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Sample records for underlying current sheet

  1. Plasma dynamics in current sheets

    International Nuclear Information System (INIS)

    Bogdanov, S.Yu.; Drejden, G.V.; Kirij, N.P.; AN SSSR, Leningrad

    1992-01-01

    Plasma dynamics in successive stages of current sheet evolution is investigated on the base of analysis of time-spatial variations of electron density and electrodynamic force fields. Current sheet formation is realized in a two-dimensional magnetic field with zero line under the action of relatively small initial disturbances (linear regimes). It is established that in the limits of the formed sheet is concentrated dense (N e ∼= 10 16 cm -3 ) (T i ≥ 100 eV, bar-Z i ≥ 2) hot pressure of which is balanced by the magnetic action of electrodynamic forces is carried out both plasma compression in the sheet limits and the acceleration along the sheet surface from a middle to narrow side edges

  2. Collisionless current sheet equilibria

    Science.gov (United States)

    Neukirch, T.; Wilson, F.; Allanson, O.

    2018-01-01

    Current sheets are important for the structure and dynamics of many plasma systems. In space and astrophysical plasmas they play a crucial role in activity processes, for example by facilitating the release of magnetic energy via processes such as magnetic reconnection. In this contribution we will focus on collisionless plasma systems. A sensible first step in any investigation of physical processes involving current sheets is to find appropriate equilibrium solutions. The theory of collisionless plasma equilibria is well established, but over the past few years there has been a renewed interest in finding equilibrium distribution functions for collisionless current sheets with particular properties, for example for cases where the current density is parallel to the magnetic field (force-free current sheets). This interest is due to a combination of scientific curiosity and potential applications to space and astrophysical plasmas. In this paper we will give an overview of some of the recent developments, discuss their potential applications and address a number of open questions.

  3. Ohm's law for a current sheet

    Science.gov (United States)

    Lyons, L. R.; Speiser, T. W.

    1985-01-01

    The paper derives an Ohm's law for single-particle motion in a current sheet, where the magnetic field reverses in direction across the sheet. The result is considerably different from the resistive Ohm's law often used in MHD studies of the geomagnetic tail. Single-particle analysis is extended to obtain a self-consistency relation for a current sheet which agrees with previous results. The results are applicable to the concept of reconnection in that the electric field parallel to the current is obtained for a one-dimensional current sheet with constant normal magnetic field. Dissipated energy goes directly into accelerating particles within the current sheet.

  4. Mars's magnetotail: Nature's current sheet laboratory

    Science.gov (United States)

    Artemyev, A. V.; Angelopoulos, V.; Halekas, J. S.; Runov, A.; Zelenyi, L. M.; McFadden, J. P.

    2017-05-01

    The configuration and stability of an important kinetic plasma structure, the current sheet, determine the efficiency of magnetic energy storage, release, and transport in surrounding plasmas. These properties depend on β (the ratio of plasma pressures to magnetic field pressures) and Mach number M (the ratio of bulk velocities to magnetosonic velocities). For the most investigated current sheet, the near-Earth magnetotail current sheet, these parameters fall within a relatively narrow range of values (high β, low M). To investigate current sheet behavior for a wider range of parameters, we explore current sheets in the magnetotail of Mars using Mars Atmosphere and Volatile Evolution (MAVEN) mission observations. We find that low-β, high-M current sheets are abundant in Mars's magnetotail, but high-β, low-M current sheets can also be found there. Low-β current sheets are nearly force-free, whereas high-M current sheets are balanced by a plasma flow gradient along the tail. We compare current sheet distributions in a (β,M) space for the Martian magnetotail, the near-Earth magnetotail (using Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission), and the distant magnetotail (using Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission). We also find that the pressure balance in the Martian magnetotail current sheet can occur by contributions from a wide range of ion species, or, in low beta cases, from field-aligned currents generation of a force-free magnetic field configuration. The Martian magnetotail is a natural laboratory where current sheet of various types can be found and investigated.

  5. Bifurcation of Jovian magnetotail current sheet

    Directory of Open Access Journals (Sweden)

    P. L. Israelevich

    2006-07-01

    Full Text Available Multiple crossings of the magnetotail current sheet by a single spacecraft give the possibility to distinguish between two types of electric current density distribution: single-peaked (Harris type current layer and double-peaked (bifurcated current sheet. Magnetic field measurements in the Jovian magnetic tail by Voyager-2 reveal bifurcation of the tail current sheet. The electric current density possesses a minimum at the point of the Bx-component reversal and two maxima at the distance where the magnetic field strength reaches 50% of its value in the tail lobe.

  6. Bifurcation of Jovian magnetotail current sheet

    Directory of Open Access Journals (Sweden)

    P. L. Israelevich

    2006-07-01

    Full Text Available Multiple crossings of the magnetotail current sheet by a single spacecraft give the possibility to distinguish between two types of electric current density distribution: single-peaked (Harris type current layer and double-peaked (bifurcated current sheet. Magnetic field measurements in the Jovian magnetic tail by Voyager-2 reveal bifurcation of the tail current sheet. The electric current density possesses a minimum at the point of the Bx-component reversal and two maxima at the distance where the magnetic field strength reaches 50% of its value in the tail lobe.

  7. Plasmoid Instability in Forming Current Sheets

    Science.gov (United States)

    Comisso, L.; Lingam, M.; Huang, Y.-M.; Bhattacharjee, A.

    2017-12-01

    The plasmoid instability has revolutionized our understanding of magnetic reconnection in astrophysical environments. By preventing the formation of highly elongated reconnection layers, it is crucial in enabling the rapid energy conversion rates that are characteristic of many astrophysical phenomena. Most previous studies have focused on Sweet-Parker current sheets, which are unattainable in typical astrophysical systems. Here we derive a general set of scaling laws for the plasmoid instability in resistive and visco-resistive current sheets that evolve over time. Our method relies on a principle of least time that enables us to determine the properties of the reconnecting current sheet (aspect ratio and elapsed time) and the plasmoid instability (growth rate, wavenumber, inner layer width) at the end of the linear phase. After this phase the reconnecting current sheet is disrupted and fast reconnection can occur. The scaling laws of the plasmoid instability are not simple power laws, and they depend on the Lundquist number (S), the magnetic Prandtl number (P m ), the noise of the system ({\\psi }0), the characteristic rate of current sheet evolution (1/τ ), and the thinning process. We also demonstrate that previous scalings are inapplicable to the vast majority of astrophysical systems. We explore the implications of the new scaling relations in astrophysical systems such as the solar corona and the interstellar medium. In both of these systems, we show that our scaling laws yield values for the growth rate, wavenumber, and aspect ratio that are much smaller than the Sweet-Parker-based scalings.

  8. Symmetry breaking bifurcations of a current sheet

    International Nuclear Information System (INIS)

    Parker, R.D.; Dewar, R.L.; Johnson, J.L.

    1988-08-01

    Using a time evolution code with periodic boundary conditions, the viscoresistive hydromagnetic equations describing an initially static, planar current sheet with large Lundquist number have been evolved for times long enough to reach a steady state. A cosh 2 x resistivity model was used. For long periodicity lengths, L p , the resistivity gradient drives flows which cause forced reconnection at X point current sheets. Using L p as a bifurcation parameter, two new symmetry breaking bifurcations were found - a transition to an asymmetric island chain with nonzero, positive or negative phase velocity, and a transition to a static state with alternating large and small islands. These states are reached after a complex transient behavior which involves a competition between secondary current sheet instability and coalescence. 31 refs., 6 figs

  9. Connections of Trapezoidal Sheets under Fire

    Directory of Open Access Journals (Sweden)

    P. Kallerová

    2009-01-01

    Full Text Available This paper describes two different experiments on connections of trapezoidal sheets under elevated temperatures. The first experiments were tensile tests carried out on four sets of tests with screwed connections under ambient and elevated temperatures. One diameter of self-drilling screws and three different thicknesses of trapezoidal sheets were used. The applied screws were without washers, or with sealed or steel washers. The second experiment was performed in a laboratory furnace to check the catenary action of a thin-walled trapezoidal sheet. The basic theory tested in this experiment was that in the first phase of the fire the sheet behaves as a simply supported beam, while in the second phase the load bearing is transferred by a tension membrane. These experiments will be used to develop a design model of connections at high temperatures. High fire resistance of the trapezoidal sheet, dependent on suitable design of the screwed connection to the bearing structure, was confirmed. The experiment with the simple beam also confirmed catenary action. 

  10. Magnetic configurations of the tilted current sheets in magnetotail

    Directory of Open Access Journals (Sweden)

    C. Shen

    2008-11-01

    Full Text Available In this research, the geometrical structures of tilted current sheet and tail flapping waves have been analysed based on multiple spacecraft measurements and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1 The magnetic field lines (MFLs in the tilted current sheet are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the equatorial plane, while the normal of the tilted current sheet leans severely to the dawn or dusk side. (2 The tilted current sheet may become very thin, the half thickness of its neutral sheet is generally much less than the minimum radius of the curvature of the MFLs. (3 In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4 In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1 RE, while the neutral sheet may be very thin, with its half thickness being several tenths of RE. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45°. The phase velocities of these flapping waves are several tens km/s, while their periods and wavelengths are several tens of minutes, and several earth radii, respectively. These tail flapping events generally last several hours and occur during quiet periods or periods of

  11. Disruption of magnetospheric current sheet by quasi-electrostatic field

    Directory of Open Access Journals (Sweden)

    W. W. Liu

    2009-05-01

    Full Text Available Recent observational evidence has indicated that local current sheet disruptions are excited by an external perturbation likely associated with the kinetic ballooning (KB instability initiating at the transition region separating the dipole- and tail-like geometries. Specifically a quasi-electrostatic field pointing to the neutral sheet was identified in the interval between the arrival of KB perturbation and local current disruption. How can such a field drive the local current sheet unstable? This question is considered through a fluid treatment of thin current sheet (TCS where the generalized Ohm's law replaces the frozen-in-flux condition. A perturbation with the wavevector along the current is applied, and eigenmodes with frequency much below the ion gyrofrequency are sought. We show that the second-order derivative of ion drift velocity along the thickness of the current sheet is a critical stability parameter. In an E-field-free Harris sheet in which the drift velocity is constant, the current sheet is stable against this particular mode. As the electrostatic field grows, however, potential for instability arises. The threshold of instability is identified through an approximate analysis of the theory. For a nominal current sheet half-thickness of 1000 km, the estimated instability threshold is E~4 mV/m. Numerical solutions indicate that the two-fluid theory gives growth rate and wave period consistent with observations.

  12. Kinetic Studies of Thin Current Sheets at Magnetosheath Jets

    Science.gov (United States)

    Eriksson, E.; Vaivads, A.; Khotyaintsev, Y. V.; Graham, D. B.; Yordanova, E.; Hietala, H.; Markidis, S.; Giles, B. L.; Andre, M.; Russell, C. T.; Le Contel, O.; Burch, J. L.

    2017-12-01

    In near-Earth space one of the most turbulent plasma environments is the magnetosheath (MSH) downstream of the quasi-parallel shock. The particle acceleration and plasma thermalization processes there are still not fully understood. Regions of strong localized currents are believed to play a key role in those processes. The Magnetospheric Multiscale (MMS) mission has sufficiently high cadence to study these processes in detail. We present details of studies of two different events that contain strong current regions inside the MSH downstream of the quasi-parallel shock. In both cases the shape of the current region is in the form of a sheet, however they show internal 3D structure on the scale of the spacecraft separation (15 and 20 km, respectively). Both current sheets have a normal magnetic field component different from zero indicating that the regions at the different sides of the current sheets are magnetically connected. Both current sheets are boundaries between two different plasma regions. Furthermore, both current sheets are observed at MSH jets. These jets are characterized by localized dynamic pressure being larger than the solar wind dynamic pressure. One current sheet does not seem to be reconnecting while the other shows reconnection signatures. Inside the non-reconnecting current sheet we observe locally accelerated electron beams along the magnetic field. At energies above the beam energy we observe a loss cone consistent with part of the hot MSH-like electrons escaping into the colder solar wind-like plasma. This suggests that the acceleration process within this current sheet is similar to the one that occurs at the bow shock, where electron beams and loss cones are also observed. Therefore, we conclude that electron beams observed in the MSH do not have to originate from the bow shock, but can also be generated locally inside the MSH. The reconnecting current sheet also shows signs of thermalization and electron acceleration processes that are

  13. Relation between current sheets and vortex sheets in stationary incompressible MHD

    Directory of Open Access Journals (Sweden)

    D. H. Nickeler

    2012-03-01

    Full Text Available Magnetohydrodynamic configurations with strong localized current concentrations and vortices play an important role in the dissipation of energy in space and astrophysical plasma. Within this work we investigate the relation between current sheets and vortex sheets in incompressible, stationary equilibria. For this approach it is helpful that the similar mathematical structure of magnetohydrostatics and stationary incompressible hydrodynamics allows us to transform static equilibria into stationary ones. The main control function for such a transformation is the profile of the Alfvén-Mach number MA, which is always constant along magnetic field lines, but can change from one field line to another. In the case of a global constant MA, vortices and electric current concentrations are parallel. More interesting is the nonlinear case, where MA varies perpendicular to the field lines. This is a typical situation at boundary layers like the magnetopause, heliopause, the solar wind flowing around helmet streamers and at the boundary of solar coronal holes. The corresponding current and vortex sheets show in some cases also an alignment, but not in every case. For special density distributions in 2-D, it is possible to have current but no vortex sheets. In 2-D, vortex sheets of field aligned-flows can also exist without strong current sheets, taking the limit of small Alfvén Mach numbers into account. The current sheet can vanish if the Alfvén Mach number is (almost constant and the density gradient is large across some boundary layer. It should be emphasized that the used theory is not only valid for small Alfvén Mach numbers MA MA ≲ 1. Connection to other theoretical approaches and observations and physical effects in space plasmas are presented. Differences in the various aspects of theoretical investigations of current sheets and vortex sheets are given.

  14. Local charge transport properties of hydrazine reduced monolayer graphene oxide sheets prepared under pressure condition

    DEFF Research Database (Denmark)

    Ryuzaki, Sou; Meyer, Jakob Abild Stengaard; Petersen, Søren Vermehren

    2014-01-01

    Charge transport properties of chemically reduced graphene oxide (RGO) sheets prepared by treatment with hydrazine were examined using conductive atomic force microscopy. The current-voltage (I-V) characteristics of monolayer RGO sheets prepared under atmospheric pressure followed an exponentially...... increase due to 2D variable-range hopping conduction through small graphene domains in an RGO sheet containing defect regions of residual sp3carbon clusters bonded to oxygen groups, whereas RGO sheets prepared in a closed container under moderate pressure showed linear I-V characteristics...... with a conductivity of 267.2-537.5S/m. It was found that the chemical reduction under pressure results in larger graphene domains (sp2networks) in the RGO sheets when compared to that prepared under atmospheric pressure, indicating that the present reduction of GO sheets under the pressure is one of the effective...

  15. Effects of electron pressure anisotropy on current sheet configuration

    International Nuclear Information System (INIS)

    Artemyev, A. V.; Angelopoulos, V.; Runov, A.; Vasko, I. Y.

    2016-01-01

    Recent spacecraft observations in the Earth's magnetosphere have demonstrated that the magnetotail current sheet can be supported by currents of anisotropic electron population. Strong electron currents are responsible for the formation of very thin (intense) current sheets playing the crucial role in stability of the Earth's magnetotail. We explore the properties of such thin current sheets with hot isotropic ions and cold anisotropic electrons. Decoupling of the motions of ions and electrons results in the generation of a polarization electric field. The distribution of the corresponding scalar potential is derived from the electron pressure balance and the quasi-neutrality condition. We find that electron pressure anisotropy is partially balanced by a field-aligned component of this polarization electric field. We propose a 2D model that describes a thin current sheet supported by currents of anisotropic electrons embedded in an ion-dominated current sheet. Current density profiles in our model agree well with THEMIS observations in the Earth's magnetotail.

  16. Phenomenological Model of Current Sheet Canting in Pulsed Electromagnetic Accelerators

    Science.gov (United States)

    Markusic, Thomas; Choueiri, E. Y.

    2003-01-01

    The phenomenon of current sheet canting in pulsed electromagnetic accelerators is the departure of the plasma sheet (that carries the current) from a plane that is perpendicular to the electrodes to one that is skewed, or tipped. Review of pulsed electromagnetic accelerator literature reveals that current sheet canting is a ubiquitous phenomenon - occurring in all of the standard accelerator geometries. Developing an understanding of current sheet canting is important because it can detract from the propellant sweeping capabilities of current sheets and, hence, negatively impact the overall efficiency of pulsed electromagnetic accelerators. In the present study, it is postulated that depletion of plasma near the anode, which results from axial density gradient induced diamagnetic drift, occurs during the early stages of the discharge, creating a density gradient normal to the anode, with a characteristic length on the order of the ion skin depth. Rapid penetration of the magnetic field through this region ensues, due to the Hall effect, leading to a canted current front ahead of the initial current conduction channel. In this model, once the current sheet reaches appreciable speeds, entrainment of stationary propellant replenishes plasma in the anode region, inhibiting further Hall-convective transport of the magnetic field; however, the previously established tilted current sheet remains at a fairly constant canting angle for the remainder of the discharge cycle, exerting a transverse J x B force which drives plasma toward the cathode and accumulates it there. This proposed sequence of events has been incorporated into a phenomenological model. The model predicts that canting can be reduced by using low atomic mass propellants with high propellant loading number density; the model results are shown to give qualitative agreement with experimentally measured canting angle mass dependence trends.

  17. Magnetoacoustic waves in diagnostics of the flare current sheets

    Science.gov (United States)

    Jelínek, P.; Karlický, M.

    2012-01-01

    Aims: To obtain diagnostics tools for solar flare current sheets, we numerically studied impulsively generated magnetoacoustic waves in the Harris current sheet. Methods: We used two-dimensional (2-D) magnetohydrodynamic (MHD) and wave dispersion models. Tests of these models were performed for waves in the density slab, where analytical solutions are known. In the MHD model, we solved the full set of ideal MHD equations by means of the modified two-step Lax-Wendroff algorithm. The initial perturbation was chosen to generate preferentially the fast sausage magnetoacoustic waves. To determine the dispersion characteristics of MHD waves in the Harris current sheet, we numerically solved the equation of plasma motions by means of the Runge-Kutta fourth order method together with the bisection iteration one. To establish some diagnostics of these waves and their corresponding flare current sheets, we used the wavelet analysis method. Results: We find that the results of tests of our 2-D MHD and wave dispersion models for the density slab are in good agreement with analytical results. We analyze the magnetoacoustic waves in the current sheet and compare them with those in the density slab. In both cases, for similar geometrical and plasma parameters, we find that wave trains were generated and propagated in a similar way. Their signals registered at selected locations of the Harris current sheet and density slab are also similar. Nevertheless, a dependence of the period of the magnetoacoustic waves on the width of the Harris current sheet differs from that for the density slab. The form of the wave front inside the current sheet similarly differs from that in the density slab. We find that the wavelet spectra of the signals of incoming magnetoacoustic waves at selected locations in the current sheet have the form of wavelet tadpoles. We distinguish that the form of these wavelet tadpoles becomes longer and the heads of the wavelet tadpoles are detected later in time as

  18. Current sheets and pressure anisotropy in the reconnection exhaust

    International Nuclear Information System (INIS)

    Le, A.; Karimabadi, H.; Roytershteyn, V.; Egedal, J.; Ng, J.; Scudder, J.; Daughton, W.; Liu, Y.-H.

    2014-01-01

    A particle-in-cell simulation shows that the exhaust during anti-parallel reconnection in the collisionless regime contains a current sheet extending 100 inertial lengths from the X line. The current sheet is supported by electron pressure anisotropy near the X line and ion anisotropy farther downstream. Field-aligned electron currents flowing outside the magnetic separatrices feed the exhaust current sheet and generate the out-of-plane, or Hall, magnetic field. Existing models based on different mechanisms for each particle species provide good estimates for the levels of pressure anisotropy. The ion anisotropy, which is strong enough to reach the firehose instability threshold, is also important for overall force balance. It reduces the outflow speed of the plasma

  19. Electrodynamic forces and plasma conductivity inside the current sheet

    International Nuclear Information System (INIS)

    Bogdanov, S.Yu.; Frank, A.G.; Markov, V.S.

    1985-01-01

    The process of accumulation and explosive release of magnetic energy was studied in a current sheet of plasma of a high-current linear discharge. The distribution of current density and of electrodynamic forces were measured and the time evolution of these quantities was determined. The evolution of the plasma conductivity was also obtained. The measured and calculated electrodynamic forces may explain the plasma acceleration up to the velocities about 3x10 4 m/s only near the sheet edges. (D.Gy.)

  20. Current disruptions in the near-earth neutral sheet region

    International Nuclear Information System (INIS)

    Liu, A.T.Y.; Anderson, B.J.; Takahashi, K.; Zanetti, L.J.; McEntire, R.W.; Potemra, T.A.; Lopez, R.E.; Klumpar, D.M.; Greene, E.M.; Strangeway, R.

    1992-01-01

    Observations from the Charge Composition Explorer in 1985 and 1986 revealed fifteen current disruption events in which the magnetic field fluctuations were large and their onsets coincided well with ground onsets of substorm expansion or intensification. Over the disruption interval, the local magnetic field can change by as much as a factor of ∼7. In general, the stronger the current buildup and the closer the neutral sheet, the larger the resultant field change. There is also a tendency for a larger subsequent enhancement in the AE index with a stronger current buildup prior to current disruption. For events with good pitch angle coverage and extended observation in the neutral sheet region the authors find that the particle pressure increases toward the disruption onset and decreases afterward. Just prior to disruption, either the total particle pressure is isotropic, or the perpendicular component (P perpendicular ) dominates the parallel component (P parallel ), the plasma beta is seen to be as high as ∼70, and the observed plasma pressure gradient at the neutral sheet is large along the tail axis. The deduced local current density associated with pressure gradient is ∼27-80 n/Am 2 and is ∼85-105 mA/m when integrated over the sheet thickness. They infer from these results that just prior to the onset of current disruption, (1) an extremely thin current sheet requiring P parallel > P perpendicular for stress balance does not develop at these distances, (2) the thermal ion orbits are in the chaotic or Speiser regime while the thermal electrons are in the adiabatic regime and, in one case, exhibit peaked fluxes perpendicular to the magnetic field, thus implying no electron orbit chaotization to possibly initiate ion tearing instability, and (3) the neutral sheet is in the unstable regime specified by the cross-field current instability

  1. Monitoring dc stray current corrosion at sheet pile structures

    NARCIS (Netherlands)

    Peelen, W.H.A.; Neeft, E.A.C.; Leegwater, G.; Kanten-Roos, W. van; Courage, W.M.G.

    2012-01-01

    Steel is discarded by railway owners as a material for underground structures near railway lines, due to uncertainty over increased corrosion by DC stray currents stemming from the traction power system. This paper presents a large scale field test in which stray currents interference of a sheet

  2. Current-sheet formation in incompressible electron magnetohydrodynamics

    DEFF Research Database (Denmark)

    Ruban, Victor P.

    2002-01-01

    The nonlinear dynamics of axisymmetric, as well as helical, frozen-in vortex structures is investigated by the Hamiltonian method in the framework of ideal incompressible electron magnetohydrodynamics. For description of current-sheet formation from a smooth initial magnetic field, local and nonl......The nonlinear dynamics of axisymmetric, as well as helical, frozen-in vortex structures is investigated by the Hamiltonian method in the framework of ideal incompressible electron magnetohydrodynamics. For description of current-sheet formation from a smooth initial magnetic field, local...... and nonlocal nonlinear approximations are introduced and partially analyzed that are generalizations of the previously known exactly solvable local model neglecting electron inertia....

  3. Solar Energetic Particle Transport Near a Heliospheric Current Sheet

    Energy Technology Data Exchange (ETDEWEB)

    Battarbee, Markus; Dalla, Silvia [Jeremiah Horrocks Institute, University of Central Lancashire, PR1 2HE (United Kingdom); Marsh, Mike S., E-mail: mbattarbee@uclan.ac.uk [Met Office, Exeter, EX1 3 PB (United Kingdom)

    2017-02-10

    Solar energetic particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the interplanetary magnetic field (IMF). In this work, we analyze the implications that a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps, and virtual observer time profiles within an energy range of 1–800 MeV. We show that protons experience significant current sheet drift to distant longitudes, causing time profiles to exhibit multiple components, which are a potential source of confusing interpretations of observations. We find that variation of the current sheet thickness within a realistic parameter range has little effect on particle propagation. We show that the IMF configuration strongly affects the deceleration of protons. We show that in our model, the presence of a flat equatorial HCS in the inner heliosphere limits the crossing of protons into the opposite hemisphere.

  4. Radiation from a current sheet at the interface between a ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. In this paper we investigate the radiation from a current sheet at the interface between semi- infinite isotropic positive refractive medium and anisotropic negative refractive medium. The distribution of the electric and magnetic fields in two regions and Poynting vectors associated with propagating and evanes-.

  5. 3-D Particle Simulation of Current Sheet Instabilities

    Science.gov (United States)

    Wang, Zhenyu; Lin, Yu; Wang, Xueyi; Tummel, Kurt; Chen, Liu

    2015-11-01

    The electrostatic (ES) and electromagnetic (EM) instabilities of a Harris current sheet are investigated using a 3-D linearized (δf) gyrokinetic (GK) electron and fully kinetic (FK) ion (GeFi) particle simulation code. The equilibrium magnetic field consists of an asymptotic anti-parallel Bx 0 and a guide field BG. The ES simulations show the excitation of lower-hybrid drift instability (LHDI) at the current sheet edge. The growth rate of the 3-D LHDI is scanned through the (kx ,ky) space. The most unstable modes are found to be at k∥ = 0 for smaller ky. As ky increases, the growth rate shows two peaks at k∥ ≠ 0 , consistent with analytical GK theory. The eigenmode structure and growth rate of LHDI obtained from the GeFi simulation agree well with those obtained from the FK PIC simulation. Decreasing BG, the asymptotic βe 0, or background density can destabilize the LHDI. In the EM simulation, tearing mode instability is dominant in the cases with ky kx , there exist two unstable modes: a kink-like (LHDI) mode at the current sheet edge and a sausage-like mode at the sheet center. The results are compared with the GK eigenmode theory and the FK simulation.

  6. A Catapult (Slingshot) Current Sheet Relaxation Model for Substorm Triggering

    Science.gov (United States)

    Machida, S.; Miyashita, Y.; Ieda, A.

    2010-12-01

    Based on the results of our superposed epoch analysis of Geotail data, we have proposed a catapult (slingshot) current sheet relaxation model in which earthward flows are produced in the central plasma sheet (CPS) due to the catapult (slingshot) current sheet relaxation, together with the rapid enhancement of Poynting flux toward the CPS in the lobe around X ~ -15 Re about 4 min before the substrom onset. These earthward flows are characterized by plasma pressure decrease and large amplitude magnetic field fluctuations. When these flows reach X ~ 12Re in the magnetotail, they give significant disturbances to the inner magnetosphere to initiate some instability such as a ballooning instability or other instabilities, and the substorm starts in the inner magnetosphere. The occurrence of the magnetic reconnection is a natural consequence of the initial convective earthward flows, because the relaxation of a highly stretched catapult current sheet produces a very thin current at its tailward edge being surrounded by intense magnetic fields which were formerly the off-equatorial lobe magnetic fields. Recently, Nishimura et al. [2010] reported that the substorm onset begins when faint poleward discrete arcs collide with equatorward quiet arcs. The region of earthward convective flows correlatively moves earthward prior to the onset. Thus, this region of the earthward convective flows seems to correspond to the faint poleward discrete arcs. Interestingly, our statistical analysis shows that the earthward convective flows are not produced by the magnetic reconnection, but they are attributed to the dominance of the earthward JxB force over the tailward pressure associated with the progress of the plasma sheet thinning.

  7. A sheet-current approach to coronal-interplanetary modeling

    International Nuclear Information System (INIS)

    Yeh, T.; Pneuman, G.W.

    1977-01-01

    The most pertinent effect of the currents in the coronal-interplanetary space is their alteration of the magnetic topology to form configurations of open field lines. The important currents seem to be those in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines in the coronal helmet-streamer structures. Thus, the coronal-interplanetary space may be regarded as being partitioned by current-sheets into several piecewise current-free regions. These current sheets overlie the photospheric neutral lines, where the vertical component of the magnetic field reverses its polarity on the solar surface. But, their locations and strengths are determined by force balance between the magnetic field and the gas pressure in the coronal-interplanetary space. Since the pressure depends on the flow velocity of the solar wind and the solar wind channels along magnetic flux tubes, there is a strong magnetohydrodynamic coupling between the magnetic field and the solar wind. The sheet-current approach presented in this paper seems to be a reasonable way to account for this complicated interaction. (Auth.)

  8. Magnetic field dissipation and fractal model of current sheets

    International Nuclear Information System (INIS)

    Yankov, V.V.

    1997-01-01

    A model of magnetic field dissipation is suggested, which possesses features of both the Kolmogorov model of turbulence of ideal fluid and the Sweet endash Parker model of magnetic reconnection. It is suggested that current sheets are smooth along the magnetic lines but have fractal structure in the transverse dimension. The fractal dimension d=2.5 of the current sheet was found instead of d=3 in Kolmogorov-like models and d=2 in the Sweet endash Parker model. The reconnection time is the geometrical mean of the Alfvacute en time and the Sweet endash Parker time. The magnetic energy dissipation time can be even shorter, up to the Alfvacute en time. copyright 1997 American Institute of Physics

  9. Intensity variation of cosmic rays near the heliospheric current sheet

    International Nuclear Information System (INIS)

    Badruddin, K.S.; Yadav, R.S.; Yadav, N.R.

    1985-01-01

    Cosmic ray intensity variations near the heliospheric current sheet-both above and below it-have been studied during 1964-76. Superposed epoch analysis of the cosmic ray neutron monitor data with respect to sector boundaries (i.e., heliospheric current sheet crossings) has been performed. In this analysis data from neutron monitors well distributed in latitude over the Earth's surface is used. First, this study has been made during the two solar activity minimum periods 1964-65 and 1975-76, using the data from Thule (cut-off rigidity O GV), Deep River (cut-off rigidity 1.02 GV), Rome (cut-off rigidity 6.32 GV) and Huancayo (cut-off rigidity 13.45 GV) neutron monitors. The data is analyzed from Deep River, Rome and Huancayo neutron monitors, for which data is available for the full period (1964-76), by dividing the periods according to the changes in solar activity, interplanetary magnetic field polarity and coronal holes. All these studies have shown a negative gradient with respect to heliomagnetic latitude (current sheet). These results have been discussed in the light of theoretical and observational evidences. Suggestions have been given to overcome the discrepancy between the observational and theoretical results. Further, possible explanations for these observational results have been suggested. (author)

  10. Morphology and Density Structure of Post-CME Current Sheets

    Science.gov (United States)

    Vrsnak, B.; Poletto, G.; Vujic, E.; Vourlidas, A.

    2009-01-01

    Eruption of a coronal mass ejection (CME) is believed to drag and open the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and field relaxation by magnetic reconnection. This paper analyzes the physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to confirm whether interpreting such phenomena in terms of a reconnecting current sheet is consistent with observations. Methods: The study focuses on UVCS/SOHO and LASCO/SOHO measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of the rays implies that they are produced by Petschek-like reconnection in the large-scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km/s, and are consistent with the narrow opening-angle of rays, which add up to a few degrees. The density of rays is an order of magnitude higher than in the ambient corona. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to higher heights by the reconnection outflow.

  11. Bank stress testing under different balance sheet assumptions

    OpenAIRE

    Busch, Ramona; Drescher, Christian; Memmel, Christoph

    2017-01-01

    Using unique supervisory survey data on the impact of a hypothetical interest rate shock on German banks, we analyse price and quantity effects on banks' net interest margin components under different balance sheet assumptions. In the first year, the cross-sectional variation of banks' simulated price effect is nearly eight times as large as the one of the simulated quantity effect. After five years, however, the importance of both effects converges. Large banks adjust their balance sheets mo...

  12. The Topology and Properties of Mercury's Tail Current Sheet

    Science.gov (United States)

    Al Asad, M.; Johnson, C.; Philpott, L. C.

    2017-12-01

    The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft orbited Mercury from March 2011 until April 2015, measuring the vector magnetic field inside and outside the magnetosphere. MESSENGER repeatedly encountered the tail current sheet (TCS) on the nightside of the planet. We examined 1s magnetic field data within 20 minutes of the magnetic equator position on 2435 orbit to characterize the shape and properties of Mercury's TCS and investigate its response to solar wind conditions. Identification of the TCS from vector magnetic field data used the following criteria: (1) a rapid rotation in the field direction from anti-sunward in the southern tail lobe to sunward in the northern lobe, accompanied by (2) a decrease in the field magnitude and (3) an increase in field variability. The current sheet was encountered on 606 orbits allowing the probability of encountering the tail current sheet in the equatorial plane to be mapped. Orbits on which the TCS was identified were binned spatially and superposed epoch analysis used to determine the field magnitude at the edge of the TCS, from which its time-averaged 3D shape was extracted. The TCS has an inner edge at 1.5 RM downtail in the midnight plane with a thickness of 0.34 RM, extends to the observation limit of 2.8 RM, decreasing in thickness to 0.28 RM. The thickness of the TCS increases in the dawn/dusk directions to 0.7 RM at 1.8 RM downtail and ± 1.5 RM from the noon-midnight plane and it warps towards the planet in the dawn/dusk directions. No strong correlations were found between the time-averaged shape and position of the TCS and solar wind conditions such as the solar wind ram pressure and the magnetic disturbance index, nor with parameters that control these conditions such as heliocentric distance. However, it is likely that the TCS does respond to these conditions on time scales too short to be characterized with MESSENGER data. In addition to mapping the shape of the

  13. Spatial Offsets in Flare-CME Current Sheets

    Energy Technology Data Exchange (ETDEWEB)

    Raymond, John C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Giordano, Silvio [INAF-Osservatorio Astrofisico di Torino, via Osservatorio 20, I-10025 Pino Torinese (Italy); Ciaravella, Angela, E-mail: jraymond@cfa.harvard.edu [INAF-Osservatorio Astronomico di Palermo, P.za Parlamento 1, I-90134 Palermo (Italy)

    2017-07-10

    Magnetic reconnection plays an integral part in nearly all models of solar flares and coronal mass ejections (CMEs). The reconnection heats and accelerates the plasma, produces energetic electrons and ions, and changes the magnetic topology to form magnetic flux ropes and to allow CMEs to escape. Structures that appear between flare loops and CME cores in optical, UV, EUV, and X-ray observations have been identified as current sheets and have been interpreted in terms of the nature of the reconnection process and the energetics of the events. Many of these studies have used UV spectral observations of high temperature emission features in the [Fe xviii] and Si xii lines. In this paper, we discuss several surprising cases in which the [Fe xviii] and Si xii emission peaks are spatially offset from each other. We discuss interpretations based on asymmetric reconnection, on a thin reconnection region within a broader streamer-like structure, and on projection effects. Some events seem to be easily interpreted as the projection of a sheet that is extended along the line of sight that is viewed an angle, but a physical interpretation in terms of asymmetric reconnection is also plausible. Other events favor an interpretation as a thin current sheet embedded in a streamer-like structure.

  14. Large scale EMF in current sheets induced by tearing modes

    Science.gov (United States)

    Mizerski, Krzysztof A.

    2018-02-01

    An extension of the analysis of resistive instabilities of a sheet pinch from a famous work by Furth et al (1963 Phys. Fluids 6 459) is presented here, to study the mean electromotive force (EMF) generated by the developing instability. In a Cartesian configuration and in the presence of a current sheet first the boundary layer technique is used to obtain global, matched asymptotic solutions for the velocity and magnetic field and then the solutions are used to calculate the large-scale EMF in the system. It is reported, that in the bulk the curl of the mean EMF is linear in {{j}}0\\cdot {{B}}0, a simple pseudo-scalar quantity constructed from the large-scale quantities.

  15. Instabilities of collisionless current sheets: Theory and simulations

    Science.gov (United States)

    Silin, I.; Büchner, J.; Zelenyi, L.

    2002-04-01

    The problem of Harris current sheet stability is investigated. A linear dispersion relation in the long-wavelength limit is derived for instabilities, propagating in the neutral plane at an arbitrary angle to the magnetic field but symmetric across the sheet. The role of electrostatic perturbations is especially investigated. It appears, that for the tearing-mode instability electrostatic effects are negligible. However, for obliquely propagating modes the modulation of the electrostatic potential φ is essential. In order to verify the theoretical results, the limiting cases of tearing and sausage instabilities are compared to the two-dimensional (2D) Vlasov code simulations. For tearing the agreement between theory and simulations is good for all mass ratios. For sausage-modes, the theory predicts fast stabilization for mass ratios mi/me⩾10. This is not observed in simulations due to the diminishing of the wavelength for higher mass ratios, which leads beyond the limit of applicability of the theory developed here.

  16. Thin current sheets observation by MMS during a near-Earth's magnetotail reconnection event

    Science.gov (United States)

    Nakamura, R.; Varsani, A.; Nakamura, T.; Genestreti, K.; Plaschke, F.; Baumjohann, W.; Nagai, T.; Burch, J.; Cohen, I. J.; Ergun, R.; Fuselier, S. A.; Giles, B. L.; Le Contel, O.; Lindqvist, P. A.; Magnes, W.; Schwartz, S. J.; Strangeway, R. J.; Torbert, R. B.

    2017-12-01

    During summer 2017, the four spacecraft of the Magnetospheric Multiscale (MMS) mission traversed the nightside magnetotail current sheet at an apogee of 25 RE. They detected a number of flow reversal events suggestive of the passage of the reconnection current sheet. Due to the mission's unprecedented high-time resolution and spatial separation well below the ion scales, structure of thin current sheets is well resolved both with plasma and field measurements. In this study we examine the detailed structure of thin current sheets during a flow reversal event from tailward flow to Earthward flow, when MMS crossed the center of the current sheet . We investigate the changes in the structure of the thin current sheet relative to the X-point based on multi-point analysis. We determine the motion and strength of the current sheet from curlometer calculations comparing these with currents obtained from the particle data. The observed structures of these current sheets are also compared with simulations.

  17. Oscillation of the current sheet velocity in plasma focus discharges

    International Nuclear Information System (INIS)

    Melzacki, K.; Nardi, V.

    1994-01-01

    The oscillation of the propagation speed of the plasma focus current sheet has been recorded with schlieren photography. The sheet stuttering in the propagation during the implosion phase has a frequency of about 60 MHz. The effect could be recorded due to application of long exposure time (60 ns) technique. It is not detectable in the subnanosecond pictures. The pictures are taken in black schlieren. The probing range of the electron density gradient, with integration along the path of the 1 J, Q-switched ruby laser beam, has been selected by the size of the stop and aperture within 3 x 10 18 cm -3 and 3 x 10 20 cm -3 . Raising the sensitivity threshold to 2 x 10 19 cm -3 (refraction angle of 4 mrad) has helped to clear the pictures by limiting their image to high gradients of density only. With this technique (and other diagnostic methods) the dynamics of 6 kJ, 16 kV plasma focus discharges in deuterium at 5 torr, with a 10% decrease of the magnetic insulation at the breech has been investigated. The average implosion velocity of the current sheath obtained with this effect, 5 x 10 6 cm/s, is consistent with those measured by the smear effect, and the electric probe. The electron density gradient has been determined at several instants; at the pinch time it is (3 ± 1.5) x 10 20 cm -4 . The data are discussed on the basis of several pictures

  18. Continuous development of current sheets near and away from magnetic nulls

    International Nuclear Information System (INIS)

    Kumar, Sanjay; Bhattacharyya, R.

    2016-01-01

    The presented computations compare the strength of current sheets which develop near and away from the magnetic nulls. To ensure the spontaneous generation of current sheets, the computations are performed congruently with Parker's magnetostatic theorem. The simulations evince current sheets near two dimensional and three dimensional magnetic nulls as well as away from them. An important finding of this work is in the demonstration of comparative scaling of peak current density with numerical resolution, for these different types of current sheets. The results document current sheets near two dimensional magnetic nulls to have larger strength while exhibiting a stronger scaling than the current sheets close to three dimensional magnetic nulls or away from any magnetic null. The comparative scaling points to a scenario where the magnetic topology near a developing current sheet is important for energetics of the subsequent reconnection.

  19. Catapult current sheet relaxation model confirmed by THEMIS observations

    Science.gov (United States)

    Machida, S.; Miyashita, Y.; Ieda, A.; Nose, M.; Angelopoulos, V.; McFadden, J. P.

    2014-12-01

    In this study, we show the result of superposed epoch analysis on the THEMIS probe data during the period from November, 2007 to April, 2009 by setting the origin of time axis to the substorm onset determined by Nishimura with THEMIS all sky imager (THEMS/ASI) data (http://www.atmos.ucla.edu/~toshi/files/paper/Toshi_THEMIS_GBO_list_distribution.xls). We confirmed the presence of earthward flows which can be associated with north-south auroral streamers during the substorm growth phase. At around X = -12 Earth radii (Re), the northward magnetic field and its elevation angle decreased markedly approximately 4 min before substorm onset. A northward magnetic-field increase associated with pre-onset earthward flows was found at around X = -17Re. This variation indicates the occurrence of the local depolarization. Interestingly, in the region earthwards of X = -18Re, earthward flows in the central plasma sheet (CPS) reduced significantly about 3min before substorm onset. However, the earthward flows enhanced again at t = -60 sec in the region around X = -14 Re, and they moved toward the Earth. At t = 0, the dipolarization of the magnetic field started at X ~ -10 Re, and simultaneously the magnetic reconnection started at X ~ -20 Re. Synthesizing these results, we can confirm the validity of our catapult current sheet relaxation model.

  20. The effect of the heliospheric current sheet on cosmic ray intensities at solar maximum: Two alternative hypotheses

    International Nuclear Information System (INIS)

    Thomas, B.T.; Goldstein, B.E.; Smith, E.J.

    1986-01-01

    There is now a growing awareness that solar cycle related changes in the large-scale structure of the heliospheric current sheet may play an important role in the modulation of galactic cosmic rays. To date, attention has been focused on the configuration of the current sheet at times near solar minimum when the current sheet structure is relatively simple. Previous analyses have explored the effect on cosmic ray intensities of a single current sheet which is tilted with respect to the heliographic equator under the assumption that the tilt of the current sheet is a minimum at solar minimum and increases as solar maximum approaches. This paper attempts to extend the previous analyses into the period near solar maximum. Two alternative hypotheses are explored: (1) that the tilt of the current sheet continues to increase as solar maximum approaches, finally becoming vertical and overturning, and (2) that the single sheet structure breaks down near solar maximum and the sun at this time sheds the poloidal flux of the previous cycle and develops a new field structure of the opposite polarity. It is found that both hypotheses lead to variations in cosmic ray intensity comparable to those actually observed over the solar cycle

  1. Geomagnetic Field Disturbances Caused by Heliospheric Current Sheet Crossings

    Science.gov (United States)

    Asenovski, S.

    2017-12-01

    The heliospheric current sheet (HCS) is modified by the solar activity. HCS is highly inclined during solar maximum and almost confined with the solar equatorial plane during solar minimum. Close to the HCS solar wind parameters as proton temperature, flow speed, proton density, etc. differ compared to the region far from the HCS. The Earth's magnetic dipole field crosses HCS several times each month. Considering interplanetary coronal mass ejections (ICME) and high speed solar wind streams (HSS) free periods an investigation of the HCS influence on the geomagnetic field disturbances is presented. The results show a drop of the Dst index and a rise of the AE index at the time of the HCS crossings and also that the behavior of these indices does not depend on the magnetic polarity.

  2. Near-earth Thin Current Sheets and Birkeland Currents during Substorm Growth Phase

    International Nuclear Information System (INIS)

    Sorin Zaharia; Cheng, C.Z.

    2003-01-01

    Two important phenomena observed during the magnetospheric substorm growth phase are modeled: the formation of a near-Earth (|X| ∼ 9 R E ) thin cross-tail current sheet, as well as the equatorward shift of the ionospheric Birkeland currents. Our study is performed by solving the 3-D force-balance equation with realistic boundary conditions and pressure distributions. The results show a cross-tail current sheet with large current (J φ ∼ 10 nA/m 2 ) and very high plasma β (β ∼ 40) between 7 and 10 R E . The obtained region-1 and region-2 Birkeland currents, formed on closed field lines due to pressure gradients, move equatorward and become more intense (J parallel max ∼ 3 (micro)A/m 2 ) compared to quiet times. Both results are in agreement with substorm growth phase observations. Our results also predict that the cross-tail current sheet maps into the ionosphere in the transition region between the region-1 and region-2 currents

  3. Global properties of magnetotail current sheet flapping: THEMIS perspectives

    Directory of Open Access Journals (Sweden)

    A. Runov

    2009-01-01

    Full Text Available A sequence of magnetic field oscillations with an amplitude of up to 30 nT and a time scale of 30 min was detected by four of the five THEMIS spacecraft in the magnetotail plasma sheet. The probes P1 and P2 were at X=−15.2 and −12.7 RE and P3 and P4 were at X=−7.9 RE. All four probes were at −6.5>Y>−7.5 RE (major conjunction. Multi-point timing analysis of the magnetic field variations shows that fronts of the oscillations propagated flankward (dawnward and Earthward nearly perpendicular to the direction of the magnetic maximum variation (B1 at velocities of 20–30 km/s. These are typical characteristics of current sheet flapping motion. The observed anti-correlation between ∂B1/∂t and the Z-component of the bulk velocity make it possible to estimate a flapping amplitude of 1 to 3 RE. The cross-tail scale wave-length was found to be about 5 RE. Thus the flapping waves are steep tail-aligned structures with a lengthwise scale of >10 RE. The intermittent plasma motion with the cross-tail velocity component changing its sign, observed during flapping, indicates that the flapping waves were propagating through the ambient plasma. Simultaneous observations of the magnetic field variations by THEMIS ground-based magnetometers show that the flapping oscillations were observed during the growth phase of a substorm.

  4. Rivers under ice: fluvial erosion beneath decaying ice sheets

    Science.gov (United States)

    Jansen, John D.; Codilean, Alexandru T.; Stroeven, Arjen P.; Fabel, Derek; Hättestrand, Clas; Kleman, Johan; Harbor, Jon M.; Heyman, Jakob; Kubik, Peter W.; Xu, Sheng

    2014-05-01

    The century-long debate over the origins of inner gorges cut within larger valleys that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. We apply cosmogenic nuclide exposure dating to seven inner gorges along ~500 km of the former Fennoscandia ice sheet margin in combination with a new deglaciation isochron map. We show that the timing of bedrock exposure matches the advent of ice-free conditions, strongly suggesting that inner gorges were cut by channelised subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for subglacial meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting akin to that currently occurring on the Greenland ice sheet. The lack of postglacial river erosion in our seven inner gorges leads us to propose that channelised subglacial meltwater-boosted possibly by abrupt supraglacial lake drainage-may be a key driver of valley deepening on the Baltic Shield over multiple glacial cycles.

  5. Development of tearing instability in a current sheet forming by sheared incompressible flow

    Science.gov (United States)

    Tolman, Elizabeth A.; Loureiro, Nuno F.; Uzdensky, Dmitri A.

    2018-02-01

    Sweet-Parker current sheets in high Lundquist number plasmas are unstable to tearing, suggesting they will not form in physical systems. Understanding magnetic reconnection thus requires study of the stability of a current sheet as it forms. Formation can occur due to sheared, sub-Alfvénic incompressible flows which narrow the sheet. Standard tearing theory (Furth et al. Phys. Fluids, vol. 6 (4), 1963, pp. 459-484, Rutherford, Phys. Fluids, vol. 16 (11), 1973, pp. 1903-1908, Coppi et al. Fizika Plazmy, vol. 2, 1976, pp. 961-966) is not immediately applicable to such forming sheets for two reasons: first, because the flow introduces terms not present in the standard calculation; second, because the changing equilibrium introduces time dependence to terms which are constant in the standard calculation, complicating the formulation of an eigenvalue problem. This paper adapts standard tearing mode analysis to confront these challenges. In an initial phase when any perturbations are primarily governed by ideal magnetohydrodynamics, a coordinate transformation reveals that the flow compresses and stretches perturbations. A multiple scale formulation describes how linear tearing mode theory (Furth et al. Phys. Fluids, vol. 6 (4), 1963, pp. 459-484, Coppi et al. Fizika Plazmy, vol. 2, 1976, pp. 961-966) can be applied to an equilibrium changing under flow, showing that the flow affects the separable exponential growth only implicitly, by making the standard scalings time dependent. In the nonlinear Rutherford stage, the coordinate transformation shows that standard theory can be adapted by adding to the stationary rates time dependence and an additional term due to the strengthening equilibrium magnetic field. Overall, this understanding supports the use of flow-free scalings with slight modifications to study tearing in a forming sheet.

  6. Sausage mode instability of thin current sheets as a cause of magnetospheric substorms

    Directory of Open Access Journals (Sweden)

    J. Büchner

    Full Text Available Observations have shown that, prior to substorm explosions, thin current sheets are formed in the plasma sheet of the Earth's magnetotail. This provokes the question, to what extent current-sheet thinning and substorm onsets are physically, maybe even causally, related. To answer this question, one has to understand the plasma stability of thin current sheets. Kinetic effects must be taken into account since particle scales are reached in the course of tail current-sheet thinning. We present the results of theoretical investigations of the stability of thin current sheets and about the most unstable mode of their decay. Our conclusions are based upon a non-local linear dispersion analysis of a cross-magnetic field instability of Harris-type current sheets. We found that a sausage-mode bulk current instability starts after a sheet has thinned down to the ion inertial length. We also present the results of three-dimensional electromagnetic PIC-code simulations carried out for mass ratios up to Mi / me=64. They verify the linearly predicted properties of the sausage mode decay of thin current sheets in the parameter range of interest.

    Key words. Magnetospheric physics (plasma waves and instabilities; storms and substorms · Space plasma physics (magnetic reconnection

  7. High-latitude Conic Current Sheets in the Solar Wind

    Energy Technology Data Exchange (ETDEWEB)

    Khabarova, Olga V.; Obridko, Vladimir N.; Kharshiladze, Alexander F. [Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN), Moscow (Russian Federation); Malova, Helmi V. [Scobeltsyn Nuclear Physics Institute of Lomonosov Moscow State University, Moscow (Russian Federation); Kislov, Roman A.; Zelenyi, Lev M. [Space Research Centre of the Polish Academy of Sciences (CBK PAN), Warsaw (Poland); Tokumaru, Munetoshi; Fujiki, Ken’ichi [Institute for Space-Earth Environmental Research, Nagoya University (Japan); Sokół, Justyna M.; Grzedzielski, Stan [Space Research Centre of the Polish Academy of Sciences (CBK), Warsaw (Poland)

    2017-02-10

    We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2–3 au several times in 1994, as the CCS was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of conic-like magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/ nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk–Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.

  8. Current sheets with inhomogeneous plasma temperature: Effects of polarization electric field and 2D solutions

    International Nuclear Information System (INIS)

    Catapano, F.; Zimbardo, G.; Artemyev, A. V.; Vasko, I. Y.

    2015-01-01

    We develop current sheet models which allow to regulate the level of plasma temperature and density inhomogeneities across the sheet. These models generalize the classical Harris model via including two current-carrying plasma populations with different temperature and the background plasma not contributing to the current density. The parameters of these plasma populations allow regulating contributions of plasma density and temperature to the pressure balance. A brief comparison with spacecraft observations demonstrates the model applicability for describing the Earth magnetotail current sheet. We also develop a two dimensional (2D) generalization of the proposed model. The interesting effect found for 2D models is the nonmonotonous profile (along the current sheet) of the magnetic field component perpendicular to the current sheet. Possible applications of the model are discussed

  9. A Hybrid Kinetic Model of Asymmetric Thin Current Sheets with Sheared Flows in a Collisionless Plasma

    Science.gov (United States)

    2010-12-27

    2010 Interim April 2010 - Sept 2010 4. TITLE AND SUBTITLE Sa . CONTRACT NUMBER A Hybrid Kinetic Model of Asymmetric Thin Current Sheets with Sheared...that charge neutrality is not an explicit assumption in this model. Rather it depends on VAle ¢: 1 and the current sheet thickness being Pa as

  10. Nonlinear instability of thin current sheets in antiparallel and guided magnetic fields

    Science.gov (United States)

    Silin, I.; Büchner, J.

    2003-09-01

    The influence of a current-aligned guide magnetic field on the nonlinear resonant instability of thin current sheets is investigated by means of three-dimensional Vlasov-code simulations. Similarly to the zero-guide field case, the pressure gradient excites lower-hybrid-drift (LHD) waves at the current sheet edges. However, since the LHD waves are excited perpendicular to the local magnetic field they propagate obliquely to the current direction. As a result, the number of resonant particles, i.e., the drift-resonance efficiency, decreases with increasing guide field strength. Hence, the driving of global current sheet kink/sausage instabilities becomes less efficient.

  11. Nonlinear instability of thin current sheets in antiparallel and guided magnetic fields

    International Nuclear Information System (INIS)

    Silin, I.; Buechner, J.

    2003-01-01

    The influence of a current-aligned guide magnetic field on the nonlinear resonant instability of thin current sheets is investigated by means of three-dimensional Vlasov-code simulations. Similarly to the zero-guide field case, the pressure gradient excites lower-hybrid-drift (LHD) waves at the current sheet edges. However, since the LHD waves are excited perpendicular to the local magnetic field they propagate obliquely to the current direction. As a result, the number of resonant particles, i.e., the drift-resonance efficiency, decreases with increasing guide field strength. Hence, the driving of global current sheet kink/sausage instabilities becomes less efficient

  12. Current and future darkening of the Greenland ice sheet

    Science.gov (United States)

    Tedesco, Marco; Stroeve, Julienne; Fettweis, Xavier; Warren, Stephen; Doherty, Sarah; Noble, Erik; Alexander, Patrick

    2015-04-01

    Surface melting over the Greenland ice sheet (GIS) promotes snow grains growth, reducing albedo and further enhancing melting through the increased amount of absorbed solar radiation. Using a combination of remote sensing data and outputs of a regional climate model, we show that albedo over the GIS decreased significantly from 1996 to 2012. Further, we show that most of this darkening can be accounted for by enhanced snow grain growth and the expansion of areas where bare ice is exposed, both of which are driven by increases in snow warming. An analysis of the impact of light-absorbing impurities on albedo trends detected from spaceborne measurements was inconclusive because the estimated impact for concentrations of impurities of order of magnitude found in Greenland is within the albedo uncertainty retrievable from space-based instruments. However, neither models nor observations show an increase in pollutants (black carbon and associated organics) in the atmosphere over the GIS in this time period. Additionally, we could not identify trends in the number of fires over North America and Russia, assumed to be among the sources of soot for Greenland. We did find that a 'dark band' of tilted ice plays a crucial role in decreasing albedo along the west margin, and there is some indication that dust deposition to the GIS may be decreasing albedo in this region but this is not conclusive. In addition to looking at the direct impact of impurities on albedo, we estimated the impact of impurities on albedo via their influence on grain growth and found it is relatively small (~ 1- 2 %), though more sophisticated analysis needs to be carried out. Projections obtained under different warming scenarios consistently point to a continued darkening, with anomalies in albedo driven solely by the effects of climate warming of as much as -0.12 along the west margin of the GIS by the end of this century (with respect to year 2000). Projected darkening is likely underestimated

  13. Plasma heating and acceleration in current sheets formed in discharges in argon

    Directory of Open Access Journals (Sweden)

    Kyrie N.P.

    2017-01-01

    Full Text Available According to present notion, flares on the sun and other stars, substorms in magnetospheres of Earth and other planets, and disruptive instabilities in tokamak plasma are connected to development of current sheets in magnetized plasma. Therefore, current sheet dynamics and magnetic reconnection processes were studied actively during the last several decades. This paper presents the results of experimental studies of plasma heating and acceleration in current sheets formed in discharges in argon. The temperature and energy of directed motion of argon ions of different degrees of ionization were measured by spectroscopic methods. It was found that Ar II, Ar III and Ar IV ions are localized in different regions of the sheet. It was shown that Ampere forces applied to the sheet can accelerate the argon ions to observed energies.

  14. Assisted crack tip flipping under Mode I thin sheet tearing

    DEFF Research Database (Denmark)

    Felter, Christian Lotz; Nielsen, Kim Lau

    2017-01-01

    Crack tip flipping, where the fracture surface alternates from side to side in roughly 45° shear bands, seems to be an overlooked propagation mode in Mode I thin sheet tearing. In fact, observations of crack tip flipping is rarely found in the literature. Unlike the already established modes...... such as slanting, cup-cone (rooftop), or cup-cup (bathtub) the flipping crack never settles in a steady-state as the near tip stress/strain field continuously change when the flip successively initiates and develops shear-lips. A recent experimental investigation has revealed new insight by exploiting 3D X......-ray tomography scanning of a developing crack tip flip. But, it remains to be understood what makes the crack flip systematically, what sets the flipping frequency, and under which material conditions this mode occurs. The present study aims at investigating the idea that a slight out-of-plane action (Mode III...

  15. Two-dimensional current-carrying plasma sheet in the near-Earth geomagnetic tail region:a quasi-stationary evolution

    Directory of Open Access Journals (Sweden)

    A. V. Manankova

    2003-12-01

    Full Text Available A problem concerning stationary configurations of an inhomogeneous, current-carrying, two-dimensional plasma sheet as the solution of the Grad–Shafranov equation with boundary conditions given on cross-sheet profiles at the  foot of the sheet and at infinity is considered, with the aim of using its solution for the description of the interaction of two current systems: the current system of the geomagnetic field, and the tail currents. The obtained solution is an exact analytical solution which contains 5 independent parameters characterizing the intensity of the current sheet. As the solution is exact, it may be applied to describe the most interesting transitional magnetospheric region: that of a strong interaction between the magnetic fields of the geodipole and of the current sheet, i.e. the region where characteristic scales of the change of all variables along and across the sheet are of the same order. This makes it possible to model the structure of the transitional region and its dynamics under quasi-stationary variation of the input parameters. The obtained solution describes the principal processes developing at various phases of magnetospheric disturbances, such as (1 formation of a very intense thin current sheet localized within the transition region, (2 changing from the quasi-dipolar magnetic field to the configuration when a "neck" is formed in this region. An important feature of the obtained solution is the existence of a critical value of one of the parameters of the problem, which leads to the change in the geomagnetic field configuration described above. The solution can be used as an initial condition in simulating dynamical processes in the magnetotail current sheet, as well as in testing the current sheet stability. In the summary a series of limitations in the model problem under consideration is discussed. Key words. Magnetospheric physics (magnetotail; plasma sheet; magnetospheric configuration and dynamics

  16. Two-dimensional current-carrying plasma sheet in the near-Earth geomagnetic tail region:a quasi-stationary evolution

    Directory of Open Access Journals (Sweden)

    A. V. Manankova

    Full Text Available A problem concerning stationary configurations of an inhomogeneous, current-carrying, two-dimensional plasma sheet as the solution of the Grad–Shafranov equation with boundary conditions given on cross-sheet profiles at the  foot of the sheet and at infinity is considered, with the aim of using its solution for the description of the interaction of two current systems: the current system of the geomagnetic field, and the tail currents. The obtained solution is an exact analytical solution which contains 5 independent parameters characterizing the intensity of the current sheet. As the solution is exact, it may be applied to describe the most interesting transitional magnetospheric region: that of a strong interaction between the magnetic fields of the geodipole and of the current sheet, i.e. the region where characteristic scales of the change of all variables along and across the sheet are of the same order. This makes it possible to model the structure of the transitional region and its dynamics under quasi-stationary variation of the input parameters. The obtained solution describes the principal processes developing at various phases of magnetospheric disturbances, such as (1 formation of a very intense thin current sheet localized within the transition region, (2 changing from the quasi-dipolar magnetic field to the configuration when a "neck" is formed in this region. An important feature of the obtained solution is the existence of a critical value of one of the parameters of the problem, which leads to the change in the geomagnetic field configuration described above. The solution can be used as an initial condition in simulating dynamical processes in the magnetotail current sheet, as well as in testing the current sheet stability. In the summary a series of limitations in the model problem under consideration is discussed. Key words. Magnetospheric physics (magnetotail; plasma sheet; magnetospheric configuration and dynamics

  17. On the internal structure of the current sheet in the pulsar wind

    Science.gov (United States)

    Prokofev, V. V.; Arzamasskiy, L. I.; Beskin, V. S.

    2018-02-01

    We investigate the internal structure of the current sheet in the pulsar wind within force-free and two-fluid MHD approximations. Within the force-free approximation we obtain general asymptotic solution of the Grad-Shafranov equation for quasi-spherical pulsar wind up to the second order in small parameter ɛ = (Ωr/c)-1. The solution allows an arbitrary latitudinal structure of the radial magnetic field, including that obtained in the numerical simulations of oblique rotators. It is also shown that the shape of the current sheet does not depend on the latitudinal structure. For the internal region of the current sheet outside the fast magnetosonic surface where the force-free approximation is not valid we use two-fluid MHD approximation. Carrying out calculations in the comoving reference frame, we succeed in determining intrinsic electric and magnetic fields of a sheet. It allows us to analyse time-dependent effects which were not investigated up to now. In particular, we estimate the efficiency of the particle acceleration inside the sheet. Finally, after investigating the motion of individual particles in the time-dependent current sheet, we find the width of the sheet and its time evolution self-consistent.

  18. CURRENT SHEET ENERGETICS, FLARE EMISSIONS, AND ENERGY PARTITION IN A SIMULATED SOLAR ERUPTION

    International Nuclear Information System (INIS)

    Reeves, Katharine K.; Linker, Jon A.; Mikic, Zoran; Forbes, Terry G.

    2010-01-01

    We investigate coronal energy flow during a simulated coronal mass ejection (CME). We model the CME in the context of the global corona using a 2.5D numerical MHD code in spherical coordinates that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The simulation domain extends from 1 to 20 R s . To our knowledge, this is the first attempt to apply detailed energy diagnostics in a flare/CME simulation when these important terms are considered in the context of the MHD equations. We find that the energy conservation properties of the code are quite good, conserving energy to within 4% for the entire simulation (more than 6 days of real time). We examine the energy release in the current sheet as the eruption takes place, and find, as expected, that the Poynting flux is the dominant carrier of energy into the current sheet. However, there is a significant flow of energy out of the sides of the current sheet into the upstream region due to thermal conduction along field lines and viscous drag. This energy outflow is spatially partitioned into three separate components, namely, the energy flux flowing out the sides of the current sheet, the energy flowing out the lower tip of the current sheet, and the energy flowing out the upper tip of the current sheet. The energy flow through the lower tip of the current sheet is the energy available for heating of the flare loops. We examine the simulated flare emissions and energetics due to the modeled CME and find reasonable agreement with flare loop morphologies and energy partitioning in observed solar eruptions. The simulation also provides an explanation for coronal dimming during eruptions and predicts that the structures surrounding the current sheet are visible in X-ray observations.

  19. Observations of the Formation, Development, and Structure of a Current Sheet in an Eruptive Solar Flare

    Energy Technology Data Exchange (ETDEWEB)

    Seaton, Daniel B.; Darnel, Jonathan M. [Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO 80305 (United States); Bartz, Allison E., E-mail: daniel.seaton@noaa.gov [Department of Physics, Grinnell College, Grinnell, IA 50112 (United States)

    2017-02-01

    We present Atmospheric Imaging Assembly observations of a structure we interpret as a current sheet associated with an X4.9 flare and coronal mass ejection that occurred on 2014 February 25 in NOAA Active Region 11990. We characterize the properties of the current sheet, finding that the sheet remains on the order of a few thousand kilometers thick for much of the duration of the event and that its temperature generally ranged between 8 and 10 MK. We also note the presence of other phenomena believed to be associated with magnetic reconnection in current sheets, including supra-arcade downflows and shrinking loops. We estimate that the rate of reconnection during the event was M{sub A} ≈ 0.004–0.007, a value consistent with model predictions. We conclude with a discussion of the implications of this event for reconnection-based eruption models.

  20. Flashover Characteristics of Silicone Rubber Sheets under Various Environmental Conditions

    Directory of Open Access Journals (Sweden)

    Arshad

    2016-08-01

    Full Text Available Silicone rubber insulators are replacing the conventional ceramic and porcelain insulators rapidly in power transmission and distribution industry. Very limited field knowledge is available about the performance of silicone rubber insulators in polluted and contaminated environments and therefore need further investigation. A comprehensive analysis of silicone rubber sheets (intended for coating outdoor insulators was carried out in this paper based on experimental results. The main performance parameters analyzed were arc inception voltage and flashover voltage. Dependence of these parameters on equivalent salt deposit density (ESDD, non-soluble salt deposit density (NSDD, relative humidity, ambient temperature, fog rate, dry band formation, dry band location and number of dry bands were investigated extensively. Insulator orientation and its effect on performance were also studied. The authors believe that this paper will provide a comprehensive knowledge about the flashover characteristics of silicone rubber insulators under humid, contaminated and dry band conditions. These results could be used in the selection and design of silicone rubber insulators for polluted environments.

  1. Field reversing magnetotail current sheets: earth, Venus, and Comet Giacobini-Zinner

    International Nuclear Information System (INIS)

    McComas, D.J.

    1986-09-01

    This dissertation examines the field reversing magnetotail current sheets at the earth, Venus, and Comet Giacobini-Zinner. In the near earth study a new analysis technique is developed to calculate the detailed current density distributions within the cross tail current sheet for the first time. This technique removes the effects of a variable sheet velocity by inverting intersatellite timings between the co-orbiting satellites ISEE-1 and -2. Case studies of three relatively geomagnetically quiet crossings are made; sheet thicknesses and peak current densities are ∼1-5 x 10 4 km and ∼5-50 nA/m 2 . Current density distributions reveal a high density central region, lower density shoulders, and considerable fine structure throughout. In the Venus study another new analysis technique is developed to reconstruct the average tail configuration from a correlation between field magnitude and draping angle in a large statistical data set. In the comet study, high resolution magnetic field and plasma electron data from the ICE traversal of Giacobini-Zinner are combined for the first time to determine the tail/current sheet geometry and calculate certain important but unmeasured local ion and upstream properties. Pressure balance across the tail gives ion temperatures and betas of ∼1.2 x 10 5 K and ∼40 in the center of the current sheet to ∼1 x 10 6 K and ∼3 in the outer lobes. Axial stress balance shows that the velocity shear upstream near the nucleus is >6 (∼1 at ICE), and that a region of strongly enhanced mass loading (ion source rate ∼24 times that upstream from lobes) exists upstream from the current sheet. The integrated downtail mass flux is ∼2.6 x 10 26 H 2 O+/sec, which is only ∼1% of the independently determined total cometary efflux. 79 refs., 37 figs

  2. Field reversing magnetotail current sheets: earth, Venus, and Comet Giacobini-Zinner

    Energy Technology Data Exchange (ETDEWEB)

    McComas, D.J.

    1986-09-01

    This dissertation examines the field reversing magnetotail current sheets at the earth, Venus, and Comet Giacobini-Zinner. In the near earth study a new analysis technique is developed to calculate the detailed current density distributions within the cross tail current sheet for the first time. This technique removes the effects of a variable sheet velocity by inverting intersatellite timings between the co-orbiting satellites ISEE-1 and -2. Case studies of three relatively geomagnetically quiet crossings are made; sheet thicknesses and peak current densities are approx.1-5 x 10/sup 4/ km and approx.5-50 nA/m/sup 2/. Current density distributions reveal a high density central region, lower density shoulders, and considerable fine structure throughout. In the Venus study another new analysis technique is developed to reconstruct the average tail configuration from a correlation between field magnitude and draping angle in a large statistical data set. In the comet study, high resolution magnetic field and plasma electron data from the ICE traversal of Giacobini-Zinner are combined for the first time to determine the tail/current sheet geometry and calculate certain important but unmeasured local ion and upstream properties. Pressure balance across the tail gives ion temperatures and betas of approx.1.2 x 10/sup 5/ K and approx.40 in the center of the current sheet to approx.1 x 10/sup 6/ K and approx.3 in the outer lobes. Axial stress balance shows that the velocity shear upstream near the nucleus is >6 (approx.1 at ICE), and that a region of strongly enhanced mass loading (ion source rate approx.24 times that upstream from lobes) exists upstream from the current sheet. The integrated downtail mass flux is approx.2.6 x 10/sup 26/ H/sub 2/O+/sec, which is only approx.1% of the independently determined total cometary efflux. 79 refs., 37 figs.

  3. Self-organization in space plasma: formation of magnetic shear in current sheets

    Science.gov (United States)

    Zelenyi, Lev; Delcourt, Dominique; Mingalev, Oleg; Malova, Helmi; Popov, Victor; Grigorenko, Elena; Petrukovich, Anatoli

    2016-07-01

    Thin current sheets are plasma structures that usually appear near reconnection regions. The presence of the shear magnetic field is characteristic for these structures. Self-consistent kinetic model of magnetotail thin current sheet (TCS) is used to understand the mechanisms of self-organization of sheared thin current sheets in a space plasma. It is shown that these configurations appear as a result of self-consistent evolution of some initial magnetic perturbation at current sheet center. Two general shapes of shear TCS components are found as a function of the transverse coordinate: symmetric and antisymmetric. We show that TCS formation goes together with the emergence of field-aligned currents in the center of the current sheet, as a result of north-south asymmetry of quasi-adiabatic ion motions. Ion drift currents can also contribute to the magnetic shear evolution, but their role is much less significant, their contribution depending upon the normal component Bz and the amplitude of the initial perturbation in TCS. Parametric maps illustrating different types of TCS equilibria are presented.

  4. Distributions of the ion temperature, ion pressure, and electron density over the current sheet surface

    Energy Technology Data Exchange (ETDEWEB)

    Kyrie, N. P., E-mail: kyrie@fpl.gpi.ru; Markov, V. S., E-mail: natalya.kyrie@yandex.ru; Frank, A. G.; Vasilkov, D. G.; Voronova, E. V. [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

    2016-06-15

    The distributions of the ion temperature, ion pressure, and electron density over the width (the major transverse dimension) of the current sheet have been studied for the first time. The current sheets were formed in discharges in argon and helium in 2D and 3D magnetic configurations. It is found that the temperature of argon ions in both 2D and 3D magnetic configurations is almost uniform over the sheet width and that argon ions are accelerated by the Ampère force. In contrast, the distributions of the electron density and the temperature of helium ions are found to be substantially nonuniform. As a result, in the 2D magnetic configuration, the ion pressure gradient across the sheet width makes a significant contribution (comparable with the Ampère force) to the acceleration of helium ions, whereas in the 3D magnetic configuration, the Ampère force is counterbalanced by the pressure gradient.

  5. Asymmetry of the Martian Current Sheet in a Multi-fluid MHD Model

    Science.gov (United States)

    Panoncillo, S. G.; Egan, H. L.; Dong, C.; Connerney, J. E. P.; Brain, D. A.; Jakosky, B. M.

    2017-12-01

    The solar wind carries interplanetary magnetic field (IMF) lines toward Mars, where they drape around the planet's conducting ionosphere, creating a current sheet behind the planet where the magnetic field has opposite polarity on either side. In its simplest form, the current sheet is often thought of as symmetric, extending behind the planet along the Mars-Sun line. Observations and model simulations, however, demonstrate that this idealized representation is only an approximation, and the actual scenario is much more complex. The current sheet can have 3D structure, move back and forth, and be situated dawnward or duskward of the Mars-Sun line. In this project, we utilized a library of global plasma model results for Mars consisting of a collection of multi-fluid MHD simulations where solar max/min, sub-solar longitude, and the orbital position of Mars are varied individually. The model includes Martian crustal fields, and was run for identical steady solar wind conditions. This library was created for the purpose of comparing model results to MAVEN data; we looked at the results of this model library to investigate current sheet asymmetries. By altering one variable at a time we were able to measure how these variables influence the location of the current sheet. We found that the current sheet is typically shifted toward the dusk side of the planet, and that modeled asymmetries are especially prevalent during solar min. Previous model studies that lack crustal fields have found that, for a Parker spiral IMF, the current sheet will shift dawnward, while our results typically show the opposite. This could expose certain limitations in the models used, or it could reveal an interaction between the solar wind and the plasma environment of Mars that has not yet been explored. MAVEN data may be compared to the model results to confirm the sense of the modeled asymmetry. These results help us to probe the physics controlling the Martian magnetotail and atmospheric

  6. A Tailward Moving Current Sheet Normal Magnetic Field Front Followed by an Earthward Moving Dipolarization Front

    Science.gov (United States)

    Hwang, K.-J.; Goldstein, M. L.; Moore, T. E.; Walsh, B. M.; Baishev, D. G.; Moiseyev, A. V.; Shevtsov, B. M.; Yumoto, K.

    2014-01-01

    A case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.

  7. Magnetotail Current Sheet in the Regime of Chaotic Dynamics of Plasma Particles

    Science.gov (United States)

    Malova, Helmi; Zelenyi, Lev; Popov, Victor; Ulkin, Alexander

    We investigate the Earth’s magnetotail current sheet which sometimes can be strongly thinned during substorms and is observed as almost 1D structure with thickness about several ion gyroradius. This extremely thin current sheet (TCS) is possibly the key element of substorms due to the accumulation of solar wind magnetic energy and its consequent release. 1D hybrid model is developed to describe TCS configuration and to determine the possible regimes of its existence, especially the states when most part of ion population move in the regime of dynamical chaos. The ion motion is described in kinetic approach, but magnetized electrons are considered as the fluid flow, providing the quasi-neutrality in the system. The convergence of current sheet model to equilibrium solutions is studied in the wide diapason of parameters of the system. It is shown that parameter adiabaticity kappa, governing particle motion, plays a general role in the current sheet structure. When kappa increases from 0.1 to 0.5 a great number of quasi-trapped ions are accumulated near current sheet. Their local currents do not contribute in the total current, but locally redistribute current density profile leading to the decrease of its central maximum and consequent TCS thickening. It is shown that the convergence of numerical codes to equilibrium state in the interval kappa ~0.4-0.5 is due to only electron curvature drifts currents, whereas the ion component shows the chaotic motion. At larger values of parameter kappa the density of quasi-trapped particles is increased substantially, leading to the destruction of current sheet equilibrium solutions. The implication of these effects to auroral manifestations of magnetotail dynamics is discussed.

  8. Pulse Current Assisted TLP Bonding of SiCP/Al Composites Sheet Using Powders Interlayer

    Directory of Open Access Journals (Sweden)

    WANG Bo

    2017-06-01

    Full Text Available The powders interlayer was applied for transient liquid phase (TLP bonding of SiCp/Al composites using pulse current heating. Pulse current got though the joint with powder interlayer and generated the effect of Joule heat and spark plasma sintering to achieve the TLP bonding of SiCp/Al composites sheet. The results show that there is the good TLP bonded joint without defects under the conditions of vacuum:1.39×103 Pa; Pulse current density: 115 A/mm2; holding time: 15-60 min; original pressure: 0.5 MPa. The results reveal the dense joint without pores composed of the Al-based solid solution, pure Ti zone, Al2Cu, and Al3Ti intermetallic phase. Furthermore, the thermal and isothermal effects of pulse current on in situ synthesis of TLP bonded joints of SiCp/Al composites using mixed Al-Cu-Ti powder interlayer are analyzed and discussed. According to microstructure of joint, pulse current promote to in situ form the intermetallic compound, which can provide higher mechanical properties of joint.

  9. Dynamical Structure of the Cross-tail Current Sheet During Substorms Observed by Cluster

    Science.gov (United States)

    Asano, Y.; Nakamura, R.; Runov, A.; Takada, T.; Baumjohann, W.; Balogh, A.; Klecker, B.; Rème, H.

    2005-12-01

    We report on the dynamical variation of the current sheet structure in the magnetotail using magnetic field and plasma data obtained by the Cluster multi-satellites. It is found that in some cases the thickness of the cross-tail current sheet shows temporal variations repeatedly. This sausage-mode-like variation is associated with substorm onsets or occurrence of fast plasma flows, with the time scale of several minutes before substorm onsets or fast flows and of a half to one minute afterwards. It frequently coexists with kink-mode-like wave or flapping motion. Such sausage-mode-like variation is mainly observed in the central part of the plasma sheet, and forms transient bifurcated currents or the intense current in the center.

  10. Nanostructure characterization of beta-sheet crystals in silk under various temperatures

    Directory of Open Access Journals (Sweden)

    Zhang Yan

    2014-01-01

    Full Text Available This paper studies the nanostructure characterizations of β-sheet in silk fiber with different reaction temperatures. A molecular dynamic model is developed and simulated by Gromacs software packages. The results reveal the change rules of the number of hydrogen bonds in β-sheet under different temperatures. The best reaction temperature for the β-sheet crystals is also found. This work provides theoretical basis for the designing of materials based on silk.

  11. MAGNETIC FIELD RELAXATION AND CURRENT SHEETS IN AN IDEAL PLASMA

    International Nuclear Information System (INIS)

    Candelaresi, S.; Pontin, D. I.; Hornig, G.

    2015-01-01

    We investigate the existence of magnetohydrostatic equilibria for topologically complex magnetic fields. The approach employed is to perform ideal numerical relaxation experiments. We use a newly developed Lagrangian relaxation scheme that exactly preserves the magnetic field topology during the relaxation. Our configurations include both twisted and sheared fields, of which some fall into the category for which Parker predicted no force-free equilibrium. The first class of field considered contains no magnetic null points, and field lines connect between two perfectly conducting plates. In these cases, we observe only resolved current layers of finite thickness. In further numerical experiments, we confirm that magnetic null points are loci of singular currents

  12. On the instability of a quasiequilibrium current sheet and the onset of impulsive bursty reconnection

    International Nuclear Information System (INIS)

    Skender, Marina; Lapenta, Giovanni

    2010-01-01

    A two-dimensional reconnecting current sheet is studied numerically in the magnetohydrodynamic approach. Different simulation setups are employed in order to follow the evolution of the formed current sheet in diverse configurations: two types of initial equilibria, Harris and force-free, two types of boundary conditions, periodic and open, with uniform and nonuniform grid set, respectively. All the simulated cases are found to exhibit qualitatively the same behavior in which a current sheet evolves slowly through a series of quasiequilibria; eventually it fragments and enters a phase of fast impulsive bursty reconnection. In order to gain more insight on the nature and characteristics of the instability taking place, physical characteristics of the simulated current sheet are related to its geometrical properties. At the adopted Lundquist number of S=10 4 and Reynolds number R=10 4 , the ratio of the length to width (aspect ratio) of the formed current sheet is observed to increase slowly in time up to a maximum value at which it fragments. Moreover, additional turbulence applied to the system is shown to exhibit the same qualitative steps, but with the sooner onset of the fragmentation and at smaller aspect ratio.

  13. Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

    International Nuclear Information System (INIS)

    Rappazzo, A. F.; Velli, M.; Matthaeus, W. H.; Ruffolo, D.; Servidio, S.

    2017-01-01

    The magnetic topology and field line random walk (FLRW) properties of a nanoflare-heated and magnetically confined corona are investigated in the reduced magnetohydrodynamic regime. Field lines originating from current sheets form coherent structures, called current sheet connected (CSC) regions, which extend around them. CSC FLRW is strongly anisotropic, with preferential diffusion along the current sheets’ in-plane length. CSC FLRW properties remain similar to those of the entire ensemble but exhibit enhanced mean square displacements and separations due to the stronger magnetic field intensities in CSC regions. The implications for particle acceleration and heat transport in the solar corona and wind, and for solar moss formation are discussed.

  14. Linear evolution of current sheets in sheared force-free magnetic fields with discontinuous connectivity

    Science.gov (United States)

    Wolfson, Richard

    1990-01-01

    Thin current sheets arising in tenuous, magnetized solar coronal plasmas may constitute an important mechanism for energy buildups and subsequent energy releases; they could arise from the continuous-and-random motion of magnetic footprints associated with photospheric velocity fields. A model is presented for study of the quasi-static evolution of current sheets due to shearing of the footpoints, in a highly idealized geometry that incorporates an abrupt jump in field-line connectivity. The model highlights that formation of thin current layers and allows large shearing motions prior to violation of the linear approximation. Excess energy comparable to that released by solar flares can be stored in a sheared field.

  15. Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

    Energy Technology Data Exchange (ETDEWEB)

    Rappazzo, A. F.; Velli, M. [Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, CA 90095 (United States); Matthaeus, W. H. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Ruffolo, D. [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); Servidio, S., E-mail: rappazzo@ucla.edu [Dipartimento di Fisica, Università della Calabria, Cosenza I-87036 (Italy)

    2017-07-20

    The magnetic topology and field line random walk (FLRW) properties of a nanoflare-heated and magnetically confined corona are investigated in the reduced magnetohydrodynamic regime. Field lines originating from current sheets form coherent structures, called current sheet connected (CSC) regions, which extend around them. CSC FLRW is strongly anisotropic, with preferential diffusion along the current sheets’ in-plane length. CSC FLRW properties remain similar to those of the entire ensemble but exhibit enhanced mean square displacements and separations due to the stronger magnetic field intensities in CSC regions. The implications for particle acceleration and heat transport in the solar corona and wind, and for solar moss formation are discussed.

  16. Impact of the storm-time plasma sheet ion composition on the ring current energy density

    Science.gov (United States)

    Mouikis, C.; Kistler, L. M.; Petrinec, S. M.; Fuselier, S. A.; Cohen, I.

    2017-12-01

    The adiabatic inward transport of the night-side near-earth ( 6 Re) hot plasma sheet is the dominant contributor to the ring current pressure during storm times. During storm times, the plasma sheet composition in the 6 - 12 Re tail region changes due to O+ entry from the lobes (from the cusp) and the direct feeding from the night side auroral region. In addition, at substorm onset the plasma sheet O+ ions can be preferentially accelerated. We use MMS and observations during two magnetic storms, 5/8/2016 and 7/16/2017, to monitor the composition changes and energization in the 6 - 12 Re plasma sheet region. For both storms the MMS apogee was in the tail. In addition, we use subsequent Van Allen Probe observations (with apogee in the dawn and dusk respectively) to test if the 6-12 Re plasma sheet, observed by MMS, is a sufficient source of the O+ in the ring current. For this we will compare the phase space density (PSD) of the plasma sheet source population and the PSD of the inner magnetosphere at constant magnetic moment values as used in Kistler et al., [2016].

  17. Fragmentation of the Current Sheet, Anomalous Resistivity, and Acceleration of Particles

    Czech Academy of Sciences Publication Activity Database

    Karlický, Marian; Bárta, Miroslav

    2008-01-01

    Roč. 247, č. 2 (2008), s. 335-342 ISSN 0038-0938 R&D Projects: GA AV ČR IAA300030701 Institutional research plan: CEZ:AV0Z10030501 Keywords : electric currents and current sheets * acceleration Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 2.774, year: 2008

  18. Current sheet formation in a sheared force-free-magnetic field. [in sun

    Science.gov (United States)

    Wolfson, Richard

    1989-01-01

    This paper presents the results of a study showing how continuous shearing motion of magnetic footpoints in a tenuous, infinitely conducting plasma can lead to the development of current sheets, despite the absence of such sheets or even of neutral points in the initial state. The calculations discussed here verify the earlier suggestion by Low and Wolfson (1988) that extended current sheets should form due to the shearing of a force-free quadrupolar magnetic field. More generally, this work augments earlier studies suggesting that the appearance of discontinuities - current sheets - may be a necessary consequence of the topological invariance imposed on the magnetic field geometry of an ideal MHD system by virtue of its infinite conductivity. In the context of solar physics, the work shows how the gradual and continuous motion of magnetic footpoints at the solar photosphere may lead to the buildup of magnetic energy that can then be released explosively when finite conductivity effects become important and lead to the rapid dissipation of current sheets. Such energy release may be important in solar flares, coronal mass ejections, and other eruptive events.

  19. The crack growth resistance of thin steel sheets under eccentric ...

    Indian Academy of Sciences (India)

    Ľ AMBRIŠKO

    2018-03-10

    Mar 10, 2018 ... for crack initiation were also estimated. The relation between Ji and J0.2 was assessed using the basic mathe- matical and statistical methods. This relation was described by a linear regression model. Keywords. Cold-formed steel; thin sheet; stable crack growth; R-curve; videoextensometry. 1. Introduction.

  20. The crack growth resistance of thin steel sheets under eccentric ...

    Indian Academy of Sciences (India)

    Ľ AMBRIŠKO

    MS received 1 August 2016; revised 13 July 2017; accepted 31 July 2017; published online 10 March 2018. Abstract. The stable crack growth in thin steel sheets is the topic of this paper. The crack ..... [26] Ambriško L', Kandra T and Pešek L 2011 Rating indentation and deformation characteristics laser welds. Chem. Listy.

  1. Kinetic models of two-dimensional plane and axially symmetric current sheets: Group theory approach

    Energy Technology Data Exchange (ETDEWEB)

    Vasko, I. Y.; Artemyev, A. V. [Space Research Institute, RAS, Moscow (Russian Federation); Popov, V. Y. [Space Research Institute, RAS, Moscow (Russian Federation); Department of Physics, Moscow State University, Moscow (Russian Federation); Malova, H. V. [Space Research Institute, RAS, Moscow (Russian Federation); Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow (Russian Federation)

    2013-02-15

    In this paper, we present new class of solutions of Grad-Shafranov-like (GS-like) equations, describing kinetic plane and axially symmetric 2D current sheets. We show that these equations admit symmetry groups only for Maxwellian and {kappa}-distributions of charged particles. The admissible symmetry groups are used to reduce GS-like equations to ordinary differential equations for invariant solutions. We derive asymptotes of invariant solutions, while invariant solutions are found analytically for the {kappa}-distribution with {kappa}=7/2. We discuss the difference of obtained solutions from equilibria widely used in other studies. We show that {kappa} regulates the decrease rate of plasma characteristics along the current sheet and determines the spatial distribution of magnetic field components. The presented class of plane and axially symmetric (disk-like) current sheets includes solutions with the inclined neutral plane.

  2. Spontaneous current sheets in magnetic fields with applications to stellar X-rays

    CERN Document Server

    Parker, Eugene N

    1994-01-01

    Expanding upon the ideas first proposed in his seminal book Cosmical Magnetic Fields, Eugene N. Parker here offers the first in-depth treatment of the magnetohydrodynamic theory of spontaneous magnetic discontinuities. In detailing his theory of the spontaneous formation of tangential discontinuities (current sheets) in a magnetic field embedded in highly conducting plasma, Parker shows how it can be used to explain the activity of the external magnetic fields of planets, stars, interstellar gas clouds, and galaxies, as well as the magnetic fields in laboratory plasmas. Provocative and fascinating, Spontaneous Current Sheets in Magnetic Fields presents a bold new theory that will excite interest and discussion throughout the space physics community.

  3. Analytical theory of neutral current sheets with a sheared magnetic field in collisionless relativistic plasma

    Science.gov (United States)

    Kocharovsky, V. V.; Kocharovsky, Vl V.; Martyanov, V. Yu; Nechaev, A. A.

    2017-12-01

    We derive and describe analytically a new wide class of self-consistent magnetostatic structures with sheared field lines and arbitrary energy distributions of particles. To do so we analyze superpositions of two planar current sheets with orthogonal magnetic fields and cylindrically symmetric momentum distribution functions, such that the magnetic field of one of them is directed along the symmetry axis of the distribution function of the other. These superpositions satisfy the pressure balance equation and allow one to construct configurations with an almost arbitrarily sheared magnetic field. We show that most of previously known current sheet families with sheared magnetic field lines are included in this novel class.

  4. Onset of reconnection in thin current sheets: Three-dimensional particle simulations

    Science.gov (United States)

    Scholer, M.; Sidorenko, I.; Jaroschek, C.; Treumann, R. A.

    2003-04-01

    The onset of reconnection in thin current sheets is investigated by means of three-dimensional full particle (PIC) simulations. Instead of imposing reconnection ab initio (as done in the GEM reconnection challenge), reconnection is allowed to develop out of the numerical noise. We do not impose symmetry about the midplane, so that the drift kink instability, the Kelvin-Helmholtz instability, and the sausage instability are allowed for, and we use a relatively high mass ratio of m_i/m_e=160. Two cases are investigated: (1) a thin current sheet with exactly anti-parallel fields,(2) a thin current sheet with a guide field of the same order as the anti-parallel field. In bothe cases the lower hybrid drift instability develops at the boundary of the current layer. The electric field in the center accelerates the electrons, while the ions are unmagnetized. The current density increase and the corresponding thinning of the current sheet results in case (1) in rapid reconnection on a time scale of about 10 inverse ion gyro-frequencies. While reconnection is initially patchy, the neutral lines merge and reconnection becomes eventually two-dimensional. In case (2) reconnection occurs after considerbly longer times and is essentially from the beginning two-dimensional.

  5. Measurement research on magnetic properties of electrical sheet steel under different temperature, harmonic and dc bias

    Directory of Open Access Journals (Sweden)

    Dezhi Chen

    2017-05-01

    Full Text Available The iron core of large power transformer is mainly composed of electrical sheet steel, which is easily affected by temperature, harmonic, and DC bias. Therefore, it is necessary to measure the magnetic properties of electrical sheet steel under different temperature, harmonic and DC Bias. This paper presents the experiment measurement system for the 30ZH120 electrical steel sheet. The B-H magnetization curve, permeability, and loss curve under different temperature, different harmonic, and different DC bias are given, respectively. The simulation of transformer is carried out by using measuring result under DC bias. The presented research provides a reference for optimizing the design of power transformer.

  6. The effect of wall friction on the current-sheet speed of a magnetically driven shock tube

    DEFF Research Database (Denmark)

    Chang, C.T.

    1971-01-01

    The effect of wall friction on the current-sheet speed is examined by taking some plausible forms of the friction into consideration. The analysis shows that the current-sheet always attains a steady state regardless of the types of friction concerned. It further shows that the experimentally...... observed velocity limitation of the current-sheet at discharge conditions of high voltage and low pressure might be attributed to a friction drag varying linearly with the driving current and the current-sheet speed....

  7. Preservation of a Preglacial Landscape Under the Center of the Greenland Ice Sheet

    Science.gov (United States)

    Bierman, Paul R.; Corbett, Lee B.; Graly, Joseph A.; Neumann, Thomas Allen; Lini, Andrea; Crosby, Benjamin T.; Rood, Dylan H.

    2014-01-01

    Continental ice sheets typically sculpt landscapes via erosion; under certain conditions, ancient landscapes can be preserved beneath ice and can survive extensive and repeated glaciation. We used concentrations of atmospherically produced cosmogenic beryllium-10, carbon, and nitrogen to show that ancient soil has been preserved in basal ice for millions of years at the center of the ice sheet at Summit, Greenland. This finding suggests ice sheet stability through the Pleistocene (i.e., the past 2.7 million years). The preservation of this soil implies that the ice has been non-erosive and frozen to the bed for much of that time, that there was no substantial exposure of central Greenland once the ice sheet became fully established, and that preglacial landscapes can remain preserved for long periods under continental ice sheets

  8. Tearing, coalescence and fragmentation processes in solar flare current sheet and drifting pulsating structures

    Czech Academy of Sciences Publication Activity Database

    Karlický, Marian

    2010-01-01

    Roč. 46, č. 4 (2010), s. 377-381 ISSN 0273-1177 R&D Projects: GA AV ČR IAA300030701 Institutional research plan: CEZ:AV0Z10030501 Keywords : solar physics * current sheets * plasma waves Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.076, year: 2010

  9. Electron Acceleration in a Turbulent Current Sheet - Comparison of GCA and HARHA Methods

    Czech Academy of Sciences Publication Activity Database

    Kramoliš, D.; Varady, Michal; Bárta, Miroslav

    2016-01-01

    Roč. 40, č. 1 (2016), s. 69-77 ISSN 1845-8319. [Hvar Astrophysical Colloquium /14./. Hvar, 26.09.2016-30.09.2016] R&D Projects: GA ČR(CZ) GA16-18495S Institutional support: RVO:67985815 Keywords : magnetic reconnection * current sheet * electron acceleration Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  10. Multispacecraft observations of the electron current sheet, neighboring magnetic islands, and electron acceleration during magnetotail reconnection

    Czech Academy of Sciences Publication Activity Database

    Chen, L. J.; Bessho, N.; Lefebvre, B.; Vaith, H.; Asnes, A.; Santolík, Ondřej; Fazakerley, A.; Puhl-Quinn, P.; Bhattacharjee, A.; Khotyaintsev, Y.; Daly, P.; Torbert, R.

    2009-01-01

    Roč. 16, - (2009), 056501/1-056501/12 ISSN 1070-664X Institutional research plan: CEZ:AV0Z30420517 Keywords : magnetotail reconnection * electron current sheet * multispacecraft observations Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.475, year: 2009

  11. Electron Cooling and Isotropization during Magnetotail Current Sheet Thinning: Implications for Parallel Electric Fields

    Science.gov (United States)

    Lu, San; Artemyev, A. V.; Angelopoulos, V.

    2017-11-01

    Magnetotail current sheet thinning is a distinctive feature of substorm growth phase, during which magnetic energy is stored in the magnetospheric lobes. Investigation of charged particle dynamics in such thinning current sheets is believed to be important for understanding the substorm energy storage and the current sheet destabilization responsible for substorm expansion phase onset. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C observations in 2008 and 2009 at 18 - 25 RE to show that during magnetotail current sheet thinning, the electron temperature decreases (cooling), and the parallel temperature decreases faster than the perpendicular temperature, leading to a decrease of the initially strong electron temperature anisotropy (isotropization). This isotropization cannot be explained by pure adiabatic cooling or by pitch angle scattering. We use test particle simulations to explore the mechanism responsible for the cooling and isotropization. We find that during the thinning, a fast decrease of a parallel electric field (directed toward the Earth) can speed up the electron parallel cooling, causing it to exceed the rate of perpendicular cooling, and thus lead to isotropization, consistent with observation. If the parallel electric field is too small or does not change fast enough, the electron parallel cooling is slower than the perpendicular cooling, so the parallel electron anisotropy grows, contrary to observation. The same isotropization can also be accomplished by an increasing parallel electric field directed toward the equatorial plane. Our study reveals the existence of a large-scale parallel electric field, which plays an important role in magnetotail particle dynamics during the current sheet thinning process.

  12. Additional acceleration of solar-wind particles in current sheets of the heliosphere

    Directory of Open Access Journals (Sweden)

    V. Zharkova

    2015-04-01

    Full Text Available Particles of fast solar wind in the vicinity of the heliospheric current sheet (HCS or in a front of interplanetary coronal mass ejections (ICMEs often reveal very peculiar energy or velocity profiles, density distributions with double or triple peaks, and well-defined streams of electrons occurring around or far away from these events. In order to interpret the parameters of energetic particles (both ions and electrons measured by the WIND spacecraft during the HCS crossings, a comparison of the data was carried out with 3-D particle-in-cell (PIC simulations for the relevant magnetic topology (Zharkova and Khabarova, 2012. The simulations showed that all the observed particle-energy distributions, densities, ion peak velocities, electron pitch angles and directivities can be fitted with the same model if the heliospheric current sheet is in a status of continuous magnetic reconnection. In this paper we present further observations of the solar-wind particles being accelerated to rather higher energies while passing through the HCS and the evidence that this acceleration happens well before the appearance of the corotating interacting region (CIR, which passes through the spacecraft position hours later. We show that the measured particle characteristics (ion velocity, electron pitch angles and the distance at which electrons are turned from the HCS are in agreement with the simulations of additional particle acceleration in a reconnecting HCS with a strong guiding field as measured by WIND. A few examples are also presented showing additional acceleration of solar-wind particles during their passage through current sheets formed in a front of ICMEs. This additional acceleration at the ICME current sheets can explain the anticorrelation of ion and electron fluxes frequently observed around the ICME's leading front. Furthermore, it may provide a plausible explanation of the appearance of bidirectional "strahls" (field-aligned most energetic

  13. Statistical and spectral properties of magnetic islands in reconnecting current sheets during two-ribbon flares

    International Nuclear Information System (INIS)

    Shen, Chengcai; Lin, Jun; Murphy, Nicholas A.; Raymond, John C.

    2013-01-01

    We perform a set of two dimensional resistive magnetohydrodynamic simulations to study the reconnection process occurring in current sheets that develop during solar eruptions. Reconnection commences gradually and produces small-scale structures inside the current sheet, which has one end anchored to the bottom boundary and the other end open. The main features we study include plasmoids (or plasma blobs) flowing in the sheet, and X-points between pairs of adjacent islands. The statistical properties of the fine structure and the dependence of the spectral energy on these properties are examined. The flux and size distribution functions of plasmoids roughly follow inverse square power laws at large scales. The mass distribution function is steep at large scales and shallow at small scales. The size distribution also shows that plasmoids are highly asymmetric soon after being formed, while older plasmoids tend to be more circular. The spectral profiles of magnetic and kinetic energy inside the current sheet are both consistent with a power law. The corresponding spectral indices γ are found to vary with the magnetic Reynolds number R m of the system, but tend to approach a constant for large R m (>10 5 ). The motion and growth of blobs change the spectral index. The growth of new islands causes the power spectrum to steepen, but it becomes shallower when old and large plasmoids leave the computational domain

  14. Hysteresis-controlled instability waves in a scale-free driven current sheet model

    Directory of Open Access Journals (Sweden)

    V. M. Uritsky

    2005-01-01

    Full Text Available Magnetospheric dynamics is a complex multiscale process whose statistical features can be successfully reproduced using high-dimensional numerical transport models exhibiting the phenomenon of self-organized criticality (SOC. Along this line of research, a 2-dimensional driven current sheet (DCS model has recently been developed that incorporates an idealized current-driven instability with a resistive MHD plasma system (Klimas et al., 2004a, b. The dynamics of the DCS model is dominated by the scale-free diffusive energy transport characterized by a set of broadband power-law distribution functions similar to those governing the evolution of multiscale precipitation regions of energetic particles in the nighttime sector of aurora (Uritsky et al., 2002b. The scale-free DCS behavior is supported by localized current-driven instabilities that can communicate in an avalanche fashion over arbitrarily long distances thus producing current sheet waves (CSW. In this paper, we derive the analytical expression for CSW speed as a function of plasma parameters controlling local anomalous resistivity dynamics. The obtained relation indicates that the CSW propagation requires sufficiently high initial current densities, and predicts a deceleration of CSWs moving from inner plasma sheet regions toward its northern and southern boundaries. We also show that the shape of time-averaged current density profile in the DCS model is in agreement with steady-state spatial configuration of critical avalanching models as described by the singular diffusion theory of the SOC. Over shorter time scales, SOC dynamics is associated with rather complex spatial patterns and, in particular, can produce bifurcated current sheets often seen in multi-satellite observations.

  15. VOYAGER OBSERVATIONS OF MAGNETIC SECTORS AND HELIOSPHERIC CURRENT SHEET CROSSINGS IN THE OUTER HELIOSPHERE

    Energy Technology Data Exchange (ETDEWEB)

    Richardson, J. D. [Kavli Center for Astrophysics and Space Science, Massachusetts Institute of Technology, Cambridge, 02139 (United States); Burlaga, L. F. [NASA Goddard Space Flight Center, Code 673, Greenbelt, MD 20771 (United States); Drake, J. F. [Department of Physics and Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 (United States); Hill, M. E. [Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20723 (United States); Opher, M., E-mail: jdr@space.mit.edu, E-mail: lburlagahsp@verizon.net, E-mail: drake@umd.edu, E-mail: Matthew.Hill@jhuapl.edu, E-mail: mopher@bu.edu [Astronomy Department, Boston University, 675 Commonwealth Avenue, Boston, MA 02215 (United States)

    2016-11-10

    Voyager 1 ( V1 ) has passed through the heliosheath and is in the local interstellar medium. Voyager 2 ( V2 ) has been in the heliosheath since 2007. The role of reconnection in the heliosheath is under debate; compression of the heliospheric current sheets (HCS) in the heliosheath could lead to rapid reconnection and a reconfiguration of the magnetic field topology. This paper compares the expected and actual amounts of time the Voyager spacecraft observe each magnetic sector and the number of HCS crossings. The predicted and observed values generally agree well. One exception is at Voyager 1 in 2008 and 2009, where the distribution of sectors is more equal than expected and the number of HCS crossings is small. Two other exceptions are at V1 in 2011–2012 and at V2 in 2012, when the spacecraft are in the opposite magnetic sector less than expected and see fewer HCS crossings than expected. These features are consistent with those predicted for reconnection, and consequently searches for other reconnection signatures should focus on these times.

  16. The most intense current sheets in the high-speed solar wind near 1 AU

    Science.gov (United States)

    Podesta, John J.

    2017-03-01

    Electric currents in the solar wind plasma are investigated using 92 ms fluxgate magnetometer data acquired in a high-speed stream near 1 AU. The minimum resolvable scale is roughly 0.18 s in the spacecraft frame or, using Taylor's "frozen turbulence" approximation, one proton inertial length di in the plasma frame. A new way of identifying current sheets is developed that utilizes a proxy for the current density J obtained from the derivatives of the three orthogonal components of the observed magnetic field B. The most intense currents are identified as 5σ events, where σ is the standard deviation of the current density. The observed 5σ events are characterized by an average scale size of approximately 3di along the flow direction of the solar wind, a median separation of around 50di or 100di along the flow direction of the solar wind, and a peak current density on the order of 0.5 pA/cm2. The associated current-carrying structures are consistent with current sheets; however, the planar geometry of these structures cannot be confirmed using single-point, single-spacecraft measurements. If Taylor's hypothesis continues to hold for the energetically dominant fluctuations at kinetic scales 1current-carrying structures in high-speed wind occur at electron scales, although the peak current densities at kinetic and electron scales are predicted to be nearly the same as those found in this study.

  17. Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator

    Science.gov (United States)

    Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

    2011-01-01

    Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration

  18. Observations of steady anomalous magnetic heating in thin current sheets. [of solar corona

    Science.gov (United States)

    Martens, P. C. H.; Van Den Oord, G. H. J.; Hoyng, P.

    1985-01-01

    The Hard X-ray Imaging Spectrometer of the Solar Maximum Mission has yielded observations of a faint, steadily emitting loop-like structure, which have allowed the thermal evolution of this loop over a period of about 15 hr to be followed. Only 0.1 percent of the volume of the loop appears to be steadily heated, at the large rate of 0.6 erg/cu cm sec; this suggests that the heating represents the dissipation of magnetic fields in thin current sheets. Ion-kinetic tearing, as proposed by Galeev et al. (1981), is noted to be especially consonant with these observations. The source of the present X-ray emission is identified with the H-alpha filament in the same region. The present findings are held to constitute the first direct evidence for the steady dissipation of coronal magnetic fields via enhanced thin current sheet resistivity.

  19. Thin and superthin ion current sheets. Quasi-adiabatic and nonadiabatic models

    Directory of Open Access Journals (Sweden)

    L. M. Zelenyi

    2000-01-01

    Full Text Available Thin anisotropic current sheets (CSs are phenomena of the general occurrence in the magnetospheric tail. We develop an analytical theory of the self-consistent thin CSs. General solitions of the Grad-Shafranov equation are obtained in a quasi-adiabatic approximation which neglects the jumps of the sheet adiabatic invariant Iz This is possible if the anisotropy of the initial distribution function is not too strong. The resulting structure of the thin CSs is interpreted as a sum of negative dia- and positive paramagnetic currents flowing near the neutral plane. In the immediate vicinity of the magnetic field reversal region the paramagnetic current arising from the meandering motion of the ions on Speiser orbits dominates. The maximum CS thick-ness is achieved in the case of weak plasma anisotropy and is of the order of the thermal ion gyroradius outside the sheet. A unified picture of thin CS scalings includes both the quasi-adiabatic regimes of weak and strong anisotropies and the nonadiabatic limit of super-strong anisotropy of the source ion distribution. The later limit corresponds to the case of almost field-aligned initial distribution, when the ratio of the drift velocity outside the CS to the thermal ion velocity exceeds the ratio of the magnetic field outside the CS to its value in-side the CS (vD/vT> B0/Bn. In this regime the jumps of Iz, become essential, and the current sheet thickness is approaching to some small but finite value, which depends upon the parameter Bn /B0. Convective electric field increases the effective anisotropy of the source distribution and might produce the essential CS thinning which could have important implications for the sub-storm dynamics.

  20. The structure of strongly tilted current sheets in the Earth magnetotail

    Directory of Open Access Journals (Sweden)

    I. Y. Vasko

    2014-02-01

    Full Text Available We investigate strongly tilted (in the y–z GSM plane current sheets (CSs in the Earth magnetotail using data from the Cluster mission. We analyze 29 CS crossings observed in 2001–2004. The characteristic current density, magnetic field at the CS boundary and the CS thickness of strongly tilted CSs are similar to those reported previously for horizontal (not tilted CSs. We confirm that strongly tilted CSs are generally characterized by a rather large northward component of the magnetic field. The field-aligned current in strongly tilted CSs is on average two times larger than the transverse current. The proton adiabaticity parameter, κp, is larger than 0.5 in 85% of strongly tilted CSs due to the large northward magnetic field. Thus, the proton dynamics is stochastic for 18 current sheets with 0.5 p p > 3, whereas electrons are magnetized for all observed current sheets. Strongly tilted CSs provide a unique opportunity to measure the electric field component perpendicular to the CS plane. We find that most of the electric field perpendicular to the CS plane is due to the decoupling of electron and ion motions (plasma polarization. For 27 CSs we determine profiles of the electrostatic potential, which is due to the plasma polarization. Drops in the potential between the neutral plane and the CS boundary are within the range of 200 V to 12 kV, while maximal values of the electric field are within the range of 0.2 mV m−1 to 8 mV m−1. For 16 CSs the observed potentials are in accordance with Ohm's law, if the electron current density is assumed to be comparable to the total current density. In 15 of these CSs the profile of the polarization potential is approximately symmetric with respect to the neutral plane and has minimum therein.

  1. The Role of Current Sheets in Solar Eruptive Events: An ISSI International Team Project

    Science.gov (United States)

    Suess, Steven T.; Poletto, Giannina

    2006-01-01

    Current sheets (CSs) are a prerequisite for magnetic reconnection. An International Space Science Institute (ISSI, of Bern, Switzerland) research team will work to empirically define current sheet properties in the solar atmosphere and their signatures in the interplanetary medium, and to understand their role in the development of solar eruptive events. The project was inspired by recently acquired ground and space based observations that reveal CS signatures at the time of flares and Coronal Mass Ejections (CMEs), in the chromosphere, in the corona and in the interplanetary medium. At the same time, theoretical studies predict the formation of CSs in different models and configurations, but theories and observational results have not yet developed an interaction efficient enough to allow us to construct a unified scenario. The team will generate synergy between observers, data analysts, and theoreticians, so as to enable a significant advance in understanding of current sheet behavior and properties. A further motivation for studying CSs is related to the expected electric fields in CSs that may be the source of solar energetic particles (SEPs). The team has 14 members from Europe and the US. The first meeting is in October 2006 and the second is late in 2007.

  2. MULTIPLE CURRENT SHEET SYSTEMS IN THE OUTER HELIOSPHERE: ENERGY RELEASE AND TURBULENCE

    Energy Technology Data Exchange (ETDEWEB)

    Burgess, D.; Gingell, P. W. [School of Physics and Astronomy, Queen Mary University of London, London E1 4NS (United Kingdom); Matteini, L. [Imperial College London, London SW7 2AZ (United Kingdom)

    2016-05-01

    In the outer heliosphere, beyond the solar wind termination shock, it is expected that the warped heliospheric current sheet forms a region of closely packed, multiple, thin current sheets. Such a system may be subject to the ion-kinetic tearing instability, and hence may generate magnetic islands and hot populations of ions associated with magnetic reconnection. Reconnection processes in this environment have important implications for local particle transport, and for particle acceleration at reconnection sites and in turbulence. We study this complex environment by means of three-dimensional hybrid simulations over long timescales, in order to capture the evolution from linear growth of the tearing instability to a fully developed turbulent state at late times. The final state develops from the highly ordered initial state via both forward and inverse cascades. Component and spectral anisotropy in the magnetic fluctuations is present when a guide field is included. The inclusion of a population of newborn interstellar pickup protons does not strongly affect these results. Finally, we conclude that reconnection between multiple current sheets can act as an important source of turbulence in the outer heliosphere, with implications for energetic particle acceleration and propagation.

  3. Conditions for the formation of nongyrotropic current sheets in slowly evolving plasmas

    International Nuclear Information System (INIS)

    Schindler, Karl; Hesse, Michael

    2010-01-01

    This paper addresses the formation of nongyrotropic current sheets resulting from slow external driving. The medium is a collisionless plasma with one spatial dimension and a three-dimensional velocity space. The study is based on particle simulation and an analytical approach. Earlier results that apply to compression of an initial Harris sheet are generalized in several ways. In a first step a general sufficient criterion for the presence of extra ion and electron currents due to nongyrotropic plasma conditions is derived. Then cases with antisymmetric magnetic and electric fields are considered. After establishing consistency of the criterion with the earlier case, the usefulness of this concept is illustrated in detail by two further particle simulations. The results indicate that the formation of nongyrotropic current sheets is a ubiquitous phenomenon for plasmas with antisymmetric fields that have evolved slowly from initial gyrotropic states. A fourth case concerns a plasma with a unidirectional magnetic field. Consistent with the general criterion, the observed final state is fluidlike in that it is approximately gyrotropic. Momentum balance is shown to include a contribution that results from accumulation of an off-diagonal pressure tensor component during the evolution. Heat flux also plays an important role.

  4. On the linear stability of sheared and magnetized jets without current sheets - relativistic case

    Science.gov (United States)

    Kim, Jinho; Balsara, Dinshaw S.; Lyutikov, Maxim; Komissarov, Serguei S.

    2018-03-01

    In our prior series of papers, we studied the non-relativistic and relativistic linear stability analysis of magnetized jets that do not have current sheets. In this paper, we extend our analysis to relativistic jets with a velocity shear and a similar current sheet free structure. The jets that we study are realistic because we include a velocity shear, a current sheet free magnetic structure, a relativistic velocity and a realistic thermal pressure so as to achieve overall pressure balance in the unperturbed jet. In order to parametrize the velocity shear, we apply a parabolic profile to the jets' 4-velocity. We find that the velocity shear significantly improves the stability of relativistic magnetized jets. This fact is completely consistent with our prior stability analysis of non-relativistic, sheared jets. The velocity shear mainly plays a role in stabilizing the short wavelength unstable modes for the pinch as well as the kink instability modes. In addition, it also stabilizes the long wavelength fundamental pinch instability mode. We also visualize the pressure fluctuations of each unstable mode to provide a better physical understanding of the enhanced stabilization by the velocity shear. Our overall conclusion is that combining velocity shear with a strong and realistic magnetic field makes relativistic jets even more stable.

  5. Modeling Solar Energetic Particle Transport near a Wavy Heliospheric Current Sheet

    Science.gov (United States)

    Battarbee, Markus; Dalla, Silvia; Marsh, Mike S.

    2018-02-01

    Understanding the transport of solar energetic particles (SEPs) from acceleration sites at the Sun into interplanetary space and to the Earth is an important question for forecasting space weather. The interplanetary magnetic field (IMF), with two distinct polarities and a complex structure, governs energetic particle transport and drifts. We analyze for the first time the effect of a wavy heliospheric current sheet (HCS) on the propagation of SEPs. We inject protons close to the Sun and propagate them by integrating fully 3D trajectories within the inner heliosphere in the presence of weak scattering. We model the HCS position using fits based on neutral lines of magnetic field source surface maps (SSMs). We map 1 au proton crossings, which show efficient transport in longitude via HCS, depending on the location of the injection region with respect to the HCS. For HCS tilt angles around 30°–40°, we find significant qualitative differences between A+ and A‑ configurations of the IMF, with stronger fluences along the HCS in the former case but with a distribution of particles across a wider range of longitudes and latitudes in the latter. We show how a wavy current sheet leads to longitudinally periodic enhancements in particle fluence. We show that for an A+ IMF configuration, a wavy HCS allows for more proton deceleration than a flat HCS. We find that A‑ IMF configurations result in larger average fluences than A+ IMF configurations, due to a radial drift component at the current sheet.

  6. Observations of Thin Current Sheets in the Solar Wind and Their Role in Magnetic Energy Dissipation

    Science.gov (United States)

    Perri, S.; Goldstein, M. L.; Dorelli, J.; Sahraoui, F.; Gurgiolo, C. A.; Karimabadi, H.; Mozer, F.; Wendel, D. E.; TenBarge, J.; Roytershteyn, V.

    2013-12-01

    A recent analysis of 450 vec/s resolution data from the STAFF search-coil magnetometer on board Cluster has revealed, for the first time, the presence of thin current sheets and discontinuities from the proton Larmor scale down to the electron Larmor scale in the solar wind. This is in the range of scales where a cascade of energy consistent with highly oblique kinetic Alfvénic fluctuations (KAW), eventually dissipated by electron Landau damping, has been detected. The current sheets have been found to have a size between 20-200 km, indicating that they are very localized. We will compare the observations with results coming from 2D Hall MHD, Gyrokinetic, and full Particle-in-Cell turbulence simulations. Preliminary work has highlighted promising qualitative agreement between the properties of the structures observed in the Cluster data and the current sheets generated in the simulations. With the aim of investigating the role played by those structures in dissipating the magnetic energy in the solar wind, E●J has been computed within each magnetic discontinuity. This has been made possible via a combined analysis of both STAFF-SC magnetic field data and the electric field data from the Electric Fields and Wave instrument (EFW). We describe procedures used to reduce the noise in the EFW data. The results obtained represent an effort to clarify the processes involved in the dissipation of magnetic energy in the solar wind.

  7. Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures

    NARCIS (Netherlands)

    Hajlasz, M.; Donkers, J.J.T.M.; Sque, S.J.; Heil, S.B.S.; Gravesteijn, Dirk J; Rietveld, F.J.R.; Schmitz, Jurriaan

    2014-01-01

    For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact

  8. THE TOPOLOGICAL CHANGES OF SOLAR CORONAL MAGNETIC FIELDS. III. RECONNECTED FIELD TOPOLOGY PRODUCED BY CURRENT-SHEET DISSIPATION

    International Nuclear Information System (INIS)

    Janse, A. M.; Low, B. C.

    2010-01-01

    In this paper, the third in a series of papers on topological changes of magnetic fields, we study how the dissipation of an initial current sheet (CS) in a closed three-dimensional (3D) field affects the field topology. The initial field is everywhere potential except at the location of the CS which is in macroscopic equilibrium under the condition of perfect conductivity. In the physical world of extremely high, but finite, conductivity, the CS dissipates and the field seeks a new equilibrium state in the form of an everywhere potential field since the initial field is everywhere untwisted. Our semi-analytical study indicates that the dissipation of the single initial CS must induce formation of additional CSs in extensive parts of the magnetic volume. The subsequent dissipation of these other sheets brings about topological changes by magnetic reconnection in order for the global field to become potential. In 2D fields, the magnetic reconnection due to the dissipation of a CS is limited to the magnetic vicinity of the dissipating sheet. Thus, the consequence of CS dissipation is physically and topologically quite different in 2D and 3D fields. A discussion of this result is given in general relation to the Parker theory of spontaneous CSs and heating in the solar corona and solar flares.

  9. Measurement of ion velocity profiles in a magnetic reconnection layer via current sheet jogging

    Science.gov (United States)

    Stein, G.; Yoo, J.; Yamada, M.; Ji, H.; Dorfman, S.; Lawrence, E.; Myers, C.; Tharp, T.

    2011-10-01

    In many laboratory plasmas, constructing stationary Langmuir and Mach probe arrays with resolution on the order of electron skin depth is technically difficult, and can introduce significant plasma perturbations. However, complete two- dimensional profiles of plasma density, electron temperature, and ion flow are important for studying the transfer of energy from magnetic fields to particles during magnetic reconnection. Through the use of extra ``Shaping Field'' coils in the Magnetic Reconnection Experiment (MRX) at the Princeton Plasma Physics Laboratory, the inward motion of the current sheet in the reconnection layer can be accelerated, or ``jogged,'' allowing the measurement of different points across the sheet with stationary probes. By acquiring data from Langmuir probes and Mach probes at different locations in the MRX with respect to the current sheet center, profiles of electron density and temperature and a vector plot of two-dimensional ion velocity in the plane of reconnection are created. Results from probe measurements will be presented and compared to profiles generated from computer simulation.

  10. The energy-based scaling of a thin current sheet: Case study

    Science.gov (United States)

    Sasunov, Yu. L.; Khodachenko, M. L.; Alexeev, I. I.; Belenkaya, E. S.; Gordeev, E. I.; Kubyshkin, I. V.

    2015-11-01

    The influence of average plasma energy on the half thickness ℓ of a thin current sheet (TCS) is investigated for three cases of TCSs crossings. The value of ℓ was estimated from the magnetic field data by means of Cluster observations. The obtained scaling values for TCSs, , where ρT is the thermal Larmor radius, were compared with the scaling , where and T are the average plasma energy and the temperature of plasma, which assumes a specific dynamics (conservation of magnetic flux through the trajectory segment) of the current carriers. The comparison of and Zμ shows a good agreement.

  11. Surface dose measurements under stretched, perforated thermoplast sheets and under protective wound dressings for high energy photon radiation

    International Nuclear Information System (INIS)

    Staudenraus, J.; Christ, G.

    2000-01-01

    Patient fixation masks made of perforated thermoplast sheets are widely used in radiotherapy. These masks in particular serve to immobilize the head and neck region during radiation treatment. We placed samples made of differently stretched, perforated mask material on the surface of a white polystyrene (RW3) phantom and measured for high energy photon beams from Co-60 radiation up to 25 MV bremsstrahlung the dose increase resulting from the build-up under the hole and bridge areas. Depending on the energy of the incident beam and the thickness of the stretched mask material we observed a dose increase under the bridges at the phantom surface of 55% up to 140% compared to the dose without a layer of mask material. Under a hole the dose increase is almost half the value found under a bridge. However, deeper than 1 mm under the phantom surface this difference in dose increase under holes and bridges decreases to less than 10%. The mean dose increase under a perforated thermoplast sheet is lower than the dose increase under a homogeneous sheet made of the same material with the same mean thickness. Radiation induced skin lesions or an ulcerating tumour, respectively, may require a protective wound dressing under a patient fixation mask during radiation therapy. Choosing a thin hydrocolloid wound dressing the additional dose increase of the skin, compared to the dose increase due to the fixation mask, can be kept low. (orig.) [de

  12. Magnetoacoustic waves in a vertical flare current-sheet in a gravitationally stratified solar atmosphere

    Science.gov (United States)

    Jelínek, P.; Karlický, M.; Murawski, K.

    2012-10-01

    Aims: We numerically studied evolution of impulsively generated magnetoacoustic waves in the vertical flare current-sheet that is embedded in the gravitationally stratified solar atmosphere and compared it with its gravity-free counterpart. Methods: We adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model, in which we solved a full set of ideal time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement (AMR) method. To initiate the fast sausage magnetoacoustic waves, we used axisymmetric Gaussian velocity perturbation. As a diagnostic tool of these magnetoacoustic waves, we used the wavelet analysis method. Results: We present a model of magnetoacoustic wave propagation with a gravity that is more realistic than that presented in previous studies. We compare our results with those of a gravity-free case. In equilibrium the current-sheet with gravity requires a non-zero horizontal component of the magnetic field, contrary to the gravity-free case. This causes differences in the parameters of the wave signal that propagates along the current sheet. In addition to these differences we find that wave signal variations and their wavelet tadpoles are more complex in the case with gravity than in the gravity-free case. Furthermore, for a shorter scale-height we found a prolongation of the wavelet tadpoles. These differences result from a variation of the dispersive properties and group velocities of the propagating magnetoacoustic waves with height in the solar atmosphere in the gravitational case. We show that these results can affect the diagnostics of physical processes in solar flares.

  13. Electrostatic Solitary Waves in the Solar Wind: Evidence for Instability at Solar Wind Current Sheets

    Science.gov (United States)

    Malaspina, David M.; Newman, David L.; Wilson, Lynn Bruce; Goetz, Keith; Kellogg, Paul J.; Kerstin, Kris

    2013-01-01

    A strong spatial association between bipolar electrostatic solitary waves (ESWs) and magnetic current sheets (CSs) in the solar wind is reported here for the first time. This association requires that the plasma instabilities (e.g., Buneman, electron two stream) which generate ESWs are preferentially localized to solar wind CSs. Distributions of CS properties (including shear angle, thickness, solar wind speed, and vector magnetic field change) are examined for differences between CSs associated with ESWs and randomly chosen CSs. Possible mechanisms for producing ESW-generating instabilities at solar wind CSs are considered, including magnetic reconnection.

  14. Thin current sheets caused by plasma flow gradients in space and astrophysical plasma

    Directory of Open Access Journals (Sweden)

    D. H. Nickeler

    2010-08-01

    Full Text Available Strong gradients in plasma flows play a major role in space and astrophysical plasmas. A typical situation is that a static plasma equilibrium is surrounded by a plasma flow, which can lead to strong plasma flow gradients at the separatrices between field lines with different magnetic topologies, e.g., planetary magnetospheres, helmet streamers in the solar corona, or at the boundary between the heliosphere and interstellar medium. Within this work we make a first step to understand the influence of these flows towards the occurrence of current sheets in a stationary state situation. We concentrate here on incompressible plasma flows and 2-D equilibria, which allow us to find analytic solutions of the stationary magnetohydrodynamics equations (SMHD. First we solve the magnetohydrostatic (MHS equations with the help of a Grad-Shafranov equation and then we transform these static equilibria into a stationary state with plasma flow. We are in particular interested to study SMHD-equilibria with strong plasma flow gradients perpendicular to separatrices. We find that induced thin current sheets occur naturally in such situations. The strength of the induced currents depend on the Alfvén Mach number and its gradient, and on the magnetic field.

  15. Analysis of Surface Roughening in AA6111 Automotive Sheet Under Pure Bending

    Science.gov (United States)

    Shi, Y.; Zhao, P. Z.; Jin, H.; Wu, P. D.; Lloyd, D. J.

    2016-02-01

    The finite element method is used to numerically simulate the topographic development in an aluminum sheet, AA6111, under pure bending. The measured electron backscatter diffraction data are directly incorporated into the finite element model, and the constitutive response at an integration point is described by the single crystal plasticity theory. The effects of strain-rate sensitivity, work hardening, and imposed initial surface roughness on surface roughening are studied. It is found that the grains in top surface layers of the sheet play a big role in controlling the outer surface roughness due to the strain gradient across sheet thickness in bending, while the grain size and texture of the surface layers have a direct impact on finishing surface qualities.

  16. Streaming sausage, kink and tearing instabilities in a current sheet with applications to the earth's magnetotail

    Science.gov (United States)

    Lee, L. C.; Wang, S.; Wei, C. Q.; Tsurutani, B. T.

    1988-01-01

    This paper investigates the growth rates and eigenmode structures of the streaming sausage, kink, and tearing instabilities in a current sheet with a super-Alfvenic flow. The growth rates and eigenmode structures are first considered in the ideal incompressible limit by using a four-layer model, as well as a more realistic case in which all plasma parameters and the magnetic field vary continuously along the direction perpendicular to the magnetic field and plasma flow. An initial-value method is applied to obtain the growth rate and eigenmode profiles of the fastest growing mode, which is either the sausage mode or kink mode. It is shown that, in the earth's magnetotail, where super-Alfvenic plasma flows are observed in the plasma sheet and the ratio between the plasma and magnetic pressures far away from the current layer is about 0.1-0.3 in the lobes, the streaming sausage and streaming tearing instabilities, but not kink modes, are likely to occur.

  17. A cylindrical current sheet over the South solar pole observed by Ulysses

    Science.gov (United States)

    Khabarova, Olga; Kislov, Roman; Malova, Helmi; Obridko, Vladimir

    2016-04-01

    We provide the first evidence for the existence of a quasi-stable cylindrical current sheet over the South solar pole as observed by Ulysses in 2006, near the solar minimum, when it reached maximal heliolatitude of 79.7 degrees at 2.4 AU. It took place inside a fast speed stream from the coronal hole, and the tube was presumably crossed rather far from the center within two degrees of heliolatitude and ~10 degrees of heliolongitude. During the spacecraft passage throughout the structure, the solar wind velocity was approximately twice as little, the solar wind density was 20 times lower than the surrounded plasma values, but the temperature was twice as large in the point closest to the pole. The interplanetary magnetic field (IMF) strongly decreased due to sharp variations in the IMF radial component (RTN) that changed its sign twice, but other components did not show changes out of usual stochastic behavior. Both the behavior of the IMF, rotation of the plasma flow direction and other features indicate the occurrence of cylindrical current sheet. We discuss its solar origin and present modeling that can explain the observations.

  18. 3D reconnection due to oblique modes: a simulation of Harris current sheets

    Directory of Open Access Journals (Sweden)

    G. Lapenta

    2000-01-01

    Full Text Available Simulations in three dimensions of a Harris current sheet with mass ratio, mi/me = 180, and current sheet thickness, pi/L = 0.5, suggest the existence of a linearly unstable oblique mode, which is independent from either the drift-kink or the tearing instability. The new oblique mode causes reconnection independently from the tearing mode. During the initial linear stage, the system is unstable to the tearing mode and the drift kink mode, with growth rates that are accurately described by existing linear theories. How-ever, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibrium and leads to a change in the growth rates of the tearing and oblique modes. In the non-linear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introduce a helical structure into the magnetic field lines.

  19. Evolution of strain-induced microstructure and texture in commercial aluminum sheet under balanced biaxial stretching

    Science.gov (United States)

    Banovic, S. W.; Foecke, T.

    2003-03-01

    The evolution of surface topography and crystallographic texture was investigated under balanced biaxial stretching in sheets of the aluminum alloy 5052-H32. Two different lots of material, with an initial nominal thickness of 1 mm, were tested in the as-received condition. Samples with increasing levels of balanced biaxial strain were deformed using a modified Marciniak in-plane stretching test. In general, the sheet materials were microstructurally and crystallographically anisotropic. Between the two lots, the initial microstructure and mechanical properties were found to be equivalent; however, the sheet texture was appreciably different. This latter variation was observed to have an effect on the additional roughening of the surface subsequent to deformation. For a given lot of material, the surface roughness was found to be proportional to the magnitude of the strain. However, while the roughening rates for the two lots were comparable, the lot having a stronger initial {220} texture component was found to roughen to a higher degree. Corresponding changes in the sheet texture were observed to have two regimes as a function of the strain level. In the first regime, typically, for strains ( ɛ) up to 0.05, the orientations were found to rotate quickly away from the initial cube {001} orientation observed in the as-received sheet toward positions along the α fiber. Above a strain level of 0.05, the {220} texture component continued to increase with deformation, but at a decreasing rate up to failure of the sheet. The difference in the grain rotation rates observed did not appear to have an effect on the surface roughening, as the relative change of the crystallographic orientations with increasing plastic strain was similar for both heats of material. Instead, it is believed that localized grain or grain-grouping interactions may play a more important role in the surface roughening process.

  20. Unified model of low-frequency electromagnetic modes in the anisotropic current sheet of the Earth's magnetotail.

    Science.gov (United States)

    Zelenyi, Lev; Malova, H.; Artemyev, A.; Popov, V.

    Experimental investigation of the Earth's magnetosphere indicates that there is close coupling between the global magnetospheric dynamics and characteristic properties of the magnetotail current sheet (CS). The investigation of CS stability is developed in a frame of analytical self-consistent model of a thin anisotropic current sheet with anisotropic pressure tensor. Ion population is considered in quasiadiabatic approximation, electrons are taken into account in Boltzman approximation. The general case of oblique perturbations with an arbitrary polarization is studied including tearing, kink, sausage and twist modes. In a frame of the linear perturbation theory it is shown that thin current sheets have larger free energy than the well known isotropic ones. It is demonstrated that, contrary to stable Harris-type current sheets, there exists certain "gaps" in the parameter space where system could become unstable for tearing perturbation. The investigation of the development of an oblique perturbation modes demonstrated the possibility of the growth of other low frequency electromagnetic instabilities such kink and sausage modes. Generally, unstable modes exist for any arbitrary angle of propagation while tearing and twist modes are most unstable for propagation along Bx, while kink and sausage modes have maximum growth rate for propagation along current. Our studies might have important implications for understanding magnetospheric dynamics during substorm activization, e.g. current sheet evolution, destruction, flapping and other dynamic plasma processes in the Earth's magnetotail.

  1. Buckling of thin viscous sheets with inhomogenous viscosity under extensional flows

    Science.gov (United States)

    Srinivasan, Siddarth; Wei, Zhiyan; Mahadevan, L.

    2016-11-01

    We investigate the dynamics, shape and stability of a thin viscous sheet subjected to an extensional flow under an imposed non-uniform temperature field. Using finite element simulations, we first solve for the stretching flow to determine the pre-buckling sheet thickness and in-plane flow velocities. Next, we use this solution as the base state and solve the linearized partial differential equation governing the out-of-plane deformation of the mid-surface as a function of two dimensionless operating parameters: the normalized stretching ratio α and a dimensionless width of the heating zone β. We show the sheet can become unstable via a buckling instability driven by the development of localized compressive stresses, and determine the global shape and growth rates of the most unstable mode. The growth rate is shown to exhibit a transition from stationary to oscillatory modes in region upstream of the heating zone. Finally, we investigate the effect of surface tension and present an operating diagram that indicates regions of the parameter space that minimizes or entirely suppresses the instability while achieving desired outlet sheet thickness. Therefore, our work is directly relevant to various industrial processes including the glass redraw & float-glass method.

  2. Numerical simulations of plasma equilibrium in a one-dimensional current sheet with a nonzero normal magnetic field component

    International Nuclear Information System (INIS)

    Mingalev, O. V.; Mingalev, I. V.; Malova, Kh. V.; Zelenyi, L. M.

    2007-01-01

    The force balance in a thin collisionless current sheet in the Earth's magnetotail with a given constant magnetic field component B z across the sheet is numerically studied for the first time in a self-consistent formulation of the problem. The current sheet is produced by oppositely directed plasma flows propagating from the periphery of the sheet toward the neutral plane. A substantially improved version of a macroparticle numerical model is used that makes it possible to simulate on the order of 10 7 macroparticles even with a personal computer and to calculate equilibrium configurations with a sufficiently low discrete noise level in the first-and second-order moments of the distribution function, which determine the stress tensor elements. Quasisteady configurations were calculated numerically for several sets of plasma parameters in some parts of the magnetotail. The force balance in the sheet was checked by calculating the longitudinal and transverse pressures as well as the elements of the full stress tensor. The stress tensor in the current sheet is found to be nondiagonal and to differ appreciably from the gyrotropic stress tensor in the Chew-Goldberger-Low model, although the Chew-Goldberger-Low theory and numerical calculations yield close results for large distances from the region of reversed magnetic field

  3. Texture evolution in thin-sheets on AISI 301 metastable stainless steel under dynamic loading

    Energy Technology Data Exchange (ETDEWEB)

    Kim, K.Y. [Posco Steels, Pohan, South Korea (Korea, Republic of); Kozaczek, K. [Oak Ridge National Lab., TN (United States); Kulkarni, S.M. [TRW Vehicle Safety Systems, Mesa, AZ (United States); Bastias, P.C.; Hahn, G.T. [Vanderbilt Univ., Nashville, TN (United States)

    1995-05-08

    The evolution of texture in thin sheets of metastable austenitic stainless steel AISI 301 is affected by external conditions such as loading rate and temperature, by inhomogeneous deformation phenomena such as twinning and shear band formation, and by the concurent strain induced phase transformation of the retained austenitc ({gamma}) into martensite ({alpha}). The present paper describes texture measurements on different gauges of AISI 301 prior and after uniaxial stretching under different conditions.

  4. Centrifugal distortion of the Jovian magnetosphere by an equatorially confined current sheet

    International Nuclear Information System (INIS)

    Hill, T.W.; Carbary, J.F.

    1978-01-01

    Ions from the Galilean satellites form a thin equatorial current sheet as they diffuse outward in the Jovian magnetosphere. We present here a self-consistent quantitative model of the magnetic field perturbation produced by such ions, assuming loss-free radial transport, strong equatorial confinement, and a static balance between magnetic tension and the corotational centrifugal force. The resulting field configuration exhibits a sharp cusplike distortion near the equatorial plane, resembling qualitatively the 'magnetodisc' configuration inferred from Pioneer encounter data. The model contains one adjustable parameter that is related to the (unknown) mass injection rate at the satellite(s); the value of this parameter determines the distance at which the outward distortion becomes important. Comparison of observed and model field configurations may provide a means of estimating the rate of mass injection from the satellites

  5. Bond-Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading.

    Science.gov (United States)

    Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

    2018-02-26

    The objective of this paper was to explore the bond-slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond-slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond-slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond-slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond-slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond-slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

  6. HEATING MECHANISMS IN THE LOW SOLAR ATMOSPHERE THROUGH MAGNETIC RECONNECTION IN CURRENT SHEETS

    Energy Technology Data Exchange (ETDEWEB)

    Ni, Lei; Lin, Jun [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Roussev, Ilia I. [Division of Geosciences, National Science Foundation Arlington, Virginia (United States); Schmieder, Brigitte, E-mail: leini@ynao.ac.cn [Observatoire de Paris, LESIA, Meudon (France)

    2016-12-01

    We simulate several magnetic reconnection processes in the low solar chromosphere/photosphere; the radiation cooling, heat conduction and ambipolar diffusion are all included. Our numerical results indicate that both the high temperature (≳8 × 10{sup 4} K) and low temperature (∼10{sup 4} K) magnetic reconnection events can happen in the low solar atmosphere (100–600 km above the solar surface). The plasma β controlled by plasma density and magnetic fields is one important factor to decide how much the plasma can be heated up. The low temperature event is formed in a high β magnetic reconnection process, Joule heating is the main mechanism to heat plasma and the maximum temperature increase is only several thousand Kelvin. The high temperature explosions can be generated in a low β magnetic reconnection process, slow and fast-mode shocks attached at the edges of the well developed plasmoids are the main physical mechanisms to heat the plasma from several thousand Kelvin to over 8 × 10{sup 4} K. Gravity in the low chromosphere can strongly hinder the plasmoid instability and the formation of slow-mode shocks in a vertical current sheet. Only small secondary islands are formed; these islands, however, are not as well developed as those in the horizontal current sheets. This work can be applied to understand the heating mechanism in the low solar atmosphere and could possibly be extended to explain the formation of common low temperature Ellerman bombs (∼10{sup 4} K) and the high temperature Interface Region Imaging Spectrograph (IRIS) bombs (≳8 × 10{sup 4}) in the future.

  7. Sheet flow measurements on a surf-zone sandbar under shoaling and breaking waves

    Science.gov (United States)

    Mieras, R.; Puleo, J. A.; Cox, D. T.; Anderson, D. L.; Kim, Y.; Hsu, T. J.

    2016-02-01

    A large-scale experiment to quantify sheet flow processes over a sandbar under varying levels of wave steepness was conducted in the wave flume at Oregon State University's O.H. Hinsdale Wave Research Laboratory. A fixed profile was constructed with concrete slabs anchored to the flume side walls, with the exception of the sandbar crest, where a steel pit was installed and filled with well-sorted sediment (d50 0.17 mm). This hybrid approach allowed for the isolation of small-scale bed response to large-scale wave forcing over the sandbar, where an array of sensors was positioned to measure hydrodynamic forcing and sediment response. Near-bed ( 0.08 m3/m3) were approximated using Conductivity Concentration Profilers. Test conditions consisted of a regular wave train with incident wave heights for individual runs ranging from 0.4 m to 0.6 m and incident wave periods from 5 s to 9 s, encompassing a variety of skewed and asymmetric wave shapes across the shoaling and breaking regimes. Ensemble-averaged sediment concentration profiles exhibit considerable variation across the different conditions. The largest variation in sheet layer thickness occurs beneath the wave crest, ranging from 30 grain diameters for 5 sec, 0.4 m waves, up to 80 grain diameters for 7 sec, 0.6 m waves. Furthermore, the initiation and duration of sheet flow relative to the wave period differs for each condition set. It is likely that more than one mechanism plays a role in determining the aforementioned sheet layer characteristics. In the present work, we focus on the relative magnitude and phase of the near-bed flow acceleration and shear stress in determining the characteristics of the sheet layer.

  8. Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites

    Directory of Open Access Journals (Sweden)

    M. Echim

    1997-04-01

    Full Text Available A case is described of multiple current sheets crossed by the MAGION-2 satellite in the near-midnight quieting auroral oval. The data were obtained by the magnetometer experiment onboard. Results show during a quieting period after a preceding substorm, or during an early growth phase of the next substorm, two double-sheet current bands, POLB and EQUB, located at respectively the polar and equatorial borders of the auroral oval separated by about 500 km in latitude. This is consistent with the double-oval structure during recovery introduced by Elphinstone et al. (1995. Within the POLB, the magnetic field data show simultaneous existence of several narrow parallel bipolar current sheets within the upward current branch (at 69.5–70.3° invariant latitude with an adjacent downward current branch at its polar side at (70.5–71.3°. The EQUB was similarly stratified and located at 61.2–63.5° invariant latitude. The narrow current sheets were separated on average by about 35 km and 15 km, respectively, within the POLB and EQUB. A similar case of double-oval current bands with small-scale structuring of their upward current branches during a quieting period is found in the data from the MAGION-3 satellite. These observations contribute to the double-oval structure of the late recovery phase, and add a small-scale structuring of the upward currents producing the auroral arcs in the double- oval pattern, at least for the cases presented here. Other observations of multiple auroral current sheets and theories of auroral arc multiplicity are briefly discussed. It is suggested that multiple X-lines in the distant tail, and/or leakage of energetic particles and FA currents from a series of plasmoids formed during preceding magnetic activity, could be one cause of highly stratified upward FA currents at the polar edge of the quieting double auroral oval.

  9. Punchless Drawing of Magnesium Alloy Sheet under Cold Condition and its Computation

    International Nuclear Information System (INIS)

    Yamashita, Minoru; Hattori, Toshio; Sato, Joji

    2011-01-01

    The punchless drawing with Maslennikov's technique was applied to the circular cup drawing of magnesium alloy AZ31B sheet under cold condition. The elastic rubber ring was used instead of the 'hard' punch, where the compressed ring dragged the sheet inward the die cavity. Attainable circumferential strain of the blank was increased by this technique with repetitive drawing operation. Thickness of the rubber pad affected little the attainable strain. The shape appearance became better when a harder rubber was used. The cup forming by single drawing operation was also tested using a small die shoulder radius. The LDR of 1.250 was obtained with the straight cup wall. Further, the computation of the punchless drawing was also conducted for the single drawing operation. The computed deformation pattern was well consistent with the corresponding experimental result.

  10. EVIDENCE FOR QUASI-ADIABATIC MOTION OF CHARGED PARTICLES IN STRONG CURRENT SHEETS IN THE SOLAR WIND

    Energy Technology Data Exchange (ETDEWEB)

    Malova, H. V. [Scobeltsyn Nuclear Physics Institute of Lomonosov Moscow State University, Moscow (Russian Federation); Popov, V. Yu.; Grigorenko, E. E.; Petrukovich, A. A.; Zelenyi, L. M. [Space Research Institute of the Russian Academy of Sciences, Moscow (Russian Federation); Delcourt, D. [Laboratoire de Physique des Plasmas, Ecole Politechnique, CNRS (France); Sharma, A. S. [Department of Astronomy, University of Maryland, College Park, MD (United States); Khabarova, O. V. [Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN), Moscow (Russian Federation)

    2017-01-01

    We investigate quasi-adiabatic dynamics of charged particles in strong current sheets (SCSs) in the solar wind, including the heliospheric current sheet (HCS), both theoretically and observationally. A self-consistent hybrid model of an SCS is developed in which ion dynamics is described at the quasi-adiabatic approximation, while the electrons are assumed to be magnetized, and their motion is described in the guiding center approximation. The model shows that the SCS profile is determined by the relative contribution of two currents: (i) the current supported by demagnetized protons that move along open quasi-adiabatic orbits, and (ii) the electron drift current. The simplest modeled SCS is found to be a multi-layered structure that consists of a thin current sheet embedded into a much thicker analog of a plasma sheet. This result is in good agreement with observations of SCSs at ∼1 au. The analysis of fine structure of different SCSs, including the HCS, shows that an SCS represents a narrow current layer (with a thickness of ∼10{sup 4} km) embedded into a wider region of about 10{sup 5} km, independently of the SCS origin. Therefore, multi-scale structuring is very likely an intrinsic feature of SCSs in the solar wind.

  11. Groundwater flow modelling under ice sheet conditions in Greenland (phase II)

    Energy Technology Data Exchange (ETDEWEB)

    Jaquet, Olivier; Namar, Rabah; Siegel, Pascal [In2Earth Modelling Ltd, Lausanne (Switzerland); Jansson, Peter [Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden)

    2012-11-15

    Within the framework of the GAP project, this second phase of geosphere modelling has enabled the development of an improved regional model that has led to a better representation of groundwater flow conditions likely to occur under ice sheet conditions. New data in relation to talik geometry and elevation, as well as to deformation zones were integrated in the geosphere model. In addition, more realistic hydraulic properties were considered for geosphere modelling; they were taken from the Laxemar site in Sweden. The geological medium with conductive deformation zones was modelled as a 3D continuum with stochastically hydraulic properties. Surface and basal glacial meltwater rates provided by a dynamic ice sheet model were assimilated into the groundwater flow model using mixed boundary conditions. The groundwater flow system is considered to be governed by infiltration of glacial meltwater in heterogeneous faulted crystalline rocks in the presence of permafrost and taliks. The characterisation of the permafrost-depth distribution was achieved using a coupled description of flow and heat transfer under steady state conditions. Using glaciological concepts and satellite data, an improved stochastic model was developed for the description at regional scale for the subglacial permafrost distribution in correlation with ice velocity and bed elevation data. Finally, the production of glacial meltwater by the ice sheet was traced for the determination of its depth and lateral extent. The major improvements are related to the type and handling of the subglacial boundary conditions. The use of meltwater rates provided by an ice sheet model applied as input to a mixed boundary condition enables to produce a more plausible flow field in the Eastern part of the domain, in comparison to previous modelling results (Jaquet et al. 2010). In addition, the integration of all potential taliks within the modelled domain provides a better characterisation of the likely groundwater

  12. Groundwater flow modelling under ice sheet conditions in Greenland (phase II)

    International Nuclear Information System (INIS)

    Jaquet, Olivier; Namar, Rabah; Siegel, Pascal; Jansson, Peter

    2012-11-01

    Within the framework of the GAP project, this second phase of geosphere modelling has enabled the development of an improved regional model that has led to a better representation of groundwater flow conditions likely to occur under ice sheet conditions. New data in relation to talik geometry and elevation, as well as to deformation zones were integrated in the geosphere model. In addition, more realistic hydraulic properties were considered for geosphere modelling; they were taken from the Laxemar site in Sweden. The geological medium with conductive deformation zones was modelled as a 3D continuum with stochastically hydraulic properties. Surface and basal glacial meltwater rates provided by a dynamic ice sheet model were assimilated into the groundwater flow model using mixed boundary conditions. The groundwater flow system is considered to be governed by infiltration of glacial meltwater in heterogeneous faulted crystalline rocks in the presence of permafrost and taliks. The characterisation of the permafrost-depth distribution was achieved using a coupled description of flow and heat transfer under steady state conditions. Using glaciological concepts and satellite data, an improved stochastic model was developed for the description at regional scale for the subglacial permafrost distribution in correlation with ice velocity and bed elevation data. Finally, the production of glacial meltwater by the ice sheet was traced for the determination of its depth and lateral extent. The major improvements are related to the type and handling of the subglacial boundary conditions. The use of meltwater rates provided by an ice sheet model applied as input to a mixed boundary condition enables to produce a more plausible flow field in the Eastern part of the domain, in comparison to previous modelling results (Jaquet et al. 2010). In addition, the integration of all potential taliks within the modelled domain provides a better characterisation of the likely groundwater

  13. Current state and future perspectives on coupled ice-sheet – sea-level modelling

    NARCIS (Netherlands)

    de Boer, Bas; Stocchi, Paolo; Whitehouse, Pippa L.; van de Wal, Roderik S.W.

    2017-01-01

    The interaction between ice-sheet growth and retreat and sea-level change has been an established field of research for many years. However, recent advances in numerical modelling have shed new light on the precise interaction of marine ice sheets with the change in near-field sea level, and the

  14. Current state and future perspectives on coupled ice-sheet - sea-level modelling

    Science.gov (United States)

    de Boer, Bas; Stocchi, Paolo; Whitehouse, Pippa L.; van de Wal, Roderik S. W.

    2017-08-01

    The interaction between ice-sheet growth and retreat and sea-level change has been an established field of research for many years. However, recent advances in numerical modelling have shed new light on the precise interaction of marine ice sheets with the change in near-field sea level, and the related stability of the grounding line position. Studies using fully coupled ice-sheet - sea-level models have shown that accounting for gravitationally self-consistent sea-level change will act to slow down the retreat and advance of marine ice-sheet grounding lines. Moreover, by simultaneously solving the 'sea-level equation' and modelling ice-sheet flow, coupled models provide a global field of relative sea-level change that is consistent with dynamic changes in ice-sheet extent. In this paper we present an overview of recent advances, possible caveats, methodologies and challenges involved in coupled ice-sheet - sea-level modelling. We conclude by presenting a first-order comparison between a suite of relative sea-level data and output from a coupled ice-sheet - sea-level model.

  15. Current state and future perspectives on coupled ice-sheet – sea-level modelling

    NARCIS (Netherlands)

    de Boer, B.; Stocchi, P.; Whitehouse, P.L.; van de Wal, R.S.W.

    2017-01-01

    The interaction between ice-sheet growth and retreat and sea-level change has been an established fieldof research for many years. However, recent advances in numerical modelling have shed new light on theprecise interaction of marine ice sheets with the change in near-field sea level, and the

  16. PROTON TEMPERATURE ANISOTROPY AND MAGNETIC RECONNECTION IN THE SOLAR WIND: EFFECTS OF KINETIC INSTABILITIES ON CURRENT SHEET STABILITY

    Energy Technology Data Exchange (ETDEWEB)

    Matteini, L.; Landi, S.; Velli, M. [Dipartimento di Fisica e Astronomia, Universita degli Studi di Firenze, Largo E. Fermi 2, I-50125 Florence (Italy); Matthaeus, W. H. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)

    2013-02-15

    We investigate the role of kinetic instabilities driven by a proton anisotropy on the onset of magnetic reconnection by means of two-dimensional hybrid simulations. The collisionless tearing of a current sheet is studied in the presence of a proton temperature anisotropy in the surrounding plasma. Our results confirm that anisotropic protons within the current sheet region can significantly enhance/stabilize the tearing instability of the current. Moreover, fluctuations associated with linear instabilities excited by large proton temperature anisotropies can significantly influence the stability of the plasma and perturb the current sheets, triggering the tearing instability. We find that such a complex coupling leads to a faster tearing evolution in the T{sub Up-Tack} > T{sub ||} regime when an ion-cyclotron instability is generated by the anisotropic proton distribution functions. On the contrary, in the presence of the opposite anisotropy, fire-hose fluctuations excited by the unstable background protons with T{sub ||} < T{sub Up-Tack} are not able to efficiently destabilize current sheets, which remain stable for a long time after fire-hose saturation. We discuss possible influences of this novel coupling on the solar wind and heliospheric plasma dynamics.

  17. Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

    Directory of Open Access Journals (Sweden)

    Ke Li

    2018-02-01

    Full Text Available The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

  18. Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

    Science.gov (United States)

    Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

    2018-01-01

    The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results. PMID:29495383

  19. Development of a current sheet in the wake of a fast coronal mass ejection

    International Nuclear Information System (INIS)

    Ling, A. G.; Webb, D. F.; Burkepile, J. T.; Cliver, E. W.

    2014-01-01

    A bright ray that developed in the wake of a fast coronal mass ejection (CME) on 2005 September 7 presents a unique opportunity to study the early development and physical characteristics of a reconnecting current sheet (CS). Polarization brightness images from the Mk4 K-Coronameter at the Mauna Loa Solar Observatory are used to determine the structure of the ray along its axis low in the corona as it progressed outward. Coverage of the early development of the ray out to ∼1.3 R ☉ for a period of ∼27 hr after the start of the event enables for the first time in white light a measurement of a CME CS from the top of the arcade to the base of the flux rope. Measured widths of the ray are combined to obtain the kinematics of the upper and lower Y- points described in reconnection flux-rope models such as that of Lin and Forbes. The time dependence of these points are used to derive values for the speed and acceleration of the growth of the CS. We note the appearance of a large structure which increases in size as it expands outward in the early development of the ray and an apparent oscillation with a period of ∼0.5 hr in the position angle of the ray.

  20. The Properties of Reconnection Current Sheets in GRMHD Simulations of Radiatively Inefficient Accretion Flows

    Science.gov (United States)

    Ball, David; Özel, Feryal; Psaltis, Dimitrios; Chan, Chi-Kwan; Sironi, Lorenzo

    2018-02-01

    Non-ideal magnetohydrodynamic (MHD) effects may play a significant role in determining the dynamics, thermal properties, and observational signatures of radiatively inefficient accretion flows onto black holes. In particular, particle acceleration during magnetic reconnection events may influence black hole spectra and flaring properties. We use representative general relativistic magnetohydrodynamic (GRMHD) simulations of black hole accretion flows to identify and explore the structures and properties of current sheets as potential sites of magnetic reconnection. In the case of standard and normal evolution (SANE) disks, we find that in the reconnection sites, the plasma beta ranges from 0.1 to 1000, the magnetization ranges from 10‑4 to 1, and the guide fields are weak compared with the reconnecting fields. In magnetically arrested (MAD) disks, we find typical values for plasma beta from 10‑2 to 103, magnetizations from 10‑3 to 10, and typically stronger guide fields, with strengths comparable to or greater than the reconnecting fields. These are critical parameters that govern the electron energy distribution resulting from magnetic reconnection and can be used in the context of plasma simulations to provide microphysics inputs to global simulations. We also find that ample magnetic energy is available in the reconnection regions to power the fluence of bright X-ray flares observed from the black hole in the center of the Milky Way.

  1. A two-fluid study of oblique tearing modes in a force-free current sheet

    Science.gov (United States)

    Akçay, Cihan; Daughton, William; Lukin, Vyacheslav S.; Liu, Yi-Hsin

    2016-01-01

    Kinetic simulations have demonstrated that three-dimensional reconnection in collisionless regimes proceeds through the formation and interaction of magnetic flux ropes, which are generated due to the growth of tearing instabilities at multiple resonance surfaces. Since kinetic simulations are intrinsically expensive, it is desirable to explore the feasibility of reduced two-fluid models to capture this complex evolution, particularly, in the strong guide field regime, where two-fluid models are better justified. With this goal in mind, this paper compares the evolution of the collisionless tearing instability in a force-free current sheet with a two-fluid model and fully kinetic simulations. Our results indicate that the most unstable modes are oblique for guide fields larger than the reconnecting field, in agreement with the kinetic results. The standard two-fluid tearing theory is extended to address the tearing instability at oblique angles. The resulting theory yields a flat oblique spectrum and underestimates the growth of oblique modes in a similar manner to kinetic theory relative to kinetic simulations.

  2. The penetration of ions into the magnetosphere through the magnetopause turbulent current sheet

    Directory of Open Access Journals (Sweden)

    A. Taktakishvili

    Full Text Available This paper reports the results of numerical modeling of magnetosheath ion motion in the magnetopause current sheet (MCS in the presence of magnetic fluctuations. Our model of magnetic field turbulence has a power law spectrum in the wave vector space, reaches maximum intensity in the center of MCS, and decreases towards the magnetosheath and magnetosphere boundaries. We calculated the density profile across the MCS. We also calculated the number of particles entering the magnetosphere, reflected from the magnetopause and escaping from the flanks, as a function of the fluctuation level of the turbulence and magnetic field shear parameter. All of these quantities appeared to be strongly dependent on the fluctuation level, but not on the magnetic field shear parameter. For the highest fluctuation levels the number of particles entering the magnetosphere does not exceed 15% of the total number of particles launched from the magnetosheath side of the MCS; the modeling also reproduced the effective reflection of the magnetosheath flow from very high levels of magnetic fluctuations.

    Key words. Magnetospheric physics (magnetosheath; magnetospheric configuration and dynamics; turbulence

  3. Metallurgical Effects of Shunting Current on Resistance Spot-Welded Joints of AA2219 Sheets

    Science.gov (United States)

    Jafari Vardanjani, M.; Araee, A.; Senkara, J.; Jakubowski, J.; Godek, J.

    2016-08-01

    Shunting effect is the loss of electrical current via the secondary circuit provided due to the existence of previous nugget in a series of welding spots. This phenomenon influences on metallurgical aspects of resistance spot-welded (RSW) joints in terms of quality and performance. In this paper RSW joints of AA2219 sheets with 1 mm thickness are investigated metallurgically for shunted and single spots. An electro-thermal finite element analysis is performed on the RSW process of shunted spot and temperature distribution and variation are obtained. These predictions are then compared with experimental micrographs. Three values of 5 mm, 20 mm, and infinite (i.e., single spot) are assumed for welding distance. Numerical and experimental results are matching each other in terms of nugget and HAZ geometry as increasing distance raised nugget size and symmetry of HAZ. In addition, important effect of shunting current on nugget thickness, microstructure, and Copper segregation on HAZ grain boundaries were discovered. A quantitative analysis is also performed about the influence of welding distance on important properties including ratio of nugget thickness and diameter ( r t), ratio of HAZ area on shunted and free side of nugget ( r HA), and ratio of equivalent segregated and total amount of Copper, measured in sample ( r Cu) on HAZ. Increasing distance from 5 mm to infinite, indicated a gain of 111.04, -45.55, and -75.15% in r t, r HA, and r Cu, respectively, while obtained ratios for 20 mm welding distance was suitable compared to single spot.

  4. Sheet resistivity of silicon wafers implanted with a high current machine

    International Nuclear Information System (INIS)

    Steeples, K.

    1985-01-01

    Silicon wafers, as used in the integrated circuits and semiconductor device industry, have been implanted with all the common dopants using Eaton Corporation's commercially available 'NV' series of high current implanters. Most detailed studies of the implanted wafers have focused on using arsenic and boron as dopants since the transport of these dopants in silicon has been found to be more compatible with the trend towards shrinking device dimensions. Four point probe measurements have been taken on implanted wafers with subsequent annealing to indicate the quality and effect of the implant. The variation of sheet resistance with dose and energy have been studied using a machine in standard condition over the range of 10 14 -10 16 ions/cm 2 and over an energy range of 5-180 keV for arsenic and boron implants into bare wafers and wafers with screen oxides. Dose control at low doses in the Eaton High Current Implanter has been studied over a range of 10 10 -10 13 ions/cm 2 using MOS devices and other measurements. Repeatability of the machines has been obtained by tracking the manufacture of over one hundred machines for nearly three years. With the use of an Eaton Standard Test Implant Procedure for each machine before shipment, it has been shown that the dose repeatability can be as good as 2% (including furnace and four point probe variations) for machine to machine. The repeatability within a single machine was found to be better than 0.5%. Arsenic ion beams have shown excellent independence of end station pressure, as may occur during photoresist outgassing or controlled gas leaks. Boron beams have a higher electron capture cross-section than other commonly used beams and require a dose control compensation for high end station pressure implants to give agreement with the low pressure regime. (orig./TW)

  5. Growth of carbon fibres, sheets and tubes on diamond films under high power plasma etching conditions

    International Nuclear Information System (INIS)

    Villalpando, I.; John, P.; Wilson, J. I. B.

    2017-01-01

    The application of diamond as a plasma facing material for fusion reactors can be limited by unknown reactions between diamond and the chamber materials transported by the plasma. Transformation of diamond to other structures can cause problems such as contamination of the plasma with loose particles or retention of gases. We have seen that diamond thin films are eroded under hydrogen plasma etching, but if silicon is present the growth of various carbon structures on diamond films is observed. We have produced carbon with different morphologies on diamond films including fibres, sheets with flower-like shapes and tubes and proposed growth mechanisms based on the results of scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Sample surfaces contain silicon and are oxidised having COO and CO groups as seen by XP S analysis. Raman analyses revealed a spectrum typical for graphite combined with that from diamond that remains on the surface after hydrogen bombardment. The results of this sturdy show the experimental conditions in which carbon fibres, sheets and tubes are produced under high-power hydrogen etching of diamond films and open the possibility to other applications such as catalysts, sensors and the production of electrodes. (Author)

  6. Growth of carbon fibres, sheets and tubes on diamond films under high power plasma etching conditions

    Energy Technology Data Exchange (ETDEWEB)

    Villalpando, I. [Centro de Investigacion de los Recursos Naturales, Antigua Normal Rural, Salaices, Lopez, Chihuahua (Mexico); John, P.; Wilson, J. I. B., E-mail: isaelav@hotmail.com [School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14-4AS (United Kingdom)

    2017-11-01

    The application of diamond as a plasma facing material for fusion reactors can be limited by unknown reactions between diamond and the chamber materials transported by the plasma. Transformation of diamond to other structures can cause problems such as contamination of the plasma with loose particles or retention of gases. We have seen that diamond thin films are eroded under hydrogen plasma etching, but if silicon is present the growth of various carbon structures on diamond films is observed. We have produced carbon with different morphologies on diamond films including fibres, sheets with flower-like shapes and tubes and proposed growth mechanisms based on the results of scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Sample surfaces contain silicon and are oxidised having COO and CO groups as seen by XP S analysis. Raman analyses revealed a spectrum typical for graphite combined with that from diamond that remains on the surface after hydrogen bombardment. The results of this sturdy show the experimental conditions in which carbon fibres, sheets and tubes are produced under high-power hydrogen etching of diamond films and open the possibility to other applications such as catalysts, sensors and the production of electrodes. (Author)

  7. Modeling of Current Transformers Under Saturation Conditions

    Directory of Open Access Journals (Sweden)

    Martin Prochazka

    2006-01-01

    Full Text Available During a short circuit the input signal of the relay can be distort by the magnetic core saturation of the current transformer. It is useful to verify the behavior of CT by a mathematical model. The paper describes one phase and three phase models and it presents some methods of how to analyze and classify a deformed secondary current

  8. CURRENT SHEET REGULATION OF SOLAR NEAR-RELATIVISTIC ELECTRON INJECTION HISTORIES

    Energy Technology Data Exchange (ETDEWEB)

    Agueda, N.; Sanahuja, B. [Departament d' Astronomia i Meteorologia, Institut de Ciencies del Cosmos, Universitat de Barcelona (Spain); Vainio, R. [Department of Physics, University of Helsinki (Finland); Dalla, S. [Jeremiah Horrocks Institute, University of Central Lancashire (United Kingdom); Lario, D. [Applied Physics Laboratory, Johns Hopkins University (United States)

    2013-03-10

    We present a sample of three large near-relativistic (>50 keV) electron events observed in 2001 by both the ACE and the Ulysses spacecraft, when Ulysses was at high-northern latitudes (>60 Degree-Sign ) and close to 2 AU. Despite the large latitudinal distance between the two spacecraft, electrons injected near the Sun reached both heliospheric locations. All three events were associated with large solar flares, strong decametric type II radio bursts and accompanied by wide (>212 Degree-Sign ) and fast (>1400 km s{sup -1}) coronal mass ejections (CMEs). We use advanced interplanetary transport simulations and make use of the directional intensities observed in situ by the spacecraft to infer the electron injection profile close to the Sun and the interplanetary transport conditions at both low and high latitudes. For the three selected events, we find similar interplanetary transport conditions at different heliolatitudes for a given event, with values of the mean free path ranging from 0.04 AU to 0.27 AU. We find differences in the injection profiles inferred for each spacecraft. We investigate the role that sector boundaries of the heliospheric current sheet (HCS) have on determining the characteristics of the electron injection profiles. Extended injection profiles, associated with coronal shocks, are found if the magnetic footpoints of the spacecraft lay in the same magnetic sector as the associated flare, while intermittent sparse injection episodes appear when the spacecraft footpoints are in the opposite sector or a wrap in the HCS bounded the CME structure.

  9. Nonlinear evolution of the Kelvin-Helmholtz instability in the double current sheet configuration

    International Nuclear Information System (INIS)

    Mao, Aohua; Li, Jiquan; Kishimoto, Yasuaki; Liu, Jinyuan

    2016-01-01

    The nonlinear evolution of the Kelvin-Helmholtz (KH) instability driven by a radially antisymmetric shear flow in the double current sheet configuration is numerically investigated based on a reduced magnetohydrodynamic model. Simulations reveal different nonlinear fate of the KH instability depending on the amplitude of the shear flow, which restricts the strength of the KH instability. For strong shear flows far above the KH instability threshold, the linear electrostatic-type KH instability saturates and achieves a vortex flow dominated quasi-steady state of the electromagnetic (EM) KH turbulence with large-amplitude zonal flows as well as zonal fields. The magnetic surfaces are twisted significantly due to strong vortices but without the formation of magnetic islands. However, for the shear flow just over the KH instability threshold, a weak EM-type KH instability is saturated and remarkably damped by zonal flows through modifying the equilibrium shear flow. Interestingly, a secondary double tearing mode (DTM) is excited subsequently in highly damped KH turbulence, behaving as a pure DTM in a flowing plasma as described in Mao et al. [Phys. Plasmas 21, 052304 (2014)]. However, the explosive growth phenomenon is replaced by a gradually growing oscillation due to the extremely twisted islands. As a result, the release of the magnetic energy becomes slow and the global magnetic reconnection tends to be gentle. A complex nonlinear interaction between the EM KH turbulence and the DTMs occurs for the medium shear flows above the KH instability threshold, turbulent EM fluctuations experience oscillatory nonlinear growth of the DTMs, finally achieves a quasi-steady state with the interplay of the fluctuations between the DTMs and the EM KH instability.

  10. Mechanical behavior and modelisation of Ti-6Al-4V titanium sheet under hot stamping conditions

    Science.gov (United States)

    Sirvin, Q.; Velay, V.; Bonnaire, R.; Penazzi, L.

    2017-10-01

    The Ti-6Al-4V titanium alloy is widely used for the manufacture of aeronautical and automotive parts (solid parts). In aeronautics, this alloy is employed for its excellent mechanical behavior associated with low density, outstanding corrosion resistance and good mechanical properties up to 600°C. It is especially used for the manufacture of fuselage frames, on the pylon for carrying out the primary structure (machining forged blocks) and the secondary structure in sheet form. In this last case, the sheet metal forming can be done through various methods: at room temperature by drawing operation, at very high temperature (≃900°C) by superplastic forming (SPF) and at intermediate temperature (≥750°C) by hot forming (HF). In order to reduce production costs and environmental troubles, the cycle times reduction associated with a decrease of temperature levels are relevant. This study focuses on the behavior modelling of Ti-6Al-4V alloy at temperatures above room temperature to obtained greater formability and below SPF condition to reduce tools workshop and energy costs. The displacement field measurement obtained by Digital Image Correlation (DIC) is based on innovative surface preparation pattern adapted to high temperature exposures. Different material parameters are identified to define a model able to predict the mechanical behavior of Ti-6Al-4V alloy under hot stamping conditions. The hardening plastic model identified is introduced in FEM to simulate an omega shape forming operation.

  11. New method for determining central axial orientation of flux rope embedded within current sheet using multipoint measurements

    Science.gov (United States)

    Li, ZhaoYu; Chen, Tao; Yan, GuangQing

    2016-10-01

    A new method for determining the central axial orientation of a two-dimensional coherent magnetic flux rope (MFR) via multipoint analysis of the magnetic-field structure is developed. The method is devised under the following geometrical assumptions: (1) on its cross section, the structure is left-right symmetric; (2) the projected structure velocity is vertical to the line of symmetry. The two conditions can be naturally satisfied for cylindrical MFRs and are expected to be satisfied for MFRs that are flattened within current sheets. The model test demonstrates that, for determining the axial orientation of such structures, the new method is more efficient and reliable than traditional techniques such as minimum-variance analysis of the magnetic field, Grad-Shafranov (GS) reconstruction, and the more recent method based on the cylindrically symmetric assumption. A total of five flux transfer events observed by Cluster are studied using the proposed approach, and the application results indicate that the observed structures, regardless of their actual physical properties, fit the assumed geometrical model well. For these events, the inferred axial orientations are all in excellent agreement with those obtained using the multi-GS reconstruction technique.

  12. Electric fields in plasmas under pulsed currents

    International Nuclear Information System (INIS)

    Tsigutkin, K.; Doron, R.; Stambulchik, E.; Bernshtam, V.; Maron, Y.; Fruchtman, A.; Commisso, R. J.

    2007-01-01

    Electric fields in a plasma that conducts a high-current pulse are measured as a function of time and space. The experiment is performed using a coaxial configuration, in which a current rising to 160 kA in 100 ns is conducted through a plasma that prefills the region between two coaxial electrodes. The electric field is determined using laser spectroscopy and line-shape analysis. Plasma doping allows for three-dimensional spatially resolved measurements. The measured peak magnitude and propagation velocity of the electric field is found to match those of the Hall electric field, inferred from the magnetic-field front propagation measured previously

  13. Icebase: A suborbital survey to map geothermal heat flux under an ice sheet

    Science.gov (United States)

    Purucker, Michael E.; Connerney, John E. P.; Blakely, Richard J.; Bracken, Robert E.; Nowicki, Sophie; Le, Guan; Sabaka, Terence J.; Bonalsky, Todd M.; Kuang, Weijia; Ravat, Dhananjay; Ritz, Catherine; Vaughan, Alan P. M.; Gaina, Carmen; McEnroe, Suzanne; Lesur, Vincent

    2013-04-01

    NASA will solicit suborbital missions as part of its Earth Venture program element in the coming year. These missions are designed as complete PI-led investigations to conduct innovative hypothesis or scientific question-driven approaches to pressing questions in Earth System science. We propose to carry out a suborbital magnetic survey of Greenland using NASA's Global Hawk unmanned aerial vehicle to produce the first-ever map of the geothermal heat flux under an ice sheet. Better constraints on geothermal heat flux will reduce the uncertainty in future sea level rise, in turn allowing a more informed assessment of its impact on society. The geothermal heat flux depends on conditions such as mantle heat flux, and the tectonic history and heat production of the crust, all of which vary spatially. Underneath ice sheets, the geothermal heat flux influences the basal ice. Therefore heat flux is an important boundary condition in ice sheet modeling. Using magnetic data to constrain heat flux is possible because the magnetic properties of rocks are temperature dependent until they reach the Curie temperature. The technique has applications to understanding the response of Greenland ice sheet to climate forcing because the basal heat flux provides one of the boundary conditions. The technique also helps to locate the oldest ice. The oldest ice in Greenland should be found in areas of very low heat flux, and the identification of those areas is provided by this technique. Ice cores from the areas of oldest ice help to decipher past temperatures and CO2 contents. Our latest model of the geothermal heat flux under the Greenland ice sheet (http://websrv.cs.umt.edu/isis/index.php/Greenland_Basal_Heat_Flux) is based on low- resolution satellite observations collected by the CHAMP satellite between 2000 and 2010. Those observations will be enhanced by the upcoming Swarm gradient satellite mission, but the resolution will improve by less than a factor of two, from 400 km

  14. Study of the generation and evolution of the current sheets in a plasma focus of hundred joules

    International Nuclear Information System (INIS)

    Silva, Patricio; Moreno, Jose; Soto, Leopoldo

    2002-01-01

    The preliminary test results are presented of the study on the initial rupture and evolution of the current sheet for optimizing a plasma focus of hundreds of joules. The main diagnostic equipment is an ICCD camera used to take images of the plasma with a time exposure of 5ns. The studies have allowed us to find operating conditions for the generation of neutrons in a 275J plasma focus (PS)

  15. Behavior of current sheets at directional magnetic discontinuities in the solar wind at 0.72 AU

    Czech Academy of Sciences Publication Activity Database

    Zhang, T. L.; Russell, C. T.; Zambelli, W.; Vörös, Zoltán; Wang, C.; Cao, J. B.; Jian l, L. K.; Strangeway, R. J.; Balikhin, M.; Baumjohann, W.; Delva, M.; Volwerk, M.; Glassmeier, K.; H.

    2008-01-01

    Roč. 35, č. 24 (2008), L24102/1-L24102/5 ISSN 0094-8276 Grant - others:Austrian Wissenschaftfonds(AT) P20131-N16; NNSFC(CN) 40628003; 973 Program(CN) 2006CB806305; NASA (US) NNG06GC62G Institutional research plan: CEZ:AV0Z30420517 Keywords : solar wind * current sheets * magnetic annihilation Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.959, year: 2008

  16. Energetic Particles of keV–MeV Energies Observed near Reconnecting Current Sheets at 1 au

    Energy Technology Data Exchange (ETDEWEB)

    Khabarova, Olga V. [Heliophysical Laboratory, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN), Moscow (Russian Federation); Zank, Gary P. [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35805 (United States)

    2017-07-01

    We provide evidence for particle acceleration up to ∼5 MeV at reconnecting current sheets in the solar wind based on both case studies and a statistical analysis of the energetic ion and electron flux data from the five Advanced Composition Explorer Electron, Proton, and Alpha Monitor (EPAM) detectors. The case study of a typical reconnection exhaust event reveals (i) a small-scale peak of the energetic ion flux observed in the vicinity of the reconnection exhaust and (ii) a long-timescale atypical energetic particle event (AEPE) encompassing the reconnection exhaust. AEPEs associated with reconnecting strong current sheets last for many hours, even days, as confirmed by statistical studies. The case study shows that time-intensity profiles of the ion flux may vary significantly from one EPAM detector to another partially because of the local topology of magnetic fields, but mainly because of the impact of upstream magnetospheric events; therefore, the occurrence of particle acceleration can be hidden. The finding of significant particle energization within a time interval of ±30 hr around reconnection exhausts is supported by a superposed epoch analysis of 126 reconnection exhaust events. We suggest that energetic particles initially accelerated via prolonged magnetic reconnection are trapped and reaccelerated in small- or medium-scale magnetic islands surrounding the reconnecting current sheet, as predicted by the transport theory of Zank et al. Other mechanisms of initial particle acceleration can contribute also.

  17. Current Sheet Structures Observed by the TESIS EUV Telescope during a Flux Rope Eruption on the Sun

    Science.gov (United States)

    Reva, A. A.; Ulyanov, A. S.; Kuzin, S. V.

    2016-11-01

    We use the TESIS EUV telescope to study the current sheet signatures observed during flux rope eruption. The special feature of the TESIS telescope was its ability to image the solar corona up to a distance of 2 {R}⊙ from the Sun’s center in the Fe 171 Å line. The Fe 171 Å line emission illuminates the magnetic field lines, and the TESIS images reveal the coronal magnetic structure at high altitudes. The analyzed coronal mass ejection (CME) had a core with a spiral—flux rope—structure. The spiral shape indicates that the flux rope radius varied along its length. The flux rope had a complex temperature structure: cold legs (70,000 K, observed in He 304 Å line) and a hotter core (0.7 MK, observed in Fe 171 Å line). Such a structure contradicts the common assumption that the CME core is a cold prominence. When the CME impulsively accelerated, a dark double Y-structure appeared below the flux rope. The Y-structure timing, location, and morphology agree with the previously performed MHD simulations of the current sheet. We interpreted the Y-structure as a hot envelope of the current sheet and hot reconnection outflows. The Y-structure had a thickness of 6.0 Mm. Its length increased over time from 79 Mm to more than 411 Mm.

  18. Thickness and fit of mouthguards adjusted by notching thermoplastic sheets under different heating conditions.

    Science.gov (United States)

    Mizuhashi, Fumi; Koide, Kaoru; Takahashi, Mutsumi

    2015-08-01

    This study examines the thickness and fit of mouthguards by notching thermoplastic copolymer ethylene vinyl acetate (EVA) sheets and then heating them to various degrees. The material used was a 3.8-mm-thick sports mouthguard. Notches with a length of 90 and 80 mm were cut into an EVA sheet 20 mm from the anterior and posterior margins and 15 mm from the right and left margins, respectively, and the sheet was compared with the original. The sheets were formed using a vacuum former when the sheets were heated until they hung 1.5, 2.0, 2.5, and 3.0 cm from the baseline. We measured the thickness and fit of the mouthguard at the central incisor and first molar. Differences in thickness and fit according to the measurement parts, sheet type, and heating conditions were analyzed by three-way anova. The measurement parts and sheet type significantly differed (P heating conditions (P heated to a hanging distance of 3.0 cm. These results suggest that the thickness and fit of the EVA sheet could be maintained by notching and heating the sheet to a hanging distance of 3.0 cm. These findings could be useful for fabricating appropriate mouthguards. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  19. Compensation of the Persistent Current Multipoles in the LHC Dipoles by making the Coil Protection Sheet from Soft Magnetic Material

    CERN Document Server

    Völlinger, C

    2000-01-01

    This note presents a scheme for compensating the persistent current multipole errors of the LHC dipoles by making the coil protection sheets from soft magnetic material of 0.5 mm thickness. The material properties assumed in this study are those of iron sheets with a very low content of impurities (99.99% pure Fe). The non-linearities in the upramp cycle on the b3 multipole component can be reduced by the factor of four (while decreasing the b5 variation by the factor of two. Using sheets of slightly different thicknesses offers a tuning possibility for the series magnet coils and can compensate deviations arising from cables of different suppliers. The calculation method is based on a semi-analytical hysteresis model for hard superconductors and an M(B) - iteration using the method of coupled boundary elements - finite elements (BEM - FEM). It is now possible to compute persistent current multipole errors of geometries with arbitrarily shaped iron yokes and thin layers of soft magnetic material such as tunin...

  20. Current and high-β sheets in CIR streams: statistics and interaction with the HCS and the magnetosphere

    Science.gov (United States)

    Potapov, A. S.

    2018-04-01

    Thirty events of CIR streams (corotating interaction regions between fast and slow solar wind) were analyzed in order to study statistically plasma structure within the CIR shear zones and to examine the interaction of the CIRs with the heliospheric current sheet (HCS) and the Earth's magnetosphere. The occurrence of current layers and high-beta plasma sheets in the CIR structure has been estimated. It was found that on average, each of the CIR streams had four current layers in its structure with a current density of more than 0.12 A/m2 and about one and a half high-beta plasma regions with a beta value of more than five. Then we traced how and how often the high-speed stream associated with the CIR can catch up with the heliospheric current sheet (HCS) and connect to it. The interface of each fourth CIR stream coincided in time within an hour with the HCS, but in two thirds of cases, the CIR connection with the HCS was completely absent. One event of the simultaneous observation of the CIR stream in front of the magnetosphere by the ACE satellite in the vicinity of the L1 libration point and the Wind satellite in the remote geomagnetic tail was considered in detail. Measurements of the components of the interplanetary magnetic field and plasma parameters showed that the overall structure of the stream is conserved. Moreover, some details of the fine structure are also transferred through the magnetosphere. In particular, the so-called "magnetic hole" almost does not change its shape when moving from L1 point to a neighborhood of L2 point.

  1. The Trajectory Method and the Description of Charged Particles Dynamics in the Current Sheet Magnetic Field Geometry.

    Science.gov (United States)

    Sasunov, Y.; Schwarzbauer, G.; Khodachenko, M. L.; Alexeev, I. I.; Belenkaya, E. S.; Gubchenko, V. M.

    2017-12-01

    The current sheets (CSs) in space plasma appear as fundamental objects which play an important role in structuring and dynamical evolution of the global magnetic environments of astrophysical and space objects. The physical nature of the current sheet consists in specific motion of the current-creating particles which has a strong non-linear character. By this, the self-consistent description of dynamics of the current-creating particles in CS is one of the key challenging tasks of the space plasma physics. The collisionless specifics of the typical space plasma flow, e.g. that of the solar wind (or the Earth magnetosphere), justifies a one-particle approach to the analysis of the dynamics of the current-creating particles in a CS. It consists in consideration of a single particle motion in an inhomogeneous magnetic field, based on the analysis of equation of motion in Cartesian coordinates. By this, particle dynamics, defined by the equation of motion, can be expressed in terms of angular variables (pitch-angle and the gyrating phase), which are specifically connected to each other along the particle trajectory in a local coordinate system related to the magnetic field. The analysis of the angular variables enables finding of easy and comprehensive solutions for a number of elementary problems which constitute the background for more complex natural cases in space physics. This approach also allows obtaining of a set of the self-consistent CS-type solutions for different geometries of the magnetic field.

  2. Polar conic current sheets as sources and channels of energetic particles in the high-latitude heliosphere

    Science.gov (United States)

    Khabarova, Olga; Malova, Helmi; Kislov, Roman; Zelenyi, Lev; Obridko, Vladimir; Kharshiladze, Alexander; Tokumaru, Munetoshi; Sokół, Justyna; Grzedzielski, Stan; Fujiki, Ken'ichi; Malandraki, Olga

    2017-04-01

    The existence of a large-scale magnetically separated conic region inside the polar coronal hole has been predicted by the Fisk-Parker hybrid heliospheric magnetic field model in the modification of Burger and co-workers (Burger et al., ApJ, 2008). Recently, long-lived conic (or cylindrical) current sheets (CCSs) have been found from Ulysses observations at high heliolatitudes (Khabarova et al., ApJ, 2017). The characteristic scale of these structures is several times lesser than the typical width of coronal holes, and the CCSs can be observed at 2-3 AU for several months. CCS crossings in 1994 and 2007 are characterized by sharp decreases in the solar wind speed and plasma beta typical for predicted profiles of CCSs. In 2007, a CCS was detected directly over the South Pole and strongly highlighted by the interaction with comet McNaught. The finding is confirmed by restorations of solar coronal magnetic field lines that reveal the occurrence of conic-like magnetic separators over the solar poles both in 1994 and 2007. Interplanetary scintillation data analysis also confirms the existence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. The occurrence of long-lived CCSs in the high-latitude solar wind could shed light on how energetic particles reach high latitudes. Energetic particle enhancements up to tens MeV were observed by Ulysses at edges of CCSs both in 1994 and 2007. In 1994 this effect was clearer, probably due to technical reasons. Accelerated particles could be produced either by magnetic reconnection at the edges of a CCS in the solar corona or in the solar wind. We discuss the role of high-latitude CCSs in propagation of energetic particles in the heliosphere and revisit previous studies of energetic particle enhancements at high heliolatitudes. We also suggest that the existence of a CCS can modify the distribution of the solar wind as a function of heliolatitude and consequently impact ionization

  3. Channelized melting drives thinning under Dotson ice shelf, Western Antarctic Ice Sheet

    Science.gov (United States)

    Gourmelen, N.; Goldberg, D.; Snow, K.; Henley, S. F.; Bingham, R. G.; Kimura, S.; Hogg, A.; Shepherd, A.; Mouginot, J.; Lenaerts, J.; Ligtenberg, S.; Van De Berg, W. J.

    2017-12-01

    The majority of meteoric ice that forms in West Antarctica leaves the ice sheet through floating ice shelves, many of which have been thinning substantially over the last 25 years. A significant proportion of ice-shelf thinning has been driven by submarine melting facilitated by increased access of relatively warm (>0.6oC) modified Circumpolar Deep Water to sub-shelf cavities. Ice shelves play a significant role in stabilising the ice sheet from runaway retreat and regulating its contribution to sea level change. Ice-shelf melting has also been implicated in sustaining high primary productivity in Antarctica's coastal seas. However, these processes vary regionally and are not fully understood. Under some ice shelves, concentrated melting leads to the formation of inverted channels. These channels guide buoyant melt-laden outflow, which can lead to localised melting of the sea ice cover. The channels may also potentially lead to heightened crevassing, which in turn affects ice-shelf stability. Meanwhile, numerical studies suggest that buttressing loss is sensitive to the location of ice removal within an ice-shelf. Thus it is important that we observe spatial patterns, as well as magnitudes, of ice-shelf thinning, in order to improve understanding of the ocean drivers of thinning and of their impacts on ice-shelf stability. Here we show from high-resolution altimetry measurements acquired between 2010 to 2016 that Dotson Ice Shelf, West Antarctica, thins in response to basal melting focussed along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. The coupled effect of geostrophic circulation and ice-shelf topography leads to the observed concentration of basal melting. Analysis of previous datasets suggests that this process has been ongoing for at least the last 25 years. If focused thinning continues at present rates, the channel would melt through within 40-50 years, almost two centuries before it is

  4. Effect of current sheets on the solar wind magnetic field power spectrum from the Ulysses observation: from Kraichnan to Kolmogorov scaling.

    Science.gov (United States)

    Li, G; Miao, B; Hu, Q; Qin, G

    2011-03-25

    The MHD turbulence theory developed by Iroshnikov and Kraichnan predicts a k(-1.5) power spectrum. Solar wind observations, however, often show a k(-5/3) Kolmogorov scaling. Based on 3 years worth of Ulysses magnetic field data where over 28,000 current sheets are identified, we propose that the current sheet is the cause of the Kolmogorov scaling. We show that for 5 longest current-sheet-free periods the magnetic field power spectra are all described by the Iroshnikov-Kraichnan scaling. In comparison, for 5 periods that have the most number of current sheets, the power spectra all exhibit Kolmogorov scaling. The implication of our results is discussed.

  5. On the Use of Maximum Force Criteria to Predict Localised Necking in Metal Sheets under Stretch-Bending

    Directory of Open Access Journals (Sweden)

    Domingo Morales-Palma

    2017-11-01

    Full Text Available The maximum force criteria and their derivatives, the Swift and Hill criteria, have been extensively used in the past to study sheet formability. Many extensions or modifications of these criteria have been proposed to improve necking predictions under only stretching conditions. This work analyses the maximum force principle under stretch-bending conditions and develops two different approaches to predict necking. The first is a generalisation of classical maximum force criteria to stretch-bending processes. The second approach is an extension of a previous work of the authors based on critical distance concepts, suggesting that necking of the sheet is controlled by the damage of a critical material volume located at the inner side of the sheet. An analytical deformation model is proposed to characterise the stretch-bending process under plane-strain conditions. Different parameters are considered, such as the thickness reduction, the gradient of variables through the sheet thickness, the thickness stress and the anisotropy of the material. The proposed necking models have been successfully applied to predict the failure in different materials, such as steel, brass and aluminium.

  6. Using Field-Particle Correlations to Show that Landau Damping Leads to Spatially Intermittent Particle Energization in Current Sheets

    Science.gov (United States)

    Howes, Gregory G.; McCubbin, Andrew J.; Klein, Kristopher G.

    2017-10-01

    Understanding the removal of energy from turbulent fluctuations in a magnetized plasma and the consequent energization of the constituent plasma particles is a major goal of heliophysics and astrophysics. Previous work has shown that nonlinear interactions among counterpropagating Alfven waves-or Alfven wave collisions-are the fundamental building block of astrophysical plasma turbulence and naturally generate current sheets in strong turbulence. A nonlinear gyrokinetic simulation of a strong Alfven wave collision is used to examine the damping of the electromagnetic fluctuations and the associated energization of particles that occurs in self-consistently generated current sheets. A simple model explains the flow of energy due to the collisionless damping and the associated particle energization, as well as the subsequent thermalization of the particle energy by collisions. Using the recently developed field-particle correlation technique, we show that particles resonant with the Alfven waves in the simulation dominate the energy transfer, demonstrating conclusively that Landau damping plays a key role in the spatially intermittent damping of the electromagnetic fluctuations and consequent energization of the particles in this strongly nonlinear simulation. NSF CAREER Award No. AGS-1054061.

  7. Nonlinear energy transfer and current sheet development in localized Alfvén wavepacket collisions in the strong turbulence limit

    Science.gov (United States)

    Verniero, J. L.; Howes, G. G.; Klein, K. G.

    2018-02-01

    In space and astrophysical plasmas, turbulence is responsible for transferring energy from large scales driven by violent events or instabilities, to smaller scales where turbulent energy is ultimately converted into plasma heat by dissipative mechanisms. The nonlinear interaction between counterpropagating Alfvén waves, denoted Alfvén wave collisions, drives this turbulent energy cascade, as recognized by early work with incompressible magnetohydrodynamic (MHD) equations. Recent work employing analytical calculations and nonlinear gyrokinetic simulations of Alfvén wave collisions in an idealized periodic initial state have demonstrated the key properties that strong Alfvén wave collisions mediate effectively the transfer of energy to smaller perpendicular scales and self-consistently generate current sheets. For the more realistic case of the collision between two initially separated Alfvén wavepackets, we use a nonlinear gyrokinetic simulation to show here that these key properties persist: strong Alfvén wavepacket collisions indeed facilitate the perpendicular cascade of energy and give rise to current sheets. Furthermore, the evolution shows that nonlinear interactions occur only while the wavepackets overlap, followed by a clean separation of the wavepackets with straight uniform magnetic fields and the cessation of nonlinear evolution in between collisions, even in the gyrokinetic simulation presented here which resolves dispersive and kinetic effects beyond the reach of the MHD theory.

  8. Spatially localized particle energization by Landau damping in current sheets produced by strong Alfvén wave collisions

    Science.gov (United States)

    Howes, Gregory G.; McCubbin, Andrew J.; Klein, Kristopher G.

    2018-02-01

    Understanding the removal of energy from turbulent fluctuations in a magnetized plasma and the consequent energization of the constituent plasma particles is a major goal of heliophysics and astrophysics. Previous work has shown that nonlinear interactions among counterpropagating Alfvén waves - or Alfvén wave collisions - are the fundamental building block of astrophysical plasma turbulence and naturally generate current sheets in the strongly nonlinear limit. A nonlinear gyrokinetic simulation of a strong Alfvén wave collision is used to examine the damping of the electromagnetic fluctuations and the associated energization of particles that occurs in self-consistently generated current sheets. A simple model explains the flow of energy due to the collisionless damping and the associated particle energization, as well as the subsequent thermalization of the particle energy by collisions. The net particle energization by the parallel electric field is shown to be spatially localized, and the nonlinear evolution is essential in enabling spatial non-uniformity. Using the recently developed field-particle correlation technique, we show that particles resonant with the Alfvén waves in the simulation dominate the energy transfer, demonstrating conclusively that Landau damping plays a key role in the spatially localized damping of the electromagnetic fluctuations and consequent energization of the particles in this strongly nonlinear simulation.

  9. Experimental study of nonlinear interaction of plasma flow with charged thin current sheets: 2. Hall dynamics, mass and momentum transfer

    Directory of Open Access Journals (Sweden)

    S. Savin

    2006-01-01

    Full Text Available Proceeding with the analysis of Amata et al. (2005, we suggest that the general feature for the local transport at a thin magnetopause (MP consists of the penetration of ions from the magnetosheath with gyroradius larger than the MP width, and that, in crossing it, the transverse potential difference at the thin current sheet (TCS is acquired by these ions, providing a field-particle energy exchange without parallel electric fields. It is suggested that a part of the surface charge is self-consistently produced by deflection of ions in the course of inertial drift in the non-uniform electric field at MP. Consideration of the partial moments of ions with different energies demonstrates that the protons having gyroradii of roughly the same size or larger than the MP width carry fluxes normal to MP that are about 20% of the total flow in the plasma jet under MP. This is close to the excess of the ion transverse velocity over the cross-field drift speed in the plasma flow just inside MP (Amata et al., 2005, which conforms to the contribution of the finite-gyroradius inflow across MP. A linkage through the TCS between different plasmas results from the momentum conservation of the higher-energy ions. If the finite-gyroradius penetration occurs along the MP over ~1.5 RE from the observation site, then it can completely account for the formation of the jet under the MP. To provide the downstream acceleration of the flow near the MP via the cross-field drift, the weak magnetic field is suggested to rotate from its nearly parallel direction to the unperturbed flow toward being almost perpendicular to the accelerated flow near the MP. We discuss a deceleration of the higher-energy ions in the MP normal direction due to the interaction with finite-scale electric field bursts in the magnetosheath flow frame, equivalent to collisions, providing a charge separation. These effective collisions, with a nonlinear frequency proxy of the order of the proton

  10. Thinning behavior of laminated sheets metal in warm deep-drawing process under various grain sizes

    Directory of Open Access Journals (Sweden)

    Kadkhodayan Mehran

    2016-01-01

    Full Text Available The purpose of present research is to investigate the thickness distribution on the warm deep-drawing process of laminated sheets consisting of aluminum alloy series 1050, 5052 and stainless steel 304 (SUS, experimentally. Individually for each layer, the influences of blank temperature and grain size on thinning behavior are clearly demonstrated. In order to survey the thinning behavior in laminate sheet behavior during warm deep-drawing process; three blank temperatures namely, 25° C, 100° C and 160° C are examined. Moreover, to obtain different grain sizes, the aluminium sheets are annealed at 350° C, 400° C and 450° C for 1 hour. Results indicate that increasing temperature and grain size lead to maximum thinning in all layers in Al 1050/SUS and Al 5052/SUS specimens increase. In addition, the most susceptible zone to fracture in aluminum sheets (Al 1050 and Al 5052 is punch profile radius region; nevertheless, for stainless steel sheets this zone switch to central zone of formed cup. These can be attributed to the fact that the adhesive layer play a crucial role in thickness distribution of steel 304 layer, therefore the distribution of thickness strain for adhesive layer is also investigated.

  11. Energy balance in current sheets: From Petschek to gravity driven reconnection

    International Nuclear Information System (INIS)

    Mercier, C.; Heyvaerts, J.

    1980-01-01

    It has been shown earlier that energy balance processes play a very important role in the determination of the reconnection regime in the central diffusive region of a steady Petschek flow (usually considered elsewhere as isothermal and incompressible): as a consequence of the plasma thermal properties, abrupt transitions in the reconnection regime may occur for special external conditions. The regime becomes then a dynamical one, and it was suggested that onset of plasma microturbulence may result and act as a primary triggering mechanism in solar flares. In this paper we will reexamine the problem of onset of such dynamical transition and conclude that plasma microturbulence does not appear in a straightforward way. However it is possible that the canonical Petschek regime may evolute into a new one in which the dissipative sheet is no longer infinitesimal with respect to the dimensions of the structure, and in which gravity plays an important role. Flare triggering, if related to the reconnection regime, must then proceed by more complex processes, possibly related to tearing mode dynamics, or to more global properties of the magnetic structure of the active region. (orig.)

  12. Balance Sheet Channel of Monetary Policy and Economic Growth under Fiscal Dominance: Evidence from Pakistan

    OpenAIRE

    Shabbir, Safia

    2012-01-01

    Using micro data on non-financial listed companies in Pakistan, over the period of 2000-2010, this paper emphasizes over the impact of monetary policy on economic growth through balance sheet channel. At first step, monetary tightening deteriorates the net worth of the firms and leads to cash flow squeeze; of which later affects the economic growth. We find this impact to last for three years over the balance sheets of the firms. Since, industrial sector drives the economic growth; we forecas...

  13. Equilibrium shape of a suspended graphene sheet under electrostatic and van der Waals forces

    Science.gov (United States)

    Inui, Norio

    2018-03-01

    The equilibrium shape of a graphene sheet suspended over a silicon substrate with a narrow gap is investigated by introducing a continuum model. The displacement of the suspended graphene sheet, subject to electrostatic and van der Waals forces, was obtained by solving the equation of motion including the dissipation terms. The van der Waals force was calculated based on the quantum theory by considering the unique optical properties of graphene and their temperature dependence. The van der Waals force has a large effect on the equilibrium shape near the threshold value, below which a pull-in phenomenon occurs.

  14. Euler potentials for two current sheets along ambient uniform magnetic field

    Czech Academy of Sciences Publication Activity Database

    Romashets, E. P.; Vandas, Marek

    2012-01-01

    Roč. 117, July (2012), A07221/1-A07221/8 ISSN 0148-0227 R&D Projects: GA ČR GA205/09/0170; GA MŠk ME09032 Institutional support: RVO:67985815 Keywords : aligned currents * birkeland currents * magnetosphere Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 3.174, year: 2012

  15. Effect of Weld Current on the Microstructure and Mechanical Properties of a Resistance Spot-Welded TWIP Steel Sheet

    Directory of Open Access Journals (Sweden)

    Mumin Tutar

    2017-11-01

    Full Text Available In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP steel sheet was investigated using optical microscopy, scanning electron microscopy–electron back-scattered diffraction (SEM–EBSD, microhardness measurements, a tensile shear test and fractography. Higher weld currents promoted the formation of a macro expulsion cavity in the fusion zone. Additionally, higher weld currents led to a higher indentation depth, a wider heat-affected zone (HAZ, coarser grain structure and thicker annealing twins in the HAZ, and a relatively equiaxed dendritic structure in the centre of the fusion zone. The hardness values in the weld zone were lower than that of the base metal. The lowest hardness values were observed in the HAZ. No strong relationship was observed between the hardness values in the weld zone and the weld current. A higher joint strength, tensile deformation and failure energy absorption capacity were obtained with a weld current of 12 kA, a welding time of 300 ms and an electrode force of 3 kN. A complex fracture surface with both brittle and limited ductile manner was observed in the joints, while the base metal exhibited a ductile fracture. Joints with a higher tensile shear load (TSL commonly exhibited more brittle fracture characteristics.

  16. Critical current of various REBCO tapes under uniaxial strain

    NARCIS (Netherlands)

    Zhou, Chao; Yagotyntsev, Kostyantyn; Gao, Peng; Haugan, T.J.; van der Laan, D.C.; Nijhuis, Arend

    2016-01-01

    For high-current REBCO superconductors in high magnet fields with currents on the order of 50 kA, single coated conductors must be assembled in a cable. Under operating conditions, such cables are subjected to combined torsion, axial, and transverse loads in the tapes and tape joints. As such, the

  17. DOES THE COMPRESSION OR THE EXPANSION OF A SIMPLE TOPOLOGY POTENTIAL MAGNETIC FIELD LEAD TO THE DEVELOPMENT OF CURRENT SHEETS?

    International Nuclear Information System (INIS)

    Aly, J. J.; Amari, T.

    2010-01-01

    Janse and Low have most recently addressed the following question. Consider a cylindrical domain containing a simple topology potential magnetic field threading its lower and upper horizontal faces, and a perfectly conducting plasma. Suppose that this domain is made to slowly contract or expand in the vertical direction, so driving the field into a quasi-static evolution through a series of force-free configurations. Then are these configurations smooth, or do they contain current sheets (CSs)? We reexamine here their three-step argument leading to the conclusion that CSs form most generally. We prove analytically that the field has to evolve through 'topologically untwisted' and 'nonpotential' configurations, thus confirming the first two steps. However, we find the third step-leading to the conclusion that a smooth untwisted force-free field is necessarily potential-to be very disputable.

  18. THE THREE-DIMENSIONAL EVOLUTION OF ION-SCALE CURRENT SHEETS: TEARING AND DRIFT-KINK INSTABILITIES IN THE PRESENCE OF PROTON TEMPERATURE ANISOTROPY

    Energy Technology Data Exchange (ETDEWEB)

    Gingell, P. W.; Burgess, D. [Queen Mary University of London, Mile End Road, London E4 1NS (United Kingdom); Matteini, L., E-mail: p.w.gingell@qmul.ac.uk [Imperial College London, London SW7 2AZ (United Kingdom)

    2015-03-20

    We present the first three-dimensional (3D) hybrid simulations of the evolution of ion-scale current sheets, with an investigation of the role of temperature anisotropy and associated kinetic instabilities on the growth of the tearing instability and particle heating. We confirm the ability of the ion cyclotron and firehose instabilities to enhance or suppress reconnection, respectively. The simulations demonstrate the emergence of persistent 3D structures, including patchy reconnection sites and the fast growth of a narrow-band drift-kink instability, which suppresses reconnection for thin current sheets with weak guide fields. Potential observational signatures of the 3D evolution of solar wind current sheets are also discussed. We conclude that kinetic instabilities, arising from non-Maxwellian ion populations, are significant to the evolution of 3D current sheets, and two-dimensional studies of heating rates by reconnection may therefore over-estimate the ability of thin, ion-scale current sheets to heat the solar wind by reconnection.

  19. Monitoring DC stray current interference of steel sheet pile structures in railway environment

    NARCIS (Netherlands)

    Peelen, W.H.A.; Neeft, E.A.C.; Leegwater, G.; Kanten-Roos, W. van; Courage, W.M.G.

    2011-01-01

    Steel structures near DC powered railways are expected to be affected by stray current interference. This causes accelerated corrosion rates. Therefore steel is often not used as a building material in these cases, although certain advantages over the alternative material concrete exist. These

  20. Cholera Fact Sheet

    Science.gov (United States)

    ... sheets Fact files Questions & answers Features Multimedia Contacts Cholera Fact sheet Updated December 2017 Key facts Cholera ... behaviour and to the control of cholera. Oral cholera vaccines Currently there are three WHO pre-qualified ...

  1. Deglacial to Holocene history of ice-sheet retreat and bottom current strength on the western Barents Sea shelf

    Science.gov (United States)

    Lantzsch, Hendrik; Hanebuth, Till J. J.; Horry, Jan; Grave, Marina; Rebesco, Michele; Schwenk, Tilmann

    2017-10-01

    High-resolution sediment echosounder data combined with radiocarbon-dated sediment cores allowed us to reconstruct the Late Quaternary stratigraphic architecture of the Kveithola Trough and surrounding Spitsbergenbanken. The deposits display the successive deglacial retreat of the Svalbard-Barents Sea Ice Sheet. Basal subglacial till indicates that the grounded ice sheet covered both bank and trough during the Late Weichselian. A glaciomarine blanket inside the trough coinciding with laminated plumites on the bank formed during the initial ice-melting phase from at least 16.1 to 13.5 cal ka BP in close proximity to the ice margin. After the establishment of open-marine conditions at around 13.5 cal ka BP, a sediment drift developed in the confined setting of the Kveithola Trough, contemporary with crudely laminated mud, an overlying lag deposit, and modern bioclastic-rich sand on Spitsbergenbanken. The Kveithola Drift shows a remarkable grain-size coarsening from the moat towards the southern flank of the trough. This trend contradicts the concept of a separated drift (which would imply coarser grain sizes in proximity of the moat) and indicates that the southern bank is the main sediment source for the coarse material building up the Kveithola Drift. This depocenter represents, therefore, a yet undescribed combination of off-bank wedge and confined drift. Although the deposits inside Kveithola Trough and on Spitsbergenbanken display different depocenter geometries, time-equivalent grain-size changes imply a region-wide sediment-dynamic connection. We thus relate a phase of coarsest sediment supply (8.8-6.3 cal ka BP) to an increase in bottom current strength, which might be related to a stronger Atlantic Water inflow from the Southeast across the bank leading to winnowing and off-bank export of sandy sediments.

  2. A modular tooling set-up for incremental sheet forming (ISF) with subsequent stress-relief annealing under partial constraints

    Science.gov (United States)

    Maqbool, Fawad; Bambach, Markus

    2017-10-01

    Incremental sheet forming (ISF) is a manufacturing process most suitable for small-batch production of sheet metal parts. In ISF, a CNC-controlled tool moves over the sheet metal, following a specified contour to form a part of the desired geometry. This study focuses on one of the dominant process limitations associated with the ISF, i.e., the limited geometrical accuracy. In this regard, a case study is performed which shows that increased geometrical accuracy of the formed part can be achieved by a using stress-relief annealing before unclamping. To keep the tooling costs low, a modular die design consisting of a stiff metal frame and inserts made from inexpensive plastics (Sika®) were devised. After forming, the plastics inserts are removed. The metal frame supports the part during stress-relief annealing. Finite Element (FE) simulations of the manufacturing process are performed. Due to the residual stresses induced during the forming, the geometry of the formed part, from FE simulation and the actual manufacturing process, shows severe distortion upon unclamping the part. Stress relief annealing of the formed part under partial constraints exerted by the tool frame shows that a part with high geometrical accuracy can be obtained.

  3. Formability of Al 5xxx Sheet Metals Using Pulsed Current for Various Heat Treatments

    Energy Technology Data Exchange (ETDEWEB)

    Salandro, Wesley A.; Jones, Joshua J.; McNeal, Timothy A.; Roth, John T.; Hong, Sung Tae; Smith, Mark T.

    2010-10-01

    Previous studies have shown that the presence of a pulsed electrical current, applied during the deformation process of an aluminum specimen, can significantly improve the formability of the aluminum without heating the metal above its maximum operating temperature range. The research herein extends these findings by examining the effect of electrical pulsing on 5052 and 5083 Aluminum Alloys. Two different parameter sets were used while pulsing three different heat treatments (As Is, 398°C, and 510°C) for each of the two aluminum alloys. For this research, the electrical pulsing is applied to the aluminum while the specimens are deformed, without halting the deformation process (a manufacturing technique known as Electrically-Assisted Manufacturing). The analysis focuses on establishing the effect the electrical pulsing has on the aluminum alloy’s various heat treatments by examining the displacement of the material throughout the testing region of dogbone-shaped specimens. The results from this research show that pulsing significantly increases the maximum achievable elongation of the aluminum (when compared to baseline tests conducted without electrical pulsing). Another beneficial effect produced by electrical pulsing is that the engineering flow stress within the material is considerably reduced. The electrical pulses also cause the aluminum to deform non-uniformly, such that the material exhibits a diffuse neck where the minimum deformation occurs near the ends of the specimen (near the clamps) and the maximum deformation occurs near the center of the specimen (where fracture ultimately occurs). This diffuse necking effect is similar to what can be experienced during superplastic deformation. However, when comparing the presence of a diffuse neck in this research, electrical pulsing does not create as significant of a diffuse neck as superplastic deformation. Electrical pulsing has the potential to be more efficient than traditional methods of incremental

  4. Durability Study of SOFCs Under Cycling Current Load Conditions

    DEFF Research Database (Denmark)

    Hagen, Anke; Hendriksen, Peter Vang; Frandsen, Henrik Lund

    2009-01-01

    In fuel cell applications, the cells must be able to withstand varying operating conditions. Anode supported solid oxide fuel cells were tested under cycling current load in order to determine the durability and possibly identify degradation mechanisms. At 750 °C and a cycling between zero and 0...

  5. DBP formation and disinfection under current and future climates - slides

    Science.gov (United States)

    How to predict and monitoring DBP formation under current and future climate is a challenge and important to water plant operations and water supply security. This presentation summarizes a system approach being developed at the EPA Water Resources Adaptation Program (WRAP).

  6. Estimation of current density distribution under electrodes for external defibrillation

    Directory of Open Access Journals (Sweden)

    Papazov Sava P

    2002-12-01

    Full Text Available Abstract Background Transthoracic defibrillation is the most common life-saving technique for the restoration of the heart rhythm of cardiac arrest victims. The procedure requires adequate application of large electrodes on the patient chest, to ensure low-resistance electrical contact. The current density distribution under the electrodes is non-uniform, leading to muscle contraction and pain, or risks of burning. The recent introduction of automatic external defibrillators and even wearable defibrillators, presents new demanding requirements for the structure of electrodes. Method and Results Using the pseudo-elliptic differential equation of Laplace type with appropriate boundary conditions and applying finite element method modeling, electrodes of various shapes and structure were studied. The non-uniformity of the current density distribution was shown to be moderately improved by adding a low resistivity layer between the metal and tissue and by a ring around the electrode perimeter. The inclusion of openings in long-term wearable electrodes additionally disturbs the current density profile. However, a number of small-size perforations may result in acceptable current density distribution. Conclusion The current density distribution non-uniformity of circular electrodes is about 30% less than that of square-shaped electrodes. The use of an interface layer of intermediate resistivity, comparable to that of the underlying tissues, and a high-resistivity perimeter ring, can further improve the distribution. The inclusion of skin aeration openings disturbs the current paths, but an appropriate selection of number and size provides a reasonable compromise.

  7. Recent aerogeophysical exploration under the East Antarctic Ice Sheet in Wilkes Land

    Science.gov (United States)

    Bozzo, E.; Ferraccioli, F.; Armadillo, E.; Jordan, T. A.; Corr, H.; Hill, D. J.

    2009-12-01

    An extensive aerogeophysical survey was flown in Wilkes Land (East Antarctica) during the 2005/06 Antarctic field-campaign as part of a joint Italian-UK exploration project, WISE (Wilkes WIlkes Basin/Transantarctic Mountains System Exploration)/ ISODYN (Icehouse Earth: Stability Or DYNamism?). The Italian Antarctic programme provided major logistic support at Mario Zucchelli Station, at two remote field camps, Talos Dome and Sitry, and at Mid-Point. 68 survey flights led to the collection of over 60,000 line-km of new aerogeophysical data over a frontier region that had not been explored since the 70’s. Airborne radar, aeromagnetic and airborne gravity data were simultaneously collected on a British Antarctic Survey Twin Otter with the overarching aim of providing new basal boundary conditions for the dynamics and stability of the East Antarctic Ice Sheet, and characterizing geological structures in the Wilkes Subglacial Basin (WSB) and adjacent Transantarctic Mountains (TAM). During the International Polar Year our efforts focused on data analysis and subsequent development of new interpretations. Here we review some of the results. Our new bedrock topography map derived from airborne radar reveals major subglacial basins with depths up to 2.1 km below sea-level within the WSB region. These sub-basins are in places up to 1.5 km deeper than imaged by BEDMAP, have different orientations, and are flanked by major bedrock plateaus that differ from alpine-type landscapes exposed over the adjacent TAM in northern Victoria Land. The new subglacial topography for the region is a critical boundary condition to develop next generation coupled ice sheet and climate models over East Antarctica. These models are targeting the contentious stability of this marine-based part of the East Antarctic Ice Sheet during warm periods in the geological past and may provide a tool for assessing its longer term future behaviour in a warmer climate. The airborne radar dataset

  8. Fault Current Characteristics of the DFIG under Asymmetrical Fault Conditions

    Directory of Open Access Journals (Sweden)

    Fan Xiao

    2015-09-01

    Full Text Available During non-severe fault conditions, crowbar protection is not activated and the rotor windings of a doubly-fed induction generator (DFIG are excited by the AC/DC/AC converter. Meanwhile, under asymmetrical fault conditions, the electrical variables oscillate at twice the grid frequency in synchronous dq frame. In the engineering practice, notch filters are usually used to extract the positive and negative sequence components. In these cases, the dynamic response of a rotor-side converter (RSC and the notch filters have a large influence on the fault current characteristics of the DFIG. In this paper, the influence of the notch filters on the proportional integral (PI parameters is discussed and the simplified calculation models of the rotor current are established. Then, the dynamic performance of the stator flux linkage under asymmetrical fault conditions is also analyzed. Based on this, the fault characteristics of the stator current under asymmetrical fault conditions are studied and the corresponding analytical expressions of the stator fault current are obtained. Finally, digital simulation results validate the analytical results. The research results are helpful to meet the requirements of a practical short-circuit calculation and the construction of a relaying protection system for the power grid with penetration of DFIGs.

  9. Step-like variations of cosmic rays and their relation to an inclination of the heliospheric current sheet

    Science.gov (United States)

    Svirzhevskaya, A. K.; Svirzhevsky, N. S.; Stozhkov, Yu. I.

    2001-08-01

    The large and fast step-like variations in the GCR intensity are examined during both the descending and recovery phases of the 20-23 solar cycles. The cosmic ray intensity data sets obtained in the stratospheric measurements in Murmansk, Mirny (Antarctica) and Moscow are used. At present the global merged interaction regions (GMIRs) are considered as a natural explanation of step-like intensity decreases. But the GMIRs are not suitable to explain the rapid intensity recovery that was as fast as the step-like decreases, for example in 1962, 1971, and 1991. According to the ULYSSES measurements, the IMF was much more disturbed within the sector zones. It means that the diffusion coefficient is smaller within the sector zone (just as inside the GMIR) than one beyond the sector zones. The changes of the heliospheric current sheet inclination cause the changes in the angular sizes of sector zones and due to that the fast decreases or increases of the GCR intensity. It is also shown that the intensity changes immediately after the step-decreases depend upon the IMF polarity. The cosmic ray intensity after the step-decrease tends to recover at 0>A and continues to decrease slowly at 0

  10. Reconstruction of a Large-scale Pre-flare Coronal Current Sheet Associated with a Homologous X-shaped Flare

    Science.gov (United States)

    Jiang, Chaowei; Yan, Xiaoli; Feng, Xueshang; Duan, Aiying; Hu, Qiang; Zuo, Pingbing; Wang, Yi

    2017-11-01

    As a fundamental magnetic structure in the solar corona, electric current sheets (CSs) can form either prior to or during a solar flare, and they are essential for magnetic energy dissipation in the solar corona because they enable magnetic reconnection. However, the static reconstruction of a CS is rare, possibly due to limitations that are inherent in the available coronal field extrapolation codes. Here we present the reconstruction of a large-scale pre-flare CS in solar active region 11967 using an MHD-relaxation model constrained by the SDO/HMI vector magnetogram. The CS is associated with a set of peculiar homologous flares that exhibit unique X-shaped ribbons and loops occurring in a quadrupolar magnetic configuration.This is evidenced by an ’X’ shape, formed from the field lines traced from the CS to the photosphere. This nearly reproduces the shape of the observed flare ribbons, suggesting that the flare is a product of the dissipation of the CS via reconnection. The CS forms in a hyperbolic flux tube, which is an intersection of two quasi-separatrix layers. The recurrence of the X-shaped flares might be attributed to the repetitive formation and dissipation of the CS, as driven by the photospheric footpoint motions. These results demonstrate the power of a data-constrained MHD model in reproducing a CS in the corona as well as providing insight into the magnetic mechanism of solar flares.

  11. Assessing the Global Climate Response to Freshwater Forcing from the Antarctic Ice Sheet Under Future Climate Scenarios

    Science.gov (United States)

    Rogstad, S.; Condron, A.; DeConto, R.; Pollard, D.

    2017-12-01

    Observational evidence indicates that the West Antarctic Ice Sheet (WAIS) is losing mass at an accelerating rate. Impacts to global climate resulting from changing ocean circulation patterns due to increased freshwater runoff from Antarctica in the future could have significant implications for global heat transport, but to-date this topic has not been investigated using complex numerical models with realistic freshwater forcing. Here, we present results from a high resolution fully coupled ocean-atmosphere model (CESM 1.2) forced with runoff from Antarctica prescribed from a high resolution regional ice sheet-ice shelf model. Results from the regional simulations indicate a potential freshwater contribution from Antarctica of up to 1 m equivalent sea level rise by the end of the century under RCP 8.5 indicating that a substantial input of freshwater into the Southern Ocean is possible. Our high resolution global simulations were performed under IPCC future climate scenarios RCP 4.5 and 8.5. We will present results showing the impact of WAIS collapse on global ocean circulation, sea ice, air temperature, and salinity in order to assess the potential for abrupt climate change triggered by WAIS collapse.

  12. Current exposure method for CCP’s under Basel III

    Directory of Open Access Journals (Sweden)

    Antonie Kotzé

    2013-04-01

    Full Text Available Exposure-at-default is one of the most interesting and most difficult parameters to estimate in counterparty credit risk. Basel I offered only the non-internal Current Exposure Method for estimating this quantity whilst Basel II further introduced the Standardized Method and an Internal Model Method. Under new Basel III rules a central counterparty is defined as being a financial institution. New principles set out by the Basel Committee on Banking Supervision forces Central Counterparties in using the Current Exposure Method when estimating the credit exposures to Clearing Member banks notwithstanding its shortcomings. The Current Exposure Method relies on the Value-at-Risk methodology and its characteristics are discussed in this note. We will particularly investigate exposures to SAFCOM, the South African clearing house and point to a mathematical discrepancy on how netting is effected through the Basel accord.

  13. How Do Icebergs Affect The Greenland Ice Sheet Under Pre-Industrial Conditions? – A Model Study With A Fully Coupled Ice Sheet – Climate Model

    NARCIS (Netherlands)

    Bügelmayer, M.; Roche, D.M.V.A.P.; Renssen, H.

    2015-01-01

    Icebergs have a potential impact on climate since they release freshwater over a widespread area and cool the ocean due to the take-up of latent heat. Yet, so far, icebergs have never been modelled using an ice-sheet model coupled to a global climate model. Thus, in climate models their impact on

  14. Towards cost optimal design and maintenance of steel structures under stray current interference

    NARCIS (Netherlands)

    Peelen, W.H.A.; Krom, A.H.M.; Polder, R.B.

    2006-01-01

    Steel is a cost-effective and durable building material. Corrosion is one of the major degradation mechanisms of steel structures, also for underground structures like sheet pile walls. Traction currents leaking into the ground (called stray currents here) and interfering with the structure can

  15. Microstructure evolution and modeling of 2024 aluminum alloy sheets during hot deformation under different stress states

    Science.gov (United States)

    Deng, Lei; Zhou, Peng; Wang, Xinyun; Jin, Junsong; Zhao, Ting

    2018-01-01

    In this work, specimens of the 2024 aluminum alloy sheet were compressed and stretched along the original rolling direction at elevated temperatures. The microstructure evolution was investigated by characterizing the metallographic structures via electron backscattered diffraction technology before and after deformation. It was found that while recrystallization occurred in the compressed specimens, it was not observed to the same extent in the stretched specimens. This difference in the grain morphology has been attributed to the different movement behaviors of the grain boundaries, i.e., their significant migration in the compression deformation and the transformation from low-angle to high-angle boundaries observed mainly during tension deformation. The empirical model, which can describe the grain size evolution during compression, is not suitable in the case of tension, and therefore, a new model which ignores the detailed recrystallization process has been proposed. This model provides a description of the grain size change during hot deformation and can be used to predict the grain size in the plastic deformation process.

  16. OSCILLATION OF CURRENT SHEETS IN THE WAKE OF A FLUX ROPE ERUPTION OBSERVED BY THE SOLAR DYNAMICS OBSERVATORY

    Energy Technology Data Exchange (ETDEWEB)

    Li, L. P.; Zhang, J.; Su, J. T. [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing (China); Liu, Y. [Department of Astronomy, Beijing Normal University, 100875 Beijing (China)

    2016-10-01

    An erupting flux rope (FR) draws its overlying coronal loops upward, causing a coronal mass ejection. The legs of the overlying loops with opposite polarities are driven together. Current sheets (CSs) form, and magnetic reconnection, producing underneath flare arcades, occurs in the CSs. Employing Solar Dynamic Observatory /Atmospheric Imaging Assembly images, we study a FR eruption on 2015 April 23, and for the first time report the oscillation of CSs underneath the erupting FR. The FR is observed in all AIA extreme-ultraviolet passbands, indicating that it has both hot and warm components. Several bright CSs, connecting the erupting FR and the underneath flare arcades, are observed only in hotter AIA channels, e.g., 131 and 94 Å. Using the differential emission measure (EM) analysis, we find that both the temperature and the EM of CSs temporally increase rapidly, reach the peaks, and then decrease slowly. A significant delay between the increases of the temperature and the EM is detected. The temperature, EM, and density spatially decrease along the CSs with increasing heights. For a well-developed CS, the temperature (EM) decreases from 9.6 MK (8 × 10{sup 28} cm{sup −5}) to 6.2 MK (5 × 10{sup 27} cm{sup −5}) in 52 Mm. Along the CSs, dark supra-arcade downflows (SADs) are observed, and one of them separates a CS into two. While flowing sunward, the speeds of the SADs decrease. The CSs oscillate with a period of 11 minutes, an amplitude of 1.5 Mm, and a phase speed of 200 ± 30 km s{sup −1}. One of the oscillations lasts for more than 2 hr. These oscillations represent fast-propagating magnetoacoustic kink waves.

  17. Discharge current distribution in stratified soil under impulse discharge

    Science.gov (United States)

    Eniola Fajingbesi, Fawwaz; Shahida Midi, Nur; Elsheikh, Elsheikh M. A.; Hajar Yusoff, Siti

    2017-06-01

    The mobility of charge particles traversing a material defines its electrical properties. Soil (earth) have long been the universal grounding before and after the inception of active ground systems for electrical appliance purpose due to it semi-conductive properties. The soil can thus be modelled as a single material exhibiting semi-complex inductive-reactive impedance. Under impulse discharge such as lightning strikes to soil this property of soil could result in electric potential level fluctuation ranging from ground potential rise/fall to electromagnetic pulse coupling that could ultimately fail connected electrical appliance. In this work we have experimentally model the soil and lightning discharge using point to plane electrode setup to observe the current distribution characteristics at different soil conductivity [mS/m] range. The result presented from this research indicate above 5% shift in conductivity before and after discharge which is significant for consideration when dealing with grounding designs. The current distribution in soil have also be successfully observed and analysed from experimental result using mean current magnitude in relation to electrode distance and location, current density variation with depth all showing strong correlation with theoretical assumptions of a semi-complex impedance material.

  18. Basic Facts about Low-Income Children: Children under 6 Years, 2013. Fact Sheet

    Science.gov (United States)

    Jiang, Yang; Ekono, Mercedes; Skinner, Curtis

    2015-01-01

    Children under 18 years represent 23 percent of the population, but they comprise 33 percent of all people in poverty. Among all children, 44 percent live in low-income families and approximately one in every five (22 percent) live in poor families. Young children under age 6 years appear to be particularly vulnerable, with 48 percent living in…

  19. Basic Facts about Low-Income Children: Children under 3 Years, 2013. Fact Sheet

    Science.gov (United States)

    Jiang, Yang; Ekono, Mercedes; Skinner, Curtis

    2015-01-01

    Children under 18 years represent 23 percent of the population, but they comprise 33 percent of all people in poverty. Among all children, 44 percent live in low-income families and approximately one in every five (22 percent) live in poor families. Our very youngest children--infants and toddlers under age 3 years--appear to be particularly…

  20. Metering error quantification under voltage and current waveform distortion

    Science.gov (United States)

    Wang, Tao; Wang, Jia; Xie, Zhi; Zhang, Ran

    2017-09-01

    With integration of more and more renewable energies and distortion loads into power grid, the voltage and current waveform distortion results in metering error in the smart meters. Because of the negative effects on the metering accuracy and fairness, it is an important subject to study energy metering combined error. In this paper, after the comparing between metering theoretical value and real recorded value under different meter modes for linear and nonlinear loads, a quantification method of metering mode error is proposed under waveform distortion. Based on the metering and time-division multiplier principles, a quantification method of metering accuracy error is proposed also. Analyzing the mode error and accuracy error, a comprehensive error analysis method is presented which is suitable for new energy and nonlinear loads. The proposed method has been proved by simulation.

  1. Antarctic Circumpolar Current Dynamics and Their Relation to Antarctic Ice Sheet and Perennial Sea-Ice Variability in the Central Drake Passage During the Last Climate Cycle

    Science.gov (United States)

    Kuhn, G.; Wu, S.; Hass, H. C.; Klages, J. P.; Zheng, X.; Arz, H. W.; Esper, O.; Hillenbrand, C. D.; Lange, C.; Lamy, F.; Lohmann, G.; Müller, J.; McCave, I. N. N.; Nürnberg, D.; Roberts, J.; Tiedemann, R.; Timmermann, A.; Titschack, J.; Zhang, X.

    2017-12-01

    The evolution of the Antarctic Ice Sheet during the last climate cycle and the interrelation to global atmospheric and ocean circulation remains controversial and plays an important role for our understanding of ice sheet response to modern global warming. The timing and sequence of deglacial warming is relevant for understanding the variability and sensitivity of the Antarctic Ice Sheet to climatic changes, and the continuing rise of atmospheric greenhouse gas concentrations. The Antarctic Ice Sheet is a pivotal component of the global water budget. Freshwater fluxes from the ice sheet may affect the Antarctic Circumpolar Current (ACC), which is strongly impacted by the westerly wind belt in the Southern Hemisphere (SHWW) and constricted to its narrowest extent in the Drake Passage. The flow of ACC water masses through Drake Passage is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global meridional overturning circulation and global climate change. In order to address orbital and millennial-scale variability of the Antarctic ice sheet and the ACC, we applied a multi-proxy approach on a sediment core from the central Drake Passage including grain size, iceberg-rafted debris, mineral dust, bulk chemical and mineralogical composition, and physical properties. In combination with already published and new sediment records from the Drake Passage and Scotia Sea, as well as high-resolution data from Antarctic ice cores (WDC, EDML), we now have evidence that during glacial times a more northerly extent of the perennial sea-ice zone decreased ACC current velocities in the central Drake Passage. During deglaciation the SHWW shifted southwards due to a decreasing temperature gradient between subtropical and polar latitudes caused by sea ice and ice sheet decline. This in turn caused Southern Hemisphere warming, a more vigorous ACC, stronger Southern Ocean ventilation, and warm Circumpolar Deep Water (CDW) upwelling on Antarctic shelves

  2. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films

    Science.gov (United States)

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-Ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-03-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.

  3. Mechanism of Antiwear Property Under High Pressure of Synthetic Oil-Soluble Ultrathin MoS2Sheets as Lubricant Additives.

    Science.gov (United States)

    Chen, Zhe; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

    2018-01-30

    Wear occurs between two rubbing surfaces. Severe wear due to seizure under high pressure leads to catastrophic failures of mechanical systems and raises wide concerns. In this paper, a kind of synthetic oil-soluble ultrathin MoS 2 sheets is synthesized and investigated as lubricant additives between steel surfaces. It is found that, with the ultrathin MoS 2 sheets, the wear can be controlled under the nominal pressure of about 1 GPa, whereas the bearable nominal pressure for traditional lubricants is only a few hundred megapascals. It is found that when wear is under control, the real pressure between the asperities agrees with the breaking strength of ultrathin MoS 2 . Therefore, it is believed that, because of the good oil solubility and ultrasmall thickness, the ultrathin MoS 2 sheets can easily enter the contact area between the contacting asperities. Then, the localized seizure and further wear are prevented because there will be no metal-to-metal contact as long as the real pressure between the asperities is below the breaking strength of ultrathin MoS 2 . In this way, the upper limit pressure the lubricant can work is dependent on the mechanical properties of the containing ultrathin two-dimensional (2D) sheets. Additionally, ultrathin MoS 2 sheets with various lateral sizes are compared, and it is found that sheets with a larger size show better lubrication performance. This work discovers the lubrication mechanism of ultrathin MoS 2 sheets as lubricant additives and provides an inspiration to develop a novel generation of lubricant additives with high-strength ultrathin 2D materials.

  4. Basic Facts about Low-Income Children: Children under 18 Years, 2013. Fact Sheet

    Science.gov (United States)

    Jiang, Yang; Ekono, Mercedes; Skinner, Curtis

    2015-01-01

    Children under 18 years represent 23 percent of the population, but they comprise 33 percent of all people in poverty. Among all children, 44 percent live in low-income families and approximately one in every five (22 percent) live in poor families. Being a child in a low-income or poor family does not happen by chance. Parental education and…

  5. Contact Behavior of Composite CrTiSiN Coated Dies in Compressing of Mg Alloy Sheets under High Pressure

    Directory of Open Access Journals (Sweden)

    T.S. Yang

    2018-01-01

    Full Text Available Hard coatings have been adopted in cutting and forming applications for nearly two decades. The major purpose of using hard coatings is to reduce the friction coefficient between contact surfaces, to increase strength, toughness and anti-wear performance of working tools and molds, and then to obtain a smooth work surface and an increase in service life of tools and molds. In this report, we deposited a composite CrTiSiN hard coating, and a traditional single-layered TiAlN coating as a reference. Then, the coatings were comparatively studied by a series of tests. A field emission SEM was used to characterize the microstructure. Hardness was measured using a nano-indentation tester. Adhesion of coatings was evaluated using a Rockwell C hardness indentation tester. A pin-on-disk wear tester with WC balls as sliding counterparts was used to determine the wear properties. A self-designed compression and friction tester, by combining a Universal Testing Machine and a wear tester, was used to evaluate the contact behavior of composite CrTiSiN coated dies in compressing of Mg alloy sheets under high pressure. The results indicated that the hardness of composite CrTiSiN coating was lower than that of the TiAlN coating. However, the CrTiSiN coating showed better anti-wear performance. The CrTiSiN coated dies achieved smooth surfaces on the Mg alloy sheet in the compressing test and lower friction coefficient in the friction test, as compared with the TiAlN coating.

  6. Contact Behavior of Composite CrTiSiN Coated Dies in Compressing of Mg Alloy Sheets under High Pressure.

    Science.gov (United States)

    Yang, T S; Yao, S H; Chang, Y Y; Deng, J H

    2018-01-08

    Hard coatings have been adopted in cutting and forming applications for nearly two decades. The major purpose of using hard coatings is to reduce the friction coefficient between contact surfaces, to increase strength, toughness and anti-wear performance of working tools and molds, and then to obtain a smooth work surface and an increase in service life of tools and molds. In this report, we deposited a composite CrTiSiN hard coating, and a traditional single-layered TiAlN coating as a reference. Then, the coatings were comparatively studied by a series of tests. A field emission SEM was used to characterize the microstructure. Hardness was measured using a nano-indentation tester. Adhesion of coatings was evaluated using a Rockwell C hardness indentation tester. A pin-on-disk wear tester with WC balls as sliding counterparts was used to determine the wear properties. A self-designed compression and friction tester, by combining a Universal Testing Machine and a wear tester, was used to evaluate the contact behavior of composite CrTiSiN coated dies in compressing of Mg alloy sheets under high pressure. The results indicated that the hardness of composite CrTiSiN coating was lower than that of the TiAlN coating. However, the CrTiSiN coating showed better anti-wear performance. The CrTiSiN coated dies achieved smooth surfaces on the Mg alloy sheet in the compressing test and lower friction coefficient in the friction test, as compared with the TiAlN coating.

  7. The plasma sheet and boundary layers under northward IMF: A multi-point and multi-instrument perspective

    Czech Academy of Sciences Publication Activity Database

    Taylor, M. G. G. T.; Lavraud, B.; Escoubet, C. P.; Milan, S.E.; Nykyri, K.; Dunlop, M. W.; Davies, J.A.; Friedel, R.H.W.; Frey, H.; Bogdanova, Y.V.; Asnes, A.; Laakso, H.; Trávníček, Pavel M.; Masson, A.; Opgenoorth, H.; Vallat, C.; Fazakerley, A. N.; Lahiff, A.; Owen, C. J.; Pitout, F.; Pu, Y.; Shen, C.; Zong, Q.-G.; Rème, H.; Scudder, J. D.; Zhang, T. L.

    2008-01-01

    Roč. 41, č. 10 (2008), s. 1619-1629 ISSN 0273-1177 Institutional research plan: CEZ:AV0Z10030501 Keywords : plasma sheet * magnetopshere * cold dense plasma sheet Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 0.860, year: 2008

  8. Current state of orthodontic patients under bisphosphonate therapy.

    Science.gov (United States)

    Krieger, Elena; Jacobs, Collin; Walter, Christian; Wehrbein, Heinrich

    2013-04-04

    Bisphosphonates are a common medication for the prevention and therapy of osteoporosis, but are also applied for tumor diseases. They affect bone metabolism, and therefore also orthodontic treatments, but how it does has yet not been definitively clarified. Therefore, the aim of this research was to evaluate and demonstrate the reported effects and the current state of scientific research regarding orthodontic treatment and bisphosphonate medication exclusively in humans. A systematic research of the literature for selected keywords in the Medline database (Pubmed) as well as a manual search was conducted. The following search terms were used: 'Bisphosphonate' in combination with: orthodontic, orthodontic treatment, tooth movement. To date, only nine reported patients (case reports/series) and one original article (retrospective cohort study) regarding orthodontic treatment under bisphosphonate medication in humans have been published. Decelerated tooth movement with increased side effects (especially in high-risk patients) and longer treatment duration was reported in some articles. Patients with initial spacing or extraction cases had a higher risk of incomplete space closure and poor root parallelism. Orthodontic tooth movement under bisphosphonate medication is possible, especially in low-risk patients (low dose and short period of intake). But the treatment is still not predictable, especially in high-risk patients. Therefore, the altered bone metabolism and higher extent of side effects should be considered in treatment planning, especially in extraction cases or high-risk patients. Regardless, longer treatment duration, decelerated tooth movement, and more side effects, e.g., incomplete space closure and poor root parallelism, should be expected, especially in extraction cases or space closure.

  9. Current state of orthodontic patients under Bisphosphonate therapy

    Science.gov (United States)

    2013-01-01

    Background Bisphosphonates are a common medication for the prevention and therapy of osteoporosis, but are also applied for tumor diseases. They affect bone metabolism, and therefore also orthodontic treatments, but how it does has yet not been definitively clarified. Therefore, the aim of this research was to evaluate and demonstrate the reported effects and the current state of scientific research regarding orthodontic treatment and bisphosphonate medication exclusively in humans. Material and methods A systematic research of the literature for selected keywords in the Medline database (Pubmed) as well as a manual search was conducted. The following search terms were used: ‘Bisphosphonate’ in combination with: orthodontic, orthodontic treatment, tooth movement. Findings To date, only nine reported patients (case reports/series) and one original article (retrospective cohort study) regarding orthodontic treatment under bisphosphonate medication in humans have been published. Decelerated tooth movement with increased side effects (especially in high-risk patients) and longer treatment duration was reported in some articles. Patients with initial spacing or extraction cases had a higher risk of incomplete space closure and poor root parallelism. Conclusions Orthodontic tooth movement under bisphosphonate medication is possible, especially in low-risk patients (low dose and short period of intake). But the treatment is still not predictable, especially in high-risk patients. Therefore, the altered bone metabolism and higher extent of side effects should be considered in treatment planning, especially in extraction cases or high-risk patients. Regardless, longer treatment duration, decelerated tooth movement, and more side effects, e.g., incomplete space closure and poor root parallelism, should be expected, especially in extraction cases or space closure. PMID:23556517

  10. The Importance of Probation under the Current Circumstances

    Directory of Open Access Journals (Sweden)

    Minodora-Ioana Balan-Rusu

    2011-05-01

    Full Text Available Implemented in our legislation with the entry into force of the Criminal Code of Charles II, theprobation system has been developed continuously, increasing its importance from one stage to another.Thus, under the current circumstances, the probation service has a crucial role in the complex activity ofrehabilitating the person sentenced to a deprivation of liberty sentence through community supervision ofthe measures and obligations imposed by the court to the convicted. Although the most important tasks ofthe service are those of monitoring sanctions and of measures ordered by the court, however, this institutionperforms other activities almost equally important in the stage of trial and of execution of custodialsentences. Among the core values of probation that were imposed in recent years both in our country and inthe European Union are: respect for persons, reconciliation between offenders and the communities towhich they belong, non-discrimination in the community of persons who have committed criminal acts,supporting and encouraging permanently these individuals to form a correct attitude towards work, the ruleof law and to obey the rules of social life. The research of the legal rules that govern the probation serviceactivity highlights some shortcomings as well, which should be corrected, the ultimate goal being that ofmaking them compatible with the EU norms, especially in the cooperating area which must be achievedbetween these institutions at European level.

  11. Comparative study of the microstructure of 5052 aluminum alloy sheets under quasi-static and high-velocity tension

    Energy Technology Data Exchange (ETDEWEB)

    Liu, D.H., E-mail: liudahai.hit@gmail.com [School of Aeronautical Manufacturing Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Yu, H.P.; Li, C.F. [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2012-08-15

    Highlights: Black-Right-Pointing-Pointer Dislocation slip mechanism works during both quasi-static and dynamic deformation. Black-Right-Pointing-Pointer Dynamic deformation induces denser dislocations and more cross-slip tendency. Black-Right-Pointing-Pointer Existed prestrain has an accommodating effect on dislocation generation and motion. - Abstract: In order to reveal the high-velocity deformation mechanisms of 5052 aluminum alloy sheets, this work compares the dynamic plastic deformation behavior and the microstructure evolutions with those of the quasi-static case by scanning electron microscopy (SEM) observations, electron back scattering diffraction (EBSD) analysis, and transmission electron microscopy (TEM) studies. Results show that the dynamic process exhibits a very different macro fracture shape and a much similar micro deformation pattern as compared with the quasi-static case, and under both conditions, the dislocation-slip mechanism works during deformation. For the shock effect of high-velocity deformation, much denser dislocations are generated and the tendency of cross-slip of dislocations increases. The dislocation bands are more narrow and denser than those shown in the quasi-static case, and a much more uniform dislocation configuration is also exhibited after dynamic loadings. In addition, under dynamic conditions, the existing of pre-strain will introduce an accommodated effect on the dynamically induced dislocations, a slight reduction of density combining with a higher movement tendency. The characteristics of multi-slips and homogenization effect of dislocations under dynamic conditions will result in much higher plasticity and strength of materials over the quasi-static ones.

  12. Synthesis of TiO2 nanorod-decorated graphene sheets and their highly efficient photocatalytic activities under visible-light irradiation

    International Nuclear Information System (INIS)

    Lee, Eunwoo; Hong, Jin-Yong; Kang, Haeyoung; Jang, Jyongsik

    2012-01-01

    Highlights: ► TiO 2 nanorods were successfully decorated on the surface of graphene sheets. ► Population of TiO 2 nanorods can be controlled by changing experimental conditions. ► TiO 2 nanorod-decorated graphene sheets have an expanded light absorption range. ► TiO 2 nanorod-decorated graphene sheets showed unprecedented photocatalytic activity. - Abstract: The titanium dioxide (TiO 2 ) nanorod-decorated graphene sheets photocatalysts with different TiO 2 nanorods population have been synthesized by a simple non-hydrolytic sol–gel approach. Electron microscopy and X-ray diffraction analysis indicated that the TiO 2 nanorods are well-dispersed and successfully anchored on the graphene sheet surface through the formation of covalent bonds between Ti and C atoms. The photocatalytic activities are evaluated in terms of the efficiencies of photodecomposition and adsorption of methylene blue (MB) in aqueous solution under visible-light irradiation. The as-synthesized TiO 2 nanorod-decorated graphene sheets showed unprecedented photodecomposition efficiency compared to the pristine TiO 2 nanorods and the commercial TiO 2 (P-25, Degussa) under visible-light. It is believed that this predominant photocatalytic activity is due to the synergistic contribution of both a retarded charge recombination rate caused by a high electronic mobility of graphene and an increased surface area originated from nanometer-sized TiO 2 nanorods. Furthermore, photoelectrochemical study is performed to give deep insights into the primary roles of graphene that determines the photocatalytic activity.

  13. Investigating the Greenland ice sheet evolution under changing climate using a three-dimensional full-Stokes model

    Science.gov (United States)

    Seddik, H.; Greve, R.; Zwinger, T.; Gillet-Chaulet, F.; Gagliardini, O.

    2010-12-01

    available data, the geothermal heat flux at the bedrock is prescribed as spatially constant and the lateral sides are open boundaries. A non-linear Weertman law is used for the basal sliding. The project goal is to better assess the effects of dynamical changes of the Greenland ice sheet on sea level rise under global-warming conditions. Hence, the simulations have been conducted in order to investigate the ice sheet evolution using the climate forcing experiments defined in the SeaRISE project. For that purpose, four different experiments have been conducted, (i) constant climate control run beginning at present (epoch 2004-1-1 0:0:0) and running up to 500 years holding the climate constant to its present state, (ii) constant climate forcing with increased basal lubrication, (iii) AR4 climate run forced by anomalies derived from results given in the IPCC 4th Assessment Report (AR4) for the A1B emission scenario, (iv) AR4 climate run with increased basal lubrication.

  14. RESULTS OF CALCULATION-EXPERIMENTAL INVESTIGATIONS OF ELECTRO-THERMAL RESISTIBILITY OF SHEET STEEL SAMPLES TO ACTION OF RATIONED COMPONENTS OF PULSED CURRENT OF ARTIFICIAL LIGHTING

    Directory of Open Access Journals (Sweden)

    M.I. Baranov

    2016-06-01

    Full Text Available Purpose. Calculation and experimental researches of the electro-thermal resistibility of the steel sheet samples to action standard pulse current components of the artificial lightning with amplitude-time parameters (ATP, corresponded the requirements of normative documents of USA for SAE ARP 5412 & SAE ARP 5416. Methodology. Electrophysics bases of technique of high tensions and large impulsive currents (LIC, and also scientific and technical bases of planning of devices of high-voltage impulsive technique and measuring in them LIC. Сurrent amplitude ImA=±200 kA (with a tolerance of ±10 %; current action integral JA=2∙106 A2•s (with a tolerance of ±20 %; time, corresponding to the amplitude of the current ImA, tmA≤50 microseconds; the duration of the current flow τpA≤500 microseconds. Results. The results of the evaluation of the calculated and experimental studies of electro-thermal resistance of the samples of plates measuring 0,5 m  0,5 m stainless steel 1 mm thickness to the action on them artificial lightning impulse currents with rationed ATP on the requirements of normative documents of USA for SAE ARP 5412 & SAE ARP 5416. A pulse A- component have a first amplitude 192 kA, the corresponding time of 34 μs, and the duration aperiodic component amplitude 804 A, corresponding to the time 9 ms. It has been shown that the long C- component current of artificial lightning can lead to keyhole these samples. The diameter of the holes in this thin steel sheet, which is formed during the flow of current C- components can reach 15 mm. The results of calculation and experiment agree within 28 %. Originality. For the first time in world practice on the generator large pulsed currents experimental studies of resistibility of sheet steel samples to the action of artificial lightning currents with critical parameters. Practical value. Using the results obtained in the practice of lightning protection will significantly improve the

  15. Development of a new biaxial testing system for generating forming limit diagrams for sheet metals under hot stamping conditions

    OpenAIRE

    Shao, Z; Li, N; Lin, J; Dean, TA

    2016-01-01

    Conventional experimental approaches used to generate forming limit diagrams (FLDs) for sheet metals at different linear strain paths are not applicable to hot stamping and cold die quenching processes because cooling occurs prior to deformation and consistent values of heating rate, cooling rate, deformation temperature and strain rate are not easy to obtain. A novel biaxial testing system for use in a Gleeble testing machine has been adopted to generate forming limits of sheet metals, inclu...

  16. Influence of Mg doping on ZnO nanoparticles decorated on graphene oxide (GO) crumpled paper like sheet and its high photo catalytic performance under sunlight

    Science.gov (United States)

    Labhane, P. K.; Sonawane, S. H.; Sonawane, G. H.; Patil, S. P.; Huse, V. R.

    2018-03-01

    Mg doped ZnO nanoparticles decorated on graphene oxide (GO) sheets were synthesized by a wet impregnation method. The effect of Mg doping on ZnO and ZnO-GO composite has been evaluated by using x-ray diffraction (XRD), Williamson-Hall Plot (Wsbnd H Plot), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDX). The physical parameters of as-prepared samples were estimated by XRD data. FESEM and HR-TEM images showed the uniform distribution of nanoparticles on GO crumpled paper like sheet. Solar light photocatalytic activities of samples were evaluated spectrophotometrically by the degradation of p-nitrophenol (PNP) and indigo carmine (IC) solution. Mgsbnd ZnO decorated on GO sheets exhibit excellent catalytic efficiency compared to all other prepared samples under identical conditions, degrading PNP and IC nearly 99% within 60 min under sunlight. The effective degradation by Mgsbnd ZnO decorated on GO sheet would be due to extended solar light absorption, enhanced adsorptivity on the composite catalyst surface and efficient charge separation of photo-induced electrons. Finally, plausible mechanism was suggested with the help of scavengers study.

  17. Three Gorges Reservoir Area: soil erosion under natural condition vs. soil erosion under current land use

    Science.gov (United States)

    Schönbrodt, Sarah; Behrens, Thorsten; Scholten, Thomas

    2010-05-01

    Apparently, the current most prominent human-induced example for large scale environmental impact is the Three Gorges Dam in China. The flooding alongside the Yangtze River, and its tributaries results in a vast loss of settlement and farmland area with productive, fertile valley soils. Due to the associated high land use dynamic on uphill-sites, the soil resources are underlying high land use pressure. Within our study, the soil erosion under natural conditions is compared to the soil erosion under current land use after the impoundment. Both were modeled using the empirical Universal Soil Loss Equation (USLE) which is able to predict long-term annual soil loss with limited data. The database consists of digital terrain data (45 m resolution DEM, erosive slope length based on Monte-Carlo-Aggregation according to Behrens et al. (2008)), field investigations of recent erosion forms, and literature studies. The natural disposition to soil erosion was calculated considering the USLE factors R, S, and K. The soil erosion under current land use was calculated taking into account all USLE factors. The study area is the catchment of the Xiangxi River in the Three Gorges Reservoir area. Within the Xiangxi Catchment (3,200 km²) the highly dynamic backwater area (580 km²), and two micro-scale study sites (Xiangjiaba with 2.8 km², and Quyuan with 88 km²) are considered more detailed as they are directly affected by the river impoundment. Central features of the Xiangxi Catchment are the subtropical monsoon climate, an extremely steep sloping relief (mean slope angle 39°, SD 22.8°) artificially fractured by farmland terraces, and a high soil erodibility (mean K factor 0.37, SD 0.13). On the catchment scale the natural disposition to soil erosion makes up to mean 518.0 t ha-1 a-1. The maximum potential soil loss of 1,730.1 t ha-1 a-1 under natural conditions is reached in the Quyuan site (mean 635.8 t ha-1 a-1) within the backwater area (mean 582.9 t ha-1 a-1). In the

  18. Experimental Characterization and Material Modelling of an AZ31 Magnesium Sheet Alloy at Elevated Temperatures under Consideration of the Tension-Compression Asymmetry

    Science.gov (United States)

    Behrens, B.-A.; Bouguecha, A.; Bonk, C.; Dykiert, M.

    2017-09-01

    Magnesium sheet alloys have a great potential as a construction material in the aerospace and automotive industry. However, the current state of research regarding temperature dependent material parameters for the description of the plastic behaviour of magnesium sheet alloys is scarce in literature and accurate statements concerning yield criteria and appropriate characterization tests to describe the plastic behaviour of a magnesium sheet alloy at elevated temperatures in deep drawing processes are to define. Hence, in this paper the plastic behaviour of the well-established magnesium sheet alloy AZ31 has been characterized by means of convenient mechanical tests (e. g. tension, compression and biaxial tests) at temperatures between 180 and 230 °C. In this manner, anisotropic and hardening behaviour as well as differences between the tension-compression asymmetry of the yield locus have been estimated. Furthermore, using the evaluated data from the above mentioned tests, two different yield criteria have been parametrized; the commonly used Hill’48 and an orthotropic yield criterion, CPB2006, which was developed especially for materials with hexagonal close packed lattice structure and is able to describe an asymmetrical yielding behaviour regarding tensile and compressive stress states. Numerical simulations have been finally carried out with both yield functions in order to assess the accuracy of the material models.

  19. THREE-DIMENSIONAL GEOMETRY OF A CURRENT SHEET IN THE HIGH SOLAR CORONA: EVIDENCE FOR RECONNECTION IN THE LATE STAGE OF THE CORONAL MASS EJECTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Ryun-Young [College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States); Vourlidas, Angelos [The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 (United States); Webb, David, E-mail: rkwon@gmu.edu [ISR, Boston College, Chestnut Hill, MA (United States)

    2016-07-20

    Motivated by the standard flare model, ray-like structures in the wake of coronal mass ejections (CMEs) have been often interpreted as proxies of the reconnecting current sheet connecting the CME with the postflare arcade. We present the three-dimensional properties of a post-CME ray derived from white light images taken from three different viewing perspectives on 2013 September 21. By using a forward modeling method, the direction, cross section, and electron density are determined within the heliocentric distance range of 5–9 R {sub ⊙}. The width and depth of the ray are 0.42 ± 0.08 R {sub ⊙} and 1.24 ± 0.35 R {sub ⊙}, respectively, and the electron density is (2.0 ± 0.5) × 10{sup 4} cm{sup 3}, which seems to be constant with height. Successive blobs moving outward along the ray are observed around 13 hr after the parent CME onset. We model the three-dimensional geometry of the parent CME with the Gradual Cylindrical Shell model and find that the CME and ray are coaxial. We suggest that coaxial post-CME rays, seen in coronagraph images, with successive formation of blobs could be associated with current sheets undergoing magnetic reconnection in the late stage of CMEs.

  20. Drift current under the action of wind and waves

    International Nuclear Information System (INIS)

    Youssef, M.; Spaulding, M.

    1993-01-01

    Accurate estimates of sea surface drift currents are critical to forecasting oil spill transport and fate. Most existing spill models employ a drift factor and deflection angle, based on local wind speed, to estimate the sea surface drift vector. The effects of wind-induced shear and wave-induced transport are lumped together in this formulation. In the present approach, the conservation of momentum, water mass, and turbulent energy equations are solved using an implicit finite difference method to predict the vertical distribution of current, turbulent energy, and eddy viscosity at one point. The model includes coupling between the wave- and shear-induced currents. Input energy from the atmosphere to the turbulent energy and current fields are represented through free-surface boundary conditions. The numerical model showed excellent agreement compared to an analytic solution of the wind-forced shear flow problem. The model was applied to predict surface drift currents for varying wind speeds and predicted results in general agreement with field observations and other numerical and theoretical studies. The model predicted drift factor F (%) and deflection angle A (degrees) decrease with increasing wind speed W (m/s), and can be approximated by the following curve fits: F=3.91-0.318W, A=23.627-7.97 log W. The model was applied to three intentional oil spills conducted on the Norwegian continental shelf in 1991 and predicted the observed trajectories with reasonable accuracy. 24 refs., 17 figs

  1. Scour at Breakwaters Under Combined Waves and Current

    DEFF Research Database (Denmark)

    Carstensen, Stefan; Sumer, B. Mutlu

    2015-01-01

    Bed profiles perpendicular to breakwater have been measured for orthogonal combined wave and current scour. The bedprofiles show the distinct features of the wave scour forming due to the presence of recirculating cells, namely deposition/scour at the antinodes/nodes depending on whether the sedi......Bed profiles perpendicular to breakwater have been measured for orthogonal combined wave and current scour. The bedprofiles show the distinct features of the wave scour forming due to the presence of recirculating cells, namely deposition/scour at the antinodes/nodes depending on whether...... the sediment transport occurs in the no-suspension or the suspension mode. Also, the current scour which forms by the presence of secondary flow as a result of the corner flow and the change in roughness is noticeable in the bed profiles. The mechanism of scour in both the fundamental cases (waves alone...... and the current alone) is that the sediment is mobilized by the primary flow while the secondaryflow/recirculating cells cause a mean transport of sediment, leading to scour. For the orthogonal combined wave andcurrent the mechanism appears to be similar....

  2. Performance of Automotive SLI Battery under Constant Current ...

    African Journals Online (AJOL)

    In this project, a cost-effective 12V battery charge controller was developed to implement constant current constant voltage charge algorithm in small-sized stand-alone solar PV systems. The algorithm was tested on automotive SLI battery instead of deep-cycle PV battery to further reduce overall system cost. The battery ...

  3. Peltier effect in multilayered nanopillars under high density charge current

    International Nuclear Information System (INIS)

    Gravier, L; Fukushima, A; Kubota, H; Yamamoto, A; Yuasa, S

    2006-01-01

    From the basic equations of thermoelectricity, we model the thermal regimes that develop in multilayered nanopillar elements experiencing continuous charge currents. The energy conservation principle was applied to all layer-layer and layer-electrode junctions. The obtained set of equations was solved to derive the temperature of each junction. The contribution of the Peltier effect is included in an effective resistance. This model gives satisfactory fits to experimental data obtained on a series of reference nanopillar elements

  4. Fact Sheet on How to Get Started Managing Hazardous Waste Laboratory Waste Under the Alternative Set of Generator Regulations

    Science.gov (United States)

    Fact sheet to help academic laboratories decide whether to opt into the alternate set of hazardous waste requirements for eligible academic laboratories found in RCRA subpart K, how to plan for the transition to subpart K, and what first steps to take.

  5. Magnetotransport in quantum cascade detectors: analyzing the current under illumination

    Directory of Open Access Journals (Sweden)

    Buffaz Amandine

    2011-01-01

    Full Text Available Abstract Photocurrent measurements have been performed on a quantum cascade detector structure under strong magnetic field applied parallel to the growth axis. The photocurrent shows oscillations as a function of B. In order to describe that behavior, we have developed a rate equation model. The interpretation of the experimental data supports the idea that an elastic scattering contribution plays a central role in the behavior of those structures. We present a calculation of electron lifetime versus magnetic field which suggests that impurities scattering in the active region is the limiting factor. These experiments lead to a better understanding of these complex structures and give key parameters to optimize them further.

  6. A Review of Current Issues Underlying Colon Cleansing before Colonoscopy

    Directory of Open Access Journals (Sweden)

    Lawrence C Hookey

    2007-01-01

    Full Text Available The present review examines four current issues related to the efficacy, patient tolerance and safety of the following bowel cleansing agents: oral sodium phosphate (NaP, polyethylene glycol (PEG and magnesium citrate (Pico-Salax, Ferring Pharmaceuticals Inc, Canada, an agent recently made available in Canada. MedLine and PubMed databases were systematically searched to identify studies related to the efficacy of altered PEG solutions combined with adjunct treatments; the efficacy, tolerability and safety of Pico-Salax; the association between nephrocalcinosis, and chronic renal failure and oral NaP use; and the role of diet. Although lower volume PEG solutions combined with adjuvant agents were generally associated with better patient tolerance, their efficacy was varied and interpretation of this end point is complicated by study design issues. There are very few reported studies of Pico-Salax, and as a result, there are insufficient data to draw conclusions about the efficacy of this agent. The available data suggest that Pico-Salax may be better tolerated by patients, than oral NaP and PEG solutions. There is a paucity of hemodynamic monitoring data pre- and postadministration, but the available data suggests that this small-volume osmotic agent could cause subclinical contraction of the intravascular space. Recent case reports suggest an association between nephrocalcinosis and oral NaP ingestion, but to date, these reports have been confined to a single centre. Preliminary studies suggest that this is not a widespread problem, but more studies are needed. There are only a few studies examining diet and patient tolerability, but they do suggest that diet may be liberalized with some cleansing regimens to enhance tolerability without decreasing efficacy. The present review highlights current controversies and advances in colon cleansing before colonoscopy, and also identifies areas for further study.

  7. Methodology to Define Delivery Accuracy Under Current Day ATC Operations

    Science.gov (United States)

    Sharma, Shivanjli; Robinson, John E., III

    2015-01-01

    In order to enable arrival management concepts and solutions in a NextGen environment, ground- based sequencing and scheduling functions have been developed to support metering operations in the National Airspace System. These sequencing and scheduling algorithms as well as tools are designed to aid air traffic controllers in developing an overall arrival strategy. The ground systems being developed will support the management of aircraft to their Scheduled Times of Arrival (STAs) at flow-constrained meter points. This paper presents a methodology for determining the undelayed delivery accuracy for current day air traffic control operations. This new method analyzes the undelayed delivery accuracy at meter points in order to understand changes of desired flow rates as well as enabling definition of metrics that will allow near-future ground automation tools to successfully achieve desired separation at the meter points. This enables aircraft to meet their STAs while performing high precision arrivals. The research presents a possible implementation that would allow delivery performance of current tools to be estimated and delivery accuracy requirements for future tools to be defined, which allows analysis of Estimated Time of Arrival (ETA) accuracy for Time-Based Flow Management (TBFM) and the FAA's Traffic Management Advisor (TMA). TMA is a deployed system that generates scheduled time-of-arrival constraints for en- route air traffic controllers in the US. This new method of automated analysis provides a repeatable evaluation of the delay metrics for current day traffic, new releases of TMA, implementation of different tools, and across different airspace environments. This method utilizes a wide set of data from the Operational TMA-TBFM Repository (OTTR) system, which processes raw data collected by the FAA from operational TMA systems at all ARTCCs in the nation. The OTTR system generates daily reports concerning ATC status, intent and actions. Due to its

  8. Anti-Influenza Treatment: Drugs Currently Used and Under Development.

    Science.gov (United States)

    Amarelle, Luciano; Lecuona, Emilia; Sznajder, Jacob I

    2017-01-01

    Influenza is a very common contagious disease that carries significant morbidity and mortality. Treatment with antiviral drugs is available, which if administered early, can reduce the risk of severe complications. However, many virus types develop resistance to those drugs, leading to a notable loss of efficacy. There has been great interest in the development of new drugs to combat this disease. A wide range of drugs has shown anti-influenza activity, but they are not yet available for use in the clinic. Many of these target viral components, which others are aimed at elements in the host cell which participate in the viral cycle. Modulating host components is a strategy which minimizes the development of resistance, since host components are not subject to the genetic variability of the virus. The main disadvantage is the risk of treatment-related side effects. The aim of this review is to describe the main pharmacological agents currently available and new drugs in the pipeline with potential benefit in the treatment of influenza. Copyright © 2016 SEPAR. Publicado por Elsevier España, S.L.U. All rights reserved.

  9. Strain rate dependent hardening of DP600 sheet metal for large strains under in-plane biaxial loadings

    Science.gov (United States)

    Liu, W.; Guines, D.; Léotoing, L.; Ragneau, E.

    2016-10-01

    In this work, an in-plane biaxial tensile test of cruciform specimen is performed to identify the visco-plastic hardening behaviour of metallic sheets for both large strains and intermediate strain rates at room temperature. Firstly, an optimal shape of the specimen is suggested. Then, dynamic biaxial tensile tests are carried out for a dual phase DP600 steel sheet. Experimental forces on the two axes of the specimen are measured during the test and strains in the central area of the specimen are post-treated by means of Digital Image Correlation (DIC) technique. Finally, considering a Hill48 anisotropic yield criterion, two strain rate dependent hardening laws are identified thanks to an inverse procedure based on a Finite Element (FE) modelling of the biaxial tensile test and on the experimental data mentioned above. The identified biaxial flow curves are then compared with the ones from a classical uniaxial tensile test.

  10. A grid side converter current controller for accurate current injection under normal and fault ride through operation

    DEFF Research Database (Denmark)

    Hadjidemetriou, Lenos; Kyriakides, Elias; Blaabjerg, Frede

    2013-01-01

    requirements. In addition, the renewable energy systems require fault ride through capability in order to support the power grid under balanced or unbalanced low voltage grid faults. Therefore, the development of advanced current controller techniques is essential for the grid side power electronic converters...... in order to increase the renewable energy systems penetration and satisfy the grid codes. This paper proposes a current controller technique, which enables the appropriate operation of the grid side converter under unbalanced grid faults and harmonic distorted grid conditions. The proposed current...... controller is designed using multiple synchronous reference frames and can inject full positive or full negative sequence balanced sinusoidal currents under abnormal grid conditions. The accurate performance with robustness against unbalanced and harmonic distorted grid voltage indicates that the proposed...

  11. 18 CFR 367.2270 - Account 227, Obligations under capital lease-Non-current.

    Science.gov (United States)

    2010-04-01

    ..., Obligations under capital lease-Non-current. 367.2270 Section 367.2270 Conservation of Power and Water....2270 Account 227, Obligations under capital lease—Non-current. This account must include the portion... recorded as assets in account 101.1, Property under capital leases (§ 367.1011). ...

  12. Balanced Current Control Strategy for Current Source Rectifier Stage of Indirect Matrix Converter under Unbalanced Grid Voltage Conditions

    Directory of Open Access Journals (Sweden)

    Yeongsu Bak

    2016-12-01

    Full Text Available This paper proposes a balanced current control strategy for the current source rectifier (CSR stage of an indirect matrix converter (IMC under unbalanced grid voltage conditions. If the three-phase grid connected to the voltage source inverter (VSI of the IMC has unbalanced voltage conditions, it affects the currents of the CSR stage and VSI stage, and the currents are distorted. Above all, the distorted currents of the CSR stage cause instability in the overall system, which can affect the life span of the system. Therefore, in this paper, a control strategy for balanced currents in the CSR stage is proposed. To achieve balanced currents in the CSR stage, the VSI stage should receive DC power without ripple components from the CSR stage. This is implemented by controlling the currents in the VSI stage. Therefore, the proposed control strategy decouples the positive and negative phase-sequence components existing in the unbalanced voltages and currents of the VSI stage. Using the proposed control strategy under unbalanced grid voltage conditions, the stability and life span of the overall system can be improved. The effectiveness of the proposed control strategy is verified by simulation and experimental results.

  13. Dense sheet Z-pinches

    International Nuclear Information System (INIS)

    Tetsu, Miyamoto

    1999-01-01

    The steady state and quasi-steady processes of infinite- and finite-width sheet z-pinches are studied. The relations corresponding to the Bennett relation and Pease-Braginskii current of cylindrical fiber z-pinches depend on a geometrical factor in the sheet z-pinches. The finite-width sheet z-pinch is approximated by a segment of infinite-width sheet z-pinch, if it is wide enough, and corresponds to a number of (width/thickness) times fiber z-pinch plasmas of the diameter that equals the sheet thickness. If the sheet current equals this number times the fiber current, the plasma created in the sheet z-pinches is as dense as in the fiber z-pinches. The total energy of plasma and magnetic field per unit mass is approximately equal in both pinches. Quasi-static transient processes are different in several aspects from the fiber z-pinch. No radiation collapse occurs in the sheet z-pinch. The stability is improved in the sheet z-pinches. The fusion criterions and the experimental arrangements to produce the sheet z-pinches are also discussed. (author)

  14. Distant plasma sheet ion distributions during reconnection

    OpenAIRE

    Owen, C. J.; Mist, R. T.

    2001-01-01

    Previous models of the plasma sheet following reconnection and current sheet acceleration predict 'lima-bean' ion distributions. These are inconsistent with observational constraints. We postulate that following initial interaction with the current sheet, a fraction of outflow ions are backscattered and re-encounter the current sheet. Fermi acceleration processes then generate an additional high-energy outflow population. In the backscatter region these ions form a complete shell in velocity ...

  15. Energy-Based Yield Criteria for Orthotropic Materials, Exhibiting Strength-Differential Effect. Specification for Sheets under Plane Stress State

    Directory of Open Access Journals (Sweden)

    Szeptyński P.

    2017-06-01

    Full Text Available A general proposition of an energy-based limit condition for anisotropic materials exhibiting strength-differential effect (SDE based on spectral decomposition of elasticity tensors and the use of scaling pressure-dependent functions is specified for the case of orthotropic materials. A detailed algorithm (based on classical solutions of cubic equations for the determination of elastic eigenstates and eigenvalues of the orthotropic stiffness tensor is presented. A yield condition is formulated for both two-dimensional and three-dimensional cases. Explicit formulas based on simple strength tests are derived for parameters of criterion in the plane case. The application of both criteria for the description of yielding and plastic deformation of metal sheets is discussed in detail. The plane case criterion is verified with experimental results from the literature.

  16. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 8 2010-10-01 2010-10-01 false Operation under current GAA/MSTS Southeast Asia Program... AUTHORITY VOYAGE DATA Sec. 7 Operation under current GAA/MSTS Southeast Asia Program. In order to adapt the provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia...

  17. Modified Johnson-Cook model incorporated with electroplasticity for uniaxial tension under a pulsed electric current

    Science.gov (United States)

    Kim, Moon-Jo; Jeong, Hye-Jin; Park, Ju-Won; Hong, Sung-Tae; Han, Heung Nam

    2018-01-01

    An empirical expression describing the electroplastic deformation behavior is suggested based on the Johnson-Cook (JC) model by adding several functions to consider both thermal and athermal electric current effects. Tensile deformation behaviors are carried out for an AZ31 magnesium alloy and an Al-Mg-Si alloy under pulsed electric current at various current densities with a fixed duration of electric current. To describe the flow curves under electric current, a modified JC model is proposed to take the electric current effect into account. Phenomenological descriptions of the adopted parameters in the equation are made. The modified JC model suggested in the present study is capable of describing the tensile deformation behaviors under pulsed electric current reasonably well.

  18. Microstructural Degradation of Ni/YSZ Electrodes in Solid Oxide Electrolysis Cells under High Current

    DEFF Research Database (Denmark)

    Chen, Ming; Liu, Yi-Lin; Bentzen, Janet Jonna

    2013-01-01

    Ni/yttria stabilized zirconia (YSZ) supported solid oxide electrolysis cells (SOECs) were exposed to long-term galvanostatic electrolysis tests, under different testing conditions (temperature, gas composition, current density etc.) with an emphasis on high current density (above −1 A/cm2...... of Ni-YSZ interfacial reactions, taking place under the conditions prevailing under strong polarization. A mechanism for the formation of ZrO2 nano-particles on the Ni surface under the electrolysis cell testing is proposed and the possibility of Ni-YSZ interfacial reactions under such conditions (T, p...

  19. Mechanical Behavior of AZ31B Mg Alloy Sheets under Monotonic and Cyclic Loadings at Room and Moderately Elevated Temperatures

    Science.gov (United States)

    Nguyen, Ngoc-Trung; Seo, Oh Suk; Lee, Chung An; Lee, Myoung-Gyu; Kim, Ji-hoon; Kim, Heon Young

    2014-01-01

    Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C. Behaviors showing significant twinning during initial in-plane compression and untwinning in subsequent tension at and slightly above room temperature were recorded. Strong yielding asymmetry and nonlinear hardening behavior were also revealed. Considerable Bauschinger effects, transient behavior, and variable permanent softening responses were observed near room temperature, but these were reduced and almost disappeared as the temperature increased. Different stress–strain responses were inherent to the activation of twinning at lower temperatures and non-basal slip systems at elevated temperatures. A critical temperature was identified to account for the transition between the twinning-dominant and slip-dominant deformation mechanisms. Accordingly, below the transition point, stress–strain curves of cyclic loading tests exhibited concave-up shapes for compression or compression following tension, and an unusual S-shape for tension following compression. This unusual shape disappeared when the temperature was above the transition point. Shrinkage of the elastic range and variation in Young’s modulus due to plastic strain deformation during stress reversals were also observed. The texture-induced anisotropy of both the elastic and plastic behaviors was characterized experimentally. PMID:28788514

  20. Mechanical Behavior of AZ31B Mg Alloy Sheets under Monotonic and Cyclic Loadings at Room and Moderately Elevated Temperatures

    Directory of Open Access Journals (Sweden)

    Ngoc-Trung Nguyen

    2014-02-01

    Full Text Available Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C. Behaviors showing significant twinning during initial in-plane compression and untwinning in subsequent tension at and slightly above room temperature were recorded. Strong yielding asymmetry and nonlinear hardening behavior were also revealed. Considerable Bauschinger effects, transient behavior, and variable permanent softening responses were observed near room temperature, but these were reduced and almost disappeared as the temperature increased. Different stress–strain responses were inherent to the activation of twinning at lower temperatures and non-basal slip systems at elevated temperatures. A critical temperature was identified to account for the transition between the twinning-dominant and slip-dominant deformation mechanisms. Accordingly, below the transition point, stress–strain curves of cyclic loading tests exhibited concave-up shapes for compression or compression following tension, and an unusual S-shape for tension following compression. This unusual shape disappeared when the temperature was above the transition point. Shrinkage of the elastic range and variation in Young’s modulus due to plastic strain deformation during stress reversals were also observed. The texture-induced anisotropy of both the elastic and plastic behaviors was characterized experimentally.

  1. Experimental and numerical determination of critical stress intensity factor of aluminum curved thin sheets under tensile stress

    Energy Technology Data Exchange (ETDEWEB)

    Heidarvand, Majid; Soltani, Naser; Hajializadeh, Farshid [University of Tehran, Tehran (Iran, Islamic Republic of)

    2017-05-15

    We determined the fracture toughness of aluminum curved thin sheets using tensile stress tests and finite element method. We applied Linear elastic fracture mechanics (LEFM) and Feddersen procedure to evaluate stress intensity factor of the samples with central wire-cut cracks and fatigue cracks with different lengths to investigate the notch radius effect. Special fixture design was utilized to establish uniform stress distribution at the crack zone. Less than 9 % difference was found between the wire-cut and the fatigue cracked samples. Since generating central fatigue crack with different lengths required so much effort, wire-cut cracked samples were used to determine critical stress intensity factor. Finite element analysis was also performed on one-quarter of the specimen using both the singular Borsum elements and the regular isoparametric elements to further investigate fracture toughness of the samples. It was observed that the singular elements presented better results than the isoparametric ones. A slight difference was also found between the results obtained from finite element method using singular elements and the experimental results.

  2. Dual-phase steel sheets under cyclic tension-compression to large strains: Experiments and crystal plasticity modeling

    Science.gov (United States)

    Zecevic, Milovan; Korkolis, Yannis P.; Kuwabara, Toshihiko; Knezevic, Marko

    2016-11-01

    In this work, we develop a physically-based crystal plasticity model for the prediction of cyclic tension-compression deformation of multi-phase materials, specifically dual-phase (DP) steels. The model is elasto-plastic in nature and integrates a hardening law based on statistically stored dislocation density, localized hardening due to geometrically necessary dislocations (GNDs), slip-system-level kinematic backstresses, and annihilation of dislocations. The model further features a two level homogenization scheme where the first level is the overall response of a two-phase polycrystalline aggregate and the second level is the homogenized response of the martensite polycrystalline regions. The model is applied to simulate a cyclic tension-compression-tension deformation behavior of DP590 steel sheets. From experiments, we observe that the material exhibits a typical decreasing hardening rate during forward loading, followed by a linear and then a non-linear unloading upon the load reversal, the Bauschinger effect, and changes in hardening rate during strain reversals. To predict these effects, we identify the model parameters using a portion of the measured data and validate and verify them using the remaining data. The developed model is capable of predicting all the particular features of the cyclic deformation of DP590 steel, with great accuracy. From the predictions, we infer and discuss the effects of GNDs, the backstresses, dislocation annihilation, and the two-level homogenization scheme on capturing the cyclic deformation behavior of the material.

  3. Horizontal electromagnetic casting of thin metal sheets

    Science.gov (United States)

    Hull, John R.; Lari, Robert J.; Praeg, Walter F.; Turner, Larry R.

    1987-01-01

    Thin metal sheets are cast by magnetically suspending molten metal deposited within a ferromagnetic yoke and between AC conducting coils and linearly displacing the magnetically levitated liquid metal while it is being cooled to form a solid metal sheet. Magnetic flux increases as the molten metal sheet moves downward and decreases as the molten metal sheet moves upward to stabilize the sheet and maintain it in equilibrium as it is linearly displaced and solidified by cooling gases. A conducting shield is electrically coupled to the molten metal sheet by means of either metal sheet engaging rollers or brushes on the solidified metal, and by means of an electrode in the vessel containing the molten metal thereby providing a return path for the eddy currents induced in the metal sheet by the AC coil generated magnetic flux. Variation in the geometry of the conducting shield allows the magnetic flux between the metal sheet and the conducting shield to be varied and the thickness in surface quality of the metal sheet to be controlled. Side guards provide lateral containment for the molten metal sheet and stabilize and shape the magnetic field while a leader sheet having electromagnetic characteristics similar to those of the metal sheet is used to start the casting process and precedes the molten metal sheet through the magnet and forms a continuous sheet therewith. The magnet may be either U-shaped with a single racetrack coil or may be rectangular with a pair of facing bedstead coils.

  4. Horizontal electromagnetic casting of thin metal sheets

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Hinsdale, IL); Lari, Robert J. (Aurora, IL); Praeg, Walter F. (Palos Park, IL); Turner, Larry R. (Naperville, IL)

    1988-01-01

    Thin metal sheets are cast by magnetically suspending molten metal deposited within a ferromagnetic yoke and between AC conducting coils and linearly displacing the magnetically levitated liquid metal while it is being cooled to form a solid metal sheet. Magnetic flux increases as the molten metal sheet moves downward and decreases as the molten metal sheet moves upward to stabilize the sheet and maintain it in equilibrium as it is linearly displaced and solidified by cooling gases. A conducting shield is electrically coupled to the molten metal sheet by means of either metal sheet engaging rollers or brushes on the solidified metal, and by means of an electrode in the vessel containing the molten metal thereby providing a return path for the eddy currents induced in the metal sheet by the AC coil generated magnetic flux. Variation in the geometry of the conducting shield allows the magnetic flux between the metal sheet and the conducting shield to be varied and the thickness in surface quality of the metal sheet to be controlled. Side guards provide lateral containment for the molten metal sheet and stabilize and shape the magnetic field while a leader sheet having electromagnetic characteristics similar to those of the metal sheet is used to start the casting process and precedes the molten metal sheet through the magnet and forms a continuous sheet therewith. The magnet may be either U-shaped with a single racetrack coil or may be rectangular with a pair of facing bedstead coils.

  5. Robust Current Control of Doubly Fed Wind Turbine Generator under Unbalanced Grid Voltage Conditions

    DEFF Research Database (Denmark)

    Wang, Yun; Gong, Wenming; Wu, Qiuwei

    2014-01-01

    This paper presents the design of a H ∞ current controller for doubly fed induction generators (DFIGs) in order to maintain stable operation under unbalanced voltage conditions. The H ∞ current controller has a multi-input and multi-output (MIMO) structure and is designed using the loop shaping...

  6. Safe current injection strategies for a STATCOM under asymmetrical grid faults

    DEFF Research Database (Denmark)

    Rodriguez, Pedro; Medeiros, Gustavo; Luna, Alvaro

    2010-01-01

    This paper explores different strategies to set the reference current of a STATCOM under unbalanced grid voltage conditions and determines the maximum deliverable reactive power in each case to guarantee the injected current is permanently within the STATCOM secure operation limits. The paper pre...

  7. Current Percolation in Medium with Boundaries under Quantum Hall Effect Conditions

    Directory of Open Access Journals (Sweden)

    M. U. Malakeeva

    2012-01-01

    Full Text Available The current percolation has been considered in the medium with boundaries under quantum Hall effect conditions. It has been shown that in that case the effective Hall conductivity has a nonzero value due to percolation of the Hall current through the finite number of singular points (in our model these are corners at the phase joints.

  8. An Improved Current Control Strategy for a Grid-Connected Inverter under Distorted Grid Conditions

    OpenAIRE

    Ngoc Bao Lai; Kyeong-Hwa Kim

    2016-01-01

    This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. The main challenge associated with the grid-connected inverter in distributed generation (DG) systems is to maintain the harmonic contents in output current below the specified values even when the grid is subject to uncertain disturbances such as harmonic distortion. To overcome such a challenge, an improved current control scheme is proposed for a grid-connecte...

  9. A model of the plasma flow and current in Saturn's polar ionosphere under conditions of strong Dungey cycle driving

    Directory of Open Access Journals (Sweden)

    C. M. Jackman

    2006-05-01

    Full Text Available We propose a simple model of the flow and currents in Saturn's polar ionosphere. This model is motivated by theoretical reasoning, and guided quantitatively by in situ field and flow data from space missions, ground-based IR Doppler measurements, and Hubble Space Telescope images. The flow pattern consists of components which represent (1 plasma sub-corotation in the middle magnetosphere region resulting from plasma pick-up and radial transport from internal sources; (2 the Vasyliunas-cycle of internal plasma mass-loss down the magnetospheric tail at higher latitudes; and (3 the polar Dungey-cycle flow driven by the solar wind interaction. Upstream measurements of the interplanetary magnetic field (IMF indicate the occurrence of both extended low-field rarefaction intervals with essentially negligible Dungey-cycle flow, and few-day high-field compression regions in which the Dungey-cycle voltage peaks at a few hundred kV. Here we model the latter conditions when the Dungey-cycle is active, advancing on previous axi-symmetric models which may be more directly applicable to quiet conditions. For theoretical convenience the overall flow pattern is constructed by adding together two components - a purely rotational flow similar to previous axi-symmetric models, and a sun-aligned twin vortex representing the dawn-dusk asymmetry effects associated with the Vasyliunas-and Dungey-cycle flows. We calculate the horizontal ionospheric current associated with the flow and the field-aligned current from its divergence. These calculations show that a sheet of upward-directed field-aligned current flows at the boundary of open field lines which is strongly modulated in local-time by the Dungey-cycle flows. We then consider implications of the field-aligned current for magnetospheric electron acceleration and aurorae using two plasma source populations (hot outer magnetospheric electrons and cool dense magnetosheath electrons. Both sources display a strong dawn

  10. Glacial transport and local ice dynamics under the Keewatin Ice Divide of the Laurentide Ice Sheet, central Nunavut

    Science.gov (United States)

    Goulet, C.; Roy, M.; McMartin, I.

    2009-12-01

    Goulet, C.; Roy, M., Department of Earth and Atmospheric Sciences, and GEOTOP, University of Quebec in Montreal, QC, H3C 3P8; McMartin, I., Geological Survey of Canada, 601 Booth Street, Ottawa, ON, K1A OE8 Recent paleogeographic reconstructions indicate that the Keewatin Ice Divide (KID) of the Laurentide Ice Sheet (LIS) was highly dynamic throughout the last glacial cycle. Extensive field measurements of cross-cutting ice-flow erosional features (striations, grooves) on multi-faceted bedrock outcrops, as well as mapping of streamlined landforms indicate significant displacements (up to 500 km) of this ice flow center during the last glacial cycle. These episodes of ice-flow reorganization likely affected the patterns of glacial transport, but the extent of the reworking of former glacial dispersal trains is often unconstrained in certain regions. Here we report ice-flow directional data and associated glacial-dynamic considerations for an area located 100 km north of Baker Lake, central Nunavut. This area lies underneath the zone of migration of the KID (essentially north of its final position), thus representing a key area for understanding the dynamics of this sector of the LIS. Measurements of ice-flow indicators indicate at least 7 ice-flow directions, going from N, NNW, NW to WNW, NNE, W, SE, and SW to WSW. A relative chronology was established from multiple intersecting striations and geometrical relations between multi-faceted outcrops, starting from older phases to younger ones with W, NW, NNW, and N. Surficial mapping using air-photo and satellite images indicate that this region is characterized by zones of fast and slower ice velocity. The presence in the centre of the study area of a drift-free positive relief formed by resistant NE-SW-oriented Proterozoic quartzite appears to have played an important role on the local ice dynamics by slowing down the velocity of the ice. Local example of varying ice velocity systems is expressed by a glacially

  11. A Bingham-plastic model for fluid mud transport under waves and currents

    Science.gov (United States)

    Liu, Chun-rong; Wu, Bo; Huhe, Ao-de

    2014-04-01

    Simplified equations of fluid mud motion, which is described as Bingham-Plastic model under waves and currents, are presented by order analysis. The simplified equations are non-linear ordinary differential equations which are solved by hybrid numerical-analytical technique. As the computational cost is very low, the effects of wave current parameters and fluid mud properties on the transportation velocity of the fluid mud are studied systematically. It is found that the fluid mud can move toward one direction even if the shear stress acting on the fluid mud bed is much smaller than the fluid mud yield stress under the condition of wave and current coexistence. Experiments of the fluid mud motion under current with fluctuation water surface are carried out. The fluid mud transportation velocity predicted by the presented mathematical model can roughly match that measured in experiments.

  12. Graphene sheets grafted three-dimensional BiOBr0.2I0.8 microspheres with excellent photocatalytic activity under visible light

    International Nuclear Information System (INIS)

    Liu, Hong; Su, Yun; Chen, Zhen; Jin, Zhitong; Wang, Yong

    2014-01-01

    Highlights: • Graphene sheets grafted 3D BiOBr 0.2 I 0.8 microspheres were synthesized. • Enhanced visible light absorption was observed in BiOBr 0.2 I 0.8 /graphene composites. • Graphene acted as an electron-acceptor to hinder the charge recombination. • The resulting composites exhibited high visible light photocatalytic activity. -- Abstract: A series of graphene sheets grafted three-dimensional BiOBr 0.2 I 0.8 microspheres with different graphene contents have been synthesized by a simple one-step solvothermal method. The BiOBr 0.2 I 0.8 microspheres were composed of numerous nanoplates with a thickness of about 10 nm and dispersed uniformly on the surface of graphene. The assembled BiOBr 0.2 I 0.8 /graphene composites exhibited excellent photocatalytic activity in the degradation of rhodamine B (RhB) and phenol under visible light irradiation (λ > 420 nm). The optimal graphene content was found to be 10.0 wt.%, and the corresponding photocatalytic activity in degradation of RhB and phenol was 3.19 and 3.27 times that of pure BiOBr 0.2 I 0.8 , respectively. The enhanced photocatalytic activity could be attributed to more effective charge transportations and separations, larger specific surface areas and the increased light absorption. A possible photocatalytic mechanism of the BiOBr 0.2 I 0.8 /graphene composites was also proposed

  13. Martian sand sheet characterization and implications for formation: A case study

    Science.gov (United States)

    Runyon, Kirby D.; Bridges, Nathan T.; Newman, Claire E.

    2017-12-01

    Windblown sand and dust dominate surface geologic processes in Mars' current environment. Besides sand dune fields, areally extensive sand sheets are common across Mars, blanketing the underlying topography with several meters of rippled sand. Earth's sand sheets commonly form upwind or cross-wind to dunes and both partially trap and source sediment to downwind dunes. In contrast, Mars' sheets are frequently located downwind of active barchan and dome sand dunes, suggesting they cannot be a sediment source for the dunes as on Earth. Here, we characterize a Martian sand sheet and its geologic context, model the regional atmospheric circulation, and more broadly consider the implications for sand sheet formation on Mars. Our case study sand sheet in central Herschel Crater is dunes, crater rims, and small hills. The sheet has actively migrating superposing ripples with estimated total sand fluxes comparable to total fluxes measured from slip faces on local, regional, and global dunes, some of which have eroded away. A smooth geologic unit interpreted as outcrops of paleo-sand sheets is adjacent to the active sheets. Our observations and atmospheric modeling-which predict wind shear stresses above the sand suspension threshold-indicate that the upwind dunes may be eroding and their sand deposited downwind in sheets in what may be a cyclical process, possibly related to Mars' axial obliquity cycles.

  14. Predicting subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.

    2013-03-01

    In this paper we use the Shreve hydraulic potential equation to predict subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. For the Antarctic Ice Sheet we are able to predict known subglacial lakes with a >70% success rate, which demonstrates the validity of this method. Despite the success in predicting known subglacial lakes the calculations produce two-orders of magnitude more lakes than are presently identified, covering 4% of the ice-sheet bed. The difference is thought to result from our poor knowledge of the bed (which has resulted in artefacts associated with the interpolation method), intrinsic errors associated with the simplified modelling approach and because thousands of subglacial lakes, particularly smaller ones, remain to be found. Applying the same modelling approach to the Greenland Ice Sheet predicts only 90 lakes under the present-day ice-sheet configuration, covering 0.2% of the bed. The paucity of subglacial lakes in Greenland is thought to be a function of steeper overall ice-surface gradients. As no lakes have currently been located under Greenland, model predictions will make suitable targets for radar surveys of Greenland to identify subglacial lakes. During deglaciation from the Last Glacial Maximum both ice sheets had more subglacial lakes at their beds, though many of these lakes have persisted to present conditions. These lakes, inherited from past ice-sheet configurations would not form under current surface conditions, suggesting a retreating ice-sheet will have many more subglacial lakes than an advancing ice sheet. This hysteresis effect has implications for ice-stream formation and flow, bed lubrication and meltwater drainage. The lake model also allows modelling of the drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Significantly, key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are shown to have

  15. Experimental study of yttrium barium copper oxide superconducting tape's critical current under twisting moment

    International Nuclear Information System (INIS)

    Khan, Ziauddin; Kundu, Ananya; Pradhan, Subrata

    2013-01-01

    Critical current (I c ) characteristics of 2G YBCO superconducting tape under the influence of twisting moment was experimentally investigated at varying current ramp rates in the self-field. Under a uniform twist, the degradation in the current-carrying capacity of YBCO tape up to 30% was observed at 77 K. The degradation is largely attributed to the shear stress and torsional shear strain resulting from the twisting. The superconductor to resistive transition index, n, is also found to behave in an identical manner with increase in the twisting. Finite element analysis (FEA) of the tape in the experimental configuration with twisting moment being applied on to it has been carried out in COMSOL. The torsional strain calculated analytically as per the experimental configuration matches closely with that of FEA results, which shows that the critical current degradation is a function of strain. (author)

  16. Dissolution of Platinum in Hydrochloric Acid Under Industrial-Scale Alternating Current Polarization

    Science.gov (United States)

    Myrzabekov, B. E.; Bayeshov, A. B.; Makhanbetov, A. B.; Mishra, B.; Baigenzhenov, O. S.

    2018-02-01

    The electrochemical behavior of platinum in a hydrochloric acid solution under polarization by an industrial-scale alternating current has been investigated. For the electrical dissolution of platinum, titanium is used as an auxiliary electrode, which increases the yield of platinum dissolution by 12.5 pct. The influence of the concentration of hydrochloric acid, the current densities of the platinum and titanium electrodes, and the temperature of the electrolyte on the efficiency of the process of dissolving platinum have all been studied.

  17. Current-voltage characteristic of a resonant tunneling diode under electromagnetic radiation

    Directory of Open Access Journals (Sweden)

    N Hatefi Kargan

    2013-09-01

    Full Text Available  In this paper, current-voltage characteristic of a resonant tunneling diode under electromagnetic radiation has been calculated and compared with the results when there is no electromagnetic radiation. For calculating current -voltage characteristic, it is required to calculate the transmission coefficient of electrons from the well and barrier structures of this device. For calculating the transmission coefficient of electrons at the presence of electromagnetic radiation, Finite Difference Time Domain (FDTD method has been used and when there is no electromagnetic radiation Transfer Matrix Method (TMM and finite diffirence time domain method have been used. The results show that the presence of electromagnetic radiation causes resonant states other than principal resonant state (without presence of electromagnetic radiation to appear on the transmition coefficient curve where they are in distances from the principal peak and from each other. Also, the presence of electromagnetic radiation causes peaks other than principal peak to appear on the current-voltage characteristics of the device. Under electromagnetic radiation, the number of peaks on the current-voltage curve is smaller than the number of peaks on the current-voltage transmission coefficient. This is due to the fact that current-voltage curve is the result of integration on the energy of electrons, Thus, the sharper and low height peaks on the transmission coefficient do not appear on the current-voltage characteristic curve.

  18. Degradation of Leakage Currents in Solid Tantalum Capacitors Under Steady-State Bias Conditions

    Science.gov (United States)

    Teverovsky, Alexander A.

    2010-01-01

    Degradation of leakage currents in various types of solid tantalum capacitors under steady-state bias conditions was investigated at temperatures from 105 oC to 170 oC and voltages up to two times the rated voltage. Variations of leakage currents with time under highly accelerated life testing (HALT) and annealing, thermally stimulated depolarization currents, and I-V characteristics were measured to understand the conduction mechanism and the reason for current degradation. During HALT the currents increase gradually up to three orders of magnitude in some cases, and then stabilize with time. This degradation is reversible and annealing can restore the initial levels of leakage currents. The results are attributed to migration of positively charged oxygen vacancies in tantalum pentoxide films that diminish the Schottky barrier at the MnO2/Ta2O5 interface and increase electron injection. A simple model allows for estimation of concentration and mobility of oxygen vacancies based on the level of current degradation.

  19. Dynamic responses of a riser under combined excitation of internal waves and background currents

    Directory of Open Access Journals (Sweden)

    Lou Min

    2014-09-01

    Full Text Available In this study, the dynamic responses of a riser under the combined excitation of internal waves and background currents are studied. A modified Taylor-Goldstein equation is used to calculate the internal waves vertical structures when background currents exist. By imposing rigid-lid boundary condition, the equation is solved by Thompson-Haskell method. Based on the principle of virtual work, a nonlinear differential equation for riser motions is established combined with the modified Morison formula. Using Newmark-β method, the motion equation is solved in time domain. It is observed that the internal waves without currents exhibit dominated effect on dynamic response of a riser in the first two modes. With the effects of the background currents, the motion displacements of the riser will increase significantly in both cases that wave goes along and against the currents. This phenomenon is most obviously observed at the motions in the first mode

  20. Dynamic responses of a riser under combined excitation of internal waves and background currents

    Directory of Open Access Journals (Sweden)

    Min Lou

    2014-09-01

    Full Text Available In this study, the dynamic responses of a riser under the combined excitation of internal waves and background currents are studied. A modified Taylor-Goldstein equation is used to calculate the internal waves vertical structures when background currents exist. By imposing rigid-lid boundary condition, the equation is solved by Thompson-Haskell method. Based on the principle of virtual work, a nonlinear differential equation for riser motions is established combined with the modified Morison formula. Using Newmark-β method, the motion equation is solved in time domain. It is observed that the internal waves without currents exhibit dominated effect on dynamic response of a riser in the first two modes. With the effects of the background currents, the motion displacements of the riser will increase significantly in both cases that wave goes along and against the currents. This phenomenon is most obviously observed at the motions in the first mode.

  1. Dynamic responses of a riser under combined excitation of internal waves and background currents

    Science.gov (United States)

    Lou, Min; Yu, Chenglong

    2014-09-01

    In this study, the dynamic responses of a riser under the combined excitation of internal waves and background currents are studied. A modified Taylor-Goldstein equation is used to calculate the internal waves vertical structures when background currents exist. By imposing rigid-lid boundary condition, the equation is solved by Thompson-Haskell method. Based on the principle of virtual work, a nonlinear differential equation for riser motions is established combined with the modified Morison formula. Using Newmark-β method, the motion equation is solved in time domain. It is observed that the internal waves without currents exhibit dominated effect on dynamic response of a riser in the first two modes. With the effects of the background currents, the motion displacements of the riser will increase significantly in both cases that wave goes along and against the currents. This phenomenon is most obviously observed at the motions in the first mode

  2. Experimental and Numerical Investigation of Local Scour Around Submarine Piggyback Pipeline Under Steady Current

    Science.gov (United States)

    Zhao, Enjin; Shi, Bing; Qu, Ke; Dong, Wenbin; Zhang, Jing

    2018-04-01

    As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few experimental studies have been published on the scour around the piggyback pipeline under steady current. This study numerically and experimentally investigates the local scour of the piggyback pipe under steady current. The influence of prominent factors such as pipe diameter, inflow Reynolds number, and gap between the main and small pipes, on the maximum scour depth have been examined and discussed in detail. Furthermore, one formula to predict the maximum scour depth under the piggyback pipeline has been derived based on the theoretical analysis of scour equilibrium. The feasibility of the proposed formula has been effectively calibrated by both experimental data and numerical results. The findings drawn from this study are instructive in the future design and application of the piggyback pipeline.

  3. Progressive current degradation and breakdown behavior in GaN LEDs under high reverse bias stress

    International Nuclear Information System (INIS)

    Zhao Linna; Yu Peihong; Yan Dawei; Zhou Hao; Wu Jinbo; Cui Zhiqiang; Gu Xiaofeng; Guo Zixiang; Sun Huarui

    2017-01-01

    The progressive current degradation and breakdown behaviors of GaN-based light emitting diodes under high reverse-bias stress are studied by combining the electrical, optical, and surface morphology characterizations. The current features a typical “soft breakdown” behavior, which is linearly correlated to an increase of the accumulative number of electroluminescence spots. The time-to-failure for each failure site approximately obeys a Weibull distribution with slopes of about 0.67 and 4.09 at the infant and wear-out periods, respectively. After breakdown, visible craters can be observed at the device surface as a result of transient electrostatic discharge. By performing focused ion beam cuts coupled with scan electron microscope, we observed a local current shunt path in the surface layer, caused by the rapid microstructure deterioration due to significant current heating effect, consistent well with the optical beam induced resistance change observations. (paper)

  4. ANALYSIS OF A COMMERCIAL PORTABLE LITHIUM-ION BATTERY UNDER LOW CURRENT CHARGE-DISCHARGE CYCLES

    Directory of Open Access Journals (Sweden)

    Stephany Pires da Silva

    Full Text Available The dependence between the transferred charge and the corresponding transference time to charge and discharge a portable cell phone Li-ion battery (LiCoO2/C under cycles of low intensity currents was studied in detail. The voltage curve profile between 3.0 and 4.2 V and the charging and discharging time are strongly influenced by the applied current intensity. A linear dependence between the stored and extracted charges, into and from the battery, with the intensity of applied current was also observed. Allometric equations were found to describe the correlation between the charge transference time and the applied current intensity to charge and discharge the battery.

  5. A tuff cone erupted under frozen-bed ice (northern Victoria Land, Antarctica): linking glaciovolcanic and cosmogenic nuclide data for ice sheet reconstructions

    Science.gov (United States)

    Smellie, J. L.; Rocchi, S.; Johnson, J. S.; Di Vincenzo, G.; Schaefer, J. M.

    2018-01-01

    The remains of a small volcanic centre are preserved on a thin bedrock ridge at Harrow Peaks, northern Victoria Land, Antarctica. The outcrop is interpreted as a monogenetic tuff cone relict formed by a hydrovolcanic (phreatomagmatic) eruption of mafic magma at 642 ± 20 ka (by 40Ar-39Ar), corresponding to the peak of the Marine Isotope Stage 16 (MIS16) glacial. Although extensively dissected and strewn with glacial erratics, the outcrop shows no evidence for erosion by ice. From interpretation of the lithofacies and eruptive mechanisms, the weight of the evidence suggests that eruptions took place under a cold-based (frozen-bed) ice sheet. This is the first time that a tuff cone erupted under cold ice has been described. The most distinctive feature of the lithofacies is the dominance of massive lapilli tuff rich in fine ash matrix and abraded lapilli. The lack of stratification is probably due to repeated eruption through a conduit blasted through the ice covering the vent. The ice thickness is uncertain but it might have been as little as 100 m and the preserved tephra accumulated mainly as a crater (or ice conduit) infill. The remainder of the tuff cone edifice was probably deposited supraglacially and underwent destruction by ice advection and, particularly, collapse during a younger interglacial. Dating using 10Be cosmogenic exposure of granitoid basement erratics indicates that the erratics are unrelated to the eruptive period. The 10Be ages suggest that the volcanic outcrop was most recently exposed by ice decay at c. 20.8 ± 0.8 ka (MIS2) and the associated ice was thicker than at 642 ka and probably polythermal rather than cold-based, which is normally assumed for the period.

  6. 17 CFR 210.6-04 - Balance sheets.

    Science.gov (United States)

    2010-04-01

    ... 17 Commodity and Securities Exchanges 2 2010-04-01 2010-04-01 false Balance sheets. 210.6-04... sheets. This rule is applicable to balance sheets filed by registered investment companies except for... of this part. Balance sheets filed under this rule shall comply with the following provisions: Assets...

  7. Anti-cyclic regulation of the Ukrainian economy under current conditions of the international markets volatility

    Directory of Open Access Journals (Sweden)

    Volodymyr Satsyk

    2009-04-01

    Full Text Available In the article there are considered the theoretical and methodological basis of anti-cyclic regulation of the countries’ economy under conditions of the world economy globalization. It suggests the analysis of practices of implementing of anti-cyclic policy in highly developed states, its defining features and directions under current global financial and economic crisis. There has been researched a practical toolkit of economic cycles diagnostics and cyclic fluctuations of total business activity in Ukraine based on this study. There are suggested recommendations concerning the formation of the effective mechanism of anti-cyclic regulation of the Ukrainian economy.

  8. Influence of Direct Current Electric Field on Corrosion Behavior of Tin Under a Thin Electrolyte Layer

    Science.gov (United States)

    Huang, H. L.; Bu, F. R.; Tian, J.; Liu, D.

    2017-12-01

    The influence of a direct current electric field (DCEF) on corrosion behavior of tin under a thin electrolyte layer was investigated based on an array electrode technology by polarization, electrochemical impedance spectroscopy and surface analysis. The experimental results indicate that the corrosion rate of tin near the positive plate of DCEF increases with increased electric field intensity, which could be attributed to the acceleration of the migration of ions, the removal of corrosion products under DCEF and the damage of tin surface oxide film. Furthermore, tin at different positions in a DCEF exhibits different corrosion behavior, which could be ascribed to the difference of the local corrosion environment caused by the DCEF.

  9. Sheet Beam Klystron Instability Analysis

    International Nuclear Information System (INIS)

    Bane, K.

    2009-01-01

    Using the principle of energy balance we develop a 2D theory for calculating growth rates of instability in a two-cavity model of a sheet beam klystron. An important ingredient is a TE-like mode in the gap that also gives a longitudinal kick to the beam. When compared with a self-consistent particle-in-cell calculation, with sheet beam klystron-type parameters, agreement is quite good up to half the design current, 65 A; at full current, however, other, current-dependent effects come in and the results deviate significantly

  10. Film sheet cassette

    International Nuclear Information System (INIS)

    1981-01-01

    A novel film sheet cassette is described for handling CAT photographic films under daylight conditions and facilitating their imaging. A detailed description of the design and operation of the cassette is given together with appropriate illustrations. The resulting cassette is a low-cost unit which is easily constructed and yet provides a sure light-tight seal for the interior contents of the cassette. The individual resilient fingers on the light-trap permit the ready removal of the slide plate for taking pictures. The stippled, non-electrostatic surface of the pressure plate ensures an air layer and free slidability of the film for removal and withdrawal of the film sheet. The advantage of the daylight system is that a darkroom need not be used for inserting and removing the film in and out of the cassette resulting in a considerable time saving. (U.K.)

  11. A theoretical analysis of the electromigration-induced void morphological evolution under high current density

    Science.gov (United States)

    Wang, Yuexing; Yao, Yao

    2017-10-01

    In this work, analysis of electromigration-induced void morphological evolution in solder interconnects is performed based on mass diffusion theory. The analysis is conducted for three typical experimentally observed void shapes: circular, ellipse, and cardioid. Void morphological evolution is governed by the competition between the electric field and surface capillary force. In the developed model, both the electric field and capillary force on the void's surface are solved analytically. Based on the mass conversation principle, the normal velocity on the void surface during diffusion is obtained. The void morphological evolution behavior is investigated, and a physical model is developed to predict void collapse to a crack or to split into sub-voids under electric current. It is noted that when the electric current is being applied from the horizontal direction, a circular void may either move stably along the electric current direction or collapse to a finger shape, depending on the relative magnitude of the electric current and surface capillary force. However, the elliptical-shaped void will elongate along the electric current direction and finally collapse to the finger shape. On the other hand, the cardioid-shaped void could bifurcate into two sub-voids when the electric current reaches a critical value. The theoretical predictions agree well with the experimental observations.

  12. GASN sheets

    International Nuclear Information System (INIS)

    2013-12-01

    This document gathers around 50 detailed sheets which describe and present various aspects, data and information related to the nuclear sector or, more generally to energy. The following items are addressed: natural and artificial radioactive environment, evolution of energy needs in the world, radioactive wastes, which energy for France tomorrow, the consequences in France of the Chernobyl accident, ammunitions containing depleted uranium, processing and recycling of used nuclear fuel, transport of radioactive materials, seismic risk for the basic nuclear installations, radon, the precautionary principle, the issue of low doses, the EPR, the greenhouse effect, the Oklo nuclear reactors, ITER on the way towards fusion reactors, simulation and nuclear deterrence, crisis management in the nuclear field, does nuclear research put a break on the development of renewable energies by monopolizing funding, nuclear safety and security, the plutonium, generation IV reactors, comparison of different modes of electricity production, medical exposure to ionizing radiations, the control of nuclear activities, food preservation by ionization, photovoltaic solar collectors, the Polonium 210, the dismantling of nuclear installations, wind energy, desalination and nuclear reactors, from non-communication to transparency about nuclear safety, the Jules Horowitz reactor, CO 2 capture and storage, hydrogen, solar energy, the radium, the subcontractors of maintenance of the nuclear fleet, biomass, internal radio-contamination, epidemiological studies, submarine nuclear propulsion, sea energy, the Three Mile Island accident, the Chernobyl accident, the Fukushima accident, the nuclear after Fukushima

  13. Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

    Science.gov (United States)

    Lin, Shi-Zeng; Saxena, Avadh

    2016-02-01

    Skyrmion lines in metallic chiral magnets carry an emergent magnetic field experienced by the conduction electrons. The inflow and outflow of this field across a closed surface is not necessarily equal, thus it allows for the existence of emergent monopoles. One example is a segment of skyrmion line inside a crystal, where a monopole and antimonopole pair is connected by the emergent magnetic flux line. This is a realization of Dirac stringlike excitations. Here we study the dynamics of monopoles in chiral magnets under an electric current. We show that in the process of creation of skyrmion lines, skyrmion line segments are first created via the proliferation of monopoles and antimonopoles. Then these line segments join and span the whole system through the annihilation of monopoles. The skyrmion lines are destroyed via the proliferation of monopoles and antimonopoles at high currents, resulting in a chiral liquid phase. We also propose to create the monopoles in a controlled way by applying an inhomogeneous current to a crystal. Remarkably, an electric field component in the magnetic field direction proportional to the current squared in the low current region is induced by the motion of distorted skyrmion lines, in addition to the Hall and longitudinal voltage. The existence of monopoles can be inferred from transport or imaging measurements.

  14. Leakage current transport mechanism under reverse bias in Au/Ni/GaN Schottky barrier diode

    Science.gov (United States)

    Peta, Koteswara Rao; Kim, Moon Deock

    2018-01-01

    The leakage current transport mechanism under reverse bias of Au/Ni/GaN Schottky diode is studied using temperature dependent current-voltage (I-V-T) and capacitance-voltage (C-V) characteristics. I-V measurement in this study is in the range of 140 K-420 K in steps of 10 K. A reduction in voltage dependent barrier height and a strong internal electric field in depletion region under reverse bias suggested electric field enhanced thermionic emission in carrier transport via defect states in Au/Ni/GaN SBD. A detailed analysis of reverse leakage current revealed two different predominant transport mechanisms namely variable-range hopping (VRH) and Poole-Frenkel (PF) emission conduction at low (260 K) temperatures respectively. The estimated thermal activation energies (0.20-0.39 eV) from Arrhenius plot indicates a trap assisted tunneling of thermally activated electrons from a deep trap state into a continuum of states associated with each conductive threading dislocation.

  15. Predicting the potential distribution in China of Euwallacea fornicates (Eichhoff) under current and future climate conditions.

    Science.gov (United States)

    Ge, Xuezhen; Jiang, Chao; Chen, Linghong; Qiu, Shuang; Zhao, Yuxiang; Wang, Tao; Zong, Shixiang

    2017-04-19

    Euwallacea fornicatus (Eichhoff) is an important forest pest that has caused serious damage in America and Vietnam. In 2014, it attacked forests of Acer trialatum in the Yunnan province of China, creating concern in China's Forestry Bureau. We used the CLIMEX model to predict and compare the potential distribution for E. fornicates in China under current (1981-2010) and projected climate conditions (2011-2040) using one scenario (RCP8.5) and one global climate model (GCM), CSIRO-Mk3-6-0. Under both current and future climate conditions, the model predicted E. fornicates to be mainly distributed in the south of China. Comparing distributions under both climate conditions showed that the area of potential distribution was projected to increase (mainly because of an increase in favourable habitat) and shift to the north. Our results help clarify the potential effect of climate change on the range of this forest pest and provide a reference and guide to facilitate its control in China.

  16. Durability assessment of concrete sheet piling in the 'De Betuweroute' railway line

    NARCIS (Netherlands)

    Peelen, W.H.A.; Polder, R.B.

    2004-01-01

    Assessment of the durability of prestressed concrete sheet piles under the interference of CP gas pipeline system current, established that due to their low magnitude, these currents do not compromise the required 100-year service life of the structures. The sophisticated numerical modelling tools

  17. Measurement of direct currents of under 10-10 ampere and of resistances of 1012 Ω for a direct current

    International Nuclear Information System (INIS)

    Vagner, J.

    1965-01-01

    Measurement of weak direct currents by Townsend's method using a vibrating condenser electrometer. Development of a current generator giving a pico-ampere independently of the resistance of the circuit used. Development of generators giving currents which may be adjusted continuously and exactly (0.1 to 1 pico-ampere, 1 to 10 pico-amperes, 10 to 100 pico-amperes). Measurement of very high resistances (10 12 Ω) by three different methods. Graphs are made by plotting the value of the resistance against the potential difference applied across it (from 50 milli-volts to 50 volts). Two methods use adjustable current generators and the third is applicable to the measurement of resistances of between 10 7 and 10 13 Ω using a series of condensers ranging from 50 pico-farads to 10 micro-farads. The accuracy of the measurements is between 0. 5 and 1 per cent. (author) [fr

  18. Morphological features of the copper surface layer under sliding with high density electric current

    Energy Technology Data Exchange (ETDEWEB)

    Fadin, V. V., E-mail: fvv@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Aleutdinova, M. I., E-mail: aleut@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Seversk Technological Institute, Branch of State Autonomous Educational Institution of Higher Professional Education “National Research Nuclear University “MEPhI”, Seversk, 636036 (Russian Federation); Rubtsov, V. Ye., E-mail: rvy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Aleutdinova, V. A., E-mail: valery-aleut@yandex.ru [National Research St. Petersburg State Polytechnical University, St. Petersburg, 195251 (Russian Federation)

    2015-10-27

    Conductivity and wear intensity of copper under the influence of dry friction and electric current with contact density higher 100 A/cm{sup 2} are presented. It is shown that an increase in hardness and heat outflow from a friction zone leads to the reduction of wear intensity and current contact density increase corresponding to the beginning of catastrophic wear. Structural changes, such as the formation of FeO oxide and α-Fe particles in the copper surface layer, have also been found. It is observed that a worn surface is deformed according to a viscous liquid mechanism. Such singularity is explained in terms of appearance of high-excited atomic states in deforming micro-volumes near contact spots that lead to easy stress relaxation by local plastic shears in the vicinity of stress concentrators. In common this effect allows to achieve high wear resistance.

  19. Investigation of assumptions underlying current safety guidelines on EM-induced nerve stimulation

    Science.gov (United States)

    Neufeld, Esra; Vogiatzis Oikonomidis, Ioannis; Iacono, Maria Ida; Angelone, Leonardo M.; Kainz, Wolfgang; Kuster, Niels

    2016-06-01

    An intricate network of a variety of nerves is embedded within the complex anatomy of the human body. Although nerves are shielded from unwanted excitation, they can still be stimulated by external electromagnetic sources that induce strongly non-uniform field distributions. Current exposure safety standards designed to limit unwanted nerve stimulation are based on a series of explicit and implicit assumptions and simplifications. This paper demonstrates the applicability of functionalized anatomical phantoms with integrated coupled electromagnetic and neuronal dynamics solvers for investigating the impact of magnetic resonance exposure on nerve excitation within the full complexity of the human anatomy. The impact of neuronal dynamics models, temperature and local hot-spots, nerve trajectory and potential smoothing, anatomical inhomogeneity, and pulse duration on nerve stimulation was evaluated. As a result, multiple assumptions underlying current safety standards are questioned. It is demonstrated that coupled EM-neuronal dynamics modeling involving realistic anatomies is valuable to establish conservative safety criteria.

  20. Path Following Control of an AUV under the Current Using the SVR-ADRC

    Directory of Open Access Journals (Sweden)

    Zheping Yan

    2014-01-01

    Full Text Available A novel active disturbance rejection control (ADRC controller is proposed based on support vector regression (SVR. The SVR-ADRC is designed to force an underactuated autonomous underwater vehicle (AUV to follow a path in the horizontal plane with the ocean current disturbance. It is derived using SVR algorithm to adjust the coefficients of the nonlinear state error feedback (ELSEF part in ADRC to deal with nonlinear variations at different operating points. The trend of change about ELSEF coefficients in the simulation proves that the designed SVR algorithm maintains the characteristics of astringency and stability. Furthermore, the path following errors under current in simulation has proved the high accuracy, strong robustness, and stability of the proposed SVR-ADRC. The contributions of the proposed controller are to improve the characteristics of ADRC considering the changing parameters in operating environment which make the controller more adaptive for the situation.

  1. Analysis of Magnetic Field Intensity and Induced Current under Live Working Based on Charge Simulation Method

    Directory of Open Access Journals (Sweden)

    Luo Yuanxiang

    2015-01-01

    Full Text Available To the problem that safety distance is insufficient for 500 kV substation live working, a magnetic field analysis method for overhead line bus is given based on the charge simulation method. In the method, charge is calculated firstly, and the space field intensity distribution calculation is completed by overlying charge. The space field intensity distribution rule is carried out based on the appropriate analysis, and space field intensity distribution rule of substation is obtained. Then according to the calculation formula of inducing current, the human body induction current under a substation busbar is simulated based on MATLAB. The simulation results have a certain guidance function for actual live working.

  2. Rotating ferro-nanofluid over stretching plate under the effect of hall current and joule heating

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Wahed, Mohamed S., E-mail: eng_moh_sayed@live.com

    2017-05-01

    The behavior of boundary layer over a stretching plate filled with ferromagnetic Fe{sub 3}O{sub 4} nanoparticles and subjected to magnetic field with hall current, joule heating and nonlinear thermal radiation has been investigated. The modeling based on nonlinear partial differential equations due to continuity, momentum and heat equations, these equations transformed to a system of nonlinear ordinary differential equations using similarity transformation technique then solved numerically. The effect of hall current, joule heating and thermal radiation on the physical quantities such as surface shear stress and heat flux have been investigated and discussed. Moreover, the velocities and temperature profiles of the boundary layer under the influence of the presented external forces plotted and discussed. - Highlights: • The existence of the hall current increases the transverse velocity, as well as has a limited impact on the longitudinal velocity. • Boundary layer temperature exposed to nonlinear thermal radiation is higher than that exposed to linear thermal radiation. • Joule heating increases the boundary layer temperature near the surface especially in the linear model of thermal radiation. • Magnetic field with hall current increases the x-direction skin friction and reduces it in the y-direction.

  3. [Mechanism of strategic management of a sanatorium-and-spa facility under current economic conditions].

    Science.gov (United States)

    Kholmogorov, N A; Fedotchenko, A A

    2010-01-01

    The existing system of management of sanatorium-and-spa facilities constitutes a major economic risk factor under current socio-economic situation. One of the most important conditions for the sustainable continuation of activities of a sanatorium-and-spa institution is its adaptability to the changing economic environment. Those health care providers are likely to have an advantage in new conditions that offer a larger scope of specialized services, simultaneously reduces their costs and prices, introduce resource-saving technologies, and stimulate motivation of the medical personnel.

  4. Enhancement of crystal homogeneity of protein crystals under application of an external alternating current electric field

    Energy Technology Data Exchange (ETDEWEB)

    Koizumi, H.; Uda, S.; Fujiwara, K.; Nozawa, J. [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577 (Japan); Tachibana, M. [Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027 (Japan); Kojima, K. [Department of Education, Yokohama Soei University, 1 Miho-tyou, Midori-ku, Yokohama, 226-0015 (Japan)

    2014-10-06

    X-ray diffraction rocking-curve measurements were performed on tetragonal hen egg white (HEW) lysozyme crystals grown with and without the application of an external alternating current (AC) electric field. The crystal quality was assessed by the full width at half maximum (FWHM) value for each rocking curve. For two-dimensional maps of the FWHMs measured on the 440 and the 12 12 0 reflection, the crystal homogeneity was improved under application of an external electric field at 1 MHz, compared with that without. In particular, the significant improvement of the crystal homogeneity was observed for the 12 12 0 reflection.

  5. Predicting the potential distribution in China of Euwallacea fornicates (Eichhoff) under current and future climate conditions

    OpenAIRE

    Ge, Xuezhen; Jiang, Chao; Chen, Linghong; Qiu, Shuang; Zhao, Yuxiang; Wang, Tao; Zong, Shixiang

    2017-01-01

    Euwallacea fornicatus (Eichhoff) is an important forest pest that has caused serious damage in America and Vietnam. In 2014, it attacked forests of Acer trialatum in the Yunnan province of China, creating concern in China?s Forestry Bureau. We used the CLIMEX model to predict and compare the potential distribution for E. fornicates in China under current (1981?2010) and projected climate conditions (2011?2040) using one scenario (RCP8.5) and one global climate model (GCM), CSIRO-Mk3-6-0. Unde...

  6. Environmental impacts of barley cultivation under current and future climatic conditions

    DEFF Research Database (Denmark)

    Dijkman, Teunis Johannes; Birkved, Morten; Saxe, Henrik

    2017-01-01

    The purpose of this work is to compare the environmental impacts of spring barley cultivation in Denmark under current (year 2010) and future (year 2050) climatic conditions. Therefore, a Life Cycle Assessment was carried out for the production of 1 kg of spring barley in Denmark, at farm gate...... for the increased impacts. This finding was confirmed by the sensitivity analysis. Because this study focused solely on the impacts of climate change, technological improvements and political measures to reduce impacts in the 2050 scenario are not taken into account. Options to mitigate the environmental impacts....... Both under 2010 and 2050 climatic conditions, four subscenarios were modelled, based on a combination of two soil types and two climates. Included in the assessment were seed production, soil preparation, fertilization, pesticide application, and harvest. When processes in the life cycle resulted in co...

  7. Hydraulic structures with defective sheet pile walls

    OpenAIRE

    Ahmed, Ashraf A.; Johnston, Harold T.; Oyedele, Lukumon

    2013-01-01

    A sheet pile wall driven to form a barrier wall below the floor of a hydraulic structure is frequently assumed to be watertight. Although the leakage through the interlocks of the sheet piles is usually small, damage and other factors can result in significant leakage. Consequently, this assumption is rarely, if ever, satisfied in reality. The present study used a finite-element model to investigate the effect of leaks through sheet piles driven under the floor of a hydraulic structure on see...

  8. Characterizing the conductance underlying depolarization-induced slow current in cerebellar Purkinje cells.

    Science.gov (United States)

    Kim, Yu Shin; Kang, Eunchai; Makino, Yuichi; Park, Sungjin; Shin, Jung Hoon; Song, Hongjun; Launay, Pierre; Linden, David J

    2013-02-01

    Brief strong depolarization of cerebellar Purkinje cells produces a slow inward cation current [depolarization-induced slow current (DISC)]. Previous work has shown that DISC is triggered by voltage-sensitive Ca influx in the Purkinje cell and is attenuated by blockers of vesicular loading and fusion. Here, we have sought to characterize the ion channel(s) underlying the DISC conductance. While the brief depolarizing steps that triggered DISC were associated with a large Ca transient, the onset of DISC current corresponded only with the Ca transient decay phase. Furthermore, substitution of external Na with the impermeant cation N-methyl-d-glucamine produced a complete and reversible block of DISC, suggesting that the DISC conductance was not Ca permeant. Transient receptor potential cation channel, subfamily M, members 4 (TRPM4) and 5 (TRPM5) are nonselective cation channels that are opened by Ca transients but do not flux Ca. They are expressed in Purkinje cells of the posterior cerebellum, where DISC is large, and, in these cells, DISC is strongly attenuated by nonselective blockers of TRPM4/5. However, measurement of DISC currents in Purkinje cells derived from TRPM4 null, TRPM5 null, and double null mice as well as wild-type mice with TRPM4 short hairpin RNA knockdown showed a partial attenuation with 35-46% of current remaining. Thus, while the DISC conductance is Ca triggered, Na permeant, and Ca impermeant, suggesting a role for TRPM4 and TRPM5, these ion channels are not absolutely required for DISC.

  9. Minimum quench power dissipation and current non-uniformity in international thermonuclear experimental reactor type NbTi cable-in-conduit conductor samples under direct current conditions

    NARCIS (Netherlands)

    Rolando, G.; van Lanen, E.P.A.; Nijhuis, Arend

    2012-01-01

    The level of current non-uniformity in NbTi cable-in-conduit conductors (CICCs) sections near the joints in combination with the magnetic field profile needs attention in view of proper joint design. The strand joule power and current distribution at quench under DC conditions of two samples of ITER

  10. The current status of cyanobacterial nomenclature under the "prokaryotic" and the "botanical" code.

    Science.gov (United States)

    Oren, Aharon; Ventura, Stefano

    2017-10-01

    Cyanobacterial taxonomy developed in the botanical world because Cyanobacteria/Cyanophyta have traditionally been identified as algae. However, they possess a prokaryotic cell structure, and phylogenetically they belong to the Bacteria. This caused nomenclature problems as the provisions of the International Code of Nomenclature for algae, fungi, and plants (ICN; the "Botanical Code") differ from those of the International Code of Nomenclature of Prokaryotes (ICNP; the "Prokaryotic Code"). While the ICN recognises names validly published under the ICNP, Article 45(1) of the ICN has not yet been reciprocated in the ICNP. Different solutions have been proposed to solve the current problems. In 2012 a Special Committee on the harmonisation of the nomenclature of Cyanobacteria was appointed, but its activity has been minimal. Two opposing proposals to regulate cyanobacterial nomenclature were recently submitted, one calling for deletion of the cyanobacteria from the groups of organisms whose nomenclature is regulated by the ICNP, the second to consistently apply the rules of the ICNP to all cyanobacteria. Following a general overview of the current status of cyanobacterial nomenclature under the two codes we present five case studies of genera for which nomenclatural aspects have been discussed in recent years: Microcystis, Planktothrix, Halothece, Gloeobacter and Nostoc.

  11. 49 CFR 236.338 - Mechanical locking required in accordance with locking sheet and dog chart.

    Science.gov (United States)

    2010-10-01

    ... locking sheet and dog chart. 236.338 Section 236.338 Transportation Other Regulations Relating to... in accordance with locking sheet and dog chart. Mechanical locking shall be in accordance with locking sheet and dog chart currently in effect. ...

  12. Current models broadly neglect specific needs of biodiversity conservation in protected areas under climate change

    Directory of Open Access Journals (Sweden)

    Moloney Kirk A

    2011-05-01

    Full Text Available Abstract Background Protected areas are the most common and important instrument for the conservation of biological diversity and are called for under the United Nations' Convention on Biological Diversity. Growing human population densities, intensified land-use, invasive species and increasing habitat fragmentation threaten ecosystems worldwide and protected areas are often the only refuge for endangered species. Climate change is posing an additional threat that may also impact ecosystems currently under protection. Therefore, it is of crucial importance to include the potential impact of climate change when designing future nature conservation strategies and implementing protected area management. This approach would go beyond reactive crisis management and, by necessity, would include anticipatory risk assessments. One avenue for doing so is being provided by simulation models that take advantage of the increase in computing capacity and performance that has occurred over the last two decades. Here we review the literature to determine the state-of-the-art in modeling terrestrial protected areas under climate change, with the aim of evaluating and detecting trends and gaps in the current approaches being employed, as well as to provide a useful overview and guidelines for future research. Results Most studies apply statistical, bioclimatic envelope models and focus primarily on plant species as compared to other taxa. Very few studies utilize a mechanistic, process-based approach and none examine biotic interactions like predation and competition. Important factors like land-use, habitat fragmentation, invasion and dispersal are rarely incorporated, restricting the informative value of the resulting predictions considerably. Conclusion The general impression that emerges is that biodiversity conservation in protected areas could benefit from the application of modern modeling approaches to a greater extent than is currently reflected in the

  13. Calculations on the current density and the voltage-current relation under a.c. conditions of filaments

    NARCIS (Netherlands)

    Hartmann, R.A.; Dijkstra, D.; van Beckum, F.P.H.; van de Klundert, L.J.M.

    1989-01-01

    Technical applications of multifilamentary wires indicate that filaments are used in complex magnetic fields (a combination of non-parallel a.c./d.c. transverse and rotating fields) carrying an a.c./d.c. transport current of various frequency. Furthermore, due to technical manufacturing processes

  14. Current algebras, measures quasi-invariant under diffeomorphism groups, and infinite quantum systems with accumulation points

    Science.gov (United States)

    Sakuraba, Takao

    The approach to quantum physics via current algebra and unitary representations of the diffeomorphism group is established. This thesis studies possible infinite Bose gas systems using this approach. Systems of locally finite configurations and systems of configurations with accumulation points are considered, with the main emphasis on the latter. In Chapter 2, canonical quantization, quantization via current algebra and unitary representations of the diffeomorphism group are reviewed. In Chapter 3, a new definition of the space of configurations is proposed and an axiom for general configuration spaces is abstracted. Various subsets of the configuration space, including those specifying the number of points in a Borel set and those specifying the number of accumulation points in a Borel set are proved to be measurable using this axiom. In Chapter 4, known results on the space of locally finite configurations and Poisson measure are reviewed in the light of the approach developed in Chapter 3, including the approach to current algebra in the Poisson space by Albeverio, Kondratiev, and Rockner. Goldin and Moschella considered unitary representations of the group of diffeomorphisms of the line based on self-similar random processes, which may describe infinite quantum gas systems with clusters. In Chapter 5, the Goldin-Moschella theory is developed further. Their construction of measures quasi-invariant under diffeomorphisms is reviewed, and a rigorous proof of their conjectures is given. It is proved that their measures with distinct correlation parameters are mutually singular. A quasi-invariant measure constructed by Ismagilov on the space of configurations with accumulation points on the circle is proved to be singular with respect to the Goldin-Moschella measures. Finally a generalization of the Goldin-Moschella measures to the higher-dimensional case is studied, where the notion of covariance matrix and the notion of condition number play important roles. A

  15. Electric Current Activated Combustion Synthesis and Chemical Ovens Under Terrestrial and Reduced Gravity Conditions

    Science.gov (United States)

    Unuvar, C.; Fredrick, D.; Anselmi-Tamburini, U.; Manerbino, A.; Guigne, J. Y.; Munir, Z. A.; Shaw, B. D.

    2004-01-01

    Combustion synthesis (CS) generally involves mixing reactants together (e.g., metal powders) and igniting the mixture. Typically, a reaction wave will pass through the sample. In field activated combustion synthesis (FACS), the addition of an electric field has a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product as well as capillary flow, mass-transport in porous media, and Marangoni flows, which are influenced by gravity. The objective is to understand the role of an electric field in CS reactions under conditions where gravity-related effects are suppressed or altered. The systems being studied are Ti+Al and Ti+3Al. Two different ignition orientations have been used to observe effects of gravity when one of the reactants becomes molten. This consequentially influences the position and concentration of the electric current, which in turn influences the entire process. Experiments have also been performed in microgravity conditions. This process has been named Microgravity Field Activated Combustion Synthesis (MFACS). Effects of gravity have been demonstrated, where the reaction wave temperature and velocity demonstrate considerable differences besides the changes of combustion mechanisms with the different high currents applied. Also the threshold for the formation of a stable reaction wave is increased under zero gravity conditions. Electric current was also utilized with a chemical oven technique, where inserts of aluminum with minute amounts of tungsten and tantalum were used to allow observation of effects of settling of the higher density solid particles in liquid aluminum at the present temperature profile and wave velocity of the reaction.

  16. Corrosion behaviour of zinc deposits obtained under pulse current electrodeposition: Effects of coumarin as additive

    International Nuclear Information System (INIS)

    Mouanga, M.; Ricq, L.; Douglade, J.; Bercot, P.

    2009-01-01

    The corrosion behaviour of zinc deposits obtained under pulsed current electrodeposition from an acidic chloride bath in the presence and absence of coumarin has been investigated. The effects of pulse peak current density (J p ) on the morphology of zinc deposits were studied by scanning electron microscopy. An increase in J p from 40 to 280 A dm -2 yields deposits with a finer grain size. The refinement of the grain size was more considerable in the presence of coumarin (J p = 280 A dm -2 ). The preferred orientation of zinc deposits was studied by X-ray diffraction. At J p = 40 A dm -2 , the preferred orientation of zinc deposits was (1 0 3) and changed to (0 0 2) at J p = 80 A dm -2 . An increase in J p to 280 A dm -2 did not change the preferred crystallographic orientations except for an increase in the peak intensity of the (0 0 2) plane. In the presence of coumarin, the preferred crystallographic orientations changed at J p = 280 A dm -2 from the (0 0 2) plane to the (1 0 3) plane. The corrosion behaviour was investigated in an aerated 3.5% NaCl solution; the anodic polarization and electrochemical impedance spectroscopy curves were performed. The corrosion resistance of zinc deposits was improved by increasing the pulse peak current density (J p ); whereas, the presence of coumarin did not improve the corrosion resistance

  17. Instrumentation for low noise nanopore-based ionic current recording under laser illumination

    Science.gov (United States)

    Roelen, Zachary; Bustamante, José A.; Carlsen, Autumn; Baker-Murray, Aidan; Tabard-Cossa, Vincent

    2018-01-01

    We describe a nanopore-based optofluidic instrument capable of performing low-noise ionic current recordings of individual biomolecules under laser illumination. In such systems, simultaneous optical measurements generally introduce significant parasitic noise in the electrical signal, which can severely reduce the instrument sensitivity, critically hindering the monitoring of single-molecule events in the ionic current traces. Here, we present design rules and describe simple adjustments to the experimental setup to mitigate the different noise sources encountered when integrating optical components to an electrical nanopore system. In particular, we address the contributions to the electrical noise spectra from illuminating the nanopore during ionic current recording and mitigate those effects through control of the illumination source and the use of a PDMS layer on the SiNx membrane. We demonstrate the effectiveness of our noise minimization strategies by showing the detection of DNA translocation events during membrane illumination with a signal-to-noise ratio of ˜10 at 10 kHz bandwidth. The instrumental guidelines for noise minimization that we report are applicable to a wide range of nanopore-based optofluidic systems and offer the possibility of enhancing the quality of synchronous optical and electrical signals obtained during single-molecule nanopore-based analysis.

  18. Optimal white spruce breeding zones for Ontario under current and future climates

    Energy Technology Data Exchange (ETDEWEB)

    Thomson, A.M.; Crowe, K.A.; Parker, W.H. [Lakehead Univ., Thunder Bay, ON (Canada). Faculty of Forestry and the Forest Environment

    2010-08-15

    Forest regeneration and tree improvement practices rely on the local adaptation of planted sources because maladaptation results in reduced growth and increased susceptibility to pests and pathogens. As such, the transfer of tree seed is usually regulated within seed and breeding zones to ensure that trees are planted within their environmental tolerance limits. The purpose of this study was to determine optimal adaptively based breeding zones of white spruce (Picea glauca (Moench) Voss) and to compare current zones with corresponding zones using a methodology for modeled future climates. Optimal breeding zones were developed for white spruce in Ontario under present and future climate conditions to examine potential shifts due to climate change. These zones were developed by determining candidate breeding zones based on the relationship between measured performance variables and climate and by using a decision support model to choose subsets of breeding zones that maximize geographic coverage. Current optimal breeding zones were based on 1961 to 1990 climate normals, and future breeding zones were based on 3 general circulation model predictions of 2041 to 2070 climate. The study showed that 14 zones were needed to cover the Ontario range of white spruce for the 1961 to 1990 data. The delimited current breeding zones for white spruce were found to be quite large, and can be used to ensure forest productivity by limiting the transfer of improved seeds to within areas where they can adapt adequately. 51 refs., 3 tabs., 6 figs.

  19. High resolution laser beam induced current images under trichromatic laser radiation: approximation to the solar irradiation.

    Science.gov (United States)

    Navas, F J; Alcántara, R; Fernández-Lorenzo, C; Martín-Calleja, J

    2010-03-01

    A laser beam induced current (LBIC) map of a photoactive surface is a very useful tool when it is necessary to study the spatial variability of properties such as photoconverter efficiency or factors connected with the recombination of carriers. Obtaining high spatial resolution LBIC maps involves irradiating the photoactive surface with a photonic beam with Gaussian power distribution and with a low dispersion coefficient. Laser emission fulfils these characteristics, but against it is the fact that it is highly monochromatic and therefore has a spectral distribution different to solar emissions. This work presents an instrumental system and procedure to obtain high spatial resolution LBIC maps in conditions approximating solar irradiation. The methodology developed consists of a trichromatic irradiation system based on three sources of laser excitation with emission in the red, green, and blue zones of the electromagnetic spectrum. The relative irradiation powers are determined by either solar spectrum distribution or Planck's emission formula which provides information approximate to the behavior of the system if it were under solar irradiation. In turn, an algorithm and a procedure have been developed to be able to form images based on the scans performed by the three lasers, providing information about the photoconverter efficiency of photovoltaic devices under the irradiation conditions used. This system has been checked with three photosensitive devices based on three different technologies: a commercial silicon photodiode, a commercial photoresistor, and a dye-sensitized solar cell. These devices make it possible to check how the superficial quantum efficiency has areas dependent upon the excitation wavelength while it has been possible to measure global incident photon-to-current efficiency values approximating those that would be obtained under irradiation conditions with sunlight.

  20. Quality evaluation of concrete under compacting by vibration using resistance of electro current

    International Nuclear Information System (INIS)

    Nozaki, Yoshisugu

    2006-01-01

    Quality of concrete in structures is affected not only quality of materials; i.e. fresh concrete delivered to site but also placing and compaction works. Factors related to the latter are not studied minutely, and the works in site are judged and controlled by skilled person under his experience, and these process are said to the neck in QC and rationalization in construction site. The study to develop the evaluation system of fresh concrete quality is described in the paper. In the experiment, electrode was attached to form work and resistance of electro current was recorded while vibrating. It can recognized that resistance is closely related to internal quality of concrete, so the resistance may be the effective index to know optimum compaction time in placing work.

  1. Quality evaluation of concrete under compacting by vibration using resistance of electro current

    International Nuclear Information System (INIS)

    Nozaki, Yoshisugu

    2006-01-01

    Quality of concrete in structures is affected not only quality of materials; i.e. fresh concrete delivered to site but also placing and compaction works. Factors related to the latter are not studied minutely, and the works in site are judged and controlled by skilled person under his experience, and these process are said to the neck in QC and rationalization in construction site. The study to develop the evaluation system of fresh concrete quality is described in the paper, In the experiment, electrode was attached to formwork and resistance of electro current was recorded while vibrating. It can recognized that resistance is closely related to internal quality of concrete, so the resistance may be the effective index to know optimum compaction time in placing work.

  2. Analysis of Three-Phase Rectifier Systems with Controlled DC-Link Current Under Unbalanced Grids

    DEFF Research Database (Denmark)

    Kumar, Dinesh; Davari, Pooya; Zare, Firuz

    2017-01-01

    Voltage unbalance is the most common disturbance in distribution networks, which give undesirable effects on many grid connected power electronics systems including Adjustable Speed Drive (ASD). Severe voltage unbalance can force three-phase rectifiers into almost single-phase operation, which...... degrades the grid power quality and also imposes a significant negative impact on the ASD system. This major power quality issue affecting the conventional rectifiers can be attenuated by controlling the DC-link current based on an Electronic Inductor (EI) technique. The purpose of this digest...... is to analyze and compare the performance of an EI with a conventional three-phase rectifier under unbalanced grid conditions. Experimental and simulation results validate the proposed mathematical modelling. Further analysis and benchmarking will be provided in the final paper....

  3. Balance velocities of the Greenland ice sheet

    DEFF Research Database (Denmark)

    Joughin, I.; Fahnestock, M.; Ekholm, Simon

    1997-01-01

    We present a map of balance velocities for the Greenland ice sheet. The resolution of the underlying DEM, which was derived primarily from radar altimetery data, yields far greater detail than earlier balance velocity estimates for Greenland. The velocity contours reveal in striking detail......, the balance map is useful for ice-sheet modelling, mass balance studies, and field planning....

  4. A global map of suitability for coastal Vibrio cholerae under current and future climate conditions.

    Science.gov (United States)

    Escobar, Luis E; Ryan, Sadie J; Stewart-Ibarra, Anna M; Finkelstein, Julia L; King, Christine A; Qiao, Huijie; Polhemus, Mark E

    2015-09-01

    Vibrio cholerae is a globally distributed water-borne pathogen that causes severe diarrheal disease and mortality, with current outbreaks as part of the seventh pandemic. Further understanding of the role of environmental factors in potential pathogen distribution and corresponding V. cholerae disease transmission over time and space is urgently needed to target surveillance of cholera and other climate and water-sensitive diseases. We used an ecological niche model (ENM) to identify environmental variables associated with V. cholerae presence in marine environments, to project a global model of V. cholerae distribution in ocean waters under current and future climate scenarios. We generated an ENM using published reports of V. cholerae in seawater and freely available remotely sensed imagery. Models indicated that factors associated with V. cholerae presence included chlorophyll-a, pH, and sea surface temperature (SST), with chlorophyll-a demonstrating the greatest explanatory power from variables selected for model calibration. We identified specific geographic areas for potential V. cholerae distribution. Coastal Bangladesh, where cholera is endemic, was found to be environmentally similar to coastal areas in Latin America. In a conservative climate change scenario, we observed a predicted increase in areas with environmental conditions suitable for V. cholerae. Findings highlight the potential for vulnerability maps to inform cholera surveillance, early warning systems, and disease prevention and control. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

  5. Numerical simulation of wave-current interaction under strong wind conditions

    Science.gov (United States)

    Larrañaga, Marco; Osuna, Pedro; Ocampo-Torres, Francisco Javier

    2017-04-01

    Although ocean surface waves are known to play an important role in the momentum and other scalar transfer between the atmosphere and the ocean, most operational numerical models do not explicitly include the terms of wave-current interaction. In this work, a numerical analysis about the relative importance of the processes associated with the wave-current interaction under strong off-shore wind conditions in Gulf of Tehuantepec (the southern Mexican Pacific) was carried out. The numerical system includes the spectral wave model WAM and the 3D hydrodynamic model POLCOMS, with the vertical turbulent mixing parametrized by the kappa-epsilon closure model. The coupling methodology is based on the vortex-force formalism. The hydrodynamic model was forced at the open boundaries using the HYCOM database and the wave model was forced at the open boundaries by remote waves from the southern Pacific. The atmospheric forcing for both models was provided by a local implementation of the WRF model, forced at the open boundaries using the CFSR database. The preliminary analysis of the model results indicates an effect of currents on the propagation of the swell throughout the study area. The Stokes-Coriolis term have an impact on the transient Ekman transport by modifying the Ekman spiral, while the Stokes drift has an effect on the momentum advection and the production of TKE, where the later induces a deepening of the mixing layer. This study is carried out in the framework of the project CONACYT CB-2015-01 255377 and RugDiSMar Project (CONACYT 155793).

  6. Stability of high current diode under 100-nanosecond-pulse voltage

    International Nuclear Information System (INIS)

    Lai Dingguo; Qiu Aici; Zhang Yongmin; Huang Jianjun; Ren Shuqing; Yang Li

    2012-01-01

    Stability of high current diode under pulse voltage with 80 ns and 34 ns rise time was studied on the flash Ⅱ accelerator. Influence of rise time of diode voltage on startup time and cathode emission uniformity and repeatability of diode impedance was analyzed by comparing the experimental results with numerically simulated results, and the influence mechanism was discussed. The startup time of diode increases with the increasing of rise time of voltage, and the repeatability of diode impedance decreases. Discal plane cathode is prone to emit rays intensely in the center area, the time that plasma covers the surface of the cathode increases and the shielding effect has more impact on cathode emission according to the increase of rise time. Local intense emission on the cathode increases expansion speed of plasma and reduces the effective emission area. The stability of characteristic impedance of diode under a pulse voltage with slow rise time is decreased by the combined action of expansion speed of plasma and the effective emission area. (authors)

  7. Automobile sheet metal part production with incremental sheet forming

    Directory of Open Access Journals (Sweden)

    İsmail DURGUN

    2016-02-01

    Full Text Available Nowadays, effect of global warming is increasing drastically so it leads to increased interest on energy efficiency and sustainable production methods. As a result of adverse conditions, national and international project platforms, OEMs (Original Equipment Manufacturers, SMEs (Small and Mid-size Manufacturers perform many studies or improve existing methodologies in scope of advanced manufacturing techniques. In this study, advanced manufacturing and sustainable production method "Incremental Sheet Metal Forming (ISF" was used for sheet metal forming process. A vehicle fender was manufactured with or without die by using different toolpath strategies and die sets. At the end of the study, Results have been investigated under the influence of method and parameters used.Keywords: Template incremental sheet metal, Metal forming

  8. Water deficit effects on maize yields modeled under current and greenhouse climates

    International Nuclear Information System (INIS)

    Muchow, R.C.; Sinclair, T.R.

    1991-01-01

    The availability of water imposes one of the major limits on rainfed maize (Zea mays L.) productivity. This analysis was undertaken in an attempt to quantify the effects of limited water on maize growth and yield by extending a simple, mechanistic model in which temperature regulates crop development and intercepted solar radiation is used to calculate crop biomass accumulation. A soil water budget was incorporated into the model by accounting for inputs from rainfall and irrigation, and water use by soil evaporation and crop transpiration. The response functions of leaf area development and crop gas exchange to the soil water budget were developed from experimental studies. The model was used to interpret a range of field experiments using observed daily values of temperature, solar radiation, and rainfall or irrigation, where water deficits of varying durations developed at different stages of growth. The relative simplicity of the model and its robustness in simulating maize yields under a range of water-availability conditions allows the model to be readily used for studies of crop performance under alternate conditions. One such study, presented here, was a yield assessment for rainfed maize under possible greenhouse climates where temperature and atmospheric CO 2 concentration were increased. An increase in temperature combined with decreased rainfall lowered grain yield, although the increase in crop water use efficiency associated with elevated CO 2 concentration ameliorated the response to the greenhouse climate. Grain yields for the greenhouse climates as compared to current conditions increased, or decreased only slightly, except when the greenhouse climate was assumed to result in severly decreased rainfall

  9. Early stages of wind wave and drift current generation under non-stationary wind conditions.

    Science.gov (United States)

    Robles-Diaz, Lucia; Ocampo-Torres, Francisco J.; Branger, Hubert

    2016-04-01

    Generation and amplification mechanisms of ocean waves are well understood under constant wind speed or limited fetch conditions. Under these situations, the momentum and energy transfers from air to water are also quite well known. However during the wind field evolution over the ocean, we may observe sometime high wind acceleration/deceleration situations (e.g. Mexican Tehuano or Mediterranean Mistral wind systems). The evolution of wave systems under these conditions is not well understood. The purpose of these laboratory experiments is to better understand the early stages of water-waves and surface-drift currents under non-stationary wind conditions and to determine the balance between transfers creating waves and surface currents during non-equilibrium situations. The experiments were conducted in the Institut Pythéas wind-wave facility in Marseille-France. The wave tank is 40 m long, 2.7 m wide and 1 m deep. The air section is 50 m long, 3 m wide and 1.8 m height. We used 11 different resistive wave-gauges located along the tank. The momentum fluxes in the air column were estimated from single and X hot-film anemometer measurements. The sampling frequency for wind velocity and surface displacement measurements was 256 Hz. Water-current measurements were performed with a profiling velocimeter. This device measures the first 3.5 cm of the water column with a frequency rate of 100Hz. During the experiments, the wind intensity was abruptly modified with a constant acceleration and deceleration over time. We observed that wind drag coefficient values for accelerated wind periods are lower than the ones reported in previous studies for constant wind speed (Large and Pond 1981; Ocampo-Torres et al. 2010; Smith 1980; Yelland and Taylor 1996). This is probably because the turbulent boundary layer is not completely developed during the increasing-wind sequence. As it was reported in some theoretical studies (Miles 1957; Phillips 1957; Kahma and Donelan 1988), we

  10. Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.; Kingslake, J.

    2013-11-01

    We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

  11. Regional scale patterns of fine root lifespan and turnover under current and future climate.

    Science.gov (United States)

    McCormack, Luke M; Eissenstat, David M; Prasad, Anantha M; Smithwick, Erica A H

    2013-06-01

    Fine root dynamics control a dominant flux of carbon from plants and into soils and mediate potential uptake and cycling of nutrients and water in terrestrial ecosystems. Understanding of these patterns is needed to accurately describe critical processes like productivity and carbon storage from ecosystem to global scales. However, limited observations of root dynamics make it difficult to define and predict patterns of root dynamics across broad spatial scales. Here, we combine species-specific estimates of fine root dynamics with a model that predicts current distribution and future suitable habitat of temperate tree species across the eastern United States (US). Estimates of fine root lifespan and turnover are based on empirical observations and relationships with fine root and whole-plant traits and apply explicitly to the fine root pool that is relatively short-lived and most active in nutrient and water uptake. Results from the combined model identified patterns of faster root turnover rates in the North Central US and slower turnover rates in the Southeastern US. Portions of Minnesota, Ohio, and Pennsylvania were also predicted to experience >10% increases in root turnover rates given potential shifts in tree species composition under future climate scenarios while root turnover rates in other portions of the eastern US were predicted to decrease. Despite potential regional changes, the average estimates of root lifespan and turnover for the entire study area remained relatively stable between the current and future climate scenarios. Our combined model provides the first empirically based, spatially explicit, and spatially extensive estimates of fine root lifespan and turnover and is a potentially powerful tool allowing researchers to identify reasonable approximations of forest fine root turnover in areas where no direct observations are available. Future efforts should focus on reducing uncertainty in estimates of root dynamics by better understanding how

  12. Evidence for superior current carrying capability of iron pnictide tapes under hydrostatic pressure

    Science.gov (United States)

    Shabbir, Babar; Huang, He; Yao, Chao; Ma, Yanwei; Dou, Shixue; Johansen, Tom H.; Hosono, Hideo; Wang, Xiaolin

    2017-09-01

    High critical current density (Jc) values in superconducting wires/tapes are desirable for high magnetic field applications. Recently developed pnictide wires/tapes exhibit exceptional superconducting properties such as high critical temperature (Tc), upper critical field (Hc 2), and almost field-independent Jc. Despite the great fabrication efforts, however, the newly discovered pnictide wires/tapes are still not able to replace low-temperature superconductors such as N b3Sn , due to their inferior Jc values. Ag-clad S r0.6K0.4F e2A s2 tapes have demonstrated significant superconducting performance, although their low Jc in comparison to N b3Sn is still a major challenge. By successfully employing hydrostatic pressure, a remarkably significant enhancement of Jc by an order of magnitude can be achieved in S r0.6K0.4F e2A s2 tapes in both low and high fields. This is a promising technological step forward towards high-field applications, as the record high Jc values (˜2 ×1 05A /c m2 at 4.2 K and 13 T, P =1.1 GPa ) obtained for S r0.6K0.4F e2A s2 tape are superior to those of N b3Sn and other pnictide wires/tapes. Here, we used magnetic Jc data for comparison to the other reported transport Jc data, due to the lack of transport measurement facility under hydrostatic pressure. Our systematic analysis shows that pressure-induced pinning centers are the main source of Jc enhancement, along with a fractional contribution from geometric changes around the grain boundaries under pressure. We expect that utilization of an appropriate pressure approach will be a way to significantly enhance Jc to beyond the cutoff (maximum) values in various superconductors produced using other existing methods for Jc enhancement.

  13. Electromagnetic augmentation for casting of thin metal sheets

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Hinsdale, IL)

    1989-01-01

    Thin metal sheets are cast by magnetically levitating molten metal deposited in a mold within a ferromagnetic yoke and between AC conducting coils and linearly displacing the magnetically levitated liquid metal while it is being cooled by the water-cooled walls of the mold to form a solid metal sheet. A conducting shield is electrically coupled to the molten metal sheet to provide a return path for eddy currents induced in the metal sheet by the current in the AC conducting coils. In another embodiment, a DC conducting coil is coupled to the metal sheet for providing a direct current therein which interacts with the magnetic field to levitate the moving metal sheet. Levitation of the metal sheet in both molten and solid forms reduces its contact pressure with the mold walls while maintaining sufficient engagement therebetween to permit efficient conductive cooling by the mold through which a coolant fluid may be circulated. The magnetic fields associated with the currents in the aforementioned coils levitate the molten metal sheet while the mold provides for its lateral and vertical confinement. A leader sheet having electromagnetic characteristics similar to those of the molten metal sheet is used to start the casing process and precedes the molten metal sheet through the yoke/coil arrangement and mold and forms a continuous sheet therewith. The yoke/coil arrangement may be either U-shaped with a single racetrack coil or may be rectangular with a pair of spaced, facing bedstead coils.

  14. Application of atelocollagen sheet for sellar reconstruction.

    Science.gov (United States)

    Goto, Yuko; Oshino, Satoru; Shimizu, Takeshi; Saitoh, Youichi

    2016-05-01

    We aimed to evaluate combined use of atelocollagen sheet and fibrin glue for sellar reconstruction. Experiment 1: A plastic chamber was prepared with a hydroxyapatite lid with a hole of 10mm in diameter at its center, covered with a Gore-Tex sheet (W.L. Gore & Associates, Tokyo, Japan) 15mm in diameter and sealed with a combination of fibrin glue sealant and either atelocollagen sheet or polyglycolic acid (PGA) sheet. Air was injected into the chamber and the pressure at which air leakage occurred was measured under each situation. Mean (±standard deviation) leakage pressure was 816±162mmH2O for atelocollagen sheet (n=5), significantly higher than the 557±130mmH2O for PGA sheet (n=5, p<0.05, Wilcoxon test). Experiment 2: Bilateral 5mm bone windows were made in the temporal bone in eight rats. The surgical cavities were filled with one of four materials (fibrin glue only; fibrin glue and atelocollagen sheet; PGA sheet; or autologous fat tissue). Histological changes including the status of implanted materials and inflammatory responses were investigated 2 and 5weeks after the procedures. Both atelocollagen and PGA sheets remained at 5weeks after implantation, whereas fibrin glue and fat tissue were absorbed and undetectable at 2weeks. Inflammatory cell accumulation was less around the atelocollagen sheet compared to the PGA sheet. The combination of atelocollagen sheet and fibrin glue sealant showed sufficient adhesion force and favorable tissue affinity, suggesting this combination as a feasible material in sellar reconstruction. Copyright © 2015 Elsevier Ltd. All rights reserved.

  15. Nanotechnology for Site Remediation: Fact Sheet

    Science.gov (United States)

    This fact sheet presents a snapshot of nanotechnology and its current uses in remediation. It presents information to help site project managers understand the potential applications of this group of technologies at their sites.

  16. Modeling the yield potential of dryland canola under current and future climates in California

    Science.gov (United States)

    George, N.; Kaffka, S.; Beeck, C.; Bucaram, S.; Zhang, J.

    2012-12-01

    -adapted canola varieties can be justified, and the potential value of a California canola industry both now and in the future. Winter annual crops like canola use rainfall in a Mediterranean climate like California more efficiently than spring or summer crops. Our results suggest that under current production costs and seed prices, dry farmed canola will have good potential in certain areas of the California. Canola yields decline with annual winter precipitation, however economically viable yields are still achieved at relatively precipitation levels (200 mm). Results from simulation, combined with related economic modeling (reported elsewhere) suggest that canola will be viable in a variety of production systems in the northern Sacramento Valley and some coastal locations, even under drier future climate scenarios. The in-field evaluation of Australian canola varieties should contribute to maintain or improving resource use efficiency and farm profitability.

  17. Neural mechanisms underlying transcranial direct current stimulation in aphasia: A feasibility study.

    Directory of Open Access Journals (Sweden)

    Lena eUlm

    2015-10-01

    Full Text Available Little is known about the neural mechanisms by which transcranial direct current stimulation (tDCS impacts on language processing in post-stroke aphasia. This was addressed in a proof-of-principle study that explored the effects of tDCS application in aphasia during simultaneous functional magnetic resonance imaging (fMRI. We employed a single subject, cross-over, sham-tDCS controlled design and the stimulation was administered to an individualized perilesional stimulation site that was identified by a baseline fMRI scan and a picture naming task. Peak activity during the baseline scan was located in the spared left inferior frontal gyrus (IFG and this area was stimulated during a subsequent cross-over phase. tDCS was successfully administered to the target region and anodal- vs. sham-tDCS resulted in selectively increased activity at the stimulation site. Our results thus demonstrate that it is feasible to precisely target an individualized stimulation site in aphasia patients during simultaneous fMRI which allows assessing the neural mechanisms underlying tDCS application. The functional imaging results of this case report highlight one possible mechanism that may have contributed to beneficial behavioural stimulation effects in previous clinical tDCS trials in aphasia. In the future, this approach will allow identifying distinct patterns of stimulation effects on neural processing in larger cohorts of patients. This may ultimately yield information about the variability of tDCS-effects on brain functions in aphasia.

  18. Modeling Hawaiian ecosystem degradation due to invasive plants under current and future climates.

    Science.gov (United States)

    Vorsino, Adam E; Fortini, Lucas B; Amidon, Fred A; Miller, Stephen E; Jacobi, James D; Price, Jonathan P; 'Ohukani'ohi'a Gon, Sam; Koob, Gregory A

    2014-01-01

    Occupation of native ecosystems by invasive plant species alters their structure and/or function. In Hawaii, a subset of introduced plants is regarded as extremely harmful due to competitive ability, ecosystem modification, and biogeochemical habitat degradation. By controlling this subset of highly invasive ecosystem modifiers, conservation managers could significantly reduce native ecosystem degradation. To assess the invasibility of vulnerable native ecosystems, we selected a proxy subset of these invasive plants and developed robust ensemble species distribution models to define their respective potential distributions. The combinations of all species models using both binary and continuous habitat suitability projections resulted in estimates of species richness and diversity that were subsequently used to define an invasibility metric. The invasibility metric was defined from species distribution models with 0.8; True Skill Statistic >0.75) as evaluated per species. Invasibility was further projected onto a 2100 Hawaii regional climate change scenario to assess the change in potential habitat degradation. The distribution defined by the invasibility metric delineates areas of known and potential invasibility under current climate conditions and, when projected into the future, estimates potential reductions in native ecosystem extent due to climate-driven invasive incursion. We have provided the code used to develop these metrics to facilitate their wider use (Code S1). This work will help determine the vulnerability of native-dominated ecosystems to the combined threats of climate change and invasive species, and thus help prioritize ecosystem and species management actions.

  19. Modeling Hawaiian ecosystem degradation due to invasive plants under current and future climates.

    Directory of Open Access Journals (Sweden)

    Adam E Vorsino

    Full Text Available Occupation of native ecosystems by invasive plant species alters their structure and/or function. In Hawaii, a subset of introduced plants is regarded as extremely harmful due to competitive ability, ecosystem modification, and biogeochemical habitat degradation. By controlling this subset of highly invasive ecosystem modifiers, conservation managers could significantly reduce native ecosystem degradation. To assess the invasibility of vulnerable native ecosystems, we selected a proxy subset of these invasive plants and developed robust ensemble species distribution models to define their respective potential distributions. The combinations of all species models using both binary and continuous habitat suitability projections resulted in estimates of species richness and diversity that were subsequently used to define an invasibility metric. The invasibility metric was defined from species distribution models with 0.8; True Skill Statistic >0.75 as evaluated per species. Invasibility was further projected onto a 2100 Hawaii regional climate change scenario to assess the change in potential habitat degradation. The distribution defined by the invasibility metric delineates areas of known and potential invasibility under current climate conditions and, when projected into the future, estimates potential reductions in native ecosystem extent due to climate-driven invasive incursion. We have provided the code used to develop these metrics to facilitate their wider use (Code S1. This work will help determine the vulnerability of native-dominated ecosystems to the combined threats of climate change and invasive species, and thus help prioritize ecosystem and species management actions.

  20. Modeling Hawaiian ecosystem degradation due to invasive plants under current and future climates

    Science.gov (United States)

    Vorsino, Adam E.; Fortini, Lucas B.; Amidon, Fred A.; Miller, Stephen E.; Jacobi, James D.; Price, Jonathan P.; `Ohukani`ohi`a Gon, Sam; Koob, Gregory A.

    2014-01-01

    Occupation of native ecosystems by invasive plant species alters their structure and/or function. In Hawaii, a subset of introduced plants is regarded as extremely harmful due to competitive ability, ecosystem modification, and biogeochemical habitat degradation. By controlling this subset of highly invasive ecosystem modifiers, conservation managers could significantly reduce native ecosystem degradation. To assess the invasibility of vulnerable native ecosystems, we selected a proxy subset of these invasive plants and developed robust ensemble species distribution models to define their respective potential distributions. The combinations of all species models using both binary and continuous habitat suitability projections resulted in estimates of species richness and diversity that were subsequently used to define an invasibility metric. The invasibility metric was defined from species distribution models with 0.8; True Skill Statistic >0.75) as evaluated per species. Invasibility was further projected onto a 2100 Hawaii regional climate change scenario to assess the change in potential habitat degradation. The distribution defined by the invasibility metric delineates areas of known and potential invasibility under current climate conditions and, when projected into the future, estimates potential reductions in native ecosystem extent due to climate-driven invasive incursion. We have provided the code used to develop these metrics to facilitate their wider use (Code S1). This work will help determine the vulnerability of native-dominated ecosystems to the combined threats of climate change and invasive species, and thus help prioritize ecosystem and species management actions.

  1. Topics in Current Science Research: Closing the Achievement Gap for Under Resourced Students of Color

    Science.gov (United States)

    Loya Villalpando, Alvaro; Daal, Miguel; Phipps, Arran; Speller, Danielle; Sadoulet, Bernard; Winheld, Rachel; Cryogenic Dark Matter Search Collaboration

    2015-04-01

    Topics in Current Science Research (TCSR) is a five-week summer course offered at the University of California, Berkeley through a collaboration between the Level Playing Field Institute's Summer Math and Science Honors Academy (SMASH) Program and the Cryogenic Dark Matter Search (CDMS) group at UC Berkeley. SMASH is an academic enrichment program geared towards under-resourced, high school students of color. The goals of the course are to expand the students' conception of STEM, to teach the students that science is a method of inquiry and not just a collection of facts that are taught in school, and to expose the scholars to critical thinking within a scientific setting. The course's curriculum engages the scholars in hands-on scientific research, project proposal writing, and presentation of their scientific work to their peers as well as to a panel of UC Berkeley scientists. In this talk, we describe the course and the impact it has had on previous scholars, we discuss how the course's pedagogy has evolved over the past 10 years to enhance students' perception and understanding of science, and we present previous participants' reflections and feedback about the course and its success in providing high school students a genuine research experience at the university level.

  2. Patterns in larval fish assemblages under the influence of the Brazil current

    Science.gov (United States)

    Katsuragawa, M.; Dias, J. F.; Harari, J.; Namiki, C.; Zani-Teixeira, M. L.

    2014-10-01

    The present work investigates the composition of larval fish assemblages in the area under the influence of the Brazil Current (BC) off the Southeastern Brazilian Bight. Ichthyoplankton was sampled during two oceanographic cruises (November-December/1997 - spring; May/2001 - autumn) with bongo nets oblique tows. Seasonal variation and a coastal-ocean pattern in the distribution of larval fish was observed and was influenced by the dynamics of the water masses, Coastal Water (CW), Tropical Water (TW) and South Atlantic Central Water (SACW), the last two of which were transported by the BC. During spring, the shelf assemblage was dominated by larvae of small pelagic fishes, such as Sardinella brasiliensis, Engraulis anchoita and Trachurus lathami, and was associated with the enrichment of shallow water by the SACW upwelling. In autumn, the abundance of coastal species larvae was reduced, and the shelf assemblage was dominated by Bregmaceros cantori. A transitional assemblage occurred during the spring, and comprised mesopelagic and coastal species. In both seasons, the oceanic assemblage was dominated by the mesopelagic families, Myctophidae, Sternopthychidae and Phosichthyidae. The oceanographic conditions also demonstrated clear differences between the northern and southern subareas, particularly in the shelf zone. This was especially the case during autumn when a latitudinal gradient in larval fish assemblages became more pronounced.

  3. The Spot Weldability of Carbon Steel Sheet

    Directory of Open Access Journals (Sweden)

    A. M. Al-Mukhtar

    2013-01-01

    Full Text Available The specimens of thickness 0.8 mm carbon steel number 1.8902 in a strip form were welded. The strips of lap joints and curved peeljoints configurations have been welded. The welding parameters such as weld current and weld time have been investigated. The relation between the weld area and the joint strength properties has been presented. The obtained results were showing that the weld joint strength and the molten area (weld nugget volume highly increase with the increasing of weld current. Therefore, the correlation between the maximum load (joint strength and area has been given. The reliable weldability under the tensile and shearing loading was considered. Therefore, the new limits of weldability have been presented to consider these two types of loading. Moreover, the experimental results were compared with the empirical relations that consider the sheet thickness only.

  4. The global impact of ozone on agricultural crop yields under current and future air quality legislation

    Science.gov (United States)

    Van Dingenen, Rita; Dentener, Frank J.; Raes, Frank; Krol, Maarten C.; Emberson, Lisa; Cofala, Janusz

    In this paper we evaluate the global impact of surface ozone on four types of agricultural crop. The study is based on modelled global hourly ozone fields for the year 2000 and 2030, using the global 1°×1° 2-way nested atmospheric chemical transport model (TM5). Projections for the year 2030 are based on the relatively optimistic "current legislation (CLE) scenario", i.e. assuming that currently approved air quality legislation will be fully implemented by the year 2030, without a further development of new abatement policies. For both runs, the relative yield loss due to ozone damage is evaluated based on two different indices (accumulated concentration above a 40 ppbV threshold and seasonal mean daytime ozone concentration respectively) on a global, regional and national scale. The cumulative metric appears to be far less robust than the seasonal mean, while the seasonal mean shows satisfactory agreement with measurements in Europe, the US, China and Southern India and South-East Asia. Present day global relative yield losses are estimated to range between 7% and 12% for wheat, between 6% and 16% for soybean, between 3% and 4% for rice, and between 3% and 5% for maize (range resulting from different metrics used). Taking into account possible biases in our assessment, introduced through the global application of "western" crop exposure-response functions, and through model performance in reproducing ozone-exposure metrics, our estimates may be considered as being conservative. Under the 2030 CLE scenario, the global situation is expected to deteriorate mainly for wheat (additional 2-6% loss globally) and rice (additional 1-2% loss globally). India, for which no mitigation measures have been assumed by 2030, accounts for 50% of these global increase in crop yield loss. On a regional-scale, significant reductions in crop losses by CLE-2030 are only predicted in Europe (soybean) and China (wheat). Translating these assumed yield losses into total global economic

  5. Ab initio-aided CALPHAD thermodynamic modeling of the Sn-Pb binary system under current stressing.

    Science.gov (United States)

    Lin, Shih-kang; Yeh, Chao-kuei; Xie, Wei; Liu, Yu-chen; Yoshimura, Masahiro

    2013-01-01

    Soldering is an ancient process, having been developed 5000 years ago. It remains a crucial process with many modern applications. In electronic devices, electric currents pass through solder joints. A new physical phenomenon--the supersaturation of solders under high electric currents--has recently been observed. It involves (1) un-expected supersaturation of the solder matrix phase, and (2) the formation of unusual "ring-shaped" grains. However, the origin of these phenomena is not yet understood. Here we provide a plausible explanation of these phenomena based on the changes in the phase stability of Pb-Sn solders. Ab initio-aided CALPHAD modeling is utilized to translate the electric current-induced effect into the excess Gibbs free energies of the phases. Hence, the phase equilibrium can be shifted by current stressing. The Pb-Sn phase diagrams with and without current stressing clearly demonstrate the change in the phase stabilities of Pb-Sn solders under current stressing.

  6. Laminin-521 Promotes Rat Bone Marrow Mesenchymal Stem Cell Sheet Formation on Light-Induced Cell Sheet Technology

    Directory of Open Access Journals (Sweden)

    Zhiwei Jiang

    2017-01-01

    Full Text Available Rat bone marrow mesenchymal stem cell sheets (rBMSC sheets are attractive for cell-based tissue engineering. However, methods of culturing rBMSC sheets are critically limited. In order to obtain intact rBMSC sheets, a light-induced cell sheet method was used in this study. TiO2 nanodot films were coated with (TL or without (TN laminin-521. We investigated the effects of laminin-521 on rBMSCs during cell sheet culturing. The fabricated rBMSC sheets were subsequently assessed to study cell sheet viability, reattachment ability, cell sheet thickness, collagen type I deposition, and multilineage potential. The results showed that laminin-521 could promote the formation of rBMSC sheets with good viability under hyperconfluent conditions. Cell sheet thickness increased from an initial 26.7 ± 1.5 μm (day 5 up to 47.7 ± 3.0 μm (day 10. Moreover, rBMSC sheets maintained their potential of osteogenic, adipogenic, and chondrogenic differentiation. This study provides a new strategy to obtain rBMSC sheets using light-induced cell sheet technology.

  7. Investments of Banks in Securities: the Essence and Development Trends under Current Conditions

    Directory of Open Access Journals (Sweden)

    Ekaterina Vladimirovna Mazikova

    2015-12-01

    Full Text Available The implementation of modern banking activities involves the realization of investments. Investment is a complex discussion economic category, characterized by a number of features. The types and forms of investment are manifold and can be transformed with account of the state of the economy and the level of development of industrial relations. The faster growth of the financial sector in the economy has stipulated the development of financial investment. Banks as financial and lending institutions actively make financial investments in securities. Banks’ investment in securities pursues a number of purposes which determine the selection of securities for investment and their quality. The article identified the targets of bank investments in securities and their development trends under current conditions on the basis of the analysis of the actual data for 2010–2014. Negative revaluation and the actual decrease in the value of corporate securities of Russian issuers reduce their commercial appeal. Banks refuse to speculate on the stock market in favor of the securities that ensure liquidity. Banks’ investments aim to purchasing securities from the Lombard List of the Bank of Russia in order to obtain loans and participate in the repo transactions. Thus, during the analyzed period, banks’ investments in securities transformed from systemically important assets that generate substantial profit into the mechanism that provides liquidity. It should be noted that a significant part of investment resources of Russian banks services the debt obligations of Russia’s Government. The article also identified a trend of banks’ increasing investment in the participation portfolios of subsidiaries and associated joint stock companies. The official data of the Central Bank of the Russian Federation (Bank of Russia [15], and the Federal State Statistics Service [14] were used as the information base for the study

  8. Prospective estimation of organ dose in CT under tube current modulation

    International Nuclear Information System (INIS)

    Tian, Xiaoyu; Li, Xiang; Segars, W. Paul; Frush, Donald P.; Samei, Ehsan

    2015-01-01

    Purpose: Computed tomography (CT) has been widely used worldwide as a tool for medical diagnosis and imaging. However, despite its significant clinical benefits, CT radiation dose at the population level has become a subject of public attention and concern. In this light, optimizing radiation dose has become a core responsibility for the CT community. As a fundamental step to manage and optimize dose, it may be beneficial to have accurate and prospective knowledge about the radiation dose for an individual patient. In this study, the authors developed a framework to prospectively estimate organ dose for chest and abdominopelvic CT exams under tube current modulation (TCM). Methods: The organ dose is mainly dependent on two key factors: patient anatomy and irradiation field. A prediction process was developed to accurately model both factors. To model the anatomical diversity and complexity in the patient population, the authors used a previously developed library of computational phantoms with broad distributions of sizes, ages, and genders. A selected clinical patient, represented by a computational phantom in the study, was optimally matched with another computational phantom in the library to obtain a representation of the patient’s anatomy. To model the irradiation field, a previously validated Monte Carlo program was used to model CT scanner systems. The tube current profiles were modeled using a ray-tracing program as previously reported that theoretically emulated the variability of modulation profiles from major CT machine manufacturers Li et al., [Phys. Med. Biol. 59, 4525–4548 (2014)]. The prediction of organ dose was achieved using the following process: (1) CTDI vol -normalized-organ dose coefficients (h organ ) for fixed tube current were first estimated as the prediction basis for the computational phantoms; (2) each computation phantom, regarded as a clinical patient, was optimally matched with one computational phantom in the library; (3) to

  9. A model of the plasma flow and current in Saturn's polar ionosphere under conditions of strong Dungey cycle driving

    Directory of Open Access Journals (Sweden)

    C. M. Jackman

    2006-05-01

    Full Text Available We propose a simple model of the flow and currents in Saturn's polar ionosphere. This model is motivated by theoretical reasoning, and guided quantitatively by in situ field and flow data from space missions, ground-based IR Doppler measurements, and Hubble Space Telescope images. The flow pattern consists of components which represent (1 plasma sub-corotation in the middle magnetosphere region resulting from plasma pick-up and radial transport from internal sources; (2 the Vasyliunas-cycle of internal plasma mass-loss down the magnetospheric tail at higher latitudes; and (3 the polar Dungey-cycle flow driven by the solar wind interaction. Upstream measurements of the interplanetary magnetic field (IMF indicate the occurrence of both extended low-field rarefaction intervals with essentially negligible Dungey-cycle flow, and few-day high-field compression regions in which the Dungey-cycle voltage peaks at a few hundred kV. Here we model the latter conditions when the Dungey-cycle is active, advancing on previous axi-symmetric models which may be more directly applicable to quiet conditions. For theoretical convenience the overall flow pattern is constructed by adding together two components - a purely rotational flow similar to previous axi-symmetric models, and a sun-aligned twin vortex representing the dawn-dusk asymmetry effects associated with the Vasyliunas-and Dungey-cycle flows. We calculate the horizontal ionospheric current associated with the flow and the field-aligned current from its divergence. These calculations show that a sheet of upward-directed field-aligned current flows at the boundary of open field lines which is strongly modulated in local-time by the Dungey-cycle flows. We then consider implications of the field-aligned current for magnetospheric electron acceleration and aurorae using two plasma source populations (hot outer magnetospheric electrons and cool dense magnetosheath electrons. Both sources display a

  10. Magnetization switching of a metallic nanomagnet via current-induced surface spin-polarization of an underlying topological insulator

    International Nuclear Information System (INIS)

    Roy, Urmimala; Dey, Rik; Pramanik, Tanmoy; Ghosh, Bahniman; Register, Leonard F.; Banerjee, Sanjay K.

    2015-01-01

    We consider a thermally stable, metallic nanoscale ferromagnet (FM) subject to spin-polarized current injection and exchange coupling from the spin-helically locked surface states of a topological insulator (TI) to evaluate possible non-volatile memory applications. We consider parallel transport in the TI and the metallic FM, and focus on the efficiency of magnetization switching as a function of transport between the TI and the FM. Transport is modeled as diffusive in the TI beneath the FM, consistent with the mobility in the TI at room temperature, and in the FM, which essentially serves as a constant potential region albeit spin-dependent except in the low conductivity, diffusive limit. Thus, it can be captured by drift-diffusion simulation, which allows for ready interpretation of the results. We calculate switching time and energy consumed per write operation using self-consistent transport, spin-transfer-torque (STT), and magnetization dynamics calculations. Calculated switching energies and times compare favorably to conventional spin-torque memory schemes for substantial interlayer conductivity. Nevertheless, we find that shunting of current from the TI to a metallic nanomagnet can substantially limit efficiency. Exacerbating the problem, STT from the TI effectively increases the TI resistivity. We show that for optimum performance, the sheet resistivity of the FM layer should be comparable to or larger than that of the TI surface layer. Thus, the effective conductivity of the FM layer becomes a critical design consideration for TI-based non-volatile memory

  11. Ice sheet hydrology - a review

    International Nuclear Information System (INIS)

    Jansson, Peter; Naeslund, Jens-Ove; Rodhe, Lars

    2007-03-01

    This report summarizes the theoretical knowledge on water flow in and beneath glaciers and ice sheets and how these theories are applied in models to simulate the hydrology of ice sheets. The purpose is to present the state of knowledge and, perhaps more importantly, identify the gaps in our understanding of ice sheet hydrology. Many general concepts in hydrology and hydraulics are applicable to water flow in glaciers. However, the unique situation of having the liquid phase flowing in conduits of the solid phase of the same material, water, is not a commonly occurring phenomena. This situation means that the heat exchange between the phases and the resulting phase changes also have to be accounted for in the analysis. The fact that the solidus in the pressure-temperature dependent phase diagram of water has a negative slope provides further complications. Ice can thus melt or freeze from both temperature and pressure variations or variations in both. In order to provide details of the current understanding of water flow in conjunction with deforming ice and to provide understanding for the development of ideas and models, emphasis has been put on the mathematical treatments, which are reproduced in detail. Qualitative results corroborating theory or, perhaps more often, questioning the simplifications made in theory, are also given. The overarching problem with our knowledge of glacier hydrology is the gap between the local theories of processes and the general flow of water in glaciers and ice sheets. Water is often channelized in non-stationary conduits through the ice, features which due to their minute size relative to the size of glaciers and ice sheets are difficult to incorporate in spatially larger models. Since the dynamic response of ice sheets to global warming is becoming a key issue in, e.g. sea-level change studies, the problems of the coupling between the hydrology of an ice sheet and its dynamics is steadily gaining interest. New work is emerging

  12. Ice sheet hydrology - a review

    Energy Technology Data Exchange (ETDEWEB)

    Jansson, Peter; Naeslund, Jens-Ove [Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden); Rodhe, Lars [Geological Survey of Sweden, Uppsala (Sweden)

    2007-03-15

    This report summarizes the theoretical knowledge on water flow in and beneath glaciers and ice sheets and how these theories are applied in models to simulate the hydrology of ice sheets. The purpose is to present the state of knowledge and, perhaps more importantly, identify the gaps in our understanding of ice sheet hydrology. Many general concepts in hydrology and hydraulics are applicable to water flow in glaciers. However, the unique situation of having the liquid phase flowing in conduits of the solid phase of the same material, water, is not a commonly occurring phenomena. This situation means that the heat exchange between the phases and the resulting phase changes also have to be accounted for in the analysis. The fact that the solidus in the pressure-temperature dependent phase diagram of water has a negative slope provides further complications. Ice can thus melt or freeze from both temperature and pressure variations or variations in both. In order to provide details of the current understanding of water flow in conjunction with deforming ice and to provide understanding for the development of ideas and models, emphasis has been put on the mathematical treatments, which are reproduced in detail. Qualitative results corroborating theory or, perhaps more often, questioning the simplifications made in theory, are also given. The overarching problem with our knowledge of glacier hydrology is the gap between the local theories of processes and the general flow of water in glaciers and ice sheets. Water is often channelized in non-stationary conduits through the ice, features which due to their minute size relative to the size of glaciers and ice sheets are difficult to incorporate in spatially larger models. Since the dynamic response of ice sheets to global warming is becoming a key issue in, e.g. sea-level change studies, the problems of the coupling between the hydrology of an ice sheet and its dynamics is steadily gaining interest. New work is emerging

  13. Strain reduced critical current in Bi-2223/Ag superconductors under axial tension and compression

    International Nuclear Information System (INIS)

    Haken, B. ten; Godeke, A.; Kate, H.H.J. ten

    1997-01-01

    The critical current of Ag sheathed Bi(Pb)SrCaCuO-2223 tape conductors is investigated as a function of various strain components. A reduction of the critical current occurs due to both tensile or a compressive strain. The critical current reduction is qualitatively similar with the results as observed in Bi-2212 conductors. An axial compression leads to an immediate critical current reduction. The critical current in an axially elongated sample remains nearly constant up to a certain limit typically close to 0.3% strain. For a larger elongation the critical current reduces rapidly. A transverse pressure acting on the tape surface leads also to an irreversible critical current reduction. This behavior is compared with the influence of an axial compression with an effective Young's modulus. The deformation induced critical current reductions in Bi-2223 conductors can be described by a model that is already proposed for Bi-2212 conductors. This model is based on the irreversible nature of the critical current reduction due to a certain deformation

  14. Ammonia-modified graphene sheets decorated with magnetic Fe{sub 3}O{sub 4} nanoparticles for the photocatalytic and photo-Fenton degradation of phenolic compounds under sunlight irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Boruah, Purna K. [Advanced Materials Group, Materials Sciences and Technology Division, CSIR-North East Institute of Science & Technology, Jorhat 785006 (India); Academy of Scientific and Innovative Research (AcSIR) (India); Sharma, Bhagyasmeeta [Advanced Materials Group, Materials Sciences and Technology Division, CSIR-North East Institute of Science & Technology, Jorhat 785006 (India); Karbhal, Indrapal; Shelke, Manjusha V. [Academy of Scientific and Innovative Research (AcSIR) (India); Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune-11008, Maharashtra (India); Das, Manash R., E-mail: mnshrdas@yahoo.com [Advanced Materials Group, Materials Sciences and Technology Division, CSIR-North East Institute of Science & Technology, Jorhat 785006 (India); Academy of Scientific and Innovative Research (AcSIR) (India)

    2017-03-05

    Highlights: • Ammonia-modified graphene sheets decorated with magnetic Fe{sub 3}O{sub 4} nanoparticles. • Photocatalytic and photo-Fenton degradation of phenolic compounds. • An excellent reusability of the nanocomposite was observed up to ten cycles. - Abstract: Synthesis of easily separable and eco-friendly efficient catalyst with both photocatalytic and photo-Fenton degradation properties is of great importance for environment remediation application. Herein, ammonia-modified graphene (AG) sheets decorated with Fe{sub 3}O{sub 4} nanoparticles (AG/Fe{sub 3}O{sub 4}) as a magnetically recoverable photocatalyst by a simple in situ solution chemistry approach. First, we have functionalized graphene oxide (GO) sheets by amide functional group and then Fe{sub 3}O{sub 4} nanoparticles (NPs) are doped onto the functionalized GO surface. The AG/Fe{sub 3}O{sub 4} nanocomposite showed efficient photocatalytic activity towards degradation of phenol (92.43%), 2-nitrophenol (2-NP) (98%) and 2-chlorophenol (2-CP) (97.15%) within 70–120 min. Consequently, in case of photo-Fenton degradation phenomenon, 93.56% phenol, 98.76% 2-NP and 98.06% of 2-CP degradation were achieved within 50–80 min using AG/Fe{sub 3}O{sub 4} nanocomposite under sunlight irradiation. The synergistic effect between amide functionalized graphene and Fe{sub 3}O{sub 4} nanoparticles (NPs) enhances the photocatalytic activity by preventing the recombination rate of electron-hole-pair in Fe{sub 3}O{sub 4} NPs. Furthermore, the remarkable reusability of the AG/Fe{sub 3}O{sub 4} nanocomposite was observed up to ten cycles during the photocatalytic degradation of these phenolic compounds.

  15. Stabilization of Inviscid Vortex Sheets

    Science.gov (United States)

    Protas, Bartosz; Sakajo, Takashi

    2017-11-01

    In this study we investigate the problem of stabilizing inviscid vortex sheets via feedback control. Such models, expressed in terms of the Birkhoff-Rott equation, are often used to describe the Kevin-Helmholtz instability of shear layers and are known to be strongly unstable to small-scale perturbations. First, we consider the linear stability of a straight vortex sheet in the periodic setting with actuation in the form of an array of point vortices or sources located a certain distance away from the sheet. We establish conditions under which this system is controllable and observable. Next, using methods of the linear control theory, we synthesize a feedback control strategy which stabilizes a straight vortex sheet in the linear regime. Given the poor conditioning of the discretized problem, reliable solution of the resulting algebraic Riccati equation requires the use of high-precision arithmetic. Finally, we demonstrate that this control approach also succeeds in the nonlinear regime, provided the magnitude of the initial perturbation is sufficiently small.

  16. Current Control Method for Distributed Generation Power Generation Plants under Grid Fault Conditions

    DEFF Research Database (Denmark)

    Rodriguez, Pedro; Luna, Alvaro; Hermoso, Juan Ramon

    2011-01-01

    The operation of distributed power generation systems under grid fault conditions is a key issue for the massive integration of renewable energy systems. Several studies have been conducted to improve the response of such distributed generation systems under voltage dips. In spite of being less s...

  17. Critical current hysteresis of superconducting proximity-effect bridges under phonon injection

    International Nuclear Information System (INIS)

    Dharmadurai, G.; Ratnam, B.A.

    1979-01-01

    A dc electric current is injected through the transverse normal-metal strip of Ag-Sn proximity-effect bridges to generate phonons which propagate through and further weaken the superconductivity in the proximity-effect-induced weak region by creating quasiparticles (by pair-breaking mechanisms). Consequently a decrease of the critical-current hysteresis is observed in the current-voltage characteristics of these bridges. These results cannot be adequately accounted for by simple heating. Further, we find that Parker's modified heating theory of nonequilibrium superconductors has to be invoked for a qualitative understanding of the observed phenomena

  18. The right to self-determination under international law: The current ...

    African Journals Online (AJOL)

    Nnamdi Azikiwe University Journal of International Law and Jurisprudence. Journal Home · ABOUT THIS JOURNAL · Advanced Search · Current Issue · Archives · Journal Home > Vol 6 (2015) >. Log in or Register to get access to full text downloads.

  19. Surface current dynamics under sea breeze conditions observed by simultaneous HF radar, ADCP and drifter measurements

    Science.gov (United States)

    Sentchev, Alexei; Forget, Philippe; Fraunié, Philippe

    2017-04-01

    Ocean surface boundary layer dynamics off the southern coast of France in the NW Mediterranean is investigated by using velocity observations by high-frequency (HF) radars, surface drifting buoys and a downward-looking drifting acoustic Doppler current profiler (ADCP). The analysis confirms that velocities measured by HF radars correspond to those observed by an ADCP at the effective depth z f = k -1, where k is wavenumber of the radio wave emitted by the radar. The radials provided by the radars were in a very good agreement with in situ measurements, with the relative errors of 1 and 9 % and root mean square (RMS) differences of 0.02 and 0.04 m/s for monostatic and bistatic radar, respectively. The total radar-based velocities appeared to be slightly underestimated in magnitude and somewhat biased in direction. At the end of the survey period, the difference in the surface current direction, based on HF radar and ADCP data, attained 10°. It was demonstrated that the surface boundary layer dynamics cannot be reconstructed successfully without taking into the account velocity variation with depth. A significant misalignment of ˜30° caused by the sea breeze was documented between the HF radar (HFR-derived) surface current and the background current. It was also found that the ocean response to a moderate wind forcing was confined to the 4-m-thick upper layer. The respective Ekman current attained the maximum value of 0.15 m/s, and the current rotation was found to be lagging the wind by approximately 40 min, with the current vector direction being 15-20° to the left of the wind. The range of velocity variability due to wind forcing was found comparable with the magnitude of the background current variability.

  20. Evolution of the MHD sheet pinch

    International Nuclear Information System (INIS)

    Matthaeus, W.H.; Montgomery, D.

    1979-01-01

    A magnetohydrodynamic (MHD) problem of recurrent interest for both astrophysical and laboratory plasmas is the evolution of the unstable sheet pinch, a current sheet across which a dc magnetic field reverses sign. The evolution of such a sheet pinch is followed with a spectral-method, incompressible, two-dimensional, MHD turbulence code. Spectral diagnostics are employed, as are contour plots of vector potential (magnetic field lines), electric current density, and velocity stream function (velocity streamlines). The nonlinear effect which seems most important is seen to be current filamentation: the concentration of the current density onto sets of small measure near a mgnetic X point. A great deal of turbulence is apparent in the current distribution, which, for high Reynolds numbers, requires large spatial grids (greater than or equal to (64) 2 ). 11 figures, 1 table

  1. Steady-state configuration and tension calculations of marine cables under complex currents via separated particle swarm optimization

    Science.gov (United States)

    Xu, Xue-song

    2014-12-01

    Under complex currents, the motion governing equations of marine cables are complex and nonlinear, and the calculations of cable configuration and tension become difficult compared with those under the uniform or simple currents. To obtain the numerical results, the usual Newton-Raphson iteration is often adopted, but its stability depends on the initial guessed solution to the governing equations. To improve the stability of numerical calculation, this paper proposed separated the particle swarm optimization, in which the variables are separated into several groups, and the dimension of search space is reduced to facilitate the particle swarm optimization. Via the separated particle swarm optimization, these governing nonlinear equations can be solved successfully with any initial solution, and the process of numerical calculation is very stable. For the calculations of cable configuration and tension of marine cables under complex currents, the proposed separated swarm particle optimization is more effective than the other particle swarm optimizations.

  2. Control Strategy for Three-Phase Grid-Connected PV Inverters Enabling Current Limitation Under Unbalanced Faults

    DEFF Research Database (Denmark)

    Afshari, Ehsan; Moradi, Gholam Reza; Rahimi, Ramin

    2017-01-01

    Power quality and voltage control are among the most important aspects of the grid-connected power converter operation under faults. Non-sinusoidal current is injected during unbalanced voltage sag and active or/and reactive power includes double frequency content. This paper introduces a novel...... control strategy to mitigate the double grid frequency oscillations in the active power and dc-link voltage of the two-stage three-phase grid-connected Photovoltaic (PV) inverters during unbalanced faults. With the proposed control method, PV inverter injects sinusoidal currents under unbalanced grid...... faults. In addition, an efficient and easy-to-implement current limitation method is introduced, which can effectively limit the injected currents to the rated value during faults. In this case, the fault-ride-through operation is ensured and it will not trigger the overcurrent protection. A non...

  3. Uncertainties in predicting rice yield by current crop models under a wide range of climatic conditions

    NARCIS (Netherlands)

    Li, T.; Hasegawa, T.; Yin, X.; Zhu, Y.; Boote, K.; Adam, M.; Bregaglio, S.; Buis, S.; Confalonieri, R.; Fumoto, T.; Gaydon, D.; Marcaida III, M.; Nakagawa, H.; Oriol, P.; Ruane, A.C.; Ruget, F.; Singh, B.; Singh, U.; Tang, L.; Yoshida, H.; Zhang, Z.; Bouman, B.

    2015-01-01

    Predicting rice (Oryza sativa) productivity under future climates is important for global food security. Ecophysiological crop models in combination with climate model outputs are commonly used in yield prediction, but uncertainties associated with crop models remain largely unquantified. We

  4. Flexible Power Regulation and Current-limited Control of Grid-connected Inverter under Unbalanced Grid Voltage Faults

    DEFF Research Database (Denmark)

    Guo, Xiaoqiang; Liu, Wenzhao; Lu, Zhigang

    2017-01-01

    The grid-connected inverters may experience excessive current stress in case of unbalanced grid voltage Fault Ride Through (FRT), which significantly affects the reliability of the power supply system. In order to solve the problem, the inherent mechanisms of the excessive current phenomenon...... of improving the system reliability under grid faults. Finally, the simulation and experiments of traditional and proposed FRT solutions are carried out. The results verify the effectiveness of the proposed method....

  5. Ice sheet in peril

    DEFF Research Database (Denmark)

    Hvidberg, Christine Schøtt

    2016-01-01

    Earth's large ice sheets in Greenland and Antarctica are major contributors to sea level change. At present, the Greenland Ice Sheet (see the photo) is losing mass in response to climate warming in Greenland (1), but the present changes also include a long-term response to past climate transitions...

  6. Final Report. Coupled simulations of Antarctic Ice-sheet/ocean interactions using POP and CISM

    Energy Technology Data Exchange (ETDEWEB)

    Asay-Davis, Xylar Storm [Potsdam Institute for Climate Impact Research, Potdam (Germany)

    2015-12-30

    The project performed under this award, referred to from here on as CLARION (CoupLed simulations of Antarctic Ice-sheet/Ocean iNteractions), included important advances in two models of ice sheet and ocean interactions. Despite its short duration (one year), the project made significant progress on its three major foci. First, together with collaborator Daniel Martin at Lawrence Berkeley National Laboratory (LBNL), I developed the POPSICLES coupled ice sheet-ocean model to the point where it could perform a number of pan-Antarctic simulations under various forcing conditions. The results were presented at a number of major conferences and workshops worldwide, and are currently being incorporated into two manuscripts in preparation.

  7. Suppressed magnetism in Ca2RuO4 under applied electric currents

    Science.gov (United States)

    Bertinshaw, Joel; Gurung, Namrata; Krautloher, Maximilian; Jain, Anil; Porras, Juan; Fabelo Rosa, Oscar; Kim, Bj; Keimer, Bernhard

    The 4 d -electron system Ca2RuO4 plays host to an exciting interplay between spin-orbit coupling and electronic correlation energies that gives rise to exotic ground states and a high sensitivity to external perturbation. Isovalent Sr-doping, hydrostatic pressure and even applied electric currents can induce dramatic changes in the exhibited electronic and magnetic properties. Here, we use single crystal neutron diffraction with in-situ applied electric currents to show that a previously identified current induced metal-insulator transition is linked to a modified distortion of the RuO6 octahedra and a concomitant suppression of antiferromagnetic order. These results indicate a close correlation among the crystal lattice, electronic, and magnetic structures.

  8. Climate Analogues Suggest Limited Potential for Intensification of Production on Current Croplands Under Climate Change

    Science.gov (United States)

    Pugh, T. A. M.; Mueller, C.; Elliott, J.; Deryng, D.; Folberth, C.; Olin, S.; Schmid, E.; Arneth, A.

    2016-01-01

    Climate change could pose a major challenge to efforts towards strongly increase food production over the coming decades. However, model simulations of future climate-impacts on crop yields differ substantially in the magnitude and even direction of the projected change. Combining observations of current maximum-attainable yield with climate analogues, we provide a complementary method of assessing the effect of climate change on crop yields. Strong reductions in attainable yields of major cereal crops are found across a large fraction of current cropland by 2050. These areas are vulnerable to climate change and have greatly reduced opportunity for agricultural intensification. However, the total land area, including regions not currently used for crops, climatically suitable for high attainable yields of maize, wheat and rice is similar by 2050 to the present-day. Large shifts in land-use patterns and crop choice will likely be necessary to sustain production growth rates and keep pace with demand.

  9. Modeling fire-driven deforestation potential in Amazonia under current and projected climate conditions

    NARCIS (Netherlands)

    Le Page, Y.; van der Werf, G.R.; Morton, D.C.; Pereira, J.M.C.

    2010-01-01

    Fire is a widely used tool to prepare deforested areas for agricultural use in Amazonia. Deforestation is currently concentrated in seasonal forest types along the arc of deforestation, where dry-season conditions facilitate burning of clear-felled vegetation. Interior Amazon forests, however, are

  10. Singular twisting moment in a cracked thin plate under an electric current flow and a magnetic field

    International Nuclear Information System (INIS)

    Shindo, Yasuhide; Tamura, Hitoshi

    1988-01-01

    This paper deals with the electromagneto-elastic problem of an elastic conducting thin plate containing a through crack under a uniform electric current flow and a constant magnetic field. The current flow is disturbed by the presence of the crack and a twisting moment is caused by the interaction between the magnetic field and the disturbed current. Two problems concerning the electric current density field and the electromagneto-elastic field are formulated by means of integral transform techniques and reduced to two pairs of dual integral equations. These integral equations are solved exactly, and the singular current densities, the displacement of the crack surface and the singular moments near the crack tip are expressed in closed forms. (author)

  11. Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments

    DEFF Research Database (Denmark)

    Vicca, S.; Bahn, M.; Estiarte, M.

    2014-01-01

    dependencies of SCE. Hence, the most justified answer to the question of whether current moisture responses of SCE can be extrapolated to predict SCE under altered precipitation regimes is 'no' - as based on the most reliable data sets available. We strongly recommend that future experiments focus more...

  12. Galvanic Couple Current and Potential Distribution between a Mg Electrode and 2024-T351 under Droplets Analyzed by Microelectrode Arrays

    Science.gov (United States)

    2015-11-04

    concentration of a given elec- trolyte varies with ambient RH.21–23 As a given deposited hygroscopic salt deliquesces on a surface it will, over time... liquid electrolyte layer. H2 bubbles could be seen to form and move under the salt cap and the magnitude of the cathodic current density on each AA2024

  13. Effect of Doubly Fed Induction GeneratorTidal Current Turbines on Stability of a Distribution Grid under Unbalanced Voltage Conditions

    Directory of Open Access Journals (Sweden)

    Dahai Zhang

    2017-02-01

    Full Text Available This paper analyses the effects of doubly fed induction generator (DFIG tidal current turbines on a distribution grid under unbalanced voltage conditions of the grid. A dynamic model of an electrical power system under the unbalanced network is described in the paper, aiming to compare the system performance when connected with and without DFIG at the same location in a distribution grid. Extensive simulations of investigating the effect of DFIG tidal current turbine on stability of the distribution grid are performed, taking into account factors such as the power rating, the connection distance of the turbine and the grid voltage dip. The dynamic responses of the distribution system are examined, especially its ability to ride through fault events under unbalanced grid voltage conditions. The research has shown that DFIG tidal current turbines can provide a good damping performance and that modern DFIG tidal current power plants, equipped with power electronics and low-voltage ride-through capability, can stay connected to weak electrical grids even under the unbalanced voltage conditions, whilst not reducing system stability.

  14. An Improved Current Controller to ensure the robust performance of grid-connected converters under weak grid conditions

    DEFF Research Database (Denmark)

    Khazraj, Hesam; Silva, Filipe Miguel Faria da; Bak, Claus Leth

    2016-01-01

    Voltage Source Converters (VSCs) operating in very weak grids with low Short Circuit Ratio (SCR) are known to meet stability challenges. This article investigates instability of a grid connected current-controlled converter under weak grid conditions, which is often attributed to the dynamic...

  15. A Review on Current Reference Calculation of Three-Phase Grid-Connected PV Converters under Grid Faults

    DEFF Research Database (Denmark)

    Afshari, Ehsan; Moradi, Gholam Reza; Yang, Yongheng

    2017-01-01

    of the most important issues that should be coped with for a reliable operation of grid-connected converters under unbalanced grid faults. Accordingly, this paper reviews the existing CRC methods and presents a current reference generation method, which can have 16 unique modes. Issues are also investigated...

  16. Rotational hysteresis and eddy current losses in electrical motor stators under non-conventional supply

    International Nuclear Information System (INIS)

    Bottauscio, Oriano.; Canova, Aldo; Chiampi, Mario; Repetto, Maurizio

    2003-01-01

    The magnetic analysis of stators of electrical motors is performed through an innovative 2D finite element formulation that takes into account the effects of eddy currents within the laminations by means of a generalized constitutive relationship also including vector hysteresis. This approach is applied to a deep estimation of magnetic flux distribution and magnetic losses in stator of induction motors supplied by high-frequency sinusoidal or six-step voltage sources

  17. Electronic health records and online medical records: an asset or a liability under current conditions?

    Science.gov (United States)

    Allen-Graham, Judith; Mitchell, Lauren; Heriot, Natalie; Armani, Roksana; Langton, David; Levinson, Michele; Young, Alan; Smith, Julian A; Kotsimbos, Tom; Wilson, John W

    2018-02-01

    Objective The aim of the present study was to audit the current use of medical records to determine completeness and concordance with other sources of medical information. Methods Medical records for 40 patients from each of five Melbourne major metropolitan hospitals were randomly selected (n=200). A quantitative audit was performed for detailed patient information and medical record keeping, as well as data collection, storage and utilisation. Using each hospital's current online clinical database, scanned files and paperwork available for each patient audited, the reviewers sourced as much relevant information as possible within a 30-min time allocation from both the record and the discharge summary. Results Of all medical records audited, 82% contained medical and surgical history, allergy information and patient demographics. All audited discharge summaries lacked at least one of the following: demographics, medication allergies, medical and surgical history, medications and adverse drug event information. Only 49% of records audited showed evidence the discharge summary was sent outside the institution. Conclusions The quality of medical data captured and information management is variable across hospitals. It is recommended that medical history documentation guidelines and standardised discharge summaries be implemented in Australian healthcare services. What is known about this topic? Australia has a complex health system, the government has approved funding to develop a universal online electronic medical record system and is currently trialling this in an opt-out style in the Napean Blue Mountains (NSW) and in Northern Queensland. The system was originally named the personally controlled electronic health record but has since been changed to MyHealth Record (2016). In Victoria, there exists a wide range of electronic health records used to varying degrees, with some hospitals still relying on paper-based records and many using scanned medical records

  18. Structural and phase transformations in zinc and brass wires under heating with high-density current pulse

    Energy Technology Data Exchange (ETDEWEB)

    Pervikov, A. V. [Laboratory of Physical Chemistry of Ultrafine Materials, Institute of Strength Physics and Materials Science, 2/4, pr. Akademicheskii, 634021 Tomsk, Russia and Department of High Voltage Electrophysics and High Current Electronics, Tomsk Polytechnic University, 30 Lenin Avenue, 634050 Tomsk (Russian Federation)

    2016-06-15

    The work is focused on revealing the mechanism of structure and phase transformations in the metal wires under heating with a high-density current pulse (the electric explosion of wires, EEWs). It has been demonstrated on the example of brass and zinc wires that the transition of a current pulse with the density of j ≈ 3.3 × 10{sup 7} A/cm{sup 2} results in homogeneous heating of the crystalline structure of the metal/alloy. It has been determined that under heating with a pulse of high-density current pulse, the electric resistance of the liquid phases of zinc and brass decreases as the temperature increases. The results obtained allow for a conclusion that the presence of the particles of the condensed phase in the expanding products of EEW is the result of overheating instabilities in the liquid metal.

  19. Thermoelectric effects in graphene at high bias current and under microwave irradiation.

    Science.gov (United States)

    Skoblin, Grigory; Sun, Jie; Yurgens, August

    2017-11-14

    We use a split top gate to induce doping of opposite signs in different parts of a graphene field-effect transistor, thereby effectively forming a graphene thermocouple. The thermocouple is sensitive to the electronic temperature in graphene, which can be several hundred kelvin higher than the ambient one at sufficiently high bias current. Combined with the high thermoelectric power of graphene, this allows for i) simple measurements of the electronic temperature and ii) building thermoelectric radiation detectors. A simple prototype graphene thermoelectric detector shows a temperature-independent optical responsivity of around 400 V/W at 94 GHz at temperatures of 4-50 K.

  20. Air Emissions Damages from Municipal Drinking Water Treatment Under Current and Proposed Regulatory Standards.

    Science.gov (United States)

    Gingerich, Daniel B; Mauter, Meagan S

    2017-09-19

    Water treatment processes present intersectoral and cross-media risk trade-offs that are not presently considered in Safe Drinking Water Act regulatory analyses. This paper develops a method for assessing the air emission implications of common municipal water treatment processes used to comply with recently promulgated and proposed regulatory standards, including concentration limits for, lead and copper, disinfection byproducts, chromium(VI), strontium, and PFOA/PFOS. Life-cycle models of electricity and chemical consumption for individual drinking water unit processes are used to estimate embedded NO x , SO 2 , PM 2.5 , and CO 2 emissions on a cubic meter basis. We estimate air emission damages from currently installed treatment processes at U.S. drinking water facilities to be on the order of $500 million USD annually. Fully complying with six promulgated and proposed rules would increase baseline air emission damages by approximately 50%, with three-quarters of these damages originating from chemical manufacturing. Despite the magnitude of these air emission damages, the net benefit of currently implemented rules remains positive. For some proposed rules, however, the promise of net benefits remains contingent on technology choice.

  1. Transcranial alternating current stimulation: A review of the underlying mechanisms and modulation of cognitive processes

    Directory of Open Access Journals (Sweden)

    Christoph S Herrmann

    2013-06-01

    Full Text Available Brain oscillations of different frequencies have been associated with a variety of cognitive functions. Convincing evidence supporting those associations has been provided by studies using intracranial stimulation, pharmacological interventions and lesion studies. The emergence of novel non-invasive brain stimulation techniques like repetitive transcranial magnetic stimulation (rTMS and transcranial alternating current stimulation (tACS now allows to modulate brain oscillations directly. Particularly, tACS offers the unique opportunity to causally link brain oscillations of a specific frequency range to cognitive processes, because it uses sinusoidal currents that are bound to one frequency only. Using tACS allows to modulate brain oscillations and in turn to influence cognitive processes, thereby demonstrating the causal link between the two. Here, we review findings about the physiological mechanism of tACS and studies that have used tACS to modulate basic motor and sensory processes as well as higher cognitive processes like memory, ambiguous perception, and decision making.

  2. The Value of CCS under Current Policy Scenarios: NDCs and Beyond

    Energy Technology Data Exchange (ETDEWEB)

    Davidson, Casie L.; Dahowski, Robert T.; McJeon, Haewon C.; Clarke, Leon E.; Iyer, Gokul C.; Muratori, Matteo

    2017-07-01

    This paper describes preliminary results of analysis using the Global Change Assessment Model (GCAM) to evaluate the potential role of CCS in addressing emissions reduction targets. Scenarios are modelled using the Paris-Increased Ambition (PIA) case developed by Fawcett et al. (2015), and a more aggressive Paris Two-Degree Ambition (P2A) case. Both cases are based upon nationally determined contributions (NDCs) agreed to at the UNFCCC Conference of Parties (COP-21) in December 2015, coupled with additional mitigation effort beyond the 2030 Paris timeframe, through the end of the century. Analysis of CCS deployment and abatement costs under both policy scenarios suggests that, as modelled, having CCS in the technological portfolio could reduce the global cost of addressing emissions reduction targets specified under the policy scenario by trillions of dollars, primarily by enabling a smoother and lower-cost transition to next-generation technologies. Through the end of the century, total global abatement costs associated with the PIA case – with five percent annual reduction in emission intensity and reaching 2.2 degrees by 2100 – are reduced by $15 trillion USD in the scenario where CCS is available to deploy by 2025 and remains available through 2100, reflecting a 47 percent savings in the cost of climate change abatement. Under the more ambitious P2A case, with 8 percent annual reduction in emission intensity and reaching 1.9 degrees by 2100, the availability of CCS reduces global abatement costs by $22 trillion USD through the end of the century, again nearly halving the costs of addressing the policy, relative to achieving the same target using an energy portfolio that does not include CCS. PIA and P2A scenarios with CCS result in 1,250 and 1,580 GtCO2 of global geologic storage by the end of the century, respectively.

  3. Experimental study on magnetically insulated transmission line electrode surface evolution process under MA/cm current density

    International Nuclear Information System (INIS)

    Zhang, PengFei; Qiu, Aici; Hu, Yang; Yang, HaiLiang; Sun, Jiang; Wang, Liangping; Cong, Peitian

    2016-01-01

    The design of high-current density magnetically insulated transmission line (MITL) is a difficult problem of current large-scale Z-pinch device. In particular, a thorough understanding of the MITL electrode surface evolution process under high current density is lacking. On the “QiangGuang-I” accelerator, the load area possesses a low inductance short-circuit structure with a diameter of 2.85 mm at the cathode, and three reflux columns with a diameter of 3 mm and uniformly distributed circumference at the anode. The length of the high density MITL area is 20 mm. A laser interferometer is used to assess and analyze the state of the MITL cathode and anode gap, and their evolution process under high current density. Experimental results indicate that evident current loss is not observed in the current density area at pulse leading edge, and peak when the surface current density reaches MA/cm. Analysis on electrode surface working conditions indicates that when the current leading edge is at 71.5% of the peak, the total evaporation of MITL cathode structure can be realized by energy deposition caused by ohmic heating. The electrode state changes, and diffusion conditions are reflected in the laser interferometer image. The MITL cathode area mainly exists in metal vapor form. The metal vapor density in the cathode central region is higher than the upper limit of laser penetration density (∼4 × 10 21 /cm 3 ), with an expansion velocity of ∼0.96 km/s. The metal vapor density in the electrode outer area may lead to evident distortion of fringes, and its expansion velocity is faster than that in the center area (1.53 km/s).

  4. Fact Sheet: Protection of the Stratospheric Ozone: New Substitute in the Motor Vehicle Air Conditioning Sector under the Significant New Alternatives Policy (SNAP) Program

    Science.gov (United States)

    Under the Significant New Alternatives Policy (SNAP) program, EPA is listing HFO-1234yf as an acceptable substitute for ozone depleting substances (ODS) in motor vehicle air conditioning (MVAC) systems in new cars and other light duty-vehicles and is speci

  5. Effects of heat and water transport on the performance of polymer electrolyte membrane fuel cell under high current density operation

    International Nuclear Information System (INIS)

    Tabuchi, Yuichiro; Shiomi, Takeshi; Aoki, Osamu; Kubo, Norio; Shinohara, Kazuhiko

    2010-01-01

    Key challenges to the acceptance of polymer electrolyte membrane fuel cells (PEMFCs) for automobiles are the cost reduction and improvement in its power density for compactness. In order to get the solution, the further improvement in a fuel cell performance is required. In particular, under higher current density operation, water and heat transport in PEMFCs has considerable effects on the cell performance. In this study, the impact of heat and water transport on the cell performance under high current density was investigated by experimental evaluation of liquid water distribution and numerical validation. Liquid water distribution in MEA between rib and channel area is evaluated by neutron radiography. In order to neglect the effect of liquid water in gas channels and reactant species concentration distribution in the flow direction, the differential cell was used in this study. Experimental results suggested that liquid water under the channel was dramatically changed with rib/channel width. From the numerical study, it is found that the change of liquid water distribution was significantly affected by temperature distribution in MEA between rib and channel area. In addition, not only heat transport but also water transport through the membrane also significantly affected the cell performance under high current density operation.

  6. Anesthesia Fact Sheet

    Science.gov (United States)

    ... Education About NIGMS NIGMS Home > Science Education > Anesthesia Anesthesia Tagline (Optional) Middle/Main Content Area En español ... Version (464 KB) Other Fact Sheets What is anesthesia? Anesthesia is a medical treatment that prevents patients ...

  7. Global ice sheet modeling

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, T.J.; Fastook, J.L. [Univ. of Maine, Orono, ME (United States). Institute for Quaternary Studies

    1994-05-01

    The University of Maine conducted this study for Pacific Northwest Laboratory (PNL) as part of a global climate modeling task for site characterization of the potential nuclear waste respository site at Yucca Mountain, NV. The purpose of the study was to develop a global ice sheet dynamics model that will forecast the three-dimensional configuration of global ice sheets for specific climate change scenarios. The objective of the third (final) year of the work was to produce ice sheet data for glaciation scenarios covering the next 100,000 years. This was accomplished using both the map-plane and flowband solutions of our time-dependent, finite-element gridpoint model. The theory and equations used to develop the ice sheet models are presented. Three future scenarios were simulated by the model and results are discussed.

  8. Global ice sheet modeling

    International Nuclear Information System (INIS)

    Hughes, T.J.; Fastook, J.L.

    1994-05-01

    The University of Maine conducted this study for Pacific Northwest Laboratory (PNL) as part of a global climate modeling task for site characterization of the potential nuclear waste respository site at Yucca Mountain, NV. The purpose of the study was to develop a global ice sheet dynamics model that will forecast the three-dimensional configuration of global ice sheets for specific climate change scenarios. The objective of the third (final) year of the work was to produce ice sheet data for glaciation scenarios covering the next 100,000 years. This was accomplished using both the map-plane and flowband solutions of our time-dependent, finite-element gridpoint model. The theory and equations used to develop the ice sheet models are presented. Three future scenarios were simulated by the model and results are discussed

  9. Structural Biology Fact Sheet

    Science.gov (United States)

    ... beta sheets (blue; thinner, tangled strands). Credit: RCSB Protein Data Bank. Even though proteins are strings of amino acids, ... structure of more than 122,000 proteins. The Protein Data Bank stores these structures and gives scientists access to ...

  10. Sepsis Fact Sheet

    Science.gov (United States)

    ... Education About NIGMS NIGMS Home > Science Education > Sepsis Sepsis Tagline (Optional) Middle/Main Content Area PDF Version ( ... KB) En español Other Fact Sheets What is sepsis? Sepsis is a serious medical condition. It is ...

  11. Respirator Fact Sheet

    Science.gov (United States)

    ... to protect myself, my family, and/or my employees? If available and used correctly, a respirator can ... Respirator Fact Sheet [PDF - 706 KB] Follow NIOSH Facebook Flickr Pinterest Twitter YouTube NIOSH Homepage NIOSH A- ...

  12. Energy information sheets

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-07-01

    The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the public. The Energy Information Sheets was developed to provide general information on various aspects of fuel production, prices, consumption, and capability. Additional information on related subject matter can be found in other Energy Information Administration (EIA) publications as referenced at the end of each sheet.

  13. Higgs pair production with SUSY QCD correction: revisited under current experimental constraints

    Energy Technology Data Exchange (ETDEWEB)

    Han, Chengcheng [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Academia Sinica,Beijing 100190 (China); Ji, Xuanting [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Academia Sinica,Beijing 100190 (China); Institute of Theoretical Physics, College of Applied Science, Beijing University of Technology,Beijing 100124 (China); Wu, Lei [ARC Centre of Excellence for Particle Physics at the Terascale, School of Physics,University of Sydney,Sydney, NSW 2006 (Australia); Wu, Peiwen; Yang, Jin Min [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Academia Sinica,Beijing 100190 (China)

    2014-04-01

    We consider the current experimental constraints on the parameter space of the MSSM and NMSSM. Then in the allowed parameter space we examine the Higgs pair production at the 14 TeV LHC via bb-macron→hh (h is the 125 GeV SM-like Higg boson) with one-loop SUSY QCD correction and compare it with the production via gg→hh. We obtain the following observations: (i) For the MSSM the production rate of bb-macron→hh can reach 50 fb and thus can be competitive with gg→hh, while for the NMSSM bb-macron→hh has a much smaller rate than gg→hh due to the suppression of the hbb-macron coupling; (ii) The SUSY-QCD correction to bb-macron→hh is sizable, which can reach 45% for the MSSM and 15% for the NMSSM within the 1σ region of the Higgs data; (iii) In the heavy SUSY limit (all soft mass parameters become heavy), the SUSY effects decouple rather slowly from the Higgs pair production (especially the gg→hh process), which, for M{sub SUSY}=5 TeV and m{sub A}<1 TeV, can enhance the production rate by a factor of 1.5 and 1.3 for the MSSM and NMSSM, respectively. So, the Higgs pair production may be helpful for unraveling the effects of heavy SUSY.

  14. Cultural aspects of the current Scandinavian identity crisis: The case of Denmark-purity under attack

    Directory of Open Access Journals (Sweden)

    Møller Tine Sørensen

    2012-01-01

    Full Text Available In this article I will attempt to show examples of the cultural manifestations of the identity crisis that is currently sweeping over Scandinavia. What is particular about this crisis is that it seems to have struck on most sides of society, while the “Scandinavian model” of the welfare state is slowly crumbling in the wake of the global financial problems. At the center of both this struggle and crisis is the notion of the Homo Scandinavicus; this seems at the same time a threat to existence (by different enemies, depending on one’s stand in the struggle and contested in its very content. In all Scandinavian countries a so-called “cultural battle” has been articulated and used as heavy artillery when articulating characteristics of either side. It is this battle I will highlight and demonstrate through examples how the “general public” has been taken hostage on this identity battle field. Furthermore, I will give examples of alternative strategies (notably found in the art worlds, and why these have also failed to provide actual functioning alternatives to the leading, rivaling, identity strategies. The nature of this crisis and the ways it manifests itself, are by no means strictly restricted to Scandinavia. Therefore, considerations about manifestations and consequences presents some highly relevant and much more general insights.

  15. Enteric disease surveillance under the AFHSC-GEIS: Current efforts, landscape analysis and vision forward

    Directory of Open Access Journals (Sweden)

    Kasper Matthew R

    2011-03-01

    Full Text Available Abstract The mission of the Armed Forces Health Surveillance Center, Division of Global Emerging Infections Surveillance and Response System (AFHSC-GEIS is to support global public health and to counter infectious disease threats to the United States Armed Forces, including newly identified agents or those increasing in incidence. Enteric diseases are a growing threat to U.S. forces, which must be ready to deploy to austere environments where the risk of exposure to enteropathogens may be significant and where routine prevention efforts may be impractical. In this report, the authors review the recent activities of AFHSC-GEIS partner laboratories in regards to enteric disease surveillance, prevention and response. Each partner identified recent accomplishments, including support for regional networks. AFHSC/GEIS partners also completed a Strengths, Weaknesses, Opportunities and Threats (SWOT survey as part of a landscape analysis of global enteric surveillance efforts. The current strengths of this network include excellent laboratory infrastructure, equipment and personnel that provide the opportunity for high-quality epidemiological studies and test platforms for point-of-care diagnostics. Weaknesses include inconsistent guidance and a splintered reporting system that hampers the comparison of data across regions or longitudinally. The newly chartered Enterics Surveillance Steering Committee (ESSC is intended to provide clear mission guidance, a structured project review process, and central data management and analysis in support of rationally directed enteric disease surveillance efforts.

  16. A computational model of the ionic currents, Ca2+ dynamics and action potentials underlying contraction of isolated uterine smooth muscle.

    Directory of Open Access Journals (Sweden)

    Wing-Chiu Tong

    2011-04-01

    Full Text Available Uterine contractions during labor are discretely regulated by rhythmic action potentials (AP of varying duration and form that serve to determine calcium-dependent force production. We have employed a computational biology approach to develop a fuller understanding of the complexity of excitation-contraction (E-C coupling of uterine smooth muscle cells (USMC. Our overall aim is to establish a mathematical platform of sufficient biophysical detail to quantitatively describe known uterine E-C coupling parameters and thereby inform future empirical investigations of physiological and pathophysiological mechanisms governing normal and dysfunctional labors. From published and unpublished data we construct mathematical models for fourteen ionic currents of USMCs: Ca2+ currents (L- and T-type, Na+ current, an hyperpolarization-activated current, three voltage-gated K+ currents, two Ca2+-activated K+ current, Ca2+-activated Cl current, non-specific cation current, Na+-Ca2+ exchanger, Na+-K+ pump and background current. The magnitudes and kinetics of each current system in a spindle shaped single cell with a specified surface area:volume ratio is described by differential equations, in terms of maximal conductances, electrochemical gradient, voltage-dependent activation/inactivation gating variables and temporal changes in intracellular Ca2+ computed from known Ca2+ fluxes. These quantifications are validated by the reconstruction of the individual experimental ionic currents obtained under voltage-clamp. Phasic contraction is modeled in relation to the time constant of changing [Ca2+]i. This integrated model is validated by its reconstruction of the different USMC AP configurations (spikes, plateau and bursts of spikes, the change from bursting to plateau type AP produced by estradiol and of simultaneous experimental recordings of spontaneous AP, [Ca2+]i and phasic force. In summary, our advanced mathematical model provides a powerful tool to

  17. Optimization of Water Management of Cranberry Fields under Current and Future Climate Conditions

    Science.gov (United States)

    Létourneau, G.; Gumiere, S.; Mailhot, E.; Rousseau, A. N.

    2016-12-01

    In North America, cranberry production is on the rise. Since 2005, land area dedicated to cranberry doubled, principally in Canada. Recent studies have shown that sub-irrigation could lead to improvements in yield, water use efficiency and pumping energy requirements compared to conventional sprinkler irrigation. However, the experimental determination of the optimal water table level of each production site may be expensiveand time-consuming. The primary objective of this study is to optimize the water table level as a function of typical soil properties, and climatic conditions observed in major production areas using a numerical modeling approach. The second objective is to evaluate the impacts of projected climatic conditions on water management of cranberry fields. To that end, cranberry-specific management operations such as harvest flooding, rapid drainage following heavy rainfall, or hydric stress management during dry weather conditions were simulated with the HYDRUS 2D software. Results have shown that maintaining the water table approximately at 60 cm provides optimal results for most of the studied soils. However, under certain extreme climatic conditions, the drainage system design may not allow maintaining optimal hydric conditions for cranberry growth. The long-term benefit of this study has potential to advance the design of drainage/sub-irrigation systems.

  18. The hydroclimatic and ecophysiological basis of cloud forest distributions under current and projected climates.

    Science.gov (United States)

    Oliveira, Rafael S; Eller, Cleiton B; Bittencourt, Paulo R L; Mulligan, Mark

    2014-05-01

    Tropical montane cloud forests (TMCFs) are characterized by a unique set of biological and hydroclimatic features, including frequent and/or persistent fog, cool temperatures, and high biodiversity and endemism. These forests are one of the most vulnerable ecosystems to climate change given their small geographic range, high endemism and dependence on a rare microclimatic envelope. The frequency of atmospheric water deficits for some TMCFs is likely to increase in the future, but the consequences for the integrity and distribution of these ecosystems are uncertain. In order to investigate plant and ecosystem responses to climate change, we need to know how TMCF species function in response to current climate, which factors shape function and ecology most and how these will change into the future. This review focuses on recent advances in ecophysiological research of TMCF plants to establish a link between TMCF hydrometeorological conditions and vegetation distribution, functioning and survival. The hydraulic characteristics of TMCF trees are discussed, together with the prevalence and ecological consequences of foliar uptake of fog water (FWU) in TMCFs, a key process that allows efficient acquisition of water during cloud immersion periods, minimizing water deficits and favouring survival of species prone to drought-induced hydraulic failure. Fog occurrence is the single most important microclimatic feature affecting the distribution and function of TMCF plants. Plants in TMCFs are very vulnerable to drought (possessing a small hydraulic safety margin), and the presence of fog and FWU minimizes the occurrence of tree water deficits and thus favours the survival of TMCF trees where such deficits may occur. Characterizing the interplay between microclimatic dynamics and plant water relations is key to foster more realistic projections about climate change effects on TMCF functioning and distribution.

  19. Weathering of Olivine during Interaction of Sulfate Aerosols with Mars Soil under Current Climate Conditions

    Science.gov (United States)

    Niles, P. B.; Golden, D. C.; Michalski, J. R.; Ming, D. W.

    2017-12-01

    Sulfur concentrations in the Mars soils are elevated above 1 wt% in nearly every location visited by landed spacecraft. This observation was first made by the Viking landers, and has been confirmed by subsequent missions. The wide distribution of sulfur in martian soils has been attributed to volcanic degassing, formation of sulfate aerosols, and later incorporation into martian soils during gravitational sedimentation. However, later discoveries of more concentrated sulfur bearing sediments by the Opportunity rover has led some to believe that sulfates may instead be a product of evaporation and aeolian redistribution. One question that has not been addressed is whether the modern surface conditions are too cold for weathering of volcanic materials by sulfate aerosols. We suggest here that mixtures of atmospheric aerosols, ice, and dust have the potential for creating small films of cryo-concentrated acidic solutions that may represent an important unexamined environment for understanding weathering processes on Mars. Laboratory experiments were conducted to simulate weathering of olivine under Mars-like conditions. The weathering rates measured in this study suggest that fine grained olivine on Mars would weather into sulfate minerals in short time periods if they are exposed to H2SO4 aerosols at temperatures at or above -40°C. In this system, the strength of the acidic solution is maximized through eutectic freezing in an environment where the silicate minerals are extremely fine grained and have high surface areas. This provides an ideal environment for olivine weathering despite the very low temperatures. The likelihood of substantial sulfur-rich volcanism on Mars and creation of abundant sulfate aerosols suggests that this process would have been important during formation of martian soils and sediments. Future work modeling sulfur release rates during volcanic eruptions and aerosol distribution over the surface will help understand how well this process

  20. Plastic flow and failure in single point incremental forming of PVC sheets

    Directory of Open Access Journals (Sweden)

    P. A. F. Martins

    2014-05-01

    Full Text Available This paper presents an innovative and effective methodology to characterize plastic flow and failure in single point incremental forming (SPIF of polymers that allows determining the stresses and the accumulated values of ductile damage directly from the experimental values of strain at various positions over the deformed polymer sheets. The approach traces the deformation path of material elements in conical and pyramidal SPIF parts, undergoing linear strain loading paths from beginning until failure, and is built upon the generalization of the analytical framework conditions assumed by Glover et al. [1] to the pressure-sensitive yield surfaces of polymers under incompressible, non-associated, plastic flow. Experimentation in conventional and multi-stage SPIF of Polyvinylchloride (PVC sheets confirms the effectiveness of the proposed methodology and demonstrates that standard non-coupled damage models currently utilized in sheet metal forming are inapplicable to describe failure in polymers. Instead fracture forming limit lines (FFL’s should be employed.

  1. Injection current dependences of electroluminescence transition energy in InGaN/GaN multiple quantum wells light emitting diodes under pulsed current conditions

    International Nuclear Information System (INIS)

    Zhang, Feng; Ikeda, Masao; Liu, Jianping; Zhang, Shuming; Zhou, Kun; Yang, Hui; Liu, Zongshun

    2015-01-01

    Injection current dependences of electroluminescence transition energy in blue InGaN/GaN multiple quantum wells light emitting diodes (LEDs) with different quantum barrier thicknesses under pulsed current conditions have been analyzed taking into account the related effects including deformation caused by lattice strain, quantum confined Stark effects due to polarization field partly screened by carriers, band gap renormalization, Stokes-like shift due to compositional fluctuations which are supposed to be random alloy fluctuations in the sub-nanometer scale, band filling effect (Burstein-Moss shift), and quantum levels in finite triangular wells. The bandgap renormalization and band filling effect occurring at high concentrations oppose one another, however, the renormalization effect dominates in the concentration range studied, since the band filling effect arising from the filling in the tail states in the valence band of quantum wells is much smaller than the case in the bulk materials. In order to correlate the carrier densities with current densities, the nonradiative recombination rates were deduced experimentally by curve-fitting to the external quantum efficiencies. The transition energies in LEDs both with 15 nm quantum barriers and 5 nm quantum barriers, calculated using full strengths of theoretical macroscopic polarization given by Barnardini and Fiorentini [Phys. Status Solidi B 216, 391 (1999)] are in excellent accordance with experimental results. The LED with 5 nm barriers has been shown to exhibit a higher transition energy and a smaller blue shift than those of LED with 15 nm barriers, which is mainly caused by the smaller internal polarization field in the quantum wells

  2. Injection current dependences of electroluminescence transition energy in InGaN/GaN multiple quantum wells light emitting diodes under pulsed current conditions

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Feng; Ikeda, Masao, E-mail: mikeda2013@sinano.ac.cn; Liu, Jianping; Zhang, Shuming [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Zhou, Kun; Yang, Hui [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Institute of Semiconductors (CAS), Beijing 100083 (China); Liu, Zongshun [Institute of Semiconductors (CAS), Beijing 100083 (China)

    2015-07-21

    Injection current dependences of electroluminescence transition energy in blue InGaN/GaN multiple quantum wells light emitting diodes (LEDs) with different quantum barrier thicknesses under pulsed current conditions have been analyzed taking into account the related effects including deformation caused by lattice strain, quantum confined Stark effects due to polarization field partly screened by carriers, band gap renormalization, Stokes-like shift due to compositional fluctuations which are supposed to be random alloy fluctuations in the sub-nanometer scale, band filling effect (Burstein-Moss shift), and quantum levels in finite triangular wells. The bandgap renormalization and band filling effect occurring at high concentrations oppose one another, however, the renormalization effect dominates in the concentration range studied, since the band filling effect arising from the filling in the tail states in the valence band of quantum wells is much smaller than the case in the bulk materials. In order to correlate the carrier densities with current densities, the nonradiative recombination rates were deduced experimentally by curve-fitting to the external quantum efficiencies. The transition energies in LEDs both with 15 nm quantum barriers and 5 nm quantum barriers, calculated using full strengths of theoretical macroscopic polarization given by Barnardini and Fiorentini [Phys. Status Solidi B 216, 391 (1999)] are in excellent accordance with experimental results. The LED with 5 nm barriers has been shown to exhibit a higher transition energy and a smaller blue shift than those of LED with 15 nm barriers, which is mainly caused by the smaller internal polarization field in the quantum wells.

  3. Minimum quench power dissipation and current non-uniformity in international thermonuclear experimental reactor type NbTi cable-in-conduit conductor samples under direct current conditions

    Science.gov (United States)

    Rolando, G.; van Lanen, E. P. A.; Nijhuis, A.

    2012-05-01

    The level of current non-uniformity in NbTi cable-in-conduit conductors (CICCs) sections near the joints in combination with the magnetic field profile needs attention in view of proper joint design. The strand joule power and current distribution at quench under DC conditions of two samples of ITER poloidal field coil conductors, as tested in the SULTAN facility, and of the so called PFCI model coil insert, have been analyzed with the numerical cable model JackPot. The precise trajectories of all individual strands, joint design, cabling configuration, spatial distribution of the magnetic field, sample geometry, and experimentally determined interstrand resistance distributions have been taken into account. Although unable to predict the quench point due to the lack of a thermal-hydraulic routine, the model allows to assess the instantaneous strand power at quench and its local distribution in the cable once the quench conditions in terms of current and temperature are experimentally known. The analysis points out the relation of the above mentioned factors with the DC quench stability of both short samples and coils. The possible small scale and local electrical-thermal interactions were ignored in order to examine the relevance of such effects in the overall prediction of the CICC performance. The electromagnetic code shows an excellent quantitative predictive potential for CICC transport properties, excluding any freedom for matching the results. The influence of the local thermal effects in the modeling is identified as being marginal and far less than the generally accepted temperature margin for safe operation.

  4. Public health argument to retain current UK national controls for tick and tapeworms under the Pet Travel Scheme.

    Science.gov (United States)

    Gover, L; Kirkbride, H; Morgan, D

    2011-02-01

    At present, the European Council is debating whether the current national controls under the Pet Travel Scheme (PETS), which aims to prevent the introduction of rabies and tapeworms or live ticks and their associated diseases into the United Kingdom (UK), should be harmonized amongst European Union (EU) Member States. There is a strong case to support the retention of control measures on human health grounds. Although many are aware of the implications of rabies infection, few realize the risk to the UK population if current tick and tapeworm controls under PETS were to be removed. If this were to occur, there is a risk that a number of diseases of human health importance may be introduced and become established in the UK. Such diseases include alveolar echinococcosis, tick borne encephalitis, tularaemia and Mediterranean spotted fever; all of which are found in other EU Member States but do not occur in the UK. These four diseases are responsible for a significant burden of disease in Europe, and current national controls under PETS have been highly effective in so far preventing their introduction into the UK. © 2009 Blackwell Verlag GmbH.

  5. Characteristic Analysis and Fault-Tolerant Control of Circulating Current for Modular Multilevel Converters under Sub-Module Faults

    Directory of Open Access Journals (Sweden)

    Wen Wu

    2017-11-01

    Full Text Available A modular multilevel converter (MMC is considered to be a promising topology for medium- or high-power applications. However, a significantly increased amount of sub-modules (SMs in each arm also increase the risk of failures. Focusing on the fault-tolerant operation issue for the MMC under SM faults, the operation characteristics of MMC with different numbers of faulty SMs in the arms are analyzed and summarized in this paper. Based on the characteristics, a novel circulating current-suppressing (CCS fault-tolerant control strategy comprised of a basic control unit (BCU and virtual resistance compensation control unit (VRCCU in two parts is proposed, which has three main features: (i it can suppress the multi-different frequency components of the circulating current under different SM fault types simultaneously; (ii it can help fast limiting of the transient fault current caused at the faulty SM bypassed moment; and (iii it does not need extra communication systems to acquire the information of the number of faulty SMs. Moreover, by analyzing the stability performance of the proposed controller using the Root-Locus criterion, the election principle of the value of virtual resistance is revealed. Finally, the efficiency of the control strategy is confirmed with the simulation and experiment studies under different fault conditions.

  6. Balance control of grid currents for UPQC under unbalanced loads based on matching-ratio compensation algorithm

    DEFF Research Database (Denmark)

    Zhao, Xiaojun; Zhang, Chunjiang; Chai, Xiuhui

    2018-01-01

    In three-phase four-wire systems, unbalanced loads can cause grid currents to be unbalanced, and this may cause the neutral point potential on the grid side to shift. The neutral point potential shift will worsen the control precision as well as the performance of the threephase four-wire unified...... power quality conditioner (UPQC), and it also leads to unbalanced three-phase output voltage, even causing damage to electric equipment. To deal with unbalanced loads, this paper proposes a matching-ratio compensation algorithm (MCA) for the fundamental active component of load currents......, and by employing this MCA, balanced three-phase grid currents can be realized under 100% unbalanced loads. The steady-state fluctuation and the transient drop of the DC bus voltage can also be restrained. This paper establishes the mathematical model of the UPQC, analyzes the mechanism of the DC bus voltage...... fluctuations, and elaborates the interaction between unbalanced grid currents and DC bus voltage fluctuations; two control strategies of UPQC under three-phase stationary coordinate based on the MCA are given, and finally, the feasibility and effectiveness of the proposed control strategy are verified...

  7. Spot welding of aluminium alloy sheets to coated steel sheets. Kakushu mekki koban to arumi gokin no spot yosetsusei

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, S.; Fukumura, K.; Soga, S. (Nisshin Steel Co. Ltd., Tokyo (Japan))

    1994-03-31

    Welding aluminum alloy sheets with coated steel sheets has become used frequently in association with weight reduction in automobiles. This paper describes investigations on the effects of spot welding aluminum alloy sheets with different kinds of coated steel sheets on optimal welding conditions and weld strength. An AC single-phase spot welding machine was used for an experiment using an aluminum alloy(5052)with a thickness of 1 mm(referred to as A)and different coated steel sheets with a thickness of 0.8 mm(referred to as B). The result may be summarized as follows: the weldable value of the electric current is closer to that for between the B steel sheets than the middle of that for between the As and between Bs; while the weldable current range is affected little by the coating materials when a CF electrode is used, it grows greater in aluminum coated steel sheets and hot-dip galvanized steel sheets than in alloyed hot-dip galvanized steel sheets and cold-rolled steel sheets when an R-type electrode is used; influence of the coating materials was observed in tensile shear strength and cross tensile shear strength; and any combination of metals shows fatigue strength lower than that in the A-A combination in a fatigue test of cross tensile system. 5 refs., 12 figs., 6 tabs.

  8. Precipitation Cluster Distributions: Current Climate Storm Statistics and Projected Changes Under Global Warming

    Science.gov (United States)

    Quinn, Kevin Martin

    The total amount of precipitation integrated across a precipitation cluster (contiguous precipitating grid cells exceeding a minimum rain rate) is a useful measure of the aggregate size of the disturbance, expressed as the rate of water mass lost or latent heat released, i.e. the power of the disturbance. Probability distributions of cluster power are examined during boreal summer (May-September) and winter (January-March) using satellite-retrieved rain rates from the Tropical Rainfall Measuring Mission (TRMM) 3B42 and Special Sensor Microwave Imager and Sounder (SSM/I and SSMIS) programs, model output from the High Resolution Atmospheric Model (HIRAM, roughly 0.25-0.5 0 resolution), seven 1-2° resolution members of the Coupled Model Intercomparison Project Phase 5 (CMIP5) experiment, and National Center for Atmospheric Research Large Ensemble (NCAR LENS). Spatial distributions of precipitation-weighted centroids are also investigated in observations (TRMM-3B42) and climate models during winter as a metric for changes in mid-latitude storm tracks. Observed probability distributions for both seasons are scale-free from the smallest clusters up to a cutoff scale at high cluster power, after which the probability density drops rapidly. When low rain rates are excluded by choosing a minimum rain rate threshold in defining clusters, the models accurately reproduce observed cluster power statistics and winter storm tracks. Changes in behavior in the tail of the distribution, above the cutoff, are important for impacts since these quantify the frequency of the most powerful storms. End-of-century cluster power distributions and storm track locations are investigated in these models under a "business as usual" global warming scenario. The probability of high cluster power events increases by end-of-century across all models, by up to an order of magnitude for the highest-power events for which statistics can be computed. For the three models in the suite with continuous

  9. Ice sheet hydrology from observations

    Energy Technology Data Exchange (ETDEWEB)

    Jansson, Peter (Dept. of Physical Geography and Quaternary Geology, Stockholm Univ-, Stockholm (Sweden))

    2010-11-15

    possible that soft beds through their ability to deform and be eroded can yield quasi-stable patterns of drainage pathways that with either erosion of critical sills or filling of temporary basins may reorganize itself periodically on time scales much shorter than the reorganization of the driving stresses for ice flow. In areas where the surface generated water (melt and rain), the basally generated fluxes dwarf the influx from the surface and hence the drainage system in such areas will be dominated by surface fluxes and variations therein. Since surface fluxes have a strong seasonal variation with no influx during winter, areas experiencing surface influx will also be subject to large seasonal variations in both flux and pressure. In addition, during the melt season, fluxes and also pressures will also vary on diurnal as well as longer time frames in response to variations in air temperature that drives melt and occurrence of precipitation events. The emerging picture of glacier drainage consists of different types of models applicable to different regimes found beneath an ice sheet (with our without surface influx, ice streams, subglacial lakes). It is not, however, clear how these systems are coupled, or even if they are. This makes it inherently difficult to assess what can be expected beneath a given sector of an ice sheet without some detailed understanding of the underlying geology (geothermal fluxes), geomorphology (possible water routing) and ice properties (cold -temperate base and ice thickness)

  10. Buckling Behavior of Substrate Supported Graphene Sheets

    Directory of Open Access Journals (Sweden)

    Kuijian Yang

    2016-01-01

    Full Text Available The buckling of graphene sheets on substrates can significantly degrade their performance in materials and devices. Therefore, a systematic investigation on the buckling behavior of monolayer graphene sheet/substrate systems is carried out in this paper by both molecular mechanics simulations and theoretical analysis. From 70 simulation cases of simple-supported graphene sheets with different sizes under uniaxial compression, two different buckling modes are investigated and revealed to be dominated by the graphene size. Especially, for graphene sheets with length larger than 3 nm and width larger than 1.1 nm, the buckling mode depends only on the length/width ratio. Besides, it is revealed that the existence of graphene substrate can increase the critical buckling stress and strain to 4.39 N/m and 1.58%, respectively, which are about 10 times those for free-standing graphene sheets. Moreover, for graphene sheets with common size (longer than 20 nm, both theoretical and simulation results show that the critical buckling stress and strain are dominated only by the adhesive interactions with substrate and independent of the graphene size. Results in this work provide valuable insight and guidelines for the design and application of graphene-derived materials and nano-electromechanical systems.

  11. Buckling Behavior of Substrate Supported Graphene Sheets.

    Science.gov (United States)

    Yang, Kuijian; Chen, Yuli; Pan, Fei; Wang, Shengtao; Ma, Yong; Liu, Qijun

    2016-01-07

    The buckling of graphene sheets on substrates can significantly degrade their performance in materials and devices. Therefore, a systematic investigation on the buckling behavior of monolayer graphene sheet/substrate systems is carried out in this paper by both molecular mechanics simulations and theoretical analysis. From 70 simulation cases of simple-supported graphene sheets with different sizes under uniaxial compression, two different buckling modes are investigated and revealed to be dominated by the graphene size. Especially, for graphene sheets with length larger than 3 nm and width larger than 1.1 nm, the buckling mode depends only on the length/width ratio. Besides, it is revealed that the existence of graphene substrate can increase the critical buckling stress and strain to 4.39 N/m and 1.58%, respectively, which are about 10 times those for free-standing graphene sheets. Moreover, for graphene sheets with common size (longer than 20 nm), both theoretical and simulation results show that the critical buckling stress and strain are dominated only by the adhesive interactions with substrate and independent of the graphene size. Results in this work provide valuable insight and guidelines for the design and application of graphene-derived materials and nano-electromechanical systems.

  12. Time evolution of secondary electron emission and trapped charge accumulation in polyimide film under various primary electron irradiation currents

    Energy Technology Data Exchange (ETDEWEB)

    Song, Bai-Peng; Zhou, Run-Dong; Su, Guo-Qiang [State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi ’ an Jiaotong University, Xi ’ an, Shaanxi 710049 (China); Mu, Hai-Bao, E-mail: haibaomu@xjtu.edu.cn [State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi ’ an Jiaotong University, Xi ’ an, Shaanxi 710049 (China); Zhang, Guan-Jun, E-mail: gjzhang@xjtu.edu.cn [State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi ’ an Jiaotong University, Xi ’ an, Shaanxi 710049 (China); Bu, Ren-An [School of Electronic and Information Engineering, Xi ’ an Jiaotong University, Xi ’ an, Shaanxi 710049 (China)

    2016-12-30

    Highlights: • Time resolved evolution of secondary electron emission and trapped charge accumulation in PI film is described. • The time constant is characterized as a function of incident current. • Evolution of SEY σ and trapped charge is dependent on incident dose but not the incident rate. • Trap density and capture cross section are discussed. - Abstract: Time-resolved evolution of secondary electron emission and trapped charge accumulation in polyimide film is investigated during two interval electrons bombardment, derived from the measurement of displacement current and secondary current via a hemispherical detector with the shielded grid. Under various irradiation current, secondary electron yield (SEY σ) at a certain injected energy decreases exponentially from initial amplitude σ{sub 0} to self-consistent steady value σ{sup ∞} close to 0.93. The time constant τ of charging process is characterized as a function of incident current I{sub p}, and the results indicate that the formula I{sub p} × τ is fitted by a hyperbolical law. The influence of I{sub p} on the amount of trapped charge is studied and no significant change in its saturation value is observed. The evolution of SEY σ and trapped charge is dependent on incident dose Q{sub p} but not the incident rate I{sub p}. Furthermore, the trap density and capture cross section are discussed.

  13. Experimental and analytical study on vibration control effects of eddy-current tuned mass dampers under seismic excitations

    Science.gov (United States)

    Lu, Zheng; Huang, Biao; Zhang, Qi; Lu, Xilin

    2018-05-01

    Eddy-current tuned mass dampers (EC-TMDs) are non-contacting passive control devices and are developed on the basis of conventional tuned mass dampers. They comprise a solid mass, a stiffness element, and a damping element, wherein the damping mechanism originates from eddy currents. By relative motion between a non-magnetic conductive metal and a permanent magnet in a dynamic system, a time-varying magnetic field is induced in the conductor, thereby generating eddy currents. The eddy currents induce a magnetic field with opposite polarity, causing repulsive forces, i.e., damping forces. This technology can overcome the drawbacks of conventional tuned mass dampers, such as limited service life, deterioration of mechanical properties, and undesired additional stiffness. The experimental and analytical study of this system installed on a multi-degree-of-freedom structure is presented in this paper. A series of shaking table tests were conducted on a five-story steel-frame model with/without an EC-TMD to evaluate the effectiveness and performance of the EC-TMD in suppressing the vibration of the model under seismic excitations. The experimental results show that the EC-TMD can effectively reduce the displacement response, acceleration response, interstory drift ratio, and maximum strain of the columns under different earthquake excitations. Moreover, an analytical method was proposed on the basis of electromagnetic and structural dynamic theories. A comparison between the test and simulation results shows that the simulation method can be used to estimate the response of structures with an EC-TMD under earthquake excitations with acceptable accuracy.

  14. Modeling and mapping the current and future distribution of Pseudomonas syringae pv. actinidiae under climate change in China.

    Science.gov (United States)

    Wang, Rulin; Li, Qing; He, Shisong; Liu, Yuan; Wang, Mingtian; Jiang, Gan

    2018-01-01

    Bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae (Psa) is a major threat to the kiwifruit industry throughout the world and accounts for substantial economic losses in China. The aim of the present study was to test and explore the possibility of using MaxEnt (maximum entropy models) to predict and analyze the future large-scale distribution of Psa in China. Based on the current environmental factors, three future climate scenarios, which were suggested by the fifth IPCC report, and the current distribution sites of Psa, MaxEnt combined with ArcGIS was applied to predict the potential suitable areas and the changing trend of Psa in China. The jackknife test and correlation analysis were used to choose dominant climatic factors. The receiver operating characteristic curve (ROC) drawn by MaxEnt was used to evaluate the accuracy of the simulation. The results showed that under current climatic conditions, the area from latitude 25° to 36°N and from longitude 101° to 122°E is the primary potential suitable area of Psa in China. The highly suitable area (with suitability between 66 and 100) was mainly concentrated in Northeast Sichuan, South Shaanxi, most of Chongqing, West Hubei and Southwest Gansu and occupied 4.94% of land in China. Under different future emission scenarios, both the areas and the centers of the suitable areas all showed differences compared with the current situation. Four climatic variables, i.e., maximum April temperature (19%), mean temperature of the coldest quarter (14%), precipitation in May (11.5%) and minimum temperature in October (10.8%), had the largest impact on the distribution of Psa. The MaxEnt model is potentially useful for forecasting the future adaptive distribution of Psa under climate change, and it provides important guidance for comprehensive management.

  15. Dipole-sheet multipole magnets for accelerators

    International Nuclear Information System (INIS)

    Walstrom, P.L.

    1993-01-01

    The dipole-sheet formalism can be used to describe both cylindrical current-sheet multipole magnets and cylindrical-bore magnets made up of permanent magnet blocks. For current sheets, the formalism provides a natural way of finding a finite set of turns that approximate a continuous distribution. The formalism is especially useful In accelerator applications where large-bore, short, high-field-quality magnets that are dominated by fringe fields are needed. A further advantage of the approach is that in systems with either open or cylindrically symmetric magnetic boundaries, analytical expressions for the three-dimensional fields that are suitable for rapid numerical evaluation can be derived. This development is described in some detail. Also, recent developments in higher-order particle-beam optics codes based on the formalism are described briefly

  16. Flux-pinning-induced stress and magnetostriction in a superconducting strip under combination of transport current and magnetic field

    Science.gov (United States)

    Yang, Yumei; Wang, Xingzhe

    2017-09-01

    The magnetoelastic properties and behaviors arising from the flux-pinning effect are investigated for a long rectangular superconducting strip subject to a combination of applied transport current and magnetic field. Based on the Bean critical state model and linear elastic theory, the flux-pinning-induced stress in the superconducting strip is analytically obtained under the zero-field cooling condition. In particular, the magnetostriction performance for the strip with a one-sided restraint condition is then investigated. The results show that the trapped magnetic flux is distributed asymmetrically along the y-direction. A non-zero resultant force is consequently observed from the magnetization arising from the applied transport current and magnetic field. An obvious tension stress emerges around the constrained side of the strip along which the highest probability for cracking occurs and leads to a structural instability. The analytical results give insight into the flux-pinning-induced stress and magnetostriction response of the superconducting strip under both complex carrying-current and applied magnetic field conditions. These results may also provide helpful guidance in avoiding the breakdown of high-temperature superconductors.

  17. Safety advice sheets

    CERN Multimedia

    HSE Unit

    2013-01-01

    You never know when you might be faced with questions such as: when/how should I dispose of a gas canister? Where can I find an inspection report? How should I handle/store/dispose of a chemical substance…?   The SI section of the DGS/SEE Group is primarily responsible for safety inspections, evaluating the safety conditions of equipment items, premises and facilities. On top of this core task, it also regularly issues “Safety Advice Sheets” on various topics, designed to be of assistance to users but also to recall and reinforce safety rules and procedures. These clear and concise sheets, complete with illustrations, are easy to display in the appropriate areas. The following safety advice sheets have been issued so far: Other sheets will be published shortly. Suggestions are welcome and should be sent to the SI section of the DGS/SEE Group. Please send enquiries to general-safety-visits.service@cern.ch.

  18. Resistance Spot Welding of AA5052 Sheet Metal of Dissimilar Thickness

    Science.gov (United States)

    Mat Din, N. A.; Zuhailawati, H.; Anasyida, A. S.

    2016-02-01

    Resistance spot welding of dissimilar thickness of AA5052 aluminum alloy was performed in order to investigate the effect of metal thickness on the weldment strength. Resistance spot welding was done using a spot welder machine available in Coraza Systems Sdn Bhd using a hemispherical of chromium copper electrode tip with radius of 6.00 mm under 14 kA of current and 0.02 bar of pressure for all thickness combinations. Lap joint configuration was produced between 2.0 mm thick sheet and 1.2 - 3.2 mm thick sheet, respectively. Microstructure of joint showed asymmetrical nugget shape that was larger on the thicker side indicating larger molten metal volume. Joint 2.0 mm x 3.2 mm sheets has the lowest hardness in both transverse direction and through thickness direction because less heat left in the weld nugget. The microstructure shows that this joint has coarse grains of HAZ. As thickness of sheet metal increased, the failure load of the joints increased. However, there was no linear correlation established between joint strength and metal thickness due to different shape of fusion zone in dissimilar thickness sheet metal.

  19. Energy information sheets

    Energy Technology Data Exchange (ETDEWEB)

    1993-12-02

    The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the general public. Written for the general public, the EIA publication Energy Information Sheets was developed to provide information on various aspects of fuel production, prices, consumption and capability. The information contained herein pertains to energy data as of December 1991. Additional information on related subject matter can be found in other EIA publications as referenced at the end of each sheet.

  20. Ultrasonic imaging of sheet metal forming.

    Science.gov (United States)

    Keitmann-Curdes, Oliver; Hansen, Christian; Knoll, Patrick; Meier, Horst; Ermert, Helmut

    2004-04-01

    With sheet metal hydroforming, a sheet metal is formed by a liquid medium under high pressure (up to 1000 bar) and a cavity contour (die). As the exact state of forming is of interest, an ultrasonic imaging system is under development. The task is to determine the geometry of a sheet metal contour with respect to the original (before forming) and the final (die) state of the sheet metal. For this purpose, two different contour reconstruction algorithms were designed, tested and compared. With the reconstruction results it will be possible to determine the optimal distribution of transmitters and receivers in the ultrasonic transducer matrix. Experiments were conducted with one pair of transducers (unfocussed, center frequency 2 MHz) and a three axis stepper motor set-up. For each experimental set of data, the contour was reconstructed with both SAFT reconstruction algorithms. Both algorithms incorporate a priori information such as original and final contour and maximal axial dislocation of the sheet metal. The results for both algorithms are compared and the relative mean error in axial direction is 0.30% and 0.48%.

  1. Shape induced (spherical, sheets and rods) optical and magnetic properties of CdS nanostructures with enhanced photocatalytic activity for photodegradation of methylene blue dye under ultra-violet irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Bilal; Kumar, Sachin; Kumar, Sumeet; Ojha, Animesh K., E-mail: animesh@mnnit.ac.in

    2016-09-15

    CdS nanostructures of different shapes such as, nanoparticles (NPs), nanosheets (NS) and nanorods (NRs) have been synthesized by one step chemical solvothermal method. The synthesized samples were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy, UV–visible (UV-VIS) spectroscopy, Raman spectroscopy (RS) and vibrating sample magnetometer (VSM) techniques. The effect of shape on optical and magnetic properties of CdS nanostructures was studied. The optical band gap and emission spectra are found to be shape dependent. CdS NRs were found to have high saturation (Ms) magnetization than that of CdS NPs and NS. The role of shape on photocatalytic performance of CdS NPs, NS and NRs was investigated by monitoring the photodegradation of methylene blue (MB) dye under the UV irradiation of wavelength 365 nm. The lower recombination rate of electron-hole pairs and larger surface area as reactive facets for adsorption of MB dye molecules in CdS NS are mainly lead to the better photocatalytic performance of CdS NS compared to NPs and NRs. - Highlights: • Synthesis of CdS nanostructures with different shapes (spherical, rod and sheet) by easy and low cost solvothermal method. • Shape induced optical and magnetic properties of CdS nanostructures have been investigated. • The shapes of nanostructures play an important role for photocatalytic performance of CdS nanostructures.

  2. Ice Sheets & Ice Cores

    DEFF Research Database (Denmark)

    Mikkelsen, Troels Bøgeholm

    Since the discovery of the Ice Ages it has been evident that Earth’s climate is liable to undergo dramatic changes. The previous climatic period known as the Last Glacial saw large oscillations in the extent of ice sheets covering the Northern hemisphere. Understanding these oscillations known...

  3. Pseudomonas - Fact Sheet

    OpenAIRE

    Public Health Agency

    2012-01-01

    Fact sheet on Pseudomonas, including:What is Pseudomonas?What infections does it cause?Who is susceptible to pseudomonas infection?How will I know if I have pseudomonas infection?How can Pseudomonas be prevented from spreading?How can I protect myself from Pseudomonas?How is Pseudomonas infection treated?

  4. Ethanol Basics (Fact Sheet)

    Energy Technology Data Exchange (ETDEWEB)

    2015-01-01

    Ethanol is a widely-used, domestically-produced renewable fuel made from corn and other plant materials. More than 96% of gasoline sold in the United States contains ethanol. Learn more about this alternative fuel in the Ethanol Basics Fact Sheet, produced by the U.S. Department of Energy's Clean Cities program.

  5. Current-density functional theory study of the H2 molecule evolving under a strong ultrashort magnetic field

    Science.gov (United States)

    Vikas, Hash(0xb7f6e60)

    2012-01-01

    Hydrogen molecule in a strong ultrashort magnetic field is investigated through a current-density functional theory (CDFT) and quantum fluid dynamics (QFD) based approach employing current-density dependent vector exchange-correlation potential and energy density functional derived with a vorticity variable. The numerical computations through the CDFT based approach are performed for the H2 molecule, starting initially from its field-free ground state, in a parallel internuclear axis and magnetic field-axis configuration with the internuclear separation R ranging from 0.1 a.u. to 14.0 a.u., and the strength of the time-dependent (TD) magnetic field varying between 0-1011 G over a few femtoseconds. The numerical results are compared with that obtained using an approach based on the current-density independent approximation under similar computational constraints but employing only scalar exchange-correlation potential dependent on the electronic charge-density alone. The current-density based approach yields exchange- and correlation energy as well as electronic charge-density of the H2 molecule drastically different from that obtained using current-independent approach, in particular, at TD magnetic field-strengths >109 G during a typical time-period of the field when the magnetic-field had attained maximum applied field-strength and is switched to a decreasing ramp function. This nonadiabatic behavior of the TD electronic charge-density is traced to the TD vorticity-dependent vector exchange-correlation potential of the CDFT based approach. The interesting electron dynamics of the H2 molecule in strong TD magnetic field is further elucidated by treating electronic charge-density as an `electron-fluid'. The present work also reveals interesting real-time dynamics on the attosecond time-scale in the electronic charge-density distribution of the hydrogen molecule.

  6. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

    Science.gov (United States)

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-04-24

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

  7. W-Band Sheet Beam Klystron Design

    International Nuclear Information System (INIS)

    Scheitrum, G.; Caryotakis, G.; Burke, A.; Jensen, A.; Jongewaard, E.; Krasnykh, A.; Neubauer, M.; Phillips, R.; Rauenbuehler, K.

    2011-01-01

    Sheet beam devices provide important advantages for very high power, narrow bandwidth RF sources like accelerator klystrons (1). Reduced current density and increased surface area result in increased power capabi1ity, reduced magnetic fields for focusing and reduced cathode loading. These advantages are offset by increased complexity, beam formation and transport issues and potential for mode competition in the ovennoded cavities and drift tube. This paper will describe the design issues encountered in developing a 100 kW peak and 2 kW average power sheet beam k1ystron at W-band including beam formation, beam transport, circuit design, circuit fabrication and mode competition.

  8. TSCA Chemical Data Reporting Fact Sheet: Articles

    Science.gov (United States)

    This fact sheet provides guidance on classifying articles under the Toxic Substances Control Act (TSCA) and determining the applicability of EPA’s articles exclusion policy for purposes of the Chemical Data Reporting (CDR) rule. The primary goal of this document is to help the regulated community comply with the requirements of the CDR rule.

  9. Chemical Data Reporting Fact Sheet: Basic Information

    Science.gov (United States)

    EPA collects information on the types and quantities of chemicals produced in the U.S under the Chemical Data Reporting (CDR) requirements. This fact sheet outlines key information about CDR, including what data are collected and how the data are used.

  10. Rubella - Fact Sheet for Parents

    Science.gov (United States)

    ... and 4 through 6 years Fact Sheet for Parents Color [2 pages] Español: Rubéola The best way ... according to the recommended schedule. Fact Sheets for Parents Diseases and the Vaccines that Prevent Them Chickenpox ...

  11. Eddy Current Testing with Giant Magnetoresistance (GMR) Sensors and a Pipe-Encircling Excitation for Evaluation of Corrosion under Insulation.

    Science.gov (United States)

    Bailey, Joseph; Long, Nicholas; Hunze, Arvid

    2017-09-28

    This work investigates an eddy current-based non-destructive testing (NDT) method to characterize corrosion of pipes under thermal insulation, one of the leading failure mechanisms for insulated pipe infrastructure. Artificial defects were machined into the pipe surface to simulate the effect of corrosion wall loss. We show that by using a giant magnetoresistance (GMR) sensor array and a high current (300 A), single sinusoidal low frequency (5-200 Hz) pipe-encircling excitation scheme it is possible to quantify wall loss defects without removing the insulation or weather shield. An analysis of the magnetic field distribution and induced currents was undertaken using the finite element method (FEM) and analytical calculations. Simple algorithms to remove spurious measured field variations not associated with defects were developed and applied. The influence of an aluminium weather shield with discontinuities and dents was ascertained and found to be small for excitation frequency values below 40 Hz. The signal dependence on the defect dimensions was analysed in detail. The excitation frequency at which the maximum field amplitude change occurred increased linearly with the depth of the defect by about 3 Hz/mm defect depth. The change in magnetic field amplitude due to defects for sensors aligned in the azimuthal and radial directions were measured and found to be linearly dependent on the defect volume between 4400-30,800 mm³ with 1.2 × 10 -3 -1.6 × 10 -3 µT/mm³. The results show that our approach is well suited for measuring wall loss defects similar to the defects from corrosion under insulation.

  12. Mixed Stimulus-Induced Mode Selection in Neural Activity Driven by High and Low Frequency Current under Electromagnetic Radiation

    Directory of Open Access Journals (Sweden)

    Lulu Lu

    2017-01-01

    Full Text Available The electrical activities of neurons are dependent on the complex electrophysiological condition in neuronal system, the three-variable Hindmarsh-Rose (HR neuron model is improved to describe the dynamical behaviors of neuronal activities with electromagnetic induction being considered, and the mode transition of electrical activities in neuron is detected when external electromagnetic radiation is imposed on the neuron. In this paper, different types of electrical stimulus impended with a high-low frequency current are imposed on new HR neuron model, and mixed stimulus-induced mode selection in neural activity is discussed in detail. It is found that mode selection of electrical activities stimulated by high-low frequency current, which also changes the excitability of neuron, can be triggered owing to adding the Gaussian white noise. Meanwhile, the mode selection of the neuron electrical activity is much dependent on the amplitude B of the high frequency current under the same noise intensity, and the high frequency response is selected preferentially by applying appropriate parameters and noise intensity. Our results provide insights into the transmission of complex signals in nerve system, which is valuable in engineering prospective applications such as information encoding.

  13. Balance Sheet Capacity and Endogenous Risk

    OpenAIRE

    Jon Danielsson; Hyun Song Shin; Jean-Pierre Zigrand

    2011-01-01

    Banks operating under Value-at-Risk constraints give rise to a well-defined aggregate balance sheet capacity for the banking sector as a whole that depends on total bank capital. Equilibrium risk and market risk premiums can be solved in closed form as functions of aggregate bank capital. We explore the empirical properties of the model in light of recent experience in the financial crisis and highlight the importance of balance sheet capacity as the driver of the financial cycle and market r...

  14. Balance Velocities of the Greenland Ice Sheet

    Science.gov (United States)

    Joughin, Ian; Fahnestock, Mark; Ekholm, Simon; Kwok, Ron

    1997-01-01

    We present a map of balance velocities for the Greenland ice sheet. The resolution of the underlying DEM, which was derived primarily from radar altimetry data, yields far greater detail than earlier balance velocity estimates for Greenland. The velocity contours reveal in striking detail the location of an ice stream in northeastern Greenland, which was only recently discovered using satellite imagery. Enhanced flow associated with all of the major outlets is clearly visible, although small errors in the source data result in less accurate estimates of the absolute flow speeds. Nevertheless, the balance map is useful for ice-sheet modelling, mass balance studies, and field planning.

  15. Bioprocessing of plant-derived virus-like particles of Norwalk virus capsid protein under current Good Manufacture Practice regulations

    Science.gov (United States)

    Lai, Huafang; Chen, Qiang

    2012-01-01

    Despite the success in expressing a variety of subunit vaccine proteins in plants and the recent stride in improving vaccine accumulation levels by transient expression systems, there is still no plant-derived vaccine that has been licensed for human use. The lack of commercial success of plant-made vaccines lies in several technical and regulatory barriers that remain to be overcome. These challenges include the lack of scalable downstream processing procedures, the uncertainty of regulatory compliance of production processes, and the lack of demonstration of plant-derived products that meet the required standards of regulatory agencies in identity, purity, potency and safety. In this study, we addressed these remaining challenges and successfully demonstrate the ability of using plants to produce a pharmaceutical grade Norwalk virus (NV) vaccine under current Good Manufacture Practice (cGMP) guidelines at multiple gram scales. Our results demonstrate that an efficient and scalable extraction and purification scheme can established for processing virus-like particles (VLP) of NV capsid protein (NVCP). We successfully operated the upstream and downstream NVCP production processes under cGMP regulations. Furthermore, plant-derived NVCP VLP demonstrates the identity, purity, potency and safety that meet the preset release specifications. This material is being tested in a Phase I human clinical trial. This research provides the first report of producing a plant-derived vaccine at scale under cGMP regulations in an academic setting and an important step for plant-produced vaccines to become a commercial reality. PMID:22134876

  16. Leakage Current Waveforms and Arcing Characteristics of Epoxy Resin for Outdoor Insulators under Clean and Salt Fogs

    Directory of Open Access Journals (Sweden)

    Suwarno

    2008-05-01

    Full Text Available Ceramic outdoor insulators have been used in high voltage transmission lines since long time ago. Due to superiority in their resistance to pollution, recently, polymeric outdoor insulators are widely used. Epoxy resin is one polymer which shows good properties for outdoor insulation. During service, outdoor insulators may severe a certain degree of pollution which may reduce their surface resistance. Leakage current (LC usually increase and degradation may take place. This paper reports experimental results on the leakage current waveforms and arcing characteristics of epoxy resin under clean and salt fog. The samples used are blocks of epoxy resin with dimension of 250 x 50 x 20 mm3. The samples were put in a test chamber with dimension of 900x900x1200 mm3 with controllable humidity and pollution conditions. Clean and salt fog were generated according to IEC 60-1 and 507. The arcing experiment was done with incline plane test in accordance with IEC 587. AC voltage in the range from 5 kV to 50 kV with frequency of 50 Hz was applied. The LC waveforms up to flash over were measured. The magnitudes as well as harmonic content of the LC were analyzed. The correlation between LC waveforms and dry band arching phenomenon was elaborated. Visual observation of the arc on the sample surfaces was observed using a video camera. Experimental results indicated that LC magnitude on clean samples was slightly affected by humidity (RH. However, under salt fog, RH greatly affected the LC magnitude. The flashover voltage of clean samples under salt fog reduced significantly for fog conductivity of more than 1.2 mS/cm. Kaolin-polluted samples under salt fog showed an Ohmic behaviour. The LC magnitude was high and a large discrepancy of LC magnitude was observed for high applied voltage of larger than 25 kV. The largest LC magnitude was observed on salt-kaolin polluted samples under clean fog at high RH. LC waveforms analysis indicated that in general LC waveforms

  17. Large-Scale Laboratory Experiments of Initiation of Motion and Burial of Objects under Currents and Waves

    Science.gov (United States)

    Landry, B. J.; Wu, H.; Wenzel, S. P.; Gates, S. J.; Fytanidis, D. K.; Garcia, M. H.

    2017-12-01

    Unexploded ordnances (UXOs) can be found at the bottom of coastal areas as the residue of military wartime activities, training or accidents. These underwater objects are hazards for humans and the coastal environment increasing the need for addressing the knowledge gaps regarding the initiation of motion, fate and transport of UXOs under currents and wave conditions. Extensive experimental analysis was conducted for the initiation of motion of UXOs under various rigid bed roughness conditions (smooth PVC, pitted steel, marbles, gravels and bed of spherical particles) for both unidirectional and oscillatory flows. Particle image velocimetry measurements were conducted under both flow conditions to resolve the flow structure estimate the critical flow conditions for initiation of motion of UXOs. Analysis of the experimental observations shows that the geometrical characteristics of the UXOs, their properties (i.e. volume, mass) and their orientation with respect to the mean flow play an important role on the reorientation and mobility of the examined objects. A novel unified initiation of motion diagram is proposed using an effective/unified hydrodynamic roughness and a new length scale which includes the effect of the projected area and the bed-UXO contact area. Both unidirectional and oscillatory critical flow conditions collapsed into a single dimensionless diagram highlighting the importance and practical applicability of the proposed work. In addition to the rigid bed experiments, the burial dynamics of proud UXOs on a mobile sand bed were also examined. The complex flow-bedform-UXOs interactions were evaluated which highlighted the effect of munition density on burial rate and final burial depth. Burial dynamics and mechanisms for motion were examined for various UXOs types, and results show that, for the case of the low density UXOs under energetic conditions, lateral transport coexists with burial. Prior to burial, UXO re-orientation was also observed

  18. Novel failure mechanism and improvement for split-gate trench MOSFET with large current under unclamped inductive switch stress

    Science.gov (United States)

    Tian, Ye; Yang, Zhuo; Xu, Zhiyuan; Liu, Siyang; Sun, Weifeng; Shi, Longxing; Zhu, Yuanzheng; Ye, Peng; Zhou, Jincheng

    2018-04-01

    In this paper, a novel failure mechanism under unclamped inductive switch (UIS) for Split-Gate Trench Metal Oxide Semiconductor Field Effect Transistor (MOSFET) with large current is investigated. The device sample is tested and analyzed in detail. The simulation results demonstrate that the nonuniform potential distribution of the source poly should be responsible for the failure. Three structures are proposed and verified available to improve the device UIS ruggedness by TCAD simulation. The best one of the structures the device with source metal inserting into source poly through contacts in the field oxide is carried out and measured. The results demonstrate that the optimized structure can balance the trade-off between the UIS ruggedness and the static characteristics.

  19. Corrosion Behavior of X80 Steel with Coupled Coating Defects under Alternating Current Interference in Alkaline Environment.

    Science.gov (United States)

    Li, Zhong; Li, Caiyu; Qian, Hongchang; Li, Jun; Huang, Liang; Du, Cuiwei

    2017-06-28

    The corrosion behavior of X80 steel in the presence of coupled coating defects was simulated and studied under the interference of alternating current (AC) in an alkaline environment. The results from electrochemical measurements showed that the electrode potential of the coating defect with the smaller exposed area was lower than that with the larger area, which indicated that the steel with the smaller coating defect was more prone to corrosion. The result of weight loss tests also showed that the smaller coating defect had induced a higher corrosion rate. However, the corrosion rate of X80 steel at the larger coating defect decreased gradually with the increase of the larger defect area at a constant smaller defect area. The corrosion morphology images showed that the coating defects with smaller areas suffered from more severe pitting corrosion.

  20. Single sheet iron oxides

    DEFF Research Database (Denmark)

    Yin, Zhou

    activity. LDH single sheets have been reported to be effective sorbents, catalysts in electrochemical and photochemical reactions, and building thin films together with other nanomaterials for designing new functionalities. Here we focus on the delamination of FeII-FeIII LDHs into single sheet iron oxide...... was rapid compared to other iron oxides, reaching equilibrium within 60 minutes. Arsenic sorption and acid-base titration data could be successfully described with a 1pk Basic Stern Model (BSM). The point of zero charge was around 8. The intrinsic surface complexation equilibrium constants (log K...... became abundant at low pH. (3) Electrochemical reduction of chlorinated compounds using an SSI modified electrode. Here, the electrochemical reactivity of SSIs coated on indium tin oxide coated glass electrodes was investigated. Iron on the SSI modified electrode showed a typical Cyclic Voltammetry...

  1. Biomolecular Science (Fact Sheet)

    Energy Technology Data Exchange (ETDEWEB)

    2012-04-01

    A brief fact sheet about NREL Photobiology and Biomolecular Science. The research goal of NREL's Biomolecular Science is to enable cost-competitive advanced lignocellulosic biofuels production by understanding the science critical for overcoming biomass recalcitrance and developing new product and product intermediate pathways. NREL's Photobiology focuses on understanding the capture of solar energy in photosynthetic systems and its use in converting carbon dioxide and water directly into hydrogen and advanced biofuels.

  2. Information sheets on energy

    International Nuclear Information System (INIS)

    2004-01-01

    These sheets, presented by the Cea, bring some information, in the energy domain, on the following topics: the world energy demand and the energy policy in France and in Europe, the part of the nuclear power in the energy of the future, the greenhouse gases emissions and the fight against the greenhouse effect, the carbon dioxide storage cost and the hydrogen economy. (A.L.B.)

  3. New aspects of plasma sheet dynamics - MHD and kinetic theory

    Directory of Open Access Journals (Sweden)

    H. Wiechen

    Full Text Available Magnetic reconnection is a process of fundamental importance for the dynamics of the Earth's plasma sheet. In this context, the development of thin current sheets in the near-Earth plasma sheet is a topic of special interest because they could be a possible cause of microscopic fluctuations acting as collective non-idealness from a macroscopic point of view. Simulations of the near-Earth plasma sheet including boundary perturbations due to localized inflow through the northern (or southern plasma sheet boundary show developing thin current sheets in the near-Earth plasma sheet about 810 RE tailwards of the Earth. This location is largely independent from the localization of the perturbation. The second part of the paper deals with the problem of the macroscopic non-ideal consequences of microscopic fluctuations. A new model is presented that allows the quantitative calculation of macroscopic non-idealness without considering details of microscopic instabilities or turbulence. This model is only based on the assumption of a strongly fluctuating, mixing dynamics on microscopic scales in phase space. The result of this approach is an expression for anomalous non-idealness formally similar to the Krook resistivity but now describing the macroscopic consequences of collective microscopic fluctuations, not of collisions.

    Key words. Magnetospheric physics (plasma sheet · Space plasma physics (kinetic and MHD theory; magnetic reconnection

  4. A glucose anode for enzymatic fuel cells optimized for current production under physiological conditions using a design of experiment approach.

    Science.gov (United States)

    Kumar, Rakesh; Leech, Dónal

    2015-12-01

    This study reports a design of experiment methodology to investigate and improve the performance of glucose oxidizing enzyme electrodes. Enzyme electrodes were constructed by co-immobilization of amine-containing osmium redox complexes, multiwalled carbon nanotubes and glucose oxidase in a carboxymethyldextran matrix at graphite electrode surfaces to provide a 3-dimensional matrix for electrocatalytic oxidation of glucose. Optimization of the amount of the enzyme electrode components to produce the highest current density under pseudo-physiological conditions of 5 mM glucose in saline buffer at 37 °C was performed using response surface methodology. A statistical analysis showed that the proposed model had a good fit with the experimental results. From the validated model, the addition of multiwalled carbon nanotubes and carboxymethyldextran components was identified as major contributing factors to the improved performance. Based on the optimized amount of components, enzyme electrodes display current densities of 1.2±0.1 mA cm(-2) and 5.2±0.2 mA cm(-2) at 0.2 V vs. Ag/AgCl in buffer containing 5 mM and 100 mM glucose, respectively, largely consistent with the predicted values. This demonstrates that use of a design of experiment approach can be applied effectively and efficiently to improve the performance of enzyme electrodes as anodes for biofuel cell device development. Copyright © 2015 Elsevier B.V. All rights reserved.

  5. More green infrastructure is required to maintain ecosystem services under current trends in land-use change in Europe.

    Science.gov (United States)

    Maes, Joachim; Barbosa, Ana; Baranzelli, Claudia; Zulian, Grazia; Batista E Silva, Filipe; Vandecasteele, Ine; Hiederer, Roland; Liquete, Camino; Paracchini, Maria Luisa; Mubareka, Sarah; Jacobs-Crisioni, Chris; Castillo, Carolina Perpiña; Lavalle, Carlo

    Green infrastructure (GI), a network of nature, semi-natural areas and green space, delivers essential ecosystem services which underpin human well-being and quality of life. Maintaining ecosystem services through the development of GI is therefore increasingly recognized by policies as a strategy to cope with potentially changing conditions in the future. This paper assessed how current trends of land-use change have an impact on the aggregated provision of eight ecosystem services at the regional scale of the European Union, measured by the Total Ecosystem Services Index (TESI8). Moreover, the paper reports how further implementation of GI across Europe can help maintain ecosystem services at baseline levels. Current demographic, economic and agricultural trends, which affect land use, were derived from the so called Reference Scenario. This scenario is established by the European Commission to assess the impact of energy and climate policy up to 2050. Under the Reference Scenario, economic growth, coupled with the total population, stimulates increasing urban and industrial expansion. TESI8 is expected to decrease across Europe between 0 and 5 % by 2020 and between 10 and 15 % by 2050 relative to the base year 2010. Based on regression analysis, we estimated that every additional percent increase of the proportion of artificial land needs to be compensated with an increase of 2.2 % of land that qualifies as green infrastructure in order to maintain ecosystem services at 2010 levels.

  6. Myocardial regenerative therapy using a scaffold-free skeletal-muscle-derived cell sheet in patients with dilated cardiomyopathy even under a left ventricular assist device: a safety and feasibility study.

    Science.gov (United States)

    Yoshikawa, Yasushi; Miyagawa, Shigeru; Toda, Koichi; Saito, Atsuhiro; Sakata, Yasushi; Sawa, Yoshiki

    2018-02-01

    Despite promising experimental results, clinically, intramyocardial myoblast injection failed to reverse remodeling and it induced arrhythmogenicity. In contrast, scaffold-free skeletal muscle-derived cell (SC) sheets attenuated cardiac dysfunction and arrhythmogenicity via paracrine effects. We report the first clinical trial of SC sheet implantation (SCSI) conducted in four patients with dilated cardiomyopathy (DCM) supported by a left ventricular assist device (LVAD). SC sheets were made from muscle fibers and multi-layered SC sheets were applied to the left ventricular (LV) anterolateral surface via left thoracotomy. There were no major cardiac adverse events. Ventricular arrhythmia decreased in all except one patient, in whom global LV function did not improve. The LV volume decreased and LV ejection fraction improved in all except the same patient. Systolic wall thickening, reflecting regional wall motion, improved in the sheet-implanted areas, and vessels in the LV apex increased in all patients, suggesting angiogenesis. The LVAD was successfully removed in two patients. SCSI induced reverse remodeling and angiogenesis, and improved LV function, allowing LVAD removal in two patients, although functional recovery failed to improve in the one non-responder, even with angiogenesis. SCSI is a promising regenerative therapy for DCM patients responsive to this strategy, even with LVAD assistance.

  7. Enhancement of Operating Efficiency Of The Central Coal-Preparation Plant of "MMK - UGOL" Ltd. Under Current Conditions

    Science.gov (United States)

    Basarygin, Maksim

    2017-11-01

    In this article the subject of enhancement of operating efficiency of the central coal-preparation plant of OOO "MMK-UGOL" is encompassed. Modern trends in the development of technologies and equipment for coal beneficiation are due to the following requirements: improving competitiveness of coal products, improvement of quality of marketable products, reduction of coal production cost, environmental requirements: polluting emission abatement, prepared coal saving, improvement of the effectiveness of resource conservation; complex mechanization and beneficiation process automation. In the article the contemporary problems of raw coal benefication under current conditions of the increased dilution of withdrawable coals with rock fractions are considered. Comparative analysis of efficiency of application of modern concentrating equipment under the conditions of the CCPP of OOO "MMK-UGOL" is carried out on the basis of research works. Particular attention is paid to dehydration of produced coal concentrate with content of volatile agents of more than 35.0% and content of fine-dispersed particles in flotation concentrate of more than 50.0%. Comparative analysis of the coal concentrate dehydration technologies is conducted.

  8. Modeling Nitrogen Losses in Conventional and Advanced Soil-Based Onsite Wastewater Treatment Systems under Current and Changing Climate Conditions.

    Science.gov (United States)

    Morales, Ivan; Cooper, Jennifer; Amador, José A; Boving, Thomas B

    2016-01-01

    Most of the non-point source nitrogen (N) load in rural areas is attributed to onsite wastewater treatment systems (OWTS). Nitrogen compounds cause eutrophication, depleting the oxygen in marine ecosystems. OWTS rely on physical, chemical and biological soil processes to treat wastewater and these processes may be affected by climate change. We simulated the fate and transport of N in different types of OWTS drainfields, or soil treatment areas (STA) under current and changing climate scenarios, using 2D/3D HYDRUS software. Experimental data from a mesocosm-scale study, including soil moisture content, and total N, ammonium (NH4+) and nitrate (NO3-) concentrations, were used to calibrate the model. A water content-dependent function was used to compute the nitrification and denitrification rates. Three types of drainfields were simulated: (1) a pipe-and-stone (P&S), (2) advanced soil drainfields, pressurized shallow narrow drainfield (PSND) and (3) Geomat (GEO), a variation of SND. The model was calibrated with acceptable goodness-of-fit between the observed and measured values. Average root mean square error (RSME) ranged from 0.18 and 2.88 mg L-1 for NH4+ and 4.45 mg L-1 to 9.65 mg L-1 for NO3- in all drainfield types. The calibrated model was used to estimate N fluxes for both conventional and advanced STAs under current and changing climate conditions, i.e. increased soil temperature and higher water table. The model computed N losses from nitrification and denitrification differed little from measured losses in all STAs. The modeled N losses occurred mostly as NO3- in water outputs, accounting for more than 82% of N inputs in all drainfields. Losses as N2 were estimated to be 10.4% and 9.7% of total N input concentration for SND and Geo, respectively. The highest N2 losses, 17.6%, were estimated for P&S. Losses as N2 increased to 22%, 37% and 21% under changing climate conditions for Geo, PSND and P&S, respectively. These findings can provide practitioners

  9. Origins of late- Pleistocene coastal dune sheets, Magdalena and Guerrero Negro, from continental shelf low-stand supply (70-20 ka), under conditions of southeast littoral- and eolian-sand transport, in Baja California Sur, Mexico

    Science.gov (United States)

    Peterson, Curt D.; Murillo-Jiménez, Janette M.; Stock, Errol; Price, David M.; Hostetler, Steve W.; Percy, David

    2017-10-01

    Shallow morpho-stratigraphic sections (n = 11) in each of two large coastal dune sheets including the Magdalena (7000 km2) and Guerrero Negro (8000 km2) dune sheets, from the Pacific Ocean side of Baja California Sur, Mexico, have been analyzed for dune deposit age. The shallow morpho-stratigraphic sections (∼2-10 m depth) include 11 new TL and 14C ages, and paleosol chronosequences, that differentiate cemented late Pleistocene dune deposits (20.7 ± 2.1 to 99.8 ± 9.4 ka) from uncemented Holocene dune deposits (0.7 ± 0.05 to at least 3.2 ± 0.3 ka). Large linear dune ridges (5-10 m in height) in the dune sheet interiors trend southeast and are generally of late Pleistocene age (∼70-20 ka). The late Pleistocene dune deposits reflect eolian transport of marine sand across the emerged continental shelf (30-50 km southeast distance) from low-stand paleo-shorelines (-100 ± 25 m elevation), which were locally oriented nearly orthogonal to modeled deep-water wave directions (∼300° TN). During the Holocene marine transgression, onshore and alongshore wave transport delivered remobilized shelf-sand deposits to the nearshore areas of the large dune sheets, building extensive barrier islands and sand spits. Submerged back-barrier lagoons generally precluded marine sand supply to dune sheet interiors in middle to late Holocene time, though exceptions occur along some ocean and lagoon shorelines. Reactivation of the late Pleistocene dune deposits in the dune sheet interiors lead to generally thin (1-3 m thickness), but widespread, covers of Holocene dune deposits (0.41 ± 0.05 to 10.5 ± 1.6 ka). Mechanical drilling will be required to penetrate indurated subsoil caliche layers to reach basal Pleistocene dune deposits.

  10. Non-Heat Treatable Alloy Sheet Products

    Energy Technology Data Exchange (ETDEWEB)

    Hayden, H.W.; Barthold, G.W.; Das, S.K.

    1999-08-01

    ALCAR is an innovative approach for conducting multi-company, pre-competitive research and development programs. ALCAR has been formed to crate a partnership of aluminum producers, the American Society of Mechanical Engineers Center for Research and Technology Development (ASME/CRTD), the United States Department of Energy (USDOE), three USDOE National Laboratories, and a Technical Advisory Committee for conducting cooperative, pre-competitive research on the development of flower-cost, non-heat treated (NHT) aluminum alloys for automotive sheet applications with strength, formability and surface appearance similar to current heat treated (HT) aluminum alloys under consideration. The effort has been supported by the USDOE, Office of Transportation Technology (OTT) through a three-year program with 50/50 cost share at a total program cost of $3 million. The program has led to the development of new and modified 5000 series aluminum ally compositions. Pilot production-size ingots have bee n melted, cast, hot rolled and cold rolled. Stamping trials on samples of rolled product for demonstrating production of typical automotive components have been successful.

  11. An empirical model for salt removal percentage in water under the effect of different current intensities of current carrying coil at different flow rates

    Directory of Open Access Journals (Sweden)

    Rameen S. AbdelHady

    2011-10-01

    Full Text Available The magnetic treatment of hard water is an alternative, simple approach by which the hard water that needs to be treated flows through a magnetic field. This field is created by inducing current in a coil wrapped around a pipe. Consequently some of its properties, such as total dissolved salts (TDS, conductivity (Ec and PH change. The primary purpose of hard water treatment is to decrease TDS in the incoming liquid stream. Using performance data from the application of different magnetic field densities on the different flow levels of water, empirical mathematical models were developed relating the salt removal percentage (SRP to operating flow rate and current of the coil. The obtained experimental results showed that the SRP increased with increasing the current at low flow rates (up to 0.75 ml/s.

  12. Bioclimatic predictions of habitat suitability for the biofuel switchgrass in North America under current and future climate scenarios

    International Nuclear Information System (INIS)

    Barney, Jacob N.; DiTomaso, Joseph M.

    2010-01-01

    Dedicated biofuel crops, while providing economic and other benefits, may adversely impact biodiversity directly via land use conversion, or indirectly via creation of novel invasive species. To mitigate negative impacts bioclimatic envelope models (BEM) can be used to estimate the potential distribution and suitable habitat based on the climate and distribution in the native range. We used CLIMEX to evaluate the regions of North America suitable for agronomic production, as well as regions potentially susceptible to an invasion of switchgrass (Panicum virgatum) under both current and future climate scenarios. Model results show that >8.7 million km 2 of North America has suitable to very favorable habitat, most of which occurs east of the Rocky Mountains. The non-native range of western North America is largely unsuitable to switchgrass as a crop or potential weed unless irrigation or permanent water is available. Under both the CGCM2 and HadCM3 climate models and A2 and B2 emissions scenarios, an overall increase in suitable habitat is predicted over the coming century, although the western US remains unsuitable. Our results suggest that much of North America is suitable for switchgrass cultivation, although this is likely to shift north in the coming century. Our results also agree with field collections of switchgrass outside its native range, which indicate that switchgrass is unlikely to establish unless it has access to water throughout the year (e.g., along a stream). Thus, it is the potential invasion of switchgrass into riparian habitats in the West that requires further investigation. (author)

  13. Pattern transitions in a compressible floating elastic sheet.

    Science.gov (United States)

    Oshri, Oz; Diamant, Haim

    2017-09-13

    Thin rigid sheets floating on a liquid substrate appear, for example, in coatings and surfactant monolayers. Upon uniaxial compression the sheet undergoes transitions from a compressed flat state to a periodic wrinkled pattern to a localized folded pattern. The stability of these states is determined by the in-plane elasticity of the sheet, its bending rigidity, and the hydrostatics of the underlying liquid. Wrinkles and folds, and the wrinkle-to-fold transition, were previously studied for incompressible sheets. In the present work we extend the theory to include finite compressibility. We analyze the details of the flat-to-wrinkle transition, the effects of compressibility on wrinkling and folding, and the compression field associated with pattern formation. The state diagram of the floating sheet including all three states is presented.

  14. Friction and bending forces evaluation of AISI 304 DDQ steel sheet forming by bending tests under deep-drawing multiaxial stresses; Evaluacion de la fuerza de doblado y de friccion en el conformado de chapa de acero inoxidable AISI 304 DDQ mediante ensayos de doblado en condiciones multiaxiales de embuticion

    Energy Technology Data Exchange (ETDEWEB)

    Coello, J.; Miguel, V.; Ferrer, C.; Calatayud, A.; Martinez, A.

    2012-11-01

    Die radius is a critical area from the viewpoint of friction in forming processes. Moreover the sheet, that has been previously deformed in flange area, suffers bending and unbending stresses. Then, die-sheet contact in die radius must be especially considered in order to guarantee the suitable lubrication conditions. In the present work, a test method is carried out for evaluating an AISI 304 DDQ steel under similar conditions to those existing in the die radius area and that, usually, are not really reproduced in traditional bending under tensions tests. Deformation under pure shear condition, the bending and the radius angle have been established as variables of the tests. Results allow to obtain the apparent pressure sheet-bending tool, that increases with bending angle and decreases with tool radius. This last variable is the most significant while the bending angle has lesser influence. Although experimental results present some concordances with values obtained by analytical methods, some corrections must be considered in them in order to improve the theoretical values. (Author) 18 refs.

  15. The use of Depletion Methods to assess Mediterranean cephalopod stocks under the current EU Data Collection Framework

    Directory of Open Access Journals (Sweden)

    S. KELLER

    2015-09-01

    Full Text Available Fuelled by the raising importance of cephalopod fisheries in Europe, there have been demands from scientists and stakeholders for their assessment and management. However, little has been done to improve the data collection in order to analyse cephalopod populations under the EU Data Collection Framework (DCF. While the DCF allows member states to design flexible national sampling programmes, it establishes the minimum data requirements (MDR each state is obliged to fulfil. In this study, it was investigated whether such MDR currently set by the DCF allow the application of depletion models (DMs to assess European cephalopod stocks. Squid and cuttlefish fisheries from the western Mediterranean were used as a case study. This exercise sheds doubt on the suitability of the MDR to properly assess and manage cephalopod stocks by means of DMs. Owing to the high plasticity of life-history traits in cephalopod populations, biological parameters should be estimated during the actual depletion period of the fished stocks, in contrast with the triennial sampling established by the DCF. In order to accurately track the depletion event, the rapid growth rates of cephalopods implies that their populations should be monitored at shorter time scales (ideally weekly or biweekly instead of quarterly as required by the DCF. These measures would not demand additional resources of the ongoing DCF, but a redistribution of sampling efforts during the depletion period. Such changes in the sampling scheme could be designed and undertaken by the member states or directly integrated as requirements.

  16. Multiscale models of metal behaviour and structural change under the action of high-current electron irradiation

    International Nuclear Information System (INIS)

    Mayer, A E; Krasnikov, V S; Mayer, P N; Pogorelko, V V

    2017-01-01

    We present our models of the tensile fracture of metals in the solid and molten states, the melting and the plastic deformation of the solid metals. Also we discuss implementation of these models for simulation of the high current electron beam impact on metals. The models are constructed in the following way: the atomistic simulations are used at the first stage for investigation of dynamics and kinetics of structural defects in material (voids, dislocations, melting cites); equations describing evolution of such defects are constructed, verified, and their parameters are identified by means of comparison with the atomistic simulation result; finally, the defects evolution equations are incorporated into the continuum model of the substance behaviour on the macroscopic scale. The obtained continuum models with accounting of defects subsystems are tested in comparison with the experimental results known from literature. The proposed models not only allow one to describe the metal behaviour under the conditions of intensive electron irradiation, but they also allow one to determine the structural changes in the irradiated material. (paper)

  17. Numerical simulation and fabrication of silicon sheet via spin casting.

    Science.gov (United States)

    Lee, Jaewoo; Kim, Hyunhui; Lee, Changbum; Kim, Joonsoo; Jang, Bo-Yun; Lee, Jinseok; Ahn, Youngsoo; Yoon, Wooyoung

    2013-05-01

    A spin-casting process for fabricating polycrystalline silicon sheets for use as solar cell wafers is proposed, and the parameters that control the sheet thickness are investigated. A numerical study of the fluidity of molten silicon indicates that the formation of thin silicon sheets without a mold and via spin casting is feasible. The faster the rotation speed of graphite mold, the thinner the thickness of sheet. After the spread of the molten silicon to cover the graphite mold with rotation speed of above 500 rpm, the solidification has to start. Silicon sheets can be produced by using the centrifugal force under appropriate experimental conditions. The spin-cast sheet had a vertical columnar microstructure due to the normal heat extraction to the substrate, and the sheet lifetime varied from 0.1 microS to 0.3 microS measured by using the microwave photoconductance decay (MW-PCD) to confirm that the spin-cast silicon sheet is applicable to photovoltaics.

  18. Long-Term Durability of Basalt Fiber-Reinforced Polymer (BFRP Sheets and the Epoxy Resin Matrix under a Wet–Dry Cyclic Condition in a Chloride-Containing Environment

    Directory of Open Access Journals (Sweden)

    Zhongyu Lu

    2017-11-01

    Full Text Available Basalt fiber-reinforced polymer (BFRP composites are receiving increasing attention as they represent a low-cost green source of raw materials. FRP composites have to face harsh environments, such as chloride ions in coastal marine environments or cold regions with salt deicing. The resistance of FRPs subjected to the above environments is critical for the safe design and application of BFRP composites. In the present paper, the long-term durability of BFRP sheets and the epoxy resin matrix in a wet–dry cyclic environment containing chloride ions was studied. The specimens of the BFRP sheet and epoxy resin matrix were exposed to alternative conditions of 8-h immersion in 3.5% NaCl solution at 40 °C and 16-h drying at 25 °C and 60% relative humidity (RH. The specimens were removed from the exposure chamber at the end of the 180th, 270th and 360th cycles of exposure and were analyzed for degradation with tensile tests, scanning electron microscopy (SEM and void volume fractions. It was found that the tensile modulus of the BFRP sheet increased by 3.4%, and the tensile strength and ultimate strain decreased by 45% and 65%, respectively, after the 360th cycle of exposure. For the epoxy resin matrix, the tensile strength, tensile modulus and ultimate strain decreased by 27.8%, 3.2% and 64.8% after the 360th cycle of exposure, respectively. The results indicated that the degradation of the BFRP sheet was dominated by the damage of the interface between the basalt fiber and epoxy resin matrix. In addition, salt precipitate accelerated the fiber–matrix interfacial debonding, and hydrolysis of the epoxy resin matrix resulted in many voids, which accelerated the degradation of the BFRP sheet.

  19. Neutral sheet crossings in the distant magnetotail

    International Nuclear Information System (INIS)

    Heikkila, W.J.; Slavin, J.A.; Smith, E.J.; Baker, D.N.; Zwickl, R.D.

    1985-01-01

    We have analyzed the magnetic field data from ISEE-3 in the distant magnetotail for 18 crossings of the cross-tail current sheet (or so-called natural sheet) to determine the direction of the normal component B/sub z/. The crossings occurred near the middle of the aberrated magnetotail (0 0.4 nT), consistent with closed field lines connected to the earth. In 3 cases B/sub z/ was very close to zero; in several instances there was structure in B/sub y/, suggesting localized currents with x or z directions. One may have been a magnetopause crossing. The strong preponderance of northward B/sub z/ favors a model of the magnetotail which is dominated by boundary layer plasma, flowing tailward on closed magnetic field lines, which requires the existence of an electric field in the sense from dusk to dawn. 37 refs., 15 figs., 1 tab

  20. Experiments on sheet metal shearing

    OpenAIRE

    Gustafsson, Emil

    2013-01-01

    Within the sheet metal industry, different shear cutting technologies are commonly used in several processing steps, e.g. in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material.Numerical models to predict forces and sheared edge geometry for different sheet metal grades and different shear parameter set-ups a...

  1. Sheet Membrane Spacesuit Water Membrane Evaporator

    Science.gov (United States)

    Bue, Grant; Trevino, Luis; Zapata, Felipe; Dillion, Paul; Castillo, Juan; Vonau, Walter; Wilkes, Robert; Vogel, Matthew; Frodge, Curtis

    2013-01-01

    A document describes a sheet membrane spacesuit water membrane evaporator (SWME), which allows for the use of one common water tank that can supply cooling water to the astronaut and to the evaporator. Test data showed that heat rejection performance dropped only 6 percent after being subjected to highly contaminated water. It also exhibited robustness with respect to freezing and Martian atmospheric simulation testing. Water was allowed to freeze in the water channels during testing that simulated a water loop failure and vapor backpressure valve failure. Upon closing the backpressure valve and energizing the pump, the ice eventually thawed and water began to flow with no apparent damage to the sheet membrane. The membrane evaporator also serves to de-gas the water loop from entrained gases, thereby eliminating the need for special degassing equipment such as is needed by the current spacesuit system. As water flows through the three annular water channels, water evaporates with the vapor flowing across the hydrophobic, porous sheet membrane to the vacuum side of the membrane. The rate at which water evaporates, and therefore, the rate at which the flowing water is cooled, is a function of the difference between the water saturation pressure on the water side of the membrane, and the pressure on the vacuum side of the membrane. The primary theory is that the hydrophobic sheet membrane retains water, but permits vapor pass-through when the vapor side pressure is less than the water saturation pressure. This results in evaporative cooling of the remaining water.

  2. Autism: General Information. Fact Sheet Number 1 = Autismo: Informacion General. Fact Sheet Number 22.

    Science.gov (United States)

    Interstate Research Associates, McLean, VA.

    This fact sheet on autism is offered in both English and Spanish, and is the same in both languages although numbered differently. It provides a definition, information on incidence, typical characteristics, and educational implications. It notes that autism is listed as a separate category under the Individuals with Disabilities Education Act.…

  3. Epilepsy: General Information. Fact Sheet Number 6 = La Epilepsia: Informacion General. Fact Sheet Number 20.

    Science.gov (United States)

    Interstate Research Associates, McLean, VA.

    This fact sheet on epilepsy is offered in both English and Spanish. It provides a definition, information on incidence, typical characteristics, and educational implications. It notes that epilepsy is classified as "other health impaired" under the Individuals with Disabilities Education Act and that students with epilepsy are eligible for special…

  4. The Plasma Sheet as Natural Symmetry Plane for Dipolarization Fronts in the Earth's Magnetotail

    Science.gov (United States)

    Frühauff, D.; Glassmeier, K.-H.

    2017-11-01

    In this work, observations of multispacecraft mission Time History of Events and Macroscale Interactions during Substorms are used for statistical investigation of dipolarization fronts in the near-Earth plasma sheet of the magnetotail. Using very stringent criteria, 460 events are detected in almost 10 years of mission data. Minimum variance analysis is used to determine the normal directions of the phase fronts, providing evidence for the existence of a natural symmetry of these phenomena, given by the neutral sheet of the magnetotail. This finding enables the definition of a local coordinate system based on the Tsyganenko model, reflecting the intrinsic orientation of the neutral sheet and, therefore, the dipolarization fronts. In this way, the comparison of events with very different background conditions is improved. Through this study, the statistical results of Liu, Angelopoulos, Runov, et al. (2013) are both confirmed and extended. In a case study, the knowledge of this plane of symmetry helps to explain the concave curvature of dipolarization fronts in the XZ plane through phase propagation speeds of magnetoacoustic waves. A second case study is presented to determine the central current system of a passing dipolarization front through a constellation of three spacecraft. With this information, a statistical analysis of spacecraft observations above and below the neutral sheet is used to provide further evidence for the neutral sheet as the symmetry plane and the central current system. Furthermore, it is shown that the signatures of dipolarization fronts are under certain conditions closely related to that of flux ropes, indicating a possible relationship between these two transient phenomena.

  5. PRODUCTION OF SHEET FROM PARTICULATE MATERIAL

    Science.gov (United States)

    Blainey, A.

    1959-05-12

    A process is presented for forming coherent sheet material from particulate material such as granular or powdered metal, granular or powdered oxide, slurries, pastes, and plastic mixes which cohere under pressure. The primary object is to avoid the use of expensive and/ or short lived pressing tools, that is, dies and specially profiled rolls, and so to reduce the cost of the product and to prcvide in a simple manner for the making of the product in a variety of shapes or sizes. The sheet material is formed when the particulate material is laterally confined in a boundary material deformable in all lateral directions under axial pressure and then axially compressing the layer of particulate material together with the boundary material.

  6. Understanding Recent Mass Balance Changes of the Greenland Ice Sheet

    Science.gov (United States)

    vanderVeen, Cornelius

    2003-01-01

    The ultimate goal of this project is to better understand the current transfer of mass between the Greenland Ice Sheet, the world's oceans and the atmosphere, and to identify processes controlling the rate of this transfer, to be able to predict with greater confidence future contributions to global sea level rise. During the first year of this project, we focused on establishing longer-term records of change of selected outlet glaciers, reevaluation of mass input to the ice sheet and analysis of climate records derived from ice cores, and modeling meltwater production and runoff from the margins of the ice sheet.

  7. Multi-scale magnetic field intermittence in the plasma sheet

    Directory of Open Access Journals (Sweden)

    Z. Vörös

    2003-09-01

    Full Text Available This paper demonstrates that intermittent magnetic field fluctuations in the plasma sheet exhibit transitory, localized, and multi-scale features. We propose a multifractal-based algorithm, which quantifies intermittence on the basis of the statistical distribution of the "strength of burstiness", estimated within a sliding window. Interesting multi-scale phenomena observed by the Cluster spacecraft include large-scale motion of the current sheet and bursty bulk flow associated turbulence, interpreted as a cross-scale coupling (CSC process.Key words. Magnetospheric physics (magnetotail; plasma sheet – Space plasma physics (turbulence

  8. Control of Power Electronic Converters in Distributed Power Generation Systems: Evaluation of Current Control Structures for Voltage Source Converters operating under Weak Grid Conditions

    OpenAIRE

    Midtsund, Tarjei

    2010-01-01

    The performance of different current controller structures for Voltage Source Converters (VSC) under weak grid conditions caused by large grid impedance is investigated. The VSC is synchronized to the grid by a Phase Locked Loop (PLL). Current control techniques and PLL techniques for handling both symmetrical and asymmetrical conditions are presented and discussed. The investigated current control structures are; the conventional Proportional Integral (PI)-controller in the synchronous rotat...

  9. Soft Costs Fact Sheet

    Energy Technology Data Exchange (ETDEWEB)

    None

    2016-05-01

    This fact sheet is an overview of the systems integration subprogram at the U.S. Department of Energy SunShot Initiative. Soft costs can vary significantly as a result of a fragmented energy marketplace. In the U.S., there are 18,000 jurisdictions and 3,000 utilities with different rules and regulations for how to go solar. The same solar equipment may vary widely in its final installation price due to process and market variations across jurisdictions, creating barriers to rapid industry growth. SunShot supports the development of innovative solutions that enable communities to build their local economies and establish clean energy initiatives that meet their needs, while at the same time creating sustainable solar market conditions.

  10. Systems Integration Fact Sheet

    Energy Technology Data Exchange (ETDEWEB)

    None

    2016-06-01

    This fact sheet is an overview of the Systems Integration subprogram at the U.S. Department of Energy SunShot Initiative. The Systems Integration subprogram enables the widespread deployment of safe, reliable, and cost-effective solar energy technologies by addressing the associated technical and non-technical challenges. These include timely and cost-effective interconnection procedures, optimal system planning, accurate prediction of solar resources, monitoring and control of solar power, maintaining grid reliability and stability, and many more. To address the challenges associated with interconnecting and integrating hundreds of gigawatts of solar power onto the electricity grid, the Systems Integration program funds research, development, and demonstration projects in four broad, interrelated focus areas: grid performance and reliability, dispatchability, power electronics, and communications.

  11. Photovoltaics Fact Sheet

    Energy Technology Data Exchange (ETDEWEB)

    None

    2016-02-01

    This fact sheet is an overview of the Photovoltaics (PV) subprogram at the U.S. Department of Energy SunShot Initiative. The U.S. Department of Energy (DOE)’s Solar Energy Technologies Office works with industry, academia, national laboratories, and other government agencies to advance solar PV, which is the direct conversion of sunlight into electricity by a semiconductor, in support of the goals of the SunShot Initiative. SunShot supports research and development to aggressively advance PV technology by improving efficiency and reliability and lowering manufacturing costs. SunShot’s PV portfolio spans work from early-stage solar cell research through technology commercialization, including work on materials, processes, and device structure and characterization techniques.

  12. The Greenland Ice Sheet Monitoring Network (GLISN)

    Science.gov (United States)

    Anderson, K. R.; Beaudoin, B. C.; Butler, R.; Clinton, J. F.; Dahl-Jensen, T.; Ekstrom, G.; Giardini, D.; Govoni, A.; Hanka, W.; Kanao, M.; Larsen, T.; Lasocki, S.; McCormack, D. A.; Mykkeltveit, S.; Nettles, M.; Agostinetti, N. P.; Stutzmann, E.; Tsuboi, S.; Voss, P.

    2010-12-01

    The GreenLand Ice Sheet monitoring Network (GLISN) is an international, broadband seismic capability for Greenland, being installed and implemented through the collaboration of Denmark, Canada, Germany, Italy, Japan, Norway, Poland, Switzerland, and USA. GLISN is a real-time sensor array of seismic stations to enhance and upgrade the performance of the sparse Greenland seismic infrastructure for detecting, locating, and characterizing glacial earthquakes and other cryo-seismic phenomena, and contributing to our understanding of Ice Sheet dynamics. Complementing data from satellites, geodesy, and other sources, and in concert with these technologies, GLISN will provide a powerful tool for detecting change, and will advance new frontiers of research in the glacial systems; the underlying geological and geophysical processes affecting the Greenland Ice Sheet; interactions between oceans, climate, and the cryosphere; and other multidisciplinary areas of interest to geoscience and climate dynamics. The glacial processes that induce seismic events (internal deformation, sliding at the base, disintegration at the calving front, drainage of supra-glacial lakes) are all integral to the overall dynamics of glaciers, and seismic observations of glaciers therefore provide a quantitative means for monitoring changes in their behavior over time. Long-term seismic monitoring of the Greenland Ice Sheet will contribute to identifying possible unsuspected mechanisms and metrics relevant to ice sheet collapse, and will provide new constraints on Ice Sheet dynamic processes and their potential roles in sea-level rise during the coming decades. GLISN will provide a new, fiducial reference network in and around Greenland for monitoring these phenomena in real-time, and for the broad seismological study of Earth and earthquakes. The 2010 summer field season saw the installation or upgrade of 9 stations in the GLISN network. Sites visited under the GLISN project include Station Nord (NOR

  13. Material Safety Data Sheets (MSDS)

    CERN Document Server

    Lalley, J

    About 250.000 Material Safety Data sheets from the U.S. Government Department of Defense MSDS database, a mirror of data from siri.uvm.edu, MSDS sheets maintained by Cornell University Environmental Health and Safety and other Cornell departments.

  14. Investigation of electrodes under flow of a submicrosecond current pulse with linear density up to 3 MA/cm

    International Nuclear Information System (INIS)

    Branitskii, A. V.; Grabovskii, E. V.; Dzhangobegov, V. V.; Laukhin, Ya. N.; Mitrofanov, K. N.; Oleinik, G. M.; Sasorov, P. V.; Tkachenko, S. I.; Frolov, I. N.

    2016-01-01

    The states of current-carrying elements at the transmission of megaampere current into load are studied. It is determined that the expansion velocity of plasma generated at the outer surface of cylindrical tubes produced of stainless steel, at flowing through them of submicrosecond current pulses with linear density of 3 MA/cm is 5.5 km/s. The evolution of various modes of instability is analyzed.

  15. Analysis of Input Currents in «Frequency Converter - Induction Motor» System under Asymmetry of Mains Voltage

    Directory of Open Access Journals (Sweden)

    B. I. Firago

    2006-01-01

    Full Text Available The influence of modem firequency converters with uncontrolled rectifiers on the supply network is investigated in this paper. The developed mathematical model permits us to analyze rectifier input currents with symmetrical and asymmetrical supply networks and in discontinuous operational mode. Results of modeling in case of asymmetrical supply network are shown in the form of mains current curves and current spectrum of one phase.

  16. Study of interactions between sediment particles in sheet flow using CFD-DEM

    Science.gov (United States)

    Sun, Rui; Xiao, Heng

    2015-11-01

    CFD-DEM simulation is a promising approach in the study of sediment transport. However, the study of sediment transport in sheet flow is still lacking. In this work, a parallelized CFD-DEM solver sediFoam, which has been extensively validated, is applied to the study of sediment transport. Numerical simulations of sediment bed of different characteristics under various waves are studied and compared with the results obtained in the literature, including sediment transport flux, solid volume fraction, and movable bed height. The micro-structures (e.g., contact network) and macroscopic solid phase stresses of the sediment bed are analyzed to gain insight into the inter-particle interactions during the transport process. Additionally, the microstructural properties and solid phase stresses in wave-induced sheet flow are compared to those obtained in unidirectional currents, and significant difference is observed.

  17. Application of Submerged Grouted Anchors in Sheet Pile Quay Walls

    OpenAIRE

    Mollahasani, Ali

    2014-01-01

    Sheet pile walls are one of the oldest earth retention systems utilized in civil engineering projects. They are used for various purposes; such as excavation support system, cofferdams, cut-off walls under dams, slope stabilization, waterfront structures, and flood walls. Sheet pile walls are one of the most common types of quay walls used in port construction. The worldwide increases in utilization of large ships for transportation have created an urgent need of deepening the seabed within p...

  18. Direct electric current treatment under physiologic saline conditions kills Staphylococcus epidermidis biofilms via electrolytic generation of hypochlorous acid.

    Directory of Open Access Journals (Sweden)

    Elizabeth L Sandvik

    Full Text Available The purpose of this study was to investigate the mechanism by which a direct electrical current reduced the viability of Staphylococcus epidermidis biofilms in conjunction with ciprofloxacin at physiologic saline conditions meant to approximate those in an infected artificial joint. Biofilms grown in CDC biofilm reactors were exposed to current for 24 hours in 1/10(th strength tryptic soy broth containing 9 g/L total NaCl. Dose-dependent log reductions up to 6.7 log(10 CFU/cm(2 were observed with the application of direct current at all four levels (0.7 to 1.8 mA/cm(2 both in the presence and absence of ciprofloxacin. There were no significant differences in log reductions for wells with ciprofloxacin compared to those without at the same current levels. When current exposures were repeated without biofilm or organics in the medium, significant generation of free chlorine was measured. Free chlorine doses equivalent to the 24 hour endpoint concentration for each current level were shown to mimic killing achieved by current application. Current exposure (1.8 mA/cm(2 in medium lacking chloride and amended with sulfate, nitrate, or phosphate as alternative electrolytes produced diminished kills of 3, 2, and 0 log reduction, respectively. Direct current also killed Pseudomonas aeruginosa biofilms when NaCl was present. Together these results indicate that electrolysis reactions generating hypochlorous acid from chloride are likely a main contributor to the efficacy of direct current application. A physiologically relevant NaCl concentration is thus a critical parameter in experimental design if direct current is to be investigated for in vivo medical applications.

  19. Direct Electric Current Treatment under Physiologic Saline Conditions Kills Staphylococcus epidermidis Biofilms via Electrolytic Generation of Hypochlorous Acid

    Science.gov (United States)

    Sandvik, Elizabeth L.; McLeod, Bruce R.; Parker, Albert E.; Stewart, Philip S.

    2013-01-01

    The purpose of this study was to investigate the mechanism by which a direct electrical current reduced the viability of Staphylococcus epidermidis biofilms in conjunction with ciprofloxacin at physiologic saline conditions meant to approximate those in an infected artificial joint. Biofilms grown in CDC biofilm reactors were exposed to current for 24 hours in 1/10th strength tryptic soy broth containing 9 g/L total NaCl. Dose-dependent log reductions up to 6.7 log10 CFU/cm2 were observed with the application of direct current at all four levels (0.7 to 1.8 mA/cm2) both in the presence and absence of ciprofloxacin. There were no significant differences in log reductions for wells with ciprofloxacin compared to those without at the same current levels. When current exposures were repeated without biofilm or organics in the medium, significant generation of free chlorine was measured. Free chlorine doses equivalent to the 24 hour endpoint concentration for each current level were shown to mimic killing achieved by current application. Current exposure (1.8 mA/cm2) in medium lacking chloride and amended with sulfate, nitrate, or phosphate as alternative electrolytes produced diminished kills of 3, 2, and 0 log reduction, respectively. Direct current also killed Pseudomonas aeruginosa biofilms when NaCl was present. Together these results indicate that electrolysis reactions generating hypochlorous acid from chloride are likely a main contributor to the efficacy of direct current application. A physiologically relevant NaCl concentration is thus a critical parameter in experimental design if direct current is to be investigated for in vivo medical applications. PMID:23390518

  20. A novel bioenergy feedstock in Latin America? Cultivation potential of Acrocomia aculeata under current and future climate conditions

    NARCIS (Netherlands)

    Plath, Mirco; Moser, Christine; Bailis, Rob; Brandt, Patric; Hirsch, Heidi; Klein, Alexandra Maria; Walmsley, David; Wehrden, von Henrik

    2016-01-01

    Plant oil is a key commodity in the global economy, particularly for food and bioenergy markets. However, current production practices often impair smallholder livelihoods, cause land use changes, and compete for food production. The neotropical palm Acrocomia aculeata is currently being promoted

  1. Enhanced Power Quality and Minimized Peak Current Control in An Inverter based Microgrid under Unbalanced Grid Faults

    DEFF Research Database (Denmark)

    Liu, Wenzhao; Guo, Xiaoqiang; Sulligoi, Giorgio

    2016-01-01

    The microgrid inverter experiences the power oscillations and current harmonics in case of the unbalanced grid voltage faults. However, there is a trade-off between power oscillations and current harmonics should be considered in three phase three wire inverter systems during the conventional fault...

  2. Folded Sheet Versus Transparent Sheet Models for Human Symmetry Judgments

    Directory of Open Access Journals (Sweden)

    Jacques Ninio

    2011-07-01

    Full Text Available As a contribution to the mysteries of human symmetry perception, reaction time data were collected on the detection of symmetry or repetition violations, in the context of short term visual memory studies. The histograms for reaction time distributions are rather narrow in the case of symmetry judgments. Their analysis was performed in terms of a simple kinetic model of a mental process in two steps, a slow one for the construction of the representation of the images to be compared, and a fast one, in the 50 ms range, for the decision. There was no need for an additional ‘mental rotation’ step. Symmetry seems to facilitate the construction step. I also present here original stimuli showing a color equalization effect across a symmetry axis, and its counterpart in periodic patterns. According to a “folded sheet model”, when a shape is perceived, the brain automatically constructs a mirror-image representation of the shape. Based in part on the reaction time analysis, I present here an alternative “transparent sheet” model in which the brain constructs a single representation, which can be accessed from two sides, thus generating simultaneously a pattern and its mirror-symmetric partner. Filtering processes, implied by current models of symmetry perception could intervene at an early stage, by nucleating the propagation of similar perceptual groupings in the two symmetric images.

  3. The Female Sexual Response: Current Models, Neurobiological Underpinnings and Agents Currently Approved or Under Investigation for the Treatment of Hypoactive Sexual Desire Disorder.

    Science.gov (United States)

    Kingsberg, Sheryl A; Clayton, Anita H; Pfaus, James G

    2015-11-01

    the agents currently being investigated as treatment options for HSDD target and influence key players within these excitatory and inhibitory pathways, including various hormone therapies and centrally acting drugs, such as buspirone, bupropion and bremelanotide.

  4. Stiffness Matrices and Anisotropy in the Trapezoidal Corrugated Composite Sheets

    Directory of Open Access Journals (Sweden)

    Mohammad Golzar

    2013-10-01

    Full Text Available In the some applications like as morphing technology, high strain and anisotropic behavior are essential design requirements. The corrugated composite sheets due to their special geometries have potential to high deflection under axial loading through longitudinal direction of corrugation. In this research, the strain and the anisotropic behavior of corrugated composite sheets are investigated by fabricating glass/epoxy samples with trapezoidal geometries. For evaluation of the mechanical behavior of the composites the samples were subjected to tension and flexural tests in the longitudinal and transverse directions of corrugation. In order to determine anisotropic behavior of the corrugated sheets, two approaches were introduced: (1 tensile anisotropic (E* and (2 flexural anisotropic (D*. The anisotropic behavior and ultimate deflections were investigated theoretically and experimentally. In this paper, mechanical behaviors based on theoretical and experimental analysis including the elastic constants and stiffness matrices of trapezoidal corrugated composite sheets were studied and the results were verified by finite element method. The results of the numerical and analytical solutions were compared with those of experimental tests. Finally, the load-displacement curves of tensile tests in longitudinal direction of corrugation, the ultimate deflection and anisotropy behavior of these exclusive composite sheets in the corrugated composite sheets were studied experimentally. The experimental results of the trapezoidal corrugated sheets showed that one of the most important parameters in the ultimate strain was amplitude of the corrugation elements. Generally, increasing the amplitude and element per length unit of trapezoidal corrugated specimen led to higher ultimate strain.

  5. Fundamental transverse mode selection and self-stabilization in large optical cavity diode lasers under high injection current densities

    Science.gov (United States)

    Avrutin, Eugene A.; Ryvkin, Boris S.; Payusov, Alexey S.; Serin, Artem A.; Gordeev, Nikita Yu

    2015-11-01

    It is shown that in high-power, large optical cavity laser diodes at high injection currents, the optical losses due to nonuniform carrier accumulation in the optical confinement layer can ensure the laser operation in the fundamental transverse mode. An experimental demonstration of switching from second order mode to fundamental mode in large optical cavity lasers with current and/or temperature increase is reported and explained, with the calculated values for the switching current and temperature in good agreement with the measurements. The results experimentally prove the nonuniform nature of carrier accumulation in the confinement layer and may aid laser design for optimizing the output.

  6. Lubricant Test Methods for Sheet Metal Forming

    DEFF Research Database (Denmark)

    Bay, Niels; Olsson, David Dam; Andreasen, Jan Lasson

    2008-01-01

    Sheet metal forming of tribologically difficult materials such as stainless steel, Al-alloys and Ti-alloys or forming in tribologically difficult operations like ironing, punching or deep drawing of thick plate requires often use of environmentally hazardous lubricants such as chlorinated paraffin...... oils in order to avoid galling. The present paper describes a systematic research in the development of new, environmentally harmless lubricants focusing on the lubricant testing aspects. A system of laboratory tests has been developed to study the lubricant performance under the very varied conditions...... appearing in different sheet forming operations such as stretch forming, deep drawing, ironing and punching. The laboratory tests have been especially designed to model the conditions in industrial production. Application of the tests for evaluating new lubricants before introducing them in production has...

  7. DC-Voltage Fluctuation Elimination Through a DC-Capacitor Current Control for DFIG Converters Under Unbalanced Grid Voltage Conditions

    DEFF Research Database (Denmark)

    Liu, Changjin; Xu, Dehong; Zhu, Nan

    2013-01-01

    Unbalanced grid voltage causes a large second-order harmonic current in the dc-link capacitors as well as dc-voltage fluctuation, which potentially will degrade the lifespan and reliability of the capacitors in voltage source converters. This paper proposes a novel dc-capacitor current control me...... grid voltage conditions. A modular implementation method of the proposed control strategy is developed for the DFIG controller. Finally, experiments are presented to validate the theoretical analysis....

  8. Modelling the Antarctic Ice Sheet

    DEFF Research Database (Denmark)

    Pedersen, Jens Olaf Pepke; Holm, A.

    2015-01-01

    Science) Antarctic Ice Sheet (DAIS) model (Shaffer 2014) is forced by reconstructed time series of Antarctic temperature, global sea level and ocean subsurface temperature over the last two glacial cycles. In this talk a modelling work of the Antarctic ice sheet over most of the Cenozoic era using...... the DAIS model will be presented. G. Shaffer (2014) Formulation, calibration and validation of the DAIS model (version 1), a simple Antarctic ice sheet model sensitive to variations of sea level and ocean subsurface temperature, Geosci. Model Dev., 7, 1803‐1818...

  9. Formation of current singularity in a topologically constrained plasma

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yao [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Huang, Yi-Min [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Qin, Hong [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Univ Sci & Technol China, Dept Modern Phys, Hefei 230026, Anhui, Peoples R China.; Bhattacharjee, A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences

    2016-02-01

    Recently a variational integrator for ideal magnetohydrodynamics in Lagrangian labeling has been developed. Its built-in frozen-in equation makes it optimal for studying current sheet formation. We use this scheme to study the Hahm-Kulsrud-Taylor problem, which considers the response of a 2D plasma magnetized by a sheared field under sinusoidal boundary forcing. We obtain an equilibrium solution that preserves the magnetic topology of the initial field exactly, with a fluid mapping that is non-differentiable. Unlike previous studies that examine the current density output, we identify a singular current sheet from the fluid mapping. These results are benchmarked with a constrained Grad-Shafranov solver. The same signature of current singularity can be found in other cases with more complex magnetic topologies.

  10. Shapeable sheet without plastic deformation

    Science.gov (United States)

    Oppenheimer, Naomi; Witten, Thomas A.

    2015-11-01

    Randomly crumpled sheets have shape memory. In order to understand the basis of this form of memory, we simulate triangular lattices of springs whose lengths are altered to create a topography with multiple potential energy minima. We then deform these lattices into different shapes and investigate their ability to retain the imposed shape when the energy is relaxed. The lattices are able to retain a range of curvatures. Under moderate forcing from a state of local equilibrium, the lattices deform by several percent but return to their retained shape when the forces are removed. By increasing the forcing until an irreversible motion occurs, we find that the transitions between remembered shapes show cooperativity among several springs. For fixed lattice structures, the shape memory tends to decrease as the lattice is enlarged; we propose ways to counter this decrease by modifying the lattice geometry. We survey the energy landscape by displacing individual nodes. An extensive fraction of these nodes proves to be bistable; they retain their displaced position when the energy is relaxed. Bending the lattice to a stable curved state alters the pattern of bistable nodes. We discuss this shapeability in the context of other forms of material memory and contrast it with the shapeability of plastic deformation. We outline the prospects for making real materials based on these principles.

  11. Photobiology Research Laboratory (Fact Sheet)

    Energy Technology Data Exchange (ETDEWEB)

    2012-06-01

    This fact sheet provides information about Photobiology Research Laboratory capabilities and applications at NREL. The photobiology group's research is in four main areas: (1) Comprehensive studies of fuel-producing photosynthetic, fermentative, and chemolithotrophic model microorganisms; (2) Characterization and engineering of redox enzymes and proteins for fuel production; (3) Genetic and pathway engineering of model organisms to improve production of hydrogen and hydrocarbon fuels; and (4) Studies of nanosystems using biological and non-biological materials in hybrid generation. NREL's photobiology research capabilities include: (1) Controlled and automated photobioreactors and fermenters for growing microorganisms under a variety of environmental conditions; (2) High-and medium-throughput screening of H{sub 2}-producing organisms; (3) Homologous and heterologous expression, purification, and biochemical/biophysical characterization of redox enzymes and proteins; (4) Qualitative and quantitative analyses of gases, metabolites, carbohydrates, lipids, and proteins; (5) Genetic and pathway engineering and development of novel genetic toolboxes; and (6) Design and spectroscopic characterization of enzyme-based biofuel cells and energy conversion nanodevices.

  12. Modeling the sensitivity of the Greenland Ice Sheet (GrIS) over the last deglaciation using improved climate reconstructions of temperature and precipitation in the Ice Sheet System Model (ISSM)

    Science.gov (United States)

    Cuzzone, J. K.; Larour, E. Y.; Morlighem, M.; Schlegel, N.; Badgeley, J.; Steig, E. J.; Buizert, C.

    2017-12-01

    Paleoclimate spinups of ice sheets can provide an important boundary condition for simulating ice sheets under present and future climate scenarios, while also providing a context on how sensitive ice sheets were to past climate change. Currently, many ice sheet models that simulate the past behavior of ice sheets rely on tuning of model specific parameter space or by adjusting the surface forcings (i.e. temperature and precipitation) to achieve the best fit with paleoclimate evidence of the ice sheet history. To create the necessary surface mass balance fields, a crude approximation based upon isotopic variations in ice core δ18O is often used to scale a modern day gridded climatology of temperature and precipitation back in time. This method is advantageous for long spinups, where variations in ice core δ18O is only needed to create the necessary surface forcings driving the past ice sheet surface mass balance. However, it cannot provide any information regarding changes in past climate seasonality and it assumes precipitation follows a purely thermodynamic relationship, therefore disregarding changes in past atmospheric circulation. Recent work has been performed to merge ice core temperature reconstructions with climate simulations during the last deglaciation, providing a continental wide Greenland Ice Sheet (GrIS) gridded temperature and precipitation reconstruction that extends back to the last glacial maximum (LGM). These new datasets resolve changes in past seasonality and incorporate changes in past atmospheric circulation by using information from climate models. This work will use two independent reconstructions of the past GrIS temperature and precipitation climatology that utilize different data assimilation techniques to drive simulations of the last deglaciation of the GrIS in the Ice Sheet System Model (ISSM). The simulation performed with ISSM relies on a 3 dimensional, thermomechanical higher order model. The results presented here will outline

  13. Finite Control Set–Model Predictive Control with Modulation to Mitigate Harmonic Component in Output Current for a Grid-Connected Inverter under Distorted Grid Conditions

    OpenAIRE

    Tien Hai Nguyen; Kyeong-Hwa Kim

    2017-01-01

    This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. In terms of performance, it is important for a grid-connected inverter to maintain the harmonic contents of inverter output currents below the specified limit even when the grid is subject to harmonic distortion. To address this problem, this paper proposes a modulated finite control set–model predictive control (FCS-MPC) scheme, which effectively mitigates the h...

  14. Current characteristic signals of aqueous solution transferring through microfluidic channel under non-continuous DC electric field

    Directory of Open Access Journals (Sweden)

    HongWei Ma

    2014-10-01

    Full Text Available The surface effect is becoming apparently significant as the miniaturization of fluidic devices. In the micro/nanochannel fluidics, the electrode surface effects have the same important influence on the current signals as the channel surface effects. In this paper, when aqueous solution are driven with non-continuous DC electric field force, the characteristics of current signals of the fluid transferring through microfluidic channel are systematically studied. Six modes of current signal are summarized, and some new significant phenomena are found, e.g. there exists a critical voltage at which the steady current value equals to zero; the absolute value of the steady current decreases at first, however, it increases with the external voltage greater than the critical voltage as the electrode area ratio of cathode and anode is 10 and 20; the critical voltage increases with the enhancing of electrode area ratio of cathode and anode and solution pH, while it decreases with the raising of ion concentration. Finally, the microscopic mechanism of the electrode surface charge effects is discussed preliminarily. The rules will be helpful for detecting and manipulating single biomolecules in the micro/nanofluidic chips and biosensors.

  15. Magneto-hydrodynamics of coupled fluid–sheet interface with mass suction and blowing

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, R., E-mail: uqrahma3@uq.edu.au

    2016-01-15

    There are large number of studies which prescribe the kinematics of the sheet and ignore the sheet's mechanics. However, the current boundary layer analysis investigates the mechanics of both the electrically conducting fluid and a permeable sheet, which makes it distinct from the other studies in the literature. One of the objectives of the current study is to (i) examine the behaviour of magnetic field effect for both the surface and the electrically conducting fluid (ii) investigate the heat and mass transfer between a permeable sheet and the surrounding electrically conducting fluid across the hydro, thermal and mass boundary layers. Self-similar solutions are obtained by considering the RK45 technique. Analytical solution is also found for the stretching sheet case. The skin friction dual solutions are presented for various types of sheet. The influence of pertinent parameters on the dimensionless velocity, shear stress, temperature, mass concentration, heat and mass transfer rates on the fluid–sheet interface is presented graphically as well as numerically. The obtained results are of potential benefit for studying the electrically conducting flow over various soft surfaces such as synthetic plastics, soft silicone sheet and soft synthetic rubber sheet. These surfaces are easily deformed by thermal fluctuations or thermal stresses. - Highlights: • The momentum equation is modelled for both the surrounding MHD fluid and the sheet with the effects of mass suction and blowing. • The current study further investigates the heat and mass transfer characteristics between a permeable sheet and the surrounding electrically conducting fluid across the thermal and mass boundary layers. • Both the approximated and analytical techniques have been included for the purpose of comparison, and the perfect numerical agreements have been established with the previous studies. • Dual solutions for the skin friction coefficients are found for various categories of

  16. Magneto-hydrodynamics of coupled fluid–sheet interface with mass suction and blowing

    International Nuclear Information System (INIS)

    Ahmad, R.

    2016-01-01

    There are large number of studies which prescribe the kinematics of the sheet and ignore the sheet's mechanics. However, the current boundary layer analysis investigates the mechanics of both the electrically conducting fluid and a permeable sheet, which makes it distinct from the other studies in the literature. One of the objectives of the current study is to (i) examine the behaviour of magnetic field effect for both the surface and the electrically conducting fluid (ii) investigate the heat and mass transfer between a permeable sheet and the surrounding electrically conducting fluid across the hydro, thermal and mass boundary layers. Self-similar solutions are obtained by considering the RK45 technique. Analytical solution is also found for the stretching sheet case. The skin friction dual solutions are presented for various types of sheet. The influence of pertinent parameters on the dimensionless velocity, shear stress, temperature, mass concentration, heat and mass transfer rates on the fluid–sheet interface is presented graphically as well as numerically. The obtained results are of potential benefit for studying the electrically conducting flow over various soft surfaces such as synthetic plastics, soft silicone sheet and soft synthetic rubber sheet. These surfaces are easily deformed by thermal fluctuations or thermal stresses. - Highlights: • The momentum equation is modelled for both the surrounding MHD fluid and the sheet with the effects of mass suction and blowing. • The current study further investigates the heat and mass transfer characteristics between a permeable sheet and the surrounding electrically conducting fluid across the thermal and mass boundary layers. • Both the approximated and analytical techniques have been included for the purpose of comparison, and the perfect numerical agreements have been established with the previous studies. • Dual solutions for the skin friction coefficients are found for various categories of

  17. Enhanced ice sheet melting driven by volcanic eruptions during the last deglaciation.

    Science.gov (United States)

    Muschitiello, Francesco; Pausata, Francesco S R; Lea, James M; Mair, Douglas W F; Wohlfarth, Barbara

    2017-10-24

    Volcanic eruptions can impact the mass balance of ice sheets through changes in climate and the radiative properties of the ice. Yet, empirical evidence highlighting the sensitivity of ancient ice sheets to volcanism is scarce. Here we present an exceptionally well-dated annual glacial varve chronology recording the melting history of the Fennoscandian Ice Sheet at the end of the last deglaciation (∼13,200-12,000 years ago). Our data indicate that abrupt ice melting events coincide with volcanogenic aerosol emissions recorded in Greenland ice cores. We suggest that enhanced ice sheet runoff is primarily associated with albedo effects due to deposition of ash sourced from high-latitude volcanic eruptions. Climate and snowpack mass-balance simulations show evidence for enhanced ice sheet runoff under volcanically forced conditions despite atmospheric cooling. The sensitivity of past ice sheets to volcanic ashfall highlights the need for an accurate coupling between atmosphere and ice sheet components in climate models.

  18. Complex world-sheets from N=2 strings

    International Nuclear Information System (INIS)

    Barbon, J.L.F.

    1996-01-01

    We study some properties of target space strings constructed from (2,1) heterotic strings. We argue that world-sheet complexification is a general property of the bosonic sector of such target world-sheets. We give a target space interpretation of this fact and relate it to the non-gaussian nature of free string field theory. We provide several one-loop calculations supporting the stringy construction of critical world-sheets in terms of (2,1) models. Using finite-temperature boundary conditions in the underlying (2,1) string we obtain non-chiral target space spin structures, and point out some of the problems arising for chiral spin structures, such as the heterotic world-sheet. To this end, we study the torus partition function of the corresponding asymmetric orbifold of the (2,1) string. (orig.)

  19. Financing gas plants using off balance sheet structures

    International Nuclear Information System (INIS)

    Best, R.J.; Malcolm, V.

    1999-01-01

    A means by which to finance oil and gas facilities using off balance sheet structures was presented. Off balance sheet facility financing means the sale by an oil and gas producer of a processing and/or transportation facility to a financial intermediary, who under a Management Agreement, appoints the producer as the operator of the facility. The financial intermediary charges a fixed processing fee to the producer and all the benefits and upside of ownership are retained by the producer. This paper deals specifically with a flexible off balance sheet facility financing structure that can be used to make effective use of discretionary capital which is committed to gas processing and to the construction of new gas processing facilities. Off balance sheet financing is an attractive alternative method of ownership that frees up capital that is locked into the facilities while allowing the producer to retain strategic control of the processing facility

  20. Research of the Ion Current Density Influence on the Glass-Ceramics Surface Defects Forming under Ion-Beam Processing

    Directory of Open Access Journals (Sweden)

    V. G. Pozdnyakov

    2015-01-01

    Full Text Available Development of modern optics is primarily determined by manufacturing accuracy of the working surfaces of optical parts. Therefore, at the last stage of manufacturing optical parts the ion-beam treatment is applied. This method uses spraying the high-energy ions of heavy gases on the surface of a solid body. After an intense ion treatment there are microscopic defects, resembling chips, on the surface of polycrystalline glass. The aim of this work is to study distribution of the surface density of defects by sizes, depending on the density of ion current.Accelerator with an anode layer and a focused ion beam was used as an ion source. The accelerator worked on argon and created ion beam with Gaussian distribution of current density along the radius. The excess positive charge of the ion beam was compensated owing to ionization of residual gas. To eliminate the influence of slow ions with peripheral regions of the ion beam, the etching was performed through a circular aperture with a diameter of 40 mm.Surface treatment of the sample was carried out at the discharge voltage of 3800 V and current of 50 mA for 30 min. The maximum ion current density on the sample surface was 20.2 A/m2 and a power density was of 5.4·104 W/m2 .Distribution of defects by size was measured in three areas of the treated surface corresponding to different densities of ion current, namely: 20.2 A/m2 , 11.3A/m2 , and 3.4 A/m2 . Their number per area unit defines a density of defects.The results show that with increasing ion current density the density of defects on the surface of polycrystalline glass decreases. Thus a view of distribution function of defect density according to size is changed: density of small defects is reduced, and density of large ones increases. Also with increasing ion current density is observed an increase in the size of defects: a 6 times increase of the average size of defects results in 1.6 times increasing ion current density.These data will

  1. Subglacial lake and meltwater flow predictions of the last North American and European Ice Sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Tarasov, L.

    2012-04-01

    There is increasing recognition that subglacial lakes act as key components within the ice sheet system, capable of influencing ice-sheet topography, ice volume and ice flow. The subglacial water systems themselves are recognised as being both active and dynamic, with large discharges of meltwater capable of flowing down hydrological pathways both between lakes and to the ice-sheet margins. At present, much glaciological research is concerned with the role of modern subglacial lake systems in Antarctica. Another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath ice sheets of the last glaciation. Investigation of such palaeo-subglacial lakes offers significant advantages because we have comprehensive information about the bed properties, they are much more accessible and we can examine and sample the sediments with ease. If we can find palaeo-subglacial lakes then we have the potential to advance understanding with regard to the topographic context and hydrological pathways that the phenomena form a part of; essentially we gain spatial and sedimentological information in relation to investigations of contemporary subglacial lakes and lose out on the short-time dynamics. In this work we present predictions of palaeo-subglacial lakes and meltwater drainage pathways under the former European and North American ice sheets during the last glaciation. We utilise data on the current topography and seafloor bathymetry, and elevation models of the ice and ground surface topography (interpolated to a 5 km grid) to calculate the hydraulic potential surface at the ice-sheet bed. Meltwater routing algorithms and the flooding of local hydraulic minima allow us to predict subglacial channels and lakes respectively. Given that specific ice-surface and bed topographies are only known from modelled outputs, and thus contain significant uncertainty, we utilise many such outputs to examine

  2. The potential of cell sheet technique on the development of hepatocellular carcinoma in rat models.

    Directory of Open Access Journals (Sweden)

    Alaa T Alshareeda

    Full Text Available Hepatocellular carcinoma (HCC is considered the 3rd leading cause of death by cancer worldwide with the majority of patients were diagnosed in the late stages. Currently, there is no effective therapy. The selection of an animal model that mimics human cancer is essential for the identification of prognostic/predictive markers, candidate genes underlying cancer induction and the examination of factors that may influence the response of cancers to therapeutic agents and regimens. In this study, we developed a HCC nude rat models using cell sheet and examined the effect of human stromal cells (SCs on the development of the HCC model and on different liver parameters such as albumin and urea.Transplanted cell sheet for HCC rat models was fabricated using thermo-responsive culture dishes. The effect of human umbilical cord mesenchymal stromal cells (UC-MSCs and human bone marrow mesenchymal stromal cells (BM-MSCs on the developed tumour was tested. Furthermore, development of tumour and detection of the liver parameter was studied. Additionally, angiogenesis assay was performed using Matrigel.HepG2 cells requires five days to form a complete cell sheet while HepG2 co-cultured with UC-MSCs or BM-MSCs took only three days. The tumour developed within 4 weeks after transplantation of the HCC sheet on the liver of nude rats. Both UC-MSCs and BM-MSCs improved the secretion of liver parameters by increasing the secretion of albumin and urea. Comparatively, the UC-MSCs were more effective than BM-MSCs, but unlike BM-MSCs, UC-MSCs prevented liver tumour formation and the tube formation of HCC.Since this is a novel study to induce liver tumour in rats using hepatocellular carcinoma sheet and stromal cells, the data obtained suggest that cell sheet is a fast and easy technique to develop HCC models as well as UC-MSCs have therapeutic potential for liver diseases. Additionally, the data procured indicates that stromal cells enhanced the fabrication of HepG2

  3. 2007 Swimming Season Fact Sheets

    Science.gov (United States)

    To help beachgoers make informed decisions about swimming at U.S. beaches, EPA annually publishes state-by-state data about beach closings and advisories for the previous year's swimming season. These fact sheets summarize that information by state.

  4. 2006 Swimming Season Fact Sheets

    Science.gov (United States)

    To help beachgoers make informed decisions about swimming at U.S. beaches, EPA annually publishes state-by-state data about beach closings and advisories for the previous year's swimming season. These fact sheets summarize that information by state.

  5. 2009 Swimming Season Fact Sheets

    Science.gov (United States)

    To help beachgoers make informed decisions about swimming at U.S. beaches, EPA annually publishes state-by-state data about beach closings and advisories for the previous year's swimming season. These fact sheets summarize that information by state.

  6. 2008 Swimming Season Fact Sheets

    Science.gov (United States)

    To help beachgoers make informed decisions about swimming at U.S. beaches, EPA annually publishes state-by-state data about beach closings and advisories for the previous year's swimming season. These fact sheets summarize that information by state.

  7. 2010 Swimming Season Fact Sheets

    Science.gov (United States)

    To help beachgoers make informed decisions about swimming at U.S. beaches, EPA annually publishes state-by-state data about beach closings and advisories for the previous year's swimming season. These fact sheets summarize that information by state.

  8. 2012 Swimming Season Fact Sheets

    Science.gov (United States)

    To help beachgoers make informed decisions about swimming at U.S. beaches, EPA annually publishes state-by-state data about beach closings and advisories for the previous year's swimming season. These fact sheets summarize that information by state.

  9. State Fact Sheets on COPD

    Science.gov (United States)

    ... Submit Search The CDC Chronic Obstructive Pulmonary Disease (COPD) Note: Javascript is disabled or is not supported ... message, please visit this page: About CDC.gov . COPD Homepage Data and Statistics Fact Sheets Publications Publications ...

  10. Fault Ride Though Control of Photovoltaic Grid-connected Inverter with Current-limited Capability under Offshore Unbalanced Voltage Conditions

    DEFF Research Database (Denmark)

    Liu, Wenzhao; Guo, Xiaoqiang; Savaghebi, Mehdi

    2016-01-01

    The photovoltaic (PV) inverter installed on board experiences the excessive current stress in case of the offshore unbalanced voltage fault ride through (FRT), which significantly affects the operation reliability of the power supply system. In order to solve the problem, the inherent mechanism o...

  11. Importance of Nisar Mission for Ice Sheet Studies

    Science.gov (United States)

    Rignot, E. J.; Scheuchl, B.; Mouginot, J.; Morlighem, M.

    2014-12-01

    This presentation addresses how the synthetic-aperture radar (SAR) satellite mission under discussion between NASA and ISRO - entitled NISAR - will help us better understand and project the evolution of ice sheets and glaciers in a changing climate. NISAR is a dedicated L-band interferometry mission that will document changes in ice flow dynamics, grounding line positions and other critical boundaries over the lifetime of its mission. Changes in ice sheet dynamics represent by far the largest uncertainty in sea level projections. NISAR will better constrain critical boundaries of ice sheets at the base (basal friction) and at the seaward margins (ice melt rate) by providing the first set of continuous, systematic and comprehensive observations of ice sheet dynamics that will help us better understand ice sheets and glaciers and enable massive data assimilation in numerical ice sheet models. NISAR will contribute observations of areas of irreversible retreat taking place in Greenland and Antarctica, provide detailed time series of glacier velocities throughout entire seasonal cycles, document grounding line dynamics on weekly time scales, enable estimations of temporal and spatial changes in basal friction during glacial retreat; it will also in combination with other data help us map the bed topography of entire ice sheets at a high spatial resolution, document changes in ice shelf melt rate around the periphery of the continents, and provide a first systematic 3D vector mapping of ice velocity. NISAR will constitute a much needed warning system for ice sheet and ice shelf changes, it will document fundamental processes poorly observed in the past (e.g. calving, ice shelf melt, grounding line dynamics) and enable robust data assimilation to play a critical role in reducing uncertainties of coupled numerical models of ocean-ice-atmosphere interactions. This work was performed at UCI and JPL under a contract with NASA.

  12. An improved synchronous reference frame current control strategy for a photovoltaic grid-connected inverter under unbalanced and nonlinear load conditions

    Science.gov (United States)

    Naderipour, Amirreza; Asuhaimi Mohd Zin, Abdullah; Bin Habibuddin, Mohd Hafiz; Miveh, Mohammad Reza; Guerrero, Josep M.

    2017-01-01

    In recent years, renewable energy sources have been considered the most encouraging resources for grid and off-grid power generation. This paper presents an improved current control strategy for a three-phase photovoltaic grid-connected inverter (GCI) under unbalanced and nonlinear load conditions. It is challenging to suppress the harmonic content in the output current below a pre-set value in the GCI. It is also difficult to compensate for unbalanced loads even when the grid is under disruption due to total harmonic distortion (THD) and unbalanced loads. The primary advantage and objective of this method is to effectively compensate for the harmonic current content of the grid current and microgrid without the use of any compensation devices, such as active and passive filters. This method leads to a very low THD in both the GCI currents and the current exchanged with the grid. The control approach is designed to control the active and reactive power and harmonic current compensation, and it also corrects the system unbalance. The proposed control method features the synchronous reference frame (SRF) method. Simulation results are presented to demonstrate the effective performance of the proposed method. PMID:28192436

  13. An improved synchronous reference frame current control strategy for a photovoltaic grid-connected inverter under unbalanced and nonlinear load conditions.

    Science.gov (United States)

    Naderipour, Amirreza; Asuhaimi Mohd Zin, Abdullah; Bin Habibuddin, Mohd Hafiz; Miveh, Mohammad Reza; Guerrero, Josep M

    2017-01-01

    In recent years, renewable energy sources have been considered the most encouraging resources for grid and off-grid power generation. This paper presents an improved current control strategy for a three-phase photovoltaic grid-connected inverter (GCI) under unbalanced and nonlinear load conditions. It is challenging to suppress the harmonic content in the output current below a pre-set value in the GCI. It is also difficult to compensate for unbalanced loads even when the grid is under disruption due to total harmonic distortion (THD) and unbalanced loads. The primary advantage and objective of this method is to effectively compensate for the harmonic current content of the grid current and microgrid without the use of any compensation devices, such as active and passive filters. This method leads to a very low THD in both the GCI currents and the current exchanged with the grid. The control approach is designed to control the active and reactive power and harmonic current compensation, and it also corrects the system unbalance. The proposed control method features the synchronous reference frame (SRF) method. Simulation results are presented to demonstrate the effective performance of the proposed method.

  14. Energy information sheets, July 1998

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-07-01

    The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the public. The Energy Information Sheets was developed to provide general information on various aspects of fuel production, prices, consumption, and capability. Additional information on related subject matter can be found in other Energy Information Administration (EIA) publications as referenced at the end of each sheet.

  15. Energy information sheets, September 1996

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1996-09-01

    The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the public. The Energy Information Sheets was developed to provide general information on various aspects of fuel production, prices, consumption, and capability. Additional information on related subject matter can be found in other Energy Information Administration (EIA) publications as referenced at the end of each sheet.

  16. In-situ repairs of pipelines using metal arc welding under oil (MAW-UO) aided by eddy current crack detection

    Science.gov (United States)

    Almostaneer, Hamad; Jones, Zachary S.; Liu, Stephen; Olson, David L.

    2012-05-01

    Metal arc welding under oil (MAW-UO) is a new process developed to make in-situ internal repairs of in-service oil industry pipelines, tanks and vessels without the need to evacuate the service from the containing fluid. High nickel alloy welding wires were used to produce a tough, relatively soft, austenitic weld metal; with reduced weld metal hardness, porosity, residual strain, and cracking susceptibility. Eddy current sensors were able to detect cracks under oil which then can be repaired in-situ using MAW-UO. The in-situ under oil crack detection and arc weld repair process will be described.

  17. Côte D’Ivoire; Fifth Review Under the Three-Year Arrangement Under the Extended Credit Facility and Requests for Modification of Performance Criteria and Extension of the Current Arrangement

    OpenAIRE

    International Monetary Fund

    2014-01-01

    This paper discusses Côte d’Ivoire’s Fifth Review Under the Three-Year Arrangement Under the Extended Credit Facility (ECF) and Requests for Modification of Performance Criteria (PC) and Extension of the Current Arrangement. Program performance has been strong. All end-December PCs and all but one indicative target were met. On the downside, fiscal discipline and structural reform momentum could be adversely affected during the run-up to the October 2015 presidential elections. The IMF staff ...

  18. Period-doubling bifurcation cascade observed in a ferromagnetic nanoparticle under the action of a spin-polarized current

    Energy Technology Data Exchange (ETDEWEB)

    Horley, Paul P., E-mail: paul.horley@cimav.edu.mx [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Kushnir, Mykola Ya. [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine); Morales-Meza, Mishel [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Sukhov, Alexander [Institut für Physik, Martin-Luther Universität Halle-Wittenberg, 06120 Halle (Saale) (Germany); Rusyn, Volodymyr [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine)

    2016-04-01

    We report on complex magnetization dynamics in a forced spin valve oscillator subjected to a varying magnetic field and a constant spin-polarized current. The transition from periodic to chaotic magnetic motion was illustrated with bifurcation diagrams and Hausdorff dimension – the methods developed for dissipative self-organizing systems. It was shown that bifurcation cascades can be obtained either by tuning the injected spin-polarized current or by changing the magnitude of applied magnetic field. The order–chaos transition in magnetization dynamics can be also directly observed from the hysteresis curves. The resulting complex oscillations are useful for development of spin-valve devices operating in harmonic and chaotic modes.

  19. Behavioral Responses Of Fish To A Current-Based Hydrokinetic Turbine Under Mutlipe Operational Conditions: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Grippo, Mark A. [Argonne National Lab. (ANL), Argonne, IL (United States); Shen, Haixue [Univ. of Maine, Orono, ME (United States); Zydlewski, Gayle [Univ. of Maine, Orono, ME (United States); Rao, Shivanesh [Univ. of Maine, Orono, ME (United States); Goodwin, Andy [United States Army Engineer R & D Center, Vicksburg, MI (United States)

    2017-02-01

    There is significant interest in the interaction of aquatic organisms with current-based marine and hydrokinetic (MHK) technologies. Determining the potential impacts of MHK devices on fish behavior is critical to addressing the environmental concerns that could act as barriers to the permitting and deployment of MHK devices. To address these concerns, we use field monitoring and fish behavior models to characterize the behavioral responses of fish to MHK turbines and infer potential stimuli that may have elicited the observed behavioral changes.

  20. The interplanetary magnetic field By-dependent field-aligned current in the dayside polar cap under quiet conditions

    International Nuclear Information System (INIS)

    Yamauchi, M.; Araki, T.

    1989-01-01

    Spatial distribution and temporal variation of the interplanetary magnetic field (IMF) B y -dependent cusp region field-aligned currents (FACs) during quiet periods were studied by use of magnetic data observed by Magsat. The analysis was made for 11 events (each event lasts more than one and a half days) when the IMF B y component was steadily large and B x was relatively small (|B z | y |). Results of the analysis of total 62 half-day periods for the IMF B y -dependent cusp region FAC are summarized as follows: (1) the IMF B y -dependent cusp region FAC is located at around 86 degree-87 degree invariant latitude local noon, which is more poleward than the location of the IMF B z -dependent cusp region FAC; (2) the current density of this FAC is greater than previous studies (≥ 4 μA/m 2 for IMF B y = 6 nT); (3) there are two time scales for the IMF B y -dependent cusp region FAC to appear: the initial rise of the current is on a short time scale, ∼ 10 min, and it is followed by a gradual increase on a time scale of several hours to a half day; (4) the seasonal change of this FAC is greater than that of the nightside region 1 or region 2 FACs; (5) the IMF B z -dependent cusp region FAC is not well observed around the cusp when the IMF B y -dependent cusp region FAC is intense