Two-center System Research Articles

Application of a computational model in simulating an endovascular clot retrieval service system within regional Australia.

The global demand for endovascular clot retrieval (ECR) has grown rapidly in recent years creating challenges to healthcare system planning and resource allocation. This study aims to apply our established computational model to predict and optimise the performance and resource allocation of ECR services within regional Australia, and applying data from the state of South Australia as a modelling exercise. Local geographic information obtained using the Google Maps application program interface and real-world data was input into the discrete event simulation model we previously developed. The results were obtained after the simulation was run over 5 years. We modelled and compared a single-centre and two-centre ECR service delivery system. Based on the input data, this model was able to simulate the ECR delivery system in the state of South Australia from the moment when emergency services were notified of a potential stroke patient to potential delivery of ECR treatment. In the model, ECR delivery improved using a two-centre system compared to a one-centre system, as the percentage of stroke patients requiring ECR was increased. When 15% of patients required ECR, the proportion of 'failure to receive ECR' cases for a single-centre system was 17.35%, compared to 3.71% for a two-centre system. Geolocation and resource utilisation within the ECR delivery system are crucial in optimising service delivery and patient outcome. Under the model assumptions, as the number of stroke cases requiring ECR increased, a two-centre ECR system resulted in increased timely ECR delivery, compared to a single-centre system. This study demonstrated the flexibility and the potential application of our DES model in simulating the stroke service within any location worldwide.

Spin-averaged effective Hamiltonian of orders mα6 and mα6(m/M) for hydrogen molecular ions

The spin-averaged effective Hamiltonian of orders $m{\ensuremath{\alpha}}^{6}$ and $m{\ensuremath{\alpha}}^{6}(m/M)$ for a one-electron two-center Coulombic system is derived by using the theory of nonrelativistic quantum electrodynamics (NRQED), without assuming the Born-Oppenheimer approximation. The separated singularities from the first- and second-order perturbations are shown to be canceled out analytically for both order $m{\ensuremath{\alpha}}^{6}$ and $m{\ensuremath{\alpha}}^{6}(m/M)$ corrections by regularizing the effective Hamiltonian. Our results can be used to perform high-precision spectroscopic calculations of hydrogen molecular ions.

Galerkin method for unsplit 3-D Dirac equation using atomically/kinetically balanced B-spline basis

A Galerkin method is developed to solve the time-dependent Dirac equation in prolate spheroidal coordinates for an electron-molecular two-center system. The initial state is evaluated from a variational principle using a kinetic/atomic balanced basis, which allows for an efficient and accurate determination of the Dirac spectrum and eigenfunctions. B-spline basis functions are used to obtain high accuracy. This numerical method is used to compute the energy spectrum of the two-center problem and then the evolution of eigenstate wavefunctions in an external electromagnetic field.

Modeling and optimization control of a demand-driven, conveyor-serviced production station

Abstract This study investigates the look-ahead control of a conveyor-serviced production station (CSPS), viewed as a production center, which is connected to a sales center. The production station is equipped with a buffer to temporarily store the parts that will flow into the product bank of the sales center after processing. The whole two-center system is characterized by random parts arrival, random customer demand, random processing time and limited buffer or bank capacities. Thus, the decision-making on the look-ahead range of such demand-driven CSPS is subject to the constraints of production and sales levels. In this paper, we will focus on modeling the stochastic control problem and providing solutions for finding the optimal look-ahead control policy under either average- or discounted-cost criteria. We first establish a detailed semi-Markov decision process for the look-ahead control of the demand-driven CSPS by combining the vacancies of both the buffer and the bank into one state, which can be solved by policy iteration or value iteration if the system parameters are known precisely. Then, to avoid the curse of dimensionality and modeling in the numerical optimization methods, we also propose a Q -learning algorithm combined with a simulated annealing technique to derive the approximate solutions. Simulation results are finally presented to show that by our established model and proposed optimization methods the system can achieve an optimal or suboptimal look-ahead control policy once the capacities of both the buffer and the bank are designed appropriately.

Multipole plasmon excitations of C60 dimers.

We study the multipole plasmon mode frequencies of a pair of C60 molecules by means of the linearized hydrodynamic theory for electronic excitations on the each C60 surface. We apply the two-center spherical coordinate system for mathematical convenience and find an explicit form of the surface plasmon energies. Numerical result shows when approaching the two C60 molecules, the coupling between the bare plasmon modes leads to the appearance of additional modes having energies that are different from those of the isolated C60 molecules.

Trinuclear Early/Late‐Transition‐Metal Thiolate Complexes

The thiolato-bridged cobalt(II)/vanadium(II) complexes [Li(thf)4]2[Co2V(SPh)8] and [Li(15-crown-5)(thf)]2[Co2V(SPh)8] as well as a related nickel(II)/vanadium(II) complex [Li(15-crown-5)(thf)]2[Ni2V(SPh)8] have been prepared by treatment of CoCl2 (NiCl2) and VCl3 {[VCl3(thf)3]} with LiSPh in THF without and in the presence of 15-crown-5, respectively. The crystal structures of the trinuclear compounds were determined by X-ray analysis of single crystals and investigated by density functional theory. Both give evidence for one very short Ni–V distance (259.41 pm) in [Li(15-crown-5)(thf)]2[Ni2V(SPh)8]. The dark-coloured compounds display absorption bands over a wide energy range with an absorption onset lying in the near-infrared region at approximately 2000 nm. Magnetic measurements show strong antiferromagnetic coupling of the metal ions through acute phenylthiolate bridges (M–S–M < 76.1°). Ab initio multireference calculations together with mapping approaches reveal that the magnetic properties of the anionic metal complexes can be described by different effective spin Hamiltonians that indicate different types of intramolecular interactions between the metal ions. In [Co2V(SPh)8]2–, we found at low temperatures an effective S = 3/2 behaviour with small zero-field splitting (ZFS) caused by a strong, symmetric antiferromagnetic exchange interaction. A weak direct Ni–V bond in [Ni2V(SPh)8]2– generates an effective two-centre system that consists of an effective spin of S = 1/2 from the weakly bound Ni–V pair and a pseudospin S = 1 located on the other nickel site, antiferromagnetically coupled to an S = 1/2 ground state.

Studies of light neutron-excess systems from bound states to continuum

The generalized two-centre cluster model (GTCM), which can handle various single-particle configurations in general two-centre systems, is applied to the light neutron-rich system, 12Be = α+α+4N. We discuss the change of the neutrons' configuration around two α cores as the excitation energy varies. We show that the excess neutrons form various chemical-bonding-like configurations around the two α cores in the unbound region above the α-decay threshold. The possibility of α-cluster formation in a heavier system with neutron excess, 28Ne, is also discussed.

Plasmon hybridization in parallel nano-wire systems

We apply the plasmon hybridization method to a double-nano-wire system, providing a simple and intuitive description of the plasmon excitations in the system. We apply the two-center cylindrical coordinate system for mathematical convenience and find an explicit form of the surface plasmon oscillations, in terms of the interaction between the bare plasmon modes of the individual surfaces of the nano-wires. We present numerical results to display how the plasmon excitations of the system depend on nano-wire separation when there is no angular momentum transfer, i.e., when m = 0.

Electronic quantum motions in hydrogen molecule ion

The hydrogen molecule ion is a two-center force system expressed under the prolate spheroidal coordinates, whose quantum motions and quantum trajectories have never been addressed in the literature before. The momentum operators in this coordinate system are derived for the first time from the Hamilton equations of motion and used to construct the Hamiltonian operator. The resulting Hamiltonian comprises a kinetic energy T and a total potential VTotal consisting of the Coulomb potential and a quantum potential. It is shown that the participation of the quantum potential and the accompanied quantum forces in the force interaction within H2+ is essential to develop an electronic motion consistent with the prediction of the probability density function |Ψ|2. The motion of the electron in H2+ can be either described by the Hamilton equations derived from the Hamiltonian H = TK + VTotal or by the Lagrange equations derived from the Lagrangian H = TK − VTotal. Solving the equations of motion with different initial positions, we show that the solutions yield an assembly of electronic quantum trajectories whose distribution and concentration reconstruct the σ and π molecular orbitals in H2+. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Oscillations in Total Photodetachment Cross Sections of a Triatomic Anion

The total photodetachment cross section of a linear triatomic anion is derived for arbitrary laser polarization direction. The cross section is shown to be strongly oscillatory when the laser polarization direction is parallel to the axis of the system; the oscillation amplitude decreases and vanishes as the angle between the laser polarization and the anion axis increases and becomes perpendicular to the axis. The average cross section over the orientations of the triatomic system is also obtained. The cross section of the triatomic anion is compared with the cross section of a two-center system. We find there are two oscillation frequencies in the triatomic anion in contrast to only one oscillation frequency in the two-center case. Closed-orbit theory is used to explain the oscillations.

Plasmon hybridization in metallic nanotubes with a nonconcentric core

We develop a theory of plasmon excitations in a metallic nanotube with a nonconcentric core using the plasmon hybridization method. We apply the two-center cylindrical coordinate system for mathematical convenience and find an explicit form of the dispersion relation for surface plasmons, in terms of interaction between the bare plasmon modes of the individual surfaces of the nanotubes. We present numerical result displaying the effect of the offset distant d of the inner core from the nanotube center, when there is no angular momentum transfer, i.e., m = 0 . For large offsets, the plasmon shifts is strong, but weak for small offset.

Oscillations in the photodetachment cross section of a two-centre model

We study analytically the photodetachment cross sections of a two-centre negative ion system based on an extension of the photodetachment model of H−. The photodetachment cross section formulae are derived and found to be strongly oscillatory. We study in detail the dependence of the cross section on the distance between the two centres, photon energy and the laser polarization direction. Closed-orbit theory is extended and used to study the origin for the oscillations in the cross sections. We also derive the oscillatory photodetachment cross section averaged over the orientations of the two-centre system. This study reveals the connection between the oscillations in the cross section and a detached-electron orbit.

Strong-Field Modulated Diffraction Effects in the Correlated Electron-Nuclear Motion in DissociatingH2+

We show that the electronic dynamics in a molecule driven by a strong field is complex and potentially even counterintuitive. As a prototype example, we simulate the interaction of a dissociating H2+ molecule with an intense infrared laser pulse. Depending on the laser intensity, the direction of the electron's motion between the two nuclei is found to follow or oppose the classical laser-electric force. We explain the sensitive dependence of the correlated electronic-nuclear motion in terms of the diffracting electronic momentum distribution of the dissociating two-center system. The distribution is dynamically modulated by the nuclear motion and periodically shifted in the oscillating infrared electric field.

Radiative Transition Line Shape in Warm and Dense Argon Plasma: a Two-Centre Model Study

A two-centre model is employed to study the electronic structure of argon plasma at a density of 1022 cm−3 and a temperature of 5eV. The model takes into account the influence of the nearest neighbour on the electronic structure of the radiator and gives a proper description of the transient molecular behaviour in dense plasmas where the mean interatomic distance can be the order of the orbital spatial extent. The orbital energies of quasi-molecular Ar2 against the interatomic distance are calculated in the framework of density functional theory. It is shown that the orbital energies are not monotonic functions of the distance because of two competitive effects: the repulsive potential between electrons and the attractive potential between electrons and nuclei. The characteristics of this two-centre system can be categorized by three regimes depending on the ratio between the electron wavelength and the interatomic distance: atomic regime, screened atomic regime, and quasi-molecular regime. This classification agrees qualitatively with the conclusion of full quantum-mechanical approach [Yonger S Met al 1988 Phys. Rev. Lett. 61 962].

Multicenter McIntosh-Cisneros-Zwanziger-Kepler system, supersymmetry and integrability

We propose the general scheme of incorporation of the Dirac monopoles into mechanical systems on the three-dimensional conformal flat space. We found that any system (without monopoles) admitting the separation of variables in the elliptic or parabolic coordinates can be extended to the integrable system with the Dirac monopoles located at the foci of the corresponding coordinate systems. Particular cases of this class of system are the two-center MICZ-Kepler system in the Euclidean space, the limiting case when one of the background dyons is located at the infinity as well as the model of particle in parabolic quantum dot in the presence of parallel constant uniform electric and magnetic fields.

Plasmon hybridization in nanoshells with a nonconcentric core

We apply the plasmon hybridization method to a nanoshell with a nonconcentric (offset) core and investigate how the energy and excitation cross section of the plasmon modes depend on the offset distance D of the inner core from the nanoshell center. A two-center spherical coordinate system is used for mathematical convenience. It is shown that the presence of an offset core shifts the plasmon energies and makes higher multipolar nanoshell plasmons dipole active and visible in the optical spectrum. The dependence of the plasmon shifts on D is weak for small offsets but strong for large offsets. The polarization dependence of the optical absorption spectra is found to be relatively weak. The electromagnetic field enhancements are shown to be much larger than on a concentric nanoshell. The results agree very well with results from finite difference time domain simulations.

Effect of microcosmic optical parameters of dopants on the signal-to-noise ratio in doubly doped LiNbO 3 crystals

We propose a united theory that describes the two-center recording system by taking scattering noise into account. The temporal evolution of the signal-to-noise ratio in doubly doped photorefractive crystals is described based on jointly solving material equations and coupled-wave equations with the fourth-order Runge–Kutta method. Roles of microcosmic optical parameters of dopants on the signal-to-noise ratio are discussed in detail. The theoretical results can confirm and predict experimental results.

Dipole transition-matrix elements of the one-electron heterodiatomic quasimolecules

The problem of dipole transition-matrix element calculation for optical transitions in multiply charged one-electron diatomic quasimolecules with unequal nuclear charges ${Z}_{1}$ and ${Z}_{2}$ has been stated and solved. The quasimolecule ${Z}_{1}e{Z}_{2}$ is a unique example of a two-center system for which the energy terms and dipole transition moments have been calculated precisely in the frame of a nonrelativistic approach. Particular examples for the optical transitions with ${Z}_{1}=1.5,2,2.5,3$ and ${Z}_{2}=1$ and with the principal quantum number of the united ion ${n}_{u}=1,2,3,4$ have been tabulated. The scaling rules make it possible to determine the matrix elements for quasimolecules having nuclear charge ratios such as 2:1, 3:1, 3:2, and 5:2. Zeros at intermediate $R$ and zero limiting values at large $R$ are the highlighted features of the matrix elements. The heteronucleus case generates a large number of asymptotically forbidden transitions corresponding to transitions of an electron from one ion to another.

Fusion Barrier of Super-heavy Elements in a Generalized Liquid Drop Model**The project supported by National Natural Science Foundation of China under Grant Nos. 10235020, 10275094, 10175092, and 10075080 and the State Key Basic Research Program of China under Grant No. G2000077400

The macroscopic deformed potential energies for super-heavy elements Z=110,112,114,116,118 are determined within a generalized liquid drop model (GLDM). A quasi-molecular mechanism is introduced to describe the deformation of a nucleus in the GLDM and the shell model simultaneously. The macroscopic energy of a two-center nuclear system in the GLDM includes the volume-, surface-, and Coulomb-energies, the proximity effect at each mass asymmetry, and accurate nuclear radius. The shell correction is calculated by the Strutinsky method and the microscopic single particle energies are derived from a shell model in an axially deformed Woods-Saxon potential with the quasi-molecular shape. The total potential energy of a nucleus can be calculated by the macro-microscopic method as the summation of the liquid-drop energy and the Strutinsky shell correction. The theory is applied to predict the fusion barriers of the cold reactions 64Ni+208Pb→ 272110*, 70Zn + 208Pb→ 278112*, 76Ge+208Pb→ 284114*, 82Se+208Pb→ 290116*, 86Kr+208Pb→ 294118*. It is found that the neck in the quasi-molecular shape is responsible for the deep valley of the fusion barrier. In the cold fusion path, double-hump fusion barriers could be predicted by the shell corrections and complete fusion events may occur.

Rigorous Aspects of the Relativistic One-Electron Two-Centre System

Several properties of the molecular Dirac operator for homonuclear diatomic systems with one electron are studied within the Born-Oppenheimer approximation. This includes the regularity of the electronic curves and a demonstration of bonding stability in relativistic H2+.