A simple, efficient, and general treatment of the singularities in Hartree-Fock and exact-exchange Kohn-Sham methods for solids

We present a general scheme for treating the integrable singular terms within exact exchange (EXX) Kohn-Sham or Hartree-Fock (HF) methods for periodic solids. We show that the singularity corrections for treating these divergencies depend only on the total number and the positions of k-points and on the lattice vectors, in particular the unit cell volume, but not on the particular positions of atoms within the unit cell. The method proposed here to treat the singularities constitutes a stable, simple to implement, and general scheme that can be applied to systems with arbitrary lattice parameters within either the EXX Kohn-Sham or the HF formalism. We apply the singularity correction to a typical symmetric structure, diamond, and to a more general structure, trans-polyacetylene. We consider the effect of the singularity corrections on volume optimisations and k-point convergence. While the singularity corrections clearly depends on the total number of k-points, it exhibits a remarkably small dependence upon the choice of the specific arrangement of the k-points.Comment: 24 pages, 5 Figures, re-submitted to Phys. Rev. B after revision

Integral Equation Analysis of Plane Wave Scattering by Coplanar Graphene-Strip Gratings in the THz Range

The plane wave scattering and absorption by finite and infinite gratings of free-space standing infinitely long graphene strips are studied in the THz range. A novel numerical approach, based on graphene surface impedance, hyper-singular integral equations, and the Nystrom method, is proposed. This technique guarantees fast convergence and controlled accuracy of computations. Reflectance, transmittance, and absorbance are carefully studied as a function of graphene and grating parameters, revealing the presence of surface plasmon resonances. Specifically, larger graphene relaxation times increases the number of resonances in the THz range, leading to higher wave transmittance due to the reduced losses; on the other hand an increase of graphene chemical potential up-shifts the frequency of plasmon resonances. It is also shown that a relatively low number of graphene strips (>10) are able to reproduce Rayleigh anomalies. These features make graphene strips good candidates for many applications, including tunable absorbers and frequency selective surfaces.Comment: 11 pages, 26 figure

Analysis of complex singularities in high-Reynolds-number Navier-Stokes solutions

Numerical solutions of the laminar Prandtl boundary-layer and Navier-Stokes equations are considered for the case of the two-dimensional uniform flow past an impulsively-started circular cylinder. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions that can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous interactions from a different perspective

Searching for solar-like oscillations in the delta Scuti star rho Puppis

Despite the shallow convective envelopes of delta Scuti pulsators, solar-like oscillations are theoretically predicted to be excited in those stars as well. To search for such stochastic oscillations we organised a spectroscopic multi-site campaign for the bright, metal-rich delta Sct star rho Puppis. We obtained a total of 2763 high-resolution spectra using four telescopes. We discuss the reduction and analysis with the iodine cell technique, developed for searching for low-amplitude radial velocity variations, in the presence of high-amplitude variability. Furthermore, we have determined the angular diameter of rho Puppis to be 1.68 \pm 0.03 mas, translating into a radius of 3.52 \pm 0.07Rsun. Using this value, the frequency of maximum power of possible solar-like oscillations, is expected at ~43 \pm 2 c/d (498 \pm 23 muHz). The dominant delta Scuti-type pulsation mode of rho Puppis is known to be the radial fundamental mode which allows us to determine the mean density of the star, and therefore an expected large frequency separation of 2.73 c/d (31.6 muHz). We conclude that 1) the radial velocity amplitudes of the delta Scuti pulsations are different for different spectral lines; 2) we can exclude solar-like oscillations to be present in rho Puppis with an amplitude per radial mode larger than 0.5 m/s.Comment: 14 pages, 12 figure, accepted for MNRA

Vector-soliton collision dynamics in nonlinear optical fibers

We consider the interactions of two identical, orthogonally polarized vector solitons in a nonlinear optical fiber with two polarization directions, described by a coupled pair of nonlinear Schroedinger equations. We study a low-dimensional model system of Hamiltonian ODE derived by Ueda and Kath and also studied by Tan and Yang. We derive a further simplified model which has similar dynamics but is more amenable to analysis. Sufficiently fast solitons move by each other without much interaction, but below a critical velocity the solitons may be captured. In certain bands of initial velocities the solitons are initially captured, but separate after passing each other twice, a phenomenon known as the two-bounce or two-pass resonance. We derive an analytic formula for the critical velocity. Using matched asymptotic expansions for separatrix crossing, we determine the location of these "resonance windows." Numerical simulations of the ODE models show they compare quite well with the asymptotic theory.Comment: 32 pages, submitted to Physical Review

CO2 and temperature effects on the asphaltene phase envelope as determined by a quartz crystal resonator

Knowledge of the asphaltene phase envelope (APE) is crucial for oil companies, especially when enhanced oil recovery is applied. An innovative quartz crystal resonator (QCR) technique was employed to assess the phase behavior of asphaltene under reservoir conditions. The effect of CO2 injection coupled to temperature changes on the APE of a recombined oil with a very low asphaltene content (0.235% w/w of C7 asphaltene in dead oil) are reported. It has been shown that QCR is an appropriate and highly sensitive nondestructive experimental technique for detecting asphaltene flocculation. Pressure onsets were found to be dependent on the depressurization rate.Knowledge of the asphaltene phase envelope (APE) is crucial for oil companies, especially when enhanced oil recovery is applied. An innovative quartz crystal resonator (QCR) technique was employed to assess the phase behavior of asphaltene under reservoir281167806787sem informaçãosem informação(2012), http://www.iea.org/publications/freepublications/publication/key_world_energy_stats-1.pdf, International Energy Agency. 2011 Key World Energy Statistics. (accessed Aug 27)Speight, J.G., (1999) The Chemistry and Technology of Petroleum, pp. 215-241. , 3 rd ed. CRC Press: New YorkFan, T., Buckley, J.S., Rapid and Accurate SARA Analysis of Medium Gravity Crude Oils (2002) Energy Fuels, 16, pp. 1571-1575Andersen, S.I., Speight, J.G., Petroleum resins separation, character, and role in petroleum (2001) Pet. Sci. Technol., 19, pp. 1-34Durand, E., Clemancey, M., Lancelin, J.-M., Verstraete, J., Espinat, D., Quoineaud, A.-A., Effect of Chemical Composition on Asphaltenes Aggregation (2010) Energy Fuels, 24, pp. 1051-1062Hammami, A., Phelps, C.H., Monger-Mcclure, T., Little, T.M., Asphaltene Precipitation from Live Oils: An Experimental Investigation of Onset Conditions and Reversibility (2000) Energy Fuels, 14, pp. 14-18Guo, B., Song, S., Chacko, J., Ghalambor, A., Flow Assurance (2005) Offshore Pipelines, pp. 169-214. , Gulf Professional Publishing: Burlington, VT, Chapter 15Zekri, A.Y., Almehaideb, R.A., A Novel Technique to Treat Asphaltene Deposition in Carbonate Rocks (2001) Soc. Pet. Eng. J.Joshi, N.B., Mullins, O.C., Jamaluddin, A., Creek, J., McFadden, J., Asphaltene Precipitation from Live Crude Oil (2001) Energy Fuels, 15, pp. 979-986Vargas, F.M., Gonzalez, D.L., Hirasaki, G.J., Chapman, W.G., Modeling Asphaltene Phase Behavior in Crude Oil Systems Using the Perturbed Chain Form of the Statistical Associating Fluid Theory (PC-SAFT) Equation of State (2009) Energy Fuels, 23, pp. 1140-1146Gonzalez, D.L., Vargas, F.M., Hirasaki, G.J., Chapman, W.G., Modeling of CO2-induced asphaltene precipitation (2008) Energy Fuels, 22, pp. 757-762Deo, M., Parra, M., Characterization of Carbon-Dioxide-Induced Asphaltene Precipitation (2012) Energy Fuels, 26, pp. 2672-2679Sarma, H.K., Can We Ignore Asphaltene in a Gas Injection Project for Light-Oils? (2003) Soc. Pet. Eng. J.Daridon, J.L., Cassiěde, M., Nasri, D., Pauly, J., Carrier, H., Probing Asphaltene Flocculation by a Quartz Crystal Resonator (2013) Energy Fuels, 27, pp. 4639-4647Abudu, A., Goual, L., Adsorption of Crude Oil on Surfaces Using Quartz Crystal Microbalance with Dissipation (QCM-D) under Flow Conditions (2009) Energy Fuels, 23, pp. 1237-1248Farooq, U., Sjöblom, J., Øye, G., Desorption of Asphaltenes from Silica-Coated Quartz Crystal Surfaces in Low Saline Aqueous Solutions (2011) J. Dispersion Sci. Technol., 32, pp. 1388-1395Tavakkoli, M., Panuganti, S.R., Vargas, F.M., Taghikhani, V., Pishvaie, M.R., Chapman, W.G., Asphaltene Deposition in Different Depositing Environments: Part 1. Model Oil (2014) Energy Fuels, 28, pp. 1617-1628Daridon, J.L., Cassiěde, M., Paillol, J.H., Pauly, J., Viscosity Measurements of Liquids under Pressure by Using the Quartz Crystal Resonators (2011) Rev. Sci. 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1997-01-23 Faculty Senate Meeting Minutes

Faculty Senate Meeting Minutes for January 23, 1997

Physical Properties of Trans-Neptunian Object (20000) Varuna

We present new time-resolved photometric observations of the bright trans-Neptunian object (20000) Varuna and use them to study the rotation period, shape, and color. In observations from 2001 February and April, we find a best-fit two-peaked lightcurve with period 6.3442 +-0.0002 hr. The peak-to-peak photometric range in the R-band is 0.42 +-0.02 mag. We find no rotational variation in colors over the 0.45 < lambda < 0.85 micron wavelength range. From the short double-peaked period and large amplitude we suggest that Varuna is an elongated, prolate body perhaps close in shape to one of the Jacobi ellipsoids. If so, the ratio of the axes projected into the plane of the sky is 1.5:1 and the density is near 1000 kg m^(-3). (20000) Varuna may be a rotationally distorted rubble pile, with a weak internal constitution due to fracturing by past impacts. The high specific angular momentum implied by our observations and recent detections of binary Trans-Neptunian Objects both point to an early, intense collisional epoch in which large Trans-Neptunian Objects were about 100 times more abundant than now. In order to maintain a cosmochemically plausible rock:ice mass ratio of about 0.5, Varuna must be internally porous.Comment: 26 pages, 6 figures, 5 tables, accepted to A

An Arbitrary Curvilinear Coordinate Method for Particle-In-Cell Modeling

A new approach to the kinetic simulation of plasmas in complex geometries, based on the Particle-in- Cell (PIC) simulation method, is explored. In the two dimensional (2d) electrostatic version of our method, called the Arbitrary Curvilinear Coordinate PIC (ACC-PIC) method, all essential PIC operations are carried out in 2d on a uniform grid on the unit square logical domain, and mapped to a nonuniform boundary-fitted grid on the physical domain. As the resulting logical grid equations of motion are not separable, we have developed an extension of the semi-implicit Modified Leapfrog (ML) integration technique to preserve the symplectic nature of the logical grid particle mover. A generalized, curvilinear coordinate formulation of Poisson's equations to solve for the electrostatic fields on the uniform logical grid is also developed. By our formulation, we compute the plasma charge density on the logical grid based on the particles' positions on the logical domain. That is, the plasma particles are weighted to the uniform logical grid and the self-consistent mean electrostatic fields obtained from the solution of the logical grid Poisson equation are interpolated to the particle positions on the logical grid. This process eliminates the complexity associated with the weighting and interpolation processes on the nonuniform physical grid and allows us to run the PIC method on arbitrary boundary-fitted meshes.Comment: Submitted to Computational Science & Discovery December 201