scholarly journals Determination of the Noise Floor of the WHISPER instrument on Cluster

2020 ◽  
Author(s):  
Helen Middleton ◽  
Harri Laakso ◽  
Arnaud Masson ◽  
Xavier Vallières
Keyword(s):  
Electric Field ◽  
Time Interval ◽  
Dipole Antennas ◽  
Technical Problems ◽  
Noise Floor ◽  
Receiving Antenna ◽  
Electric Dipole Antennas ◽  
Behaviour Changes ◽  
Different Characteristics ◽  
Configuration Changes

<p>The WHISPER (Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation) instrument is part of the WEC (Wave Experiment Consortium) of the ongoing Cluster mission, launched almost 20 years ago in 2000. It uses the long double sphere electric dipole antennas of the EFW (Electric Field and Wave) instrument to measure the electric field spectra in the frequency range 2-80 kHz.<span> </span></p><p>The characteristic signatures of natural or actively triggered waves indicate the nature of the ambient plasma regime and, combined with the spacecraft position, reveals the position of key magnetospheric boundaries encountered during a specific time interval.</p><p>Most of the time, WHISPER observes natural waves in the 2-80 kHz band, using one of the two EFW antennae pairs: Ey or Ez, which can have different characteristics. After successive technical problems with the EFW sensors, the receiving antenna had to be changed on 3 of the 4 spacecraft over the years, and Cluster 1 (C1) WHISPER measurements are currently being made with only one probe (the spacecraft acts as the second probe).</p><p>In order to understand the signals observed by the WHISPER experiment, one needs to know the instrumental noise floor, around which the measurements are meaningless. It is a frequent feature of wave detectors that this noise floor is temporally static - it does not degrade with time. However, what this noise floor actually is, and how its behaviour changes around the failure of probes and switching to other probes is the purpose of this study.<span> </span></p><p>The NATURAL spectra were processed orbit by orbit, in order to avoid strong emissions from any one region, then the minimum value for the low-energy spectra was picked out for each frequency. Individually, these show a large amount of variation, but the median of 20 orbits gives a very reproducible curve showing how the noise floor varies with frequency. The periods before, during and after probe failures and configuration changes were investigated and show the limited changes to the curves and strength of interference lines.</p>

Comparison of Meta-heuristic Algorithms on Benchmark Functions

2019 ◽  
Vol 2 (3) ◽  
pp. 508-517
Author(s):  
FerdaNur Arıcı ◽  
Ersin Kaya
Keyword(s):  
Heuristic Algorithms ◽  
Optimization Problems ◽  
Search Algorithm ◽  
Optimization Algorithms ◽  
Gravitational Search Algorithm ◽  
Differential Evolution Algorithm ◽  
Population Based ◽  
Time Interval ◽  
Bee Colony ◽  
Different Characteristics

Optimization is a process to search the most suitable solution for a problem within an acceptable time interval. The algorithms that solve the optimization problems are called as optimization algorithms. In the literature, there are many optimization algorithms with different characteristics. The optimization algorithms can exhibit different behaviors depending on the size, characteristics and complexity of the optimization problem. In this study, six well-known population based optimization algorithms (artificial algae algorithm - AAA, artificial bee colony algorithm - ABC, differential evolution algorithm - DE, genetic algorithm - GA, gravitational search algorithm - GSA and particle swarm optimization - PSO) were used. These six algorithms were performed on the CEC’17 test functions. According to the experimental results, the algorithms were compared and performances of the algorithms were evaluated.

scholarly journals Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

2013 ◽  
Vol 31 (11) ◽  
pp. 2097-2121 ◽  
Author(s):  
P. M. E. Décréau ◽  
S. Kougblénou ◽  
G. Lointier ◽  
J.-L. Rauch ◽  
J.-G. Trotignon ◽  
...  
Keyword(s):  
Electric Field ◽  
Circular Polarization ◽  
Source Region ◽  
Plane Waves ◽  
Geomagnetic Latitude ◽  
Magnetic Activity ◽  
Spectral Signature ◽  
Time Interval ◽  
Field Polarization ◽  
Electric Field Polarization

Abstract. The Cluster mission operated a "tilt campaign" during the month of May 2008. Two of the four identical Cluster spacecraft were placed at a close distance (~50 km) from each other and the spin axis of one of the spacecraft pair was tilted by an angle of ~46°. This gave the opportunity, for the first time in space, to measure global characteristics of AC electric field, at the sensitivity available with long boom (88 m) antennas, simultaneously from the specific configuration of the tilted pair of satellites and from the available base of three satellites placed at a large characteristic separation (~1 RE). This paper describes how global characteristics of radio waves, in this case the configuration of the electric field polarization ellipse in 3-D-space, are identified from in situ measurements of spin modulation features by the tilted pair, validating a novel experimental concept. In the event selected for analysis, non-thermal continuum (NTC) waves in the 15–25 kHz frequency range are observed from the Cluster constellation placed above the polar cap. The observed intensity variations with spin angle are those of plane waves, with an electric field polarization close to circular, at an ellipticity ratio e = 0.87. We derive the source position in 3-D by two different methods. The first one uses ray path orientation (measured by the tilted pair) combined with spectral signature of magnetic field magnitude at source. The second one is obtained via triangulation from the three spacecraft baseline, using estimation of directivity angles under assumption of circular polarization. The two results are not compatible, placing sources widely apart. We present a general study of the level of systematic errors due to the assumption of circular polarization, linked to the second approach, and show how this approach can lead to poor triangulation and wrong source positioning. The estimation derived from the first method places the NTC source region in the dawn sector, at a large L value (L ~ 10) and a medium geomagnetic latitude (35° S). We discuss these untypical results within the frame of the geophysical conditions prevailing that day, i.e. a particularly quiet long time interval, followed by a short increase of magnetic activity.

scholarly journals Spiral wave unpinning facilitated by wave emitting sites in cardiac monolayers

2019 ◽  
Vol 475 (2230) ◽  
pp. 20190420
Author(s):  
Shreyas Punacha ◽  
Sebastian Berg ◽  
Anupama Sebastian ◽  
Valentin I. Krinski ◽  
Stefan Luther ◽  
...  
Keyword(s):  
Electric Field ◽  
Electrical Activity ◽  
Spiral Wave ◽  
Electrical Stimulus ◽  
Spiral Waves ◽  
Time Interval ◽  
Field Pulse ◽  
The Core ◽  
Rotating Wave ◽  
Multiple Obstacles

Rotating spiral waves of electrical activity in the heart can anchor to unexcitable tissue (an obstacle) and become stable pinned waves. A pinned rotating wave can be unpinned either by a local electrical stimulus applied close to the spiral core, or by an electric field pulse that excites the core of a pinned wave independently of its localization. The wave will be unpinned only when the pulse is delivered inside a narrow time interval called the unpinning window (UW) of the spiral. In experiments with cardiac monolayers, we found that other obstacles situated near the pinning centre of the spiral can facilitate unpinning. In numerical simulations, we found increasing or decreasing of the UW depending on the location, orientation and distance between the pinning centre and an obstacle. Our study indicates that multiple obstacles could contribute to unpinning in experiments with intact hearts.

scholarly journals Optimal Planar Electric Dipole Antennas: Searching for antennas reaching the fundamental bounds on selected metrics

2019 ◽  
Vol 61 (4) ◽  
pp. 19-29 ◽  
Author(s):  
Miloslav Capek ◽  
Lukas Jelinek ◽  
Kurt Schab ◽  
Mats Gustafsson ◽  
B.L.G. Jonsson ◽  
...  
Keyword(s):  
Electric Dipole ◽  
Dipole Antennas ◽  
Electric Dipole Antennas

An Investigation on Resistive Switching Characteristics Induced by HfOx and Electrode Interfaces

2015 ◽  
Vol 645-646 ◽  
pp. 169-177
Author(s):  
Xiao Rong Chen ◽  
Jie Feng
Keyword(s):  
Electric Field ◽  
Resistive Switching ◽  
Joule Heat ◽  
Negative Bias ◽  
Bipolar Resistive Switching ◽  
Comparison And Analysis ◽  
Switching Characteristics ◽  
Different Characteristics ◽  
Unipolar Devices ◽  
Switching Devices

Pt/HfOx/Pt resistive switching devices with symmetric electrodes were fabricated. Bipolar resistive switching (RS) behaviors and unipolar behaviors were then observed under a positive/negative bias applied to the top electrode (TE). A comparison and analysis of bipolar/unipolar RS behaviors under different voltage polarities was then performed.The results demonstrated that bipolar RS was achieved via a drift of anion (O2-) under the electric field resulting in the rupture and recovery of filaments at the interface. When the filaments dissolved and formed at the interface near BE, the performance of the bipolar RS devices was better. However, for unipolar RS devices, when filaments dissolved and formed at the interface near TE, the performance was even better. These results indicated that a drift of O2-caused by electric field and a diffusion of O2-induced by Joule heat were the main reasons for unipolar RS. The different characteristics of the bipolar and unipolar devices can be attributed to the existence of a different number of defects at the active interface of the devices. This was where the rupture and recovery of filaments occurred. The results also indicate that the active interface is more important than other interfaces for RRAM performance.

Loading Rate Effect on the Domain Switching of Ferroelectric Materials

2008 ◽  
Author(s):  
Ajit Achuthan ◽  
Chin-Teh Sun
Keyword(s):  
Electric Field ◽  
Loading Rate ◽  
Domain Switching ◽  
Underlying Mechanism ◽  
Ferroelectric Materials ◽  
Switching Behavior ◽  
Switching Mechanism ◽  
Two Factors ◽  
Different Characteristics ◽  
Butterfly Behavior

A method to characterize the strain electric field butterfly behavior based on the underlying domain switching mechanism is presented at first. The effect of loading rate on the different characteristics of the strain electric-field-butterfly behavior is then studied. By comparing the changes in these characteristics under different loading rates, it is established that the loading rate dependence of the strain electric field butterfly behavior is mainly due to two factors, 1) the dependence of the switching of individual domains on the magnitude and duration of the loading time and 2) the variation of the transition electric field with the loading rate. Several interesting attributes of the domain switching behavior that may shed light on understanding the underlying mechanism of domain switching further is illustrated in the present study. The present study also demonstrates that the method of characterizing the strain electric butterfly based on the underlying domain switching mechanism is very effective in studying ferroelectric behavior under different loading conditions.

scholarly journals Search for magnetically quiet CHAMP polar passes and the characteristics of ionospheric currents during the dark season

2006 ◽  
Vol 24 (11) ◽  
pp. 2997-3009 ◽  
Author(s):  
P. Ritter ◽  
H. Lühr
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Transverse Field ◽  
Transverse Component ◽  
Local Times ◽  
Time Interval ◽  
Polar Regions ◽  
Ionospheric Currents ◽  
Ionospheric Conductivity ◽  
Field Modelling

Abstract. The magnetic activity at auroral latitudes is strongly dependent on season. During the dark season, when the solar zenith angle in the polar region is larger than 100° at all local times, the ionospheric conductivity is much reduced, and generally low activity is encountered. These time intervals are of special interest for the main field modelling, because then the geomagnetic field readings, in particular the field magnitude, are only slightly affected by ionospheric currents. Based on CHAMP data, this study examines how these quiet periods are reflected in the different magnetic field components. The peak FAC density is used as a possible proxy for the deviation of the total field. As a second option, the transverse field component, which is aligned with the auroral oval, is investigated, because it presents a measure for the FAC total current. Correlation analyses with the scalar residuals are performed and both proxies are tested for their suitability of predicting the intensity of the auroral electrojet during the dark polar seasons. The indicators based on the local FAC strength or on the amplitude of the transverse component show a reasonable correlation with the electrojet intensity for these periods, but fail when limited to small amplitudes. The predictability improves considerably if the time sector is limited to dayside hours (08:00–16:00 MLT). As the activity at high latitudes is strongly controlled by the solar wind input, we also consider IMF quantities which may support very quiet conditions. Correlations of the magnetic field scalar residuals with the merging electric field are strongest if only passes in the dayside sector are considered. Best selection results for quiet passes are obtained by combining four conditions: dark season, small average merging electric field, Em<0.8 mV/m, absence of peak values of Em>1.2 mV/m during a time interval of 40 min centred at the polar crossing, and limitation to the dayside sector (08:00–16:00 MLT). The set of quiet polar passes identified by these criteria may be used beneficially in crustal field modelling of the polar regions.

Dielectrophoresis velocities response on tapered electrode profile: simulation and experimental

2019 ◽  
Vol 36 (2) ◽  
pp. 45-53
Author(s):  
Muhammad Izzuddin Abd Samad ◽  
Muhamad Ramdzan Buyong ◽  
Shyong Siow Kim ◽  
Burhanuddin Yeop Majlis
Keyword(s):  
Electric Field ◽  
Field Intensity ◽  
Particle Velocity ◽  
Applied Voltage ◽  
Electric Field Intensity ◽  
Particle Trajectory ◽  
Numerical Study ◽  
Time Interval ◽  
Content Type ◽  
Field Density

Purpose The purpose of this paper is to use a particle velocity measurement technique on a tapered microelectrode device via changes of an applied voltage, which is an enhancement of the electric field density in influencing the dipole moment particles. Polystyrene microbeads (PM) have used to determine the responses of the dielectrophoresis (DEP) voltage based on the particle velocity technique. Design/methodology/approach Analytical modelling was used to simulate the particles’ polarization and their velocity based on the Clausius–Mossotti Factor (CMF) equation. The electric field intensity and DEP forces were simulated through the COMSOL numerical study of the variation of applied voltages such as 5 V p-p, 7 V p-p and 10 V p-p. Experimentally, the particle velocity on a tapered DEP response was quantified via the particle travelling distance over a time interval through a high-speed camera adapted to a high-precision non-contact depth measuring microscope. Findings The result of the particle velocity was found to increase, and the applied voltage has enhanced the particle trajectory on the tapered microelectrode, which confirmed its dependency on the electric field intensity at the top and bottom edges of the electrode. A higher magnitude of particle levitation was recorded with the highest particle velocity of 11.19 ± 4.43 µm/s at 1 MHz on 10 V p-p, compared to the lowest particle velocity with 0.62 ± 0.11 µm/s at 10 kHz on 7 V p-p. Practical implications This research can be applied for high throughout sensitivity and selectivity of particle manipulation in isolating and concentrating biological fluid for biomedical implications. Originality/value The comprehensive manipulation method based on the changes of the electrical potential of the tapered electrode was able to quantify the magnitude of the particle trajectory in accordance with the strong electric field density.

ER EFFECT OF LOW MOLECULAR LIQUID CRYSTAL ON ONE-SIDED PATTERNED ELECTRODES

2007 ◽  
Vol 21 (28n29) ◽  
pp. 4988-4995 ◽  
Author(s):  
TAKEHITO KIKUCHI ◽  
AKIO INOUE ◽  
JUNJI FURUSHO ◽  
RYOHEI KAWAMUKI
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Short Circuit ◽  
Flow Characteristics ◽  
Electrode System ◽  
Processing Technologies ◽  
Pattern Type ◽  
Molecular Liquid ◽  
Er Fluids ◽  
Different Characteristics

Several kinds of ER fluids (ERF) have been developed and have been applied to some mechatronics devices and processing technologies. In many conventional applications of ERFs, these devices consist of bilateral electrodes to apply electric field in ERF. However, the electric field of several kV/mm may be necessary to generate an ER effect sufficiently for practical purposes. The gap between a pair of electrodes should be, therefore, maintained narrowly and exactly for fears of short-circuit. At the same time, this electrode system also requires an interconnection on driving parts. To improve these disadvantages, we proposed "one-sided patterned electrode" (OSPE) systems in previous works. In this report, we confirmed the flow characteristics of low molecular liquid crystal (LMLC) on OSPE. Next, we also confirmed the different characteristics depending on the pattern type. Depending on results of electro-static analysis, we conclude that such a difference may results from the directors of LC molecules derived by electric field.

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