Small Electric Field Strength Research Articles

Dissipation of field-aligned currents in the topside ionosphere

Field-aligned currents (FACs) are electric currents parallel to the geomagnetic field and connecting the Earth’s magnetosphere to the high-latitude ionosphere. Part of the energy injected into the ionosphere by FACs is converted into kinetic energy of the surrounding plasma. Such a current dissipation is poorly investigated, mainly due to the high electrical conductivity and the small electric field strength expected in direction parallel to the geomagnetic field. However, previous results in literature have shown that parallel electric field is not null (and may be locally not negligible), and that parallel electrical conductivity is high but finite. Thus, dissipation of FACs may occur. In this work, for the first time, we show maps of power density dissipation features associated with FACs in the topside ionosphere of the Northern hemisphere. To this aim, we use a 6-year time series of data at one second cadence acquired by the European Space Agency’s “Swarm A” satellite flying at an altitude of about 460 km. In particular, we use data from the Langmuir probe together with the FAC product provided by the Swarm team. The results obtained point out that dissipation of FACs, even if small when compared to that associated with horizontal currents flowing about 350 km lower, is not null and shows evident features co-located with electron temperature at the same altitude. In particular, power density dissipation features are enhanced mainly in the ionospheric regions where intense energy injection from the magnetosphere occurs. In addition, these features depend on geomagnetic activity, which quantifies the response of the Earth’s environment to energetic forcing from magnetized plasma of solar origin.

Electronic properties and tunable Schottky barrier of non-Janus MoSSe/graphene heterostructures

We investigate the stability and electronic properties of van der Waals junctions composed with graphene and non-Janus MoSSe in comparison with graphene/Janus MoSSe configuration, and furthermore explore its Schottky barrier as well as the effect of external electric field. Based on first-principles calculations, we compare the interlayer distance and binding energy between them. It is found that with the adhesion of graphene, the less-stable Janus MoSSe becomes the most stable configuration. The graphene/non-Janus MoSSe configuration has the minimum interlayer distance, and the weak vdW interactions indicates the preservation of unique electronic properties in both two materials. An n-type Schottky contact with the Schottky barrier height (SBH) of 0.38 eV is formed at the equilibrium state for graphene/non-Janus MoSSe, while the n-type SBH for two configurations of graphene/Janus MoSSe is 0.67 and 0.10 eV, respectively. With the application of an external electric field perpendicularly to the surface, not only the Schottky barrier height but also the transition of n-type and p-type Schottky contacts as well as Ohmic contacts can be modulated within a relatively small electric field strength. This property distinguishes graphene/non-Janus MoSSe from graphene/Janus MoSSe configuration, and provides great potential for applications in optoelectronic and nanoelectronic and devices.

Flat panel detector based on a shadow mask plasma display panel

AbstractA flat panel detector based on the structure of a shadow mask plasma display panel is analyzed in terms of the electron amplification factor when used in the Townsend mode. The detector consists of a metal shadow mask and two ultra‐thin glass substrates with electrodes depositing on them. The shadow mask divides the detecting area into arrays of independent cells. The electron gain and linearity of the device are investigated by simulation based on the particle‐in‐cell/Monte Carlo collision model. Similar experiments are carried out. Both experimental and simulation results show that the linearity of the detector is significant. The applied voltages and the effective cathode area are parameters affecting its gain. As the avalanche process in the center of the cell with small electric field strength is much smaller than that near the shadow mask edge, the gain increases exponentially with the anode voltage but decreases with the negative shadow mask voltage. The balance between effective cathode area and high electric field intensity near the shadow mask edge provides room for future optimization of the detector. In conclusion, the flat panel detector is a promising component in a detection system for high energy radiation, and the wide application of the device is expected.

Liquid crystal electrography: Electric field mapping and detection of peak electric field strength in AlGaN/GaN high electron mobility transistors

The liquid crystal mixture E7, based on cyanobiphenyl, has been successfully employed to map electric field strength and distribution in AlGaN/GaN high electron mobility transistors. Using a transmitted light image through crossed polarizers the optical response of the liquid crystal deposited onto the surface of the devices was recorded as a function of source–drain bias, Vds. At a critical voltage of 4V the preferred direction of orientation of the long axes of the liquid crystal molecules in the drain access region aligned with one of the polarizers resulting in reduced transmitted light intensity. This indicates that at this electric field strength molecule orientation in most of the liquid crystal film is dominated by the electric field effect rather than the influence of surface anchoring. The experimental results were compared to device simulations. Electric field strength above the surface at Vds=4V was simulated to reach or exceed 0.006MV/cm. This electric field is consistent with the field expected for E7 to overcome internal elastic energy. This result illustrates the usefulness of liquid crystals to directly determine and map electric fields in electronic devices, including small electric field strengths.

Electrohydrodynamics of a compound drop

The behavior of a compound drop, comprising two concentric fluid spheres, in a uniform electric field is studied analytically. The governing electrohydrodynamic equations are solved for Newtonian and immiscible fluids in the framework of leaky-dielectric theory and in the limit of small electric field strength and fluid inertia. A detailed analysis of the electric and flow fields is presented and it is shown that there will be four possible flow patterns in and around the globule, in terms of the direction of the external flow (pole-to-equator vs equator-to-pole) and the number of vortices (single-vortex vs double vortices) in the shell, and that the senses of the net electric shear stresses at the surfaces of the inner and the outer drops and their relative importance are the key parameters in setting these patterns. A circulation map is constructed, which is used to infer about the likelihood of the flow patterns and transition from one pattern to another for representative fluid systems. For small distortion from the spherical shape, the deformations of the inner and the outer drops are found using normal stress balances at the corresponding surfaces. It is shown that there will be four possible modes for the deformation of the compound drop, which are determined by the net normal electric and hydrodynamic stresses at the pertinent surfaces. The dynamic responses of the inner and the outer drops for representative fluid systems are studied using a deformation map, which characterizes the possibilities of the deformation modes and transition from one mode to another as a function of the fluid properties.

Branched nanotrees with immobilized acetylcholine esterase for nanobiosensorapplications

A novel lab-on-a-chip nanotree enzyme reactor is demonstrated for the detection of acetylcholine.The reactors are intended for use in the RISFET (regional ion sensitive field effect transistor)nanosensor, and are constructed from gold-tipped branched nanorod structures grown onSiNx-covered wafers. Two different reactors are shown: one with simple, one-dimensionalnanorods and one with branched nanorod structures (nanotrees). Significantly higherenzymatic activity is found for the nanotree reactors than for the nanorod reactors, mostlikely due to the increased gold surface area and thereby higher enzyme bindingcapacity. A theoretical calculation is included to show how the enzyme kinetics andhence the sensitivity can be influenced and increased by the control of electricalfields in relation to the active sites of enzymes in an electronic biosensor. Thepossible effects of electrical fields employed in the RISFET on the function ofacetylcholine esterase is investigated using quantum chemical methods, which showthat the small electric field strengths used are unlikely to affect enzyme kinetics.Acetylcholine esterase activity is determined using choline oxidase and peroxidase bymeasuring the amount of choline formed using the chemiluminescent luminol reaction.

Moderate Electric Field Treatment of Sugarbeet Tissues

The effects of thermal and moderate electric field (MEF) treatment on the damage of sugarbeet tissue were discussed. The activation energy ΔUT was estimated as 170 kJ mol−1 using the temperature dependences of the characteristic thermal damage time within the temperature interval 50–70 °C. The temperature dependences of electrical conductivity were measured for the maximally damaged and intact sugarbeet tissues; these data were used for estimation of the conductivity disintegration index at different MEF treatments. The results evidenced that the electrically stimulated damage of a sugarbeet tissue occurs even at a rather small electric field strength E of 20 V cm−1 if treatment time is large enough (t≈1 h). The energy consumption caused by MEF-treatment is mainly related to temperature elevation inside the tissue and noticeably decreases with increasing electric field strength E. MEF-treatment experiments in the aqueous media reveal the dependence of damage efficiency on sample orientation with respect to the external electric field.

A corona-discharge-based aerosol neutralizer designed for use with the SMPS-system

The widely used scanning mobility particle sizer (SMPS) for measuring submicron particles uses radioactivity to charge aerosol particles to a known charge distribution. Because of numerous restrictions and safety issues concerning radioactive sources, corona-discharge-based neutralizers are an attractive alternative. The newly developed electrical neutralizer consists of an aerosol chamber with an AC electrical discharge. Combining small residence times, high ion concentrations, small electric field strengths, discharge in the aerosol chamber itself and an automatic regulation of the ion input results in a very effective neutralizing device. Experiments with an initially uncharged aerosol have shown that charging of submicron particles to the bipolar equilibrium charge distribution was possible for volumetric flow rates of up to 1.5 L/min and concentrations of at least 5 × 1 0 6 1 / cm 3 . Particle loss (>3 nm) and particle production (>3 nm) were not observed.

DIFFERENCES IN STEADY CHARACTERISTICS AND RESPONSE TIME OF ERF ON ROTATIONAL FLOW BETWEEN ROTATING DISK AND CONCENTRIC CYLINDER

We made an experimental investigation of the steady characteristics of torque, current density, and response time of ERF on rotational flow of the disk and the concentric cylinder. We used smectite particles suspension ERF and D.C. electric field. We compared the steady shearstress, current density, and the rise and settling time of the concentric cylinder and with those of the rotating disk. Then we clarified the differences. At a larger electric field strength, the shear stress, yield stress, and apparent viscosity to a constant shear rate in the case of the rotating disk are larger than they are in the case of the rotating concentric cylinder. However, at a larger electric field strength, the current density to a constant shear rate in the case of the rotating disk is smaller than it is in the case of the rotating concentric cylinder. Rise time of torque in the case of the rotating disk is faster than it is in the case of the rotating concentric cylinder. However, rise time of current density in the case of the rotating disk is slower than it is in the case of the rotating concentric cylinder at a small electric field strength. On the other hand, the difference of settling time of torque and current density between the rotating disk and the rotating concentric cylinder is changed by the electric field strength and shear rate. The settling time of torque in the case of the rotating disk is faster than it is in the case of the rotating concentric cylinder at a large electric field strength and large shear rate. The settling time of current density in the case of the rotating disk is slower than it is in the case of rotating concentric cylinder at a small electric field strength. Based on these results, the rotating disk has an efficiency of obtained torque to given electric power greater than that of the rotating concentric cylinder.

Anticrossing effects in Rydberg states of lithium in the presence of parallel magnetic and electric fields.

Rydberg states in lithium have been excited from the ground state by absorption of \ensuremath{\pi}-polarized photons in the presence of parallel electric F and magnetic B fields. The magnetic field strength (B=3.11 T) is high enough to reach the inter-n-mixing regime, and a small electric field strength (F\ensuremath{\simeq}25 V/cm) is sufficient for the lowest state of the n=30 manifold to penetrate into the high-energy part of the n=29 manifold. The first anticrossing is thoroughly studied. Away from the anticrossing the spectrum exhibits two lines, but at the anticrossing a third component appears in the structure in the same energy range. This provides an experimental confirmation for the existence of pairs of almost-degenerate states with opposite parities in the high-energy part of the diamagnetic manifold of lithium. The two components of this doublet behave differently at the anticrossing. The experimental data have been interpreted in a global treatment in which core effects and intermanifold couplings are simultaneously taken into account. The different behavior of low- and high-lying states of the multiplet with respect to these two interactions is analyzed in detail.

Rotational diffusion of short DNA fragments in polyacrylamide gels: an electric birefringence study.

AbstractUsing electric birefringence we have examined the rotational diffusion of five short DNA fragments (55 to 256 base pairs) both in polyacrylamide gels as a function of gel concentration and in solution. The length dependence of the measured rotational relaxation times in the gels is in good agreement with the prediction from the Odijk theory for the dynamics of slightly flexible rods in a network. The rotational relaxation times were found to depend on the gel concentration, contrary to the prediction from the Odijk theory. Possible reasons for this observation are discussed. The birefringence decay curves for DNA fragments in the gel were single exponential only at small electric field strength.

Nonlinear and frequency-dependent transport phenomena in low-dimensional conductors

Nonlinear and frequency-dependent electrical conductivity is more a rule than an exception in materials with highly anisotropic electronic structure. Disorder leads to localization of the electronic wave functions, and the temperature-( T), electric field-( E), and frequency (ω)-dependent transport are due to random transfer rates between localized single particle states, a process fundamentally different from band transport. Interactions lead to collective modes, represented by a periodic modulation of the charge or spin density. The charge density wave (CDW) mode is pinned by impurities, but for small pinning forces, it can be depinned by moderate electric fields, leading to nonlinear conductivity due to a sliding CDW. Both classical and quantum models account for the field and frequency dependent response; they also describe current oscillation phenomena and effects which arise when both dc and ac excitations are applied. For strong pinning the collective mode cannot be depinned at small electric field strengths, but nonlinear (soliton) excitations of the collective modes may be responsible for the nonlinear conductivity observed. In all these cases field-and frequency-dependent transport is strongly related. This feature is reproduced by various models, and therefore a detailed study of σ( T, E,ω) is called for to distinguish between the various sources of novel transport phenomena in these new types of solids.

Mobility of Ions in Hydrogen

The drift velocity of positive ions in hydrogen was measured over a range of $\frac{E}{{p}_{0}}$ (ratio of electric field strength to pressure) from 0.6-110 V per cm per mm Hg by means of a double-shutter velocity spectrometer. From these data the mobility (ratio of drift velocity to electric field) at a standard gas density of 2.69\ifmmode\times\else\texttimes\fi{}${10}^{19}$ molecules per ${\mathrm{cm}}^{3}$ could be calculated. At low electric-field strengths the observed mobility was 10.2 cm per sec per V per cm at room temperature. At an $\frac{E}{{p}_{0}}$ of 10 the mobility began to rise, passing through a maximum of 14.3 at an $\frac{E}{{p}_{0}}$ of 60. The mobility at small electric field strengths was also measured as a function of temperature from 77-470\ifmmode^\circ\else\textdegree\fi{}K. Its value remained nearly constant at about 10 from 77\ifmmode^\circ\else\textdegree\fi{}K to room temperature and then rose abruptly to 11.5 at 375\ifmmode^\circ\else\textdegree\fi{}K. These results are compared with other recent measurements and it is suggested that ${\mathrm{H}}_{5}^{+}$ cluster formation may be responsible for the unusual behavior of the mobility of the hydrogen ion.