Value Of External Electric Field Research Articles

A strategy toward therapeutic improvement of electric field-sensitive gemcitabine prodrugs in 2D metal–organic frameworks in view of their structure and interactions

• The interaction energy of the drug-polymer with MON stronger than the free drug. • Higher value of external electric field will help in better absorption. • A 10% defect leads to a 50% increase in the total interaction energies of the carrier with the PPY-GEM molecules. Gemcitabine, among other chemotherapeutic agents, helps to save many lives in fighting cancers of various types. Nevertheless, many side effects arise from the high dosage required for effective treatment. Nanotechnology-based drug delivery systems (DDSs) are among the newly proposed strategies proposed to send chemotherapeutic agents directly to tumor cells and reduce their hazardous concentrations in healthy tissues. In this paper, through density functional theory (DFT) calculations and molecular dynamics (MD) simulations, a new DDS is designed in which gemcitabine is conjugated to an electric field-responsive polymer called polypyrrole and loaded on a metal–organic nanosheet (MON). DFT calculations reveal that covalent bonding between the drug and polymer has a limited impact on the chemical properties of the drug. On the other hand, the MD simulation suggested that the adsorption of the drug on the CuBDC nanoparticle is highly improved by conjunction with polymer. The interaction energy of the drug-polymer complex with MON is approximately 138 kJ/mol stronger than the corresponding value for the free drug. Furthermore, implementation of a lower magnitude of the external electric field may reduce the adsorption interaction energies, while a higher value will help in better absorption.

Electronic bandstructure modulation of MoX2/ZnO(X:S,Se) heterostructure by applying external electric field

The electronic properties of 2-Dimensional Van der Waals heterostructure of MX2(M:Mo, X:S, Se) and graphene-like ZnO by applying an external electric field(EF) in the range -0.50V/Å to 1.0V/Å is studied using first-principles calculations. The effect of the transverse electric field is measured in terms of modulation of the electronic energy bandgap and change in the band alignment properties. The bandstructure of MoS2/ZnO heterostructure(HS) shows an indirect bandgap of 1.61eV with a type-II band alignment and a large built-in electric field of 7.42eV with a valence band offset of 1.22eV across the interface. The bandstructure of MoSe2/ZnO shows a direct bandgap of 1.81eV with type-I alignment and a built-in electric field of 3.64eV with a band offset of 0.31eV. The charge density is localized on MoS2 and ZnO in VBM and CBM respectively in MoS2/ZnO HS, whereas in MoSe2/ZnO, both VBM and CBM are localized on MoSe2. With a perpendicular electric field applied across the HS, re-alignment of bandstructure and modulation of bandgap in both the HSs occurs. The energy bandgap increases linearly with the applied electric field for MoS2/ZnO(1.1–2.2eV) and remains almost constant(1.81eV) in the range -0.50V/Å to 0.50V/Å followed by a small decrease with an increase in electric field (1.60 for EF=±1.0V/Å). A cross-over in the bandgap type from indirect(type-II)→direct(type-I) in MoS2-ZnO and direct(type-I) to indirect(type-II) in MoSe2/ZnO has been observed at a critical value of electric field EF=0.75V/Å. The cross-over in band structure is consistent with the charge transfer pattern observed on the application of electric field. Tuning the electronic bandgap and changing the band-alignment with an external electric field opens a way to design futuristic electronic and optical devices.

The stability of two layer dielectric-electrolyte micro-flow subjected to an external electric field

The two-phase microflow of conductive (electrolyte) and non-conductive (dielectric) viscous liquids bounded by two solid walls in an external electric field is scrutinized. The lower solid wall, which is adjoined to the electrolyte, is a charged dielectric surface; the upper wall which bounds the dielectric is insulated. The problem has a steady one-dimensional (1D) solution. The theoretical results for a plug-like velocity profile are successfully compared with available theoretical and experimental data from the literature. The linear stability of the steady-state flow is investigated numerically with spectral Galerkin’s method for solving linearized eigenvalue problem. This method was successfully applied for related problem of electroosmosis of ultrathin film. The numerical analysis provides insights on the coexistence of long and short-wave instabilities. The influence of control parameters such as the ratio of the viscosities of both liquids and the ratio of the channel heights on the stability of one-dimensional flow was investigated for different values of external electric field. The influence of an external pressure gradient on the flow stability is also investigated. The experimental facts established by other authors, according to which the system destabilizes if the electroosmotic flow is oppositely directed to the external pressure gradient, is confirmed in this work. Otherwise stabilization takes place.

Exploring the Applicability of Nano-Poration for Remote Control in Smart Drug Delivery Systems.

Smart drug delivery systems represent an interesting tool to significantly improve the efficiency and the precision in the treatment of a broad category of diseases. In this context, a drug delivery mediated by nanosecond pulsed electric fields seems a promising technique, allowing for a controlled release and uptake of drugs by the synergy between the electropulsation and nanocarriers with encapsulated drugs. The main concern about the use of electroporation for drug delivery applications is the difference in dimension between the liposome (nanometer range) and the cell (micrometer range). The choice of liposome dimension is not trivial. Liposomes larger than 500nm of diameter could be recognized as pathogen agents by the immune system, while liposomes of smaller size would require external electric field of high amplitudes for the membrane electroporation that could compromise the cell viability. The aim of this work is to theoretically study the possibility of a simultaneous cell and liposomes electroporation. The numerical simulations reported the possibility to electroporate the cell and a significant percentage of liposomes with comparable values of external electric field, when a 12nsPEF is used.

Compensation of asymmetry of diffraction characteristics of holographic chirped photonic structures in PDLC by the impact of spatially non-uniform electric field

In this work we have proposed the method of asymmetry compensation of diffraction characteristics of chirped photonic structures in PDLC by the impact of electric field, which has different forms of spatial inhomogeneity. It's shown that for each area of external electric field values the function of inhomogeneity has its optimal form.

A holographic description of the Schwinger effect in a confining gauge theory

This is a review of the recent progress on a holographic description of the Schwinger effect. In 2011, Semenoff and Zarembo proposed a scenario to study the Schwinger effect in the context of the AdS/CFT correspondence. The production rate of quark–antiquark pairs was computed in the Coulomb phase. In particular, it provided the critical value of external electric field, above which particles are freely created and the vacuum decays catastrophically. Then the potential analysis in the holographic approach was invented and it enabled us to study the Schwinger effect in the confining phase as well. A remarkable feature of the Schwinger effect in the confining phase is to exhibit another kind of the critical value, below which the pair production cannot occur and the vacuum of the system is nonperturbatively stable. The critical value is tantamount to the confining string tension. We computed the pair production rate numerically and introduced new exponents associated with the critical electric fields.

Trapping Effect on Electrical Behavior of Polyester Film: I. Unipolar Injection

Charging current-time J(t) characteristics for a polar polymer were simulated via a simple one-carrier model including traps with effective density N t. This model is used to reproduce the conduction current-time component J c(t) in the case of a typical polar polymer (PET) containing traps levels, which allows understanding the electrical behavior of the current at different values of external electric field via the effect of trapping factors.

A comparison of foetal SAR in three sets of pregnant female models

This paper compares the foetal SAR in the HPA hybrid mathematical phantoms with the 26-week foetal model developed at the National Institute of Information and Communications Technology, Tokyo, and the set of 13-, 26- and 38-week boundary representation models produced at Rensselaer Polytechnic Institute. FDTD calculations are performed at a resolution of 2 mm for a plane wave with a vertically aligned electric field incident upon the body from the front, back and two sides from 20 MHz to 3 GHz under isolated conditions. The external electric field values required to produce the ICNIRP public exposure localized restriction of 2 W kg−1 when averaged over 10 g of the foetus are compared with the ICNIRP reference levels.

SAR Changes in a Human Head Model for Plane Wave Exposure (500–2500 MHz) and a Comparison with IEEE 2005 Safety Limits

In this paper, external electric field values that are derived from the largest peak average 10 g SAR (Specific Absorption Rate) results in a realistic human head model are compared with current IEEE and ICNIRP reference levels. The head is illuminated by a plane wave source at seven different frequencies ranging from 500 MHz to 2500 MHz, with five different incident directions and three polarizations. Results reveal that the presence of metallic wire spectacles reduces the external electric field levels in the region above 900 MHz. Comparison of derived electric field values shows that the current IEEE and ICNIRP safety limits provide a conservative estimate.

FDTD calculations of specific energy absorption rate in a seated voxel model of the human body from 10 MHz to 3 GHz

Finite-difference time-domain (FDTD) calculations have been performed to investigate the frequency dependence of the specific energy absorption rate (SAR) in a seated voxel model of the human body. The seated model was derived from NORMAN (NORmalized MAN), an anatomically realistic voxel phantom in the standing posture with arms to the side. Exposure conditions included both vertically and horizontally polarized plane wave electric fields between 10 MHz and 3 GHz. The resolution of the voxel model was 4 mm for frequencies up to 360 MHz and 2 mm for calculations in the higher frequency range. The reduction in voxel size permitted the calculation of SAR at these higher frequencies using the FDTD method. SAR values have been calculated for the seated adult phantom and scaled versions representing 10-, 5- and 1-year-old children under isolated and grounded conditions. These scaled models do not exactly reproduce the dimensions and anatomy of children, but represent good geometric information for a seated child. Results show that, when the field is vertically polarized, the sitting position causes a second, smaller resonance condition not seen in resonance curves for the phantom in the standing posture. This occurs at ∼130 MHz for the adult model when grounded. Partial-body SAR calculations indicate that the upper and lower regions of the body have their own resonant frequency at ∼120 MHz and ∼160 MHz, respectively, when the grounded adult model is orientated in the sitting position. These combine to produce this second resonance peak in the whole-body averaged SAR values calculated. Two resonance peaks also occur for the sitting posture when the incident electric field is horizontally polarized. For the adult model, the peaks in the whole-body averaged SAR occur at ∼180 and ∼600 MHz. These peaks are due to resonance in the arms and feet, respectively. Layer absorption plots and colour images of SAR in individual voxels show the specific regions in which the seated human body absorbs the incident field. External electric field values required to produce the ICNIRP basic restrictions were derived from SAR calculations and compared with ICNIRP reference levels. This comparison shows that the reference levels provide a conservative estimate of the ICNIRP whole-body averaged SAR restriction, with the exception of the region above 1.4 GHz for the scaled 1-year-old model.

Effects of posture on FDTD calculations of specific absorption rate in a voxel model of the human body

A change in the posture of the human body can significantly affect the way in which it absorbs radiofrequency electromagnetic radiation. To study this, an anatomically realistic model of the body has been modified to develop new voxel models in postures other than the standard standing position with arms to the side. These postures were sitting, arms stretched out horizontally to the side and vertically above the head. Finite-difference time-domain (FDTD) calculations of the whole-body averaged specific energy absorption rate (SAR) have been performed from 10 MHz to 300 MHz at a resolution of 4 mm. Calculations show that the effect of a raised arm above the head posture was to increase the value of the whole-body averaged SAR at resonance by up to 35% when compared to the standard, arms by the side position. SAR values, both whole-body averaged and localized in the ankle, were used to derive the external electric field values required to produce the SAR basic restrictions of the ICNIRP guidelines. It was found that, in certain postures, external electric field reference levels alone would not provide a conservative estimate of localized SAR exposure and it would be necessary to invoke secondary reference levels on limb currents to provide compliance with restrictions.

Non-stationary charging of a dust grain in decaying streamer-channel plasma

The process of a dust grain charging in non-stationary (decaying) air plasma in external electric fields typical of a streamer channel at atmospheric air pressure is investigated numerically using two-dimensional spherical coordinates. The characteristic timescale on which the grain acquires maximal electric charge is found to be determined by the rate of electron attachment. For zero external field, the process of charging in decaying air plasma is compared with the analogous process in nitrogen (non-attaching gas). For non-zero external electric fields in air plasma, the correlation between the charging time and the field dependence of the attachment rate is revealed. For high values of external electric fields, a streamer discharge starting from the dust grain is observed, analogous to Trichel pulses in a negative corona.

FDTD calculations of the whole-body averaged SAR in an anatomically realistic voxel model of the human body from 1 MHz to 1 GHz

This paper presents finite-difference time-domain (FDTD) calculations of the whole-body averaged SAR in an anatomically realistic voxel model of the human body. This model, NORMAN, consists of million voxels, of 2 mm dimension in the adult phantom, segmented into 37 tissue types. SAR values are presented for an adult phantom and for scaled 10, 5 and 1 year old models, grounded and isolated in air from 1 MHz to 1 GHz for plane wave exposure. External electric field values corresponding to a whole-body averaged SAR of are also presented.

Quenching mechanisms of nonlocal transport in laterally confined two-dimensional systems.

Non-Ohmic and sample-size-dependent transport effects [i.e., Shubnikov--de Haas (SdH) and quantum Hall effect] of mesoscopic two-dimensional (2D) systems prove the occurrence of nonlocal contributions to the electronic conductance in these systems. However, this nonlocal regime accompanied by a non- equilibrium population of the edge states with respect to the 2D bulk state is quenched at rather low values of external electric fields or flowing currents, respectively. Beyond this quench, the bulk state is coupled to the edge by an increasing amount of electron transitions between the corresponding states. We analyze the non-Ohmic behavior of SdH oscillations at GaAs/${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum Hall conductors on the basis of a model including edge and bulk transport. We deduce the current-dependent non- equilibrium population of edge and bulk states quantitatively. Further, we give estimates for the current ranges in which transitions of electrons between edge and bulk states due to elastic and inelastic scattering are relevant. The change of the typical nonequilibrium parameters as the equilibration length and the maximal difference of chemical potentials of edge and bulk states in tilted magnetic fields are also discussed.

Detection of specifically oriented impurities in an amorphous host through interference between holograms stored as spectral holes

The constructive interference between two Stark-effect-broadened holograms produced by spectral hole burning is discussed. The holograms are burned at the same frequency but at different external electric-field values. The phase difference is selected to be zero so that constructive interference between the waves diffracted by each grating occurs. Experimentally it is found that a dip in the hologram efficiency that is not predicted by previous theory occurs for all reconstruction external electric-field values in the region between the original burn values. This dip is interpreted as being due to the time nonlinearity of the hologram burn process. The dip corresponds to those molecules, oriented in a specific direction with respect to the electric field, for which no Stark shift occurs and that are therefore resonant with the laser during the production of both holograms. The width of the anomalous feature is close to that of the hologram when the hologram is reconstructed at the original burn external electric-field strength. Other molecular orientations may be selected by burning pairs of holographic gratings at other combinations of the frequency and the electric field.

The transient current in a one-dimensional molecular crystal with traps

The transient current, due to the hopping transport of a carrier in a one-dimensional molecular crystal, in the presence of a random distribution of traps and an arbitrary value of external electric field, is determined exactly. The trapping time as a function of electric field is derived from the current decay curves. It is shown that the current ∝exp(−At1/2) for all t at low fields. This is in agreement with the simple kinetic approach to one-dimensional trapping and not with more recent sophisticated approaches. The current decays asymptotically as exp(−Bt) for high field.

Design and development of a bubble chamber technique for the study of electric-field induced nucleation in liquids

A description is given of a method for the study of electric-field induced nucleation (phase transition) in liquids. The device used is a miniature bubble chamber in which intense electric stress is applied to the liquid by means of a sharp edge of thin ( approximately 10-5 cm), transparent and highly conducting film of tin oxide. A capacitor manometer has been used for the dynamic pressure measurements. The change in scattered light intensity from the liquid at 90 degrees to the incident light is utilized as an indication of the nucleation. The instantaneous pressure, scattered light intensity and the instant of the application of the electric field are registered simultaneously on the oscilloscope. Typical sets of results are shown at different temperatures and pressures for three organic liquids namely n-hexane, n-pentane and iso-pentane. The extrapolation of these results to the zero value of external electric field gives the limit of thermodynamic stability of the liquids. The results thus obtained are compared with those obtained from kinetic and Furth's theories of liquids.