Field Energies Research Articles

Localized plasmonic field enhancement in shaped graphene nanoribbons.

Graphene nanoribbon (GNR), as a fundamental component to support the surface plasmon waves, are envisioned to play an important role in graphene plasmonics. However, to achieve extremely confinement of the graphene surface plasmons (GSPs) is still a challenging. Here, we propose a scheme to realize the excitation of localized surface plasmons with very strong field enhancement at the resonant frequency. By sinusoidally patterning the boundaries of GNRs, a new type of plasmon mode with field energy concentrated on the shaped grating crest (crest mode) can be efficiently excited, creating a sharp notch on the transmission spectra. Specifically, the enhanced field energies are featured by 3 times of magnitude stronger than that of the unpatterned classical GNRs. Through theoretical analyses and numerical calculations, we confirm that the enhanced fields of the crest modes can be tuned not only by changing the width, period and Fermi energy as traditional ribbons, but also by varying the grating amplitude and period. This new technique of manipulating the light-graphene interaction gives an insight of modulating plasmon resonances on graphene nanostrutures, making the proposed pattern method an attractive candidate for designing optical filters, spatial light modulators, and other active plasmonic devices.

Vibration analysis of the embedded piezoelectric polymeric nano-composite panels in the elastic substrate

Abstract In the present study the vibrations of a smart thin micro panel of polymeric nano-composite reinforced by the Single-Walled Boron-Nitride Nano-Tubes (SWBNNTs) and the matrix Poly-VinyliDene Fluoride (PVDF) on an elastic substrate is studied. Using the micromechanics method, the nano-composite structural equations are obtained for a sample volume element and by considering a unidirectional electric field and stress in the field. The stress-strain relationships that include mechanical and electric terms are obtained for the micro-tubes. The micro-panel is considered as the thin wall shell and Donnell’s non-linear theory is used for the strain-displacement relations. To obtain the equations of motion, the minimum energy method or Hamilton’s principle is used. The external work is caused by the elastic environment as well as the magnetic field energies. Given that the work has been in small micro scale the strain gradient, modified coupled stress and classic theories are used to consider the small-scale effect in the equations. The results showed Stiffness of the panel is reduced by increasing length and reducing volume fraction of BNNT and lower frequencies are obtained. Angling nanotubes is reduced panel frequency and the severity of this reduction is increased at higher volume percentages. The maximum frequency is happened in the full cylinder sector.

Electromagnetic field energy revisited

Electromagnetic field energy is often invoked in introductory physics courses as a mechanism for describing energy exchanges among charged objects. In this paper, we examine field energy in two relatively simple scenarios: a charged particle in a locally uniform electric field and a charged particle moving with a uniform velocity. In both cases, detailed calculations of field energies unveil several surprises about where field energy is located and how it changes when the charge is moving. We argue that these complexities indicate that potential (configuration) energy is a more useful concept than field energy for introductory physics courses.

SU‐F‐T‐409: Modelling of the Magnetic Port in Temporary Breast Tissue Expanders for a Treatment Planning System

Purpose:To model the magnetic port in the temporary breast tissue expanders and to improve accuracy of dose calculation in Pinnacle, a commercial treatment planning system (TPS).Methods:A magnetic port in the tissue expander was modeled with a radiological measurement‐basis; we have determined the dimension and the density of the model by film images and ion chamber measurement under the magnetic port, respectively. The model was then evaluated for various field sizes and photon energies by comparing depth dose values calculated by TPS (using our new model) and ion chamber measurement in a water tank. Also, the model was further evaluated by using a simplified anthropomorphic phantom with realistic geometry by placing thermoluminescent dosimeters (TLD)s around the magnetic port. Dose perturbations in a real patient's treatment plan from the new model and a current clinical model, which is based on the subjective contouring created by the dosimetrist, were also compared.Results:Dose calculations based on our model showed less than 1% difference from ion chamber measurements for various field sizes and energies under the magnetic port when the magnetic port was placed parallel to the phantom surface. When it was placed perpendicular to the phantom surface, the maximum difference was 3.5%, while average differences were less than 3.1% for all cases. For the simplified anthropomorphic phantom, the calculated point doses agreed with TLD measurements within 5.2%. By comparing with the current model which is being used in clinic by TPS, it was found that current clinical model overestimates the effect from the magnetic port.Conclusion:Our new model showed good agreement with measurement for all cases. It could potentially improve the accuracy of dose delivery to the breast cancer patients.

Nanoscale periodic domain patterns in tetragonal ferroelectrics: A phase-field study

Ferroelectrics form domain patterns that minimize their energy subject to imposed boundary conditions. In a linear, constrained theory, that neglects domain wall energy, periodic domain patterns in the form of multi-rank laminates can be identified as minimum-energy states. However, when these laminates (formed in a macroscopic crystal) comprise domains that are a few nanometers in size, the domain-wall energy becomes significant, and the behaviour of laminate patterns at this scale is not known. Here, a phase-field model, which accounts for gradient energy and strain energy contributions, is employed to explore the stability and evolution of the nanoscale multi-rank laminates. The stress, electric field, and domain wall energies in the laminates are computed. The effect of scaling is also discussed. In the absence of external loading, stripe domain patterns are found to be lower energy states than the more complex, multi-rank laminates, which mostly collapse into simpler patterns. However, complex laminates can be stabilized by imposing external loads such as electric field, average strain and polarization. The study provides insight into the domain patterns that may form on a macroscopic single crystal but comprising of nanoscale periodic patterns, and on the effect of external loads on these patterns.

An empirical model for calculation of the collimator contamination dose in therapeutic proton beams

Collimators are used as lateral beam shaping devices in proton therapy with passive scattering beam lines. The dose contamination due to collimator scattering can be as high as 10% of the maximum dose and influences calculation of the output factor or monitor units (MU). To date, commercial treatment planning systems generally use a zero-thickness collimator approximation ignoring edge scattering in the aperture collimator and few analytical models have been proposed to take scattering effects into account, mainly limited to the inner collimator face component. The aim of this study was to characterize and model aperture contamination by means of a fast and accurate analytical model. The entrance face collimator scatter distribution was modeled as a 3D secondary dose source. Predicted dose contaminations were compared to measurements and Monte Carlo simulations. Measurements were performed on two different proton beam lines (a fixed horizontal beam line and a gantry beam line) with divergent apertures and for several field sizes and energies. Discrepancies between analytical algorithm dose prediction and measurements were decreased from 10% to 2% using the proposed model. Gamma-index (2%/1 mm) was respected for more than 90% of pixels. The proposed analytical algorithm increases the accuracy of analytical dose calculations with reasonable computation times.

Parameterization of photon beam dosimetry for a linear accelerator.

In radiation therapy, accurate data acquisition of photon beam dosimetric quantities is important for (1) beam modeling data input into a treatment planning system (TPS), (2) comparing measured and TPS modeled data, (3) the quality assurance process of a linear accelerator's (Linac) beam characteristics, (4) the establishment of a standard data set for comparison with other data, etcetera. Parameterization of the photon beam dosimetry creates a data set that is portable and easy to implement for different applications such as those previously mentioned. The aim of this study is to develop methods to parameterize photon beam dosimetric quantities, including percentage depth doses (PDDs), profiles, and total scatter output factors (S(cp)). S(cp), PDDs, and profiles for different field sizes, depths, and energies were measured for a Linac using a cylindrical 3D water scanning system. All data were smoothed for the analysis and profile data were also centered, symmetrized, and geometrically scaled. The S(cp) data were analyzed using an exponential function. The inverse square factor was removed from the PDD data before modeling and the data were subsequently analyzed using exponential functions. For profile modeling, one halfside of the profile was divided into three regions described by exponential, sigmoid, and Gaussian equations. All of the analytical functions are field size, energy, depth, and, in the case of profiles, scan direction specific. The model's parameters were determined using the minimal amount of measured data necessary. The model's accuracy was evaluated via the calculation of absolute differences between the measured (processed) and calculated data in low gradient regions and distance-to-agreement analysis in high gradient regions. Finally, the results of dosimetric quantities obtained by the fitted models for a different machine were also assessed. All of the differences in the PDDs' buildup and the profiles' penumbra regions were less than 2 and 0.5 mm, respectively. The differences in the low gradient regions were 0.20% ± 0.20% (<1% for all) and 0.50% ± 0.35% (<1% for all) for PDDs and profiles, respectively. For S(cp) data, all of the absolute differences were less than 0.5%. This novel analytical model with minimum measurement requirements was proved to accurately calculate PDDs, profiles, and S(cp) for different field sizes, depths, and energies.

Ground state magnetic response of two coupled dodecahedra

The antiferromagnetic Heisenberg model on the dodecahedron possesses a number of ground state magnetization discontinuities in a field at the classical and quantum level, even though it lacks magnetic anisotropy. Here the model is considered for two dodecahedra coupled antiferromagnetically along one of their faces, as a first step to determine the magnetic response of collections of fullerene molecules. The magnetic response is determined from the competition among the intra-, interdodecahedral exchange and magnetic field energies. At the classical level the discontinuities of the isolated dodecahedron are renormalized by the interdodecahedral coupling, while new ones show up, with the maximum number of ground state discontinuities being six for a specific range of the coupling. In the full quantum limit where the individual spin magnitude , there are two ground state discontinuities originating in the single discontinuity of the isolated dodecahedron, and another one due to the intermolecular coupling, generating a total of three discontinuities which come one right after the other. These results show that the magnetic response of more than one dodecahedra interacting together is quite richer than the one of a single dodecahedron.

A test on reactive force fields for the study of silica dimerization reactions.

We studied silica dimerization reactions in the gas and aqueous phase by density functional theory (DFT) and reactive force fields based on two parameterizations of ReaxFF. For each method (both ReaxFF force fields and DFT), we performed constrained geometry optimizations, which were subsequently evaluated in single point energy calculations using the other two methods. Standard fitting procedures typically compare the force field energies and geometries with those from quantum mechanical data after a geometry optimization. The initial configurations for the force field optimization are usually the minimum energy structures of the ab initio database. Hence, the ab initio method dictates which structures are being examined and force field parameters are being adjusted in order to minimize the differences with the ab initio data. As a result, this approach will not exclude the possibility that the force field predicts stable geometries or low transition states which are realistically very high in energy and, therefore, never considered by the ab initio method. Our analysis reveals the existence of such unphysical geometries even at unreactive conditions where the distance between the reactants is large. To test the effect of these discrepancies, we launched molecular dynamics simulations using DFT and ReaxFF and observed spurious reactions for both ReaxFF force fields. Our results suggest that the standard procedures for parameter fitting need to be improved by a mutual comparative method.

Impact of currents on surface flux computations and their feedback on dynamics at regional scales

Abstract. A twin numerical experiment was conducted in the seas around the island of Sardinia (Western Mediterranean) to assess the impact, at regional and coastal scales, of the use of relative winds (i.e., taking into account ocean surface currents) in the computation of heat and momentum fluxes through standard (Fairall et al., 2003) bulk formulas. The Regional Ocean Modelling System (ROMS) was implemented at 3 km resolution in order to well resolve mesoscale processes, which are known to have a large influence in the dynamics of the area. Small changes (few percent points) in terms of spatially averaged fluxes correspond to quite large differences of such quantities (about 15 %) in spatial terms and in terms of kinetics (more than 20 %). As a consequence, wind power input P is also reduced by ~ 14 % on average. Quantitative validation with satellite SST suggests that such a modification of the fluxes improves the model solution especially in the western side of the domain, where mesoscale activity (as suggested by eddy kinetic energy) is stronger. Surface currents change both in their stable and fluctuating part. In particular, the path and intensity of the Algerian Current and of the Western Sardinia Current (WSC) are impacted by the modification in fluxes. Both total and eddy kinetic energies of the surface current field are reduced in the experiment where fluxes took into account the surface currents. The main dynamical correction is observed in the SW area, where the different location and strength of the eddies influence the path and intensity of the WSC. Our results suggest that, even at local scales and in temperate regions, it would be preferable to take into account such a contribution in flux computations. The modification of the original code, substantially cost-less in terms of numerical computation, improves the model response in terms of surface fluxes (SST validated) and it also likely improves the dynamics as suggested by qualitative comparison with satellite data.

SU‐E‐T‐597: Parameterization of the Photon Beam Dosimetry for a Commercial Linear Accelerator

Purpose:In radiation therapy, accurate data acquisition of photon beam dosimetric quantities is important for (1) beam modeling data input into a treatment planning system (TPS), (2) comparing measured and TPS modelled data, (3) a linear accelerator's (linac) beam characteristics quality assurance process, and (4) establishing a standard data set for data comparison, etcetera. Parameterization of the photon beam dosimetry creates a portable data set that is easy to implement for different applications such as those previously mentioned. The aim of this study is to develop methods to parameterize photon percentage depth doses(PDD), profiles, and total scatter output factors(Scp).Methods:Scp, PDDs and profiles for different field sizes (from 2×2 to 40×40cm2), depths and energies were measured in a linac using a three‐dimensional water tank. All data were smoothed and profile data were also centered, symmetrized and geometrically scaled. The Scp and PDD data were analyzed using exponential functions. For modelling of open and wedge field profiles, each side was divided into three regions described by exponential, sigmoid and Gaussian equations. The model's equations were chosen based on the physical principles described by these dosimetric quantities. The equations’ parameters were determined using a least square optimization method with the minimal amount of measured data necessary. The model's accuracy was then evaluated via the calculation of absolute differences and distance–to–agreement analysis in low gradient and high gradient regions, respectively.Results:All differences in the PDDs’ buildup and the profiles’ penumbra regions were less than 2 mm and 0.5 mm, respectively. Differences in the low gradient regions were 0.20 ± 0.20% and 0.50 ± 0.35% for PDDs and profiles, respectively. For Scp data, all differences were less than 0.5%.Conclusion:This novel analytical model with minimum measurement requirements proved to accurately calculate PDDs, profiles, and Scp for different field sizes, depths and energies.

Modeling an unmitigated thermal quench event in a large field magnet in a DEMO reactor

The superconducting magnet systems of future fusion reactors, such as a demonstration power plant (DEMO), will produce magnetic field energies in the 10s of GJ range. The release of this energy during a fault condition could produce arcs that can damage the magnets of these systems. The public safety consequences of such events must be explored for a DEMO reactor because the magnets are located near the DEMO's primary radioactive confinement barrier, the reactor's vacuum vessel (VV). Great care will be taken in the design of DEMO's magnet systems to detect and provide a rapid field energy dump to avoid any accidents conditions. During an event when a fault condition proceeds undetected, the potential of producing melting of the magnet exists. If molten material from the magnet impinges on the walls of the VV, these walls could fail, resulting in a pathway for release of radioactive material from the VV. A model is under development at Idaho National Laboratory (INL) called MAGARC to investigate the consequences of this accident in a large toroidal field (TF) coil. Recent improvements to this model are described in this paper, along with predictions for a DEMO relevant event in a toroidal field magnet.

Structures and hydrogen bonding investigation of 1,3-dimethylimidazolium methylsulfate and 1,3-dimethylimidazolium dimethylphosphate with theoretical methods

The structures and H-bonds for 1,3-dimethylimidazolium methylsulfate ([DMIM][MS]) and 1,3-dimethylimidazolium dimethylphosphate ([DMIM][DMP]) have been investigated with density functional theory (DFT) method. The optimized geometries of for each ion pair as well as their ion pair dimer are identified by analyzing the relative self-consistent field (SCF) energies. The results show that the major intermolecular interaction in the ion pairs and their clusters is multiple C–H⋯O type H-bond. Atoms in molecules (AIM) theory and natural bond orbital (NBO) analysis are employed for the complexes under study, to gain a deeper understanding of the detail of these hydrogen bonding interactions. In addition, the results of energy decomposition analysis (EDA) show that the interaction of these anions with cation is electrostatic in the nature.

Some aspects of configuration interaction of the 4f(N) configurations of tripositive lanthanide ions.

Some features of the interaction of the 4f(N) configuration of tripositive lanthanide ions (Ln(3+)) with excited configurations have been investigated. The calculated barycenter energies of the same parity 4f(N-1)6p, 4f(N+1)5p(5), and 4f(N-1)5f configurations for Ln(3+), relative to those of 4f(N), are fitted well by exponential functions. The 4f(N) barycenter energies of Ln(3+) in Y3Al5O12/Ln(3+) lie in the band gap, with the exceptions of Tb(3+) and Yb(3+), where they are situated in the conduction and valence bands, respectively. The configuration interaction parameters α, β, and γ, which are fitted in the usual phenomenological Hamiltonian to calculate the crystal field energies of Ln(3+), exhibit quite variable magnitudes in the literature due to incomplete energy level data sets, energy level misassignments and fitting errors. For LaCl3/Ln(3+), 83% of the variation of α and 50% of that for β can be explained by the change in the difference in barycenter energy with the predominant interacting configuration. The parameter γ is strongly correlated with the Slater parameter F(2) and is not well-determined in most calculations. The values of the electrostatically correlated spin-other orbit parameter P(2) vary smoothly across the Ln(3+) series with the barycenter difference between the 4f(N) and 4f(N-1)5f configurations. Calculations of the P(k) (k = 2, 4, and 6) values for Pr(3+) show that 4f → nf excitations only account for ∼65% of the value of P(2) for LaCl3/Pr(3+) and 35% of that in Y3Al5O12/Pr(3+). The role of the ligand is therefore important in determining the value, and a discussion is included of the present state of configuration-interaction-assisted crystal field calculations. Further progress cannot be made in the above areas until more reliable and complete energy level data sets are available for the Ln(3+) series of ions in crystals.

The Effect of K Substitution on Magnetoresistivity and Activation Energy of Bi-2212 System

In the present work, magnetoresistivity performance of polycrystalline Bi2Sr2Ca1−x K x Cu2 O 8+y superconductor with x=0.0,0.05,0.075, and 0.1 has been studied by change of flux pinning mechanism, using magnetoresistivity measurements. The samples were prepared using a polymer solution technique. The effects of K substitution for Ca on the irreversibility field, upper critical magnetic field, coherence length, and activation energies have been investigated. The magnetoresistivity of the samples has been measured under applied magnetic fields ranging from 0 to 9 T. Broadening of superconducting transition is observed under magnetic field, explained on the basis of thermally activated flux flow (TAFF) model. The upper critical magnetic field H C2(0) and the coherence length (ζ(0)) at T = 0 K were calculated using the resistivity data and from H C2(0) ,respectively. H C2(0) and ξ(0) values have been calculated as 62, 72, 75, and 53 T and 23, 21, 20, and 25 A for the 0.0, 0.05, 0.075, and 0.10 K doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi2Sr2Ca1−x K x Cu2 O 8+y where x = 0.075 are calculated as 0.0147 eV for 9 T and 0.29 eV for 0 T.

Exploring Hamiltonian dielectric solvent molecular dynamics

Hamiltonian dielectric solvent (HADES) is a recent method [7,25], which enables Hamiltonian molecular dynamics (MD) simulations of peptides and proteins in dielectric continua. Sample simulations of an α-helical decapeptide with and without explicit solvent demonstrate the high efficiency of HADES-MD. Addressing the folding of this peptide by replica exchange MD we study the properties of HADES by comparing melting curves, secondary structure motifs and salt bridges with explicit solvent results. Despite the unoptimized ad hoc parametrization of HADES, calculated reaction field energies correlate well with numerical grid solutions of the dielectric Poisson equation.

Relaxation character of the rheological behavior of cellulose ether solutions in a magnetic field

The relaxation character of the rheological behavior of hydroxypropyl cellulose and ethyl cellulose solutions in a magnetic field and without it was studied. Application of magnetic field leads to an increase in the viscosity of cellulose ether solutions. The mechanical and magnetic field energies stored by the solutions at flow were calculated.

Inductive crystal field control in layered metal oxides with correlated electrons

We show that the NiO6 crystal field energies can be tailored indirectly via heterovalent A cation ordering in layered (La,A)NiO4 Ruddlesden–Popper (RP) oxides, where A = Sr, Ca, or Ba, using density functional calculations. We leverage as a driving force the electrostatic interactions between charged [LaO]1 + and neutral [AO]0 planes to inductively tune the Ni–O bond distortions, without intentional doping or epitaxial strain, altering the correlated d-orbital energies. We use this strategy to design cation ordered LaCaNiO4 and LaBaNiO4 with distortions favoring enhanced Ni eg orbital polarization, and find local electronic structure signatures analogous to those in RP La-cuprates, i.e., parent phases of the high-temperature superconducting oxides.

Analytical gradients of complete active space self-consistent field energies using Cholesky decomposition: Geometry optimization and spin-state energetics of a ruthenium nitrosyl complex

We present a formulation of analytical energy gradients at the complete active space self-consistent field (CASSCF) level of theory employing density fitting (DF) techniques to enable efficient geometry optimizations of large systems. As an example, the ground and lowest triplet state geometries of a ruthenium nitrosyl complex are computed at the DF-CASSCF level of theory and compared with structures obtained from density functional theory (DFT) using the B3LYP, BP86, and M06L functionals. The average deviation of all bond lengths compared to the crystal structure is 0.042Å at the DF-CASSCF level of theory, which is slightly larger but still comparable with the deviations obtained by the tested DFT functionals, e.g., 0.032Å with M06L. Specifically, the root-mean-square deviation between the DF-CASSCF and best DFT coordinates, delivered by BP86, is only 0.08Å for S0 and 0.11Å for T1, indicating that the geometries are very similar. While keeping the mean energy gradient errors below 0.25%, the DF technique results in a 13-fold speedup compared to the conventional CASSCF geometry optimization algorithm. Additionally, we assess the singlet-triplet energy vertical and adiabatic differences with multiconfigurational second-order perturbation theory (CASPT2) using the DF-CASSCF and DFT optimized geometries. It is found that the vertical CASPT2 energies are relatively similar regardless of the geometry employed whereas the adiabatic singlet-triplet gaps are more sensitive to the chosen triplet geometry.

Strength of Axial Water Ligation in Substrate-Free Cytochrome P450s Is Isoform Dependent

The heme-containing cytochrome P450s exhibit isoform-dependent ferric spin equilibria in the resting state and differential substrate-dependent spin equilibria. The basis for these differences is not well understood. Here, magnetic circular dichroism (MCD) reveals significant differences in the resting low spin ligand field of CYPs 3A4, 2E1, 2C9, 125A1, and 51B1, which indicates differences in the strength of axial water ligation to the heme. The near-infrared bands that specifically correspond to charge-transfer porphyrin-to-metal transitions span a range of energies of nearly 2 kcal/mol. In addition, the experimentally determined MCD bands are not entirely in agreement with the expected MCD energies calculated from electron paramagnetic resonance parameters, thus emphasizing the need for the experimental data. MCD marker bands of the high spin heme between 500 and 680 nm were also measured and suggest only a narrow range of energies for this ensemble of high spin Cys(S–) → Fe3+ transitions among these isoforms. The differences in axial ligand energies between CYP isoforms of the low spin states likely contribute to the energetics of substrate-dependent spin state perturbation. However, these ligand field energies do not correlate with the fraction of high spin vs low spin in the resting state enzyme, suggestive of differences in water access to the heme or isoform-dependent differences in the substrate-free high spin states as well.