Top PDF Current-voltage relationship in the auroral particle acceleration region

Current-voltage relationship in the auroral particle acceleration region

Current-voltage relationship in the auroral particle acceleration region

Abstract. The current-voltage relationship in the auroral particle acceleration region has been studied statistically by the Akebono (EXOS-D) satellite in terms of the charge carri- ers of the upward field-aligned current. The Akebono satel- lite often observed field-aligned currents which were sig- nificantly larger than the model value predicted by Knight (1973). We compared the upward field-aligned current esti- mated by three different methods, and found that low-energy electrons often play an important role as additional cur- rent carriers, together with the high-energy primary electrons which are expected from Knight’s relation. Such additional currents have been observed especially at high and middle altitudes of the particle acceleration region. Some particular features of electron distribution functions, such as “cylindri- cal distribution functions” and “electron conics”, have often been observed coinciding with the additional currents. They indicated time variability of the particle acceleration region. Therefore, we have concluded that the low-energy electrons within the “forbidden” region of electron phase space in the stationary model often contribute to charge carriers of the current because of the rapid time variability of the particle acceleration region. “Cylindrical distribution functions” are expected to be found below the time-varying potential differ- ence. We statistically examined the locations of “cylindrical distribution function”, and found that their altitudes are re- lated to the location where the additional currents have been observed. This result is consistent with the idea that the low- energy electrons can also carry significant current when the acceleration region changes in time.
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Observations of nightside auroral plasma upflows in the F-region and topside ionosphere

Observations of nightside auroral plasma upflows in the F-region and topside ionosphere

In terms of the magnitude of the maximum vertical ion velocity and the duration of the event, the upflow ob- served around 0030 UT is comparable with the earlier feature. However, in this case we observe only modest increases in the vertical ion temperature during the up- flow, which is consistent with the moderate measured convection velocities. Furthermore, in the earlier event the electron temperature at the lower altitudes was seen to increase subsequent to the upflow, whereas here there appears to be a direct correlation between enhanced elec- tron temperature and vertical ion velocity at 500-km alti- tude. The electron heating might be due to a downward heatflux of magnetospheric origin, or the result of particle precipitation; evidence of a discrete feature is apparent as a slight increase in electron density at 200 km, and there is certainly a correlation between this and enhancements in both ion and electron temperatures at that altitude. It has previously been discussed how particle precipitation can result in enhanced F-region and topside electron temper- atures, which can induce upward plasma acceleration via thermal diffusion and enhanced field-parallel electric fields. Again, temperature measurements above 500-km altitude are not available, but we might infer elevated temperatures above this range from the observations at the lower altitudes. Thus we conclude that the observed upflows were associated with precipitation-induced elec- tron heating in the F-region and topside ionosphere. It is interesting that in this event enhanced electron temper- atures at 500 km were accompanied by large vertical vel- ocities at the same altitude, whereas in the previous event somewhat greater electron temperatures at 300 and 500 km were not coincident with upward flows. The rea- son for this is not readily apparent, but it might simply be due to differences in field-aligned pressure gradients be- tween the two events, which cannot be quantitatively examined from vertical observations for such transient features.
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Additional acceleration of solar-wind particles in current sheets of the heliosphere

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

Again, similarly to the ion flux in the HCS, an increase in high-energy particle flux occurs earlier than the ICME- associated shock comes (seen in the far right corner of each plot in Fig. 5a); this cannot, then, be responsible for this par- ticle acceleration. Also, there is a sharp change in the direc- tion of motion by suprathermal electrons observed at the mo- ment of the shock crossing and after the passage of the lead- ing edge, indicated by grey arrows in Fig. 4. The fluxes of all energies are increased inside the investigated area (wide red section in Fig. 5a–c), which means that the acceleration of particles occurs in this region. It is easy to see multiple crossings of the neutral lines (current sheets) during this pe- riod. The zero line is represented in red in Fig. 5d–f in order to indicate such crossings.
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On the relationship between auroral absorption, electrojet currents and plasma convection

On the relationship between auroral absorption, electrojet currents and plasma convection

Previous studies of the current-conductance-E-field rela- tionship have mostly used the data collected using incoher- ent scatter radars (ISRs) that provide plasma convection ve- locity (electric field) data and information on conductivi- ties in the limited range of altitudes (typically 90–300 km). From this information the ionospheric currents are inferred using Ohm’s law (e.g. Davies and Lester, 1999; Sugino et al., 2002). In this approach all 3 parameters are provided by the same instrument at the same resolution and all the measure- ments are coincident and simultaneous. On the other hand, ISR is an expensive instrument with which to observe pro- cesses in the upper atmosphere. As a result they typically do not operate continuously for extended periods of time, i.e. months or years. Riometers and magnetometers, on the other hand, are passive instruments and are inexpensive to operate. As a result they function nearly continuously, under all con- ditions. They also provide observations integrated over the full ionospheric height profile. In addition, in previous stud- ies, the solar and particle components of conductances were not considered separately as current depends on the total Hall and Pedersen conductances. Previous studies have also con- centrated on nightside observations with the full MLT depen- dence including dayside sectors still less investigated.
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An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

Abstract. An auroral westward flow channel (AWFC) is a latitudinally narrow channel of unstable F-region plasma with intense westward drift in the dusk-to-midnight sector ionosphere. AWFCs tend to overlap the equatorward edge of the auroral oval, and their life cycle is often synchronised to that of substorms: they commence close to substorm expan- sion phase onset, intensify during the expansion phase, and then decay during the recovery phase. Here we define for the first time the relationship between an AWFC, large-scale field-aligned current (FAC), the ring current, and plasma- pause location. The Tasman International Geospace Envi- ronment Radar (TIGER), a Southern Hemisphere HF Super- DARN radar, observed a jet-like AWFC during ∼08:35 to 13:28 UT on 7 April 2001. The initiation of the AWFC was preceded by a band of equatorward expanding ionospheric scatter (BEES) which conveyed an intense poleward elec- tric field through the inner plasma sheet. Unlike previous AWFCs, this event was not associated with a distinct sub- storm surge; rather it occurred during an interval of per- sistent, moderate magnetic activity characterised by AL∼ −200 nT. The four Cluster spacecraft had perigees within the dusk sector plasmasphere, and their trajectories were mag- netically conjugate to the radar observations. The Waves of High frequency and Sounder for Probing Electron den- sity by Relaxation (WHISPER) instruments on board Clus- ter were used to identify the plasmapause location. The Im- ager for Magnetopause-to-Aurora Global Exploration (IM- AGE) EUV experiment also provided global-scale obser- vations of the plasmapause. The Cluster fluxgate magne- tometers (FGM) provided successive measurements specify- ing the relative location of the ring current and filamentary Correspondence to: M. L. Parkinson
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Particle acceleration in tangential discontinuities by lower hybrid waves

Particle acceleration in tangential discontinuities by lower hybrid waves

To accomplish our goal, we first summarize the conditions needed to excite the LHDI. In particular, we assume that the magnetic merging process is a steady state, permitting the assumption of marginal stability. This allows us to ob- tain an expression for the characteristic scale length required to maintain the LHDI at marginal stability. In the steady- state Petchek reconnection, we assume the LHDI is driven by the gradients in the magnetic field produced by the in- flowing plasma. This allows us to obtain the level of anoma- lous resistivity required to achieve a steady state in terms of the length of the reconnection region, L, and the magnitude of the magnetic field B. The incompressibility assumption permits a relationship between L and the thickness of the re- connection dissipation region, 1x ⊥ , which closes the system and provides a complete set of equations in terms of space- craft “observables”. Once this is determined, we derive the level of ion density fluctuations at marginal stability. Esti- mates of the electron and ion temperatures are then obtained, together with non-thermal electron energies and numbers.
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Anomalous width variation of rarefactive ion acoustic solitary waves in the context of auroral plasmas

Anomalous width variation of rarefactive ion acoustic solitary waves in the context of auroral plasmas

The discrepancies between the weakly nonlinear theory (Washimi and Taniuti, 1966) and the observations of the au- roral acceleration region (B¨ostrom et al., 1989) was known for a long time. However, not many attempts were taken to cover the particular lacuna in the width-amplitude vari- ation pattern. Previous theoretical analysis have suggested both the presence of ion acoustic modes (Lotko, 1983), or BGK ion holes in the phase space (M¨aikii and Koskinen, 1989). It was considered that an ion acoustic mode neces- sarily show a decrease in the width with increasing ampli- tude while an opposite trend indicates the presence of BGK modes in the space. However, unlike electron solitary holes (Muschietti et al., 1999b; Maslov and Schamel, 1993), the observed rarefactive structures in the auroral region (Temerin et al., 1982; B¨ostrom et al., 1989) were mainly interpreted as the evolution of ion acoustic mode (Reddy and Lakhina, 1991). Berthomier et al. (1998) have shown that a fully nonlinear rarefactive ion acoustic wave in an unmagnetized plasma may show an increase in the width with increasing amplitude. Previous satellite observations showed an appar- ently “random” variation of the width with amplitude where no regular correlation could be observed but recent satel- lites are more capable with higher data rates and high res- olution particle detectors which have opened a wide oppor- tunity to analyze different nonlinear structures. Significant works have been done by Cattell et al. (2001); Crumley et al. (2001) and Dombeck et al. (2001) in the auroral region on the basis of POLAR data. A particularly interesting finding was the width-amplitude variation of the low altitude rarefactive ion structures in the auroral region (Dombeck et al., 2001). It shows a clear trend of increasing width with increasing amplitude. Figure 6 shows one of the three EFI bursts as studied and presented by Dombeck et al. (2001). Though the
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Crossing a narrow-in-altitude turbulent auroral acceleration region

Crossing a narrow-in-altitude turbulent auroral acceleration region

for a large fraction of the acceleration of electrons and ions. Hence a small number of such layers are required only to pro- vide the total “inverted-V” electron energy in bright aurorae. It should be stressed that the observations discussed in the present paper are in good agreement with recent numerical simulation results on generation of holes (Singh et al., 1987; Singh and Khazanov, 2003). In particular, Singh et al. (1987) predicted the main features of panel (e) in Fig. 1 from simu- lations, namely a wide upward current sheet sandwiched be- tween two return current regions. The self-consistent poten- tial structure accelerating the upward and downward acceler- ated electrons and ions was found from 2-D PIC simulations of current sheet equilibrium by varying the width of the up- ward current sheet. In addition, they predicted the different types of turbulence above and in the center of the accelera- tion layer (their Figs. 10 and 13, the contours H, there, show the spiky fields of transient double layers, which contribute to the downward accelerations of electrons and upward ac- celerations of ions).
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Ion dynamics and acceleration in relativistic shocks

Ion dynamics and acceleration in relativistic shocks

Ab initio numerical study of collisionless shocks in electron–ion unmagnetized plasmas is performed with fully relativistic particle in cell simulations. The main properties of the shock are shown, focusing on the implications for particle acceleration. Results from previous works with a distinct numerical framework are recovered, including the shock structure and the overall acceleration features. Particle tracking is then used to analyze in detail the particle dynamics and the acceleration process. We observe an energy growth in time that can be reproduced by a Fermi-like mechanism with a reduced number of scatterings, in which the time between collisions increases as the particle gains energy, and the average acceleration efficiency is not ideal. The in depth analysis of the underlying physics is relevant to understanding the generation of high- energy cosmic rays, the impact on the astrophysical shock dynamics, and the consequent emission of radiation. Key words: acceleration of particles – gamma rays: bursts – methods: numerical
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Dopaminergic modulation of the voltage-gated sodium current in the cochlear afferent neurons of the rat.

Dopaminergic modulation of the voltage-gated sodium current in the cochlear afferent neurons of the rat.

We found that under current pulse stimulation most of the SGN adapted quickly and dis- charged a single action potential. These results coincide with those described by other authors [46,47]. Applying DA to cells stimulated with sinusoidal current injection allowed us to show the inhibitory action of DA in the action potential discharge of SGNs. The use of dihydrexidine in cells with repetitive discharge showed that there is an increase in the duration of the action potential in the cells that discharged throughout the pulse. This change in the AP duration is reflected by a change in the number of action potentials throughout the current pulse. These results support the notion that DA released from the olivocochlear efferent neurons depresses the discharge of the afferent neurons, constituting a protective mechanism in conditions of is- chemia or acoustic overstimulation, which may lead to an excitotoxic damage from excess glu- tamate release and sustained action potential discharge [48,49]. The DA neurotransmission enhancer rasagiline (a monoamine oxidase type B inhibitor) has been approved as an otopro- tectant, showing that DA release from lateral olivocochlear fibers exert a protective action against excitotoxicity, a pathological factor in the aminoglycoside-induced sensorineural hear- ing loss [50]. Also pramipexole (a D2/D3 receptor agonist) is an effective agent against subjec- tive tinnitus, action that may involve both central and peripheral targets in the auditory system [51].
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Comment on "Danish auroral science history" by P. Stauning in Hist. Geo Space Sci., 2, 1–28, 2011

Comment on "Danish auroral science history" by P. Stauning in Hist. Geo Space Sci., 2, 1–28, 2011

During the IGY ground-based recordings of VLF (Very Low Frequency) electromagnetic emissions were initiated in Greenland by the Ionosphere Laboratory at the Techni- cal University of Denmark, and it was demonstrated in the 1960s, that the emission type called auroral hiss was pro- duced by the auroral particle precipitation (e.g. Jørgensen, 1966).

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Sba Controle & Automação  vol.19 número4

Sba Controle & Automação vol.19 número4

Section 2 has demonstrated why the current-source PV array model is more convenient than the voltage-source one for the purpose of modeling this input-controlled PV system. Al- though neither of the models represents the array in its full operating range, the current-source model may be adopted and considered as a suitable representation of the PV array. Section 3 has presented the development of converter transfer functions for the input voltage control of the buck converter operating with duty-cycle control (voltage mode) and with inductor peak current control (current-programmed mode). The transfer functions reveal important dynamic characteris- tics of the input-controlled buck converter when it is fed by a PV array. With these transfer functions it is possible to de- sign compensators and feedback controllers for the control of the input voltage of the buck converter.
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Nonlinear wave structures in collisional plasma of auroral E-region ionosphere

Nonlinear wave structures in collisional plasma of auroral E-region ionosphere

We shall consider here quasi-stationary electrostatic non- linear moving plasma structures, and apply the so-called stationary wave approach (see Karpman, 1973). It is sup- posed further that the only variable is S"x!»t#hz, where z is along the magnetic field, x is perpendicular to the magnetic field in the direction of the electron drift velocity due to external field, » is the parameter with the velocity dimension (the velocity of the structure) which will be defined from the conditions for the solution exist- ence. For the one-dimensional problem considered in this section, h"0, while for the two- and three-dimensional models, h defines the angle of the plane in which the nonlinear structure can move, with the plane perpendicu- lar to the magnetic field, Blo, i.e., the aspect angle for auroral radar reflections (see Sect. 4). Thus, a class of stationary solutions is sought which describes stationary electrostatic structures moving with a constant velocity » in respect to the plasma.
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REVIEW_AN INTERDISCIPLINARY APPROACH TO THE RELATIONSHIP BETWEEN MASS-MEDIA AND DEMOCRACY IN POST-COMMUNIST ROMANIA

REVIEW_AN INTERDISCIPLINARY APPROACH TO THE RELATIONSHIP BETWEEN MASS-MEDIA AND DEMOCRACY IN POST-COMMUNIST ROMANIA

The events of 1989 helped Romanian mass-media to escape from the prison of censorship and conformism, of imposed but also self-imposed servitude. The changes happening in the political area also brought along a revolution of communication means. But not all was nice and good since in the new political framework, which featured a democracy in search of its own identity, the evolution of the mass-media also experienced such phenomena as the monopolisation of the public space, the cartelisation of the mass-media or the usage of media trusts as tools serving political interests.
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Preliminary results of ion trajectory tracking in the acceleration region of the VINCY cyclotron

Preliminary results of ion trajectory tracking in the acceleration region of the VINCY cyclotron

In cy clo tron de sign and beam dy nam ics anal - y sis, it is com mon to treat sep a rately the cen tral, ac - cel er a tion and ex trac tion re gions. This is be cause each of these re gions im poses dif fer ent re quire - ments and chal lenges. In the ac cel er a tion re gion, ions travel through an isochronized mag netic field, trac ing a spi ral or bit. A very large num ber of turns are per formed, re sult ing in a sub stan tial tra jec tory length. As a con se quence, the cru cial re quire ment is to im prove com pu ta tional speed while pre serv - ing high ac cu racy, along the long nu mer i cally in te - grated trajectory. The VINDY soft ware pack age, pri mar ily tai lored to ac com mo date ex trac tion re - gion beam dy nam ics and anal y sis, has been de vel - oped pre vi ously, as shown in [1, 2]. It has a mod u - lar struc ture and is or ga nized in such a man ner as to en able easy ad just ments and im ple men ta tion in sim i lar beam dy nam ics prob lems. A beam tra jec - tory in the ex trac tion re gion is sev eral hun dreds times shorter than the one in the ac cel er a tion re -
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Three Phase High Power Quality Two- Stage Boost Rectifier

Three Phase High Power Quality Two- Stage Boost Rectifier

The sensed instantaneous value i of the input current is converted into the absolute value , which is one of the two inputs to the comparator. A read only memory (ROM) contains the digital data of a full-wave rectified sinusoidal signal with unity amplitude. A digital-to-analogue (D/A) converter changes the output of ROM into the continuous signal, which is kept in phase with the supply voltage. The reference [i*] of the input current is provided from the multiplier and it is given as a product of the signal u and the D/A converter output. The reference is the second input to the comparator. The switching timings of the two IGBTs labelled Q 1 and Q 2
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Power Quality Improvement And Mitigation Of Voltage Sag And  Current Swell Using Distributed Power Flow Controller

Power Quality Improvement And Mitigation Of Voltage Sag And Current Swell Using Distributed Power Flow Controller

Within the DPFC, the transmission line is used as a connection between shunt converter output and AC port of series converters, instead of using DC- link for power exchange between converters. The method of power exchange in DPFC is based on power theory of non-sinusoidal components [9]. Non- sinusoidal voltage and current can be presented as the sum of sinusoidal components at different frequencies. It is the main result of Fourier analysis. The product of voltage and current components provides the active power. Since the integral of some terms with different frequencies are zero, so the active power equation is as follow:
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Braz. J. Phys.  vol.39 número1

Braz. J. Phys. vol.39 número1

mass spectrometers, detector optics, time of flight instruments, ion traps, magnetic sectors and much more. SIMION 3D 7.0 is intended to provide direct and highly interactive methods for simulating a wide variety of general ion optics problems. In general, the fundamental steps for simulating the properties of a model extraction system are to define the physical and electrical boundaries of the electrodes. SIMION defines the ions that make up the beam, selects output data to be recorded and simulates ion accelerated trajectories through the extrac- tion system. Each electrode of the triode extraction system is separately designed using a potential array. Such a potential array is a two or three dimensional array of points, consisting of a collection of equally spaced points forming a rectangular grid. Points in the potential array will be bound within a certain shape creating an electrode or non-electrode. Using a finite dif- ference method, SIMION takes the potentials of the electrode points to calculate the potential at the non-electrode points. Once all three electrodes are designed and defined within a potential array, SIMION solves Laplace’s equation:
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Unified Power Quality Conditioner for voltage and current compensation

Unified Power Quality Conditioner for voltage and current compensation

The UPQC is aimed for simultaneous compensation of the load current distortion and the supply voltage disturbance.UPQC has two voltage-source inverters of three-phase three wire configuration connected back to back through same DC link capacitor [2]. Source side inverter, called the series inverter is connected through coupling transformers between the point of common connection and load. The load side inverter, called the shunt inverter is connected in parallel through the transformers or directly connected. The series inverter operates as a controlled voltage source, while the shunt inverter operates as a controlled current source [4]. So, the UPQC has compensation capabilities for the load harmonic current, the reactive power compensation, the source voltage disturbances (including sag / swell), and the unbalance (load and source) compensation [1].
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Short term generation scheduling of cascaded hydro electric system using time varying acceleration coefficients PSO

Short term generation scheduling of cascaded hydro electric system using time varying acceleration coefficients PSO

The NCHES generation scheduling has been done by Time Varying Acceleration Coefficients PSO (TVAC_PSO) on hourly basis, assuming all reservoirs full at starting of the schedule horizon. The above problem also approached by the NSAIW_PSO with same population size, PSO parameters (as given in Table 3) and load demand. Program has been coded in MATLAB and the performance of both algorithms have been obtained by using MATLAB 7.0.1 on a core 2 duo, 2 GHz, 2.99 GB RAM. The effectiveness of TVAC_PSO & NSAIW_PSO in various trials is judged by the three criteria’s first is the probability to get best solution or objective function (robustness), second is the solution quality and third is dynamic convergence characteristics. Dynamic convergence behavior has been analyzed by the mean and standard deviation of swarm as given in eq. (16) & eq. (17) at each generation. Out of 10 trials of each individual hour best results are chosen based on above criteria. The final optimal hourly power generation through hydro power plants of NCHES has shown in Figure 2. The number subscript in increasing order with parameters P, X and Q in Figure 2 to Figure 4 means parameters related to Rani Avanti Bai Sagar, Indira Sagar, Omkareshwar and Sardar Sarovar hydro power plant respectively.
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