Adiabatic approximation for the density matrix
NASA Astrophysics Data System (ADS)
Band, Yehuda B.
1992-05-01
An adiabatic approximation for the Liouville density-matrix equation which includes decay terms is developed. The adiabatic approximation employs the eigenvectors of the non-normal Liouville operator. The approximation is valid when there exists a complete set of eigenvectors of the non-normal Liouville operator (i.e., the eigenvectors span the density-matrix space), the time rate of change of the Liouville operator is small, and an auxiliary matrix is nonsingular. Numerical examples are presented involving efficient population transfer in a molecule by stimulated Raman scattering, with the intermediate level of the molecule decaying on a time scale that is fast compared with the pulse durations of the pump and Stokes fields. The adiabatic density-matrix approximation can be simply used to determine the density matrix for atomic or molecular systems interacting with cw electromagnetic fields when spontaneous emission or other decay mechanisms prevail.
Anderson localization makes adiabatic quantum optimization fail
Altshuler, Boris; Krovi, Hari; Roland, Jérémie
2010-01-01
Understanding NP-complete problems is a central topic in computer science (NP stands for nondeterministic polynomial time). This is why adiabatic quantum optimization has attracted so much attention, as it provided a new approach to tackle NP-complete problems using a quantum computer. The efficiency of this approach is limited by small spectral gaps between the ground and excited states of the quantum computer’s Hamiltonian. We show that the statistics of the gaps can be analyzed in a novel way, borrowed from the study of quantum disordered systems in statistical mechanics. It turns out that due to a phenomenon similar to Anderson localization, exponentially small gaps appear close to the end of the adiabatic algorithm for large random instances of NP-complete problems. This implies that unfortunately, adiabatic quantum optimization fails: The system gets trapped in one of the numerous local minima. PMID:20616043
Adiabatic corrections to density functional theory energies and wave functions.
Mohallem, José R; Coura, Thiago de O; Diniz, Leonardo G; de Castro, Gustavo; Assafrão, Denise; Heine, Thomas
2008-09-25
The adiabatic finite-nuclear-mass-correction (FNMC) to the electronic energies and wave functions of atoms and molecules is formulated for density-functional theory and implemented in the deMon code. The approach is tested for a series of local and gradient corrected density functionals, using MP2 results and diagonal-Born-Oppenheimer corrections from the literature for comparison. In the evaluation of absolute energy corrections of nonorganic molecules the LDA PZ81 functional works surprisingly better than the others. For organic molecules the GGA BLYP functional has the best performance. FNMC with GGA functionals, mainly BLYP, show a good performance in the evaluation of relative corrections, except for nonorganic molecules containing H atoms. The PW86 functional stands out with the best evaluation of the barrier of linearity of H2O and the isotopic dipole moment of HDO. In general, DFT functionals display an accuracy superior than the common belief and because the corrections are based on a change of the electronic kinetic energy they are here ranked in a new appropriate way. The approach is applied to obtain the adiabatic correction for full atomization of alcanes C(n)H(2n+2), n = 4-10. The barrier of 1 mHartree is approached for adiabatic corrections, justifying its insertion into DFT. PMID:18537228
The density temperature and the dry and wet virtual adiabats
NASA Technical Reports Server (NTRS)
Bartlo, J.; Betts, Alan K.
1991-01-01
A density temperature is introduced to represent virtual temperature and potential temperature on thermodynamic diagrams. This study reviews how the dry and wet virtual adiabats can be used to represent stability and air parcel density for unsaturated and cloudy air, and present formula and tabulations.
Local entanglement generation in the adiabatic regime
Cliche, M.; Veitia, Andrzej
2010-09-15
We study entanglement generation in a pair of qubits interacting with an initially correlated system. Using time-independent perturbation theory and the adiabatic theorem, we show conditions under which the qubits become entangled as the joint system evolves into the ground state of the interacting theory. We then apply these results to the case of qubits interacting with a scalar quantum field. We study three different variations of this setup; a quantum field subject to Dirichlet boundary conditions, a quantum field interacting with a classical potential, and a quantum field that starts in a thermal state.
Turbulent Density Variations in Non-Adiabatic Interstellar Fluids
NASA Astrophysics Data System (ADS)
Higdon, J. C.; Conley, Alex
1998-05-01
Analyses of radio scintillation measurements have demonstrated (e.g., Rickett, ARAA, 28, 561, 1990) the existence of ubiquitous turbulent density fluctuations in the interstellar medium. Higdon (ApJ, 309, 342, 1986) and Goldreich and Sridhar (ApJ, 438, 763 1995) have modeled successfully these density variations as entropy structures distorted by convection in anisotropic magnetohydrodynamic turbulent flows. However, the interstellar medium is a heterogeneous non-adiabatic fluid whose thermal properties result ( Field, ApJ, 142, 531 1965) from a balance of heating and cooling rates. The effect of the non-adiabatic nature of interstellar fluids on the properties of turbulent cascades to small scales has not been considered previously. We find that in thermally stable fluids that the required balance of heating and cooling decreases the amplitudes of entropy structures independently of their spatial scale. Consequently, we show that if the time scale for turbulent flows to cascade to small scales is significantly greater than the cooling time of an interstellar fluid, the generation of turbulent denisty density variations at large wave numbers is greatly suppressed. Such results constrain possible values for the turbulent outer scale in models of interstellar turbulent flows.
Exchange–Correlation Functionals via Local Interpolation along the Adiabatic Connection
2016-01-01
The construction of density-functional approximations is explored by modeling the adiabatic connection locally, using energy densities defined in terms of the electrostatic potential of the exchange–correlation hole. These local models are more amenable to the construction of size-consistent approximations than their global counterparts. In this work we use accurate input local ingredients to assess the accuracy of a range of local interpolation models against accurate exchange–correlation energy densities. The importance of the strictly correlated electrons (SCE) functional describing the strong coupling limit is emphasized, enabling the corresponding interpolated functionals to treat strong correlation effects. In addition to exploring the performance of such models numerically for the helium and beryllium isoelectronic series and the dissociation of the hydrogen molecule, an approximate analytic model is presented for the initial slope of the local adiabatic connection. Comparisons are made with approaches based on global models, and prospects for future approximations based on the local adiabatic connection are discussed. PMID:27116427
Exchange-Correlation Functionals via Local Interpolation along the Adiabatic Connection.
Vuckovic, Stefan; Irons, Tom J P; Savin, Andreas; Teale, Andrew M; Gori-Giorgi, Paola
2016-06-14
The construction of density-functional approximations is explored by modeling the adiabatic connection locally, using energy densities defined in terms of the electrostatic potential of the exchange-correlation hole. These local models are more amenable to the construction of size-consistent approximations than their global counterparts. In this work we use accurate input local ingredients to assess the accuracy of a range of local interpolation models against accurate exchange-correlation energy densities. The importance of the strictly correlated electrons (SCE) functional describing the strong coupling limit is emphasized, enabling the corresponding interpolated functionals to treat strong correlation effects. In addition to exploring the performance of such models numerically for the helium and beryllium isoelectronic series and the dissociation of the hydrogen molecule, an approximate analytic model is presented for the initial slope of the local adiabatic connection. Comparisons are made with approaches based on global models, and prospects for future approximations based on the local adiabatic connection are discussed. PMID:27116427
Local shortcut to adiabaticity for quantum many-body systems
NASA Astrophysics Data System (ADS)
Mukherjee, Victor; Montangero, Simone; Fazio, Rosario
2016-06-01
We study the environmentally assisted local transitionless dynamics in closed spin systems driven through quantum critical points. In general the shortcut to adaiabaticity (STA) in quantum critical systems requires highly nonlocal control Hamiltonians. In this work we develop an approach to achieve local shortcuts to adiabaticity (LSTA) in spin chains, using local control fields which scale polynomially with the system size, following universal critical exponents. We relate the control fields to reduced fidelity susceptibility and use the transverse Ising model in one dimension to exemplify our generic results. We also extend our analysis to achieve LSTA in central spin models.
NASA Astrophysics Data System (ADS)
Park, Young Choon; Krykunov, Mykhaylo; Ziegler, Tom
2015-07-01
In ΔSCF density functional theory studies of a i → a transition one performs separate fully self-consistent field calculations on the ground state configuration (i)n (n = 1,2) and the excited state configuration (i)n - 1a. The excitation energy for the transition i → a is subsequently determined as the Kohn-Sham energy difference ΔEi → a = E[in - 1a] - E[in] between the ground state (i)n and the excited state configuration (i)n - 1a. The ΔSCF scheme has been applied extensively and works well for lower energy excitations provided that they can be represented by a single orbital replacement or transition i → a. However, for excitations of higher energy ΔSCF tends to become numerically unstable with a variational collapse to transitions of lower energy. We demonstrate here a numerically stable ΔSCF scheme for local functionals that is guaranteed not to collapse on excited configurations of lower energy as well as the ground state. The new scheme is based on constricted variational density functional theory in which the canonical ground state orbitals are allowed to relax (R-CV(∞)-DFT). Since it is restricted to a single orbital replacement i → a it is termed SOR-R-CV(∞)-DFT.
Gidopoulos, Nikitas I.; Gross, E. K. U.
2014-01-01
A novel treatment of non-adiabatic couplings is proposed. The derivation is based on a theorem by Hunter stating that the wave function of the complete system of electrons and nuclei can be written, without approximation, as a Born–Oppenheimer (BO)-type product of a nuclear wave function, X(R), and an electronic one, ΦR(r), which depends parametrically on the nuclear configuration R. From the variational principle, we deduce formally exact equations for ΦR(r) and X(R). The algebraic structure of the exact nuclear equation coincides with the corresponding one in the adiabatic approximation. The electronic equation, however, contains terms not appearing in the adiabatic case, which couple the electronic and the nuclear wave functions and account for the electron–nuclear correlation beyond the BO level. It is proposed that these terms can be incorporated using an optimized local effective potential. PMID:24516183
Vashaee, S; Newling, B; Balcom, B J
2015-12-01
Band selective adiabatic inversion radio frequency pulses were employed for multi-slice T2 distribution measurements in porous media samples. Multi-slice T2 measurement employing longitudinal Hadamard encoding has an inherent sensitivity advantage over slice-by-slice local T2 measurements. The slice selection process is rendered largely immune to B1 variation by employing hyperbolic secant adiabatic inversion pulses, which simultaneously invert spins in several well-defined slices. While Hadamard encoding is well established for local spectroscopy, the current work is the first use of Hadamard encoding for local T2 measurement. PMID:26580063
NASA Astrophysics Data System (ADS)
Vashaee, S.; Newling, B.; Balcom, B. J.
2015-12-01
Band selective adiabatic inversion radio frequency pulses were employed for multi-slice T2 distribution measurements in porous media samples. Multi-slice T2 measurement employing longitudinal Hadamard encoding has an inherent sensitivity advantage over slice-by-slice local T2 measurements. The slice selection process is rendered largely immune to B1 variation by employing hyperbolic secant adiabatic inversion pulses, which simultaneously invert spins in several well-defined slices. While Hadamard encoding is well established for local spectroscopy, the current work is the first use of Hadamard encoding for local T2 measurement.
Borovsky, Joseph E; Denton, Michael H
2008-01-01
Using temperature and number-density measurements of the energetic-electron population from multiple spacecraft in geosynchronous orbit, the specific entropy S = T/n{sup 2/3} of the outer electron radiation belt is calculated. Then 955,527 half-hour-long data intervals are statistically analyzed. Local-time and solar-cycle variations in S are examined. The median value of the specific entropy (2.8 x 10{sup 7} eVcm{sup 2}) is much larger than the specific entropy of other particle populations in and around the magnetosphere. The evolution of the specific entropy through high-speed-stream-driven geomagnetic storms and through magnetic-cloud-driven geomagnetic storms is studied using superposed-epoch analysis. For high-speed-stream-driven storms, systematic variations in the entropy associated with electron loss and gain and with radiation-belt heating are observed in the various storm phases. For magnetic-cloud-driven storms, multiple trigger choices for the data superpositions reveal the effects of interplanetary shock arrival, sheath driving, cloud driving, and recovery phase. The specific entropy S = T/n{sup 2/3} is algebraically expressed in terms of the first and second adiabatic invariants of the electrons: this allows a relativistic expression for S in terms of T and n to be derived. For the outer electron radiation belt at geosynchronous orbit, the relativistic corrections to the specific entropy expression are -15%.
Andronesi, Ovidiu C.; Ramadan, Saadallah; Mountford, Carolyn E.; Sorensen, A. Gregory
2011-01-01
Novel low-power adiabatic sequences are demonstrated for in-vivo localized two-dimensional (2D) correlated MR spectroscopy, such as COSY (Correlated Spectroscopy) and TOCSY (Total Correlated Spectroscopy). The design is based on three new elements for in-vivo 2D MRS: the use of gradient modulated constant adiabaticity GOIA-W(16,4) pulses for i) localization (COSY and TOCSY) and ii) mixing (TOCSY), and iii) the use of longitudinal mixing (z-filter) for magnetization transfer during TOCSY. GOIA-W(16,4) provides accurate signal localization, and more importantly, lowers the SAR for both TOCSY mixing and localization. Longitudinal mixing improves considerably (five-folds) the efficiency of TOCSY transfer. These are markedly different from previous 1D editing TOCSY sequences using spatially non-selective pulses and transverse mixing. Fully adiabatic (adiabatic mixing with adiabatic localization) and semi-adiabatic (adiabatic mixing with non-adiabatic localization) methods for 2D TOCSY are compared. Results are presented for simulations, phantoms, and in-vivo 2D spectra from healthy volunteers and patients with brain tumors obtained on 3T clinical platforms equipped with standard hardware. To the best of our knowledge this is the first demonstration of in-vivo adiabatic 2D TOCSY and fully adiabatic 2D COSY. It is expected that these methodological developments will advance the in-vivo applicability of multi(spectrally)dimensional MRS to reliably identify metabolic biomarkers. PMID:20890988
Diestler, D J
2012-03-22
The Born-Oppenheimer (BO) description of electronically adiabatic molecular processes predicts a vanishing electronic flux density (j(e)),
Wilken, F.; Bauer, D.
2006-11-17
The ionization of a one-dimensional model helium atom in short laser pulses using time-dependent density-functional theory is investigated. We calculate ionization probabilities as a function of laser intensity by approximating the correlation function of the system adiabatically with an explicit dependence on the fractional number of bound electrons. For the correlation potential we take the derivative discontinuity at integer numbers of bound electrons explicitly into account. This approach reproduces ionization probabilities from the solution of the time-dependent Schroedinger equation, in particular, the so-called knee due to nonsequential ionization.
Adiabatic approximation in time-dependent reduced-density-matrix functional theory
Requist, Ryan; Pankratov, Oleg
2010-04-15
With the aim of describing real-time electron dynamics, we introduce an adiabatic approximation for the equation of motion of the one-body reduced density matrix (one-matrix). The eigenvalues of the one-matrix, which represent the occupation numbers of single-particle orbitals, are obtained from the constrained minimization of the instantaneous ground-state energy functional rather than from their dynamical equations. The performance of the approximation vis-a-vis nonadiabatic effects is assessed in real-time simulations of a two-site Hubbard model. Due to Landau-Zener-type transitions, the system evolves into a nonstationary state with persistent oscillations in the observables. The amplitude of the oscillations displays a strongly nonmonotonic dependence on the strength of the electron-electron interaction and the rate of variation of the external potential. We interpret an associated resonance behavior in the phase of the oscillations in terms of 'scattering' with spectator energy levels. To clarify the motivation for the minimization condition, we derive a sequence of energy functionals E{sub v}{sup (n)}, for which the corresponding sequence of minimizing one-matrices is asymptotic to the exact one-matrix in the adiabatic limit.
Quantum Lattice Fluctuations in the Charge Density Wave State beyond the Adiabatic Approximation
NASA Astrophysics Data System (ADS)
Shida, Keisuke; Watanabe, Yuko; Gomi, Hiroki; Takahashi, Akira; Tomita, Norikazu
2015-12-01
We have developed a tractable numerical method in which large-amplitude quantum lattice fluctuations can be described beyond the adiabatic approximation using the coherent state representation of phonons. A many-body wave function is constructed by the superposition of direct products of non-orthogonal Slater determinants for electrons and coherent states of phonons. Both orbitals in all the Slater determinants and the amplitudes of all the coherent states are simultaneously optimized. We apply the method to the one-dimensional Su-Schrieffer-Heeger model with the on-site and nearest-neighbor-site Coulomb interactions. It is shown the lattice fluctuations in doped charge density wave (CDW) systems are described by the translational and vibrational motion of lattice solitons. Such lattice solitons induce bond alternation in the doped CDW system while the lattice becomes equidistant in the half-filled CDW system.
Habershon, Scott
2013-09-14
We introduce a new approach for calculating quantum time-correlation functions and time-dependent expectation values in many-body thermal systems; both electronically adiabatic and non-adiabatic cases can be treated. Our approach uses a path integral simulation to sample an initial thermal density matrix; subsequent evolution of this density matrix is equivalent to solution of the time-dependent Schrödinger equation, which we perform using a linear expansion of Gaussian wavepacket basis functions which evolve according to simple classical-like trajectories. Overall, this methodology represents a formally exact approach for calculating time-dependent quantum properties; by introducing approximations into both the imaginary-time and real-time propagations, this approach can be adapted for complex many-particle systems interacting through arbitrary potentials. We demonstrate this method for the spin Boson model, where we find good agreement with numerically exact calculations. We also discuss future directions of improvement for our approach with a view to improving accuracy and efficiency.
Adiabatic transport, Kubo formula and Anderson localization in some lattice and continuum models
NASA Astrophysics Data System (ADS)
Elgart, A.
2006-03-01
The different explanations of the Quantum Hall Effect rely on the validity of the linear response theory for a system that has infinite extent. We will present recent results on the adiabatic charge transport in this context for two dimensional lattice (joint work with M. Aizenman and J. Schenker) and continuum (joint work with B. Schlein) models of a non-interacting electron gas. It is proved that if the Fermi energy falls in the localization regime then the Hall transport is correctly described by the linear response Kubo formula. The localization condition is set forth by the fractional moment method, which is by now extended also to continuum models (joint work with M. Aizenman, S. Naboko, J. Schenker and G. Stoltz). In the present talk, besides localization criteria, we will discuss some ideas -- Nenciu's asymptotic expansion, generalized space-momentum inequalities, and finite speed of propagation estimates -- which enter the proof.
NASA Astrophysics Data System (ADS)
Read, J. I.
2014-06-01
I review current efforts to measure the mean density of dark matter near the Sun. This encodes valuable dynamical information about our Galaxy and is also of great importance for ‘direct detection’ dark matter experiments. I discuss theoretical expectations in our current cosmology; the theory behind mass modelling of the Galaxy; and I show how combining local and global measures probes the shape of the Milky Way dark matter halo and the possible presence of a ‘dark disc’. I stress the strengths and weaknesses of different methodologies and highlight the continuing need for detailed tests on mock data—particularly in the light of recently discovered evidence for disequilibria in the Milky Way disc. I collate the latest measurements of ρdm and show that, once the baryonic surface density contribution Σb is normalized across different groups, there is remarkably good agreement. Compiling data from the literature, I estimate Σb = 54.2 ± 4.9 M⊙pc-2, where the dominant source of uncertainty is in the H i gas contribution. Assuming this contribution from the baryons, I highlight several recent measurements of ρdm in order of increasing data complexity and prior, and, correspondingly, decreasing formal error bars. Comparing these measurements with spherical extrapolations from the Milky Way’s rotation curve, I show that the Milky Way is consistent with having a spherical dark matter halo at R0 ˜ 8 kpc. The very latest measures of ρdm based on ˜10 000 stars from the Sloan Digital Sky Survey appear to favour little halo flattening at R0, suggesting that the Galaxy has a rather weak dark matter disc, with a correspondingly quiescent merger history. I caution, however, that this result hinges on there being no large systematics that remain to be uncovered in the SDSS data, and on the local baryonic surface density being Σb ˜ 55 M⊙pc-2. I conclude by discussing how the new Gaia satellite will be transformative. We will obtain much tighter
Bailey, Nicholas P.; Bøhling, Lasse; Veldhorst, Arno A.; Schrøder, Thomas B.; Dyre, Jeppe C.
2013-11-14
We derive exact results for the rate of change of thermodynamic quantities, in particular, the configurational specific heat at constant volume, C{sub V}, along configurational adiabats (curves of constant excess entropy S{sub ex}). Such curves are designated isomorphs for so-called Roskilde liquids, in view of the invariance of various structural and dynamical quantities along them. The slope of the isomorphs in a double logarithmic representation of the density-temperature phase diagram, γ, can be interpreted as one third of an effective inverse power-law potential exponent. We show that in liquids where γ increases (decreases) with density, the contours of C{sub V} have smaller (larger) slope than configurational adiabats. We clarify also the connection between γ and the pair potential. A fluctuation formula for the slope of the C{sub V}-contours is derived. The theoretical results are supported with data from computer simulations of two systems, the Lennard-Jones fluid, and the Girifalco fluid. The sign of dγ/dρ is thus a third key parameter in characterizing Roskilde liquids, after γ and the virial-potential energy correlation coefficient R. To go beyond isomorph theory we compare invariance of a dynamical quantity, the self-diffusion coefficient, along adiabats and C{sub V}-contours, finding it more invariant along adiabats.
Spatial Symmetries of the Local Densities
Rohozinski, S.; Dobaczewski, J.; Nazarewicz, Witold
2010-01-01
Spatial symmetries of the densities appearing in the nuclear Density Functional Theory are discussed. General forms of the local densities are derived by using methods of construction of isotropic tensor fields. The spherical and axial cases are considered.
Accurate calculation and modeling of the adiabatic connection in density functional theory
NASA Astrophysics Data System (ADS)
Teale, A. M.; Coriani, S.; Helgaker, T.
2010-04-01
Using a recently implemented technique for the calculation of the adiabatic connection (AC) of density functional theory (DFT) based on Lieb maximization with respect to the external potential, the AC is studied for atoms and molecules containing up to ten electrons: the helium isoelectronic series, the hydrogen molecule, the beryllium isoelectronic series, the neon atom, and the water molecule. The calculation of AC curves by Lieb maximization at various levels of electronic-structure theory is discussed. For each system, the AC curve is calculated using Hartree-Fock (HF) theory, second-order Møller-Plesset (MP2) theory, coupled-cluster singles-and-doubles (CCSD) theory, and coupled-cluster singles-doubles-perturbative-triples [CCSD(T)] theory, expanding the molecular orbitals and the effective external potential in large Gaussian basis sets. The HF AC curve includes a small correlation-energy contribution in the context of DFT, arising from orbital relaxation as the electron-electron interaction is switched on under the constraint that the wave function is always a single determinant. The MP2 and CCSD AC curves recover the bulk of the dynamical correlation energy and their shapes can be understood in terms of a simple energy model constructed from a consideration of the doubles-energy expression at different interaction strengths. Differentiation of this energy expression with respect to the interaction strength leads to a simple two-parameter doubles model (AC-D) for the AC integrand (and hence the correlation energy of DFT) as a function of the interaction strength. The structure of the triples-energy contribution is considered in a similar fashion, leading to a quadratic model for the triples correction to the AC curve (AC-T). From a consideration of the structure of a two-level configuration-interaction (CI) energy expression of the hydrogen molecule, a simple two-parameter CI model (AC-CI) is proposed to account for the effects of static correlation on the
Quasi-Adiabatic Quantum Computing Treated with c-Numbers Using the Local-Field Response
NASA Astrophysics Data System (ADS)
Tomaru, Tatsuya
2016-03-01
A computational method called the local-field response method is proposed, where spins evolve by responding to an effective field consisting of gradually decreasing external fields and spin-spin interactions, similarly to what is carried out in adiabatic quantum computing (AQC). This method is partly quantum-mechanical. That is, spins are treated as classical variables, but the response function of the spins to the effective field is determined a priori by referring to a quantum-mechanical calculation that was carried out for similar problems. This novel response function improves the performance of the ground state being maintained in the time evolution compared with the case without a priori information. The performance is numerically checked in an eight-qubit system by solving random-interaction problems of finding their ground states. The false probability decreases by about half as a result of using a priori information. The operation of this method is classical, but it has a quantum-mechanical advantage through a priori information. This method is practically useful because obtaining a complete quantum system is difficult as it stands.
NASA Astrophysics Data System (ADS)
Haruyama, Jun; Suzuki, Takahiro; Hu, Chunping; Watanabe, Kazuyuki
2012-01-01
We present a simple and computationally efficient method to calculate excited-state nuclear forces on adiabatic potential-energy surfaces (APES) from linear-response time-dependent density-functional theory within a real-space framework. The Casida ansatz, which has been validated for computing first-order nonadiabatic couplings in previous studies, was applied to the calculation of the excited-state forces. Our method is validated by the consistency of results in the lower excited states, which reproduce well those obtained by the numerical derivative of each APES. We emphasize the usefulness of this technique by demonstrating the excited-state molecular-dynamics simulation.
Locality of correlation in density functional theory
NASA Astrophysics Data System (ADS)
Burke, Kieron; Cancio, Antonio; Gould, Tim; Pittalis, Stefano
2016-08-01
The Hohenberg-Kohn density functional was long ago shown to reduce to the Thomas-Fermi (TF) approximation in the non-relativistic semiclassical (or large-Z) limit for all matter, i.e., the kinetic energy becomes local. Exchange also becomes local in this limit. Numerical data on the correlation energy of atoms support the conjecture that this is also true for correlation, but much less relevant to atoms. We illustrate how expansions around a large particle number are equivalent to local density approximations and their strong relevance to density functional approximations. Analyzing highly accurate atomic correlation energies, we show that EC → -AC ZlnZ + BCZ as Z → ∞, where Z is the atomic number, AC is known, and we estimate BC to be about 37 mhartree. The local density approximation yields AC exactly, but a very incorrect value for BC, showing that the local approximation is less relevant for the correlation alone. This limit is a benchmark for the non-empirical construction of density functional approximations. We conjecture that, beyond atoms, the leading correction to the local density approximation in the large-Z limit generally takes this form, but with BC a functional of the TF density for the system. The implications for the construction of approximate density functionals are discussed.
Locality of correlation in density functional theory.
Burke, Kieron; Cancio, Antonio; Gould, Tim; Pittalis, Stefano
2016-08-01
The Hohenberg-Kohn density functional was long ago shown to reduce to the Thomas-Fermi (TF) approximation in the non-relativistic semiclassical (or large-Z) limit for all matter, i.e., the kinetic energy becomes local. Exchange also becomes local in this limit. Numerical data on the correlation energy of atoms support the conjecture that this is also true for correlation, but much less relevant to atoms. We illustrate how expansions around a large particle number are equivalent to local density approximations and their strong relevance to density functional approximations. Analyzing highly accurate atomic correlation energies, we show that EC → -AC ZlnZ + BCZ as Z → ∞, where Z is the atomic number, AC is known, and we estimate BC to be about 37 mhartree. The local density approximation yields AC exactly, but a very incorrect value for BC, showing that the local approximation is less relevant for the correlation alone. This limit is a benchmark for the non-empirical construction of density functional approximations. We conjecture that, beyond atoms, the leading correction to the local density approximation in the large-Z limit generally takes this form, but with BC a functional of the TF density for the system. The implications for the construction of approximate density functionals are discussed. PMID:27497544
Robitaille, P M; Merkle, H; Sublett, E; Hendrich, K; Lew, B; Path, G; From, A H; Bache, R J; Garwood, M; Uğurbil, K
1989-04-01
Adiabatic pulses have been employed in spectroscopic imaging and relaxation rate measurements at 4.7 T to demonstrate the feasibility of obtaining spectroscopic data from the complete sensitive volume of a surface coil using the surface coil as a transmitter and receiver. With conventional B1 sensitive pulses, spectroscopic localization or imaging techniques, such as chemical-shift imaging, yield resonance intensities that are distorted severely as a function of space, and maximal signal is detected from a small region within the complete sensitive volume of the coil. With adiabatic pulses, however, this problem is eliminated completely. In addition, a new method of spatial localization is introduced. This method, referred to as FLAX-ISIS, is a derivative of longitudinally modulated Fourier series window and ISIS approaches and utilizes adiabatic inversion and excitation pulses. The method allows construction of localized spectra for multiple regions along the surface coil axis by postacquisition data manipulation of a single set of free induction decays. These techniques were applied to the study of the myocardium using an implanted surface coil in an instrumented closed-chest canine model and in an open-chest preparation. The results demonstrate that one-dimensional techniques are adequate for transmural detection of metabolites provided signal origin is restricted to a column perpendicular to the left ventricle wall. PMID:2755331
Local density dependent potential for compressible mesoparticles
NASA Astrophysics Data System (ADS)
Faure, Gérôme; Maillet, Jean-Bernard; Stoltz, Gabriel
2014-03-01
This work proposes a coarse grained description of molecular systems based on mesoparticles representing several molecules, where interactions between mesoparticles are modelled by an interparticle potential of molecular type. Since strong non-equilibrium situations over a wide range of pressure and density are targeted, the internal compressibility of the mesoparticles has to be considered. This is done by introducing a dependence of the potential on the local environment of the mesoparticles. To define local densities, we resort to a three-dimensional Voronoi tessellation instead of standard local, spherical averages. As an example, a local density dependent potential is fitted to reproduce the Hugoniot curve of a model of nitromethane over a large range of pressures and densities.
Moll, Jochen
2016-09-01
This work is based on the experimental observation that the phase and group velocity of the fundamental antisymmetric wave mode in a composite structure with linearly varying thickness changes as it propagates along the nonuniform waveguide (Moll et al., 2015). This adiabatic wave motion leads to systematic damage localization errors of conventional algorithms because a constant wave velocity is assumed in the reconstruction process. This paper presents a generalized beamforming approach for composite structures with nonuniform cross section that eliminates this systematic error. Damage localization results will be presented and discussed in comparison to existing techniques. PMID:27317966
Local Atomic Density of Microporous Carbons
Dmowski, Wojtek; Contescu, Cristian I.; Llobet, Anna; Gallego, Nidia C.; Egami, Takeskhi
2012-07-12
We investigated the structure of two disordered carbons: activated carbon fibers (ACF) and ultramicroporous carbon (UMC). These carbons have highly porous structure with large surface areas and consequently low macroscopic density that should enhance adsorption of hydrogen. We used the atomic pair distribution function to probe the local atomic arrangements. The results show that the carbons maintain an in-plane local atomic structure similar to regular graphite, but the stacking of graphitic layers is strongly disordered. Although the local atomic density of these carbons is lower than graphite, it is only {approx}20% lower and is much higher than the macroscopic density due to the porosity of the structure. For this reason, the density of graphene sheets that have optimum separation for hydrogen adsorption is lower than anticipated.
Local atomic density of microporous carbons
Dmowski, Wojtek; Contescu, Cristian I; Llobet, Anna; Gallego, Nidia C; Egami, Takeshi
2011-01-01
We investigated the structure of two disordered carbons: activated carbon fibers (ACF) and ultramicroporous carbon (UMC). These carbons have highly porous structure with large surface areas and consequently low macroscopic density that should enhance adsorption of hydrogen. We used the atomic pair distribution function to probe the local atomic arrangements. The results show that the carbons maintain an in-plane local atomic structure similar to regular graphite, but the stacking of graphitic layers is strongly disordered. Although the local atomic density of these carbons is lower than graphite, it is only ~20% lower and is much higher than the macroscopic density due to the porosity of the structure. For this reason, the density of graphene sheets that have optimum separation for hydrogen adsorption is lower than anticipated.
The local density of halo giants
NASA Technical Reports Server (NTRS)
Morrison, Heather L.
1993-01-01
A new estimate of the local density of halo giants - 36 +/- 7 with M(V) less than 0.5 per cu kpc - is presented. This number is derived from an objective-prism survey for nearby metal-weak stars, and so is free from many of the assumptions needed to derive the local halo density in the traditional way, from high proper motion surveys. This number agrees well with estimates of the local density of halo horizontal-branch stars, but is approximately a factor of 2 smaller than the density derived by Bahcall and Casertano (1986). This may be due to the inclusion of some thick disk stars in their proper-motion selected sample. The halo density derived from giants can be expressed as a disk-to-halo ratio of 850:1 (+/- 35 percent). Using these results, a simple model is built to predict numbers of halo giants in specified directions in the Galaxy. It is shown that it performs much better than the Bahcall-Soniera model, in the specific case of halo giants. The surface brightness due to the halo at the solar radius is calculated to be 27.7 V magnitudes per sq arcsec, if the Galaxy was viewed from the outside, edge-on, thus raising the possibility of detecting light from halo field stars in other galaxies similar to our own.
Entropy density of an adiabatic relativistic Bose-Einstein condensate star
Khaidir, Ahmad Firdaus; Kassim, Hasan Abu; Yusof, Norhasliza
2015-04-24
Inspired by recent works, we investigate how the thermodynamics parameters (entropy, temperature, number density, energy density, etc) of Bose-Einstein Condensate star scale with the structure of the star. Below the critical temperature in which the condensation starts to occur, we study how the entropy behaves with varying temperature till it reaches its own stability against gravitational collapse and singularity. Compared to photon gases (pressure is described by radiation) where the chemical potential, μ is zero, entropy of photon gases obeys the Stefan-Boltzmann Law for a small values of T while forming a spiral structure for a large values of T due to general relativity. The entropy density of Bose-Einstein Condensate is obtained following the similar sequence but limited under critical temperature condition. We adopt the scalar field equation of state in Thomas-Fermi limit to study the characteristics of relativistic Bose-Einstein condensate under varying temperature and entropy. Finally, we obtain the entropy density proportional to (σT{sup 3}-3T) which obeys the Stefan-Boltzmann Law in ultra-relativistic condition.
Generalized local-spin-density-functional theory
NASA Astrophysics Data System (ADS)
Guo, Yufei; Whitehead, M. A.
1991-01-01
An alternative density-functional theory, the generalized local-spin-density-functional (G-LSD) theory, is proposed based on the boundary conditions and sum rule of the Fermi-correlation factor in the Hartree-Fock (HF) limit. It avoids the physical restrictions to the boundary conditions and the sum rule used in the generalized exchange local-spin-density-functional (GX-LSD) theory completely, the homogeneous electron-density approximation in the Hartree-Fock-Slater (HFS) theory and in the Gáspár-Kohn-Sham (GKS) theory partly, and the time-consuming step to search for the optimal exchange parameter for each atom or ion in the Xα and Ξa theories. The alternative G-LSD theory generates the GX-LSD, HFS, GKS, Xα, and Ξa theories, when additional approximations or certain Fermi-hole shapes or high electron-density limit in a system are used. Theoretically, the G-LSD theory is more rigorous than the GX-LSD, HFS, GKS, and Ξa theories. Numerically, the statistical total energies for atoms in the G-LSD theory are in excellent agreement with the HF results, when the Gopinathan, Whitehead, and Bogdanovic [Phys. Rev. A 14, 1 (1976)] Fermi-hole parameters are used.
Local-density-driven clustered star formation
NASA Astrophysics Data System (ADS)
Parmentier, G.; Pfalzner, S.
2013-01-01
Context. A positive power-law trend between the local surface densities of molecular gas, Σgas, and young stellar objects, Σ ⋆ , in molecular clouds of the solar neighbourhood has recently been identified. How it relates to the properties of embedded clusters, in particular to the recently established radius-density relation, has so far not been investigated. Aims: We model the development of the stellar component of molecular clumps as a function of time and initial local volume density. Our study provides a coherent framework able to explain both the molecular-cloud and embedded-cluster relations quoted above. Methods: We associate the observed volume density gradient of molecular clumps to a density-dependent free-fall time. The molecular clump star formation history is obtained by applying a constant star formation efficiency per free-fall time, ɛff. Results: For the volume density profiles typical of observed molecular clumps (i.e. power-law slope ≃ -1.7), our model gives a star-gas surface-density relation of the form Σ⋆ ∝ Σgas2, which agrees very well with the observations. Taking the case of a molecular clump of mass M0 ≃ 104 M⊙ and radius R ≃ 6 pc experiencing star formation during 2 Myr, we derive what star formation efficiency per free-fall time matches the normalizations of the observed and predicted (Σ ⋆ , Σgas) relations best. We find ɛff ≃ 0.1. We show that the observed growth of embedded clusters, embodied by their radius-density relation, corresponds to a surface density threshold being applied to developing star-forming regions. The consequences of our model in terms of cluster survivability after residual star-forming gas expulsion are that, owing to the locally high star formation efficiency in the inner part of star-forming regions, global star formation efficiency as low as 10% can lead to the formation of bound gas-free star clusters.
NASA Astrophysics Data System (ADS)
Regnier, D.; Dubray, N.; Schunck, N.; Verrière, M.
2016-05-01
Background: Accurate knowledge of fission fragment yields is an essential ingredient of numerous applications ranging from the formation of elements in the r process to fuel cycle optimization for nuclear energy. The need for a predictive theory applicable where no data are available, together with the variety of potential applications, is an incentive to develop a fully microscopic approach to fission dynamics. Purpose: In this work, we calculate the pre-neutron emission charge and mass distributions of the fission fragments formed in the neutron-induced fission of 239Pu using a microscopic method based on nuclear density functional theory (DFT). Methods: Our theoretical framework is the nuclear energy density functional (EDF) method, where large-amplitude collective motion is treated adiabatically by using the time-dependent generator coordinate method (TDGCM) under the Gaussian overlap approximation (GOA). In practice, the TDGCM is implemented in two steps. First, a series of constrained EDF calculations map the configuration and potential-energy landscape of the fissioning system for a small set of collective variables (in this work, the axial quadrupole and octupole moments of the nucleus). Then, nuclear dynamics is modeled by propagating a collective wave packet on the potential-energy surface. Fission fragment distributions are extracted from the flux of the collective wave packet through the scission line. Results: We find that the main characteristics of the fission charge and mass distributions can be well reproduced by existing energy functionals even in two-dimensional collective spaces. Theory and experiment agree typically within two mass units for the position of the asymmetric peak. As expected, calculations are sensitive to the structure of the initial state and the prescription for the collective inertia. We emphasize that results are also sensitive to the continuity of the collective landscape near scission. Conclusions: Our analysis confirms
Local spin analyses using density functional theory
NASA Astrophysics Data System (ADS)
Abate, Bayileyegn; Peralta, Juan
Local spin analysis is a valuable technique in computational investigations magnetic interactions on mono- and polynuclear transition metal complexes, which play vital roles in catalysis, molecular magnetism, artificial photosynthesis, and several other commercially important materials. The relative size and complex electronic structure of transition metal complexes often prohibits the use of multi-determinant approaches, and hence, practical calculations are often limited to single-determinant methods. Density functional theory (DFT) has become one of the most successful and widely used computational tools for the electronic structure study of complex chemical systems; transition metal complexes in particular. Within the DFT formalism, a more flexible and complete theoretical modeling of transition metal complexes can be achieved by considering noncollinear spins, in which the spin density is 'allowed to' adopt noncollinear structures in stead of being constrained to align parallel/antiparallel to a universal axis of magnetization. In this meeting, I will present local spin analyses results obtained using different DFT functionals. Local projection operators are used to decompose the expectation value
Statistical density modification using local pattern matching
Terwilliger, Thomas C.
2007-01-23
A computer implemented method modifies an experimental electron density map. A set of selected known experimental and model electron density maps is provided and standard templates of electron density are created from the selected experimental and model electron density maps by clustering and averaging values of electron density in a spherical region about each point in a grid that defines each selected known experimental and model electron density maps. Histograms are also created from the selected experimental and model electron density maps that relate the value of electron density at the center of each of the spherical regions to a correlation coefficient of a density surrounding each corresponding grid point in each one of the standard templates. The standard templates and the histograms are applied to grid points on the experimental electron density map to form new estimates of electron density at each grid point in the experimental electron density map.
NASA Astrophysics Data System (ADS)
Lu, Deyu
The adiabatic-connection fluctuation-dissipation theorem (ACFDT) is a formal theoretical framework to treat van der Waals (vdW) dispersion interactions. Under the random phase approximation (RPA), it yields the correct asymptotic behavior at large distances, but the short-range correlation is overestimated. It has been demonstrated that non-local exchange-correlation kernels can systematically correct the errors of RPA for homogenous electron gas. However, direct extension of non-local kernels derived from the electron gas model to inhomogeneous systems raises several issues. In addition to the high computational expense, the non-local kernels worsen the rare gas dimer binding curve as compared to RPA. In this study, we propose a quasi-local approximation of the non-local kernel in order to address these issues. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.
NASA Astrophysics Data System (ADS)
Subotnik, Joseph E.; Yeganeh, Sina; Cave, Robert J.; Ratner, Mark A.
2008-12-01
This article shows that, although Boys localization is usually applied to single-electron orbitals, the Boys method itself can be applied to many electron molecular states. For the two-state charge-transfer problem, we show analytically that Boys localization yields the same charge-localized diabatic states as those found by generalized Mulliken-Hush theory. We suggest that for future work in electron transfer, where systems have more than two charge centers, one may benefit by using a variant of Boys localization to construct diabatic potential energy surfaces and extract electronic coupling matrix elements. We discuss two chemical examples of Boys localization and propose a generalization of the Boys algorithm for creating diabatic states with localized spin density that should be useful for Dexter triplet-triplet energy transfer.
NASA Astrophysics Data System (ADS)
Wehrenberg, Christopher; Prisbrey, Shon T.; Park, Hye-Sook; Benedetti, L. Robin; Huntington, Channing; McNaney, James; Smith, Ray; Panas, Cynthia; Cook, Angela; Remington, Bruce; Arsenlis, Tom; Graham, Peter
2015-11-01
A series of experiments were performed on NIF to develop a planar, 3-shock, low-adiabat drive for material science experiments. Physics samples (Ta, Pb, etc.) are loaded to 3-4 Mbar while staying well below the melt temperature. X-ray ablation from an indirect drive launches a strong (~ 50 Mbar), decaying shock through a precision fabricated ``reservoir,'' consisting of a CH ablator, followed by layers of Al, CH(18.75%I), ~ 375 mg/cc carbonized resorcinol formaldehyde foam, and a final layer of low density (10-35) mg/cc foam. As the releasing reservoir stagnates on a Ta drive plate, VISAR is used to measures the resulting compression waves. The lowest density reservoir layer is responsible for the leading shock and induces the most entropy during the drive. LLNL has developed a new, low-density foam called JX6 (C20H30) for the purpose of controlling the leading shock. We will describe a series of experiments done on NIF to test the combined release and recompression properties of JX6 and to develop a new, lower-adiabat drive. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
Connection between Hybrid Functionals and Importance of the Local Density Approximation.
Mosquera, Martín A; Borca, Carlos H; Ratner, Mark A; Schatz, George C
2016-03-10
The exchange-correlation (XC) local density approximation (LDA) is the original density functional used to investigate the electronic structure of molecules and solids within the formulation of Kohn and Sham. The LDA is fundamental for the development of density-functional approximations. In this work we consider the generalized Kohn-Sham (GKS) theory of hybrid functionals. The GKS formalism is an extension of the Kohn-Sham theory for electronic ground states and leads to a vast set of alternative density functionals, which can be estimated by the LDA and related methods. Herein we study auxiliary electronic systems with parametrized interactions and derive (i) a set of exact equations relating the GKS XC energies in the parameter space and (ii) a formal relation between the parameters and the standard XC derivative discontinuity. In view of the new results and previously reported findings, we discuss why the inclusion of Fock exchange, and its long-range-corrected form (in the ground-state calculations and in linear-response Kohn-Sham equations), dominate over the generalized gradient corrections to enhance the quality of the fundamental gap and to enhance excitation-energy estimations. As an example, we show that the adiabatic CAM-LDA0 (a functional with 1/4 global and 1/2 long-range Hartree-Fock interaction, respectively, a range separation factor of 1/3, and pure LDA exchange and correlation) works for electronic excitations as well as the adiabatic CAM-B3LYP functional. PMID:26901359
Zhan, Hongyi; Zeng, Weidong; Wang, Gui; Kent, Damon; Dargusch, Matthew
2015-04-15
The microstructural evolution and grain refinement within adiabatic shear bands in the Ti6554 alloy deformed at high strain rates and elevated temperatures have been characterized using transmission electron microscopy. No stress drops were observed in the corresponding stress–strain curve, indicating that the initiation of adiabatic shear bands does not lead to the loss of load capacity for the Ti6554 alloy. The outer region of the shear bands mainly consists of cell structures bounded by dislocation clusters. Equiaxed subgrains in the core area of the shear band can be evolved from the subdivision of cell structures or reconstruction and transverse segmentation of dislocation clusters. It is proposed that dislocation activity dominates the grain refinement process. The rotational recrystallization mechanism may operate as the kinetic requirements for it are fulfilled. The coexistence of different substructures across the shear bands implies that the microstructural evolution inside the shear bands is not homogeneous and different grain refinement mechanisms may operate simultaneously to refine the structure. - Graphical abstract: Display Omitted - Highlights: • The microstructure within the adiabatic shear band was characterized by TEM. • No stress drops were observed in the corresponding stress–strain curve. • Dislocation activity dominated the grain refinement process. • The kinetic requirements for rotational recrystallization mechanism were fulfilled. • Different grain refinement mechanisms operated simultaneously to refine the structure.
Measure the local dark matter density with LAMOST spectroscopic survey
NASA Astrophysics Data System (ADS)
Liu, Chao; Xia, Qiran; Mao, Shude
2016-08-01
The local dark matter density plays the key role in the distribution of the dark matter halo near the Galactic disk. It will also answer whether a dark matter disk exists in the Milky Way. We measure the local dark matter density with LAMOST observed stars located at around the north Galactic pole. The selection effects of the observations are well considered and corrected. We find that the derived DM density, which is around 0.0159+0.0047 -0.0057 M ⊙ pc-3 providing a flat local rotation curve.
CORRELATION BETWEEN GROUP LOCAL DENSITY AND GROUP LUMINOSITY
Deng Xinfa; Yu Guisheng
2012-11-10
In this study, we investigate the correlation between group local number density and total luminosity of groups. In four volume-limited group catalogs, we can conclude that groups with high luminosity exist preferentially in high-density regions, while groups with low luminosity are located preferentially in low-density regions, and that in a volume-limited group sample with absolute magnitude limit M{sub r} = -18, the correlation between group local number density and total luminosity of groups is the weakest. These results basically are consistent with the environmental dependence of galaxy luminosity.
Local mammographic density as a predictor of breast cancer
NASA Astrophysics Data System (ADS)
Otsuka, Mayu; Harkness, Elaine F.; Chen, Xin; Moschidis, Emmanouil; Bydder, Megan; Gadde, Soujanya; Lim, Yit Y.; Maxwell, Anthony J.; Evans, Gareth D.; Howell, Anthony; Stavrinos, Paula; Wilson, Mary; Astley, Susan M.
2015-03-01
High overall mammographic density is associated with both an increased risk of developing breast cancer and the risk of cancer being masked. We compared local density at cancer sites in diagnostic images with corresponding previous screening mammograms (priors), and matched controls. VolparaTM density maps were obtained for 54 mammograms showing unilateral breast cancer and their priors which had been previously read as normal. These were each matched to 3 controls on age, menopausal status, hormone replacement therapy usage, body mass index and year of prior. Local percent density was computed in 15mm square regions at lesion sites and similar locations in the corresponding images. Conditional logistic regression was used to predict case-control status. In diagnostic and prior images, local density was increased at the lesion site compared with the opposite breast (medians 21.58%, 9.18%, p<0.001 diagnostic; 18.82%, 9.45%, p <0.001 prior). Women in the highest tertile of local density in priors were more likely to develop cancer than those in the lowest tertile (OR 42.09, 95% CI 5.37-329.94). Those in the highest tertile of VolparaTM gland volume were also more likely to develop cancer (OR 2.89, 95% CI 1.30-6.42). Local density is increased where cancer will develop compared with corresponding regions in the opposite breast and matched controls, and its measurement could enhance computer-aided mammography.
A new upper limit to the local population II density.
NASA Technical Reports Server (NTRS)
Weistrop, D.
1972-01-01
An upper limit to the local population II density is derived, in terms of the mass-luminosity ratio, on the basis of U, B, and V photometric observations of several thousand stars with V magnitudes between 12 and 18 in a region near the North Galactic Pole. The photographic and photoelectric photometry and the reduction procedures are discussed. Models of the density distribution and luminosity function of the population II stars are used to predict their distribution in color and apparent magnitude. The derived local density of population II is found to be significantly lower than previous estimates. Possible causes for this discrepancy are considered.
Localized density matrix minimization and linear-scaling algorithms
NASA Astrophysics Data System (ADS)
Lai, Rongjie; Lu, Jianfeng
2016-06-01
We propose a convex variational approach to compute localized density matrices for both zero temperature and finite temperature cases, by adding an entry-wise ℓ1 regularization to the free energy of the quantum system. Based on the fact that the density matrix decays exponentially away from the diagonal for insulating systems or systems at finite temperature, the proposed ℓ1 regularized variational method provides an effective way to approximate the original quantum system. We provide theoretical analysis of the approximation behavior and also design convergence guaranteed numerical algorithms based on Bregman iteration. More importantly, the ℓ1 regularized system naturally leads to localized density matrices with banded structure, which enables us to develop approximating algorithms to find the localized density matrices with computation cost linearly dependent on the problem size.
Krykunov, Mykhaylo; Seth, Mike; Ziegler, Tom
2014-05-14
We have applied the relaxed and self-consistent extension of constricted variational density functional theory (RSCF-CV-DFT) for the calculation of the lowest charge transfer transitions in the molecular complex X-TCNE between X = benzene and TCNE = tetracyanoethylene. Use was made of functionals with a fixed fraction (α) of Hartree-Fock exchange ranging from α = 0 to α = 0.5 as well as functionals with a long range correction (LC) that introduces Hartree-Fock exchange for longer inter-electronic distances. A detailed comparison and analysis is given for each functional between the performance of RSCF-CV-DFT and adiabatic time-dependent density functional theory (TDDFT) within the Tamm-Dancoff approximation. It is shown that in this particular case, all functionals afford the same reasonable agreement with experiment for RSCF-CV-DFT whereas only the LC-functionals afford a fair agreement with experiment using TDDFT. We have in addition calculated the CT transition energy for X-TCNE with X = toluene, o-xylene, and naphthalene employing the same functionals as for X = benzene. It is shown that the calculated charge transfer excitation energies are in as good agreement with experiment as those obtained from highly optimized LC-functionals using adiabatic TDDFT. We finally discuss the relation between the optimization of length separation parameters and orbital relaxation in the RSCF-CV-DFT scheme.
The dynamic instability of adiabatic blast waves
NASA Technical Reports Server (NTRS)
Ryu, Dongsu; Vishniac, Ethan T.
1991-01-01
Adiabatic blastwaves, which have a total energy injected from the center E varies as t(sup q) and propagate through a preshock medium with a density rho(sub E) varies as r(sup -omega) are described by a family of similarity solutions. Previous work has shown that adiabatic blastwaves with increasing or constant postshock entropy behind the shock front are susceptible to an oscillatory instability, caused by the difference between the nature of the forces on the two sides of the dense shell behind the shock front. This instability sets in if the dense postshock layer is sufficiently thin. The stability of adiabatic blastwaves with a decreasing postshock entropy is considered. Such blastwaves, if they are decelerating, always have a region behind the shock front which is subject to convection. Some accelerating blastwaves also have such region, depending on the values of q, omega, and gamma where gamma is the adiabatic index. However, since the shock interface stabilizes dynamically induced perturbations, blastwaves become convectively unstable only if the convective zone is localized around the origin or a contact discontinuity far from the shock front. On the other hand, the contact discontinuity of accelerating blastwaves is subject to a strong Rayleigh-Taylor instability. The frequency spectra of the nonradial, normal modes of adiabatic blastwaves have been calculated. The results have been applied to the shocks propagating through supernovae envelopes. It is shown that the metal/He and He/H interfaces are strongly unstable against the Rayleigh-Taylor instability. This instability will induce mixing in supernovae envelopes. In addition the implications of this work for the evolution of planetary nebulae is discussed.
The dynamic instability of adiabatic blast waves
NASA Astrophysics Data System (ADS)
Ryu, Dongsu; Vishniac, Ethan T.
1991-02-01
Adiabatic blastwaves, which have a total energy injected from the center E varies as tq and propagate through a preshock medium with a density rhoE varies as r-omega are described by a family of similarity solutions. Previous work has shown that adiabatic blastwaves with increasing or constant postshock entropy behind the shock front are susceptible to an oscillatory instability, caused by the difference between the nature of the forces on the two sides of the dense shell behind the shock front. This instability sets in if the dense postshock layer is sufficiently thin. The stability of adiabatic blastwaves with a decreasing postshock entropy is considered. Such blastwaves, if they are decelerating, always have a region behind the shock front which is subject to convection. Some accelerating blastwaves also have such region, depending on the values of q, omega, and gamma where gamma is the adiabatic index. However, since the shock interface stabilizes dynamically induced perturbations, blastwaves become convectively unstable only if the convective zone is localized around the origin or a contact discontinuity far from the shock front. On the other hand, the contact discontinuity of accelerating blastwaves is subject to a strong Rayleigh-Taylor instability. The frequency spectra of the nonradial, normal modes of adiabatic blastwaves have been calculated. The results have been applied to the shocks propagating through supernovae envelopes. It is shown that the metal/He and He/H interfaces are strongly unstable against the Rayleigh-Taylor instability. This instability will induce mixing in supernovae envelopes. In addition the implications of this work for the evolution of planetary nebulae is discussed.
The dynamic instability of adiabatic blastwaves
NASA Astrophysics Data System (ADS)
Ryu, Dongsu; Vishniac, Ethan T.
1990-05-01
Adiabatic blastwaves, which have a total energy injected from the center E varies as t(sup q) and propagate through a preshock medium with a density rho(sub E) varies as r(sup -omega) are described by a family of similarity solutions. Previous work has shown that adiabatic blastwaves with increasing or constant postshock entropy behind the shock front are susceptible to an oscillatory instability, caused by the difference between the nature of the forces on the two sides of the dense shell behind the shock front. This instability sets in if the dense postshock layer is sufficiently thin. The stability of adiabatic blastwaves with a decreasing postshock entropy is considered. Such blastwaves, if they are decelerating, always have a region behind the shock front which is subject to convection. Some accelerating blastwaves also have such region, depending on the values of q, omega, and gamma where gamma is the adiabatic index. However, since the shock interface stabilizes dynamically induced perturbations, blastwaves become convectively unstable only if the convective zone is localized around the origin or a contact discontinuity far from the shock front. On the other hand, the contact discontinuity of accelerating blastwaves is subject to a strong Rayleigh-Taylor instability. The frequency spectra of the nonradial, normal modes of adiabatic blastwaves have been calculated. The results have been applied to the shocks propagating through supernovae envelopes. It is shown that the metal/He and He/H interfaces are strongly unstable against the Rayleigh-Taylor instability. This instability will induce mixing in supernovae envelopes. In addition the implications of this work for the evolution of planetary nebulae is discussed.
NASA Astrophysics Data System (ADS)
Baxter, Matthew; Kirchner, Tom
2016-01-01
A recent model to describe electron correlations in time-dependent density-functional-theory (TDDFT) studies of antiproton-helium collisions is extended to deal with positively charged projectiles. The main complication is that a positively charged projectile can capture electrons in addition to ionizing them to the continuum. As a consequence, within the TDDFT framework one needs to consider three, instead of just one, correlation integrals (Ic's) when formally expressing the probabilities for the one- and two-electron processes in terms of the density. We discuss an extension of an adiabatic model for Ic to a two-centered system. Total cross sections for single ionization, double ionization, single capture, transfer ionization, and double capture are presented for both proton-helium and He2+-He collisions for impact energies in the approximate range 10-1000 keV/amu. One- and two-electron removal cross sections are also presented for the p -He system, with a comparison to updated antiproton-helium results. Our results, while mixed, demonstrate the relative importance of dynamic and functional correlations in a TDDFT description of collision processes.
Adiabatic topological quantum computing
NASA Astrophysics Data System (ADS)
Cesare, Chris; Landahl, Andrew J.; Bacon, Dave; Flammia, Steven T.; Neels, Alice
2015-07-01
Topological quantum computing promises error-resistant quantum computation without active error correction. However, there is a worry that during the process of executing quantum gates by braiding anyons around each other, extra anyonic excitations will be created that will disorder the encoded quantum information. Here, we explore this question in detail by studying adiabatic code deformations on Hamiltonians based on topological codes, notably Kitaev's surface codes and the more recently discovered color codes. We develop protocols that enable universal quantum computing by adiabatic evolution in a way that keeps the energy gap of the system constant with respect to the computation size and introduces only simple local Hamiltonian interactions. This allows one to perform holonomic quantum computing with these topological quantum computing systems. The tools we develop allow one to go beyond numerical simulations and understand these processes analytically.
Charge density waves and local states in quasi-one-dimensional mixed valence inorganic complexes
NASA Astrophysics Data System (ADS)
Conradson, S. D.; Stroud, M. A.; Zietlow, M. H.; Swanson, B. I.; Baeriswyl, D.; Bishop, A. R.
1988-02-01
The ground state structures and local states associated with chemical defects in quasi-one-dimensional halogen ( X) bridged transition metal ( M) mixed valence solids of MX and MMX type have been studied. An adiabatic Hartree-Fock theoretical framework is presented and representative members are classified. The MX materials provide a class whose strong electron-phonon coupling usually favors a charge-density-wave (CDW) ground state. However, the coupling strength can be chemically tuned (e.g., by extension to MMX systems) or altered by pressure, driving the ground state structures towards, e.g., a bond-order-wave (BOW) phase. Electron-phonon driven self-trapped states are expected in both the CDW or BOW regimes. Resonance Raman spectra of the MMX solid K 4[Pt 2(P 2O 5H 2) 4Cl]·H 2O show, in addition to the homogeneous ground state modes, sharp new features with excitation profiles shifted to the red of the intervalence-charge-transfer (IVCT) band. We attribute these new bands to a local polaron state formed by oxidation of the Pt 2Cl chain by a chemical defect. The observed spectral characteristics of this local state are in good agreement with theoretical predictions.
Local and Total Density Measurements in Ice Shapes
NASA Technical Reports Server (NTRS)
Vargas, Mario; Broughton, Howard; Sims, James J.; Bleeze, Brian; Gaines, Vatanna
2005-01-01
Preliminary measurements of local and total densities inside ice shapes were obtained from ice shapes grown in the NASA Glenn Research Tunnel for a range of glaze ice, rime ice, and mixed phase ice conditions on a NACA 0012 airfoil at 0 angle of attack. The ice shapes were removed from the airfoil and a slice of ice 3 mm thick was obtained using a microtome. The resulting samples were then x-rayed to obtain a micro-radiography, the film was digitized, and image processing techniques were used to extract the local and total density values.
Pairing renormalization and regularization within the local density approximation
Borycki, P.J.; Dobaczewski, J.; Nazarewicz, W.; Stoitsov, M.V.
2006-04-15
We discuss methods used in mean-field theories to treat pairing correlations within the local density approximation. Pairing renormalization and regularization procedures are compared in spherical and deformed nuclei. Both prescriptions give fairly similar results, although the theoretical motivation, simplicity, and stability of the regularization procedure make it a method of choice for future applications.
Non-local crime density estimation incorporating housing information
Woodworth, J. T.; Mohler, G. O.; Bertozzi, A. L.; Brantingham, P. J.
2014-01-01
Given a discrete sample of event locations, we wish to produce a probability density that models the relative probability of events occurring in a spatial domain. Standard density estimation techniques do not incorporate priors informed by spatial data. Such methods can result in assigning significant positive probability to locations where events cannot realistically occur. In particular, when modelling residential burglaries, standard density estimation can predict residential burglaries occurring where there are no residences. Incorporating the spatial data can inform the valid region for the density. When modelling very few events, additional priors can help to correctly fill in the gaps. Learning and enforcing correlation between spatial data and event data can yield better estimates from fewer events. We propose a non-local version of maximum penalized likelihood estimation based on the H1 Sobolev seminorm regularizer that computes non-local weights from spatial data to obtain more spatially accurate density estimates. We evaluate this method in application to a residential burglary dataset from San Fernando Valley with the non-local weights informed by housing data or a satellite image. PMID:25288817
Localized Density/Drag Prediction for Improved Onboard Orbit Propagation
NASA Astrophysics Data System (ADS)
Stastny, N.; Lin, C.; Lovell, A.; Luck, J.; Chavez, F.
Since the development of Luigi G. Jacchia's first density model in 1970 (J70), atmospheric density modeling has steadily focused on large monolithic codes that provide global density coverage. The most recent instantiation of the global density model is the Jacchia-Bowman 2008 (JB08) model developed by Bruce Bowman of the Air Force Space Command. As the models have evolved and improved, their complexity has grown as well. Where the J70 model required 2 indices and various time averages to determine density, the JB08 model requires 5 indices to determine density. Due to computational complexity, the number of real-time inputs required, and limited forecasting abilities, these models are not well suited for onboard satellite orbit propagation. In contrast to the global models, this paper proposes the development of a density prediction tool that is only concerned with the trajectory of a specific satellite. Since the orbital parameters of most low Earth orbiting satellites remain relatively constant in the short term, there is also minimal variation in the density profile observed by the satellite. Limiting the density model to a smaller orbit regime will also increase the ability to forecast the density along that orbital track. As a first step, this paper evaluates the feasibility of using a localized density prediction algorithm to generate the density profile that will be seen by satellite, allowing for high-accuracy orbit propagation with minimal or no input from the ground. The algorithm evaluated in this paper is a simple Yule-Walker auto-regressive filter that, given previously measured density values, provides predictions on the upcoming density profile. This first approach requires zero information about the satellite's current orbit, but does require an onboard method for determining the current, local density. Though this aspect of the onboard system is not analyzed here, it is envisioned that this current, local density (or equivalently drag acceleration
The difficulty of measuring the local dark matter density
NASA Astrophysics Data System (ADS)
Hessman, F. V.
2015-07-01
The analysis of the vertical velocity dispersion of disc stars in the local Milky Way is the most direct astronomical means of estimating the local dark matter density, ρDM. Current estimates for ρDM based on the mid-plane dynamic density use a local baryonic correction that ignores the non-local effects of spiral structure and significantly underestimates the amount of dynamically relevant gas now known to be present in the ISM; the additional gas plus the remaining uncertainties make it practically impossible to measure ρDM from mid-plane kinematics alone. The sampling of inhomogeneous tracer populations with different scale-heights and scale-lengths results in a systematic increase in the observed dispersion gradients and changes in the nominal density distributions that, if not properly considered, can be misinterpreted as a sign of more dark matter. If the disc gravity is modelled locally using an infinite disc, the local variation in the vertical gravity due to the globally exponential disc components results in an underestimation of the baryonic contribution by as much as ~40%. Given only the assumptions of stationarity, an axially and vertically symmetric disc, doubly exponential tracer and mass-component density profiles, a phenomenologically justified model for the cross-dispersion component σRz, and a realistic model for gz(z), it is possible to solve the full vertical Jeans equation analytically for the vertical dispersion σz(z) and hence test the robustness of previous attempts at measuring ρDM. When the model parameters for σRz are estimated from SEGUE G dwarf star data, it is still not possible to explain the difference in behaviour seen in the simple thick- and thin-disc datasets reported by Buedenbender et al. (2014, MNRAS, submitted). Rather than being a fundamental problem with the kinematical model, this effect appears to be a further sign of the difficulty of defining and handling kinematically homogeneous tracer populations.
Comments on the locality in density-functional theory
Lindgren, Ingvar; Salomonson, Sten
2003-05-01
The 'locality hypothesis' in density-functional theory (DFT), implying that the functional derivative is equivalent to a multiplicative local function, forms the basis of models of Kohn-Sham type. This has been generally accepted by the community since the advent of the model, and has later been formally proved for a large class of functionals. The hypothesis has recently been questioned by Nesbet [Phys. Rev. A 58, R12 (1998) and Phys. Rev. A 65, 010502 (2001)], who claims that it fails for the kinetic-energy functional for a system with more than two noninteracting electrons with a nondegenerate ground state. This conclusion has been questioned by Gal [Phys. Rev. A 62, 044501 (2000)] and by Holas and March [Phys. Rev. A 64, 016501 (2001)]. We claim that the arguments of Nesbet are incorrect, since the orbital functional used for the kinetic energy is not a unique functional of the total density in the domain of unnormalized orbitals. We have demonstrated that with a proper definition of the kinetic energy, which is a unique density functional also in the unnormalized region, the derivative can be represented by a single local multiplicative function for all v-representable densities. Therefore, we consider the controversy connected with the issue raised by Nesbet as resolved. We believe that the proof of the differentiability given here can be extended to larger groups of DFT functionals, and works along these lines are in progress.
Determining the local dark matter density with LAMOST data
NASA Astrophysics Data System (ADS)
Xia, Qiran; Liu, Chao; Mao, Shude; Song, Yingyi; Zhang, Lan; Long, R. J.; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Wu, Yue
2016-06-01
Measurement of the local dark matter density plays an important role in both Galactic dynamics and dark matter direct detection experiments. However, the estimated values from previous works are far from agreeing with each other. In this work, we provide a well-defined observed sample with 1427 G- and K-type main-sequence stars from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope spectroscopic survey, taking into account selection effects, volume completeness, and the stellar populations. We apply a vertical Jeans equation method containing a single exponential stellar disc, a razor thin gas disc, and a constant dark matter density distribution to the sample, and obtain a total surface mass density of 78.7 ^{+3.9}_{-4.7} M_{{⊙}} pc^{-2} up to 1 kpc and a local dark matter density of 0.018± 0.0054 M_{{⊙}} pc^{-3}. We find that the sampling density (i.e. number of stars per unit volume) of the spectroscopic data contributes to about two-third of the uncertainty in the estimated values. We discuss the effect of the tilt term in the Jeans equation and find it has little impact on our measurement. Other issues, such as a non-equilibrium component due to perturbations and contamination by the thick-disc population, are also discussed.
Local thermodynamic mapping for effective liquid density-functional theory
NASA Technical Reports Server (NTRS)
Kyrlidis, Agathagelos; Brown, Robert A.
1992-01-01
The structural-mapping approximation introduced by Lutsko and Baus (1990) in the generalized effective-liquid approximation is extended to include a local thermodynamic mapping based on a spatially dependent effective density for approximating the solid phase in terms of the uniform liquid. This latter approximation, called the local generalized effective-liquid approximation (LGELA) yields excellent predictions for the free energy of hard-sphere solids and for the conditions of coexistence of a hard-sphere fcc solid with a liquid. Moreover, the predicted free energy remains single valued for calculations with more loosely packed crystalline structures, such as the diamond lattice. The spatial dependence of the weighted density makes the LGELA useful in the study of inhomogeneous solids.
NEUTRONIC REACTOR HAVING LOCALIZED AREAS OF HIGH THERMAL NEUTRON DENSITIES
Newson, H.W.
1958-06-01
A nuclear reactor for the irradiation of materials designed to provide a localized area of high thermal neutron flux density in which the materials to be irradiated are inserted is described. The active portion of the reactor is comprised of a cubicle graphite moderator of about 25 feet in length along each axis which has a plurality of cylindrical channels for accommodatirg elongated tubular-shaped fuel elements. The fuel elements have radial fins for spacing the fuel elements from the channel walls, thereby providing spaces through which a coolant may be passed, and also to serve as a heatconductirg means. Ducts for accommnodating the sample material to be irradiated extend through the moderator material perpendicular to and between parallel rows of fuel channels. The improvement is in the provision of additional fuel element channels spaced midway between 2 rows of the regular fuel channels in the localized area surrounding the duct where the high thermal neutron flux density is desired. The fuel elements normally disposed in the channels directly adjacent the duct are placed in the additional channels, and the channels directly adjacent the duct are plugged with moderator material. This design provides localized areas of high thermal neutron flux density without the necessity of providing additional fuel material.
Local thermodynamic equilibrium in rapidly heated high energy density plasmas
Aslanyan, V.; Tallents, G. J.
2014-06-15
Emission spectra and the dynamics of high energy density plasmas created by optical and Free Electron Lasers (FELs) depend on the populations of atomic levels. Calculations of plasma emission and ionization may be simplified by assuming Local Thermodynamic Equilibrium (LTE), where populations are given by the Saha-Boltzmann equation. LTE can be achieved at high densities when collisional processes are much more significant than radiative processes, but may not be valid if plasma conditions change rapidly. A collisional-radiative model has been used to calculate the times taken by carbon and iron plasmas to reach LTE at varying densities and heating rates. The effect of different energy deposition methods, as well as Ionization Potential Depression are explored. This work shows regimes in rapidly changing plasmas, such as those created by optical lasers and FELs, where the use of LTE is justified, because timescales for plasma changes are significantly longer than the times needed to achieve an LTE ionization balance.
Local thermodynamic equilibrium in rapidly heated high energy density plasmas
NASA Astrophysics Data System (ADS)
Aslanyan, V.; Tallents, G. J.
2014-06-01
Emission spectra and the dynamics of high energy density plasmas created by optical and Free Electron Lasers (FELs) depend on the populations of atomic levels. Calculations of plasma emission and ionization may be simplified by assuming Local Thermodynamic Equilibrium (LTE), where populations are given by the Saha-Boltzmann equation. LTE can be achieved at high densities when collisional processes are much more significant than radiative processes, but may not be valid if plasma conditions change rapidly. A collisional-radiative model has been used to calculate the times taken by carbon and iron plasmas to reach LTE at varying densities and heating rates. The effect of different energy deposition methods, as well as Ionization Potential Depression are explored. This work shows regimes in rapidly changing plasmas, such as those created by optical lasers and FELs, where the use of LTE is justified, because timescales for plasma changes are significantly longer than the times needed to achieve an LTE ionization balance.
NASA Astrophysics Data System (ADS)
Li, J.; Yang, P.; Mao, W. M.; Cui, F. E.
2015-04-01
Local shear textures in ASBs of high manganese TRIP steels under high rate straining are determined and the influences of initial microstructure is analyzed using EBSD technique. It is seen that even at the presence of majority of two types of martensite before deformation, ASB is preferred to evolve in austenite, rather than in martenite, due to reverse transformation. Ultrafine grains of thress phases due to dynamic recrystallization are formed and all show shear textures. The less ε-martensite in ASB is distributed as islands and its preferred orientation can be found to originate from the variants in matrix. The grain orientation rotation around ASB in multi-phase alloy reveals significant influence of α'- martensite on texture in ASB. The mechanism of local texture formation in ASB of high manganese TRIP steel is proposed in terms of the interaction of early TRIP and later reverse transformation.
Gene flow in maize fields with different local pollen densities
NASA Astrophysics Data System (ADS)
Goggi, A. Susana; Lopez-Sanchez, Higinio; Caragea, Petrutza; Westgate, Mark; Arritt, Raymond; Clark, Craig A.
2007-08-01
The development of maize ( Zea mays L.) varieties as factories of pharmaceutical and industrial compounds has renewed interest in controlling pollen dispersal. The objective of this study was to compare gene flow into maize fields of different local pollen densities under the same environmental conditions. Two fields of approximately 36 ha were planted with a nontransgenic, white hybrid, in Ankeny, Iowa, USA. In the center of both fields, a 1-ha plot of a yellow-seeded stacked RR/Bt transgenic hybrid was planted as a pollen source. Before flowering, the white receiver maize of one field was detasseled in a 4:1 ratio to reduce the local pollen density (RPD). The percentage of outcross in the field with RPD was 42.2%, 6.3%, and 1.3% at 1, 10, and 35 m from the central plot, respectively. The percentage of outcross in the white maize with normal pollen density (NPD) was 30.1%, 2.7%, and 0.4%, respectively, at these distances. At distances greater than 100 m, the outcross frequency decreased below 0.1 and 0.03% in the field with RPD and NPD, respectively. A statistical model was used to compare pollen dispersal based on observed outcross percentages. The likelihood ratio test confirmed that the models of outcrossing in the two fields were significantly different ( P is practically 0). Results indicated that when local pollen is low, the incoming pollen has a competitive advantage and the level of outcross is significantly greater than when the local pollen is abundant.
NASA Astrophysics Data System (ADS)
Portwood, Gavin; de Bruyn Kops, Stephen; Turbulence Simulation Laboratory Team
2015-11-01
In stratified flows, the maximum amount of potential energy that can be converted to kinetic energy is the difference between the potential energy in the instantaneous flow and that in the flow if the fluid parcels were adiabatically sorted to produce the lowest energy configuration. Lorentz (1955) defines this global quantity as available potential energy (APE). Holliday and McIntyre (1981) introduces the concept of local available potential energy (Ea) associated with a fluid parcel, and Molemaker and McWilliams (2010) develop the transport for this quantity for a viscous, Boussinesq fluid. Here, we characterize Ea in simulations of a vortex street with uniform and non-uniform stabilizing ambient density gradients. In pseudo-spectral direct numerical simulations resolved on up to 4096 × 2048 × 2048 grid points, we find that the majority of APE is due to fluid parcels displaced a small distance, relative to the buoyancy length scale, from their locations in the sorted density field. By computing each term in the transport equation for Ea, we observe by how much Ea of a fluid parcel changes in time due to local dipycnal mixing, and by how much global mixing alters the position of the local parcel in the sorted density field. This work is funded by DoD HPCMP though Frontier Project FPCFD-FY14-007 and the Office of Naval Research via grant N00014-15-1-2248.
The Local-Density Theory: Application to Atoms and Molecules
NASA Astrophysics Data System (ADS)
Guo, Yufei
1990-01-01
The generalized local-spin-density functional (G-LSD) theory is proposed which avoids (a) the physical restriction used in the generalized exchange local-spin -density functional (GX-LSD) theory; (b) the homogeneous electron-density approximation in the Hartree-Fock-Slater (HFS) theory and in the Gaspar-Kohn-Sham (GKS) theory; and (c) the time-consuming step to search the optimal exchange parameter for each atom or ion in the Xalpha and Xia theories. Theoretically, the G-LSD theory is more rigorous than the GX-LSD, HFS, GKS, and Xia theories. Numerically, the statistical total energies for atoms are better in the G-LSD theory than in the GKS theory. Ionization potentials and electron affinities of atoms, the stability of singly and doubly charged negative ions, and the electronegativities, and hardnesses of the fractional charged atoms with Z < 37 are calculated by the SIC-GX-LSD theory with the GWB Fermi -hole parameters and electron-correlation correction. The self-interaction correction (SIC) is introduced into the multiple-Scattering Xalpha (MS-Xalpha) method and used to calculate some molecules and molecular anions. The results show that the ionization potentials from the negative of the one-electron eigenvalues are as good as those obtained in the transition state calculation and in very good agreement with experiment.
Density overturns and local stability measures in early stratified wakes
NASA Astrophysics Data System (ADS)
Madison, Trystan; Sellappan, Prabu; Xiang, Xinjiang; Spedding, Geoffrey
2015-11-01
Though the dynamics of decaying stratified turbulence are sensitive to certain details of the initial generating conditions, the late-time evolution has also general characteristics that depend only on local stratification parameters, often characterised by a buoyancy Reynolds number, Reb =Re . Fr2 . Bluff-body wakes, for example, have been shown to have universal characteristics that do not depend on details of the generator. Recent experiments on the near wake of a towed grid (Xiang et al. J. Fluid Mech. 775, 149-177, 2015) show that the trajectory of solutions entering the late stratified turbulence regime vary significantly with both Re and Fr , reflecting different balance between wake-edge shear instabilities and local, grid turbulence-generated motions. Here we show density profiles taken through the grid wakes for Re = 2700 and Fr = { 2 , 4 , 9 } . The relative importance of stabilising density gradients vs. destabilising shear flows is customarily measured by a global and/or local Richardson number, Ri , and such measures will be compared and contrasted to form a more complete and quantitative picture of the early wake instabilities than has been available hitherto. Support from ONR N00014-11-1-0553 is most gratefully acknowledged.
Range Separation and Local Hybridization in Density Functional Theory†
Henderson, Thomas M.; Janesko, Benjamin G.; Scuseria, Gustavo E.
2016-01-01
Kohn–Sham density functional theory has become a standard method for modeling energetic, spectroscopic, and chemical reactivity properties of large molecules and solids. Density functional theory provides a rigorous theoretical framework for modeling the many-body exchange-correlation effects that dominate the computational cost of traditional wave function approaches. The advent of hybrid exchange-correlation functionals which incorporate a fraction of nonlocal exact exchange has solidified the prominence of density functional theory within computational chemistry. Hybrids provide accurate treatments of properties such as thermochemistry and molecular geometry. But they also exhibit some rather spectacular failures, and often contain multiple empirical parameters. This article reviews our work on developing novel exchange-correlation functionals that build upon the successes of global hybrids. We focus on more flexible functional forms, including local and range-separated hybrid functionals, constructed to obey known exact constraints and (ideally) to incorporate a minimum of empirical parametrization. The article places our work within the context of some other new approximate density functionals and discusses prospects for future work. PMID:19006280
A novel determination of the local dark matter density
Catena, Riccardo; Ullio, Piero E-mail: ullio@sissa.it
2010-08-01
We present a novel study on the problem of constructing mass models for the Milky Way, concentrating on features regarding the dark matter halo component. We have considered a variegated sample of dynamical observables for the Galaxy, including several results which have appeared recently, and studied a 7- or 8-dimensional parameter space - defining the Galaxy model - by implementing a Bayesian approach to the parameter estimation based on a Markov Chain Monte Carlo method. The main result of this analysis is a novel determination of the local dark matter halo density which, assuming spherical symmetry and either an Einasto or an NFW density profile is found to be around 0.39 GeV cm{sup −3} with a 1-σ error bar of about 7%; more precisely we find a ρ{sub DM}(R{sub 0}) = 0.385±0.027 GeV cm{sup −3} for the Einasto profile and ρ{sub DM}(R{sub 0}) = 0.389±0.025 GeV cm{sup −3} for the NFW. This is in contrast to the standard assumption that ρ{sub DM}(R{sub 0}) is about 0.3 GeV cm{sup −3} with an uncertainty of a factor of 2 to 3. A very precise determination of the local halo density is very important for interpreting direct dark matter detection experiments. Indeed the results we produced, together with the recent accurate determination of the local circular velocity, should be very useful to considerably narrow astrophysical uncertainties on direct dark matter detection.
The local density of optical states of a metasurface
Lunnemann, Per; Koenderink, A. Femius
2016-01-01
While metamaterials are often desirable for near-field functions, such as perfect lensing, or cloaking, they are often quantified by their response to plane waves from the far field. Here, we present a theoretical analysis of the local density of states near lattices of discrete magnetic scatterers, i.e., the response to near field excitation by a point source. Based on a pointdipole theory using Ewald summation and an array scanning method, we can swiftly and semi-analytically evaluate the local density of states (LDOS) for magnetoelectric point sources in front of an infinite two-dimensional (2D) lattice composed of arbitrary magnetoelectric dipole scatterers. The method takes into account radiation damping as well as all retarded electrodynamic interactions in a self-consistent manner. We show that a lattice of magnetic scatterers evidences characteristic Drexhage oscillations. However, the oscillations are phase shifted relative to the electrically scattering lattice consistent with the difference expected for reflection off homogeneous magnetic respectively electric mirrors. Furthermore, we identify in which source-surface separation regimes the metasurface may be treated as a homogeneous interface, and in which homogenization fails. A strong frequency and in-plane position dependence of the LDOS close to the lattice reveals coupling to guided modes supported by the lattice. PMID:26868601
The local density of optical states of a metasurface.
Lunnemann, Per; Koenderink, A Femius
2016-01-01
While metamaterials are often desirable for near-field functions, such as perfect lensing, or cloaking, they are often quantified by their response to plane waves from the far field. Here, we present a theoretical analysis of the local density of states near lattices of discrete magnetic scatterers, i.e., the response to near field excitation by a point source. Based on a pointdipole theory using Ewald summation and an array scanning method, we can swiftly and semi-analytically evaluate the local density of states (LDOS) for magnetoelectric point sources in front of an infinite two-dimensional (2D) lattice composed of arbitrary magnetoelectric dipole scatterers. The method takes into account radiation damping as well as all retarded electrodynamic interactions in a self-consistent manner. We show that a lattice of magnetic scatterers evidences characteristic Drexhage oscillations. However, the oscillations are phase shifted relative to the electrically scattering lattice consistent with the difference expected for reflection off homogeneous magnetic respectively electric mirrors. Furthermore, we identify in which source-surface separation regimes the metasurface may be treated as a homogeneous interface, and in which homogenization fails. A strong frequency and in-plane position dependence of the LDOS close to the lattice reveals coupling to guided modes supported by the lattice. PMID:26868601
The local density of optical states of a metasurface
NASA Astrophysics Data System (ADS)
Lunnemann, Per; Koenderink, A. Femius
2016-02-01
While metamaterials are often desirable for near-field functions, such as perfect lensing, or cloaking, they are often quantified by their response to plane waves from the far field. Here, we present a theoretical analysis of the local density of states near lattices of discrete magnetic scatterers, i.e., the response to near field excitation by a point source. Based on a pointdipole theory using Ewald summation and an array scanning method, we can swiftly and semi-analytically evaluate the local density of states (LDOS) for magnetoelectric point sources in front of an infinite two-dimensional (2D) lattice composed of arbitrary magnetoelectric dipole scatterers. The method takes into account radiation damping as well as all retarded electrodynamic interactions in a self-consistent manner. We show that a lattice of magnetic scatterers evidences characteristic Drexhage oscillations. However, the oscillations are phase shifted relative to the electrically scattering lattice consistent with the difference expected for reflection off homogeneous magnetic respectively electric mirrors. Furthermore, we identify in which source-surface separation regimes the metasurface may be treated as a homogeneous interface, and in which homogenization fails. A strong frequency and in-plane position dependence of the LDOS close to the lattice reveals coupling to guided modes supported by the lattice.
Global and local curvature in density functional theory
NASA Astrophysics Data System (ADS)
Zhao, Qing; Ioannidis, Efthymios I.; Kulik, Heather J.
2016-08-01
Piecewise linearity of the energy with respect to fractional electron removal or addition is a requirement of an electronic structure method that necessitates the presence of a derivative discontinuity at integer electron occupation. Semi-local exchange-correlation (xc) approximations within density functional theory (DFT) fail to reproduce this behavior, giving rise to deviations from linearity with a convex global curvature that is evidence of many-electron, self-interaction error and electron delocalization. Popular functional tuning strategies focus on reproducing piecewise linearity, especially to improve predictions of optical properties. In a divergent approach, Hubbard U-augmented DFT (i.e., DFT+U) treats self-interaction errors by reducing the local curvature of the energy with respect to electron removal or addition from one localized subshell to the surrounding system. Although it has been suggested that DFT+U should simultaneously alleviate global and local curvature in the atomic limit, no detailed study on real systems has been carried out to probe the validity of this statement. In this work, we show when DFT+U should minimize deviations from linearity and demonstrate that a "+U" correction will never worsen the deviation from linearity of the underlying xc approximation. However, we explain varying degrees of efficiency of the approach over 27 octahedral transition metal complexes with respect to transition metal (Sc-Cu) and ligand strength (CO, NH3, and H2O) and investigate select pathological cases where the delocalization error is invisible to DFT+U within an atomic projection framework. Finally, we demonstrate that the global and local curvatures represent different quantities that show opposing behavior with increasing ligand field strength, and we identify where these two may still coincide.
Global and local curvature in density functional theory.
Zhao, Qing; Ioannidis, Efthymios I; Kulik, Heather J
2016-08-01
Piecewise linearity of the energy with respect to fractional electron removal or addition is a requirement of an electronic structure method that necessitates the presence of a derivative discontinuity at integer electron occupation. Semi-local exchange-correlation (xc) approximations within density functional theory (DFT) fail to reproduce this behavior, giving rise to deviations from linearity with a convex global curvature that is evidence of many-electron, self-interaction error and electron delocalization. Popular functional tuning strategies focus on reproducing piecewise linearity, especially to improve predictions of optical properties. In a divergent approach, Hubbard U-augmented DFT (i.e., DFT+U) treats self-interaction errors by reducing the local curvature of the energy with respect to electron removal or addition from one localized subshell to the surrounding system. Although it has been suggested that DFT+U should simultaneously alleviate global and local curvature in the atomic limit, no detailed study on real systems has been carried out to probe the validity of this statement. In this work, we show when DFT+U should minimize deviations from linearity and demonstrate that a "+U" correction will never worsen the deviation from linearity of the underlying xc approximation. However, we explain varying degrees of efficiency of the approach over 27 octahedral transition metal complexes with respect to transition metal (Sc-Cu) and ligand strength (CO, NH3, and H2O) and investigate select pathological cases where the delocalization error is invisible to DFT+U within an atomic projection framework. Finally, we demonstrate that the global and local curvatures represent different quantities that show opposing behavior with increasing ligand field strength, and we identify where these two may still coincide. PMID:27497541
The LC resonance probe for determining local plasma density
NASA Astrophysics Data System (ADS)
Boris, D. R.; Fernsler, R. F.; Walton, S. G.
2011-04-01
We present a novel plasma diagnostic for measuring local plasma density in reactive-gas plasmas, and depositing plasmas. The diagnostic uses a network analyzer to measure the LC resonance (LCR) frequency of a parallel plate capacitor with inductive leads. The location of the LCR (ωR) in frequency space is then used as a measure of the plasma dielectric constant bold varepsilonp between the plates. By properly constructing the LCR probe, ωR can be tuned such that ωR Gt ωce, where ωce is the electron-cyclotron frequency. Thus, the probe can be used in plasmas with varying degrees of magnetization while avoiding complications introduced to bold varepsilonp when ω is comparable to ωce. Density measurements from the LCR probe are compared with Langmuir probe measurements in an electron-beam generated plasma in which density varied from 109 to 1011 cm-3. An axial magnetic field, typically used to confine the electron beam, was varied between 0 to 300 G. The LCR probe showed good agreement with a Langmuir probe across the entire range of magnetic fields.
NASA Astrophysics Data System (ADS)
Lemaire, Joseph; Pierrard, Viviane; Darrouzet, Fabien
2013-04-01
Using European arrays of magnetometers and the cross-phase analysis to determine magnetic field line resonance frequencies, it has been found by Kale et al. (2009) that the plasma mass density within plasmaspheric flux tubes increased rapidly after the SSC of the Hallowe'en 2003 geomagnetic storms. These observations tend to confirm other independent experimental results, suggesting that heavy ion up-flow from the ionosphere is responsible for the observed plasma density increases during main phases of geomagnetic storms. The aim of our contribution is to point out that, during main phases, reversible Betatron effect induced by the increase of the southward Dst-magnetic field component (|Δ Bz|), diminishes slightly the perpendicular kinetic energy (W?) of charged particles spiraling along field lines. Furthermore, due to the conservation of the first adiabatic invariant (μ = Wm/ Bm) the mirror points of all ionospheric ions and electrons are lifted up to higher altitudes i.e. where the mirror point magnetic field (Bm) is slightly smaller. Note that the change of the mirror point altitude is given by: Δ hm = -1/3 (RE + hm) Δ Bm / Bm. It is independent of the ion species and it does not depend of their kinetic energy. The change of kinetic energy is determined by: Δ Wm = Wm Δ Bm / Bm. Both of these equations have been verified numerically by Lemaire et al. (2005; doi: 10.1016/S0273-1177(03)00099-1) using trajectory calculations in a simple time-dependant B-field model: i.e. the Earth's magnetic dipole, plus an increasing southward B-field component: i.e. the Dst magnetic field whose intensity becomes more and more negative during the main phase of magnetic storms. They showed that a variation of Bz (or Dst) by more than - 50 nT significantly increases the mirror point altitudes by more than 100 km which is about equal to scale height of the plasma density in the topside ionosphere where particles are almost collisionless (see Fig. 2 in Lemaire et al., 2005
Probability density function transformation using seeded localized averaging
Dimitrov, N. B.; Jordanov, V. T.
2011-07-01
Seeded Localized Averaging (SLA) is a spectrum acquisition method that averages pulse-heights in dynamic windows. SLA sharpens peaks in the acquired spectra. This work investigates the transformation of the original probability density function (PDF) in the process of applying SLA procedure. We derive an analytical expression for the resulting probability density function after an application of SLA. In addition, we prove the following properties: 1) for symmetric distributions, SLA preserves both the mean and symmetry. 2) for uni-modal symmetric distributions, SLA reduces variance, sharpening the distributions peak. Our results are the first to prove these properties, reinforcing past experimental observations. Specifically, our results imply that in the typical case of a spectral peak with Gaussian PDF the full width at half maximum (FWHM) of the transformed peak becomes narrower even with averaging of only two pulse-heights. While the Gaussian shape is no longer preserved, our results include an analytical expression for the resulting distribution. Examples of the transformation of other PDFs are presented. (authors)
Local density of states in parabolic quantum corrals
NASA Astrophysics Data System (ADS)
Trallero-Giner, C.; Ulloa, S. E.; López-Richard, V.
2004-03-01
Atomic manipulation and scanning tunnel microscope experiments on metal surfaces have shown that electronic states in a “quantum corral” can be locally monitored and used to analyze the nonlocal effects of perturbations. We study new corral geometries defined by families of confocal parabolas. General solutions of the Schrödinger equation for the interior problem with Dirichlet (hard wall) boundary conditions are found exactly in terms of zeroes of hypergeometric functions. We show that the Hilbert space of solutions is separated in subspaces with odd and even symmetry. We perform numerical evaluation of the zeroes and study the effects of the parabolic curvatures on the eigenvalues and eigenfunctions of the parabolic quantum corral. The evolution of the local density of states with energy as a function of parabolic corral geometry is also analyzed. We find that under suitable conditions, the distribution of state antinodes can be described as directed intensity beams, which could be used as “quantum beacons” in future generations of “quantum mirage” experiments or optical and acoustic analogs of quantum corrals for the state node distribution.
Localized end states in density modulated quantum wires and rings.
Gangadharaiah, Suhas; Trifunovic, Luka; Loss, Daniel
2012-03-30
We study finite quantum wires and rings in the presence of a charge-density wave gap induced by a periodic modulation of the chemical potential. We show that the Tamm-Shockley bound states emerging at the ends of the wire are stable against weak disorder and interactions, for discrete open chains and for continuum systems. The low-energy physics can be mapped onto the Jackiw-Rebbi equations describing massive Dirac fermions and bound end states. We treat interactions via the continuum model and show that they increase the charge gap and further localize the end states. The electrons placed in the two localized states on the opposite ends of the wire can interact via exchange interactions and this setup can be used as a double quantum dot hosting spin qubits. The existence of these states could be experimentally detected through the presence of an unusual 4π Aharonov-Bohm periodicity in the spectrum and persistent current as a function of the external flux. PMID:22540720
Recovery of local density of states using scanning tunneling spectroscopy
NASA Astrophysics Data System (ADS)
Passoni, M.; Donati, F.; Li Bassi, A.; Casari, C. S.; Bottani, C. E.
2009-01-01
Scanning tunneling spectroscopy (STS) provides a unique method for the investigation of the local surface-projected electron density of states (DOS), mostly for its capability of reaching atomic resolution. Such information is contained in a nonobvious way in STS data, and a proper understanding of the overall features of the system (sample+tip) is mandatory in order to obtain quantitative information. Several approaches have been proposed in the literature to tackle this problem. A common feature of these methods is that they are mostly based on a one-dimensional (1D) WKB description of the tunneling current. We present a critical analysis and an extension of the methods so far proposed, with the main goal of applying the results to STS experimental data. This study has been conducted by modeling the tip-sample system within the frame of 1D-WKB theory, investigating key open issues, such as the estimation of required but usually experimentally unknown parameters such as the tip-sample distance and the role played by the presence of a nonconstant tip local DOS on STS data. This investigation allows us to ascertain strengths and weaknesses of the existing methods and leads to an optimized and improved strategy which we propose for the analysis of STS data. We tested our conclusions on STS measurements of the Si(111)-7×7 and Au(111) surfaces, acquired with W and Cr tips.
Taylor, John S.; Folta, James A.; Montcalm, Claude
2005-01-18
Figure errors are corrected on optical or other precision surfaces by changing the local density of material in a zone at or near the surface. Optical surface height is correlated with the localized density of the material within the same region. A change in the height of the optical surface can then be caused by a change in the localized density of the material at or near the surface.
Wireless adiabatic power transfer
Rangelov, A.A.; Suchowski, H.; Silberberg, Y.; Vitanov, N.V.
2011-03-15
Research Highlights: > Efficient and robust mid-range wireless energy transfer between two coils. > The adiabatic energy transfer is analogous to adiabatic passage in quantum optics. > Wireless energy transfer is insensitive to any resonant constraints. > Wireless energy transfer is insensitive to noise in the neighborhood of the coils. - Abstract: We propose a technique for efficient mid-range wireless power transfer between two coils, by adapting the process of adiabatic passage for a coherently driven two-state quantum system to the realm of wireless energy transfer. The proposed technique is shown to be robust to noise, resonant constraints, and other interferences that exist in the neighborhood of the coils.
Adiabatic invariance of oscillons/I -balls
NASA Astrophysics Data System (ADS)
Kawasaki, Masahiro; Takahashi, Fuminobu; Takeda, Naoyuki
2015-11-01
Real scalar fields are known to fragment into spatially localized and long-lived solitons called oscillons or I -balls. We prove the adiabatic invariance of the oscillons/I -balls for a potential that allows periodic motion even in the presence of non-negligible spatial gradient energy. We show that such a potential is uniquely determined to be the quadratic one with a logarithmic correction, for which the oscillons/I -balls are absolutely stable. For slightly different forms of the scalar potential dominated by the quadratic one, the oscillons/I -balls are only quasistable, because the adiabatic charge is only approximately conserved. We check the conservation of the adiabatic charge of the I -balls in numerical simulation by slowly varying the coefficient of logarithmic corrections. This unambiguously shows that the longevity of oscillons/I -balls is due to the adiabatic invariance.
Analysis of the local-density approximation of density-functional theory
NASA Astrophysics Data System (ADS)
Sahni, Viraht; Bohnen, K.-P.; Harbola, Manoj K.
1988-03-01
In this paper we perform a configuration-space analysis of the local-density approximation (LDA) for the exchange-correlation energy functional of Kohn-Sham density-functional theory in terms of the corresponding average exchange-correlation charge (hole) and energy densities. According to our analysis, the explanation for the quantitative success of the LDA based on the hole charge-conservation sum rule and the assumed consequent cancellation of errors in the spherical averages of the hole is inadequate. The principal conclusion of our work is that the constraint of charge neutrality is a necessary but not sufficient condition for an approximate energy functional to lead to accurate ground-state energies and ionization potentials. The significant additional requirement for the functional is that it must, at least qualitatively, reproduce correctly the structure of the hole as a function of electron position. We perform our calculations within the exchange-only approximation as applied to atoms and jellium metal surfaces. In atoms the Fermi hole is localized about the nucleus; as a consequence the LDA Fermi hole is accurate only for electron positions close to it. However, we show that the spherically averaged LDA hole is accurate for electron positions in the shell regions; it is substantially in error in the intershell and classically forbidden regions. The fact that the principal contribution to the exchange energy comes from the inner-shell region of the atom, where the LDA hole is accurate, explains why the errors in the LDA ground-state energies are small. However, the ionization potential, which depends on the structure of the hole in the outer regions of the atom, is substantially in error in the LDA since here the LDA hole differs significantly from the exact one. For metallic surfaces, on the other hand, as an electron is pulled from within the metal to infinity outside, the Fermi hole is delocalized and spread throughout the crystal. As a consequence
Adiabatically driven Brownian pumps.
Rozenbaum, Viktor M; Makhnovskii, Yurii A; Shapochkina, Irina V; Sheu, Sheh-Yi; Yang, Dah-Yen; Lin, Sheng Hsien
2013-07-01
We investigate a Brownian pump which, being powered by a flashing ratchet mechanism, produces net particle transport through a membrane. The extension of the Parrondo's approach developed for reversible Brownian motors [Parrondo, Phys. Rev. E 57, 7297 (1998)] to adiabatically driven pumps is given. We demonstrate that the pumping mechanism becomes especially efficient when the time variation of the potential occurs adiabatically fast or adiabatically slow, in perfect analogy with adiabatically driven Brownian motors which exhibit high efficiency [Rozenbaum et al., Phys. Rev. E 85, 041116 (2012)]. At the same time, the efficiency of the pumping mechanism is shown to be less than that of Brownian motors due to fluctuations of the number of particles in the membrane. PMID:23944411
Delgado, Juan C; Selsby, Ronald G
2013-01-01
The ground state configuration of the gas phase cationic dyes pinacyanol chloride and rhodamine B are optimized with HF/6-311 + G(2d,2p) method and basis set. B3PW91/6-311 + G(2df,2p) functional and basis set is used to calculate the Mulliken atom charge distribution, total molecular energy, the dipole moment, the vertical ionization potential, the adiabatic electron affinity and the lowest excited triplet state, the last three as an energy difference between separately calculated open shell and ground states. The triplet and extra electron states are optimized to find the relaxation energy. In the ground state optimization of both dyes the chloride anion migrates to a position near the center of the chromophore. For rhodamine B the benzoidal group turns perpendicular to the chromophore plane. For both dyes, the LUMO is mostly of π character associated with the aromatic part of the molecule containing the chromophore. The highest occupied MOs consist of three almost degenerate eigenvectors involving the chloride anion coordinated with σ electrons in the molecular framework. The fourth highest MO is of π character. For both molecules in the gas phase ionization process the chloride anion loses the significant fraction of electric charge. In electron capture, the excess charge goes mainly on the dye cation. PMID:22891949
Parallelizable adiabatic gate teleportation
NASA Astrophysics Data System (ADS)
Nakago, Kosuke; Hajdušek, Michal; Nakayama, Shojun; Murao, Mio
2015-12-01
To investigate how a temporally ordered gate sequence can be parallelized in adiabatic implementations of quantum computation, we modify adiabatic gate teleportation, a model of quantum computation proposed by Bacon and Flammia [Phys. Rev. Lett. 103, 120504 (2009), 10.1103/PhysRevLett.103.120504], to a form deterministically simulating parallelized gate teleportation, which is achievable only by postselection. We introduce a twisted Heisenberg-type interaction Hamiltonian, a Heisenberg-type spin interaction where the coordinates of the second qubit are twisted according to a unitary gate. We develop parallelizable adiabatic gate teleportation (PAGT) where a sequence of unitary gates is performed in a single step of the adiabatic process. In PAGT, numeric calculations suggest the necessary time for the adiabatic evolution implementing a sequence of L unitary gates increases at most as O (L5) . However, we show that it has the interesting property that it can map the temporal order of gates to the spatial order of interactions specified by the final Hamiltonian. Using this property, we present a controlled-PAGT scheme to manipulate the order of gates by a control qubit. In the controlled-PAGT scheme, two differently ordered sequential unitary gates F G and G F are coherently performed depending on the state of a control qubit by simultaneously applying the twisted Heisenberg-type interaction Hamiltonians implementing unitary gates F and G . We investigate why the twisted Heisenberg-type interaction Hamiltonian allows PAGT. We show that the twisted Heisenberg-type interaction Hamiltonian has an ability to perform a transposed unitary gate by just modifying the space ordering of the final Hamiltonian implementing a unitary gate in adiabatic gate teleportation. The dynamics generated by the time-reversed Hamiltonian represented by the transposed unitary gate enables deterministic simulation of a postselected event of parallelized gate teleportation in adiabatic
Local Current Density Calculations for Molecular Films from Ab Initio.
Walz, Michael; Bagrets, Alexei; Evers, Ferdinand
2015-11-10
We present a formalism relying on density functional theory for the calculation of the spatially continuous electron current density j(r) and induced magnetic fields B(r) in molecular films in dc transport. The proposed method treats electron transport in graphene ribbons containing on the of order 10(3) atoms. The employed computational techniques scale efficiently when using several thousand CPUs. An application to transport through hydrogenated graphene will be presented. As we will show, the adatoms have an impact on the transmission function not only because they introduce additional states but also because their presence modifies the geometry of the carbon host lattice (lattice relaxation). PMID:26574313
On the Role of Prior Probability in Adiabatic Quantum Algorithms
NASA Astrophysics Data System (ADS)
Sun, Jie; Lu, Songfeng; Yang, Liping
2016-03-01
In this paper, we study the role of prior probability on the efficiency of quantum local adiabatic search algorithm. The following aspects for prior probability are found here: firstly, only the probabilities of marked states affect the running time of the adiabatic evolution; secondly, the prior probability can be used for improving the efficiency of the adiabatic algorithm; thirdly, like the usual quantum adiabatic evolution, the running time for the case of multiple solution states where the number of marked elements are smaller enough than the size of the set assigned that contains them can be significantly bigger than that of the case where the assigned set only contains all the marked states.
Adiabatic cooling of antiprotons.
Gabrielse, G; Kolthammer, W S; McConnell, R; Richerme, P; Kalra, R; Novitski, E; Grzonka, D; Oelert, W; Sefzick, T; Zielinski, M; Fitzakerley, D; George, M C; Hessels, E A; Storry, C H; Weel, M; Müllers, A; Walz, J
2011-02-18
Adiabatic cooling is shown to be a simple and effective method to cool many charged particles in a trap to very low temperatures. Up to 3×10(6) p are cooled to 3.5 K-10(3) times more cold p and a 3 times lower p temperature than previously reported. A second cooling method cools p plasmas via the synchrotron radiation of embedded e(-) (with many fewer e(-) than p in preparation for adiabatic cooling. No p are lost during either process-a significant advantage for rare particles. PMID:21405511
Adiabatic Cooling of Antiprotons
Gabrielse, G.; Kolthammer, W. S.; McConnell, R.; Richerme, P.; Kalra, R.; Novitski, E.; Oelert, W.; Grzonka, D.; Sefzick, T.; Zielinski, M.; Fitzakerley, D.; George, M. C.; Hessels, E. A.; Storry, C. H.; Weel, M.; Muellers, A.; Walz, J.
2011-02-18
Adiabatic cooling is shown to be a simple and effective method to cool many charged particles in a trap to very low temperatures. Up to 3x10{sup 6} p are cooled to 3.5 K--10{sup 3} times more cold p and a 3 times lower p temperature than previously reported. A second cooling method cools p plasmas via the synchrotron radiation of embedded e{sup -} (with many fewer e{sup -} than p) in preparation for adiabatic cooling. No p are lost during either process--a significant advantage for rare particles.
Electron density power spectrum in the local interstellar medium
NASA Technical Reports Server (NTRS)
Armstrong, J. W.; Rickett, B. J.; Spangler, S. R.
1995-01-01
Interstellar scintillation (ISS), fluctuations in the amplitude and phase of radio waves caused by scattering in the interstellar medium, is important as a diagnostic of interstellar plasma turbulence. ISS is also of interest because it is noise for other radio astronomical observations. The unifying concern is the power spectrum of the interstellar electron density. Here we use ISS observations through the nearby (less than or approximately =1 kpc) (ISM) to estimate the spectrum. From measurements of angular broadening of pulsars and extragalactic sources, decorrelation bandwidth of pulsars, refractive steering of features in pulsar dynamic spectra, dispersion measured fluctuations of pulsars, and refractive scintillation index measurements, we construct a composite structure function that is approximately power law over 2 x 10(exp 6) m less than scale less than 10(exp 13) m. The data are consistent with the structure function having a logarithmic slope versus baseline less than 2; thus there is a meaningful connection between scales in the radiowave fluctuation field and the scales in the electron density field causing the scattering. The data give an upper limit to the inner scale, l(sub o) less than or approximately 10(exp 8) m and are consistent with much smaller values. We construct a composite electron density spectrum that is approximately power law over at least the approximately = 5 decade wavenumber range 10(exp -13)/m less than wavenumber less than 10(exp -8)/m and that may extend to higher wavenumbers. The average spectral index of electron density over this wavenumber range is approximately = 3.7, very close to the value expected for a Kolmogorov process. The outer scale size, L(sub o), must be greater than or approximately = 10(exp 13) m (determined from dispersion measure fluctuations). When the ISS data are combined with measurements of differential Faraday rotation angle, and gradients in the average electron density, constraints can be put on the
Spontaneous emission in stimulated Raman adiabatic passage
Ivanov, P. A.; Vitanov, N. V.; Bergmann, K.
2005-11-15
This work explores the effect of spontaneous emission on the population transfer efficiency in stimulated Raman adiabatic passage (STIRAP). The approach uses adiabatic elimination of weakly coupled density matrix elements in the Liouville equation, from which a very accurate analytic approximation is derived. The loss of population transfer efficiency is found to decrease exponentially with the factor {omega}{sub 0}{sup 2}/{gamma}, where {gamma} is the spontaneous emission rate and {omega}{sub 0} is the peak Rabi frequency. The transfer efficiency increases with the pulse delay and reaches a steady value. For large pulse delay and large spontaneous emission rate STIRAP degenerates into optical pumping.
LOCALIZED PLASMA DENSITY ENHANCEMENTS OBSERVED IN STEREO COR1
Jones, Shaela I.; Davila, Joseph M.
2009-08-20
Measurements of solar wind speed in the solar corona, where it is primarily accelerated, have proven elusive. One of the more successful attempts has been the tracking of outward-moving density inhomogeneities in white-light coronagraph images. These inhomogeneities, or 'blobs', have been treated as passive tracers of the ambient solar wind. Here we report on the extension of these observations to lower altitudes using the STEREO COR1 coronagraph, and discuss the implications of these measurements for theories about the origin of these features.
Adiabatically implementing quantum gates
Sun, Jie; Lu, Songfeng Liu, Fang
2014-06-14
We show that, through the approach of quantum adiabatic evolution, all of the usual quantum gates can be implemented efficiently, yielding running time of order O(1). This may be considered as a useful alternative to the standard quantum computing approach, which involves quantum gates transforming quantum states during the computing process.
Entanglement and adiabatic quantum computation
NASA Astrophysics Data System (ADS)
Ahrensmeier, D.
2006-06-01
Adiabatic quantum computation provides an alternative approach to quantum computation using a time-dependent Hamiltonian. The time evolution of entanglement during the adiabatic quantum search algorithm is studied, and its relevance as a resource is discussed.
Time-dependent local density measurements in unsteady flows
NASA Technical Reports Server (NTRS)
Mckenzie, R. L.; Monson, D. J.; Exberger, R. J.
1979-01-01
A laser-induced fluorescence technique for measuring the relative time-dependent density fluctuations in unsteady or turbulent flows is demonstrated. Using a 1.5-W continuous-wave Kr(+) laser, measurements have been obtained in 0.1-mm diameter by 1-mm-long sampling volumes in a Mach 3 flow of N2 seeded with biacetyl vapor. A signal amplitude resolution of 2% was achieved for a detection frequency bandwidth of 10 kHz. The measurement uncertainty was found to be dominated by noise behaving as photon statistical noise. The practical limits of signal-to-noise ratios have been characterized for a wide range of detection frequency bandwidths that encompasses those of interest in supersonic turbulence measurements.
Time-dependent local density measurements in unsteady flows
NASA Technical Reports Server (NTRS)
Mckenzie, R. L.; Monson, D. J.; Exberger, R. J.
1979-01-01
A laser-induced fluorescence technique for measuring the relative time-dependent density fluctuations in unsteady or turbulent flows is demonstrated. Using a 1.5-W continuous-wave Kr(+) laser, measurements have been obtained in 0.1-mm-diameter by 1-mm-long sampling volumes in a Mach 3 flow of N2 seeded with biacetyl vapor. A signal amplitude resolution of 2% was achieved for a detection frequency bandwidth of 10 kHz. The measurement uncertainty was found to be dominated by noise behaving as photon statistical noise. The practical limits of signal-to-noise ratios have been characterized for a wide range of detection frequency bandwidths that encompasses those of interest in supersonic turbulence measurements.
Generalized local-density approximation for spherical potentials
Zhang, X.; Nicholson, D.M.
1999-08-01
An alternative density functional for the spherical approximation of cell potentials is formulated. It relies on overlapping atomic spheres for the calculation of the kinetic energy, similar to the atomic sphere approximation (ASA), however, a shape correction is used that has the same form as the interstitial treatment in the nonoverlapping muffin-tin (MT) approach. The intersite Coulomb energy is evaluated using the Madelung energy as computed in the MT approach, while the on-site Coulomb energy is calculated using the ASA. The Kohn-Sham equations for the functional are then solved self-consistently. The ASA is known to give poor elastic constants and good point defect energies. Conversely the MT approach gives good elastic constants and poor point defect energies. The proposed new functional maintains the simplicity of the spherical potentials found in the ASA and MT approaches, but gives good values for both elastic constants and point defects. This solution avoids a problem, absent in the ASA but suffered by the MT approximation, of incorrect distribution of site charges when charge transfer is large. Relaxation of atomic positions is thus facilitated. Calculations confirm that the approach gives similar elastic constants to the MT approximation, and defect formation energies similar to those obtained with ASA. {copyright} {ital 1999} {ital The American Physical Society}
Multifluorophore localization as a percolation problem: limits to density and precision.
Small, Alex
2016-07-01
We show that the maximum desirable density of activated fluorophores in a superresolution experiment can be determined by treating the overlapping point spread functions as a problem in percolation theory. We derive a bound on the density of activated fluorophores, taking into account the desired localization accuracy and precision, as well as the number of photons emitted. Our bound on density is close to that reported in experimental work, suggesting that further increases in the density of imaged fluorophores will come at the expense of localization accuracy and precision. PMID:27409704
NASA Technical Reports Server (NTRS)
Scarf, F. L.; Chappell, C. R.
1973-01-01
We use OGO 5 measurements made within the plasmapause on May 15, 1969, to investigate the possible association between changes in lightning whistler dispersion characteristics and local density fluctuations. It is shown that groups of whistlers with relatively constant dispersions tended to be detected in regions where the local ion concentration was significantly enhanced. It is assumed that these local density fluctuations represent characteristics of large-scale field-aligned variations. The results are then compared with ray refraction estimates appropriate for low-frequency whistler mode propagation (wave components with frequencies comparable to the local lower hybrid frequency) in a nonuniform medium.
Ziegler, Tom; Krykunov, Mykhaylo; Autschbach, Jochen
2014-09-01
The random phase approximation (RPA) equation of adiabatic time dependent density functional ground state response theory (ATDDFT) has been used extensively in studies of excited states. It extracts information about excited states from frequency dependent ground state response properties and avoids, thus, in an elegant way, direct Kohn-Sham calculations on excited states in accordance with the status of DFT as a ground state theory. Thus, excitation energies can be found as resonance poles of frequency dependent ground state polarizability from the eigenvalues of the RPA equation. ATDDFT is approximate in that it makes use of a frequency independent energy kernel derived from the ground state functional. It is shown in this study that one can derive the RPA equation of ATDDFT from a purely variational approach in which stationary states above the ground state are located using our constricted variational DFT (CV-DFT) method and the ground state functional. Thus, locating stationary states above the ground state due to one-electron excitations with a ground state functional is completely equivalent to solving the RPA equation of TDDFT employing the same functional. The present study is an extension of a previous work in which we demonstrated the equivalence between ATDDFT and CV-DFT within the Tamm-Dancoff approximation. PMID:26588541
Shortcut to adiabatic gate teleportation
NASA Astrophysics Data System (ADS)
Santos, Alan C.; Silva, Raphael D.; Sarandy, Marcelo S.
2016-01-01
We introduce a shortcut to the adiabatic gate teleportation model of quantum computation. More specifically, we determine fast local counterdiabatic Hamiltonians able to implement teleportation as a universal computational primitive. In this scenario, we provide the counterdiabatic driving for arbitrary n -qubit gates, which allows to achieve universality through a variety of gate sets. Remarkably, our approach maps the superadiabatic Hamiltonian HSA for an arbitrary n -qubit gate teleportation into the implementation of a rotated superadiabatic dynamics of an n -qubit state teleportation. This result is rather general, with the speed of the evolution only dictated by the quantum speed limit. In particular, we analyze the energetic cost for different Hamiltonian interpolations in the context of the energy-time complementarity.
Spatially heterogeneous populations with mixed negative and positive local density dependence.
Knipl, Diána; Röst, Gergely
2016-06-01
Identifying the steady states of a population is a key issue in theoretical ecology, that includes the study of spatially heterogeneous populations. There are several examples of real ecosystems in patchy environments where the habitats are heterogeneous in their local density dependence. We investigate a multi-patch model of a single species with spatial dispersal, where the growth of the local population is logistic in some localities (negative density dependence) while other patches exhibit a strong Allee effect (positive density dependence). When the local dynamics is logistic in each patch and the habitats are interconnected by dispersal then the total population has only the extinction steady state and a componentwise positive equilibrium, corresponding to persistence in each patch. We show that animal populations in patchy environments can have a large number of steady states if local density dependence varies over the locations. It is demonstrated that, depending on the network topology of migration routes between the patches, the interaction of spatial dispersal and local density dependence can create a variety of coexisting stable positive equilibria. We give a detailed description of the multiple ways dispersal can rescue local populations from extinction. PMID:26801607
Local Tobacco Policy and Tobacco Outlet Density: Associations With Youth Smoking
Grube, Joel W.; Friend, Karen B.
2011-01-01
Purpose This study investigates the associations between tobacco outlet density, local tobacco policy, and youth smoking. A primary focus is on whether local tobacco policy moderates the relation between outlet density and youth smoking. Methods 1,491 youth (51.9% male, M age = 14.7 years, SD =1.05) in 50 midsized California cities were surveyed through a computer-assisted telephone interview. Measures of local clean air policy and youth access policy were created based on a review of tobacco policies in these cities. Outlet density was calculated as the number of retail tobacco outlets per 10,000 persons and city characteristics were obtained from 2000 U.S. Census data. Results Using multilevel regression analyses controlling for city characteristics, tobacco outlet density was positively associated with youth smoking. No significant main effects were found for the two tobacco policy types on any of the smoking outcomes after controlling for interactions and covariates. However, statistically significant interactions were found between local clean air policy and tobacco outlet density for ever smoked and past-12-month cigarette smoking. Comparisons of simple slopes indicated that the positive associations between tobacco outlet density and youth smoking behaviors were stronger at the lowest level of local clean air policy compared to the moderate and high levels. Conclusions Our results suggest that outlet density is related to youth smoking. In addition, local clean air policy may act as a moderator of relationship between outlet density and youth smoking, such that density is less important at moderate and high levels of this tobacco policy. PMID:22626479
A Tomographic Method for the Reconstruction of Local Probability Density Functions
NASA Technical Reports Server (NTRS)
Sivathanu, Y. R.; Gore, J. P.
1993-01-01
A method of obtaining the probability density function (PDF) of local properties from path integrated measurements is described. The approach uses a discrete probability function (DPF) method to infer the PDF of the local extinction coefficient from measurements of the PDFs of the path integrated transmittance. The local PDFs obtained using the method are compared with those obtained from direct intrusive measurements in propylene/air and ethylene/air diffusion flames. The results of this comparison are good.
Bazzani, A.; Turchetti, G.; Benedetti, C.; Rambaldi, S.; Servizi, G.
2005-06-08
In a high intensity circular accelerator the synchrotron dynamics introduces a slow modulation in the betatronic tune due to the space-charge tune depression. When the transverse motion is non-linear due to the presence of multipolar effects, resonance islands move in the phase space and change their amplitude. This effect introduces the trapping and detrapping phenomenon and a slow diffusion in the phase space. We apply the neo-adiabatic theory to describe this diffusion mechanism that can contribute to halo formation.
Towards improved local hybrid functionals by calibration of exchange-energy densities
Arbuznikov, Alexei V. E-mail: martin.kaupp@tu-berlin.de; Kaupp, Martin E-mail: martin.kaupp@tu-berlin.de
2014-11-28
A new approach for the calibration of (semi-)local and exact exchange-energy densities in the context of local hybrid functionals is reported. The calibration functions are derived from only the electron density and its spatial derivatives, avoiding spatial derivatives of the exact-exchange energy density or other computationally unfavorable contributions. The calibration functions fulfill the seven more important out of nine known exact constraints. It is shown that calibration improves substantially the definition of a non-dynamical correlation energy term for generalized gradient approximation (GGA)-based local hybrids. Moreover, gauge artifacts in the potential-energy curves of noble-gas dimers may be corrected by calibration. The developed calibration functions are then evaluated for a large range of energy-related properties (atomization energies, reaction barriers, ionization potentials, electron affinities, and total atomic energies) of three sets of local hybrids, using a simple one-parameter local-mixing. The functionals are based on (a) local spin-density approximation (LSDA) or (b) Perdew-Burke-Ernzerhof (PBE) exchange and correlation, and on (c) Becke-88 (B88) exchange and Lee-Yang-Parr (LYP) correlation. While the uncalibrated GGA-based functionals usually provide very poor thermochemical data, calibration allows a dramatic improvement, accompanied by only a small deterioration of reaction barriers. In particular, an optimized BLYP-based local-hybrid functional has been found that is a substantial improvement over the underlying global hybrids, as well as over previously reported LSDA-based local hybrids. It is expected that the present calibration approach will pave the way towards new generations of more accurate hyper-GGA functionals based on a local mixing of exchange-energy densities.
Towards improved local hybrid functionals by calibration of exchange-energy densities
NASA Astrophysics Data System (ADS)
Arbuznikov, Alexei V.; Kaupp, Martin
2014-11-01
A new approach for the calibration of (semi-)local and exact exchange-energy densities in the context of local hybrid functionals is reported. The calibration functions are derived from only the electron density and its spatial derivatives, avoiding spatial derivatives of the exact-exchange energy density or other computationally unfavorable contributions. The calibration functions fulfill the seven more important out of nine known exact constraints. It is shown that calibration improves substantially the definition of a non-dynamical correlation energy term for generalized gradient approximation (GGA)-based local hybrids. Moreover, gauge artifacts in the potential-energy curves of noble-gas dimers may be corrected by calibration. The developed calibration functions are then evaluated for a large range of energy-related properties (atomization energies, reaction barriers, ionization potentials, electron affinities, and total atomic energies) of three sets of local hybrids, using a simple one-parameter local-mixing. The functionals are based on (a) local spin-density approximation (LSDA) or (b) Perdew-Burke-Ernzerhof (PBE) exchange and correlation, and on (c) Becke-88 (B88) exchange and Lee-Yang-Parr (LYP) correlation. While the uncalibrated GGA-based functionals usually provide very poor thermochemical data, calibration allows a dramatic improvement, accompanied by only a small deterioration of reaction barriers. In particular, an optimized BLYP-based local-hybrid functional has been found that is a substantial improvement over the underlying global hybrids, as well as over previously reported LSDA-based local hybrids. It is expected that the present calibration approach will pave the way towards new generations of more accurate hyper-GGA functionals based on a local mixing of exchange-energy densities.
Franco-Pérez, Marco; Ayers, Paul W; Gázquez, José L; Vela, Alberto
2015-12-28
We explore the local and nonlocal response functions of the grand canonical potential density functional at nonzero temperature. In analogy to the zero-temperature treatment, local (e.g., the average electron density and the local softness) and nonlocal (e.g., the softness kernel) intrinsic response functions are defined as partial derivatives of the grand canonical potential with respect to its thermodynamic variables (i.e., the chemical potential of the electron reservoir and the external potential generated by the atomic nuclei). To define the local and nonlocal response functions of the electron density (e.g., the Fukui function, the linear density response function, and the dual descriptor), we differentiate with respect to the average electron number and the external potential. The well-known mathematical relationships between the intrinsic response functions and the electron-density responses are generalized to nonzero temperature, and we prove that in the zero-temperature limit, our results recover well-known identities from the density functional theory of chemical reactivity. Specific working equations and numerical results are provided for the 3-state ensemble model. PMID:26723661
Franco-Pérez, Marco E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx; Ayers, Paul W. E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx; Gázquez, José L. E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx; Vela, Alberto E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx
2015-12-28
We explore the local and nonlocal response functions of the grand canonical potential density functional at nonzero temperature. In analogy to the zero-temperature treatment, local (e.g., the average electron density and the local softness) and nonlocal (e.g., the softness kernel) intrinsic response functions are defined as partial derivatives of the grand canonical potential with respect to its thermodynamic variables (i.e., the chemical potential of the electron reservoir and the external potential generated by the atomic nuclei). To define the local and nonlocal response functions of the electron density (e.g., the Fukui function, the linear density response function, and the dual descriptor), we differentiate with respect to the average electron number and the external potential. The well-known mathematical relationships between the intrinsic response functions and the electron-density responses are generalized to nonzero temperature, and we prove that in the zero-temperature limit, our results recover well-known identities from the density functional theory of chemical reactivity. Specific working equations and numerical results are provided for the 3-state ensemble model.
A non-parametric method for measuring the local dark matter density
NASA Astrophysics Data System (ADS)
Silverwood, H.; Sivertsson, S.; Steger, P.; Read, J. I.; Bertone, G.
2016-04-01
We present a new method for determining the local dark matter density using kinematic data for a population of tracer stars. The Jeans equation in the z-direction is integrated to yield an equation that gives the velocity dispersion as a function of the total mass density, tracer density, and the `tilt' term that describes the coupling of vertical and radial motions. We then fit a dark matter mass profile to tracer density and velocity dispersion data to derive credible regions on the vertical dark matter density profile. Our method avoids numerical differentiation, leading to lower numerical noise, and is able to deal with the tilt term while remaining one dimensional. In this study we present the method and perform initial tests on idealised mock data. We also demonstrate the importance of dealing with the tilt term for tracers that sample ≳ 1 kpc above the disc plane. If ignored, this results in a systematic underestimation of the dark matter density.
A non-parametric method for measuring the local dark matter density
NASA Astrophysics Data System (ADS)
Silverwood, H.; Sivertsson, S.; Steger, P.; Read, J. I.; Bertone, G.
2016-07-01
We present a new method for determining the local dark matter density using kinematic data for a population of tracer stars. The Jeans equation in the z-direction is integrated to yield an equation that gives the velocity dispersion as a function of the total mass density, tracer density, and the `tilt' term that describes the coupling of vertical and radial motions. We then fit a dark matter mass profile to tracer density and velocity dispersion data to derive credible regions on the vertical dark matter density profile. Our method avoids numerical differentiation, leading to lower numerical noise, and is able to deal with the tilt term while remaining one dimensional. In this study we present the method and perform initial tests on idealized mock data. We also demonstrate the importance of dealing with the tilt term for tracers that sample ≳1 kpc above the disc plane. If ignored, this results in a systematic underestimation of the dark matter density.
Star Formation as a Function of Neutral Hydrogen Gas Density in Local Group Galaxies
NASA Astrophysics Data System (ADS)
Carlson, Erika K.; Madore, Barry F.; Freedman, Wendy L.
2016-06-01
We present a study of the efficiency and timescales of star formation as a function of local neutral hydrogen gas density in four Local Group galaxies: M33, NGC 6822, the LMC, and the SMC. In this work, we conceptualize the process of star formation as a cycle of two major phases – (1) a gas dynamics phase in which neutral hydrogen gas coalesces into clouds, and (2) a stellar phase in which stars have formed and interrupt further gas coalescence during their active lifetimes. By examining the spatial distribution and number densities of stars on maps of neutral hydrogen, we estimate the timescale of the gas coalescence phase relative to the timescale of the stellar phase and infer an efficiency of star formation as a function of neutral hydrogen gas density. From these timescales and efficiencies, we will calculate star formation rates as a function of neutral hydrogen gas density in these galaxies.
NASA Astrophysics Data System (ADS)
Landahl, Andrew
2012-10-01
Quantum computers promise to exploit counterintuitive quantum physics principles like superposition, entanglement, and uncertainty to solve problems using fundamentally fewer steps than any conventional computer ever could. The mere possibility of such a device has sharpened our understanding of quantum coherent information, just as lasers did for our understanding of coherent light. The chief obstacle to developing quantum computer technology is decoherence--one of the fastest phenomena in all of physics. In principle, decoherence can be overcome by using clever entangled redundancies in a process called fault-tolerant quantum error correction. However, the quality and scale of technology required to realize this solution appears distant. An exciting alternative is a proposal called ``adiabatic'' quantum computing (AQC), in which adiabatic quantum physics keeps the computer in its lowest-energy configuration throughout its operation, rendering it immune to many decoherence sources. The Adiabatic Quantum Architectures In Ultracold Systems (AQUARIUS) Grand Challenge Project at Sandia seeks to demonstrate this robustness in the laboratory and point a path forward for future hardware development. We are building devices in AQUARIUS that realize the AQC architecture on up to three quantum bits (``qubits'') in two platforms: Cs atoms laser-cooled to below 5 microkelvin and Si quantum dots cryo-cooled to below 100 millikelvin. We are also expanding theoretical frontiers by developing methods for scalable universal AQC in these platforms. We have successfully demonstrated operational qubits in both platforms and have even run modest one-qubit calculations using our Cs device. In the course of reaching our primary proof-of-principle demonstrations, we have developed multiple spinoff technologies including nanofabricated diffractive optical elements that define optical-tweezer trap arrays and atomic-scale Si lithography commensurate with placing individual donor atoms with
Adiabatic nanofocusing: spectroscopy, transport and imaging investigation of the nano world
NASA Astrophysics Data System (ADS)
Giugni, A.; Allione, M.; Torre, B.; Das, G.; Francardi, M.; Moretti, M.; Malerba, M.; Perozziello, G.; Candeloro, P.; Di Fabrizio, E.
2014-11-01
Adiabatic compression plays a fundamental role in the realization of localized enhanced electromagnetic field hot spots, it provides the possibility to focus at nanoscale optical excitation. It differs from the well-known lightning rod effect since it is based on the lossless propagation of surface plasmon polaritons (SPPs) up to a nano-sized metal tip where the energy density is largely enhanced. Here we discuss two important applications of adiabatic compression: Raman and hot electron spectroscopy at nanometric resolution. The underlying phenomena are the conversion of SPPs into photons or hot electrons. New scanning probe spectroscopy techniques along with experimental results are discussed. We foresee that these techniques will play a key role in relating the functional and structural properties of matter at the nanoscale.
Shahmoradi, Amir; Wilke, Claus O
2016-06-01
What are the structural determinants of protein sequence evolution? A number of site-specific structural characteristics have been proposed, most of which are broadly related to either the density of contacts or the solvent accessibility of individual residues. Most importantly, there has been disagreement in the literature over the relative importance of solvent accessibility and local packing density for explaining site-specific sequence variability in proteins. We show that this discussion has been confounded by the definition of local packing density. The most commonly used measures of local packing, such as contact number and the weighted contact number, represent the combined effects of local packing density and longer-range effects. As an alternative, we propose a truly local measure of packing density around a single residue, based on the Voronoi cell volume. We show that the Voronoi cell volume, when calculated relative to the geometric center of amino-acid side chains, behaves nearly identically to the relative solvent accessibility, and each individually can explain, on average, approximately 34% of the site-specific variation in evolutionary rate in a data set of 209 enzymes. An additional 10% of variation can be explained by nonlocal effects that are captured in the weighted contact number. Consequently, evolutionary variation at a site is determined by the combined effects of the immediate amino-acid neighbors of that site and effects mediated by more distant amino acids. We conclude that instead of contrasting solvent accessibility and local packing density, future research should emphasize on the relative importance of immediate contacts and longer-range effects on evolutionary variation. Proteins 2016; 84:841-854. © 2016 Wiley Periodicals, Inc. PMID:26990194
Adiabatic burst evaporation from bicontinuous nanoporous membranes
Ichilmann, Sachar; Rücker, Kerstin; Haase, Markus; Enke, Dirk
2015-01-01
Evaporation of volatile liquids from nanoporous media with bicontinuous morphology and pore diameters of a few 10 nm is an ubiquitous process. For example, such drying processes occur during syntheses of nanoporous materials by sol–gel chemistry or by spinodal decomposition in the presence of solvents as well as during solution impregnation of nanoporous hosts with functional guests. It is commonly assumed that drying is endothermic and driven by non-equilibrium partial pressures of the evaporating species in the gas phase. We show that nearly half of the liquid evaporates in an adiabatic mode involving burst-like liquid-to-gas conversions. During single adiabatic burst evaporation events liquid volumes of up to 107 μm3 are converted to gas. The adiabatic liquid-to-gas conversions occur if air invasion fronts get unstable because of the built-up of high capillary pressures. Adiabatic evaporation bursts propagate avalanche-like through the nanopore systems until the air invasion fronts have reached new stable configurations. Adiabatic cavitation bursts thus compete with Haines jumps involving air invasion front relaxation by local liquid flow without enhanced mass transport out of the nanoporous medium and prevail if the mean pore diameter is in the range of a few 10 nm. The results reported here may help optimize membrane preparation via solvent-based approaches, solution-loading of nanopore systems with guest materials as well as routine use of nanoporous membranes with bicontinuous morphology and may contribute to better understanding of adsorption/desorption processes in nanoporous media. PMID:25926406
Ground-state properties of Ag/sub 2/: A local-density pseudopotential approach
Luis Martins, J.; Andreoni, W.
1983-12-01
The local-density approximation of the density-functional theory is applied to calculate the ground-state properties of Ag/sub 2/, within the framework of the pseudopotential method. The calculated values of the bond length and the harmonic vibrational frequency are in good agreement with experiment. The bonding properties are found to be influenced by the d-electron states in a significant way. The results are compared with those of configuration-interaction calculations.
Local-spin-density calculations for iron: Effect of spin interpolation on ground-state properties
NASA Astrophysics Data System (ADS)
MacLaren, J. M.; Clougherty, D. P.; Albers, R. C.
1990-08-01
Scalar-relativistic self-consistent linear muffin-tin orbital (LMTO) calculations for bcc and fcc Fe have been performed with several different local approximations to the exchange and correlation energy density and potential. Overall, in contrast to the conclusions of previous studies, we find that the local-spin-density approximation to exchange and correlation can provide an adequate description of bulk Fe provided that a proper parametrization of the correlation energy density and potential of the homogeneous electron gas over both spin and density is used. Lattice constants, found from the position of the minimum of the total energy as a function of Wigner-Seitz radius, agree to within 1% (for s,p,d LMTO's only) and within 1-2% (for s,p,d,f LMTO's) of the experimental lattice constants for all forms used for the local correlation. The best agreement, however, was obtained using a local correlation potential derived from the Vosko-Wilk-Nusair form for the spin dependence of the correlation energy density. The calculation performed with this correlation potential was also the only calculation to correctly predict a bcc ferromagnetic ground state.
NASA Astrophysics Data System (ADS)
Hao, Pan
Density functional theory (DFT) is a widely used quantum mechanical method for the simulation of the electronic structure of atoms, molecules, and solids. The only part that needs to be approximated is the exchange-correlation energy as a functional of the electron density. After many-year development, there is a huge variety of exchange-correlation functionals. According to the ingredients, an exchange-correlation functional can be classified as a semi-local functional or beyond. A semi-local functional can be nonempirical or empirical and only uses locality information, such as electron density, gradient of the density, Laplacian of the density, and kinetic energy density. Unlike a non-local functional that uses non-locality information, a semi-local functional is computationally efficient and can be applied to large systems. The meta-generalized gradient approximation (meta-GGA), which is the highest-level semi-local functional, has the potential to give a good description for condensed matter physics and quantum chemistry. We built the self-consistent revised Tao-Perdew-Staroverov-Scuseria (revTPSS) meta-GGA into the band-structure program BAND to test the performances of some self-consistent semi-local functionals on lattice constant with a 58-solid test set. The self-consistent effect of revTPSS was also discussed. The vibration of a crystal has a contribution to the ground state energy of a system, which is the zero-point energy at zero temperature. It has anharmonicity at the equilibrium geometry. The standard DFT doesn't consider the zero-point energy of a crystal. We used density functional perturbation theory (DFPT), which is a powerful and flexible theoretical technique within the density functional framework, to study the zero-point energy and make a correction to the lattice constant. The method was compared to a traditional zero-point anharmonic expansion method that is based on the Debye and Dugdale-MacDonald approximations. We also tested some new
Geometry of the Adiabatic Theorem
ERIC Educational Resources Information Center
Lobo, Augusto Cesar; Ribeiro, Rafael Antunes; Ribeiro, Clyffe de Assis; Dieguez, Pedro Ruas
2012-01-01
We present a simple and pedagogical derivation of the quantum adiabatic theorem for two-level systems (a single qubit) based on geometrical structures of quantum mechanics developed by Anandan and Aharonov, among others. We have chosen to use only the minimum geometric structure needed for the understanding of the adiabatic theorem for this case.…
Kathu Townlands: A High Density Earlier Stone Age Locality in the Interior of South Africa
Walker, Steven J. H.; Lukich, Vasa; Chazan, Michael
2014-01-01
Kathu Townlands is a high density Earlier Stone Age locality in the Northern Cape Province, South Africa. Here we present the first detailed information on this locality based on analysis of a sample of lithic material from excavations by P. Beaumont and field observations made in the course of fieldwork in 2013. The results confirm the remarkably high artefact density at Kathu Townlands and do not provide evidence consistent with high energy transport as a mechanism of site formation, suggesting that Kathu Townlands was the site of intensive exploitation of highly siliceous outcroppings of banded iron formation. The results presented here provide a first step towards understanding this complex locality and point to the need for further research and the importance of preserving this locality in the face of intensive and rapid development. PMID:25058317
Localized electron heating and downstream density rise in expanding helicon plasma
NASA Astrophysics Data System (ADS)
Ghosh, Soumen; Barada, Kshitish; Chattopadhyay, Prabal; Ghosh, Joydeep; Bora, Dhiraj
2015-11-01
Localized electron heating and downstream density rise have been observed in presence of diverging magnetic fields in a linear expanding helicon plasma system. Axial wave field measurement shows the presence of damped helicon waves with standing wave character folded into it even at low densities (1016 m-3) . Helicon wavelength is just about twice the antenna length and the phase velocity (vp) is almost equal to the speed required for electron impact ionization. Observations advocate the Landau damping heating by the helicon waves, particularly in our low density plasma. Electron heating, confined away from the antenna centre, strongly indicates a source of local power absorption, occurring due to damped helicon waves. Further downstream from the location of electron heating, a density peak is observed. Location of both electron heating and density peaking can be varied by changing the axial magnetic field topology. A comprehensive discussion regarding the cause behind both the localized electron heating and downstream density rise will be discussed in this presentation.
Non-adiabatic perturbations in Ricci dark energy model
Karwan, Khamphee; Thitapura, Thiti E-mail: nanodsci2523@hotmail.com
2012-01-01
We show that the non-adiabatic perturbations between Ricci dark energy and matter can grow both on superhorizon and subhorizon scales, and these non-adiabatic perturbations on subhorizon scales can lead to instability in this dark energy model. The rapidly growing non-adiabatic modes on subhorizon scales always occur when the equation of state parameter of dark energy starts to drop towards -1 near the end of matter era, except that the parameter α of Ricci dark energy equals to 1/2. In the case where α = 1/2, the rapidly growing non-adiabatic modes disappear when the perturbations in dark energy and matter are adiabatic initially. However, an adiabaticity between dark energy and matter perturbations at early time implies a non-adiabaticity between matter and radiation, this can influence the ordinary Sachs-Wolfe (OSW) effect. Since the amount of Ricci dark energy is not small during matter domination, the integrated Sachs-Wolfe (ISW) effect is greatly modified by density perturbations of dark energy, leading to a wrong shape of CMB power spectrum. The instability in Ricci dark energy is difficult to be alleviated if the effects of coupling between baryon and photon on dark energy perturbations are included.
New approaches for the calibration of exchange-energy densities in local hybrid functionals.
Maier, Toni M; Haasler, Matthias; Arbuznikov, Alexei V; Kaupp, Martin
2016-08-21
The ambiguity of exchange-energy densities is a fundamental challenge for the development of local hybrid functionals, or of other functionals based on a local mixing of exchange-energy densities. In this work, a systematic construction of semi-local calibration functions (CFs) for adjusting the exchange-energy densities in local hybrid functionals is provided, which directly links a given CF to an underlying semi-local exchange functional, as well as to the second-order gradient expansion of the exchange hole. Using successive steps of integration by parts allows the derivation of correction terms of increasing order, resulting in more and more complicated but also more flexible CFs. We derive explicit first- and second-order CFs (pig1 and pig2) based on B88 generalized-gradient approximation (GGA) exchange, and a first-order CF (tpig1) based on τ-dependent B98 meta-GGA exchange. We combine these CFs with different long-range damping functions and evaluate them for calibration of LDA, B88 GGA, and TPSS meta-GGA exchange-energy densities. Based on a minimization of unphysical nondynamical correlation contributions in three noble-gas dimer potential-energy curves, free parameters in the CFs are optimized, and performance of various approaches in the calibration of different exchange-energy densities is compared. Most notably, the second-order pig2 CF provides the largest flexibility with respect to the diffuseness of the damping function. This suggests that higher-order CFs based on the present integration-by-parts scheme may be particularly suitable for the flexible construction of local hybrid functionals. PMID:27080804
Cembran, Alessandro; Song, Lingchun; Mo, Yirong; Gao, Jiali
2010-01-01
A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between Kohn–Sham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized Kohn–Sham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant Kohn–Sham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the SN2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three
Wilson, B.; Liberman, D.A.
1995-01-18
The plasma polarization shift computed with a Local Density Functional model of an ion-sphere model is compared with results calculated using an optimum central field effective exchange potential. Indications are that the bulk of the shift is an artifact of the approximate exchange functional describing the interaction between bound and continuum orbitals in the LDA.
Green Function Approach to the Calculation of the Local Density of States in the Graphitic Nanocone
NASA Astrophysics Data System (ADS)
Smotlacha, Jan; Pinčák, Richard
2016-02-01
Graphene and other nanostructures belong to the center of interest of today's physics research. The local density of states of the graphitic nanocone influenced by the spin-orbit interaction was calculated. Numerical calculations and the Green function approach were used to solve this problem. It was proven in the second case that the second order approximation is not sufficient for this purpose.
Sun, Jianwei; Perdew, John P; Yang, Zenghui; Peng, Haowei
2016-05-21
The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin density approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound. PMID:27208927
NASA Astrophysics Data System (ADS)
Sun, Jianwei; Perdew, John P.; Yang, Zenghui; Peng, Haowei
2016-05-01
The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin density approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound.
Local electric dipole moments for periodic systems via density functional theory embedding.
Luber, Sandra
2014-12-21
We describe a novel approach for the calculation of local electric dipole moments for periodic systems. Since the position operator is ill-defined in periodic systems, maximally localized Wannier functions based on the Berry-phase approach are usually employed for the evaluation of local contributions to the total electric dipole moment of the system. We propose an alternative approach: within a subsystem-density functional theory based embedding scheme, subset electric dipole moments are derived without any additional localization procedure, both for hybrid and non-hybrid exchange-correlation functionals. This opens the way to a computationally efficient evaluation of local electric dipole moments in (molecular) periodic systems as well as their rigorous splitting into atomic electric dipole moments. As examples, Infrared spectra of liquid ethylene carbonate and dimethyl carbonate are presented, which are commonly employed as solvents in Lithium ion batteries. PMID:25527922
Local electric dipole moments for periodic systems via density functional theory embedding
NASA Astrophysics Data System (ADS)
Luber, Sandra
2014-12-01
We describe a novel approach for the calculation of local electric dipole moments for periodic systems. Since the position operator is ill-defined in periodic systems, maximally localized Wannier functions based on the Berry-phase approach are usually employed for the evaluation of local contributions to the total electric dipole moment of the system. We propose an alternative approach: within a subsystem-density functional theory based embedding scheme, subset electric dipole moments are derived without any additional localization procedure, both for hybrid and non-hybrid exchange-correlation functionals. This opens the way to a computationally efficient evaluation of local electric dipole moments in (molecular) periodic systems as well as their rigorous splitting into atomic electric dipole moments. As examples, Infrared spectra of liquid ethylene carbonate and dimethyl carbonate are presented, which are commonly employed as solvents in Lithium ion batteries.
Coral reef degradation is not correlated with local human population density
Bruno, John F.; Valdivia, Abel
2016-01-01
The global decline of reef-building corals is understood to be due to a combination of local and global stressors. However, many reef scientists assume that local factors predominate and that isolated reefs, far from human activities, are generally healthier and more resilient. Here we show that coral reef degradation is not correlated with human population density. This suggests that local factors such as fishing and pollution are having minimal effects or that their impacts are masked by global drivers such as ocean warming. Our results also suggest that the effects of local and global stressors are antagonistic, rather than synergistic as widely assumed. These findings indicate that local management alone cannot restore coral populations or increase the resilience of reefs to large-scale impacts. They also highlight the truly global reach of anthropogenic warming and the immediate need for drastic and sustained cuts in carbon emissions. PMID:27435659
Coral reef degradation is not correlated with local human population density.
Bruno, John F; Valdivia, Abel
2016-01-01
The global decline of reef-building corals is understood to be due to a combination of local and global stressors. However, many reef scientists assume that local factors predominate and that isolated reefs, far from human activities, are generally healthier and more resilient. Here we show that coral reef degradation is not correlated with human population density. This suggests that local factors such as fishing and pollution are having minimal effects or that their impacts are masked by global drivers such as ocean warming. Our results also suggest that the effects of local and global stressors are antagonistic, rather than synergistic as widely assumed. These findings indicate that local management alone cannot restore coral populations or increase the resilience of reefs to large-scale impacts. They also highlight the truly global reach of anthropogenic warming and the immediate need for drastic and sustained cuts in carbon emissions. PMID:27435659
Local electric dipole moments for periodic systems via density functional theory embedding
Luber, Sandra
2014-12-21
We describe a novel approach for the calculation of local electric dipole moments for periodic systems. Since the position operator is ill-defined in periodic systems, maximally localized Wannier functions based on the Berry-phase approach are usually employed for the evaluation of local contributions to the total electric dipole moment of the system. We propose an alternative approach: within a subsystem-density functional theory based embedding scheme, subset electric dipole moments are derived without any additional localization procedure, both for hybrid and non-hybrid exchange–correlation functionals. This opens the way to a computationally efficient evaluation of local electric dipole moments in (molecular) periodic systems as well as their rigorous splitting into atomic electric dipole moments. As examples, Infrared spectra of liquid ethylene carbonate and dimethyl carbonate are presented, which are commonly employed as solvents in Lithium ion batteries.
Li, Arvin H.-T.; Chao, S.D.
2006-01-15
To verify the recently calculated intermolecular interaction potentials of the methane dimer within the density functional theory using the (Perdew) local density approximation (LDA) [Chen et al., Phys. Rev. A 69, 034701 (2004)], we have performed a parallel series of calculations using the LDA/6-311++G (3df, 3pd) level of theory with selected exchange functionals (B, G96, MPW, O, PBE, PW91, S, and XA). None of the above calculated intermolecular interaction potentials from the local density approximation reproduce the results reported in the commented paper. In addition, we point out the inappropriateness of using the Lennard-Jones function to model the long-range parts of the calculated intermolecular interaction potentials, as suggested positively by Chen et al.
Measurement of local current density of all-vanadium redox flow batteries
NASA Astrophysics Data System (ADS)
Hsieh, Wen-Yen; Leu, Chih-Hsing; Wu, Chun-Hsing; Chen, Yong-Song
2014-12-01
This article presents a preliminary study of the measurement of local current density in all-vanadium redox flow batteries. Two batteries are designed and manufactured in this study, and the experimental results are compared. In the first cell, the current collector is divided into 25 segments, and the flow field plate is not segmented, whereas in the other cell, the flow field plate is segmented. The effects of the electrolyte flow rate on the battery efficiencies and the local current density variation are investigated. The experimental results show that the current density near the outlet significantly decreases when the discharge capacity approaches zero. In addition, the battery has a larger discharge depth at a higher electrolyte flow rate.
RECONSTRUCTING THE INITIAL DENSITY FIELD OF THE LOCAL UNIVERSE: METHODS AND TESTS WITH MOCK CATALOGS
Wang Huiyuan; Mo, H. J.; Yang Xiaohu; Van den Bosch, Frank C.
2013-07-20
Our research objective in this paper is to reconstruct an initial linear density field, which follows the multivariate Gaussian distribution with variances given by the linear power spectrum of the current cold dark matter model and evolves through gravitational instabilities to the present-day density field in the local universe. For this purpose, we develop a Hamiltonian Markov Chain Monte Carlo method to obtain the linear density field from a posterior probability function that consists of two components: a prior of a Gaussian density field with a given linear spectrum and a likelihood term that is given by the current density field. The present-day density field can be reconstructed from galaxy groups using the method developed in Wang et al. Using a realistic mock Sloan Digital Sky Survey DR7, obtained by populating dark matter halos in the Millennium simulation (MS) with galaxies, we show that our method can effectively and accurately recover both the amplitudes and phases of the initial, linear density field. To examine the accuracy of our method, we use N-body simulations to evolve these reconstructed initial conditions to the present day. The resimulated density field thus obtained accurately matches the original density field of the MS in the density range 0.3{approx}<{rho}/ {rho}-bar {approx}<20 without any significant bias. In particular, the Fourier phases of the resimulated density fields are tightly correlated with those of the original simulation down to a scale corresponding to a wavenumber of {approx}1 h Mpc{sup -1}, much smaller than the translinear scale, which corresponds to a wavenumber of {approx}0.15 h Mpc{sup -1}.
NASA Astrophysics Data System (ADS)
Fredriksson, C.; Lazzaroni, R.; Brédas, J. L.; Ouhlal, A.; Selmani, A.
1994-06-01
The interactions between aluminum atoms and model molecules representing trans-polyacetylene are studied quantum chemically by a local density functional method. We focus on the chemical and electronic structure of the organoaluminum complexes. Special emphasis is put on a comparison between results at the local spin density approximation and ab initio Hartree-Fock levels. In unmetallized polyenes, the density functional method provides a very good description of the carbon-carbon bond lengths of conjugated systems; in the case of hexatriene, it reproduces the bond dimerization in very good agreement with experimental measurements. Upon metallization, a strong covalent interaction between aluminum and carbon is found. The Al-C bond formation induces an interruption of the bond alternation pattern and reduces the π-conjugation in the oligomer, in qualitative agreement with photoelectron spectroscopy data and previous theoretical results at the Hartree-Fock level. Notably, the π-electron levels in the organoaluminum complexes maintain delocalization. In contrast to Hartree-Fock results where an aluminum atom binds to a single carbon, the interactions calculated with the local spin density approximation lead to (i) formation of multicenter aluminum-carbon bonding; (ii) near planarity of the polyene molecule; and (iii) a lower degree of charge transfer from the metal atom to the polymer.
Adiabatic heating in impulsive solar flares
NASA Technical Reports Server (NTRS)
Maetzler, C.; Bai, T.; Crannell, C. J.; Frost, K. J.
1978-01-01
A study is made of adiabatic heating in two impulsive solar flares on the basis of dynamic X-ray spectra in the 28-254 keV range, H-alpha, microwave, and meter-wave radio observations. It is found that the X-ray spectra of the events are like those of thermal bremsstrahlung from single-temperature plasmas in the 10-60 keV range if photospheric albedo is taken into account. The temperature-emission correlation indicates adiabatic compression followed by adiabatic expansion and that the electron distribution remains isotropic. H-alpha data suggest compressive energy transfer. The projected areas and volumes of the flares are estimated assuming that X-ray and microwave emissions are produced in a single thermal plasma. Electron densities of about 10 to the 9th/cu cm are found for homogeneous, spherically symmetric sources. It is noted that the strong self-absorption of hot-plasma gyrosynchrotron radiation reveals low magnetic field strengths.
Non-adiabatic effect on quantum pumping
NASA Astrophysics Data System (ADS)
Uchiyama, Chikako
2014-03-01
We study quantum pumping for an anharmonic junction model which interacts with two kinds of bosonic environments. We provide an expression for the quantum pumping under a piecewise modulation of environmental temperatures with including non-adiabatic effect under Markovian approximation. The obtained formula is an extension of the one expressed with the geometrical phase(Phys. Rev. Lett. 104,170601 (2010)). This extension shows that the quantum pumping depends on the initial condition of the anharmonic junction just before the modulation, as well as the characteristic environmental parameters such as interaction strength and cut-off frequencies of spectral density other than the conditions of modulation. We clarify that the pumping current including non-adiabatic effect can be larger than that under the adiabatic condition. This means that we can find the optimal condition of the current by adjusting these parameters. (The article has been submitted as http://arxiv.org/submit/848201 and will be appeared soon.) This work is supported by a Grant-in-Aid for Scientific Research (B) (KAKENHI 25287098).
Local and Landscape Correlates of Spider Activity Density and Species Richness in Urban Gardens.
Otoshi, Michelle D; Bichier, Peter; Philpott, Stacy M
2015-08-01
Urbanization is a major threat to arthropod biodiversity and abundance due to reduction and loss of suitable natural habitat. Green spaces and small-scale agricultural areas may provide habitat and resources for arthropods within densely developed cities. We studied spider activity density (a measure of both abundance and degree of movement) and diversity in urban gardens in Santa Cruz, Santa Clara, and Monterey counties in central California, USA. We sampled for spiders with pitfall traps and sampled 38 local site characteristics for 5 mo in 19 garden sites to determine the relative importance of individual local factors. We also analyzed 16 landscape variables at 500-m and 1-km buffers surrounding each garden to determine the significance of landscape factors. We identified individuals from the most common families to species and identified individuals from other families to morphospecies. Species from the families Lycosidae and Gnaphosidae composed 81% of total adult spider individuals. Most of the significant factors that correlated with spider activity density and richness were local rather than landscape factors. Spider activity density and richness increased with mulch cover and flowering plant species, and decreased with bare soil. Thus, changes in local garden management have the potential to promote diversity of functionally important spiders in urban environments. PMID:26314049
The local dark matter phase-space density and impact on WIMP direct detection
Catena, Riccardo; Ullio, Piero E-mail: ullio@sissa.it
2012-05-01
We present a new determination of the local dark matter phase-space density. This result is obtained implementing, in the limit of isotropic velocity distribution and spherical symmetry, Eddington's inversion formula, which links univocally the dark matter distribution function to the density profile, and applying, within a Bayesian framework, a Markov Chain Monte Carlo algorithm to sample mass models for the Milky Way against a broad and variegated sample of dynamical constraints. We consider three possible choices for the dark matter density profile, namely the Einasto, NFW and Burkert profiles, finding that the velocity dispersion, which characterizes the width in the distribution, tends to be larger for the Burkert case, while the escape velocity depends very weakly on the profile, with the mean value we obtain being in very good agreement with estimates from stellar kinematics. The derived dark matter phase-space densities differ significantly — most dramatically in the high velocity tails — from the model usually taken as a reference in dark matter detection studies, a Maxwell-Boltzmann distribution with velocity dispersion fixed in terms of the local circular velocity and with a sharp truncation at a given value of the escape velocity. We discuss the impact of astrophysical uncertainties on dark matter scattering rates and direct detection exclusion limits, considering a few sample cases and showing that the most sensitive ones are those for light dark matter particles and for particles scattering inelastically. As a general trend, regardless of the assumed profile, when adopting a self-consistent phase-space density, we find that rates are larger, and hence exclusion limits stronger, than with the standard Maxwell-Boltzmann approximation. Tools for applying our result on the local dark matter phase-space density to other dark matter candidates or experimental setups are provided.
Quasi-particle energy spectra in local reduced density matrix functional theory.
Lathiotakis, Nektarios N; Helbig, Nicole; Rubio, Angel; Gidopoulos, Nikitas I
2014-10-28
Recently, we introduced [N. N. Lathiotakis, N. Helbig, A. Rubio, and N. I. Gidopoulos, Phys. Rev. A 90, 032511 (2014)] local reduced density matrix functional theory (local RDMFT), a theoretical scheme capable of incorporating static correlation effects in Kohn-Sham equations. Here, we apply local RDMFT to molecular systems of relatively large size, as a demonstration of its computational efficiency and its accuracy in predicting single-electron properties from the eigenvalue spectrum of the single-particle Hamiltonian with a local effective potential. We present encouraging results on the photoelectron spectrum of molecular systems and the relative stability of C20 isotopes. In addition, we propose a modelling of the fractional occupancies as functions of the orbital energies that further improves the efficiency of the method useful in applications to large systems and solids. PMID:25362285
Zhang, Feihu; Buckl, Christian; Knoll, Alois
2014-01-01
This paper studies the problem of multiple vehicle cooperative localization with spatial registration in the formulation of the probability hypothesis density (PHD) filter. Assuming vehicles are equipped with proprioceptive and exteroceptive sensors (with biases) to cooperatively localize positions, a simultaneous solution for joint spatial registration and state estimation is proposed. For this, we rely on the sequential Monte Carlo implementation of the PHD filtering. Compared to other methods, the concept of multiple vehicle cooperative localization with spatial registration is first proposed under Random Finite Set Theory. In addition, the proposed solution also addresses the challenges for multiple vehicle cooperative localization, e.g., the communication bandwidth issue and data association uncertainty. The simulation result demonstrates its reliability and feasibility in large-scale environments. PMID:24406860
Quasi-particle energy spectra in local reduced density matrix functional theory
Lathiotakis, Nektarios N.; Helbig, Nicole; Rubio, Angel
2014-10-28
Recently, we introduced [N. N. Lathiotakis, N. Helbig, A. Rubio, and N. I. Gidopoulos, Phys. Rev. A 90, 032511 (2014)] local reduced density matrix functional theory (local RDMFT), a theoretical scheme capable of incorporating static correlation effects in Kohn-Sham equations. Here, we apply local RDMFT to molecular systems of relatively large size, as a demonstration of its computational efficiency and its accuracy in predicting single-electron properties from the eigenvalue spectrum of the single-particle Hamiltonian with a local effective potential. We present encouraging results on the photoelectron spectrum of molecular systems and the relative stability of C{sub 20} isotopes. In addition, we propose a modelling of the fractional occupancies as functions of the orbital energies that further improves the efficiency of the method useful in applications to large systems and solids.
Phototactic number-density flux in the localized bioconvection of Euglena gracilis
NASA Astrophysics Data System (ADS)
Shoji, Erika; Suematsu, Nobuhiko; Nishimori, Hiraku; Awazu, Akinori; Izumi, Shunsuke; Iima, Makoto
2014-11-01
Euglena gracilis is a unicellular phototactic flagellate; it escapes from light sources if the light intensity is higher than 200 W/m2 (negative phototaxis). When the suspension of E. gracilis is illuminated from the bottom by strong light, bioconvection patterns are generated. In the case of E. gracilis, the patterns can be spatially localized. The localization mechanism has not been clarified. We report experimental results related to the localization mechanism. In particular, we experimentally measured the strength of the phototaxis in the lateral direction as well as vertical direction. We prepared a thin container in which the suspension is included, and gave the linearly-changing light intensity. We found the number density gets a peak at a particular light intensity, which never happens if the suspension has the vertical phototaxis only. Further, we succeeded in getting the function representing lateral phototaxis. The relationship between the measured functions and the localized convection cells will be also reported.
State pre-emption, local control, and alcohol retail outlet density regulation.
Mosher, James F; Treffers, Ryan D
2013-04-01
The substantial health and economic costs of excessive alcohol consumption make its reduction a major public health and economic concern. The Community Preventive Services Task Force, based on a systematic review of the research literature, concluded that restricting alcohol retail outlet density through local land use and zoning regulations is an effective strategy for reducing these costs. Yet the implementation of the Task Force's recommendation is limited by state pre-emption, which determines the extent to which states allow local government to adopt policies and enact legislation. This article summarizes the state pre-emption doctrine, its status in the 50 states pertaining to alcohol retail outlet density regulation, and findings from state legal analyses conducted in six states. Data reflect state laws in effect as of January 1, 2012. Analyses were conducted during the 2012 calendar year. An examination of relevant state laws found five distinct pre-emption categories: exclusive state licensing, exclusive state licensing and concurrent local zoning, joint licensing, exclusive local licensing, and a mixed system. The analysis demonstrated wide variability across the states, ranging from exclusive state pre-emption to broad state delegation of authority to local governments. Pre-emption is applied differentially in many states based on retail outlet characteristics. In many cases, state pre-emption laws are ambiguous in terms of their application, leading to inconsistent and confusing court interpretations. Reforms targeting the adverse impact of state pre-emption on alcohol retail outlet density have the potential for reducing the harm associated with excessive alcohol consumption. State and local public health departments can support such reforms by implementing educational, analytic, monitoring, and technical assistance activities. PMID:23498107
Adiabatic fluctuations from cosmic strings in a contracting universe
Brandenberger, Robert H.; Takahashi, Tomo; Yamaguchi, Masahide E-mail: tomot@cc.saga-u.ac.jp
2009-07-01
We show that adiabatic, super-Hubble, and almost scale invariant density fluctuations are produced by cosmic strings in a contracting universe. An essential point is that isocurvature perturbations produced by topological defects such as cosmic strings on super-Hubble scales lead to a source term which seeds the growth of curvature fluctuations on these scales. Once the symmetry has been restored at high temperatures, the isocurvature seeds disappear, and the fluctuations evolve as adiabatic ones in the expanding phase. Thus, cosmic strings may be resurrected as a mechanism for generating the primordial density fluctuations observed today.
Exact density functional and wave function embedding schemes based on orbital localization
NASA Astrophysics Data System (ADS)
Hégely, Bence; Nagy, Péter R.; Ferenczy, György G.; Kállay, Mihály
2016-08-01
Exact schemes for the embedding of density functional theory (DFT) and wave function theory (WFT) methods into lower-level DFT or WFT approaches are introduced utilizing orbital localization. First, a simple modification of the projector-based embedding scheme of Manby and co-workers [J. Chem. Phys. 140, 18A507 (2014)] is proposed. We also use localized orbitals to partition the system, but instead of augmenting the Fock operator with a somewhat arbitrary level-shift projector we solve the Huzinaga-equation, which strictly enforces the Pauli exclusion principle. Second, the embedding of WFT methods in local correlation approaches is studied. Since the latter methods split up the system into local domains, very simple embedding theories can be defined if the domains of the active subsystem and the environment are treated at a different level. The considered embedding schemes are benchmarked for reaction energies and compared to quantum mechanics (QM)/molecular mechanics (MM) and vacuum embedding. We conclude that for DFT-in-DFT embedding, the Huzinaga-equation-based scheme is more efficient than the other approaches, but QM/MM or even simple vacuum embedding is still competitive in particular cases. Concerning the embedding of wave function methods, the clear winner is the embedding of WFT into low-level local correlation approaches, and WFT-in-DFT embedding can only be more advantageous if a non-hybrid density functional is employed.
The local projection in the density functional theory plus U approach: A critical assessment
NASA Astrophysics Data System (ADS)
Wang, Yue-Chao; Chen, Ze-Hua; Jiang, Hong
2016-04-01
Density-functional theory plus the Hubbard U correction (DFT + U) method is widely used in first-principles studies of strongly correlated systems, as it can give qualitatively (and sometimes, semi-quantitatively) correct description of energetic and structural properties of many strongly correlated systems with similar computational cost as local density approximation or generalized gradient approximation. On the other hand, the DFT + U approach is limited both theoretically and practically in several important aspects. In particular, the results of DFT + U often depend on the choice of local orbitals (the local projection) defining the subspace in which the Hubbard U correction is applied. In this work we have systematically investigated the issue of the local projection by considering typical transition metal oxides, β-MnO2 and MnO, and comparing the results obtained from different implementations of DFT + U. We found that the choice of the local projection has significant effects on the DFT + U results, which are more significant for systems with stronger covalent bonding (e.g., MnO2) than those with more ionic bonding (e.g., MnO). These findings can help to clarify some confusion arising from the practical use of DFT + U and may also provide insights for the development of new first-principles approaches beyond DFT + U.
The local projection in the density functional theory plus U approach: A critical assessment.
Wang, Yue-Chao; Chen, Ze-Hua; Jiang, Hong
2016-04-14
Density-functional theory plus the Hubbard U correction (DFT + U) method is widely used in first-principles studies of strongly correlated systems, as it can give qualitatively (and sometimes, semi-quantitatively) correct description of energetic and structural properties of many strongly correlated systems with similar computational cost as local density approximation or generalized gradient approximation. On the other hand, the DFT + U approach is limited both theoretically and practically in several important aspects. In particular, the results of DFT + U often depend on the choice of local orbitals (the local projection) defining the subspace in which the Hubbard U correction is applied. In this work we have systematically investigated the issue of the local projection by considering typical transition metal oxides, β-MnO2 and MnO, and comparing the results obtained from different implementations of DFT + U. We found that the choice of the local projection has significant effects on the DFT + U results, which are more significant for systems with stronger covalent bonding (e.g., MnO2) than those with more ionic bonding (e.g., MnO). These findings can help to clarify some confusion arising from the practical use of DFT + U and may also provide insights for the development of new first-principles approaches beyond DFT + U. PMID:27083707
The electron localization as the information content of the conditional pair density
NASA Astrophysics Data System (ADS)
Urbina, Andres S.; Torres, F. Javier; Rincon, Luis
2016-06-01
In the present work, the information gained by an electron for "knowing" about the position of another electron with the same spin is calculated using the Kullback-Leibler divergence (DKL) between the same-spin conditional pair probability density and the marginal probability. DKL is proposed as an electron localization measurement, based on the observation that regions of the space with high information gain can be associated with strong correlated localized electrons. Taking into consideration the scaling of DKL with the number of σ-spin electrons of a system (Nσ), the quantity χ = (Nσ - 1) DKLfcut is introduced as a general descriptor that allows the quantification of the electron localization in the space. fcut is defined such that it goes smoothly to zero for negligible densities. χ is computed for a selection of atomic and molecular systems in order to test its capability to determine the region in space where electrons are localized. As a general conclusion, χ is able to explain the electron structure of molecules on the basis of chemical grounds with a high degree of success and to produce a clear differentiation of the localization of electrons that can be traced to the fluctuation in the average number of electrons in these regions.
The electron localization as the information content of the conditional pair density.
Urbina, Andres S; Torres, F Javier; Rincon, Luis
2016-06-28
In the present work, the information gained by an electron for "knowing" about the position of another electron with the same spin is calculated using the Kullback-Leibler divergence (DKL) between the same-spin conditional pair probability density and the marginal probability. DKL is proposed as an electron localization measurement, based on the observation that regions of the space with high information gain can be associated with strong correlated localized electrons. Taking into consideration the scaling of DKL with the number of σ-spin electrons of a system (N(σ)), the quantity χ = (N(σ) - 1) DKLfcut is introduced as a general descriptor that allows the quantification of the electron localization in the space. fcut is defined such that it goes smoothly to zero for negligible densities. χ is computed for a selection of atomic and molecular systems in order to test its capability to determine the region in space where electrons are localized. As a general conclusion, χ is able to explain the electron structure of molecules on the basis of chemical grounds with a high degree of success and to produce a clear differentiation of the localization of electrons that can be traced to the fluctuation in the average number of electrons in these regions. PMID:27369494
Scanning tunneling microscopy current from localized basis orbital density functional theory
NASA Astrophysics Data System (ADS)
Gustafsson, Alexander; Paulsson, Magnus
2016-03-01
We present a method capable of calculating elastic scanning tunneling microscopy (STM) currents from localized atomic orbital density functional theory (DFT). To overcome the poor accuracy of the localized orbital description of the wave functions far away from the atoms, we propagate the wave functions, using the total DFT potential. From the propagated wave functions, the Bardeen's perturbative approach provides the tunneling current. To illustrate the method we investigate carbon monoxide adsorbed on a Cu(111) surface and recover the depression/protrusion observed experimentally with normal/CO-functionalized STM tips. The theory furthermore allows us to discuss the significance of s - and p -wave tips.
Measurement of local gain and electron density in an yttrium x-ray laser amplifier
Cauble, R.; Da Silva, L.B.; Barbee, T.Jr.; Celliers, P.; Decker, C.; London, R.A.; Moreno, J.C.; Trebes, J.E.; Wan, A.S.; Weber, F.
1996-05-01
X-ray lasers have measured average gains significantly less than calculated and a persistently low level of spatial coherence. We have used an X-ray laser both as an injected signal to a short X-ray laser amplifier and as an interferometer beam to measure two dimensional local gain and density profiles of the X-ray laser plasma with near-1- mm resolution. The measured local gain is in agreement with atomic models, but its gain is unexpectedly spatially inhomogeneous. This inhomogeneity explains the low level of spatial coherence observed and helps explain the disparity between observed and simulated gains.
NASA Astrophysics Data System (ADS)
Jones, B.; Deeney, C.; McKenney, J. L.; Ampleford, D. J.; Coverdale, C. A.; Lepell, P. D.; Shelton, K. P.; Safronova, A. S.; Kantsyrev, V. L.; Osborne, G.; Sotnikov, V. I.; Ivanov, V. V.; Fedin, D.; Nalajala, V.; Yilmaz, F.; Shrestha, I.
2008-03-01
Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.
Local-density approximation for confined bosons in an optical lattice
Bergkvist, Sara; Henelius, Patrik; Rosengren, Anders
2004-11-01
We investigate local and global properties of the one-dimensional Bose-Hubbard model with an external confining potential, describing an atomic condensate in an optical lattice. Using quantum Monte Carlo techniques we demonstrate that a local-density approximation, which relates the unconfined and the confined model, yields quantitatively correct results in most of the interesting parameter range. We also examine claims of universal behavior in the confined system, and demonstrate the origin of a previously calculated fine structure in the experimentally accessible momentum distribution.
Ionization potentials of cobalt and nickel ions in the local-spin-density approximation
Dhar, S. ); Kestner, N.R. )
1990-06-15
In this article we report on the ionization potentials of all configurations of the Co{sup {ital n}+} and Ni{sup {ital n}+} ions obtained via transition-state calculations using local-spin-density (LSD) potentials. The calculations were performed numerically with and without modifications of the local exchange potential for fractional occupation numbers. When the exchange potential is corrected for noninteger occupation numbers, a more consistent picture of the ionization process is obtained than that given by the LSD Kohn-Sham exchange. The agreement with experimental results is also significantly improved.
Lv, Caixia; Stewart, William J; Akanyeti, Otar; Frederick, Courtney; Zhu, Jie; Santos-Sacchi, Joseph; Sheets, Lavinia; Liao, James C; Zenisek, David
2016-06-21
Synaptic ribbons are structures made largely of the protein Ribeye that hold synaptic vesicles near release sites in non-spiking cells in some sensory systems. Here, we introduce frameshift mutations in the two zebrafish genes encoding for Ribeye and thus remove Ribeye protein from neuromast hair cells. Despite Ribeye depletion, vesicles collect around ribbon-like structures that lack electron density, which we term "ghost ribbons." Ghost ribbons are smaller in size but possess a similar number of smaller vesicles and are poorly localized to synapses and calcium channels. These hair cells exhibit enhanced exocytosis, as measured by capacitance, and recordings from afferent neurons post-synaptic to hair cells show no significant difference in spike rates. Our results suggest that Ribeye makes up most of the synaptic ribbon density in neuromast hair cells and is necessary for proper localization of calcium channels and synaptic ribbons. PMID:27292637
NASA Astrophysics Data System (ADS)
Finzel, Kati
2016-01-01
The local conditions for the Pauli potential that are necessary in order to yield self-consistent electron densities from orbital-free calculations are investigated for approximations that are expressed with the help of a local position variable. It is shown that those local conditions also apply when the Pauli potential is given in terms of the electron density. An explicit formula for the Ne atom is given, preserving the local conditions during the iterative procedure. The resulting orbital-free electron density exhibits proper shell structure behavior and is in close agreement with the Kohn-Sham electron density. This study demonstrates that it is possible to obtain self-consistent orbital-free electron densities with proper atomic shell structure from simple one-point approximations for the Pauli potential at local density level.
NASA Astrophysics Data System (ADS)
Nara, Takaaki; Koike, Masanori; Ando, Shigeru; Gotoh, Yuji; Izumi, Masaaki
2016-05-01
In this paper, we propose novel inversion methods to estimate defects or localized current anomalies in membrane electrode assemblies (MEAs) in polymer electrolyte fuel cells (PEFCs). One method is an imaging approach with L1-norm regularization that is suitable for estimation of focal anomalies compared to Tikhonov regularization. The second is a complex analysis based method in which multiple pointwise current anomalies can be identified directly and algebraically from the measured magnetic flux density.
Ultraviolet observations of cool stars. V - The local density of interstellar matter
NASA Technical Reports Server (NTRS)
Mcclintock, W.; Henry, R. C.; Moos, H. W.; Linsky, J. L.
1976-01-01
A high-resolution Copernicus observation of the chromospheric Ly-alpha emission line of the nearby (3.3 pc) K dwarf epsilon Eri sets limits on the velocity, the velocity dispersion, and the density of atomic hydrogen in the local interstellar medium. Analysis shows that the interstellar Ly-alpha absorption is on the flat portion of the curve of growth. An upper limit of 0.12 per cu cm is derived for the atomic-hydrogen density. The value of this density is 0.08 (plus or minus 0.04 per cu cm if the velocity-dispersion parameter is 9 km/s, corresponding to a temperature of 5000 K. Also, the interstellar deuterium Ly-alpha line may be present in the spectrum.
Typical density of states as an order parameter for the Anderson localization
NASA Astrophysics Data System (ADS)
Tam, Ka-Ming; Moore, Conrad; Moreno, Juana; Jarrell, Mark
2015-03-01
The typical medium theory and its recently proposed extensions for models with off-diagonal disorder and multiple bands are significant progress towards the study of localization phenomenon in real materials. The fundamental assumption of these methods is that the typical density of states can be treated as an order parameter. However, its justifications in lattice model is largely lacking. This is predominantly due to two factors. First, the lattice sizes amenable for exact diagonalization is rather limited. Second, the small lattice sizes lead to a very sensitive dependence on the broadening factor. In this work, we use the kernel polynomial method to perform simulation for large system sizes. By adapting the method for the study of criticality, we find that the typical density of states has a well defined finite size scaling behavior. In particular, from the kurtosis, Binder ratio, of the distribution of the density of states for different lattice sizes, we find a clear crossing to identify the critical point. This provides further support that the typical density of states can be used as an order parameter for the localization transition.
Local suppression of the superfluid density of PuCoGa5 by strong onsite disorder
NASA Astrophysics Data System (ADS)
Das, Tanmoy; Zhu, Jian-Xin; Graf, Matthias J.
2011-10-01
We present superfluid density calculations for the unconventional superconductor PuCoGa5 by solving the real-space Bogoliubov-de Gennes equations on a square lattice within the Swiss-cheese model in the presence of strong onsite disorder. We find that, despite strong electronic inhomogeneity, one can establish a one-to-one correspondence between the local maps of the density of states, superconducting order parameter, and superfluid density. In this model, strong onsite impurity scattering punches localized holes into the fabric of d-wave superconductivity similar to a Swiss cheese. Already, a two-dimensional impurity concentration of nimp=4% gives rise to a pronounced short-range suppression of the order parameter and a suppression of the superconducting transition temperature Tc by roughly 20% compared to its pure limit value Tc0, whereas the superfluid density ρs is reduced drastically by about 70%. This result is consistent with available experimental data for aged (400-day-old) and fresh (25-day-old) PuCoGa5 superconducting samples. In addition, we show that the T2 dependence of the low-T superfluid density, a signature of dirty d-wave superconductivity, originates from a combined effect in the density of states of “gap filling” and “gap closing.” Finally, we demonstrate that the Uemuera plot of Tc versus ρs deviates sharply from the conventional Abrikosov-Gor’kov theory for radiation-induced defects in PuCoGa5, but follows the same trend of short-coherence-length high-Tc cuprate superconductors.
Hao, Feng Mattsson, Ann E.; Armiento, Rickard
2014-05-14
We have previously proposed that further improved functionals for density functional theory can be constructed based on the Armiento-Mattsson subsystem functional scheme if, in addition to the uniform electron gas and surface models used in the Armiento-Mattsson 2005 functional, a model for the strongly confined electron gas is also added. However, of central importance for this scheme is an index that identifies regions in space where the correction provided by the confined electron gas should be applied. The electron localization function (ELF) is a well-known indicator of strongly localized electrons. We use a model of a confined electron gas based on the harmonic oscillator to show that regions with high ELF directly coincide with regions where common exchange energy functionals have large errors. This suggests that the harmonic oscillator model together with an index based on the ELF provides the crucial ingredients for future improved semi-local functionals. For a practical illustration of how the proposed scheme is intended to work for a physical system we discuss monoclinic cupric oxide, CuO. A thorough discussion of this system leads us to promote the cell geometry of CuO as a useful benchmark for future semi-local functionals. Very high ELF values are found in a shell around the O ions, and take its maximum value along the Cu–O directions. An estimate of the exchange functional error from the effect of electron confinement in these regions suggests a magnitude and sign that could account for the error in cell geometry.
Parallel and Low-Order Scaling Implementation of Hartree-Fock Exchange Using Local Density Fitting.
Köppl, Christoph; Werner, Hans-Joachim
2016-07-12
Calculations using modern linear-scaling electron-correlation methods are often much faster than the necessary reference Hartree-Fock (HF) calculations. We report a newly implemented HF program that speeds up the most time-consuming step, namely, the evaluation of the exchange contributions to the Fock matrix. Using localized orbitals and their sparsity, local density fitting (LDF), and atomic orbital domains, we demonstrate that the calculation of the exchange matrix scales asymptotically linearly with molecular size. The remaining parts of the HF calculation scale cubically but become dominant only for very large molecular sizes or with many processing cores. The method is well parallelized, and the speedup scales well with up to about 100 CPU cores on multiple compute nodes. The effect of the local approximations on the accuracy of computed HF and local second-order Møller-Plesset perturbation theory energies is systematically investigated, and default values are established for the parameters that determine the domain sizes. Using these values, calculations for molecules with hundreds of atoms in combination with triple-ζ basis sets can be carried out in less than 1 h, with just a few compute nodes. The method can also be used to speed up density functional theory calculations with hybrid functionals that contain HF exchange. PMID:27267488
Imaging the local forward current density of solar cells by dynamical precision contact thermography
Breitenstein, O.; Eberhardt, W.; Iwig, K.
1994-12-31
In spite of many techniques of measuring the local lifetime or the local short circuit current, no non-destructive technique has been available for imaging the local forward current density, which determines the open circuit voltage and the fill factor of solar cells. The authors demonstrate the application of a new analyzing technique, enabling non-destructive shunt hunting in forward direction. A periodical forward current is applied to the cell, and only the dynamical temperature response is measured in contact mode with a resolution below 10 {micro}K. Mechanical scanning of the T-sensor position yields a thermogram with a spatial resolution well below 1 mm and a current density resolution well below 1 mA/cm{sup 2}. First results show that both the edges of solar cells and their interior may have sites of a locally increased forward current. Hot spots measured in reverse bias direction only occasionally coincide with these warm spots measured in forward direction.
NASA Astrophysics Data System (ADS)
Chen, Xiaolong; Li, Wei; Wang, Lin; He, Yuheng; Wu, Zefei; Cai, Yuan; Zhang, Mingwei; Wang, Yang; Han, Yu; Lortz, Rolf W.; Zhang, Zhao-Qing; Sheng, Ping; Wang, Ning
2013-03-01
We demonstrate that local fluctuations of the density of states (DOS) in strongly disordered graphene play an important role in determining the quantum capacitance of the top-gate device geometry. Depending on the strength of the disorder induced by metal-cluster decoration, the measured quantum capacitance of disordered graphene could dramatically decrease in comparison with pristine graphene (previous work on transport of metal-cluster decoration has been published on Phys. Rev. B 84, 045431, 2011). A quantitative model for correlating fluctuations of local density of states with the disorder strength and quantum capacitance is presented and discussed. The DOS of disordered graphene obeys a non-universal power law. By measuring the quantum capacitance of disordered graphene, we simultaneously determined both the DOS and its local fluctuations, which is in agreement with the lognormal distributions reported previously for localized samples. Financial support from the Research Grants Council of Hong Kong (Project Nos. HKUST9/CRF/08, 604112) and technical support of the Raith-HKUST Nanotechnology Laboratory (Project No. SEG_HKUST08) are hereby acknowledged.
Bao, Peng
2013-01-01
An interaction energy decomposition analysis method based on the block-localized wavefunction (BLW-ED) approach is described. The first main feature of the BLW-ED method is that it combines concepts of valence bond and molecular orbital theories such that the intermediate and physically intuitive electron-localized states are variationally optimized by self-consistent field calculations. Furthermore, the block-localization scheme can be used both in wave function theory and in density functional theory, providing a useful tool to gain insights on intermolecular interactions that would otherwise be difficult to obtain using the delocalized Kohn–Sham DFT. These features allow broad applications of the BLW method to energy decomposition (BLW-ED) analysis for intermolecular interactions. In this perspective, we outline theoretical aspects of the BLW-ED method, and illustrate its applications in hydrogen-bonding and π–cation intermolecular interactions as well as metal–carbonyl complexes. Future prospects on the development of a multistate density functional theory (MSDFT) are presented, making use of block-localized electronic states as the basis configurations. PMID:21369567
High-density three-dimensional localization microscopy across large volumes.
Legant, Wesley R; Shao, Lin; Grimm, Jonathan B; Brown, Timothy A; Milkie, Daniel E; Avants, Brian B; Lavis, Luke D; Betzig, Eric
2016-04-01
Extending three-dimensional (3D) single-molecule localization microscopy away from the coverslip and into thicker specimens will greatly broaden its biological utility. However, because of the limitations of both conventional imaging modalities and conventional labeling techniques, it is a challenge to localize molecules in three dimensions with high precision in such samples while simultaneously achieving the labeling densities required for high resolution of densely crowded structures. Here we combined lattice light-sheet microscopy with newly developed, freely diffusing, cell-permeable chemical probes with targeted affinity for DNA, intracellular membranes or the plasma membrane. We used this combination to perform high-localization precision, ultrahigh-labeling density, multicolor localization microscopy in samples up to 20 μm thick, including dividing cells and the neuromast organ of a zebrafish embryo. We also demonstrate super-resolution correlative imaging with protein-specific photoactivable fluorophores, providing a mutually compatible, single-platform alternative to correlative light-electron microscopy over large volumes. PMID:26950745
Image denoising via Bayesian estimation of local variance with Maxwell density prior
NASA Astrophysics Data System (ADS)
Kittisuwan, Pichid
2015-10-01
The need for efficient image denoising methods has grown with the massive production of digital images and movies of all kinds. The distortion of images by additive white Gaussian noise (AWGN) is common during its processing and transmission. This paper is concerned with dual-tree complex wavelet-based image denoising using Bayesian techniques. Indeed, one of the cruxes of the Bayesian image denoising algorithms is to estimate the local variance of the image. Here, we employ maximum a posteriori (MAP) estimation to calculate local observed variance with Maxwell density prior for local observed variance and Gaussian distribution for noisy wavelet coefficients. Evidently, our selection of prior distribution is motivated by analytical and computational tractability. The experimental results show that the proposed method yields good denoising results.
Autonomous bacterial localization and gene expression based on nearby cell receptor density
Wu, Hsuan-Chen; Tsao, Chen-Yu; Quan, David N; Cheng, Yi; Servinsky, Matthew D; Carter, Karen K; Jee, Kathleen J; Terrell, Jessica L; Zargar, Amin; Rubloff, Gary W; Payne, Gregory F; Valdes, James J; Bentley, William E
2013-01-01
Escherichia coli were genetically modified to enable programmed motility, sensing, and actuation based on the density of features on nearby surfaces. Then, based on calculated feature density, these cells expressed marker proteins to indicate phenotypic response. Specifically, site-specific synthesis of bacterial quorum sensing autoinducer-2 (AI-2) is used to initiate and recruit motile cells. In our model system, we rewired E. coli's AI-2 signaling pathway to direct bacteria to a squamous cancer cell line of head and neck (SCCHN), where they initiate synthesis of a reporter (drug surrogate) based on a threshold density of epidermal growth factor receptor (EGFR). This represents a new type of controller for targeted drug delivery as actuation (synthesis and delivery) depends on a receptor density marking the diseased cell. The ability to survey local surfaces and initiate gene expression based on feature density represents a new area-based switch in synthetic biology that will find use beyond the proposed cancer model here. PMID:23340842
Pressure sensitivity of adiabatic shear banding in metals
NASA Astrophysics Data System (ADS)
Hanina, E.; Rittel, D.; Rosenberg, Z.
2007-01-01
Adiabatic shear banding (ASB) is a dynamic failure mode characterized by large plastic strains in a narrow localized band. ASB occurs at high strain rates (ɛ˙⩾103s-1), under adiabatic conditions leading to a significant temperature rise inside the band [H. Tresca, Annales du Conservatoire des Arts et Métiers 4, (1879); Y. L. Bai and B. Dodd, Adiabatic Shear Localization-Occurrence, Theories, and Applications (Pergamon, Oxford, 1992); M. A. Meyers, Dynamic Behavior of Materials (Wiley, New York, 1994).; and J. J. Lewandowski and L. M. Greer, Nat. Mater. 5, 15 (2006)]. Large hydrostatic pressures are experienced in many dynamic applications involving ASB formation (e.g., ballistic penetration, impact, and machining). The relationship between hydrostatic pressure and ASB development remains an open question, although its importance has been often noted. This letter reports original experimental results indicating a linear relationship between the (normalized) dynamic deformation energy and the (normalized) hydrostatic pressure.
Density Functional Modeling of the Local Structure of Kaolinite Subjected to Thermal Dehydroxylation
White, Claire E.; Provis, John L.; Proffen, Thomas; Riley, Daniel P.; van Deventer, Jannie S.J.
2010-11-19
Understanding the atomic-level changes that occur as kaolinite is converted (thermally dehydroxylated) to metakaolin is critical to the optimization of this large-scale industrial process. Metakaolin is X-ray amorphous; therefore, conventional crystallographic techniques do not reveal the changes in local structure during its formation. Local structure-based experimental techniques are useful in understanding the atomic structure but do not provide the thermodynamic information which is necessary to ensure plausibility of refined structures. Here, kaolinite dehydroxylation is modeled using density functional theory, and a stepwise methodology, where several water molecules are removed from the structure, geometry optimization is carried out, and then the process is repeated. Hence, the structure remains in an energetically and thermodynamically feasible state while transitioning from kaolinite to metakaolin. The structures generated during the dehydroxylation process are validated by comparison with X-ray and neutron pair distribution function data. Thus, this study illustrates one possible route by which dehydroxylation of kaolinite can take place, revealing a chemically, energetically, and experimentally plausible structure of metakaolin. This methodology of density functional modeling of the stepwise changes in a material is not limited in application to kaolinite or other aluminosilicates and provides an accurate representation of the local structural changes occurring in materials used in industrially important processes.
NASA Astrophysics Data System (ADS)
Sato, Takeshi; Nakai, Hiromi
2009-12-01
A new method to calculate the atom-atom dispersion coefficients in a molecule is proposed for the use in density functional theory with dispersion (DFT-D) correction. The method is based on the local response approximation due to Dobson and Dinte [Phys. Rev. Lett. 76, 1780 (1996)], with modified dielectric model recently proposed by Vydrov and van Voorhis [J. Chem. Phys. 130, 104105 (2009)]. The local response model is used to calculate the distributed multipole polarizabilities of atoms in a molecule, from which the dispersion coefficients are obtained by an explicit frequency integral of the Casimir-Polder type. Thus obtained atomic polarizabilities are also used in the damping function for the short-range singularity. Unlike empirical DFT-D methods, the local response dispersion (LRD) method is able to calculate the dispersion energy from the ground-state electron density only. It is applicable to any geometry, free from physical constants such as van der Waals radii or atomic polarizabilities, and computationally very efficient. The LRD method combined with the long-range corrected DFT functional (LC-BOP) is applied to calculations of S22 weakly bound complex set [Phys. Chem. Chem. Phys. 8, 1985 (2006)]. Binding energies obtained by the LC-BOP+LRD agree remarkably well with ab initio references.
NASA Astrophysics Data System (ADS)
Sato, Takeshi; Nakai, Hiromi
2009-12-01
A new method to calculate the atom-atom dispersion coefficients in a molecule is proposed for the use in density functional theory with dispersion (DFT-D) correction. The method is based on the local response approximation due to Dobson and Dinte [Phys. Rev. Lett. 76, 1780 (1996)], with modified dielectric model recently proposed by Vydrov and van Voorhis [J. Chem. Phys. 130, 104105 (2009)]. The local response model is used to calculate the distributed multipole polarizabilities of atoms in a molecule, from which the dispersion coefficients are obtained by an explicit frequency integral of the Casimir-Polder type. Thus obtained atomic polarizabilities are also used in the damping function for the short-range singularity. Unlike empirical DFT-D methods, the local response dispersion (LRD) method is able to calculate the dispersion energy from the ground-state electron density only. It is applicable to any geometry, free from physical constants such as van der Waals radii or atomic polarizabilities, and computationally very efficient. The LRD method combined with the long-range corrected DFT functional (LC-BOP) is applied to calculations of S22 weakly bound complex set [Phys. Chem. Chem. Phys. 8, 1985 (2006)]. Binding energies obtained by the LC-BOP + LRD agree remarkably well with ab initio references.
NASA Astrophysics Data System (ADS)
Marchukov, Oleksandr V.; Eriksen, Emil H.; Midtgaard, Jonatan M.; Kalaee, Alex A. S.; Fedorov, Dmitri V.; Jensen, Aksel S.; Zinner, Nikolaj T.
2016-02-01
One-dimensional multi-component Fermi or Bose systems with strong zero-range interactions can be described in terms of local exchange coefficients and mapping the problem into a spin model is thus possible. For arbitrary external confining potentials the local exchanges are given by highly non-trivial geometric factors that depend solely on the geometry of the confinement through the single-particle eigenstates of the external potential. To obtain accurate effective Hamiltonians to describe such systems one needs to be able to compute these geometric factors with high precision which is difficult due to the computational complexity of the high-dimensional integrals involved. An approach using the local density approximation would therefore be a most welcome approximation due to its simplicity. Here we assess the accuracy of the local density approximation by going beyond the simple harmonic oscillator that has been the focus of previous studies and consider some double-wells of current experimental interest. We find that the local density approximation works quite well as long as the potentials resemble harmonic wells but break down for larger barriers. In order to explore the consequences of applying the local density approximation in a concrete setup we consider quantum state transfer in the effective spin models that one obtains. Here we find that even minute deviations in the local exchange coefficients between the exact and the local density approximation can induce large deviations in the fidelity of state transfer for four, five, and six particles.
Adiabatic evolution of plasma equilibrium
Grad, H.; Hu, P. N.; Stevens, D. C.
1975-01-01
A new theory of plasma equilibrium is introduced in which adiabatic constraints are specified. This leads to a mathematically nonstandard structure, as compared to the usual equilibrium theory, in which prescription of pressure and current profiles leads to an elliptic partial differential equation. Topologically complex configurations require further generalization of the concept of adiabaticity to allow irreversible mixing of plasma and magnetic flux among islands. Matching conditions across a boundary layer at the separatrix are obtained from appropriate conservation laws. Applications are made to configurations with planned islands (as in Doublet) and accidental islands (as in Tokamaks). Two-dimensional, axially symmetric, helically symmetric, and closed line equilibria are included. PMID:16578729
Charge density stabilised local electron spin pair states in insulating polymers
Serra, S.; Dissado, L. A.
2014-12-14
A model is presented that addresses the energy stability of localized electron states in insulating polymers with respect to delocalized free electron-like states at variable charge densities. The model was derived using an effective Hamiltonian for the total energy of electrons trapped in large polarons and spin-paired bipolarons, which includes the electrostatic interaction between charges that occurs when the charge density exceeds the infinite dilution limit. The phase diagram of the various electronic states with respect to the charge density is derived using parameters determined from experimental data for polyethylene, and it is found that a phase transition from excess charge in the form of stable polarons to a stable state of bipolarons with charge = 2 and spin number S = 0 is predicted for a charge density between 0.2 C/m{sup 3} and ∼2 C/m{sup 3}. This transition is consistent with a change from low mobility charge transport to charge transport in the form of pulses with a mobility orders of magnitude higher that has been observed in several insulating polymers.
Symmetry-broken local-density approximation for one-dimensional systems
NASA Astrophysics Data System (ADS)
Rogers, Fergus J. M.; Ball, Caleb J.; Loos, Pierre-François
2016-06-01
Within density-functional theory, the local-density approximation (LDA) correlation functional is typically built by fitting the difference between the near-exact and Hartree-Fock (HF) energies of the uniform electron gas (UEG), together with analytic perturbative results from the high- and low-density regimes. Near-exact energies are obtained by performing accurate diffusion Monte Carlo calculations, while HF energies are usually assumed to be the Fermi fluid HF energy. However, it has been known since the seminal work of A. W. Overhauser [Phys. Rev. Lett. 3, 414 (1959), 10.1103/PhysRevLett.3.414; Phys. Rev. 128, 1437 (1962), 10.1103/PhysRev.128.1437] that one can obtain lower, symmetry-broken (SB) HF energies at any density. Here, we have computed the SBHF energies of the one-dimensional UEG and constructed a SB version of the LDA (SBLDA) from the results. We compare the performance of the LDA and SBLDA functionals when applied to one-dimensional systems, including atoms and molecules. Generalization to higher dimensions is also discussed.
Richardson, E.A.; Hill, S.E.; Mitchell, R.; Pearce, J.; Shortt, N.K.
2015-01-01
Alcohol consumption may be influenced by the local alcohol retailing environment. This study is the first to examine neighbourhood alcohol outlet availability (on- and off-sales outlets) and alcohol-related health outcomes in Scotland. Alcohol-related hospitalisations and deaths were significantly higher in neighbourhoods with higher outlet densities, and off-sales outlets were more important than on-sales outlets. The relationships held for most age groups, including those under the legal minimum drinking age, although were not significant for the youngest legal drinkers (18–25 years). Alcohol-related deaths and hospitalisations were higher in more income-deprived neighbourhoods, and the gradient in deaths (but not hospitalisations) was marginally larger in neighbourhoods with higher off-sales outlet densities. Efforts to reduce alcohol-related harm should consider the potentially important role of the alcohol retail environment. PMID:25840352
Uniform electron gases. II. The generalized local density approximation in one dimension
Loos, Pierre-François Ball, Caleb J.; Gill, Peter M. W.
2014-05-14
We introduce a generalization (gLDA) of the traditional Local Density Approximation (LDA) within density functional theory. The gLDA uses both the one-electron Seitz radius r{sub s} and a two-electron hole curvature parameter η at each point in space. The gLDA reduces to the LDA when applied to the infinite homogeneous electron gas but, unlike the LDA, it is also exact for finite uniform electron gases on spheres. We present an explicit gLDA functional for the correlation energy of electrons that are confined to a one-dimensional space and compare its accuracy with LDA, second- and third-order Møller-Plesset perturbation energies, and exact calculations for a variety of inhomogeneous systems.
Evolution of the local packing density in a sheared granular material
NASA Astrophysics Data System (ADS)
Umbanhowar, Paul; van Hecke, Martin; Sakaie, Ken
2005-11-01
The local particle packing density, η, in a bed of poppy seeds sheared in a vertical, split-bottom cylindrical container is measured using magnetic resonance imaging. Wide shear zones away from the wall are generated when a thin concentric disk at the bottom of the cylinder, and with radius less than the cylinder radius, is rotated slowly. Experiments reveal that, initially, a shear band forms at the outer edge of the disk which decreases in radius with decreasing depth. Material near the shear zone dilates with a corresponding decrease in η of about 15%. The radial extent of the dilated region increases approximately logarithmically with increasing rotation in shallow layers. In relatively deep layers, the shear zone is at first entirely below the free surface, but with further rotation grows vertically creating a low η core. We discuss the relation between the previously reported universal velocity profiles across the shear zone and the spatial and temporal evolution of the packing density.
Relativistic Coulomb excitation within the time dependent superfluid local density approximation
Stetcu, I.; Bertulani, C. A.; Bulgac, A.; Magierski, P.; Roche, K. J.
2015-01-06
Within the framework of the unrestricted time-dependent density functional theory, we present for the first time an analysis of the relativistic Coulomb excitation of the heavy deformed open shell nucleus ^{238}U. The approach is based on the superfluid local density approximation formulated on a spatial lattice that can take into account coupling to the continuum, enabling self-consistent studies of superfluid dynamics of any nuclear shape. We compute the energy deposited in the target nucleus as a function of the impact parameter, finding it to be significantly larger than the estimate using the Goldhaber-Teller model. The isovector giant dipole resonance, the dipole pygmy resonance, and giant quadrupole modes are excited during the process. As a result, the one-body dissipation of collective dipole modes is shown to lead a damping width Γ↓≈0.4 MeV and the number of preequilibrium neutrons emitted has been quantified.
Richardson, E A; Hill, S E; Mitchell, R; Pearce, J; Shortt, N K
2015-05-01
Alcohol consumption may be influenced by the local alcohol retailing environment. This study is the first to examine neighbourhood alcohol outlet availability (on- and off-sales outlets) and alcohol-related health outcomes in Scotland. Alcohol-related hospitalisations and deaths were significantly higher in neighbourhoods with higher outlet densities, and off-sales outlets were more important than on-sales outlets. The relationships held for most age groups, including those under the legal minimum drinking age, although were not significant for the youngest legal drinkers (18-25 years). Alcohol-related deaths and hospitalisations were higher in more income-deprived neighbourhoods, and the gradient in deaths (but not hospitalisations) was marginally larger in neighbourhoods with higher off-sales outlet densities. Efforts to reduce alcohol-related harm should consider the potentially important role of the alcohol retail environment. PMID:25840352
The dipole moment of the spin density as a local indicator for phase transitions
Schmitz, D.; Schmitz-Antoniak, C.; Warland, A.; Darbandi, M.; Haldar, S.; Bhandary, S.; Eriksson, O.; Sanyal, B.; Wende, H.
2014-01-01
The intra-atomic magnetic dipole moment - frequently called 〈Tz〉 term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe2+ and Fe3+ sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry. PMID:25041757
Jeans Analysis of the Galactic Thick Disk and the Local Dark Matter Density
NASA Astrophysics Data System (ADS)
Sánchez-Salcedo, F. J.; Flynn, Chris; de Diego, J. A.
2016-01-01
Dynamical estimates of the mass surface density at the solar radius can be made up to a height of 4 kpc using thick disk stars as tracers of the potential. We investigate why different Jeans estimators of the local surface density lead to puzzling and conflicting results. Using the Jeans equations, we compute the vertical (Fz) and radial (FR) components of the gravitational force, as well as Γ(z), which is defined as {{Γ }}\\equiv \\partial {V}{{c}}2/\\partial R, with {V}{{c}}2\\equiv -R{F}R. If we assume that the thick disk does not flare and that all the components of the velocity dispersion tensor of the thick disk have a uniform radial scalelength of 3.5 kpc, Γ takes implausibly large negative values when using the currently available kinematical data of the thick disk. This implies that the input parameters or the model assumptions must be revised. We have explored, using a simulated thick disk, the impact of the assumption that the scalelengths of the density and velocity dispersions do not depend on the vertical height z above the midplane. In the absence of any information about how these scale radii depend on z, we define a different strategy. By using a parameterized Galactic potential, we find that acceptable fits to Fz, FR, and Γ are obtained for a flaring thick disk and a spherical dark matter (DM) halo with a local density ≳0.0064 M⊙ pc-3. Disk-like DM distributions may be also compatible with the current data of the thick disk. A precise measurement of Γ at the midplane could be very useful for discriminating between models.
Existence of minimizers for Kohn-Sham within the local spin density approximation
NASA Astrophysics Data System (ADS)
Gontier, David
2015-01-01
The purpose of this article is to extend the work by Anantharaman and Cancès (2009 Ann. Inst. Henri Poincaré (C) 26 2425-55) and prove the existence of minimizers for the spin-polarized Kohn-Sham model in the presence of a magnetic field within the local spin density approximation. We show that for any magnetic field that vanishes at infinity, the existence of minimizers is ensured for neutral or positively charged systems. The proof relies on classical concentration-compactness techniques.
Local-density approximation study of p-Si/ n-Si nanoscale junctions
NASA Astrophysics Data System (ADS)
Zavodinsky, V. G.; Kuyanov, I. A.
1996-09-01
We have performed a first-principles local-density cluster investigation of nanoscale p-Si/ n-Si junctions. Al and P atoms were used as dopants and Al-P distances were of order a few Ångstroms. The thermoemission current-voltage characteristics were calculated in addition to the electronic structure. It was shown that a rectifying nanoscale p-njunction can be formed in silicon if the distance between donor and acceptor atoms is not too small (about 1 nm).
Staggered Local Density of States around the Vortex in Underdoped Cuprates
Kishine, Jun-ichiro; Lee, Patrick A.; Wen, Xiao-Gang
2001-06-04
We have studied a single vortex with the staggered flux (SF) core based on the SU(2) slave-boson theory of high T{sub c} superconductors. We find that, whereas the center in the vortex core is a SF state, as one moves away from the core center a correlated staggered modulation of the hopping amplitude {chi} and pairing amplitude {Delta} becomes predominant. We predict that in this region the local density of states exhibits staggered modulation when measured on the bonds, which may be directly detected by STM experiments.
Electron affinities for rare gases and some actinides from local-spin-density-functional theory
Guo, Y.; Wrinn, M.C.; Whitehead, M.A. )
1989-12-01
The negative ions of the rare gases (He, Ne, Ar, Kr, Xe, and Rn) and some actinides (Pu, Am, Bk, Cf, and Es) have been calculated self-consistently by the generalized exchange local-spin-density-functional theory with self-interaction correction and correlation. The electron affinities were obtained as the differences between the statistical total energies of the negative ions and neutral atoms; the electron affinities were positive around several millirydbergs. Consequently, the negative ions are predicted stable for the rare gases and actinides.
NASA Astrophysics Data System (ADS)
Zachary, Chase E.; Torquato, Salvatore
2011-05-01
We provide numerical constructions of one-dimensional hyperuniform many-particle distributions that exhibit unusual clustering and asymptotic local number density fluctuations growing more slowly than the volume of an observation window but faster than the surface area. Hyperuniformity, defined by vanishing infinite-wavelength local density fluctuations, provides a quantitative metric of global order within a many-particle configuration and signals the onset of an “inverted” critical point in which the direct correlation function becomes long ranged. By targeting a specified form of the structure factor at small wavenumbers (S(k)~kα for 0<α<1) using collective density variables, we are able to tailor the form of asymptotic local density fluctuations while simultaneously measuring the effect of imposing weak and strong constraints on the available degrees of freedom within the system. This procedure is equivalent to finding the (possibly disordered) classical ground state of an interacting many-particle system with up to four-body interactions. Even in one dimension, the long-range effective interactions induce clustering and nontrivial phase transitions in the resulting ground-state configurations. We provide an analytical connection between the fraction of constrained degrees of freedom within the system and the disorder-order phase transition for a class of target structure factors by examining the realizability of the constrained contribution to the pair correlation function. Our results explicitly demonstrate that disordered hyperuniform many-particle ground states, and therefore also point distributions, with substantial clustering can be constructed. We directly relate the local coordination structure of our point patterns to the distribution of the void space external to the particles, and we provide a scaling argument for the configurational entropy (analogous to spin-frustated system) of the disordered ground states. By emphasizing the intimate
NASA Astrophysics Data System (ADS)
Stankov, S. M.; Warnant, R.; Stegen, K.
2009-04-01
The purpose of the LIEDR (Local Ionospheric Electron Density Reconstruction) system is to acquire and process data from simultaneous ground-based GNSS TEC and digital ionosonde measurements, and subsequently to deduce the vertical electron density distribution in the local ionosphere. LIEDR is primarily designed to operate in real time for service applications, and, if sufficient data from solar and geomagnetic observations are available, to provide short-term forecast as well. For research applications and further development of the system, a post-processing mode of operation is also envisaged. In essence, the reconstruction procedure consists in the following. The high-precision ionosonde measurements are used for directly obtaining the bottom part of the electron density profile. The ionospheric profiler for the lower side (i.e. below the density peak height, hmF2) is based on the Epstein layer functions using the known values of the critical frequencies, foF2 and foE, and the propagation factor, M3000F2. The corresponding bottom-side part of the total electron content is calculated from this profile and is then subtracted from the GPS TEC value in order to obtain the unknown portion of the TEC in the upper side (i.e. above the hmF2). Ionosonde data, together with the simultaneously-measured TEC and empirically obtained O+/H+ ion transition level values, are all required for the determination of the topside electron density scale height. The topside electron density is considered as a sum of the constituent oxygen and hydrogen ion densities with unknown vertical scale heights. The latter are calculated by solving a system of transcendental equations that arise from the incorporation of a suitable ionospheric profiler (Chapman, Epstein, or Exponential) into formulae describing ionospheric conditions (plasma quasi-neutrality, ion transition level). Once the topside scale heights are determined, the construction of the vertical electron density distribution in the
NASA Astrophysics Data System (ADS)
Singh, D.; Clougherty, D. P.; MacLaren, J. M.; Albers, R. C.; Wang, C. S.
1991-10-01
The influence of local-spin-dependent correlation effects on the predicted stable ground-state phase of iron is reexamined with use of general-potential linearized augmented-plane-wave calculations. Differences in the form of the Vosko-Wilk-Nusair (VWN) local-spin-density functional used in previous studies are noted, since in previous studies significant additional approximations were made with respect to those of Vosko, Wilk, and Nusan [Can. J. Phys. 58, 1200 (1980)] and of MacLaren, Clougherty, and Albers [Phys. Rev. B 42, 3205 (1990)]. While the results of previous linear muffin-tin orbital calculations using the VWN functional predict a bcc ferromagnetic ground state, the present calculations show that the VWN spin-correlation effects fail to stabilize a bcc ground state. Considerable sensitivity to the form of the spin interpolation is found.
Self-interaction-corrected local-spin-density calculations for rare earth materials
Svane, A.; Temmerman, W.M.; Szotek, Z.; Laegsgaard, J.; Winter, H.
2000-04-20
The ab initio self-interaction-corrected (SIC) local-spin-density (LSD) approximation is discussed with emphasis on the ability to describe localized f-electron states in rare earth solids. Two methods for minimizing the SIC-LSD total energy functional are discussed, one using a unified Hamiltonian for all electron states, thus having the advantages of Bloch's theorem, the other one employing an iterative scheme in real space. Results for cerium and cerium compounds as well as other rare earths are presented. For the cerium compounds the onset of f-electron delocalization can be accurately described, including the intricate isostructural phase transitions in elemental cerium and CeP. In Pr and Sm the equilibrium lattice constant and zero temperature equation of state is greatly improved in comparison with the LSD results.
Navarrete-López, Alejandra M; Garza, Jorge; Vargas, Rubicelia
2008-03-14
In this report, it is shown that the Kohn-Sham (KS) kinetic energy density (KED) contains the average local electrostatic potential (ALEP) and the average local ionization energy (ALIE); the shell structure in atomic systems is presented as one application of the KS-KED. By writing the KS-KED from the KS equations, this quantity was divided in three contributions: orbital, Coulomb, and exchange correlation. By studying several closed and open shell atoms, the shell structure was established by the maxima presented by the Coulomb contribution and the minima in the orbital contribution of the KS-KED. The exchange-correlation contribution to the KS-KED does not show maxima or minima, but this quantity shows bumps where the division between shells is expected. The results obtained in this work were compared with other shell structure indicators such as the electron localization function, the ALEP, the ALIE, and the radial distribution function. The most important result in this work is related to the fact that even when the ALEP and the ALIE functions were built with different arguments to each other, they are contained in the KS-KED. In this way, the KS-KED shows its importance to reveal the electron localization in atomic systems. PMID:18345880
Carrara, Francesco; Rinaldo, Andrea; Holyoak, Marcel
2011-01-01
Metacommunity theory poses that the occurrence and abundance of species is a product of local factors, including disturbance, and regional factors, like dispersal among patches. While metacommunity ideas have been broadly tested there is relatively little work on metacommunities subject to disturbance. We focused on how localized disturbance and dispersal interact to determine species composition in metacommunities. Experiments conducted in simple two-patch habitats containing eight protozoa and rotifer species tested how dispersal altered community composition in both communities that were disturbed and communities that connected to refuge communities not subject to disturbance. While disturbance lowered population densities, in disturbed patches connected to undisturbed patches this was ameliorated by immigration. Furthermore, species with high dispersal abilities or growth rates showed the fastest post-disturbance recovery in presence of immigration. Connectivity helped to counteract the negative effect of disturbances on local populations, allowing mass-effect-driven dispersal of individuals from undisturbed to disturbed patches. In undisturbed patches, however, local population sizes were not significantly reduced by emigration. The absence of a cost of dispersal for undisturbed source populations is consistent with a lack of complex demography in our system, such as age- or sex-specific emigration. Our approach provides an improved way to separate components of population growth from organisms' movement in post-disturbance recovery of (meta)communities. Further studies are required in a variety of ecosystems to investigate the transient dynamics resulting from disturbance and dispersal. PMID:21559336
Energy Densities in the Strong-Interaction Limit of Density Functional Theory.
Mirtschink, André; Seidl, Michael; Gori-Giorgi, Paola
2012-09-11
We discuss energy densities in the strong-interaction limit of density functional theory, deriving an exact expression within the definition (gauge) of the electrostatic potential of the exchange-correlation hole. Exact results for small atoms and small model quantum dots (Hooke's atoms) are compared with available approximations defined in the same gauge. The idea of a local interpolation along the adiabatic connection is discussed, comparing the energy densities of the Kohn-Sham, the physical, and the strong-interacting systems. We also use our results to analyze the local version of the Lieb-Oxford bound, widely used in the construction of approximate exchange-correlation functionals. PMID:26605721
Adiabatic connection at negative coupling strengths
Seidl, Michael; Gori-Giorgi, Paola
2010-01-15
The adiabatic connection of density functional theory (DFT) for electronic systems is generalized here to negative values of the coupling strength alpha (with attractive electrons). In the extreme limit alpha->-infinity a simple physical solution is presented and its implications for DFT (as well as its limitations) are discussed. For two-electron systems (a case in which the present solution can be calculated exactly), we find that an interpolation between the limit alpha->-infinity and the opposite limit of infinitely strong repulsion (alpha->+infinity) yields a rather accurate estimate of the second-order correlation energy E{sub c}{sup GL2}[rho] for several different densities rho, without using virtual orbitals. The same procedure is also applied to the Be isoelectronic series, analyzing the effects of near degeneracy.
Local interstellar cloud electron density from magnesium and sodium ionization: a comparison.
NASA Astrophysics Data System (ADS)
Lallement, R.; Ferlet, R.
1997-08-01
The ambient interstellar plasma density (i.e. the plasma density of the interstellar medium surrounding the Sun) directly governs the structure and the size of our heliosphere. Information on this density can be derived from the ionization states of the interstellar species which can be detected in absorption along the paths to the nearby stars, and which can be shown to belong to the Local Interstellar Cloud (LIC). Echelle spectra around the resonance lines of neutral and singly ionized magnesium have been obtained for the nearby star δ Cas with the Goddard High-Resolution Spectrograph (GHRS) on board the Hubble Space Telescope. While apparently a unique velocity component (a unique cloudlet) is detected in both lines of the MgII λλ2800 resonance doublet, at the expected Doppler shift for the LIC, an extremely small λλ2853 Mg line is also detected at a Doppler shift compatible with the LIC motion, allowing a measurement of the LIC MgII/MgI ratio, here found to be 400 (-130,+190). This ratio implies a mean electron density of about 0.28 (-0.14, +0.34)cm^-3^ along this line-of-sight, if equilibrium conditions prevail, and if T=7000K, when using the most recent recombination and charge-exchange rates. This MgII/MgI ratio is larger than for Sirius (R=~220), which lies at 110^o^ from δ Cas, providing some evidence for an ionization gradient in the local cloud. Such an electron density implies a surprisingly large ionization degree, and the upper range of the interval is incompatible with the minimum size of our heliosphere. A second and independent way to derive the electron density along the path to δ Cas uses the simplicity of the LIC geometry in the sky region surrounding the star, which allows an estimate of the H column-density to the star, as well as previous ground-based CaII data, and the measured NaI/CaII ratio and calcium depletion in the LIC. The resulting most probable electron density at 7000K, 0.05cm^-3^, provides a new evidence for a significant
The flat Grothendieck-Riemann-Roch theorem without adiabatic techniques
NASA Astrophysics Data System (ADS)
Ho, Man-Ho
2016-09-01
In this paper we give a simplified proof of the flat Grothendieck-Riemann-Roch theorem. The proof makes use of the local family index theorem and basic computations of the Chern-Simons form. In particular, it does not involve any adiabatic limit computation of the reduced eta-invariant.
Pressure Oscillations in Adiabatic Compression
ERIC Educational Resources Information Center
Stout, Roland
2011-01-01
After finding Moloney and McGarvey's modified adiabatic compression apparatus, I decided to insert this experiment into my physical chemistry laboratory at the last minute, replacing a problematic experiment. With insufficient time to build the apparatus, we placed a bottle between two thick textbooks and compressed it with a third textbook forced…
Adiabatic dynamics of magnetic vortices
NASA Astrophysics Data System (ADS)
Papanicolaou, N.
1994-03-01
We formulate a reasonably detailed adiabatic conjecture concerning the dynamics of skew deflection of magnetic vortices in a field gradient, which is expected to be valid at sufficiently large values of the winding number. The conjecture is consistent with the golden rule used to describe the dynamics of realistic magnetic bubbles and is verified here numerically within the 2-D isotropic Heisenberg model.
Power-law singularity in the local density of states due to the point defect in graphene
NASA Astrophysics Data System (ADS)
Huang, Wen-Min; Tang, Jian-Ming; Lin, Hsiu-Hau
2009-09-01
Defects in graphene give rise to zero modes that are often related to the sharp peak in the local density of states near the defect site. Here we solved all zero modes induced by a single defect in the finite-size graphene and show that their contributions to the local density of states vanish in the thermodynamic limit. Instead, lots of resonant states emerge at low energies and eventually lead to a power-law singularity in the local density of states. Our findings show that the impurity problem in graphene should be treated as a collective phenomenon rather than a single impurity state.
Floral herbivory increases with inflorescence size and local plant density in Digitalis purpurea
NASA Astrophysics Data System (ADS)
Sletvold, Nina; Grindeland, John M.
2008-07-01
Insect herbivores search for their host plants in heterogeneous environments, and the efficiency of host location may be influenced by plant architecture and abundance. In this study, we ask how plant and habitat characteristics traditionally thought to attract pollinators are related to attack rates by floral herbivores. Patterns of floral herbivory by the moth larva Eupithecia pulchellata were studied in relation to inflorescence size and local plant density in two years in a natural population of the facultative biennial Digitalis purpurea. Overall levels of herbivory were low, 84% of the infested plants lost less than 10% of their flowers. Only 9% of the plants lost more than 20% of their flowers. Probability of herbivory at the plant level increased strongly with inflorescence height, and it was considerably higher in dense patches compared to sparse ones. There was no effect of local plant density on the functional relationship between inflorescence size and probability of herbivory. Both number and proportion of damaged flowers per plant increased with inflorescence height. The results suggest that E. pulchellata is attracted to dense patches and large individuals of D. purpurea, and that negative effects of herbivory increase with plant size. This implies diminishing returns for investment in more flowers in D. purpurea, and indicates that herbivory may select for smaller flowering size and flower number in this monocarpic species.
Global hybrids from the semiclassical atom theory satisfying the local density linear response.
Fabiano, Eduardo; Constantin, Lucian A; Cortona, Pietro; Della Sala, Fabio
2015-01-13
We propose global hybrid approximations of the exchange-correlation (XC) energy functional which reproduce well the modified fourth-order gradient expansion of the exchange energy in the semiclassical limit of many-electron neutral atoms and recover the full local density approximation (LDA) linear response. These XC functionals represent the hybrid versions of the APBE functional [Phys. Rev. Lett. 2011, 106, 186406] yet employing an additional correlation functional which uses the localization concept of the correlation energy density to improve the compatibility with the Hartree-Fock exchange as well as the coupling-constant-resolved XC potential energy. Broad energetic and structural testing, including thermochemistry and geometry, transition metal complexes, noncovalent interactions, gold clusters and small gold-molecule interfaces, as well as an analysis of the hybrid parameters, show that our construction is quite robust. In particular, our testing shows that the resulting hybrid, including 20% of Hartree-Fock exchange and named hAPBE, performs remarkably well for a broad palette of systems and properties, being generally better than popular hybrids (PBE0 and B3LYP). Semiempirical dispersion corrections are also provided. PMID:26574210
Transitionless driving on adiabatic search algorithm
Oh, Sangchul; Kais, Sabre
2014-12-14
We study quantum dynamics of the adiabatic search algorithm with the equivalent two-level system. Its adiabatic and non-adiabatic evolution is studied and visualized as trajectories of Bloch vectors on a Bloch sphere. We find the change in the non-adiabatic transition probability from exponential decay for the short running time to inverse-square decay in asymptotic running time. The scaling of the critical running time is expressed in terms of the Lambert W function. We derive the transitionless driving Hamiltonian for the adiabatic search algorithm, which makes a quantum state follow the adiabatic path. We demonstrate that a uniform transitionless driving Hamiltonian, approximate to the exact time-dependent driving Hamiltonian, can alter the non-adiabatic transition probability from the inverse square decay to the inverse fourth power decay with the running time. This may open up a new but simple way of speeding up adiabatic quantum dynamics.
Transitionless driving on adiabatic search algorithm
NASA Astrophysics Data System (ADS)
Oh, Sangchul; Kais, Sabre
2014-12-01
We study quantum dynamics of the adiabatic search algorithm with the equivalent two-level system. Its adiabatic and non-adiabatic evolution is studied and visualized as trajectories of Bloch vectors on a Bloch sphere. We find the change in the non-adiabatic transition probability from exponential decay for the short running time to inverse-square decay in asymptotic running time. The scaling of the critical running time is expressed in terms of the Lambert W function. We derive the transitionless driving Hamiltonian for the adiabatic search algorithm, which makes a quantum state follow the adiabatic path. We demonstrate that a uniform transitionless driving Hamiltonian, approximate to the exact time-dependent driving Hamiltonian, can alter the non-adiabatic transition probability from the inverse square decay to the inverse fourth power decay with the running time. This may open up a new but simple way of speeding up adiabatic quantum dynamics.
Transitionless driving on adiabatic search algorithm.
Oh, Sangchul; Kais, Sabre
2014-12-14
We study quantum dynamics of the adiabatic search algorithm with the equivalent two-level system. Its adiabatic and non-adiabatic evolution is studied and visualized as trajectories of Bloch vectors on a Bloch sphere. We find the change in the non-adiabatic transition probability from exponential decay for the short running time to inverse-square decay in asymptotic running time. The scaling of the critical running time is expressed in terms of the Lambert W function. We derive the transitionless driving Hamiltonian for the adiabatic search algorithm, which makes a quantum state follow the adiabatic path. We demonstrate that a uniform transitionless driving Hamiltonian, approximate to the exact time-dependent driving Hamiltonian, can alter the non-adiabatic transition probability from the inverse square decay to the inverse fourth power decay with the running time. This may open up a new but simple way of speeding up adiabatic quantum dynamics. PMID:25494733
Characterization of adiabatic shear bands in AM60B magnesium alloy under ballistic impact
Zou, D.L.; Zhen, L. Xu, C.Y.; Shao, W.Z.
2011-05-15
Adiabatic shear bands in Mg alloy under ballistic impact at a velocity of 0.5 km.s{sup -1} were characterized by means of optical microscope, scanning electron microscope, transmission electron microscope and indenter technique. The results show that adiabatic shear bands were formed around the impacted crater, and the deformed and transformed bands were distinguished by etching colors in metallographic observation. TEM observation shows that the deformed bands were composed of the elongated grains and high density dislocations, while the transformed bands composed of the ultrafine and equiaxed grains were confirmed. In initial stage, the severe localized plastic deformation led to the formation of elongated grains in the deformed bands. With localized strain increasing, the severe localized deformation assisted with the plastic temperature rising led to the severe deformation grains evolved into the ultrafine and equiaxed grains, while the deformed bands were developed into transformed bands. The formation of the ultrafine and equiaxed grains in the transformed bands should be attributed to the twinning-induced rotational dynamic recrystallization mechanism. High microhardness in the bands was obtained because of the strain hardening, grain refining and content concentration. - Research Highlights: {yields} Deformed and transformed bands are found in Mg alloy under ballistic impact. {yields} The microstructures in the deformed and transformed bands are characterized. {yields} The evolution process of the microstructure in the bands is discussed.
Studies in Chaotic adiabatic dynamics
Jarzynski, C.
1994-01-01
Chaotic adiabatic dynamics refers to the study of systems exhibiting chaotic evolution under slowly time-dependent equations of motion. In this dissertation the author restricts his attention to Hamiltonian chaotic adiabatic systems. The results presented are organized around a central theme, namely, that the energies of such systems evolve diffusively. He begins with a general analysis, in which he motivates and derives a Fokker-Planck equation governing this process of energy diffusion. He applies this equation to study the {open_quotes}goodness{close_quotes} of an adiabatic invariant associated with chaotic motion. This formalism is then applied to two specific examples. The first is that of a gas of noninteracting point particles inside a hard container that deforms slowly with time. Both the two- and three-dimensional cases are considered. The results are discussed in the context of the Wall Formula for one-body dissipation in nuclear physics, and it is shown that such a gas approaches, asymptotically with time, an exponential velocity distribution. The second example involves the Fermi mechanism for the acceleration of cosmic rays. Explicit evolution equations are obtained for the distribution of cosmic ray energies within this model, and the steady-state energy distribution that arises when this equation is modified to account for the injection and removal of cosmic rays is discussed. Finally, the author re-examines the multiple-time-scale approach as applied to the study of phase space evolution under a chaotic adiabatic Hamiltonian. This leads to a more rigorous derivation of the above-mentioned Fokker-Planck equation, and also to a new term which has relevance to the problem of chaotic adiabatic reaction forces (the forces acting on slow, heavy degrees of freedom due to their coupling to light, fast chaotic degrees).
Non Adiabatic Evolution of Elliptical Galaxies by Dynamical Friction
NASA Astrophysics Data System (ADS)
Arena, S. E.; Bertin, G.; Liseikina, T.; Pegoraro, F.
2007-05-01
Many astrophysical problems, ranging from structure formation in cosmology to dynamics of elliptical galaxies, refer to slow processes of evolution of essentially collisionless self-gravitating systems. In order to determine the relevant quasi-equilibrium configuration at time t from given initial conditions, it is often argued that such slow evolution may be approximated in terms of adiabatic evolution, for the calculation of which efficient semi--analytical techniques are available. Here we focus on the slow process of evolution, induced by dynamical friction of a host stellar system on a minority component of "satellites", to determine to what extent an adiabatic description might be applied. The study is realized by means of N--body simulations of the evolution of the total system (the stellar system plus the minority component), in a controlled numerical environment. In particular, we compare the evolution from initial to final configurations of the system subject to dynamical friction with that of the same system evolved adiabatically (in the absence of dynamical friction). We consider two classes of galaxy models characterized by significantly different density and pressure anisotropy profiles. We demonstrate that, for the examined process, the evolution driven by dynamical friction is significantly different from the adiabatic case, not only quantitatively, but also qualitatively. The two classes of galaxy models considered in this investigation exhibit generally similar trends in evolution, with one exception: concentrated models reach a final total density profile, in the internal region, shallower than the initial one, while galaxy models with a broad core show the opposite behaviour. The evolution of elliptical galaxies induced by dynamical friction is a slow process but it is not adiabatic. The results of our investigation should be taken as a warning against the indiscriminate use of adiabatic growth prescriptions in studies of the structure of
Adiabatic cooling of solar wind electrons
NASA Technical Reports Server (NTRS)
Sandbaek, Ornulf; Leer, Egil
1992-01-01
In thermally driven winds emanating from regions in the solar corona with base electron densities of n0 not less than 10 exp 8/cu cm, a substantial fraction of the heat conductive flux from the base is transfered into flow energy by the pressure gradient force. The adiabatic cooling of the electrons causes the electron temperature profile to fall off more rapidly than in heat conduction dominated flows. Alfven waves of solar origin, accelerating the basically thermally driven solar wind, lead to an increased mass flux and enhanced adiabatic cooling. The reduction in electron temperature may be significant also in the subsonic region of the flow and lead to a moderate increase of solar wind mass flux with increasing Alfven wave amplitude. In the solar wind model presented here the Alfven wave energy flux per unit mass is larger than that in models where the temperature in the subsonic flow is not reduced by the wave, and consequently the asymptotic flow speed is higher.
NASA Astrophysics Data System (ADS)
Mintmire, J. W.; White, C. T.
1987-03-01
We report the results of a computational study of the dimerization of the all-trans-polyacetylene chain within the local-density-func- tional formalism employing the Gáspár-Kohn-Sham exchange-correlation potential. Our calculated bond alternation at equilibrium is less than experimentally implied by roughly a factor of 3. Evidence is presented that suggests that this underestimation of dimerization is closely connected with the much discussed band-gap problem in local-density-functional theory.
Li, Wei; Chen, Xiaolong; Wang, Lin; He, Yuheng; Wu, Zefei; Cai, Yuan; Zhang, Mingwei; Wang, Yang; Han, Yu; Lortz, Rolf W.; Zhang, Zhao-Qing; Sheng, Ping; Wang, Ning
2013-01-01
We demonstrate that fluctuations of the local density of states (LDOS) in strongly disordered graphene play an important role in determining the quantum capacitance of the top-gate graphene devices. Depending on the strength of the disorder induced by metal-cluster decoration, the measured quantum capacitance of disordered graphene can dramatically decrease in comparison with pristine graphene. This is opposite to the common belief that quantum capacitance should increase with disorder. To explain this counterintuitive behavior, we present a two-parameter model which incorporates both the non-universal power law behavior for the ADOS and a lognormal distribution of LDOS. We find excellent quantitative agreements between the model and measured quantum capacitance for three disordered samples in a wide range of Fermi energies. Thus, by measuring the quantum capacitance, we can simultaneously determine the ADOS and its fluctuations. It is the LDOS fluctuations that cause the dramatic reduction of the quantum capacitance.
Vallée, R A L; Tomczak, N; Vancso, G J; Kuipers, L; van Hulst, N F
2005-03-15
We investigated the nanometer scale mobility of polymers in the glassy state by monitoring the dynamics of embedded single fluorophores. Recently we reported on fluorescence lifetime fluctuations which reflect the segmental rearrangement dynamics of the polymer in the surroundings of the single molecule probe. Here we focus on the nature of these fluorescence lifetime fluctuations. First the potential role of quenching and molecular conformational changes is discussed. Next we concentrate on the influence of the radiative density of states on the spontaneous emission of individual dye molecules embedded in a polymer. To this end we present a theory connecting the effective-medium theory to a cell-hole model, originating from the Simha-Somcynsky free-volume theory. The relation between the derived distributions of free volume and fluorescence lifetime allows one to determine the number of segments involved in the local rearrangement directly from experimental data. Results for two different polymers as a function of temperature are presented. PMID:15836240
Liang, Xiangdong; Johnson, Steven G
2013-12-16
We present a technique for large-scale optimization of optical microcavities based on the frequency-averaged local density of states (LDOS), which circumvents computational difficulties posed by previous eigenproblem-based formulations and allows us to perform full topology optimization of three-dimensional (3d) leaky cavity modes. We present theoretical results for both 2d and fully 3d computations in which every pixel of the design pattern is a degree of freedom ("topology optimization"), e.g. for lithographic patterning of dielectric slabs in 3d. More importantly, we argue that such optimization techniques can be applied to design cavities for which (unlike silicon-slab single-mode cavities) hand designs are difficult or unavailable, and in particular we design minimal-volume multi-mode cavities (e.g. for nonlinear frequency-conversion applications). PMID:24514656
Determination of Local Densities in Accreted Ice Samples Using X-Rays and Digital Imaging
NASA Technical Reports Server (NTRS)
Broughton, Howard; Sims, James; Vargas, Mario
1996-01-01
At the NASA Lewis Research Center's Icing Research Tunnel ice shapes, similar to those which develop in-flight icing conditions, were formed on an airfoil. Under cold room conditions these experimental samples were carefully removed from the airfoil, sliced into thin sections, and x-rayed. The resulting microradiographs were developed and the film digitized using a high resolution scanner to extract fine detail in the radiographs. A procedure was devised to calibrate the scanner and to maintain repeatability during the experiment. The techniques of image acquisition and analysis provide accurate local density measurements and reveal the internal characteristics of the accreted ice with greater detail. This paper will discuss the methodology by which these samples were prepared with emphasis on the digital imaging techniques.
NASA Astrophysics Data System (ADS)
Mattsson, Ann E.; Wills, John M.
2013-03-01
The inability to computationally describe the physics governing the properties of actinides and their alloys is the poster child of failure of existing Density Functional Theory exchange-correlation functionals. The intricate competition between localization and delocalization of the electrons, present in these materials, exposes the limitations of functionals only designed to properly describe one or the other situation. We will discuss the manifestation of this competition in real materials and propositions on how to construct a functional able to accurately describe properties of these materials. I addition we will discuss both the importance of using the Dirac equation to describe the relativistic effects in these materials, and the connection to the physics of transition metal oxides. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Quantifying local density of optical states of nanorods by fluorescence lifetime imaging
Liu, Jing; Jiang, Xunpeng; Ishii, Satoshi; Shalaev, Vladimir; Irudayaraj, Joseph
2014-01-01
In this letter, we demonstrate a facile far-field approach to quantify the near-field local density of optical states (LDOS) of a nanorod using CdTe quantum dots (QDs) emitters tethered to the surface of nanorods as beacons for optical read-outs. Radiative decay rate was extracted to quantify the LDOS; our analysis indicates that the LDOS of the nanorod enhance both the radiative and nonradiative decay of QD, particularly radiative decay of QDs at the end of nanorod is enhanced by 1.17 times greater than that at the waist, while the nonradiative decay was uniformly enhanced over the nanorod. To the best of our knowledge, our effort constitutes the first to map the LDOS of a nanostructure via far-field method, to provide clarity on the interaction mechanism between emitters and the nanostructure, and to be potentially employed in the LDOS mapping of high-throughput nanostructures. PMID:25408619
Broadband enhancement of local density of states using silicon-compatible hyperbolic metamaterials
Wang, Yu; Inampudi, Sandeep; Capretti, Antonio; Sugimoto, Hiroshi; Fujii, Minoru; Dal Negro, Luca
2015-06-15
Light emitting silicon quantum dots by colloidal synthesis were uniformly spin-coated into a 20 nm-thick film and deposited atop a hyperbolic metamaterial of alternating TiN and SiO{sub 2} sub-wavelength layers. Using steady-state and time-resolved photoluminescence spectroscopy as a function of the emission wavelength in partnership with rigorous electromagnetic modeling of dipolar emission, we demonstrate enhanced Local Density of States and coupling to high-k modes in a broad spectral range. These findings provide an alternative approach for the engineering of novel Si-compatible broadband sources that leverage the control of radiative transitions in hyperbolic metamaterials and the flexibility of the widespread Si platform.
NASA Astrophysics Data System (ADS)
Magrakvelidze, Maia; Madjet, Mohamed; Chakraborty, Himadri
2016-05-01
We investigate Wigner-Smith (WS) time delays of the photoionization from various subshells of xenon using the time-dependent local density approximation (TDLDA) with the Leeuwen and Baerends exchange-correlation functional. At the 4d giant dipole resonance region as well as near all the Cooper minimum anti-resonances in 5p, 5s and 4d photoemissions, effects of electron correlations uniquely determine the shapes of the emission quantum phase. The Wigner-Smith time delay derived from this phase indicates significant variations as a function of energy. The results qualitatively support our TDLDA predictions at the fullerene plasmon region and at 3p Cooper minimum in argon, and should encourage attosecond measurements of Xe photoemission via two-photon interferometric techniques, such as RABITT. The work is supported by the NSF, USA.
NASA Astrophysics Data System (ADS)
Mariani, Davide; Guyennon, Nicolas; Maggioni, Margherita; Salerno, Franco; Romano, Emanuele
2015-04-01
Snowpack melting can represent a major contribution to the seasonal variability of the surface and ground water budget at basin scale: the snow pack, acting as a natural reservoir, stores water during the winter season and releases it during spring and summer. The radiative budget driving the melting process depends on numerous variables that may be affected by the ongoing climatic changes. As a result, a shift in time during the spring and summer discharge may significantly affect surface water management at basin scale. For this reason, a reliable model able to quantitatively describe the snow melting processes is very important also for management purposes. The estimation of snow melt rate requires a full energy (mass) balance snowpack assessment. The limited availability of necessary data often does not allow implementing a radiative (mass) balance model. As an alternative we propose here a simple methodology to reconstruct the daily snowmelt and associated melt rate function based only on solid precipitation, air mean temperature and snowpack depth measurements, while snow density observations are often missing. The model differentiates between the melting and the compaction processes based on a daily mean temperature threshold (i.e. above or below the freezing point) and the snowpack state. The snow pack is described as two-layer model, each of them considers its own depth and density. The first one is a fresh snow surface layer whose density is a constant parameter. It is modulated by the daily snowfall/melting budget or it can be compacted and embedded within the second layer. The second one is the ripe snow, whose density is a weighted average with depths of antecedent snowpack and possible first layer contribution. The two snow layers allow starting the fusion by the snowpack's top where the density is lower, while much water is released when the ripe snow starts melting during the late melting season. Finally, we estimate the associated degree-day and
NASA Astrophysics Data System (ADS)
Lim, S. P.; Sheng, D. N.
2016-07-01
A many-body localized (MBL) state is a new state of matter emerging in a disordered interacting system at high-energy densities through a disorder-driven dynamic phase transition. The nature of the phase transition and the evolution of the MBL phase near the transition are the focus of intense theoretical studies with open issues in the field. We develop an entanglement density matrix renormalization group (En-DMRG) algorithm to accurately target highly excited states for MBL systems. By studying the one-dimensional Heisenberg spin chain in a random field, we demonstrate the accuracy of the method in obtaining energy eigenstates and the corresponding statistical results of quantum states in the MBL phase. Based on large system simulations by En-DMRG for excited states, we demonstrate some interesting features in the entanglement entropy distribution function, which is characterized by two peaks: one at zero and another one at the quantized entropy S =ln2 with an exponential decay tail on the S >ln2 side. Combining En-DMRG with exact diagonalization simulations, we demonstrate that the transition from the MBL phase to the delocalized ergodic phase is driven by rare events where the locally entangled spin pairs develop power-law correlations. The corresponding phase diagram contains an intermediate or crossover regime, which has power-law spin-z correlations resulting from contributions of the rare events. We discuss the physical picture for the numerical observations in this regime, where various distribution functions are distinctly different from results deep in the ergodic and MBL phases for finite-size systems. Our results may provide new insights for understanding the phase transition in such systems.
Microscopic expression for heat in the adiabatic basis.
Polkovnikov, Anatoli
2008-11-28
We derive a microscopic expression for the instantaneous diagonal elements of the density matrix rho(nn)(t) in the adiabatic basis for an arbitrary time-dependent process in a closed Hamiltonian system. If the initial density matrix is stationary (diagonal) then this expression contains only squares of absolute values of matrix elements of the evolution operator, which can be interpreted as transition probabilities. We then derive the microscopic expression for the heat defined as the energy generated due to transitions between instantaneous energy levels. If the initial density matrix is passive [diagonal with rho(nn)(0) monotonically decreasing with energy] then the heat is non-negative in agreement with basic expectations of thermodynamics. Our findings also can be used for systematic expansion of various observables around the adiabatic limit. PMID:19113464
Robust adiabatic sum frequency conversion.
Suchowski, Haim; Prabhudesai, Vaibhav; Oron, Dan; Arie, Ady; Silberberg, Yaron
2009-07-20
We discuss theoretically and demonstrate experimentally the robustness of the adiabatic sum frequency conversion method. This technique, borrowed from an analogous scheme of robust population transfer in atomic physics and nuclear magnetic resonance, enables the achievement of nearly full frequency conversion in a sum frequency generation process for a bandwidth up to two orders of magnitude wider than in conventional conversion schemes. We show that this scheme is robust to variations in the parameters of both the nonlinear crystal and of the incoming light. These include the crystal temperature, the frequency of the incoming field, the pump intensity, the crystal length and the angle of incidence. Also, we show that this extremely broad bandwidth can be tuned to higher or lower central wavelengths by changing either the pump frequency or the crystal temperature. The detailed study of the properties of this converter is done using the Landau-Zener theory dealing with the adiabatic transitions in two level systems. PMID:19654679
Nonadiabatic quantum Liouville and master equations in the adiabatic basis
Jang, Seogjoo
2012-12-14
A compact form of nonadiabatic molecular Hamiltonian in the basis of adiabatic electronic states and nuclear position states is presented. The Hamiltonian, which includes both the first and the second derivative couplings, is Hermitian and thus leads to a standard expression for the quantum Liouville equation for the density operator. With the application of a projection operator technique, a quantum master equation for the diagonal components of the density operator is derived. Under the assumption that nuclear states are much more short ranged compared to electronic states and assuming no singularity, a semi-adiabatic approximation is invoked, which results in expressions for the nonadiabatic molecular Hamiltonian and the quantum Liouville equation that are much more amenable to advanced quantum dynamics calculation. The semi-adiabatic approximation is also applied to a resonance energy transfer system consisting of a donor and an acceptor interacting via Coulomb terms, and explicit detailed expressions for exciton-bath Hamiltonian including all the non-adiabatic terms are derived.
Equations for Adiabatic but Rotational Steady Gas Flows without Friction
NASA Technical Reports Server (NTRS)
Schaefer, Manfred
1947-01-01
This paper makes the following assumptions: 1) The flowing gases are assumed to have uniform energy distribution. ("Isoenergetic gas flows," that is valid with the same constants for the the energy equation entire flow.) This is correct, for example, for gas flows issuing from a region of constant pressure, density, temperature, end velocity. This property is not destroyed by compression shocks because of the universal validity of the energy law. 2) The gas behaves adiabatically, not during the compression shock itself but both before and after the shock. However, the adiabatic equation (p/rho(sup kappa) = C) is not valid for the entire gas flow with the same constant C but rather with an appropriate individual constant for each portion of the gas. For steady flows, this means that the constant C of the adiabatic equation is a function of the stream function. Consequently, a gas that has been flowing "isentropically",that is, with the same constant C of the adiabatic equation throughout (for example, in origination from a region of constant density, temperature, and velocity) no longer remains isentropic after a compression shock if the compression shock is not extremely simple (wedge shaped in a two-dimensional flow or cone shaped in a rotationally symmetrical flow). The solution of nonisentropic flows is therefore an urgent necessity.
Cs diffusion in local Taiwan laterite with different solution concentration, pH and packing density.
Wang, Tsing-Hai; Li, Ming-Hsu; Teng, Shi-Ping
2008-09-01
In this work we used an "in-diffusion" method to study the effects of pH, solution concentration and packing density on Cs diffusion by packing local Taiwan laterite (LTL) into modified capillary columns with 5mm diameter. These packed columns were first pre-equilibrated with synthetic groundwater (GW) for 3 weeks. The diffusion experiments were then carried out at ambient condition for 2 weeks. Our experimental results showed that the Cs diffusion profile fits Fick's second law very well in given experimental conditions, indicating the validity of modified capillary column method. Generally speaking, Cs diffusion in LTL decreases as the pH increases and as Cs concentration decreases. The apparent diffusion coefficient (D(a)) increases from 5.52 x 10(-12) (10(-7)M) to 2.18 x 10(-11) (10(-3)M)m(2)/s, while the effective diffusion coefficient (D(e)) shows slight variation as the Cs concentration changes. Both the derived D(a) and D(e) values decrease as the pH increases, implying that the diffusion mechanisms of Cs nuclide in alkaline and acid environment are different. In addition, our results show that Cs diffusion is unaffected by the given packing density, indicating the interlaminary space is not the major determinant of Cs adsorption and diffusion in LTL. PMID:18321721
Relativistic Coulomb excitation within the time dependent superfluid local density approximation
Stetcu, I.; Bertulani, C. A.; Bulgac, A.; Magierski, P.; Roche, K. J.
2015-01-06
Within the framework of the unrestricted time-dependent density functional theory, we present for the first time an analysis of the relativistic Coulomb excitation of the heavy deformed open shell nucleus 238U. The approach is based on the superfluid local density approximation formulated on a spatial lattice that can take into account coupling to the continuum, enabling self-consistent studies of superfluid dynamics of any nuclear shape. We compute the energy deposited in the target nucleus as a function of the impact parameter, finding it to be significantly larger than the estimate using the Goldhaber-Teller model. The isovector giant dipole resonance, themore » dipole pygmy resonance, and giant quadrupole modes are excited during the process. As a result, the one-body dissipation of collective dipole modes is shown to lead a damping width Γ↓≈0.4 MeV and the number of preequilibrium neutrons emitted has been quantified.« less
Gide, Milind S; Karam, Lina J
2016-08-01
With the increased focus on visual attention (VA) in the last decade, a large number of computational visual saliency methods have been developed over the past few years. These models are traditionally evaluated by using performance evaluation metrics that quantify the match between predicted saliency and fixation data obtained from eye-tracking experiments on human observers. Though a considerable number of such metrics have been proposed in the literature, there are notable problems in them. In this paper, we discuss shortcomings in the existing metrics through illustrative examples and propose a new metric that uses local weights based on fixation density, which overcomes these flaws. To compare the performance of our proposed metric at assessing the quality of saliency prediction with other existing metrics, we construct a ground-truth subjective database in which saliency maps obtained from 17 different VA models are evaluated by 16 human observers on a five-point categorical scale in terms of their visual resemblance with corresponding ground-truth fixation density maps obtained from eye-tracking data. The metrics are evaluated by correlating metric scores with the human subjective ratings. The correlation results show that the proposed evaluation metric outperforms all other popular existing metrics. In addition, the constructed database and corresponding subjective ratings provide an insight into which of the existing metrics and future metrics are better at estimating the quality of saliency prediction and can be used as a benchmark. PMID:27295671
Adiabaticity in open quantum systems
NASA Astrophysics Data System (ADS)
Venuti, Lorenzo Campos; Albash, Tameem; Lidar, Daniel A.; Zanardi, Paolo
2016-03-01
We provide a rigorous generalization of the quantum adiabatic theorem for open systems described by a Markovian master equation with time-dependent Liouvillian L (t ) . We focus on the finite system case relevant for adiabatic quantum computing and quantum annealing. Adiabaticity is defined in terms of closeness to the instantaneous steady state. While the general result is conceptually similar to the closed-system case, there are important differences. Namely, a system initialized in the zero-eigenvalue eigenspace of L (t ) will remain in this eigenspace with a deviation that is inversely proportional to the total evolution time T . In the case of a finite number of level crossings, the scaling becomes T-η with an exponent η that we relate to the rate of the gap closing. For master equations that describe relaxation to thermal equilibrium, we show that the evolution time T should be long compared to the corresponding minimum inverse gap squared of L (t ) . Our results are illustrated with several examples.
Sun, Bo; Zhang, Ping; Zhao, Xian-Geng
2008-02-28
The electronic structure and properties of PuO2 and Pu2O3 have been studied from first principles by the all-electron projector-augmented-wave method. The local density approximation+U and the generalized gradient approximation+U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by the choice of U as well as the choice of exchange-correlation potential. Also, oxidation reaction of Pu2O3, leading to formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U, it is promising to correctly and consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modeling of redox process involving Pu-based materials possible. PMID:18315070
Color of pure and alkali-doped cerium sulfide: A local-density-functional study
NASA Astrophysics Data System (ADS)
Perrin, M.-A.; Wimmer, E.
1996-07-01
The electronic structure and mechanisms for the optical excitations of pure and Na-doped γ-Ce2S3 have been investigated using first-principles local-density-functional theory. The energy-band structures from augmented-spherical-wave calculations indicate that the S 3p-->Ce 5d interband transitions give rise to absorptions in the ultraviolet, whereas the observed red color of γ-Ce2S3 is associated with localized Ce 4f-->5d excitations. The cationic vacancies in γ-Ce2S3 (which is derived from the cubic Th3P4 structure) lead to the formation of vacancy bands, which are split off from the top of the S 3p valence band. Na doping removes these vacancy bands and homogenizes the band edges of the valence and conduction bands. As a consequence, the onset of the f-->d transitions is shifted slightly to larger energies and becomes sharper, which is consistent with an observed change in the color of γ-Ce2S3 from maroon to red-orange upon doping with Na.
Localization of fused in sarcoma (FUS) protein to the post-synaptic density in the brain.
Aoki, Naoya; Higashi, Shinji; Kawakami, Ito; Kobayashi, Zen; Hosokawa, Masato; Katsuse, Omi; Togo, Takashi; Hirayasu, Yoshio; Akiyama, Haruhiko
2012-09-01
Mutations in the fused in sarcoma (FUS) gene are linked to a form of familial amyotrophic lateral sclerosis (ALS), ALS6. The FUS protein is a major component of the ubiquitin-positive neuronal cytoplasmic inclusions in both ALS6 and some rare forms of frontotemporal lobar degeneration (FTLD). The latter are now collectively referred to as FTLD-FUS. In the present study, we investigated the localization of FUS in human and mouse brains. FUS was detected by western blot as an approximately 72 kDa protein in both human and mouse brains. Immunohistochemistry using lightly fixed tissue sections of human and mouse brains revealed FUS-positive granular staining in the neuropil, in addition to nuclear staining. Such granules are abundant in the gray matter of the brainstem and spinal cord. They are not frequent in the telencephalon. At the light microscopic level, FUS-positive granules are often co-localized with synaptophysin and present in association with microtubule-associated protein 2-positive dendrites. In the synaptosomal fraction of mouse brain, FUS is detected mainly in the post-synaptic density fraction. Thus, while FUS is primarily a nuclear protein, it may also play a role in dendrites. In the brains of patients with FTLD with TDP-43 deposition (FTLD-TDP), the number of FUS-positive granules in the cortex is increased compared with control cases. The increase in Alzheimer's disease (AD) is less remarkable but still significant. The dendritic localization of FUS and its increase in FTLD-TDP and AD may have some implication for the pathophysiology of neurodegenerative diseases. PMID:22526020
NASA Astrophysics Data System (ADS)
Li, Dafa
2016-05-01
The adiabatic theorem was proposed about 90 years ago and has played an important role in quantum physics. The quantitative adiabatic condition constructed from eigenstates and eigenvalues of a Hamiltonian is a traditional tool to estimate adiabaticity and has proven to be the necessary and sufficient condition for adiabaticity. However, recently the condition has become a controversial subject. In this paper, we list some expressions to estimate the validity of the adiabatic approximation. We show that the quantitative adiabatic condition is invalid for the adiabatic approximation via the Euclidean distance between the adiabatic state and the evolution state. Furthermore, we deduce general necessary and sufficient conditions for the validity of the adiabatic approximation by different definitions.
Symmetry-protected adiabatic quantum transistors
NASA Astrophysics Data System (ADS)
Williamson, Dominic J.; Bartlett, Stephen D.
2015-05-01
Adiabatic quantum transistors (AQT) allow quantum logic gates to be performed by applying a large field to a quantum many-body system prepared in its ground state, without the need for local control. The basic operation of such a device can be viewed as driving a spin chain from a symmetry-protected (SP) phase to a trivial phase. This perspective offers an avenue to generalize the AQT and to design several improvements. The performance of quantum logic gates is shown to depend only on universal symmetry properties of a SP phase rather than any fine tuning of the Hamiltonian, and it is possible to implement a universal set of logic gates in this way by combining several different types of SP matter. Such SP AQTs are argued to be robust to a range of relevant noise processes.
NASA Astrophysics Data System (ADS)
Hollen, S. M.; Fernandes, G. E.; Xu, J. M.; Valles, J. M.
2014-10-01
A Bose insulator composed of a low density of strongly localized Cooper pairs develops at the two-dimensional superconductor to insulator transition (SIT) in a number of thin film systems. Investigations of ultrathin amorphous PbBi films far from the SIT described here provide evidence that the Bose insulator gives way to a second insulating phase with decreasing film thickness. At a critical film thickness dc the magnetoresistance changes sign from positive, as expected for boson transport, to negative, as expected for fermion transport, signs of local Cooper-pair phase coherence effects on transport vanish, and the transport activation energy exhibits a kink. Below dc pairing fluctuation effects remain visible in the high-temperature transport while the activation energy continues to rise. These features show that Cooper pairing persists and suggest that the localized unpaired electron states involved in transport are interspersed among regions of strongly localized Cooper pairs in this strongly localized, low Cooper-pair density phase.
Archer, A J; Evans, R
2013-01-01
The local molecular field theory (LMF) developed by Weeks and co-workers has proved successful for treating the structure and thermodynamics of a variety of non-uniform liquids. By reformulating LMF in terms of one-body direct correlation functions we recast the theory in the framework of classical density functional theory (DFT). We show that the general LMF equation for the effective reference potential φ(R)(r) follows directly from the standard mean-field DFT treatment of attractive interatomic forces. Using an accurate (fundamental measures) DFT for the non-uniform hard-sphere reference fluid we determine φ(R)(r) for a hard-core Yukawa liquid adsorbed at a planar hard wall. In the approach to bulk liquid-gas coexistence we find the effective potentials exhibit rich structure that can include damped oscillations at large distances from the wall as well as the repulsive hump near the wall required to generate the low density "gas" layer characteristic of complete drying. We argue that it would be difficult to obtain the same level of detail from other (non-DFT based) implementations of LMF. LMF emphasizes the importance of making an intelligent division of the interatomic pair potential of the full system into a reference part and a remainder that can be treated in mean-field approximation. We investigate different divisions for an exactly solvable one-dimensional model where the pair potential has a hard-core plus a linear attractive tail. Results for the structure factor and the equation of state of the uniform fluid show that including a significant portion of the attraction in the reference system can be much more accurate than treating the full attractive tail in mean-field approximation. We discuss further aspects of the relationship between LMF and DFT. PMID:23298050
Adiabatic Wankel type rotary engine
NASA Technical Reports Server (NTRS)
Kamo, R.; Badgley, P.; Doup, D.
1988-01-01
This SBIR Phase program accomplished the objective of advancing the technology of the Wankel type rotary engine for aircraft applications through the use of adiabatic engine technology. Based on the results of this program, technology is in place to provide a rotor and side and intermediate housings with thermal barrier coatings. A detailed cycle analysis of the NASA 1007R Direct Injection Stratified Charge (DISC) rotary engine was performed which concluded that applying thermal barrier coatings to the rotor should be successful and that it was unlikely that the rotor housing could be successfully run with thermal barrier coatings as the thermal stresses were extensive.
LCAO-local-spin-density calculations for V 2 and Mn 2
NASA Astrophysics Data System (ADS)
Salahub, D. R.; Baykara, N. A.
1985-06-01
Binding-energy curves for V 2 and Mn 2 have been obtained through spin-polarized, broken-symmetry LCAO-local-spin-density (LSD) calculations. For V 2 the region near Re is characterized by full-symmetry ( D∞h) molecular orbitals. The LSD ground state (configuration 1π 4u 1σ 2g 1δ 2g 2σ 2g) is a triplet with R e = 1.75 Å, ω e = 594 cm -1. There is a state with αβ spin about 0.4 eV higher. These results are in good agreement with recent beam spectroscopy experiments. The large- R part of the V 2 potential curve is, however, inaccurate since the molecule dissociates into two d 4s 1 atoms (the LSD ground state for a spherical V atom) rather than two ground-state (d 3s 2) atoms. For Mn 2 the magnetic aspects are more dominant; symmetry breaking is essential. We find a long ( R e = 2.52 Å), relatively weak ( De = 0.86 eV) bond with ωe = 144 cm-1, for an "antiferro magnetic" 1σ 2 1δ 4 1π 4 2σ 2 3σ 2 configuration. These results are in good agreement with experimental data, where available.