Magnetosphere

Abstract The most important aspect of job scheduling is the ability to create a multi-tasking environment. A single user cannot keep either the CPU or the I/O devices busy at all times. Multiprogramming increases CPU utilization by organizing jobs so that the CPU always ...

Over the last decade, Diversified Technologies Inc. (DTI) has designed and built solid-state pulse modulators to support high power radar transmitters employing large klystrons and TWT amplifiers. The reliability and performance of these modulators indicate that they can deliver similar benefits to a wide range of high power magnetron oscillators. DTI's modulators use standard circuit components and topologies in a specialized form adapted to insure highly stable operation of magnetron-based radar transmitters. This paper describes several approaches to the design of the modulator circuits, and provides examples of recent fielded transmitters, ranging from low power magnetron systems to turn-key, high power transmitters with multiple TWTs.

Plasmas are ubiquitous in nature, surround our local geospace environment, and permeate the universe. Plasma phenomena in space give rise to energetic particles, the aurora, solar flares and coronal mass ejections, as well as many energetic phenomena in interstellar space. Although plasmas can be studied in laboratory settings, it is often difficult, if not impossible, to replicate the conditions (density, temperature, magnetic and electric fields, etc.) of space. Single-point space missions too numerous to list have described many properties of near-Earth and heliospheric plasmas as measured both in situ and remotely (see http://www.nasa.gov/missions/#.U1mcVmeweRY for a list of NASA-related missions). However, a full description of our plasma environment requires three-dimensional spatial measurements. Cluster is the first, and until data begin flowing from the Magnetospheric Multiscale Mission (MMS), the only mission designed to describe the three-dimensional spatial structure of plasma phenomena in geospace. In this paper, we concentrate on some of the many plasma phenomena that have been studied using data from Cluster. To date, there have been more than 2000 refereed papers published using Cluster data but in this paper we will, of necessity, refer to only a small fraction of the published work. We have focused on a few basic plasma phenomena, but, for example, have not dealt with most of the vast body of work describing dynamical phenomena in Earth's magnetosphere, including the dynamics of current sheets in Earth's magnetotail and the morphology of the dayside high latitude cusp. Several review articles and special publications are available that describe aspects of that research in detail and interested readers are referred to them (see for example, Escoubet et al.

The focus of this thesis is to identify the role and dynamics of different current systems for storm-time activity at mid-latitude ground level and their relation with other solar, interplanetary and geomagnetic  parameters, in the 2007-2016 time interval. For this purpose, I compared the synthetic series of six magnetospheric current systems computed with the data-based semi-empirical model of Tsyganenko and Sitnov 2005 (TS05), with the measurements of four mid-latitude geomagnetic stations at very near geomagnetic latitudes, but well apart in longitude (Coimbra (COI), Portugal; Panagyurishte (PAG), Bulgary; Novosibirsk (NVS), Russia; Boulder (BOU), USA), and with other ground and satellite-based solar, interplanetary and geomagnetic parameters obtained from the OMNI/NASA database. An evaluation of TS05 model is presented, in order to determine the model ability to reproduce both the total  magnetospheric transient signal and to explain this signal through the contribution of each TS05 magnetospheric current system at ground level, comparing them with hourly data of the four geomagnetic stations selected.

It was found that TS05 model is a useful tool to explain ground-based North-South (or X) component of geomagnetic activity at mid-latitudes, in terms of main current sources. It was verified that TS05 is efficient to reproduce the X component of terrestrial magnetospheric field at mid-latitudes during high geomagnetic activity time, with correlations r ≥ 0.7 in ∼50% of compared data, presenting a lower efficiency during calm time, with correlations r ≥ 0.7 only in ∼30% of data compared. Results
are less favourable for the East-West (or Y ) component, probably due to the fact that TS05 model closes Birkeland (or field-aligned, FAC) currents through the Earth’s centre instead of through the ionosphere. It was found that currents that contribute most to the X component during geomagnetic active periods are the cross-tail (TAIL), the symmetric ring (SRC) and the partial ring (PRC) currents. The currents that contribute
most to Y component are FAC and PRC currents. For all stations the highest correlations among observations and TS05 simulations are obtained for stronger geomagnetic activity. The results in this study indicate that the implementation of TAIL and SRC currents in TS05 model is more successful than that for the FAC current.
The quiet daily (QD) variation has a main contribution from ionospheric currents, which are not considered in TS05 model. For observatories at Northern Hemisphere’s mid-latitudes that are localized close to the ionospheric current vortex center (COI and PAG), it was possible to separate efficiently the QD ionospheric contribution using Principal Component Analysis (PCA). For the other two stations (NVS and BOU) it
was found a relatively higher contribution of magnetospheric signal in the QD variation. After removing the QD variation from data, COI and PAG are better correlated with TS05 series than BOU and NVS. However, BOU and NVS are better correlated with geomagnetic indices Dst (disturbance storm-time) and RC (ring current), with RC showing a slightly less good performance with respect to Dst. Correlations between 33 solar, interplanetary magnetic field (IMF) and geomagnetic activity proxies were analysed for the 2009-2016 time interval. It was found that series of 27-day averages (Bartels’ rotation) give higher correlations than daily or annual series. Parameters that show higher cross-correlations among different groups are the Sun’s northern and southern facular areas (FA-N and FA-S), two geomagnetic indices derived from TS05 model (T-SRC and T-PRC), the total IMF intensity (B), the percentage of IMF southward component (BZS GSM) and the interplanetary coupling Newell’s function. We propose that these parameters are the best candidates to use if we want to relate meaningfully the solar surface events to geomagnetic activity felt on the Earth’s surface. Two new proxies were tested, 1) TI-indices, calculated from the X TS05-derived series of TAIL, SRC, PRC and FAC contributions for the four observatories and 2) BZS GSM, calculated as the daily percentage of IMF southward component along the GSM Z-axis.

Helio-magnetic asymmetries were calculated for the 33 parameters, as the difference between their averaged values in the towards and away magnetic sectors of the interplanetary medium. Improvement in 27-day correlations with respect to annual correlations is the result of an annual oscillation in this asymmetry, which is present in most studied proxies and is probably due to the Russell-McPherron effect. Due to this effect, BZS GSM and BZ GSM have a well-defined annual modulation, and geomagnetic activity indices (GAI) also have annual oscillation and good correlations with BZS GSM and BZ GSM. TI-indices have annual oscillation at declining phase of the cycle, but insignificant oscillation near the minimum. Major percentage of towards days in negative polarity epoch and of away days in positive polarity epoch means that the Earth has been mostly at the northern magnetic hemisphere during the solar cycle 24.

In conclusion, the main part of this Ph.D. thesis was dedicated to the design and implementation of a statistical approach that was applied to test the performance of the TS05 model in explaining geomagnetic activity observed at Earth’s Northern Hemisphere mid-latitudes. This approach can be applied to test any other magnetospheric model. At the end of this work, a prospective study was made using different proxies that describe the Sun surface, the interplanetary medium and geomagnetic activity, to identify those parameters that should be more meaningfully used to relate the Sun to the geomagnetic activity observed on Earth.

Keywords: Sun-Earth interaction, solar activity, solar and geomagnetic data, space weather.

1] We present observations of periodic magnetospheric substorms and corresponding ionospheric disturbances. Since the periodic substorms occur during a stable interplanetary magnetic field, we are able to identify which ionospheric signatures are caused solely by substorms. We find that the low-latitude ionospheric electric field perturbation after substorm onsets is eastward on the dayside and westward on the nightside and that the ground magnetometer northward (H) deviations at middle and low latitudes show an increase (a positive bay) after each substorm onset, no matter whether the magnetometers are located on the dayside or on the nightside. The nightside magnetometer H deviations are closely correlated with the inner magnetospheric magnetic field B z component during the dipolarization process. The Dst index shows a significant increase of 20-40 nT after each substorm onset. We propose that the increase in the magnetometer H field and Dst index in response to substorm onsets is related to the field dipolarization. In this scenario the nightside magnetosphere earthward of the near-Earth neutral line is highly compressed during the dipolarization, and the magnetic flux density within the inner magnetosphere is greatly enhanced, resulting in an increase in the ground magnetometer H component and in Dst.

Though the works on geomagnetic storms have many research articles but still the mechanism through which magnetosphere is coupled with low latitude ionosphere during the density pulse events is not comprehensively understood. So the topic is still challenging the present study is of a sudden commencement storm on July 2006 and November 2007 , both the years considered to be in low solar active period was taken into consideration. A detailed comparison of the solar wind parameters with reversal enhancements of IMF Bz and Dst is discussed. Index Terms— Geomagnetic storm, IMF Bz, low solar active period, solar wind parameters and ionospheric parameters.

The dayside magnetosphere contains a region where the field strength has a local maximum. This region, located just inside the magnetopause around the equatorial plane and between the cusps, has a width of 2-3Re. When a drift shell with a sufficiently small mirror field intersects this region, it will bifurcate into two branches near local noon, each branch going across one cusp and joining together at the symmetrical local time. The particle then drifts around the Earth over a single branch until it comes back to local noon.

In the neighborhood of the bifurcation points, the bounce period tends to infinity, and thus the adiabaticity of the bounce motion is broken there, but not elsewhere. This breaking causes a small but finite jump ∆I in the second invariant. Repeated crossings lead to a random walk in second invariant space, and thus to radial diffusion.
We use theory and simulations to determine the magnitude of ∆I. Our study is limited to static magnetic fields, but it can be extended to general fields.

Our results indicate that ∆I is sensitively dependent on bounce phase at bifurcation, and it can grow significantly for some initial conditions. When the initial second invariant I_0 is much larger than the mirror gyroradius ρ_m , we use separatrix crossing
theory. The average of ∆I over bounce phases is zero, and the rms ∆I is of the order of ρ_m . When I_0 is comparable to ρ_m , the equation of bounce motion is approximated as the second Painlevé equation, whose asymptotic solutions are used to determine ∆I. In this limit, the rms ∆I is still O(ρ_m); however, the average is nonzero, in the form exp(−I 0 /ρ m ).

Drift-shell bifurcation leads to significant radial diffusion. For MeV electrons, the diffusion coefficient can be several R_e per day. Also, because of bifurcation, some quasitrapped particles can remain in the magnetosphere for a finite number of drifts before they leave permanently. Such behavior leads to metastable particles, a new
kind of trapping. These results can be useful for radiation-belt modeling efforts.

The progress in the study of ULF waves in the Earth's magnetosphere made between 1987 and 1989 is reviewed. Topics addressed in the review include satellite and ground-based observations of ULF wave spatial structure, ULF wave resonators and waveguides in the magnetosphere and ionosphere, the ionosphere as a 'passive screen' and an 'active source' for MHD disturbances, 'non-linear language' for ULF waves, and their applications.

1] We use a nonstationary generalization of the higher-order structure function technique to investigate statistical properties of the magnetic field fluctuations recorded by MESSENGER spacecraft during its first flyby (01/14/2008) through the near-Mercury space environment, with the emphasis on key boundary regions participating in the solar windmagnetosphere interaction. Our analysis shows, for the first time, that kinetic-scale fluctuations play a significant role in the Mercury's magnetosphere up to the largest resolvable timescale (∼20 s) imposed by the signal nonstationarity, suggesting that turbulence at this planet is largely controlled by finite Larmor radius effects. In particular, we report the presence of a highly turbulent and extended foreshock system filled with packets of ULF oscillations, broad-band intermittent fluctuations in the magnetosheath, ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail, and kinetic-scale fluctuations in the inner current sheet encountered at the outbound (dawn-side) magnetopause. Overall, our measurements indicate that the Hermean magnetosphere, as well as the surrounding region, are strongly affected by non-MHD effects introduced by finite sizes of cyclotron orbits of the constituting ion species. Physical mechanisms of these effects and their potentially critical impact on the structure and dynamics of Mercury's magnetic field remain to be understood.

1] We perform a statistical study of the decay times for the recovery phase of the 300 most intense magnetic storms that occurred from 1 January 1957 to 31 December 1998. The Dst index in the decaying stage has been fitted by an exponential function, and a very good correlation has been obtained for most of the storms. Statistically representative values for the decay time (t) are obtained by averaging the most reliable t values, which resulted from applying a least squares method to the Dst index time series during every recovery phase. The mean value of t turned out to be $14 ± 4 hours. We have also found that for very intense storms (Dst min < À250 nT) the values of t tend to decrease as the intensity of the storm increases.

The multipole magnetization of the permanent magnet components in an electrical magnet machine is a key stage in its manufacture, and can exert a considerable influence on the final machine performance. Accurate design of the magnetizing fixture is essential if the properties of the permanent magnet material are to be fully exploited. A comprehensive design methodology i s presented for radial-field multipole impulse magnetizing fixtures, which embraces all the various facets from the initial specification to the modeling of the performance of the machine into which the magnet is ultimately incorporated. The various techniques used in the design synthesis are validated by means of a case study on a 4-pole brushless permanent magnet machine, which also serves to highlight the utility of an integrated approach to the design of the magnetizing fixture and the machine. I. INTRODUCTION HE various grades of Magnequench isotropic NdFeB

VERY MUCH A PRECURSOR TO THE 3 DAYS OF DARKNESS EVENT – LETTING US KNOW THAT IT IS A GOOD THING THAT WE DESIGNED FOR THIS TIME.  A CLEANSING PULSE – THE EVENT IS MEANT TO CLEAR ALL OF THE PLASTIC OUT OF THE OCEANS, RETURN THE ENTIRE PLANET TO PRISTINE, RETURN ALL PEOPLE TO THEIR 20 YEAR OLD PRISTINE BODIES AND CAUSE MOST FEARFUL BEINGS TO PERISH OF THEIR OWN ACCORD, WHICH HAPPENS AROUND THE ORGANMIC BUBBLE NOW.

It has generally been assumed in the past that the plasmapause is a preferred region for the generation and propagation of electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere. One assumption invoked the overlap of the expanding cold plasmapause with the inner edge of the hot ring current during storm recovery to provide favourable conditions for EMIC instability. The plasmapause was also expected to provide a convenient gradient for guiding the waves from equatorial sources to higher latitudes. The paper commences from a historic perspective and reviews the development of the ideas from the 1960s that relate the source of EMIC waves to the plasmapause. CRRES spacecraft observations of EMIC wave events over L = 3:5-8 and associated plasmapause locations indicate that the plasmapause is a region of wave generation and propagation, with signiÿcant wave power seen in the plasmatrough, but is not necessarily the preferred region. Other results show that wave occurrence predominates in the afternoon and increases with radial distance and a He + slot is seen in the data. These agree with earlier AMPTE-CCE results from Anderson et al. (J. Geophys. Res. 97 (1992) 3075, 3089). New results from CRRES show all wave polarisations (left-hand, linear, and right-hand) are seen within 8 • of the equator whereas linear predominates over 20-30 • latitude. Waves are observed in background plasma densities of 4-300 cm −3 . Wave frequencies above the He + cyclotron frequency are concentrated outside the plasmapause in lower density regions of 2-30 cm −3 .

Previous studies suggested that seismoelectromagnetic signals were generated during earthquake preparation phase. While the anomalous signals in Japan, Russia, and Greece are rather clear; observational results in some regions including America and Indonesian have not conclusive yet, whether the signals are really exist or normal magnetic storm phenomena only. Some problems in measuring instrumentations might also result in anomalous signals. This paper reviews further possibilities by processing a nearly continuous geomagnetic data of INTERMAGNET observatories in three regions (Japan, America, and Indonesia) during the last twelve years (2000-2011). MATLAB ® with digital signal processing and statistical toolboxes is used for night-time data filtering, thereafter processing methods of differentiation and moving average are applied. To get relationship between these anomalous signals and natural processes, tectonic settings of the regions and global geomagnetic conditions are also considered in the analysis.

Abstract Unshielded magnetic tunnel junction (MTJ) sensors stabilized by insulating hard magnetic tails have been fabricated. Testing results showed that the control of oxidation condition was important for obtaining MTJ with low junction resistances and high TMR ...

Some properties of nonlinear dust acoustic waves in magnetized dusty plasma with variable charges by reductive perturbation technique have been studied. The effect of adiabatic dust charge variations under the assumption that the ratio of dust charging time to the dust hydrodynamical time is very small, and the nonadiabatic dust charges variations under the assumption that the same ratio is small but finite, are also incorporated. It is seen that the magnetic field and the dust charge variations significantly modify the wave amplitude. It is also seen that in case of adiabatic charge variations, the Korteweg-de Vries (KdV) equation governs the nonlinear dust acoustic wave, whereas in case of nonadiabatic dust charge variations, the wave is governed by the KdV Burger equation. Nonadiabaticity generated anomalous dissipative effect causes generation of the dust acoustic shock wave. Numerical integration of KdV Burger equation shows that the dust acoustic wave admits oscillatory (dispersion dominant) or monotone (dissipation dominant) shock solutions depending on the magnitude of the coefficient of the Burger term. Index Terms-Charge fluctuations, magnetized dusty plasma, nonlinear dust acoustic waves.

A method for determining many new magnetohydrodynamic shock normal expressions is described that uses both magnetic-field and plasma-flow parameters. These shock normal expressions are useful as a check on the usual magnetic coplanarity expression or for cases in which the most reliable data are mixed. For high Alfv,•n Mach numbers, the exact results are well approximated by the simple velocity coplanarity formula. This is illustrated by calculating shock normals for the 1965 bow shock crossing of Pioneer 6. We present a generalization of the method of calculation using magnetic coplanarity for the unit vector normal to a magnetohydrodynamic shock wave [Colburn and Soneft, 1966; Spreiter et al., 1966]. Two approximate methods for shocks in plasmas with high Alfv•n Mach numbers have also been used. These assumed either

Episodes of southward (Bz<0) interplanetary magnetic field (IMF) which lead to disturbed geomagnetic conditions are associated either with coronal mass ejections (CMEs) and possess long and continuous negative IMF Bz excursions, or with high speed solar wind streams (HSS) whose geoeffectiveness is due to IMF Bz profiles fluctuating about zero with various amplitudes and duration. We simulate ring current evolution during a HSS-driven storm that occurred during 24-26 October 2002 and compare its dynamics with a CME-driven storm of similar strength during 22-23 April 2001. We use our kinetic ring current-atmosphere interactions model (RAM), and investigate the mechanisms responsible for trapping particles and for causing their loss. Ring current evolution depends on the interplay of time-dependent inflow of plasma from the magnetotail, particle acceleration and loss (mainly due to charge exchange) along adiabatic drift paths, and outflow of plasma from the dayside magnetopause; all of these processes are incorporated in our model. We compare results from simulations using a newly developed, Cluster data based, University of New Hampshire inner magnetospheric electric field (UNH-IMEF) convection model with simulations using a Volland-Stern (V-S) type convection model. We find that, first, periods of increased magnetospheric convection coinciding with enhancements of plasma sheet density are needed for strong ring current buildup. Second, during the HSS-driven storm the convection potential from UNH-IMEF model is highly variable and causes sporadic shallow injections resulting in a weak ring current. The long period of enhanced convection during the CME-driven storm causes a continuous ion injection penetrating to lower L shells and stronger ring current buildup. V-S model predicts larger ring current injection during both storms. Third, the RAM driven by either convection model underestimates the total ring current energy during the recovery phase of the HSS storm, thus indicating that additional injections from substorm-induced electric fields and/or radial diffusion are needed to better reproduce its several-day long geomagnetic activity.

1] Studies using all-sky imagers have revealed the presence of various ionospheric irregularities in the nighttime midlatitude F region. The most prevalent and well known of these are the medium-scale traveling ionospheric disturbances (MSTIDs) that usually occur when the geomagnetic activity is low and midlatitude spread F plumes that are often observed when the geomagnetic activity is high. The inverse and direct relations between geomagnetic activity and the occurrence rate of MSTIDs and midlatitude plumes, respectively, have been observed by several studies using different instruments; however, most of them focus on MSTIDs only and use only Kp to characterize geomagnetic activity. In order to understand the underlying causes of these two relations and to distinguish between MSTIDs and plumes, it is illuminating to better characterize the occurrence of MSTIDs and plumes using multiple magnetospheric state parameters. Here we statistically compare multiple geomagnetic driver and response parameters (such as Kp, AE, Dst, and solar wind parameters) with the occurrence rates of nighttime MSTIDs and plumes observed using an all-sky imager at Arecibo Observatory (AO) between 2003 and 2008. We also present seasonal and annual variations of MSTIDs and plumes at AO. The results not only allow us to better distinguish MSTIDs and plumes, but also to shed further light on the generation mechanism and electrodynamics of these two different phenomena occurring at nighttime in the midlatitude F region.

Thumbnail link to Figure 1 Figure 1.(a) RPI plasmagram showing signal amplitude (dBnV/m) as a function of frequency and time delay expressed in terms of virtual range in units of Earth radius (RE). The local plasma and gyro resonances appear as vertical line segments, and ...

... Twisted magnet wire transmission lines using the wire size range from 4 to 44 can be realized with characteristic impedances ranging from 10 to 85 R. More practical examples would be a 50-a line made with a pair of number 40 wires and a 25,a line made with a pair of number ...

In order to isolate the effects of IrMn film grain size, texture and roughness on the temperature dependence of exchange bias field ( ) different multilayers of the configuration UL/CoFe4/IrMn5/Ta3nm (top) and UL/IrMn5/CoFe4/Ta3nm (bottom) were deposited. Underlayers (UL) used were Cu, Ru and [Cu1/Ru1nm]n with thickness varying between 5-100 nm. The vs. temperature curve shows a change in shape from a convex type to concave type with increasing the grain size. A qualitative explanation is given based on a thermal fluctuation after effect model.

The newly discovered phenomenon of stressd e p m a t u r a t i o n magnetostriction, observed in lowmagnetostrictive metallic glasses, is discussed. Its influence on the measurements of saturation magnetostriction is seen when the experiments are carried out by means of indirect methods based on the Villari effect. A procedure is proposed by which reliable results of measurements can be obtained.

This work attempts to fill a gap in comparative studies of upstream-generated Pc3-4 waves and broad band ULF noise observed at cusp latitudes. We performed a statistical analysis of the spectral properties of three years of cusp-latitude ground magnetometer data, finding that the average daytime Pc3-4 spectra are characterized by two principal components: an upstream-related band-limited enhancement ('signal') and a power-law background ('noise') with S(f) ∝ f −4. Based on this information we developed an algorithm allowing for the deconvolution of these two components in the spectral domain. The frequency of the signal enhancement increases linearly with IMF magnitude as f [mHz] 4.4|B IMF |[nT], and its power maximizes around IMF cone angles θ xB 20 and 160 • and at 10:30-11:00 MLT. Both spectral components exhibit similar semiannual variations with equinoctial maxima. The background noise power grows with increasing southward B z and remains nearly constant for northward B z. Its diurnal variation resembles that of Pc5 field-line resonance power, with a maximum near 09:00 MLT. Both the band-limited signal and broad band noise components show power-law growth with solar wind velocity ∝ V 5.71 sw and ∝ V 4.12 sw , respectively. Thus, the effective signal-to-noise ratio increases with increasing V sw. The observations suggest that the noise generation is associated with reconnection processes.

A new self-reconfigurable robot is presented. The robot is a hybrid chain/lattice design with several novel features. An active mechanical docking mechanism provides intermodule connection, along with optical and electrical interface. The docking mechanisms function additionally as driven wheels. Internal slip rings provide unlimited rotary motion to the wheels, allowing the modules to move independently by driving on flat surfaces, or in assemblies negotiating more complex terrain. Modules in the system are mechanically homogeneous, with three identical docking mechanisms within a module. Each mechanical dock is driven by a high torque actuator to enable movement of large segments within a multi-module structure, as well as low-speed driving. Preliminary experimental results demonstrate locomotion, mechanical docking, and lifting of a single module. Index Terms-cellular and modular robots, robotics in hazardous fields, mechanism design of mobile robots

, the Cassini spacecraft performed its Saturn orbit insertion, twice crossing the equatorial plane between the G and F rings. The radio HF receiver observed a peak at the upper-hybrid frequency and weakly banded emissions having well-defined minima at gyroharmonics. We show that through most of the encounter, these emissions do not result from instabilities, but instead are the quasi-thermal noise that can be calculated from the classical theory of plasma fluctuations. The spectroscopy of this noise yields the electron density, the core and the halo temperatures in the range 2.3 < L/R S < 7, À1.2 < z/R S < +0.1. For the first time, we measure the core temperature of the Kronian plasma torus to be about 0.

Energetic neutral atom (ENA) images in the energy range 16-50 keV obtained by the High-Energy Neutral Atom (HENA) imager on board the IMAGE satellite are presented from the period 23-26 May 2000. Two events during this period are investigated: (1) A rapid decrease on 23 May of the entire dayside ring current fluxes and (2) an unexpected local time distribution of the ring current during the storm commencing on 24 May. In the first event, ENA fluxes from the dayside ring current decrease rapidly for 10 min. The start of the decrease is associated with a sharp, southward turning of the interplanetary magnetic field (IMF) and a steep increase of the cross polar cap potential. Simulated equatorial ion fluxes are able to reproduce the event using a kinetic ion drift model. The observations are explained in terms of rapidly changing drift paths during a reconfiguration of the convectional electric field in the magnetosphere. The reconfiguration timescale ($10 min) is too short to modify the pitch angle distribution (PAD). The results show that the solar wind electric field over the dayside magnetosphere penetrates to the inner magnetosphere within a few minutes. In the second event an enhanced ring current develops during the storm on 24 May. Below 27 keV at L < 4 the ring current extends from midnight clockwise through noon toward the dawn sector. At energies above 27 keV the images show an enhancement in the ENA emissions coming from the noon region and a lack of ENA emissions from the duskside. Apart from the main phase of the storm the convection through the magnetosphere was steady throughout the 3-day recovery phase. Images in extreme ultraviolet (EUV) of the plasmasphere reveal a spatial relation between the ENA emissions and a plasmaspheric tail. Data from the Polar satellite together with preliminary ENA simulations suggest that the lack of ENA emissions is an effect of ion PADs peaked around 90°. We discuss possible explanations for the modification of the PADs, such as adiabatic drifts, charge exchange, and waveparticle interaction.

Magnetohydrodynamic (MHD) models of the global magnetosphere are very good research tools for investigating the topology and dynamics of the near-Earth space environment. While these models have obvious limitations in regions that are not well described by the MHD equations, they can typically be used (or are used) to investigate the majority of magnetosphere. Often, a secondary consideration is overlooked by researchers when utilizing global models-the effects of solving the MHD equations on a grid, instead of analytically. Any discretization unavoidably introduces numerical artifacts that affect the solution to various degrees. This paper investigates some of the consequences of the numerical schemes and grids that are used to solve the MHD equations in the global magnetosphere. Specifically, the University of Michigan's MHD code is used to investigate the role of grid resolution, numerical schemes, limiters, inner magnetospheric density boundary conditions, and the artificial lowering of the speed of light on the strength of the ionospheric cross polar cap potential and the build up of the ring current in the inner magnetosphere. It is concluded that even with a very good solver and the highest affordable grid resolution, the inner magnetosphere is not grid converged. Artificially reducing the speed of light reduces the numerical diffusion that helps to achieve better agreement with data. It is further concluded that many numerical effects work nonlinearly to complicate the interpretation of the physics within the magnetosphere, and so simulation results should be scrutinized very carefully before a physical interpretation of the results is made. Our conclusions are not limited to the Michigan MHD code, but apply to all MHD models due to the limitations of computational resources.

This paper deals with the benefits of using a nonlinear model-based approach for controlling magnetically guided therapeutic microrobots in the cardiovascular system. Such robots used for minimally invasive interventions consist of a polymer binded aggregate of nanosized ferromagnetic particles functionalized by drug-conjugated micelles. The proposed modeling addresses wall effects (blood velocity in minor and major vessels' bifurcations, pulsatile blood flow and vessel walls, and effect of robot-to-vessel diameter ratio), wall interactions (contact, van der Waals, electrostatic and steric forces), non-Newtonian behaviour of blood and different driving designs as well. Despite nonlinear and thorough, the resulting model can both be exploited to improve the targeting ability and be controlled in closed-loop using nonlinear control theory tools. In particular, we infer from the model an optimization of both the designs and the reference trajectory to minimize the control efforts. Efficiency and robustness to noise and model parameter's uncertainties are then illustrated through simulations results for a bead pulled robot of radius 250µm in a small artery.

The 24-year-old pulsar problem is reconsidered. New results are obtained by replacing the assumption of steady-state discharges near the polar caps by oscillatory discharges, and by creating the neutral-excess pair plasma via inverse-Compton collisions rather than via curvature radiation. As a result, the electrons and positrons which compose the pulsar wind have different bulk velocities and an oscillating space density, and (strong) coherent curvature radiation is implied (without invoking the excitation of instabilities, and contrary to existing proofs of its impossibility). The magnetospheres of young pulsars are likely to have considerable higher-order multipole components, in particular octupole. Radiation transfer through the pulsar magnetosphere results in fan beams whose polarization is dictated by the bottom of the radiation zone, hence, looks like curvature radiation from dipole-like poiar caps. Wind generation depends mainly on the quantity B~ 2 which takes similar values for the ms pulsars; the latter compensate for (somewhat) weaker fields by wider polar caps and smaller curvature radii.

A review of periodic and quasiperiodic VLF emissions observed at ground-based stations and in the Earth's magnetosphere is presented. Emissions with periods below 10 s are divided into three main groups : periodic emissions, hisslers and pulsing hiss, while the quasiperiodic emissions with periods above 10 s are divided into two main groups: QPl, which are definitely related to geomagnetic pulsations, and QP2, which are not obviously related to them, based on ground observations. However, it is pointed out that all types of quasiperiodic emissions with periods over 10 s observed onboard satellites show some association with geomagnetic pulsations which suggests that both QPl and QP2 can have similar mechanisms for their generation. Different approaches to the theoretical modelling of periodic and quasiperiodic emissions are discussed.

We have used a global model of the solar wind magnetosphere interaction to model the high latitude part of the external contributions to the geomagnetic field near the Earth. The model also provides corresponding values for the electric field. Geomagnetic quiet conditions were modeled to provide simulated external contributions relevant for internal field modeling. These have proven very valuable for