Electric Charge Separation Research Articles

Attosecond X-ray generation driven by the relativistic laser pulse based on the semi-analytical self-consistent theory

A semi-analytical theory of the interaction between a relativistic laser pulse and the overdense plasma to generate an attosecond X-ray source is presented.The physical parameters such as plasma oscillation trajectory,surface electric field and magnetic field can be given by this model,and the high-order harmonic spectrum is also calculated accurately from the solution of the plasma surface oscillations,the obtained result is consistent with the result from the PIC simulation program.This model can be valid for arbitrary laser duration,solid densities,and a large set of laser peak intensities (1018-1021 W/cm2).In addition,the model is not applicable for the small laser focal spots (less than ten times the laser wavelength),although two-dimensional effects such as the pulse finite size may significantly change the movement progress of the electrons,the laser spot can be larger than ten times the laser wavelength under the general laboratory conditions. In this model,the laser energy absorption is small,and the electron kinetic pressure is also small.Due to the radiation pressure of the laser pulse,the electrons are pushed into the solid,forming a very steep density profile.As a result,the relevant forces makes the electrons ponderomotive and the longitudinal electric field is caused by the strong electric charge separation effect.This semi-analytical self-consistent theory can give us a reasonable physical description, and the momentum equation and the continuity equation of the electric and magnetic field at the boundary allow us to determine the plasma surface oscillations.The spatiotemporal characteristics of the reflected magnetic and electric field at the boundary can allow us to determine the emitting characteristics of the high order harmonic. Our results show that the radiation of the attosecond X-ray source is dependent on the plasma surface oscillation. The plasma surface oscillates with a duration about twice the laser optical cycle,and the high-order harmonics also emit twice the laser optical cycle,thus an attosecond pulse train driven by the multi-cycle laser pulse can be formed.By using a few-cycle laser field,the smooth high-order harmonics can be obtained,which leads to a single attosecond pulse with high signal-to-noise ratio.In a word,our calculation results show that the time evolution progress of plasma surface can be controlled by changing the carrier envelope phase of the few-cycle laser pulse,and then the radiation progress of the high-order harmonics can be influenced as result of a single attosecond X-ray pulse.

Charge-Separation Kinetics of Photoexcited Oxygen Vacancies in ZnO Nanowire Field-Effect Transistors

Shining light on a semiconductor can create electron-hole pairs---the well known basis of all photovoltaic cells. However, the processes behind photogeneration and recombination of pairs remain unclear at the nanoscale, where Coulombic attraction becomes quite strong. The authors use FET structures to control the surface electric field and study charge separation in photoexcited ZnO nanowires Their results aid our understanding of the physics behind the responses of phototransistors and photosensors, the quantum efficiencies of solar cells, and the reactivities of photocatalytic and photochemical systems at the nanoscale.

Power Source for Wireless Sensors in Pipes

In this paper, we present investigations on wireless sensors for fluid control inside a pipe. Autarkic sensors are in the technical trend. They are typically connected with a transceiver unit for data transmission. Sensors usually need a lower amount of energy than data transceivers. Therefore, they are commonly supplied via wires or batteries with electricity. With common technologies, this request leads to high requirements on tightness in liquids since poor sealing could easily lead to failures. Replacement of batteries inside pipes is complicated and almost accompanied by a flow interruption. The application of energy harvesters as power supply is therefore a good alternative. In our studies we used flexible piezoelectric energy harvesters of PVDF (Poly-Vinylidene-Di-Fluoride). All harvesting units consist of piezoelectric PVDF-foils as active layers and Aluminum-foils as electrodes. The layers were stacked alternating on each other and wound to a spool. A LDPE-film wraps the spool and prevents the inflow of liquids. The device has following parameters: No. of windings: 4 in air, 4, 5, 7 in water Dimensions: 15 mm O 22mm Materials: PDVF: 25μm; Aluminimum: 6μm, LDPE: 25μm A ring shaped bluff body was placed inside the pipe to induce turbulence in the fluid stream. As the harvesters have been arranged downstream of the bluff body, they were forced to oscillate independent of the media. In each case, deformation of the active layers led to a polarization and a separation of electrical charges. Experiments were carried out in a wind channel as well as in a water pipe. In air, the spool oscillates with a frequency of about 30Hz, at a wind speed of about 7m/s. A -Voltage of about 4V (peak-peak) was measured. This delivers in case of power adjustment, power values of about 0.54μW. In water, the velocity of the fluid was limited to nearly one tenth. Oscillation starts only at a water speed above 0.6m/s. The average oscillation frequency is about 18Hz. At a velocity of 0.74m/s, a peak-peak-Voltage up to about 2.3V was found. In case of impedance adjustment, the power was about 0.33μW. This power is stored in a capacitor. Assuming a data transmission unit consumes about 0.2 mWs during one operational period of 1 second, the duty cycle time can be calculated to about 6.2 minutes for air harvesting and 10.1 minutes for harvesting in water.

Nonlinear oscillations of coalescing magnetic flux ropes.

An analytical model of highly nonlinear oscillations occurring during a coalescence of two magnetic flux ropes, based upon two-fluid hydrodynamics, is developed. The model accounts for the effect of electric charge separation, and describes perpendicular oscillations of the current sheet formed by the coalescence. The oscillation period is determined by the current sheet thickness, the plasma parameter β, and the oscillation amplitude. The oscillation periods are typically greater or about the ion plasma oscillation period. In the nonlinear regime, the oscillations of the ion and electron concentrations have a shape of a narrow symmetric spikes.

(Invited) A Spontaneously Generated Electrical Charge of an Aqueous Droplet by Pipetting and Its Use of a Self-Powered Sensor

We report that pipetting dispenses an electrically charged aqueous droplet by a spontaneous electrical charging process. This electrification originated from the electrical charge separation between the droplet and the inner surface of the tip of the pipet. Methods to suppress and control the electrical charge of a droplet should be developed because such unexpected phenomenon is mostly undesirable in many experiments. Two different methods for controlling the electrical charge, i.e., passive and active methods, have been developed and reported. Utilizing these methods, it is possible to intentionally control the behavior of droplets in oil environment. Furthermore, since this spontaneous generation of the net electrical charge is equivalent with the generation of the electrical power, the potential use of the electrification as a self-powered sensor is briefly discussed.

(Invited) A Spontaneously Generated Electrical Charge of an Aqueous Droplet by Pipetting and Its Use of a Self-Powered Sensor

Recently, we reported that pipetting always dispenses an electrically charged aqueous droplet by spontaneous electrical charging process between the pipet tip inner surface and the aqueous droplet. The amount of an electrical charge depends on the constituents of the droplet, on coating material of a pipet tip, and on atmospheric humidity. It is clarified that this spontaneous electrical charging of an aqueous droplet is originated from the electrical charge separation between the droplet and the pipet tip inner surface through performing consecutive measurement of the electrical charge amount of the pipet tip and the droplet during a pipetting process. Since this unexpected electrification phenomenon could influence the localization and combination of charged bio-molecules inside the aqueous solution, controlling and suppressing the spontaneous electrification phenomenon are important. To suggest the way to suppress the electrification phenomenon, a graphene-based nanocomposite coated pipet tip, which we called a zeta-pipet tip, is fabricated, as a proof-of-concept example to reduce the zeta potential of the pipet tip inner surface. Since the electrical charge is always spontaneously generated in the case of solid-water contact, it could be potentially utilized with a self-powered sensor.

Is It Beneficial for the Major Photosynthetic Antenna Complex of Plants To Form Trimers?

The process of primary electric charge separation in photosynthesis takes place in the reaction centers, but photosynthesis can operate efficiently and fluently due to the activity of several pigment-protein complexes called antenna, which absorb light quanta and transfer electronic excitations toward the reaction centers. LHCII is the major photosynthetic pigment-protein antenna complex of plants and appears in the trimeric form. Several recent reports point to trimeric organization of LHCII as a key factor responsible for the chloroplast architecture via stabilization of granal organization of the thylakoid membranes. In the present work, we address the question of whether such an organization could also directly influence the antenna properties of this pigment-protein complex. Chlorophyll fluorescence analysis reveals that excitation energy transfer in LHCII is substantially more efficient in trimers and dissipative energy losses are higher in monomers. It could be concluded that trimers are exceptionally well suited to perform the antenna function. Possibility of fine regulation of the photosynthetic antenna function via the LHCII trimer-monomer transition is also discussed, based on the fluorescence lifetime analysis in a single chloroplast.

A high-resolution global Vlasov simulation of a small dielectric body with a weak intrinsic magnetic field on the K computer

The interaction between the solar wind and solar system bodies, such as planets, satellites, and asteroids, is one of the fundamental global-scale phenomena in space plasma physics. In the present study, the electromagnetic environment around a small dielectric body with a weak intrinsic magnetic field is studied by means of a first-principle kinetic plasma simulation, which is a challenging task in space plasma physics as well as high-performance computing. Due to several computational limitations, five-dimensional full electromagnetic Vlasov simulations with two configuration space and three velocity space coordinates are performed with two different spatial resolutions. The Debye-scale charge separation is not solved correctly in the simulation run with a low spatial resolution, while all the physical processes in collisionless plasma are included in the simulation run with a high spatial resolution. The direction comparison of electromagnetic fields between the two runs shows that there is small difference in the structure of magnetic field lines. On the other hand, small-scale fine structures of electrostatic fields are enhanced by the electric charge separation and the charge accumulation on the surface of the body in the high-resolution run, while these structures are absent in the low-resolution runs. These results are consistent with the conventional understanding of plasma physics that the structure and dynamics of global magnetic fields, which are generally described by the magneto-hydro-dynamics (MHD) equations, are not affected by electron-scale microphysics.

Chiral magnetic wave in an expanding QCD fluid

As a consequence of the chiral anomaly, the hydrodynamics of hot QCD matter coupled to QED allows for a long-wavelength mode of chiral charge density, the chiral magnetic wave (CMW), that provides for a mechanism of electric charge separation along the direction of an external magnetic field. Here, we investigate the efficiency of this mechanism for values of the time-dependent magnetic field and of the energy density attained in the hot QCD matter of ultra-relativistic heavy ion collisions. To this end, we derive the CMW equations of motion for expanding systems by treating the CMW as a charge perturbation on top of an expanding Bjorken-type background field in the limit of small chemical potential. Both, approximate analytical and full numerical solutions to these equations of motion indicate that for the lifetime and thermodynamic conditions of ultra-relativistic heavy ion collisions, the efficiency of CMW-induced electric charge separation decreases with increasing center of mass energy and that the effect is numerically very small. We note, however, that if sizable oriented asymmetries in the axial charge distribution (that are not induced by the CMW) are present in the early fluid dynamic evolution, then the mechanism of CMW-induced electric charge separation can be much more efficient.

A Stochastic Relationship

A Stochastic Relationship

Computational Modeling of Electrostatic Charge and Fields Produced by Hypervelocity Impact

Following prior experimental evidence of electrostatic charge separation, electric and magnetic fields produced by hypervelocity impact, we have developed a model of electrostatic charge separation based on plasma sheath theory and implemented it into the CTH shock physics code. Preliminary assessment of the model shows good qualitative and quantitative agreement between the model and prior experiments at least in the hypervelocity regime for the porous carbonate material tested. Moreover, the model agrees with the scaling analysis of experimental data performed in the prior work, suggesting that electric charge separation and the resulting electric and magnetic fields can be a substantial effect at larger scales, higher impact velocities, or both.

The electric field in sandstorm can strongly affect the sand׳s scattering properties

It has been found that the particle in the sandstorm is always associated with the separation of electric charge, which in turn produces a strong electrostatic field. A few papers have reported that the surplus charge on particle has a significant effect on particles׳ optical properties, but no any reports on the influence of the environmental electric field. In order to fill this gap, this paper proposed a theoretical model and carried out a numerical simulation. The calculated results show that the environmental electric field, when it is more than 50kV/m, should have a significant influence on particle׳s optical properties, and the stronger the environmental electric field is, the more obvious the influence is. This paper also shows that both the charged angle and the charge density on particle have some influences on it. The above findings offer a theoretical guidance to understand the effect of electric field on the microwave propagation on the sandstorm.

Local CP-violation and electric charge separation by magnetic fields from lattice QCD

We study local CP-violation on the lattice by measuring the local correlation between the topological charge density and the electric dipole moment of quarks, induced by a constant external magnetic field. This correlator is found to increase linearly with the external field, with the coefficient of proportionality depending only weakly on temperature. Results are obtained on lattices with various spacings, and are extrapolated to the continuum limit after the renormalization of the observables is carried out. This renormalization utilizes the gradient flow for the quark and gluon fields. Our findings suggest that the strength of local CP-violation in QCD with physical quark masses is about an order of magnitude smaller than a model prediction based on nearly massless quarks in domains of constant gluon backgrounds with topological charge. We also show numerical evidence that the observed local CP-violation correlates with spatially extended electric dipole structures in the QCD vacuum.

Applications of Oxide Coatings in Photovoltaic Devices

Metalloid and metal based oxides are an almost unavoidable component in the majority of solar cell technologies used at the time of writing this review. Numerous studies have shown increases of ≥1% absolute in solar cell efficiency by simply substituting a given layer in the material stack with an oxide. Depending on the stoichiometry and whether other elements are present, oxides can be used for the purpose of light management, passivation of electrical defects, photo-carrier generation, charge separation, and charge transport in a solar cell. In this review, the most commonly used oxides whose benefits for solar cells have been proven both in a laboratory and industrial environment are discussed. Additionally, developing trends in the use of oxides, as well as newer oxide materials, and deposition technologies for solar cells are reported.

Correlations between electrical and mechanical signals during granular stick-slip events

Powders and grains exhibit unpredictable jamming-to-flow transitions that manifest themselves on geophysical scales in catastrophic slip events such as landslides and earthquakes, and on laboratory/industrial scales in profound processing difficulties. Over the past few years, insight into these transitions has been provided by new evidence that slip events may be accompanied, or even preceded, by electrical effects. In the present work, we quantify the correlation between slip and the separation of electrical charges, using an archetypal granular material: photoelastic polymers. We measure a strong correlation between material displacement, acoustic emissions, and voltage. We find that the generation of voltage is associated with surface, rather than bulk properties of the granular materials. While voltage precursors are only occasionally observed in this system, there is some asymmetry in the cross-correlation between the slip and voltage signals that indicates differences between the pre- and post-slip dynamics.

Spatial separation and motion of electric charges arisingdue to the interaction of high-power IR laser radiation with water

We have studied temporal and amplitude characteristics of the electrical signal arising under irradiation of the free water surface by a 2.94-μm high-power laser. The investigations have been conducted using a specially designed electrode system, which makes it possible to record the motion of the electric charge after the end of the laser pulse. We have measured the dependences of the signal parameters on the radiation energy density at the water surface.

“Capacitive Sensor” to Measure Flow Electrification and Prevent Electrostatic Hazards

At a solid/liquid interface, physico-chemical phenomena occur that lead to the separation of electrical charges, establishing a zone called electrical double layer. The convection of one part of these charges by the liquid flow is the cause of the flow electrification phenomenon which is suspected of being responsible of incidents in the industry. The P' Institute of Poitiers University and CNRS has developed an original sensor called “capacitive sensor” that allows the characterization of the mechanisms involved in the generation, accumulation and transfer of charges. As an example, this sensor included in the design of high power transformers, could easily show the evolution of electrostatic charge generation developed during the operating time of the transformer and, therefore, point out the operations leading to electrostatic hazards and, then, monitor the transformer to prevent such risks.

Pyroelectric Nanogenerators for Harvesting Thermoelectric Energy

Harvesting thermoelectric energy mainly relies on the Seebeck effect that utilizes a temperature difference between two ends of the device for driving the diffusion of charge carriers. However, in an environment that the temperature is spatially uniform without a gradient, the pyroelectric effect has to be the choice, which is based on the spontaneous polarization in certain anisotropic solids due to a time-dependent temperature variation. Using this effect, we experimentally demonstrate the first application of pyroelectric ZnO nanowire arrays for converting heat energy into electricity. The coupling of the pyroelectric and semiconducting properties in ZnO creates a polarization electric field and charge separation along the ZnO nanowire as a result of the time-dependent change in temperature. The fabricated nanogenerator has a good stability, and the characteristic coefficient of heat flow conversion into electricity is estimated to be ∼0.05-0.08 Vm(2)/W. Our study has the potential of using pyroelectric nanowires to convert wasted energy into electricity for powering nanodevices.

Spectroscopy of Photosynthetic Pigment-Protein Complex LHCII

Light-harvesting pigment–protein complex of photosystem II is the most abundant membrane protein in the biosphere, comprising more than half chlorophyll molecules. The protein plays a role of photosynthetic antenna, collecting solar radiation and transferring excitations towards the reaction centers, where electric charge separation takes place. Efficient excitation energy capture and transfer requires unique organization of the complex and unique photophysical properties of the accessory pigments: chlorophylls and carotenoids. LHCII is also a place where extremely harmful singlet oxygen may be generated, under strong illumination conditions. Several physical mechanisms have been found in LHCII, operating to protect the photosynthetic apparatus against light-induced damage, including chlorophyll triplet and singlet excitations quenching by carotenoids. In this paper we discuss the results of our recent studies, carried out with the application of several molecular spectroscopy techniques (electronic absorption, fluorescence, resonance Raman and FTIR), designed to investigate molecular mechanisms responsible for regulation of excitation density in LHCII. Among the most interesting findings are the light-induced molecular configuration changes of the LHCII-bound xanthophylls, leading to conformational rearrangements of the protein. These mechanisms are discussed in terms of excessive excitation quenching in the pigment–protein complex subjected to overexcitation. Such an activity seems to represent a vital regulatory process in the photosynthetic apparatus, at the molecular level, protecting plants against photodegradation.

Feel the force: Bio-electricity and the sensing of electric fields

In an issue devoted to sensory phenomena, it may seem odd to include an article on sensing something that we cannot consciously perceive: electric force. Of course, we can sense the dramatic power of a lightning bolt: we see the flash, hear the boom, feel the rumble, and, if we're close enough, smell and taste the ozone produced. Lightning is caused by an enormous electric field that develops under a thundercloud due to the separation of electrical charges between the cloud and the earth. Almost 250 years after Benjamin Franklin's kite-in-the-storm experiment, we still don't fully understand how this charge separation is generated. But it's nevertheless a fact that if you are standing under a thundercloud, you are immersed in a large vertically directed electric field, typically a few hundred volts between your head and your feet. Just before a lightning strike, this electric field becomes large enough to literally rip gas molecules in the air apart by pulling negatively charged electrons in one direction – towards the positively charged ground – and positive nuclei towards the negative cloud. Once a column of air becomes ionized in this way, the charged particles zoom to their respective ‘electrodes’, discharging the cloud–ground capacitor in a bright, hot flash of enormous electrical current. Lightning is a manifestation of a phenomenon called ‘dielectric breakdown’, something we've all seen in more controlled contexts, such as cheesy horror movies, Ask-Dr-Science demos at science museums and aluminium foil mistakenly placed in the microwave oven. Dielectric breakdown of most materials occurs at electric fields on the order of a few million volts per metre. But there is a great irony here: whereas we sense all of the secondary consequences of lightning, we are utterly blind to its most fundamental element – the electric field that gets the whole thing going. Humans just never evolved electric-force sensors. (But fish did – and migratory birds and turtles navigate by ‘feeling’ the earth's weak magnetic field.