Sulaksono, A; Agrawal, B K
2014-01-01
The model dependence and the symmetry energy dependence of the core-crust transition properties for the neutron stars are studied using three different families of systematically varied extended relativistic mean field model. Several forces within each of the families are so considered that they yield wide variations in the values of the nuclear symmetry energy $a_{\\rm sym}$ and its slope parameter $L$ at the saturation density. The core-crust transition density is calculated using a method based on random-phase-approximation. The core-crust transition density is strongly correlated, in a model independent manner, with the symmetry energy slope parameter evaluated at the saturation density. The pressure at the transition point dose not show any meaningful correlations with the symmetry energy parameters at the saturation density. At best, pressure at the transition point is correlated with the symmetry energy parameters and their linear combination evaluated at the some sub-saturation density. Yet, such corre...
Core-crust transition and crustal fraction of moment of inertia in neutron stars
Atta, Debasis; Basu, D N
2015-01-01
The crustal fraction of moment of inertia in neutron stars is calculated using $\\beta$-equilibrated nuclear matter obtained from density dependent M3Y effective interaction. The transition density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of the neutron stars determined from the thermodynamic stability conditions are found to be $\\rho_t=$ 0.0938 fm$^{-3}$, P$_t=$ 0.5006 MeV fm$^{-3}$ and $x_{p(t)}=$ 0.0308, respectively. The crustal fraction of the moment of inertia can be extracted from studying pulsar glitches and is most sensitive to the pressure as well as density at the transition from the crust to the core. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a new limit for the radius of the Vela pulsar: $R \\geq 4.10 + 3.36 M/M_\\odot$ kms.
Core-crust transition pressure for relativistic slowly rotating neutron stars
González-Romero, L M
2013-01-01
We study the influence of core-\\textit{crust} transition pressure changes on the general dynamical properties of neutron star configurations. First we study the matching conditions in core-\\textit{crust} transition pressure region, where phase transitions in the equation of state causes energy density jumps. Then using a surface \\textit{crust} approximation, we can construct configurations where the matter is described by the equation of state of the core of the star and the core-\\textit{crust} transition pressure. We will consider neutron stars in the slow rotation limit, considering perturbation theory up to second order in the angular velocity so that the deformation of the star is also taken into account. The junction determines the parameters of the star such as total mass, angular and quadrupolar momentum.
Phase transitions at finite density
Friman, Bengt
2012-01-01
I discuss the analytic structure of thermodynamic quantities for complex values of thermodynamic variables within Landau theory. In particular, the singularities connected with phase transitions of second order, first order and cross over types are examined. A conformal mapping is introduced, which may be used to explore the thermodynamics of strongly interacting matter at finite values of the baryon chemical potential $\\mu$ starting from lattice QCD results at $\\mu^{2}\\leq 0$. This method allows us to improve the convergence of a Taylor expansion about $\\mu=0$ and to enhance the sensitivity to physical singularities in the complex $\\mu$ plane. The technique is illustrated by an application to a second-order transition in a chiral effective model.
The transition to the metallic state in low density hydrogen.
McMinis, Jeremy; Morales, Miguel A; Ceperley, David M; Kim, Jeongnim
2015-11-21
Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work, we use diffusion quantum Monte Carlo to benchmark the transition between paramagnetic and anti-ferromagnetic body centered cubic atomic hydrogen in its ground state. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of rs = 2.27(3) a0. We compare our results to previously reported density functional theory, Hedin's GW approximation, and dynamical mean field theory results.
A density-independent rigidity transition in biological tissues
Bi, Dapeng; Lopez, J. H.; Schwarz, J. M.; Manning, M. Lisa
2015-12-01
Cell migration is important in many biological processes, including embryonic development, cancer metastasis and wound healing. In these tissues, a cell’s motion is often strongly constrained by its neighbours, leading to glassy dynamics. Although self-propelled particle models exhibit a density-driven glass transition, this does not explain liquid-to-solid transitions in confluent tissues, where there are no gaps between cells and therefore the density is constant. Here we demonstrate the existence of a new type of rigidity transition that occurs in the well-studied vertex model for confluent tissue monolayers at constant density. We find that the onset of rigidity is governed by a model parameter that encodes single-cell properties such as cell-cell adhesion and cortical tension, providing an explanation for liquid-to-solid transitions in confluent tissues and making testable predictions about how these transitions differ from those in particulate matter.
Transition matrices and orbitals from reduced density matrix theory
Energy Technology Data Exchange (ETDEWEB)
Etienne, Thibaud [Université de Lorraine – Nancy, Théorie-Modélisation-Simulation, SRSMC, Boulevard des Aiguillettes 54506, Vandoeuvre-lès-Nancy (France); CNRS, Théorie-Modélisation-Simulation, SRSMC, Boulevard des Aiguillettes 54506, Vandoeuvre-lès-Nancy (France); Unité de Chimie Physique Théorique et Structurale, Université de Namur, Rue de Bruxelles 61, 5000 Namur (Belgium)
2015-06-28
In this contribution, we report two different methodologies for characterizing the electronic structure reorganization occurring when a chromophore undergoes an electronic transition. For the first method, we start by setting the theoretical background necessary to the reinterpretation through simple tensor analysis of (i) the transition density matrix and (ii) the natural transition orbitals in the scope of reduced density matrix theory. This novel interpretation is made more clear thanks to a short compendium of the one-particle reduced density matrix theory in a Fock space. The formalism is further applied to two different classes of excited states calculation methods, both requiring a single-determinant reference, that express an excited state as a hole-particle mono-excited configurations expansion, to which particle-hole correlation is coupled (time-dependent Hartree-Fock/time-dependent density functional theory) or not (configuration interaction single/Tamm-Dancoff approximation). For the second methodology presented in this paper, we introduce a novel and complementary concept related to electronic transitions with the canonical transition density matrix and the canonical transition orbitals. Their expression actually reflects the electronic cloud polarisation in the orbital space with a decomposition based on the actual contribution of one-particle excitations from occupied canonical orbitals to virtual ones. This approach validates our novel interpretation of the transition density matrix elements in terms of the Euclidean norm of elementary transition vectors in a linear tensor space. A proper use of these new concepts leads to the conclusion that despite the different principles underlying their construction, they provide two equivalent excited states topological analyses. This connexion is evidenced through simple illustrations of (in)organic dyes electronic transitions analysis.
Transition matrices and orbitals from reduced density matrix theory
Etienne, Thibaud
2015-06-01
In this contribution, we report two different methodologies for characterizing the electronic structure reorganization occurring when a chromophore undergoes an electronic transition. For the first method, we start by setting the theoretical background necessary to the reinterpretation through simple tensor analysis of (i) the transition density matrix and (ii) the natural transition orbitals in the scope of reduced density matrix theory. This novel interpretation is made more clear thanks to a short compendium of the one-particle reduced density matrix theory in a Fock space. The formalism is further applied to two different classes of excited states calculation methods, both requiring a single-determinant reference, that express an excited state as a hole-particle mono-excited configurations expansion, to which particle-hole correlation is coupled (time-dependent Hartree-Fock/time-dependent density functional theory) or not (configuration interaction single/Tamm-Dancoff approximation). For the second methodology presented in this paper, we introduce a novel and complementary concept related to electronic transitions with the canonical transition density matrix and the canonical transition orbitals. Their expression actually reflects the electronic cloud polarisation in the orbital space with a decomposition based on the actual contribution of one-particle excitations from occupied canonical orbitals to virtual ones. This approach validates our novel interpretation of the transition density matrix elements in terms of the Euclidean norm of elementary transition vectors in a linear tensor space. A proper use of these new concepts leads to the conclusion that despite the different principles underlying their construction, they provide two equivalent excited states topological analyses. This connexion is evidenced through simple illustrations of (in)organic dyes electronic transitions analysis.
Transition matrices and orbitals from reduced density matrix theory.
Etienne, Thibaud
2015-06-28
In this contribution, we report two different methodologies for characterizing the electronic structure reorganization occurring when a chromophore undergoes an electronic transition. For the first method, we start by setting the theoretical background necessary to the reinterpretation through simple tensor analysis of (i) the transition density matrix and (ii) the natural transition orbitals in the scope of reduced density matrix theory. This novel interpretation is made more clear thanks to a short compendium of the one-particle reduced density matrix theory in a Fock space. The formalism is further applied to two different classes of excited states calculation methods, both requiring a single-determinant reference, that express an excited state as a hole-particle mono-excited configurations expansion, to which particle-hole correlation is coupled (time-dependent Hartree-Fock/time-dependent density functional theory) or not (configuration interaction single/Tamm-Dancoff approximation). For the second methodology presented in this paper, we introduce a novel and complementary concept related to electronic transitions with the canonical transition density matrix and the canonical transition orbitals. Their expression actually reflects the electronic cloud polarisation in the orbital space with a decomposition based on the actual contribution of one-particle excitations from occupied canonical orbitals to virtual ones. This approach validates our novel interpretation of the transition density matrix elements in terms of the Euclidean norm of elementary transition vectors in a linear tensor space. A proper use of these new concepts leads to the conclusion that despite the different principles underlying their construction, they provide two equivalent excited states topological analyses. This connexion is evidenced through simple illustrations of (in)organic dyes electronic transitions analysis.
The transition to the metallic state in low density hydrogen
Energy Technology Data Exchange (ETDEWEB)
McMinis, Jeremy; Morales, Miguel A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Ceperley, David M. [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States); Kim, Jeongnim [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
2015-11-21
Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work, we use diffusion quantum Monte Carlo to benchmark the transition between paramagnetic and anti-ferromagnetic body centered cubic atomic hydrogen in its ground state. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of r{sub s} = 2.27(3) a{sub 0}. We compare our results to previously reported density functional theory, Hedin’s GW approximation, and dynamical mean field theory results.
Effects of phase transition induced density fluctuations on pulsar dynamics
Directory of Open Access Journals (Sweden)
Partha Bagchi
2015-07-01
Full Text Available We show that density fluctuations during phase transitions in pulsar cores may have non-trivial effects on pulsar timings, and may also possibly account for glitches and anti-glitches. These density fluctuations invariably lead to non-zero off-diagonal components of the moment of inertia, leading to transient wobbling of star. Thus, accurate measurements of pulsar timing and intensity modulations (from wobbling may be used to identify the specific pattern of density fluctuations, hence the particular phase transition, occurring inside the pulsar core. Changes in quadrupole moment from rapidly evolving density fluctuations during the transition, with very short time scales, may provide a new source for gravitational waves.
Nuclear shape transitions, level density, and underlying interactions
Karampagia, S
2016-01-01
The configuration interaction approach to nuclear structure uses the effective Hamiltonian in a finite orbital space. The various parts of this Hamiltonian and their interplay are responsible for specific features of physics including the shape of the mean field and level density. This interrelation is not sufficiently understood. We intend to study phase transitions between spherical and deformed shapes driven by different parts of the nuclear Hamiltonian and to establish the presence of the collective enhancement of the nuclear level density by varying the shell-model matrix elements. Varying the interaction matrix elements we define, for nuclei in the sd and pf shells, the sectors with spherical and deformed shapes. Using the moments method that does not require the full diagonalization we relate the shape transitions with the corresponding level density. Enhancement of the level density in the low-energy part of the spectrum is observed in clear correlation with a deformation phase transition induced main...
Insight into Structural Phase Transitions from Density Functional Theory
Ruzsinszky, Adrienn
2014-03-01
Structural phase transitions caused by high pressure or temperature are very relevant in materials science. The high pressure transitions are essential to understand the interior of planets. Pressure or temperature induced phase transitions can be relevant to understand other phase transitions in strongly correlated systems or molecular crystals.Phase transitions are important also from the aspect of method development. Lower level density functionals, LSDA and GGAs all fail to predict the lattice parameters of different polymorphs and the phase transition parameters at the same time. At this time only nonlocal density functionals like HSE and RPA have been proved to resolve the geometry-energy dilemma to some extent in structural phase transitions. In this talk I will report new results from the MGGA_MS family of meta-GGAs and give an insight why this type of meta-GGAs can give a systematic improvement of the geometry and phase transition parameters together. I will also present results from the RPA and show a possible way to improve beyond RPA.
Electron Momentum Density and Phase Transition in ZnS
Directory of Open Access Journals (Sweden)
N. Munjal
2013-01-01
Full Text Available The electron momentum density distribution and phase transition in ZnS are reported in this paper. The calculations are performed on the basis of density functional theory (DFT based on the linear combination of atomic orbitals (LCAO method. To compare the theoretical Compton profile, the measurement on polycrystalline ZnS has been made using a Compton spectrometer employing 59.54 keV gamma rays. The spherically averaged theoretical Compton profile is in agreement with the measurement. On the basis of equal valence-electron-density Compton profiles, it is found that ZnS is less covalent as compared to ZnSe. The present study suggests zincblende (ZB to rocksalt (RS phase transition at 13.7 GPa. The calculated transition pressure is found in good agreement with the previous investigations.
A density-independent glass transition in biological tissues
Bi, Dapeng; Schwarz, J M; Manning, M Lisa
2014-01-01
Cells must move through tissues in many important biological processes, including embryonic development, cancer metastasis, and wound healing. In these tissues, a cell's motion is often strongly constrained by its neighbors, leading to glassy dynamics. Recent work has demonstrated the existence of a non-equilibrium glass transition in self-propelled particle models for active matter, where the transition is driven by changes in density. However, this may not explain liquid-to-solid transitions in confluent tissues, where there are no gaps between cells and the packing fraction remains fixed and equal to unity. Here we demonstrate the existence of a different type of glass transition that occurs in the well-studied vertex model for confluent tissue monolayers. In this model, the onset of rigidity is governed by changes to single-cell properties such as cell-cell adhesion, cortical tension, and volume compressibility, providing an explanation for a liquid-to-solid transitions in confluent tissues.
Topological deconfinement transition in QCD at finite isospin density
Kashiwa, Kouji; Ohnishi, Akira
2017-09-01
The confinement-deconfinement transition is discussed from topological viewpoints. The topological change of the system is achieved by introducing the dimensionless imaginary chemical potential (θ). Then, the non-trivial free-energy degeneracy becomes the signal of the deconfinement transition and it can be visualized by using the map of the thermodynamic quantities to the circle S1 along θ. To understand this "topological" deconfinement transition at finite real quark chemical potential (μR), we consider the isospin chemical potential (μiso) in the effective model of QCD. The phase diagram at finite μiso is identical with that at finite μR outside of the pion-condensed phase at least in the large-Nc limit via the well-known orbifold equivalence. In the present effective model, the topological deconfinement transition does not show a significant dependence on μiso and then we can expect that this tendency also appears at small μR. Also, the chiral transition and the topological deconfinement transition seems to be weakly correlated. If we will access lattice QCD data for the temperature dependence of the quark number density at finite μiso with θ = π / 3, our surmise can be judged.
Asymptotic Expansions of Transition Densities for Hybrid Jump-Diffusions
Institute of Scientific and Technical Information of China (English)
Yuan-jin Liu; G.Yin
2004-01-01
A class of hybrid jump diffusions modulated by a Markov chain is considered in this work.The motivation stems from insurance risk models,and emerging applications in production planning and wireless communications.The models are hybrid in that they involve both continuous dynamics and discrete events.Under suitable conditions,asymptotic expansions of the transition densities for the underlying processes are developed.The formal expansions are validated and the error bounds obtained.
Thermal Rounding of the Charge Density Wave Depinning Transition
Middleton, A. Alan
1992-01-01
The rounding of the charge density wave depinning transition by thermal noise is examined. Hops by localized modes over small barriers trigger ``avalanches'', resulting in a creep velocity much larger than that expected from comparing thermal energies with typical barriers. For a field equal to the $T=0$ depinning field, the creep velocity is predicted to have a {\\em power-law} dependence on the temperature $T$; numerical computations confirm this result. The predicted order of magnitude of t...
Density shift and broadening of transition lines in antiprotonic helium
Bakalov; Jeziorski; Korona; Szalewicz; Tchoukova
2000-03-13
The density shift and broadening of the transition lines of antiprotonic helium have been evaluated in the impact approximation using an interatomic potential calculated ab initio with the symmetry-adapted perturbation theory. The results help to remove an uncertainty of up to 10 ppm in the laser spectroscopy data on antiprotonic helium and are of importance in experimental tests of bound state QED and CPT invariance.
Density functional theory studies of transition metal nanoparticles in catalysis
DEFF Research Database (Denmark)
Greeley, Jeffrey Philip; Rankin, Rees; Zeng, Zhenhua
2013-01-01
Periodic Density Functional Theory calculations are capable of providing powerful insights into the structural, energetics, and electronic phenomena that underlie heterogeneous catalysis on transition metal nanoparticles. Such calculations are now routinely applied to single crystal metal surfaces...... and to subnanometer metal clusters. Descriptions of catalysis on truly nanosized structures, however, are generally not as well developed. In this talk, I will illustrate different approaches to analyzing nanocatalytic phenomena with DFT calculations. I will describe case studies from heterogeneous catalysis...
Density Functional Theory for Phase-Ordering Transitions
Energy Technology Data Exchange (ETDEWEB)
Wu, Jianzhong [Univ. of California, Riverside, CA (United States)
2016-03-30
Colloids display astonishing structural and dynamic properties that can be dramatically altered by modest changes in the solution condition or an external field. This complex behavior stems from a subtle balance of colloidal forces and intriguing mesoscopic and macroscopic phase transitions that are sensitive to the processing conditions and the dispersing environment. Whereas the knowledge on the microscopic structure and phase behavior of colloidal systems at equilibrium is now well-advanced, quantitative predictions of the dynamic properties and the kinetics of phase-ordering transitions in colloids are not always realized. Many important mesoscopic and off-equilibrium colloidal states remain poorly understood. The proposed research aims to develop a new, unifying approach to describe colloidal dynamics and the kinetics of phase-ordering transitions based on accomplishments from previous work for the equilibrium properties of both uniform and inhomogeneous systems and on novel concepts from the state-of-the-art dynamic density functional theory. In addition to theoretical developments, computational research is designed to address a number of fundamental questions on phase-ordering transitions in colloids, in particular those pertinent to a competition of the dynamic pathways leading to various mesoscopic structures, off-equilibrium states, and crystalline phases. By providing a generic theoretical framework to describe equilibrium, metastable as well as non-ergodic phase transitions concurrent with the colloidal self-assembly processes, accomplishments from this work will have major impacts on both fundamental research and technological applications.
Detection of a Transiting Low-Density Super-Earth
Henry, Gregory W; Marcy, Geoffrey W; Fischer, Debra A; Johnson, John Asher
2011-01-01
We present evidence for photometric transits of the low-mass planet HD 97658b across the disk of its host star, an early K dwarf. This planet was previously discovered in radial velocities (RVs) from Keck/HIRES as part of the Eta-Earth Survey. Using photometry from the Automated Photometric Telescopes at Fairborn Observatory, we detected four separate planetary egress events at times predicted from the RV orbit. We measured a transit depth of 1470 +/- 260 ppm, a result that should be confirmed and refined with space-based photometry. We also collected additional Keck-HIRES RV measurements that refined the transit ephemeris and planet mass. With an orbital period of 9.4957 +/- 0.0022 days, HD 97658b is a close-in planet that had been classified as a `super-Earth' based on its mass of 6.4 +/- 0.7 Mearth. However, the planet radius of 2.93 +/- 0.28 Rearth implies a density of 1.40 g/cc and suggests `sub-Neptune' status. The low density can be explained by an extended atmosphere of volatiles such as hydrogen, hel...
Insights into phase transitions and entanglement from density functional theory
Wei, Bo-Bo
2016-11-01
Density functional theory (DFT) has met great success in solid state physics, quantum chemistry and in computational material sciences. In this work we show that DFT could shed light on phase transitions and entanglement at finite temperatures. Specifically, we show that the equilibrium state of an interacting quantum many-body system which is in thermal equilibrium with a heat bath at a fixed temperature is a universal functional of the first derivatives of the free energy with respect to temperature and other control parameters respectively. This insight from DFT enables us to express the average value of any physical observable and any entanglement measure as a universal functional of the first derivatives of the free energy with respect to temperature and other control parameters. Since phase transitions are marked by the nonanalytic behavior of free energy with respect to control parameters, the physical quantities and entanglement measures may present nonanalytic behavior at critical point inherited from their dependence on the first derivative of free energy. We use two solvable models to demonstrate these ideas. These results give new insights for phase transitions and provide new profound connections between entanglement and phase transitions in interacting quantum many-body physics.
Uejima, Motoyuki; Sato, Tohru; Yokoyama, Daisuke; Tanaka, Kazuyoshi; Park, Jong-Wook
2014-07-21
A theoretical design principle for enhancement of the quantum yield of light-emitting molecules is desired. For the establishment of the principle, we focused on the S1 states of blue-emitting anthracene derivatives: 2-methyl-9,10-di(2'-naphthyl)anthracene (MADN), 4,9,10-bis(3',5'-diphenylphenyl)anthracene (MAM), 9-(3',5'-diphenylphenyl)-10-(3'',5''-diphenylbiphenyl-4''-yl) anthracene (MAT), and 9,10-bis(3''',5'''-diphenylbiphenyl-4'-yl) anthracene (TAT) [Kim et al., J. Mater. Chem., 2008, 18, 3376]. The vibronic coupling constants and transition dipole moments were calculated and analyzed by using the concepts of vibronic coupling density (VCD) and transition dipole moment density (TDMD), respectively. It is found that the driving force of the internal conversions and vibrational relaxations originate mainly from the anthracenylene group. On the other hand, fluorescence enhancement results from the large torsional distortion of the side groups in the S1 state. The torsional distortion is caused by the diagonal vibronic coupling for the lowest-frequency mode in the Franck-Condon (FC) S1 state, which originates from a small portion of the electron density difference on the side groups. These findings lead to the following design principles for anthracene derivatives with a high quantum yield: (1) reduction in the electron density difference and overlap density between the S0 and S1 states in the anthracenylene group to suppress vibrational relaxation and radiationless transitions, respectively; (2) increase in the overlap density in the side group to enhance the fluorescence.
Electron star birth: a continuous phase transition at nonzero density.
Hartnoll, Sean A; Petrov, Pavel
2011-03-25
We show that charged black holes in anti-de Sitter spacetime can undergo a third-order phase transition at a critical temperature in the presence of charged fermions. In the low temperature phase, a fraction of the charge is carried by a fermion fluid located a finite distance from the black hole. In the zero temperature limit, the black hole is no longer present and all charge is sourced by the fermions. The solutions exhibit the low temperature entropy density scaling s~T(2/z) anticipated from the emergent IR criticality of recently discussed electron stars.
Chiral Phase Transition at Finite Isospin Density in Linear Sigma Model
Institute of Scientific and Technical Information of China (English)
SHU Song; LI Jia-Rong
2005-01-01
Using the linear sigma model, we have introduced the pion isospin chemical potential. The chiral phase transition is studied at finite temperatures and finite isospin densities. We have studied the μ - T phase diagram for the chiral phase transition and found the transition cannot happen below a certain low temperature because of the BoseEinstein condensation in this system. Above that temperature, the chiral phase transition is studied by the isotherms of pressure versus density. We indicate that the transition, in the chiral limit, is a first-order transition from a low-density phase to a high-density phase like a gas-liquid phase transition.
Kepler-7b: A Transiting Planet with Unusually Low Density
Latham, David W; Koch, David G; Brown, Timothy M; Buchhave, Lars A; Basri, Gibor; Batalha, Natalie M; Caldwell, Douglas A; Cochran, William D; Dunham, Edward W; Furesz, Gabor; Gautier, Thomas N; Geary, John C; Gilliland, Ronald L; Howell, Steve B; Jenkins, Jon M; Lissauer, Jack J; Marcy, Geoffrey W; Monet, David G; Rowe, Jason F; Sasselov, Dimitar D
2010-01-01
We report the discovery and confirmation of Kepler-7b, a transiting planet with unusually low density. The mass is less than half that of Jupiter, Mp = 0.43 Mj, but the radius is fifty percent larger, Rp = 1.48 Rj. The resulting density, 0.17 g/cc, is the second lowest reported so far for an extrasolar planet. The orbital period is fairly long, P = 4.886 days, and the host star is not much hotter than the Sun, Teff = 6000 K. However, it is more massive and considerably larger than the sun, Mstar = 1.35 Msun and Rstar = 1.84 Rsun, and must be near the end of its life on the Main Sequence.
Incommensurate Chirality Density Wave Transition in a Hybrid Molecular Framework
Hill, Joshua A.; Christensen, Kirsten E.; Goodwin, Andrew L.
2017-09-01
Using single-crystal x-ray diffraction we characterize the 235 K incommensurate phase transition in the hybrid molecular framework tetraethylammonium silver(I) dicyanoargentate, [NEt4]Ag3(CN )4 . We demonstrate the transition to involve spontaneous resolution of chiral [NEt4]+ conformations, giving rise to a state in which molecular chirality is incommensurately modulated throughout the crystal lattice. We refer to this state as an incommensurate chirality density wave (XDW) phase, which represents a fundamentally new type of chiral symmetry breaking in the solid state. Drawing on parallels to the incommensurate ferroelectric transition of NaNO2 , we suggest the XDW state arises through coupling between acoustic (shear) and molecular rotoinversion modes. Such coupling is symmetry forbidden at the Brillouin zone center but symmetry allowed for small but finite modulation vectors q =[0 ,0 ,qz]* . The importance of long-wavelength chirality modulations in the physics of this hybrid framework may have implications for the generation of mesoscale chiral textures, as required for advanced photonic materials.
Energy boost in laser wakefield accelerators using sharp density transitions
Döpp, A; Thaury, C; Lifschitz, A; Phuoc, K Ta; Malka, V
2015-01-01
The energy gain in laser wakefield accelerators is limited by dephasing between the driving laser pulse and the highly relativistic electrons in its wake. Since this phase depends on both the driver and the cavity length, the effects of dephasing can be mitigated with appropriate tailoring of the plasma density along propagation. Preceding studies have discussed the prospects of continuous phase-locking in the linear wakefield regime. However, most experiments are performed in the highly non-linear regime and rely on self-guiding of the laser pulse. Due to the complexity of the driver evolution in this regime it is much more difficult to achieve phase locking. As an alternative we study the scenario of rapid rephasing in sharp density transitions, as was recently demonstrated experimentally. Starting from a phenomenological model we deduce expressions for the electron energy gain in such density profiles. The results are in accordance with particle-in-cell simulations and we present gain estimations for singl...
E→H mode transition density and power in two types of inductively coupled plasma configuration
Energy Technology Data Exchange (ETDEWEB)
Wang, Jian; Du, Yin-chang; Zhang, Xiao; Zheng, Zhe; Liu, Yu; Xu, Liang; Wang, Pi; Cao, Jin-xiang, E-mail: jxcao@ustc.edu.cn [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2014-07-15
E → H transition power and density were investigated at various argon pressures in inductively coupled plasma (ICP) in a cylindrical interlaid chamber. The transition power versus the pressure shows a minimum transition power at 4 Pa (ν/ω=1) for argon. Then the transition density hardly changes at low pressures (ν/ω≪1), but it increases clearly when argon pressure exceeds an appropriate value. In addition, both the transition power and transition density are lower in the re-entrant configuration of ICP compared with that in the cylindrical configuration of ICP. The result may be caused from the decrease of stochastic heating in the re-entrant configuration of ICP. This work is useful to understand E → H mode transition and control the transition points in real plasma processes.
Institute of Scientific and Technical Information of China (English)
Jeffrey L. BOERSEMA
2007-01-01
We prove analogs of the Kaplansky Density Theorem and the Kadison Transitivity Theorem for irreducible representations of a real C*-algebra on a real Hilbert space. Specifically, if a C*-algebra is acting irreducibly on a real Hilbert space, then the Hilbert space has either a real, complex, or quaternionic structure with respect to which the density and transitivity theorems hold.
Molecular dynamics simulation for the baryon-quark phase transition at finite baryon density
Energy Technology Data Exchange (ETDEWEB)
Akimura, Y. [Saitama University, Department of physics, Sakura-Ku, Saitama City (Japan); Japan Atomic Energy Research Institute, Advanced Science Research Center, Tokai (Japan); Maruyama, T.; Chiba, S. [Japan Atomic Energy Research Institute, Advanced Science Research Center, Tokai (Japan); Yoshinaga, N. [Saitama University, Department of physics, Sakura-Ku, Saitama City (Japan)
2005-09-01
We study the baryon-quark phase transition in the molecular dynamics (MD) of the quark degrees of freedom at finite baryon density. The baryon state at low baryon density, and the deconfined quark state at high baryon density are reproduced. We investigate the equations of state of matters with different u-d-s compositions. It is found that the baryon-quark transition is sensitive to the quark width. (orig.)
Experiments on Transitional Subaqueous Density Flows and Resulting Sediment Deposits
Barnaal, Z. D.; Parker, G.
2016-12-01
Much remains unknown regarding the sedimentary deposits of submarine gravity flows. Flows with large concentrations of suspended sediment may transition from a more turbulent to a more coherent flow type. Such transitional flows may be produced when turbulence becomes suppressed due to entrainment of cohesive sediment or from flow deceleration. Argillaceous sandstones and linked turbidite-debrites are types of submarine sediment deposits in a category known as hybrid event beds, and are interpreted to be emplaced by transitional regime flows (Talling, 2007; Davis, 2009; Haughton, 2009; Hodgson, 2009; Sumner, 2009; Baas, 2011; Lee, 2013; and Talling, 2013). Here we report on the physical modelling of such transitional flows. The sediment consists of mixtures of non-cohesive silica flour with a median grain size of 30 microns and kaolin clay with a median size of 4 microns. These sediments were mixed in ratios including 100%, 70%, 60%, 50%, 30% and 0% kaolin. Total volume concentration of the input slurry varied from 0.01 to 0.2, allowing coverage of wide range of transitional flow types. The flow passed over a 4.9-m-long bed with a slope of 7 degrees, and continued another 4.9 m over a horizontal bed before exiting the tank. Measurements of flow velocity profiles, flow concentrations, deposit geometry, and deposit grain-size distributions were conducted. The results of experiments help us to better understand the rheology, and to determine the structure and patterns of deposits including argillaceous sandstones.
Shape transition of state density for bosonic systems
Indian Academy of Sciences (India)
Harshal N Deota; N D Chavda; V Potbhare
2013-12-01
For a finite boson system, the ensemble-averaged state density has been computed with respect to the body interaction rank . The shape of such a state density changes from Gaussian to semicircle as the body rank of the interaction increases. This state density is expressed as a linear superposition of Gaussian and semicircular states. The nearest-neighbour spacing distribution (NNSD), which is one of the most important spectral properties of a system, is studied. The NNSDs are rather independent of body rank and show a Wigner distribution throughout.
Molecular dynamics simulation for baryon-quark phase transition at finite temperature and density
Akimura, Y; Yoshinaga, N; Chiba, S; Akimura, Yuka; Maruyama, Toshiki; Yoshinaga, Naotaka; Chiba, Satoshi
2005-01-01
We study the baryon-quark phase transition in a molecular dynamics (MD) of quark degrees of freedom at finite temperature and density. The baryon state at low density and temperature, and the deconfined quark state at high density and temperature are reproduced. We investigate the equations of state of matters with different $u$-$d$-$s$ compositions. Then we draw phase diagrams in the temperature-density plane by this simulation. It is found that the baryon-quark transition is sensitive to the quark width.
Closed-Form Expansions for Transition Densities of Convenience Yield Processes
Directory of Open Access Journals (Sweden)
Sanae RUJIVAN
2009-01-01
Full Text Available In this paper, we derive closed-form expansions for transition densities of convenience yield processes modeled by using extended Cox-Ingersoll-Ross (ECIR processes. The closed-form expansions can be used for all cases of model having appropriate drift and diffusion coefficients. In terms of the efficiency, the closed-form expansions are close to the exact transition densities when the number of terms in the expansions is large and the time step size is small.
Empirical transverse charge densities in the nucleon and the nucleon-to-Delta transition
Energy Technology Data Exchange (ETDEWEB)
Carl Carlson; Marc Vanderhaeghen
2008-01-01
Using only the current empirical information on the nucleon electromagnetic form factors we map out the transverse charge density in proton and neutron as viewed from a light front moving towards a transversely polarized nucleon. These charge densities are characterized by a dipole pattern, in addition to the monopole field corresponding with the unpolarized density. Furthermore, we use the latest empirical information on the $N \\to \\Delta$ transition form factors to map out the transition charge density which induces the $N \\to \\Delta$ excitation. This transition charge density in a transversely polarized $N$ and $\\Delta$ contains both monopole, dipole and quadrupole patterns, the latter corresponding with a deformation of the hadron's charge distribution.
THEORY OF THE THRESHOLD FIELD FOR THE DEPINNING TRANSITION OF A CHARGE-DENSITY WAVE
PIETRONERO, L; VERSTEEG, M
1991-01-01
The Hamiltonian of an elastic string pinned by random potentials is often used to describe the depinning transition of a charge density wave in the presence of impurity pinning. The properties of the pinned states show close analogies to those of glassy systems, while the depinning transition resemb
Metal-insulator transition and local moment formation: A spin-density functional approach
Ghazali, A.; Leroux-Hugon, P.
1980-01-01
A more thorough description of the metal-insulator transition in correlated systems including local moment formation may be achieved through the spin-density functional method when compared to the Hubbard model. We have applied this method to doped semiconductors and found a transition between an insulating phase with local moments and a metallic one without moments.
Exploring effective interactions through transition charge density study of 70,72,74,76Ge nuclei
Indian Academy of Sciences (India)
A Shukla; P K Raina; P K Rath
2005-02-01
Transition charge densities (TCD) for $0^{+} → 2_{1}^{+}$ excitation have been calculated for 70, 72, 74, 76Ge nuclei within microscopic variational framework employing 23/2, 15/2, 21/2 and 19/2 valence space. The calculated TCDs for different monopole variants of Kuo interaction are compared with available experimental results. Other systematics like reduced transition probabilities (2) and static quadrupole moments (2) are also presented. It is observed that the transition density study acts as a sensitive probe for discriminating the response of different parts of effective interactions.
Energy Technology Data Exchange (ETDEWEB)
Sato, K.; Koide, Tomoi; Maruyama, Masahiro [Tohoku Univ., Faculty of Science, Sendai, Miyagi (Japan)
1999-08-01
There are various approaches to nonequilibrium system. We use the projection operator method investigated by F. Shibata and N. Hashitsume on the linear sigma model at finite temperature and density. We derive a differential equation of the time evolution for the order parameter and pion number density in chiral phase transition. (author)
Phase transition in finite density and temperature lattice QCD
Wang, Rui; Gong, Ming; Liu, Chuan; Liu, Yu-Bin; Liu, Zhao-Feng; Ma, Jian-Ping; Meng, Xiang-Fei; Zhang, Jian-Bo
2015-01-01
We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of $\\beta$ and $ma$ at the lattice size $24\\times12^{2}\\times6$. The calculation was done in the Taylar expansion formalism. We are able to calculate the first and second order derivatives of $\\langle\\bar{\\psi}\\psi\\rangle$ in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and the magnitude of $\\bar{\\psi}\\psi$ decreases under the influence of finite chemical potential in both channels.
Finite density QCD phase transition in the heavy quark region
Saito, H; Kanaya, K; Ohno, H; Ejiri, S; Nakagawa, Y; Hatsuda, T; Umeda, T
2012-01-01
We extend our previous study of the QCD phase structure in the heavy quark region to non-zero chemical potentials. To identify the critical point where the first order deconfining transition terminates, we study an effective potential defined by the probability distribution function of the plaquette and the Polyakov loop. The reweighting technique is shown to be powerful in evaluating the effective potential in a wide range of the plaquette and Polyakov loop expectation values. We adopt the cumulant expansion to overcome the sign problem in the calculation of complex phase of the quark determinant. We find that the method provides us with an intuitive and powerful way to study the phase structure. We estimate the location of the critical point at finite chemical potential in the heavy quark region.
Kota, V K B
2015-01-01
Embedded random matrix ensembles are generic models for describing statistical properties of finite isolated interacting quantum many-particle systems. For the simplest spinless systems, with say $m$ particles in $N$ single particle states and interacting via $k$-body interactions, we have EGUE($k$) and the embedding algebra is $U(N)$. A finite quantum system, induced by a transition operator, makes transitions from its states to the states of the same system or to those of another system. Examples are electromagnetic transitions (same initial and final systems), nuclear beta and double beta decay (different initial and final systems), particle addition to/removal from a given system and so on. Towards developing a complete statistical theory for transition strength densities, we have derived formulas for lower order bivariate moments of the strength densities generated by a variety of transition operators. For a spinless fermion system, using EGUE($k$) representation for Hamiltonian and an independent EGUE($...
Interfacial stick–slip transition in hydroxyapatite filled high density polyethylene composite
Indian Academy of Sciences (India)
Roy Joseph; M T Martyn; K E Tanner; P D Coates
2006-02-01
Effect of filler addition and temperature on the stick–slip transition in high density polyethylene melt was studied. Results showed that shear stresses corresponding to stick–slip transition increases with the addition of filler. Increase in temperature also increases the shear stresses for stick–slip transition. The features of the flow curves of composites and that of unfilled system remain identical. Filler addition lowers the shear rate at which the transition occurs. The composite extrudate did not show characteristic extrudate distortions associated with the unfilled polymer.
Transition densities in the context of the generalized rotation-vibration model
Morales Botero, D. F.; Chamon, L. C.; Carlson, B. V.
2017-10-01
A collective model for the description of heavy-ion nuclear structure, called the generalized rotation-vibration model (GRVM), was proposed in an earlier paper. In the present work, we use this model to study transition densities for the low-lying states of several nuclei. In order to evaluate the accuracy of the model, we test the GRVM transition densities in the description of experimental results corresponding to elastic and inelastic electron-nucleus scattering. We also compare the GRVM densities with those arising from microscopic Dirac-Hartree-Bogoliubov theoretical calculations. The GRVM transition densities can be used in future works to calculate folding-type coupling potentials in coupled-channel data analyses for heavy-ion systems.
Time-dependent renormalized Redfield theory II for off-diagonal transition in reduced density matrix
Kimura, Akihiro
2016-09-01
In our previous letter (Kimura, 2016), we constructed time-dependent renormalized Redfield theory (TRRT) only for diagonal transition in a reduced density matrix. In this letter, we formulate the general expression for off-diagonal transition in the reduced density matrix. We discuss the applicability of TRRT by numerically comparing the dependencies on the energy gap of the exciton relaxation rate by using the TRRT and the modified Redfield theory (MRT). In particular, we roughly show that TRRT improves MRT for the detailed balance about the excitation energy transfer reaction.
Calaminici, Patrizia; Janetzko, Florian; Köster, Andreas M; Mejia-Olvera, Roberto; Zuniga-Gutierrez, Bernardo
2007-01-28
Density functional theory optimized basis sets for gradient corrected functionals for 3d transition metal atoms are presented. Double zeta valence polarization and triple zeta valence polarization basis sets are optimized with the PW86 functional. The performance of the newly optimized basis sets is tested in atomic and molecular calculations. Excitation energies of 3d transition metal atoms, as well as electronic configurations, structural parameters, dissociation energies, and harmonic vibrational frequencies of a large number of molecules containing 3d transition metal elements, are presented. The obtained results are compared with available experimental data as well as with other theoretical data from the literature.
DEFF Research Database (Denmark)
Vallejo, Federico Calle; Martinez, Jose Ignacio; Rossmeisl, Jan
2011-01-01
) at the cathode. In this contribution, on the basis of Density Functional Theory (DFT) calculations, we show that graphitic materials with active sites composed of 4 nitrogen atoms and transition metal atoms belonging to groups 7 to 9 in the periodic table are active towards ORR, and also towards Oxygen Evolution...
H2 adsorption on 3d transition metal clusters: a combined infrared and density functional study
Swart, I.; de Groot, F.M.F.; Weckhuysen, B.M.; Gruene, P.; Meijer, G.; Fielicke, A.
2008-01-01
The adsorption of H2 on a series of gas-phase transition metal (scandium, vanadium, iron, cobalt, and nickel) clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations. Comparison of the exper
Damping-Growth Transition for Ion-Acoustic Waves in a Density Gradient
DEFF Research Database (Denmark)
D'Angelo, N.; Michelsen, Poul; Pécseli, Hans
1975-01-01
A damping-growth transition for ion-acoustic waves propagating in a nonuniform plasma (e-folding length for the density ln) is observed at a wavelength λ∼2πln. This result supports calculations performed in connection with the problem of heating of the solar corona by ion-acoustic waves generated...
TREATMENT OF NONADIABATIC TRANSITIONS BY DENSITY-MATRIX EVOLUTION AND MOLECULAR-DYNAMICS SIMULATIONS
MAVRI, J; BERENDSEN, HJC
1994-01-01
A density matrix evolution (DME) method (H.J.C. Berendsen and J. Mavri, J. Phys. Chem., 97 (1993) 13469) to simulate the dynamics of quantum systems embedded in a classical environment is presented. The DME method allows treatment of nonadiabatic transitions. As numerical examples the collinear coll
Separable Transition Density in the Hybrid Model for Tumor-Immune System Competition
Directory of Open Access Journals (Sweden)
Carlo Cattani
2012-01-01
Full Text Available A hybrid model, on the competition tumor cells immune system, is studied under suitable hypotheses. The explicit form for the equations is obtained in the case where the density function of transition is expressed as the product of separable functions. A concrete application is given starting from a modified Lotka-Volterra system of equations.
Universal dynamics of density correlations at the transition to the many-body localized state
Mierzejewski, M.; Herbrych, J.; Prelovšek, P.
2016-12-01
Within one-dimensional disordered models of interacting fermions, we perform a numerical study of several dynamical density correlations, which can serve as hallmarks of the transition to the many-body localized state. The results confirm that density-wave correlations exhibit quite an abrupt change with increasing disorder, with a nonvanishing long-time value characteristic for the nonergodic phase. In addition, our results reveal a logarithmic variation of correlations in time in a wide time window, which we can bring in connection with the anomalous behavior of the dynamical conductivity near the transition. Our results support the view that the transition to many-body localization can be characterized by universal dynamical exponents.
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.
2014-07-01
The intra-atomic magnetic dipole moment - frequently called 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.
Analysis on insulator–metal transition in yttrium doped LSMO from electron density distribution
Indian Academy of Sciences (India)
S Israel; S Saravana Kumar; R Renuretson; R A J R Sheeba; R Saravanan
2012-02-01
Yttrium doped LSMO (La1−SrMnO3) was prepared using sol–gel technique and analysed for the insulator–metal transition fromcharge density variation in the unit cell with respect to different stoichiometric inclusion of yttrium. X-ray powder diffraction profiles of the samples were obtained and the well known Rietveld method and a versatile tool called maximum entropy method (MEM) were used for structural and profile refinement. The charge density in the unit cell was constructed using refined structure factors and was analysed. The charge ordering taking place in the insulator–metal transition was investigated and quantified. The insulator–metal transition was found to occur when 20% of La/Sr atoms were replaced by yttrium. The changes in the charge environment have also been analysed.
Ultrafast Spin Density Wave Transition in Chromium Governed by Thermalized Electron Gas
Nicholson, C. W.; Monney, C.; Carley, R.; Frietsch, B.; Bowlan, J.; Weinelt, M.; Wolf, M.
2016-09-01
The energy and momentum selectivity of time- and angle-resolved photoemission spectroscopy is exploited to address the ultrafast dynamics of the antiferromagnetic spin density wave (SDW) transition photoexcited in epitaxial thin films of chromium. We are able to quantitatively extract the evolution of the SDW order parameter Δ through the ultrafast phase transition and show that Δ is governed by the transient temperature of the thermalized electron gas, in a mean field description. The complete destruction of SDW order on a sub-100 fs time scale is observed, much faster than for conventional charge density wave materials. Our results reveal that equilibrium concepts for phase transitions such as the order parameter may be utilized even in the strongly nonadiabatic regime of ultrafast photoexcitation.
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
2014-07-21
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 Fe(2+) and Fe(3+) 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.
Characterization of Phase Transition in Heisenberg Fluids from Density Functional Theory
Li, Liang-Sheng; Li, Li; Chen, Xiao-Song
2009-02-01
The phase transition of Heisenberg fluid has been investigated with the density functional theory in mean-field approximation (MF). The matrix of the second derivatives of the grand canonical potential Ω with respect to the particle density fluctuations and the magnetization fluctuations has been investigated and diagonalized. The smallest eigenvalue being 0 signalizes the phase instability and the related eigenvector characterizes this phase transition. We find a Curie line where the order parameter is pure magnetization and a spinodal where the order parameter is a mixture of particle density and magnetization. Along the spinodal, the character of phase instability changes continuously from predominant condensation to predominant ferromagnetic phase transition with the decrease of total density. The spinodal meets the Curie line at the critical endpoint with the reduced density ρ* = ρσ3 = 0.224 and the reduced temperature T* = kT/in = 1.87 (σ is the diameter of Heisenberg hard sphere and in is the coupling constant).
Characterization of Phase Transition in Heisenberg Fluids from Density Functional Theory
Institute of Scientific and Technical Information of China (English)
LI Liang-Sheng; LI Li; CHEN Xiao-Song
2009-01-01
The phase transition of Heisenberg fluid has been investigated with the density functional theory in mean-field approximation (MF).The matrix of the second derivatives of the grand canonical potential Ω with respect to the particle density fluctuations and the magnetization fluctuations has been investigated and diagonalized.The smallest eigenvalue being 0 signalizes the phase instability and the related eigenvector characterizes this phase transition.We find a Curie line where the order parameter is pure magnetization and a spinodM where the order parameter is a mixture of particle density and magnetization.Along the spinodal, the character of phase instability changes continuously from predominant condensation to predominant ferromagnetic phase transition with the decrease of total density.The spinodal meets the Curie line at the critical endpoint with the reduced density ρ*= ρσ3=0.224 and the reduced temperature T* = kT/ε = 1.87 (σ is the diameter of Heisenberg hard sphere and e is the coupling constant).
Chen, Shaohao; Qing, Bo; Li, Jiaming
2007-10-01
Using the multiconfiguration Dirac-Fock method, including the quantum electrodynamics corrections, especially with the Breit interactions, we calculate the electric quadrupole (E2) and magnetic dipole (M1) transition rates for the two transitions D5/2,3/2o2→S3/2o4 of OII . We show systematically that the correlation effects owing to core electron excitations and the Breit interactions are vitally important for the transition rates. We present a benchmark for the intensity ratio between the two transitions in the limit of high electron density in planetary nebulas, i.e., r(∞)=0.345-0.014+0.028 , which is in good agreement with modern astronomical observations.
Turning reduced density matrix theory into a practical tool for studying the Mott transition
Pernal, Katarzyna
2015-11-01
Strongly correlated systems pose a challenge for theoretical methods based on an independent electron approximation. Such methods struggle to predict a nonzero gap in Mott insulators or to capture the correct physics of the insulator-to-metal phase transition in strongly correlated materials. In a recent paper by Shinohara et al (2015 New J. Phys. 17 093038) it is shown that strongly correlated materials and correct descriptions of their phase transitions are within the reach of reduced density matrix functional theory (RDMFT) approximations. For a doping-induced phase transition, not only is a satisfactory agreement with experimental spectra found for NiO but it is also shown that the physical picture of the observed Mott transition stays in line with more computationally demanding many-body theories. This is an important step toward providing an RDMFT-based computation tool for studying strongly correlated materials.
Carlson, Rebecca K; Li Manni, Giovanni; Sonnenberger, Andrew L; Truhlar, Donald G; Gagliardi, Laura
2015-01-13
Kohn-Sham density functional theory, resting on the representation of the electronic density and kinetic energy by a single Slater determinant, has revolutionized chemistry, but for open-shell systems, the Kohn-Sham Slater determinant has the wrong symmetry properties as compared to an accurate wave function. We have recently proposed a theory, called multiconfiguration pair-density functional theory (MC-PDFT), in which the electronic kinetic energy and classical Coulomb energy are calculated from a multiconfiguration wave function with the correct symmetry properties, and the rest of the energy is calculated from a density functional, called the on-top density functional, that depends on the density and the on-top pair density calculated from this wave function. We also proposed a simple way to approximate the on-top density functional by translation of Kohn-Sham exchange-correlation functionals. The method is much less expensive than other post-SCF methods for calculating the dynamical correlation energy starting with a multiconfiguration self-consistent-field wave function as the reference wave function, and initial tests of the theory were quite encouraging. Here, we provide a broader test of the theory by applying it to bond energies of main-group molecules and transition metal complexes, barrier heights and reaction energies for diverse chemical reactions, proton affinities, and the water dimerization energy. Averaged over 56 data points, the mean unsigned error is 3.2 kcal/mol for MC-PDFT, as compared to 6.9 kcal/mol for Kohn-Sham theory with a comparable density functional. MC-PDFT is more accurate on average than complete active space second-order perturbation theory (CASPT2) for main-group small-molecule bond energies, alkyl bond dissociation energies, transition-metal-ligand bond energies, proton affinities, and the water dimerization energy.
Thermal transitions in the low-density lipoprotein and lipids of the egg yolk of hens.
Smith, M B; Back, J F
1975-05-22
1. Differential sanning calorimetry and light-scattering have been used to investigate temperature-dependent transitions in low-density lipoprotein and in lipids from hens' egg yolk. Yolks of different fatty acid composition were obtained by varying the dietary lipid and by adding methyl sterculate to the hen's diet. 2. Lipoprotein solutions in 50 percent glycerol/water gave characteristic melting curves between -25 degrees C and 50 degrees C, and on cooling showed increases in light-scattering between 10 degrees C and -20 degrees C. The temperatures at which major changes occurred depended on the proportions of saturated and unsaturated fatty acids. 3. The thermal transitions in the intact lipoprotein in glycerol solution were reversible, but with marked hysteresis. Lipid extracted from the lipoprotein did not show temperature hystersis but the transition heats and melting curves similar to those of the intact lipoprotein. The results support the hypothesis of a "lipid-core" structure for low-density lipoproteins. 4. Scanning calorimetry of egg-yolk lecithins indicated a strong dependence of transition temperature on water content in the rane 3 percent-20 percent water. A rise in the mid-temperature of the liquid-crystalline to gel transition as the water content is lowered on freezing may be the primary event in the irreversible gelation of egg yolk and aggregation of lipoprotein.
Phase transitions in Core-Collapse Supernova Matter at sub-saturation densities
Pais, Helena; Stone, Jirina R
2014-01-01
We perform a three-dimensional, finite temperature Skyrme-Hartree-Fock study of inhomogeneous nuclear matter to determine the critical density and temperature for the phase transition between the pasta phase and homogeneous matter and its properties. We employ four different parametrizations of the Skyrme nuclear energy-density functional, SkM$^*$, SLy4, NRAPR and SQMC700, which span a range of saturation-density symmetry energy behaviours constrained by a variety of nuclear experimental probes. For each of these interactions we calculate free energy, pressure, entropy and chemical potentials in the range of particle number densities where the nuclear pasta phases are expected to exist, 0.02 - 0.12 fm$^{-3}$, temperatures 2 - 8 MeV and a proton fraction of 0.3. We find unambiguous evidence for a first-order phase transition to uniform matter, unsoftened by the presence of the pasta phases. No conclusive signs of first-order phase transition between the pasta phases is observed, and it is argued that the therm...
Bulk Properties of Transition Metals: A Challenge for the Design of Universal Density Functionals.
Janthon, Patanachai; Luo, Sijie Andy; Kozlov, Sergey M; Viñes, Francesc; Limtrakul, Jumras; Truhlar, Donald G; Illas, Francesc
2014-09-09
Systematic evaluation of the accuracy of exchange-correlation functionals is essential to guide scientists in their choice of an optimal method for a given problem when using density functional theory. In this work, accuracy of one Generalized Gradient Approximation (GGA) functional, three meta-GGA functionals, one Nonseparable Gradient Approximation (NGA) functional, one meta-NGA, and three hybrid GGA functionals was evaluated for calculations of the closest interatomic distances, cohesive energies, and bulk moduli of all 3d, 4d, and 5d bulk transition metals that have face centered cubic (fcc), hexagonal closed packed (hcp), or body centered cubic (bcc) structures (a total of 27 cases). Our results show that including the extra elements of kinetic energy density and Hartree-Fock exchange energy density into gradient approximation density functionals does not usually improve them. Nevertheless, the accuracies of the Tao-Perdew-Staroverov-Scuseria (TPSS) and M06-L meta-GGAs and the MN12-L meta-NGA approach the accuracy of the Perdew-Burke-Ernzerhof (PBE) GGA, so usage of these functionals may be advisable for systems containing both solid-state transition metals and molecular species. The N12 NGA functional is also shown to be almost as accurate as PBE for bulk transition metals, and thus it could be a good choice for studies of catalysis given its proven good performance for molecular species.
Molecular Dynamical Simulation of Ice Phase Transition: Ice Ih to High-Density Amorphous
Institute of Scientific and Technical Information of China (English)
DONG Shun-Le; WANG Yan
2005-01-01
@@ We put 5kbar and 12kbar on perfect ice Ih lattice at 77K and 180K. After 30000 simulation steps (in units of 10-15 s), high-density amorphous ice is formed. Four-site simple-pair potential TIP4P is used for molecular interactions and the rigid molecular model is employed. Phase transition processes are fitted by an exponential function, and different phase transition times τ are obtained from O-O radial distribution functions (366 and 359fs for 77K and 180K) and O-O-O angle distribution functions (126 and 116fs for 77K and 180K).
Identification of transition bias in oxidized low density lipoprotein receptor 1 gene in buffalo
Directory of Open Access Journals (Sweden)
N. Shabir
2014-03-01
Full Text Available Aim: Though transition bias has been previously demonstrated in cattle, however, there has not been any study that has explored transition bias in buffalo nuclear genome. The aim of the present study was to evaluate the nucleotide substitution pattern in the Intron I of Oxidised Low Density Lipoprotein Receptor 1 (OLR1 gene in four breeds of Indian buffalo using 24 different nucleotide substitution models and evaluate their association with DNA methylation. Materials and Methods: Transition/transversion bias (R was estimated by 24 different nucleotide substitution models available in MEGA 5.0. The transition/transversion bias (R was estimated under the Kimura 2-parameter model. Substitution patterns and the transitions/transversions rates (r were then estimated by Tamura-Nei-I and Tamura-Nei-II models. The CpG Island search was done by using CpG Plot Island online Software available at European Bioinformatics Institute (EBI website. Results: The frequency of transition was found to be 3.5 times higher than that of the transversion mutation frequency. Out of 9 nucleotide substitutions, 7 transitions and 2 transversions were found. Among all the nucleotide substitutions, thymine to cytosine substitutions was observed to be very high. CpG Island search tool revealed that IntronI of OLR1 genes is a CpG rich region, thus prone to methylation. Conclusions: Higher transition frequency was found in the intronI of OLR1 gene, however due to the richness of methylated CpGs in the evaluated stretch of genome, the higher T↔C transitions could likely be a result of frequent deaminations of the methylated cytosines into thymines during the evolution of four buffalo breeds.
D'Escamard, Gabriella; De Rosa, Claudio; Auriemma, Finizia
2016-05-01
Crosslink sulfur density in rubber compounds and interactions in polymer blends are two of the composition elements that affect the rubber compound properties and glass transition temperature (Tg), which is a marker of polymer properties related to its applications. Natural rubber (NR), butadiene rubber (BR) and styrene-butadiene rubber (SBR) compounds were investigated using calorimetry (DSC) and dynamic mechanical analysis (DMA). The results indicate that the Di Marzio's and Schneider's Models predict with accuracy the dependence of Tg on crosslink density and composition in miscible blends, respectively, and that the two model may represent the base to study the relevant "in service" properties of real rubber compounds.
Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas
DEFF Research Database (Denmark)
Basse, N.P.; Zoletnik, S.; Baumel, S.
2003-01-01
Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper...... of the fluctuation level associated with the transition from NC- to HDH-mode. Correlation calculations on a 20 mus timescale between magnetic and density fluctuations lead to the result that the fluctuations are correlated in NC- but not in HDH-mode. Finally, a comparative analysis between the enhanced D-alpha H...
Large-Scale Density Functional Theory Transition State Searching in Enzymes.
Lever, Greg; Cole, Daniel J; Lonsdale, Richard; Ranaghan, Kara E; Wales, David J; Mulholland, Adrian J; Skylaris, Chris-Kriton; Payne, Mike C
2014-11-06
Linear-scaling quantum mechanical density functional theory calculations have been applied to study the rearrangement of chorismate to prephenate in large-scale models of the Bacillus subtilis chorismate mutase enzyme. By treating up to 2000 atoms at a consistent quantum mechanical level of theory, we obtain an unbiased, almost parameter-free description of the transition state geometry and energetics. The activation energy barrier is calculated to be lowered by 10.5 kcal mol(-1) in the enzyme, compared with the equivalent reaction in water, which is in good agreement with experiment. Natural bond orbital analysis identifies a number of active site residues that are important for transition state stabilization in chorismate mutase. This benchmark study demonstrates that linear-scaling density functional theory techniques are capable of simulating entire enzymes at the ab initio quantum mechanical level of accuracy.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Fan; Li, Cheng; Wen, Pei-Wei [Beijing Normal University, The Key Laboratory of Beam Technology of Ministry of Education, College of Nuclear Science and Technology, Beijing (China); Beijing Radiation Center, Beijing (China); Liu, Hang [Texas Advanced Computing Center University of Texas at Austin, Austin, TX (United States); Zhang, Feng-Shou [Beijing Normal University, The Key Laboratory of Beam Technology of Ministry of Education, College of Nuclear Science and Technology, Beijing (China); Beijing Radiation Center, Beijing (China); National Laboratory of Heavy Ion Accelerator of Lanzhou, Center of Theoretical Nuclear Physics, Lanzhou (China)
2016-09-15
Heavy-ion collisions at relativistic energy are studied by the isospin-dependent quantum molecular dynamics model in the company of the GEMINI model. The present study mainly focuses on the liquid-gas phase transition in nuclear matter. We calculate the shear-viscosity-to-entropy-density ratio η/s, γ{sub 2} and the multiplicity of intermediate-mass fragment (M{sub IMF}) in finite-size nuclear sources. At excitation energy 8 MeV a minimum of η/s is found in the coexistence phase of intermediate-mass fragments and light particles. At similar excitation energy a maximum of the M{sub IMF} is also observed at the same density condition which is an indication of the liquid-gas phase transition. (orig.)
Metal-insulator transition in disordered systems from the one-body density matrix
DEFF Research Database (Denmark)
Olsen, Thomas; Resta, Raffaele; Souza, Ivo
2017-01-01
systems. In particular, for noninteracting systems the geometrical marker can be obtained from the configurational average of the norm-squared one-body density matrix, which can be calculated within open as well as periodic boundary conditions. This is in sharp contrast to a classification based...... on the static conductivity, which is only sensible within periodic boundary conditions. We exemplify the method by considering a simple lattice model, known to have a metal-insulator transition as a function of the disorder strength, and demonstrate that the transition point can be obtained accurately from...... the one-body density matrix. The approach has a general ab initio formulation and could in principle be applied to realistic disordered materials by standard electronic structure methods....
Steam Reforming on Transition-metal Carbides from Density-functional Theory
Energy Technology Data Exchange (ETDEWEB)
Vojvodic, Aleksandra
2012-05-11
A screening study of the steam reforming reaction on clean and oxygen covered early transition-metal carbides surfaces is performed by means of density-functional theory calculations. It is found that carbides provide a wide spectrum of reactivities, from too reactive via suitable to too inert. Several molybdenum-based systems are identified as possible steam reforming catalysts. The findings suggest that carbides provide a playground for reactivity tuning, comparable to the one for pure metals.
Sun, Xu; Yao, Tao; Hu, Zhenpeng; Guo, Yuqiao; Liu, Qinghua; Wei, Shiqiang; Wu, Changzheng
2015-05-28
A deep understanding of the relationship between electronic and structure ordering across the charge-density-wave (CDW) transition is crucial for both fundamental study and technological applications. Herein, using in situ X-ray absorption fine structure (XAFS) spectroscopy coupled with high-resolution transmission electron microscopy (HRTEM), we have illustrated the atomic-level information on the local structural evolution across the CDW transition and its influence on the intrinsic electrical properties in VS2 system. The structure transformation, which is highlighted by the formation of vanadium trimers with derivation of V-V bond length (ΔR = 0.10 Å), was clearly observed across the CDW process. Moreover, the corresponding influence of lattice variation on the electronic behavior was clearly characterized by experimental results as well as theoretical analysis, which demonstrated that vanadium trimers drive the deformation of space charge density distribution into √3 ×√3 periodicity, with the conductivity of a1g band reducing by half. These observations directly unveiled the close connection between lattice evolution and electronic property variation, paving a new avenue for understanding the intrinsic nature of electron-lattice interactions in the VS2 system and other isostructural transition metal dichalcogenides across the CDW transition process.
HATS-8b: A Low-Density Transiting Super-Neptune
Bayliss, D; Bakos, G Á; Penev, K; Zhou, G; Brahm, R; Rabus, M; Jordán, A; Mancini, L; de Val-Borro, M; Bhatti, W; Espinoza, N; Csubry, Z; Howard, A W; Fulton, B J; Buchhave, L A; Henning, T; Schmidt, B; Ciceri, S; Noyes, R W; Isaacson, H; Marcy, G W; Suc, V; Lázár, J; Papp, I; Sári, P
2015-01-01
HATS-8b is a low density transiting super-Neptune discovered as part of the HATSouth project. The planet orbits its solar-like G dwarf host (V=14.03 $\\pm$ 0.10 and T$_{eff}$ =5679 $\\pm$ 50 K) with a period of 3.5839 d. HATS-8b is the third lowest mass transiting exoplanet to be discovered from a wide-field ground based search, and with a mass of 0.138 $\\pm$ 0.019 M$_J$ it is approximately half-way between the masses of Neptune and Saturn. However HATS-8b has a radius of 0.873 (+0.123,-0.075) R$_J$, resulting in a bulk density of just 0.259 $\\pm$ 0.091 g.cm$^{-3}$. The metallicity of the host star is super-Solar ([Fe/H]=0.210 $\\pm$ 0.080), arguing against the idea that low density exoplanets form from metal-poor environments. The low density and large radius of HATS-8b results in an atmospheric scale height of almost 1000 km, and in addition to this there is an excellent reference star of near equal magnitude at just 19 arcsecond separation on the sky. These factors make HATS-8b an exciting target for future a...
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.
Autschbach, Jochen; Jorge, Francisco E; Ziegler, Tom
2003-05-05
Time-dependent density functional theory (TD-DFT) has for the first time been applied to the computation of circular dichroism (CD) spectra of transition metal complexes, and a detailed comparison with experimental spectra has been made. Absorption spectra are also reported. Various Co(III) complexes as well as [Rh(en)(3)](3+) are studied in this work. The resulting simulated CD spectra are generally in good agreement with experimental spectra after corrections for systematic errors in a few of the lowest excitation energies are applied. This allows for an interpretation and assignment of the spectra for the whole experimentally accessible energy range (UV/vis). Solvent effects on the excitations are estimated via inclusion of a continuum solvent model. This significantly improves the computed excitation energies for charge-transfer bands for complexes of charge +3, but has only a small effect on those for neutral or singly charged complexes. The energies of the weak d-to-d transitions of the Co complexes are systematically overestimated due to deficiencies of the density functionals. These errors are much smaller for the 4d metal complex. Taking these systematic errors and the effect of a solvent into consideration, TD-DFT computations are demonstrated to be a reliable tool in order to assist with the assignment and interpretation of CD spectra of chiral transition metal complexes.
Institute of Scientific and Technical Information of China (English)
ZHOU Bang-Rong
2004-01-01
By means of critical behaviors of the dynamical fermion mass in four-fermion interaction models, we show by explicit calculations that when T ＝ 0 the particle density will have a discontinuous jumping across the critical chemical potential μc in 2D and 3D Gross-Neveu (GN) model and these physically explain the first-order feature of the corresponding symmetry restoring phase transitions. For the second-order phase transitions in the 3D GN model when T → 0 and in 4D Nambu-Jona-Lasinio (NJL) model when T ＝ 0, it is proven that the particle density itself will be continuous across μc but its derivative over the chemical potential μ will have a discontinuous jumping. The results give a physical explanation of implications of the tricritical point (T, μ) = (0,μc) in the 3D GN model. The discussions also show effectiveness of the critical analysis approach of phase transitions.
Directory of Open Access Journals (Sweden)
Hyeon-Dong Son
2015-07-01
Full Text Available We investigate the generalized K→π transition vector and tensor form factors, from which we derive the transverse quark spin density in the course of the K→π transition, based on the nonlocal chiral quark model from the instanton vacuum. The results of the transition tensor form factor are in good agreement with recent data of lattice QCD. The behavior of the transverse quark spin density of the K→π transition turns out to be very similar to those of the pion and the kaon.
Electronic and magnetic properties of spiral spin-density-wave states in transition-metal chains
Tanveer, M.; Ruiz-Díaz, P.; Pastor, G. M.
2016-09-01
The electronic and magnetic properties of one-dimensional (1D) 3 d transition-metal nanowires are investigated in the framework of density functional theory. The relative stability of collinear and noncollinear (NC) ground-state magnetic orders in V, Mn, and Fe monoatomic chains is quantified by computing the frozen-magnon dispersion relation Δ E (q ⃗) as a function of the spin-density-wave vector q ⃗. The dependence on the local environment of the atoms is analyzed by varying systematically the lattice parameter a of the chains. Electron correlation effects are explored by comparing local spin-density and generalized-gradient approximations to the exchange and correlation functional. Results are given for Δ E (q ⃗) , the local magnetic moments μ⃗i at atom i , the magnetization-vector density m ⃗(r ⃗) , and the local electronic density of states ρi σ(ɛ ) . The frozen-magnon dispersion relations are analyzed from a local perspective. Effective exchange interactions Ji j between the local magnetic moments μ⃗i and μ⃗j are derived by fitting the ab initio Δ E (q ⃗) to a classical 1D Heisenberg model. The dominant competing interactions Ji j at the origin of the NC magnetic order are identified. The interplay between the various Ji j is revealed as a function of a in the framework of the corresponding magnetic phase diagrams.
Observation and modeling of deflagration-to-detonation transition (DDT) in low-density HMX
Tringe, Joseph W.; Vandersall, Kevin S.; Reaugh, John E.; Levie, Harold W.; Henson, Bryan F.; Smilowitz, Laura B.; Parker, Gary R.
2017-01-01
We employ simultaneous flash x-ray radiography and streak imaging, together with a multi-phase finite element model, to understand deflagration-to-detonation transition (DDT) phenomena in low-density (˜1.2 gm/cm3) powder of the explosive cyclotetramethylene-tetranitramine (HMX). HMX powder was lightly hand-tamped in a 12.7 mm diameter column, relatively lightly-confined in an optically-transparent polycarbonate cylinder with wall thickness 25.4 mm. We observe apparent compaction of the powder in advance of the detonation transition by the motion of small steel spheres pre-emplaced throughout the length of explosive. High-speed imaging along the explosive cylinder length provides a more temporally continuous record of the transition that is correlated with the high-resolution x-ray image record. Preliminary simulation of these experiments with the HERMES model implemented in the ALE3D code enables improved understanding of the explosive particle burning, compaction and detonation phenomena which are implied by the observed reaction rate and transition location within the cylinder.
Observation and modeling of deflagration-to-detonation (DDT) transition in low-density HMX
Tringe, Joseph; Vandersall, Kevin; Reaugh, Jack; Levie, Harold; Henson, Bryan; Smilowitz, Laura; Parker, Gary
2015-06-01
We employ simultaneous flash x-ray radiography and streak imaging, together with a multi-phase finite element model, to understand deflagration-to-detonation transition (DDT) phenomena in low-density (~ 1.2 gm/cm3) powder of the explosive cyclotetramethylene-tetranitramine (HMX). HMX powder was lightly hand-tamped in a 12.7 mm diameter column, relatively lightly-confined in an optically-transparent polycarbonate cylinder with wall thickness 25.4 mm. We observe apparent compaction of the powder in advance of the detonation transition, both by x-ray contrast and by the motion of small steel spheres pre-emplaced throughout the length of explosive. High-speed imaging along the explosive cylinder length provides a temporally continuous record of the transition that is correlated with the high-resolution x-ray image record. Preliminary simulation of these experiments with the HERMES model implemented in the ALE3D code enables improved understanding of the explosive particle burning, compaction and detonation phenomena which are implied by the observed reaction rate and transition location within the cylinder. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Possibility of charge density wave transition in a SrPt2Sb2 superconductor.
Ibuka, Soshi; Imai, Motoharu
2016-04-27
The first-order transition at T(0) = 270 K for the platinum-based SrPt2Sb2 superconductor was investigated using x-ray diffraction and magnetic susceptibility measurements. When polycrystalline SrPt2Sb2 was cooled down through T(0), the structure was transformed from monoclinic to a modulated orthorhombic structure, and no magnetic order was formed, which illustrates the possibility of a charge density wave (CDW) transition at T(0). SrPt2Sb2 can thus be a new example to examine the interplay of CDW and superconductivity in addition to SrPt2As2, BaPt2As2, and LaPt2Si2. It is unique that the average structure of the low-temperature phase has higher symmetry than that of the high-temperature phase.
Density-transition based electron injector for laser driven wakefield accelerators
Schmid, K.; Buck, A.; Sears, C. M. S.; Mikhailova, J. M.; Tautz, R.; Herrmann, D.; Geissler, M.; Krausz, F.; Veisz, L.
2010-09-01
We demonstrate a laser wakefield accelerator with a novel electron injection scheme resulting in enhanced stability, reproducibility, and ease of use. In order to inject electrons into the accelerating phase of the plasma wave, a sharp downward density transition is employed. Prior to ionization by the laser pulse this transition is formed by a shock front induced by a knife edge inserted into a supersonic gas jet. With laser pulses of 8 fs duration and with only 65 mJ energy on target, the accelerator produces a monoenergetic electron beam with tunable energy between 15 and 25 MeV and on average 3.3 pC charge per electron bunch. The shock-front injector is a simple and powerful new tool to enhance the reproducibility of laser-driven electron accelerators, is easily adapted to different laser parameters, and should therefore allow scaling to the energy range of several hundred MeV.
Drying and wetting transitions of a Lennard-Jones fluid: Simulations and density functional theory
Evans, Robert; Stewart, Maria C.; Wilding, Nigel B.
2017-07-01
We report a theoretical and simulation study of the drying and wetting phase transitions of a truncated Lennard-Jones fluid at a flat structureless wall. Binding potential calculations predict that the nature of these transitions depends on whether the wall-fluid attraction has a long ranged (LR) power law decay or is instead truncated, rendering it short ranged (SR). Using grand canonical Monte Carlo simulation and classical density functional theory, we examine both cases in detail. We find that for the LR case wetting is first order, while drying is continuous (critical) and occurs exactly at zero attractive wall strength, i.e., in the limit of a hard wall. In the SR case, drying is also critical but the order of the wetting transition depends on the truncation range of the wall-fluid potential. We characterize the approach to critical drying and wetting in terms of the density and local compressibility profiles and via the finite-size scaling properties of the probability distribution of the overall density. For the LR case, where the drying point is known exactly, this analysis allows us to estimate the exponent ν∥, which controls the parallel correlation length, i.e., the extent of vapor bubbles at the wall. Surprisingly, the value we obtain is over twice that predicted by mean field and renormalization group calculations, despite the fact that our three dimensional system is at the upper critical dimension where mean field theory for critical exponents is expected to hold. Possible reasons for this discrepancy are discussed in the light of fresh insights into the nature of near critical finite-size effects.
Energy Technology Data Exchange (ETDEWEB)
Stoessel, J.P.; Wolynes, P.G.
1989-01-01
With analogy to the ''highly accurate'' summation of cluster diagrams for hard sphere fluids a la Carnahan-Starling, we present a simple, real space free energy density functional for arbitrary potential systems, based on the generalization of the second virial coefficient to inhomogeneous systems which, when applied to hard sphere, soft-sphere, and Lennard-Jones freezing, yield melting characteristics in remarkable agreement with experiment. Implications for the liquid-glass transition in all three potential systems are also presented. 45 refs., 7 figs., 1 tab.
Superfluid density and superconducting transition temperature in Bi-based cuprate single crystals.
Gasparov, L.; Tanner, D.; Berger, H.; Forro, L.; Margaritondo, G.
2000-03-01
We present temperature-dependent reflectance measurements for Bi-based cuprate single crystals in the frequency range from 100 to 40,000 cm-1 (0.012--5 eV). The optical conductivity is obtained by Kramers-Kronig analysis. We compare differently doped Bi-2212 (particularly in the underdoped regime) as well as Pr-doped Bi-2212 crystals by analyzing optical conductivity in the framework of a two-fluid approach. This approach allows us to study correlations between superfluid density and superconducting transition temperature of these materials.
First order phase transition in finite density QCD using the modulus of the Dirac determinant
Aloisio, R; Di Carlo, G; Galante, A; Grillo, A F
1998-01-01
We report results of simulations of strong coupling, finite density QCD obtained within a MFA inspired approach where the fermion determinant in the integration measure is replaced by its absolute value. Contrary to the standard wisdom, we show that within this approach a clear signal of a phase transition appears with a critical chemical potential in extremely good agreement with the results obtained with the Glasgow algorithm. The modulus of the fermion determinant seems therefore to preserve some of the relevant physical properties of the system. We also analyze the dependence of our results on the quark mass, including both the chiral and large mass limit, and the theory in the quenched approximation.
Calculation of the Nuclear Transition Charge Density in a Microscopic sdgIBM-1
Institute of Scientific and Technical Information of China (English)
ZHANG Zhan-Jun; SANG Jian-ping; LIU Yong
2000-01-01
Formulae of proton and neutron boson structure functions (BSF's) are deduced in terms of a microscopic approach of sdgIBM (namely, microscopic sdgIBM). For the nucleus 190Os, the value of BSF's is worked out. Due to the high similarity, the maximum F-spin truncation is made under the full-symmetry approximation. Thereafter, calculations of E2 and E4 transition charge densities (TCD's) are performed in the sdgIBM-1. It is found that the E2 and E4 TCD's can be reproduced quite satisfactorily in the uniform frame of microscopic sdgIBM-1.
Density-functional theory for fluid-solid and solid-solid phase transitions
Bharadwaj, Atul S.; Singh, Yashwant
2017-03-01
We develop a theory to describe solid-solid phase transitions. The density functional formalism of classical statistical mechanics is used to find an exact expression for the difference in the grand thermodynamic potentials of the two coexisting phases. The expression involves both the symmetry conserving and the symmetry broken parts of the direct pair correlation function. The theory is used to calculate phase diagram of systems of soft spheres interacting via inverse power potentials u (r ) =ɛ "close="1 /n )">σ /r n , where parameter n measures softness of the potential. We find that for 1 /n ≥0.154 the body-centred-cubic (bcc) structure is preferred. The bcc structure transforms into the fcc structure upon increasing the density. The calculated phase diagram is in good agreement with the one found from molecular simulations.
Self-Focusing of Hermite-Cosh-Gaussian Laser Beams in Plasma under Density Transition
Directory of Open Access Journals (Sweden)
Manzoor Ahmad Wani
2014-01-01
Full Text Available Self-focusing of Hermite-Cosh-Gaussian (HChG laser beam in plasma under density transition has been discussed here. The field distribution in the medium is expressed in terms of beam-width parameters and decentered parameter. The differential equations for the beam-width parameters are established by a parabolic wave equation approach under paraxial approximation. To overcome the defocusing, localized upward plasma density ramp is considered, so that the laser beam is focused on a small spot size. Plasma density ramp plays an important role in reducing the defocusing effect and maintaining the focal spot size up to several Rayleigh lengths. To discuss the nature of self-focusing, the behaviour of beam-width parameters with dimensionless distance of propagation for various values of decentered parameters is examined by numerical estimates. The results are presented graphically and the effect of plasma density ramp and decentered parameter on self-focusing of the beams has been discussed.
[Validity of PSA density of the transition zone in the diagnosis of prostate cancer].
Anastasi, G; Magno, C; Carmignani, A; Inferrera, A; Petrelli, A; Broccio, G
2000-12-01
One hundred four patients (mean age 70.6 years) with prostatic specific antigen (PSA) values between 4 and 10 ng/ml (average 7.9 ng/ml), and with no suspects for neoplasia by digital rectal examination (DRE) and transrectal ultrasound (TRUS) were studied. In all patients PSA density for the entire prostate (PSAD) and PSA density for the transition zone (PSAT) were calculated. TRUS was performed using a 5 MHz probe. Prostate and transition zone volumes were obtained by ellipsoid formula. Aim of the study was to evaluate the PSAT predictivity for prostate cancer compared to the PSAD. Sixteen out of 104 patients (15.4%) had histologically confirmed prostate cancer, and 88 (84.6%) had benign prostatic hyperplasia. When cut-off for PSAD was 0.15 ng/ml/cc, specificity and sensitivity were respectively 75% and 68% with positive and negative predictive values of 54% and 17%; when cut-off for PSAT was 0.34% ng/ml/cc, sensitivity and specificity were respectively 100% and 68% with positive and negative predictive values of 60% and 18%. Our results, according to the literature data, suggest that PSAT seems to have a higher predictivity for prostate cancer than PSAD, providing an optimization for the employ of prostatic biopsy, especially for those patients with PSA values between 4 and 10 ng/ml.
Directory of Open Access Journals (Sweden)
Gian Carlo Gazzadi
2015-06-01
Full Text Available Suspended nanowires (SNWs have been deposited from Co–carbonyl precursor (Co2(CO8 by focused electron beam induced deposition (FEBID. The SNWs dimensions are about 30–50 nm in diameter and 600–850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC and hexagonal close-packed (HCP Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM analysis and by energy-dispersive X-ray (EDX spectroscopy, respectively. Current (I–voltage (V measurements with current densities up to 107 A/cm2 determine different structural transitions in the SNWs, depending on the I–V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 107 A/cm2. The role played by resistive heating and electromigration in these transitions is discussed.
Gazzadi, Gian Carlo; Frabboni, Stefano
2015-01-01
Suspended nanowires (SNWs) have been deposited from Co-carbonyl precursor (Co2(CO)8) by focused electron beam induced deposition (FEBID). The SNWs dimensions are about 30-50 nm in diameter and 600-850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC) and hexagonal close-packed (HCP) Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM) analysis and by energy-dispersive X-ray (EDX) spectroscopy, respectively. Current (I)-voltage (V) measurements with current densities up to 10(7) A/cm(2) determine different structural transitions in the SNWs, depending on the I-V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 10(7) A/cm(2). The role played by resistive heating and electromigration in these transitions is discussed.
Song, Yun S; Steinrücken, Matthias
2012-03-01
The transition density function of the Wright-Fisher diffusion describes the evolution of population-wide allele frequencies over time. This function has important practical applications in population genetics, but finding an explicit formula under a general diploid selection model has remained a difficult open problem. In this article, we develop a new computational method to tackle this classic problem. Specifically, our method explicitly finds the eigenvalues and eigenfunctions of the diffusion generator associated with the Wright-Fisher diffusion with recurrent mutation and arbitrary diploid selection, thus allowing one to obtain an accurate spectral representation of the transition density function. Simplicity is one of the appealing features of our approach. Although our derivation involves somewhat advanced mathematical concepts, the resulting algorithm is quite simple and efficient, only involving standard linear algebra. Furthermore, unlike previous approaches based on perturbation, which is applicable only when the population-scaled selection coefficient is small, our method is nonperturbative and is valid for a broad range of parameter values. As a by-product of our work, we obtain the rate of convergence to the stationary distribution under mutation-selection balance.
Novel charge density wave transition in crystals of R5Ir4Si10
Indian Academy of Sciences (India)
S Ramakrishnan
2002-05-01
We review the observation of novel charge density wave (CDW) transitions in ternary R5Ir4Si10 compounds. A high quality single crystal of Lu5Ir4Si10 shows the formation of a commensurate CDW along -axis below 80 K in the (ℎ, 0, ) plane that coexists with BCS type superconductivity below 3.9 K. However, in a single crystal of Er5Ir4Si10, one observes the development of a 1D-incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er3 moments are antiferromagnetically ordered below 2.8 K which results in the coexistence of strongly coupled CDW with local moment antiferromagnetism in Er5Ir4Si10. Unlike conventional CDW systems, extremely sharp transition (width ∼ 1.5 K) in all bulk properties along with huge heat capacity anomalies in these compounds makes this CDW transition an interesting one.
Andrews, Lester
2004-02-20
Metal hydrides are of considerable importance in chemical synthesis as intermediates in catalytic hydrogenation reactions. Transition metal atoms react with dihydrogen to produce metal dihydrides or dihydrogen complexes and these may be trapped in solid matrix samples for infrared spectroscopic study. The MH(2) or M(H(2)) molecules so formed react further to form higher MH(4), (H(2))MH(2), or M(H(2))(2), and MH(6), (H(2))(2)MH(2), or M(H(2))(3) hydrides or complexes depending on the metal. In this critical review these transition metal and dihydrogen reaction products are surveyed for Groups 3 though 12 and the contrasting behaviour in Groups 6 and 10 is discussed. Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate. 104 references are cited.
Quantum phase transitions and collective enhancement of level density in odd–A and odd–odd nuclei
Energy Technology Data Exchange (ETDEWEB)
Karampagia, S., E-mail: karampag@nscl.msu.edu [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321 (United States); Renzaglia, A. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-1321 (United States); Zelevinsky, V. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321 (United States); Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-1321 (United States)
2017-06-15
The nuclear shell model assumes an effective mean-field plus interaction Hamiltonian in a specific configuration space. We want to understand how various interaction matrix elements affect the observables, the collectivity in nuclei and the nuclear level density for odd–A and odd–odd nuclei. Using the sd and pf shells, we vary specific groups of matrix elements and study the evolution of energy levels, transition rates and the level density. In all cases studied, a transition between a “normal” and a collective phase is induced, accompanied by an enhancement of the level density in the collective phase. In distinction to neighboring even–even nuclei, the enhancement of the level density is observed already at the transition point. The collective phase is reached when the single-particle transfer matrix elements are dominant in the shell model Hamiltonian, providing a sign of their fundamental role.
Oka, Shotaro
2015-01-01
The canonical approach for finite density lattice QCD has a numerical instability. This instability makes it difficult to use the method reliably at the finite real chemical potential region. We studied this instability in detail and found that it is caused by the cancellation of significant digits. In order to reduce the effect of this cancellation, we adopt the multiple precision calculation for our discrete Fourier transformation (DFT) program, and we get the canonical partition function Zc(n,T) with required accuracy. From the obtained Zc(n,T), we calculate Lee--Yang zero distribution varying the number of significant digits. As a result, some curves surround the origin in the fugacity plane, but they are moved by varying the number of significant digits. Hence, we conclude that these curves are pseudo phase transition lines, and not real ones.
Comment on the "Influence of Cosmological Transitions on the Evolution of Density Perturbations"
Grishchuk, L P
1998-01-01
The "standard inflationary result" has been confirmed once again. This time, by Martin and Schwarz [1]. The fallacy - "the closer the inflationary epoch is to the de Sitter space-time, the less important are large-scale gravitational waves in the CMBR today" - has been repeated and has been claimed to be finally proved. The paper [1] is somewhat better than many other incorrect inflationary papers on the subject of cosmological perurbations. This paper at least operates with correct equations (taken from the criticized work of Grishchuk [2, 3]). Martin and Schwarz say that Grishchuk's conclusion about approximate equality of metric amplitudes for gravitational waves and density perturbations "is wrong because the time evolution of the scalar metric perturbation through the (smooth) reheating transition was not calculated correctly". They reiterate an old inflationary fantasy about "big amplification" of scalar perturbations (in contrast to gravitational waves) during "reheating". They say that after appropria...
Schickling, Tobias; Bünemann, Jörg; Gebhard, Florian; Boeri, Lilia
2016-05-01
We use the Gutzwiller density-functional theory to calculate ground-state properties and band structures of iron in its body-centered-cubic (bcc) and hexagonal-close-packed (hcp) phases. For a Hubbard interaction U =9 eV and Hund's-rule coupling J =0.54 eV , we reproduce the lattice parameter, magnetic moment, and bulk modulus of bcc iron. For these parameters, bcc is the ground-state lattice structure at ambient pressure up to a pressure of pc=41 GPa where a transition to the nonmagnetic hcp structure is predicted, in qualitative agreement with experiment (pcexp=10 ,...,15 GPa ) . The calculated band structure for bcc iron is in good agreement with ARPES measurements. The agreement improves when we perturbatively include the spin-orbit coupling.
Phase Transition in the Density of States of Quantum Spin Glasses
Energy Technology Data Exchange (ETDEWEB)
Erdős, László, E-mail: lerdos@ist.ac.at [IST Austria (Austria); Schröder, Dominik, E-mail: schroeder.dominik@gmail.com [Ludwig-Maximilians-Universität München (Germany)
2014-12-15
We prove that the empirical density of states of quantum spin glasses on arbitrary graphs converges to a normal distribution as long as the maximal degree is negligible compared with the total number of edges. This extends the recent results of Keating et al. (2014) that were proved for graphs with bounded chromatic number and with symmetric coupling distribution. Furthermore, we generalise the result to arbitrary hypergraphs. We test the optimality of our condition on the maximal degree for p-uniform hypergraphs that correspond to p-spin glass Hamiltonians acting on n distinguishable spin- 1/2 particles. At the critical threshold p = n{sup 1/2} we find a sharp classical-quantum phase transition between the normal distribution and the Wigner semicircle law. The former is characteristic to classical systems with commuting variables, while the latter is a signature of noncommutative random matrix theory.
Density-transition based electron injector for laser driven wakefield accelerators
Directory of Open Access Journals (Sweden)
K. Schmid
2010-09-01
Full Text Available We demonstrate a laser wakefield accelerator with a novel electron injection scheme resulting in enhanced stability, reproducibility, and ease of use. In order to inject electrons into the accelerating phase of the plasma wave, a sharp downward density transition is employed. Prior to ionization by the laser pulse this transition is formed by a shock front induced by a knife edge inserted into a supersonic gas jet. With laser pulses of 8 fs duration and with only 65 mJ energy on target, the accelerator produces a monoenergetic electron beam with tunable energy between 15 and 25 MeV and on average 3.3 pC charge per electron bunch. The shock-front injector is a simple and powerful new tool to enhance the reproducibility of laser-driven electron accelerators, is easily adapted to different laser parameters, and should therefore allow scaling to the energy range of several hundred MeV.
Multiple charge density wave transitions in the antiferromagnets R NiC2 (R =Gd ,Tb)
Shimomura, S.; Hayashi, C.; Hanasaki, N.; Ohnuma, K.; Kobayashi, Y.; Nakao, H.; Mizumaki, M.; Onodera, H.
2016-04-01
X-ray scattering and electrical resistivity measurements were performed on GdNiC2 and TbNiC2. We found a set of satellite peaks characterized by q1=(0.5 ,η ,0 ) below T1, at which the resistivity shows a sharp inflection, suggesting the charge density wave (CDW) formation. The value of η decreases with decreasing temperature below T1, and then a transition to a commensurate phase with q1 C=(0.5 ,0.5 ,0 ) takes place. The diffuse scattering observed above T1 indicates the presence of soft phonon modes associated with CDW instabilities at q1 and q2=(0.5 ,0.5 ,0.5 ) . The long-range order given by q2 is developed in addition to that given by q1 C in TbNiC2, while the short-range correlation with q2 persists even at 6 K in GdNiC2. The amplitude of the q1 C lattice modulation is anomalously reduced below an antiferromagnetic transition temperature TN in GdNiC2. In contrast, the q2 order vanishes below TN in TbNiC2. We demonstrate that R NiC2 (R = rare earth) compounds exhibit similarities with respect to their CDW phenomena, and discuss the effects of magnetic transitions on CDWs. We offer a possible displacement pattern of the modulated structure characterized by q1 C and q2 in terms of frustration.
Institute of Scientific and Technical Information of China (English)
Li Cheng-Bin; Li Ming-Kai; Yin Dong; Liu Fu-Qing; Fan Xiang-Jun
2005-01-01
A first principles study of the electronic properties and bulk modulus (B0) of the fcc and bcc transition metals,transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.
The influence of topological phase transition on the superfluid density of overdoped copper oxides.
Shaginyan, V R; Stephanovich, V A; Msezane, A Z; Japaridze, G S; Popov, K G
2017-08-23
We show that a quantum phase transition, generating flat bands and altering Fermi surface topology, is a primary reason for the exotic behavior of the overdoped high-temperature superconductors represented by La2-xSrxCuO4, whose superconductivity features differ from what is predicted by the classical Bardeen-Cooper-Schrieffer theory. This observation can open avenues for chemical preparation of high-Tc materials. We demonstrate that (1) at temperature T = 0, the superfluid density ns turns out to be considerably smaller than the total electron density; (2) the critical temperature Tc is controlled by ns rather than by doping, and is a linear function of the ns; (3) at T > Tc the resistivity ρ(T) varies linearly with temperature, ρ(T) ∝ αT, where α diminishes with Tc → 0, whereas in the normal (non superconducting) region induced by overdoping, Tc = 0, and ρ(T) ∝ T(2). Our results are in good agreement with recent experimental observations.
Hydrostatic pressure effects on the state density and optical transitions in quantum dots
Energy Technology Data Exchange (ETDEWEB)
Galindez-Ramirez, G; Perez-Merchancano, S T [Departamento de Fisica, Universidad del Cauca, calle 5 4-70, Popayan (Colombia); Paredes Gutierrez, H [Escuela de Fisica, Universidad Industrial de Santander, A. A. 678, Bucaramanga (Colombia); Gonzalez, J D, E-mail: jdavid0831@gmail.co [Grupo de Investigacion en teorIa de la Materia Condensada, Universidad del Magdalena, A.A. 731, Santa Marta (Colombia)
2010-09-01
Using the effective mass approximation and variational method we have computed the effects of hydrostatic pressure on the absorption and photoluminescence spectra in spherical quantum dot GaAs-(Ga, Al) As, considering a finite confinement potential of this particular work we show the optical transitions in quantum of various sizes in the presence of hydrogenic impurities and hydrostatic pressure effects. Our first result describes the spectrum of optical absorption of 500 A QD for different values of hydrostatic pressure P = 0, 20 and 40 Kbar. The absorption peaks are sensitive to the displacement of the impurity center to the edge of the quantum dot and even more when the hydrostatic pressure changes in both cases showing that to the extent that these two effects are stronger quantum dots respond more efficiently. Also this result can be seen in the study of the photoluminescence spectrum as in the case of acceptor impurities consider them more efficiently capture carriers or electrons that pass from the conduction band to the valence band. Density states with randomly distributed impurity show that the additional peaks in the curves of the density of impurity states appear due to the presence of the additional hydrostatic pressure effects.
Laser reflection method for determination of shear stress in low density transitional flows
Sathian, Sarith P.; Kurian, Job
2006-03-01
The details of laser reflection method (LRM) for the determination of shear stress in low density transitional flows are presented. The method is employed to determine the shear stress due to impingement of a low density supersonic free jet issuing out from a convergent divergent nozzle on a flat plate. The plate is smeared with a thin oil film and kept parallel to the nozzle axis. For a thin oil film moving under the action of aerodynamic boundary layer, the shear stress at the air-oil interface is equal to the shear stress between the surface and air. A direct and dynamic measurement of the oil film slope generated by the shear force is done using a position sensing detector (PSD). The thinning rate of the oil film is directly measured which is the major advantage of the LRM. From the oil film slope history, calculation of the shear stress is done using a three-point formula. The range of Knudsen numbers investigated is from 0.028 to 0.516. Pressure ratio across the nozzle varied from 3,500 to 8,500 giving highly under expanded free jets. The measured values of shear, in the overlapping region of experimental parameters, show fair agreement with those obtained by force balance method and laser interferometric method.
Superfluid density in He II near the lambda transition: First principles theory
Energy Technology Data Exchange (ETDEWEB)
Jackson, H.W., E-mail: hwjackson2@gmail.com
2015-03-15
A first principles theory of the λ transition in liquid {sup 4}He was introduced in a recent paper [H. W. Jackson, J. Low Temp. Phys. 155, 1 (2009)]. In that theory critical fluctuations consisting of isothermal fourth sound waves are treated with quantum statistical mechanics methods in deriving formulas for constant volume conditions for specific heat, correlation length, equal time pair correlation function, and isothermal compressibility. To leading order terms in (T{sub λ}−T) the theory yields exact results α′=0 and ν′=2/3 for critical exponents at constant volume. A follow-up study in the present paper demonstrates by a least squares fit that a logarithmic function accurately describes the specific heat at svp when (T{sub λ}−T) is between 10{sup −9} K and 10{sup −5} K. This logarithmic divergent behavior conflicts with previous analyses of experimental data and predictions of renormalization group theory that constant pressure specific heat is finite at T{sub λ}, but Is thermodynamically consistent with logarithmic asymptotic behavior of specific heat at constant volume predicted in the new theory. The first principles theory is extended in this paper to derive formulas for superfluid density and for a relation between superfluid density and correlation length in He II near T{sub λ}. Numerical results based on these formulas are in good agreement with experimental data produced by second sound measurements.
Quantum Monte Carlo studies of a metallic spin-density wave transition
Energy Technology Data Exchange (ETDEWEB)
Gerlach, Max Henner
2017-01-20
Plenty experimental evidence indicates that quantum critical phenomena give rise to much of the rich physics observed in strongly correlated itinerant electron systems such as the high temperature superconductors. A quantum critical point of particular interest is found at the zero-temperature onset of spin-density wave order in two-dimensional metals. The appropriate low-energy theory poses an exceptionally hard problem to analytic theory, therefore the unbiased and controlled numerical approach pursued in this thesis provides important contributions on the road to comprehensive understanding. After discussing the phenomenology of quantum criticality, a sign-problem-free determinantal quantum Monte Carlo approach is introduced and an extensive toolbox of numerical methods is described in a self-contained way. By the means of large-scale computer simulations we have solved a lattice realization of the universal effective theory of interest. The finite-temperature phase diagram, showing both a quasi-long-range spin-density wave ordered phase and a d-wave superconducting dome, is discussed in its entirety. Close to the quantum phase transition we find evidence for unusual scaling of the order parameter correlations and for non-Fermi liquid behavior at isolated hot spots on the Fermi surface.
Densities and eccentricities of 139 Kepler planets from transit time variations
Energy Technology Data Exchange (ETDEWEB)
Hadden, Sam; Lithwick, Yoram [Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States)
2014-05-20
We extract densities and eccentricities of 139 sub-Jovian planets by analyzing transit time variations (TTVs) obtained by the Kepler mission through Quarter 12. We partially circumvent the degeneracies that plague TTV inversion with the help of an analytical formula for the TTV. From the observed TTV phases, we find that most of these planets have eccentricities of the order of a few percent. More precisely, the rms eccentricity is 0.018{sub −0.004}{sup +0.005}, and planets smaller than 2.5 R {sub ⊕} are around twice as eccentric as those bigger than 2.5 R {sub ⊕}. We also find a best-fit density-radius relationship ρ ≈ 3 g cm{sup –3} × (R/3 R {sub ⊕}){sup –2.3} for the 56 planets that likely have small eccentricity and hence small statistical correction to their masses. Many planets larger than 2.5 R {sub ⊕} are less dense than water, implying that their radii are largely set by a massive hydrogen atmosphere.
Nanda, Kaushik D; Krylov, Anna I
2017-07-20
Observables such as two-photon absorption cross sections cannot be computed from the wave functions of initial and final states alone because of their nonlinear nature. Rather, they depend on the entire manifold of the excited states, which follows from the familiar sum-over-states expressions of second- and higher-order properties. Consequently, the interpretation of the computed nonlinear optical properties in terms of molecular orbitals is not straightforward and usually relies on approximate few-states models. Here, we show that the two-photon absorption (2PA) transitions can be visualized using response one-particle transition density matrices, which are defined as transition density matrices between the zero-order and first-order perturbed states. We also extend the concept of natural transition orbitals to 2PA transitions. We illustrate the utility of this new tool, which provides a rigorous black box alternative to traditional qualitative few-states analysis, by considering 2PA transitions in ethylene, trans-stilbene, and para-nitroaniline.
Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W; Poole, Peter H
2016-12-14
The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.
Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W.; Poole, Peter H.
2016-12-01
The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.
Phase transitions to dipolar clusters and charge density waves in high T{sub c} superconductors
Energy Technology Data Exchange (ETDEWEB)
Saarela, M., E-mail: Mikko.Saarela@oulu.fi [Department of Physics, University of Oulu, P.O. Box 3000, FIN-90014 (Finland); Kusmartsev, F.V. [Department of Physics, Loughborough University, LE11 3TU (United Kingdom)
2017-02-15
We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.
Quantum critical properties of a metallic spin-density-wave transition
Gerlach, Max H.; Schattner, Yoni; Berg, Erez; Trebst, Simon
2017-01-01
We report on numerically exact determinantal quantum Monte Carlo simulations of the onset of spin-density-wave (SDW) order in itinerant electron systems captured by a sign-problem-free two-dimensional lattice model. Extensive measurements of the SDW correlations in the vicinity of the phase transition reveal that the critical dynamics of the bosonic order parameter are well described by a dynamical critical exponent z =2 , consistent with Hertz-Millis theory, but are found to follow a finite-temperature dependence that does not fit the predicted behavior of the same theory. The presence of critical SDW fluctuations is found to have a strong impact on the fermionic quasiparticles, giving rise to a dome-shaped superconducting phase near the quantum critical point. In the superconducting state we find a gap function that has an opposite sign between the two bands of the model and is nearly constant along the Fermi surface of each band. Above the superconducting Tc, our numerical simulations reveal a nearly temperature and frequency independent self-energy causing a strong suppression of the low-energy quasiparticle weight in the vicinity of the hot spots on the Fermi surface. This indicates a clear breakdown of Fermi liquid theory around these points.
AC-field-induced quantum phase transitions in density of states
Yang, Kai-Hua; Liu, Kai-Di; Wang, Huai-Yu; Qin, Chang-Dong
2016-02-01
We investigate the joint effects of the intralead electron interaction and an external alternating gate voltage on the time-averaged local density of states (DOSs) of a quantum dot coupled to two Luttinger-liquid leads in the Kondo regime. A rich dependence of the DOSs on the driving amplitude and intralead interaction is demonstrated. We show that the feature is quite different for different interaction strengths in the presence of the ac field. It is shown that the photon-assisted transport processes cause an additional splitting of the Kondo peak or dip, which exhibits photon-assisted single-channel (1CK) or two-channel Kondo (2CK) physics behavior. The phase transition between photon-assisted 1CK and 2CK physics occurs when the interaction strength is moderately strong. The inelastic channels associated with photon-assisted electron tunneling can dominate electron transport for weak interaction when the ac amplitude is greater than the frequency by one order of magnitude. In the limit of strong interaction the DOSs scale as a power-law behavior which is strongly affected by the ac field.
Seo, Dong-Kyun
2007-11-14
We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.
Phase transitions to dipolar clusters and charge density waves in high Tc superconductors
Saarela, M.; Kusmartsev, F. V.
2017-02-01
We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.
Liu, Kai; Cheng, Chun; Cheng, Zhenting; Wang, Kevin; Ramesh, Ramamoorthy; Wu, Junqiao
2012-12-12
Various mechanisms are currently exploited to transduce a wide range of stimulating sources into mechanical motion. At the microscale, simultaneously high amplitude, high work output, and high speed in actuation are hindered by limitations of these actuation mechanisms. Here we demonstrate a set of microactuators fabricated by a simple microfabrication process, showing simultaneously high performance by these metrics, operated on the structural phase transition in vanadium dioxide responding to diverse stimuli of heat, electric current, and light. In both ambient and aqueous conditions, the actuators bend with exceedingly high displacement-to-length ratios up to 1 in the sub-100 μm length scale, work densities over 0.63 J/cm(3), and at frequencies up to 6 kHz. The functionalities of actuation can be further enriched with integrated designs of planar as well as three-dimensional geometries. Combining the superior performance, high durability, diversity in responsive stimuli, versatile working environments, and microscale manufacturability, these actuators offer potential applications in microelectromechanical systems, microfluidics, robotics, drug delivery, and artificial muscles.
DEFF Research Database (Denmark)
Hummelshøj, Jens Strabo; Landis, David; Voss, Johannes
2009-01-01
We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K (M1); and 1 alkali, alkaline earth or 3d/4d transition...
Hussain, Tanveer; Maark, Tuhina Adit; Pathak, Biswarup; Ahuja, Rajeev
2013-10-01
This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs) by means of hybrid density functional theory (PBE0). On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM's. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies.
Energy Technology Data Exchange (ETDEWEB)
Singh, Ram Chandra [Department of Physics, Hindustan Institute of Technology, 32, 34 Knowledge Park-III, Greater Noida-201306, UP (India)
2007-09-19
We have used the density-functional theory to study the effect of varying temperature on the isotropic-nematic transition of a fluid of molecules interacting via the Gay-Berne intermolecular potential. The nematic phase is found to be stable with respect to isotropic phase in the temperature range 0.80{<=}T*{<=}1.25. Pair correlation functions needed as input information in density-functional theory is calculated using the Percus-Yevick integral equation theory. We find that the density-functional theory is good for studying the isotropic-nematic transition in molecular fluids if the values of the pair-correlation functions in the isotropic phase are known accurately. We have also compared our results with computer simulation results wherever they are available.
Ovchinnikov, Vasily A; Sundholm, Dage
2014-04-21
The 0-0 transitions of the electronic excitation spectra of the lowest tautomers of the four nucleotide (DNA) bases have been studied using linear-response approximate coupled-cluster singles and doubles (CC2) calculations. Excitation energies have also been calculated at the linear-response time-dependent density functional theory (TDDFT) level using the B3LYP functional. Large basis sets have been employed for ensuring that the obtained excitation energies are close to the basis-set limit. Zero-point vibrational energy corrections have been calculated at the B3LYP and CC2 levels for the ground and excited states rendering direct comparisons with high-precision spectroscopy measurements feasible. The obtained excitation energies for the 0-0 transitions of the first excited states of guanine tautomers are in good agreement with experimental values confirming the experimental assignment of the energetic order of the tautomers of the DNA bases. For the experimentally detected guanine tautomers, the first excited state corresponds to a π→π* transition, whereas for the tautomers of adenine, thymine, and the lowest tautomer of cytosine the transition to the first excited state has n →π* character. The calculations suggest that the 0-0 transitions of adenine, thymine, and cytosine are not observed in the absorption spectrum due to the weak oscillator strength of the formally symmetry-forbidden transitions, while 0-0 transitions of thymine have been detected in fluorescence excitation spectra.
Misra, D.; Kundu, T. K.
2016-09-01
Density functional theory with appropriate functional has been employed to investigate the metal to insulator transition in oxygen deficient LaNiO3-x (x = 0.0, 0.25, 0.5, 1.0) compounds. While the metallic nature of LaNiO3 is characterized by the low temperature Fermi liquid behavior of resistivity and a finite density of states at the Fermi level, the density of states and the transport properties clearly identify LaNiO2.75 as a semiconductor, and LaNiO2.5 as an insulator, which is followed by another insulator to semiconductor transition with further increase of x to ‘1’ in LaNiO2. This oxygen vacancy controlled metal to insulator transition is explained on the basis of non-adiabatic polaronic transport. From the covalency metric calculation of the chemical bonding and the Bader charge transfer analysis, this metal to insulator transition is attributed to the enhanced covalent part in the chemical bonding and reduced charge transfer from Ni to O atoms in LaNiO3-x compounds.
DNA conformational transitions inferred from re-evaluation of m|Fo| - D|Fc| electron-density maps.
Sunami, Tomoko; Chatake, Toshiyuki; Kono, Hidetoshi
2017-07-01
Conformational flexibility of DNA plays important roles in biological processes such as transcriptional regulation and DNA packaging etc. To understand the mechanisms of these processes, it is important to analyse when, where and how DNA shows conformational variations. Recent analyses have indicated that conventional refinement methods do not always provide accurate models of crystallographic heterogeneities and that some information on polymorphism has been overlooked in previous crystallographic studies. In the present study, the m|Fo| - D|Fc| electron-density maps of double-helical DNA crystal structures were calculated at a resolution equal to or better than 1.5 Å and potential conformational transitions were found in 27% of DNA phosphates. Detailed analyses of the m|Fo| - D|Fc| peaks indicated that some of these unassigned densities correspond to ZI ↔ ZII or A/B → BI conformational transitions. A relationship was also found between ZI/ZII transitions and metal coordination in Z-DNA from the detected peaks. The present study highlights that frequent transitions of phosphate backbones occur even in crystals and that some of these transitions are affected by the local molecular environment.
A Closely-Packed System of Low-Mass, Low-Density Planets Transiting Kepler-11
Lissauer, Jack J; Ford, Eric B; Borucki, William J; Fressin, Francois; Marcy, Geoffrey W; Orosz, Jerome A; Rowe, Jason F; Torres, Guillermo; Welsh, William F; Batalha, Natalie M; Bryson, Stephen T; Buchhave, Lars A; Caldwell, Douglas A; Carter, Joshua A; Charbonneau, David; Christiansen, Jessie L; Cochran, William D; Desert, Jean-Michel; Dunham, Edward W; Fanelli, Michael N; Fortney, Jonathan J; Gautier, Thomas N; Geary, John C; Gilliland, Ronald L; Haas, Michael R; Hall, Jennifer R; Holman, Matthew J; Koch, David G; Latham, David W; Lopez, Eric; McCauliff, Sean; Miller, Neil; Morehead, Robert C; Quintana, Elisa V; Ragozzine, Darin; Sasselov, Dimitar; Short, Donald R; Steffen, Jason H
2011-01-01
When an extrasolar planet passes in front of its star (transits), its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star that reveal six transiting planets, five with orbital periods between 10 and 47 days plus a sixth one with a longer period. The five inner planets are among the smallest whose masses and sizes have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end o...
Evolution of the phonon density of states of LaCoO3 over the spin state transition
Energy Technology Data Exchange (ETDEWEB)
Golosova, N. O. [Joint Institute for Nuclear Research, Dubna, Russia; Kozlenko, D. P. [Joint Institute for Nuclear Research, Dubna, Russia; Kolesnikov, Alexander I [ORNL; Kazimirov, V. Yu. [Joint Institute for Nuclear Research, Dubna, Russia; Smirnov, M. B. [St. Petersburg State University, St. Petersburg, Russia; Jirak, Z. [Institute of Physics, Czech Republic; Savenko, B. N. [Joint Institute for Nuclear Research, Dubna, Russia
2011-01-01
The phonon spectra of LaCoO3 were studied by inelastic neutron scattering in the temperature range of 4 120 K. The DFT calculations of the lattice dynamics have been made for interpretation of the experimental data. The observed and calculated phonon frequencies were found to be in a reasonable agreement. The evolution of the phonon density of states over the spin state transition was analyzed. In the low-temperature range (T < 50 K), an increase in the energy of resolved breathing, stretching, and bending phonon modes was found, followed by their softening and broadening at higher temperatures due to the spin state transition and relevant orbital-phonon coupling.
Li, Yonghui; Ullrich, Carsten
2013-03-01
The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. This work is supported by NSF Grant DMR-1005651
Ejiri, S; Aoki, S; Kanaya, K; Ohno, H; Saito, H; Hatsuda, T; Maezawa, Y; Umeda, T
2010-01-01
We study scaling behavior of a chiral order parameter performing a simulation of two-flavor QCD with improved Wilson quarks. It has been shown that the scaling behavior of the chiral order parameter defined by a Ward-Takahashi identity agrees with the scaling function of the three-dimensional O(4) spin model at zero chemical potential. We extend the scaling study to finite density QCD. Calculating derivatives of the chiral order parameter with respect to the chemical potential in two-flavor QCD, the scaling property of chiral phase transition is discussed in the low density region. We moreover calculate the curvature of the phase boundary of the chirl phase transition in the temperature and chemical potential plane assuming the O(4) scaling relation.
Hirano, Y; Kiyama, S; Fujiwara, Y; Koguchi, H; Sakakita, H
2015-11-01
A high current density (≈3 mA/cm(2)) hydrogen ion beam source operating in an extremely low-energy region (E(ib) ≈ 150-200 eV) has been realized by using a transition to a highly focused state, where the beam is extracted from the ion source chamber through three concave electrodes with nominal focal lengths of ≈350 mm. The transition occurs when the beam energy exceeds a threshold value between 145 and 170 eV. Low-level hysteresis is observed in the transition when E(ib) is being reduced. The radial profiles of the ion beam current density and the low temperature ion current density can be obtained separately using a Faraday cup with a grid in front. The measured profiles confirm that more than a half of the extracted beam ions reaches the target plate with a good focusing profile with a full width at half maximum of ≈3 cm. Estimation of the particle balances in beam ions, the slow ions, and the electrons indicates the possibility that the secondary electron emission from the target plate and electron impact ionization of hydrogen may play roles as particle sources in this extremely low-energy beam after the compensation of beam ion space charge.
Evidence for a Peierls phase-transition in a three-dimensional multiple charge-density waves solid.
Mansart, Barbara; Cottet, Mathieu J G; Penfold, Thomas J; Dugdale, Stephen B; Tediosi, Riccardo; Chergui, Majed; Carbone, Fabrizio
2012-04-10
The effect of dimensionality on materials properties has become strikingly evident with the recent discovery of graphene. Charge ordering phenomena can be induced in one dimension by periodic distortions of a material's crystal structure, termed Peierls ordering transition. Charge-density waves can also be induced in solids by strong coulomb repulsion between carriers, and at the extreme limit, Wigner predicted that crystallization itself can be induced in an electrons gas in free space close to the absolute zero of temperature. Similar phenomena are observed also in higher dimensions, but the microscopic description of the corresponding phase transition is often controversial, and remains an open field of research for fundamental physics. Here, we photoinduce the melting of the charge ordering in a complex three-dimensional solid and monitor the consequent charge redistribution by probing the optical response over a broad spectral range with ultrashort laser pulses. Although the photoinduced electronic temperature far exceeds the critical value, the charge-density wave is preserved until the lattice is sufficiently distorted to induce the phase transition. Combining this result with ab initio electronic structure calculations, we identified the Peierls origin of multiple charge-density waves in a three-dimensional system for the first time.
Approach to nonadiabatic transitions by density matrix evolution and molecular dynamics simulations
Berendsen, H.J.C.; Mavri, J.
1996-01-01
Many biological processes are characterized by an essentially quantum dynamical event, such as electron or proton transfer, in a complex classical environment. To treat such processes properly by computer simulation, allowing nonadiabatic transitions involving excited states, we recently developed a
Tretyakov, Nikita; Vollmer, Doris; Butt, Hans-Jürgen; Dünweg, Burkhard; Daoulas, Kostas Ch
2016-01-01
Classical density functional theory is applied to investigate the validity of a phenomenological force-balance description of the stability of the Cassie state of liquids on substrates with nanoscale corrugation. A bulk free-energy functional of third order in local density is combined with a square-gradient term, describing the liquid-vapor interface. The bulk free energy is parameterized to reproduce the liquid density and the compressibility of water. The square-gradient term is adjusted to model the width of the water-vapor interface. The substrate is modeled by an external potential, based upon Lennard-Jones interactions. The three-dimensional calculation focuses on substrates patterned with nanostripes and square-shaped nanopillars. Using both the force-balance relation and density-functional theory, we locate the Cassie-to-Wenzel transition as a function of the corrugation parameters. We demonstrate that the force-balance relation gives a qualitatively reasonable description of the transition even on t...
Directory of Open Access Journals (Sweden)
Tanveer Hussain
2013-10-01
Full Text Available This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs by means of hybrid density functional theory (PBE0. On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM’s. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies.
Institute of Scientific and Technical Information of China (English)
LIU Yan-Hui; TIAN Fu-Bo; MA Yan-Ming; HE Zhi; CUI Tian; LIU Bing-Bing; ZOU Guang-Tian
2008-01-01
Crystal structures and optical properties of the δ-O,2 phase and the ε-O,8 phase have been investigated by using the ab initio pseudopotential plane-wave method. It is found that the phase transition is of the first order with a discontinuous volumetric change from the antiferromagnetic δ-O,2 phase to the nonmagnetic ε-O8 phase, consistent with the experimental findings. The energy band calculations show that the direct band gap changes into an indirect band gap after the phase transition. The apparent change in the optical properties can be used for identifying the phase transition from δ-O2 to ε-O,8.
Implications of cosmic string-induced density ﬂuctuations at the quark–hadron transition
Indian Academy of Sciences (India)
Biswanath Layek; Soma Sanyal; Ajit M Srivastava
2003-11-01
We show that cosmic strings moving through the plasma at the time of a ﬁrst-order quark–hadron transition in the early universe generate baryon inhomogeneities, which can survive till the nucleosynthesis epoch. We ﬁnd out how these inhomogeneities actually affect the calculated values of the light element abundances. Recently a wealth of observational data from various experiments have helped to reduce the uncertainties in the values of these abundances. Using these we show that it is possible to derive constraints in the presence of cosmic strings during the quark–hadron transition.
Kawano, Hiroyuki; Bivard, Andrew; Lin, Longting; Spratt, Neil J; Miteff, Ferdinand; Parsons, Mark W; Levi, Christopher R
2016-03-01
Collateral circulation is recognized to influence the life expectancy of the ischemic penumbra in acute ischemic stroke. The best method to quantify collateral status on acute imaging is uncertain. We aimed to determine the relationship between visual collateral status, quantitative collateral assessments, baseline computed tomographic perfusion measures, and tissue outcomes on follow-up imaging. Sixty-six consecutive patients with acute ischemic stroke clinically eligible for recanalization therapy and with M1 or M2 middle cerebral artery occlusion were evaluated. We compared the visual collateral scoring with measures of contrast peak time delay and contrast peak density. We also compared these measures for their ability to predict perfusion lesion and infarct core volumes, final infarct, and infarct growth. Shorter contrast peak time delay (P=0.041) and higher contrast peak density (P=0.002) were associated with good collateral status. Shorter contrast peak time delay correlated with higher contrast peak density (β=-4.413; P=0.037). In logistic regression analysis after adjustment for age, sex, onset-computed tomographic time, and occlusion site, higher contrast peak density was independently associated with good collateral status (P=0.009). Multiple regression analysis showed that higher contrast peak density was an independent predictor of smaller perfusion lesion volume (P=0.029), smaller ischemic core volume (P=0.044), smaller follow-up infarct volume (P=0.005), and smaller infarct growth volume (P=0.010). Visual collateral status, contrast peak density, and contrast peak time delay were inter-related, and good collateral status was strongly associated with contrast peak density. Contrast peak density in collateral vessel may be an important factor in tissue fate in acute ischemic stroke. © 2016 American Heart Association, Inc.
H I-to-H{sub 2} transitions and H I column densities in galaxy star-forming regions
Energy Technology Data Exchange (ETDEWEB)
Sternberg, Amiel [Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978 (Israel); Le Petit, Franck; Roueff, Evelyne; Le Bourlot, Jacques [LERMA, Observatoire de Paris, CNRS, 5 place Jules Janssen, F-92190 Meudon (France)
2014-07-20
We present new analytic theory and radiative transfer computations for the atomic-to-molecular (H I-to-H{sub 2}) transitions and the buildup of atomic hydrogen (H I) gas columns in optically thick interstellar clouds irradiated by far-UV (FUV) photodissociating radiation fields. We derive analytic expressions for the total H I column densities for (one-dimensional (1D)) planar slabs, for beamed or isotropic radiation fields, from the weak- to strong-field limits, for gradual or sharp atomic-to-molecular transitions, and for arbitrary metallicity. Our expressions may be used to evaluate the H I column densities as functions of the radiation field intensity and the H{sub 2}-dust-limited dissociation flux, the hydrogen gas density, and the metallicity-dependent H{sub 2} formation rate coefficient and FUV dust grain absorption cross section. We make the distinction between 'H I-dust' and 'H{sub 2}-dust' opacity, and we present computations for the 'universal H{sub 2}-dust-limited effective dissociation bandwidth'. We validate our analytic formulae with Meudon PDR code computations for the H I-to-H{sub 2} density profiles and total H I column densities. We show that our general 1D formulae predict H I columns and H{sub 2} mass fractions that are essentially identical to those found in more complicated (and approximate) spherical (shell-core) models. We apply our theory to compute H{sub 2} mass fractions and star-formation thresholds for individual clouds in self-regulated galaxy disks, for a wide range of metallicities. Our formulae for the H I columns and H{sub 2} mass fractions may be incorporated into hydrodynamics simulations for galaxy evolution.
HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
Sternberg, Amiel; Roueff, Evelyne; Bourlot, Jacques Le
2014-01-01
We present new analytic theory and radiative transfer computations for the atomic to molecular (HI-to-H2) transitions, and the build-up of atomic-hydrogen (HI) gas columns, in optically thick interstellar clouds, irradiated by far-ultraviolet photodissociating radiation fields. We derive analytic expressions for the total HI column densities for (1D) planar slabs, for beamed or isotropic radiation fields, from the weak- to strong-field limits, for gradual or sharp atomic to molecular transitions, and for arbitrary metallicity. Our expressions may be used to evaluate the HI column densities as functions of the radiation field intensity and the H2-dust-limited dissociation flux, the hydrogen gas density, and the metallicity-dependent H2 formation rate-coefficient and far-UV dust-grain absorption cross-section. We make the distinction between "HI-dust" and "H2-dust" opacity, and we present computations for the "universal H2-dust-limited effective dissociation bandwidth". We validate our analytic formulae with Me...
Exact versus Taylor-expanded energy density in the study of the neutron star crust-core transition
Routray, T. R.; Viñas, X.; Basu, D. N.; Pattnaik, S. P.; Centelles, M.; Robledo, L. B.; Behera, B.
2016-10-01
The importance of the fourth and higher order terms in the Taylor series expansion of energy of isospin asymmetric nuclear matter in studies of the neutron star crust-core phase transition is investigated using the finite-range simple effective interaction. Analytic expressions for the evaluation of the second and fourth order derivative terms in the Taylor series expansion for any general finite-range interaction of Yukawa, exponential or Gaussian form have been obtained. The effect of the nuclear matter incompressibility, symmetry energy and slope parameters on the predictions for the crust-core transition density is examined. The crustal moment of inertia is calculated and the prediction for the radius of the Vela pulsar is analyzed using different equations of state.
Exact versus Taylor-expanded energy density in the study of the neutron star crust-core transition
Routray, T R; Basu, D N; Pattnaik, S P; Centelles, M; Robledo, L; Behera, B
2016-01-01
The importance of the fourth and higher order terms in the Taylor series expansion of the energy of the isospin asymmetric nuclear matter in the study of the neutron star crust-core phase transition is investigated using the finite range simple effective interaction. Analytic expressions for the evaluation of the second and fourth order derivative terms in the Taylor series expansion for any general finite range interaction of Yukawa, exponential or Gaussian form have been obtained. The effect of the nuclear matter incompressibility, symmetry energy and slope parameters on the predictions for the crust-core transition density is examined. The crustal moment of inertia is calculated and the prediction for the radius of the Vela pulsar is analyzed using different equations of state.
Wang, Ying; Feng, Chenglian; Liu, Yuedan; Zhao, Yujie; Li, Huixian; Zhao, Tianhui; Guo, Wenjing
2017-02-01
Transition metals in the fourth period of the periodic table of the elements are widely widespread in aquatic environments. They could often occur at certain concentrations to cause adverse effects on aquatic life and human health. Generally, parametric models are mostly used to construct species sensitivity distributions (SSDs), which result in comparison for water quality criteria (WQC) of elements in the same period or group of the periodic table might be inaccurate and the results could be biased. To address this inadequacy, the non-parametric kernel density estimation (NPKDE) with its optimal bandwidths and testing methods were developed for establishing SSDs. The NPKDE was better fit, more robustness and better predicted than conventional normal and logistic parametric density estimations for constructing SSDs and deriving acute HC5 and WQC for transition metals in the fourth period of the periodic table. The decreasing sequence of HC5 values for the transition metals in the fourth period was Ti > Mn > V > Ni > Zn > Cu > Fe > Co > Cr(VI), which were not proportional to atomic number in the periodic table, and for different metals the relatively sensitive species were also different. The results indicated that except for physical and chemical properties there are other factors affecting toxicity mechanisms of transition metals. The proposed method enriched the methodological foundation for WQC. Meanwhile, it also provided a relatively innovative, accurate approach for the WQC derivation and risk assessment of the same group and period metals in aquatic environments to support protection of aquatic organisms.
Energy Technology Data Exchange (ETDEWEB)
Nanda, Vikas; Kant, Niti, E-mail: nitikant@yahoo.com [Department of Physics, Lovely Professional University, Phagwara 144411, Punjab (India)
2014-04-15
Enhanced and early relativistic self-focusing of Hermite-cosh-Gaussian (HChG) beam in the plasmas under density transition has been investigated theoretically using Wentzel-Kramers-Brillouin and paraxial ray approximation for mode indices m=0, 1, and 2. The variation of beam width parameter with normalized propagation distance for m=0, 1, and 2 is reported, and it is observed that strong self-focusing occurs as the HChG beam propagates deeper inside the nonlinear medium as spot size shrinks due to highly dense plasmas and the results are presented graphically. A comparative study between self-focusing of HChG beam in the presence and absence of plasmas density transition is reported. The dependency of beam width parameter on the normalized propagation distance for different values of decentered parameter “b” has also been presented graphically. For m=0 and 1, strong self-focusing is reported for b=1.8, and for m=2 and b=1.8, beam gets diffracted. The results obtained indicate the dependency of the self-focusing of the HChG beam on the selected values of decentered parameter. Moreover, proper selection of decentered parameter results strong self-focusing of HChG beam. Stronger self-focusing of laser beam is observed due to the presence of plasma density transition which might be very useful in the applications like the generation of inertial fusion energy driven by lasers, laser driven accelerators, etc.
Fluid-solid transition in simple systems using density functional theory
Energy Technology Data Exchange (ETDEWEB)
Bharadwaj, Atul S.; Singh, Yashwant [Department of Physics, Banaras Hindu University, Varanasi-221 005 (India)
2015-09-28
A free energy functional for a crystal which contains both the symmetry-conserved and symmetry-broken parts of the direct pair correlation function has been used to investigate the fluid-solid transition in systems interacting via purely repulsive Weeks-Chandler-Anderson Lennard–Jones potential and the full Lennard–Jones potential. The results found for freezing parameters for the fluid-face centred cubic crystal transition are in very good agreement with simulation results. It is shown that although the contribution made by the symmetry broken part to the grand thermodynamic potential at the freezing point is small compared to that of the symmetry conserving part, its role is crucial in stabilizing the crystalline structure and on values of the freezing parameters.
Energy Technology Data Exchange (ETDEWEB)
Yi, M.
2010-06-02
Through a systematic high-resolution angle-resolved photoemission study of the iron pnictide compounds (Ba,Sr)Fe{sub 2}As{sub 2}, we show that the electronic structures of these compounds are significantly reconstructed across the spin density wave transition, which cannot be described by a simple folding scenario of conventional density wave ordering. Moreover, we find that LDA calculations with an incorporated suppressed magnetic moment of 0.5{mu}{sub B} can match well the details in the reconstructed electronic structure, suggesting that the nature of magnetism in the pnictides is more itinerant than local, while the origin of suppressed magnetic moment remains an important issue for future investigations.
Li, Wenqing; Walther, Christian F J; Kuc, Agnieszka; Heine, Thomas
2013-07-09
The performance of a wide variety of commonly used density functionals, as well as two screened hybrid functionals (HSE06 and TB-mBJ), on predicting electronic structures of a large class of en vogue materials, such as metal oxides, chalcogenides, and nitrides, is discussed in terms of band gaps, band structures, and projected electronic densities of states. Contrary to GGA, hybrid functionals and GGA+U, both HSE06 and TB-mBJ are able to predict band gaps with an appreciable accuracy of 25% and thus allow the screening of various classes of transition-metal-based compounds, i.e., mixed or doped materials, at modest computational cost. The calculated electronic structures are largely unaffected by the choice of basis functions and software implementation, however, might be subject to the treatment of the core electrons.
Tretyakov, Nikita; Papadopoulos, Periklis; Vollmer, Doris; Butt, Hans-Jürgen; Dünweg, Burkhard; Daoulas, Kostas Ch.
2016-10-01
Classical density functional theory is applied to investigate the validity of a phenomenological force-balance description of the stability of the Cassie state of liquids on substrates with nanoscale corrugation. A bulk free-energy functional of third order in local density is combined with a square-gradient term, describing the liquid-vapor interface. The bulk free energy is parameterized to reproduce the liquid density and the compressibility of water. The square-gradient term is adjusted to model the width of the water-vapor interface. The substrate is modeled by an external potential, based upon the Lennard-Jones interactions. The three-dimensional calculation focuses on substrates patterned with nanostripes and square-shaped nanopillars. Using both the force-balance relation and density-functional theory, we locate the Cassie-to-Wenzel transition as a function of the corrugation parameters. We demonstrate that the force-balance relation gives a qualitatively reasonable description of the transition even on the nanoscale. The force balance utilizes an effective contact angle between the fluid and the vertical wall of the corrugation to parameterize the impalement pressure. This effective angle is found to have values smaller than the Young contact angle. This observation corresponds to an impalement pressure that is smaller than the value predicted by macroscopic theory. Therefore, this effective angle embodies effects specific to nanoscopically corrugated surfaces, including the finite range of the liquid-solid potential (which has both repulsive and attractive parts), line tension, and the finite interface thickness. Consistently with this picture, both patterns (stripes and pillars) yield the same effective contact angles for large periods of corrugation.
Density induced phase transitions in QED$_\\mathrm{2}$ - A study with matrix product states
Bañuls, Mari Carmen; Cirac, J Ignacio; Jansen, Karl; Kühn, Stefan
2016-01-01
We numerically study the zero temperature phase structure of the multi-flavor Schwinger model at non-zero chemical potential. Using matrix product states, we reproduce analytical results for the phase structure for two flavors in the massless case and extend the computation to the massive case, where no analytical predictions are available. Our calculations allow us to locate phase transitions in the mass-chemical potential plane with great precision, and provide a concrete example of tensor networks overcoming the sign problem in a lattice gauge theory calculation.
Density induced phase transitions in the Schwinger model. A study with matrix product states
Energy Technology Data Exchange (ETDEWEB)
Banuls, Mari Carmen; Cirac, J. Ignacio; Kuehn, Stefan [Max-Planck-Institut fuer Quantenoptik (MPQ), Garching (Germany); Cichy, Krzysztof [Frankfurt Univ. (Germany). Inst. fuer Theoretische Physik; Adam Mickiewicz Univ., Poznan (Poland). Faculty of Physics; Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC
2017-02-15
We numerically study the zero temperature phase structure of the multiflavor Schwinger model at nonzero chemical potential. Using matrix product states, we reproduce analytical results for the phase structure for two flavors in the massless case and extend the computation to the massive case, where no analytical predictions are available. Our calculations allow us to locate phase transitions in the mass-chemical potential plane with great precision and provide a concrete example of tensor networks overcoming the sign problem in a lattice gauge theory calculation.
Institute of Scientific and Technical Information of China (English)
HE Xiang; WANG Fan
2006-01-01
@@ Thioaldehydes and thioketones are candidates of new photoluminescence materials. The time-dependent density functional theory is applied to calculate the absorption and emission wavelengths of ten thiocarbonyl compounds using both B3LYP and PBE0 functionals. The theoretical results are in agreement with the measurable ones.Furthermore, it is found that the maximum absorption and emission wavelengths are linearly correlated to the C-S bond lengths.
Energy Technology Data Exchange (ETDEWEB)
Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg, E-mail: thorsten.arnold@physik.uni-erlangen.de, E-mail: marc.siegmund@physik.uni-erlangen.de [Lehrstuhl fuer Theoretische Festkoerperphysik, Universitaet Erlangen-Nuernberg, Staudtstrasse 7 B2, D-91058 Erlangen (Germany)
2011-08-24
We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r{sub S} is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r{sub S}. We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r{sub S}{sup c} at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r{sub S} the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.
Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg
2011-08-24
We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.
A density spike on astrophysical scales from an N-field waterfall transition
Directory of Open Access Journals (Sweden)
Illan F. Halpern
2015-09-01
Full Text Available Hybrid inflation models are especially interesting as they lead to a spike in the density power spectrum on small scales, compared to the CMB, while also satisfying current bounds on tensor modes. Here we study hybrid inflation with N waterfall fields sharing a global SO(N symmetry. The inclusion of many waterfall fields has the obvious advantage of avoiding topologically stable defects for N>3. We find that it also has another advantage: it is easier to engineer models that can simultaneously (i be compatible with constraints on the primordial spectral index, which tends to otherwise disfavor hybrid models, and (ii produce a spike on astrophysically large length scales. The latter may have significant consequences, possibly seeding the formation of astrophysically large black holes. We calculate correlation functions of the time-delay, a measure of density perturbations, produced by the waterfall fields, as a convergent power series in both 1/N and the field's correlation function Δ(x. We show that for large N, the two-point function is 〈δt(xδt(0〉∝Δ2(|x|/N and the three-point function is 〈δt(xδt(yδt(0〉∝Δ(|x−y|Δ(|x|Δ(|y|/N2. In accordance with the central limit theorem, the density perturbations on the scale of the spike are Gaussian for large N and non-Gaussian for small N.
Weymuth, Thomas; Chen, Peter; Reiher, Markus
2014-01-01
We present the WCCR10 data set of ten ligand dissociation energies of large cationic transition metal complexes for the assessment of approximate exchange--correlation functionals. We analyze nine popular functionals, namely BP86, BP86-D3, B3LYP, B3LYP-D3, B97-D-D2, PBE, TPSS, PBE0, and TPSSh by mutual comparison and by comparison to experimental gas-phase data measured with well-known precision. The comparison of all calculated data reveals a large, system-dependent scattering of results with nonnegligible consequences for computational chemistry studies on transition metal compounds. Considering further the comparison with experiment, the non-empirical functionals PBE and TPSS turn out to be among the best functionals for our reference data set. The deviation can be lowered further by including Hartree--Fock exchange. Accordingly, PBE0 and TPSSh are the two most accurate functionals for our test set, but also these functionals exhibit deviations from experiment by up to 50 kJ/mol for individual reactions. A...
Pressure-induced changes in the electron density distribution in α-Ge near the α-β transition
Energy Technology Data Exchange (ETDEWEB)
Li, Rui [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); HPCAT Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439 (United States); University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049 (China); Liu, Jing [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Bai, Ligang; Shen, Guoyin, E-mail: gshen@ciw.edu [HPCAT Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439 (United States); Tse, John S. [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2 (Canada)
2015-08-17
Electron density distributions in α-Ge have been determined under high pressure using maximum entropy method with structure factors obtained from single crystal synchrotron x-ray diffraction in a diamond anvil cell. The results show that the sp{sup 3} bonding is enhanced with increasing pressure up to 7.7(1) GPa. At higher pressures but below the α-β transition pressure of 11.0(1) GPa, the sp{sup 3}-like electron distribution progressively weakens with a concomitant increase of d-orbitals hybridization. The participation of d-orbitals in the electronic structure is supported by Ge Kβ{sub 2} (4p-1s) x-ray emission spectroscopy measurements showing the reduction of 4s character in the valence band at pressures far below the α-β transition. The gradual increase of d-orbitals in the valence level in the stability field of α-Ge is directly related to the eventual structural transition.
Energy Technology Data Exchange (ETDEWEB)
Shamim, Md; Harbola, Manoj K, E-mail: sami@iitk.ac.i, E-mail: mkh@iitk.ac.i [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India)
2010-11-14
Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.
A transition radiation detector interleaved with low-density targets for the NOE experiment
Alexandrov, K V; Bernardini, P; Brigida, M; Campana, D; Candela, A M; Caruso, R; Cassese, F; Ceres, A; D'Aquino, B; De Cataldo, G; De Mitri, I; Di Credico, A; Favuzzi, C; Fusco, P; Gargano, F; Giglietto, N; Giordano, F; Grillo, A; Guarino, F; Gustavino, C; Lamanna, E; Lauro, A; Leone, A; Loparco, F; Mancarella, G; Martello, D; Mazziotta, M N; Mikheyev, S P; Mongelli, M; Osteria, G; Palladino, Vittorio; Passeggio, G; Perchiazzi, M; Pontoniere, G; Rainó, A; Rocco, R; Romanucci, E; Rubizzo, U; Sacchetti, A; Scapparone, E; Spinelli, P; Tikhomirov, V; Vaccina, A; Vanzanella, E; Weber, M
2001-01-01
The NOE Collaboration has proposed a transition radiation detector (TRD) interleaved with marble targets to tag the electron decay channel of tau leptons produced by nu /sub tau /, eventually originated by nu /sub mu / oscillations in a long base line experiment. A reduced scale TRD detector prototype has been built and exposed to an electron/pion beam at the CERN PS. Discrimination capabilities between electrons and both charged and neutral pions, representing the main source of background for our measurement, have been determined obtaining rejection factors of the order of the tenth of percent for charged pions, and of a few percent for the neutral pion, matching the experiment requirements. The capabilities of this detector to measure the energy released by particles that start showering inside the targets are shown. A momentum resolution sigma /sub p//P
Phase transitions and gluodynamics in 2-colour matter at high density
Boz, Tamer; Fister, Leonard; Mehta, Dhagash; Skullerud, Jon-Ivar
2013-01-01
We investigate 2-colour QCD with 2 flavours of Wilson fermion at nonzero temperature T and quark chemical potential mu. From temperature scans at fixed mu we find that the critical temperature for the superfluid to normal transition depends only very weakly on mu above the onset chemical potential, while the deconfinement crossover temperature is clearly decreasing with mu. We find indications of a region of superfluid but deconfined matter at high mu and intermediate T. The static quark potential determined from the Wilson loop is found to exhibit a 'string tension' that increases at large mu in the 'deconfined' region. The electric (longitudinal) gluon propagator in Landau gauge becomes strongly screened with increasing temperature and chemical potential. The magnetic (transverse) gluon shows little sensitivity to temperature, and exhibits a mild enhancement at intermediate mu before becoming suppressed at large mu.
HAT-P-26b: A Low-density Neptune-mass Planet Transiting a K Star
Hartman, J. D.; Bakos, G. Á.; Kipping, D. M.; Torres, G.; Kovács, G.; Noyes, R. W.; Latham, D. W.; Howard, A. W.; Fischer, D. A.; Johnson, J. A.; Marcy, G. W.; Isaacson, H.; Quinn, S. N.; Buchhave, L. A.; Béky, B.; Sasselov, D. D.; Stefanik, R. P.; Esquerdo, G. A.; Everett, M.; Perumpilly, G.; Lázár, J.; Papp, I.; Sári, P.
2011-02-01
We report the discovery of HAT-P-26b, a transiting extrasolar planet orbiting the moderately bright V = 11.744 K1 dwarf star GSC 0320-01027, with a period P = 4.234516 ± 0.000015 days, transit epoch Tc = 2455304.65122 ± 0.00035 (BJD; Barycentric Julian dates throughout the paper are calculated from Coordinated Universal Time (UTC)), and transit duration 0.1023 ± 0.0010 days. The host star has a mass of 0.82 ± 0.03 M sun, radius of 0.79+0.10 -0.04 R sun, effective temperature 5079 ± 88 K, and metallicity [Fe/H] = -0.04 ± 0.08. The planetary companion has a mass of 0.059 ± 0.007 M J, and radius of 0.565+0.072 -0.032 R J yielding a mean density of 0.40 ± 0.10 g cm-3. HAT-P-26b is the fourth Neptune-mass transiting planet discovered to date. It has a mass that is comparable to those of Neptune and Uranus, and slightly smaller than those of the other transiting Super-Neptunes, but a radius that is ~65% larger than those of Neptune and Uranus, and also larger than those of the other transiting Super-Neptunes. HAT-P-26b is consistent with theoretical models of an irradiated Neptune-mass planet with a 10 M ⊕ heavy element core that comprises gsim50% of its mass with the remainder contained in a significant hydrogen-helium envelope, though the exact composition is uncertain as there are significant differences between various theoretical models at the Neptune-mass regime. The equatorial declination of the star makes it easily accessible to both Northern and Southern ground-based facilities for follow-up observations. Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NASA (N018Hr and N167Hr).
Indian Academy of Sciences (India)
Vijayanand Kalamse; Sanjay Gaikwad; Ajay Chaudhari
2010-06-01
5-metal mononitrides and monoborides viz. X–N and X–B (X = La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg) are studied using density functional method based B3LYP functional with LANL2DZ and SDD basis set. The lowest spin state, electron affinities, ionization potentials and binding energies for mononitrides and monoborides are obtained. The electronic state and electronic configuration of mononitrides and monoborides are discussed. Orbitals involved in bond formation are identified. The properties of mononitrides and monoborides are compared. It is found that 5-metal atoms form stronger bond with nitrogen atom than the boron atom. The range of binding energy, electron affinity and ionization potential is wider for mononitrides than that for monoborides. The properties of 5-metal mononitrides and 3-metal mononitrides are also compared. The binding energies for the former are lower than those for the latter.
Fermi Surface Evolution Across Multiple Charge Density Wave Transitions in ErTe3
Energy Technology Data Exchange (ETDEWEB)
Moore, R.G.; /SLAC, SSRL /Stanford U., Geballe Lab.; Brouet, V.; /Orsay, LPS; He, R.; /SLAC, SSRL /Stanford U., Geballe Lab.; Lu, D.H.; /SLAC, SSRL; Ru, N.; Chu, J.-H.; Fisher, I.R.; /Stanford U., Geballe Lab.; Shen, Z.-X.; /SLAC, SSRL /Stanford U., Geballe Lab.
2010-02-15
The Fermi surface (FS) of ErTe{sub 3} is investigated using angle-resolved photoemission spectroscopy (ARPES). Low temperature measurements reveal two incommensurate charge density wave (CDW) gaps created by perpendicular FS nesting vectors. A large {Delta}{sub 1} = 175 meV gap arising from a CDW with c* - q{sub CDW1} {approx} 0.70(0)c* is in good agreement with the expected value. A second, smaller {Delta}{sub 2} = 50 meV gap is due to a second CDW with a* - q{sub CDW2} {approx} 0.68(5)a*. The temperature dependence of the FS, the two gaps and possible interaction between the CDWs are examined.
Elabbady, Ahmed; Hashad, Mohamed Mohieeldin; Kotb, Ahmed Fouad; Abdullah, Dina Mohamed; Beltagy, Ahmad
2017-01-01
The prognosis of bladder cancer patients with positive lymph node (LN) disease is affected by both the extent of lymphadenectomy and LN density retrieved during radical cystectomy. This study aimed at assessing the differences in LN metastasis between patients who presented primarily with muscle-invasive transitional cell carcinoma of the bladder "de novo disease" versus "progressive disease." The latter is defined as patients who progressed to muscle-invasive bladder cancer (MIBC) following prior conservative management of a non-muscle-invasive disease. Data were prospectively collected from consecutive 41 radical cystectomies that were divided into two groups: Group I included de novo MIBC cases and Group II included progressive MIBC cases. The median age was 60 years (44-75). Thirty-four patients exhibited de novo disease versus 7 patients who presented as progressive MIBC with a median duration of 9 months between the resection of the first non-invasive tumor and the diagnosis of progressive MIBC (range: 6-56 months). The median number of retrieved LNs in both groups was 15 LNs (range: 4-36). Ten patients (24.39%) had positive pathological LN disease; distributed as 9 patients in Group I and 1 patient in Group II. The median LN density of LN-positive patients was 15.73% (6.46 % in Group I, 28.57% in Group II). Five patients had LN density >20%. Although non-muscle-invasive urothelial bladder tumor may progress to muscle-invasive disease, it still carries less aggressive course than de novo MIBC based on differences in LN metastasis and density.
Schwerdtfeger, Christine A; Mazziotti, David A
2009-06-14
Quantum phase transitions in N-particle systems can be identified and characterized by the movement of the two-particle reduced density matrix (2-RDM) along the boundary of its N-representable convex set as a function of the Hamiltonian parameter controlling the phase transition [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 74, 012501 (2006)]. For the one-dimensional transverse Ising model quantum phase transitions as well as their finite-lattice analogs are computed and characterized by the 2-RDM movement with respect to the transverse magnetic field strength g. The definition of a 2-RDM "speed" quantifies the movement of the 2-RDM per unit of g, which reaches its maximum at the critical point of the phase transition. For the infinite lattice the convex set of 2-RDMs and the 2-RDM speed are computed from the exact solution of the 2-RDM in the thermodynamic limit of infinite N [P. Pfeuty, Ann. Phys. 57, 79 (1970)]. For the finite lattices we compute the 2-RDM convex set and its speed by the variational 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)] in which approximate ground-state 2-RDMs are calculated without N-particle wave functions by using constraints, known as N-representability conditions, to restrict the 2-RDMs to represent quantum system of N fermions. Advantages of the method include: (i) rigorous lower bounds on the ground-state energies, (ii) polynomial scaling of the calculation with N, and (iii) independence of the N-representability conditions from a reference wave function, which enables the modeling of multiple quantum phases. Comparing the 2-RDM convex sets for the finite- and infinite-site lattices reveals that the variational 2-RDM method accurately captures the shape of the convex set and the signature of the phase transition in the 2-RDM movement. From the 2-RDM all one- and two-particle expectation values (or order parameters) of the quantum Ising model can also be computed including the pair correlation function, which
Das, Tanmoy
2016-07-01
We study directional dependent band gap evolutions and metal-insulator transitions (MITs) in model quantum wire systems within the spin-orbit density wave (SODW) model. The evolution of MIT is studied as a function of varying anisotropy between the intra-wire hopping ({{t}\\parallel} ) and inter-wire hopping ({{t}\\bot} ) with Rashba spin-orbit coupling. We find that as long as the anisotropy ratio (β ={{t}\\bot}/{{t}\\parallel} ) remains below 0.5, and the Fermi surface nesting is tuned to {{\\mathbf{Q}}1}=≤ft(π,0\\right) , an exotic SODW induced MIT easily develops, with its critical interaction strength increasing with increasing anisotropy. As β \\to 1 (2D system), the nesting vector switches to {{\\mathbf{Q}}2}=≤ft(π,π \\right) , making this state again suitable for an isotropic MIT. Finally, we discuss various physical consequences and possible applications of the directional dependent MIT.
Magnetic field-induced charge-density-wave transitions: The role of the orbital and Pauli effects
Kartsovnik, M. V.; Andres, D.; Biberacher, W.; Müller, H.
2009-03-01
Due to a low transition temperature and, correspondingly, a small energy gap, the charge-density-wave (CDW) state of the layered organic metal α-(BEDT-TTF)2KHg(SCN)4 is very sensitive to pressure and magnetic field. The latter couples to the CDW via two competing mechanisms: Pauli paramagnetism and orbital motion of charge carriers in a magnetic field. We study the interplay between the Pauli and orbital effects under a pressure of 2.8 kbar, in the region of the field-induced CDW (FICDW) instability. We find that, in agreement with theoretical predictions, the FICDW state is enhanced when the Zeeman splitting becomes commensurate with the orbital quantization.
Magnetic field-induced charge-density-wave transitions: The role of the orbital and Pauli effects
Energy Technology Data Exchange (ETDEWEB)
Kartsovnik, M.V. [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany)], E-mail: mark.kartsovnik@wmi.badw.de; Andres, D.; Biberacher, W. [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany); Mueller, H. [European Synchrotron Radiation Facility, F-38043 Grenoble (France)
2009-03-01
Due to a low transition temperature and, correspondingly, a small energy gap, the charge-density-wave (CDW) state of the layered organic metal {alpha}-(BEDT-TTF){sub 2}KHg(SCN){sub 4} is very sensitive to pressure and magnetic field. The latter couples to the CDW via two competing mechanisms: Pauli paramagnetism and orbital motion of charge carriers in a magnetic field. We study the interplay between the Pauli and orbital effects under a pressure of 2.8 kbar, in the region of the field-induced CDW (FICDW) instability. We find that, in agreement with theoretical predictions, the FICDW state is enhanced when the Zeeman splitting becomes commensurate with the orbital quantization.
XX. CoRoT-20b: A very high density, high eccentricity transiting giant planet
Deleuil, M; Ferraz-Mello, S; Erikson, A; Bouchy, F; Havel, M; Aigrain, S; Almenara, J -M; Alonso, R; Auvergne, M; Baglin, A; Barge, P; Bordé, P; Bruntt, H; Cabrera, J; Carpano, S; Cavarroc, C; Csizmadia, Sz; Damiani, C; Deeg, H J; Dvorak, R; Fridlund, M; Hébrard, G; Gandolfi, D; Gillon, M; Guenther, E; Guillot, T; Hatzes, A; Jorda, L; Léger, A; Lammer, H; Mazeh, T; Moutou, C; Ollivier, M; Ofir, A; Parviainen, H; Queloz, D; Rauer, H; Rodríguez, A; Rouan, D; Santerne, A; Schneider, J; Tal-Or, L; Tingley, B; Weingrill, J; Wuchterl, G
2011-01-01
We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/- 0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most compact planets known so far. Evolution models for the planet suggest a mass of heavy elements of the order of 800 ME if embedded in a central core, requiring a revision either of the planet formation models or of planet evolution and structure models. We note however that smaller amounts of heavy elements are expected from more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56. The star's projected rotational velocity is vsini = 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of t...
Institute of Scientific and Technical Information of China (English)
Liu Li; Wei Jian-Jun; An Xin-You; Wang Xue-Min; Liu Hui-Na; Wu Wei-Dong
2011-01-01
The phase transition of gallium phosphide (GaP) from zinc-blende (ZB) to a rocksalt (RS) structure is investigated by the plane-wave pseudopotential density functional theory (DFT).Lattice constant a0,elastic constants cij,bulk modulus B0 and the pressure derivative of bulk modulus B'0 are calculated.The results are in good agreement with numerous experimental and theoretical data.From the usual condition of equal enthalpies,the phase transition from the ZB to the RS structure occurs at 21.9 GPa,which is close to the experimental value of 22.0 GPa.The elastic properties of GaP with the ZB structure in a pressure range from 0 GPa to 21.9 GPa and those of the RS structure in a pressure range of pressures from 21.9 GPa to 40 GPa are obtained.According to the quasi-harmonic Debye model,in which the phononic effects are considered,the normalized volume V/Vo,the Debye temperature θ,the heat capacity Cv and the thermal expansion coefficient α are also discussed in a pressure range from 0 GPa to 40 GPa and a temperature range from 0 K to 1500 K.
A FRAMEWORK FOR CHARACTERIZING THE ATMOSPHERES OF LOW-MASS LOW-DENSITY TRANSITING PLANETS
Energy Technology Data Exchange (ETDEWEB)
Fortney, Jonathan J.; Nettelmann, Nadine [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Mordasini, Christoph [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Kempton, Eliza M.-R. [Department of Physics, Grinnell College, Grinnell, IA (United States); Greene, Thomas P.; Zahnle, Kevin, E-mail: jfortney@ucolick.org [Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA (United States)
2013-09-20
We perform modeling investigations to aid in understanding the atmospheres and composition of small planets of ∼2-4 Earth radii, which are now known to be common in our Galaxy. GJ 1214b is a well-studied example whose atmospheric transmission spectrum has been observed by many investigators. Here we take a step back from GJ 1214b to investigate the role that planetary mass, composition, and temperature play in impacting the transmission spectra of these low-mass low-density (LMLD) planets. Under the assumption that these planets accrete modest hydrogen-dominated atmospheres and planetesimals, we use population synthesis models to show that predicted metal enrichments of the H/He envelope are high, with metal mass fraction Z{sub env} values commonly 0.6-0.9, or ∼100-400+ times solar. The high mean molecular weight of such atmospheres (μ ≈ 5-12) would naturally help to flatten the transmission spectrum of most LMLD planets. The high metal abundance would also provide significant condensible material for cloud formation. It is known that the H/He abundance in Uranus and Neptune decreases with depth, and we show that atmospheric evaporation of LMLD planets could expose atmospheric layers with gradually higher Z{sub env}. However, values of Z{sub env} close to solar composition can also arise, so diversity should be expected. Photochemically produced hazes, potentially due to methane photolysis, are another possibility for obscuring transmission spectra. Such hazes may not form above T{sub eq} of ∼800-1100 K, which is testable if such warm, otherwise low mean molecular weight atmospheres are stable against atmospheric evaporation. We find that available transmission data are consistent with relatively high mean molecular weight atmospheres for GJ 1214b and 'warm Neptune' GJ 436b. We examine future prospects for characterizing GJ 1214b with Hubble and the James Webb Space Telescope.
Truhlik, Vladimir; Triskova, Ludmila; Benson, Robert; Bilitza, Dieter; Chu, Philip; Richards, Phil G.; Wang, Yongli
The upper transition height (Ht) (the altitude of the transition from heavy atomic ions to light ions or in the simplest form the transition from O+ to H+) is an important parameter, representing the boundary between the ionosphere and the plasmasphere. Ht is very sensitive to various geophysical parameters, like solar and magnetic activity and strongly depends on latitude and local time. There were numerous studies of this parameter in past decades. In spite of these efforts, no model satisfactorily represents this parameter so far. Moreover, surprising evidence of very low transition heights during the last prolonged solar minimum, of a level never obtained before, have been reported. We investigate the upper transition height on the global scale. We made progress in processing large data sets of Ht deduced from the Alouette/ISIS topside sounder and from the Formosat-3/COSMIC vertical electron-density profiles Ne(h) using the theoretical Global Plasma Ionosphere Density (GPID) model (Webb and Essex, 2004) and a revised non-linear function describing the scale height vs. altitude (Titheridge, 1976) to fit the vertical density profiles to the observed profiles and to determine the upper transition height. Since both methods require the plasma temperatures and their gradients as input, these are calculated using the IRI2012 model. Both methods are verified using a large amount of electron and ion density profiles simulated by the FLIP theoretical model and their accuracy is discussed. We compare the results from Alouette/ISIS and Formosat-3/COSMIC and present a global distribution of the calculated Ht and its dependence on geophysical parameters. Finally we compare it with Ht calculated using the IRI ion composition model. Titheridge, J.E., 1976. Ion Transition Heights from Topside Electron-Density Profiles. Planetary and Space Science 24 (3), 229-245. Webb, P.A., Essex, E.A., 2004. A dynamic global model of the plasmasphere. Journal of Atmospheric and Solar
Luo, Sijie; Averkiev, Boris; Yang, Ke R; Xu, Xuefei; Truhlar, Donald G
2014-01-14
The 3d-series transition metals (also called the fourth-period transition metals), Sc to Zn, are very important in industry and biology, but they provide unique challenges to computing the electronic structure of their compounds. In order to successfully describe the compounds by theory, one must be able to describe their components, in particular the constituent atoms and cations. In order to understand the ingredients required for successful computations with density functional theory, it is useful to examine the performance of various exchange-correlation functionals; we do this here for 4s(N)3d(N') transition-metal atoms and their cations. We analyze the results using three ways to compute the energy of the open-shell states: the direct variational method, the weighted-averaged broken symmetry (WABS) method, and a new broken-symmetry method called the reinterpreted broken symmetry (RBS) method. We find the RBS method to be comparable in accuracy with the WABS method. By examining the overall accuracy in treating 18 multiplicity-changing excitations and 10 ionization potentials with the RBS method, 10 functionals are found to have a mean-unsigned error of systems, the M06-L functional is the most accurate. And by combining the results with our previous studies of p-block and 4d-series elements as well as databases for alkyl bond dissociation, main-group atomization energies, and π-π noncovalent interactions, we find five functionals, namely, PW6B95, MPW1B95, M08-SO, SOGGA11-X, and MPWB1K, to be highly recommended. We also studied the performance of PW86 and C09 exchange functionals, which have drawn wide interest in recent studies due to their claimed ability to reproduce Hartree-Fock exchange at long distance. By combining them with four correlation functionals, we find the performance of the resulting functionals disappointing both for 3d transition-metal chemistry and in broader tests, and thus we do not recommend PW86 and C09 as components of generalized
DEFF Research Database (Denmark)
Zoletnik, S,; Basse, Nils Plesner; Saffman, Mark;
2002-01-01
or by a small plasma current, these transitions offer a precise way to systematically analyse differences in plasma turbulence between bad and good confinement cases. This paper presents results of the study of electron density fluctuations associated with confinement changes. Wavenumber and frequency spectra...... and radial profiles are compared., A slow and reproducible transition is induced by a small plasma current and the sequence of events leading to bad confinement is investigated. The laser scattering core plasma density fluctuation measurements are complemented by edge beam emission spectroscopy results...
Rêgo, Celso R. C.; Tereshchuk, Polina; Oliveira, Luiz N.; Da Silva, Juarez L. F.
2017-06-01
Transition-metal nanoparticles adsorbed on graphene are of great interest due to the unique catalytic and magnetic properties resulting from nanoparticles-graphene interactions. Comparison between the physical properties of such systems and those of the same nanoparticles in the gas phase is especially important. Here we report a systematic density functional investigation of the structural, energetic, and magnetic properties of small Nin, Pdn, and Ptn clusters, comprising from n =1 to 6 atoms, in the gas phase and adsorbed on a graphene monolayer. Our results show that the Ni adatom binds to the graphene hollow site, with -1.47 -meV adsorption energy, while Pd and Pt prefer the bridge sites, with -1.14 - and -1.62 -meV adsorption energies, respectively. This difference is determined by a competition between quantum and classical forces. Ni2 and Pt2 dimers bind perpendicularly on hollow and bridge sites, respectively, while Pd2 lies parallel to the graphene sheet, with each adatom on a bridge site. For larger TMn (TM = Ni , Pd , Pt ; n =3 -6 ) clusters, either two or three atoms bind to bridge graphene sites. In almost all cases the adsorbed clusters retain their gas-phase structures. The exceptions are Ni5 and Pt4, which acquire more compact structures with effective coordination number 12 and 19 % larger than in the gas phase, respectively. As the number of atoms grows, the cluster binds more weakly to the graphene, while its binding energy mounts up. Van der Waals corrections to the plain density functional theory (DFT) total energy raise the adsorption energy, but leave the cluster structure unchanged, in the gas phase or upon adsorption. Bader charge analysis shows that adsorption causes minor charge redistribution: the TM atoms bound to C atoms become positively charged, while the remaining metal atoms acquire negative charge. We have derived an approximate analytical expression for the local densities of states for the d orbitals of Ni , Pd , and Pt adatoms
Wegner, Th; Küllig, C.; Meichsner, J.
2017-02-01
In this series of two papers, the E-H transition in a planar inductively coupled radio frequency discharge (13.56 MHz) in pure oxygen is studied using comprehensive plasma diagnostic methods. The electron density serves as the main plasma parameter to distinguish between the operation modes. The (effective) electron temperature, which is calculated from the electron energy distribution function and the difference between the floating and plasma potential, halves during the E-H transition. Furthermore, the pressure dependency of the RF sheath extension in the E-mode implies a collisional RF sheath for the considered total gas pressures. The gas temperature increases with the electron density during the E-H transition and doubles in the H-mode compared to the E-mode, whereas the molecular ground state density halves at the given total gas pressure. Moreover, the singlet molecular metastable density reaches 2% in the E-mode and 4% in the H-mode of the molecular ground state density. These measured plasma parameters can be used as input parameters for global rate equation calculations to analyze several elementary processes. Here, the ionization rate for the molecular oxygen ions is exemplarily determined and reveals, together with the optical excitation rate patterns, a change in electronegativity during the mode transition.
Imamura, Yutaka; Kamiya, Muneaki; Nakajima, Takahito
2016-03-01
We study spin-forbidden transitions of Os polypyridyl sensitizers by two-component relativistic time-dependent density functional theory with the spin-orbit interaction based on Tamm-Dancoff approximation. The absorption spectra, including spin-forbidden-transition peaks, for the Os complexes are reasonably reproduced in comparison with the experimental ones. The extension of the conjugated lengths in the Os complexes is investigated and found to be effective to enhance photo absorption for spin-allowed transitions as well as spin-forbidden ones. This study provides fruitful information for a design of new dyes in terms of conjugation lengths.
Goodpaster, Jason D; Barnes, Taylor A; Manby, Frederick R; Miller, Thomas F
2012-12-14
Density functional theory (DFT) embedding provides a formally exact framework for interfacing correlated wave-function theory (WFT) methods with lower-level descriptions of electronic structure. Here, we report techniques to improve the accuracy and stability of WFT-in-DFT embedding calculations. In particular, we develop spin-dependent embedding potentials in both restricted and unrestricted orbital formulations to enable WFT-in-DFT embedding for open-shell systems, and develop an orbital-occupation-freezing technique to improve the convergence of optimized effective potential calculations that arise in the evaluation of the embedding potential. The new techniques are demonstrated in applications to the van-der-Waals-bound ethylene-propylene dimer and to the hexa-aquairon(II) transition-metal cation. Calculation of the dissociation curve for the ethylene-propylene dimer reveals that WFT-in-DFT embedding reproduces full CCSD(T) energies to within 0.1 kcal/mol at all distances, eliminating errors in the dispersion interactions due to conventional exchange-correlation (XC) functionals while simultaneously avoiding errors due to subsystem partitioning across covalent bonds. Application of WFT-in-DFT embedding to the calculation of the low-spin/high-spin splitting energy in the hexaaquairon(II) cation reveals that the majority of the dependence on the DFT XC functional can be eliminated by treating only the single transition-metal atom at the WFT level; furthermore, these calculations demonstrate the substantial effects of open-shell contributions to the embedding potential, and they suggest that restricted open-shell WFT-in-DFT embedding provides better accuracy than unrestricted open-shell WFT-in-DFT embedding due to the removal of spin contamination.
Mayoral, E.; Klapp, J.; Gama Goicochea, A.
2017-01-01
Nonequilibrium coarse-grained, dissipative particle dynamics simulations of complex fluids, made up of polymer brushes tethered to planar surfaces immersed in a solvent yield nonmonotonic behavior of the friction coefficient as a function of the polymer grating density on the substrates, Γ , while the viscosity shows a monotonically increasing dependence on Γ . This effect is shown to be independent of the degree of polymerization, N , and the size of the system. It arises from the composition and the structure of the first particle layer adjacent to each surface that results from the confinement of the fluid. Whenever such layers are made up of as close a proportion of polymer beads to solvent particles as there are in the fluid, the friction coefficient shows a minimum, while for disparate proportions the friction coefficient grows. At the mushroom-to-brush transition (MBT) the viscosity scales with an exponent that depends on the characteristic exponent of the MBT (6/5) and the solvent quality exponent (ν =0.5 , for θsolvent), but it is independent of the polymerization degree (N ). On the other hand, the friction coefficient at the MBT scales as μ ˜N6 /5 , while the grafting density at the MBT scales as Γ ˜N-6 /5 when friction is minimal, in agreement with previous scaling theories. We argue these aspects are the result of cooperative phenomena that have important implications for the understanding of biological brushes and the design of microfluidics devices, among other applications of current academic and industrial interest.
Ricca, Alessandra; Bauschlicher, Charles W.; Langhoff, Stephen R. (Technical Monitor)
1994-01-01
Density functional theory (DFT) is found to give a better description of the geometries and vibrational frequencies of FeL and FeL(sup +) systems than second order Moller Plesset perturbation theory (MP2). Namely, the DFT correctly predicts the shift in the CO vibrational frequency between free CO and the Sigma(sup -) state of FeCO and yields a good result for the Fe-C distance in the quartet states of FeCH4(+) 4 These are properties where the MP2 results are unsatisfactory. Thus DFT appears to be an excellent approach for optimizing the geometries and computing the zero-point energies of systems containing first transition row atoms. Because the DFT approach is biased in favor of the 3d(exp 7) occupation, whereas the more traditional approaches are biased in favor of the 3d(exp 6) occupation, differences are found in the relative ordering of states. It is shown that if the dissociation is computed to the most appropriate atomic asymptote and corrected to the ground state asymptote using the experimental separations, the DFT results are in good agreement with high levels of theory. The energetics at the DFT level are much superior to the MP2 and in most cases in good agreement with high levels of theory.
Carles, R.; Benzo, P.; Pécassou, B.; Bonafos, C.
2016-12-01
Surface enhanced Raman scattering (SERS) is generally and widely used to enhance the vibrational fingerprint of molecules located at the vicinity of noble metal nanoparticles. In this work, SERS is originally used to enhance the own vibrational density of states (VDOS) of nude and isolated gold nanoparticles. This offers the opportunity of analyzing finite size effects on the lattice dynamics which remains unattainable with conventional techniques based on neutron or x-ray inelastic scattering. By reducing the size down to few nanometers, the role of surface atoms versus volume atoms become dominant, and the “text-book” 3D-2D transition on the dynamical behavior is experimentally emphasized. “Anomalies” that have been predicted by a large panel of simulations at the atomic scale, are really observed, like the enhancement of the VDOS at low frequencies or the occurrence of localized modes at frequencies beyond the cut-off in bulk. Consequences on the thermodynamic properties at the nanoscale, like the reduction of the Debye temperature or the excess of the specific heat, have been evaluated. Finally the high sensitivity of reminiscent bulk-like phonons on the arrangements at the atomic scale is used to access the morphology and internal disorder of the nanoparticles.
Escudero, Daniel; Thiel, Walter
2014-05-21
We report an assessment of the performance of density functional theory-based multireference configuration interaction (DFT/MRCI) calculations for a set of 3d- and 4d-transition metal (TM) complexes. The DFT/MRCI results are compared to published reference data from reliable high-level multi-configurational ab initio studies. The assessment covers the relative energies of different ground-state minima of the highly correlated CrF6 complex, the singlet and triplet electronically excited states of seven typical TM complexes (MnO4(-), Cr(CO)6, [Fe(CN)6](4-), four larger Fe and Ru complexes), and the corresponding electronic spectra (vertical excitation energies and oscillator strengths). It includes comparisons with results from different flavors of time-dependent DFT (TD-DFT) calculations using pure, hybrid, and long-range corrected functionals. The DFT/MRCI method is found to be superior to the tested TD-DFT approaches and is thus recommended for exploring the excited-state properties of TM complexes.
Liu, Ping; Rodriguez, José A.
2004-03-01
Density functional theory was employed to study the stabilities and chemical activities of transition metal carbides. Here we take the well-known Mo carbides and Ti carbides as an example. Different kinds of structures including the bulk surfaces [Mo2C(001), MoC(001), and TiC(001)] and metcars [Mo8C12 and Ti8C12] are taken into consideration. Systematic studies show that by raising the C coordination number of the metal atoms in the carbides, in general the stability of the carbides increases (metcars are an exception since they include both high-coordinated and low-coordinated metal atoms.); at the same time, the chemical activities of the carbides decrease due to a downshift of the metal d-band center (ligand effect). Considering the better catalysts those that combine high stability and moderate chemical activity, our results suggest that the catalytic potential of Mo carbide systems should decrease in the following sequence: Mo8C12>Mo2C(001) or MoC(001)>pure Mo(110). In spite of having the largest C/Mo ratio, the metcar appears as the most attractive system. Our studies also indicate that the "magic" behavior of metcars is not unique for Mo carbides. Similar behavior is also observed for Ti carbides. This implies that nanoparticles like metcar species could exhibit better performances than the corresponding bulk metal carbides as catalysts.
Goodpaster, Jason D; Manby, Frederick R; Miller, Thomas F
2012-01-01
Density functional theory (DFT) embedding provides a formally exact framework for interfacing correlated wave-function theory (WFT) methods with lower-level descriptions of electronic structure. Here, we report techniques to improve the accuracy and stability of WFT-in-DFT embedding calculations. In particular, we develop spin-dependent embedding potentials in both restricted and unrestricted orbital formulations to enable WFT-in-DFT embedding for open-shell systems, and we develop an orbital-occupation-freezing technique to improve the convergence of optimized effective potential (OEP) calculations that arise in the evaluation of the embedding potential. The new techniques are demonstrated in applications to the van-der-Waals-bound ethylene-propylene dimer and to the hexaaquairon(II) transition-metal cation. Calculation of the dissociation curve for the ethylene-propylene dimer reveals that WFT-in-DFT embedding reproduces full CCSD(T) energies to within 0.1 kcal/mol at all distances, eliminating errors in th...
Kolincio, Kamil; Pérez, Olivier; Hébert, Sylvie; Fertey, Pierre; Pautrat, Alain
2016-06-01
Detailed structural and magnetotransport properties of monophosphate tungsten bronze Kx(PO2)4(WO3)8 single crystals are reported. Both galvanomagnetic and thermal properties are shown to be consistent with a charge density wave electronic transition due to hidden nesting of the quasi-1D portion of the Fermi surface. We also observe the enhancement of electronic anisotropy due to reconstruction of the Fermi surface at the Peierls transition. The resistivity presents a thermal hysteresis suggesting a first-order nature characteristic of a strong-coupling scenario. However, other measurements such as the change of carrier density demonstrate a second-order Peierls scenario with weak-coupling features. We suggest that the structural transition driven by the residual strain in the K-P-O environment is responsible for the resistivity hysteresis and modifies the Fermi surface which then helps the rise to the second-order Peierls instability.
Carlson, Rebecca K; Truhlar, Donald G; Gagliardi, Laura
2015-09-08
We extend the on-top density functional of multiconfiguration pair-density functional theory (MC-PDFT) to include the gradient of the on-top density as well as the gradient of the density. We find that the theory is reasonably stable to this extension; furthermore, it provides improved accuracy for molecules containing transition metals. We illustrate the extended on-top density functionals by applying them to Cr2, Cu2, Ag2, Os2, and Re2Cl8(2-) as well as to our previous database of 56 data for bond dissociation energies, barrier heights, reaction energies, proton affinities, and the water dimer. The performance of MC-PDFT is comparable to or better than that of CASPT2.
Andres, D.; Kartsovnik, M. V.; Biberacher, W.; Neumaier, K.; Sheikin, I.; Müller, H.; Kushch, N. D.
2011-10-01
Successive magnetic-field-induced charge-density-wave transitions in the layered molecular conductor α-(BEDT-TTF)2KHg(SCN)4 are studied in a hydrostatic pressure regime in which the zero field charge-density- wave (CDW) state is completely suppressed. It is shown that the orbital effect of the magnetic field restores the density wave, while orbital quantization induces transitions between different CDW states as the field strength is varied. The latter show up as distinct anomalies in the magnetoresistance as a function of field. The interplay between the orbital and Pauli paramagnetic effects, which act, respectively, to enhance and to suppress the CDW instability, is particularly manifest in the angular dependence of the field-induced anomalies.
Umeda, T; Kanaya, K; Maezawa, Y; Nakagawa, Y; Ohno, H; Saito, H; Yoshida, S
2013-01-01
We study scaling behavior of a chiral order parameter in the low density region, performing a simulation of two-flavor QCD with improved Wilson quarks. The scaling behavior of the chiral order parameter defined by a Ward-Takahashi identity agrees with the scaling function of the three-dimensional O(4) spin model at zero chemical potential. We extend the scaling study to finite density QCD. Applying the reweighting method and calculating derivatives of the chiral order parameter with respect to the chemical potential, the scaling properties of the chiral phase transition are discussed in the low density region. We moreover calculate the curvature of the phase boundary of the chiral phase transition in the temperature and chemical potential plane assuming the O(4) scaling relation.
Tekarli, Sammer M; Drummond, Michael L; Williams, T Gavin; Cundari, Thomas R; Wilson, Angela K
2009-07-30
The performance of 44 density functionals used in conjunction with the correlation consistent basis sets (cc-pVnZ where n = T and Q) has been assessed for the gas-phase enthalpies of formation at 298.15 K of 3d transition metal (TM) containing systems. Nineteen molecules were examined: ScS, VO, VO(2), Cr(CO)(6), MnS, MnCl(2), Mn(CO)(5)Cl, FeCl(3), Fe(CO)(5), CoH(CO)(4), NiCl(2), Ni(CO)(4), CuH, CuF, CuCl, ZnH, ZnO, ZnCl, and Zn(CH(3))(2). Of the functionals examined, the functionals that resulted in the smallest mean absolute deviation (MAD, in parentheses, kcal mol(-1)) from experiment were B97-1 (6.9), PBE1KCIS (8.1), TPSS1KCIS (9.6), B97-2 (9.7), and B98 (10.7). All five of these functionals include some degree of Hartree-Fock (HF) exchange. The impact of increasing the basis set from cc-pVTZ to cc-pVQZ was found to be slight for the generalized gradient approximation (GGA) and meta-GGA (MGGA) functionals studied, indicating basis set saturation at the triple-zeta level. By contrast, for most of the generalized gradient exchange (GGE), hybrid GGA (HGGA), and hybrid meta-GGA (HMGGA) functionals considered, improvements in the average MAD of 2-3 kcal mol(-1) were seen upon progressing to a quadruple-zeta level basis set. Overall, it was found that the functionals that include Hartree-Fock exchange performed best overall, but those with greater than 40% HF exchange exhibit significantly poor performance for the prediction of enthalpies of formation for 3d TM complexes. Carbonyl-containing complexes, a mainstay in organometallic TM chemistry, are demonstrated to be exceedingly difficult to describe accurately with all but 2 of the 44 functionals considered. The most accurate functional, for both CO-containing and CO-free compounds, is B97-1/cc-pVQZ, which is shown to be capable of yielding results within 1 kcal mol(-1) of high-level ab initio composite methodologies.
DEFF Research Database (Denmark)
Vojvodic, Aleksandra; Ruberto, C.; Lundqvist, Bengt
2010-01-01
This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMCs) in NaCl structure by means of density-functional theory calculations. The investigated substrates are the TM-terminated TMC(111) surfaces, of interest because of the presence of different types......, surface relaxations, Bader charges, and surface-localized densities of states (DOSs). Detailed comparisons between surface and bulk DOSs reveal the existence of transition-metal localized SRs (TMSRs) in the pseudogap and of several C-localized SRs (CSRs) in the upper valence band on all considered TMC(111......C, delta-MoC, TaC, and WC (in NaCl structure) and the adsorbates H, B, C, N, O, F, NH, NH2, and NH3. Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption-energy values with the calculated surface electronic structures. The results...
Zuev, Yuri; Kim, Mun Seog; Lemberger, Thomas R
2005-09-23
We report measurements of the ab-plane superfluid density n(s) (magnetic penetration depth lambda) of heavily underdoped films of YBa2Cu3O6+x, with T(C)'s from 6 to 50 K. We find the characteristic length for vortex unbinding transition equal to the film thickness, suggesting strongly coupled CuO2 layers. At the lowest dopings, T(C) is as much as 5 times larger than the upper limit set by the 2D Kosterlitz-Thouless-Berezinskii transition temperature calculated for individual CuO2 bilayers. Our main finding is that T(C) is not proportional to n(s)(0); instead, we find T(C) proportional to ns(1/2.3+/-0.4). This conflicts with a popular point of view that quasi-2D thermal phase fluctuations determine the transition temperature.
Institute of Scientific and Technical Information of China (English)
ZHOUBang-Rong
2003-01-01
High density phase transitions in a 4-dimensional Nambu-dona-Lasinio model containing a single symmetry breaking order parameter coming from the fermion-antifermion condensates are researched and expounded by means of both the gap equation and the effective potential approach. The phase transitions are proven to be second-order at a high temperature T; however at T = 0 they are first- or second-order, depending on whether A/m(0), the ratio of the momentum cutoff A in the fermion-loop integrals to the dynamical fermion mass m(0) at zero temperature, is lessthan 3.387 or not. The former condition cannot be satisfied in some models. The discussions further show complete effectiveness of the critical analysis based on the gap equation for second order phase transitions including determination of the condition of their occurrence.
Incommensurate spin-density wave and magnetic lock-in transition in CaFe{sub 4}As{sub 3}.
Energy Technology Data Exchange (ETDEWEB)
Manuel, P.; Chapon, L. C.; Todorov, I. S.; Chung, D. Y.; Castellan, J.-P.; Rosenkranz, S.; Osborn, R.; Toledano, P.; Kanatzidis, M. G.; Materials Science Division; Rutherford Appleton Lab.; Univ. of Picardie; Northwestern Univ.
2010-05-01
The magnetic structure for the recently synthesized iron-arsenide compound CaFe4As3 has been studied by neutron-powder diffraction. Long-range magnetic order is detected below 85 K, with an incommensurate modulation described by the propagation vector k=(0,?,0), ??0.39. Below ?25 K, our measurements detect a first-order phase transition where ? locks into the commensurate value 3/8. A model of the magnetic structure is proposed for both temperature regimes, based on Rietveld refinements of the powder data and symmetry considerations. The structures correspond to longitudinal spin-density waves with magnetic moments directed along the b axis. A Landau analysis captures the change in thermodynamic quantities observed at the two magnetic transitions, in particular, the drop in resistivity at the lock-in transition.
Kanno, Shohei; Imamura, Yutaka; Hada, Masahiko
2016-05-25
We explore spin-forbidden transitions for a Ru dye with an N3 skeleton and an Fe dye with a DX1 skeleton by time-dependent density functional theory with spin-orbit interaction. The modified N3-based Ru dye with iodine anions has an absorption edge in the long wavelength region which is not observed in the original N3 dye. The long wavelength absorption edge originates from the spin-orbit interaction with iodine. Although the Fe dye has a small spin-orbit interaction, because of less spin-orbit interaction from the light metal, spin-forbidden transitions also occur for DX1-based Fe dye systems with iodine anions. This result indicates that the introduction of iodine can strengthen the spin-orbit interaction for a dye sensitizer and offers a new approach for designing spin-forbidden transitions.
Institute of Scientific and Technical Information of China (English)
ZHOU Bang-Rong
2003-01-01
High density phase transitions in a 4-dimensional Nambu-Jona-Lasinio model containing a single symmetry breaking order parameter coming from the fermion-antifermion condensates are researched and expounded by means of both the gap equation and the effective potential approach. The phase transitions are proven to be second-order at a high temperature T; however at T = 0 they are first- or second-order, depending on whether A/m(0), the ratio of the momentum cutoff A in the fermion-loop integrals to the dynamicalfermion mass m(0) at zero temperature, is less than 3.387 or not. The former condition cannot be satisfied in some models. The discussions further show complete effectiveness of the critical analysis based on the gap equation for second order phase transitions including determination of the condition of their occurrence.
Jug, Giancarlo; Ziegler, Klaus
1997-10-01
We present a calculation for the second moment of the local density of states in a model of a two-dimensional quantum dot array near the quantum Hall transition. The quantum dot array model is a realistic adaptation of the lattice model for the quantum Hall transition in the two-dimensional electron gas in an external magnetic field proposed by Ludwig, Fisher, Shankar, and Grinstein. We make use of a Dirac fermion representation for the Green's functions in the presence of fluctuations for the quantum dot energy levels. A saddle-point approximation yields nonperturbative results for the first and second moments of the local density of states, showing interesting fluctuation behavior near the quantum Hall transition. To our knowledge we discuss here one of the first analytic characterizations of chaotic behavior for a two-dimensional mesoscopic structure. The connection with possible experimental investigations of the local density of states in the quantum dot array structures (by means of NMR Knight-shift or single-electron-tunneling techniques) and our work is also established.
Dong, Shunle; Chen, Zhuo; Wang, Yan
2010-03-01
This article has been retracted: please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editors of Chemical Physics. A large part of this article (text as well as measured data) has been published previously in Canadian Journal of Physics (Neutron-scattering studies of the phase transitions in high-pressure ices during annealing, by Y. Wang, A.I. Kolesnikov, S.L. Dong, and J.C. Li, Can. J. Phys., 81 (2003) 401-407, doi: 10.1139/p03-045).
Energy Technology Data Exchange (ETDEWEB)
Jungsuttiwong, Siriporn, E-mail: siriporn.j@ubu.ac.th [Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ubon Ratchathani University, Ubon Ratchathani 34190 (Thailand); Wongnongwa, Yutthana [Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ubon Ratchathani University, Ubon Ratchathani 34190 (Thailand); Namuangruk, Supawadee [National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), Klong Luang, Pathum Thani 12120 (Thailand); Kungwan, Nawee [Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Promarak, Vinich [Department of Material Science and Engineering, School of Molecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology, Rayong 21210 (Thailand); Kunaseth, Manaschai, E-mail: manaschai@nanotec.or.th [National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), Klong Luang, Pathum Thani 12120 (Thailand)
2016-01-30
Graphical abstract: Decoration of Pd{sub 4}-A (square planar) on B-doped graphene significantly promotes Hg{sup 0} adsorption, a single site of Pd{sub 4} cluster on BDG could strongly adsorb up to six Hg atoms. - Highlights: • Transition metal atom and cluster binds strongly on B-doped graphene surface. • Decoration of transition metal on B-doped graphene significantly promotes Hg{sup 0} adsorption. • Adsorption strength of Hg{sup 0} atom on metal decorated B-doped graphene: Pd > Pt > Ru > W > Cu. • One site decorated Pd4 cluster adsorbed Hg{sup 0} strongly up to six atoms.
Parisi, Filippo; Sciascia, Luciana; Princivalle, Francesco; Merli, Marcello
2012-02-01
In order to characterize the pressure-induced decomposition of ringwoodite (γ-Mg2SiO4), the topological analysis of the electron density ρ( r), based upon the theory of atoms in molecules (AIM) developed by Bader in the framework of the catastrophe theory, has been performed. Calculations have been carried out by means of the ab initio CRYSTAL09 code at the HF/DFT level, using Hamiltonians based on the Becke- LYP scheme containing hybrid Hartree-Fock/density functional exchange-correlation terms. The equation of state at 0 K has been constructed for the three phases involved in the post-spinel phase transition (ringwoodite → Mg-perovskite + periclase) occurring at the transition zone-lower mantel boundary. The topological results show that the decomposition of the ringwoodite at high pressures is caused by a conflict catastrophe. Furthermore, topological evidences of the central role played by the oxygen atoms to facilitate the pressure-induced ringwoodite decomposition and the subsequent phase transition have been noticed.
DEFF Research Database (Denmark)
Verma, Ashok K.; Modak, P.; Sharma, Surinder M.;
2013-01-01
First-principles calculations have been performed for americium (Am) metal using the generalized gradient approximation + orbital-dependent onsite Coulomb repulsion via Hubbard interaction (GGA+U) and hybrid density functional theory (HYB-DFT) methods to investigate various ground state properties...... spectrum at ambient pressure relate, for some parameter choices, well to peak positions in the calculated density of states function of Am-I....
Merli, Marcello; Sciascia, Luciana
2013-06-01
In this work, the Bader's topological analysis of the electron density, coupled with Thom's catastrophe theory, was used to characterize the pressure-induced transformations in α-quartz. In particular, ab initio calculations of the α-quartz structures in the range 0-105 Gpa have been performed at the HF/DFT exchange-correlation terms level, using Hamiltonians based on a WC1LYP hybrid scheme. The electron densities calculated throughout the ab initio wave functions have been analysed by means of the Bader's theory, seeking for some catastrophic mechanism in the sense of Thom's theory. The analysis mainly showed that there is a typical fold catastrophe feature involving an O-O interaction at the quartz-coesite transition pressure, while the amorphization of α-quartz is coincident with an average distribution of the gradient field of the electron density around the oxygen atom which is typically observed in the free atoms. This approach is addressed to depict a phase transition from a novel viewpoint, particularly useful in predicting the stability of a compound at extreme conditions, especially in the absence of experimental data.
Huerta, Adrian; Pizio, Orest; Bryk, Pawel; Sokolowski, Stefan
A density functional approach is used to study the adsorption of the four-bonding-site model associating Lennard-Jones fluid in slit-like pores with energetically heterogeneous walls. The fluid-wall potential is qualitatively similar to that invoked by Röcken, P., Somoza, A., Tarazona, P., and Findenegg, G. H., 1999, J. chem. Phys., 108, 8089, i.e. it consists of a homogeneous part that varies in the direction perpendicular to the wall and a periodic part, varying also in one direction parallel to the wall. Both parts are modelled by Lennard-Jones 9,3-type functions. The structure of the adsorbed film is characterized by the local densities of all particles and the densities of the monomers. The phase diagrams are evaluated for several systems characterized by different corrugation of the adsorbing potential. The adsorbing field is strong enough to allow for the layering transition. As well as the formation of the so-called bridge phase that fills the pore space over the most energetic parts of the wall and of capillary condensation, the layering transition is observed within the first layer adjacent to the pore walls. If the adsorbing potential due to each pore wall is shifted in phase by pi/2, the bridge phase is not formed.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yu; Mukamel, Shaul; Khalil, Munira; Govind, Niranjan
2015-11-09
Valence-to-core (VtC) X-ray emission spectroscopy (XES) has emerged as a power- ful technique for the structural characterization of complex organometallic compounds in realistic environments. Since the spectrum represents electronic transitions from the ligand molecular orbitals to the core holes of the metal centers, the approach is more chemically sensitive to the metal-ligand bonding character compared with con- ventional X-ray absorption techniques. In this paper we study how linear-response time-dependent density functional theory (LR-TDDFT) can be harnessed to simulate K-edge VtC X-ray emission spectra reliably. LR-TDDFT allows one to go beyond the single-particle picture that has been extensively used to simulate VtC-XES. We con- sider seven low- and high-spin model complexes involving chromium, manganese and iron transition metal centers. Our results are in good agreement with experiment.
Dlimi, S.; El kaaouachi, A.; Narjis, A.; Limouny, L.; Sybous, A.; Errai, M.
2013-10-01
We investigated the temperature dependence of resistivity of a high mobility two-dimensional holes system grown on the (311) GaAs surface in the absence of the magnetic field near the metal-insulator transition. The Coulomb hopping was found in a wide range of temperature and carrier density. Quantitative analysis of our results suggests that a crossover from Efros-Shklovskii to Mott variable range hopping due to screening phenomenon when the hopping distance increases. We found that using the 2D single particle hopping amplitude CES gives unreasonably high localization lengths. Therefore, we believe that electrical transport is dominated by correlated hopping and the hopping amplitude must be renormalized by a reduction factor A≈1.6. The localization length appears to diverge in a power-law fashion near the transition point. The analysis of the hopping gives results consistent with the prediction of the critical point from a recent study of percolation and other experiences.
Stojchevska, L.; Borovšak, M.; Foury-Leylekian, P.; Pouget, J.-P.; Mertelj, T.; Mihailovic, D.
2017-07-01
All-optical femtosecond relaxation dynamics in a single crystal of monophosphate tungsten bronze (PO2)4(WO3)2m with alternate stacking m =6 of WO3 layers was studied through the three consequent charge-density-wave (CDW) transitions. Several transient coherent collective modes associated with the different CDW transitions were observed and analyzed in the framework of the time-dependent Ginzburg-Landau theory. Remarkably, the interference of the modes leads to an apparent rectification effect in the transient reflectivity response. A saturation of the coherent-mode amplitudes with increasing pump fluence well below the CDWs destruction threshold fluence indicates a decoupling of the electronic and lattice parts of the order parameter on the femtosecond timescale.
Energy Technology Data Exchange (ETDEWEB)
Wei, S. H.; Ma, J.; Gessert, T. A.; Chin, K. K.
2011-07-01
Doping is one of the most important issues in semiconductor physics. The charge carrier generated by doping can profoundly change the properties of semiconductors and their performance in optoelectronic device applications, such as solar cells. Using detailed balance theory and first-principles calculated defect formation energies and transition energy levels, we derive general formulae to calculate carrier density for semiconductors with multi dopants and multi transition energy levels. As an example, we studied CdTe doped with Cu, in which VCd, CuCd, and Cui are the dominant defects/impurities. We show that in this system, when Cu concentration increases, the doping properties of the system can change from a poor p-type, to a poorer p-type, to a better p-type, and then to a poor p-type again, in good agreement with experimental observation of CdTe-based solar cells.
Urban, Daniel F.; Elsässer, Christian
2017-09-01
A density functional theory study of atomic defects and dopants in ternary Z-phase transition-metal nitrides Cr M N with M =V , Nb, or Ta is presented. Various defect formation energies of native point defects and of substitutional atoms of other metal elements which are abundant in the steel as well are evaluated. The dependence thereof on the thermodynamic environment, i.e., the chemical conditions of a growing Z-phase precipitate, is studied, and different growth scenarios are compared. The results obtained may help to relate results of experimental atomic-scale analysis by atom probe tomography or transmission electron microscopy to the theoretical modeling of the formation process of the Z phase from binary transition-metal nitrides.
Petit, Laurence; Maldivi, Pascale; Adamo, Carlo
2005-09-01
The calculation of the absorption spectra of four families of transition-metal complexes (Ni(CO)4, MnO4(-), MF6 (M = Cr, Mo, W) and CpM(CO)2 (M = Rh, Ir)) has been undertaken to unravel the influence of basis sets onto excitation energies, oscillator strengths, and assignments. Three among the most common pseudopotentials, with the corresponding valence basis sets, and two all-electron basis sets have been used for the metal center description in the framework of the time dependent Density Functional Theory (TD-DFT). Our results show that this approach does not particularly depend on the basis set used on the metal atoms. Furthermore, the chosen functional PBE0 provides transitions in good agreement with experiments, and it provides an accuracy of about 0.3 eV, comparable to that of refined post-Hartree-Fock methods.
Gibbs, G V; Spackman, M A; Jayatilaka, D; Rosso, K M; Cox, D F
2006-11-01
For a variety of molecules and earth materials, the theoretical local kinetic energy density, G(r(c)), increases and the local potential energy density, V(r(c)), decreases as the M-O bond lengths (M = first- and second-row metal atoms bonded to O) decrease and the electron density, rho(r(c)), accumulates at the bond critical points, r(c). Despite the claim that the local kinetic energy density per electronic charge, G(r(c))/rho(r(c)), classifies bonded interactions as shared interactions when less than unity and closed-shell when greater, the ratio was found to increase from 0.5 to 2.5 au as the local electronic energy density, H(r(c)) = G(r(c)) + V(r(c)), decreases and becomes progressively more negative. The ratio appears to be a measure of the character of a given M-O bonded interaction, the greater the ratio, the larger the value of rho(r(c)), the smaller the coordination number of the M atom and the more shared the bonded interaction. H(r(c))/rho(r(c)) versus G(r(c))/rho(r(c)) scatter diagrams categorize the M-O bonded interactions into domains with the local electronic energy density per electron charge, H(r(c))/rho(r(c)), tending to decrease as the electronegativity differences for the bonded pairs of atoms decrease. The values of G(r(c)) and V(r(c)), estimated with a gradient-corrected electron gas theory expression and the local virial theorem, are in good agreement with theoretical values, particularly for the bonded interactions involving second-row M atoms. The agreement is poorer for shared C-O and N-O bonded interactions.
DEFF Research Database (Denmark)
Martinez, Jose Ignacio; García Lastra, Juan Maria; Lopez, M. J.
2010-01-01
The optical spectra of sandwich clusters formed by transition metal atoms (titanium, vanadium, and chromium) intercalated between parallel benzene molecules have been studied by time-dependent density functional theory (TDDFT) and many-body perturbation theory. Sandwiches with different number...... the optical properties according to specific functionality targets. The differences in the spectra could be used to identify relative abundances of isomers with different spins in experimental studies. As a salient feature, this theoretical spectroscopic analysis predicts the metallization of the infinite (Ti...
Shirayama, Masaki; Kadowaki, Hideyuki; Miyadera, Tetsuhiko; Sugita, Takeshi; Tamakoshi, Masato; Kato, Masato; Fujiseki, Takemasa; Murata, Daisuke; Hara, Shota; Murakami, Takurou N.; Fujimoto, Shohei; Chikamatsu, Masayuki; FUJIWARA, HIROYUKI
2015-01-01
We report artifact-free CH3NH3PbI3 optical constants extracted from ultra-smooth perovskite layers without air exposure and assign all the optical transitions in the visible/ultraviolet region unambiguously based on density functional theory (DFT) analysis that assumes a simple pseudo-cubic crystal structure. From the self-consistent spectroscopic ellipsometry analysis of the ultra-smooth CH3NH3PbI3 layers, we find that the absorption coefficients of CH3NH3PbI3 (alpha = 3.8 x 10^4 cm-1 at 2.0...
Rapid and controllable a-Si:H-to-nc-Si:H transition induced by a high-density plasma route
Zhou, H. P.; Xu, M.; Xu, S.; Xu, L. X.; Ji, H.; Xiao, S. Q.; Feng, Y. Y.
2017-09-01
The low-temperature rapid solid phase crystallization route of amorphous silicon is fundamentally and technologically significant. Micrometer thick hydrogenated amorphous silicon (a-Si:H) films were exposed to a low-frequency inductively coupled hydrogen plasma under a low substrate temperature of 300 °C. The plasma treated a-Si:H was completely crystallized within half an hour. The evolution of microstructures, optical and electric properties with respect to plasma exposure duration deterministically demonstrates that the present low-temperature rapid crystallization process enables the controllable phase transition from amorphous to nanocrystalline (nc) silicon. The crystallization mechanism is discussed in terms of the unique characteristics of low-frequency inductively coupled plasma (LFICP) and the LFICP-grown precursor a-Si:H film itself. The crucial role of hydrogen atoms in the phase transition is also discussed.
Tl sub 2 Mo sub 6 Se sub 6 : reentrant normal-superconductor-density wave phase transition
Energy Technology Data Exchange (ETDEWEB)
Tessema, G.X.; Tseng, Y.T.; Skove, M.J.; Stillwell, E.P. (Dept. of Physics and Astronomy, Clemson Univ., SC (USA)); Brusetti, R.; Monceau, P. (C.R.T.B.T., C.N.R.S., 38 - Grenoble (France))
1991-06-14
We report experimental results showing that uniaxial stress ({epsilon}) increases the resistance in the full range of temperature and leads to a metal to nonmetal phase transition. It suppresses T{sub c}. And, for {epsilon}{>=}0.50%, a peak appears at T{sub p}=15{+-}3 K in d(logR({epsilon},T))/d(1/T)vs 1/T plots. We speculate a Peierls phase transition takes place at T{sub p} with a fully developed gap E{sub g}=57 K below T=10 K. We summarize our results in a phase diagram in the {epsilon} vs T plane which, in the case of type-A samples exhibits a reentrant metal-superconductor-semiconductor characteristics. (orig.).
Gillon, M; Csizmadia, Sz; Fridlund, M; Deleuil, M; Aigrain, S; Alonso, R; Auvergne, M; Baglin, A; Barge, P; Barnes, S I; Bonomo, A S; Bordé, P; Bouchy, F; Bruntt, H; Cabrera, J; Carone, L; Carpano, S; Cochran, W D; Deeg, H J; Dvorak, R; Endl, M; Erikson, A; Ferraz-Mello, S; Gandolfi, D; Gazzano, J C; Guenther, E; Guillot, T; Havel, M; Hébrard, G; Jorda, L; Léger, A; Llebaria, A; Lammer, H; Lovis, C; Mayor, M; Mazeh, T; Montalbán, J; Moutou, C; Ofir, A; Ollivier, M; Pätzold, M; Pepe, F; Queloz, D; Rauer, H; Rouan, D; Samuel, B; Santerne, A; Schneider, J; Tingley, B; Udry, S; Weingrill, J; Wuchterl, G
2010-01-01
We report the discovery by the CoRoT satellite of a new transiting giant planet in a 2.83 days orbit about a V=15.5 solar analog star (M_* = 1.08 +- 0.08 M_sun, R_* = 1.1 +- 0.1 R_sun, T_eff = 5675 +- 80 K). This new planet, CoRoT-12b, has a mass of 0.92 +- 0.07 M_Jup and a radius of 1.44 +- 0.13 R_Jup. Its low density can be explained by standard models for irradiated planets.
Energy Technology Data Exchange (ETDEWEB)
Vinod, K., E-mail: vinod@igcar.gov.in; Sharma, Shilpam; Sundar, C. S.; Bharathi, A. [Low Temperature Studies Section, Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam-603102 (India)
2015-06-24
Heat capacity measurements were done on sub-micron sized BaFe{sub 2−x}Ru{sub x}As{sub 2} single crystals using thin film membrane based the AC steady state calorimetry technique. Noticeable thermal hysteresis is observed in the heat capacity of the BaFe{sub 2−x}Ru{sub x}As{sub 2} during cooling and warming cycles, indicating first order nature of the SDW transition.
Bogdan, T. J.
1983-01-01
The problem of one-dimensional gas flow through a sinusoidal gravitational potential with a series of equally spaced shock fronts is considered. For time-independent and spatially periodic flows, an integral equation relates the flow velocity to the gravitational potential and source functions of energy and momentum densities. It is suggested that this problem simulates some of the dynamical effects of the azimuthal flow on a parcel of gas at a fixed radius in a galactic disk that supports a spiral density wave structure. It omits the radial motions. In this context, a typical azimuthal velocity across a spiral arm is specified and the resultant source functions are obtained. The implications of this calculation suggest heating of the gaseous disk by O and B stars behind the shock front, and subsequent interarm cooling is a plausible mechanism for maintaining the periodic cycling of the gaseous component of the galactic disk.
Deleuil, M.; Bonomo, A. S.; Ferraz-Mello, S.; Erikson, A.; Bouchy, F.; Havel, M.; Aigrain, S.; Almenara, J.-M.; Alonso, R.; Auvergne, M.; Baglin, A.; Barge, P.; Bordé, P.; Bruntt, H.; Cabrera, J.; Carpano, S.; Cavarroc, C.; Csizmadia, Sz.; Damiani, C.; Deeg, H. J.; Dvorak, R.; Fridlund, M.; Hébrard, G.; Gandolfi, D.; Gillon, M.; Guenther, E.; Guillot, T.; Hatzes, A.; Jorda, L.; Léger, A.; Lammer, H.; Mazeh, T.; Moutou, C.; Ollivier, M.; Ofir, A.; Parviainen, H.; Queloz, D.; Rauer, H.; Rodríguez, A.; Rouan, D.; Santerne, A.; Schneider, J.; Tal-Or, L.; Tingley, B.; Weingrill, J.; Wuchterl, G.
2012-02-01
We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 ± 0.23 MJup and a radius of 0.84 ± 0.04 RJup. With a mean density of 8.87 ± 1.10 g cm-3, it is among the most compact planets known so far. Evolutionary models for the planet suggest a mass of heavy elements of the order of 800 M⊕ if embedded in a central core, requiring a revision either of the planet formation models or both planet evolution and structure models. We note however that smaller amounts of heavy elements are expected by more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56.The star's projected rotational velocity is vsini = 4.5 ± 1.0 km s-1, corresponding to a spin period of 11.5 ± 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving toward a triple synchronous state with equality of the orbital, planetary and stellar spin periods. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain.
Cai, Weihua; Lai, Ting; Lai, Jianwei; Xie, Haoting; Ouyang, Liuzhang; Ye, Jianshan; Yu, Chengzhong
2016-06-01
Fiber shaped supercapacitors are promising candidates for wearable electronics because they are flexible and light-weight. However, a critical challenge of the widespread application of these energy storage devices is their low cell voltages and low energy densities, resulting in limited run-time of the electronics. Here, we demonstrate a 1.5 V high cell voltage and high volumetric energy density asymmetric fiber supercapacitor in aqueous electrolyte. The lightweight (0.24 g cm‑3), highly conductive (39 S cm‑1), and mechanically robust (221 MPa) graphene fibers were firstly fabricated and then coated by NiCo2S4 nanoparticles (GF/NiCo2S4) via the solvothermal deposition method. The GF/NiCo2S4 display high volumetric capacitance up to 388 F cm‑3 at 2 mV s‑1 in a three-electrode cell and 300 F cm‑3 at 175.7 mA cm‑3 (568 mF cm‑2 at 0.5 mA cm‑2) in a two-electrode cell. The electrochemical characterizations show 1000% higher capacitance of the GF/NiCo2S4 as compared to that of neat graphene fibers. The fabricated device achieves high energy density up to 12.3 mWh cm‑3 with a maximum power density of 1600 mW cm‑3, outperforming the thin-film lithium battery. Therefore, these supercapacitors are promising for the next generation flexible and wearable electronic devices.
Cai, Weihua; Lai, Ting; Lai, Jianwei; Xie, Haoting; Ouyang, Liuzhang; Ye, Jianshan; Yu, Chengzhong
2016-06-01
Fiber shaped supercapacitors are promising candidates for wearable electronics because they are flexible and light-weight. However, a critical challenge of the widespread application of these energy storage devices is their low cell voltages and low energy densities, resulting in limited run-time of the electronics. Here, we demonstrate a 1.5 V high cell voltage and high volumetric energy density asymmetric fiber supercapacitor in aqueous electrolyte. The lightweight (0.24 g cm(-3)), highly conductive (39 S cm(-1)), and mechanically robust (221 MPa) graphene fibers were firstly fabricated and then coated by NiCo2S4 nanoparticles (GF/NiCo2S4) via the solvothermal deposition method. The GF/NiCo2S4 display high volumetric capacitance up to 388 F cm(-3) at 2 mV s(-1) in a three-electrode cell and 300 F cm(-3) at 175.7 mA cm(-3) (568 mF cm(-2) at 0.5 mA cm(-2)) in a two-electrode cell. The electrochemical characterizations show 1000% higher capacitance of the GF/NiCo2S4 as compared to that of neat graphene fibers. The fabricated device achieves high energy density up to 12.3 mWh cm(-3) with a maximum power density of 1600 mW cm(-3), outperforming the thin-film lithium battery. Therefore, these supercapacitors are promising for the next generation flexible and wearable electronic devices.
Kabita, Kh; Maibam, Jameson; Indrajit Sharma, B.; Brojen Singh, R. K.; Thapa, R. K.
2016-01-01
We report first principles phase transition, elastic properties and electronic structure for cadmium telluride (CdTe) under induced pressure in the light of density functional theory using the local density approximation (LDA), generalised gradient approximation (GGA) and modified Becke-Johnson (mBJ) potential. The structural phase transition of CdTe from a zinc blende (ZB) to a rock salt (RS) structure within the LDA calculation is 2.2 GPa while that within GGA is found to be at 4 GPa pressure with a volume collapse of 20.9%. The elastic constants and parameters (Zener anisotropy factor, Shear modulus, Poisson’s ratio, Young’s modulus, Kleinmann parameter and Debye’s temperature) of CdTe at different pressures of both the phases have been calculated. The band diagram of the CdTe ZB structure shows a direct band gap of 1.46 eV as predicted by mBJ calculation which gives better results in close agreement with experimental results as compared to LDA and GGA. An increase in the band gap of the CdTe ZB phase is predicted under induced pressure while the metallic nature is retained in the CdTe RS phase.
Zobač, Vladimír; Lewis, James P; Abad, Enrique; Mendieta-Moreno, Jesús I; Hapala, Prokop; Jelínek, Pavel; Ortega, José
2015-05-08
The computational simulation of photo-induced processes in large molecular systems is a very challenging problem. Firstly, to properly simulate photo-induced reactions the potential energy surfaces corresponding to excited states must be appropriately accessed; secondly, understanding the mechanisms of these processes requires the exploration of complex configurational spaces and the localization of conical intersections; finally, photo-induced reactions are probability events, that require the simulation of hundreds of trajectories to obtain the statistical information for the analysis of the reaction profiles. Here, we present a detailed description of our implementation of a molecular dynamics with electronic transitions algorithm within the local-orbital density functional theory code FIREBALL, suitable for the computational study of these problems. As an example of the application of this approach, we also report results on the [2 + 2] cycloaddition of ethylene with maleic anhydride and on the [2 + 2] photo-induced polymerization reaction of two C60 molecules. We identify different deactivation channels of the initial electron excitation, depending on the time of the electronic transition from LUMO to HOMO, and the character of the HOMO after the transition.
Nakata, Ayako; Tsuneda, Takao; Hirao, Kimihiko
2011-12-14
A long-range corrected (LC) time-dependent density functional theory (TDDFT) incorporating relativistic effects with spin-orbit couplings is presented. The relativistic effects are based on the two-component zeroth-order regular approximation Hamiltonian. Before calculating the electronic excitations, we calculated the ionization potentials (IPs) of alkaline metal, alkaline-earth metal, group 12 transition metal, and rare gas atoms as the minus orbital (spinor) energies on the basis of Koopmans' theorem. We found that both long-range exchange and spin-orbit coupling effects are required to obtain Koopmans' IPs, i.e., the orbital (spinor) energies, quantitatively in DFT calculations even for first-row transition metals and systems containing large short-range exchange effects. We then calculated the valence excitations of group 12 transition metal atoms and the Rydberg excitations of rare gas atoms using spin-orbit relativistic LC-TDDFT. We found that the long-range exchange and spin-orbit coupling effects significantly contribute to the electronic spectra of even light atoms if the atoms have low-lying excitations between orbital spinors of quite different electron distributions.
Gyanchandani, Jyoti; Sikka, S. K.
2011-05-01
We have calculated some of the physical properties of the recently discovered 6d elements by density functional theory. Comparison with those of the 5d metals shows that there is a close analogy for the crystal structures, for parabolic variation of equilibrium atomic volumes and bulk moduli, and an almost linearly increasing behavior of the pressure derivative of the bulk modulus across the 6d series. The Friedel model that is used to explain these trends for homologous series also holds for 6d metals. These elements also seem to be placed correctly in the Periodic Table.
Bjornsson, Ragnar; Bühl, Michael
2010-06-14
Electric field gradients (EFGs) were computed for the first-row transition metal nuclei in Cr(C(6)H(6))(CO)(3), MnO(3)F, Mn(CO)(5)H, MnCp(CO)(3), Co(CO)(4)H, Co(CO)(3)(NO) and VCp(CO)(4), for which experimental gas-phase data (in form of nuclear quadrupole coupling constants) are available from microwave spectroscopy. A variety of exchange-correlation functionals were assessed, among which range-separated hybrids (such as CAM-B3LYP or LC-omegaPBE) perform best, followed by global hybrids (such as B3LYP and PBE0) and gradient-corrected functionals (such as BP86). While large basis sets are required on the metal atom for converged EFGs, smaller basis sets can be employed on the ligands. In most cases, EFGs show little sensitivity toward the geometrical parameters.
Crossfield, Ian J M
2012-01-01
The ACME Spectra project provides absolutely calibrated, mostly empirical spectra of exoplanet host stars for use in analysis of the stars and their planets. Spectra are obtained from ground-based telescopes and are tied directly to calibrated ground- and space-based photometry. The spectra remain only "mostly" empirical because of telluric absorption, but interpolation of stellar models over the gaps in wavelength coverage provides continuous stellar spectra. Among other uses, the spectra are suitable for precisely converting observed secondary eclipses (occultations) into absolute flux units with minimal recourse to models. In this letter I introduce ACME's methods and present a calibrated spectrum of the nearby, super-Earth hosting star 55 Cancri that spans the range from 0.81-5.05 micron. With this spectrum I show that the brightness temperature of the transiting planet 55 Cnc e is 1950 (+260/-190) K at 4.5 micron (cooler than previously reported), which corresponds to a planetary flux of 0.44 (+0.12/-0.0...
Directory of Open Access Journals (Sweden)
Vinit Sharma
2011-09-01
Full Text Available The formation of magnetic moment due to the dopants with p-orbital (d-orbital is named d0 (d − magnetism, where the ion without (with partially filled d states is found to be responsible for the observed magnetic properties. To study the origin of magnetism at a fundamental electronic level in such materials, as a representative case, we theoretically investigate ferromagnetism in MgO doped with transition metal (Mn and non-metal (C. The generalized gradient approximation based first-principles calculations are used to investigate substitutional doping of metal (Mn and non-metal (C, both with and without the presence of neighboring oxygen vacancy sites. Furthermore, the case of co-doping of (Mn, C in MgO system is also investigated. It is observed that the oxygen vacancies do not play a role in tuning the ferromagnetism in presence of Mn dopants, but have a significant influence on total magnetism of the C doped system. In fact, we find that in MgO the d0 magnetism through C doping is curtailed by pairing of the substitutional dopant with naturally occurring O vacancies. On the other hand, in case of (Mn, C co-doped MgO the strong hybridization between the C (2p and the Mn(3d states suggests that co-doping is a promising approach to enhance the ferromagnetic coupling between the nearest-neighboring dopant and host atoms. Therefore, (Mn,C co-doped MgO is expected to be a ferromagnetic semiconductor with long ranged ferromagnetism and high Curie temperature.
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Fang, Zongtang; Both, Johan; Li, Shenggang; Yue, Shuwen; Aprà, Edoardo; Keçeli, Murat; Wagner, Albert F.; Dixon, David A.
2016-08-09
The heats of formation and the normalized clustering energies (NCEs) for the group 4 and group 6 transition metal oxide (TMO) trimers and tetramers have been calculated by the Feller-Peterson-Dixon (FPD) method. The heats of formation predicted by the FPD method do not differ much from those previously derived from the NCEs at the CCSD(T)/aT level except for the CrO3 nanoclusters. New and improved heats of formation for Cr3O9 and Cr4O12 were obtained using PW91 orbitals instead of Hartree-Fock (HF) orbitals. Diffuse functions are necessary to predict accurate heats of formation. The fluoride affinities (FAs) are calculated with the CCSD(T) method. The relative energies (REs) of different isomers, NCEs, electron affinities (EAs), and FAs of (MO2)n ( M = Ti, Zr, Hf, n = 1 – 4 ) and (MO3)n ( M = Cr, Mo, W, n = 1 – 3) clusters have been benchmarked with 55 exchange-correlation DFT functionals including both pure and hybrid types. The absolute errors of the DFT results are mostly less than ±10 kcal/mol for the NCEs and the EAs, and less than ±15 kcal/mol for the FAs. Hybrid functionals usually perform better than the pure functionals for the REs and NCEs. The performance of the two types of functionals in predicting EAs and FAs is comparable. The B1B95 and PBE1PBE functionals provide reliable energetic properties for most isomers. Long range corrected pure functionals usually give poor FAs. The standard deviation of the absolute error is always close to the mean errors and the probability distributions of the DFT errors are often not Gaussian (normal). The breadth of the distribution of errors and the maximum probability are dependent on the energy property and the isomer.
HAT-P-18b and HAT-P-19b: Two Low-density Saturn-mass Planets Transiting Metal-rich K Stars
Hartman, J. D.; Bakos, G. Á.; Sato, B.; Torres, G.; Noyes, R. W.; Latham, D. W.; Kovács, G.; Fischer, D. A.; Howard, A. W.; Johnson, J. A.; Marcy, G. W.; Buchhave, L. A.; Füresz, G.; Perumpilly, G.; Béky, B.; Stefanik, R. P.; Sasselov, D. D.; Esquerdo, G. A.; Everett, M.; Csubry, Z.; Lázár, J.; Papp, I.; Sári, P.
2011-01-01
We report the discovery of two new transiting extrasolar planets. HAT-P-18b orbits the V = 12.759 K2 dwarf star GSC 2594-00646, with a period P = 5.508023 ± 0.000006 days, transit epoch Tc = 2454715.02174 ± 0.00020 (BJD), and transit duration 0.1131 ± 0.0009 days. The host star has a mass of 0.77 ± 0.03 M sun, radius of 0.75 ± 0.04 R sun, effective temperature 4803 ± 80 K, and metallicity [Fe/H] = +0.10 ± 0.08. The planetary companion has a mass of 0.197 ± 0.013 M J and radius of 0.995 ± 0.052 R J, yielding a mean density of 0.25 ± 0.04 g cm-3. HAT-P-19b orbits the V = 12.901 K1 dwarf star GSC 2283-00589, with a period P = 4.008778 ± 0.000006 days, transit epoch Tc = 2455091.53417 ± 0.00034 (BJD), and transit duration 0.1182 ± 0.0014 days. The host star has a mass of 0.84 ± 0.04 M sun, radius of 0.82 ± 0.05 R sun, effective temperature 4990 ± 130 K, and metallicity [Fe/H] = +0.23 ± 0.08. The planetary companion has a mass of 0.292 ± 0.018 M J and radius of 1.132 ± 0.072 R J, yielding a mean density of 0.25 ± 0.04 g cm-3. The radial velocity residuals for HAT-P-19 exhibit a linear trend in time, which indicates the presence of a third body in the system. Comparing these observations with theoretical models, we find that HAT-P-18b and HAT-P-19b are each consistent with a hydrogen-helium-dominated gas giant planet with negligible core mass. HAT-P-18b and HAT-P-19b join HAT-P-12b and WASP-21b in an emerging group of low-density Saturn-mass planets, with negligible inferred core masses. However, unlike HAT-P-12b and WASP-21b, both HAT-P-18b and HAT-P-19b orbit stars with super-solar metallicity. This calls into question the heretofore suggestive correlation between the inferred core mass and host star metallicity for Saturn-mass planets. Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NOAO (A146Hr, A201Hr
Ruggieri, M
2016-01-01
In this article we study spontaneous chiral symmetry breaking for quark matter in the background of an electric-magnetic flux tube with static, homogeneous and parallel electric field $\\bm E$ and magnetic field $\\bm B$. We use a Nambu-Jona-Lasinio model with a local kernel interaction to compute the relevant quantities to describe chiral symmetry breaking at finite temperature for a wide range of $E$ and $B$. We study the effect of the flux tube background on inverse catalysis of chiral symmetry breaking for $E$ and $B$ of the same order of magnitude. We then focus on the effect of equilibration of chiral density, $n_5$, produced dynamically by axial anomaly on the critical temperature. The equilibration of $n_5$, a consequence of chirality flipping processes in the thermal bath, allows for the introduction of the chiral chemical potential, $\\mu_5$, which is computed self-consistently as a function of temperature and field strength by coupling the number equation to the gap equation. We find that even if chir...
Ruggieri, M.; Peng, G. X.
2016-05-01
In this article, we study spontaneous chiral symmetry breaking for quark matter in the background of static and homogeneous parallel electric field E and magnetic field B . We use a Nambu-Jona-Lasinio model with a local kernel interaction to compute the relevant quantities to describe chiral symmetry breaking at a finite temperature for a wide range of E and B . We study the effect of this background on the inverse catalysis of chiral symmetry breaking for E and B of the same order of magnitude. We then focus on the effect of the equilibration of chiral density n5 , produced dynamically by an axial anomaly on the critical temperature. The equilibration of n5 , a consequence of chirality-flipping processes in the thermal bath, allows for the introduction of the chiral chemical potential μ5, which is computed self-consistently as a function of the temperature and field strength by coupling the number equation to the gap equation and solving the two within an expansion in E /T2 , B /T2 , and μ52/T2 . We find that even if chirality is produced and equilibrates within a relaxation time τM , it does not change drastically the thermodynamics, with particular reference to the inverse catalysis induced by the external fields, as long as the average μ5 at equilibrium is not too large.
Shirayama, Masaki; Kadowaki, Hideyuki; Miyadera, Tetsuhiko; Sugita, Takeshi; Tamakoshi, Masato; Kato, Masato; Fujiseki, Takemasa; Murata, Daisuke; Hara, Shota; Murakami, Takurou N.; Fujimoto, Shohei; Chikamatsu, Masayuki; Fujiwara, Hiroyuki
2016-01-01
Light-induced photocarrier generation is an essential process in all solar cells, including organic-inorganic hybrid (CH3NH3PbI3 ) solar cells, which exhibit a high short-circuit current density (Jsc ) of approximately 20 mA /cm2 . Although the high Jsc observed in the hybrid solar cells relies on strong electron-photon interaction, the optical transitions in the perovskite material remain unclear. Here, we report artifact-free CH3NH3PbI3 optical constants extracted from ultrasmooth perovskite layers without air exposure and assign all of the optical transitions in the visible and ultraviolet region unambiguously, based on density-functional theory (DFT) analysis that assumes a simple pseudocubic crystal structure. From the self-consistent spectroscopic ellipsometry analysis of the ultrasmooth CH3NH3PbI3 layers, we find that the absorption coefficients of CH3NH3PbI3 (α =3.8 ×104 cm-1 at 2.0 eV) are comparable to those of CuInGaSe2 and CdTe, and high α values reported in earlier studies are overestimated seriously by the extensive surface roughness of CH3NH3PbI3 layers. The polarization-dependent DFT calculations show that CH3NH3 + interacts strongly with the PbI3 - cage, modifying the CH3NH3PbI3 dielectric function in the visible region rather significantly. In particular, the transition matrix element of CH3NH3PbI3 varies, depending on the position of CH3NH3 + within the Pb—I network. When the effect of CH3NH3 + on the optical transition is eliminated in the DFT calculation, the CH3NH3PbI3 dielectric function deduced from DFT shows an excellent agreement with the experimental result. As a result, distinct optical transitions observed at E0(Eg)=1.61 eV , E1=2.53 eV , and E2=3.24 eV in CH3NH3PbI3 are attributed to the direct semiconductor-type transitions at the R , M , and X points in the pseudocubic Brillouin zone, respectively. We further perform the quantum efficiency (QE) analysis for a standard hybrid-perovskite solar cell incorporating a mesoporous TiO2
Lu, Cheng; Kuang, Xiao-Yu; Zhu, Qin-Sheng
2008-11-06
Using first-principles calculations, the elastic constants, the thermodynamic properties, and the structural phase transition between the B1 (rocksalt) and the B2 (cesium chloride) phases of NaCl are investigated by means of the pseudopotential plane-waves method. The calculations are performed within the generalized gradient approximation to density functional theory with the Perdew-Burke-Ernzerhof exchange-correlation functional. On the basis of the third-order Birch-Murnaghan equation of states, the transition pressure Pt between the B1 phase and the B2 phase of NaCl is determined. The calculated values are generally speaking in good agreement with experiments and with similar theoretical calculations. From the theoretical calculations, the shear modulus, Young's modulus, rigidity modulus, and Poisson's ratio of NaCl are derived. According to the quasi-harmonic Debye model, we estimated the Debye temperature of NaCl from the average sound velocity. Moreover, the pressure derivatives of elastic constants, partial differentialC11/partial differentialP, partial differentialC12/partial differentialP, partial differentialC44/partial differentialP, partial differentialS11/partial differential P, partial differentialS12/partial differentialP, and partial differentialS44/partial differentialP, for NaCl crystal are investigated for the first time. This is a quantitative theoretical prediction of the elastic and thermodynamic properties of NaCl, and it still awaits experimental confirmation.
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Liu, Qi-Jun, E-mail: qijunliu@home.swjtu.edu.cn [Bond and Band Engineering Group, Sichuan Provincial Key Laboratory (for Universities) of High Pressure Science and Technology, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhang, Ning-Chao; Sun, Yan-Yun; Zhang, Ming-Jian; Liu, Fu-Sheng [Bond and Band Engineering Group, Sichuan Provincial Key Laboratory (for Universities) of High Pressure Science and Technology, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Liu, Zheng-Tang [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China)
2014-03-01
Using first-principles density-functional theory, we have investigated the pressure-induced phase transition in hydronitrogen compound N{sub 4}H{sub 4} and discussed the potential tetragonal structure. We find that tetragonal structure with P4{sub 2}/n space group is mechanically stable and ductile. The thermodynamic stability of Pmna>P1{sup ¯}>P4{sub 2}/n>P2{sub 1}/m has been obtained. With increasing pressure, the phase transition pressures of T{sub Pmna→P4{sub 2/n}}, T{sub P4{sub 2/n→Pmna}}, T{sub Pmna→P1{sup ¯}} and T{sub P1{sup ¯}→P2{sub 1/m}} are 5.6, 15.0, 30.0 and 69.2 GPa, respectively, which are in agreement with the available data. Moreover, the mechanical stability of four structures under pressure has been analyzed.
Ramanantoanina, Harry; Urland, Werner; Cimpoesu, Fanica; Daul, Claude
2013-09-07
Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4f(n)→ 4f(n-1)5d(1) transitions in rare earth compounds and apply it for the characterization of the 4f(2)→ 4f(1)5d(1) transitions in the quantum cutter Cs2KYF6:Pr(3+) with the elpasolite structure type. The methodological advances are relevant for the analysis and prospection of materials acting as phosphors in light-emitting diodes. The positions of the zero-phonon energy corresponding to the states of the electron configurations 4f(2) and 4f(1)5d(1) are calculated, where the praseodymium ion may occupy either the Cs(+)-, K(+)- or the Y(3+)-site, and are compared with available experimental data. The theoretical results show that the occupation of the three undistorted sites allows a quantum-cutting process. However size effects due to the difference between the ionic radii of Pr(3+) and K(+) as well as Cs(+) lead to the distortion of the K(+)- and the Cs(+)-site, which finally exclude these sites for quantum-cutting. A detailed discussion about the origin of this distortion is also described.
Shil, Suranjan; Bhattacharya, Debojit; Sarkar, Sonali; Misra, Anirban
2013-06-13
We have computed and investigated the performance of Minnesota density functionals especially the M05, M06, and M08 suite of complementary density functionals for the prediction of the heat of formations (HOFs) and the ionization potentials (IPs) of various benchmark complexes containing nine different first row transition metals. The eight functionals of M0X family, namely, the M05, M05-2X, M06-L, M06, M06-2X, M06-HF, M08-SO, and M08-HX are taken for the computation of the above-mentioned physical properties of such metal complexes along with popular Los Alamos National Laboratory 2 double-ζ (LANL2DZ) basis set. Total 54 benchmark systems are taken for HOF calculation, whereas the 47 systems among these benchmark complexes are chosen for the calculation of IPs because of lack of experimental results on rest of the seven systems. The computed values of HOFs and IPs are compared with the experimental results obtained from the literature. The deviation of these computed values from the actual experimental results is calculated for each eight different M0X functionals to judge their performances in evaluating these properties. Finally, a clear relationship between the exchange correlation energy of eight M0X functionals and their efficiency are made to predict the different physical properties.
Khitrov, V A
2001-01-01
The new, model-independent method to estimate simultaneously the level densities excited in the (n,gamma) reaction and the radiative strength functions of dipole transitions is developed. The method can be applied for any nucleus and reaction followed by cascade gamma-emission. It is just necessary to measure the intensities of two-step gamma-cascades depopulating one or several high-excited states and determine the quanta ordering in the main portion of the observed cascades. The method provides a sufficiently narrow interval of most probable densities of levels with given J suppi and radiative strength functions of dipole transitions populating them.
Adamescu, Adrian; Hamilton, Ian P; Al-Abadleh, Hind A
2014-07-31
Aromatic organoarsenicals, such as p-arsanilic acid (pAsA), are still used today as feed additives in the poultry and swine industries in developing countries. Through the application of contaminated litter as a fertilizer, these compounds enter the environment and interact with reactive soil components such as iron and aluminum oxides. Little is known about these surface interactions at the molecular level. We report density functional theory (DFT) calculations on the energies, optimal geometries, and vibrational frequencies for hydrated pAsA/iron oxide complexes, as well as changes in Gibbs free energy, enthalpy, and entropy for various types of ligand exchange reactions leading to both inner- and outer-sphere complexes. Similar calculations using arsenate are also shown for comparison, along with activation barriers and transition state geometries between inner-sphere complexes. Minimum energy calculations show that the formation of inner- and outer-sphere pAsA/iron oxide complexes is thermodynamically favorable, with the monodentate mononuclear complexes being the most favorable. Interatomic As-Fe distances are calculated to be between 3.3 and 3.5 Å for inner-sphere complexes and between 5.2 and 5.6 Å for outer-sphere complexes. In addition, transition state calculations show that activation energies greater than 23 kJ/mol are required to form the bidentate binuclear pAsA/iron oxide complexes, and that formation of arsenate bidentate binuclear complexes is thermodynamically -rather than kinetically- driven. Desorption thermodynamics using phosphate ions show that reactions are most favorable using HPO4(2-) species. The significance of our results for the overall surface complexation mechanism of pAsA and arsenate is discussed.
Vojvodic, A; Ruberto, C; Lundqvist, B I
2010-09-22
This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMCs) in NaCl structure by means of density-functional theory calculations. The investigated substrates are the TM-terminated TMC(111) surfaces, of interest because of the presence of different types of surface resonances (SRs) on them and because of their technological importance in growth processes. Also, TM compounds have shown potential in catalysis applications. Trend studies are conducted with respect to both period and group in the periodic table, choosing the substrates ScC, TiC, VC, ZrC, NbC, δ-MoC, TaC, and WC (in NaCl structure) and the adsorbates H, B, C, N, O, F, NH, NH(2), and NH(3). Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption-energy values with the calculated surface electronic structures. The results are rationalized by use of a concerted-coupling model (CCM), which has previously been applied successfully to the description of adsorption on TiC(111) and TiN(111) surfaces (Ruberto et al 2007 Solid State Commun. 141 48). First, the clean TMC(111) surfaces are characterized by calculating surface energies, surface relaxations, Bader charges, and surface-localized densities of states (DOSs). Detailed comparisons between surface and bulk DOSs reveal the existence of transition-metal localized SRs (TMSRs) in the pseudogap and of several C-localized SRs (CSRs) in the upper valence band on all considered TMC(111) surfaces. The spatial extent and the dangling bond nature of these SRs are supported by real-space analyses of the calculated Kohn-Sham wavefunctions. Then, atomic and molecular adsorption energies, geometries, and charge transfers are presented. An analysis of the adsorbate-induced changes in surface DOSs reveals a presence of both adsorbate-TMSR and adsorbate-CSRs interactions, of varying strengths depending on the surface and the adsorbate. These variations are
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Lima, C P; Lima, F M S; Fonseca, A L A; Nunes, O A C, E-mail: fabio@fis.unb.br [Institute of Physics, University of Brasilia and International Center of Condensed Matter Physics, PO Box 04455, 70919-970, Brasilia-DF (Brazil)
2011-07-15
The influence of a uniform magnetic field on the density of states (DoS) for carriers confined in a cylindrical semiconductor quantum wire irradiated by a monochromatic, linearly polarized, intense laser field is computed here non-perturbatively, following the Green's function scheme introduced by some of the authors in a recent work (Lima et al 2009 Solid State Commun. 149 678). Besides the known changes in the DoS provoked by an intense terahertz laser field-namely, a significant reduction and the appearance of Franz-Keldysh-like oscillations-our model reveals that the inclusion of a longitudinal magnetic field induces additional blueshifts on the energy levels of the allowed states. Our results show that the increase of the blueshifts with the magnitude of the magnetic field depends only on the azimuthal quantum number m (m=0, 1, 2, ...), being more pronounced for states with higher values of m, which leads to some energy crossovers. For all states, we have obtained, even in the absence of a magnetic field, a localization effect that leads to a transition in the DoS from the usual profile of quasi-1D systems to a peaked profile typical of quasi-0D systems, as e.g. those found for electrons confined in a quantum dot.
Schmiedeberg, Michael
2013-05-01
By using molecular-dynamics simulations, we determine the jamming phase diagrams at high densities for a bidisperse mixture of soft spheres that interact according to repulsive power-law pair potentials. We observe that the relaxation time varies nonmonotonically as a function of density at constant temperature. Therefore, the jamming phase diagrams contain multiple reentrant glass transitions if temperature and density are used as control parameters. However, if we consider a new formulation of the jamming phase diagrams where temperature over pressure and pressure are employed as control parameters, no nonmonotonic behavior is observed.
DEFF Research Database (Denmark)
Guenther, E. W.; Díaz, R. F.; Gazzano, J.-C.
2012-01-01
Context. Observations of transiting extrasolar planets are of key importance to our understanding of planets because their mass, radius, and mass density can be determined. These measurements indicate that planets of similar mass can have very different radii. For low-density planets, it is gener......Context. Observations of transiting extrasolar planets are of key importance to our understanding of planets because their mass, radius, and mass density can be determined. These measurements indicate that planets of similar mass can have very different radii. For low-density planets...... physical configurations mimicking a planetary transit signal, we determine the radius and mass of the planet by combining CoRoT photometry with high-resolution spectroscopy obtained with the echelle spectrographs SOPHIE, HARPS, FIES, and SANDIFORD. To improve the precision of its ephemeris and the epoch...... to the end of its main-sequence life. The host star has a mass M∗ = 1.21 ± 0.05 M⊙ and radius R∗ = 1.65 ± 0.04 R⊙. The planet has a mass of MP = 1.11 ± 0.06 MJup and radius of RP = 1.29 ± 0.03 RJup. The resulting bulk density is only ρ = 0.71 ± 0.06 g cm-3, which is much lower than that for Jupiter...
Sokolowsky, Kathleen P; Bailey, Heather E; Hoffman, David J; Andersen, Hans C; Fayer, Michael D
2016-07-21
Two-dimensional infrared (2D IR) data are presented for a vibrational probe in three nematogens: 4-cyano-4'-pentylbiphenyl, 4-cyano-4'-octylbiphenyl, and 4-(trans-4-amylcyclohexyl)-benzonitrile. The spectral diffusion time constants in all three liquids in the isotropic phase are proportional to [T*/(T - T*)](1/2), where T* is 0.5-1 K below the isotropic-nematic phase transition temperature (TNI). Rescaling to a reduced temperature shows that the decays of the frequency-frequency correlation function (FFCF) for all three nematogens fall on the same curve, suggesting a universal dynamic behavior of nematogens above TNI. Spectral diffusion is complete before significant orientational relaxation in the liquid, as measured by optically heterodyne detected-optical Kerr effect (OHD-OKE) spectroscopy, and before any significant orientational randomization of the probe measured by polarization selective IR pump-probe experiments. To interpret the OHD-OKE and FFCF data, we constructed a mode coupling theory (MCT) schematic model for the relationships among three correlation functions: ϕ1, a correlator for large wave vector density fluctuations; ϕ2, the orientational correlation function whose time derivative is the observable in the OHD-OKE experiment; and ϕ3, the FFCF for the 2D IR experiment. The equations for ϕ1 and ϕ2 match those in the previous MCT schematic model for nematogens, and ϕ3 is coupled to the first two correlators in a straightforward manner. Resulting models fit the data very well. Across liquid crystals, the temperature dependences of the coupling constants show consistent, nonmonotonic behavior. A remarkable change in coupling occurs at ∼5 K above TNI, precisely where the rate of spectral diffusion in 5CB was observed to deviate from that of a similar nonmesogenic liquid.
Tian, Dong; Zeng, Chunhua; Wang, Hua; Cheng, Xianming; Zheng, Yane; Xiang, Chao; Wei, Yonggang; Li, Kongzhai; Zhu, Xing
2017-09-01
Methane activation and oxygen vacancy formation over transition metal Fe adsorption on CeO2 (110) are studied by using the method of density functional theory (DFT) + U method. A set of model configurations are generated by placing Fe at five surface sites, viz., O-top site, O-bridge site, Ce-bridge site, Ce-top and double oxygen-bridge sites. The study shows that the energetically most favorable configuration is Fe adsorption at the double oxygen-bridge site. Based on the calculated surface, subsurface and the second oxygen vacancies formation energy with (or without) Fe adsorption, it shows that the Fe adsorption is in favor of the surface, subsurface and second oxygen vacancies formation. For the surface and subsurface oxygen vacancy on the Fe/CeO2 (110) surface, the main factor responsible for lowering of Evac is that the adsorption induces structural distortions, whereas, for the second oxygen vacancy, half can be attributed to the large structural relaxation, half can be attributed to the electronic effects. After calculating and discussing about the CH4 activation on CeO2 (110) and Fe/CeO2 (110) surface with (or without) the surface or subsurface oxygen vacancies at the possible adsorption sites, the results show that when the CH4 adsorbed on the Fe/CeO2 (110) with the surface oxygen vacancy at the Ce1 and Ce2 sites, the CH4 decomposed into the CH(ads) and H(ads), its belongs to the chemical absorption, whereas, when the CH4 adsorbed on the other possible sites, the mentioned phenomenon is not occurred, its belongs to the physical absorption. This study reveals the correlation between surface reducibility and catalytic activity for methane oxidation on cerium-based materials, which might be beneficial in developing improved catalysts for methane combustion.
Freire, Rafael L H; Kiejna, Adam; Da Silva, Juarez L F
2016-10-26
We report the results of extensive computational investigation of the adsorption properties of water and ethanol on several Cu-, Pt-, and Au-based substrates, including the close-packed unreconstructed Cu(111), Pt(111), and Au(111) surfaces, defected metal substrates with on-surface low-coordinated sites generated by the intermixing of Pt-Cu and Pt-Au in the topmost surface layers and strained on-surface and sub-surface Pt-layers at Cu(111) and Au(111) substrates. The calculations are based on the density functional theory (DFT) within the van der Waals (vdW) correction. For all the substrates, we found that water and ethanol bind via the anionic O atom to the cationic one-fold coordinated on-top metal sites, which enhances the adsorbate-substrate Coulomb interactions. For water, both DFT and DFT + vdW calculations predict a flat geometry. For ethanol, the DFT and DFT + vdW results are in contrast, namely, DFT yields a perpendicular orientation of the C-C bond with respect to the surface, while we obtained a parallel orientation of the C-C bond using DFT + vdW, which maximizes the adsorption energies. Despite expected deviations due to the nature of the weak adsorbate-substrate interactions, we found that the adsorption energy of water and ethanol shows a linear dependence as a function of the position of the center of gravity of the occupied d-band, and hence, the magnitude of the adsorption energy increases as the d-band center position shifts towards the Fermi energy. Thus, it indicates hybridization between the O p- and metal d-states, which determines the magnitude of the adsorption energy of water and ethanol on clean, low-coordinated, and strained noble and transition-metal substrates.
X-ray study of the charge-density-wave transition in single-layer $\mathrm{TiS}{{e}}_{2}$
Energy Technology Data Exchange (ETDEWEB)
Fang, Xin-Yue; Hong, Hawoong; Chen, Peng; Chiang, T. -C.
2017-05-01
Synchrotron x-ray studies of single-layer TiSe2 reveal displacements of the Ti and Se atoms as a function of temperature. The measurements, with a high sensitivity of 0.001 Å, show a (2x2) charge density wave (CDW) structure at temperatures below a critical temperature of TC1 = 233 K. The temperature dependence follows a BCS-like second-order mean-field behavior. A fivelayer TiSe2 film also exhibits a CDW transition of the same character but at a lower transition temperature of TC5 = 204 K, which is the same as that for bulk TiSe2. The results demonstrate that lattice distortion is an integral part of the CDW transition that must also involve renormalization of the electronic structure.
Guenther, E W; Gazzano, J -C; Mazeh, T; Rouan, D; Gibson, N; Csizmadia, Sz; Aigrain, S; Alonso, R; Almenara, J M; Auvergne, M; Baglin, A; Barge, P; Bonomo, A S; Borde, P; Bouchy, F; Bruntt, H; Cabrera, J; Carone, L; Carpano, S; Cavarroc, C; Deeg, H J; Deleuil, M; Dreizler, S; Dvorak, R; Erikson, A; Ferraz-Mello, S; Fridlund, M; Gandolfi, D; Gillon, M; Guillot, T; Hatzes, A; Havel, M; Hebrard, G; Jehin, E; Jorda, L; Lammer, H; Leger, A; Moutou, C; Nortmann, L; Ollivier, M; Ofir, A; Pasternacki, Th; Paetzold, M; Parviainen, H; Queloz, D; Rauer, H; Samuel, B; Santerne, A; Schneider, J; Tal-Or, L; Tingley, B; Weingrill, J; Wuchterl, G
2011-01-01
Observations of transiting extrasolar planets are of key importance to our understanding of planets because their mass, radius, and mass density can be determined. The CoRoT space mission allows us to achieve a very high photometric accuracy. By combining CoRoT data with high-precision radial velocity measurements, we derive precise planetary radii and masses. We report the discovery of CoRoT-19b, a gas-giant planet transiting an old, inactive F9V-type star with a period of four days. After excluding alternative physical configurations mimicking a planetary transit signal, we determine the radius and mass of the planet by combining CoRoT photometry with high-resolution spectroscopy obtained with the echelle spectrographs SOPHIE, HARPS, FIES, and SANDIFORD. To improve the precision of its ephemeris and the epoch, we observed additional transits with the TRAPPIST and Euler telescopes. Using HARPS spectra obtained during the transit, we then determine the projected angle between the spin of the star and the orbi...
Heydari Gharahcheshmeh, M.; Galstyan, E.; Xu, A.; Kukunuru, J.; Katta, R.; Zhang, Y.; Majkic, G.; Li, X.-F.; Selvamanickam, V.
2017-01-01
The superconducting transition width (∆T c) characteristics of REBa2Cu3O7-δ (REBCO and RE = Gd, Y) superconductor tapes with Zr content of 25 mol% with high lift factor (ratio of critical current density (J c) at 30 K, 3 T (B||c) to the J c at 77 K, 0 T) has been determined. In this work, heavily doped (Gd, Y)Ba2Cu3O7-δ superconductor tapes with 25 mol% Zr addition were fabricated by metal organic chemical vapor deposition using a reel-to reel process. The optimal chemical composition range of (Gd, Y)Ba2Cu3O7-δ superconductor tapes with Zr content of 25 mol% to achieve critical current densities above 3.5 MA cm-2 at 77 K in zero applied magnetic field has been determined. A superconducting transition width (∆T c) as narrow as 0.4 K and an onset critical transition temperature (T c-onset) as high as 92 K were obtained in the 25 mol% Zr-added (Gd, Y)BaCuO superconductor tapes. Based on the mapped compositional phase diagram of the ∆Tc and lift factor, ∆T c in the range of 0.7-0.9 K is observed in 25 mol% Zr-added (Gd, Y)BaCuO superconductor tapes with a high lift factor.
DEFF Research Database (Denmark)
Grivel, Jean-Claude; Eltsev, Y.; Andersson, M.
1999-01-01
R(T) measurements have been performed on optimally and overdoped heavily twinned high-purity YBa2Cu3O7-delta single crystals, under a magnetic field B oriented parallel to the twin boundary planes (B parallel to c). The characteristic feature attributed to the flux line lattice melting transition...
He, Xiao; Ryu, Shinsei; Hirata, So
2014-01-14
Finite-temperature extensions of ab initio Gaussian-basis-set spin-restricted Hartree-Fock (HF) and second-order many-body perturbation (MP2) theories are implemented for infinitely extended, periodic, one-dimensional solids and applied to the Peierls and charge-density-wave (CDW) transitions in polyyne and all-trans polyacetylene. The HF theory predicts insulating CDW ground states for both systems in their equidistant structures at low temperatures. In the same structures, they turn metallic at high temperatures. Starting from the "dimerized" low-temperature equilibrium structures, the systems need even higher temperatures to undergo a Peierls transition, which is accompanied by geometric as well as electronic distortions from dimerized to non-dimerized forms. The conventional finite-temperature MP2 theory shows a sign of divergence in any phase at any nonzero temperature and is useless. The renormalized finite-temperature MP2 (MP2R) theory is divergent only near metallic electronic structures, but is well behaved elsewhere. MP2R also predicts CDW and Peierls transitions occurring at two different temperatures. The effect of electron correlation is primarily to lower the Peierls transition temperature.
Caffarel, Michel; Giner, Emmanuel; Scemama, Anthony; Ramírez-Solís, Alejandro
2014-12-09
We present a comparative study of the spatial distribution of the spin density of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wave function theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell and the delocalization of the 3d hole over the chlorine atoms. More generally, this problem is representative of the difficulties encountered when studying open-shell metal-containing molecular systems. Here, it is shown that qualitatively different results for the spin density distribution are obtained from the various quantum-mechanical approaches. At the DFT level, the spin density distribution is found to be very dependent on the functional employed. At the QMC level, Fixed-Node Diffusion Monte Carlo (FN-DMC) results are strongly dependent on the nodal structure of the trial wave function. Regarding wave function methods, most approaches not including a very high amount of dynamic correlation effects lead to a much too high localization of the spin density on the copper atom, in sharp contrast with DFT. To shed some light on these conflicting results Full CI-type (FCI) calculations using the 6-31G basis set and based on a selection process of the most important determinants, the so-called CIPSI approach (Configuration Interaction with Perturbative Selection done Iteratively) are performed. Quite remarkably, it is found that for this 63-electron molecule and a full CI space including about 10(18) determinants, the FCI limit can almost be reached. Putting all results together, a natural and coherent picture for the spin distribution is proposed.
Bao, Junwei Lucas; Odoh, Samuel O; Gagliardi, Laura; Truhlar, Donald G
2017-02-14
We study the performance of multiconfiguration pair-density functional theory (MC-PDFT) and multireference perturbation theory for the computation of the bond dissociation energies in 12 transition-metal-containing diatomic molecules and three small transition-metal-containing polyatomic molecules and in two transition-metal dimers. The first step is a multiconfiguration self-consistent-field calculation, for which two choices must be made: (i) the active space and (ii) its partition into subspaces, if the generalized active space formulation is used. In the present work, the active space is chosen systematically by using three correlated-participating-orbitals (CPO) schemes, and the partition is chosen by using the separated-pair (SP) approximation. Our calculations show that MC-PDFT generally has similar accuracy to CASPT2, and the active-space dependence of MC-PDFT is not very great for transition-metal-ligand bond dissociation energies. We also find that the SP approximation works very well, and in particular SP with the fully translated BLYP functional SP-ftBLYP is more accurate than CASPT2. SP greatly reduces the number of configuration state functions relative to CASSCF. For the cases of FeO and NiO with extended-CPO active space, for which complete active space calculations are unaffordable, SP calculations are not only affordable but also of satisfactory accuracy. All of the MC-PDFT results are significantly better than the corresponding results with broken-symmetry spin-unrestricted Kohn-Sham density functional theory. Finally we test a perturbation theory method based on the SP reference and find that it performs slightly worse than CASPT2 calculations, and for most cases of the nominal-CPO active space, the approximate SP perturbation theory calculations are less accurate than the much less expensive SP-PDFT calculations.
Caffarel, Michel; Scemama, Anthony; Ramírez-Solís, Alejandro
2014-01-01
We present a comparative study of the spatial distribution of the spin density (SD) of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wavefunction theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell of the copper atom and the delocalization of the 3d hole over the chlorine atoms. It is shown here that qualitatively different results for SD are obtained from these various quantum-chemical approaches. At the DFT level, the spin density distribution is directly related to the amount of Hartree-Fock exchange introduced in hybrid functionals. At the QMC level, Fixed-node Diffusion Monte Carlo (FN-DMC) results for SD are strongly dependent on the nodal structure of the trial wavefunction employed (here, Hartree-Fock or Kohn-Sham with a particula...
Jiang, Jiang; DeAngelis, Donald L.; Zhang, B.; Cohen, J.E.
2014-01-01
Taylor's power law describes an empirical relationship between the mean and variance of population densities in field data, in which the variance varies as a power, b, of the mean. Most studies report values of b varying between 1 and 2. However, Cohen (2014a) showed recently that smooth changes in environmental conditions in a model can lead to an abrupt, infinite change in b. To understand what factors can influence the occurrence of an abrupt change in b, we used both mathematical analysis and Monte Carlo samples from a model in which populations of the same species settled on patches, and each population followed independently a stochastic linear birth-and-death process. We investigated how the power relationship responds to a smooth change of population growth rate, under different sampling strategies, initial population density, and population age. We showed analytically that, if the initial populations differ only in density, and samples are taken from all patches after the same time period following a major invasion event, Taylor's law holds with exponent b=1, regardless of the population growth rate. If samples are taken at different times from patches that have the same initial population densities, we calculate an abrupt shift of b, as predicted by Cohen (2014a). The loss of linearity between log variance and log mean is a leading indicator of the abrupt shift. If both initial population densities and population ages vary among patches, estimates of b lie between 1 and 2, as in most empirical studies. But the value of b declines to ~1 as the system approaches a critical point. Our results can inform empirical studies that might be designed to demonstrate an abrupt shift in Taylor's law.
López Arvizu, Gregorio; Calaminici, Patrizia
2007-05-21
Density functional calculations have been performed for small nickel clusters, Ni(n), Ni(n) (+), and Ni(n)(-) (ntheory approach. Newly developed nickel all-electron basis sets optimized for generalized gradient approximation (GGA) as well as an all-electron basis set optimized for the local density approximation were employed. For both neutral and charged systems, several isomers and different multiplicities were studied in order to determine the lowest energy structures. A vibrational analysis was performed in order to characterize these isomers. Structural parameters, harmonic frequencies, binding energies, ionization potentials, and electron affinities are reported. This work shows that the employed GGA basis sets for the nickel atom are important for the correct prediction of the ground state structures of small nickel clusters and that the structural assignment of these systems can be performed, with a good resolution, over the ionization potential.
Carmona, A; Kamp, I; Baruteau, C; Matter, A; Ancker, M van den; Pinte, C; Kóspál, A; Audard, M; Liebhart, A; Sicilia-Aguilar, A; Pinilla, P; Regály, Zs; Güdel, M; Henning, Th; Cieza, L A; Baldovin-Saavedra, C; Meeus, G; Eiroa, C
2016-01-01
Context: Quantifying the gas content inside the dust gaps of transition disks is important to establish their origin. Aims: We seek to constrain the surface density of warm gas in the disk of HD 139614, a Herbig Ae star with a transition disk exhibiting a dust gap from 2.3 to 6 AU. Methods: We have obtained ESO/VLT CRIRES high-resolution spectra of CO ro-vibrational emission. We derive disk structure constraints by modeling the line profiles, the spectroastrometric signal, and the rotational diagrams using flat Keplerian disk models. Results: We detected v=1-0 12CO, 2-1 12CO, 1-0 13CO, 1-0 C18O, and 1-0 C17O ro-vibrational lines. 12CO v=1-0 lines have an average width of 14 km/s, Tgas of 450 K and an emitting region from 1 to 15 AU. 13CO and C18O lines are on average 70 and 100 K colder, 1 and 4 km/s narrower, and are dominated by emission at R>6 AU. The 12CO v=1-0 line profile indicates that if there is a gap in the gas it must be narrower than 2 AU. We find that a drop in the gas surface density (delta_gas)...
Zhang, Wei-Bing; Li, Jie; Tang, Bi-Yu
2013-06-28
The structural, electronic, magnetic, and elastic properties of hexagonal nickel sulfide (NiS) have been investigated comparatively by Density Functional theory (DFT) and DFT plus correction for on-site Coulomb interaction (DFT+U), in which two different exchange correlation functionals local density approximations (LDA) and general gradient approximations (GGA) in the form of Perdew-Burke-Ernzerhof (PBE) are used. Our results indicate LDA and PBE methods predict hexagonal NiS to be a paramagnetic metal whereas LDA(PBE)+U calculations with reasonable on-site Coulomb interaction energy give the antiferromagnetic insulating state of low temperature hexagonal NiS successfully. Meanwhile, compared with LDA(PBE) results, LDA(PBE)+U methods give larger lattice parameters, crystal volume, and shear constant c44, consistent with the experimental picture during high-low temperature phase transition of hexagonal NiS, in which an increase of the shear constant c44 and lattice parameters were found in the low-temperature antiferromagnetic phase. The present DFT and DFT+U calculations provide a reasonable description for the properties of high temperature and low temperature hexagonal NiS respectively, which indicates that electronic correlation is responsible for this high-low temperature phase transition.
Wave-vector-dependent electron-phonon coupling and the charge-density-wave transition in TbT e3
Maschek, M.; Rosenkranz, S.; Heid, R.; Said, A. H.; Giraldo-Gallo, P.; Fisher, I. R.; Weber, F.
2015-06-01
We present a high-energy-resolution inelastic x-ray scattering investigation of the soft phonon mode in the charge-density-wave (CDW) system TbT e3 . We analyze our data based on lattice dynamical calculations using density-functional-perturbation theory and find clear evidence that strongly momentum-dependent electron-phonon coupling defines the periodicity of the CDW superstructure: Our experiment reveals strong phonon softening and increased phonon linewidths over a large part in reciprocal space adjacent to the CDW ordering vector qCDW=(0 ,0 ,0.3 ) . Further, qCDW is clearly offset from the wave vector of (weak) Fermi surface nesting qFS=(0 ,0 ,0.25 ) , and our detailed analysis indicates that electron-phonon coupling is responsible for this shift. Hence, we can add TbT e3 , which was previously considered as a canonical CDW compound following the Peierls scenario, to the list of distinct charge-density-wave materials characterized by momentum-dependent electron-phonon coupling.
Matsui, Toru; Kitagawa, Yasutaka; Shigeta, Yasuteru; Okumura, Mitsutaka
2013-07-09
We propose an accurate scheme to evaluate the redox potential of a wide variety of transition metal complexes by adding a charge-dependent correction term for a counterion around the charged complexes, which is based on Generalized Born theory, to the solvation energy. The mean absolute error (MAE) toward experimental redox potentials of charged complexes is considerably reduced from 0.81 V (maximum error 1.22 V) to 0.22 V (maximum error 0.50 V). We found a remarkable exchange-correlation functional dependence on the results rather than the basis set ones. The combination of Wachters+f (for metal) and 6-31++G(d,p) (for other atoms) with the B3LYP functional gives the least MAE 0.15 V for the test complexes. This scheme is applicable to other solvents, and heavier transition metal complexes such as M1(CO)5(pycn) (M1 = Cr, Mo, W), M2(mnt)2 (M2 = Ni, Pd, Pt), and M3(bpy)3 (M3 = Fe, Ru, Os) with the same quality.
Schaper, Danielle; McElroy, Kyle; Calleja, Eduardo; Dai, Jixia; Li, Lijun; Lu, Wenjian; Sun, Yuping; Zhu, Xiangde
2014-03-01
Charged ordered states are becoming a common feature in the phase diagrams of correlated materials. In many cased there are indications that doping controlled quantum critical points between the CO state and others are related to interesting properties including superconductivity. An interesting test case is the ordered 2D CDW found in the transition metal dichalcogenides. We performed an analytical study on the dichalcogenides tantalum disulfide (TaS2) and tantalum diselenide (TaSe2) to observe how CDWs present in the material can be melted as disorder is introduced into the system via copper doping. Data was taken using a scanning tunneling microscope (STM) below the transition to the CDW state, both with and without copper dopants added. The resulting topographs were then analyzed to investigate the relationship between the phase and the amplitude of the disordered CDW. We found that the copper doping caused disorder in the CDW state characterized by phase wanderings and 2 π phase winding ``point defects'' in the CDW not present in the undoped parent compound. The locations of these point defects and windings were, in turn, found to have the characteristics of topological defects. Implications for studies of other disordered CO states seen in STM will be discussed.
Li, Hong; Draxl, Claudia; Wurster, Stefan; Pippan, Reinhard; Romaner, Lorenz
2017-03-01
We address the impact of tantalum alloying on dislocation properties of tungsten. To that aim, we calculate elastic constants, atomic-row displacement energy, dislocation core energy, and Peierls stress for different degrees of alloying within the framework of density-functional theory. We show that the elastic shear constants decrease monotonously with Ta content. Conversely, atomic-row displacement energy and, consequently, core energy and Peierls stress show a nonmonotonous behavior. These quantities peak at 25 at% Ta, indicating a tendency for embrittlement of W at such alloying concentrations. Our findings are in agreement with the experimental literature.
Woutersen, Sander; Zhao, Zuofeng; Angell, C Austen
2016-01-01
The striking anomalies in physical properties of supercooled water that were discovered in the 1960-70s, remain incompletely understood and so provide both a source of controversy amongst theoreticians, and a stimulus to experimentalists and simulators to find new ways of penetrating the "crystallization curtain" that effectively shields the problem from solution. Recently a new door on the problem was opened by showing that, in ideal solutions, made using ionic liquid solutes, water anomalies are not destroyed as earlier found for common salt and most molecular solutes, but instead are enhanced to the point of precipitating an apparently first order liquid-liquid transition. The evidence was a spike in apparent heat capacity during cooling that could be fully reversed during reheating before any sign of ice crystallization appeared. Here, we use decoupled-oscillator infrared spectroscopy to define the structural character of this phenomenon using similar down and upscan rates as in the calorimetric study. Th...
Burel, Maxym; Martin, Sylvain; Bonnefoy, Olivier
2017-06-01
We present the results of an experimental study on the jamming/flowing transition. A suspension of neutrally buoyant large particles flows in an horizontal rectangular duct, where an artificial restriction triggers jamming. We show that the avalanche distribution size is exponential, that is memoryless. We further demonstrate that the avalanche size diverges when the restriction size approaches a critical value and that this divergence is well described by a power law. The parameters (critical opening size and divergence velocity) are compared to literature values and show a strong similarity with others systems. Another result of this paper is the study of the influence of the particle morphology. We show that, for a moderate restriction size, the dead-zone formed right upstream of the restriction is larger for angular particles but, paradoxically, that the avalanche size is larger for polyhedra compared to spheres by at least one order of magnitude.
Energy Technology Data Exchange (ETDEWEB)
Porcar, L.; Bourgault, D.; Chaud, X.; Noudem, J.G.; Tournier, R. [CNRS, Grenoble (France). EPM-Matformag; Belmont, O.; Barbut, J.M.; Barrault, M. [Schneider Electric SA, Usine A, Rue Volta, 38050 Grenoble cedex 09 (France); Tixador, P. [CRTBT, CNRS, BP 166, 38042 Grenoble cedex 09 (France)
1998-05-01
High transport currents along the (a,b) planes and along the c-axis have been measured in pulsed current of different pseudo-frequencies. Self field losses and transport current of 8000 A (20000 A cm{sup -2}) have been measured in Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} bars textured by the melting zone technique. Critical currents as high as 500 A (90000 A cm{sup -2}) along the (a,b) planes or 3000 A (7500 A cm{sup -2}) along the c-axis have been measured. For both orientations, the transition from the normal state to the superconducting state has been observed. Electric field of 1000 V m{sup -1} and study of the superconducting state recovery are reported. (orig.) 6 refs.
Transitive spaces of operators
Davidson, K R; Radjavi, H
2007-01-01
We investigate algebraic and topological transitivity and, more generally, k-transitivity for linear spaces of operators. In finite dimensions, we determine minimal dimensions of k-transitive spaces for every k, and find relations between the degree of transitivity of a product or tensor product on the one hand and those of the factors on the other. We present counterexamples to some natural conjectures. Some infinite dimensional analogues are discussed. A simple proof is given of Arveson's result on the weak-operator density of transitive spaces that are masa bimodules.
DEFF Research Database (Denmark)
Guenther, E. W.; Díaz, R. F.; Gazzano, J.-C.
2012-01-01
to the end of its main-sequence life. The host star has a mass M∗ = 1.21 ± 0.05 M⊙ and radius R∗ = 1.65 ± 0.04 R⊙. The planet has a mass of MP = 1.11 ± 0.06 MJup and radius of RP = 1.29 ± 0.03 RJup. The resulting bulk density is only ρ = 0.71 ± 0.06 g cm-3, which is much lower than that for Jupiter......Context. Observations of transiting extrasolar planets are of key importance to our understanding of planets because their mass, radius, and mass density can be determined. These measurements indicate that planets of similar mass can have very different radii. For low-density planets......, it is generally assumed that they are inflated owing to their proximity to the host-star. To determine the causes of this inflation, it is necessary to obtain a statistically significant sample of planets with precisely measured masses and radii. Aims. The CoRoT space mission allows us to achieve a very high...
Li, Zhendong; Liu, Wenjian
2016-06-14
Compared with closed-shell systems, open-shell systems place three additional challenges to time-dependent density functional theory (TD-DFT) for electronically excited states: (a) the spin-contamination problem is a serious issue; (b) the exchange-correlation (XC) kernel may be numerically instable; and (c) the single-determinant description of open-shell ground states readily becomes energetically instable. Confined to flip-up single excitations, the spin-contamination problem can largely be avoided by using the spin-flip TD-DFT (SF-TD-DFT) formalism, provided that a noncollinear XC kernel is employed. As for the numerical instabilities associated with such a kernel, only an ad hoc scheme has been proposed so far, viz., the ALDA0 kernel, which amounts to setting the divergent components (arising from density gradients and kinetic energy density) simply to zero. The ground-state instability problem can effectively be avoided by introducing the Tamm-Dancoff approximation (TDA) to TD-DFT. Therefore, on a general basis, the SF-TDA/ALDA0 Ansatz is so far the only promising means within the TD-DFT framework for flip-up single excitations of open-shell systems. To assess systematically the performance of SF-TDA/ALDA0, in total 61 low-lying quartet excited states of the benchmark set of 11 small radicals [J. Chem. Theory Comput. 2016, 12, 238] are investigated with various XC functionals. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as benchmark, it is found that the mean absolute errors of SF-TDA/ALDA0 with the SAOP (statistical averaging of model orbital potentials), global hybrid, and range-separated hybrid functionals are in the range of 0.2-0.4 eV. This is in line not only with the typical accuracy of TD-DFT for singlet and triplet excited states of closed-shell systems but also with the gross accuracy of spin-adapted TD-DFT for spin-conserving excited states of open-shell systems.
Liu, Bin; Cheng, Lei; Curtiss, Larry; Greeley, Jeffrey
2014-04-01
The hydrogenation of furfural to furfuryl alcohol on Pd(111), Cu(111) and Pt(111) is studied with both standard Density Functional Theory (DFT)-GGA functionals and with van der Waals-corrected density functionals. VdW-DF functionals, including optPBE, optB88, optB86b, and Grimme's method, are used to optimize the adsorption configurations of furfural, furfuryl alcohol, and related intermediates resulting from hydrogenation of furfural, and the results are compared to corresponding values determined with GGA functionals, including PW91 and PBE. On Pd(111) and Pt(111), the adsorption geometries of the intermediates are not noticeably different between the two classes of functionals, while on Cu(111), modest changes are seen in both the perpendicular distance and the orientation of the aromatic ring with respect to the planar surface. In general, the binding energies increase substantially in magnitude as a result of van der Waals contributions on all metals. In contrast, however, dispersion effects on the kinetics of hydrogenation are relatively small. It is found that activation barriers are not significantly affected by the inclusion of dispersion effects, and a Brønsted-Evans-Polanyi relationship developed solely from PW91 calculations on Pd(111) is capable of describing corresponding results on Cu(111) and Pt(111), even when the dispersion effects are included. Finally, the reaction energies and barriers derived from the dispersion-corrected and pure GGA calculations are used to plot simple potential energy profiles for furfural hydrogenation to furfuryl alcohol on the three considered metals, and an approximately constant downshift of the energetics due to the dispersion corrections is observed.
Energy Technology Data Exchange (ETDEWEB)
Liu, Bin; Cheng, Lei; Curtiss, Larry A.; Greeley, Jeffrey P.
2014-04-01
The hydrogenation of furfural to furfuryl alcohol on Pd(111), Cu(111) and Pt(111) is studied with both standard Density Functional Theory (DFT)-GGA functionals and with van der Waals-corrected density functionals. VdWDF functionals, including optPBE, optB88, optB86b, and Grimme's method, are used to optimize the adsorption configurations of furfural, furfuryl alcohol, and related intermediates resulting from hydrogenation of furfural, and the results are compared to corresponding values determined with GGA functionals, including PW91 and PBE. On Pd(111) and Pt(111), the adsorption geometries of the intermediates are not noticeably different between the two classes of functionals, while on Cu(111), modest changes are seen in both the erpendicular distance and the orientation of the aromatic ringwith respect to the planar surface. In general, the binding energies increase substantially in magnitude as a result of van derWaals contributions on all metals. In contrast, however, dispersion effects on the kinetics of hydrogenation are relatively small. It is found that activation barriers are not significantly affected by the inclusion of dispersion effects, and a Brønsted–Evans–Polanyi relationship developed solely fromPW91 calculations on Pd(111) is capable of describing corresponding results on Cu(111) and Pt(111), even when the dispersion effects are included. Finally, the reaction energies and barriers derived from the dispersion-corrected and pure GGA calculations are used to plot simple potential energy profiles for furfural hydrogenation to furfuryl alcohol on the three considered metals, and an approximately constant downshift of the energetics due to the dispersion corrections is observed.
Carmona, A.; Thi, W. F.; Kamp, I.; Baruteau, C.; Matter, A.; van den Ancker, M.; Pinte, C.; Kóspál, A.; Audard, M.; Liebhart, A.; Sicilia-Aguilar, A.; Pinilla, P.; Regály, Zs.; Güdel, M.; Henning, Th.; Cieza, L. A.; Baldovin-Saavedra, C.; Meeus, G.; Eiroa, C.
2017-02-01
Context. Quantifying the gas surface density inside the dust cavities and gaps of transition disks is important to establish their origin. Aims: We seek to constrain the surface density of warm gas in the inner disk of HD 139614, an accreting 9 Myr Herbig Ae star with a (pre-)transition disk exhibiting a dust gap from 2.3 ± 0.1 to 5.3 ± 0.3 AU. Methods: We observed HD 139614 with ESO/VLT CRIRES and obtained high-resolution (R 90 000) spectra of CO ro-vibrational emission at 4.7 μm. We derived constraints on the disk's structure by modeling the CO isotopolog line-profiles, the spectroastrometric signal, and the rotational diagrams using grids of flat Keplerian disk models. Results: We detected υ = 1 → 0 12CO, 2→1 12CO, 1→0 13CO, 1→0 C18O, and 1→0 C17O ro-vibrational lines. Lines are consistent with disk emission and thermal excitation. 12CO υ = 1 → 0 lines have an average width of 14 km s-1, Tgas of 450 K and an emitting region from 1 to 15 AU. 13CO and C18O lines are on average 70 and 100 K colder, 1 and 4 km s-1 narrower than 12CO υ = 1 → 0, and are dominated by emission at R ≥ 6 AU. The 12CO υ = 1 → 0 composite line-profile indicates that if there is a gap devoid of gas it must have a width narrower than 2 AU. We find that a drop in the gas surface density (δgas) at R R R R ≤ 1 AU of 5 × 1015 cm-2 (NH ≤ 5 × 1019 cm-2). Conclusions: The dust gap in the disk of HD 139614 has molecular gas. The distribution and amount of gas at R ≤ 6 AU in HD 139614 is very different from that of a primordial disk. The gas surface density in the disk at R ≤ 1 AU and at 1 R 2 AU) gas gap, suggest the presence of an embedded program 091.C-0671(B).
Dong, X. L.; Lu, W.; Yang, J.; Yi, W.; Li, Z. C.; Zhang, C.; Ren, Z. A.; Che, G. C.; Sun, L. L.; Zhou, F.; Zhou, X. J.; Zhao, Z. X.
2010-12-01
We have measured magnetic susceptibility of iron pnictide superconductors SmFeAsO0.85 and PrFe0.925Co0.075AsO under hydrostatic pressure up to 1.15 GPa. The superconducting transition temperature (TC) deceases linearly and the Meissner signal size also decreases with increasing pressure for SmFeAsO0.85 . In contrast, the TC of PrFe0.925Co0.075AsO initially increases with pressure then saturates above ˜0.8GPa . Meanwhile its Meissner signal exhibits the similar pressure dependence. Our results indicate that the pressure dependences of TC and superfluid density in both systems are positively correlated which suggests that these quaternary iron-based superconductors are not conventional BCS ones.
Gilson, Ronan; Durrant, Marcus C
2009-12-14
The deprotonation energies of the water ligands in a set of 40 d-block metal complexes have been calculated using density functional theory with polarized continuum model solvent corrections. The complexes include 13 aqua ions [M(OH(2))(n)](2+/3+) and a variety of aqua complexes with organic co-ligands, whose experimental pK(a) values have been reported in the literature. For comparison, the deprotonation energies of a set of 60 organic and inorganic molecules with experimental pK(a) values ranging from -25 (HSbF(6)) to +52 (C(2)H(6)) have also been calculated. Three different classes of acids are identified as giving different slopes in plots of pK(a) versus deprotonation energies; namely non-hydroxy acids, hydroxy acids, and the metal complexes. The correlation coefficients for the straight lines obtained for these three classes are 0.96, 0.97 and 0.92 respectively. Better correlations are found for sub-sets of the complexes, such as the 31 first row complexes (correlation coefficient 0.95).For several of the complexes, comparison of the calculated and observed pK(a) values, together with changes in the geometry upon optimization, offer new insights into the possible solution structures. It is concluded that DFT calculations incorporating solvent corrections can be used to give reasonable estimates of pK(a) values for the aqua ligands in a range of complex types.
Roper, Ian P E; Besley, Nicholas A
2016-03-21
The simulation of X-ray emission spectra of transition metal complexes with time-dependent density functional theory (TDDFT) is investigated. X-ray emission spectra can be computed within TDDFT in conjunction with the Tamm-Dancoff approximation by using a reference determinant with a vacancy in the relevant core orbital, and these calculations can be performed using the frozen orbital approximation or with the relaxation of the orbitals of the intermediate core-ionised state included. Both standard exchange-correlation functionals and functionals specifically designed for X-ray emission spectroscopy are studied, and it is shown that the computed spectral band profiles are sensitive to the exchange-correlation functional used. The computed intensities of the spectral bands can be rationalised by considering the metal p orbital character of the valence molecular orbitals. To compute X-ray emission spectra with the correct energy scale allowing a direct comparison with experiment requires the relaxation of the core-ionised state to be included and the use of specifically designed functionals with increased amounts of Hartree-Fock exchange in conjunction with high quality basis sets. A range-corrected functional with increased Hartree-Fock exchange in the short range provides transition energies close to experiment and spectral band profiles that have a similar accuracy to those from standard functionals.
Zein, Samir; Neese, Frank
2008-08-28
The paper presents a method comparison for the prediction of zero-field splitting (ZFS) parameters in a series of Mn (II) coordination complexes. The test set consists of Mn (II) complexes that are experimentally well-characterized by X-ray diffraction and high-field electron paramagnetic resonance. Their ZFS parameters have been calculated using density functional theory (DFT) as well as complete active space self-consistent field (CASSCF) methods. It is shown that the recently introduced coupled-perturbed spin-orbit coupling (CP-SOC) approach [ Neese, F. J. Chem. Phys. 2007, 127, 164112 ] together with hybrid-DFT functionals leads to a slope of the correlation line (plot of experimental vs calculated D values) that is essentially unity provided that the direct spin-spin interaction is properly included in the treatment. This is different from our previous DFT study on the same series of complexes where a severe overestimation of the D parameter has been found [ Zein, S. ; Duboc, C. ; Lubitz, W. ; Neese, F. Inorg. Chem. 2008, 47, 134 ]. CASSCF methods have been used to evaluate the ZFS in an "ab initio ligand-field" type treatment. The study demonstrates that a substantial part of the relevant physics is lost in such a treatment since only excitations within the manganese d-manifold are accounted for. Thus, a severe underestimation of the D parameter has been found. Because the CASSCF calculations in combination with quasidegenerate perturbation theory treats the SOC to all orders, we have nevertheless verified that second-order perturbation theory is an adequate approximation in the case of the high-spin d (5) configuration.
Mikhailov, Ivan A.; Tafur, Sergio; Masunov, Artëm E.
2008-01-01
The effect of static and dynamic electron correlation on the nature of excited states and state-to-state transition dipole moments is studied with a multideterminant wave function approach on the example of all-trans linear polyenes ( C4H6 , C6H8 , and C8H10 ). Symmetry-forbidden singlet nAg states were found to separate into three groups: purely single, mostly single, and mostly double excitations. The excited-state absorption spectrum is dominated by two bright transitions: 1Bu-2Ag and 1Bu-mAg , where mAg is the state, corresponding to two-electron excitation from the highest occupied to lowest unoccupied molecular orbital. The richness of the excited-state absorption spectra and strong mixing of the doubly excited determinants into lower- nAg states, reported previously at the complete active space self-consistent field level of theory, were found to be an artifact of the smaller active space, limited to π orbitals. When dynamic σ-π correlation is taken into account, single- and double-excited states become relatively well separated at least at the equilibrium geometry of the ground state. This electronic structure is closely reproduced within time-dependent density-functional theory (TD DFT), where double excitations appear in a second-order coupled electronic oscillator formalism and do not mix with the single excitations obtained within the linear response. An extension of TD DFT is proposed, where the Tamm-Dancoff approximation (TDA) is invoked after the linear response equations are solved (a posteriori TDA). The numerical performance of this extension is validated against multideterminant-wave-function and quadratic-response TD DFT results. It is recommended for use with a sum-over-states approach to predict the nonlinear optical properties of conjugated molecules.
Indian Academy of Sciences (India)
Amit S Tiwary; Asok K Mukherjee
2013-07-01
The inductive effect of methyl group has been quantified by expressing highest occupied molecular orbital (HOMO) and HOMO-1 energies of indole and a series of methylated indoles using a combination of graph theory (GT) and the Coulson-Longuett-Higgins perturbation method. By correlating these expressions with the corresponding Kohn-Sham orbital energies of the indoles obtained by density functional theory (DFT) calculation at the B3LYP/6-31++G(d,p) and M06-2X/6-31++G(d,p) levels of theory, the inductive effect parameter ℎ has been estimated; the Coulomb integral of -conjugated carbon atom also comes out from the analysis. A correlation of the GT results with the HOMO and HOMO-1 energies obtained by the HF/STO-3G method yield almost the same values of ℎ and . Finally, when these estimated ℎ and are used to calculate the vertical ionization potentials of the methylated indoles in the series, an excellent correlation with experimental charge transfer transition energies of their molecular complexes with tetracyanoethylene is obtained which complies with Mulliken’s theory of charge transfer.
Nguyen Lan, Tran; Kurashige, Yuki; Yanai, Takeshi
2015-01-13
We have developed a new computational scheme for high-accuracy prediction of the isotropic hyperfine coupling constant (HFCC) of heavy molecules, accounting for the high-level electron correlation effects, as well as the scalar-relativistic effects. For electron correlation, we employed the ab initio density matrix renormalization group (DMRG) method in conjunction with a complete active space model. The orbital-optimization procedure was employed to obtain the optimized orbitals required for accurately determining the isotropic HFCC. For the scalar-relativistic effects, we initially derived and implemented the Douglas-Kroll-Hess (DKH) hyperfine coupling operators up to the third order (DKH3) by using the direct transformation scheme. A set of 4d transition-metal radicals consisting of Ag atom, PdH, and RhH2 were chosen as test cases. Good agreement between the isotropic HFCC values obtained from DMRG/DKH3 and experiment was archived. Because there are no available gas-phase values for PdH and RhH2 radicals in the literature, the results from the present high-level theory may serve as benchmark data.
Bakos, G Á; Torres, G; Latham, D W; Sato, B; Bieryla, A; Shporer, A; Howard, A W; Fulton, B J; Buchhave, L A; Penev, K; Kovács, G; Kovács, T; Csubry, Z; Esquerdo, G A; Everett, M; Szklenár, T; Quinn, S N; Béky, B; Marcy, G W; Noyes, R W; Lázár, J; Papp, I; Sári, P
2016-01-01
We report the discovery of two new transiting extrasolar planets orbiting moderately bright (V = 10.7 and 12.2 mag) F stars (masses of 1.39 Msun and 1.10 Msun, respectively). The planets have periods of P = 4.7322 d and 4.4087 d, and masses of 0.21 MJ and 0.17 MJ which are almost half-way between those of Neptune and Saturn. With radii of 1.31 RJ and 1.13 RJ, these very low density planets are the two lowest mass planets with radii in excess that of Jupiter. Comparing with other recent planet discoveries, we find that sub-Saturns (0.18MJ < Mp < 0.3MJ) and super-Neptunes (0.05MJ < Mp < 0.18MJ) exhibit a wide range of radii, and their radii exhibit a weaker correlation with irradiation than higher mass planets. The two planets are both suitable for measuring the Rossiter-McLaughlin effect and for atmospheric characterization. Measuring the former effect would allow an interesting test of the theory that star-planet tidal interactions are responsible for the tendency of close-in giant planets around ...
Li, Can; Zhang, Jie; Wu, Hao; Li, Lili; Yang, Caiting; Song, Shushu; Peng, Peike; Shao, Miaomiao; Zhang, Mingming; Zhao, Junjie; Zhao, Ran; Wu, Weicheng; Ruan, Yuanyuan; Wang, Lan; Gu, Jianxin
2017-01-01
Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a pattern recognition receptor that plays a critical role in vascular diseases and host immune response. Recently, our research discovered that LOX-1 could facilitate the uptake of dying cells and cross-presentation of cellular antigen via binding with heat shock proteins, which have a close relationship with gastric neoplasia. Therefore, we speculated that LOX-1 may serve as an oncogene in gastric cancer (GC) development and progression. In this study, through immunohistochemistry staining assay and cancer-related databases, we found that LOX-1 expression was up-regulated in GC tissues and correlated with a poor prognosis in GC patients. The expression of LOX-1 was an independent prognostic factor for OS in GC patients, and the incorporation of LOX-1 with TNM stage is more accurate for predicting prognosis. Additionally, in vitro study by transwell assay and western blot analysis confirmed that LOX-1 could promote the migration and invasion of GC cells by driving epithelial-mesenchymal transition and PI3K/Akt/GSK3β activation. Taken together, we first explored the expression profiles, clinical significance and biological function of LOX-1 in GC, and these data suggest that LOX-1 may represent a promising prognostic biomarker for GC and offer a novel molecular target for GC therapies. PMID:28345638
U.S. Environmental Protection Agency — Road density is generally highly correlated with amount of developed land cover. High road densities usually indicate high levels of ecological disturbance. More...
Aloisio, R; Di Carlo, G; Galante, A; Grillo, A F
2000-01-01
Lattice formulation of Finite Baryon Density QCD is problematic from computer simulation point of view; it is well known that for light quark masses the reconstructed partition function fails to be positive in a wide region of parameter space. For large bare quark masses, instead, it is possible to obtain more sensible results; problems are still present but restricted to a small region. We present evidence for a saturation transition independent from the gauge coupling $\\beta$ and for a transition line that, starting from the temperature critical point at $\\mu=0$, moves towards smaller $\\beta$ with increasing $\\mu$ as expected from simplified phenomenological arguments.
Holographic Magnetisation Density Waves
Donos, Aristomenis
2016-01-01
We numerically construct asymptotically $AdS$ black brane solutions of $D=4$ Einstein theory coupled to a scalar and two $U(1)$ gauge fields. The solutions are holographically dual to $d=3$ CFTs in a constant external magnetic field along one of the $U(1)$'s. Below a critical temperature the system's magnetisation density becomes inhomogeneous, leading to spontaneous formation of current density waves. We find that the transition can be of second order and that the solutions which minimise the free energy locally in the parameter space of solutions have averaged stressed tensor of a perfect fluid.
DEFF Research Database (Denmark)
Garnett, E S; Webber, C E; Coates, G
1977-01-01
The density of a defined volume of the human lung can be measured in vivo by a new noninvasive technique. A beam of gamma-rays is directed at the lung and, by measuring the scattered gamma-rays, lung density is calculated. The density in the lower lobe of the right lung in normal man during quiet...... breathing in the sitting position ranged from 0.25 to 0.37 g.cm-3. Subnormal values were found in patients with emphsema. In patients with pulmonary congestion and edema, lung density values ranged from 0.33 to 0.93 g.cm-3. The lung density measurement correlated well with the findings in chest radiographs...... but the lung density values were more sensitive indices. This was particularly evident in serial observations of individual patients....
Gibbs, G V; Downs, R T; Cox, D F; Rosso, K M; Ross, N L; Kirfel, A; Lippmann, T; Morgenroth, W; Crawford, T D
2008-09-18
Bond critical point (bcp) and local energy density properties for the electron density (ED) distributions, calculated with first-principle quantum mechanical methods for divalent transition metal Mn-, Co-, and Fe-containing silicates and oxides are compared with experimental model ED properties for tephroite, Mn 2SiO 4, fayalite, Fe 2SiO 4, and Co 2SiO 4 olivine, each determined with high-energy synchrotron single-crystal X-ray diffraction data. Trends between the experimental bond lengths, R(M-O), (M = Mn, Fe, Co), and the calculated bcp properties are comparable with those observed for non-transition M-O bonded interactions. The bcp properties, local total energy density, H( r c), and bond length trends determined for the Mn-O, Co-O, and Fe-O interactions are also comparable. A comparison is also made with model experimental bcp properties determined for several Mn-O, Fe-O, and Co-O bonded interactions for selected organometallic complexes and several oxides. Despite the complexities of the structures of the organometallic complexes, the agreement between the calculated and model experimental bcp properties is fair to good in several cases. The G( r c)/rho( r c) versus R(M-O) trends established for non-transition metal M-O bonded interactions hold for the transition metal M-O bonded interactions with G( r c)/rho( r c) increasing in value as H( r c) becomes progressively more negative in value, indicating an increasing shared character of the interaction as G( r c)/rho( r c) increases in value. As observed for the non-transition metal M-O bonded interactions, the Laplacian, nabla (2)rho( r c), increases in value as rho( r c) increases and as H( r c) decreases and becomes progressive more negative in value. The Mn-O, Fe-O, and Co-O bonded interactions are indicated to be of intermediate character with a substantial component of closed-shell character compared with Fe-S and Ni-S bonded interactions, which show greater shared character based on the | V( r c)|/ G( r c
Level density for deformations of the Gaussian orthogonal ensemble
Bertuola, A C; Hussein, M S; Pato, M P; Sargeant, A J
2004-01-01
Formulas are derived for the average level density of deformed, or transition, Gaussian orthogonal random matrix ensembles. After some general considerations about Gaussian ensembles we derive formulas for the average level density for (i) the transition from the Gaussian orthogonal ensemble (GOE) to the Poisson ensemble and (ii) the transition from the GOE to $m$ GOEs.
Spin polarization in high density quark matter
DEFF Research Database (Denmark)
Bohr, Henrik; Panda, Prafulla K.; Providênci, Constanca
2013-01-01
We investigate the occurrence of a ferromagnetic phase transition in high density hadronic matter (e.g., in the interior of a neutron star). This could be induced by a four-fermion interaction analogous to the one which is responsible for chiral symmetry breaking in the Nambu-Jona-Lasinio model......, to which it is related through a Fierz transformation. Flavor SU(2) and flavor SU(3) quark matter are considered. A second-order phase transition is predicted at densities about 5 times the normal nuclear matter density. It is also found that in flavor SU(3) quark matter, a first-order transition from...
Energy Technology Data Exchange (ETDEWEB)
Young, Bruce Kai Fong
1988-09-01
The determination of level populations and detailed population mechanisms in dense plasmas has become an increasingly important problem in atomic physics. In this work, the density variation of line intensities and level populations in aluminum K-shell and molybdenum and silver L-shell emission spectra have been measured from high-powered, laser-produced plasmas. For each case, the density dependence of the observed line emission is due to the effect of high frequency electron-ion collisions on metastable levels. The density dependent line intensities vary greatly in laser-produced plasmas and can be used to extract detailed information concerning the population kinetics and level populations of the ions. The laser-plasmas had to be fully characterized in order to clearly compare the observed density dependence with atomic theory predictions. This has been achieved through the combined use of new diagnostic instruments and microdot targets which provided simultaneously space, time, and spectrally resolved data. The plasma temperatures were determined from the slope of the hydrogen-like recombination continuum. The time resolved electron density profiles were measured using multiple frame holographic interferometry. Thus, the density dependence of K-shell spectral lines could be clearly examined, independent of assumptions concerning the dynamics of the plasma. In aluminum, the electron density dependence of various helium-like line intensity ratios were measured. Standard collisional radiative equilibrium models fail to account for the observed density dependence measured for the ''He/sub ..cap alpha..//IC'' ratio. Instead, a quasi-steady state atomic model based on a purely recombining plasma is shown to accurately predict the measured density dependence. This same recombining plasma calculation successfully models the density dependence of the high-n ''He/sub ..gamma..//He/sub ..beta../'' and ''He/sub delta
Microscopic Charge Density Wave Transport
Slot, Erwin
2005-01-01
This thesis describes the work performed on crystals with a phase transition to a Charge-Density Wave (CDW). The electrical transport properties change when crystal sizes are smaller than characteristic length scales for CDWs, typically 1 micrometer. In contrast to metals, semiconductors and superco
Comparison of approximations to the transition rate in the DDHMS preequilibrium model
Energy Technology Data Exchange (ETDEWEB)
Brito, L.; Carlson, B.V., E-mail: britoluc@ita.br [Instituto Tecnologia de Aeronautica (ITA), Sao Jose dos Campos, SP (Brazil)
2014-07-01
The double differential hybrid Monte Carlo simulation model (DDHMS) originally used exciton model densities and transition densities with approximate angular distributions obtained using linear momentum conservation. Because the model uses only the simplest transition rates, calculations using more complex approximations to these are still viable. We compare calculations using the original approximation to one using a nonrelativistic Fermi gas transition densities with the approximate angular distributions and with exact nonrelativistic and relativistic transition transition densities. (author)
Topological Transitions in Metamaterials
Krishnamoorthy, Harish N S; Narimanov, Evgenii; Kretzschmar, Ilona; Menon, Vinod M
2011-01-01
The ideas of mathematical topology play an important role in many aspects of modern physics - from phase transitions to field theory to nonlinear dynamics (1, 2). An important example of this is the Lifshitz transition (3), where the transformation of the Fermi surface of a metal from a closed to an open geometry (due to e.g. external pressure) leads to a dramatic effect on the electron magneto-transport (4). Here, we present the optical equivalent of the Lifshitz transition in strongly anisotropic metamaterials. When one of the components of the dielectric permittivity tensor of such a composite changes sign, the corresponding iso-frequency surface transforms from an ellipsoid to a hyperboloid. Since the photonic density of states can be related to the volume enclosed by the iso-frequency surface (5), such a topological transition in a metamaterial leads to a dramatic change in the photonic density of states, with a resulting effect on every single physical parameter related to the metamaterial - from thermo...
Aspects of unconventional density waves
Maki, Kazumi; Dóra, Balázs; Virosztek, Attila
2003-12-01
Recently many people discuss unconventional density waves (i.e. unconventional charge density waves (UCDW) and unconventional spin density waves (USDW)). Unlike in conventional density waves, the quasiparticle spectrum in these systems is gapless. Also these systems remain metallic. Indeed it appears that there are many candidates for UDW. The low temperature phase of α-(BEDT-TTF)2KHg(SCN)4, the antiferromagnetic phase in URu2Si2, the CDW in transition metal dichalcogenite NbSe2, the pseudogap phase in high Tc cuprate superconductors, the glassy phase in organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br. After a brief introduction on UCDW and USDW, we shall discuss some of the above systems, where we believe we have evidence for unconventional density waves.
Baird, Matthew David
2012-01-01
I study three separate questions in this dissertation. In Chapter 1, I develop and estimate a structural dynamic model of occupation and job choice to test hypotheses of the importance of wages and non-wages and learning in occupational transitions, and find that wages are approximately 3 times as important as non-wage benefits in decisions and…
Baird, Matthew David
2012-01-01
I study three separate questions in this dissertation. In Chapter 1, I develop and estimate a structural dynamic model of occupation and job choice to test hypotheses of the importance of wages and non-wages and learning in occupational transitions, and find that wages are approximately 3 times as important as non-wage benefits in decisions and…
Solé, Ricard V
2011-01-01
Phase transitions--changes between different states of organization in a complex system--have long helped to explain physics concepts, such as why water freezes into a solid or boils to become a gas. How might phase transitions shed light on important problems in biological and ecological complex systems? Exploring the origins and implications of sudden changes in nature and society, Phase Transitions examines different dynamical behaviors in a broad range of complex systems. Using a compelling set of examples, from gene networks and ant colonies to human language and the degradation o
Density limits investigation and high density operation in EAST tokamak
Zheng, Xingwei; Li, Jiangang; Hu, Jiansheng; Liu, Haiqing; Jie, Yinxian; Wang, Shouxin; Li, Jiahong; Duan, Yanming; Li, Miaohui; Li, Yongchun; Zhang, Ling; Ye, Yang; Yang, Qingquan; Zhang, Tao; Cheng, Yingjie; Xu, Jichan; Wang, Liang; Xu, Liqing; Zhao, Hailin; Wang, Fudi; Lin, Shiyao; Wu, Bin; Lyu, Bo; Xu, Guosheng; Gao, Xiang; Shi, Tonghui; He, Kaiyang; Lan, Heng; Chu, Nan; Cao, Bin; Sun, Zhen; Zuo, Guizhong; Ren, Jun; Zhuang, Huidong; Li, Changzheng; Yuan, Xiaolin; Yu, Yaowei; Wang, Houyin; Chen, Yue; Wu, Jinhua; EAST Team
2016-05-01
Increasing the density in a tokamak is limited by the so-called density limit, which is generally performed as an appearance of disruption causing loss of plasma confinement, or a degradation of high confinement mode which could further lead to a H → L transition. The L-mode and H-mode density limit has been investigated in EAST tokamak. Experimental results suggest that density limits could be triggered by either edge cooling or excessive central radiation. The L-mode density limit disruption is generally triggered by edge cooling, which leads to the current profile shrinkage and then destabilizes a 2/1 tearing mode, ultimately resulting in a disruption. The L-mode density limit scaling agrees well with the Greenwald limit in EAST. The observed H-mode density limit in EAST is an operational-space limit with a value of 0.8∼ 0.9{{n}\\text{GW}} . High density H-mode heated by neutral beam injection (NBI) and lower hybrid current drive (LHCD) are analyzed, respectively. The constancy of the edge density gradients in H-mode indicates a critical limit caused perhaps by e.g. ballooning induced transport. The maximum density is accessed at the H → L transition which is generally caused by the excessive core radiation due to high Z impurities (Fe, Cu). Operating at a high density (>2.8× {{10}19} {{\\text{m}}-3} ) is favorable for suppressing the beam shine through NBI. High density H-mode up to 5.3× {{10}19}{{\\text{m}}-3}~≤ft(∼ 0.8{{n}\\text{GW}}\\right) could be sustained by 2 MW 4.6 GHz LHCD alone, and its current drive efficiency is studied. Statistics show that good control of impurities and recycling facilitate high density operation. With careful control of these factors, high density up to 0.93{{n}\\text{GW}} stable H-mode operation was carried out heated by 1.7 MW LHCD and 1.9 MW ion cyclotron resonance heating with supersonic molecular beam injection fueling.
Kuindersma, S. R.; Boudewijn, Pieter Reinder
1978-01-01
The absorption and MCD spectra of the 3A2g → 1Eg transition of CdI2:Ni2+ at ∼ 12,500 cm-1 were measured. The unusual vibronic fine structure is explained by the coupling of the phonons of the CdI2 lattice to the electronic states of Ni2+. The dispersion curves for the acoustical and optical branches
Vucic, Z; Gladic, J; Haas, C; DeBoer, JL
1996-01-01
An X-ray study of the quasi-one-dimensional charge density wave (CDW) system (NbSe4)(10)I-3 as a function of temperature from room temperature down to 130 K has been performed by taking oscillation and zeroth level Weissenberg photographs. A reversible transformation of the room temperature tetragon
Kang, W.; Osada, T.; Konoike, T.; Uchida, K.
2013-11-01
The stereoscopic angle-dependent magnetoresistance oscillations (AMRO) in an organic conductor α-(BEDT-TTF)2KHg(SCN)4 were measured across the temperature-pressure boundary that separates the charge-density-wave state from the metallic state. The gnomonic projections of the data clearly resolved the contributions from different parts of the Fermi surfaces. The temperature and pressure dependencies of the AMRO results revealed the progressive formation of a quasi-one-dimensional orbit in the charge-density-wave state. The AMRO measurements at ambient pressures and at low temperatures revealed the presence of two sets of quasi-one-dimensional Fermi surfaces. Additional evidence for multiple quasi-one-dimensional orbits was obtained from the data collected in conjunction with the in-plane field rotations.
Lee, Min-Young; Murray, Claire E; Heiles, Carl; Miller, Jesse
2015-01-01
We investigate the impact of high optical depth on the HI surface density (Sigma_HI) saturation observed in the Perseus molecular cloud. We use Arecibo HI emission and absorption measurements obtained toward 26 radio continuum sources to derive the spin temperature and optical depth of individual HI components along each line of sight. The derived properties are used to estimate the correction for high optical depth. We examine two different methods for the correction, Gaussian decomposition and isothermal approximation methods, and find that they are consistent as having the maximum correction factor of ~1.2 likely due to the relatively low optical depth and insignificant contribution from the diffuse radio continuum emission for Perseus. We apply the correction to the HI column density image derived in the optically thin approximation on a pixel-by-pixel basis, and find that the total HI mass increases by only ~10%. Using the corrected HI column density image and far-infrared data from the Improved Reproces...
Barge, P; Auvergne, M; Rauer, H; Léger, A; Schneider, J; Pont, F; Aigrain, S; Almenara, J -M; Alonso, R; Barbieri, M; Borde, P; Bouchy, F; Deeg, H -J; De la Reza, R; Deleuil, M; Dvorak, R; Erikson, A; Fridlund, M; Gillon, M; Gondoin, P; Guillot, T; Hatzes, A; Hébrard, G; Jorda, L; Kabath, P; Lammer, H; Llebaria, A; Loeillet, B; Magain, P; Mazeh, T; Moutou, C; Ollivier, M; Patzold, M; Queloz, D; Rouan, D; Shporer, A; Wuchterl, G
2008-01-01
Context. The pioneer space mission for photometric planet searches, CoRoT, steadily monitors about 12,000 stars in each of its fields of view; it is able to detect transit candidates early in the processing of the data and before the end of a run. Aims. We report the detection of the first planet discovered by CoRoT and characterizing it with the help of follow-up observations. Methods. Raw data were filtered from outliers and residuals at the orbital period of the satellite. The orbital parameters and the radius of the planet were estimated by best fitting the phase folded light curve with 34 successive transits. Doppler measurements with the SOPHIE spectrograph permitted us to secure the detection and to estimate the planet mass. Results. The accuracy of the data is very high with a dispersion in the 2.17 min binned phase-folded light curve that does not exceed 3.10-4 in flux unit. The planet orbits a mildly metal-poor G0V star of magnitude V=13.6 in 1.5 days. The estimated mass and radius of the star are 0...
Cassidy, Joan
1998-01-01
Describes two sixth-grade lessons on the work of M. C. Escher: (1) the first lesson instructs students on tessellations, or tiles that interlock in a repeated pattern; (2) the second lesson explores Escher's drawings of transitions from two- to three-dimensional space. (DSK)
2006-06-09
Morton Mintz and Stuart Auerbach, “Ford Solicits Suggestions on No. 2 Man,” Washington Post, Aug. 11, 1974, p. A1. 64 Fred Austin, “Ford Begins Move...representatives of the federal departments and agencies to ensure a smooth transition. Management and organizational issues should be CRS-23 105 Carl Brauer
... Information › Bone Density Exam/Testing › Low Bone Density Low Bone Density Low bone density is when your ... compared to people with normal bone density. Detecting Low Bone Density A bone density test will determine ...
Symmetry structure and phase transitions
Indian Academy of Sciences (India)
Ashok Goyal; Meenu Dahiya; Deepak Chandra
2003-05-01
We study chiral symmetry structure at ﬁnite density and temperature in the presence of external magnetic ﬁeld and gravity, a situation relevant in the early Universe and in the core of compact stars. We then investigate the dynamical evolution of phase transition in the expanding early Universe and possible formation of quark nuggets and their survival.
Probabilistic nature in L/H transition
Energy Technology Data Exchange (ETDEWEB)
Toda, Shinichiro; Itoh, Sanae-I.; Yagi, Masatoshi [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Itoh, Kimitaka; Fukuyama, Atsushi
1999-11-01
Statistical picture for an excitation of a plasma transition is examined, which occurs in a strongly turbulent state. The physical picture of transition phenomena is extended to include the statistical variances. The dynamics of the plasma density and turbulent-driven flux is studied with hysteresis nature in the flux-density relation. The probabilistic excitation is predicted and the critical conditions are described by the probabilistic distribution function. The stability for the model equations is also discussed. (author)
Transition from Poisson to circular unitary ensemble
Indian Academy of Sciences (India)
Vinayak; Akhilesh Pandey
2009-09-01
Transitions to universality classes of random matrix ensembles have been useful in the study of weakly-broken symmetries in quantum chaotic systems. Transitions involving Poisson as the initial ensemble have been particularly interesting. The exact two-point correlation function was derived by one of the present authors for the Poisson to circular unitary ensemble (CUE) transition with uniform initial density. This is given in terms of a rescaled symmetry breaking parameter Λ. The same result was obtained for Poisson to Gaussian unitary ensemble (GUE) transition by Kunz and Shapiro, using the contour-integral method of Brezin and Hikami. We show that their method is applicable to Poisson to CUE transition with arbitrary initial density. Their method is also applicable to the more general ℓ CUE to CUE transition where CUE refers to the superposition of ℓ independent CUE spectra in arbitrary ratio.
DEFF Research Database (Denmark)
2014-01-01
What. The chapter addresses designing for sustainability as interventions in socio-technical systems and social practices of users and communities. It calls for reflexive design practices challenging dominant regimes and shaping alternative design spaces. The specific case is the reconfiguration...... of agendas/vision, technologies, actors and institutions in the emergent design of an urban mobility system based on an electric car sharing system. Why. Designing for sustainability is a fundamental challenge for future design practices; designers have to obtain an ability to contribute to sustainable...... transition processes. Where. Addresses design processes aimed at sustainable transition enacted in complex social settings, socio-technical systems involving many different actors and agendas. How. The chapter outlines a conceptual and analytic framework for a reflexive design practice for sustainability...
Alcock-Zeilinger, Judith
2016-01-01
In this paper, we give a generic algorithm of the transition operators between Hermitian Young projection operators corresponding to equivalent irreducible representations of SU(N), using the compact expressions of Hermitian Young projection operators derived in a companion paper. We show that the Hermitian Young projection operators together with their transition operators constitute a fully orthogonal basis for the algebra of invariants of $V^{\\otimes m}$ that exhibits a systematically simplified multiplication table. We discuss the full algebra of invariants over $V^{\\otimes 3}$ and $V^{\\otimes 4}$ as explicit examples. In our presentation we make use of various standard concepts such as Young projection operators, Clebsch-Gordan operators, and invariants (in birdtrack notation). We tie these perspectives together and use them to shed light on each other.
Czerminski, Ryszard; Roitberg, Adrian; Choi, Chyung; Ulitsky, Alexander; Elber, Ron
1991-10-01
Two computational approaches to study plausible conformations of biological molecules and the transitions between them are presented and discussed. The first approach is a new search algorithm which enhances the sampling of alternative conformers using a mean field approximation. It is argued and demonstrated that the mean field approximation has a small effect on the location of the minima. The method is a combination of the LES protocol (Locally Enhanced Sampling) and simulated annealing. The LES method was used in the past to study the diffusion pathways of ligands from buried active sites in myoglobin and leghemoglobin to the exterior of the protein. The present formulation of LES and its implementation in a Molecular Dynamics program is described. An application for side chain placement in a tetrapeptide is presented. The computational effort associated with conformational searches using LES grows only linearly with the number of degrees of freedom, whereas in the exact case the computational effort grows exponentially. Such saving is of course associated with a mean field approximation. The second branch of studies pertains to the calculation of reaction paths in large and flexible biological systems. An extensive mapping of minima and barriers for two different tetrapeptides is calculated from the known minima and barriers of alanine tetrapeptide which we calculated recently.1 The tetrapeptides are useful models for the formation of secondary structure elements since they are the shortest possible polymers of this type which can still form a complete helical turn. The tetrapeptides are isobutyryl-val(χ1=60)-ala-ala and isobutyryl-val(χ1=-60)-ala-ala. Properties of the hundreds of minima and of the hundreds intervening barriers are discussed. Estimates for thermal transition times between the many conformers (and times to explore the complete phase space) are calculated and compared. It is suggested that the most significant effect of the side chain size is
Energy Technology Data Exchange (ETDEWEB)
Hamrin, J.G.
1980-01-01
Solar energy programs are entering a critical transitional period as we move from the initial marketing of solar technologies into a phase of widespread commercialization. We face the dual challenge of trying to get enough solar systems in place fast enough to prove solar is a viable alternative, while trying to ensure the systems are designed and installed properly, proving the energy savings as promised. This is a period of both great opportunity and high risk as the field becomes crowded with new solar cheerleaders and supporters but seldom enough competent players. The status of existing and proposed programs for the accelerated commercialization of solar energy in California is described.
DEFF Research Database (Denmark)
Raahauge, Kirsten Marie
2008-01-01
This article deals with representations of one specific city, Århus, Denmark, especially its central district. The analysis is based on anthropological fieldwork conducted in Skåde Bakker and Fedet, two well-off neighborhoods. The overall purpose of the project is to study perceptions of space...... and the interaction of cultural, social, and spatial organizations, as seen from the point of view of people living in Skåde Bakker and Fedet. The focus is on the city dwellers’ representations of the central district of Århus with specific reference to the concept of transit space. When applied to various Århusian...
Liquid-Gas Phase Transition in Nuclear Equation of State
Lee, S J
1997-01-01
A canonical ensemble model is used to describe a caloric curve of nuclear liquid-gas phase transition. Allowing a discontinuity in the freeze out density from one spinodal density to another for a given initial temperature, the nuclear liquid-gas phase transition can be described as first order. Averaging over various freeze out densities of all the possible initial temperatures for a given total reaction energy, the first order characteristics of liquid-gas phase transition is smeared out to a smooth transition. Two experiments, one at low beam energy and one at high beam energy show different caloric behaviors and are discussed.
vanden-Eijnden, E.
The dynamical behavior of many systems arising in physics, chemistry, biology, etc. is dominated by rare but important transition events between long lived states. For over 70 years, transition state theory (TST) has provided the main theoretical framework for the description of these events [17,33,34]. Yet, while TST and evolutions thereof based on the reactive flux formalism [1, 5] (see also [30,31]) give an accurate estimate of the transition rate of a reaction, at least in principle, the theory tells very little in terms of the mechanism of this reaction. Recent advances, such as transition path sampling (TPS) of Bolhuis, Chandler, Dellago, and Geissler [3, 7] or the action method of Elber [15, 16], may seem to go beyond TST in that respect: these techniques allow indeed to sample the ensemble of reactive trajectories, i.e. the trajectories by which the reaction occurs. And yet, the reactive trajectories may again be rather uninformative about the mechanism of the reaction. This may sound paradoxical at first: what more than actual reactive trajectories could one need to understand a reaction? The problem, however, is that the reactive trajectories by themselves give only a very indirect information about the statistical properties of these trajectories. This is similar to why statistical mechanics is not simply a footnote in books about classical mechanics. What is the probability density that a trajectory be at a given location in state-space conditional on it being reactive? What is the probability current of these reactive trajectories? What is their rate of appearance? These are the questions of interest and they are not easy to answer directly from the ensemble of reactive trajectories. The right framework to tackle these questions also goes beyond standard equilibrium statistical mechanics because of the nontrivial bias that the very definition of the reactive trajectories imply - they must be involved in a reaction. The aim of this chapter is to
Single-charge-exchange reactions and the neutron density at the surface of the nucleus
Loc, Bui Minh; Auerbach, Naftali; Khoa, Dao T.
2017-07-01
In this paper, we study the charge-exchange reaction to the isobaric analog state using two types of transition densities. One transition density is equal to the difference of the total neutron density minus the total proton density and the other one is the density of the excess neutrons only. We show that for projectiles that do not probe the interior of the nucleus but mostly the surface of this nucleus, distinct differences in the cross section arise when two types of transition densities are employed. We demonstrate this by considering the (3He,t ) reaction.
Indian Academy of Sciences (India)
Thomas S Ullrich
2004-02-01
QCD predicts a phase transition between hadronic matter and a quark-gluon plasma at high energy density. The relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory is a new facility dedicated to the experimental study of matter under extreme conditions. Already the first round of experimental results at RHIC indicated that the conditions to create a new state of matter are indeed reached in the collisions of heavy nuclei. Studies of particle spectra and their correlations at low transverse momenta provide evidence of strong pressure gradients in the highly interacting dense medium and hint that we observe a system in thermal equilibrium. Recent runs with high statistics allow us to explore the regime of hard-scattering processes where the suppression of hadrons at large transverse momentum, and quenching of di-jets are observed thus providing further evidence for extreme high density matter created in collisions at RHIC.
... Quick summary of transition IDEA’s definition of transition services Considering the definition Students at the heart of planning their transition ... fix that! Keep reading… Back to top IDEA’s Definition of Transition Services Any discussion of transition services must begin with ...
Laboratory Density Functionals
Giraud, B. G.
2007-01-01
We compare several definitions of the density of a self-bound system, such as a nucleus, in relation with its center-of-mass zero-point motion. A trivial deconvolution relates the internal density to the density defined in the laboratory frame. This result is useful for the practical definition of density functionals.
Laboratory Density Functionals
Giraud, B G
2007-01-01
We compare several definitions of the density of a self-bound system, such as a nucleus, in relation with its center-of-mass zero-point motion. A trivial deconvolution relates the internal density to the density defined in the laboratory frame. This result is useful for the practical definition of density functionals.
Quantum phase transitions with dynamical flavors
Bea, Yago; Ramallo, Alfonso V
2016-01-01
We study the properties of a D6-brane probe in the ABJM background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and non-vanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at non-zero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number $N_f$ of unquenched quarks of the background.
Quantum phase transitions with dynamical flavors
Bea, Yago; Jokela, Niko; Ramallo, Alfonso V.
2016-07-01
We study the properties of a D6-brane probe in the Aharony-Bergman-Jafferis-Maldacena (ABJM) background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and nonvanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at nonzero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number Nf of unquenched quarks of the background.
Meson Effects on the Chiral Condensate at Finite Density
Institute of Scientific and Technical Information of China (English)
HUANG Mei; ZHUANG Peng-Fei; ZHAO Wei-Qin
2002-01-01
Meson corrections on the chiral condensate up to next-to-leading order in a 1/Nc expansion at finite densityare investigated in the NJL model with explicit chiral symmetry breaking. Compared with mean-field results, the chiralphase transition is still of the first order while the properties near the critical density for chiral phase transition are foundto change significantly.
Kepler-7b: A Transiting Planet With Unusually Low Density
2010-04-20
Marcy with HIRES on Keck 1 was analyzed by D. Fischer using Spectroscopy Made Easy (SME) (Valenti & Piskunov 1996), with very similar results: Teff...arXiv:1001.0305 Pál, A., et al. 2010, MNRAS, 401, 2665 Valenti, J. A., & Piskunov , N. 1996, A&AS, 118, 595 Yi, S. K., Demarque, P., Kim, Y.-C., Lee, Y.-W., Ree, C. H., Lejeune, T., & Barnes, S. 2001, ApJS, 136, 417
Density induced transition in a school of fish
Cambuí, Dorílson Silva; Rosas, Alexandre
2012-08-01
Collective behaviour has been studied in various fields of science. As an example, we may consider the patterns observed in living systems, whose aggregates form organized groups such as flocks of birds, herds of mammals and schools of fish. These aggregates may be formed as a consequence of an external stimulus or due to the local interaction among nearby specimens. As an example of the latter case one may think about a school of fish, where each individual bases its behaviour on its perception of the position and velocity of its nearest neighbours. As a result of these interactions, global collective behaviour may emerge, originating and maintaining the cohesion of the aggregate. In this work, we model the collective movement of a school of fish using an agent-based model which follows biologically motivated behavioural rules previously proposed. The distributions of nearest neighbour distance and relative orientations between neighbouring fishes are measured and the results are found to be in good agreement with previous experimental measurements.
Sleep spindle density in narcolepsy.
Christensen, Julie Anja Engelhard; Nikolic, Miki; Hvidtfelt, Mathias; Kornum, Birgitte Rahbek; Jennum, Poul
2017-06-01
Patients with narcolepsy type 1 (NT1) show alterations in sleep stage transitions, rapid-eye-movement (REM) and non-REM sleep due to the loss of hypocretinergic signaling. However, the sleep microstructure has not yet been evaluated in these patients. We aimed to evaluate whether the sleep spindle (SS) density is altered in patients with NT1 compared to controls and patients with narcolepsy type 2 (NT2). All-night polysomnographic recordings from 28 NT1 patients, 19 NT2 patients, 20 controls (C) with narcolepsy-like symptoms, but with normal cerebrospinal fluid hypocretin levels and multiple sleep latency tests, and 18 healthy controls (HC) were included. Unspecified, slow, and fast SS were automatically detected, and SS densities were defined as number per minute and were computed across sleep stages and sleep cycles. The between-cycle trends of SS densities in N2 and NREM sleep were evaluated within and between groups. Between-group comparisons in sleep stages revealed no significant differences in any type of SS. Within-group analyses of the SS trends revealed significant decreasing trends for NT1, HC, and C between first and last sleep cycle. Between-group analyses of SS trends between first and last sleep cycle revealed that NT2 differ from NT1 patients in the unspecified SS density in NREM sleep, and from HC in the slow SS density in N2 sleep. SS activity is preserved in NT1, suggesting that the ascending neurons to thalamic activation of SS are not significantly affected by the hypocretinergic system. NT2 patients show an abnormal pattern of SS distribution. Copyright © 2017 Elsevier B.V. All rights reserved.
PyTransit: Transit light curve modeling
Parviainen, Hannu
2015-05-01
PyTransit implements optimized versions of the Giménez and Mandel & Agol transit models for exoplanet transit light-curves. The two models are implemented natively in Fortran with OpenMP parallelization, and are accessed by an object-oriented python interface. PyTransit facilitates the analysis of photometric time series of exoplanet transits consisting of hundreds of thousands of data points, and of multipassband transit light curves from spectrophotometric observations. It offers efficient model evaluation for multicolour observations and transmission spectroscopy, built-in supersampling to account for extended exposure times, and routines to calculate the projected planet-to-star distance for circular and eccentric orbits, transit durations, and more.
Thermodynamics of Phase Transitions of a Kerr Nonlinear Blackbody
Institute of Scientific and Technical Information of China (English)
CHENG Ze
2008-01-01
We study the thermodynamics of phase transitions of a blackbody whose interior is filled by a Kerr nonlinear crystal. There is a transition temperature To, above which the Kerr nonlinear blackbody is in the normal thermal radiation state, and below which it is in the squeezed thermal radiation state. At To, the Gibbs free energy of the two phases is continuous but the entropy density of the two phases is discontinuous. Hence, there is a jump in the entropy density and this leads to a latent heat density. The photon system undergoes a first-order phase transition from the normal to the squeezed thermal radiation state.
Holographic phase transitions at finite chemical potential
Mateos, David; Matsuura, Shunji; Myers, Robert C.; Thomson, Rowan M.
2007-11-01
Recently, holographic techniques have been used to study the thermal properties of Script N = 2 super-Yang-Mills theory, with gauge group SU(Nc) and coupled to Nf coupling. Here we consider the phase diagram as a function of temperature and baryon chemical potential μb. For fixed μb transitions separating a region with vanishing baryon density and one with nonzero density. For fixed μb>Nc Mq there is no phase transition as a function of the temperature and the baryon density is always nonzero. We also compare the present results for the grand canonical ensemble with those for canonical ensemble in which the baryon density is held fixed [1].
Inner crust of neutron stars with mass-fitted Skyrme interaction
Madhuri, K; Routray, T R; Pattnaik, S P
2016-01-01
The mass, radius and crustal fraction of moment of inertia in neutron stars are calculated using $\\beta$-equilibrated nuclear matter obtained from Skyrme effective interaction. The transition density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of the neutron stars are determined from the thermodynamic stability conditions using the KDE0v1 set. The neutron star masses obtained by solving the Tolman-Oppenheimer-Volkoff equations using neutron star matter obtained from this set is able to describe highly massive compact stars $\\sim$2$M_{\\odot}$. The crustal fraction of the moment of inertia can be extracted from studying pulsar glitches. This fraction is highly dependent on the core-crust transition pressure and corresponding density. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a limit for the radius of the Vela pulsar:$R\\geq$ 3.69+3.44 M/$M_{\\odot}$. ...
U.S. Environmental Protection Agency — Road density is generally highly correlated with amount of developed land cover. High road densities usually indicate high levels of ecological disturbance. More...
Holographic phase transitions at finite chemical potential
Mateos, David; Myers, Robert C; Thomson, Rowan M
2007-01-01
Recently holographic techniques have been used to study the thermal properties of N=2 SYM theory, with gauge group SU(Nc) and coupled to Nf Nc Mq there is no phase transition as a function of the temperature and the baryon density is always nonzero. We also compare the present results for the grand canonical ensemble with those for canonical ensemble in which the baryon density is held fixed [1].
The Actinide Transition Revisited by Gutzwiller Approximation
Xu, Wenhu; Lanata, Nicola; Yao, Yongxin; Kotliar, Gabriel
2015-03-01
We revisit the problem of the actinide transition using the Gutzwiller approximation (GA) in combination with the local density approximation (LDA). In particular, we compute the equilibrium volumes of the actinide series and reproduce the abrupt change of density found experimentally near plutonium as a function of the atomic number. We discuss how this behavior relates with the electron correlations in the 5 f states, the lattice structure, and the spin-orbit interaction. Our results are in good agreement with the experiments.
Bioinorganic Chemistry Modeled with the TPSSh Density Functional
DEFF Research Database (Denmark)
Kepp, Kasper Planeta
2008-01-01
In this work, the TPSSh density functional has been benchmarked against a test set of experimental structures and bond energies for 80 transition-metal-containing diatomics. It is found that the TPSSh functional gives structures of the same quality as other commonly used hybrid and nonhybrid func...... promising density functional for use and further development within the field of bioinorganic chemistry....
Design and Environment, 1972
1972-01-01
Three-part report pinpointing problems and uncovering solutions for the dual concepts of density (ratio of people to space) and crowding (psychological response to density). Section one, A Primer on Crowding,'' reviews new psychological and social findings; section two, Density in the Suburbs,'' shows conflict between status quo and increased…
The density limit in JET diverted plasmas
Energy Technology Data Exchange (ETDEWEB)
Campbell, D.J.; Clement, S.; Gottardi, N.; Gowers, C.; Harbour, P.; Loarte, A.; Horton, L.; Lingertat, J.; Lowry, C.G.; Saibene, G.; Stamp, M.; Stork, D. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Monk, R. [Royal Holloway Coll., London (United Kingdom). Dept. of Physics
1994-07-01
In JET limiter plasmas the density limit is associated with radiated power fractions of 100% and, in plasmas with carbon limiters, it is invariably disruptive. However, in discharges with solid beryllium limiters the limit is identified with the formation of a MARFE and disruptions are less frequent. In addition, the improved conditioning of the vessel arising from the use of beryllium has significantly improved the density limit scaling, so that the maximum density rises with the square root of the input power. In diverted plasmas several confinement regimes exist, making the characterization of the density limit more complex. While the density limit in L-mode plasmas is generally disruptive, the limit in ELMy and ELM-free H-modes generally prompts a return to the L-mode and a disruption is not inevitable. The density limit does rise with the increasing power, but the L-to-H transition complicates the analysis. Nevertheless, at low plasma currents (<2 MA), densities significantly above the Greenwald limit can be achieved, while at higher currents power handling limitations have constrained the range of density which can be achieved. (authors). 7 refs., 4 figs.
Institute of Scientific and Technical Information of China (English)
凯蕾·柯提思
2012-01-01
与以往依赖于小汽车的出行定位相比，珀斯对公共交通基础设施的投入不断增强。然而，为低密度城市设计一个能与小汽车抗衡的交通系统却面临着严峻挑战。珀斯最新的一条客运铁路的规划和线路设计主要以土地利用规划为基础，并积极寻求公交导向型开发的契机。它带来了不同的融合模式，包括吸引过往客流和舒缓剑拔弩张的机动车环境的公交导向型开发，以及通过西澳大利亚州的交通管理机构协调交通换乘站中的各种运输模式，从而使公交出行的吸引力最大化。本文旨在考察各种模型所带来的机遇和局限。%Perth has seen strong investment in public transport infrastructure compared with its past approach of a city designed for mobility by car. Designing a transport system to compete with the car in a low-density city has raised significant challenges. The planning and routing of Perth' s newest passenger railway has been strongly grounded in land use planning with active pursuit of opportunities for transit-oriented development (TOD). This has resulted in different models of integration from TODs designed around walk-on patronage, to TODs designed to calm hostile car-based environments, to transitransfer stations relying on state transit agency coordination between transport modes to maximize the attractiveness of the public transport travel. This paper examines the opportunities and constraints presented by each model.
Quarkonium at non-zero isospin density
Detmold, William; Shi, Zhifeng
2014-01-01
We calculate the energies of quarkonium bound states in the presence of a medium of nonzero isospin density using lattice QCD. The medium, created using a canonical (fixed isospin charge) approach, induces a reduction of the quarkonium energies. As the isospin density increases, the energy shifts first increase linearly and then saturate at an isospin density where a qualitative change in the behaviour of the energy density of the medium has been previously observed. This provides further support to the conjecture that the medium undergoes a transition from a pion gas to a Bose-Einstein condensed phase at this point. The reduction of the quarkonium energies becomes more pronounced as the heavy-quark mass is decreased, similar to the behaviour seen in two-colour QCD at non-zero quark chemical potential. In the process of our analysis, the Upsilon-pi and eta_b-pi scattering phase shifts are determined at low momentum and found to be small.
Density shock waves in confined microswimmers
Tsang, Alan Cheng Hou
2015-01-01
Motile and driven particles confined in microfluidic channels exhibit interesting emergent behavior from propagating density bands to density shock waves. A deeper understanding of the physical mechanisms responsible for these emergent structures is relevant to a number of physical and biomedical applications. Here, we study the formation of density shock waves in the context of an idealized model of microswimmers confined in a narrow channel and subject to a uniform external flow. Interestingly, these density shock waves exhibit a transition from `subsonic' with compression at the back to `supersonic' with compression at the front of the population as the intensity of the external flow increases. This behavior is the result of a non-trivial interplay between hydrodynamic interactions and geometric confinement, and is confirmed by a novel quasilinear wave model that properly captures the dependence of the shock formation on the external flow. These findings can be used to guide the development of novel mechan...
Transiting Exoplanet Survey Satellite (TESS)
Ricker, G. R.; Clampin, M.; Latham, D. W.; Seager, S.; Vanderspek, R. K.; Villasenor, J. S.; Winn, J. N.
2012-01-01
The Transiting Exoplanet Survey Satellite (TESS) will discover thousands of exoplanets in orbit around the brightest stars in the sky. In a two-year survey, TESS will monitor more than 500,000 stars for temporary drops in brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey will identify planets ranging from Earth-sized to gas giants, around a wide range of stellar types and orbital distances. No ground-based survey can achieve this feat. A large fraction of TESS target stars will be 30-100 times brighter than those observed by Kepler satellite, and therefore TESS . planets will be far easier to characterize with follow-up observations. TESS will make it possible to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. TESS will provide prime targets for observation with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes of the future. TESS data will be released with minimal delay (no proprietary period), inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the very nearest and brightest main-sequence stars hosting transiting exoplanets, thus providing future observers with the most favorable targets for detailed investigations.
Probability densities and Lévy densities
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole Eiler
For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated.......For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated....
Probability densities and Lévy densities
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole Eiler
For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated.......For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated....
Neutron drip transition in accreting and nonaccreting neutron star crusts
Chamel, N; Zdunik, J L; Haensel, P
2015-01-01
The neutron-drip transition in the dense matter constituting the interior of neutron stars generally refers to the appearance of unbound neutrons as the matter density reaches some threshold density $\\rho_\\textrm{drip}$. This transition has been mainly studied under the cold catalyzed matter hypothesis. However, this assumption is unrealistic for accreting neutron stars. After examining the physical processes that are thought to be allowed in both accreting and nonaccreting neutron stars, suitable conditions for the onset of neutron drip are derived and general analytical expressions for the neutron drip density and pressure are obtained. Moreover, we show that the neutron-drip transition occurs at lower density and pressure than those predicted within the mean-nucleus approximation. This transition is studied numerically for various initial composition of the ashes from X-ray bursts and superbursts using microscopic nuclear mass models.
Neutrino Oscillation Induced by Chiral Phase Transition
Institute of Scientific and Technical Information of China (English)
MU Cheng-Fu; SUN Gao-Feng; ZHUANG Peng-Fei
2009-01-01
Electric charge neutrality provides a relationship between chiral dynamics and neutrino propagation in compact stars.Due to the sudden drop of the electron density at the first-order chiral phase transition,the oscillation for low energy neutrinos is significant and can be regarded as a signature of chiral symmetry restoration in the core of compact stars.
Population Density Modeling Tool
2014-02-05
194 POPULATION DENSITY MODELING TOOL by Davy Andrew Michael Knott David Burke 26 June 2012 Distribution...MARYLAND NAWCADPAX/TR-2012/194 26 June 2012 POPULATION DENSITY MODELING TOOL by Davy Andrew Michael Knott David Burke...Density Modeling Tool 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Davy Andrew Michael Knott David Burke 5d. PROJECT NUMBER
Higher-order symmetry energy of nuclear matter and the inner edge of neutron star crusts
Seif, W M
2014-01-01
The parabolic approximation to the equation of state of the isospin asymmetric nuclear matter (ANM) is widely used in the literature to make predictions for the nuclear structure and the neutron star properties. Based on the realistic M3Y-Paris and M3Y-Reid nucleon-nucleon interactions, we investigate the effects of the higher-order symmetry energy on the proton fraction in neutron stars and the location of the inner edge of their crusts and their core-crust transition density and pressure, thermodynamically. Analytical expressions for different-order symmetry energy coefficients of ANM are derived using the realistic interactions mentioned above. It is found that the higher-order terms of the symmetry energy coefficients up to its eighth-order (E$_{sym8}$) contributes substantially to the proton fraction in $\\beta$ stable neutron star matter at different nuclear matter densities, the core-crust transition density and pressure. Even by considering the symmetry energy coefficients up to E$_{sym8}$, we obtain a...
The QCD phase transitions: From mechanism to observables
Energy Technology Data Exchange (ETDEWEB)
Shuryak, E.V.
1997-09-22
This paper contains viewgraphs on quantum chromodynamic phase transformations during heavy ion collisions. Some topics briefly described are: finite T transitions of I molecule pairs; finite density transitions of diquarks polymers; and the softtest point of the equation of state as a source of discontinuous behavior as a function of collision energy or centrality.
Electronic transitions of fluorene, dibenzofuran, carbazole, and dibenzothiophene
DEFF Research Database (Denmark)
Nguyen, Duy Duc; Trunk, John; Nakhimovsky, Lina
2010-01-01
. Prediction of electronic transitions to excited singlet states was performed by using time-dependent density functional theory TD-B3LYP/6-31+G(d,p). Based on the experimental and theoretical results, symmetry assignments of electronic transitions in the vacuum and near-UV region are suggested...
Deconfinement phase transition in neutron star matter
Institute of Scientific and Technical Information of China (English)
LI Ang; PENG Guang-Xiong; Lombardo U
2009-01-01
The transition from hadron phase to strange quark phase in dense matter is investigated. Instead of using the conventional bag model in quark sect, we achieve the confinement by a density-dependent quark mass derived from in-medium chiral condensates, with a thermodynamic problem improved. In nuclear slot,we adopt the equation of state from Brueckner-Bethe-Goldstone approach with three-body force. It is found that the mixed phase can occur, for reasonable confinement parameter, near the normal saturation density,and transit to pure quark matter at 4-5 times the saturation, which is quite different from the previous results from other quark models that pure quark phase can not appear at neutron-star densities.
Kneeland, Steven J.
1980-01-01
Having identified the problem of managerial transition in a previous article (CE 510 277), the author outlines a strategy for change which includes performance appraisal, definition of the management structure, and counselling for the individual in transition. (SK)
Department of Homeland Security — fixed rail transit stations within the Continental United States, Alaska, Hawaii, the District of Columbia, and Puerto Rico. The modes of transit that are serviced...
Density dependent neurodynamics.
Halnes, Geir; Liljenström, Hans; Arhem, Peter
2007-01-01
The dynamics of a neural network depends on density parameters at (at least) two different levels: the subcellular density of ion channels in single neurons, and the density of cells and synapses at a network level. For the Frankenhaeuser-Huxley (FH) neural model, the density of sodium (Na) and potassium (K) channels determines the behaviour of a single neuron when exposed to an external stimulus. The features of the onset of single neuron oscillations vary qualitatively among different regions in the channel density plane. At a network level, the density of neurons is reflected in the global connectivity. We study the relation between the two density levels in a network of oscillatory FH neurons, by qualitatively distinguishing between three regions, where the mean network activity is (1) spiking, (2) oscillating with enveloped frequencies, and (3) bursting, respectively. We demonstrate that the global activity can be shifted between regions by changing either the density of ion channels at the subcellular level, or the connectivity at the network level, suggesting that different underlying mechanisms can explain similar global phenomena. Finally, we model a possible effect of anaesthesia by blocking specific inhibitory ion channels.
On density forecast evaluation
Diks, C.
2008-01-01
Traditionally, probability integral transforms (PITs) have been popular means for evaluating density forecasts. For an ideal density forecast, the PITs should be uniformly distributed on the unit interval and independent. However, this is only a necessary condition, and not a sufficient one, as
Institute of Scientific and Technical Information of China (English)
冯跟胜; 党金春; 等
1995-01-01
A method used for on line determining the change of wheat density with a automatic watering machine in a lqarge flour mill has been studied.The results show that the higher distinguishing ability is obtained when using 241Am as a γ-ray source for measuring the wheat density than using 137Cs.
Regenwetter, Michel; Dana, Jason; Davis-Stober, Clintin P.
2011-01-01
Transitivity of preferences is a fundamental principle shared by most major contemporary rational, prescriptive, and descriptive models of decision making. To have transitive preferences, a person, group, or society that prefers choice option "x" to "y" and "y" to "z" must prefer "x" to "z". Any claim of empirical violations of transitivity by…
Learning Grasp Affordance Densities
DEFF Research Database (Denmark)
Detry, Renaud; Kraft, Dirk; Kroemer, Oliver
2011-01-01
We address the issue of learning and representing object grasp affordance models. We model grasp affordances with continuous probability density functions (grasp densities) which link object-relative grasp poses to their success probability. The underlying function representation is nonparametric...... and relies on kernel density estimation to provide a continuous model. Grasp densities are learned and refined from exploration, by letting a robot “play” with an object in a sequence of graspand-drop actions: The robot uses visual cues to generate a set of grasp hypotheses; it then executes...... these and records their outcomes. When a satisfactory number of grasp data is available, an importance-sampling algorithm turns these into a grasp density. We evaluate our method in a largely autonomous learning experiment run on three objects of distinct shapes. The experiment shows how learning increases success...
Trautmann, Wolfgang; Russotto, Paolo
2016-01-01
The nuclear equation-of-state is a topic of highest current interest in nuclear structure and reactions as well as in astrophysics. In particular, the equation-of-state of asymmetric matter and the symmetry energy representing the difference between the energy densities of neutron matter and of symmetric nuclear matter are not sufficiently well constrained at present. The density dependence of the symmetry energy is conventionally expressed in the form of the slope parameter L describing the derivative with respect to density of the symmetry energy at saturation. Results deduced from nuclear structure and heavy-ion reaction data are distributed around a mean value L=60 MeV. Recent studies have more thoroughly investigated the density range that a particular observable is predominantly sensitive to. Two thirds of the saturation density is a value typical for the information contained in nuclear-structure data. Higher values exceeding saturation have been shown to be probed with meson production and collective ...
Strongly Interacting Matter at High Energy Density
Energy Technology Data Exchange (ETDEWEB)
McLerran,L.
2008-09-07
This lecture concerns the properties of strongly interacting matter (which is described by Quantum Chromodynamics) at very high energy density. I review the properties of matter at high temperature, discussing the deconfinement phase transition. At high baryon density and low temperature, large N{sub c} arguments are developed which suggest that high baryonic density matter is a third form of matter, Quarkyonic Matter, that is distinct from confined hadronic matter and deconfined matter. I finally discuss the Color Glass Condensate which controls the high energy limit of QCD, and forms the low x part of a hadron wavefunction. The Glasma is introduced as matter formed by the Color Glass Condensate which eventually thermalizes into a Quark Gluon Plasma.
Structural transition of FeSe under high pressure
Institute of Scientific and Technical Information of China (English)
Li Wei; Chen Jun-Fang; He Qin-Yu; Wang Teng; Pan Zhong-Liang
2011-01-01
The density functional calculations of the energy band structure and density of state for the tetragonal PbO-type phase α-FeSe and hexagonal NiAs-type phase β-FeSe are reported in this paper. The structural phase transition from tetragonal to hexagonal FeSe under high pressure is investigated, it is found that the calculated transition pressure for the α→β phase transformation is 8.5 GPa. Some fluctuations in the transition pressure maybe occurred by different external factors such as temperature and stress condition. There is about 17% volume collapse accompanying the α→β phase transformation.
Model for continuous thermal metal to insulator transition
Jian, Chao-Ming; Bi, Zhen; Xu, Cenke
2017-09-01
We propose a d -dimensional interacting Majorana fermion model with quenched disorder, which gives us a continuous quantum phase transition between a diffusive thermal metal phase with a finite entropy density to an insulator phase with zero entropy density. This model is based on coupled Sachdev-Ye-Kitaev model clusters, and hence has a controlled large-N limit. The metal-insulator transition is accompanied by a spontaneous time-reversal symmetry breaking. We perform controlled calculations to show that the energy diffusion constant jumps to zero discontinuously at the metal-insulator transition, while the time-reversal symmetry-breaking order parameter increases continuously.
Joint density of states in low dimensional semiconductors
Cabrera, C. I.; Contreras-Solorio, D. A.; Hernández, L.
2016-02-01
We present a different approach to evaluate density of states for quasi-bidimensional systems, which bonds density of states in the confinement direction with in-plane 2D density of states. Applying the convolution operation, we propose an accurately mathematical expression that combines directly the valence band and conduction band density of states functions to generate a joint density of states for direct transitions. When considering low dimensional semiconductors, another expression is found which shows that the density of states for electrons (holes) can be calculated by convolution operations between the confinement direction and in-plane electron (hole) density of states. Using both expressions, we have calculated the quantum well and superlattice absorption coefficient, resulting in positive alignment with experimental data. A more complete description of physical absorption is achieved with this new approach.
Transition Theory – Sustainable Transition of Socio-Technical Systems
DEFF Research Database (Denmark)
Søndergård, Bent; Holm, Jesper; Stauning, Inger
2015-01-01
Theories of transition management, transition studies and social practise theory Applied to studies of hosuing and construction......Theories of transition management, transition studies and social practise theory Applied to studies of hosuing and construction...
Density Functionals with Broad Applicability in Chemistry
Energy Technology Data Exchange (ETDEWEB)
Zhao, Yan; Truhlar, Donald G.
2008-02-01
The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Although density functional theory is widely used in the computational chemistry community, the most popular density functional, B3LYP, has some serious shortcomings: (i) it is better for main-group chemistry than for transition metals; (ii) it systematically underestimates reaction barrier heights; (iii) it is inaccurate for interactions dominated by mediumrange correlation energy, such as van der Waals attraction, aromatic-aromatic stacking, and alkane isomerization energies. We have developed a variety of databases for testing and designing new density functionals. We used these data to design new density functionals, called M06-class (and, earlier, M05-class) functionals, for which we enforced some fundamental exact constraints such as the uniform-electron-gas limit and the absence of self-correlation energy. Our M06-class functionals depend on spin-up and spin-down electron densities (i.e., spin densities), spin density gradients, spin kinetic energy densities, and, for nonlocal (also called hybrid) functionals, Hartree-Fock exchange. We have developed four new functionals that overcome the above-mentioned difficulties: (a) M06, a hybrid meta functional, is a functional with good accuracy “across-theboard” for transition metals, main group thermochemistry, medium-range correlation energy, and barrier heights; (b) M06- 2X, another hybrid meta functional, is not good for transition metals but has excellent performance for main group chemistry, predicts accurate valence and Rydberg electronic excitation energies, and is an excellent functional for aromatic-aromatic stacking interactions; (c) M06-L is not as accurate as M06 for barrier heights but is the most accurate
Big bang nucleosynthesis and the quark-hadron transition
Kurki-Suonio, Hannu; Matzner, Richard A.; Olive, Keith A.; Schramm, David N.
1990-01-01
An examination and brief review is made of the effects of quark-hadron transition induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp e), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).
Big bang nucleosynthesis and the quark-hadron transition
Kurki-Suonio, Hannu; Matzner, Richard A.; Olive, Keith A.; Schramm, David N.
1990-01-01
An examination and brief review is made of the effects of quark-hadron transition induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp e), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).
Intermolecular forces and the glass transition.
Hall, Randall W; Wolynes, Peter G
2008-01-17
Random first-order transition theory is used to determine the role of attractive and repulsive interactions in the dynamics of supercooled liquids. Self-consistent phonon theory, an approximate mean field treatment consistent with random first-order transition theory, is used to treat individual glassy configurations, whereas the liquid phase is treated using common liquid-state approximations. Free energies are calculated using liquid-state perturbation theory. The transition temperature, T*A, the temperature where the onset of activated behavior is predicted by mean field theory; the lower crossover temperature, T*C, where barrierless motions actually occur through fractal or stringy motions (corresponding to the phenomenological mode coupling transition temperature); and T*K, the Kauzmann temperature (corresponding to an extrapolated entropy crisis), are calculated in addition to T*g, the glass transition temperature that corresponds to laboratory cooling rates. Relationships between these quantities agree well with existing experimental and simulation data on van der Waals liquids. Both the isobaric and isochoric behavior in the supercooled regime are studied, providing results for DeltaCV and DeltaCp that can be used to calculate the fragility as a function of density and pressure, respectively. The predicted variations in the alpha-relaxation time with temperature and density conform to the empirical density-temperature scaling relations found by Casalini and Roland. We thereby demonstrate the microscopic origin of their observations. Finally, the relationship first suggested by Sastry between the spinodal temperature and the Kauzmann temperatures, as a function of density, is examined. The present microscopic calculations support the existence of an intersection of these two temperatures at sufficiently low temperatures.
Engel, J
2006-01-01
The Hohenberg-Kohn theorem and Kohn-Sham procedure are extended to functionals of the localized intrinsic density of a self-bound system such as a nucleus. After defining the intrinsic-density functional, we modify the usual Kohn-Sham procedure slightly to evaluate the mean-field approximation to the functional, and carefully describe the construction of the leading corrections for a system of fermions in one dimension with a spin-degeneracy equal to the number of particles N. Despite the fact that the corrections are complicated and nonlocal, we are able to construct a local Skyrme-like intrinsic-density functional that, while different from the exact functional, shares with it a minimum value equal to the exact ground-state energy at the exact ground-state intrinsic density, to next-to-leading order in 1/N. We briefly discuss implications for real Skyrme functionals.
BMD test; Bone density test; Bone densitometry; DEXA scan; DXA; Dual-energy x-ray absorptiometry; p-DEXA; Osteoporosis-BMD ... need to undress. This scan is the best test to predict your risk of fractures. Peripheral DEXA ( ...
Veeder, G. J.
1974-01-01
An improved mass-luminosity relation for faint main-sequence stars derived from recently revised masses for some faint double stars is presented. The total local mass density is increased to nearly 0.2 solar masses per cu pc. This estimate is as large as the mass density required by Oort's (1965) dynamical analysis of stellar motions perpendicular to the galactic plane if the mass is concentrated in a narrow layer.
Distribution of current in nonequilibrium diffusive systems and phase transitions
Bodineau, T.; Derrida, B.
2005-12-01
We consider diffusive lattice gases on a ring and analyze the stability of their density profiles conditionally to a current deviation. Depending on the current, one observes a phase transition between a regime where the density remains constant and another regime where the density becomes time dependent. Numerical data confirm this phase transition. This time dependent profile persists in the large drift limit and allows one to understand on physical grounds the results obtained earlier for the totally asymmetric exclusion process on a ring.
Phase Transition in the Simplest Plasma Model
Iosilevskiy, Igor
2009-01-01
We have investigated the phase transition of the gas-liquid type, with an upper critical point, in a variant of the One Component Plasma model (OCP) that has a uniform but compressible compensating background. We have calculated the parameters of the critical and triple points, spinodals, and two-phase coexistence curves (binodals). We have analyzed the connection of this simplest plasma phase transition with anomalies in the spatial charge profiles of equilibrium non-uniform plasma in the local-density approximations of Thomas-Fermi or Poisson-Boltzmann-type.
Exceptional Points and Dynamical Phase Transitions
Directory of Open Access Journals (Sweden)
I. Rotter
2010-01-01
Full Text Available In the framework of non-Hermitian quantum physics, the relation between exceptional points,dynamical phase transitions and the counter intuitive behavior of quantum systems at high level density is considered. The theoretical results obtained for open quantum systems and proven experimentally some years ago on a microwave cavity, may explain environmentally induce deffects (including dynamical phase transitions, which have been observed in various experimental studies. They also agree(qualitatively with the experimental results reported recently in PT symmetric optical lattices.
Simulation of transition dynamics to high confinement in fusion plasmas
Nielsen, A H; Madsen, J; Naulin, V; Rasmussen, J Juul; Wan, B N
2014-01-01
The transition dynamics from the low (L) to the high (H) confinement mode in magnetically confined plasmas is investigated using a first-principles four-field fluid model. Numerical results are in close agreement with measurements from the Experimental Advanced Superconducting Tokamak - EAST. Particularly, the slow transition with an intermediate dithering phase is well reproduced by the numerical solutions. Additionally, the model reproduces the experimentally determined L-H transition power threshold scaling that the ion power threshold increases with increasing particle density. The results hold promise for developing predictive models of the transition, essential for understanding and optimizing future fusion power reactors.
Phase Transition Induced by Small Molecules in Confined Copolymer Films
Institute of Scientific and Technical Information of China (English)
ZHOU Ling
2007-01-01
We investigate the phase transition induced by small molecules in confined copolymer films by using density functional theory.It is found that the addition of small molecules can effectively promote the phase separation of copolymers.In a symmetric diblock copolymer film,the affinity and concentration of small molecules play an important role in the structure transjtions.The disordered-lamellar transitions lamellar-lamellar transitions and the re-entrant transitions of the same structures are observed.Our results have potential applications in the fabrication of new functional materials.
Chaotic jam and phase transition in traffic flow with passing.
Nagatani, T
1999-08-01
The lattice hydrodynamic model is presented to take into account the passing effect in one-dimensional traffic flow. When the passing constant gamma is small, the conventional jamming transition occurs between the uniform traffic and kink density wave flows. When passing constant gamma is larger than the critical value, the jamming transitions occur from the uniform traffic flow, through the chaotic density wave flow, to the kink density wave flow, with an increasing delay time. The chaotic region increases with passing constant gamma. The neutral stability line is derived from the linear stability analysis. The neutral stability line coincides with the transition line between the uniform traffic and density wave flows. The modified Korteweg-de Vries equation describing the kink jam is derived for small values of gamma by use of a nonlinear analysis.
DIFFUSE MOLECULAR CLOUD DENSITIES FROM UV MEASUREMENTS OF CO ABSORPTION
Energy Technology Data Exchange (ETDEWEB)
Goldsmith, Paul F. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
2013-09-10
We use UV measurements of interstellar CO toward nearby stars to calculate the density in the diffuse molecular clouds containing the molecules responsible for the observed absorption. Chemical models and recent calculations of the excitation rate coefficients indicate that the regions in which CO is found have hydrogen predominantly in molecular form and that collisional excitation is by collisions with H{sub 2} molecules. We carry out statistical equilibrium calculations using CO-H{sub 2} collision rates to solve for the H{sub 2} density in the observed sources without including effects of radiative trapping. We have assumed kinetic temperatures of 50 K and 100 K, finding this choice to make relatively little difference to the lowest transition. For the sources having T{sup ex}{sub 10} only for which we could determine upper and lower density limits, we find (n(H{sub 2})) = 49 cm{sup -3}. While we can find a consistent density range for a good fraction of the sources having either two or three values of the excitation temperature, there is a suggestion that the higher-J transitions are sampling clouds or regions within diffuse molecular cloud material that have higher densities than the material sampled by the J = 1-0 transition. The assumed kinetic temperature and derived H{sub 2} density are anticorrelated when the J = 2-1 transition data, the J = 3-2 transition data, or both are included. For sources with either two or three values of the excitation temperature, we find average values of the midpoint of the density range that is consistent with all of the observations equal to 68 cm{sup -3} for T{sup k} = 100 K and 92 cm{sup -3} for T{sup k} = 50 K. The data for this set of sources imply that diffuse molecular clouds are characterized by an average thermal pressure between 4600 and 6800 K cm{sup -3}.
Dissociation of N2, NO, and CO on transition metal surfaces
DEFF Research Database (Denmark)
Mavrikakis, Manos; Hansen, Lars Bruno; Mortensen, Jens Jørgen;
1999-01-01
Using density functional theory we study the dissociation of N2, NO, and CO on transition metal surfaces. We discuss an efficient method to locate the minimum energy path and the transition state, and review recent calculations using this method to determine the transition state for dissociation...
Gravitationally induced quantum transitions
Landry, A.; Paranjape, M. B.
2016-06-01
In this paper, we calculate the probability for resonantly inducing transitions in quantum states due to time-dependent gravitational perturbations. Contrary to common wisdom, the probability of inducing transitions is not infinitesimally small. We consider a system of ultracold neutrons, which are organized according to the energy levels of the Schrödinger equation in the presence of the Earth's gravitational field. Transitions between energy levels are induced by an oscillating driving force of frequency ω . The driving force is created by oscillating a macroscopic mass in the neighborhood of the system of neutrons. The neutron lifetime is approximately 880 sec while the probability of transitions increases as t2. Hence, the optimal strategy is to drive the system for two lifetimes. The transition amplitude then is of the order of 1.06 ×10-5, and hence with a million ultracold neutrons, one should be able to observe transitions.
Gravitationally induced quantum transitions
Landry, A
2016-01-01
In this letter, we calculate the probability for resonantly induced transitions in quantum states due to time dependent gravitational perturbations. Contrary to common wisdom, the probability of inducing transitions is not infinitesimally small. We consider a system of ultra cold neutrons (UCN), which are organized according to the energy levels of the Schr\\"odinger equation in the presence of the earth's gravitational field. Transitions between energy levels are induced by an oscillating driving force of frequency $\\omega$. The driving force is created by oscillating a macroscopic mass in the neighbourhood of the system of neutrons. The neutrons decay in 880 seconds while the probability of transitions increase as $t^2$. Hence the optimal strategy is to drive the system for 2 lifetimes. The transition amplitude then is of the order of $1.06\\times 10^{-5}$ hence with a million ultra cold neutrons, one should be able to observe transitions.
Predictability of Critical Transitions
Zhang, Xiaozhu; Hallerberg, Sarah
2015-01-01
Critical transitions in multistable systems have been discussed as models for a variety of phenomena ranging from the extinctions of species to socio-economic changes and climate transitions between ice-ages and warm-ages. From bifurcation theory we can expect certain critical transitions to be preceded by a decreased recovery from external perturbations. The consequences of this critical slowing down have been observed as an increase in variance and autocorrelation prior to the transition. However especially in the presence of noise it is not clear, whether these changes in observation variables are statistically relevant such that they could be used as indicators for critical transitions. In this contribution we investigate the predictability of critical transitions in conceptual models. We study the the quadratic integrate-and-fire model and the van der Pol model, under the influence of external noise. We focus especially on the statistical analysis of the success of predictions and the overall predictabil...
Turning Forbidden Transitions into Dominant Transitions
Rivera, Nicholas; Soljacic, Marin
2016-01-01
Surface phonon polaritons are hybrid modes of photons and optical phonons that can propagate on the surface of a polar dielectric. In this work, we show that the precise combination of confinement and bandwidth offered by surface phonon polaritons allows for the ability to take forbidden transitions and turn them into the primary means by which an electron emits light. We show that high-order multipolar transitions and two-photon emission processes can be over an order of magnitude faster than competing dipole transitions, as opposed to being as much as eight to ten orders of magnitude slower in free space. Our results have direct implications for the design of fundamentally new types of emitters in the mid and far IR: ones which prefer to change their angular momentum by large amounts and also ones that prefer to emit a relatively broad spectrum of entangled photons - potentially allowing for new sources of both single and multiple photons.
Effect of Muons on the Phase Transition in Magnetised Proto-Neutron Star Matter
Sen-Gupta, A; Singh, S; Anand, J D; Gupta, Asha
2002-01-01
We study the effect of inclusion of muons and the muon neutrinos on the phase transition from nuclear to quark matter in a magnetised proto-neutron star and compare our results with those obtained by us without the muons. We find that the inclusion of muons changes slightly the nuclear density at which transition occurs.However the dependence of this transition density on various chemical potentials, temperature and the magnetic field remains quantitatively the same.
Transit Benefit Program Data -
Department of Transportation — This data set contains information about any US government agency participating in the transit benefits program, funding agreements, individual participating Federal...
Directory of Open Access Journals (Sweden)
Stone J.R.
2013-12-01
Full Text Available The microscopic composition and properties of matter at super-saturation densities have been the subject of intense investigation for decades. The scarcity of experimental and observational data has led to the necessary reliance on theoretical models. There remains great uncertainty in these models which, of necessity, have to go beyond the over-simple assumption that high density matter consists only of nucleons and leptons. Heavy strange baryons, mesons and quark matter in different forms and phases have to be included to fulfil basic requirements of fundamental laws of physics. In this contribution latest developments in construction of the Equation of State (EoS of high-density matter at zero and finite temperature assuming different composition of matter will be discussed. Critical comparison of model EoS with available experimental data from heavy ion collisions and observations on neutron stars, including gravitational mass, radii and cooling patterns and data on X-ray burst sources and low mass X-ray binaries are made. Fundamental differences between the EoS of low-density, high temperature matter, such as is created in heavy ion collisions and of high-density, low temperature compact objects is discussed.
Energy Technology Data Exchange (ETDEWEB)
McCall, G.H.
1988-01-01
During the past few years techniques have been developed for producing pinches in solid deuterium. The conditions which exist in these plasmas are quiet different from those produced earlier. The pinch is formed from a fiber of solid deuterium rather than from a low density gas, and the current is driven by a low impedance, high voltage pulse generator. Because of the high initial density, it is not necessary to compress the pinch to reach thermonuclear conditions, and the confinement time required for energy production is much shorter than for a gas. The experimental results, which have been verified by experiments performed at higher current were quite surprising and encouraging. The pinch appeared to be stable for a time much longer than the Alfven radial transit time. In this paper, however, I argue that the pinch is not strictly stable, but it does not appear to disassemble in a catastrophic fashion. It appears that there may be a distinction between stability and confinement in the high density pinch. In the discussion below I will present the status of the high density Z-pinch experiments at laboratories around the world, and I will describe some of the calculational and experimental results. I will confine my remarks to recent work on the high density pinch. 17 refs. 10 figs.
Mott transitions in three-component Falicov-Kimball model
Nguyen, Duong-Bo; Tran, Minh-Tien
2013-01-01
Metal-insulator transitions are studied within a three-component Falicov-Kimball model, which mimics a mixture of one-component and two-component fermionic particles with local repulsive interactions in optical lattices. Within the model, the two-component fermionic particles are able to hop in the lattice, while the one-component fermionic particles are localized. The model is studied by using the dynamical mean-field theory with exact diagonalization. Its homogeneous solutions establish Mott transitions for both commensurate and incommensurate fillings between one-third and two-thirds. At commensurate one-third and two-thirds fillings, the Mott transition occurs for any density of hopping particles, while at incommensurate fillings, the Mott transition can occur only for density one-half of hopping particles. At half-filling, depending on the repulsive interactions, the reentrant effect of the Mott insulator is observed. As increasing local interaction of hopping particles, the first insulator-metal transition is continuous, whereas the second metal-insulator transition is discontinuous. The second metal-insulator transition crosses a finite region where both metallic and insulating phase coexist. At third-filling, the Mott transition is established only for strong repulsive interactions. A phase separation occurs together with the phase transition.
Faranoff-Riley type I jet deceleration at density discontinuities
Meliani, Z.; Keppens, R.; Giacomazzo, B.
2008-01-01
Aims. We propose a model that could explain the sudden jet deceleration in active galactic nuclei, thereby invoking density discontinuities. Motivated particularly by recent indications from HYbrid MOrphology Radio Sources (HYMORS) that Fanaroff-Riley classification is induced in some cases by variations in the density of the external medium. We explore how one-sided jet deceleration and a transition to FR I type can occur in HYMORS, which start as FR II (and remain so on the other side). Met...
Particle transport in density gradient driven TE mode turbulence
Skyman, Andreas; Strand, P I
2011-01-01
The turbulent transport of main ion and trace impurities in a tokamak device in the presence of steep electron density gradients has been studied. The parameters are chosen for trapped electron (TE) mode turbulence, driven primarily by steep electron density gradients relevant to H-mode physics, but with a transition to temperature gradient driven turbulence as the density gradient flattens. Results obtained through non-linear (NL) and quasilinear (QL) gyrokinetic simulations using the GENE code are compared with results obtained from a fluid model. Main ion and impurity transport is studied by examining the balance of convective and diffusive transport, as quantified by the density gradient corresponding to zero particle flux (peaking factor). Scalings are obtained for the impurity peaking with the background electron density gradient and the impurity charge number. It is shown that the impurity peaking factor is weakly dependent on impurity charge and significantly smaller than the driving electron density ...
Safety models incorporating graph theory based transit indicators.
Quintero, Liliana; Sayed, Tarek; Wahba, Mohamed M
2013-01-01
There is a considerable need for tools to enable the evaluation of the safety of transit networks at the planning stage. One interesting approach for the planning of public transportation systems is the study of networks. Network techniques involve the analysis of systems by viewing them as a graph composed of a set of vertices (nodes) and edges (links). Once the transport system is visualized as a graph, various network properties can be evaluated based on the relationships between the network elements. Several indicators can be calculated including connectivity, coverage, directness and complexity, among others. The main objective of this study is to investigate the relationship between network-based transit indicators and safety. The study develops macro-level collision prediction models that explicitly incorporate transit physical and operational elements and transit network indicators as explanatory variables. Several macro-level (zonal) collision prediction models were developed using a generalized linear regression technique, assuming a negative binomial error structure. The models were grouped into four main themes: transit infrastructure, transit network topology, transit route design, and transit performance and operations. The safety models showed that collisions were significantly associated with transit network properties such as: connectivity, coverage, overlapping degree and the Local Index of Transit Availability. As well, the models showed a significant relationship between collisions and some transit physical and operational attributes such as the number of routes, frequency of routes, bus density, length of bus and 3+ priority lanes.
Nuclear level density predictions
Directory of Open Access Journals (Sweden)
Bucurescu Dorel
2015-01-01
Full Text Available Simple formulas depending only on nuclear masses were previously proposed for the parameters of the Back-Shifted Fermi Gas (BSFG model and of the Constant Temperature (CT model of the nuclear level density, respectively. They are now applied for the prediction of the level density parameters of all nuclei with available masses. Both masses from the new 2012 mass table and from different models are considered and the predictions are discussed in connection with nuclear regions most affected by shell corrections and nuclear structure effects and relevant for the nucleosynthesis.
Density Distribution Sunflower Plots
Dupont, William D; W. Dale Plummer Jr.
2003-01-01
Density distribution sunflower plots are used to display high-density bivariate data. They are useful for data where a conventional scatter plot is difficult to read due to overstriking of the plot symbol. The x-y plane is subdivided into a lattice of regular hexagonal bins of width w specified by the user. The user also specifies the values of l, d, and k that affect the plot as follows. Individual observations are plotted when there are less than l observations per bin as in a conventio...
DEFF Research Database (Denmark)
Olsen, Jógvan Magnus Haugaard; Steinmann, Casper; Ruud, Kenneth
2015-01-01
We present a new QM/QM/MM-based model for calculating molecular properties and excited states of solute-solvent systems. We denote this new approach the polarizable density embedding (PDE) model and it represents an extension of our previously developed polarizable embedding (PE) strategy. The PDE...... model is a focused computational approach in which a core region of the system studied is represented by a quantum-chemical method, whereas the environment is divided into two other regions: an inner and an outer region. Molecules belonging to the inner region are described by their exact densities...
Holographic charge density waves
Donos, Aristomenis
2013-01-01
We show that strongly coupled holographic matter at finite charge density can exhibit charge density wave phases which spontaneously break translation invariance while preserving time-reversal and parity invariance. We show that such phases are possible within Einstein-Maxwell-dilaton theory in general spacetime dimensions. We also discuss related spatially modulated phases when there is an additional coupling to a second vector field, possibly with non-zero mass. We discuss how these constructions, and others, should be associated with novel spatially modulated ground states.
Holographic charge density waves
Donos, Aristomenis; Gauntlett, Jerome P.
2013-06-01
We show that strongly coupled holographic matter at finite charge density can exhibit charge density wave phases which spontaneously break translation invariance while preserving time-reversal and parity invariance. We show that such phases are possible within Einstein-Maxwell-dilaton theory in general spacetime dimensions. We also discuss related spatially modulated phases when there is an additional coupling to a second vector field, possibly with nonzero mass. We discuss how these constructions, and others, should be associated with novel spatially modulated ground states.
Density matrix perturbation theory.
Niklasson, Anders M N; Challacombe, Matt
2004-05-14
An orbital-free quantum perturbation theory is proposed. It gives the response of the density matrix upon variation of the Hamiltonian by quadratically convergent recursions based on perturbed projections. The technique allows treatment of embedded quantum subsystems with a computational cost scaling linearly with the size of the perturbed region, O(N(pert.)), and as O(1) with the total system size. The method allows efficient high order perturbation expansions, as demonstrated with an example involving a 10th order expansion. Density matrix analogs of Wigner's 2n+1 rule are also presented.
Levinson, N
1940-01-01
A typical gap theorem of the type discussed in the book deals with a set of exponential functions { \\{e^{{{i\\lambda}_n} x}\\} } on an interval of the real line and explores the conditions under which this set generates the entire L_2 space on this interval. A typical gap theorem deals with functions f on the real line such that many Fourier coefficients of f vanish. The main goal of this book is to investigate relations between density and gap theorems and to study various cases where these theorems hold. The author also shows that density- and gap-type theorems are related to various propertie
Origins of evolutionary transitions
Indian Academy of Sciences (India)
Ellen Clarke
2014-04-01
An `evolutionary transition in individuality’ or `major transition’ is a transformation in the hierarchical level at which natural selection operates on a population. In this article I give an abstract (i.e. level-neutral and substrate-neutral) articulation of the transition process in order to precisely understand how such processes can happen, especially how they can get started.
Institute of Scientific and Technical Information of China (English)
Yueh-Yi Lai; Wen-Kai Tai
2008-01-01
Synthesis of transition textures is essential for displaying visually acceptable appearances on a terrain. This investigation presents a modified method for synthesizing the transition texture to be tiled on a terrain. All transition pattern types are recognized for a number of input textures. The proposed modified patch-based sampling texture synthesis approach, using the extra feature map of the input source and target textures for patch matching, can synthesize any transition texture on a succession pattern by initializing the output texture using a portion of the source texture enclosed in a transition cut. The transition boundary is further enhanced to improve the visual effect by tracing out the integral texture elements. Either the Game of Life model or Wang tiles method are exploited to present a good-looking profile of successions on a terrain for tiling transition textures. Experimental results indicate that the proposed method requires few input textures, yet synthesizes numerous tileable transition textures, which are useful for obtaining a vivid appearance of a terrain.
Anderson, Lara B.; Gray, James; Raghuram, Nikhil; Taylor, Washington
2016-04-01
We explore a novel type of transition in certain 6D and 4D quantum field theories, in which the matter content of the theory changes while the gauge group and other parts of the spectrum remain invariant. Such transitions can occur, for example, for SU(6) and SU(7) gauge groups, where matter fields in a three-index antisymmetric representation and the fundamental representation are exchanged in the transition for matter in the two-index antisymmetric representation. These matter transitions are realized by passing through superconformal theories at the transition point. We explore these transitions in dual F-theory and heterotic descriptions, where a number of novel features arise. For example, in the heterotic description the relevant 6D SU(7) theories are described by bundles on K3 surfaces where the geometry of the K3 is constrained in addition to the bundle structure. On the F-theory side, non-standard representations such as the three-index antisymmetric representation of SU( N) require Weierstrass models that cannot be realized from the standard SU( N) Tate form. We also briefly describe some other situations, with groups such as Sp(3), SO(12), and SU(3), where analogous matter transitions can occur between different representations. For SU(3), in particular, we find a matter transition between adjoint matter and matter in the symmetric representation, giving an explicit Weierstrass model for the F-theory description of the symmetric representation that complements another recent analogous construction.
An accelerated nutrition transition in Iran.
Ghassemi, Hossein; Harrison, Gail; Mohammad, Kazem
2002-02-01
To describe the emergence of the nutrition transition, and associated morbidity shifts, in the Islamic Republic of Iran. Review and analysis of secondary data relating to the socio-political and nutritional context, demographic trends, food utilisation and consumption patterns, obesity, and diet-related morbidity. The nutrition transition in Iran is occurring rapidly, secondary to the rapid change in fertility and mortality patterns and to urbanisation. The transition is occurring against the backdrop of lack of sustained economic growth. There is considerable imbalance in food consumption with low nutrient density characterising diets at all income levels, over-consumption evident among more than a third of households, and food insecurity among 20% of the population. Obesity is an emerging problem, particularly in urban areas and for women, and both diabetes and other risk factors for heart disease are becoming significant problems.
Mixed phases during the phase transitions
Tatsumi, Toshitaka; Maruyama, Toshiki
2011-01-01
Quest for a new form of matter inside compact stars compels us to examine the thermodynamical properties of the phase transitions. We closely consider the first-order phase transitions and the phase equilibrium on the basis of the Gibbs conditions, taking the liquid-gas phase transition in asymmetric nuclear matter as an example. Characteristic features of the mixed phase are figured out by solving the coupled equations for mean-fields and densities of constituent particles self-consistently within the Thomas-Fermi approximation. The mixed phase is inhomogeneous matter composed of two phases in equilibrium; it takes a crystalline structure with a unit of various geometrical shapes, inside of which one phase with a characteristic shape, called "pasta", is embedded in another phase by some volume fraction. This framework enables us to properly take into account the Coulomb interaction and the interface energy, and thereby sometimes we see the mechanical instability of the geometric structures of the mixed phase...
Pressure-induced phase transition in CrO2.
Alptekin, Sebahaddin
2015-12-01
The ab initio constant pressure molecular dynamics technique and density functional theory with generalized gradient approximation (GGA) was used to study the pressure-induced phase transition of CrO2. The phase transition of the rutile (P42/mnm) to the orthorhombic CaCl2 (Pnnm) structure at 30 GPa was determined successfully in a constant pressure simulation. This phase transition was analyzed from total energy calculations and, from the enthalpy calculation, occurred at around 17 GPa. Structural properties such as bulk modules, lattice parameters and phase transition were compared with experimental results. The phase transition at 12 ± 3 GPa was in good agreement with experimental results, as was the phase transition from the orthorhombic CaCl2 (Pnnm) to the monoclinic (P21/c) structure also found at 35 GPa.
Transition radiation by neutrinos
Energy Technology Data Exchange (ETDEWEB)
Ioannisian, A.N., E-mail: ara.ioannisyan@cern.ch [Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan (Armenia); CERN, Theory Division, CH-1211 Geneva 23 (Switzerland); Institute for Theoretical Physics and Modeling, 375036 Yerevan (Armenia); Ioannisian, D.A. [Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan (Armenia); Institute for Theoretical Physics and Modeling, 375036 Yerevan (Armenia); Physics Department, Yerevan State University, 1 Alex Manoogian (Armenia); Kazarian, N.A. [Institute for Theoretical Physics and Modeling, 375036 Yerevan (Armenia)
2011-08-19
We calculate the transition radiation process {nu}{yields}{nu}{gamma} at an interface of two media. The neutrinos are taken to be with only standard-model couplings. The medium fulfills the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation. The transition radiation occurs when at least one of those quantities have different values in different media. The neutrino mass is ignored due to its negligible contribution. We present a result for the probability of the transition radiation which is both accurate and analytic. For E{sub {nu}=}1 MeV neutrino crossing polyethylene-vacuum interface the transition radiation probability is about 10{sup -39} and the energy intensity is about 10{sup -34} eV. At the surface of the neutron stars the transition radiation probability may be {approx}10{sup -20}. Our result is by the three orders of magnitude larger than those of previous calculations.
Transition radiation by neutrinos
Ioannisian, A. N.; Ioannisian, D. A.; Kazarian, N. A.
2011-08-01
We calculate the transition radiation process ν→νγ at an interface of two media. The neutrinos are taken to be with only standard-model couplings. The medium fulfills the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation. The transition radiation occurs when at least one of those quantities have different values in different media. The neutrino mass is ignored due to its negligible contribution. We present a result for the probability of the transition radiation which is both accurate and analytic. For Eν=1 MeV neutrino crossing polyethylene-vacuum interface the transition radiation probability is about 10 and the energy intensity is about 10 eV. At the surface of the neutron stars the transition radiation probability may be ˜10. Our result is by the three orders of magnitude larger than those of previous calculations.
Vranjes, J
2015-01-01
Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindric configuration. This is of practical importance for drift wave instability in various plasmas, and in particular in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit ...
DEFF Research Database (Denmark)
Christensen, Ole; Heil, Christopher; Deng, Baiqiao
1999-01-01
Beurling densities of Lambda = boolean ORk=1r Lambda(k) satisfy D- (Lambda) greater than or equal to 1 and D+(Lambda) Ramanathan and Steger. Additionally, we prove the conjecture that no collection boolean ORk=1r {g(k)(x - a)}(a is an element of Gamma k) of pure...
Energy Technology Data Exchange (ETDEWEB)
Vranjes, J., E-mail: jvranjes@yahoo.com [Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife (Spain); Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife (Spain); Kono, M., E-mail: kono@fps.chuo-u.ac.jp [Faculty of Policy Studies, Chuo University, Tokyo (Japan)
2015-01-15
Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work, the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindrical configuration. This is of practical importance for drift wave instability in various plasmas, and, in particular, in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit volume (per second) in quiet regions in the corona. Consequently, within the life-time of a magnetic structure such energy losses can easily be compensated by the stochastic drift wave heating.
Culture systems: embryo density.
Reed, Michael L
2012-01-01
Embryo density is defined as the embryo-to-volume ratio achieved during in vitro culture; in other words, it is the number of embryos in a defined volume of culture medium. The same density can be achieved by manipulating either the number of embryos in a given volume of medium, or manipulating the volume of the medium for a given number of embryos: for example, a microdrop with five embryos in a 50 μl volume under oil has the same embryo-to-volume ratio (1:10 μl) as a microdrop with one embryo in a 10 μl volume under oil (1:10 μl). Increased embryo density can improve mammalian embryo development in vitro; however, the mechanism(s) responsible for this effect may be different with respect to which method is used to increase embryo density.Standard, flat sterile plastic petri dishes are the most common, traditional platform for embryo culture. Microdrops under a mineral oil overlay can be prepared to control embryo density, but it is critical that dish preparation is consistent, where appropriate techniques are applied to prevent microdrop dehydration during preparation, and results of any data collection are reliable, and repeatable. There are newer dishes available from several manufacturers that are specifically designed for embryo culture; most are readily available for use with human embryos. The concept behind these newer dishes relies on fabrication of conical and smaller volume wells into the dish design, so that embryos rest at the lowest point in the wells, and where putative embryotrophic factors may concentrate.Embryo density is not usually considered by the embryologist as a technique in and of itself; rather, the decision to culture embryos in groups or individually is protocol-driven, and is based more on convenience or the need to collect data on individual embryos. Embryo density can be controlled, and as such, it can be utilized as a simple, yet effective tool to improve in vitro development of human embryos.
Partition density functional theory
Nafziger, Jonathan
Partition density functional theory (PDFT) is a method for dividing a molecular electronic structure calculation into fragment calculations. The molecular density and energy corresponding to Kohn Sham density-functional theory (KS-DFT) may be exactly recovered from these fragments. Each fragment acts as an isolated system except for the influence of a global one-body 'partition' potential which deforms the fragment densities. In this work, the developments of PDFT are put into the context of other fragment-based density functional methods. We developed three numerical implementations of PDFT: One within the NWChem computational chemistry package using basis sets, and the other two developed from scratch using real-space grids. It is shown that all three of these programs can exactly reproduce a KS-DFT calculation via fragment calculations. The first of our in-house codes handles non-interacting electrons in arbitrary one-dimensional potentials with any number of fragments. This code is used to explore how the exact partition potential changes for different partitionings of the same system and also to study features which determine which systems yield non-integer PDFT occupations and which systems are locked into integer PDFT occupations. The second in-house code, CADMium, performs real-space calculations of diatomic molecules. Features of the exact partition potential are studied for a variety of cases and an analytical formula determining singularities in the partition potential is derived. We introduce an approximation for the non-additive kinetic energy and show how this quantity can be computed exactly. Finally a PDFT functional is developed to address the issues of static correlation and delocalization errors in approximations within DFT. The functional is applied to the dissociation of H2 + and H2.
2D transition metal dichalcogenides
Manzeli, Sajedeh; Ovchinnikov, Dmitry; Pasquier, Diego; Yazyev, Oleg V.; Kis, Andras
2017-08-01
Graphene is very popular because of its many fascinating properties, but its lack of an electronic bandgap has stimulated the search for 2D materials with semiconducting character. Transition metal dichalcogenides (TMDCs), which are semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), provide a promising alternative. Because of its robustness, MoS2 is the most studied material in this family. TMDCs exhibit a unique combination of atomic-scale thickness, direct bandgap, strong spin-orbit coupling and favourable electronic and mechanical properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. In this Review, the methods used to synthesize TMDCs are examined and their properties are discussed, with particular attention to their charge density wave, superconductive and topological phases. The use of TMCDs in nanoelectronic devices is also explored, along with strategies to improve charge carrier mobility, high frequency operation and the use of strain engineering to tailor their properties.
Spin in Density-Functional Theory
Jacob, Christoph R; 10.1002/qua.24309
2012-01-01
The accurate description of open-shell molecules, in particular of transition metal complexes and clusters, is still an important challenge for quantum chemistry. While density-functional theory (DFT) is widely applied in this area, the sometimes severe limitations of its currently available approximate realizations often preclude its application as a predictive theory. Here, we review the foundations of DFT applied to open-shell systems, both within the nonrelativistic and the relativistic framework. In particular, we provide an in-depth discussion of the exact theory, with a focus on the role of the spin density and possibilities for targeting specific spin states. It turns out that different options exist for setting up Kohn-Sham DFT schemes for open-shell systems, which imply different definitions of the exchange-correlation energy functional and lead to different exact conditions on this functional. Finally, we suggest some possible directions for future developments.
Form the density-of-states method to finite density quantum field theory
Langfeld, Kurt
2016-01-01
During the last 40 years, Monte Carlo calculations based upon Importance Sampling have matured into the most widely employed method for determinig first principle results in QCD. Nevertheless, Importance Sampling leads to spectacular failures in situations in which certain rare configurations play a non-secondary role as it is the case for Yang-Mills theories near a first order phase transition or quantum field theories at finite matter density when studied with the re-weighting method. The density-of-states method in its LLR formulation has the potential to solve such overlap or sign problems by means of an exponential error suppression. We here introduce the LLR approach and its generalisation to complex action systems. Applications include U(1), SU(2) and SU(3) gauge theories as well as the Z3 spin model at finite densities and heavy-dense QCD.
Dependence of the critical current density on the first matching field density
Energy Technology Data Exchange (ETDEWEB)
Obaidat, I.M. [Department of Physics, United Arab Emirates University, Al-Ain 17551 (United Arab Emirates)], E-mail: iobaidat@uaeu.ac.ae; Benkraouda, M.; Khawaja, U. Al [Department of Physics, United Arab Emirates University, Al-Ain 17551 (United Arab Emirates)
2008-10-01
Molecular dynamic simulations were carried out to investigate the properties of the critical depinning force in high temperature superconductors at several vortex densities at the first matching field. The study was conducted on samples with periodic square arrays of vortices and pinning sites. The variables in the simulations were the vortex density, the pinning sites density, the temperature, the pinning strength, the size of pinning sites. The critical depinning force is found to decrease with temperature for all first matching field densities. The rate of this decrease was found to be slower as the pinning strength and size of pinning site gets larger. At low temperatures and for large pinning strengths, the critical depinning force was found to decrease with increasing the first matching field density. But very interesting results were obtained at moderate temperatures where the critical depinning force was found to increase as the first matching field density increases. The same behavior of the critical depinning force was found at low temperatures, for small pinning strengths. These unexpected results were attributed to a vortex structural phase transition from a disordered state to an ordered state.
VARIOUS REGIMES OF CHARGE-DENSITY WAVES IN LAYERED COMPOUNDS
Bakel, G.P.E.M. van; Hosson, J.Th.M. De
1992-01-01
In this paper we have subjected different layered transition-metal dichalcogenides to scanning tunneling microscopy to reveal the electronic charge distribution associated with the charge-density-wave (CDW) part of the superstructure, in addition to the atomic corrugation. The observations presented
Method to reduce dislocation density in silicon using stress
Buonassisi, Anthony; Bertoni, Mariana; Argon, Ali; Castellanos, Sergio; Fecych, Alexandria; Powell, Douglas; Vogl, Michelle
2013-03-05
A crystalline material structure with reduced dislocation density and method of producing same is provided. The crystalline material structure is annealed at temperatures above the brittle-to-ductile transition temperature of the crystalline material structure. One or more stress elements are formed on the crystalline material structure so as to annihilate dislocations or to move them into less harmful locations.
Audible reflection density for different late reflection criteria in rooms
DEFF Research Database (Denmark)
Krueger, Donata; Jeong, Cheol-Ho; Brunskog, Jonas
2012-01-01
only specular reflections. Therefore in this study, the upper threshold for audible reflection density is investigated for four different transition times of 25, 50, 75, and 100 ms through a headphone listening test. Binaural impulse responses and speech signals simulated in three rooms with different...
Dynamical quorum sensing: Population density encoded in cellular dynamics
De Monte, Silvia; d'Ovidio, Francesco; Danø, Sune; Sørensen, Preben Graae
2007-01-01
Mutual synchronization by exchange of chemicals is a mechanism for the emergence of collective dynamics in cellular populations. General theories exist on the transition to coherence, but no quantitative, experimental demonstration has been given. Here, we present a modeling and experimental analysis of cell-density-dependent glycolytic oscillations in yeast. We study the disappearance of oscillations at low cell density and show that this phenomenon occurs synchronously in all cells and not by desynchronization, as previously expected. This study identifies a general scenario for the emergence of collective cellular oscillations and suggests a quorum-sensing mechanism by which the cell density information is encoded in the intracellular dynamical state. PMID:18003917
Degenerate Density Perturbation Theory
Palenik, Mark C
2016-01-01
Fractional occupation numbers can be used in density functional theory to create a symmetric Kohn-Sham potential, resulting in orbitals with degenerate eigenvalues. We develop the corresponding perturbation theory and apply it to a system of $N_d$ degenerate electrons in a harmonic oscillator potential. The order-by-order expansions of both the fractional occupation numbers and unitary transformations within the degenerate subspace are determined by the requirement that a differentiable map exists connecting the initial and perturbed states. Using the X$\\alpha$ exchange-correlation (XC) functional, we find an analytic solution for the first-order density and first through third-order energies as a function of $\\alpha$, with and without a self-interaction correction. The fact that the XC Hessian is not positive definite plays an important role in the behavior of the occupation numbers.
Ayala, A P; Levin, E M
1996-01-01
In this talk we present our detail study ( theory and numbers) [1] on the shadowing corrections to the gluon structure functions for nuclei. Starting from rather contraversial information on the nucleon structure function which is originated by the recent HERA data, we develop the Glauber approach for the gluon density in a nucleus based on Mueller formula [2] and estimate the value of the shadowing corrections in this case. Than we calculate the first corrections to the Glauber approach and show that these corrections are big. Based on this practical observation we suggest the new evolution equation which takes into account the shadowing corrections and solve it. We hope to convince you that the new evolution equation gives a good theoretical tool to treat the shadowing corrections for the gluons density in a nucleus and, therefore, it is able to provide the theoretically reliable initial conditions for the time evolution of the nucleus - nucleus cascade.
Quantal density functional theory
Sahni, Viraht
2016-01-01
This book deals with quantal density functional theory (QDFT) which is a time-dependent local effective potential theory of the electronic structure of matter. The treated time-independent QDFT constitutes a special case. In the 2nd edition, the theory is extended to include the presence of external magnetostatic fields. The theory is a description of matter based on the ‘quantal Newtonian’ first and second laws which is in terms of “classical” fields that pervade all space, and their quantal sources. The fields, which are explicitly defined, are separately representative of electron correlations due to the Pauli exclusion principle, Coulomb repulsion, correlation-kinetic, correlation-current-density, and correlation-magnetic effects. The book further describes Schrödinger theory from the new physical perspective of fields and quantal sources. It also describes traditional Hohenberg-Kohn-Sham DFT, and explains via QDFT the physics underlying the various energy functionals and functional derivatives o...
Langfeld, Kurt
2016-01-01
Although Monte Carlo calculations using Importance Sampling have matured into the most widely employed method for determining first principle results in QCD, they spectacularly fail for theories with a sign problem or for which certain rare configurations play an important role. Non-Markovian Random walks, based upon iterative refinements of the density-of-states, overcome such overlap problems. I will review the Linear Logarithmic Relaxation (LLR) method and, in particular, focus onto ergodicity and exponential error suppression. Applications include the high-state Potts model, SU(2) and SU(3) Yang-Mills theories as well as a quantum field theory with a strong sign problem: QCD at finite densities of heavy quarks.
Degenerate density perturbation theory
Palenik, Mark C.; Dunlap, Brett I.
2016-09-01
Fractional occupation numbers can be used in density functional theory to create a symmetric Kohn-Sham potential, resulting in orbitals with degenerate eigenvalues. We develop the corresponding perturbation theory and apply it to a system of Nd degenerate electrons in a harmonic oscillator potential. The order-by-order expansions of both the fractional occupation numbers and unitary transformations within the degenerate subspace are determined by the requirement that a differentiable map exists connecting the initial and perturbed states. Using the X α exchange-correlation (XC) functional, we find an analytic solution for the first-order density and first- through third-order energies as a function of α , with and without a self-interaction correction. The fact that the XC Hessian is not positive definite plays an important role in the behavior of the occupation numbers.
Energy Technology Data Exchange (ETDEWEB)
Petry, W.; Neuhaus, J. [Techn. Universitaet Muenchen, Physik Department E13, Munich (Germany)
1996-11-01
Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs.
Variational Transition State Theory
Energy Technology Data Exchange (ETDEWEB)
Truhlar, Donald G. [Univ. of Minnesota, Minneapolis, MN (United States)
2016-09-29
This is the final report on a project involving the development and applications of variational transition state theory. This project involved the development of variational transition state theory for gas-phase reactions, including optimized multidimensional tunneling contributions and the application of this theory to gas-phase reactions with a special emphasis on developing reaction rate theory in directions that are important for applications to combustion. The development of variational transition state theory with optimized multidimensional tunneling as a useful computational tool for combustion kinetics involved eight objectives.
Anomalous radiative transitions
Ishikawa, Kenzo; Tobita, Yutaka
2014-01-01
Anomalous transitions involving photons derived by many-body interaction of the form, $\\partial_{\\mu} G^{\\mu}$, in the standard model are studied. This does not affect the equation of motion in the bulk, but makes wave functions modified, and causes the unusual transition characterized by the time-independent probability. In the transition probability at a time-interval T expressed generally in the form $P=T \\Gamma_0 +P^{(d)}$, now with $\\Gamma_0=0, P^{(d)} \
Transition nozzle combustion system
Energy Technology Data Exchange (ETDEWEB)
Kim, Won-Wook; McMahan, Kevin Weston; Maldonado, Jaime Javier
2016-11-29
The present application provides a combustion system for use with a cooling flow. The combustion system may include a head end, an aft end, a transition nozzle extending from the head end to the aft end, and an impingement sleeve surrounding the transition nozzle. The impingement sleeve may define a first cavity in communication with the head end for a first portion of the cooling flow and a second cavity in communication with the aft end for a second portion of the cooling flow. The transition nozzle may include a number of cooling holes thereon in communication with the second portion of the cooling flow.
The density of reactive levels in NO2 unimolecular decomposition
Ionov, S. I.; Davis, H. F.; Mikhaylichenko, K.; Valachovic, L.; Beaudet, R. A.; Wittig, C.
1994-09-01
Laser induced fluorescence spectra of expansion-cooled NO2/Ne samples (1 and 2 K) are reported for transitions that originate from the lowest rovibronic levels and terminate on levels near D0. At 1 K, nearly all transitions originate from N`=0. With the present resolution of 0.02 cm-1, the 1 K spectra are resolved rather well. The high density of transitions is due to couplings between rovibronic levels with different N and K quantum numbers and with electronic characters that borrow oscillator strength from bright B2 vibronic species of the mixed 2A1/2B2 electronic system. Just above reaction threshold, such rovibronic species comprise the manifold of levels sampled by optically prepared wave packets. However, at higher energies we argue that the density of B2 vibronic species is a more relevant parameter to describe the nature of unimolecular reactions. Nuances of the optical excitation process are discussed.
Airborne Crowd Density Estimation
Meynberg, O.; Kuschk, G.
2013-10-01
This paper proposes a new method for estimating human crowd densities from aerial imagery. Applications benefiting from an accurate crowd monitoring system are mainly found in the security sector. Normally crowd density estimation is done through in-situ camera systems mounted on high locations although this is not appropriate in case of very large crowds with thousands of people. Using airborne camera systems in these scenarios is a new research topic. Our method uses a preliminary filtering of the whole image space by suitable and fast interest point detection resulting in a number of image regions, possibly containing human crowds. Validation of these candidates is done by transforming the corresponding image patches into a low-dimensional and discriminative feature space and classifying the results using a support vector machine (SVM). The feature space is spanned by texture features computed by applying a Gabor filter bank with varying scale and orientation to the image patches. For evaluation, we use 5 different image datasets acquired by the 3K+ aerial camera system of the German Aerospace Center during real mass events like concerts or football games. To evaluate the robustness and generality of our method, these datasets are taken from different flight heights between 800 m and 1500 m above ground (keeping a fixed focal length) and varying daylight and shadow conditions. The results of our crowd density estimation are evaluated against a reference data set obtained by manually labeling tens of thousands individual persons in the corresponding datasets and show that our method is able to estimate human crowd densities in challenging realistic scenarios.
Spatial Density Maps from a Debris Cloud
Healy, L.; Kindl, S.; Binz, C.
2016-09-01
A debris cloud from a fragmentation on orbit may be modeled by transformation of variables from the instantaneous velocity distribution at the fragmentation time to the spatial distribution at some elapsed time later. There are no Gaussian distributions assumed and the evolution map is quite nonlinear, being derived from the solution of the Lambert, two-point boundary value, problem and the state transition matrix for unperturbed propagation, so the traditional tools of analysis that assume these qualities fail dramatically. The transformation of variables technique does not suffer from any such assumptions, and unlike the Monte Carlo method, is not subject to sampling errors or approximations. Structures and features are evident in the density maps, and these structures show promise for simplified approximation of the density map. Most prominent of the structures is the well-known pinch point at the fragmentation location in inertial space. The anti-pinch line, or wedge, is also observed. Bands on the opposite side of the fragmentation are very noticeable, and their existence may be motivated from simple orbit dynamics. These bands make the anti-pinch line actually more of a set of anti-pinch line segments. By computing these density maps over time, the evolution may be studied. There is a density generator, a density band at roughly the same altitude as the pinch point, that cycles around the earth and appears a source of the bands, with newly created bands moving radially outward and diminishing in density. Although the initial velocity distribution affects the final spatial distribution, the Lambert solutions, which are the most time consuming to compute, need only be computed once. Therefore, different initial distributions may be changed and the results recomputed with relative speed. A comparison of the effects of initial distributions is shown in this paper.
Contingent kernel density estimation.
Directory of Open Access Journals (Sweden)
Scott Fortmann-Roe
Full Text Available Kernel density estimation is a widely used method for estimating a distribution based on a sample of points drawn from that distribution. Generally, in practice some form of error contaminates the sample of observed points. Such error can be the result of imprecise measurements or observation bias. Often this error is negligible and may be disregarded in analysis. In cases where the error is non-negligible, estimation methods should be adjusted to reduce resulting bias. Several modifications of kernel density estimation have been developed to address specific forms of errors. One form of error that has not yet been addressed is the case where observations are nominally placed at the centers of areas from which the points are assumed to have been drawn, where these areas are of varying sizes. In this scenario, the bias arises because the size of the error can vary among points and some subset of points can be known to have smaller error than another subset or the form of the error may change among points. This paper proposes a "contingent kernel density estimation" technique to address this form of error. This new technique adjusts the standard kernel on a point-by-point basis in an adaptive response to changing structure and magnitude of error. In this paper, equations for our contingent kernel technique are derived, the technique is validated using numerical simulations, and an example using the geographic locations of social networking users is worked to demonstrate the utility of the method.
Signals of the QCD Phase Transition in the Heavens
Schaffner-Bielich, J
2007-01-01
The modern phase diagram of strongly interacting matter reveals a rich structure at high-densities due to phase transitions related to the chiral symmetry of quantum chromodynamics (QCD) and the phenomenon of color superconductivity. These exotic phases have significant impacts on high-density astrophysics as the properties of neutron stars and the evolution of astrophysical systems as proto-neutron stars, core-collapse supernovae and neutron star mergers. Most recent pulsar mass measurements and constraints on neutron star radii are critically discussed. Astrophysical signals for exotic matter and phase transitions in high-density matter proposed recently in the literature are outlined. A strong first order phase transition leads to the emergence of a third family of compact stars besides white dwarfs and neutron stars. The different microphysics of quark matter results in an enhanced r-mode stability window for rotating compact stars compared to normal neutron stars. Future telescope and satellite data will...
Antigen-Independent Restriction of Pneumococcal Density by Mucosal Adjuvant Cholera Toxin Subunit B
Kuipers, Kirsten; Diavatopoulos, Dimitri A.; van Opzeeland, Fred; Simonetti, Elles; van den Kieboom, Corne H.; Kerstholt, Mariska; Borczyk, Malgorzata; van IngenSchenau, D.; Brandsma, Eelke T.; Netea, Mihai G.; de Jonge, Marien I.
2016-01-01
For many bacterial respiratory infections, development of (severe) disease is preceded by asymptomatic colonization of the upper airways. For Streptococcus pneumoniae, the transition to severe lower respiratory tract infection is associated with an increase in nasopharyngeal colonization density. In
Antigen-Independent Restriction of Pneumococcal Density by Mucosal Adjuvant Cholera Toxin Subunit B
Kuipers, K.; Diavatopoulos, D.A.; Opzeeland, F. van; Simonetti, E.; Kieboom, C.H. van den; Kerstholt, M; Borczyk, M.; IngenSchenau, D. van; Brandsma, E.T.; Netea, M.G.; Jonge, M.I. de
2016-01-01
For many bacterial respiratory infections, development of (severe) disease is preceded by asymptomatic colonization of the upper airways. For Streptococcus pneumoniae, the transition to severe lower respiratory tract infection is associated with an increase in nasopharyngeal colonization density.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A four-parameter model based on the extended Miedema's cellular model of alloy phases and pattern recognition methods has been used to study the regularities of the formation of binary intermetallic compounds between transition element and non-transition element. The formation criterion can be expressed as some inequities of electronegativity φ, the valence electron density in Wagner-Seitz cell nws1/3, Pauling's metallic radius R and the number of valence electrons in atom Z or their functions. According to these empirical criterions, the "unknown" binary alloy system can be predicted, the predicted result is better than that of Miedema's two-parameter model.
Density measures and additive property
Kunisada, Ryoichi
2015-01-01
We deal with finitely additive measures defined on all subsets of natural numbers which extend the asymptotic density (density measures). We consider a class of density measures which are constructed from free ultrafilters on natural numbers and study a certain additivity property of such density measures.
Density measures and additive property
Kunisada, Ryoichi
2015-01-01
We deal with finitely additive measures defined on all subsets of natural numbers which extend the asymptotic density (density measures). We consider a class of density measures which are constructed from free ultrafilters on natural numbers and study a certain additivity property of such density measures.
Electronic entanglement in late transition metal oxides.
Thunström, Patrik; Di Marco, Igor; Eriksson, Olle
2012-11-01
We present a study of the entanglement in the electronic structure of the late transition metal monoxides--MnO, FeO, CoO, and NiO--obtained by means of density-functional theory in the local density approximation combined with dynamical mean-field theory. The impurity problem is solved through exact diagonalization, which grants full access to the thermally mixed many-body ground state density operator. The quality of the electronic structure is affirmed through a direct comparison between the calculated electronic excitation spectrum and photoemission experiments. Our treatment allows for a quantitative investigation of the entanglement in the electronic structure. Two main sources of entanglement are explicitly resolved through the use of a fidelity based geometrical entanglement measure, and additional information is gained from a complementary entropic entanglement measure. We show that the interplay of crystal field effects and Coulomb interaction causes the entanglement in CoO to take a particularly intricate form.
Density waves in the organic metal α-(BEDT-TTF) 2KHg(SCN) 4
Kato, Masaru
2003-05-01
We have investigated possible spin and charge density waves in the organic metal α-(BEDT-TTF) 2KHg(SCN) 4. This system shows density wave like transition at T=8 K, and the nature of the density wave is not clarified up to now. Using a realistic tight binding model and an inhomogeneous mean-field theory, we obtained several stable density wave states. Especially, spin density wave states (SDW) are stable only for large on-site Coulomb interaction U⩾400 meV. Their spin moments are tiny and inhomogeneous even in the unit cell. Also charge density wave appears simultaneously with the SDW.
Transiting Exoplanets with JWST
Seager, S; Valenti, J A
2008-01-01
The era of exoplanet characterization is upon us. For a subset of exoplanets -- the transiting planets -- physical properties can be measured, including mass, radius, and atmosphere characteristics. Indeed, measuring the atmospheres of a further subset of transiting planets, the hot Jupiters, is now routine with the Spitzer Space Telescope. The James Webb Space Telescope (JWST) will continue Spitzer's legacy with its large mirror size and precise thermal stability. JWST is poised for the significant achievement of identifying habitable planets around bright M through G stars--rocky planets lacking extensive gas envelopes, with water vapor and signs of chemical disequilibrium in their atmospheres. Favorable transiting planet systems, are, however, anticipated to be rare and their atmosphere observations will require tens to hundreds of hours of JWST time per planet. We review what is known about the physical characteristics of transiting planets, summarize lessons learned from Spitzer high-contrast exoplanet m...
Energy Technology Data Exchange (ETDEWEB)
Ross, M; Japel, S; Boehler, R
2005-04-11
We review the transition melting studies carried out at Mainz, and describe a recently developed model used to explain that the relatively low melting slopes are due to the partially filled d-bands, and the persistence of the pressure induced s-d transition. The basic tenets of the model have now been reconfirmed by new measurements for Cu and Ni. The measurements show that Cu which has a filled 3d-band, has a melt slope that is about 2.5 greater than its neighbor Ni. In the case of Mo, the apparent discrepancy of DAC melting measurements with shock melting can be explained by accounting for the change in melt slope due to the bcc-cp transition observed in the shock studies. The Fe melt curve is revisited. The possible relevance of the Jahn-Teller effect and recently observed transition metal melts with Icosahedral Short-Range Order (ISRO) is discussed.
Phase transitions modern applications
Gitterman, Moshe
2014-01-01
This book provides a comprehensive review of the theory of phase transitions and its modern applications, based on the five pillars of the modern theory of phase transitions i.e. the Ising model, mean field, scaling, renormalization group and universality. This expanded second edition includes, along with a description of vortices and high temperature superconductivity, a discussion of phase transitions in chemical reaction and moving systems. The book covers a close connection between phase transitions and small world phenomena as well as scale-free systems such as the stock market and the Internet. Readership: Scientists working in different fields of physics, chemistry, biology and economics as well as teaching material for undergraduate and graduate courses.
Transitivity on Weierstrass points
Laing, Zoe
2010-01-01
We look for Riemann surfaces whose automorphism group acts transitively on the Weierstrass points. We concentrate on hyperelliptic surfaces, surfaces with PSL(2, q) as automorphism group, Platonic surfaces and Fermat curves.
Oligocyclopentadienyl transition metal complexes
Energy Technology Data Exchange (ETDEWEB)
de Azevedo, Cristina G.; Vollhardt, K. Peter C.
2002-01-18
Synthesis, characterization, and reactivity studies of oligocyclopentadienyl transition metal complexes, namely those of fulvalene, tercyclopentadienyl, quatercyclopentadienyl, and pentacyclopentadienyl(cyclopentadienyl) are the subject of this account. Thermal-, photo-, and redox chemistries of homo- and heteropolynuclear complexes are described.
Superconductivity in transition metals.
Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P
2015-03-13
A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified.
Metal-semiconductor-metal transition in zigzag carbon nanoscrolls
Dong, Haixia; Zhang, Yang; Fang, Dangqi; Gong, Baihua; Zhang, Erhu; Zhang, Shengli
2016-01-01
Similar to rolling up paper, carbon nanoscrolls (CNSs) can be rolled from graphene nanoribbons (GNRs) using physical approaches. Owing to their peculiar one-dimensional nanostructures, CNSs have attracted great attention over the past few years. In this study, we have investigated the effects of bending deformation on the electronic properties of zigzag CNSs (ZCNSs) during the rolling process from zigzag GNRs (ZGNRs) by means of first-principles calculations. It is found that a metal-semiconductor-metal transition is observed. By analyzing charge density and density of states, the origin of this electronic property transition is discussed. Furthermore, we find that the metal-semiconductor-metal transition in ZCNSs is independent of ribbon width as well as spin-orbit interaction. Our results of the metal-semiconductor-metal transition in the ZCNSs are robust and may open potential applications in nano-electromechanical devices based on the ZCNSs.Similar to rolling up paper, carbon nanoscrolls (CNSs) can be rolled from graphene nanoribbons (GNRs) using physical approaches. Owing to their peculiar one-dimensional nanostructures, CNSs have attracted great attention over the past few years. In this study, we have investigated the effects of bending deformation on the electronic properties of zigzag CNSs (ZCNSs) during the rolling process from zigzag GNRs (ZGNRs) by means of first-principles calculations. It is found that a metal-semiconductor-metal transition is observed. By analyzing charge density and density of states, the origin of this electronic property transition is discussed. Furthermore, we find that the metal-semiconductor-metal transition in ZCNSs is independent of ribbon width as well as spin-orbit interaction. Our results of the metal-semiconductor-metal transition in the ZCNSs are robust and may open potential applications in nano-electromechanical devices based on the ZCNSs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07628
Universal properties of large N phase transitions in Wilson loops
Narayanan, R
2007-01-01
Numerical studies support the conjecture that in continuum planar QCD the eigenvalue density of a Wilson loop operator undergoes a transition as the loop is dilated while keeping the loop shape fixed. A second part of the conjecture is that the transition obeys large N universality and that this universality class is the same in 2, 3 and 4 Euclidean space-time dimensions. The focus of the talk will be on clarifying precisely what the conjecture is claiming.
Transition-Metal-Free Biomolecule-Based Flexible Asymmetric Supercapacitors.
Yang, Yun; Wang, Hua; Hao, Rui; Guo, Lin
2016-09-01
A transition-metal-free asymmetric supercapacitor (ASC) is successfully fabricated based on an earth-abundant biomass derived redox-active biomolecule, named lawsone. Such an ASC exhibits comparable or even higher energy densities than most of the recently reported transition-metal-based ASCs, and this green ASC generation from renewable resources is promising for addressing current issues of electronic hazard processing, high cost, and unsustainability.
Trends in catalytic NO decomposition over transition metal surfaces
DEFF Research Database (Denmark)
Falsig, Hanne; Bligaard, Thomas; Rass-Hansen, Jeppe
2007-01-01
The formation of NOx from combustion of fossil and renewable fuels continues to be a dominant environmental issue. We take one step towards rationalizing trends in catalytic activity of transition metal catalysts for NO decomposition by combining microkinetic modelling with density functional...... theory calculations. We show specifically why the key problem in using transition metal surfaces to catalyze direct NO decomposition is their significant relative overbinding of atomic oxygen compared to atomic nitrogen....
Freezing of low energy excitations in charge density wave glasses.
Staresinic, D; Zaitsev-Zotov, S V; Baklanov, N I; Biljaković, K
2008-03-07
Thermally stimulated discharge current measurements were performed to study slow relaxation processes in two canonical charge density wave systems K(0.3)MoO(3) and o-TaS(3). Two relaxation processes were observed and characterized in each system, corroborating the results of dielectric spectroscopy. Our results are consistent with the scenario of the glass transition on the charge density wave superstructure level. In particular, the results directly prove the previously proposed criterion of charge density wave freezing based on the interplay of charge density wave pinning by impurities and screening by free carriers. In addition, we obtained new information on distribution of relaxation parameters, as well as on nonlinear dielectric response both below and above the threshold field for charge density wave sliding.
Institute of Scientific and Technical Information of China (English)
许可; 李未
1999-01-01
Phase transition is an important feature of SAT problem. For random k-SAT model, it is proved that as r（ratio of clauses to variables） increases, the structure of solutions will undergo a sudden change like satisfiability phase transition when r reaches a threshold point (r=rcr). This phenomenon shows that the satisfying truth assignments suddenly shift from being relatively different from each other to being very similar to each other.##属性不符
Grubler, A.
2004-01-01
Patterns of energy use have changed dramatically since the onset of the industrial revolution in terms of both energy quantities and energy quality. These changing patterns of energy use, where energy quantities and quality interact in numerous important ways, are referred to in this article as energy transitions and are described from a historical perspective as well as through future scenarios. Far from being completed, many of these transitions are continuing to unfold in industrial and de...
Directory of Open Access Journals (Sweden)
Hodgkin S.
2011-02-01
Full Text Available The WFCAM Transit Survey (WTS has been obtaining data on the United Kingdom Infrared Telescope since 2007. The WTS targets about 8,000 M dwarfs over several square degrees of sky, and aims to ﬁnd low-mass eclipsing binaries and planets, down to the size of the Earth, transiting M dwarf stars with periods up to a few days.
Stateless Transitive Signature Schemes
Institute of Scientific and Technical Information of China (English)
MA Chun-guang; CAI Man-chun; YANG Yi-xian
2004-01-01
A new practical method is introduced to transform the stateful transitive signature scheme to stateless one without the loss of security. According to the approach, two concrete stateless transitive signature schemes based on Factoring and RSA are presented respectively. Under the assumption of the hardness of factoring and one-more- RSA-inversion problem, both two schemes are secure under the adaptive chosen-message attacks in random oracle model.
Energy Technology Data Exchange (ETDEWEB)
Fujimoto, Kazuhiro J., E-mail: fujimoto@ruby.kobe-u.ac.jp [Department of Computational Science, Graduate School of System Informatics, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan)
2014-12-07
A transition charge, dipole, and quadrupole from electrostatic potential (TrESP-CDQ) method for electronic coupling calculations is proposed. The TrESP method is based on the classical description of electronic Coulomb interaction between transition densities for individual molecules. In the original TrESP method, only the transition charge interactions were considered as the electronic coupling. In the present study, the TrESP method is extended to include the contributions from the transition dipoles and quadrupoles as well as the transition charges. Hence, the self-consistent transition density is employed in the ESP fitting procedure. To check the accuracy of the present approach, several test calculations are performed to a helium dimer, a methane dimer, and an ethylene dimer. As a result, the TrESP-CDQ method gives a much improved description of the electronic coupling, compared with the original TrESP method. The calculated results also show that the self-consistent treatment to the transition densities contributes significantly to the accuracy of the electronic coupling calculations. Based on the successful description of the electronic coupling, the contributions to the electronic coupling are also analyzed. This analysis clearly shows a negligible contribution of the transition charge interaction to the electronic coupling. Hence, the distribution of the transition density is found to strongly influence the magnitudes of the transition charges, dipoles, and quadrupoles. The present approach is useful for analyzing and understanding the mechanism of excitation-energy transfer.
Semiclassics in Density Functional Theory
Lee, Donghyung; Cangi, Attila; Elliott, Peter; Burke, Kieron
2009-03-01
Recently, we published an article [1] about the semiclassical origin of density functional theory. We showed that the density and the kinetic energy density of one dimensional finite systems with hard walls can be expressed in terms of the external potential using the semiclassical Green's function method. Here, we show a uniformization scheme for the semiclassical density and the kinetic energy density for turning-point problems.[1] P. Elliott, D. Lee, A. Cangi, and K. Burke, Phys. Rev. Lett. 100, 256406 (2008).
Anderson, Lara B; Raghuram, Nikhil; Taylor, Washington
2015-01-01
We explore a novel type of transition in certain 6D and 4D quantum field theories, in which the matter content of the theory changes while the gauge group and other parts of the spectrum remain invariant. Such transitions can occur, for example, for SU(6) and SU(7) gauge groups, where matter fields in a three-index antisymmetric representation and the fundamental representation are exchanged in the transition for matter in the two-index antisymmetric representation. These matter transitions are realized by passing through superconformal theories at the transition point. We explore these transitions in dual F-theory and heterotic descriptions, where a number of novel features arise. For example, in the heterotic description the relevant 6D SU(7) theories are described by bundles on K3 surfaces where the geometry of the K3 is constrained in addition to the bundle structure. On the F-theory side, non-standard representations such as the three-index antisymmetric representation of SU(N) require Weierstrass models...
Phase transition in traffic jam experiment on a circuit
Tadaki, Shin-ichi; Kikuchi, Macoto; Fukui, Minoru; Nakayama, Akihiro; Nishinari, Katsuhiro; Shibata, Akihiro; Sugiyama, Yuki; Yosida, Taturu; Yukawa, Satoshi
2013-10-01
The emergence of a traffic jam is considered to be a dynamical phase transition in a physics point of view; traffic flow becomes unstable and changes phase into a traffic jam when the car density exceeds a critical value. In order to verify this view, we have been performing a series of circuit experiments. In our previous work (2008 New J. Phys. 10 033001), we demonstrated that a traffic jam emerges even in the absence of bottlenecks at a certain high density. In this study, we performed a larger indoor circuit experiment in the Nagoya Dome in which the positions of cars were observed using a high-resolution laser scanner. Over a series of sessions at various values of density, we found that jammed flow occurred at high densities, whereas free flow was conserved at low densities. We also found indications of metastability at an intermediate density. The critical density is estimated by analyzing the fluctuations in speed and the density-flow relation. The value of this critical density is consistent with that observed on real expressways. This experiment provides strong support for physical interpretations of the emergence of traffic jams as a dynamical phase transition.
Du, Yanjun; Peng, Zhimin; Ding, Yanjun; Sadeghi, Nader; Bruggeman, Peter J.
2016-08-01
The measurement of absolute densities of reactive species and radicals such as OH is of growing interest for many plasma applications. In this paper, we extend the use of a self-absorption model for atomic emission spectroscopy to molecular emission spectroscopy. The proposed analysis of self-absorbed molecular emission spectra is a simple and inexpensive method to determine OH(X) densities and rotational temperatures compared to laser induced fluorescence. We compare the recorded absolute OH density in a non-equilibrium diffuse atmospheric-pressure RF glow discharge by this method with broadband UV absorption considering a number of rotational lines with J‧ ⩽ 6.5, the detection limit of the line integrated OH(X) density with this method is of the order of 2 × 1019 m-2. The accuracy of the density is sensitive to the rotational temperature of the OH(A) state and the non-equilibrium rotational population distribution.
Charge fluctuations in chiral models and the QCD phase transition
Skokov, V; Karsch, F; Redlich, K
2011-01-01
We consider the Polyakov loop-extended two flavor chiral quark--meson model and discuss critical phenomena related with the spontaneous breaking of the chiral symmetry. The model is explored beyond the mean-field approximation in the framework of the functional renormalisation group. We discuss properties of the net-quark number density fluctuations as well as their higher cumulants. We show that with the increasing net-quark number density, the higher order cumulants exhibit a strong sensitivity to the chiral crossover transition. We discuss their role as probes of the chiral phase transition in heavy-ion collisions at RHIC and LHC.
Background field functional renormalization group for absorbing state phase transitions.
Buchhold, Michael; Diehl, Sebastian
2016-07-01
We present a functional renormalization group approach for the active to inactive phase transition in directed percolation-type systems, in which the transition is approached from the active, finite density phase. By expanding the effective potential for the density field around its minimum, we obtain a background field action functional, which serves as a starting point for the functional renormalization group approach. Due to the presence of the background field, the corresponding nonperturbative flow equations yield remarkably good estimates for the critical exponents of the directed percolation universality class, even in low dimensions.
Non-equilibrium quantum phase transition via entanglement decoherence dynamics
Lin, Yu-Chen; Yang, Pei-Yun; Zhang, Wei-Min
2016-01-01
We investigate the decoherence dynamics of continuous variable entanglement as the system-environment coupling strength varies from the weak-coupling to the strong-coupling regimes. Due to the existence of localized modes in the strong-coupling regime, the system cannot approach equilibrium with its environment, which induces a nonequilibrium quantum phase transition. We analytically solve the entanglement decoherence dynamics for an arbitrary spectral density. The nonequilibrium quantum phase transition is demonstrated as the system-environment coupling strength varies for all the Ohmic-type spectral densities. The 3-D entanglement quantum phase diagram is obtained. PMID:27713556
Density Distribution Sunflower Plots
Directory of Open Access Journals (Sweden)
William D. Dupont
2003-01-01
Full Text Available Density distribution sunflower plots are used to display high-density bivariate data. They are useful for data where a conventional scatter plot is difficult to read due to overstriking of the plot symbol. The x-y plane is subdivided into a lattice of regular hexagonal bins of width w specified by the user. The user also specifies the values of l, d, and k that affect the plot as follows. Individual observations are plotted when there are less than l observations per bin as in a conventional scatter plot. Each bin with from l to d observations contains a light sunflower. Other bins contain a dark sunflower. In a light sunflower each petal represents one observation. In a dark sunflower, each petal represents k observations. (A dark sunflower with p petals represents between /2-pk k and /2+pk k observations. The user can control the sizes and colors of the sunflowers. By selecting appropriate colors and sizes for the light and dark sunflowers, plots can be obtained that give both the overall sense of the data density distribution as well as the number of data points in any given region. The use of this graphic is illustrated with data from the Framingham Heart Study. A documented Stata program, called sunflower, is available to draw these graphs. It can be downloaded from the Statistical Software Components archive at http://ideas.repec.org/c/boc/bocode/s430201.html . (Journal of Statistical Software 2003; 8 (3: 1-5. Posted at http://www.jstatsoft.org/index.php?vol=8 .
Moreau, F; Romani, R
1982-11-01
Mitochondria from avocado (Persea americana Mill, var. Fuerte and Hass) can be rapidly prepared at every stage of ripening using differential centrifugation and self-generated Percoll gradients. The procedure results in improved oxidative and phosphorylative properties, especially for mitochondria isolated from preclimacteric fruits.A gradual change in the buoyant density of avocado mitochondria takes place during ripening. Climacteric and postclimacteric avocado mitochondria have the same buoyant density as other plant mitochondria (potato, cauliflower), whereas mitochondria from preclimacteric fruit have a lower density. The transition in buoyant density occurs during the climacteric rise, and two populations of intact mitochondria (p = 1.060 and p = 1.075) can be separated at this stage. Evidence indicates that the difference in mitochondrial buoyant density between preclimacteric and postclimacteric mitochondria is likely due to interactions with soluble cytosolic components.
Aydin, Alhun; Sisman, Altug
2016-03-01
By considering the quantum-mechanically minimum allowable energy interval, we exactly count number of states (NOS) and introduce discrete density of states (DOS) concept for a particle in a box for various dimensions. Expressions for bounded and unbounded continua are analytically recovered from discrete ones. Even though substantial fluctuations prevail in discrete DOS, they're almost completely flattened out after summation or integration operation. It's seen that relative errors of analytical expressions of bounded/unbounded continua rapidly decrease for high NOS values (weak confinement or high energy conditions), while the proposed analytical expressions based on Weyl's conjecture always preserve their lower error characteristic.
Analysis of compaction shock interactions during DDT of low density HMX
Rao, Pratap T.; Gonthier, Keith A.
2017-01-01
Deflagration-to-Detonation Transition (DDT) in confined, low density granular HMX occurs by a complex mechanism that involves compaction shock interactions within the material. Piston driven DDT experiments indicate that detonation is abruptly triggered by the interaction of a strong combustion-supported secondary shock and a piston-supported primary (input) shock, where the nature of the interaction depends on initial packing density and primary shock strength. These interactions influence transition by affecting dissipative heating within the microstructure during pore collapse. Inert meso-scale simulations of successive shock loading of low density HMX are performed to examine how dissipation and hot-spot formation are affected by the initial density, and the primary and secondary shock strengths. This information is used to formulate an ignition and burn model for low density HMX that accounts for the effect of shock densensitization on burn. Preliminary DDT predictions are presented that illustrate how primary shock strength affects the transition mechanism.
Generalizing smooth transition autoregressions
DEFF Research Database (Denmark)
Chini, Emilio Zanetti
forecasting experiment to evaluate its point and density forecasting performances. In all the cases, the dynamic asymmetry in the cycle is efficiently captured by the new model. The GSTAR beats AR and STAR competitors in point forecasting, while this superiority becomes less evident in density forecasting...
Gas-liquid phase transition in modified pseudopotential and “shelf Coulomb” ultracold plasma models
Butlitsky, M. A.; Zelener, B. B.; Zelener, B. V.
2016-11-01
Phase diagrams for the “shelf Coulomb” and the modified pseudopotential plasma models developed in our previous works are compared. Qualitative agreement is observed between gas-liquid phase transition region of “shelf Coulomb” model and liquid-gas structure region of modified pseudopotential one. The possibility of experimental finding of the phase transition in nonequilibrium ultracold Rydberg plasma is considered. Parameters (density, temperature, levels of Rydberg atoms) for such a transition are estimated. Conclusion is made that “shelf Coulomb” model phase transition is practically impossible to observe in equilibrium strongly coupled plasmas due to high neutral atoms density at low temperatures: T crit ≈ 0.076.
Structural Transitions of Solvent-Free Oligomer-Grafted Nanoparticles
Chremos, Alexandros
2011-09-01
Novel structural transitions of solvent-free oligomer-grafted nanoparticles are investigated by using molecular dynamics simulations of a coarse-grained bead-spring model. Variations in core size and grafting density lead to self-assembly of the nanoparticles into a variety of distinct structures. At the boundaries between different structures, the nanoparticle systems undergo thermoreversible transitions. This structural behavior, which has not been previously reported, deviates significantly from that of simple liquids. The reversible nature of these transitions in solvent-free conditions offers new ways to control self-assembly of nanoparticles at experimentally accessible conditions. © 2011 American Physical Society.
Topology-driven magnetic quantum phase transition in topological insulators.
Zhang, Jinsong; Chang, Cui-Zu; Tang, Peizhe; Zhang, Zuocheng; Feng, Xiao; Li, Kang; Wang, Li-Li; Chen, Xi; Liu, Chaoxing; Duan, Wenhui; He, Ke; Xue, Qi-Kun; Ma, Xucun; Wang, Yayu
2013-03-29
The breaking of time reversal symmetry in topological insulators may create previously unknown quantum effects. We observed a magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 topological insulator films grown by means of molecular beam epitaxy. Across the critical point, a topological quantum phase transition is revealed through both angle-resolved photoemission measurements and density functional theory calculations. We present strong evidence that the bulk band topology is the fundamental driving force for the magnetic quantum phase transition. The tunable topological and magnetic properties in this system are well suited for realizing the exotic topological quantum phenomena in magnetic topological insulators.
Thermodynamic signature of the dynamic glass transition in hard spheres.
Hermes, Michiel; Dijkstra, Marjolein
2010-03-17
We use extensive event-driven molecular dynamics simulations to study the thermodynamic, structural and dynamic properties of hard-sphere glasses. We determine the equation of state of the metastable fluid branch for hard spheres with a size polydispersity of 10%. Our results show a clear jump in the slope of the isothermal compressibility. The observation of a thermodynamic signature at the transition from a metastable fluid to a glassy state is analogous to the abrupt change in the specific heat or thermal expansion coefficient as observed for molecular liquids at the glass transition. The dynamic glass transition becomes more pronounced and shifts to higher densities for longer equilibration times.
Probability of statistical L-H transition in tokamaks
Energy Technology Data Exchange (ETDEWEB)
Itoh, Sanae-I. [Kyushu Univ., Research Institute for Applied Mechanics, Kasuga, Fukuoka (Japan); Itoh, Kimitaka; Toda, Shinichiro [National Inst. for Fusion Science, Toki, Gifu (Japan)
2002-08-01
A statistical model of bifurcation of radial electric field E{sub r} is analyzed in relation with L-H transitions of tokamaks. A noise from micro fluctuations leads to random noise for E{sub r}. The transition of E{sub r} occurs in a probabilistic manner. Probability density function and ensemble average of E{sub r} are obtained, when hysteresis of E{sub r} exists. Forward- and backward-transition probabilities are calculated. The phase boundary is shown. Due to the suppression of turbulence by E{sub r} shear, the boundary deviates from the Maxwell's construction rule. (author)
Using connectivity for measuring equity in transit provision
DEFF Research Database (Denmark)
Kaplan, Sigal; Popoks, Dmitrijs; Prato, Carlo Giacomo
2014-01-01
This study proposes the assessment of equity in transit provision by using transit connectivity as a comprehensive impedance measure. Transit connectivity considers in-vehicle time, access/egress times, waiting time, service reliability, frequency, and ‘seamless’ transfers along multi-modal paths...... connectivity provision for students to higher-education and job opportunities. Also, results show that the north-west ‘finger’ is less equitable with lower connectivity for low population density and lower connectivity to higher-education opportunities regardless of the high number of students....
Piel, Alexander; Arp, Oliver; Menzel, Kristoffer; Klindworth, Markus
2007-11-01
We report on experimental observations of dust density waves in a complex (dusty) plasma under microgravity. The plasma is produced in a radio-frequency parallel-plate discharge (argon, p=15Pa, U=65Vpp). Different sizes of dust particles were used (3.4 μm and 6.4μm diameter). The low-frequency (f 11Hz) dust density waves are naturally unstable modes, which are driven by the ion flow in the plasma. Surprisingly, the wave propagation direction is aligned with the ion flow direction in the bulk plasma but becomes oblique at the boundary of the dust cloud with an inclination of 60^o with respect to the plasma boundary. The experimental results are compared with a kinetic model in the electrostatic approximation [1] and a fluid model [2]. Moreover, the role of dust surface waves is discussed. [1] M. Rosenberg, J. Vac. Sci. Technol. A 14, 631 (1996) [2] A. Piel et al, Phys. Rev. Lett. 97, 205009 (2006)
Energy Technology Data Exchange (ETDEWEB)
Ayala, A.L. [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil). Inst. de Fisica][Pelotas Univ., RS (Brazil). Inst. de Fisica e Matematica; Ducati, M.B.G. [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil). Inst. de Fisica; Levin, E.M. [Fermi National Accelerator Lab., Batavia, IL (United States)][Nuclear Physics Inst., St. Petersburg (Russian Federation)
1996-10-01
In this talk we present our detailed study (theory and numbers) on the shadowing corrections to the gluon structure functions for nuclei. Starting from rather controversial information on the nucleon structure function which is originated by the recent HERA data, we develop the Glauber approach for the gluon density in a nucleus based on Mueller formula and estimate the value of the shadowing corrections in this case. Then we calculate the first corrections to the Glauber approach and show that these corrections are big. Based on this practical observation we suggest the new evolution equation which takes into account the shadowing corrections and solve it. We hope to convince you that the new evolution equation gives a good theoretical tool to treat the shadowing corrections for the gluons density in a nucleus and, therefore, it is able to provide the theoretically reliable initial conditions for the time evolution of the nucleus-nucleus cascade. The initial conditions should be fixed both theoretically and phenomenologically before to attack such complicated problems as the mixture of hard and soft processes in nucleus-nucleus interactions at high energy or the theoretically reliable approach to hadron or/and parton cascades for high energy nucleus-nucleus interaction. 35 refs., 24 figs., 1 tab.
The Evolution of Transition Region Loops Using IRIS and AIA
Winebarger, Amy R.; DePontieu, Bart
2014-01-01
Over the past 50 years, the model for the structure of the solar transition region has evolved from a simple transition layer between the cooler chromosphere to the hotter corona to a complex and diverse region that is dominated by complete loops that never reach coronal temperatures. The IRIS slitjaw images show many complete transition region loops. Several of the "coronal" channels in the SDO AIA instrument include contributions from weak transition region lines. In this work, we combine slitjaw images from IRIS with these channels to determine the evolution of the loops. We develop a simple model for the temperature and density evolution of the loops that can explain the simultaneous observations. Finally, we estimate the percentage of AIA emission that originates in the transition region.
Population pressure and fertility in pre-transition Thailand.
VanLandingham, M; Hirschman, C
2001-11-01
Before the demographic transition in Thailand, fertility was high, but not uniformly so. As in other pre-transition settings, Thai fertility responded to pressures and opportunities created by socioeconomic structure and land availability. Drawing upon provincial data from the 1947 and 1960 censuses of Thailand, we find a strong 'frontier effect' on Thai fertility in the 1950s. Fertility was higher in sparsely settled frontier provinces and lower in provinces with higher population density relative to cultivatable land. This finding is robust and holds up with controls for agricultural employment, land quality, and the sex ratio (an indicator of sex-selective migration). The effect of population pressure lowers the likelihood of marriage and of marital fertility. The findings from Thailand are consistent with the research of Easterlin on the nineteenth century United States and with other pre-transition societies. We suggest how demographic transition theory might be broadened to include fertility dynamics in pre-transition societies.
Magnetic endohedral transition-metal-doped semiconducting-nanoclusters.
Matxain, Jon M; Formoso, Elena; Mercero, Jose M; Piris, Mario; Lopez, Xabier; Ugalde, Jesus M
2008-01-01
Endohedral first-row transition-metal-doped TM@Zn(i)S(i) nanoclusters, in which TM stands for the first-row transition-metals from Sc to Zn, and i=12, 16, have been characterized. In these structures the dopant metals are trapped inside spheroidal hollow semiconducting nanoclusters. It is observed that some of the transition metals are trapped in the center of mass of the cluster, whereas others are found to be displaced from that center, leading to structures in which the transition metals display a complex dynamical behavior upon encapsulation. This fact was confirmed by quantum molecular dynamics calculations, which further confirmed the thermal stability of endohedral compounds. In the endohedrally-doped nanoclusters in which the transition-metal atom sits on the center of mass, the host hollow cluster structure remains undistorted after dopant encapsulation. Conversely, if the encapsulated transition-metal atom is displaced from the center of mass, the host hollow cluster structure suffers a very tiny distortion. Additionally, it is found that there is negligible charge transfer between the dopant transition-metal atom and its hollow cluster host and, after encapsulation, the spin densities remain localized on the transition-metal atom. This allows for the atomic-like behavior of the trapped transition-metal atom, which gives rise to their atomic-like magnetic properties. The encapsulation free energies are negative, suggesting that these compounds are thermodynamically stable.
Examining hydrogen transitions.
Energy Technology Data Exchange (ETDEWEB)
Plotkin, S. E.; Energy Systems
2007-03-01
This report describes the results of an effort to identify key analytic issues associated with modeling a transition to hydrogen as a fuel for light duty vehicles, and using insights gained from this effort to suggest ways to improve ongoing modeling efforts. The study reported on here examined multiple hydrogen scenarios reported in the literature, identified modeling issues associated with those scenario analyses, and examined three DOE-sponsored hydrogen transition models in the context of those modeling issues. The three hydrogen transition models are HyTrans (contractor: Oak Ridge National Laboratory), MARKAL/DOE* (Brookhaven National Laboratory), and NEMS-H2 (OnLocation, Inc). The goals of these models are (1) to help DOE improve its R&D effort by identifying key technology and other roadblocks to a transition and testing its technical program goals to determine whether they are likely to lead to the market success of hydrogen technologies, (2) to evaluate alternative policies to promote a transition, and (3) to estimate the costs and benefits of alternative pathways to hydrogen development.
Scaling and universality in glass transition
de Candia, Antonio; Fierro, Annalisa; Coniglio, Antonio
2016-05-01
Kinetic facilitated models and the Mode Coupling Theory (MCT) model B are within those systems known to exhibit a discontinuous dynamical transition with a two step relaxation. We consider a general scaling approach, within mean field theory, for such systems by considering the behavior of the density correlator and the dynamical susceptibility - 2. Focusing on the Fredrickson and Andersen (FA) facilitated spin model on the Bethe lattice, we extend a cluster approach that was previously developed for continuous glass transitions by Arenzon et al. (Phys. Rev. E 90, 020301(R) (2014)) to describe the decay to the plateau, and consider a damage spreading mechanism to describe the departure from the plateau. We predict scaling laws, which relate dynamical exponents to the static exponents of mean field bootstrap percolation. The dynamical behavior and the scaling laws for both density correlator and dynamical susceptibility coincide with those predicted by MCT. These results explain the origin of scaling laws and the universal behavior associated with the glass transition in mean field, which is characterized by the divergence of the static length of the bootstrap percolation model with an upper critical dimension dc = 8.
Fast Radial Flows in Transition Disk Holes
Rosenfeld, Katherine A; Andrews, Sean M
2013-01-01
Protoplanetary "transition" disks have large, mass-depleted central cavities, yet also deliver gas onto their host stars at rates comparable to disks without holes. The paradox of simultaneous transparency and accretion can be explained if gas flows inward at much higher radial speeds inside the cavity than outside the cavity, since surface density (and by extension optical depth) varies inversely with inflow velocity at fixed accretion rate. Radial speeds within the cavity might even have to approach free-fall values to explain the huge surface density contrasts inferred for transition disks. We identify observational diagnostics of fast radial inflow in channel maps made in optically thick spectral lines. Signatures include (1) twisted isophotes in maps made at low systemic velocities and (2) rotation of structures observed between maps made in high-velocity line wings. As a test case, we apply our new diagnostic tools to archival ALMA data on the transition disk HD 142527, and uncover evidence for free-fal...
Gedanken Densities and Exact Constraints in Density Functional Theory
Perdew, John P; Sun, Jianwei; Burke, Kieron
2014-01-01
Approximations to the exact density functional for the exchange-correlation energy of a many-electron ground state can be constructed by satisfying constraints that are universal, i.e., valid for all electron densities. Gedanken densities are designed for the purpose of this construction, but need not be realistic. The uniform electron gas is an old gedanken density. Here, we propose a spherical two-electron gedanken density in which the dimensionless density gradient can be an arbitrary positive constant wherever the density is non-zero. The Lieb-Oxford lower bound on the exchange energy can be satisfied within a generalized gradient approximation (GGA) by bounding its enhancement factor or simplest GGA exchange-energy density. This enhancement-factor bound is well known to be sufficient, but our gedanken density shows that it is also necessary. The conventional exact exchange-energy density satisfies no such local bound, but energy densities are not unique, and the simplest GGA exchange-energy density is no...
Lin, Yue; Li, Cheng
2012-01-01
Nearest neighbors search is a fundamental problem in various research fields like machine learning, data mining and pattern recognition. Recently, hashing-based approaches, e.g., Locality Sensitive Hashing (LSH), are proved to be effective for scalable high dimensional nearest neighbors search. Many hashing algorithms found their theoretic root in random projection. Since these algorithms generate the hash tables (projections) randomly, a large number of hash tables (i.e., long codewords) are required in order to achieve both high precision and recall. To address this limitation, we propose a novel hashing algorithm called {\\em Density Sensitive Hashing} (DSH) in this paper. DSH can be regarded as an extension of LSH. By exploring the geometric structure of the data, DSH avoids the purely random projections selection and uses those projective functions which best agree with the distribution of the data. Extensive experimental results on real-world data sets have shown that the proposed method achieves better ...
Ducati, M B G
2001-01-01
The dynamics of high partonic density QCD is presented considering, in the double logarithm approximation, the parton recombination mechanism built in the AGL formalism, developed including unitarity corrections for the nucleon as well for nucleus. It is shown that these corrections are under theoretical control. The resulting non linear evolution equation is solved in the asymptotic regime, and a comprehensive phenomenology concerning Deep Inelastic Scattering like $F_2$, $F_L$, $F_2^c$. $\\partial F_2/ \\partial \\ln Q^2$, $\\partial F^A_2/ \\partial \\ln Q^2$, etc, is presented. The connection of our formalism with the DGLAP and BFKL dynamics, and with other perturbative (K) and non-perturbative (MV-JKLW) approaches is analised in detail. The phenomena of saturation due to shadowing corrections and the relevance of this effect in ion physics and heavy quark production is emphasized. The implications to e-RHIC, HERA-A, and LHC physics and some open questions are mentioned.
Oberacker, V E
2015-01-01
In this manuscript we provide an outline of the numerical methods used in implementing the density constrained time-dependent Hartree-Fock (DC-TDHF) method and provide a few examples of its application to nuclear fusion. In this approach, dynamic microscopic calculations are carried out on a three-dimensional lattice and there are no adjustable parameters, the only input is the Skyrme effective NN interaction. After a review of the DC-TDHF theory and the numerical methods, we present results for heavy-ion potentials $V(R)$, coordinate-dependent mass parameters $M(R)$, and precompound excitation energies $E^{*}(R)$ for a variety of heavy-ion reactions. Using fusion barrier penetrabilities, we calculate total fusion cross sections $\\sigma(E_\\mathrm{c.m.})$ for reactions between both stable and neutron-rich nuclei. We also determine capture cross sections for hot fusion reactions leading to the formation of superheavy elements.
Citizens in sustainable transitions
DEFF Research Database (Denmark)
Hoffmann, Birgitte; Agger, Annika
2013-01-01
The paper explores how local public authorities can support and facilitate citizens’ participa-tion and learning in sustainable transition in urban neighbourhoods, by supporting local in-termediaries. The role of intermediaries can be performed by a variety of actors such as public housing...... associations; NGO´s, or semi public institutions. Our claim is that intermediary actors have the potential to facilitate new platforms for citizens’ participation in urban sustainable transition due to their particular role in between public authorities and civil society. The key question of the paper is how...... the intermediary actors facilitate citizens' participatory processes in sustainable urban transitions, and the paper explores the concept of institutional capacity building as a way to develop learning processes and new practises? The aim is to analyse approaches of creating platforms for involving citizens...
DEFF Research Database (Denmark)
Theil, Peter Kappel
2015-01-01
The transition period from late gestation to early lactation is rather short, but it is nonetheless of major importance for the productivity of high-prolific sows. The transition period, here defined as the last 10 d of gestation and the first 10 d of lactation, encompasses substantial changes...... for the sow. More specifically, fetal growth, mammary growth, colostrum production and sow maintenance require substantial amounts of nutrients during late gestation. After parturition, nutrients are mainly required for milk synthesis and sow maintenance, but the regressing uterus supplies considerable...... practices do not acknowledge these changes. Development of new feeding strategies specifically adapted for the transition sow is likely of importance to match the rapid changes in nutrient requirements....
Parametric modal transition systems
DEFF Research Database (Denmark)
Beneš, Nikola; Křetínský, Jan; Larsen, Kim Guldstrand;
2011-01-01
Modal transition systems (MTS) is a well-studied specification formalism of reactive systems supporting a step-wise refinement methodology. Despite its many advantages, the formalism as well as its currently known extensions are incapable of expressing some practically needed aspects in the refin......Modal transition systems (MTS) is a well-studied specification formalism of reactive systems supporting a step-wise refinement methodology. Despite its many advantages, the formalism as well as its currently known extensions are incapable of expressing some practically needed aspects...... in the refinement process like exclusive, conditional and persistent choices. We introduce a new model called parametric modal transition systems (PMTS) together with a general modal refinement notion that overcome many of the limitations and we investigate the computational complexity of modal refinement checking....
DEFF Research Database (Denmark)
Fjællegaard, Cecilie Bryld
The degree of transferability of skills and knowledge from an creative occupation in the creative industries to the wider economy is a great point of discussion within research in the arts and cultural and creative industries. By applying human capital theory on the labor market for creatives......, this paper investigates the relationship between creative occupation and industry human capital and hourly wage after transitioning to a non-creative occupation and/ or industry. Further, it is investigated how the distance of the transition mediates the relationship between creative occupation and industry...... specific human capital and hourly wage. By making use of a matched employer-employee dataset from the Denmark from 1994 to 2007, wage equation are estimated. The results suggest that a transition from a creative occupation to a non-creative occupation results in an increase in the hourly wage...
Planets transiting non-eclipsing binaries
Martin, David V.; Triaud, Amaury H. M. J.
2014-10-01
The majority of binary stars do not eclipse. Current searches for transiting circumbinary planets concentrate on eclipsing binaries, and are therefore restricted to a small fraction of potential hosts. We investigate the concept of finding planets transiting non-eclipsing binaries, whose geometry would require mutually inclined planes. Using an N-body code we explore how the number and sequence of transits vary as functions of observing time and orbital parameters. The concept is then generalised thanks to a suite of simulated circumbinary systems. Binaries are constructed from radial-velocity surveys of the solar neighbourhood. They are then populated with orbiting gas giants, drawn from a range of distributions. The binary population is shown to be compatible with the Kepler eclipsing binary catalogue, indicating that the properties of binaries may be as universal as the initial mass function. These synthetic systems produce transiting circumbinary planets occurring on both eclipsing and non-eclipsing binaries. Simulated planets transiting eclipsing binaries are compared with published Kepler detections. We find 1) that planets transiting non-eclipsing binaries are probably present in the Kepler data; 2) that observational biases alone cannot account for the observed over-density of circumbinary planets near the stability limit, which implies a physical pile-up; and 3) that the distributions of gas giants orbiting single and binary stars are likely different. Estimating the frequency of circumbinary planets is degenerate with the spread in mutual inclination. Only a minimum occurrence rate can be produced, which we find to be compatible with 9%. Searching for inclined circumbinary planets may significantly increase the population of known objects and will test our conclusions. Their presence, or absence, will reveal the true occurrence rate and help develop circumbinary planet formation theories.
Pannell, C
1995-01-01
This article describes recent changes in urban patterns in Shanghai-Nanjing, Beijing-Tianjin-Tangshan, Canton-Hong Kong, and Dalian-Shenyang. The urban patterns in these metropolitan areas are viewed as part of an urban transition that is responding to population growth, a structural shift in employment, relaxed rules on migration and household registration, and foreign investment and trade. It is argued that these metropolitan coastal areas will form the key growth centers and will lead China's economic development. Urban transition is defined as the shift from rural to urban and from agricultural employment to industrial, commercial, or service employment. China's large cities always dominated as important centers of politics and trade. The recent shift is from interior to coastal cities due to a new world view and a movement away from the isolationism of prior centuries. It is assumed that cities are formed to take advantage of economies of scale in production, consumption, and distribution and to conform to regional specialization. Governments can intervene in growth processes. China's development of cities reflects state controls and market forces. The size and scale of China's population influenced the development process, which resulted in differences in the shape and process of the urban transition. It was under Chinese communism that cities became more than a set of discrete regional urban systems. Reference is made to Oshima's model of change that is specific to monsoon countries. Oshima argues that monsoon agricultural conditions require a distinct strategy based on full employment in order to achieve industrial transition. Rice cultivation requires a large and disciplined labor force. The discussion focuses on other models as well, such as the McGee's model of the extended metropolis and its extension by Zhou Yixing to China. China's changes may not follow Skeldon's models of urbanization in developing countries, because of state control of migration
Bone Densitometry (Bone Density Scan)
... News Physician Resources Professions Site Index A-Z Bone Densitometry (DEXA) Bone densitometry, also called dual-energy ... limitations of DEXA Bone Densitometry? What is a Bone Density Scan (DEXA)? Bone density scanning, also called ...
Dynamical phase transitions in quantum mechanics
Directory of Open Access Journals (Sweden)
Rotter Ingrid
2012-02-01
Full Text Available The nucleus is described as an open many-body quantum system with a non-Hermitian Hamilton operator the eigenvalues of which are complex, in general. The eigenvalues may cross in the complex plane (exceptional points, the phases of the eigenfunctions are not rigid in approaching the crossing points and the widths bifurcate. By varying only one parameter, the eigenvalue trajectories usually avoid crossing and width bifurcation occurs at the critical value of avoided crossing. An analog spectroscopic redistribution takes place for discrete states below the particle decay threshold. By this means, a dynamical phase transition occurs in the many-level system starting at a critical value of the level density. Hence the properties of the low-lying nuclear states (described well by the shell model and those of highly excited nuclear states (described by random ensembles differ fundamentally from one another. The statement of Niels Bohr on the collective features of compound nucleus states at high level density is therefore not in contradiction to the shell-model description of nuclear (and atomic states at low level density. Dynamical phase transitions are observed experimentally in different quantum mechanical systems by varying one or two parameters.
DEFF Research Database (Denmark)
Lange, Ida Sofie Gøtzsche; Laursen, Lea Louise Holst; Lassen, Claus
Thinking of Transit Places, the first sites that comes to mind will probably be airports, train stations and motorways. Such places are overall mono-functional with the embedded rationales of people's desires to move (themselves or goods) from one place to another. Often different service functions...... how a town primarily characterized by ferry transit is being challenged on its capacity to be a 'place' of meaning and social importance to its inhabitants. The paper raises the key question: Can a place become too well connected and this in such a manner that its identity and key character becomes...
DEFF Research Database (Denmark)
Bygbjerg, Ib Christian; Meyrowitsch, Dan W
2006-01-01
, and by degenerative, and man-made diseases in ageing populations. Omran could not foresee the HIV/AIDS pandemic or the dramatic fall in longevity and fertility in, for example, Russia. But his model remains of value for health planners and politicians. We advocate for research in the interplay between diseases......Global epidemiological transition reflected in changed patterns of death and diseases was first described by Omran; decreasing death and disease rates from infectious diseases, particularly in children and the young, are followed by decreased fertility rate and increased longevity......, populations and systems in a world in fast transition. Udgivelsesdato: 2006-Sep-4...
DEFF Research Database (Denmark)
Bygbjerg, Ib Christian; Meyrowitsch, Dan W
2007-01-01
"Tempora mutantur et nos in illis" King Lothar I remarked by year 900 AD. What exactly changed in us over time, i.e. how patterns of the epidemiological transition in populations locally and globally might appear, was described by Omran in 1971 [1]. The effect of transition on health and diseases...... diseases like child diseases, malaria, HIV/AIDS and tuberculosis. It is remarkable that the specific chronic diseases of major public health relevance are in fact not mentioned in the MDG, even if these diseases increasingly are hitting populations in low- and middle-income societies, i.e. developing...
Network observability transitions.
Yang, Yang; Wang, Jianhui; Motter, Adilson E
2012-12-21
In the modeling, monitoring, and control of complex networks, a fundamental problem concerns the comprehensive determination of the state of the system from limited measurements. Using power grids as example networks, we show that this problem leads to a new type of percolation transition, here termed a network observability transition, which we solve analytically for the configuration model. We also demonstrate a dual role of the network's community structure, which both facilitates optimal measurement placement and renders the networks substantially more sensitive to "observability attacks." Aside from their immediate implications for the development of smart grids, these results provide insights into decentralized biological, social, and technological networks.
Garcia, Y.; Ksenofontov, V.; Campbell, S. J.; Lord, J. S.; Boland, Y.; Gütlich, P.
2004-12-01
The reversible thermal spin transition which occurs in [Fe(phen)2(NCS)2] around T1/2 177 K has been investigated by muon spin relaxation (μSR) (10-280 K). The depolarisation curves are well described by two Lorentzian lines represent fast and slow components in the decay curves, with the initial asymmetry parameter of the fast component found to track the spin transition in [Fe(phen)2(NCS)2]. Comparison of zero-field and transverse field (20 Oe) μSR measurements shows that diamagnetic muonic species occur over the entire temperature range.
Kopaev, YuV
1992-01-01
Electronic Phase Transitions deals with topics, which are presently at the forefront of scientific research in modern solid-state theory. Anderson localization, which has fundamental implications in many areas of solid-state physics as well as spin glasses, with its influence on quite different research activities such as neural networks, are two examples that are reviewed in this book. The ab initio statistical mechanics of structural phase transitions is another prime example, where the interplay and connection of two unrelated disciplines of solid-state theory - first principle ele
Pinocchio: Geppetto's transitional object
Directory of Open Access Journals (Sweden)
Gabriele Zeloni
2015-01-01
Full Text Available The literature has been considered by Freud and others after him, a form of unaware exploration of mind that can leads to discoveries similar to psychoanalysis’s discoveries. From this perspective, the author puts forward the following hypothesis: Pinocchio is a puppet who comes to life and is therefore, from a child's perception, a transitional object according to Winnicott. Consequently Geppetto is nothing more than the involuntary representation of any child interacting with the transitional object. The author explains the results of the analysis of the text in support of the hypothesis and reflects on the impact of The adventure of Pinocchio on the reader.
DEFF Research Database (Denmark)
Hedman, Jonas; Xiao, Xiao
2016-01-01
companies operate. In this paper, we present a case study of an ERP vendor for SMB (small and mediumsize business) in making a transition towards a cloud-based business model. Through the theoretical lens of ecosystem, we are able to analyze the evolution of the vendor and its business network as a whole......The rising of cloud computing has dramatically changed the way software companies provide and distribute their IT product and related services over the last decades. Today, most software is bought offthe-shelf and distributed over the Internet. This transition is greatly influencing how software...
Lee-Yang zeros analysis of finite density lattice QCD
Crompton, P
2001-01-01
coefficients from different ensembles (through the ratio of the normalisations) we are thus able to alleviate the bias in our sampling. We then further develop this method for SU(3) with static quarks by generating a range of canonical ensembles which we combine with our new re-weighting approach. From our SU(2) measurements we establish the existence of a diquark superfluid at high densities and low temperatures. We also determine the position and order of the associated symmetry breaking transitions in the mass - chemical potential plane. From our measurements of static SU(3) we establish that the finite density transition at intermediate coupling is a first order percolation transition. Having addressed the pathologies of the re-weighting method in two nonabelian gauge field theories which are simpler to evaluate numerically, in future work SU(3) QCD can be evaluated at finite density. Recent results from four-fermion interaction models have suggested that new exotic phases form at finite baryon density wh...
Orbital quantization in the high-magnetic-field state of a charge-density-wave system
Andres, D.; Kartsovnik, M. V.; Grigoriev, P. D.; Biberacher, W.; Müller, H.
2003-11-01
A superposition of the Pauli and orbital couplings of a high magnetic field to charge carriers in a charge-density-wave (CDW) system is proposed to give rise to transitions between subphases with quantized values of the CDW wave vector. By contrast to the purely orbital field-induced density-wave effects which require a strongly imperfect nesting of the Fermi surface, the new transitions can occur even if the Fermi surface is well nested at zero field. We suggest that such transitions are observed in the organic metal α-(BEDT-TTF)2KHg(SCN)4 under a strongly tilted magnetic field.
Density of states of Frenkel excitons in strongly disordered two-dimensional systems
Siemann, Robert; Boukahil, Abdelkrim
2014-03-01
We present the calculation of the density of states of Frenkel excitons in strongly disordered two-dimensional systems. A random distribution of transition frequencies with variance σ2 characterizes the disorder. The Coherent Potential Approximation (CPA) calculations show a strong dependence of the density of states (DOS) on the disorder parameter σ.