Measuring short range stray electric fields with a force quantum sensor

Electrical influence on molecular conformation in glyoxal and glycine

This paper analyzes the two-dimensional motion of a charged particle in constant mutually perpendicular electric and magnetic fields. The magnetic field is assumed to be uniform, and the electric field components are assumed to be linear functions of the Cartesian coordinates. Under these assumptions, the equations of particle motion can be solved analytically. This solution is used to study the stability of particle motion and to assess the accuracy of the guiding center approximation in the presence of electric field gradients. It is well known that if the gradient of a one-dimensional electric field is sufficiently large, the motion of the charged particles becomes unstable and the particles are effectively energized by the electric field. This paper, however, demonstrates that the instability threshold depends on the spatial derivatives of both electric field components and is, under certain conditions, very sensitive to both. The analytical solution is averaged over the gyroperiod to derive simple expressions for the drift speed and the position of the gyrocenter, which explicitly account for the electric field gradient. The results of this averaging are used to develop equations for tracing the particle gyrocenter location, which incorporate the effects of non-uniformity of the electric field. These equations are shown to be noticeably more accurate than those based on the standard E × B drift velocity, which is exact only for uniform electric and magnetic fields. Simple expressions for the local errors in the E × B drift velocity are also derived, which arise from the electric field gradients.

We present a benchmark study of a combined multipole shielding polarizability/reaction field (MSP/RF) approach to the calculation of both specific and bulk solvation effects on nuclear magnetic shielding constants of solvated molecules. The MSP/RF scheme is defined by an expansion of the shielding constants of the solvated molecule in terms of electric field and field gradient property derivatives derived from single molecule ab initio calculations. The solvent electric field and electric field gradient are calculated based on data derived from molecular dynamics simulations, thereby accounting for solute-solvent dynamical effects. The MSP/RF method is benchmarked against polarizable quantum mechanics/molecular mechanics (QM/MM) calculations. The best agreement between the MSP/RF and QM/MM approaches is found by truncating the electric field expansion in the MSP/RF approach at the linear electric field level which is due to the cancelation of errors. In addition, we investigate the sensitivity of the results due to the choice of one-electron basis set in the ab initio calculations of the property derivatives and find that these derivatives are affected by the basis set in a way similar to the shielding constants themselves.

Effects of electric field and strain gradients on cracks in piezoelectric solids

In this paper, we investigate the photodetachment of \(H^{-}\) in parallel-gradient electric and magnetic fields on the basis of a semiclassical closed-orbit theory. Firstly, we give a clear physical picture of a detached electron's movement in parallel-gradient electric and magnetic fields. Then we derive the analytical formula for the photodetachment cross section of this system. It is found that parallel gradient electric and magnetic fields can produce some interesting effects. Aside from the closed orbits previously reported for the photodetachment of \(H^{-}\) in a parallel-gradient electric field, some additional closed orbits are produced owing to the effect of the magnetic field. Compared with the cross section of \(H^{-}\) in a gradient electric field, the oscillation in the cross section of our system becomes much more complicated. Moreover, our study shows that the oscillation amplitude in the photodetachment cross section sensitively depends on the electric field gradient and external field s...

A unified treatment of multicenter electronic attraction (EA), electric field (EF), and electric-field gradient (EFG) integrals of Yukawa-like screened and nonscreened Coulomb potentials with Slater-type orbitals (STOs) is described. Using different sets of series expansion formulas of two-center distributions for STOs in terms of STOs at a displaced center the EA, EF, and EFG integrals over STOs are expressed through the overlap integrals between potentials or their derivatives and STOs. These two-center overlap integrals are evaluated by the use of rotational transformation for overlap integrals established by the author. The final results expressed through the overlap integrals of STOs with the same screening constants are valid for the arbitrary parameters of STOs and potentials. PACS No.: 31.15.–p

The conditions under which direct lattice sums of electric potential, field, and field gradient converge are discussed. The analogous conditions under which differences in these lattice sums, for two points in the crystal, converge are also outlined. These conditions are applied to direct lattice sum calculations in crystals in which the ideal lattice is distorted close to a defect of some kind. The conver- gence conditions are then applied to the case of determining the direct lattice sums in crystals in which higher symmetry properties can be invoked, which leads to a knowledge by inspection of the lattice sum at one point in the unit cell.

A coupled cluster (CC) investigation is presented for the (generalized) Sternheimer shieldings and the electric field gradient (EFG) polarizabilities which describe the effect of external electric fields and field gradients on the electric field gradient at the nuclei. Calculations are performed for the linear molecules N2, CO, HF, C2H2, HCl, HCN, and HNC. Correlation effects are monitored by employing a hierarchy of CC models consisting of CCS, CC2, CCSD, and CC3. The effect of tight basis functions and core correlation is investigated by carrying out CCSD calculations with core-valence basis sets. Accurate theoretical estimates for EFGs, Sternheimer shieldings, and EFG polarizabilities are given and the effects of vibrational corrections are discussed. Our final estimates for the considered EFG properties can be used, for example, in simulations of electric field effects on the EFG at the nuclei in interacting molecules.

The calculation of the electric field gradient in ionic crystals assumed to consist of discrete deformable ions is discussed, the ions being characterized by their multipolar polarizabilities. A set of linear self-consistent equations for calculating the electric field and field gradient components at all inequivalent lattice sites is derived with particular reference to long-range effects, and including terms up to the quadrupole moment. The calculation of antishielding factors is not considered. Some of the lattice sums involved are conditionally convergent and the implications of this on their evaluation are discussed. It is shown that the conditional convergence and the existence of Lorentz factors is intimately related. The lattice sums are transformed into a rapidly convergent form by the method of plane-wise summation used by de Wette in 1961. The field gradient at the site of 127I in hexagonal AgI is calculated and found to be critically dependent on the relative displacement of the Ag+ and I- sublattices, its value changing sign over the experimental range of this crystal parameter. An upper bound of 1.7 Mc/s for the nuclear quadrupole coupling constant is deduced on the basis of the ionic model.

Directed cell migration is critical across biological processes spanning healing to cancer invasion, yet no existing tools allow real-time interactive guidance over such migration. We present a new bioreactor that harnesses electrotaxis-directed cell migration along electric field gradients-by integrating four independent electrodes under computer control to dynamically program electric field patterns, and hence steer cell migration. Using this platform, we programmed and characterized multiple precise, two-dimensional collective migration maneuvers in renal epithelia and primary skin keratinocyte ensembles. First, we demonstrated on-demand, 90-degree collective turning. Next, we developed a universal electrical stimulation scheme capable of programming arbitrary 2D migration maneuvers such as precise angular turns and migration in a complete circle. Our stimulation scheme proves that cells effectively time-average electric field cues, helping to elucidate the transduction timescales in electrotaxis. Together, this work represents an enabling platform for controlling cell migration with broad utility across many cell types.

Flexoelectric effect is a novel electro-mechanical coupling effect that has drawn a lot of attention in the past few decades. Compared with piezoelectric materials, flexoelectric materials have the inherent characteristics of gradient coupling effect between electric field and elastic field. Since no complex pre-polarization process is required, the flexoelectric materials do not have depolarization or aging problems during the trial period. Similar to piezoelectricity, flexoelectricity exhibits two different effects: direct and converse flexoelectric effect. The direct flexoelectric effect indicates that the strain gradient produces an electrical response, and can be used in sensor design and energy harvesting. The converse flexoelectric effect represents mechanical stress or strain caused by inhomogeneous electric field or polarization gradient, and then as a response, the induced membrane force and the corresponding control moment will occur in the structure. This study will take the mechanic electric coupling characteristics of flexoelectric effect as the core, establish the dynamic equation, deduce the modal response of plate structure under the effect of flexoelectric and obtain the relationship between modal response and electric field gradient. To validate the theoretical method, a finite element model of flexoelectric actuated plate will be established in the commercial software COMSOL Multiphysics. With no existing flexoelectric module, the finite element model of flexoelectric plate will be built based on the original dynamic model. A non-uniform electric field is firstly constructed in COMSOL with the electrostatic module. The influence of different structural parameters on the vibration control effect caused by flexoelectric excitation will be analyzed and optimized, which will provide a theoretical basis for the application of flexoelectric materials in the vibration control of novel smart structures.

Tip-enhanced Raman spectroscopy (TERS) is a promising label-free super-resolving imaging technique, and the electric field gradient of nanofocusing plays a role in TERS performance. In this paper, we theoretically investigated the enhancement and manipulation of the electric field gradient in a bottom-illumination TERS configuration through a tightly focused perfect radially polarized beam (PRPB). Improvement and manipulation in electric field enhancement and field gradient of the gap-plasmon mode between a plasmonic tip and a virtual surface plasmons (SPs) probe are achieved by adjusting the ring radius of the incident PRPB. Our results demonstrate that the method of optimizing the ring radius of PRPB is to make the illumination angle of incident light as close to the surface plasmon resonance (SPR) excitation angle as possible. Under the excitation of optimal parameters, more than 10 folds improvement of field enhancement and 3 times of field gradient of the gap-plasmon mode is realized compared with that of the conventional focused RPB. By this feat, our results indicate that such a method can further enhance the gradient Raman mode in TERS. We envision that the proposed method, to achieve the dynamic manipulation and enhancement of the nanofocusing field and field gradient, can be more broadly used to control light-matter interactions and extend the reach of tip-enhanced spectroscopy.

A description of the guiding field line (GFL) model is presented for spherical torus geometry. The model is extended to cover small banana orbits that are trapped either above or below the midplane. Comparison of the model with the fluid and neoclassical theories demonstrates correctness of the model, though it shows that the model is not exactly equivalent to them. The GFL model provides a more general description for the orbit-squeezing effect resulting from the large gradient of the radial electric field. It shows that not only does the deformation of banana orbits, but also the change of the passing particles' orbits, affect the current in plasma. Besides, it appears that the change of the orbits' shape, as projected on the magnetic surface, contributes to modification of the current along with the radial squeezing/expanding. Distortion of the current by the gradient of the electric field is found to be predominantly in the direction parallel to the magnetic field, while almost no effect is seen for the perpendicular component.

Characterisation of stray electric fields in niobium cavities using ultra-high resolution spectroscopy

The kinetics of photoconductivity and the spectral photosensitivity of a semiconductor with anisotropic electroconductivity in nonhomogeneous electric field has been investigated. Photoconductivity of germanium samples of ring geometry was studied experimentally and theoretically. The main results are: decay of the photocurrent in a semiconductor in the presence of a transverse gradient of electric field differs from the exponential one and depends on mutual directions of the gradient and the drift of the carriers; a photodetector with parameters reversibly controlled by electric and magnetic fields is possible. It was found that spectral photosensitivity either selective or bolometric depending on mutual directions of incident light, the gradient of electric field, and of drift of carriers.