WorldWideScience

Sample records for program called dynamo

  1. The Climate Variability & Predictability (CVP) Program at NOAA - DYNAMO Recent Project Advancements

    Science.gov (United States)

    Lucas, S. E.; Todd, J. F.; Higgins, W.

    2013-12-01

    The Climate Variability & Predictability (CVP) Program supports research aimed at providing process-level understanding of the climate system through observation, modeling, analysis, and field studies. This vital knowledge is needed to improve climate models and predictions so that scientists can better anticipate the impacts of future climate variability and change. To achieve its mission, the CVP Program supports research carried out at NOAA and other federal laboratories, NOAA Cooperative Institutes, and academic institutions. The Program also coordinates its sponsored projects with major national and international scientific bodies including the World Climate Research Programme (WCRP), the International Geosphere-Biosphere Programme (IGBP), and the U.S. Global Change Research Program (USGCRP). The CVP program sits within the Earth System Science (ESS) Division at NOAA's Climate Program Office. Dynamics of the Madden-Julian Oscillation (DYNAMO): The Indian Ocean is one of Earth's most sensitive regions because the interactions between ocean and atmosphere there have a discernable effect on global climate patterns. The tropical weather that brews in that region can move eastward along the equator and reverberate around the globe, shaping weather and climate in far-off places. The vehicle for this variability is a phenomenon called the Madden-Julian Oscillation, or MJO. The MJO, which originates over the Indian Ocean roughly every 30 to 90 days, is known to influence the Asian and Australian monsoons. It can also enhance hurricane activity in the northeast Pacific and Gulf of Mexico, trigger torrential rainfall along the west coast of North America, and affect the onset of El Niño. CVP-funded scientists participated in the DYNAMO field campaign in 2011-12. Results from this international campaign are expected to improve researcher's insights into this influential phenomenon. A better understanding of the processes governing MJO is an essential step toward

  2. Magnetized Turbulent Dynamo in Protogalaxies

    Energy Technology Data Exchange (ETDEWEB)

    Leonid Malyshkin; Russell M. Kulsrud

    2002-01-28

    The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium. Up to now, in calculation of the turbulent dynamo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy. This assumption leads to the kinematic dynamo theory. However, the applicability of this theory to protogalaxies is rather limited. The reason is that in protogalaxies the temperature is very high, and the viscosity is dominated by magnetized ions. As the magnetic field strength grows in time, the ion cyclotron time becomes shorter than the ion collision time, and the plasma becomes strongly magnetized. As a result, the ion viscosity becomes the Braginskii viscosity. Thus, in protogalaxies the back reaction sets in much earlier, at field strengths much lower than those which correspond to field-turbulence energy equipartition, and the turbulent dynamo becomes what we call the magnetized turbulent dynamo. In this paper we lay the theoretical groundwork for the magnetized turbulent dynamo. In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the development of the inverse cascade of magnetic energy after the energy equipartition is reached.

  3. Sharing programming resources between Bio* projects through remote procedure call and native call stack strategies.

    Science.gov (United States)

    Prins, Pjotr; Goto, Naohisa; Yates, Andrew; Gautier, Laurent; Willis, Scooter; Fields, Christopher; Katayama, Toshiaki

    2012-01-01

    Open-source software (OSS) encourages computer programmers to reuse software components written by others. In evolutionary bioinformatics, OSS comes in a broad range of programming languages, including C/C++, Perl, Python, Ruby, Java, and R. To avoid writing the same functionality multiple times for different languages, it is possible to share components by bridging computer languages and Bio* projects, such as BioPerl, Biopython, BioRuby, BioJava, and R/Bioconductor. In this chapter, we compare the two principal approaches for sharing software between different programming languages: either by remote procedure call (RPC) or by sharing a local call stack. RPC provides a language-independent protocol over a network interface; examples are RSOAP and Rserve. The local call stack provides a between-language mapping not over the network interface, but directly in computer memory; examples are R bindings, RPy, and languages sharing the Java Virtual Machine stack. This functionality provides strategies for sharing of software between Bio* projects, which can be exploited more often. Here, we present cross-language examples for sequence translation, and measure throughput of the different options. We compare calling into R through native R, RSOAP, Rserve, and RPy interfaces, with the performance of native BioPerl, Biopython, BioJava, and BioRuby implementations, and with call stack bindings to BioJava and the European Molecular Biology Open Software Suite. In general, call stack approaches outperform native Bio* implementations and these, in turn, outperform RPC-based approaches. To test and compare strategies, we provide a downloadable BioNode image with all examples, tools, and libraries included. The BioNode image can be run on VirtualBox-supported operating systems, including Windows, OSX, and Linux.

  4. How is Mercury's dynamo powered?

    Science.gov (United States)

    Cox, G. A.; Delbridge, B. G.; Irving, J. C. E.; Matsui, H.; McDonough, W. F.; Rose, I.; Shahar, A.; Wahl, S. M.

    2014-12-01

    One of the more surprising findings of the MESSENGER spacecraft is the confirmation that the smallest terrestrial planet has an internally generated, dipolar magnetic field, which is likely driven by a combination of thermal and compositional buoyancy sources. This observation places constraints on the thermal and energetic state of Mercury's large iron core and on mantle dynamics because dynamo operation is strongly dependent on the amount of heat extracted from the core by the mantle. However, other observations point to several factors that should inhibit a present-day dynamo. These include physical constraints on a thin, possibly non-convecting mantle, as well as properties of liquid iron alloys that promote compositional stratification in the core. We consider a range of self-consistent internal structures, core compositions and thermal evolution models that are also consistent with observational constraints, and assess the circumstances under which a dynamo is permitted to operate in Mercury's core. We present the thermal evolution models, 1D parameterized convection models and planetary entropy calculations. We attempt to account for the large uncertainties on some parameters by considering various end member cases. We examine the thermal and magnetic implications of a long-lived lateral temperature difference resulting from Mercury's orbital resonance and how it may play a role in driving the planetary dynamo. We compare simulations of mantle heat flow using the ASPECT convection code to predictions from the parameterized models and produce heat flow maps at the CMB. To represent fluid dynamics and magnetic field generation inside Mercury's core, a numerical dynamo model is performed by using the obtained heat flux maps. Lastly, we also investigate the seismic observability of the different structural models of Mercury to determine the extent to which any future single-seismometer mission will be able to provide alternative insights into Mercury's internal

  5. The lunar dynamo.

    Science.gov (United States)

    Weiss, Benjamin P; Tikoo, Sonia M

    2014-12-05

    The inductive generation of magnetic fields in fluid planetary interiors is known as the dynamo process. Although the Moon today has no global magnetic field, it has been known since the Apollo era that the lunar rocks and crust are magnetized. Until recently, it was unclear whether this magnetization was the product of a core dynamo or fields generated externally to the Moon. New laboratory and spacecraft measurements strongly indicate that much of this magnetization is the product of an ancient core dynamo. The dynamo field persisted from at least 4.25 to 3.56 billion years ago (Ga), with an intensity reaching that of the present Earth. The field then declined by at least an order of magnitude by ∼3.3 Ga. The mechanisms for sustaining such an intense and long-lived dynamo are uncertain but may include mechanical stirring by the mantle and core crystallization. Copyright © 2014, American Association for the Advancement of Science.

  6. Growth rate degeneracies in kinematic dynamos

    CERN Document Server

    Favier, B

    2013-01-01

    We consider the classical problem of kinematic dynamo action in simple steady flows. Due to the adjointness of the induction operator, we show that the growth rate of the dynamo will be exactly the same for two types of magnetic boundary conditions: the magnetic field can be normal (infinite magnetic permeability, also called pseudo-vacuum) or tangent (perfect electrical conductor) to the boundaries of the domain. These boundary conditions correspond to well-defined physical limits often used in numerical models and relevant to laboratory experiments. The only constraint is for the velocity field u to be reversible, meaning there exists a transformation changing u into -u. We illustrate this surprising property using S2T2 type of flows in spherical geometry inspired by Dudley and James (1989). Using both types of boundary conditions, it is shown that the growth rates of the dynamos are identical, although the corresponding magnetic eigenmodes are drastically different.

  7. Dynamo Scaling Relationships

    Science.gov (United States)

    Augustson, Kyle; Mathis, Stéphane; Brun, Sacha; Toomre, Juri

    2017-11-01

    This paper provides a brief look at dynamo scaling relationships for the degree of equipartition between magnetic and kinetic energies. Two simple models are examined, where one that assumes magnetostrophy and another that includes the effects of inertia. These models are then compared to a suite of convective dynamo simulations of the convective core of a main-sequence B-type star and applied to its later evolutionary stages.

  8. The Solar Dynamo Zoo

    Science.gov (United States)

    Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W.

    2016-07-01

    We present composite time series of Ca II H & K line core emission indices of up to 50 years in length for a set of 27 solar-analog stars (spectral types G0-G5; within 10% of the solar mass) and the Sun. These unique data are available thanks to the long-term dedicated efforts of the Mount Wilson Observatory HK project, the Lowell Observatory Solar-Stellar Spectrograph, and the National Solar Observatory/Air Force Research Laboratory/Sacramento Peak K-line monitoring program. The Ca II H & K emission originates in the lower chromosphere and is strongly correlated with the presence of magnetic plage regions in the Sun. These synoptic observations allow us to trace the patterns long-term magnetic variability and explore dynamo behavior over a wide range of rotation regimes and stellar evolution timescales.In this poster, the Ca HK observations are expressed using the Mount Wilson S-index. Each time series is accompanied by a Lomb-Scargle periodogram, fundemental stellar parameters derived from the Geneva-Copenhagen Survey, and statistics derived from the time series including the median S-index value and seasonal and long-term amplitudes. Statistically significant periodogram peaks are ranked according to a new cycle quality metric. We find that clear, simple, Sun-like cycles are the minority in this sample.

  9. Magnetic Helicity and Planetary Dynamos

    Science.gov (United States)

    Shebalin, John V.

    2012-01-01

    A model planetary dynamo based on the Boussinesq approximation along with homogeneous boundary conditions is considered. A statistical theory describing a large-scale MHD dynamo is found, in which magnetic helicity is the critical parameter

  10. The Solar Dynamo

    Science.gov (United States)

    Hathaway, David H.

    1998-01-01

    The solar dynamo is the process by which the Sun's magnetic field is generated through the interaction of the field with convection and rotation. In this, it is kin to planetary dynamos and other stellar dynamos. Although the precise mechanism by which the Sun generates its field remains poorly understood despite decades of theoretical and observational work, recent advances suggest that solutions to this solar dynamo problem may be forthcoming. Two basic processes are involved in dynamo activity. When the fluid stresses dominate the magnetic stresses (high plasma beta = 8(pi)rho/B(sup 2)), shear flows can stretch magnetic field lines in the direction of the shear (the "alpha effect") and helical flows can lift and twist field lines into orthogonal planes (the "alpha effect"). These two processes can be active anywhere in the solar convection zone but with different results depending upon their relative strengths and signs. Little is known about how and where these processes occur. Other processes, such as magnetic diffusion and the effects of the fine scale structure of the solar magnetic field, pose additional problems.

  11. Strong Field Spherical Dynamos

    CERN Document Server

    Dormy, Emmanuel

    2014-01-01

    Numerical models of the geodynamo are usually classified in two categories: those denominated dipolar modes, observed when the inertial term is small enough, and multipolar fluctuating dynamos, for stronger forcing. I show that a third dynamo branch corresponding to a dominant force balance between the Coriolis force and the Lorentz force can be produced numerically. This force balance is usually referred to as the strong field limit. This solution co-exists with the often described viscous branch. Direct numerical simulations exhibit a transition from a weak-field dynamo branch, in which viscous effects set the dominant length scale, and the strong field branch in which viscous and inertial effects are largely negligible. These results indicate that a distinguished limit needs to be sought to produce numerical models relevant to the geodynamo and that the usual approach of minimizing the magnetic Prandtl number (ratio of the fluid kinematic viscosity to its magnetic diffusivity) at a given Ekman number is mi...

  12. Sharing programming resources between Bio* projects through remote procedure call and native call stack strategies

    DEFF Research Database (Denmark)

    Prins, Pjotr; Goto, Naohisa; Yates, Andrew

    2012-01-01

    , and languages sharing the Java Virtual Machine stack. This functionality provides strategies for sharing of software between Bio* projects, which can be exploited more often. Here, we present cross-language examples for sequence translation, and measure throughput of the different options. We compare calling...... into R through native R, RSOAP, Rserve, and RPy interfaces, with the performance of native BioPerl, Biopython, BioJava, and BioRuby implementations, and with call stack bindings to BioJava and the European Molecular Biology Open Software Suite. In general, call stack approaches outperform native Bio...

  13. Kinematic dynamo induced by helical waves

    OpenAIRE

    Wei, Xing

    2014-01-01

    We investigate numerically the kinematic dynamo induced by the superposition of two helical waves in a periodic box as a simplified model to understand the dynamo action in astronomical bodies. The effects of magnetic Reynolds number, wavenumber and wave frequency on the dynamo action are studied. It is found that this helical-wave dynamo is a slow dynamo. There exists an optimal wavenumber for the dynamo growth rate. A lower wave frequency facilitates the dynamo action and the oscillations o...

  14. The 3D Elevation Program initiative: a call for action

    Science.gov (United States)

    Sugarbaker, Larry J.; Constance, Eric W.; Heidemann, Hans Karl; Jason, Allyson L.; Lukas, Vicki; Saghy, David L.; Stoker, Jason M.

    2014-01-01

    The 3D Elevation Program (3DEP) initiative is accelerating the rate of three-dimensional (3D) elevation data collection in response to a call for action to address a wide range of urgent needs nationwide. It began in 2012 with the recommendation to collect (1) high-quality light detection and ranging (lidar) data for the conterminous United States (CONUS), Hawaii, and the U.S. territories and (2) interferometric synthetic aperture radar (ifsar) data for Alaska. Specifications were created for collecting 3D elevation data, and the data management and delivery systems are being modernized. The National Elevation Dataset (NED) will be completely refreshed with new elevation data products and services. The call for action requires broad support from a large partnership community committed to the achievement of national 3D elevation data coverage. The initiative is being led by the U.S. Geological Survey (USGS) and includes many partners—Federal agencies and State, Tribal, and local governments—who will work together to build on existing programs to complete the national collection of 3D elevation data in 8 years. Private sector firms, under contract to the Government, will continue to collect the data and provide essential technology solutions for the Government to manage and deliver these data and services. The 3DEP governance structure includes (1) an executive forum established in May 2013 to have oversight functions and (2) a multiagency coordinating committee based upon the committee structure already in place under the National Digital Elevation Program (NDEP). The 3DEP initiative is based on the results of the National Enhanced Elevation Assessment (NEEA) that was funded by NDEP agencies and completed in 2011. The study, led by the USGS, identified more than 600 requirements for enhanced (3D) elevation data to address mission-critical information requirements of 34 Federal agencies, all 50 States, and a sample of private sector companies and Tribal and local

  15. Converting DYNAMO simulations to Powersim Studio simulations

    Energy Technology Data Exchange (ETDEWEB)

    Walker, La Tonya Nicole; Malczynski, Leonard A.

    2014-02-01

    DYNAMO is a computer program for building and running 'continuous' simulation models. It was developed by the Industrial Dynamics Group at the Massachusetts Institute of Technology for simulating dynamic feedback models of business, economic, and social systems. The history of the system dynamics method since 1957 includes many classic models built in DYANMO. It was not until the late 1980s that software was built to take advantage of the rise of personal computers and graphical user interfaces that DYNAMO was supplanted. There is much learning and insight to be gained from examining the DYANMO models and their accompanying research papers. We believe that it is a worthwhile exercise to convert DYNAMO models to more recent software packages. We have made an attempt to make it easier to turn these models into a more current system dynamics software language, Powersim © Studio produced by Powersim AS2 of Bergen, Norway. This guide shows how to convert DYNAMO syntax into Studio syntax.

  16. Sharing Programming Resources Between Bio* Projects Through Remote Procedure Call and Native Call Stack Strategies

    NARCIS (Netherlands)

    Prins, J.C.P.; Goto, N.; Yates, A.; Gautier, L.; Willis, S.; Fields, C.; Katayama, T.

    2012-01-01

    Open-source software (OSS) encourages computer programmers to reuse software components written by others. In evolutionary bioinformatics, OSS comes in a broad range of programming languages, including C/C++, Perl, Python, Ruby, Java, and R. To avoid writing the same functionality multiple times for

  17. Radiative transfer dynamo effect.

    Science.gov (United States)

    Munirov, Vadim R; Fisch, Nathaniel J

    2017-01-01

    Magnetic fields in rotating and radiating astrophysical plasma can be produced due to a radiative interaction between plasma layers moving relative to each other. The efficiency of current drive, and with it the associated dynamo effect, is considered in a number of limits. It is shown here, however, that predictions for these generated magnetic fields can be significantly higher when kinetic effects, previously neglected, are taken into account.

  18. Mathematical aspects of natural dynamos

    CERN Document Server

    Dormy, Emmanuel

    2007-01-01

    Although the origin of Earth's and other celestial bodies' magnetic fields remains unknown, we do know that the motion of electrically conducting fluids generates and maintains these fields, forming the basis of magnetohydrodynamics (MHD) and, to a larger extent, dynamo theory. Answering the need for a comprehensive, interdisciplinary introduction to this area, ""Mathematical Aspects of Natural Dynamos"" provides a foundation in dynamo theory before moving on to modeling aspects of natural dynamos.Bringing together eminent international contributors, the book first introduces governing equatio

  19. Dynamo waves in Friedmann and Misner cosmologies

    OpenAIRE

    de Andrade, Garcia

    2015-01-01

    It is shown that Misner metric can be obtained as solution of dynamo waves equations and Friedmann hyperbolic metrics are obtained when the dynamo waves are absent. In the case of dynamo waves ICM fields are computed and galactic dynamos are obtained.

  20. Multiple scale dynamo

    Science.gov (United States)

    Le Mouël, Jean-Louis; Allègre, Claude J.; Narteau, Clément

    1997-01-01

    A scaling law approach is used to simulate the dynamo process of the Earth’s core. The model is made of embedded turbulent domains of increasing dimensions, until the largest whose size is comparable with the site of the core, pervaded by large-scale magnetic fields. Left-handed or right-handed cyclones appear at the lowest scale, the scale of the elementary domains of the hierarchical model, and disappear. These elementary domains then behave like electromotor generators with opposite polarities depending on whether they contain a left-handed or a right-handed cyclone. To transfer the behavior of the elementary domains to larger ones, a dynamic renormalization approach is used. A simple rule is adopted to determine whether a domain of scale l is a generator—and what its polarity is—in function of the state of the (l − 1) domains it is made of. This mechanism is used as the main ingredient of a kinematic dynamo model, which displays polarity intervals, excursions, and reversals of the geomagnetic field. PMID:11038547

  1. Program Design Called Crucial across Array of School Choices

    Science.gov (United States)

    Viadero, Debra

    2008-01-01

    While school choice may be one of the most polarizing issues in education today, a new volume of research papers makes the case that innovations aimed at giving families more say in where their children go to school can be whatever their architects make of them. Programs such as magnet schools, charters, tuition tax credits, or open-enrollment…

  2. Teachers are students in ZPG program called 'Pop Ed.'.

    Science.gov (United States)

    Schline, S

    1977-01-01

    Zero Population Growth's Population Education (Pop Ed) program began in 1975 as an ongoing effort to bring the "real world" into the classroom by demonstrating the relationships among population trends, food and energy resources, and environmental and economic problems. The training workshops which last for a day or 2 have the following goals: 1) to offer a brief demographic overview for teachers, 2) to provide lesson plans and techniques readily usable in the classroom, 3) to alert teachers to the best written and audiovisual materials available, 4) to identify local resources for teaching Pop Ed, and 5) to provide sample materials. In the 1st year of program operation 10 workshops were held. These workshops are credited, at least partly, with the subsequent population instruction that reached over 10,400 students and 1600 teachers. Another 15 workshops were held in the 2nd year of operation. Obstacles to the program are the assumption on the part of some teachers that Pop Ed belongs in disciplines other than their own and the belief on the part of many teachers that they will require extensive training.

  3. Turbulent Dynamos and Magnetic Helicity

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Hantao

    1999-04-01

    It is shown that the turbulent dynamo alpha-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is elcetrostatic or due to the elcetron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity expect for a battery effect which vanishes in the limit of magnetohydrodynamics. Implications for astrophysical situations, especially for the solar dynamo, are discussed.

  4. A Call for an Integrated Program of Assessment

    Science.gov (United States)

    Regehr, Glenn

    2017-01-01

    An integrated curriculum that does not incorporate equally integrated assessment strategies is likely to prove ineffective in achieving the desired educational outcomes. We suggest it is time for colleges and schools of pharmacy to re-engineer their approach to assessment. To build the case, we first discuss the challenges leading to the need for curricular developments in pharmacy education. We then turn to the literature that informs how assessment can influence learning, introduce an approach to learning assessment that is being used by several medical education programs, and provide some examples of this approach in operation. Finally, we identify some of the challenges faced in adopting such an integrated approach to assessment and suggest that this is an area ripe with research opportunities for pharmacy educators. PMID:28630518

  5. On the saturation of astrophysical dynamos

    DEFF Research Database (Denmark)

    Dorch, Bertil; Archontis, Vasilis

    2004-01-01

    In the context of astrophysical dynamos we illustrate that the no-cosines flow, with zero mean helicity, can drive fast dynamo action and we study the dynamo's mode of operation during both the linear and non-linear saturation regimes. It turns out that in addition to a high growth rate in the li......In the context of astrophysical dynamos we illustrate that the no-cosines flow, with zero mean helicity, can drive fast dynamo action and we study the dynamo's mode of operation during both the linear and non-linear saturation regimes. It turns out that in addition to a high growth rate...

  6. 78 FR 68814 - Call for Applications for the International Buyer Program Calendar Year 2015

    Science.gov (United States)

    2013-11-15

    ... accommodating large numbers of attendees whose native language will not be English. (i) Level of Cooperation... International Trade Administration Call for Applications for the International Buyer Program Calendar Year 2015 AGENCY: International Trade Administration, Department of Commerce. ACTION: Notice and call for...

  7. Tsunami: ocean dynamo generator.

    Science.gov (United States)

    Sugioka, Hiroko; Hamano, Yozo; Baba, Kiyoshi; Kasaya, Takafumi; Tada, Noriko; Suetsugu, Daisuke

    2014-01-08

    Secondary magnetic fields are induced by the flow of electrically conducting seawater through the Earth's primary magnetic field ('ocean dynamo effect'), and hence it has long been speculated that tsunami flows should produce measurable magnetic field perturbations, although the signal-to-noise ratio would be small because of the influence of the solar magnetic fields. Here, we report on the detection of deep-seafloor electromagnetic perturbations of 10-micron-order induced by a tsunami, which propagated through a seafloor electromagnetometer array network. The observed data extracted tsunami characteristics, including the direction and velocity of propagation as well as sea-level change, first to verify the induction theory. Presently, offshore observation systems for the early forecasting of tsunami are based on the sea-level measurement by seafloor pressure gauges. In terms of tsunami forecasting accuracy, the integration of vectored electromagnetic measurements into existing scalar observation systems would represent a substantial improvement in the performance of tsunami early-warning systems.

  8. Do steady fast magnetic dynamos exist?

    Science.gov (United States)

    Finn, John M.; Ott, Edward; Hanson, James D.; Kan, Ittai

    1989-01-01

    This paper considers the question of the existense of a steady fast kinematic magnetic dynamo for a conducting fluid with a steady velocity field and vanishingly small electrical resistivity. The analysis of examples of steady dynamos, found by considering the zero-resistivity dynamics, indicated that, for sufficiently small resistivity, dynamo action can indeed occur in steady smooth three-dimensional chaotic fluid flows and that fast dynamos should consequently be a typical occurrence for such flows.

  9. Computation of Program Source Code Similarity by Composition of Parse Tree and Call Graph

    Directory of Open Access Journals (Sweden)

    Hyun-Je Song

    2015-01-01

    Full Text Available This paper proposes a novel method to compute how similar two program source codes are. Since a program source code is represented as a structural form, the proposed method adopts convolution kernel functions as a similarity measure. Actually, a program source code has two kinds of structural information. One is syntactic information and the other is the dependencies of function calls lying on the program. Since the syntactic information of a program is expressed as its parse tree, the syntactic similarity between two programs is computed by a parse tree kernel. The function calls within a program provide a global structure of a program and can be represented as a graph. Therefore, the similarity of function calls is computed with a graph kernel. Then, both structural similarities are reflected simultaneously into comparing program source codes by composing the parse tree and the graph kernels based on a cyclomatic complexity. According to the experimental results on a real data set for program plagiarism detection, the proposed method is proved to be effective in capturing the similarity between programs. The experiments show that the plagiarized pairs of programs are found correctly and thoroughly by the proposed method.

  10. Kinematic dynamos in spheroidal geometries

    Science.gov (United States)

    Ivers, D. J.

    2017-10-01

    The kinematic dynamo problem is solved numerically for a spheroidal conducting fluid of possibly large aspect ratio with an insulating exterior. The solution method uses solenoidal representations of the magnetic field and the velocity by spheroidal toroidal and poloidal fields in a non-orthogonal coordinate system. Scaling of coordinates and fields to a spherical geometry leads to a modified form of the kinematic dynamo problem with a geometric anisotropic diffusion and an anisotropic current-free condition in the exterior, which is solved explicitly. The scaling allows the use of well-developed spherical harmonic techniques in angle. Dynamo solutions are found for three axisymmetric flows in oblate spheroids with semi-axis ratios 1≤a/c≤25. For larger aspect ratios strong magnetic fields may occur in any region of the spheroid, depending on the flow, but the external fields for all three flows are weak and concentrated near the axis or periphery of the spheroid.

  11. Reconnecting flux-rope dynamo.

    Science.gov (United States)

    Baggaley, Andrew W; Barenghi, Carlo F; Shukurov, Anvar; Subramanian, Kandaswamy

    2009-11-01

    We develop a model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multiscale model of turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. This model can be viewed as an implementation of the asymptotic limit R_{m}-->infinity for a continuous magnetic field, where magnetic dissipation is strongly localized to small regions of strong-field gradients. We investigate the kinetic-energy release into heat mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux-rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3 , consistent with the solar corona heating by nanoflares.

  12. 77 FR 24766 - Call for Proposals for a Micro Support Program on International Conflict Resolution and...

    Science.gov (United States)

    2012-04-25

    ... funding, and provide financial and report management oversight. Deadline: Friday, May 11, 2012 at 3 p.m... PEACE Call for Proposals for a Micro Support Program on International Conflict Resolution and... Support Program on International Conflict Resolution and Peacebuilding. The United States Institute of...

  13. A Set of Free Cross-Platform Authoring Programs for Flexible Web-Based CALL Exercises

    Science.gov (United States)

    O'Brien, Myles

    2012-01-01

    The Mango Suite is a set of three freely downloadable cross-platform authoring programs for flexible network-based CALL exercises. They are Adobe Air applications, so they can be used on Windows, Macintosh, or Linux computers, provided the freely-available Adobe Air has been installed on the computer. The exercises which the programs generate are…

  14. Global Simulations of Dynamo and Magnetorotational Instability in Madison Plasma Experiments and Astrophysical Disks

    Energy Technology Data Exchange (ETDEWEB)

    Ebrahimi, Fatima [Univ. of New Hampshire, Durham, NH (United States)

    2014-07-31

    Large-scale magnetic fields have been observed in widely different types of astrophysical objects. These magnetic fields are believed to be caused by the so-called dynamo effect. Could a large-scale magnetic field grow out of turbulence (i.e. the alpha dynamo effect)? How could the topological properties and the complexity of magnetic field as a global quantity, the so called magnetic helicity, be important in the dynamo effect? In addition to understanding the dynamo mechanism in astrophysical accretion disks, anomalous angular momentum transport has also been a longstanding problem in accretion disks and laboratory plasmas. To investigate both dynamo and momentum transport, we have performed both numerical modeling of laboratory experiments that are intended to simulate nature and modeling of configurations with direct relevance to astrophysical disks. Our simulations use fluid approximations (Magnetohydrodynamics - MHD model), where plasma is treated as a single fluid, or two fluids, in the presence of electromagnetic forces. Our major physics objective is to study the possibility of magnetic field generation (so called MRI small-scale and large-scale dynamos) and its role in Magneto-rotational Instability (MRI) saturation through nonlinear simulations in both MHD and Hall regimes.

  15. CALL English Courses in the General Studies Program : A Case Study in Iwate Prefectural University

    OpenAIRE

    Eishiro, Ito

    2006-01-01

    This article aims to define English language education at the university level, especially English courses in "Zengaku Kyotsu Kamoku" (Course Offered by the University General Studies Program) and to introduce an example of CALL English courses carried out in Iwate Prefectural University with the result of the survey for Ito's six courses dated between October 24 (Mon)-27 (Thu), 2005. CALL (Computer Assisted Language Learning) is an efficient and effective method of learning a foreign languag...

  16. Statistical dynamo theory: Mode excitation.

    Science.gov (United States)

    Hoyng, P

    2009-04-01

    We compute statistical properties of the lowest-order multipole coefficients of the magnetic field generated by a dynamo of arbitrary shape. To this end we expand the field in a complete biorthogonal set of base functions, viz. B= summation operator_{k}a;{k}(t)b;{k}(r) . The properties of these biorthogonal function sets are treated in detail. We consider a linear problem and the statistical properties of the fluid flow are supposed to be given. The turbulent convection may have an arbitrary distribution of spatial scales. The time evolution of the expansion coefficients a;{k} is governed by a stochastic differential equation from which we infer their averages a;{k} , autocorrelation functions a;{k}(t)a;{k *}(t+tau) , and an equation for the cross correlations a;{k}a;{l *} . The eigenfunctions of the dynamo equation (with eigenvalues lambda_{k} ) turn out to be a preferred set in terms of which our results assume their simplest form. The magnetic field of the dynamo is shown to consist of transiently excited eigenmodes whose frequency and coherence time is given by Ilambda_{k} and -1/Rlambda_{k} , respectively. The relative rms excitation level of the eigenmodes, and hence the distribution of magnetic energy over spatial scales, is determined by linear theory. An expression is derived for |a;{k}|;{2}/|a;{0}|;{2} in case the fundamental mode b;{0} has a dominant amplitude, and we outline how this expression may be evaluated. It is estimated that |a;{k}|;{2}/|a;{0}|;{2} approximately 1/N , where N is the number of convective cells in the dynamo. We show that the old problem of a short correlation time (or first-order smoothing approximation) has been partially eliminated. Finally we prove that for a simple statistically steady dynamo with finite resistivity all eigenvalues obey Rlambda_{k}<0 .

  17. 75 FR 53640 - Call for Applications for the International Buyer Program Calendar Year 2012

    Science.gov (United States)

    2010-09-01

    ... large numbers of attendees whose native language will not be English. (j) Level of Cooperation: The...-53642] [FR Doc No: 2010-21838] DEPARTMENT OF COMMERCE International Trade Administration [Docket No.: 100806330-0330-01] Call for Applications for the International Buyer Program Calendar Year 2012 AGENCY...

  18. Preventing Boys' Problems in Schools through Psychoeducational Programming: A Call to Action

    Science.gov (United States)

    O'Neil, James M.; Lujan, Melissa L.

    2009-01-01

    Controversy currently exists on whether boys are in crises and, if so, what to do about it. Research is reviewed that indicates that boys have problems that affect their emotional and interpersonal functioning. Psychoeducational and preventive programs for boys are recommended as a call to action in schools. Thematic areas for boys' programming…

  19. Experimental Bullard-von Karman dynamo: MHD saturated regimes

    Science.gov (United States)

    Miralles, Sophie; Plihon, Nicolas; Pinton, Jean-François

    2014-05-01

    The dynamo instability, converting kinetic energy into magnetic energy, creates the magnetic fields of many astrophysical bodies for which the flows are highly turbulent. Those turbulent fluctuations restricts the range of parameters of numerical and theoretical predictions. As laboratory experiments are closer from natural parameters, this approach is favored in this work. In the past decades, dynamo action has been observed in experiments involving laminar flows [1] or fully turbulent flows [2] in liquid sodium. Nevertheless, the saturation of the velocity field by the Lorentz force due to the dynamo magnetic field is weak in those experiment because the control parameter is always close to the threshold of the instability (which is not the case in astrophysical situations). The details of the mechanism of the back reaction of Lorentz force on the flow are not known. We present here an experimental semi-synthetic dynamo, for which a fluid turbulent induction mechanism ('omega' effect) is associated to an external amplification applying a current into a pair of coils. The flow, called von-Karman, is produced by the counter rotation of two coaxial propellers in a cylindrical tank filled with liquid gallium. The resulting flow is highly turbulent (Re > 10 ^ 5). The amplification, mimicking a turbulent 'alpha' effect, allow to observe the dynamo instability at low magnetic Reynolds number (Rm ~ 2), far below the threshold of natural homogeneous dynamo. This experiment reaches non linear regimes, for which the saturation is a MHD process, at control parameter several times the critical value. The instability grows through an on-off intermittent regime evolving into a full MHD saturated regime for which the Lorentz force is in balance with the inertial one. The power budget is strongly modified by the dynamo magnetic field and we give an insight of the estimated rate of conversion of kinetic energy into magnetic one from experimental data. Very rich regimes such as

  20. CARIAA Call - Call Document

    International Development Research Centre (IDRC) Digital Library (Canada)

    CARIAA

    2013-02-19

    Feb 19, 2013 ... Canada's International Development Research Centre (IDRC) is pleased to announce a call for concept notes as part of the Collaborative Adaptation Research Initiative in Africa and Asia (CARIAA) program. Funded by IDRC and the United Kingdom's Department for International Development (DFID), ...

  1. Radiology residency call in the northeastern United States: comparison of difficulty and frequency in programs of different size.

    Science.gov (United States)

    Rozenshtein, Anna; Bauman-Fishkin, Olga; Fishkin, Igor; Homel, Peter

    2003-05-01

    The purpose of this study was to develop objective measures of residency call frequency and difficulty, to establish mean values for the northeastern United States, and to test those values for correlation with program size. A survey questionnaire was sent to 104 radiology residency programs in the northeastern United States. The programs were classified according to number of residents, as small ( or = 31 residents). The call difficulty index was defined as the number of emergency examinations per resident per year. Call frequency indexes were defined as the numbers of evenings and of nights during the 4-year residency when residents were scheduled for call. The average call difficulty index and standard deviation for the respondent programs was 3,855 +/- 1,779. The average call frequency index and standard deviation for evenings was 140 +/- 53 and for nights was 120 +/- 59. A significant negative correlation was found between program size on one hand and call difficulty index (r = -0.36, P = .01), evening call frequency index (r = -0.29, P = .033), and night call frequency index (r = -0.51, P < .001) on the other. Residents in small programs could expect to be on call 192 evenings and 192 nights in the 4-year residency and to perform 4,866 emergency examinations per year, as opposed to the 110 evenings and 89 nights on call and the 3,213 emergency examinations that residents in very large programs could expect. In other words, the smaller the program, the more calls residents can expect to take, and the more emergency examinations they will interpret. The mean call difficulty and off-hours call frequency indexes established for residency programs of different size in the Northeast demonstrate increasing call difficulty and increasing off-hours call frequency with decreasing program size.

  2. Magnetic reversals from planetary dynamo waves

    DEFF Research Database (Denmark)

    Sheyko, Andrey; Finlay, Chris; Jackson, Andrew

    2016-01-01

    A striking feature of many natural dynamos is their ability to undergo polarity reversals. The best documented example is Earth's magnetic field, which has reversed hundreds of times during its history. The origin of geomagnetic polarity reversals lies in a magnetohydrodynamic process that takes ...... to kinematic dynamo waves. Because our results are relevant in a regime of low viscosity and high magnetic diffusivity, and with geophysically appropriate boundary conditions, this form of dynamo wave may also be involved in geomagnetic reversals....

  3. Optimization of the magnetic dynamo.

    Science.gov (United States)

    Willis, Ashley P

    2012-12-21

    In stars and planets, magnetic fields are believed to originate from the motion of electrically conducting fluids in their interior, through a process known as the dynamo mechanism. In this Letter, an optimization procedure is used to simultaneously address two fundamental questions of dynamo theory: "Which velocity field leads to the most magnetic energy growth?" and "How large does the velocity need to be relative to magnetic diffusion?" In general, this requires optimization over the full space of continuous solenoidal velocity fields possible within the geometry. Here the case of a periodic box is considered. Measuring the strength of the flow with the root-mean-square amplitude, an optimal velocity field is shown to exist, but without limitation on the strain rate, optimization is prone to divergence. Measuring the flow in terms of its associated dissipation leads to the identification of a single optimal at the critical magnetic Reynolds number necessary for a dynamo. This magnetic Reynolds number is found to be only 15% higher than that necessary for transient growth of the magnetic field.

  4. Transition to Turbulent Dynamo Saturation

    Science.gov (United States)

    Seshasayanan, Kannabiran; Gallet, Basile; Alexakis, Alexandros

    2017-11-01

    While the saturated magnetic energy is independent of viscosity in dynamo experiments, it remains viscosity dependent in state-of-the-art 3D direct numerical simulations (DNS). Extrapolating such viscous scaling laws to realistic parameter values leads to an underestimation of the magnetic energy by several orders of magnitude. The origin of this discrepancy is that fully 3D DNS cannot reach low enough values of the magnetic Prandtl number Pm. To bypass this limitation and investigate dynamo saturation at very low Pm, we focus on the vicinity of the dynamo threshold in a rapidly rotating flow: the velocity field then depends on two spatial coordinates only, while the magnetic field consists of a single Fourier mode in the third direction. We perform numerical simulations of the resulting set of reduced equations for Pm down to 2 ×10-5. This parameter regime is currently out of reach to fully 3D DNS. We show that the magnetic energy transitions from a high-Pm viscous scaling regime to a low-Pm turbulent scaling regime, the latter being independent of viscosity. The transition to the turbulent saturation regime occurs at a low value of the magnetic Prandtl number, Pm ≃10-3 , which explains why it has been overlooked by numerical studies so far.

  5. Inverse problem in Parker's dynamo

    CERN Document Server

    Reshetnyak, M Yu

    2015-01-01

    The inverse solution of the 1D Parker dynamo equations is considered. The method is based on minimization of the cost-function, which characterize deviation of the model solution properties from the desired ones. The output is the latitude distribution of the magnetic field generation sources: the $\\alpha$- and $\\omega$-effects. Minimization is made using the Monte-Carlo method. The details of the method, as well as some applications, which can be interesting for the broad dynamo community, are considered: conditions when the invisible for the observer at the surface of the planet toroidal part of the magnetic field is much larger than the poloidal counterpart. It is shown that at some particular distributions of $\\alpha$ and $\\omega$ the well-known thesis that sign of the dynamo-number defines equatorial symmetry of the magnetic field to the equator plane, is violated. It is also demonstrated in what circumstances magnetic field in the both hemispheres have different properties, and simple physical explanati...

  6. Statistical Mechanics of Turbulent Dynamos

    Science.gov (United States)

    Shebalin, John V.

    2014-01-01

    Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much

  7. MHD Turbulence and Magnetic Dynamos

    Science.gov (United States)

    Shebalin, John V

    2014-01-01

    Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much

  8. FPGA Implementation of Blue Whale Calls Classifier Using High-Level Programming Tool

    Directory of Open Access Journals (Sweden)

    Mohammed Bahoura

    2016-02-01

    Full Text Available In this paper, we propose a hardware-based architecture for automatic blue whale calls classification based on short-time Fourier transform and multilayer perceptron neural network. The proposed architecture is implemented on field programmable gate array (FPGA using Xilinx System Generator (XSG and the Nexys-4 Artix-7 FPGA board. This high-level programming tool allows us to design, simulate and execute the compiled design in Matlab/Simulink environment quickly and easily. Intermediate signals obtained at various steps of the proposed system are presented for typical blue whale calls. Classification performances based on the fixed-point XSG/FPGA implementation are compared to those obtained by the floating-point Matlab simulation, using a representative database of the blue whale calls.

  9. Periodic magnetorotational dynamo action as a prototype of nonlinear magnetic-field generation in shear flows.

    Science.gov (United States)

    Herault, J; Rincon, F; Cossu, C; Lesur, G; Ogilvie, G I; Longaretti, P-Y

    2011-09-01

    The nature of dynamo action in shear flows prone to magnetohydrodynamc instabilities is investigated using the magnetorotational dynamo in Keplerian shear flow as a prototype problem. Using direct numerical simulations and Newton's method, we compute an exact time-periodic magnetorotational dynamo solution to three-dimensional dissipative incompressible magnetohydrodynamic equations with rotation and shear. We discuss the physical mechanism behind the cycle and show that it results from a combination of linear and nonlinear interactions between a large-scale axisymmetric toroidal magnetic field and nonaxisymmetric perturbations amplified by the magnetorotational instability. We demonstrate that this large-scale dynamo mechanism is overall intrinsically nonlinear and not reducible to the standard mean-field dynamo formalism. Our results therefore provide clear evidence for a generic nonlinear generation mechanism of time-dependent coherent large-scale magnetic fields in shear flows and call for new theoretical dynamo models. These findings may offer important clues to understanding the transitional and statistical properties of subcritical magnetorotational turbulence.

  10. Periodic magnetorotational dynamo action as a prototype of nonlinear magnetic-field generation in shear flows

    Science.gov (United States)

    Herault, J.; Rincon, F.; Cossu, C.; Lesur, G.; Ogilvie, G. I.; Longaretti, P.-Y.

    2011-09-01

    The nature of dynamo action in shear flows prone to magnetohydrodynamc instabilities is investigated using the magnetorotational dynamo in Keplerian shear flow as a prototype problem. Using direct numerical simulations and Newton’s method, we compute an exact time-periodic magnetorotational dynamo solution to three-dimensional dissipative incompressible magnetohydrodynamic equations with rotation and shear. We discuss the physical mechanism behind the cycle and show that it results from a combination of linear and nonlinear interactions between a large-scale axisymmetric toroidal magnetic field and nonaxisymmetric perturbations amplified by the magnetorotational instability. We demonstrate that this large-scale dynamo mechanism is overall intrinsically nonlinear and not reducible to the standard mean-field dynamo formalism. Our results therefore provide clear evidence for a generic nonlinear generation mechanism of time-dependent coherent large-scale magnetic fields in shear flows and call for new theoretical dynamo models. These findings may offer important clues to understanding the transitional and statistical properties of subcritical magnetorotational turbulence.

  11. Some Recent Developments in Solar Dynamo Theory

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... We discuss the current status of solar dynamo theory and describe the dynamo model developed by our group. The toroidal magnetic field is generated in the tachocline by the strong differential rotation and rises to the solar surface due to magnetic buoyancy to create active regions. The decay of these ...

  12. Global Solar Dynamo Models: Simulations and Predictions

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Home; Journals; Journal of Astrophysics and Astronomy; Volume 29; Issue 1-2 ... Flux-transport type solar dynamos have achieved considerable success in correctly simulating many solar cycle features, and are now being used for ... We first define flux-transport dynamos and demonstrate how they work.

  13. Recent Progress in Understanding the Sun's Magnetic Dynamo

    Science.gov (United States)

    Hathaway, David. H.

    2004-01-01

    100 years ago we thought that the Sun and stars shone as a result of slow gravitational contraction over a few tens of millions of years - putting astronomers at odds with geologists who claimed that the Earth was much, much older. That mystery was solved in the 1920s and 30s with the discovery of nuclear energy (proving that the geologists had it right all along). Other scientific mysteries concerning the Sun have come and gone but three major mysteries remain: 1) How does the Sun produce sunspots with an 11-year cycle? 2) What produces the huge explosions that result in solar flares, prominence eruptions, and coronal mass ejections? and 3) Why is the Sun's outer atmosphere, the corona, so darned hot? Recent progress in solar astronomy reveals a single key to understanding all three of these mysteries.The 11-year time scale for the sunspot cycle indicates the presence of a magnetic dynamo within the Sun. For decades this dynamo was though to operate within the Sun's convection zone - the outmost 30% of the Sun where convective currents transport heat and advect magnetic lines of force. The two leading theories for the dynamo had very different models for the dynamics of the convection zone. Actual measurements of the dynamics using the techniques of helioseismology showed that both of these models had to be wrong some 20 years ago. A thin layer of strongly sheared flow at the base of the convection zone (now called the tachocline) was then taken to be the seat of the dynamo. Over the last 10 years it has become apparent that a weak meridional circulation within the convection zone also plays a key role in the dynamo. This meridional circulation has plasma rising up from the tachocline in the equatorial regions, spreading out toward the poles at a top speed of about 10-20 m/s at the surface, sinking back down to the tachocline in the polar regions, and then flowing back toward the equator at a top speed of about 1-2 m/s in the tachocline itself. Recent dynamo

  14. Dynamo transition in low-dimensional models.

    Science.gov (United States)

    Verma, Mahendra K; Lessinnes, Thomas; Carati, Daniele; Sarris, Ioannis; Kumar, Krishna; Singh, Meenakshi

    2008-09-01

    Two low-dimensional magnetohydrodynamic models containing three velocity and three magnetic modes are described. One of them (nonhelical model) has zero kinetic and current helicity, while the other model (helical) has nonzero kinetic and current helicity. The velocity modes are forced in both these models. These low-dimensional models exhibit a dynamo transition at a critical forcing amplitude that depends on the Prandtl number. In the nonhelical model, dynamo exists only for magnetic Prandtl number beyond 1, while the helical model exhibits dynamo for all magnetic Prandtl number. Although the model is far from reproducing all the possible features of dynamo mechanisms, its simplicity allows a very detailed study and the observed dynamo transition is shown to bear similarities with recent numerical and experimental results.

  15. A long-lived lunar core dynamo.

    Science.gov (United States)

    Shea, Erin K; Weiss, Benjamin P; Cassata, William S; Shuster, David L; Tikoo, Sonia M; Gattacceca, Jérôme; Grove, Timothy L; Fuller, Michael D

    2012-01-27

    Paleomagnetic measurements indicate that a core dynamo probably existed on the Moon 4.2 billion years ago. However, the subsequent history of the lunar core dynamo is unknown. Here we report paleomagnetic, petrologic, and (40)Ar/(39)Ar thermochronometry measurements on the 3.7-billion-year-old mare basalt sample 10020. This sample contains a high-coercivity magnetization acquired in a stable field of at least ~12 microteslas. These data extend the known lifetime of the lunar dynamo by 500 million years. Such a long-lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior. The inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory.

  16. Mixed sequence reader: a program for analyzing DNA sequences with heterozygous base calling.

    Science.gov (United States)

    Chang, Chun-Tien; Tsai, Chi-Neu; Tang, Chuan Yi; Chen, Chun-Houh; Lian, Jang-Hau; Hu, Chi-Yu; Tsai, Chia-Lung; Chao, Angel; Lai, Chyong-Huey; Wang, Tzu-Hao; Lee, Yun-Shien

    2012-01-01

    The direct sequencing of PCR products generates heterozygous base-calling fluorescence chromatograms that are useful for identifying single-nucleotide polymorphisms (SNPs), insertion-deletions (indels), short tandem repeats (STRs), and paralogous genes. Indels and STRs can be easily detected using the currently available Indelligent or ShiftDetector programs, which do not search reference sequences. However, the detection of other genomic variants remains a challenge due to the lack of appropriate tools for heterozygous base-calling fluorescence chromatogram data analysis. In this study, we developed a free web-based program, Mixed Sequence Reader (MSR), which can directly analyze heterozygous base-calling fluorescence chromatogram data in .abi file format using comparisons with reference sequences. The heterozygous sequences are identified as two distinct sequences and aligned with reference sequences. Our results showed that MSR may be used to (i) physically locate indel and STR sequences and determine STR copy number by searching NCBI reference sequences; (ii) predict combinations of microsatellite patterns using the Federal Bureau of Investigation Combined DNA Index System (CODIS); (iii) determine human papilloma virus (HPV) genotypes by searching current viral databases in cases of double infections; (iv) estimate the copy number of paralogous genes, such as β-defensin 4 (DEFB4) and its paralog HSPDP3.

  17. Mixed Sequence Reader: A Program for Analyzing DNA Sequences with Heterozygous Base Calling

    Directory of Open Access Journals (Sweden)

    Chun-Tien Chang

    2012-01-01

    Full Text Available The direct sequencing of PCR products generates heterozygous base-calling fluorescence chromatograms that are useful for identifying single-nucleotide polymorphisms (SNPs, insertion-deletions (indels, short tandem repeats (STRs, and paralogous genes. Indels and STRs can be easily detected using the currently available Indelligent or ShiftDetector programs, which do not search reference sequences. However, the detection of other genomic variants remains a challenge due to the lack of appropriate tools for heterozygous base-calling fluorescence chromatogram data analysis. In this study, we developed a free web-based program, Mixed Sequence Reader (MSR, which can directly analyze heterozygous base-calling fluorescence chromatogram data in .abi file format using comparisons with reference sequences. The heterozygous sequences are identified as two distinct sequences and aligned with reference sequences. Our results showed that MSR may be used to (i physically locate indel and STR sequences and determine STR copy number by searching NCBI reference sequences; (ii predict combinations of microsatellite patterns using the Federal Bureau of Investigation Combined DNA Index System (CODIS; (iii determine human papilloma virus (HPV genotypes by searching current viral databases in cases of double infections; (iv estimate the copy number of paralogous genes, such as β-defensin 4 (DEFB4 and its paralog HSPDP3.

  18. Mechanically-forced dynamos (Invited)

    Science.gov (United States)

    Le Bars, M.

    2013-12-01

    It is a commonly accepted hypothesis that convection is responsible for planetary dynamos. However, the validity of the convective dynamo model can be questioned in various planets and moons as well as in asteroids, where the constraints from thermal evolution and compositional core models are sometimes difficult to reconcile with available data from paleomagnetism and in situ measurements. Over the last few years, researches have thus been pursued to find alternative mechanisms for sustaining intense three-dimensional motions in liquid cores, a necessary ingredient for planetary dynamo. In particular, mechanical forcings driven by libration, precession, nutation and tides, have received a renewed interest, following the first studies by Malkus in the 60's. A huge reservoir of energy is available in the rotational and orbital motions of all planetary systems. If planetary bodies were completely rigid and rotating at a constant spin rate, their fluid layers in the absence of convection would also behave rigidly and follow the spin of their boundaries. But small periodic perturbations of the shape of the core/mantle boundary (i.e. dynamic tides) and/or small periodic perturbations of the direction of the spin vector (i.e. precession and nutation) and/or small periodic perturbations of the spin rate (i.e. libration) systematically perturb this rigid state. Then, each of these small perturbations is capable of triggering instabilities in fluid layers, conveying energy from the spin and orbital motions to drive intense three-dimensional flows in the liquid cores. With the view to establish a general framework for planetary applications, I will present here the basic physical ingredients of these instabilities, which involve a resonance between the considered mechanical forcing and two inertial waves of the core. I will then review the numerical and experimental validations of this generic principle, and the few magnetohydrodynamic validations of their dynamo capacity

  19. Learning Based Approach for Optimal Clustering of Distributed Program's Call Flow Graph

    Science.gov (United States)

    Abofathi, Yousef; Zarei, Bager; Parsa, Saeed

    Optimal clustering of call flow graph for reaching maximum concurrency in execution of distributable components is one of the NP-Complete problems. Learning automatas (LAs) are search tools which are used for solving many NP-Complete problems. In this paper a learning based algorithm is proposed to optimal clustering of call flow graph and appropriate distributing of programs in network level. The algorithm uses learning feature of LAs to search in state space. It has been shown that the speed of reaching to solution increases remarkably using LA in search process, and it also prevents algorithm from being trapped in local minimums. Experimental results show the superiority of proposed algorithm over others.

  20. The DYNAMO Project: An Introduction

    Directory of Open Access Journals (Sweden)

    R. C. Ferrier

    1998-01-01

    Full Text Available European concerns about the consequences of anthropogenic impacts on environmental quality have led to the establishment of various dynamic modelling approaches through which the consequences of impacts over time can be assessed. Similarly, throughout Europe, there has been extensive collection of regional data on 'environmental capital' resulting in the production of wide area mapping of environmental quality (soils, land use etc. The aim of the DYNAMO was to integrate data and models, specifically; (1 to enhance the existing process based models to evaluate the impacts of multiple drivers of environmental change; (2 to evaluate these models at intensively studied (and manipulated catchments and stands; (3 to scale up in time from observations collected over several years to predict the long term impacts over decades, and (4 to scale up in space from the individual site level to regional, National and European scale. The project aims to develop and enhance regional modelling approaches so that European scale impacts of acidic deposition, land use (forestry practices and global change can be determined without compromising process level understanding of ecosystem function. The DYNAMO project contributes to the EU TERI (Terrestrial Ecosystems Research Initiative framework of the Environment and Climate Programme of the European Commission.

  1. Dynamo transition in a five-mode helical model

    OpenAIRE

    Kumar, Rohit; Wahi, Pankaj

    2017-01-01

    We construct a five-mode helical dynamo model containing three velocity and two magnetic modes and solve it analytically. This model exhibits dynamo transition via supercritical pitchfork bifurcation. We show that the critical magnetic Reynolds number for dynamo transition ($\\mathrm{Rm}_c$) asymptotes to constant values for very low and very high magnetic Prandtl numbers ($\\mathrm{Pm}$). Beyond dynamo transition, secondary bifurcations lead to periodic, quasi-periodic, and chaotic dynamo stat...

  2. Nonlinear MHD dynamo operating at equipartition

    DEFF Research Database (Denmark)

    Archontis, V.; Dorch, Bertil; Nordlund, Åke

    2007-01-01

    Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy-equipartition a......Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy......-equipartition and a turbulent state. The generation and evolution of such strong magnetic fields is relevant for the understanding of dynamo action that occurs in stars and other astrophysical objects. Aims.We study the mode of operation of this dynamo, in the linear and non-linear saturation regimes. We also consider......, and that it can saturate at a level significantly higher than intermittent turbulent dynamos, namely at energy equipartition, for high values of the magnetic and fluid Reynolds numbers. The equipartition solution however does not remain time-independent during the simulation but exhibits a much more intricate...

  3. HYSTERESIS BETWEEN DISTINCT MODES OF TURBULENT DYNAMOS

    Energy Technology Data Exchange (ETDEWEB)

    Karak, Bidya Binay; Brandenburg, Axel [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden); Kitchatinov, Leonid L., E-mail: bbkarak@nordita.org [Institute of Solar-Terrestrial Physics, P.O. Box 291, Irkutsk 664033 (Russian Federation)

    2015-04-20

    Nonlinear mean-field models of the solar dynamo show long-term variability, which may be relevant to different states of activity inferred from long-term radiocarbon data. This paper is aimed at probing the dynamo hysteresis predicted by the recent mean-field models of Kitchatinov and Olemskoy with direct numerical simulations. We perform three-dimensional (3D) simulations of large-scale dynamos in a shearing box with helically forced turbulence. As an initial condition, we either take a weak random magnetic field or we start from a snapshot of an earlier simulation. Two quasi-stable states are found to coexist in a certain range of parameters close to the onset of the large-scale dynamo. The simulations converge to one of these states depending on the initial conditions. When either the fractional helicity or the magnetic Prandtl number is increased between successive runs above the critical value for onset of the dynamo, the field strength jumps to a finite value. However, when the fractional helicity or the magnetic Prandtl number is then decreased again, the field strength stays at a similar value (strong field branch) even below the original onset. We also observe intermittent decaying phases away from the strong field branch close to the point where large-scale dynamo action is just possible. The dynamo hysteresis seen previously in mean-field models is thus reproduced by 3D simulations. Its possible relation to distinct modes of solar activity such as grand minima is discussed.

  4. Solar Dynamo Near Tachocline and Magnetic Monopoly

    Science.gov (United States)

    Kryvodubskyj, Valery N.

    To explain the observed magnetic anomaly of the polar Sun's field the turbulent dynamo mechanism based on the joint action of mean helical turbulence and differential rotation (alpha-omega-dynamo) was used near tachocline in the solar convection zone (SCZ). The global magnetic field modes (odd or even ones) excited by dynamo depend on the eigenvalue Kh for a Parker dynamo-wave (K is the wave number of the dynamo-wave and h is the extent of the dynamo region). Estimations of the helicity-parameter and radial angular-velocity gradient based on the most recent helioseismological measurements at the growth phase of solar cycle 23 were obtained using the mixing-length approximation. For the SCZ model by Stix (1989) these estimations indicate that the alpha-omega-dynamo mechanism near the tachocline most efficiency excites the poloidal field main odd mode dipole (Kh ~ -7); while the physical conditions at latitudes above 50 degrees are more favourable for the exitation of the lowest even mode quadrupole (Kh ~ +8). The resulting north-south magnetic asymmetry of the poloidal field can explain the magnetic anomaly (""monopoly"" structure) of the polar fields observed near solar-cycle maxima.

  5. Soft iron and axisymetric eigenmodes in the von-Karman-Sodium dynamo

    Science.gov (United States)

    Giesecke, A.; Stefani, F.; Gerbeth, G.

    2012-04-01

    In the Cadarache von-Karman-Sodium (VKS) dynamo experiment magnetic field excitation is generated by a turbulent flow of liquid sodium. In the experiment this so called von-Karman-like flow is driven by two counter-rotating impellers that are located close to the end-caps of a cylindrical vessel. Despite of extensive numerical and experimental efforts the very nature of the VKS dynamo and its surprising properties still remain unclear. Firstly, dynamo action is obtained only when (at least one of) the flow driving impellers are made of soft iron with a relative permeability around 65. Moreover, and in apparent contradiction with Cowling's anti-dynamo theorem, the geometric structure of the observed magnetic field is dominated by an axisymmetric field. Our kinematic simulations of an axisymmetric model of the Cadarache dynamo show a close connection between the exclusive occurrence of dynamo action with soft iron impellers and the axisymmetry of the magnetic field. We observe two distinct classes of axisymmetric eigenmodes, a purely toroidal mode that is amplified by paramagnetic pumping at the fluid-disk interface and a mixed mode consisting of a poloidal and a toroidal contribution that is rather insensitive to the disk permeability. In the limit of large permeability, the purely toroidal mode is close to the onset of dynamo action with a growth-rate that is rather independent of the flow field. This mode is located near to and in the high permeability disks and becomes the leading mode when the disk permeability exceeds a critical value. However, since in our axisymmetric configuration the purely toroidal mode is decoupled from any poloidal field component no dynamo action can be expected from this mode. The purely toroidal mode and its strong amplification by paramagnetic pumping at the fluid-disks interface can be obtained only by explicitly considering the internal permeability distribution. This mode does not exist in case of highly conducting disks or in

  6. Statistical simulation of the magnetorotational dynamo.

    Science.gov (United States)

    Squire, J; Bhattacharjee, A

    2015-02-27

    Turbulence and dynamo induced by the magnetorotational instability (MRI) are analyzed using quasilinear statistical simulation methods. It is found that homogenous turbulence is unstable to a large-scale dynamo instability, which saturates to an inhomogenous equilibrium with a strong dependence on the magnetic Prandtl number (Pm). Despite its enormously reduced nonlinearity, the dependence of the angular momentum transport on Pm in the quasilinear model is qualitatively similar to that of nonlinear MRI turbulence. This demonstrates the importance of the large-scale dynamo and suggests how dramatically simplified models may be used to gain insight into the astrophysically relevant regimes of very low or high Pm.

  7. Statistical Simulation of the Magnetorotational Dynamo

    Energy Technology Data Exchange (ETDEWEB)

    Squire, Jonathan [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Bhattacharjee, Amitava [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Max Planck Society, Garching (Germany). Max Planck Inst. for Astrophysik

    2015-02-01

    Turbulence and dynamo induced by the magnetorotational instability (MRI) are analyzed using quasilinear statistical simulation methods. It is found that homogenous turbulence is unstable to a large-scale dynamo instability, which saturates to an inhomogenous equilibrium with a strong dependence on the magnetic Prandtl number (Pm). Despite its enormously reduced nonlinearity, the dependence of the angular momentum transport on Pm in the quasilinear model is qualitatively similar to that of nonlinear MRI turbulence. This demonstrates the importance of the large-scale dynamo and suggests how dramatically simplified models may be used to gain insight into the astrophysically relevant regimes of very low or high Pm.

  8. The magnetic universe geophysical and astrophysical dynamo theory

    CERN Document Server

    Rüdiger, Günther

    2004-01-01

    Magnetism is one of the most pervasive features of the Universe, with planets, stars and entire galaxies all having associated magnetic fields. All of these fields are generated by the motion of electrically conducting fluids, the so-called dynamo effect. The precise details of what drives the motion, and indeed what the fluid consists of, differ widely though. In this work the authors draw upon their expertise in geophysical and astrophysical MHD to explore some of these phenomena, and describe the similarities and differences between different magnetized objects. They also explain why magn

  9. Parity fluctuations in stellar dynamos

    Science.gov (United States)

    Moss, D. L.; Sokoloff, D. D.

    2017-10-01

    Observations of the solar butterfly diagram from sunspot records suggest persistent fluctuations in parity, away from the overall, approximately dipolar pattern. A simple mean-field dynamo model is used with a solar-like rotation law and perturbed α effect. The parity of the magnetic field relative to the rotational equator can demonstrate can be described as resonance behavior, while the magnetic energy behaves in a more or less expected way. Possible applications of this effect are discussed in the context of various deviations of the solar magnetic field from dipolar symmetry, as reported from analyses of archival sunspot data. The model produces fluctuations in field parity, and hence in the butterfly diagram, that are consistent with observed fluctuaions in solar behavior.

  10. Dynamo Models of the Solar Cycle

    Directory of Open Access Journals (Sweden)

    Paul Charbonneau

    2010-09-01

    Full Text Available This paper reviews recent advances and current debates in modeling the solar cycle as a hydromagnetic dynamo process. Emphasis is placed on (relatively simple dynamo models that are nonetheless detailed enough to be comparable to solar cycle observations. After a brief overview of the dynamo problem and of key observational constraints, we begin by reviewing the various magnetic field regeneration mechanisms that have been proposed in the solar context. We move on to a presentation and critical discussion of extant solar cycle models based on these mechanisms. We then turn to the origin and consequences of fluctuations in these models, including amplitude and parity modulation, chaotic behavior, intermittency, and predictability. The paper concludes with a discussion of our current state of ignorance regarding various key questions relating to the explanatory framework offered by dynamo models of the solar cycle.

  11. Saturation of the turbulent dynamo.

    Science.gov (United States)

    Schober, J; Schleicher, D R G; Federrath, C; Bovino, S; Klessen, R S

    2015-08-01

    The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence.

  12. Calling the lp_solve Linear Program Software from R, S-PLUS and Excel

    Directory of Open Access Journals (Sweden)

    Samuel E. Buttrey

    2005-05-01

    Full Text Available We present a link that allows R, S-PLUS and Excel to call the functions in the lp_solve system. lp_solve is free software (licensed under the GNU Lesser GPL that solves linear and mixed integer linear programs of moderate size (on the order of 10,000 variables and 50,000 constraints. R does not include this ability (though two add-on packages offer linear programs without integer variables, while S-PLUS users need to pay extra for the NuOPT library in order to solve these problems. Our link manages the interface between these statistical packages and lp_solve. Excel has a built-in add-in named Solver that is capable of solving mixed integer programs, but only with fewer than 200 variables. This link allows Excel users to handle substantially larger problems at no extra cost. While our primary concern has been the Windows operating system, the package has been tested on some Unix-type systems as well.

  13. New results on an equipartition dynamo

    DEFF Research Database (Denmark)

    Dorch, S. B. F.; Archontis, V.

    2006-01-01

    linear and non-linear saturation regimes. The means were 3-d non-linear MHD simulations and visualization using the high resolution numerical scheme by Nordlund, Galsgaard and others. We have found that the dynamo has a high growth rate in the linear regime, and that it can saturate at a level...... is amplified and sustained, between experiments with varying Reynolds numbers are illustrated. The conclusion is that strong astrophysical magnetic fields at equipartition are not necessarily generated by turbulent dynamos....

  14. Time scales separation for dynamo action

    OpenAIRE

    Dormy, Emmanuel; Gerard-Varet, David

    2008-01-01

    International audience; The study of dynamo action in astrophysical objects classically involves two timescales: the slow diffusive one and the fast advective one. We investigate the possibility of field amplification on an intermediate timescale associated with time dependent modulations of the flow. We consider a simple steady configuration for which dynamo action is not realised. We study the effect of time dependent perturbations of the flow. We show that {some} vanishing {low frequency} ...

  15. Planetary Dynamos from a Solar Perspective

    Science.gov (United States)

    Christensen, U. R.; Schmitt, D.; Rempel, M.

    2009-04-01

    Direct numerical simulations of the geodynamo and other planetary dynamos have been successful in reproducing the observed magnetic fields. We first give an overview on the fundamental properties of planetary magnetism. We review the concepts and main results of planetary dynamo modeling, contrasting them with the solar dynamo. In planetary dynamos the density stratification plays no major role and the magnetic Reynolds number is low enough to allow a direct simulation of the magnetic induction process using microscopic values of the magnetic diffusivity. The small-scale turbulence of the flow cannot be resolved and is suppressed by assuming a viscosity far in excess of the microscopic value. Systematic parameter studies lead to scaling laws for the magnetic field strength or the flow velocity that are independent of viscosity, indicating that the models are in the same dynamical regime as the flow in planetary cores. Helical flow in convection columns that are aligned with the rotation axis play an important role for magnetic field generation and forms the basis for a macroscopic α-effect. Depending on the importance of inertial forces relative to rotational forces, either dynamos with a dominant axial dipole or with a small-scale multipolar magnetic field are found. Earth is predicted to lie close to the transition point between both classes, which may explain why the dipole undergoes reversals. Some models fit the properties of the geomagnetic field in terms of spatial power spectra, magnetic field morphology and details of the reversal behavior remarkably well. Magnetic field strength in the dipolar dynamo regime is controlled by the available power and found to be independent of rotation rate. Predictions for the dipole moment agree well with the observed field strength of Earth and Jupiter and moderately well for other planets. Dedicated dynamo models for Mercury, Saturn, Uranus and Neptune, which assume stably stratified layers above or below the dynamo

  16. A deep dynamo generating Mercury's magnetic field.

    Science.gov (United States)

    Christensen, Ulrich R

    2006-12-21

    Mercury has a global magnetic field of internal origin and it is thought that a dynamo operating in the fluid part of Mercury's large iron core is the most probable cause. However, the low intensity of Mercury's magnetic field--about 1% the strength of the Earth's field--cannot be reconciled with an Earth-like dynamo. With the common assumption that Coriolis and Lorentz forces balance in planetary dynamos, a field thirty times stronger is expected. Here I present a numerical model of a dynamo driven by thermo-compositional convection associated with inner core solidification. The thermal gradient at the core-mantle boundary is subadiabatic, and hence the outer region of the liquid core is stably stratified with the dynamo operating only at depth, where a strong field is generated. Because of the planet's slow rotation the resulting magnetic field is dominated by small-scale components that fluctuate rapidly with time. The dynamo field diffuses through the stable conducting region, where rapidly varying parts are strongly attenuated by the skin effect, while the slowly varying dipole and quadrupole components pass to some degree. The model explains the observed structure and strength of Mercury's surface magnetic field and makes predictions that are testable with space missions both presently flying and planned.

  17. Approximate Dynamic Programming techniques for skill-based routing in call centres

    NARCIS (Netherlands)

    Roubos, D.; Bhulai, S.

    2012-01-01

    We consider the problem of dynamic multi-skill routing in call centers. Calls from different customer classes are offered to the call center according to a Poisson process. The agents are grouped into pools according to their heterogeneous skill sets that determine the calls that they can handle.

  18. High Performance Computing Application: Solar Dynamo Model Project II, Corona and Heliosphere Component Initialization, Integration and Validation

    Science.gov (United States)

    2015-06-24

    AFRL-RD-PS- TR-2015-0028 AFRL-RD-PS- TR-2015-0028 HIGH PERFORMANCE COMPUTING APPLICATION: SOLAR DYNAMO MODEL PROJECT II; CORONA AND HELIOSPHERE...Dynamo Model Project II, Corona and Heliosphere Component Initialization, Integration and Validation 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6...Approved for public release; distribution is unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT This report reviews the status of current day solar corona and

  19. Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?

    Science.gov (United States)

    Riols, A.; Rincon, F.; Cossu, C.; Lesur, G.; Ogilvie, G. I.; Longaretti, P.-Y.

    2017-02-01

    In Keplerian accretion disks, turbulence and magnetic fields may be jointly excited through a subcritical dynamo mechanisminvolving magnetorotational instability (MRI). This dynamo may notably contribute to explaining the time-variability of various accreting systems, as high-resolution simulations of MRI dynamo turbulence exhibit statistical self-organization into large-scale cyclic dynamics. However, understanding the physics underlying these statistical states and assessing their exact astrophysical relevance is theoretically challenging. The study of simple periodic nonlinear MRI dynamo solutions has recently proven useful in this respect, and has highlighted the role of turbulent magnetic diffusion in the seeming impossibility of a dynamo at low magnetic Prandtl number (Pm), a common regime in disks. Arguably though, these simple laminar structures may not be fully representative of the complex, statistically self-organized states expected in astrophysical regimes. Here, we aim at closing this seeming discrepancy by reporting the numerical discovery of exactly periodic, yet semi-statistical "chimeral MRI dynamo states" which are the organized outcome of a succession of MRI-unstable, non-axisymmetric dynamical stages of different forms and amplitudes. Interestingly, these states, while reminiscent of the statistical complexity of turbulent simulations, involve the same physical principles as simpler laminar cycles, and their analysis further confirms the theory that subcritical turbulent magnetic diffusion impedes the sustainment of an MRI dynamo at low Pm. Overall, chimera dynamo cycles therefore offer an unprecedented dual physical and statistical perspective on dynamos in rotating shear flows, which may prove useful in devising more accurate, yet intuitive mean-field models of time-dependent turbulent disk dynamos. Movies associated to Fig. 1 are available at http://www.aanda.org

  20. The Ghost in the Machine: Are "Teacherless" CALL Programs Really Possible?

    Science.gov (United States)

    Davies, Ted; Williamson, Rodney

    1998-01-01

    Reflects critically on pedagogical issues in the production of computer-assisted language learning (CALL) courseware and ways CALL has affected the practice of language learning. Concludes that if CALL is to reach full potential, it must be more than a simple medium of information; it should provide a teaching/learning process, with the real…

  1. Core and Dynamo Evolution in Small Solar System Bodies

    Science.gov (United States)

    Scheinberg, A.; Elkins-Tanton, L. T.; Schubert, G.

    2013-10-01

    We produce a core solidification timeline and core chemical profile for planetesimals, then explore the potential strength and longevity of a dynamo. Different sulfur content and adiabat slope may create a dynamo qualitatively different than Earth's.

  2. Turbulent dynamo in a collisionless plasma.

    Science.gov (United States)

    Rincon, François; Califano, Francesco; Schekochihin, Alexander A; Valentini, Francesco

    2016-04-12

    Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.

  3. Magnetorotational dynamo action in the shearing box

    Science.gov (United States)

    Walker, Justin; Boldyrev, Stanislav

    2017-09-01

    Magnetic dynamo action caused by the magnetorotational instability is studied in the shearing-box approximation with no imposed net magnetic flux. Consistent with recent studies, the dynamo action is found to be sensitive to the aspect ratio of the box: it is much easier to obtain in tall boxes (stretched in the direction normal to the disc plane) than in long boxes (stretched in the radial direction). Our direct numerical simulations indicate that the dynamo is possible in both cases, given a large enough magnetic Reynolds number. To explain the relatively larger effort required to obtain the dynamo action in a long box, we propose that the turbulent eddies caused by the instability most efficiently fold and mix the magnetic field lines in the radial direction. As a result, in the long box the scale of the generated strong azimuthal (stream-wise directed) magnetic field is always comparable to the scale of the turbulent eddies. In contrast, in the tall box the azimuthal magnetic flux spreads in the vertical direction over a distance exceeding the scale of the turbulent eddies. As a result, different vertical sections of the tall box are permeated by large-scale non-zero azimuthal magnetic fluxes, facilitating the instability. In agreement with this picture, the cases when the dynamo is efficient are characterized by a strong intermittency of the local azimuthal magnetic fluxes.

  4. Dynamic motif occupancy (DynaMO) analysis identifies transcription factors and their binding sites driving dynamic biological processes.

    Science.gov (United States)

    Kuang, Zheng; Ji, Zhicheng; Boeke, Jef D; Ji, Hongkai

    2018-01-09

    Biological processes are usually associated with genome-wide remodeling of transcription driven by transcription factors (TFs). Identifying key TFs and their spatiotemporal binding patterns are indispensable to understanding how dynamic processes are programmed. However, most methods are designed to predict TF binding sites only. We present a computational method, dynamic motif occupancy analysis (DynaMO), to infer important TFs and their spatiotemporal binding activities in dynamic biological processes using chromatin profiling data from multiple biological conditions such as time-course histone modification ChIP-seq data. In the first step, DynaMO predicts TF binding sites with a random forests approach. Next and uniquely, DynaMO infers dynamic TF binding activities at predicted binding sites using their local chromatin profiles from multiple biological conditions. Another landmark of DynaMO is to identify key TFs in a dynamic process using a clustering and enrichment analysis of dynamic TF binding patterns. Application of DynaMO to the yeast ultradian cycle, mouse circadian clock and human neural differentiation exhibits its accuracy and versatility. We anticipate DynaMO will be generally useful for elucidating transcriptional programs in dynamic processes. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

  5. Competing kinematic dynamo mechanisms in rotating convection with shear

    Science.gov (United States)

    Proctor, Michael R. E.; Hughes, David W.

    2011-08-01

    Following earlier work by Hughes & Proctor (2009) on the role of velocity shear in convectively driven dynamos, we present preliminary results on the nature of dynamo action due to modified flows derived by filtration from the full convective flow. The results suggest that filtering the flow fields has surprisingly little effect on the dynamo growth rates.

  6. Dynamo Models of the Solar Cycle

    Directory of Open Access Journals (Sweden)

    Charbonneau Paul

    2005-06-01

    Full Text Available This paper reviews recent advances and current debates in modeling the solar cycle as a hydromagnetic dynamo process. Emphasis is placed on (relatively simple dynamo models that are nonetheless detailed enough to be comparable to solar cycle observations. After a brief overview of the dynamo problem and of key observational constraints, we begin by reviewing the various magnetic field regeneration mechanisms that have been proposed in the solar context. We move on to a presentation and critical discussion of extant solar cycle models based on these mechanisms. We then turn to the origin of fluctuations in these models, including amplitude and parity modulation, chaotic behavior, and intermittency. The paper concludes with a discussion of our current state of ignorance regarding various key questions, the most pressing perhaps being the identification of the physical mechanism(s responsible for the generation of the Sun's poloidal magnetic field component.

  7. Shear dynamo problem: Quasilinear kinematic theory.

    Science.gov (United States)

    Sridhar, S; Subramanian, Kandaswamy

    2009-04-01

    Large-scale dynamo action due to turbulence in the presence of a linear shear flow is studied. Our treatment is quasilinear and kinematic but is nonperturbative in the shear strength. We derive the integrodifferential equation for the evolution of the mean magnetic field by systematic use of the shearing coordinate transformation and the Galilean invariance of the linear shear flow. For nonhelical turbulence the time evolution of the cross-shear components of the mean field does not depend on any other components excepting themselves. This is valid for any Galilean-invariant velocity field, independent of its dynamics. Hence the shear-current assisted dynamo is essentially absent, although large-scale nonhelical dynamo action is not ruled out.

  8. Planetary dynamo and protocore concept

    Science.gov (United States)

    Pushkarev, Y.; Starchenko, S. V.

    2013-09-01

    the core of just formatted Earth. This protocore is slowly melted under the surface influence of the overheated liquid core (figure 1). It grows up to its modern size when the solid core is small relic of the protocore. Such protocore concept [5] resolves the problem of the energy source for geodynamo and for plume activity in the mantle. In case of validity of this concept the mantle should be supplemented by silicate material from the protocore with primitive isotope composition of the lead but which can't be the result of the liquid core crystallization. The preliminary results are in our interpretation of compilation from [2] shown in figure 2 below. Additional argument to the validity of our protocore concept could be the primitive isotope composition of lead in combination with the primary helium enriched by isotope He-3. Following the currently accepted crystallization concept Martian dynamo should be stopped only when the central solid core occupies almost all the volume of Martian core. So, nowadays the liquid core should be sufficiently smaller than the solid one. That contradicts to all the available models of the Martian interior. To resolve this paradox we apply our protocore concept to Mars following figure 3. Paleomagnetic samples from Moon demonstrate very high (a few times larger than on the modern Earth surface) intensity of the magnetic field that was in operation from about 4.2 till 3.6 billion years ago [1]. The currently accepted compositional (under crystallization concept) and thermal dynamo of the Moon are not able to provide enough energy to support so higher magnetic intensity and for so long period. While a Lunar dynamo under our protocore concept could easy provide required energy source for the intensive compositional convection during that long period. Lunar paleomagnetic samples indicate magnetic intensity of order geomagnetic one at about 3.5-3 GA that could be supported by the known crystallization of a liquid core. Sufficiently

  9. Planetary dynamos driven by helical waves - II

    Science.gov (United States)

    Davidson, P. A.; Ranjan, A.

    2015-09-01

    In most numerical simulations of the Earth's core the dynamo resides outside the tangent cylinder and may be crudely classified as being of the α2 type. In this region the flow comprises a sea of thin columnar vortices aligned with the rotation axis, taking the form of alternating cyclones and anticyclones. The dynamo is thought to be driven by these columnar vortices within which the flow is observed to be highly helical, helicity being a crucial ingredient of planetary dynamos. As noted in Davidson, one of the mysteries of this dynamo cartoon is the origin of the helicity, which is observed to be positive in the south and negative in the north. While Ekman pumping at the mantle can induce helicity in some of the overly viscous numerical simulations, it is extremely unlikely to be a significant source within planets. In this paper we return to the suggestion of Davidson that the helicity observed in the less viscous simulations owes its existence to helical wave packets, launched in and around the equatorial plane where the buoyancy flux is observed to be strong. Here we show that such wave packets act as a potent source of planetary helicity, constituting a simple, robust mechanism that yields the correct sign for h north and south of the equator. Since such a mechanism does not rely on the presence of a mantle, it can operate within both the Earth and the gas giants. Moreover, our numerical simulations show that helical wave packets dispersing from the equator produce a random sea of thin, columnar cyclone/anticyclone pairs, very like those observed in the more strongly forced dynamo simulations. We examine the local dynamics of helical wave packets dispersing from the equatorial regions, as well as the overall nature of an α2-dynamo driven by such wave packets. Our local analysis predicts the mean emf induced by helical waves, an analysis that rests on a number of simple approximations which are consistent with our numerical experiments, while our global

  10. Mean-field magnetohydrodynamics and dynamo theory

    CERN Document Server

    Krause, F

    2013-01-01

    Mean-Field Magnetohydrodynamics and Dynamo Theory provides a systematic introduction to mean-field magnetohydrodynamics and the dynamo theory, along with the results achieved. Topics covered include turbulence and large-scale structures; general properties of the turbulent electromotive force; homogeneity, isotropy, and mirror symmetry of turbulent fields; and turbulent electromotive force in the case of non-vanishing mean flow. The turbulent electromotive force in the case of rotational mean motion is also considered. This book is comprised of 17 chapters and opens with an overview of the gen

  11. Dynamo transition in a five-mode helical model

    Science.gov (United States)

    Kumar, Rohit; Wahi, Pankaj

    2017-09-01

    We construct a five-mode helical dynamo model containing three velocity and two magnetic modes and solve it analytically. This model exhibits dynamo transition via supercritical pitchfork bifurcation. We show that the critical magnetic Reynolds number for dynamo transition (Rmc) asymptotes to constant values for very low and very high magnetic Prandtl numbers (Pm). Beyond dynamo transition, secondary bifurcations lead to periodic, quasi-periodic, and chaotic dynamo states as the forcing amplitude is increased and chaos appears through a quasi-periodic route.

  12. Pembuatan Kakas Pendeteksi Unused Method pada Kode Program PHP dengan Framework CodeIgniter Menggunakan Call Graph

    Directory of Open Access Journals (Sweden)

    Divi Galih Prasetyo Putri

    2014-03-01

    Full Text Available Proses evolusi dan perawatan dari sebuah sistem merupakan proses yang sangat penting dalam rekayasa perangkat lunak tidak terkecuali pada aplikasi web. Pada proses ini kebanyakan pengembang tidak lagi berpatokan pada rancangan sistem. Hal ini menyebabkan munculnya unused method. Bagian-bagian program ini tidak lagi terpakai namun masih berada dalam sistem. Keadaan ini meningkatkan kompleksitas dan mengurangi tingkat understandability sistem. Guna mendeteksi adanya unused method pada progam diperlukan teknik untuk melakukan code analysis. Teknik static analysis yang digunakan memanfaatkan call graph yang dibangun dari kode program untuk mengetahui adanya unused method. Call graph dibangun berdasarkan pemanggilan antar method. Aplikasi ini mendeteksi unused method pada kode program PHP yang dibangun menggunakan framework CodeIgniter. Kode program sebagai inputan diurai kedalam bentuk Abstract Syntax Tree (AST yang kemudian dimanfaatkan untuk melakukan analisis terhadap kode program. Proses analisis tersebut kemudian menghasilkan sebuah call graph. Dari call graph yang dihasilkan dapat dideteksi method-method mana saja yang tidak berhasil ditelusuri dan tergolong kedalam unused method. Kakas telah diuji coba pada 5 aplikasi PHP dengan hasil  rata-rata nilai presisi sistem sebesar 0.749 dan recall sebesar 1.

  13. Limited role of spectra in dynamo theory: coherent versus random dynamos.

    Science.gov (United States)

    Tobias, Steven M; Cattaneo, Fausto

    2008-09-19

    We discuss the importance of phase information and coherence times in determining the dynamo properties of turbulent flows. We compare the kinematic dynamo properties of three flows with the same energy spectrum. The first flow is dominated by coherent structures with nontrivial phase information and long eddy coherence times, the second has random phases and long-coherence time, the third has nontrivial phase information, but short coherence time. We demonstrate that the first flow is the most efficient kinematic dynamo, owing to the presence of sustained stretching and constructive folding. We argue that these results place limitations on the possible inferences of the dynamo properties of flows from the use of spectra alone, and that the role of coherent structures must always be accounted for.

  14. Feasibility of a magma ocean dynamo on Mars

    Science.gov (United States)

    Helffrich, George

    2017-12-01

    Crustal magnetization of rocks in regions of Mars surface testifies to an era of dynamo activity. I examine the possibility that the dynamo that operated then, in the first 400-600 Ma after Mars formed, was powered by a crystallizing subsurface magma ocean. Of the ways that a magma ocean dynamo could operate, on Mars only turbulent and magnetostrophic dynamos seem feasible; geostrophic dynamos do not seem so unless very high heat flows, 100-1000 times present, are invoked. Given the anticipated information from the future InSight lander mission, it will be difficult to assess where the dynamo originated unless an inner core is discovered, rendering the dynamo likely to have operated in the core. [Figure not available: see fulltext.

  15. Kinematic dynamo action in square and hexagonal patterns.

    Science.gov (United States)

    Favier, B; Proctor, M R E

    2013-11-01

    We consider kinematic dynamo action in rapidly rotating Boussinesq convection just above onset. The velocity is constrained to have either a square or a hexagonal pattern. For the square pattern, large-scale dynamo action is observed at onset, with most of the magnetic energy being contained in the horizontally averaged component. As the magnetic Reynolds number increases, small-scale dynamo action becomes possible, reducing the overall growth rate of the dynamo. For the hexagonal pattern, the breaking of symmetry between up and down flows results in an effective pumping velocity. For intermediate rotation rates, this additional effect can prevent the growth of any mean-field dynamo, so that only a small-scale dynamo is eventually possible at large enough magnetic Reynolds number. For very large rotation rates, this pumping term becomes negligible, and the dynamo properties of square and hexagonal patterns are qualitatively similar. These results hold for both perfectly conducting and infinite magnetic permeability boundary conditions.

  16. Kinematic dynamo action in square and hexagonal patterns

    CERN Document Server

    Favier, B

    2013-01-01

    We consider kinematic dynamo action in rapidly rotating Boussinesq convection just above onset. The velocity is constrained to have either a square or a hexagonal pattern. For the square pattern, large-scale dynamo action is observed at onset, with most of the magnetic energy being contained in the horizontally-averaged component. As the magnetic Reynolds number increases, small-scale dynamo action becomes possible, reducing the overall growth rate of the dynamo. For the hexagonal pattern, the breaking of symmetry between up and down flows results in an effective pumping velocity. For intermediate rotation rates, this additional effect can prevent the growth of any mean-field dynamo, so that only a small-scale dynamo is eventually possible at large enough magnetic Reynolds number. For very large rotation rates, this pumping term becomes negligible, and the dynamo properties of square and hexagonal patterns are qualitatively similar. These results hold for both perfectly conducting and infinite magnetic permea...

  17. 77 FR 61740 - Call for Applications for the International Buyer Program-Calendar Years 2014 and 2015

    Science.gov (United States)

    2012-10-11

    ... attendees whose native language will not be English. (j) Level of Cooperation: The applicant demonstrates a... International Trade Administration Call for Applications for the International Buyer Program-- Calendar Years 2014 and 2015 AGENCY: International Trade Administration, Department of Commerce. ACTION: Notice and...

  18. 75 FR 16125 - Call for Co-Sponsors for Office of Healthcare Quality's Programs to Strengthen Coordination and...

    Science.gov (United States)

    2010-03-31

    ...), Office of Public Health and Science (OPHS), Office for Healthcare Quality (OHQ) announces the opportunity... Healthcare Quality, Office of Public Health and Science. BILLING CODE 4150-28-P ... HUMAN SERVICES Call for Co-Sponsors for Office of Healthcare Quality's Programs to Strengthen...

  19. Stochastic flux freezing and magnetic dynamo.

    Science.gov (United States)

    Eyink, Gregory L

    2011-05-01

    Magnetic flux conservation in turbulent plasmas at high magnetic Reynolds numbers is argued neither to hold in the conventional sense nor to be entirely broken, but instead to be valid in a statistical sense associated to the "spontaneous stochasticity" of Lagrangian particle trajectories. The latter phenomenon is due to the explosive separation of particles undergoing turbulent Richardson diffusion, which leads to a breakdown of Laplacian determinism for classical dynamics. Empirical evidence is presented for spontaneous stochasticity, including numerical results. A Lagrangian path-integral approach is then exploited to establish stochastic flux freezing for resistive hydromagnetic equations and to argue, based on the properties of Richardson diffusion, that flux conservation must remain stochastic at infinite magnetic Reynolds number. An important application of these results is the kinematic, fluctuation dynamo in nonhelical, incompressible turbulence at magnetic Prandtl number (Pr(m)) equal to unity. Numerical results on the Lagrangian dynamo mechanisms by a stochastic particle method demonstrate a strong similarity between the Pr(m)=1 and 0 dynamos. Stochasticity of field-line motion is an essential ingredient of both. Finally, some consequences for nonlinear magnetohydrodynamic turbulence, dynamo, and reconnection are briefly considered. © 2011 American Physical Society

  20. Magnetic Helicity and the Solar Dynamo

    Science.gov (United States)

    Canfield, Richard C.

    1997-01-01

    The objective of this investigation is to open a new window into the solar dynamo, convection, and magnetic reconnection through measurement of the helicity density of magnetic fields in the photosphere and tracing of large-scale patterns of magnetic helicity in the corona.

  1. Magnetic reversals from planetary dynamo waves.

    Science.gov (United States)

    Sheyko, Andrey; Finlay, Christopher C; Jackson, Andrew

    2016-11-24

    A striking feature of many natural dynamos is their ability to undergo polarity reversals. The best documented example is Earth's magnetic field, which has reversed hundreds of times during its history. The origin of geomagnetic polarity reversals lies in a magnetohydrodynamic process that takes place in Earth's core, but the precise mechanism is debated. The majority of numerical geodynamo simulations that exhibit reversals operate in a regime in which the viscosity of the fluid remains important, and in which the dynamo mechanism primarily involves stretching and twisting of field lines by columnar convection. Here we present an example of another class of reversing-geodynamo model, which operates in a regime of comparatively low viscosity and high magnetic diffusivity. This class does not fit into the paradigm of reversal regimes that are dictated by the value of the local Rossby number (the ratio of advection to Coriolis force). Instead, stretching of the magnetic field by a strong shear in the east-west flow near the imaginary cylinder just touching the inner core and parallel to the axis of rotation is crucial to the reversal mechanism in our models, which involves a process akin to kinematic dynamo waves. Because our results are relevant in a regime of low viscosity and high magnetic diffusivity, and with geophysically appropriate boundary conditions, this form of dynamo wave may also be involved in geomagnetic reversals.

  2. Symbolic Computations in Simulations of Hydromagnetic Dynamo

    Directory of Open Access Journals (Sweden)

    Vodinchar Gleb

    2017-01-01

    Full Text Available The compilation of spectral models of geophysical fluid dynamics and hydromagnetic dynamo involves the calculation of a large number of volume integrals from complex combinations of basis fields. In this paper we describe the automation of this computation with the help of systems of symbolic computations.

  3. Extrapolating Solar Dynamo Models Throughout the Heliosphere

    Science.gov (United States)

    Cox, B. T.; Miesch, M. S.; Augustson, K.; Featherstone, N. A.

    2014-12-01

    There are multiple theories that aim to explain the behavior of the solar dynamo, and their associated models have been fiercely contested. The two prevailing theories investigated in this project are the Convective Dynamo model that arises from the pure solving of the magnetohydrodynamic equations, as well as the Babcock-Leighton model that relies on sunspot dissipation and reconnection. Recently, the supercomputer simulations CASH and BASH have formed models of the behavior of the Convective and Babcock-Leighton models, respectively, in the convective zone of the sun. These models show the behavior of the models within the sun, while much less is known about the effects these models may have further away from the solar surface. The goal of this work is to investigate any fundamental differences between the Convective and Babcock-Leighton models of the solar dynamo outside of the sun and extending into the solar system via the use of potential field source surface extrapolations implemented via python code that operates on data from CASH and BASH. The use of real solar data to visualize supergranular flow data in the BASH model is also used to learn more about the behavior of the Babcock-Leighton Dynamo. From the process of these extrapolations it has been determined that the Babcock-Leighton model, as represented by BASH, maintains complex magnetic fields much further into the heliosphere before reverting into a basic dipole field, providing 3D visualisations of the models distant from the sun.

  4. Solar Cycle #24 and the Solar Dynamo

    Science.gov (United States)

    Schatten, Kenneth; Pesnell, W. Dean

    2007-01-01

    We focus on two solar aspects related to flight dynamics. These are the solar dynamo and long-term solar activity predictions. The nature of the solar dynamo is central to solar activity predictions, and these predictions are important for orbital planning of satellites in low earth orbit (LEO). The reason is that the solar ultraviolet (UV) and extreme ultraviolet (EUV) spectral irradiances inflate the upper atmospheric layers of the Earth, forming the thermosphere and exosphere through which these satellites orbit. Concerning the dynamo, we discuss some recent novel approaches towards its understanding. For solar predictions we concentrate on a solar precursor method, in which the Sun's polar field plays a major role in forecasting the next cycle s activity based upon the Babcock-Leighton dynamo. With a current low value for the Sun s polar field, this method predicts that solar cycle #24 will be one of the lowest in recent times, with smoothed F10.7 radio flux values peaking near 130 plus or minus 30 (2 sigma), in the 2013 timeframe. One may have to consider solar activity as far back as the early 20th century to find a cycle of comparable magnitude. Concomitant effects of low solar activity upon satellites in LEO will need to be considered, such as enhancements in orbital debris. Support for our prediction of a low solar cycle #24 is borne out by the lack of new cycle sunspots at least through the first half of 2007. Usually at the present epoch in the solar cycle (approx. 7+ years after the last solar maximum), for a normal size following cycle, new cycle sunspots would be seen. The lack of their appearance at this time is only consistent with a low cycle #24. Polar field observations of a weak magnitude are consistent with unusual structures seen in the Sun s corona. Polar coronal holes are the hallmarks of the Sun's open field structures. At present, it appears that the polar coronal holes are relatively weak, and there have been many equatorial coronal holes

  5. The Crisis among Contemporary American Adolescents: A Call for the Integration of Research, Policies, and Programs.

    Science.gov (United States)

    Lerner, Richard M.; And Others

    1994-01-01

    Points out the growing crisis among American adolescents, with approximately half of adolescents at moderate or greater risk for engaging in unsafe sexual behaviors, teenage pregnancy, and teenage child-bearing; drug and alcohol use and abuse; school underachievement, failure, and dropout; and delinquency and crime. Calls for increased research on…

  6. Integrated Program on Malaria in sub-Saharan Africa (IPMA) : Call ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    The Integrated Program on Malaria in sub-Saharan Africa (IPMA) will offer a shared and synergistic approach to existing malaria control programs. It will do so by supporting research aimed at understanding the complex societal and environmental dynamics affecting malaria in the region, and testing interventions that ...

  7. A potential thermal dynamo and its astrophysical applications

    Energy Technology Data Exchange (ETDEWEB)

    Lingam, Manasvi, E-mail: mlingam@princeton.edu [Department of Physics and Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States); Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States); Mahajan, Swadesh M., E-mail: mahajan@mail.utexas.edu [Department of Physics and Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States); Department of Physics, School of Natural Sciences, Shiv Nadar University, Uttar Pradesh 201314 (India)

    2016-05-15

    It is shown that thermal turbulence, not unlike the standard kinetic and magnetic turbulence, can be an effective driver of a mean-field dynamo. In simple models, such as hydrodynamics and magnetohydrodynamics, both vorticity and induction equations can have strong thermal drives that resemble the α and γ effects in conventional dynamo theories; the thermal drives are likely to be dominant in systems that are endowed with subsonic, low-β turbulence. A pure thermal dynamo is quite different from the conventional dynamo in which the same kinetic/magnetic mix in the ambient turbulence can yield a different ratio of macroscopic magnetic/vortical fields. The possible implications of the similarities and differences between the thermal and non-thermal dynamos are discussed. The thermal dynamo is shown to be highly important in the stellar and planetary context, and yields results broadly consistent with other theoretical and experimental approaches.

  8. Seeking Information on Behalf of Others: An Analysis of Calls to a Spanish-Language Radio Health Program.

    Science.gov (United States)

    Ramirez, A Susana; Leyva, Bryan; Graff, Kaitlin; Nelson, David E; Huerta, Elmer

    2015-07-01

    Spanish-monolingual Latinos account for 13% of U.S. residents and experience multiple barriers to effective health communication. Information intermediaries/proxies mediate between the linguistically isolated and health care providers. This study characterizes the information needs of surrogate callers and their subjects to a U.S.-based Spanish-language radio health program. Content analysis of calls placed (N = 281 calls). Women made 70% of calls; 39.1% of calls were on behalf of children, 11.0% on behalf of parents/older adults, and 18.5% on behalf of spouses/siblings/contemporary adults. Most common topics were disease symptoms/conditions (19.6%), cancer (13.9%), and reproduction/sexuality (12.9%). Calls for children were more likely than those for parents/other adults to pertain to current illness symptoms or conditions; calls for parents were more likely to be about cancer/chronic conditions. Half of all calls sought clarification about a previous medical encounter. Information-seeking surrogates may represent a useful strategy for linguistic minorities to overcome structural and individual barriers to health information access. Results suggest that Latinos are willing to seek information on behalf of friends and family and highlight the need for improved, culturally and linguistically appropriate health communication sources. Leveraging Latinos' natural familial social networks/willingness to share information may improve dissemination of culturally and linguistically appropriate health information. Further implications for patient activation and doctor-patient communication are discussed. © 2015 Society for Public Health Education.

  9. Preserving the educational value of call in a diagnostic radiology residency program.

    Science.gov (United States)

    Dell, Carol M; Deloney, Linda A; Jambhekar, Kedar; Brandon, Hicks

    2014-01-01

    Our study was designed to determine residents' opinions of the advantages, disadvantages and educational value of a traditional "Tandem Call" (TC) model as compared to night float (NF). Because TC is more representative of adult learning principles and constructivist theory, we hypothesized that resident satisfaction and educational outcomes would demonstrate a preference for, and the educational efficacy of, the TC model. We surveyed all residents in a university-based radiology residency on their opinions of TC and its educational value. Aggregate data from annual Graduate Medical Education Committee institutional surveys (2008-2012) and annual radiology alumni surveys (2009-2012) were reviewed as measures of satisfaction with TC. Performance on the ABR oral exam was a proxy for educational outcome. Quality data for the year of study and prior years in which TC was in effect were reviewed as a measure of patient safety. The great majority of respondents attributed confidence/competence on call and added value to their education directly to TC. A majority believed that teamwork required for TC facilitated more positive relationships among residents and more peer teaching. Most said that they would not prefer NF. Almost all believed indirect supervision with attending backup aided in developing confidence in performance. Quality data confirmed a low number of discrepancies between preliminary resident and final attending reads. TC provides a more consistent call experience throughout residency than NF. TC is valued by residents, facilitates retrieval-based learning and development of independence and efficiency, and parallels essential elements of team-based learning. Quality data suggests that lack of 24-hour attending supervision is not detrimental to patient safety. Published by Elsevier Inc.

  10. Predictability and Coupled Dynamics of MJO During DYNAMO

    Science.gov (United States)

    2015-02-03

    3. DATES COVERED (From - To) Jan 2013-Dec 2014 4. TITLE AND SUBTITLE Predictability and Coupled Dynamics of MJO During DYNAMO 5a. CONTRACT...release: distribution is unlimited. Predictability and Coupled Dynamics of MJO During DYNAMO Hyodae Seo Woods Hole Oceanographic Institution Woods...scientific goals of the proposed research are: 1. Examine the process by which the SST variability affects the MJO during the DYNAMO using a SCOAR2 regional

  11. Universal nonlinear small-scale dynamo.

    Science.gov (United States)

    Beresnyak, A

    2012-01-20

    We consider astrophysically relevant nonlinear MHD dynamo at large Reynolds numbers (Re). We argue that it is universal in a sense that magnetic energy grows at a rate which is a constant fraction C(E) of the total turbulent dissipation rate. On the basis of locality bounds we claim that this "efficiency of the small-scale dynamo", C(E), is a true constant for large Re and is determined only by strongly nonlinear dynamics at the equipartition scale. We measured C(E) in numerical simulations and observed a value around 0.05 in the highest resolution simulations. We address the issue of C(E) being small, unlike the Kolmogorov constant which is of order unity. © 2012 American Physical Society

  12. An ancient core dynamo in asteroid Vesta.

    Science.gov (United States)

    Fu, Roger R; Weiss, Benjamin P; Shuster, David L; Gattacceca, Jérôme; Grove, Timothy L; Suavet, Clément; Lima, Eduardo A; Li, Luyao; Kuan, Aaron T

    2012-10-12

    The asteroid Vesta is the smallest known planetary body that has experienced large-scale igneous differentiation. However, it has been previously uncertain whether Vesta and similarly sized planetesimals formed advecting metallic cores and dynamo magnetic fields. Here we show that remanent magnetization in the eucrite meteorite Allan Hills A81001 formed during cooling on Vesta 3.69 billion years ago in a surface magnetic field of at least 2 microteslas. This field most likely originated from crustal remanence produced by an earlier dynamo, suggesting that Vesta formed an advecting liquid metallic core. Furthermore, the inferred present-day crustal fields can account for the lack of solar wind ion-generated space weathering effects on Vesta.

  13. Magnetic dynamo action at low magnetic Prandtl numbers.

    Science.gov (United States)

    Malyshkin, Leonid M; Boldyrev, Stanislav

    2010-11-19

    Amplification of magnetic field due to kinematic turbulent dynamo action is studied in the regime of small magnetic Prandtl numbers. Such a regime is relevant for planets and stars interiors, as well as for liquid-metal laboratory experiments. A comprehensive analysis based on the Kazantsev-Kraichnan model is reported, which establishes the dynamo threshold and the dynamo growth rates for varying kinetic helicity of turbulent fluctuations. It is proposed that in contrast with the case of large magnetic Prandtl numbers, the kinematic dynamo action at small magnetic Prandtl numbers is significantly affected by kinetic helicity, and it can be made quite efficient with an appropriate choice of the helicity spectrum.

  14. Bistability and chaos in the Taylor-Green dynamo.

    Science.gov (United States)

    Yadav, Rakesh K; Verma, Mahendra K; Wahi, Pankaj

    2012-03-01

    Using direct numerical simulations, we study dynamo action under Taylor-Green forcing for a magnetic Prandtl number of 0.5. We observe bistability with weak- and strong-magnetic-field branches. Both the dynamo branches undergo subcritical dynamo transition. We also observe a host of dynamo states including constant, periodic, quasiperiodic, and chaotic magnetic fields. One of the chaotic states originates through a quasiperiodic route with phase locking, while the other chaotic attractor appears to follow the Newhouse-Ruelle-Takens route to chaos. We also observe intermittent transitions between quasiperiodic and chaotic states for a given Taylor-Green forcing.

  15. Nonlinear dynamo action in a precessing cylindrical container.

    Science.gov (United States)

    Nore, C; Léorat, J; Guermond, J-L; Luddens, F

    2011-07-01

    It is numerically demonstrated by means of a magnetohydrodynamics code that precession can trigger the dynamo effect in a cylindrical container. When the Reynolds number, based on the radius of the cylinder and its angular velocity, increases, the flow, which is initially centrosymmetric, loses its stability and bifurcates to a quasiperiodic motion. This unsteady and asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field thus generated is unsteady and quadrupolar. These numerical evidences of dynamo action in a precessing cylindrical container may be useful for an experiment now planned at the Dresden sodium facility for dynamo and thermohydraulic studies in Germany.

  16. Evidence for a Second Martian Dynamo from Electron Reflection Magnetometry

    Science.gov (United States)

    Lillis, R. J.; Manga, M.; Mitchell, D. L.; Lin, R. P.; Acuna, M. H.

    2005-01-01

    Present-day Mars does not possess an active core dynamo and associated global magnetic field. However, the discovery of intensely magnetized crust in Mars Southern hemisphere implies that a Martian dynamo has existed in the past. Resolving the history of the Martian core dynamo is important for understanding the evolution of the planet's interior. Moreover, because the global magnetic field provided by an active dynamo can shield the atmosphere from erosion by the solar wind, it may have influenced past Martian climate. Additional information is included in the original extended abstract.

  17. The Hottest Hot Jupiters May Host Atmospheric Dynamos

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, T. M. [Department of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne (United Kingdom); McElwaine, J. N. [Planetary Science Institute, Tucson, AZ 85721 (United States)

    2017-06-01

    Hot Jupiters have proven themselves to be a rich class of exoplanets that test our theories of planetary evolution and atmospheric dynamics under extreme conditions. Here, we present three-dimensional magnetohydrodynamic simulations and analytic results that demonstrate that a dynamo can be maintained in the thin, stably stratified atmosphere of a hot Jupiter, independent of the presumed deep-seated dynamo. This dynamo is maintained by conductivity variations arising from strong asymmetric heating from the planets’ host star. The presence of a dynamo significantly increases the surface magnetic field strength and alters the overall planetary magnetic field geometry, possibly affecting star–planet magnetic interactions.

  18. Bridging the Otolaryngology Peer Review Knowledge Gap: A Call for a Residency Development Program.

    Science.gov (United States)

    Schmalbach, Cecelia E

    2016-07-01

    Current otolaryngology literature and future scientific direction rely heavily on a rigorous peer review process. Just as manuscripts warrant thoughtful review with constructive feedback to the authors, the same can be said for critiques written by novice peer reviewers. Formal scientific peer review training programs are lacking. Recognizing this knowledge gap, Otolaryngology-Head and Neck Surgery is excited to offer its new Resident Reviewer Development Program. All otolaryngology residents who are postgraduate year 2 and above and in excellent academic standing are eligible to participate in this mentored program, during which they will conduct 6 manuscript reviews under the direction of a seasoned reviewer in his or her subspecialty area of interest. By completing reviews alongside a mentor, participants gain the required skills to master the peer review process-a first step that often leads to journal editorial board and associate editor invitations. © American Academy of Otolaryngology—Head and Neck Surgery Foundation 2016.

  19. The Writing Program and the Call to Service: A Progress Report from a Land Grant University

    Science.gov (United States)

    Sawyer, Paul

    2009-01-01

    Although a vibrant literature on the social justice advantages of writing service-learning programs has existed for many years, the focus has tended to be on specific projects and courses, often accompanied by an understandable suspicion that entrenched institutions like universities have interests inimical to radical social change. As a result,…

  20. A Call to Action: Addressing the Childhood Obesity Epidemic through Comprehensive School Counseling Programs

    Science.gov (United States)

    Belser, Christopher T.; Morris, Jessica A.; Hasselbeck, Jennifer M.

    2012-01-01

    The need for school-based interventions targeting the childhood obesity epidemic has been well documented. The risk factors associated with childhood obesity are physical, mental, psychosocial, academic, and economic. With training in developing comprehensive programs and interventions, professional school counselors are positioned to assist…

  1. A Call for Sustainability Education in Post-Secondary Outdoor Recreation Programs

    Science.gov (United States)

    O'Connell, Timothy S.; Potter, Tom G.; Curthoys, Lesley P.; Dyment, Janet E.; Cuthbertson, Brent

    2005-01-01

    Purpose: The purpose of this paper is to examine the link between sustainability education and outdoor education and to encourage outdoor recreation educators to evaluate their programs with regard to sustainability and sustainable living. Design/methodology/approach: This paper starts by presenting several factors that currently hinder the…

  2. Solar Physics at Evergreen: Solar Dynamo and Chromospheric MHD

    Science.gov (United States)

    Zita, E. J.; Maxwell, J.; Song, N.; Dikpati, M.

    2006-12-01

    We describe our five year old solar physics research program at The Evergreen State College. Famed for its cloudy skies, the Pacific Northwest is an ideal location for theoretical and remote solar physics research activities. Why does the Sun's magnetic field flip polarity every 11 years or so? How does this contribute to the magnetic storms Earth experiences when the Sun's field reverses? Why is the temperature in the Sun's upper atmosphere millions of degrees higher than the Sun's surface temperature? How do magnetic waves transport energy in the Sun’s chromosphere and the Earth’s atmosphere? How does solar variability affect climate change? Faculty and undergraduates investigate questions such as these in collaboration with the High Altitude Observatory (HAO) at the National Center for Atmospheric Research (NCAR) in Boulder. We will describe successful student research projects, logistics of remote computing, and our current physics investigations into (1) the solar dynamo and (2) chromospheric magnetohydrodynamics.

  3. Measuring and reporting attrition from obesity treatment programs: A call to action!

    Science.gov (United States)

    Miller, Beth M L; Brennan, Leah

    2015-01-01

    The high attrition rates in obesity interventions are associated with poorer weight loss and maintenance for the individual and poorer overall treatment effectiveness and cost-effectiveness for the treatment provider. Increased knowledge about factors associated with attrition can facilitate the identification of individuals at risk of drop-out and inform treatment program improvements with the aim of maximising treatment retention. To date, a relatively small body of literature has explored attrition from weight-loss interventions using two methods of attrition assessment: identification of pre-treatment predictors of attrition and eliciting post-treatment reasons for attrition. A range of attrition rates have been reported and no reliable or consistent predictors of attrition have been found. It is unknown whether the lack of consistent findings reflects population or treatment differences, or if the discrepant findings simply reflect differences in definition and measurement of attrition. Further research is required to address these limitations. There is a need for a recognised definition of obesity treatment attrition, the consideration of predictors that are theoretically and empirically associated with attrition, the development of a well-validated and standardised measure of barriers to attendance, and assessment of both treatment completers and drop-outs. Understanding the factors that influence attrition can be used to inform the modification of treatment programs and to target those most at risk of drop-out so as to maximise the success of obesity interventions. Copyright © 2014 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.

  4. The Current Status of Kinematic Solar Dynamo Models

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... This review provides a historical overview of how research in kinematic solar dynamo modeling evolved during the last few decades and assesses the present state of research. The early pioneering papers assumed the dynamo to operate in the convection zone. It was suggested in the 1980s that the ...

  5. Numerical insights into magnetic dynamo action in a turbulent regime

    NARCIS (Netherlands)

    Kenjeres, S.; Hanjalic, K.

    2007-01-01

    We report on hybrid numerical simulations of a turbulent magnetic dynamo. The simulated set-up mimics the Riga dynamo experiment characterized by Re ? 3.5 × 106 and (Gailitis et al 2000 Phys. Rev. Lett. 84 4365–8). The simulations were performed by a simultaneous fully coupled solution of the

  6. Polar spots and stellar spindown: is dynamo saturation needed?

    NARCIS (Netherlands)

    Solanki, S. K.; Motamen, S.; Keppens, R.

    1997-01-01

    Dynamo saturation is often invoked when calculating the rotational evolution of cool stars. At rapid rotation rates a saturated dynamo reduces the angular momentum carried away by the stellar wind. This, in turn, may explain the high rotation rates present in the distribution of rotation periods in

  7. Polar spots and stellar spindown: Is dynamo saturation needed?

    NARCIS (Netherlands)

    Solanki, S. K.; Motamen, S.; Keppens, R.

    1997-01-01

    Dynamo saturation is often invoked when calculating the rotational evolution of cool stars. At rapid rotation rates a saturated dynamo reduces the angular momentum carried away by the stellar wind. This, in turn, may explain the high rotation rates present in the distribution of rotation periods in

  8. The Current Status of Kinematic Solar Dynamo Models

    Indian Academy of Sciences (India)

    tribpo

    kinematic solar dynamo modeling evolved during the last few decades and assesses the present state of research. .... towards the equator, early dynamo theorists used to choose their parameters in such a way that the inequality (5) was .... sunspots and weak magnetic fields in a unified way. We are, however, still far from.

  9. Some Recent Developments in Solar Dynamo Theory Arnab Rai ...

    Indian Academy of Sciences (India)

    Abstract. We discuss the current status of solar dynamo theory and describe the dynamo model developed by our group. The toroidal magnetic field is generated in the tachocline by the strong differential rotation and rises to the solar surface due to magnetic buoyancy to create active regions. The decay of these active ...

  10. Efficiency Measurement Using a Motor-Dynamo Module

    Science.gov (United States)

    Ng, Pun-hon; Wong, Siu-ling; Mak, Se-yuen

    2009-01-01

    In this article, we describe a simple method which can be used to measure the efficiency of a low power dc motor, a motor-converted dynamo and a coupled motor-dynamo module as a function of the speed of rotation. The result can also be used to verify Faraday's law of electromagnetic induction. (Contains 1 table and 8 figures.)

  11. Axial dipolar dynamo action in the Taylor-Green vortex.

    Science.gov (United States)

    Krstulovic, Giorgio; Thorner, Gentien; Vest, Julien-Piera; Fauve, Stephan; Brachet, Marc

    2011-12-01

    We present a numerical study of the magnetic field generated by the Taylor-Green vortex. We show that periodic boundary conditions can be used to mimic realistic boundary conditions by prescribing the symmetries of the velocity and magnetic fields. This gives insight into some problems of central interest for dynamos: the possible effect of velocity fluctuations on the dynamo threshold, and the role of boundary conditions on the threshold and on the geometry of the magnetic field generated by dynamo action. In particular, we show that an axial dipolar dynamo similar to the one observed in a recent experiment can be obtained with an appropriate choice of the symmetries of the magnetic field. The nonlinear saturation is studied and a simple model explaining the magnetic Prandtl number dependence of the super- and subcritical nature of the dynamo transition is given.

  12. Persistence and origin of the lunar core dynamo.

    Science.gov (United States)

    Suavet, Clément; Weiss, Benjamin P; Cassata, William S; Shuster, David L; Gattacceca, Jérôme; Chan, Lindsey; Garrick-Bethell, Ian; Head, James W; Grove, Timothy L; Fuller, Michael D

    2013-05-21

    The lifetime of the ancient lunar core dynamo has implications for its power source and the mechanism of field generation. Here, we report analyses of two 3.56-Gy-old mare basalts demonstrating that they were magnetized in a stable and surprisingly intense dynamo magnetic field of at least ~13 μT. These data extend the known lifetime of the lunar dynamo by ~160 My and indicate that the field was likely continuously active until well after the final large basin-forming impact. This likely excludes impact-driven changes in rotation rate as the source of the dynamo at this time in lunar history. Rather, our results require a persistent power source like precession of the lunar mantle or a compositional convection dynamo.

  13. Could Giant Basin-Forming Impacts Have Killed Martian Dynamo?

    Science.gov (United States)

    Kuang, W.; Jiang, W.; Roberts, J.; Frey, H. V.

    2014-01-01

    The observed strong remanent crustal magnetization at the surface of Mars suggests an active dynamo in the past and ceased to exist around early to middle Noachian era, estimated by examining remagnetization strengths in extant and buried impact basins. We investigate whether the Martian dynamo could have been killed by these large basin-forming impacts, via numerical simulation of subcritical dynamos with impact-induced thermal heterogeneity across the core-mantle boundary. We find that subcritical dynamos are prone to the impacts centered on locations within 30 deg of the equator but can easily survive those at higher latitudes. Our results further suggest that magnetic timing places a strong constraint on postimpact polar reorientation, e.g., a minimum 16 deg polar reorientation is needed if Utopia is the dynamo killer.

  14. Transition from large-scale to small-scale dynamo.

    Science.gov (United States)

    Ponty, Y; Plunian, F

    2011-04-15

    The dynamo equations are solved numerically with a helical forcing corresponding to the Roberts flow. In the fully turbulent regime the flow behaves as a Roberts flow on long time scales, plus turbulent fluctuations at short time scales. The dynamo onset is controlled by the long time scales of the flow, in agreement with the former Karlsruhe experimental results. The dynamo mechanism is governed by a generalized α effect, which includes both the usual α effect and turbulent diffusion, plus all higher order effects. Beyond the onset we find that this generalized α effect scales as O(Rm(-1)), suggesting the takeover of small-scale dynamo action. This is confirmed by simulations in which dynamo occurs even if the large-scale field is artificially suppressed.

  15. Solar Cycle 24 and the Solar Dynamo

    Science.gov (United States)

    Pesnell, W. D.; Schatten, K.

    2007-01-01

    We will discuss the polar field precursor method for solar activity prediction, which predicts cycle 24 will be significantly lower than recent activity cycles, and some new ideas rejuvenating Babcock's shallow surface dynamo. The polar field precursor method is based on Babcock and Leighton's dynamo models wherein the polar field at solar minimum plays a major role in generating the next cycle's toroidal field and sunspots. Thus, by examining the polar fields of the Sun near solar minimum, a forecast for the next cycle's activity is obtained. With the current low value for the Sun's polar fields, this method predicts solar cycle 24 will be one of the lowest in recent times, with smoothed F10.7 radio flux values peaking near 135 plus or minus 35 (2 sigma), in the 2012-2013 timeframe (equivalent to smoothed Rz near 80 plus or minus 35 [2 sigma]). One may have to consider solar activity as far back as the early 20th century to find a cycle of comparable magnitude. We discuss unusual behavior in the Sun's polar fields that support this prediction. Normally, the solar precursor method is consistent with the geomagnetic precursor method, wherein geomagnetic variations are thought to be a good measure of the Sun's polar field strength. Because of the unusual polar field, the Earth does not appear to be currently bathed in the Sun's extended polar field (the interplanetary field), hence negating the primal cause behind the geomagnetic precursor technique. We also discuss how percolation may support Babcock's original shallow solar dynamo. In this process ephemeral regions from the solar magnetic carpet, guided by shallow surface fields, may collect to form pores and sunspots.

  16. Promoting health after gestational diabetes: a National Diabetes Education Program call to action.

    Science.gov (United States)

    Gabbe, Steven G; Landon, Mark B; Warren-Boulton, Elizabeth; Fradkin, Judith

    2012-01-01

    The National Diabetes Education Program joins the American College of Obstetricians and Gynecologists (the College) to promote opportunities for obstetrician-gynecologists (ob-gyns) and other primary care providers to better meet the long-term health needs of women with prior gestational diabetes mellitus (GDM) and their children. Up to one third of GDM women may have diabetes or prediabetes postpartum, yet only about half of these women are tested postpartum, and about a quarter are tested 6-12 weeks postpartum. Women with GDM face a lifelong increased risk for subsequent diabetes, primarily type 2 diabetes mellitus. Timely testing for prediabetes may provide an opportunity for ob-gyns to prevent or delay the onset of type 2 diabetes mellitus through diet, physical activity, weight management, and pharmacologic intervention. The College and the American Diabetes Association recommend testing women with a history of GDM at 6-12 weeks postpartum. If the postpartum test is normal, retest every 3 years and at the first prenatal visit in a subsequent pregnancy. If prediabetes is diagnosed, test annually. Because children of GDM pregnancies face an increased risk for obesity and type 2 diabetes mellitus, families need support to develop healthy eating and physical activity behaviors. Current criteria indicate that GDM occurs in 2% to 10% of all pregnancies. If new GDM diagnostic criteria are used, the frequency of GDM may increase to about 18% of pregnancies annually. The projected increase in the number of women with GDM and the potential subsequent associated risks underscore the need for proactive long-term primary care treatment of the mother and her children.

  17. On a certain laminar dynamo model

    Science.gov (United States)

    Novikov, V. V.; Fevralskikh, L. N.

    2017-11-01

    We consider the motion of a conducting incompressible viscous fluid in the space between two rotating spheres. We assume the centres of symmetry of spheres to lie a short distance from each other in a plane perpendicular to the axes of rotation. If we ignore the effect of the magnetic field on the motion of the liquid and regard the flow as laminar, then we are able to solve the hydrodynamics system of equations analytically. We use this solution to assess the possibility of a magnetic dynamo.

  18. The dynamo bifurcation in rotating spherical shells

    CERN Document Server

    Morin, Vincent; 10.1142/S021797920906378X

    2010-01-01

    We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core, i.e. in a rotating spherical shell with thermally driven motions. We show that the nature of the bifurcation, which can be either supercritical or subcritical or even take the form of isola (or detached lobes) strongly depends on the parameters. This dependence is described in a range of parameters numerically accessible (which unfortunately remains remote from geophysical application), and we show how the magnetic Prandtl number and the Ekman number control these transitions.

  19. FamSeq: a variant calling program for family-based sequencing data using graphics processing units.

    Science.gov (United States)

    Peng, Gang; Fan, Yu; Wang, Wenyi

    2014-10-01

    Various algorithms have been developed for variant calling using next-generation sequencing data, and various methods have been applied to reduce the associated false positive and false negative rates. Few variant calling programs, however, utilize the pedigree information when the family-based sequencing data are available. Here, we present a program, FamSeq, which reduces both false positive and false negative rates by incorporating the pedigree information from the Mendelian genetic model into variant calling. To accommodate variations in data complexity, FamSeq consists of four distinct implementations of the Mendelian genetic model: the Bayesian network algorithm, a graphics processing unit version of the Bayesian network algorithm, the Elston-Stewart algorithm and the Markov chain Monte Carlo algorithm. To make the software efficient and applicable to large families, we parallelized the Bayesian network algorithm that copes with pedigrees with inbreeding loops without losing calculation precision on an NVIDIA graphics processing unit. In order to compare the difference in the four methods, we applied FamSeq to pedigree sequencing data with family sizes that varied from 7 to 12. When there is no inbreeding loop in the pedigree, the Elston-Stewart algorithm gives analytical results in a short time. If there are inbreeding loops in the pedigree, we recommend the Bayesian network method, which provides exact answers. To improve the computing speed of the Bayesian network method, we parallelized the computation on a graphics processing unit. This allowed the Bayesian network method to process the whole genome sequencing data of a family of 12 individuals within two days, which was a 10-fold time reduction compared to the time required for this computation on a central processing unit.

  20. The Dynamo package for tomography and subtomogram averaging: components for MATLAB, GPU computing and EC2 Amazon Web Services.

    Science.gov (United States)

    Castaño-Díez, Daniel

    2017-06-01

    Dynamo is a package for the processing of tomographic data. As a tool for subtomogram averaging, it includes different alignment and classification strategies. Furthermore, its data-management module allows experiments to be organized in groups of tomograms, while offering specialized three-dimensional tomographic browsers that facilitate visualization, location of regions of interest, modelling and particle extraction in complex geometries. Here, a technical description of the package is presented, focusing on its diverse strategies for optimizing computing performance. Dynamo is built upon mbtools (middle layer toolbox), a general-purpose MATLAB library for object-oriented scientific programming specifically developed to underpin Dynamo but usable as an independent tool. Its structure intertwines a flexible MATLAB codebase with precompiled C++ functions that carry the burden of numerically intensive operations. The package can be delivered as a precompiled standalone ready for execution without a MATLAB license. Multicore parallelization on a single node is directly inherited from the high-level parallelization engine provided for MATLAB, automatically imparting a balanced workload among the threads in computationally intense tasks such as alignment and classification, but also in logistic-oriented tasks such as tomogram binning and particle extraction. Dynamo supports the use of graphical processing units (GPUs), yielding considerable speedup factors both for native Dynamo procedures (such as the numerically intensive subtomogram alignment) and procedures defined by the user through its MATLAB-based GPU library for three-dimensional operations. Cloud-based virtual computing environments supplied with a pre-installed version of Dynamo can be publicly accessed through the Amazon Elastic Compute Cloud (EC2), enabling users to rent GPU computing time on a pay-as-you-go basis, thus avoiding upfront investments in hardware and longterm software maintenance.

  1. Two spinning ways for precession dynamo.

    Science.gov (United States)

    Cappanera, L; Guermond, J-L; Léorat, J; Nore, C

    2016-04-01

    It is numerically demonstrated by means of a magnetohydrodynamic code that precession can trigger dynamo action in a cylindrical container. Fixing the angle between the spin and the precession axis to be 1/2π, two limit configurations of the spinning axis are explored: either the symmetry axis of the cylinder is parallel to the spin axis (this configuration is henceforth referred to as the axial spin case), or it is perpendicular to the spin axis (this configuration is referred to as the equatorial spin case). In both cases, the centro-symmetry of the flow breaks when the kinetic Reynolds number increases. Equatorial spinning is found to be more efficient in breaking the centro-symmetry of the flow. In both cases, the average flow in the reference frame of the mantle converges to a counter-rotation with respect to the spin axis as the Reynolds number grows. We find a scaling law for the average kinetic energy in term of the Reynolds number in the axial spin case. In the equatorial spin case, the unsteady asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field is mainly dipolar in the equatorial spin case, while it is is mainly quadrupolar in the axial spin case.

  2. Optimal Length Scale for a Turbulent Dynamo.

    Science.gov (United States)

    Sadek, Mira; Alexakis, Alexandros; Fauve, Stephan

    2016-02-19

    We demonstrate that there is an optimal forcing length scale for low Prandtl number dynamo flows that can significantly reduce the required energy injection rate. The investigation is based on simulations of the induction equation in a periodic box of size 2πL. The flows considered are the laminar and turbulent ABC flows forced at different forcing wave numbers k_{f}, where the turbulent case is simulated using a subgrid turbulence model. At the smallest allowed forcing wave number k_{f}=k_{min}=1/L the laminar critical magnetic Reynolds number Rm_{c}^{lam} is more than an order of magnitude smaller than the turbulent critical magnetic Reynolds number Rm_{c}^{turb} due to the hindering effect of turbulent fluctuations. We show that this hindering effect is almost suppressed when the forcing wave number k_{f} is increased above an optimum wave number k_{f}L≃4 for which Rm_{c}^{turb} is minimum. At this optimal wave number, Rm_{c}^{turb} is smaller by more than a factor of 10 than the case forced in k_{f}=1. This leads to a reduction of the energy injection rate by 3 orders of magnitude when compared to the case where the system is forced at the largest scales and thus provides a new strategy for the design of a fully turbulent experimental dynamo.

  3. Constraints on dynamo action in plasmas

    CERN Document Server

    Helander, P; Schekochihin, A A

    2016-01-01

    Upper bounds are derived on the amount of magnetic energy that can be generated by dynamo action in collisional and collisionless plasmas with and without external forcing. A hierarchy of mathematical descriptions is considered for the plasma dynamics: ideal MHD, visco-resistive MHD, the double-adiabatic theory of Chew, Goldberger and Low (CGL), kinetic MHD, and other kinetic models. It is found that dynamo action is greatly constrained in models where the magnetic moment of any particle species is conserved. In the absence of external forcing, the magnetic energy then remains small at all times if it is small in the initial state. In other words, a small "seed" magnetic field cannot be amplified significantly, regardless of the nature of flow, as long as the collision frequency and gyroradius are small enough to be negligible. A similar conclusion also holds if the system is subject to external forcing as long as this forcing conserves the magnetic moment of at least one plasma species and does not greatly i...

  4. On the mean-field theory of the Karlsruhe Dynamo Experiment

    Directory of Open Access Journals (Sweden)

    K.-H. Rädler

    2002-01-01

    Full Text Available In the Forschungszentrum Karlsruhe an experiment has been constructed which demonstrates a homogeneous dynamo as is expected to exist in the Earth's interior. This experiment is discussed within the framework of mean-field dynamo theory. The main predictions of this theory are explained and compared with the experimental results. Key words. Dynamo, geodynamo, dynamo experiment, mean-field dynamo theory, a-effect

  5. A two-billion-year history for the lunar dynamo.

    Science.gov (United States)

    Tikoo, Sonia M; Weiss, Benjamin P; Shuster, David L; Suavet, Clément; Wang, Huapei; Grove, Timothy L

    2017-08-01

    Magnetic studies of lunar rocks indicate that the Moon generated a core dynamo with surface field intensities of ~20 to 110 μT between at least 4.25 and 3.56 billion years ago (Ga). The field subsequently declined to dynamo had terminated by this time or just greatly weakened in intensity. We present analyses that demonstrate that the melt glass matrix of a young regolith breccia was magnetized in a ~5 ± 2 μT dynamo field at ~1 to ~2.5 Ga. These data extend the known lifetime of the lunar dynamo by at least 1 billion years. Such a protracted history requires an extraordinarily long-lived power source like core crystallization or precession. No single dynamo mechanism proposed thus far can explain the strong fields inferred for the period before 3.56 Ga while also allowing the dynamo to persist in such a weakened state beyond ~2.5 Ga. Therefore, our results suggest that the dynamo was powered by at least two distinct mechanisms operating during early and late lunar history.

  6. Experimental observation of spatially localized dynamo magnetic fields.

    Science.gov (United States)

    Gallet, B; Aumaître, S; Boisson, J; Daviaud, F; Dubrulle, B; Bonnefoy, N; Bourgoin, M; Odier, Ph; Pinton, J-F; Plihon, N; Verhille, G; Fauve, S; Pétrélis, F

    2012-04-06

    We report the first experimental observation of a spatially localized dynamo magnetic field, a common feature of astrophysical dynamos and convective dynamo simulations. When the two propellers of the von Kármán sodium experiment are driven at frequencies that differ by 15%, the mean magnetic field's energy measured close to the slower disk is nearly 10 times larger than the one close to the faster one. This strong localization of the magnetic field when a symmetry of the forcing is broken is in good agreement with a prediction based on the interaction between a dipolar and a quadrupolar magnetic mode. © 2012 American Physical Society

  7. Facilitating dynamo action via control of large-scale turbulence.

    Science.gov (United States)

    Limone, A; Hatch, D R; Forest, C B; Jenko, F

    2012-12-01

    The magnetohydrodynamic dynamo effect is considered to be the major cause of magnetic field generation in geo- and astrophysical systems. Recent experimental and numerical results show that turbulence constitutes an obstacle to dynamos; yet its role in this context is not totally clear. Via numerical simulations, we identify large-scale turbulent vortices with a detrimental effect on the amplification of the magnetic field in a geometry of experimental interest and propose a strategy for facilitating the dynamo instability by manipulating these detrimental "hidden" dynamics.

  8. Mean-field theory and self-consistent dynamo modeling

    Energy Technology Data Exchange (ETDEWEB)

    Yoshizawa, Akira; Yokoi, Nobumitsu [Tokyo Univ. (Japan). Inst. of Industrial Science; Itoh, Sanae-I [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan)

    2001-12-01

    Mean-field theory of dynamo is discussed with emphasis on the statistical formulation of turbulence effects on the magnetohydrodynamic equations and the construction of a self-consistent dynamo model. The dynamo mechanism is sought in the combination of the turbulent residual-helicity and cross-helicity effects. On the basis of this mechanism, discussions are made on the generation of planetary magnetic fields such as geomagnetic field and sunspots and on the occurrence of flow by magnetic fields in planetary and fusion phenomena. (author)

  9. Solar Dynamo Driven by Periodic Flow Oscillation

    Science.gov (United States)

    Mayr, Hans G.; Hartle, Richard E.; Einaudi, Franco (Technical Monitor)

    2001-01-01

    We have proposed that the periodicity of the solar magnetic cycle is determined by wave mean flow interactions analogous to those driving the Quasi Biennial Oscillation in the Earth's atmosphere. Upward propagating gravity waves would produce oscillating flows near the top of the radiation zone that in turn would drive a kinematic dynamo to generate the 22-year solar magnetic cycle. The dynamo we propose is built on a given time independent magnetic field B, which allows us to estimate the time dependent, oscillating components of the magnetic field, (Delta)B. The toroidal magnetic field (Delta)B(sub phi) is directly driven by zonal flow and is relatively large in the source region, (Delta)(sub phi)/B(sub Theta) much greater than 1. Consistent with observations, this field peaks at low latitudes and has opposite polarities in both hemispheres. The oscillating poloidal magnetic field component, (Delta)B(sub Theta), is driven by the meridional circulation, which is difficult to assess without a numerical model that properly accounts for the solar atmosphere dynamics. Scale-analysis suggests that (Delta)B(sub Theta) is small compared to B(sub Theta) in the dynamo region. Relative to B(sub Theta), however, the oscillating magnetic field perturbations are expected to be transported more rapidly upwards in the convection zone to the solar surface. As a result, (Delta)B(sub Theta) (and (Delta)B(sub phi)) should grow relative to B(sub Theta), so that the magnetic fields reverse at the surface as observed. Since the meridional and zonai flow oscillations are out of phase, the poloidal magnetic field peaks during times when the toroidal field reverses direction, which is observed. With the proposed wave driven flow oscillation, the magnitude of the oscillating poloidal magnetic field increases with the mean rotation rate of the fluid. This is consistent with the Bode-Blackett empirical scaling law, which reveals that in massive astrophysical bodies the magnetic moment tends

  10. DynamO: a free O(N) general event-driven molecular dynamics simulator.

    Science.gov (United States)

    Bannerman, M N; Sargant, R; Lue, L

    2011-11-30

    Molecular dynamics algorithms for systems of particles interacting through discrete or "hard" potentials are fundamentally different to the methods for continuous or "soft" potential systems. Although many software packages have been developed for continuous potential systems, software for discrete potential systems based on event-driven algorithms are relatively scarce and specialized. We present DynamO, a general event-driven simulation package, which displays the optimal O(N) asymptotic scaling of the computational cost with the number of particles N, rather than the O(N) scaling found in most standard algorithms. DynamO provides reference implementations of the best available event-driven algorithms. These techniques allow the rapid simulation of both complex and large (>10(6) particles) systems for long times. The performance of the program is benchmarked for elastic hard sphere systems, homogeneous cooling and sheared inelastic hard spheres, and equilibrium Lennard-Jones fluids. This software and its documentation are distributed under the GNU General Public license and can be freely downloaded from http://marcusbannerman.co.uk/dynamo. Copyright © 2011 Wiley Periodicals, Inc.

  11. Dynamo efficiency controlled by hydrodynamic bistability.

    Science.gov (United States)

    Miralles, Sophie; Herault, Johann; Herault, Johann; Fauve, Stephan; Gissinger, Christophe; Pétrélis, François; Daviaud, François; Dubrulle, Bérengère; Boisson, Jean; Bourgoin, Mickaël; Verhille, Gautier; Odier, Philippe; Pinton, Jean-François; Plihon, Nicolas

    2014-06-01

    Hydrodynamic and magnetic behaviors in a modified experimental setup of the von Kármán sodium flow-where one disk has been replaced by a propeller-are investigated. When the rotation frequencies of the disk and the propeller are different, we show that the fully turbulent hydrodynamic flow undergoes a global bifurcation between two configurations. The bistability of these flow configurations is associated with the dynamics of the central shear layer. The bistable flows are shown to have different dynamo efficiencies; thus for a given rotation rate of the soft-iron disk, two distinct magnetic behaviors are observed depending on the flow configuration. The hydrodynamic transition controls the magnetic field behavior, and bifurcations between high and low magnetic field branches are investigated.

  12. Starspots: A Key to the Stellar Dynamo

    Directory of Open Access Journals (Sweden)

    Berdyugina Svetlana V.

    2005-12-01

    Full Text Available Magnetic activity similar to that of the Sun is observed on a variety of cool stars with external convection envelopes. Stellar rotation coupled with convective motions generate strong magnetic fields in the stellar interior and produce a multitude of magnetic phenomena including starspots in the photosphere, chromospheric plages, coronal loops, UV, X-ray, and radio emission and flares. Here I review the phenomenon of starspots on different types of cool stars, observational tools and diagnostic techniques for studying starspots as well as starspot properties including their temperatures, areas, magnetic field strengths, lifetimes, active latitudes and longitudes, etc. Evolution of starspots on various time scales allows us to investigate stellar differential rotation, activity cycles, and global magnetic fields. Together these constitute the basis for our understanding of stellar and solar dynamos and provide valuable constraints for theoretical models.

  13. Introduction to Plasma Dynamo, Reconnection and Shocks

    Energy Technology Data Exchange (ETDEWEB)

    Intrator, Thomas P. [Los Alamos National Laboratory

    2012-08-30

    In our plasma universe, most of what we can observe is composed of ionized gas, or plasma. This plasma is a conducting fluid, which advects magnetic fields when it flows. Magnetic structure occurs from the smallest planetary to the largest cosmic scales. We introduce at a basic level some interesting features of non linear magnetohydrodynamics (MHD). For example, in our plasma universe, dynamo creates magnetic fields from gravitationally driven flow energy in an electrically conducting medium, and conversely magnetic reconnection annihilates magnetic field and accelerates particles. Shocks occur when flows move faster than the local velocity (sonic or Alfven speed) for the propagation of information. Both reconnection and shocks can accelerate particles, perhaps to gigantic energies, for example as observed with 10{sup 20} eV cosmic rays.

  14. Wave-driven dynamo action in spherical magnetohydrodynamic systems.

    Science.gov (United States)

    Reuter, K; Jenko, F; Tilgner, A; Forest, C B

    2009-11-01

    Hydrodynamic and magnetohydrodynamic numerical studies of a mechanically forced two-vortex flow inside a sphere are reported. The simulations are performed in the intermediate regime between the laminar flow and developed turbulence, where a hydrodynamic instability is found to generate internal waves with a characteristic m=2 zonal wave number. It is shown that this time-periodic flow acts as a dynamo, although snapshots of the flow as well as the mean flow are not dynamos. The magnetic fields' growth rate exhibits resonance effects depending on the wave frequency. Furthermore, a cyclic self-killing and self-recovering dynamo based on the relative alignment of the velocity and magnetic fields is presented. The phenomena are explained in terms of a mixing of nonorthogonal eigenstates of the time-dependent linear operator of the magnetic induction equation. The potential relevance of this mechanism to dynamo experiments is discussed.

  15. Strong horizontal photospheric magnetic field in a surface dynamo simulation

    NARCIS (Netherlands)

    SchÜssler, M.; Vögler, A.|info:eu-repo/dai/nl/323397212

    2008-01-01

    Context. Observations with the Hinode spectro-polarimeter have revealed strong horizontal internetwork magnetic fields in the quiet solar photosphere. Aims. We aim to interpret the observations with results from numerical simulations. Methods. Radiative MHD simulations of dynamo action by

  16. Energy transfers in dynamos with small magnetic Prandtl numbers

    KAUST Repository

    Kumar, Rohit

    2015-06-25

    We perform numerical simulation of dynamo with magnetic Prandtl number Pm = 0.2 on 10243 grid, and compute the energy fluxes and the shell-to-shell energy transfers. These computations indicate that the magnetic energy growth takes place mainly due to the energy transfers from large-scale velocity field to large-scale magnetic field and that the magnetic energy flux is forward. The steady-state magnetic energy is much smaller than the kinetic energy, rather than equipartition; this is because the magnetic Reynolds number is near the dynamo transition regime. We also contrast our results with those for dynamo with Pm = 20 and decaying dynamo. © 2015 Taylor & Francis.

  17. Early MARS Chronology: When and How did the Dynamo Die?

    Science.gov (United States)

    Lillis, R. J.; Vervilidou, F.; Weiss, B. P.; Manga, M.; Frey, H. V.; Robbins, S. J.

    2017-10-01

    Mars’ dynamo is a key aspect of early Mars evolution. It likely started sometime after primordial crust formation and ceased before the Utopia impact. Its total duration depends on impactor flux following accretion and the timing of the LHB.

  18. Planetary Dynamos: Investigations of Saturn and Ancient Mars

    Energy Technology Data Exchange (ETDEWEB)

    Stanley, Sabine [University of Toronto

    2012-04-18

    Magnetic field observations by spacecraft missions have provided vital information on planetary dynamos. The four giant planets as well as Earth, Mercury and Ganymede have observable magnetic fields generated by active dynamos. In contrast, Moon and Mars only have remanent crustal fields from dynamo action in their early histories. A variety of magnetic field morphologies and intensities can be found in the solar system. We have found that some of the differences between planetary magnetic fields can be explained as the result of the presence of boundary thermal variations or stably-stratified layers. In this talk, I will discuss how dynamos are affected by these complications and discuss the implications for Mars’ magnetic dichotomy and Saturn’s extremely axisymmetric magnetic field.

  19. Direct numerical simulation of dynamo transition for nonhelical MHD

    Energy Technology Data Exchange (ETDEWEB)

    Nath, Dinesh; Verma, Mahendra K [Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Lessinnes, Thomas; Carati, Daniele [Physique Statistique et Plasmas, Universite Libre de Bruxellers, B-1050 Bruxelles (Belgium); Sarris, Ioannis [Department of Mechanical and Industrial Engineering, University of Thessaly, Volos (Greece)

    2010-02-01

    Pseudospectral Direct Numerical Simulation (DNS) has been performed to simulate dynamo transition for nonhelical magnetohydrodynamics turbulence. The numerical results are compared with a recent low-dimensional model [Verma et al. [13

  20. Sharp magnetic structures from dynamos with density stratification

    Science.gov (United States)

    Jabbari, Sarah; Brandenburg, Axel; Kleeorin, Nathan; Rogachevskii, Igor

    2017-05-01

    Recent direct numerical simulations (DNS) of large-scale turbulent dynamos in strongly stratified layers have resulted in surprisingly sharp bipolar structures at the surface. Here, we present new DNS of helically and non-helically forced turbulence with and without rotation and compare with corresponding mean-field simulations (MFS) to show that these structures are a generic outcome of a broader class of dynamos in density-stratified layers. The MFS agree qualitatively with the DNS, but the period of oscillations tends to be longer in the DNS. In both DNS and MFS, the sharp structures are produced by converging flows at the surface and might be driven in non-linear stage of evolution by the Lorentz force associated with the large-scale dynamo-driven magnetic field if the dynamo number is at least 2.5 times supercritical.

  1. Searching for the fastest dynamo: laminar ABC flows.

    Science.gov (United States)

    Alexakis, Alexandros

    2011-08-01

    The growth rate of the dynamo instability as a function of the magnetic Reynolds number R(M) is investigated by means of numerical simulations for the family of the Arnold-Beltrami-Childress (ABC) flows and for two different forcing scales. For the ABC flows that are driven at the largest available length scale, it is found that, as the magnetic Reynolds number is increased: (a) The flow that results first in a dynamo is the 2 1/2-dimensional flow for which A=B and C=0 (and all permutations). (b) The second type of flow that results in a dynamo is the one for which A=B≃2C/5 (and permutations). (c) The most symmetric flow, A=B=C, is the third type of flow that results in a dynamo. (d) As R(M) is increased, the A=B=C flow stops being a dynamo and transitions from a local maximum to a third-order saddle point. (e) At larger R(M), the A=B=C flow reestablishes itself as a dynamo but remains a saddle point. (f) At the largest examined R(M), the growth rate of the 2 1/2-dimensional flows starts to decay, the A=B=C flow comes close to a local maximum again, and the flow A=B≃2C/5 (and permutations) results in the fastest dynamo with growth rate γ≃0.12 at the largest examined R(M). For the ABC flows that are driven at the second largest available length scale, it is found that (a) the 2 1/2-dimensional flows A=B,C=0 (and permutations) are again the first flows that result in a dynamo with a decreased onset. (b) The most symmetric flow, A=B=C, is the second type of flow that results in a dynamo. It is, and it remains, a local maximum. (c) At larger R(M), the flow A=B≃2C/5 (and permutations) appears as the third type of flow that results in a dynamo. As R(M) is increased, it becomes the flow with the largest growth rate. The growth rates appear to have some correlation with the Lyapunov exponents, but constructive refolding of the field lines appears equally important in determining the fastest dynamo flow.

  2. Hysteresis of dynamos in rotating spherical shell convection

    Science.gov (United States)

    Feudel, F.; Tuckerman, L. S.; Zaks, M.; Hollerbach, R.

    2017-05-01

    Bifurcations of dynamos in rotating and buoyancy-driven spherical Rayleigh-Bénard convection in an electrically conducting fluid are investigated numerically. Both nonmagnetic and magnetic solution branches comprised of rotating waves are traced by path-following techniques, and their bifurcations and interconnections for different Ekman numbers are determined. In particular, the question of whether the dynamo branches bifurcate super- or subcritically and whether a direct link to the primary pure convective states exists is answered.

  3. Numerical investigations of spherical boundary-driven dynamos

    Science.gov (United States)

    White, Katelyn Rose

    A fundamental process in physics is dynamo action which concerns how magnetic fields are generated and maintained against dissipative effects by motion in electrically conducting fluids. This process is ubiquitous in many astrophysical and geophysical contexts. Of particular interest are situations where the polarity of the large scale magnetic field reverses in planets and stars, for example in the Earth and the Sun. This thesis aims to shed light on fundamental aspects of these dynamo processes, motivated by these ultimate applications but also by their relationship to physical experiments designed to explore this problem. The most recent dynamo experiments have been mechanically forced through a boundary effect, such as impellers. We therefore investigate dynamos in a spherical shell forced mechanically by the motion of the boundary via numerical simulations in order to shed light on both the experiments and fundamental processes. We examine and elucidate dynamo mechanisms in such geometries and in particular the role of boundary conditions, and then extend such calculations to asymmetric velocity forcings at the boundary, which is a condition seen experimentally to be necessary for magnetic reversals. Ultimately we focus on localization of the boundary velocity forcing towards the spherical poles in efforts to more closely align our numerical simulations with current dynamo experiments.

  4. Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence

    Science.gov (United States)

    Bodo, G.; Cattaneo, F.; Mignone, A.; Rossi, P.

    2017-07-01

    We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by magneto-rotational turbulence (MRT) within the shearing-box approximation. We consider magnetically open boundary conditions that allow a flux of helicity in or out of the computational domain. We circumvent the problem of the lack of gauge invariance in open domains by choosing a particular gauge—the winding gauge—that provides a natural interpretation in terms of the average winding number of pairwise field lines. We use this gauge precisely to define and measure the helicity and the helicity flux for several realizations of dynamo action. We find in these cases that the system as a whole does not break reflectional symmetry and that the total helicity remains small even in cases when substantial magnetic flux is generated. We find no particular connection between the generation of magnetic flux and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.

  5. Are professional psychology training programs willing the future to economic illiterates?: a clarion call for pedagogical action.

    Science.gov (United States)

    Friedberg, Robert D

    2016-10-01

    The behavioral health care environment in the United States is changing and many experts expect seismic shifts in access, accountability and reimbursement policies. Students in professional psychology training programs will be called upon to administer, manage, supervise and deliver clinically sound as well as cost effective services. While in general, traditional professional psychology training curricula prepare students well for clinical challenges, most students enter the profession naïve to the economic, financial and business enterprise crucibles in the behavioral health care marketplace. This article examines the problem of such naiveté and offers several recommendations for improving graduate students' economic literacy. Moreover, the article argues that increased business and economic acumen may serve to close the research-practice gap in professional psychology. The article reviews literature pertinent to training psychologists and highlights pedagogical gaps. Several recommendations for curricular development are offered. Specifically, adding courses in health care economics and basic business principles is suggested. Integrating cost-effectiveness analyses across all course content is proposed. The article also emphasizes both didactic and experiential learning opportunities. Course work should be augmented with training opportunities at the practicum, internship, and post-doctoral fellowship level.

  6. On the computation of steady, self - consistent spherical dynamos

    Science.gov (United States)

    Fearn, D. R.; Proctor, M. R. E.

    In an earlier paper (Fearn and Proctor, 1984) we described results from a preliminary model of a spherical hydromagnetic dynamo driven by convection. An iterative approach was used. Starting from some guess for the mean toroidal field B we solved for the form of the convective instability in the presence of this field. The mean e.m.f. E [defined in (2.13)] associated with the convection was calculated, and from this, an-effect was constructed (=E/B). We then solved a mean field-dynamo model to produce a new "B". This cycle was repeated until B converged. For a preliminary investigation, there were good reasons for using an-effect formalism. However, a more straightforward and physically more realistic approach is to use the e.m.f. E directly to force the mean field dynamo. This "EΩ-dynamo" is used here. The converged results of Fearn and Proctor (1984) are successfully reproduced and in addition we have found converged steady dynamos in the absence of any poloidal flow (cf. Roberts, 1972). Our iterative dynamo is still far from being completely self-consistent since several parameters and the mean fluid flow have had to be arbitrarily prescribed. The next step is to incorporate more of the dynamics. We use the mean momentum equation to determine the mean flow and, in particular, apply Taylor's (1963) constraint to determine the otherwise arbitrary geostrophic flow UG(s)? The EΩ-dynamo permits this to be done with relative ease (see Fearn and Proctor, 1987). No converged results were found. Solutions either became too detailed to resolve, magnetic instabilities became present, or the solution jumped between two different modes of convection.

  7. ON THE ROLE OF TACHOCLINES IN SOLAR AND STELLAR DYNAMOS

    Energy Technology Data Exchange (ETDEWEB)

    Guerrero, G. [Physics Department, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627, Belo Horizonte, MG, 31270-901 (Brazil); Smolarkiewicz, P. K. [European Centre for Medium-Range Weather Forecasts, Reading RG2 9AX (United Kingdom); De Gouveia Dal Pino, E. M. [Astronomy Department, IAG-USP Rua do mato, 1226, São Paulo, SP, 05508-090 (Brazil); Kosovichev, A. G. [New Jersey Institute of Technology, Newark, NJ 07103 (United States); Mansour, N. N., E-mail: guerrero@fisica.ufmg.br, E-mail: smolar@ecmwf.int, E-mail: dalpino@astro.iag.usp.br, E-mail: sasha@bbso.njit.edu, E-mail: Nagi.N.Mansour@nasa.gov [NASA, Ames Research Center, Moffett Field, Mountain View, CA 94040 (United States)

    2016-03-10

    Rotational shear layers at the boundary between radiative and convective zones, tachoclines, play a key role in the process of magnetic field generation in solar-like stars. We present two sets of global simulations of rotating turbulent convection and dynamo. The first set considers a stellar convective envelope only; the second one, aiming at the formation of a tachocline, also considers the upper part of the radiative zone. Our results indicate that the resulting properties of the mean flows and dynamo, such as the growth rate, saturation energy, and mode, depend on the Rossby number (Ro). For the first set of models either oscillatory (with ∼2 yr period) or steady dynamo solutions are obtained. The models in the second set naturally develop a tachocline, which in turn leads to the generation of a strong mean magnetic field. Since the field is also deposited in the stable deeper layer, its evolutionary timescale is much longer than in the models without a tachocline. Surprisingly, the magnetic field in the upper turbulent convection zone evolves on the same timescale as the deep field. These models result in either an oscillatory dynamo with a ∼30 yr period or a steady dynamo depending on Ro. In terms of the mean-field dynamo coefficients computed using the first-order smoothing approximation, the field evolution in the oscillatory models without a tachocline seems to be consistent with dynamo waves propagating according to the Parker–Yoshimura sign rule. In the models with tachoclines the dynamics is more complex and involves other transport mechanisms as well as tachocline instabilities.

  8. Shear-driven dynamo waves at high magnetic Reynolds number.

    Science.gov (United States)

    Tobias, S M; Cattaneo, F

    2013-05-23

    Astrophysical magnetic fields often display remarkable organization, despite being generated by dynamo action driven by turbulent flows at high conductivity. An example is the eleven-year solar cycle, which shows spatial coherence over the entire solar surface. The difficulty in understanding the emergence of this large-scale organization is that whereas at low conductivity (measured by the magnetic Reynolds number, Rm) dynamo fields are well organized, at high Rm their structure is dominated by rapidly varying small-scale fluctuations. This arises because the smallest scales have the highest rate of strain, and can amplify magnetic field most efficiently. Therefore most of the effort to find flows whose large-scale dynamo properties persist at high Rm has been frustrated. Here we report high-resolution simulations of a dynamo that can generate organized fields at high Rm; indeed, the generation mechanism, which involves the interaction between helical flows and shear, only becomes effective at large Rm. The shear does not enhance generation at large scales, as is commonly thought; instead it reduces generation at small scales. The solution consists of propagating dynamo waves, whose existence was postulated more than 60 years ago and which have since been used to model the solar cycle.

  9. The fate of alpha dynamos at large $Rm$

    CERN Document Server

    Cameron, Alexandre

    2016-01-01

    At the heart of today's solar magnetic field evolution models lies the alpha dynamo description. In this work, we investigate the fate of alpha-dynamos as the magnetic Reynolds number $Rm$ is increased. Using Floquet theory, we are able to precisely quantify mean field effects like the alpha and beta effect (i) by rigorously distinguishing dynamo modes that involve large scale components from the ones that only involve small scales, and by (ii) providing a way to investigate arbitrary large scale separations with minimal computational cost. We apply this framework to helical and non-helical flows as well as to random flows with short correlation time. Our results determine that the alpha-description is valid for $Rm$ smaller than a critical value $Rm_c$ at which small scale dynamo instability starts. When $Rm$ is above $Rm_c$ the dynamo ceases to follow the mean field description and the growth rate of the large scale modes becomes independent of the scale separation while the energy in the large scale modes ...

  10. Numerical Simulations of Dynamos Generated in Spherical Couette Flows

    CERN Document Server

    Guervilly, Céline; 10.1080/03091920903550955

    2010-01-01

    We numerically investigate the efficiency of a spherical Couette flow at generating a self-sustained magnetic field. No dynamo action occurs for axisymmetric flow while we always found a dynamo when non-axisymmetric hydrodynamical instabilities are excited. Without rotation of the outer sphere, typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few thousands. They increase as the mechanical forcing imposed by the inner core on the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\\sim 1$. Oscillating quadrupolar dynamos are present in the vicinity of the dynamo onset. Saturated magnetic fields obtained in supercritical regimes (either $Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3}, 10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic Prandtl number, but we find a peculi...

  11. Magnetic helicity and higher helicity invariants as constraints for dynamo action

    Science.gov (United States)

    Sokoloff, Dmitry; Akhmetyev, Peter; Illarionov, Egor

    2018-01-01

    We consider classical magnetic helicity (a Gauss invariant of magnetic lines) and higher helicity invariants as nonlinear constraints for dynamo action. We argue that the Gauss invariant has several properties absent from higher helicity invariants which prevents use of the latter to constrain dynamo action. We consider other helicities (hydrodynamic helicity and cross helicity) in the context of the dynamo problem.

  12. Predicting cycle 24 using various dynamo-based tools

    Directory of Open Access Journals (Sweden)

    M. Dikpati

    2008-02-01

    Full Text Available Various dynamo-based techniques have been used to predict the mean solar cycle features, namely the amplitude and the timings of onset and peak. All methods use information from previous cycles, including particularly polar fields, drift-speed of the sunspot zone to the equator, and remnant magnetic flux from the decay of active regions. Polar fields predict a low cycle 24, while spot zone migration and remnant flux both lead to predictions of a high cycle 24. These methods both predict delayed onset for cycle 24. We will describe how each of these methods relates to dynamo processes. We will present the latest results from our flux-transport dynamo, including some sensitivity tests and how our model relates to polar fields and spot zone drift methods.

  13. Dynamo regimes and transitions in the VKS experiment

    CERN Document Server

    Berhanu, M; Boisson, J; Gallet, B; Gissinger, C; Fauve, S; Mordant, N; Pétrélis, F; Bourgoin, M; Odier, P; Pinton, J -F; Plihon, N; Aumaître, S; Chiffaudel, A; Daviaud, F; Dubrulle, B; Pirat, C

    2015-01-01

    The Von K{\\'a}rm{\\'a}n Sodium experiment yields a variety of dynamo regimes, when asymmetry is imparted to the flow by rotating impellers at different speed F1 and F2. We show that as the intensity of forcing, measured as F1 + F2, is increased, the transition to a self-sustained magnetic field is always observed via a supercritical bifurcation to a stationary state. For some values of the asymmetry parameter $\\\\theta$ = (F1--F2)/(F1+F2), time dependent dynamo regimes develop. They are observed either when the forcing is increased for a given value of asymmetry, or when the amount of asymmetry is varied at sufficiently high forcing. Two qualitatively different transitions between oscillatory and stationary regimes are reported, involving or not a strong divergence of the period of oscillations. These transitions can be interpreted using a low dimensional model based on the interactions of two dynamo modes.

  14. Persistence of the lunar dynamo: The role of compositional convection

    Science.gov (United States)

    Soderlund, K. M.; Schubert, G.; Scheinberg, A. L.

    2013-12-01

    Although the Moon does not currently have an active magnetic field, it does have magnetic anomalies associated with magnetized materials in the lunar crust. The crustal magnetic anomalies, originally detected during the Apollo era, have been mapped in detail by instruments on the Lunar Prospector and Kaguya (SELENE) spacecraft. Laboratory analyses of the magnetization of some lunar basalts returned from Apollo suggest that a field of approximately 10 microTesla persisted until 3.56 Gyr. Seismic measurements further imply that the Moon has a metallic core with both solid iron and liquid iron alloy components at present day. Thus, it is generally agreed that the early lunar magnetic field was generated by a dynamo. However, the mechanism driving the dynamo is a subject of current debate. Thermal convection alone is likely not sufficient to explain the duration of the dynamo because thermal evolution models predict lunar heat flow through the core to become sub-adiabatic within a few hundred million years. Alternatively, power for the dynamo may be derived from precession of the lunar mantle, impact-induced changes in the Moon's rotation rate, and/or compositional convection due to the formation of a solid inner core. Here, we will present results from a numerical dynamo model designed to simulate magnetic field generation at a number of different times during the Moon's history as predicted by thermal evolution models. These simulations will test the hypothesis that thermo-compositional convection can explain the persistence of the lunar dynamo and advance our understanding of how terrestrial bodies evolve through geologic time.

  15. The solar cycle and solar dynamo models: past accomplishments, present status and a strategy for the 21st century

    Science.gov (United States)

    Dikpati, Mausumi

    2016-07-01

    We describe the primary observational features of solar cycles, as seen in the photosphere, and review progress made over the past sixty years to simulate and predict these features using magneto-hydrodynamic dynamo models. The focus is on the so-called Babcock-Leighton flux-transport (BLFT) dynamo models, calibrated for the Sun, which so far have been the most successful in simulation, and the only ones tested for prediction. The proposed 21st century strategy for progress emphasizes the need (a) to use modern data assimilation techniques, so successful for Earth's atmosphere simulation and prediction, to exploit all available solar observations, and (b) to generalize BLFT dynamo models to 3D to simulate and predict longitude-dependent cycle features. The 3D models must include (a) global HD and MHD instabilities in the solar tachocline, which probably create spatial patterns and time dependence that is reflected in surface observations, such as active longitudes, and (b) processes that capture the statistics and effects of emerging active regions that are tilted with respect to latitude circles, in order to accurately represent the surface source of poloidal fields, whose transport to the poles is responsible for polar field reversals.

  16. On the role of thermal boundary conditions in dynamo scaling laws

    CERN Document Server

    Oruba, Ludivine

    2016-01-01

    In dynamo power-based scaling laws, the power $P$ injected by buoyancy forces is measured by a so-called flux-based Rayleigh number, denoted as ${\\rm Ra}_Q^*$ (see Christensen and Aubert, 2006). Whereas it is widely accepted that this parameter is measured (as opposite to controlled) in dynamos driven by differential heating, the literature is much less clear concerning its nature in the case of imposed heat flux. We clarify this issue by highlighting that in that case, the ${\\rm Ra}_{Q}^*$ parameter becomes controlled only in the limit of large Nusselt numbers (${\\rm Nu} \\gg 1$). We then address the issue of the robustness of the original relation between $P$ and ${\\rm Ra}_Q^*$ with the geometry and the thermal boundary conditions. We show that in the cartesian geometry, as in the spherical geometry with a central mass distribution, this relation is purely linear, in both differential and fixed-flux heating. However, we show that in the geometry commonly studied by geophysicists (spherical with uniform mass ...

  17. Let Your Life Speak: Assessing the Effectiveness of a Program to Explore Meaning, Purpose, and Calling with College Students

    Science.gov (United States)

    Thompson, Elizabeth; Feldman, David B.

    2010-01-01

    Typical career planning courses assist students with the self-assessment process, career exploration, and decision making. Although this assistance is helpful, college students are increasingly concerned with issues of meaning and calling (P. Braun, 2005). The authors describe and test the effectiveness of the Let Your Life Speak course, a program…

  18. A Critical Assessment of the Flux Transport Dynamo

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... We first discuss how the flux transport dynamo with reasonably high diffusion can explain both the regular and the irregular features of the solar cycle quite well. Then, we critically examine the inadequacies of the model and the challenge posed by some recent observational data about meridional ...

  19. Fluctuation dynamo and turbulent induction at small Prandtl number.

    Science.gov (United States)

    Eyink, Gregory L

    2010-10-01

    We study the Lagrangian mechanism of the fluctuation dynamo at zero Prandtl number and infinite magnetic Reynolds number, in the Kazantsev-Kraichnan model of white-noise advection. With a rough velocity field corresponding to a turbulent inertial range, flux freezing holds only in a stochastic sense. We show that field lines arriving to the same point which were initially separated by many resistive lengths are important to the dynamo. Magnetic vectors of the seed field that point parallel to the initial separation vector arrive anticorrelated and produce an "antidynamo" effect. We also study the problem of "magnetic induction" of a spatially uniform seed field. We find no essential distinction between this process and fluctuation dynamo, both producing the same growth rates and small-scale magnetic correlations. In the regime of very rough velocity fields where fluctuation dynamo fails, we obtain the induced magnetic energy spectra. We use these results to evaluate theories proposed for magnetic spectra in laboratory experiments of turbulent induction.

  20. Mean-field dynamo action in renovating shearing flows.

    Science.gov (United States)

    Kolekar, Sanved; Subramanian, Kandaswamy; Sridhar, S

    2012-08-01

    We study mean-field dynamo action in renovating flows with finite and nonzero correlation time (τ) in the presence of shear. Previous results obtained when shear was absent are generalized to the case with shear. The question of whether the mean magnetic field can grow in the presence of shear and nonhelical turbulence, as seen in numerical simulations, is examined. We show in a general manner that, if the motions are strictly nonhelical, then such mean-field dynamo action is not possible. This result is not limited to low (fluid or magnetic) Reynolds numbers nor does it use any closure approximation; it only assumes that the flow renovates itself after each time interval τ. Specifying to a particular form of the renovating flow with helicity, we recover the standard dispersion relation of the α(2)Ω dynamo, in the small τ or large wavelength limit. Thus mean fields grow even in the presence of rapidly growing fluctuations, surprisingly, in a manner predicted by the standard quasilinear closure, even though such a closure is not strictly justified. Our work also suggests the possibility of obtaining mean-field dynamo growth in the presence of helicity fluctuations, although having a coherent helicity will be more efficient.

  1. Solar Internal Rotation and Dynamo Waves: A Two Dimensional ...

    Indian Academy of Sciences (India)

    tribpo

    3Moscow State University, Department of Physics, 119899 Moscow, Russia. * e mail: gbelvedere@alpha4. ct. astro, it. Key words. Sun: magnetic fields, rotation, activity. Extended abstract. Here we outline how asymptotic models may contribute to the investigation of mean field dynamos applied to the solar convective zone.

  2. Colloidal Plasmas: Dynamo transformation of the collisional RT in a ...

    Indian Academy of Sciences (India)

    mechanical nature was first time reported by Dwivedi and Das in 1992 in the context of mesospheric modeling of observed neutral induced turbulence. Local dynamo action (due to relative neutral flow) governs the basic physical principle for linear ...

  3. Energy fluxes in helical magnetohydrodynamics and dynamo action

    Indian Academy of Sciences (India)

    his sabbatical leave. This work was supported in part by the Department of Science and. Technology, India. References. [1] H K Moffatt, Magnetic fields generation in electrically conducting fluids (Cambridge University. Press, Cambridge, 1978). [2] F Krause and K H Rädler, Mean-field magnetohydrodynamics and dynamo ...

  4. Analytic solution of an oscillatory migratory α2 stellar dynamo

    Science.gov (United States)

    Brandenburg, A.

    2017-02-01

    Context. Analytic solutions of the mean-field induction equation predict a nonoscillatory dynamo for homogeneous helical turbulence or constant α effect in unbounded or periodic domains. Oscillatory dynamos are generally thought impossible for constant α. Aims: We present an analytic solution for a one-dimensional bounded domain resulting in oscillatory solutions for constant α, but different (Dirichlet and von Neumann or perfect conductor and vacuum) boundary conditions on the two boundaries. Methods: We solve a second order complex equation and superimpose two independent solutions to obey both boundary conditions. Results: The solution has time-independent energy density. On one end where the function value vanishes, the second derivative is finite, which would not be correctly reproduced with sine-like expansion functions where a node coincides with an inflection point. The field always migrates away from the perfect conductor boundary toward the vacuum boundary, independently of the sign of α. Conclusions: The obtained solution may serve as a benchmark for numerical dynamo experiments and as a pedagogical illustration that oscillatory migratory dynamos are possible with constant α.

  5. Integration of Environmental Sensors with BIM: case studies using Arduino, Dynamo, and the Revit API

    Directory of Open Access Journals (Sweden)

    Kensek, K. M.

    2014-12-01

    Full Text Available This paper investigates the feasibility of connecting environmental sensors such as light, humidity, or CO2 receptors to a building information model (BIM. A base case was created in Rhino; using Grasshopper and Firefly, a simple digital model responded to lighting-levels detected by a photoresistor on an Arduino board. The case study was duplicated using Revit Architecture, a popular BIM software, and Dynamo, a visual programming environment, in an innovative application. Another case study followed a similar procedure by implementing the Revit API directly instead of using Dynamo. Then the process was reversed to demonstrate that not only could data could be sent from sensors to change the 3D model, but changes to parameters of a 3D model could effect a physical model through the use of actuators. It is intended that these virtual/physical prototypes could be used as the basis for testing intelligent façade systems before constructing full size mock-ups.Este estudio investiga la posibilidad de conectar sensores ambientales como de luz, humedad, o dióxido de carbono con un modelo de información de un edificio (siglas BIM en inglés. Un caso base fue creado en Rhino; usando Grasshopper and Firefly, donde un simple modelo digital respondió a niveles de luz detectados por un foto resistor en una tarjeta Arduino. El caso de estudio fue duplicado usando Revit Architecture, una herramienta popular en BIM, y Dynamo, un ambiente de programación gráfica, en una creativa aplicación. Un segundo caso de estudio siguió un procedimiento similar implementando Revit API directamente en vez de usar Dynamo. Entonces el proceso fue revertido para demostrar que no solamente la información podría ser enviada desde sensores para cambiar el modelo tridimensional, pero cambios en los parámetros de un modelo tridimensional podrían afectar un modelo físico mediante el uso de actuadores. Se espera que esos modelos virtuales puedan ser usados como base para

  6. Physical conditions for Jupiter-like dynamo models

    Science.gov (United States)

    Duarte, Lúcia D. V.; Wicht, Johannes; Gastine, Thomas

    2018-01-01

    The Juno mission will measure Jupiter's magnetic field with unprecedented precision and provide a wealth of additional data that will allow us to constrain the planet's interior structure and dynamics. Here we analyse 66 different numerical simulations in order to explore the sensitivity of the dynamo-generated magnetic field to the planets interior properties. Jupiter field models based on pre-Juno data and up-to-date interior models based on ab initio simulations serve as benchmarks. Our results suggest that Jupiter-like magnetic fields can be found for a number of different models. These complement the steep density gradients in the outer part of the simulated shell with an electrical conductivity profile that mimics the low conductivity in the molecular hydrogen layer and thus renders the dynamo action in this region largely unimportant. We find that whether we assume an ideal gas or use the more realistic interior model based on ab initio simulations makes no difference. However, two other factors are important. A low Rayleigh number leads to a too strong axial dipole contribution while the axial dipole dominance is lost altogether when the convective driving is too strong. The required intermediate range that yields Jupiter-like magnetic fields depends on the other system properties. The second important factor is the convective magnetic Reynolds number radial profile Rmc(r), basically a product of the non-axisymmetric flow velocity and electrical conductivity. We find that the depth where Rmc exceeds about 50 is a good proxy for the top of the dynamo region. When the dynamo region sits too deep, the axial dipole is once more too dominant due to geometric reasons. Extrapolating our results to Jupiter and the result suggests that the Jovian dynamo extends to 95% of the planetary radius. The zonal flow system in our simulations is dominated by an equatorial jet which remains largely confined to the molecular layer. Where the jet reaches down to higher

  7. EMERGENCY CALLS

    CERN Document Server

    2001-01-01

    IN URGENT NEED OF A DOCTOR GENEVA EMERGENCY SERVICES GENEVA AND VAUD 144 FIRE BRIGADE 118 POLICE 117 CERN FIREMEN 767-44-44 ANTI-POISONS CENTRE Open 24h/24h 01-251-51-51 Patient not fit to be moved, call family doctor, or: GP AT HOME, open 24h/24h 748-49-50 Association Of Geneva Doctors Emergency Doctors at home 07h-23h 322 20 20 Patient fit to be moved: HOPITAL CANTONAL CENTRAL 24 Micheli-du-Crest 372-33-11 ou 382-33-11 EMERGENCIES 382-33-11 ou 372-33-11 CHILDREN'S HOSPITAL 6 rue Willy-Donzé 372-33-11 MATERNITY 32 bvd.de la Cluse 382-68-16 ou 382-33-11 OPHTHALMOLOGY 22 Alcide Jentzer 382-33-11 ou 372-33-11 MEDICAL CENTRE CORNAVIN 1-3 rue du Jura 345 45 50 HOPITAL DE LA TOUR Meyrin EMERGENCIES 719-61-11 URGENCES PEDIATRIQUES 719-61-00 LA TOUR MEDICAL CENTRE 719-74-00 European Emergency Call 112 FRANCE EMERGENCY SERVICES 15 FIRE BRIGADE 18 POLICE 17 CERN FIREMEN AT HOME 00-41-22-767-44-44 ANTI-POISONS CENTRE Open 24h/24h 04-72-11-69-11 All doctors ...

  8. Small-scale dynamo at low magnetic Prandtl numbers.

    Science.gov (United States)

    Schober, Jennifer; Schleicher, Dominik; Bovino, Stefano; Klessen, Ralf S

    2012-12-01

    The present-day Universe is highly magnetized, even though the first magnetic seed fields were most probably extremely weak. To explain the growth of the magnetic field strength over many orders of magnitude, fast amplification processes need to operate. The most efficient mechanism known today is the small-scale dynamo, which converts turbulent kinetic energy into magnetic energy leading to an exponential growth of the magnetic field. The efficiency of the dynamo depends on the type of turbulence indicated by the slope of the turbulence spectrum v(ℓ)∝ℓ^{ϑ}, where v(ℓ) is the eddy velocity at a scale ℓ. We explore turbulent spectra ranging from incompressible Kolmogorov turbulence with ϑ=1/3 to highly compressible Burgers turbulence with ϑ=1/2. In this work, we analyze the properties of the small-scale dynamo for low magnetic Prandtl numbers Pm, which denotes the ratio of the magnetic Reynolds number, Rm, to the hydrodynamical one, Re. We solve the Kazantsev equation, which describes the evolution of the small-scale magnetic field, using the WKB approximation. In the limit of low magnetic Prandtl numbers, the growth rate is proportional to Rm^{(1-ϑ)/(1+ϑ)}. We furthermore discuss the critical magnetic Reynolds number Rm_{crit}, which is required for small-scale dynamo action. The value of Rm_{crit} is roughly 100 for Kolmogorov turbulence and 2700 for Burgers. Furthermore, we discuss that Rm_{crit} provides a stronger constraint in the limit of low Pm than it does for large Pm. We conclude that the small-scale dynamo can operate in the regime of low magnetic Prandtl numbers if the magnetic Reynolds number is large enough. Thus, the magnetic field amplification on small scales can take place in a broad range of physical environments and amplify week magnetic seed fields on short time scales.

  9. Does the Food Stamp Program cause obesity? A realist review and a call for place-based research.

    Science.gov (United States)

    DeBono, Nathaniel L; Ross, Nancy A; Berrang-Ford, Lea

    2012-07-01

    The high prevalence of obesity among low income groups has led some to question the role of food assistance programs in contributing to the problem. The USDA's Food Stamp Program (now known as the Supplemental Nutrition Assistance Program - SNAP) is the largest food assistance program in the United States with over 40 million participants. This paper employed systematic realist review methods to determine whether participation in the Food Stamp Program causes obesity and the causal pathways through which this relationship may exist. Findings indicate a more consistent positive relationship for women than for men, especially for women who are long term users of the program. All studies discussed the "food stamp cycle" and an "income effect" as explanations for the role of food stamps in increased obesity yet evidence for these factors is limited. Curiously, the research in this field does not address obesogenic environments and we suggest that the absence of an understanding of household behavior in local contexts is a significant impediment to the reform of the Food Stamp Program. Copyright © 2012 Elsevier Ltd. All rights reserved.

  10. CALL English

    DEFF Research Database (Denmark)

    Barlach, Else

    This multimedia program of English grammar caters specifically for Danish students at Bachelor level. The handbook introduces students to well-established grammatical terminology within the traditional areas of English grammar, and the CD-ROM, which contains about 120 exercises, offers students...

  11. VNA HouseCalls of greater Cleveland, Ohio: development and pilot evaluation of a program for high-risk older adults offering primary medical care in the home.

    Science.gov (United States)

    Anetzberger, Georgia J; Stricklin, Mary Lou; Gauntner, Daniel; Banozic, Richard; Laurie, Roberta

    2006-01-01

    The need for primary medical care in the home will increase with a growing elderly and disabled population. The effectiveness of the service must be assessed in light of its relatively high costs. The aim of this study was to evaluate VNA HouseCalls of Greater Cleveland, Ohio during its first year of operations. The program targets high-risk older adults using teams of advanced practice nurses and physicians. The pilot evaluation focused on the attainment of identified program goals. Data collection techniques included clinical record review (N = 139), mailed referral source satisfaction survey, and both mailed and telephone interview patient satisfaction surveys. The results showed that the typical patient served by VNA HouseCalls was a homebound woman in advanced old age with regular family contact and both physical and mental disorders. When asked, the typical patient indicated that without the program she would not have received the care that she needed.VNA HouseCalls helped in preventing functional decline and reducing hospitalization. It received high satisfaction ratings from both referral sources and patients. Study findings suggest that primary care in the home bears further examination for addressing community need and affecting positive patient outcomes for high risk older adults.

  12. Solar and Stellar Dynamos Saas-Fee Advanced Course 39 Swiss Society for Astrophysics and Astronomy

    CERN Document Server

    2013-01-01

    Astrophysical dynamos are at the heart of cosmic magnetic fields of a wide range of scales, from planets and stars to entire galaxies. This book presents a thorough, step-by-step introduction to solar and stellar dynamos. Looking first at the ultimate origin of cosmic seed magnetic fields, the antagonists of field amplification are next considered: resistive decay, flux expulsion, and flows ruled out by anti-dynamo theorems. Two kinematic flows that can act as dynamos are then studied: the Roberts cell and the CP-flow. Mean-field electrodynamics and derivation of the mean-field dynamo equations lead to the alpha Omega-dynamo, the flux transport dynamo, and dynamos based on the Babcock-Leighton mechanism. Alternatives to the mean-field theory are also presented, as are global MHD dynamo simulations. Fluctuations and grand minima in the solar cycle are discussed in terms of dynamo modulations through stochastic forcing and nonlinear effects. The book concludes with an overview of the major challenges in underst...

  13. What Are We Missing A Call for Red Teaming Within the Domestic Maritime Domain for Anti-Terrorism Programs

    Science.gov (United States)

    2015-12-01

    is entrepreneurship . “Anyone who is creating a new product or business under conditions of extreme uncertainty is an entrepreneur whether he or she...and sustain the proposed set of red teaming programs, it will be important to have those working within, and customers of Coast Guard terrorism risk...Business (New York: Collins Business Essentials, 1997), 2. 54 of the organization. Failure to achieve and sustain these efforts would put considerable

  14. Dynamo onset as a first-order transition: lessons from a shell model for magnetohydrodynamics.

    Science.gov (United States)

    Sahoo, Ganapati; Mitra, Dhrubaditya; Pandit, Rahul

    2010-03-01

    We carry out systematic and high-resolution studies of dynamo action in a shell model for magnetohydrodynamic (MHD) turbulence over wide ranges of the magnetic Prandtl number PrM and the magnetic Reynolds number ReM. Our study suggests that it is natural to think of dynamo onset as a nonequilibrium first-order phase transition between two different turbulent, but statistically steady, states. The ratio of the magnetic and kinetic energies is a convenient order parameter for this transition. By using this order parameter, we obtain the stability diagram (or nonequilibrium phase diagram) for dynamo formation in our MHD shell model in the (PrM-1,ReM) plane. The dynamo boundary, which separates dynamo and no-dynamo regions, appears to have a fractal character. We obtain a hysteretic behavior of the order parameter across this boundary and suggestions of nucleation-type phenomena.

  15. Fluid Dynamics Prize Lecture: Homogeneous Dynamos in Planets and in the Laboratory

    Science.gov (United States)

    Busse, F. H.

    2000-11-01

    Numerical simulations of the dynamo problem of the generation of magnetic fields by convection flows in rotating spherical fluid shells have been extended to a sufficiently large parameter regime such that extrapolation to the condition of planetary cores have become feasible. Besides dipolar fields, hemispherical and quadrupolar fields are preferred in various regimes of the parameter space. In the latter two cases oscillating time dependances are always found inspite of the chaotic nature of the dynamos. Subcritical dynamo states are typical and multiple dynamo states are possible. On the experimental side the homogeneous dynamo process has recently been demonstrated without the use of ferromagnetic material in Riga and Karlsruhe. Further experiments at other laboratories are expected to realize dynamos under conditions of strong turbulence.

  16. Gender-Based Violence Against Transgender People in the United States: A Call for Research and Programming.

    Science.gov (United States)

    Wirtz, Andrea L; Poteat, Tonia C; Malik, Mannat; Glass, Nancy

    2018-01-01

    Gender-based violence (GBV) is an umbrella term for any harm that is perpetrated against a person's will and that results from power inequalities based on gender roles. Most global estimates of GBV implicitly refer only to the experiences of cisgender, heterosexually identified women, which often comes at the exclusion of transgender and gender nonconforming (trans) populations. Those who perpetrate violence against trans populations often target gender nonconformity, gender expression or identity, and perceived sexual orientation and thus these forms of violence should be considered within broader discussions of GBV. Nascent epidemiologic research suggests a high burden of GBV among trans populations, with an estimated prevalence that ranges from 7% to 89% among trans populations and subpopulations. Further, 165 trans persons have been reported murdered in the United States between 2008 and 2016. GBV is associated with multiple poor health outcomes and has been broadly posited as a component of syndemics, a term used to describe an interaction of diseases with underlying social forces, concomitant with limited prevention and response programs. The interaction of social stigma, inadequate laws, and punitive policies as well as a lack of effective GBV programs limits access to and use of GBV prevention and response programs among trans populations. This commentary summarizes the current body of research on GBV among trans populations and highlights areas for future research, intervention, and policy.

  17. Impact of Convection on Surface Fluxes Observed During LASP/DYNAMO 2011

    Science.gov (United States)

    2014-12-01

    CONVECTION ON SURFACE FLUXES OBSERVED DURING LASP/ DYNAMO 2011 by Matthew S. Cushanick December 2014 Thesis Advisor: Qing Wang Second Reader...December 2014 Master’s Thesis 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS IMPACT OF CONVECTION ON SURFACE FLUXES OBSERVED DURING LASP/ DYNAMO 2011 6...during the Littoral Air-Sea Processes (LASP)/Dynamics of Madden-Julian Oscillation ( DYNAMO ) experiment. The low-level measurements from the WP-30 are

  18. Dynamo Enhancement and Mode Selection Triggered by High Magnetic Permeability

    Science.gov (United States)

    Kreuzahler, S.; Ponty, Y.; Plihon, N.; Homann, H.; Grauer, R.

    2017-12-01

    We present results from consistent dynamo simulations, where the electrically conducting and incompressible flow inside a cylinder vessel is forced by moving impellers numerically implemented by a penalization method. The numerical scheme models jumps of magnetic permeability for the solid impellers, resembling various configurations tested experimentally in the von Kármán sodium experiment. The most striking experimental observations are reproduced in our set of simulations. In particular, we report on the existence of a time-averaged axisymmetric dynamo mode, self-consistently generated when the magnetic permeability of the impellers exceeds a threshold. We describe a possible scenario involving both the turbulent flow in the vicinity of the impellers and the high magnetic permeability of the impellers.

  19. Constraining Substellar Magnetic Dynamos using Auroral Radio Emission

    Science.gov (United States)

    Kao, Melodie; Hallinan, Gregg; Pineda, J. Sebastian; Escala, Ivanna; Burgasser, Adam J.; Stevenson, David J.

    2017-01-01

    An important outstanding problem in dynamo theory is understanding how magnetic fields are generated and sustained in fully convective stellar objects. A number of models for possible dynamo mechanisms in this regime have been proposed but constraining data on magnetic field strengths and topologies across a wide range of mass, age, rotation rate, and temperature are sorely lacking, particularly in the brown dwarf regime. Detections of highly circularly polarized pulsed radio emission provide our only window into magnetic field measurements for objects in the ultracool brown dwarf regime. However, these detections are very rare; previous radio surveys encompassing ˜60 L6 or later targets have yielded only one detection. We have developed a selection strategy for biasing survey targets based on possible optical and infrared tracers of auroral activity. Using our selection strategy, we previously observed six late L and T dwarfs with the Jansky Very Large Array (VLA) and detected the presence of highly circularly polarized radio emission for five targets. Our initial detections at 4-8 GHz provided the most robust constraints on dynamo theory in this regime, confirming magnetic fields >2.5 kG. To further develop our understanding of magnetic fields in the ultracool brown dwarf mass regime bridging planets and stars, we present constraints on surface magnetic field strengths for two Y-dwarfs as well as higher frequency observations of the previously detected L/T dwarfs corresponding ~3.6 kG fields. By carefully comparing magnetic field measurements derived from auroral radio emission to measurements derived from Zeeman broadening and Zeeman Doppler imaging, we provide tentative evidence that the dynamo operating in this mass regime may be inconsistent with predicted values from currently in vogue models. This suggests that parameters beyond convective flux may influence magnetic field generation in brown dwarfs.

  20. Mars' paleomagnetic field as the result of a single-hemisphere dynamo.

    Science.gov (United States)

    Stanley, Sabine; Elkins-Tanton, Linda; Zuber, Maria T; Parmentier, E Marc

    2008-09-26

    Mars' crustal magnetic field was most likely generated by dynamo action in the planet's early history. Unexplained characteristics of the field include its strength, concentration in the southern hemisphere, and lack of correlation with any surface features except for the hemispheric crustal dichotomy. We used numerical dynamo modeling to demonstrate that the mechanisms proposed to explain crustal dichotomy formation can result in a single-hemisphere dynamo. This dynamo produces strong magnetic fields in only the southern hemisphere. This magnetic field morphology can explain why Mars' crustal magnetic field intensities are substantially stronger in the southern hemisphere without relying on any postdynamo mechanisms.

  1. Effect of small scale motions on dynamo actions generated by the Beltrami-like flows

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Mingtian, E-mail: mingtian@sdu.edu.cn

    2016-08-12

    The geodynamo and solar dynamo are driven by the turbulent flows which involve motions of various scales. Of particular interest is what role is played by the small scale motions in these dynamos. In this paper, the integral equation approach is employed to investigate the effect of the small scale motions on dynamo actions driven by multiscale Beltrami-like flows in a cylindrical vessel. The result shows that some small scale motions can trigger a transition of a dynamo from a steady to an unsteady state. Our results also show that when the poloidal components of the small and large scale flows share the same direction in the equatorial plane, the small scale flows have more positive or less detrimental effect on the onsets of the dynamo actions in comparison with the case that the poloidal components have different directions. These findings shed light on the effect of the small scale turbulence on dynamo actions. - Highlights: • Dynamo actions driven by multiscale Beltrami-like flows are investigated. • Some small scale motions induce transition of dynamo from steady to unsteady state. • Direction of small scale poloidal flow has a significant effect on dynamo threshold.

  2. DYNAMO: A Dynamic Architectural Memory On-line

    Directory of Open Access Journals (Sweden)

    Ann Heylighen

    2000-01-01

    Full Text Available This paper describes the current status of DYNAMO, a web-based design assistant for students and professional designers in the field of architecture. The tool can be considered a Case-Based Design (CBD system in so far that it was inspired by the view of cognition underlying CBD. The paper points out how DYNAMO incorporates this view, and at the same time extrapolates it beyond the individual. In this way, the tool attempts to embrace and profit from several kinds of interaction that are crucial for the development and renewal of design knowledge. This should result in a design tool that both feels cognitively comfortable to (student- designers, and offers them a platform for exchanging knowledge and insights with colleagues in different contexts and at different levels of experience. In addition, the paper describes the implementation of these theoretical ideas as a working prototype, which has recently been tested by 4th year design students. Finally, DYNAMO is situated in the context of other comparable tools that have been or are being developed in the field of architectural design.

  3. An impact-driven dynamo for the early Moon.

    Science.gov (United States)

    Le Bars, M; Wieczorek, M A; Karatekin, O; Cébron, D; Laneuville, M

    2011-11-09

    The origin of lunar magnetic anomalies remains unresolved after their discovery more than four decades ago. A commonly invoked hypothesis is that the Moon might once have possessed a thermally driven core dynamo, but this theory is problematical given the small size of the core and the required surface magnetic field strengths. An alternative hypothesis is that impact events might have amplified ambient fields near the antipodes of the largest basins, but many magnetic anomalies exist that are not associated with basin antipodes. Here we propose a new model for magnetic field generation, in which dynamo action comes from impact-induced changes in the Moon's rotation rate. Basin-forming impact events are energetic enough to have unlocked the Moon from synchronous rotation, and we demonstrate that the subsequent large-scale fluid flows in the core, excited by the tidal distortion of the core-mantle boundary, could have powered a lunar dynamo. Predicted surface magnetic field strengths are on the order of several microteslas, consistent with palaeomagnetic measurements, and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins.

  4. Faraday rotation signatures of fluctuation dynamos in young galaxies

    Science.gov (United States)

    Sur, Sharanya; Bhat, Pallavi; Subramanian, Kandaswamy

    2018-01-01

    Observations of Faraday rotation through high-redshift galaxies has revealed that they host coherent magnetic fields that are of comparable strengths to those observed in nearby galaxies. These fields could be generated by fluctuation dynamos. We use idealized numerical simulations of such dynamos in forced compressible turbulence up to rms Mach number of 2.4 to probe the resulting rotation measure (RM) and the degree of coherence of the magnetic field. We obtain rms values of RM at dynamo saturation of the order of 45 - 55 per cent of the value expected in a model where fields are assumed to be coherent on the forcing scale of turbulence. We show that the dominant contribution to the RM in subsonic and transonic cases comes from the general sea of volume filling fields, rather than from the rarer structures. However, in the supersonic case, strong field regions as well as moderately overdense regions contribute significantly. Our results can account for the observed RMs in young galaxies.

  5. Some consequences of shear on galactic dynamos with helicity fluxes

    Science.gov (United States)

    Zhou, Hongzhe; Blackman, Eric G.

    2017-08-01

    Galactic dynamo models sustained by supernova (SN) driven turbulence and differential rotation have revealed that the sustenance of large-scale fields requires a flux of small-scale magnetic helicity to be viable. Here we generalize a minimalist analytic version of such galactic dynamos to explore some heretofore unincluded contributions from shear on the total turbulent energy and turbulent correlation time, with the helicity fluxes maintained by either winds, diffusion or magnetic buoyancy. We construct an analytic framework for modelling the turbulent energy and correlation time as a function of SN rate and shear. We compare our prescription with previous approaches that include only rotation. The solutions depend separately on the rotation period and the eddy turnover time and not just on their ratio (the Rossby number). We consider models in which these two time-scales are allowed to be independent and also a case in which they are mutually dependent on radius when a radial-dependent SN rate model is invoked. For the case of a fixed rotation period (or a fixed radius), we show that the influence of shear is dramatic for low Rossby numbers, reducing the correlation time of the turbulence, which, in turn, strongly reduces the saturation value of the dynamo compared to the case when the shear is ignored. We also show that even in the absence of winds or diffusive fluxes, magnetic buoyancy may be able to sustain sufficient helicity fluxes to avoid quenching.

  6. A hemispherical dynamo model: Implications for the Martian crustal magnetization

    Science.gov (United States)

    Dietrich, W.; Wicht, J.; Christensen, U. R.

    2011-12-01

    In 1999 the Mars Global Surveyor detected a strong but very heterogeneous crustal magnetization mainly localized in the southern hemisphere. Their magnetization dichotomy may have either an external or an internal origin. In the first scenario, the Martian crust was fully magnetized by a dipolar dynamo induced in the Martian liquid core. After the core dynamo cessation, the crust was demagnetized by volcanoes, impacts or any other resurfacing event distributed not homogeneously over the surface. The internal origin, which is investigated here, relies on a per se hemispherical internal magnetric field. For this, we rely on that Mars never developed an inner core. The planets ancient dynamo was thus exclusively driven by secular cooling and radiogenic heating. Due to the small planetary size, the core mantle boundary (CMB) heat flux may be not as homogeneous, as in e.g. Earth. Mantle convection in smaller planets is thought to develope larger scales, maybe even a huge single-plume structure. Giant impacts might have played a crucial role in the thermal history of Mars, hence they are heating mainly one hemisphere. Giant plumes and major impact events would both cause a hemispherical CMB heat flux pattern. Therefore, we model the ancient Martian dynamo as rotating, convecting and conducting fluid heated by an internal heat source and contained in a spherical shell, where the CMB heat flux is perturbed by a sinusoidal anomaly. Compared to the classical columnar convection, we find a drastically different flow pattern. There meridional circulation seeking to equilibrate the heat difference between both hemispheres is diverted into two counterdirected cells of axisymmetric zonal flows (thermal winds) by the strong Coriolis force. Convective plumes are confined to the region of high heat flux in the vicinity of the southern pole. Core convection is thus dominated by equatorially antisymmetric and axisymmetric (EAA) modes. In the columnar regime, poloidal and toroidal

  7. Southeast regional and state trends in anuran occupancy from calling survey data (2001-2013) from the North American Amphibian Monitoring Program

    Science.gov (United States)

    Villena Carpio, Oswaldo; Royle, J. Andrew; Weir, Linda; Foreman, Tasha M.; Gazenski, Kimberly D.; Campbell Grant, Evan H.

    2016-01-01

    We present the first regional trends in anuran occupancy for eight states of the southeastern United States, based on 13 y (2001–2013) of North American Amphibian Monitoring Program (NAAMP) data. The NAAMP is a longterm monitoring program in which observers collect anuran calling observation data at fixed locations along random roadside routes. We assessed occupancy trends for 14 species. We found weak evidence for a general regional pattern of decline in calling anurans within breeding habitats along roads in the southeastern USA over the last 13 y. Two species had positive regional trends with 95% posterior intervals that did not include zero (Hyla cinerea and Pseudacris crucifer). Five other species also showed an increasing trend, while eight species showed a declining trend, although 95% posterior intervals included zero. We also assessed state level trends for 107 species/state combinations. Of these, 14 showed a significant decline and 12 showed a significant increase in occupancy (i.e., credible intervals did not include zero for these 26 trends).

  8. Coupled fluid-flow and magnetic-field simulation of the Riga dynamo experiment

    NARCIS (Netherlands)

    Kenjereš, S.; Hanjali?, K.; Renaudier, S.; Stefani, F.; Gerbeth, G.; Gailitis, A.

    2006-01-01

    Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electroconducting fluids, also known as the dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment [ A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000) ; A. Gailitis et

  9. Observations of non-solar-type dynamo processes in stars with shallow convective zones

    NARCIS (Netherlands)

    Jeffers, S.V.|info:eu-repo/dai/nl/326052658; Donati, J.F.; Alecian, E.; Marsden, S.C.

    2010-01-01

    The magnetic field topology and differential rotation are fundamental signatures of the dynamo processes that generate the magnetic activity observed in the Sun and solar-type stars. To investigate how these dynamo processes evolve in stars with shallow convective zones, we present high-resolution

  10. COHERENT NONHELICAL SHEAR DYNAMOS DRIVEN BY MAGNETIC FLUCTUATIONS AT LOW REYNOLDS NUMBERS

    Energy Technology Data Exchange (ETDEWEB)

    Squire, J.; Bhattacharjee, A., E-mail: jsquire@caltech.edu [Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States)

    2015-11-01

    Nonhelical shear dynamos are studied with a particular focus on the possibility of coherent dynamo action. The primary results—serving as a follow up to the results of Squire and Bhattacharjee—pertain to the “magnetic shear-current effect” as a viable mechanism to drive large-scale magnetic field generation. This effect raises the interesting possibility that the saturated state of the small-scale dynamo could drive large-scale dynamo action, and is likely to be important in the unstratified regions of accretion disk turbulence. In this paper, the effect is studied at low Reynolds numbers, removing the complications of small-scale dynamo excitation and aiding analysis by enabling the use of quasi-linear statistical simulation methods. In addition to the magnetically driven dynamo, new results on the kinematic nonhelical shear dynamo are presented. These illustrate the relationship between coherent and incoherent driving in such dynamos, demonstrating the importance of rotation in determining the relative dominance of each mechanism.

  11. A Three-dimensional Multilayered Spherical Dynamic Interface Dynamo Using the Malkus-Proctor Formulation

    Science.gov (United States)

    Chan, K. H.; Liao, X.; Zhang, K.

    2008-08-01

    We investigate a fully three-dimensional and multilayered spherical dynamic interface dynamo using a finite-element method based on the three-dimensional tetrahedralization of the whole spherical system. The dynamic interface dynamo model consists of four magnetically coupled zones: an electrically conducting and uniformly rotating core, a thin differentially rotating tachocline, a turbulent convection envelope, and a nearly insulating exterior. In the thin tachocline at the base of the convection zone, a differential rotation, similar to that of the observed solar differential rotation, is imposed. In the convection zone, the Malkus-Proctor formulation with a prescribed α-effect is employed while the fully three-dimensional dynamic feedback of Lorentz forces is taken into account. Our numerical simulations of the dynamic interface dynamo are focused on the Taylor number Ta = 105 with a unity magnetic Prandtl number. It is shown that the dynamic interface dynamo, depending on the size of the magnetic Reynolds number Rem based on the differential rotation, can be either nonaxisymmetric or axisymmetric. When Rem is small or moderate, the dynamic dynamo is characterized by quasi-periodic and nonaxisymmetric azimuthally traveling waves. When Rem is sufficiently large, the dynamo is characterized by a strong toroidal magnetic field, axisymmetric or nearly axisymmetric, that selects dipolar symmetry and propagates equatorward. Implications of our dynamic interface dynamo for the solar dynamo are also discussed.

  12. Effect of the Lorentz force on on-off dynamo intermittency.

    Science.gov (United States)

    Alexakis, Alexandros; Ponty, Yannick

    2008-05-01

    An investigation of the dynamo instability close to the threshold produced by an ABC forced flow is presented. We focus on the on-off intermittency behavior of the dynamo and the countereffect of the Lorentz force in the nonlinear stage of the dynamo. The Lorentz force drastically alters the statistics of the turbulent fluctuations of the flow and reduces their amplitude. As a result, much longer bursts (on phases) are observed than is expected based on the amplitude of the fluctuations in the kinematic regime of the dynamo. For large Reynolds numbers, the duration time of the on phase follows a power law distribution, while for smaller Reynolds numbers the Lorentz force completely kills the noise and the system transits from a chaotic state into a laminar time periodic flow. The behavior of the on-off intermittency as the Reynolds number is increased is also examined. The connections with dynamo experiments and theoretical modeling are discussed.

  13. Role of large-scale velocity fluctuations in a two-vortex kinematic dynamo.

    Science.gov (United States)

    Kaplan, E J; Brown, B P; Rahbarnia, K; Forest, C B

    2012-06-01

    This paper presents an analysis of the Dudley-James two-vortex flow, which inspired several laboratory-scale liquid-metal experiments, in order to better demonstrate its relation to astrophysical dynamos. A coordinate transformation splits the flow into components that are axisymmetric and nonaxisymmetric relative to the induced magnetic dipole moment. The reformulation gives the flow the same dynamo ingredients as are present in more complicated convection-driven dynamo simulations. These ingredients are currents driven by the mean flow and currents driven by correlations between fluctuations in the flow and fluctuations in the magnetic field. The simple model allows us to isolate the dynamics of the growing eigenvector and trace them back to individual three-wave couplings between the magnetic field and the flow. This simple model demonstrates the necessity of poloidal advection in sustaining the dynamo and points to the effect of large-scale flow fluctuations in exciting a dynamo magnetic field.

  14. F-region dynamo current as deduced from the magnetic-field observations by CHAMP

    Science.gov (United States)

    Park, Jaeheung; Luehr, Hermann; Rother, Martin; Min, Kyoung; Michaelis, Ingo

    Thermospheric neutral winds generate dynamo currents through ion-neutral collision. In ease of the equatorial F-region dynamo the current forms a meridional circuit in each hemisphere, leading to asymmetric zonal deflections of the geomagnetic field [Lühr and Maus, 2006]. Us-u ing magnetic observations of the CHAMP satellite, we investigate variations of the F-region dynamo current with season, longitude, local time, and solar activity. Dynamo currents show pronounced seasonal/longitudinal (S/L) variations. Around noon they show different longitu-dinal structures in each season. At dusk its S/L variation shows a rough correlation with that of the evening pre-reversal enhancement (PRE) of vertical drift. The dynamo current increases with solar activity. All the results imply that magnetic field data can be a useful proxy for ionospheric E-fields. Precise magnetic observations and accurate models will further improve this technique.

  15. The Spherically Symmetric a2–dynamo and Some of its Spectral Peculiarities

    Directory of Open Access Journals (Sweden)

    U. Günther

    2007-01-01

    Full Text Available A brief overview is given of recent results on the spectral properties of spherically symmetric MHD α2-dynamos. In particular, the spectra of sphere-confined fluid or plasma configurations with physically realistic boundary conditions (BCs (surrounding vacuum and with idealized BCs (super-conducting surrounding are discussed. The subjects comprise third-order branch points of the spectrum, self-adjointness of the dynamo operator in a Krein space as well as the resonant unfolding of diabolical points. It is sketched how certain classes of dynamos with a strongly localized α-profile embedded in a conducting surrounding can be mode decoupled by a diagonalization ofthe dynamo operator matrix. A mapping of the dynamo eigenvalue problem to that of a quantum mechanical Hamiltonian with energy dependent potential is used to obtain qualitative information about the spectral behavior. Links to supersymmetric Quantum Mechanics and to the Dirac equation are indicated.

  16. A simplified model of collision-driven dynamo action in small bodies

    CERN Document Server

    Wei, Xing

    2013-01-01

    We investigate numerically the self-sustained dynamo action in a spinning sphere whose sense of rotation reverses periodically. This system serves as a simple model of a dynamo in small bodies powered by frequent collisions. It is found that dynamo action is possible in some intervals of collision rates. At high Ekman numbers the laminar spin-up flow is helical in the boundary layers and the Ekman circulation together with the azimuthal shear powers the dynamo action. At low Ekman number a non-axisymmetric instability helps the dynamo action. The intermittency of magnetic field occurs at low Ekman number. A lower bound of magnetic energy is numerically obtained, and the space-averaged field in the fluid core and the surface field of a small body are roughly estimated.

  17. Solar Field Mapping and Dynamo Behavior

    Directory of Open Access Journals (Sweden)

    Kenneth H. Schatten

    2012-01-01

    Full Text Available We discuss the importance of the Sun’s large-scale magnetic field to the Sun-Planetary environment. This paper narrows its focus down to the motion and evolution of the photospheric large-scale magnetic field which affects many environments throughout this region. For this purpose we utilize a newly developed Netlogo cellular automata model. The domain of this algorithmic model is the Sun’s photosphere. Within this computational space are placed two types of entities or agents; one may refer to them as bluebirds and cardinals; the former carries outward magnetic flux and the latter carries out inward magnetic flux. One may simply call them blue and red agents. The agents provide a granularity with discrete changes not present in smooth MHD models; they undergo three processes: birth, motion, and death within the photospheric domain. We discuss these processes, as well as how we are able to develop a model that restricts its domain to the photosphere and allows the deeper layers to be considered only through boundary conditions. We show the model’s ability to mimic a number of photospheric magnetic phenomena: the solar cycle (11-year oscillations, the Waldmeier effect, unipolar magnetic regions (e.g. sectors and coronal holes, Maunder minima, and the march/rush to the poles involving the geometry of magnetic field reversals. We also discuss why the Sun sometimes appears as a magnetic monopole, which of course requires no alteration of Maxwell’s equations.

  18. Variational data assimilation for the initial-value dynamo problem.

    Science.gov (United States)

    Li, Kuan; Jackson, Andrew; Livermore, Philip W

    2011-11-01

    The secular variation of the geomagnetic field as observed at the Earth's surface results from the complex magnetohydrodynamics taking place in the fluid core of the Earth. One way to analyze this system is to use the data in concert with an underlying dynamical model of the system through the technique of variational data assimilation, in much the same way as is employed in meteorology and oceanography. The aim is to discover an optimal initial condition that leads to a trajectory of the system in agreement with observations. Taking the Earth's core to be an electrically conducting fluid sphere in which convection takes place, we develop the continuous adjoint forms of the magnetohydrodynamic equations that govern the dynamical system together with the corresponding numerical algorithms appropriate for a fully spectral method. These adjoint equations enable a computationally fast iterative improvement of the initial condition that determines the system evolution. The initial condition depends on the three dimensional form of quantities such as the magnetic field in the entire sphere. For the magnetic field, conservation of the divergence-free condition for the adjoint magnetic field requires the introduction of an adjoint pressure term satisfying a zero boundary condition. We thus find that solving the forward and adjoint dynamo system requires different numerical algorithms. In this paper, an efficient algorithm for numerically solving this problem is developed and tested for two illustrative problems in a whole sphere: one is a kinematic problem with prescribed velocity field, and the second is associated with the Hall-effect dynamo, exhibiting considerable nonlinearity. The algorithm exhibits reliable numerical accuracy and stability. Using both the analytical and the numerical techniques of this paper, the adjoint dynamo system can be solved directly with the same order of computational complexity as that required to solve the forward problem. These numerical

  19. Using Jupiter's gravitational field to probe the Jovian convective dynamo.

    Science.gov (United States)

    Kong, Dali; Zhang, Keke; Schubert, Gerald

    2016-03-23

    Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection.

  20. CALL-BASED INSTRUCTION MODEL OF SPEAKING ENGLISH (A Developmental Research at the English Language Education Study Program of STKIP Kusuma Negara, Jakarta

    Directory of Open Access Journals (Sweden)

    Siti Yulidhar Harunasari

    2015-06-01

    Full Text Available The objective of this research is to develop a model of learning speaking English for students majoring in English Language Education in STKIP Kusuma Jakarta, and to examine the effectiveness of CALL-Based instruction the model in improving students’ speaking skill. The research was conducted using system approach model of Dick and Carey, and was carried out from October 2012 to July 2014 in 3 stages i.e. preliminary stage; model development stage; validation, evaluation, and revision stage. The data were obtained through tests, questionnaires, interviews, observation, and expert judgments. The English speaking test was designed to measure students speaking skill before and after the implementation of the model. Then, the data were analyzed qualitatively and quantitatively. The research findings showed that the development of the model can improve the students’ speaking skill through the increase in the mean score before the implementation of the model, 61 to 69 after implementation of the model. The testing of hypothesis using paired-samples t-test resulted in a probability value (sig 0.000 < α = 0.05 which means that there is a significant difference on students speaking skill before and after implementing the CALL-based instruction model. It can be concluded that the model is effective in improving the students speaking skill in English Education Study Program of STKIP Kusuma Negara Jakarta.

  1. CARIAA Call - Frequently Asked Questions

    International Development Research Centre (IDRC) Digital Library (Canada)

    IDRC CRDI

    2013-03-28

    Mar 28, 2013 ... The call states that CARIAA will also collaborate with the consortia on programmatic functions that support the program as a whole, including communication, outreach and engagement, knowledge management, and monitoring and evaluation. What kind of activities are envisaged? 48). The call states that ...

  2. Dramatically Enhanced Spin Dynamo with Plasmonic Diabolo Cavity.

    Science.gov (United States)

    Gou, Peng; Qian, Jie; Xi, Fuchun; Zou, Yuexin; Cao, Jun; Yu, Haochi; Zhao, Ziyi; Yang, Le; Xu, Jie; Wang, Hengliang; Zhang, Lijian; An, Zhenghua

    2017-07-13

    The applications of spin dynamos, which could potentially power complex nanoscopic devices, have so far been limited owing to their extremely low energy conversion efficiencies. Here, we present a unique plasmonic diabolo cavity (PDC) that dramatically improves the spin rectification signal (enhancement of more than three orders of magnitude) under microwave excitation; further, it enables an energy conversion efficiency of up to ~0.69 mV/mW, compared with ~0.27 μV/mW without a PDC. This remarkable improvement arises from the simultaneous enhancement of the microwave electric field (~13-fold) and the magnetic field (~195-fold), which cooperate in the spin precession process generates photovoltage (PV) efficiently under ferromagnetic resonance (FMR) conditions. The interplay of the microwave electromagnetic resonance and the ferromagnetic resonance originates from a hybridized mode based on the plasmonic resonance of the diabolo structure and Fabry-Perot-like modes in the PDC. Our work sheds light on how more efficient spin dynamo devices for practical applications could be realized and paves the way for future studies utilizing both artificial and natural magnetism for applications in many disciplines, such as for the design of future efficient wireless energy conversion devices, high frequent resonant spintronic devices, and magnonic metamaterials.

  3. The Role of Kinetic Instabilities in the Collisionless Turbulent Dynamo

    Science.gov (United States)

    St-Onge, D. A.; Kunz, M. W.

    2017-10-01

    Conservation of the first adiabatic invariant μ in a magnetized, collisionless plasma precludes turbulent amplification of the magnetic field. This is because any increase in magnetic-field strength would adiabatically increase the perpendicular pressure, whose growth is stringently limited by the finite free energy in the system. A mechanism is then needed to break μ conservation in order to enable the amplification of a weak, primordial seed magnetic field to dynamically important strengths. Conveniently, amplification of the magnetic field in a high-beta plasma leads to pressure anisotropies large enough to trigger kinetic instabilities at ion-Larmor scales (e.g., firehose, mirror). These instabilities saturate by causing anomalous scattering of particles, breaking μ conservation. This interplay between magnetic-field growth and kinetic instabilities adds a new layer of complexity to the more conventional (and much better understood) magnetohydrodynamic turbulent dynamo. Using self-consistent hybrid-kinetic, particle-in-cell simulations, we investigate the impact of these kinetic instabilities on the turbulent dynamo in a collisionless plasma, with a particular focus on how kinetic effects enable the amplification of magnetic fields and modify their structure. This work was supported by U.S. DOE contract DE-AC02-09CH11466.

  4. Dynamo tests for stratification below the core-mantle boundary

    Science.gov (United States)

    Olson, Peter; Landeau, Maylis; Reynolds, Evan

    2017-10-01

    Evidence from seismology, mineral physics, and core dynamics suggests a layer with an overall stable stratification in the Earth's outer core, possibly thermal in origin, extending below the core-mantle boundary (CMB) for several hundred kilometers. Yet vigorous deep mantle convection with locally elevated heat flux implies locally unstable thermal stratification below the CMB, consistent with interpretations of non-dipole geomagnetic field behavior that favor upwelling flows in places below the CMB. To resolve this apparent inconsistency, we investigate the structure of convection and magnetic fields in the core using numerical dynamos with laterally heterogeneous boundary heat flux. Strongly heterogeneous boundary heat flux generates localized convection beneath the CMB that coexists with an overall stable stratification there. Our partially stratified dynamos are distinguished by their time average magnetic field structures. Without stratification or with stratification confined to a thin layer, the octupole component is small and the CMB magnetic field structure includes polar intensity minima. With more extensive stratification, the octupole component is large and the magnetic field structure includes intense patches or high intensity lobes in the polar regions. Comparisons with the time-averaged geomagnetic field are generally favorable for partial stratification in a thin (<400 km) layer but unfavorable for stratification in a thick (∼1000 km) layer beneath the CMB.

  5. Dynamo action in dissipative, forced, rotating MHD turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Shebalin, John V. [Astromaterials Research Office, NASA Johnson Space Center, Houston, Texas 77058-3696 (United States)

    2016-06-15

    Magnetohydrodynamic (MHD) turbulence is an inherent feature of large-scale, energetic astrophysical and geophysical magnetofluids. In general, these are rotating and are energized through buoyancy and shear, while viscosity and resistivity provide a means of dissipation of kinetic and magnetic energy. Studies of unforced, rotating, ideal (i.e., non-dissipative) MHD turbulence have produced interesting results, but it is important to determine how these results are affected by dissipation and forcing. Here, we extend our previous work and examine dissipative, forced, and rotating MHD turbulence. Incompressibility is assumed, and finite Fourier series represent turbulent velocity and magnetic field on a 64{sup 3} grid. Forcing occurs at an intermediate wave number by a method that keeps total energy relatively constant and allows for injection of kinetic and magnetic helicity. We find that 3-D energy spectra are asymmetric when forcing is present. We also find that dynamo action occurs when forcing has either kinetic or magnetic helicity, with magnetic helicity injection being more important. In forced, dissipative MHD turbulence, the dynamo manifests itself as a large-scale coherent structure that is similar to that seen in the ideal case. These results imply that MHD turbulence, per se, may play a fundamental role in the creation and maintenance of large-scale (i.e., dipolar) stellar and planetary magnetic fields.

  6. Quantifying paleosecular variation: Insights from numerical dynamo simulations

    Science.gov (United States)

    Lhuillier, F.; Gilder, S. A.

    2013-12-01

    Numerical dynamo simulations can be used to investigate paleosecular variation of Earth-like magnetic fields over several million-year timescales. Using a set of five numerical models integrated over the equivalent of 40-50 Myr, we generated synthetic data analogous to paleomagnetic data. We show that paleosecular variation among the five models is best discriminated by the relative variability in paleointensity (ɛ_F) and the precision parameter (k) of directions or poles. Whether the geodynamo operated in different regimes in its past can be best tested with these parameters in combination. Roughly one million years of time with 200 time-independent samples is required to achieve convergence of ɛ_F and k. The quantities ɛ_F and k correlate well with the average chron duration (μ_chr), which suggests that excursions and reversals are an integral part of palaeosecular variation. If applicable to the geodynamo, the linear dependence of k on μ_chr could help to predict μ_chr for the Earth during geologic times with no available reversal frequency data; it also predicts much higher average k for directions during superchrons (k ≈ 2500 for the Cretaceous normal superchron) than during actively reversing times (k ≈ 35 for the last 80 Myr). As such high k values are not observed, either this family of dynamo models is not applicable to the geodynamo, or the geodynamo regime acting during superchrons lies statistically within the same energy state as at present.

  7. Effect of an art brut therapy program called go beyond the schizophrenia (GBTS) on prison inmates with schizophrenia in mainland China-A randomized, longitudinal, and controlled trial.

    Science.gov (United States)

    Qiu, Hong-Zhong; Ye, Zeng-Jie; Liang, Mu-Zi; Huang, Yue-Qun; Liu, Wei; Lu, Zhi-Dong

    2017-09-01

    Creative arts therapies are proven to promote an interconnection between body and mind, but there are major obstacles for providing therapeutic services in prisons due to inmates' inherent mistrust for verbal disclosure and rigid self-defenses, especially among inmates with schizophrenia. Thus, we developed a structured and quantitative art brut therapy program called go beyond the schizophrenia to actually measure the benefits of art therapy on prison inmates in mainland China. Upon completion of the program, the intervention group reported a decrease in anxiety, depression, anger, and negative psychiatric symptoms and showed better compliance with rules, socialization with peers, compliance with medications, and regular sleeping patterns after 16 weekly sessions of go beyond the schizophrenia. This article concludes that the art brut therapy was effective for the inmates with schizophrenia in mainland China and provides encouraging data on how to enhance mental health for inmates with schizophrenia. Art brut therapy can reduce emotional distress and negative psychiatric symptoms among Chinese inmates. Arts brut therapy can enhance Chinese inmates' compliance with rules, socialization with peers, compliance with medicines, and regular sleeping patterns. Arts brut therapy in conjunction with medication is highly recommended for recovery of Chinese inmates with schizophrenia, especially for patients with negative symptoms. Copyright © 2017 John Wiley & Sons, Ltd.

  8. Implication of kinematic dynamo studies for the geodynamo

    Science.gov (United States)

    Gubbins, David

    2008-04-01

    In the kinematic dynamo problem Maxwell's equations are solved for the magnetic field given a prescribed fluid velocity. Although no dynamic equations are involved, it does provide an accurate link between the magnetic field and fluid velocity and can therefore be used to infer something about the flow underlying the observed geomagnetic field. In this sense it complements the commonly used frozen-flux theory for inverting secular variation for core flow, in which electrical diffusion is neglected, and can be used to show up some of the strengths and weaknesses of the frozen-flux approximation. It might be thought that kinematic models have been superceded by dynamic models that include the momentum and heat equations, but this is not the case. Even the biggest numerical simulation cannot approach the correct parameters for the Earth's core, and the classes of flows that result are, in fact, quite restricted as well as being too complex for simple physical interpretation. A variety of simple flows have been studied for dynamo action; of particular interest here are a broad class of flows, based loosely on extensions of the early simple choice of Bullard & Gellman and to some extent representative of what might be generated by convection in the Earth's rapidly rotating core: this paper reviews the implications of the solutions for geomagnetism. The non-axisymmetric flows mimic convection rolls in a rotating sphere, the axisymmetric poloidal flows describe meridional circulation, a likely secondary flow, and the axisymmetric toroidal flow is a simple differential rotation. Helicity, which seems to be important for dynamo action, is related to spiralling of the rolls. Dipole, rather than quadrupole, fields are preferred when spiralling is eastward and differential rotation westward at the surface. Magnetic flux tends to be concentrated at stagnation points of the flow, and dynamo action fails when this concentration becomes so intense that steep gradients develop so

  9. A long-lived lunar dynamo driven by continuous mechanical stirring.

    Science.gov (United States)

    Dwyer, C A; Stevenson, D J; Nimmo, F

    2011-11-09

    Lunar rocks contain a record of an ancient magnetic field that seems to have persisted for more than 400 million years and which has been attributed to a lunar dynamo. Models of conventional dynamos driven by thermal or compositional convection have had difficulty reproducing the existence and apparently long duration of the lunar dynamo. Here we investigate an alternative mechanism of dynamo generation: continuous mechanical stirring arising from the differential motion, due to Earth-driven precession of the lunar spin axis, between the solid silicate mantle and the liquid core beneath. We show that the fluid motions and the power required to drive a dynamo operating continuously for more than one billion years and generating a magnetic field that had an intensity of more than one microtesla 4.2 billion years ago are readily obtained by mechanical stirring. The magnetic field is predicted to decrease with time and to shut off naturally when the Moon recedes far enough from Earth that the dissipated power is insufficient to drive a dynamo; in our nominal model, this occurred at about 48 Earth radii (2.7 billion years ago). Thus, lunar palaeomagnetic measurements may be able to constrain the poorly known early orbital evolution of the Moon. This mechanism may also be applicable to dynamos in other bodies, such as large asteroids.

  10. Dynamo generation of magnetic field in the white dwarf GD 358

    Science.gov (United States)

    Markiel, J. Andrew; Thomas, John H.; Van Horn, H. M.

    1994-01-01

    On the basis of Whole Earth Telescope observations of the g-mode oscillation spectrum of the white dwarf GD 358, Winget et al. find evidence for significant differential rotation and for a time-varying magnetic field concentrated in the surface layers of this star. Here we argue on theoretical grounds that this magnetic field is produced by an alpha omega dynamo operating in the lower part of a surface convection zone in GD 358. Our argument is based on numerical solutions of the nonlinear, local dynamo equations of Robinson & Durney, with specific parameters based on our detailed models of white-dwarf convective envelopes, and universal constants determined by a calibration with the the Sun's dynamo. The calculations suggest a dynamo cycle period of about 6 years for the fundamental mode, and periods as short as 1 year for the higher-order modes that are expected to dominate in view of the large dynamo number we estimate for GD 358. These dynamo periods are consistent with the changes in the magnetic field of GD 358 over the span of 1 month inferred by Winget et. al. from their observations. Our calculations also suggest a peak dynamo magnetic field strength at the base of the surface convection zone of about 1800 G, which is consistent with the field strength inferred from the observations.

  11. Call Forecasting for Inbound Call Center

    Directory of Open Access Journals (Sweden)

    Peter Vinje

    2009-01-01

    Full Text Available In a scenario of inbound call center customer service, the ability to forecast calls is a key element and advantage. By forecasting the correct number of calls a company can predict staffing needs, meet service level requirements, improve customer satisfaction, and benefit from many other optimizations. This project will show how elementary statistics can be used to predict calls for a specific company, forecast the rate at which calls are increasing/decreasing, and determine if the calls may stop at some point.

  12. IS THE SMALL-SCALE MAGNETIC FIELD CORRELATED WITH THE DYNAMO CYCLE?

    Energy Technology Data Exchange (ETDEWEB)

    Karak, Bidya Binay; Brandenburg, Axel, E-mail: bbkarak@nordita.org [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)

    2016-01-01

    The small-scale magnetic field is ubiquitous at the solar surface—even at high latitudes. From observations we know that this field is uncorrelated (or perhaps even weakly anticorrelated) with the global sunspot cycle. Our aim is to explore the origin, and particularly the cycle dependence, of such a phenomenon using three-dimensional dynamo simulations. We adopt a simple model of a turbulent dynamo in a shearing box driven by helically forced turbulence. Depending on the dynamo parameters, large-scale (global) and small-scale (local) dynamos can be excited independently in this model. Based on simulations in different parameter regimes, we find that, when only the large-scale dynamo is operating in the system, the small-scale magnetic field generated through shredding and tangling of the large-scale magnetic field is positively correlated with the global magnetic cycle. However, when both dynamos are operating, the small-scale field is produced from both the small-scale dynamo and the tangling of the large-scale field. In this situation, when the large-scale field is weaker than the equipartition value of the turbulence, the small-scale field is almost uncorrelated with the large-scale magnetic cycle. On the other hand, when the large-scale field is stronger than the equipartition value, we observe an anticorrelation between the small-scale field and the large-scale magnetic cycle. This anticorrelation can be interpreted as a suppression of the small-scale dynamo. Based on our studies we conclude that the observed small-scale magnetic field in the Sun is generated by the combined mechanisms of a small-scale dynamo and tangling of the large-scale field.

  13. Kinematic α tensors and dynamo mechanisms in a von Kármán swirling flow.

    Science.gov (United States)

    Ravelet, F; Dubrulle, B; Daviaud, F; Ratié, P-A

    2012-07-13

    We provide experimental and numerical evidence of in-blades vortices in the von Kármán swirling flow. We estimate the associated kinematic α-effect tensor and show that it is compatible with recent models of the von Kármán sodium (VKS) dynamo. We further show that depending on the relative frequency of the two impellers, the dominant dynamo mechanism may switch from α2 to α - Ω dynamo. We discuss some implications of these results for VKS experiments.

  14. The energy coupling function and the power generated by the solar wind-magnetosphere dynamo

    Science.gov (United States)

    Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

    1980-01-01

    A solar wind parameter epsilon, known as the energy coupling function, has been shown to correlate with the power consumption in the magnetosphere. It is shown in the present paper that the parameter epsilon can be identified semi-quantitatively as the dynamo power delivered from the solar wind to an open magnetosphere. This identification not only provides a theoretical basis for the energy coupling function, but also constitutes an observational verification of the solar wind-magnetosphere dynamo along the magnetotail. Moreover, one can now conclude that a substorm results when the dynamo power exceeds 10 to the 18th erg/s.

  15. Thellier-Thellier Paleointensity of the Lunar Core Dynamo

    Science.gov (United States)

    Suavet, C. R.; Weiss, B. P.; Andrade Lima, E.; Tikoo, S. M.; Fu, R. R.; Wang, H.; Wang, J.; Chen-Wiegart, Y. C. K.

    2014-12-01

    A number of paleomagnetic studies based on Alternating Field (AF) demagnetization of lunar samples have recently shown that the Moon had a dynamo magnetic field of several tens of μT at 4.2 Ga, 3.72 Ga, 3.56 Ga, and that the field had declined to below a few μT by 3.2 Ga. Although uncertainties associated with AF-derived paleointensity estimates are up to a factor of 3, these values are too high to be explained by current lunar dynamo models: based on estimates of the power available to drive a dynamo in the early history of the Moon, it is expected that the field intensity should have been of the order of a few μT. Thermal demagnetization-based techniques such as the Thellier-Thellier paleointensity method have much lower uncertainties on the paleofield, but attempts have consistently failed due to alteration of the metal-bearing lunar samples when heated. We have recently designed the first system to conduct thermal demagnetization with oxygen fugacity control using mixtures of H2 and CO2to mitigate alteration. We are applying this method to the following lunar samples: - Regolith breccia 15498. Impact melt from this breccia acquired a magnetization at 1.0-1.3 Ga. We conducted a Thellier-Thellier paleointensity experiment in a controlled atmosphere with oxygen fugacity at IW-1 log(atm). pTRM checks indicate that alteration is negligible up to 500°C. A paleointensity of 3.2 μT is obtained for the origin-trending high-temperature (>250°C) component. This is consistent with estimates based on AF-demagnetization data. - Troctolite 76535. A single plagioclase crystal from 4.2 Gyr-old troctolite 76535 was thermally demagnetized in a controlled atmosphere with oxygen fugacity at IW-1 log(atm). The synchrotron transmission X-ray microscopy and hysteresis parameters show that the major magnetization carriers are fine-grained pseudo-single domain metal inclusions. Due to the small size and weak magnetization of the sample (natural remanent magnetization (NRM) ~5x10

  16. THE SMALL-SCALE DYNAMO AND NON-IDEAL MAGNETOHYDRODYNAMICS IN PRIMORDIAL STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Schober, Jennifer; Federrath, Christoph; Glover, Simon; Klessen, Ralf S. [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Schleicher, Dominik [Institut fuer Astrophysik, Georg-August-Universitaet Goettingen, Friedrich-Hund-Platz, D-37077 Goettingen (Germany); Banerjee, Robi, E-mail: schober@stud.uni-heidelberg.de, E-mail: christoph.federrath@monash.edu, E-mail: glover@uni-heidelberg.de, E-mail: klessen@uni-heidelberg.de, E-mail: dschleic@astro.physik.uni-goettingen.de, E-mail: banerjee@hs.uni-hamburg.de [Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg (Germany)

    2012-08-01

    We study the amplification of magnetic fields during the formation of primordial halos. The turbulence generated by gravitational infall motions during the formation of the first stars and galaxies can amplify magnetic fields very efficiently and on short timescales up to dynamically significant values. Using the Kazantsev theory, which describes the so-called small-scale dynamo-a magnetohydrodynamical process converting kinetic energy from turbulence into magnetic energy-we can then calculate the growth rate of the small-scale magnetic field. Our calculations are based on a detailed chemical network and we include non-ideal magnetohydrodynamical effects such as ambipolar diffusion and Ohmic dissipation. We follow the evolution of the magnetic field up to larger scales until saturation occurs on the Jeans scale. Assuming a weak magnetic seed field generated by the Biermann battery process, both Burgers and Kolmogorov turbulence lead to saturation within a rather small density range. Such fields are likely to become relevant after the formation of a protostellar disk and, thus, could influence the formation of the first stars and galaxies in the universe.

  17. Reconciling solar and stellar magnetic cycles with nonlinear dynamo simulations.

    Science.gov (United States)

    Strugarek, A; Beaudoin, P; Charbonneau, P; Brun, A S; do Nascimento, J-D

    2017-07-14

    The magnetic fields of solar-type stars are observed to cycle over decadal periods-11 years in the case of the Sun. The fields originate in the turbulent convective layers of stars and have a complex dependency upon stellar rotation rate. We have performed a set of turbulent global simulations that exhibit magnetic cycles varying systematically with stellar rotation and luminosity. We find that the magnetic cycle period is inversely proportional to the Rossby number, which quantifies the influence of rotation on turbulent convection. The trend relies on a fundamentally nonlinear dynamo process and is compatible with the Sun's cycle and those of other solar-type stars. Copyright © 2017, American Association for the Advancement of Science.

  18. Modeling of the Coupled Magnetospheric and Neutral Wind Dynamos

    Science.gov (United States)

    Thayer, Jeffrey P.

    1997-01-01

    Over the past four years of funding, SRI, in collaboration with the University of Texas at Dallas, has been involved in assessing the influence of thermospheric neutral winds on the electric field and current systems at high latitudes. The initial direction of the project was to perform a set of numerical experiments concerning the contribution of the magnetospheric and neutral wind dynamo processes, under specific boundary conditions, to the polarization electric field and/or the field-aligned current distribution at high latitudes. To facilitate these numerical experiments we developed a numerical scheme that relied on using output from the NCAR Thermosphere-Ionosphere General Circulation Model (NCAR-TIGCM), expanding them in the form of spherical harmonics and solving the dynamo equations spectrally. Once initial calculations were completed, it was recognized that the neutral wind contribution could be significant but its actual contribution to the electric field or currents depended strongly on the generator properties of the magnetosphere. Solutions to this problem are not unique because of the unknown characteristics of the magnetospheric generator, therefore the focus was on two limiting cases. One limiting case was to consider the magnetosphere as a voltage generator delivering a fixed voltage to the high-latitude ionosphere and allowing for the neutral wind dynamo to contribute only to the current system. The second limiting case was to consider the magnetosphere as a current generator and allowing for the neutral wind dynamo to contribute only to the generation of polarization electric fields. This work was completed and presented at the l994 Fall AGU meeting. The direction of the project then shifted to applying the Poynting flux concept to the high-latitude ionosphere. This concept was more attractive as it evaluated the influence of neutral winds on the high-latitude electrodynamics without actually having to determine the generator characteristics of

  19. MAGNETIC HELICITY REVERSALS IN A CYCLIC CONVECTIVE DYNAMO

    Energy Technology Data Exchange (ETDEWEB)

    Miesch, Mark S. [High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307-3000 (United States); Zhang, Mei [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Datun Road A20, Chaoyang District, Beijing 100012 (China); Augustson, Kyle C., E-mail: miesch@ucar.edu [CEA/DRF/IRFU Service d’Astrophysique, CEA-Saclay, Batiment 709, F-91191 Gif-sur-Yvette Cedex (France)

    2016-06-10

    We investigate the role of magnetic helicity in promoting cyclic magnetic activity in a global, 3D, magnetohydrodynamic (MHD) simulation of a convective dynamo. This simulation is characterized by coherent bands of toroidal field that exist within the convection zone, with opposite polarities in the northern hemisphere (NH) and southern hemisphere (SH). Throughout most of the cycle, the magnetic helicity in these bands is negative in the NH and positive in the SH. However, during the declining phase of each cycle, this hemispheric rule reverses. We attribute this to a global restructuring of the magnetic topology that is induced by the interaction of the bands across the equator. This band interaction appears to be ultimately responsible for, or at least associated with, the decay and subsequent reversal of both the toroidal bands and the polar fields. We briefly discuss the implications of these results within the context of solar observations, which also show some potential evidence for toroidal band interactions and helicity reversals.

  20. Spherical convective dynamos in the rapidly rotating asymptotic regime

    CERN Document Server

    Aubert, Julien; Fournier, Alexandre

    2016-01-01

    Self-sustained convective dynamos in planetary systems operate in an asymptotic regime of rapid rotation, where a balance is thought to hold between the Coriolis, pressure, buoyancy and Lorentz forces (the MAC balance). Classical numerical solutions have previously been obtained in a regime of moderate rotation where viscous and inertial forces are still significant. We define a unidimensional path in parameter space between classical models and asymptotic conditions from the requirements to enforce a MAC balance and to preserve the ratio between the magnetic diffusion and convective overturn times (the magnetic Reynolds number). Direct numerical simulations performed along this path show that the spatial structure of the solution at scales larger than the magnetic dissipation length is largely invariant. This enables the definition of large-eddy simulations resting on the assumption that small-scale details of the hydrodynamic turbulence are irrelevant to the determination of the large-scale asymptotic state...

  1. The DYNAMO Simulation Language--An Alternate Approach to Computer Science Education.

    Science.gov (United States)

    Bronson, Richard

    1986-01-01

    Suggests the use of computer simulation of continuous systems as a problem solving approach to computer languages. Outlines the procedures that the system dynamics approach employs in computer simulations. Explains the advantages of the special purpose language, DYNAMO. (ML)

  2. A solar dynamo surface wave at the interface between convection and nonuniform rotation

    Science.gov (United States)

    Parker, E. N.

    1993-01-01

    A simple dynamo surface wave is presented to illustrate the basic principles of a dynamo operating in the thin layer of shear and suppressed eddy diffusion beneath the cyclonic convection in the convection zone of the sun. It is shown that the restriction of the shear delta(Omega)/delta(r) to a region below the convective zone provides the basic mode with a greatly reduced turbulent diffusion coefficient in the region of strong azimuthal field. The dynamo takes on the character of a surface wave tied to the lower surface z = 0 of the convective zone. There is a substantial body of evidence suggesting a fibril state for the principal flux bundles beneath the surface of the sun, with fundamental implications for the solar dynamo.

  3. Generation of Large-Scale Magnetic Fields by Small-Scale Dynamo in Shear Flows.

    Science.gov (United States)

    Squire, J; Bhattacharjee, A

    2015-10-23

    We propose a new mechanism for a turbulent mean-field dynamo in which the magnetic fluctuations resulting from a small-scale dynamo drive the generation of large-scale magnetic fields. This is in stark contrast to the common idea that small-scale magnetic fields should be harmful to large-scale dynamo action. These dynamos occur in the presence of a large-scale velocity shear and do not require net helicity, resulting from off-diagonal components of the turbulent resistivity tensor as the magnetic analogue of the "shear-current" effect. Given the inevitable existence of nonhelical small-scale magnetic fields in turbulent plasmas, as well as the generic nature of velocity shear, the suggested mechanism may help explain the generation of large-scale magnetic fields across a wide range of astrophysical objects.

  4. Magnetism, dynamo action and the solar-stellar connection

    Science.gov (United States)

    Brun, Allan Sacha; Browning, Matthew K.

    2017-09-01

    The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star's life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism—e.g., its dependence on stellar age, mass, or rotation rate—that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the "Solar-stellar connection": i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief summary of what we have learned, and a sampling of issues that remain uncertain or unsolved.

  5. Magnetism, dynamo action and the solar-stellar connection

    Directory of Open Access Journals (Sweden)

    Allan Sacha Brun

    2017-09-01

    Full Text Available Abstract The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star’s life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism—e.g., its dependence on stellar age, mass, or rotation rate—that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the “Solar-stellar connection”: i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief summary of what we have learned, and a sampling of issues that remain uncertain or unsolved.

  6. Implementing an Evidence-based Tobacco Control Program at Five 2-1-1 Call Centers: An Evaluation Using the Consolidated Framework for Implementation Research.

    Science.gov (United States)

    Thompson, Tess; Kreuter, Matthew W; Caito, Nicole; Williams, Rebecca S; Escoffery, Cam; Fernandez, Maria E; Kegler, Michelle C

    2017-10-10

    The Smoke-Free Homes Program (SFH) is an evidence-based intervention offered within 2-1-1 information and referral call centers to promote smoke-free homes in low-income populations. We used the Consolidated Framework for Implementation Research to conduct a mixed-methods analysis of facilitators and barriers to scaling up SFH to five 2-1-1 sites in the United States. Data were collected from staff in 2015-2016 via online surveys administered before (N = 120) and after SFH training (N = 101) and after SFH implementation (N = 79). Semi-structured telephone interviews were conducted in 2016 with 25 staff to examine attitudes towards SFH, ways local context affected implementation, and unintended benefits and consequences of implementing SFH. Post-implementation, 79% of respondents reported SFH was consistent with their 2-1-1's mission, 70% thought it led to more smoke-free homes in their population, 62% thought it was easy to adapt, and 56% thought participants were satisfied. Composite measures of perceived appropriateness of SFH for 2-1-1 callers and staff positivity toward SFH were significantly lower post-implementation than pre-implementation. In interviews, staff said SFH fit with their 2-1-1's mission but expressed concerns about intervention sustainability, time and resources needed for delivery, and how SFH fit into their workflow. Sites' SFH implementation experiences were affected both by demands of intervention delivery and by SFH's perceived effectiveness and fit with organizational mission. Future implementation of SFH and other tobacco control programs should address identified barriers by securing ongoing funding, providing dedicated staff time, and ensuring programs fit with staff workflow. Smoke-free homes policies reduce exposure to second-hand smoke. Partnering with social service agencies offers a promising way to scale up evidence-based smoke-free homes interventions among low-income populations. We found that the SFH intervention was acceptable

  7. A magnetic betelgeuse? Numerical simulations of non-linear dynamo action

    DEFF Research Database (Denmark)

    Dorch, S. B. F.

    2004-01-01

    question regarding the nature of Betelgeuse and supergiants in general is whether these stars may be magnetically active. If so, that may in turn also contribute to their variability. By performing detailed numerical simulations, I find that both linear kinematic and non-linear dynamo action are possible...... and that the non-linear magnetic field saturates at a value somewhat below equipartition: in the linear regime there are two modes of dynamo action....

  8. Towards the geophysical regime in numerical dynamo models: studies of rapidly-rotating convection driven dynamos with low Pm and constant heat flux boundary conditions

    DEFF Research Database (Denmark)

    Sheyko, A.A.; Finlay, Chris; Marti, P.

    We present a set of numerical dynamo models with the convection strength varied by a factor of 30 and the ratio of magnetic to viscous diffusivities by a factor of 20 at rapid rotation rates (E =nu/(2 Omega d^2 ) = 10-6 and 10-7 ) using a heat flux outer BC. This regime has been little explored...... on the structure of the dynamos and how this changes in relation to the selection of control parameters, a comparison with the proposed rotating convection and dynamo scaling laws, energy spectra of steady solutions and inner core rotation rates. Magnetic field on the CMB. E=2.959*10-7, Ra=6591.0, Pm=0.05, Pr=1....

  9. Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow

    Science.gov (United States)

    Riols, A.; Rincon, F.; Cossu, C.; Lesur, G.; Ogilvie, G. I.; Longaretti, P.-Y.

    2015-03-01

    The magnetorotational (MRI) dynamo has long been considered one of the possible drivers of turbulent angular momentum transport in astrophysical accretion disks. However, various numerical results suggest that this dynamo may be difficult to excite in the astrophysically relevant regime of magnetic Prandtl number (Pm) significantly smaller than unity, for reasons currently not well understood. The aim of this article is to present the first results of an ongoing numerical investigation of the role of both linear and nonlinear dissipative effects in this problem. Combining a parametric exploration and an energy analysis of incompressible nonlinear MRI dynamo cycles representative of the transitional dynamics in large aspect ratio shearing boxes, we find that turbulent magnetic diffusion makes the excitation and sustainment of this dynamo at moderate magnetic Reynolds number (Rm) increasingly difficult for decreasing Pm. This results in an increase in the critical Rm of the dynamo for increasing kinematic Reynolds number (Re), in agreement with earlier numerical results. Given its very generic nature, we argue that turbulent magnetic diffusion could be an important determinant of MRI dynamo excitation in disks, and may also limit the efficiency of angular momentum transport by MRI turbulence in low Pm regimes.

  10. Solar-type dynamo behaviour in fully convective stars without a tachocline.

    Science.gov (United States)

    Wright, Nicholas J; Drake, Jeremy J

    2016-07-28

    In solar-type stars (with radiative cores and convective envelopes like our Sun), the magnetic field powers star spots, flares and other solar phenomena, as well as chromospheric and coronal emission at ultraviolet to X-ray wavelengths. The dynamo responsible for generating the field depends on the shearing of internal magnetic fields by differential rotation. The shearing has long been thought to take place in a boundary layer known as the tachocline between the radiative core and the convective envelope. Fully convective stars do not have a tachocline and their dynamo mechanism is expected to be very different, although its exact form and physical dependencies are not known. Here we report observations of four fully convective stars whose X-ray emission correlates with their rotation periods in the same way as in solar-type stars. As the X-ray activity-rotation relationship is a well-established proxy for the behaviour of the magnetic dynamo, these results imply that fully convective stars also operate a solar-type dynamo. The lack of a tachocline in fully convective stars therefore suggests that this is not a critical ingredient in the solar dynamo and supports models in which the dynamo originates throughout the convection zone.

  11. Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars

    Science.gov (United States)

    Warnecke, J.; Rheinhardt, M.; Tuomisto, S.; Käpylä, P. J.; Käpylä, M. J.; Brandenburg, A.

    2018-01-01

    Aims: We investigate dynamo action in global compressible solar-like convective dynamos in the framework of mean-field theory. Methods: We simulate a solar-type star in a wedge-shaped spherical shell, where the interplay between convection and rotation self-consistently drives a large-scale dynamo. To analyze the dynamo mechanism we apply the test-field method for azimuthally (φ) averaged fields to determine the 27 turbulent transport coefficients of the electromotive force, of which six are related to the α tensor. This method has previously been used either in simulations in Cartesian coordinates or in the geodynamo context and is applied here for the first time to fully compressible simulations of solar-like dynamos. Results: We find that the φφ-component of the α tensor does not follow the profile expected from that of kinetic helicity. The turbulent pumping velocities significantly alter the effective mean flows acting on the magnetic field and therefore challenge the flux transport dynamo concept. All coefficients are significantly affected by dynamically important magnetic fields. Quenching as well as enhancement are being observed. This leads to a modulation of the coefficients with the activity cycle. The temporal variations are found to be comparable to the time-averaged values and seem to be responsible for a nonlinear feedback on the magnetic field generation. Furthermore, we quantify the validity of the Parker-Yoshimura rule for the equatorward propagation of the mean magnetic field in the present case.

  12. INTERIOR STRUCTURE OF WATER PLANETS: IMPLICATIONS FOR THEIR DYNAMO SOURCE REGIONS

    Energy Technology Data Exchange (ETDEWEB)

    Yunsheng Tian, Bob; Stanley, Sabine, E-mail: ytian@physics.utoronto.ca [Department of Physics, University of Toronto (Canada)

    2013-05-10

    Recent discoveries of water-rich, sub-Neptunian- to Neptunian-massed exoplanets with short-period orbits present a new parameter space for the study of exoplanetary dynamos. We explore the geometry of the dynamo source region within this parameter space using 1D interior structure models. We model planets with four chemically distinct layers that consist of (1) an iron core, (2) a silicate layer, (3) an H{sub 2}O layer, and (4) an H/He envelope. By varying the total planetary mass in the range of 1-19 M{sub Circled-Plus }, the mass fraction of the H/He envelope between 0.1% and 5.1%, and the equilibrium temperature between 100 K and 1000 K, a survey of the parameter space for potential dynamo source region geometries is conducted. We find that due to the nature of the phase diagram of water at pressure and temperature conditions of planetary interiors, two different dynamo source region geometries are obtainable. Specifically, we find that smaller planets, and planets with thicker H/He envelopes, are likely to be in the regime of a thick-shelled dynamo. Massive planets, and planets with thin H/He envelopes, are likely to be in the regime of a thin-shelled dynamo. Also, small variations of these parameters can produce large interior structure differences. This implies the potential to constrain these parameters based on observations of a planet's magnetic field signature.

  13. Joint and Coordinated Calls for Science and Technology Programs between Ukraine and the European Commission as a Potential Tool for Harmonization of the EU-Ukraine Priorities

    Directory of Open Access Journals (Sweden)

    M. Gorohovatska

    2013-07-01

    Full Text Available Results of scientific cooperation between European countries, including Ukraine, within the Seventh Framework Programme for Research and Technological Development are reviewed. Terms of preparation of joint and coordinated EUUkraine calls within the Framework Programme «Horizon 2020» are discussed; terms and conditions of participation in these calls are determined.

  14. Processing Doppler Lidar and Cloud Radar Observations for Analysis of Convective Mass Flux Parameterizations Using DYNAMO Direct Observations

    Science.gov (United States)

    2014-09-30

    for Analysis of Convective Mass Flux Parameterizations Using DYNAMO Direct Observations R. Michael Hardesty CIRES/University of Colorado/NOAA 325...the RV-Revell during legs 2 & 3 of the DYNAMO experiement to help characterize vertical transport through the boundary layer and to build statistics...obtained during DYNAMO , and to investigate whether cold pools that emanate from convection organize the interplay between humidity and convection and

  15. CALL-BASED INSTRUCTION MODEL OF SPEAKING ENGLISH (A Developmental Research at the English Language Education Study Program of STKIP Kusuma Negara, Jakarta)

    National Research Council Canada - National Science Library

    Siti Yulidhar Harunasari; Aceng Rahmat

    2015-01-01

    The objective of this research is to develop a model of learning speaking English for students majoring in English Language Education in STKIP Kusuma Jakarta, and to examine the effectiveness of CALL...

  16. Global bifurcations to subcritical magnetorotational dynamo action in Keplerian shear flow

    Science.gov (United States)

    Riols, A.; Rincon, F.; Cossu, C.; Lesur, G.; Longaretti, P.-Y.; Ogilvie, G. I.; Herault, J.

    2013-09-01

    Magnetorotational dynamo action in Keplerian shear flow is a three-dimensional, nonlinear magnetohydrodynamic process whose study is relevant to the understanding of accretion and magnetic field generation in astrophysics. Transition to this form of dynamo is subcritical and shares many characteristics of transition to turbulence in non-rotating hydrodynamic shear flows. This suggests that these different fluid systems become active through similar generic bifurcation mechanisms, which in both cases have eluded detailed understanding so far. In this paper, we investigate numerically the bifurcation mechanisms at work in the incompressible Keplerian magnetorotational dynamo problem in the shearing box framework. Using numerical techniques imported from dynamical systems research, we show that the onset of chaotic dynamo action at magnetic Prandtl numbers larger than unity is primarily associated with global homoclinic and heteroclinic bifurcations of nonlinear magnetorotational dynamo cycles. These global bifurcations are supplemented by local bifurcations of cycles marking the beginning of period-doubling cascades. This suggests that nonlinear magnetorotational dynamo cycles provide the pathway to turbulent injection of both kinetic and magnetic energy in incompressible magnetohydrodynamic Keplerian shear flow in the absence of an externally imposed magnetic field. Studying the nonlinear physics and bifurcations of these cycles in different regimes and configurations may subsequently help to better understand the conditions of excitation of magnetohydrodynamic turbulence and instability-driven dynamos in various astrophysical systems and laboratory experiments. The detailed characterization of global bifurcations provided for this three-dimensional subcritical fluid dynamics problem may also prove useful for the problem of transition to turbulence in hydrodynamic shear flows.

  17. A GLOBAL GALACTIC DYNAMO WITH A CORONA CONSTRAINED BY RELATIVE HELICITY

    Energy Technology Data Exchange (ETDEWEB)

    Prasad, A.; Mangalam, A., E-mail: avijeet@iiap.res.in, E-mail: mangalam@iiap.res.in [Indian Institute of Astrophysics, Sarjapur Road, Koramangala, Bangalore, 560034 (India)

    2016-01-20

    We present a model for a global axisymmetric turbulent dynamo operating in a galaxy with a corona that treats the parameters of turbulence driven by supernovae and by magneto-rotational instability under a common formalism. The nonlinear quenching of the dynamo is alleviated by the inclusion of small-scale advective and diffusive magnetic helicity fluxes, which allow the gauge-invariant magnetic helicity to be transferred outside the disk and consequently to build up a corona during the course of dynamo action. The time-dependent dynamo equations are expressed in a separable form and solved through an eigenvector expansion constructed using the steady-state solutions of the dynamo equation. The parametric evolution of the dynamo solution allows us to estimate the final structure of the global magnetic field and the saturated value of the turbulence parameter α{sub m}, even before solving the dynamical equations for evolution of magnetic fields in the disk and the corona, along with α-quenching. We then solve these equations simultaneously to study the saturation of the large-scale magnetic field, its dependence on the small-scale magnetic helicity fluxes, and the corresponding evolution of the force-free field in the corona. The quadrupolar large-scale magnetic field in the disk is found to reach equipartition strength within a timescale of 1 Gyr. The large-scale magnetic field in the corona obtained is much weaker than the field inside the disk and has only a weak impact on the dynamo operation.

  18. Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo

    Science.gov (United States)

    Augustson, Kyle C.; Brun, Allan Sacha; Miesch, Mark; Toomre, Juri

    2015-08-01

    The 3-D magnetohydrodynamic (MHD) Anelastic Spherical Harmonic (ASH) code, using slope-limited diffusion, is employed to capture convective and dynamo processes achieved in a global-scale stellar convection simulation for a model solar-mass star rotating at three times the solar rate. The dynamo generated magnetic fields possesses many time scales, with a prominent polarity cycle occurring roughly every 6.2 years. The magnetic field forms large-scale toroidal wreaths, whose formation is tied to the low Rossby number of the convection in this simulation. The polarity reversals are linked to the weakened differential rotation and a resistive collapse of the large-scale magnetic field. An equatorial migration of the magnetic field is seen, which is due to the strong modulation of the differential rotation rather than a dynamo wave. A poleward migration of magnetic flux from the equator eventually leads to the reversal of the polarity of the high-latitude magnetic field. This simulation also enters an interval with reduced magnetic energy at low latitudes lasting roughly 16 years (about 2.5 polarity cycles), during which the polarity cycles are disrupted and after which the dynamo recovers its regular polarity cycles. An analysis of this grand minimum reveals that it likely arises through the interplay of symmetric and antisymmetric dynamo families. This intermittent dynamo state potentially results from the simulations relatively low magnetic Prandtl number. A mean-field-based analysis of this dynamo simulation demonstrates that it is of the α-Ω type. The time scales that appear to be relevant to the magnetic polarity reversal are also identified.

  19. Magnetorotational Turbulence and Dynamo in a Collisionless Plasma.

    Science.gov (United States)

    Kunz, Matthew W; Stone, James M; Quataert, Eliot

    2016-12-02

    We present results from the first 3D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model of a collisionless accretion disk. The kinetic magnetorotational instability grows from a subthermal magnetic field having zero net flux over the computational domain to generate self-sustained turbulence and outward angular-momentum transport. Significant Maxwell and Reynolds stresses are accompanied by comparable viscous stresses produced by field-aligned ion pressure anisotropy, which is regulated primarily by the mirror and ion-cyclotron instabilities through particle trapping and pitch-angle scattering. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatiotemporally variable. Energy spectra suggest an Alfvén-wave cascade at large scales and a kinetic-Alfvén-wave cascade at small scales, with strong small-scale density fluctuations and weak nonaxisymmetric density waves. Ions undergo nonthermal particle acceleration, their distribution accurately described by a κ distribution. These results have implications for the properties of low-collisionality accretion flows, such as that near the black hole at the Galactic center.

  20. Resolved magnetic dynamo action in the simulated intracluster medium

    Science.gov (United States)

    Vazza, F.; Brunetti, G.; Brüggen, M.; Bonafede, A.

    2018-02-01

    Faraday rotation and synchrotron emission from extragalactic radio sources give evidence for the presence of magnetic fields extending over ˜ Mpc scales. However, the origin of these fields remains elusive. With new high-resolution grid simulations, we studied the growth of magnetic fields in a massive galaxy cluster that in several aspects is similar to the Coma cluster. We investigated models in which magnetic fields originate from primordial seed fields with comoving strengths of 0.1 nG at redshift z = 30. The simulations show evidence of significant magnetic field amplification. At the best spatial resolution (3.95 kpc), we are able to resolve the scale where magnetic tension balances the bending of magnetic lines by turbulence. This allows us to observe the final growth stage of the small-scale dynamo. To our knowledge, this is the first time that this is seen in cosmological simulations of the intracluster medium. Our mock observations of Faraday rotation provide a good match to observations of the Coma cluster. However, the distribution of magnetic fields shows strong departures from a simple Maxwellian distribution, suggesting that the three-dimensional structure of magnetic fields in real clusters may be significantly different than what is usually assumed when inferring magnetic field values from rotation measure observations.

  1. BIPOLAR MAGNETIC SPOTS FROM DYNAMOS IN STRATIFIED SPHERICAL SHELL TURBULENCE

    Energy Technology Data Exchange (ETDEWEB)

    Jabbari, Sarah; Brandenburg, Axel; Kleeorin, Nathan; Mitra, Dhrubaditya; Rogachevskii, Igor, E-mail: sarahjab@kth.se [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)

    2015-06-01

    Recent work by Mitra et al. (2014) has shown that in strongly stratified forced two-layer turbulence with helicity and corresponding large-scale dynamo action in the lower layer, and nonhelical turbulence in the upper, a magnetic field occurs in the upper layer in the form of sharply bounded bipolar magnetic spots. Here we extend this model to spherical wedge geometry covering the northern hemisphere up to 75° latitude and an azimuthal extent of 180°. The kinetic helicity and therefore also the large-scale magnetic field are strongest at low latitudes. For moderately strong stratification, several bipolar spots form that eventually fill the full longitudinal extent. At early times, the polarity of spots reflects the orientation of the underlying azimuthal field, as expected from Parker’s Ω-shaped flux loops. At late times their tilt changes such that there is a radial field of opposite orientation at different latitudes separated by about 10°. Our model demonstrates the spontaneous formation of spots of sizes much larger than the pressure scale height. Their tendency to produce filling factors close to unity is argued to be reminiscent of highly active stars. We confirm that strong stratification and strong scale separation are essential ingredients behind magnetic spot formation, which appears to be associated with downflows at larger depths.

  2. Magnetic reversal frequency scaling in dynamos with thermochemical convection

    Science.gov (United States)

    Olson, Peter; Amit, Hagay

    2014-05-01

    Scaling relationships are derived for the frequency of magnetic polarity reversals in numerical dynamos powered by thermochemical convection. We show that the average number of reversals per unit of time scales with the local Rossby number Rol of the convection. With uniform core-mantle boundary (CMB) heat flux, polarity reversals are absent below a critical value Rol_crit ~ 0.05, beyond which reversal frequency increases approximately linearly with Rol. The relative standard deviation of the dipole intensity fluctuations increases with reversal frequency and Rol. With heterogeneous CMB heat flux that models the large-scale seismic heterogeneity in Earth's lower mantle, reversal frequency also exhibits linear dependence on Rol, and increases approximately as the square root of the amplitude of the CMB heterogeneity. Applied to the history of the geodynamo, these results imply that outer core convection was relatively weak with low CMB heat flux and RolRol_crit during magnetic superchrons and relatively vigorous with higher, more heterogeneous CMB heat flux and Rol>Rol_crit when geomagnetic reversals were frequent. They also suggest that polarity reversals may have been commonplace in the early history of other terrestrial planets. We find that zonal heterogeneity in CMB heat flux produces special effects. Close to Rol_crit, enhanced equatorial cooling at the CMB increases reversal frequency by concentrating magnetic field at low latitudes, whereas far beyond Rol_crit, enhanced polar cooling at the CMB increases reversal frequency by amplifying outer core convection.

  3. Magnetorotational Turbulence and Dynamo in a Collisionless Plasma

    Science.gov (United States)

    Kunz, Matthew

    2017-10-01

    Low-luminosity black-hole accretion flows are collisionless. A kinetic approach is thus necessary to understand the transport of heat and angular momentum, the acceleration of particles, and the growth and structure of the magnetic field in these systems. I present results from the first 6D kinetic simulation of magnetorotational turbulence and dynamo, which was performed using the hybrid-kinetic particle-in-cell code Pegasus. Special attention will be paid to the transport of angular momentum by the anisotropic-pressure stress, as well as to the ion-Larmor-scale kinetic instabilities (firehose, mirror, ion-cyclotron) that regulate it. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatiotemporally variable. Energy spectra suggest an Alfvén-wave cascade at large scales and a kinetic-Alfvén-wave cascade at small scales, with strong small-scale density fluctuations and weak nonaxisymmetric density waves. Ions undergo nonthermal particle acceleration, their distribution accurately described by a κ distribution. Dedicated nonlinear studies of firehose and mirror instabilities in a shearing plasma will also be presented as a complement to the study of the magnetorotational instability. The profits, perils, and price of using a kinetic approach are discussed.

  4. Observing and modeling the poloidal and toroidal fields of the solar dynamo

    Science.gov (United States)

    Cameron, R. H.; Duvall, T. L.; Schüssler, M.; Schunker, H.

    2018-01-01

    Context. The solar dynamo consists of a process that converts poloidal magnetic field to toroidal magnetic field followed by a process that creates new poloidal field from the toroidal field. Aims: Our aim is to observe the poloidal and toroidal fields relevant to the global solar dynamo and to see if their evolution is captured by a Babcock-Leighton dynamo. Methods: We used synoptic maps of the surface radial field from the KPNSO/VT and SOLIS observatories, to construct the poloidal field as a function of time and latitude; we also used full disk images from Wilcox Solar Observatory and SOHO/MDI to infer the longitudinally averaged surface azimuthal field. We show that the latter is consistent with an estimate of the longitudinally averaged surface azimuthal field due to flux emergence and therefore is closely related to the subsurface toroidal field. Results: We present maps of the poloidal and toroidal magnetic fields of the global solar dynamo. The longitude-averaged azimuthal field observed at the surface results from flux emergence. At high latitudes this component follows the radial component of the polar fields with a short time lag of between 1-3 years. The lag increases at lower latitudes. The observed evolution of the poloidal and toroidal magnetic fields is described by the (updated) Babcock-Leighton dynamo model.

  5. Dynamo threshold detection in the von Kármán sodium experiment.

    Science.gov (United States)

    Miralles, Sophie; Bonnefoy, Nicolas; Bourgoin, Mickael; Odier, Philippe; Pinton, Jean-François; Plihon, Nicolas; Verhille, Gautier; Boisson, Jean; Daviaud, François; Dubrulle, Bérengère

    2013-07-01

    Predicting dynamo self-generation in liquid metal experiments has been an ongoing question for many years. In contrast to simple dynamical systems for which reliable techniques have been developed, the ability to predict the dynamo capacity of a flow and the estimate of the corresponding critical value of the magnetic Reynolds number (the control parameter of the instability) has been elusive, partly due to the high level of turbulent fluctuations of flows in such experiments (with kinetic Reynolds numbers in excess of 10(6)). We address these issues here, using the von Kármán sodium experiment and studying its response to an externally applied magnetic field. We first show that a dynamo threshold can be estimated from analysis related to critical slowing down and susceptibility divergence, in configurations for which dynamo action is indeed observed. These approaches are then applied to flow configurations that have failed to self-generate magnetic fields within operational limits, and we quantify the dynamo capacity of these configurations.

  6. Influence of high-permeability discs in an axisymmetric model of the Cadarache dynamo experiment

    Science.gov (United States)

    Giesecke, A.; Nore, C.; Stefani, F.; Gerbeth, G.; Léorat, J.; Herreman, W.; Luddens, F.; Guermond, J.-L.

    2012-05-01

    Numerical simulations of the kinematic induction equation are performed on a model configuration of the Cadarache von-Kármán-sodium dynamo experiment. The effect of a localized axisymmetric distribution of relative permeability μr that represents soft iron material within the conducting fluid flow is investigated. The critical magnetic Reynolds number Rmc for dynamo action of the first non-axisymmetric mode roughly scales like Rmcμr - Rmc∞∝μ-1/2r, i.e. the threshold decreases as μr increases. This scaling law suggests a skin effect mechanism in the soft iron discs. More important with regard to the Cadarache dynamo experiment, we observe a purely toroidal axisymmetric mode localized in the high-permeability discs which becomes dominant for large μr. In this limit, the toroidal mode is close to the onset of dynamo action with a (negative) growth rate that is rather independent of the magnetic Reynolds number. We qualitatively explain this effect by paramagnetic pumping at the fluid/disc interface and propose a simplified model that quantitatively reproduces numerical results. The crucial role of the high-permeability discs in the mode selection in the Cadarache dynamo experiment cannot be inferred from computations using idealized pseudo-vacuum boundary conditions (H × n = 0).

  7. 77 FR 64978 - Dynamo Power LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes Request for...

    Science.gov (United States)

    2012-10-24

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Dynamo Power LLC; Supplemental Notice That Initial Market-Based Rate Filing...-referenced proceeding of Dynamo Power LLC's application for market-based rate authority, with an accompanying...

  8. 77 FR 58124 - Dynamo Power LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes Request for...

    Science.gov (United States)

    2012-09-19

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Dynamo Power LLC; Supplemental Notice That Initial Market-Based Rate Filing...-referenced proceeding, of Dynamo Power LLC's application for market-based rate authority, with an...

  9. The gravitomagnetic dynamo effect in accretion disks of rotating black holes

    Science.gov (United States)

    Khanna, Ramon; Camenzind, Max

    1994-11-01

    We present a previously unknown dynamo effect that arises from the coupling of the gravitomagnetic field of a Kerr black hole with electromagnetic fields. The axisymmetric dynamo equations are derived in the 3 + 1 split of Kerr spacetime. They are formally identical to their equivalents in flat space, augmented by a general relativistic source term for the poloidal magnetic field provided by the gravitomagnetic field. There is no need for any particular small-scale plasma motions. The effect does, however, require finite conductivity and is enhanced by anomalous or turbulent magnetic diffusivity. The results of our time-dependent numerical simulations of the mean field dyanmo in a turbulent accretion disk prove that the gravitomagnetic dynamo has growing modes in the vicinity of a rotating black hole.

  10. Simulations of the kinematic dynamo onset of spherical Couette flows with smooth and rough boundaries.

    Science.gov (United States)

    Finke, K; Tilgner, A

    2012-07-01

    We study numerically the dynamo transition of an incompressible electrically conducting fluid filling the gap between two concentric spheres. In a first series of simulations, the fluid is driven by the rotation of a smooth inner sphere through no-slip boundary conditions, whereas the outer sphere is stationary. In a second series a volume force intended to simulate a rough surface drives the fluid next to the inner sphere within a layer of thickness one-tenth of the gap width. We investigate the effect of the boundary layer thickness on the dynamo threshold in the turbulent regime. The simulations show that the boundary forcing simulating the rough surface lowers the necessary rotation rate, which may help to improve spherical dynamo experiments.

  11. Evidence from numerical experiments for a feedback dynamo generating Mercury's magnetic field.

    Science.gov (United States)

    Heyner, Daniel; Wicht, Johannes; Gómez-Pérez, Natalia; Schmitt, Dieter; Auster, Hans-Ulrich; Glassmeier, Karl-Heinz

    2011-12-23

    The observed weakness of Mercury's magnetic field poses a long-standing puzzle to dynamo theory. Using numerical dynamo simulations, we show that it could be explained by a negative feedback between the magnetospheric and the internal magnetic fields. Without feedback, a small internal field was amplified by the dynamo process up to Earth-like values. With feedback, the field strength saturated at a much lower level, compatible with the observations at Mercury. The classical saturation mechanism via the Lorentz force was replaced by the external field impact. The resulting surface field was dominated by uneven harmonic components. This will allow the feedback model to be distinguished from other models once a more accurate field model is constructed from MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and BepiColombo data.

  12. Dynamo Action in a Quasi-Keplerian Taylor-Couette Flow

    Science.gov (United States)

    Guseva, Anna; Hollerbach, Rainer; Willis, Ashley P.; Avila, Marc

    2017-10-01

    We numerically compute the flow of an electrically conducting fluid in a Taylor-Couette geometry where the rotation rates of the inner and outer cylinders satisfy Ωo/Ωi=(ro/ri)-3/2. In this quasi-Keplerian regime, a nonmagnetic system would be Rayleigh stable for all Reynolds numbers Re, and the resulting purely azimuthal flow incapable of kinematic dynamo action for all magnetic Reynolds numbers R m . For Re = 104 and R m =105 , we demonstrate the existence of a finite-amplitude dynamo, whereby a suitable initial condition yields mutually sustaining turbulence and magnetic fields, even though neither could exist without the other. This dynamo solution results in significantly increased outward angular momentum transport, with the bulk of the transport being by Maxwell rather than Reynolds stresses.

  13. Are tachoclines important for solar and stellar dynamos? What can we learn from global simulations

    Science.gov (United States)

    Guerrero, G.; Smolarkiewicz, P. K.; de Gouveia Dal Pino, E. M.; Kosovichev, A. G.; Zaire, B.; Mansour, N. N.

    2017-10-01

    The role of tachoclines, the thin shear layers that separate solid body from differential rotation in the interior of late-type stars, in stellar dynamos is still controversial. In this work we discuss their relevance in view of recent results from global dynamo simulations performed with the EULAG-MHD code. The models have solar-like stratification and different rotation rates (i.e., different Rossby number). Three arguments supporting the key role of tachoclines are presented: the solar dynamo cycle period, the origin of torsional oscillations and the scaling law of stellar magnetic fields as function of the Rossby number. This scaling shows a regime where the field strength increases with the rotation and a saturated regime for fast rotating stars. These properties are better reproduced by models that consider the convection zone and a fraction of the radiative core, naturally developing a tachocline, than by those that consider only the convection zone.

  14. Energy transfers and magnetic energy growth in small-scale dynamo

    KAUST Repository

    Kumar, Rohit Raj

    2013-12-01

    In this letter we investigate the dynamics of magnetic energy growth in small-scale dynamo by studying energy transfers, mainly energy fluxes and shell-to-shell energy transfers. We perform dynamo simulations for the magnetic Prandtl number Pm = 20 on 10243 grid using the pseudospectral method. We demonstrate that the magnetic energy growth is caused by nonlocal energy transfers from the large-scale or forcing-scale velocity field to small-scale magnetic field. The peak of these energy transfers moves towards lower wave numbers as dynamo evolves, which is the reason why the integral scale of the magnetic field increases with time. The energy transfers U2U (velocity to velocity) and B2B (magnetic to magnetic) are forward and local. Copyright © EPLA, 2013.

  15. Marshall N. Rosenbluth Outstanding Doctoral Thesis Award: Magnetorotational turbulence and dynamo

    Science.gov (United States)

    Squire, Jonathan

    2017-10-01

    Accretion disks are ubiquitous in astrophysics and power some of the most luminous sources in the universe. In many disks, the transport of angular momentum, and thus the mass accretion itself, is thought to be caused by the magnetorotational instability (MRI). As the MRI saturates into strong turbulence, it also generates ordered magnetic fields, acting as a magnetic dynamo powered by the background shear flow. However, despite its importance for astrophysical accretion processes, basic aspects of MRI turbulence-including its saturation amplitude-remain poorly understood. In this talk, I will outline progress towards improving this situation, focusing in particular on the nonlinear shear dynamo and how this controls the turbulence. I will discuss how novel statistical simulation methods can be used to better understand this shear dynamo, in particular the distinct mechanisms that may play a role in MRI turbulence and how these depend on important physical parameters.

  16. Fast dynamos with finite resistivity in steady flows with stagnation points

    Science.gov (United States)

    Lau, Yun-Tung; Finn, John M.

    1993-01-01

    Results are presented of a kinematic fast dynamo problem for two classes of steady incompressible flows: the ABC flow and the spatially aperiodic flow of Lau and Finn (1992). The numerical method used to find the solutions is described, together with convergence studies with respect to the time step and the number of points N of the spatial grid. It is shown that the growth rate and frequency can be extrapolated to N = infinity. Results are presented indicating that fast kinematic dynamos can exist in both these flows and that chaotic flow is a necessary condition. It was found that, for the ABC flow with A = B = C, there are two dynamo modes: an oscillating mode and a purely growing mode.

  17. What Do Numerical Simulations Tell Us About Solar/Stellar Dynamos?

    Science.gov (United States)

    Jouve, L.

    2016-09-01

    In this talk, we will review some aspects of the stellar magnetism and in particular what numerical simulations tell us about the physical processes underlying the observations. In cool stars, a convective dynamo is thought to be responsible for the presence and evolution of magnetic fields. The question of the impact of the internal stellar structure on the magnetic field topology will be addressed. We will focus in particular on the role of differential rotation and of a tachocline. Another important aspect of stellar dynamos is the possible presence of magnetic cycles and how its period depends on the stellar parameters. Numerical simulations addressing this issue will be presented. Finally, one step of the dynamo process is the emergence of magnetic flux from the interior where it is created and organised to the exterior where it emerges as starspots. We will also show results of global 3D MHD numerical simulations of such a process.

  18. Precession-driven dynamos in a full sphere and the role of large scale cyclonic vortices

    CERN Document Server

    Lin, Yufeng; Noir, Jerome; Jackson, Andrew

    2016-01-01

    Precession has been proposed as an alternative power source for planetary dynamos. Previous hydrodynamic simulations suggested that precession can generate very complex flows in planetary liquid cores [Y. Lin, P. Marti, and J. Noir, "Shear-driven parametric instability in a precessing sphere," Physics of Fluids 27, 046601 (2015)]. In the present study, we numerically investigate the magnetohydrodynamics of a precessing sphere. We demonstrate precession driven dynamos in different flow regimes, from laminar to turbulent flows. In particular, we highlight the magnetic field generation by large scale cyclonic vortices, which has not been explored previously. In this regime, dynamos can be sustained at relatively low Ekman numbers and magnetic Prandtl numbers, which paves the way for planetary applications.

  19. Non-linear dynamo waves in an incompressible medium when the turbulence dissipative coefficients depend on temperature

    Directory of Open Access Journals (Sweden)

    A. D. Pataraya

    1997-01-01

    Full Text Available Non-linear α-ω; dynamo waves existing in an incompressible medium with the turbulence dissipative coefficients depending on temperature are studied in this paper. We investigate of α-ω solar non-linear dynamo waves when only the first harmonics of magnetic induction components are included. If we ignore the second harmonics in the non-linear equation, the turbulent magnetic diffusion coefficient increases together with the temperature, the coefficient of turbulent viscosity decreases, and for an interval of time the value of dynamo number is greater than 1. In these conditions a stationary solution of the non-linear equation for the dynamo wave's amplitude exists; meaning that the magnetic field is sufficiently excited. The amplitude of the dynamo waves oscillates and becomes stationary. Using these results we can explain the existence of Maunder's minimum.

  20. Community Alternatives for Love and Limits (CALL): A community-based family strengthening multi-family intervention program to respond to adolescents at risk

    OpenAIRE

    David Wilkerson; Philip M. Ouellette

    2005-01-01

    Family strengthening has become a source of growing interest, research, and program design in the fields of prevention and treatment for problems of youth delinquency, school failure, alcohol, tobacco and other drug abuse (ATOD). Despite many studies that illustrate the positive outcomes of family strengthening programs and family-focused interventions, their use in communities has not advanced commensurate with their promise. This article offers a rationale for why programming efforts shou...

  1. Procyon: New Candidate for the Dynamo Clinical Trial

    Science.gov (United States)

    Ayres, Thomas

    2017-08-01

    This is the third year of a joint Chandra/HST program to follow the evolution of the high-energy (X-ray and UV) activity cycles of the nearby mid-F subgiant Procyon. This bright star has high-energy attributes that are similar to the Sun, yet it is a hotter star, at the edge of the region in the H-R diagram where surface convection occurs (the power source for stellar magnetic activity). The HST part is to record STIS UV spectra of the bright star on a semiannual basis at high echelle resolution and high S/N, especially to capture the FUV Fe XII 124,134 nm coronal forbidden lines, which can tie together the non-simultaneous Chandra X-ray and HST pointings; as well as to record other key high-energy species like Si IV, C IV, and N V. The latter display Doppler-shifted, bimodal distorted emission profiles that signify high-powered dynamics in the interface regions of the stellar atmosphere between the super-hot corona (>1 MK) and the cold photosphere (<6000 K). The associated flows are a hot topic in contemporary solar physics, and one focus of a new space-based solar imaging spectrometer called IRIS. The solar and stellar FUV views are strongly complementary. The HST part of the program has two general objectives: (1) follow changes in the FUV spectra associated with any slowly evolving X-ray activity cycle of Procyon; and (2) combine the multiple epochs of echelle spectra to provide the highest possible S/N for identifying weak, but diagnostically important, emission lines (absorption, in some cases), and for decomposing the high-temperature line profiles (e.g., Si IV, C IV) into multiple dynamical components (which are though to be symptomatic of coronal heating and cooling processes).

  2. The cross-over to magnetostrophic convection in planetary dynamo systems.

    Science.gov (United States)

    Aurnou, J M; King, E M

    2017-03-01

    Global scale magnetostrophic balance, in which Lorentz and Coriolis forces comprise the leading-order force balance, has long been thought to describe the natural state of planetary dynamo systems. This argument arises from consideration of the linear theory of rotating magnetoconvection. Here we test this long-held tenet by directly comparing linear predictions against dynamo modelling results. This comparison shows that dynamo modelling results are not typically in the global magnetostrophic state predicted by linear theory. Then, in order to estimate at what scale (if any) magnetostrophic balance will arise in nonlinear dynamo systems, we carry out a simple scaling analysis of the Elsasser number Λ, yielding an improved estimate of the ratio of Lorentz and Coriolis forces. From this, we deduce that there is a magnetostrophic cross-over length scale, [Formula: see text], where Λo is the linear (or traditional) Elsasser number, Rmo is the system scale magnetic Reynolds number and D is the length scale of the system. On scales well above [Formula: see text], magnetostrophic convection dynamics should not be possible. Only on scales smaller than [Formula: see text] should it be possible for the convective behaviours to follow the predictions for the magnetostrophic branch of convection. Because [Formula: see text] is significantly smaller than the system scale in most dynamo models, their large-scale flows should be quasi-geostrophic, as is confirmed in many dynamo simulations. Estimating Λo ≃1 and Rmo ≃103 in Earth's core, the cross-over scale is approximately 1/1000 that of the system scale, suggesting that magnetostrophic convection dynamics exists in the core only on small scales below those that can be characterized by geomagnetic observations.

  3. DYNAMO-HIA--a Dynamic Modeling tool for generic Health Impact Assessments.

    Science.gov (United States)

    Lhachimi, Stefan K; Nusselder, Wilma J; Smit, Henriette A; van Baal, Pieter; Baili, Paolo; Bennett, Kathleen; Fernández, Esteve; Kulik, Margarete C; Lobstein, Tim; Pomerleau, Joceline; Mackenbach, Johan P; Boshuizen, Hendriek C

    2012-01-01

    Currently, no standard tool is publicly available that allows researchers or policy-makers to quantify the impact of policies using epidemiological evidence within the causal framework of Health Impact Assessment (HIA). A standard tool should comply with three technical criteria (real-life population, dynamic projection, explicit risk-factor states) and three usability criteria (modest data requirements, rich model output, generally accessible) to be useful in the applied setting of HIA. With DYNAMO-HIA (Dynamic Modeling for Health Impact Assessment), we introduce such a generic software tool specifically designed to facilitate quantification in the assessment of the health impacts of policies. DYNAMO-HIA quantifies the impact of user-specified risk-factor changes on multiple diseases and in turn on overall population health, comparing one reference scenario with one or more intervention scenarios. The Markov-based modeling approach allows for explicit risk-factor states and simulation of a real-life population. A built-in parameter estimation module ensures that only standard population-level epidemiological evidence is required, i.e. data on incidence, prevalence, relative risks, and mortality. DYNAMO-HIA provides a rich output of summary measures--e.g. life expectancy and disease-free life expectancy--and detailed data--e.g. prevalences and mortality/survival rates--by age, sex, and risk-factor status over time. DYNAMO-HIA is controlled via a graphical user interface and is publicly available from the internet, ensuring general accessibility. We illustrate the use of DYNAMO-HIA with two example applications: a policy causing an overall increase in alcohol consumption and quantifying the disease-burden of smoking. By combining modest data needs with general accessibility and user friendliness within the causal framework of HIA, DYNAMO-HIA is a potential standard tool for health impact assessment based on epidemiologic evidence.

  4. DYNAMO-HIA–A Dynamic Modeling Tool for Generic Health Impact Assessments

    Science.gov (United States)

    Lhachimi, Stefan K.; Nusselder, Wilma J.; Smit, Henriette A.; van Baal, Pieter; Baili, Paolo; Bennett, Kathleen; Fernández, Esteve; Kulik, Margarete C.; Lobstein, Tim; Pomerleau, Joceline; Mackenbach, Johan P.; Boshuizen, Hendriek C.

    2012-01-01

    Background Currently, no standard tool is publicly available that allows researchers or policy-makers to quantify the impact of policies using epidemiological evidence within the causal framework of Health Impact Assessment (HIA). A standard tool should comply with three technical criteria (real-life population, dynamic projection, explicit risk-factor states) and three usability criteria (modest data requirements, rich model output, generally accessible) to be useful in the applied setting of HIA. With DYNAMO-HIA (Dynamic Modeling for Health Impact Assessment), we introduce such a generic software tool specifically designed to facilitate quantification in the assessment of the health impacts of policies. Methods and Results DYNAMO-HIA quantifies the impact of user-specified risk-factor changes on multiple diseases and in turn on overall population health, comparing one reference scenario with one or more intervention scenarios. The Markov-based modeling approach allows for explicit risk-factor states and simulation of a real-life population. A built-in parameter estimation module ensures that only standard population-level epidemiological evidence is required, i.e. data on incidence, prevalence, relative risks, and mortality. DYNAMO-HIA provides a rich output of summary measures – e.g. life expectancy and disease-free life expectancy – and detailed data – e.g. prevalences and mortality/survival rates – by age, sex, and risk-factor status over time. DYNAMO-HIA is controlled via a graphical user interface and is publicly available from the internet, ensuring general accessibility. We illustrate the use of DYNAMO-HIA with two example applications: a policy causing an overall increase in alcohol consumption and quantifying the disease-burden of smoking. Conclusion By combining modest data needs with general accessibility and user friendliness within the causal framework of HIA, DYNAMO-HIA is a potential standard tool for health impact assessment based on

  5. DYNAMO-HIA--a Dynamic Modeling tool for generic Health Impact Assessments.

    Directory of Open Access Journals (Sweden)

    Stefan K Lhachimi

    Full Text Available BACKGROUND: Currently, no standard tool is publicly available that allows researchers or policy-makers to quantify the impact of policies using epidemiological evidence within the causal framework of Health Impact Assessment (HIA. A standard tool should comply with three technical criteria (real-life population, dynamic projection, explicit risk-factor states and three usability criteria (modest data requirements, rich model output, generally accessible to be useful in the applied setting of HIA. With DYNAMO-HIA (Dynamic Modeling for Health Impact Assessment, we introduce such a generic software tool specifically designed to facilitate quantification in the assessment of the health impacts of policies. METHODS AND RESULTS: DYNAMO-HIA quantifies the impact of user-specified risk-factor changes on multiple diseases and in turn on overall population health, comparing one reference scenario with one or more intervention scenarios. The Markov-based modeling approach allows for explicit risk-factor states and simulation of a real-life population. A built-in parameter estimation module ensures that only standard population-level epidemiological evidence is required, i.e. data on incidence, prevalence, relative risks, and mortality. DYNAMO-HIA provides a rich output of summary measures--e.g. life expectancy and disease-free life expectancy--and detailed data--e.g. prevalences and mortality/survival rates--by age, sex, and risk-factor status over time. DYNAMO-HIA is controlled via a graphical user interface and is publicly available from the internet, ensuring general accessibility. We illustrate the use of DYNAMO-HIA with two example applications: a policy causing an overall increase in alcohol consumption and quantifying the disease-burden of smoking. CONCLUSION: By combining modest data needs with general accessibility and user friendliness within the causal framework of HIA, DYNAMO-HIA is a potential standard tool for health impact assessment based

  6. The cross-over to magnetostrophic convection in planetary dynamo systems

    Science.gov (United States)

    King, E. M.

    2017-01-01

    Global scale magnetostrophic balance, in which Lorentz and Coriolis forces comprise the leading-order force balance, has long been thought to describe the natural state of planetary dynamo systems. This argument arises from consideration of the linear theory of rotating magnetoconvection. Here we test this long-held tenet by directly comparing linear predictions against dynamo modelling results. This comparison shows that dynamo modelling results are not typically in the global magnetostrophic state predicted by linear theory. Then, in order to estimate at what scale (if any) magnetostrophic balance will arise in nonlinear dynamo systems, we carry out a simple scaling analysis of the Elsasser number Λ, yielding an improved estimate of the ratio of Lorentz and Coriolis forces. From this, we deduce that there is a magnetostrophic cross-over length scale, LX≈(Λo2/Rmo)D, where Λo is the linear (or traditional) Elsasser number, Rmo is the system scale magnetic Reynolds number and D is the length scale of the system. On scales well above LX, magnetostrophic convection dynamics should not be possible. Only on scales smaller than LX should it be possible for the convective behaviours to follow the predictions for the magnetostrophic branch of convection. Because LX is significantly smaller than the system scale in most dynamo models, their large-scale flows should be quasi-geostrophic, as is confirmed in many dynamo simulations. Estimating Λo≃1 and Rmo≃103 in Earth’s core, the cross-over scale is approximately 1/1000 that of the system scale, suggesting that magnetostrophic convection dynamics exists in the core only on small scales below those that can be characterized by geomagnetic observations. PMID:28413338

  7. Powering Earth's dynamo with magnesium precipitation from the core.

    Science.gov (United States)

    O'Rourke, Joseph G; Stevenson, David J

    2016-01-21

    Earth's global magnetic field arises from vigorous convection within the liquid outer core. Palaeomagnetic evidence reveals that the geodynamo has operated for at least 3.4 billion years, which places constraints on Earth's formation and evolution. Available power sources in standard models include compositional convection (driven by the solidifying inner core's expulsion of light elements), thermal convection (from slow cooling), and perhaps heat from the decay of radioactive isotopes. However, recent first-principles calculations and diamond-anvil cell experiments indicate that the thermal conductivity of iron is two or three times larger than typically assumed in these models. This presents a problem: a large increase in the conductive heat flux along the adiabat (due to the higher conductivity of iron) implies that the inner core is young (less than one billion years old), but thermal convection and radiogenic heating alone may not have been able to sustain the geodynamo during earlier epochs. Here we show that the precipitation of magnesium-bearing minerals from the core could have served as an alternative power source. Equilibration at high temperatures in the aftermath of giant impacts allows a small amount of magnesium (one or two weight per cent) to partition into the core while still producing the observed abundances of siderophile elements in the mantle and avoiding an excess of silicon and oxygen in the core. The transport of magnesium as oxide or silicate from the cooling core to underneath the mantle is an order of magnitude more efficient per unit mass as a source of buoyancy than inner-core growth. We therefore conclude that Earth's dynamo would survive throughout geologic time (from at least 3.4 billion years ago to the present) even if core radiogenic heating were minimal and core cooling were slow.

  8. Meridional circulation dynamics in a cyclic convective dynamo

    Science.gov (United States)

    Passos, D.; Miesch, M.; Guerrero, G.; Charbonneau, P.

    2017-11-01

    Surface observations indicate that the speed of the solar meridional circulation in the photosphere varies in anti-phase with the solar cycle. The current explanation for the source of this variation is that inflows into active regions alter the global surface pattern of the meridional circulation. When these localized inflows are integrated over a full hemisphere, they contribute to slowing down the axisymmetric poleward horizontal component. The behavior of this large-scale flow deep inside the convection zone remains largely unknown. Present helioseismic techniques are not sensitive enough to capture the dynamics of this weak large-scale flow. Moreover, the large time of integration needed to map the meridional circulation inside the convection zone, also masks some of the possible dynamics on shorter timescales. In this work we examine the dynamics of the meridional circulation that emerges from a 3D MHD global simulation of the solar convection zone. Our aim is to assess and quantify the behavior of meridional circulation deep inside the convection zone where the cyclic large-scale magnetic field can reach considerable strength. Our analyses indicate that the meridional circulation morphology and amplitude are both highly influenced by the magnetic field via the impact of magnetic torques on the global angular momentum distribution. A dynamic feature induced by these magnetic torques is the development of a prominent upward flow at mid-latitudes in the lower convection zone that occurs near the equatorward edge of the toroidal bands and that peaks during cycle maximum. Globally, the dynamo-generated large-scale magnetic field drives variations in the meridional flow, in stark contrast to the conventional kinematic flux transport view of the magnetic field being advected passively by the flow.

  9. CALL-BASED INSTRUCTION MODEL OF SPEAKING ENGLISH (A Developmental Research at the English Language Education Study Program of STKIP Kusuma Negara, Jakarta)

    OpenAIRE

    Siti Yulidhar Harunasari; Aceng Rahmat

    2015-01-01

    The objective of this research is to develop a model of learning speaking English for students majoring in English Language Education in STKIP Kusuma Jakarta, and to examine the effectiveness of CALL-Based instruction the model in improving students’ speaking skill. The research was conducted using system approach model of Dick and Carey, and was carried out from October 2012 to July 2014 in 3 stages i.e. preliminary stage; model development stage; validation, evaluation, and revision stage. ...

  10. Optimum reduction of the dynamo threshold by a ferromagnetic layer located in the flow.

    Science.gov (United States)

    Herault, J; Pétrélis, F

    2014-09-01

    We consider a fluid dynamo model generated by the flow on both sides of a moving layer. The magnetic permeability of the layer is larger than that of the flow. We show that there exists an optimum value of magnetic permeability for which the critical magnetic Reynolds number for dynamo onset is smaller than for a nonmagnetic material and also smaller than for a layer of infinite magnetic permeability. We present a mechanism that provides an explanation for recent experimental results. A similar effect occurs when the electrical conductivity of the layer is large.

  11. Magnetic field variation caused by rotational speed change in a magnetohydrodynamic dynamo.

    Science.gov (United States)

    Miyagoshi, Takehiro; Hamano, Yozo

    2013-09-20

    We have performed numerical magnetohydrodynamic dynamo simulations in a spherical shell with rotational speed or length-of-day (LOD) variation, which is motivated by correlations between geomagnetic field and climatic variations with ice and non-ice ages. The results show that LOD variation leads to magnetic field variation whose amplitude is considerably larger than that of LOD variation. The heat flux at the outer sphere and the zonal flow also change. The mechanism of the magnetic field variation due to LOD variation is also found. The keys are changes of dynamo activity and Joule heating.

  12. Call Center Capacity Planning

    DEFF Research Database (Denmark)

    Nielsen, Thomas Bang

    The main topics of the thesis are theoretical and applied queueing theory within a call center setting. Call centers have in recent years become the main means of communication between customers and companies, and between citizens and public institutions. The extensively computerized infrastructu...

  13. Call 1 FAQ (ENG)

    International Development Research Centre (IDRC) Digital Library (Canada)

    Francine Sinzinkayo

    What is your definition of “improvement” in this Call for proposals? “Improvement” as used in this call implies all innovations that may be applied by research teams to ... perform their expected roles and to participate in the overall coordination of partnership activities (including monitoring, reporting, communication, etc.).

  14. Callings and Organizational Behavior

    Science.gov (United States)

    Elangovan, A. R.; Pinder, Craig C.; McLean, Murdith

    2010-01-01

    Current literature on careers, social identity and meaning in work tends to understate the multiplicity, historical significance, and nuances of the concept of calling(s). In this article, we trace the evolution of the concept from its religious roots into secular realms and develop a typology of interpretations using occupation and religious…

  15. Dimensioning large call centers

    NARCIS (Netherlands)

    S.C. Borst (Sem); A. Mandelbaum; M.I. Reiman

    2000-01-01

    textabstractWe develop a framework for asymptotic optimization of a queueing system. The motivation is the staffing problem of call centers with 100's of agents (or more). Such a call center is modeled as an M/M/N queue, where the number of agents~$N$ is large. Within our framework, we determine the

  16. CALL FOR PROPOSALS

    International Development Research Centre (IDRC) Digital Library (Canada)

    Charles

    CALL FOR PROPOSALS. Research Project on: Gender and Enterprise Development in Africa: A Cross-Country Comparative Study. The Institute of Statistical, Social and Economic Research ... calling for research proposals from researchers based in Kenya, Uganda, Mozambique or ... For example, many more women work.

  17. Call 1 FAQ (ENG)

    International Development Research Centre (IDRC) Digital Library (Canada)

    Francine Sinzinkayo

    What is your definition of “improvement” in this Call for proposals? “Improvement” as used in this call implies all innovations that may be applied by research teams to develop a vaccine that is superior to a current one. Examples of improvement are better adjuvant, vaccine delivery systems or formulations that present ...

  18. Community Alternatives for Love and Limits (CALL: A community-based family strengthening multi-family intervention program to respond to adolescents at risk

    Directory of Open Access Journals (Sweden)

    David Wilkerson

    2005-12-01

    Full Text Available Family strengthening has become a source of growing interest, research, and program design in the fields of prevention and treatment for problems of youth delinquency, school failure, alcohol, tobacco and other drug abuse (ATOD. Despite many studies that illustrate the positive outcomes of family strengthening programs and family-focused interventions, their use in communities has not advanced commensurate with their promise. This article offers a rationale for why programming efforts should continue to be directed towards family strengthening efforts as opposed to youth-focused only interventions. In addition, a community-based, family-strengthening alternative is described that addresses issues of youth delinquency while reducing barriers associated with availability, accessibility, and cost.

  19. Mean-field dynamo in a turbulence with shear and kinetic helicity fluctuations.

    Science.gov (United States)

    Kleeorin, Nathan; Rogachevskii, Igor

    2008-03-01

    We study the effects of kinetic helicity fluctuations in a turbulence with large-scale shear using two different approaches: the spectral tau approximation and the second-order correlation approximation (or first-order smoothing approximation). These two approaches demonstrate that homogeneous kinetic helicity fluctuations alone with zero mean value in a sheared homogeneous turbulence cannot cause a large-scale dynamo. A mean-field dynamo is possible when the kinetic helicity fluctuations are inhomogeneous, which causes a nonzero mean alpha effect in a sheared turbulence. On the other hand, the shear-current effect can generate a large-scale magnetic field even in a homogeneous nonhelical turbulence with large-scale shear. This effect was investigated previously for large hydrodynamic and magnetic Reynolds numbers. In this study we examine the threshold required for the shear-current dynamo versus Reynolds number. We demonstrate that there is no need for a developed inertial range in order to maintain the shear-current dynamo (e.g., the threshold in the Reynolds number is of the order of 1).

  20. Dynamo transformation of the collisional R-T in a weakly ionized ...

    Indian Academy of Sciences (India)

    where the interstellar neutrals undergo charge exchange collisions with ions in the solar wind [1]. The presence of neutrals in plasmas can drive new instability in many ways. For ... to be based on the dynamo principle of a.c. generator. However, a pertinent question remains to be addressed: what happens to the collisional ...

  1. Flux-transport and mean-field dynamo theories of solar cycles

    Science.gov (United States)

    Choudhuri, Arnab Rai

    2013-07-01

    We point out the difficulties in carrying out direct numerical simulation of the solar dynamo problem and argue that kinematic mean-field models are our best theoretical tools at present for explaining various aspects of the solar cycle in detail. The most promising kinematic mean-field model is the flux transport dynamo model, in which the toroidal field is produced by differential rotation in the tachocline, the poloidal field is produced by the Babcock-Leighton mechanism at the solar surface and the meridional circulation plays a crucial role. Depending on whether the diffusivity is high or low, either the diffusivity or the meridional circulation provides the main transport mechanism for the poloidal field to reach the bottom of the convection zone from the top. We point out that the high-diffusivity flux transport dynamo model is consistent with various aspects of observational data. The irregularities of the solar cycle are primarily produced by fluctuations in the Babcock-Leighton mechanism and in the meridional circulation. We summarize recent work on the fluctuations of meridional circulation in the flux transport dynamo, leading to explanations of such things as the Waldmeier effect.

  2. Dynamo Scaling Laws for Uranus and Neptune: The Role of Convective Shell Thickness on Dipolarity

    Science.gov (United States)

    Stanley, Sabine; Yunsheng Tian, Bob

    2017-10-01

    Previous dynamo scaling law studies (Christensen and Aubert, 2006) have demonstrated that the morphology of a planet’s magnetic field is determined by the local Rossby number (Ro_l): a non-dimensional diagnostic variable that quantifies the ratio of inertial forces to Coriolis forces on the average length scale of the flow. Dynamos with Ro_l ~ 0.1 produce multipolar magnetic fields. Scaling studies have also determined the dependence of the local Rossby number on non-dimensional parameters governing the system - specifically the Ekman, Prandtl, magnetic Prandtl and flux-based Rayleigh numbers (Olson and Christensen, 2006). When these scaling laws are applied to the planets, it appears that Uranus and Neptune should have dipole-dominated fields, contrary to observations. However, those scaling laws were derived using the specific convective shell thickness of the Earth’s core. Here we investigate the role of convective shell thickness on dynamo scaling laws. We find that the local Rossby number depends exponentially on the convective shell thickness. Including this new dependence on convective shell thickness, we find that the dynamo scaling laws now predict that Uranus and Neptune reside deeply in the multipolar regime, thereby resolving the previous contradiction with observations.

  3. New Mexico Liquid Metal αω -dynamo experiment: Most Recent Progress

    Science.gov (United States)

    Si, Jiahe; Sonnenfeld, Richard; Colgate, Art; Li, Hui

    2017-10-01

    The goal of the New Mexico Liquid Metal αω -dynamo experiment is to demonstrate a galactic dynamo can be generated through two phases, the ω-phase and α-phase by two semi-coherent flows in laboratory. We have demonstrated an 8-fold poloidal-to-toroidal flux amplification from differential rotation (the ω-effect) by minimizing turbulence in our apparatus. To demonstrate the α-effect, major upgrades are needed. The upgrades include building a helicity injection facility, mounting new 100hp motors and new sensors, designing a new data acquisition system capable of transmitting data from about 80 sensors in a high speed rotating frame with an overall 200kS/sec sampling rate. We hope the upgrade can be utilized to answer the question of whether a self-sustaining αω -dynamo can be implemented with a realistic lab fluid flow field, as well as to obtain more details to understand dynamo action in highly turbulent Couette flow.

  4. Predicting Juno's Possible Internal Field and Secular Variation Models Based on Numerical Dynamo Simulations

    Science.gov (United States)

    Wicht, J.; Holme, R. T.; Gastine, T.; Duarte, L.

    2016-12-01

    We use numerical simulations to model Jupiter's internal dynamo and to predict the information Juno's magnetometer may reveal about the internal magnetic field and dynamics. The simulations were performed with the MHD code MagIC, cover 99% of Jupiter's radius below the one bar level, and use an electrical conductivity profile that includes the metallic inner as well as the molecular outer hydrogen layer. Surface magnetic fields closely resemble known magnetic field models. The flow is dominated by a realistic prograde equatorial jet but lacks multiple mid to high latitude jets which, according to our simulations, seem incompatible with a Jupiter like magnetic field. Using the Juno mission trajectory and assuming an isotropic measurement error of 100 nT we could recover the numerical model field to spheric harmonic degree 18, and secular variation (SV) perhaps to degree 5. The field shows characteristic bands where the equatorial jet reaches down to higher conductivities and promotes a secondary local dynamo effect. The presence of these bands as well as the SV caused by zonal flow advection may offer important clues on the depth of the zonal jets. The form of the spectrum can provide additional information on the general depth of the dynamo region: The numerical simulations suggest that dynamo action starts at the radius where the magnetic Reynolds number, the ratio of Ohmic dissipation time to convective turnover time, exceeds about 50. This roughly agrees with the depth where the magnetic power spectrum is white for spherical harmonics degrees beyond four.

  5. Degenerate Hopf bifurcation in a self-exciting Faraday disc dynamo

    Science.gov (United States)

    Pan, Weiquan; Li, Lijie

    2017-06-01

    In order to further understand a self-exciting Faraday disc dynamo (Hide et al, in Proc. R. Soc. A 452, 1369 1996), showing chaotic attractors with very complicated topological structures, we present codimension one and two (degenerate) Hopf bifurcations and prove the existence of periodic solutions. In addition, numerical simulations are given for confirming the theoretical results.

  6. Analysis, Control, Synchronization and SPICE Implementation of a Novel 4-D Hyperchaotic Rikitake Dynamo System without Equilibrium

    Directory of Open Access Journals (Sweden)

    S. Vaidyanathan

    2014-11-01

    Full Text Available Chaos theory has wide applications and its importance can be seen by the voluminous publications on various applications in several branches of science, commerce and engineering. Control, tracking or regulation and synchronization of different types of chaotic systems are importance areas of research in the control literature and various methods have been adopted over the past few decades for tackling these research problems. Also, the discovery of novel chaotic and hyperchaotic systems in various applications, their qualitative properties and the control of such systems are also important research areas in chaos theory. This paper announces a novel 4-D hyperchaotic Rikitake dynamo system, which is derived by adding a state feedback control to the famous 3-D Rikitake two-disk dynamo system (1958. The frequent and irregular reversals of the Earth’s magnetic field inspired a number of early studies involving electrical currents within the Earth’s molten core. One of the first such models to exhibit reversals was Rikitake’s two-disk dynamo system (Rikitake, 1958. This paper discusses the qualitative properties of the novel hyperchaotic Rikitake dynamo system. We note that the novel hyperchaotic Rikitake dynamo system has no equilibrium points. The Lyapunov exponents of the hyperchaotic Rikitake dynamo system are found as �! = 0.09136, �! = 0.02198, �! = 0 and �! = −2.11190. The Kaplan-Yorke fractional dimension of the novel hyperchaotic Rikitake dynamo system is found as �!" = 3.05367. Next, this paper discusses control and synchronization of the novel hyperchaotic Rikitake dynamo system with unknown parameters using adaptive control method. The main results are established using Lyapunov stability theory and numerically illustrated using MATLAB. Finally, for the 4-D novel hyperchaotic system, an electronic circuit realization in SPICE has been described to confirm the feasibility of the theoretical hyperchaotic Rikitake dynamo

  7. Approximate Dynamic Programming techniques for the control of time-varying queueing systems applied to call centers with abandonments and retrials

    NARCIS (Netherlands)

    Roubos, D.; Bhulai, S.

    2010-01-01

    In this article we develop techniques for applying Approximate Dynamic Programming (ADP) to the control of time-varying queuing systems. First, we show that the classical state space representation in queuing systems leads to approximations that can be significantly improved by increasing the

  8. Opening the black box: the impact of an oncology management program consisting of level I pathways and an outbound nurse call system.

    Science.gov (United States)

    Hoverman, J Russell; Klein, Ira; Harrison, Debra W; Hayes, Jad E; Garey, Jody S; Harrell, Robyn; Sipala, Maria; Houldin, Scott; Jameson, Melissa D; Abdullahpour, Mitra; McQueen, Jessica; Nelson, Greg; Verrilli, Diana K; Neubauer, Marcus

    2014-01-01

    The Innovent Oncology Program aims to improve the value of cancer care delivered to patients. McKesson Specialty Health and Texas Oncology (TXO) collaborated with Aetna to launch a pilot program. The study objectives were to evaluate the impact of Innovent on Level I Pathway compliance, implement the Patient Support Services program, and measure the rate and costs associated with chemotherapy-related emergency room (ER) visits and hospital admissions. This was a prospective, nonrandomized evaluation of patients enrolled in Innovent from June 1, 2010, through May 31, 2012. Data from the iKnowMed electronic health record, the McKesson Specialty Health financial data warehouse, and Aetna claims data warehouse were analyzed. A total of 221 patients were included and stratified according to disease and age groups; 76% of ordered regimens were on pathway; 24% were off pathway. Pathway adherence improved from TXO baseline adherence of 63%. Of the 221 patients, 81% enrolled in PSS. Within the breast, colorectal, and lung cancer groups, 14% and 24% of patients had an ER visit and in-patient admission (IPA; baseline) versus 10% and 18% in Innovent, respectively; average in-patient days decreased from 2.1 to 1.2 days, respectively. Total savings combined for the program was $506,481. Implementation of Innovent positively affected patient care in several ways: Fewer ER visits and IPAs occurred, in-patient days decreased, cancer-related use costs were reduced, and on-pathway adherence increased.

  9. 75 FR 13537 - Clean Water Act Section 303(d): Notice of Call for Public Comment on 303(d) Program and Ocean...

    Science.gov (United States)

    2010-03-22

    ..., Tribal, and Territorial managers of water quality programs, including the Total Maximum Daily Load... measure ocean acidification impacts? i. Are there emerging remote sensing technologies that might be... States to make attainment determinations consistent with water quality standards related to ocean...

  10. Magnetic Cycles in a Convective Dynamo Simulation of a Young Solar-type Star

    Science.gov (United States)

    Brown, Benjamin P.; Miesch, Mark S.; Browning, Matthew K.; Brun, Allan Sacha; Toomre, Juri

    2011-04-01

    Young solar-type stars rotate rapidly and many are magnetically active. Some appear to undergo magnetic cycles similar to the 22 yr solar activity cycle. We conduct simulations of dynamo action in rapidly rotating suns with the three-dimensional magnetohydrodynamic anelastic spherical harmonic (ASH) code to explore dynamo action achieved in the convective envelope of a solar-type star rotating at five times the current solar rotation rate. We find that dynamo action builds substantial organized global-scale magnetic fields in the midst of the convection zone. Striking magnetic wreaths span the convection zone and coexist with the turbulent convection. A surprising feature of this wreath-building dynamo is its rich time dependence. The dynamo exhibits cyclic activity and undergoes quasi-periodic polarity reversals where both the global-scale poloidal and toroidal fields change in sense on a roughly 1500 day timescale. These magnetic activity patterns emerge spontaneously from the turbulent flow and are more organized temporally and spatially than those realized in our previous simulations of the solar dynamo. We assess in detail the competing processes of magnetic field creation and destruction within our simulations that contribute to the global-scale reversals. We find that the mean toroidal fields are built primarily through an Ω-effect, while the mean poloidal fields are built by turbulent correlations which are not well represented by a simple α-effect. During a reversal the magnetic wreaths propagate toward the polar regions, and this appears to arise from a poleward propagating dynamo wave. As the magnetic fields wax and wane in strength and flip in polarity, the primary response in the convective flows involves the axisymmetric differential rotation which varies on similar timescales. Bands of relatively fast and slow fluid propagate toward the poles on timescales of roughly 500 days and are associated with the magnetic structures that propagate in the

  11. A High-Resolution Merged Wind Dataset for DYNAMO: Progress and Future Plans

    Science.gov (United States)

    Lang, Timothy J.; Mecikalski, John; Li, Xuanli; Chronis, Themis; Castillo, Tyler; Hoover, Kacie; Brewer, Alan; Churnside, James; McCarty, Brandi; Hein, Paul; hide

    2015-01-01

    In order to support research on optimal data assimilation methods for the Cyclone Global Navigation Satellite System (CYGNSS), launching in 2016, work has been ongoing to produce a high-resolution merged wind dataset for the Dynamics of the Madden Julian Oscillation (DYNAMO) field campaign, which took place during late 2011/early 2012. The winds are produced by assimilating DYNAMO observations into the Weather Research and Forecasting (WRF) three-dimensional variational (3DVAR) system. Data sources from the DYNAMO campaign include the upper-air sounding network, radial velocities from the radar network, vector winds from the Advanced Scatterometer (ASCAT) and Oceansat-2 Scatterometer (OSCAT) satellite instruments, the NOAA High Resolution Doppler Lidar (HRDL), and several others. In order the prep them for 3DVAR, significant additional quality control work is being done for the currently available TOGA and SMART-R radar datasets, including automatically dealiasing radial velocities and correcting for intermittent TOGA antenna azimuth angle errors. The assimilated winds are being made available as model output fields from WRF on two separate grids with different horizontal resolutions - a 3-km grid focusing on the main DYNAMO quadrilateral (i.e., Gan Island, the R/V Revelle, the R/V Mirai, and Diego Garcia), and a 1-km grid focusing on the Revelle. The wind dataset is focused on three separate approximately 2-week periods during the Madden Julian Oscillation (MJO) onsets that occurred in October, November, and December 2011. Work is ongoing to convert the 10-m surface winds from these model fields to simulated CYGNSS observations using the CYGNSS End-To-End Simulator (E2ES), and these simulated satellite observations are being compared to radar observations of DYNAMO precipitation systems to document the anticipated ability of CYGNSS to provide information on the relationships between surface winds and oceanic precipitation at the mesoscale level. This research will

  12. Cyclic Evolution of Coronal Fields from a Coupled Dynamo Potential-Field Source-Surface Model.

    Science.gov (United States)

    Dikpati, Mausumi; Suresh, Akshaya; Burkepile, Joan

    The structure of the Sun's corona varies with the solar-cycle phase, from a near spherical symmetry at solar maximum to an axial dipole at solar minimum. It is widely accepted that the large-scale coronal structure is governed by magnetic fields that are most likely generated by dynamo action in the solar interior. In order to understand the variation in coronal structure, we couple a potential-field source-surface model with a cyclic dynamo model. In this coupled model, the magnetic field inside the convection zone is governed by the dynamo equation; these dynamo-generated fields are extended from the photosphere to the corona using a potential-field source-surface model. Assuming axisymmetry, we take linear combinations of associated Legendre polynomials that match the more complex coronal structures. Choosing images of the global corona from the Mauna Loa Solar Observatory at each Carrington rotation over half a cycle (1986 - 1991), we compute the coefficients of the associated Legendre polynomials up to degree eight and compare with observations. We show that at minimum the dipole term dominates, but it fades as the cycle progresses; higher-order multipolar terms begin to dominate. The amplitudes of these terms are not exactly the same for the two limbs, indicating that there is a longitude dependence. While both the 1986 and the 1996 minimum coronas were dipolar, the minimum in 2008 was unusual, since there was a substantial departure from a dipole. We investigate the physical cause of this departure by including a North-South asymmetry in the surface source of the magnetic fields in our flux-transport dynamo model, and find that this asymmetry could be one of the reasons for departure from the dipole in the 2008 minimum.

  13. Constraining the Date of the Martian Dynamo Shutdown by Means of Crater Magnetization Signatures

    Science.gov (United States)

    Vervelidou, Foteini; Lesur, Vincent; Grott, Matthias; Morschhauser, Achim; Lillis, Robert J.

    2017-11-01

    Mars is believed to have possessed a dynamo that ceased operating approximately 4 Ga ago, although the exact time is still under debate. The scope of this study is to constrain the possible timing of its cessation by studying the magnetization signatures of craters. The study uses the latest available model of the lithospheric magnetic field of Mars, which is based on Mars Global Surveyor data. We tackle the problem of nonuniqueness that characterizes the inversion of magnetic field data for the magnetization by inferring only the visible part of the magnetization, that is, the part of the magnetization that gives rise to the observed magnetic field. Further on, we demonstrate that a zero visible magnetization is a valid proxy for the entire magnetization being zero under the assumption of a magnetization distribution of induced geometry. This assumption holds for craters whose thermoremanent magnetization has not been significantly altered since its acquisition. Our results show that the dynamo shut off after the impacts that created the Acidalia and SE Elysium basins and before the crust within the Utopia basin cooled below its magnetic blocking temperature. Accounting for the age uncertainties in the dating of these craters, we estimate that the dynamo shut off at an N(300) crater retention age of 2.5-3.2 or an absolute model age of 4.12-4.14 Ga. Moreover, the Martian dynamo may have been weaker in its early stage, which if true implies that the driving mechanism of the Martian dynamo was not the same throughout its history.

  14. Impact of DYNAMO observations on NASA GEOS-5 reanalyses and the representation of MJO initiation

    Science.gov (United States)

    Achuthavarier, D.; Wang, H.; Schubert, S. D.; Sienkiewicz, M.

    2017-01-01

    This study examines the impact of the Dynamics of the Madden-Julian Oscillation (DYNAMO) campaign in situ observations on NASA Goddard Earth Observing System version 5 (GEOS-5) reanalyses and the improvements gained thereby in the representation of the Madden-Julian Oscillation (MJO) initiation processes. To this end, we produced a global, high-resolution (1/4° spatially) reanalysis that assimilates the level-4, quality-controlled DYNAMO upper air soundings from about 87 stations in the equatorial Indian Ocean region along with a companion data-denied control reanalysis. The DYNAMO reanalysis produces a more realistic vertical structure of the temperature and moisture in the central tropical Indian Ocean by correcting the model biases, namely, the cold and dry biases in the lower troposphere and warm bias in the upper troposphere. The reanalysis horizontal winds are substantially improved, in that, the westerly acceleration and vertical shear of the zonal wind are enhanced. The DYNAMO reanalysis shows enhanced low-level diabatic heating, moisture anomalies and vertical velocity during the MJO initiation. Due to the warmer lower troposphere, the deep convection is invigorated, which is evident in convective cloud fraction. The GEOS-5 atmospheric general circulation model (AGCM) employed in the reanalysis is overall successful in assimilating the additional DYNAMO observations, except for an erroneous model response for medium rain rates, between 700 and 600 hPa, reminiscent of a bias in earlier versions of the AGCM. The moist heating profile shows a sharp decrease there due to the excessive convective rain re-evaporation, which is partly offset by the temperature increment produced by the analysis.

  15. The call and rise of disability leaders in Uganda: The first Christian-based bachelors program in disability studies and special education at Africa Renewal University

    Directory of Open Access Journals (Sweden)

    Ashley A Hall

    2015-01-01

    Full Text Available This paper investigates the epidemic that prevails in the lives of persons and families affected by disabilities in developing countries, mainly East Africa and Uganda. Grating data and demography are exposed, along with some of the common dilemmas found in the Ugandan educational systems, churches, and communities, in order to express the palpable realities of families and persons with disabilities. Patrons will discover the features and attributes that constructs the disability studies and special education bachelor’s program at Africa Renewal University, including course listings and course content, and how this program seeks to alleviate some of the major wounds for persons and families affected by disabilities in East Africa, which all contribute to identifying the problem and bringing forth resolution. Lastly, this paper highlights bouyant outcomes, strategies for moving forward, and a scope of the next steps for Christlike front-runners and the souls affected by disabilities subsiding in Uganda and East Africa.

  16. 76 FR 17934 - Infrastructure Protection Data Call

    Science.gov (United States)

    2011-03-31

    ... infrastructure and key resources (CIKR). At DHS, this responsibility is managed by IP within NPPD. Beginning in...: Infrastructure Protection Data Call. OMB Number: 1670-NEW. Frequency: On occasion. Affected Public: Federal... SECURITY Infrastructure Protection Data Call AGENCY: National Protection and Programs Directorate, DHS...

  17. Monitoring method call sequences using annotations

    NARCIS (Netherlands)

    B. Nobakht (Behrooz); F.S. de Boer (Frank); M.M. Bonsangue (Marcello); C.P.T. de Gouw (Stijn); M.M. Jaghouri (MohammadMahdi)

    2014-01-01

    htmlabstractIn this paper we introduce JMSeq, a Java-based tool for monitoring sequences of method calls. JMSeq provides a simple but expressive language to specify the observables of a Java program in terms of sequences of possibly nested method calls. Similar to many monitoring-oriented

  18. Assessing call centers’ success:

    Directory of Open Access Journals (Sweden)

    Hesham A. Baraka

    2013-07-01

    This paper introduces a model to evaluate the performance of call centers based on the Delone and McLean Information Systems success model. A number of indicators are identified to track the call center’s performance. Mapping of the proposed indicators to the six dimensions of the D&M model is presented. A Weighted Call Center Performance Index is proposed to assess the call center performance; the index is used to analyze the effect of the identified indicators. Policy-Weighted approach was used to assume the weights with an analysis of different weights for each dimension. The analysis of the different weights cases gave priority to the User satisfaction and net Benefits dimension as the two outcomes from the system. For the input dimensions, higher priority was given to the system quality and the service quality dimension. Call centers decision makers can use the tool to tune the different weights in order to reach the objectives set by the organization. Multiple linear regression analysis was used in order to provide a linear formula for the User Satisfaction dimension and the Net Benefits dimension in order to be able to forecast the values for these two dimensions as function of the other dimensions

  19. Enhanced nurse call systems.

    Science.gov (United States)

    2001-04-01

    This Evaluation focuses on high-end computerized nurse call systems--what we call enhanced systems. These are highly flexible systems that incorporate microprocessor and communications technologies to expand the capabilities of the nurse call function. Enhanced systems, which vary in configuration from one installation to the next, typically consist of a basic system that provides standard nurse call functionality and a combination of additional enhancements that provide the added functionality the facility desires. In this study, we examine the features that distinguish enhanced nurse call systems from nonenhanced systems, focusing on their application and benefit to healthcare facilities. We evaluated seven systems to determine how well they help (1) improve patient care, as well as increase satisfaction with the care provided, and (2) improve caregiver efficiency, as well as increase satisfaction with the work environment. We found that all systems meet these objectives, but not all systems perform equally well for all implementations. Our ratings will help facilities identify those systems that offer the most effective features for their intended use. The study also includes a Technology Management Guide to help readers (1) determine whether they'll benefit from the capabilities offered by enhanced systems and (2) target a system for purchase and equip the system for optimum performance and cost-effective operation.

  20. Robust estimate of dynamo thresholds in the von K\\'arm\\'an sodium experiment using the Extreme Value Theory

    CERN Document Server

    Faranda, Davide; Miralles, Sophie; Odier, Philippe; Pinton, Jean-Francois; Plihon, Nicolas; Daviaud, François; Dubrulle, Bérengère

    2014-01-01

    We apply a new threshold detection method based on the extreme value theory to the von K\\'arm\\'an sodium (VKS) experiment data. The VKS experiment is a successful attempt to get a dynamo magnetic field in a laboratory liquid-metal experiment. We first show that the dynamo threshold is associated to a change of the probability density function of the extreme values of the magnetic field. This method does not require the measurement of response functions from applied external perturbations, and thus provides a simple threshold estimate. We apply our method to different configurations in the VKS experiment showing that it yields a robust indication of the dynamo threshold as well as evidence of hysteretic behaviors. Moreover, for the experimental configurations in which a dynamo transition is not observed, the method provides a way to extrapolate an interval of possible threshold values.

  1. Lorentz violation bounds from torsion trace fermion sector and galaxy M 51 data and chiral dynamos

    Science.gov (United States)

    Garcia de Andrade, L. C.

    2017-06-01

    Earlier we have computed a Lorentz violation (LV) bound for torsion terms via galactic dynamos and found bounds similar to the one obtained by Kostelecky et al. (Phys Rev Lett 100:111102, 2008) which is of the order of 10^{-31} GeV. Their result was found making use of the axial torsion vector in terms of Dirac spinors and minimal torsion coupling in flat space-time of fermions. In this paper, a torsion dynamo equation obtained using the variation of the torsion trace and galaxy M51 data of 500 pc are used to place an upper bound of 10^{-26} GeV in LV, which agrees with the one by Kostelecky and his group using an astrophysical framework background. Their lowest bound was obtained in earth laboratory using dual masers. One of the purposes of this paper is to apply the Faraday self-induction magnetic equation, recently extended to torsioned space-time, by the author to show that it lends support to physics in Riemann-Cartan space-time, in several distinct physical backgrounds. Backreaction magnetic effects are used to obtain the LV bounds. Previously Bamba et al. (JCAP 10:058, 2012) have used the torsion trace in their teleparallel investigation of the IGMF, with the argument that the torsion trace leads to less weaker effects than the other irreducible components of the torsion tensor. LV is computed in terms of a chiral-torsion-like current in the new dynamo equation analogous to the Dvornikov and Semikoz dynamo equation with chiral magnetic currents. Making use of the chiral-torsion dynamo equation we estimate the LV bounds in the early universe to be of the order of 10^{-24} GeV, which was the order of the charged-lepton sector. Our main result is that it is possible to obtain more stringent bounds than the ones found in the fermion sector of astrophysics in the new revised 2017 data table for CPT and Lorentz violation by Kostelecky and Mewes. They found in several astrophysical backgrounds, orders of magnitude such as 10^{-24} and 10^{-23} GeV which are not so

  2. Lorentz violation bounds from torsion trace fermion sector and galaxy M51 data and chiral dynamos

    Energy Technology Data Exchange (ETDEWEB)

    Garcia de Andrade, L.C. [IF-UERJ, Departamento de Fisica Teorica, Rio de Janeiro, RJ (Brazil)

    2017-06-15

    Earlier we have computed a Lorentz violation (LV) bound for torsion terms via galactic dynamos and found bounds similar to the one obtained by Kostelecky et al. (Phys Rev Lett 100:111102, 2008) which is of the order of 10{sup -31} GeV. Their result was found making use of the axial torsion vector in terms of Dirac spinors and minimal torsion coupling in flat space-time of fermions. In this paper, a torsion dynamo equation obtained using the variation of the torsion trace and galaxy M51 data of 500 pc are used to place an upper bound of 10{sup -26} GeV in LV, which agrees with the one by Kostelecky and his group using an astrophysical framework background. Their lowest bound was obtained in earth laboratory using dual masers. One of the purposes of this paper is to apply the Faraday self-induction magnetic equation, recently extended to torsioned space-time, by the author to show that it lends support to physics in Riemann-Cartan space-time, in several distinct physical backgrounds. Backreaction magnetic effects are used to obtain the LV bounds. Previously Bamba et al. (JCAP 10:058, 2012) have used the torsion trace in their teleparallel investigation of the IGMF, with the argument that the torsion trace leads to less weaker effects than the other irreducible components of the torsion tensor. LV is computed in terms of a chiral-torsion-like current in the new dynamo equation analogous to the Dvornikov and Semikoz dynamo equation with chiral magnetic currents. Making use of the chiral-torsion dynamo equation we estimate the LV bounds in the early universe to be of the order of 10{sup -24} GeV, which was the order of the charged-lepton sector. Our main result is that it is possible to obtain more stringent bounds than the ones found in the fermion sector of astrophysics in the new revised 2017 data table for CPT and Lorentz violation by Kostelecky and Mewes. They found in several astrophysical backgrounds, orders of magnitude such as 10{sup -24} and 10{sup -23} Ge

  3. Call Me Sisyphus

    Science.gov (United States)

    2009-02-01

    Gordon MacKenzie (au- thor of Orbiting the Giant Hairball: A Corporate Fool’s Guide to Surviving with Grace) calls a “plum tree structure” and looked at...ghting.” Editor’s note: In Greek mythology , Sisyphus was condemned to an eternity of punishment in Hades that consisted of rolling a huge boulder to

  4. CALLING AQUARIUM LOVERS...

    CERN Multimedia

    2002-01-01

    CERN's anemones will soon be orphans. We are looking for someone willing to look after the aquarium in the main building, for one year. If you are interested, or if you would like more information, please call 73830. (The anemones living in the aquarium thank you in anticipation.)

  5. Post-call delirium.

    Science.gov (United States)

    Rush, Raphael

    2016-12-01

    Although frequently diagnosed in hospital in-patients, delirium is often recognised but under-reported in the housestaff population. It is estimated that more than 90% of housestaff will experience regular episodes of post-call delirium. This paper identifies diagnostic criteria and discusses approaches to treatment. © 2016 John Wiley & Sons Ltd and The Association for the Study of Medical Education.

  6. A call for surveys

    DEFF Research Database (Denmark)

    Bernstein, Philip A.; Jensen, Christian S.; Tan, Kian-Lee

    2012-01-01

    The database field is experiencing an increasing need for survey papers. We call on more researchers to set aside time for this important writing activity. The database field is growing in population, scope of topics covered, and the number of papers published. Each year, thousands of new papers ...

  7. CIFSRF 2015 Call Document

    International Development Research Centre (IDRC) Digital Library (Canada)

    wmanchur

    2015-02-02

    Feb 2, 2015 ... Cross-cutting priorities. All proposals seeking funds from this call shall clearly speak to the three CIFSRF cross-cutting priorities: a. Gender equality. Proposals need to demonstrate how the project will include women as important players in the scaling up of innovations, as well as key clients and end users.

  8. A Remarkable Recent Transition in the Solar Dynamo

    NARCIS (Netherlands)

    de Jager, C.; Akasofu, S.-I.; Duhau, S.; Livingston, W.C.; Nieuwenhuijzen, H.; Potgieter, M.S.

    2016-01-01

    We summarize the major aspects of the remarkable, fairly long lasting period(∼ 2005 to ∼ 2010) of low solar activity, that we will call the Transition. It is the transitionalstage between the Grand Maximum of the 20th century and a forthcoming (most probablyRegular) episode of solar activity. The

  9. High Prevalence of Vitamin D Deficiency in Native versus Migrant Mothers and Newborns in the North of Italy: A Call to Act with a Stronger Prevention Program.

    Directory of Open Access Journals (Sweden)

    Francesco Cadario

    Full Text Available Vitamin D status during pregnancy is related to neonatal vitamin D status. Vitamin D deficiency has been associated with an increased risk of rickets in children and osteomalacia in adults. Aim of this study was to investigate 25OHD levels in maternal serum and in neonatal blood spots in native and migrant populations living in Novara (North Italy, 45°N latitude.We carried out a cross sectional study from April 1st 2012 to March 30th 2013, in a tertiary Care Center. Maternal blood samples after delivery and newborns' blood spots were analyzed for 25OHD levels in 533 pairs. Maternal country of origin, skin phototype, vitamin D dietary intake and supplementation during pregnancy were recorded. Multivariate regression analysis, showed a link between neonatal and maternal 25OHD levels (R-square:0.664. Severely deficient 25OHD values (<25 nmol/L were found in 38% of Italian and in 76.2% of migrant's newborns (p <0.0001, and in 18% of Italian and 48,4% of migrant mothers (p <0.0001 while 25OHD deficiency (≥25 and <50 nmol/L was shown in 40.1% of Italian and 21.7% of migrant's newborns (p <0.0001, and in 43.6% of Italian and 41.3% of migrant mothers (p <0.0001. Italian newborns and mothers had higher 25OHD levels (34.4±19.2 and 44.9±21.2 nmol/L than migrants (17.7±13.7 and 29.7±16.5 nmol/L; p<0.0001. A linear decrease of 25OHD levels was found with increasing skin pigmentation (phototype I 42.1 ±18.2 vs phototype VI 17.9±10.1 nmol/l; p<0.0001. Vitamin D supplementation resulted in higher 25OHD values both in mothers and in their newborns (p<0.0001.Vitamin D insufficiency in pregnancy and in newborns is frequent especially among migrants. A prevention program in Piedmont should urgently be considered and people identified as being at risk should be closely monitored. Vitamin D supplementation should be taken into account when considering a preventative health care policy.

  10. Investigation of the Air-Wave-Sea Interaction Modes Using an Airborne Doppler Wind Lidar: Analyses of the HRDL Data Taken using DYNAMO

    Science.gov (United States)

    2013-10-07

    Interaction Modes Using an Airborne Doppler Wind Lidar: Analyses of the HRDL data taken using DYNAMO 5a. CONTRACT NUMBER N0001411C0464 5b. GRANT...efficiency of energy, mass and momentum exchange at the bottom and top of the ABL. 15. SUBJECT TERMS DYNAMO , ABL 16. SECURITY CLASSIFICATION OF: 17...Investigation of the Air-Wave-Sea Interaction Modes Using an Airborne Doppler Wind Lidar: Analyses of the HRDL data taken during DYNAMO George

  11. Non-kinematic Flux-transport Dynamos Including the Effects of Diffusivity Quenching

    Energy Technology Data Exchange (ETDEWEB)

    Ichimura, Chiaki; Yokoyama, Takaaki [Department of Earth and Planetary Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2017-04-10

    Turbulent magnetic diffusivity is quenched when strong magnetic fields suppress turbulent motion in a phenomenon known as diffusivity quenching. Diffusivity quenching can provide a mechanism for amplifying magnetic field and influencing global velocity fields through Lorentz force feedback. To investigate this effect, we conducted mean field flux-transport dynamo simulations that included the effects of diffusivity quenching in a non-kinematic regime. We found that toroidal magnetic field strength is amplified by up to approximately 1.5 times in the convection zone as a result of diffusivity quenching. This amplification is much weaker than that in kinematic cases as a result of Lorentz force feedback on the system’s differential rotation. While amplified toroidal fields lead to the suppression of equatorward meridional flow locally near the base of the convection zone, large-scale equatorward transport of magnetic flux via meridional flow, which is the essential process of the flux-transport dynamo, is sustainable in our calculations.

  12. Large-scale dynamo of accretion disks around supermassive nonrotating black holes

    Directory of Open Access Journals (Sweden)

    Poplavsky A.L.

    2006-01-01

    Full Text Available In this paper one presents an analytical model of accretion disk magnetosphere dynamics around supermassive nonrotating black holes in the centers of active galactic nuclei. Based on general relativistic equations of magneto hydrodynamics, the nonstationary solutions for time-dependent dynamo action in the accretion disks, spatial and temporal distribution of magnetic field are found. It is shown that there are two distinct stages of dynamo process: the transient and the steady-state regimes, the induction of magnetic field at t > 6:6665 x 1011GM/c3 s becomes stationary, magnetic field is located near the innermost stable circular orbit, and its value rises up to ~ 105 G. Applications of such systems with nonrotating black holes in real active galactic nuclei are discussed.

  13. Dynamo effects and geometrical origin of the alpha term in affine theory of gravity

    Science.gov (United States)

    Cirilo-Lombardo, Diego Julio

    2017-11-01

    Dynamo effect is considered in the context of an Unified field theoretical model based in affine geometries. We show that there exists an analog "α-term" in the equations that has a purely geometric origin, in sharp contrast with the turbulent one. Some high energy and astrophysical implicancies (primordial magnetic field, compact objects dynamics, chiral magnetic effects, etc) coming from this type of alternative model of gravitation are briefly discussed.

  14. Large-scale dynamo growth rates from numerical simulations and implications for mean-field theories.

    Science.gov (United States)

    Park, Kiwan; Blackman, Eric G; Subramanian, Kandaswamy

    2013-05-01

    Understanding large-scale magnetic field growth in turbulent plasmas in the magnetohydrodynamic limit is a goal of magnetic dynamo theory. In particular, assessing how well large-scale helical field growth and saturation in simulations match those predicted by existing theories is important for progress. Using numerical simulations of isotropically forced turbulence without large-scale shear with its implications, we focus on several additional aspects of this comparison: (1) Leading mean-field dynamo theories which break the field into large and small scales predict that large-scale helical field growth rates are determined by the difference between kinetic helicity and current helicity with no dependence on the nonhelical energy in small-scale magnetic fields. Our simulations show that the growth rate of the large-scale field from fully helical forcing is indeed unaffected by the presence or absence of small-scale magnetic fields amplified in a precursor nonhelical dynamo. However, because the precursor nonhelical dynamo in our simulations produced fields that were strongly subequipartition with respect to the kinetic energy, we cannot yet rule out the potential influence of stronger nonhelical small-scale fields. (2) We have identified two features in our simulations which cannot be explained by the most minimalist versions of two-scale mean-field theory: (i) fully helical small-scale forcing produces significant nonhelical large-scale magnetic energy and (ii) the saturation of the large-scale field growth is time delayed with respect to what minimalist theory predicts. We comment on desirable generalizations to the theory in this context and future desired work.

  15. Quasi-cyclic behaviour in non-linear simulations of the shear dynamo

    Science.gov (United States)

    Teed, Robert J.; Proctor, Michael R. E.

    2017-06-01

    The solar magnetic field displays features on a wide range of length-scales including spatial and temporal coherence on scales considerably larger than the chaotic convection that generates the field. Explaining how the Sun generates and sustains such large-scale magnetic field has been a major challenge of dynamo theory for many decades. Traditionally, the 'mean-field' approach, utilizing the well-known α-effect, has been used to explain the generation of large-scale field from small-scale turbulence. However, with the advent of increasingly high-resolution computer simulations there is doubt as to whether the mean-field method is applicable under solar conditions. Models such as the 'shear dynamo' provide an alternative mechanism for the generation of large-scale field. In recent work, we showed that while coherent magnetic field was possible under kinematic conditions (where the kinetic energy is far greater than magnetic energy), the saturated state typically displayed a destruction of large-scale field and a transition to a small-scale state. In this paper, we report that the quenching of large-scale field in this way is not the only regime possible in the saturated state of this model. Across a range of simulations, we find a quasi-cyclic behaviour where a large-scale field is preserved and oscillates between two preferred length-scales. In this regime, the kinetic and magnetic energies can be of a similar order of magnitude. These results demonstrate that there is mileage in the shear dynamo as a model for the solar dynamo.

  16. Cosmological magnetic fields as string dynamo seeds and axion fields in torsioned spacetime

    Energy Technology Data Exchange (ETDEWEB)

    De Andrade, L.C. Garcia, E-mail: garcia@dft.if.uerj.br [Departamento de Física Teórica — IF — Universidade do Estado do Rio de Janeiro-UERJ, Rua São Francisco Xavier, 524, Maracanã, Rio de Janeiro, RJ, Cep 20550-003 (Brazil)

    2014-08-01

    In this paper two examples of the generation cosmological magnetic fields (CMF) are given. The first is the string dynamo seed cosmological magnetic field estimated as B{sub seed}∼10{sup -24} Gauss from a static spin polarised cylinder in Einstein-Cartan-Maxwell spacetime. The string dynamo seeds from a static spin polarised cylinder is given by B∼σ{sup 2}R{sup 2} where σ is the spin-torsion density while R is the string radius. The B-field value above is able to seed galactic dynamo. In the BBN the magnetic fields around 10{sup 12} Gauss give rise to a string radius as small as 10{sup 17}l{sub P} where l{sub P} is the Planck length. The second is the CMF from axionic torsion field which is given by B{sub seed}∼10{sup -27} Gauss which is stronger than the primordial magnetic field B{sub BICEP2}∼10{sup -30} Gauss from the BICEP2 recent experiment on primordial gravitational waves and cosmological inflation to axionic torsion. The interaction Lagrangean between axionic torsion scalar φ and magnetic fields used in this last example is given by f{sup 2}(φ)F{sub μν}F{sup μν}. A similar lagrangean has been used by K. Bamba et al. [JCAP 10 (2012) 058] so generate magnetic fields without dynamo action. Since axionic torsion can be associated with axionic domain walls both examples discussed here could be consider as topological defects examples of the generation of primordial magnetic fields in universes endowed with spacetime torsion.

  17. Global Solar Convective Dynamo with Cycles, Equatorward Propagation and Grand Minima

    Science.gov (United States)

    Toomre, Juri; Augustson, Kyle C.; Brun, Allan Sacha; Miesch, Mark S.

    2016-05-01

    The 3-D MHD Anelastic Spherical Harmonic (ASH) code, using slope-limited diffusion, is used to study the interaction of turbulent convection, rotation and magnetism in a full spherical shell comparable to the solar convection zone. Here a star of one solar mass, with a solar luminosity, is considered that is rotating at three times the solar rate. The dynamo generated magnetic field forms large-scale toroidal wreaths, whose formation is tied to the low Rossby number of the convection in this simulation which we have labeled K3S. This case displays prominent polarity cycles with regular reversals occurring roughly every 6.2 years. These reversals are linked to the weakened differential rotation and a resistive collapse of the large-scale magnetic field. Distinctive equatorial migration of the strong magnetic wreaths is seen, arising from modulation of the differential rotation rather than a dynamo wave. As the wreaths approach the equator, cross-equatorial magnetic flux is achieved that permits the low-latitude convection to generate poloidal magnetic field with opposite polarity. Poleward migration of such magnetic flux from the equator eventually leads to the reversal of the polarity of the high-latitude magnetic field. This K3S simulation also enters an interval with reduced magnetic energy at low latitudes lasting roughly 16 years (about 2.5 polarity cycles), during which the polarity cycles are disrupted and after which the dynamo recovers its regular polarity cycles. An analysis of this striking grand minimum reveals that it likely arises through the interplay of symmetric and antisymmetric dynamo families.

  18. Flight calls and orientation

    DEFF Research Database (Denmark)

    Larsen, Ole Næsbye; Andersen, Bent Bach; Kropp, Wibke

    2008-01-01

    flight calls was simulated by sequential computer controlled activation of five loudspeakers placed in a linear array perpendicular to the bird's migration course. The bird responded to this stimulation by changing its migratory course in the direction of that of the ‘flying conspecifics' but after about...... 30 minutes it drifted back to its original migration course. The results suggest that songbirds migrating alone at night can use the flight calls from conspecifics as additional cues for orientation and that they may compare this information with other cues to decide what course to keep.......  In a pilot experiment a European Robin, Erithacus rubecula, expressing migratory restlessness with a stable orientation, was video filmed in the dark with an infrared camera and its directional migratory activity was recorded. The flight overhead of migrating conspecifics uttering nocturnal...

  19. The DYNAMO Orbiter Project: High Resolution Mapping of Gravity/Magnetic Fields and In Situ Investigation of Mars Atmospheric Escape

    Science.gov (United States)

    Smrekar, S.; Chassefiere, E.; Forget, F.; Reme, H.; Mazelle, C.; Blelly, P. -L.; Acuna, M.; Connerney, J.; Purucker, M.; Lin, R.

    2000-01-01

    Dynamo is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for Dynamo of 120-130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere, and water, from the planet. There is much room for debate on the importance of current atmosphere escape processes in the evolution of the Martian atmosphere, as early "exotic" processes including hydrodynamic escape and impact erosion are traditionally invoked to explain the apparent sparse inventory of present-day volatiles. Yet, the combination of low surface gravity and the absence of a substantial internally generated magnetic field have undeniable effects on what we observe today. In addition to the current losses in the forms of Jeans and photochemical escape of neutrals, there are solar wind interaction-related erosion mechanisms because the upper atmosphere is directly exposed to the solar wind. The solar wind related loss rates, while now comparable to those of a modest comet, nonetheless occur continuously, with the intriguing possibility of important cumulative and

  20. A Call for Justice

    OpenAIRE

    Brahmachari, Debahuti

    2015-01-01

    Abstract A new development can be identified within the civil society in Malaysia. A development that has resulted in a general call for justice, voiced through coalition groups that cut across categories of affiliation. This development is triggered by an increasing inculcation of Islamic values into the political system, which has interfered with the understanding of Malaysia as a country that can provide a framework for coexistence within a multicultural society. This thesis seeks ...

  1. Multimodality and CALL

    OpenAIRE

    Guichon, Nicolas; Cohen, Cathy

    2016-01-01

    International audience; This chapter explores the issues pertaining to multimodality, which has always been considered as a defining characteristic of CALL (Chapelle 2009). The chapter begins by critically examining the various definitions of multimodality, especially in the field of second language acquisition and cognitive psychology and explores the distinction between mode, modality and channel. With reference to specific studies conducted in the field, we then investigate the potential o...

  2. Magnetic Cycles in a Dynamo Simulation of Fully Convective M-star Proxima Centauri

    Science.gov (United States)

    Yadav, Rakesh K.; Christensen, Ulrich R.; Wolk, Scott J.; Poppenhaeger, Katja

    2016-12-01

    The recent discovery of an Earth-like exoplanet around Proxima Centauri has shined a spot light on slowly rotating fully convective M-stars. When such stars rotate rapidly (period ≲20 days), they are known to generate very high levels of activity that is powered by a magnetic field much stronger than the solar magnetic field. Recent theoretical efforts are beginning to understand the dynamo process that generates such strong magnetic fields. However, the observational and theoretical landscape remains relatively uncharted for fully convective M-stars that rotate slowly. Here, we present an anelastic dynamo simulation designed to mimic some of the physical characteristics of Proxima Centauri, a representative case for slowly rotating fully convective M-stars. The rotating convection spontaneously generates differential rotation in the convection zone that drives coherent magnetic cycles where the axisymmetric magnetic field repeatedly changes polarity at all latitudes as time progress. The typical length of the “activity” cycle in the simulation is about nine years, in good agreement with the recently proposed activity cycle length of about seven years for Proxima Centauri. Comparing our results with earlier work, we hypothesis that the dynamo mechanism undergoes a fundamental change in nature as fully convective stars spin down with age.

  3. Effect of soft-iron impellers on the von Kármán-sodium dynamo.

    Science.gov (United States)

    Xu, Mingtian

    2014-01-01

    The explanation for the observed axisymmetric magnetic field in the von Kármán-sodium (VKS) dynamo experiment is still an unresolved question. In this paper, the integral equation approach is extended to investigate the VKS dynamo action by taking into account the discontinuity of the magnetic permeability and electrical conductivity in the conducting region. When the relative magnetic permeability of the soft-iron impellers is set to 65, a steady toroidal field that is apparently axisymmetric is excited at the critical magnetic Reynolds number, Rmc≈27.23, which is close to the experimental result, Rmc≈30. Our results show that the critical magnetic Reynolds number declines as the relative magnetic permeability of the impellers increases. Furthermore, when the relative magnetic permeability is not greater than 37, an equatorial magnetic field with an azimuthal wave number m=1 is the dominant mode, otherwise a steady toroidal field with an azimuthal wave number m=0 predominates the magnetic field generated by the VKS dynamo action.

  4. Nonlinear Large Scale Flow in a Precessing Cylinder and Its Ability To Drive Dynamo Action.

    Science.gov (United States)

    Giesecke, André; Vogt, Tobias; Gundrum, Thomas; Stefani, Frank

    2018-01-12

    We have conducted experimental measurements and numerical simulations of a precession-driven flow in a cylindrical cavity. The study is dedicated to the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf and aims at the evaluation of the hydrodynamic flow with respect to its ability to drive a dynamo. We focus on the strongly nonlinear regime in which the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves arising from nonlinear self-interactions. We obtain an excellent agreement between experiment and simulation with regard to both flow amplitudes and flow geometry. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rm^{c}≈430, which is well within the range of the planned liquid sodium experiment.

  5. Helioseismic Observations of Two Solar Cycles and Constraints on Dynamo Theory

    Science.gov (United States)

    Kosovichev, Alexander

    2018-01-01

    Helioseismology data from the SOHO and SDO, obtained in 1996-2017 for almost two solar cycles, provide a unique opportunity to investigate variations of the solar interior structure and dynamics, and link these variations to the current dynamo models and simulations. The solar oscillation frequencies and frequency splitting of medium-degree p- and f-modes, as well as helioseismic inversions have been used to analyze variations of the differential rotation (“torsional oscillations”) and the global asphericity. By comparing the helioseismology results with the synoptic surface magnetic fields we identify characteristic changes associated the initiation and evolution of the solar cycles, 23 and 24. The observational results are compared with the current mean-field dynamo models and 3D MHD dynamo simulations. It is shown that the helioseismology inferences provide important constraints on the dynamics of the tachocline and near-surface shear layer, and also may explain the fundamental difference between the two solar cycles and detect the onset of the next cycle.

  6. Energy transfers in large-scale and small-scale dynamos

    Science.gov (United States)

    Samtaney, Ravi; Kumar, Rohit; Verma, Mahendra

    2015-11-01

    We present the energy transfers, mainly energy fluxes and shell-to-shell energy transfers in small-scale dynamo (SSD) and large-scale dynamo (LSD) using numerical simulations of MHD turbulence for Pm = 20 (SSD) and for Pm = 0.2 on 10243 grid. For SSD, we demonstrate that the magnetic energy growth is caused by nonlocal energy transfers from the large-scale or forcing-scale velocity field to small-scale magnetic field. The peak of these energy transfers move towards lower wavenumbers as dynamo evolves, which is the reason for the growth of the magnetic fields at the large scales. The energy transfers U2U (velocity to velocity) and B2B (magnetic to magnetic) are forward and local. For LSD, we show that the magnetic energy growth takes place via energy transfers from large-scale velocity field to large-scale magnetic field. We observe forward U2U and B2B energy flux, similar to SSD.

  7. Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

    Science.gov (United States)

    Butsky, Iryna; Zrake, Jonathan; Kim, Ji-hoon; Yang, Hung-I.; Abel, Tom

    2017-07-01

    We study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way-mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulent dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk’s spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.

  8. The magnetospheric clock of Saturn—A self-organized plasma dynamo

    Energy Technology Data Exchange (ETDEWEB)

    Olson, J.; Brenning, N. [Space and Plasma Physics, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden)

    2013-08-15

    The plasma in the inner magnetosphere of Saturn is characterized by large-amplitude azimuthal density variations in the equatorial plane, with approximately a sinusoidal dependence on the azimuthal angle [D. A. Gurnett et al., Science 316, 442 (2007)]. This structure rotates with close to the period of the planet itself and has been proposed to steer other nonaxisymmetric phenomena, e.g., the Saturn kilometric radiation SKR [W. S. Kurth et al., Geophys. Res. Lett. 34, L02201 (2007)], and inner-magnetosphere magnetic field perturbations [D. J. Southwood and M. G. Kivelson, J. Geophys. Res. 112(A12), A12222 (2007)]. There is today no consensus regarding the basic driving mechanism. We here propose it to be a plasma dynamo, located in the neutral gas torus of Enceladus but coupled both inwards, through electric currents along the magnetic field lines down to the planet, and outwards through the plasma flow pattern there. Such a dynamo mechanism is shown to self-regulate towards a state that, with realistic parameters, can reproduce the observed configuration of the magnetosphere. This state is characterized by three quantities: the Pedersen conductivity in the polar cap, the ionization time constant in the neutral gas torus, and a parameter characterizing the plasma flow pattern. A particularly interesting property of the dynamo is that regular (i.e., constant-amplitude, sinusoidal) variations in the last parameter can lead to complicated, non-periodic, oscillations around the steady-state configuration.

  9. Electrically driving large magnetic Reynolds number flows on the Madison plasma dynamo experiment

    Science.gov (United States)

    Weisberg, David; Wallace, John; Peterson, Ethan; Endrezzi, Douglass; Forest, Cary B.; Desangles, Victor

    2015-11-01

    Electrically-driven plasma flows, predicted to excite a large-scale dynamo instability, have been generated in the Madison plasma dynamo experiment (MPDX), at the Wisconsin Plasma Astrophysics Laboratory. Numerical simulations show that certain topologies of these simply-connected flows may be optimal for creating a plasma dynamo and predict critical thresholds as low as Rmcrit =μ0 σLV = 250 . MPDX plasmas are shown to exceed this critical Rm , generating large (L = 1 . 4 m), warm (Te > 10 eV), unmagnetized (MA > 1) plasmas where Rm torque in Helium plasmas. Detailed Mach probe measurements of plasma velocity for two flow topologies will be presented: edge-localized drive using the multi-cusp boundary field, and volumetric drive using an axial Helmholtz field. Radial velocity profiles show that edge-driven flow is established via ion viscosity but is limited by a volumetric neutral drag force (χ ~ 1 / (ντin)), and measurements of velocity shear compare favorably to Braginskii transport theory. Volumetric flow drive is shown to produce stronger velocity shear, and is characterized by the radial potential gradient as determined by global charge balance.

  10. The Double-Ring Algorithm: Reconciling Surface Flux Transport Simulations and Kinematic Dynamo Models

    Science.gov (United States)

    Munoz-Jaramillo, Andres; Nandy, D.; Martens, P. C. H.; Yeates, A. R.

    2011-05-01

    The emergence of tilted bipolar active regions and the dispersal of their flux, mediated via processes such as diffusion, differential rotation and meridional circulation is believed to be responsible for the reversal of the Sun's polar field. This process (commonly known as the Babcock-Leighton mechanism) is usually modeled as a near-surface, spatially distributed α-effect in kinematic mean-field dynamo models. However, this formulation leads to a relationship between polar field strength and meridional flow speed which is opposite to that suggested by physical insight and predicted by surface flux-transport simulations. With this in mind, we present an improved double-ring algorithm for modeling the Babcock-Leighton mechanism based on active region eruption, within the framework of an axisymmetric dynamo model. We demonstrate that our treatment of the Babcock-Leighton mechanism through double-ring eruption leads to an inverse relationship between polar field strength and meridional flow speed as expected, reconciling the discrepancy between surface flux-transport simulations and kinematic dynamo models. Finally, we show how this new formulation paves the way for applications, which were not possible before, like understanding the nature of the extended minimum of sunspot cycle 23 and direct assimilation of active region data. This work is funded by NASA Living With a Star Grant NNX08AW53G to Montana State University/Harvard-Smithsonian Center for Astrophysics and the Government of India's Ramanujan Fellowship.

  11. Numerical simulation of laminar plasma dynamos in a cylindrical von K\\'arm\\'an flow

    CERN Document Server

    Khalzov, I V; Ebrahimi, F; Schnack, D D; Forest, C B; 10.1063/1.3559472

    2011-01-01

    The results of a numerical study of the magnetic dynamo effect in cylindrical von K\\'arm\\'an plasma flow are presented with parameters relevant to the Madison Plasma Couette Experiment. This experiment is designed to investigate a broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl number Pm can be of order unity (i.e., the fluid Reynolds number Re is comparable to the magnetic Reynolds number Rm). This is in contrast to liquid metal experiments, where Pm is small (so, Re>>Rm) and the flows are always turbulent. We explore dynamo action through simulations using the extended magnetohydrodynamic NIMROD code for an isothermal and compressible plasma model.We also study two-fluid effects in simulations by including the Hall term in Ohm's law. We find that the counter-rotating von K\\'arm\\'an flow results in sustained dynamo action and the self-generation of magnetic field when the magnetic Reynolds number exceeds a critical value. For the plasma parameters of the experiment, this field ...

  12. Final Technical Report for DOE DE-FG02-05ER54831 "Laboratory Studies of Dynamos."

    Energy Technology Data Exchange (ETDEWEB)

    Forest, Cary B. [Univ. of Wisconsin, Madison, WI (United States)

    2014-11-06

    Laboratory Studies of Dynamos: Executive Summary. The self-generation of magnetic fields by astrophysical bodies like planets, stars, accretion disks, galaxies, and even galaxy clusters arises due to a mechanism referred to as a homogeneous dynamo. It is quite simple to demonstrate the generation of a magnetic fi eld from a rotating copper disk coupled with a coil of wire, a device known as the homopolar dynamo. The device works like a magnetic fi eld ampli er with a feedback circuit: the differential rotation of a metal disk past an infinitesimally small seed magnetic field induces currents in the disk which, when coupled to a coil winding, can amplify the field until it becomes strong enough to slow the rotation of the disk. What is remarkable is that the same type of circuit may be achieved in a flowing conducting fluid such as a liquid metal in the case of planetary dynamos or a plasma in the case of astrophysical dynamos. The complexity of describing planetary and stellar dynamos despite their ubiquity and the plethora of observational data from the Earth and the Sun motivates the demonstration of a laboratory homogenous dynamo. To create a homogenous dynamo, one first needs a su fficiently large, fast flow of a highly conducting fluid that the velocity shear in the fluid can bend magnetic field lines. With a high Rm-flow, the magnetic fi eld can be ampli ed by the stretching action provided by di fferential rotation. The other critical ingredient is a flow geometry that provides feedback so that the ampli ed eld reinforces the initial in nitesimal seed field - a mechanism that recreates the feedback provided by the coil of wire in the homopolar dynamo. In the Madison Dynamo Experiment, this combination of magnetic ampli cation and feedback is feasible in the simple geometry of two counter-rotating helical vortices in a 1 meter-diameter spherical vessel lled with liquid sodium. For an optimal helical pitch of the flow the threshold for exciting a dynamo is

  13. Plasma response to sustainment with imposed-dynamo current drive in HIT-SI and HIT-SI3

    Science.gov (United States)

    Hossack, A. C.; Jarboe, T. R.; Chandra, R. N.; Morgan, K. D.; Sutherland, D. A.; Penna, J. M.; Everson, C. J.; Nelson, B. A.

    2017-07-01

    The helicity injected torus—steady inductive (HIT-SI) program studies efficient, steady-state current drive for magnetic confinement plasmas using a novel experimental method. Stable, high-beta spheromaks have been sustained using steady, inductive current drive. Externally induced loop voltage and magnetic flux are oscillated together so that helicity and power injection are always positive, sustaining the edge plasma current indefinitely. Imposed-dynamo current drive (IDCD) theory further shows that the entire plasma current is sustained. The method is ideal for low aspect ratio, toroidal geometries with closed flux surfaces. Experimental studies of spheromak plasmas sustained with IDCD have shown stable magnetic profiles with evidence of pressure confinement. New measurements show coherent motion of a stable spheromak in response to the imposed perturbations. On the original device two helicity injectors were mounted on either side of the spheromak and the injected mode spectrum was predominantly n  =  1. Coherent, rigid motion indicates that the spheromak is stable and a lack of plasma-generated n  =  1 energy indicates that the maximum q is maintained below 1 during sustainment. Results from the HIT-SI3 device are also presented. Three inductive helicity injectors are mounted on one side of the spheromak flux conserver. Varying the relative injector phasing changes the injected mode spectrum which includes n  =  2, 3, and higher modes.

  14. The dynamics and scaling laws of planetary dynamos driven by inertial waves

    Science.gov (United States)

    Davidson, P. A.

    2014-09-01

    Great progress has been made in the numerical simulation of planetary dynamos, though these numerical experiments still operate in a regime very far from the planets. For example, it seems unlikely that viscous forces are at all significant in planetary interiors, yet some of the simulations display a significant dependence on viscosity, and indeed in some of the simulations the dynamo mechanism is itself viscously driven, taking the form of helical Ekman pumping within columnar convection rolls. Given the similarity of the external magnetic fields observed in the terrestrial planets and gas giants, and the extremely small value of the Ekman number in all such cases, it seems natural to suppose that the underlying dynamo mechanism in these planets is simple, robust, independent of viscosity and insensitive to mechanical boundary conditions. A key step to identifying this mechanism is to determine the source of helicity in planetary cores, which itself should be robust, independent of viscosity and insensitive to boundary conditions. In this paper, we explore the possibility that the helicity in the core of the Earth arises from the spontaneous emission of inertial waves, driven by the equatorial heat flux in the outer core. We also ask if a similar mechanism might operate in other planets, and perhaps act to supplement the helicity driven by Ekman pumping in the (viscous) numerical simulations. We demonstrate that such waves do indeed produce the required helicity distribution outside the tangent cylinder. Moreover, we show that these waves inevitably propagate along the axis of the columnar vortices, and indeed they are the very mechanism by which the columnar vortices form in the first place and the means by which the columns subsequently evolve. We also calculate the emf induced by such axially propagating inertial waves and show that, in principle, this emf is sufficient to support a self-sustaining dynamo of the α2 type. Finally, we derive the scaling laws

  15. To be called upon

    DEFF Research Database (Denmark)

    Kublitz, Anja

    2015-01-01

    of the responses to the Arab spring among Danish Muslims, this paper will offer some preliminary reflections on how we can understand ‘the mass’ and an ‘intimacy of the mass’ when the mass is no longer a crowd. According to Marx the mass grows quantitatively from the local to the global, but what happens......When Danish Muslims explain what made them decide to travel to the Middle East and take up arms in the wake of the Arab Spring, they say that they were called upon. Displayed on videos on social media, women and sometimes children begged them to come to their rescue. In light of some...

  16. An Island Called Cuba

    Directory of Open Access Journals (Sweden)

    Jean Stubbs

    2011-06-01

    Full Text Available Review of: An Island Called Home: Returning to Jewish Cuba. Ruth Behar, photographs by Humberto Mayol. New Brunswick NJ: Rutgers University Press, 2007. xiii + 297 pp. (Cloth US$ 29.95 Fidel Castro: My Life: A Spoken Autobiography. Fidel Castro & Ignacio Ramonet. New York: Scribner/Simon & Schuster, 2008. vii + 724 pp. (Paper US$ 22.00, e-book US$ 14.99 Cuba: What Everyone Needs to Know. Julia E. Sweig. New York: Oxford University Press, 2009. xiv + 279 pp. (Paper US$ 16.95 [First paragraph] These three ostensibly very different books tell a compelling story of each author’s approach, as much as the subject matter itself. Fidel Castro: My Life: A Spoken Autobiography is based on a series of long interviews granted by the then-president of Cuba, Fidel Castro, to Spanish-Franco journalist Ignacio Ramonet. Cuba: What Everyone Needs to Know, by U.S. political analyst Julia Sweig, is one of a set country series, and, like Ramonet’s, presented in question/answer format. An Island Called Home: Returning to Jewish Cuba, with a narrative by Cuban-American anthropologist Ruth Behar and photographs by Cuban photographer Humberto Mayol, is a retrospective/introspective account of the Jewish presence in Cuba. While from Ramonet and Sweig we learn much about the revolutionary project, Behar and Mayol convey the lived experience of the small Jewish community against that backdrop.

  17. CALL FOR PARTICIPATION

    Directory of Open Access Journals (Sweden)

    Alejandro Jimenez M.

    2008-10-01

    Full Text Available TRIPLE HELIX VII 7TH BIENNIAL INTERNATIONAL CONFERENCE ON UNIVERSITY, INDUSTRY AND GOVERNMENT LINKAGES “THE ROLE OF TRIPLE HELIX IN THE GLOBAL AGENDA FOR INNOVATION, COMPETITIVENESS AND SUSTAINABILITY” UNIVERSITY OF STRATHCLYDE, GLASGOW, SCOTLAND 17-19 JUNE 2009 CALL FOR PARTICIPATION CLOSING DATE FOR ABSTRACT SUBMISSION – 14 NOVEMBER 2008 Triple Helix VII is an important occasion offering a major platform for the exchange of ideas and experiences - academics will share their insights into the dynamics of collaboration; business and industry will review their plans and indicate future directions; and for government decision makers, will explore new avenues for supporting developments, analysing innovation frameworks and their impact on national and regional economies. A Call for Papers is attached, and further details can be obtained from the Triple Helix VII website: http://www.triple-helix-7.org. We hope the Conference will be of interest to you and look forward to seeing you in Glasgow next year taking part in the Triple Helix VII proceedings. Sheila Forbes Conference Administrator Triple Helix VII

  18. MEDICAL SERVICE - URGENT CALLS

    CERN Document Server

    Service Médical

    2000-01-01

    IN URGENT NEED OF A DOCTOR GENEVA: EMERGENCY SERVICES GENEVA AND VAUD 144 FIRE BRIGADE 118 POLICE 117 CERN FIREMEN 767-44-44 ANTI-POISONS CENTRE Open 24h/24h 01-251-51-51 Patient not fit to be moved, call family doctor, or: GP AT HOME: Open 24h/24h 748-49-50 AMG- Association Of Geneva Doctors: Emergency Doctors at home 07h-23h 322 20 20 Patient fit to be moved: HOPITAL CANTONAL CENTRAL 24 Micheli-du-Crest 372-33-11 ou 382-33-11 EMERGENCIES 382-33-11 ou 372-33-11 CHILDREN'S HOSPITAL 6 rue Willy-Donzé 372-33-11 MATERNITY 32 bvd.de la Cluse 382-68-16 ou 382-33-11 OPHTHALMOLOGY 22 Alcide Jentzer 382-33-11 ou 372-33-11 MEDICAL CENTRE CORNAVIN 1-3 rue du Jura 345 45 50 HOPITAL DE LA TOUR Meyrin 719-61-11 EMERGENCIES 719-61-11 CHILDREN'S EMERGENCIES 719-61-00 LA TOUR MEDICAL CENTRE 719-74-00 European Emergency Call 112   FRANCE: EMERGENCY SERVICES 15 FIRE BRIGADE 18 POLICE 17 CERN FIREMEN AT HOME 00-41-22-767-44-44 ...

  19. Call for volunteers

    CERN Multimedia

    2008-01-01

    CERN is calling for volunteers from all members of the Laboratory for organizing the two exceptional Open days.CERN is calling for volunteers from all members of the Laboratory’s personnel to help with the organisation of these two exceptional Open Days, for the visits of CERN personnel and their families on the Saturday and above all for the major public Open Day on the Sunday. As for the 50th anniversary in 2004, the success of the Open Days will depend on a large number of volunteers. All those working for CERN as well as retired members of the personnel can contribute to making this event a success. Many guides will be needed at the LHC points, for the activities at the surface and to man the reception and information points. The aim of these major Open Days is to give the local populations the opportunity to discover the fruits of almost 20 years of work carried out at CERN. We are hoping for some 2000 volunteers for the two Open Days, on the Saturday from 9 a.m. to ...

  20. Influence of thermal boundary conditions on convection and dynamos in early and present earth-like cores

    Science.gov (United States)

    Hori, K.; Wicht, J.; Dietrich, W.; Christensen, U. R.

    2012-12-01

    The early dynamos of Earth and Mars probably operated without an inner core being present. They were thus exclusively driven by secular cooling and radiogenic heating, whereas the present geodynamo is thought to be predominantly driven by buoyancy fluxes which arise from the release of latent heat and the compositional enrichment associated with inner core solidification. Dynamo simulations model the secular cooling by volumetric internal buoyancy sources and the inner core-related driving by bottom sources. The impact of the inner core growth on the ancient geodynamo has been discussed extensively but is still controversial. As for Mars, the Mars Global Surveyor detected a strong northern-southern dichotomy in the crustal magnetization. A scenario proposed so far is due to such an ancient dynamo, where thermal heterogeneities at the core mantle boundary (CMB) were imposed by the lower mantle structure. A key issue here is how easily influence of the boundary anomalies emerges. Here we show that the dynamos without inner core solidification are much more sensitive to the CMB heat flows imposed by the lower mantle structure. We compare three-dimensional convection-driven MHD dynamo simulations either driven by homogeneously distributed internal heat sources or by buoyancy sources at the inner core boundary (ICB). Several different boundary heat-flux patterns are used. The effects are found even when boundaries are homogeneous. The impact of the outer boundary condition, fixed temperature or fixed heat flux, is large when convection is predominantly driven by volumetric internal heating. In the dynamos driven by ICB buoyancy sources, the lower boundary condition becomes more important. In both cases, a fixed flux condition promotes larger convective scales than a fixed temperature condition. A dipolar magnetic field can further increase the flow scale. This different sensitivity may also extend to cases when CMB heat flows are laterally inhomogeneous. In the dynamos

  1. Call of Duty

    Science.gov (United States)

    Shea, Rich

    2007-01-01

    Army National Guard Sergeant James Reynolds is one of about 10,000 former and current military service members who, since 1994, have arrived in the classroom via the federal Troops to Teachers program. Reynolds, who was serving as rear gunner on a Humvee patrolling a Bosnian town, is currently teaching 6th grade students at Hybla Valley…

  2. The importance of wind-flux feedbacks during the November CINDY-DYNAMO MJO event

    Science.gov (United States)

    Riley Dellaripa, Emily; Maloney, Eric; van den Heever, Susan

    2015-04-01

    High-resolution, large-domain cloud resolving model (CRM) simulations probing the importance of wind-flux feedbacks to Madden-Julian Oscillation (MJO) convection are performed for the November 2011 CINDY-DYNAMO MJO event. The work is motivated by observational analysis from RAMA buoys in the Indian Ocean and TRMM precipitation retrievals that show a positive correlation between MJO precipitation and wind-induced surface fluxes, especially latent heat fluxes, during and beyond the CINDY-DYNAMO time period. Simulations are done using Colorado State University's Regional Atmospheric Modeling System (RAMS). The domain setup is oceanic and spans 1000 km x 1000 km with 1.5 km horizontal resolution and 65 stretched vertical levels centered on the location of Gan Island - one of the major CINDY-DYNAMO observation points. The model is initialized with ECMWF reanalysis and Aqua MODIS sea surface temperatures. Nudging from ECMWF reanalysis is applied at the domain periphery to encourage realistic evolution of MJO convection. The control experiment is run for the entire month of November so both suppressed and active, as well as, transitional phases of the MJO are modeled. In the control experiment, wind-induced surface fluxes are activated through the surface bulk aerodynamic formula and allowed to evolve organically. Sensitivity experiments are done by restarting the control run one week into the simulation and controlling the wind-induced flux feedbacks. In one sensitivity experiment, wind-induced surface flux feedbacks are completely denied, while in another experiment the winds are kept constant at the control simulations mean surface wind speed. The evolution of convection, especially on the mesoscale, is compared between the control and sensitivity simulations.

  3. EFFECTS OF LARGE-SCALE NON-AXISYMMETRIC PERTURBATIONS IN THE MEAN-FIELD SOLAR DYNAMO

    Energy Technology Data Exchange (ETDEWEB)

    Pipin, V. V. [Institute of Solar-Terrestrial Physics, Russian Academy of Sciences (Russian Federation); Kosovichev, A. G. [W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)

    2015-11-10

    We explore the response of a nonlinear non-axisymmetric mean-field solar dynamo model to shallow non-axisymmetric perturbations. After a relaxation period, the amplitude of the non-axisymmetric field depends on the initial condition, helicity conservation, and the depth of perturbation. It is found that a perturbation that is anchored at 0.9 R{sub ⊙} has a profound effect on the dynamo process, producing a transient magnetic cycle of the axisymmetric magnetic field, if it is initiated at the growing phase of the cycle. The non-symmetric, with respect to the equator, perturbation results in a hemispheric asymmetry of the magnetic activity. The evolution of the axisymmetric and non-axisymmetric fields depends on the turbulent magnetic Reynolds number R{sub m}. In the range of R{sub m} = 10{sup 4}–10{sup 6} the evolution returns to the normal course in the next cycle, in which the non-axisymmetric field is generated due to a nonlinear α-effect and magnetic buoyancy. In the stationary state, the large-scale magnetic field demonstrates a phenomenon of “active longitudes” with cyclic 180° “flip-flop” changes of the large-scale magnetic field orientation. The flip-flop effect is known from observations of solar and stellar magnetic cycles. However, this effect disappears in the model, which includes the meridional circulation pattern determined by helioseismology. The rotation rate of the non-axisymmetric field components varies during the relaxation period and carries important information about the dynamo process.

  4. Simulations of cloud-radiation interaction with imposed largescale dynamics from the DYNAMO northern sounding array

    Science.gov (United States)

    Wang, S.; Sobel, A. H.; Fridlind, A. M.

    2014-12-01

    The recently accomplished CINDY/DYNAMO project observed three MJO events in the equatorial Indian Ocean from October to December 2011. Analysis of the moist static energy budget by Sobel et al. (2014) indicates that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of the same DYNAMO MJO events. The simulations are driven by the large scale forcing dataset from the DYNAMO northern sounding array, and carried out in doubly-periodic domains using the WRF model. Simulated cloud properties and radiative fluxes are compared to the observed reflectivity from the SPolka radar and observed radiative fluxes from the CERES and VISST datasets. To accommodate the uncertainty in cloud microphysics, we have tested a number of single-moment (SM) and double-moment (DM) microphysical schemes in the WRF model. We find that in general the SM schemes tend to underestimate radiative flux anomalies in the active phase of the MJOs, while the DM schemes perform better but can instead overestimate radiative fluxes. All the microphysics schemes tested exhibit bias in the shape of the histograms of radiative fluxes and radar reflectivity. Analysis of CRM-simulated radar reflectivity indicates that this microphysics-related radiative flux uncertainty is closely related to how much stratiform clouds the CRM can simulate. SM schemes underestimate stratiform clouds by a factor of 2, while DM schemes simulate much more stratiform cloud, closer to observation, but shows a peak in the histogram at 15-20 dBz that is absent in observations. The double-moment Morrison scheme appears to give the best results in TOA fluxes associated with the MJO convective anomalies despite biases in the histograms of cloud and radiative fluxes.

  5. The Effect of an Electrically Conducting Lower Mantle on Dynamo Generated Planetary Magnetic Fields

    Science.gov (United States)

    Vilim, R.; Stanley, S.

    2012-12-01

    Recent studies have shown that the lower mantles of Earth[1], Mercury[2], and large terrestrial exoplanets[3, 4] may be good conductors of electricity. This raises questions about the effect of an electrically conducting lower mantle on magnetic field generation in these planets. A core dynamo generated magnetic field can interact with an electrically conducting mantle in two ways. First, magnetic fields lines can be be frozen into the solid mantle. The flows in the core can then stretch the magnetic field lines at the core mantle boundary increasing their strength. Second, any field observed at the surface will be attenuated due to the screening effect, which preferentially attenuates the components of the magnetic field that vary quickest in time. We use a numerical dynamo model to investigate the effect of a conducting mantle on dynamo generated planetary magnetic fields. [1] Ohta, K., Cohen, R. E., Hirose, K., Haule, K., Shimizu, K., and Ohishi, Y. (2012). Experimental and Theoretical Evidence for Pressure-Induced Metallization in FeO with Rocksalt-Type Structure. PRL, 108, 026403 [2] Smith, D. E., Zuber, M. T., Phillips, R. J., Solomon, S. C., Hauck, S. A. II, Lemoine, F. G., Mazarico, E., Neumann, G.A., Peale, S.J., Margot, J.L., Johnson C.L., Torrence, M.H., Perry, M.E., Rowlands D.D., Goossens, S., Head, J.W., Taylor, A.H. (2012). Gravity Field and Internal Structure of Mercury from MESSENGER. Science [3] Nellis, W. J. (2011). Metallic liquid hydrogen and likely Al2O3 metallic glass. The European Physical Journal Special Topics, 196, 121-130 [4] Tsuchiya, T. (2011). Prediction of a hexagonal SiO2 phase affecting stabilities of MgSiO3 and CaSiO3 at multimegabar pressures. PNAS, 108, 1252-1255

  6. Dynamo dominated accretion and energy flow: The mechanism of active galactic nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Colgate, S.A.; Li, H.

    1998-12-31

    An explanation of the magnetic fields of the universe, the central mass concentration of galaxies, the massive black hole of every galaxy, and the AGN phenomena has been an elusive goal. The authors suggest here the outlines of such a theoretical understanding and point out where the physical understanding is missing. They believe there is an imperative to the sequence of mass flow and hence energy flow in the collapse of a galactic mass starting from the first non-linearity appearing in structure formation following decoupling. This first non-linearity of a two to one density fluctuation, the Lyman-{alpha} clouds, ultimately leads to the emission spectra of the phenomenon of AGN, quasars, blazars, etc. The over-arching physical principle is the various mechanisms for the transport of angular momentum. They believe they have now understood the new physics of two of these mechanisms that have previously been illusive and as a consequence they impose strong constraints on the initial conditions of the mechanisms for the subsequent emission of the gravitational binding energy. The new phenomena described are: (1) the Rossby vortex mechanism of the accretion disk {alpha}-viscosity, and (2) the mechanism of the {alpha}-{Omega} dynamo in the accretion disk. The Rossby vortex mechanism leads to a prediction of the black hole mass and rate of energy release and the {alpha}-{Omega} dynamo leads to the generation of the magnetic flux of the galaxy (and the far greater magnetic flux of clusters) and separately explains the primary flux of energy emission as force-free magnetic energy density. This magnetic flux and magnetic energy density separately are the necessary consequence of the saturation of a dynamo created by the accretion disk with a gain greater than unity.

  7. Disorder in the Disk: The Influence of Accretion Disk Thickness on the Large-scale Magnetic Dynamo.

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2018-01-01

    The evolution of the magnetic field from the enigmatic large-scale dynamo is often considered a central feature of the accretion disk around a black hole. The resulting low-frequency oscillations introduced from the growth and decay of the field strength, along with the change in field orientation, are thought to be intimately tied to variability from the disk. Several factors are at play, but the dynamo can either be directly tied to observable signatures through modulation of the heating rate, or indirectly as the source of quasiperiodic oscillations, the driver of nonlinear structure from propagating fluctuations in mass accretion rate, or even the trigger of state transitions. We present a selection of results from a recent study of this process using a suite of four global, high-resolution, MHD accretion disk simulations. We systematically vary the scale height ratio and find the large-scale dynamo fails to develop above a scale height ratio of h/r ≥ 0.2. Using “butterfly” diagrams of the azimuthal magnetic field, we show the large-scale dynamo exists in the thinner accretion disk models, but fails to excite when the scale height ratio is increased, a feature which is also reflected in 2D Fourier transforms. Additionally, we calculate the dynamo α-parameter through correlations in the averaged magnetic field and turbulent electromotive force, and also generate synthetic light curves from the disk cooling. Using our emission proxy, we find the disks have markedly different characters as photometric fluctuations are larger and less ordered when the disk is thicker and the dynamo is absent.

  8. Decay rates of magnetic modes below the threshold of a turbulent dynamo.

    Science.gov (United States)

    Herault, J; Pétrélis, F; Fauve, S

    2014-04-01

    We measure the decay rates of magnetic field modes in a turbulent flow of liquid sodium below the dynamo threshold. We observe that turbulent fluctuations induce energy transfers between modes with different symmetries (dipolar and quadrupolar). Using symmetry properties, we show how to measure the decay rate of each mode without being restricted to the one with the smallest damping rate. We observe that the respective values of the decay rates of these modes depend on the shape of the propellers driving the flow. Dynamical regimes, including field reversals, are observed only when the modes are both nearly marginal. This is in line with a recently proposed model.

  9. Using Jupiter’s gravitational field to probe the Jovian convective dynamo

    Science.gov (United States)

    Kong, Dali; Zhang, Keke; Schubert, Gerald

    2016-01-01

    Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection. PMID:27005472

  10. Cloud Resolving Simulations of Convection during AMIE/DYNAMO: Microphysics and Heat / Moisture Budget

    Science.gov (United States)

    Janiga, M. A.; Li, X.; Hagos, S.; Feng, Z.; Wang, S.; Rowe, A.; Tao, W. K.; Zhang, C.

    2014-12-01

    This study compares simulations of convection during the AMIE/DYNAMO field campaign performed using three doubly-periodic cloud-resolving models (CRMs) and one regional CRM. A variety of microphysics parameterizations are used in these simulations. The target of these simulations is the second MJO event of the campaign, including suppressed periods before and after the passage of the convective envelope. The properties of convection in the CRM simulations are compared to observations of reflectivity and hydrometeor type from the dual-polarimetric SPOL radar. Contrasts in the properties of convection between the various simulations are related to their effect on the heat and moisture budgets.

  11. Nonlinear quenching of current fluctuations in a self-exciting homopolar dynamo

    Directory of Open Access Journals (Sweden)

    R. Hide

    1997-01-01

    Full Text Available In the interpretation of geomagnetic polarity reversals with their highly variable frequency over geological time it is necessary, as with other irregularly fluctuating geophysical phenomena, to consider the relative importance of forced contributions associated with changing boundary conditions and of free contributions characteristic of the behaviour of nonlinear systems operating under fixed boundary conditions.  New evidence -albeit indirect- in favour of the likely predominance of forced contributions is provided by the discovery reported here of the possibility of complete quenching by nonlineax effects of current fluctuations in a self-exciting homopolar dynamo with its single Faraday disk driven into rotation with angular speed y(τ (where τ denotes time by a steady applied couple.  The armature of an electric motor connected in series with the coil of the dynamo is driven into rotation' with angular speed z(τ by a torque xf (x due to Lorentz forces associated with the electric current x(τ in the system (just as certain parts of the spectrum of eddies within the liquid outer core are generated largely by Lorentz forces associated with currents generated by the self-exciting magnetohydrodynamic (MHD geodynamo.   The discovery is based on bifurcation analysis supported by computational studies of the following (mathematically novel autonomous set of nonlinear ordinary differential equations: dx/dt = x(y - 1 - βzf(x, dy/dt = α(1 - x² - κy, dz/dt = xf (x -λz,          where f (x = 1 - ε + εσx, in cases when the dimensionless parameters (α, β, κ, λ, σ are all positive and 0 ≤ ε ≤ 1. Within those regions of (α, β, κ, λ, σ parameter space where the applied couple, as measured by α, is strong enough for persistent dynamo action (i.e. x ≠ 0 to occur at all, there are in general extensive regions where x(τ exhibits large amplitude regular or irregular (chaotic fluctuations.  But these fluctuating r

  12. Using dynamo theory to predict the sunspot number during solar cycle 21

    Science.gov (United States)

    Schatten, K. H.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M.

    1978-01-01

    On physical grounds it is suggested that the polar field strength of the sun near a solar minimum is closely related to the solar activity of the following cycle. Four methods of estimating the polar magnetic field strength of the sun near solar minimum are employed to provide an estimate of the yearly mean sunspot number of cycle 21 at solar maximum of 140 + or - 20. This estimate may be considered a first-order attempt to predict the cycle activity using one parameter of physical importance based upon dynamo theory.

  13. Paleomagnetic evidence for dynamo activity driven by inward crystallisation of a metallic asteroid

    Science.gov (United States)

    Bryson, James F. J.; Weiss, Benjamin P.; Harrison, Richard J.; Herrero-Albillos, Julia; Kronast, Florian

    2017-08-01

    The direction in which a planetary core solidifies has fundamental implications for the feasibility and nature of dynamo generation. Although Earth's core is outwardly solidifying, the cores of certain smaller planetary bodies have been proposed to inwardly solidify due to their lower central pressures. However, there have been no unambiguous observations of inwardly solidified cores or the relationship between this solidification regime and planetary magnetic activity. To address this gap, we present the results of complimentary paleomagnetic techniques applied to the matrix metal and silicate inclusions within the IVA iron meteorites. This family of meteorites has been suggested to originate from a planetary core that had its overlaying silicate mantle removed by collisions during the early solar system. This process is thought to have produced a molten ball of metal that cooled rapidly and has been proposed to have inwardly solidified. Recent thermal evolution models of such a body predict that it should have generated an intense, multipolar and time-varying dynamo field. This field could have been recorded as a remanent magnetisation in the outer, cool layers of a solid crust on the IVA parent core. We find that the different components in the IVA iron meteorites display a range of paleomagnetic fidelities, depending crucially on the cooling rate of the meteorite. In particular, silicate inclusions in the quickly cooled São João Nepomuceno meteorite are poor paleomagnetic recorders. On the other hand, the matrix metal and some silicate subsamples from the relatively slowly cooled Steinbach meteorite are far better paleomagnetic recorders and provide evidence of an intense (≳100 μT) and directionally varying (exhibiting significant changes on a timescale ≲200 kyr) magnetic field. This is the first demonstration that some iron meteorites record ancient planetary magnetic fields. Furthermore, the observed field intensity, temporal variability and dynamo

  14. Design and construction of the small wind generator called “AR-SF-500” for the ore milling to a laborator y scale

    OpenAIRE

    Romero Baylón, Alfonso; UNMSM; Flores Chávez, Silvana; UNMSM; Pacheco, Werner; UNMSM

    2014-01-01

    The small wind generator called “AR-SFWP- 500” has a dynamo that generated a potency of 500 watts, which characterize for having in its internal structure, the called “permanent magnet” for working with small wind generators, such as employing in rural zones, where there is a lack of electric energy. In this sense, the purpose of the paper, treats explaining the process of design and construction of the Small Wind Generator AR-SFWP- 500, whose principle of functioning is based in transform th...

  15. 47 CFR 74.791 - Digital call signs.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Digital call signs. 74.791 Section 74.791..., AUXILIARY, SPECIAL BROADCAST AND OTHER PROGRAM DISTRIBUTIONAL SERVICES Low Power TV, TV Translator, and TV Booster Stations § 74.791 Digital call signs. (a) Digital low power stations. Call signs for digital low...

  16. Behavior based adaptive call predictor

    OpenAIRE

    Phithakkitnukoon, Santi; Dantu, Ram; Claxton, Rob; Eagle, Nathan

    2011-01-01

    Predicting future calls can be the next advanced feature of the next-generation telecommunication networks as the service providers are looking to offer new services to their customers. Call prediction can be useful to many applications such as planning daily schedules, avoiding unwanted communications (e.g. voice spam), and resource planning in call centers. Predicting calls is a very challenging task. We believe that this is an emerging area of research in ambient intelligence where the ele...

  17. Mericitabine and Either Boceprevir or Telaprevir in Combination with Peginterferon Alfa-2a plus Ribavirin for Patients with Chronic Hepatitis C Genotype 1 Infection and Prior Null Response: The Randomized DYNAMO 1 and DYNAMO 2 Studies.

    Science.gov (United States)

    Wedemeyer, Heiner; Forns, Xavier; Hézode, Christophe; Lee, Samuel S; Scalori, Astrid; Voulgari, Athina; Le Pogam, Sophie; Nájera, Isabel; Thommes, James A

    2016-01-01

    Most patients with chronic hepatitis C virus (HCV) genotype 1 infection who have had a previous null response (DYNAMO 1, and with telaprevir in DYNAMO 2). The primary endpoint in both trials was SVR, defined as HCV RNA DYNAMO 1 and of 71-96% in DYNAMO 2. SVR12 rates were similar in patients infected with HCV genotype 1a and 1b in both trials. The placebo control arms in both studies were stopped because of high rates of virological failure. Numerically lower relapse rates were associated with longer treatment with mericitabine (24 versus 12 weeks), telaprevir-containing regimens, and regimens that included 48 weeks of PegIFN alfa-2a/RBV therapy. No mericitabine resistance mutations were identified in any patient in either trial. The addition of mericitabine did not add to the safety burden associated with either telaprevir or boceprevir-based regimens. These studies demonstrate increased SVR rates and reduced relapse rates in difficult-to-treat patients when a nucleoside polymerase inhibitor with intermediate antiviral potency is added to regimens containing a first-generation PI. ClinicalTrials.gov NCT01482403 and ClinicalTrials.gov NCT01482390.

  18. Strong-field dynamo action in rapidly rotating convection with no inertia.

    Science.gov (United States)

    Hughes, David W; Cattaneo, Fausto

    2016-06-01

    The earth's magnetic field is generated by dynamo action driven by convection in the outer core. For numerical reasons, inertial and viscous forces play an important role in geodynamo models; however, the primary dynamical balance in the earth's core is believed to be between buoyancy, Coriolis, and magnetic forces. The hope has been that by setting the Ekman number to be as small as computationally feasible, an asymptotic regime would be reached in which the correct force balance is achieved. However, recent analyses of geodynamo models suggest that the desired balance has still not yet been attained. Here we adopt a complementary approach consisting of a model of rapidly rotating convection in which inertial forces are neglected from the outset. Within this framework we are able to construct a branch of solutions in which the dynamo generates a strong magnetic field that satisfies the expected force balance. The resulting strongly magnetized convection is dramatically different from the corresponding solutions in which the field is weak.

  19. Hidden hyperchaos and electronic circuit application in a 5D self-exciting homopolar disc dynamo.

    Science.gov (United States)

    Wei, Zhouchao; Moroz, Irene; Sprott, J C; Akgul, Akif; Zhang, Wei

    2017-03-01

    We report on the finding of hidden hyperchaos in a 5D extension to a known 3D self-exciting homopolar disc dynamo. The hidden hyperchaos is identified through three positive Lyapunov exponents under the condition that the proposed model has just two stable equilibrium states in certain regions of parameter space. The new 5D hyperchaotic self-exciting homopolar disc dynamo has multiple attractors including point attractors, limit cycles, quasi-periodic dynamics, hidden chaos or hyperchaos, as well as coexisting attractors. We use numerical integrations to create the phase plane trajectories, produce bifurcation diagram, and compute Lyapunov exponents to verify the hidden attractors. Because no unstable equilibria exist in two parameter regions, the system has a multistability and six kinds of complex dynamic behaviors. To the best of our knowledge, this feature has not been previously reported in any other high-dimensional system. Moreover, the 5D hyperchaotic system has been simulated using a specially designed electronic circuit and viewed on an oscilloscope, thereby confirming the results of the numerical integrations. Both Matlab and the oscilloscope outputs produce similar phase portraits. Such implementations in real time represent a new type of hidden attractor with important consequences for engineering applications.

  20. Enhancement of Small-scale Turbulent Dynamo by Large-scale Shear

    Science.gov (United States)

    Singh, Nishant K.; Rogachevskii, Igor; Brandenburg, Axel

    2017-11-01

    Small-scale dynamos (SSDs) are ubiquitous in a broad range of turbulent flows with large-scale shear, ranging from solar and galactic magnetism to accretion disks, cosmology, and structure formation. Using high-resolution direct numerical simulations, we show that in non-helically forced turbulence with zero mean magnetic field, large-scale shear supports SSD action, I.e., the dynamo growth rate increases with shear and shear enhances or even produces turbulence, which, in turn, further increases the growth rate. When the production rates of turbulent kinetic energy due to shear and forcing are comparable, we find scalings for the growth rate γ of the SSD and the turbulent rms velocity {u}{rms} with shear rate S that are independent of the magnetic Prandtl number: γ \\propto | S| and {u}{rms}\\propto | S{| }2/3. For large fluid and magnetic Reynolds numbers, γ, normalized by its shear-free value, depends only on shear. Having compensated for shear-induced effects on turbulent velocity, we find that the normalized growth rate of the SSD exhibits the scaling, \\widetilde{γ }\\propto | S{| }2/3, arising solely from the induction equation for a given velocity field.

  1. Transport coefficients for the shear dynamo problem at small Reynolds numbers.

    Science.gov (United States)

    Singh, Nishant K; Sridhar, S

    2011-05-01

    We build on the formulation developed in S. Sridhar and N. K. Singh [J. Fluid Mech. 664, 265 (2010)] and present a theory of the shear dynamo problem for small magnetic and fluid Reynolds numbers, but for arbitrary values of the shear parameter. Specializing to the case of a mean magnetic field that is slowly varying in time, explicit expressions for the transport coefficients α(il) and η(il) are derived. We prove that when the velocity field is nonhelical, the transport coefficient α(il) vanishes. We then consider forced, stochastic dynamics for the incompressible velocity field at low Reynolds number. An exact, explicit solution for the velocity field is derived, and the velocity spectrum tensor is calculated in terms of the Galilean-invariant forcing statistics. We consider forcing statistics that are nonhelical, isotropic, and delta correlated in time, and specialize to the case when the mean field is a function only of the spatial coordinate X(3) and time τ; this reduction is necessary for comparison with the numerical experiments of A. Brandenburg, K. H. Rädler, M. Rheinhardt, and P. J. Käpylä [Astrophys. J. 676, 740 (2008)]. Explicit expressions are derived for all four components of the magnetic diffusivity tensor η(il)(τ). These are used to prove that the shear-current effect cannot be responsible for dynamo action at small Re and Rm, but for all values of the shear parameter. © 2011 American Physical Society

  2. No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry.

    Science.gov (United States)

    Roettenbacher, R M; Monnier, J D; Korhonen, H; Aarnio, A N; Baron, F; Che, X; Harmon, R O; Kővári, Zs; Kraus, S; Schaefer, G H; Torres, G; Zhao, M; ten Brummelaar, T A; Sturmann, J; Sturmann, L

    2016-05-12

    Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection. Moreover, strong magnetic fields can alter the average atmospheric structure, degrading our ability to measure stellar masses and ages. Stars that are more active than the Sun have more and stronger dark spots than does the Sun, including on the rotational pole. Doppler imaging, which has so far produced the most detailed images of surface structures on other stars, cannot always distinguish the hemisphere in which the starspots are located, especially in the equatorial region and if the data quality is not optimal. This leads to problems in investigating the north-south distribution of starspot active latitudes (those latitudes with more starspot activity); this distribution is a crucial constraint of dynamo theory. Polar spots, whose existence is inferred from Doppler tomography, could plausibly be observational artefacts. Here we report imaging of the old, magnetically active star ζ Andromedae using long-baseline infrared interferometry. In our data, a dark polar spot is seen in each of two observation epochs, whereas lower-latitude spot structures in both hemispheres do not persist between observations, revealing global starspot asymmetries. The north-south symmetry of active latitudes observed on the Sun is absent on ζ And, which hosts global spot patterns that cannot be produced by solar-type dynamos.

  3. A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars.

    Science.gov (United States)

    Stello, Dennis; Cantiello, Matteo; Fuller, Jim; Huber, Daniel; García, Rafael A; Bedding, Timothy R; Bildsten, Lars; Aguirre, Victor Silva

    2016-01-21

    Magnetic fields play a part in almost all stages of stellar evolution. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes. Intermediate-mass stars do not have deep convective envelopes, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process. These stars do have convective cores that might produce internal magnetic fields, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface. Here we report the strength of dipolar oscillation modes for a sample of 3,600 red giant stars. About 20 per cent of our sample show mode suppression, by strong magnetic fields in the cores, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6-2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.

  4. Turbulent Dynamo Amplification of Magnetic Fields in Laser-Produced Plasmas: Simulations and Experiments

    Science.gov (United States)

    Tzeferacos, P.; Rigby, A.; Bott, A.; Bell, A.; Bingham, R.; Casner, A.; Cattaneo, F.; Churazov, E.; Forest, C.; Katz, J.; Koenig, M.; Li, C.-K.; Meinecke, J.; Petrasso, R.; Park, H.-S.; Remington, B.; Ross, J.; Ryutov, D.; Ryu, D.; Reville, B.; Miniati, F.; Schekochihin, A.; Froula, D.; Lamb, D.; Gregori, G.

    2017-10-01

    The universe is permeated by magnetic fields, with strengths ranging from a femtogauss in the voids between the filaments of galaxy clusters to several teragauss in black holes and neutron stars. The standard model for cosmological magnetic fields is the nonlinear amplification of seed fields via turbulent dynamo. We have conceived experiments to demonstrate and study the turbulent dynamo mechanism in the laboratory. Here, we describe the design of these experiments through large-scale 3D FLASH simulations on the Mira supercomputer at ANL, and the laser-driven experiments we conducted with the OMEGA laser at LLE. Our results indicate that turbulence is capable of rapidly amplifying seed fields to near equipartition with the turbulent fluid motions. This work was supported in part from the ERC (FP7/2007-2013, No. 256973 and 247039), and the U.S. DOE, Contract No. B591485 to LLNL, FWP 57789 to ANL, Grant No. DE-NA0002724 and DE-SC0016566 to the University of Chicago, and DE-AC02-06CH11357 to ANL.

  5. ESTIMATING THE DEEP SOLAR MERIDIONAL CIRCULATION USING MAGNETIC OBSERVATIONS AND A DYNAMO MODEL: A VARIATIONAL APPROACH

    Energy Technology Data Exchange (ETDEWEB)

    Hung, Ching Pui; Jouve, Laurène; Brun, Allan Sacha [Laboratoire AIM Paris-Saclay, CEA/IRFU Université Paris-Diderot CNRS/INSU, F-91191 Gif-Sur-Yvette (France); Fournier, Alexandre [Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot UMR 7154 CNRS, F-75005 Paris (France); Talagrand, Olivier [Laboratoire de météorologie dynamique, UMR 8539, Ecole Normale Supérieure, Paris Cedex 05 (France)

    2015-12-01

    We show how magnetic observations of the Sun can be used in conjunction with an axisymmetric flux-transport solar dynamo model in order to estimate the large-scale meridional circulation throughout the convection zone. Our innovative approach rests on variational data assimilation, whereby the distance between predictions and observations (measured by an objective function) is iteratively minimized by means of an optimization algorithm seeking the meridional flow that best accounts for the data. The minimization is performed using a quasi-Newton technique, which requires knowledge of the sensitivity of the objective function to the meridional flow. That sensitivity is efficiently computed via the integration of the adjoint flux-transport dynamo model. Closed-loop (also known as twin) experiments using synthetic data demonstrate the validity and accuracy of this technique for a variety of meridional flow configurations, ranging from unicellular and equatorially symmetric to multicellular and equatorially asymmetric. In this well-controlled synthetic context, we perform a systematic study of the behavior of our variational approach under different observational configurations by varying their spatial density, temporal density, and noise level, as well as the width of the assimilation window. We find that the method is remarkably robust, leading in most cases to a recovery of the true meridional flow to within better than 1%. These encouraging results are a first step toward using this technique to (i) better constrain the physical processes occurring inside the Sun and (ii) better predict solar activity on decadal timescales.

  6. Study of electrode slice forming of bicycle dynamo hub power connector

    Science.gov (United States)

    Chen, Dyi-Cheng; Jao, Chih-Hsuan

    2013-12-01

    Taiwan's bicycle industry has been an international reputation as bicycle kingdom, but the problem in the world makes global warming green energy rise, the development of electrode slice of hub dynamo and power output connector to bring new hope to bike industry. In this study connector power output to gather public opinion related to patent, basis of collected documents as basis for design, structural components in least drawn to power output with simple connector. Power output of this study objectives connector hope at least cost, structure strongest, highest efficiency in output performance characteristics such as use of computer-aided drawing software Solid works to establish power output connector parts of 3D model, the overall portfolio should be considered part types including assembly ideas, weather resistance, water resistance, corrosion resistance to vibration and power flow stability. Moreover the 3D model import computer-aided finite element analysis software simulation of expected the power output of the connector parts manufacturing process. A series of simulation analyses, in which the variables relied on first stage and second stage forming, were run to examine the effective stress, effective strain, press speed, and die radial load distribution when forming electrode slice of bicycle dynamo hub.

  7. DynAMo: A Modular Platform for Monitoring Process, Outcome, and Algorithm-Based Treatment Planning in Psychotherapy.

    Science.gov (United States)

    Kaiser, Tim; Laireiter, Anton Rupert

    2017-07-20

    In recent years, the assessment of mental disorders has become more and more personalized. Modern advancements such as Internet-enabled mobile phones and increased computing capacity make it possible to tap sources of information that have long been unavailable to mental health practitioners. Software packages that combine algorithm-based treatment planning, process monitoring, and outcome monitoring are scarce. The objective of this study was to assess whether the DynAMo Web application can fill this gap by providing a software solution that can be used by both researchers to conduct state-of-the-art psychotherapy process research and clinicians to plan treatments and monitor psychotherapeutic processes. In this paper, we report on the current state of a Web application that can be used for assessing the temporal structure of mental disorders using information on their temporal and synchronous associations. A treatment planning algorithm automatically interprets the data and delivers priority scores of symptoms to practitioners. The application is also capable of monitoring psychotherapeutic processes during therapy and of monitoring treatment outcomes. This application was developed using the R programming language (R Core Team, Vienna) and the Shiny Web application framework (RStudio, Inc, Boston). It is made entirely from open-source software packages and thus is easily extensible. The capabilities of the proposed application are demonstrated. Case illustrations are provided to exemplify its usefulness in clinical practice. With the broad availability of Internet-enabled mobile phones and similar devices, collecting data on psychopathology and psychotherapeutic processes has become easier than ever. The proposed application is a valuable tool for capturing, processing, and visualizing these data. The combination of dynamic assessment and process- and outcome monitoring has the potential to improve the efficacy and effectiveness of psychotherapy.

  8. DynAMo: A Modular Platform for Monitoring Process, Outcome, and Algorithm-Based Treatment Planning in Psychotherapy

    Science.gov (United States)

    Laireiter, Anton Rupert

    2017-01-01

    Background In recent years, the assessment of mental disorders has become more and more personalized. Modern advancements such as Internet-enabled mobile phones and increased computing capacity make it possible to tap sources of information that have long been unavailable to mental health practitioners. Objective Software packages that combine algorithm-based treatment planning, process monitoring, and outcome monitoring are scarce. The objective of this study was to assess whether the DynAMo Web application can fill this gap by providing a software solution that can be used by both researchers to conduct state-of-the-art psychotherapy process research and clinicians to plan treatments and monitor psychotherapeutic processes. Methods In this paper, we report on the current state of a Web application that can be used for assessing the temporal structure of mental disorders using information on their temporal and synchronous associations. A treatment planning algorithm automatically interprets the data and delivers priority scores of symptoms to practitioners. The application is also capable of monitoring psychotherapeutic processes during therapy and of monitoring treatment outcomes. This application was developed using the R programming language (R Core Team, Vienna) and the Shiny Web application framework (RStudio, Inc, Boston). It is made entirely from open-source software packages and thus is easily extensible. Results The capabilities of the proposed application are demonstrated. Case illustrations are provided to exemplify its usefulness in clinical practice. Conclusions With the broad availability of Internet-enabled mobile phones and similar devices, collecting data on psychopathology and psychotherapeutic processes has become easier than ever. The proposed application is a valuable tool for capturing, processing, and visualizing these data. The combination of dynamic assessment and process- and outcome monitoring has the potential to improve the efficacy

  9. Call Centre- Computer Telephone Integration

    Directory of Open Access Journals (Sweden)

    Dražen Kovačević

    2012-10-01

    Full Text Available Call centre largely came into being as a result of consumerneeds converging with enabling technology- and by the companiesrecognising the revenue opportunities generated by meetingthose needs thereby increasing customer satisfaction. Regardlessof the specific application or activity of a Call centre, customersatisfaction with the interaction is critical to the revenuegenerated or protected by the Call centre. Physical(v, Call centreset up is a place that includes computer, telephone and supervisorstation. Call centre can be available 24 hours a day - whenthe customer wants to make a purchase, needs information, orsimply wishes to register a complaint.

  10. Mean-field model of the von Kármán sodium dynamo experiment using soft iron impellers.

    Science.gov (United States)

    Nore, C; Léorat, J; Guermond, J-L; Giesecke, A

    2015-01-01

    It has been observed that dynamo action occurs in the von-Kármán-Sodium (VKS) experiment only when the rotating disks and the blades are made of soft iron. The purpose of this paper is to numerically investigate the role of soft iron in the VKS dynamo scenario. This is done by using a mean-field model based on an axisymmetric mean flow, a localized permeability distribution, and a localized α effect modeling the action of the small velocity scales between the blades. The action of the rotating blades is modeled by an axisymmetric effective permeability field. Key properties of the flow giving to the numerical magnetic field a geometric structure similar to that observed experimentally are identified. Depending on the permeability of the disks and the effective permeability of the blades, the dynamo that is obtained is either oscillatory or stationary. Our numerical results confirm the leading role played by the ferromagnetic impellers. A scenario for the VKS dynamo is proposed.

  11. A BABCOCK–LEIGHTON SOLAR DYNAMO MODEL WITH MULTI-CELLULAR MERIDIONAL CIRCULATION IN ADVECTION- AND DIFFUSION-DOMINATED REGIMES

    Energy Technology Data Exchange (ETDEWEB)

    Belucz, Bernadett; Forgács-Dajka, Emese [Eötvös University, Department of Astronomy, 1518 Budapest, Pf. 32 (Hungary); Dikpati, Mausumi, E-mail: bbelucz@astro.elte.hu, E-mail: dikpati@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green, Boulder, CO 80307-3000 (United States)

    2015-06-20

    Babcock–Leighton type-solar dynamo models with single-celled meridional circulation are successful in reproducing many solar cycle features. Recent observations and theoretical models of meridional circulation do not indicate a single-celled flow pattern. We examine the role of complex multi-cellular circulation patterns in a Babcock–Leighton solar dynamo in advection- and diffusion-dominated regimes. We show from simulations that the presence of a weak, second, high-latitude reverse cell speeds up the cycle and slightly enhances the poleward branch in the butterfly diagram, whereas the presence of a second cell in depth reverses the tilt of the butterfly wing to an antisolar type. A butterfly diagram constructed from the middle of convection zone yields a solar-like pattern, but this may be difficult to realize in the Sun because of magnetic buoyancy effects. Each of the above cases behaves similarly in higher and lower magnetic diffusivity regimes. However, our dynamo with a meridional circulation containing four cells in latitude behaves distinctly differently in the two regimes, producing solar-like butterfly diagrams with fast cycles in the higher diffusivity regime, and complex branches in butterfly diagrams in the lower diffusivity regime. We also find that dynamo solutions for a four-celled pattern, two in radius and two in latitude, prefer to quickly relax to quadrupolar parity if the bottom flow speed is strong enough, of similar order of magnitude as the surface flow speed.

  12. Self-consistent simulations of a von Kármán type dynamo in a spherical domain with metallic walls.

    Science.gov (United States)

    Guervilly, Céline; Brummell, Nicholas H

    2012-10-01

    We have performed numerical simulations of boundary-driven dynamos using a three-dimensional nonlinear magnetohydrodynamical model in a spherical shell geometry. A conducting fluid of magnetic Prandtl number Pm=0.01 is driven into motion by the counter-rotation of the two hemispheric walls. The resulting flow is of von Kármán type, consisting of a layer of zonal velocity close to the outer wall and a secondary meridional circulation. Above a certain forcing threshold, the mean flow is unstable to non-axisymmetric motions within an equatorial belt. For fixed forcing above this threshold, we have studied the dynamo properties of this flow. The presence of a conducting outer wall is essential to the existence of a dynamo at these parameters. We have therefore studied the effect of changing the material parameters of the wall (magnetic permeability, electrical conductivity, and thickness) on the dynamo. In common with previous studies, we find that dynamos are obtained only when either the conductivity or the permeability is sufficiently large. However, we find that the effect of these two parameters on the dynamo process are different and can even compete to the detriment of the dynamo. Our self-consistent approach allow us to analyze in detail the dynamo feedback loop. The dynamos we obtain are typically dominated by an axisymmetric toroidal magnetic field and an axial dipole component. We show that the ability of the outer shear layer to produce a strong toroidal field depends critically on the presence of a conducting outer wall, which shields the fluid from the vacuum outside. The generation of the axisymmetric poloidal field, on the other hand, occurs in the equatorial belt and does not depend on the wall properties.

  13. Dynamo: a flexible, user-friendly development tool for subtomogram averaging of cryo-EM data in high-performance computing environments.

    Science.gov (United States)

    Castaño-Díez, Daniel; Kudryashev, Mikhail; Arheit, Marcel; Stahlberg, Henning

    2012-05-01

    Dynamo is a new software package for subtomogram averaging of cryo Electron Tomography (cryo-ET) data with three main goals: first, Dynamo allows user-transparent adaptation to a variety of high-performance computing platforms such as GPUs or CPU clusters. Second, Dynamo implements user-friendliness through GUI interfaces and scripting resources. Third, Dynamo offers user-flexibility through a plugin API. Besides the alignment and averaging procedures, Dynamo includes native tools for visualization and analysis of results and data, as well as support for third party visualization software, such as Chimera UCSF or EMAN2. As a demonstration of these functionalities, we studied bacterial flagellar motors and showed automatically detected classes with absent and present C-rings. Subtomogram averaging is a common task in current cryo-ET pipelines, which requires extensive computational resources and follows a well-established workflow. However, due to the data diversity, many existing packages offer slight variations of the same algorithm to improve results. One of the main purposes behind Dynamo is to provide explicit tools to allow the user the insertion of custom designed procedures - or plugins - to replace or complement the native algorithms in the different steps of the processing pipeline for subtomogram averaging without the burden of handling parallelization. Custom scripts that implement new approaches devised by the user are integrated into the Dynamo data management system, so that they can be controlled by the GUI or the scripting capacities. Dynamo executables do not require licenses for third party commercial software. Sources, executables and documentation are freely distributed on http://www.dynamo-em.org. Copyright © 2012 Elsevier Inc. All rights reserved.

  14. Role of soft-iron impellers on the mode selection in the von kármán-sodium dynamo experiment.

    Science.gov (United States)

    Giesecke, André; Stefani, Frank; Gerbeth, Gunter

    2010-01-29

    A crucial point for the understanding of the von Kármán-sodium (VKS) dynamo experiment is the influence of soft-iron impellers. We present numerical simulations of a VKS-like dynamo with a localized permeability distribution that resembles the shape of the flow driving impellers. It is shown that the presence of soft-iron material essentially determines the dynamo process in the VKS experiment. An axisymmetric magnetic field mode can be explained by the combined action of the soft-iron disk and a rather small alpha effect parametrizing the induction effects of unresolved small scale flow fluctuations.

  15. Dynamo-driven plasmoid formation from a current-sheet instability

    CERN Document Server

    Ebrahimi, F

    2016-01-01

    Axisymmetric current-carrying plasmoids are formed in the presence of nonaxisymmetric fluctuations during nonlinear three-dimensional resistive MHD simulations in a global toroidal geometry. We utilize the helicity injection technique to form an initial poloidal flux in the presence of a toroidal guide field. As helicity is injected, two types of current sheets are formed from 1) the oppositely directed field lines in the injector region (primary reconnecting current sheet), and 2) the poloidal flux compression near the plasma edge (edge current sheet). We first find that nonaxisymmetic fluctuations arising from the current-sheet instability isolated near the plasma edge have tearing parity but can nevertheless grow fast (on the poloidal Alfven time scale). These modes saturate by breaking up the current sheet. Second, for the first time a dynamo poloidal flux amplification is observed at the reconnetion site (in the region of the oppositely directed magnetic field). This fluctuation-induced flux amplificatio...

  16. The difficult medical emergency call

    DEFF Research Database (Denmark)

    Møller, Thea Palsgaard; Kjærulff, Thora Majlund; Viereck, Søren

    2017-01-01

    BACKGROUND: Pre-hospital emergency care requires proper categorization of emergency calls and assessment of emergency priority levels by the medical dispatchers. We investigated predictors for emergency call categorization as "unclear problem" in contrast to "symptom-specific" categories and the ...

  17. Latitude Distribution of Sunspots: Analysis Using Sunspot Data and a Dynamo Model

    Science.gov (United States)

    Mandal, Sudip; Karak, Bidya Binay; Banerjee, Dipankar

    2017-12-01

    In this paper, we explore the evolution of sunspot latitude distribution and explore its relations with the cycle strength. With the progress of the solar cycle, the distributions in two hemispheres from mid-latitudes propagate toward the equator and then (before the usual solar minimum) these two distributions touch each other. By visualizing the evolution of the distributions in two hemispheres, we separate the solar cycles by excluding this hemispheric overlap. From these isolated solar cycles in two hemispheres, we generate latitude distributions for each cycle, starting from cycle 8 to cycle 23. We find that the parameters of these distributions, namely the central latitude (C), width (δ), and height (H), evolve with the cycle number, and they show some hemispheric asymmetries. Although the asymmetries in these parameters persist for a few successive cycles, they get corrected within a few cycles, and the new asymmetries appear again. In agreement with the previous study, we find that distribution parameters are correlated with the strengths of the cycles, although these correlations are significantly different in two hemispheres. The general trend features, i.e., (i) stronger cycles that begin sunspot eruptions at relatively higher latitudes, and (ii) stronger cycles that have wider bands of sunspot emergence latitudes, are confirmed when combining the data from two hemispheres. We explore these features using a flux transport dynamo model with stochastic fluctuations. We find that these features are correctly reproduced in this model. The solar cycle evolution of the distribution center is also in good agreement with observations. Possible explanations of the observed features based on this dynamo model are presented.

  18. Impact of time-dependent nonaxisymmetric velocity perturbations on dynamo action of von Kármán-like flows.

    Science.gov (United States)

    Giesecke, André; Stefani, Frank; Burguete, Javier

    2012-12-01

    We present numerical simulations of the kinematic induction equation in order to examine the dynamo efficiency of an axisymmetric von Kármán-like flow subject to time-dependent nonaxisymmetric velocity perturbations. The numerical model is based on the setup of the French von Kármán-sodium dynamo (VKS) and on the flow measurements from a water experiment conducted at the University of Navarra in Pamplona, Spain. The principal experimental observations that are modeled in our simulations are nonaxisymmetric vortexlike structures which perform an azimuthal drift motion in the equatorial plane. Our simulations show that the interactions of these periodic flow perturbations with the fundamental drift of the magnetic eigenmode (including the special case of nondrifting fields) essentially determine the temporal behavior of the dynamo state. We find two distinct regimes of dynamo action that depend on the (prescribed) drift frequency of an (m=2) vortexlike flow perturbation. For comparatively slowly drifting vortices we observe a narrow window with enhanced growth rates and a drift of the magnetic eigenmode that is synchronized with the perturbation drift. The resonance-like enhancement of the growth rates takes place when the vortex drift frequency roughly equals the drift frequency of the magnetic eigenmode in the unperturbed system. Outside of this small window, the field generation is hampered compared to the unperturbed case, and the field amplitude of the magnetic eigenmode is modulated with approximately twice the vortex drift frequency. The abrupt transition between the resonant regime and the modulated regime is identified as a spectral exceptional point where eigenvalues (growth rates and frequencies) and eigenfunctions of two previously independent modes collapse. In the actual configuration the drift frequencies of the velocity perturbations that are observed in the water experiment are much larger than the fundamental drift frequency of the magnetic

  19. Impact of time-dependent nonaxisymmetric velocity perturbations on dynamo action of von Kármán-like flows

    Science.gov (United States)

    Giesecke, André; Stefani, Frank; Burguete, Javier

    2012-12-01

    We present numerical simulations of the kinematic induction equation in order to examine the dynamo efficiency of an axisymmetric von Kármán-like flow subject to time-dependent nonaxisymmetric velocity perturbations. The numerical model is based on the setup of the French von Kármán-sodium dynamo (VKS) and on the flow measurements from a water experiment conducted at the University of Navarra in Pamplona, Spain. The principal experimental observations that are modeled in our simulations are nonaxisymmetric vortexlike structures which perform an azimuthal drift motion in the equatorial plane. Our simulations show that the interactions of these periodic flow perturbations with the fundamental drift of the magnetic eigenmode (including the special case of nondrifting fields) essentially determine the temporal behavior of the dynamo state. We find two distinct regimes of dynamo action that depend on the (prescribed) drift frequency of an (m=2) vortexlike flow perturbation. For comparatively slowly drifting vortices we observe a narrow window with enhanced growth rates and a drift of the magnetic eigenmode that is synchronized with the perturbation drift. The resonance-like enhancement of the growth rates takes place when the vortex drift frequency roughly equals the drift frequency of the magnetic eigenmode in the unperturbed system. Outside of this small window, the field generation is hampered compared to the unperturbed case, and the field amplitude of the magnetic eigenmode is modulated with approximately twice the vortex drift frequency. The abrupt transition between the resonant regime and the modulated regime is identified as a spectral exceptional point where eigenvalues (growth rates and frequencies) and eigenfunctions of two previously independent modes collapse. In the actual configuration the drift frequencies of the velocity perturbations that are observed in the water experiment are much larger than the fundamental drift frequency of the magnetic

  20. The difficult medical emergency call

    DEFF Research Database (Denmark)

    Møller, Thea Palsgaard; Kjærulff, Thora Majlund; Viereck, Søren

    2017-01-01

    BACKGROUND: Pre-hospital emergency care requires proper categorization of emergency calls and assessment of emergency priority levels by the medical dispatchers. We investigated predictors for emergency call categorization as "unclear problem" in contrast to "symptom-specific" categories...... and the effect of categorization on mortality. METHODS: Register-based study in a 2-year period based on emergency call data from the emergency medical dispatch center in Copenhagen combined with nationwide register data. Logistic regression analysis (N = 78,040 individuals) was used for identification...

  1. Impact Of A Uniform Plasma Resistivity In MHD Modelling Of Helical Solutions For The Reversed Field Pinch Dynamo

    CERN Document Server

    Bonfiglio, D; Escande, D F

    2016-01-01

    Till now the magnetohydrodynamic (MHD) simulation of the reversed field pinch (RFP) has been performed by assuming axis-symmetric radial time independent dissipation profiles. In helical states this assumption is not correct since these dissipations should be flux functions, and should exhibit a helical symmetry as well. Therefore more correct simulations should incorporate self-consistent dissipation profiles. As a first step in this direction, the case of uniform dissipation profiles was considered by using the 3D nonlinear visco-resistive MHD code SpeCyl. It is found that a flattening of the resistivity profile results in the reduction of the dynamo action, which brings to marginally-reversed or even non-reversed equilibrium solutions. The physical origin of this result is discussed in relation to the electrostatic drift explanation of the RFP dynamo. This sets constraints on the functional choice of dissipations in future self-consistent simulations.

  2. Nanomagnetic intergrowths in Fe-Ni meteoritic metal: The potential for time-resolved records of planetesimal dynamo fields

    DEFF Research Database (Denmark)

    Bryson, James F.J.; Church, Nathan S.; Kasama, Takeshi

    2014-01-01

    Nanoscale intergrowths unique to the cloudy zones (CZs) of meteoritic metal display novel magnetic behaviour with the potential to reveal new insight into the early development of magnetic fields on protoplanetary bodies. The nanomagnetic state of the CZ within the Tazewell IIICD iron meteorite h...... and direction variations over time (10–100 Ma), which would enable events such as magnetic reversals and the decay of an asteroid dynamo to be observed....

  3. Simulations of Magnetic Flux Emergence in Cool, Low-Mass Stars: Toward Linking Dynamo Action with Starspots

    Science.gov (United States)

    Weber, Maria Ann; Browning, Matthew; Nelson, Nicholas

    2018-01-01

    Starspots are windows into a star’s internal dynamo mechanism. However, the manner by which the dynamo-generated magnetic field traverses the stellar interior to emerge at the surface is not especially well understood. Establishing the details of magnetic flux emergence plays a key role in deciphering stellar dynamos and observed starspot properties. In the solar context, insight into this process has been obtained by assuming the magnetism giving rise to sunspots consists partly of idealized thin flux tubes (TFTs). Here, we present three sets of TFT simulations in rotating spherical shells of convection: one representative of the Sun, the second of a solar-like rapid rotator, and the third of a fully convective M dwarf. Our solar simulations reproduce sunspot observables such as low-latitude emergence, tilting action toward the equator following the Joy’s Law trend, and a phenomenon akin to active longitudes. Further, we compare the evolution of rising flux tubes in our (computationally inexpensive) TFT simulations to buoyant magnetic structures that arise naturally in a unique global simulation of a rapidly rotating Sun. We comment on the role of rapid rotation, the Coriolis force, and external torques imparted by the surrounding convection in establishing the trajectories of the flux tubes across the convection zone. In our fully convective M dwarf simulations, the expected starspot latitudes deviate from the solar trend, favoring significantly poleward latitudes unless the differential rotation is sufficiently prograde or the magnetic field is strongly super-equipartition. Together our work provides a link between dynamo-generated magnetic fields, turbulent convection, and observations of starspots along the lower main sequence.

  4. Magnetic field amplification by small-scale dynamo action: dependence on turbulence models and Reynolds and Prandtl numbers.

    Science.gov (United States)

    Schober, Jennifer; Schleicher, Dominik; Federrath, Christoph; Klessen, Ralf; Banerjee, Robi

    2012-02-01

    The small-scale dynamo is a process by which turbulent kinetic energy is converted into magnetic energy, and thus it is expected to depend crucially on the nature of the turbulence. In this paper, we present a model for the small-scale dynamo that takes into account the slope of the turbulent velocity spectrum v(ℓ)proportional ℓ([symbol see text])V}, where ℓ and v(ℓ) are the size of a turbulent fluctuation and the typical velocity on that scale. The time evolution of the fluctuation component of the magnetic field, i.e., the small-scale field, is described by the Kazantsev equation. We solve this linear differential equation for its eigenvalues with the quantum-mechanical WKB approximation. The validity of this method is estimated as a function of the magnetic Prandtl number Pm. We calculate the minimal magnetic Reynolds number for dynamo action, Rm_{crit}, using our model of the turbulent velocity correlation function. For Kolmogorov turbulence ([symbol see text] = 1/3), we find that the critical magnetic Reynolds number is Rm(crit) (K) ≈ 110 and for Burgers turbulence ([symbol see text] = 1/2) Rm(crit)(B) ≈ 2700. Furthermore, we derive that the growth rate of the small-scale magnetic field for a general type of turbulence is Γ proportional Re((1-[symbol see text])/(1+[symbol see text])) in the limit of infinite magnetic Prandtl number. For decreasing magnetic Prandtl number (down to Pm >/~ 10), the growth rate of the small-scale dynamo decreases. The details of this drop depend on the WKB approximation, which becomes invalid for a magnetic Prandtl number of about unity.

  5. Dynamo action and magnetic activity during the pre-main sequence: Influence of rotation and structural changes

    Science.gov (United States)

    Emeriau-Viard, Constance; Brun, Allan Sacha

    2017-10-01

    During the PMS, structure and rotation rate of stars evolve significantly. We wish to assess the consequences of these drastic changes on stellar dynamo, internal magnetic field topology and activity level by mean of HPC simulations with the ASH code. To answer this question, we develop 3D MHD simulations that represent specific stages of stellar evolution along the PMS. We choose five different models characterized by the radius of their radiative zone following an evolutionary track, from 1 Myr to 50 Myr, computed by a 1D stellar evolution code. We introduce a seed magnetic field in the youngest model and then we spread it through all simulations. First of all, we study the consequences that the increase of rotation rate and the change of geometry of the convective zone have on the dynamo field that exists in the convective envelop. The magnetic energy increases, the topology of the magnetic field becomes more complex and the axisymmetric magnetic field becomes less predominant as the star ages. The computation of the fully convective MHD model shows that a strong dynamo develops with a ratio of magnetic to kinetic energy reaching equipartition and even super-equipartition states in the faster rotating cases. Magnetic fields resulting from our MHD simulations possess a mixed poloidal-toroidal topology with no obvious dominant component. We also study the relaxation of the vestige dynamo magnetic field within the radiative core and found that it satisfies stability criteria. Hence it does not experience a global reconfiguration and instead slowly relaxes by retaining its mixed poloidal-toroidal topology.

  6. The role of DYNAMO in situ observations in improving NASA CERES-like daily surface and atmospheric radiative flux estimates

    Science.gov (United States)

    Wang, Hailan; Su, Wenying; Loeb, Norman G.; Achuthavarier, Deepthi; Schubert, Siegfried D.

    2017-04-01

    The daily surface and atmospheric radiative fluxes from NASA Clouds and the Earth's Radiant Energy System (CERES) Synoptic 1 degree (SYN1deg) Ed3A are among the most widely used data to study cloud-radiative feedback. The CERES SYN1deg data are based on Fu-Liou radiative transfer computations that use specific humidity (Q) and air temperature (T) from NASA Global Modeling and Assimilation Office (GMAO) reanalyses as inputs and are therefore subject to the quality of those fields. This study uses in situ Q and T observations collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign to augment the input stream used in the NASA GMAO reanalysis and assess the impact on the CERES daily surface and atmospheric longwave estimates. The results show that the assimilation of DYNAMO observations considerably improves the vertical profiles of analyzed Q and T over and near DYNAMO stations by moistening and warming the lower troposphere and upper troposphere and drying and cooling the mid-upper troposphere. As a result of these changes in Q and T, the computed CERES daily surface downward longwave flux increases by about 5 W m-2, due mainly to the warming and moistening in the lower troposphere; the computed daily top-of-atmosphere (TOA) outgoing longwave radiation increases by 2-3 W m-2 during dry periods only. Correspondingly, the estimated local atmospheric longwave radiative cooling enhances by about 5 W m-2 (7-8 W m-2) during wet (dry) periods. These changes reduce the bias in the CERES SYN1deg-like daily longwave estimates at both the TOA and surface and represent an improvement over the DYNAMO region.

  7. Reinforcement of double dynamo waves as a source of solar activity and its prediction on millennium timescale

    Science.gov (United States)

    Popova, E.; Zharkova, V. V.; Shepherd, S. J.; Zharkov, S.

    2016-12-01

    Using the principal components of solar magnetic field variations derived from the synoptic maps for solar cycles 21-24 with Principal Components Analysis (PCA) (Zharkova et al, 2015) we confirm our previous prediction of the upcoming Maunder minimum to occur in cycles 25-27, or in 2020-2055. We also use a summary curve of the two eigen vectors of solar magnetic field oscillations (or two dynamo waves) to extrapolate solar activity backwards to the three millennia and to compare it with relevant historic and Holocene data. Extrapolation of the summary curve confirms the eight grand cycles of 350-400-years superimposed on 22 year-cycles caused by beating effect of the two dynamo waves generated in the two (deep and shallow) layers of the solar interior. The grand cycles in different periods comprise a different number of individual 22-year cycles; the longer the grand cycles the larger number of 22 year cycles and the smaller their amplitudes. We also report the super-grand cycle of about 2000 years often found in solas activity with spectral analysis. Furthermore, the summary curve reproduces a remarkable resemblance to the sunspot and terrestrial activity reported in the past: the recent Maunder Minimum (1645-1715), Dalton minimum (1790-1815), Wolf minimum (1200), Homeric minimum (800-900 BC), the Medieval Warmth Period (900-1200), the Roman Warmth Period (400-10BC) and so on. Temporal variations of these dynamo waves are modelled with the two layer mean dynamo model with meridional circulation revealing a remarkable resemblance of the butterfly diagram to the one derived for the last Maunder minimum in 17 century and predicting the one for the upcoming Maunder minimum in 2020-2055.

  8. Inhibitors of calling behavior of Plodia interpunctella.

    Science.gov (United States)

    Hirashima, Akinori; Shigeta, Yoko; Eiraku, Tomohiko; Kuwano, Eiichi

    2003-01-01

    Some octopamine agonists were found to suppress the calling behavior of the stored product Indian meal moth, Plodia interpunctella. Compounds were screened using a calling behavior bioassay using female P. interpunctella. Four active derivatives, with inhibitory activity at the nanomolar range, were identified in order of decreasing activity: 2-(1-phenylethylamino)-2-oxazoline > 2-(2-ethyl,6-methylanilino)oxazolidine > 2-(2-methyl benzylamino)-2-thiazoline > 2-(2,6-diethylanilino)thiazolidine. Three-dimensional pharmacophore hypotheses were built from a set of 15 compounds. Among the ten common-featured models generated by the program Catalyst/HipHop, a hypothesis including a hydrogen-bond acceptor lipid, a hydrophobic aromatic and two hydrophobic aliphatic features was considered to be essential for inhibitory activity in the calling behavior. Active compounds mapped well onto all the hydrogen-bond acceptor lipid, hydrophobic aromatic and hydrophobic aliphatic features of the hypothesis. On the other hand, less active compounds were shown not to achieve the energetically favorable conformation that is found in the active molecules in order to fit the 3D common-feature pharmacophore models. The present studies demonstrate that inhibition of calling behavior is via an octopamine receptor.

  9. Inhibitors of calling behavior of Plodia interpunctella

    Directory of Open Access Journals (Sweden)

    Akinori Hirashima

    2003-01-01

    Full Text Available Some octopamine agonists were found to suppress the calling behavior of the stored product Indian meal moth, Plodia interpunctella. Compounds were screened using a calling behavior bioassay using female P. interpunctella. Four active derivatives, with inhibitory activity at the nanomolar range, were identified in order of decreasing activity: 2-(1-phenylethylamino-2-oxazoline > 2-(2-ethyl,6-methylanilinooxazolidine > 2-(2-methyl benzylamino-2-thiazoline > 2-(2,6-diethylanilinothiazolidine. Three-dimensional pharmacophore hypotheses were built from a set of 15 compounds. Among the ten common-featured models generated by the program Catalyst/HipHop, a hypothesis including a hydrogen-bond acceptor lipid, a hydrophobic aromatic and two hydrophobic aliphatic features was considered to be essential for inhibitory activity in the calling behavior. Active compounds mapped well onto all the hydrogen-bond acceptor lipid, hydrophobic aromatic and hydrophobic aliphatic features of the hypothesis. On the other hand, less active compounds were shown not to achieve the energetically favorable conformation that is found in the active molecules in order to fit the 3D common-feature pharmacophore models. The present studies demonstrate that inhibition of calling behavior is via an octopamine receptor.

  10. Quantifying uncertainty in genotype calls.

    Science.gov (United States)

    Carvalho, Benilton S; Louis, Thomas A; Irizarry, Rafael A

    2010-01-15

    Genome-wide association studies (GWAS) are used to discover genes underlying complex, heritable disorders for which less powerful study designs have failed in the past. The number of GWAS has skyrocketed recently with findings reported in top journals and the mainstream media. Microarrays are the genotype calling technology of choice in GWAS as they permit exploration of more than a million single nucleotide polymorphisms (SNPs) simultaneously. The starting point for the statistical analyses used by GWAS to determine association between loci and disease is making genotype calls (AA, AB or BB). However, the raw data, microarray probe intensities, are heavily processed before arriving at these calls. Various sophisticated statistical procedures have been proposed for transforming raw data into genotype calls. We find that variability in microarray output quality across different SNPs, different arrays and different sample batches have substantial influence on the accuracy of genotype calls made by existing algorithms. Failure to account for these sources of variability can adversely affect the quality of findings reported by the GWAS. We developed a method based on an enhanced version of the multi-level model used by CRLMM version 1. Two key differences are that we now account for variability across batches and improve the call-specific assessment of each call. The new model permits the development of quality metrics for SNPs, samples and batches of samples. Using three independent datasets, we demonstrate that the CRLMM version 2 outperforms CRLMM version 1 and the algorithm provided by Affymetrix, Birdseed. The main advantage of the new approach is that it enables the identification of low-quality SNPs, samples and batches. Software implementing of the method described in this article is available as free and open source code in the crlmm R/BioConductor package. Supplementary data are available at Bioinformatics online.

  11. Dynamo Catalogue: Geometrical tools and data management for particle picking in subtomogram averaging of cryo-electron tomograms.

    Science.gov (United States)

    Castaño-Díez, Daniel; Kudryashev, Mikhail; Stahlberg, Henning

    2017-02-01

    Cryo electron tomography allows macromolecular complexes within vitrified, intact, thin cells or sections thereof to be visualized, and structural analysis to be performed in situ by averaging over multiple copies of the same molecules. Image processing for subtomogram averaging is specific and cumbersome, due to the large amount of data and its three dimensional nature and anisotropic resolution. Here, we streamline data processing for subtomogram averaging by introducing an archiving system, Dynamo Catalogue. This system manages tomographic data from multiple tomograms and allows visual feedback during all processing steps, including particle picking, extraction, alignment and classification. The file structure of a processing project file structure includes logfiles of performed operations, and can be backed up and shared between users. Command line commands, database queries and a set of GUIs give the user versatile control over the process. Here, we introduce a set of geometric tools that streamline particle picking from simple (filaments, spheres, tubes, vesicles) and complex geometries (arbitrary 2D surfaces, rare instances on proteins with geometric restrictions, and 2D and 3D crystals). Advanced functionality, such as manual alignment and subboxing, is useful when initial templates are generated for alignment and for project customization. Dynamo Catalogue is part of the open source package Dynamo and includes tools to ensure format compatibility with the subtomogram averaging functionalities of other packages, such as Jsubtomo, PyTom, PEET, EMAN2, XMIPP and Relion. Copyright © 2016. Published by Elsevier Inc.

  12. Seasonal Environmental Characteristics for the Tropical Cyclone Genesis in the Indian Ocean during the CINDY2011/DYNAMO Field Experiment

    Directory of Open Access Journals (Sweden)

    Aya Tsuboi

    2016-05-01

    Full Text Available This study investigated the seasonal environmental characteristics for tropical cyclone genesis (TCG over the Indian Ocean during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 and the Dynamics of the Madden–Julian Oscillation (MJO (CINDY2011/DYNAMO field experiment and compare them with long-term climatological features. It was found that the spatial pattern of an empirical environmental index for TCG over the tropical Indian Ocean in 2011 is very similar to the feature composited over the years with high activity of MJO. The analyses of the contributions from each environmental factor indicated that relative humidity, absolute vorticity, and vertical velocity contribute to generate positive influences on the conditions for TCG in 2011. The influences of La Niña appear only through a shear effect over the Indian Ocean in 2011. Under the influences of active MJO events during the CINDY2011/DYNAMO period, the environmental conditions for TCG over the Indian Ocean are determined more strongly by MJO than by La Niña, through modifications of some environmental properties favorable for TCG. The environmental characteristics during CINDY2011/DYNAMO seem to be quite typical of the MJO active years; in such a case, the influences of El Niño/La Niña would not appear in determining the environmental conditions for TCG over the Indian Ocean.

  13. How can I help you? User instructions in telephone calls

    NARCIS (Netherlands)

    Steehouder, M.F.; Hartman, Daniel

    2003-01-01

    We a small corpus of instructions given in phone calls to customers who need support for programming their universal remote control, to make it suitable for their particular TV set VCR, Audio, etc. Typically, in these calls the operator or 'agent' coaches the client while the client is performing

  14. Steven MacCall: Winner of LJ's 2010 Teaching Award

    Science.gov (United States)

    Berry, John N., III

    2010-01-01

    This article profiles Steven L. MacCall, winner of "Library Journal's" 2010 Teaching Award. An associate professor at the School of Library and Information Studies (SLIS) at the University of Alabama, Tuscaloosa, MacCall was nominated by Kathie Popadin, known as "Kpop" to the members of her cohort in the online MLIS program at SLIS. Sixteen of…

  15. Prompting in CALL: A Longitudinal Study of Learner Uptake

    Science.gov (United States)

    Heift, Trude

    2010-01-01

    This research presents a longitudinal study of learner uptake in a computer-assisted language learning (CALL) environment. Over the course of 3 semesters, 10 second language learners of German at a Canadian university used an online, parser-based CALL program that, for the purpose of this research, provided 2 different types of feedback of varying…

  16. The Wireless Nursing Call System

    DEFF Research Database (Denmark)

    Jensen, Casper Bruun

    2006-01-01

    This paper discusses a research project in which social scientists were involved both as analysts and supporters during a pilot with a new wireless nursing call system. The case thus exemplifies an attempt to participate in developing dependable health care systems and offers insight into the cha......This paper discusses a research project in which social scientists were involved both as analysts and supporters during a pilot with a new wireless nursing call system. The case thus exemplifies an attempt to participate in developing dependable health care systems and offers insight...

  17. Radar-Based and Large-Scale Views of Convection and Tropospheric Humidity during DYNAMO/AMIE

    Science.gov (United States)

    Powell, S.; Houze, R.

    2013-12-01

    Unresolved issues remain concerning the onset of a Madden-Julian Oscillation (MJO). Particularly, the mechanism(s) through which widespread deep convection develops before propagating toward the east is (are) unknown. One hypothesized mechanism involves a positive feedback between environmental humidity and convection: Convection deepens as humidity builds vertically, and the taller convection detrains more moisture into the environment. The DYNAMO and AMIE field campaigns in 2011-2012 provided an unprecedented amount of radar and rawinsonde data over the central equatorial Indian Ocean during three realizations of the MJO. Several early papers using DYNAMO/AMIE radar and sounding data have already documented the evolution of humidity fields near the radar sites as well as the evolution of convection leading up to and during an MJO. While extremely valuable, the DYNAMO/AMIE data alone only yield information about convection and humidity within a fairly small volume immediately near the radar site. Humidity fields from AIRS and reflectivity from the TRMM PR examined in conjunction with observations of humidity and convection near Addu Atoll and the R/V Revelle show that the evolution of humidity and convection over each of the equatorial radar sites during DYNAMO is representative of that seen throughout a much larger domain. The time scale involved for the vertical build-up of humidity and convective depth is on the order of one week or less. On this time scale, over the three MJO events, no consistent relationship is observed between humidification of the lower troposphere and deepening of convection. Thus, the results cast doubt on the role of a cloud-humidity feedback mechanism (also known as the 'discharge-recharge' mechanism) in causing MJO onset. Preliminary modeling results using a regional model with non-parameterized convection are also briefly shown. With its boundary conditions updated regularly, the model is capable of reproducing the MJOs observed

  18. CALL and the Speaking Skill.

    Science.gov (United States)

    James, Robert

    1996-01-01

    Using common technologies listed in the conversation class, the article suggests a computer-aided language learning (CALL) speaking methodology that is interaction rather than machine centered and outlines ways to ensure the success of speaking activities at the computer. (31 references) (Author/CK)

  19. Calling to Nursing: Concept Analysis.

    Science.gov (United States)

    Emerson, Christie

    The aims of this article are (a) to analyze the concept of a calling as it relates nursing and (b) to develop a definition of calling to nursing with the detail and clarity needed to guide reliable and valid research. The classic steps described by Walker and Avant are used for the analysis. Literature from several disciplines is reviewed including vocational psychology, Christian career counseling, sociology, organizational management, and nursing. The analysis provides an operational definition of a calling to nursing and establishes 3 defining attributes of the concept: (a) a passionate intrinsic motivation or desire (perhaps with a religious component), (b) an aspiration to engage in nursing practice, as a means of fulfilling one's purpose in life, and (c) the desire to help others as one's purpose in life. Antecedents to the concept are personal introspection and cognitive awareness. Positive consequences to the concept are improved work meaningfulness, work engagement, career commitment, personal well-being, and satisfaction. Negative consequences of having a calling might include willingness to sacrifice well-being for work and problems with work-life balance. Following the concept analysis, philosophical assumptions, contextual factors, interdisciplinary work, research opportunities, and practice implications are discussed.

  20. An Evaluation Framework for CALL

    Science.gov (United States)

    McMurry, Benjamin L.; Williams, David Dwayne; Rich, Peter J.; Hartshorn, K. James

    2016-01-01

    Searching prestigious Computer-assisted Language Learning (CALL) journals for references to key publications and authors in the field of evaluation yields a short list. The "American Journal of Evaluation"--the flagship journal of the American Evaluation Association--is only cited once in both the "CALICO Journal and Language…

  1. A large-scale dynamo and magnetoturbulence in rapidly rotating core-collapse supernovae.

    Science.gov (United States)

    Mösta, Philipp; Ott, Christian D; Radice, David; Roberts, Luke F; Schnetter, Erik; Haas, Roland

    2015-12-17

    Magnetohydrodynamic turbulence is important in many high-energy astrophysical systems, where instabilities can amplify the local magnetic field over very short timescales. Specifically, the magnetorotational instability and dynamo action have been suggested as a mechanism for the growth of magnetar-strength magnetic fields (of 10(15) gauss and above) and for powering the explosion of a rotating massive star. Such stars are candidate progenitors of type Ic-bl hypernovae, which make up all supernovae that are connected to long γ-ray bursts. The magnetorotational instability has been studied with local high-resolution shearing-box simulations in three dimensions, and with global two-dimensional simulations, but it is not known whether turbulence driven by this instability can result in the creation of a large-scale, ordered and dynamically relevant field. Here we report results from global, three-dimensional, general-relativistic magnetohydrodynamic turbulence simulations. We show that hydromagnetic turbulence in rapidly rotating protoneutron stars produces an inverse cascade of energy. We find a large-scale, ordered toroidal field that is consistent with the formation of bipolar magnetorotationally driven outflows. Our results demonstrate that rapidly rotating massive stars are plausible progenitors for both type Ic-bl supernovae and long γ-ray bursts, and provide a viable mechanism for the formation of magnetars. Moreover, our findings suggest that rapidly rotating massive stars might lie behind potentially magnetar-powered superluminous supernovae.

  2. Can Core Flows inferred from Geomagnetic Field Models explain the Earth's Dynamo?

    CERN Document Server

    Schaeffer, Nathanaël; Pais, Maria Alexandra

    2015-01-01

    We test the ability of velocity fields inferred from geomagnetic secular variation data to produce the global magnetic field of the Earth. Our kinematic dynamo calculations use quasi-geostrophic (QG) flows inverted from geomagnetic field models which, as such, incorporate flow structures that are Earth-like and may be important for the geodynamo. Furthermore, the QG hypothesis allows straightforward prolongation of the flow from the core surface to the bulk. As expected from previous studies, we check that a simple quasi-geostrophic flow is not able to sustain the magnetic field against ohmic decay. Additional complexity is then introduced in the flow, inspired by the action of the Lorentz force. Indeed, on centenial timescales, the Lorentz force can balance the Coriolis force and strict quasi-geostrophy may not be the best ansatz. When the columnar flow is modified to account for the action of the Lorentz force, magnetic field is generated for Elsasser numbers larger than 0.25 and magnetic Reynolds numbers l...

  3. Magnetorotational instability and dynamo action in gravito-turbulent astrophysical discs

    Science.gov (United States)

    Riols, A.; Latter, H.

    2018-02-01

    Though usually treated in isolation, the magnetorotational and gravitational instabilities (MRI and GI) may coincide at certain radii and evolutionary stages of protoplanetary discs and active galactic nuclei. Their mutual interactions could profoundly influence several important processes, such as accretion variability and outbursts, fragmentation and disc truncation, or large-scale magnetic field production. Direct numerical simulations of both instabilities are computationally challenging and remain relatively unexplored. In this paper, we aim to redress this neglect via a set of 3D vertically stratified shearing-box simulations, combining self-gravity and magnetic fields. We show that gravito-turbulence greatly weakens the zero-net-flux MRI. In the limit of efficient cooling (and thus enhanced GI), the MRI is completely suppressed, and yet strong magnetic fields are sustained by the gravito-turbulence. This turbulent `spiral wave' dynamo may have widespread application, especially in galactic discs. Finally, we present preliminary work showing that a strong net-vertical-flux revives the MRI and supports a magnetically dominated state in which the GI is secondary.

  4. Reducing juvenile delinquency with automated cell phone calls.

    Science.gov (United States)

    Burraston, Bert O; Bahr, Stephen J; Cherrington, David J

    2014-05-01

    Using a sample of 70 juvenile probationers (39 treatment and 31 controls), we evaluated the effectiveness of a rehabilitation program that combined cognitive-behavioral training and automated phone calls. The cognitive-behavioral training contained six 90-min sessions, one per week, and the phone calls occurred twice per day for the year following treatment. Recidivism was measured by whether they were rearrested and the total number of rearrests during the 1st year. To test the impact of the phone calls, those who received phone calls were divided into high and low groups depending on whether they answered more or less than half of their phone calls. Those who completed the class and answered at least half of their phone calls were less likely to have been arrested and had fewer total arrests.

  5. impact of queuing on call c queuing on call c queuing on call ...

    African Journals Online (AJOL)

    eobe

    work resource reduces the probability that a call arriving at the base sta formance evaluation plays an important role in modelling and network resource. network resource. This objective is achieved by an accurate traffic characte. This objective is achieved by an accurate traffic characte rformance metrics in terms of traffic ...

  6. “Computer Assisted Language Learning” (CALL

    Directory of Open Access Journals (Sweden)

    Nazlı Gündüz

    2005-10-01

    Full Text Available This article will provide an overview of computers; an overview of the history of CALL, itspros and cons, the internet, World Wide Web, Multimedia, and research related to the uses of computers in the language classroom. Also, it also aims to provide some background for the beginnerson using the Internet in language classes today. It discusses some of the common types of Internetactivities that are being used today, what the minimum requirements are for using the Internet forlanguage learning, and some easy activities you can adapt for your classes. Some special terminology related to computers will also be used in this paper. For example, computer assisted language learning(CALL refers to the sets of instructions which need to be loaded into the computer for it to be able to work in the language classroom. It should be borne in mind that CALL does not refer to the use of acomputer by a teacher to type out a worksheet or a class list or preparing his/her own teaching alone.Hardware refers to any computer equipment used, including the computer itself, the keyboard, screen (or the monitor, the disc-drive, and the printer. Software (computer programs refers to the sets of instructions which need to be loaded into the computer for it to be able to work.

  7. Calle y Saberes en Movimiento

    Directory of Open Access Journals (Sweden)

    Laura Daniela Aguirre Aguilar

    2010-05-01

    Full Text Available En México el rezago, el ausentismo, la deserción escolar, el trabajo a temprana edad y el inicio de una vida en la calle, en repetidas ocasiones son consecuencia de un núcleo familiar desarticulado o de una débil relación intrafamiliar, así como de una condición socioeconómica en desventaja. Ante esta problemática, la Secretaría de Educación Pública, instancia gubernamental encargada de garantizar una educación de calidad para la población, trabaja coordinadamente con organizaciones de la sociedad civil e instancias públicas, para la reintegración a los espacios educativos de los niños, niñas y jóvenes en situación de calle.

  8. Calle y Saberes en Movimiento

    Directory of Open Access Journals (Sweden)

    Laura Daniela Aguirre Aguilar

    2010-01-01

    Full Text Available En México el rezago, el ausentismo, la deserción escolar, el trabajo a temprana edad y el inicio de una vida en la calle, en repetidas ocasiones son consecuencia de un núcleo familiar desarticulado o de una débil relación intrafamiliar, así como de una condición socioeconómica en desventaja. Ante esta problemática, la Secretaría de Educación Pública, instancia gubernamental encargada de garantizar una educación de calidad para la población, trabaja coordinadamente con organizaciones de la sociedad civil e instancias públicas, para la reintegración a los espacios educativos de los niños, niñas y jóvenes en situación de calle.

  9. Armed calling for sur plus

    Directory of Open Access Journals (Sweden)

    Andréa Limberto Leite

    2013-12-01

    Full Text Available The most recent work by researcher José Luiz Aidar Prado, Convocações biopolíticas dos dispositivos comunicacionais (freely translated as Biopolitic convoking of communicational dispositives puts the reader straight in the face of the calling to enter circulating discourses. They are directed to all subjects and also accomodate the discourses with urgence for consumption. 

  10. Ultrasound call detection in capybara

    Directory of Open Access Journals (Sweden)

    Selene S.C. Nogueira

    2012-07-01

    Full Text Available The vocal repertoire of some animal species has been considered a non-invasive tool to predict distress reactivity. In rats ultrasound emissions were reported as distress indicator. Capybaras[ vocal repertoire was reported recently and seems to have ultrasound calls, but this has not yet been confirmed. Thus, in order to check if a poor state of welfare was linked to ultrasound calls in the capybara vocal repertoire, the aim of this study was to track the presence of ultrasound emissions in 11 animals under three conditions: 1 unrestrained; 2 intermediately restrained, and 3 highly restrained. The ultrasound track identified frequencies in the range of 31.8±3.5 kHz in adults and 33.2±8.5 kHz in juveniles. These ultrasound frequencies occurred only when animals were highly restrained, physically restrained or injured during handling. We concluded that these calls with ultrasound components are related to pain and restraint because they did not occur when animals were free of restraint. Thus we suggest that this vocalization may be used as an additional tool to assess capybaras[ welfare.

  11. 78 FR 76257 - Rural Call Completion

    Science.gov (United States)

    2013-12-17

    ... such service offers the capability to place calls to or receive calls from the PSTN. 6. In addition... traffic in response to continued complaints about rural call completion issues from rural associations... Project offering providers the opportunity to test call completion issues identified on calls destined to...

  12. A Call for Cultural Democracy

    Science.gov (United States)

    Graves, Daniel E.

    2015-01-01

    In this chapter, an incarcerated student in Illinois discusses the issue of cheating/plagiarism in the prison context and weighs in on the value of vocational education compared to degree-granting academic programs in prison.

  13. Comparison of tobacco control scenarios: quantifying estimates of long-term health impact using the DYNAMO-HIA modeling tool.

    Science.gov (United States)

    Kulik, Margarete C; Nusselder, Wilma J; Boshuizen, Hendriek C; Lhachimi, Stefan K; Fernández, Esteve; Baili, Paolo; Bennett, Kathleen; Mackenbach, Johan P; Smit, H A

    2012-01-01

    There are several types of tobacco control interventions/policies which can change future smoking exposure. The most basic intervention types are 1) smoking cessation interventions 2) preventing smoking initiation and 3) implementation of a nationwide policy affecting quitters and starters simultaneously. The possibility for dynamic quantification of such different interventions is key for comparing the timing and size of their effects. We developed a software tool, DYNAMO-HIA, which allows for a quantitative comparison of the health impact of different policy scenarios. We illustrate the outcomes of the tool for the three typical types of tobacco control interventions if these were applied in the Netherlands. The tool was used to model the effects of different types of smoking interventions on future smoking prevalence and on health outcomes, comparing these three scenarios with the business-as-usual scenario. The necessary data input was obtained from the DYNAMO-HIA database which was assembled as part of this project. All smoking interventions will be effective in the long run. The population-wide strategy will be most effective in both the short and long term. The smoking cessation scenario will be second-most effective in the short run, though in the long run the smoking initiation scenario will become almost as effective. Interventions aimed at preventing the initiation of smoking need a long time horizon to become manifest in terms of health effects. The outcomes strongly depend on the groups targeted by the intervention. We calculated how much more effective the population-wide strategy is, in both the short and long term, compared to quit smoking interventions and measures aimed at preventing the initiation of smoking. By allowing a great variety of user-specified choices, the DYNAMO-HIA tool is a powerful instrument by which the consequences of different tobacco control policies and interventions can be assessed.

  14. The Role of DYNAMO in Situ Observations in Improving NASA Ceres-like Daily Surface and Atmospheric Radiative Flux Estimates

    Science.gov (United States)

    Wang, Hailan; Su, Wenying; Loeb, Norman G.; Achuthavarier, Deepthi; Schubert, Siegfried D.

    2017-01-01

    The daily surface and atmospheric radiative fluxes from NASA Clouds and the Earths RadiantEnergy System (CERES) Synoptic 1 degree (SYN1deg) Ed3A are among the most widely used data to studycloud-radiative feedback. The CERES SYN1deg data are based on Fu-Liou radiative transfer computations thatuse specific humidity (Q) and air temperature (T) from NASA Global Modeling and Assimilation Office (GMAO)reanalyses as inputs and are therefore subject to the quality of those fields. This study uses in situ Q and Tobservations collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign toaugment the input stream used in the NASA GMAO reanalysis and assess the impact on the CERES dailysurface and atmospheric longwave estimates. The results show that the assimilation of DYNAMOobservations considerably improves the vertical profiles of analyzed Q and T over and near DYNAMO stationsby moistening and warming the lower troposphere and upper troposphere and drying and cooling themid-upper troposphere. As a result of these changes in Q and T, the computed CERES daily surface downwardlongwave flux increases by about 5 W m(exp -2), due mainly to the warming and moistening in the lowertroposphere; the computed daily top-of-atmosphere (TOA) outgoing longwave radiation increases by2-3 W m(exp -2) during dry periods only. Correspondingly, the estimated local atmospheric longwave radiativecooling enhances by about 5 W m(exp -2) (7-8 W m(exp -2)) during wet (dry) periods. These changes reduce the bias inthe CERES SYN1deg-like daily longwave estimates at both the TOA and surface and represent animprovement over the DYNAMO region.

  15. Role of asymmetric meridional circulation in producing north-south asymmetry in a solar cycle dynamo model

    Energy Technology Data Exchange (ETDEWEB)

    Belucz, Bernadett [Eötvös University, Department of Astronomy, 1518 Budapest, Pf. 32 (Hungary); Dikpati, Mausumi [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green, Boulder, CO 80307-3000 (United States)

    2013-12-10

    Solar cycles in the north and south hemispheres differ in cycle length, amplitude, profile, polar fields, and coronal structure. To show what role differences in meridional flow could play in producing these differences, we present the results of three sets of numerical simulations from a flux transport dynamo in which one property of meridional circulation has been changed in the south only. The changes are in amplitude and the presence of a second cell in latitude or in depth. An ascending phase speedup causes weakening of polar and toroidal fields; a speed decrease in a late descending phase does not change amplitudes. A long-duration speed increase leads to lower toroidal field peaks but unchanged polar field peaks. A second high-latitude circulation cell in an ascending phase weakens the next polar and toroidal field peaks, and the ascending phase is lengthened. A second cell in a late descending phase speeds up the cycle. A long-duration second cell leads to a poleward branch of the butterfly diagram and weaker polar fields. A second cell in depth reverses the tilt of the butterfly wing, decreasing polar fields when added during an ascending phase and increasing them during a late descending phase. A long-duration presence of a second cell in radius evolves the butterfly diagram far away from the observed one, with different dynamo periods in low and high latitudes. Thus, a second cell in depth is unlikely to persist more than a few years if the solar dynamo is advection-dominated. Our results show the importance of time variation and north-south asymmetry in meridional circulation in producing differing cycles in the north and south.

  16. Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander

    Science.gov (United States)

    Nayak, Michael; Hemingway, Doug; Garrick-Bethell, Ian

    2017-04-01

    A number of magnetic anomalies are present along the northern edge of the lunar South Pole-Aitken (SPA) basin. A variety of hypotheses for their formation have been proposed, but an in-depth study of their properties has not been performed. Here we use two different methods to invert for their source body characteristics: one that completely searches a small parameter space of less than ten uniform-strength dipoles per anomaly, and another that uses grids of hundreds of dipoles with variable magnetization strengths. Both methods assume uniform magnetization directions at each anomaly and with one exception, produce nearly the same results. We introduce new Monte Carlo methods to quantify errors in our inversions arising from Gaussian time-dependent changes in the external field and the uncertain geometry of the source bodies. We find the errors from uncertainty in source body geometry are almost always higher. We also find a diverse set of magnetization directions around SPA, which we combine with other physical arguments to conclude that the source bodies were likely magnetized in a dynamo field. Igneous intrusions are a reasonable explanation (Purucker et al., 2012) for the directional variability, since they could be intruded over different magnetic epochs. However, the directional variability also implies either surprisingly large amounts of true polar wander or a dynamo not aligned with the lunar spin axis. We also explore the possibility that true polar wander caused by the SPA impact could allow iron-rich SPA ejecta to record a diverse set of magnetic field directions. Some of this material may have also become "sesquinary" ejecta and re-impacted across the Moon on 104-106 year timescales to capture such changes. No completely satisfactory answer emerges, except that the dipole-axis of the lunar dynamo may have been variable in direction.

  17. A Proposed Paradigm for Solar Cycle Dynamics Mediated via Turbulent Pumping of Magnetic Flux in Babcock-Leighton-type Solar Dynamos

    Science.gov (United States)

    Hazra, Soumitra; Nandy, Dibyendu

    2016-11-01

    At present, the Babcock-Leighton flux transport solar dynamo models appear to be the most promising models for explaining diverse observational aspects of the sunspot cycle. The success of these flux transport dynamo models is largely dependent upon a single-cell meridional circulation with a deep equatorward component at the base of the Sun’s convection zone. However, recent observations suggest that the meridional flow may in fact be very shallow (confined to the top 10% of the Sun) and more complex than previously thought. Taken together, these observations raise serious concerns on the validity of the flux transport paradigm. By accounting for the turbulent pumping of magnetic flux, as evidenced in magnetohydrodynamic simulations of solar convection, we demonstrate that flux transport dynamo models can generate solar-like magnetic cycles even if the meridional flow is shallow. Solar-like periodic reversals are recovered even when meridional circulation is altogether absent. However, in this case, the solar surface magnetic field dynamics does not extend all the way to the polar regions. Very importantly, our results demonstrate that the Parker-Yoshimura sign rule for dynamo wave propagation can be circumvented in Babcock-Leighton dynamo models by the latitudinal component of turbulent pumping, which can generate equatorward propagating sunspot belts in the absence of a deep, equatorward meridional flow. We also show that variations in turbulent pumping coefficients can modulate the solar cycle amplitude and periodicity. Our results suggest the viability of an alternate magnetic flux transport paradigm—mediated via turbulent pumping—for sustaining solar-stellar dynamo action.

  18. Spinning Unmagnetized Plasma for Laboratory Studies of Astrophysical Accretion Disks & Dynamos

    Science.gov (United States)

    Collins, Cami

    2015-11-01

    A technique for creating a large, fast-flowing, unmagnetized plasma has been demonstrated experimentally. This marks an important first step towards laboratory studies of phenomenon such as magnetic field generation through self-excited dynamos, or the magnetorotational instability (MRI), the mechanism of interest for its role in the efficient outward transport of angular momentum in accretion disks. In the Plasma Couette Experiment (PCX), a sufficiently hot, steady-state plasma is confined in a cylindrical, axisymmetric multicusp magnetic field, with Tetorque using toroidally localized, biased hot cathodes in the magnetized edge region. Measurements show that momentum couples viscously from the magnetized edge to the unmagnetized core, and the core rotates when collisional ion viscosity overcomes the drag due to ion-neutral collisions. Torque can be applied at the inner or outer boundaries, resulting in controlled, differential rotation. Maximum speeds are observed (He ~ 12 km/s, Ne ~ 4 km/s, Ar ~ 3.2 km/s, Xe ~ 1.4 km/s), consistent with a critical ionization velocity limit reported to occur in partially ionized plasmas. PCX has achieved magnetic Reynolds numbers of Rm ~ 65 and magnetic Prandtl numbers of Pm ~ 0.2-10, which are approaching regimes shown to excite the MRI in a global Hall-MHD stability analysis. Ion-neutral collisions effectively add a body force that undesirably changes the flow profile shape. Recent upgrades have increased the ionization fraction with an additional 6 kW of microwave heating power and stronger magnets that reduce loss area and increase plasma volume by 150%. In addition, an alternative scheme using volume-applied JxB force will maintain the shear profile and destabilize the MRI at more easily achievable plasma parameters.

  19. Small-scale dynamo magnetism as the driver for heating the solar atmosphere.

    Science.gov (United States)

    Amari, Tahar; Luciani, Jean-François; Aly, Jean-Jacques

    2015-06-11

    The long-standing problem of how the solar atmosphere is heated has been addressed by many theoretical studies, which have stressed the relevance of two specific mechanisms, involving magnetic reconnection and waves, as well as the necessity of treating the chromosphere and corona together. But a fully consistent model has not yet been constructed and debate continues, in particular about the possibility of coronal plasma being heated by energetic phenomena observed in the chromosphere. Here we report modelling of the heating of the quiet Sun, in which magnetic fields are generated by a subphotospheric fluid dynamo intrinsically connected to granulation. We find that the fields expand into the chromosphere, where plasma is heated at the rate required to match observations (4,500 watts per square metre) by small-scale eruptions that release magnetic energy and drive sonic motions. Some energetic eruptions can even reach heights of 10 million metres above the surface of the Sun, thereby affecting the very low corona. Extending the model by also taking into account the vertical weak network magnetic field allows for the existence of a mechanism able to heat the corona above, while leaving unchanged the physics of chromospheric eruptions. Such a mechanism rests on the eventual dissipation of Alfvén waves generated inside the chromosphere and that carry upwards the required energy flux of 300 watts per square metre. The model shows a topologically complex magnetic field of 160 gauss on the Sun's surface, agreeing with inferences obtained from spectropolarimetric observations, chromospheric features (contributing only weakly to the coronal heating) that can be identified with observed spicules and blinkers, and vortices that may be possibly associated with observed solar tornadoes.

  20. A small-scale dynamo in feedback-dominated galaxies - III. Cosmological simulations

    Science.gov (United States)

    Rieder, Michael; Teyssier, Romain

    2017-12-01

    Magnetic fields are widely observed in the Universe in virtually all astrophysical objects, from individual stars to entire galaxies, even in the intergalactic medium, but their specific genesis has long been debated. Due to the development of more realistic models of galaxy formation, viable scenarios are emerging to explain cosmic magnetism, thanks to both deeper observations and more efficient and accurate computer simulations. We present here a new cosmological high-resolution zoom-in magnetohydrodynamic (MHD) simulation, using the adaptive mesh refinement technique, of a dwarf galaxy with an initially weak and uniform magnetic seed field that is amplified by a small-scale dynamo (SSD) driven by supernova-induced turbulence. As first structures form from the gravitational collapse of small density fluctuations, the frozen-in magnetic field separates from the cosmic expansion and grows through compression. In a second step, star formation sets in and establishes a strong galactic fountain, self-regulated by supernova explosions. Inside the galaxy, the interstellar medium becomes highly turbulent, dominated by strong supersonic shocks, as demonstrated by the spectral analysis of the gas kinetic energy. In this turbulent environment, the magnetic field is quickly amplified via a SSD process and is finally carried out into the circumgalactic medium by a galactic wind. This realistic cosmological simulation explains how initially weak magnetic seed fields can be amplified quickly in early, feedback-dominated galaxies, and predicts, as a consequence of the SSD process, that high-redshift magnetic fields are likely to be dominated by their small-scale components.

  1. A dynamo theory prediction for solar cycle 22 - Sunspot number, radio flux, exospheric temperature, and total density at 400 km

    Science.gov (United States)

    Schatten, K. H.; Hedin, A. E.

    1984-01-01

    Using the 'dynamo theory' method to predict solar activity, a value for the smoothed sunspot number of 109 + or - 20 is obtained for solar cycle 22. The predicted cycle is expected to peak near December, 1990 + or - 1 year. Concommitantly, F(10.7) radio flux is expected to reach a smoothed value of 158 + or - 18 flux units. Global mean exospheric temperature is expected to reach 1060 + or - 50 K and global total average total thermospheric density at 400 km is expected to reach 4.3 x 10 to the -15th gm/cu cm + or - 25 percent.

  2. A dynamo theory prediction for solar cycle 22: Sunspot number, radio flux, exospheric temperature, and total density at 400 km

    Science.gov (United States)

    Schatten, K. H.; Hedin, A. E.

    1986-01-01

    Using the dynamo theory method to predict solar activity, a value for the smoothed sunspot number of 109 + or - 20 is obtained for solar cycle 22. The predicted cycle is expected to peak near December, 1990 + or - 1 year. Concommitantly, F(10.7) radio flux is expected to reach a smoothed value of 158 + or - 18 flux units. Global mean exospheric temperature is expected to reach 1060 + or - 50 K and global total average total thermospheric density at 400 km is expected to reach 4.3 x 10 to the -15th gm/cu cm + or - 25 percent.

  3. The nonlinear differential equations governing a hierarchy of self-exciting coupled Faraday-disk homopolar dynamos

    Science.gov (United States)

    Hide, Raymond

    1997-02-01

    This paper discusses the derivation of the autonomous sets of dimensionless nonlinear ordinary differential equations (ODE's) that govern the behaviour of a hierarchy of related electro-mechanical self-exciting Faraday-disk homopolar dynamo systems driven by steady mechanical couples. Each system comprises N interacting units which could be arranged in a ring or lattice. Within each unit and connected in parallel or in series with the coil are electric motors driven into motion by the dynamo, all having linear characteristics, so that nonlinearity arises entirely through the coupling between components. By introducing simple extra terms into the equations it is possible to represent biasing effects arising from impressed electromotive forces due to thermoelectric or chemical processes and from the presence of ambient magnetic fields. Dissipation in the system is due not only to ohmic heating but also to mechanical friction in the disk and the motors, with the latter agency, no matter how weak, playing an unexpectedly crucial rôle in the production of régimes of chaotic behaviour. This has already been demonstrated in recent work on a case of a single unit incorporating just one series motor, which is governed by a novel autonomous set of nonlinear ODE's with three time-dependent variables and four control parameters. It will be of mathematical as well as geophysical and astrophysical interest to investigate systematically phase and amplitude locking and other types of behaviour in the more complicated cases that arise when N > 1, which can typically involve up to 6 N dependent variables and 19 N-5 control parameters. Even the simplest members of the hierarchy, with N as low as 1, 2 or 3, could prove useful as physically-realistic low-dimensional models in theoretical studies of fluctuating stellar and planetary magnetic fields. Geomagnetic polarity reversals could be affected by the presence of the Earth's solid metallic inner core, driven like an electric motor

  4. Call for Outline Research Proposals

    International Development Research Centre (IDRC) Digital Library (Canada)

    IDRC CRDI

    2013-07-25

    Jul 25, 2013 ... The program will support a variety of research methodologies and approaches, with an emphasis .... Proposals from all social-science disciplines that can contribute to the theme are encouraged. Multi- .... IDRC has concluded general agreements for scientific and technical cooperation with a number of.

  5. 78 FR 76218 - Rural Call Completion

    Science.gov (United States)

    2013-12-17

    ..., to the extent such service offers the capability to place calls to or receive calls from the PSTN. 6... restricting telephone traffic in response to continued complaints about rural call completion issues from.... In August 2013, ATIS and NECA announced a voluntary Joint National Call Testing Project offering...

  6. 47 CFR 2.302 - Call signs.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false Call signs. 2.302 Section 2.302... RULES AND REGULATIONS Call Signs and Other Forms of Identifying Radio Transmissions § 2.302 Call signs. The table which follows indicates the composition and blocks of international call signs available for...

  7. Impact of time-dependent non-axisymmetric velocity perturbations on dynamo action of von-K\\'arm\\'an-like flows

    CERN Document Server

    Giesecke, Andre; Burguete, Javier

    2012-01-01

    We have performed numerical simulations of the kinematic induction equation in order to examine the dynamo efficiency of an axisymmetric von-K\\'arm\\'an-like flow subject to time-dependent non-axisymmetric velocity perturbations. The numerical model is based on the setup of the French Von-K\\'arm\\'an-Sodium dynamo (VKS) and on the flow measurements from a model water experiment conducted at the University of Navarra in Pamplona, Spain. Our simulations show that the interactions of azimuthally drifting flow perturbations with the fundamental drift of the magnetic eigenmode (caused by the inevitable equatorial symmetry breaking of the basic flow) essentially determine the temporal behavior of the dynamo state. We find two distinct regimes of dynamo action that depend on the (prescribed) drift frequency of an ($m=2$) vortex-like flow perturbation. For comparatively slowly drifting vortices we observe a narrow window with enhanced growth-rates and a drift of the magnetic eigenmode that is synchronized with the pert...

  8. From Systematic Review to Call for Action.

    Science.gov (United States)

    Sawin, Erika Metzler; Sobel, Linda L; Annan, Sandra L; Schminkey, Donna L

    2017-06-01

    Intimate partner violence (IPV) is a global public health and criminal justice concern with significant impacts; especially high rates are seen among rural Hispanic American (HA) communities, the fastest growing population in the United States. They experience additional barriers to care including extreme poverty, lesser education, gender norms, and language and immigration issues. A systematic literature review was conducted using Cooper's framework to identify evidence supporting associations between interventions and prevention, reduction, and elimination of IPV among rural HA women. Searches conducted on databases including CINAHL, PubMed, Medline, Women's Studies International, MedicLatina, and JSTOR used the MeSH terms Hispanic Americans (Latino/a and Hispanic), domestic violence, and intimate partner violence. Selected studies were published between January 1, 2000, and January 1, 2014. Of the 617 yielded articles, only 6 met the inclusion criteria. Of these, none closely examined rurality or provided valid and reliable measures of outcomes, instead reporting program descriptions and suggested interventions. We identify key findings to guide program, screening, and tool development. Our study identifies a gap in knowledge, research, and effective practices and issues a call for action to create evidence-based tools to prevent, reduce, and eliminate IPV in these underserved populations.

  9. Indico CONFERENCE: Define the Call for Abstracts

    CERN Multimedia

    CERN. Geneva; Ferreira, Pedro

    2017-01-01

    In this tutorial, you will learn how to define and open a call for abstracts. When defining a call for abstracts, you will be able to define settings related to the type of questions asked during a review of an abstract, select the users who will review the abstracts, decide when to open the call for abstracts, and more.

  10. HOW TO CALL THE CERN FIRE BRIGADE

    CERN Multimedia

    2002-01-01

    The telephone numbers of the CERN Fire Brigade are: 74444 for emergency calls 74848 for other calls Note The number 112 will stay in use for emergency calls from 'wired' telephones, however, from mobile phones it leads to non-CERN emergency services.

  11. How to call the Fire Brigade

    CERN Multimedia

    2003-01-01

    The telephone numbers for the CERN Fire Brigade are: 74444 for emergency calls 74848 for other calls Note The number 112 will stay in use for emergency calls from "wired" telephones, however, from mobile phones it leads to non-CERN emergency services.

  12. HOW TO CALL THE CERN FIRE BRIGADE

    CERN Multimedia

    2002-01-01

    The telephone numbers of the CERN Fire Brigade are: 74444 for emergency calls 74848 for other calls Note The number 112 will stay in use for emergency calls from 'wired' telephones, however, from mobile phones it leads to non-CERN emergency services.  

  13. Do market participants learn from conference calls?

    NARCIS (Netherlands)

    Roelofsen, E.; Verbeeten, F.; Mertens, G.

    2014-01-01

    We examine whether market participants learn from the information that is disseminated during the Q-and-A section of conference calls. Specifically, we investigate whether stock prices react to information on intangible assets provided during conference calls, and whether conference calls

  14. HOW TO CALL THE CERN FIRE BRIGADE

    CERN Multimedia

    2001-01-01

    The telephone numbers of the CERN Fire Brigade are: 74444 for emergency calls 74848 for other calls Note: the number 112 will stay in use for emergency calls from 'wired' telephones, however, from mobile phones it leads to non-CERN emergency services.

  15. HOW TO CALL THE CERN FIRE BRIGADE

    CERN Multimedia

    2001-01-01

    The telephone numbers of the CERN Fire Brigade are: 74444 for emergency calls 74848 for other calls Note The number 112 will stay in use for emergency calls from 'wired' telephones, however, from mobile phones it leads to non-CERN emergency services.

  16. ICALL's Relevance to CALL

    Science.gov (United States)

    Ward, Monica

    2017-01-01

    The term Intelligent Computer Assisted Language Learning (ICALL) covers many different aspects of CALL that add something extra to a CALL resource. This could be with the use of computational linguistics or Artificial Intelligence (AI). ICALL tends to be not very well understood within the CALL community. There may also be the slight fear factor…

  17. Pursuing the plasma dynamo and MRI in the laboratory: Hydrodynamic studies of unmagnetized plasmas at large magnetic Reynolds number

    Science.gov (United States)

    Weisberg, David B.

    A new method for studying flow-driven MHD instabilities in the laboratory has been developed, using a highly conductive, low viscosity, spherical plasma. The confinement, heating, and stirring of this unmagnetized plasma has been demonstrated experimentally, laying the foundations for the laboratory studies of a diverse collection of astrophysically-relevant instabilities. Specifically, plasma flows conducive to studies of the dynamo effect and the magnetorotational instability (MRI) are measured using a wide array of plasma diagnostics, and compare favorably to hydrodynamic numerical models. The Madison plasma dynamo experiment (MPDX) uses a cylindrically symmetric spherical boundary ring cusp geometry built from strong permanent magnets to confine a large (R=1.5 m), warm (Te torques using current drawn from emissive LaB6 cathodes located at the magnetized plasma edge, which also ionize and heat the plasma via sizable discharge current injection. Combination Langmuir/Mach probes measure maximum velocities of 6 km/s and 3 km/s in helium and argon plasmas, respectively, and ion viscosity is shown to be an efficient mechanism for transporting momentum from the magnetized edge into the unmagnetized core. Momentum loss to neutral charge-exchange collisions serves as the main source of drag on the bulk plasma velocity, and ionization fraction (He ˜ 0.6, Ar ˜ 0.95) is shown to be a limiting factor in momentum penetration. High Alfven Mach number flows have also been generated by drawing current across a global axial magnetic field, resulting in a velocity geometry conducive to MRI experiments. The experiment has achieved magnetic Reynolds numbers of Rm < 250 and fluid Reynolds numbers of Re < 200 (significantly higher than previous flow experiments in cusp-confined plasmas), setting the stage for future research of flow-driven MHD instabilities.

  18. Simulations of Cloud-Radiation Interaction Using Large-Scale Forcing Derived from the CINDY/DYNAMO Northern Sounding Array

    Science.gov (United States)

    Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; Feng, Zhe; Comstock, Jennifer M.; Minnis, Patrick; Nordeen, Michele L.

    2015-01-01

    The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large-scale forcing data set derived from the DYNAMO northern sounding array observations, and carried out in a doubly periodic domain using the Weather Research and Forecasting (WRF) model. Simulated cloud properties and radiative fluxes are compared to those derived from the S-PolKa radar and satellite observations. To accommodate the uncertainty in simulated cloud microphysics, a number of single-moment (1M) and double-moment (2M) microphysical schemes in the WRF model are tested. The 1M schemes tend to underestimate radiative flux anomalies in the active phases of the MJO events, while the 2M schemes perform better, but can overestimate radiative flux anomalies. All the tested microphysics schemes exhibit biases in the shapes of the histograms of radiative fluxes and radar reflectivity. Histograms of radiative fluxes and brightness temperature indicate that radiative biases are not evenly distributed; the most significant bias occurs in rainy areas with OLR less than 150 W/ cu sq in the 2M schemes. Analysis of simulated radar reflectivities indicates that this radiative flux uncertainty is closely related to the simulated stratiform cloud coverage. Single-moment schemes underestimate stratiform cloudiness by a factor of 2, whereas 2M schemes simulate much more stratiform cloud.

  19. A small-scale dynamo in feedback-dominated galaxies - II. The saturation phase and the final magnetic configuration

    Science.gov (United States)

    Rieder, Michael; Teyssier, Romain

    2017-11-01

    Magnetic fields in galaxies are believed to be the result of dynamo amplification of initially weak seed fields, reaching equipartition strength inside the interstellar medium. The small-scale dynamo (SSD) appears to be a viable mechanism to explain observations of strong magnetic fields in present-day and high-redshift galaxies, considering the extreme weakness of viable seed fields. Performing high-resolution adaptive mesh magnetohydrodynamic simulations of a small-mass, isolated cooling halo with an initial magnetic seed field strength well below equipartition, we follow the SSD amplification from supernova-induced turbulence up to saturation of the field. We find that saturation occurs when the average magnetic pressure reaches only 3 per cent of the turbulent pressure. The magnetic energy growth transitions from exponential to linear, and finally comes to halt. The saturation level increases slightly with grid resolution. These results are in good agreement with theoretical predictions for magnetic Prandtl numbers of the order ofPm ˜ 1 and turbulent Mach numbers of the order of M ˜ 10. When we suppress supernova feedback after our simulation has reached saturation, we find that turbulence decays and that the gas falls back on to a thin disc with the magnetic field in local equipartition in most of the dense gas arms. We propose a scenario in which galactic magnetic fields are amplified from weak seed fields in the early stages of the Universe to sub-equipartition fields, owing to the turbulent environment of feedback-dominated galaxies at high redshift, and are evolved further in a later stage up to equipartition, as galaxies transformed into more quiescent, large spiral discs.

  20. Assessment of health impacts of decreased smoking prevalence in Copenhagen: Application of the DYNAMO-HIA model.

    Science.gov (United States)

    Holm, Astrid Ledgaard; Brønnum-Hansen, Henrik; Robinson, Kirstine Magtengaard; Diderichsen, Finn

    2014-07-01

    Tobacco smoking is among the leading risk factors for chronic disease and early death in developed countries, including Denmark, where smoking causes 14% of the disease burden. In Denmark, many public health interventions, including smoking prevention, are undertaken by the municipalities, but models to estimate potential health effects of local interventions are lacking. The aim of the current study was to model the effects of decreased smoking prevalence in Copenhagen, Denmark. The DYNAMO-HIA model was applied to the population of Copenhagen, by using health survey data and data from Danish population registers. We modelled the effects of four intervention scenarios aimed at different target groups, compared to a reference scenario. The potential effects of each scenario were modelled until 2040. A combined scenario affecting both initiation rates among youth, and cessation and re-initiation rates among adults, which reduced the smoking prevalence to 4% by 2025, would have large beneficial effects on incidence and prevalence of smoking-related diseases and mortality. Health benefits could also be obtained through interventions targeting only cessation or re-initiation rates, whereas an intervention targeting only initiation among youth had marginal effects on morbidity and mortality within the modelled time frame. By modifying the DYNAMO-HIA model, we were able to estimate the potential health effects of four interventions to reduce smoking prevalence in the population of Copenhagen. The effect of the interventions on future public health depended on population subgroup(s) targeted, duration of implementation and intervention reach. © 2014 the Nordic Societies of Public Health.

  1. Predicting the health impact of lowering salt consumption in Turkey using the DYNAMO health impact assessment tool.

    Science.gov (United States)

    Erkoyun, E; Sözmen, K; Bennett, K; Unal, B; Boshuizen, H C

    2016-11-01

    To estimate the impact of three daily salt consumption scenarios on the prevalence and incidence of ischaemic heart disease (IHD) and cerebrovascular disease in 2025 in the Turkish population aged ≥30 years using the DYNAMO Health Impact Assessment tool. Statistical disease modelling study. DYNAMO health impact assessment was populated using data from Turkey to estimate the prevalence and incidence of IHD and cerebrovascular disease in 2025. TurkSTAT data were used for demographic data, and national surveys were used for salt consumption and disease-specific burden. Three salt consumption scenarios were modelled: (1) reference scenario: mean salt consumption stays the same from 2012-2013 until 2025; (2) gradual decline: daily salt intake reduces steadily by 0.47 g per year by lowering salt intake from bread by 50% and from table salt by 40% by 2025; and (3) World Health Organization (WHO) advice: daily salt intake of 5 g per day from 2013 until 2025. The gradual decline scenario would lead to a decrease in the prevalence of IHD and cerebrovascular disease by 0.3% and 0.2%, respectively, and a decrease in the incidence by 0.6 and 0.4 per 1000, respectively. Following WHO's advice would lead to a decrease in the prevalence of IHD and cerebrovascular disease by 0.8% and 0.5%, respectively, and a decrease in the incidence by 1.0 and 0.7 per 1000, respectively. This model indicates that Turkey can lower its future cardiovascular disease burden by following the gradual decline scenario. Following WHO's advice would achieve an even greater benefit. Copyright © 2016 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.

  2. A gray-box DPDA-based intrusion detection technique using system-call monitoring

    NARCIS (Netherlands)

    Jafarian, Jafar Haadi; Abbasi, Ali; Safaei Sheikhabadi, Siavash

    2011-01-01

    In this paper, we present a novel technique for automatic and efficient intrusion detection based on learning program behaviors. Program behavior is captured in terms of issued system calls augmented with point-of-system-call information, and is modeled according to an efficient deterministic

  3. Bonobos extract meaning from call sequences.

    Directory of Open Access Journals (Sweden)

    Zanna Clay

    Full Text Available Studies on language-trained bonobos have revealed their remarkable abilities in representational and communication tasks. Surprisingly, however, corresponding research into their natural communication has largely been neglected. We address this issue with a first playback study on the natural vocal behaviour of bonobos. Bonobos produce five acoustically distinct call types when finding food, which they regularly mix together into longer call sequences. We found that individual call types were relatively poor indicators of food quality, while context specificity was much greater at the call sequence level. We therefore investigated whether receivers could extract meaning about the quality of food encountered by the caller by integrating across different call sequences. We first trained four captive individuals to find two types of foods, kiwi (preferred and apples (less preferred at two different locations. We then conducted naturalistic playback experiments during which we broadcasted sequences of four calls, originally produced by a familiar individual responding to either kiwi or apples. All sequences contained the same number of calls but varied in the composition of call types. Following playbacks, we found that subjects devoted significantly more search effort to the field indicated by the call sequence. Rather than attending to individual calls, bonobos attended to the entire sequences to make inferences about the food encountered by a caller. These results provide the first empirical evidence that bonobos are able to extract information about external events by attending to vocal sequences of other individuals and highlight the importance of call combinations in their natural communication system.

  4. McNamara calls for action now.

    Science.gov (United States)

    1992-05-01

    Robert McNamara outlined a 6 point global family planning (FP) program he designed to expand FP services to answer unmet need. The plan calls for Fp spending to increase to US$8 billion by 2000. For the US this would mean an increase from US$800 million to US$3.5 billion. This amount is very, very small compared to the total amount spent on official development assistance projected for Organization for Economic Cooperation and Development (OECD) countries. It is easily within the capabilities of OECD countries to meet this goal. The plan would develop a system in which the World Bank and the UNFPA would work together with each developing country to establish population target levels. The World Bank would assume responsibility for organizing external financing and serve as a last resort source of financing. Japan must also begin to take a leadership role more in line with its economic power. Currently it spends only .32% of its GNP to aid developing countries, despite the fact that its per capita income is 20% larger than any other OECD member. This means raising spending form US$9 billion to US$14.5 billion. This could be done easily by raising it US$500 million/year and planning to increase this US$1 billion by 2000.

  5. Generation of Electrojets in Weakly Ionized Plasmas through a Collisional Dynamo

    CERN Document Server

    Dimant, Yakov S; Fletcher, Alex C

    2016-01-01

    Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. This letter argues that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for electrojet formation, $\

  6. Synchronization and Electronic Circuit Application of Hidden Hyperchaos in a Four-Dimensional Self-Exciting Homopolar Disc Dynamo without Equilibria

    Directory of Open Access Journals (Sweden)

    Yu Feng

    2017-01-01

    Full Text Available We introduce and investigate a four-dimensional hidden hyperchaotic system without equilibria, which is obtained by augmenting the three-dimensional self-exciting homopolar disc dynamo due to Moffatt with an additional control variable. Synchronization of two such coupled disc dynamo models is investigated by active control and sliding mode control methods. Numerical integrations show that sliding mode control provides a better synchronization in time but causes chattering. The solution is obtained by switching to active control when the synchronization errors become very small. In addition, the electronic circuit of the four-dimensional hyperchaotic system has been realized in ORCAD-PSpice and on the oscilloscope by amplitude values, verifying the results from the numerical experiments.

  7. Educación de calle

    OpenAIRE

    Aguado Alonso, Carmen María

    2014-01-01

    Los cambios que está sufriendo nuestra sociedad generan nuevas realidades sociales y nuevos métodos de socialización modificando nuestro entorno. Uno de los principales lugares donde ocurre esto es en la calle. La Calle tiene un potencial educativo muy valioso. En ocasiones puede ser utilizado para “des - educar”, olvidado por instituciones sociales, políticas y educativas. Es importante que la Calle se convierta en un espacio de socialización educativa. La Calle tiene un pa...

  8. Call Duration Characteristics based on Customers Location

    Directory of Open Access Journals (Sweden)

    Žvinys Karolis

    2014-05-01

    Full Text Available Nowadays a lot of different researches are performed based on call duration distributions (CDD analysis. However, the majority of studies are linked with social relationships between the people. Therefore the scarcity of information, how the call duration is associated with a user's location, is appreciable. The goal of this paper is to reveal the ties between user's voice call duration and the location of call. For this reason we analyzed more than 5 million calls from real mobile network, which were made over the base stations located in rural areas, roads, small towns, business and entertainment centers, residential districts. According to these site types CDD’s and characteristic features for call durations are given and discussed. Submitted analysis presents the users habits and behavior as a group (not an individual. The research showed that CDD’s of customers being them in different locations are not equal. It has been found that users at entertainment, business centers are tend to talk much shortly, than people being at home. Even more CDD can be distorted strongly, when machinery calls are evaluated. Hence to apply a common CDD for a whole network it is not recommended. The study also deals with specific parameters of call duration for distinguished user groups, the influence of network technology for call duration is considered.

  9. Time series modeling of daily abandoned calls in a call centre ...

    African Journals Online (AJOL)

    Models for evaluating and predicting the short periodic time series in daily abandoned calls in a call center are developed. Abandonment of calls due to impatient is an identified problem among most call centers. The two competing models were derived using Fourier series and the Box and Jenkins modeling approaches.

  10. Chemotherapeutic Impact on Pain and Global Health-Related Quality of Life in Hormone-Refractory Prostate Cancer: Dynamically Modified Outcomes Analysis (DYNAMO) of a Randomized Controlled Trial

    Science.gov (United States)

    Moinpour, Carol M.; Donaldson, Gary W.; Nakamura, Yoshio

    2010-01-01

    Purpose This paper applies the Dynamically Modified Outcomes (DYNAMO) model to a clinical trial of two chemotherapeutic regimens on global health-related quality of life (GHRQL) in hormone-refractory prostate cancer. Methods DYNAMO identifies the causal influences operating in a clinical trial and their mediation, moderation, and modulation by uncontrolled variables. Southwest Oncology Group Trial S9916 randomized assignment to mitoxantrone plus prednisone (M+P) versus docetaxel plus estramustine (D+E) treatments. In this application, we examine baseline-adjusted impacts of Worst Pain (McGill Pain Questionnaire) on GHRQL (EORTC Quality of Life Questionnaire-C30)at 10 weeks. Results Average treatment levels of Pain did not differ, hence the average mediated effect of treatment on GHRQL was zero. Nonetheless, M+P reduced the impact (the relational outcome) of Pain on GHRQL by 54% relative to D+E. Individual variation in the relational outcome (modulation) was of the same magnitude as the average difference between arms. Performance status moderated the direct effects of treatment, with D+E more effective in good, but not poor, performance strata. Conclusions The DYNAMO approach comprehensively accounted for treatment effects. Rather than a single average effect, there were three distinct treatment effects: one direct effect for each performance status level, and a direct effect on the relationship between pain and GHRQL. PMID:19130298

  11. Answering the "Call of the Mountain"

    NARCIS (Netherlands)

    Chaves Villegas, Martha

    2016-01-01

    In response to the age of the ‘anthropocene,’ as some authors are calling this epoch in which one single species is disrupting major natural systems (Steffen et al 2011), there are calls for more radical, learning-based sustainability that generates deep transformations in individuals

  12. Kindness Curbs Kids' Name-Calling

    Science.gov (United States)

    Saxon, Rebekah

    2005-01-01

    In this article, the author discusses the impact of name-calling towards the student's academic performance and emotions and cites some measures on how should teachers address this problem in order to facilitate effective learning among students. Psychologists recognize that name-calling and other forms of verbal bullying and harassment are more…

  13. 17 CFR 31.18 - Margin calls.

    Science.gov (United States)

    2010-04-01

    ... 17 Commodity and Securities Exchanges 1 2010-04-01 2010-04-01 false Margin calls. 31.18 Section 31....18 Margin calls. (a) No leverage transaction merchant shall liquidate a leverage contract because of a margin deficiency without effecting personal contact with the leverage customer. If a leverage...

  14. Help Options in CALL: A Systematic Review

    Science.gov (United States)

    Cardenas-Claros, Monica S.; Gruba, Paul A.

    2009-01-01

    This paper is a systematic review of research investigating help options in the different language skills in computer-assisted language learning (CALL). In this review, emerging themes along with is-sues affecting help option research are identified and discussed. We argue that help options in CALL are application resources that do not only seem…

  15. 78 FR 21891 - Rural Call Completion

    Science.gov (United States)

    2013-04-12

    ... one of two proposed safe harbor provisions. We also propose to prohibit both originating and... these proposed rules, particularly for originating providers whose call-routing practices do not appear... in presentations at the Commission's October 18, 2011 workshop on rural call routing and termination...

  16. Call Admission Control in Mobile Cellular Networks

    CERN Document Server

    Ghosh, Sanchita

    2013-01-01

    Call Admission Control (CAC) and Dynamic Channel Assignments (DCA) are important decision-making problems in mobile cellular communication systems. Current research in mobile communication considers them as two independent problems, although the former greatly depends on the resulting free channels obtained as the outcome of the latter. This book provides a solution to the CAC problem, considering DCA as an integral part of decision-making for call admission. Further, current technical resources ignore movement issues of mobile stations and fluctuation in network load (incoming calls) in the control strategy used for call admission. In addition, the present techniques on call admission offers solution globally for the entire network, instead of considering the cells independently.      CAC here has been formulated by two alternative approaches. The first approach aimed at handling the uncertainty in the CAC problem by employing fuzzy comparators.  The second approach is concerned with formulation of CAC ...

  17. Source levels of foraging humpback whale calls.

    Science.gov (United States)

    Fournet, Michelle E H; Matthews, Leanna P; Gabriele, Christine M; Mellinger, David K; Klinck, Holger

    2018-02-01

    Humpback whales produce a wide range of low- to mid-frequency vocalizations throughout their migratory range. Non-song "calls" dominate this species' vocal repertoire while on high-latitude foraging grounds. The source levels of 426 humpback whale calls in four vocal classes were estimated using a four-element planar array deployed in Glacier Bay National Park and Preserve, Southeast Alaska. There was no significant difference in source levels between humpback whale vocal classes. The mean call source level was 137 dB RMS re 1 μPa @ 1 m in the bandwidth of the call (range 113-157 dB RMS re 1 μPa @ 1 m), where bandwidth is defined as the frequency range from the lowest to the highest frequency component of the call. These values represent a robust estimate of humpback whale source levels on foraging grounds and should append earlier estimates.

  18. Call Cultures in Orang-Utans?

    Science.gov (United States)

    Wich, Serge A.; Nater, Alexander; Arora, Natasha; Bastian, Meredith L.; Meulman, Ellen; Morrogh-Bernard, Helen C.; Atmoko, S. Suci Utami; Pamungkas, Joko; Perwitasari-Farajallah, Dyah; Hardus, Madeleine E.; van Noordwijk, Maria; van Schaik, Carel P.

    2012-01-01

    Background Several studies suggested great ape cultures, arguing that human cumulative culture presumably evolved from such a foundation. These focused on conspicuous behaviours, and showed rich geographic variation, which could not be attributed to known ecological or genetic differences. Although geographic variation within call types (accents) has previously been reported for orang-utans and other primate species, we examine geographic variation in the presence/absence of discrete call types (dialects). Because orang-utans have been shown to have geographic variation that is not completely explicable by genetic or ecological factors we hypothesized that this will be similar in the call domain and predict that discrete call type variation between populations will be found. Methodology/Principal Findings We examined long-term behavioural data from five orang-utan populations and collected fecal samples for genetic analyses. We show that there is geographic variation in the presence of discrete types of calls. In exactly the same behavioural context (nest building and infant retrieval), individuals in different wild populations customarily emit either qualitatively different calls or calls in some but not in others. By comparing patterns in call-type and genetic similarity, we suggest that the observed variation is not likely to be explained by genetic or ecological differences. Conclusion/Significance These results are consistent with the potential presence of ‘call cultures’ and suggest that wild orang-utans possess the ability to invent arbitrary calls, which spread through social learning. These findings differ substantially from those that have been reported for primates before. First, the results reported here are on dialect and not on accent. Second, this study presents cases of production learning whereas most primate studies on vocal learning were cases of contextual learning. We conclude with speculating on how these findings might assist in bridging

  19. Call cultures in orang-utans?

    Directory of Open Access Journals (Sweden)

    Serge A Wich

    Full Text Available BACKGROUND: Several studies suggested great ape cultures, arguing that human cumulative culture presumably evolved from such a foundation. These focused on conspicuous behaviours, and showed rich geographic variation, which could not be attributed to known ecological or genetic differences. Although geographic variation within call types (accents has previously been reported for orang-utans and other primate species, we examine geographic variation in the presence/absence of discrete call types (dialects. Because orang-utans have been shown to have geographic variation that is not completely explicable by genetic or ecological factors we hypothesized that this will be similar in the call domain and predict that discrete call type variation between populations will be found. METHODOLOGY/PRINCIPAL FINDINGS: We examined long-term behavioural data from five orang-utan populations and collected fecal samples for genetic analyses. We show that there is geographic variation in the presence of discrete types of calls. In exactly the same behavioural context (nest building and infant retrieval, individuals in different wild populations customarily emit either qualitatively different calls or calls in some but not in others. By comparing patterns in call-type and genetic similarity, we suggest that the observed variation is not likely to be explained by genetic or ecological differences. CONCLUSION/SIGNIFICANCE: These results are consistent with the potential presence of 'call cultures' and suggest that wild orang-utans possess the ability to invent arbitrary calls, which spread through social learning. These findings differ substantially from those that have been reported for primates before. First, the results reported here are on dialect and not on accent. Second, this study presents cases of production learning whereas most primate studies on vocal learning were cases of contextual learning. We conclude with speculating on how these findings might

  20. Call-Center Based Disease Management of Pediatric Asthmatics

    Science.gov (United States)

    2006-04-01

    Cagnani CE. Allergic rhinitis and asthma in children: disease management and outcomes. Current Allergy & Asthma Reports. 1(6):515-22, 2001. 58. Chan...of Pediatric Asthmatics PRINCIPAL INVESTIGATOR: James M. Quinn, M.D. CONTRACTING ORGANIZATION: The Geneva Foundation...CONTRACT NUMBER Call-Center Based Disease Management of Pediatric Asthmatics 5b. GRANT NUMBER DAMD17-02-1-0182 5c. PROGRAM ELEMENT NUMBER 6

  1. X-Ray and Optical Variations in the Classical Be Star γ Cassiopeia: The Discovery of a Possible Magnetic Dynamo

    Science.gov (United States)

    Robinson, Richard D.; Smith, Myron A.; Henry, Gregory W.

    2002-08-01

    The classical B0.5e star γ Cassiopeia is known to be a unique X-ray source by virtue of its moderate LX (1033 ergs s-1), hard X-ray spectrum, and light curve punctuated by ubiquitous flares and slow undulations. The peculiarities of this star have led to a controversy concerning the origin of these emissions: whether they are from wind infall onto a putative degenerate companion, as in the case of normal Be/X-ray binaries, or from the Be star itself. Recently, much progress has been made to resolve this question: (1) the discovery that γ Cas is a moderately eccentric binary system (P=203.59 days) with unknown secondary type, (2) the addition of RXTE observations at six epochs in 2000, adding to three others in 1996-1998, and (3) the collation of robotic telescope (Automated Photometric Telescope) B- and V-band photometric observations over four seasons that show a 3%, cyclical flux variation with cycle lengths of 55-93 days. We find that X-ray fluxes at all nine epochs show random variations with orbital phase, thereby contradicting the binary accretion model, which predicts a substantial modulation. However, these fluxes correlate well with the cyclical optical variations. In particular, the six flux measurements in 2000, which vary by a factor of 3, closely track the interpolated optical variations between the 2000 and 2001 observing seasons. The energy associated with the optical variations greatly exceeds the energy in the X-rays, so that the optical variability cannot simply be due to reprocessing of X-ray flux. However, the strong correlation between the two suggests that they are driven by a common mechanism. We propose that this mechanism is a cyclical magnetic dynamo excited by a Balbus-Hawley instability located within the inner part of the circumstellar disk. According to our model, variations in the field strength directly produce the changes in the magnetically related X-ray activity. Turbulence associated with the dynamo results in changes to the

  2. External GSM phone calls now made simpler

    CERN Multimedia

    2007-01-01

    On 2 July, the IT/CS Telecom Service introduced a new service making external calls from CERN GSM phones easier. A specific prefix is no longer needed for calls outside CERN. External calls from CERN GSM phones are to be simplified. It is no longer necessary to use a special prefix to call an external number from the CERN GSM network.The Telecom Section of the IT/CS Group is introducing a new system that will make life easier for GSM users. It is no longer necessary to use a special prefix (333) to call an external number from the CERN GSM network. Simply dial the number directly like any other Swiss GSM customer. CERN currently has its own private GSM network with the Swiss mobile operator, Sunrise, covering the whole of Switzerland. This network was initially intended exclusively for calls between CERN numbers (replacing the old beeper system). A special system was later introduced for external calls, allowing them to pass thr...

  3. Attitude of Farmers towards Kisan Call Centres

    Directory of Open Access Journals (Sweden)

    Shely Mary Koshy

    2017-09-01

    Full Text Available The present study was conducted to measure the attitude of farmers in Kerala, India towards Kisan Call Centre (KCC. Kisan Call Centre provides free agricultural advisory services to every citizen involved in agriculture through a toll free number. One hundred and fifty farmers who have utilized the Kisan Call Centre service were selected from the database of KCC. The results showed that the respondents had moderately favourable attitude towards KCC followed by highly favourable attitude. The variables digital divide, temporal awareness on KCC, satisfaction towards KCC and utilization of KCC were found to have a positive correlation with the attitude of respondents towards KCC.

  4. Role of boundary conditions in helicoidal flow collimation: Consequences for the von Kármán sodium dynamo experiment.

    Science.gov (United States)

    Varela, J; Brun, S; Dubrulle, B; Nore, C

    2015-12-01

    We present hydrodynamic and magnetohydrodynamic (MHD) simulations of liquid sodium flow with the PLUTO compressible MHD code to investigate influence of magnetic boundary conditions on the collimation of helicoidal motions. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multiblades impeller inspired by those used in the Von-Kármán-sodium (VKS) experiment. We show that the impinging of the large-scale flow upon the impeller generates a coherent helicoidal vortex inside the blades, located at a distance from the upstream blade piloted by the incident angle of the flow. This vortex collimates any existing magnetic field lines leading to an enhancement of the radial magnetic field that is stronger for ferromagnetic than for conducting blades. The induced magnetic field modifies locally the velocity fluctuations, resulting in an enhanced helicity. This process possibly explains why dynamo action is more easily triggered in the VKS experiment when using soft iron impellers.

  5. Moist Process Biases in Simulations of the Madden–Julian Oscillation Episodes Observed during the AMIE/DYNAMO Field Campaign

    Energy Technology Data Exchange (ETDEWEB)

    Hagos, Samson M.; Feng, Zhe; Burleyson, Casey D.; Zhao, Chun; Martini, Matus N.; Berg, Larry K.

    2016-02-01

    Two Madden-Julian Oscillation (MJO) episodes observed during the 2011 AMIE/DYNAMO field campaign are simulated using a regional cloud-permitting model, a regional model with various cumulus parameterizations, and a global variable-resolution model with a high-resolution region centered over the tropical Indian Ocean. Model biases associated with moisture mode instability, wind-induced surface heat exchange (WISHE), and convective momentum transport (CMT) are examined and their relative contributions to the overall model errors are quantified using a linear statistical model. Linear relationships are found among the normalized root mean square errors of precipitation, saturation fraction, evaporation, and surface wind speed suggesting that errors may propagate across the processes involving these variables. Analysis using a linear statistical model shows the relationship between convection and local surface wind speed (related to CMT processes) is the source of the largest uncertainty. In comparison, WISHE processes in the simulations tend to be biased consistently, with excess evaporation for the same wind speeds as the observations, which suggests they are likely related to biases in boundary layer and/or surface schemes. The relationship between precipitation and saturation fraction (which is associated with moisture mode instability) is captured relatively well with slightly larger model precipitation in the simulations in comparison to observations for the same saturation fraction, especially for weak rain rates. By linking developments in theoretical understanding of MJO processes and cumulus parameterizations, this study provides guidance to future improvements of MJO simulation by in high-resolution regional and global models.

  6. Where Do Data Go When They Die? Attaining Data Salvation Through the Establishment of a Solar Dynamo Dataverse

    Science.gov (United States)

    Munoz-Jaramillo, Andres

    2016-05-01

    The arrival of a highly interconnected digital age with practically limitless data storage capacity has brought with it a significant shift in which scientific data is stored and distributed (i.e. from being in the hands of a small group of scientists to being openly and freely distributed for anyone to use). However, the vertiginous speed at which hardware, software, and the nature of the internet changes has also sped up the rate at which data is lost due to formatting obsolescence and loss of access.This poster is meant to advertise the creation of a highly permanent data repository (within the context of Harvard's Dataverse), curated to contain datasets of high relevance for the study, and prediction of the solar dynamo, solar cycle, and long-term solar variability. This repository has many advantages over traditional data storage like the assignment of unique DOI identifiers for each database (making it easier for scientist to directly cite them), and the automatic versioning of each database so that all data are able to attain salvation.

  7. Mourning Dove Call-count Survey

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The Mourning Dove (Zenaida macroura) Call-Count Survey was developed to provide an index to population size and to detect annual changes in mourning dove breeding...

  8. Evaluating erroneous offside calls in soccer

    OpenAIRE

    H?ttermann, Stefanie; No?l, Benjamin; Memmert, Daniel

    2017-01-01

    The ability to simultaneously attend to multiple objects declines with increases in the visual angle separating distant objects. We explored whether these laboratory-measured limits on visual attentional spread generalize to a real life context: offside calls by soccer assistant referees. We coded all offside calls from a full year of first division German soccer matches. By determining the x-y coordinates of the relevant players and assistant referee on the soccer field we were able to calcu...

  9. Partition Decomposition for Roll Call Data

    CERN Document Server

    Leibon, Greg; Rockmore, Daniel N; Savell, Robert

    2011-01-01

    In this paper we bring to bear some new tools from statistical learning on the analysis of roll call data. We present a new data-driven model for roll call voting that is geometric in nature. We construct the model by adapting the "Partition Decoupling Method," an unsupervised learning technique originally developed for the analysis of families of time series, to produce a multiscale geometric description of a weighted network associated to a set of roll call votes. Central to this approach is the quantitative notion of a "motivation," a cluster-based and learned basis element that serves as a building block in the representation of roll call data. Motivations enable the formulation of a quantitative description of ideology and their data-dependent nature makes possible a quantitative analysis of the evolution of ideological factors. This approach is generally applicable to roll call data and we apply it in particular to the historical roll call voting of the U.S. House and Senate. This methodology provides a...

  10. An automated device for provoking and capturing wildlife calls

    Science.gov (United States)

    Ausband, David E.; Skrivseth, Jesse; Mitchell, Michael S.

    2011-01-01

    Some animals exhibit call-and-response behaviors that can be exploited to facilitate detection. Traditionally, acoustic surveys that use call-and-respond techniques have required an observer's presence to perform the broadcast, record the response, or both events. This can be labor-intensive and may influence animal behavior and, thus, survey results. We developed an automated acoustic survey device using commercially available hardware (e.g., laptop computer, speaker, microphone) and an author-created (JS) software program ("HOOT") that can be used to survey for any animal that calls. We tested this device to determine 1) deployment longevity, 2) effective sampling area, and 3) ability to detect known packs of gray wolves (Canis lupus) in Idaho, USA. Our device was able to broadcast and record twice daily for 6–7 days using the internal computer battery and surveyed an area of 3.3–17.5 km2 in relatively open habitat depending on the hardware components used. We surveyed for wolves at 2 active rendezvous sites used by closely monitored, radiocollared wolf packs and obtained 4 responses across both packs over 3 days of sampling. We confirmed reproduction in these 2 packs by detecting pup howls aurally from the resulting device recordings. Our device can broadcast and record animal calls and the computer software is freely downloadable. This automated survey device can be used to collect reliable data while reducing the labor costs traditionally associated with acoustic surveys.

  11. CALL Evaluation: Students' Perception and Use of LoMasTv

    Science.gov (United States)

    Pardo-Ballester, Cristina

    2012-01-01

    In order to integrate technology into the language curriculum, it is essential not only to evaluate a program within a second language acquisition (SLA) framework but also to seek the students' attitudes towards the use of computer-assisted language learning (CALL) materials. Guided by Chapelle's (2001) framework for CALL evaluation, this paper…

  12. An Evaluation Study of a CALL Application: With BELT or without BELT

    Science.gov (United States)

    Genc, Humeyra

    2012-01-01

    The present study tried to evaluate the 6th grade students' attitudes towards the use of a CALL program which is called BELT Success used in English language learning course in a private school, the relationship to students' attitudes to their English language proficiency level, and finally teachers` experiences and opinions towards the use of…

  13. Hourly associations between heat and ambulance calls.

    Science.gov (United States)

    Guo, Yuming

    2017-01-01

    The response speed of ambulance calls is very crucial to rescue patients suffering immediately life threatening conditions. The serious health outcomes might be caused by exposing to extreme heat only several hours before. However, limited evidence is available on this topic. This study aims to examine the hourly association between heat and ambulance calls, to improve the ambulance services and to better protect health. Hourly data on ambulance calls for non-accidental causes, temperature and air pollutants (PM10, NO2, and O3) were collected from Brisbane, Australia, during 2001 and 2007. A time-stratified case-crossover design was used to examine the associations between hourly ambulance calls and temperature during warm season (Nov, Dec, Jan, Feb, and Mar), while adjusting for potential confounders. Stratified analyses were performed for sex and age groups. Ambulance calls peaked at 10am for all groups, except those aged 27 °C) increase the demands of ambulance. This information is helpful to increase the efficiency of ambulance service then save lives, for example, preparing more ambulance before appearance of extremely hot temperature in combination with weather forecast. Also, people should better arrange their time for outdoor activities to avoid exposing to extreme hot temperatures. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. Automated detection of Antarctic blue whale calls.

    Science.gov (United States)

    Socheleau, Francois-Xavier; Leroy, Emmanuelle; Pecci, Andres Carvallo; Samaran, Flore; Bonnel, Julien; Royer, Jean-Yves

    2015-11-01

    This paper addresses the problem of automated detection of Z-calls emitted by Antarctic blue whales (B. m. intermedia). The proposed solution is based on a subspace detector of sigmoidal-frequency signals with unknown time-varying amplitude. This detection strategy takes into account frequency variations of blue whale calls as well as the presence of other transient sounds that can interfere with Z-calls (such as airguns or other whale calls). The proposed method has been tested on more than 105 h of acoustic data containing about 2200 Z-calls (as found by an experienced human operator). This method is shown to have a correct-detection rate of up to more than 15% better than the extensible bioacoustic tool package, a spectrogram-based correlation detector commonly used to study blue whales. Because the proposed method relies on subspace detection, it does not suffer from some drawbacks of correlation-based detectors. In particular, it does not require the choice of an a priori fixed and subjective template. The analytic expression of the detection performance is also derived, which provides crucial information for higher level analyses such as animal density estimation from acoustic data. Finally, the detection threshold automatically adapts to the soundscape in order not to violate a user-specified false alarm rate.

  15. Restoring rape survivors: justice, advocacy, and a call to action.

    Science.gov (United States)

    Koss, Mary P

    2006-11-01

    Rape results in mental and physical health, social, and legal consequences. For the latter, restorative justice-based programs might augment community response, but they generate controversy among advocates and policy makers. This article identifies survivors' needs and existing community responses to them. Survivors feel their legal needs are most poorly met due to justice system problems that can be summarized as attrition, retraumatization, and disparate treatment across gender, class, and ethnic lines. Empirical data support each problem and the conclusion that present justice options are inadequate. The article concludes by identifying common ground in advocacy and restorative justice goals and calls for a holistic approach to the needs of rape survivors that includes advocating for expanded justice alternatives. A call to action is issued to implement restorative alternatives to expand survivor choice and offender accountability. Conventional and restorative justice are often viewed as mutually exclusive whereas the author argues they are complementary.

  16. Soft calls and broadcast calls in the corncrake as adaptations to short and long range communication.

    Science.gov (United States)

    Ręk, Paweł

    2013-10-01

    Because birds' acoustic signals function in antagonistic interactions between males and in female attraction, a majority of vocalisations are loud. In contrast, some birds, additionally produce soft vocalisations in escalated agonistic and sexual contexts. Nevertheless, the relationship between the acoustic parameters of such signals and their function is not clear. Here I investigate the sound transmission degradation properties of soft and broadcast (loud) calls in the corncrake using calls with natural and changed amplitude. I show that, if played at the same amplitude, the maximum limit for communication distance with soft calls was significantly shorter than that of broadcast calls, indicating that frequency structure is important in determining the range of both signals independently of their amplitude. At the same time, the values of excess attenuation were lower for soft calls than for broadcast calls at most distances, which suggests that the short transmission of soft calls is achieved mostly due to their low and narrow frequency ranges, promoting their masking by ambient noise. Finally, contrary to soft calls, changes in the energy of tails of echoes in broadcast calls were associated with the distance of propagation, which might be useful in assessing the distance to senders. I suggest that the acoustic structure of soft vocalisations can be used to limit the range of the signal, which might be helpful in eavesdropping avoidance, whereas broadcast calls are designed for long-range transmission. Copyright © 2013 Elsevier B.V. All rights reserved.

  17. Echolocation calls and communication calls are controlled differentially in the brainstem of the bat Phyllostomus discolor

    Directory of Open Access Journals (Sweden)

    Schuller Gerd

    2005-08-01

    Full Text Available Abstract Background Echolocating bats emit vocalizations that can be classified either as echolocation calls or communication calls. Neural control of both types of calls must govern the same pool of motoneurons responsible for vocalizations. Electrical microstimulation in the periaqueductal gray matter (PAG elicits both communication and echolocation calls, whereas stimulation of the paralemniscal area (PLA induces only echolocation calls. In both the PAG and the PLA, the current thresholds for triggering natural vocalizations do not habituate to stimuli and remain low even for long stimulation periods, indicating that these structures have relative direct access to the final common pathway for vocalization. This study intended to clarify whether echolocation calls and communication calls are controlled differentially below the level of the PAG via separate vocal pathways before converging on the motoneurons used in vocalization. Results Both structures were probed simultaneously in a single experimental approach. Two stimulation electrodes were chronically implanted within the PAG in order to elicit either echolocation or communication calls. Blockade of the ipsilateral PLA site with iontophoretically application of the glutamate antagonist kynurenic acid did not impede either echolocation or communication calls elicited from the PAG. However, blockade of the contralateral PLA suppresses PAG-elicited echolocation calls but not communication calls. In both cases the blockade was reversible. Conclusion The neural control of echolocation and communication calls seems to be differentially organized below the level of the PAG. The PLA is an essential functional unit for echolocation call control before the descending pathways share again the final common pathway for vocalization.

  18. Data acquisition in a high-speed rotating frame for New Mexico Institute of Mining and Technology liquid sodium αω dynamo experiment.

    Science.gov (United States)

    Si, Jiahe; Colgate, Stirling A; Li, Hui; Martinic, Joe; Westpfahl, David

    2013-10-01

    New Mexico Institute of Mining and Technology liquid sodium αω-dynamo experiment models the magnetic field generation in the universe as discussed in detail by Colgate, Li, and Pariev [Phys. Plasmas 8, 2425 (2001)]. To obtain a quasi-laminar flow with magnetic Reynolds number R(m) ~ 120, the dynamo experiment consists of two co-axial cylinders of 30.5 cm and 61 cm in diameter spinning up to 70 Hz and 17.5 Hz, respectively. During the experiment, the temperature of the cylinders must be maintained to 110 °C to ensure that the sodium remains fluid. This presents a challenge to implement a data acquisition (DAQ) system in such high temperature, high-speed rotating frame, in which the sensors (including 18 Hall sensors, 5 pressure sensors, and 5 temperature sensors, etc.) are under the centrifugal acceleration up to 376g. In addition, the data must be transmitted and stored in a computer 100 ft away for safety. The analog signals are digitized, converted to serial signals by an analog-to-digital converter and a field-programmable gate array. Power is provided through brush/ring sets. The serial signals are sent through ring/shoe sets capacitively, then reshaped with cross-talk noises removed. A microcontroller-based interface circuit is used to decode the serial signals and communicate with the data acquisition computer. The DAQ accommodates pressure up to 1000 psi, temperature up to more than 130 °C, and magnetic field up to 1000 G. First physics results have been analyzed and published. The next stage of the αω-dynamo experiment includes the DAQ system upgrade.

  19. Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

    Science.gov (United States)

    Varela, J.; Brun, S.; Dubrulle, B.; Nore, C.

    2017-05-01

    We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Kármán-Sodium dynamo experiment. The aim of the study is to analyze the influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified Cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Kármán-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbers between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically, the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and the impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and the impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller compared to a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.

  20. Assessing Health Impacts of Pictorial Health Warning Labels on Cigarette Packs in Korea Using DYNAMO-HIA.

    Science.gov (United States)

    Kang, Eunjeong

    2017-07-01

    This study aimed to predict the 10-year impacts of the introduction of pictorial warning labels (PWLs) on cigarette packaging in 2016 in Korea for adults using DYNAMO-HIA. In total, four scenarios were constructed to better understand the potential health impacts of PWLs: two for PWLs and the other two for a hypothetical cigarette tax increase. In both policies, an optimistic and a conservative scenario were constructed. The reference scenario assumed the 2015 smoking rate would remain the same. Demographic data and epidemiological data were obtained from various sources. Differences in the predicted smoking prevalence and prevalence, incidence, and mortality from diseases were compared between the reference scenario and the four policy scenarios. It was predicted that the optimistic PWLs scenario (PWO) would lower the smoking rate by 4.79% in males and 0.66% in females compared to the reference scenario in 2017. However, the impact on the reduction of the smoking rate was expected to diminish over time. PWO will prevent 85 238 cases of diabetes, 67 948 of chronic obstructive pulmonary disease, 31 526 of ischemic heart disease, 21 036 of lung cancer, and 3972 prevalent cases of oral cancer in total over the 10-year span due to the reductions in smoking prevalence. The impacts of PWO are expected to be between the impact of the optimistic and the conservative cigarette tax increase scenarios. The results were sensitive to the transition probability of smoking status. The introduction of PWLs in 2016 in Korea is expected reduce smoking prevalence and disease cases for the next 10 years, but regular replacements of PWLs are needed for persistent impacts.