Energy Variation Range Research Articles

Quantum mechanics and molecular dynamics strategies to investigate self-aggregation of Quinolin-65

Asphaltene is the heaviest and most polar component of the crude oil. Asphaltene precipitation and deposition results in some adverse processes in both upstream and downstream petroleum industry such as formation of water-in-oil emulsions, wettability alteration of the reservoir rock, pore blockage leading to permeability impairment, blockage of transportation pipeline, and catalyst poisoning in refineries. Asphaltene self-aggregation plays a major role in all these operational difficulties. Although several studies have been carried out on asphaltene aggregation, there is limited scientific understanding of asphaltene self-aggregation at the microscopic level. In this study, Quinolin-65 molecule is considered as a model asphaltene structure. The effect of various factors contributing to self-aggregation of Quinolin-65 molecules including intermolecular interactions, temperature, pressure, solvent, and molecular structure are investigated using quantum mechanics analysis and molecular dynamics (MD) simulations. Results of reduced density gradient (RDG) analysis demonstrated that the strong van der Waals interaction between aromatic rings in two Quinolin-65 molecules is a critical factor in their dimerization and self-aggregation. Radial distribution function, potential of mean force, and mean square displacement are calculated using MD simulation. The Quinolin-65 aggregation tendency in the toluene medium is significantly decreased compared to that in the water and heptane media, due to the interactions between the Quinolin-65 molecules and toluene. According to the MD simulation results, the solubility parameter of the medium can affect the Quinolin-65 aggregation process. The stability of Quinolin-65 molecule in the medium is increased by increasing the temperature. Upon a change in the Quinolin-65 aggregation behavior, the free energy variation range with pressure and temperature is from −4.01 to −0.23 kjmol and −3.49 to −0.56 kjmol, respectively. This study provides new insights/findings to better understand the interaction force(s) between the Quinolin-65 molecules as well as the effect of different thermodynamic conditions on Quinolin-65 molecules self-aggregation at the molecular level. Moreover, this research work assesses the synergistic effects of influential parameters (e.g., thermodynamic conditions, solvent, and structure) on the Quinolin-65 self-aggregation behavior, which can help predict some serious flow assurance issues associated with the precipitation/deposition of asphaltene particles.

Zeroing dynamics method for motion control of industrial upper-limb exoskeleton system with minimal potential energy modulation

Abstract Accurate motion control of industrial upper-limb exoskeleton can provide efficient assistance for subjects to perform various industrial manipulation tasks. In most motion control scenarios of upper-limb exoskeletons, the variations of potential energy frequently reach to a high level of oscillations, leading to the reconstructed motion uncomfortable or dangerous. In this paper, in order to achieve minimal potential energy variation and accurate motion control of the upper-limb exoskeleton, we propose a novel motion planning strategy with minimal potential energy modulation. Such motion resolution scheme is formulated as an optimization problem and solved by the zeroing dynamics (ZD) to achieve elegant global convergence. Simulation and experiment results show that the potential energy variation range of the upper-limb exoskeleton can be significantly decreased by average 99.34 % in both X-Y and X-Z planes, in addition to finishing tracking the desired motion path accurately. All of these demonstrate that the efficiency and superiority of the proposed method for potential energy minimization during achieving accurate motion planning and control.

Resonance Enhancement by Suitably Chosen Frequency Detuning

The theory of exact resonances (kinematics and dynamics) is well developed while even the very concept of detuned resonance is ambiguous and only studies of their kinematic characteristics (that is, those not depending on time) are available in the literature. In this paper, we report novel effects enforced by the resonance detuning on solutions of the dynamical system describing interactions of three spherical planetary waves. We establish that the energy variation range can significantly exceed the range of the exact resonance for suitably chosen values of the detuning. The asymmetry of system’s solutions with respect to the sign of the detuning parameter is demonstrated. Finally, a non-monotonic dependence of the energy oscillation period with respect to detuning magnitude is discovered. These results have direct implications in physics of atmosphere, e.g., for prediction of weather extremes in the Northern Hemisphere midlatitudes (Proc. Nat. Acad. Sci. USA 2016, 133(25), 6862–6867). Moreover, similar study can be conducted for a generic three-wave system taken in the Hamiltonian form which makes our results applicable for an arbitrary Hamiltonian three-wave system met in climate prediction theory, geophysical fluid dynamics, plasma physics, etc.

A novel sine wave modulation method of pulse current during double wire MIG welding

As a highly efficient welding method that guarantees good weld quality, double wire pulse welding has broken the neck bottle of single wire welding in terms of weld speed and tackled such problems as undercut and hump during single wire high-speed welding. During double wire welding, double current waveform modulation is a key that affects weld quality and efficiency. Based on single wire sine wave modulation, this paper proposes a new double wire sine wave modulation method. Front and back wire pulse currents with the same peak value and basic current variation amplitude were obtained by performing sine wave modulation on ordinary double current pulse waveform. An in-depth analysis was made in terms of the energy distribution coefficient m, amplitude coefficient k, and the negative half-cycle sine wave pulse number Nn to discuss how double wire sine wave modulation affects weld seam imaging quality. Experimental results show that with the application of sine wave modulation, double wire pulse welding can effectively enhance instantaneous energy density and broaden the energy variation range between pulse current base value and peak value. Also, enhancing weld speed appropriately helps to improve weld quality and efficiency to a great extent.

Two-dimensional power-type electronic spectrographs with a symmetry plane

The electronic and optical characteristics of 2D electric fields with a complex potential of the type Ω = i(x + iy)n, where n is a real number, are investigated. Particle dynamics is studied in the symmetry plane and in its neighborhood for constructing an effective spectrograph of electron flows. It is shown that in the range of exponents 0 < n < 1, spatial focusing in the angles of incidence of conical bunches is effected in the system, which has second order in the symmetry plane and at least the first order across it. The line of images of a point source (focal line) is a straight line lying in the symmetry plane, the focusing order being independent of particle energy W. Thus, the spectrographic principle holds, and partial electron fluxes can be detected simultaneously by a position-sensitive detector in a wide range of energy variation. The electrode configuration of these systems is quite simple and can be used in practice for constructing spectrographs. The prospects of application of such spectrographs in energy analysis are considered.

Superconducting, energy variable heavy ion linac with constantβ, multicell cavities of CH-type

An energy variable ion linac consisting of multigap, constant-$\ensuremath{\beta}$ cavities was developed. The effect of phase sliding, unavoidable in any constant-$\ensuremath{\beta}$ section, is leading to a coherent rf phase motion, which fits well to the H-type structures with their long $\ensuremath{\pi}$-mode sections and separated lenses. The exact periodicity of the cell lengths within each cavity results in technical advantages, such as higher calculation accuracy when only one single period can be simulated, simpler manufacturing, and tuning. This is most important in the case of superconducting cavities. By using this concept, an improved design for a 217 MHz cw superconducting heavy ion linac with energy variation has been worked out. The small output energy spread of $\ifmmode\pm\else\textpm\fi{}3\text{ }\text{ }\mathrm{AkeV}$ is provided over the whole range of energy variation from 3.5 to 7.3 AMeV. These capabilities would allow for a competitive research in the field of radiochemistry and for a production of super heavy elements (SHE), especially. A first 19-cell cavity of that type was designed, built, and rf tested successfully at the Institute for Applied Physics (IAP) Frankfurt. A 325.224 MHz, seven-cell cavity with constant $\ensuremath{\beta}=0.16$ is under development and will be operated in a frequency controlled mode. It will be equipped with a power coupler and beam tests with Unilac beams at GSI are foreseen.

Variation of Bandgap in Nanocrystalline Silicon as Monitored by Subgap Photoluminescence

ABSTRACTInfrared PL from νc-Si and nc-Si thin films is a potential spectroscopic tool for sensitive diagnostics of structure and defects. Bhat et al. have shown that the dominant PL band found in νc-Si centered at 0.9 eV cannot be assigned to the amorphous phase, as the energeticaly similar defect band found in a-Si:H (i.e., at 0.9 eV) shows a different temperature dependence and is much broader (i.e., FWHM of 0.15 eV compared to 0.35 eV) [1]. Recently, Carius et al. have observed a gradual lower energy shift of the 0.9 eV PL down to 0.82 eV for nc-Si as the plasma deposition excitation frequency is increased with a corresponding decrease in FWHM from 0.15 0.12 eV, respectively [2]. However, a lower energy shift in optical absorption was not observed, nor did they look for a correlation with the variation of any other physical property. Here, we report a broader range of energy variation for PL from our ECR-PECVD deposited nc-Si films accompanied with an energy shift in optical absorption and variation in dark conductivity and crystallite size. It has been argued that this PL peak in question could arise from the radiative transitions between bandtail states as in the case of ∼1.3 eV PL in a-Si:H or it may be associated with structural defects [2,3]. Our observations support both possibilities.

γ-quanta radiation field in a layered system

A method was developed to calculate the γ-quanta spectra in a plane-parallel barrier geometry, irradiated by an isotropic source of γ-quanta, 60Co, when the most significant effects are brought about by multiple Compton scattering in the quanta propagation processes. This method is a variant of a successive collision's method that assumes the γ-quantum's spectrum to be an infinite sum of particular spectra of γ-quanta that underwent a certain number of Compton scatterings from electrons in the medium. Despite the approximations, the convergence of the sum of particular spectra has been analytically proved for an actual range of the γ-quantum's energy variation range. Numerical data on spectral and spatial distributions of γ-quanta in a system simulating a common isotopic unit have been obtained. It has been shown that the scattered radiation, given the irradiation above, is significant and comparable with the source primary radiation.

Asymmetry of Low-Energy Positrons from Muon Decay

An investigation of the angular asymmetry of lowenergy positrons from the decay of polarized muons coming to rest in a propane bubble chamber is reported. The energy dependence of the asymmetry parimeter alpha is predicted by the two-component theory of the neutrino, while according to the four- component theory, with arbitrary parity-nonconserving interactions, this parameter can have a wide range of energy variations depending on the values of the interaction constants. Berley et al., have recently investigated the energy dependence of the asymmetry parameter for the upper half of the energy spectrum by an absorption technique and found approximate agreement with the prediction of the two-component theory. The results of the present work support this view. (A.C.)