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Sample records for regular magnetic clouds

  1. Infrared radiative transfer through a regular array of cuboidal clouds

    NASA Technical Reports Server (NTRS)

    HARSHVARDHAN; Weinman, J. A.

    1981-01-01

    Infrared radiative transfer through a regular array of cuboidal clouds is studied and the interaction of the sides of the clouds with each other and the ground is considered. The theory is developed for black clouds and is extended to scattering clouds using a variable azimuth two-stream approximation. It is shown that geometrical considerations often dominate over the microphysical aspects of radiative transfer through the clouds. For example, the difference in simulated 10 micron brightness temperature between black isothermal cubic clouds and cubic clouds of optical depth 10, is less than 2 deg for zenith angles less than 50 deg for all cloud fractions when viewed parallel to the array. The results show that serious errors are made in flux and cooling rate computations if broken clouds are modeled as planiform. Radiances computed by the usual practice of area-weighting cloudy and clear sky radiances are in error by 2 to 8 K in brightness temperature for cubic clouds over a wide range of cloud fractions and zenith angles. It is also shown that the lapse rate does not markedly affect the exiting radiances for cuboidal clouds of unit aspect ratio and optical depth 10.

  2. Waves Within Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Siu Tapia, A. L.; Blanco-Cano, X.; Kajdic, P.; Aguilar-Rodriguez, E.; Russell, C. T.; Jian, L. K.; Luhmann, J. G.

    2013-05-01

    Complex events are formed by two or more large-scale structures which interact in the solar wind. Typical cases are interactions of: (i) a magnetic cloud/interplanetary coronal mass ejection (MC/ICME) with another MC/ICME transient; (ii) a MC/ICME embedded within a stream interaction region (SIR); and (iii) a MC/ICME followed by a fast stream. Using data from the STEREO mission during the years 2007-2011 we found 17 ICMEs forming complex events with an associated shock wave. All the ICMEs included in this study showed a smooth rotation of the magnetic field and low proton beta plasma, and were classified as MCs. We use magnetic field and plasma data to study the waves observed within these MCs. To determine wave characteristics we perform Power Spectra and Minimum Variance Analysis. We also analyze 10 MCs driving shocks which were not associated with complex events. We compare wave characteristics within the Magnetic Clouds forming Complex Events (MCCE), with those waves observed within the Magnetic Clouds that were isolated (IMC), i. e., not associated with complex events. Transverse and almost parallel propagating ion cyclotron waves were observed within both, MCCE and IMC. Compressive mirror mode waves were observed only within MCCE. Both modes can grow due to temperature anisotropy. Most of the mirror mode events found within MCCE are observed in regions with enhanced plasma beta. This is in agreement with kinetic theory, which predicts that mirror mode growth is favored by high plasma beta values. It is possible that the observed enhancements in plasma beta are due to compressions inside MCCE.

  3. Magnetic confinement of cosmic clouds

    NASA Technical Reports Server (NTRS)

    Azar, Michel; Thompson, W. B.

    1988-01-01

    The role of the magnetic field in the confinement or compression of interstellar gas clouds is reconsidered. The virial theorem for an isolated magnetized cloud in the presence of distant magnetic sources is reformulated in terms of moments of the internal and external currents, and an equilibrium condition is derived. This condition is applied to the interaction between isolated clouds for the simple- and artificial-case in which the field of each cloud is a dipole. With the simplest of statistical assumptions, the probability of any given cloud being compressed is calculated as about 10 percent, the magnetic field acting as a medium which transmits the kinetic pressure between clouds. Even when compression occurs the magnetic pressure 1/2 B-squared may decrease on leaving the cloud surface.

  4. Polytropic relationship in interplanetary magnetic clouds

    NASA Technical Reports Server (NTRS)

    Osherovich, V. A.; Farrugia, C. J.; Burlaga, L. F.; Lepping, R. P.; Fainberg, J.; Stone, R. G.

    1993-01-01

    High time-resolution data from the ISEE 3 and IMP 8 spacecraft are presented for the magnetic field and the proton and electron populations of a number of magnetic clouds, in order to investigate such clouds' thermodynamics and the relationship between their magnetic and thermodynamic structures. It is judged on the basis of these data that while the magnetic flield of the cloud expands, the ions are cooled. Hot electrons are trapped by the magnetic field in the magnetic cloud's core. These conditions are favorable for the generation of ion-acoustic waves.

  5. Study of an expanding magnetic cloud

    NASA Astrophysics Data System (ADS)

    Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Démoulin, P.

    Magnetic Clouds (MCs) transport into the interplanetary medium the magnetic flux and helicity released in coronal mass ejections by the Sun. At 1 AU from the Sun, MCs are generally modelled as static flux ropes. However, the velocity profile of some MCs presents signatures of expansion. We analise here the magnetic structure of an expanding magnetic cloud observed by Wind spacecraft. We consider a dynamical model, based on a self-similar behaviour for the cloud radial velocity. We assume a free expansion for the cloud, and a cylindrical linear force free field (i.e., the Lundquist's field) as the initial condition for its magnetic configuration. We derive theoretical expressions for the magnetic flux across a surface perpendicular to the cloud axis, for the magnetic helicity and magnetic energy per unit length along the tube using the self-similar model. Finally, we compute these magntitudes with the fitted parameters. FULL TEXT IN SPANISH

  6. Magnetic clouds in the solar wind

    NASA Technical Reports Server (NTRS)

    Burlaga, L. F.; Klein, L.

    1980-01-01

    Two interplanetary magnetic clouds, characterized by anomalous magnetic field directions and unusually high magnetic field strengths with a scale of the order of 0.25 AU, are identified and described. As the clouds moved past a spacecraft located in the solar wind near Earth, the magnetic field direction changed by rotating approximately 180 deg nearly parallel to a plane which was essentially perpendicular to the ecliptic. The configuration of the magnetic field in the clouds might be that of a tightly wound cylindrical helix or a series of closed circular loops. One of the magnetic clouds was in a cold stream preceded by a shock, and it caused both a geomagnetic storm and a depression in the galactic cosmic ray intensity. No stream, geomagnetic storm, or large cosmic ray decrease was associated with the other magnetic cloud.

  7. Interplanetary magnetic clouds at 1 AU

    NASA Technical Reports Server (NTRS)

    Klein, L. W.; Burlaga, L. F.

    1981-01-01

    Magnetic clouds are defined as regions with a radial dimension approximately 0.25 AU (at 1 AU) in which the magnetic field strength is high and the magnetic field direction changes appreciably by means of rotation of one component of B nearly parallel to a plane. The magnetic field geometry in such a magnetic cloud is consistent with that of a magnetic loop, but it cannot be determined uniquely. Forty-five clouds were identified in interplanetary data obtained near Earth between 1967 and 1978; at least one cloud passed the Earth every three months. Three classes of clouds were identified, corresponding to the association of a cloud with a shock, a stream interface, or a CME. There are approximately equal numbers of clouds in each class, and the three types of clouds might be different manifestations of a coronal transient. The magnetic pressure inside the clouds is higher than the ion pressure and the sum is higher than the pressure of the material outside of the cloud.

  8. Interplanetary magnetic clouds: Topology and driving mechanism

    NASA Astrophysics Data System (ADS)

    Chen, James; Garren, David A.

    1993-11-01

    A model is developed to study the origin and propagation of magnetic clouds. Starting with an equilibrium current loop embedded in an ambient plasma consistent with the solar corona, magnetic energy is injected by increasing the loop current. This causes the loop to rise, propelling plasma and magnetic field away from the Sun. Using a simple model of the interplanetary medium, the subsequent dynamics of the loop is calculated to 1 AU and beyond. The macroscopic properties of the resulting structures at 1 AU closely resemble those of observed magnetic clouds. Thermal effects indicate that clouds remain magnetically connected to the Sun in order to yield observed temperatures near 1 AU.

  9. Global configuration of a magnetic cloud

    NASA Astrophysics Data System (ADS)

    Burlaga, L. F.; Lepping, R. P.; Jones, J. A.

    A magnetic cloud associated with a 2N flare on January 1, 1978 was observed by IMP-8, Helios A, Helios B, and Voyager 2. The variation of the magnetic field observed at each spacecraft is represented to good approximation by Lundquist's solution for a cylindrically symmetric force-free magnetic field with constant alpha. A least-squares fit of Lundquist's solution to the data from each spacecraft gives the local orientation of the axis of the magnetic cloud. The times of the estimated boundaries of the magnetic cloud at each spacecraft, together with the speeds of the boundaries and the spacecraft position, give the positions of the boundaries at a given time. From these results the magnetic cloud is determined to resemble a flux rope whose minor radius is approximately 0.15 AU at 1 AU, and whose radius of curvature at 1 AU is approximately 1/3 AU.

  10. Ionospheric Geo-effectiveness of Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Bronder, T. J.; Knipp, D. J.; Lynch, B.; Zurbuchen, T.; McHarg, M. G.; Chun, F. K.

    2002-12-01

    We present an analysis of the geo-effectiveness of magnetic clouds and the disturbed solar wind surrounding them. Estimates of the ionospheric Joule heating rates based on two ground magnetic indices and estimates of auroral zone particle heating from polar satellites will be combined to provide a summary of the total geomagnetic heating during magnetic cloud passage. Preliminary estimates suggest that intervals of magnetic cloud passage experience about 50 percent greater heating rates than intervals associated with the more general class of interplanetary coronal mass ejection. Heating rates for magnetic clouds are about four times greater than heating rates estimated for intervals of background slow solar wind flow. Preliminary work also indicates that magnetic clouds lying in the ecliptic plane (leading or trailing fields oriented N-S or S-N) have heating rates about 50 percent greater than clouds with leading or trailing fields perpendicular to the ecliptic plane. We will provide hourly heating profiles for more than 50 magnetic clouds passing the earth during the rise and peak of solar cycle 23.

  11. Exploring Regularities for Improving FAÇADE Reconstruction from Point Clouds

    NASA Astrophysics Data System (ADS)

    Zhou, K.; Gorte, B.; Zlatanova, S.

    2016-06-01

    (Semi)-automatic facade reconstruction from terrestrial LiDAR point clouds is often affected by both quality of point cloud itself and imperfectness of object recognition algorithms. In this paper, we employ regularities, which exist on façades, to mitigate these problems. For example, doors, windows and balconies often have orthogonal and parallel boundaries. Many windows are constructed with the same shape. They may be arranged at the same lines and distance intervals, so do different windows. By identifying regularities among objects with relatively poor quality, these can be applied to calibrate the objects and improve their quality. The paper focuses on the regularities among the windows, which is the majority of objects on the wall. Regularities are classified into three categories: within an individual window, among similar windows and among different windows. Nine cases are specified as a reference for exploration. A hierarchical clustering method is employed to identify and apply regularities in a feature space, where regularities can be identified from clusters. To find the corresponding features in the nine cases of regularities, two phases are distinguished for similar and different windows. In the first phase, ICP (iterative closest points) is used to identify groups of similar windows. The registered points and a number of transformation matrices are used to identify and apply regularities among similar windows. In the second phase, features are extracted from the boundaries of the different windows. When applying regularities by relocating windows, the connections, called chains, established among the similar windows in the first phase are preserved. To test the performance of the algorithms, two datasets from terrestrial LiDAR point clouds are used. Both show good effects on the reconstructed model, while still matching with original point cloud, preventing over or under-regularization.

  12. Charged scalar perturbations around a regular magnetic black hole

    NASA Astrophysics Data System (ADS)

    Huang, Yang; Liu, Dao-Jun

    2016-05-01

    We study charged scalar perturbations in the background of a regular magnetic black hole. In this case, the charged scalar perturbation does not result in superradiance. By using a careful time-domain analysis, we show that the charge of the scalar field can change the real part of the quasinormal frequency, but has little impact on the imaginary part of the quasinormal frequency and the behavior of the late-time tail. Therefore, the regular magnetic black hole may be stable under the perturbations of a charged scalar field at the linear level.

  13. ANCHORING MAGNETIC FIELD IN TURBULENT MOLECULAR CLOUDS

    SciTech Connect

    Li Huabai; Goodman, Alyssa; Darren Dowell, C.; Hildebrand, Roger; Novak, Giles

    2009-10-20

    One of the key problems in star formation research is to determine the role of magnetic fields. Starting from the atomic intercloud medium which has density n {sub H} approx 1 cm{sup -3}, gas must accumulate from a volume several hundred pc across in order to form a typical molecular cloud. Star formation usually occurs in cloud cores, which have linear sizes below 1 pc and densities n {sub H2} > 10{sup 5} cm{sup -3}. With current technologies, it is hard to probe magnetic fields at scales lying between the accumulation length and the size of cloud cores, a range corresponds to many levels of turbulent eddy cascade, and many orders of magnitude of density amplification. For field directions detected from the two extremes, however, we show here that a significant correlation is found. Comparing this result with molecular cloud simulations, only the sub-Alfvenic cases result in field orientations consistent with our observations.

  14. Comment on the polarity of magnetic clouds

    NASA Technical Reports Server (NTRS)

    Gonzalez, W. D.; Lee, L.-C.; Tsurutani, B. T.

    1990-01-01

    The initial description of magnetic clouds by Klein and Burlaga (1982) and the models that have been developed for their representation (e.g., by Goldstein, 1983) are examined. The results show that a definition of the cloud's polarity only in terms of the Bz component of the IMF is not always correct. It is suggested that, for the description polarities of quasi-transverse and quasi-parallel clouds, a combination of directions in the Bz and By components of the IMF should be used.

  15. Influence of magnetic clouds on cosmic ray intensity variations

    NASA Technical Reports Server (NTRS)

    Yadav, R. S.; Yadav, N. R.; BADRUDDIN; Agrawal, S. P.

    1985-01-01

    Neutron monitor data has been analyzed to study the nature of galactic cosmic ray transient modulation associated with three types of interplanetary magnetic clouds - clouds associated with shocks, stream interfaces and cold magnetic enhancements.

  16. Probing the magnetic topologies of magnetic clouds by means of solar energetic particles

    NASA Technical Reports Server (NTRS)

    Kahler, S. W.; Reames, D. V.

    1991-01-01

    Solar energetic particles (SEPs) have been used as probes of magnetic cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

  17. Cosmic ray decreases and magnetic clouds

    NASA Technical Reports Server (NTRS)

    Cane, H. V.

    1993-01-01

    A study has been made of energetic particle data, obtained from IMP 8, in conjunction with solar wind field and plasma data at the times of reported magnetic clouds. It is shown that magnetic clouds can cause a depression of the cosmic ray flux but high fields are required. A depression of 3 percent in a neutron monitor requires a field of about 25 nT. Such high fields are found only in a subset of coronal ejecta. The principal cause for Forbush decreases associated with energetic shocks is probably turbulence in the postshock region, although some shocks will be followed by an ejecta with a high field. Each event is different. The lower-energy particles can help in identifying the dominant processes in individual events.

  18. Cosmic ray decreases and magnetic clouds

    NASA Technical Reports Server (NTRS)

    Cane, H. V.

    1992-01-01

    Energetic particle data, obtained from IMP 8, in conjunction with solar wind field and plasma data at the times of reported magnetic clouds was studied. It is shown that magnetic clouds can cause a depression of the cosmic ray flux but high fields are required. A depression of 3 percent in a neutron monitor requires a field of about 25 nT. Such high fields are found only in a subset of coronal ejecta. The principal cause for Forbush decreases associated with energetic shocks is probably turbulence in the post-shock region although some shocks will be followed by an ejecta with a high field. Each event is different. The lower energy particles can help in identifying the dominant processes in individual events.

  19. Magnetic Cloud Field Intensities and Solar Wind Velocities

    NASA Technical Reports Server (NTRS)

    Gonzalez, Walter D.; Clau de Gonzalez, Alicia D.; Tsurutani, Bruce T.; Arballo, John K.

    1997-01-01

    For the sets of magnetic clouds studied in this work we have shown that there is a general relationship between their magnetic fields strength and velocities. With a clear tendency that the faster the speed of the cloud the higher the magnetic field.

  20. Magnetic clouds, helicity conservation, and intrinsic scale flux ropes

    NASA Technical Reports Server (NTRS)

    Kumar, A.; Rust, D. M.

    1995-01-01

    An intrinsic-scale flux-rope model for interplanetary magnetic clouds, incorporating conservation of magnetic helicity, flux and mass is found to adequately explain clouds' average thermodynamic and magnetic properties. In spite their continuous expansion as they balloon into interplanetary space, magnetic clouds maintain high temperatures. This is shown to be due to magnetic energy dissipation. The temperature of an expanding cloud is shown to pass through a maximum above its starting temperature if the initial plasma beta in the cloud is less than 2/3. Excess magnetic pressure inside the cloud is not an important driver of the expansion as it is almost balanced by the tension in the helical field lines. It is conservation of magnetic helicity and flux that requires that clouds expand radially as they move away from the Sun. Comparison with published data shows good agreement between measured cloud properties and theory. Parameters determined from theoretical fits to the data, when extended back to the Sun, are consistent with the origin of interplanetary magnetic clouds in solar filament eruptions. A possible extension of the heating mechanism discussed here to heating of the solar corona is discussed.

  1. A Global Magnetic Topology Model for Magnetic Clouds. III

    NASA Astrophysics Data System (ADS)

    Hidalgo, M. A.

    2014-03-01

    In two previous papers, we presented a global model for the analysis of magnetic clouds (MCs), where the three components of the magnetic field were fitted to the corresponding Geocentric Solar Ecliptic experimental data, obtaining reliable information, for example, about the orientation of these events in the interplanetary medium. That model, due to its non-force-free character, (∇p ≠ 0), could be extended to determine the plasma behavior. In the present work, we develop that extension, now including the plasma behavior inside the cloud through the analysis of the plasma pressure, and define a fitting procedure where the pressure and the magnetic field components are fitted simultaneously. After deducing the magnetic field topology and the current density components of the model, we calculate the expression of the pressure tensor and, in particular, its trace. In light of the results, we conclude that incorporating the plasma behavior in the analysis of the MCs can give us a better scenario in which to understand the physical mechanisms involved in the evolution of such magnetic structures in the interplanetary medium.

  2. A global magnetic topology model for magnetic clouds. III

    SciTech Connect

    Hidalgo, M. A.

    2014-03-20

    In two previous papers, we presented a global model for the analysis of magnetic clouds (MCs), where the three components of the magnetic field were fitted to the corresponding Geocentric Solar Ecliptic experimental data, obtaining reliable information, for example, about the orientation of these events in the interplanetary medium. That model, due to its non-force-free character, (∇p ≠ 0), could be extended to determine the plasma behavior. In the present work, we develop that extension, now including the plasma behavior inside the cloud through the analysis of the plasma pressure, and define a fitting procedure where the pressure and the magnetic field components are fitted simultaneously. After deducing the magnetic field topology and the current density components of the model, we calculate the expression of the pressure tensor and, in particular, its trace. In light of the results, we conclude that incorporating the plasma behavior in the analysis of the MCs can give us a better scenario in which to understand the physical mechanisms involved in the evolution of such magnetic structures in the interplanetary medium.

  3. Observations in the sheath region ahead of a magnetic cloud and in the dayside magnetosheath during magnetic cloud passage

    NASA Technical Reports Server (NTRS)

    Farrugia, C. J.; Fitzenreiter, R. J.; Burlaga, L. F.; Erkaev, N. V.; Osherovich, V. A.; Biernat, H. K.; Fazakerley, A.

    1994-01-01

    We present magnetic field and particle (protons and electrons) observations in the sheath region behind an interplanetary shock driven by a magnetic cloud, and in the magnetic cloud itself. We also discuss observations in the dayside terrestrial magnetosheath during cloud passage. We find that the region ahead of the cloud is in pressure balance. Further, throughout its extent (greater than 0.06 AU), the magnetic field strength is anticorrelated with the plasma density, with the latter decreasing steadily as the cloud is approached. This behavior is indicative of magnetic forces influencing the flow topology and highlights a large-scale breakdown of predictions based solely on gas dynamical considerations. We also study density structures inside the cloud which result in an undulating dynamic pressure being applied to the magnetopause causing it to oscillate with amplitudes of approximately 1-3 Re and period approximately 2h.

  4. Prominence material identified in magnetic cloud

    NASA Astrophysics Data System (ADS)

    Yao, Shuo; Marsch, E.; Tu, C.-Y.

    2010-03-01

    Coronal mass ejections (CMEs) often appear in coronagraph images as three-part structures composed of a leading bright front, a dark cavity and a bright core, which are believed to be associated with the sheath of compressed solar wind, the erupting magnetic flux rope and the cool and dense prominence plasma, respectively. However, a convincing identification of this three-part structure in the in-situ solar wind is extremely rare. Therefore, there still remains an open question as to what kind of signatures these three CME parts will reveal in the in situ data ([5]). Our work presents a clear identification of prominence material from in situ observations of the solar wind magnetic field and plasma parameters. The Helios 2 solar probe detected a magnetic cloud at 0.5 AU on 30 March 1976. In this event, we found a region with lower proton temperature and higher proton number density than outside, which is consistent with key features of a prominence as cold and dense solar material. During the same time we also found the occurrence of what possibly is He+, which is a special ion expected to occur only in prominence ejecta. Furthermore, the above observations were all made at a location related to the turning point of a bipolar structure of the interplanetary magnetic field, which is coincident with the notion that a solar prominence lies under the magnetic field lines of a bipolar region and is oriented along the neutral line. Furthermore, from our analysis of solar wind velocity distribution functions (VDFs) we can confirm by kinetic evidence that the plasma inside this special region is colder and more isotropic than outside. Above all, our observations circumstantially confirm the 3-part CME model as described in references [10] and [7].

  5. Energetic Particles Events inside Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Medina, Jose; Hidalgo, Miguel Angel; Blanco, Juan Jose; Rodriguez-Pacheco, Javier

    The effect of the magnetic topology of the Magnetic Clouds (MCs) over the energetic particle event (EPe) fluxes (0.5-100 MeV) have been simulated. In the data corresponding to the ion and electron fluxes, a depression after a strong maximum is observed when a EPe passes through a MC. Using our cross-section circular and elliptical MC models (Journal of Geophysical Research 107(1), doi:10.1029/2001JA900100 (2002) and Solar Physics 207(1), 187-198 (2002)) we have tried to explain that effect, understanding the importance of the topology of the MC. In sight of the results of the preliminary analysis we conclude that the magnitude of the magnetic field seems not to play a significant role but the helicoidal topology associated with topology of the MCs. This work has been supported by the Spanish Comisín Internacional de o Ciencia y Tecnoloǵ (CICYT), grant ESP2005-07290-C02-01 and ESP2006-08459. This work ıa is performed inside COST Action 724.

  6. Regular and chaotic precession of magnetization in magnetic films with a stripe domain structure

    NASA Astrophysics Data System (ADS)

    Shutyĭ, A. M.

    2008-12-01

    Based on a numerical solution of the equations of motion found over a wide range of frequencies of an alternating magnetic field, the nonlinear precession dynamics of magnetization are studied in thin-film structures of the (100) type with a stripe domain structure in a perpendicular bias field. The conditions are determined under which high-amplitude regular and chaotic dynamic regimes occur. Bifurcational variations in the precession of coupled magnetic moments and dynamic-bistability states are detected. The specific features of the spectrum of Lyapunov exponents and of time analogs of Poincaré cross sections of trajectories in chaotic regimes are considered.

  7. Automatic Extraction and Regularization of Building Outlines from Airborne LIDAR Point Clouds

    NASA Astrophysics Data System (ADS)

    Albers, Bastian; Kada, Martin; Wichmann, Andreas

    2016-06-01

    Building outlines are needed for various applications like urban planning, 3D city modelling and updating cadaster. Their automatic reconstruction, e.g. from airborne laser scanning data, as regularized shapes is therefore of high relevance. Today's airborne laser scanning technology can produce dense 3D point clouds with high accuracy, which makes it an eligible data source to reconstruct 2D building outlines or even 3D building models. In this paper, we propose an automatic building outline extraction and regularization method that implements a trade-off between enforcing strict shape restriction and allowing flexible angles using an energy minimization approach. The proposed procedure can be summarized for each building as follows: (1) an initial building outline is created from a given set of building points with the alpha shape algorithm; (2) a Hough transform is used to determine the main directions of the building and to extract line segments which are oriented accordingly; (3) the alpha shape boundary points are then repositioned to both follow these segments, but also to respect their original location, favoring long line segments and certain angles. The energy function that guides this trade-off is evaluated with the Viterbi algorithm.

  8. A GLOBAL MAGNETIC TOPOLOGY MODEL FOR MAGNETIC CLOUDS. II

    SciTech Connect

    Hidalgo, M. A.

    2013-04-01

    In the present work, we extensively used our analytical approach to the global magnetic field topology of magnetic clouds (MCs), introduced in a previous paper, in order to show its potential and to study its physical consistency. The model assumes toroidal topology with a non-uniform (variable maximum radius) cross-section along them. Moreover, it has a non-force-free character and also includes the expansion of its cross-section. As is shown, the model allows us, first, to analyze MC magnetic structures-determining their physical parameters-with a variety of magnetic field shapes, and second, to reconstruct their relative orientation in the interplanetary medium from the observations obtained by several spacecraft. Therefore, multipoint spacecraft observations give the opportunity to infer the structure of this large-scale magnetic flux rope structure in the solar wind. For these tasks, we use data from Helios (A and B), STEREO (A and B), and Advanced Composition Explorer. We show that the proposed analytical model can explain quite well the topology of several MCs in the interplanetary medium and is a good starting point for understanding the physical mechanisms under these phenomena.

  9. Evidence linking coronal mass ejections with interplanetary magnetic clouds

    NASA Technical Reports Server (NTRS)

    Wilson, R. M.; Hildner, E.

    1983-01-01

    Using proxy data for the occurrence of those mass ejections from the solar corona which are directed earthward, we investigate the association between the post-1970 interplanetary magnetic clouds of Klein and Burlaga and coronal mass ejections. The evidence linking magnetic clouds following shocks with coronal mass ejections is striking; six of nine clouds observed at Earth were preceded an appropriate time earlier by meter-wave type II radio bursts indicative of coronal shock waves and coronal mass ejections occurring near central meridian. During the selected periods when no clouds were detected near Earth, the only type II bursts reported were associated with solar activity near the limbs. Where the proxy solar data to be sought are not so clearly suggested, that is, for clouds preceding interaction regions and clouds within cold magnetic enhancements, the evidence linking the clouds and coronal mass ejections is not as clear; proxy data usually suggest many candidate mass-ejection events for each cloud. Overall, the data are consistent with and support the hypothesis suggested by Klein and Burlaga that magnetic clouds observed with spacecraft at 1 AU are manifestations of solar coronal mass ejection transients.

  10. OH Zeeman Studies of Magnetic Field Strengths in Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Thompson, Kristen L.; Troland, Thomas H.; Heiles, Carl E.

    2016-01-01

    Although stars have long been known to form in the gravitational collapse of molecular clouds, the details of the formation process are not well understood. There are many questions surrounding the formation mechanism of the clouds and the timescales on which they collapse. Star formation within the Galaxy has been found to be extremely inefficient, with stars forming at only 1-3% of the expected rate. Multiple theories addressing this inefficiency have emerged, placing varying degrees of emphasis on the magnetic fields and turbulence within the interstellar medium. One major difference in leading theories is the strength of the magnetic fields permeating the clouds and the extent to which they can provide support against cloud collapse. One way to determine the effect of magnetic fields is to determine the ratio between the gravitational and magnetic energies, called the mass-to-flux ratio, within the clouds to determine whether they are magnetically subcritical or supercritical. Much work has been done to determine this ratio in the cores of molecular clouds, but little is currently known about the fields in the envelopes of the clouds where most of the mass resides. We present the results of an extensive observational survey aimed at characterizing the fields in molecular clouds as a whole. We use the Arecibo telescope to determine mass-to-flux ratios in clouds distributed throughout the sky via the Zeeman effect in 18 cm OH absorption lines. This statistical study provides magnetic field and mass-to-flux results for 41 clouds located along 22 lines-of-sight. We find the first evidence for subcritical molecular gas along individual lines-of-sight, and a statistical analysis suggests that the mass-to-flux ratio in the envelopes of molecular clouds is approximately critical overall.

  11. Multi-tube model for interplanetary magnetic clouds

    NASA Astrophysics Data System (ADS)

    Osherovich, Vladimir A.; Fainberg, J.; Stone, R. G.

    Measurements of the polytropic index γ inside a magnetic cloud showed that there are two non-equal tubes inside the cloud [Fainberg et al., 1996; Osherovich et al., 1997]. For both tubes, γ < 1, but each tube has its own polytrope. We test equilibrium solutions which are a superposition of solutions with cylindrical and helical symmetry [Krat and Osherovich, 1978] as a new paradigm for a multi-tube model. Comparison of magnetic and gas pressure profiles for these bounded MHD states with observations suggests that complex magnetic clouds can be viewed as multiple helices embedded in a cylindrically symmetric flux rope.

  12. A Global Magnetic Topology Model for Magnetic Clouds. IV.

    NASA Astrophysics Data System (ADS)

    Hidalgo, M. A.

    2016-05-01

    In the first paper of this series, we introduced a global topology model for the study of magnetic clouds (MCs), fitting it to the experimental magnetic field components and obtaining, for example, the orientation of the axis of the MCs in the interplanetary medium. In the third paper, we extended the model to include theoretical hydrostatic plasma pressure, also incorporating it in the fitting procedure. The present work is complementary to the previous ones, now incorporating the proton current density as deduced from the continuity equation. In particular, we are interested in the component of the proton current density parallel to the magnetic field lines of the MC, {\\boldsymbol{j}} \\parallel , because the perpendicular component is expected to have information similar to the plasma pressure. Under all of these conditions, our fitting procedure now involves simultaneous analysis of the three components of the magnetic field, the trace of the plasma pressure, and the parallel proton current density. This provides us with more information about the physical mechanisms taking place inside MCs, thus helping us to understand the propagation and evolution of these structures in the interplanetary medium.

  13. The heliospheric sector boundary as a distented magnetic cloud

    NASA Technical Reports Server (NTRS)

    Crooker, N. U.; Intriligator, D. S.

    1995-01-01

    A magnetic cloud was detected both near Earth and by Pioneer 11 located 43 deg east of Earth at 4.8 AU. The magnetic field within the cloud rotated smoothly from toward to away polarity, marking sector boundary passage. Interpreted as a flux rope, the cloud had a vertical axis, implying that its cylindrical cross-section in the ecliptic plane was distended along the sector boundary by at least 43, forming an extensive occlusion in the heliospheric current sheet. At 1 AU the cloud had plasma signatures typical of a fast coronal mass ejection with low temperature and a leading shock. In contrast, at 4.8 AU, only the cloud signature remained. Its radial dimension was the same at both locations, consistent with little expansion beyond 1 AU. Energetic particle data at 4.8 AU show high fluxes preceding the cloud but not extending forward to the corotating shock that marked entry into the interaction region containing the cloud. The streaming direction was antisunward, consistent with possible acceleration in a low-beta region of field line draping around the cloud's western (upstream) end. The fluxes dropped upon entry into the cloud and became essentially isotropic one third of the way through it. On the basis of sector boundary characteristics published in the past, we suggest that distended clouds may be common heliospheric current sheet occlusions.

  14. Spiral structures and regularities in magnetic field variations and auroras

    NASA Astrophysics Data System (ADS)

    Feldstein, Y. I.; Gromova, L. I.; Förster, M.; Levitin, A. E.

    2012-02-01

    The conception of spiral shaped precipitation regions, where solar corpuscles penetrate the upper atmosphere, was introduced into geophysics by C. Störmer and K. Birkeland at the beginning of the last century. Later, in the course of the XX-th century, spiral distributions were disclosed and studied in various geophysical phenomena. Most attention was devoted to spiral shapes in the analysis of regularities pertaining to the geomagnetic activity and auroras. We review the historical succession of perceptions about the number and positions of spiral shapes, that characterize the spatial-temporal distribution of magnetic disturbances. We describe the processes in the upper atmosphere, which are responsible for the appearance of spiral patterns. We considered the zones of maximal aurora frequency and of maximal particle precipitation intensity, as offered in the literature, in their connection with the spirals. We discuss the current system model, that is closely related to the spirals and that appears to be the source for geomagnetic field variations during magnetospheric substorms and storms. The currents in ionosphere and magnetosphere constitute together with field-aligned (along the geomagnetic field lines) currents (FACs) a common 3-D current system. At ionospheric heights, the westward and eastward electrojets represent characteristic elements of the current system. The westward electrojet covers the longitudinal range from the morning to the evening hours, while the eastward electrojet ranges from afternoon to near-midnight hours. The polar electrojet is positioned in the dayside sector at cusp latitudes. All these electrojets map along the magnetic field lines to certain plasma structures in the near-Earth space. The first spiral distribution of auroras was found based on observations in Antarctica for the nighttime-evening sector (N-spiral), and later in the nighttime-evening (N-spiral) and morning (M-spiral) sectors both in the Northern and Southern

  15. Simulation of Electron Cloud Multipacting in Solenoidal Magnetic Field

    SciTech Connect

    Novokhatski, A

    2004-01-27

    A simulation algorithm is based on a numerical solution of the Vlasov equation for the distribution function of an electron cloud density in a cylindrical vacuum chamber with solenoidal magnetic field. The algorithm takes into consideration space charge effects. This approach improves the simulation of multipacting effects as it is free of statistical fluctuations. Simulation studies were carried for the SLAC B-factory vacuum chamber for different bunch patterns and solenoidal field strength. Space charge and the magnetic field limit the maximum density of the electron cloud. Magnetic resonant damping of multipacting was found in special cases of positron beam parameters and magnetic field amplitude.

  16. Self-similar evolution of interplanetary magnetic clouds and Ulysses measurements of the polytropic index inside the cloud

    NASA Technical Reports Server (NTRS)

    Osherovich, Vladimir A.; Fainberg, J.; Stone, R. G.; MacDowall, R. J.; Berdichevsky, D.

    1997-01-01

    A self similar model for the expanding flux rope is developed for a magnetohydrodynamic model of interplanetary magnetic clouds. It is suggested that the dependence of the maximum magnetic field on the distance from the sun and the polytropic index gamma has the form B = r exp (-1/gamma), and that the ratio of the electron temperature to the proton temperature increases with distance from the sun. It is deduced that ion acoustic waves should be observed in the cloud. Both predictions were confirmed by Ulysses observations of a 1993 magnetic cloud. Measurements of gamma inside the cloud demonstrate sensitivity to the internal topology of the magnetic field in the cloud.

  17. DISPERSION OF MAGNETIC FIELDS IN MOLECULAR CLOUDS. II

    SciTech Connect

    Houde, Martin; Chitsazzadeh, Shadi; Vaillancourt, John E.; Hildebrand, Roger H.; Kirby, Larry

    2009-12-01

    We expand our study on the dispersion of polarization angles in molecular clouds. We show how the effect of signal integration through the thickness of the cloud as well as across the area subtended by the telescope beam inherent to dust continuum measurements can be incorporated in our analysis to correctly account for its effect on the measured angular dispersion and inferred turbulent to large-scale magnetic field strength ratio. We further show how to evaluate the turbulent magnetic field correlation scale from polarization data of sufficient spatial resolution and high enough spatial sampling rate. We apply our results to the molecular cloud OMC-1, where we find a turbulent correlation length of delta approx 16 mpc, a turbulent to large-scale magnetic field strength ratio of approximately 0.5, and a plane-of-the-sky large-scale magnetic field strength of approximately 760 muG.

  18. Full particle orbit effects in regular and stochastic magnetic fields

    NASA Astrophysics Data System (ADS)

    Ogawa, Shun; Cambon, Benjamin; Leoncini, Xavier; Vittot, Michel; del Castillo-Negrete, Diego; Dif-Pradalier, Guilhem; Garbet, Xavier

    2016-07-01

    We present a numerical study of charged particle motion in a time-independent magnetic field in cylindrical geometry. The magnetic field model consists of an unperturbed reversed-shear (non-monotonic q-profile) helical part and a perturbation consisting of a superposition of modes. Contrary to most of the previous studies, the particle trajectories are computed by directly solving the full Lorentz force equations of motion in a six-dimensional phase space using a sixth-order, implicit, symplectic Gauss-Legendre method. The level of stochasticity in the particle orbits is diagnosed using averaged, effective Poincare sections. It is shown that when only one mode is present, the particle orbits can be stochastic even though the magnetic field line orbits are not stochastic (i.e., fully integrable). The lack of integrability of the particle orbits in this case is related to separatrix crossing and the breakdown of the global conservation of the magnetic moment. Some perturbation consisting of two modes creates resonance overlapping, leading to Hamiltonian chaos in magnetic field lines. Then, the particle orbits exhibit a nontrivial dynamics depending on their energy and pitch angle. It is shown that the regions where the particle motion is stochastic decrease as the energy increases. The non-monotonicity of the q-profile implies the existence of magnetic ITBs (internal transport barriers) which correspond to shearless flux surfaces located in the vicinity of the q-profile minimum. It is shown that depending on the energy, these magnetic ITBs might or might not confine particles. That is, magnetic ITBs act as an energy-dependent particle confinement filter. Magnetic field lines in reversed-shear configurations exhibit topological bifurcations (from homoclinic to heteroclinic) due to separatrix reconnection. We show that a similar but more complex scenario appears in the case of particle orbits that depend in a non-trivial way on the energy and pitch angle of the

  19. Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields

    NASA Astrophysics Data System (ADS)

    Magnet, C.; Kuzhir, P.; Bossis, G.; Meunier, A.; Nave, S.; Zubarev, A.; Lomenech, C.; Bashtovoi, V.

    2014-03-01

    When a micron-sized magnetizable particle is introduced into a suspension of nanosized magnetic particles, the nanoparticles accumulate around the microparticle and form thick anisotropic clouds extended in the direction of the applied magnetic field. This phenomenon promotes colloidal stabilization of bimodal magnetic suspensions and allows efficient magnetic separation of nanoparticles used in bioanalysis and water purification. In the present work, the size and shape of nanoparticle clouds under the simultaneous action of an external uniform magnetic field and the flow have been studied in detail. In experiments, a dilute suspension of iron oxide nanoclusters (of a mean diameter of 60 nm) was pushed through a thin slit channel with the nickel microspheres (of a mean diameter of 50 μm) attached to the channel wall. The behavior of nanocluster clouds was observed in the steady state using an optical microscope. In the presence of strong enough flow, the size of the clouds monotonically decreases with increasing flow speed in both longitudinal and transverse magnetic fields. This is qualitatively explained by enhancement of hydrodynamic forces washing the nanoclusters away from the clouds. In the longitudinal field, the flow induces asymmetry of the front and the back clouds. To explain the flow and the field effects on the clouds, we have developed a simple model based on the balance of the stresses and particle fluxes on the cloud surface. This model, applied to the case of the magnetic field parallel to the flow, captures reasonably well the flow effect on the size and shape of the cloud and reveals that the only dimensionless parameter governing the cloud size is the ratio of hydrodynamic-to-magnetic forces—the Mason number. At strong magnetic interactions considered in the present work (dipolar coupling parameter α ≥2), the Brownian motion seems not to affect the cloud behavior.

  20. Regularities in temperature, magnetic field and pressure effect on the resistive properties of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Polyakov, P. I.; Kucherenko, S. S.

    2002-08-01

    The influence of hydrostatic pressure, magnetic field and temperature on resistivity behaviour of bulk and film samples La 0.9Mn 1.1O 3 and La 0.56Ca 0.24Mn 1.2O 3 at action of magnetic field and temperature has been analysed. It is established that the maximum of magnetoresistive and the revealed baroresistive, magnetobaroresistive effects coincide at the same temperature Tpp. This temperature is equal to the "metal-semiconductor" phase transition temperature Tms. "Cooling" and "heating" effects of pressure and magnetic field have been revealed. A mutual correspondence of T- P- H (6.2 K, 1 kbar, 2.7 kOe) influence on polycrystalline sample La 0.9Mn 1.1O 3 resistivity has been determined. The linear change of Tms( P) and Tms( H) in La 0.9Mn 1.1O 3, La 0.56Ca 0.24Mn 1.2O 3 resistivity have been found. An importance of the regularities of elastic-deforming correspondence of T- H- P influence on magnetic, resistivity properties, phase transitions and effects was elucidated and explained. An alternating influence of T- H- P and its role in resistivity has been pointed. A correlation between structural, elastic and resistive properties is specified.

  1. Beam induced electron cloud resonances in dipole magnetic fields

    NASA Astrophysics Data System (ADS)

    Calvey, J. R.; Hartung, W.; Makita, J.; Venturini, M.

    2016-07-01

    The buildup of low energy electrons in an accelerator, known as electron cloud, can be severely detrimental to machine performance. Under certain beam conditions, the beam can become resonant with the cloud dynamics, accelerating the buildup of electrons. This paper will examine two such effects: multipacting resonances, in which the cloud development time is resonant with the bunch spacing, and cyclotron resonances, in which the cyclotron period of electrons in a magnetic field is a multiple of bunch spacing. Both resonances have been studied directly in dipole fields using retarding field analyzers installed in the Cornell Electron Storage Ring. These measurements are supported by both analytical models and computer simulations.

  2. MAGNETIZED GAS IN THE SMITH HIGH VELOCITY CLOUD

    SciTech Connect

    Hill, Alex S.; McClure-Griffiths, Naomi M.; Mao, S. A.; Benjamin, Robert A.; Lockman, Felix J. E-mail: naomi.mcclure-griffiths@csiro.au E-mail: benjamir@uww.edu

    2013-11-01

    We report the first detection of magnetic fields associated with the Smith High Velocity Cloud. We use a catalog of Faraday rotation measures toward extragalactic radio sources behind the Smith Cloud, new H I observations from the Robert C. Byrd Green Bank Telescope, and a spectroscopic map of Hα from the Wisconsin H-Alpha Mapper Northern Sky Survey. There are enhancements in rotation measure (RM) of ≈100 rad m{sup –2} which are generally well correlated with decelerated Hα emission. We estimate a lower limit on the line-of-sight component of the field of ≈8 μG along a decelerated filament; this is a lower limit due to our assumptions about the geometry. No RM excess is evident in sightlines dominated by H I or Hα at the velocity of the Smith Cloud. The smooth Hα morphology of the emission at the Smith Cloud velocity suggests photoionization by the Galactic ionizing radiation field as the dominant ionization mechanism, while the filamentary morphology and high (≈1 Rayleigh) Hα intensity of the lower-velocity magnetized ionized gas suggests an ionization process associated with shocks due to interaction with the Galactic interstellar medium. The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the Galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas.

  3. Two Models of Magnetic Support for Photoevaporated Molecular Clouds

    SciTech Connect

    Ryutov, D; Kane, J; Mizuta, A; Pound, M; Remington, B

    2004-05-05

    The thermal pressure inside molecular clouds is insufficient for maintaining the pressure balance at an ablation front at the cloud surface illuminated by nearby UV stars. Most probably, the required stiffness is provided by the magnetic pressure. After surveying existing models of this type, we concentrate on two of them: the model of a quasi-homogeneous magnetic field and the recently proposed model of a ''magnetostatic turbulence''. We discuss observational consequences of the two models, in particular, the structure and the strength of the magnetic field inside the cloud and in the ionized outflow. We comment on the possible role of reconnection events and their observational signatures. We mention laboratory experiments where the most significant features of the models can be tested.

  4. Probing the magnetic topologies of magnetic clouds by means of solar energetic particles

    SciTech Connect

    Kahler, S.W. ); Reames, D.V. )

    1991-06-01

    Magnetic clouds are large (<0.25 AU) interplanetary regions with topologies consistent with those of magnetic loops. They are of interest because they may be an interplanetary signature of coronal mass ejections. Clouds have been identified in solar wind data by their magnetic properties and by the presence of bidirectional particle fluxes. Two possible closed magnetic topologies have been considered for clouds: (1) an elongated bottle with field lines rooted at both ends in the Sun and (2) a detached magnetic bubble or plasmoid consisting of closed field lines. The inferred topologies are also consistent with open field lines that converge beyond 1 AU. The authors have used solar energetic particles (SEPs) as probes of the cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the Sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

  5. DISPERSION OF MAGNETIC FIELDS IN MOLECULAR CLOUDS. I

    SciTech Connect

    Hildebrand, Roger H.; Kirby, Larry; Dotson, Jessie L.; Houde, Martin; Vaillancourt, John E.

    2009-05-01

    We describe a method for determining the dispersion of magnetic field vectors about large-scale fields in turbulent molecular clouds. The method is designed to avoid inaccurate estimates of magnetohydrodynamic or turbulent dispersion-and help avoiding inaccurate estimates of field strengths-due to a large-scale, nonturbulent field structure when using the well known method of Chandrasekhar and Fermi. Our method also provides accurate, independent estimates of the turbulent to large-scale magnetic field strength ratio. We discuss applications to the molecular clouds OMC-1, M17, and DR21(Main)

  6. Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud

    NASA Astrophysics Data System (ADS)

    Galyardt, Jason; Shelton, Robin L.

    2016-01-01

    The Galaxy’s population of High Velocity Clouds (HVCs) may include a subpopulation that is confined by dark matter minihalos and falling toward the Galactic disk. We present the first magnetohydrodynamic simulational study of dark-matter-dominated HVCs colliding with a weakly magnetized galactic disk. Our HVCs have baryonic masses of 5 × 106M⊙ and dark matter minihalo masses of 0, 3 × 108, or 1 × 109 M⊙. They are modeled on the Smith Cloud, which is said to have collided with the disk 70 Myr ago. We find that, in all cases, the cloud’s collision with the galactic disk creates a hole in the disk, completely disperses the cloud, and forms a bubble-shaped structure on the far side of the disk. In contrast, when present, the dark matter minihalo continues unimpeded along its trajectory. Later, as the minihalo passes through the bubble structure and galactic halo, it accretes up to 6.0 × 105 M⊙ in baryonic material, depending on the strengths of the magnetic field and minihalo gravity. These simulations suggest that if the Smith Cloud is associated with a dark matter minihalo and collided with the Galactic disk, the minihalo has accreted the observed gas. However, if the Smith Cloud is dark-matter-free, it is on its first approach toward the disk. These simulations also suggest that the dark matter is most concentrated either at the head of the cloud or near the cloud, depending upon the strength of the magnetic field, a point that could inform indirect dark matter searches.

  7. The magnetic field of cloud 3 in L204

    SciTech Connect

    Cashman, Lauren R.; Clemens, D. P. E-mail: clemens@bu.edu

    2014-10-01

    The L204 dark cloud complex is a nearby filamentary structure in Ophiuchus North that has no signs of active star formation. Past studies show that L204 is interacting with the nearby runaway O star, ζ Oph, and hosts a magnetic field that is coherent across parsec-length scales. Near-infrared H-band (1.6 μm) linear polarization measurements were obtained for 3896 background stars across a 1° × 1.°5 region centered on the dense Cloud 3 in L204, using the Mimir near-infrared instrument on the 1.8 m Perkins Telescope. Analysis of these observations reveals both large-scale properties and small-scale changes in the magnetic field direction in Cloud 3. In the northern and western ζ Oph facing regions of the cloud, the magnetic field appears to be pushed up against the face of the cloud. This may indicate that the UV flux from ζ Oph has compressed the magnetic field on the western edge of L204. The plane-of-sky magnetic field strength is estimated to be ∼11-26 μG using the Chandrasekhar-Fermi method. The polarimetry data also reveal that the polarization efficiency (PE ≡ P {sub H}/A {sub V}) steadily decreases with distance from ζ Oph (–0.09% ± 0.03% mag{sup –1} pc{sup –1}). Additionally, power-law fits of PE versus A {sub V} for localized samples of probe stars show steeper negative indices with distance from ζ Oph. Both findings highlight the importance of external illumination, here from ζ Oph, in aligning dust grains to embedded magnetic fields.

  8. A Study of Magnetic Fields on Bright-Rimmed Clouds

    NASA Astrophysics Data System (ADS)

    Kusune, Takayoshi; Sugitani, Koji

    2015-08-01

    Bright-rimmed clouds (BRCs), which are located at periphery of HII regions, are considered to be potential sites for induced star formation by UV radiation from nearby massive stars. Many theorists have developed 2D/3D hydrodynamical models to understand dynamical evolution of such molecular clouds. Most simulations, however, did not always include the magnetic field effect, which is of importance in the astrophysics. This is because that there are few observation results examining the magnetic field configuration of BRCs in detail. In order to obtain information on magnetic field in and around BRCs, we have made near-infrared (JHKs) imaging polarimetry toward 24 BRCs showing strong interaction with HII region (Urquhart et al. 2009). We used the imaging polarimeter SIRPOL/SIRIUS (FOV ~7.7’ x 7.7’) mounted on IRSF 1.4 m telescope at the South African Astronomical Observatory.We found that polarization vectors, i.e., magnetic fields inside the clouds, follow the curved bright rim just behind the bright rim for almost all of the observed BRCs. Our investigation into the relation between the ambient magnetic field direction and the UV radiation direction suggests a following tendency. In the case that the ambient magnetic field is perpendicular to the direction of incident UV radiation, the clouds are likely to have bright rims with small curvatures. On the other hand, in the case that the ambient field is parallel to the UV radiation, they would have those with larger curvatures. In this presentation, we will present the physical quantities for these BRCs (i.e., magnetic field strength, the post shock pressure by the ionization front, etc.) as well as these morphological results.

  9. Anisotropic Formation of Magnetized Cores in Turbulent Clouds

    NASA Astrophysics Data System (ADS)

    Chen, Che-Yu; Ostriker, Eve C.

    2015-09-01

    In giant molecular clouds (GMCs), shocks driven by converging turbulent flows create high-density, strongly magnetized regions that are locally sheetlike. In previous work, we showed that within these layers, dense filaments and embedded self-gravitating cores form by gathering material along the magnetic field lines. Here, we extend the parameter space of our three-dimensional, turbulent MHD core formation simulations. We confirm the anisotropic core formation model we previously proposed and quantify the dependence of median core properties on the pre-shock inflow velocity and upstream magnetic field strength. Our results suggest that bound core properties are set by the total dynamic pressure (dominated by large-scale turbulence) and thermal sound speed cs in GMCs, independent of magnetic field strength. For models with a Mach number between 5 and 20, the median core masses and radii are comparable to the critical Bonnor-Ebert mass and radius defined using the dynamic pressure for Pext. Our results correspond to Mcore=1.2cs4 (G3ρ0v02)-1/2 and Rcore=0.34 cs2 (Gρ0v02)-1/2 for ρ0 and v0 the large-scale mean density and velocity. For our parameter range, the median Mcore 0.1-1M⊙, but a very high pressure cloud could have lower characteristic core mass. We find cores and filaments form simultaneously, and filament column densities are a factor of 2 greater than the surrounding cloud when cores first collapse. We also show that cores identified in our simulations have physical properties comparable to those observed in the Perseus cloud. Superthermal cores in our models are generally also magnetically supercritical, suggesting that the same may be true in observed clouds.

  10. MAGNETIC FIELDS IN HIGH-MASS INFRARED DARK CLOUDS

    SciTech Connect

    Pillai, T.; Kauffmann, J.; Tan, J. C.; Goldsmith, P. F.; Carey, S. J.; Menten, K. M.

    2015-01-20

    High-mass stars are cosmic engines known to dominate the energetics in the Milky Way and other galaxies. However, their formation is still not well understood. Massive, cold, dense clouds, often appearing as infrared dark clouds (IRDCs), are the nurseries of massive stars. No measurements of magnetic fields in IRDCs in a state prior to the onset of high-mass star formation (HMSF) have previously been available, and prevailing HMSF theories do not consider strong magnetic fields. Here, we report observations of magnetic fields in two of the most massive IRDCs in the Milky Way. We show that IRDCs G11.11–0.12 and G0.253+0.016 are strongly magnetized and that the strong magnetic field is as important as turbulence and gravity for HMSF. The main dense filament in G11.11–0.12 is perpendicular to the magnetic field, while the lower density filament merging onto the main filament is parallel to the magnetic field. The implied magnetic field is strong enough to suppress fragmentation sufficiently to allow HMSF. Other mechanisms reducing fragmentation, such as the entrapment of heating from young stars via high-mass surface densities, are not required to facilitate HMSF.

  11. Regular and chaotic dynamics of magnetization precession in ferrite-garnet films

    NASA Astrophysics Data System (ADS)

    Shutyĭ, Anatoliy M.; Sementsov, Dmitriy I.

    2009-03-01

    By numerically solving equations of motion and constructing the spectrum of Lyapunov exponents, nonlinear dynamics of uniformly precessing magnetization in (110) thin film structures with perpendicular magnetic bias is investigated over a wide frequency range of the alternating field. Bifurcational changes in magnetization precession and the states of dynamical bistability are discovered. Conditions for the realization of high-amplitude regular and chaotic dynamic regimes are revealed. The possibility of controlling those precession regimes by using external magnetic fields is shown. The features of time analogs of the Poincaré section of trajectories in the chaotic regimes are studied.

  12. Ionization-regulated star formation in magnetized molecular clouds

    NASA Astrophysics Data System (ADS)

    Pudritz, Ralph E.; Silk, Joseph

    1987-05-01

    The authors present a theory for the early evolution of contracting magnetized flattened clouds in molecular clouds which undergo magnetic braking and field slip (ambipolar diffusion). If magnetic torques are the means by which angular momentum is removed from disks, then accretion rates and protostellar masses depend on how efficient braking is with respect to field line slip and hence can depend sensitively on ionization conditions. The authors discuss homologously evolving structures and calculate the evolution of the disk rotation frequency, toroidal field, accretion velocity, accretion rate, and core mass. It is found that cores which accrete out of very weakly ionized pancakes may have their masses increased by factors of 5 - 10 by increasing the ionization rate of the material by a decade.

  13. Gas Dynamics and Magnetic Fields in Infrared Dark Clouds

    NASA Astrophysics Data System (ADS)

    Pillai, T.

    2016-05-01

    Almost two decades ago, the discovery of a handful of Infrared Dark Clouds (IRDCs) heralded a new avenue for exploring the elusive early phases of massive star formation (Egan et al. 1998). Since then tremendous progress has been made in our understanding of these clouds. It is now well established that IRDCs are ubiquitous and harbor a broad spectrum of star forming stages. Thus studies of star formation and IRDCs are intricately tied together. I summarize some of the recent progress in understanding the magnetic field structure and gas dynamics in IRDCs in the context of high-mass star formation formation.

  14. Magnetic Field Structure of the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Magalhaes, A. M.; Margoniner, V. E.; Pereyra, A.; Rodrigues, C. V.; Coyne, G. V.

    1996-05-01

    We describe an on-going observational program to determine the magnetic field structure of the Small Magellanic Cloud (SMC). The project employs CCD images which allow the determination of the linear polarization of a large number of stars in each field. The data are being collected at the CTIO 1.5m telescope using a visitor polarimetry unit on the direct CCD camera. The data are been gathered mainly in the Northeast and Wing sections of the SMC. These regions have been presumably affected by past interactions with the Large Magellanic Cloud. Support by FAPESP, CNPq, CAPES and USP is gratefully acknowledged.

  15. PROBING PRIMORDIAL MAGNETIC FIELDS USING Ly{alpha} CLOUDS

    SciTech Connect

    Pandey, Kanhaiya L.; Sethi, Shiv K.

    2013-01-01

    From previous studies of the effect of primordial magnetic fields on early structure formation, we know that the presence of primordial magnetic fields during early structure formation could induce more perturbations at small scales (at present 1-10 h {sup -1} Mpc) as compared to the usual {Lambda}CDM theory. Matter power spectra over these scales are effectively probed by cosmological observables such as shear correlation and Ly{alpha} clouds. In this paper we discuss the implications of primordial magnetic fields on the distribution of Ly{alpha} clouds. We simulate the line-of-sight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Ly{alpha} opacity for this case and compare our theoretical estimates of Ly{alpha} opacity with the existing data to constrain the parameters of the primordial magnetic fields. We also discuss the case when the two density fields are correlated. Our analysis yields an upper bound of roughly 0.3-0.6 nG on the magnetic field strength for a range of nearly scale-invariant models, corresponding to a magnetic field power spectrum index n {approx_equal} -3.

  16. Regular nonminimal magnetic black holes in spacetimes with a cosmological constant

    NASA Astrophysics Data System (ADS)

    Balakin, Alexander B.; Lemos, José P. S.; Zayats, Alexei E.

    2016-01-01

    We consider new regular exact spherically symmetric solutions of a nonminimal Einstein-Yang-Mills theory with a cosmological constant and a gauge field of magnetic Wu-Yang type. The most interesting solutions found are black holes with metric and curvature invariants that are regular everywhere, i.e., regular black holes. We set up a classification of the solutions according to the number and type of horizons. The structure of these regular black holes is characterized by four specific features: a small cavity in the neighborhood of the center, a repulsion barrier off the small cavity, a distant equilibrium point, in which the metric function has a minimum, and a region of Newtonian attraction. Depending on the sign and value of the cosmological constant, the solutions are asymptotically de Sitter (dS), asymptotically flat, or asymptotically anti-de Sitter (AdS).

  17. Magnetic Field Generation During the Collision of Narrow Plasma Clouds

    NASA Astrophysics Data System (ADS)

    Sakai, Jun-ichi; Kazimura, Yoshihiro; Haruki, Takayuki

    1999-06-01

    We investigate the dynamics of the collision of narrow plasma clouds,whose transverse dimension is on the order of the electron skin depth.A 2D3V (two dimensions in space and three dimensions in velocity space)particle-in-cell (PIC) collisionless relativistic code is used toshow the generation of a quasi-staticmagnetic field during the collision of narrow plasma clouds both inelectron-ion and electron-positron (pair) plasmas. The localizedstrong magnetic fluxes result in the generation of the charge separationwith complicated structures, which may be sources of electromagneticas well as Langmuir waves. We also present one applicationof this process, which occurs during coalescence of magnetic islandsin a current sheet of pair plasmas.

  18. Magnetic clouds in the Earth's magnetosheath: a statistical study

    NASA Astrophysics Data System (ADS)

    Turc, Lucile; Fontaine, Dominique; Kilpua, Emilia; Escoubet, Philippe

    2016-04-01

    Magnetic clouds (MCs) are highly geoeffective solar wind transients. In the interplanetary space, they possess a well-defined magnetic structure, characterised by an enhanced and smoothly rotating magnetic field. We examine here whether their magnetic structure is modified when they encounter the outer regions of the geospace, namely the bow shock and the magnetosheath. Significant changes in the magnetic structure of MCs could in turn affect the level of geomagnetic activity they induce in the near-Earth's space. In this work, we study 82 MCs during which spacecraft observations are available simultaneously in the solar wind and in the magnetosheath. The observations inside the magnetosheath are related to the bow shock properties using a magnetosheath model (Turc et al., 2014, Ann. Geophys.). We find that the variation of an MC's magnetic field orientation from the solar wind to the magnetosheath is directly related to the encountered shock configuration. The angle between the magnetic field in the magnetosheath and that in the solar wind shows a very good correlation with the ΘBn angle (between the upstream magnetic field and the normal to the shock's surface) encountered at the bow shock's crossing. Because of its importance for the geoeffectivity, we examine how the magnetic field North-South (Bz) component is modified across the bow shock. In some cases, we find that Bz reverses in the magnetosheath. The conditions during which such reversals occur are investigated and their implications in terms of the MCs' geoeffectivity are discussed.

  19. Molecular cloud formation in high-shear, magnetized colliding flows

    NASA Astrophysics Data System (ADS)

    Fogerty, E.; Frank, A.; Heitsch, F.; Carroll-Nellenback, J.; Haig, C.; Adams, M.

    2016-08-01

    The colliding flows (CF) model is a well-supported mechanism for generating molecular clouds. However, to-date most CF simulations have focused on the formation of clouds in the normal-shock layer between head-on colliding flows. We performed simulations of magnetized colliding flows that instead meet at an oblique-shock layer. Oblique shocks generate shear in the post-shock environment, and this shear creates inhospitable environments for star formation. As the degree of shear increases (i.e. the obliquity of the shock increases), we find that it takes longer for sink particles to form, they form in lower numbers, and they tend to be less massive. With regard to magnetic fields, we find that even a weak field stalls gravitational collapse within forming clouds. Additionally, an initially oblique collision interface tends to reorient over time in the presence of a magnetic field, so that it becomes normal to the oncoming flows. This was demonstrated by our most oblique shock interface, which became fully normal by the end of the simulation.

  20. Typical Profiles and Distributions of Plasma and Magnetic Field Parameters in Magnetic Clouds at 1 AU

    NASA Astrophysics Data System (ADS)

    Rodriguez, L.; Masías-Meza, J. J.; Dasso, S.; Démoulin, P.; Zhukov, A. N.; Gulisano, A. M.; Mierla, M.; Kilpua, E.; West, M.; Lacatus, D.; Paraschiv, A.; Janvier, M.

    2016-07-01

    Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs). They are important because of their simple internal magnetic field configuration, which resembles a magnetic flux rope, and because they represent one of the most geoeffective types of solar transients. In this study, we analyze their internal structure using a superposed epoch method on 63 events observed at L1 by the Advance Composition Explorer (ACE), between 1998 and 2006. In this way, we obtain an average profile for each plasma and magnetic field parameter at each point of the cloud. Furthermore, we take a fixed time-window upstream and downstream from the MC to also sample the regions preceding the cloud and the wake trailing it. We then perform a detailed analysis of the internal characteristics of the clouds and their surrounding solar wind environments. We find that the parameters studied are compatible with log-normal distribution functions. The plasma β and the level of fluctuations in the magnetic field vector are the best parameters to define the boundaries of MCs. We find that one third of the events shows a peak in plasma density close to the trailing edge of the flux ropes. We provide several possible explanations for this result and investigate if the density peak is of a solar origin (e.g. erupting prominence material) or formed during the magnetic cloud travel from the Sun to 1 AU. The most plausible explanation is the compression due to a fast overtaking flow, coming from a coronal hole located to the east of the solar source region of the magnetic cloud.

  1. Typical Profiles and Distributions of Plasma and Magnetic Field Parameters in Magnetic Clouds at 1 AU

    NASA Astrophysics Data System (ADS)

    Rodriguez, L.; Masías-Meza, J. J.; Dasso, S.; Démoulin, P.; Zhukov, A. N.; Gulisano, A. M.; Mierla, M.; Kilpua, E.; West, M.; Lacatus, D.; Paraschiv, A.; Janvier, M.

    2016-08-01

    Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs). They are important because of their simple internal magnetic field configuration, which resembles a magnetic flux rope, and because they represent one of the most geoeffective types of solar transients. In this study, we analyze their internal structure using a superposed epoch method on 63 events observed at L1 by the Advance Composition Explorer (ACE), between 1998 and 2006. In this way, we obtain an average profile for each plasma and magnetic field parameter at each point of the cloud. Furthermore, we take a fixed time-window upstream and downstream from the MC to also sample the regions preceding the cloud and the wake trailing it. We then perform a detailed analysis of the internal characteristics of the clouds and their surrounding solar wind environments. We find that the parameters studied are compatible with log-normal distribution functions. The plasma β and the level of fluctuations in the magnetic field vector are the best parameters to define the boundaries of MCs. We find that one third of the events shows a peak in plasma density close to the trailing edge of the flux ropes. We provide several possible explanations for this result and investigate if the density peak is of a solar origin ( e.g. erupting prominence material) or formed during the magnetic cloud travel from the Sun to 1 AU. The most plausible explanation is the compression due to a fast overtaking flow, coming from a coronal hole located to the east of the solar source region of the magnetic cloud.

  2. Solar energetic particles as probes of the structures of magnetic clouds

    NASA Astrophysics Data System (ADS)

    Kahler, S. W.; Reames, D. V.

    Two possible closed magnetic topologies are considered for clouds: an elongated bottle with field lines rooted at both ends in the sun and a magnetic bubble or plasmoid consisting of closed field lines. Solar energetic particles (SEPs) are used as probes of the cloud topologies. The rapid access of SEPs to clouds in many events indicates that the cloud field lines extend back to the sun.

  3. Solar energetic particles as probes of the structures of magnetic clouds

    NASA Technical Reports Server (NTRS)

    Kahler, S. W.; Reames, D. V.

    1990-01-01

    Two possible closed magnetic topologies are considered for clouds: an elongated bottle with field lines rooted at both ends in the sun and a magnetic bubble or plasmoid consisting of closed field lines. Solar energetic particles (SEPs) are used as probes of the cloud topologies. The rapid access of SEPs to clouds in many events indicates that the cloud field lines extend back to the sun.

  4. Formation of Magnetized Prestellar Cores in Turbulent Cloud

    NASA Astrophysics Data System (ADS)

    Chen, Che-Yu; Ostriker, Eve C.; Classy Team

    2015-01-01

    In GMCs, shocks in the turbulent flow create high-density regions, in which filaments grow and then fragment gravitationally into prestellar cores. This process is influenced by the cloud's magnetic field, which is also amplified during the shock. We showed in three-dimensional simulations that in typical GMC environments, the turbulence-compressed regions are strongly-magnetized sheet-like layers. Within these layers, dense filaments and embedded self-gravitating cores form via gathering material along the magnetic field lines. As a result of the preferred-direction mass collection, velocity gradients perpendicular to the filament major axis are a common feature seen in our simulations, which is in good agreement with the most recent results from CARMA Large Area Star Formation Survey (CLASSy). From our simulations, we identified hundreds of self-gravitating cores with masses, sizes, and mass-to-magnetic flux ratios comparable to observations. We found that core masses and sizes do not depend on the coupling strength between neutrals and ions, and ambipolar diffusion is not necessary to form low-mass supercritical cores. This is a result of anisotropic contraction along field lines, which can explain the fact that magnetically supercritical cores are commonly observed even in a strongly magnetized medium. We then confirmed the anisotropic core formation model by extending the parameter space of the three-dimensional, turbulent MHD core formation simulations, and quantified how the scalings of median core properties depend on the pre-shock inflow velocity and upstream magnetic field strength.

  5. Nonlinear amplification of Langmuir waves in a plasma with regular and random magnetic fields

    NASA Astrophysics Data System (ADS)

    Krivitskii, V. S.; Priadko, Iu. M.; Tsytovich, V. N.

    1990-07-01

    The nonlinear interaction of Langmuir waves in a turbulent plasma with random resonance magnetic fields in the presence of an external regular magnetic field is investigated analytically. In particular, attention is given to the possibility of Langmuir wave amplification using the plasma maser effect. The frequency and angle dependences of the amplification increment (attenuation decrement) of Langmuir waves are determined in the isotropic case and in the presence of anisotropy. For an anisotropic particle distribution function, the amplification increment of Langmuir waves may reach values of the order of the plasma frequency.

  6. Regular and chaotic dynamics of a chain of magnetic dipoles with moments of inertia

    SciTech Connect

    Shutyi, A. M.

    2009-05-15

    The nonlinear dynamic modes of a chain of coupled spherical bodies having dipole magnetic moments that are excited by a homogeneous ac magnetic field are studied using numerical analysis. Bifurcation diagrams are constructed and used to find conditions for the presence of several types of regular, chaotic, and quasi-periodic oscillations. The effect of the coupling of dipoles on the excited dynamics of the system is revealed. The specific features of the Poincare time sections are considered for the cases of synchronous chaos with antiphase synchronization and asynchronous chaos. The spectrum of Lyapunov exponents is calculated for the dynamic modes of an individual dipole.

  7. Orientation Of Interplanetary Magnetic Clouds Associated With Filament Eruptions And Major Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Ye, P.; Zhou, G.; Wang, S.; Wang, J.

    2004-12-01

    As a major source of non-recurrent geomagnetic storms, more than half of magnetic clouds in the interplanetary medium are associated with filament eruptions [Subramanian and Dere, 2001]. The strength of south component of the magnetic field inside magnetic cloud and its duration are consider the very important factors in causing geomagnetic storm. Obviously, these factors are related to the orientation of magnetic cloud in terms of flux rope model. By investigating the observations of SOHO and ACE spacecraft from 2000 to 2003, the relationship between the orientation of interplanetary magnetic clouds which were associated with filament eruptions and major geomagnetic storms are studied. Two issues are discussed: (1) the effect of magnetic cloud's orientation on the intensity of geomagnetic storm, and (2) the possible factors in influencing the cloud's orientation. The results will be worked out.

  8. Formation of giant molecular clouds and helical magnetic fields by the Parker instability

    NASA Astrophysics Data System (ADS)

    Shibata, Kazunari; Matsumoto, Ryoji

    1991-10-01

    It is suggested that the Orion molecular cloud complex formed through the Parker instability (the buoyancy of a magnetic field entrained in matter) and that the helical filament found by Uchida et al. (1991) in the L1641 in the Orion cloud complex is the result of spinning gas falling along the magnetic field and twisting it. The twisted magnetic field, unlike a purely planar field, suppresses the Parker instability on small scales, allowing the generation of finite clouds rather than general turbulence.

  9. Interaction of a neutral cloud moving through a magnetized plasma

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.; Lu, G.

    1990-01-01

    Current collection by outgassing probes in motion relative to a magnetized plasma may be significantly affected by plasma processes that cause electron heating and cross field transport. Simulations of a neutral gas cloud moving across a static magnetic field are discussed. The authors treat a low-Beta plasma and use a 2-1/2 D electrostatic code linked with the authors' Plasma and Neutral Interaction Code (PANIC). This study emphasizes the understanding of the interface between the neutral gas cloud and the surrounding plasma where electrons are heated and can diffuse across field lines. When ionization or charge exchange collisions occur a sheath-like structure is formed at the surface of the neutral gas. In that region the crossfield component of the electric field causes the electron to E times B drift with a velocity of the order of the neutral gas velocity times the square root of the ion to electron mass ratio. In addition a diamagnetic drift of the electron occurs due to the number density and temperature inhomogeneity in the front. These drift currents excite the lower-hybrid waves with the wave k-vectors almost perpendicular to the neutral flow and magnetic field again resulting in electron heating. The thermal electron current is significantly enhanced due to this heating.

  10. Simulations of Supersonic Turbulence in Magnetized Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Kritsuk, Alexei; Ustyugov, S. D.; Norman, M. L.; Padoan, P.

    2009-01-01

    We report first results from three-dimensional numerical simulations of supersonic magnetohydrodynamic (MHD) turbulence with the Piecewise Parabolic Method on Local Stencil (PPML, Popov & Ustyugov 2008). PPML is a multi-dimensional higher-order Godunov scheme that preserves monotonicity of solutions in the vicinity of strong discontinuities, and maintains zero divergence of the magnetic field through a constrained transport approach. The method is very accurate, extremely low-dissipation, and perfectly stable for super-Alfv'enic turbulence, where many other MHD schemes experience difficulties. We solve the equations of ideal MHD in a periodic domain on Cartesian grids of up to 1024^3 points. Our models describe driven turbulence at Mach 10 and assume an isothermal equation of state to mimic the conditions in molecular clouds. We start with uniform gas density and uniform magnetic field aligned with one of the coordinate directions and apply large-scale solenoidal force to develop a saturated turbulent state in a statistical equilibrium. Depending on the initial field strength, B_0, a saturation is reached within three-to-six dynamical times of driving. We then collect the turbulence statistics and compare those for different models. As predicted by Kritsuk et al. (2007), for weak initial fields we get Kolmogorov spectra for the density-weighted velocities ρ^{1/3}u. With stronger fields, the spectra tend to get shallower, but the -5/3 scaling still appears to hold (even in these highly compressible, magnetized flows) for a combination of kinetic and magnetic variables constructed in the spirit of Politano & Pouquet (1998). We compare PDFs, structure functions, and power spectra from runs with different B_0 and discuss the signature of magnetic field in the statistical properties of molecular cloud turbulence and their role in overall flow dynamics. This research was partially supported by NSF grants AST0607675, AST0808184, and by NRAC allocation MCA07S014. We

  11. Geospace Response to a Slow Moving Unipolar Magnetic Cloud

    NASA Astrophysics Data System (ADS)

    Knipp, D. J.; Matsuo, T.; Kilcommons, L. M.; Anderson, B. J.; Korth, H.; Richmond, A. D.

    2013-12-01

    The passage at Earth of a unipolar, southward-directed magnetic cloud on 28-29 May 2010 provided a unique opportunity to investigate magnetosphere-ionosphere coupling in response to a slow-moving transient in the solar wind and the subsequent higher speed flow. Despite more than 8 hours of IMF Bz < -10 nT, the Dst Index did not intensify below -100 nT. However, there was an extraordinary 16-hour stretch with the AE index exceeding 500 nT throughout. We use magnetic perturbation data from the constellation of more than 70 Iridium satellites forming the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) and from four satellites of the Defense Meteorological Satellite Program to map the large-scale field-aligned currents during this interval. Of particular interest are: 1) the prolonged interval of AE index greater than 500 nT and 2) the dayside response to a full rotation of the interplanetary east-west (IMF By) component while the IMF is southward. During the magnetic cloud passage we are able to isolate the IMF By response without the intervening effects of solar wind pressure pulses or other IMF discontinuities. In addition to the unusual storm features, we discuss the "observational error" characteristics of the space-based magnetic field measurements incorporated into the data assimilation algorithm used in the field-aligned current mapping The independent satellite measurements allow us to quantify the uncertainty in the mapping procedure. We report on the spatial and temporal uncertainties.

  12. A comparative study among different regularization techniques for solving ill-posed magnetic inverse problem

    NASA Astrophysics Data System (ADS)

    Abdelazeem, Maha; Gobashy, Mohamed

    2015-04-01

    The magnetic inverse problem is, intrinsically, non-unique and its numerical solution is unstable. This means that any small perturbation in the data (noise) causes large variation in the solution. This ill-posedness is not only due to complex geological situations, but it may arise because of ill-conditioned kernel matrix. Procedures adopted to stabilize the inversion of ill-posed problem are called regularization, so the selection of regularization parameter is very important to invert the earth model causing the measured magnetic field. Two strategies are commonly used, techniques based on Tikhonov formula and techniques using the trust region sub-problem TRS and the controlling factor will be the radius of such region. In this study, the two categories are compared to examine the stability of solutions with noise. A MATLAB-based inversion code is implemented and tested on some synthetic total magnetic fields with different noise levels added to simulate real fields. The capability of such techniques have been further tested by applying it to real data.

  13. Magnetic Cloud Polarity and Geomagnetic Activities over Three Solar Cycles

    NASA Astrophysics Data System (ADS)

    Li, Y.; Luhmann, J.

    2006-12-01

    Interplanetary coronal mass ejections (ICMEs) that show fluxrope magnetic structures are named magnetic clouds (MCs). Majority of the MCs exhibit bipolar signature in their north-south component (Bz) in IMF measurements. The Bz component of a bipolar cloud is either NS (north first then turning south as the MC traverses the spacecraft) or SN. Studies show that the occurrence of these two types of MCs has some solar cycle dependence. However it appears to be a complex relationship as the switch between the two types of MCs is not concurrent with either the solar polar reversal or the time of the sunspot minimum when the new cycle sunspots start to appear. In this paper, we use ACE solar wind and IMF observations to obtain the most updated MC signatures and their temporal variation. In combination with our previously published results, we analyze MC polarity variations over the three solar cycles of 21, 22 and 23. Interpretations in terms of their solar sources will be attempted. On the other hand, the geomagnetic activities over the same solar cycles will be studied using geomagnetic indices. The geoeffectiveness of the MC will be evaluated in the aid of Dst indices.

  14. THE SUBMILLIMETER AND MILLIMETER EXCESS OF THE SMALL MAGELLANIC CLOUD: MAGNETIC DIPOLE EMISSION FROM MAGNETIC NANOPARTICLES?

    SciTech Connect

    Draine, B. T.; Hensley, Brandon

    2012-09-20

    The Small Magellanic Cloud (SMC) has surprisingly strong submillimeter- and millimeter-wavelength emission that is inconsistent with standard dust models, including those with emission from spinning dust. Here, we show that the emission from the SMC may be understood if the interstellar dust mixture includes magnetic nanoparticles, emitting magnetic dipole radiation resulting from thermal fluctuations in the magnetization. The magnetic grains can be metallic iron, magnetite Fe{sub 3}O{sub 4}, or maghemite {gamma}-Fe{sub 2}O{sub 3}. The required mass of iron is consistent with elemental abundance constraints. The magnetic dipole emission is predicted to be polarized orthogonally to the normal electric dipole radiation if the nanoparticles are inclusions in larger grains. We speculate that other low-metallicity galaxies may also have a large fraction of the interstellar Fe in magnetic materials.

  15. Energetic Electrons Associated with Magnetic Reconnection in the Magnetic Cloud Boundary Layer

    SciTech Connect

    Wang, Y.; Zhang, S. H.; Wei, F. S.; Feng, X. S.; Zuo, P. B.; Sun, T. R.

    2010-11-05

    Here is reported in situ observation of energetic electrons ({approx}100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi-type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy.

  16. Energetic electrons associated with magnetic reconnection in the magnetic cloud boundary layer.

    PubMed

    Wang, Y; Wei, F S; Feng, X S; Zhang, S H; Zuo, P B; Sun, T R

    2010-11-01

    Here is reported in situ observation of energetic electrons (∼100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi-type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy. PMID:21231178

  17. Turbulence-induced disc formation in strongly magnetized cloud cores

    NASA Astrophysics Data System (ADS)

    Seifried, D.; Banerjee, R.; Pudritz, R. E.; Klessen, R. S.

    2013-07-01

    We present collapse simulations of strongly magnetized, turbulent molecular cloud cores with masses ranging from 2.6 to 1000 M⊙ in order to study the influence of the initial conditions on the turbulence-induced disc formation mechanism proposed recently by Seifried et al. We find that Keplerian discs are formed in all cases independently of the core mass, the strength of turbulence or the presence of global rotation. The discs appear within a few kyr after the formation of the protostar, are 50-150 au in size, and have masses between 0.05 and a few 0.1 M⊙. During the formation of the discs the mass-to-flux ratio stays well below the critical value of 10 for Keplerian disc formation. Hence, flux-loss alone cannot explain the formation of Keplerian discs. The formation of rotationally supported discs at such early phases is rather due to the disordered magnetic field structure and due to turbulent motions in the surroundings of the discs, two effects lowering the classical magnetic braking efficiency. Binary systems occurring in the discs are mainly formed via the disc capturing mechanism rather than via disc fragmentation, which is largely suppressed by the presence of magnetic fields.

  18. Observation of Magnetic Resonances in Electron Clouds in a Positron Storage Ring

    SciTech Connect

    Pivi, M.T.F.; Ng, J.S.T.; Cooper, F.; Kharakh, D.; King, F.; Kirby, R.E.; Kuekan, B.; Spencer, Cherrill M.; Raubenheimer, T.O.; Wang, L.F.; /SLAC

    2011-08-24

    The first experimental observation of magnetic resonances in electron clouds is reported. The resonance was observed as a modulation in cloud intensity for uncoated as well as TiN-coated aluminum surfaces in the positron storage ring of the PEP-II collider at SLAC. Electron clouds frequently arise in accelerators of positively charged particles, and severely impact the machines performance. The TiN coating was found to be an effective remedy, reducing the cloud intensity by three orders of magnitude.

  19. Ulysses observations of electron and proton components in a magnetic cloud and related wave activity

    NASA Technical Reports Server (NTRS)

    Osherovich, V. A.; Fainberg, J.; Stone, R. G.; MacDowall, R. J.; Phillips, J. L.; Balogh, A.

    1995-01-01

    In addition to a smooth rotation of the magnetic field vector, magnetic clouds have a low proton temperature T(sub p). Their expansion in the solar wind leads to depletion and therefore the ion component cools down. It has been shown recently that the electron component in magnetic clouds behaves differently: when the cloud expands, electron temperature Te anti correlates with density and therefore Te increases in the cloud, creating favorable conditions for the rise of ion-acoustic waves. For the magnetic cloud observed by Ulysses on June 10 - 12, 1993 at 4.64 AU at S 32.5 deg, we present observations for both electron and proton components and related plasma wave activity. Our results confirm the anti correlation between T(sub e) and electron density and also exhibit a high ratio of T(sub e)/T(sub P) in the cloud. Since Landau damping is not effective for T(sub e)/T(sub p) much greater than 1, Doppler shifted ion acoustic waves are expected in the cloud. Calculation of ion acoustic wave frequencies in the cloud and comparison with observed wave activity confirm this expectation. As in our previous work, we show that the electron component in the cloud obeys a polytropic law with gamma is less than 1 (gamma approximately equals 0.3-0.4). The dynamics of the magnetic cloud are determined to a large degree by the dominating electron pressure.

  20. Solar energetic particles inside magnetic clouds observed with the Wind spacecraft

    NASA Astrophysics Data System (ADS)

    Mazur, J. E.; Mason, G. M.; Dwyer, J. R.; von Rosenvinge, T. T.

    Solar energetic particles can be used to probe the structure of magnetic clouds. Since impulsive flare particles are accelerated within active regions, their presence inside a magnetic cloud implies that the cloud's magnetic field connects to an active region at the sun. We report on the fluxes and composition of low energy ions inside 13 magnetic clouds observed with instrumentation on the Wind spacecraft from November 1994 to February 1997. The STEP subsystem of the EPACT experiment on Wind resolves ³He and 4He and the most abundant heavy ion species from ∼20 keV/nucleon to ∼1 MeV/nucleon. Using STEP, we are able to measure the energetic particle composition in an energy range previously unexplored in the context of magnetic clouds. We find that when STEP measured significant ion fluxes inside a cloud, they were most likely from impulsive solar flares; this was the case in 4 events. We find that the 1/10/97 magnetic cloud decreased the interplanetary fluxes of ∼100 keV/nucleon ions by a factor of ∼10² this was probably because the cloud disconnected Wind from the interplanetary particle source beyond 1 AU. In contrast, we observed particles from several impulsive solar flares inside the 10/18/95 event with fluxes ∼10³ higher than the fluxes measured inside the 1/10/97 cloud.

  1. Predicting the magnetic structure of interplanetary magnetic clouds and their sheath regions: Space weather perspective

    NASA Astrophysics Data System (ADS)

    Kilpua, Emilia

    2016-04-01

    Magnetic clouds and their turbulent sheath regions drive the majority of intense space weather storms. The magnitude and the details of the magnetic storm (timing, affected current systems, response of the high energy radiation belt electron fluxes, etc.) depend strongly on the magnetic topology of the CME flux rope and whether the sheath region makes a significant contribution. Sheath regions are particularly geoeffective due to their large-amplitude magnetic field fluctuations and high Alfven Mach numbers, which may enhance solar wind - magnetospheric coupling efficiency. In this presentation I will present examples of space weather responses driven by different CME structures to demonstrate the necessity to develop detailed prediction models/scenarios for different magnetic field configurations and characteristics. The constraints for solar observations and models will be also discussed.

  2. Probing the magnetic topologies of magnetic clouds by means of solar energetic particles. (Reannouncement with new availability information)

    SciTech Connect

    Kahler, S.W.; Reames, D.V.

    1991-06-01

    Magnetic clouds are large (<0.25 AU) interplanetary regions with topologies consistent with those of magnetic loops. They are of interest because they may be an interplanetary signature of coronal mass ejections. Clouds have been identified in solar wind data by their magnetic properties and by the presence of bidirectional particle fluxes. Two possible closed magnetic topologies have been considered for clouds: (1) an elongated bottle with field lines rooted at both ends in the Sun and (2) a detached magnetic bubble or plasmoid consisting of closed field lines. The inferred topologies are also consistent with open field lines that converge beyond 1 AU. We have used solar energetic particles (SEPs) as probes of the cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the Sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

  3. On the association of magnetic clouds with disappearing filaments. [interplanetary phenomena associated with coronal mass ejection

    NASA Technical Reports Server (NTRS)

    Wilson, R. M.; Hildner, E.

    1986-01-01

    Evidence is presented that an interplanetary magnetic cloud preceding an interaction region, observed at earth on January 24, 1974, is associated with the eruptive filament of disparition brusque (DB) near central meridian on January 18. The DB was also associated with a long-decay soft X ray transient and a long-duration gradual-rise-and-fall radio burst. To assess whether magnetic clouds are generally associated with DBs, results from statistical testing of the relation of 33 magnetic clouds (and 33 control samples without magnetic clouds) to disappearing filaments near central meridian (approximately less than 45 deg central meridian distance) are presented. The hypothesis that magnetic cloud are the 1-AU counterparts of either eruptive filaments or the coronal mass ejections which probably accompany them is supported. The major result is that disappearing filaments occur more frequently on the days when magnetic clouds are launched than on control days, a result obtained with greater than 99 pct confidence. There is a suggestion that clouds following shocks, probably launched at times of solar flares, are not as strongly associated with disappearing filaments as are clouds launched less violently.

  4. DISPERSION OF MAGNETIC FIELDS IN MOLECULAR CLOUDS. III

    SciTech Connect

    Houde, Martin; Rao, Ramprasad; Vaillancourt, John E.; Hildebrand, Roger H.

    2011-06-01

    We apply our technique on the dispersion of magnetic fields in molecular clouds to high spatial resolution Submillimeter Array polarization data obtained for Orion KL in OMC-1, IRAS 16293, and NGC 1333 IRAS 4A. We show how one can take advantage of such high-resolution data to characterize the magnetized turbulence power spectrum in the inertial and dissipation ranges. For Orion KL we determine that in the inertial range the spectrum can be approximately fitted with a power law k{sup -(2.9{+-}0.9)} and we report a value of 9.9 mpc for {lambda}{sub AD}, the high spatial frequency cutoff presumably due to turbulent ambipolar diffusion. For the same parameters we have {approx}k{sup -(1.4{+-}0.4)} and a tentative value of {lambda}{sub AD} {approx_equal} 2.2 mpc for NGC 1333 IRAS 4A, and {approx}k{sup -(1.8{+-}0.3)} with an upper limit of {lambda}{sub AD} {approx}< 1.8 mpc for IRAS 16293. We also discuss the application of the technique to interferometry measurements and the effects of the inherent spatial filtering process on the interpretation of the results.

  5. Spatio-spectral regularization to improve magnetic resonance spectroscopic imaging quantification.

    PubMed

    Laruelo, Andrea; Chaari, Lotfi; Tourneret, Jean-Yves; Batatia, Hadj; Ken, Soléakhéna; Rowland, Ben; Ferrand, Régis; Laprie, Anne

    2016-07-01

    Magnetic resonance spectroscopic imaging (MRSI) is a non-invasive technique able to provide the spatial distribution of relevant biochemical compounds commonly used as biomarkers of disease. Information provided by MRSI can be used as a valuable insight for the diagnosis, treatment and follow-up of several diseases such as cancer or neurological disorders. Obtaining accurate metabolite concentrations from in vivo MRSI signals is a crucial requirement for the clinical utility of this technique. Despite the numerous publications on the topic, accurate quantification is still a challenging problem due to the low signal-to-noise ratio of the data, overlap of spectral lines and the presence of nuisance components. We propose a novel quantification method, which alleviates these limitations by exploiting a spatio-spectral regularization scheme. In contrast to previous methods, the regularization terms are not expressed directly on the parameters being sought, but on appropriate transformed domains. In order to quantify all signals simultaneously in the MRSI grid, while introducing prior information, a fast proximal optimization algorithm is proposed. Experiments on synthetic MRSI data demonstrate that the error in the estimated metabolite concentrations is reduced by a mean of 41% with the proposed scheme. Results on in vivo brain MRSI data show the benefit of the proposed approach, which is able to fit overlapping peaks correctly and to capture metabolites that are missed by single-voxel methods due to their lower concentrations. Copyright © 2016 John Wiley & Sons, Ltd. PMID:27166741

  6. Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field.

    PubMed

    Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

    2016-04-01

    Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2×10^{3}regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra/Q=10, where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach. PMID:27176392

  7. Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field

    NASA Astrophysics Data System (ADS)

    Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

    2016-04-01

    Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q . We explored convection regimes in a parameter range, at 2 ×103regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra /Q =10 , where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.

  8. TRANSITION FROM REGULAR TO CHAOTIC CIRCULATION IN MAGNETIZED CORONAE NEAR COMPACT OBJECTS

    SciTech Connect

    Kopacek, O.; Karas, V.; Kovar, J.; StuchlIk, Z.

    2010-10-20

    Accretion onto black holes and compact stars brings material in a zone of strong gravitational and electromagnetic fields. We study dynamical properties of motion of electrically charged particles forming a highly diluted medium (a corona) in the regime of strong gravity and large-scale (ordered) magnetic field. We start our work from a system that allows regular motion, then we focus on the onset of chaos. To this end, we investigate the case of a rotating black hole immersed in a weak, asymptotically uniform magnetic field. We also consider a magnetic star, approximated by the Schwarzschild metric and a test magnetic field of a rotating dipole. These are two model examples of systems permitting energetically bound, off-equatorial motion of matter confined to the halo lobes that encircle the central body. Our approach allows us to address the question of whether the spin parameter of the black hole plays any major role in determining the degree of the chaoticness. To characterize the motion, we construct the recurrence plots (RPs) and we compare them with Poincare surfaces of section. We describe the RPs in terms of the recurrence quantification analysis, which allows us to identify the transition between different dynamical regimes. We demonstrate that this new technique is able to detect the chaos onset very efficiently and provide its quantitative measure. The chaos typically occurs when the conserved energy is raised to a sufficiently high level that allows the particles to traverse the equatorial plane. We find that the role of the black hole spin in setting the chaos is more complicated than initially thought.

  9. Diffusion of Magnetic Field and Removal of Magnetic Flux from Clouds Via Turbulent Reconnection

    NASA Astrophysics Data System (ADS)

    Santos-Lima, R.; Lazarian, A.; de Gouveia Dal Pino, E. M.; Cho, J.

    2010-05-01

    The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence reassures that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our three-dimensional MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e., without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our three-dimensional simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus, the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the

  10. EFFECTS OF MAGNETIC FIELD STRENGTH AND ORIENTATION ON MOLECULAR CLOUD FORMATION

    SciTech Connect

    Heitsch, Fabian; Hartmann, Lee W.; Stone, James M.

    2009-04-10

    We present a set of numerical simulations addressing the effects of magnetic field strength and orientation on the flow-driven formation of molecular clouds. Fields perpendicular to the flows sweeping up the cloud can efficiently prevent the formation of massive clouds but permit the buildup of cold, diffuse filaments. Fields aligned with the flows lead to substantial clouds, whose degree of fragmentation and turbulence strongly depends on the background field strength. Adding a random field component leads to a 'selection effect' for molecular cloud formation: high column densities are only reached at locations where the field component perpendicular to the flows is vanishing. Searching for signatures of colliding flows should focus on the diffuse, warm gas, since the cold gas phase making up the cloud will have lost the information about the original flow direction because the magnetic fields redistribute the kinetic energy of the inflows.

  11. Dynamics of Finite Dust Clouds in a Magnetized Anodic Plasma

    SciTech Connect

    Piel, A.; Pilch, I.; Trottenberg, T.; Koepke, M. E.

    2008-09-07

    The response to an external modulation voltage of small dust clouds confined in an anodic plasma is studied. Dust density waves are excited when the cloud is larger than a wavelength, whereas a sloshing and stretching motion is found for smaller clouds. The wave dispersion shows similarities with waveguide modes.

  12. The Evolution of Gas Clouds Falling in the Magnetized Galactic Halo: High-Velocity Clouds (HVCs) Originated in the Galactic Fountain

    NASA Astrophysics Data System (ADS)

    Kwak, Kyujin; Shelton, Robin L.; Raley, Elizabeth A.

    2009-07-01

    In the Galactic fountain scenario, supernovae and/or stellar winds propel material into the Galactic halo. As the material cools, it condenses into clouds. By using FLASH three-dimensional magnetohydrodynamic simulations, we model and study the dynamical evolution of these gas clouds after they form and begin to fall toward the Galactic plane. In our simulations, we assume that the gas clouds form at a height of z = 5 kpc above the Galactic midplane, then begin to fall from rest. We investigate how the cloud's evolution, dynamics, and interaction with the interstellar medium (ISM) are affected by the initial mass of the cloud. We find that clouds with sufficiently large initial densities (n >= 0.1 H atoms cm-3) accelerate sufficiently and maintain sufficiently large column densities as to be observed and identified as high-velocity clouds (HVCs) even if the ISM is weakly magnetized (1.3 μG). However, the ISM can provide noticeable resistance to the motion of a low-density cloud (n <= 0.01 H atoms cm-3) thus making it more probable that a low-density cloud will attain the speed of an intermediate-velocity cloud rather than the speed of an HVC. We also investigate the effects of various possible magnetic field configurations. As expected, the ISM's resistance is greatest when the magnetic field is strong and perpendicular to the motion of the cloud. The trajectory of the cloud is guided by the magnetic field lines in cases where the magnetic field is oriented diagonal to the Galactic plane. The model cloud simulations show that the interactions between the cloud and the ISM can be understood via analogy to the shock tube problem which involves shock and rarefaction waves. We also discuss accelerated ambient gas, streamers of material ablated from the clouds, and the cloud's evolution from a sphere-shaped to a disk- or cigar-shaped object.

  13. Magnetized color superconducting cold quark matter within the SU(2 ) f NJL model: A novel regularization scheme

    NASA Astrophysics Data System (ADS)

    Allen, P.; Grunfeld, A. G.; Scoccola, N. N.

    2015-10-01

    The influence of intense magnetic fields on the behavior of color superconducting cold quark matter is investigated using an SU(2 ) f Nambu-Jona-Lasinio-type model for which a novel regulation scheme is introduced. In such a scheme the contributions which are explicitly dependent on the magnetic field turn out to be finite and, thus, do not require to be regularized. As a result of this, nonphysical oscillations that might arise in the alternative regularization schemes previously used in the literature are naturally removed. In this way, a clearer interpretation of the physical oscillations is possible. The sensitivity of our results to the model parametrization is analyzed.

  14. Comparisons of Characteristics of Magnetic Clouds and Cloud-Like Structures During 1995-2012

    NASA Technical Reports Server (NTRS)

    Wu, Chin-Chun; Lepping, Ronald P.

    2015-01-01

    Using eighteen years (1995 - 2012) of solar wind plasma and magnetic field data (observed by the Wind spacecraft), solar activity (e.g. sunspot number: SSN), and the geomagnetic activity index (Dst), we have identified 168 magnetic clouds (MCs) and 197 magnetic cloud - like structures (MCLs), and we have made relevant comparisons. The following features are found during seven different periods (TP: Total period during 1995 - 2012, P1 and P2: first and second half period during 1995 - 2003 and 2004 - 2012, Q1 and Q2: quiet periods during 1995 - 1997 and 2007 - 2009, A1 and A2: active periods during 1998 - 2006 and 2010 - 2012). (1) During the total period the yearly occurrence frequency is 9.3 for MCs and 10.9 for MCLs. (2) In the quiet periods Q1 > Q1 and Q2 > Q2, but in the active periods A1 < A1 and A2 < A2. (3) The minimum Bz (Bzmin) inside of a MC is well correlated with the intensity of geomagnetic activity, Dstmin (minimum Dst found within a storm event) for MCs (with a Pearson correlation coefficient, c.c. = 0.75, and the fitting function is Dstmin = 0.90+7.78Bzmin), but Bzmin for MCLs is not well correlated with the Dst index (c.c. = 0.56, and the fitting function is Dstmin = -9.40+ 4.58 Bzmin). (4) MCs play a major role in producing geomagnetic storms: the absolute value of the average Dstmin (MC = -70 nT) for MCs associated geomagnetic storms is two times stronger than that for MCLs (MCL = -35 nT), due to the difference in the IMF (interplanetary magnetic field) strength. (5) The SSN is not correlated with MCs (TP, c.c. = 0.27), but is well associated with MCLs (TP, c.c. = 0.85). Note that the c.c. for SSN vs. P2 is higher than that for SSN vs. P2. (6) Averages of IMF, solar wind speed, and density inside of the MCs are higher than those inside of the MCLs. (7) The average of MC duration (approx. = 18.82 hours) is approx. = 20 % longer than the average of MCL

  15. Comparisons of Characteristics of Magnetic Clouds and Cloud-Like Structures During 1995 - 2012

    NASA Astrophysics Data System (ADS)

    Wu, Chin-Chun; Lepping, Ronald P.

    2015-04-01

    Using eighteen years (1995 - 2012) of solar wind plasma and magnetic field data (observed by the Wind spacecraft), solar activity ( e.g. sunspot number: SSN), and the geomagnetic-activity index (Dst), we have identified 168 magnetic clouds (MCs) and 197 magnetic-cloud-like structures (MCLs), and we have made relevant comparisons. The following features are found during seven different periods (TP: total period during 1995 - 2012, P1 and P2: first and second half-period during 1995 - 2003 and 2004 - 2012, Q1 and Q2: quiet periods during 1995 - 1997 and 2007 - 2009, A1 and A2: active periods during 1998 - 2006 and 2010 - 2012). (1) During the total period, the yearly occurrence frequency is 9.3 for MCs and 10.9 for MCLs. (2) In the quiet periods < N MCs>Q1 > < N MCLs>Q1 and < N MCs>Q2 > < N MCLs>Q2, but in the active periods < N MCs>A1 < < N MCLs>A1 and < N MCs>A2 < < N MCLs>A2. (3) The minimum Bz ( Bz min) inside of an MC is well correlated with the intensity of geomagnetic activity, Dstmin (minimum Dst found within a storm event) for MCs (with a Pearson correlation coefficient, , and the fitting function is Dstmin=0.90+7.78 Bz min), but Bz min for MCLs is not well correlated with the Dst index (, and the fitting function is Dstmin=-9.40+4.58 Bz min). (4) MCs play a major role in producing geomagnetic storms: the absolute value of the average Dstmin (MC=-70 nT) for MCs associated geomagnetic storms is twice as strong as that for MCLs (MCL=-35 nT) because of the difference in the IMF (interplanetary magnetic field) strength. (5) The SSN is uncorrelated with MCs (< N MCs>TP, ), but is well associated with MCLs (< N MCLs>TP, ). Note that the c.c. for SSN vs. < N MCs>P2 is higher than that for SSN vs. < N MCLs>P2. (6) Averages of IMF, solar wind speed, and density inside of the MCs are higher than those inside of the MCLs. (7) The average of MC duration (≈ 18.82 hours) is ≈ 20 % longer than the average of MCL duration (≈ 15.69 hours). (8) There are

  16. Zeroth order regular approximation approach to parity violating nuclear magnetic resonance shielding tensors.

    PubMed

    Nahrwold, Sophie; Berger, Robert

    2009-06-01

    In this paper, a quasirelativistic two-component zeroth order regular approximation (ZORA) density functional theory (DFT) approach to the calculation of parity violating (PV) resonance frequency differences between the nuclear magnetic resonance (NMR) spectra of enantiomers is presented and the systematics of PV NMR shielding constants in C(2)-symmetric dihydrogen dichalcogenides (H(2)X(2) with X=(17)O, (33)S, (77)Se, (125)Te, (209)Po) are investigated. The typical sin(2alpha)-like dependence of the PV NMR frequency splittings on the dihedral angle alpha is observed for the entire series. As for the scaling behavior of the effect with the nuclear charge Z of X, the previously reported Z(2.5+/-0.5) scaling in the nonrelativistic limit is reproduced and a scaling of approximately Z(3) for the paramagnetic and Z(5) for the spin-orbit coupling contribution to the frequency splitting is observed in the relativistic framework. The paramagnetic and spin-orbit coupling contributions are typically of opposite sign for the molecular structures studied herein and the maximum scaling of the total ZORA frequency splitting (i.e., the sum of the two contributions) is Z(3.9) for H(2)Po(2). Thus, an earlier claim for a spin-orbit coupling contribution scaling with up to Z(7) for H(2)Po(2) and the erratic dihedral angle dependence obtained for this compound within a four-component Dirac-Hartree-Fock-Coulomb study is not confirmed at the DFT level. The maximum NMR frequency splitting reported here is of the order of 10 mHz for certain clamped conformations of H(2)Po(2) inside a static magnetic field with magnetic flux density of 11.7 T. Frequency splittings of this size have been estimated to be detectable with present day NMR spectrometers. Thus, a NMR route toward molecular PV appears promising once suitable compounds have been identified. PMID:19508050

  17. Do the Legs of Magnetic Clouds Contain Twisted Flux-rope Magnetic Fields?

    NASA Astrophysics Data System (ADS)

    Owens, M. J.

    2016-02-01

    Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized primarily by a smooth rotation in the magnetic field direction indicative of the presence of a magnetic flux rope. Energetic particle signatures suggest MC flux ropes remain magnetically connected to the Sun at both ends, leading to widely used model of global MC structure as an extended flux rope, with a loop-like axis stretching out from the Sun into the heliosphere and back to the Sun. The time of flight of energetic particles, however, suggests shorter magnetic field line lengths than such a continuous twisted flux rope would produce. In this study, two simple models are compared with observed flux rope axis orientations of 196 MCs to show that the flux rope structure is confined to the MC leading edge. The MC “legs,” which magnetically connect the flux rope to the Sun, are not recognizable as MCs and thus are unlikely to contain twisted flux rope fields. Spacecraft encounters with these non-flux rope legs may provide an explanation for the frequent observation of non-MC ICMEs.

  18. Propagation Characteristics of CMEs Associated Magnetic Clouds and Ejecta

    NASA Astrophysics Data System (ADS)

    Kim, Roksoon; Gopalswamy, N.; Cho, K.; Moon, Y.; Yashiro, S.

    2012-05-01

    We have investigated the characteristics of magnetic cloud (MC) and ejecta (EJ) associated coronal mass ejections (CMEs) based on the assumption that all CMEs have a flux rope structure. For this, we used 54 CMEs and their interplanetary counter parts (interplanetary CMEs: ICMEs) that constitute the list of events used by the NASA/LWS Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We considered the location, angular width, speed, and direction parameter, D, that quantifies the propagation direction of a CME. For the 54 CDAW events, we found several properties of the CMEs as follows: (1) the average value of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49), which indicates that the MC-associated CMEs propagate more directly to the Earth than the EJ-associated CMEs; (2) comparison between the direction parameter and the source location shows that the majority of the MC-associated CMEs are ejected along the radial direction, while many of the EJ-associated CMEs are ejected non-radially; (3) the mean speed of MC-associated CMEs (946 km/s) is faster than that of EJ-associated CMEs (771 km/s). For seven very fast CMEs (> 1500 km/s), all CMEs with large D (> 0.4) are associated with MCs and the CMEs with small D are associated with EJs. On the basis of these results, we suggest that the CME trajectory essentially decides the observed ICME structure.

  19. An interplanetary magnetic cloud from the solar flare of November 22, 1977.

    NASA Astrophysics Data System (ADS)

    Ivanov, K. G.; Styazhkin, V. A.; Kharshiladze, A. F.

    1989-10-01

    Experimental profiles of Bx, By, and Bz, the components of the IMF, obtained by the Prognoz-6, ISEE-2, and IMP-8 satellites during their passage through a magnetic cloud from the powerful solar flare of November 22 are compared with the theoretical model of a force-free magnetic field of a diffusion pinch. It is found that qualitative agreement between theory and experiment occurs for the permissible configuration and kinematic characteristics of a circular cylinder approximating the cloud.

  20. Electron Velocity Distribution Function in Magnetic Clouds in the Solar Wind

    NASA Technical Reports Server (NTRS)

    Nieves-Chinchil, Teresa; Vinas, Adolfo F.; Bale, Stuart D.

    2006-01-01

    We present a study of the kinetic properties of the electron velocity distribution functions within magnetic clouds, since they are the dominant thermal component. The study is based on high time resolution data from the GSFC WIND/SWE electron spectrometer and the Berkeley 3DP electron plasma instruments. Recent studies on magnetic clouds have shown observational evidence of anti-correlation between the total electron density and electron temperature, which suggest a polytrope law P(sub e) = alpha(Nu(sub e) (sup gamma)) for electrons with the constant gamma approximates 0.5 < 1. This anti-correlation and small polytropic gamma-values is interpreted in the context of the presence of highly non-Maxwellian electron distributions (i.e. non-thermal) within magnetic clouds. These works suggested that the non-thermal electrons can contribute as much as 50% of the total electron pressure within magnetic clouds. We have revisited some of the magnetic cloud events previously studied and attempted to quantify the nature of the non-thermal electrons by modeling the electron velocity distribution function using a kappa distribution function to characterize the kinetic non-thermal effects. If non-thermal tail effects are the source for the anti-correlation between the moment electron temperature and density and if the kappa distribution is a reasonable representative model of non-thermal effects, then the electron velocity distribution within magnetic clouds should show indication for small K-values when gamma < 1.

  1. Some Peculiar Properties of Magnetic Clouds as Observed by the WIND Spacecraft

    NASA Technical Reports Server (NTRS)

    Berdichevsky, D.; Lepping, R. P.; Szabo, A.; Burlaga, L. F.; Thompson, B. J.; Lazarus, A. J.; Steinburg, J. T.; Mariani, F.

    1999-01-01

    We aimed at understanding the common characteristics of magnetic clouds, relevant to solar-interplanetary connections, but exceptional ones were noted and are stressed here through a short compendium. The study is based on analyses of 28 good or better events (Out of 33 candidates) as identified in WIND magnetic field and plasma data. These cloud intervals are provided by WIND-MFI's Website under the URL (http://lepmfi.gsfc.nasa.gov/mfi/mag_cloud_publ.html#table). The period covered is from early 1995 to November 1998. A force free, cylindrically symmetric, magnetic field model has been applied to the field data in usually 1-hour averaged form for the cloud analyses. Some of the findings are: (1) one small duration event turned out to have an approximately normal size which was due to a distant almost "skimming" passage by the spacecraft; (2) One truly small event was observed, where 10 min averages had to be used in the model fitting; it had an excellent model fit and the usual properties of a magnetic cloud, except it possessed a small axial magnetic flux; (3) One cloud ha a dual axial-field-polarity, in the sense that the "core" had one polarity and the annular region around it had an opposite polarity. This event also satisfied the model and with a ve3ry good chi-squared value. Some others show a hint of this dual polarity; (4) The temporal distribution of occurrence clouds over the 4 years show a dip in 1996; (5) About 50 % of the clouds had upstream shocks; any others had upstream pressure pulses; (6) The overall average speed (390 km/s) of the best 28 events is less than the normally quoted for the average solar wind speed (420 km/s) The average of central cloud speed to the upstream solar wind speed was not much greater than one (1.08), even though many of these clouds were drivers of interplanetary shocks. Cloud expansion is partly the reason for the existence of upstream shocks; (7) The cloud axes often (about 50 % of the time) revealed reasonable

  2. Simultaneous observations of solar MeV particles in a magnetic cloud and in the earth's northern tail lobe - Implications for the global field line topology of magnetic clouds and for the entry of solar particles into the magnetosphere during cloud passage

    NASA Technical Reports Server (NTRS)

    Farrugia, C. J.; Richardson, I. G.; Burlaga, L. F.; Lepping, R. P.; Osherovich, V. A.

    1993-01-01

    Simultaneous ISEE 3 and IMP 8 spacecraft observations of magnetic fields and flow anisotropies of solar energetic protons and electrons during the passage of an interplanetary magnetic cloud show various particle signature differences at the two spacecraft. These differences are interpretable in terms of the magnetic line topology of the cloud, the connectivity of the cloud field lines to the solar surface, and the interconnection between the magnetic fields of the magnetic clouds and of the earth. These observations are consistent with a magnetic cloud model in which these mesoscale configurations are curved magnetic flux ropes attached at both ends to the sun's surface, extending out to 1 AU.

  3. Collision of the Smith Cloud and its dark matter halo with the magnetized Galactic disk

    NASA Astrophysics Data System (ADS)

    Galyardt, Jason; Shelton, Robin L.

    2015-01-01

    The Smith Cloud is a massive High Velocity Cloud (HVC) that may have passed through the Milky Way disk in the recent past. Previous studies using hydrodynamic simulations suggest that a dark matter halo may have provided the confinement neccessary for the Smith Cloud to survive passage through the Galactic corona and disk. However, the models of the Galaxy that were used in these studies did not include a magnetic field, while magnetic fields are known to have confining properties. Other studies have shown that the Galactic magnetic field can inhibit mass exchange between the corona and the disk due to magnetic field compression. We extend upon these studies via FLASH magnetohydrodynamic simulations to consider the effects of a Galactic magnetic field on an infalling, dark matter confined HVC.

  4. The application of a priori structural information based regularization in image reconstruction in magnetic induction tomography

    NASA Astrophysics Data System (ADS)

    Dekdouk, B.; Ktistis, C.; Yin, W.; Armitage, D. W.; Peyton, A. J.

    2010-04-01

    Magnetic induction tomography (MIT) is a non-invasive contactless modality that could be capable of imaging the conductivity distribution of biological tissues. In this paper we consider the possibility of using absolute MIT voltage measurements for monitoring the progress of a peripheral hemorrhagic stroke in a human brain. The pathology is modelled as a local blood accumulation in the white matter. The solution of the MIT inverse problem is nonlinear and ill-posed and hence requires the use of a regularisation method. In this paper, we describe the construction and present the performance of a regularisation matrix based on a priori structural information of the head tissues obtained from a very recent MRI scan. The method takes the MRI scan as an initial state of the stroke and constructs a learning set containing the possible conductivity distributions of the current state of the stroke. This data is used to calculate an approximation of the covariance matrix and then a subspace is constructed using principal component analysis (PCA). It is shown by simulations the method is capable of producing a representative reconstruction of a stroke compared to smoothing Tikhonov regularization in a simplified model of the head.

  5. Torus-Shaped Dust Clouds in Magnetized Anodic Plasmas

    SciTech Connect

    Pilch, I.; Reichstein, T.; Greiner, F.; Piel, A.

    2008-09-07

    The generation of a torus-shaped dust cloud in an anodic plasma is decribed. The confined dust particles perfom a rotational motion around the torus major axis. The structure of the cloud in dependence of the external parameters are observed and the rotation velocity of the particles was measured and compared with a simple estimate.

  6. Geo-effectiveness and radial dependence of magnetic cloud erosion by magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Lavraud, Benoit; Ruffenach, Alexis; Rouillard, Alexis P.; Kajdic, Primoz; Manchester, Ward B.; Lugaz, Noé

    2014-01-01

    flux erosion by magnetic reconnection occurs at the front of at least some magnetic clouds (MCs). We first investigate how erosion influences the geo-effectiveness of MCs in a general sense and using a south-north magnetic polarity MC observed on 18-20 October 1995. Although the magnetic shear at its front may not be known during propagation, measurements at 1 AU show signatures of local reconnection. Using a standard MC model, an empirical model of the geomagnetic response (Dst), and an observational estimate of the magnetic flux erosion, we find that the strength of the observed ensuing storm was ~30% lower than if no erosion had occurred. We then discuss the interplay between adiabatic compression and magnetic erosion at the front of MCs. We conclude that the most geo-effective configuration for a south-north polarity MC is to be preceded by a solar wind with southward IMF. This stems not only from the formation of a geo-effective sheath ahead of it but also from the adiabatic compression and reduced (or lack thereof) magnetic erosion which constructively conspire for the structure to be more geo-effective. Finally, assuming simple semiempirical and theoretical Alfvén speed profiles expected from expansion to 1 AU, we provide first-order estimates of the erosion process radial evolution. We find that the expected reconnection rates during propagation allow for significant erosion, on the order of those reported. Calculations also suggest that most of the erosion should occur in the inner heliosphere, and up to ~50% may yet occur beyond Mercury's orbit.

  7. MAGNETIC FIELDS IN INTERSTELLAR CLOUDS FROM ZEEMAN OBSERVATIONS: INFERENCE OF TOTAL FIELD STRENGTHS BY BAYESIAN ANALYSIS

    SciTech Connect

    Crutcher, Richard M.; Wandelt, Benjamin; Heiles, Carl; Falgarone, Edith

    2010-12-10

    The only direct measurements of interstellar magnetic field strengths depend on the Zeeman effect, which samples the line-of-sight component B{sub z} of the magnetic vector. In this paper, we use a Bayesian approach to analyze the observed probability density function (PDF) of B{sub z} from Zeeman surveys of H I, OH, and CN spectral lines in order to infer a density-dependent stochastic model of the total field strength B in diffuse and molecular clouds. We find that at n < 300 cm{sup -3} (in the diffuse interstellar medium sampled by H I lines), B does not scale with density. This suggests that diffuse clouds are assembled by flows along magnetic field lines, which would increase the density but not the magnetic field strength. We further find strong evidence for B in molecular clouds being randomly distributed between very small values and a maximum that scales with volume density n as B {proportional_to} n {sup 0.65} for n>300 cm{sup -3}, with an uncertainty at the 50% level in the power-law exponent of about {+-}0.05. This break-point density could be interpreted as the average density at which parsec-scale clouds become self-gravitating. Both the uniform PDF of total field strengths and the scaling with density suggest that magnetic fields in molecular clouds are often too weak to dominate the star formation process. The stochasticity of the total field strength B implies that many fields are so weak that the mass/flux ratio in many clouds must be significantly supercritical. A two-thirds power law comes from isotropic contraction of gas too weakly magnetized for the magnetic field to affect the morphology of the collapse. On the other hand, our study does not rule out some clouds having strong magnetic fields with critical mass/flux ratios.

  8. A numerical study of the effects of ambipolar diffusion on the collapse of magnetic gas clouds

    NASA Technical Reports Server (NTRS)

    Black, D. C.; Scott, E. H.

    1982-01-01

    The gravitational collapse of isothermal, nonrotating magnetic gas clouds have been calculated numerically, including the effects of ambipolar diffusion. The fractional ionization in the clouds is approximated by a power-law function of the gas density, f = K/n to the q-power, where K and q are adjustable parameters. Eleven numerical experiments were run, and the results indicate that the asymptotic character of collapse is determined mainly by the value of q and is largely independent of the other parameters characterizing a cloud (e.g., K, cloud mass). In particular, there is nearly a one-to-one correspondence between q and the slope, x, of the central magnetic field strength-gas density relationship. If q is no more than 0.8, a cloud collapses asymptotically, as though the magnetic field were 'frozen' to the neutral matter. The magnetic field strength at the center of a collapsing cloud is strongly amplified during collapse even for values of q of about 1, despite extremely low values of fractional ionization. A discussion of the theoretical basis for this unexpected behavior is given. Possible implications of our results for the problems of magnetic braking of rotating protostars and star formation in general are also presented.

  9. New OH Zeeman Measurements of Magnetic Field Strengths in Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Bourke, Tyler L.; Myers, Philip C.; Robinson, Garry; Hyland, A. R.

    2001-06-01

    We present the results of a new survey of 23 molecular clouds for the Zeeman effect in OH undertaken with the Australia Telescope National Facility Parkes 64 m radio telescope and the National Radio Astronomy Observatory Green Bank 43 m radio telescope. The Zeeman effect was clearly detected in the cloud associated with the H II region RCW 38, with a field strength of 38+/-3 μG, and possibly detected in a cloud associated with the H II region RCW 57, with a field strength of -203+/-24 μG. The remaining 21 measurements give formal upper limits to the magnetic field strength, with typical 1 σ sensitivities less than 20 μG. For 22 of the molecular clouds we are also able to determine the column density of the gas in which we have made a sensitive search for the Zeeman effect. We combine these results with previous Zeeman studies of 29 molecular clouds, most of which were compiled by Crutcher, for a comparison of theoretical models with the data. This comparison implies that if the clouds can be modeled as initially spherical with uniform magnetic fields and densities that evolve to their final equilibrium state assuming flux freezing, then the typical cloud is magnetically supercritical, as was found by Crutcher. If the clouds can be modeled as highly flattened sheets threaded by uniform perpendicular fields, then the typical cloud is approximately magnetically critical, in agreement with Shu et al., but only if the true values of the field for the nondetections are close to the 3 σ upper limits. If instead these values are significantly lower (for example, similar to the 1 σ limits), then the typical cloud is generally magnetically supercritical. When all observations of the Zeeman effect are considered, the single-dish detection rate of the OH Zeeman effect is relatively low. This result may be due to low mean field strengths, but a more realistic explanation may be significant field structure within the beam. As an example, for clouds associated with H II

  10. Propagation Characteristics of CMEs Associated with Magnetic Clouds and Ejecta

    NASA Astrophysics Data System (ADS)

    Kim, R.-S.; Gopalswamy, N.; Cho, K.-S.; Moon, Y.-J.; Yashiro, S.

    2013-05-01

    We have investigated the characteristics of magnetic cloud (MC) and ejecta (EJ) associated coronal mass ejections (CMEs) based on the assumption that all CMEs have a flux rope structure. For this, we used 54 CMEs and their interplanetary counterparts (interplanetary CMEs: ICMEs) that constitute the list of events used by the NASA/LWS Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We considered the location, angular width, and speed as well as the direction parameter, D. The direction parameter quantifies the degree of asymmetry of the CME shape in coronagraph images, and shows how closely the CME propagation is directed to Earth. For the 54 CDAW events, we found the following properties of the CMEs: i) the average value of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49), which indicates that the MC-associated CMEs propagate more directly toward the Earth than the EJ-associated CMEs; ii) comparison between the direction parameter and the source location shows that the majority of the MC-associated CMEs are ejected along the radial direction, while many of the EJ-associated CMEs are ejected non-radially; iii) the mean speed of MC-associated CMEs (946 km s-1) is faster than that of EJ-associated CMEs (771 km s-1). For seven very fast CMEs (≥ 1500 km s-1), all CMEs with large D (≥ 0.4) are associated with MCs and the CMEs with small D are associated with EJs. From the statistical analysis of CME parameters, we found the superiority of the direction parameter. Based on these results, we suggest that the CME trajectory essentially determines the observed ICME structure.

  11. Interplanetary magnetic cloud from the solar flare of Nov. 22, 1977

    NASA Astrophysics Data System (ADS)

    Ivanov, K. G.; Stiazhkin, V. A.; Kharshiladze, A. F.

    1989-04-01

    Attention is given to experimental Bx, By, and Bz profiles of the IMF measured by the Prognoz-6, ISEE-2, and IMP-8 satellites during the passage of a magnetic cloud from the intense solar flare of Nov. 22, 1977. These profiles are compared with a theoretical model of a force-free diffusion-pinch magnetic field.

  12. A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

    NASA Astrophysics Data System (ADS)

    Eswaraiah, C.; Maheswar, G.; Pandey, A. K.; Jose, J.; Ramaprakash, A. N.; Bhatt, H. C.

    2013-08-01

    Aims: We aim to map the magnetic field geometry and to study the dust properties of the starless cloud, L1570, using multi-wavelength optical polarimetry and photometry of the stars projected on the cloud. Methods: The direction of the magnetic field component parallel to the plane of the sky of a cloud can be obtained using polarimetry of the stars projected on and located behind the cloud. It is believed that the unpolarized light from the stars background to the cloud undergoes selective extinction while passing through non-spherical dust grains that are aligned with their minor axes parallel to the cloud magnetic field. The emerging light becomes partially plane polarized. The observed polarization vectors trace the direction of the projected magnetic field of the cloud. We made R-band imaging polarimetry of the stars projected on a cloud, L1570, to trace the magnetic field orientation. We also made multi-wavelength polarimetric and photometric observations to constrain the properties of dust in L1570. Results: We estimated a distance of 394 ± 70 pc to the cloud using 2MASS JHKs colors. Using the values of the Serkowski parameters, σ1, overlineɛ, λmax, and the position of the stars on the near-infrared color-color diagram, we identified 13 stars that could possibly have intrinsic polarization and/or rotation in their polarization angles. One star, 2MASS J06075075+1934177, which is a B4Ve spectral type, shows diffuse interstellar bands in the spectrum in addition to the Hα line in emission. There is an indication for slightly bigger dust grains toward L1570 on the basis of the dust grain size-indicators such as λmax and RV values. The magnetic field lines are found to be parallel to the cloud structures seen in the 250 μm images (also in the 8 μm and 12 μm shadow images) of L1570. Based on the magnetic field geometry, the cloud structure, and the complex velocity structure, we conclude that L1570 is in the process of formation due to the converging flow

  13. The Bastille Day Magnetic Clouds and Upstream Shocks: Near Earth Interplanetary Observations

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Berdichevsky, D. B.; Burlaga, L. F.; Lazarus, A. J.; Kasper, J.; Desch, M. D.; Wu, C.-C.; Reames, D. V.; Singer, H. J.; Singer, H. J.; Vondrak, Richard R. (Technical Monitor)

    2001-01-01

    The energetic charged particle, interplanetary magnetic field, and plasma characteristics of the 'Bastille Day' shock and ejecta/magnetic cloud events at 1 AU occurring over the days 14-16 July 2000 are described. Profiles of MeV (WIND/LEMT) energetic ions help to organize the overall sequence of events from the solar source to 1 AU. Stressed are analyses of an outstanding magnetic cloud (MC2) starting late on 15 July and its upstream shock about 4 hours earlier in WIND magnetic field and plasma data. Also analyzed is a less certain, but likely, magnetic cloud (MC1) occurring early on 15 July; this was separated from MC2 by its upstream shock and many heliospheric current sheet (HCS) crossings. Other HCS crossings occurred throughout the 3-day period. Overall this dramatic series of interplanetary events caused a large multi-phase magnetic storm with min Dst lower than -300 nT. The very fast solar wind speed (greater than or equal to 1100 km/s) in and around the front of MC2 (for near average densities) was responsible for a very high solar wind ram pressure driving in the front of the magnetosphere to geocentric distances estimated to be as low as approx. 5 R(sub E), much lower than the geosynchronous orbit radius. This was consistent with magnetic field observations from two GOES satellites which indicated they were in the magnetosheath for extended times. A static force free field model is used to fit the two magnetic cloud profiles providing estimates of the clouds' physical and geometrical properties. MC2 was much larger than MCI, but their axes were nearly antiparallel, and their magnetic fields had the same left-handed helicity. MC2's axis and its upstream shock normal were very close to being perpendicular to each other, as might be expected if the cloud were driving the shock at the time of observation. The estimated axial magnetic flux carried by MC2 was 52 x 10(exp 20) Mx, which is about 5 times the typical magnetic flux estimated for other magnetic

  14. Evidence in Magnetic Clouds for Systematic Open Flux Transport on the Sun

    NASA Technical Reports Server (NTRS)

    Crooker, N. U.; Kahler, S. W.; Gosling, J. T.; Lepping, R. P.

    2008-01-01

    Most magnetic clouds encountered by spacecraft at 1 AU display a mix of unidirectional suprathermal electrons signaling open field lines and counterstreaming electrons signaling loops connected to the Sun at both ends. Assuming the open fields were originally loops that underwent interchange reconnection with open fields at the Sun, we determine the sense of connectedness of the open fields found in 72 of 97 magnetic clouds identified by the Wind spacecraft in order to obtain information on the location and sense of the reconnection and resulting flux transport at the Sun. The true polarity of the open fields in each magnetic cloud was determined from the direction of the suprathermal electron flow relative to the magnetic field direction. Results indicate that the polarity of all open fields within a given magnetic cloud is the same 89% of the time, implying that interchange reconnection at the Sun most often occurs in only one leg of a flux rope loop, thus transporting open flux in a single direction, from a coronal hole near that leg to the foot point of the opposite leg. This pattern is consistent with the view that interchange reconnection in coronal mass ejections systematically transports an amount of open flux sufficient to reverse the polarity of the heliospheric field through the course of the solar cycle. Using the same electron data, we also find that the fields encountered in magnetic clouds are only a third as likely to be locally inverted as not. While one might expect inversions to be equally as common as not in flux rope coils, consideration of the geometry of spacecraft trajectories relative to the modeled magnetic cloud axes leads us to conclude that the result is reasonable.

  15. Radial Evolution of a Magnetic Cloud: MESSENGER, STEREO, and Venus Express Observations

    NASA Astrophysics Data System (ADS)

    Good, S. W.; Forsyth, R. J.; Raines, J. M.; Gershman, D. J.; Slavin, J. A.; Zurbuchen, T. H.

    2015-07-01

    The Solar Orbiter and Solar Probe Plus missions will provide observations of magnetic clouds closer to the Sun than ever before, and it will be good preparation for these missions to make full use of the most recent in situ data sets from the inner heliosphere—namely, those provided by MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and Venus Express—for magnetic cloud studies. We present observations of the same magnetic cloud made by MESSENGER at Mercury and later by Solar TErrestrial RElations Observatory-B (STEREO-B), while the spacecraft were radially aligned in 2011 November. Few such radial observations of magnetic clouds have been previously reported. Estimates of the solar wind speed at MESSENGER are also presented, calculated through the application of a previously established technique. The cloud's flux rope has been analyzed using force-free fitting; the rope diameter increased from 0.18 to 0.41 AU (corresponding to an {r}{{H}}0.94 dependence on heliocentric distance, rH), and the axial magnetic field strength dropped from 46.0 to 8.7 nT (an {r}{{H}}-1.84 dependence) between the spacecraft, clear indications of an expanding structure. The axial magnetic flux was ˜0.50 nT AU2 at both spacecraft, suggesting that the rope underwent no significant erosion through magnetic reconnection between MESSENGER and STEREO-B. Further, we estimate the change in the cloud's angular width by assuming helicity conservation. It has also been found that the rope axis rotated by 30° between the spacecraft to lie close to the solar equatorial plane at STEREO-B. Such a rotation, if it is a common feature of coronal mass ejection propagation, would have important implications for space weather forecasting.

  16. Dst prediction for a period of high-density plasmas in magnetic clouds

    NASA Astrophysics Data System (ADS)

    Adachi, H.; Sakurai, T.

    We examine geomagnetic effects for high-density plasmas in magnetic clouds and their relationship to solar sources. It is well known that Bz component of interplanetary magnetic field plays an important role for estimation of Dst from solar wind parameters (Burton et al.1975). However, magnetic clouds frequently carry high-density plasmas, which are interpreted as the remnants of filament. In order to clarify their geomagnetic effects, we try to estimate Dst by adopting different methods introducing effects of solar wind parameters. In our estimation the most important point is laid on the sense of Dst variation rather than its magnitude. The most suitable estimation is obtained by setting up a threshold for plasma density, in which for a case of plasma density greater than 20 /cc the Fenrich and Luhmann (1998)'s formula should be used, while in the other cases the Burton's formula are adopted. In both estimations the O'Brien and McPherron (2000)'s ring current decay time is employed. Furthermore, we examine the solar origin corresponding to the magnetic clouds and then compared characteristic signatures of the magnetic cloud with those observed on the solar surface. As a result, we confirm that the magnetic structure of interplanetary flux rope is in good agreement with the structures of the magnetic neutral line near disappearing filaments and heliospheric current sheet (HCS). On the basis of these studies, we suggest that for the geomagnetic disturbance forecast, the effect of high-density plasmas carried with magnetic clouds should be taken into account of as well as that of interplanetary magnetic field.

  17. Using baryon octet magnetic moments and masses to fix the pion cloud contribution

    SciTech Connect

    Franz Gross, Gilberto Ramalho, Kazuo Tsushima

    2010-06-01

    Using SU(3) symmetry to constrain the $\\pi BB'$ couplings, assuming SU(3) breaking comes only from one-loop pion cloud contributions, and using the the covariant spectator theory to describe the photon coupling to the quark core, we show how the experimental masses and magnetic moments of the baryon octet can be used to set a model independent constraint on the strength of the pion cloud contributions to the octet, and hence the nucleon, form factors at $Q^2=0$.

  18. Magnetic field and plasma wave observations in a plasma cloud at Venus

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Luhmann, J. G.; Elphic, R. C.; Scarf, F. L.; Brace, L. H.

    1982-01-01

    Pioneer Venus magnetic field and plasma wave data are examined in a particularly clear example of a plasma cloud above the Venus ionosphere. The magnetic configuration is suggestive of acceleration of the plasma cloud by magnetic tension. If the plasma is at rest at the subsolar point, it could be accelerated to approximately 90 km/sec by the observed stress at the location of the measurement. This far exceeds the escape velocity and suggests that plasma clouds do form a significant loss mechanism for the Venus ionosphere but does not necessarily indicate that the plasma cloud is detached from the ionosphere proper. The plasma cloud is accompanied by strong plasma wave activity and is significantly hotter than the ionospheric plasma encountered later on the same pass. A loss rate of the order of 2 x 10 to the 25th ions/sec is estimated during this event. The geometry suggested by these observations is one of a ridge of dense cold plasma starting in the subsolar regions and flowing over the poles of the planet. Thus, these plasma clouds may be the planetary analog of cometary tail rays.

  19. Magnetic cloud erosion by magnetic reconnection: occurrence statistics, radial evolution and geo-effectiveness

    NASA Astrophysics Data System (ADS)

    Lavraud, B.; Ruffenach, A.; Farrugia, C. J.; Demoulin, P.; Dasso, S.; Sauvaud, J.; Rouillard, A.; Foullon, C.; Owens, M. J.; Savani, N.; Kajdic, P.; Manchester, W.; Lugaz, N.; Luhmann, J. G.

    2013-12-01

    We present results regarding the occurrence statistics of magnetic flux erosion due to magnetic reconnection at the front of all magnetic clouds (MC) observed near Earth during solar cycle 23. We show that the process commonly occurs. It often occurs in large amounts, and at both the front and back boundaries of MCs. The statistics of reconnection jets at these boundaries confirms the significance of the process even up to 1 AU. Indeed, we also estimate the radial evolution of this process based on simple models. We conclude that most of the erosion occurs within Mercury's orbit, but up to 50% of the erosion seen at 1 AU may occur beyond Mercury's orbit. Using a standard MC model and an empirical model of the Dst index we also study the impact of this process on MC geo-effectiveness. We conclude that the most geo-effective configuration for a south-north polarity MC is to be preceded by a slow solar wind with southward IMF. This stems not only from the formation of a geo-effective sheath region with southward IMF ahead of it, but also from the fact that adiabatic compression and reduced (or lack thereof) magnetic erosion constructively conspire for the structure to be more geo-effective. Future missions such as Bepi-Colombo, Solar Orbiter and Solar Probe Plus will be able to further quantify this process and determine its radial dependence. Multi-spacecraft observations would be particularly useful for understanding the large-scale 3D topology changes associated with this process.

  20. The resolved magnetic fields of the quiescent cloud GRSMC 45.60+0.30

    NASA Astrophysics Data System (ADS)

    Pavel, Michael D.; Marchwinski, Robert C.; Clemens, Dan P.

    2015-03-01

    Marchwinski et al. (2012) mapped the magnetic field strength across the quiescent cloud GRSMC 45.60+0.30 (shown in Figure 1 subtending 40x10 pc at a distance of 1.88 kpc) with the Chandrasekhar-Fermi method CF; Chandrasekhar & Fermi 1953) using near-infrared starlight polarimetry from the Galactic Plane Infrared Polarization Survey (Clemens et al. 2012a, b) and gas properties from the Galactic Ring Survey (Jackson et al. 2006). The large-scale magnetic field is oriented parallel to the gas-traced `spine' of the cloud. Seven `magnetic cores' with high magnetic field strength were identified and are coincident with peaks in the gas column density. Calculation of the mass-to-flux ratio (Crutcher 1999) shows that these cores are exclusively magnetically subcritical and that magnetostatic pressure can support them against gravitational collapse.

  1. Transverse deflection and dissipation of small plasma beams and clouds in magnetized media

    NASA Technical Reports Server (NTRS)

    Cheng, Andrew F.

    1987-01-01

    Propagation of a quasi-neutral plasma beam or cloud across a magnetic field is considered for the case where the transverse dimension of the beam or cloud is sufficiently small compared to ion gyroradii. This situation commonly arises for active experiments in near-earth space. Two mechanisms are presented for transverse deflection of a beam or cloud in the -v0 x B0 direction where v0 is the velocity relative to the ambient medium. In the first, asymmetric escape of ions from an electrically polarized beam or cloud causes transverse deflection by means of a rocket effect. The transverse deflection distance is estimated to be a few times the initial transverse dimension of the beam or cloud. Dissipation occurs within a few times the thermal ion transverse crossing time. In the second mechanism, asymmetric charging results from localized accumulation of incident ions from the ambient medium. This excess positive charge distorts electric equipotentials and drives electron Hall currents that maintain an asymmetric compressed magnetic field region. The asymmetry of the magnetic stress contributes to transverse deflection with the same sign as the rocket effect. The asymmetric magnetic field also focuses incident ions to yield the localized charge accumulation. These ideas are qualitatively consistent with observations of the Active Magnetospheric Particle Tracer Explorers artificial comet releases.

  2. Near-IR Imaging Polarimetry toward a Bright-rimmed Cloud: Magnetic Field in SFO 74

    NASA Astrophysics Data System (ADS)

    Kusune, Takayoshi; Sugitani, Koji; Miao, Jingqi; Tamura, Motohide; Sato, Yaeko; Kwon, Jungmi; Watanabe, Makoto; Nishiyama, Shogo; Nagayama, Takahiro; Sato, Shuji

    2015-01-01

    We have made near-infrared (JHK s) imaging polarimetry of a bright-rimmed cloud (SFO 74). The polarization vector maps clearly show that the magnetic field in the layer just behind the bright rim is running along the rim, quite different from its ambient magnetic field. The direction of the magnetic field just behind the tip rim is almost perpendicular to that of the incident UV radiation, and the magnetic field configuration appears to be symmetric as a whole with respect to the cloud symmetry axis. We estimated the column and number densities in the two regions (just inside and far inside the tip rim) and then derived the magnetic field strength, applying the Chandrasekhar-Fermi method. The estimated magnetic field strength just inside the tip rim, ~90 μG, is stronger than that far inside, ~30 μG. This suggests that the magnetic field strength just inside the tip rim is enhanced by the UV-radiation-induced shock. The shock increases the density within the top layer around the tip and thus increases the strength of the magnetic field. The magnetic pressure seems to be comparable to the turbulent one just inside the tip rim, implying a significant contribution of the magnetic field to the total internal pressure. The mass-to-flux ratio was estimated to be close to the critical value just inside the tip rim. We speculate that the flat-topped bright rim of SFO 74 could be formed by the magnetic field effect.

  3. Torus-shaped dust clouds trapped in a magnetized anodic plasma

    SciTech Connect

    Pilch, Iris; Reichstein, Torben; Piel, Alexander

    2008-10-15

    Dust particles confined in a magnetized anodic plasma can form a torus-shaped cloud with a dust-free region (void) in the center. Most of the dust particles perform a rotational motion about the major axis of the torus. The torus-shaped dust cloud and the velocity of the particles are studied by varying the external plasma parameters like magnetic field strength and rf-power of the source plasma. Two-dimensional potential contours are measured with an emissive probe. The results are used to discuss the force balance between electric field force and ion drag acting on the dust particles that determines the void size.

  4. A Comprehensive Automated 3D Approach for Building Extraction, Reconstruction, and Regularization from Airborne Laser Scanning Point Clouds

    PubMed Central

    Dorninger, Peter; Pfeifer, Norbert

    2008-01-01

    Three dimensional city models are necessary for supporting numerous management applications. For the determination of city models for visualization purposes, several standardized workflows do exist. They are either based on photogrammetry or on LiDAR or on a combination of both data acquisition techniques. However, the automated determination of reliable and highly accurate city models is still a challenging task, requiring a workflow comprising several processing steps. The most relevant are building detection, building outline generation, building modeling, and finally, building quality analysis. Commercial software tools for building modeling require, generally, a high degree of human interaction and most automated approaches described in literature stress the steps of such a workflow individually. In this article, we propose a comprehensive approach for automated determination of 3D city models from airborne acquired point cloud data. It is based on the assumption that individual buildings can be modeled properly by a composition of a set of planar faces. Hence, it is based on a reliable 3D segmentation algorithm, detecting planar faces in a point cloud. This segmentation is of crucial importance for the outline detection and for the modeling approach. We describe the theoretical background, the segmentation algorithm, the outline detection, and the modeling approach, and we present and discuss several actual projects.

  5. Magnetic field geometry of an unusual cometary cloud Gal 110-13

    NASA Astrophysics Data System (ADS)

    Neha, S.; Maheswar, G.; Soam, A.; Lee, C. W.; Tej, A.

    2016-04-01

    Aims: We carried out optical polarimetry of an isolated cloud, Gal 110-13, to map the plane-of-the-sky magnetic field geometry. The main aim of the study is to understand the most plausible mechanism responsible for the unusual cometary shape of the cloud in the context of its magnetic field geometry. Methods: When unpolarized starlight passes through the intervening interstellar dust grains that are aligned with their short axes parallel to the local magnetic field, it gets linearly polarized. The plane-of-the-sky magnetic field component can therefore be traced by doing polarization measurements of background stars projected on clouds. Because the light in the optical wavelength range is most efficiently polarized by the dust grains typically found in the outer layers of the molecular clouds, optical polarimetry enables us to trace the magnetic field geometry of the outer layers of the clouds. Results: We made R-band polarization measurements of 207 stars in the direction of Gal 110-13. The distance of Gal 110-13 was determined as ~450 ± 80 pc using our polarization and 2MASS near-infrared data. The foreground interstellar contribution was removed from the observed polarization values by observing a number of stars located in the vicinity of Gal 110-13 which has Hipparcos parallax measurements. The plane-of-the-sky magnetic field lines are found to be well ordered and aligned with the elongated structure of Gal 110-13. Using structure function analysis, we estimated the strength of the plane-of-the-sky component of the magnetic field as ~25 μG. Conclusions: Based on our results and comparing them with those from simulations, we conclude that compression by the ionization fronts from 10 Lac is the most plausible cause of the comet-like morphology of Gal 110-13 and of the initiation of subsequent star formation.

  6. Magnetic Fields in Star-Forming Clouds: How Can FIRST Contribute?

    NASA Astrophysics Data System (ADS)

    Matthews, B. C.; Wilson, C. D.; Fiege, J. D.

    2001-07-01

    The SCUBA polarimeter at the James Clerk Maxwell Telescope has been used to probe the magnetic field geometry within the OMC-3 region of the Integral Filament of Orion A, the Barnard 1 cloud in Perseus and the B2 core in the rho Ophiuchus dark cloud. In the submillimetre, polarized dust emission arises from rapidly spinning dust grains aligned by the local magnetic field. Although the polarized emission from each grain is orthogonal to the local field direction, a variation of the magnetic field orientation through the cloud can produce complex polarization patterns from which the field geometry cannot easily be determined without modelling. In each of the regions observed, the polarization patterns are inconsistent with strictly uniform or unidirectional magnetic fields on extended spatial scales. In each case, a decrease in polarization percentage is observed toward higher total intensities. In OMC-3, we have modelled the polarization pattern as arising from a bent filamentary cloud threaded by a helical magnetic field. The model is remarkably consistent with the polarization pattern observed.

  7. VLBA Provides Best Detail Yet of Star-Forming Cloud's Magnetic Field

    NASA Astrophysics Data System (ADS)

    2001-07-01

    Astronomers have used the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope to do a very detailed map of the magnetic field within a star-forming cloud, an achievement that will help scientists unravel the mysterious first steps of the stellar birth process. "This study provides new and important data needed by theorists to understand how magnetic fields affect the early stages of star formation," said Anuj Sarma, an astronomer at the University of Illinois at Urbana-Champaign. Sarma worked with Thomas Troland of the University of Kentucky and Jonathan Romney of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. Their research results were published in the Astrophysical Journal Letters. Stars are formed when gas in giant interstellar clouds collapses gravitationally. Magnetic fields are believed to support such gas clouds, helping them resist gravitational collapse, so the beginning stages of star formation arise from a complex interplay of the magnetic fields and gravity that is not yet well understood. "In order to understand how star formation gets started, we need to know in detail the structure of the magnetic fields in a star-forming cloud," Sarma said. "Our observations with the VLBA have provided one more big step in this direction," he added. The astronomers studied a cloud of molecular gas more than 5,000 light- years from Earth in a spiral arm of our own Milky Way Galaxy. The cloud, known as W3 IRS5, contains seven newly-formed stars. In addition, it contains a number of regions, somewhat smaller than the diameter of Earth's orbit, in which water vapor molecules act to amplify, or strengthen, radio emission. Such regions, called masers, are a radio- wave parallel to lasers, which amplify light. The scientists used the VLBA to make a detailed study of the radio waves coming from these maser regions in the gas cloud. They detected a phenomenon called the Zeeman effect, in which a very precise frequency

  8. Coronal Mass Ejections and Magnetic Clouds Modeled as MHD Bounded States

    NASA Astrophysics Data System (ADS)

    Fainberg, J.; Osherovich, V. A.

    2004-12-01

    Multiple loops can be seen in the solar corona before the onset of a coronal mass ejection (CME), during and after the event. We apply multi-toroidal configurations to model CMEs and their interplanetary counterparts - magnetic clouds. In the laboratory, plasma confinement is often achieved by conducting metal walls which introduce elastic forces to maintain equilibrium. Such walls, carrying electric surface currents, usually are taken as boundaries where the magnetic field is truncated to provide finite energy for the configuration. The idea of MHD bounded states as solutions with continuous magnetic field and finite magnetic energy was put forward in 1975 [1]. Such solutions describe a single toroid (ground state) and multiple toroids (excited states) [1],[2]. We analyze noncircular cross sections of such toroids and compare the components of the magnetic field vector with in situ observations in interplanetary magnetic clouds. We present Ulysses spacecraft observations in support of our multi-tube model for interplanetary magnetic clouds based on bounded state MHD configurations with axial and helical symmetry [3],[4]. The interaction of CMEs with the global coronal field will also be discussed. In our presentation, we stress the difference in boundary conditions for magnetic configurations in laboratory and space plasmas. [1] Osherovich, V.A., `On an equilibrium of an MHD config-uration with axial symmetry 1', Soln Dann, 5, p. 70, 1975. [2] Osherovich, V.A. and Lawrence, J.K., `Elaboration of the new magnetohydrostatic sunspot theory (Double return flux model)', Sol. Phys., 88, p. 117, 1983. [3] Krat, V.A. and Osherovich, V.A., `Note on the asymmetry of bipolar sunspot groups', Solar Phys., 59, pp. 43-47, 1978. [4] Osherovich, V.A., Fainberg, J. and Stone, R.G., `Multi-tube model for interplanetary magnetic clouds', Geophys. Res. L., 26(3), pp. 401-404, 1999.

  9. Analysis of 20 magnetic clouds at 1 AU during a solar minimum

    NASA Astrophysics Data System (ADS)

    Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P.

    We study 20 magnetic clouds, observed in situ by the spacecraft Wind, at the Lagrangian point L1, from 22 August, 1995, to 7 November, 1997. In previous works, assuming a cylindrical symmetry for the local magnetic configuration and a satellite trajectory crossing the axis of the cloud, we obtained their orientations using a minimum variance analysis. In this work we compute the orientations and magnetic configurations using a non-linear simultaneous fit of the geometric and physical parameters for a linear force-free model, including the possibility of a not null impact parameter. We quantify global magnitudes such as the relative magnetic helicity per unit length and compare the values found with both methods (minimum variance and the simultaneous fit). FULL TEXT IN SPANISH

  10. Trapping of Electron Cloud LLC/Cesrta Quadrupole and Sextupole Magnets

    SciTech Connect

    Wang, L; Pivi, M.; /SLAC

    2011-08-18

    The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R&D [1]. One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in CESRTA and ILC quadrupole and sextupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with a long lifetime in a quadrupole and sextupole magnet due to the mirror field trapping mechanism. We study the effects of magnet strength, bunch current, ante-chamber effect, bunch spacing effect and secondary emission yield (SEY) in great detail. The development of an electron cloud in magnets is the main concern where a weak solenoid field is not effective. Quadrupole and sextupole magnets have mirror field configurations which may trap electrons by the mirror field trapping mechanism [2]. Fig.1 shows the orbit of a trapped electron in a quadrupole magnet. The electron makes gyration motion (called transverse motion) and also moves along the field line (called longitudinal motion). At the mirror point (middle of the field line), there is a maximum longitudinal energy and minimum transverse energy. When the electron moves away from the mirror point, its longitudinal energy reduces and the transverse energy increases as the magnetic field increases. If the magnetic field is strong enough, the longitudinal energy becomes zero at one point and then the electron is turned back by the strong field. Note that the electrons are trapped in the region near the middle of the field lines. Although all quadrupole and sextupole magnets can trap electrons in principle, the trapping

  11. Typical and Unusual Properties of Magnetic Clouds during the WIND Era

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Berdichevsky, D.; Szabo, A.; Burlaga, L. F.; Thompson, B. J.; Mariani, F.; Lazarus, A. J.; Steinberg, J. T.

    1999-01-01

    A list of 33 magnetic clouds as identified in WIND magnetic field and plasma data has been compiled. The intervals for these events are provided as part of NASA/GSFC, WIND-MFI's Website under the URL http://lepmfi.qsfc.nasa.gov/mfi/mag_cloud publ.html#table The period covered in this study is from early 1995 to November 1998 which primarily occurs in the quiet part of the solar cycle. A force free, cylindrically symmetric, magnetic field model has been applied to the field data in 1-hour averaged form for all of these events (except one small event where 10 min avg's were used) and the resulting fit-parameters examined. Each event was provided a semi-quantitatively determined quality factor (excellent, good or poor). A set of 28 good or better cases, spanning a surprisingly large range of values for its various properties, was used for further analysis. These properties are, for example, durations, attitudes, sizes, asymmetries, axial field strengths, speeds, and relative impact parameters. They will be displayed and analyzed, along with some related derived quantities, with emphasis on typical vs unusual properties and on the magnetic fields magnetic clouds' relationships to the Sun and to upstream interplanetary shocks, where possible. For example, it is remarkable how narrowly distributed the speeds of these clouds are, and the overall average speed (390 techniques km/s) is less than that normally quoted for the average solar wind speed (420 km/s) despite the fact that many of these clouds are d"drivers" of interplanetary shocks. On average, a cloud appears to be a little less symmetric when the spacecraft is able to pass close to the cloud's axis as compared to a farther out passage. The average longitude and latitude (in GSE) of the axes of the clouds are 85 degrees and 8 degrees, respectively, with standard deviations near 40 degrees. Also, the half=yearly averaged axial magnetic flux has approximately tripled. almost monotonically, from about 6 to 17 X 10

  12. LONG-LIVED MAGNETIC-TENSION-DRIVEN MODES IN A MOLECULAR CLOUD

    SciTech Connect

    Basu, Shantanu; Dapp, Wolf B. E-mail: wdapp@uwo.c

    2010-06-10

    We calculate and analyze the longevity of magnetohydrodynamic (MHD) wave modes that occur in the plane of a magnetic thin sheet. Initial turbulent conditions applied to a magnetically subcritical cloud are shown to lead to relatively rapid energy decay if ambipolar diffusion is introduced at a level corresponding to partial ionization primarily by cosmic rays. However, in the flux-freezing limit, as may be applicable to photoionized molecular cloud envelopes, the turbulence persists at 'nonlinear' levels in comparison with the isothermal sound speed c {sub s}, with one-dimensional rms material motions in the range of {approx} 2 c {sub s}-5 c {sub s} for cloud sizes in the range of {approx} 2 pc-16 pc. These fluctuations persist indefinitely, maintaining a significant portion of the initial turbulent kinetic energy. We find the analytic explanation for these persistent fluctuations. They are magnetic-tension-driven modes associated with the interaction of the sheet with the external magnetic field. The phase speed of such modes is quite large, allowing residual motions to persist without dissipation in the flux-freezing limit, even as they are nonlinear with respect to the sound speed. We speculate that long-lived large-scale MHD modes such as these may provide the key to understanding observed supersonic motions in molecular clouds.

  13. Magnetohydrostatic equilibrium structure and mass of filamentary isothermal cloud threaded by lateral magnetic field

    SciTech Connect

    Tomisaka, Kohji

    2014-04-10

    Herschel observations have recently revealed that interstellar molecular clouds consist of many filaments. Polarization observations in optical and infrared wavelengths indicate that the magnetic field often runs perpendicular to the filament. In this article, we study the magnetohydrostatic configuration of isothermal gas in which the thermal pressure and the Lorentz force are balanced against the self-gravity, and the magnetic field is globally perpendicular to the axis of the filament. The model is controlled by three parameters: center-to-surface density ratio (ρ {sub c}/ρ {sub s}), plasma β of surrounding interstellar gas (β{sub 0}), and the radius of the hypothetical parent cloud normalized by the scale-height (R{sub 0}{sup ′}), although there remains freedom in how the mass is distributed against the magnetic flux (mass loading). In the case where R{sub 0}{sup ′} is small enough, the magnetic field plays a role in confining the gas. However, the magnetic field generally has the effect of supporting the cloud. There is a maximum line-mass (mass per unit length) above which the cloud is not supported against gravity. Compared with the maximum line-mass of a nonmagnetized cloud (2c{sub s}{sup 2}/G, where c{sub s} and G represent, respectively, the isothermal sound speed and the gravitational constant), that of the magnetized filament is larger than the nonmagnetized one. The maximum line-mass is numerically obtained as λ{sub max}≃0.24Φ{sub cl}/G{sup 1/2}+1.66c{sub s}{sup 2}/G, where Φ{sub cl} represents one half of the magnetic flux threading the filament per unit length. The maximum mass of the filamentary cloud is shown to be significantly affected by the magnetic field when the magnetic flux per unit length exceeds Φ{sub cl} ≳ 3 pc μG (c{sub s} /190 m s{sup –1}){sup 2}.

  14. Energetic ion observations in the magnetic cloud of 14-15 January 1988 and their implications for the magnetic field topology

    NASA Technical Reports Server (NTRS)

    Richardson, I. G.; Farrugia, C. J.; Burlaga, L. F.

    1991-01-01

    On 14-15 January 1988, a magnetic cloud with a local field topology consistent with an east-west aligned cylindrical flux-rope and which formed the driver of an interplanetary shock passed the earth. Using 0.5-4 MeV/n ion data from the instrument on IMP 8, the paper addresses the question of whether or not magnetic field lines within the magnetic cloud were connected to the sun. An impulsive solar particle event was detected inside the magnetic cloud strongly suggesting that the field lines were rooted at the sun.

  15. Tracing the Magnetic Field Morphology of the Lupus I Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Franco, G. A. P.; Alves, F. O.

    2015-07-01

    Deep R-band CCD linear polarimetry collected for fields with lines of sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with a polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large-scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 μm dust emission map shows that the principal filament of Lupus I is constituted by three main clumps that are acted on by magnetic fields that have different large-scale structural properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and the cloud’s apparent evolutionary stage. On the other hand, assuming that the magnetic field is composed of large-scale and turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 to 200 μG in these clumps. The intensity increases toward the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales. Based on observations collected at the Observatório do Pico dos Dias, operated by Laboratório Nacional de Astrofísica (LNA/MCTI, Brazil).

  16. Temperature and phase-space density of a cold atom cloud in a quadrupole magnetic trap

    NASA Astrophysics Data System (ADS)

    Ram, S. P.; Mishra, S. R.; Tiwari, S. K.; Rawat, H. S.

    2014-08-01

    We present studies on modifications in the temperature, number density and phase-space density when a laser-cooled atom cloud from optical molasses is trapped in a quadrupole magnetic trap. Theoretically, for a given temperature and size of the cloud from the molasses, the phase-space density in the magnetic trap is shown first to increase with increasing magnetic field gradient and then to decrease with it after attaining a maximum value at an optimum value of the magnetic-field gradient. The experimentally-measured variation in the phase-space density in the magnetic trap with changing magnetic field gradient is shown to exhibit a similar trend. However, the experimentally-measured values of the number density and the phase-space density are much lower than the theoretically-predicted values. This is attributed to the experimentally-observed temperature in the magnetic trap being higher than the theoretically-predicted temperature. Nevertheless, these studies can be useful for setting a higher phase-space density in the trap by establishing an optimal value of the field gradient for a quadrupole magnetic trap.

  17. STEREO Observations of an SEP Event Injected Into Both Loop Legs of a Magnetic Cloud

    NASA Astrophysics Data System (ADS)

    Dresing, N.; Gomez-Herrero, R.; Heber, B.; Hidalgo, M. A. U.; Klassen, A.; Temmer, M.; Veronig, A.

    2015-12-01

    On 7 Nov 2013 STEREO B was embedded in a magnetic-cloud (MC) like structure when an SEP event occurred reaching both STEREO spacecraft. The bi-drectional near relativistic electron distribution observed by STEREO B reveals such timing and relative intensity characteristics suggesting that the SEPs were injected separately into both loop legs of the MC. Observations by the Nancay Radioheliograph (NRH) of two distinct radio sources at the same time further support the above scenario. In order to derive the 3D morphology and average speed of the CME close to the Sun, we use the graduated cylindrical shell model (GCS) which is applied to the white-light coronagraph observations by the STEREO spacecraft and SOHO. Furthermore, a global magnetic topology model for magnetic clouds is applied to the in-situ measurements of the magnetic field. Both models suggest that the MC is strongly inclined with respect to the ecliptic yielding a north/south orientation. The energetic electron observations are used to probe the structure of the magnetic cloud: We determine the electron path lengths along both loop legs of the structure to infer the amount of field line twist inside the MC. The resulting path lengths are around 50% longer than the estimated lengths of the loop legs of the MC itself suggesting that the amount of field line winding is moderate.

  18. The magnetic field of the Large Magellanic Cloud revealed through Faraday rotation.

    PubMed

    Gaensler, B M; Haverkorn, M; Staveley-Smith, L; Dickey, J M; McClure-Griffiths, N M; Dickel, J R; Wolleben, M

    2005-03-11

    We have measured the Faraday rotation toward a large sample of polarized radio sources behind the Large Magellanic Cloud (LMC) to determine the structure of this galaxy's magnetic field. The magnetic field of the LMC consists of a coherent axisymmetric spiral of field strength approximately 1 microgauss. Strong fluctuations in the magnetic field are also seen on small (<0.5 parsec) and large (approximately 100 parsecs) scales. The large bursts of recent star formation and supernova activity in the LMC argue against standard dynamo theory, adding to the growing evidence for rapid field amplification in galaxies. PMID:15761149

  19. Virial theorem analysis of the structure and stability of magnetized clouds

    NASA Technical Reports Server (NTRS)

    Zweibel, Ellen G.

    1990-01-01

    The tensor virial theorem is used to analyze the structure and stability of self-gravitating, magnetized spheroids surrounded by a low-density medium with pressure and magnetic field. Analytical expressions are developed for the effect of a weak field and calculate critical states when the effect of the field is arbitrarily strong, comparing the results with full magnetohydrostatic calculations. This analysis suggests that a magnetic field may prevent gravitational collapse but may also be destabilizing, depending on its degree of concentration within the cloud.

  20. Coronal mass ejections, magnetic clouds, and relativistic magnetospheric electron events: ISTP

    SciTech Connect

    Baker, D.N.; Pulkkinen, T.I.; Li, X.; Kanekal, S.G.; Blake, J.B.; Selesnick, R.S.; Henderson, M.G.; Reeves, G.D.; Spence, H.E.

    1998-08-01

    The role of high-speed solar wind streams in driving relativistic electron acceleration within the Earth{close_quote}s magnetosphere during solar activity minimum conditions has been well documented. The rising phase of the new solar activity cycle (cycle 23) commenced in 1996, and there have recently been a number of coronal mass ejections (CMEs) and related {open_quotes}magnetic clouds{close_quotes} at 1 AU. As these CME/cloud systems interact with the Earth{close_quote}s magnetosphere, some events produce substantial enhancements in the magnetospheric energetic particle population while others do not. This paper compares and contrasts relativistic electron signatures observed by the POLAR, SAMPEX, Highly Elliptical Orbit, and geostationary orbit spacecraft during two magnetic cloud events: May 27{endash}29, 1996, and January 10{endash}11, 1997. Sequences were observed in each case in which the interplanetary magnetic field was first strongly southward and then rotated northward. In both cases, there were large solar wind density enhancements toward the end of the cloud passage at 1 AU. Strong energetic electron acceleration was observed in the January event, but not in the May event. The relative geoeffectiveness for these two cases is assessed, and it is concluded that large induced electric fields ({partial_derivative}B/{partial_derivative}t) caused in situ acceleration of electrons throughout the outer radiation zone during the January 1997 event. {copyright} 1998 American Geophysical Union

  1. Segmentation of Brain Tissues from Magnetic Resonance Images Using Adaptively Regularized Kernel-Based Fuzzy C-Means Clustering.

    PubMed

    Elazab, Ahmed; Wang, Changmiao; Jia, Fucang; Wu, Jianhuang; Li, Guanglin; Hu, Qingmao

    2015-01-01

    An adaptively regularized kernel-based fuzzy C-means clustering framework is proposed for segmentation of brain magnetic resonance images. The framework can be in the form of three algorithms for the local average grayscale being replaced by the grayscale of the average filter, median filter, and devised weighted images, respectively. The algorithms employ the heterogeneity of grayscales in the neighborhood and exploit this measure for local contextual information and replace the standard Euclidean distance with Gaussian radial basis kernel functions. The main advantages are adaptiveness to local context, enhanced robustness to preserve image details, independence of clustering parameters, and decreased computational costs. The algorithms have been validated against both synthetic and clinical magnetic resonance images with different types and levels of noises and compared with 6 recent soft clustering algorithms. Experimental results show that the proposed algorithms are superior in preserving image details and segmentation accuracy while maintaining a low computational complexity. PMID:26793269

  2. Segmentation of Brain Tissues from Magnetic Resonance Images Using Adaptively Regularized Kernel-Based Fuzzy C-Means Clustering

    PubMed Central

    Wang, Changmiao; Jia, Fucang; Wu, Jianhuang; Li, Guanglin

    2015-01-01

    An adaptively regularized kernel-based fuzzy C-means clustering framework is proposed for segmentation of brain magnetic resonance images. The framework can be in the form of three algorithms for the local average grayscale being replaced by the grayscale of the average filter, median filter, and devised weighted images, respectively. The algorithms employ the heterogeneity of grayscales in the neighborhood and exploit this measure for local contextual information and replace the standard Euclidean distance with Gaussian radial basis kernel functions. The main advantages are adaptiveness to local context, enhanced robustness to preserve image details, independence of clustering parameters, and decreased computational costs. The algorithms have been validated against both synthetic and clinical magnetic resonance images with different types and levels of noises and compared with 6 recent soft clustering algorithms. Experimental results show that the proposed algorithms are superior in preserving image details and segmentation accuracy while maintaining a low computational complexity. PMID:26793269

  3. Magnetically Regulated Star Formation in Three Dimensions: The Case of the Taurus Molecular Cloud Complex

    NASA Astrophysics Data System (ADS)

    Nakamura, Fumitaka; Li, Zhi-Yun

    2008-11-01

    We carry out three-dimensional MHD simulations of star formation in turbulent, magnetized clouds, including ambipolar diffusion and feedback from protostellar outflows. The calculations focus on relatively diffuse clouds threaded by a strong magnetic field capable of resisting severe tangling by turbulent motions and retarding global gravitational contraction in the cross field direction. They are motivated by observations of the Taurus molecular cloud complex (and, to a lesser extent, Pipe Nebula), which shows an ordered large-scale magnetic field, as well as elongated condensations that are generally perpendicular to the large-scale field. We find that stars form in earnest in such clouds when enough material has settled gravitationally along the field lines that the mass-to-flux ratios of the condensations approach the critical value. Only a small fraction (of order 1% or less) of the nearly magnetically critical, condensed material is turned into stars per local free-fall time, however. The slow star formation takes place in condensations that are moderately supersonic; it is regulated primarily by magnetic fields, rather than turbulence. The quiescent condensations are surrounded by diffuse halos that are much more turbulent, as observed in the Taurus complex. Strong support for magnetic regulation of star formation in this complex comes from the extremely slow conversion of the already condensed, relatively quiescent C18O gas into stars, at a rate 2 orders of magnitude below the maximum, free-fall value. We analyze the properties of dense cores, including their mass spectrum, which resembles the stellar initial mass function.

  4. Using baryon octet magnetic moments and masses to fix the pion cloud contribution

    SciTech Connect

    Franz L. Gross; Ramalho, Gilberto T. F.; Tsushima, Kazuo

    2010-05-12

    In this study, using SU(3) symmetry to constrain the $\\pi BB'$ couplings, assuming SU(3) breaking comes only from one-loop pion cloud contributions, and using the the covariant spectator theory to describe the photon coupling to the quark core, we show how the experimental masses and magnetic moments of the baryon octet can be used to set a model independent constraint on the strength of the pion cloud contributions to the octet, and hence the nucleon, form factors at $Q^2=0$.

  5. Using baryon octet magnetic moments and masses to fix the pion cloud contribution

    DOE PAGESBeta

    Franz L. Gross; Ramalho, Gilberto T. F.; Tsushima, Kazuo

    2010-05-12

    In this study, using SU(3) symmetry to constrain themore » $$\\pi BB'$$ couplings, assuming SU(3) breaking comes only from one-loop pion cloud contributions, and using the the covariant spectator theory to describe the photon coupling to the quark core, we show how the experimental masses and magnetic moments of the baryon octet can be used to set a model independent constraint on the strength of the pion cloud contributions to the octet, and hence the nucleon, form factors at $Q^2=0$.« less

  6. NEAR-IR IMAGING POLARIMETRY TOWARD A BRIGHT-RIMMED CLOUD: MAGNETIC FIELD IN SFO 74

    SciTech Connect

    Kusune, Takayoshi; Sugitani, Koji; Miao, Jingqi; Tamura, Motohide; Kwon, Jungmi; Sato, Yaeko; Watanabe, Makoto; Nishiyama, Shogo; Nagayama, Takahiro; Sato, Shuji

    2015-01-01

    We have made near-infrared (JHK {sub s}) imaging polarimetry of a bright-rimmed cloud (SFO 74). The polarization vector maps clearly show that the magnetic field in the layer just behind the bright rim is running along the rim, quite different from its ambient magnetic field. The direction of the magnetic field just behind the tip rim is almost perpendicular to that of the incident UV radiation, and the magnetic field configuration appears to be symmetric as a whole with respect to the cloud symmetry axis. We estimated the column and number densities in the two regions (just inside and far inside the tip rim) and then derived the magnetic field strength, applying the Chandrasekhar-Fermi method. The estimated magnetic field strength just inside the tip rim, ∼90 μG, is stronger than that far inside, ∼30 μG. This suggests that the magnetic field strength just inside the tip rim is enhanced by the UV-radiation-induced shock. The shock increases the density within the top layer around the tip and thus increases the strength of the magnetic field. The magnetic pressure seems to be comparable to the turbulent one just inside the tip rim, implying a significant contribution of the magnetic field to the total internal pressure. The mass-to-flux ratio was estimated to be close to the critical value just inside the tip rim. We speculate that the flat-topped bright rim of SFO 74 could be formed by the magnetic field effect.

  7. Finite-time singularities and flow regularization in a hydromagnetic shell model at extreme magnetic Prandtl numbers

    NASA Astrophysics Data System (ADS)

    Nigro, G.; Carbone, V.

    2015-07-01

    Conventional surveys on the existence of singularities in fluid systems for vanishing dissipation have hitherto tried to infer some insight by searching for spatial features developing in asymptotic regimes. This approach has not yet produced a conclusive answer. One of the difficulties preventing us from getting a definitive answer is the limitations of direct numerical simulations which do not yet have a high enough resolution so far as to properly describe spatial fine structures in asymptotic regimes. In this paper, instead of searching for spatial details, we suggest seeking a principle, that would be able to discriminate between singular or not-singular behavior, among the integral and purely dynamical properties of a fluid system. We investigate the singularities developed by a hydromagnetic shell model during the magnetohydrodynamic turbulent cascade. Our results show that when the viscosity is equal to the magnetic diffusivity (unit magnetic Prandtl number) singularities appear in a finite time. A complex behavior is observed at extreme magnetic Prandtl numbers. In particular, the singularities persist in the limit of vanishing viscosity, while a complete regularization is observed in the limit of vanishing diffusivity. This dynamics is related to differences between the magnetic and the kinetic energy cascades towards small scales. Finally a comparison between the three-dimensional and the two-dimensional cases leads to conjecture that the existence of singularities may be related to the conservation of different ideal invariants.

  8. Experimental Investigation of Electron Cloud Containment in a Nonuniform Magnetic Field

    NASA Technical Reports Server (NTRS)

    Eninger, J. E.

    1974-01-01

    Dense clouds of electrons were generated and studied in an axisymmetric, nonuniform magnetic field created by a short solenoid. The operation of the experiment was similar to that of a low-pressure (approximately 0.000001 Torr) magnetron discharge. Discharge current characteristics are presented as a function of pressure, magnetic field strength, voltage, and cathode end-plate location. The rotation of the electron cloud is determined from the frequency of diocotron waves. In the space charge saturated regime of operation, the cloud is found to rotate as a solid body with frequency close to V sub a/phi sub a where V sub a is the anode voltage and phi suba is the total magnetic flux. This result indicates that, in regions where electrons are present, the magnetic field lines are electrostatic equipotentials (E bar, B bar = 0). Equilibrium electron density distributions suggested by this conditions are integrated with respect to total ionizing power and are found consistent with measured discharge currents.

  9. First MHD simulation of collapse and fragmentation of magnetized molecular cloud cores

    NASA Astrophysics Data System (ADS)

    Machida, Masahiro N.; Tomisaka, Kohji; Matsumoto, Tomoaki

    2004-02-01

    This is the first paper about fragmentation and mass outflow in molecular clouds by using three-dimensional magnetohydrodynamical (MHD) nested-grid simulations. The binary star formation process is studied, paying particular attention to the fragmentation of a rotating magnetized molecular cloud. We assume an isothermal rotating and magnetized cylindrical cloud in hydrostatic balance. Non-axisymmetric as well as axisymmetric perturbations are added to the initial state and the subsequent evolutions are studied. The evolution is characterized by three parameters: the amplitude of the non-axisymmetric perturbations, the rotation speed and the magnetic field strength. As a result, it is found that non-axisymmetry hardly evolves in the early phase, but begins to grow after the gas contracts and forms a thin disc. Disc formation is strongly promoted by the rotation speed and the magnetic field strength. There are two types of fragmentation: that from a ring and that from a bar. Thin adiabatic cores fragment if their thickness is less than 1/4 of the radius. For the fragments to survive, they should be formed in a heavily elongated barred core or a flat round disc. In the models showing fragmentation, outflows from respective fragments are found as well as those driven by the rotating bar or the disc.

  10. Matching dust emission structures and magnetic field in high-latitude cloud L1642: comparing Herschel and Planck maps★

    NASA Astrophysics Data System (ADS)

    Malinen, J.; Montier, L.; Montillaud, J.; Juvela, M.; Ristorcelli, I.; Clark, S. E.; Berné, O.; Bernard, J.-Ph.; Pelkonen, V.-M.; Collins, D. C.

    2016-05-01

    The nearby cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. It is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g., of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642. The high-resolution (˜20″) Herschel data reveal a complex structure including a dense, compressed central clump, and low density striations. The Planck polarization data (at 10' resolution) reveal an ordered magnetic field pervading the cloud and aligned with the surrounding striations. There is a complex interplay between the cloud structure and large scale magnetic field. This suggests that the magnetic field is closely linked to the formation and evolution of the cloud. CO rotational emission confirms that the striations are connected with the main clumps and likely to contain material either falling into or flowing out of the clumps. There is a clear transition from aligned to perpendicular structures approximately at a column density of NH = 1.6 × 1021 cm-2. Comparing the Herschel maps with the Planck polarization maps shows the close connection between the magnetic field and cloud structure even in the finest details of the cloud.

  11. Matching dust emission structures and magnetic field in high-latitude cloud L1642: comparing Herschel and Planck maps★

    NASA Astrophysics Data System (ADS)

    Malinen, J.; Montier, L.; Montillaud, J.; Juvela, M.; Ristorcelli, I.; Clark, S. E.; Berné, O.; Bernard, J.-Ph.; Pelkonen, V.-M.; Collins, D. C.

    2016-08-01

    The nearby cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. It is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g. of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642. The high-resolution (˜20 arcsec) Herschel data reveal a complex structure including a dense, compressed central clump, and low-density striations. The Planck polarization data (at 10 arcmin resolution) reveal an ordered magnetic field pervading the cloud and aligned with the surrounding striations. There is a complex interplay between the cloud structure and large-scale magnetic field. This suggests that the magnetic field is closely linked to the formation and evolution of the cloud. CO rotational emission confirms that the striations are connected with the main clumps and likely to contain material either falling into or flowing out of the clumps. There is a clear transition from aligned to perpendicular structures approximately at a column density of NH = 1.6 × 1021 cm-2. Comparing the Herschel maps with the Planck polarization maps shows the close connection between the magnetic field and cloud structure even in the finest details of the cloud.

  12. Cone angle control of the interaction of magnetic clouds with the Earth's bow shock

    NASA Astrophysics Data System (ADS)

    Turc, L.; Escoubet, C. P.; Fontaine, D.; Kilpua, E. K. J.; Enestam, S.

    2016-05-01

    We study the interaction of magnetic clouds (MCs) with the near-Earth environment. Recent works suggest that the bow shock crossing may modify significantly the magnetic structure of an MC, and thus its ability to drive geomagnetic storms. This change is largely controlled by the bow shock configuration, which depends on the upstream interplanetary magnetic field (IMF) orientation. From the distribution of the magnetic field orientation in 152 Earth-impacting MCs, we determine for the first time the typical shock configuration during MC events. We find that 56% (6.3%) of the time, the subsolar bow shock configuration is exclusively quasi-perpendicular (quasi-parallel). The rest of the time, both configurations coexist. Furthermore, using a subset of 63 MCs observed simultaneously in the solar wind and in the dayside magnetosheath, we determine the magnitude of the magnetic field alteration, how it depends on the shock configuration, and how it relates to the IMF cone angle.

  13. Passive shimming of a superconducting magnet using the L1-norm regularized least square algorithm

    NASA Astrophysics Data System (ADS)

    Kong, Xia; Zhu, Minhua; Xia, Ling; Wang, Qiuliang; Li, Yi; Zhu, Xuchen; Liu, Feng; Crozier, Stuart

    2016-02-01

    The uniformity of the static magnetic field B0 is of prime importance for an MRI system. The passive shimming technique is usually applied to improve the uniformity of the static field by optimizing the layout of a series of steel shims. The steel pieces are fixed in the drawers in the inner bore of the superconducting magnet, and produce a magnetizing field in the imaging region to compensate for the inhomogeneity of the B0 field. In practice, the total mass of steel used for shimming should be minimized, in addition to the field uniformity requirement. This is because the presence of steel shims may introduce a thermal stability problem. The passive shimming procedure is typically realized using the linear programming (LP) method. The LP approach however, is generally slow and also has difficulty balancing the field quality and the total amount of steel for shimming. In this paper, we have developed a new algorithm that is better able to balance the dual constraints of field uniformity and the total mass of the shims. The least square method is used to minimize the magnetic field inhomogeneity over the imaging surface with the total mass of steel being controlled by an L1-norm based constraint. The proposed algorithm has been tested with practical field data, and the results show that, with similar computational cost and mass of shim material, the new algorithm achieves superior field uniformity (43% better for the test case) compared with the conventional linear programming approach.

  14. Low virial parameters in molecular clouds: Implications for high-mass star formation and magnetic fields

    SciTech Connect

    Kauffmann, Jens; Pillai, Thushara; Goldsmith, Paul F. E-mail: tpillai@astro.caltech.edu

    2013-12-20

    Whether or not molecular clouds and embedded cloud fragments are stable against collapse is of utmost importance for the study of the star formation process. Only 'supercritical' cloud fragments are able to collapse and form stars. The virial parameter α = M {sub vir}/M, which compares the virial mass to the actual mass, provides one way to gauge stability against collapse. Supercritical cloud fragments are characterized by α ≲ 2, as indicated by a comprehensive stability analysis considering perturbations in pressure and density gradients. Past research has suggested that virial parameters α ≳ 2 prevail in clouds. This would suggest that collapse toward star formation is a gradual and relatively slow process and that magnetic fields are not needed to explain the observed cloud structure. Here, we review a range of very recent observational studies that derive virial parameters <<2 and compile a catalog of 1325 virial parameter estimates. Low values of α are in particular observed for regions of high-mass star formation (HMSF). These observations may argue for a more rapid and violent evolution during collapse. This would enable 'competitive accretion' in HMSF, constrain some models of 'monolithic collapse', and might explain the absence of high-mass starless cores. Alternatively, the data could point at the presence of significant magnetic fields ∼1 mG at high gas densities. We examine to what extent the derived observational properties might be biased by observational or theoretical uncertainties. For a wide range of reasonable parameters, our conclusions appear to be robust with respect to such biases.

  15. A Radio and Optical Polarization Study of the Magnetic Field in the Small Magellanic Cloud

    SciTech Connect

    Mao, S. A.; Gaensler, B. M.; Stanimirovic, S.; Haverkorn, M.; McClure-Griffiths, N. M.; Staveley-Smith, L.; Dickey, J. M.

    2008-12-01

    We present a study of the magnetic field of the Small Magellanic Cloud (SMC), carried out using radio Faraday rotation and optical starlight polarization data. Consistent negative rotation measures (RMs) across the SMC indicate that the line-of-sight magnetic field is directed uniformly away from us with a strength 0.19 {+-} 0.06 {mu}G. Applying the Chandrasekhar-Fermi method to starlight polarization data yields an ordered magnetic field in the plane of the sky of strength 1.6 {+-} 0.4 {mu}G oriented at a position angle 4deg {+-} 12deg , measured counterclockwise from the great circle on the sky joining the SMC to the Large Magellanic Cloud (LMC). We construct a three-dimensional magnetic field model of the SMC, under the assumption that the RMs and starlight polarization probe the same underlying large-scale field. The vector defining the overall orientation of the SMC magnetic field shows a potential alignment with the vector joining the center of the SMC to the center of the LMC, suggesting the possibility of a 'pan-Magellanic' magnetic field. A cosmic-ray-driven dynamo is the most viable explanation of the observed field geometry, but has difficulties accounting for the observed unidirectional field lines. A study of Faraday rotation through the Magellanic Bridge is needed to further test the pan-Magellanic field hypothesis.

  16. A Radio and Optical Polarization Study of the Magnetic Field in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Mao, S. A.; Gaensler, B. M.; Stanimirović, S.; Haverkorn, M.; McClure-Griffiths, N. M.; Staveley-Smith, L.; Dickey, J. M.

    2008-12-01

    We present a study of the magnetic field of the Small Magellanic Cloud (SMC), carried out using radio Faraday rotation and optical starlight polarization data. Consistent negative rotation measures (RMs) across the SMC indicate that the line-of-sight magnetic field is directed uniformly away from us with a strength 0.19 +/- 0.06 μG. Applying the Chandrasekhar-Fermi method to starlight polarization data yields an ordered magnetic field in the plane of the sky of strength 1.6 +/- 0.4 μG oriented at a position angle 4°+/- 12°, measured counterclockwise from the great circle on the sky joining the SMC to the Large Magellanic Cloud (LMC). We construct a three-dimensional magnetic field model of the SMC, under the assumption that the RMs and starlight polarization probe the same underlying large-scale field. The vector defining the overall orientation of the SMC magnetic field shows a potential alignment with the vector joining the center of the SMC to the center of the LMC, suggesting the possibility of a "pan-Magellanic" magnetic field. A cosmic-ray-driven dynamo is the most viable explanation of the observed field geometry, but has difficulties accounting for the observed unidirectional field lines. A study of Faraday rotation through the Magellanic Bridge is needed to further test the pan-Magellanic field hypothesis.

  17. Correlation of electron path lengths observed in the highly wound outer region of magnetic clouds with the slab fraction of magnetic turbulence in the dissipation range

    SciTech Connect

    Tan, Lun C.; Shao, Xi; Reames, Donald V.; Ng, Chee K.; Wang, Linghua

    2014-05-10

    Three magnetic cloud events, in which solar impulsive electron events occurred in their outer region, are employed to investigate the difference of path lengths L {sub 0eIII} traveled by non-relativistic electrons from their release site near the Sun to the observer at 1 AU, where L {sub 0eIII} = v {sub l} × (t {sub l} – t {sub III}), v {sub l} and t {sub l} being the velocity and arrival time of electrons in the lowest energy channel (∼27 keV) of the Wind/3DP/SST sensor, respectively, and t {sub III} being the onset time of type III radio bursts. The deduced L {sub 0eIII} value ranges from 1.3 to 3.3 AU. Since a negligible interplanetary scattering level can be seen in both L {sub 0eIII} > 3 AU and ∼1.2 AU events, the difference in L {sub 0eIII} could be linked to the turbulence geometry (slab or two-dimensional) in the solar wind. By using the Wind/MFI magnetic field data with a time resolution of 92 ms, we examine the turbulence geometry in the dissipation range. In our examination, ∼6 minutes of sampled subintervals are used in order to improve time resolution. We have found that, in the transverse turbulence, the observed slab fraction is increased with an increasing L {sub 0eIII} value, reaching ∼100% in the L {sub 0eIII} > 3 AU event. Our observation implies that when only the slab spectral component exists, magnetic flux tubes (magnetic surfaces) are closed and regular for a very long distance along the transport route of particles.

  18. Detailed Magnetic Field Morphology of the Vela C Molecular Cloud from the BLASTPol 2012 flight

    NASA Astrophysics Data System (ADS)

    Fissel, Laura Marion; Ade, Peter; Angilè, Francesco E.; Ashton, Peter; Benton, Steven J.; Devlin, Mark J.; Dober, Bradley; Fukui, Yasuo; Galitzki, Nicholas B.; Gandilo, Natalie; Klein, Jeff; Korotkov, Andrei; Li, Zhi-Yun; Moncelsi, Lorenzo; Matthews, Tristan; nakamura, fumitaka; Barth Netterfield, Calvin; Novak, Giles; Pascale, Enzo; Poidevin, Frédérick; Savini, Giorgio; Pereira Santos, Fábio; Scott, Douglas; Shariff, Jamil; Soler, Juan Diego; Thomas, Nicholas; tucker, carole; Tucker, Gregory S.; Ward-Thompson, Derek

    2015-01-01

    In order to understand the role of magnetic fields in the process of star formation, we require detailed observations of field morphology on scales ranging from clouds to cores. However, ground based millimetre/submillimetre polarimetry is usually limited to small maps of relatively dense regions. BLASTPol, the Balloon-borne Large Aperture Sub-mm Telescope for Polarimetry, maps linear polarization at 250, 350 and 500 microns with arcminute resolution. Its high sensitivity and resolving power allow BLASTPol to bridge the gap in spatial scales between the polarization capabilities of Planck and ALMA.I will present early results from the second flight of BLASTPol, focusing on our observations of the Vela C molecular cloud, an early stage intermediate mass star forming region (d~700 pc). With thousands of independent measurements of magnetic field direction, this is the most detailed sub-mm polarization map of a GMC to date. The field we observe in this elongated cloud exhibits a coherent, large-scale ~ 90 degree bend between its high latitude and low latitude edges. I will discuss what we can learn about star formation in Vela C from the combination of BLASTPol polarization maps and velocity information from molecular line observations, and what the variation of polarization strength across the cloud can tell us about dust grain alignment in GMCs.

  19. Contraction and Fragmentation of Magnetized Rotating Clouds and Formation of Binary Systems

    NASA Astrophysics Data System (ADS)

    Tomisaka, Kohji; Machida, Masahiro N.; Matsumoto, Tomoaki

    2004-08-01

    Using three-dimensional (3D) magnetohydrodynamical (MHD) nested-grid simulations, the fragmentation of a rotating magnetized molecular cloud core is studied. An isothermal rotating magnetized cylindrical cloud in hydrostatic balance is considered. We studied non-axisymmetric evolution of the cloud. It is found that non-axisymmetry hardly evolves in the early phase, but it begins to grow after the gas contracts and forms a thin disk. The disk formation and thus growth of non-axisymmetric perturbation are strongly promoted by rotation and magnetic field strength. We found two types of fragmentations: fragmentation from a ring and that from a bar. These two types of fragmentations occur in thin adiabatic cores with the thickness being smaller than 1/4 of the radial size. For the fragments to survive, they should be formed in a heavily elongated barred core or a flat round disk. In the models showing fragmentation, outflows from respective fragments are found as well as that driven by the rotating bar or the disk.

  20. Multiple spacecraft flux rope modeling of the Bastille Day magnetic cloud

    NASA Astrophysics Data System (ADS)

    Mulligan, T.; Russell, C. T.; Anderson, B. J.; Acuna, M. H.

    The Bastille Day magnetic cloud in July 2000 occurred with NEAR in conjunction with the Earth at a radial distance of 1.76 AU and 1.9° from the Earth-Sun line. Propagation time from ACE at 0.99 AU to NEAR indicates the cloud did not decelerate significantly between the Earth and 1.76 AU. Using a non-force-free, kinematic flux rope model we find the rope contained 130 TWb of magnetic flux, was oriented with clock and cone angles of 50° and 83°, and had a radius of 0.25 AU at ACE. At NEAR its radius had expanded to 0.43 AU. Simultaneous modeling of ACE and NEAR data indicate the axial and poloidal magnetic fields vary as R-1.4 and R-1.2 where R is heliocentric distance. Magnetosheath thicknesses of 0.14 AU and 0.23 AU indicate the rope cross section is elongated normal to the cloud axis and the radial direction.

  1. Injection of solar energetic particles into both loop legs of a magnetic cloud

    NASA Astrophysics Data System (ADS)

    Dresing, N.; Gómez-Herrero, R.; Heber, B.; Hidalgo, M. A.; Klassen, A.; Temmer, M.; Veronig, A.

    2016-02-01

    Context. Each of the two Solar TErrestrial RElations Observatory (STEREO) spacecraft carries a Solar Electron and Proton Telescope (SEPT) which measures electrons and protons. Anisotropy observations are provided in four viewing directions: along the nominal magnetic field Parker spiral in the ecliptic towards the Sun (SUN) and away from the Sun (Anti-Sun/ASUN), and towards the north (NORTH) and south (SOUTH). The solar energetic particle (SEP) event on 7 November 2013 was observed by both STEREO spacecraft, which were longitudinally separated by 68° at that time. While STEREO A observed the expected characteristics of an SEP event at a well-connected position, STEREO B detected a very anisotropic bi-directional distribution of near-relativistic electrons and was situated inside a magnetic-cloud-like structure during the early phase of the event. Aims: We examine the source of the bi-directional SEP distribution at STEREO B. On the one hand this distribution could be caused by a double injection into both loop legs of the magnetic cloud (MC). On the other hand, a mirroring scenario where the incident beam is reflected in the opposite loop leg could be the reason. Furthermore, the energetic electron observations are used to probe the magnetic structure inside the magnetic cloud. Methods: We investigate in situ plasma and magnetic field observations and show that STEREO B was embedded in an MC-like structure ejected three days earlier on 4 November from the same active region. We apply a Graduated Cylindrical Shell (GCS) model to the coronagraph observations from three viewpoints as well as the Global Magnetic Cloud (GMC) model to the in situ measurements at STEREO B to determine the orientation and topology of the MC close to the Sun and at 1 AU. We also estimate the path lengths of the electrons propagating through the MC to estimate the amount of magnetic field line winding inside the structure. Results: The relative intensity and timing of the energetic electron

  2. Comparing Herschel dust emission structures, magnetic fields observed by Planck, and dynamics: high-latitude star forming cloud L1642

    NASA Astrophysics Data System (ADS)

    Malinen, Johanna

    2016-01-01

    The nearby high-latitude cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. This cloud is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g., of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642, and also combine these with dynamic information from molecular line observations. The high-resolution Herschel data reveal a complex structure including a dense, compressed central blob with elongated extensions, low density striations, "fishbone" like structures with a spine and perpendicular striations, and a spiraling "tail". The Planck polarization data reveal an ordered magnetic field that pervades the cloud and is aligned with the surrounding low density striations. We show that there is a complex interplay between the cloud structure and large scale magnetic fields revealed by Planck polarization data at 10' resolution. This suggests that the magnetic field is closely linked to the formation and evolution of the cloud. We see a clear transition from aligned to perpendicular structures approximately at a column density of NH = 2x10^21 cm-2. We conclude that Planck polarization data revealing the large scale magnetic field orientation can be very useful even when comparing to the finest structures in higher resolution data, e.g. Herschel at ~18" resolution.

  3. Energetic secondary electrons and the nonthermal galactic radio background - A probe of the magnetic field in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Marscher, A. P.; Brown, R. L.

    1978-01-01

    A previous analysis of the manifestations of charged-pion-decay secondary electrons in interstellar cloud material is extended to include those contributions to the Galactic radio and soft gamma-ray backgrounds that are directly attributable to energetic secondaries. The equilibrium distribution of secondary electrons in dense interstellar clouds is calculated, synchrotron emissivity from isolated interstellar clouds is examined, and it is shown how the value of the magnetic field in these clouds may be determined by observing the radio emission in their directions. The contribution that such clouds make to the integrated radio background is evaluated, and the Galactic distribution of bremsstrahlung gamma rays that arise from interactions of secondary electrons with thermal material in dense clouds is computed. The results indicate that a magnetic field of no more than 80 microgauss is characteristic of dense clouds and that the integrated synchrotron radiation from secondary electrons in interstellar clouds will contribute a significant fraction of the nonthermal brightness along the Galactic equator even if the mean cloud field is as low as 35 microgauss.

  4. Disc formation in turbulent cloud cores: is magnetic flux loss necessary to stop the magnetic braking catastrophe or not?

    NASA Astrophysics Data System (ADS)

    Santos-Lima, R.; de Gouveia Dal Pino, E. M.; Lazarian, A.

    2013-03-01

    Recent numerical analysis of Keplerian disc formation in turbulent, magnetized cloud cores by Santos-Lima et al. demonstrated that reconnection diffusion is an efficient process to remove the magnetic flux excess during the buildup of a rotationally supported disc. This process is induced by fast reconnection of the magnetic fields in a turbulent flow. In a similar numerical study, Seifried et al. concluded that reconnection diffusion or any other non-ideal magnetohydrodynamic effects would not be necessary and turbulence shear alone would provide a natural way to build up a rotating disc without requiring magnetic flux loss. Their conclusion was based on the fact that the mean mass-to-flux ratio (μ) evaluated over a spherical region with a radius much larger than the disc is nearly constant in their models. In this paper, we compare the two sets of simulations and show that this averaging over large scales can mask significant real increases of μ in the inner regions where the disc is built up. We demonstrate that turbulence-induced reconnection diffusion of the magnetic field happens in the initial stages of the disc formation in the turbulent envelope material that is accreting. Our analysis is suggestive that reconnection diffusion is present in both sets of simulations and provides a simple solution for the `magnetic braking catastrophe' which is discussed in the literature in relation to the formation of protostellar accretion discs.

  5. COLLAPSE AND FRAGMENTATION OF MAGNETIC MOLECULAR CLOUD CORES WITH THE ENZO AMR MHD CODE. I. UNIFORM DENSITY SPHERES

    SciTech Connect

    Boss, Alan P.; Keiser, Sandra A.

    2013-02-20

    Magnetic fields are important contributors to the dynamics of collapsing molecular cloud cores, and can have a major effect on whether collapse results in a single protostar or fragmentation into a binary or multiple protostar system. New models are presented of the collapse of magnetic cloud cores using the adaptive mesh refinement code Enzo2.0. The code was used to calculate the ideal magnetohydrodynamics (MHD) of initially spherical, uniform density, and rotation clouds with density perturbations, i.e., the Boss and Bodenheimer standard isothermal test case for three-dimensional (3D) hydrodynamics codes. After first verifying that Enzo reproduces the binary fragmentation expected for the non-magnetic test case, a large set of models was computed with varied initial magnetic field strengths and directions with respect to the cloud core axis of rotation (parallel or perpendicular), density perturbation amplitudes, and equations of state. Three significantly different outcomes resulted: (1) contraction without sustained collapse, forming a denser cloud core; (2) collapse to form a single protostar with significant spiral arms; and (3) collapse and fragmentation into binary or multiple protostar systems, with multiple spiral arms. Comparisons are also made with previous MHD calculations of similar clouds with a barotropic equations of state. These results for the collapse of initially uniform density spheres illustrate the central importance of both magnetic field direction and field strength for determining the outcome of dynamic protostellar collapse.

  6. Observations of galactic magnetic fields

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    Magnetic fields are enchored in gas clouds. Field lines are tangled in spiral arms, but highly regular between the arms. The similarity of pitch angles between gaseous and magnetic arms suggests a coupling between the density wave and the magnetic wave. Observations of large-scale patterns in Faraday rotation favour a dynamo origin of the regular fields. Fields in barred galaxies do not reveal the strong shearing shocks observed in the cold gas, but swing smoothly from the upstream region into the bar. Magnetic fields are important for the dynamcis of gas clouds, for the formation of spiral structures, bars and halos, and for mass and angular momentum transport in central regions.

  7. Rigid-body rotation of an electron cloud in divergent magnetic fields

    SciTech Connect

    Fruchtman, A.; Gueroult, R.; Fisch, N. J.

    2013-07-10

    For a given voltage across a divergent poloidal magnetic field, two electric potential distributions, each supported by a rigid-rotor electron cloud rotating with a different frequency, are found analytically. The two rotation frequencies correspond to the slow and fast rotation frequencies known in uniform plasma. Due to the centrifugal force, the equipotential surfaces, that correspond to the two electric potential distributions, diverge more than the magnetic surfaces do, the equipotential surfaces in the fast mode diverge largely in particular. The departure of the equipotential surfaces from the magnetic field surfaces may have a significant focusing effect on the ions accelerated by the electric field. Furthermore, the focusing effect could be important for laboratory plasma accelerators as well as for collimation of astrophysical jets.

  8. Rigid-body rotation of an electron cloud in divergent magnetic fields

    DOE PAGESBeta

    Fruchtman, A.; Gueroult, R.; Fisch, N. J.

    2013-07-10

    For a given voltage across a divergent poloidal magnetic field, two electric potential distributions, each supported by a rigid-rotor electron cloud rotating with a different frequency, are found analytically. The two rotation frequencies correspond to the slow and fast rotation frequencies known in uniform plasma. Due to the centrifugal force, the equipotential surfaces, that correspond to the two electric potential distributions, diverge more than the magnetic surfaces do, the equipotential surfaces in the fast mode diverge largely in particular. The departure of the equipotential surfaces from the magnetic field surfaces may have a significant focusing effect on the ions acceleratedmore » by the electric field. Furthermore, the focusing effect could be important for laboratory plasma accelerators as well as for collimation of astrophysical jets.« less

  9. On the magnetic fields of Be/X-ray pulsars in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Ikhsanov, N. R.; Mereghetti, S.

    2015-12-01

    We explore the possibility of explaining the properties of the Be/X-ray pulsars observed in the Small Magellanic Cloud (SMC) within the magnetic levitation accretion scenario. This implies that their X-ray emission is powered by a wind-fed accretion on to a neutron star (NS) which captures matter from a magnetized stellar wind. The NS in this case is accreting matter from a non-Keplerian magnetically levitating disc which is surrounding its magnetosphere. This allows us to explain the observed periods of the pulsars in terms of spin equilibrium without the need of invoking dipole magnetic fields outside the usual range ˜1011-1013 G inferred from cyclotron features of Galactic high-mass X-ray binaries. We find that the equilibrium period of a NS, under certain conditions, depends strongly on the magnetization of the stellar wind of its massive companion and, correspondingly, on the magnetic field of the massive companion itself. This may help to explain why similar NSs in binaries with similar properties rotate with different periods yielding a large scatter of periods of the accretion-powered pulsar observed in SMC and our galaxy.

  10. Collapse and fragmentation of magnetic molecular cloud cores with the Enzo AMR MHD code. II. Prolate and oblate cores

    SciTech Connect

    Boss, Alan P.; Keiser, Sandra A.

    2014-10-10

    We present the results of a large suite of three-dimensional models of the collapse of magnetic molecular cloud cores using the adaptive mesh refinement code Enzo2.2 in the ideal magnetohydrodynamics approximation. The cloud cores are initially either prolate or oblate, centrally condensed clouds with masses of 1.73 or 2.73 M {sub ☉}, respectively. The radial density profiles are Gaussian, with central densities 20 times higher than boundary densities. A barotropic equation of state is used to represent the transition from low density isothermal phases, to high density optically thick phases. The initial magnetic field strength ranges from 6.3 to 100 μG, corresponding to clouds that are strongly to marginally supercritical, respectively, in terms of the mass to magnetic flux ratio. The magnetic field is initially uniform and aligned with the clouds' rotation axes, with initial ratios of rotational to gravitational energy ranging from 10{sup –4} to 0.1. Two significantly different outcomes for collapse result: (1) formation of single protostars with spiral arms, and (2) fragmentation into multiple protostar systems. The transition between these two outcomes depends primarily on the initial magnetic field strength, with fragmentation occurring for mass to flux ratios greater than about 14 times the critical ratio for prolate clouds. Oblate clouds typically fragment into several times more clumps than prolate clouds. Multiple, rather than binary, system formation is the general rule in either case, suggesting that binary stars are primarily the result of the orbital dissolution of multiple protostar systems.

  11. MULTI-SCALE ANALYSIS OF MAGNETIC FIELDS IN FILAMENTARY MOLECULAR CLOUDS IN ORION A

    SciTech Connect

    Poidevin, Frederick; Bastien, P.; Jones, T. J. E-mail: Bastien@astro.umontreal.ca

    2011-11-10

    New visible and K-band polarization measurements of stars surrounding molecular clouds in Orion A and stars in the Becklin-Neugebauer (BN) vicinity are presented. Our results confirm that magnetic fields located inside the Orion A molecular clouds and in their close neighborhood are spatially connected. On and around the BN object, we measured the angular offsets between the K-band polarization data and available submillimeter (submm) data. We find high values of the polarization degree, P{sub K} , and of the optical depth, {tau}{sub K}, close to an angular offset position of 90 Degree-Sign whereas lower values of P{sub K} and {tau}{sub K} are observed for smaller angular offsets. We interpret these results as evidence for the presence of various magnetic field components toward lines of sight in the vicinity of BN. On a larger scale, we measured the distribution of angular offsets between available H-band polarization data and the same submm data set. Here we find an increase of (P{sub H}) with angular offset, which we interpret as a rotation of the magnetic field by {approx}< 60 Degree-Sign . This trend generalizes previous results on small scales toward and around lines of sight to BN and is consistent with a twist of the magnetic field on a larger scale toward OMC-1. A comparison of our results with several other studies suggests that a two-component magnetic field, perhaps helical, could be wrapping the OMC-1 filament.

  12. Electron Cloud Generation And Trapping in a Quadrupole Magnet at the Los Alamos PSR

    SciTech Connect

    Macek, R.J.; Browman, A.A.; Ledford, J.E.; Borden, M.J.; O'Hara, J.F.; McCrady, R.C.; Rybarcyk, L.J.; Spickermann, T.; Zaugg, T.J.; Pivi, M.T.F.; /SLAC

    2007-11-14

    A diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies with this diagnostic show that the electron flux striking the wall in the quadrupole is comparable to or larger than in an adjacent drift. In addition, the trapped electron signal, obtained using the sweeping feature of diagnostic, was larger than expected and decayed very slowly with an exponential time constant of 50 to 100 {micro}s. Experimental results were also obtained which suggest that a significant fraction of the electrons observed in the adjacent drift space were seeded by electrons ejected from the quadrupole.

  13. Relativistic nuclear magnetic resonance J-coupling with ultrasoft pseudopotentials and the zeroth-order regular approximation

    NASA Astrophysics Data System (ADS)

    Green, Timothy F. G.; Yates, Jonathan R.

    2014-06-01

    We present a method for the first-principles calculation of nuclear magnetic resonance (NMR) J-coupling in extended systems using state-of-the-art ultrasoft pseudopotentials and including scalar-relativistic effects. The use of ultrasoft pseudopotentials is allowed by extending the projector augmented wave (PAW) method of Joyce et al. [J. Chem. Phys. 127, 204107 (2007)]. We benchmark it against existing local-orbital quantum chemical calculations and experiments for small molecules containing light elements, with good agreement. Scalar-relativistic effects are included at the zeroth-order regular approximation level of theory and benchmarked against existing local-orbital quantum chemical calculations and experiments for a number of small molecules containing the heavy row six elements W, Pt, Hg, Tl, and Pb, with good agreement. Finally, 1J(P-Ag) and 2J(P-Ag-P) couplings are calculated in some larger molecular crystals and compared against solid-state NMR experiments. Some remarks are also made as to improving the numerical stability of dipole perturbations using PAW.

  14. Relativistic nuclear magnetic resonance J-coupling with ultrasoft pseudopotentials and the zeroth-order regular approximation

    SciTech Connect

    Green, Timothy F. G. Yates, Jonathan R.

    2014-06-21

    We present a method for the first-principles calculation of nuclear magnetic resonance (NMR) J-coupling in extended systems using state-of-the-art ultrasoft pseudopotentials and including scalar-relativistic effects. The use of ultrasoft pseudopotentials is allowed by extending the projector augmented wave (PAW) method of Joyce et al. [J. Chem. Phys. 127, 204107 (2007)]. We benchmark it against existing local-orbital quantum chemical calculations and experiments for small molecules containing light elements, with good agreement. Scalar-relativistic effects are included at the zeroth-order regular approximation level of theory and benchmarked against existing local-orbital quantum chemical calculations and experiments for a number of small molecules containing the heavy row six elements W, Pt, Hg, Tl, and Pb, with good agreement. Finally, {sup 1}J(P-Ag) and {sup 2}J(P-Ag-P) couplings are calculated in some larger molecular crystals and compared against solid-state NMR experiments. Some remarks are also made as to improving the numerical stability of dipole perturbations using PAW.

  15. Use of Incident and Reflected Solar Particle Beams to Trace the Topology of Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Tan, Lun C.; Malandraki, Olga E.; Reames, Donald V.; Ng, Chee K.; Wang, Linghua; Dorrian, Gareth

    2012-05-01

    Occasionally, large solar energetic particle (SEP) events occur inside magnetic clouds (MCs). In this work, the onset time analysis, the peak intensity analysis, and the decay phase analysis of SEPs are used to investigate two large SEP events inside MCs: the 1998 May 2 and 2002 April 21 events. The onset time analysis of non-relativistic electrons and ~MeV nucleon-1 heavy ions shows the stability of the magnetic loop structure during a period of a few hours in the events examined. The joint analysis of pitch-angle distributions and peak intensities of electrons exhibits that, depending on the particle pitch angle observed at 1 AU, in the April event the reflection point of particles may be distributed along a wide spatial range, implying that the magnetic loop is a magnetic bottle connected to the Sun with both legs. In contrast, in the May event particle reflection occurs abruptly at the magnetic mirror formed by a compressed field enhancement behind the interplanetary shock, consistent with its open field line topology.

  16. Use of incident and reflected solar particle beams to trace the topology of magnetic clouds

    NASA Astrophysics Data System (ADS)

    Malandraki, O.; Tan, L.; Reames, D.; Ng, C.; Wang, L.; Dorrian, G.

    2012-04-01

    Occasionally, large solar energetic particle (SEP) events occur inside magnetic clouds (MCs). In this work the onset time analysis, the peak intensity analysis, and the decay phase analysis of SEPs are used to investigate two large SEP events inside MCs: the 1998 May 2 and 2002 April 21 events. The onset time analysis of non-relativistic electrons and ~MeVnucleon-1 heavy ions exhibits the stability of the magnetic loop structure during a period of a few hours in the events examined. The joint analysis of pitch-angle distributions (PADs) and peak intensities of electrons indicates that in the April event the reflected particles with nearly zero pitch-angle at 1 AU could reach the vicinity of the Sun, implying that the magnetic loop was a magnetic bottle connected to the Sun with both legs. In contrast, in the May event the magnetic mirror was formed by a compressed field enhancement behind the interplanetary shock driven by a preceding coronal mass ejection, being consistent with its open field line topology. We have also measured the anisotropy characteristic of SEPs in the solar wind frame. At the MC boundary the PADs of both non-relativistic electrons and ~MeVnucleon-1 heavy ions are nearly isotropic, suggesting a diffusive transport environment of SEPs there. This work has received funding from the European Commission FP7 Project COMESEP (263252)

  17. USE OF INCIDENT AND REFLECTED SOLAR PARTICLE BEAMS TO TRACE THE TOPOLOGY OF MAGNETIC CLOUDS

    SciTech Connect

    Tan, Lun C.; Malandraki, Olga E.; Dorrian, Gareth; Reames, Donald V.; Ng, Chee K.; Wang Linghua

    2012-05-10

    Occasionally, large solar energetic particle (SEP) events occur inside magnetic clouds (MCs). In this work, the onset time analysis, the peak intensity analysis, and the decay phase analysis of SEPs are used to investigate two large SEP events inside MCs: the 1998 May 2 and 2002 April 21 events. The onset time analysis of non-relativistic electrons and {approx}MeV nucleon{sup -1} heavy ions shows the stability of the magnetic loop structure during a period of a few hours in the events examined. The joint analysis of pitch-angle distributions and peak intensities of electrons exhibits that, depending on the particle pitch angle observed at 1 AU, in the April event the reflection point of particles may be distributed along a wide spatial range, implying that the magnetic loop is a magnetic bottle connected to the Sun with both legs. In contrast, in the May event particle reflection occurs abruptly at the magnetic mirror formed by a compressed field enhancement behind the interplanetary shock, consistent with its open field line topology.

  18. Comparison of Magnetic Properties in a Magnetic Cloud and Its Solar Source on 2013 April 11–14

    NASA Astrophysics Data System (ADS)

    Vemareddy, P.; Möstl, C.; Amerstorfer, T.; Mishra, W.; Farrugia, C.; Leitner, M.

    2016-09-01

    In the context of the Sun–Earth connection of coronal mass ejections and magnetic flux ropes (MFRs), we studied the solar active region (AR) and the magnetic properties of magnetic cloud (MC) event during 2013 April 14–15. We use in situ observations from the Advanced Composition Explorer and source AR measurements from the Solar Dynamics Observatory. The MCs magnetic structure is reconstructed from the Grad–Shafranov method, which reveals a northern component of the axial field with left handed helicity. The MC invariant axis is highly inclined to the ecliptic plane pointing northward and is rotated by 117° with respect to the source region PIL. The net axial flux and current in the MC are comparatively higher than from the source region. Linear force-free alpha distribution (10‑7–10‑6 m‑1) at the sigmoid leg matches the range of twist number in the MC of 1–2 au MFR. The MFR is nonlinear force-free with decreasing twist from the axis (9 turns/au) toward the edge. Therefore, a Gold–Hoyle (GH) configuration, assuming a constant twist, is more consistent with the MC structure than the Lundquist configuration of increasing twist from the axis to boundary. As an indication of that, the GH configuration yields a better fitting to the global trend of in situ magnetic field components, in terms of rms, than the Lundquist model. These cylindrical configurations improved the MC fitting results when the effect of self-similar expansion of MFR was considered. For such twisting behavior, this study suggests an alternative fitting procedure to better characterize the MC magnetic structure and its source region links.

  19. Kinetic and Structural Evolution of Self-gravitating, Magnetized Clouds: 2.5-dimensional Simulations of Decaying Turbulence

    NASA Astrophysics Data System (ADS)

    Ostriker, Eve C.; Gammie, Charles F.; Stone, James M.

    1999-03-01

    The molecular component of the Galaxy is comprised of turbulent, magnetized clouds, many of which are self-gravitating and form stars. To develop an understanding of how these clouds' kinetic and structural evolution may depend on their level of turbulence, mean magnetization, and degree of self-gravity, we perform a survey of direct numerical MHD simulations in which three parameters are independently varied. Our simulations consist of solutions to the time-dependent MHD equations on a two-dimensional grid with periodic boundary conditions; an additional ``half'' dimension is also incorporated as dependent variables in the third Cartesian direction. Two of our survey parameters, the mean magnetization parameter β≡c2sound/v2Alfven and the Jeans number nJ≡Lcloud/LJeans, allow us to model clouds that either meet or fail conditions for magneto-Jeans stability and magnetic criticality. Our third survey parameter, the sonic Mach number M≡σvelocity/csound, allows us to initiate turbulence of either sub- or super-Alfvénic amplitude; we employ an isothermal equation of state throughout. We evaluate the times for each cloud model to become gravitationally bound and measure each model's kinetic energy loss over the fluid-flow crossing time. We compare the evolution of density and magnetic field structural morphology and quantify the differences in the density contrast generated by internal stresses for models of differing mean magnetization. We find that the values of β and nJ, but not the initial Mach number M, determine the time for cloud gravitational binding and collapse: for mean cloud density nH2=100 cm-3, unmagnetized models collapse after ~5 Myr, and magnetically supercritical models generally collapse after 5-10 Myr (although the smallest magneto-Jeans stable clouds survive gravitational collapse until t~15 Myr), while magnetically subcritical clouds remain uncollapsed over the entire simulations; these cloud collapse times scale with the mean density as

  20. Electron Cloud Generation and Trapping in a Quadrupole Magnet at the Los Alamos Proton Storage Ring

    SciTech Connect

    Macek, Robert J.; Browman, Andrew A.; Ledford, John E.; Borden, Michael J.; O'Hara, James F.; McCrady, Rodney C.; Rybarcyk, Lawrence J.; Spickermann, Thomas; Zaugg, Thomas J.; Pivi, Mauro T.F.; /SLAC

    2008-03-17

    Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR) have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the 'prompt' electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the 'swept' electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100 {micro}s. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the quadrupole.

  1. Solar Sources and Geospace Consequences of Interplanetary Magnetic Clouds Observed During Solar Cycle 23

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Michalek, G.; Lepping, R. P.

    2007-01-01

    We present results of a statistical investigation of 99 magnetic clouds (MCs) observed during 1995-2005. The MC-associated coronal mass ejections (CMEs) are faster and wider on the average and originate within +/-30deg from the solar disk center. The solar sources of MCs also followed the butterfly diagram. The correlation between the magnetic field strength and speed of MCs was found to be valid over a much wider range of speeds. The number of south-north (SN) MCs was dominant and decreased with solar cycle, while the number of north-south (NS) MCs increased confirming the odd-cycle behavior. Two-thirds of MCs were geoeffective; the Dst index was highly correlated with speed and magnetic field in MCs as well as their product. Many (55%) fully northward (FN) MCs were geoeffective solely due to their sheaths. The non-geoeffective MCs were slower (average speed approx. 382 km/s), had a weaker southward magnetic field (average approx. -5.2nT), and occurred mostly during the rise phase of the solar activity cycle.

  2. The collective gyration of a heavy ion cloud in a magnetized plasma

    NASA Technical Reports Server (NTRS)

    Brenning, N.; Swenson, C.; Kelley, M. C.; Providakes, J.; Torbert, R.

    1990-01-01

    In both the ionospheric barium injection experiments CRIT 1 and CRIT 2, a long duration oscillation was seen with a frequency close to the gyro frequency of barium and a time duration of about one second. A model for the phenomena which was proposed for the CRIT 1 experiment is compared to the results from CRIT 2 which made a much more complete set of measurements. The model follows the motion of a low Beta ion cloud through a larger ambient plasma. The internal field of the model is close to antiparallel to the injection direction v sub i but slightly tilted towards the self polarization direction E sub p = -V sub i by B. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic field aligned electron currents from the ambient ionosphere, drawn by the divergence in the perpendicular electric field. These currents give a perturbation of the magnetic field related to the electric field perturbation by Delta E/Delta B approximately equal to V sub A. The model predictions agree quite well with the observed vector directions, field strengths, and decay times of the electric and magnetic fields in CRIT 2. The possibility to extend the model to the active region, where the ions are produces in this type of self-ionizing injection experiments, is discussed.

  3. Mixed micelle cloud point-magnetic dispersive μ-solid phase extraction of doxazosin and alfuzosin.

    PubMed

    Gao, Nannan; Wu, Hao; Chang, Yafen; Guo, Xiaozhen; Zhang, Lizhen; Du, Liming; Fu, Yunlong

    2015-01-01

    Mixed micelle cloud point extraction (MM-CPE) combined with magnetic dispersive μ-solid phase extraction (MD-μ-SPE) has been developed as a new approach for the extraction of doxazosin (DOX) and alfuzosin (ALF) prior to fluorescence analysis. The mixed micelle anionic surfactant sodium dodecyl sulfate and non-ionic polyoxyethylene(7.5)nonylphenylether was used as the extraction solvent in MM-CPE, and diatomite bonding Fe₃O₄ magnetic nanoparticles were used as the adsorbent in MD-μ-SPE. The method was based on MM-CPE of DOX and ALF in the surfactant-rich phase. Magnetic materials were used to retrieve the surfactant-rich phase, which easily separated from the aqueous phase under magnetic field. At optimum conditions, a linear relationship between DOX and ALF was obtained in the range of 5-300 ng mL(-1), and the limits of detection were 0.21 and 0.16 ng mL(-1), respectively. The proposed method was successfully applied for the determination of the drugs in pharmaceutical preparations, urine samples, and plasma samples. PMID:24995413

  4. A Circular-cylindrical Flux-rope Analytical Model for Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Nieves-Chinchilla, T.; Linton, M. G.; Hidalgo, M. A.; Vourlidas, A.; Savani, N. P.; Szabo, A.; Farrugia, C.; Yu, W.

    2016-05-01

    We present an analytical model to describe magnetic flux-rope topologies. When these structures are observed embedded in Interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton temperature, they are called Magnetic Clouds (MCs). Our model extends the circular-cylindrical concept of Hidalgo et al. by introducing a general form for the radial dependence of the current density. This generalization provides information on the force distribution inside the flux rope in addition to the usual parameters of MC geometrical information and orientation. The generalized model provides flexibility for implementation in 3D MHD simulations. Here, we evaluate its performance in the reconstruction of MCs in in situ observations. Four Earth-directed ICME events, observed by the Wind spacecraft, are used to validate the technique. The events are selected from the ICME Wind list with the magnetic obstacle boundaries chosen consistently with the magnetic field and plasma in situ observations and with a new parameter (EPP, the Electron Pitch angle distribution Parameter) which quantifies the bidirectionally of the plasma electrons. The goodness of the fit is evaluated with a single correlation parameter to enable comparative analysis of the events. In general, at first glance, the model fits the selected events very well. However, a detailed analysis of events with signatures of significant compression indicates the need to explore geometries other than the circular-cylindrical. An extension of our current modeling framework to account for such non-circular CMEs will be presented in a forthcoming publication.

  5. Circular-cylindrical flux-rope analytical model for Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Nieves-Chinchilla, Teresa; Linton, Mark; Hidalgo, Miguel A.; Vourlidas, Angelos; Savani, Neel P.; Szabo, Adam; Farrugia, Charlie; Yu, Wenyuan

    2016-05-01

    We present an analytical model to describe magnetic flux-rope topologies. When these structures are observed embedded in Interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton temperature, they are called Magnetic Clouds ( MCs). The model extends the circular-cylindrical concept of Hidalgo et al. (2000) by introducing a general form for the radial dependence of the current density. This generalization provides information on the force distribution inside the flux rope in addition to the usual parameters of MC geometrical information and orientation.The generalized model provides flexibility for implementation in 3D MHD simulations. Here, we evaluate its performance in the reconstruction of MCs in in-situ observations. Four Earth directed ICME events, observed by the Wind spacecraft, are used to validate the technique. The events are selected from the ICME Wind list with the magnetic obstacle boundaries chosen consistently with the magnetic fi eld and plasma in situ observations and with a new parameter (EPP, Electron Pitch angle distribution Parameter) which quantifies the bidirectionally of theplasma electrons. The goodness of the fit is evaluated with a single correlation parameter to enable comparative analysis of the events. In general, at first glance, the model fits the selected events very well. However, a detailed analysis of events with signatures of significant compression indicates the need to explore geometries other than the circular-cylindrical.

  6. Mid-Infrared Spectropolarimetry of Molecular Cloud Sources: Magnetic Fields and Dust Properties

    NASA Astrophysics Data System (ADS)

    Wright, Christopher Mathew

    1994-12-01

    One of the earliest phases of the star formation process is the bipolar outflow. It is not presently understood how the outflow is generated, but a number of theories propose that a dynamically important magnetic field, embedded in the disk and acting in concert with rotation, is able to tap the gravitational potential well of the star plus disk system to drive material off the disk surface. Spectropolarimetric observations between 8 and 13 micrometers provide information on the chemical and physical nature of dust grains, as well as on the direction of the transverse (to the line-of-sight) component of an aligning magnetic field. In this thesis, such observations toward a selection of mainly high mass young stellar objects (YSO's) are presented. The field directions inferred from the polarization position angle are compared with the axes of disks and bipolar outflows associated with the sources. A strong correlation is found such that the field tends to lie in the plane of the disk, thereby providing support for the magnetic pressure mechanism for bipolar outflows. The observed field directions are also compared with the interstellar field configuration determined from optical polarization of field stars and obtained from the literature. Two distributions are observed, one in which the difference between the position angles of the two fields is less than 30 deg, and the other for which the difference is greater than 30 deg. The existence of the second group implies that the evolution of the YSO has a significant perturbing effect on its ambient magnetic field. Together with the disk field finding, the results are discussed in terms of the initial collapse phase of the molecular cloud in which the YSO is embedded, specifically whether the cloud was supercritical or subcritical. For instance, for two high mass objects, AFGL 2591 and AFGL 989, and one low mass object, SVS13, the source and interstellar fields, and interstellar field and disk major axes, are inclined

  7. EFFECTS OF MAGNETIC FIELD AND FAR-ULTRAVIOLET RADIATION ON THE STRUCTURES OF BRIGHT-RIMMED CLOUDS

    SciTech Connect

    Motoyama, Kazutaka; Umemoto, Tomofumi; Shang, Hsien; Hasegawa, Tatsuhiko

    2013-03-20

    The bright-rimmed cloud SFO 22 was observed with the 45 m telescope of Nobeyama Radio Observatory in the {sup 12}CO (J = 1-0), {sup 13}CO (J = 1-0), and C{sup 18}O (J = 1-0) lines, where well-developed head-tail structure and small line widths were found. Such features were predicted by radiation-driven implosion models, suggesting that SFO 22 may be in a quasi-stationary equilibrium state. We compare the observed properties with those from numerical models of a photoevaporating cloud, which include effects of magnetic pressure and heating due to strong far-ultraviolet (FUV) radiation from an exciting star. The magnetic pressure may play a more important role in the density structures of bright-rimmed clouds than the thermal pressure that is enhanced by the FUV radiation. The FUV radiation can heat the cloud surface to near 30 K; however, its effect is not enough to reproduce the observed density structure of SFO 22. An initial magnetic field of 5 {mu}G in our numerical models produces the best agreement with the observations, and its direction can affect the structures of bright-rimmed clouds.

  8. Magnetized interstellar molecular clouds - I. Comparison between simulations and Zeeman observations

    NASA Astrophysics Data System (ADS)

    Li, Pak Shing; McKee, Christopher F.; Klein, Richard I.

    2015-09-01

    The most accurate measurements of magnetic fields in star-forming gas are based on the Zeeman observations analysed by Crutcher et al. We show that their finding that the 3D magnetic field scales approximately as density0.65 can also be obtained from analysis of the observed line-of-sight fields. We present two large-scale adaptive-mesh-refinement magnetohydrodynamic simulations of several thousand M⊙ of turbulent, isothermal, self-gravitating gas, one with a strong initial magnetic field (Alfvén Mach number M_A,0=1) and one with a weak initial field (M_A,0=10). We construct samples of the 100 most massive clumps in each simulation and show that they exhibit a power-law relation between field strength and density (bar{n}_H) in excellent agreement with the observed one. Our results imply that the average field in molecular clumps in the interstellar medium (ISM) is < B_tot(bar{n}_H) > ≈ 42 bar{n}_{H, 4}^{0.65} μ G. Furthermore, the median value of the ratio of the line-of-sight field to density0.65 in the simulations is within a factor of about (1.3, 1.7) of the observed value for the strong- and weak-field cases, respectively. The median value of the mass-to-flux ratio, normalized to the critical value, is 70 per cent of the line-of-sight value. This is larger than the 50 per cent usually cited for spherical clouds because the actual mass-to-flux ratio depends on the volume-weighted field, whereas the observed one depends on the mass-weighted field. Our results indicate that the typical molecular clump in the ISM is significantly supercritical (˜ factor of 3). The results of our strong-field model are in very good quantitative agreement with the observations of Li et al., which show a strong correlation in field orientation between small and large scales. Because there is a negligible correlation in the weak-field model, we conclude that molecular clouds form from strongly magnetized (although magnetically supercritical) gas, in agreement with the conclusion

  9. 3D hybrid simulations of the interaction of a magnetic cloud with a bow shock

    NASA Astrophysics Data System (ADS)

    Turc, L.; Fontaine, D.; Savoini, P.; Modolo, R.

    2015-08-01

    In this paper, we investigate the interaction of a magnetic cloud (MC) with a planetary bow shock using hybrid simulations. It is the first time to our knowledge that this interaction is studied using kinetic simulations which include self-consistently both the ion foreshock and the shock wave dynamics. We show that when the shock is in a quasi-perpendicular configuration, the MC's magnetic structure in the magnetosheath remains similar to that in the solar wind, whereas it is strongly altered downstream of a quasi-parallel shock. The latter can result in a reversal of the magnetic field north-south component in some parts of the magnetosheath. We also investigate how the MC affects in turn the outer parts of the planetary environment, i.e., from the foreshock to the magnetopause. We find the following: (i) The decrease of the Alfvén Mach number at the MC's arrival causes an attenuation of the foreshock region because of the weakening of the bow shock. (ii) The foreshock moves along the bow shock's surface, following the rotation of the MC's magnetic field. (iii) Owing to the low plasma beta, asymmetric flows arise inside the magnetosheath, due to the magnetic tension force which accelerates the particles in some parts of the magnetosheath and slows them down in others. (iv) The quasi-parallel region forms a depression in the shock's surface. Other deformations of the magnetopause and the bow shock are also highlighted. All these effects can contribute to significantly modify the solar wind/magnetosphere coupling during MC events.

  10. Relativistic calculation of nuclear magnetic shielding tensor using the regular approximation to the normalized elimination of the small component. II. Consideration of perturbations in the metric operator

    NASA Astrophysics Data System (ADS)

    Maeda, H.; Ootani, Y.; Fukui, H.

    2007-05-01

    A previous relativistic shielding calculation theory based on the regular approximation to the normalized elimination of the small component approach is improved by the inclusion of the magnetic interaction term contained in the metric operator. In order to consider effects of the metric perturbation, the self-consistent perturbation theory is used for the case of perturbation-dependent overlap integrals. The calculation results show that the second-order regular approximation results obtained for the isotropic shielding constants of halogen nuclei are well improved by the inclusion of the metric perturbation to reproduce the fully relativistic four-component Dirac-Hartree-Fock results. However, it is shown that the metric perturbation hardly or does not affect the anisotropy of the halogen shielding tensors and the proton magnetic shieldings.

  11. The collective gyration of a heavy ion cloud in a magnetized plasma. [in earth ionosphere

    NASA Technical Reports Server (NTRS)

    Brenning, N.; Swenson, C.; Kelley, M. C.; Providakes, J.; Torbert, R.

    1992-01-01

    Results are reported from the ionospheric barium injection experiments CRIT I and CRIT II, during both of which a long-duration oscillation was observed with a frequency close to the gyrofrequency of barium and a time duration of about 1 sec. A model for the phenomenon which was proposed for CRIT I is compared to the results from CRIT II, which made a much more complete set of measurements. The model follows the motion of a low-beta ion cloud through a larger ambient plasma. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic-field aligned electron currents from the ambient ionosphere, drawn by the divergence in the perpendicular electric field. These currents yield a perturbation of the magnetic field related to the electric perturbation by Delta-E/Delta-B is approximately equal to V sub A. The possibility of extending the model to the active region, where the ions are produced in this type of self-ionizing injection experiments, is discussed.

  12. A model for the behaviour of the Solar Energetic Particle Events inside Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Medina, J.; Hidalgo, M. A.

    2006-12-01

    The modulation effects of the solar ejecta over the solar energetic particle event SEPe fluxes (0,5-100 MeV) provided by solar flares have recently been highlighted. Especially important is the behaviour of these fluxes inside MCs where, in spite of the low magnetic field intensities of these interplanetary structures (about 30 nT), a decrease in the population of the energetic particles is observed. In the present work it is shown a simple theoretical model we have developed to analyse the behaviour of those fluxes inside the magnetic clouds (MCs) using, as a starting point, our previous magnetic field model for MCs. The experimental data from ACE, GOES, SAMPEX, SOHO, Ulysses and WIND satellites are presented, both from MC coincident with SEPe and not coincident. This work has been supported by the Spanish Comisión Internacional de Ciencia y Tecnología (CICYT), grant ESP2005-07290-C02-01 and ESP2006-08459 and Madrid Autonomous Community / University of Alcala grant CAM-UAH 2005/007. This work is performed inside COST Action 724.

  13. Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.; Arnaud, M.; Arzoumanian, D.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Burigana, C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Chiang, H. C.; Christensen, P. R.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falceta-Gonçalves, D.; Falgarone, E.; Ferrière, K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Ghosh, T.; Giard, M.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Guillet, V.; Harrison, D. L.; Helou, G.; Hennebelle, P.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Holmes, W. A.; Hornstrup, A.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Netterfield, C. B.; Noviello, F.; Novikov, D.; Novikov, I.; Oppermann, N.; Oxborrow, C. A.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Pasian, F.; Perotto, L.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Soler, J. D.; Stolyarov, V.; Sudiwala, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Ysard, N.; Yvon, D.; Zonca, A.

    2016-02-01

    Within ten nearby (d < 450 pc) Gould belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The selected regions, covering several degrees in size, are analysed at an effective angular resolution of 10' FWHM, thus sampling physical scales from 0.4 to 40 pc in the nearest cloud. The column densities in the selected regions range from NH≈ 1021 to1023 cm-2, and hence they correspond to the bulk of the molecular clouds. The relative orientation is evaluated pixel by pixel and analysed in bins of column density using the novel statistical tool called "histogram of relative orientations". Throughout this study, we assume that the polarized emission observed by Planck at 353 GHz is representative of the projected morphology of the magnetic field in each region, i.e., we assume a constant dust grain alignment efficiency, independent of the local environment. Within most clouds we find that the relative orientation changes progressively with increasing NH, from mostly parallel or having no preferred orientation to mostly perpendicular. In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck. We compare the deduced magnetic field strength with estimates we obtain from other methods and discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.

  14. Properties and geoeffectiveness of magnetic clouds during solar cycles 23 and 24

    NASA Astrophysics Data System (ADS)

    Gopalswamy, N.; Yashiro, S.; Xie, H.; Akiyama, S.; Mäkelä, P.

    2015-11-01

    We report on a study that compares the properties of magnetic clouds (MCs) during the first 73 months of solar cycles 23 and 24 in order to understand the weak geomagnetic activity in cycle 24. We find that the number of MCs did not decline in cycle 24, although the average sunspot number is known to have declined by ~40%. Despite the large number of MCs, their geoeffectiveness in cycle 24 was very low. The average Dst index in the sheath and cloud portions in cycle 24 was -33 nT and -23 nT, compared to -66 nT and -55 nT, respectively, in cycle 23. One of the key outcomes of this investigation is that the reduction in the strength of geomagnetic storms as measured by the Dst index is a direct consequence of the reduction in the factor VBz (the product of the MC speed and the out-of-the-ecliptic component of the MC magnetic field). The reduction in MC-to-ambient total pressure in cycle 24 is compensated for by the reduction in the mean MC speed, resulting in the constancy of the dimensionless expansion rate at 1 AU. However, the MC size in cycle 24 was significantly smaller, which can be traced to the anomalous expansion of coronal mass ejections near the Sun reported by Gopalswamy et al. (2014a). One of the consequences of the anomalous expansion seems to be the larger heliocentric distance where the pressure balance between the CME flux ropes and the ambient medium occurs in cycle 24.

  15. Probing the role of the magnetic field in the formation of structure in molecular clouds with Planck

    NASA Astrophysics Data System (ADS)

    Diego Soler, Juan

    2015-08-01

    The Planck observations of intensity and polarization of thermal emission from Galactic dust over the whole sky, and down to scales that probe the interiors of nearby molecular clouds, constitute an unprecedented data set for the study of the morphology of the magnetic field.Within ten nearby (d < 450 pc) Gould Belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The relative orientation is evaluated pixel by pixel and analyzed in bins of column density using the novel statistical tool called "Histogram of Relative Orientations".Within most clouds we find that the relative orientation changes progressively with increasing NH, from preferentially parallel or having no preferred orientation to preferentially perpendicular.In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck.We compare the deduced plane-of-the-sky magnetic field strength with estimates we obtain from the Davis-Chandrasekhar-Fermi method and with the line-of-sight magnetic field strengths derived from Zeeman splitting observations towards some of the studied regions.Finally, we discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.This work is presented on behalf of the Planck Collaboration.

  16. Remote Numerical Simulations of the Interaction of High Velocity Clouds with Random Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Santillan, Alfredo; Hernandez--Cervantes, Liliana; Gonzalez--Ponce, Alejandro; Kim, Jongsoo

    The numerical simulations associated with the interaction of High Velocity Clouds (HVC) with the Magnetized Galactic Interstellar Medium (ISM) are a powerful tool to describe the evolution of the interaction of these objects in our Galaxy. In this work we present a new project referred to as Theoretical Virtual i Observatories. It is oriented toward to perform numerical simulations in real time through a Web page. This is a powerful astrophysical computational tool that consists of an intuitive graphical user interface (GUI) and a database produced by numerical calculations. In this Website the user can make use of the existing numerical simulations from the database or run a new simulation introducing initial conditions such as temperatures, densities, velocities, and magnetic field intensities for both the ISM and HVC. The prototype is programmed using Linux, Apache, MySQL, and PHP (LAMP), based on the open source philosophy. All simulations were performed with the MHD code ZEUS-3D, which solves the ideal MHD equations by finite differences on a fixed Eulerian mesh. Finally, we present typical results that can be obtained with this tool.

  17. The Structure of Magnetic Clouds in the Inner Heliosphere: An Approach Through Grad-Shafranov Reconstruction

    NASA Astrophysics Data System (ADS)

    Hu, Q.; Farrugia, C. J.; Osherovich, V. A.; Moestl, C.; Qiu, J.; Sonnerup, B. U.

    2011-12-01

    Magnetic Clouds (MCs), as a subset of Interplanetary Coronal Mass Ejections (ICMEs), are commonly observed in space. They have been extensively studied with respect to their origin at the Sun, their propagation, and their structures in the inner heliosphere between Sun and Earth. A method, based on the in-situ spacecraft measurements across such structures and the Grad-Shafranov (GS) equation, has been developed and widely used to derive their 2.5D cross-section from the single-spacecraft magnetic field and plasma data. We provide a brief review of the GS reconstruction of MC structures and its applications to various spacecraft mission data and Sun-Solar System Connection science. We then report the recent progress on the application of GS method to the MC structures by examining the effect of (1) inclusion of electron temperature (pressure), since Te is often >> Tp in these configurations, and (2) a locally torus-shape geometry of the MC flux rope, as opposed to the commonly assumed straight-cylinder geometry. Case studies will be presented to illustrate our results.

  18. Relationships Among Geomagnetic Storms, Interplanetary Shocks, Magnetic Clouds, and Sunspot Number During 1995 - 2012

    NASA Astrophysics Data System (ADS)

    Wu, Chin-Chun; Lepping, Ronald P.

    2016-01-01

    During 1995 - 2012, the Wind spacecraft has recorded 168 magnetic clouds (MCs), 197 magnetic cloud-like structures (MCLs), and 358 interplanetary (IP) shocks. Ninety-four MCs and 56 MCLs had upstream shock waves. The following features are found: i) The averages of the solar wind speed, interplanetary magnetic field (IMF), duration (< Δ t >), the minimum of B_{min}, and intensity of the associated geomagnetic storm/activity (Dst_{min}) for MCs with upstream shock waves (MC_{shock}) are higher (or stronger) than those averages for the MCs without upstream shock waves (MC_{no-shock}). ii) The average < Δ t > of MC_{shock} events ({≈} 19.8 h) is 9 % longer than that for MC_{no-shock} events ({≈} 17.6 h). iii) For the MC_{shock} events, the average duration of the sheath (<Δ t_{sheath}>) is 12.1 h. These findings could be very useful for space weather predictions, i.e. IP shocks driven by MCs are expected to arrive at Wind (or at 1 AU) about 12 h ahead of the front of the MCs on average. iv) The occurrence frequency of IP shocks is well associated with sunspot number (SSN). The average intensity of geomagnetic storms measured by < Dst_{min}> for MC_{shock} and MC_{no-shock} events is -102 and -31 nT, respectively. The average values < {Dst}_{min} > are -78, -70, and -35 nT for the 358 IP shocks, 168 MCs, and 197 MCLs, respectively. These results imply that IP shocks, when they occur with MCs/MCLs, must play an important role in the strength of geomagnetic storms. We speculate about the reason for this. Yearly occurrence frequencies of MC_{shock} and IP shocks are well correlated with solar activity ( e.g., SSN). Choosing the correct Dst_{min} estimating formula for predicting the intensity of MC-associated geomagnetic storms is crucial for space weather predictions.

  19. Formation of Dense Clumps/Cores in Infrared Dark Clouds and Their Magnetic Field Properties from AMR MHD Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Li, Pak Shing; Klein, Richard I.

    2014-07-01

    Massive infrared dark clouds (IRDCs) are believed to be the precursors to star clusters and massive stars (e.g. Bergin & Tafalla 2007). The supersonic turbulent nature of molecular clouds in the presence of magnetic fields poses a great challenge in understanding the structure and dynamics of molecular clouds and the star formation therein (e.g. Falgarone et al. 2008, Crutcher et al. 2010, Peretto & Fuller 2010, Hernandez & Tan 2011, Harcar et al. 2013, Kainulainen & Tan 2013). We perform two high resolution ideal MHD AMR simulations with supersonically driven turbulence on the formation of massive infrared dark clouds, using our radiative-MHD AMR code ORION2 (P.S. Li, et al. 2012), to reveal the complex 3D filamentary structure and the subsequent formation of dense clumps and cores inside the dark clouds. The two models differ only in field strength, with one model having an initial field 10 times as strong as the other. The magnetic properties of the clumps from the two models are compared with the Zeeman observations summarized in Crutcher et al. (2010). Our dense clumps exhibit a power-law relation between magnetic field strength and density similar to the observations. Despite the order of magnitude difference in initial field strength, with the magnetic field enhancement and fragmentation as the result of turbulence, the magnetic properties of clumps in the weak field model are remarkably similar to those in the strong field model, except for a clear difference in the magnetic field orientation with respect to the global mean field direction. The almost random orientation of the weak field simulation is inconsistent with the observation of the field orientation on large and small scales by H.-b. Li, et al. (2009). I will briefly summarize the physical properties of the filamentary dark clouds in the simulations and report a detailed comparison of the magnetic properties of dense clumps in the simulations with the Zeeman observations. We have continued the

  20. Swift J045106.8-694803: a highly magnetized neutron star in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Klus, H.; Bartlett, E. S.; Bird, A. J.; Coe, M.; Corbet, R. H. D.; Udalski, A.

    2013-02-01

    We report the analysis of a highly magnetized neutron star in the Large Magellanic Cloud (LMC). The high-mass X-ray binary pulsar Swift J045106.8-694803 has been observed with Swift X-ray telescope (XRT) in 2008, the Rossi X-ray Timing Explorer (RXTE) in 2011 and the X-ray Multi-Mirror Mission-Newton (XMM-Newton) in 2012. The change in spin period over these four years indicates a spin-up rate of -5.01 ± 0.06 s yr-1, amongst the highest observed for an accreting pulsar. This spin-up rate can be accounted for using Ghosh & Lamb accretion theory assuming it has a magnetic field of (1.2 ± 0.20.7) × 1014 G. This is over the quantum critical field value. There are very few accreting pulsars with such high surface magnetic fields and this is the first of which to be discovered in the LMC. The large spin-up rate is consistent with Swift Burst Alert Telescope (BAT) observations which show that Swift J045106.8-694803 has had a consistently high X-ray luminosity for at least five years. Optical spectra have been used to classify the optical counterpart of Swift J045106.8-694803 as a B0-1 III-V star and a possible orbital period of 21.631 ± 0.005 d has been found from Massive Compact Halo Object (MACHO) optical photometry.

  1. Interplanetary Charged Dust Magnetic Clouds Striking the Magnetosphere: Coordinated Space-based and Ground-based Observations

    NASA Astrophysics Data System (ADS)

    Russell, C. T.; Chi, Peter; Lai, Hairong

    In general, asteroids, meteoroids and dust do not interact with the plasma structures in the solar system, but after a collision between fast moving bodies the debris cloud contains nanoscale dust particles that are charged and behave like heavy ions. Dusty magnetic clouds are then accelerated to the solar wind speed. While they pose no threat to spacecraft because of the particle size, the coherency imposed by the magnetization of the cloud allows the cloud to interact with the Earth’s magnetosphere as well as the plasma in the immediate vicinity of the cloud. We call these clouds Interplanetary Field Enhancements (IFEs). These IFEs are a unique class of interplanetary field structures that feature cusp-shaped increases and decreases in the interplanetary magnetic field and a thin current sheet. The occurrence of IFEs is attributed to the interaction between the solar wind and dust particles produced in inter-bolide collisions. Previous spacecraft observations have confirmed that IFEs move with the solar wind. When IFEs strike the magnetosphere, they may distort the magnetosphere in several possible ways, such as producing a small indentation, a large scale compression, or a glancing blow. In any event if the IFE is slowed by the magnetosphere, the compression of the Earth’s field should be seen in the ground-based magnetic records that are continuously recorded. Thus it is important to understand the magnetospheric response to IFE arrival. In this study, we investigate the IFE structure observed by spacecraft upstream of the magnetosphere and the induced magnetic field perturbations observed by networks of ground magnetometers, including the THEMIS, CARISMA, McMAC arrays in North America and the IMAGE array in Europe. We find that, in a well-observed IFE event on December 24, 2006, all ground magnetometer stations observed an impulse at approximately 1217 UT when the IFE was expected to arrive at the Earth’s magnetopause. These ground stations spread across

  2. Galactic Cosmic Ray Intensity Response to Interplanetary Coronal Mass Ejections/Magnetic Clouds in 1995-2009

    NASA Technical Reports Server (NTRS)

    Richardson, I. G.; Cane, H. V.

    2011-01-01

    We summarize the response of the galactic cosmic ray (CGR) intensity to the passage of the more than 300 interplanetary coronal mass ejections (ICMEs) and their associated shocks that passed the Earth during 1995-2009, a period that encompasses the whole of Solar Cycle 23. In approx.80% of cases, the GCR intensity decreased during the passage of these structures, i.e., a "Forbush decrease" occurred, while in approx.10% there was no significant change. In the remaining cases, the GCR intensity increased. Where there was an intensity decrease, minimum intensity was observed inside the ICME in approx.90% of these events. The observations confirm the role of both post-shock regions and ICMEs in the generation of these decreases, consistent with many previous studies, but contrary to the conclusion of Reames, Kahler, and Tylka (Astrophys. 1. Lett. 700, L199, 2009) who, from examining a subset of ICMEs with flux-rope-like magnetic fields (magnetic clouds) argued that these are "open structures" that allow free access of particles including GCRs to their interior. In fact, we find that magnetic clouds are more likely to participate in the deepest GCR decreases than ICMEs that are not magnetic clouds.

  3. Spatial and Temporal Energy Characterization of Precipitating Electrons for the January 10th, 1997 Magnetic Cloud Event

    NASA Technical Reports Server (NTRS)

    Spann, J. F., Jr.; Germany, G. A.; Brittnacher, M. J.; Parks, G. K.; Elsen, R.

    1997-01-01

    The January 10-11, 1997 magnetic cloud event provided a rare opportunity to study auroral energy deposition under varying but intense IMF conditions. The Wind spacecraft located about 100 RE upstream monitored the IMF and plasma parameters during the passing of the cloud. The Polar Ultraviolet Imager (UVI) observed the aurora[ precipitation during the first encounter of the cloud with Earth's magnetosphere and during several subsequent substorm events. The UVI has the unique capability of measuring the energy flux and characteristic energy of the precipitating electrons through the use of narrow band filters that distinguish short and long wavelength molecular nitrogen emissions. The spatial and temporal characteristics of the precipitating electron energy will be discussed beginning with the inception of the event at the Earth early January 1 Oth and continuing through the subsidence of auroral activity on January 11th.

  4. Krein regularization of QED

    NASA Astrophysics Data System (ADS)

    Forghan, B.; Takook, M. V.; Zarei, A.

    2012-09-01

    In this paper, the electron self-energy, photon self-energy and vertex functions are explicitly calculated in Krein space quantization including quantum metric fluctuation. The results are automatically regularized or finite. The magnetic anomaly and Lamb shift are also calculated in the one loop approximation in this method. Finally, the obtained results are compared to conventional QED results.

  5. Optimization of Regularization Parameters in Compressed Sensing of Magnetic Resonance Angiography: Can Statistical Image Metrics Mimic Radiologists' Perception?

    PubMed Central

    Akasaka, Thai; Fujimoto, Koji; Yamamoto, Takayuki; Okada, Tomohisa; Fushumi, Yasutaka; Yamamoto, Akira; Tanaka, Toshiyuki; Togashi, Kaori

    2016-01-01

    In Compressed Sensing (CS) of MRI, optimization of the regularization parameters is not a trivial task. We aimed to establish a method that could determine the optimal weights for regularization parameters in CS of time-of-flight MR angiography (TOF-MRA) by comparing various image metrics with radiologists’ visual evaluation. TOF-MRA of a healthy volunteer was scanned using a 3T-MR system. Images were reconstructed by CS from retrospectively under-sampled data by varying the weights for the L1 norm of wavelet coefficients and that of total variation. The reconstructed images were evaluated both quantitatively by statistical image metrics including structural similarity (SSIM), scale invariant feature transform (SIFT) and contrast-to-noise ratio (CNR), and qualitatively by radiologists’ scoring. The results of quantitative metrics and qualitative scorings were compared. SSIM and SIFT in conjunction with brain masks and CNR of artery-to-parenchyma correlated very well with radiologists’ visual evaluation. By carefully selecting a region to measure, we have shown that statistical image metrics can reflect radiologists’ visual evaluation, thus enabling an appropriate optimization of regularization parameters for CS. PMID:26744843

  6. Propagation and Evolution of Interplanetary Magnetic Clouds: Global Simulations and Comparisons with Observations

    NASA Astrophysics Data System (ADS)

    Riley, P.; Ben-Nun, M.; Linker, J.; Torok, T.; Lionello, R.; Downs, C.

    2014-12-01

    In this talk, we explore the evolution of interplanetary coronal mass ejections (ICMEs), and fast magnetic clouds (MCs) in particular. We address three specific issues. First, What are the large-scale forces acting on ejecta as they travel from the Sun to 1 AU through a realistic ambient solar wind, and how does they affect the large-scale structure of the event? Second, what are the dominant waves/shocks associated with fast ICMEs? And third, how are the properties of ICMEs different during cycle 24 than during the previous cycle? To accomplish these objectives, we employ a variety of numerical approaches, including global resistive MHD models that incorporate realistic energy transport processes. We also compare and contrast model results with both remote solar and in-situ measurements of ICMEs at 1 AU and elsewhere, including the so-called ``Bastille Day'' event of July 14, 2000, and the more recent ``extreme ICME'' observed by STEREO-A on July 23, 2012.

  7. Selection Effects in Identifying Magnetic Clouds and the Importance of the Closest Approach Parameter

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Wu, Chin-Chun

    2010-01-01

    This study is motivated by the unusually low number of magnetic clouds (MCs) that are strictly identified within interplanetary coronal mass ejections (ICMEs), as observed at 1 AU; this is usually estimated to be around 30% or lower. But a looser definition of MCs may significantly increase this percentage. Another motivation is the unexpected shape of the occurrence distribution of the observers' "closest approach distances" (measured from a MC's axis, and called CA) which drops off somewhat rapidly as |CA| (in % of MC radius) approaches 100%, based on earlier studies. We suggest, for various geometrical and physical reasons, that the |CA|-distribution should be somewhere between a uniform one and the one actually observed, and therefore the 30% estimate should be higher. So we ask, When there is a failure to identify a MC within an ICME, is it occasionally due to a large |CA| passage, making MC identification more difficult, i.e., is it due to an event selection effect? In attempting to answer this question we examine WIND data to obtain an accurate distribution of the number of MCs vs. |CA| distance, whether the event is ICME-related or not, where initially a large number of cases (N=98) are considered. This gives a frequence distribution that is far from uniform, confirming earlier studies. This along with the fact that there are many ICME identification-parameters that do not depend on |CA| suggest that, indeed an MC event selection effect may explain at least part of the low ratio of (No. MCs)/(No. ICMEs). We also show that there is an acceptable geometrical and physical consistency in the relationships for both average "normalized" magnetic field intensity change and field direction change vs. |CA| within a MC, suggesting that our estimates of |CA|, B(sub 0) (magnetic field intensity on the axis), and choice of a proper "cloud coordinate" system (all needed in the analysis) are acceptably accurate. Therefore the MC fitting model (Lepping et al., 1990) is

  8. Dust Properties and Magnetic Fields in MSX Infrared-Dark Clouds

    NASA Astrophysics Data System (ADS)

    Carey, S. J.; Feldman, P. A.; Redman, R. O.; Egan, M. P.; Mizuno, D.; Kuchar, T.; Price, S.

    1999-12-01

    The Midcourse Space Experiment (MSX) infrared-dark clouds (IRDCs) are a population of a few thousand molecular cores that have been identified by their substantial mid-infrared (8-25 μ m) extinctions in the MSX Galactic Plane survey images (Egan et al. 1998, ApJL, 494, L199). Subsequent observations have revealed IRDCs to contain cold (T < 15 K), dense (n 106 cm-3) molecular gas (Carey et al. 1998, ApJ, 508, 721). The IRDCs are distributed along spiral arms and are located near but do not contain star formation tracers such as HII regions and H2O maser emission. Continuum maps at 450 and 850 μ m taken with SCUBA on the JCMT reveal bright knots of emission within the envelope of emission associated with the IRDCs. Many IRDCs are filamentary in nature. The bright emission knots have HCO+ and CO line profiles indicative of outflow and/or infall with several sources exhibiting the blue-red asymmetry characteristic of infall. The IRDCs appear to be large, cold molecular cores in the earliest stages of star formation. We present a detailed comparison of the extinction at 8 μ m derived from the soon-to-be released MSX Galactic Plane survey images ( 18'' resolution) to the 450/850 μ m emission (14'' resolution). The morphologies of the submillimeter emission and mid-infrared extinction are in good agreement. From the comparison, we will determine the dust column density and constrain dust temperature and emissivity. In addition, we present very recent polarimetric imaging of IRDCs at 850 μ m. A relatively high degree of polarization at 850 μ m is seen, suggesting that a well-ordered magnetic field may be present within most IRDCs. In general, the magnetic fields thread the filaments with a more complicated structure near the embedded sources. We will examine the structure of the magnetic field and the star formation properties of IRDCs using the mid-infrared and submillimeter images, submillimeter polarimetry and CO and HCO+ line maps.

  9. Reconnection Remnants in the Magnetic Cloud of October 18-19, 1995: A Shock, Monochromatic Wave, Heat Flux Dropout and Energetic Ion Beam

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Szabo, A.; Farrell, W.; Slavin, J. A.; Lepping, R. P.; Fitzenreiter, R.; Thompson, B.; Hamilton, D. C.; Gloeckler, G.; Ho, G. C.

    2000-01-01

    Evidence is presented that the WIND spacecraft observed particle and field signatures on October 18-19, 1995 due to reconnection near the footpoints of a magnetic cloud (i.e., between 1 and 5 solar radii). These signatures include: (1) an internal shock traveling approximately along the axis of the magnetic cloud, (2) a simple compression of the magnetic field consistent with the footpoint magnetic fields being thrust outwards at speeds much greater than the solar wind speed, (3) an electron heat flux dropout occurring within minutes of the shock indicating a topological change resulting from disconnection from the solar surface, (4) a very cold 5 keV proton beam and (5) an associated monochromatic wave. We expect that, given observations of enough magnetic clouds, Wind and other spacecraft will see signatures similar to the ones reported here indicating reconnection. However, these observations require the spacecraft to be fortuitously positioned to observe the passing shock and other signatures and will therefore be associated with only a small fraction of magnetic clouds. Consistent with this, a few magnetic clouds observed by Wind have been found to possess internal shock waves.

  10. Effect of surface conductivity on the peak magnetic field radiated by first return strokes in cloud-to-ground lightning

    NASA Technical Reports Server (NTRS)

    Tyahla, Lori J.; Lopez, Raul E.

    1994-01-01

    The effect of surface conductivity on the peak magnetic field radiated by the first return stroke in cloud-to-ground lightning was investigated by comparing the peak magnetic fields from return strokes that struck water with those that struck land. The data were obtained from a network of three gated, wideband magnetic direction finders (DFs) at the NASA Kennedy Space Center during the summer of 1985. Two geographical areas that were equidistant from two of the direction finders were compared where the flash distances ranged from approximately 40 to 60 km. An unbiased data set was obtained by correcting site errors, equalizing differences in sensor gain, eliminating directional biases in DF triggering, and keeping differences in signal attenuation over the two surfaces to a minimum. When a statistical analysis was performed on the frequency distributions of the signal amplitudes, there was no statistically significant difference in the peak amplitudes of first return strokes over land (lambda = 8.2 x 10(exp -3) mho/m) and over water (lambda = 4 mho/m). Therefore we infer that the conductivity of the underlying surface does not significantly affect the magnitude of the peak magnetic field, and hence the peak current, in the first return stroke of a cloud-to-ground lightning flash.

  11. Low-frequency waves within isolated magnetic clouds and complex structures: STEREO observations

    NASA Astrophysics Data System (ADS)

    Siu-Tapia, A.; Blanco-Cano, X.; Kajdic, P.; Aguilar-Rodriguez, E.; Russell, C. T.; Jian, L. K.; Luhmann, J. G.

    2015-04-01

    Complex Structures (CSs) formed by the interaction of magnetic cloud (MC)-like structures with other transients (e.g., another MC, a stream interaction region, or a fast stream of solar wind) were frequently observed in the interplanetary space by STEREO spacecraft during the solar minimum 23 and the rising phase of the solar cycle 24. Here we report the presence of low-frequency waves (LFWs) inside some isolated MCs (IMCs) and inside the CSs observed by STEREO during such period (2007-2011). It is important to study in detail the properties of waves in space plasmas since particle distribution functions can be modified by wave-particle interactions. We compare wave characteristics within IMCs with those waves observed inside CSs. Both left-handed (LH) and right-handed (RH), near-circularly polarized, transverse and almost parallel-propagating LFWs (around the proton cyclotron frequency) were sporadically observed inside both IMCs and CSs. In contrast, compressive mirror-mode waves (MMs) were observed only within CSs. We studied local plasma conditions inside the IMCs and CSs to gain insight about wave origin: most of the MMs within CSs were observed in regions with enhanced plasma beta (β>1) the majority of the LH waves were found in low beta plasmas (β<1), and the RH waves were predominantly observed at moderate betas (0.4<β≤2). These observations are in agreement with linear kinetic theory predictions for the growth of the mirror, the LH ion cyclotron, and the RH ion firehose instability, respectively. It is possible that the waves were generated locally inside the IMCs and CSs via temperature anisotropies. The plasma beta enhancements that were frequently observed inside the CSs may be the result of compressions and heating taking place inside the interacting structures.

  12. Arrival time of solar eruptive CMEs associated with ICMEs of magnetic cloud and ejecta

    NASA Astrophysics Data System (ADS)

    Shanmugaraju, A.; Syed Ibrahim, M.; Moon, Y.-J.; Kasro Lourdhina, K.; Dharanya, M.

    2015-05-01

    The Coronal Mass Ejection (CME) is an eruptive event in which magnetic plasma is ejected from the Sun into space through the solar corona. We considered a set of 51 Interplanetary Coronal Mass Ejections (ICMEs) listed by Kim et al. (Solar Phys. 184:77, 2013) from Coordinated Data Analysis Workshop (CDAW, Gopalswamy et al. in Astrophys. J. 710:1111, 2010). Among the 51 events, 22 events are classified as Magnetic Clouds (MC) and 29 events are classified as Ejecta (EJ) where the MC and EJ are subsets of ICMEs. We have analyzed the physical properties of CMEs and ICMEs associated with MC and EJ, and correlated them with the CME's transit time/arrival time from the Sun to the Earth. Main aims of the present study are to examine (a) dependence of transit time on the properties of CMEs and ICMEs, and (b) differences between MC and EJ. It is found that CME's initial speed decides the transit time which is in support of the known results in literature. Apart from this, some important results from the present study are: (i) transit time predicted using an empirical relation obtained in the present work is found comparable with the observations (correlation coefficient=0.70). (ii) The transit time of MC and EJ-associated CMEs ranges from 20 to 120 hours and IP acceleration lies between -10 m/s2 to 5 m/s2. (iii) There are certain differences between MC and EJ such as: (a) Ejecta takes slightly more time to travel and only 30 % of them are accelerated in the interplanetary medium. Whereas, MC takes less time to travel and nearly 50 % of them are accelerated, (b) The correlations of IP acceleration and speed with transit time are higher for MC than that of EJ, (c) A weak relationship between the deflection and transit time is found for MC, but it is absent in the case of EJ and (d) Only EJ-type CMEs have wider range of direction parameter and acceleration. Further, we checked the solar wind speed as another parameter has any influence on CME acceleration and it shows that there

  13. Characterization of a double flux-rope magnetic cloud observed by ACE spacecraft on August 19-21, 1998

    NASA Astrophysics Data System (ADS)

    Ojeda González, A.; Mendes, O.; Domingues Oliveira, M.; Moestl, C.; Farrugia, C. J.; Gonzalez, W. D.

    2013-05-01

    Investigations have studied MC cases of double flux rope configuration with apparent asymmetry. Grad-Shafranov reconstruction technique allows deriving the local magnetic structure from data of a single spacecraft. The results obtained show two cylindrical flux ropes next to each other, where a single X point forms between them. In all possible combinations of two bipolar MCs, the magnetic field between them is antiparallel in eight cases SWN-SWN, SWN-SEN, SEN-SWN, SEN-SEN, NWS-NWS, NWS-NES, NES-NWS, NES-NWS. If clouds are under magnetic coupling, reconnection evidences are expected from the interaction between them. In this work, we examine the event that occurred at Aug. 19-21, 1998 using solar wind measurements collected by ACE. In Fig. 1 a) presents the recovered cross-section of the two bipolar MCs (SEN-SWN). The black contour lines show the transverse magnetic field lines (calculated as the contours of the magnetic potential function A(x,y)), and the colors show the axial magnetic field Bz distribution. The yellow arrows along y=0 denote measured transverse magnetic field vectors, direction and magnitude measurements at ACE utilized as initial input into the numerical solver. The green arrows are residual velocities in the deHoffmann-Teller frame at ACE. The spacecraft crosses the X point and observes the exact moment of the magnetic reconnection, from 0.13 to 0.15 AU in x axis. In the opposite corners of the X point, the magnetic fields are antiparallel (see yellow arrows in this region). The residual velocity (green arrow in y=0) in the deHoffmann-Teller frame at ACE is perpendicular to the magnetic field line in the reconnection region. In principle, it is possible to adjust a two-dimension model considering the most common separator reconnection, in which four separate magnetic domains exchange magnetic field lines. In Fig. 1 b), the cross-section through four magnetic domains undergoing separator reconnection is represented. The green array in the top

  14. On the alignment of Classical T Tauri stars with the magnetic field in the Taurus-Auriga molecular cloud

    NASA Astrophysics Data System (ADS)

    Ménard, F.; Duchêne, G.

    2004-10-01

    In this paper we readdress the issue of the alignment of Classical T Tauri stars (CTTS) with the magnetic field in the Taurus-Auriga molecular cloud. Previous studies have claimed that the jet axis of active young stellar objects (YSO), projected in the plane of the sky, is aligned preferentially along the projected direction of the local magnetic field. We re-examine this issue in view of the numerous high angular resolution images of circumstellar disks and micro-jets now available. The images show that T Tauri stars as a group are oriented randomly with respect to the local magnetic field, contrary to previous claims. This indicates that the magnetic field may play a lesser role in the final stages of collapse of an individual prestellar core than previously envisioned. The current database also suggests that a subsample of CTTS with resolved disks but without observations of bright and extended outflows have a tendency to align perpendicularly to the magnetic field. We discuss the possibility that this may trace a less favorable topology, e.g., quadrupolar, for the magnetic field in the inner disk, resulting in a weaker collimated outflow.

  15. Magnetospheric Response to the Arrival of the Shock Wave in Front of the Magnetic Cloud of January 10, 1997

    NASA Technical Reports Server (NTRS)

    Wuest, M.; Huddleston, M. M.; Burch, J. L.; Dempsey, D. L.; Craven, P. D.; Chandler, M. O.; Spann, J. F.; Peterson, W. K.; Collin, H. L.; Lennartsson, W.

    1999-01-01

    We are Studying the magnetic cloud event of January 6 - 11, 1997. Specifically, we have investigated the response of the magnetosphere to the shock wave in front of the magnetic cloud on January 10, 1997 using data from WIND, GEOTAIL and POLAR spacecraft as well as ground magnetometer data. The WIND spacecraft, which was located as about 104 Re upstream from the Earth (85.1, -55.2, -22.1) Re(sub GSM), observed the arrival of the shock wave front at 0050 UT. Geotail was located at the equatorial magnetopause (approx. 8.7 Re, 10.7 MLT, -7.46 MLAT), while POLAR was located in the northern dawn sector above the auroral zone at 8.4 Re, 6.1 MLT and 61.1 MLAT. A magnetic signature was nearly simultaneously observed at about 0104 UT at the POLAR and Geotail spacecraft. The Geotail spacecraft entered from the magnetosphere into the magnetosheath. Particle density increases were observed on WIND and Geotail, but not on POLAR. Two instruments on the Polar spacecraft (TIDE and TIMAS) actually observed a slight reduction in energy, density and temperature. The UV aurora shows a dawnside intensification. The shock wave did not cause an auroral substorm and therefore was not geoeffective.

  16. The (non-)variability of magnetic chemically peculiar candidates in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Paunzen, E.; Mikulášek, Z.; Poleski, R.; Krtička, J.; Netopil, M.; Zejda, M.

    2013-08-01

    Context. The galactic magnetic chemically peculiar (mCP) stars of the upper main sequence are well known as periodic spectral and light variables. The observed variability is obviously caused by the uneven distribution of overabundant chemical elements on the surfaces of rigidly rotating stars. The mechanism causing the clustering of some chemical elements into disparate structures on mCP stars has not been fully understood up to now. The observations of light changes of mCP candidates recently revealed in the nearby Large Magellanic Cloud (LMC) should provide us with information about their rotational periods and about the distribution of optically active elements on mCP stars born in other galaxies. Aims: We queried for photometry at the Optical Gravitational Lensing Experiment (OGLE)-III survey of published mCP candidates selected because of the presence of the characteristic λ5200 Å flux depression. In total, the intersection of both sources resulted in twelve stars. For these objects and two control stars, we searched for a periodic variability. Methods: We performed our own and standard periodogram time series analyses of all available data. The final results are, amongst others, the frequency of the maximum peak and the bootstrap probability of its reality. Results: We detected that only two mCP candidates, 190.1 1581 and 190.1 15527, may show some weak rotationally modulated light variations with periods of 1.23 and 0.49 days; however, the 49% and 32% probabilities of their reality are not very satisfying. The variability of the other 10 mCP candidates is too low to be detectable by their V and I OGLE photometry. Conclusions: The relatively low amplitude variability of the studied LMC mCP candidates sample can be explained by the absence of photometric spots of overabundant optically active chemical elements. The unexpected LMC mCPs behaviour is probably caused by different conditions during the star formation in the LMC and the Galaxy. Figures 11-22 are

  17. Multi-Physics Feedback Simulations with Realistic Initial Conditions of the Formation of Star Clusters: From Large Scale Magnetized Clouds to Turbulent Clumps to Cores to Stars

    NASA Astrophysics Data System (ADS)

    Klein, R. I.; Li, P.; McKee, C. F.

    2015-10-01

    Multi-physics zoom-in adaptive mesh refinement simulations with feedback and realistic initial conditions, starting from large scale turbulent molecular clouds through the formation of clumps and cores to the formation os stellar clusters are presented. I give a summary of results at the different scales undergoing gravitational collapse from cloud to core to cluster formation. Detailed comparisons with observations are made at each stage of the simulations. In particular, properties of the magnetized clumps are compared with recent observations of Crutcher et al. 2010 and Crutcher 2012 and the magnetic field orientation in cloud clumps relative to the global mean field of the inter-cloud medium (Li et al. 2009). The Initial Mass Function (IMF) obtained is compared with the Chabrier IMF and the protostellar mass function of the cluster is compared with different theories.

  18. The Fraction of Interplanetary Coronal Mass Ejections That Are Magnetic Clouds: Evidence for a Solar Cycle Variation

    NASA Technical Reports Server (NTRS)

    Richardson, I. G.; Cane, H. V.

    2004-01-01

    "Magnetic clouds" (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized by enhanced magnetic fields with an organized rotation in direction, and low plasma beta. Though intensely studied, MCs only constitute a fraction of all the ICMEs that are detected in the solar wind. A comprehensive survey of ICMEs in the near- Earth solar wind during the ascending, maximum and early declining phases of solar cycle 23 in 1996 - 2003 shows that the MC fraction varies with the phase of the solar cycle, from approximately 100% (though with low statistics) at solar minimum to approximately 15% at solar maximum. A similar trend is evident in near-Earth observations during solar cycles 20 - 21, while Helios 1/2 spacecraft observations at 0.3 - 1.0 AU show a weaker trend and larger MC fraction.

  19. Regularly scheduled, day-time, slow-onset 60 Hz electric and magnetic field exposure does not depress serum melatonin concentration in nonhuman primates

    SciTech Connect

    Rogers, W.R.; Smith, H.D.; Orr, J.L.; Reiter, R.J.; Barlow-Walden, L.

    1995-12-31

    Experiments conducted with laboratory rodents indicate that exposure to 60 Hz electric fields or magnetic fields can suppress nocturnal melatonin concentrations in pineal gland and blood. In three experiments employing three field-exposed and three sham-exposed nonhuman primates, each implanted with an indwelling venous cannula to allow repeated blood sampling, the authors studied the effects of either 6 kV/m and 50 {micro}T (0.5 G) or 30 kV/m and 100 {micro}T (1.0 G) on serum melatonin patterns. The fields were ramped on and off slowly, so that no transients occurred. Extensive quality control for the melatonin assay, computerized control and monitoring of field intensities, and consistent exposure protocols were used. No changes in nocturnal serum melatonin concentration resulted from 6 weeks of day-time exposure with slow field onset/offset and a highly regular exposure protocol. These results indicate that, under the conditions tested, day-time exposure to 60 Hz electric and magnetic fields in combination does not result in melatonin suppression in primates.

  20. Reconstruction of the 2007 May 22 Magnetic Cloud: How Much Can We Trust the Flux-Rope Geometry of CMEs?

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Luhmann, J. G.; Huttunen, K. E. J.; Lin, R. P.; Bale, S. D.; Russell, C. T.; Galvin, A. B.

    2008-04-01

    Coronal mass ejections (CMEs) are often assumed to be magnetic flux ropes, but direct proof has been lacking. A key feature, resulting from the translational symmetry of a flux rope, is that the total transverse pressure as well as the axial magnetic field has the same functional form over the vector potential along any crossing of the flux rope. We test this feature (and hence the flux-rope structure) by reconstructing the 2007 May 22 magnetic cloud (MC) observed at STEREO B, Wind/ACE, and possibly STEREO A with the Grad-Shafranov (GS) method. The model output from reconstruction at STEREO B agrees fairly well with the magnetic field and thermal pressure observed at ACE/Wind; the separation between STEREO B and ACE/Wind is about 0.06 AU, almost half of the MC radial width. For the first time, we reproduce observations at one spacecraft with data from another well-separated spacecraft, which provides compelling evidence for the flux-rope geometry and is of importance for understanding CME initiation and propagation. We also discuss the global configuration of the MC at different spacecraft on the basis of the reconstruction results.

  1. Wind Magnetic Clouds for 2010-2012: Model Parameter Fittings, Associated Shock Waves, and Comparisons to Earlier Periods

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Wu, C.-C.; Berdichevsky, D. B.; Szabo, A.

    2015-01-01

    We fitted the parameters of magnetic clouds (MCs) as identified in the Wind spacecraft data from early 2010 to the end of 2012 using the model of Lepping, Jones, and Burlaga (J. Geophys. Res. 95, 1195, 1990). The interval contains 48 MCs and 39 magnetic cloud-like (MCL) events. This work is a continuation of MC model fittings of the earlier Wind sets, including those in a recent publication, which covers 2007 to 2009. This period (2010 - 2012) mainly covers the maximum portion of Solar Cycle 24. Between the previous and current interval, we document 5.7 years of MCs observations. For this interval, the occurrence frequency of MCs markedly increased in the last third of the time. In addition, over approximately the last six years, the MC type (i.e. the profile of the magnetic-field direction within an MC, such as North-to-South, South-to-North, all South) dramatically evolved to mainly North-to-South types when compared to earlier years. Furthermore, this evolution of MC type is consistent with global solar magnetic-field changes predicted by Bothmer and Rust (Coronal Mass Ejections, 139, 1997). Model fit parameters for the MCs are listed for 2010 - 2012. For the 5.7 year interval, the observed MCs are found to be slower, weaker in estimated axial magnetic-field intensity, and shorter in duration than those of the earlier 12.3 years, yielding much lower axial magnetic-field fluxes. For about the first half of this 5.7 year period, i.e. up to the end of 2009, there were very few associated MC-driven shock waves (distinctly fewer than the long-term average of about 50 % of MCs). But since 2010, such driven shocks have increased markedly, reflecting similar statistics as the long-term averages. We estimate that 56 % of the total observed MCs have upstream shocks when the full interval of 1995 - 2012 is considered. However, only 28 % of the total number of MCLs have driven shocks over the same period. Some interplanetary shocks during the 2010 - 2012 interval are seen

  2. Origins of Giant Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Ostriker, E. C.; Kim, W.-T.

    2004-12-01

    The material in giant molecular clouds (GMCs) constitutes a large proportion of the Milky Way's ISM, and determining how cloud-formation processes affect the properties and spatial distribution of GMCs is important to understanding the structure of the Milky Way. Understanding the formation of GMCs is also key to theories of galactic evolution because it represents the first stage in the overall process of star formation. Several lines of evidence point to a need for relatively rapid GMC formation via coherent dynamical instabilities, and both Parker- and Jeans- type modes have been proposed as potential cloud-forming mechanisms. Recent numerical simulations have investigated these instabilities directly, using spatially-localized models of the interstellar medium that self-consistently incorporate rotational shear, self-gravity, and magnetic fields, as well as the effects of stellar spiral arms. These models have demonstrated that condensation via gravitational instability, aided by magnetic torques, is the most likely candidate for explaining the formation of GMCs. The models have also shown that spiral arm ``spurs'' -- clearly seen as regular projections from dust lanes in at least one external galaxy -- may originate as magneto-gravitational instabilities of the ISM within the dense portions of stellar spiral arms. This raises the interesting possibility that spur structures with similar dynamical origins could potentially be present in the Milky Way as well.

  3. The Distribution of Cloud to Ground Lightning Strike Intensities and Associated Magnetic Inductance Fields Near the Kennedy Space Center

    NASA Technical Reports Server (NTRS)

    Burns, Lee; Decker, Ryan

    2005-01-01

    Lightning strike location and peak current are monitored operationally in the Kennedy Space Center (KSC) Cape Canaveral Air Force Station (CCAFS) area by the Cloud to Ground Lightning Surveillance System (CGLSS). The present study compiles ten years worth of CGLSS data into a database of near strikes. Using shuffle launch platform LP39A as a convenient central point, all strikes recorded within a 20-mile radius for the period of record O R ) from January 1, 1993 to December 31,2002 were included in the subset database. Histograms and cumulative probability curves are produced for both strike intensity (peak current, in kA) and the corresponding magnetic inductance fields (in A/m). Results for the full POR have application to launch operations lightning monitoring and post-strike test procedures.

  4. Differences in generation of magnetic storms driven by magnetic clouds, ejecta, sheath region before ICME and CIR

    NASA Astrophysics Data System (ADS)

    Nikolaeva, Nadezhda; Yermolaev, Yuri; Lodkina, Irina

    2016-07-01

    We investigate the efficiency of main phase storm generation by different solar wind (SW) streams when using 12 functions coupling (FC) various interplanetary parameters with magnetospheric state. By using our Catalog of Solar Wind Phenomena [Yermolaev et al., 2009] created on the basis of the OMNI database for 1976-2000, we selected the magnetic storms with Dst ≤ -50 nT for which interplanetary sources were following: MC (10 storms); Ejecta (31 storms); Sheath (21 storms); CIRs (31magnetic storms). To compare the interplanetary drivers we estimate an efficiency of magnetic storm generation by type of solar wind stream with using 12 coupling functions. We obtained that in average Sheath has more large efficiency of the magnetic storm generation and MC has more low efficiency in agreement with our previous results which show that by using a modification of formula by Burton et al. [1975] for connection of interplanetary conditions with Dst and Dst* indices the efficiency of storm generation by Sheath and CIR was ~50% higher than generation by ICME [Nikolaeva et al., 2013; 2015]. The most part of FCs has sufficiently high correlation coefficients. In particular the highest values of coefficients (~ 0.5 up to 0.63) are observed for Sheath- driven storms. In a small part of FCs with low coefficients it is necessary to increase the number of magnetic storms to increase the statistical significance of results. The reliability of the obtained data and possible reasons of divergences for various FCs and various SW types require further researches. The authors are grateful for the opportunity to use the OMNI database. This work was supported by the Russian Foundation for Basic Research, project 16-02-00125, and by Program of Presidium of the Russian Academy of Sciences. References: Nikolaeva, N. S., Y. I. Yermolaev, and I. G. Lodkina (2013), Modeling of Dst-index temporal profile on the main phase of the magnetic storms generated by different types of solar wind, Cosmic

  5. Induced core formation time in subcritical magnetic clouds by large-scale trans-Alfvénic flows

    SciTech Connect

    Kudoh, Takahiro; Basu, Shantanu E-mail: basu@uwo.ca

    2014-10-20

    We clarify the mechanism of accelerated core formation by large-scale nonlinear flows in subcritical magnetic clouds by finding a semi-analytical formula for the core formation time and describing the physical processes that lead to them. Recent numerical simulations show that nonlinear flows induce rapid ambipolar diffusion that leads to localized supercritical regions that can collapse. Here, we employ non-ideal magnetohydrodynamic simulations including ambipolar diffusion for gravitationally stratified sheets threaded by vertical magnetic fields. One of the horizontal dimensions is eliminated, resulting in a simpler two-dimensional simulation that can clarify the basic process of accelerated core formation. A parameter study of simulations shows that the core formation time is inversely proportional to the square of the flow speed when the flow speed is greater than the Alfvén speed. We find a semi-analytical formula that explains this numerical result. The formula also predicts that the core formation time is about three times shorter than that with no turbulence, when the turbulent speed is comparable to the Alfvén speed.

  6. A Statistical Study of the Average Iron Charge State Distributions inside Magnetic Clouds for Solar Cycle 23

    NASA Astrophysics Data System (ADS)

    Song, H. Q.; Zhong, Z.; Chen, Y.; Zhang, J.; Cheng, X.; Zhao, L.; Hu, Q.; Li, G.

    2016-06-01

    Magnetic clouds (MCs) are the interplanetary counterparts of coronal magnetic flux ropes. They can provide valuable information regarding flux rope characteristics at their eruption stage in the corona, which is unable to be explored in situ at present. In this paper, we make a comprehensive survey of the average iron charge-state (< Q> {Fe}) distributions inside 96 MCs for solar cycle 23 using Advanced Composition Explorer (ACE) data. Since the < Q> {Fe} in the solar wind are typically around 9+ to 11+, the Fe charge state is defined as being high when the < Q> {Fe} is larger than 12+, which implies the existence of a considerable amount of Fe ions with high charge states (e.g., ≥16+). The statistical results show that the < Q> {Fe} distributions of 92 (∼96%) MCs can be classified into four groups with different characteristics. In group A (11 MCs), the < Q> {Fe} shows a bi-modal distribution with both peaks being higher than 12+. Group B (4 MCs) presents a unimodal distribution of < Q> {Fe}, with its peak being higher than 12+. In groups C (29 MCs) and D (48 MCs), the < Q> {Fe} remains higher and lower than 12+ throughout ACE’s passage through the MC, respectively. Possible explanations of these distributions are discussed.

  7. Dispersion of Magnetic Fields in Molecular Clouds. IV. Analysis of Interferometry Data

    NASA Astrophysics Data System (ADS)

    Houde, Martin; Hull, Charles L. H.; Plambeck, Richard L.; Vaillancourt, John E.; Hildebrand, Roger H.

    2016-03-01

    We expand on the dispersion analysis of polarimetry maps toward applications to interferometry data. We show how the filtering of low spatial frequencies can be accounted for within the idealized Gaussian turbulence model, initially introduced for single-dish data analysis, to recover reliable estimates for correlation lengths of magnetized turbulence, as well as magnetic field strengths (plane-of-the-sky component) using the Davis-Chandrasekhar-Fermi method. We apply our updated technique to TADPOL/CARMA data obtained on W3(OH), W3 Main, and DR21(OH). For W3(OH), our analysis yields a turbulence correlation length δ ≃ 19 mpc, a ratio of turbulent-to-total magnetic energy < {B}{{t}}2> /< {B}2> ≃ 0.58, and a magnetic field strength {B}0˜ 1.1 {mG}; for W3 Main δ ≃ 22 mpc, < {B}{{t}}2> /< {B}2> ≃ 0.74, and {B}0˜ 0.7 {mG}; while for DR21(OH) δ ≃ 12 mpc, < {B}{{t}}2> /< {B}2> ≃ 0.70, and {B}0˜ 1.2 {mG}.

  8. Chandra Observations of a Young Embedded Magnetic B Star in the p Ophiuchus Cloud

    NASA Technical Reports Server (NTRS)

    Hamaguchi, Kenji; Imanishi, Kensuke

    2002-01-01

    This paper reports the analysis of two Chandra X-ray observations of the young magnetic B star rho Ophiuchus S1. X-ray emission from the star was detected in both observations. The average flux is almost the same in both, but during each observation the flux shows significant time variations by a factor of two on timescales of 20-40 ksec. Each spectrum can be fit by either an absorbed power law model with a photon index of approx. -3 or a thin-thermal plasma model with a temperature of approx. 2 keV and an extremely low metal abundance (approx. less than 0.1 solar). The spectrum of the first observation has an apparent line feature at about 6.8 keV, which likely corresponds to highly ionized iron K alpha. In contrast, the spectrum of the second observation shows an anomalous edge absorption component at E approx. 1 keV. The continuum emission and log (L(sub X)/L(sub bol)) approx. -6 are similar to those of young intermediate-mass stars (Herbig Ae/Be stars) although the presence of the magnetic field inferred from the detection of non-thermal radio emission has drawn an analogy between rho Ophiuchus S1 and magnetic chemically peculiar (MCP) stars. If the X-ray emission is thermal, the highest plasma temperature observed is too high to be explained by the conventional theories of magnetic stars, and favors some kind of magnetic dynamo activity, while if the emission is nonthermal, it might be related to mass infall. The 6.8 keV line and 4 keV edge features are marginal but they give important information near the stellar body if they are real. Their physical interpretation is discussed.

  9. FORMATION OF MASSIVE MOLECULAR CLOUD CORES BY CLOUD-CLOUD COLLISION

    SciTech Connect

    Inoue, Tsuyoshi; Fukui, Yasuo

    2013-09-10

    Recent observations of molecular clouds around rich massive star clusters including NGC 3603, Westerlund 2, and M20 revealed that the formation of massive stars could be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we demonstrate that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by cloud-cloud collision. We find that the massive molecular cloud cores have large effective Jeans mass owing to the enhancement of the magnetic field strength by shock compression and turbulence in the compressed layer. Our results predict that massive molecular cloud cores formed by the cloud-cloud collision are filamentary and threaded by magnetic fields perpendicular to the filament.

  10. Magnetohydrodynamic simulation of the interaction between two interplanetary magnetic clouds and its consequent geoeffectiveness: 2. Oblique collision

    NASA Astrophysics Data System (ADS)

    Xiong, Ming; Zheng, Huinan; Wang, Shui

    2009-11-01

    The numerical studies of the interplanetary coupling between multiple magnetic clouds (MCs) are continued by a 2.5-dimensional ideal magnetohydrodynamic (MHD) model in the heliospheric meridional plane. The interplanetary direct collision (DC)/oblique collision (OC) between both MCs results from their same/different initial propagation orientations. Here the OC is explored in contrast to the results of the DC. Both the slow MC1 and fast MC2 are consequently injected from the different heliospheric latitudes to form a compound stream during the interplanetary propagation. The MC1 and MC2 undergo contrary deflections during the process of oblique collision. Their deflection angles of ∣δ$\\theta$1∣ and ∣δ$\\theta$2∣ continuously increase until both MC-driven shock fronts are merged into a stronger compound one. The ∣δ$\\theta$1∣, ∣δ$\\theta$2∣, and total deflection angle Δ$\\theta$ (Δ$\\theta$ = ∣δ$\\theta$1∣ + ∣δ$\\theta$2∣) reach their corresponding maxima when the initial eruptions of both MCs are at an appropriate angular difference. Moreover, with the increase of MC2's initial speed, the OC becomes more intense, and the enhancement of δ$\\theta$1 is much more sensitive to δ$\\theta$2. The ∣δ$\\theta$1∣ is generally far less than the ∣δ$\\theta$2∣, and the unusual case of ∣δ$\\theta$1∣ $\\simeq$ ∣δ$\\theta$2∣ only occurs for an extremely violent OC. But because of the elasticity of the MC body to buffer the collision, this deflection would gradually approach an asymptotic degree. As a result, the opposite deflection between the two MCs, together with the inherent magnetic elasticity of each MC, could efficiently relieve the external compression for the OC in the interplanetary space. Such a deflection effect for the OC case is essentially absent for the DC case. Therefore, besides the magnetic elasticity, magnetic helicity, and reciprocal compression, the deflection due to the OC should be considered for the

  11. The interaction of a magnetic cloud with the Earth - Ionospheric convection in the Northern and Southern Hemispheres for a wide range of quasi-steady interplanetary magnetic field conditions

    NASA Technical Reports Server (NTRS)

    Freeman, M. P.; Farrugia, C. J.; Burlaga, L. F.; Hairston, M. R.; Greenspan, M. E.; Ruohoniemi, J. M.; Lepping, R. P.

    1993-01-01

    Observations are presented of the ionospheric convection in cross sections of the polar cap and auroral zone as part of the study of the interaction of the Earth's magnetosphere with the magnetic cloud of January 13-15, 1988. For strongly northward IMF, the convection in the Southern Hemisphere is characterized by a two-cell convection pattern comfined to high latitudes with sunward flow over the pole. The strength of the flows is comparable to that later seen under southward IMF. Superimposed on this convection pattern there are clear dawn-dusk asymmetries associated with a one-cell convection component whose sense depends on the polarity of the magnetic cloud's large east-west magnetic field component. When the cloud's magnetic field turns southward, the convection is characterized by a two-cell pattern extending to lower latitude with antisunward flow over the pole. There is no evident interhemispheric difference in the structure and strength of the convection. Superimposed dawn-dusk asymmetries in the flow patterns are observed which are only in part attributable to the east-west component of the magnetic field.

  12. Erratum to "Solar Sources and Geospace Consequences of Interplanetary Magnetic Clouds Observed During Solar Cycle 23-Paper 1" [J. Atmos. Sol.-Terr. Phys. 70(2-4) (2008) 245-253

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Michalek, G.; Lepping, R. P.

    2009-01-01

    One of the figures (Fig. 4) in "Solar sources and geospace consequences of interplanetary magnetic Clouds observed during solar cycle 23 -- Paper 1" by Gopalswamy et al. (2008, JASTP, Vol. 70, Issues 2-4, February 2008, pp. 245-253) is incorrect because of a software error in t he routine that was used to make the plot. The source positions of various magnetic cloud (MC) types are therefore not plotted correctly.

  13. Transport and entry of plasma clouds/jets across transverse magnetic discontinuities: Three-dimensional electromagnetic particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Voitcu, Gabriel; Echim, Marius

    2016-05-01

    In this paper we use three-dimensional electromagnetic particle-in-cell simulations to investigate the interaction of a small Larmor radius plasma cloud/jet with a transverse nonuniform magnetic field typical to a tangential discontinuity in a parallel geometry. The simulation setup corresponds to an idealized, yet relevant, magnetospheric configuration likely to be observed at the magnetopause during northward orientation of the interplanetary magnetic field. The numerical simulations are adapted to study the kinetic effects and their role on the transport and entry of localized plasma jets similar to those identified inside the Earth's magnetosheath propagating toward the magnetopause. The simulations reveal the formation of a perpendicular polarization electric field inside the main bulk of the plasma cloud that enables its forward transport and entry across the transverse magnetic field. The jet is able to penetrate the transition region when the height of the magnetic barrier does not exceed a certain critical threshold. Otherwise, the forward transport along the injection direction is stopped before full penetration of the magnetopause. Moreover, the jet is pushed back and simultaneously deflected in the perpendicular plane to the magnetic field. Our simulations evidence physical processes advocated previously by the theoretical model of impulsive penetration and revealed in laboratory experiments.

  14. Lack of relationship between geoeffectiveness and orientations of magnetic clouds with bipolar Bz and unipolar southward Bz

    NASA Astrophysics Data System (ADS)

    Teh, W.-L.; Abdullah, M.; Hasbi, A. M.

    2015-09-01

    In this study, 38 magnetic clouds (MCs) that caused significant geomagnetic storms (the minimum SYM-H, SHmin, ≤-50 nT) are examined, in which 17 MCs were unipolar Bz in south (S-type) and 21 MCs were bipolar Bz (north-to-south, NS-type, or south-to-north, SN-type). For S-type MC, inclination angle of the axis of the MC, |θ|, is ≥45°, while |θ|<45° for bipolar MC. This paper aims to address a question: is the intensity of a MC-driven storm correlated with the orientations of bipolar and S-type MCs? Our results demonstrate that there is no direct and significant relationship between geoeffectiveness and orientations of bipolar and S-type MCs. In other words, there is no MC preference (bipolar or S-type MC) to regulate the SHmin of the storm. On the whole, the SHmin is found to strongly correlate with southward field Bz (cc=0.96) and with the y component of the solar wind convective electric field (cc=-0.91) but to weakly correlate with solar wind speed (cc=-0.65). This result is consistent with previous studies by Wu and Lepping (2002), J. Geophys. Res. 107 (A10), 1314. doi:10.1029/2001JA000161. By separating MC-driven storms by size into moderate (-100 nTcloud's southward field Bz and the y component of the electric field, regardless of whether the MC is bipolar or S-type. Also, the ambient solar wind structure (e.g., shock) ahead of MC may play a role in regulating the storm's intensity.

  15. Yearly Comparison of Magnetic Cloud Parameters, Sunspot Number, and Interplanetary Quantities for the First 18 Years of the Wind Mission

    NASA Astrophysics Data System (ADS)

    Lepping, R. P.; Wu, C.-C.; Berdichevsky, D. B.

    2015-02-01

    In the scalar part of this study, we determine various statistical relationships between estimated magnetic cloud (MC) model fit-parameters and sunspot number (SSN) for the interval defined by the Wind mission, i.e., early 1995 until the end of 2012, all in terms of yearly averages. The MC-fitting model used is that of Lepping, Jones, and Burlaga ( J. Geophys. Res. 95, 11957 - 11965, 1990). We also statistically compare the MC fit-parameters and other derived MC quantities [ e.g., axial magnetic flux (ΦO) and total axial current density ( J O)] with some associated ambient interplanetary quantities (including the interplanetary magnetic field ( B IMF), proton number density ( N P), and others). Some of the main findings are that the minimum SSN is nearly simultaneous with the minimum in the number of MCs per year ( N MC), which occurs in 2008. There are various fluctuations in N MC and the MC model-fit quality ( Q') throughout the mission, but the last four years (2009 - 2012) are markedly different from the others; Q' is low and N MC is large over these four years. N MC is especially large for 2012. The linear correlation coefficient (c.c.≈0.75) between the SSN and each of the three quantities J O, MC diameter (2 R O), and B IMF, is moderately high, but none of the MC parameters track the SSN well in the sense defined in this article. However, there is good statistical tracking among the following: MC axial field, B IMF, 2 R O, average MC speed ( V MC), and yearly average solar wind speed ( V SW) with relatively high c.c.s among most of these. From the start of the mission until late 2005, J O gradually increases, with a slight violation in 2003, but then a dramatic decrease (by more than a factor of five) occurs to an almost steady and low value of ≈ 3 μA km-2 until the end of the interval of interest, i.e., lasting for at least seven years. This tends to split the overall 18-year interval into two phases with a separator at

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  18. The Magnetic Field of the L1544 Starless Dark Cloud, Traced Using Near-Infrared Background Starlight

    NASA Astrophysics Data System (ADS)

    Clemens, Dan P.; Goldsmith, Paul; Tassis, Konstantinos

    2016-06-01

    What roles do interstellar magnetic fields play in star formation processes? We have studied the B-field of L1544, a dark cloud with a starless dense core showing active gas infall, and located only 140 pc away in Taurus, via deep near-infrared (NIR) imaging polarimetry with the Mimir instrument. We find the B-field orientations in the plane of the sky change significantly at L1544, mimicking its shape and extent. The elongated spine of L1544 is also where the dispersion of NIR linear polarization position angles is smallest, suggesting strengthening of the B-field. Archival WISE, SCUPOL, Herschel, and Planck data were analyzed to characterize dust extinction and emission across L1544 and the field around it. Three-dimensional modeling, constrained through matching two-dimensional integrated model properties to observed dust distributions, led us to develop maps of effective gas mass densities and non-thermal gas velocity dispersions. These were combined with the NIR polarimetry, under the Chandrasekhar & Fermi (1953) approach, to yield a map of B-field strength across the entire 400 sq-arcmin region surveyed. The trends of B-field strength with gas volume density, mass-to-flux ratio with radius, and plane-of-sky B-field strengths with Zeeman-traced line-of-sight B-field strengths were found and compared to previous published work to establish the role of B-fields in L1544. We find field strengths in the 3 - 30 uG range, quite similar to the OH Zeeman values found by Crutcher et al. (2009) for L1544.This work was partially supported by grants to Boston University from NSF (AST-0907790, 1412269) and NASA (NNX15AE51G).

  19. Magnetohydrodynamic simulation of the interaction between interplanetary strong shock and magnetic cloud and its consequent geoeffectiveness: 2. Oblique collision

    NASA Astrophysics Data System (ADS)

    Xiong, Ming; Zheng, Huinan; Wang, Yuming; Wang, Shui

    2006-11-01

    Numerical studies of the interplanetary "shock overtaking magnetic cloud (MC)" event are continued by a 2.5-dimensional magnetohydrodynamic (MHD) model in heliospheric meridional plane. Interplanetary direct collision (DC)/oblique collision (OC) between an MC and a shock results from their same/different initial propagation orientations. For radially erupted MC and shock in solar corona, the orientations are only determined respectively by their heliographic locations. OC is investigated in contrast with the results in DC (Xiong, 2006). The shock front behaves as a smooth arc. The cannibalized part of MC is highly compressed by the shock front along its normal. As the shock propagates gradually into the preceding MC body, the most violent interaction is transferred sideways with an accompanying significant narrowing of the MC's angular width. The opposite deflections of MC body and shock aphelion in OC occur simultaneously through the process of the shock penetrating the MC. After the shock's passage, the MC is restored to its oblate morphology. With the decrease of MC-shock commencement interval, the shock front at 1 AU traverses MC body and is responsible for the same change trend of the latitude of the greatest geoeffectiveness of MC-shock compound. Regardless of shock orientation, shock penetration location regarding the maximum geoeffectiveness is right at MC core on the condition of very strong shock intensity. An appropriate angular difference between the initial eruption of an MC and an overtaking shock leads to the maximum deflection of the MC body. The larger the shock intensity is, the greater is the deflection angle. The interaction of MCs with other disturbances could be a cause of deflected propagation of interplanetary coronal mass ejection (ICME).

  20. Multiple, Distant (40 deg) in situ Observations of a Magnetic Cloud and a Corotating Interaction Region Complex

    NASA Astrophysics Data System (ADS)

    Farrugia, C. J.; Berdichevsky, D. B.; Moestl, C.; Galvin, A. B.; Leitner, M.; Popecki, M.; Simunac, K. D.; Opitz, A.; Lavraud, B.; Ogilvie, K.; Veronig, A.; Temmer, M.; Luhmann, J. G.; Sauvaud, J.

    2010-12-01

    We report a comprehensive analysis of in situ observations made by Wind and the STEREO probes (STA, STB) of a complex interaction between a magnetic cloud (MC) and a corotating interaction region (CIR) occurring near the heliospheric current sheet (HCS) on November 19-21, 2007. The probes were separated by 0.7 AU (~40 deg) with a spread in heliographic latitudes (4.8, 2.2, and -0.4 deg for STB, Wind and STA, respectively). We employ data from the MFI, SWE and 3DP instruments on Wind, and the PLASTIC and IMPACT suites on STEREO. STB, located east of Earth, observed a forward shock followed by signatures of a MC. The MC took the role of the HCS in that the polarity of the interplanetary magnetic field (IMF) on exit was the reverse of that on entry. A passage through a plasma sheet is observed. Along the Sun-Earth line Wind observed a stream interface (SI) between a forward and a reverse shock. A MC, compressed by the CIR, was entrained in this. STA, located 20 deg to the west of Earth, saw a MC which was not preceded by a shock. A SI trailed the transient. The shocks are examined using various methods and from this it is concluded that the forward shock at Wind - but not at STB - was driven by the MC. Examining the MC by Grad-Shafranov reconstruction, we find evidence of a double-flux rope structure at Wind and STA and possibly also at STB. The orientations are at variance with the notion of a large-scale flux tube being observed at the three spacecraft. We find consistency of this with the directional properties of the solar wind "strahl" electrons. We examine aspects of the geomagnetic response and find a double-dip storm corresponding to the two interplanetary triggers. The minimum Dst phase was prolonged and the geoffects were intensified due to the interaction. We conclude that while the formation of compound streams is a common feature of interplanetary space, understanding their components when CIRs are involved is a complicated matter needing numerical

  1. Multiple, distant (40°) in situ observations of a magnetic cloud and a corotating interaction region complex

    NASA Astrophysics Data System (ADS)

    Farrugia, C. J.; Berdichevsky, D. B.; Möstl, C.; Galvin, A. B.; Leitner, M.; Popecki, M. A.; Simunac, K. D. C.; Opitz, A.; Lavraud, B.; Ogilvie, K. W.; Veronig, A. M.; Temmer, M.; Luhmann, J. G.; Sauvaud, J. A.

    2011-06-01

    We report a comprehensive analysis of in situ observations made by Wind and the STEREO probes (STA, STB) of a complex interaction between a magnetic cloud (MC) and a corotating interaction region (CIR) occurring near the heliospheric current sheet (HCS) on November 19-21, 2007. The probes were separated by 0.7 AU (˜40∘) with a spread in heliographic latitudes (4.8,° 2.2,° and -0.4,° for STB, Wind and STA, respectively). We employ data from the MFI, SWE and 3DP instruments on Wind, and the PLASTIC and IMPACT suites on STEREO. STB, located east of Earth, observed a forward shock followed by signatures of a MC. The MC took the role of the HCS in that the polarity of the interplanetary magnetic field (IMF) on exit was the reverse of that on entry. A passage through a plasma sheet was observed. Along the Sun-Earth line Wind observed a stream interface (SI) between a forward and a reverse shock. A MC, compressed by the CIR, was entrained in this. STA, located 20° to the west of Earth, saw a MC which was not preceded by a shock. A SI trailed the transient. The shocks are examined using various methods and from this it is concluded that the forward shock at Wind—but not at STB—was driven by the MC. Examining the MC by Grad-Shafranov reconstruction, we find evidence of a double-flux rope structure at Wind and STA and possibly also at STB. The orientations are at variance with the notion of a large-scale flux tube being observed at the three spacecraft. We find consistency of this with the directional properties of the solar wind "strahl" electrons. We examine aspects of the geomagnetic response and find a double-dip storm corresponding to the two interplanetary triggers. The minimum Dst phase was prolonged and the geoeffects were intensified due to the interaction. We conclude that while the formation of compound streams is a common feature of interplanetary space, understanding their components when CIRs are involved is a complicated matter needing numerical

  2. Magnetic Clouds at/near the 2007 - 2009 Solar Minimum: Frequency of Occurrence and Some Unusual Properties

    NASA Technical Reports Server (NTRS)

    Lepping. R. P.; Wu, C.-C.; Berdichevsky, D. B.; Szabo, A.

    2011-01-01

    Magnetic clouds (MCs) have been identified for the period 2007 2009 (at/near the recent solar minimum) from Wind data, then confirmed through MC parameter fitting using a force-free model. A dramatic increase in the frequency of occurrence of these events took place from the two early years of 2007 (with five MCs) and 2008 (one MC) compared to 2009 (12 MCs). This pattern approximately mirrors the occurrence-frequency profile that was observed over a three-year interval 12 years earlier, with eight events in 1995, four in 1996, and 17 in 1997, but decreased overall by a factor of 0.62 in number. However, the average estimated axial field strength taken over all of the 18 events of 2007 - 2009 (called the "recent period" here) was only 11.0 nT, whereas |BO| for the 29 events of 1995 - 1997 (called the "earlier period" ) was 16.5 nT. This 33% average drop in |BO| is more or less consistent with the decreased three-year average interplanetary magnetic field intensity between these two periods, which shows a 23% drop. In the earlier period, the MCs were clearly of mixed types but predominantly of the South-to-North type, whereas those in the recent period are almost exclusively the North-to-South type; this change is consistent with global solar field changes predicted by Bothmer and Rust (Geophys. Monogr. Ser. 99, 139, 1997). As we have argued in earlier work (Lepping and Wu, J. Geophys. Res. 112, A10103, 2007), this change should make it possible to carry out (accurate short-term) magnetic storm forecasting by predicting the latter part of an MC from the earlier part, using a good MC parameter-fitting model with real-time data from a spacecraft at L1, for example. The recent set s average duration is 15.2 hours, which is a 27% decrease compared to that of the earlier set, which had an average duration of 20.9 hours. In fact, all physical aspects of the recent MC set are shown to drop with respect to the earlier set; e.g., as well as the average internal magnetic field

  3. Mesoscale cloud phenomena observed by LANDSAT

    NASA Technical Reports Server (NTRS)

    Ormsby, J. P.

    1977-01-01

    Examples of certain mesoscale cloud features - jet cirrus, eddies/vortices, cloud banding, and wave clouds - were collected from LANDSAT imagery and placed into Mason's four groups of causes of cloud formation based on the mechanism of vertical motion which produces condensation. These groups are as follows: (1) layer clouds formed by widespread regular ascent; (2) layer clouds caused by irregular stirring motions; (3) convective clouds; and (4) clouds formed by orographic disturbances. These mechanisms explain general cloud formation. Once formed, other forces may play a role in the deformation of a cloud or cloud mass into unusual and unique meso- and microscale patterns. Each example presented is followed by a brief discussion describing the synoptic situation, and some inference into the formation and occurrence of the more salient features. No major attempt was made to discuss in detail the meteorological and topographic interplay producing these mesoscale features.

  4. Relativistic calculation of nuclear magnetic shielding tensor using the regular approximation to the normalized elimination of the small component. III. Introduction of gauge-including atomic orbitals and a finite-size nuclear model

    NASA Astrophysics Data System (ADS)

    Hamaya, S.; Maeda, H.; Funaki, M.; Fukui, H.

    2008-12-01

    The relativistic calculation of nuclear magnetic shielding tensors in hydrogen halides is performed using the second-order regular approximation to the normalized elimination of the small component (SORA-NESC) method with the inclusion of the perturbation terms from the metric operator. This computational scheme is denoted as SORA-Met. The SORA-Met calculation yields anisotropies, Δσ =σ∥-σ⊥, for the halogen nuclei in hydrogen halides that are too small. In the NESC theory, the small component of the spinor is combined to the large component via the operator σ⃗ṡπ⃗U/2c, in which π⃗=p⃗+A⃗, U is a nonunitary transformation operator, and c ≅137.036 a.u. is the velocity of light. The operator U depends on the vector potential A⃗ (i.e., the magnetic perturbations in the system) with the leading order c-2 and the magnetic perturbation terms of U contribute to the Hamiltonian and metric operators of the system in the leading order c-4. It is shown that the small Δσ for halogen nuclei found in our previous studies is related to the neglect of the U(0,1) perturbation operator of U, which is independent of the external magnetic field and of the first order with respect to the nuclear magnetic dipole moment. Introduction of gauge-including atomic orbitals and a finite-size nuclear model is also discussed.

  5. Artist's Rendering of Multiple Whirlpools in a Sodium Gas Cloud

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image depicts the formation of multiple whirlpools in a sodium gas cloud. Scientists who cooled the cloud and made it spin created the whirlpools in a Massachusetts Institute of Technology laboratory, as part of NASA-funded research. This process is similar to a phenomenon called starquakes that appear as glitches in the rotation of pulsars in space. MIT's Wolgang Ketterle and his colleagues, who conducted the research under a grant from the Biological and Physical Research Program through NASA's Jet Propulsion Laboratory, Pasadena, Calif., cooled the sodium gas to less than one millionth of a degree above absolute zero (-273 Celsius or -460 Fahrenheit). At such extreme cold, the gas cloud converts to a peculiar form of matter called Bose-Einstein condensate, as predicted by Albert Einstein and Satyendra Bose of India in 1927. No physical container can hold such ultra-cold matter, so Ketterle's team used magnets to keep the cloud in place. They then used a laser beam to make the gas cloud spin, a process Ketterle compares to stroking a ping-pong ball with a feather until it starts spirning. The spinning sodium gas cloud, whose volume was one- millionth of a cubic centimeter, much smaller than a raindrop, developed a regular pattern of more than 100 whirlpools.

  6. On Regularity Criteria for the 2D Generalized MHD System

    NASA Astrophysics Data System (ADS)

    Jiang, Zaihong; Wang, Yanan; Zhou, Yong

    2016-06-01

    This paper deals with the problem of regularity criteria for the 2D generalized MHD system with fractional dissipative terms {-Λ^{2α}u} for the velocity field and {-Λ^{2β}b} for the magnetic field respectively. Various regularity criteria are established to guarantee smoothness of solutions. It turns out that our regularity criteria imply previous global existence results naturally.

  7. Regular FPGA based on regular fabric

    NASA Astrophysics Data System (ADS)

    Xun, Chen; Jianwen, Zhu; Minxuan, Zhang

    2011-08-01

    In the sub-wavelength regime, design for manufacturability (DFM) becomes increasingly important for field programmable gate arrays (FPGAs). In this paper, an automated tile generation flow targeting micro-regular fabric is reported. Using a publicly accessible, well-documented academic FPGA as a case study, we found that compared to the tile generators previously reported, our generated micro-regular tile incurs less than 10% area overhead, which could be potentially recovered by process window optimization, thanks to its superior printability. In addition, we demonstrate that on 45 nm technology, the generated FPGA tile reduces lithography induced process variation by 33%, and reduce probability of failure by 21.2%. If a further overhead of 10% area can be recovered by enhanced resolution, we can achieve the variation reduction of 93.8% and reduce the probability of failure by 16.2%.

  8. Scalar relativistic computations of nuclear magnetic shielding and g-shifts with the zeroth-order regular approximation and range-separated hybrid density functionals

    SciTech Connect

    Aquino, Fredy W.; Govind, Niranjan; Autschbach, Jochen

    2011-10-01

    Density functional theory (DFT) calculations of NMR chemical shifts and molecular g-tensors with Gaussian-type orbitals are implemented via second-order energy derivatives within the scalar relativistic zeroth order regular approximation (ZORA) framework. Nonhybrid functionals, standard (global) hybrids, and range-separated (Coulomb-attenuated, long-range corrected) hybrid functionals are tested. Origin invariance of the results is ensured by use of gauge-including atomic orbital (GIAO) basis functions. The new implementation in the NWChem quantum chemistry package is verified by calculations of nuclear shielding constants for the heavy atoms in HX (X=F, Cl, Br, I, At) and H2X (X = O, S, Se, Te, Po), and Te chemical shifts in a number of tellurium compounds. The basis set and functional dependence of g-shifts is investigated for 14 radicals with light and heavy atoms. The problem of accurately predicting F NMR shielding in UF6-nCln, n = 1 to 6, is revisited. The results are sensitive to approximations in the density functionals, indicating a delicate balance of DFT self-interaction vs. correlation. For the uranium halides, the results with the range-separated functionals are mixed.

  9. Regular gravitational lagrangians

    NASA Astrophysics Data System (ADS)

    Dragon, Norbert

    1992-02-01

    The Einstein action with vanishing cosmological constant is for appropriate field content the unique local action which is regular at the fixed point of affine coordinate transformations. Imposing this regularity requirement one excludes also Wess-Zumino counterterms which trade gravitational anomalies for Lorentz anomalies. One has to expect dilatational and SL (D) anomalies. If these anomalies are absent and if the regularity of the quantum vertex functional can be controlled then Einstein gravity is renormalizable. On leave of absence from Institut für Theoretische Physik, Universität Hannover, W-3000 Hannover 1, FRG.

  10. REGULAR VERSUS DIFFUSIVE PHOTOSPHERIC FLUX CANCELLATION

    SciTech Connect

    Litvinenko, Yuri E.

    2011-04-20

    Observations of photospheric flux cancellation on the Sun imply that cancellation can be a diffusive rather than regular process. A criterion is derived, which quantifies the parameter range in which diffusive photospheric cancellation should occur. Numerical estimates show that regular cancellation models should be expected to give a quantitatively accurate description of photospheric cancellation. The estimates rely on a recently suggested scaling for a turbulent magnetic diffusivity, which is consistent with the diffusivity measurements on spatial scales varying by almost two orders of magnitude. Application of the turbulent diffusivity to large-scale dispersal of the photospheric magnetic flux is discussed.

  11. Plasma clouds and snowplows: Bulk plasma escape from Mars observed by MAVEN

    NASA Astrophysics Data System (ADS)

    Halekas, J. S.; Brain, D. A.; Ruhunusiri, S.; McFadden, J. P.; Mitchell, D. L.; Mazelle, C.; Connerney, J. E. P.; Harada, Y.; Hara, T.; Espley, J. R.; DiBraccio, G. A.; Jakosky, B. M.

    2016-02-01

    We present initial Mars Atmosphere and Volatile EvolutioN (MAVEN) observations and preliminary interpretation of bulk plasma loss from Mars. MAVEN particle and field measurements show that planetary heavy ions derived from the Martian atmosphere can escape in the form of discrete coherent structures or "clouds." The ions in these clouds are unmagnetized or weakly magnetized, have velocities well above the escape speed, and lie directly downstream from magnetic field amplifications, suggesting a "snowplow" effect. This postulated escape process, similar to that successfully used to explain the dynamics of active gas releases in the solar wind and terrestrial magnetosheath, relies on momentum transfer from the shocked solar wind protons to the planetary heavy ions, with the electrons and magnetic field acting as intermediaries. Fluxes of planetary ions on the order of 107 cm-2 s-1 can escape by this process, and if it operates regularly, it could contribute 10-20% of the current ion escape from Mars.

  12. 3D Reconstruction of the 22 May 2007 Magnetic Cloud: How Much Can We Trust the Flux- Rope Geometry of CMEs?

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Luhmann, J.; Wang, L.; Lynch, B.; Huttunen, E.; Lin, R.; Bale, S.; Russell, C.; Galvin, T.

    2008-05-01

    Coronal mass ejections (CMEs) are often assumed to be magnetic flux ropes, but direct proof has been lacking. A key feature, resulting from the translational symmetry of a flux rope, is that the total transverse pressure as well as the axial magnetic field has the same functional form over the vector potential along any crossing of the flux rope. We test this feature (and hence the flux-rope structure) by reconstructing the 22 May 2007 magnetic cloud (MC) observed at STEREO B, Wind/ACE and possibly STEREO A with the Grad-Shafranov (GS) method. The model output from reconstruction at STEREO B agrees fairly well with the magnetic field and thermal pressure observed at ACE/Wind; the separation between STEREO B and ACE/Wind is about 0.06 AU, almost half of the MC radial width. For the first time, we reproduce observations at one spacecraft with data from another well- separated spacecraft, which provides compelling evidence for the flux-rope geometry and is of importance for understanding CME initiation and propagation. The magnetic field line length, calculated from the velocity dispersion of energetic electrons within the MC, is substantially longer than the nominal Parker spiral field, which is consistent with a flux-rope structure. The reconstruction gives a global configuration of the MC at different spacecraft with a flattened cross section owing to the solar wind radial expansion. A similar approach is also performed with a force-free flux-rope fitting model in an effort to compare with the GS reconstruction results.

  13. Spin period change and the magnetic fields of neutron stars in Be X-ray binaries in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Klus, H.; Ho, W. C. G.; Coe, M. J.; Corbet, R. H. D.; Townsend, L. J.

    2014-02-01

    We report on the long-term average spin period, rate of change of spin period and X-ray luminosity during outbursts for 42 Be X-ray binary systems in the Small Magellanic Cloud. We also collect and calculate parameters of each system and use these data to determine that all systems contain a neutron star which is accreting via a disc, rather than a wind, and that if these neutron stars are near spin equilibrium, then over half of them, including all with spin periods over about 100 s, have magnetic fields over the quantum critical level of 4.4 × 1013 G. If these neutron stars are not close to spin equilibrium, then their magnetic fields are inferred to be much lower, of the order of 106-1010 G, comparable to the fields of neutron stars in low-mass X-ray binaries. Both results are unexpected and have implications for the rate of magnetic field decay and the isolated neutron star population.

  14. Effect of geomagnetic activity, solar wind and parameters of interplanetary magnetic field on regularities in intermittency of Pi2 geomagnetic pulsations

    NASA Astrophysics Data System (ADS)

    Kurazhkovskaya, Nadezhda; Klain, Boris

    2015-09-01

    We present the results of investigation of the influence of geomagnetic activity, solar wind and parameters of the interplanetary magnetic field (IMF) on properties of the intermittency of midlatitude burst series of Pi2 geomagnetic pulsations observed during magnetospheric substorms on the nightside (substorm Pi2) and in the absence of these phenomena (nonsubstorm Pi2). We considered the index α as a main characteristic of intermittency of substorm and nonsubstorm Pi2 pulsations. The index α characterizes the slope of the cumulative distribution function of Pi2 burst amplitudes. The study indicated that the value and dynamics of the index α varies depending on the planetary geomagnetic activity, auroral activity and the intensity of magnetospheric ring currents. In addition, the forms of dependences of the index α; on the density n, velocity V, dynamic pressure Pd of the solar wind and IMF Bx-component are different. The behavior of the index α depending on the module of B, By- and Bz-components is similar. We found some critical values of V, Pd, B, By- and Bz-components, after reaching of which the turbulence of the magnetotail plasma during substorm development is decreased. The revealed patterns of the intermittency of Pi2 pulsations can be used for qualitative assessment of turbulence level in the magnetotail plasma depending on changing interplanetary conditions.

  15. Comparison of Dawn and Dusk Precipitating Electron Energy Populations Shortly After the Initial Shock for the January 10th, 1997 Magnetic Cloud

    NASA Technical Reports Server (NTRS)

    Spann, J.; Germany, G.; Swift, W.; Parks, G.; Brittnacher, M.; Elsen, R.

    1997-01-01

    The observed precipitating electron energy between 0130 UT and 0400 UT of January 10 th, 1997, indicates that there is a more energetic precipitating electron population that appears in the auroral oval at 1800-2200 UT at 030) UT. This increase in energy occurs after the initial shock of the magnetic cloud reaches the Earth (0114 UT) and after faint but dynamic polar cap precipitation has been cleared out. The more energetic population is observed to remain rather constant in MLT through the onset of auroral activity (0330 UT) and to the end of the Polar spacecraft apogee pass. Data from the Ultraviolet Imager LBH long and LBH short images are used to quantify the average energy of the precipitating auroral electrons. The Wind spacecraft located about 100 RE upstream monitored the IMF and plasma parameters during the passing of the cloud. The affects of oblique angle viewing are included in the analysis. Suggestions as to the source of this hot electron population will be presented.

  16. Regularized Structural Equation Modeling

    PubMed Central

    Jacobucci, Ross; Grimm, Kevin J.; McArdle, John J.

    2016-01-01

    A new method is proposed that extends the use of regularization in both lasso and ridge regression to structural equation models. The method is termed regularized structural equation modeling (RegSEM). RegSEM penalizes specific parameters in structural equation models, with the goal of creating easier to understand and simpler models. Although regularization has gained wide adoption in regression, very little has transferred to models with latent variables. By adding penalties to specific parameters in a structural equation model, researchers have a high level of flexibility in reducing model complexity, overcoming poor fitting models, and the creation of models that are more likely to generalize to new samples. The proposed method was evaluated through a simulation study, two illustrative examples involving a measurement model, and one empirical example involving the structural part of the model to demonstrate RegSEM’s utility. PMID:27398019

  17. Using a magnetized plasma jet colliding with a heavy gas cloud to investigate MIF adiabatic heating and compression mechanisms

    NASA Astrophysics Data System (ADS)

    Bellan, Paul; Wongwaitayakornkul, Pakorn; Chai, Kil-Byoung; Greig, Amelia; Li, Hui

    2015-11-01

    Magnetized inertial fusion (MIF) is based on having an imploding liner adiabatically compress a magnetized plasma to the density and temperature required for thermonuclear fusion. The goal of the Caltech research program is to determine the scaling of the temperature and density increase when an actual experimental plasma is adiabatically compressed. The plasma parameters will be more modest than a fusion-grade configuration, but in compensation, the shot repetition rate will be much higher and the experiments will be non-destructive. The non-destructive feature results from having a high-speed magnetized plasma jet impact a localized heavy gas. From the point of view of an observer in the frame of the magnetized plasma jet, it will look as if the heavy gas is impacting and compressing the magnetized plasma and so, except for some geometrical differences, the configuration is equivalent to a liner impacting and compressing a stationary magnetized plasma. The experiment will be modeled by 3D numerical MHD and PIC codes. (as of approximately September 15).

  18. QUANTIFYING THE SIGNIFICANCE OF THE MAGNETIC FIELD FROM LARGE-SCALE CLOUD TO COLLAPSING CORE: SELF-SIMILARITY, MASS-TO-FLUX RATIO, AND STAR FORMATION EFFICIENCY

    SciTech Connect

    Koch, Patrick M.; Ho, Paul T. P.; Tang, Ya-Wen

    2012-03-01

    Dust polarization observational results are analyzed for the high-mass star formation region W51 from the largest parent cloud ({approx}2 pc, James Clerk Maxwell Telescope) to the large-scale envelope ({approx}0.5 pc, BIMA array) down to the collapsing core e2 ({approx}60 mpc, Submillimeter Array). Magnetic field and dust emission gradient orientations reveal a correlation which becomes increasingly more tight with higher resolution. The previously developed polarization-intensity-gradient method is applied in order to quantify the magnetic field significance. This technique provides a way to estimate the local magnetic field force compared to gravity without the need of any mass or field strength measurements, solely making use of measured angles which reflect the geometrical imprint of the various forces. All three data sets clearly show regions with distinct features in the field-to-gravity force ratio. Azimuthally averaged radial profiles of this force ratio reveal a transition from a field dominance at larger distances to a gravity dominance closer to the emission peaks. Normalizing these profiles to a characteristic core scale points toward self-similarity. Furthermore, the polarization-intensity-gradient method is linked to the mass-to-flux ratio, providing a new approach to estimate the latter one without mass and field strength inputs. A transition from a magnetically supercritical to a subcritical state as a function of distance from the emission peak is found for the e2 core. Finally, based on the measured radius-dependent field-to-gravity force ratio we derive a modified star formation efficiency with a diluted gravity force. Compared to a standard (free-fall) efficiency, the observed field is capable of reducing the efficiency down to 10% or less.

  19. Geometry of spinor regularization

    NASA Technical Reports Server (NTRS)

    Hestenes, D.; Lounesto, P.

    1983-01-01

    The Kustaanheimo theory of spinor regularization is given a new formulation in terms of geometric algebra. The Kustaanheimo-Stiefel matrix and its subsidiary condition are put in a spinor form directly related to the geometry of the orbit in physical space. A physically significant alternative to the KS subsidiary condition is discussed. Derivations are carried out without using coordinates.

  20. Cloud Computing

    SciTech Connect

    Pete Beckman and Ian Foster

    2009-12-04

    Chicago Matters: Beyond Burnham (WTTW). Chicago has become a world center of "cloud computing." Argonne experts Pete Beckman and Ian Foster explain what "cloud computing" is and how you probably already use it on a daily basis.

  1. Arctic Clouds

    Atmospheric Science Data Center

    2013-04-19

    ...     View Larger Image Stratus clouds are common in the Arctic during the summer months, and are ... formats available at JPL August 23, 2000 - Stratus clouds help modulate the arctic climate. project:  ...

  2. Non-equilibrium ionization around clouds evaporating in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Ballet, J.; Luciani, J. F.; Mora, P.

    1986-01-01

    It is of prime importance for global models of the interstellar medium to know whether dense clouds do or do not evaporate in the hot coronal gas. The rate of mass exchanges between phases depends very much on that. McKee and Ostriker's model, for instance, assumes that evaporation is important enough to control the expansion of supernova remnants, and that mass loss obeys the law derived by Cowie and McKee. In fact, the geometry of the magnetic field is nearly unknown, and it might totally inhibit evaporation, if the clouds are not regularly connected to the hot gas. Up to now, the only test of the theory is the U.V. observation (by the Copernicus and IUE satellites) of absorption lines of ions such as OVI or NV, that exist at temperatures of a few 100,000 K typical of transition layers around evaporating clouds. Other means of testing the theory are discussed.

  3. Magnetohydrodynamic stability of broad line region clouds

    NASA Astrophysics Data System (ADS)

    Krause, Martin; Schartmann, Marc; Burkert, Andreas

    2012-10-01

    Hydrodynamic stability has been a longstanding issue for the cloud model of the broad line region in active galactic nuclei. We argue that the clouds may be gravitationally bound to the supermassive black hole. If true, stabilization by thermal pressure alone becomes even more difficult. We further argue that if magnetic fields are present in such clouds at a level that could affect the stability properties, they need to be strong enough to compete with the radiation pressure on the cloud. This would imply magnetic field values of a few gauss for a sample of active galactic nuclei we draw from the literature. We then investigate the effect of several magnetic configurations on cloud stability in axisymmetric magnetohydrodynamic simulations. For a purely azimuthal magnetic field which provides the dominant pressure support, the cloud first gets compressed by the opposing radiative and gravitational forces. The pressure inside the cloud then increases, and it expands vertically. Kelvin-Helmholtz and column density instabilities lead to a filamentary fragmentation of the cloud. This radiative dispersion continues until the cloud is shredded down to the resolution level. For a helical magnetic field configuration, a much more stable cloud core survives with a stationary density histogram which takes the form of a power law. Our simulated clouds develop sub-Alfvénic internal motions on the level of a few hundred km s-1.

  4. Optical/Near-infrared Polarization Survey of Sh 2-29: Magnetic Fields, Dense Cloud Fragmentations, and Anomalous Dust Grain Sizes

    NASA Astrophysics Data System (ADS)

    Santos, Fábio P.; Franco, Gabriel A. P.; Roman-Lopes, Alexandre; Reis, Wilson; Román-Zúñiga, Carlos G.

    2014-03-01

    Sh 2-29 is a conspicuous star-forming region marked by the presence of massive embedded stars as well as several notable interstellar structures. In this research, our goals were to determine the role of magnetic fields and to study the size distribution of interstellar dust particles within this turbulent environment. We have used a set of optical and near-infrared polarimetric data obtained at OPD/LNA (Brazil) and CTIO (Chile), correlated with extinction maps, Two Micron All Sky Survey data, and images from the Digitized Sky Survey and Spitzer. The region's most striking feature is a swept out interstellar cavity whose polarimetric maps indicate that magnetic field lines were dragged outward, piling up along its borders. This led to a higher magnetic strength value (≈400 μG) and an abrupt increase in polarization degree, probably due to an enhancement in alignment efficiency. Furthermore, dense cloud fragmentations with peak AV between 20 and 37 mag were probably triggered by its expansion. The presence of 24 μm point-like sources indicates possible newborn stars inside this dense environment. A statistical analysis of the angular dispersion function revealed areas where field lines are aligned in a well-ordered pattern, seemingly due to compression effects from the H II region expansion. Finally, Serkowski function fits were used to study the ratio of the total-to-selective extinction, revealing a dual population of anomalous grain particle sizes. This trend suggests that both effects of coagulation and fragmentation of interstellar grains are present in the region. Based on observations collected at the National Optical Astronomy Observatory (CTIO, Chile) and Observatório do Pico dos Dias, operated by Laboratório Nacional de Astrofísica (LNA/MCT, Brazil).

  5. Optical/near-infrared polarization survey of Sh 2-29: Magnetic fields, dense cloud fragmentations, and anomalous dust grain sizes

    SciTech Connect

    Santos, Fábio P.; Franco, Gabriel A. P.; Reis, Wilson; Roman-Lopes, Alexandre; Román-Zúñiga, Carlos G. E-mail: franco@fisica.ufmg.br E-mail: roman@dfuls.cl

    2014-03-01

    Sh 2-29 is a conspicuous star-forming region marked by the presence of massive embedded stars as well as several notable interstellar structures. In this research, our goals were to determine the role of magnetic fields and to study the size distribution of interstellar dust particles within this turbulent environment. We have used a set of optical and near-infrared polarimetric data obtained at OPD/LNA (Brazil) and CTIO (Chile), correlated with extinction maps, Two Micron All Sky Survey data, and images from the Digitized Sky Survey and Spitzer. The region's most striking feature is a swept out interstellar cavity whose polarimetric maps indicate that magnetic field lines were dragged outward, piling up along its borders. This led to a higher magnetic strength value (≈400 μG) and an abrupt increase in polarization degree, probably due to an enhancement in alignment efficiency. Furthermore, dense cloud fragmentations with peak A{sub V} between 20 and 37 mag were probably triggered by its expansion. The presence of 24 μm point-like sources indicates possible newborn stars inside this dense environment. A statistical analysis of the angular dispersion function revealed areas where field lines are aligned in a well-ordered pattern, seemingly due to compression effects from the H II region expansion. Finally, Serkowski function fits were used to study the ratio of the total-to-selective extinction, revealing a dual population of anomalous grain particle sizes. This trend suggests that both effects of coagulation and fragmentation of interstellar grains are present in the region.

  6. Electron cloud in the Fermilab Booster

    SciTech Connect

    Ng, K.Y.; /Fermilab

    2007-06-01

    Simulations of the Fermilab Booster reveal a substantial electron-cloud buildup both inside the unshielded combined-function magnets and the beam pipes joining the magnets, when the second-emission yield (SEY) is larger than {approx}1.6. The implication of the electron-cloud effects on space charge and collective instabilities of the beam is discussed.

  7. Interstellar Cloud Collisions

    NASA Astrophysics Data System (ADS)

    Lattanzio, J. C.; Monaghan, J. J.; Pongracic, H.; Schwarz, M. P.

    1985-07-01

    We describe the results of a three-dimensional numerical simulation of isothermal interstellar clouds in the absence of magnetic fields. A wide variety of high and low Mach number, head-on and off-centre collisions of clouds with mass ratios 1, 2.5, 5.0 and 10.1 have been studied. The results show that a necessary, but not sufficient, condition for the gravitational instability of a substantial fraction of the matter is that the initial clouds should be either marginally stable or unstable according to the usual Jeans criterion. The collisions, in general, do not result in one or more clouds. Instead we find, in most cases, that the matter disperses in an irregular way. The calculations therefore suggest that if the initial state of the interstellar medium is one of cool dense clouds in a hotter more tenuous background, collisions will rapidly mix the medium rather than produce a steady-state spectrum of cool clouds.

  8. Shadow of rotating regular black holes

    NASA Astrophysics Data System (ADS)

    Abdujabbarov, Ahmadjon; Amir, Muhammed; Ahmedov, Bobomurat; Ghosh, Sushant G.

    2016-05-01

    We study the shadows cast by the different types of rotating regular black holes viz. Ayón-Beato-García (ABG), Hayward, and Bardeen. These black holes have in addition to the total mass (M ) and rotation parameter (a ), different parameters as electric charge (Q ), deviation parameter (g ), and magnetic charge (g*). Interestingly, the size of the shadow is affected by these parameters in addition to the rotation parameter. We found that the radius of the shadow in each case decreases monotonically, and the distortion parameter increases when the values of these parameters increase. A comparison with the standard Kerr case is also investigated. We have also studied the influence of the plasma environment around regular black holes to discuss its shadow. The presence of the plasma affects the apparent size of the regular black hole's shadow to be increased due to two effects: (i) gravitational redshift of the photons and (ii) radial dependence of plasma density.

  9. Higher-Order Global Regularity of an Inviscid Voigt-Regularization of the Three-Dimensional Inviscid Resistive Magnetohydrodynamic Equations

    NASA Astrophysics Data System (ADS)

    Larios, Adam; Titi, Edriss S.

    2014-03-01

    We prove existence, uniqueness, and higher-order global regularity of strong solutions to a particular Voigt-regularization of the three-dimensional inviscid resistive magnetohydrodynamic (MHD) equations. Specifically, the coupling of a resistive magnetic field to the Euler-Voigt model is introduced to form an inviscid regularization of the inviscid resistive MHD system. The results hold in both the whole space and in the context of periodic boundary conditions. Weak solutions for this regularized model are also considered, and proven to exist globally in time, but the question of uniqueness for weak solutions is still open. Furthermore, we show that the solutions of the Voigt regularized system converge, as the regularization parameter , to strong solutions of the original inviscid resistive MHD, on the corresponding time interval of existence of the latter. Moreover, we also establish a new criterion for blow-up of solutions to the original MHD system inspired by this Voigt regularization.

  10. Higher-Order Global Regularity of an Inviscid Voigt-Regularization of the Three-Dimensional Inviscid Resistive Magnetohydrodynamic Equations

    NASA Astrophysics Data System (ADS)

    Larios, Adam; Titi, Edriss S.

    2013-05-01

    We prove existence, uniqueness, and higher-order global regularity of strong solutions to a particular Voigt-regularization of the three-dimensional inviscid resistive magnetohydrodynamic (MHD) equations. Specifically, the coupling of a resistive magnetic field to the Euler-Voigt model is introduced to form an inviscid regularization of the inviscid resistive MHD system. The results hold in both the whole space {{R}^3} and in the context of periodic boundary conditions. Weak solutions for this regularized model are also considered, and proven to exist globally in time, but the question of uniqueness for weak solutions is still open. Furthermore, we show that the solutions of the Voigt regularized system converge, as the regularization parameter {α → 0}, to strong solutions of the original inviscid resistive MHD, on the corresponding time interval of existence of the latter. Moreover, we also establish a new criterion for blow-up of solutions to the original MHD system inspired by this Voigt regularization.

  11. An enhanced neighborhood similar pixel interpolator approach for removing thick clouds in landsat images

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Thick cloud contaminations in Landsat images limit their regular usage for land applications. A few methods have been developed to remove thick clouds using additional cloud-free images. Unfortunately, the cloud-free composition image produced by existing methods commonly lacks from the desired spat...

  12. Investigating Plasma Motion of Magnetic Clouds at 1 AU through a Velocity-modified Cylindrical Force-free Flux Rope Model

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Shen, C.; Liu, R.; Zhou, Z.

    2014-12-01

    Magnetic clouds (MCs) are the interplanetary counterparts of coronal mass ejections (CMEs). Due to the very low value of Can't connect to bucket.int.confex.com:4201 (Connection refused) LWP::Protocol::http::Socket: connect: Connection refused at /usr/local/lib/perl5/site_perl/5.8.8/LWP/Protocol/http.pm line 51. in MCs, they are believed to be in a nearly force-free state and therefore are able to be modeled by a cylindrical force-free flux rope. However, the force-free state only describes the magnetic field topology but not the plasma motion of a MC. For a MC propagating in interplanetary space, the global plasma motion has three possible components: linear propagating motion of a MC away from the Sun, expanding motion and circular motion with respect to the axis of the MC. By assuming the quasi-steady evolution and self-similar expansion, we introduced the three-component motion into the cylindrical force-free flux rope model, and developed a velocity-modified model. Then we applied the model to 73 MCs observed by Wind spacecraft to investigate the properties of the plasma motion of MCs. It is found that (1) some MCs did not propagate along the Sun-Earth line, suggesting the direct evidence of the CME's deflected propagation and/or rotation in interplanetary space, (2) the expansion speed is correlated with the radial propagation speed and 62%/17% of MCs underwent a under/over-expansion at 1 AU, and (3) the circular motion does exists though it is only on the order of 10 km s-1. These findings advance our understanding of the MC's properties at 1 AU as well as the dynamic evolution of CMEs from the Sun to interplanetary space.

  13. Comparison of Cloud Properties from CALIPSO-CloudSat and Geostationary Satellite Data

    NASA Technical Reports Server (NTRS)

    Nguyen, L.; Minnis, P.; Chang, F.; Winker, D.; Sun-Mack, S.; Spangenberg, D.; Austin, R.

    2007-01-01

    Cloud properties are being derived in near-real time from geostationary satellite imager data for a variety of weather and climate applications and research. Assessment of the uncertainties in each of the derived cloud parameters is essential for confident use of the products. Determination of cloud amount, cloud top height, and cloud layering is especially important for using these real -time products for applications such as aircraft icing condition diagnosis and numerical weather prediction model assimilation. Furthermore, the distribution of clouds as a function of altitude has become a central component of efforts to evaluate climate model cloud simulations. Validation of those parameters has been difficult except over limited areas where ground-based active sensors, such as cloud radars or lidars, have been available on a regular basis. Retrievals of cloud properties are sensitive to the surface background, time of day, and the clouds themselves. Thus, it is essential to assess the geostationary satellite retrievals over a variety of locations. The availability of cloud radar data from CloudSat and lidar data from CALIPSO make it possible to perform those assessments over each geostationary domain at 0130 and 1330 LT. In this paper, CloudSat and CALIPSO data are matched with contemporaneous Geostationary Operational Environmental Satellite (GOES), Multi-functional Transport Satellite (MTSAT), and Meteosat-8 data. Unlike comparisons with cloud products derived from A-Train imagers, this study considers comparisons of nadir active sensor data with off-nadir retrievals. These matched data are used to determine the uncertainties in cloud-top heights and cloud amounts derived from the geostationary satellite data using the Clouds and the Earth s Radiant Energy System (CERES) cloud retrieval algorithms. The CERES multi-layer cloud detection method is also evaluated to determine its accuracy and limitations in the off-nadir mode. The results will be useful for

  14. Hubble Space Telescope and HI Imaging of Strong Ram Pressure Stripping in the Coma Spiral NGC 4921: Dense Cloud Decoupling and Evidence for Magnetic Binding in the ISM

    NASA Astrophysics Data System (ADS)

    Kenney, Jeffrey D. P.; Abramson, Anne; Bravo-Alfaro, Hector

    2015-08-01

    Remarkable dust extinction features in the deep Hubble Space Telescope (HST) V and I images of the face-on Coma cluster spiral galaxy NGC 4921 show in unprecedented ways how ram pressure strips the ISM from the disk of a spiral galaxy. New VLA HI maps show a truncated and highly asymmetric HI disk with a compressed HI distribution in the NW, providing evidence for ram pressure acting from the NW. Where the HI distribution is truncated in the NW region, HST images show a well-defined, continuous front of dust that extends over 90° and 20 kpc. This dust front separates the dusty from dust-free regions of the galaxy, and we interpret it as galaxy ISM swept up near the leading side of the ICM-ISM interaction. We identify and characterize 100 pc-1 kpc scale substructure within this dust front caused by ram pressure, including head-tail filaments, C-shaped filaments, and long smooth dust fronts. The morphology of these features strongly suggests that dense gas clouds partially decouple from surrounding lower density gas during stripping, but decoupling is inhibited, possibly by magnetic fields that link and bind distant parts of the ISM.

  15. Cloud Control

    ERIC Educational Resources Information Center

    Ramaswami, Rama; Raths, David; Schaffhauser, Dian; Skelly, Jennifer

    2011-01-01

    For many IT shops, the cloud offers an opportunity not only to improve operations but also to align themselves more closely with their schools' strategic goals. The cloud is not a plug-and-play proposition, however--it is a complex, evolving landscape that demands one's full attention. Security, privacy, contracts, and contingency planning are all…

  16. Cloud Cover

    ERIC Educational Resources Information Center

    Schaffhauser, Dian

    2012-01-01

    This article features a major statewide initiative in North Carolina that is showing how a consortium model can minimize risks for districts and help them exploit the advantages of cloud computing. Edgecombe County Public Schools in Tarboro, North Carolina, intends to exploit a major cloud initiative being refined in the state and involving every…

  17. Cloud Control

    ERIC Educational Resources Information Center

    Weinstein, Margery

    2012-01-01

    Your learning curriculum needs a new technological platform, but you don't have the expertise or IT equipment to pull it off in-house. The answer is a learning system that exists online, "in the cloud," where learners can access it anywhere, anytime. For trainers, cloud-based coursework often means greater ease of instruction resulting in greater…

  18. Fast Image Reconstruction with L2-Regularization

    PubMed Central

    Bilgic, Berkin; Chatnuntawech, Itthi; Fan, Audrey P.; Setsompop, Kawin; Cauley, Stephen F.; Wald, Lawrence L.; Adalsteinsson, Elfar

    2014-01-01

    Purpose We introduce L2-regularized reconstruction algorithms with closed-form solutions that achieve dramatic computational speed-up relative to state of the art L1- and L2-based iterative algorithms while maintaining similar image quality for various applications in MRI reconstruction. Materials and Methods We compare fast L2-based methods to state of the art algorithms employing iterative L1- and L2-regularization in numerical phantom and in vivo data in three applications; 1) Fast Quantitative Susceptibility Mapping (QSD), 2) Lipid artifact suppression in Magnetic Resonance Spectroscopic Imaging (MRSI), and 3) Diffusion Spectrum Imaging (DSI). In all cases, proposed L2-based methods are compared with the state of the art algorithms, and two to three orders of magnitude speed up is demonstrated with similar reconstruction quality. Results The closed-form solution developed for regularized QSM allows processing of a 3D volume under 5 seconds, the proposed lipid suppression algorithm takes under 1 second to reconstruct single-slice MRSI data, while the PCA based DSI algorithm estimates diffusion propagators from undersampled q-space for a single slice under 30 seconds, all running in Matlab using a standard workstation. Conclusion For the applications considered herein, closed-form L2-regularization can be a faster alternative to its iterative counterpart or L1-based iterative algorithms, without compromising image quality. PMID:24395184

  19. Cloud point-dispersive μ-solid phase extraction of hydrophobic organic compounds onto highly hydrophobic core-shell Fe₂O₃@C magnetic nanoparticles.

    PubMed

    Giokas, Dimosthenis L; Zhu, Qing; Pan, Qinmin; Chisvert, Alberto

    2012-08-17

    A novel two-step extraction technique combining cloud point extraction (CPE) with dispersive micro-solid phase extraction (D-μ-SPE) is presented in this work for the first time. The method involves initial extraction of the target analytes by CPE in the micelles of a non-ionic surfactant medium; then highly hydrophobic polysiloxane-coated core-shell Fe(2)O(3)@C magnetic nanoparticles (MNPs) are used to retrieve the micellar phase. In that manner, the micellar phase containing the analytes is the target of the D-μ-SPE step rather than the analytes directly. MNPs are then collected by the application of an adscititious magnetic field overcoming the need for specific steps associated with CPE such as centrifugation to separate the surfactant-rich phase, refrigeration of the condensed micellar phase to reduce its viscosity or appropriate apparatus that enable direct sampling of the surfactant-rich phase. A noteworthy feature of the method is the introduction of highly oleophilic MNPs, which afford rapid and quantitative mass transfer of the surfactant phase, as opposed to other more conventional hydrophobic nanoparticles. In that manner, fast and reproducible extraction is accomplished, lending improved analytical features compared to conventional CPE, such as reduced analysis time and relative inertness to surfactant concentration and equilibration temperature. The analytes were recovered from the surface of MNPs by ultrasound-assisted back-extraction in a water-immiscible organic solvent where analytes are readily partitioned but the surfactant has limited solubility, thus minimizing its interference during chromatographic detection. As an analytical demonstration, different UV absorbing chemicals with various physico-chemical properties were used as model organic compounds for optimizing the parameters associated with this novel two-step extraction approach. The proposed method, combining two different and efficient techniques, offers satisfactory analytical

  20. Generalized Higher Degree Total Variation (HDTV) Regularization

    PubMed Central

    Hu, Yue; Ongie, Greg; Ramani, Sathish; Jacob, Mathews

    2015-01-01

    We introduce a family of novel image regularization penalties called generalized higher degree total variation (HDTV). These penalties further extend our previously introduced HDTV penalties, which generalize the popular total variation (TV) penalty to incorporate higher degree image derivatives. We show that many of the proposed second degree extensions of TV are special cases or are closely approximated by a generalized HDTV penalty. Additionally, we propose a novel fast alternating minimization algorithm for solving image recovery problems with HDTV and generalized HDTV regularization. The new algorithm enjoys a ten-fold speed up compared to the iteratively reweighted majorize minimize algorithm proposed in a previous work. Numerical experiments on 3D magnetic resonance images and 3D microscopy images show that HDTV and generalized HDTV improve the image quality significantly compared with TV. PMID:24710832

  1. Regularized Generalized Canonical Correlation Analysis

    ERIC Educational Resources Information Center

    Tenenhaus, Arthur; Tenenhaus, Michel

    2011-01-01

    Regularized generalized canonical correlation analysis (RGCCA) is a generalization of regularized canonical correlation analysis to three or more sets of variables. It constitutes a general framework for many multi-block data analysis methods. It combines the power of multi-block data analysis methods (maximization of well identified criteria) and…

  2. 75 FR 53966 - Regular Meeting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-02

    ... CORPORATION Regular Meeting AGENCY: Farm Credit System Insurance Corporation Board. SUMMARY: Notice is hereby given of the regular meeting of the Farm Credit System Insurance Corporation Board (Board). DATE AND TIME: The meeting of the Board will be held at the offices of the Farm Credit Administration in...

  3. Regularly timed events amid chaos.

    PubMed

    Blakely, Jonathan N; Cooper, Roy M; Corron, Ned J

    2015-11-01

    We show rigorously that the solutions of a class of chaotic oscillators are characterized by regularly timed events in which the derivative of the solution is instantaneously zero. The perfect regularity of these events is in stark contrast with the well-known unpredictability of chaos. We explore some consequences of these regularly timed events through experiments using chaotic electronic circuits. First, we show that a feedback loop can be implemented to phase lock the regularly timed events to a periodic external signal. In this arrangement the external signal regulates the timing of the chaotic signal but does not strictly lock its phase. That is, phase slips of the chaotic oscillation persist without disturbing timing of the regular events. Second, we couple the regularly timed events of one chaotic oscillator to those of another. A state of synchronization is observed where the oscillators exhibit synchronized regular events while their chaotic amplitudes and phases evolve independently. Finally, we add additional coupling to synchronize the amplitudes, as well, however in the opposite direction illustrating the independence of the amplitudes from the regularly timed events. PMID:26651759

  4. CLOUD CONDENSATION NUCLEI MEASUREMENTS WITHIN CLOUDS

    EPA Science Inventory

    Measurements of the spectra of cloud condensation nuclei (CCN) within and near the boundaries of clouds are presented. Some of the in-cloud measurements excluded the nuclei within cloud droplets (interstitial CCN) while others included all nuclei inside the cloud (total CCN). The...

  5. Natural selection and mechanistic regularity.

    PubMed

    DesAutels, Lane

    2016-06-01

    In this article, I address the question of whether natural selection operates regularly enough to qualify as a mechanism of the sort characterized by Machamer, Darden, and Craver (2000). Contrary to an influential critique by Skipper and Millstein (2005), I argue that natural selection can be seen to be regular enough to qualify as an MDC mechanism just fine-as long as we pay careful attention to some important distinctions regarding mechanistic regularity and abstraction. Specifically, I suggest that when we distinguish between process vs. product regularity, mechanism-internal vs. mechanism-external sources of irregularity, and abstract vs. concrete regularity, we can see that natural selection is only irregular in senses that are unthreatening to its status as an MDC mechanism. PMID:26921876

  6. CLOUD CHEMISTRY.

    SciTech Connect

    SCHWARTZ,S.E.

    2001-03-01

    Clouds present substantial concentrations of liquid-phase water, which can potentially serve as a medium for dissolution and reaction of atmospheric gases. The important precursors of acid deposition, SO{sub 2} and nitrogen oxides NO and NO{sub 2} are only sparingly soluble in clouds without further oxidation to sulfuric and nitric acids. In the case of SO{sub 2} aqueous-phase reaction with hydrogen peroxide, and to lesser extent ozone, are identified as important processes leading to this oxidation, and methods have been described by which to evaluate the rates of these reactions. The limited solubility of the nitrogen oxides precludes significant aqueous-phase reaction of these species, but gas-phase reactions in clouds can be important especially at night.

  7. Neptune's clouds

    NASA Technical Reports Server (NTRS)

    1999-01-01

    The bright cirrus-like clouds of Neptune change rapidly, often forming and dissipating over periods of several to tens of hours. In this sequence Voyager 2 observed cloud evolution in the region around the Great Dark Spot (GDS). The surprisingly rapid changes which occur separating each panel shows that in this region Neptune's weather is perhaps as dynamic and variable as that of the Earth. However, the scale is immense by our standards -- the Earth and the GDS are of similar size -- and in Neptune's frigid atmosphere, where temperatures are as low as 55 degrees Kelvin (-360 F), the cirrus clouds are composed of frozen methane rather than Earth's crystals of water ice. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications

  8. Our World: Cool Clouds

    NASA Video Gallery

    Learn how clouds are formed and watch an experiment to make a cloud using liquid nitrogen. Find out how scientists classify clouds according to their altitude and how clouds reflect and absorb ligh...

  9. Complex Clouds

    Atmospheric Science Data Center

    2013-04-16

    ...     View Larger Image The complex structure and beauty of polar clouds are highlighted by these images acquired ... Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously from pole to pole, and every 9 days views the entire globe ...

  10. Cloud Front

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA02171 Cloud Front

    These clouds formed in the south polar region. The faintness of the cloud system likely indicates that these are mainly ice clouds, with relatively little dust content.

    Image information: VIS instrument. Latitude -86.7N, Longitude 212.3E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  11. Thin Clouds

    Atmospheric Science Data Center

    2013-04-18

    ... of this montage is a natural-color view of the Caribbean Sea east of the Yucatan Peninsula as seen by MISR's most steeply ... - Thin, feathery clouds of ice crystals over the Caribbean Sea. project:  MISR category:  gallery ...

  12. NONCONVEX REGULARIZATION FOR SHAPE PRESERVATION

    SciTech Connect

    CHARTRAND, RICK

    2007-01-16

    The authors show that using a nonconvex penalty term to regularize image reconstruction can substantially improve the preservation of object shapes. The commonly-used total-variation regularization, {integral}|{del}u|, penalizes the length of the object edges. They show that {integral}|{del}u|{sup p}, 0 < p < 1, only penalizes edges of dimension at least 2-p, and thus finite-length edges not at all. We give numerical examples showing the resulting improvement in shape preservation.

  13. Geometric continuum regularization of quantum field theory

    SciTech Connect

    Halpern, M.B. . Dept. of Physics)

    1989-11-08

    An overview of the continuum regularization program is given. The program is traced from its roots in stochastic quantization, with emphasis on the examples of regularized gauge theory, the regularized general nonlinear sigma model and regularized quantum gravity. In its coordinate-invariant form, the regularization is seen as entirely geometric: only the supermetric on field deformations is regularized, and the prescription provides universal nonperturbative invariant continuum regularization across all quantum field theory. 54 refs.

  14. Regular patterns stabilize auditory streams.

    PubMed

    Bendixen, Alexandra; Denham, Susan L; Gyimesi, Kinga; Winkler, István

    2010-12-01

    The auditory system continuously parses the acoustic environment into auditory objects, usually representing separate sound sources. Sound sources typically show characteristic emission patterns. These regular temporal sound patterns are possible cues for distinguishing sound sources. The present study was designed to test whether regular patterns are used as cues for source distinction and to specify the role that detecting these regularities may play in the process of auditory stream segregation. Participants were presented with tone sequences, and they were asked to continuously indicate whether they perceived the tones in terms of a single coherent sequence of sounds (integrated) or as two concurrent sound streams (segregated). Unknown to the participant, in some stimulus conditions, regular patterns were present in one or both putative streams. In all stimulus conditions, participants' perception switched back and forth between the two sound organizations. Importantly, regular patterns occurring in either one or both streams prolonged the mean duration of two-stream percepts, whereas the duration of one-stream percepts was unaffected. These results suggest that temporal regularities are utilized in auditory scene analysis. It appears that the role of this cue lies in stabilizing streams once they have been formed on the basis of simpler acoustic cues. PMID:21218898

  15. Extended Locus of Regular Nuclei

    SciTech Connect

    Amon, L.; Casten, R. F.

    2007-04-23

    A new family of IBM Hamiltonians, characterized by certain parameter values, was found about 15 years ago by Alhassid and Whelan to display almost regular dynamics, and yet these solutions to the IBM do not belong to any of the known dynamical symmetry limits (vibrational, rotational and {gamma} - unstable). Rather, they comprise an 'Arc of Regularity' cutting through the interior of the symmetry triangle from U(5) to SU(3) where suddenly there is a decrease in chaoticity and a significant increase in regularity. A few years ago, the first set of nuclei lying along this arc was discovered. The purpose of the present work is to search more broadly in the nuclear chart at all nuclei from Z = 40 - 100 for other examples of such 'regular' nuclei. Using a unique signature for such nuclei involving energy differences of certain excited states, we have identified an additional set of 12 nuclei lying near or along the arc. Some of these nuclei are known to have low-lying intruder states and therefore care must be taken, however, in judging their structure. The regularity exhibited by nuclei near the arc presumably reflects the validity or partial validity of some new, as yet unknown, quantum number describing these systems and giving the regularity found for them.

  16. Model of E-Cloud Instability in the Fermilab Recycler

    SciTech Connect

    Balbekov, V.

    2015-06-24

    Simple model of electron cloud is developed in the paper to explain e-cloud instability of bunched proton beam in the Fermilab Recycler. The cloud is presented as an immobile snake in strong vertical magnetic field. The instability is treated as an amplification of the bunch injection errors from the batch head to its tail. Nonlinearity of the e-cloud field is taken into account. Results of calculations are compared with experimental data demonstrating good correlation.

  17. Plasma cloud behavior

    NASA Astrophysics Data System (ADS)

    Linson, Lewis M.

    1991-08-01

    Participation in PLACES (Position Location And Communications Effects Simulations) and Midnight Sky field operations is described. In the former, four barium releases were made during the period 4 to 12 December 1980. The range of velocities experienced was greater than before at this location. The principal challenge was to perform real-time tracking of the ion cloud so as to predict a future aim point for use in targeting beacon and probe rockets. Recommendations for obtaining smoother tracking data involve determining the motion of a field line through the ion cloud rather than an indeterminate point in the cloud, making measurements at set intervals, and coordinating measurements by more than one observer. During Midnight Sky, 2 barium releases were made on 29 March 81 and 2 April 81. The first went westerly at 450 m/s while the second was nearly motionless. A small aircraft was positioned so as to take photographs up the magnetic field line during the second release. It is strongly urged that a complete dry run including all participants, communications links, and necessary operations be carried out before a test event.

  18. The Giant Molecular Cloud Environments of Infrared Dark Clouds

    NASA Astrophysics Data System (ADS)

    Hernandez, Audra K.; Tan, Jonathan C.

    2015-08-01

    We study giant molecular cloud (GMC) environments surrounding 10 infrared dark clouds (IRDCs), using {}13{CO}(1-0) emission from the Galactic Ring Survey. We measure physical properties of these IRDCs/GMCs on a range of scales extending to radii, R, of 30 pc. By comparing different methods for defining cloud boundaries and for deriving mass surface densities and velocity dispersions, we settle on a preferred “CE,τ,G” method of “Connected Extraction” in position-velocity space plus Gaussian fitting to opacity-corrected line profiles for velocity dispersion and mass estimation. We examine how cloud definition affects measurements of the magnitude and direction of line-of-sight velocity gradients and velocity dispersions, including associated dependencies on size scale. CE,τ,G-defined GMCs show velocity dispersion versus size relations σ ∝ s1/2, which are consistent with the large-scale gradients being caused by turbulence. However, IRDCs have velocity dispersions that are moderately enhanced above those predicted by this scaling relation. We examine the dynamical state of the clouds, finding mean virial parameters {\\bar{α }}{vir}≃ 1.0 for GMCs and 1.6 for IRDCs, broadly consistent with models of magnetized virialized pressure-confined polytropic clouds, but potentially indicating that IRDCs have more disturbed kinematics. CE,τ, G-defined clouds exhibit a tight correlation of σ /{R}1/2\\propto {{{Σ }}}n, with n ≃ 0.7 for GMCs and 1.3 for IRDCs (cf. a value of 0.5 expected for a population of virialized clouds). We conclude that while GMCs show evidence for virialization over a range of scales, IRDCs may be moderately supervirial. Alternatively, IRDCs could be virialized but have systematically different {}13{CO} gas-phase abundances, i.e., owing to freeze-out, affecting mass estimations.

  19. Linear Clouds

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA03667 Linear Clouds

    These clouds are located near the edge of the south polar region. The cloud tops are the puffy white features in the bottom half of the image.

    Image information: VIS instrument. Latitude -80.1N, Longitude 52.1E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  20. The origin of ferromagnetic interaction between bound magnetic polarons in diluted magnetic semiconductors: A minimal model

    NASA Astrophysics Data System (ADS)

    Bednarski, Henryk

    2014-01-01

    We present a detailed analysis of the role of various interaction mechanisms contributing to the bound magnetic polaron (BMP) molecule Hamiltonian with the purpose of gaining an insight into the origin of the ferromagnetic interaction between BMPs. Explicitly, it appears that the BMP molecule Hamiltonian without interatomic direct exchange interaction does not lead to appearance of the parallel alignment of polaronic clouds in the lowest energy state even for large magnitudes of the polaronic exchange fields (up to ~65 meV in Cd0.95Mn0.05Se). Also, it appears that for the range of moderate values of polaronic exchange fields (16-25 meV in Cd0.95Mn0.05Se), the regular Hubbard BMP pair Hamiltonian must be supplemented with the direct interatomic (Heisenberg) exchange interaction to form a minimal model Hamiltonian of BMP molecule with the parallel alignment of the polaronic clouds in the lowest energy state.

  1. Cloud Interactions

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 1 July 2004 The atmosphere of Mars is a dynamic system. Water-ice clouds, fog, and hazes can make imaging the surface from space difficult. Dust storms can grow from local disturbances to global sizes, through which imaging is impossible. Seasonal temperature changes are the usual drivers in cloud and dust storm development and growth.

    Eons of atmospheric dust storm activity has left its mark on the surface of Mars. Dust carried aloft by the wind has settled out on every available surface; sand dunes have been created and moved by centuries of wind; and the effect of continual sand-blasting has modified many regions of Mars, creating yardangs and other unusual surface forms.

    This image was acquired during mid-spring near the North Pole. The linear water-ice clouds are now regional in extent and often interact with neighboring cloud system, as seen in this image. The bottom of the image shows how the interaction can destroy the linear nature. While the surface is still visible through most of the clouds, there is evidence that dust is also starting to enter the atmosphere.

    Image information: VIS instrument. Latitude 68.4, Longitude 258.8 East (101.2 West). 38 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration

  2. Regularization Analysis of SAR Superresolution

    SciTech Connect

    DELAURENTIS,JOHN M.; DICKEY,FRED M.

    2002-04-01

    Superresolution concepts offer the potential of resolution beyond the classical limit. This great promise has not generally been realized. In this study we investigate the potential application of superresolution concepts to synthetic aperture radar. The analytical basis for superresolution theory is discussed. In a previous report the application of the concept to synthetic aperture radar was investigated as an operator inversion problem. Generally, the operator inversion problem is ill posed. This work treats the problem from the standpoint of regularization. Both the operator inversion approach and the regularization approach show that the ability to superresolve SAR imagery is severely limited by system noise.

  3. Dimensional regularization in configuration space

    SciTech Connect

    Bollini, C.G. |; Giambiagi, J.J.

    1996-05-01

    Dimensional regularization is introduced in configuration space by Fourier transforming in {nu} dimensions the perturbative momentum space Green functions. For this transformation, the Bochner theorem is used; no extra parameters, such as those of Feynman or Bogoliubov and Shirkov, are needed for convolutions. The regularized causal functions in {ital x} space have {nu}-dependent moderated singularities at the origin. They can be multiplied together and Fourier transformed (Bochner) without divergence problems. The usual ultraviolet divergences appear as poles of the resultant analytic functions of {nu}. Several examples are discussed. {copyright} {ital 1996 The American Physical Society.}

  4. Estimating Cloud Cover

    ERIC Educational Resources Information Center

    Moseley, Christine

    2007-01-01

    The purpose of this activity was to help students understand the percentage of cloud cover and make more accurate cloud cover observations. Students estimated the percentage of cloud cover represented by simulated clouds and assigned a cloud cover classification to those simulations. (Contains 2 notes and 3 tables.)

  5. Instrument measures cloud cover

    NASA Technical Reports Server (NTRS)

    Laue, E. G.

    1981-01-01

    Eight solar sensing cells comprise inexpensive monitoring instrument. Four cells always track Sun while other four face sky and clouds. On overcast day, cloud-irradiance sensors generate as much short-circuit current as Sun sensor cells. As clouds disappear, output of cloud sensors decreases. Ratio of two sensor type outputs determines fractional cloud cover.

  6. MAGNETS

    DOEpatents

    Hofacker, H.B.

    1958-09-23

    This patent relates to nmgnets used in a calutron and more particularly to means fur clamping an assembly of magnet coils and coil spacers into tightly assembled relation in a fluid-tight vessel. The magnet comprises windings made up of an assembly of alternate pan-cake type coils and spacers disposed in a fluid-tight vessel. At one end of the tank a plurality of clamping strips are held firmly against the assembly by adjustable bolts extending through the adjacent wall. The foregoing arrangement permits taking up any looseness which may develop in the assembly of coils and spacers.

  7. Nonlinear waves and solitons in molecular clouds

    NASA Technical Reports Server (NTRS)

    Adams, Fred C.; Fatuzzo, Marco

    1993-01-01

    We begin a study of nonlinear wave phenomena in molecular clouds. These clouds exhibit highly nonlinear structure that is often described in terms of 'clumps' and 'filaments' which are bouncing around, twisting, and colliding within the cloud. These clouds are important because they ultimately produce the initial conditions for the star formation process. Our motivation is to explore the possibility that solitons (i.e., spatially localized, single-hump wave entities which often exhibit remarkable stability) can live in these molecular clouds and produce their observed structure. In this paper we focus on the case of one spatial dimension, and we show that a rich variety of nonlinear waves can exist in molecular cloud fluid systems (where self-gravity is included). We show that in the absence of magnetic fields no true soliton solutions are allowed, although highly nonlinear waves (whose crests become widely spaced and thus soliton-like) do exist. For clouds with embedded magnetic fields, we derive a model equation which describes the behavior of wave phenomena; this model equation allows solutions which correspond to nonlinear waves, solitons, and topological solitons. We briefly consider the stability of these wave entities and discuss the possible role they play in molecular cloud dynamics.

  8. Rotations of the Regular Polyhedra

    ERIC Educational Resources Information Center

    Jones, MaryClara; Soto-Johnson, Hortensia

    2006-01-01

    The study of the rotational symmetries of the regular polyhedra is important in the classroom for many reasons. Besides giving the students an opportunity to visualize in three dimensions, it is also an opportunity to relate two-dimensional and three-dimensional concepts. For example, rotations in R[superscript 2] require a point and an angle of…

  9. Regularized Generalized Structured Component Analysis

    ERIC Educational Resources Information Center

    Hwang, Heungsun

    2009-01-01

    Generalized structured component analysis (GSCA) has been proposed as a component-based approach to structural equation modeling. In practice, GSCA may suffer from multi-collinearity, i.e., high correlations among exogenous variables. GSCA has yet no remedy for this problem. Thus, a regularized extension of GSCA is proposed that integrates a ridge…

  10. Academic Improvement through Regular Assessment

    ERIC Educational Resources Information Center

    Wolf, Patrick J.

    2007-01-01

    Media reports are rife with claims that students in the United States are overtested and that they and their education are suffering as result. Here I argue the opposite--that students would benefit in numerous ways from more frequent assessment, especially of diagnostic testing. The regular assessment of students serves critical educational and…

  11. A cloud/particle model of the interstellar medium - Galactic spiral structure

    NASA Technical Reports Server (NTRS)

    Levinson, F. H.; Roberts, W. W., Jr.

    1981-01-01

    A cloud/particle model for gas flow in galaxies is developed that incorporates cloud-cloud collisions and supernovae as dominant local processes. Cloud-cloud collisions are the main means of dissipation. To counter this dissipation and maintain local dispersion, supernova explosions in the medium administer radial snowplow pushes to all nearby clouds. The causal link between these processes is that cloud-cloud collisions will form stars and that these stars will rapidly become supernovae. The cloud/particle model is tested and used to investigate the gas dynamics and spiral structures in galaxies where these assumptions may be reasonable. Particular attention is given to whether large-scale galactic shock waves, which are thought to underlie the regular well-delineated spiral structure in some galaxies, form and persist in a cloud-supernova dominated interstellar medium; this question is answered in the affirmative.

  12. Martian Clouds

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 28 June 2004 The atmosphere of Mars is a dynamic system. Water-ice clouds, fog, and hazes can make imaging the surface from space difficult. Dust storms can grow from local disturbances to global sizes, through which imaging is impossible. Seasonal temperature changes are the usual drivers in cloud and dust storm development and growth.

    Eons of atmospheric dust storm activity has left its mark on the surface of Mars. Dust carried aloft by the wind has settled out on every available surface; sand dunes have been created and moved by centuries of wind; and the effect of continual sand-blasting has modified many regions of Mars, creating yardangs and other unusual surface forms.

    This image was acquired during early spring near the North Pole. The linear 'ripples' are transparent water-ice clouds. This linear form is typical for polar clouds. The black regions on the margins of this image are areas of saturation caused by the build up of scattered light from the bright polar material during the long image exposure.

    Image information: VIS instrument. Latitude 68.1, Longitude 147.9 East (212.1 West). 38 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS

  13. Operator regularization and quantum gravity

    NASA Astrophysics Data System (ADS)

    Mann, R. B.; Tarasov, L.; Mckeon, D. G. C.; Steele, T.

    1989-01-01

    Operator regularization has been shown to be a symmetry preserving means of computing Green functions in gauge symmetric and supersymmetric theories which avoids the explicit occurrence of divergences. In this paper we examine how this technique can be applied to computing quantities in non-renormalizable theories in general and quantum gravity in particular. Specifically, we consider various processes to one- and two-loop order in φ4N theory for N > 4 for which the theory is non-renormalizable. We then apply operator regularization to determine the one-loop graviton correction to the spinor propagator. The effective action for quantum scalars in a background gravitational field is evaluated in operator regularization using both the weak-field method and the normal coordinate expansion. This latter case yields a new derivation of the Schwinger-de Witt expansion which avoids the use of recursion relations. Finally we consider quantum gravity coupled to scalar fields in n dimensions, evaluating those parts of the effective action that (in other methods) diverge as n → 4. We recover the same divergence structure as is found using dimensional regularization if n ≠ 4, but if n = 4 at the outset no divergence arises at any stage of the calculation. The non-renormalizability of such theories manifests itself in the scale-dependence at one-loop order of terms that do not appear in the original lagrangian. In all cases our regularization procedure does not break any invariances present in the theory and avoids the occurence of explicit divergences.

  14. Temporal regularity in speech perception: Is regularity beneficial or deleterious?

    PubMed Central

    Geiser, Eveline; Shattuck-Hufnagel, Stefanie

    2012-01-01

    Speech rhythm has been proposed to be of crucial importance for correct speech perception and language learning. This study investigated the influence of speech rhythm in second language processing. German pseudo-sentences were presented to participants in two conditions: ‘naturally regular speech rhythm’ and an ‘emphasized regular rhythm'. Nine expert English speakers with 3.5±1.6 years of German training repeated each sentence after hearing it once over headphones. Responses were transcribed using the International Phonetic Alphabet and analyzed for the number of correct, false and missing consonants as well as for consonant additions. The over-all number of correct reproductions of consonants did not differ between the two experimental conditions. However, speech rhythmicization significantly affected the serial position curve of correctly reproduced syllables. The results of this pilot study are consistent with the view that speech rhythm is important for speech perception. PMID:22701753

  15. Crater Clouds

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA06085 Crater Clouds

    The crater on the right side of this image is affecting the local wind regime. Note the bright line of clouds streaming off the north rim of the crater.

    Image information: VIS instrument. Latitude -78.8N, Longitude 320.0E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  16. Structure of interplanetary fluxes based on plasma and magnetic field measurements by Prognoz-6 satellite on 25-26 November 1977

    NASA Astrophysics Data System (ADS)

    Yeroshenko, Ye. G.; Ivanov, K. G.; Verigin, M. I.; Kotova, G. A.; Styazhkin, V. A.

    1989-01-01

    Two fluxes from a flare and a coronal hole on 25 to 26 November 1977 were observed aboard the Prognoz-6 satellite. A comparative analysis is presented of the magnetic and plasma data based on these observations and observations of other Soviet and American spacecraft which were located at that time near a line between the Sun and the Earth. The Prognoz-6 data recored disturbances in the magnetic field and plasma near the Earth during passage of the isolated flare flux and the quasisteady flux from the coronal hole. A perpendicular to the head of the shock wave of the flare flux was found. The magnetic cloud from the flare was measured over a period of 19 hours as an area of relatively strong field, sparse plasma with near regular variations of all B components. The normal and inner structure of the magnetic cloud magnetopause were measured. More than 10 intersections with the leading edge of the magnetospheric shock wave were recorded while the geomagnetosphere was within the magnetic cloud, indicating an increase in the cross section of the transient area as the magnetosphere and cloud interacted. The boundary of the quasisteady flux was identified and had almost the same changes in plasma and magnetic field parameters as the flare flux boundary.

  17. Distributional Stress Regularity: A Corpus Study

    ERIC Educational Resources Information Center

    Temperley, David

    2009-01-01

    The regularity of stress patterns in a language depends on "distributional stress regularity", which arises from the pattern of stressed and unstressed syllables, and "durational stress regularity", which arises from the timing of syllables. Here we focus on distributional regularity, which depends on three factors. "Lexical stress patterning"…

  18. Cloud Infrastructure & Applications - CloudIA

    NASA Astrophysics Data System (ADS)

    Sulistio, Anthony; Reich, Christoph; Doelitzscher, Frank

    The idea behind Cloud Computing is to deliver Infrastructure-as-a-Services and Software-as-a-Service over the Internet on an easy pay-per-use business model. To harness the potentials of Cloud Computing for e-Learning and research purposes, and to small- and medium-sized enterprises, the Hochschule Furtwangen University establishes a new project, called Cloud Infrastructure & Applications (CloudIA). The CloudIA project is a market-oriented cloud infrastructure that leverages different virtualization technologies, by supporting Service-Level Agreements for various service offerings. This paper describes the CloudIA project in details and mentions our early experiences in building a private cloud using an existing infrastructure.

  19. Venus ionospheric 'clouds' - Relationship to the magnetosheath field geometry

    NASA Technical Reports Server (NTRS)

    Ong, M.; Luhmann, J. G.; Russell, C. T.; Strangeway, R. J.; Brace, L. H.

    1991-01-01

    The magnetic field control of Venus plasma 'clouds' relative to the planet has been analyzed by rotating the observed locations of the clouds into a coordinate system in which all of the transverse upstream magnetic fields were aligned. The results indicate that clouds are scattered around the periphery of the planet in the terminator plane. There is no evidence of a concentration of clouds where the magnetosheath magnetic field is most strongly 'draped'. On the other hand, statistics show that the change in the orientation of the transverse upstream magnetic field between the inbound and outbound bow shock crossings, for the orbits where clouds are seen is about 30 deg greater than the average upstream change at Venus over the same time intervals.

  20. Fragmentation of interstellar clouds and star formation

    NASA Technical Reports Server (NTRS)

    Silk, J.

    1982-01-01

    The principal issues are addressed: the fragmentation of molecular clouds into units of stellar mass and the impact of star formation on molecular clouds. The observational evidence for fragmentation is summarized, and the gravitational instability described of a uniform spherical cloud collapsing from rest. The implications are considered of a finite pressure for the minimum fragment mass that is attainable in opacity-limited fragmentation. The role of magnetic fields is discussed in resolving the angular momentum problem and in making the collapse anisotropic, with notable consequences for fragmentation theory. Interactions between fragments are described, with emphasis on the effect of protostellar winds on the ambient cloud matter and on inhibiting further star formation. Such interactions are likely to have profound consequences for regulating the rate of star formation and on the energetics and dynamics of molecular clouds.

  1. Absolute Measurement of Electron Cloud Density

    SciTech Connect

    Covo, M K; Molvik, A W; Cohen, R H; Friedman, A; Seidl, P A; Logan, G; Bieniosek, F; Baca, D; Vay, J; Orlando, E; Vujic, J L

    2007-06-21

    Beam interaction with background gas and walls produces ubiquitous clouds of stray electrons that frequently limit the performance of particle accelerator and storage rings. Counterintuitively we obtained the electron cloud accumulation by measuring the expelled ions that are originated from the beam-background gas interaction, rather than by measuring electrons that reach the walls. The kinetic ion energy measured with a retarding field analyzer (RFA) maps the depressed beam space-charge potential and provides the dynamic electron cloud density. Clearing electrode current measurements give the static electron cloud background that complements and corroborates with the RFA measurements, providing an absolute measurement of electron cloud density during a 5 {micro}s duration beam pulse in a drift region of the magnetic transport section of the High-Current Experiment (HCX) at LBNL.

  2. Adaptive regularization of earthquake slip distribution inversion

    NASA Astrophysics Data System (ADS)

    Wang, Chisheng; Ding, Xiaoli; Li, Qingquan; Shan, Xinjian; Zhu, Jiasong; Guo, Bo; Liu, Peng

    2016-04-01

    Regularization is a routine approach used in earthquake slip distribution inversion to avoid numerically abnormal solutions. To date, most slip inversion studies have imposed uniform regularization on all the fault patches. However, adaptive regularization, where each retrieved parameter is regularized differently, has exhibited better performances in other research fields such as image restoration. In this paper, we implement an investigation into adaptive regularization for earthquake slip distribution inversion. It is found that adaptive regularization can achieve a significantly smaller mean square error (MSE) than uniform regularization, if it is set properly. We propose an adaptive regularization method based on weighted total least squares (WTLS). This approach assumes that errors exist in both the regularization matrix and observation, and an iterative algorithm is used to solve the solution. A weight coefficient is used to balance the regularization matrix residual and the observation residual. An experiment using four slip patterns was carried out to validate the proposed method. The results show that the proposed regularization method can derive a smaller MSE than uniform regularization and resolution-based adaptive regularization, and the improvement in MSE is more significant for slip patterns with low-resolution slip patches. In this paper, we apply the proposed regularization method to study the slip distribution of the 2011 Mw 9.0 Tohoku earthquake. The retrieved slip distribution is less smooth and more detailed than the one retrieved with the uniform regularization method, and is closer to the existing slip model from joint inversion of the geodetic and seismic data.

  3. Localizing the Frequency x Regularity Word Reading Interaction in the Cerebral Cortex

    ERIC Educational Resources Information Center

    Cummine, Jacqueline; Sarty, Gordon E.; Borowsky, Ron

    2010-01-01

    The aim of this work is to combine behavioural and functional magnetic resonance imaging (fMRI) data to advance our knowledge of where the Frequency x Regularity interaction on word naming is located in the cerebral cortex. Participants named high and low frequency, regular and exception words in a behavioural lab (Experiment 1) and during an fMRI…

  4. The effect of brokenness on cloud-climate sensitivity

    NASA Technical Reports Server (NTRS)

    Harshvardhan, MR.

    1982-01-01

    A study has been made of the effect of brokenness on the infrared and albedo feedback of clouds in climate models using a simplified treatment of broken cloudiness. It is shown that the individual feedback terms computed using the plane-parallel assumption differ markedly from the computations performed for a regular array of cuboidal clouds. If the cloudiness changes such that clear areas become cloudy but the nature of the broken cloud field remains unchanged, then both the feedbacks are magnified, the infrared more so than the albedo. However, if individual elements in the cloud field are increased horizontally in a constrained area, the feedbacks can be enhanced or diminished depending on the cloud fraction and aspect ratio of the elements. It is also shown that, in the global average, the ratio of the change in outgoing infrared flux to global albedo, as deduced from satellite measurements, will be larger than model simulations using planiform clouds.

  5. Filamentary structure in the Orion molecular cloud

    NASA Astrophysics Data System (ADS)

    Bally, J.; Dragovan, M.; Langer, W. D.; Stark, A. A.; Wilson, R. W.

    1986-10-01

    A large scale 13CO map (containing 33,000 spectra) of the giant molecular cloud located in the southern part of Orion is presented which contains the Orion Nebula, NGC1977, and the LI641 dark cloud complex. The overall structure of the cloud is filamentary, with individual features having a length up to 40 times their width. This morphology may result from the effects of star formation in the region or embedded magnetic fields in the cloud. We suggest a simple picture for the evolution of the Orion-A cloud and the formation of the major filament. A rotating proto-cloud (counter rotating with respect to the galaxy) contians a b-field aligned with the galaxtic plane. The northern portion of this cloud collapsed first, perhaps triggered by the pressure of the Ori I OB association. The magnetic field combined with the anisotropic pressure produced by the OB-association breaks the symmetry of the pancake instability, a filament rather than a disc is produced. The growth of instabilities in the filament formed sub-condensations which are recent sites of star formation.

  6. Filamentary structure in the Orion molecular cloud

    NASA Technical Reports Server (NTRS)

    Bally, J.; Langer, W. D.; Bally, J.; Langer, W. D.; Bally, J.; Langer, W. D.

    1986-01-01

    A large scale 13CO map (containing 33,000 spectra) of the giant molecular cloud located in the southern part of Orion is presented which contains the Orion Nebula, NGC1977, and the LI641 dark cloud complex. The overall structure of the cloud is filamentary, with individual features having a length up to 40 times their width. This morphology may result from the effects of star formation in the region or embedded magnetic fields in the cloud. We suggest a simple picture for the evolution of the Orion-A cloud and the formation of the major filament. A rotating proto-cloud (counter rotating with respect to the galaxy) contians a b-field aligned with the galaxtic plane. The northern protion of this cloud collapsed first, perhaps triggered by the pressure of the Ori I OB association. The magnetic field combined with the anisotropic pressure produced by the OB-association breaks the symmetry of the pancake instability, a filament rather than a disc is produced. The growth of instabilities in the filament formed sub-condensations which are recent sites of star formation.

  7. Knowledge and regularity in planning

    NASA Technical Reports Server (NTRS)

    Allen, John A.; Langley, Pat; Matwin, Stan

    1992-01-01

    The field of planning has focused on several methods of using domain-specific knowledge. The three most common methods, use of search control, use of macro-operators, and analogy, are part of a continuum of techniques differing in the amount of reused plan information. This paper describes TALUS, a planner that exploits this continuum, and is used for comparing the relative utility of these methods. We present results showing how search control, macro-operators, and analogy are affected by domain regularity and the amount of stored knowledge.

  8. The Oort cloud

    NASA Technical Reports Server (NTRS)

    Marochnik, Leonid S.; Mukhin, Lev M.; Sagdeev, Roald Z.

    1991-01-01

    Views of the large-scale structure of the solar system, consisting of the Sun, the nine planets and their satellites, changed when Oort demonstrated that a gigantic cloud of comets (the Oort cloud) is located on the periphery of the solar system. The following subject areas are covered: (1) the Oort cloud's mass; (2) Hill's cloud mass; (3) angular momentum distribution in the solar system; and (4) the cometary cloud around other stars.

  9. MIT image reconstruction based on edge-preserving regularization.

    PubMed

    Casanova, R; Silva, A; Borges, A R

    2004-02-01

    Tikhonov regularization has been widely used in electrical tomography to deal with the ill-posedness of the inverse problem. However, due to the fact that discontinuities are strongly penalized, this approach tends to produce blurred images. Recently, a lot of interest has been devoted to methods with edge-preserving properties, such as those related to total variation, wavelets and half-quadratic regularization. In the present work, the performance of an edge-preserving regularization method, called ARTUR, is evaluated in the context of magnetic induction tomography (MIT). ARTUR is a deterministic method based on half-quadratic regularization, where complementary a priori information may be introduced in the reconstruction algorithm by the use of a nonnegativity constraint. The method is first tested using an MIT analytical model that generates projection data given the position, the radius and the magnetic permeability of a single nonconductive cylindrical object. It is shown that even in the presence of strong Gaussian additive noise, it is still able to recover the main features of the object. Secondly, reconstructions based on real data for different configurations of conductive nonmagnetic cylindrical objects are presented and some of their parameters estimated. PMID:15005316

  10. RES: Regularized Stochastic BFGS Algorithm

    NASA Astrophysics Data System (ADS)

    Mokhtari, Aryan; Ribeiro, Alejandro

    2014-12-01

    RES, a regularized stochastic version of the Broyden-Fletcher-Goldfarb-Shanno (BFGS) quasi-Newton method is proposed to solve convex optimization problems with stochastic objectives. The use of stochastic gradient descent algorithms is widespread, but the number of iterations required to approximate optimal arguments can be prohibitive in high dimensional problems. Application of second order methods, on the other hand, is impracticable because computation of objective function Hessian inverses incurs excessive computational cost. BFGS modifies gradient descent by introducing a Hessian approximation matrix computed from finite gradient differences. RES utilizes stochastic gradients in lieu of deterministic gradients for both, the determination of descent directions and the approximation of the objective function's curvature. Since stochastic gradients can be computed at manageable computational cost RES is realizable and retains the convergence rate advantages of its deterministic counterparts. Convergence results show that lower and upper bounds on the Hessian egeinvalues of the sample functions are sufficient to guarantee convergence to optimal arguments. Numerical experiments showcase reductions in convergence time relative to stochastic gradient descent algorithms and non-regularized stochastic versions of BFGS. An application of RES to the implementation of support vector machines is developed.

  11. Incorporating anatomical side information into PET reconstruction using nonlocal regularization.

    PubMed

    Nguyen, Van-Giang; Lee, Soo-Jin

    2013-10-01

    With the introduction of combined positron emission tomography (PET)/computed tomography (CT) or PET/magnetic resonance imaging (MRI) scanners, there is an increasing emphasis on reconstructing PET images with the aid of the anatomical side information obtained from X-ray CT or MRI scanners. In this paper, we propose a new approach to incorporating prior anatomical information into PET reconstruction using the nonlocal regularization method. The nonlocal regularizer developed for this application is designed to selectively consider the anatomical information only when it is reliable. As our proposed nonlocal regularization method does not directly use anatomical edges or boundaries which are often used in conventional methods, it is not only free from additional processes to extract anatomical boundaries or segmented regions, but also more robust to the signal mismatch problem that is caused by the indirect relationship between the PET image and the anatomical image. We perform simulations with digital phantoms. According to our experimental results, compared to the conventional method based on the traditional local regularization method, our nonlocal regularization method performs well even with the imperfect prior anatomical information or in the presence of signal mismatch between the PET image and the anatomical image. PMID:23744678

  12. Quantum spin chains with regularly alternating bonds and fields

    NASA Astrophysics Data System (ADS)

    Derzhko, Oleg

    2002-01-01

    We consider the spin-1/2 XY chain in a transverse field with regularly varying exchange interactions and on-site fields. In two limiting cases of the isotropic ( XX) and extremely anisotropic (Ising) exchange interaction the thermodynamic quantities are calculated rigorously with the help of continued fractions. We discuss peculiarities of the low-temperature magnetic properties and a possibility of the spin-Peierls instability.

  13. Research on cloud-based remote measurement and analysis system

    NASA Astrophysics Data System (ADS)

    Gao, Zhiqiang; He, Lingsong; Su, Wei; Wang, Can; Zhang, Changfan

    2015-02-01

    The promising potential of cloud computing and its convergence with technologies such as cloud storage, cloud push, mobile computing allows for creation and delivery of newer type of cloud service. Combined with the thought of cloud computing, this paper presents a cloud-based remote measurement and analysis system. This system mainly consists of three parts: signal acquisition client, web server deployed on the cloud service, and remote client. This system is a special website developed using asp.net and Flex RIA technology, which solves the selective contradiction between two monitoring modes, B/S and C/S. This platform supplies customer condition monitoring and data analysis service by Internet, which was deployed on the cloud server. Signal acquisition device is responsible for data (sensor data, audio, video, etc.) collection and pushes the monitoring data to the cloud storage database regularly. Data acquisition equipment in this system is only conditioned with the function of data collection and network function such as smartphone and smart sensor. This system's scale can adjust dynamically according to the amount of applications and users, so it won't cause waste of resources. As a representative case study, we developed a prototype system based on Ali cloud service using the rotor test rig as the research object. Experimental results demonstrate that the proposed system architecture is feasible.

  14. Tessellating the Sphere with Regular Polygons

    ERIC Educational Resources Information Center

    Soto-Johnson, Hortensia; Bechthold, Dawn

    2004-01-01

    Tessellations in the Euclidean plane and regular polygons that tessellate the sphere are reviewed. The regular polygons that can possibly tesellate the sphere are spherical triangles, squares and pentagons.

  15. Magnetic

    NASA Astrophysics Data System (ADS)

    Aboud, Essam; El-Masry, Nabil; Qaddah, Atef; Alqahtani, Faisal; Moufti, Mohammed R. H.

    2015-06-01

    The Rahat volcanic field represents one of the widely distributed Cenozoic volcanic fields across the western regions of the Arabian Peninsula. Its human significance stems from the fact that its northern fringes, where the historical eruption of 1256 A.D. took place, are very close to the holy city of Al-Madinah Al-Monawarah. In the present work, we analyzed aeromagnetic data from the northern part of Rahat volcanic field as well as carried out a ground gravity survey. A joint interpretation and inversion of gravity and magnetic data were used to estimate the thickness of the lava flows, delineate the subsurface structures of the study area, and estimate the depth to basement using various geophysical methods, such as Tilt Derivative, Euler Deconvolution and 2D modeling inversion. Results indicated that the thickness of the lava flows in the study area ranges between 100 m (above Sea Level) at the eastern and western boundaries of Rahat Volcanic field and getting deeper at the middle as 300-500 m. It also showed that, major structural trend is in the NW direction (Red Sea trend) with some minor trends in EW direction.

  16. Some Cosine Relations and the Regular Heptagon

    ERIC Educational Resources Information Center

    Osler, Thomas J.; Heng, Phongthong

    2007-01-01

    The ancient Greek mathematicians sought to construct, by use of straight edge and compass only, all regular polygons. They had no difficulty with regular polygons having 3, 4, 5 and 6 sides, but the 7-sided heptagon eluded all their attempts. In this article, the authors discuss some cosine relations and the regular heptagon. (Contains 1 figure.)

  17. Regular Pentagons and the Fibonacci Sequence.

    ERIC Educational Resources Information Center

    French, Doug

    1989-01-01

    Illustrates how to draw a regular pentagon. Shows the sequence of a succession of regular pentagons formed by extending the sides. Calculates the general formula of the Lucas and Fibonacci sequences. Presents a regular icosahedron as an example of the golden ratio. (YP)

  18. 22 CFR 120.39 - Regular employee.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 22 Foreign Relations 1 2013-04-01 2013-04-01 false Regular employee. 120.39 Section 120.39 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.39 Regular employee. (a) A regular employee means for purposes of this subchapter: (1) An...

  19. 22 CFR 120.39 - Regular employee.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 22 Foreign Relations 1 2012-04-01 2012-04-01 false Regular employee. 120.39 Section 120.39 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.39 Regular employee. (a) A regular employee means for purposes of this subchapter: (1) An...

  20. 22 CFR 120.39 - Regular employee.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 22 Foreign Relations 1 2014-04-01 2014-04-01 false Regular employee. 120.39 Section 120.39 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.39 Regular employee. (a) A regular employee means for purposes of this subchapter: (1) An...

  1. Cloud CCN feedback

    SciTech Connect

    Hudson, J.G.

    1992-12-31

    Cloud microphysics affects cloud albedo precipitation efficiency and the extent of cloud feedback in response to global warming. Compared to other cloud parameters, microphysics is unique in its large range of variability and the fact that much of the variability is anthropogenic. Probably the most important determinant of cloud microphysics is the spectra of cloud condensation nuclei (CCN) which display considerable variability and have a large anthropogenic component. When analyzed in combination three field observation projects display the interrelationship between CCN and cloud microphysics. CCN were measured with the Desert Research Institute (DRI) instantaneous CCN spectrometer. Cloud microphysical measurements were obtained with the National Center for Atmospheric Research Lockheed Electra. Since CCN and cloud microphysics each affect the other a positive feedback mechanism can result.

  2. Natural frequency of regular basins

    NASA Astrophysics Data System (ADS)

    Tjandra, Sugih S.; Pudjaprasetya, S. R.

    2014-03-01

    Similar to the vibration of a guitar string or an elastic membrane, water waves in an enclosed basin undergo standing oscillatory waves, also known as seiches. The resonant (eigen) periods of seiches are determined by water depth and geometry of the basin. For regular basins, explicit formulas are available. Resonance occurs when the dominant frequency of external force matches the eigen frequency of the basin. In this paper, we implement the conservative finite volume scheme to 2D shallow water equation to simulate resonance in closed basins. Further, we would like to use this scheme and utilizing energy spectra of the recorded signal to extract resonant periods of arbitrary basins. But here we first test the procedure for getting resonant periods of a square closed basin. The numerical resonant periods that we obtain are comparable with those from analytical formulas.

  3. Pairing effect and misleading regularity

    NASA Astrophysics Data System (ADS)

    Al-Sayed, A.

    2015-11-01

    We study the nearest neighbor spacing distribution of energy levels of even-even nuclei classified according to their reduced electric quadrupole transition probability B (E2) ↑ using the available experimental data. We compare between Brody, and Abul-Magd distributions that extract the degree of chaoticity within nuclear dynamics. The results show that Abul-Magd parameter f can represents the chaotic behavior in more acceptable way than Brody, especially if a statistically significant study is desired. A smooth transition from chaos to order is observed as B (E2) ↑ increases. An apparent regularity was located at the second interval, namely: at 0.05 ≤ B (E2) < 0.1 in e2b2 units, and at 10 ≤ B (E2) < 15 in Weisskopf unit. Finally, the chaotic behavior parameterized in terms of B (E2) ↑ does not depend on the unit used.

  4. Pion Cloud and the Sea of the Nucleon

    SciTech Connect

    Wally Melnitchouk

    2009-05-01

    I review recent progress in understanding the structure of the nucleon sea and the role of the nucleon's pion cloud. In particular, I discuss the consequences of the pion cloud for the d-bar - u-bar asymmetry in the proton, the neutron's electric form factor, and the proton's electric to magnetic form factor ratio.

  5. Molecular clouds in Orion and Monoceros

    SciTech Connect

    Maddalena, R.J.

    1986-01-01

    About one-eighth of a well-sampled 850 deg/sup 2/ region of Orion and Monoceros, extending from the Taurus dark cloud complex to the CMa OB 1 association, shows emission at the frequency of the J = 1 ..-->.. 0 transition of CO coming from either local clouds (d < 1 kpc) lying as much as 25/sup 8/ from the galactic plane or from more distant objects located within a few degrees of the plane and well outside the solar circle. Local giant molecular clouds associated with Orion A and B have enhanced temperatures and densities near their western edges possibly due to compression of molecular gas by a high pressure region created by the cumulative effects of approx.10 supernovae that occurred in the Orion OB association. Another giant molecular cloud found to be associated with Mon R2 may be related to the Orion clouds. Two filamentary clouds (one possible 200 pc long but only 3-10 pc wide) were found that may represent a new class of object; magnetic fields probably play a role in confining these filaments. An expanding ring of clouds concentric with the H II region S 264 and its ionizing 08 star lambda Ori was also investigated, and a possible evolutionary sequence for the ring is given in detail: the clouds probably constitute fragments of the original cloud from which lambda Ori formed, the gas pressure of the H II region and the rocket effect having disrupted the cloud and accelerated the fragments to their present velocities.

  6. On the virial theorem for turbulent molecular clouds

    NASA Technical Reports Server (NTRS)

    Mckee, Christopher F.; Zweibel, Ellen G.

    1992-01-01

    An Eulerian, rather than Lagrangian, form of the virial theorem is derived for a turbulent, magnetized cloud embedded in a steady, turbulent, low-density intercloud medium. The role of turbulent pressure in cloud confinement is clarified, and it is shown that, in the absence of a magnetic field, a cloud can be at a somewhat lower pressure than the intercloud medium. Simple forms for the magnetic term in the virial equation are obtained. Radiation pressure is considered; its effects are relatively small under average conditions in the interstellar medium. Under typical conditions, external pressure and magnetic fields are shown to have a relatively small effect on virial estimates of the mass of self-gravitating clouds.

  7. Cloud Processed CCN Affect Cloud Microphysics

    NASA Astrophysics Data System (ADS)

    Hudson, J. G.; Noble, S. R., Jr.; Tabor, S. S.

    2015-12-01

    Variations in the bimodality/monomodality of CCN spectra (Hudson et al. 2015) exert opposite effects on cloud microphysics in two aircraft field projects. The figure shows two examples, droplet concentration, Nc, and drizzle liquid water content, Ld, against classification of CCN spectral modality. Low ratings go to balanced separated bimodal spectra, high ratings go to single mode spectra, strictly monomodal 8. Intermediate ratings go merged modes, e.g., one mode a shoulder of another. Bimodality is caused by mass or hygroscopicity increases that go only to CCN that made activated cloud droplets. In the Ice in Clouds Experiment-Tropical (ICE-T) small cumuli with lower Nc, greater droplet mean diameters, MD, effective radii, re, spectral widths, σ, cloud liquid water contents, Lc, and Ld were closer to more bimodal (lower modal ratings) below cloud CCN spectra whereas clouds with higher Nc, smaller MD, re, σ, and Ld were closer to more monomodal CCN (higher modal ratings). In polluted stratus clouds of the MArine Stratus/Stratocumulus Experiment (MASE) clouds that had greater Nc, and smaller MD, re, σ, Lc, and Ld were closer to more bimodal CCN spectra whereas clouds with lower Nc, and greater MD, re, σ, Lc, and Ld were closer to more monomodal CCN. These relationships are opposite because the dominant ICE-T cloud processing was coalescence whereas chemical transformations (e.g., SO2 to SO4) were dominant in MASE. Coalescence reduces Nc and thus also CCN concentrations (NCCN) when droplets evaporate. In subsequent clouds the reduced competition increases MD and σ, which further enhance coalescence and drizzle. Chemical transformations do not change Nc but added sulfate enhances droplet and CCN solubility. Thus, lower critical supersaturation (S) CCN can produce more cloud droplets in subsequent cloud cycles, especially for the low W and effective S of stratus. The increased competition reduces MD, re, and σ, which inhibit coalescence and thus reduce drizzle

  8. Identifying Cognitive States Using Regularity Partitions

    PubMed Central

    2015-01-01

    Functional Magnetic Resonance (fMRI) data can be used to depict functional connectivity of the brain. Standard techniques have been developed to construct brain networks from this data; typically nodes are considered as voxels or sets of voxels with weighted edges between them representing measures of correlation. Identifying cognitive states based on fMRI data is connected with recording voxel activity over a certain time interval. Using this information, network and machine learning techniques can be applied to discriminate the cognitive states of the subjects by exploring different features of data. In this work we wish to describe and understand the organization of brain connectivity networks under cognitive tasks. In particular, we use a regularity partitioning algorithm that finds clusters of vertices such that they all behave with each other almost like random bipartite graphs. Based on the random approximation of the graph, we calculate a lower bound on the number of triangles as well as the expectation of the distribution of the edges in each subject and state. We investigate the results by comparing them to the state of the art algorithms for exploring connectivity and we argue that during epochs that the subject is exposed to stimulus, the inspected part of the brain is organized in an efficient way that enables enhanced functionality. PMID:26317983

  9. Molecular clouds in Orion and Monoceros

    NASA Technical Reports Server (NTRS)

    Morris, M.; Montani, J.; Thaddeus, P.

    1980-01-01

    A 1.2-m millimeter-wave telescope has been used to survey CO in the constellations of Orion and Monoceros. Many new molecular clouds have been found. The distribution of molecular material shows two striking characteristics: (1) Most of the molecular clouds in this region appear to be connected by continuous extensions and filaments. To judge from continuity in radial velocity, most of these connections appear to be real, and are not merely the result of projection along the line of sight; (2) There are at least two slender filamentary features longer than 10 deg in angular extent. These filaments may connect the molecular clouds lying well out of the Galactic plane to clouds lying in the plane. Their shape and orientation suggest that magnetic fields may play a role in their evolution. The observed velocity gradients may be explained by accelerated gas flow along the filament.

  10. Gamma rays from giant molecular clouds

    NASA Technical Reports Server (NTRS)

    Hunter, Stanley D.; Kanbach, Gottfried

    1990-01-01

    Giant Molecular Clouds (GMCs) are massive, bounded, cool, dense regions containing mostly H2, but also H I, CO, and other molecules. These clouds occupy less than 1 percent of the galactic volume, but are a substantial part of the interstellar mass. They are irradiated by the high energy cosmic rays which are possibly modulated by the matter and magnetic fields within the clouds. The product of cosmic-ray flux and matter density is traced by the emission of high energy gamma-rays. A spherical cloud model is considered and the gamma ray flux from several GMCs within 1 kpc of the sun which should be detectable by the EGRET (Energetic Gamma-Ray Experimental Telescope) instrument on GRO (Gamma Ray Observatory).

  11. A simulation study exploring the effects of sensor spatial resolution on estimates of cloud cover from satellites.

    NASA Technical Reports Server (NTRS)

    Shenk, W. E.; Salomonson, V. V.

    1972-01-01

    Investigation of the effects of sensor spatial resolution on estimating the amount of clouds covering the earth by simulating various cloud distributions and sizes, and measuring the known cloud amount with resolution of different sizes using a cloud-no cloud threshold technique often applied in automatic data processing. Cloud amount statistics have been tabulated for a three-orders-of-magnitude range in the ratio (R) of areal cloud size to areal resolution size for seven cloud amounts between 6 and 90%. Three different cloud patterns were used. These were 1) a regularly spaced pattern of homogeneous dots arranged in rows and columns (to simulate cloud streets), 2) a randomly spaced pattern of the same dots (to simulate randomly oriented cumulus clouds), and 3) a heterogeneous cloud size distribution irregularly spaced (to simulate a view of different cloud types and sizes). Two cloud amount estimation techniques were tested. Cloud amounts of 100% (method 1) and 50% (method 2) were assigned to partially filled resolution elements. Using criteria applicable to some studies carried out in the past, it is shown that cloud amount estimations can be in error by as much as 86 and 38%, respectively, for the two methods. Nomograms have been developed which subtantially improve the estimate of the true cloud cover for R less than 100, provided that R can be determined.

  12. Cloud Computing for radiologists.

    PubMed

    Kharat, Amit T; Safvi, Amjad; Thind, Ss; Singh, Amarjit

    2012-07-01

    Cloud computing is a concept wherein a computer grid is created using the Internet with the sole purpose of utilizing shared resources such as computer software, hardware, on a pay-per-use model. Using Cloud computing, radiology users can efficiently manage multimodality imaging units by using the latest software and hardware without paying huge upfront costs. Cloud computing systems usually work on public, private, hybrid, or community models. Using the various components of a Cloud, such as applications, client, infrastructure, storage, services, and processing power, Cloud computing can help imaging units rapidly scale and descale operations and avoid huge spending on maintenance of costly applications and storage. Cloud computing allows flexibility in imaging. It sets free radiology from the confines of a hospital and creates a virtual mobile office. The downsides to Cloud computing involve security and privacy issues which need to be addressed to ensure the success of Cloud computing in the future. PMID:23599560

  13. Noctilucent Cloud Sightings

    NASA Video Gallery

    Polar Mesospheric Clouds form during each polar region's summer months in the coldest place in the atmosphere, 50 miles above Earth's surface. Noctilucent Clouds were first observed in 1885 by an a...

  14. Closed Small Cell Clouds

    Atmospheric Science Data Center

    2013-04-19

    article title:  Closed Small Cell Clouds in the South Pacific     ... the Multi-angle Imaging SpectroRadiometer (MISR). Closed cell clouds are formed under conditions of widespread sinking of the air above. ...

  15. Modeling Electrical Structure of the Artificial Charged Aerosol Cloud

    NASA Astrophysics Data System (ADS)

    Davydenko, S.; Iudin, D.; Klimashov, V.; Kostinskiy, A. J.; Syssoev, V.

    2014-12-01

    The electric structure of the unipolar charged aerosol cloud is considered. The cloud of the volume about 30 cubic meters is generated in the open atmosphere by the original aeroelectrical facility consisting of the source of the aquated ions and the high-voltage discharger. Representing the charge density distribution as a superposition of regular and irregular parts, a model of the electrical structure of the cloud is developed. The regular part is calculated under the stationary current approximation taking into account the source current structure, the shape of the cloud, and results of the multi-point measurements of the electric field and conductivity in the vicinity of the cloud. The irregular part describes random spatiotemporal fluctuations of the charge density which are assumed to be proportional to the aerosol number density. It is shown that a quasi-electrostatic field of the charged aerosol is characterized by significant spatial fluctuations showing the scale invariance. The mean-square fluctuations of the voltage between different parts of the cloud are proportional to the square root of its linear dimensions and may reach significant values even in the absence of the regular field. The basic parameters of the fluctuating spatial structure of the electric field inside the charged aerosol cloud are estimated. It is shown that the charge density fluctuations could lead to a significant (up to 2,5 times) local enhancement of the electric field as compared to the field of the regular part of the charge density. The above effect could serve as one of the important mechanisms of the spark initiation.

  16. Computer animation of clouds

    SciTech Connect

    Max, N.

    1994-01-28

    Computer animation of outdoor scenes is enhanced by realistic clouds. I will discuss several different modeling and rendering schemes for clouds, and show how they evolved in my animation work. These include transparency-textured clouds on a 2-D plane, smooth shaded or textured 3-D clouds surfaces, and 3-D volume rendering. For the volume rendering, I will present various illumination schemes, including the density emitter, single scattering, and multiple scattering models.

  17. Cloud Scaling Properties and Cloud Parameterization

    NASA Technical Reports Server (NTRS)

    Cahalan, R. F.; Morcrette, J. J.

    1998-01-01

    Cloud liquid and cloud traction variability is studied as a function of horizontal scale in the ECMWF forecast model during several 10-day runs at the highest available model resolution, recently refined from approximately 60 km (T213) down to approximately 20 km (T639). At higher resolutions, model plane-parallel albedo biases are reduced, so that models may be tuned to have larger, more realistic, cloud liquid water amounts, However, the distribution of cloud liquid assumed -within- each gridbox, for radiative and thermodynamic computations, depends on ad hoc assumptions that are not necessarily consistent with observed scaling properties, or with scaling properties produced by the model at larger scales. To study the larger-scale cloud properties, ten locations on the Earth are chosen to coincide with locations having considerable surface data available for validation, and representing a variety of climatic regimes, scaling exponents are determined from a range or scales down to model resolution, and are re-computed every three hours, separately for low, medium and high clouds, as well as column-integrated cloudiness. Cloud variability fluctuates in time, due to diurnal, synoptic and other' processes, but scaling exponents are found to be relatively stable. various approaches are considered for applying computed cloud scaling to subgrid cloud distributions used for radiation, beyond simple random or maximal overlap now in common use. Considerably more work is needed to compare model cloud scaling with observations. This will be aided by increased availability of high-resolution surface, aircraft and satellite data, and by the increasing resolution of global models,

  18. Cloud Computing Explained

    ERIC Educational Resources Information Center

    Metz, Rosalyn

    2010-01-01

    While many talk about the cloud, few actually understand it. Three organizations' definitions come to the forefront when defining the cloud: Gartner, Forrester, and the National Institutes of Standards and Technology (NIST). Although both Gartner and Forrester provide definitions of cloud computing, the NIST definition is concise and uses…

  19. A Population of Dark Clouds Detected in Radio Continuum Images

    NASA Astrophysics Data System (ADS)

    Yusef-Zadeh, Farhad

    2013-01-01

    Using the VLA and GBT, radio continuum images of the inner Galaxy reveal the presence of numerous dark features. These dark features coincide with dense molecular and dust clouds. Unlike infrared dark clouds or extinction clouds at optical wavelengths, these features which we call ``radio dark clouds'' are produced by a deficiency in radio continuum emission from molecular clouds that are embedded in a bath of UV radiation field or synchrotron emitting cosmic ray particles. The contribution of the continuum emission along different pathlengths results in dark features that trace embedded molecular clouds. The new technique of identifying cold clouds can place constraints on the depth and the strength of diffuse magnetic field of molecular clouds. We present several examples of radio dark clouds and demonstrate an anti-correlation between the distributions of radio continuum and molecular line and dust emission. The level at which the continuum flux is suppressed in these sources suggests that the depth of the molecular cloud is similar to the size of the continuum emission within a factor of two. These examples suggest that radio continuum survey images can be powerful probes of interacting molecular clouds with massive stars and supernova remnants in the Galaxy as well as in the nuclei of active galaxies.

  20. Corona Discharge in Clouds

    NASA Astrophysics Data System (ADS)

    Sin'kevich, A. A.; Dovgalyuk, Yu. A.

    2014-04-01

    We present a review of the results of theoretical studies and laboratory modeling of corona discharge initiation in clouds. The influence of corona discharges on the evolution of the cloud microstructure and electrification is analyzed. It is shown that corona discharges are initiated when large-size hydrometeors approach each other, whereas in some cases, corona discharges from crystals, ice pellets, and hailstones can appear. The corona discharges lead to significant air ionization, charging of cloud particles, and separation of charges in clouds and initiate streamers and lightnings. The influence of corona discharges on changes in the phase composition of clouds is analyzed.

  1. Cloud microstructure studies

    NASA Technical Reports Server (NTRS)

    Blau, H. H., Jr.; Fowler, M. G.; Chang, D. T.; Ryan, R. T.

    1972-01-01

    Over two thousand individual cloud droplet size distributions were measured with an optical cloud particle spectrometer flown on the NASA Convair 990 aircraft. Representative droplet spectra and liquid water content, L (gm/cu m) were obtained for oceanic stratiform and cumuliform clouds. For non-precipitating clouds, values of L range from 0.1 gm/cu m to 0.5 gm/cu m; with precipitation, L is often greater than 1 gm/cu m. Measurements were also made in a newly formed contrail and in cirrus clouds.

  2. Methane Clouds on Titan

    NASA Astrophysics Data System (ADS)

    Griffith, Caitlin A.

    Following the Voyager encounter with Titan in 1981 Saturn's largest moon was hypothesized sport a liquid cycle similar that on Earth with clouds rain and seas. On Titan methane is the condensible playing the role that water plays on Earth. Although the presence of seas is difficult to establish from ground methane clouds have been detected on Titan. Ground-based observations reveal that Titan's clouds differ remarkedly from their terrestrial counterparts. Titan's clouds are sparse reside primarily at particular altitude and concentrate presently in the south pole. That Titan's clouds are exotic is not surprising. Titan receives ~100 times less sunlight than Earth to drive weather. In addition Titan's radiative time constant is 180 years large compared to the 3 month terrestrial value. With little power and sluggish conditions it is not clear how clouds form on Titan. This talk will compare Titan to Earth to explore the nature of clouds under Titan's foreign conditions.

  3. Clouds Over Crater Rim

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Clouds above the rim of 'Endurance Crater' in this image from NASA's Mars Exploration Rover Opportunity can remind the viewer that Mars, our celestial neighbor, is subject to weather. On Earth, clouds like these would be referred to as 'cirrus' or the aptly nicknamed 'mares' tails.' These clouds occur in a region of strong vertical shear. The cloud particles (ice in this martian case) fall out, and get dragged along away from the location where they originally condensed, forming characteristic streamers. Opportunity took this picture with its navigation camera during the rover's 269th martian day (Oct. 26, 2004).

    The mission's atmospheric science team is studying cloud observations to deduce seasonal and time-of-day behavior of the clouds. This helps them gain a better understanding of processes that control cloud formation.

  4. Resolving intravoxel fiber architecture using nonconvex regularized blind compressed sensing

    NASA Astrophysics Data System (ADS)

    Chu, C. Y.; Huang, J. P.; Sun, C. Y.; Liu, W. Y.; Zhu, Y. M.

    2015-03-01

    In diffusion magnetic resonance imaging, accurate and reliable estimation of intravoxel fiber architectures is a major prerequisite for tractography algorithms or any other derived statistical analysis. Several methods have been proposed that estimate intravoxel fiber architectures using low angular resolution acquisitions owing to their shorter acquisition time and relatively low b-values. But these methods are highly sensitive to noise. In this work, we propose a nonconvex regularized blind compressed sensing approach to estimate intravoxel fiber architectures in low angular resolution acquisitions. The method models diffusion-weighted (DW) signals as a sparse linear combination of unfixed reconstruction basis functions and introduces a nonconvex regularizer to enhance the noise immunity. We present a general solving framework to simultaneously estimate the sparse coefficients and the reconstruction basis. Experiments on synthetic, phantom, and real human brain DW images demonstrate the superiority of the proposed approach.

  5. Proper time regularization at finite quark chemical potential

    NASA Astrophysics Data System (ADS)

    Zhang, Jin-Li; Shi, Yuan-Mei; Xu, Shu-Sheng; Zong, Hong-Shi

    2016-04-01

    In this paper, we use the two-flavor Nambu-Jona-Lasinio (NJL) model to study the quantum chromodynamics (QCD) chiral phase transition. To deal with the ultraviolet (UV) issue, we adopt the popular proper time regularization (PTR), which is commonly used not only for hadron physics but also for the studies with magnetic fields. This regularization scheme can introduce the infrared (IR) cutoff to include quark confinement. We generalize the PTR to zero temperature and finite chemical potential case use a completely new method, and then study the chiral susceptibility, both in the chiral limit case and with finite current quark mass. The chiral phase transition is second-order in μ = 0 and T = 0 and crossover at μ≠0 and T = 0. Three sets of parameters are used to make sure that the results do not depend on the parameter choice.

  6. Wavelet Regularization Per Nullspace Shuttle

    NASA Astrophysics Data System (ADS)

    Charléty, J.; Nolet, G.; Sigloch, K.; Voronin, S.; Loris, I.; Simons, F. J.; Daubechies, I.; Judd, S.

    2010-12-01

    Wavelet decomposition of models in an over-parameterized Earth and L1-norm minimization in wavelet space is a promising strategy to deal with the very heterogeneous data coverage in the Earth without sacrificing detail in the solution where this is resolved (see Loris et al., abstract this session). However, L1-norm minimizations are nonlinear, and pose problems of convergence speed when applied to large data sets. In an effort to speed up computations we investigate the application of the nullspace shuttle (Deal and Nolet, GJI 1996). The nullspace shuttle is a filter that adds components from the nullspace to the minimum norm solution so as to have the model satisfy additional conditions not imposed by the data. In our case, the nullspace shuttle projects the model on a truncated basis of wavelets. The convergence of this strategy is unproven, in contrast to algorithms using Landweber iteration or one of its variants, but initial computations using a very large data base give reason for optimism. We invert 430,554 P delay times measured by cross-correlation in different frequency windows. The data are dominated by observations with US Array, leading to a major discrepancy in the resolution beneath North America and the rest of the world. This is a subset of the data set inverted by Sigloch et al (Nature Geosci, 2008), excluding only a small number of ISC delays at short distance and all amplitude data. The model is a cubed Earth model with 3,637,248 voxels spanning mantle and crust, with a resolution everywhere better than 70 km, to which 1912 event corrections are added. In each iteration we determine the optimal solution by a least squares inversion with minimal damping, after which we regularize the model in wavelet space. We then compute the residual data vector (after an intermediate scaling step), and solve for a model correction until a satisfactory chi-square fit for the truncated model is obtained. We present our final results on convergence as well as a

  7. Cyclotron Resonances in Electron Cloud Dynamics

    SciTech Connect

    Celata, C. M.; Furman, Miguel A.; Vay, J.-L.; Ng, J. S.T.; Grote, D. P.; Pivi, M. T. F.; Wang, L. F.

    2009-04-29

    A new set of resonances for electron cloud dynamics in the presence of a magnetic field has been found. For short beam bunch lengths and low magnetic fields where lb<< 2pi c/omega c (with lb = bunch length, omega c = non-relativistic cyclotron frequency) resonances between the bunch frequency and harmonics of the electron cyclotron frequency cause an increase in the electron cloud density in narrow ranges of magnetic field near the resonances. For ILC parameters the increase in the density is up to a factor ~;;3, and the spatial distribution of the electrons is broader near resonances, lacking the well-defined vertical density"stripes" found for non-resonant cases. Simulations with the 2D computer code POSINST, as well as a single-particle tracking code, were used to elucidate the physics of the dynamics. The existence of the resonances has been confirmed in experiments at PEP-II. The resonances are expected to affect the electron cloud dynamics in the fringe fields of conventional lattice magnets and in wigglers, where the magnetic fields are low. Results of the simulations and experimental observations, the reason for the bunch-length dependence, and details of the dynamics are discussed here.

  8. Cyclotron Resonances in Electron Cloud Dynamics

    SciTech Connect

    Celata, C M; Furman, M A; Vay, J L; Grote, D P; Ng, J T; Pivi, M F; Wang, L F

    2009-05-05

    A new set of resonances for electron cloud dynamics in the presence of a magnetic field has been found. For short beam bunch lengths and low magnetic fields where l{sub b} << 2{pi}{omega}{sub c}, (l{sub b} = bunch duration, {omega}{sub c} = non-relativistic cyclotron frequency) resonances between the bunch frequency and harmonics of the cyclotron frequency cause an increase in the electron cloud density in narrow ranges of magnetic field near the resonances. For ILC parameters the increase in the density is up to a factor {approx} 3, and the spatial distribution of the electrons is broader near resonances, lacking the well-defined density 'stripes' of multipactoring found for non-resonant cases. Simulations with the 2D computer code POSINST, as well as a single-particle tracking code, were used to elucidate the physics of the dynamics. The resonances are expected to affect the electron cloud dynamics in the fringe fields of conventional lattice magnets and in wigglers, where the magnetic fields are low. Results of the simulations, the reason for the bunch-length dependence, and details of the dynamics will be discussed.

  9. Electron cloud detection and characterization in the CERN Proton Synchrotron

    NASA Astrophysics Data System (ADS)

    Mahner, Edgar; Kroyer, Tom; Caspers, Fritz

    2008-09-01

    We describe a dedicated electron cloud experiment which was installed in the CERN Proton Synchrotron in 2007. The setup comprises shielded button-type pickups, a fast vacuum logging, a dipole magnet, and a stripline electrode to experimentally verify the beneficial effect of electron cloud clearing. The electron cloud effect was observed within the last milliseconds before ejection of the nominal LHC proton beam consisting of 72 bunches with 25 ns spacing. Measurements of electron flux at the wall and vacuum pressure are presented for a set of magnetic fields and bias voltages on the clearing electrode, showing that efficient electron cloud suppression can be obtained for appropriate clearing voltages but revealing an unexpectedly complex dependence on magnetic field and voltage.

  10. Conditions for Circumstellar Disc Formation II: Effects of Initial Cloud Stability and Mass Accretion Rate

    NASA Astrophysics Data System (ADS)

    Machida, Masahiro N.; Matsumoto, Tomoaki; Inutsuka, Shu-ichiro

    2016-09-01

    Disc formation in strongly magnetized cloud cores is investigated using a three-dimensional magnetohydrodynamic simulation with a focus on the effects of the initial cloud stability and the mass accretion rate. The initial cloud stability greatly alters the disc formation process even for prestellar clouds with the same mass-to-flux ratio. A high mass accretion rate onto the disc-forming region is realized in initially unstable clouds, and a large angular momentum is introduced into the circumstellar region in a short time. The region around the protostar has both a thin infalling envelope and a weak magnetic field, which both weaken the effect of magnetic braking. The growth of the rotation-supported disc is promoted in such unstable clouds. Conversely, clouds in an initially near-equilibrium state show lower accretion rates of mass and angular momentum. The angular momentum is transported to the outer envelope before protostar formation. After protostar formation, the circumstellar region has a thick infalling envelope and a strong magnetic field that effectively brake the disc. As a result, disc formation is suppressed when the initial cloud is in a nearly stable state. The density distribution of the initial cloud also affects the disc formation process. Disc growth strongly depends on the initial conditions when the prestellar cloud has a uniform density, whereas there is no significant difference in the disc formation process in prestellar clouds with nonuniform densities.

  11. Electron cloud wakefields in bunch trains

    NASA Astrophysics Data System (ADS)

    Petrov, F. B.; Boine-Frankenheim, Oliver

    2016-02-01

    Electron cloud is a concern for many modern and future accelerator facilities. There are a number of undesired effects attributed to the presence of electron clouds. Among them are coherent instabilities, emittance growth, cryogenic heat load, synchronous phase shift and pressure rise. In long bunch trains one can observe the emittance growth getting faster along the bunch train. The interaction between the beam and the electron cloud is a two-stream interaction. The prameters of the electron cloud wakefields depend on the beam intensity, beam centroid perturbations, and on the electron density and perturbations. If the electron cloud forgets the bunch centroid perturbation very fast, the buildup itself, via growing density, becomes a way of coupling between the bunches. In the present paper we address how the bunch perturbation shape affects the multi-bunch wakefields under the conditions similar to the CERN LHC and SPS. We study the interplay between the single-bunch and multi-bunch electron cloud wakefields. The effect of the dipole magnetic field on the multi-bunch wakefields is studied.

  12. Overview of New Cloud Optical Properties in Air Force Weather Worldwide Merged Cloud Analysis

    NASA Astrophysics Data System (ADS)

    Nobis, T. E.; Conner, M. D.

    2013-12-01

    Air Force Weather (AFW) has documented requirements for real-time cloud analysis to support DoD missions around the world. To meet these needs, AFW utilizes the Cloud Depiction and Forecast System (CDFS) II system to develop an hourly cloud analysis. The system creates cloud masks at pixel level from 16 different satellite sources, diagnoses cloud layers, reconciles the pixel level data to a regular grid by instrument class, and optimally merges the various instrument classes to create a final multi-satellite analysis. In Jan, 2013, Northrop Grumman Corp. delivered a new CDFS II baseline which included the addition of new Atmospheric and Environmental Research Inc (AER) developed Cloud Optical Property (COP) variables in the analysis. The new variables include phase (ice/water), optical depth, ice/water path, and particle size. In addition, the COP schemes have radically changed the derivation of cloud properties like cloud top height and thickness. The Northrop-developed CDFS II Test Bed was used to examine and characterize the behavior of these new variables in order to understand how the variables are performing, especially between instrument classes. Understanding this behavior allows performance tuning and uncertainty estimation which will assist users seeking to reason with the data and will be necessary for use in model development and climatology development. This presentation will provide a basic overview of the CDFS II produced COP variables and show results from experiments conducted on the CDFS II Testbed. Results will include a basic comparison of COP derived using different instrument classes as well as comparison between pixel level and derived gridded products with an eye towards better characterization of uncertainty.

  13. Electromagnetic wave propagation with negative phase velocity in regular black holes

    SciTech Connect

    Sharif, M. Manzoor, R.

    2012-12-15

    We discuss the propagation of electromagnetic plane waves with negative phase velocity in regular black holes. For this purpose, we consider the Bardeen model as a nonlinear magnetic monopole and the Bardeen model coupled to nonlinear electrodynamics with a cosmological constant. It turns out that the region outside the event horizon of each regular black hole does not support negative phase velocity propagation, while its possibility in the region inside the event horizon is discussed.

  14. 12 CFR 725.3 - Regular membership.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... advances without approval of the NCUA Board for a period of six months after becoming a member. This subsection shall not apply to any credit union which becomes a Regular member of the Facility within six... member of the Facility at any time within six months prior to becoming a Regular member of the Facility....

  15. Transport Code for Regular Triangular Geometry

    Energy Science and Technology Software Center (ESTSC)

    1993-06-09

    DIAMANT2 solves the two-dimensional static multigroup neutron transport equation in planar regular triangular geometry. Both regular and adjoint, inhomogeneous and homogeneous problems subject to vacuum, reflective or input specified boundary flux conditions are solved. Anisotropy is allowed for the scattering source. Volume and surface sources are allowed for inhomogeneous problems.

  16. Continuum regularization of quantum field theory

    SciTech Connect

    Bern, Z.

    1986-04-01

    Possible nonperturbative continuum regularization schemes for quantum field theory are discussed which are based upon the Langevin equation of Parisi and Wu. Breit, Gupta and Zaks made the first proposal for new gauge invariant nonperturbative regularization. The scheme is based on smearing in the ''fifth-time'' of the Langevin equation. An analysis of their stochastic regularization scheme for the case of scalar electrodynamics with the standard covariant gauge fixing is given. Their scheme is shown to preserve the masslessness of the photon and the tensor structure of the photon vacuum polarization at the one-loop level. Although stochastic regularization is viable in one-loop electrodynamics, two difficulties arise which, in general, ruins the scheme. One problem is that the superficial quadratic divergences force a bottomless action for the noise. Another difficulty is that stochastic regularization by fifth-time smearing is incompatible with Zwanziger's gauge fixing, which is the only known nonperturbaive covariant gauge fixing for nonabelian gauge theories. Finally, a successful covariant derivative scheme is discussed which avoids the difficulties encountered with the earlier stochastic regularization by fifth-time smearing. For QCD the regularized formulation is manifestly Lorentz invariant, gauge invariant, ghost free and finite to all orders. A vanishing gluon mass is explicitly verified at one loop. The method is designed to respect relevant symmetries, and is expected to provide suitable regularization for any theory of interest. Hopefully, the scheme will lend itself to nonperturbative analysis. 44 refs., 16 figs.

  17. Regular Decompositions for H(div) Spaces

    SciTech Connect

    Kolev, Tzanio; Vassilevski, Panayot

    2012-01-01

    We study regular decompositions for H(div) spaces. In particular, we show that such regular decompositions are closely related to a previously studied “inf-sup” condition for parameter-dependent Stokes problems, for which we provide an alternative, more direct, proof.

  18. Silicon photonics cloud (SiCloud)

    NASA Astrophysics Data System (ADS)

    DeVore, Peter T. S.; Jiang, Yunshan; Lynch, Michael; Miyatake, Taira; Carmona, Christopher; Chan, Andrew C.; Muniam, Kuhan; Jalali, Bahram

    2015-02-01

    We present SiCloud (Silicon Photonics Cloud), the first free, instructional web-based research and education tool for silicon photonics. SiCloud's vision is to provide a host of instructional and research web-based tools. Such interactive learning tools enhance traditional teaching methods by extending access to a very large audience, resulting in very high impact. Interactive tools engage the brain in a way different from merely reading, and so enhance and reinforce the learning experience. Understanding silicon photonics is challenging as the topic involves a wide range of disciplines, including material science, semiconductor physics, electronics and waveguide optics. This web-based calculator is an interactive analysis tool for optical properties of silicon and related material (SiO2, Si3N4, Al2O3, etc.). It is designed to be a one stop resource for students, researchers and design engineers. The first and most basic aspect of Silicon Photonics is the Material Parameters, which provides the foundation for the Device, Sub-System and System levels. SiCloud includes the common dielectrics and semiconductors for waveguide core, cladding, and photodetection, as well as metals for electrical contacts. SiCloud is a work in progress and its capability is being expanded. SiCloud is being developed at UCLA with funding from the National Science Foundation's Center for Integrated Access Networks (CIAN) Engineering Research Center.

  19. On regularizations of the Dirac delta distribution

    NASA Astrophysics Data System (ADS)

    Hosseini, Bamdad; Nigam, Nilima; Stockie, John M.

    2016-01-01

    In this article we consider regularizations of the Dirac delta distribution with applications to prototypical elliptic and hyperbolic partial differential equations (PDEs). We study the convergence of a sequence of distributions SH to a singular term S as a parameter H (associated with the support size of SH) shrinks to zero. We characterize this convergence in both the weak-* topology of distributions and a weighted Sobolev norm. These notions motivate a framework for constructing regularizations of the delta distribution that includes a large class of existing methods in the literature. This framework allows different regularizations to be compared. The convergence of solutions of PDEs with these regularized source terms is then studied in various topologies such as pointwise convergence on a deleted neighborhood and weighted Sobolev norms. We also examine the lack of symmetry in tensor product regularizations and effects of dissipative error in hyperbolic problems.

  20. Interpretation of MODIS Cloud Images by CloudSat/CALIPSO Cloud Vertical Profiles

    NASA Astrophysics Data System (ADS)

    Wang, T.; Fetzer, E. J.; Wong, S.; Yue, Q.

    2015-12-01

    Clouds observed by passive remote-sensing imager (Aqua-MODIS) are collocated to cloud vertical profiles observed by active profiling sensors (CloudSat radar and CALIPSO lidar) at the pixel-scale. By comparing different layers of cloud types classified in the 2B-CLDCLASS-LIDAR product from CloudSat+CALIPSO to those cloud properties observed by MODIS, we evaluate the occurrence frequencies of cloud types and cloud-overlap in CloudSat+CALIPSO for each MODIS cloud regime defined by cloud optical depth (τ) and cloud-top pressure (P) histograms. We find that about 70% of MODIS clear sky agrees with the clear category in CloudSat+CALIPSO; whereas the remainder is either single layer (~25%) cirrus (Ci), low-level cumulus (Cu), stratocumulus (Sc), or multi-layer (<5%) clouds in CloudSat+CALIPSO. Under MODIS cloudy conditions, 60%, 28%, and 8% of the occurrences show single-, double-, and triple-layer clouds, respectively in CloudSat+CALIPSO. When MODIS identifies single-layer clouds, 50-60% of the MODIS low-level clouds are categorized as stratus (Sc) in CloudSat+CALIPSO. Over the tropics, ~70% of MODIS high and optically thin clouds (considered as cirrus in the histogram) is also identified as Ci in CloudSat+CALIPSO, and ~40% of MODIS high and optically thick clouds (considered as convective in the histogram) agrees with CloudSat+CALIPSO deep convections (DC). Over mid-latitudes these numbers drop to 45% and 10%, respectively. The best agreement occurs in tropical single-layer cloud regimes, where 90% of MODIS high-thin clouds are identified as Ci by CloudSat+CALIPSO and 60% of MODIS high-thick clouds are identified as DC. Worst agreement is found for multi-layer clouds, where cirrus on top of low- and mid-level clouds in MODIS are frequently categorized as high-thick clouds by passive imaging - among these only 5-12% are DC in CloudSat+CALIPSO. It is encouraging that both MODIS low-level clouds (regardless of optical thickness) and high-level thin clouds are consistently

  1. What is a Cloud?

    NASA Astrophysics Data System (ADS)

    Long, C. N.; Wu, W.

    2013-12-01

    There are multiple factors that cause disagreements between differing methods using differing instruments to infer cloud amounts. But along with these issues is a fundamental concern that has permeated all comparisons and supersedes such questions as what are the uncertainty estimates of a given retrieval. To wit: what is a cloud? How can uncertainty of a cloud amount measurement be determined when there is no absolute 'truth' on what defines a cloud, as opposed to cloud-free? Recent research comparing a decade of surface- and satellite-based retrievals of cloud amount for the ARM Southern Great Plains site shows significant disagreements. While Total Sky Imager 100-degree FOV, Shortwave (SW) Radiative Flux Analysis, GOES satellite and PATMOS-x satellite amounts agree relatively well, ISCCP satellite and ARSCL time-series cloud amounts are significantly greater, 15% (ISCCP) and 8% (ARSCL) larger in average diurnal variations. In both cases, it appears that optically thin high ice is counted as 'cloud' in ARSCL and ISCCP that is not categorized as cloud by all the others. Additionally, cloud amounts from three methods (ISCCP, ARSCL, and GOES) show an overall increase of 8%-10% in the annually averaged cloud fractions from 1998 to 2009, while those from the other three (TSI, SWFA, PATMOS-x) show little trend for this period. So one wonders: are cloud amounts increasing or not over this period? The SW Flux Analysis used sky imager retrievals as 'truth' in development of the methodology (Long et al, 2006a), where sky imagery itself used human observations as the model (Long et al., 2006b). Min et al. (2008) then used SW Flux Analysis retrievals as 'truth' to develop an MFRSR-based spectral SW retrieval method. Dupont et al. (2008) show that the SW-based retrievals allow up to a visible optical depth of 0.15 (95% of occurrences) under the 'clear-sky' category which primarily consists of sub-visual cirrus, which by ancestry applies to spectral SW, sky imager and human

  2. Stratus Cloud Supersaturations

    NASA Astrophysics Data System (ADS)

    Noble, S.; Hudson, J. G.; Jha, V.

    2009-12-01

    Extensive aircraft measurements of cloud microphysics and complete CCN spectra from 15 flights in central California stratus clouds are presented. Cloud droplet and CCN concentrations varied over an order of magnitude in this July-August, 2008 POST project. Correlation coefficients (R) between CCN and average total cloud droplet concentrations within parcels with specific minimal liquid water contents (LWC) are shown in the table. For most LWC thresholds R is greatest for CCN concentrations at rather high supersaturations (S); i.e., 1%. The highest R for the 0.1 gm-3 are for the 300’ altitude CCN measurements but the number of cases is very small. The 0.5 g-3 R values are higher at lower S but the number of cases is also very small. The high cloud S implied by most R values goes against conventional wisdom that low stratus cloud updraft velocities limit cloud S to < 0.3%. On the other hand average droplet concentrations for most LWC thresholds match best the CCN concentrations at 0.2-0.3% S, which is more in keeping with conventional wisdom. However, these average droplet concentrations were probably reduced from adiabatic values by entrainment, which would suggest higher initial cloud S. Yum and Hudson (2002, Tellus) did report S > 1% in some maritime clouds. Further research is ongoing with this data set to substantiate stratus cloud S values. If stratus cloud S is determined to be higher than previous estimates this would imply that a much larger subset of particles (even smaller sizes) influence cloud microphysics and this would have important climate implications. As has recently been reported for small cumulus clouds (Hudson et al. 2009 JGR and Hudson and Noble 2009 GRL) negative R values were found for CCN with larger cloud droplets and drizzle drop concentrations. Correlation coefficients (R) between average droplet and CCN concentrations. 1st row (1 min)is for CCN measurements in ascents or descents closest to cloud base. 2nd row is for CCN averaged in

  3. Hydrodynamics of Cloud Collisions in Two Dimensions: The Fate of Clouds in a Multiphase Medium

    NASA Astrophysics Data System (ADS)

    Miniati, Francesco; Jones, T. W.; Ferrara, Andrea; Ryu, Dongsu

    1997-12-01

    depend on the initial conditions, the two colliding clouds are converted into a few low-density contrast (χ ~ 5) clumps at the end of the simulations. By contrast, for symmetric radiative cases, we find that the two clouds coalesce, and there are good chances for a new massive cloud to be formed. Almost all the initial kinetic energy of the two clouds is radiated away during such collisions. On the other hand, for both adiabatic and radiative collisions, symmetry breaking leads to major differences. Most importantly, asymmetric collisions have a much greater tendency to disrupt the two clouds. Portions of individual clouds may be sheared away, and instabilities along the interfaces between the clouds and with the intercloud medium are enhanced. In addition, radiative cooling is less efficient in our asymmetric interactions, so that those parts of the clouds that initially seem to merge are more likely to reexpand and fade into the warm intercloud medium. Since the majority of real cloud collisions should be asymmetric for one reason or another, we conclude that most gasdynamical diffuse cloud collisions will be disruptive, at least in the absence of significant self-gravity or a significant magnetic field.

  4. Energy Aware Clouds

    NASA Astrophysics Data System (ADS)

    Orgerie, Anne-Cécile; de Assunção, Marcos Dias; Lefèvre, Laurent

    Cloud infrastructures are increasingly becoming essential components for providing Internet services. By benefiting from economies of scale, Clouds can efficiently manage and offer a virtually unlimited number of resources and can minimize the costs incurred by organizations when providing Internet services. However, as Cloud providers often rely on large data centres to sustain their business and offer the resources that users need, the energy consumed by Cloud infrastructures has become a key environmental and economical concern. This chapter presents an overview of techniques that can improve the energy efficiency of Cloud infrastructures. We propose a framework termed as Green Open Cloud, which uses energy efficient solutions for virtualized environments; the framework is validated on a reference scenario.

  5. Ammonia Clouds on Jupiter

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Click on the image for movie of Ammonia Ice Clouds on Jupiter

    In this movie, put together from false-color images taken by the New Horizons Ralph instrument as the spacecraft flew past Jupiter in early 2007, show ammonia clouds (appearing as bright blue areas) as they form and disperse over five successive Jupiter 'days.' Scientists noted how the larger cloud travels along with a small, local deep hole.

  6. Quantitative regularities in floodplain formation

    NASA Astrophysics Data System (ADS)

    Nevidimova, O.

    2009-04-01

    Quantitative regularities in floodplain formation Modern methods of the theory of complex systems allow to build mathematical models of complex systems where self-organizing processes are largely determined by nonlinear effects and feedback. However, there exist some factors that exert significant influence on the dynamics of geomorphosystems, but hardly can be adequately expressed in the language of mathematical models. Conceptual modeling allows us to overcome this difficulty. It is based on the methods of synergetic, which, together with the theory of dynamic systems and classical geomorphology, enable to display the dynamics of geomorphological systems. The most adequate for mathematical modeling of complex systems is the concept of model dynamics based on equilibrium. This concept is based on dynamic equilibrium, the tendency to which is observed in the evolution of all geomorphosystems. As an objective law, it is revealed in the evolution of fluvial relief in general, and in river channel processes in particular, demonstrating the ability of these systems to self-organization. Channel process is expressed in the formation of river reaches, rifts, meanders and floodplain. As floodplain is a periodically flooded surface during high waters, it naturally connects river channel with slopes, being one of boundary expressions of the water stream activity. Floodplain dynamics is inseparable from the channel dynamics. It is formed at simultaneous horizontal and vertical displacement of the river channel, that is at Y=Y(x, y), where х, y - horizontal and vertical coordinates, Y - floodplain height. When dу/dt=0 (for not lowering river channel), the river, being displaced in a horizontal plane, leaves behind a low surface, which flooding during high waters (total duration of flooding) changes from the maximum during the initial moment of time t0 to zero in the moment tn. In a similar manner changed is the total amount of accumulated material on the floodplain surface

  7. Quantitative regularities in floodplain formation

    NASA Astrophysics Data System (ADS)

    Nevidimova, O.

    2009-04-01

    Quantitative regularities in floodplain formation Modern methods of the theory of complex systems allow to build mathematical models of complex systems where self-organizing processes are largely determined by nonlinear effects and feedback. However, there exist some factors that exert significant influence on the dynamics of geomorphosystems, but hardly can be adequately expressed in the language of mathematical models. Conceptual modeling allows us to overcome this difficulty. It is based on the methods of synergetic, which, together with the theory of dynamic systems and classical geomorphology, enable to display the dynamics of geomorphological systems. The most adequate for mathematical modeling of complex systems is the concept of model dynamics based on equilibrium. This concept is based on dynamic equilibrium, the tendency to which is observed in the evolution of all geomorphosystems. As an objective law, it is revealed in the evolution of fluvial relief in general, and in river channel processes in particular, demonstrating the ability of these systems to self-organization. Channel process is expressed in the formation of river reaches, rifts, meanders and floodplain. As floodplain is a periodically flooded surface during high waters, it naturally connects river channel with slopes, being one of boundary expressions of the water stream activity. Floodplain dynamics is inseparable from the channel dynamics. It is formed at simultaneous horizontal and vertical displacement of the river channel, that is at Y=Y(x, y), where х, y - horizontal and vertical coordinates, Y - floodplain height. When dу/dt=0 (for not lowering river channel), the river, being displaced in a horizontal plane, leaves behind a low surface, which flooding during high waters (total duration of flooding) changes from the maximum during the initial moment of time t0 to zero in the moment tn. In a similar manner changed is the total amount of accumulated material on the floodplain surface

  8. Functional MRI Using Regularized Parallel Imaging Acquisition

    PubMed Central

    Lin, Fa-Hsuan; Huang, Teng-Yi; Chen, Nan-Kuei; Wang, Fu-Nien; Stufflebeam, Steven M.; Belliveau, John W.; Wald, Lawrence L.; Kwong, Kenneth K.

    2013-01-01

    Parallel MRI techniques reconstruct full-FOV images from undersampled k-space data by using the uncorrelated information from RF array coil elements. One disadvantage of parallel MRI is that the image signal-to-noise ratio (SNR) is degraded because of the reduced data samples and the spatially correlated nature of multiple RF receivers. Regularization has been proposed to mitigate the SNR loss originating due to the latter reason. Since it is necessary to utilize static prior to regularization, the dynamic contrast-to-noise ratio (CNR) in parallel MRI will be affected. In this paper we investigate the CNR of regularized sensitivity encoding (SENSE) acquisitions. We propose to implement regularized parallel MRI acquisitions in functional MRI (fMRI) experiments by incorporating the prior from combined segmented echo-planar imaging (EPI) acquisition into SENSE reconstructions. We investigated the impact of regularization on the CNR by performing parametric simulations at various BOLD contrasts, acceleration rates, and sizes of the active brain areas. As quantified by receiver operating characteristic (ROC) analysis, the simulations suggest that the detection power of SENSE fMRI can be improved by regularized reconstructions, compared to unregularized reconstructions. Human motor and visual fMRI data acquired at different field strengths and array coils also demonstrate that regularized SENSE improves the detection of functionally active brain regions. PMID:16032694

  9. Partitioning of regular computation on multiprocessor systems

    NASA Technical Reports Server (NTRS)

    Lee, Fung Fung

    1988-01-01

    Problem partitioning of regular computation over two dimensional meshes on multiprocessor systems is examined. The regular computation model considered involves repetitive evaluation of values at each mesh point with local communication. The computational workload and the communication pattern are the same at each mesh point. The regular computation model arises in numerical solutions of partial differential equations and simulations of cellular automata. Given a communication pattern, a systematic way to generate a family of partitions is presented. The influence of various partitioning schemes on performance is compared on the basis of computation to communication ratio.

  10. Oseledets Regularity Functions for Anosov Flows

    NASA Astrophysics Data System (ADS)

    Simić, Slobodan N.

    2011-07-01

    Oseledets regularity functions quantify the deviation of the growth associated with a dynamical system along its Lyapunov bundles from the corresponding uniform exponential growth. The precise degree of regularity of these functions is unknown. We show that for every invariant Lyapunov bundle of a volume preserving Anosov flow on a closed smooth Riemannian manifold, the corresponding Oseledets regularity functions are in L p ( m), for some p > 0, where m is the probability measure defined by the volume form. We prove an analogous result for essentially bounded cocycles over volume preserving Anosov flows.

  11. Continuum regularization of gauge theory with fermions

    SciTech Connect

    Chan, H.S.

    1987-03-01

    The continuum regularization program is discussed in the case of d-dimensional gauge theory coupled to fermions in an arbitrary representation. Two physically equivalent formulations are given. First, a Grassmann formulation is presented, which is based on the two-noise Langevin equations of Sakita, Ishikawa and Alfaro and Gavela. Second, a non-Grassmann formulation is obtained by regularized integration of the matter fields within the regularized Grassmann system. Explicit perturbation expansions are studied in both formulations, and considerable simplification is found in the integrated non-Grassmann formalism.

  12. Magnetic alignment of grains. [in interstellar space

    NASA Technical Reports Server (NTRS)

    Hildebrand, Roger H.

    1988-01-01

    This paper reviews mechanisms that have been proposed to account for alignment of dust grains in diffuse clouds and in dense clouds. The mechanisms that have proved inadequate are considered, including alignment by nonmagnetic and magnetic processes. The results thus far favor the Davis-Greenstein mechanism, in which paramagnetic relaxation of spinning grains removes components of rotation perpendicular to the magnetic field. Polarization measurements showing the alignment of grains in cool dense clouds are discussed.

  13. Magnetic Fields in Galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    Magnetic fields are a major agent in the interstellar medium. They contribute significantly to the total pressure which balances the gas disk against gravitation. They affect the gas flows in spiral arms (Gómez and Cox, 2002). The effective sound speed of the gas is increased by the presence of strong fields which reduce the shock strength. The interstellar fields are closely connected to gas clouds. They affect the dynamics of the gas clouds (Elmegreen, 1981; de Avillez and Breitschwerdt, 2004). The stability and evolution of gas clouds are also influenced by magnetic fields, but it is not understood how (Crutcher, 1999; see Chap. 7). Magnetic fields are essential for the onset of star formation as they enable the removal of angular momentum from the protostellar cloud during its collapse (magnetic braking, Mouschovias, 1990). Strong fields may shift the stellar mass spectrum towards the more massive stars (Mestel, 1990). MHD turbulence distributes energy from supernova explosions within the ISM (Subramanian, 1998) and regenerates the field via the dynamo process (Wielebinski, R., Krause, 1993, Beck et al., 1996; Sect. 6). Magnetic reconnection is a possible heating source for the ISM and halo gas (Birk et al., 1998). Magnetic fields also control the density and distribution of cosmic rays in the ISM. A realistic model for any process in the ISM needs basic information about the magnetic field which has to be provided by observations.

  14. Functional neuroimaging study in identical twin pairs discordant for regular cigarette smoking.

    PubMed

    Lessov-Schlaggar, Christina N; Lepore, Rebecca L; Kristjansson, Sean D; Schlaggar, Bradley L; Barnes, Kelly Anne; Petersen, Steven E; Madden, Pamela A F; Heath, Andrew C; Barch, Deanna M

    2013-01-01

    Despite the tremendous public health and financial burden of cigarette smoking, relatively little is understood about brain mechanisms that subserve smoking behavior. This study investigated the effect of lifetime regular smoking on brain processing in a reward guessing task using functional magnetic resonance imaging and a co-twin control study design in monozygotic (MZ) twin pairs that maximally controls for genetic and family background factors. Young adult (24-34 years) MZ female twin pairs (n = 15 pairs), discordant for regular smoking defined using Centers for Disease Control criteria as having smoked ≥100 cigarettes in their lifetime, were recruited from an ongoing genetic epidemiological longitudinal study of substance use and psychopathology. We applied hypothesis-driven region of interest (ROI) and whole-brain analyses to investigate the effect of regular smoking on reward processing. Reduced response to reward and punishment in regular compared with never-regular smokers was seen in hypothesis-driven ROI analysis of bilateral ventral striatum. Whole-brain analysis identified bilateral reward-processing regions that showed activation differences in response to winning or losing money but no effect of regular smoking; and frontal/parietal regions, predominantly in the right hemisphere, that showed robust effect of regular smoking but no effect of winning or losing money. Altogether, using a study design that maximally controls for group differences, we found that regular smoking had modest effects on striatal reward processing regions but robust effects on cognitive control/attentional systems. PMID:22340136

  15. Clouds blown by the solar wind

    NASA Astrophysics Data System (ADS)

    Voiculescu, M.; Usoskin, I.; Condurache-Bota, S.

    2013-12-01

    In this letter we investigate possible relationships between the cloud cover (CC) and the interplanetary electric field (IEF), which is modulated by the solar wind speed and the interplanetary magnetic field. We show that CC at mid-high latitudes systematically correlates with positive IEF, which has a clear energetic input into the atmosphere, but not with negative IEF, in general agreement with predictions of the global electric circuit (GEC)-related mechanism. Thus, our results suggest that mid-high latitude clouds might be affected by the solar wind via the GEC. Since IEF responds differently to solar activity than, for instance, cosmic ray flux or solar irradiance, we also show that such a study allows distinguishing one solar-driven mechanism of cloud evolution, via the GEC, from others.

  16. Lost in Cloud

    NASA Technical Reports Server (NTRS)

    Maluf, David A.; Shetye, Sandeep D.; Chilukuri, Sri; Sturken, Ian

    2012-01-01

    Cloud computing can reduce cost significantly because businesses can share computing resources. In recent years Small and Medium Businesses (SMB) have used Cloud effectively for cost saving and for sharing IT expenses. With the success of SMBs, many perceive that the larger enterprises ought to move into Cloud environment as well. Government agency s stove-piped environments are being considered as candidates for potential use of Cloud either as an enterprise entity or pockets of small communities. Cloud Computing is the delivery of computing as a service rather than as a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network. Underneath the offered services, there exists a modern infrastructure cost of which is often spread across its services or its investors. As NASA is considered as an Enterprise class organization, like other enterprises, a shift has been occurring in perceiving its IT services as candidates for Cloud services. This paper discusses market trends in cloud computing from an enterprise angle and then addresses the topic of Cloud Computing for NASA in two possible forms. First, in the form of a public Cloud to support it as an enterprise, as well as to share it with the commercial and public at large. Second, as a private Cloud wherein the infrastructure is operated solely for NASA, whether managed internally or by a third-party and hosted internally or externally. The paper addresses the strengths and weaknesses of both paradigms of public and private Clouds, in both internally and externally operated settings. The content of the paper is from a NASA perspective but is applicable to any large enterprise with thousands of employees and contractors.

  17. The Volume of the Regular Octahedron

    ERIC Educational Resources Information Center

    Trigg, Charles W.

    1974-01-01

    Five methods are given for computing the area of a regular octahedron. It is suggested that students first construct an octahedron as this will aid in space visualization. Six further extensions are left for the reader to try. (LS)

  18. Regular Exercise May Boost Prostate Cancer Survival

    MedlinePlus

    ... nih.gov/medlineplus/news/fullstory_158374.html Regular Exercise May Boost Prostate Cancer Survival Study found that ... HealthDay News) -- Sticking to a moderate or intense exercise regimen may improve a man's odds of surviving ...

  19. Regular Exercise: Antidote for Deadly Diseases?

    MedlinePlus

    ... https://medlineplus.gov/news/fullstory_160326.html Regular Exercise: Antidote for Deadly Diseases? High levels of physical ... Aug. 9, 2016 (HealthDay News) -- Getting lots of exercise may reduce your risk for five common diseases, ...

  20. Scaling behavior of regularized bosonic strings

    NASA Astrophysics Data System (ADS)

    Ambjørn, J.; Makeenko, Y.

    2016-03-01

    We implement a proper-time UV regularization of the Nambu-Goto string, introducing an independent metric tensor and the corresponding Lagrange multiplier, and treating them in the mean-field approximation justified for long strings and/or when the dimension of space-time is large. We compute the regularized determinant of the 2D Laplacian for the closed string winding around a compact dimension, obtaining in this way the effective action, whose minimization determines the energy of the string ground state in the mean-field approximation. We discuss the existence of two scaling limits when the cutoff is taken to infinity. One scaling limit reproduces the results obtained by the hypercubic regularization of the Nambu-Goto string as well as by the use of the dynamical triangulation regularization of the Polyakov string. The other scaling limit reproduces the results obtained by canonical quantization of the Nambu-Goto string.

  1. Nonminimal black holes with regular electric field

    NASA Astrophysics Data System (ADS)

    Balakin, Alexander B.; Zayats, Alexei E.

    2015-05-01

    We discuss the problem of identification of coupling constants, which describe interactions between photons and spacetime curvature, using exact regular solutions to the extended equations of the nonminimal Einstein-Maxwell theory. We argue the idea that three nonminimal coupling constants in this theory can be reduced to the single guiding parameter, which plays the role of nonminimal radius. We base our consideration on two examples of exact solutions obtained earlier in our works: the first of them describes a nonminimal spherically symmetric object (star or black hole) with regular radial electric field; the second example represents a nonminimal Dirac-type object (monopole or black hole) with regular metric. We demonstrate that one of the inflexion points of the regular metric function identifies a specific nonminimal radius, thus marking the domain of dominance of nonminimal interactions.

  2. Parallelization of irregularly coupled regular meshes

    NASA Technical Reports Server (NTRS)

    Chase, Craig; Crowley, Kay; Saltz, Joel; Reeves, Anthony

    1992-01-01

    Regular meshes are frequently used for modeling physical phenomena on both serial and parallel computers. One advantage of regular meshes is that efficient discretization schemes can be implemented in a straight forward manner. However, geometrically-complex objects, such as aircraft, cannot be easily described using a single regular mesh. Multiple interacting regular meshes are frequently used to describe complex geometries. Each mesh models a subregion of the physical domain. The meshes, or subdomains, can be processed in parallel, with periodic updates carried out to move information between the coupled meshes. In many cases, there are a relatively small number (one to a few dozen) subdomains, so that each subdomain may also be partitioned among several processors. We outline a composite run-time/compile-time approach for supporting these problems efficiently on distributed-memory machines. These methods are described in the context of a multiblock fluid dynamics problem developed at LaRC.

  3. Blind Poissonian images deconvolution with framelet regularization.

    PubMed

    Fang, Houzhang; Yan, Luxin; Liu, Hai; Chang, Yi

    2013-02-15

    We propose a maximum a posteriori blind Poissonian images deconvolution approach with framelet regularization for the image and total variation (TV) regularization for the point spread function. Compared with the TV based methods, our algorithm not only suppresses noise effectively but also recovers edges and detailed information. Moreover, the split Bregman method is exploited to solve the resulting minimization problem. Comparative results on both simulated and real images are reported. PMID:23455078

  4. Cloud Resolving Modeling

    NASA Technical Reports Server (NTRS)

    Tao, Wei-Kuo

    2007-01-01

    One of the most promising methods to test the representation of cloud processes used in climate models is to use observations together with cloud-resolving models (CRMs). CRMs use more sophisticated and realistic representations of cloud microphysical processes, and they can reasonably well resolve the time evolution, structure, and life cycles of clouds and cloud systems (with sizes ranging from about 2-200 km). CRMs also allow for explicit interaction between clouds, outgoing longwave (cooling) and incoming solar (heating) radiation, and ocean and land surface processes. Observations are required to initialize CRMs and to validate their results. This paper provides a brief discussion and review of the main characteristics of CRMs as well as some of their major applications. These include the use of CRMs to improve our understanding of: (1) convective organization, (2) cloud temperature and water vapor budgets, and convective momentum transport, (3) diurnal variation of precipitation processes, (4) radiative-convective quasi-equilibrium states, (5) cloud-chemistry interaction, (6) aerosol-precipitation interaction, and (7) improving moist processes in large-scale models. In addition, current and future developments and applications of CRMs will be presented.

  5. On Cloud Nine

    ERIC Educational Resources Information Center

    McCrea, Bridget; Weil, Marty

    2011-01-01

    Across the U.S., innovative collaboration practices are happening in the cloud: Sixth-graders participate in literary salons. Fourth-graders mentor kindergarteners. And teachers use virtual Post-it notes to advise students as they create their own television shows. In other words, cloud computing is no longer just used to manage administrative…

  6. Weather Fundamentals: Clouds. [Videotape].

    ERIC Educational Resources Information Center

    1998

    The videos in this educational series, for grades 4-7, help students understand the science behind weather phenomena through dramatic live-action footage, vivid animated graphics, detailed weather maps, and hands-on experiments. This episode (23 minutes) discusses how clouds form, the different types of clouds, and the important role they play in…

  7. Smoke Above Clouds

    NASA Technical Reports Server (NTRS)

    Remer, Lorraine A.

    2009-01-01

    Aerosols in the atmosphere alter the radiative balance of the Earth by reflecting or absorbing solar radiation. Spaceborne measurements of clouds and aerosols advected over the southeastern Atlantic Ocean indicate that the greater the cloud cover below the aerosols, the more likely the aerosols are to heat the planet.

  8. Cloud shadow speed sensor

    NASA Astrophysics Data System (ADS)

    Fung, V.; Bosch, J. L.; Roberts, S. W.; Kleissl, J.

    2014-06-01

    Changing cloud cover is a major source of solar radiation variability and poses challenges for the integration of solar energy. A compact and economical system is presented that measures cloud shadow motion vectors to estimate power plant ramp rates and provide short-term solar irradiance forecasts. The cloud shadow speed sensor (CSS) is constructed using an array of luminance sensors and a high-speed data acquisition system to resolve the progression of cloud passages across the sensor footprint. An embedded microcontroller acquires the sensor data and uses a cross-correlation algorithm to determine cloud shadow motion vectors. The CSS was validated against an artificial shading test apparatus, an alternative method of cloud motion detection from ground-measured irradiance (linear cloud edge, LCE), and a UC San Diego sky imager (USI). The CSS detected artificial shadow directions and speeds to within 15° and 6% accuracy, respectively. The CSS detected (real) cloud shadow directions and speeds with average weighted root-mean-square difference of 22° and 1.9 m s-1 when compared to USI and 33° and 1.5 m s-1 when compared to LCE results.

  9. Cloud speed sensor

    NASA Astrophysics Data System (ADS)

    Fung, V.; Bosch, J. L.; Roberts, S. W.; Kleissl, J.

    2013-10-01

    Changing cloud cover is a major source of solar radiation variability and poses challenges for the integration of solar energy. A compact and economical system that measures cloud motion vectors to estimate power plant ramp rates and provide short term solar irradiance forecasts is presented. The Cloud Speed Sensor (CSS) is constructed using an array of luminance sensors and high-speed data acquisition to resolve the progression of cloud passages across the sensor footprint. An embedded microcontroller acquires the sensor data and uses a cross-correlation algorithm to determine cloud motion vectors. The CSS was validated against an artificial shading test apparatus, an alternative method of cloud motion detection from ground measured irradiance (Linear Cloud Edge, LCE), and a UC San Diego Sky Imager (USI). The CSS detected artificial shadow directions and speeds to within 15 and 6% accuracy, respectively. The CSS detected (real) cloud directions and speeds without average bias and with average weighted root mean square difference of 22° and 1.9 m s-1 when compared to USI and 33° and 1.5 m s-1 when compared to LCE results.

  10. Kernel structures for Clouds

    NASA Technical Reports Server (NTRS)

    Spafford, Eugene H.; Mckendry, Martin S.

    1986-01-01

    An overview of the internal structure of the Clouds kernel was presented. An indication of how these structures will interact in the prototype Clouds implementation is given. Many specific details have yet to be determined and await experimentation with an actual working system.

  11. Learning in the Clouds?

    ERIC Educational Resources Information Center

    Butin, Dan W.

    2013-01-01

    Engaged learning--the type that happens outside textbooks and beyond the four walls of the classroom--moves beyond right and wrong answers to grappling with the uncertainties and contradictions of a complex world. iPhones back up to the "cloud." GoogleDocs is all about "cloud computing." Facebook is as ubiquitous as the sky.…

  12. Clouds over Open Ocean

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The heavy concentration of these cirrocumulus and nimbostratus clouds over open ocean - location unknown, indicate that a heavy downpouring of rain is occuring on the Earth's surface below. Towering anvils, seen rising high above the base cloud cover and casting long shadows, also indicate high winds and possible tornado activity.

  13. Regularized CT reconstruction on unstructured grid

    NASA Astrophysics Data System (ADS)

    Chen, Yun; Lu, Yao; Ma, Xiangyuan; Xu, Yuesheng

    2016-04-01

    Computed tomography (CT) is an ill-posed problem. Reconstruction on unstructured grid reduces the computational cost and alleviates the ill-posedness by decreasing the dimension of the solution space. However, there was no systematic study on edge-preserving regularization methods for CT reconstruction on unstructured grid. In this work, we propose a novel regularization method for CT reconstruction on unstructured grid, such as triangular or tetrahedral meshes generated from the initial images reconstructed via analysis reconstruction method (e.g., filtered back-projection). The proposed regularization method is modeled as a three-term optimization problem, containing a weighted least square fidelity term motivated by the simultaneous algebraic reconstruction technique (SART). The related cost function contains two non-differentiable terms, which bring difficulty to the development of the fast solver. A fixed-point proximity algorithm with SART is developed for solving the related optimization problem, and accelerating the convergence. Finally, we compare the regularized CT reconstruction method to SART with different regularization methods. Numerical experiments demonstrated that the proposed regularization method on unstructured grid is effective to suppress noise and preserve edge features.

  14. Continuum regularization of quantum field theory

    SciTech Connect

    Bern, Z.

    1986-01-01

    Breit, Gupta, and Zaks made the first proposal for new gauge invariant nonperturbative regularization. The scheme is based on smearing in the fifth-time of the Langevin equation. An analysis of their stochastic regularization scheme for the case of scalar electrodynamics with the standard covariant gauge fixing is given. Their scheme is shown to preserve the masslessness of the photon and the tensor structure of the photon vacuum polarization at the one-loop level. Although stochastic regularization is viable in one-loop electrodynamics, difficulties arise which, in general, ruins the scheme. A successful covariant derivative scheme is discussed which avoids the difficulties encountered with the earlier stochastic regularization by fifth-time smearing. For QCD the regularized formulation is manifestly Lorentz invariant, gauge invariant, ghost free and finite to all orders. A vanishing gluon mass is explicitly verified at one loop. The method is designed to respect relevant symmetries, and is expected to provide suitable regularization for any theory of interest.

  15. Io's sodium cloud

    NASA Astrophysics Data System (ADS)

    Goldberg, B. A.; Garneau, G. W.; Lavoie, S. K.

    1984-11-01

    The first two-dimensional images of the source region of Io's neutral sodium cloud have been acquired by ground-based observation. Observed asymmetries in its spatial brightness distribution provide new evidence that the cloud is supplied by sodium that is ejected nonisotropically from Io or its atmosphere. Complementary, high-time-resolution, calibrated image sequences that give the first comprehensive picture of the variations of the fainter regions of the cloud extending more than 100,000 kilometers from Io were also obtained. These data demonstrate that the cloud exhibits a persistent systematic behavior coupled with Io's orbital position, a distinct 'east-west orbital asymmetry', a variety of spatial morphologies, and true temporal changes. The geometric stability of the sodium source is also indicated. Isolation of the cloud's temporal changes constitutes an important milestone toward its utilization as a long-term probe of Io and the inner Jovian magnetosphere.

  16. SMILES ice cloud products

    NASA Astrophysics Data System (ADS)

    MilláN, L.; Read, W.; Kasai, Y.; Lambert, A.; Livesey, N.; Mendrok, J.; Sagawa, H.; Sano, T.; Shiotani, M.; Wu, D. L.

    2013-06-01

    Upper tropospheric water vapor and clouds play an important role in Earth's climate, but knowledge of them, in particular diurnal variation in deep convective clouds, is limited. An essential variable to understand them is cloud ice water content. The Japanese Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on board the International Space Station (ISS) samples the atmosphere at different local times allowing the study of diurnal variability of atmospheric parameters. We describe a new ice cloud data set consisting of partial Ice Water Path and Ice Water Content. Preliminary comparisons with EOS-MLS, CloudSat-CPR and CALIOP-CALIPSO are presented. Then, the diurnal variation over land and over open ocean for partial ice water path is reported. Over land, a pronounced diurnal variation peaking strongly in the afternoon/early evening was found. Over the open ocean, little temporal dependence was encountered. This data set is publicly available for download in HDF5 format.

  17. Cloud computing security.

    SciTech Connect

    Shin, Dongwan; Claycomb, William R.; Urias, Vincent E.

    2010-10-01

    Cloud computing is a paradigm rapidly being embraced by government and industry as a solution for cost-savings, scalability, and collaboration. While a multitude of applications and services are available commercially for cloud-based solutions, research in this area has yet to fully embrace the full spectrum of potential challenges facing cloud computing. This tutorial aims to provide researchers with a fundamental understanding of cloud computing, with the goals of identifying a broad range of potential research topics, and inspiring a new surge in research to address current issues. We will also discuss real implementations of research-oriented cloud computing systems for both academia and government, including configuration options, hardware issues, challenges, and solutions.

  18. Polarization of clouds

    NASA Astrophysics Data System (ADS)

    Goloub, Philippe; Herman, Maurice; Parol, Frederic

    1995-12-01

    This paper reports the main results concerning polarization by clouds derived from POLDER (polarization and directionality of earth's reflectances) airborne version. These results tend to confirm the high information content in the polarization (phase, altimetry). The preliminary results of EUCREX'94 (European Cloud Radiation Experiment) evidenced the drastically different polarized signatures for ice crystals and water droplets. Here we report systematic and statistically significative observations over the whole EUCREX data set. The results show that the cirrus exhibit their own signature. Preliminary observations performed during CLEOPATRA'91 (Cloud Experiment Ober Pfaffenhofen And Transport) and EUCREX'94 campaigns have shown the feasibility of cloud altimetry using spectral information (443 nm and 865 nm) of the polarized light over liquid water droplets clouds. Altimetry technique has been generalized on ASTEX-SOFIA'92 and EUCREX'94 data sets. All these results are presented and discussed in this paper.

  19. Cloud model bat algorithm.

    PubMed

    Zhou, Yongquan; Xie, Jian; Li, Liangliang; Ma, Mingzhi

    2014-01-01

    Bat algorithm (BA) is a novel stochastic global optimization algorithm. Cloud model is an effective tool in transforming between qualitative concepts and their quantitative representation. Based on the bat echolocation mechanism and excellent characteristics of cloud model on uncertainty knowledge representation, a new cloud model bat algorithm (CBA) is proposed. This paper focuses on remodeling echolocation model based on living and preying characteristics of bats, utilizing the transformation theory of cloud model to depict the qualitative concept: "bats approach their prey." Furthermore, Lévy flight mode and population information communication mechanism of bats are introduced to balance the advantage between exploration and exploitation. The simulation results show that the cloud model bat algorithm has good performance on functions optimization. PMID:24967425

  20. Prebiotic chemistry in clouds

    NASA Technical Reports Server (NTRS)

    Oberbeck, Verne R.; Marshall, John; Shen, Thomas

    1991-01-01

    The chemical evolution hypothesis of Woese (1979), according to which prebiotic reactions occurred rapidly in droplets in giant atmospheric reflux columns was criticized by Scherer (1985). This paper proposes a mechanism for prebiotic chemistry in clouds that answers Scherer's concerns and supports Woese's hypothesis. According to this mechanism, rapid prebiotic chemical evolution was facilitated on the primordial earth by cycles of condensation and evaporation of cloud drops containing clay condensation nuclei and nonvolatile monomers. For example, amino acids supplied by, or synthesized during entry of meteorites, comets, and interplanetary dust, would have been scavenged by cloud drops containing clay condensation nuclei and would be polymerized within cloud systems during cycles of condensation, freezing, melting, and evaporation of cloud drops.

  1. The cyanopolyynes as a chemical clock for molecular clouds

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.

    1984-01-01

    A new method is proposed for determining the ages of molecular clouds. The method utilizes the properties of the long-chain organic molecules known as the cyanopolyynes (HC/2k + 1/N, k = 0, 1, 2, 3 ...), which are found in a variety of clouds. The observed regular abundance decline of these molecules as a function of chain length suggests that they are formed sequentially. If so, the age of the cloud can be read off as the time to grow the longest chain present. Although the creation process for the chains is still unknown, the age can be obtained from knowledge of the chain destruction mechanism. Destruction is probably due to adsorption onto the surfaces of interstellar grains. Using the known properties of grains, the age can be obtained from the cloud density and the abundance ratios of the cyanopolyynes. As a first application, minimum ages for the four dark clouds B335, TMC-1, TMC-2, and L183 are obtained. These minimum ages are 1.3 x 10 to the 6th yr, 9.7 x 10 to the 5th yr, 3.4 x 10 to the 5th yr, and 3.3 x 10 to the 5th yr, respectively. In each case, the ages are greater than or equal to the cloud's free-fall collapse time. These four clouds are therefore either in a state of hydrostatic balance or have only recently begun to collapse, following an earlier period of hydrostatic support.

  2. Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

    SciTech Connect

    Liu, Y.; Wu, W.; Jensen, M. P.; Toto, T.

    2011-07-21

    This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surface-based approach for measuring cloud albedo; (3) multiscale (diurnal, annual and inter-annual) variations and covariations of surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo. An analytical expression is first derived to quantify the relationship between cloud radiative forcing, cloud fraction, and cloud albedo. The analytical expression is then used to deduce a new approach for inferring cloud albedo from concurrent surface-based measurements of downwelling surface shortwave radiation and cloud fraction. High-resolution decade-long data on cloud albedos are obtained by use of this surface-based approach over the US Department of Energy's Atmospheric Radiaton Measurement (ARM) Program at the Great Southern Plains (SGP) site. The surface-based cloud albedos are further compared against those derived from the coincident GOES satellite measurements. The three long-term (1997-2009) sets of hourly data on shortwave cloud radiative forcing, cloud fraction and cloud albedo collected over the SGP site are analyzed to explore the multiscale (diurnal, annual and inter-annual) variations and covariations. The analytical formulation is useful for diagnosing deficiencies of cloud-radiation parameterizations in climate models.

  3. Usual Source of Care in Preventive Service Use: A Regular Doctor versus a Regular Site

    PubMed Central

    Xu, K Tom

    2002-01-01

    Objective To compare the effects of having a regular doctor and having a regular site on five preventive services, controlling for the endogeneity of having a usual source of care. Data Source The Medical Expenditure Panel Survey 1996 conducted by the Agency for Healthcare Research and Quality and the National Center for Health Statistics. Study Design Mammograms, pap smears, blood pressure checkups, cholesterol level checkups, and flu shots were examined. A modified behavioral model framework was presented, which controlled for the endogeneity of having a usual source of care. Based on this framework, a two-equation empirical model was established to predict the probabilities of having a regular doctor and having a regular site, and use of each type of preventive service. Principal Findings Having a regular doctor was found to have a greater impact than having a regular site on discretional preventive services, such as blood pressure and cholesterol level checkups. No statistically significant differences were found between the effects a having a regular doctor and having a regular site on the use of flu shots, pap smears, and mammograms. Among the five preventive services, having a usual source of care had the greatest impact on cholesterol level checkups and pap smears. Conclusions Promoting a stable physician–patient relationship can improve patients’ timely receipt of clinical prevention. For certain preventive services, having a regular doctor is more effective than having a regular site. PMID:12546284

  4. Venus ionopause 'clouds' and IMF sector boundaries

    NASA Astrophysics Data System (ADS)

    Luhmann, Janet G.; Russell, C. T.; Wei, Hanying; Ma, Yingjuan; Zhang, Tielong; McEnulty, T.

    Disconnected or partially connected structures observed by the PVO Langmuir Probe near the ionopause of Venus were called 'clouds' by Brace et al. (1980). These authors speculated that the loss of atmosphere represented by these features could be significant compared to other loss processes. Russell et al. (1982) subsequently showed that the clouds occurred together with sharp rotations in the magnetic field. They suggested that the extreme draping of the interplanetary field that occurs near the ionopause at the draping poles could exert JxB forces sufficient to pull the ionospheric plasma in the cloud tailward and out into the heliosphere. But in 1991, Ong et al. demonstrated via analysis of many clouds that they are not generally seen in the polar regions of the draped magnetosheath field. Instead they occur at times when the interplanetary magnetic field undergoes a sudden rotation, as in interplanetary field sector boundaries. We discuss the statistics of such rotations at the orbit of Venus and their frequency as a function of solar cycle. Whether they enable or enhance escape or not requires simulation studies, but this study calls attention to the potential importance of time dependent external conditions.

  5. Magnetic fields of chemically peculiar and related stars. I. Main results of 2014 and near-future prospects

    NASA Astrophysics Data System (ADS)

    Romanyuk, I. I.

    2015-04-01

    We make a critical analysis of the results of studies of magnetic fields in chemically peculiar and related stars, published mostly in 2014. Methodological matters are discussed, and research results are analyzed. Most of the measurements of magnetic fields were obtained with well-known instruments. In 2014 a large observational project MiMeS was accomplished, the observations of more than 500 objects were performed, magnetic fields were found in 35 of them. Twenty new magnetic stars have been detected from the observations with the SAORAS 6-m telescope. Regular measurements of magnetic fields with an accuracy of units of gauss are conducted on a number of telescopes using the HARPS, ESPaDOnS, and NARVAL spectropolarimeters. The fields of complex topology have been studied, magnetic maps have been built, a connection with the distribution of anomalies of chemical composition has been found. The debate about the existence of a magnetic field of about 1 G in Vega and some other objects is ongoing. Apparently, the absence of a large-scale magnetic field greater than tens of gauss in the mercury-manganese and Am stars is confirmed. First CP stars were detected outside the Galaxy, in the Large Magellanic Cloud. Observations of magnetic fields in solar-type stars are continued, a strong correlation between the field strength and the degree of chromospheric activity was discovered.

  6. Electron Cyclotron Resonances in Electron Cloud Dynamics

    SciTech Connect

    Celata, Christine; Celata, C.M.; Furman, Miguel A.; Vay, J.-L.; Yu, Jennifer W.

    2008-06-25

    We report a previously unknown resonance for electron cloud dynamics. The 2D simulation code"POSINST" was used to study the electron cloud buildup at different z positions in the International Linear Collider positron damping ring wiggler. An electron equilibrium density enhancement of up to a factor of 3 was found at magnetic field values for which the bunch frequency is an integral multiple of the electron cyclotron frequency. At low magnetic fields the effects of the resonance are prominent, but when B exceeds ~;;(2 pi mec/(elb)), with lb = bunch length, effects of the resonance disappear. Thus short bunches and low B fields are required for observing the effect. The reason for the B field dependence, an explanation of the dynamics, and the results of the 2D simulations and of a single-particle tracking code used to elucidate details of the dynamics are discussed.

  7. Improvements in GRACE Gravity Fields Using Regularization

    NASA Astrophysics Data System (ADS)

    Save, H.; Bettadpur, S.; Tapley, B. D.

    2008-12-01

    The unconstrained global gravity field models derived from GRACE are susceptible to systematic errors that show up as broad "stripes" aligned in a North-South direction on the global maps of mass flux. These errors are believed to be a consequence of both systematic and random errors in the data that are amplified by the nature of the gravity field inverse problem. These errors impede scientific exploitation of the GRACE data products, and limit the realizable spatial resolution of the GRACE global gravity fields in certain regions. We use regularization techniques to reduce these "stripe" errors in the gravity field products. The regularization criteria are designed such that there is no attenuation of the signal and that the solutions fit the observations as well as an unconstrained solution. We have used a computationally inexpensive method, normally referred to as "L-ribbon", to find the regularization parameter. This paper discusses the characteristics and statistics of a 5-year time-series of regularized gravity field solutions. The solutions show markedly reduced stripes, are of uniformly good quality over time, and leave little or no systematic observation residuals, which is a frequent consequence of signal suppression from regularization. Up to degree 14, the signal in regularized solution shows correlation greater than 0.8 with the un-regularized CSR Release-04 solutions. Signals from large-amplitude and small-spatial extent events - such as the Great Sumatra Andaman Earthquake of 2004 - are visible in the global solutions without using special post-facto error reduction techniques employed previously in the literature. Hydrological signals as small as 5 cm water-layer equivalent in the small river basins, like Indus and Nile for example, are clearly evident, in contrast to noisy estimates from RL04. The residual variability over the oceans relative to a seasonal fit is small except at higher latitudes, and is evident without the need for de-striping or

  8. Molecular clouds. [significance in stellar evolution

    NASA Technical Reports Server (NTRS)

    Thaddeus, P.

    1977-01-01

    An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

  9. Community Cloud Computing

    NASA Astrophysics Data System (ADS)

    Marinos, Alexandros; Briscoe, Gerard

    Cloud Computing is rising fast, with its data centres growing at an unprecedented rate. However, this has come with concerns over privacy, efficiency at the expense of resilience, and environmental sustainability, because of the dependence on Cloud vendors such as Google, Amazon and Microsoft. Our response is an alternative model for the Cloud conceptualisation, providing a paradigm for Clouds in the community, utilising networked personal computers for liberation from the centralised vendor model. Community Cloud Computing (C3) offers an alternative architecture, created by combing the Cloud with paradigms from Grid Computing, principles from Digital Ecosystems, and sustainability from Green Computing, while remaining true to the original vision of the Internet. It is more technically challenging than Cloud Computing, having to deal with distributed computing issues, including heterogeneous nodes, varying quality of service, and additional security constraints. However, these are not insurmountable challenges, and with the need to retain control over our digital lives and the potential environmental consequences, it is a challenge we must pursue.

  10. Clouds in GEOS-5

    NASA Technical Reports Server (NTRS)

    Bacmeister, Julio; Rienecker, Michele; Suarez, Max; Norris, Peter

    2007-01-01

    The GEOS-5 atmospheric model is being developed as a weather-and-climate capable model. It must perform well in assimilation mode as well as in weather and climate simulations and forecasts and in coupled chemistry-climate simulations. In developing GEOS-5, attention has focused on the representation of moist processes. The moist physics package uses a single phase prognostic condensate and a prognostic cloud fraction. Two separate cloud types are distinguished by their source: "anvil" cloud originates in detraining convection, and large-scale cloud originates in a PDF-based condensation calculation. Ice and liquid phases for each cloud type are considered. Once created, condensate and fraction from the anvil and statistical cloud types experience the same loss processes: evaporation of condensate and fraction, auto-conversion of liquid or mixed phase condensate, sedimentation of frozen condensate, and accretion of condensate by falling precipitation. The convective parameterization scheme is the Relaxed Arakawa-Schubert, or RAS, scheme. Satellite data are used to evaluate the performance of the moist physics packages and help in their tuning. In addition, analysis of and comparisons to cloud-resolving models such as the Goddard Cumulus Ensemble model are used to help improve the PDFs used in the moist physics. The presentation will show some of our evaluations including precipitation diagnostics.

  11. Oxygen saturation resolution influences regularity measurements.

    PubMed

    Garde, Ainara; Karlen, Walter; Dehkordi, Parastoo; Ansermino, J Mark; Dumont, Guy A

    2014-01-01

    The measurement of regularity in the oxygen saturation (SpO(2)) signal has been suggested for use in identifying subjects with sleep disordered breathing (SDB). Previous work has shown that children with SDB have lower SpO(2) regularity than subjects without SDB (NonSDB). Regularity was measured using non-linear methods like approximate entropy (ApEn), sample entropy (SamEn) and Lempel-Ziv (LZ) complexity. Different manufacturer's pulse oximeters provide SpO(2) at various resolutions and the effect of this resolution difference on SpO(2) regularity, has not been studied. To investigate this effect, we used the SpO(2) signal of children with and without SDB, recorded from the Phone Oximeter (0.1% resolution) and the same SpO(2) signal rounded to the nearest integer (artificial 1% resolution). To further validate the effect of rounding, we also used the SpO(2) signal (1% resolution) recorded simultaneously from polysomnography (PSG), as a control signal. We estimated SpO(2) regularity by computing the ApEn, SamEn and LZ complexity, using a 5-min sliding window and showed that different resolutions provided significantly different results. The regularity calculated using 0.1% SpO(2) resolution provided no significant differences between SDB and NonSDB. However, the artificial 1% resolution SpO(2) provided significant differences between SDB and NonSDB, showing a more random SpO(2) pattern (lower SpO(2) regularity) in SDB children, as suggested in the past. Similar results were obtained with the SpO(2) recorded from PSG (1% resolution), which further validated that this SpO(2) regularity change was due to the rounding effect. Therefore, the SpO(2) resolution has a great influence in regularity measurements like ApEn, SamEn and LZ complexity that should be considered when studying the SpO(2) pattern in children with SDB. PMID:25570437

  12. Diagnosing AIRS Sampling with CloudSat Cloud Classes

    NASA Technical Reports Server (NTRS)

    Fetzer, Eric; Yue, Qing; Guillaume, Alexandre; Kahn, Brian

    2011-01-01

    AIRS yield and sampling vary with cloud state. Careful utilization of collocated multiple satellite sensors is necessary. Profile differences between AIRS and ECMWF model analyses indicate that AIRS has high sampling and excellent accuracy for certain meteorological conditions. Cloud-dependent sampling biases may have large impact on AIRS L2 and L3 data in climate research. MBL clouds / lower tropospheric stability relationship is one example. AIRS and CloudSat reveal a reasonable climatology in the MBL cloud regime despite limited sampling in stratocumulus. Thermodynamic parameters such as EIS derived from AIRS data map these cloud conditions successfully. We are working on characterizing AIRS scenes with mixed cloud types.

  13. TRACING TURBULENT AMBIPOLAR DIFFUSION IN MOLECULAR CLOUDS

    SciTech Connect

    Li Huabai; Houde, Martin; Lai Shihping; Sridharan, T. K.

    2010-08-01

    Though flux freezing is a good approximation frequently assumed for molecular clouds, ambipolar diffusion (AD) is inevitable at certain scales. The scale at which AD sets in can be a crucial parameter for turbulence and the star formation process. However, both observation and simulation of AD are very challenging and our knowledge of it is very limited. We recently proposed that the difference between ion and neutral velocity spectra is a signature of turbulent AD and can be used to estimate the AD scales and magnetic field strengths. Here, we present observational evidence showing that this difference between the velocity dispersions from coexistent ions and neutrals is indeed correlated with magnetic field strength.

  14. Aerosol and Plasma Measurements in Noctilucent Clouds

    NASA Technical Reports Server (NTRS)

    Robertson, Scott

    2000-01-01

    The purpose of this project was to develop rocket-borne probes to detect charged aerosol layers in the mesosphere. These include sporadic E layers, which have their origin in meteoric dust, and noctilucent clouds, which form in the arctic summer and are composed of ice crystals. The probe being developed consists of a charge collecting patch connected to a sensitive electrometer which measures the charge deposited on the patch by impacting aerosols. The ambient electrons and light ions in the mesosphere are prevented from being collected by a magnetic field. The magnetic force causes these lighter particles to turn so that they miss the collecting patch.

  15. Evolution of Ion Clouds in the Equatorial Ionosphere

    NASA Astrophysics Data System (ADS)

    Petrochuk, Yevgeny; Blaunstein, Nathan; Mishin, Evgeny; Pedersen, Todd; Caton, Ron; Viggiano, Al; Schuman, Nick

    2015-11-01

    We report on the results of 2- and 3-dimentional numerical investigations of the evolution of samarium ion clouds injected in the equatorial ionosphere, alike the recent MOSC experiments. The ambient conditions are described by a standard model of the quiet-time equatorial ionosphere from 90 to 350 km. The altitudinal distribution of the transport processes and ambient electric and magnetic fields is taken into account. The fast process of stratification of ion clouds and breaking into small plasmoids occur only during the late stage of the cloud evolution. The role of the background plasma and its depletion zones formed due to the short-circuiting currents is not as evident as in mid latitudes. It is also revealed that the altitudinal dependence of the diffusion and drift plays a minor role in the cloud evolution at the equator. Likewise, the cloud remains stable with respect to the Raleigh-Taylor and gradient-drift instabilities. These two features are defined by the equatorial near-horizontal magnetic field which leads to a strongly-elongated ellipsoid-like plasma cloud. The critical dip angle separating the stable (equatorial) and unstable (mid-latitude) cloud regimes will be defined in future simulation studies, as well as the dependence on the ambient electric field and neutral wind. 2Space Vehicles Directorate, Air Force Research Laboratory

  16. Modified sparse regularization for electrical impedance tomography.

    PubMed

    Fan, Wenru; Wang, Huaxiang; Xue, Qian; Cui, Ziqiang; Sun, Benyuan; Wang, Qi

    2016-03-01

    Electrical impedance tomography (EIT) aims to estimate the electrical properties at the interior of an object from current-voltage measurements on its boundary. It has been widely investigated due to its advantages of low cost, non-radiation, non-invasiveness, and high speed. Image reconstruction of EIT is a nonlinear and ill-posed inverse problem. Therefore, regularization techniques like Tikhonov regularization are used to solve the inverse problem. A sparse regularization based on L1 norm exhibits superiority in preserving boundary information at sharp changes or discontinuous areas in the image. However, the limitation of sparse regularization lies in the time consumption for solving the problem. In order to further improve the calculation speed of sparse regularization, a modified method based on separable approximation algorithm is proposed by using adaptive step-size and preconditioning technique. Both simulation and experimental results show the effectiveness of the proposed method in improving the image quality and real-time performance in the presence of different noise intensities and conductivity contrasts. PMID:27036798

  17. Assessment of regularization techniques for electrocardiographic imaging

    PubMed Central

    Milanič, Matija; Jazbinšek, Vojko; MacLeod, Robert S.; Brooks, Dana H.; Hren, Rok

    2014-01-01

    A widely used approach to solving the inverse problem in electrocardiography involves computing potentials on the epicardium from measured electrocardiograms (ECGs) on the torso surface. The main challenge of solving this electrocardiographic imaging (ECGI) problem lies in its intrinsic ill-posedness. While many regularization techniques have been developed to control wild oscillations of the solution, the choice of proper regularization methods for obtaining clinically acceptable solutions is still a subject of ongoing research. However there has been little rigorous comparison across methods proposed by different groups. This study systematically compared various regularization techniques for solving the ECGI problem under a unified simulation framework, consisting of both 1) progressively more complex idealized source models (from single dipole to triplet of dipoles), and 2) an electrolytic human torso tank containing a live canine heart, with the cardiac source being modeled by potentials measured on a cylindrical cage placed around the heart. We tested 13 different regularization techniques to solve the inverse problem of recovering epicardial potentials, and found that non-quadratic methods (total variation algorithms) and first-order and second-order Tikhonov regularizations outperformed other methodologies and resulted in similar average reconstruction errors. PMID:24369741

  18. Cloud computing basics for librarians.

    PubMed

    Hoy, Matthew B

    2012-01-01

    "Cloud computing" is the name for the recent trend of moving software and computing resources to an online, shared-service model. This article briefly defines cloud computing, discusses different models, explores the advantages and disadvantages, and describes some of the ways cloud computing can be used in libraries. Examples of cloud services are included at the end of the article. PMID:22289098

  19. Perturbations in a regular bouncing universe

    SciTech Connect

    Battefeld, T.J.; Geshnizjani, G.

    2006-03-15

    We consider a simple toy model of a regular bouncing universe. The bounce is caused by an extra timelike dimension, which leads to a sign flip of the {rho}{sup 2} term in the effective four dimensional Randall Sundrum-like description. We find a wide class of possible bounces: big bang avoiding ones for regular matter content, and big rip avoiding ones for phantom matter. Focusing on radiation as the matter content, we discuss the evolution of scalar, vector and tensor perturbations. We compute a spectral index of n{sub s}=-1 for scalar perturbations and a deep blue index for tensor perturbations after invoking vacuum initial conditions, ruling out such a model as a realistic one. We also find that the spectrum (evaluated at Hubble crossing) is sensitive to the bounce. We conclude that it is challenging, but not impossible, for cyclic/ekpyrotic models to succeed, if one can find a regularized version.

  20. Strong regularizing effect of integrable systems

    SciTech Connect

    Zhou, Xin

    1997-11-01

    Many time evolution problems have the so-called strong regularization effect, that is, with any irregular initial data, as soon as becomes greater than 0, the solution becomes C{sup {infinity}} for both spacial and temporal variables. This paper studies 1 x 1 dimension integrable systems for such regularizing effect. In the work by Sachs, Kappler [S][K], (see also earlier works [KFJ] and [Ka]), strong regularizing effect is proved for KdV with rapidly decaying irregular initial data, using the inverse scattering method. There are two equivalent Gel`fand-Levitan-Marchenko (GLM) equations associated to an inverse scattering problem, one is normalized at x = {infinity} and another at x = {infinity}. The method of [S][K] relies on the fact that the KdV waves propagate only in one direction and therefore one of the two GLM equations remains normalized and can be differentiated infinitely many times. 15 refs.

  1. Regularized image recovery in scattering media.

    PubMed

    Schechner, Yoav Y; Averbuch, Yuval

    2007-09-01

    When imaging in scattering media, visibility degrades as objects become more distant. Visibility can be significantly restored by computer vision methods that account for physical processes occurring during image formation. Nevertheless, such recovery is prone to noise amplification in pixels corresponding to distant objects, where the medium transmittance is low. We present an adaptive filtering approach that counters the above problems: while significantly improving visibility relative to raw images, it inhibits noise amplification. Essentially, the recovery formulation is regularized, where the regularization adapts to the spatially varying medium transmittance. Thus, this regularization does not blur close objects. We demonstrate the approach in atmospheric and underwater experiments, based on an automatic method for determining the medium transmittance. PMID:17627052

  2. Cloud Distribution Statistics from LITE

    NASA Technical Reports Server (NTRS)

    Winker, David M.

    1998-01-01

    The Lidar In-Space Technology Experiment (LITE) mission has demonstrated the utility of spaceborne lidar in observing multilayer clouds and has provided a dataset showing the distribution of tropospheric clouds and aerosols. These unambiguous observations of the vertical distribution of clouds will allow improved verification of current cloud climatologies and GCM cloud parameterizations. Although there is now great interest in cloud profiling radar, operating in the mm-wave region, for the spacebased observation of cloud heights the results of the LITE mission have shown that satellite lidars can also make significant contributions in this area.

  3. Entrainment, Drizzle, and Cloud Albedo

    NASA Technical Reports Server (NTRS)

    Ackerman, A. S.; Kirkpatrick, J. P.; Stevens, D. E.; Toon, O. B.

    2004-01-01

    Increased aerosol and hence droplet concentrations in polluted clouds are expected to inhibit precipitation and thereby increase cloud water, leading to more reflective clouds that partially offset global warming. Yet polluted clouds are not generally observed to hold more water. Much of the uncertainty regarding the indirect aerosol effect stems from inadequate understanding of such changes in cloud water. Detailed simulations show that the relative humidity of air overlying stratocumulus is a leading factor determining whether cloud water increases or decreases when precipitation is suppressed. When the overlying air is dry, cloud water can decrease as droplet concentrations increase.

  4. [Why regular physical activity favors longevity].

    PubMed

    Pentimone, F; Del Corso, L

    1998-06-01

    Regular physical exercise is useful at all ages. In the elderly, even a gentle exercise programme consisting of walking, bicycling, playing golf if performed constantly increases longevity by preventing the onset of the main diseases or alleviating the handicaps they may have caused. Cardiovascular diseases, which represent the main cause of death in the elderly, and osteoporosis, a disabling disease potentially capable of shortening life expectancy, benefit from physical exercise which if performed regularly well before the start of old age may help to prevent them. Over the past few years there has been growing evidence of the concrete protection offered against neoplasia and even the ageing process itself. PMID:9739351

  5. Learning with regularizers in multilayer neural networks

    NASA Astrophysics Data System (ADS)

    Saad, David; Rattray, Magnus

    1998-02-01

    We study the effect of regularization in an on-line gradient-descent learning scenario for a general two-layer student network with an arbitrary number of hidden units. Training examples are randomly drawn input vectors labeled by a two-layer teacher network with an arbitrary number of hidden units that may be corrupted by Gaussian output noise. We examine the effect of weight decay regularization on the dynamical evolution of the order parameters and generalization error in various phases of the learning process, in both noiseless and noisy scenarios.

  6. Regular transport dynamics produce chaotic travel times.

    PubMed

    Villalobos, Jorge; Muñoz, Víctor; Rogan, José; Zarama, Roberto; Johnson, Neil F; Toledo, Benjamín; Valdivia, Juan Alejandro

    2014-06-01

    In the hope of making passenger travel times shorter and more reliable, many cities are introducing dedicated bus lanes (e.g., Bogota, London, Miami). Here we show that chaotic travel times are actually a natural consequence of individual bus function, and hence of public transport systems more generally, i.e., chaotic dynamics emerge even when the route is empty and straight, stops and lights are equidistant and regular, and loading times are negligible. More generally, our findings provide a novel example of chaotic dynamics emerging from a single object following Newton's laws of motion in a regularized one-dimensional system. PMID:25019866

  7. Demosaicing as the problem of regularization

    NASA Astrophysics Data System (ADS)

    Kunina, Irina; Volkov, Aleksey; Gladilin, Sergey; Nikolaev, Dmitry

    2015-12-01

    Demosaicing is the process of reconstruction of a full-color image from Bayer mosaic, which is used in digital cameras for image formation. This problem is usually considered as an interpolation problem. In this paper, we propose to consider the demosaicing problem as a problem of solving an underdetermined system of algebraic equations using regularization methods. We consider regularization with standard l1/2-, l1 -, l2- norms and their effect on quality image reconstruction. The experimental results showed that the proposed technique can both be used in existing methods and become the base for new ones

  8. Methanol in dark clouds

    NASA Astrophysics Data System (ADS)

    Friberg, P.; Hjalmarson, A.; Madden, S. C.; Irvine, W. M.

    1988-04-01

    The authors report observations, for the first time, of the 20 - 10A+ and E, 2-1 - 1-1 E, and 10 - 00A+ lines of methanol (CH3OH) in three dark cold clouds, TMC 1, L 134N, and B 335. The CH3OH emission is extended in these clouds and shows a complex velocity structure. Clear indications of non LTE excitation are observed in TMC 1. Estimated column densities are a few×1013cm-2. Although less abundant than formaldehyde (H2CO), methanol is almost an order of magnitude more abundant than acetaldehyde (CH3CHO), in these clouds. Dimethyl ether was searched for in L 134N, to an upper limit of 4×1012cm-2 (3σ). Implications for dark cloud excitation and chemistry are discussed.

  9. Fingerprinting the Clouds

    NASA Astrophysics Data System (ADS)

    Orellana, M. V.; Caballero, J.; Lee, A. M.; Matrai, P. A.; Leck, C.; Madan, A.; Collins, H.

    2012-12-01

    Marine microgels play an important role in regulating ocean-basin-scale biogeochemical dynamics. We have found them in surface waters, in airborne aerosol, fog, and cloud water in the high Arctic (north of 80oN). Microgels dominated the available cloud condensation nuclei number population during the summer season. These microgels have unique physicochemical characteristics and originate from the ice algae and/or phytoplankton in the surface water. We have sequenced the genomic material found in the microgels from the sea surface and cloud waters with next-generation sequencing technology. The sequence analysis and annotation, show a high abundance of proteins of microbial and diatom origin, including a high number of proteins from different taxonomical origin associated with antifreeze functions. Our results have implications not only for cloud droplet activation but also for ice nucleation.

  10. My NASA Data Clouds

    NASA Video Gallery

    This lesson has two activities that help students develop a basic understanding of the relationship between cloud type and the form of precipitation and the relationship between the amount of water...

  11. Noctilucent Clouds in Motion

    NASA Video Gallery

    Swedish photographer Peter Rosén took this close-up, time-lapse movieof Noctilucent Clouds (NLCs) over Stockholm, Sweden on the evening ofJuly 16, 2012. "What looked like a serene view from a di...

  12. GEOS-5 Modeled Clouds

    NASA Video Gallery

    This visualization shows clouds from a simulation using the Goddard Earth Observing System Model, Verison 5 (GEOS-5). The global atmospheric simulation covers a period from Feb 3, 2010 through Feb ...

  13. Methanol in dark clouds

    NASA Technical Reports Server (NTRS)

    Friberg, P.; Hjalmarson, A.; Madden, S. C.; Irvine, W. M.

    1988-01-01

    The first observation of methanol in cold dark clouds TMC 1, L 134 N, and B 335 is reported. In all three clouds, the relative abundance of methanol was found to be in the range of 10 to the -9th (i.e., almost an order of magnitude more abundant than acetaldehyde), with no observable variation between the clouds. Methanol emission showed a complex velocity structure; in TMC 1, clear indications of non-LTE were observed. Dimethyl ether was searched for in L 134 N; the upper limit of the column density of dimethyl ether in L 134 N was estimated to be 4 x 10 to the 12th/sq cm, assuming 5 K rotation temperature and LTE. This limit makes the abundance ratio (CH3)2O/CH3OH not higher than 1/5, indicating that dimethyl ether is not overabundant in this dark cloud.

  14. Closed Large Cell Clouds

    Atmospheric Science Data Center

    2013-04-19

    article title:  Closed Large Cell Clouds in the South Pacific     ... unperturbed by cyclonic or frontal activity. When the cell centers are cloudy and the main sinking motion is concentrated at cell ...

  15. Scanning Cloud Radar Observations at Azores: Preliminary 3D Cloud Products

    SciTech Connect

    Kollias, P.; Johnson, K.; Jo, I.; Tatarevic, A.; Giangrande, S.; Widener, K.; Bharadwaj, N.; Mead, J.

    2010-03-15

    The deployment of the Scanning W-Band ARM Cloud Radar (SWACR) during the AMF campaign at Azores signals the first deployment of an ARM Facility-owned scanning cloud radar and offers a prelude for the type of 3D cloud observations that ARM will have the capability to provide at all the ARM Climate Research Facility sites by the end of 2010. The primary objective of the deployment of Scanning ARM Cloud Radars (SACRs) at the ARM Facility sites is to map continuously (operationally) the 3D structure of clouds and shallow precipitation and to provide 3D microphysical and dynamical retrievals for cloud life cycle and cloud-scale process studies. This is a challenging task, never attempted before, and requires significant research and development efforts in order to understand the radar's capabilities and limitations. At the same time, we need to look beyond the radar meteorology aspects of the challenge and ensure that the hardware and software capabilities of the new systems are utilized for the development of 3D data products that address the scientific needs of the new Atmospheric System Research (ASR) program. The SWACR observations at Azores provide a first look at such observations and the challenges associated with their analysis and interpretation. The set of scan strategies applied during the SWACR deployment and their merit is discussed. The scan strategies were adjusted for the detection of marine stratocumulus and shallow cumulus that were frequently observed at the Azores deployment. Quality control procedures for the radar reflectivity and Doppler products are presented. Finally, preliminary 3D-Active Remote Sensing of Cloud Locations (3D-ARSCL) products on a regular grid will be presented, and the challenges associated with their development discussed. In addition to data from the Azores deployment, limited data from the follow-up deployment of the SWACR at the ARM SGP site will be presented. This effort provides a blueprint for the effort required for the

  16. Clouds and the Near-Earth Environment: Possible Links

    NASA Astrophysics Data System (ADS)

    Condurache-Bota, Simona; Voiculescu, Mirela; Dragomir, Carmelia

    2015-12-01

    Climate variability is a hot topic not only for scientists and policy-makers, but also for each and every one of us. The anthropogenic activities are considered to be responsible for most climate change, however there are large uncertainties about the magnitude of effects of solar variability and other extraterrestrial influences, such as galactic cosmic rays on terrestrial climate. Clouds play an important role due to feedbacks of the radiation budget: variation of cloud cover/composition affects climate, which, in turn, affects cloud cover via atmospheric dynamics and sea temperature variations. Cloud formation and evolution are still under scientific scrutiny, since their microphysics is still not understood. Besides atmospheric dynamics and other internal climatic parameters, extraterrestrial sources of cloud cover variation are considered. One of these is the solar wind, whose effect on cloud cover might be modulated by the global atmospheric electrical circuit. Clouds height and composition, their seasonal variation and latitudinal distribution should be considered when trying to identify possible mechanisms by which solar energy is transferred to clouds. The influence of the solar wind on cloud formation can be assessed also through the ap index - the geomagnetic storm index, which can be readily connected with interplanetary magnetic field, IMF structure. This paper proposes to assess the possible relationship between both cloud cover and solar wind proxies, as the ap index, function of cloud height and composition and also through seasonal studies. The data covers almost three solar cycles (1984-2009). Mechanisms are looked for by investigating observed trends or correlation at local/seasonal scale

  17. Cloud Inhomogeneity from MODIS

    NASA Technical Reports Server (NTRS)

    Oreopoulos, Lazaros; Cahalan, Robert F.

    2004-01-01

    Two full months (July 2003 and January 2004) of MODIS Atmosphere Level-3 data from the Terra and Aqua satellites are analyzed in order to characterize the horizontal variability of cloud optical thickness and water path at global scales. Various options to derive cloud variability parameters are discussed. The climatology of cloud inhomogeneity is built by first calculating daily parameter values at spatial scales of l degree x 1 degree, and then at zonal and global scales, followed by averaging over monthly time scales. Geographical, diurnal, and seasonal changes of inhomogeneity parameters are examined separately for the two cloud phases, and separately over land and ocean. We find that cloud inhomogeneity is weaker in summer than in winter, weaker over land than ocean for liquid clouds, weaker for local morning than local afternoon, about the same for liquid and ice clouds on a global scale, but with wider probability distribution functions (PDFs) and larger latitudinal variations for ice, and relatively insensitive to whether water path or optical thickness products are used. Typical mean values at hemispheric and global scales of the inhomogeneity parameter nu (roughly the mean over the standard deviation of water path or optical thickness), range from approximately 2.5 to 3, while for the inhomogeneity parameter chi (the ratio of the logarithmic to linear mean) from approximately 0.7 to 0.8. Values of chi for zonal averages can occasionally fall below 0.6 and for individual gridpoints below 0.5. Our results demonstrate that MODIS is capable of revealing significant fluctuations in cloud horizontal inhomogenity and stress the need to model their global radiative effect in future studies.

  18. Mesospheric cloud formations

    NASA Technical Reports Server (NTRS)

    Forbes, J. M.

    1980-01-01

    Formation of mesospheric clouds as a result of deposition of large amounts of H2O by the heavy lift launch vehicle (HLLV) of the solar power satellite system is discussed. The conditions which must be met in order to form and maintain clouds near the mesopause are described. The frequency and magnitude of H2O injections from the HLLV rocket exhaust are considered.

  19. Marine Cloud Brightening

    SciTech Connect

    Latham, John; Bower, Keith; Choularton, Tom; Coe, H.; Connolly, P.; Cooper, Gary; Craft, Tim; Foster, Jack; Gadian, Alan; Galbraith, Lee; Iacovides, Hector; Johnston, David; Launder, Brian; Leslie, Brian; Meyer, John; Neukermans, Armand; Ormond, Bob; Parkes, Ben; Rasch, Philip J.; Rush, John; Salter, Stephen; Stevenson, Tom; Wang, Hailong; Wang, Qin; Wood, Robert

    2012-09-07

    The idea behind the marine cloud-brightening (MCB) geoengineering technique is that seeding marine stratocumulus clouds with copious quantities of roughly monodisperse sub-micrometre sea water particles might significantly enhance the cloud droplet number concentration, and thereby the cloud albedo and possibly longevity. This would produce a cooling, which general circulation model (GCM) computations suggest could - subject to satisfactory resolution of technical and scientific problems identified herein - have the capacity to balance global warming up to the carbon dioxide-doubling point. We describe herein an account of our recent research on a number of critical issues associated with MCB. This involves (i) GCM studies, which are our primary tools for evaluating globally the effectiveness of MCB, and assessing its climate impacts on rainfall amounts and distribution, and also polar sea-ice cover and thickness; (ii) high-resolution modelling of the effects of seeding on marine stratocumulus, which are required to understand the complex array of interacting processes involved in cloud brightening; (iii) microphysical modelling sensitivity studies, examining the influence of seeding amount, seedparticle salt-mass, air-mass characteristics, updraught speed and other parameters on cloud-albedo change; (iv) sea water spray-production techniques; (v) computational fluid dynamics studies of possible large-scale periodicities in Flettner rotors; and (vi) the planning of a three-stage limited-area field research experiment, with the primary objectives of technology testing and determining to what extent, if any, cloud albedo might be enhanced by seeding marine stratocumulus clouds on a spatial scale of around 100 km. We stress that there would be no justification for deployment of MCB unless it was clearly established that no significant adverse consequences would result. There would also need to be an international agreement firmly in favour of such action.

  20. Observations of orographic Cloud Base Heights from satellite and in-situ measurements at the Monteverde Cloud Mist Forest Reserve, Costa Rica

    NASA Astrophysics Data System (ADS)

    Asefi, S.; Zeng, J.; Han, Q.; Welch, R. M.; Lawton, R. O.; Nair, U. S.; Ray, D.; McCarty, W. R.; Jedlovec, G.

    2005-12-01

    Tropical montane cloud mist forests are among the most biologically rich and diverse ecosystems, providing habitats for many of the world's endangered species. Survival of these habitats depends strongly on regular and frequent immersion in orographic clouds. At the Monteverde Cloud Mist Forest Reserve in Costa Rica, the bases of the clouds have shifted upslope, leading to anuran population crashes, an increase in the upper elevation of bird ranges on the Pacific slope, and longer dry season mist-free intervals. Satellite remote sensing techniques have been developed to determine the orographic cloud base heights; these are tested for the dry season month of March 2003 over the Monteverde cloud forests. The approach derives MODIS cloud top pressures and then converts them to cloud top heights using geopotential height profiles. The NCAR Land Use and Cloud Interaction Experiment (LUCIE), consisting of paired mobile radiosonde systems deployed in Costa Rica, provided the means for validating the retrievals. Results show that the four MODIS CO2 slicing channels do not provide sufficiently accurate cloud top height values, although some of the differences are due to a mismatch in the observational periods. In order to improve the results, two alternative approaches are examined. Simulated geopotential height profiles from the CSU Regional Atmospheric Modeling System (RAMS) initialized with soundings provided superior results. Another approach investigated the utility of multiple combinations of channels in the CO2 slicing technique using Atmospheric Infrared Sounder (AIRS) data for cloud height assignment. Using AIRS a more accurate determination of cloud top height is achieved. Cloud thicknesses are estimated using three different approaches: 1) constant liquid water content (CLWC); 2) an empirical relationship; and 3) an adiabatic model. The CLWC approach provided the most consistent results. Cloud base heights are computed from subtracting cloud thickness from cloud

  1. FIRE Arctic Clouds Experiment

    NASA Technical Reports Server (NTRS)

    Curry, J. A.; Hobbs, P. V.; King, M. D.; Randall, D. A.; Minnis, P.; Issac, G. A.; Pinto, J. O.; Uttal, T.; Bucholtz, A.; Cripe, D. G.; Gerber, H.; Fairall, C. W.; Garrett, T. J.; Hudson, J.; Intrieri, J. M.; Jakob, C.; Jensen, T.; Lawson, P.; Marcotte, D.; Nguyen, L.

    1998-01-01

    An overview is given of the First ISCCP Regional Experiment (FIRE) Arctic Clouds Experiment that was conducted in the Arctic during April through July, 1998. The principal goal of the field experiment was to gather the data needed to examine the impact of arctic clouds on the radiation exchange between the surface, atmosphere, and space, and to study how the surface influences the evolution of boundary layer clouds. The observations will be used to evaluate and improve climate model parameterizations of cloud and radiation processes, satellite remote sensing of cloud and surface characteristics, and understanding of cloud-radiation feedbacks in the Arctic. The experiment utilized four research aircraft that flew over surface-based observational sites in the Arctic Ocean and Barrow, Alaska. In this paper we describe the programmatic and science objectives of the project, the experimental design (including research platforms and instrumentation), conditions that were encountered during the field experiment, and some highlights of preliminary observations, modelling, and satellite remote sensing studies.

  2. A cloud physics radiometer

    NASA Technical Reports Server (NTRS)

    Kyle, H. L.; Curran, R. J.; Barnes, W. L.; Escoe, D.

    1978-01-01

    The paper describes the design features and capabilities of a seven-channel cloud physics radiometer (CPR) for remote sensing of cloud properties. The CPR channel characteristics and functions are tabulated and diagrammed. Each of the first three channels utilizes a photo-multipler detector, with the high-voltage power supply integrated with the tube into a single unit. In operation a heater is used to keep the optics temperature at or above 273 K and this temperature is constantly monitored. The last four channel detectors and filters are all cooled to the temperature of liquid nitrogen. The inclined scanning mirror rotates at a rate of 3.48 rps. Registration pulses are triggered and recorded as the mirror enters and leaves the + or -45 deg earth observation region. The ice-cloud, water cloud, snow discriminator detector has worked quite well in general. Interesting radiometer data have been obtained and their analysis is under way. The combination of the CPR and the Cloud Lidar System will make possible sophisticated remote sensing cloud studies.

  3. Molecules in interstellar clouds

    NASA Astrophysics Data System (ADS)

    Irvine, W. M.; Hjalmarson, A.; Rydbeck, O. E. H.

    The physical conditions and chemical compositions of the gas in interstellar clouds are reviewed in light of the importance of interstellar clouds for star formation and the origin of life. The Orion A region is discussed as an example of a giant molecular cloud where massive stars are being formed, and it is pointed out that conditions in the core of the cloud, with a kinetic temperature of about 75 K and a density of 100,000-1,000,000 molecules/cu cm, may support gas phase ion-molecule chemistry. The Taurus Molecular Clouds are then considered as examples of cold, dark, relatively dense interstellar clouds which may be the birthplaces of solar-type stars and which have been found to contain the heaviest interstellar molecules yet discovered. The molecular species identified in each of these regions are tabulated, including such building blocks of biological monomers as H2O, NH3, H2CO, CO, H2S, CH3CN and H2, and more complex species such as HCOOCH3 and CH3CH2CN.

  4. Electron cloud and space charge effects in the Fermilab Booster

    SciTech Connect

    Ng, K.Y.; /Fermilab

    2007-06-01

    The stable region of the Fermilab Booster beam in the complex coherent-tune-shift plane appears to have been shifted far away from the origin by its intense space charge making Landau damping appear impossible. Simulations reveal a substantial buildup of electron cloud in the whole Booster ramping cycle, both inside the unshielded combined-function magnets and the beam pipes joining the magnets, whenever the secondary-emission yield (SEY) is larger than {approx}1.6. The implication of the electron-cloud effects on the space charge and collective instabilities of the beam is investigated.

  5. Magnetohydrodynamic shock waves in molecular clouds

    SciTech Connect

    Draine, B.T.; Roberge, W.G.; Dalgarno, A.

    1983-01-15

    The structure of shock waves in molecular clouds is calculated, including the effects of ion-neutral streaming driven by the magnetic field. It is found that shock waves in molecular clouds will usually be C-type shock waves, mediated entirely by the dissipation accompanying ion-neutral streaming, and in which all of the hydrodynamic variables are continuous. Detailed results are presented for magnetohydrodynamic shock waves propagating at speeds in the range of 5--50 km s/sup -1/ in molecular clouds with preshock densities n/sub H/ = 10/sup 2/, 10/sup 4/, and 10/sup 6/ cm/sup -3/. Graphs are constructed of the effective ''excitation temperatures'' of the rotational and vibrational levels of H/sub 2/ in the shocked gas. The effects of chemical changes in the composition of oxygen-bearing molecules are investigated, and the contributions to the cooling of the shocked gas by emission from H/sub 2/, CO, OH, and H/sub 2/O are evaluated. Predictions are made of the intensities of the rotation-vibration lines of H/sub 2/ and of the fine-structure lines of O I and C I. Magnetic fields may lead to a substantial increase in the limiting shock velocity above which dissociation of H/sub 2/ takes place: for a cloud of density eta/sub H/ = 10/sup 6/ cm/sup -3/, the limiting shock speed is approx.45 km s/sup -1/. The fractional ionization is a critical parameter affecting the shock structure, and the processes acting to change the ionization in the shock are examined. Magnetic field effects enhance the sputtering of grain mantles in dense gas: H/sub 2/O ice mantles can be substantially eroded in v/sub s/> or =25 km s/sup -1/ shock waves. Grain erosion may contribute to the enhancement of some molecular species in the shocked gas.

  6. First observations of tracking clouds using scanning ARM cloud radars

    SciTech Connect

    Borque, Paloma; Giangrande, Scott; Kollias, Pavlos

    2014-12-01

    Tracking clouds using scanning cloud radars can help to document the temporal evolution of cloud properties well before large drop formation (‘‘first echo’’). These measurements complement cloud and precipitation tracking using geostationary satellites and weather radars. Here, two-dimensional (2-D) Along-Wind Range Height Indicator (AW-RHI) observations of a population of shallow cumuli (with and without precipitation) from the 35-GHz scanning ARM cloud radar (SACR) at the DOE Atmospheric Radiation Measurements (ARM) program Southern Great Plains (SGP) site are presented. Observations from the ARM SGP network of scanning precipitation radars are used to provide the larger scale context of the cloud field and to highlight the advantages of the SACR to detect the numerous, small, non-precipitating cloud elements. A new Cloud Identification and Tracking Algorithm (CITA) is developed to track cloud elements. In CITA, a cloud element is identified as a region having a contiguous set of pixels exceeding a preset reflectivity and size threshold. The high temporal resolution of the SACR 2-D observations (30 sec) allows for an area superposition criteria algorithm to match cloud elements at consecutive times. Following CITA, the temporal evolution of cloud element properties (number, size, and maximum reflectivity) is presented. The vast majority of the designated elements during this cumulus event were short-lived non-precipitating clouds having an apparent life cycle shorter than 15 minutes. The advantages and disadvantages of cloud tracking using an SACR are discussed.

  7. 12 CFR 725.3 - Regular membership.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... and Banking NATIONAL CREDIT UNION ADMINISTRATION REGULATIONS AFFECTING CREDIT UNIONS NATIONAL CREDIT UNION ADMINISTRATION CENTRAL LIQUIDITY FACILITY § 725.3 Regular membership. (a) A natural person credit... the credit union's paid-in and unimpaired capital and surplus, as determined in accordance with §...

  8. 12 CFR 725.3 - Regular membership.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... and Banking NATIONAL CREDIT UNION ADMINISTRATION REGULATIONS AFFECTING CREDIT UNIONS NATIONAL CREDIT UNION ADMINISTRATION CENTRAL LIQUIDITY FACILITY § 725.3 Regular membership. (a) A natural person credit... the credit union's paid-in and unimpaired capital and surplus, as determined in accordance with §...

  9. 12 CFR 725.3 - Regular membership.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... and Banking NATIONAL CREDIT UNION ADMINISTRATION REGULATIONS AFFECTING CREDIT UNIONS NATIONAL CREDIT UNION ADMINISTRATION CENTRAL LIQUIDITY FACILITY § 725.3 Regular membership. (a) A natural person credit... the credit union's paid-in and unimpaired capital and surplus, as determined in accordance with §...

  10. 12 CFR 725.3 - Regular membership.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... and Banking NATIONAL CREDIT UNION ADMINISTRATION REGULATIONS AFFECTING CREDIT UNIONS NATIONAL CREDIT UNION ADMINISTRATION CENTRAL LIQUIDITY FACILITY § 725.3 Regular membership. (a) A natural person credit... the credit union's paid-in and unimpaired capital and surplus, as determined in accordance with §...

  11. Commitment and Dependence Upon Regular Running.

    ERIC Educational Resources Information Center

    Sachs, Michael L.; Pargman, David

    The linear relationship between intellectual commitment to running and psychobiological dependence upon running is examined. A sample of 540 regular runners (running frequency greater than three days per week for the past year for the majority) was surveyed with a questionnaire. Measures of commitment and dependence on running, as well as…

  12. RBOOST: RIEMANNIAN DISTANCE BASED REGULARIZED BOOSTING.

    PubMed

    Liu, Meizhu; Vemuri, Baba C

    2011-03-30

    Boosting is a versatile machine learning technique that has numerous applications including but not limited to image processing, computer vision, data mining etc. It is based on the premise that the classification performance of a set of weak learners can be boosted by some weighted combination of them. There have been a number of boosting methods proposed in the literature, such as the AdaBoost, LPBoost, SoftBoost and their variations. However, the learning update strategies used in these methods usually lead to overfitting and instabilities in the classification accuracy. Improved boosting methods via regularization can overcome such difficulties. In this paper, we propose a Riemannian distance regularized LPBoost, dubbed RBoost. RBoost uses Riemannian distance between two square-root densities (in closed form) - used to represent the distribution over the training data and the classification error respectively - to regularize the error distribution in an iterative update formula. Since this distance is in closed form, RBoost requires much less computational cost compared to other regularized Boosting algorithms. We present several experimental results depicting the performance of our algorithm in comparison to recently published methods, LP-Boost and CAVIAR, on a variety of datasets including the publicly available OASIS database, a home grown Epilepsy database and the well known UCI repository. Results depict that the RBoost algorithm performs better than the competing methods in terms of accuracy and efficiency. PMID:21927643

  13. Generalisation of Regular and Irregular Morphological Patterns.

    ERIC Educational Resources Information Center

    Prasada, Sandeep; and Pinker, Steven

    1993-01-01

    When it comes to explaining English verbs' patterns of regular and irregular generalization, single-network theories have difficulty with the former, rule-only theories with the latter process. Linguistic and psycholinguistic evidence, based on observation during experiments and simulations in morphological pattern generation, independently call…

  14. Observing Special and Regular Education Classrooms.

    ERIC Educational Resources Information Center

    Hersh, Susan B.

    The paper describes an observation instrument originally developed as a research tool to assess both the special setting and the regular classroom. The instrument can also be used in determining appropriate placement for students with learning disabilities and for programming the transfer of skills learned in the special setting to the regular…

  15. Starting flow in regular polygonal ducts

    NASA Astrophysics Data System (ADS)

    Wang, C. Y.

    2016-06-01

    The starting flows in regular polygonal ducts of S = 3, 4, 5, 6, 8 sides are determined by the method of eigenfunction superposition. The necessary S-fold symmetric eigenfunctions and eigenvalues of the Helmholtz equation are found either exactly or by boundary point match. The results show the starting time is governed by the first eigenvalue.

  16. 28 CFR 540.44 - Regular visitors.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... PERSONS IN THE COMMUNITY Visiting Regulations § 540.44 Regular visitors. An inmate desiring to have... ordinarily will be extended to friends and associates having an established relationship with the inmate... of the institution. Exceptions to the prior relationship rule may be made, particularly for...

  17. Regular Classroom Teachers' Perceptions of Mainstreaming Effects.

    ERIC Educational Resources Information Center

    Ringlaben, Ravic P.; Price, Jay R.

    To assess regular classroom teachers' perceptions of mainstreaming, a 22 item questionnaire was completed by 117 teachers (K through 12). Among results were that nearly half of the Ss indicated a lack of preparation for implementing mainstreaming; 47% tended to be very willing to accept aminstreamed students; 42% said mainstreaming was working…

  18. Regularizing cosmological singularities by varying physical constants

    SciTech Connect

    Dąbrowski, Mariusz P.; Marosek, Konrad E-mail: k.marosek@wmf.univ.szczecin.pl

    2013-02-01

    Varying physical constant cosmologies were claimed to solve standard cosmological problems such as the horizon, the flatness and the Λ-problem. In this paper, we suggest yet another possible application of these theories: solving the singularity problem. By specifying some examples we show that various cosmological singularities may be regularized provided the physical constants evolve in time in an appropriate way.

  19. Exploring the structural regularities in networks

    NASA Astrophysics Data System (ADS)

    Shen, Hua-Wei; Cheng, Xue-Qi; Guo, Jia-Feng

    2011-11-01

    In this paper, we consider the problem of exploring structural regularities of networks by dividing the nodes of a network into groups such that the members of each group have similar patterns of connections to other groups. Specifically, we propose a general statistical model to describe network structure. In this model, a group is viewed as a hidden or unobserved quantity and it is learned by fitting the observed network data using the expectation-maximization algorithm. Compared with existing models, the most prominent strength of our model is the high flexibility. This strength enables it to possess the advantages of existing models and to overcome their shortcomings in a unified way. As a result, not only can broad types of structure be detected without prior knowledge of the type of intrinsic regularities existing in the target network, but also the type of identified structure can be directly learned from the network. Moreover, by differentiating outgoing edges from incoming edges, our model can detect several types of structural regularities beyond competing models. Tests on a number of real world and artificial networks demonstrate that our model outperforms the state-of-the-art model in shedding light on the structural regularities of networks, including the overlapping community structure, multipartite structure, and several other types of structure, which are beyond the capability of existing models.

  20. Dyslexia in Regular Orthographies: Manifestation and Causation

    ERIC Educational Resources Information Center

    Wimmer, Heinz; Schurz, Matthias

    2010-01-01

    This article summarizes our research on the manifestation of dyslexia in German and on cognitive deficits, which may account for the severe reading speed deficit and the poor orthographic spelling performance that characterize dyslexia in regular orthographies. An only limited causal role of phonological deficits (phonological awareness,…

  1. Regularities in Spearman's Law of Diminishing Returns.

    ERIC Educational Resources Information Center

    Jensen, Arthur R.

    2003-01-01

    Examined the assumption that Spearman's law acts unsystematically and approximately uniformly for various subtests of cognitive ability in an IQ test battery when high- and low-ability IQ groups are selected. Data from national standardization samples for Wechsler adult and child IQ tests affirm regularities in Spearman's "Law of Diminishing…

  2. Handicapped Children in the Regular Classroom.

    ERIC Educational Resources Information Center

    Fountain Valley School District, CA.

    Reported was a project in which 60 educable mentally retarded (EMR) and 30 educationally handicapped (EH) elementary school students were placed in regular classrooms to determine whether they could be effectively educated in those settings. Effective education was defined in terms of improvement in reading, mathematics, student and teacher…

  3. Characterizing the functional MRI response using Tikhonov regularization.

    PubMed

    Vakorin, Vasily A; Borowsky, Ron; Sarty, Gordon E

    2007-09-20

    The problem of evaluating an averaged functional magnetic resonance imaging (fMRI) response for repeated block design experiments was considered within a semiparametric regression model with autocorrelated residuals. We applied functional data analysis (FDA) techniques that use a least-squares fitting of B-spline expansions with Tikhonov regularization. To deal with the noise autocorrelation, we proposed a regularization parameter selection method based on the idea of combining temporal smoothing with residual whitening. A criterion based on a generalized chi(2)-test of the residuals for white noise was compared with a generalized cross-validation scheme. We evaluated and compared the performance of the two criteria, based on their effect on the quality of the fMRI response. We found that the regularization parameter can be tuned to improve the noise autocorrelation structure, but the whitening criterion provides too much smoothing when compared with the cross-validation criterion. The ultimate goal of the proposed smoothing techniques is to facilitate the extraction of temporal features in the hemodynamic response for further analysis. In particular, these FDA methods allow us to compute derivatives and integrals of the fMRI signal so that fMRI data may be correlated with behavioral and physiological models. For example, positive and negative hemodynamic responses may be easily and robustly identified on the basis of the first derivative at an early time point in the response. Ultimately, these methods allow us to verify previously reported correlations between the hemodynamic response and the behavioral measures of accuracy and reaction time, showing the potential to recover new information from fMRI data. PMID:17634970

  4. The statistical difference between bending arcs and regular polar arcs

    NASA Astrophysics Data System (ADS)

    Kullen, A.; Fear, R. C.; Milan, S. E.; Carter, J. A.; Karlsson, T.

    2015-12-01

    In this work, the Polar UVI data set by Kullen et al. (2002) of 74 polar arcs is reinvestigated, focusing on bending arcs. Bending arcs are typically faint and form (depending on interplanetary magnetic field (IMF) By direction) on the dawnside or duskside oval with the tip of the arc splitting off the dayside oval. The tip subsequently moves into the polar cap in the antisunward direction, while the arc's nightside end remains attached to the oval, eventually becoming hook-shaped. Our investigation shows that bending arcs appear on the opposite oval side from and farther sunward than most regular polar arcs. They form during By-dominated IMF conditions: typically, the IMF clock angle increases from 60 to 90° about 20 min before the arc forms. Antisunward plasma flows from the oval into the polar cap just poleward of bending arcs are seen in Super Dual Auroral Radar Network data, indicating dayside reconnection. For regular polar arcs, recently reported characteristics are confirmed in contrast to bending arcs. This includes plasma flows along the nightside oval that originate close to the initial arc location and a significant delay in the correlation between IMF By and initial arc location. In our data set, the highest correlations are found with IMF By appearing at least 1-2 h before arc formation. In summary, bending arcs are distinctly different from regular arcs and cannot be explained by existing polar arc models. Instead, these results are consistent with the formation mechanism described in Carter et al. (2015), suggesting that bending arcs are caused by dayside reconnection.

  5. Learning regular expressions for clinical text classification

    PubMed Central

    Bui, Duy Duc An; Zeng-Treitler, Qing

    2014-01-01

    Objectives Natural language processing (NLP) applications typically use regular expressions that have been developed manually by human experts. Our goal is to automate both the creation and utilization of regular expressions in text classification. Methods We designed a novel regular expression discovery (RED) algorithm and implemented two text classifiers based on RED. The RED+ALIGN classifier combines RED with an alignment algorithm, and RED+SVM combines RED with a support vector machine (SVM) classifier. Two clinical datasets were used for testing and evaluation: the SMOKE dataset, containing 1091 text snippets describing smoking status; and the PAIN dataset, containing 702 snippets describing pain status. We performed 10-fold cross-validation to calculate accuracy, precision, recall, and F-measure metrics. In the evaluation, an SVM classifier was trained as the control. Results The two RED classifiers achieved 80.9–83.0% in overall accuracy on the two datasets, which is 1.3–3% higher than SVM's accuracy (p<0.001). Similarly, small but consistent improvements have been observed in precision, recall, and F-measure when RED classifiers are compared with SVM alone. More significantly, RED+ALIGN correctly classified many instances that were misclassified by the SVM classifier (8.1–10.3% of the total instances and 43.8–53.0% of SVM's misclassifications). Conclusions Machine-generated regular expressions can be effectively used in clinical text classification. The regular expression-based classifier can be combined with other classifiers, like SVM, to improve classification performance. PMID:24578357

  6. Marine cloud brightening

    PubMed Central

    Latham, John; Bower, Keith; Choularton, Tom; Coe, Hugh; Connolly, Paul; Cooper, Gary; Craft, Tim; Foster, Jack; Gadian, Alan; Galbraith, Lee; Iacovides, Hector; Johnston, David; Launder, Brian; Leslie, Brian; Meyer, John; Neukermans, Armand; Ormond, Bob; Parkes, Ben; Rasch, Phillip; Rush, John; Salter, Stephen; Stevenson, Tom; Wang, Hailong; Wang, Qin; Wood, Rob

    2012-01-01

    The idea behind the marine cloud-brightening (MCB) geoengineering technique is that seeding marine stratocumulus clouds with copious quantities of roughly monodisperse sub-micrometre sea water particles might significantly enhance the cloud droplet number concentration, and thereby the cloud albedo and possibly longevity. This would produce a cooling, which general circulation model (GCM) computations suggest could—subject to satisfactory resolution of technical and scientific problems identified herein—have the capacity to balance global warming up to the carbon dioxide-doubling point. We describe herein an account of our recent research on a number of critical issues associated with MCB. This involves (i) GCM studies, which are our primary tools for evaluating globally the effectiveness of MCB, and assessing its climate impacts on rainfall amounts and distribution, and also polar sea-ice cover and thickness; (ii) high-resolution modelling of the effects of seeding on marine stratocumulus, which are required to understand the complex array of interacting processes involved in cloud brightening; (iii) microphysical modelling sensitivity studies, examining the influence of seeding amount, seed-particle salt-mass, air-mass characteristics, updraught speed and other parameters on cloud–albedo change; (iv) sea water spray-production techniques; (v) computational fluid dynamics studies of possible large-scale periodicities in Flettner rotors; and (vi) the planning of a three-stage limited-area field research experiment, with the primary objectives of technology testing and determining to what extent, if any, cloud albedo might be enhanced by seeding marine stratocumulus clouds on a spatial scale of around 100×100 km. We stress that there would be no justification for deployment of MCB unless it was clearly established that no significant adverse consequences would result. There would also need to be an international agreement firmly in favour of such action

  7. Stratocumulus cloud evolution

    SciTech Connect

    Yang, X.; Rogers, D.P.; Norris, P.M.; Johnson, D.W.; Martin, G.M.

    1994-12-31

    The structure and evolution of the extra-tropical marine atmospheric boundary layer (MABL) depends largely on the variability of stratus and stratocumulus clouds. The typical boundary-layer is capped by a temperature inversion that limits exchange with the free atmosphere. Cloud-top is usually coincident with the base of the inversion. Stratus clouds are generally associated with a well-mixed MABL, whereas daytime observations of stratocumulus-topped boundary-layers indicate that the cloud and subcloud layers are often decoupled due to shortwave radiative heating of the cloud layer. In this case the surface-based mixed layer is separated from the base of the stratocumulus (Sc) by a layer that is stable to dry turbulent mixing. This is sometimes referred to as the transition layer. Often cumulus clouds (Cu) develop in the transition layer. The cumulus tops may remain below the Sc base or they may penetrate into the Sc layer and occasionally through the capping temperature inversion. While this cloud structure is characteristic of the daytime MABL, it may persist at night also. The Cu play an important role in connecting the mixed layer to the Sc layer. If the Cu are active they transport water vapor from the sea surface that maintains the Sc against the dissipating effects of shortwave heating. The Cu, however, are very sensitive to small changes in the heat and moisture in the boundary-layer and are transient features. Here the authors discuss the effect of these small Cu on the turbulent structure of the MABL.

  8. The Launching of Cold Clouds by Galaxy Outflows. I. Hydrodynamic Interactions with Radiative Cooling

    NASA Astrophysics Data System (ADS)

    Scannapieco, Evan; Brüggen, Marcus

    2015-06-01

    To better understand the nature of the multiphase material found in outflowing galaxies, we study the evolution of cold clouds embedded in flows of hot and fast material. Using a suite of adaptive mesh refinement simulations that include radiative cooling, we investigate both cloud mass loss and cloud acceleration under the full range of conditions observed in galaxy outflows. The simulations are designed to track the cloud center of mass, enabling us to study the cloud evolution at long disruption times. For supersonic flows, a Mach cone forms around the cloud, which damps the Kelvin-Helmholtz instability but also establishes a streamwise pressure gradient that stretches the cloud apart. If time is expressed in units of the cloud crushing time, both the cloud lifetime and the cloud acceleration rate are independent of cloud radius, and we find simple scalings for these quantities as a function of the Mach number of the external medium. A resolution study suggests that our simulations accurately describe the evolution of cold clouds in the absence of thermal conduction and magnetic fields, physical processes whose roles will be studied in forthcoming papers.

  9. MHD Turbulence in the Taurus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Heyer, M.; Gong, H.; Brunt, C.; Ostriker, E.

    2005-12-01

    The presence of MHD turbulence in the Taurus Molecular Cloud is examined from 12CO and 13CO J=1-0 imaging observations using the FCRAO 14 meter telescope. The degree of velocity anisotropy is measured from velocity structure functions derived separately along the x and y axes using Principal Component Analysis of spectroscopic imaging data (Brunt & Heyer 2002). Such anisotropy is predicted from model descriptions and computational simulations of MHD turbulence in the case of strong magnetic fields (Goldreich & Sridhar 1995; Cho, Lazarian, & Vishniac 2002; Vestuto, Ostriker, & Stone 2003). Within a subfield of the Taurus image where the column densities are low, this velocity anisotropy is largest along an angle that is coincident with the local magnetic field direction determined independently from optical polarization of background stars.The structure function derived from data perpendicular to the local field shows a shallower scaling exponent and a larger scaling coefficient than the values that describe the structure function constructed along the magnetic field as predicted by the MHD models. This alignment provides strong evidence that the magnetic field is a significant dynamical force within this column density regime of the Taurus cloud.

  10. Maximum-likelihood constrained regularized algorithms: an objective criterion for the determination of regularization parameters

    NASA Astrophysics Data System (ADS)

    Lanteri, Henri; Roche, Muriel; Cuevas, Olga; Aime, Claude

    1999-12-01

    We propose regularized versions of Maximum Likelihood algorithms for Poisson process with non-negativity constraint. For such process, the best-known (non- regularized) algorithm is that of Richardson-Lucy, extensively used for astronomical applications. Regularization is necessary to prevent an amplification of the noise during the iterative reconstruction; this can be done either by limiting the iteration number or by introducing a penalty term. In this Communication, we focus our attention on the explicit regularization using Tikhonov (Identity and Laplacian operator) or entropy terms (Kullback-Leibler and Csiszar divergences). The algorithms are established from the Kuhn-Tucker first order optimality conditions for the minimization of the Lagrange function and from the method of successive substitutions. The algorithms may be written in a `product form'. Numerical illustrations are given for simulated images corrupted by photon noise. The effects of the regularization are shown in the Fourier plane. The tests we have made indicate that a noticeable improvement of the results may be obtained for some of these explicitly regularized algorithms. We also show that a comparison with a Wiener filter can give the optimal regularizing conditions (operator and strength).

  11. Cloud Photogrammetry from Space

    NASA Astrophysics Data System (ADS)

    Zaksek, K.; Gerst, A.; von der Lieth, J.; Ganci, G.; Hort, M.

    2015-04-01

    The most commonly used method for satellite cloud top height (CTH) compares brightness temperature of the cloud with the atmospheric temperature profile. Because of the uncertainties of this method, we propose a photogrammetric approach. As clouds can move with high velocities, even instruments with multiple cameras are not appropriate for accurate CTH estimation. Here we present two solutions. The first is based on the parallax between data retrieved from geostationary (SEVIRI, HRV band; 1000 m spatial resolution) and polar orbiting satellites (MODIS, band 1; 250 m spatial resolution). The procedure works well if the data from both satellites are retrieved nearly simultaneously. However, MODIS does not retrieve the data at exactly the same time as SEVIRI. To compensate for advection in the atmosphere we use two sequential SEVIRI images (one before and one after the MODIS retrieval) and interpolate the cloud position from SEVIRI data to the time of MODIS retrieval. CTH is then estimated by intersection of corresponding lines-of-view from MODIS and interpolated SEVIRI data. The second method is based on NASA program Crew Earth observations from the International Space Station (ISS). The ISS has a lower orbit than most operational satellites, resulting in a shorter minimal time between two images, which is needed to produce a suitable parallax. In addition, images made by the ISS crew are taken by a full frame sensor and not a push broom scanner that most operational satellites use. Such data make it possible to observe also short time evolution of clouds.

  12. Microphysics of Pyrocumulonimbus Clouds

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Ackerman, Andrew S.; Fridlind, Ann

    2004-01-01

    The intense heat from forest fires can generate explosive deep convective cloud systems that inject pollutants to high altitudes. Both satellite and high-altitude aircraft measurements have documented cases in which these pyrocumulonimbus clouds inject large amounts of smoke well into the stratosphere (Fromm and Servranckx 2003; Jost et al. 2004). This smoke can remain in the stratosphere, be transported large distances, and affect lower stratospheric chemistry. In addition recent in situ measurements in pyrocumulus updrafts have shown that the high concentrations of smoke particles have significant impacts on cloud microphysical properties. Very high droplet number densities result in delayed precipitation and may enhance lightning (Andrew et al. 2004). Presumably, the smoke particles will also lead to changes in the properties of anvil cirrus produces by the deep convection, with resulting influences on cloud radiative forcing. In situ sampling near the tops of mature pyrocumulonimbus is difficult due to the high altitude and violence of the storms. In this study, we use large eddy simulations (LES) with size-resolved microphysics to elucidate physical processes in pyrocumulonimbus clouds.

  13. Counting the clouds

    NASA Astrophysics Data System (ADS)

    Randall, David A.

    2005-01-01

    Cloud processes are very important for the global circulation of the atmosphere. It is now possible, though very expensive, to simulate the global circulation of the atmosphere using a model with resolution fine enough to explicitly represent the larger individual clouds. An impressive preliminary calculation of this type has already been performed by Japanese scientists, using the Earth Simulator. Within the next few years, such global cloud-resolving models (GCRMs) will be applied to weather prediction, and later they will be used in climatechange simulations. The tremendous advantage of GCRMs, relative to conventional lowerresolution global models, is that GCRMs can avoid many of the questionable "parameterizations" used to represent cloud effects in lower-resolution global models. Although cloud microphysics, turbulence, and radiation must still be parameterized in GCRMs, the high resolution of a GCRM simplifies these problems considerably, relative to conventional models. The United States currently has no project to develop a GCRM, although we have both the computer power and the expertise to do it. A research program aimed at development and applications of GCRMs is outlined.

  14. 42 CFR 61.3 - Purpose of regular fellowships.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 42 Public Health 1 2010-10-01 2010-10-01 false Purpose of regular fellowships. 61.3 Section 61.3 Public Health PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES FELLOWSHIPS, INTERNSHIPS, TRAINING FELLOWSHIPS Regular Fellowships § 61.3 Purpose of regular fellowships. Regular fellowships...

  15. 42 CFR 61.3 - Purpose of regular fellowships.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 42 Public Health 1 2011-10-01 2011-10-01 false Purpose of regular fellowships. 61.3 Section 61.3 Public Health PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES FELLOWSHIPS, INTERNSHIPS, TRAINING FELLOWSHIPS Regular Fellowships § 61.3 Purpose of regular fellowships. Regular fellowships...

  16. 42 CFR 61.3 - Purpose of regular fellowships.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 42 Public Health 1 2014-10-01 2014-10-01 false Purpose of regular fellowships. 61.3 Section 61.3 Public Health PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES FELLOWSHIPS, INTERNSHIPS, TRAINING FELLOWSHIPS Regular Fellowships § 61.3 Purpose of regular fellowships. Regular fellowships...

  17. 42 CFR 61.3 - Purpose of regular fellowships.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 42 Public Health 1 2012-10-01 2012-10-01 false Purpose of regular fellowships. 61.3 Section 61.3 Public Health PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES FELLOWSHIPS, INTERNSHIPS, TRAINING FELLOWSHIPS Regular Fellowships § 61.3 Purpose of regular fellowships. Regular fellowships...

  18. 42 CFR 61.3 - Purpose of regular fellowships.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 42 Public Health 1 2013-10-01 2013-10-01 false Purpose of regular fellowships. 61.3 Section 61.3 Public Health PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES FELLOWSHIPS, INTERNSHIPS, TRAINING FELLOWSHIPS Regular Fellowships § 61.3 Purpose of regular fellowships. Regular fellowships...

  19. Imprints of Molecular Clouds in Radio Continuum Images

    NASA Astrophysics Data System (ADS)

    Yusef-Zadeh, F.

    2012-11-01

    We show radio continuum images of several molecular complexes in the inner Galaxy and report the presence of dark features that coincide with dense molecular clouds. Unlike infrared dark clouds, these features which we call "radio dark clouds" are produced by a deficiency in radio continuum emission from molecular clouds that are embedded in a bath of UV radiation field or synchrotron emitting cosmic-ray particles. The contribution of the continuum emission along different path lengths results in dark features that trace embedded molecular clouds. The new technique of identifying cold clouds can place constraints on the depth and the magnetic field of molecular clouds when compared to those of the surrounding hot plasma radiating at radio wavelengths. The study of five molecular complexes in the inner Galaxy, Sgr A, Sgr B2, radio Arc, the Snake filament, and G359.75-0.13 demonstrates an anti-correlation between the distributions of radio continuum and molecular line and dust emission. Radio dark clouds are identified in Green Bank Telescope maps and Very Large Array images taken with uniform sampling of uv coverage. The level at which the continuum flux is suppressed in these sources suggests that the depth of the molecular cloud is similar to the size of the continuum emission within a factor of two. These examples suggest that high-resolution, high-dynamic-range continuum images can be powerful probes of interacting molecular clouds with massive stars and supernova remnants in regions where the kinematic distance estimates are ambiguous as well as in the nuclei of active galaxies.

  20. Cloud condensation nucleus-sulfate mass relationship and cloud albedo

    NASA Technical Reports Server (NTRS)

    Hegg, Dean A.

    1994-01-01

    Analysis of previously published, simultaneous measurements of cloud condensation nucleus number concentration and sulfate mass concentration suggest a nonlinear relationship between the two variables. This nonlinearity reduces the sensitivity of cloud albedo to changes in the sulfur cycle.