Kinds Of Orbits Research Articles

Superconductivity in metal-insulator composite bands: A realization of negative-U pairing in purely repulsive systems.

We consider the multiband, purely repulsive Hubbard model on a class of systems in which there are two (or more) kinds of orbitals per unit cell such that one metallic band interacts with the other insulating band. From both perturbational canonical transformation and quantum Monte Carlo studies we have shown that superconductivity due to nonretarded attraction (negative U) is a generic feature of this class of metal-insulator composite many-body systems. Remarkably, the superconductivity arises, under appropriate conditions, for various types of insulating bands (a charge-transfer insulator, Mott-Hubbard insulator, etc.). Superconductivity is unambiguously identified from the pairing correlation function, which agrees with that of the attractive Hubbard model surprisingly well even in the nonperturbative regime. The superconductivity revealed here is in a sense an opposite limit to conventional superconductivity with retarded attraction from boson-exchange mechanisms. We also show that the present mechanism is distinct from existing multiband models such as d-${\mathit{p}}_{\mathrm{\ensuremath{\sigma}}}$ models. As we increase the magnitude of the attraction in the present model by changing some parameters (e.g., to make the accompanying band metallic), the similarity with the attractive Hubbard model becomes eventually degraded, so that the optimum condition for superconductivity is determined by this kind of tradeoff. We also discuss the relevance of the present model to high-${\mathit{T}}_{\mathit{c}}$ superconductivity in cuprates and fullerenes.

US 4,966,935 Fire retardant PBT

The stable near rectilinear halo orbits (NRHOs) and distant retrograde orbits (DROs) are both considered as potential parking orbits for cis-lunar stations. Transfer orbits between NRHOs and DROs can promote the exploitation of their distinct advantages and be helpful for possible cooperations between cis-lunar stations in different kinds of orbits. By using the symmetry of the dynamics in the circular restricted three body problem (CR3BP), the transfers between NRHOs and DROs are investigated through the transfers from southern NRHOs to DROs, which are obtained by using a two-step approach, consisting of the search and optimization phases. Four NRHOs and three DROs, including those in previous studies and the 9:2 L2 NRHO considered as the nominal orbit for the Lunar Orbital Platform-Gateway (LOP-G), are considered in this study. Both the interior and exterior transfer orbits are found, and the exterior transfer orbits always have relatively low transfer costs. The transfer orbits with better performances than the best previous results are successfully constructed. In the cases of some transfers, the close lunar flyby has shown great advantages in changing the orbital plane and adjusting the velocity without fuel consumption. The comparison between transfer orbits to different DROs indicates that the dynamical structures have more significant effects on the transfer cost than the Jacobi energy. Then, some representative transfer orbits are refined in the high-fidelity ephemeris model for real mission scenarios. The comparisons between transfer orbits departing at different epochs indicate that the lunar orbit eccentricity has significant effects on the transfer time and cost, and some transfer orbits with specific epochs can have better performances than the nominal ones in the CR3BP. The results are of great significance for constructing connections between cis-lunar space stations, as well as for designing transport systems in the Earth-Moon system.

Trajectories of zero rest-mass particles and gravitational trapping in interior geometries

Trajectories of zero rest-mass particles (ZRP) are quite well studied in Schwarzschild geometry but not in interior geometries. In this paper the trajectories of ZRP have been obtained and discussed for Tolman's IV solution. It is found that the inward moving ZRP approaches the centre up to a minimum distance and then draws away from it if the angle of emittance is less than that for the ‘cone of avoidance’. If, however, the angle of emittance is greater than the angle of ‘cone of avoidance’, the ZRP moves inwards up to a certain minimum distance from the centre and then stays at this distance in a circular orbit. In this regard four different kinds of orbits have been identified. Calculations have also been done for the number of ZRP that will escape such massive configuration.

A new kind of stellar orbit in a galactic potential

Numerical integrations of a star's motion in an axisymmetric galactic potential have unveiled a new kind of orbit in the meridional plane. Especially, neutron stars can be expected to move on such orbits.

Symbolic dynamics of the cubic map

A symmetric cubic map on the interval describing isolated stable or bistable orbits and different kind of bifurcation was analyzed. Stable orbits were presented by itineraries, permutation parentheses and matrices. Itineraries were used to order the cycles with respect to the parameter and also to order the coordinates of the cycle in the interval. Linear symbolic dynamics was introduced to study the periodic unstable points coexisting with stable orbits by means of a matrix of intervals. The non-zero entries of these matrices have an N-shape corresponding to the N-shape of the cubic. The characteristic polynomial of the matrix of intervals was in one-to-one correspondence with the itinerary. Equations to calculate the number of different kind of orbits were explicitly written and used to calculate those numbers for a small number of periods.

On active and passive CETI from an earth satellite orbit

Scientific and technical problems of the project (Subotowicz, 1976) were discussed in detail (e.g., single- or multiantenna system, frequency range, kind of orbit, corrections to antenna shape, role of thermal heating, gain of antenna, possible perturbations of the orbit, undesirable motion of the antenna, possibilities of long-term and exact pointing at a particular star, optimal dimensions of the antenna for different frequencies and distances in active and passive communication, modulation modes, etc.). Problems of the CETI antenna coupling with the solar power station (noise level, screening of the antenna from the power station, role of antenna mechanical oscillations, etc.) are discussed, as well as the shape and nature of the beacons and that of the S N ratio; the laws of pulse distortion in the interstellar medium, and the role of Doppler shift of the signal.

Perturbation theory for configuration interaction wavefunctions

A zeroth order hamiltonian is given for configuration interaction wavefunctions constructed from orbitals which may be open shell Hartree-Fock orbitals, multiconfiguration self consistent field orbitals, or some other kind of orbitals which are eigenfunctions of a common one-electron hamiltonian. The perturbation expansion for the wavefunction in each order may be decoupled into equations for internal, single, pair, etc., excitations.

The electronic spectra of substituted aromatic hydrocarbons

IN THIS paper I wish to give a critical comparison of the quantum mechanical models which may be used for interpreting the spectra of substituted aromatic hydrocarbons. The first point to be decided when entering into a calculation of electronic energy levels, is what kind of orbitals are to be used to build up the electronic states. I f one is going to work within the valence bond framework, then one uses just the atomic orbitals, and constructs wave functions from these according to the Heit ler-London description of the electron pair bond. This approach will give satisfactory wave functions and energies if the basic set of states is large enough. However, the crude theory (which we may refer to as resonance theory), in which one includes only those wave functions which are associated with chemical structures having most of the electrons paired, and an electron distribution which is favoured by the electronegativity of the atoms in the molecule, does not give sensible results.1 For example, if benzene is substituted by one donor group (e.g. OMe, NH2) and one acceptor (e.g. NO2, COOH) then one finds that the spectra of the ortho and meta substituted compounds are very similar to one another but different from that of the para compound. Moreover, the para compound absorbs at shorter wavelengths than the other two. Resonance theory however, would say that it is the meta compound which should be the odd one out, since it is the only one which cannot be given a quinonoid structure of the type.

Electronic Structure and Hyperfine Coupling Constants for NO2 and Related Molecules

The electronic structure of NO2 and related molecules is discussed by means of a correlation diagram between the molecular orbitals of O3 and CO2. The general properties of the hyperfine structure constants for the different kinds of orbitals are discussed and compared with the experimental results of NO2 and ClO2. The hyperfine structure constants are used to identify the symmetry properties of the ground states of NO2 and ClO2 and also to estimate some coefficients of the atomic orbitals in the LCAO MO.