Spontaneous Electric Field Research Articles

A human brain microphysiological system derived from induced pluripotent stem cells to study neurological diseases and toxicity.

SummaryHuman in vitro models of brain neurophysiology are needed to investigate molecular and cellular mechanisms associated with neurological disorders and neurotoxicity. We have developed a reproducible iPSC-derived human 3D brain microphysiological system (BMPS), comprised of differentiated mature neurons and glial cells (astrocytes and oligodendrocytes) that reproduce neuronal-glial interactions and connectivity. BMPS mature over eight weeks and show the critical elements of neuronal function: synaptogenesis and neuron-to-neuron (e.g., spontaneous electric field potentials) and neuronal-glial interactions (e.g., myelination), which mimic the microenvironment of the central nervous system, rarely seen in vitro before. The BMPS shows 40% overall myelination after 8 weeks of differentiation. Myelin was observed by immunohistochemistry and confirmed by confocal microscopy 3D reconstruction and electron microscopy. These findings are of particular relevance since myelin is crucial for proper neuronal function and development. The ability to assess oligodendroglial function and mechanisms associated with myelination in this BMPS model provide an excellent tool for future studies of neurological disorders such as multiple sclerosis and other demyelinating diseases. The BMPS provides a suitable and reliable model to investigate neuron-neuroglia function as well as pathogenic mechanisms in neurotoxicology.

Electrical and optical anisotropy in rutile TiO2

ABSTRACTWe present a theoretical approach for studying the electrical and optical properties of rutile titanium dioxide at room temperature. The quantum mechanics microscopic model bases on the orbital approximation in correlation with the dipole-dipole approximation and takes into account the anisotropy in the first-, second-, and third-order electronic polarizabilities of the constituent ions, their ionic shifts as well as the crystalline deformations. Our theoretical calculations show that the experimental data of the refractive indices and the large optical birefringence of rutile titanium dioxide can be mainly explained by considering nonlinearity and anisotropy of the electronic polarizabilities of the oxygen ions. The spontaneous local electric field acting on the oxygen ions plays a major role in these calculations.

Observation of the variations of the domain structure of a spontaneous electric field in a two-dimensional electron system under microwave irradiation

It has been found on a sample of the GaAs/AlGaAs heterostructure with the two-dimensional electron system that different configurations of domains of a spontaneous electric field are possible within one microwave- induced state with the resistance tending to zero. Transitions between such configurations are observed at the variation of the radiation power and magnetic field. In the general case, the configuration of domains is more complicated than existing models. The fragment of the distribution of the electric field in the sample for one of the observed configurations is in agreement with the rhombic domain structure considered by I. G. Finkler and B. I. Halperin, Phys. Rev. B 79, 085315 (2009).

Spontaneous polarization induced electric field in zinc oxide nanowires and nanostars

We report on the detection mechanism of spontaneous polarization using electrostatic force microscopy in zinc oxide nanowires and nanostars grown by vapor-liquid-solid technique. Optical and structural properties are investigated in detail to understand the complex ZnO nanostructures comprehensively. Calculations are carried out to estimate the electric field from the change in interleave amplitude induced by the electrostatic force due to the spontaneous polarization effects. Attraction of the probe between the tip and the sample varies for different structures with a stronger attraction for nanostars as compared to nanowires. Strength of electric field is dependent on the orientation of nanowires and nanostars c-axis with measured magnitude of electric field to be ∼107 V/m and 108 V/m respectively. This technique presents a unique detection mechanism of built-in spontaneous polarization and electric field from polar ZnO nanowires with applications in voltage gated ion channels, nano-bio interfaces, optoelectronic and photonic devices.

A human brain microphysiological system derived from induced pluripotent stem cells to study neurological diseases and toxicity_suppl1

Human in vitro models of brain neurophysiology are needed to investigate molecular and cellular mechanisms associated with neurological disorders and neurotoxicity. We have developed a reproducible iPSC-derived human 3D brain microphysiological system (BMPS), comprised of differentiated mature neurons and glial cells (astrocytes and oligodendrocytes) that reproduce neuronal-glial interactions and connectivity. BMPS mature over eight weeks and show the critical elements of neuronal function: synaptogenesis and neuron-to-neuron (e.g., spontaneous electric field potentials) and neuronal-glial interactions (e.g., myelination), which mimic the microenvironment of the central nervous system, rarely seen in vitro before. The BMPS shows 40% overall myelination after 8 weeks of differentiation. Myelin was observed by immunohistochemistry and confirmed by confocal microscopy 3D reconstruction and electron microscopy. These findings are of particular relevance since myelin is crucial for proper neuronal function and development. The ability to assess oligodendroglial function and mechanisms associated with myelination in this BMPS model provide an excellent tool for future studies of neurological disorders such as multiple sclerosis and other demyelinating diseases. The BMPS provides a suitable and reliable model to investigate neuron-neuroglia function as well as pathogenic mechanisms in neurotoxicology.

Emission color-tuned light-emitting diode microarrays of nonpolar In(x)Ga(1-x)N/GaN multishell nanotube heterostructures.

Integration of nanostructure lighting source arrays with well-defined emission wavelengths is of great importance for optoelectronic integrated monolithic circuitry. We report on the fabrication and optical properties of GaN-based p–n junction multishell nanotube microarrays with composition-modulated nonpolar m-plane InxGa1–xN/GaN multiple quantum wells (MQWs) integrated on c-sapphire or Si substrates. The emission wavelengths were controlled in the visible spectral range of green to violet by varying the indium mole fraction of the InxGa1–xN MQWs in the range 0.13 ≤ x ≤ 0.36. Homogeneous emission from the entire area of the nanotube LED arrays was achieved via the formation of MQWs with uniform QW widths and composition by heteroepitaxy on the well-ordered nanotube arrays. Importantly, the wavelength-invariant electroluminescence emission was observed above a turn-on of 3.0 V because both the quantum-confinement Stark effect and band filling were suppressed due to the lack of spontaneous inherent electric field in the m-plane nanotube nonpolar MQWs. The method of fabricating the multishell nanotube LED microarrays with controlled emission colors has potential applications in monolithic nonpolar photonic and optoelectronic devices on commonly used c-sapphire and Si substrates.

Self-Oscillations of a spontaneous electric field in a nonequilibrium two-dimensional electron system under microwave irradiation

Self-oscillations of a microwave photovoltage with irregular interruptions have been discovered in the states with vanishing dc dissipation emerging in two-dimensional electron systems under microwave irradiation. The observed picture can be caused by transitions between a stable pole and a limiting cycle in the phase space of the systems (Andronov–Hopf bifurcation) that occur owing to fluctuations.

Effect of effective mass and spontaneous polarization on photocatalytic activity of wurtzite and zinc-blende ZnS

Semiconductor zinc sulphide (ZnS) has two common phases: hexagonal wurtzite and cubic zinc-blende structures. The crystal structures, energy band structures, density of states (DOS), bond populations, and optical properties of wurtzite and zinc-blende ZnS were investigated by the density functional theory of first-principles. The similar band gaps and DOS of wurtzite and zinc-blende ZnS were found and implied the similarities in crystal structures. However, the distortion of ZnS4 tetrahedron in wurtzite ZnS resulted in the production of spontaneous polarization and internal electric field, which was beneficial for the transfer and separation of photogenerated electrons and holes.

Spontaneous electric fields in solid carbon monoxide.

Reflection-absorption infrared spectroscopy (RAIRS) is shown to provide a means of observing the spontelectric phase of matter, the defining characteristic of which is the occurrence of a spontaneous and powerful static electric field within a film of material. The presence of such a field is demonstrated here through the study of longitudinal-transverse optical splitting in RAIR spectra in films of carbon monoxide, based upon the deposition temperature dependence of this splitting. Analysis of spectral data, in terms of the vibrational Stark effect, allows the measurement of the polarization of spontelectric films, showing for example that solid carbon monoxide at 20 K may maintain a spontelectric field of 3.78 × 10(7) V m(-1), representing a polarization of 3.34 × 10(-4) cm(-2). We comment on the astrophysical implications of polarized carbon monoxide ices, on the surface of cosmic grains in star-forming regions.

Intrinsic Hysteresis Loops Calculation of BZT Thin Films

The Landau Devonshire (LK) simulation is utilized to calculate the intrinsic hysteresis properties of Barium Zirconium Titanate (BZT) doped by Indium and Lanthanum. A Delphi program run on Windows platform is used to facilitate the calculation. The simulation is very useful to calculate and understand the Gibbs free energy and the relationship between spontaneous polarization and electric field.

Electrical properties and Pockels effect in BaTiO $$_{3}$$ 3 /SrTiO $$_{3}$$ 3 superlattices

The electrical and linear electro-optical properties of BaTiO $$_{3}$$ (BT)/SrTiO $$_{3}$$ (ST) superlattices epitaxially grown on ST substrate are theoretically investigated using a microscopic quantum mechanical model based on the orbital approximation in correlation with the dipole–dipole interaction. Both the first-, second-, and third-order electronic polarizabilities were considered in this calculation in order to obtain accurate results for both the spontaneous local electric field, spontaneous polarization, relative dielectric constant, and linear electro-optic coefficients (Pockels constants) of BT/ST superlattices. The calculations show that the spontaneous local electric field, spontaneous polarization and linear electro-optic coefficients of BT/ST superlattices increase with their content in BT while the relative dielectric constant increases with their content in ST. Moreover, we have shown that significant enhancement of the linear electro-optic coefficients can be achieved in BT/ST superlattices. This enhancement, which concerns the ST as well as the BT layers, arises from the combined effects of strain, induced in the BT layers by the epitaxial growth, and internal polarizing electric field originating in the BT layers and acting on the electronic clouds of the polarizable constituent ions of the system.

Ferroelectric phase transition in graphene with the Hubbard interaction

It has been revealed that, as an external dc electric field is applied to graphene with the Hubbard interaction between electrons, a spontaneous electric field perpendicular to the applied field can appear. This effect can be due to the nonequilibrium electron subsystem in graphene. The spontaneous field characteristics have been found as a function of the parameters of the problem.

Crystal orientation effects on wurtzite quantum well electromechanical fields

A one-dimensional continuum model for calculating strain and electric field in wurtzite semiconductor heterostructures with arbitrary crystal orientation is presented and applied to GaN/AlGaN and ZnO/MgZnO heterostructure combinations. The model is self-consistent involving feedback couplings of spontaneous polarization, strain, and electric field. Significant differences between fully coupled and semicoupled models are found for the longitudinal and shear-strain components as a function of the crystal-growth direction. In particular, we find that the semicoupled model, typically used in the literature for semiconductors, is inaccurate for ZnO/MgZnO heterostructures where shear-strain components play an important role. An interesting observation is that a growth direction apart from $[\overline{1}2\overline{1}0]$ exists for which the electric field in the quantum well region becomes zero. This is important for, e.g., optimization of light-emitting-diode quantum efficiency.

Quantum wells on 3C-SiC/NH-SiC heterojunctions. Calculation of spontaneous polarization and electric field strength in experiments

The results of experiments with quantum wells on 3C-SiC/4H-SiC and 3C-SiC/6H-SiC heterojunctions obtained by various methods are reconsidered. Spontaneous polarizations, field strengths, and energies of local levels in quantum wells on 3C-SiC/NH-SiC heterojunctions were calculated within a unified model. The values obtained are in agreement with the results of all considered experiments. Heterojunction types are determined. Approximations for valence band offsets on heterojunctions between silicon carbide polytypes and the expression for calculating local levels in quantum wells on the 3C-SiC/NH-SiC heterojunction are presented. The spontaneous polarizations and field strengths induced by spontaneous polarization on 3C-SiC/4H-SiC and 3C-SiC/6H-SiC heterojunctions were calculated as 0.71 and 0.47 C/m2 and 0.825 and 0.55 MV/cm, respectively.

The role of electric field gradient in modeling elastic ferroelectrics

In this article a continuum model for simulating the microscopic behavior of ferroelectrics is proposed. The model is based on an alternative phase field formulation, where spontaneous polarization, mechanical strain, electric field and electric field gradient are used as constitutive variables. The electric field gradient is energetically conjugated to the quadrupole polarization, thus it is about a theory with electric quadrupoles. A variational principle has been used for the derivation of the field equations and the appropriate boundary conditions. Like polarization vector, it is assumed that electric quadrupole tensor is separated into a reversible and a spontaneous part, too. It is proved that spontaneous quadrupole tensor is responsible for the domain wall thickness. Computational examples concerning ferroelectric materials with charge and dipole defects are carried out with the proposed model. The additional boundary conditions provided by the variational principle seem to be useful especially to handle dipole defects.

Highly nonlinear phenomena of self‐organization of quasi‐two‐dimensional electron gas in high magnetic and electric fields

AbstractThe transverse electric field Ey that appears in lateral superlattices (2SLs) under Hall‐measurement conditions, i.e. in the presence of a longitudinal applied electric field Ex and applied magnetic field H normal to the SL plane (H ∥ OZ) is calculated. In contrast to previous works devoted to this problem both applied electric and magnetic fields are treated as control parameters. By introducing the generalized function of entropy production (the synergetic potential) the kinetic behavior of a quasi‐two‐dimensional nonequilibrium electron gas is investigated from the viewpoint of self‐organization and catastrophe theory. The field Ey contains both the Hall field and the spontaneous transverse electric field that exists without H. The magnetoresistance caused by the appearance of a spontaneous transverse EMF is investigated. Spontaneous transverse EMF, current–voltage characteristics and magnetoresistance are multivalued and sign‐changing functions of applied electric and magnetic fields. From the model computer simulations the observed multistability exhibits a large difference in the behavior of the system in high magnetic fields as compared to low one. The novel nonlinear effects such as first‐order nonequilibrium phase transitions and hysteresis, induced by magnetic field are predicted. As the magnetic field is increased the nonlinear behaviors show self‐organized hierarchical complexity, which manifests itself in fractalization of bifurcation set, whose self‐similar fine structure leading to fractal‐like folds of critical manifold sheets, resulting in fuzzy bifurcations, was discovered. Complex nonlinear behaviors including macrostate crisis and chaotic‐looking intermittency of Hall‐effect characteristics were discovered in limited narrow ranges of the control parameter space. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Drift current dominated terahertz radiation from InN at low-density excitation

This letter investigates the polarity of terahertz radiation from indium nitride (InN) excited by femtosecond optical pulses wherein a central wavelength of around 790nm is measured. The InN epilayers are grown by metalorganic chemical vapor deposition on sapphire and silicon substrates. The polarity of the terahertz radiation field from InN is opposite to that from p-InAs whose radiation mechanism is dominated by the photo-Dember effect indicating that the dominant radiation mechanism in InN is the drift current induced by the internal electric field at low-density excitation below 590nJ∕cm2. The internal electric field consists of the surface accumulation field and the spontaneous polarization-induced electric field. In addition, since no azimuthal angle dependence of the terahertz radiation is observed, the optical rectification effect is ruled out. By comparing the wave forms of terahertz radiation from the front and the back of the InN sample grown on sapphire in reflection geometry, the N polarity of the InN sample is confirmed.

Theoretical Study of the Site-Dependent Stabilities of Intrinsic Defects in a Polar BN Nanotube with Finite Length

Intrinsic defects, including single vacancy and Stone−Wales defects in a finite-length (8, 0) BN tube are investigated using density functional theory calculations. It is found that the stabilities of all defects are enhanced as they get close to the tube ends. We propose the possible physical origins for the defect energetic preference toward the tube ends and prove that the spontaneous electric polarization field of the BN tube can affect the stability of the defect by making the different electrostatic potential to the defect at different site. We also discuss the potential experimental consequences and provide the theoretical support for one experimental method for the synthesis of BN tubes.

Physics models of centriole replication

Our previous pre-clinic experimental results have showed that the epithelialization can be enhanced by the externally applied rectangular pulsed electrical current stimulation (RPECS). The results are clinically significant for patients, especially for those difficult patients whose skin wounds need long periods to heal. However, the results also raise questions: How does the RPECS accelerate the epithelium cell proliferation? To answer these questions, we have previously developed several models for animal cells, in a view of physics, to explain mechanisms of mitosis and cytokinesis at a cellular level, and separation of nucleotide sequences and the unwinding of a double helix during DNA replication at a bio-molecular level. In this paper, we further model the mechanism of centriole replication during a natural and normal mitosis and cytokinesis to explore the mechanism of epithelialization enhanced with the externally applied RPECS at a bio-molecular level. Our models suggest: (1) Centriole replication is an information flowing. The direction of the information flowing is from centrioles to centrioles based on a cylindrical template of 9 x 3 protein microtubules (MTs) pattern. (2) A spontaneous and strong electromagnetic field (EMF) force is a pushing force that separates a mother and a daughter centrioles in centrosomes or in cells, while a pulling force of interacting fibers and pericentriolar materials delivers new babies. The newly born babies inherit the pattern information from their mother(s) and grow using microtubule fragments that come through the centrosome pores. A daughter centriole is always born and grows along stronger EMF. The EMF mostly determines centrioles positions and plays key role in centriole replication. We also hypothesize that the normal centriole replication could not been disturbed in centrosome in the epithelium cells by our RPECS, because the centrioles have two non-conducting envelope (cell and centrosome membranes), that protect the normal duplication. The induced electric field by externally applied RPECS could be mild compared with the spontaneous and natural electric field of the centrioles. Therefore, the centriole replication during the epithelium cellular proliferation may be directly, as well as indirectly (e.g., somatic reflex) accelerated by the RPECS.

Self-Organization Process with Dynamo Activity in Ultra-Low q and Reversed-Field-Pinch Plasmas

Dynamo activity is highly important for formation and confinement of ultra-low q (ULQ) and reversed-field-pinch (RFP) plasmas. These configurations are self-organized by a spontaneous dynamo electric field. In order to investigate the properties of this self-organization process, an inductive poloidal electric field is applied to standard ULQ and RFP plasmas. Synchronized to the application of poloidal electric fields, remarkable responses of plasma parameters are observed. In the ULQ experiment, toroidal plasma current increases with decrease in loop voltage. In this experiment, fluctuation levels are almost constant. On the other hand, dIp/dt decreases with the reduction of plasma fluctuations in the RFP experiment. In these processes, plasmas will self-organize to maintain a state of nearly minimum energy. In general, the self-organization process changes the total dissipation in the system through the enhancement of the plasma fluctuation. To improve the plasma confinement for ULQ and RFP plasmas, it is important to understand the properties of this self-organization process in detail.