Fast Fermi acceleration in the plasma sheet boundary layer

International Nuclear Information System (INIS)

Wu, C.S.; Lui, A.T.Y.

1989-01-01

A longstanding question in the field of magnetospheric physics is the source of the energetic particles which are commonly observed along the plasma sheet boundary layer (PSBL). Several models have been suggested for the acceleration of these particles. We suggest a means by which the fast Fermi acceleration mechanism [Wu, 1984] can accelerate electrons at the plasma sheet and perhaps account for some of the observations. We propose the following: A localized hydromagnetic disturbance propagating through the tail lobe region impinges upon the PSBL deforming it and displacing it in towards the central plasma sheet. The boundary layer can then act like a moving magnetic mirror. If the disturbance is propagating nearly perpendicular to the layer then its velocity projected parallel to the layer (and the magnetic field) can be very large resulting in significant acceleration of reflected particles. copyright American Geophysical Union 1989

Particle pitch angle diffusion due to nonadiabatic effects in the plasma sheet

International Nuclear Information System (INIS)

Gray, P.C.; Lee, L.C.

1982-01-01

In order to understand certain aspects of the plasma sheet dynamics, a numerical study of the nonadiabatic behavior of particles in a model field geometry is performed. The particle's magnetic moment as a function of time is calculated for various initial parameters, corresponding to various particle energies and degrees of field curvature. It is shown that the magnetic moment changes as the particle passes through the plasma sheet and that the magnitude of the change is related to the curvature of the field at the middle of the plasma sheet. The relation of the magnitude of the change in magnetic moment to the particle's pitch and phase angles as it passes through the sheet is numerically resolved. The nature of the change may be considered as a mechanism for pitch angle diffusion, and the diffusion coefficient is calculated. This scattering mechanism is significant for plasma sheet ions (1--10 keV) as well as energetic electrons (>100 keV)

Bi-directional electrons in the near-Earth plasma sheet

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K. Shiokawa

2003-07-01

Full Text Available We have studied the occurrence characteristics of bi-directional electron pitch angle anisotropy (enhanced flux in field-aligned directions, F^ /F|| > 1.5 at energies of 0.1–30 keV using plasma and magnetic field data from the AMPTE/IRM satellite in the near-Earth plasma sheet. The occurrence rate increases in the tailward direction from XGSM = - 9 RE to - 19 RE . The occurrence rate is also enhanced in the midnight sector, and furthermore, whenever the elevation angle of the magnetic field is large while the magnetic field intensity is small, B ~ 15 nT. From these facts, we conclude that the bi-directional electrons in the central plasma sheet are produced mainly in the vicinity of the neutral sheet and that the contribution from ionospheric electrons is minor. A high occurrence is also found after earthward high-speed ion flows, suggesting Fermi-type field-aligned electron acceleration in the neutral sheet. Occurrence characteristics of bi-directional electrons in the plasma sheet boundary layer are also discussed.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; magnetotail; plasma sheet

Cross-tail velocity component in the plasma sheet fast flows

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N. P. Dmitrieva

2008-06-01

Full Text Available The flux transfer in the magnetotail plasma sheet is mainly provided by the tail-aligned fast plasma flows (Bursty Bulk Flows – BBFs. In this paper we study the events with a large cross-tail velocity component, including their occurrence and relationship to the standard BBFs. We found out that a significant part of large Vy events are a subgroup connected with the BBFs propagation. The maximal deviation of the velocity vector from the X direction (about 40–50 degrees, on average is observed near the BBFs' leading front in the sheath, where the fast flow interacts with surrounding plasma. The average variation of the velocity direction in the vicinity of the BBF resembles a plasma vortex. Our results support the model, in which the BBF represents a polarized, bubble-like flux tube, propagating through the plasma sheet.

Slow convection of a magnetized plasma and the earth plasma sheet

International Nuclear Information System (INIS)

Hruska, A.

1980-01-01

Stationary convection of an isotropic, infinitely conducting plasma in a magnetic field with non-trivial geometry is discussed under the assumption that the inertial term in the equation of motion may be ignored. The energy gained or lost by a volume element of plasma per unit time does not vary along the field-lines. Simple relations between the components of the current density, depending on the field-line geometry, exist. Similar relations hold for the components of the plasma velocity. The theoretical analysis is applied to the geomagnetically-quiet plasma sheet and a qualitative physical picture of the sheet is suggested. The observed structure of the sheet is compatible with Axford-Hines type of convection perhaps combined with a low-speed flow from a distant neutral point. The magnetic-field-aligned currents are driven by the deformations of the closed field-lines which are enforced by the solar wind. (orig.)

Two-and-one-half-dimensional magnetohydrodynamic simulations of the plasma sheet in the presence of oxygen ions: The plasma sheet oscillation and compressional Pc 5 waves

International Nuclear Information System (INIS)

Lu Li; Liu Zhenxing; Cao Jinbin

2002-01-01

Two-and-one-half-dimensional magnetohydrodynamic simulations of the multicomponent plasma sheet with the velocity curl term in the magnetic equation are represented. The simulation results can be summarized as follows: (1) There is an oscillation of the plasma sheet with the period on the order of 400 s (Pc 5 range); (2) the magnetic equator is a node of the magnetic field disturbance; (3) the magnetic energy integral varies antiphase with the internal energy integral; (4) disturbed waves have a propagating speed on the order of 10 km/s earthward; (5) the abundance of oxygen ions influences amplitude, period, and dissipation of the plasma sheet oscillation. It is suggested that the compressional Pc 5 waves, which are observed in the plasma sheet close to the magnetic equator, may be caused by the plasma sheet oscillation, or may be generated from the resonance of the plasma sheet oscillation with some Pc 5 perturbation waves coming from the outer magnetosphere

Multi-scale magnetic field intermittence in the plasma sheet

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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

The Interaction of C-Band Microwaves with Large Plasma Sheets

International Nuclear Information System (INIS)

Ding Liang; Huo Wenqing; Yang Xinjie; Xu Yuemin

2012-01-01

A large plasma sheet 60 cm×60 cm×2 cm in size was generated using a hollow cathode, and measurements were conducted for interactions including transmission, reflection and absorption. With different discharge parameters, plasma sheets can vary and influence microwave strength. Microwave reflection decreases when the discharge current rises, and the opposite occurs in transmission. The C-band microwave is absorbed when it is propagated through large plasma sheets at higher pressure. When plasma density and collision frequency are fitted with incident microwave frequency, a large amount of microwave energy is consumed. Reflection, transmission and absorption all exist simultaneously. Plasma sheets are an attractive alternative to microwave steering at low pressure, and the microwave reflection used in receiving radar can be altered by changing the discharge parameters.

Interaction of a charge with a thin plasma sheet

International Nuclear Information System (INIS)

Bordag, M.

2007-01-01

The interaction of the electromagnetic field with a two-dimensional plasma sheet intended to describe the pi-electrons of a carbon nanotube or a C 60 molecule is investigated. By first integrating out the displacement field of the plasma or the electromagnetic field, different representations for quantities like the Casimir energy are derived which are shown to be consistent with one another. Starting from the covariant gauge for the electromagnetic field, it is shown that the matching conditions to which the presence of the plasma sheet can be reduced are different from the commonly used ones. The difference in the treatments does not show up in the Casimir force between two parallel sheets, but it is present in the Casimir-Polder force between a charge or a neutral atom and a sheet. At once, since the plasma sheet is a regularization of the conductor boundary conditions, this sheds light on the difference in physics found earlier in the realization of conductor boundary conditions as 'thin' or 'thick' boundary conditions in Phys. Rev. D 70, 085010 (2004)

Composition and plasma properties of the plasma sheet in the Earth's magnetotail

International Nuclear Information System (INIS)

Orsini, S.; Altwegg, K.; Balsiger, H.

1986-01-01

A statistical study of the plasma sheet properties, based on 300 h of data from the ISEE-1 Ion Composition Experiment, yiels a description of H + and He ++ densities and temperatures as functions of magnetospheric substorm activity and geocentric distance. The H + and He ++ temperatures are found to be well correlated, such that a ratio T(He ++ )/T(H + ) = 2.7±0.1 is typical. However, linear-regression analysis typically yields a nonvanishing T(He ++ ) in the limit T(H + ) #-> # 0, a limit that is approached through the addition of cold ionospheric H + to the plasma sheet during active periods. The plasma sheet proton temperature T(H + ) varies inversely with geocentric distance, and the radial gradient of T(H + ) increases with increasing activity index AE. The density ratio N (He ++ )/N(H + ) increases with geocentric distance, irrespective of AE

Geomagnetic activity effects on plasma sheet energy conversion

Directory of Open Access Journals (Sweden)

M. Hamrin

2010-10-01

Full Text Available In this article we use three years (2001, 2002, and 2004 of Cluster plasma sheet data to investigate what happens to localized energy conversion regions (ECRs in the plasma sheet during times of high magnetospheric activity. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have studied the influence on Concentrated Load Regions (CLRs and Concentrated Generator Regions (CGRs from variations in the geomagnetic disturbance level as expressed by the Kp, the AE, and the Dst indices. We find that the ECR occurrence frequency increases during higher magnetospheric activities, and that the ECRs become stronger. This is true both for CLRs and for CGRs, and the localized energy conversion therefore concerns energy conversion in both directions between the particles and the fields in the plasma sheet. A higher geomagnetic activity hence increases the general level of energy conversion in the plasma sheet. Moreover, we have shown that CLRs live longer during magnetically disturbed times, hence converting more electromagnetic energy. The CGR lifetime, on the other hand, seems to be unaffected by the geomagnetic activity level. The evidence for increased energy conversion during geomagnetically disturbed times is most clear for Kp and for AE, but there are also some indications that energy conversion increases during large negative Dst. This is consistent with the plasma sheet magnetically mapping to the auroral zone, and therefore being more tightly coupled to auroral activities and variations in the AE and Kp indices, than to variations in the ring current region as described by the Dst index.

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.)

Singular Sheet Etching of Graphene with Oxygen Plasma

Institute of Scientific and Technical Information of China (English)

Haider Al-Mumen; Fubo Rao; Wen Li; Lixin Dong

2014-01-01

This paper reports a simple and controllable post-synthesis method for engineering the number of graphene layers based on oxygen plasma etching. Singular sheet etching(SSE) of graphene was achieved with the optimum process duration of 38 seconds. As a demonstration of this SSE process, monolayer graphene films were produced from bilayer graphenes. Experimental investigations verified that the oxygen plasma etching removes a single layer graphene sheet in an anisotropic fashion rather than anisotropic mode. In addition,etching via the oxygen plasma at the ground electrodes introduced fewer defects to the bottom graphene layer compared with the conventional oxygen reactive ion etching using the powered electrodes. Such defects can further be reduced with an effective annealing treatment in an argon environment at 900-1000?C. These results demonstrate that our developed SSE method has enabled a microelectronics manufacturing compatible way for single sheet precision subtraction of graphene layers and a potential technique for producing large size graphenes with high yield from multilayer graphite materials.

Singular Sheet Etching of Graphene with Oxygen Plasma

Institute of Scientific and Technical Information of China (English)

Haider Al-Mumen; Fubo Rao; Wen Li; Lixin Dong

2014-01-01

This paper reports a simple and controllable post-synthesis method for engineering the number of graphene layers based on oxygen plasma etching. Singular sheet etching (SSE) of graphene was achieved with the optimum process duration of 38 seconds. As a demonstration of this SSE process, monolayer graphene films were produced from bilayer graphenes. Experimental investigations verified that the oxygen plasma etching removes a single layer graphene sheet in an anisotropic fashion rather than anisotropic mode. In addition, etching via the oxygen plasma at the ground electrodes introduced fewer defects to the bottom graphene layer compared with the conventional oxygen reactive ion etching using the powered electrodes. Such defects can further be reduced with an effective annealing treatment in an argon environment at 900-1000◦C. These results demonstrate that our developed SSE method has enabled a microelectronics manufacturing compatible way for single sheet precision subtraction of graphene layers and a potential technique for producing large size graphenes with high yield from multilayer graphite materials.

Radial evolution of the finite-width plasma sheet in a z-pinch: A parametric analysis based on conservation laws

International Nuclear Information System (INIS)

Sherar, A.G.

1996-01-01

A simple method that allows to estimate the macroscopic variables (width, temperature, density, radial velocity, etc.) of the plasma sheet in the first compression of a z-pinch, is presented. Following the snow-plow model, the radial compression is assumed as a process in which the mass is swept by a sheet of finite width. Very high pressures can be reached inside the sheet due to magnetic compression, higher than the filling gas pressure. A quasi-equilibrium hypothesis for the pressure of the layer is defined. From this assumption the thickness of the dense plasma sheet can be estimated. A set of MHD equations that include a term to compute total energy losses is used. The system of equations is written in the interface reference system in which the internal boundary of the sheet is at rest. In this early stage of the compression, the plasma temperature is mainly due to heavy particles. The results obtained using this model can explain ionic temperatures measured in cold plasmas which cannot be explained from electron-ion collisions. From an analytical study of the formation solution, a well-defined range of validity for each parameter of the model has been found. Based on physical conditions, these ranges of validity give a criterion to understanding the necessary conditions to build and maintain a moving plasma sheet. Using this model, other geometries besides the cylindrical one can be analyzed in the future

On the nature of the plasma sheet boundary layer

Energy Technology Data Exchange (ETDEWEB)

Hones, E.W. Jr. (Mission Research Corp., Los Alamos, NM (USA) Los Alamos National Lab., NM (USA))

1990-01-01

The regions of the plasma sheet adjacent to the north and south lobes of the magnetotail have been described by many experimenters as locations of beams of energetic ions and fast-moving plasma directed primarily earthward and tailward along magnetic field lines. Measurements taken as satellites passed through one or the other of these boundary layers have frequently revealed near-earth mirroring of ions and a vertical segregation of velocities of both earthward-moving and mirroring ions with the fastest ions being found nearest the lobe-plasma sheet interface. These are features expected for particles from a distant tail source {bar E} {times} {bar B} drifting in a dawn-to-dusk electric field and are consistent with the source being a magnetic reconnection region. The plasma sheet boundary layers are thus understood as separatrix layers, bounded at their lobeward surfaces by the separatrices from the distant neutral line. This paper will review the observations that support this interpretation. 10 refs., 7 figs.

Energization of the Ring Current through Convection of Substorm Enhancements of the Plasma Sheet Source.

Science.gov (United States)

Menz, A.; Kistler, L. M.; Mouikis, C.; Spence, H. E.; Henderson, M. G.; Matsui, H.

2017-12-01

It has been shown that electric field strength and night-side plasma sheet density are the two best predictors of the adiabatic energy gain of the ring current during geomagnetic storms (Liemohn and Khazanov, 2005). While H+ dominates the ring current during quiet times, O+ can contribute substantially during geomagnetic storms. Substorm activity provides a mechanism to enhance the energy density of O+ in the plasma sheet during geomagnetic storms, which is then convected adiabatically into the inner-magnetosphere. Using the Van Allen Probes data in the the plasma sheet source region (defined as L>5.5 during storms) and the inner magnetosphere, along with LANL-GEO data to identify substorm injection times, we show that adiabatic convection of O+ enhancements in the source region can explain the observed enhancements in the inner magnetosphere. We use the UNH-IMEF electric field model to calculate drift times from the source region to the inner magnetosphere to test whether enhancements in the inner-magnetosphere can be explained by dipolarization driven enhancements in the plasma sheet source hours before.

Nonadiabatic heating of the central plasma sheet at substorm onset

International Nuclear Information System (INIS)

Huang, C.Y.; Frank, L.A.; Rostoker, G.; Fennell, J.; Mitchell, D.G.

1992-01-01

Heating events in the plasma sheet boundary layer and central plasma sheet are found to occur at the onset of expansive phase activity. The main effect is a dramatic increase in plasma temperature, coincident with a partial dipolarization of the magnetic field. Fluxes of energetic particles increase without dispersion during these events which occur at all radial distances up to 23 R E , the apogee of the ISEIE spacecraft. A major difference between these heating events and those observed at geosynchronous distances lies in the heating mechanism which is nonadiabatic beyond 10 R E but may be adiabatic closer to Earth. The energy required to account for the increase in plasma thermal energy is comparable with that required for Joule heating of the ionosphere. The plasma sheet must be considered as a major sink in the energy balance of substorm. The authors estimate lobe magnetic pressures during these events. Changes in lobe pressure are generally not correlated with onsets or intensifications of expansive phase activity

The lobe to plasma sheet boundary layer transition: Theory and observations

International Nuclear Information System (INIS)

Schriver, D.; Ashour-Abdalla, M.; Treumann, R.; Nakamura, M.; Kistler, L.M.

1990-01-01

The lobe and the plasma sheet boundary layer in the Earth's magnetotail are regions of different plasma conditions and share a common interface. The transition from the lobe to the plasma sheet boundary layer is examined here using AMPTE/IRM data. When the satellite crossed from the lobe to the plasma sheet boundary layer, intense narrow banded wave bursts at 1 kHz were observed an d then broadband electrostatic noise (BEN) immediately followed. Simultaneous with the onset of BEN, high energy earthward streaming proton beams at > 40 keV (> 2,700 km/s) were detected. These results are used as input into a numerical simulation to study ion beam instabilities in the PSBL

A triggering of solar flare by magnetosonic waves in a neutral sheet plasma

International Nuclear Information System (INIS)

Sakai, Jun-ichi; Washimi, Haruichi.

1981-09-01

A theoretical model of the triggering of a solar flare by magnetosonic waves in a neutral sheet plasma is discussed. It is shown that the ponderomotive force due to the magnetosonic waves strongly excites the plasma convection flow in the magnetic neutral sheet which in turn enhances the tearing instability. The system of basic equations for the tearing mode including the time-averaged nonlinear effects due to the magnetosonic waves is derived and the boundary value problem is solved. The results show that the growth time of the instability is shortened to about 100 sec for reasonable magnetosonic wave intensity. (author)

Upper Hybrid Resonance of Microwaves with a Large Magnetized Plasma Sheet

International Nuclear Information System (INIS)

Huo Wenqing; Guo Shijie; Ding Liang; Xu Yuemin

2013-01-01

A large magnetized plasma sheet with size of 60 cm × 60 cm × 2 cm was generated by a linear hollow cathode discharge under the confinement of a uniform magnetic field generated by a Helmholtz Coil. The microwave transmission characteristic of the plasma sheet was measured for different incident frequencies, in cases with the electric field polarization of the incident microwave either perpendicular or parallel to the magnetic field. In this measurement, parameters of the plasma sheet were changed by varying the discharge current and magnetic field intensity. In the experiment, upper hybrid resonance phenomena were observed when the electric field polarization of the incident wave was perpendicular to the magnetic field. These resonance phenomena cannot be found in the case of parallel polarization incidence. This result is consistent with theoretical consideration. According to the resonance condition, the electron density values at the resonance points are calculated under various experimental conditions. This kind of resonance phenomena can be used to develop a specific method to diagnose the electron density of this magnetized plasma sheet apparatus. Moreover, it is pointed out that the operating parameters of the large plasma sheet in practical applications should be selected to keep away from the upper hybrid resonance point to prevent signals from polarization distortion

Relationship between energetic particles and plasmas in the distant plasma sheet

International Nuclear Information System (INIS)

Sarris, E.T.; Krimigis, S.M.; Lui, A.T.Y.; Ackerson, K.L.; Frank, L.A.; Williams, D.J.

1981-01-01

Measurements of ions from three different instruments on the IMP-7 and 8 spacecraft are combined to yield with differential energy spectra of ions over the entire energy range of approx.100 eV to 4 MeV in the earth's distant (approx.30 to approx.40 R/sub e/) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from approx.10 -5 to 10 5 (cm 2 sec sr keV) -1 , varying smoothly over the entire energy range both when the plasma is cold (approx.1 keV) and hot (approx.9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (> or approx. =50 keV) tail described well by a power law (proportionalE -7 ). The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. The transition between the Maxwellian and the power law occurs at Eapprox. =(g+1)kT. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas

Associations of geomagnetic activity with plasma sheet thinning and expansion: A statistical study

International Nuclear Information System (INIS)

Hones, E.W. Jr.; Pytte, T.; West, H.I. Jr.

1984-01-01

Associations of geomagnetic activity in the auroral zone with thinnings and expansions of the magnetotail plasma sheet are examined statistically in this paper. We first identified many plasma sheet thinnings and expansions in plasma and particle data from VELA satellites and from OGO 5 without reference to the ground magnetic data. These events were grouped according to the location of the detecting satellite in the magnetotail. For each such group the times of thinning or expansion were then used as fiducial times in a superposed-epoch analysis of the geomagnetic AL index values that were recorded in 8-hour intervals centered on the event times. The results show that many plasma sheet thinnings and expansions are related to discrete negative bay structures that are the classical signature of substorms. Furthermore, they support earlier findings that plasma sheet thinning and expansion at the VELA orbit (rroughly-equal18 R/sub E/) tend to be associated with the onset of the auroral zone negative bay and the beginning of its subsidence, respectively. Earthward of rroughly-equal13-15 R/sub E/, plasma sheet expansion occurs near the time of the onset of the negative bay, again in agreement with earlier findings. A large fraction of plasma sheet expansions to half thicknesses of > or approx. =6 R/sub E/ at the VELA orbit are associated not with a baylike geomagnetic disturbance but with subsidence of a prolonged interval of disturbance. The study also shows that many plasma sheet expansions are related simply to generally enhanced geomagnetic activity showing no baylike or other distinctive features

Production of free radical by magnetized sheet plasma with vertical gas-flow

International Nuclear Information System (INIS)

Tonegawa, Akira; Takatori, Masahiko; Kawamura, Kazutaka

1995-01-01

Free radicals play an important role in plasma processing, environment problem, and space plasma and so on because of their outstanding physical properties. Although much work has been done on the free radicals in the reactive plasma, very little is known about the production mechanism of the free radicals against various plasma parameters. To overcome this problem, we have proposed to do a new system of a magnetized sheet plasma with vertical gas-flow. The sheet plasma is a special type of strongly magnetized highly ionized slab plasma. This system is controlled to the parameters of radicals and plasma independently. Therefore, it is possible to make a quantitative analysis of free radicals as the simple one. In this paper, we describe the magnetized sheet plasma with vertical gas-flow system and report the preliminary results of production of the free radical. In particular, we show to produce and control the OH free radical which has been the most commonly studied combustion species

Distribution of energetic oxygen and hydrogen in the near-Earth plasma sheet

Science.gov (United States)

Kronberg, E. A.; Grigorenko, E. E.; Haaland, S. E.; Daly, P. W.; Delcourt, D. C.; Luo, H.; Kistler, L. M.; Dandouras, I.

2015-05-01

The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn-dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure (Pdyn) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near-Earth duskside during disturbed geomagnetic conditions, enhanced SW Pdyn, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near-Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW Pdyn. These observations are in agreement with theoretical models.

A statistical study on the correlations between plasma sheet and solar wind based on DSP explorations

Directory of Open Access Journals (Sweden)

G. Q. Yan

2005-11-01

Full Text Available By using the data of two spacecraft, TC-1 and ACE (Advanced Composition Explorer, a statistical study on the correlations between plasma sheet and solar wind has been carried out. The results obtained show that the plasma sheet at geocentric distances of about 9~13.4 Re has an apparent driving relationship with the solar wind. It is found that (1 there is a positive correlation between the duskward component of the interplanetary magnetic field (IMF and the duskward component of the geomagnetic field in the plasma sheet, with a proportionality constant of about 1.09. It indicates that the duskward component of the IMF can effectively penetrate into the near-Earth plasma sheet, and can be amplified by sunward convection in the corresponding region at geocentric distances of about 9~13.4 Re; (2 the increase in the density or the dynamic pressure of the solar wind will generally lead to the increase in the density of the plasma sheet; (3 the ion thermal pressure in the near-Earth plasma sheet is significantly controlled by the dynamic pressure of solar wind; (4 under the northward IMF condition, the ion temperature and ion thermal pressure in the plasma sheet decrease as the solar wind speed increases. This feature indicates that plasmas in the near-Earth plasma sheet can come from the magnetosheath through the LLBL. Northward IMF is one important condition for the transport of the cold plasmas of the magnetosheath into the plasma sheet through the LLBL, and fast solar wind will enhance such a transport process.

Pressure balance inconsistency exhibited in a statistical model of magnetospheric plasma

Science.gov (United States)

Garner, T. W.; Wolf, R. A.; Spiro, R. W.; Thomsen, M. F.; Korth, H.

2003-08-01

While quantitative theories of plasma flow from the magnetotail to the inner magnetosphere typically assume adiabatic convection, it has long been understood that these convection models tend to overestimate the plasma pressure in the inner magnetosphere. This phenomenon is called the pressure crisis or the pressure balance inconsistency. In order to analyze it in a new and more detailed manner we utilize an empirical model of the proton and electron distribution functions in the near-Earth plasma sheet (-50 RE attributed to gradient/curvature drift for large isotropic energy invariants but not for small invariants. The tailward gradient of the distribution function indicates a violation of the adiabatic drift condition in the plasma sheet. It also confirms the existence of a "number crisis" in addition to the pressure crisis. In addition, plasma sheet pressure gradients, when crossed with the gradient of flux tube volume computed from the [1989] magnetic field model, indicate Region 1 currents on the dawn and dusk sides of the outer plasma sheet.

Estimates of magnetic flux, and energy balance in the plasma sheet during substorm expansion

Science.gov (United States)

Hesse, Michael; Birn, Joachim; Pulkkinen, Tuija

1996-01-01

The energy and magnetic flux budgets of the magnetotail plasma sheet during substorm expansion are investigated. The possible mechanisms that change the energy content of the closed field line region which contains all the major dissipation mechanisms of relevance during substorms, are considered. The compression of the plasma sheet mechanism and the diffusion mechanism are considered and excluded. It is concluded that the magnetic reconnection mechanism can accomplish the required transport. Data-based empirical magnetic field models are used to investigate the magnetic flux transport required to account for the observed magnetic field dipolarizations in the inner magnetosphere. It is found that the magnetic flux permeating the current sheet is typically insufficient to supply the required magnetic flux. It is concluded that no major substorm-type magnetospheric reconfiguration is possible in the absence of magnetic reconnection.

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].

Thinning and functionalization of few-layer graphene sheets by CF4 plasma treatment

KAUST Repository

Shen, Chao

2012-05-24

Structural changes of few-layer graphene sheets induced by CF4 plasma treatment are studied by optical microscopy and Raman spectroscopy, together with theoretical simulation. Experimental results suggest a thickness reduction of few-layer graphene sheets subjected to prolonged CF4 plasma treatment while plasma treatment with short time only leads to fluorine functionalization on the surface layer by formation of covalent bonds. Raman spectra reveal an increase in disorder by physical disruption of the graphene lattice as well as functionalization during the plasma treatment. The F/CF3 adsorption and the lattice distortion produced are proved by theoretical simulation using density functional theory, which also predicts p-type doping and Dirac cone splitting in CF4 plasma-treated graphene sheets that may have potential in future graphene-based micro/nanodevices.

Plasma sheet behavior during substorms

International Nuclear Information System (INIS)

Hones, E.W. Jr.

1983-01-01

Auroral or magnetic substorms are periods of enhanced auroral and geomagnetic activity lasting one to a few hours that signify increased dissipation of energy from the magnetosphere to the earth. Data acquired during the past decade from satellites in the near-earth sector of the magnetotail have suggested that during a substorm part of the plasma sheet is severed from earth by magnetic reconnection, forming a plasmoid, i.e., a body of plasma and closed magnetic loops, that flows out of the tail into the solar wind, thus returning plasma and energy that have earlier been accumulated from the solar wind. Very recently this picture has been dramatically confirmed by observations, with the ISEE 3 spacecraft in the magnetotail 220 R/sub E/ from earth, of plasmoids passing that location in clear delayed response to substorms. It now appears that plasmoid release is a fundamental process whereby the magnetosphere gives up excess stored energy and plasma, much like comets are seen to do, and that the phenomena of the substorm seen at earth are a by-product of that fundamental process

Superposed epoch analysis of pressure and magnetic field configuration changes in the plasma sheet

International Nuclear Information System (INIS)

Kistler, L.M.; Moebius, E.; Baumjohann, W.; Nagai, T.

1993-01-01

The authors report on an analysis of pressure and magnetic configuration within the plasma sheet following the initiation of substorm events. They have constructed this time dependent picture by using an epoch analysis of data from the AMPTE/IRM spacecraft. This analysis procedure can be used to construct a unified picture of events, provided they are reproducible, from a statistical analysis of a series of point measurements. The authors first determine the time dependent pressure changes in the plasma sheet. With some simplifying assumptions they then determine the z dependence of the pressure profiles, and from this distribution determine how field lines in the plasma sheet map to the neutral sheet

Convective growth of broadband turbulence in the plasma sheet boundary layer

International Nuclear Information System (INIS)

Dusenbery, P.B.

1987-01-01

Convective growth of slow and fast beam acoustic waves in the plasma sheet boundary layer (PSBL) is investigated. It has been shown previously that a could ion population must be present in order to excite beam acoustic waves in the PSBL. However, growth rates are significantly enhanced when warm plasma sheet boundary layer ions are present. Net wave growth along a ray path is determined by convective growth. This quantity is calculated for particle distribution models consistent with the PSBL where the intensity of broadband turbulence is observed to peak. Total number density dependence on beam acoustic convective growth is evaluated, and it is found that even for low density conditions of ∼0.01 cm -3 , a measurable level of broadband turbulence is expected. Relative drift effects between cold and warm ion populations are also considered. In particular, it is found that slow mode convective growth can be enhanced when slowly streaming cold ions are present, compared to fast ion streams

Acceleration of O+ from the cusp to the plasma sheet

Science.gov (United States)

Liao, J.; Kistler, L. M.; Mouikis, C. G.; Klecker, B.; Dandouras, I.

2015-02-01

Heavy ions from the ionosphere that are accelerated in the cusp/cleft have been identified as a direct source for the hot plasma in the plasma sheet. However, the details of the acceleration and transport that transforms the originally cold ions into the hot plasma sheet population are not fully understood. The polar orbit of the Cluster satellites covers the main transport path of the O+ from the cusp to the plasma sheet, so Cluster is ideal for tracking its velocity changes. However, because the cusp outflow is dispersed according to its velocity as it is transported to the tail, due to the velocity filter effect, the observed changes in beam velocity over the Cluster orbit may simply be the result of the spacecraft accessing different spatial regions and not necessarily evidence of acceleration. Using the Cluster Ion Spectrometry/Composition Distribution Function instrument onboard Cluster, we compare the distribution function of streaming O+ in the tail lobes with the initial distribution function observed over the cusp and reveal that the observations of energetic streaming O+ in the lobes around -20 RE are predominantly due to the velocity filter effect during nonstorm times. During storm times, the cusp distribution is further accelerated. In the plasma sheet boundary layer, however, the average O+ distribution function is above the upper range of the outflow distributions at the same velocity during both storm and nonstorm times, indicating that acceleration has taken place. Some of the velocity increase is in the direction perpendicular to the magnetic field, indicating that the E × B velocity is enhanced. However, there is also an increase in the parallel direction, which could be due to nonadiabatic acceleration at the boundary or wave heating.

High-beta plasma blobs in the morningside plasma sheet

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G. Haerendel

1999-12-01

Full Text Available Equator-S frequently encountered, i.e. on 30% of the orbits between 1 March and 17 April 1998, strong variations of the magnetic field strength of typically 5–15-min duration outside about 9RE during the late-night/early-morning hours. Very high-plasma beta values were found, varying between 1 and 10 or more. Close conjunctions between Equator-S and Geotail revealed the spatial structure of these "plasma blobs" and their lifetime. They are typically 5–10° wide in longitude and have an antisymmetric plasma or magnetic pressure distribution with respect to the equator, while being altogether low-latitude phenomena  (≤ 15°. They drift slowly sunward, exchange plasma across the equator and have a lifetime of at least 15–30 min. While their spatial structure may be due to some sort of mirror instability, little is known about the origin of the high-beta plasma. It is speculated that the morningside boundary layer somewhat further tailward may be the source of this plasma. This would be consistent with the preference of the plasma blobs to occur during quiet conditions, although they are also found during substorm periods. The relation to auroral phenomena in the morningside oval is uncertain. The energy deposition may be mostly too weak to generate a visible signature. However, patchy aurora remains a candidate for more disturbed periods.Key words. Magnetospheric physics (plasma convection; plasma sheet; plasma waves and instabilities

Thermomechanical processing of plasma sprayed intermetallic sheets

Science.gov (United States)

Hajaligol, Mohammad R.; Scorey, Clive; Sikka, Vinod K.; Deevi, Seetharama C.; Fleischhauer, Grier; Lilly, Jr., A. Clifton; German, Randall M.

2001-01-01

A powder metallurgical process of preparing a sheet from a powder having an intermetallic alloy composition such as an iron, nickel or titanium aluminide. The sheet can be manufactured into electrical resistance heating elements having improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The iron aluminide has an entirely ferritic microstructure which is free of austenite and can include, in weight %, 4 to 32% Al, and optional additions such as .ltoreq.1% Cr, .gtoreq.0.05% Zr .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Ni, .ltoreq.0.75% C, .ltoreq.0.1% B, .ltoreq.1% submicron oxide particles and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, and/or .ltoreq.3% Cu. The process includes forming a non-densified metal sheet by consolidating a powder having an intermetallic alloy composition such as by roll compaction, tape casting or plasma spraying, forming a cold rolled sheet by cold rolling the non-densified metal sheet so as to increase the density and reduce the thickness thereof and annealing the cold rolled sheet. The powder can be a water, polymer or gas atomized powder which is subjecting to sieving and/or blending with a binder prior to the consolidation step. After the consolidation step, the sheet can be partially sintered. The cold rolling and/or annealing steps can be repeated to achieve the desired sheet thickness and properties. The annealing can be carried out in a vacuum furnace with a vacuum or inert atmosphere. During final annealing, the cold rolled sheet recrystallizes to an average grain size of about 10 to 30 .mu.m. Final stress relief annealing can be carried out in the B2 phase temperature range.

Experimental investigation of a 1 kA/cm² sheet beam plasma cathode electron gun.

Science.gov (United States)

Kumar, Niraj; Pal, Udit Narayan; Pal, Dharmendra Kumar; Prajesh, Rahul; Prakash, Ram

2015-01-01

In this paper, a cold cathode based sheet-beam plasma cathode electron gun is reported with achieved sheet-beam current density ∼1 kA/cm(2) from pseudospark based argon plasma for pulse length of ∼200 ns in a single shot experiment. For the qualitative assessment of the sheet-beam, an arrangement of three isolated metallic-sheets is proposed. The actual shape and size of the sheet-electron-beam are obtained through a non-conventional method by proposing a dielectric charging technique and scanning electron microscope based imaging. As distinct from the earlier developed sheet beam sources, the generated sheet-beam has been propagated more than 190 mm distance in a drift space region maintaining sheet structure without assistance of any external magnetic field.

Plasma sheet fast flows and auroral dynamics during substorm: a case study

Directory of Open Access Journals (Sweden)

N. L. Borodkova

2002-03-01

Full Text Available Interball-1 observations of a substorm development in the mid-tail on 16 December 1998 are compared with the auroral dynamics obtained from the Polar UV imager. Using these data, the relationship between plasma flow directions in the tail and the location of the auroral activation is examined. Main attention is given to tailward and earth-ward plasma flows, interpreted as signatures of a Near Earth Neutral Line (NENL. It is unambiguously shown that in the mid-plasma sheet the flows were directed tailward when the auroral bulge developed equatorward of the spacecraft ionospheric footprint. On the contrary, when active auroras moved poleward of the Interball-1 projection, earthward fast flow bursts were observed. This confirms the concept that the NENL (or flow reversal region is the source of auroras forming the poleward edge of the auroral bulge. The observed earthward flow bursts have all typical signatures of Bursty Bulk Flows (BBFs, described by Angelopolous et al. (1992. These BBFs are related to substorm activations starting at the poleward edge of the expanded auroral bulge. We interpret the BBFs as a result of reconnection pulses occurring tail-ward of Interball-1. In addition, some non-typically observed phenomena were detected in the plasma sheet during this substorm: (i tailward/earthward flows were superimposed on a very strong duskward flow, and (ii wavy structures of both magnetic field and plasma density were registered. The latter observation is probably linked to the filamentary structure of the current sheet.Key words. Magnetospheric physics (auroral phenomena; plasma sheet; storms and substorms

Substorms in the Inner Plasma Sheet

Science.gov (United States)

Le Contel, O.; Perraut, S.; Roux, A.; Pellat, R.; Korth, A.

Thin Current Sheets (TCS) are regularly formed prior to substorm breakup, even in the near-Earth plasma sheet, as close as the geostationary orbit. A self-consistent kinetic theory describing the response of the plasma sheet to an electromagnetic perturbation is given. This perturbation corresponds to an external forcing, for instance caused by the solar wind (not an internal instability). The equilibrium of the configuration of this TCS in the presence of a time varying perturbation is shown to produce a strong parallel thermal anisotropy (T∥ > T⊺) of energetic electrons and ions (E>50keV) as well as an enhanced diamagnetic current carried by low energy ions (Ecurrents tend to enhance the confinement of this current sheet near the magnetic equator. These results are compared with data gathered by GEOS-2 at the geostationary orbit, where the magnetic signatures of TCS, and parallel anisotropies are regularly observed prior to breakup. By ensuring quasi-neutrality everywhere we find, when low frequency electromagnetic perturbations are applied, that although the magnetic field line remains an equipotential to the lowest order in Te/Ti, a field-aligned potential drop exists to the next order in (Te/Ti). Thus the development of a TCS implies the formation of a field-aligned potential drop (~= few hundred volts) to ensure the quasi-neutrality everywhere. For an earthward directed pressure gradient, a field-aligned electric field, directed towards the ionosphere, is obtained, on the western edge of the perturbation (i.e. western edge of the current sheet). Thus field aligned beams of electrons are expected to flow towards the equatorial region on the western edge of the current sheet. We study the stability of these electron beams and show that they are unstable to ``High Frequency'' (HF) waves. These ``HF'' waves are regularly observed at frequencies of the order of the proton gyrofrequency (fH+) just before, or at breakup. The amplitude of these HF waves is so

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

High-beta plasma blobs in the morningside plasma sheet

Directory of Open Access Journals (Sweden)

G. Haerendel

Full Text Available Equator-S frequently encountered, i.e. on 30% of the orbits between 1 March and 17 April 1998, strong variations of the magnetic field strength of typically 5–15-min duration outside about 9R_E during the late-night/early-morning hours. Very high-plasma beta values were found, varying between 1 and 10 or more. Close conjunctions between Equator-S and Geotail revealed the spatial structure of these "plasma blobs" and their lifetime. They are typically 5–10^° wide in longitude and have an antisymmetric plasma or magnetic pressure distribution with respect to the equator, while being altogether low-latitude phenomena 
(≤ 15^°. They drift slowly sunward, exchange plasma across the equator and have a lifetime of at least 15–30 min. While their spatial structure may be due to some sort of mirror instability, little is known about the origin of the high-beta plasma. It is speculated that the morningside boundary layer somewhat further tailward may be the source of this plasma. This would be consistent with the preference of the plasma blobs to occur during quiet conditions, although they are also found during substorm periods. The relation to auroral phenomena in the morningside oval is uncertain. The energy deposition may be mostly too weak to generate a visible signature. However, patchy aurora remains a candidate for more disturbed periods.

Key words. Magnetospheric physics (plasma convection; plasma sheet; plasma waves and instabilities

Gas isotope separation method using plasma sheet

International Nuclear Information System (INIS)

Takayama, K.; Takagi, K.; Fukvi, R.

1988-03-01

A high frequency electric field is applied to a plasma sheet with a frequency equal to the cyclotronic frequency of the ions to be separated. Because of resonance the cyclotronic radius of the isotope has increased and the electric charge is eliminated by collision with a separator and the isotope is separated in neutral particles [fr

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

A Modified Porous Titanium Sheet Prepared by Plasma-Activated Sintering for Biomedical Applications

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Yukimichi Tamaki

2010-01-01

Full Text Available This study aimed to develop a contamination-free porous titanium scaffold by a plasma-activated sintering within an originally developed TiN-coated graphite mold. The surface of porous titanium sheet with or without a coated graphite mold was characterized. The cell adhesion property of porous titanium sheet was also evaluated in this study. The peak of TiC was detected on the titanium sheet processed with the graphite mold without a TiN coating. Since the titanium fiber elements were directly in contact with the carbon graphite mold during processing, surface contamination was unavoidable event in this condition. The TiC peak was not detectable on the titanium sheet processed within the TiN-coated carbon graphite mold. This modified plasma-activated sintering with the TiN-coated graphite mold would be useful to fabricate a contamination-free titanium sheet. The number of adherent cells on the modified titanium sheet was greater than that of the bare titanium plate. Stress fiber formation and the extension of the cells were observed on the titanium sheets. This modified titanium sheet is expected to be a new tissue engineering material in orthopedic bone repair.

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

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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.

Predicting Pulsar Scintillation from Refractive Plasma Sheets

Science.gov (United States)

Simard, Dana; Pen, Ue-Li

2018-05-01

The dynamic and secondary spectra of many pulsars show evidence for long-lived, aligned images of the pulsar that are stationary on a thin scattering sheet. One explanation for this phenomenon considers the effects of wave crests along sheets in the ionized interstellar medium, such as those due to Alfvén waves propagating along current sheets. If these sheets are closely aligned to our line-of-sight to the pulsar, high bending angles arise at the wave crests and a selection effect causes alignment of images produced at different crests, similar to grazing reflection off of a lake. Using geometric optics, we develop a simple parameterized model of these corrugated sheets that can be constrained with a single observation and that makes observable predictions for variations in the scintillation of the pulsar over time and frequency. This model reveals qualitative differences between lensing from overdense and underdense corrugated sheets: Only if the sheet is overdense compared to the surrounding interstellar medium can the lensed images be brighter than the line-of-sight image to the pulsar, and the faint lensed images are closer to the pulsar at higher frequencies if the sheet is underdense, but at lower frequencies if the sheet is overdense.

Ion and electron Kappa distribution functions in the plasma sheet.

Science.gov (United States)

Moya, P. S.; Stepanova, M. V.; Espinoza, C.; Antonova, E. E.; Valdivia, J. A.

2017-12-01

We present a study of ion and electron flux spectra in the Earth's plasma sheet using kappa distribution functions. Satellite data from the THEMIS mission were collected for thousands of crossings through the plasma sheet, between 7 and 35 Re and during the years 2008-2009. The events were separated according to the geomagnetic activity at the time. Our results show the distribution of the kappa index and characteristic energies across the plasma sheet and its evolution with distance to Earth for quiet times and for the substorm expansion and recovery phases. For the ions, it is observed that the kappa values tend to decrease outwards and that this effect is more significant in the dusk sector, where the smallest values are found for distances beyond 15 Re. The main effect of the substorms appears as an enhancement of this behavior. The electrons show a much more homogeneous distribution in quiet times, with a mild tendency for larger kappa values at larger distances. During substorms, the kappa values tend to equalize and appear very homogenous during expansion. However, they exhibit a significant increase in the dusk sector during the recovery substorm phase. Finally, we observe that the characteristic energy of the particles during substorms increases and concentrate at distances less than 15 Re.

Survey of 0.1- to 16-keV/e plasma sheet ion composition

International Nuclear Information System (INIS)

Lennartsson, W.; Shelley, E.G.

1986-01-01

A large statistical survey of the 0.1- to 16-keV/e plasma sheet ion composition has been carried out using data obtained by the Plasma Composition Experiment on ISEE 1 between 10 and 23 R/sub E/ during 1978 and 1979. This survey includes more than 10 times the quantity of data used in earlier studies of the same topic and makes it possible to investigate in finer detail the relationship between the ion composition and the substorm activity. The larger data base also makes it possible for the first time to study the spatial distribution of the principal ion species. As found in previous studies, the ion composition has a large variance at any given value of the AE index, but a number of distinct trends emerge when the data are averaged at each activity level. During quiet conditions the plasma sheet is dominated by ions of solar origin (H + and He ++ ), as found in earlier studies, and these ions are most numerous during extended periods of very low activity (AE< or approx. =30 γ). The quiet time density of these ions is particularly large in the flanks of the plasma sheet (GSM Yapprox. +- 10 R/sub E/), where it is about twice as large as it is near the central axis of the plasma sheet (Y = Z = 0). In contrast, the energy of these ions peaks near the central axis

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

Sheet Fluorescence and Annular Analysis of Ultracold Neutral Plasmas

International Nuclear Information System (INIS)

Castro, J.; Gao, H.; Killian, T. C.

2009-01-01

Annular analysis of fluorescence imaging measurements on Ultracold Neutral Plasmas (UNPs) is demonstrated. Spatially-resolved fluorescence imaging of the strontium ions produces a spectrum that is Doppler-broadened due to the thermal ion velocity and shifted due to the ion expansion velocity. The fluorescence excitation beam is spatially narrowed into a sheet, allowing for localized analysis of ion temperatures within a volume of the plasma with small density variation. Annular analysis of fluorescence images permits an enhanced signal-to-noise ratio compared to previous fluorescence measurements done in strontium UNPs. Using this technique and analysis, plasma ion temperatures are measured and shown to display characteristics of plasmas with strong coupling such as disorder induced heating and kinetic energy oscillations.

The quiet evening auroral arc and the structure of the growth phase near-Earth plasma sheet

Science.gov (United States)

Coroniti, F. V.; Pritchett, P. L.

2014-03-01

The plasma pressure and current configuration of the near-Earth plasma sheet that creates and sustains the quiet evening auroral arc during the growth phase of magnetospheric substorms is investigated. We propose that the quiet evening arc (QEA) connects to the thin near-Earth current sheet, which forms during the development of the growth phase enhancement of convection. The current sheet's large polarization electric fields are shielded from the ionosphere by an Inverted-V parallel potential drop, thereby producing the electron precipitation responsible for the arc's luminosity. The QEA is located in the plasma sheet region of maximal radial pressure gradient and, in the east-west direction, follows the vanishing of the approximately dawn-dusk-directed gradient or fold in the plasma pressure. In the evening sector, the boundary between the Region1 and Region 2 current systems occurs where the pressure maximizes (approximately radial gradient of the pressure vanishes) and where the approximately radial gradient of the magnetic flux tube volume also vanishes in an inflection region. The proposed intricate balance of plasma sheet pressure and currents may well be very sensitive to disruption by the arrival of equatorward traveling auroral streamers and their associated earthward traveling dipolarization fronts.

Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet

Directory of Open Access Journals (Sweden)

M. Hamrin

2009-11-01

Full Text Available Here, and in a companion paper by Hamrin et al. (2009 [Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs in the Earth's plasma sheet. In total we have studied 151 ECRs within 660 h of plasma sheet data from the summer and fall of 2001 when Cluster was close to apogee at an altitude of about 15–20 R_E. Cluster offers appropriate conditions for the investigation of energy conversion by the evaluation of the power density, E·J, where E is the electric field and J the current density. From the sign of the power density, we have identified more than three times as many Concentrated Load Regions (CLRs as Concentrated Generator Regions (CGRs. We also note that the CLRs appear to be stronger. To our knowledge, these are the first in situ observations confirming the general notion of the plasma sheet, on the average, behaving as a load. At the same time the plasma sheet appears to be highly structured, with energy conversion occurring in both directions between the fields and the particles. From our data we also find that the CLRs appear to be located closer to the neutral sheet, while CGRs prefer locations towards the plasma sheet boundary layer (PSBL. For both CLRs and CGRs, E and J in the GSM y (cross-tail direction dominate the total power density, even though the z contribution occasionally can be significant. The prevalence of the y-direction seems to be weaker for the CGRs, possibly related to a higher fluctuation level near the PSBL.

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

Modeling magnetospheric plasma; Proceedings of the First Huntsville Workshop on Magnetosphere/Ionosphere Plasma Models, Guntersville, AL, Oct. 14-16, 1987

International Nuclear Information System (INIS)

Moore, T.E.; Waite, J.H. Jr.

1988-01-01

The conference presents papers on the global modeling of magnetospheric plasma processes, the modeling of the midlatitude ionosphere and plasmasphere, the modeling of the auroral zone and boundary layer, the modeling of the polar magnetosphere and ionosphere, and the modeling of the plasma sheet and ring current. Particular attention is given to the kinetic approach in magnetospheric plasma transport modeling, self-consistent neutral point current and fields from single particle dynamics, preliminary statistical survey of plasmaspheric ion properties from observations by DE 1/RIMS, and a model of auroral potential structures based on dynamics explorer plasma data. Other topics include internal shear layers in auroral dynamics, quantitative parameterization of energetic ionospheric ion outflow, and open flux merging in an expanding polarcap model

Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet

Directory of Open Access Journals (Sweden)

M. Hamrin

2009-11-01

Full Text Available In this article, and in a companion paper by Hamrin et al. (2009 [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data at the altitude of about 15–20 RE in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs and 35 Concentrated Generator Regions (CGRs. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 RE≲ΔSECR≲5 RE. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1–10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005. The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1–10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.

Three-dimensional earthward fast flow in the near-Earth plasma sheet in a sheared field: comparisons between simulations and observations

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K. Kondoh

2009-06-01

Full Text Available Three-dimensional configuration of earthward fast flow in the near-Earth plasma sheet is studied using three-dimensional magnetohydrodynamics (MHD simulations on the basis of the spontaneous fast reconnection model. In this study, the sheared magnetic field in the plasma sheet is newly considered in order to investigate the effects of it to the earthward fast flow, and the results are discussed in comparison with no-shear simulations. The virtual probes located at different positions in our simulation domain in shear/no-shear cases could explain different behavior of fast flows in the real observations.

The statistical studies of the inner boundary of plasma sheet

Directory of Open Access Journals (Sweden)

J. B. Cao

2011-02-01

Full Text Available The penetration of plasma sheet ions into the inner magnetosphere is very important to the inner magnetospheric dynamics since plasma sheet ions are one of the major particle sources of ring current during storm times. However, the direct observations of the inner boundary of the plasma sheet are fairly rare due to the limited number of satellites in near equatorial orbits outside 6.6 RE. In this paper, we used the ion data recorded by TC-1 from 2004 to 2006 to study the distribution of inner boundary of ion plasma sheet (IBIPS and for the first time show the observational distribution of IBIPS in the equatorial plane. The IBIPS has a dawn-dusk asymmetry, being farthest to the Earth in the 06:00 08:00 LT bin and closest to the Earth in the 18:00–20:00 LT bin. Besides, the IBIPS has also a day-night asymmetry, which may be due to the fact that the ions on the dayside are exposed more time to loss mechanisms on their drift paths. The radial distance of IBIPS decrease generally with the increase of Kp index. The mean radial distance of IBIPS is basically larger than 6.6 RE during quiet times and smaller than 6.6 RE during active times. When the strength of convection electric field increases, the inward shift of IBIPS is most significant on the night side (22:00–02:00 LT. For Kp ≤ 0+, only 16% of IBIPSs penetrate inside the geosynchronous orbit. For 2 ≤ Kp +, however, 70% of IBIPSs penetrate inside the geosynchronous orbit. The IBIPS has weak correlations with the AE and Dst indexes. The average correlation coefficient between Ri and Kp is −0.58 while the correlation coefficient between Ri and AE/Dst is only −0.29/0.17. The correlation coefficients are local time dependent. Particularly, Ri and Kp are highly correlated (r=−0.72 in the night sector, meaning that the radial distance of IBIPS Ri in the night sector has the good response to the Kp index These observations indicate that Kp plays a key role in determining the position of

An ice sheet model validation framework for the Greenland ice sheet

Science.gov (United States)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

2017-01-01

We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.

Latitudinal distribution of the Jovian plasma sheet ions observed by Juno JADE-I

Science.gov (United States)

Kim, T. K. H.; Valek, P. W.; McComas, D. J.; Allegrini, F.; Bagenal, F.; Bolton, S. J.; Connerney, J. E. P.; Ebert, R. W.; Levin, S.; Louarn, P.; Pollock, C. J.; Ranquist, D. A.; Szalay, J.; Thomsen, M. F.; Wilson, R. J.

2017-12-01

The Jovian plasma sheet is a region where the centrifugal force dominates the heavy ion plasma. Properties of the plasma sheet ions near the equatorial plane have been studied with in-situ measurements from the Pioneer, Voyager, and Galileo spacecraft. However, the ion properties for the off-equator regions are not well known due to the limited measurements. Juno is the first polar orbiting spacecraft that can investigate the high latitude region of the Jovian magnetosphere. With Juno's unique trajectory, we will investigate the latitudinal distribution of the Jovian plasma sheet ions using measurements from the Jovian Auroral Distributions Experiment Ion sensor (JADE-I). JADE-I measures an ion's energy-per-charge (E/Q) from 0.01 keV/q to 46.2 keV/q with an electrostatic analyzer (ESA) and a mass-per-charge (M/Q) up to 64 amu/q with a carbon-foil-based time-of-flight (TOF) mass spectrometer. We have shown that the ambiguity between and (both have M/Q of 16) can be resolved in JADE-I using a semi-empirical simulation tool based on carbon foil effects (i.e., charge state modification, angular scattering, and energy loss) from incident ions passing through the TOF mass spectrometer. Based on the simulation results, we have developed an Ion Composition Analysis Tool (ICAT) that determines ion composition at each energy step of JADE-I (total of 64 steps). The velocity distribution for each ion species can be obtained from the ion composition as a function of each energy step. Since there is an ambipolar electric field due to mobile electrons and equatorially confined heavy ions, we expect to see acceleration along the field line. This study will show the species separated velocity distribution at various latitudes to investigate how the plasma sheet ions evolve along the field line.

Ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves

International Nuclear Information System (INIS)

Moghaddam-Taaheri, E.; Goertz, C.K.; Smith, R.A.

1989-01-01

The kinetic Alfven wave, an Alfven wave with a perpendicular wavelength comparable to the ion gyroradius, can diffuse ions both in velocity and coordinate spaces with comparable transport rates. This may lead to the generation of ion beams in the plasma sheet boundary layer (PSBL). To investigate the ion beam generation process numerically, a two-dimensional quasi-linear code was constructed. Assuming that the plasma β (the ratio of plasma pressure to the magnetic pressure) varies from β = 1 to β << 1 across the magnetic field, the dynamics of the ion beam generation in the PSBL was studied. It was found that if your start with an ion distribution function which monotonically decreases with velocity along the magnetic field and a density gradient across the magnetic field, ions diffuse in velocity-coordinate space until nearly a plateau is established along the diffusion path. Depending on the topology of the magnetic field at the lobe side of the simulation system, i.e., open or closed field lines, the ion distribution function may or may not reach a steady state. If the field lines are open there, i.e., if the diffusion extends into the lobe, the double diffusion process may provide a mechanism for continuously transferring the ions from the central plasma sheet to the lobe. The authors comment on the effect of the particle loss on the establishment of the pressure balance in the plasma sheet

Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet

Directory of Open Access Journals (Sweden)

M. Hamrin

2009-11-01

Full Text Available In this article, and in a companion paper by Hamrin et al. (2009 [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data at the altitude of about 15–20 R_E in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs and 35 Concentrated Generator Regions (CGRs. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 R_E≲ΔS_ECR≲5 R_E. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1–10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005. The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1–10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.

Compression Models for Plasma Focus Devices

International Nuclear Information System (INIS)

Gonzalez, Jose; Calusse, Alejandro; Ramos, Ruben; Rodriguez Palomino, Luis

2003-01-01

Using a numerical model that calculates the dynamics of Plasma Focus devices, we compared the results of three different compression models of the plasma pinch.One of the main objectives in this area is to develop a simplified model to calculate the neutron production of Plasma Focus devices, to study the influence of the main parameters in this neutron yield.The dynamics is thoroughly studied, and the model predicts fairly well values such as maximum currents and times for pinch collapse.Therefore, we evaluate here different models of pinch compression, to try to predict the neutron production with good agreement with the rest of the variables involved.To fulfill this requirement, we have experimental results of neutron production as a function of deuterium filling pressure in the chamber, and typical values of other main variables in the dynamics of the current sheet

Frequency-dependent absorbance of broadband terahertz wave in dense plasma sheet

Science.gov (United States)

Peng, Yan; Qi, Binbin; Jiang, Xiankai; Zhu, Zhi; Zhao, Hongwei; Zhu, Yiming

2018-05-01

Due to the ability of accurate fingerprinting and low-ionization for different substances, terahertz (THz) technology has a lot of crucial applications in material analysis, information transfer, and safety inspection, etc. However, the spectral characteristic of atmospheric gas and ionized gas has not been widely investigated, which is important for the remote sensing application. Here, in this paper, we investigate the absorbance of broadband terahertz wave in dense plasma sheet generated by femtosecond laser pulses. It was found that as the terahertz wave transmits through the plasma sheet formed, respectively, in carbon dioxide, oxygen, argon and nitrogen, spectrum presents completely different and frequency-dependent absorbance. The reasons for these absorption peaks are related to the molecular polarity, electric charge, intermolecular and intramolecular interactions, and collisional absorption of gas molecules. These results have significant implications for the remote sensing of gas medium.

Localized fast flow disturbance observed in the plasma sheet and in the ionosphere

Directory of Open Access Journals (Sweden)

R. Nakamura

2005-02-01

Full Text Available An isolated plasma sheet flow burst took place at 22:02 UT, 1 September 2002, when the Cluster footpoint was located within the area covered by the Magnetometers-Ionospheric Radars-All-sky Cameras Large Experiment (MIRACLE. The event was associated with a clear but weak ionospheric disturbance and took place during a steady southward IMF interval, about 1h preceding a major substorm onset. Multipoint observations, both in space and from the ground, allow us to discuss the temporal and spatial scale of the disturbance both in the magnetosphere and ionosphere. Based on measurements from four Cluster spacecraft it is inferred that Cluster observed the dusk side part of a localized flow channel in the plasma sheet with a flow shear at the front, suggesting a field-aligned current out from the ionosphere. In the ionosphere the equivalent current pattern and possible field-aligned current location show a pattern similar to the auroral streamers previously obtained during an active period, except for its spatial scale and amplitude. It is inferred that the footpoint of Cluster was located in the region of an upward field-aligned current, consistent with the magnetospheric observations. The entire disturbance in the ionosphere lasted about 10min, consistent with the time scale of the current sheet disturbance in the magnetosphere. The plasma sheet bulk flow, on the other hand, had a time scale of about 2min, corresponding to the time scale of an equatorward excursion of the enhanced electrojet. These observations confirm that localized enhanced convection in the magnetosphere and associated changes in the current sheet structure produce a signature with consistent temporal and spatial scale at the conjugate ionosphere.

Polar Plasma at Ganymede: Ionospheric outflow and discovery of the plasma sheet

Science.gov (United States)

Collinson, G.; Paterson, W.; Dorelli, J.; Glocer, A.; Sarantos, M.; Wilson, R. J.; Bard, C.

2017-12-01

On the 27th of June 1996, the NASA Galileo spacecraft made humanities first flyby of Jupiter's largest moon, Ganymede, discovering that it is unique to science in being the only moon known to possess an internally generated magnetic dynamo field. Although Galileo carried a plasma spectrometer, the Plasma Subsystem (PLS), converting its highly complex raw data stream into meaningful plasma moments (density, temperature, velocity) is extremely challenging, and was only ever performed for the second (out of six) Ganymede flybys. Resurrecting the original Galileo PLS data analysis software, we processed the raw PLS data from G01, and for the first time present the properties of plasmas encountered. Dense, cold ions were observed outflowing from the moon's north pole (presumed to be dominated by H+ from the icy surface), with more diffuse, warmer field-aligned outflows in the lobes. Dropouts in plasma density combined with velocity perturbations either side of this suggest that Galileo briefly crossed the cusps onto closed magnetic field lines. PLS observations show that upon entry into the magnetosphere, Galileo crossed through the plasma sheet, observing plasma flows consistent with reconnection-driven convection, highly energized 105 eV ions, and a reversal in the magnetic field. The densities of plasmas flowing upwards from Ganymede's ionosphere were higher on open "lobe" field lines than on closed field lines, suggesting that the ionospheric source of these plasmas may be denser at the poles, there may be additional acceleration mechanisms at play, or the balance of ions were outside the energy range of PLS.

Static current-sheet models of quiescent prominences

Science.gov (United States)

Wu, F.; Low, B. C.

1986-12-01

A particular class of theoretical models idealize the prominence to be a discrete flat electric-current sheet suspended vertically in a potential magnetic field. The weight of the prominence is supported by the Lorentz force in the current sheet. These models can be extended to have curved electric-current sheets and to vary three-dimensionally. The equation for force balance is 1 over 4 pi (del times B) times Bdel p- p9 z=zero. Using Cartesian coordinates we take, for simplicity, a uniform gravity with constant acceleration g in the direction -z. If we are interested not in the detailed internal structure of the prominence, but in the global magnetic configuration around the prominence, we may take prominence plasma to be cold. Consideration is given to how such equilibrium states can be constructed. To simplify the mathematical problem, suppose there is no electric current in the atmosphere except for the discrete currents in the cold prominence sheet. Let us take the plane z =0 to be the base of the atmosphere and restrict our attention to the domain z greater than 0. The task we have is to solve for a magnetic field which is everywhere potential except on some free surface S, subject to suit able to boundary conditions. The surface S is determined by requiring that it possesses a discrete electric current density such that the Lorentz force on it is everywhere vertically upward to balance the weight of the material m(S). Since the magnetic field is potential in the external atmosphere, the latter is decoupled from the magnetic field and its plane parallel hydrostatic pressure and density can be prescribed.

Casimir effects for a flat plasma sheet: II. Fields and stresses

International Nuclear Information System (INIS)

Barton, G

2005-01-01

We study the self-stresses experienced by the single plasma sheet modelled in the preceding paper, and determine the exact mean-squared Maxwell fields in vacuum around it. These are effects that probe the physics of such systems further than do the ground-state eigenvalues responsible for the cohesive energy β; in particular, unlike β they depend not only on the collective properties but also on the self-fields of the charge carriers. The classical part of the interaction between the sheet and a slowly moving charged particle follows as a byproduct. The main object is to illustrate, in simple closed or almost closed form, the consequences of imperfect (dispersive) reflectivity. The largely artificial limit of perfect reflection reduces all the results to those long familiar outside a half-space taken to reflect perfectly from the outset; but a careful examination of the approach to this limit is needed in order to resolve paradoxes associated with the surface energy, and with the mechanism which, in the limit, disjoins the two flanking half-spaces both electromagnetically and quantally

Spatial variations in the suprathermal ion distributions during substorms in the plasma sheet

International Nuclear Information System (INIS)

Kistler, L.M.; Moebius, E.; Klecker, B.; Gloeckler, G.; Ipavich, F.M.; Hamilton, D.C.

1990-01-01

Using data from AMPTE IRM and AMPTE CCE, the authors have determined the pre- and post-injection suprathermal energy spectra for the ion species H + , O + , He + , and He ++ for six events in which substorm-associated particle injections are observed in both the near-Earth plasma sheet and farther down the tail. They find similar spectral changes in both locations, with the spectra becoming harder with the injection. Post-injection, the flux decreases exponentially with radial distance. Approximately the same gradient is observed in all species. In addition, they find that although the O + /H + and the He ++ /H + ratios increase with energy per charge, the ratios are approximately the same at the same energy per charge at the two spacecraft. The observations are difficult to explain either with a model in which the ions are accelerated at a neutral line and transported toward Earth or with a model in which the ions are accelerated in the near-Earth region by current disruption/diversion and transported down the tail. In either case, the ions would have to be transported throughout the tail without much energization or deenergization in order to explain the energy per charge correlations. Further, earthward transport without energization would not lead to the observed radial gradient. A combination of these acceleration mechanisms, a disturbance that propagates throughout the plasma sheet, or a more global mechanism may explain the observations

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)

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...

On the possible eigenoscillations of neutral sheets

International Nuclear Information System (INIS)

Almeida, W.A.; Costa, J.M. da; Aruquipa, E.G.; Sudano, J.P.

1974-12-01

A neutral sheet model with hyperbolic tangent equilibrium magnetic field and hyperbolic square secant density profiles is considered. It is shown that the equation for small oscillations takes the form of an eigenvalue oscillation problem. Computed eigenfrequencies of the geomagnetic neutral sheet were found to be in the range of the resonant frequencies of the geomagnetic plasma sheet computed by other authors

FDTD modeling of thin impedance sheets

Science.gov (United States)

Luebbers, Raymond J.; Kunz, Karl S.

1991-01-01

Thin sheets of resistive or dielectric material are commonly encountered in radar cross section calculations. Analysis of such sheets is simplified by using sheet impedances. In this paper it is shown that sheet impedances can be modeled easily and accurately using Finite Difference Time Domain (FDTD) methods.

A lumped parameter model of plasma focus

International Nuclear Information System (INIS)

Gonzalez, Jose H.; Florido, Pablo C.; Bruzzone, H.; Clausse, Alejandro

1999-01-01

A lumped parameter model to estimate neutron emission of a plasma focus (PF) device is developed. The dynamic of the current sheet is calculated using a snowplow model, and the neutron production with the thermal fusion cross section for a deuterium filling gas. The results were contrasted as a function of the filling pressure with experimental measurements of a 3.68 KJ Mather-type PF. (author)

Computational numerical modelling of plasma focus

International Nuclear Information System (INIS)

Brollo, Fabricio

2005-01-01

Several models for calculation of the dynamics of Plasma Focus have been developed. All of them begin from the same physic principle: the current sheet run down the anode length, ionizing and collecting the gas that finds in its way.This is known as snow-plow model.Concerning pinch's compression, a MHD model is proposed.The plasma is treated as a fluid , particularly as a high ionized gas.However, there are not many models that, taking into account thermal equilibrium inside the plasma, make approximated calculations of the maximum temperatures reached in the pinch.Besides, there are no models which use those temperatures to estimate the termofusion neutron yield for the Deuterium or Deuterium-Tritium gas filled cases.In the PLADEMA network (Dense Magnetized Plasmas) a code was developed with the objective of describe the plasma focus dynamics, in a conceptual engineering stage.The codes calculates the principal variables (currents, time to focus, etc) and estimates the neutron yield in Deuterium-filled plasma focus devices.It can be affirmed that the code's experimental validation, in its axial and radial stages, was very successfully. However, it was accepted that the compression stage should be formulated again, to find a solution for a large variation of a parameter related with velocity profiles for the particles trapped inside the pinch.The objectives of this work can be stated in the next way : - Check the compression's model hypothesis. Develop a new model .- Implement the new model in the code. Compare results against experimental data of Plasma Focus devices from all around the world [es

NON-EQUILIBRIUM IONIZATION MODELING OF THE CURRENT SHEET IN A SIMULATED SOLAR ERUPTION

International Nuclear Information System (INIS)

Shen Chengcai; Reeves, Katharine K.; Raymond, John C.; Murphy, Nicholas A.; Ko, Yuan-Kuen; Lin Jun; Mikić, Zoran; Linker, Jon A.

2013-01-01

The current sheet that extends from the top of flare loops and connects to an associated flux rope is a common structure in models of coronal mass ejections (CMEs). To understand the observational properties of CME current sheets, we generated predictions from a flare/CME model to be compared with observations. We use a simulation of a large-scale CME current sheet previously reported by Reeves et al. This simulation includes ohmic and coronal heating, thermal conduction, and radiative cooling in the energy equation. Using the results of this simulation, we perform time-dependent ionization calculations of the flow in a CME current sheet and construct two-dimensional spatial distributions of ionic charge states for multiple chemical elements. We use the filter responses from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory and the predicted intensities of emission lines to compute the count rates for each of the AIA bands. The results show differences in the emission line intensities between equilibrium and non-equilibrium ionization. The current sheet plasma is underionized at low heights and overionized at large heights. At low heights in the current sheet, the intensities of the AIA 94 Å and 131 Å channels are lower for non-equilibrium ionization than for equilibrium ionization. At large heights, these intensities are higher for non-equilibrium ionization than for equilibrium ionization inside the current sheet. The assumption of ionization equilibrium would lead to a significant underestimate of the temperature low in the current sheet and overestimate at larger heights. We also calculate the intensities of ultraviolet lines and predict emission features to be compared with events from the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, including a low-intensity region around the current sheet corresponding to this model

Spatial structure of the plasma sheet boundary layer at distances greater than 180 RE as derived from energetic particle measurements on GEOTAIL

Directory of Open Access Journals (Sweden)

T. Yamamoto

Full Text Available We have analyzed the onsets of energetic particle bursts detected by the ICS and STICS sensors of the EPIC instrument on board the GEOTAIL spacecraft in the deep magnetotail (i.e., at distances greater than 180 RE. Such bursts are commonly observed at the plasma-sheet boundary layer (PSBL and are highly collimated along the magnetic field. The bursts display a normal velocity dispersion (i.e., the higher-speed particles are seen first, while the progressively lower speed particles are seen later when observed upon entry of the spacecraft from the magnetotail lobes into the plasma sheet. Upon exit from the plasma sheet a reverse velocity dispersion is observed (i.e., lower-speed particles disappear first and higher-speed particles disappear last. Three major findings are as follows. First, the tailward-jetting energetic particle populations of the distant-tail plasma sheet display an energy layering: the energetic electrons stream along open PSBL field lines with peak fluxes at the lobes. Energetic protons occupy the next layer, and as the spacecraft moves towards the neutral sheet progressively decreasing energies are encountered systematically. These plasma-sheet layers display spatial symmetry, with the plane of symmetry the neutral sheet. Second, if we consider the same energy level of energetic particles, then the H+ layer is confined within that of the energetic electron, the He++ layer is confined within that of the proton, and the oxygen layer is confined within the alpha particle layer. Third, whenever the energetic electrons show higher fluxes inside the plasma sheet as compared to those at the boundary layer, their angular distribution is isotropic irrespective of the Earthward or tailward character of fluxes, suggesting a closed field line topology.

Spatial structure of the plasma sheet boundary layer at distances greater than 180 RE as derived from energetic particle measurements on GEOTAIL

Directory of Open Access Journals (Sweden)

D. V. Sarafopoulos

1997-10-01

Full Text Available We have analyzed the onsets of energetic particle bursts detected by the ICS and STICS sensors of the EPIC instrument on board the GEOTAIL spacecraft in the deep magnetotail (i.e., at distances greater than 180 RE. Such bursts are commonly observed at the plasma-sheet boundary layer (PSBL and are highly collimated along the magnetic field. The bursts display a normal velocity dispersion (i.e., the higher-speed particles are seen first, while the progressively lower speed particles are seen later when observed upon entry of the spacecraft from the magnetotail lobes into the plasma sheet. Upon exit from the plasma sheet a reverse velocity dispersion is observed (i.e., lower-speed particles disappear first and higher-speed particles disappear last. Three major findings are as follows. First, the tailward-jetting energetic particle populations of the distant-tail plasma sheet display an energy layering: the energetic electrons stream along open PSBL field lines with peak fluxes at the lobes. Energetic protons occupy the next layer, and as the spacecraft moves towards the neutral sheet progressively decreasing energies are encountered systematically. These plasma-sheet layers display spatial symmetry, with the plane of symmetry the neutral sheet. Second, if we consider the same energy level of energetic particles, then the H+ layer is confined within that of the energetic electron, the He++ layer is confined within that of the proton, and the oxygen layer is confined within the alpha particle layer. Third, whenever the energetic electrons show higher fluxes inside the plasma sheet as compared to those at the boundary layer, their angular distribution is isotropic irrespective of the Earthward or tailward character of fluxes, suggesting a closed field line topology.

Equilibrium structure of the plasma sheet boundary layer-lobe interface

Science.gov (United States)

Romero, H.; Ganguli, G.; Palmadesso, P.; Dusenbery, P. B.

1990-01-01

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential is established in order to maintain quasi-neutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.

Interpretation of magnetosonic waves in the boundary regions of the plasma sheet as seen by the ISEE 3 spacecraft

International Nuclear Information System (INIS)

Smith, P.R.; Hopcraft, K.I.; Murphy, N.

1987-01-01

Recent calculations that derive the normal-mode spectrum of an idealized magnetic current sheet are discussed. The Harris neutral-sheet equilibrium is perturbed with an ideal MHD displacement. The longitudinal polarization of the fundamental modes is calculated as a function of the position in the sheet. Using data from the energetic-ion instrument aboard ISEE 3, the thickness of the plasma sheet in the deep geomagnetic tail is estimated. This parameter enables a quantitative comparison between the boundary oscillations reported by Tsurutani and Smith (1984) and the normal mode oscillations derived by Hopcraft and Smith (1985) to be performed. The normal-mode solutions are found to be consistent with observation. Further aspects of the MHD wave spectrum that may lead to an observable variation of the mode character across the boundary of the plasma sheet are pointed out. 12 references

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.

Generation mechanism of the whistler-mode waves in the plasma sheet prior to magnetic reconnection

Czech Academy of Sciences Publication Activity Database

Wei, X. H.; Cao, J. B.; Zhou, G. C.; Fu, H. S.; Santolík, Ondřej; Reme, H.; Dandouras, I.; Cornilleau, N.; Fazakerley, A.

2013-01-01

Roč. 52, č. 1 (2013), s. 205-210 ISSN 0273-1177 Institutional support: RVO:68378289 Keywords : whistler-mode waves * electron temperature anisotropy * Reconnection * the plasma sheet Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.238, year: 2013 http://www.sciencedirect.com/science/article/pii/S0273117713001221

Transient, Small-Scale Field-Aligned Currents in the Plasma Sheet Boundary Layer During Storm Time Substorms

Science.gov (United States)

Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Plaschke, F.; Magnes, W.; Fischer, D.; Varsani, A.; Schmid, D.; Nakamura, T. K. M.; Russell, C. T.;

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.

Observation of enhanced electric field in an RF-plugged sheet plasma in the RFC-XX-M open-ended machine

International Nuclear Information System (INIS)

Oda, T.; Takiyama, K.; Kadota, K.

1987-12-01

We report nonperturbing observation of the electric field in the sheet plasma for RF end-plugging on the RFC XX-M open-ended machine by using the Stark effect with a combined technique of beam-probe and laser-induced fluorescence. Under the optimum condition for the RF plugging, enhanced electric field is found in the sheet plasma by about 2.5 times with respect to the electric field when no plasma is produced. The field spatial profile is also measured, which is discussed in connection with the electrostatic eigenmode. (author)

Current sheet characteristics of a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode

Science.gov (United States)

Liu, Shuai; Huang, Yizhi; Guo, Haishan; Lin, Tianyu; Huang, Dong; Yang, Lanjun

2018-05-01

The axial characteristics of a current sheet in a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode are reported. The accelerator is powered by a fourteen stage pulse forming network. The capacitor and inductor in each stage are 1.5 μF and 300 nH, respectively, and yield a damped oscillation square wave of current with a pulse width of 20.6 μs. Magnetic probes and photodiodes are placed at various axial positions to measure the behavior of the current sheet. Both magnetic probe and photodiode signals reveal a secondary breakdown when the current reverses the direction. An increase in the discharge current amplitude and a decrease in pressure lead to a decrease in the current shedding factor. The current sheet velocity and thickness are nearly constant during the run-down phase under the first half-period of the current. The current sheet thicknesses are typically in the range of 25 mm to 40 mm. The current sheet velocities are in the range of 10 km/s to 45 km/s when the discharge current is between 10 kA and 55 kA and the gas prefill pressure is between 30 Pa and 800 Pa. The experimental velocities are about 75% to 90% of the theoretical velocities calculated with the current shedding factor. One reason for this could be that the idealized snowplow analysis model ignores the surface drag force.

Distribution of O+ ions in the plasma sheet and locations of substorm onsets

Science.gov (United States)

Ono, Y.; Christon, S. P.; Frey, H. U.; Lui, A. T. Y.

2010-09-01

We discuss the effect of O+ ions on substorm onsets by examining the relation between the substorm onset location and the distribution of the O+/H+ number density ratio before the onset in the various regions within the plasma sheet (-8 RE > XGSM > -32 RE). We use 9-212 keV/e ion flux data observed by Geotail/Energetic Particles and Ion Composition (EPIC)/Suprathermal Ion Composition Spectrometer (STICS) instrument and the IMAGE/Far Ultra-Violet (FUV) substorm onset list presented by Frey et al. [Frey, H. U., S. B. Mende, V. Angelopoulos, and E. F. Donovan (2004), Substorm onset observations by IMAGE-FUV, J. Geophys. Res., 109, A10304, doi:10.1029/2004JA010607]. The results are summarized as follows. Substorm onsets, which we identify by auroral initial brightenings, are likely to occur in the more dusk-(dawn-)ward region when the O+/H+ number density ratio is high in the dusk (dawn) side. This property is observed only in the near-Earth plasma sheet (at -8 RE > XGSM > -14 RE). The above-mentioned property holds in each of two groups: substorm events due to internal instability of the magnetosphere (i.e., internally triggered substorms) and events due to external changes in the solar wind or the interplanetary magnetic field (i.e., externally triggered substorms). Thus, we conclude that the substorm onset location depends on the density of O+ ions in the near-Earth plasma sheet prior to onset, whether the substorm is triggered internally or externally.

Latitude-energy structure of multiple ion beamlets in Polar/TIMAS data in plasma sheet boundary layer and boundary plasma sheet below 6 RE radial distance: basic properties and statistical analysis

Directory of Open Access Journals (Sweden)

P. Janhunen

2005-03-01

Full Text Available Velocity dispersed ion signatures (VDIS occurring at the plasma sheet boundary layer (PSBL are a well reported feature. Theory has, however, predicted the existence of multiple ion beamlets, similar to VDIS, in the boundary plasma sheet (BPS, i.e. at latitudes below the PSBL. In this study we show evidence for the multiple ion beamlets in Polar/TIMAS ion data and basic properties of the ion beamlets will be presented. Statistics of the occurrence frequency of ion multiple beamlets show that they are most common in the midnight MLT sector and for altitudes above 4 RE, while at low altitude (≤3 RE, single beamlets at PSBL (VDIS are more common. Distribution functions of ion beamlets in velocity space have recently been shown to correspond to 3-dimensional hollow spheres, containing a large amount of free energy. We also study correlation with ~100 Hz waves and electron anisotropies and consider the possibility that ion beamlets correspond to stable auroral arcs.

Physical models for the description of an electrodynamically accelerated plasma sheath

International Nuclear Information System (INIS)

Zambreanu, V.

1977-01-01

An analysis of the models proposed for the description of the plasma sheath dynamics in a coaxial system (of the same type as that operating at the Bucharest Institute of Physics) is presented. A particular attention is paid to the physical structure of the accelerated plasma. It has been shown that a self-consistent model could be derived from a phenomenological description of the sheath structure. The physical models presented so far in the literature have been classified into three groups: the hydrodynamic models, the plasma sheet models and the shock wave models. Each of these models is briefly described. The simplifying assumptions used in the construction of these models have been pointed out. The final conclusion has been that, under these assumptions, none of these models taken separately could completely and correctly describe the dynamical state of the plasma sheath. (author)

Compressional Pc5 type pulsations in the morningside plasma sheet

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A. Vaivads

Full Text Available We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000–1700 UT on 9 March 1998, and 0200–0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode, and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.

Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma sheet

Compressional Pc5 type pulsations in the morningside plasma sheet

Directory of Open Access Journals (Sweden)

A. Vaivads

2001-03-01

Full Text Available We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000–1700 UT on 9 March 1998, and 0200–0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode, and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma sheet

Coupling of climate models and ice sheet models by surface mass balance gradients: application to the Greenland Ice Sheet

Directory of Open Access Journals (Sweden)

M. M. Helsen

2012-03-01

Full Text Available It is notoriously difficult to couple surface mass balance (SMB results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature, which is often related to surface elevation (H_s. In this study, we propose a new strategy to calculate SMB, to allow a direct adjustment of SMB to a change in ice sheet topography and/or a change in climate forcing. This method is based on elevational gradients in the SMB field as computed by a regional climate model. Separate linear relations are derived for ablation and accumulation, using pairs of H_s and SMB within a minimum search radius. The continuously adjusting SMB forcing is consistent with climate model forcing fields, also for initially non-glaciated areas in the peripheral areas of an ice sheet. When applied to an asynchronous coupled ice sheet – climate model setup, this method circumvents traditional temperature lapse rate assumptions. Here we apply it to the Greenland Ice Sheet (GrIS. Experiments using both steady-state forcing and glacial-interglacial forcing result in realistic ice sheet reconstructions.

Spatial Distribution and Semiannual Variation of Cold-Dense Plasma Sheet

Science.gov (United States)

Bai, Shichen; Shi, Quanqi; Tian, Anmin; Nowada, Motoharu; Degeling, Alexander W.; Zhou, Xu-Zhi; Zong, Qiu-Gang; Rae, I. Jonathan; Fu, Suiyan; Zhang, Hui; Pu, Zuyin; Fazakerly, Andrew N.

2018-01-01

The cold-dense plasma sheet (CDPS) plays an important role in the entry process of the solar wind plasma into the magnetosphere. Investigating the seasonal variation of CDPS occurrences will help us better understand the long-term variation of plasma exchange between the solar wind and magnetosphere, but any seasonal variation of CDPS occurrences has not yet been reported in the literature. In this paper, we investigate the seasonal variation of the occurrence rate of CDPS using Geotail data from 1996 to 2015 and find a semiannual variation of the CDPS occurrences. Given the higher probability of solar wind entry under stronger northward interplanetary magnetic field (IMF) conditions, 20 years of IMF data (1996-2015) are used to investigate the seasonal variation of IMF Bz under northward IMF conditions. We find a semiannual variation of IMF Bz, which is consistent with the Russell-McPherron (R-M) effect. We therefore suggest that the semiannual variation of CDPS may be related to the R-M effect.

A MODEL FOR THE ELECTRICALLY CHARGED CURRENT SHEET OF A PULSAR

Energy Technology Data Exchange (ETDEWEB)

DeVore, C. R.; Antiochos, S. K.; Black, C. E. [Heliophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); Harding, A. K.; Kalapotharakos, C.; Kazanas, D.; Timokhin, A. N., E-mail: c.richard.devore@nasa.gov [Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)

2015-03-10

Global-scale solutions for the magnetosphere of a pulsar consist of a region of low-lying, closed magnetic field near the star, bounded by opposite-polarity regions of open magnetic field along which the pulsar wind flows into space. Separating these open-field regions is a magnetic discontinuity—an electric current sheet—consisting of generally nonneutral plasma. We have developed a self-consistent model for the internal equilibrium structure of the sheet by generalizing the charge-neutral Vlasov/Maxwell equilibria of Harris and Hoh to allow for net electric charge. The resulting equations for the electromagnetic field are solved analytically and numerically. Our results show that the internal thermal pressure needed to establish equilibrium force balance, and the associated effective current-sheet thickness and magnetization, can differ by orders of magnitude from the Harris/Hoh charge-neutral limit. The new model provides a starting point for kinetic or fluid investigations of instabilities that can cause magnetic reconnection and flaring in pulsar magnetospheres.

Compressional wave events in the dawn plasma sheet observed by Interball-1

Directory of Open Access Journals (Sweden)

O. Verkhoglyadova

1999-09-01

Full Text Available Compressional waves with periods greater than 2 min (about 10-30 min at low geomagnetic latitudes, namely compressional Pc5 waves, are studied. The data set obtained with magnetometer MIF-M and plasma analyzer instrument CORALL on board the Interball-1 are analyzed. Measurements performed in October 1995 and October 1996 in the dawn plasma sheet at -30 RE ≤ XGSM and |ZGSM| ≤ 10 RE are considered. Anti-phase variations of magnetic field and ion plasma pressures are analyzed by searching for morphological similarities in the two time series. It is found that longitudinal and transverse magnetic field variations with respect to the background magnetic field are of the same order of magnitude. Plasma velocities are processed for each time period of the local dissimilarity in the pressure time series. Velocity disturbances occur mainly transversely to the local field line. The data reveal the rotation of the velocity vector. Because of the field line curvature, there is no fixed position of the rotational plane in the space. These vortices are localized in the regions of anti-phase variations of the magnetic field and plasma pressures, and the vortical flows are associated with the compressional Pc5 wave process. A theoretical model is proposed to explain the main features of the nonlinear wave processes. Our main goal is to study coupling of drift Alfven wave and magnetosonic wave in a warm inhomogeneous plasma. A vortex is the partial solution of the set of the equations when the compression is neglected. A compression effect gives rise to a nonlinear soliton-like solution.Key words. Magnetosphere physics (magnetotail · Space plasma physics (kinetic and MHD theory; non-linear phenomena

Characteristics of electrostatic solitary waves observed in the plasma sheet boundary: Statistical analyses

Directory of Open Access Journals (Sweden)

H. Kojima

1999-01-01

Full Text Available We present the characteristics of the Electrostatic Solitary Waves (ESW observed by the Geotail spacecraft in the plasma sheet boundary layer based on the statistical analyses. We also discuss the results referring to a model of ESW generation due to electron beams, which is proposed by computer simulations. In this generation model, the nonlinear evolution of Langmuir waves excited by electron bump-on-tail instabilities leads to formation of isolated electrostatic potential structures corresponding to "electron hole" in the phase space. The statistical analyses of the Geotail data, which we conducted under the assumption that polarity of ESW potentials is positive, show that most of ESW propagate in the same direction of electron beams, which are observed by the plasma instrument, simultaneously. Further, we also find that the ESW potential energy is much smaller than the background electron thermal energy and that the ESW potential widths are typically shorter than 60 times of local electron Debye length when we assume that the ESW potentials travel in the same velocity of electron beams. These results are very consistent with the ESW generation model that the nonlinear evolution of electron bump-on-tail instability leads to the formation of electron holes in the phase space.

Cluster view of the plasma sheet boundary layer and bursty bulk flow connection

Directory of Open Access Journals (Sweden)

O. W. Lennartsson

2009-04-01

Full Text Available The high-latitude boundaries of the plasma sheet (PSBL are dynamic latitude zones of recurring and transient (minutes to tens of minutes earthward and magnetic field-aligned bursts of plasma, each being more or less confined in longitude as well, whose ionic component is dominated by protons with flux, energies and density that are consistent with a central plasma sheet (CPS source at varying distance (varying rates of energy time dispersion, sometimes as close as the ~19 RE Cluster apogees, or closer still. The arguably most plausible source consists of so called "bursty bulk flows" (BBFs, i.e. proton bulk flow events with large, positive and bursty GSE vx. Known mainly from CPS observations made at GSE x>−30 RE, the BBF type events probably take place much further downtail as well. What makes the BBFs an especially plausible source are (1 their earthward bulk flow, which helps explain the lack of distinctive latitudinal PSBL energy dispersion, and (2 their association with a transient strong increase of the local tail Bz component ("local dipolarization". The enhanced Bz provides intermittent access to higher latitudes for the CPS plasma, resulting in local density reductions in the tail midplane, as illustrated here by proton data from the Cluster CIS CODIF instruments. Another sign of kinship between the PSBL bursts and the BBFs is their similar spatial fine structure. The PSBL bursts have prominent filaments aligned along the magnetic field with transverse flux gradients that are often characterized by local ~10 keV proton gyroradii scale size (or even smaller, as evidenced by Cluster measurements. The same kind of fine structure is also found during Cluster near-apogee traversals of the tail midplane, as illustrated here and implied by recently published statistics on BBFs obtained with Cluster multipoint observations at varying satellite separations. Altogether, the Cluster observations described here mesh rather well with theories

Electron precipitation morphology and plasma sheet dynamics: ground and magnetotail studies of the magnetospheric substorm

International Nuclear Information System (INIS)

Pytte, T.

1976-12-01

The main results of some recent studies of the magnetospheric substorm are summarised and discussed in view of the fundamental role of magnetospheric convection. The substorm growth phase is described in terms of a temporary imbalance between the rates of magnetic field-line merging on the dayside, and reconnection on the nightside, of the magnetosphere following a southward turning of the interplanetary magnetic field. Some new understanding of the possible causal relationship between growth-phase and expansion-phase phenomena is provided through studies of multiple-onset substorms, during which substorm expansions are observed to occur at intervals of 10-15 min. Detailed observations have revealed new features of the radial and azimuthal dynamics of these substorms that are not consistent with recent models proposed by Akasofu and by Rostoker and his co-workers. It is shown that the behaviour of the near-earth plasma sheet early in a substorm cannot be inferred from measurements at larger distances (e.g., in the Vela satellite orbits), and that the triggering of a substorm expansion may well be directly related to pre-substorm thinning of the near-earth plasma sheet, even though the most significant thinning in the tailward region may occur at the onset, and therefore appears to be an effect rather than a cause of triggering. Initial results from studies of a new type of magnetospheric activity, characterised by strong auroral-zone bay activity but no other indications of substorm expansions, are shown to be consistent with current models of the growth and expansion phases of substorms and of substorm triggering. (JIW)

Advanced friction modeling for sheet metal forming

NARCIS (Netherlands)

Hol, J.; Cid Alfaro, M.V.; de Rooij, Matthias B.; Meinders, Vincent T.

2012-01-01

The Coulomb friction model is frequently used for sheet metal forming simulations. This model incorporates a constant coefficient of friction and does not take the influence of important parameters such as contact pressure or deformation of the sheet material into account. This article presents a

Advanced friction modeling in sheet metal forming

NARCIS (Netherlands)

Hol, J.; Cid Alfaro, M.V.; Meinders, Vincent T.; Huetink, Han

2011-01-01

The Coulomb friction model is frequently used for sheet metal forming simulations. This model incorporates a constant coefficient of friction and does not take the influence of important parameters such as contact pressure or deformation of the sheet material into account. This article presents a

The effect of plasma actuator on the depreciation of the aerodynamic drag on box model

Science.gov (United States)

Harinaldi, Budiarso, Julian, James; Rabbani M., N.

2016-06-01

Recent active control research advances have provided many benefits some of which in the field of transportation by land, sea as well as by air. Flow engineering by using active control has proven advantages in energy saving significantly. One of the active control equipment that is being developed, especially in the 21st century, is a plasma actuator, with the ability to modify the flow of fluid by the approach of ion particles makes these actuators a very powerful and promising tool. This actuator can be said to be better to the previously active control such as suction, blowing and synthetic jets because it is easier to control, more flexible because it has no moving parts, easy to be manufactured and installed, and consumes a small amount of energy with maximum capability. Plasma actuator itself is the composition of a material composed of copper and a dielectric sheet, where the copper sheets act as an electricity conductor and the dielectric sheet as electricity insulator. Products from the plasma actuators are ion wind which is the result of the suction of free air around the actuator to the plasma zone. This study investigates the ability of plasma actuators in lowering aerodynamic drag which is commonly formed in the models of vehicles by varying the shape of geometry models and the flow speed.

Sheet pinch devices

International Nuclear Information System (INIS)

Anderson, O.A.; Baker, W.R.; Ise, J. Jr.; Kunkel, W.B.; Pyle, R.V.; Stone, J.M.

1958-01-01

Three types of sheet-like discharges are being studied at Berkeley. The first of these, which has been given the name 'Triax', consists of a cylindrical plasma sleeve contained between two coaxial conducting cylinders A theoretical analysis of the stability of the cylindrical sheet plasma predicts the existence of a 'sausage-mode' instability which is, however, expected to grow more slowly than in the case of the unstabilized linear pinch (by the ratio of the radial dimensions). The second pinch device employs a disk shaped discharge with radial current guided between flat metal plates, this configuration being identical to that of the flat hydromagnetic capacitor without external magnetic field. A significant feature of these configurations is the absence of a plasma edge, i.e., there are no regions of sharply curved magnetic field lines anywhere in these discharges. The importance of this fact for stability is not yet fully investigated theoretically. As a third configuration a rectangular, flat pinch tube has been constructed, and the behaviour of a flat plasma sheet with edges is being studied experimentally

Spontaneous magnetic fluctuations and collisionless regulation of the Earth's plasma sheet

Science.gov (United States)

Moya, P. S.; Espinoza, C.; Stepanova, M. V.; Antonova, E. E.; Valdivia, J. A.

2017-12-01

Even in the absence of instabilities, plasmas often exhibit inherent electromagnetic fluctuations which are present due to the thermal motion of charged particles, sometimes called thermal (quasi-thermal) noise. One of the fundamental and challenging problems of laboratory, space, and astrophysical plasma physics is the understanding of the relaxation processes of nearly collisionless plasmas, and the resultant state of electromagnetic plasma turbulence. The study of thermal fluctuations can be elegantly addressed by using the Fluctuation-Dissipation Theorem that describes the average amplitude of the fluctuations through correlations of the linear response of the media with the perturbations of the equilibrium state (the dissipation). Recently, it has been shown that solar wind plasma beta and temperature anisotropy observations are bounded by kinetic instabilities such as the ion cyclotron, mirror, and firehose instabilities. The magnetic fluctuations observed within the bounded area are consistent with the predictions of the Fluctuation-Dissipation theorem even far below the kinetic instability thresholds, with an enhancement of the fluctuation level near the thresholds. Here, for the very first time, using in-situ magnetic field and plasma data from the THEMIS spacecraft, we show that such regulation also occurs in the Earth's plasma sheet at the ion scales and that, regardless of the clear differences between the solar wind and the magnetosphere environments, spontaneous fluctuation and their collisionless regulation seem to be fundamental features of space and astrophysical plasmas, suggesting the universality of the processes.

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)

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)

Simultaneous Measurements of Substorm-Related Electron Energization in the Ionosphere and the Plasma Sheet

Science.gov (United States)

Sivadas, N.; Semeter, J.; Nishimura, Y.; Kero, A.

2017-10-01

On 26 March 2008, simultaneous measurements of a large substorm were made using the Poker Flat Incoherent Scatter Radar, Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft, and all sky cameras. After the onset, electron precipitation reached energies ≳100 keV leading to intense D region ionization. Identifying the source of energetic precipitation has been a challenge because of lack of quantitative and magnetically conjugate measurements of loss cone electrons. In this study, we use the maximum entropy inversion technique to invert altitude profiles of ionization measured by the radar to estimate the loss cone energy spectra of primary electrons. By comparing them with magnetically conjugate measurements from THEMIS-D spacecraft in the nightside plasma sheet, we constrain the source location and acceleration mechanism of precipitating electrons of different energy ranges. Our analysis suggests that the observed electrons ≳100 keV are a result of pitch angle scattering of electrons originating from or tailward of the inner plasma sheet at 9RE, possibly through interaction with electromagnetic ion cyclotron waves. The electrons of energy 10-100 keV are produced by pitch angle scattering due to a potential drop of ≲10 kV in the auroral acceleration region (AAR) as well as wave-particle interactions in and tailward of the AAR. This work demonstrates the utility of magnetically conjugate ground- and space-based measurements in constraining the source of energetic electron precipitation. Unlike in situ spacecraft measurements, ground-based incoherent scatter radars combined with an appropriate inversion technique can be used to provide remote and continuous-time estimates of loss cone electrons in the plasma sheet.

Survey of Galileo Plasma Observations in Jupiter's Plasma Sheet

Science.gov (United States)

Bagenal, Fran; Wilson, Robert J.; Siler, Scott; Paterson, William R.; Kurth, William S.

2016-01-01

The plasma science (PLS) Instrument on the Galileo spacecraft (orbiting Jupiter from December 1995 to September 2003) measured properties of the ions that were trapped in the magnetic field. The PLS data provide a survey of the plasma properties between approx. 5 and 30 Jupiter radii [R(sub J)] in the equatorial region. We present plasma properties derived via two analysis methods: numerical moments and forward modeling. We find that the density decreases with radial distance by nearly 5 orders of magnitude from approx. 2 to 3000 cm(exp.-3) at 6R(sub j) to approx. 0.05cm(sub -3) at 30 R(sub j). The density profile did not show major changes from orbit to orbit, suggesting that the plasma production and transport remained constant within about a factor of 2. The radial profile of ion temperature increased with distance which implied that contrary to the concept of adiabatic cooling on expansion, the plasma heats up as it expands out from Io's orbit (where TI is approx.60-80 eV) at approx. 6R(sub j) to a few keV at 30R(sub j).There does not seem to be a long-term, systematic variation in ion temperature with either local time or longitude. This latter finding differs from earlier analysis of Galileo PLS data from a selection of orbits. Further examination of all data from all Galileo orbits suggests that System Ill variations are transitory on timescales of weeks, consistent with the modeling of Cassini Ultraviolet Imaging Spectrograph observations. The plasma flow is dominated by azimuthal flow that is between 80% and 100% of corotation out to 25 R(sub j).

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

Ice Sheet Model Intercomparison Project (ISMIP6) contribution to CMIP6

Science.gov (United States)

Nowicki, Sophie M.J.; Payne, Tony; Larour, Eric; Seroussi, Helene; Goelzer, Heiko; Lipscomb, William; Gregory, Jonathan; Abe-Ouchi, Ayako; Shepherd, Andrew

2018-01-01

Reducing the uncertainty in the past, present and future contribution of ice sheets to sea-level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project – phase 6 (CMIP6) focusing on the Greenland and Antarctic Ice Sheets. In this paper, we describe the framework for ISMIP6 and its relationship to other activities within CMIP6. The ISMIP6 experimental design relies on CMIP6 climate models and includes, for the first time within CMIP, coupled ice sheet – climate models as well as standalone ice sheet models. To facilitate analysis of the multi-model ensemble and to generate a set of standard climate inputs for standalone ice sheet models, ISMIP6 defines a protocol for all variables related to ice sheets. ISMIP6 will provide a basis for investigating the feedbacks, impacts, and sea-level changes associated with dynamic ice sheets and for quantifying the uncertainty in ice-sheet-sourced global sea-level change. PMID:29697697

Single clay sheets inside electrospun polymer nanofibers

Science.gov (United States)

Sun, Zhaohui

2005-03-01

Nanofibers were prepared from polymer solution with clay sheets by electrospinning. Plasma etching, as a well controlled process, was used to supply electrically excited gas molecules from a glow discharge. To reveal the structure and arrangement of clay layers in the polymer matrix, plasma etching was used to remove the polymer by controlled gasification to expose the clay sheets due to the difference in reactivity. The shape, flexibility, and orientation of clay sheets were studied by transmission and scanning electron microscopy. Additional quantitative information on size distribution and degree of exfoliation of clay sheets were obtained by analyzing electron micrograph of sample after plasma etching. Samples in various forms including fiber, film and bulk, were thinned by plasma etching. Morphology and dispersion of inorganic fillers were studied by electron microscopy.

Ice flow Modelling of the Greenland Ice Sheet

DEFF Research Database (Denmark)

Nielsen, Lisbeth Tangaa

Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others. In t...... a steady state with respect to the reference climate at the end of the simulation and that the mass balance of the ice sheet at this time was more sensitive to recent climate fluctuations than the temperature forcing in the early or mid-Holocene.......Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others....... In this PhD project, the use of ice flow models for the interpretation of the age-structure of the Greenland ice sheet, i.e. the depth within the ice, at which ice deposited at given times are found at present day. Two different observational data sets of this archive were investigated. Further, paleo...

Early results of microwave transmission experiments through an overly dense rectangular plasma sheet with microparticle injection

Energy Technology Data Exchange (ETDEWEB)

Gillman, Eric D., E-mail: eric.gillman.ctr@nrl.navy.mil [National Research Council Postdoctoral Associate at the U.S. Naval Research Laboratory, Washington, DC 20375 (United States); Amatucci, W. E. [U.S. Naval Research Laboratory, Washington, DC 20375 (United States)

2014-06-15

These experiments utilize a linear hollow cathode to create a dense, rectangular plasma sheet to simulate the plasma layer surrounding vehicles traveling at hypersonic velocities within the Earth's atmosphere. Injection of fine dielectric microparticles significantly reduces the electron density and therefore lowers the electron plasma frequency by binding a significant portion of the bulk free electrons to the relatively massive microparticles. Measurements show that microwave transmission through this previously overly dense, impenetrable plasma layer increases with the injection of alumina microparticles approximately 60 μm in diameter. This method of electron depletion is a potential means of mitigating the radio communications blackout experienced by hypersonic vehicles.

Modeling an emittance-dominated elliptical sheet beam with a 212-dimensional particle-in-cell code

International Nuclear Information System (INIS)

Carlsten, Bruce E.

2005-01-01

Modeling a 3-dimensional (3-D) elliptical beam with a 212-D particle-in-cell (PIC) code requires a reduction in the beam parameters. The 212-D PIC code can only model the center slice of the sheet beam, but that can still provide useful information about the beam transport and distribution evolution, even if the beam is emittance dominated. The reduction of beam parameters and resulting interpretation of the simulation is straightforward, but not trivial. In this paper, we describe the beam parameter reduction and emittance issues related to the initial beam distribution. As a numerical example, we use the case of a sheet beam designed for use with a planar traveling-wave amplifier for high power generator for RF ranging from 95 to 300GHz [Carlsten et al., IEEE Trans. Plasma Sci. 33 (2005) 85]. These numerical techniques also apply to modeling high-energy elliptical bunches in RF accelerators

Numerical modeling of the plasma ring acceleration experiment

International Nuclear Information System (INIS)

Eddleman, J.L.; Hammer, J.H.; Hartman, C.W.

1987-01-01

Modeling of the LLNL RACE experiment and its many applications has necessitated the development and use of a wide array of computational tools. The two-dimensional MHD code, HAM, has been used to model the formation of a compact torus plasma ring in a magnetized coaxial gun and its subsequent acceleration by an additional applied toroidal field. Features included in the 2-D calculations are self-consistent models for (1) the time-dependent poloidal field produced by a capacitor bank discharge through a solenoid field coil (located either inside the gun inner electrode or outside the outer gun electrode) and the associated diffusion of magnetic flux through neighboring conductors, (2) gas flow into the gun annular region from a simulated puffed gas valve plenum, (3) formation and motion of a current sheet produced by J x B forces resulting from discharge of the gun capacitor bank through the plasma load between the coaxial gun electrodes, (4) the subsequent stretching and reconnection of the poloidal field lines to form a compact torus plasma ring, and (5) finally the discharge of the accelerator capacitor bank producing an additional toroidal field for acceleration of the plasma ring. The code has been extended to include various models for gas breakdown, plasma anomalous resistivity, and mass entrainment from ablation of electrode material

Ice Sheet Model Intercomparison Project (ISMIP6) Contribution to CMIP6

Science.gov (United States)

Nowicki, Sophie M. J.; Payne, Tony; Larour, Eric; Seroussi, Helene; Goelzer, Heiko; Lipscomb, William; Gregory, Jonathan; Abe-Ouchi, Ayako; Shepherd, Andrew

2016-01-01

Reducing the uncertainty in the past, present, and future contribution of ice sheets to sea-level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project phase 6 (CMIP6) focusing on the Greenland and Antarctic ice sheets. In this paper, we describe the framework for ISMIP6 and its relationship with other activities within CMIP6. The ISMIP6 experimental design relies on CMIP6 climate models and includes, for the first time within CMIP, coupled ice-sheetclimate models as well as standalone ice-sheet models. To facilitate analysis of the multi-model ensemble and to generate a set of standard climate inputs for standalone ice-sheet models, ISMIP6 defines a protocol for all variables related to ice sheets. ISMIP6 will provide a basis for investigating the feedbacks, impacts, and sea-level changes associated with dynamic ice sheets and for quantifying the uncertainty in ice-sheet-sourced global sea-level change.

Theoretical models of non-Maxwellian equilibria for one-dimensional collisionless plasmas

Science.gov (United States)

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

2016-12-01

It is ideal to use exact equilibrium solutions of the steady state Vlasov-Maxwell system to intialise collsionless simulations. However, exact equilibrium distribution functions (DFs) for a given macroscopic configuration are typically unknown, and it is common to resort to using `flow-shifted' Maxwellian DFs in their stead. These DFs may be consistent with a macrosopic system with the target number density and current density, but could well have inaccurate higher order moments. We present recent theoretical work on the `inverse problem in Vlasov-Maxwell equilibria', namely calculating an exact solution of the Vlasov equation for a specific given magnetic field. In particular, we focus on one-dimensional geometries in Cartesian (current sheets) coordinates.1. From 1D fields to Vlasov equilibria: Theory and application of Hermite Polynomials: (O. Allanson, T. Neukirch, S. Troscheit and F. Wilson, Journal of Plasma Physics, 82, 905820306 (2016) [28 pages, Open Access] )2. An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta: (O. Allanson, T. Neukirch, F. Wilson and S. Troscheit, Physics of Plasmas, 22, 102116 (2015) [11 pages, Open Access])3. Neutral and non-neutral collisionless plasma equilibria for twisted flux tubes: The Gold-Hoyle model in a background field (O. Allanson, F. Wilson and T. Neukirch, (2016)) (accepted, Physics of Plasmas)

An Exploration of Heating Mechanisms in a Supra-arcade Plasma Sheet Formed after a Coronal Mass Ejection

Energy Technology Data Exchange (ETDEWEB)

Reeves, Katharine K. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St. MS 58, Cambridge, MA 02138 (United States); Freed, Michael S.; McKenzie, David E. [Montana State University, Bozeman, MT 59717 (United States); Savage, Sabrina L., E-mail: kreeves@cfa.harvard.edu [NASA Marshall Space Flight Center, Huntsville, AL 35812 (United States)

2017-02-10

We perform a detailed analysis of the thermal structure of the region above the post-eruption arcade for a flare that occurred on 2011 October 22. During this event, a sheet of hot plasma is visible above the flare loops in the 131 Å bandpass of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory . Supra-arcade downflows (SADs) are observed traveling sunward through the post-eruption plasma sheet. We calculate differential emission measures using the AIA data and derive an emission measure weighted average temperature in the supra-arcade region. In areas where many SADs occur, the temperature of the supra-arcade plasma tends to increase, while in areas where no SADs are observed, the temperature tends to decrease. We calculate the plane-of-sky velocities in the supra-arcade plasma and use them to determine the potential heating due to adiabatic compression and viscous heating. Of the 13 SADs studied, 10 have noticeable signatures in both the adiabatic and the viscous terms. The adiabatic heating due to compression of plasma in front of the SADs is on the order of 0.1–0.2 MK/s, which is similar in magnitude to the estimated conductive cooling rate. This result supports the notion that SADs contribute locally to the heating of plasma in the supra-arcade region. We also find that in the region without SADs, the plasma cools at a rate that is slower than the estimated conductive cooling, indicating that additional heating mechanisms may act globally to keep the plasma temperature high.

An Exploration of Heating Mechanisms in a Supra-arcade Plasma Sheet Formed after a Coronal Mass Ejection

International Nuclear Information System (INIS)

Reeves, Katharine K.; Freed, Michael S.; McKenzie, David E.; Savage, Sabrina L.

2017-01-01

We perform a detailed analysis of the thermal structure of the region above the post-eruption arcade for a flare that occurred on 2011 October 22. During this event, a sheet of hot plasma is visible above the flare loops in the 131 Å bandpass of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory . Supra-arcade downflows (SADs) are observed traveling sunward through the post-eruption plasma sheet. We calculate differential emission measures using the AIA data and derive an emission measure weighted average temperature in the supra-arcade region. In areas where many SADs occur, the temperature of the supra-arcade plasma tends to increase, while in areas where no SADs are observed, the temperature tends to decrease. We calculate the plane-of-sky velocities in the supra-arcade plasma and use them to determine the potential heating due to adiabatic compression and viscous heating. Of the 13 SADs studied, 10 have noticeable signatures in both the adiabatic and the viscous terms. The adiabatic heating due to compression of plasma in front of the SADs is on the order of 0.1–0.2 MK/s, which is similar in magnitude to the estimated conductive cooling rate. This result supports the notion that SADs contribute locally to the heating of plasma in the supra-arcade region. We also find that in the region without SADs, the plasma cools at a rate that is slower than the estimated conductive cooling, indicating that additional heating mechanisms may act globally to keep the plasma temperature high.

Grounding line transient response in marine ice sheet models

Directory of Open Access Journals (Sweden)

A. S. Drouet

2013-03-01

Full Text Available Marine ice-sheet stability is mostly controlled by the dynamics of the grounding line, i.e. the junction between the grounded ice sheet and the floating ice shelf. Grounding line migration has been investigated within the framework of MISMIP (Marine Ice Sheet Model Intercomparison Project, which mainly aimed at investigating steady state solutions. Here we focus on transient behaviour, executing short-term simulations (200 yr of a steady ice sheet perturbed by the release of the buttressing restraint exerted by the ice shelf on the grounded ice upstream. The transient grounding line behaviour of four different flowline ice-sheet models has been compared. The models differ in the physics implemented (full Stokes and shallow shelf approximation, the numerical approach, as well as the grounding line treatment. Their overall response to the loss of buttressing is found to be broadly consistent in terms of grounding line position, rate of surface elevation change and surface velocity. However, still small differences appear for these latter variables, and they can lead to large discrepancies (> 100% observed in terms of ice sheet contribution to sea level when cumulated over time. Despite the recent important improvements of marine ice-sheet models in their ability to compute steady state configurations, our results question the capacity of these models to compute short-term reliable sea-level rise projections.

Spectral functions for the flat plasma sheet model

International Nuclear Information System (INIS)

Pirozhenko, I G

2006-01-01

The present work is based on Bordag M et al 2005 (J. Phys. A: Math. Gen. 38 11027) where the spectral analysis of the electromagnetic field on the background of an infinitely thin flat plasma layer is carried out. The solutions to Maxwell equations with the appropriate matching conditions at the plasma layer are derived and the spectrum of electromagnetic oscillations is determined. The spectral zeta function and the integrated heat kernel are constructed for different branches of the spectrum in an explicit form. The asymptotic expansion of the integrated heat kernel at small values of the evolution parameter is derived. The local heat kernels are considered also

Energetic particle beams in the plasma sheet boundary layer following substorm expansion - Simultaneous near-earth and distant tail observations

Science.gov (United States)

Scholer, M.; Baker, D. N.; Gloeckler, G.; Ipavich, F. M.; Galvin, A. B.; Klecker, B.; Terasawa, T.; Tsurutani, B. T.

1986-01-01

Simultaneous observations of ions and electron beams in the near-earth and deep magnetotail following the onset of substorm are analyzed in terms of the substorm neutral line model. The observations were collected on March 20, 1983 with ISSE 1 and 3. Energy fluxes and intensity-time profiles of protons and electrons are studied. The data reveal that the reconnection at the near-earth neutral line produces ions and electrons for the plasma sheet boundary layer. The maximum electric potential along the neutral line is evaluated.

Global ice sheet/RSL simulations using the higher-order Ice Sheet System Model.

Science.gov (United States)

Larour, E. Y.; Ivins, E. R.; Adhikari, S.; Schlegel, N.; Seroussi, H. L.; Morlighem, M.

2017-12-01

Relative sea-level rise is driven by processes that are intimately linked to the evolution ofglacial areas and ice sheets in particular. So far, most Earth System models capable of projecting theevolution of RSL on decadal to centennial time scales have relied on offline interactions between RSL andice sheets. In particular, grounding line and calving front dynamics have not been modeled in a way that istightly coupled with Elasto-Static Adjustment (ESA) and/or Glacial-Isostatic Adjustment (GIA). Here, we presenta new simulation of the entire Earth System in which both Greenland and Antarctica ice sheets are tightly coupledto an RSL model that includes both ESA and GIA at resolutions and time scales compatible with processes suchas grounding line dynamics for Antarctica ice shelves and calving front dynamics for Greenland marine-terminatingglaciers. The simulations rely on the Ice Sheet System Model (ISSM) and show the impact of higher-orderice flow dynamics and coupling feedbacks between ice flow and RSL. We quantify the exact impact of ESA andGIA inclusion on grounding line evolution for large ice shelves such as the Ronne and Ross ice shelves, as well asthe Agasea Embayment ice streams, and demonstate how offline vs online RSL simulations diverge in the long run,and the consequences for predictions of sea-level rise.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

PERISTALTIC PUMPING NEAR POST-CORONAL MASS EJECTION SUPRA-ARCADE CURRENT SHEETS

Energy Technology Data Exchange (ETDEWEB)

Scott, Roger B.; Longcope, Dana W.; McKenzie, David E., E-mail: rscott@physics.montana.edu [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717 (United States)

2013-10-10

Temperature and density measurements near supra-arcade current sheets suggest that plasma on unreconnected field lines may experience some degree of 'pre-heating' and 'pre-densification' prior to reconnection. Models of patchy reconnection allow for heating and acceleration of plasma along reconnected field lines but do not offer a mechanism for transport of thermal energy across field lines. Here, we present a model in which a reconnected flux tube retracts, deforming the surrounding layer of unreconnected field. The deformation creates constrictions that act as peristaltic pumps, driving plasma flow along affected field lines. Under certain circumstances, these flows lead to shocks that can extend far out into the unreconnected field, altering the plasma properties in the affected region. These findings have direct implications for observations in the solar corona, particularly in regard to such phenomena as high temperatures near current sheets in eruptive solar flares and wakes seen in the form of descending regions of density depletion or supra-arcade downflows.

Electron energization in the geomagnetic tail current sheet

International Nuclear Information System (INIS)

Lyons, L.R.

1984-01-01

Electron motion in the distant tail current sheet is evaluated and found to violate the guiding center approximation at energies > or approx. =100 eV. Most electrons within the energy range approx.10 -1 -10 2 keV that enter the current sheet become trapped within the magnetic field reversal region. These electrons then convect earthward and gain energy from the cross-tail electric field. If the energy spectrum of electrons entering the current sheet is similar to that of electrons from the boundary layer surrounding the magnetotail, the energy gain from the electric field produces electron energy spectra comparable to those observed in the earth's plasma sheet. Thus current sheet interactions can be a significant source of particles and energy for plasma sheet electrons as well as for plasma sheet ions. A small fraction of electrons within the current sheet has its pitch angles scattered so as to be ejected from the current sheet within the atmospheric loss cone. These electrons can account for the electron precipitation near the high-latitude boundary of energetic electrons, which is approximately isotropic in pitch angle up to at least several hundred keV. Current sheet interaction should cause approximately isotropic auroral precipitation up to several hundred keV energies, which extends to significantly lower latitudes for ions than for electrons in agreement with low-altitude satellite observations. Electron precipitation associated with diffuse aurora generally has a transition at 1-10 keV to anisotropic pitch angle distributions. Such electron precipitation cannot be explained by current sheet interactions, but it can be explained by pitch angle diffusion driven by plasma turbulence

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.

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.

A Novel Method of Modeling the Deformation Resistance for Clad Sheet

International Nuclear Information System (INIS)

Hu Jianliang; Yi Youping; Xie Mantang

2011-01-01

Because of the excellent thermal conductivity, the clad sheet (3003/4004/3003) of aluminum alloy is extensively used in various heat exchangers, such as radiator, motorcar air conditioning, evaporator, and so on. The deformation resistance model plays an important role in designing the process parameters of hot continuous rolling. However, the complex behaviors of the plastic deformation of the clad sheet make the modeling very difficult. In this work, a novel method for modeling the deformation resistance of clad sheet was proposed by combining the finite element analysis with experiments. The deformation resistance model of aluminum 3003 and 4004 was proposed through hot compression test on the Gleeble-1500 thermo-simulation machine. And the deformation resistance model of clad sheet was proposed through finite element analysis using DEFORM-2D software. The relationship between cladding ratio and the deformation resistance was discussed in detail. The results of hot compression simulation demonstrate that the cladding ratio has great effects on the resistance of the clad sheet. Taking the cladding ratio into consideration, the mathematical model of the deformation resistance for clad sheet has been proved to have perfect forecasting precision of different cladding ratio. Therefore, the presented model can be used to predict the rolling force of clad sheet during the hot continuous rolling process.

Particle balance analysis on carbon sheet pump applied to the GAMMA10 tandem mirror plasmas

International Nuclear Information System (INIS)

Ishimoto, Yuki; Nakashima, Yousuke; Ishinuki, Eiichi; Kobayashi, Shinji; Yoshikawa, Masayuki; Tamano, Teruo; Yatsu, Kiyoshi; Sagara, Akio

2000-01-01

Carbon Sheet Pump (CSP) is expected as a tool for reduction of hydrogen recycling. In this paper, particle balance in the CSP is described. The pumping efficiencies estimated from the time evolution of hydrogen pressures during plasma discharges and those estimated from the thermal desorption experiments have no remarkable difference between the cases of 30degC and 200degC within experimental errors. In cases that CSP is used in actual plasma conditions, we established a method which reduces adsorbed gases on the CSP surface with sustaining a sufficient pumping efficiency by continuously heating CSP. (author)

Model of an electric field produced by viscous interaction in the plasma sheet of the magnetotail

International Nuclear Information System (INIS)

Erkaev, N.V.

1996-01-01

Two-dimensional model of flow in a plasma layer of magnetotail is considered with account of low viscosity. The general Ohm's law is used for electric current. The role of viscous forces is most sufficient in boundary layers, which expand with moving away along the flow and located along the boundaries of plasma layer and solar wind. Auto model solution, describing the distribution of potential and velocity in boundary layers was obtained. The solution for boundary layers dictates boundary conditions for determination of large-scale distribution of electric potential in plasma layer. 7 refs., 4 figs

ULF hydromagnetic oscillations with the discrete spectrum as eigenmodes of MHD-resonator in the near-Earth part of the plasma sheet

Directory of Open Access Journals (Sweden)

V. A. Mazur

2006-07-01

Full Text Available A new concept is proposed for the emergence of ULF geomagnetic oscillations with a discrete spectrum of frequencies (0.8, 1.3, 1.9, 2.6 ...mHz registered in the magnetosphere's midnight-morning sector. The concept relies on the assumption that these oscillations are MHD-resonator eigenmodes in the near-Earth plasma sheet. This magnetospheric area is where conditions are met for fast magnetosonic waves to be confined. The confinement is a result of the velocity values of fast magnetosonic waves in the near-Earth plasma sheet which differ greatly from those in the magnetotail lobes, leading to turning points forming in the tailward direction for the waves under study. To compute the eigenfrequency spectrum of such a resonator, we used a model magnetosphere with parabolic geometry. The fundamental harmonics of this resonator's eigenfrequencies are shown to be capable of being clustered into groups with average frequencies matching, with good accuracy, the frequencies of the observed oscillations. A possible explanation for the stability of the observed oscillation frequencies is that such a resonator might only form when the magnetosphere is in a certain unperturbed state.

ULF hydromagnetic oscillations with the discrete spectrum as eigenmodes of MHD-resonator in the near-Earth part of the plasma sheet

Directory of Open Access Journals (Sweden)

V. A. Mazur

2006-07-01

Full Text Available A new concept is proposed for the emergence of ULF geomagnetic oscillations with a discrete spectrum of frequencies (0.8, 1.3, 1.9, 2.6 ...mHz registered in the magnetosphere's midnight-morning sector. The concept relies on the assumption that these oscillations are MHD-resonator eigenmodes in the near-Earth plasma sheet. This magnetospheric area is where conditions are met for fast magnetosonic waves to be confined. The confinement is a result of the velocity values of fast magnetosonic waves in the near-Earth plasma sheet which differ greatly from those in the magnetotail lobes, leading to turning points forming in the tailward direction for the waves under study. To compute the eigenfrequency spectrum of such a resonator, we used a model magnetosphere with parabolic geometry. The fundamental harmonics of this resonator's eigenfrequencies are shown to be capable of being clustered into groups with average frequencies matching, with good accuracy, the frequencies of the observed oscillations. A possible explanation for the stability of the observed oscillation frequencies is that such a resonator might only form when the magnetosphere is in a certain unperturbed state.

Modeling of AlMg Sheet Forming at Elevated Temperatures

NARCIS (Netherlands)

van den Boogaard, Antonius H.; Bolt, P.; Werkhoven, R.

2001-01-01

The process limits of aluminum sheet forming processes can be improved by control-ling local flow behavior by means of elevated temperatures and temperature gradients. In order to accurately model the deep drawing or stretching of aluminum sheet at elevated temperatures, a model is required that

A Multicell Converter Model of DBD Plasma Discharges

International Nuclear Information System (INIS)

Flores-Fuentes, A. A.; Piedad-Beneitez, A. de la; Pena-Eguiluz, R.; Mercado-Cabrera, A.; Valencia A, R.; Barocio, S. R.; Lopez-Callejas, R.; Godoy-Cabrera, O. G.; Benitez-Read, J. S.; Pacheco-Sotelo, J. O.

2006-01-01

A compact Matlab model of plasma discharges in a DBD reactor consisting of two parallel electrode plates with a small gap and a thin dielectric sheet between them is reported. Its DBD plasma is modelled as a voltage controlled current-source switched on when the voltage across the gap exceeds the breakdown voltage. A three cell voltage-source inverter, configured in half-bridge, has been used as a power supply. This configuration has an excellent performance when operating as an open-loop. The distribution of total energy between a large number of low power converters proofs to be advantageous, allowing an efficient high power drive. Simulation results show that the current source and its output current tend to follow an exponential behaviour. A phenomenological characteristic of the voltage-current behaviour of DBD is then described by power laws with different voltage exponent function values

TURBULENT DYNAMICS IN SOLAR FLARE SHEET STRUCTURES MEASURED WITH LOCAL CORRELATION TRACKING

Energy Technology Data Exchange (ETDEWEB)

McKenzie, D. E., E-mail: mckenzie@physics.montana.edu [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717-3840 (United States)

2013-03-20

High-resolution observations of the Sun's corona in extreme ultraviolet and soft X-rays have revealed a new world of complexity in the sheet-like structures connecting coronal mass ejections (CMEs) to the post-eruption flare arcades. This article presents initial findings from an exploration of dynamic flows in two flares observed with Hinode/XRT and SDO/AIA. The flows are observed in the hot ({approx}> 10 MK) plasma above the post-eruption arcades and measured with local correlation tracking. The observations demonstrate significant shears in velocity, giving the appearance of vortices and stagnations. Plasma diagnostics indicate that the plasma {beta} exceeds unity in at least one of the studied events, suggesting that the coronal magnetic fields may be significantly affected by the turbulent flows. Although reconnection models of eruptive flares tend to predict a macroscopic current sheet in the region between the CME and the flare arcade, it is not yet clear whether the observed sheet-like structures are identifiable as the current sheets or 'thermal halos' surrounding the current sheets. Regardless, the relationship between the turbulent motions and the embedded magnetic field is likely to be complicated, involving dynamic fluid processes that produce small length scales in the current sheet. Such processes may be crucial for triggering, accelerating, and/or prolonging reconnection in the corona.

Modelling the Antarctic Ice Sheet

DEFF Research Database (Denmark)

Pedersen, Jens Olaf Pepke; Holm, A.

2015-01-01

to sea level high stands during past interglacial periods. A number of AIS models have been developed and applied to try to understand the workings of the AIS and to form a robust basis for future projections of the AIS contribution to sea level change. The recent DCESS (Danish Center for Earth System......The Antarctic ice sheet is a major player in the Earth’s climate system and is by far the largest depository of fresh water on the planet. Ice stored in the Antarctic ice sheet (AIS) contains enough water to raise sea level by about 58 m, and ice loss from Antarctica contributed significantly...

Two-dimensional model of a freely expanding plasma

International Nuclear Information System (INIS)

Khalid, Q.

1975-01-01

The free expansion of an initially confined plasma is studied by the computer experiment technique. The research is an extension to two dimensions of earlier work on the free expansion of a collisionless plasma in one dimension. In the two-dimensional rod model, developed in this research, the plasma particles, electrons and ions are modeled as infinitely long line charges or rods. The line charges move freely in two dimensions normal to their parallel axes, subject only to a self-consistent electric field. Two approximations, the grid approximation and the periodic boundary condition are made in order to reduce the computation time. In the grid approximation, the space occupied by the plasma at a given time is divided into boxes. The particles are subject to an average electric field calculated for that box assuming that the total charge within each box is located at the center of the box. However, the motion of each particle is exactly followed. The periodic boundary condition allows us to consider only one-fourth of the total number of particles of the plasma, representing the remaining three-fourths of the particles as symmetrically placed images of those whose positions are calculated. This approximation follows from the expected azimuthal symmetry of the plasma. The dynamics of the expansion are analyzed in terms of average ion and electron positions, average velocities, oscillation frequencies and relative distribution of energy between thermal, flow and electric field energies. Comparison is made with previous calculations of one-dimensional models which employed plane, spherical or cylindrical sheets as charged particles. In order to analyze the effect of the grid approximation, the model is solved for two different grid sizes and for each grid size the plasma dynamics is determined. For the initial phase of expansion, the agreement for the two grid sizes is found to be good

Ice shelf fracture parameterization in an ice sheet model

Science.gov (United States)

Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

2017-11-01

Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

Sawtooth events and O+ in the plasma sheet and boundary layer: CME- and SIR-driven events

Science.gov (United States)

Lund, E. J.; Nowrouzi, N.; Kistler, L. M.; Cai, X.; Liao, J.

2017-12-01

The role of ionospheric ions in sawtooth events is an open question. Simulations[1,2,3] suggest that O+ from the ionosphere produces a feedback mechanism for driving sawtooth events. However, observational evidence[4,5] suggest that the presence of O+ in the plasma sheet is neither necessary nor sufficient. In this study we investigate whether the solar wind driver of the geomagnetic storm has an effect on the result. Building on an earlier study[4] that used events for which Cluster data is available in the plasma sheet and boundary layer, we perform a superposed epoch analysis for coronal mass ejection (CME) driven storms and streaming interaction region (SIR) driven storms separately, to investigate the hypothesis that ionospheric O+ is an important contributor for CME-driven storms but not SIR-driven storms[2]. [1]O. J. Brambles et al. (2011), Science 332, 1183.[2]O. J. Brambles et al. (2013), JGR 118, 6026.[3]R. H. Varney et al. (2016), JGR 121, 9688.[4]J. Liao et al. (2014), JGR 119, 1572.[5]E. J. Lund et al. (2017), JGR, submitted.

The formation of solar prominences by thermal instability in a current sheet

International Nuclear Information System (INIS)

Smith, E.A.; Priest, E.R.

1977-01-01

The energy balance equation for the upper chromosphere or lower corona contains a radiative loss term which is destabilizing, because of slight decrease in temperature from the equilibrium value causes more radiation and hence a cooling of the plasma; also a slight increase in temperature has the effect of heating the plasma. In spite of this tendency towards thermal instability, most of the solar atmosphere is remarkably stable, since thermal conduction is very efficient at equalizing any temperature irregularity which may arise. However, the effectiveness of thermal conduction in transporting heat is decreased considerably in a current sheet or a magnetic flux tube, since heat can be conducted quickly only along the magnetic field lines. This paper presents a simple model for the thermal equilibrium and stability of a current sheet. It is found that, when its length exceeds a certain maximum value, no equilibrium is possible and the plasma in the sheet cools. The results may be relevant for the formation of a quiescent prominence. (Auth.)

Combination of platelet-rich plasma within periodontal ligament stem cell sheets enhances cell differentiation and matrix production.

Science.gov (United States)

Xu, Qiu; Li, Bei; Yuan, Lin; Dong, Zhiwei; Zhang, Hao; Wang, Han; Sun, Jin; Ge, Song; Jin, Yan

2017-03-01

The longstanding goal of periodontal therapy is to regenerate periodontal tissues. Although platelet-rich plasma (PRP) has been gaining increasing popularity for use in the orofacial region, whether PRP is useful for periodontal regeneration is still unknown. The purpose of this study was to determine whether a mixture of periodontal ligament stem cell (PDLSC) sheets and PRP promoted bone regeneration, one of the most important measurement indices of periodontal tissue regenerative capability in vitro and in vivo. In this study, we evaluated the effects of different doses of PRP on the differentiation of human PDLSCs. Then cell sheet formation, extracellular matrix deposition and osteogenic gene expression in response to different doses of PRP treatment during sheet grafting was investigated. Furthermore, we implanted PDLSC sheets treated with 1% PRP subcutaneously into immunocompromised mice to evaluate their bone-regenerative capability. The results revealed that 1% PRP significantly enhanced the osteogenic differentiation of PDLSCs. Based on the production of extracellular matrix proteins, the results of scanning electron microscopy and the expression of the osteogenic genes ALP, Runx2, Col-1 and OCN, the provision of 1% PRP for PDLSC sheets was the most effective PRP administration mode for cell sheet formation. The results of in vivo transplantation showed that 1% PRP-mediated PDLSC sheets exhibited better periodontal tissue regenerative capability than those obtained without PRP intervention. These data suggest that a suitable concentration of PRP stimulation may enhance extracellular matrix production and positively affect cell behaviour in PDLSC sheets. Copyright © 2014 John Wiley & Sons, Ltd. Copyright © 2014 John Wiley & Sons, Ltd.

Glacial Cycles and ice-sheet modelling

NARCIS (Netherlands)

Oerlemans, J.

1982-01-01

An attempt is made to simulate the Pleistocene glacial cycles with a numerical model of the Northern Hemisphere ice sheets. This model treats the vertically-integrated ice flow along a meridian, including computation of bedrock adjustment and temperature distribution in the ice. Basal melt water is

Solar wind and substorm excitation of the wavy current sheet

Directory of Open Access Journals (Sweden)

C. Forsyth

2009-06-01

Full Text Available Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the ZGSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −YGSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002. We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005 and Erkaev et al. (2008. We find that the Erkaev et al. (2008 model gives the best fit to the observations.

Groundwater flow modelling under ice sheet conditions. Scoping calculations

International Nuclear Information System (INIS)

Jaquet, O.; Namar, R.; Jansson, P.

2010-10-01

The potential impact of long-term climate changes has to be evaluated with respect to repository performance and safety. In particular, glacial periods of advancing and retreating ice sheet and prolonged permafrost conditions are likely to occur over the repository site. The growth and decay of ice sheets and the associated distribution of permafrost will affect the groundwater flow field and its composition. As large changes may take place, the understanding of groundwater flow patterns in connection to glaciations is an important issue for the geological disposal at long term. During a glacial period, the performance of the repository could be weakened by some of the following conditions and associated processes: - Maximum pressure at repository depth (canister failure). - Maximum permafrost depth (canister failure, buffer function). - Concentration of groundwater oxygen (canister corrosion). - Groundwater salinity (buffer stability). - Glacially induced earthquakes (canister failure). Therefore, the GAP project aims at understanding key hydrogeological issues as well as answering specific questions: - Regional groundwater flow system under ice sheet conditions. - Flow and infiltration conditions at the ice sheet bed. - Penetration depth of glacial meltwater into the bedrock. - Water chemical composition at repository depth in presence of glacial effects. - Role of the taliks, located in front of the ice sheet, likely to act as potential discharge zones of deep groundwater flow. - Influence of permafrost distribution on the groundwater flow system in relation to build-up and thawing periods. - Consequences of glacially induced earthquakes on the groundwater flow system. Some answers will be provided by the field data and investigations; the integration of the information and the dynamic characterisation of the key processes will be obtained using numerical modelling. Since most of the data are not yet available, some scoping calculations are performed using the

Groundwater flow modelling under ice sheet conditions. Scoping calculations

Energy Technology Data Exchange (ETDEWEB)

Jaquet, O.; Namar, R. (In2Earth Modelling Ltd (Switzerland)); Jansson, P. (Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden))

2010-10-15

The potential impact of long-term climate changes has to be evaluated with respect to repository performance and safety. In particular, glacial periods of advancing and retreating ice sheet and prolonged permafrost conditions are likely to occur over the repository site. The growth and decay of ice sheets and the associated distribution of permafrost will affect the groundwater flow field and its composition. As large changes may take place, the understanding of groundwater flow patterns in connection to glaciations is an important issue for the geological disposal at long term. During a glacial period, the performance of the repository could be weakened by some of the following conditions and associated processes: - Maximum pressure at repository depth (canister failure). - Maximum permafrost depth (canister failure, buffer function). - Concentration of groundwater oxygen (canister corrosion). - Groundwater salinity (buffer stability). - Glacially induced earthquakes (canister failure). Therefore, the GAP project aims at understanding key hydrogeological issues as well as answering specific questions: - Regional groundwater flow system under ice sheet conditions. - Flow and infiltration conditions at the ice sheet bed. - Penetration depth of glacial meltwater into the bedrock. - Water chemical composition at repository depth in presence of glacial effects. - Role of the taliks, located in front of the ice sheet, likely to act as potential discharge zones of deep groundwater flow. - Influence of permafrost distribution on the groundwater flow system in relation to build-up and thawing periods. - Consequences of glacially induced earthquakes on the groundwater flow system. Some answers will be provided by the field data and investigations; the integration of the information and the dynamic characterisation of the key processes will be obtained using numerical modelling. Since most of the data are not yet available, some scoping calculations are performed using the

Uncertainty Quantification for Large-Scale Ice Sheet Modeling

Energy Technology Data Exchange (ETDEWEB)

Ghattas, Omar [Univ. of Texas, Austin, TX (United States)

2016-02-05

This report summarizes our work to develop advanced forward and inverse solvers and uncertainty quantification capabilities for a nonlinear 3D full Stokes continental-scale ice sheet flow model. The components include: (1) forward solver: a new state-of-the-art parallel adaptive scalable high-order-accurate mass-conservative Newton-based 3D nonlinear full Stokes ice sheet flow simulator; (2) inverse solver: a new adjoint-based inexact Newton method for solution of deterministic inverse problems governed by the above 3D nonlinear full Stokes ice flow model; and (3) uncertainty quantification: a novel Hessian-based Bayesian method for quantifying uncertainties in the inverse ice sheet flow solution and propagating them forward into predictions of quantities of interest such as ice mass flux to the ocean.

Ice shelf fracture parameterization in an ice sheet model

Directory of Open Access Journals (Sweden)

S. Sun

2017-11-01

Full Text Available Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ∼ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

Science.gov (United States)

Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2011-09-01

We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011).

3-D MHD modeling and stability analysis of jet and spheromak plasmas launched into a magnetized plasma

Science.gov (United States)

Fisher, Dustin; Zhang, Yue; Wallace, Ben; Gilmore, Mark; Manchester, Ward; Arge, C. Nick

2016-10-01

The Plasma Bubble Expansion Experiment (PBEX) at the University of New Mexico uses a coaxial plasma gun to launch jet and spheromak magnetic plasma configurations into the Helicon-Cathode (HelCat) plasma device. Plasma structures launched from the gun drag frozen-in magnetic flux into the background magnetic field of the chamber providing a rich set of dynamics to study magnetic turbulence, force-free magnetic spheromaks, and shocks. Preliminary modeling is presented using the highly-developed 3-D, MHD, BATS-R-US code developed at the University of Michigan. BATS-R-US employs an adaptive mesh refinement grid that enables the capture and resolution of shock structures and current sheets, and is particularly suited to model the parameter regime under investigation. CCD images and magnetic field data from the experiment suggest the stabilization of an m =1 kink mode trailing a plasma jet launched into a background magnetic field. Results from a linear stability code investigating the effect of shear-flow as a cause of this stabilization from magnetic tension forces on the jet will be presented. Initial analyses of a possible magnetic Rayleigh Taylor instability seen at the interface between launched spheromaks and their entraining background magnetic field will also be presented. Work supported by the Army Research Office Award No. W911NF1510480.

Modeling the Alzheimer Abeta17-42 fibril architecture: tight intermolecular sheet-sheet association and intramolecular hydrated cavities.

Science.gov (United States)

Zheng, Jie; Jang, Hyunbum; Ma, Buyong; Tsai, Chung-Jun; Nussinov, Ruth

2007-11-01

We investigate Abeta(17-42) protofibril structures in solution using molecular dynamics simulations. Recently, NMR and computations modeled the Abeta protofibril as a longitudinal stack of U-shaped molecules, creating an in-parallel beta-sheet and loop spine. Here we study the molecular architecture of the fibril formed by spine-spine association. We model in-register intermolecular beta-sheet-beta-sheet associations and study the consequences of Alzheimer's mutations (E22G, E22Q, E22K, and M35A) on the organization. We assess the structural stability and association force of Abeta oligomers with different sheet-sheet interfaces. Double-layered oligomers associating through the C-terminal-C-terminal interface are energetically more favorable than those with the N-terminal-N-terminal interface, although both interfaces exhibit high structural stability. The C-terminal-C-terminal interface is essentially stabilized by hydrophobic and van der Waals (shape complementarity via M35-M35 contacts) intermolecular interactions, whereas the N-terminal-N-terminal interface is stabilized by hydrophobic and electrostatic interactions. Hence, shape complementarity, or the "steric zipper" motif plays an important role in amyloid formation. On the other hand, the intramolecular Abeta beta-strand-loop-beta-strand U-shaped motif creates a hydrophobic cavity with a diameter of 6-7 A, allowing water molecules and ions to conduct through. The hydrated hydrophobic cavities may allow optimization of the sheet association and constitute a typical feature of fibrils, in addition to the tight sheet-sheet association. Thus, we propose that Abeta fiber architecture consists of alternating layers of tight packing and hydrated cavities running along the fibrillar axis, which might be possibly detected by high-resolution imaging.

Large-scale Modeling of the Greenland Ice Sheet on Long Timescales

DEFF Research Database (Denmark)

Solgaard, Anne Munck

is investigated as well as its early history. The studies are performed using an ice-sheet model in combination with relevant forcing from observed and modeled climate. Changes in ice-sheet geometry influences atmospheric flow (and vice versa) hereby changing the forcing patterns. Changes in the overall climate...... and climate model is included shows, however, that a Föhn effect is activated and hereby increasing temperatures inland and inhibiting further ice-sheet expansion into the interior. This indicates that colder than present temperatures are needed in order for the ice sheet to regrow to the current geometry....... Accordingto this hypothesis, two stages of uplift since the Late Miocene lead to the present-day topography. The results of the ice-sheet simulations show geometries in line with geologicobservations through the period, and it is found that the uplift events enhance the effect of the climatic deterioration...

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

Current sheets and pressure anisotropy in the reconnection exhaust

Energy Technology Data Exchange (ETDEWEB)

Le, A.; Karimabadi, H.; Roytershteyn, V. [SciberQuest, Inc., Del Mar, California 92014 (United States); Egedal, J. [University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States); Ng, J. [PPPL, Princeton University, Princeton, New Jersey 08543 (United States); Scudder, J. [University of Iowa, Iowa City, Iowa 52242 (United States); Daughton, W.; Liu, Y.-H. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2014-01-15

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.

Modeling sheet-flow sand transport under progressive surface waves

NARCIS (Netherlands)

Kranenburg, Wouter

2013-01-01

In the near-shore zone, energetic sea waves generate sheet-flow sand transport. In present day coastal models, wave-induced sheet-flow sand transport rates are usually predicted with semi-empirical transport formulas, based on extensive research on this phenomenon in oscillatory flow tunnels.

Multiscale friction modeling for sheet metal forming

NARCIS (Netherlands)

Hol, J.; Cid Alfaro, M.V.; de Rooij, Matthias B.; Meinders, Vincent T.; Felder, Eric; Montmitonnet, Pierre

2010-01-01

The most often used friction model for sheet metal forming simulations is the relative simple Coulomb friction model. This paper presents a more advanced friction model for large scale forming simulations based on the surface change on the micro-scale. The surface texture of a material changes when

Solar wind and substorm excitation of the wavy current sheet

Directory of Open Access Journals (Sweden)

C. Forsyth

2009-06-01

Full Text Available Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the Z_GSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −Y_GSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002. We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005 and Erkaev et al. (2008. We find that the Erkaev et al. (2008 model gives the best fit to the observations.

Surface Energy and Mass Balance Model for Greenland Ice Sheet and Future Projections

Science.gov (United States)

Liu, Xiaojian

The Greenland Ice Sheet contains nearly 3 million cubic kilometers of glacial ice. If the entire ice sheet completely melted, sea level would raise by nearly 7 meters. There is thus considerable interest in monitoring the mass balance of the Greenland Ice Sheet. Each year, the ice sheet gains ice from snowfall and loses ice through iceberg calving and surface melting. In this thesis, we develop, validate and apply a physics based numerical model to estimate current and future surface mass balance of the Greenland Ice Sheet. The numerical model consists of a coupled surface energy balance and englacial model that is simple enough that it can be used for long time scale model runs, but unlike previous empirical parameterizations, has a physical basis. The surface energy balance model predicts ice sheet surface temperature and melt production. The englacial model predicts the evolution of temperature and meltwater within the ice sheet. These two models can be combined with estimates of precipitation (snowfall) to estimate the mass balance over the Greenland Ice Sheet. We first compare model performance with in-situ observations to demonstrate that the model works well. We next evaluate how predictions are degraded when we statistically downscale global climate data. We find that a simple, nearest neighbor interpolation scheme with a lapse rate correction is able to adequately reproduce melt patterns on the Greenland Ice Sheet. These results are comparable to those obtained using empirical Positive Degree Day (PDD) methods. Having validated the model, we next drove the ice sheet model using the suite of atmospheric model runs available through the CMIP5 atmospheric model inter-comparison, which in turn built upon the RCP 8.5 (business as usual) scenarios. From this exercise we predict how much surface melt production will increase in the coming century. This results in 4-10 cm sea level equivalent, depending on the CMIP5 models. Finally, we try to bound melt water

Modeling the Fracture of Ice Sheets on Parallel Computers

Energy Technology Data Exchange (ETDEWEB)

Waisman, Haim [Columbia Univ., New York, NY (United States); Tuminaro, Ray [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2013-10-10

The objective of this project was to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. This objective was achieved by developing novel physics based models for ice, novel numerical tools to enable the modeling of the physics and by collaboration with the ice community experts. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. To this end, our research findings through this project offers significant advancement to the field and closes a large gap of knowledge in understanding and modeling the fracture of ice sheets in the polar regions. Thus, we believe that our objective has been achieved and our research accomplishments are significant. This is corroborated through a set of published papers, posters and presentations at technical conferences in the field. In particular significant progress has been made in the mechanics of ice, fracture of ice sheets and ice shelves in polar regions and sophisticated numerical methods that enable the solution of the physics in an efficient way.

Mechanical characterization and constitutive modeling of Mg alloy sheets

International Nuclear Information System (INIS)

Mekonen, M. Nebebe; Steglich, D.; Bohlen, J.; Letzig, D.; Mosler, J.

2012-01-01

Highlights: ► Material characterization of the Mg alloys AZ31 and ZE10 at elevated temperatures. ► Distortion of the yield locus does not depend on the strain rate. ► Novel constitutive model suitable for the analysis of sheet forming of magnesium. ► Strain-dependent r-values are included within the model. ► The model is thermodynamically consistent and accounts for distortional hardening. - Abstract: In this paper, an experimental mechanical characterization of the magnesium alloys ZE10 and AZ31 is performed and a suitable constitutive model is established. The mechanical characterization is based on uniaxial tensile tests. In order to avoid poor formability at room temperature, the tests were conducted at elevated temperature (200 °C). The uniaxial tensile tests reveal sufficient ductility allowing sheet forming processes at this temperature. The differences in yield stresses and plastic strain ratios (r-values) confirm the anisotropic response of the materials under study. The constitutive model is established so that the characteristic mechanical features observed in magnesium alloys such as anisotropy and compression-tension asymmetry can be accommodated. This model is thermodynamically consistent, incorporates rate effect, is formulated based on finite strain plasticity theory and is applicable in sheet forming simulations of magnesium alloys. More precisely, a model originally proposed by Cazacu and Barlat in 2004 and later modified to account for the evolution of the material anisotropy is rewritten in a thermodynamically consistent framework. The calibrated constitutive model is shown to capture the characteristic mechanical features observed in magnesium alloy sheets.

Magnetospheric Multiscale Mission Observations of Magnetic Flux Ropes in the Earth's Plasma Sheet

Science.gov (United States)

Slavin, J. A.; Akhavan-Tafti, M.; Poh, G.; Le, G.; Russell, C. T.; Nakamura, R.; Baumjohann, W.; Torbert, R. B.; Gershman, D. J.; Pollock, C. J.; Giles, B. L.; Moore, T. E.; Burch, J. L.

2017-12-01

A major discovery by the Cluster mission and the previous generation of science missions is the presence of earthward and tailward moving magnetic flux ropes in the Earth's plasma sheet. However, the lack of high-time resolution plasma measurements severely limited progress concerning the formation and evolution of these reconnection generated structures. We use high-time resolution magnetic and electric field and plasma measurements from the Magnetospheric Multiscale mission's first tail season to investigate: 1) the distribution of flux rope diameters relative to the local ion and electron inertial lengths; 2) the internal force balance sustaining these structures; and 3) the magnetic connectivity of the flux ropes to the Earth and/or the interplanetary medium; 4) the specific entropy of earthward moving flux ropes and the possible effect of "buoyancy" on how deep they penetrate into the inner magnetosphere; and 5) evidence for coalescence of adjacent flux ropes and/or the division of existing flux ropes through the formation of secondary X-lines. The results of these initial analyses will be discussed in terms of their implications for reconnection-driven magnetospheric dynamics and substorms.

An Imminent Revolution in Modeling Interactions of Ice Sheets With Climate

Science.gov (United States)

Hughes, T.

2008-12-01

Modeling continental ice sheets was inaugurated by meteorologists William Budd and Uwe Radok, with mathematician Richard Jenssen, in 1971. Their model calculated the thermal and mechanical regime using measured surface accumulation rates, temperatures, and elevations, and bed topography. This top-down approach delivered a basal thermal regime of temperatures or melting rates for an assumed basal geothermal heat flux. When Philippe Huybrechts and others incorporated time, largely unknownpast surface conditions had a major effect on present basal thermal conditions. This approach produced ice-sheet models with only a slow response to external forcing, whereas the glacial geological record and climate records from ice and ocean cores show that ice sheets can have rapid changes in size and shape independent of external forcing. These top-down models were wholly inadequate for reconstructing former ice sheets at the LGM for CLIMAP in 1981. Ice-sheet areas,elevations, and volumes provided the albedo, surface topography, and sea-surface area as input to climate models. A bottom-up model based on dated glacial geology was developed to provide the areal extent and basal thermal regime of ice sheets at the LGM. Basal thermal conditions determined ice-bed coupling and therefore the elevation of ice sheets. High convex ice surfaces for slow sheet flow lower about 20 percent when a frozen bed becomes thawed. As further basal melting drowns bedrock bumps that "pin" basal ice, the ice surface becomes concave in fast stream flow that ends as low floating ice shelves at marine ice margins. A revolution in modeling interactions between glaciation, climate, and sea level is driven by new Greenland and Antarctic data from Earth-orbiting satellites, airborne and surface traverses, and deep drilling. We anticipate continuous data acquisition of surface albedo, accumulation/ablation rates, elevations, velocities, and temperatures over a whole ice sheet, mapping basal thermal conditions

Estimates on the mean current in a sphere of plasma

International Nuclear Information System (INIS)

Nunez, Manuel

2003-01-01

Several turbulent dynamo models predict the concentration of the magnetic field in chaotic plasmas in sheets with the field vector pointing alternatively in opposite directions, which should produce strong current sheets. It is proved that if the plasma is contained in a rigid sphere with perfectly conducting boundary the geometry of these sheets must be balanced so that the mean current remains essentially bounded by the Coulomb gauged mean vector potential of the field. This magnitude remains regular even for the sharp field variations expected in a chaotic flow. For resistive plasmas the same arguments imply that the contribution to the total current of the regions near the boundary compensates the current of the central part of the sphere

Energized Oxygen : Speiser Current Sheet Bifurcation

Science.gov (United States)

George, D. E.; Jahn, J. M.

2017-12-01

A single population of energized Oxygen (O+) is shown to produce a cross-tail bifurcated current sheet in 2.5D PIC simulations of the magnetotail without the influence of magnetic reconnection. Treatment of oxygen in simulations of space plasmas, specifically a magnetotail current sheet, has been limited to thermal energies despite observations of and mechanisms which explain energized ions. We performed simulations of a homogeneous oxygen background, that has been energized in a physically appropriate manner, to study the behavior of current sheets and magnetic reconnection, specifically their bifurcation. This work uses a 2.5D explicit Particle-In-a-Cell (PIC) code to investigate the dynamics of energized heavy ions as they stream Dawn-to-Dusk in the magnetotail current sheet. We present a simulation study dealing with the response of a current sheet system to energized oxygen ions. We establish a, well known and studied, 2-species GEM Challenge Harris current sheet as a starting point. This system is known to eventually evolve and produce magnetic reconnection upon thinning of the current sheet. We added a uniform distribution of thermal O+ to the background. This 3-species system is also known to eventually evolve and produce magnetic reconnection. We add one additional variable to the system by providing an initial duskward velocity to energize the O+. We also traced individual particle motion within the PIC simulation. Three main results are shown. First, energized dawn- dusk streaming ions are clearly seen to exhibit sustained Speiser motion. Second, a single population of heavy ions clearly produces a stable bifurcated current sheet. Third, magnetic reconnection is not required to produce the bifurcated current sheet. Finally a bifurcated current sheet is compatible with the Harris current sheet model. This work is the first step in a series of investigations aimed at studying the effects of energized heavy ions on magnetic reconnection. This work differs

Ice Sheet Model Intercomparison Project (ISMIP6) contribution to CMIP6

NARCIS (Netherlands)

Nowicki, Sophie M J; Payne, Anthony; Larour, Eric; Seroussi, Helene; Goelzer, Heiko|info:eu-repo/dai/nl/412549123; Lipscomb, William; Gregory, Jonathan; Abe-Ouchi, Ayako; Shepherd, Andrew

2016-01-01

Reducing the uncertainty in the past, present, and future contribution of ice sheets to sea-level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model

Ice Sheet System Model as Educational Entertainment

Science.gov (United States)

Perez, G.

2013-12-01

Understanding the importance of polar ice sheets and their role in the evolution of Sea Level Rise (SLR), as well as Climate Change, is of paramount importance for policy makers as well as the public and schools at large. For example, polar ice sheets and glaciers currently account for 1/3 of the SLR signal, a ratio that will increase in the near to long-term future, which has tremendous societal ramifications. Consequently, it is important to increase awareness about our changing planet. In our increasingly digital society, mobile and web applications are burgeoning venues for such outreach. The Ice Sheet System Model (ISSM) is a software that was developed at the Jet Propulsion Laboratory/CalTech/NASA, in collaboration with University of California Irvine (UCI), with the goal of better understanding the evolution of polar ice sheets. It is a state-of-the-art framework, which relies on higher-end cluster-computing to address some of the aforementioned challenges. In addition, it is a flexible framework that can be deployed on any hardware; in particular, on mobile platforms such as Android or iOS smart phones. Here, we look at how the ISSM development team managed to port their model to these platforms, what the implications are for improving how scientists disseminate their results, and how a broader audience may familiarize themselves with running complex climate models in simplified scenarios which are highly educational and entertaining in content. We also look at the future plans toward a web portal fully integrated with mobile technologies to deliver the best content to the public, and to provide educational plans/lessons that can be used in grades K-12 as well as collegiate under-graduate and graduate programs.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

Science.gov (United States)

Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2011-09-01

We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

The Potsdam Parallel Ice Sheet Model (PISM-PIK – Part 1: Model description

Directory of Open Access Journals (Sweden)

R. Winkelmann

2011-09-01

Full Text Available We present the Potsdam Parallel Ice Sheet Model (PISM-PIK, developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009. Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011 and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP. A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011.

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 M_i / m_e=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

Plasma pressure and anisotropy inferred from the Tsyganenkomagnetic field model

Directory of Open Access Journals (Sweden)

F. Cao

Full Text Available A numerical procedure has been developed to deduce the plasma pressure and anisotropy from the Tsyganenko magnetic field model. The Tsyganenko empirical field model, which is based on vast satellite field data, provides a realistic description of magnetic field configuration in the magnetosphere. When the force balance under the static condition is assumed, the electromagnetic J×B force from the Tsyganenko field model can be used to infer the plasma pressure and anisotropy distributions consistent with the field model. It is found that the J×B force obtained from the Tsyganenko field model is not curl-free. The curl-free part of the J×B force in an empirical field model can be balanced by the gradient of the isotropic pressure, while the nonzero curl of the J×B force can only be associated with the pressure anisotropy. The plasma pressure and anisotropy in the near-Earth plasma sheet are numerically calculated to obtain a static equilibrium consistent with the Tsyganenko field model both in the noon-midnight meridian and in the equatorial plane. The plasma pressure distribution deduced from the Tsyganenko 1989 field model is highly anisotropic and shows this feature early in the substorm growth phase. The pressure anisotropy parameter α_P, defined as α_P=1-P_VertP_⊥, is typically ~0.3 at x ≈ -4.5R_E and gradually decreases to a small negative value with an increasing tailward distance. The pressure anisotropy from the Tsyganenko 1989 model accounts for 50% of the cross-tail current at maximum and only in a highly localized region near xsim-10R_E. In comparison, the plasma pressure anisotropy inferred from the Tsyganenko 1987 model is much smaller. We also find that the boundary

Outreach/education interface for Cryosphere models using the Virtual Ice Sheet Laboratory

Science.gov (United States)

Larour, E. Y.; Halkides, D. J.; Romero, V.; Cheng, D. L.; Perez, G.

2014-12-01

In the past decade, great strides have been made in the development of models capable of projecting the future evolution of glaciers and the polar ice sheets in a changing climate. These models are now capable of replicating some of the trends apparent in satellite observations. However, because this field is just now maturing, very few efforts have been dedicated to adapting these capabilities to education. Technologies that have been used in outreach efforts in Atmospheric and Oceanic sciences still have not been extended to Cryospheric Science. We present a cutting-edge, technologically driven virtual laboratory, geared towards outreach and k-12 education, dedicated to the polar ice sheets on Antarctica and Greenland, and their role as major contributors to sea level rise in coming decades. VISL (Virtual Ice Sheet Laboratory) relies on state-of-the art Web GL rendering of polar ice sheets, Android/iPhone and web portability using Javascript, as well as C++ simulations (back-end) based on the Ice Sheet System Model, the NASA model for simulating the evolution of polar ice sheets. Using VISL, educators and students can have an immersive experience into the world of polar ice sheets, while at the same exercising the capabilities of a state-of-the-art climate model, all of it embedded into an education experience that follows the new STEM standards for education.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

Incorporation of ice sheet models into an Earth system model: Focus on methodology of coupling

Science.gov (United States)

Rybak, Oleg; Volodin, Evgeny; Morozova, Polina; Nevecherja, Artiom

2018-03-01

Elaboration of a modern Earth system model (ESM) requires incorporation of ice sheet dynamics. Coupling of an ice sheet model (ICM) to an AOGCM is complicated by essential differences in spatial and temporal scales of cryospheric, atmospheric and oceanic components. To overcome this difficulty, we apply two different approaches for the incorporation of ice sheets into an ESM. Coupling of the Antarctic ice sheet model (AISM) to the AOGCM is accomplished via using procedures of resampling, interpolation and assigning to the AISM grid points annually averaged meanings of air surface temperature and precipitation fields generated by the AOGCM. Surface melting, which takes place mainly on the margins of the Antarctic peninsula and on ice shelves fringing the continent, is currently ignored. AISM returns anomalies of surface topography back to the AOGCM. To couple the Greenland ice sheet model (GrISM) to the AOGCM, we use a simple buffer energy- and water-balance model (EWBM-G) to account for orographically-driven precipitation and other sub-grid AOGCM-generated quantities. The output of the EWBM-G consists of surface mass balance and air surface temperature to force the GrISM, and freshwater run-off to force thermohaline circulation in the oceanic block of the AOGCM. Because of a rather complex coupling procedure of GrIS compared to AIS, the paper mostly focuses on Greenland.

Constitutive Modeling for Sheet Metal Forming

International Nuclear Information System (INIS)

Barlat, Frederic

2005-01-01

This paper reviews aspects of the plastic behaviour common in sheet metals. Macroscopic and microscopic phenomena occurring during plastic deformation are described succinctly. Constitutive models of plasticity suitable for applications to forming, are discussed in a very broad manner. Approaches to plastic anisotropy are described in a somewhat more detailed manner

The double layers in the plasma sheet boundary layer during magnetic reconnection

Science.gov (United States)

Guo, J.; Yu, B.

2014-11-01

We studied the evolutions of double layers which appear after the magnetic reconnection through two-dimensional electromagnetic particle-in-cell simulation. The simulation results show that the double layers are formed in the plasma sheet boundary layer after magnetic reconnection. At first, the double layers which have unipolar structures are formed. And then the double layers turn into bipolar structures, which will couple with another new weak bipolar structure. Thus a new double layer or tripolar structure comes into being. The double layers found in our work are about several ten Debye lengths, which accords with the observation results. It is suggested that the electron beam formed during the magnetic reconnection is responsible for the production of the double layers.

Deposition Rate and Energy Enhancements of TiN Thin-Film in a Magnetized Sheet Plasma Source

OpenAIRE

Hamdi Muhyuddin D. Barra; Henry J. Ramos

2011-01-01

Titanium nitride (TiN) has been synthesized using the sheet plasma negative ion source (SPNIS). The parameters used for its effective synthesis has been determined from previous experiments and studies. In this study, further enhancement of the deposition rate of TiN synthesis and advancement of the SPNIS operation is presented. This is primarily achieved by the addition of Sm-Co permanent magnets and a modification of the configuration in the TiN deposition process. The ...

Ion flow ripples in the Earth's plasma sheet

Science.gov (United States)

De Spiegeleer, Alexandre; Hamrin, Maria; Pitkänen, Timo; Norqvist, Patrik; Mann, Ingrid

2016-04-01

For a long time, magnetotail flows were considered rather smooth and laminar, and primarily dominated by a simple convection flow pattern. However, in the early 90's, high speed bursty bulk flows (BBFs) were discovered and found to commonly perturb the underlying convection flows. In addition, there are other disturbances complicating the magnetotail flow pattern. Instabilities such as the Kelvin-Helmholz instability and the kink instability can cause different types of magnetic field oscillations, such as field line resonances. It is expected that ions will follow these oscillations if the typical time and length scales are larger than the gyroperiod and gyroradius of the ions. Though low-velocity sloshing and ripple disturbances of the average magnetotail convection flows have been observed, their connection with magnetic field oscillations is not fully understood. Furthermore, when studying BFFs, these "Ion Flow Ripples" (IFRs) are often neglected, dismissed as noise or can even erroneously be identified as BBFs. It is therefore of utter importance to find out and understand the role of IFRs in magnetotail dynamics. In a statistical investigation, we use several years of Cluster plasma sheet data to study the low-speed flows in the magnetotail. We investigate different types of IFRs, study their occurrence, and discuss their possible causes.

Interactive Ice Sheet Flowline Model for High School and College Students

Science.gov (United States)

Stearns, L. A.; Rezvanbehbahani, S.; Shankar, S.

2017-12-01

Teaching about climate and climate change is conceptually challenging. While teaching tools and lesson plans are rapidly evolving to help teachers and students improve their understanding of climate processes, there are very few tools targeting ice sheet and glacier dynamics. We have built an interactive ice sheet model that allows students to explore how Antarctic glaciers respond to different climate perturbations. Interactive models offer advantages that are hard to obtain in traditional classroom settings; users can systematically investigate hypothetical situations, explore the effects of modifying systems, and repeatedly observe how systems interrelate. As a result, this project provides a much-needed bridge between the data and models used by the scientific community and students in high school and college. We target our instructional and assessment activities to three high school and college students with the overall aim of increasing understanding of ice sheet dynamics and the different ways that ice sheets are impacted by climate change, while also improving their fundamental math skills.

The influence of atmospheric grid resolution in a climate model-forced ice sheet simulation

Science.gov (United States)

Lofverstrom, Marcus; Liakka, Johan

2018-04-01

Coupled climate-ice sheet simulations have been growing in popularity in recent years. Experiments of this type are however challenging as ice sheets evolve over multi-millennial timescales, which is beyond the practical integration limit of most Earth system models. A common method to increase model throughput is to trade resolution for computational efficiency (compromise accuracy for speed). Here we analyze how the resolution of an atmospheric general circulation model (AGCM) influences the simulation quality in a stand-alone ice sheet model. Four identical AGCM simulations of the Last Glacial Maximum (LGM) were run at different horizontal resolutions: T85 (1.4°), T42 (2.8°), T31 (3.8°), and T21 (5.6°). These simulations were subsequently used as forcing of an ice sheet model. While the T85 climate forcing reproduces the LGM ice sheets to a high accuracy, the intermediate resolution cases (T42 and T31) fail to build the Eurasian ice sheet. The T21 case fails in both Eurasia and North America. Sensitivity experiments using different surface mass balance parameterizations improve the simulations of the Eurasian ice sheet in the T42 case, but the compromise is a substantial ice buildup in Siberia. The T31 and T21 cases do not improve in the same way in Eurasia, though the latter simulates the continent-wide Laurentide ice sheet in North America. The difficulty to reproduce the LGM ice sheets in the T21 case is in broad agreement with previous studies using low-resolution atmospheric models, and is caused by a substantial deterioration of the model climate between the T31 and T21 resolutions. It is speculated that this deficiency may demonstrate a fundamental problem with using low-resolution atmospheric models in these types of experiments.

Sea-level and solid-Earth deformation feedbacks in ice sheet modelling

Science.gov (United States)

Konrad, Hannes; Sasgen, Ingo; Klemann, Volker; Thoma, Malte; Grosfeld, Klaus; Martinec, Zdeněk

2014-05-01

The interactions of ice sheets with the sea level and the solid Earth are important factors for the stability of the ice shelves and the tributary inland ice (e.g. Thomas and Bentley, 1978; Gomez et al, 2012). First, changes in ice extent and ice thickness induce viscoelastic deformation of the Earth surface and Earth's gravity field. In turn, global and local changes in sea level and bathymetry affect the grounding line and, subsequently, alter the ice dynamic behaviour. Here, we investigate these feedbacks for a synthetic ice sheet configuration as well as for the Antarctic ice sheet using a three-dimensional thermomechanical ice sheet and shelf model, coupled to a viscoelastic solid-Earth and gravitationally self-consistent sea-level model. The respective ice sheet undergoes a forcing from rising sea level, warming ocean, and/or changing surface mass balance. The coupling is realized by exchanging ice thickness, Earth surface deformation and sea level periodically. We apply several sets of viscoelastic Earth parameters to our coupled model, e.g. simulating a low-viscous upper mantle present at the Antarctic Peninsula (Ivins et al., 2011). Special focus of our study lies on the evolution of Earth surface deformation and local sea level changes, as well as on the accompanying grounding line evolution. N. Gomez, D. Pollard, J. X. Mitrovica, P. Huybers, and P. U. Clark 2012. Evolution of a coupled marine ice sheet-sea level model, J. Geophys. Res., 117, F01013, doi:10.1029/2011JF002128. E. R. Ivins, M. M. Watkins, D.-N. Yuan, R. Dietrich, G. Casassa, and A. Rülke 2011. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009, J. Geophys. Res. 116, B02403, doi: 10.1029/2010JB007607 R. H. Thomas and C. R. Bentley 1978. A model for Holocene retreat of the West Antarctic Ice Sheet, Quaternary Research, 10 (2), pages 150-170, doi: 10.1016/0033-5894(78)90098-4.

Current sheet particle acceleration - theory and observations for the geomagnetic tail

International Nuclear Information System (INIS)

Speiser, T.W.

1984-01-01

It has been found that the current sheet in the geomagnetic tail is a source of plasma and energetic particles for the magnetospheric ring current and radiation belts. It is also a seat for instabilities and magnetospheric substorms. Theoretical studies related to the geomagnetic tail are discussed, taking into account Dungey's (1953) original ideas concerning neutral point acceleration, and studies of particle motion in current sheets conducted by many authors. A description of observations concerning the geomagnetic tail is also provided, taking into account plasma sheet populations, and the plasma sheet boundary layer. Some remaining problems are partly related to the location and the behavior of the distant source, the nature of the relative (time-dependent) ionospheric versus solar wind contributions, and the role of the solar wind in the initiation of distant or near-earth neutral lines. 56 references

VESL: The Virtual Earth Sheet Laboratory for Ice Sheet Modeling and Visualization

Science.gov (United States)

Cheng, D. L. C.; Larour, E. Y.; Quinn, J. D.; Halkides, D. J.

2017-12-01

We present the Virtual Earth System Laboratory (VESL), a scientific modeling and visualization tool delivered through an integrated web portal. This allows for the dissemination of data, simulation of physical processes, and promotion of climate literacy. The current iteration leverages NASA's Ice Sheet System Model (ISSM), a state-of-the-art polar ice sheet dynamics model developed at the Jet Propulsion Lab and UC Irvine. We utilize the Emscripten source-to-source compiler to convert the C/C++ ISSM engine core to JavaScript, and bundled pre/post-processing JS scripts to be compatible with the existing ISSM Python/Matlab API. Researchers using VESL will be able to effectively present their work for public dissemination with little-to-no additional post-processing. Moreover, the portal allows for real time visualization and editing of models, cloud based computational simulation, and downloads of relevant data. This allows for faster publication in peer-reviewed journals and adaption of results for educational applications. Through application of this concept to multiple aspects of the Earth System, VESL is able to broaden data applications in the geosciences and beyond. At this stage, we still seek feedback from the greater scientific and public outreach communities regarding the ease of use and feature set of VESL. As we plan its expansion, we aim to achieve more rapid communication and presentation of scientific results.

The Potsdam Parallel Ice Sheet Model (PISM-PIK – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

Directory of Open Access Journals (Sweden)

M. A. Martin

2011-09-01

Full Text Available We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK. The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

VESL: The Virtual Earth Sheet Laboratory for Ice Sheet Modeling and Visualization

Science.gov (United States)

Cheng, D. L. C.; Larour, E. Y.; Quinn, J. D.; Halkides, D. J.

2016-12-01

We introduce the Virtual Earth System Laboratory (VESL), a scientific modeling and visualization tool delivered through an integrated web portal for dissemination of data, simulation of physical processes, and promotion of climate literacy. The current prototype leverages NASA's Ice Sheet System Model (ISSM), a state-of-the-art polar ice sheet dynamics model developed at the Jet Propulsion Lab and UC Irvine. We utilize the Emscripten source-to-source compiler to convert the C/C++ ISSM engine core to JavaScript, and bundled pre/post-processing JS scripts to be compatible with the existing ISSM Python/Matlab API. Researchers using VESL will be able to effectively present their work for public dissemination with little-to-no additional post-processing. This will allow for faster publication in peer-reviewed journals and adaption of results for educational applications. Through future application of this concept to multiple aspects of the Earth System, VESL has the potential to broaden data applications in the geosciences and beyond. At this stage, we seek feedback from the greater scientific and public outreach communities regarding the ease of use and feature set of VESL, as we plan its expansion, and aim to achieve more rapid communication and presentation of scientific results.

Acceleration Modes and Transitions in Pulsed Plasma Accelerators

Science.gov (United States)

Polzin, Kurt A.; Greve, Christine M.

2018-01-01

accelerators was developed by Cheng, et al. The Coaxial High ENerGy (CHENG) thruster operated on the 10-microseconds timescales of pulsed plasma thrusters, but claimed high thrust density, high efficiency and low electrode erosion rates, which are more consistent with the deflagration mode of acceleration. Separate work on gas-fed pulsed plasma thrusters (PPTs) by Ziemer, et al. identified two separate regimes of performance. The regime at higher mass bits (termed Mode I in that work) possessed relatively constant thrust efficiency (ratio of jet kinetic energy to input electrical energy) as a function of mass bit. In the second regime at very low mass bits (termed Mode II), the efficiency increased with decreasing mass bit. Work by Poehlmann et al. and by Sitaraman and Raja sought to understand the performance of the CHENG thruster and the Mode I / Mode II performance in PPTs by modeling the acceleration using the Hugoniot Relation, with the detonation and deflagration modes representing two distinct sets of solutions to the relevant conservation laws. These works studied the proposal that, depending upon the values of the various controllable parameters, the accelerator would operate in either the detonation or deflagration mode. In the present work, we propose a variation on the explanation for the differences in performance between the various pulsed plasma accelerators. Instead of treating the accelerator as if it were only operating in one mode or the other during a pulse, we model the initial stage of the discharge in all cases as an accelerating current sheet (detonation mode). If the current sheet reaches the exit of the accelerator before the discharge is completed, the acceleration mode transitions to the deflagration mode type found in the quasi-steady MPD thrusters. This modeling method is used to demonstrate that standard gas-fed pulsed plasma accelerators, the CHENG thruster, and the quasi-steady MPD accelerator are variations of the same device, with the overall

Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy

Directory of Open Access Journals (Sweden)

L. M. Zelenyi

2004-01-01

Full Text Available Thin current sheets represent important and puzzling sites of magnetic energy storage and subsequent fast release. Such structures are observed in planetary magnetospheres, solar atmosphere and are expected to be widespread in nature. The thin current sheet structure resembles a collapsing MHD solution with a plane singularity. Being potential sites of effective energy accumulation, these structures have received a good deal of attention during the last decade, especially after the launch of the multiprobe CLUSTER mission which is capable of resolving their 3D features. Many theoretical models of thin current sheet dynamics, including the well-known current sheet bifurcation, have been developed recently. A self-consistent 1D analytical model of thin current sheets in which the tension of the magnetic field lines is balanced by the ion inertia rather than by the plasma pressure gradients was developed earlier. The influence of the anisotropic electron population and of the corresponding electrostatic field that acts to restore quasi-neutrality of the plasma is taken into account. It is assumed that the electron motion is fluid-like in the direction perpendicular to the magnetic field and fast enough to support quasi-equilibrium Boltzmann distribution along the field lines. Electrostatic effects lead to an interesting feature of the current density profile inside the current sheet, i.e. a narrow sharp peak of electron current in the very center of the sheet due to fast curvature drift of the particles in this region. The corresponding magnetic field profile becomes much steeper near the neutral plane although the total cross-tail current is in all cases dominated by the ion contribution. The dependence of electrostatic effects on the ion to electron temperature ratio, the curvature of the magnetic field lines, and the average electron magnetic moment is also analyzed. The implications of these effects on the fine structure of thin current sheets

Evolution of three-dimensional relativistic current sheets and development of self-generated turbulence

Science.gov (United States)

Takamoto, M.

2018-05-01

In this paper, the temporal evolution of three-dimensional relativistic current sheets in Poynting-dominated plasma is studied for the first time. Over the past few decades, a lot of efforts have been conducted on studying the evolution of current sheets in two-dimensional space, and concluded that sufficiently long current sheets always evolve into the so-called plasmoid chain, which provides a fast reconnection rate independent of its resistivity. However, it is suspected that plasmoid chain can exist only in the case of two-dimensional approximation, and would show transition to turbulence in three-dimensional space. We performed three-dimensional numerical simulation of relativistic current sheet using resistive relativistic magnetohydrodynamic approximation. The results showed that the three-dimensional current sheets evolve not into plasmoid chain but turbulence. The resulting reconnection rate is 0.004, which is much smaller than that of plasmoid chain. The energy conversion from magnetic field to kinetic energy of turbulence is just 0.01 per cent, which is much smaller than typical non-relativistic cases. Using the energy principle, we also showed that the plasmoid is always unstable for a displacement in the opposite direction to its acceleration, probably interchange-type instability, and this always results in seeds of turbulence behind the plasmoids. Finally, the temperature distribution along the sheet is discussed, and it is found that the sheet is less active than plasmoid chain. Our finding can be applied for many high-energy astrophysical phenomena, and can provide a basic model of the general current sheet in Poynting-dominated plasma.

Motion and shape of snowplough sheets in coaxial accelerators

International Nuclear Information System (INIS)

Tsagas, N.F.; Mair, G.L.R.; Prinn, A.E.

1978-01-01

A long coaxial accelerator is filled with helium at initial gas pressure between 0.2 and 4 Torr. When connected to a large capacitor at < - 10 kV a discharge is started at one end; the central electrode has negative polarity. The velocity of the plasma sheet, the snowplough, and its shape have been derived from streak photographs for terminal currents between about 100 and 300 kA. The motion of the sheet has been analysed by balancing the electromagnetic driving force against the inertia of the mass of the gas swept up by a plane sheet taken to be impenetrable to gas atoms. The calculated positions and average sheet velocities, which involve simplifying assumptions, have been found to be in good agreement with observations at different positions and pressures. Also the shape of the sheet has been derived by allowing for the sheet's curvature in the linear momentum equation while net radial motions causing variations in profile have, at first, been excluded. The calculated shape of the sheet is very nearly that photographically observed. The axial velocity of a sheet element is evaluated under the assumption that the plasma is azimuthally uniform, free of spikes and that the vessel's wall does not affect the shape. (author)

Rapid model building of beta-sheets in electron-density maps.

Science.gov (United States)

Terwilliger, Thomas C

2010-03-01

A method for rapidly building beta-sheets into electron-density maps is presented. beta-Strands are identified as tubes of high density adjacent to and nearly parallel to other tubes of density. The alignment and direction of each strand are identified from the pattern of high density corresponding to carbonyl and C(beta) atoms along the strand averaged over all repeats present in the strand. The beta-strands obtained are then assembled into a single atomic model of the beta-sheet regions. The method was tested on a set of 42 experimental electron-density maps at resolutions ranging from 1.5 to 3.8 A. The beta-sheet regions were nearly completely built in all but two cases, the exceptions being one structure at 2.5 A resolution in which a third of the residues in beta-sheets were built and a structure at 3.8 A in which under 10% were built. The overall average r.m.s.d. of main-chain atoms in the residues built using this method compared with refined models of the structures was 1.5 A.

Plasma cutting or laser cutting. Plasma setsudan ka laser setsudan ka

Energy Technology Data Exchange (ETDEWEB)

Nakamura, A. (Tanaka Engineering Works Ltd., Saitama (Japan))

1991-05-01

Comparisons and discussions were made on the plasma cutting and laser cutting in sheet steel cutting, referring partly to gas cutting. Historically, the cutting has been developed from gas, plasma, and laser in that order, and currently these three methods are used mixedly. Generally, the plasma cutting is superior in cutting speed, but inferior in cut face quality, and it requires measures of dust collection. Due to high accuracy and quality in cut face, the laser cutting has been practically used for quite some time in the thin sheet industry, but medium to thick sheet cutting had a problem of unavailability of high output laser suitable for these ranges. However, the recent technologies have overcome the problem as a result of development at the authors {prime} company of a 2 kW class laser cutter capable of cutting 19 mm thick sheet. The cutter has been proven being particularly excellent in controllability. Choice of whether plasma or laser would depend upon which priority is to be taken, cost or accuracy. 15 figs., 3 tabs.

A Dislocation based Constitutive Model for Warm Forming of Aluminum Sheet

NARCIS (Netherlands)

Kurukuri, S.; Ghosh, M.; van den Boogaard, Antonius H.

2008-01-01

The formability of aluminum sheet can be improved considerably by increasing the temperature. At elevated temperatures, the mechanical response of the material becomes strain rate dependent. To accurately simulate warm forming of aluminum sheet, a material model is required that incorporates the

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.

Design and results of the ice sheet model initialisation initMIP-Greenland: an ISMIP6 intercomparison

Directory of Open Access Journals (Sweden)

H. Goelzer

2018-04-01

Full Text Available Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6, which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6 focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1 the initial present-day state of the ice sheet and (2 the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing and in response to a large perturbation (prescribed surface mass balance anomaly; they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.

Friction and lubrication modelling in sheet metal forming: Influence of lubrication amount, tool roughness and sheet coating on product quality

Science.gov (United States)

Hol, J.; Wiebenga, J. H.; Carleer, B.

2017-09-01

In the stamping of automotive parts, friction and lubrication play a key role in achieving high quality products. In the development process of new automotive parts, it is therefore crucial to accurately account for these effects in sheet metal forming simulations. This paper presents a selection of results considering friction and lubrication modelling in sheet metal forming simulations of a front fender product. For varying lubrication conditions, the front fender can either show wrinkling or fractures. The front fender is modelled using different lubrication amounts, tool roughness’s and sheet coatings to show the strong influence of friction on both part quality and the overall production stability. For this purpose, the TriboForm software is used in combination with the AutoForm software. The results demonstrate that the TriboForm software enables the simulation of friction behaviour for varying lubrication conditions, i.e. resulting in a generally applicable approach for friction characterization under industrial sheet metal forming process conditions.

Thin sheet numerical modelling of continental collision

NARCIS (Netherlands)

Jimenez-Munt, I.; Garcia-Gastellanos, D.; Fernandez, M.

2005-01-01

We study the effects of incorporating surface mass transport and the gravitational potential energy of both crust and lithospheric mantle to the viscous thin sheet approach. Recent 2D (cross-section) numerical models show that surface erosion and sediment transport can play a major role in shaping

Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial

Directory of Open Access Journals (Sweden)

A. Robinson

2011-04-01

Full Text Available Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate-ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. The sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i the diagnosed present-day surface mass balance partition between surface melting and ice discharge at the margin, (ii the modeled present-day elevation at GRIP; and (iii the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 360 simulations with 90 different model realizations were filtered down to 46 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations resulted in a range of Eemian ice loss of 0.4–4.4 m sea level equivalent, with a more likely range of about 3.7–4.4 m sea level if the GRIP δ¹⁸O isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures.

Three-fluid magnetohydrodynamical simulation of plasma focus discharges

International Nuclear Information System (INIS)

Behler, K.; Bruhns, H.

1987-01-01

A two-dimensional, three-fluid code based on the two-fluid Potter code [Methods in Computational Physics (Academic, New York, 1970), Vol. 9, p. 340] was developed for simulating the plasma focus discharge. With this code it is possible to treat the neutral gas in addition to the plasma components and to model the ionization and recombination phenomena. Thus the sheet dynamics in a plasma focus can be studied and effects investigated such as the occurrence of residual gas (or plasma) density behind the current sheet in the run-down phase. This is a prerequisite to the occurrence of leak currents, which are one of the causes limiting the performance of large plasma focus devices. It is shown that fast operating foci with small dimensions behave favorably compared with the ''classical'' Mather focus [Methods of Experimental Physics (Academic, New York, 1971), Vol. 9B, p. 187] with long coaxial electrodes

Particle modeling of plasmas computational plasma physics

International Nuclear Information System (INIS)

Dawson, J.M.

1991-01-01

Recently, through the development of supercomputers, a powerful new method for exploring plasmas has emerged; it is computer modeling of plasmas. Such modeling can duplicate many of the complex processes that go on in a plasma and allow scientists to understand what the important processes are. It helps scientists gain an intuition about this complex state of matter. It allows scientists and engineers to explore new ideas on how to use plasma before building costly experiments; it allows them to determine if they are on the right track. It can duplicate the operation of devices and thus reduce the need to build complex and expensive devices for research and development. This is an exciting new endeavor that is in its infancy, but which can play an important role in the scientific and technological competitiveness of the US. There are a wide range of plasma models that are in use. There are particle models, fluid models, hybrid particle fluid models. These can come in many forms, such as explicit models, implicit models, reduced dimensional models, electrostatic models, magnetostatic models, electromagnetic models, and almost an endless variety of other models. Here the author will only discuss particle models. He will give a few examples of the use of such models; these will be taken from work done by the Plasma Modeling Group at UCLA because he is most familiar with work. However, it only gives a small view of the wide range of work being done around the US, or for that matter around the world

Improving Climate Literacy Using The Ice Sheet System Model (ISSM): A Prototype Virtual Ice Sheet Laboratory For Use In K-12 Classrooms

Science.gov (United States)

Halkides, D. J.; Larour, E. Y.; Perez, G.; Petrie, K.; Nguyen, L.

2013-12-01

Statistics indicate that most Americans learn what they will know about science within the confines of our public K-12 education system and the media. Next Generation Science Standards (NGSS) aim to remedy science illiteracy and provide guidelines to exceed the Common Core State Standards that most U.S. state governments have adopted, by integrating disciplinary cores with crosscutting ideas and real life practices. In this vein, we present a prototype ';Virtual Ice Sheet Laboratory' (I-Lab), geared to K-12 students, educators and interested members of the general public. I-Lab will allow users to perform experiments using a state-of-the-art dynamical ice sheet model and provide detailed downloadable lesson plans, which incorporate this model and are consistent with NGSS Physical Science criteria for different grade bands (K-2, 3-5, 6-8, and 9-12). The ultimate goal of this website is to improve public climate science literacy, especially in regards to the crucial role of the polar ice sheets in Earth's climate and sea level. The model used will be the Ice Sheet System Model (ISSM), an ice flow model developed at NASA's Jet Propulsion Laboratory and UC Irvine, that simulates the near-term evolution of polar ice sheets (Greenland and Antarctica) and includes high spatial resolution capabilities and data assimilation to produce realistic simulations of ice sheet dynamics at the continental scale. Open sourced since 2011, ISSM is used in cutting edge cryosphere research around the globe. Thru I-Lab, students will be able to access ISSM using a simple, online graphical interface that can be launched from a web browser on a computer, tablet or smart phone. The interface will allow users to select different climate conditions and watch how the polar ice sheets evolve in time under those conditions. Lesson contents will include links to background material and activities that teach observation recording, concept articulation, hypothesis formulation and testing, and

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

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

Modelling large-scale ice-sheet-climate interactions at the last glacial inception

Science.gov (United States)

Browne, O. J. H.; Gregory, J. M.; Payne, A. J.; Ridley, J. K.; Rutt, I. C.

2010-05-01

In order to investigate the interactions between coevolving climate and ice-sheets on multimillenial timescales, a low-resolution atmosphere-ocean general circulation model (AOGCM) has been coupled to a three-dimensional thermomechanical ice-sheet model. We use the FAMOUS AOGCM, which is almost identical in formulation to the widely used HadCM3 AOGCM, but on account of its lower resolution (7.5° longitude × 5° latitude in the atmosphere, 3.75°× 2.5° in the ocean) it runs about ten times faster. We use the community ice-sheet model Glimmer at 20 km resolution, with the shallow ice approximation and an annual degree-day scheme for surface mass balance. With the FAMOUS-Glimmer coupled model, we have simulated the growth of the Laurentide and Fennoscandian ice sheets at the last glacial inception, under constant orbital forcing and atmospheric composition for 116 ka BP. Ice grows in both regions, totalling 5.8 m of sea-level equivalent in 10 ka, slower than proxy records suggest. Positive climate feedbacks reinforce this growth at local scales (order hundreds of kilometres), where changes are an order of magnitude larger than on the global average. The albedo feedback (higher local albedo means a cooler climate) is important in the initial expansion of the ice-sheet area. The topography feedback (higher surface means a cooler climate) affects ice-sheet thickness and is not noticeable for the first 1 ka. These two feedbacks reinforce each other. Without them, the ice volume is ~90% less after 10 ka. In Laurentia, ice expands initially on the Canadian Arctic islands. The glaciation of the islands eventually cools the nearby mainland climate sufficiently to produce a positive mass balance there. Adjacent to the ice-sheets, cloud feedbacks tend to reduce the surface mass balance and restrain ice growth; this is an example of a local feedback whose simulation requires a model that includes detailed atmospheric physics.

Thermal modeling of the forced convection Sandwich Greenhouse drying system for rubber sheets

International Nuclear Information System (INIS)

Tanwanichkul, B.; Thepa, S.; Rordprapat, W.

2013-01-01

Highlights: • Sandwich Greenhouse is designed for better quality and efficiency of rubber sheet drying. • Thermal models are developed to predict the convection heat transfer coefficient. • The models are validated and show good agreement with the actual experimental data. • The proposed greenhouse can maintain 40–60 °C, suitable for rubber sheet drying. • This greenhouse can bring down the moisture content to 2.8% in fewer than 2 days. - Abstract: In this paper, a novel “Sandwich Greenhouse” for rubber sheet drying is proposed. Using solar energy as the only heat source instead of traditional smoke house that requires firewood, it eliminates shortcomings such as skilled labor monitoring requirement, possible fire hazard, and darken-color rubber sheets due to soot particle contamination. Our greenhouse is specially designed to retain solar energy within, while minimizing the heat loss to the outside environment. The mathematical models are developed to predict the convection mass transfer coefficient and to study the thermal behavior during the drying of rubber sheets under our proposed greenhouse design. Validated with experimental observations, the models show good agreement with the actual experimental data. The experiment demonstrates an effectiveness of our proposed Sandwich Greenhouse, as the temperature of the rubber sheet is 15 °C and 5 °C higher than the ambient temperature during the daytime and nighttime, respectively. As a result, the moisture content of the rubber sheets can decrease from 36.4% to 2.8% in fewer than 2 days

Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

Science.gov (United States)

Greenwood, Sarah L.; Clark, Chris D.

2009-12-01

The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid

Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

Directory of Open Access Journals (Sweden)

F. Pattyn

2012-05-01

Full Text Available Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing. Unique steady state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including fixed grid models that generally perform poorly at coarse resolution. Fixed grid models, with nested grid representations of the grounding line, are able to generate accurate steady state positions, but can be inaccurate over transients. Only one full-Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full-Stokes models remains to be determined in detail, especially during transients.

Simulation of the last glacial cycle with a coupled climate ice-sheet model of intermediate complexity

Directory of Open Access Journals (Sweden)

A. Ganopolski

2010-04-01

Full Text Available A new version of the Earth system model of intermediate complexity, CLIMBER-2, which includes the three-dimensional polythermal ice-sheet model SICOPOLIS, is used to simulate the last glacial cycle forced by variations of the Earth's orbital parameters and atmospheric concentration of major greenhouse gases. The climate and ice-sheet components of the model are coupled bi-directionally through a physically-based surface energy and mass balance interface. The model accounts for the time-dependent effect of aeolian dust on planetary and snow albedo. The model successfully simulates the temporal and spatial dynamics of the major Northern Hemisphere (NH ice sheets, including rapid glacial inception and strong asymmetry between the ice-sheet growth phase and glacial termination. Spatial extent and elevation of the ice sheets during the last glacial maximum agree reasonably well with palaeoclimate reconstructions. A suite of sensitivity experiments demonstrates that simulated ice-sheet evolution during the last glacial cycle is very sensitive to some parameters of the surface energy and mass-balance interface and dust module. The possibility of a considerable acceleration of the climate ice-sheet model is discussed.

One-Dimensional Vlasov-Maxwell Equilibrium for the Force-Free Harris Sheet

International Nuclear Information System (INIS)

Harrison, Michael G.; Neukirch, Thomas

2009-01-01

In this Letter, the first nonlinear force-free Vlasov-Maxwell equilibrium is presented. One component of the equilibrium magnetic field has the same spatial structure as the Harris sheet, but whereas the Harris sheet is kept in force balance by pressure gradients, in the force-free solution presented here force balance is maintained by magnetic shear. Magnetic pressure, plasma pressure and plasma density are constant. The method used to find the equilibrium is based on the analogy of the one-dimensional Vlasov-Maxwell equilibrium problem to the motion of a pseudoparticle in a two-dimensional conservative potential. The force-free solution can be generalized to a complete family of equilibria that describe the transition between the purely pressure-balanced Harris sheet to the force-free Harris sheet

Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison

Science.gov (United States)

Goelzer, Heiko; Nowicki, Sophie; Edwards, Tamsin; Beckley, Matthew; Abe-Ouchi, Ayako; Aschwanden, Andy; Calov, Reinhard; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Golledge, Nicholas R.; Gregory, Jonathan; Greve, Ralf; Humbert, Angelika; Huybrechts, Philippe; Kennedy, Joseph H.; Larour, Eric; Lipscomb, William H.; Le clec'h, Sébastien; Lee, Victoria; Morlighem, Mathieu; Pattyn, Frank; Payne, Antony J.; Rodehacke, Christian; Rückamp, Martin; Saito, Fuyuki; Schlegel, Nicole; Seroussi, Helene; Shepherd, Andrew; Sun, Sainan; van de Wal, Roderik; Ziemen, Florian A.

2018-04-01

Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.

Multi Scale Models for Flexure Deformation in Sheet Metal Forming

Directory of Open Access Journals (Sweden)

Di Pasquale Edmondo

2016-01-01

Full Text Available This paper presents the application of multi scale techniques to the simulation of sheet metal forming using the one-step method. When a blank flows over the die radius, it undergoes a complex cycle of bending and unbending. First, we describe an original model for the prediction of residual plastic deformation and stresses in the blank section. This model, working on a scale about one hundred times smaller than the element size, has been implemented in SIMEX, one-step sheet metal forming simulation code. The utilisation of this multi-scale modeling technique improves greatly the accuracy of the solution. Finally, we discuss the implications of this analysis on the prediction of springback in metal forming.

Capabilities and performance of Elmer/Ice, a new-generation ice sheet model

Directory of Open Access Journals (Sweden)

O. Gagliardini

2013-08-01

Full Text Available The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

Model of detached plasmas

International Nuclear Information System (INIS)

Yoshikawa, S.; Chance, M.

1986-07-01

Recently a tokamak plasma was observed in TFTR that was not limited by a limiter or a divertor. A model is proposed to explain this equilibrium, which is called a detached plasma. The model consists of (1) the core plasma where ohmic heating power is lost by anomalous heat conduction and (2) the shell plasma where the heat from the core plasma is radiated away by the atomic processes of impurity ions. A simple scaling law is proposed to test the validity of this model

Modeling plasma behavior in a plasma electrode Pockels cell

International Nuclear Information System (INIS)

Boley, C.D.; Rhodes, M.A.

1999-01-01

The authors present three interrelated models of plasma behavior in a plasma electrode Pockels cell (PEPC). In a PEPC, plasma discharges are formed on both sides of a thin, large-aperture electro-optic crystal (typically KDP). The plasmas act as optically transparent, highly conductive electrodes, allowing uniform application of a longitudinal field to induce birefringence in the crystal. First, they model the plasma in the thin direction, perpendicular to the crystal, via a one-dimensional fluid model. This yields the electron temperature and the density and velocity profiles in this direction as functions of the neutral pressure, the plasma channel width, and the discharge current density. Next, they model the temporal response of the crystal to the charging process, combining a circuit model with a model of the sheath which forms near the crystal boundary. This model gives the time-dependent voltage drop across the sheath as a function of electron density at the sheath entrance. Finally, they develop a two-dimensional MHD model of the planar plasma, in order to calculate the response of the plasma to magnetic fields. They show how the plasma uniformity is affected by the design of the current return, by the longitudinal field from the cathode magnetron, and by fields from other sources. This model also gives the plasma sensitivity to the boundary potential at which the top and bottom of the discharge are held. They validate these models by showing how they explain observations in three large Pockels cells built at Lawrence Livermore National Laboratory

Translating hydrologically-relevant variables from the ice sheet model SICOPOLIS to the Greenland Analog Project hydrologic modeling domain

Science.gov (United States)

Vallot, Dorothée; Applegate, Patrick; Pettersson, Rickard

2013-04-01

Projecting future climate and ice sheet development requires sophisticated models and extensive field observations. Given the present state of our knowledge, it is very difficult to say what will happen with certainty. Despite the ongoing increase in atmospheric greenhouse gas concentrations, the possibility that a new ice sheet might form over Scandinavia in the far distant future cannot be excluded. The growth of a new Scandinavian Ice Sheet would have important consequences for buried nuclear waste repositories. The Greenland Analogue Project, initiated by the Swedish Nuclear Fuel and Waste Management Company (SKB), is working to assess the effects of a possible future ice sheet on groundwater flow by studying a constrained domain in Western Greenland by field measurements (including deep bedrock drilling in front of the ice sheet) combined with numerical modeling. To address the needs of the GAP project, we interpolated results from an ensemble of ice sheet model runs to the smaller and more finely resolved modeling domain used in the GAP project's hydrologic modeling. Three runs have been chosen with three fairly different positive degree-day factors among those that reproduced the modern ice margin at the borehole position. The interpolated results describe changes in hydrologically-relevant variables over two time periods, 115 ka to 80 ka, and 20 ka to 1 ka. In the first of these time periods, the ice margin advances over the model domain; in the second time period, the ice margin retreats over the model domain. The spatially-and temporally dependent variables that we treated include the ice thickness, basal melting rate, surface mass balance, basal temperature, basal thermal regime (frozen or thawed), surface temperature, and basal water pressure. The melt flux is also calculated.

Formability models for warm sheet metal forming analysis

Science.gov (United States)

Jiang, Sen

Several closed form models for the prediction of strain space sheet metal formability as a function of temperature and strain rate are proposed. The proposed models require only failure strain information from the uniaxial tension test at an elevated temperature setting and failure strain information from the traditionally defined strain space forming limit diagram at room temperature, thereby featuring the advantage of offering a full forming limit description without having to carry out expensive experimental studies for multiple modes of deformation under the elevated temperature. The Power law, Voce, and Johnson-Cook hardening models are considered along with the yield criterions of Hill's 48 and Logan-Hosford yield criteria. Acceptable correlations between the theory and experiment are reported for all the models under a plane strain condition. Among all the proposed models, the model featuring Johnson-Cook hardening model and Logan-Hosford yield behavior (LHJC model) was shown to best correlate with experiment. The sensitivity of the model with respect to various forming parameters is discussed. This work is significant to those aiming to incorporate closed-form formability models directly into numerical simulation programs for the purpose of design and analysis of products manufactured through the warm sheet metal forming process. An improvement based upon Swift's diffuse necking theory, is suggested in order to enhance the reliability of the model for biaxial stretch conditions. Theory relating to this improvement is provided in Appendix B.

A material model for aluminium sheet forming at elevated temperatures

NARCIS (Netherlands)

van den Boogaard, Antonius H.; Werkhoven, R.J.; Bolt, P.J.

2001-01-01

In order to accurately simulate the deep drawing or stretching of aluminum sheet at elevated temperatures, a model is required that incorporates the temperature and strain-rate dependency of the material. In this paper two models are compared: a phenomenological material model in which the

Heliospheric current sheet and effects of its interaction with solar cosmic rays

Energy Technology Data Exchange (ETDEWEB)

Malova, H. V., E-mail: hmalova@yandex.ru [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation); Popov, V. Yu.; Grigorenko, E. E.; Dunko, A. V.; Petrukovich, A. A. [Russian Academy of Sciences, Space Research Institute (Russian Federation)

2016-08-15

The effects of interaction of solar cosmic rays (SCRs) with the heliospheric current sheet (HCS) in the solar wind are analyzed. A self-consistent kinetic model of the HCS is developed in which ions with quasiadiabatic dynamics can present. The HCS is considered an equilibrium embedded current structure in which two main plasma species with different temperatures (the low-energy background plasma of the solar wind and the higher energy SCR component) contribute to the current. The obtained results are verified by comparing with the results of numerical simulations based on solving equations of motion by the particle tracing method in the given HCS magnetic field with allowance for SCR particles. It is shown that the HCS is a relatively thin multiscale current configuration embedded in a thicker plasma layer. In this case, as a rule, the shear (tangential to the sheet current) component of the magnetic field is present in the HCS. Taking into account high-energy SCR particles in the HCS can lead to a change of its configuration and the formation of a multiscale embedded structure. Parametric family of solutions is considered in which the current balance in the HCS is provided at different SCR temperatures and different densities of the high-energy plasma. The SCR densities are determined at which an appreciable (detectable by satellites) HCS thickening can occur. Possible applications of this modeling to explain experimental observations are discussed.

Controllable preparation of vertically standing graphene sheets and their wettability and supercapacitive properties

International Nuclear Information System (INIS)

Zhou Hai-Tao; Zou Fei; Gao Ge; Yu Ning; Yao Zhao-Hui; Shen Cheng-Min

2016-01-01

Vertically standing graphene (VSG) sheets have been fabricated by using plasma enhanced chemical vapor deposition (PECVD) method. The lateral size of VSG nanosheets could be well controlled by varying the substrate temperature. The higher temperature usually gives rise to a smaller sheet size. The wettability of VSG films was tuned between hydrophobicity and hydrophilicity by means of oxygen and hydrogen plasma treatment. The supercapacitor electrode made of VSG sheets exhibited an ideal double-layer-capacitor feature and the specific capacitance reached a value up to 9.62 F·m −2 . (rapid communication)

Several features of the earthward and tailward streaming of energetic protons (0.29--0.5 MeV) in the earth's plasma sheet

International Nuclear Information System (INIS)

Lui, A.T.Y.; Krimigis, S.M.

1981-01-01

The characteristics of earthward and tailward streaming of energetic protons (0.29--0.50 MeV) in the magnetotial at downstream distances of 20 to 40 R/sub E/ are examined with approx.5.5-min averaged data from the APL/JHU Charged Particle Measurements Experiment on board the IMP 7 and IMP 8 spacecraft. On the basis of observations from September 1972 to May 1978 it is found that the occurrence frequency of energetic magnetospheric protons streaming either tailward or earthward with a front-to-back flux ratio of >2 is at least 23%. Tailward streaming is found to be prevalent in the postmidnight plasma sheet, while earthward streaming is more frequent in the premidnight sector. The particle spectrum is progressively harder from the dawn flank to the dusk flank of the plasma sheet and is generally harder for tailward streaming than for earthward streaming. It is suggested that the dawn-dusk reversal in the dominant streaming direction results from an underlying circulation pattern of energetic protons in the magnetotail, tailward in the postmidnight region and earthward in the premidnight region

An object-oriented, coprocessor-accelerated model for ice sheet simulations

Science.gov (United States)

Seddik, H.; Greve, R.

2013-12-01

Recently, numerous models capable of modeling the thermo-dynamics of ice sheets have been developed within the ice sheet modeling community. Their capabilities have been characterized by a wide range of features with different numerical methods (finite difference or finite element), different implementations of the ice flow mechanics (shallow-ice, higher-order, full Stokes) and different treatments for the basal and coastal areas (basal hydrology, basal sliding, ice shelves). Shallow-ice models (SICOPOLIS, IcIES, PISM, etc) have been widely used for modeling whole ice sheets (Greenland and Antarctica) due to the relatively low computational cost of the shallow-ice approximation but higher order (ISSM, AIF) and full Stokes (Elmer/Ice) models have been recently used to model the Greenland ice sheet. The advance in processor speed and the decrease in cost for accessing large amount of memory and storage have undoubtedly been the driving force in the commoditization of models with higher capabilities, and the popularity of Elmer/Ice (http://elmerice.elmerfem.com) with an active user base is a notable representation of this trend. Elmer/Ice is a full Stokes model built on top of the multi-physics package Elmer (http://www.csc.fi/english/pages/elmer) which provides the full machinery for the complex finite element procedure and is fully parallel (mesh partitioning with OpenMPI communication). Elmer is mainly written in Fortran 90 and targets essentially traditional processors as the code base was not initially written to run on modern coprocessors (yet adding support for the recently introduced x86 based coprocessors is possible). Furthermore, a truly modular and object-oriented implementation is required for quick adaptation to fast evolving capabilities in hardware (Fortran 2003 provides an object-oriented programming model while not being clean and requiring a tricky refactoring of Elmer code). In this work, the object-oriented, coprocessor-accelerated finite element

An energy balance model for the Greenland ice sheet

NARCIS (Netherlands)

Wal, R.S.W. van de; Oerlemans, J.

1994-01-01

The sensitivity of the mass balance of the Greenland Ice Sheet is studied by means of an energy balance model. The model calculates the shortwave and longwave radiation and the turbulent fluxes on a grid with a grid point spacing of 20 km. Special attention is given to the parameterization of the

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

The modelled liquid water balance of the Greenland Ice Sheet

Science.gov (United States)

Steger, Christian R.; Reijmer, Carleen H.; van den Broeke, Michiel R.

2017-11-01

Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with the SNOWPACK model for the GrIS and over the period 1960-2014 with a special focus on the LWB and refreezing. Evaluations of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model-observation agreement. Results of the LWB analysis reveal a spatially uniform increase in surface melt (0.16 m w.e. a-1) during 1990-2014. As a response, refreezing and run-off also indicate positive changes during this period (0.05 and 0.11 m w.e. a-1, respectively), where refreezing increases at only half the rate of run-off, implying that the majority of the additional liquid input runs off the ice sheet. This pattern of refreeze and run-off is spatially variable. For instance, in the south-eastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. Modelled increase in refreezing leads to a decrease in firn air content and to a substantial increase in near-surface firn temperature. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases are more gradual and are associated with the migration of firn aquifers to higher elevations.

BRITICE-CHRONO: Constraining rates and style of marine-influenced ice sheet decay to provide a data-rich playground for ice sheet modellers

Science.gov (United States)

Clark, Chris

2014-05-01

Uncertainty exists regarding the fate of the Antarctic and Greenland ice sheets and how they will respond to forcings from sea level and atmospheric and ocean temperatures. If we want to know more about the mechanisms and rate of change of shrinking ice sheets, then why not examine an ice sheet that has fully disappeared and track its retreat through time? If achieved in enough detail such information could become a data-rich playground for improving the next breed of numerical ice sheet models to be used in ice and sea level forecasting. We regard that the last British-Irish Ice Sheet is a good target for this work, on account of its small size, density of information and with its numerous researchers already investigating it. BRITICE-CHRONO is a large (>45 researchers) NERC-funded consortium project comprising Quaternary scientists and glaciologists who will search the seafloor around Britain and Ireland and parts of the landmass in order to find and extract samples of sand, rock and organic matter that can be dated (OSL; Cosmogenic; 14C) to reveal the timing and rate of change of the collapsing British-Irish Ice Sheet. The purpose is to produce a high resolution dataset on the demise on an ice sheet - from the continental shelf edge and across the marine to terrestrial transition. Some 800 new date assessments will be added to those that already exist. This poster reports on the hypotheses that underpin the work. Data on retreat will be collected by focusing on 8 transects running from the continental shelf edge to a short distance (10s km) onshore and acquiring marine and terrestrial samples for geochronometric dating. The project includes funding for 587 radiocarbon, 140 OSL and 158 TCN samples for surface exposure dating; with sampling accomplished by two research cruises and 16 fieldwork campaigns. Results will reveal the timing and rate of change of ice margin recession for each transect, and combined with existing landform and dating databases, will be

Modeling Antarctic Ice Sheet retreat in warm climates: a historical perspective.

Science.gov (United States)

Pollard, D.; Deconto, R. M.; Gasson, E.

2016-12-01

Early modeling of Antarctic Ice Sheet size vs. climate focused on asymmetry between retreat and growth, with much greater warming needed to cause retreat from full ice cover, due to Height Mass Balance Feedback and albedo feedback. This led to a long-standing model-data conflict, with models needing 1000 to2000 ppmv atmospheric CO2 to produce retreat from full size, vs. proxy data of large ice fluctuations despite much lower CO2 since the Miocene.Subsequent modeling with marine ice physics found that the West Antarctic Ice Sheet could undergo repeated warm-period collapses with realistic past forcing. However, that yields only 3 to 7 m equivalent sea-level rise above modern, compared to 10 to 20 m or more suggested by some geologic data. Large subglacial basins in East Antarctica could be vulnerable to the same processes,but did not retreat in most models due to narrower and shallower sills.After recent modifications, some ice sheet models were able to produce warm-period collapse of major East Antarctic basins, with sea-level rise of up to 15 m. The modifications are (i) hydrofracturing by surface melt, and structural failure of ice cliffs, or (ii) numerical treatment at the grounding line. In these models, large retreat occurs both for past warmintervals, and also for future business-as-usual scenarios.Some interpretations of data in the late Oligocene and Miocene suggest yet larger fluctuations, between 50 to 100% of modern Antarctic size. That would require surface-melt driven retreat of some terrestrial East Antarctic ice, despite the hysteresis issue raised above. A recent study using a coupled climate-ice sheet model found that with a finer climate gridand more frequent coupling exchange, substantial retreat of terrestrial Antarctica can occur with 500 to 840 ppmv CO2, much lower than in earlier models. This will allow meaningful interactions between modeling and deeper-time geologic interpretations since the late Oligocene.

Process control for sheet-metal stamping process modeling, controller design and shop-floor implementation

CERN Document Server

Lim, Yongseob; Ulsoy, A Galip

2014-01-01

Process Control for Sheet-Metal Stamping presents a comprehensive and structured approach to the design and implementation of controllers for the sheet metal stamping process. The use of process control for sheet-metal stamping greatly reduces defects in deep-drawn parts and can also yield large material savings from reduced scrap. Sheet-metal forming is a complex process and most often characterized by partial differential equations that are numerically solved using finite-element techniques. In this book, twenty years of academic research are reviewed and the resulting technology transitioned to the industrial environment. The sheet-metal stamping process is modeled in a manner suitable for multiple-input multiple-output control system design, with commercially available sensors and actuators. These models are then used to design adaptive controllers and real-time controller implementation is discussed. Finally, experimental results from actual shopfloor deployment are presented along with ideas for further...

The Cryosphere Model Comparison Tool (CmCt): Ice Sheet Model Validation and Comparison Tool for Greenland and Antarctica

Science.gov (United States)

Simon, E.; Nowicki, S.; Neumann, T.; Tyahla, L.; Saba, J. L.; Guerber, J. R.; Bonin, J. A.; DiMarzio, J. P.

2017-12-01

The Cryosphere model Comparison tool (CmCt) is a web based ice sheet model validation tool that is being developed by NASA to facilitate direct comparison between observational data and various ice sheet models. The CmCt allows the user to take advantage of several decades worth of observations from Greenland and Antarctica. Currently, the CmCt can be used to compare ice sheet models provided by the user with remotely sensed satellite data from ICESat (Ice, Cloud, and land Elevation Satellite) laser altimetry, GRACE (Gravity Recovery and Climate Experiment) satellite, and radar altimetry (ERS-1, ERS-2, and Envisat). One or more models can be uploaded through the CmCt website and compared with observational data, or compared to each other or other models. The CmCt calculates statistics on the differences between the model and observations, and other quantitative and qualitative metrics, which can be used to evaluate the different model simulations against the observations. The qualitative metrics consist of a range of visual outputs and the quantitative metrics consist of several whole-ice-sheet scalar values that can be used to assign an overall score to a particular simulation. The comparison results from CmCt are useful in quantifying improvements within a specific model (or within a class of models) as a result of differences in model dynamics (e.g., shallow vs. higher-order dynamics approximations), model physics (e.g., representations of ice sheet rheological or basal processes), or model resolution (mesh resolution and/or changes in the spatial resolution of input datasets). The framework and metrics could also be used for use as a model-to-model intercomparison tool, simply by swapping outputs from another model as the observational datasets. Future versions of the tool will include comparisons with other datasets that are of interest to the modeling community, such as ice velocity, ice thickness, and surface mass balance.

Prototypical model for tensional wrinkling in thin sheets

KAUST Repository

Davidovitch, B.; Schroll, R. D.; Vella, D.; Adda-Bedia, M.; Cerda, E. A.

2011-01-01

The buckling and wrinkling of thin films has recently seen a surge of interest among physicists, biologists, mathematicians, and engineers. This activity has been triggered by the growing interest in developing technologies at ever-decreasing scales and the resulting necessity to control the mechanics of tiny structures, as well as by the realization that morphogenetic processes, such as the tissue-shaping instabilities occurring in animal epithelia or plant leaves, often emerge from mechanical instabilities of cell sheets. Although the most basic buckling instability of uniaxially compressed plates was understood by Euler more than two centuries ago, recent experiments on nanometrically thin (ultrathin) films have shown significant deviations from predictions of standard buckling theory. Motivated by this puzzle, we introduce here a theoretical model that allows for a systematic analysis of wrinkling in sheets far from their instability threshold. We focus on the simplest extension of Euler buckling that exhibits wrinkles of finite length--a sheet under axisymmetric tensile loads. The first study of this geometry, which is attributed to Lamé, allows us to construct a phase diagram that demonstrates the dramatic variation of wrinkling patterns from near-threshold to far-from-threshold conditions. Theoretical arguments and comparison to experiments show that the thinner the sheet is, the smaller is the compressive load above which the far-from-threshold regime emerges. This observation emphasizes the relevance of our analysis for nanomechanics applications.

Prototypical model for tensional wrinkling in thin sheets

KAUST Repository

Davidovitch, B.

2011-10-31

The buckling and wrinkling of thin films has recently seen a surge of interest among physicists, biologists, mathematicians, and engineers. This activity has been triggered by the growing interest in developing technologies at ever-decreasing scales and the resulting necessity to control the mechanics of tiny structures, as well as by the realization that morphogenetic processes, such as the tissue-shaping instabilities occurring in animal epithelia or plant leaves, often emerge from mechanical instabilities of cell sheets. Although the most basic buckling instability of uniaxially compressed plates was understood by Euler more than two centuries ago, recent experiments on nanometrically thin (ultrathin) films have shown significant deviations from predictions of standard buckling theory. Motivated by this puzzle, we introduce here a theoretical model that allows for a systematic analysis of wrinkling in sheets far from their instability threshold. We focus on the simplest extension of Euler buckling that exhibits wrinkles of finite length--a sheet under axisymmetric tensile loads. The first study of this geometry, which is attributed to Lamé, allows us to construct a phase diagram that demonstrates the dramatic variation of wrinkling patterns from near-threshold to far-from-threshold conditions. Theoretical arguments and comparison to experiments show that the thinner the sheet is, the smaller is the compressive load above which the far-from-threshold regime emerges. This observation emphasizes the relevance of our analysis for nanomechanics applications.

Pulsar current sheet C̆erenkov radiation

Science.gov (United States)

Zhang, Fan

2018-04-01

Plasma-filled pulsar magnetospheres contain thin current sheets wherein the charged particles are accelerated by magnetic reconnections to travel at ultra-relativistic speeds. On the other hand, the plasma frequency of the more regular force-free regions of the magnetosphere rests almost precisely on the upper limit of radio frequencies, with the cyclotron frequency being far higher due to the strong magnetic field. This combination produces a peculiar situation, whereby radio-frequency waves can travel at subluminal speeds without becoming evanescent. The conditions are thus conducive to C̆erenkov radiation originating from current sheets, which could plausibly serve as a coherent radio emission mechanism. In this paper we aim to provide a portrait of the relevant processes involved, and show that this mechanism can possibly account for some of the most salient features of the observed radio signals.

Class of analytic solutions for the thermally balanced magnetostatic prominence sheet

International Nuclear Information System (INIS)

Low, B.C.; Wu, S.T.

1981-01-01

This is a theoretical study of the nonlinear interplay between magnetostatic equilibrium and energy balance in a Kippenhahn-Schlueter type prominence sheet. The basic effects are illustrated explicitly with an analytic model in which a radiative loss proportional to rho 2 T balances against wave heating proportional to rho, with thermal conduction confined along magnetic field lines, where rho and T denote the plasma density and temperature, respectively. The particular choices of heat sink and source enable us to integrate the governing equations exactly while they are of the basic mathematical forms to simulate radiative loss in an optically thin plasma which is heated by wave dissipation. The steady solutions exhibit three different basic behaviors, characterized by the total wave heating in the prominence sheet being more than, equal to, or less than the total radiative loss. It is the compaction of the plasma along the field lines under its own weight combined with the effects of energy transport that determines which of the three basic behaviors obtains in a particular situation. The implications of the steady solutions for the formation of prominences are discussed. The exact solutions presented do not support the conclusion of Milne, Priest, and Roberts that there is an upper bound on the plasma beta for an equilibrium of the Kippenhahn-Schlueter prominence

Dispersive O+ conics observed in the plasma-sheet boundary layer with CRRES/LOMICS during a magnetic storm

Directory of Open Access Journals (Sweden)

M. Wüest

1996-06-01

Full Text Available We present initial results from the Low-energy magnetospheric ion composition sensor (LOMICS on the Combined release and radiation effects satellite (CRRES together with electron, magnetic field, and electric field wave data. LOMICS measures all important magnetospheric ion species (H+, He++, He+, O++, O+ simultaneously in the energy range 60 eV to 45 keV, as well as their pitch-angle distributions, within the time resolution afforded by the spacecraft spin period of 30 s. During the geomagnetic storm of 9 July 1991, over a period of 42 min (0734 UT to 0816 UT the LOMICS ion mass spectrometer observed an apparent O+ conic flowing away from the southern hemisphere with a bulk velocity that decreased exponentially with time from 300 km/s to 50 km/s, while its temperature also decreased exponentially from 700 to 5 eV. At the onset of the O+ conic, intense low-frequency electromagnetic wave activity and strong pitch-angle scattering were also observed. At the time of the observations the CRRES spacecraft was inbound at L~7.5 near dusk, magnetic local time (MLT, and at a magnetic latitude of –23°. Our analysis using several CRRES instruments suggests that the spacecraft was skimming along the plasma sheet boundary layer (PSBL when the upward-flowing ion conic arrived. The conic appears to have evolved in time, both slowing and cooling, due to wave-particle interactions. We are unable to conclude whether the conic was causally associated with spatial structures of the PSBL or the central plasma sheet.

Free oscillations in a climate model with ice-sheet dynamics

Science.gov (United States)

Kallen, E.; Crafoord, C.; Ghil, M.

1979-01-01

A study of stable periodic solutions to a simple nonlinear model of the ocean-atmosphere-ice system is presented. The model has two dependent variables: ocean-atmosphere temperature and latitudinal extent of the ice cover. No explicit dependence on latitude is considered in the model. Hence all variables depend only on time and the model consists of a coupled set of nonlinear ordinary differential equations. The globally averaged ocean-atmosphere temperature in the model is governed by the radiation balance. The reflectivity to incoming solar radiation, i.e., the planetary albedo, includes separate contributions from sea ice and from continental ice sheets. The major physical mechanisms active in the model are (1) albedo-temperature feedback, (2) continental ice-sheet dynamics and (3) precipitation-rate variations. The model has three-equilibrium solutions, two of which are linearly unstable, while one is linearly stable. For some choices of parameters, the stability picture changes and sustained, finite-amplitude oscillations obtain around the previously stable equilibrium solution. The physical interpretation of these oscillations points to the possibility of internal mechanisms playing a role in glaciation cycles.

Reconstructing the post-LGM decay of the Eurasian Ice Sheets with Ice Sheet Models; data-model comparison and focus on the Storfjorden (Svalbard) ice stream dynamics history

Science.gov (United States)

Petrini, Michele; Kirchner, Nina; Colleoni, Florence; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata G.; Forte, Emanuele; Colucci, Renato R.

2017-04-01

The challenge of reconstructing palaeo-ice sheets past growth and decay represent a critical task to better understand mechanisms of present and future global climate change. Last Glacial Maximum (LGM), and the subsequent deglaciation until Pre-Industrial time (PI) represent an excellent testing ground for numerical Ice Sheet Models (ISMs), due to the abundant data available that can be used in an ISM as boundary conditions, forcings or constraints to test the ISMs results. In our study, we simulate with ISMs the post-LGM decay of the Eurasian Ice Sheets, with a focus on the marine-based Svalbard-Barents Sea-Kara Sea Ice Sheet. In particular, we aim to reconstruct the Storfjorden ice stream dynamics history by comparing the model results with the marine geological data (MSGLs, GZWs, sediment cores analysis) available from the area, e.g., Pedrosa et al. 2011, Rebesco et al. 2011, 2013, Lucchi et al. 2013. Two hybrid SIA/SSA ISMs are employed, GRISLI, Ritz et al. 2001, and PSU, Pollard&DeConto 2012. These models differ mainly in the complexity with which grounding line migration is treated. Climate forcing is interpolated by means of climate indexes between LGM and PI climate. Regional climate indexes are constructed based on the non-accelerated deglaciation transient experiment carried out with CCSM3, Liu et al. 2009. Indexes representative of the climate evolution over Siberia, Svalbard and Scandinavia are employed. The impact of such refined representation as opposed to the common use of the NGRIP δ18O index for transient experiments is analysed. In this study, the ice-ocean interaction is crucial to reconstruct the Storfjorden ice stream dynamics history. To investigate the sensitivity of the ice shelf/stream retreat to ocean temperature, we allow for a space-time variation of basal melting under the ice shelves by testing two-equations implementations based on Martin et al. 2011 forced with simulated ocean temperature and salinity from the TraCE-21ka coupled

Application of GRACE to the Evaluation of an Ice Flow Model of the Greenland Ice Sheet

Science.gov (United States)

Schlegel, N.; Wiese, D. N.; Watkins, M. M.; Larour, E. Y.; Box, J. E.; Fettweis, X.; van den Broeke, M. R.; Morlighem, M.; Boening, C.; Seroussi, H. L.

2014-12-01

Quantifying Greenland's future contribution to sea level rise is a challenging task and requires accurate estimates of ice flow sensitivity to climate change. Transient ice flow models are promising tools for estimating future ice sheet behavior. However, confidence in these types of future projections is low, especially because evaluation of model historical runs is so challenging due to the scarcity of continental-wide data for validation. For more than a decade, NASA's GRACE has continuously acquired time-variable measurements of the Earth's gravity field and has provided unprecedented surveillance of mass balance of the ice sheets, offering an opportunity for ice sheet model evaluation. Here, we take advantage of a new high-resolution (~300 km) monthly mascon solution for the purpose of mass balance comparison with an independent, historical ice flow model simulation using the Ice Sheet System Model (ISSM). The comparison highlights which regions of the ice sheet differ most from GRACE. Investigation of regional differences in trends and seasonal amplitudes between simulations forced with three different Regional Climate Model (RCM)-based estimates of surface mass balance (SMB) allows us to make conclusions about the relative contributions of various error sources in the model hindcast. This study constitutes the first regional comparison of GRACE data and an ice sheet model. Conclusions will aid in the improvement of RCM SMB estimates as well as ice sheet simulation estimates of present and future rates of sea level rise. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Program and President's and Director's Fund Program.

Pulsed Electromagnetic Acceleration of Plasma: A Review

Science.gov (United States)

Thio, Y. C. Francis; Turchi, Peter J.; Markusic, Thomas E.; Cassibry, Jason T.; Sommer, James; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

Much have been learned in the acceleration mechanisms involved in accelerating a plasma electromagnetically in the laboratory over the last 40 years since the early review by Winston Bostik of 1963, but the accumulated understanding is very much scattered throughout the literature. This literature extends back at least to the early sixties and includes Rosenbluth's snowplow model, discussions by Ralph Lovberg, Colgate's boundary-layer model of a current sheet, many papers from the activity at Columbia by Robert Gross and his colleagues, and the relevant, 1-D unsteady descriptions developed from the U. of Maryland theta-pinch studies. Recent progress on the understanding of the pulsed penetration of magnetic fields into collisionless or nearly collisionless plasmas are also be reviewed. Somewhat more recently, we have the two-dimensional, unsteady results in the collisional regime associated with so-called wall-instability in large radius pinch discharges and also in coaxial plasma guns (e.g., Plasma Flow Switch). Among other things, for example, we have the phenomenon of a high- density plasma discharge propagating in a cooaxial gun as an apparently straight sheet (vs paraboloid) because mass re-distribution (on a microsecond timescale) compensates for the 1/r- squared variation of magnetic pressure. We will attempt to collate some of this vast material and bring some coherence tc the development of the subject.

Extraction of volume produced H- or D- ions from a sheet plasma, 2

International Nuclear Information System (INIS)

Uramoto, Joshin.

1984-02-01

A development to large area H - or D - ion source is tried by using three extraction electrodes: The first electrode bias voltage is set near the wall potential (floating), the second electrode is set near 13 % of main extraction voltage and the third electrode is the main acceleration electrode. An ion current of 13 mA (3.3 mA/cm 2 ) for H - or 11 mA (2.8 mA/ cm 2 ) for D - at 3 KeV is extracted from 9 apertures of 6 mm phi in 4 cm 2 outside of the sheet plasma (14 cm wide and 1.0 cm thick) under a pressure of 7.7 x 10 -4 H2 or D2 gas and a weak magnetic field 50 gauss. Then, it is noted that the corresponding electron current is suppressed below 1/10 of the H - or D - ion current. (author)

Mapping of a Hydrological Ice Sheet Drainage Basin on the West Greenland Ice Sheet Margin from ERS-1/2 SAR Interferometry, Ice-Radar Measurement, and Modelling

DEFF Research Database (Denmark)

Ahlstrøm, Andreas P.; Bøggild, C.E.; Stenseng, L.

2002-01-01

importance of the potential of the ice overburden pressure compared to the bedrock topography. The meltwater run-off for the basin delineations was modelled with an energy-balance model calibrated with observed ice-sheet ablation and compared to a 25 year time series of measured basin run-off. The standard......The hydrological ice-sheet basin draining into the Tasersiaq lake, West Greenland (66°13'N, 50°30'W), was delineated, First using standard digital elevation models (DEMs) for ice-sheet surface and bedrock, and subsequently using a new high-resolution dataset, with a surface DEM derived from repeat......-track interferometric synthetic aperture radar (SAR) and a bedrock topography derived from an airborne 60 MHz ice-penetrating radar. The extent of the delineation was calculated from a water-pressure potential as a function of the ice-sheet surface and bedrock elevations and a hydraulic factor κ describing the relative...

Vlasov-Maxwell equilibrium solutions for Harris sheet magnetic field with Kappa velocity distribution

International Nuclear Information System (INIS)

Fu, W.-Z.; Hau, L.-N.

2005-01-01

An exact solution of the steady-state, one-dimensional Vlasov-Maxwell equations for a plasma current sheet with oppositely directed magnetic field was found by Harris in 1962. The so-called Harris magnetic field model assumes Maxwellian velocity distributions for oppositely drifting ions and electrons and has been widely used for plasma stability studies. This paper extends Harris solutions by using more general κ distribution functions that incorporate Maxwellian distribution in the limit of κ→∞. A new functional form for the plasma pressure as a function of the magnetic vector potential p(A) is found and the magnetic field is a modified tanh z function. In the extended solutions the effective temperature is no longer spatially uniform like in the Harris model and the thickness of the current layer decreases with decreasing κ

Spatially Localized Particle Energization by Landau Damping in Current Sheets

Science.gov (United States)

Howes, G. G.; Klein, K. G.; McCubbin, A. J.

2017-12-01

Understanding the mechanisms of particle energization through the removal of energy from turbulent fluctuations in heliospheric plasmas is a grand challenge problem in heliophysics. Under the weakly collisional conditions typical of heliospheric plasma, kinetic mechanisms must be responsible for this energization, but the nature of those mechanisms remains elusive. In recent years, the spatial localization of plasma heating near current sheets in the solar wind and numerical simulations has gained much attention. Here we show, using the innovative and new field-particle correlation technique, that the spatially localized particle energization occurring in a nonlinear gyrokinetic simulation has the velocity space signature of Landau damping, suggesting that this well-known collisionless damping mechanism indeed actively leads to spatially localized heating in the vicinity of current sheets.

Application of plasma focus device to compression of toroidal plasma

International Nuclear Information System (INIS)

Ikuta, Kazunari

1980-01-01

A new concept of compressing a toroidal plasma using a plasma focus device is considered. Maximum compression ratio of toroidal plasma is determined merely by the initial density ratio of the toroidal plasma to a sheet plasma in a focus device because of the Rayleigh-Taylor instability. An initiation senario of plasma-linear is also proposed with a possible application of this concepts to the creation of a burning plasma in reversed field configurations, i.e., burning plasma vortex. (author)

Multi-instrument observations of the ionospheric counterpart of a bursty bulk flow in the near-Earth plasma sheet

Directory of Open Access Journals (Sweden)

A. Grocott

2004-04-01

Full Text Available On 07 September 2001 the Cluster spacecraft observed a "bursty bulk flow" event in the near-Earth central plasma sheet. This paper presents a detailed study of the coincident ground-based observations and attempts to place them within a simple physical framework. The event in question occurs at ~22:30 UT, some 10min after a southward turning of the IMF. IMAGE and SAMNET magnetometer measurements of the ground magnetic field reveal perturbations of a few tens of nT and small amplitude Pi2 pulsations. CUTLASS radar observations of ionospheric plasma convection show enhanced flows out of the polar cap near midnight, accompanied by an elevated transpolar voltage. Optical data from the IMAGE satellite also show that there is a transient, localised ~1 kR brightening in the UV aurora. These observations are consistent with the earthward transport of plasma in the tail, but also indicate the absence of a typical "large-scale" substorm current wedge. An analysis of the field-aligned current system implied by the radar measurements does suggest the existence of a small-scale current "wedgelet", but one which lacks the global scale and high conductivities observed during substorm expansions.

Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphere interactions; plasma convection

Modelling the formation of sheeting joints with FRACOD2D (FRActure propagation CODe)

International Nuclear Information System (INIS)

Lanaro, Flavio; Amemiya, Kiyoshi; Yamada, Atsuo

2008-01-01

This contribution shows an application of the newly developed gravity acceleration function in the BEM-DDM code FRACOD 2D . The influence of the model geometry, material parameters and boundary stresses on the initiation and propagation of sheeting joints due to rebound by removal of the overburden is studied. The models seem to capture the pattern of sheeting joints and the depth of their occurrence. The influence of the sheeting joints on the stress distributions in the rock mass also seem to be realistic and in agreement with field observations. The results indicate that the stresses measured in-situ at several sites in crystalline rock might exhibit the same features as the numerical results by FRACOD 2D . For example, the horizontal stress is found to be rather high at the surface of the models as it was observed in Forsmark, Sweden. Moreover, stresses where sheeting joints are developing are so severe to justify damage and fracturing of the intact rock observed in terms of fracture frequency and laboratory sample damage close to the surface at the Shobasama and MIU Construction Site, Mizunami, Japan. (author)

Magnetic reconnection and current sheet formation in 3D magnetic configurations

International Nuclear Information System (INIS)

Frank, A.G.

1999-01-01

The problem of magnetic reconnection in three-dimensional (3D) magnetic configurations has been studied experimentally. The research has concentrated on the possibilities of formation of current sheets, which represent crucial objects for a realization of magnetic reconnection phenomena. Different types of 3D magnetic configurations were examined, including configurations with singular lines of the X-type, non-uniform fields containing isolated magnetic null-points and without null-points. It was revealed that formation of quasi-one-dimensional current sheets is the universal process for plasma dynamics in 3D magnetic fields both with null-points and without. At the same time the peculiarities of current sheets, plasma dynamics and magnetic reconnection processes depend essentially on characteristics of 3D magnetic configurations. The result of principal significance obtained was that magnetic reconnection phenomena can take place in a wide range of 3D magnetic configurations as a consequence of their ability to form current sheets. (author)

An advanced constitutive model in the sheet metal forming simulation: the Teodosiu microstructural model and the Cazacu Barlat yield criterion

International Nuclear Information System (INIS)

Alves, J.L.; Oliveira, M.C.; Menezes, L.F.

2004-01-01

Two constitutive models used to describe the plastic behavior of sheet metals in the numerical simulation of sheet metal forming process are studied: a recently proposed advanced constitutive model based on the Teodosiu microstructural model and the Cazacu Barlat yield criterion is compared with a more classical one, based on the Swift law and the Hill 1948 yield criterion. These constitutive models are implemented into DD3IMP, a finite element home code specifically developed to simulate sheet metal forming processes, which generically is a 3-D elastoplastic finite element code with an updated Lagrangian formulation, following a fully implicit time integration scheme, large elastoplastic strains and rotations. Solid finite elements and parametric surfaces are used to model the blank sheet and tool surfaces, respectively. Some details of the numerical implementation of the constitutive models are given. Finally, the theory is illustrated with the numerical simulation of the deep drawing of a cylindrical cup. The results show that the proposed advanced constitutive model predicts with more exactness the final shape (medium height and ears profile) of the formed part, as one can conclude from the comparison with the experimental results

Cryosphere Science Outreach using the Ice Sheet System Model and a Virtual Ice Sheet Laboratory

Science.gov (United States)

Cheng, D. L. C.; Halkides, D. J.; Larour, E. Y.

2015-12-01

Understanding the role of Cryosphere Science within the larger context of Sea Level Rise is both a technical and educational challenge that needs to be addressed if the public at large is to trulyunderstand the implications and consequences of Climate Change. Within this context, we propose a new approach in which scientific tools are used directly inside a mobile/website platform geared towards Education/Outreach. Here, we apply this approach by using the Ice Sheet System Model, a state of the art Cryosphere model developed at NASA, and integrated within a Virtual Ice Sheet Laboratory, with the goal is to outreach Cryospherescience to K-12 and College level students. The approach mixes laboratory experiments, interactive classes/lessons on a website, and a simplified interface to a full-fledged instance of ISSM to validate the classes/lessons. This novel approach leverages new insights from the Outreach/Educational community and the interest of new generations in web based technologies and simulation tools, all of it delivered in a seamlessly integrated web platform. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

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

Hindcasting to measure ice sheet model sensitivity to initial states

Directory of Open Access Journals (Sweden)

A. Aschwanden

2013-07-01

Full Text Available Validation is a critical component of model development, yet notoriously challenging in ice sheet modeling. Here we evaluate how an ice sheet system model responds to a given forcing. We show that hindcasting, i.e. forcing a model with known or closely estimated inputs for past events to see how well the output matches observations, is a viable method of assessing model performance. By simulating the recent past of Greenland, and comparing to observations of ice thickness, ice discharge, surface speeds, mass loss and surface elevation changes for validation, we find that the short term model response is strongly influenced by the initial state. We show that the thermal and dynamical states (i.e. the distribution of internal energy and momentum can be misrepresented despite a good agreement with some observations, stressing the importance of using multiple observations. In particular we identify rates of change of spatially dense observations as preferred validation metrics. Hindcasting enables a qualitative assessment of model performance relative to observed rates of change. It thereby reduces the number of admissible initial states more rigorously than validation efforts that do not take advantage of observed rates of change.

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.

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

Robot-based additive manufacturing for flexible die-modelling in incremental sheet forming

Science.gov (United States)

Rieger, Michael; Störkle, Denis Daniel; Thyssen, Lars; Kuhlenkötter, Bernd

2017-10-01

The paper describes the application concept of additive manufactured dies to support the robot-based incremental sheet metal forming process (`Roboforming') for the production of sheet metal components in small batch sizes. Compared to the dieless kinematic-based generation of a shape by means of two cooperating industrial robots, the supporting robot models a die on the back of the metal sheet by using the robot-based fused layer manufacturing process (FLM). This tool chain is software-defined and preserves the high geometrical form flexibility of Roboforming while flexibly generating support structures adapted to the final part's geometry. Test series serve to confirm the feasibility of the concept by investigating the process challenges of the adhesion to the sheet surface and the general stability as well as the influence on the geometric accuracy compared to the well-known forming strategies.

Representing grounding line migration in synchronous coupling between a marine ice sheet model and a z-coordinate ocean model

Science.gov (United States)

Goldberg, D. N.; Snow, K.; Holland, P.; Jordan, J. R.; Campin, J.-M.; Heimbach, P.; Arthern, R.; Jenkins, A.

2018-05-01

Synchronous coupling is developed between an ice sheet model and a z-coordinate ocean model (the MITgcm). A previously-developed scheme to allow continuous vertical movement of the ice-ocean interface of a floating ice shelf ("vertical coupling") is built upon to allow continuous movement of the grounding line, or point of floatation of the ice sheet ("horizontal coupling"). Horizontal coupling is implemented through the maintenance of a thin layer of ocean ( ∼ 1 m) under grounded ice, which is inflated into the real ocean as the ice ungrounds. This is accomplished through a modification of the ocean model's nonlinear free surface evolution in a manner akin to a hydrological model in the presence of steep bathymetry. The coupled model is applied to a number of idealized geometries and shown to successfully represent ocean-forced marine ice sheet retreat while maintaining a continuous ocean circulation.

An Excursion Set Model of the Cosmic Web: the Abundance of Sheets, Filaments And Halos

Energy Technology Data Exchange (ETDEWEB)

Shen, Jiajian; /Penn State U., Astron. Astrophys.; Abel, Tom; /KIPAC, Menlo Park; Mo, Houjun; /Massachusetts U., Amherst; Sheth, Ravi; /Pennsylvania U.

2006-01-11

We discuss an analytic approach for modeling structure formation in sheets, filaments and knots. This is accomplished by combining models of triaxial collapse with the excursion set approach: sheets are defined as objects which have collapsed along only one axis, filaments have collapsed along two axes, and halos are objects in which triaxial collapse is complete. In the simplest version of this approach, which we develop here, large scale structure shows a clear hierarchy of morphologies: the mass in large-scale sheets is partitioned up among lower mass filaments, which themselves are made-up of still lower mass halos. Our approach provides analytic estimates of the mass fraction in sheets, filaments and halos, and its evolution, for any background cosmological model and any initial fluctuation spectrum. In the currently popular {Lambda}CDM model, our analysis suggests that more than 99% of the mass in sheets, and 72% of the mass in filaments, is stored in objects more massive than 10{sup 10}M{sub {circle_dot}} at the present time. For halos, this number is only 46%. Our approach also provides analytic estimates of how halo abundances at any given time correlate with the morphology of the surrounding large-scale structure, and how halo evolution correlates with the morphology of large scale structure.

Plasma modelling and numerical simulation

International Nuclear Information System (INIS)

Van Dijk, J; Kroesen, G M W; Bogaerts, A

2009-01-01

Plasma modelling is an exciting subject in which virtually all physical disciplines are represented. Plasma models combine the electromagnetic, statistical and fluid dynamical theories that have their roots in the 19th century with the modern insights concerning the structure of matter that were developed throughout the 20th century. The present cluster issue consists of 20 invited contributions, which are representative of the state of the art in plasma modelling and numerical simulation. These contributions provide an in-depth discussion of the major theories and modelling and simulation strategies, and their applications to contemporary plasma-based technologies. In this editorial review, we introduce and complement those papers by providing a bird's eye perspective on plasma modelling and discussing the historical context in which it has surfaced. (editorial review)

Modeling of optimization strategies in the incremental CNC sheet metal forming process

International Nuclear Information System (INIS)

Bambach, M.; Hirt, G.; Ames, J.

2004-01-01

Incremental CNC sheet forming (ISF) is a relatively new sheet metal forming process for small batch production and prototyping. In ISF, a blank is shaped by the CNC movements of a simple tool in combination with a simplified die. The standard forming strategies in ISF entail two major drawbacks: (i) the inherent forming kinematics set limits on the maximum wall angle that can be formed with ISF. (ii) since elastic parts of the imposed deformation can currently not be accounted for in CNC code generation, the standard strategies can lead to undesired deviations between the target and the sample geometry.Several enhancements have recently been put forward to overcome the above limitations, among them a multistage forming strategy to manufacture steep flanges, and a correction algorithm to improve the geometric accuracy. Both strategies have been successful in improving the forming of simple parts. However, the high experimental effort to empirically optimize the tool paths motivates the use of process modeling techniques.This paper deals with finite element modeling of the ISF process. In particular, the outcome of different multistage strategies is modeled and compared to collated experimental results regarding aspects such as sheet thickness and the onset of wrinkling. Moreover, the feasibility of modeling the geometry of a part is investigated as this is of major importance with respect to optimizing the geometric accuracy. Experimental validation is achieved by optical deformation measurement that gives the local displacements and strains of the sheet during forming as benchmark quantities for the simulation

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet-climate model

Science.gov (United States)

Stap, Lennert B.; van de Wal, Roderik S. W.; de Boer, Bas; Bintanja, Richard; Lourens, Lucas J.

2017-09-01

Since the inception of the Antarctic ice sheet at the Eocene-Oligocene transition (˜ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice-albedo and surface-height-temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO2. Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO2 and temperature is subject to hysteresis. When the climate cools from very high CO2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO2, temperature, ice-volume-equivalent sea level, and benthic δ18O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet-climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice-albedo and surface

Current Sheets in Pulsar Magnetospheres and Winds: Particle Acceleration and Pulsed Gamma Ray Emission

Science.gov (United States)

Arons, Jonathan

The research proposed addresses understanding of the origin of non-thermal energy in the Universe, a subject beginning with the discovery of Cosmic Rays and continues, including the study of relativistic compact objects - neutron stars and black holes. Observed Rotation Powered Pulsars (RPPs) have rotational energy loss implying they have TeraGauss magnetic fields and electric potentials as large as 40 PetaVolts. The rotational energy lost is reprocessed into particles which manifest themselves in high energy gamma ray photon emission (GeV to TeV). Observations of pulsars from the FERMI Gamma Ray Observatory, launched into orbit in 2008, have revealed 130 of these stars (and still counting), thus demonstrating the presence of efficient cosmic accelerators within the strongly magnetized regions surrounding the rotating neutron stars. Understanding the physics of these and other Cosmic Accelerators is a major goal of astrophysical research. A new model for particle acceleration in the current sheets separating the closed and open field line regions of pulsars' magnetospheres, and separating regions of opposite magnetization in the relativistic winds emerging from those magnetopsheres, will be developed. The currents established in recent global models of the magnetosphere will be used as input to a magnetic field aligned acceleration model that takes account of the current carrying particles' inertia, generalizing models of the terrestrial aurora to the relativistic regime. The results will be applied to the spectacular new results from the FERMI gamma ray observatory on gamma ray pulsars, to probe the physics of the generation of the relativistic wind that carries rotational energy away from the compact stars, illuminating the whole problem of how compact objects can energize their surroundings. The work to be performed if this proposal is funded involves extending and developing concepts from plasma physics on dissipation of magnetic energy in thin sheets of

Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

Science.gov (United States)

Goelzer, Heiko; Huybrechts, Philippe; Loutre, Marie-France; Fichefet, Thierry

2016-12-01

As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ˜ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate-ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet-climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

Experimental Investigation of the Neutral sheet Profile During Magnetic Reconnection

International Nuclear Information System (INIS)

Trintchouk, F.; Ji, H.; Yamada, M.; Kulsrud, R.; Hsu, S.; Carter, T.

1999-01-01

During magnetic reconnection, a ''neutral sheet'' current is induced, heating the plasma. The resultant plasma thermal pressure forms a stationary equilibrium with the opposing magnetic fields. The reconnection layer profile holds significant clues about the physical mechanisms which control reconnection. On the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)], a quasi steady-state and axisymmetric neutral sheet profile has been measured precisely using a magnetic probe array with spatial resolution equal to one quarter of the ion gyro-radius. It was found that the reconnecting field profile fits well with a Harris-type profile [E. G. Harris, Il Nuovo Cimento 23, 115 (1962)], B(x) approximately tanh(x/delta). This agreement is remarkable since the Harris theory does not take into account reconnection and associated electric fields and dissipation. An explanation for this agreement is presented. The sheet thickness delta is found to be approximately 0.4 times the ion skin depth, which agrees with a generalized Harris theory incorporating non-isothermal electron and ion temperatures and finite electric field. The detailed study of additional local features of the reconnection region is also presented

Uses of dense magnetized plasmas as neutron sources

International Nuclear Information System (INIS)

Gonzalez, Jose Hector

2004-01-01

In this work, a lumped parameter model for Plasma Focus is presented.A fast running computer code was developed, specially focused to the calculation of the neutron production in Deuterium-filled devices.This code is suitable to parameters optimization at the conceptual engineering stage.The kinematics of the current sheet is represented by a plane, 2D snowplow model.It is complemented with sensible estimations for the current sheet characteristics (density n and temperature T).After the radial collapse, a one fluid MHD model with velocity profiles for the particles trapped inside the pinch is proposed.Then, assuming thermal equilibrium in the plasma, the neutron production by termofusion can be estimated.The dynamics equations are coupled with the electrical circuit. A computer code in FORTRAN language was programmed to solve this set of equations.A powerful numerical integrator for first order differential equations is used, and the code can perform an estimation of the neutron production very quickly.The resulting neutron yield and dynamics predictions have been compared against experimental results of Plasma Focus devices from all around the world, for different geometric and energetic conditions.The effective parameters of the model were validated using those experimental measurements. The presented model ultimately calculates the neutron production given the geometric and energetic parameters, and the filling pressure

Plasma Reactors and Plasma Thrusters Modeling by Ar Complete Global Models

Directory of Open Access Journals (Sweden)

Chloe Berenguer

2012-01-01

Full Text Available A complete global model for argon was developed and adapted to plasma reactor and plasma thruster modeling. It takes into consideration ground level and excited Ar and Ar+ species and the reactor and thruster form factors. The electronic temperature, the species densities, and the ionization percentage, depending mainly on the pressure and the absorbed power, have been obtained and commented for various physical conditions.

Modelling of friction anisotropy of deepdrawing sheet in ABAQUS/EXPLICIT

Directory of Open Access Journals (Sweden)

F. Stachowicz

2010-07-01

Full Text Available This paper presents the experimental and numerical results of rectangular cup drawing of steel sheets. The aim of the experimental study was to analyze material behavior under deformation. The received results were further used to verify the results from numerical simulation by taking friction and material anisotropy into consideration. A 3D parametric finite element (FE model was built using the FE-package ABAQUS/Standard. ABAQUS allows analyzing physical models of real processes putting special emphasis on geometrical non-linearities caused by large deformations, material non-linearities and complex friction conditions. Frictional properties of the deep drawing quality steel sheet were determined by using the pin-on-disc tribometer. It shows that the friction coefficient value depends on the measured angle from the rolling direction and corresponds to the surface topography. A quadratic Hill anisotropic yield criterion was compared with Huber-Mises yield criterion having isotropic hardening. Plastic anisotropy is the result of the distortion of the yield surface shape due to the material microstructural state. The sensitivity of constitutive laws to the initial data characterizing material behavior isalso presented. It is found that plastic anisotropy of the matrix in ductile sheet metal has influence on deformation behavior of the material. If the material and friction anisotropy are taken into account in the finite element analysis, this approach undoubtedly gives the most approximate numerical results to real processes. This paper is the first part of the study of numerical investigation using ABAQUS and mainly deals with the most influencing parameters in a forming process to simulate the sheet metal forming of rectangular cup.

Observations and modeling of magnetized plasma jets and bubbles launched into a transverse B-field

Science.gov (United States)

Fisher, Dustin M.; Zhang, Yue; Wallace, Ben; Gilmore, Mark; Manchester, Ward B., IV; van der Holst, Bart; Rogers, Barrett N.; Hsu, Scott C.

2017-10-01

Hot, dense, plasma structures launched from a coaxial plasma gun on the HelCat dual-source plasma device at the University of New Mexico drag frozen-in magnetic flux into the chamber's background magnetic field providing a rich set of dynamics to study magnetic turbulence, force-free magnetic spheromaks, shocks, as well as CME-like dynamics possibly relevant to the solar corona. Vector magnetic field data from an eleven-tipped B-dot rake probe and images from an ultra-fast camera will be presented in comparison with ongoing MHD modeling using the 3-D MHD BATS-R-US code developed at the University of Michigan. BATS-R-US employs an adaptive mesh refinement grid (AMR) that enables the capture and resolution of shock structures and current sheets and is uniquely suited for flux-rope expansion modeling. Recent experiments show a possible magnetic Rayleigh-Taylor (MRT) instability that appears asymmetrically at the interface between launched spheromaks (bubbles) and their entraining background magnetic field. Efforts to understand this instability using in situ measurements, new chamber boundary conditions, and ultra-fast camera data will be presented. Work supported by the Army Research Office Award No. W911NF1510480.

Pressure changes in the plasma sheet during substorm injections

International Nuclear Information System (INIS)

Kistler, L.M.; Moebuis, E.; Baumjohann, W.; Paschmann, G.; Hamilton, D.C.

1992-01-01

The authors have determined the particle pressure and total pressure as a function of radial distance in the plasma sheet for periods before and after the onset of substorm-associated ion enhancements over the radial range 7-19 R E . They have chosen events occurring during times of increasing magnetospheric activity, as determined by an increasing AE index, in which a sudden increase, or injection, of energetic particle flux is observed. During these events the particle energy of maximum contribution to the pressure increases from about 12 to about 27 keV. In addition, the particle pressure increases, and the magnetic pressure decreases, with the total pressure only changing slightly. For radial distances of less than 10 R E the total pressure tends to increase with the injection, while outside 10 R E it tends to decrease or remain the same. Because the fraction of the pressure due to particles has increased and higher energies are contributing to the pressure, a radial gradient is evident in the postinjection, but not preinjection, flux measurements. These observations show that the simulations appearance of energetic particles and changes in the magnetic field results naturally from pressure balance and does not necessarily indicate that the local changing field is accelerating the particles. The changes in the total pressure outside 10 R E are consistent with previous measurements of pressure changes at substorm onset and can be understood in terms of the unloading of energy in the magnetotail and the resulting change in the magnetic field configuration

Finite element simulation of aluminum sheet warm forming using alflow hardening model

NARCIS (Netherlands)

Kurukuri, S.; van den Boogaard, Antonius H.; Huetink, Han

2007-01-01

In order to accurately model the plastic deformation of Aluminum sheet at elevated temperatures, a model is required that incorporate the temperature and strain rate dependency of the material. In this article, two physically based models are compared: Bergstr¨om and Alflow model. Although both

Reconstruction of the Greenland ice sheet dynamics in a fully coupled Earth System Model

Science.gov (United States)

Rybak, Oleg; Volodin, Evgeny; Huybrechts, Philippe

2016-04-01

Earth system models (ESMs) are undoubtedly effective tools for studying climate dynamics. Incorporation of evolving ice sheets to ESMs is a challenging task because response times of the climate system and of ice sheets differ by several orders of magnitude. Besides, AO GCMs operate on spatial and temporal resolutions substantially differing from those of ice sheet models (ICMs). Therefore elaboration of an effective coupling methodology of an AO GCM and an ICM is the key problem of an ESM construction and utilization. Several downscaling strategies of varying complexity exist now of data exchange between modeled climate system and ice sheets. Application of a particular strategy depends on the research objectives. In our view, the optimum approach for model studying of significant environmental changes (e.g. glacial/interglacial transitions) when ice sheets undergo substantial evolution of geometry and volume would be an asynchronous coupling. The latter allows simulation in the interactive way of growth and decay of ice sheets in the changing climatic conditions. In the focus of the presentation, is the overview of coupling aspects of an AO GCM INMCM32 elaborated in the Institute of Numerical Mathematics (Moscow, Russia) to the Greenland ice sheet model (GrISM, Vrije Uninersiteit Brussel, Belgium). To provide interactive coupling of INMCM32 (spatial resolution 5°×4°, 21 vertical layers and temporal resolution 6 min. in the atmospheric block) and GrISM (spatial resolution 20×20 km, 51 vertical layers and 1 yr temporal resolution), we employ a special energy- and water balance model (EWBM-G), which serves as a buffer providing effective data exchange between INMCM32 and GrISM. EWBM-G operates in a rectangle domain including Greenland. Transfer of daily meanings of simulated climatic variables (air surface temperature and specific humidity) is provided on the lateral boundarias of the domain and inside the domain (sea level air pressure, wind speed and total

A sensitivity analysis for a thermomechanical model of the Antarctic ice sheet and ice shelves

Science.gov (United States)

Baratelli, F.; Castellani, G.; Vassena, C.; Giudici, M.

2012-04-01

The outcomes of an ice sheet model depend on a number of parameters and physical quantities which are often estimated with large uncertainty, because of lack of sufficient experimental measurements in such remote environments. Therefore, the efforts to improve the accuracy of the predictions of ice sheet models by including more physical processes and interactions with atmosphere, hydrosphere and lithosphere can be affected by the inaccuracy of the fundamental input data. A sensitivity analysis can help to understand which are the input data that most affect the different predictions of the model. In this context, a finite difference thermomechanical ice sheet model based on the Shallow-Ice Approximation (SIA) and on the Shallow-Shelf Approximation (SSA) has been developed and applied for the simulation of the evolution of the Antarctic ice sheet and ice shelves for the last 200 000 years. The sensitivity analysis of the model outcomes (e.g., the volume of the ice sheet and of the ice shelves, the basal melt rate of the ice sheet, the mean velocity of the Ross and Ronne-Filchner ice shelves, the wet area at the base of the ice sheet) with respect to the model parameters (e.g., the basal sliding coefficient, the geothermal heat flux, the present-day surface accumulation and temperature, the mean ice shelves viscosity, the melt rate at the base of the ice shelves) has been performed by computing three synthetic numerical indices: two local sensitivity indices and a global sensitivity index. Local sensitivity indices imply a linearization of the model and neglect both non-linear and joint effects of the parameters. The global variance-based sensitivity index, instead, takes into account the complete variability of the input parameters but is usually conducted with a Monte Carlo approach which is computationally very demanding for non-linear complex models. Therefore, the global sensitivity index has been computed using a development of the model outputs in a

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

Constitutive modeling for analysis and design of aluminum sheet forming processes

International Nuclear Information System (INIS)

Barlat, F.; Chung, K.; Yoon, J-W.; Choi, S-H.

2000-01-01

Finite element modeling (FEM) technology is one of the most powerful tools used to design new products, i.e. appliances, automotive, rigid packaging and aerospace parts, etc., and processes. However, FEM users need data and models to characterize the materials used to fabricate the new products. In fact, they need more information than the traditional and standard yield strength, ultimate strength, elongation, etc. Constitutive models and their associated coefficients represent a new way to describe material properties, a way that can be used by FEM users. In order to help manufacturers use more aluminum alloy sheet in their products, appropriate material models are needed to analyze and design specifically for these materials. This work describes a methodology that provides phenomenological constitutive equations based on three main microstructure components of aluminum alloys: dislocation density, second-phase particles and crystallographic texture. Examples of constitutive equations and their applications to numerical sheet forming process analysis and design are provided in this work. (author)

Research on NC laser combined cutting optimization model of sheet metal parts

Science.gov (United States)

Wu, Z. Y.; Zhang, Y. L.; Li, L.; Wu, L. H.; Liu, N. B.

2017-09-01

The optimization problem for NC laser combined cutting of sheet metal parts was taken as the research object in this paper. The problem included two contents: combined packing optimization and combined cutting path optimization. In the problem of combined packing optimization, the method of “genetic algorithm + gravity center NFP + geometric transformation” was used to optimize the packing of sheet metal parts. In the problem of combined cutting path optimization, the mathematical model of cutting path optimization was established based on the parts cutting constraint rules of internal contour priority and cross cutting. The model played an important role in the optimization calculation of NC laser combined cutting.

Inception of the Laurentide Ice Sheet using asynchronous coupling of a regional atmospheric model and an ice model

Science.gov (United States)

Birch, L.; Cronin, T.; Tziperman, E.

2017-12-01

The climate over the past 0.8 million years has been dominated by ice ages. Ice sheets have grown about every 100 kyrs, starting from warm interglacials, until they spanned continents. State-of-the-art global climate models (GCMs) have difficulty simulating glacial inception, or the transition of Earth's climate from an interglacial to a glacial state. It has been suggested that this failure may be related to their poorly resolved local mountain topography, due to their coarse spatial resolution. We examine this idea as well as the possible role of ice flow dynamics missing in GCMs. We investigate the growth of the Laurentide Ice Sheet at 115 kya by focusing on the mountain glaciers of Canada's Baffin Island, where geologic evidence indicates the last inception occurred. We use the Weather Research and Forecasting model (WRF) in a regional, cloud-resolving configuration with resolved mountain terrain to explore how quickly Baffin Island could become glaciated with the favorable yet realizable conditions of 115 kya insolation, cool summers, and wet winters. Using the model-derived mountain glacier mass balance, we force an ice sheet model based on the shallow-ice approximation, capturing the ice flow that may be critical to the spread of ice sheets away from mountain ice caps. The ice sheet model calculates the surface area newly covered by ice and the change in the ice surface elevation, which we then use to run WRF again. Through this type of iterated asynchronous coupling, we investigate how the regional climate responds to both larger areas of ice cover and changes in ice surface elevation. In addition, we use the NOAH-MP Land model to characterize the importance of land processes, like refreezing. We find that initial ice growth on the Penny Ice Cap causes regional cooling that increases the accumulation on the Barnes Ice Cap. We investigate how ice and topography changes on Baffin Island may impact both the regional climate and the large-scale circulation.

Implementation of virtual models from sheet metal forming simulation into physical 3D colour models using 3D printing

Science.gov (United States)

Junk, S.

2016-08-01

Today the methods of numerical simulation of sheet metal forming offer a great diversity of possibilities for optimization in product development and in process design. However, the results from simulation are only available as virtual models. Because there are any forming tools available during the early stages of product development, physical models that could serve to represent the virtual results are therefore lacking. Physical 3D-models can be created using 3D-printing and serve as an illustration and present a better understanding of the simulation results. In this way, the results from the simulation can be made more “comprehensible” within a development team. This paper presents the possibilities of 3D-colour printing with particular consideration of the requirements regarding the implementation of sheet metal forming simulation. Using concrete examples of sheet metal forming, the manufacturing of 3D colour models will be expounded upon on the basis of simulation results.

Pre-LGM Northern Hemisphere ice sheet topography

Directory of Open Access Journals (Sweden)

J. Kleman

2013-10-01

Full Text Available We here reconstruct the paleotopography of Northern Hemisphere ice sheets during the glacial maxima of marine isotope stages (MIS 5b and 4.We employ a combined approach, blending geologically based reconstruction and numerical modeling, to arrive at probable ice sheet extents and topographies for each of these two time slices. For a physically based 3-D calculation based on geologically derived 2-D constraints, we use the University of Maine Ice Sheet Model (UMISM to calculate ice sheet thickness and topography. The approach and ice sheet modeling strategy is designed to provide robust data sets of sufficient resolution for atmospheric circulation experiments for these previously elusive time periods. Two tunable parameters, a temperature scaling function applied to a spliced Vostok–GRIP record, and spatial adjustment of the climatic pole position, were employed iteratively to achieve a good fit to geological constraints where such were available. The model credibly reproduces the first-order pattern of size and location of geologically indicated ice sheets during marine isotope stages (MIS 5b (86.2 kyr model age and 4 (64 kyr model age. From the interglacial state of two north–south obstacles to atmospheric circulation (Rocky Mountains and Greenland, by MIS 5b the emergence of combined Quebec–central Arctic and Scandinavian–Barents-Kara ice sheets had increased the number of such highland obstacles to four. The number of major ice sheets remained constant through MIS 4, but the merging of the Cordilleran and the proto-Laurentide Ice Sheet produced a single continent-wide North American ice sheet at the LGM.

Vibrational characteristics of graphene sheets elucidated using an elastic network model.

Science.gov (United States)

Kim, Min Hyeok; Kim, Daejoong; Choi, Jae Boong; Kim, Moon Ki

2014-08-07

Recent studies of graphene have demonstrated its great potential for highly sensitive resonators. In order to capture the intrinsic vibrational characteristics of graphene, we propose an atomistic modeling method called the elastic network model (ENM), in which a graphene sheet is modeled as a mass-spring network of adjacent atoms connected by various linear springs with specific bond ratios. Normal mode analysis (NMA) reveals the various vibrational features of bi-layer graphene sheets (BLGSs) clamped at two edges. We also propose a coarse-graining (CG) method to extend our graphene study into the meso- and macroscales, at which experimental measurements and synthesis of graphene become practical. The simulation results show good agreement with experimental observations. Therefore, the proposed ENM approach will not only shed light on the theoretical study of graphene mechanics, but also play an important role in the design of highly-sensitive graphene-based resonators.

Quite time convection electric field properties derived from keV electron measurements at the inner edge of the plasma sheet by means of GEOS 2

International Nuclear Information System (INIS)

Reme, H.; Kremser, G.; Bahnsen, A.; Jespersen, M.; Hultqvist, B.; Borg, H.; Holmgren, L.Aa.

1981-04-01

From an analysis of the local time distribution of the electron upper energy limit reached by the geostationary satellite GEOS 2 in cutting through the innermost part of the electron plasma sheet during fairly quite condition the following results have been obtained, among others: An electric field model given by E = -grad(AR 4 sinphi), with the dusk singular point of the forbidden region boundary at 1500, instead of at 1800 MLT, is in quite good agreement with the observations. This means that effects due to the shielding by the hot plasma of the inner magnetosphere from the convection electric field are quite strong in situations of low disturbance level. The quiet time convection electric field strength at 2100 MLT in the geostationary orbit obtained from this analysis varies in the range 0.15 - 0.3 keV/Rsub(e). Six hours earlier or later in the satellite orbit the convection field is 4 times stronger. Also when the convection field varies, some information about its magnitude can be obtained from the keV electron measurements. (author)

Assessing the formability of metallic sheets by means of localized and diffuse necking models

Science.gov (United States)

Comşa, Dan-Sorin; Lǎzǎrescu, Lucian; Banabic, Dorel

2016-10-01

The main objective of the paper consists in elaborating a unified framework that allows the theoretical assessment of sheet metal formability. Hill's localized necking model and the Extended Maximum Force Criterion proposed by Mattiasson, Sigvant, and Larsson have been selected for this purpose. Both models are thoroughly described together with their solution procedures. A comparison of the theoretical predictions with experimental data referring to the formability of a DP600 steel sheet is also presented by the authors.

Ion motion in the wake driven by long particle bunches in plasmas

International Nuclear Information System (INIS)

Vieira, J.; Silva, L. O.; Fonseca, R. A.; Mori, W. B.

2014-01-01

We explore the role of the background plasma ion motion in self-modulated plasma wakefield accelerators. We employ Dawson's plasma sheet model to derive expressions for the transverse plasma electric field and ponderomotive force in the narrow bunch limit. We use these results to determine the on-set of the ion dynamics and demonstrate that the ion motion could occur in self-modulated plasma wakefield accelerators. Simulations show the motion of the plasma ions can lead to the early suppression of the self-modulation instability and of the accelerating fields. The background plasma ion motion can nevertheless be fully mitigated by using plasmas with heavier plasmas

New developments in tribomechanical modeling of automotive sheet steel forming

Science.gov (United States)

Khandeparkar, Tushar; Chezan, Toni; van Beeck, Jeroen

2018-05-01

Forming of automotive sheet metal body panels is a complex process influenced by both the material properties and contact conditions in the forming tooling. Material properties are described by the material constitutive behavior and the material flow into the forming die can be described by the tribological system. This paper investigates the prediction accuracy of the forming process using the Tata Steel state of the art description of the material constitutive behavior in combination with different friction models. A cross-die experiment is used to investigate the accuracy of local deformation modes typically seen in automotive sheet metal forming operations. Results of advanced friction models as well as the classical Coulomb friction description are compared to the experimentally measured strain distribution and material draw-in. Two hot-dip galvanized coated steel forming grades were used for the investigations. The results show that the accuracy of the simulation is not guaranteed by the advanced friction models for the entire investigated blank holder force range, both globally and locally. A measurable difference between the calculated and measured local strains is seen for both studied models even in the case where the global indicator, i.e. the draw-in, is well predicted.

MHD waveguides in space plasma

International Nuclear Information System (INIS)

Mazur, N. G.; Fedorov, E. N.; Pilipenko, V. A.

2010-01-01

The waveguide properties of two characteristic formations in the Earth's magnetotail-the plasma sheet and the current (neutral) sheet-are considered. The question of how the domains of existence of different types of MHD waveguide modes (fast and slow, body and surface) in the (k, ω) plane and their dispersion properties depend on the waveguide parameters is studied. Investigation of the dispersion relation in a number of particular (limiting) cases makes it possible to obtain a fairly complete qualitative pattern of all the branches of the dispersion curve. Accounting for the finite size of perturbations across the wave propagation direction reveals new additional effects such as a change in the critical waveguide frequencies, the excitation of longitudinal current at the boundaries of the sheets, and a change in the symmetry of the fundamental mode. Knowledge of the waveguide properties of the plasma and current sheets can explain the occurrence of preferred frequencies in the low-frequency fluctuation spectra in the magnetotail. In satellite observations, the type of waveguide mode can be determined from the spectral properties, as well as from the phase relationships between plasma oscillations and magnetic field oscillations that are presented in this paper.

Alfven-wave particle interaction in finite-dimensional self-consistent field model

International Nuclear Information System (INIS)

Padhye, N.; Horton, W.

1998-01-01

A low-dimensional Hamiltonian model is derived for the acceleration of ions in finite amplitude Alfven waves in a finite pressure plasma sheet. The reduced low-dimensional wave-particle Hamiltonian is useful for describing the reaction of the accelerated ions on the wave amplitudes and phases through the self-consistent fields within the envelope approximation. As an example, the authors show for a single Alfven wave in the central plasma sheet of the Earth's geotail, modeled by the linear pinch geometry called the Harris sheet, the time variation of the wave amplitude during the acceleration of fast protons

Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003-2012)

Science.gov (United States)

Alexander, Patrick M.; Tedesco, Marco; Schlegel, Nicole-Jeanne; Luthcke, Scott B.; Fettweis, Xavier; Larour, Eric

2016-06-01

Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003-December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of -178.9 ± 4.4 and -239.4 ± 7.7 Gt yr-1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related

Analysis of 16 plasma vortex events in the geomagnetic tail

International Nuclear Information System (INIS)

Birn, J.; Hones, E.W. Jr.; Bame, S.J.; Russel, C.T.

1985-01-01

The analysis of 16 plasma vortex occurrences in the magnetotail plasma sheet of Hones et al. (1983) is extended. We used two- and three-dimensional plasma measurements and three-dimensional magnetic field measurements to study phase relations, energy propagation, and polarization properties. The results point toward an interpretation as a slow strongly damped MHD eigenmode which is generated by tailward traveling perturbations at the low-latitude interface between plasma sheet and magnetosheath

Determination of the Number of Fixture Locating Points for Sheet Metal By Grey Model

Directory of Open Access Journals (Sweden)

Yang Bo

2017-01-01

Full Text Available In the process of the traditional fixture design for sheet metal part based on the "N-2-1" locating principle, the number of fixture locating points is determined by trial and error or the experience of the designer. To that end, a new design method based on grey theory is proposed to determine the number of sheet metal fixture locating points in this paper. Firstly, the training sample set is generated by Latin hypercube sampling (LHS and finite element analysis (FEA. Secondly, the GM(1, 1 grey model is constructed based on the established training sample set to approximate the mapping relationship between the number of fixture locating points and the concerned sheet metal maximum deformation. Thirdly, the final number of fixture locating points for sheet metal can be inversely calculated under the allowable maximum deformation. Finally, a sheet metal case is conducted and the results indicate that the proposed approach is effective and efficient in determining the number of fixture locating points for sheet metal.

A feature of negative hydrogen ion production in the Uramoto-type sheet plasma

Energy Technology Data Exchange (ETDEWEB)

Jimbo, Kouichi [Kyoto Univ., Uji (Japan). Inst. of Atomic Energy

1997-02-01

It seems that negative hydrogen ions H{sup -} are formed directly from atomic hydrogens H. When the chamber was biased more negative against the anode potential at constant are power, forming a much deeper electrostatic well in the Uramoto-type sheet plasma negative ion source, more negative hydrogen ion currents were extracted. The chamber potential V{sub B} was biased down to -100V in the 150V discharge. The negative ion current J{sup -} was evaluated by the JAERI-probe measurement. J{sup -} increases linearly with the chamber current I{sub B}. The largest J{sup -} value was obtained at absolute value of |V{sub prob,f}|=15V and absolute value of |V{sub B}|=100V; the discharge was not operated for absolute value of |V{sub B}|>100V. We speculate the following collisional (three-body) electron attachment to H as a possible production process for H{sup -}; e+e+H{yields}e+H{sup -}. This process may explain the linear increase of J{sup -} with absolute value of |V{sub prob,f}|. (S.Y.)

A model for plasma evolution in Filipov type plasma focus facilities

International Nuclear Information System (INIS)

Siahpoush, V.; Sobhanian, S.; Tafreshi, M. A.; Lamehi, M.

2003-01-01

A model is presented in this paper for the evolution of plasma in Filipov type plasma focus facilities. With the help of this model, one can predict some of the main parameters of the produced plasma and obtain the optimized geometrical an physical properties (anode radius and length, gas pressure, capacitance, bank energy etc) for the primary design purposes. The results obtained by this model will be compared with the experimental data obtained from the 90 kJ plasma focus facility D ena

SEMIC: an efficient surface energy and mass balance model applied to the Greenland ice sheet

Directory of Open Access Journals (Sweden)

M. Krapp

2017-07-01

Full Text Available We present SEMIC, a Surface Energy and Mass balance model of Intermediate Complexity for snow- and ice-covered surfaces such as the Greenland ice sheet. SEMIC is fast enough for glacial cycle applications, making it a suitable replacement for simpler methods such as the positive degree day (PDD method often used in ice sheet modelling. Our model explicitly calculates the main processes involved in the surface energy and mass balance, while maintaining a simple interface and requiring minimal data input to drive it. In this novel approach, we parameterise diurnal temperature variations in order to more realistically capture the daily thaw–freeze cycles that characterise the ice sheet mass balance. We show how to derive optimal model parameters for SEMIC specifically to reproduce surface characteristics and day-to-day variations similar to the regional climate model MAR (Modèle Atmosphérique Régional, version 2 and its incorporated multilayer snowpack model SISVAT (Soil Ice Snow Vegetation Atmosphere Transfer. A validation test shows that SEMIC simulates future changes in surface temperature and surface mass balance in good agreement with the more sophisticated multilayer snowpack model SISVAT included in MAR. With this paper, we present a physically based surface model to the ice sheet modelling community that is general enough to be used with in situ observations, climate model, or reanalysis data, and that is at the same time computationally fast enough for long-term integrations, such as glacial cycles or future climate change scenarios.

An advanced material model for aluminum sheet forming at elevated temperatures

NARCIS (Netherlands)

Kurukuri, S.; Miroux, Alexis; Ghosh, Manojit; van den Boogaard, Antonius H.; Oñate, E.; Owen, D.R.J; Suárez, B.

2009-01-01

A physically-based material model according to Nes is used to simulate the warm forming of Al-Mg-Si sheet. This model incorporates the influence of the temperature and strain rate on the flow stress and on the hardening rate based on storage and dynamic recovery of dislocations. The effect of size

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

VARIATIONAL PRINCIPLES FOR NONLOCAL CONTINUUM MODEL OF ORTHOTROPIC GRAPHENE SHEETS EMBEDDED IN AN ELASTIC MEDIUM

Institute of Scientific and Technical Information of China (English)

Sarp Adali

2012-01-01

Equations governing the vibrations and buckling of multilayered orthotropic graphene sheets can be expressed as a system of n partial differential equations where n refers to the number of sheets.This description is based on the continuum model of the graphene sheets which can also take the small scale effects into account by employing a nonlocal theory.In the present article a variational principle is derived for the nonlocal elastic theory of rectangular graphene sheets embedded in an elastic medium and undergoing transverse vibrations.Moreover the graphene sheets are subject to biaxial compression.Rayleigh quotients are obtained for the frequencies of freely vibrating graphene sheets and for the buckling load. The influence of small scale effects on the frequencies and the buckling load can be observed qualiatively from the expressions of the Rayleigh quotients.Elastic medium is modeled as a combination of Winkler and Pasternak foundations acting on the top and bottom layers of the mutilayered nano-structure.Natural boundary conditions of the problem are derived using the variational principle formulated in the study.It is observed that free boundaries lead to coupled boundary conditions due to nonlocal theory used in the continuum formulation while the local (classical) elasticity theory leads to uncoupled boundary conditions.The mathematical methods used in the study involve calculus of variations and the semi-inverse method for deriving the variational integrals.

Integrated models for plasma/material interaction during loss of plasma confinement

International Nuclear Information System (INIS)

Hassanein, A.

1998-01-01

A comprehensive computer package, High Energy Interaction with General Heterogeneous Target Systems (HEIGHTS), has been developed to evaluate the damage incurred on plasma-facing materials during loss of plasma confinement. The HEIGHTS package consists of several integrated computer models that follow the start of a plasma disruption at the scrape-off layer (SOL) through the transport of the eroded debris and splashed target materials to nearby locations as a result of the energy deposited. The package includes new models to study turbulent plasma behavior in the SOL and predicts the plasma parameters and conditions at the divertor plate. Full two-dimensional comprehensive radiation magnetohydrodynamic models are coupled with target thermodynamics and liquid hydrodynamics to evaluate the integrated response of plasma-facing materials. A brief description of the HEIGHTS package and its capabilities are given in this work with emphasis on turbulent plasma behavior in the SOL during disruptions

Quasi-adiabatic particle acceleration in a magnetic field reversals and the formation of the plasma sheet boundary layer in the earth's magnetotail

International Nuclear Information System (INIS)

Zelenyi, L.M.; Vogin, D.V.; Buechner, J.

1989-01-01

Two types of regularity exist for the particle motion in the two-dimensional magnetic field reversals (MFR) with the strongly curves magnetic field lines - the usual adiabatic and another one which we called 'quasiadiabatic'. Here we consider the acceleration of MFR particles in stationary and homogeneous electric field induced by the motion of MFR through the ambient plasma (i.e. solar wind). Assuming that the time scale of acceleration is slow in comparison with the period of orbital motion we introduce the new longitudinal invariant I κ . This enables to describe the process of acceleration in a closed form and to obtain for the first time the laws governing the quasiadiabatic ion acceleration in the Earth's mangetotail. The similarities and differences in adiabatic and quasiadiabatic acceleration mechanisms are discussed. The obtained results give and important insights to the problem of the particle heating in hte Earth's magnetotail and to the formation of accelerated plasma streams along the edges of the plasma sheet. (author). 17 refs.; 7 figs

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.

Plasma disruption modeling and simulation

International Nuclear Information System (INIS)

Hassanein, A.

1994-01-01

Disruptions in tokamak reactors are considered a limiting factor to successful operation and reliable design. The behavior of plasma-facing components during a disruption is critical to the overall integrity of the reactor. Erosion of plasma facing-material (PFM) surfaces due to thermal energy dump during the disruption can severely limit the lifetime of these components and thus diminish the economic feasibility of the reactor. A comprehensive understanding of the interplay of various physical processes during a disruption is essential for determining component lifetime and potentially improving the performance of such components. There are three principal stages in modeling the behavior of PFM during a disruption. Initially, the incident plasma particles will deposit their energy directly on the PFM surface, heating it to a very high temperature where ablation occurs. Models for plasma-material interactions have been developed and used to predict material thermal evolution during the disruption. Within a few microseconds after the start of the disruption, enough material is vaporized to intercept most of the incoming plasma particles. Models for plasma-vapor interactions are necessary to predict vapor cloud expansion and hydrodynamics. Continuous heating of the vapor cloud above the material surface by the incident plasma particles will excite, ionize, and cause vapor atoms to emit thermal radiation. Accurate models for radiation transport in the vapor are essential for calculating the net radiated flux to the material surface which determines the final erosion thickness and consequently component lifetime. A comprehensive model that takes into account various stages of plasma-material interaction has been developed and used to predict erosion rates during reactor disruption, as well during induced disruption in laboratory experiments

On hot tenuous plasmas, fireballs, and boundary layers in the earth's magnetotail

International Nuclear Information System (INIS)

Frank, L.A.; Ackerson, K.L.; Lepping, R.P.

1976-01-01

Intensive correlative studies of magnetic fields and plasmas within the earth's magnetotail at geocentric radial distances of approx. 23--46 R/sub E/ during March--October 1974 revealed striking new features. The hot tenuous plasmas within the plasma sheet were found to be in a state of almost continual flow and were threaded with northward, or closed, geomagnetic field lines. Proton bulk speeds were in the range 50--500 km s -1 . The magnetic fields are directed northward. These observations demand a strong persistent source of magnetic flux and hot plasmas for the plasma sheet. No characteristic proton bulk flows were evident during crossings of the neutral sheet. Occasionally, the satellite encountered the region of acceleration in the magnetotail, the 'fireball.' This spectacular phenomenon exhibits strong jetting of plasmas in exces of 1000 km s -1 , proton temperatures of approx. 10 7 degreeK (kT approx. 1 keV), disordered magnetic fields, southward magnetic fields during tailward jetting of the plasmas. Earthward plasma flows within the fireball are threaded with closed geomagnetic field lines, and open magnetic field lines are embedded in the tailward jetting plasmas. The magnetosheathlike plasmas within the boundary layers which are positioned contiguous to the plasma sheet display striking evidences of plasma heating, great changes in bulk flow velocities and acceleration of energetic electrons with E > 45 keV. Persistent zones of southward magnetic fields are detected, which are often positioned adjacent to the plasma sheet and within the boundary layer plasmas. Rotations of the magnetic fields from southward to northward, or vice versa, in these boundary layers are accompanied by large enhancements of energetic electron intensities, substantial heating of the low-energy electron distributions, and strong perturbations of the proton velocity distribution functions

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

Chaotic jumps in the generalized first adiabatic invariant in current sheets

International Nuclear Information System (INIS)

Brittnacher, M.J.; Whipple, E.C.

1991-01-01

In attempting to develop a fluidlike model of plasma dynamics in a current sheet, kinetic effects due to chaotic non-adiabatic particle motion must be included in any realistic description. Using drift variables, derived by the Kruskal averaging procedure, to construct distribution functions may provide an approach in which to develop the fluid description. However, the drift motion is influenced by abrupt changes in the value of the generalized first adiabatic invariant J. In this letter, the authors indicate how the changes in J derived from separatrix crossing theory can be incorporated into the drift variable approach to generating distribution functions. In particular, the authors propose a method to determine distribution functions for an ensemble of particles following interactions with the tail current sheet by treating the interaction as a scattering problem characterized by changes in the invariant

An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

Science.gov (United States)

Pollard, D.

1978-01-01

The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

Light manipulation with flat and conformal inhomogeneous dispersive impedance sheets: an efficient FDTD modeling.

Science.gov (United States)

Jafar-Zanjani, Samad; Cheng, Jierong; Mosallaei, Hossein

2016-04-10

An efficient auxiliary differential equation method for incorporating 2D inhomogeneous dispersive impedance sheets in the finite-difference time-domain solver is presented. This unique proposed method can successfully solve optical problems of current interest involving 2D sheets. It eliminates the need for ultrafine meshing in the thickness direction, resulting in a significant reduction of computation time and memory requirements. We apply the method to characterize a novel broad-beam leaky-wave antenna created by cascading three sinusoidally modulated reactance surfaces and also to study the effect of curvature on the radiation characteristic of a conformal impedance sheet holographic antenna. Considerable improvement in the simulation time based on our technique in comparison with the traditional volumetric model is reported. Both applications are of great interest in the field of antennas and 2D sheets.

Electrical model of cold atmospheric plasma gun

Science.gov (United States)

Slutsker, Ya. Z.; Semenov, V. E.; Krasik, Ya. E.; Ryzhkov, M. A.; Felsteiner, J.; Binenbaum, Y.; Gil, Z.; Shtrichman, R.; Cohen, J. T.

2017-10-01

We present an analytical model of cold atmospheric plasma formed by a dielectric barrier discharge (DBD), which is based on the lumped and distributed elements of an equivalent electric circuit of this plasma. This model is applicable for a wide range of frequencies and amplitudes of the applied voltage pulses, no matter whether or not the generated plasma plume interacts with a target. The model allows quantitative estimation of the plasma plume length and the energy delivered to the plasma. Also, the results of this model can be used for the design of DBD guns which efficiently generate cold atmospheric plasma. A comparison of the results of the model with those obtained in experiments shows a fairly good agreement.

EVOLUTION OF RELATIVISTIC PLASMOID CHAINS IN A POYNTING-DOMINATED PLASMA

International Nuclear Information System (INIS)

Takamoto, Makoto

2013-01-01

In this paper, we investigate the evolution of plasmoid chains in a Poynting-dominated plasma. We model the relativistic current sheet with a cold background plasma using the relativistic resistive magnetohydrodynamic approximation and solve for its temporal evolution numerically. We perform various calculations using different magnetization parameters of the background plasma and different Lundquist numbers. Numerical results show that the initially induced plasmoid triggers a secondary tearing instability, which gradually fills the current sheet with plasmoids, as has also been observed in the non-relativistic case. We find that plasmoid chains greatly enhance the reconnection rate, which becomes independent of the Lundquist number when the Lundquist number exceeds a critical value. In addition, we show that the distribution of plasmoid size becomes a power law. Since magnetic reconnection is expected to play an important role in various high-energy astrophysical phenomena, our results can be used for explaining the physical mechanisms of those phenomena

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.

On the energy release rate in a turbulent current sheet on the Sun

International Nuclear Information System (INIS)

Bardakov, V.M.

1986-01-01

It is shown that turbulent current sheets on the Sun, realizing in the form of the Parker - Sweet flow, are in quasilinear regime of turbulence (or in the regime of instability threshold). The energy release rate in such sheets does not exceed 10 26 erg/s for typical plasma parameters in active regions

Modelling of boundary plasma in TOKES

International Nuclear Information System (INIS)

Igitkhanov, Yu.; Pestchanyi, S.; Landman, I.

2009-12-01

The main purpose of this report is the development of analytical and numerical transport models of tokamak plasmas, suitable for implementation into the integrated transport code TOKES [1-4]. Therefore this work is presented as an executive guideline for numerical implementation. The tokamak edge plasma in reactor configurations is expected to be rather thin outmost area with strong radial plasma gradients inside the separatrix and the area outside the separatrix, a scrape-off layer (SOL), with open magnetic field surfaces, terminated at the divertor plates. The region beyond the separatrix plays an important role because it serves as a shield, protecting the wall from the hot plasma and bulk plasma from the penetration of impurities and because it is mostly affected by transients. The transport model, proposed here, provides plasma density, temperature and velocity distribution along and across the magnetic field lines in bulk and the edge plasma region. It describes the dependence of temperature and density at the separatrix on the plasma conditions at the plate and the efficiency of the divertor operation in detached or attached conditions, depending on power and particle sources. The calculation gives eventually the power and particle loads on the divertor plates and side walls. During numerical implementation some simple models, allowing an analytical solution, were developed and used for comparison and checking. Some parts of the transport models were also benchmarked with experimental data from various tokamaks. In the frame of this work the following tasks have been completed: - The transport model with neoclassical and anomalous coefficients for bulk plasma and 2D transport model for the SOL have been prepared and implemented into the TOKES code. The coefficients are suitable for description of stationary plasma processes in the bulk and edge tokamak plasmas. - The model of pedestal formation at the plasma edge in H-mode operation was implemented in TOKES

Imaging a seizure model in zebrafish with structured illumination light sheet microscopy

Science.gov (United States)

Liu, Yang; Dale, Savannah; Ball, Rebecca; VanLeuven, Ariel J.; Baraban, Scott; Sornborger, Andrew; Lauderdale, James D.; Kner, Peter

2018-02-01

Zebrafish are a promising vertebrate model for elucidating how neural circuits generate behavior under normal and pathological conditions. The Baraban group first demonstrated that zebrafish larvae are valuable for investigating seizure events and can be used as a model for epilepsy in humans. Because of their small size and transparency, zebrafish embryos are ideal for imaging seizure activity using calcium indicators. Light-sheet microscopy is well suited to capturing neural activity in zebrafish because it is capable of optical sectioning, high frame rates, and low excitation intensities. We describe work in our lab to use light-sheet microscopy for high-speed long-time imaging of neural activity in wildtype and mutant zebrafish to better understand the connectivity and activity of inhibitory neural networks when GABAergic signaling is altered in vivo. We show that, with light-sheet microscopy, neural activity can be recorded at 23 frames per second in twocolors for over 10 minutes allowing us to capture rare seizure events in mutants. We have further implemented structured illumination to increase resolution and contrast in the vertical and axial directions during high-speed imaging at an effective frame rate of over 7 frames per second.

Measurement of OH free radical in magnetized sheet plasma crossed with vertical gas-flow by laser-induced fluorescence spectroscopy

International Nuclear Information System (INIS)

Tonegawa, Akira; Takatori, Masahiko; Kobayashi, Yukihiro; Kawamura, Kazutaka; Takayama, Kazuo

1997-01-01

We demonstrated the production of OH free radicals in an argon magnetized sheet plasma crossed with vertical gas-flow mixed with an oxygen gas O 2 and a hydrogen gas H 2 . The density and the rotational-vibrational temperature of the OH free radicals were measured by a laser-induced fluorescence (LIF). The density of OH free radicals increases with increasing O 2 gas-flow, while the high energy part of the electron-energy-distribution-function f e (E) above 8 eV decreases. These results suggest the high energy part of f e (E) is contributed to the dissociation of O 2 and the production of OH free radicals. (author)

Implementation of higher-order vertical finite elements in ISSM v4.13 for improved ice sheet flow modeling over paleoclimate timescales

Science.gov (United States)

Cuzzone, Joshua K.; Morlighem, Mathieu; Larour, Eric; Schlegel, Nicole; Seroussi, Helene

2018-05-01

Paleoclimate proxies are being used in conjunction with ice sheet modeling experiments to determine how the Greenland ice sheet responded to past changes, particularly during the last deglaciation. Although these comparisons have been a critical component in our understanding of the Greenland ice sheet sensitivity to past warming, they often rely on modeling experiments that favor minimizing computational expense over increased model physics. Over Paleoclimate timescales, simulating the thermal structure of the ice sheet has large implications on the modeled ice viscosity, which can feedback onto the basal sliding and ice flow. To accurately capture the thermal field, models often require a high number of vertical layers. This is not the case for the stress balance computation, however, where a high vertical resolution is not necessary. Consequently, since stress balance and thermal equations are generally performed on the same mesh, more time is spent on the stress balance computation than is otherwise necessary. For these reasons, running a higher-order ice sheet model (e.g., Blatter-Pattyn) over timescales equivalent to the paleoclimate record has not been possible without incurring a large computational expense. To mitigate this issue, we propose a method that can be implemented within ice sheet models, whereby the vertical interpolation along the z axis relies on higher-order polynomials, rather than the traditional linear interpolation. This method is tested within the Ice Sheet System Model (ISSM) using quadratic and cubic finite elements for the vertical interpolation on an idealized case and a realistic Greenland configuration. A transient experiment for the ice thickness evolution of a single-dome ice sheet demonstrates improved accuracy using the higher-order vertical interpolation compared to models using the linear vertical interpolation, despite having fewer degrees of freedom. This method is also shown to improve a model's ability to capture sharp

A balanced water layer concept for subglacial hydrology in large-scale ice sheet models

Directory of Open Access Journals (Sweden)

S. Goeller

2013-07-01

Full Text Available There is currently no doubt about the existence of a widespread hydrological network under the Antarctic Ice Sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux–basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

A balanced water layer concept for subglacial hydrology in large scale ice sheet models

Science.gov (United States)

Goeller, S.; Thoma, M.; Grosfeld, K.; Miller, H.

2012-12-01

There is currently no doubt about the existence of a wide-spread hydrological network under the Antarctic ice sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain inspired by the Gamburtsev Mountains, Antarctica. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux-basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out, that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

Synthesis of N-graphene using microwave plasma-based methods

Science.gov (United States)

Dias, Ana; Tatarova, Elena; Henriques, Julio; Dias, Francisco; Felizardo, Edgar; Abrashev, Miroslav; Bundaleski, Nenad; Cvelbar, Uros

2016-09-01

In this work a microwave atmospheric plasma driven by surface waves is used to produce free-standing graphene sheets (FSG). Carbonaceous precursors are injected into a microwave plasma environment, where decomposition processes take place. The transport of plasma generated gas-phase carbon atoms and molecules into colder zones of plasma reactor results in carbon nuclei formation. The main part of the solid carbon is gradually carried from the ``hot'' plasma zone into the outlet plasma stream where carbon nanostructures assemble and grow. Subsequently, the graphene sheets have been N-doped using a N2-Ar large-scale remote plasma treatment, which consists on placing the FSG on a substrate in a remote zone of the N2-Ar plasma. The samples were treated with different compositions of N2-Ar gas mixtures, while maintaining 1 mbar pressure in the chamber and a power applied of 600 W. The N-doped graphene sheets were characterized by scanning and by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Plasma characterization was also performed by optical emission spectroscopy. Work partially funded by Portuguese FCT - Fundacao para a Ciencia e a Tecnologia, under grant SFRH/BD/52413/2013 (PD-F APPLAuSE).

Sensitivity analysis for the coupling of a subglacial hydrology model with a 3D ice-sheet model.

Science.gov (United States)

Bertagna, L.; Perego, M.; Gunzburger, M.; Hoffman, M. J.; Price, S. F.

2017-12-01

When studying the movement of ice sheets, one of the most important factors that influence the velocity of the ice is the amount of friction against the bedrock. Usually, this is modeled by a friction coefficient that may depend on the bed geometry and other quantities, such as the temperature and/or water pressure at the ice-bedrock interface. These quantities are often assumed to be known (either by indirect measurements or by means of parameter estimation) and constant in time. Here, we present a 3D computational model for the simulation of the ice dynamics which incorporates a 2D model proposed by Hewitt (2011) for the subglacial water pressure. The hydrology model is fully coupled with the Blatter-Pattyn model for the ice sheet flow, as the subglacial water pressure appears in the expression for the ice friction coefficient, and the ice velocity appears as a source term in the hydrology model. We will present results on real geometries, and perform a sensitivity analysis with respect to the hydrology model parameters.

Jovian Plasma Modeling for Mission Design

Science.gov (United States)

Garrett, Henry B.; Kim, Wousik; Belland, Brent; Evans, Robin

2015-01-01

The purpose of this report is to address uncertainties in the plasma models at Jupiter responsible for surface charging and to update the jovian plasma models using the most recent data available. The updated plasma environment models were then used to evaluate two proposed Europa mission designs for spacecraft charging effects using the Nascap-2k code. The original Divine/Garrett jovian plasma model (or "DG1", T. N. Divine and H. B. Garrett, "Charged particle distributions in Jupiter's magnetosphere," J. Geophys. Res., vol. 88, pp. 6889-6903,1983) has not been updated in 30 years, and there are known errors in the model. As an example, the cold ion plasma temperatures between approx.5 and 10 Jupiter radii (Rj) were found by the experimenters who originally published the data to have been underestimated by approx.2 shortly after publication of the original DG1 model. As knowledge of the plasma environment is critical to any evaluation of the surface charging at Jupiter, the original DG1 model needed to be updated to correct for this and other changes in our interpretation of the data so that charging levels could beproperly estimated using the Nascap-2k charging code. As an additional task, the Nascap-2k spacecraft charging tool has been adapted to incorporate the so-called Kappa plasma distribution function--an important component of the plasma model necessary to compute the particle fluxes between approx.5 keV and 100 keV (at the outset of this study,Nascap-2k did not directly incorporate this common representation of the plasma thus limiting the accuracy of our charging estimates). The updating of the DG1 model and its integration into the Nascap-2k design tool means that charging concerns can now be more efficiently evaluated and mitigated. (We note that, given the subsequent decision by the Europa project to utilize solar arrays for its baseline design, surface charging effects have becomeeven more of an issue for its mission design). The modifications and

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

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

The transposition of the balance sheet to financial and functional balance sheet. Research and development

Directory of Open Access Journals (Sweden)

Liana GĂDĂU

2015-09-01

Full Text Available As the title suggests, through this paper we want to highlight the necessity of treating again the content and the form of the balance sheet in order to adapt it to a more efficient analysis, this way surpassing the informational valences of the classic balance sheet. The functional and the financial balance sheet will be taken into account. These models of balance sheet permit the complex analyses regarding the solvability or the bankruptcy risk of an enterprise to take place, and also other analyses, like the analysis of the structure and the financial/ functional equilibrium, the analysis of the company on operating cycles and their role in the functioning of the company. Through the particularities offered by each of these two models of balance sheet, we want to present the advantages of a superior informing. This content of this material is based on a vast investigation of the specialized literature.

Generation of sheet currents by high frequency fast MHD waves

Energy Technology Data Exchange (ETDEWEB)

Núñez, Manuel, E-mail: mnjmhd@am.uva.es

2016-07-01

The evolution of fast magnetosonic waves of high frequency propagating into an axisymmetric equilibrium plasma is studied. By using the methods of weakly nonlinear geometrical optics, it is shown that the perturbation travels in the equatorial plane while satisfying a transport equation which enables us to predict the time and location of formation of shock waves. For plasmas of large magnetic Prandtl number, this would result into the creation of sheet currents which may give rise to magnetic reconnection and destruction of the original equilibrium. - Highlights: • Regular solutions of quasilinear hyperbolic systems may evolve into shocks. • The shock location is found for high frequency fast MHD waves. • The result is applied to static axisymmetric equilibria. • The previous process may lead to the formation of sheet currents and destruction of the equilibrium.

Calculation of mass discharge of the Greenland ice sheet in the Earth System Model

Directory of Open Access Journals (Sweden)

O. O. Rybak

2016-01-01

Full Text Available Mass discharge calculation is a challenging task for the ice sheet modeling aimed at evaluation of their contribution to the global sea level rise during past interglacials, as well as one of the consequences of future climate change. In Greenland, ablation is the major source of fresh water runoff. It is approximately equal to the dynamical discharge (iceberg calving. Its share might have still larger during the past interglacials when the margins of the GrIS retreated inland. Refreezing of the melted water and its retention are two poorly known processes playing as a counterpart of melting and, thus, exerting influence on the run off. Interaction of ice sheets and climate is driven by energy and mass exchange processes and is complicated by numerous feed-backs. To study the complex of these processes, coupling of an ice sheet model and a climate model (i.e. models of the atmosphere and the ocean in one model is required, which is often called the Earth System Model (ESM. Formalization of processes of interaction between the ice sheets and climate within the ESM requires elaboration of special techniques to deal with dramatic differences in spatial and temporal variability scales within each of three ESM’s blocks. In this paper, we focus on the method of coupling of a Greenland ice sheet model (GrISM with the climate model INMCM having been developed in the Institute of Numerical Mathematics of Russian Academy of Sciences. Our coupling approach consists in applying of a special buffer model, which serves as an interface between GrISM and INMCM. A simple energy and water exchange model (EWBM-G allows realistic description of surface air temperature and precipitation fields adjusted to a relief of elevation of the GrIS surface. In a series of diagnostic numerical experiments with the present-day GrIS geometry and the modeled climate we studied sensitivity of the modeled surface mass balance and run off to the key EWBM-G parameters and compared

Ice-sheet modelling accelerated by graphics cards

Science.gov (United States)

Brædstrup, Christian Fredborg; Damsgaard, Anders; Egholm, David Lundbek

2014-11-01

Studies of glaciers and ice sheets have increased the demand for high performance numerical ice flow models over the past decades. When exploring the highly non-linear dynamics of fast flowing glaciers and ice streams, or when coupling multiple flow processes for ice, water, and sediment, researchers are often forced to use super-computing clusters. As an alternative to conventional high-performance computing hardware, the Graphical Processing Unit (GPU) is capable of massively parallel computing while retaining a compact design and low cost. In this study, we present a strategy for accelerating a higher-order ice flow model using a GPU. By applying the newest GPU hardware, we achieve up to 180× speedup compared to a similar but serial CPU implementation. Our results suggest that GPU acceleration is a competitive option for ice-flow modelling when compared to CPU-optimised algorithms parallelised by the OpenMP or Message Passing Interface (MPI) protocols.

Magnetic reconnection through the current sheets as the universal process for plasma dynamics in nonuniform magnetic fields

International Nuclear Information System (INIS)

Frank, A.G.; Bogdanov, S.Yu.; Burilina, V.B.; Kyrie, N.P.

1997-01-01

Laboratory experiments are reported, in which we studied the possibilities of the formation of current sheets (CS) in different magnetic configurations, as well as the magnetic reconnection phenomena. In 2D magnetic fields with null-lines the CS formation was shown to be a typical process in both linear and nonlinear regimes. The problem of CS formation is of a fundamental importance in the general case of 3D magnetic configurations. We have revealed experimentally, that the formation of CS occurs in the various 3D configurations, both containing magnetic null-points and without them. At the same time, the CS parameters essentially depend on the local characteristics of the configuration. We may conclude therefore, that the self-organization of CS represents the universal process for the plasma dynamics in the nonuniform magnetic fields. (author)

Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

Directory of Open Access Journals (Sweden)

Mahmoud Fathy

2016-07-01

Full Text Available Abstract Sorption of calcium ion from the hard underground water using novel oxidized graphene (GO sheets was studied in this paper. Physicochemical properties and microstructure of graphene sheets were investigated using Raman spectrometer, thermogravimetry analyzer, transmission electron microscope, scanning electron microscope. The kinetics adsorption of calcium on graphene oxide sheets was examined using Lagergren first and second orders. The results show that the Lagergren second-order was the best-fit model that suggests the conception process of calcium ion adsorption on the Go sheets. For isothermal studies, the Langmuir and Freundlich isotherm models were used at temperatures ranging between 283 and 313 K. Thermodynamic parameters resolved at 283, 298 and 313 K indicating that the GO adsorption was exothermic spontaneous process. Finally, the graphene sheets show high partiality toward calcium particles and it will be useful in softening and treatment of hard water.

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.

Modelling of aluminium sheet forming at elevated temperatures

NARCIS (Netherlands)

van den Boogaard, Antonius H.; Huetink, Han

2004-01-01

The formability of Al–Mg sheet can be improved considerably, by increasing the temperature. By heating the sheet in areas with large shear strains, but cooling it on places where the risk of necking is high, the limiting drawing ratio can be increased to values above 2.5. At elevated temperatures,

Implementation of higher-order vertical finite elements in ISSM v4.13 for improved ice sheet flow modeling over paleoclimate timescales

Directory of Open Access Journals (Sweden)

J. K. Cuzzone

2018-05-01

Full Text Available Paleoclimate proxies are being used in conjunction with ice sheet modeling experiments to determine how the Greenland ice sheet responded to past changes, particularly during the last deglaciation. Although these comparisons have been a critical component in our understanding of the Greenland ice sheet sensitivity to past warming, they often rely on modeling experiments that favor minimizing computational expense over increased model physics. Over Paleoclimate timescales, simulating the thermal structure of the ice sheet has large implications on the modeled ice viscosity, which can feedback onto the basal sliding and ice flow. To accurately capture the thermal field, models often require a high number of vertical layers. This is not the case for the stress balance computation, however, where a high vertical resolution is not necessary. Consequently, since stress balance and thermal equations are generally performed on the same mesh, more time is spent on the stress balance computation than is otherwise necessary. For these reasons, running a higher-order ice sheet model (e.g., Blatter-Pattyn over timescales equivalent to the paleoclimate record has not been possible without incurring a large computational expense. To mitigate this issue, we propose a method that can be implemented within ice sheet models, whereby the vertical interpolation along the z axis relies on higher-order polynomials, rather than the traditional linear interpolation. This method is tested within the Ice Sheet System Model (ISSM using quadratic and cubic finite elements for the vertical interpolation on an idealized case and a realistic Greenland configuration. A transient experiment for the ice thickness evolution of a single-dome ice sheet demonstrates improved accuracy using the higher-order vertical interpolation compared to models using the linear vertical interpolation, despite having fewer degrees of freedom. This method is also shown to improve a model's ability

Rotator cuff repair using cell sheets derived from human rotator cuff in a rat model.

Science.gov (United States)

Harada, Yoshifumi; Mifune, Yutaka; Inui, Atsuyuki; Sakata, Ryosuke; Muto, Tomoyuki; Takase, Fumiaki; Ueda, Yasuhiro; Kataoka, Takeshi; Kokubu, Takeshi; Kuroda, Ryosuke; Kurosaka, Masahiro

2017-02-01

To achieve biological regeneration of tendon-bone junctions, cell sheets of human rotator-cuff derived cells were used in a rat rotator cuff injury model. Human rotator-cuff derived cells were isolated, and cell sheets were made using temperature-responsive culture plates. Infraspinatus tendons in immunodeficient rats were resected bilaterally at the enthesis. In right shoulders, infraspinatus tendons were repaired by the transosseous method and covered with the cell sheet (sheet group), whereas the left infraspinatus tendons were repaired in the same way without the cell sheet (control group). Histological examinations (safranin-O and fast green staining, isolectin B4, type II collagen, and human-specific CD31) and mRNA expression (vascular endothelial growth factor; VEGF, type II collagen; Col2, and tenomodulin; TeM) were analyzed 4 weeks after surgery. Biomechanical tests were performed at 8 weeks. In the sheet group, proteoglycan at the enthesis with more type II collagen and isolectin B4 positive cells were seen compared with in the control group. Human specific CD31-positive cells were detected only in the sheet group. VEGF and Col2 gene expressions were higher and TeM gene expression was lower in the sheet group than in the control group. In mechanical testing, the sheet group showed a significantly higher ultimate failure load than the control group at 8 weeks. Our results indicated that the rotator-cuff derived cell sheet could promote cartilage regeneration and angiogenesis at the enthesis, with superior mechanical strength compared with the control. Treatment for rotator cuff injury using cell sheets could be a promising strategy for enthesis of tendon tissue engineering. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:289-296, 2017. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Integrated modelling of the edge plasma and plasma facing components

International Nuclear Information System (INIS)

Coster, D.P.; Bonnin, X.; Mutzke, A.; Schneider, R.; Warrier, M.

2007-01-01

Modelling of the interaction between the edge plasma and plasma facing components (PFCs) has tended to place more emphasis on either the plasma or the PFCs. Either the PFCs do not change with time and the plasma evolution is studied, or the plasma is assumed to remain static and the detailed interaction of the plasma and the PFCs are examined, with no back-reaction on the plasma taken into consideration. Recent changes to the edge simulation code, SOLPS, now allow for changes in both the plasma and the PFCs to be considered. This has been done by augmenting the code to track the time-development of the properties of plasma facing components (PFCs). Results of standard mixed-materials scenarios (base and redeposited C; Be) are presented

Contribution of energetic and heavy ions to the plasma pressure: The 27 September to 3 October 2002 storm

Science.gov (United States)

Kronberg, E. A.; Welling, D.; Kistler, L. M.; Mouikis, C.; Daly, P. W.; Grigorenko, E. E.; Klecker, B.; Dandouras, I.

2017-09-01

Magnetospheric plasma sheet ions drift toward the Earth and populate the ring current. The ring current plasma pressure distorts the terrestrial internal magnetic field at the surface, and this disturbance strongly affects the strength of a magnetic storm. The contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure in the near-Earth plasma sheet is not always considered. In this study, we evaluate the contribution of low-energy and energetic ions of different species to the total plasma pressure for the storm observed by the Cluster mission from 27 September until 3 October 2002. We show that the contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure is ≃76-98.6% in the ring current and ≃14-59% in the magnetotail. The main source of oxygen ions, responsible for ≃56% of the plasma pressure of the ring current, is located at distances earthward of XGSE ≃ -13.5 RE during the main phase of the storm. The contribution of the ring current particles agrees with the observed Dst index. We model the magnetic storm using the Space Weather Modeling Framework (SWMF). We assess the plasma pressure output in the ring current for two different ion outflow models in the SWMF through comparison with observations. Both models yield reasonable results. The model which produces the most heavy ions agrees best with the observations. However, the data suggest that there is still potential for refinement in the simulations.

Enhancement of the guide field during the current sheet formation in the three-dimensional magnetic configuration with an X line

International Nuclear Information System (INIS)

Frank, Anna; Bugrov, Sergey; Markov, Vladimir

2009-01-01

Results are presented from studies of the formation of current sheets during exciting a current aligned with the X line of the 3D magnetic configuration, in the CS-3D device. Enhancement of the guide field (parallel to the X line) was directly observed for the first time, on the basis of magnetic measurements. After the current sheet formation, the guide field inside the sheet exceeds its initial value, as well as the field outside. It is convincingly demonstrated that an enhancement of the guide field is due to its transportation by plasma flows on the early stage of the sheet formation. The in-plane plasma currents, which produce the excess guide field, are comparable to the total current along the X line that initiates the sheet itself.

Further determination of the characteristics of magnetospheric plasma vortices with Isee 1 and 2

International Nuclear Information System (INIS)

Hones, E.W. Jr.; Birn, J.; Bame, S.J.; Asbridge, J.R.; Paschmann, G.; Sckopke, N.; Haerendel, G.

1981-01-01

Further studies of the vortices in magnetospheric plasma flow with the Los Alamos Scientific Laboratory/Max-Planck-Institut (LASL/MPI) fast plasma experiment on Isee 1 and 2 have revealed that the pattern of vortical flow has a wavelength of approx.20-40 R/sub E/ and moves tailward through the magnetosphere at speed of several hundred kilometers per second. The tendency toward vorticity pervades the total breadth of the plasma sheet tailward of the dawn-dusk meridian. The sense of rotation of the plasma flow (as viewed from above the ecliptic plane) is clockwise in the morningside of the plasma sheet and counterclockwise in the eveningside. The sense of rotation in the morning and evening boundary layers is reversed from that in the contiguous regions of the plasma sheet. The occurrence of vortical flow is independent of the level of geomagnetic activity but is associated with long-period geomagnetic pulsations. We believe that the source of the vortical motion is a Kelvin-Helmholtz instability of the plasma boundary layer's inner surface (i.e., the interface between the plasma sheet and the boundary layer) that has recently been proposed by Sonnerup [1980

Electron conductivity model for dense plasmas

International Nuclear Information System (INIS)

Lee, Y.T.; More, R.M.

1984-01-01

An electron conductivity model for dense plasmas is described which gives a consistent and complete set of transport coefficients including not only electrical conductivity and thermal conductivity, but also thermoelectric power, and Hall, Nernst, Ettinghausen, and Leduc--Righi coefficients. The model is useful for simulating plasma experiments with strong magnetic fields. The coefficients apply over a wide range of plasma temperature and density and are expressed in a computationally simple form. Different formulas are used for the electron relaxation time in plasma, liquid, and solid phases. Comparisons with recent calculations and available experimental measurement show the model gives results which are sufficiently accurate for many practical applications

Spatial Evolution of Electrostatic Solitary Waves along Plasma Sheet Boundary Layer Adjacent to the Magnetic Reconnection X-Line

International Nuclear Information System (INIS)

Li Shi-You; Zhang Shi-Feng; Cai Hong; Deng Xiao-Hua

2012-01-01

Analysis on the spatial structure of electrostatic solitary waves (ESWs) along the plasma sheet boundary layer (PSBL) near an on-going magnetic reconnection X-line is performed. Most of the ESWs in the PSBL of R3 region near reconnection X-line are propagating earthwards away from the reconnecting site. An analysis of their spatial structure shows that, when ESWs propagate along the ambient field in the PSBL, outwards from the magnetic reconnection X-line, their amplitude will finally attenuate and thus the electron hole will fade away but their spatial scale remains unchanged. However, the spatial structure of propagating ESWs evolves from 1-D-like to 2-D-like though totally in a 1-D structure. (geophysics, astronomy, and astrophysics)

Multi-physics modeling of plasma-material interactions

Science.gov (United States)

Lasa, Ane; Green, David; Canik, John; Younkin, Timothy; Blondel, Sophie; Wirth, Brian; Drobny, Jon; Curreli, Davide

2017-10-01

Plasma-material interactions (PMI) can degrade both plasma and material properties. Often, PMI modeling focuses on either the plasma or surface. Here, we present an integrated model with high-fidelity codes coupled within the IPS framework that self-consistently addresses PMI. The model includes, calculation of spatially resolved influx of plasma and impurities to the surface and their implantation; surface erosion and roughening; evolution of implanted species and sub-surface composition; and transport of eroded particles across the plasma and their re-deposition. The model is applied and successfully compared to dedicated PISCES linear device experiments, where a tungsten (W) target was exposed to helium (He) plasma. The present contribution will focus on the analysis of W erosion, He retention and sub-surface gas bubble and surface composition evolution, under the different He plasma conditions across the surface that are calculated by impurity transport modeling. Impact of code coupling, reflected as interplay between surface erosion, fuel / impurity implantation and retention, and evolution of target composition, as well as sensitivity of these processes to plasma exposure conditions is also analyzed in detail. This work is supported by the US DOE under contract DE-AC05-00OR22725.

Model for resonant plasma probe.

Energy Technology Data Exchange (ETDEWEB)

Warne, Larry Kevin; Johnson, William Arthur; Hebner, Gregory Albert; Jorgenson, Roy E.; Coats, Rebecca Sue

2007-04-01

This report constructs simple circuit models for a hairpin shaped resonant plasma probe. Effects of the plasma sheath region surrounding the wires making up the probe are determined. Electromagnetic simulations of the probe are compared to the circuit model results. The perturbing effects of the disc cavity in which the probe operates are also found.

Modeling of Unsteady Sheet Cavitation on Marine Propeller Blades

Directory of Open Access Journals (Sweden)

Spyros A. Kinnas

2003-01-01

Full Text Available Unsteady sheet cavitation is very common on marine propulsor blades. The authors summarize a lifting-surface and a surface-panel model to solve for the unsteady cavitating flow around a propeller that is subject to nonaxisymmetric inflow. The time-dependent extent and thickness of the cavity were determined by using an iterative method. The cavity detachment was determined by applying the smooth detachment criterion in an iterative manner. A nonzeroradius developed vortex cavity model was utilized at the tip of the blade, and the trailing wake geometry was determined using a fully unsteady wake-alignment process. Comparisons of predictions by the two models and measurements from several experiments are given.

Research on Al-alloy sheet forming formability during warm/hot sheet hydroforming based on elliptical warm bulging test

Science.gov (United States)

Cai, Gaoshen; Wu, Chuanyu; Gao, Zepu; Lang, Lihui; Alexandrov, Sergei

2018-05-01

An elliptical warm/hot sheet bulging test under different temperatures and pressure rates was carried out to predict Al-alloy sheet forming limit during warm/hot sheet hydroforming. Using relevant formulas of ultimate strain to calculate and dispose experimental data, forming limit curves (FLCS) in tension-tension state of strain (TTSS) area are obtained. Combining with the basic experimental data obtained by uniaxial tensile test under the equivalent condition with bulging test, complete forming limit diagrams (FLDS) of Al-alloy are established. Using a quadratic polynomial curve fitting method, material constants of fitting function are calculated and a prediction model equation for sheet metal forming limit is established, by which the corresponding forming limit curves in TTSS area can be obtained. The bulging test and fitting results indicated that the sheet metal FLCS obtained were very accurate. Also, the model equation can be used to instruct warm/hot sheet bulging test.

Plasma Transport at the Magnetospheric Flank Boundary. Final report

International Nuclear Information System (INIS)

Otto, Antonius

2012-01-01

Progress is highlighted in these areas: 1. Model of magnetic reconnection induced by three-dimensional Kelvin Helmholtz (KH) modes at the magnetospheric flank boundary; 2. Quantitative evaluation of mass transport from the magnetosheath onto closed geomagnetic field for northward IMF; 3. Comparison of mass transfer by cusp reconnection and Flank Kelvin Helmholtz modes; 4. Entropy constraint and plasma transport in the magnetotail - a new mechanism for current sheet thinning; 5. Test particle model for mass transport onto closed geomagnetic field for northward IMF; 6. Influence of density asymmetry and magnetic shear on (a) the linear and nonlinear growth of 3D Kelvin Helmholtz (KH) modes, and (b) three-dimensional KH mediated mass transport; 7. Examination of entropy and plasma transport in the magnetotail; 8. Entropy change and plasma transport by KH mediated reconnection - mixing and heating of plasma; 9. Entropy and plasma transport in the magnetotail - tail reconnection; and, 10. Wave coupling at the magnetospheric boundary and generation of kinetic Alfven waves

A study of plasma focus

International Nuclear Information System (INIS)

Hirano, Katsumi; Majima, Kazuo

1976-01-01

The behavior of the plasma acceleration between electrodes, the phenomena due to the pinch effect at the top of the electrodes and the neutron emission mechanism were experimentally studied. The plasma focus device was a Mather type coaxial discharge device, and the instruments used for the present purpose were a Rogoski coil, an image converter camera, a scintillation detector and a silver foil activation counter. The results of the present experiment were as follows. Plasma focus was not definitely made under the same condition. When the focus was seen, a dip was observed in the discharge wave form, and the emissions of X-ray and neutrons were detected. The angular anisotropy of neutron emission was observed, and corresponds to a beam target model. The phenomena showing the occurrence of focus were seen, when the current sheet was produced at a delayed time after discharge, and arrived at the muzzle with large velocity. The relation between the number of emitted neutrons and the velocity of the current sheet was obtained, whereas no systematic relation exists between the number of emitted neutrons and the velocity of pinch. When the focus was not observed, no dip was seen in current wave form, and the emissions of X-ray and neutrons were not detected. The reason of no focus was considered. (Kato, T.)

The Effect of Solar Forcing on the Greenland Ice Sheet during the Holocene - A Model Study

Science.gov (United States)

Bügelmayer, Marianne; Roche, Didier; Renssen, Hans

2014-05-01

Abrupt climate changes did not only happen during glacials but also during interglacials such as the Holocene. Marine sediments provide evidence for the periodic occurrence of centennial-scale events with enhanced iceberg discharge during the past 11.000 years (Bond et al., 2001). These events were chronologically linked to reduced solar activity as reconstructed using cosmogenic isotopes (Bond et al., 2001), indicating that even an external forcing that is considered to be small, has a potential impact on climate due to several feedback mechanisms (Renssen et al., 2006). The interactions between climate and solar irradiance have been investigated using numerical models (e.g. Haigh, 1996; Renssen et al, 2006), but so far without dynamically computing the Greenland ice sheet and iceberg calving. Thus, the impact of solar variations on iceberg discharge and the underlying mechanisms have not been analysed so far. To analyse the effect of variations in solar activity on the Greenland ice sheet (GIS) and the iceberg calving, as well as possible feedback mechanisms that enhance the impact of the total solar irradiance, we use the earth system model of intermediate complexity (iLOVECLIM, Roche et al., 2013), coupled to the ice sheet/ice shelf model GRISLI (Ritz et al., 2001) and to a dynamic-thermodynamic iceberg module (Jongma et al., 2009, Bügelmayer et al., 2014) to perform transient experiments of the last 6000 years. The experiments are conducted applying reconstructed atmospheric greenhouse gas concentrations, volcanic aerosol loads, orbital parameters and variations in the total solar irradiance. We present the response of the coupled model to different solar irradiance scenarios to evaluate modeled GIS sensitivity to relatively modest variations in radiative forcing. Moreover, we investigate the dependence of the model results on the chosen model sensitivity. References: Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M. N., Showers, W., … Bonani, G

Anomalous resistivity due to kink modes in a thin current sheet

International Nuclear Information System (INIS)

Moritaka, Toseo; Horiuchi, Ritoku; Ohtani, Hiroaki

2007-01-01

The roles of microscopic plasma instabilities on the violation of the frozen-in constraint are investigated by examining the force balance equation based on explicit electromagnetic particle simulation for a thin current sheet. Wave-particle interactions associated with lower hybrid drift instability and drift kink instability (DKI) contribute to the wavy electric force term at the periphery of the current sheet and the wavy magnetic force term at the neutral sheet, respectively. In the linear growing phase of DKI, the wavy magnetic force term balances with the electric force term due to the dc electric field at the neutral sheet. It is concluded that the growth of DKI can create anomalous resistivity and result in the violation of the frozen-in constraint as well as the diffusion of current density

Development of a Prediction Model Based on RBF Neural Network for Sheet Metal Fixture Locating Layout Design and Optimization.

Science.gov (United States)

Wang, Zhongqi; Yang, Bo; Kang, Yonggang; Yang, Yuan

2016-01-01

Fixture plays an important part in constraining excessive sheet metal part deformation at machining, assembly, and measuring stages during the whole manufacturing process. However, it is still a difficult and nontrivial task to design and optimize sheet metal fixture locating layout at present because there is always no direct and explicit expression describing sheet metal fixture locating layout and responding deformation. To that end, an RBF neural network prediction model is proposed in this paper to assist design and optimization of sheet metal fixture locating layout. The RBF neural network model is constructed by training data set selected by uniform sampling and finite element simulation analysis. Finally, a case study is conducted to verify the proposed method.

Simulations of the Scandinavian ice sheet and its subsurface conditions

International Nuclear Information System (INIS)

Boulton, G.S.; Caban, P.; Hulton, N.

1999-12-01

An ice sheet model has been applied to an approximate flow line through the area of the Fennoscandian ice sheet. The modelled ice sheet fluctuations have been matched with stratigraphic evidence of Weichselian ice sheet fluctuation in order to simulate ice sheet attributes through time along the flowline. The model predicts extensive melting at the base of the ice sheet. This output has been used as an input to a simplified model of hydrogeology along the southern flank of the ice sheet so as to reconstruct patterns of subglacial groundwater flow. The output from the model is also used to estimate patterns of subglacial stress and strain. Results suggest that large scale subglacial groundwater catchment are formed which were quite different in extent from modern catchment; that fossil subglacial groundwaters should be found at sampling depths; and much fracturing in shallow bedrock in Sweden could be glacially generated

Simulations of the Scandinavian ice sheet and its subsurface conditions

Energy Technology Data Exchange (ETDEWEB)

Boulton, G.S.; Caban, P.; Hulton, N. [Edinburgh Univ. (United Kingdom). Dept of Geology and Geophysics

1999-12-01

An ice sheet model has been applied to an approximate flow line through the area of the Fennoscandian ice sheet. The modelled ice sheet fluctuations have been matched with stratigraphic evidence of Weichselian ice sheet fluctuation in order to simulate ice sheet attributes through time along the flowline. The model predicts extensive melting at the base of the ice sheet. This output has been used as an input to a simplified model of hydrogeology along the southern flank of the ice sheet so as to reconstruct patterns of subglacial groundwater flow. The output from the model is also used to estimate patterns of subglacial stress and strain. Results suggest that large scale subglacial groundwater catchment are formed which were quite differentin extent from modern catchment; that fossil subglacial groundwaters should be found at sampling depths; and much fracturing in shallow bedrock in Sweden could be glacially generated.

Current sheets in the Earth’s magnetosphere and in laboratory experiments: The magnetic field structure and the Hall effect

International Nuclear Information System (INIS)

Frank, A. G.; Artemyev, A. V.; Zelenyi, L. M.

2016-01-01

The main characteristics of current sheets (CSs) formed in laboratory experiments are compared with the results of satellite observations of CSs in the Earth’s magnetotail. We show that many significant features of the magnetic field structure and the distributions of plasma parameters in laboratory and magnetospheric CSs exhibit a qualitative similarity, despite the enormous differences of scales, absolute values of plasma parameters, magnetic fields, and currents. In addition to a qualitative comparison, we give a number of dimensionless parameters that demonstrate the possibility of laboratory modeling of the processes occurring in the magnetosphere.

Effect of Temperature and Sheet Temper on Isothermal Solidification Kinetics in Clad Aluminum Brazing Sheet

Science.gov (United States)

Benoit, Michael J.; Whitney, Mark A.; Wells, Mary A.; Winkler, Sooky

2016-09-01

Isothermal solidification (IS) is a phenomenon observed in clad aluminum brazing sheets, wherein the amount of liquid clad metal is reduced by penetration of the liquid clad into the core. The objective of the current investigation is to quantify the rate of IS through the use of a previously derived parameter, the Interface Rate Constant (IRC). The effect of peak temperature and initial sheet temper on IS kinetics were investigated. The results demonstrated that IS is due to the diffusion of silicon (Si) from the liquid clad layer into the solid core. Reduced amounts of liquid clad at long liquid duration times, a roughened sheet surface, and differences in resolidified clad layer morphology between sheet tempers were observed. Increased IS kinetics were predicted at higher temperatures by an IRC model as well as by experimentally determined IRC values; however, the magnitudes of these values are not in good agreement due to deficiencies in the model when applied to alloys. IS kinetics were found to be higher for sheets in the fully annealed condition when compared with work-hardened sheets, due to the influence of core grain boundaries providing high diffusivity pathways for Si diffusion, resulting in more rapid liquid clad penetration.

Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition

International Nuclear Information System (INIS)

Davami, Keivan; Jiang, Yijie; Cortes, John; Lin, Chen; Turner, Kevin T; Bargatin, Igor; Shaygan, Mehrdad

2016-01-01

We report the fabrication and characterization of graphene nanostructures with mechanical properties that are tuned by conformal deposition of alumina. Vertical graphene (VG) sheets, also called carbon nanowalls (CNWs), were grown on copper foil substrates using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and conformally coated with different thicknesses of alumina (Al_2O_3) using atomic layer deposition (ALD). Nanoindentation was used to characterize the mechanical properties of pristine and alumina-coated VG sheets. Results show a significant increase in the effective Young’s modulus of the VG sheets with increasing thickness of deposited alumina. Deposition of only a 5 nm thick alumina layer on the VG sheets nearly triples the effective Young’s modulus of the VG structures. Both energy absorption and strain recovery were lower in VG sheets coated with alumina than in pure VG sheets (for the same peak force). This may be attributed to the increase in bending stiffness of the VG sheets and the creation of connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed. (paper)

Modeling of Plasma-Induced Ignition and Combustion

National Research Council Canada - National Science Library

Boyd, Iain D; Keidar, Michael

2008-01-01

.... Phenomena that must be considered in an electrothermal chemical gun model include the initial capillary plasma properties, the plasma-air interaction, plasma sheath effects, and the plasma-propellant interaction itself...

Modelling the short-term response of the Greenland ice-sheet to global warming

NARCIS (Netherlands)

Wal, R.S.W. van de; Oerlemans, J.

1997-01-01

A two-dimensional vertically integrated ice flow model has been developed to test the importance of various processes and concepts used for the prediction of the contribution of the Greenland ice-sheet to sea-level rise over the next 350 y (short-term response). The mass balance is modelled by the

21st century changes in the surface mass balance of the Greenland ice sheet simulated with the global model CESM

Science.gov (United States)

Vizcaíno, M.; Lipscomb, W. H.; Van den Broeke, M.

2012-04-01

We present here the first projections of 21st century surface mass balance change of the Greenland ice sheet simulated with the Community Earth System Model (CESM). CESM is a fully-coupled, global climate model developed at many research centers and universities, primarily in the U.S. The model calculates the surface mass balance in the land component (the Community Land Model, CLM), at the same resolution as the atmosphere (1 degree), with an energy-balance scheme. The snow physics included in CLM for non-glaciated surfaces (SNiCAR model, Flanner and Zender, 2005) are used over the ice sheet. The surface mass balance is calculated for 10 elevation classes, and then downscaled to the grid of the ice sheet model (5 km in this case) via vertical linear interpolation between elevation classes combined with horizontal bilinear interpolation. The ice sheet topography is fixed at present-day values for the simulations presented here. The use of elevation classes reduces computational costs while giving results that reproduce well the mass balance gradients at the steep margins of the ice sheet. The simulated present-day surface mass balance agrees well with results from regional models. We focus on the regional model RACMO (Ettema et al. 2009) to compare the results on 20th-century surface mass balance evolution and two-dimensional patterns. The surface mass balance of the ice sheet under RCP8.5. forcing becomes negative in the last decades of the 21st century. The equilibrium line becomes ~500 m higher on average. Accumulation changes are positive in the accumulation zone. We examine changes in refreezing, accumulation, albedo, surface fluxes, and the timing of the melt season.

Development of a Prediction Model Based on RBF Neural Network for Sheet Metal Fixture Locating Layout Design and Optimization

Directory of Open Access Journals (Sweden)

Zhongqi Wang

2016-01-01

Full Text Available Fixture plays an important part in constraining excessive sheet metal part deformation at machining, assembly, and measuring stages during the whole manufacturing process. However, it is still a difficult and nontrivial task to design and optimize sheet metal fixture locating layout at present because there is always no direct and explicit expression describing sheet metal fixture locating layout and responding deformation. To that end, an RBF neural network prediction model is proposed in this paper to assist design and optimization of sheet metal fixture locating layout. The RBF neural network model is constructed by training data set selected by uniform sampling and finite element simulation analysis. Finally, a case study is conducted to verify the proposed method.

Impact of improved Greenland ice sheet surface representation in the NASA GISS ModelE2 GCM on simulated surface mass balance and regional climate

Science.gov (United States)

Alexander, P. M.; LeGrande, A. N.; Fischer, E.; Tedesco, M.; Kelley, M.; Schmidt, G. A.; Fettweis, X.

2017-12-01

Towards achieving coupled simulations between the NASA Goddard Institute for Space Studies (GISS) ModelE2 general circulation model (GCM) and ice sheet models (ISMs), improvements have been made to the representation of the ice sheet surface in ModelE2. These include a sub-grid-scale elevation class scheme, a multi-layer snow model, a time-variable surface albedo scheme, and adjustments to parameterization of sublimation/evaporation. These changes improve the spatial resolution and physical representation of the ice sheet surface such that the surface is represented at a level of detail closer to that of Regional Climate Models (RCMs). We assess the impact of these changes on simulated Greenland Ice Sheet (GrIS) surface mass balance (SMB). We also compare ModelE2 simulations in which winds have been nudged to match the European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis with simulations from the Modèle Atmosphérique Régionale (MAR) RCM forced by the same reanalysis. Adding surface elevation classes results in a much higher spatial resolution representation of the surface necessary for coupling with ISMs, but has a negligible impact on overall SMB. Implementing a variable surface albedo scheme increases melt by 100%, bringing it closer to melt simulated by MAR. Adjustments made to the representation of topography-influenced surface roughness length in ModelE2 reduce a positive bias in evaporation relative to MAR. We also examine the impact of changes to the GrIS surface on regional atmospheric and oceanic climate in coupled ocean-atmosphere simulations with ModelE2, finding a general warming of the Arctic due to a warmer GrIS, and a cooler North Atlantic in scenarios with doubled atmospheric CO2 relative to pre-industrial levels. The substantial influence of changes to the GrIS surface on the oceans and atmosphere highlight the importance of including these processes in the GCM, in view of potential feedbacks between the ice sheet

Modeling the astrophysical dynamical process with laser-plasmas

International Nuclear Information System (INIS)

Xia Jiangfan; Zhang Jun; Zhang Jie

2001-01-01

The use of the state-of-the-art laser facility makes it possible to create conditions of the same or similar to those in the astrophysical processes. The introduction of the astrophysics-relevant ideas in laser-plasma experiments is propitious to the understanding of the astrophysical phenomena. However, the great difference between the laser-produced plasmas and the astrophysical processes makes it awkward to model the latter by laser-plasma experiments. The author addresses the physical backgrounds for modeling the astrophysical plasmas by laser plasmas, connecting these two kinds of plasmas by scaling laws. Thus, allowing the creation of experimental test beds where observations and models can be quantitatively compared with laser-plasma data. Special attentions are paid on the possibilities of using home-made laser facilities to model astrophysical phenomena

Spatial and Temporal Extent of Ion Spectral Structures at the Inner Edge of the Plasma Sheet

Science.gov (United States)

Ferradas, C.; Reeves, G. D.; Zhang, J.; Spence, H. E.; Kistler, L. M.; Larsen, B.; Skoug, R. M.; Funsten, H. O.

2017-12-01

Several ion spectral structures are observed near the inner edge of the plasma sheet and constitute the signatures of ion drift and loss in the highly dynamic environment of the inner magnetosphere. Their study helps us understand ion access and losses in this region. Several studies have found that these structures vary with geomagnetic activity, local time, and ion species, but their spatial and temporal extent remain undetermined. We use data from the Helium, Oxygen, Proton, and Electron (HOPE) mass spectrometers onboard the Van Allen Probes to analyze the spectral structures in the energy range of 1- 50 keV. HOPE measurements on both Van Allen Probes spacecraft enable us to resolve the extent of these ion structures in space and time. As the structures respond to changes in the convection electric field on a variety of time scales, the lapping of the two spacecraft on time scales of minutes to hours helps determine their spatial and temporal evolution.

Buckling and stretching of thin viscous sheets

Science.gov (United States)

O'Kiely, Doireann; Breward, Chris; Griffiths, Ian; Howell, Peter; Lange, Ulrich

2016-11-01

Thin glass sheets are used in smartphone, battery and semiconductor technology, and may be manufactured by producing a relatively thick glass slab and subsequently redrawing it to a required thickness. The resulting sheets commonly possess undesired centerline ripples and thick edges. We present a mathematical model in which a viscous sheet undergoes redraw in the direction of gravity, and show that, in a sufficiently strong gravitational field, buckling is driven by compression in a region near the bottom of the sheet, and limited by viscous resistance to stretching of the sheet. We use asymptotic analysis in the thin-sheet, low-Reynolds-number limit to determine the centerline profile and growth rate of such a viscous sheet.

Long-term ice sheet-climate interactions under anthropogenic greenhouse forcing simulated with a complex Earth System Model

Energy Technology Data Exchange (ETDEWEB)

Vizcaino, Miren [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); University of California, Department of Geography, Berkeley, CA (United States); Mikolajewicz, Uwe; Maier-Reimer, Ernst [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Groeger, Matthias [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); IFM-GEOMAR, Kiel (Germany); Schurgers, Guy [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Lund University, Department of Physical Geography and Ecosystems Analysis, Lund (Sweden); Winguth, Arne M.E. [Center for Climatic Research, Department of Atmospheric and Oceanic Sciences, Madison (United States)

2008-11-15

Several multi-century and multi-millennia simulations have been performed with a complex Earth System Model (ESM) for different anthropogenic climate change scenarios in order to study the long-term evolution of sea level and the impact of ice sheet changes on the climate system. The core of the ESM is a coupled coarse-resolution Atmosphere-Ocean General Circulation Model (AOGCM). Ocean biogeochemistry, land vegetation and ice sheets are included as components of the ESM. The Greenland Ice Sheet (GrIS) decays in all simulations, while the Antarctic ice sheet contributes negatively to sea level rise, due to enhanced storage of water caused by larger snowfall rates. Freshwater flux increases from Greenland are one order of magnitude smaller than total freshwater flux increases into the North Atlantic basin (the sum of the contribution from changes in precipitation, evaporation, run-off and Greenland meltwater) and do not play an important role in changes in the strength of the North Atlantic Meridional Overturning Circulation (NAMOC). The regional climate change associated with weakening/collapse of the NAMOC drastically reduces the decay rate of the GrIS. The dynamical changes due to GrIS topography modification driven by mass balance changes act first as a negative feedback for the decay of the ice sheet, but accelerate the decay at a later stage. The increase of surface temperature due to reduced topographic heights causes a strong acceleration of the decay of the ice sheet in the long term. Other feedbacks between ice sheet and atmosphere are not important for the mass balance of the GrIS until it is reduced to 3/4 of the original size. From then, the reduction in the albedo of Greenland strongly accelerates the decay of the ice sheet. (orig.)