumped by the anisotropic radiation from the sun is influenced by the magnetic alignment, which happens for sub-gausian magnetic field. As a result, the linear polarization becomes an excellent tracer of the embedded magnetic field. The method is illustrated by our synthetic obser- vation of the Jupiter's Io and comet Halley. A uniform density distribution of Na was considered and polar- ization at each point was then constructed. Both spa- tial and temporal variations of turbulent magnetic field can be traced with this technique as well. Instead of sending thousands of space probes, ground state alignment allows magnetic mapping with any ground telescope facilities equipped with spectrometer and polarimeter. For remote regions like the the boundary of interstellar medium, ground state alignment provides a unique diagnostics of magnetic field, which is crucial for understanding the physical processes such as the IBEX ribbons.

  7. Imaging optical fields through heavily scattering media.

    PubMed

    Newman, Jason A; Webb, Kevin J

    2014-12-31

    Coherent imaging and communication through or within heavily scattering random media has been considered impossible due to the randomization of the information contained in the scattered electromagnetic field. We report a remarkable result based on speckle correlations over incident field position that demonstrates that the field incident on a heavily scattering random medium can be obtained using a method that is not restricted to weak scatter and is, in principle, independent of the thickness of the scattering medium. Natural motion can be exploited, and the approach can be extended to other geometries. The near-infrared optical results presented indicate that the approach is applicable to other frequency regimes, as well as other wave types. This work presents opportunities to enhance communication channel capacity in the large source and detector number regime, for a new method to view binary stars from Earth, and in biomedical applications. PMID:25615337

  8. Relations between transverse electric fields and field-aligned currents. [in magnetosphere and ionosphere

    NASA Technical Reports Server (NTRS)

    Mallinckrodt, A. J.; Carlson, C. W.

    1978-01-01

    A model for the field-aligned propagation of transverse electric fields and associated field-aligned sheet currents is presented which takes into account the wave nature of the process. The model is applied to the separate cases of ionospheric and magnetospheric sources, and the resulting ionospheric electric field to field-aligned sheet current ratios are determined for comparison with experimental observations. It is found that the magnetospheric wave 'conductivity' for shear mode Alfven waves is small with respect to typical values of the height-integrated ionospheric Pedersen conductivity. For plasma convecting across a stationary disturbance a dynamic equilibrium is achieved in which field-aligned currents flow continuously away from the source on convecting field lines. Consistency with typical ionospheric electric fields requires that the field-aligned sheet currents are limited to around 0.1 A/m for ionospheric polarization sources, while magnetospheric sources are easily capable of 1 A/m or more.

  9. Field-free molecular alignment for probing collisional relaxation dynamics

    NASA Astrophysics Data System (ADS)

    Vieillard, Th.; Chaussard, F.; Billard, F.; Sugny, D.; Faucher, O.; Ivanov, S.; Hartmann, J.-M.; Boulet, C.; Lavorel, B.

    2013-02-01

    We report the experimental study of field-free molecular alignment in CO2 gas mixtures induced by intense femtosecond laser pulses in the presence of collisional processes. We demonstrate that the alignment signals exhibit specific features due to nontrivial collisional propensity rules that tend to preserve the orientation of the rotational angular momentum of the molecules. The analysis is performed with a quantum approach based on the modeling of rotational J- and M-dependent state-to-state transfer rates. The present work paves the way for strong-field spectroscopy of collisional dynamics.

  10. Field-aligned electron flux oscillations that produce flickering aurora

    NASA Technical Reports Server (NTRS)

    Mcfadden, J. P.; Carlson, C. W.; Boehm, M. H.; Hallinan, T. J.

    1987-01-01

    Measurements of energetic electrons that produce flickering aurora were made by a pair of sounding rockets, launched during a slowly evolving auroral breakup. Both payloads passed through a broad inverted-V structure. A component of the electron distribution function was closely aligned with the magnetic field over a broad energy range that extended from low energies up to the inverted-V differential energy flux peak. Measurements of the field-aligned component showed the presence of order of magnitude coherent flux oscillations. Source altitudes between 4000 and 8000 km were derived from velocity dispersion of the flux oscillations.

  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. Field-aligned particle currents near an auroral arc.

    NASA Technical Reports Server (NTRS)

    Choy, L. W.; Arnoldy, R. L.; Potter, W.; Kintner, P.; Cahill, L. J., Jr.

    1971-01-01

    A Nike-Tomahawk rocket equipped to measure electric and magnetic fields and charged particles from a few eV to several hundred keV energy was flown into an auroral band on April 11, 1970. The purpose of this flight was to obtain evidence of the low-energy electrons and protons that constitute a field-aligned sheet current, and also to obtain the magnetic signature of such a current and the electric field in and near the auroral-arc electric current system. Particular attention was given to a sudden increase in the field-aligned current associated with a prior sudden increase in the electric field and a sudden change in the magnetic field, all occurring near the edge of a visual auroral arc. Data obtained are discussed and analyzed; they present an important contribution to the problem of mapping of atmospheric auroral phenomena to the magnetospheric equatorial plane.

  13. Reversibility of scattered fields (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Zhou, Renjie; Kim, Taewoo; Popescu, Gabriel

    2016-03-01

    In recent years, tremendous efforts have been spent on deep tissue imaging using phase conjugation, a technique used to undo the effects of light scattering in a thick tissue. Despite the early debates between Yariv and Wolf, it is still not well understood physically how deep can a field propagate into biological tissue and still be phase conjugated. In order to answer this question, we developed a light scattering theory to describe the evolution of the phase associated with a field scattered by a thick tissue block. The multiple scattering through the sample is simplified to a series of single scattering through consecutive thin tissue slices. With this theory, we identify the limits of the phase conjugation operation and recover the previous results by Yariv and Wolf, which asserts that phase conjugation is rooted in small angle approximation. Importantly, we discover the fundamental principle that rules phase conjugation: the mean axial wavenumber of a field progressively decreases to zero as it scatters multiple times. At this point, phase becomes a spatially random variable and phase conjugation becomes impossible. This result describes a fundamental phenomenon: the interaction between a deterministic object and a deterministic field can result in a random scattered field. We show that this phenomenon is rooted into Heisenberg's uncertainty principle.

  14. Towards the adaptive optimization of field-free molecular alignment

    NASA Astrophysics Data System (ADS)

    Rouzée, Arnaud; Hertz, Edouard; Lavorel, Bruno; Faucher, Olivier

    2008-04-01

    We theoretically report the optimization of field-free molecular alignment by spectral phase shaping of femtosecond laser pulses. Optimal pulse shapes are designed iteratively by an evolutionary algorithm in conjunction with a non-perturbative regime calculation. The investigation is conducted in O2 and N2 under realistic conditions of intensity, temperature and pulse shaping. We demonstrate that specific tailored pulses can provide significant maximization of field-free alignment compared to the Fourier transform limited pulses of the same energy. The underlying control mechanism is discussed. The effect of pulse energy and temperature is analysed leading to the identification of a general criteria for a successful optimization. Finally, the optimal spectral phase learned from the algorithm is rather smooth and can be described by a representation in terms of a sigmoidal function. We show that the use of a low-dimensional parametrization of the phase yields an efficient optimization of the alignment within a highly reduced convergence time.

  15. 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.

  16. Field-Aligned Electric Potential in the Polar Cap

    NASA Astrophysics Data System (ADS)

    Wing, S.; Hildebrand, L.

    2014-12-01

    Reconnection with the interplanetary magnetic field (IMF) on the dayside magnetosphere opens the previously closed Earth's field line, allowing solar wind particles to enter the magnetosphere, some of which precipitate into the ionosphere. As the open-field line ExB convects to the nightside, fewer ions can enter the magnetosphere. As a result, field-aligned (parallel) electric potential increases with latitude to prevent more electrons from entering, in order to maintain charge quasi-neutrality. The APL open-field line model predicts that the parallel potential drop increases from cusp to mantle to polar rain. This trend has been confirmed in a study that compared phase space densities of ACE solar wind electrons to those of DMSP precipitating electrons. However, the same study also found that sometimes there is an anomaly: the parallel potential drop would have the opposite polarity such that solar wind electrons are accelerated downward in the afternoon polar cap. Using DMSP magnetometer and particle precipitation data, we show that this accelerating potential drop can be found often in the poleward upward field-aligned current region. The velocity shear at the magnetopause boundary leads to a voltage drop across the boundary, which drives the upward field-aligned currents. At higher latitude or further away from noon, the field line maps to the magnetopause location that is further down the magnetotail where the magnetosheath velocity shear is higher and density is lower. When the velocity shear and hence field-aligned current density (J//) is too high or density too low, parallel potential develops to accelerate more electron downward, in accordance with Knight relation.

  17. Cavity-Enhanced Field-Free Molecular Alignment at a High Repetition Rate

    NASA Astrophysics Data System (ADS)

    Benko, Craig; Hua, Linqiang; Allison, Thomas K.; Labaye, François; Ye, Jun

    2015-04-01

    Extreme ultraviolet frequency combs are a versatile tool with applications including precision measurement, strong-field physics, and solid-state physics. Here we report on an application of extreme ultraviolet frequency combs and their driving lasers for studying strong-field effects in molecular systems. We perform field-free molecular alignment and high-order harmonic generation with aligned molecules in a gas jet at a repetition rate of 154 MHz using a high-powered optical frequency comb inside a femtosecond enhancement cavity. The cavity-enhanced system provides a means to reach suitable intensities to study field-free molecular alignment and enhance the observable effects of the molecule-field interaction. We observe modulations of the driving field, arising from the nature of impulsive stimulated Raman scattering responsible for coherent molecular rotations. We foresee the impact of this work on the study of molecule-based strong-field physics, with improved precision and a more fundamental understanding of the interaction effects on both the field and molecules.

  18. Cavity-enhanced field-free molecular alignment at a high repetition rate.

    PubMed

    Benko, Craig; Hua, Linqiang; Allison, Thomas K; Labaye, François; Ye, Jun

    2015-04-17

    Extreme ultraviolet frequency combs are a versatile tool with applications including precision measurement, strong-field physics, and solid-state physics. Here we report on an application of extreme ultraviolet frequency combs and their driving lasers for studying strong-field effects in molecular systems. We perform field-free molecular alignment and high-order harmonic generation with aligned molecules in a gas jet at a repetition rate of 154 MHz using a high-powered optical frequency comb inside a femtosecond enhancement cavity. The cavity-enhanced system provides a means to reach suitable intensities to study field-free molecular alignment and enhance the observable effects of the molecule-field interaction. We observe modulations of the driving field, arising from the nature of impulsive stimulated Raman scattering responsible for coherent molecular rotations. We foresee the impact of this work on the study of molecule-based strong-field physics, with improved precision and a more fundamental understanding of the interaction effects on both the field and molecules. PMID:25933311

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Thermally Switchable Aligned Nanopores by Magnetic-Field Directed Self-Assembly of Block Copolymers

    NASA Astrophysics Data System (ADS)

    Osuji, Chinedum

    2014-03-01

    Magnetic fields provide a facile approach to direct the self-assembly of magnetically anisotropic block copolymer nanostructures in a scalable manner. Here we combine such field-based processing with materials design to enable the fabrication of polymer films with highly aligned stimuli-responsive nanopores. Etch removal of a poly(D,L-lactide) (PLA) brush that is the minority component of a liquid crystalline block copolymer is used to produce nanopores of ~ 8 nm diameter. The pores can be reversibly closed and opened while retaining their alignment by appropriate heating and cooling. We present TEM and temperture resolved scattering data during pore closure and re-opening to explore the mechanism and kinetics of pore collapse. NSF DMR-0847534; DMR-1119826.

  4. 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 .

  5. 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.

  6. Magnetic field-aligned electric potentials in nonideal plasma flows

    NASA Technical Reports Server (NTRS)

    Schindler, K.; Hesse, M.; Birn, J.

    1991-01-01

    The electric field component parallel to the magnetic field arising from plasma flows which violate the frozen-in field condition of ideal magnetohydrodynamics is discussed. The quantity of interest is the potential U = integral E parallel ds where the integral is extended along field lines. It is shown that U can be directly related to magnetic field properties, expressed by Euler potentials, even when time-dependence is included. These results are applicable to earth's magnetosphere, to solar flares, to aligned-rotator models of compact objects, and to galactic rotation. On the basis of order-of-magnitude estimates, these results support the view that parallel electric fields associated with nonideal plasma flows might play an important role in cosmic particle acceleration.

  7. High-latitude field-aligned current sources and induced electric fields

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1979-01-01

    Using a simple, planar model of the high latitude ionosphere with an enhanced conductivity auroral ring, the electric potential is computed for a pair of field-aligned current sheets inferred from observations. The relationship of various characteristics of the electric potential pattern to features of the field-aligned current distribution are elucidated in the context of a generalized field-aligned current Fourier analysis. On the basis of the analysis and observations to date, it is concluded that boundary layer dynamo action is the prevalent mechanism in the solar wind/magnetosphere/ionosphere interaction.

  8. [Three-dimensional vertically aligned CNTs coated by Ag nanoparticles for surface-enhanced Raman scattering].

    PubMed

    Zhang, Xiao-Lei; Zhang, Jie; Fan, Tuo; Ren, Wen-Jie; Lai, Chun-Hong

    2014-09-01

    In order to make surface-enhanced Raman scattering (SERS) substrates contained more "hot spots" in a three-dimensional (3D) focal volume, and can be adsorbed more probe molecules and metal nanoparticles, to obtain stronger Raman spectral signal, a new structure based on vertically aligned carbon nanotubes (CNTs) coated by Ag nanoparticles for surface Raman enhancement is presented. The vertically aligned CNTs are synthesized by chemical vapor deposition (CVD). A silver film is first deposited on the vertically aligned CNTs by magnetron sputtering. The samples are then annealed at different temperature to cause the different size silver nanoparticles to coat on the surface and sidewalls of vertically aligned CNTs. The result of scanning electron microscopy(SEM) shows that Ag nanoparticles are attached onto the sidewalls and tips of the vertically aligned CNTs, as the annealing temperature is different , pitch size, morphology and space between the silver nanoparticles is vary. Rhodamine 6G is served as the probe analyte. Raman spectrum measurement indicates that: the higher the concentration of R6G, the stronger the Raman intensity, but R6G concentration increase with the enhanced Raman intensity varies nonlinearly; when annealing temperature is 450 °C, the average size of silver nanoparticles is about 100 to 120 nm, while annealing temperature is 400 °C, the average size is about 70 nm, and the Raman intensity of 450 °C is superior to the annealing temperature that of 400 °C and 350 °C. PMID:25532342

  9. 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.

  10. On the field-aligned electric field in the polar cap

    NASA Astrophysics Data System (ADS)

    Wing, Simon; Fairfield, Donald H.; Johnson, Jay R.; Ohtani, Shin-I.

    2015-07-01

    The Johns Hopkins University Applied Physics Laboratory open-field line particle precipitation model predicts downward field-aligned electric field to maintain charge quasi-neutrality. Previous studies confirmed the existence of such electric fields. However, the present study shows that upward field-aligned electric field can be found within upward field-aligned current (FAC) region. In the upward FAC region, upward electric field that accelerates electron downward is seen with the occurrence rates of 82%-96%. In contrast, the occurrence rates in the downward FAC regions are 3%-11%. Polar rain electrons located in the upward FAC region adjacent to closed field lines often show a ramping up of energy with increasing latitude before reaching a plateau. This plateau may be attributed to the magnetosheath electrons that progressively have higher antisunward velocity and lower density with increasing distance from the subsolar point before they asymptotically reach the solar wind values.

  11. Finite geometry effects of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.; Hoffman, R. A.

    1992-01-01

    Results are presented of model calculations of the magnetic field produced by finite current regions that would be measured by a spaceborne magnetometer. Conditions were examined under which the infinite current sheet approximation can be applied to the calculation of the field-aligned current (FAC) density, using satellite magnetometer data. The accuracy of the three methods used for calculating the current sheet normal direction with respect to the spacecraft trajectory was assessed. It is shown that the model can be used to obtain the position and the orientation of the spacecraft trajectory through the FAC region.

  12. Thermoreversible Changes in Aligned and Cross-Linked Block Copolymer Melts Studied by Two Color Depolarized Light Scattering

    SciTech Connect

    Wilbur, Jeffrey D.; Gomez, Enrique D.; Ellsworth, Mark W.; Garetz, Bruce A.; Balsara, Nitash P.

    2012-09-04

    A procedure for creating samples that can be repeatedly cycled between weakly aligned and strongly aligned states is described. Poly(styrene-b-isoprene) block copolymer samples were first shear-aligned and then cross-linked using a high energy electron beam. Samples with more than 1.0 cross-links per chain on average showed almost complete recovery of their initial alignment state even after 20 cycles of heating above the order–disorder transition temperature of the un-cross-linked block copolymer. Samples with 1.1 cross-links per chain, which showed over 90% loss of alignment on heating and almost 100% recovery of alignment on cooling, provided the best example of a reversible aligned-to-unaligned transition. Samples with lower cross-linking densities exhibited irreversible loss of alignment upon heating, while those with higher cross-linking densities exhibited less than 90% loss of alignment upon heating. Alignment was quantified by a technique that we call two color depolarized light scattering (TCDLS), an extension of the traditional depolarized light scattering experiment used to determine the state of order in block copolymers. Qualitative confirmation of our interpretation of TCDLS data was obtained by small-angle X-ray scattering and transmission electron microscopy.

  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. 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.

  15. 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.

  16. Far field elastodynamic Born scattering revisited

    NASA Astrophysics Data System (ADS)

    Geerits, Tim W.; Veile, Ines; Hellwig, Olaf

    2013-02-01

    This paper summarizes part of an ongoing feasibility study that investigates the possible use of the full elastic Born approximation in multipole borehole acoustics. As a first step we exclude the fluid-filled borehole with the motivation that one or two wavelengths away from the fluid-filled borehole, radiating borehole mode amplitudes (e.g., Stoneley wave, formation dipole wave, etc.) are small compared to body wave amplitudes (P-, SV- and SH-waves). Consequently, for scatterers one or two wavelengths away from the fluid-filled borehole, it suffices to only consider their interaction with body waves. In this paper we apply the contrast-source stress-velocity forward scattering (integral equation) formulation for solid configurations in its first order (Born-) approximation (De Hoop, 1995) assuming a multipole force source excitation in a zero-offset configuration. To scrutinize the validity of the Born approximation, we consider the simplest type of scatterer, i.e., one characterized by a (Heaviside) step function change in one or more of the contrast (perturbation) parameters and we derive analytic zero-offset formulas for the scattered wave particle velocity and displacement in both the space-frequency and space-time domain, respectively. We assume the scatterer to be located in the far-field. More complicated layered configurations can easily be derived by superposition of the given solution types. Explicit results are given for the dipole and quadrupole excitation, where the former is allowed to have an arbitrary orientation relative to the scatterer and where the latter one is located in a plane perpendicular to the scatterer. In the time domain it is shown, how the scattered wave field decomposes in a specular and diffuse wave field (two terms borrowed from ‘Optics'), where the former contribution vanishes in the absence of an imaging condition and where the latter is always present. For the dipole case, we subject our results to a sensitivity analysis

  17. 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.

  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. Probing ultrafast thermalization with field-free molecular alignment

    NASA Astrophysics Data System (ADS)

    Houzet, J.; Gateau, J.; Hertz, E.; Billard, F.; Lavorel, B.; Hartmann, J.-M.; Boulet, C.; Faucher, O.

    2012-09-01

    The rotation-translation thermalization of CO2 gas is investigated 500 ps after its preheating by a nonresonant short and intense laser pulse. The temperature of thermalization is optically determined with two additional short laser pulses enabling a field-free molecular alignment process and its probing, respectively. The measurements are performed for various intensities of the preheat pulse, leading to the observation of different temperatures which are in very good agreement with classical molecular dynamics simulations. The results can be regarded as a step towards real-time tracking of ultrafast relaxation pathways in molecular motion.

  20. 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.

  1. 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.

  2. 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.

  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. 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.

  5. Self aligned hysteresis free carbon nanotube field-effect transistors

    NASA Astrophysics Data System (ADS)

    Shlafman, M.; Tabachnik, T.; Shtempluk, O.; Razin, A.; Kochetkov, V.; Yaish, Y. E.

    2016-04-01

    Hysteresis phenomenon in the transfer characteristics of carbon nanotube field effect transistor (CNT FET) is being considered as the main obstacle for successful realization of electronic devices based on CNTs. In this study, we prepare four kinds of CNTFETs and explore their hysteretic behavior. Two kinds of devices comprise on-surface CNTs (type I) and suspended CNTs (type II) with thin insulating layer underneath and a single global gate which modulates the CNT conductance. The third and fourth types (types III and IV) consist of suspended CNT over a metallic local gate underneath, where for type IV the local gate was patterned self aligned with the source and drain electrodes. The first two types of devices, i.e., type I and II, exhibit substantial hysteresis which increases with scanning range and sweeping time. Under high vacuum conditions and moderate electric fields ( |E |>4 ×106 V /cm ), the hysteresis for on-surface devices cannot be eliminated, as opposed to suspended devices. Interestingly, type IV devices exhibit no hysteresis at all at ambient conditions, and from the different roles which the global and local gates play for the four types of devices, we could learn about the hysteresis mechanism of this system. We believe that these self aligned hysteresis free FETs will enable the realization of different electronic devices and sensors based on CNTs.

  6. Magnetic Field Alignment of PS-P4VP: a Non-Liquid Crystalline Coil-Coil Block Copolymer

    NASA Astrophysics Data System (ADS)

    Rokhlenko, Yekaterina; Zhang, Kai; Larson, Steven; Gopalan, Padma; O'Hern, Corey; Osuji, Chinedum

    2015-03-01

    Magnetic fields provide the ability to control alignment of self-assembled soft materials such as block copolymers. Most prior work in this area has relied on the presence of ordered assemblies of anisotropic liquid crystalline species to ensure sufficient magnetic anisotropy to drive alignment. Recent experiments with poly(styrene-b-4-vinylpyridine), a non-liquid crystalline BCP, however, show field-induced alignment of a lamellar microstructure during cooling across the order-disorder transition. Using in situ x-ray scattering, we examine the roles of field strength and cooling rate on the alignment response of this low MW coil-coil BCP. Alignment is first observed at field strengths as low as 1 Tesla and improves markedly with both increasing field strength and slower cooling. We present a geometric argument to illustrate the origin of a finite, non-trivial magnetic susceptibility anisotropy for highly stretched surface-tethered polymer chains and corroborate this using coarse-grained molecular dynamics simulations. We rationalize the magnetic field response of the system in terms of the mobility afforded by the absence of entanglements, the intrinsic anisotropy resulting from the stretched polymer chains and sterically constrained conjugated rings, and the large grain size in these low molecular weight materials.

  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. 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.

  9. 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.

  10. 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. PMID:24675572

  11. ALIGNMENT BETWEEN FLATTENED PROTOSTELLAR INFALL ENVELOPES AND AMBIENT MAGNETIC FIELDS

    SciTech Connect

    Chapman, Nicholas L.; Matthews, Tristan G.; Novak, Giles; Davidson, Jacqueline A.; Goldsmith, Paul F.; Houde, Martin; Kwon, Woojin; Looney, Leslie W.; Li Zhiyun; Matthews, Brenda; Peng Ruisheng; Vaillancourt, John E.; Volgenau, Nikolaus H.

    2013-06-20

    We present 350 {mu}m polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened young stellar object inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hourglass-shaped morphology as gravity drags the field inward toward the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 {mu}m polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15 Degree-Sign ). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis.

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

    DOE PAGESBeta

    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.

  13. Field-free molecular alignment of asymmetric top molecules using elliptically polarized laser pulses

    NASA Astrophysics Data System (ADS)

    Rouzée, A.; Guérin, S.; Faucher, O.; Lavorel, B.

    2008-04-01

    We show theoretically that a short specific elliptically polarized laser pulse driving an asymmetric top molecule can induce postpulse revivals of three-dimensional (3D) alignment. By choosing the field ellipticity resulting in the best compromise between the alignment of two molecular axes, we demonstrate that efficient 3D alignment can be achieved at low temperature. In the experiment, the field-free alignment of moderately cool ethylene molecules is probed by using a technique based on the optical Kerr effect. Control of 3D field-free alignment opens the door to a large range of applications in chemistry as well as in molecular optics.

  14. Field-aligned Electron Density Measurements and Comparison with Diffusive Equilibrium Models

    NASA Astrophysics Data System (ADS)

    Ozhogin, P.; Song, P.; Tu, J.; Reinisch, B. W.

    2012-12-01

    The diffusive equilibrium model describes the electron and ion densities along the magnetic field line in the plasmasphere and has been widely used in, for example, ray tracing and pitch-angle scattering calculations. It is based on the hydrostatic equilibrium with the electrostatic force that acts on ions and electrons along geomagnetic field lines while there is actually no motion or diffusion of the plasma involved. The model requires multiple input parameters: electron density and ion composition (H+, He+, O+) at a base level for a magnetic field line in the ionosphere, and the (electron or ion) temperature in the plasmasphere. It has been recognized that these input parameters have to be flexible from one field line to another so that the model output does not contradict some known observed relationship. However, while the flexibility provides the possibility to fit any individual observed density distribution which is measured across many different field lines, the model prediction becomes questionable along a single field line. Since the plasma density measurements along a single field line were not available until recently, the validity of the diffusive equilibrium models has not been verified independently. This study is to investigate both qualitatively and quantitatively whether the fundamental functional form of the diffusive equilibrium model can be useful and consistent with a large database of field-aligned electron density distributions from the radio plasma imager (RPI) instrument onboard the IMAGE satellite.

  15. Interplanetary Electric Field Control of Field-Aligned Currents: Polar Magnetometer Observations

    NASA Astrophysics Data System (ADS)

    Fleishman, M.; Russell, C. T.

    2001-05-01

    ACE and Wind measurements of the solar wind velocity and interplanetary magnetic field have been used to calculate the interplanetary electric field during passages of the Polar spacecraft above the southern auroral oval. Periods of the quasi-steady interplanetary electric field have been identified when the Polar spacecraft was transiting the auroral and polar regions both just in front of the terminator above the lit ionosphere and just behind the terminator above the dark ionosphere. The east-west magnetic perturbation observed was then used as a measure of the local field-aligned current density and extrapolated to a common altitude. Independent of whether the interplanetary electric field (IEF) is from dawn to dusk or dusk to dawn a significant field-aligned current always exists. The magnitude of its perturbation field for dusk to dawn IEF is about 180 nT. For dawn to dusk IEF the magnetic perturbation is roughly proportional to the dawn-dusk component of the IEF. The strength of the field-aligned current does not depend on whether the ionosphere under the spacecraft is in sunlight or in darkness.

  16. Low-latitude field-aligned currents deduced by Swarm

    NASA Astrophysics Data System (ADS)

    Lühr, Hermann; Kervalishvili, Guram; Rauberg, Jan

    2015-04-01

    ESA's constellation mission Swarm was successfully launched on 22 November 2013. The three satellites are orbiting the Earth at 470 km and 520 km altitude. The lower pair Swarm-A and C is flying side-by-side separated by only 1.4° in latitude. Magnetic field readings of this pair are used to determine for the first time field-aligned currents (FAC) uniquely in the ionosphere. Of particular interest for this presentation are FACs at low and equatorial latitudes. Indications for several of such current systems have been deduced from CHAMP observations. Examples to be studied are meridional and vertical currents driven by the F-region dynamo. They are expected to show opposite polarities between noon and sunset. Likewise there are FACs expected to balance the electric potential differences between the foci of the Sq current vortices in the two hemispheres, which should be most prominent during solstice seasons. Another example is the FAC associated with equatorial plasma bubbles. They are expected to flow along the walls of the electron density depleted volume. Due to the limited amount of suitable Swarm data we will focus on June solstice and September equinox 2014 for this presentation.

  17. Polarization electric field in subalfvenic plasma jet under condition of field- aligned currents generation

    NASA Astrophysics Data System (ADS)

    Sobyanin, D.; Gavrilov, B.; Podgorny, I.

    The subalfvenic magnetized plasma jet propagating across the geomagnetic field generates field-aligned currents in the ionospheric plasma. As a result the transverse polarization electric field Ep =-VxB/c in the jet should be reduced (plasma jet depolarization). These phenomena are investigated in the laboratory experiment. It was revealed that the depolarization is accompanied by the appearing of the electric field E along the plasma velocity vector. The value of E is comparable with theaa transverse electric field. It results in the plasma jet deflection. The possibility of manifestation of these effects in the NORTH STAR Russian-American active rocket experiment is discussed.

  18. Currents and electric fields in the ionosphere due to field-aligned auroral currents

    NASA Technical Reports Server (NTRS)

    Nisbet, J. S.; Miller, M. J.; Carpenter, L. A.

    1978-01-01

    Birkeland (1908, 1913) did a detailed analysis of the upper atmospheric current system in the high-latitude region, and suggested that field-aligned currents flowing into and out of the auroral ionosphere were the driving mechanism for this current system. In the present paper, static electric field and current patterns due to the field-aligned Birkeland currents are examined, using a model in which currents approximating those reported by Iijima and Potemra (1976) are used as input to a global model of the ionospheric conductivities, in which interhemispheric coupling along field lines is included. The model reproduces the main features of the high-latitude current and voltage system and the penetration of these currents within the plasmasphere.

  19. Extracting Electron-Ion Differential Scattering Cross Sections for Partially Aligned Molecules by Laser-Induced Rescattering Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Okunishi, Misaki; Niikura, Hiromichi; Lucchese, R. R.; Morishita, Toru; Ueda, Kiyoshi

    2011-02-01

    We extract large-angle elastic differential cross sections (DCSs) for electrons scattering from partially aligned O2+ and CO2+ molecules using rescattering photoelectrons generated by infrared laser pulses. The extracted DCSs are in good agreement with those calculated theoretically, demonstrating that accurate DCSs for electron-ion scattering can be extracted from the laser-induced rescattering spectra, thus paving the way for dynamic imaging of chemical reactions by rescattering photoelectron spectroscopy.

  20. 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.

  1. Field-Free Alignment and Strong Field Control of Molecular Rotors

    NASA Astrophysics Data System (ADS)

    Spanner, Michael

    2004-12-01

    Methods of controlling molecular rotations using linearly polarized femtosecond and picosecond pulses are considered and analyzed theoretically. These laser pulses, typically in the infrared, are highly non-resonant with respect to the electronic degrees of freedom of the molecules and have intensities of ~ 10^13 to 10^14 W/cm?. It is shown how these laser pulses can force small linear molecules to align with the direction of the electric field vector of the laser both in the presence of the laser field as well as after the application of a short laser pulse. Recent experiments on laser-induced molecular alignment are modeled and excellent agreement between experiment and theory is found. Additional methods of controlling molecular rotational dynamics are outlined. The first method considers the forced rotational acceleration of diatomic molecules, called the optical centrifuge. Here, the direction of polarization of a linearly polarized laser field is made to smoothly rotate faster and faster. The molecules, which tend to align with the polarization vector of the laser field, follow the rotation of the laser polarization and are accelerated to high angular momentum. The second method considers the control of field-free rotational dynamics by applying phase shifts to the molecular wave function at select times called fractional revivals. At these select moments, an initially localized wave function splits into several copies of the initial state. Adding phase shifts to the copies then induces interference effects which can be used to control the subsequent evolution of the rotational wave function. This same control scheme has a close link to quantum information and this connection is outlined. Finally, a recently proposed method of controlling the quantum dynamics of the classically chaotic kicked rotor system [J. Gong and P. Brumer, Phys. Rev. Lett. 86, 1741 (2001)] is analyzed from a phase space perspective. It is shown that the proposed quantum control can be

  2. Shear Induced Alignment of Multi-Walled Carbon Nanotube Dispersions via Small Angle X-Ray Scattering

    NASA Astrophysics Data System (ADS)

    Pujari, Saswati; Burghardt, Wesley R.; Rahatekar, Sameer S.; Windle, Alan H.; Koziol, Krzysztof K.

    2008-07-01

    We report small-angle x-ray scattering studies of shear-induced alignment of multi-walled carbon nanotube (MWCNT) dispersions. Uncured epoxy was used as a viscous, Newtonian suspending medium, and samples were prepared from `aligned' MWCNTs using methods previously reported (Rahatekar et al. J Rheol 40:599, 2006); here we emphasize measurements on rather dilute dispersions. Flow-induced alignment was studied in both the flow-gradient (1-2) plane, and the flow-vorticity (1-3) plane using, respectively, annular cone and plate and rotating disk x-ray shear cells. Small-angle x-ray scattering patterns were rendered anisotropic under application of shear flow. Measurements in the 1-2 plane indicate that the average MWCNT orientation direction is intermediate between the flow and gradient directions. Transient measurements of structure evolution enabled by high flux synchrotron radiation allowed study of time-dependent behavior following flow reversal and flow cessation.

  3. 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.

  4. 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.

  5. Field-aligned Currents in Io's Plasma Wake

    NASA Astrophysics Data System (ADS)

    Chen, Chuxin

    2008-09-01

    Since the discovery of Io-controlled decametric radio emissions, the interaction between Io and Jovian magnetosphere has been studied intensively. Two types of interaction have been proposed so far. One is electric circuit model, in which the induced currents flow between Io and the Jovian ionosphere along the magnetic flux tube threading Io. The other is Alfvén wing model. A wing forms in the perturbed magnetic field lines behind Io, the Alfvénic currents develop in the wing rather than along the magnetic flux tubes. More recently, auroral emission associated with Io's footprint and its trailing emission were observed. Such auroral arc may extend longitudinally westward for more than 100 degrees. This trail of aurora is brightest near Io and dims with increasing downstream distance. There is no clear theoretical understanding of the physics that generates this downstream aurora. However it is generally believed that Io's plasma wake is associated with this phenomenon and field-aligned currents lead to downstream emissions. Along with the above two types of the interaction between Io and its surrounding medium, there are also two theoretical frameworks in which these downstream emissions can be interpreted. The first one is corotational lag. When an Io-perturbed (mass loading and/or Io's conductivity) magnetic flux tube moves slowly relative to Jovian magnetosphere, an electric field would be induced at the equatorial plane of the flux tube, which in turn causes a current perpendicular to the field lines that is connected by field-aligned currents. The Lorentz force due to the perpendicular current would play the role of bring the lagged plasma up to corotation. The second is Alfvén wave, in which the Io-perturbed Alfvén wave is reflected between the Jovian ionosphere and the torus edge, driving particles into loss cone. Our present study attempts to use a MHD method to solve the above problem. MHD simulations of Io-Jupiter interaction has been carried out by

  6. Quasistatic electric field structures and field-aligned currents in the polar cusp region

    NASA Astrophysics Data System (ADS)

    Jacobsen, Knut; Moen, Joran; Pedersen, Arne

    2010-05-01

    Quasistatic electric field structures in the vicinity of the cusp have been studied using Cluster data. There are two categories of electric potential structures, S-shaped and U-shaped. In previous studies in the nightside auroral region, the S-shaped potential was uniquely related to the boundary transition between low density and high density plasma regimes, leading to the conclusion that the electric field profile depends on whether the plasma populations on each side of the boundary can support intense field-aligned and Pedersen currents. In this study in the dayside cusp this is not the case, and a different explanation has to be sought. Most electric field structures are associated with the start of the cusp ion dispersion or with injection signatures within the cusp, and the field-aligned currents associated with these structures are found to be consistent with the cusp currents expected for the IMF By polarity at the time. This indicates that the electric field structures are generated by the cusp current system, or modified by the cusp current system to be consistent with the required currents. Furthermore, we provide firm evidence for the dayside Region 1 current to be located on open field lines, which have been postulated but to our knowledge heretofore not experimentally verified.

  7. 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.

  8. 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.

  9. Field-free molecular alignment for measuring ionization probability

    NASA Astrophysics Data System (ADS)

    Loriot, V.; Hertz, E.; Lavorel, B.; Faucher, O.

    2008-01-01

    We have shown in a recent letter (Loriot et al 2006 Opt. Lett. 31 2897) the possibility of determining the ionization probability of linear molecules by using an all-optical technique that takes advantage of post-pulse molecular alignment. To that end, we have implemented a 'cross-defocusing' technique producing a signal sensitive to both alignment and ionization. The analysis of the signal provides a quantitative measurement of the ionization probability calibrated with molecular alignment. In the present work, the method is discussed in more detail and applied to the measurement of the ionization probability of N2 as well as to the determination of the ionization ratio between (i) N2 and Ar and (ii) O2 and Xe. We demonstrate in addition a progress in the scheme in order to improve the accuracy at low intensity.

  10. 30 MHz radar observations of artificial E region field-aligned plasma irregularities

    NASA Astrophysics Data System (ADS)

    Hysell, D. L.

    2008-02-01

    Artificial E region field aligned irregularities (FAIs) have been observed during heating experiments at the HAARP facility using a new 30 MHz coherent scatter radar imager deployed near Homer, Alaska. Irregularities were observed during brief experiments on three quiet days in July and August, 2007, when the daytime E region critical frequency was close to 3 MHz. Irregularities were consistently generated and detected during experiments with O-mode HF pumping on zenith with a 1-min on, 1-min off CW modulation. The scattering cross sections, rise, and fall times of the echoes were observed as well as their spectral properties. Results were found to be mainly in agreement with observations from other mid- and high-latitude sites with some discrepancies. Radar images of the irregularity-filled volume on one case exhibited clear variations in backscatter power and Doppler shift across the volume. The images furthermore show the emergence of a small irregularity-filled region to the south southwest of the main region in the approximate direction of magnetic zenith.

  11. 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.

  12. 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.

  13. The role of magnetic-field-aligned electric fields in auroral acceleration

    SciTech Connect

    Block, L.P.; Faelthammar, C.G. )

    1990-05-01

    Electric field measurements on the Swedish satellite Viking have confirmed and extended earlier observations on S3-3 and provided further evidence of the role of dc electric fields in auroral acceleration processes. On auroral magnetic field lines the electric field is strongly fluctuating both transverse and parallel to the magnetic field. The significance of these fluctuations for the auroral acceleration process is discussed. A definition of dc electric fields is given in terms of their effects on charged particles. Fluctuations below several hertz are experienced as dc by typical auroral electrons if the acceleration length is a few thousand kilometers. For ions the same is true below about 0.1 Hz. The magnetic-field-aligned (as well as the transverse) component of the electric field fluctuations has a maximum below 1 Hz, in a frequency range that appears as dc to the electrons but not to the ions. This allows it to cause a selective acceleration, which may be important in explaining some of the observed characteristics of auroral particle distributions. The electric field observations on Viking support the conclusion that magnetic-field-aligned potential drops play an important role in auroral acceleration, in good agreement with particle observations boht on Viking and on the DE satellites. They also show that a large part, or even all, of the accelerating potential drop may be accounted for by numerous weak (about a volt) electric double layers, in agreement with earlier observations on the S3-3 satellite and with an early theoretical suggestion by L. Block.

  14. Quasistatic electric field structures and field-aligned currents in the polar cusp region

    NASA Astrophysics Data System (ADS)

    Jacobsen, K. S.; Moen, J. I.; Pedersen, A.

    2010-10-01

    Cluster data have been examined for quasi-stationary electric field structures and field-aligned currents (FACs) in the vicinity of the dayside cusp region. We have related the measurements to the Region 1/Region 2 (R1/R2) current system and the cusp current system. It has been theoretically proposed that the dayside R1 current may be located on open field lines, and experimental evidence has been shown for R1 currents partially on open field lines. We document that R1 currents may flow entirely on open field lines. The electric field structures are found to occur at plasma density gradients in the cusp. They are associated with strong FACs with current directions that are consistent with the cusp currents. This indicates that the electric field structures are closely coupled to the cusp current system. The electric equipotential structures linking the perpendicular electric fields seen at Cluster altitudes to field-aligned electric fields at lower altitudes fall into one of two categories: S shape or U shape. Both types are found at both the equatorward edge of the cusp ion dispersion and at the equatorward edge of injection events within the cusp. Previous studies in the nightside auroral region attributed the S-shaped potential structures to the boundary transition between the low-density polar cap and the high-density plasma sheet, concluding that the shape of the electric potential structure depends on whether the plasma populations on each side of the structure can support intense currents. This explanation is not applicable for the S-shaped structures observed in the dayside cusp region.

  15. 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.

  16. 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.

  17. Plateau structures in potential scattering in a strong laser field

    SciTech Connect

    Cerkic, A.; Milosevic, D.B.

    2004-11-01

    Electron-atom scattering in a strong laser field is analyzed using the strong-field approximation and modeling elastic scattering of electrons by atoms with a realistic analytical potential derived from an independent-particle model. The results that include both direct scattering and scattering with a repeated scattering (rescattering) are presented. In the latter case, in the intermediate step of the process, the electron can absorb the energy from the laser field and additional plateau structures appear. The features of these plateaus and their cutoffs are analyzed for various incident electron energies and scattering angles, for different laser intensities, and for various atomic gases. The boundaries of these plateaus are compared with classical estimates.

  18. Metrology systems for active alignment control of the Hobby-Eberly Telescope wide field corrector

    NASA Astrophysics Data System (ADS)

    Lee, Hanshin; Hill, Gary J.; Hart, Michael; Cornell, Mark E.; Savage, Richard; Vattiat, Brian; Perry, Dave; Moller, William M.; Rafferty, Tom; Taylor, Trey; Rafal, Marc D.

    2010-07-01

    The Hobby-Eberly Telescope (HET) Wide-Field Upgrade (WFU) will be equipped with new metrology systems to actively control the optical alignment of the new four-mirror Wide-Field Corrector (WFC) as it tracks sidereal motion with respect to the fixed primary mirror. These systems include a tip/tilt sensor (TTS), distance measuring interferometers (DMI), guide probes (GP), and wavefront sensors (WFS). While the TTS and DMIs are to monitor the mechanical alignment of the WFC, the WFSs and GPs will produce direct measurement of the optical alignment of the WFC with respect to the HET primary mirror. Together, these systems provide fully redundant alignment and pointing information for the telescope, thereby keeping the WFC in focus and suppressing alignment-driven field aberrations. We describe the current snapshot of these systems and discuss their roles, expected performance, and operation plans.

  19. 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.

  20. 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.

  1. Scattered field generation and optical forces in transformation optics

    NASA Astrophysics Data System (ADS)

    Novitsky, A. V.

    2016-04-01

    In this paper we develop an approach for making various scattered electromagnetic fields on the transformation-optics ground. To do so, we use the a special coordinate transformation from the a vacuum virtual space to physical space, which changes the boundary of the scattering device upon transformation. We explore this approach for small scatterers compared with radiation wavelength, which allows us to predict the arbitrarily directed optical forces. Obtaining scattered fields and optical forces can be useful in nano-optics and optical micromanipulation.

  2. Field-free molecular alignment detection by 4 f coherent imaging

    NASA Astrophysics Data System (ADS)

    Houzet, J.; Billard, F.; Hertz, E.; Chateau, D.; Chaussard, F.; Lavorel, B.; Faucher, O.

    2012-09-01

    Time-resolved detection of field-free molecular alignment is investigated by phase contrast. The technique based on a 4 f imager operating as an inverted Zernike spatial filter makes it possible to discriminate between positive and negative molecular alignment revivals produced in a linear molecule. The measurements are performed in a way that minimizes the contamination of the signal by the plasma generated during the aligning pulse. The observations are supported by a semi-analytical model, from which the degree of alignment produced at the beam focus is estimated.

  3. 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.

  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. Average field-aligned current configuration parameterized by solar wind conditions

    NASA Astrophysics Data System (ADS)

    Carter, J. A.; Milan, S. E.; Coxon, J. C.; Walach, M.-T.; Anderson, B. J.

    2016-02-01

    We present the first large-scale comparison of the spatial distribution of field-aligned currents as measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment, with the location and brightness of the average auroral oval, determined from the Imager for Magnetopause-to-Aurora Global Exploration far ultraviolet instrument. These distributions are compared under the same interplanetary magnetic field magnitude and clock angle conditions. The field-aligned currents and auroral oval drop to lower latitudes, as the interplanetary magnetic field becomes both increasingly stronger in magnitude and increasingly southward. We find that the region 2 currents are more closely aligned with the distribution of auroral UV emission, whether that be in the discrete auroral zone about dusk or in the postmidnight diffuse aurora sector. The lack of coincidence between the region 1 field-aligned currents with the auroral oval in the dusk sector is contrary to expectation.

  6. Single molecule spectroscopy of conjugated polymer chains in an electric field-aligned liquid crystal.

    PubMed

    Chang, Wei-Shun; Link, Stephan; Yethiraj, Arun; Barbara, Paul F

    2008-01-17

    Using single molecule polarization spectroscopy, we investigated the alignment of a polymer solute with respect to the liquid crystal (LC) director in an LC device while applying an external electric field. The polymer solute is poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (or MEH-PPV), and the LC solvent is 5CB. The electric field induces a change in the LC director orientation from a planar alignment (no electric field) to a perpendicular (homeotropic) alignment with an applied field of 5.5 x 103 V/cm. We find that the polymer chains align with the LC director in both planar and homeotropic alignment when measured in the bulk of the LC solution away from the device interface. Single molecule polarization distributions measured as a function of distance from the LC device interface reveal a continuous change of the MEH-PPV alignment from planar to homeotropic. The observed polarization distributions are modeled using a conventional elastic model that predicts the depth profile of the LC director orientation for the applied electric field. The excellent agreement between experiment and simulations shows that the alignment of MEH-PPV follows the LC director throughout the LC sample. Furthermore, our results suggest that conjugated polymers such as MEH-PPV can be used as sensitive local probes to explore complex (and unknown) structures in anisotropic media. PMID:17975912

  7. 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.

  8. Swarm and ESR observations of the ionospheric response to a field-aligned current system in the high-latitude midnight sector

    NASA Astrophysics Data System (ADS)

    Pitout, F.; Marchaudon, A.; Blelly, P.-L.; Bai, X.; Forme, F.; Buchert, S. C.; Lorentzen, D. A.

    2015-06-01

    We present a conjunction between the Swarm fleet and the European Incoherent Scatter Svalbard Radar (ESR) on 9 January 2014. The Swarm orbit in the early phase of the mission gives us the unique opportunity of sequencing the temporal evolution of the observed field-aligned current system in the nightside, near magnetic local midnight. These field-aligned currents are seen to move poleward through the radar field of view and to affect the observed ionosphere. The upward field-aligned current (FAC) is responsible, at least in part, for the heating of the ionospheric electrons. It is less clear whether the downward FAC cools the ionosphere. We use the TRANSCAR model of the ionosphere to quantify the thermoelectric effect that comes into play. Finally, we compare the plasma parameters measured by the Langmuir probe on board Swarm and the ESR and conclude on an agreement within the errors.

  9. Alignment of iron nanoparticles in a magnetic field due to shape anisotropy

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, B.; Nicholson, D. M.; Eisenbach, M.; Parish, C.; Ludtka, G. M.; Rios, O.

    2015-11-01

    During high magnetic field solidification processing there is evidence for the alignment of nanoscale metallic particles with elongated morphologies that nucleate from a liquid metal. Such alignment occurs well above the Curie temperature of the particle where the magneto-crystalline anisotropy energy and exchange energy contributions are negligible. 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 a scaling law for the dipole-dipole interaction energy as a function of the particle size to identify the conditions under which such alignment is possible.

  10. The alignment of galaxy spin with the shear field in observations

    NASA Astrophysics Data System (ADS)

    Pahwa, Isha; Libeskind, Noam I.; Tempel, Elmo; Hoffman, Yehuda; Tully, R. Brent; Courtois, Hélène M.; Gottlöber, Stefan; Steinmetz, Matthias; Sorce, Jenny G.

    2016-03-01

    Tidal torque theory suggests that galaxies gain angular momentum in the linear stage of structure formation. Such a theory predicts alignments between the spin of haloes and tidal shear field. However, non-linear evolution and angular momentum acquisition may alter this prediction significantly. In this paper, we use a reconstruction of the cosmic shear field from observed peculiar velocities combined with spin axes extracted from galaxies within 115 Mpc (˜8000 km s-1) from 2MASS Redshift Survey (2MRS) catalogue to test whether or not galaxies appear aligned with principal axes of shear field. Although linear reconstructions of the tidal field have looked at similar issues, this is the first such study to examine galaxy alignments with velocity shear field. Ellipticals in the 2MRS sample show a statistically significant alignment with two of the principal axes of the shear field. In general, elliptical galaxies have their short axis aligned with the axis of greatest compression and perpendicular to the axis of slowest compression. Spiral galaxies show no signal. Such an alignment is significantly strengthened when considering only those galaxies that are used in velocity field reconstruction. When examining such a subsample, a weak alignment with the axis of greatest compression emerges for spiral galaxies as well. This result indicates that although velocity field reconstructions still rely on fairly noisy and sparse data, the underlying alignment with shear field is strong enough to be visible even when small numbers of galaxies are considered - especially if those galaxies are used as constraints in the reconstruction.

  11. Field-aligned electron precipitation at the edge of an arc

    NASA Technical Reports Server (NTRS)

    Mcfadden, J. P.; Carlson, C. W.; Boehm, M. H.

    1986-01-01

    Measurements of field-aligned electrons at the edge of an arc are presented from a sounding rocket flight through a quiet afternoon auroral arc. High time resolution measurements show the evolution of the electron distribution function over the 2.3-km width of field-aligned precipitation. A nearly constant 1.2-eV perpendicular temperature was found for these field-aligned fluxes over a broad range of parallel energies (100 - 900 eV). The small perpendicular temperature indicates that the acceleration region is located at a low altitude. Two models of cold plasma convection into the edge of a V-shaped potential structure are examined and found to be consistent with both the observed fluxes and spatial width of the edge precipitation. Both models predict an average source plasma density less than 130/cu cm to account for the observed field-aligned fluxes and thus an acceleration region well above 1000 km.

  12. A Topologically-Informed Hyperstreamline Seeding Method for Alignment Tensor Fields.

    PubMed

    Fu, Fred; Abukhdeir, Nasser Mohieddin

    2015-03-01

    A topologically-informed hyperstreamline seeding method is presented for visualization of alignment tensor fields. The method is inspired by and applied to visualization of nematic liquid crystal (LC) orientation dynamics simulations. The method distributes hyperstreamlines along domain boundaries and edges of a nearest-neighbor graph whose vertices are degenerate regions of the alignment tensor field, which correspond to orientational defects in a nematic LC domain. This is accomplished without iteration while conforming to a user-specified spacing between hyperstreamlines and avoids possible failure modes associated with hyperstreamline integration in the vicinity of degeneracies in alignment (orientational defects). It is shown that the presented seeding method enables automated hyperstreamline-based visualization of a broad range of alignment tensor fields which enhances the ability of researchers to interpret these fields and provides an alternative to using glyph-based techniques. PMID:26357072

  13. Field-theoretical description of deep inelastic scattering

    SciTech Connect

    Geyer, B.; Robaschik, D.; Wieczorek, E.

    1980-01-01

    The most important theoretical notions concerning deep inelastic scattering are reviewed. Topics discussed are the model-independent approach, which is based on the general principles of quantum field theory, the application of quantum chromodynamics to deep inelastic scattering, approaches based on the quark--parton model, the light cone algebra, and conformal invariance, and also investigations in the framework of perturbation theory.

  14. 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.

  15. Analysing collimator structure effects in head-scatter calculations for IMRT class fields using scatter raytracing.

    PubMed

    Naqvi, S A; Sarfaraz, M; Holmes, T; Yu, C X; Li, X A

    2001-07-01

    The frequent blocking of the irradiated volume in intensity modulated radiation therapy (IMRT) makes the head-scatter fraction of the incident photon fluence more significant than that in conventional therapy with open fields. On the other hand. certain collimator configurations block scatter photons directed to a given observation point while allowing primary photons to be transmitted. The 'anomalous blocking' makes the primary field a poor indicator of the scatter fluence. Since large MU-to-cGy ratios in IMRT can magnify head-scatter uncertainties, it becomes necessary to accurately model both the effective scatter source and the collimator structure that limits the scatter reaching the irradiated volume. First we obtain a dual-source model, using a Taylor series expansion to derive the effective scatter source distribution from the data measured for the Elekta SL20 linac equipped with a multi-leaf collimator (MLC). Then, using a raytracing algorithm, we calculate the transmission of scatter rays from the effective scatter source plane to points in the patient plane. The method can account for the anomalous blocking of scatter by the MLC leaves and the backup diaphragms. For a variety of collimator settings tested, the calculations agree with measurements to an accuracy of 0.002psi10 x 10, where psi10 x 10 is the total (primary + scatter) photon fluence of an open 10 x 10 cm2 field for the same MU delivered. Although the significance of collimator structure in IMRT depends strongly on fields shapes employed for the delivery, potential cumulative errors on the order of a few per cent can be avoided in fluence calculations if the proposed method is used. PMID:11474941

  16. Field-aligned currents, plasma waves, and anomalous resistivity in the disturbed polar cusp.

    NASA Technical Reports Server (NTRS)

    Fredricks, R. W.; Scarf, F. L.; Russell, C. T.

    1973-01-01

    During the magnetic storm of November 1, 1968, the Ogo 5 spacecraft encountered the polar cusp region at low magnetic latitudes. We show that the region just outside the last closed field lines contained a warm magnetosheath plasma, magnetic field perturbations interpretable as field-aligned current layers, and electrostatic waves possibly due to plasma instabilities driven by these currents. Estimates of anomalous resistivity extrapolated along the field lines due to these electrostatic waves lead to estimates of field-aligned potential drops between Ogo 5 and the ionosphere on the order of 2 kV.

  17. 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.

  18. Fresnel field interaction applied to scattering from a vegetation layer

    NASA Technical Reports Server (NTRS)

    Fung, A. K.; Chen, M. F.; Lee, K. K.

    1987-01-01

    Models for scattering from a vegetation layer treated as a collection of discrete scatterers usually assume far field interaction among scatterers. In a real vegetation medium such as a deciduous forest or a soybean field it is not always true that each leaf is in the far field of other leaves. This paper examines the additional effect when scatterers are permitted to be in the Fresnel zone of one another. Both disc-shaped and needle-shaped leaves are considered. It is found that in general this causes the backscattering coefficient to be lower for the disk-shaped leaves and may be higher or lower for the needle-shaped leaves depending upon polarization, incidence angle, and frequency than those computed under the assumption of conventional far field interaction.

  19. Extremely low-frequency electromagnetic fields disrupt magnetic alignment of ruminants

    PubMed Central

    Burda, Hynek; Begall, Sabine; Červený, Jaroslav; Neef, Julia; Němec, Pavel

    2009-01-01

    Resting and grazing cattle and deer tend to align their body axes in the geomagnetic North-South direction. The mechanism(s) that underlie this behavior remain unknown. Here, we show that extremely low-frequency magnetic fields (ELFMFs) generated by high-voltage power lines disrupt alignment of the bodies of these animals with the geomagnetic field. Body orientation of cattle and roe deer was random on pastures under or near power lines. Moreover, cattle exposed to various magnetic fields directly beneath or in the vicinity of power lines trending in various magnetic directions exhibited distinct patterns of alignment. The disturbing effect of the ELFMFs on body alignment diminished with the distance from conductors. These findings constitute evidence for magnetic sensation in large mammals as well as evidence of an overt behavioral reaction to weak ELFMFs in vertebrates. The demonstrated reaction to weak ELFMFs implies effects at the cellular and molecular levels. PMID:19299504

  20. Unified theory of near-field analysis and measurement - Scattering and inverse scattering

    NASA Astrophysics Data System (ADS)

    Wacker, P. F.

    1981-03-01

    The scanning procedures of unified theory of near-field analysis and measurement are adapted to the determination of scattering patterns of electromagnetic and scalar systems from measurements made in the near, intermediate, or far field, with emphasis on high accuracy and efficient data processing. The scanning procedures include spherical, improved plane polar, and many types of plane rectangular, plane radial, and circular cylindrical scanning. Application of group representation to inverse scattering analysis is discussed.

  1. 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

  2. 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.

  3. Deuterium NMR investigations of field-induced director alignment in nematic liquid crystals.

    PubMed

    Sugimura, Akihiko; Luckhurst, Geoffrey R

    2016-05-01

    There have been many investigations of the alignment of nematic liquid crystals by either a magnetic and/or an electric field. The basic features of the important hydrodynamic processes for low molar mass nematics have been characterized for the systems in their equilibrium and non-equilibrium states. These have been created using electric and magnetic fields to align the director and deuterium nuclear magnetic resonance ((2)H NMR) spectroscopy has been used to explore this alignment. Theoretical models based on continuum theory have been developed to complement the experiments and found to describe successfully the static and the dynamic phenomena observed. Such macroscopic behaviour has been investigated with (2)H NMR spectroscopy, in which an electric field in addition to the magnetic field of the spectrometer is used to rotate the director and produce a non-equilibrium state. This powerful technique has proved to be especially valuable for the investigation of nematic liquid crystals. Since the quadrupolar splitting for deuterons observed in the liquid crystal phase is determined by the angle between the director and the magnetic field, time-resolved and time-averaged (2)H NMR spectroscopies can be employed to investigate the dynamic director alignment process in a thin nematic film following the application or removal of an electric field. In this article, we describe some seminal studies to illustrate the field-induced static and dynamic director alignment for low molar mass nematics. PMID:27247284

  4. 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

  5. Far-field detection system for laser beam and crystal alignment

    NASA Astrophysics Data System (ADS)

    Zhang, Jiachen; Liu, Daizhong; Zhu, Baoqiang; Tang, Shunxing; Gao, Yanqi

    2016-03-01

    Laser beam far-field alignment as well as frequency-doubling and frequency-tripling crystal adjustment is very important for high-power laser facility. Separate systems for beam and crystal alignment are generally used while the proposed approach by off-axial grating sampling share common optics for these two functions, reducing both space and cost requirements. This detection system has been demonstrated on the National Laser Facility of Israel. The experimental results indicate that the average far-field alignment error is <5% of the spatial filter pinhole diameter, average autocollimation angle error of crystals is <10 μrad, and average frequency-tripling conversion efficiency is 69.3%, which meet the alignment system requirements on the beam direction and crystals.

  6. 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.

  7. In-situ SAXS observation of magnetic field effects on block copolymer ordering and alignment

    NASA Astrophysics Data System (ADS)

    Osuji, Chinedum; Gopinadhan, Manesh; Majewksi, Pawel

    2012-02-01

    The use of external fields to direct block copolymer self-assembly is well documented. Magnetic fields offer particular promise due to their space-pervasive nature and the ability to produce arbitrary alignments over truly macroscopic length scales in appropriate systems. We present here the results of in-situ SAXS studies of side-chain liquid crystalline diblock copolymers ordering under high magnetic fields and ex-situ GISAXS data on thin films. Despite the coincidence of the block copolymer order-disorder transition (ODT) and the LC clearing temperature in these weakly segregated materials, there is no measurable effect of the field on the ODT of the system, up to 6 T. This is in line with rough estimates based simply on the magnitudes of the relevant energy scales - the free energy of field interaction and the enthalpy of the isotropic-LC transition. We show that the alignment of the system is critically limited by the viscosity of the mesophase such that alignment can only be advanced by residence in a small temperature window near TODT. This residence produces a weakly aligned system which thereafter transitions to a strongly aligned state on cooling even in the absence of the field.

  8. Magnetic field-aligned coupling effects on ionospheric plasma structure

    NASA Technical Reports Server (NTRS)

    Heelis, R. A.; Vickrey, J. F.

    1990-01-01

    This paper presents a mathematical description of the electrical coupling and dynamics of plasma structure in the E and F regions. The scale size dependence of the electric field coupling along the magnetic field is examined for a realistic background ionosphere and atmosphere. It is shown that, while normalized potentials map reciprocally between two altitudes, the potential disturbance caused by a fixed amplitude plasma density perturbation does not. The magnitude of electrostatic potential created by structured ionization is also shown to be strongly dependent on the altitude of the structure. The role of diffusion parallel to the magnetic field in the redistribution and decay of plasma structure is illustrated.

  9. 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.

  10. 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.

  11. Field-induced alignment of oxygen and nitrogen by intense femtosecond laser pulses.

    PubMed

    Huang, Juan; Wu, Chengyin; Xu, Nan; Liang, Qingqing; Wu, Zhifeng; Yang, Hong; Gong, Qihuang

    2006-08-31

    Field-induced alignment of O2 and N2 was experimentally studied with laser intensities varying from 10(13) to 10(15) W/cm2. When the laser intensity was below the ionization threshold for these molecules, the interaction between the induced dipole moment of molecules and the laser electric field aligned the molecules along the laser polarization direction. After extinction of the exciting laser, the transient alignment revived periodically. Thus macroscopic ensembles of highly aligned O2 and N2 molecules were obtained under field-free conditions. When the laser intensity exceeded the ionization threshold for these molecules, multielectron ionization and Coulomb explosion occurred. Using two linearly polarized laser pulses with crossed polarization, we demonstrated that the rising edge of the laser pulse aligned the molecules along the laser polarization direction prior to ionization, which resulted in strong anisotropic angular distributions of exploding fragments. These results suggest that the degree of alignment should be taken into account when qualitatively comparing the ion yield of these molecules with their companion atoms. PMID:16928105

  12. 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. PMID:18572626

  13. On the alignment of plasma anisotropies and the magnetic field direction in the solar wind

    NASA Technical Reports Server (NTRS)

    Asbridge, J. R.; Bame, S. J.; Feldman, W. C.; Gosling, J. T.; Ness, N. F.

    1977-01-01

    One year's Imp 6 solar wind plasma and magnetic field data are examined to determine whether anisotropies in particle velocity distributions are aligned with the measured interplanetary magnetic field vector. Alignment of components in the analysis plane was generally found to be excellent whenever plasma parameter magnitudes were larger than determination uncertainties, although some spread exists (typical rms approximately equal to 10 deg). By assuming cylindrical symmetry about the simultaneously measured magnetic field vector during the 1-year interval under study, three-dimensional values of selected solar wind plasma thermal parameters were constructed from the two-dimensional plasma measurements, and the statistical properties of their distributions have been tabulated.

  14. 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.

  15. Field-aligned currents and the auroral electrojet

    NASA Technical Reports Server (NTRS)

    Cahill, L. J.; Potter, W. E.; Kintner, P. M.; Arnoldy, R. L.; Choy, L. W.

    1974-01-01

    A Nike Tomahawk with fields and particles payload was launched on Nov. 18, 1970, over a strong westward electrojet current and auroral forms moving rapidly to the east. Electron fluxes moving up and down the magnetic field lines were measured. Upward-moving electrons below 1-keV energy were dominant and were equivalent to a net downward electric current that fluctuated between .2 and .6 microamp/sq m during the flight above 130 km. As the rocket traversed this broad region of downward electric current over and to the north of the auroral forms, the horizontal electric field slowly rotated from east to west. The magnetic measurements indicate that the westward electrojet was a horizontal sheet of current several hundred kilometers in north-south extent.

  16. 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.

  17. Chorus intensity modulation driven by time-varying field-aligned low-energy plasma

    NASA Astrophysics Data System (ADS)

    Nishimura, Y.; Bortnik, J.; Li, W.; Liang, J.; Thorne, R. M.; Angelopoulos, V.; Le Contel, O.; Auster, U.; Bonnell, J. W.

    2015-09-01

    Recent studies have shown that chorus waves are responsible for scattering and precipitating the energetic electrons that drive the pulsating aurora. While some of the chorus intensity modulation events are correlated with <~100 eV electron density modulation, most of the chorus intensity modulation events in the postmidnight sector occur without apparent density changes. Although it is generally difficult to measure evolution of low-energy (<~20 eV) electron fluxes due to constraints imposed by the spacecraft potential and electrostatic analyzer (ESA) energy range limit, we identified using Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data that low-energy ions of ~100 eV show density modulation that is correlated with chorus intensity modulation. Those low-energy ions and electrons are field-aligned with major peaks in 0° (for northern hemisphere winter event) and 180° (for northern hemisphere summer event) pitch angle, indicating that outflowing plasma from the sunlit hemisphere is the source of the low-energy plasma density modulation near the equator. Plasma sheet plasma density, and ambient electric and magnetic fields do not show modulations that are correlated with the chorus intensity modulation. Assuming charge neutrality, the low-energy ions can be used to represent cold plasma density in wave growth rate calculations, and the enhancements of the low-energy plasma density are found to contribute most effectively to chorus linear growth rates. These results suggest that chorus intensity modulation is driven by a feedback process where outflowing plasma due to energetic electron precipitation increases the equatorial density that drives further electron precipitation.

  18. Spurious fields in time domain computations of scattering problems

    NASA Technical Reports Server (NTRS)

    Kangro, Urve; Nicolaides, Roy

    1995-01-01

    In this paper two-dimensional electromagnetic scattering problems with a time-periodic incident field are considered. The scatterer is a perfect conductor, and an artificial boundary condition is used. The large time behavior of solutions, depending on (divergence-free) initial conditions, is characterized. It turns out that in addition to the expected time-periodic solution the limiting solution may also contain a spurious stationary field. The source of the stationary field is explained and equations describing it are obtained. Several avoidance strategies are discussed, and numerical comparisons of these techniques are given.

  19. Study of multiple scattering in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Kaplan, Daniel M.; Roberts, Thomas J.

    2013-02-01

    Muon cooling for a neutrino factory or muon collider can be achieved using low-Z absorbers in strong focusing fields. Proposed cooling lattices place absorbers in solenoidal fields ranging up to 30 to 40 T. The cooling performance of these lattices is determined by the interplay of ionization energy loss and Molière scattering, but Bethe's classic treatment of Moliere scattering ignores the helical motion of charged particles in solenoidal fields. When this motion is taken into account, the performance of these lattices can be better than predicted by simulations using the standard treatment.

  20. 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

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

    PubMed

    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. PMID:24475923

  2. Alignment of four-mirror wide field corrector for the Hobby-Eberly Telescope

    NASA Astrophysics Data System (ADS)

    Oh, Chang Jin; Frater, Eric H.; Coyle, Laura; Dubin, Matt; Lowman, Andrew; Zhao, Chunyu; Burge, James H.

    2013-09-01

    The Hobby-Eberly Telescope (HET) Wide Field Corrector (WFC) is a four-mirror optical system which corrects for aberrations from the 10-m segmented spherical primary mirror. The WFC mirror alignments must meet particularly tight tolerances for the system to meet performance requirements. The system uses 1-m class highly aspheric mirrors, which precludes conventional alignment methods. For the WFC system alignment a "center reference fixture" has been used as the reference for each mirror's vertex and optical axis. The center reference fixtures have both a CGH and sphere mounted retroreflector (SMR) nests. The CGH is aligned to the mirror's optical axis to provide a reference for mirror decenter and tilt. The vertex of each mirror is registered to the SMR nests on the center reference fixtures using a laser tracker. The spacing between the mirror vertices is measured during the system alignment using these SMR nest locations to determine the vertex locations. In this paper we present the procedures and results from creating and characterizing these center reference fixtures. As a verification of our alignment methods we also present results from their application in the WFC system alignment are also presented.

  3. The applicability of Brillouin scattering to flow field diagnostics

    NASA Technical Reports Server (NTRS)

    Laiosa, J.; Lederman, S.

    1979-01-01

    To fill the void between turbulence theory and experiment; particularly in the flow fields consisting of monatomic gases, for example in wind tunnels, means of measuring fluctuating quantities are needed. In the area of density fluctuation measurement, the optical method of Brillouin scattering was suggested. This was based on the theory, that the Brillouin scattered intensity is proportional to a function of density. In this investigation the potential of this method as a diagnostic tool was studied. Here the density fluctuations in gases were sought. Continuous wave lasers and interferometers were used as the primary illuminating source and scattered light filters respectively.

  4. 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.

  5. 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.

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

    PubMed

    Korobenko, A; Milner, V

    2016-05-01

    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. PMID:27203318

  7. Theoretical study of alignment dynamics of magnetic oblate spheroids in rotating magnetic fields

    NASA Astrophysics Data System (ADS)

    Tan, Mingyang; Song, Han; Dhagat, Pallavi; Jander, Albrecht; Walker, Travis W.

    2016-06-01

    Magnetic composites containing anisotropic magnetic particles can achieve properties not possible in corresponding bulk or thin films of the magnetic material. In this work, we discuss how planar magnetic anisotropy may be achieved in a composite by aligning disk-shaped particles in an in-plane rotating magnetic field. Previous efforts have reported a simple model of aligning particles in a high-frequency rotating magnetic field. However, no complete analytic solution was proposed. Here, we provide a full analytic solution that describes the alignment dynamics of microdisks in a rotating field that covers the entire frequency range. We also provide simplified solutions at both high-frequency and low-frequency limits through asymptotic expansions for easy implementation into industrial settings. The analytic solution is confirmed by numerical simulation and shows agreement with experiments.

  8. 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.

  9. 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.

  10. Eastward propagation of transient field-aligned currents and Pi 2 pulsations at auroral latitudes

    SciTech Connect

    Webster, D.J.; Samson, J.C.; Rostoker, G. )

    1989-04-01

    Transient field-aligned currents associated with the substorm expansive phase produce the damped, quasisinusoidal, geomagnetic pulsations called Pi 2's. Mid-latitude and auroral latitude measurements of the fields of these pulsations have indicated that they are produced, for the most part, by westward propagating field-aligned currents at auroral latitudes, although some studies have shown hints of eastward propagation, particularly far to the east of the longitude of the onset of the expansive phase. This study uses data from the University of Alberta magnetometer array to identify the characteristics of the eastward propagating mode at high latitudes by measuring polarizations and apparent group and phase velocities in regions far to the east of the expansive phase. The results show that eastward propagating Pi 2's have very high phase velocities (typically 40 km/s) which are comparable with those of the westward propagating mode. The polarizations and field configurations are compatible with a field-aligned and ionospheric current model which is very similar to that for the westward propagating component. These current models suggest that Pi 2's may be caused by shear Alfven waves produced by an azimuthally expanding, fast mode wave. The shear Alfven waves are reflected from the auroral ionosphere to produce the latitudinally localized field-aligned and ionospheric currents in the eastward (and westward) propagating modes.

  11. 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)].

  12. Paramagnetic alignment of small grains: A novel method for measuring interstellar magnetic fields

    SciTech Connect

    Hoang, Thiem; Martin, P. G.; Lazarian, A.

    2014-07-20

    We present a novel method to measure the strength of interstellar magnetic fields using ultraviolet (UV) polarization of starlight that is in part produced by weakly aligned, small dust grains. We begin with calculating the degrees of the paramagnetic alignment of small (size a ∼ 0.01 μm) and very small (a ∼ 0.001 μm) grains in the interstellar magnetic field due to the Davis-Greenstein relaxation and resonance relaxation. To calculate the degrees of paramagnetic alignment, we use Langevin equations and take into account various interaction processes essential for the rotational dynamics of small grains. We find that the alignment of small grains is necessary to reproduce the observed polarization in the UV, although the polarization arising from these small grains is negligible at the optical and infrared (IR) wavelengths. Based on fitting theoretical models to observed extinction and polarization curves, we find that the best-fit model for the case with the peak wavelength of polarization λ{sub max} < 0.55 μm requires a higher degree of alignment of small grains than for the typical case with λ{sub max} = 0.55 μm. We interpret the correlation between the systematic increase of the UV polarization relative to maximum polarization (i.e., of p(6 μm{sup –1})/p{sub max}) with λ{sub max}{sup −1} for cases of low λ{sub max} by appealing to the higher degree of alignment of small grains. We utilize the correlation of the paramagnetic alignment of small grains with the magnetic field strength B to suggest a new way to measure B using the observable parameters λ{sub max} and p(6 μm{sup –1})/p{sub max}.

  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. Synthesis models of dayside field-aligned currents for strong interplanetary magnetic field By

    NASA Astrophysics Data System (ADS)

    Watanabe, Masakazu; Iijima, Takesi; Rich, Frederick J.

    1996-06-01

    Using particle and magnetic field data acquired with DMSP-F6 and DMSP-F7 satellites, we have investigated interplanetary magnetic field (IMF) By dependence of the global pattern of plasma regime and field-aligned currents (FACs) on dayside high latitudes during strong IMF By (averaged |By|>3.7 nT) and geomagnetically disturbed (mainly IMF Bz<0) periods. From particle data we have identified five plasma regimes: inner plasma sheet, outer plasma sheet, cleft, cusp, and mantle. All the plasma domains except the inner plasma sheet show By dependence in spatial distribution. Region 1 and ``traditional cusp'' currents appear in cusp/mantle domains, which we call midday region 1 and region 0 currents, respectively, in this paper. These currents perfectly reverse their flow directions depending on IMF By polarity. Traditional region 1 currents occurring in cleft and outer plasma sheet almost always flow into the ionosphere in the prenoon sector and flow away from the ionosphere in the postnoon sector regardless of By polarity. Thus the midday region 1 and region 0 current system that appears at local noon is not a simple continuation of flankside region 1/region 2 current system. Midday region 1 and region 0 currents are not necessarily balanced in intensity; region 0 current intensity occasionally exceeds midday region 1 current intensity. Furthermore, intensity imbalance also appears in cleft-associated region 1 currents; that is, region 1 current in the farside cleft from the reconnection site (``downstreamside'' cleft) is larger than region 1 current in the nearside cleft (``upstreamside'' cleft). On the basis of these observational facts we discuss the source mechanisms of the dayside FAC system: (1) directly coupled generation of region 0 and midday region 1 current in the cusp/mantle domains around noon and (2) generation of extra region 0 current in the tail magnetopause which is connected to the extra downstreamside cleft-associated region 1 current.

  15. Strong ionospheric field-aligned currents for radial interplanetary magnetic fields

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Lühr, Hermann; Shue, Jih-Hong; Frey, Harald. U.; Kervalishvili, Guram; Huang, Tao; Cao, Xue; Pi, Gilbert; Ridley, Aaron J.

    2014-05-01

    The present work has investigated the configuration of field-aligned currents (FACs) during a long period of radial interplanetary magnetic field (IMF) on 19 May 2002 by using high-resolution and precise vector magnetic field measurements of CHAMP satellite. During the interest period IMF By and Bz are weakly positive and Bx keeps pointing to the Earth for almost 10 h. The geomagnetic indices Dst is about -40 nT and AE about 100 nT on average. The cross polar cap potential calculated from Assimilative Mapping of Ionospheric Electrodynamics and derived from DMSP observations have average values of 10-20 kV. Obvious hemispheric differences are shown in the configurations of FACs on the dayside and nightside. At the south pole FACs diminish in intensity to magnitudes of about 0.1 μA/m2, the plasma convection maintains two-cell flow pattern, and the thermospheric density is quite low. However, there are obvious activities in the northern cusp region. One pair of FACs with a downward leg toward the pole and upward leg on the equatorward side emerge in the northern cusp region, exhibiting opposite polarity to FACs typical for duskward IMF orientation. An obvious sunward plasma flow channel persists during the whole period. These ionospheric features might be manifestations of an efficient magnetic reconnection process occurring in the northern magnetospheric flanks at high latitude. The enhanced ionospheric current systems might deposit large amount of Joule heating into the thermosphere. The air densities in the cusp region get enhanced and subsequently propagate equatorward on the dayside. Although geomagnetic indices during the radial IMF indicate low-level activity, the present study demonstrates that there are prevailing energy inputs from the magnetosphere to both the ionosphere and thermosphere in the northern polar cusp region.

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

    NASA Astrophysics Data System (ADS)

    Vechinski, Douglas A.; Rao, Sadasiva M.

    1992-10-01

    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.

  17. 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.

  18. Broadband electrostatic noise and field-aligned currents in Jupiter's middle magnetosphere

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.; Scarf, F. L.; Kurth, W. S.; Gurnett, D. A.

    1981-01-01

    Voyager 1 plasma wave observations have revealed the presence of an impulsive electrostatic emission localized to the Jovian middle magnetosphere that appears on the edges of the plasma sheet. This plasma mode has the same spectral and morphological characteristics of an emission that has been extensively studied in the earth's magnetosphere and has been associated with the presence of field-aligned currents. The results of a detailed study of the properties of this Jovian emission are presented by using comparisons with terrestrial observations as a basis for mode identification. The occurrence regions of the waves are compared with the measured magnetic field configuration to establish a correspondence with the plasma sheet. It is argued that this is a quasi-permanent global system of field-aligned currents linking the ionosphere of Jupiter to the middle magnetosphere, which powers energetic plasma heating processes occurring there. On the basis of knowledge of the consequences of field-aligned currents in the terrestrial magnetosphere, a scenario for acceleration/precipitation of inverted V electrons, concomitant aurorae, and energetic (approximately 10 keV) proton deposition into the middle magnetosphere resulting from field-aligned potential drops associated with this current system is suggested.

  19. 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.

  20. Molecular alignment and filamentation: Comparison between weak- and strong-field models

    NASA Astrophysics Data System (ADS)

    Berti, N.; Béjot, P.; Wolf, J.-P.; Faucher, O.

    2014-11-01

    The impact of nonadiabatic laser-induced molecular alignment on filamentation is numerically studied. Weak- and strong-field models of impulsive molecular alignment are compared in the context of nonlinear pulse propagation. It is shown that the widely used weak-field model describing the refractive index modification induced by impulsive molecular alignment accurately reproduces the propagation dynamics providing that only a single pulse is involved during the experiment. On the contrary, it fails at reproducing the nonlinear propagation experienced by an intense laser pulse traveling in the wake of a second strong laser pulse. The discrepancy depends on the relative delay between the two pulses and is maximal for delays corresponding to half the rotational period of the molecule.

  1. 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. PMID:25362298

  2. 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.

  3. IMF By-controlled field-aligned currents in the magnetotail during northward interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Cheng, Z. W.; Shi, J. K.; Dunlop, M.; Liu, Z. X.

    2014-08-01

    The influence of the interplanetary magnetic field (IMF) By component on the field-aligned currents (FACs) in the plasma sheet boundary layer (PSBL) in the magnetotail during the northward IMF were investigated using the data from Cluster. There are 748 FACs cases selected to do analysis. We present that the IMF By component plays a very important role in controlling the flow direction of the FACs in the PSBL in the magnetotail. In the northern hemisphere, the influence of the positive (negative) IMF By is an earthward (tailward) FACs. To the contrary, in the southern hemisphere, the effect of the positive (negative) IMF By is a tailward (earthward) FACs. There is a clear north-south asymmetry of the polarity of the FACs in the PSBL when IMF By is positive or negative, and this asymmetry of the polarity is more distinct when IMF By is positive. The FAC density is controlled by IMF By only when |IMF By| is large. When |IMF By| is more than 10 nT the absolute FAC density in the PSBL has an obvious positive correlation with the |IMF By|. When |IMF By| is less than 10 nT, there is no correlation between the absolute FAC density and |IMF By|. There is a clear dusk-dawn asymmetry in the current densities for the FACs in the PSBL, with the dawn currents appearing larger than the dusk currents. The FAC with the largest (smallest) density is located in the range of 0100≤MLT<0200 (2100≤MLT<2200).

  4. Terminator field-aligned current system: Its dependencies on solar, seasonal, and geomagnetic conditions

    NASA Astrophysics Data System (ADS)

    Zhu, L.; Schunk, R. W.; Eccles, V.; Scherliess, L.; Sojka, J. J.; Gardner, L. C.

    2014-12-01

    A new field-aligned current system in the high-latitude ionosphere was reported recently by Zhu et al. (2014). The current system develops and evolves along the ionospheric terminator and it is thus termed as the terminator field-aligned currents. The discovery was based on the reconstructions from the Ionospheric Dynamics and Electrodynamics Data Assimilation Model (IDED-DA) with the ingestion of observational measurements. In this presentation, we show the results of a follow-on study using the IDED-DA, in which the solar, seasonal, and geomagnetic dependencies of the terminator field-aligned currents are explored. The new current system is the first field-aligned current system in the high-latitude ionosphere that is not directly driven by the magnetospheric dynamics and has an ionospheric origin. A systematic study of its electrodynamic and plasma dynamics as well as dependencies on various solar-terrestrial conditions will help us to explore the active role of the ionosphere in the magnetosphere-ionosphere coupling and improve the physical understanding of the electrodynamics and plasma dynamics of many small-scale structures in the polar ionosphere.

  5. 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.

  6. 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.

  7. 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.

  8. Pair-eigenstates and mutual alignment of coupled molecular rotors in a magnetic field.

    PubMed

    Sharma, Ketan; Friedrich, Bretislav

    2016-05-11

    We examine the rotational states of a pair of polar (2)Σ molecules subject to a uniform magnetic field. The electric dipole-dipole interaction between the molecules creates entangled pair-eigenstates of two types. In one type, the Zeeman interaction between the inherently paramagnetic molecules and the magnetic field destroys the entanglement of the pair-eigenstates, whereas in the other type it does not. The pair-eigenstates exhibit numerous intersections, which become avoided for pair-eigenstates comprised of individual states that meet the selection rules ΔJi = 0, ± 1, ΔNi = 2n (n = 0, ±1, ±2,…), and ΔMi = 0, ± 1 imposed by the electric dipole-dipole operator. Here Ji, Ni and Mi are the total, rotational and projection angular momentum quantum numbers of molecules i = 1, 2 in the absence of the electric dipole-dipole interaction. We evaluate the mutual alignment of the pair-eigenstates and find it to be independent of the magnetic field, except for states that undergo avoided crossings, in which case the alignment of the interacting states is interchanged at the magnetic field corresponding to the crossing point. We present an analytic model which provides ready estimates of the pairwise alignment cosine that characterises the mutual alignment of the pair of coupled rotors. PMID:27126576

  9. 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.

  10. Mie scattering of highly focused, scalar fields: an analytic approach.

    PubMed

    Moore, Nicole J; Alonso, Miguel A

    2016-07-01

    We present a method for modeling the scattering of a focused scalar field incident on a spherical particle. This approach involves the expansion of the incident field in an orthonormal basis of closed-form solutions of the Helmholtz equation which are nonparaxial counterparts of Laguerre-Gaussian beams. This method also allows for the analytic calculation of the forces and torques exerted on a particle at any position with respect to the beam's focus. PMID:27409679

  11. Coulomb field scattering in Born-Infeld electrodynamics

    SciTech Connect

    Tennant, Daniel

    2011-02-15

    In the context of Born-Infeld electrodynamics, the electromagnetic fields interact with each other via their nonlinear couplings. A calculation will be performed where an incoming electromagnetic plane wave scatters off a Coulomb field in the geometrical optics approximation. In addition to finding the first-order angle of deflection, exact solutions for the trajectory will also be found. The possibility of electromagnetic bound states will be discussed.

  12. 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.

  13. Electric-field-driven alignment of chiral conductive polymer thin films.

    PubMed

    Tassinari, Francesco; Mathew, Shinto P; Fontanesi, Claudio; Schenetti, Luisa; Naaman, Ron

    2014-04-29

    We investigated the effect of an electric field on the alignment and structural properties of thin films of a chiral polybithiophene-based conductive polymer, functionalized with a protected l-cysteine amino acid. Thin films were obtained by exploiting both drop-casting and spin-coating procedures. The electric properties, the polarized Raman spectrum, the UV-vis spectrum, and the CD spectra were measured as a function of the electric field intensity applied during film formation. It was found that beyond the enhancement of the conductivity observed when the electric field aligns the polymer, the electric field significantly affects the chiral properties and the effect depends on the method of deposition. PMID:24731141

  14. Conoscopic analysis of electric field driven planar aligned nematic liquid crystal.

    PubMed

    Ranjini, Radhakrishnan; Matham, Murukeshan Vadakke; Nguyen, Nam-Trung

    2014-05-01

    This paper illustrates the conoscopic observation of a molecular reconstruction occurring across a nematic liquid crystal (NLC) medium in the presence of an external electric field. Conoscopy is an optical interferometric method, employed to determine the orientation of an optic axis in uniaxial crystals. Here a planar aligned NLC medium is used, and the topological changes with respect to various applied voltages are monitored simultaneously. Homogenous planar alignment is obtained by providing suitable surface treatments to the ITO coated cell walls. The variation in the conoscopic interferometric patterns clearly demonstrates the transition from planar to homeotropic state through various intermediate states. PMID:24921859

  15. Microwave Characterization of a Field Effect Transistor with Dielectrophoretically-Aligned Single Silicon Nanowire

    NASA Astrophysics Data System (ADS)

    Kang, Myung-Gil; Ahn, Jae-Hyun; Lee, Jongwoon; Hwang, Dong-Hoon; Kim, Hee-Tae; Rieh, Jae-Seong; Whang, Dongmok; Son, Maeng-Ho; Ahn, Doyeol; Yu, Yun-Seop; Hwang, Sung-Woo

    2010-06-01

    Microwave (MW) characteristics of a field effect transistor (FET) incorporating a single silicon nanowire (SiNW) were obtained from S-parameter measurements in the frequency range of 0.05 to 20 GHz. The single SiNW was aligned, using the alternating current (ac) dielectrophoresis alignment method, between the drain and source electrode forming a coplanar waveguide (CPW) structure. Analysis of the FET was performed using equivalent circuit modeling by advanced device system (ADS) simulation. By fitting the measured data with the simulation results, the parameters of the single SiNW FET were obtained and the cutoff frequency was derived.

  16. Mapping Field-Aligned Currents as a Function of the Interplanetary Electric Field

    NASA Astrophysics Data System (ADS)

    Edwards, T.; Weimer, D. R.; Luhr, H.; Olsen, N.; Stauning, P.

    2015-12-01

    Magnetometer measurements from both the Oersted and CHAMP satellite have been combined together to create a database that is used to construct maps of the polar, magnetic field-aligned currents (FAC). As these satellite data span the time range of years 1999 to 2005 for Oersted and 2001 to 2010 for CHAMP, this large quantity is useful to investigate how the currents change under various conditions. This presentation will focus on the magnitude of the total current as a function of the interplanetary electric field (IEF), the product of the interplanetary magnetic field (IMF) and solar wind velocity. This topic is of particular interest due to the numerous prior studies in the past, both experimental and theoretical, about the behavior of the polar cap electric potentials. Specifically, the electric potentials increase and then level off to a saturated value as the IMF and IEF increase in magnitude. The majority of the theoretical explanations for this saturation involve the "Region 1" currents. What has been found in this investigation is that the total FAC is highly linear as a function of the IEF, up to values of 8 mV/m, for all IMF clock angles. This is more than double the value of the IEF where the electric potentials exhibit the roll-off toward saturation. The linear slope does vary as a function of dipole tilt angle, which correlates with season; the summer hemisphere has a larger slope and higher currents than the winter hemisphere. In addition to looking at the total FAC values, the totals within the Regions 0, 1, and 2 have also been extracted from the FAC patterns, and it has been found that the linearity of the response curve is maintained. Above IEF values of 8 mV/m, corresponding to IMF magnitudes around 20 nT, the volume of data is very low, resulting in much uncertainty in the FAC values that are obtained, although there is some evidence that the total FAC does begin to saturate above 8 mV/m.

  17. Field Fluctuation Spectroscopy in a Reverberant Cavity with Moving Scatterers

    NASA Astrophysics Data System (ADS)

    de Rosny, Julien; Roux, Philippe; Fink, Mathias; Page, J. H.

    2003-03-01

    We report a study of transient ultrasonic waves inside a reverberant cavity containing moving scatterers. We show that the elastic mean free path and the dynamics of the scatterers govern the evolution of the autocorrelation of acoustic wave field. A parallel is established between these results and a closely related technique, diffusing acoustic wave spectroscopy. Excellent agreement is found between experiment and theory for a moving stainless steel ball in a water tank, thereby elucidating the underlying physics, and a potential application, fish monitoring inside aquariums, is demonstrated.

  18. 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.

  19. 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).

  20. Dynamics of Dollard asymptotic variables. Asymptotic fields in Coulomb scattering

    NASA Astrophysics Data System (ADS)

    Morchio, G.; Strocchi, F.

    2016-03-01

    Generalizing Dollard’s strategy, we investigate the structure of the scattering theory associated to any large time reference dynamics UD(t) allowing for the existence of Møller operators. We show that (for each scattering channel) UD(t) uniquely identifies, for t →±∞, asymptotic dynamics U±(t); they are unitary groups acting on the scattering spaces, satisfy the Møller interpolation formulas and are interpolated by the S-matrix. In view of the application to field theory models, we extend the result to the adiabatic procedure. In the Heisenberg picture, asymptotic variables are obtained as LSZ-like limits of Heisenberg variables; their time evolution is induced by U±(t), which replace the usual free asymptotic dynamics. On the asymptotic states, (for each channel) the Hamiltonian can by written in terms of the asymptotic variables as H = H±(qout/in,pout/in), H±(q,p) the generator of the asymptotic dynamics. As an application, we obtain the asymptotic fields ψout/in in repulsive Coulomb scattering by an LSZ modified formula; in this case, U±(t) = U0(t), so that ψout/in are free canonical fields and H = H0(ψout/in).

  1. Application of field-modulated birefringence and light scattering to biosensing

    NASA Astrophysics Data System (ADS)

    Strong, Louis H.; Hall, Daniel B.; Edson, Clark M.; Nguyen, Hiep-hoa; Whitt, Michael A.; Varadi, Gyula

    2011-03-01

    Superparamagnetic nanoparticles (NPs) coated with surface ligands are shown to be an effective means to impart magnetic field modulation to optical signals from targeted receptor complexes. The modulated signals they produce can be used for a number of important high throughput applications in bio-sensing including: detecting (weaponized) viruses, screening recombinant libraries of proteins, identifying pathogenic conversions of microbes, and monitoring gene amplification. We compare the results of two dynamic methods of measuring target binding to NPs: birefringence and field modulated light scattering (FMLS). These measurements reflect complementary manifestations of NP alignment (orientation) and de-alignment (relaxation) dynamics. Birefringence originates from the specific crystalline properties of a small subset of paramagnetic NPs (for example, maghemite) when oriented in a magnetic field. Upon quenching the field, it decays at a rate exhibiting the Debye-Stokes-Einstein rotational relaxation constant of target-NP complexes. Birefringence relaxation reflects the particle dynamics of the mixed suspension of NPs, with signal components weighted in proportion to the free and complexed NP size distributions. FMLS relaxation signals, on the other hand, originate predominately from the inherent optical anisotropy of the target complexes, show little contribution from non-complexed NPs when the targets are more optically anisotropic than the NPs, and provide a more direct and accurate method for determining target receptor concentrations. Several illustrations of the broad range of applications possible using these dynamic measurements and the kind of information to be derived from each detection modality will be discussed.

  2. Solution Processing of Ordered Thin Film Nanowire Composites by Magnetic Field Alignment

    NASA Astrophysics Data System (ADS)

    Singer, Jonathan; Pelligra, Candice; Huang, Su; Osuji, Chinedum

    2014-03-01

    Vertically aligned nanowire forests are a desirable geometry for many applications, including as electrodes, heterojunctions, and high surface energy interfaces. Most conventional aligned nanowire structures, however, are generated by methods that require (i) high temperatures, (ii) a specific substrate, or (iii) high cost lithographic techniques. We seek to utilize the magnetic alignment of cobalt-doped zinc oxide nanowires to enable the solution processing of thin films of aligned nanowires on a generalized substrate at a fraction of the cost of other methods. By functionalization of the nanowires with various surface modifications, they can be dispersed in several solvent systems and aligned by a 6 T field. Further, by including polymer in the wire solution, we can both control the areal density and also incorporate additional functionalities to the final composite device. As an example, the use of a conjugated polymer (such as poly(3-hexylthiophene-2,5-diyl) (P3HT)) allows for the final structures to act as inorganic-organic ordered heterojunction solar cells. While final device quality depends on the simultaneous optimization of several key processing parameters, the process does not rely on top-down fabrication or costly materials. Supported by ONR YIP Award N000141210657.

  3. Markov random field based automatic alignment for low SNR imagesfor cryo electron tomography

    SciTech Connect

    Amat, Fernando; Moussavi, Farshid; Comolli, Luis R.; Elidan, Gal; Horowitz, Mark

    2007-07-21

    We present a method for automatic full precision alignmentof the images in a tomographic tilt series. Full-precision automaticalignment of cryo electron microscopy images has remained a difficultchallenge to date, due to the limited electron dose and low imagecontrast. These facts lead to poor signal to noise ratio (SNR) in theimages, which causes automatic feature trackers to generate errors, evenwith high contrast gold particles as fiducial features. To enable fullyautomatic alignment for full-precision reconstructions, we frame theproblem probabilistically as finding the most likely particle tracksgiven a set of noisy images, using contextual information to make thesolution more robust to the noise in each image. To solve this maximumlikelihood problem, we use Markov Random Fields (MRF) to establish thecorrespondence of features in alignment and robust optimization forprojection model estimation. The resultingalgorithm, called RobustAlignment and Projection Estimation for Tomographic Reconstruction, orRAPTOR, has not needed any manual intervention for the difficult datasets we have tried, and has provided sub-pixel alignment that is as goodas the manual approach by an expert user. We are able to automaticallymap complete and partial marker trajectories and thus obtain highlyaccurate image alignment. Our method has been applied to challenging cryoelectron tomographic datasets with low SNR from intact bacterial cells,as well as several plastic section and x-ray datasets.

  4. 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.

  5. 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.

  6. Field-aligned currents in the Jovian magnetosphere during the Ulysses flyby

    NASA Technical Reports Server (NTRS)

    Dougherty, M. K.; Southwood, D. J.; Balogh, A.; Smith, E. J.

    1993-01-01

    The data recorded by the dual vector helium/fluxgate magnetometer flown onboard the Ulysses spacecraft during the flyby of Jupiter in February 1992 are analyzed with the aim of identifying the presence of field-aligned current signatures. Field-aligned current flow is expected wherever stress is being transmitted electromagnetically along the magnetic field direction. Sources of such currents at Jupiter are departures within the magnetosphere from corotation, momentum transfer from the solar wind, or centrifugally driven magnetospheric outflow. It is pointed out that the azimuthal field component provides a simple first-order means of monitoring the presence of currents, the currents occurring in regions where the azimuthal component changes significantly. The data from both inbound and outbound passes show evidence of 'leading' and 'lagging' azimuthal field signatures where the field bends out of the meridian, and which are signatures symptomatic of current systems associated with departures from corotation. On the outbound pass, the most intense signatures are found where the field switches from a configuration symptomatic of the field lagging corotation to a configuration representing the field leading. The latter configuration also corresponds to a tail-like displacement of the field and, indeed, the magnetometer data alone cannot distinguish the source of the current system, which could be due to solar wind magnetosphere coupling or which may arise from internal stress imbalance.

  7. Molecular simulation of model liquid crystals in a strong aligning field

    NASA Astrophysics Data System (ADS)

    de Miguel, Enrique; Blas, Felipe J.; Martín Del Río, Elvira

    We report a computer simulation study of systems of perfectly aligned molecules interacting through the Gay-Berne (GB) potential model for two different values of the molecular anisotropy parameter κ, namely 3 and 4.4. The models are appropriate to gauge the effects of strong aligning fields on the thermodynamics and structural properties of thermotropic liquid crystals. According to our results, one of the main effects of the external field is to increase the range of stability of the smectic A phase, which indicates the existence of a strong coupling between orientational and translational order. For the κ = 3 GB model the smectic phase, which is not stable in the absence of the field, is promoted when the molecules are constrained to be parallel. According to the simulation results, the smectic A-nematic transition is, in general, continuous; however, this transition appears to be first order at low pressure for the κ = 4.4 GB fluid model.

  8. 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.

  9. Comparison of Iridium Determined Field-Aligned Current Patterns with MHD Simulations

    NASA Astrophysics Data System (ADS)

    Korth, H.; Anderson, B. J.; Goodrich, C. C.; Waters, C. L.; Merkine, V. G.

    2002-05-01

    The engineering magnetometers aboard the 70+ Iridium satellites arranged in six equally spaced polar orbital planes provide a unique database for determination of global field-aligned currents [Waters et al., 2001]. In this study we compare these field-aligned currents with MHD simulation results to quantitatively evaluate the MHD results in a global way. We report analysis for three events of steady interplanetary magnetic field (IMF) orientation, stable to within 25o of the average direction. The start times of these intervals are August~11, 1999 (22:36), November~23, 1999 (07:15), and August~10, 2000 (22:11), and the events extend between eight and ten hours in duration. The IMF clock angles for the events are -124o, 125o, and 160o, respectively, and the IMF cone angles for all three intervals are within 25o of 90o. The solar wind flow speeds for the events averages 430, 453, and 386~km/s, and the mean solar wind densities are 3.7, 3.6, and 12.0 {cm}-3, respectively. The field aligned current densities in the MHD simulations are evaluated at the inner simulation boundary (2~Re) and mapped on dipole field lines to ionospheric altitudes. Preliminary results show a reasonably good agreement in the morphology of the Region-1 currents, although the field-aligned currents of the MHD simulations are displaced somewhat poleward with respect to the Iridium patterns. DMSP particle source identifications are used to compare source regions of Region 1 in the observed FAC maps with those in the MHD simulations. The Region-2 currents show expectedly larger differences since ring current drift physics necessary to drive these currents in the magnetosphere is not implemented in the MHD evaluations. The ratio between Region~1 and Region~2 is used to measure the relative deficit of Region-2 currents in the MHD simulation results.

  10. Magnetic Field and Pressure Dependence of Small Angle Neutron Scattering in MnSi

    SciTech Connect

    Pfleiderer, C.; Reznik, D.; Pintschovius, L.; Haug, J.

    2007-10-12

    We report small angle neutron scattering of spontaneous and magnetic field aligned components of the helical spin polarization in MnSi for temperatures T down to 0.35 K, at pressures p up to 21 kbar, and magnetic field B up to 0.7 T. The parameter range of our study spans the first order transition between helical order and partial magnetic order at p{sub c}=14.6 kbar, which coincides with the onset of an extended regime of non-Fermi liquid resistivity. Our study suggests that MnSi above p{sub c} is not dominated by the remnants of the first order transition at p{sub c}, but that an unidentified mechanism favors stabilization of a new ground state other than helical order.

  11. 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

  12. Magnetic Alignment of Magnetically Biaxial Diamagnetic Rods under Rotating Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Tsukui, Shu; Kimura, Tsunehisa

    2012-05-01

    The alignment behavior of magnetically biaxial diamagnetic rods under rotating magnetic fields is studied to elucidate the effects of particle shape and rotation speed on alignment manner. Three types of rod (ca. 1.1 mmφ × 3 mm) are prepared: (i) rod axes parallel to χ1, (ii) parallel to χ2, and (iii) parallel to χ3, where χs are the principal axes of the diamagnetic susceptibility tensor and χ1 > χ2 > χ3. The motion of the rod is recorded on video and the angles required for the comparison with simulation are measured. Simulation is performed by numerically solving a torque equation including magnetic and hydrodynamic torques. The experimental results show a good agreement with simulation results. It is shown that the χ3-axis of rod sample (ii) does not align parallel to the axis of the rotating magnetic field under most experimental conditions; this is in marked contrast to the case with magnetically uniaxial particles (χ1 = χ2 > χ3), for which the χ3-axis aligns irrespective of particle shape and/or rotation speed. This observation is interpreted in terms of magnetic energy and orientation kinetics.

  13. 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.

  14. 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. PMID:25927488

  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. A High Resolution Magnetohydrodynamic Simulation Study of Kronian Field-Aligned Currents and Aurora

    NASA Astrophysics Data System (ADS)

    Fukazawa, K.; Ogino, T.; Walker, R. J.

    2011-12-01

    Magnetohydrodynamic simulations of the interaction of Saturn's magnetosphere with the solar wind indicate that Kelvin-Helmholtz (K-H) waves can form on the dayside magnetopause when the interplanetary magnetic field (IMF) is northward. Dayside magnetic reconnection occurs at Saturn for northward IMF. The combination of K-H waves and reconnection caused enhanced vorticity in Saturn's magnetosphere. We have used a very high resolution version (grid interval is 0.1 RS) of our simulation code to study the consequences of the vortices and reconnection for the generation of field aligned currents (FAC) and aurorae in Saturn's ionosphere. We found three bands of alternating FAC toward and away from the dawn side of the ionosphere and two sets on the dusk side. The K-H waves generated a series of toward and away currents along the dayside side magnetopause. In the ionosphere they appear as a series of spots of up and down current. The K-H field aligned currents are adjacent to nearly continuous currents located from 1600 LT around past midnight to about 0700 LT The largest currents (jpara> 5×10-8 A /m-2) are found are at the highest latitudes. They map to the magnetopause and to the near-Earth tail region. In analogy with the Earth's ionosphere the field aligned currents away from Saturn can serve as a proxy for discrete aurorae. We used the away current density and the Knight relationship to estimate the energy flux from discrete aurorae and obtained ~1 mW /m-2 in the region with the strongest currents. Similar energy fluxes were found in the K-H related aurorae. This gave approximately 70 GW for the auroral power. We also investigated diffuse aurorae by using the energy flux in the absence of the field aligned currents. We found a region of enhanced thermal energy flux in the region where cusp aurorae are observed.

  17. 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.

  18. 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.

  19. Field-aligned currents associated with Pc 5 pulsations: STARE and TRIAD observations

    SciTech Connect

    Poulter, E.M.; Nielsen, E.; Potemra, T.A.

    1982-04-01

    The resonance theory for monochromatic Pc 5 micropulsations predicts that the toroidal mode resonance should be accompanied by field-aligned current systems. These currents close via Pedersen current in the ionosphere, and the drifting irregularities observed by the STARE radars are thought to be generated by the associated electric fields. Recent theoretical calculations by Walker (1980) are used to estimate the micropulsation current systems and accompanying magnetic perturbations. STARE radar observations of the pulsation electric field in the ionosphere are then compared with the corresponding magnetic perturbation observed with the TRIAD satellite magnetometer.

  20. Tailoring the Optical Dipole Force for Molecules by Field-Induced Alignment

    NASA Astrophysics Data System (ADS)

    Purcell, S. M.; Barker, P. F.

    2009-10-01

    We report on the ability to tailor the optical dipole force for molecules by tuning their effective polarizability with strong field alignment using polarized fields. We have measured a difference of 20% in the dipole force on cold CS2 molecules when changing from linear to near-circular polarization using peak field intensities of 5.7×1011Wcm-2. A variation in the focal length with laser polarization of a molecular-optical lens formed by a single focused laser beam was also measured. This provides a new way of modifying this force for many molecules.

  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. A flux-coordinate independent field-aligned approach to plasma turbulence simulations

    NASA Astrophysics Data System (ADS)

    Hariri, F.; Ottaviani, M.

    2013-11-01

    This work illustrates a new approach to field-aligned coordinates for plasma turbulence simulations which is not based on flux variables. The method employs standard Cartesian or polar coordinates to discretize the fields. Parallel derivatives are computed directly along a coordinate that follows the local field, and poloidal derivatives are computed in the original Cartesian frame. Several advantages of this approach are presented. The tests on a drift-wave model demonstrate that the method is well suited to exploit the flute property of small parallel gradients by minimizing the number of degrees of freedom needed to treat a given problem in an accurate and efficient manner.

  3. 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. PMID:27472632

  4. 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.

  5. Small-scale field-aligned currents observed by the AKEBONO (EXOS-D) satellite

    SciTech Connect

    Fukunishi, H.; Oya, H. ); Kokubun, S. ); Tohyama, F. ); Mukai, T.; Fujii, R.

    1991-02-01

    The EXOS-D fluxgate magnetometer data obtained at 3,000-10,000 km altitude have shown that small-scale field-aligned currents always exist in large-scale region 1, region 2, cusp and polar cap current systems. Assuming that these small-scale field-aligned currents have current sheet structure, the width of current sheet is estimated to be 5-20 km at ionospheric altitude. By comparing the magnetometer data with charged particle and high frequency plasma wave data simultaneously obtained from EXOS-D, it is found that small-scale currents have one-to-one correspondence with localized electron precipitation events characterized by flux enhancement over a wide energy range from 10 eV to several keV and broadband electrostatic bursts occasionally extending above local plasma frequencies or electron cyclotron frequencies.

  6. 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.

  7. Draping of strongly flow-aligned interplanetary magnetic field about the magnetopause

    NASA Astrophysics Data System (ADS)

    Petrinec, S. M.

    2016-07-01

    Many dynamic processes of the magnetosphere are directly driven by the solar wind and the occurrence of magnetic merging at the magnetopause. The location of magnetopause magnetic merging, or reconnection, is now fairly well understood when the interplanetary magnetic field (IMF) contains large By and Bz components in relation to the Bx component (in Geocentric Solar Magnetospheric (GSM) coordinates). However, when the IMF contains a large X-component (i.e., is closely flow-aligned), it is not yet well understood how the shocked IMF drapes about the magnetopause, and how this affects the occurrence and location of magnetic merging. In this initial study, we examine from observations how a nearly flow-aligned IMF drapes about the magnetopause. The results of this study are expected to be useful for comparisons with both analytic and global numerical models of the magnetosheath magnetic field.

  8. Space Technology 5 measurements of auroral field-aligned current sheet motion

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

    During the 90-day Space Technology 5 (ST-5) mission, a total of 2535 auroral field-aligned current (FAC) signatures were identified. Of these 1030 were suitable to be modeled as semi-infinite current sheets aligned with L-shells and moving with constant speed in the north or south directions (hereafter called FAC speed). FAC speeds were found to range from -1 to 1 km/s with larger mean magnitude during intervals of higher geomagnetic activity. At ST-5 altitudes, ~300 to 4500 km, the median relative errors in FAC thickness and current density, when stationary FAC is assumed, are 4%. When the ST-5 FAC speed determinations are extrapolated along the IGRF-10 magnetic field lines, these errors increase to 23% and 24% at 4 RE, and 65% and 124% at 8 RE, respectively.

  9. Field-aligned currents in the Jovian magnetosphere - Pioneer 10 and 11

    NASA Technical Reports Server (NTRS)

    Kivelson, M. G.; Winge, C. R.

    1976-01-01

    Field-aligned currents, which are known to play an important role in the dynamics of the earth's magnetosphere, would also be expected to flow in the Jovian magnetosphere during magnetically active periods. Such currents are difficult to observe largely because of their limited spatial extent and intermittent nature, but on the Pioneer 11 inbound pass to Jupiter on day 336, 1800 GRT, near the L shell of Ganymede, the helium vector magnetometer recorded a structured perturbation with the characteristic signature of a field-aligned current. No analogous structure was found on a similar Pioneer 10 inbound pass (day 337, 1200 GRT). The perturbation could have been caused by turbulence with the wake of Ganymede through which the spacecraft was moving or the perturbation could represent the first observation of a Jovian substorm. The observations are discussed in terms of both models, and difficulties are examined.

  10. Full field strain measurements of collagenous tissue by tracking fiber alignment through vector correlation.

    PubMed

    Quinn, Kyle P; Winkelstein, Beth A

    2010-09-17

    Full field strain measurements of biological tissue during loading are often limited to the quantification of fiduciary marker displacements on the tissue surface. These marker measurements can lack the necessary spatial resolution to characterize non-uniform deformation and may not represent the deformation of the load-bearing collagen microstructure. To overcome these potential limitations, a method was developed to track the deformation of the collagen fiber microstructure in ligament tissue. Using quantitative polarized light imaging, fiber alignment maps incorporating both direction and alignment strength at each pixel were generated during facet capsular ligament loading. A grid of virtual markers was superimposed over the tissue in the alignment maps, and the maximization of a vector correlation calculation between fiber alignment maps was used to track marker displacement. Tracking error was quantified through comparisons to the displacements of excised ligament tissue (n=3); separate studies applied uniaxial tension to isolated facet capsular ligament tissue (n=4) to evaluate tracking capabilities during large tissue deformations. The average difference between virtual marker and tissue displacements was 0.07+/-0.06pixels. This error in marker location produced principal strain measurements of 1.2+/-1.6% when markers were spaced 4pixels apart. During tensile tissue loading, substantial inhomogeneity was detected in the strain field using vector correlation tracking, and the location of maximum strain differed from that produced by standard tracking techniques using coarser meshes. These findings provide a method to directly measure fiber network strains using quantitative fiber alignment data, enabling a better understanding of structure-function relationships in tissues at different length scales. PMID:20494363

  11. 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.

  12. Alignments in quasar polarizations: Pseudoscalar-photon mixing in the presence of correlated magnetic fields

    SciTech Connect

    Agarwal, Nishant; Kamal, Archana; Jain, Pankaj

    2011-03-15

    We investigate the effects of pseudoscalar-photon mixing on electromagnetic radiation in the presence of correlated extragalactic magnetic fields. We model the Universe as a collection of magnetic domains and study the propagation of radiation through them. This leads to correlations between Stokes parameters over large scales and consistently explains the observed large-scale alignment of quasar polarizations at different redshifts within the framework of the big bang model.

  13. 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.

  14. Vertically-Aligned Single-Crystal Nanocone Arrays: Controlled Fabrication and Enhanced Field Emission.

    PubMed

    Duan, Jing Lai; Lei, Dang Yuan; Chen, Fei; Lau, Shu Ping; Milne, William I; Toimil-Molares, M E; Trautmann, Christina; Liu, Jie

    2016-01-13

    Metal nanostructures with conical shape, vertical alignment, large ratio of cone height and curvature radius at the apex, controlled cone angle, and single-crystal structure are ideal candidates for enhancing field electron-emission efficiency with additional merits, such as good mechanical and thermal stability. However, fabrication of such nanostructures possessing all these features is challenging. Here, we report on the controlled fabrication of large scale, vertically aligned, and mechanically self-supported single-crystal Cu nanocones with controlled cone angle and enhanced field emission. The Cu nanocones were fabricated by ion-track templates in combination with electrochemical deposition. Their cone angle is controlled in the range from 0.3° to 6.2° by asymmetrically selective etching of the ion tracks and the minimum tip curvature diameter reaches down to 6 nm. The field emission measurements show that the turn-on electric field of the Cu nanocone field emitters can be as low as 1.9 V/μm at current density of 10 μA/cm(2) (a record low value for Cu nanostructures, to the best of our knowledge). The maximum field enhancement factor we measured was as large as 6068, indicating that the Cu nanocones are promising candidates for field emission applications. PMID:26666466

  15. Enhancing field-free molecular alignment by a polynomial phase modulation

    NASA Astrophysics Data System (ADS)

    Huang, Yunxia; Xu, Shuwu; Yao, Yunhua; Jia, Tianqing; Zhang, Shian; Sun, Zhenrong

    2016-01-01

    A feasible scheme is proposed to enhance the molecular alignment by shaping the femtosecond laser pulse with a polynomial phase modulation that involves the second and third order dispersions. It is shown that the field-free molecular alignment can be obtained adiabatically during the interaction with the shaped femtosecond laser pulse, and can be reproduced at full rotational periods with the same degree as that at the peak of laser pulse when the shaped femtosecond laser pulse is gone off. It is also shown that the molecular alignment behavior by the shaped femtosecond laser pulse is same as that by the slow turn-on and rapid turn-off laser pulse in previous study, but the shaped femtosecond laser pulse can induce slightly higher alignment degree due to the different rising edge. In addition, it is indicated that our proposed scheme can be experimentally realized by using a programmable 4f-configuration zero-dispersion pulse shaper combined with a one-dimensional liquid-crystal spatial light modulator.

  16. Vertically aligned self-assembled gold nanorods as low turn-on, stable field emitters

    NASA Astrophysics Data System (ADS)

    Apte, Amey; Joshi, Padmashree; Bhaskar, Prashant; Joag, Dilip; Kulkarni, Sulabha

    2015-11-01

    In this work we have investigated field emission from self-assembled, vertically aligned, gold nanorod arrays, which were synthesized via a colloidal growth method. A field emission current density of ∼1 mA/cm2 was measured for these gold nanorod arrays using an anode-cathode separation of ∼3.5 mm. The field emission investigation of these gold nanorod arrays was carried out at a base pressure of ∼10-8 mbar. The turn on field, defined as the electric field required to obtain a current density of 1 μA/cm2, is observed to be 1.9 V/μm. Assuming a work function value of 5.3 eV, the field enhancement factor β is estimated to be ∼2931, which is higher than the reported values for other gold nanostructures/arrays.

  17. 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.

  18. High-Field Magneto-Photoluminescence Spectroscopy of Highly-Aligned Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Shaver, J.; Kono, J.; Crooker, S. A.; Fagan, J. A.; Hobbie, E. K.

    2008-03-01

    We have investigated excitons in semiconducting single-walled carbon nanotubes (SWNTs) through low-temperature magneto-photoluminescence (PL) of highly-aligned SWNT films in magnetic fields (B) up to 55 T. The magnetic field was generated using the 60 T long pulse magnet powered by a 1.4 GVA motor-generator at the National High Magnetic Field Lab in Los Alamos, NM. Polyacrylic acid films containing DNA suspended CoMoCAT SWNTs were stretch-aligned, and the alignment factor was analyzed by polarized Raman spectroscopy^1. Utilizing two well-defined measurement geometries, SWNTs B and SWNTs B, we provide unambiguous evidence that the PL from excitons in SWNTs is sensitive only to the B-component parallel to the tube axis. We developed a theoretical model of one-dimensional magneto-excitons, based on recently-proposed exchange-split bright and dark exciton bands with Aharonov-Bohm-phase-dependent energies, masses, and oscillator strengths, which successfully reproduces our observations^2. 1. Fagan et al. Phys. Rev. Lett. 98, 147402 (2007) 2. Shaver et al. Nano Lett. 7, 1851 (2007)

  19. 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. PMID:26114376

  20. 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.

  1. Spatial distribution and alignments of volcanic centers: Clues to the formation of monogenetic volcanic fields

    NASA Astrophysics Data System (ADS)

    Le Corvec, Nicolas; Spörli, K. Bernhard; Rowland, Julie; Lindsay, Jan

    2013-09-01

    Monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent. Understanding similarities and differences between these fields may help to characterize key controls on their generation. Such volcanic fields consist of numerous volcanic centers, each of which represents a pathway of magma from its source to the surface. We analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields, and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle, applied the following methods for each: (1) the Poisson Nearest Neighbor (PNN) analysis, representing the degree to which the distribution of the volcanic centers departs from a predicted Poisson distribution, and (2) a volcanic alignment analysis to ascertain the preferential pathways, if any, used by the magma to reach the surface. This is the first comprehensive global comparison of such analyses. Magma pathways within the brittle upper crust are influenced to various degrees by two end-member situations: (1) formation of new extension fractures perpendicular to the least compressive stress (σ3) and (2) re-activation of pre-existing fractures that are near-parallel to the maximum principal stress (σ1). The results of the PNN analysis show that, independently of the tectonic environment, most volcanic fields display a clustered distribution of their volcanic centers. Alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments, or that it is in competition with other factors (e.g., pre-existing structures, local stress changes due to older intrusions). Overall, these results indicate that the propagation of the magma (and therefore the spatial distribution of the volcanic centers within volcanic fields) is the product of an interplay between deep level influences (i

  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. f-mode interaction with models of sunspot: near-field scattering and multifrequency effects

    NASA Astrophysics Data System (ADS)

    Daiffallah, Khalil

    2016-07-01

    We use numerical simulations to investigate the interaction of an f-mode wave packet with small and large models of a sunspot in a stratified atmosphere. While a loose cluster model has been largely studied before, we focus in this study on the scattering from an ensemble of tightly compact tubes. We showed that the small compact cluster produces a slight distorted scattered wave field in the transverse direction, which can be attributed to the simultaneous oscillations of the pairs of tubes within the cluster aligned in a perpendicular direction to the incoming wave. However, no signature of a multiple-scattering regime has been observed from this model, while it has been clearly observable for the large compact cluster model. Furthermore, we pointed out the importance of the geometrical shape of the monolithic model on the interaction of f-mode waves with a sunspot in a high-frequency range (ν = 5 mHz). These results are a contribution to the observational effort to distinguish seismically between different configurations of magnetic flux tubes within sunspots and plage.

  4. Production of flickering aurora and field-aligned electron flux by electromagnetic ion cyclotron waves

    NASA Technical Reports Server (NTRS)

    Temerin, M.; Mcfadden, J.; Boehm, M.; Carlson, C. W.; Lotko, W.

    1986-01-01

    Recent observations have suggested that flickering aurora is produced by a modulation of the field-aligned component of the electron flux within an auroral arc. It is proposed that a portion of the field-aligned electrons are of ionospheric origin and that these electrons are accelerated and their flux modulated by electromagnetic ion cyclotron waves that occur below the main acceleration region on auroral arc field lines. A model of the electromagnetic ion cyclotron wave shows that the parallel phase velocity of the wave increase as the wave propagates toward the ionosphere. A test particle calculation shows that ionospheric electrons trapped or reflected by the wave are accelerated to energies of several keV and that their flux is modulated at the wave frequency. The relative amplitudes of the model wave electric fields are consistent with the observations of small-scale low-frequency ionospheric and magnetospheric electric fields near auroral arcs of approximately 10 mV/m and 100 mV/m, respectively. The large-amplitude ion cyclotron waves also produce a ponderomotive force and a self-consistent ambipolar electric field. Energy considerations show that the downward energy flux in the electromagnetic ion cyclotron wave can be several percent of the total downward auroral electron energy flux.

  5. 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.

  6. Alignment of Red-Sequence Cluster Dwarf Galaxies: From the Frontier Fields to the Local Universe

    NASA Astrophysics Data System (ADS)

    Barkhouse, Wayne Alan; Archer, Haylee; Burgad, Jaford; Foote, Gregory; Rude, Cody; Lopez-Cruz, Omar

    2015-08-01

    Galaxy clusters are the largest virialized structures in the universe. Due to their high density and mass, they are an excellent laboratory for studying the environmental effects on galaxy evolution. Numerical simulations have predicted that tidal torques acting on dwarf galaxies as they fall into the cluster environment will cause the major axis of the galaxies to align with their radial position vector (a line that extends from the cluster center to the galaxy's center). We have undertaken a study to measure the redshift evolution of the alignment of red-sequence cluster dwarf galaxies based on a sample of 57 low-redshift Abell clusters imaged at KPNO using the 0.9-meter telescope, and 64 clusters from the WINGS dataset. To supplement our low-redshift sample, we have included galaxies selected from the Hubble Space Telescope Frontier fields. Leveraging the HST data allows us to look for evolutionary changes in the alignment of red-sequence cluster dwarf galaxies over a redshift range of 0 < z < 0.35. The alignment of the major axis of the dwarf galaxies is measured by fitting a Sersic function to each red-sequence galaxy using GALFIT. The quality of each model is checked visually after subtracting the model from the galaxy. The cluster sample is then combined by scaling each cluster by r200. We present our preliminary results based on the alignment of the red-sequence dwarf galaxies with: 1) the major axis of the brightest cluster galaxy, 2) the major axis of the cluster defined by the position of cluster members, and 3) a radius vector pointing from the cluster center to individual dwarf galaxies. Our combined cluster sample is sub-divided into different radial regions and redshift bins.

  7. Strong-field cyclotron scattering. I - Scattering amplitudes and natural line width

    NASA Astrophysics Data System (ADS)

    Graziani, Carlo

    1993-07-01

    The introduction of resonance line width into the QED cyclotron scattering amplitudes is considered. It is shown that the width arises from loop corrections to the electron propagator, which also bring about shifts in the Landau energy levels. A formalism is developed that allows the dressed electron propagator to be derived. It is shown that the states of Herold et al. (1982) and of Sokolov and Ternov (1968), which diagonalize the component of the magnetic moment operator parallel to the external magnetic field, are appropriate for calculation of the scattering amplitudes, whereas the states of Johnson and Lippmann (1949) are not. In addition, it is shown that the Breit-Wigner broadening approximation E tends to E - i(Gamma)/2 is consistent with the perturbation-theoretic order of the calculation, if the former basis states are chosen, but not the latter.

  8. Field-aligned ion beams upstream of the earth's bow shock Evidence for a magnetosheath source

    NASA Technical Reports Server (NTRS)

    Thomsen, M. F.; Gosling, J. T.; Bame, S. J.; Feldman, W. C.; Paschmann, G.; Sckopke, N.

    1983-01-01

    High time resolution ISEE-1 and -2 observations of upstream field-aligned ion beams at several crossings of the earth's bow shock indicate that some beams are due to high energy magnetosheath particles leaking through the shock into the upstream region. The distribution immediately downstream of these oblique shocks consists of a 'core' of directly transmitted, slightly heated ions, plus a crescent-shaped, high-velocity distribution, centered roughly on the magnetic field in the direction toward the upstream region, with a fairly well defined low velocity cutoff.

  9. Beam-Based Alignment of Magnetic Field in the Fermilab Electron Cooler Cooling Section

    SciTech Connect

    Seletskiy, S. M.; Tupikov, V.

    2006-03-20

    The Fermilab Electron Cooling Project requires low effective anglular spread of electrons in the cooling section. One of the main components of the effective electron angles is an angle of electron beam centroid with respect to antiproton beam. This angle is caused by the poor quality of magnetic field in the 20 m long cooling section solenoid and by the mismatch of the beam centroid to the entrance of the cooling section. This paper focuses on the beam-based procedure of the alignment of the cooling section field and beam centroid matching. The discussed procedure allows to suppress the beam centroid angles below the critical value of 0.1 mrad.

  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. PMID:26183388