Electric Dipole Potential Research Articles

Long-Range Influence of a Pump on a Critical Fluid.

A pump coupled to a conserved density generates long-range modulations, resulting from the non-equilibrium nature of the dynamics. We study how these modulations are modified at the critical point where the system exhibits intrinsic long-range correlations. To do so, we consider a pump in a diffusive fluid, which is known to generate a density profile in the form of an electric dipole potential and a current in the form of a dipolar field above the critical point. We demonstrate that while the current retains its form at the critical point, the density profile changes drastically. At criticality, in d<4 dimensions, the deviation of the density from the average is given by sgn[cos(θ)]|cos(θ)/r^{(d-1)}|^{1/δ} at large distance r from the pump and angle θ with respect to the pump's orientation. At short distances, there is a crossover to a cos(θ)/r^{d-3+η} profile. Here δ and η are Ising critical exponents. The effect of the local pump on the domain wall structure below the critical point is also considered.

Virtual Electric Dipole Field Applied to Autonomous Formation Flight Control of Unmanned Aerial Vehicles.

The following paper presents a method for the use of a virtual electric dipole potential field to control a leader-follower formation of autonomous Unmanned Aerial Vehicles (UAVs). The proposed control algorithm uses a virtual electric dipole potential field to determine the desired heading for a UAV follower. This method’s greatest advantage is the ability to rapidly change the potential field function depending on the position of the independent leader. Another advantage is that it ensures formation flight safety regardless of the positions of the initial leader or follower. Moreover, it is also possible to generate additional potential fields which guarantee obstacle and vehicle collision avoidance. The considered control system can easily be adapted to vehicles with different dynamics without the need to retune heading control channel gains and parameters. The paper closely describes and presents in detail the synthesis of the control algorithm based on vector fields obtained using scalar virtual electric dipole potential fields. The proposed control system was tested and its operation was verified through simulations. Generated potential fields as well as leader-follower flight parameters have been presented and thoroughly discussed within the paper. The obtained research results validate the effectiveness of this formation flight control method as well as prove that the described algorithm improves flight formation organization and helps ensure collision-free conditions.

Teaching the electrical origins of the electrocardiogram: An introductory physics laboratory for life science students

We present the design, pedagogical logic, and assessment of a laboratory and supporting materials that integrate a clinical academic cardiologist's understanding of the origins of the electrocardiogram (ECG) with a physics educator's insights into how to teach the underlying physics at the introductory level to life science students. In this article, we explain the choices made throughout the design process, connect a more advanced treatment of the physics to our approach, and present our assessment of the curriculum. Before the laboratory, students learn the cellular origins of the electric dipole potential produced by the heart on the body's surface, including a simple physical model for the electrical activity of excitable cells, and learn to interpret the measured voltages of an ECG as probing components of the heart's time-varying electric dipole moment. In the laboratory, students measure their own ECGs and analyze the data accordingly; they animate their data to display their own heart's dipole moment for a single heartbeat. Our results from the assessment of student understanding and attitudes indicate that although students find the content challenging, nearly all students find it at least moderately interesting, and for about a quarter of the students in the course, this lab plays a highly meaningful part in connecting physics to medicine.

Electron collisions with F2CO molecules

In this paper we present elastic differential, integral, and momentum-transfer cross sections for electron collisions with carbonyl fluoride $({\mathrm{F}}_{2}\mathrm{CO})$ molecules for the incident electron's energy from 0.5 eV to 20 eV. The Schwinger multichannel method with pseudopotentials was employed to obtain the cross sections in the static-exchange and static-exchange plus polarization approximations. The present results were compared with the available data in the literature, in particular, with the results of Kaur, Mason, and Antony [Phys. Rev. A 92, 052702 (2015)] for the differential, total, and momentum-transfer cross sections. We have found a ${\ensuremath{\pi}}^{*}$ shape resonance centered at 2.6 eV in the ${B}_{1}$ symmetry and other resonance, in the ${B}_{2}$ symmetry, located at around 9.7 eV. A systematic study of the inclusion of polarization effects was performed in order to have a well balanced description of this negative-ion transient state. The effects of the long-range electric dipole potential were included by the Born closure scheme. Electronic structure calculations were also performed to help in the interpretation of the scattering results, and associate the transient states to the unoccupied orbitals.

Pinwheel-dipole configuration in cat early visual cortex

In the early visual cortex, information is processed within functional maps whose layouts are thought to underlie visual perception. However, the precise organization of these functional maps as well as their interrelationships remain unsettled. Here, we show that spatial frequency representation in cat early visual cortex exhibits singularities around which the map organizes like an electric dipole potential. These singularities are precisely co-located with singularities of the orientation map: the pinwheel centers. To show this, we used high resolution intrinsic optical imaging in cat areas 17 and 18. First, we show that a majority of pinwheel centers exhibit in their neighborhood both semi-global maximum and minimum in the spatial frequency map (i.e. extreme values of the spatial frequency in a hypercolumn). This contradicts pioneering studies suggesting that pinwheel centers are placed at the locus of a single spatial frequency extremum. Based on an analogy with electromagnetism, we proposed a mathematical model for a dipolar structure, accurately fitting optical imaging data. We conclude that a majority of orientation pinwheel centers form spatial frequency dipoles in cat early visual cortex. Given the functional specificities of neurons at singularities in the visual cortex, it is argued that the dipolar organization of spatial frequency around pinwheel centers could be fundamental for visual processing.

Inversion Layer Mobility in High-k Dielectric MOSFETs - Intrinsic Mobility Degradation by Electric Dipoles at High-k/SiO2 Interface

An intrinsic mobility degradation mechanism in high-k gate stacks is proposed. Scattering, due to the electric dipole potential formed at the high-k/SiO2 interface, strongly affects the electron mobility in a metal/high-k gate stack. Comparison of the mobilities in HfO2 gate stacks with different optical phonon structures also revealed that the contribution of remote phonon scattering to mobility degradation is rather small.

Analytic solution of the wave equation for an electron in the field of a molecule with an electric dipole moment

We relax the usual diagonal constraint on the matrix representation of the eigenvalue wave equation by allowing it to be tridiagonal. This results in a larger representation space that incorporates an analytic solution for the non-central electric dipole potential cos θ/ r 2, which was believed not to belong to the class of exactly solvable potentials. Therefore, we were able to obtain a closed form solution of the three-dimensional time-independent Schrödinger equation for a charged particle in the field of a point electric dipole that could carry a nonzero net charge. This problem models the interaction of an electron with a molecule (neutral or ionized) that has a permanent electric dipole moment. The solution is written as a series in a basis composed of special functions that support a tridiagonal matrix representation for the angular and radial components of the wave operator. Moreover, this solution is for all energies, the discrete (for bound states) as well as the continuous (for scattering states). The expansion coefficients of the radial and angular components of the wavefunction are written in terms of orthogonal polynomials satisfying three-term recursion relations. For the Coulomb-free case, where the molecule is neutral, we calculate critical values for its dipole moment below which no electron capture is allowed. These critical values are obtained not only for the ground state, where it agrees with already known results, but also for excited states as well.

Effects of the Charge-Dipole Interaction on the Coagulation of Fractal Aggregates

A numerical model with broad applications to complex (dusty) plasmas is presented. The self-consistent N-body code allows simulation of the coagulation of fractal aggregates, including the charge-dipole interaction of the clusters due to the spatial arrangement of charge on the aggregate. It is shown that not only does a population of oppositely charged particles increase the coagulation rate, the inclusion of the charge-dipole interaction of the aggregates as well as the electric dipole potential of the dust ensemble decreases the gelation time by a factor of up to 20. It is further shown that these interactions can also stimulate the onset of gelation, or growth, even in a population of particles charged to a monopotential where previously it was believed that like-charged grains would inhibit coagulation. Gelation is observed to occur due to the formation of high-mass aggregates with fractal dimensions greater than two, which act as seeds for runaway growth.

An approximate analytical solution of the Klein–Gordon equation for the finite electric dipole potential

The Klein–Gordon equation for the finite electric-dipole potential is solved approximately by the method of matching of asymptotic solutions. Near-continuum state energies are found analytically.

Bound electronic states in a statically screened electric-dipole potential.

Bound electronic states in a statically screened electric-dipole potential.

Electron scattering with H2S and PH3 molecules

Calculated total, differential and momentum transfer cross sections are reported for the vibrationally elastic scattering of electrons from H2S and PH3 molecules in the range of energy 0.1–50 eV. The scattering process is approximated by two incoherent scatterings caused, separately, by a central field and a long-range electric dipole interaction. The central field is calculated with a spherical approximate molecular wave function, in which the exchange interaction is treated in two ways: (i) exactly within the accuracy of the molecular wave function; (ii) approximately by a local model potential. The scattering by the central field is calculated with partial wave expansion technique, while the scattering by the electric dipole potential is calculated by using the first Born approximation for a rotating dipole model with experimental values of the dipole moments of H2S and PH3. The total cross sections are approximated by the incoherent sum of the cross section due to the central potential and the cross section of 00→10 rotational transition caused by the electric dipole potential. The effects of the polarization interaction are also tested. The contribution of small-angle scattering to the integral cross section is analyzed for these weakly polar molecules with some quantitative comparison.

A laser-T-jump study of the adsorption of dipolar molecules to planar lipid membranes. II. Phloretin and phloretin analogues.

Phloretin and structurally related neutral molecules adsorb to the interface of lipid membranes and modify the electric dipole potential of the membrane/water interface. The adsorption process has been studied using a laser-T-jump relaxation technique in combination with an analysis of nonactin mediated potassium transport (see part I, Awiszus and Stark 1988). Deviations from the Langmuir isotherm were observed for most of the substances. The discrepancies were most pronounced at large surface densities, whereas good agreement was found at low concentrations in many cases. The partition coefficient in the limit of low concentrations was compared with that of octanol/water bulk phases. No correlation was found. The individual values of the two partition coefficients differed by more than three orders of magnitude. The contribution, b, of a single adsorbed molecule to the dipole potential could not be predicted from the dipole moment, microL, of the molecule measured in the bulk phase. Different values of b were found at identical values of microL. The study shows the limitations of the use of bulk phase data to predict molecular properties in lipid membranes.

Non-linear effects in rotational dynamics in the liquid state

Through general theoretical considerations, based only on the Markoffian assumption, it is shown that equilibrium non-gaussian properties can be used to predict how the decay of excited states deviates from a linear response theory behaviour. To check this prediction, a computer experiment on a ‘two-dimensional liquid’ of discs interacting via a Lennard-Jones plus electric dipole potential is carried out. The results obtained for both equilibrium and excited correlation functions confirm completely the intimate relation between equilibrium non-gaussian properties and excitation behaviour. Via approximate analytical expressions and exact solutions, it is also shown that a non-linear version of the popular itinerant oscillator provides the same equilibrium non-gaussian properties and, in consequence of that, the same kind of deviation from linear response as the two-dimensional system.

Negative hydrophobic ions as transport-mediators for positive ions. Evidence for a carrier mechanism

The permeability of hydrophobic cations, such as tetraphenylarsonium across biological membranes and artificial lipid membranes is strongly increased in the presence of trace amounts of hydrophobic anions like tetraphenylborate (Liberman, Y.A. and Topaly, V.P. (1969) Biofizika 14, 452–461). Voltage-jump relaxation experiments performed on thin lipid membranes support the idea that the anions, A −, act as carriers for the cations, B +, by the formation of neutral ion pairs, A −B +. Their permeability is not affected by the electric dipole potential, which hinders the movement of free cations, B +.

WKB Treatment of Bound States in an Electric-Dipole Potential

The WKB method is applied to the problem of bound states of an electron in the field of a finite dipole. A necessary condition for binding is derived which suggests that bound states may exist only if the dipole moment is larger than a certain minimum value. It is also shown that the number of bound states given by the WKB method is comparable to the exact number for the one- and three-dimensional square-well potentials.

Neglected Quadrupole

The usual textbook developments of the electric dipole potential are discussed and the limitations, some inherent and some arbitrary, are noted. Introducing Legendre polynomials by their generating function an alternate derivation is presented. This latter approach offers the double advantage of introducing the undergraduate to quadrupoles and higher multipoles and providing him with a powerful mathematical tool for treating electrostatic and many other problems. The importance of the quadrupole concept in modern physics is emphasized.