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Sample records for charge densities determined

  1. Photo-detachment signal analysis to accurately determine electronegativity, electron temperature, and charged species density

    NASA Astrophysics Data System (ADS)

    Oudini, N.; Sirse, N.; Taccogna, F.; Ellingboe, A. R.; Bendib, A.

    2016-09-01

    Laser pulse induced photo-detachment combined with Langmuir probing has been introduced to diagnose plasma electronegativity. This technique uses a laser pulse to convert negative ions into electron-atom pairs and tracks the change of electron saturation current by a Langmuir probe. The existing model determines plasma electronegativity as the ratio of electron saturation current before and after detachment. However, this model depends on various assumptions and neglects the formation of a potential barrier between the laser channel and surrounding electronegative plasma. In this letter, we present a new analytical model to analyze photo-detachment signals in order to improve the accuracy of electronegativity measurements and extend this technique for measuring electron temperature and charged species density. This analytical model is supported by Particle-In-Cell simulation of electronegative plasma dynamics following laser photo-detachment. The analysis of the signal, detected on a simulated probe, shows that the present analytical model determines electronegativity, electron temperature, and plasma density with a relative error of ˜20%, ˜20%, and ˜50%, respectively, whereas the electronegativity obtained from a previous model is underestimated by an order of magnitude.

  2. Structure-dependent charge density as a determinant of antimicrobial activity of peptide analogues of defensin.

    PubMed

    Bai, Yang; Liu, Shouping; Jiang, Ping; Zhou, Lei; Li, Jing; Tang, Charles; Verma, Chandra; Mu, Yuguang; Beuerman, Roger W; Pervushin, Konstantin

    2009-08-01

    Defensins are small (3-5 kDa) cysteine-rich cationic proteins found in both vertebrates and invertebrates constituting the front line of host innate immunity. Despite intensive research, bactericidal and cytotoxic mechanisms of defensins are still largely unknown. Moreover, we recently demonstrated that small peptides derived from defensins are even more potent bactericidal agents with less toxicity toward host cells. In this paper, structures of three C-terminal (R36-K45) analogues of human beta-defensin-3 were studied by 1H NMR spectroscopy and extensive molecular dynamics simulations. Because of indications that these peptides might target the inner bacterial membrane, they were reconstituted in dodecylphosphocholine or dodecylphosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] mixed micelles, and lipid bicelles mimicking the phospholipid-constituted bilayer membrane of mammalian and bacterial cells. The results show that the binding affinity and partitioning into the lipid phase and the ability to dimerize and accrete well-defined structures upon interactions with lipid membranes contribute to compactization of positive charges within peptide oligomers. The peptide charge density, mediated by corresponding three-dimensional structures, was found to directly correlate with the antimicrobial activity. These novel observations may provide a new rationale for the design of improved antimicrobial agents.

  3. Self-Consistent Determination of Atomic Charges of Ionic Liquid through a Combination of Molecular Dynamics Simulation and Density Functional Theory.

    PubMed

    Ishizuka, Ryosuke; Matubayasi, Nobuyuki

    2016-02-01

    A self-consistent scheme is developed to determine the atomic partial charges of ionic liquid. Molecular dynamics (MD) simulation was conducted to sample a set of ion configurations, and these configurations were subject to density functional theory (DFT) calculations to determine the partial charges. The charges were then averaged and used as inputs for the subsequent MD simulation, and MD and DFT calculations were repeated until the MD results are not altered any more. We applied this scheme to 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide ([C1mim][NTf2]) and investigated its structure and dynamics as a function of temperature. At convergence, the average ionic charges were ±0.84 e at 350 K due to charge transfer among ions, where e is the elementary charge, while the reduced ionic charges do not affect strongly the density of [C1mim][NTf2] and radial distribution function. Instead, major effects are found on the energetics and dynamics, with improvements of the overestimated heat of vaporization and the too slow motions of ions observed in MD simulations using commonly used force fields.

  4. Density functional theory of charged colloidal systems

    NASA Astrophysics Data System (ADS)

    Chan, Derek Y.

    2001-06-01

    The phase behavior of charged colloidal systems has been studied recently by the density functional theory formalism (DFT) [R. van Roij, M. Dijkstra, and J. P. Hansen, Phys. Rev. E 59, 2010 (1999)]. A key feature of this approach is the appearance of a density and temperature-dependent effective Hamiltonian between the charged colloids. Under certain approximations, the effective Hamiltonian is made up only of a sum of position-independent one-body or volume terms and two-body colloid-separation dependent terms. In the limit of low colloidal densities, the DFT results do not reduce to the familiar Debye-Hückel limiting law nor do the results agree with previous work based on an identical approach but were developed using traditional statistical-mechanical methods [B. Beresford-Smith, D. Y. C. Chan, and D. J. Mitchell J. Colloid Interface Sci. 105, 216 (1985)]. This paper provides a reconciliation of these differences and comments on the significance of the one-body volume terms in the effective Hamiltonian of a system of charged colloids in determining thermodynamics and phase behavior.

  5. Central depression of nuclear charge density distribution

    SciTech Connect

    Chu Yanyun; Ren Zhongzhou; Wang Zaijun; Dong Tiekuang

    2010-08-15

    The center-depressed nuclear charge distributions are investigated with the parametrized distribution and the relativistic mean-field theory, and their corresponding charge form factors are worked out with the phase shift analysis method. The central depression of nuclear charge distribution of {sup 46}Ar and {sup 44}S is supported by the relativistic mean-field calculation. According to the calculation, the valence protons in {sup 46}Ar and {sup 44}S prefer to occupy the 1d{sub 3/2} state rather than the 2s{sub 1/2} state, which is different from that in the less neutron-rich argon and sulfur isotopes. As a result, the central proton densities of {sup 46}Ar and {sup 44}S are highly depressed, and so are their central charge densities. The charge form factors of some argon and sulfur isotopes are presented, and the minima of the charge form factors shift upward and inward when the central nuclear charge distributions are more depressed. Besides, the effect of the central depression on the charge form factors is studied with a parametrized distribution, when the root-mean-square charge radii remain constant.

  6. Charge properties of low density lipoprotein subclasses.

    PubMed

    La Belle, M; Blanche, P J; Krauss, R M

    1997-04-01

    Measurements of electrophoretic mobility and particle size of low density lipoproteins (LDL) allowed use of standard electrokinetic theory to quantitate LDL charge characteristics from subjects with predominance of large LDL (pattern A, n = 9) or small LDL (pattern B, n = 8). Pattern A LDL was found to have significantly lower (P < or = 0.001) mobility (-0.22 +/- 0.01 micron s-1 cm V-1), surface potential (-4.2 +/- 0.3 mV) and charge density (-500 +/- 34 esu/cm2) than pattern B LDL (-0.25 +/- 0.01 micron s-1 cm V-1, -4.9 +/- 0.3 mV, and -580 +/- 30 esu/cm2), but no significant difference in particle valence (-22.0 +/- 1.4 for pattern A vs. -21.8 +/- 1.9 for pattern B). Thus, the greater mobility of pattern B LDL is due to similar net charge residing on a smaller particle. Comparison of subfractions in pattern B relative to pattern A LDL revealed greater surface potential in all pattern B subfractions and greater charge density in fractions of d > or = 1.032 g/ml. In a subset of subjects incubation with neuraminidase produced significant reductions in all LDL charge parameters for all subfractions, but did not abolish the differences between pattern A and B. Thus increased surface potential and charge density of unfractionated pattern B LDL is due both to charge properties of particles across the size and density spectrum as well as enrichment of pattern B LDL with smaller, denser particles that have higher surface charge density.

  7. Core thresholds and charge-density waves in alkali metals

    NASA Astrophysics Data System (ADS)

    Bruhwiler, P. A.; Schnatterly, S. E.

    1988-07-01

    We have determined experimental upper limits on any broadening which could be due to a charge-density wave in Na and K metal soft x-ray-absorption and emisssion spectra. The upper limit for absorption in Na is a factor of 4 below the expected theoretical value. These results contradict expectations based on the present theory of charge-density waves in alkali metals.

  8. Transport and Structure of Charge Density Waves

    NASA Astrophysics Data System (ADS)

    Dicarlo, David Anthony

    Experimental studies are presented concerning the transport properties and structure of charge-density waves (CDWs) in rm NbSe_3 and rm K_{0.3}MoO_3. Transport measurements were performed to determine how charged impurities affect the CDW and how the narrow -band noise is created in sliding CDWs. Ti-doped rm NbSe_3 is shown to have a weakly pinned CDW even though Ti is incorporated as a charged impurity. The narrow-band-noise amplitude versus sample volume and impurity concentration is consistent with the narrow-band-noise being generated in the bulk by impurities and a weakly pinned CDW. X-ray scattering measurements were performed to determine how impurities, temperature, normal carriers, and electric fields affect the CDW structure. The periodic CDW scatters x-rays and the sharpness of the scattering is a reflection of the CDW structure. The CDW correlation function and its characteristic length are determined through the competition between the disordering impurity forces and the ordering elastic forces. Added impurities and high temperatures decrease the correlations by increasing the disorder forces and decreasing the CDW order parameter Delta , respectively. For rm NbSe_3, the correlation length l was much greater than the average impurity spacing and depends on impurity density n _{i} and temperature as l ~ Delta^2/n_{i}. In addition, the CDW correlation function decays exponentially in real space; ~ e^{-| {bf r}| /l}. These results are consistent with weak pinning. In rm K_{0.3}MoO _3, the CDW exhibits a different structure than that in rm NbSe_3. Changes occur in the correlation function and peak width at low temperatures. These are possibly due to the freeze out of normal carriers in semiconducting rm K _{0.3}MoO_3.. Longitudinal CDW deformations are observed when the CDW was driven by an external electric field. The electric field, temperature, and position dependence of these deformations are consistent with those required for CDW

  9. Counterion density profiles at charged flexible membranes.

    PubMed

    Fleck, Christian C; Netz, Roland R

    2005-09-16

    Counterion distributions at charged flexible membranes are studied using analytical and simulation methods in both Poisson-Boltzmann and strong-coupling limits. The softer the membrane, the more smeared out the counterion-density profile becomes and counterions penetrate through the mean-membrane surface location, in agreement with anomalous scattering results. Repulsion between membrane charges enhances protrusions and induces short-scale membrane roughening.

  10. Quantum crystallographic charge density of urea

    DOE PAGES

    Wall, Michael E.

    2016-06-08

    Standard X-ray crystallography methods use free-atom models to calculate mean unit-cell charge densities. Real molecules, however, have shared charge that is not captured accurately using free-atom models. To address this limitation, a charge density model of crystalline urea was calculated using high-level quantum theory and was refined against publicly available ultra-high-resolution experimental Bragg data, including the effects of atomic displacement parameters. The resulting quantum crystallographic model was compared with models obtained using spherical atom or multipole methods. Despite using only the same number of free parameters as the spherical atom model, the agreement of the quantum model with the datamore » is comparable to the multipole model. The static, theoretical crystalline charge density of the quantum model is distinct from the multipole model, indicating the quantum model provides substantially new information. Hydrogen thermal ellipsoids in the quantum model were very similar to those obtained using neutron crystallography, indicating that quantum crystallography can increase the accuracy of the X-ray crystallographic atomic displacement parameters. Lastly, the results demonstrate the feasibility and benefits of integrating fully periodic quantum charge density calculations into ultra-high-resolution X-ray crystallographic model building and refinement.« less

  11. Quantum crystallographic charge density of urea

    PubMed Central

    Wall, Michael E.

    2016-01-01

    Standard X-ray crystallography methods use free-atom models to calculate mean unit-cell charge densities. Real molecules, however, have shared charge that is not captured accurately using free-atom models. To address this limitation, a charge density model of crystalline urea was calculated using high-level quantum theory and was refined against publicly available ultra-high-resolution experimental Bragg data, including the effects of atomic displacement parameters. The resulting quantum crystallographic model was compared with models obtained using spherical atom or multipole methods. Despite using only the same number of free parameters as the spherical atom model, the agreement of the quantum model with the data is comparable to the multipole model. The static, theoretical crystalline charge density of the quantum model is distinct from the multipole model, indicating the quantum model provides substantially new information. Hydrogen thermal ellipsoids in the quantum model were very similar to those obtained using neutron crystallography, indicating that quantum crystallography can increase the accuracy of the X-ray crystallographic atomic displacement parameters. The results demonstrate the feasibility and benefits of integrating fully periodic quantum charge density calculations into ultra-high-resolution X-ray crystallographic model building and refinement. PMID:27437111

  12. Quantum crystallographic charge density of urea.

    PubMed

    Wall, Michael E

    2016-07-01

    Standard X-ray crystallography methods use free-atom models to calculate mean unit-cell charge densities. Real molecules, however, have shared charge that is not captured accurately using free-atom models. To address this limitation, a charge density model of crystalline urea was calculated using high-level quantum theory and was refined against publicly available ultra-high-resolution experimental Bragg data, including the effects of atomic displacement parameters. The resulting quantum crystallographic model was compared with models obtained using spherical atom or multipole methods. Despite using only the same number of free parameters as the spherical atom model, the agreement of the quantum model with the data is comparable to the multipole model. The static, theoretical crystalline charge density of the quantum model is distinct from the multipole model, indicating the quantum model provides substantially new information. Hydrogen thermal ellipsoids in the quantum model were very similar to those obtained using neutron crystallography, indicating that quantum crystallography can increase the accuracy of the X-ray crystallographic atomic displacement parameters. The results demonstrate the feasibility and benefits of integrating fully periodic quantum charge density calculations into ultra-high-resolution X-ray crystallographic model building and refinement. PMID:27437111

  13. Quantum crystallographic charge density of urea.

    PubMed

    Wall, Michael E

    2016-07-01

    Standard X-ray crystallography methods use free-atom models to calculate mean unit-cell charge densities. Real molecules, however, have shared charge that is not captured accurately using free-atom models. To address this limitation, a charge density model of crystalline urea was calculated using high-level quantum theory and was refined against publicly available ultra-high-resolution experimental Bragg data, including the effects of atomic displacement parameters. The resulting quantum crystallographic model was compared with models obtained using spherical atom or multipole methods. Despite using only the same number of free parameters as the spherical atom model, the agreement of the quantum model with the data is comparable to the multipole model. The static, theoretical crystalline charge density of the quantum model is distinct from the multipole model, indicating the quantum model provides substantially new information. Hydrogen thermal ellipsoids in the quantum model were very similar to those obtained using neutron crystallography, indicating that quantum crystallography can increase the accuracy of the X-ray crystallographic atomic displacement parameters. The results demonstrate the feasibility and benefits of integrating fully periodic quantum charge density calculations into ultra-high-resolution X-ray crystallographic model building and refinement.

  14. On the extraction of interface trap density in the Pt/La2O3/Ge gate stack and the determination of the charge neutrality level in Ge

    NASA Astrophysics Data System (ADS)

    Bozyigit, D.; Rossel, C.

    2009-06-01

    The study of trap densities at the oxide-semiconductor interface of the new generation of field-effect transistors is essential for the optimization of their electrical performance. The conventional conductance method, which was efficiently applied to Si, turns out to be less appropriate on alternative substrates, such as the lower band gap germanium (Ge), because of the strong influence of minority carrier processes. Recent investigations show that these restrictions might be severe and lead to incorrect conclusions. We identify here the appearance of such processes, compare the conventional conductance method with the full conductance method of Martens et al., IEEE Electron Device Lett. 27, 405 (2006), and propose an extension of the latter. By applying a reverse bias to source and drain with respect to the substrate, it becomes possible to separate, on the same device, the contribution of electron and hole trap distributions. Our approach allows us to determine the position of the charge neutrality level at the surface of the semiconductor, which is found to be at 0.14 eV above the valence band.

  15. Doping-induced Charge-Density-Wave

    NASA Astrophysics Data System (ADS)

    Nomura, Atsushi; Yamaya, Kazuhiko; Takayanagi, Shigeru; Ichimura, Koichi; Matsuura, Toru; Tanda, Satoshi; Hokkaido University Team

    Doping is a useful method for searching new characters in solids, as we can see in the discoveries of impurity semiconductors and high-temperature superconductors. If a Charge-Density-Wave (CDW) is induced in materials which do not exhibit a CDW, new CDW properties might be brought there. TaSe3 exhibits no CDW transition but a superconductivity transition at about 2 K while it has a quasi-one-dimensional chain structure as well as typical CDW conductors, NbSe3, TaS3, and NbS3. Therefore, TaSe3 is one of the suitable materials for the induction of a CDW by doping, and we tried to induce a CDW in TaSe3 by doping Cu. Cu concentration was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The high Cu concentration was consistent with the high value of residual resistance (R (4 . 5 K) / (R (280 K) - R (4 . 5 K))). Single-crystal X-ray diffraction pattern (XRD) showed an expansion of the c-axis in Cu-doped TaSe3. The temperature dependence of the resistivity showed the anomaly at 80-100 K in Cu-doped TaSe3, which was never observed in pure TaSe3. These results suggest that the Cu-doping induces a CDW. We will discuss the relation between the resistivity anomaly and superconductivity.

  16. Alternative route to charge density wave formation in multiband systems.

    PubMed

    Eiter, Hans-Martin; Lavagnini, Michela; Hackl, Rudi; Nowadnick, Elizabeth A; Kemper, Alexander F; Devereaux, Thomas P; Chu, Jiun-Haw; Analytis, James G; Fisher, Ian R; Degiorgi, Leonardo

    2013-01-01

    Charge and spin density waves, periodic modulations of the electron, and magnetization densities, respectively, are among the most abundant and nontrivial low-temperature ordered phases in condensed matter. The ordering direction is widely believed to result from the Fermi surface topology. However, several recent studies indicate that this common view needs to be supplemented. Here, we show how an enhanced electron-lattice interaction can contribute to or even determine the selection of the ordering vector in the model charge density wave system ErTe(3). Our joint experimental and theoretical study allows us to establish a relation between the selection rules of the electronic light scattering spectra and the enhanced electron-phonon coupling in the vicinity of band degeneracy points. This alternative proposal for charge density wave formation may be of general relevance for driving phase transitions into other broken-symmetry ground states, particularly in multiband systems, such as the iron-based superconductors.

  17. Do plasma proteins distinguish between liposomes of varying charge density?

    PubMed

    Capriotti, Anna Laura; Caracciolo, Giulio; Cavaliere, Chiara; Foglia, Patrizia; Pozzi, Daniela; Samperi, Roberto; Laganà, Aldo

    2012-03-16

    Cationic liposomes (CLs) are one of the most employed nonviral nanovector systems in gene therapy. However, their transfection efficiency is strongly affected by interactions with plasma components, that lead to the formation of a "protein corona" onto CL surface. The interactions between nanoparticles entering the body and biomolecules have an essential role for their biodistribution. Because the knowledge of proteins adsorbed onto vector surface could be useful in the screening of new, more efficient and more biocompatible liposomal formulations, the behavior of three CLs with different membrane charge densities was investigated. The proteins of the three coronas were identified by nano-liquid chromatography-tandem mass spectrometry, and quantified with label-free spectral counting strategy. Fibrinogen displayed higher association with CLs with high membrane charge density, while apolipoproteins and C4b-binding protein with CLs with low membrane charge density. These results are discussed in terms of the different lipid compositions of CLs and may have a deep biological impact for in vivo applications. Surface charge of nanoparticles is emerging as a relevant factor determining the corona composition after interaction with plasma proteins. Remarkably, it is also shown that the charge of the protein corona formed around CLs is strongly related to their membrane charge density.

  18. Contributions of charge-density research to medicinal chemistry

    PubMed Central

    Dittrich, Birger; Matta, Chérif F.

    2014-01-01

    This article reviews efforts in accurate experimental charge-density studies with relevance to medicinal chemistry. Initially, classical charge-density studies that measure electron density distribution via least-squares refinement of aspherical-atom population parameters are summarized. Next, interaction density is discussed as an idealized situation resembling drug–receptor interactions. Scattering-factor databases play an increasing role in charge-density research, and they can be applied both to small-molecule and macromolecular structures in refinement and analysis; software development facilitates their use. Therefore combining both of these complementary branches of X-ray crystallography is recommended, and examples are given where such a combination already proved useful. On the side of the experiment, new pixel detectors are allowing rapid measurements, thereby enabling both high-throughput small-molecule studies and macromolecular structure determination to higher resolutions. Currently, the most ambitious studies compute intermolecular interaction energies of drug–receptor complexes, and it is recommended that future studies benefit from recent method developments. Selected new developments in theoretical charge-density studies are discussed with emphasis on its symbiotic relation to crystallography. PMID:25485126

  19. Transverse charge densities of N* resonances

    SciTech Connect

    Tiator, L.; Vanderhaeghen, M.

    2011-10-24

    The unitary isobar model MAID2007 has been used to analyze the recent data of pion electroproduction. The model contains all four-star resonances in the region below W = 2 GeV. Both single-Q{sup 2} and Q{sup 2} dependent transition form factors could be obtained for the Delta, Roper, D{sub 13}(1520), S{sub 11}(1535), D{sub 15}(1675), and F{sub 15}(1680) nucleon resonances. Furthermore, we show the empirical transverse charge densities for the Roper, the S11 and D13 resonances, which are evaluated from Fourier transforms of the transition form factors.

  20. Determination of colloidal particle surface charge from dielectrophoresis

    NASA Astrophysics Data System (ADS)

    Chavez, Marko; Nuansri, Rittirong; Mazza, Jacob; Ou-Yang, H. Daniel

    2015-03-01

    Electrophoresis (EP) is used to determine colloidal particle surface charge. However, when the Debye length is comparable to or larger than the particle size, electrophoresis cannot be reliably used to determine the surface charge due to counter ion retardation flow. Alexander et al. developed a theory relating colloidal osmotic pressure and particle surface charge. We use dielectrophoresis (DEP) to obtain a potential landscape based on the number density distribution of the particles in a non-uniform AC electric field. We determine the osmotic pressure from the DEP force and density profiles using Einstein's osmotic equilibrium equation. Surface charge obtained by DEP (thermodynamics) will be compared to that obtained by EP (electrokinetics).

  1. SOP - Determination of Requirement Density

    SciTech Connect

    Reynolds, John G.; Martz, Jr., Harry E.

    2010-10-26

    The purpose of this Standard Operating Procedure (SOP) is to give guidelines on how to determine the density of a sample that will be used as the requirement density. This will be the requirement density of record for the specimens examined by Micro CT and EDS measurements. This density will then be set as the formulation requirement for radiography measurements. This SOP is referred to in TP 48— Preparation of Hydrogen Peroxide/Icing Sugar Specimens for X-ray Measurements by J. G. Reynolds and H. E. Martz.

  2. Pion transverse charge density from timelike form factor data

    SciTech Connect

    Gerald Miller, Mark Strikman, Christian Weiss

    2011-01-01

    The transverse charge density in the pion can be represented as a dispersion integral of the imaginary part of the pion form factor in the timelike region. This formulation incorporates information from e+e- annihilation experiments and allows one to reconstruct the transverse density much more accurately than from the spacelike pion form factor data alone. We calculate the transverse density using an empirical parametrization of the timelike pion form factor and estimate that it is determined to an accuracy of ~10% at a distance b ~ 0.1 fm, and significantly better at larger distances. The density is found to be close to that obtained from a zero-width rho meson pole over a wide range and shows a pronounced rise at small distances. The resulting two-dimensional image of the fast-moving pion can be interpreted in terms of its partonic structure in QCD. We argue that the singular behavior of the charge density at the center requires a substantial presence of pointlike configurations in the pion's partonic wave function, which can be probed in other high-momentum transfer processes.

  3. The diamagnetic charge-density wave

    NASA Astrophysics Data System (ADS)

    Harrison, Neil; Mielke, Charles H.; Balicas, Luis; Brooks, James S.; Tokumoto, M.

    2001-03-01

    Organic charge-transfer salts of the form α-(BEDT-TTF)_2MHg(SCN)4 (with M= K or Tl) possess exotic charge-density wave (CDW) ground states. The low transition temperature T_p ~ 8 K implies that the low temperature ground state is characterized by an order parameter (Δ ~ 2 meV) that is exceptionally small for a CDW, making it especially vulnerable both to magnetic fields and to oscillatory chemical potentials. Notably, this is probably the only CDW system for which the Pauli paramagnetic limit (B_P ~ 23 T) is accessed in DC magnetic fields. Above this field, theory predicts a new CDWx phase that is expected to be a modulated CDW phase for which the Q vector continually shifts with B or a CDW-SDW hybrid phase. A high magnetic field phase that is thermodynamically consistent with the theory is observed experimentally, but does not resemble a CDW (or a spin-density wave (SDW) for that matter) in any way. One of the first unusual effects that was observed is the apparent induction of currents in pulsed magnetic fields. These have since been confirmed to be real currents by measurement of their AC susceptibility in DC magnetic fields. They have also been observed in strictly DC magnetic fields by means of magnetic torque. This means that the currents are persistent. These currents exhibit hysteretic magnetic phenomena (i.e. a Bean model-like critical state) closely resembling that of extreme type II superconductors. While the time-, temperature- and field-dependence of the currents is sensitive to the location of the chemical potential with respect to the Landau levels of the 2D Fermi surface pocket (that happens to survive the CDW order), they do occur at all fields above 23 T, irrespective of the Landau level filling factor. This rules out the involvement of the QHE. Furthermore, the resistivity is observed to drop abruptly below 2-3 K for constant magnetic fields above 23 T, particularly at integral Landau level filling factors, where the resistivity drops by as

  4. Charge Density Quantification of Polyelectrolyte Polysaccharides by Conductometric Titration: An Analytical Chemistry Experiment

    ERIC Educational Resources Information Center

    Farris, Stefano; Mora, Luigi; Capretti, Giorgio; Piergiovanni, Luciano

    2012-01-01

    An easy analytical method for determination of the charge density of polyelectrolytes, including polysaccharides and other biopolymers, is presented. The basic principles of conductometric titration, which is used in the pulp and paper industry as well as in colloid and interface science, were adapted to quantify the charge densities of a…

  5. Plasma digital density determining device

    DOEpatents

    Sprott, Julien C.; Lovell, Thomas W.; Holly, Donald J.

    1976-01-01

    The density of a decaying plasma in an electrically conducting enclosure is determined by applying an excitation to the cavity formed by the enclosure and counting digitally the number of resonant frequencies traversed by the combination of the cavity and the decaying plasma.

  6. Electron (charge) density studies of cellulose models

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Introductory material first describes electron density approaches and demonstrates visualization of electron lone pairs and bonding as concentrations of electron density. Then it focuses on the application of Bader’s Quantum Theory of Atoms-in-Molecules (AIM) to cellulose models. The purpose of the ...

  7. Surface-charge-density relaxation of Ni(113)

    SciTech Connect

    Rieder, K.H.; Baumberger, M.; Stocker, W.

    1985-07-22

    Symmetric in-plane and extremely asymmetric out-of-plane Ne-diffraction rainbows obtained from Ni(113) along (332) show that the close-packed (111) facets are more strongly corrugated than the more open (100) ones, in surprising contrast to expectation. Surface-charge-density calculations with overlapping atomic densities indicate that surface bonding causes appreciable electronic charge flow from the (111) to the (100) facets, filling up the fourfold hollows completely.

  8. Spacecraft dielectric surface charging property determination

    NASA Technical Reports Server (NTRS)

    Williamson, W. S.

    1987-01-01

    The charging properties of 127 micron thick polyimide, (a commonly used spacecraft dielectric material) was measured under conditions of irradiation by a low-current-density electron beam with energy between 2 and 14 keV. The observed charging characteristics were consistent with predictions of the NASCAP computer model. The use of low electron current density results in a nonlinearity in the sample-potential versus beam-energy characteristic which is attributed to conduction leakage through the sample. Microdischarges were present at relatively low beam energies.

  9. Charge and spin fluctuations in the density functional theory

    SciTech Connect

    Gyoerffy, B.L.; Barbieri, A. . H.H. Wills Physics Lab.); Staunton, J.B. . Dept. of Physics); Shelton, W.A.; Stocks, G.M. )

    1990-01-01

    We introduce a conceptual framework which allow us to treat charge and spin fluctuations about the Local density Approximation (LDA) to the Density Functional Theory (DFT). We illustrate the approach by explicit study of the Disordered Local Moment (DLM) state in Fe above the Curie Temperature {Tc} and the Mott insulating state in MnO. 27 refs., 6 figs.

  10. Pion transverse charge density and the edge of hadrons

    NASA Astrophysics Data System (ADS)

    Carmignotto, Marco; Horn, Tanja; Miller, Gerald A.

    2014-08-01

    We use the world data on the pion form factor for space-like kinematics and a technique previously used to extract the proton transverse densities to extract the transverse pion charge density and its uncertainty due the incomplete knowledge of the pion form factor at large values of Q2 and the experimental uncertainties. The pion charge density at small values of impact parameter b < 0.1 fm is dominated by this incompleteness error while the range between 0.1-0.3 fm is relatively well constrained. A comparison of pion and proton transverse charge densities shows that the pion is denser than the proton for values of b <0.2fm. The pion and proton transverse charge densities seem to be the same for values of b =0.3-0.6 fm. Future data from Thomas Jefferson National Accelerator Facility (JLab) 12 GeV and the Electron-Ion Collider (EIC) will increase the dynamic extent of the form factor data to higher values of Q2 and thus reduce the uncertainties in the extracted pion transverse charge density.

  11. Mining for elastic constants of intermetallics from the charge density landscape

    NASA Astrophysics Data System (ADS)

    Kong, Chang Sun; Broderick, Scott R.; Jones, Travis E.; Loyola, Claudia; Eberhart, Mark E.; Rajan, Krishna

    2015-02-01

    There is a significant challenge in designing new materials for targeted properties based on their electronic structure. While in principle this goal can be met using knowledge of the electron charge density, the relationships between the density and properties are largely unknown. To help overcome this problem we develop a quantitative structure-property relationship (QSPR) between the charge density and the elastic constants for B2 intermetallics. Using a combination of informatics techniques for screening all the potentially relevant charge density descriptors, we find that C11 and C44 are determined solely from the magnitude of the charge density at its critical points, while C12 is determined by the shape of the charge density at its critical points. From this reduced charge density selection space, we develop models for predicting the elastic constants of an expanded number of intermetallic systems, which we then use to predict the mechanical stability of new systems. Having reduced the descriptors necessary for modeling elastic constants, statistical learning approaches may then be used to predict the reduced knowledge-based required as a function of the constituent characteristics.

  12. Current, charge, and capacitance during scanning probe oxidation of silicon. I. Maximum charge density and lateral diffusion

    NASA Astrophysics Data System (ADS)

    Dagata, J. A.; Perez-Murano, F.; Martin, C.; Kuramochi, H.; Yokoyama, H.

    2004-08-01

    A comprehensive analysis of the electrical current passing through the tip-substrate junction during oxidation of silicon by scanning probe microscopy (SPM) is presented. This analysis of experimental results under dc-bias conditions resolves the role of electronic and ionic contributions, especially for the initial stages of the reaction, determines the effective contact area of the tip-substrate junction, and unifies the roles of space charge and meniscus formation. In Part I of this work, we demonstrate that SPM oxidation is governed by a maximum charge density generated by electronic species within the junction at the onset of the oxidation process. Excess charge is channeled into lateral diffusion, keeping the charge density within the reaction zone constant and reducing the aspect ratio of the resulting oxide features. A uniform charge density implies that SPM oxides contain a fixed defect concentration, in accordance with the space-charge model. The effective (electrical) thickness of SPM oxides determined by these defects is investigated by Fowler-Nordheim analysis. We conclude that most of the electrical current involved in high voltage SPM oxidation of Si does not actually induce surface oxide growth, and that lateral diffusion and small aspect ratios are unavoidable aspects of contact-mode conditions.

  13. Effect of dilute strongly pinning impurities on charge density waves

    NASA Astrophysics Data System (ADS)

    Okamoto, Jun-ichi; Millis, Andrew J.

    2015-05-01

    We study theoretically the effects of strong pinning centers on a charge density wave in the limit that the charge density wave coherence length is shorter than the average interimpurity distance. An analysis based on a Ginzburg-Landau model shows that long-range forces arising from the elastic response of the charge density wave induce a kind of collective pinning which suppresses impurity-induced phase fluctuations, leading to a long-range ordered ground state. The correlations induced by impurities are characterized by a length scale parametrically longer than the average interimpurity distance. Long-wavelength fluctuations are found to be gapped, implying the stability of the ground state. We also present Monte Carlo simulations that confirm the basic features of the analytical results.

  14. Pion transverse charge density and the edge of hadrons

    SciTech Connect

    Carmignotto, Marco; Horn, Tanja; Miller, Gerald A.

    2014-08-01

    We use the world data on the pion form factor for space-like kinematics and a technique used to extract the proton transverse densities, to extract the transverse pion charge density and its uncertainty due to experimental uncertainties and incomplete knowledge of the pion form factor at large values of Q2. The pion charge density at small values of b<0.1 fm is dominated by this incompleteness error while the range between 0.1-0.3 fm is relatively well constrained. A comparison of pion and proton charge densities shows that the pion is denser than the proton for values of b<0.2 fm. The pion and proton distributions seem to be the same for values of b=0.2-0.6 fm. Future data from Jlab 12 GeV and the EIC will increase the dynamic extent of the data to higher values of Q2 and thus reduce the uncertainties in the extracted pion charge density.

  15. Realizing vector meson dominance with transverse charge densities

    SciTech Connect

    Gerald Miller, Mark Strikman, Christian Weiss

    2011-10-01

    The transverse charge density in a fast-moving nucleon is represented as a dispersion integral of the imaginary part of the Dirac form factor in the timelike region (spectral function). At a given transverse distance b the integration effectively extends over energies in a range {radical}t {approx}< 1/b, with exponential suppression of larger values. The transverse charge density at peripheral distances thus acts as a low-pass filter for the spectral function and allows one to select energy regions dominated by specific t-channel states, corresponding to definite exchange mechanisms in the spacelike form factor. We show that distances b {approx} 0.5 - 1.5 fm in the isovector density are maximally sensitive to the {rho} meson region, with only a {approx}10% contribution from higher-mass states. Soft-pion exchange governed by chiral dynamics becomes relevant only at larger distances. In the isoscalar density higher-mass states beyond the {omega} are comparatively more important. The dispersion approach suggests that the positive transverse charge density in the neutron at b {approx} 1 fm, found previously in a Fourier analysis of spacelike form factor data, could serve as a sensitive test of the isoscalar strength in the {approx}1 GeV mass region. In terms of partonic structure, the transverse densities in the vector meson region b {approx} 1 fm support an approximate mean-field picture of the motion of valence quarks in the nucleon.

  16. An Analytical Planning Model to Estimate the Optimal Density of Charging Stations for Electric Vehicles.

    PubMed

    Ahn, Yongjun; Yeo, Hwasoo

    2015-01-01

    The charging infrastructure location problem is becoming more significant due to the extensive adoption of electric vehicles. Efficient charging station planning can solve deeply rooted problems, such as driving-range anxiety and the stagnation of new electric vehicle consumers. In the initial stage of introducing electric vehicles, the allocation of charging stations is difficult to determine due to the uncertainty of candidate sites and unidentified charging demands, which are determined by diverse variables. This paper introduces the Estimating the Required Density of EV Charging (ERDEC) stations model, which is an analytical approach to estimating the optimal density of charging stations for certain urban areas, which are subsequently aggregated to city level planning. The optimal charging station's density is derived to minimize the total cost. A numerical study is conducted to obtain the correlations among the various parameters in the proposed model, such as regional parameters, technological parameters and coefficient factors. To investigate the effect of technological advances, the corresponding changes in the optimal density and total cost are also examined by various combinations of technological parameters. Daejeon city in South Korea is selected for the case study to examine the applicability of the model to real-world problems. With real taxi trajectory data, the optimal density map of charging stations is generated. These results can provide the optimal number of chargers for driving without driving-range anxiety. In the initial planning phase of installing charging infrastructure, the proposed model can be applied to a relatively extensive area to encourage the usage of electric vehicles, especially areas that lack information, such as exact candidate sites for charging stations and other data related with electric vehicles. The methods and results of this paper can serve as a planning guideline to facilitate the extensive adoption of electric

  17. An Analytical Planning Model to Estimate the Optimal Density of Charging Stations for Electric Vehicles

    PubMed Central

    Ahn, Yongjun; Yeo, Hwasoo

    2015-01-01

    The charging infrastructure location problem is becoming more significant due to the extensive adoption of electric vehicles. Efficient charging station planning can solve deeply rooted problems, such as driving-range anxiety and the stagnation of new electric vehicle consumers. In the initial stage of introducing electric vehicles, the allocation of charging stations is difficult to determine due to the uncertainty of candidate sites and unidentified charging demands, which are determined by diverse variables. This paper introduces the Estimating the Required Density of EV Charging (ERDEC) stations model, which is an analytical approach to estimating the optimal density of charging stations for certain urban areas, which are subsequently aggregated to city level planning. The optimal charging station’s density is derived to minimize the total cost. A numerical study is conducted to obtain the correlations among the various parameters in the proposed model, such as regional parameters, technological parameters and coefficient factors. To investigate the effect of technological advances, the corresponding changes in the optimal density and total cost are also examined by various combinations of technological parameters. Daejeon city in South Korea is selected for the case study to examine the applicability of the model to real-world problems. With real taxi trajectory data, the optimal density map of charging stations is generated. These results can provide the optimal number of chargers for driving without driving-range anxiety. In the initial planning phase of installing charging infrastructure, the proposed model can be applied to a relatively extensive area to encourage the usage of electric vehicles, especially areas that lack information, such as exact candidate sites for charging stations and other data related with electric vehicles. The methods and results of this paper can serve as a planning guideline to facilitate the extensive adoption of electric

  18. An Analytical Planning Model to Estimate the Optimal Density of Charging Stations for Electric Vehicles.

    PubMed

    Ahn, Yongjun; Yeo, Hwasoo

    2015-01-01

    The charging infrastructure location problem is becoming more significant due to the extensive adoption of electric vehicles. Efficient charging station planning can solve deeply rooted problems, such as driving-range anxiety and the stagnation of new electric vehicle consumers. In the initial stage of introducing electric vehicles, the allocation of charging stations is difficult to determine due to the uncertainty of candidate sites and unidentified charging demands, which are determined by diverse variables. This paper introduces the Estimating the Required Density of EV Charging (ERDEC) stations model, which is an analytical approach to estimating the optimal density of charging stations for certain urban areas, which are subsequently aggregated to city level planning. The optimal charging station's density is derived to minimize the total cost. A numerical study is conducted to obtain the correlations among the various parameters in the proposed model, such as regional parameters, technological parameters and coefficient factors. To investigate the effect of technological advances, the corresponding changes in the optimal density and total cost are also examined by various combinations of technological parameters. Daejeon city in South Korea is selected for the case study to examine the applicability of the model to real-world problems. With real taxi trajectory data, the optimal density map of charging stations is generated. These results can provide the optimal number of chargers for driving without driving-range anxiety. In the initial planning phase of installing charging infrastructure, the proposed model can be applied to a relatively extensive area to encourage the usage of electric vehicles, especially areas that lack information, such as exact candidate sites for charging stations and other data related with electric vehicles. The methods and results of this paper can serve as a planning guideline to facilitate the extensive adoption of electric

  19. Charge density stabilised local electron spin pair states in insulating polymers

    SciTech Connect

    Serra, S.; Dissado, L. A.

    2014-12-14

    A model is presented that addresses the energy stability of localized electron states in insulating polymers with respect to delocalized free electron-like states at variable charge densities. The model was derived using an effective Hamiltonian for the total energy of electrons trapped in large polarons and spin-paired bipolarons, which includes the electrostatic interaction between charges that occurs when the charge density exceeds the infinite dilution limit. The phase diagram of the various electronic states with respect to the charge density is derived using parameters determined from experimental data for polyethylene, and it is found that a phase transition from excess charge in the form of stable polarons to a stable state of bipolarons with charge = 2 and spin number S = 0 is predicted for a charge density between 0.2 C/m{sup 3} and ∼2 C/m{sup 3}. This transition is consistent with a change from low mobility charge transport to charge transport in the form of pulses with a mobility orders of magnitude higher that has been observed in several insulating polymers.

  20. Mapping surface charge density with a scanning nanopipette

    NASA Astrophysics Data System (ADS)

    Klausen, Lasse Hyldgaard; Fuhs, Thomas; Besenbacher, Flemming; Dong, Mingdong

    2015-03-01

    Characterisation of the surface charge density (SCD) is important in interface and colloid science, and especially local variations in SCD of biological samples are of keen interest. The surface charge of lipid bilayers governs the uptake of charged particles and guides cell-cell interactions. As the electrostatic potential is screened by high physiological salt concentrations, direct probing of the potential can only be performed at a sub nanometer distance; therefore it was impossible to directly measure the SCD under physiological conditions. Yet the charged surface attracts counter ions leading to an enhanced ionic concentration near the surface, creating a measurable surface conductivity. In this study we measure SCD using a scanning ion-conductance microscope (SICM) setup, where the electrolyte current through a nanopipette is monitored as the pipette is positioned in the vicinity of the sample. We investigate the current dependency of SCD and pipette potential using numerical solutions to Poisson and Nernst-Planck equations and characterise a complex system governed by a multitude of factors such as pipette size, geometry and charge. We then propose an imaging method and prove its feasibility by mapping the surface charge density of phase separated lipid bilayers.

  1. Pressure induced Superconductivity in the Charge Density Wave Compound Tritelluride

    SciTech Connect

    Hamlin, J.J.; Zocco, D.A.; Sayles, T.A.; Maple, M.B.; Chu, J.-H.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2010-02-15

    A series of high-pressure electrical resistivity measurements on single crystals of TbTe{sub 3} reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge density wave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near {approx} 12.4 GPa.

  2. Modelling charge transfer reactions with the frozen density embedding formalism

    SciTech Connect

    Pavanello, Michele; Neugebauer, Johannes

    2011-12-21

    The frozen density embedding (FDE) subsystem formulation of density-functional theory is a useful tool for studying charge transfer reactions. In this work charge-localized, diabatic states are generated directly with FDE and used to calculate electronic couplings of hole transfer reactions in two {pi}-stacked nucleobase dimers of B-DNA: 5{sup '}-GG-3{sup '} and 5{sup '}-GT-3{sup '}. The calculations rely on two assumptions: the two-state model, and a small differential overlap between donor and acceptor subsystem densities. The resulting electronic couplings agree well with benchmark values for those exchange-correlation functionals that contain a high percentage of exact exchange. Instead, when semilocal GGA functionals are used the electronic couplings are grossly overestimated.

  3. Transverse charge and magnetization densities in the nucleon's chiral periphery

    SciTech Connect

    Granados, Carlos G.; Weiss, Christian

    2014-01-01

    In the light-front description of nucleon structure the electromagnetic form factors are expressed in terms of frame-independent transverse densities of charge and magnetization. Recent work has studied the transverse densities at peripheral distances b = O(M{pi}{sup -1}), where they are governed by universal chiral dynamics and can be computed in a model-independent manner. Of particular interest is the comparison of the peripheral charge and magnetization densities. We summarize (a) their interpretation as spin-independent and -dependent current matrix elements; (b) the leading-order chiral effective field theory results; (c) their mechanical interpretation in the light-front formulation; (d) the large-N_c limit of QCD and the role of {Delta} intermediate states; (e) the connection with generalized parton distributions and peripheral high-energy scattering processes.

  4. Transverse Charge and Magnetization Densities in the Nucleon's Chiral Periphery

    NASA Astrophysics Data System (ADS)

    Granados, C.; Weiss, C.

    2014-01-01

    In the light-front description of nucleon structure the electromagnetic form factors are expressed in terms of frame-independent transverse densities of charge and magnetization. Recent work has studied the transverse densities at peripheral distances $b = O(M_{\\pi}^{-1}), where they are governed by universal chiral dynamics and can be computed in a model-independent manner. Of particular interest is the comparison of the peripheral charge and magnetization densities. We summarize (a) their interpretation as spin-independent and -dependent current matrix elements; (b) the leading-order chiral effective field theory results; (c) their mechanical interpretation in the light-front formulation; (d) the large-Nc limit of QCD and the role of Δ intermediate states; (e) the connection with generalized parton distributions and peripheral high-energy scattering processes.

  5. Reactivity of biogenic silica: Surface versus bulk charge density

    NASA Astrophysics Data System (ADS)

    Loucaides, Socratis; Behrends, Thilo; Van Cappellen, Philippe

    2010-01-01

    Acid-base titrations were carried out at three different ionic strengths (0.01, 0.1 and 0.7 M NaCl) on a range of marine and continental biosiliceous materials. The large variability in electrical charging behavior of the various materials is consistent with the existence of two pools of ionizable groups, one on the outer surface of and the other within the silica particles. The relative amounts of internal and external silanols were estimated by fitting a two-site complexation model to excess proton versus pH curves obtained at the different ionic strengths. For fresh diatom frustules and phytoliths, as well as recently deposited biosiliceous sediments, the abundance of internal silanols was of the same order of magnitude as, or exceeded, that of silanols on the external surface. Older biosiliceous materials exhibited lower proportions of internal groups, while a decrease in the relative amount of internal silanols was also observed for diatom frustules artificially aged in seawater. The existence of internal ionizable functional groups explains measured charge densities of biogenic silicas that largely exceed the theoretical site density of silica surfaces. Variations in the relative abundance of internal versus surface silanols further explain the non-uniform dependence of electrical charging on ionic strength, the lack of correlation between total charge density and dissolution kinetics, and the variable 950 cm -1 peak intensity in the infrared spectra of biogenic silicas. Dissolution rates correlate positively with the external charge, rather than the total charge build-up, as expected if dissolution only involves the removal of silicate units from the external surfaces of the particles. The progressive reduction with time of the internal to external silanol concentration ratio represents one of the mechanisms altering the material properties that affect the recycling and preservation of biogenic silica in earth surface environments.

  6. Battery peak charge voltage monitor for dual air density satellite

    NASA Technical Reports Server (NTRS)

    Shull, T. A.

    1975-01-01

    A battery peak charge voltage monitor was developed for use on the dual air density satellite (DADS). This device retains a reading of the maximum voltage reached by the spacecraft battery during periods of charging, and makes it available during periods of data transmission. The monitor is connected across the battery and operates solely from the battery; it is powered continuously with quiescent input current of only 3 milliamperes. Standard integrated circuits and a thin-film resistor network are utilized. The monitor occupies approximately 40 square centimeters of a printed-circuit board within a larger electronic package.

  7. Magnetic catalysis and axionic charge density wave in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Roy, Bitan; Sau, Jay D.

    2015-09-01

    Three-dimensional Weyl and Dirac semimetals can support a chiral-symmetry-breaking, fully gapped, charge-density-wave order even for sufficiently weak repulsive electron-electron interactions, when placed in strong magnetic fields. In the former systems, due to the natural momentum space separation of Weyl nodes the ordered phase lacks the translational symmetry and represents an axionic phase of matter, while that in a Dirac semimetal (neglecting the Zeeman coupling) is only a trivial insulator. We present the scaling of this spectral gap for a wide range of subcritical (weak) interactions as well as that of the diamagnetic susceptibility with the magnetic field. A similar mechanism for charge-density-wave ordering at weak coupling is shown to be operative in double- and triple-Weyl semimetals, where the dispersion is linear (quadratic and cubic, respectively) for the z (planar) component(s) of the momentum. We here also address the competition between the charge-density-wave and a spin-density-wave orders, both of which breaks the chiral symmetry and leads to gapped spectrum, and show that at least in the weak coupling regime the former is energetically favored. The anomalous surface Hall conductivity, role of topological defects such as axion strings, existence of one-dimensional gapless dispersive modes along the core of such defects, and anomaly cancellation through the Callan-Harvey mechanism are discussed.

  8. Determination of experimental charge density in model nickel macrocycle: [3,11-bis(methoxycarbonyl)-1,5,9,13-tetraazacyclohexadeca-1,3,9,11-tetraenato-(2-)-kappa(4)N]nickel(II).

    PubMed

    Domagała, Sławomir; Korybut-Daszkiewicz, Bohdan; Straver, Leo; Woźniak, Krzysztof

    2009-05-01

    Experimental and theoretical atomic charges and d-orbital populations were obtained for [3,11-bis(methoxycarbonyl)-1,5,9,13-tetraazacyclohexadeca-1,3,9,11-tetraenato(2-)-kappa(4)N]nickel(II) monocrystal (16Ni) using the Hansen and Coppens formalism. Several models of this structure were tested as a function of quality of the fit, convergence of the refinement, value of residual peaks and holes, and Hirshfeld's rigid-bond test. The models with Ni-atomic scattering factors applied for the metal center are significantly better than those with the Ni-ionic scattering factors. The properties of the final electron density distributions are very consistent and similar for all of the models tested. The values of the d-orbital populations for Ni roughly agree with the occupation order of the d-electron levels for square-planar complexes derived from crystal field theory and are comparable with those obtained by the natural population analysis method. Experimental atoms-in-molecules charges calculated for four different models agree quite well for models with different symmetry restrictions and the same scattering factor for the Ni. Both experimental and theoretical methods predict relatively high negative values of charges for the nitrogen and oxygen atoms and also a quite high positive charge for the C(7) atom. The values of rho(r(BCP)) for the Ni-N bonds are in the range from 0.60 up to 0.75e A(-3), with positive laplacian values indicating noncovalent bonding. For the laplacian of the electron density evaluated in the plane of the macrocyclic ring, a typical map for a square-planar complex was obtained with four charge concentrations--3d(xy) orbitals--pointing toward the regions between the M-N bonds and charge depletions directed toward the (3,-1) critical points of the negative laplacian for the nitrogen atoms. PMID:19354267

  9. Fast electronic resistance switching involving hidden charge density wave states

    NASA Astrophysics Data System (ADS)

    Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.

    2016-05-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states.

  10. Fast electronic resistance switching involving hidden charge density wave states

    PubMed Central

    Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.

    2016-01-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T–TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483

  11. Comparison of density determination of liquid samples by density meters

    NASA Astrophysics Data System (ADS)

    Buchner, C.; Wolf, H.; Vámossy, C.; Lorefice, S.; Lenard, E.; Spohr, I.; Mares, G.; Perkin, M.; Parlic-Risovic, T.; Grue, L.-L.; Tammik, K.; van Andel, I.; Zelenka, Z.

    2016-01-01

    Hydrostatic density determinations of liquids as reference material are mainly performed by National Metrology Institutes to provide means for calibrating or checking liquid density measuring instruments such as oscillation-type density meters. These density meters are used by most of the metrology institutes for their calibration and scientific work. The aim of this project was to compare the results of the liquid density determination by oscillating density meters of the participating laboratories. The results were linked to CCM.D.K-2 partly via Project EURAMET.M.D.K-2 (1019) "Comparison of liquid density standards" by hydrostatic weighing piloted by BEV in 2008. In this comparison pentadecane, water and of oil with a high viscosity were measured at atmospheric pressure using oscillation type density meter. The temperature range was from 15 °C to 40 °C. The measurement results were in some cases discrepant. Further studies, comparisons are essential to explore the capability and uncertainty of the density meters Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  12. Study of the Charge Density Control Method Including the Space Charge Effect in the Proton Synchrotron

    NASA Astrophysics Data System (ADS)

    Kato, Shinichi; Harada, Hiroyuki; Hotchi, Hideaki; Okabe, Kota; Yamamoto, Kazami; Kinsho, Michikazu

    For high intensity proton accelerators, one of the beam loss sources is the incoherent tune spread caused by the space charge force. In the 3 GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex, beams are injected sequentially and shifted slightly from the central orbit in order to increase the beam size intentionally and suppress the charge density and incoherent tune spread. This injection method has been adopted and suppressed the beam loss. However, simulations clarified that beams did not spread as much as expected because of the space charge effect in the high current case. As simulation results of the optimized beam shift pattern when the space charge effect is considered, it was obtained that the incoherent tune spread could be suppressed to an extent that has not been achieved previously.

  13. Coupled commensurate charge density wave and lattice distortion in Na2Ti2P n2O (P n =As ,Sb ) determined by x-ray diffraction and angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Davies, N. R.; Johnson, R. D.; Princep, A. J.; Gannon, L. A.; Ma, J.-Z.; Qian, T.; Richard, P.; Li, H.; Shi, M.; Nowell, H.; Baker, P. J.; Shi, Y. G.; Ding, H.; Luo, J.; Guo, Y. F.; Boothroyd, A. T.

    2016-09-01

    We report single-crystal x-ray-diffraction measurements on Na2Ti2P n2O (P n =As ,Sb ) which reveal a charge superstructure that appears below the density wave transitions previously observed in bulk data. From symmetry-constrained structure refinements we establish that the associated distortion mode can be described by two propagation vectors q1=(1 /2 ,0 ,l ) and q2=(0 ,1 /2 ,l ) with l =0 (Sb) or l =1 /2 (As) and primarily involves in-plane displacements of the Ti atoms perpendicular to the Ti-O bonds. We also present angle-resolved photoemission spectroscopy measurements, which show band folding and backbending consistent with a density wave with the same wave-vectors q1 and q2 associated with Fermi-surface nesting, and muon-spin relaxation data, which show no indication of spin density wave order. The results provide direct evidence for phonon-assisted charge density wave order in Na2Ti2P n2O and fully characterize a proximate ordered phase that could compete with superconductivity in doped BaTi2Sb2O .

  14. 42 CFR 405.503 - Determining customary charges.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... charges for charity patients and substandard charges for welfare and other low income patients are to be... to determine the customary charge on the basis of reliable statistical data (for example, because...

  15. 42 CFR 405.503 - Determining customary charges.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... charges for charity patients and substandard charges for welfare and other low income patients are to be... to determine the customary charge on the basis of reliable statistical data (for example, because...

  16. 42 CFR 405.503 - Determining customary charges.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... charges for charity patients and substandard charges for welfare and other low income patients are to be... to determine the customary charge on the basis of reliable statistical data (for example, because...

  17. 42 CFR 405.503 - Determining customary charges.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... charges for charity patients and substandard charges for welfare and other low income patients are to be... to determine the customary charge on the basis of reliable statistical data (for example, because...

  18. 42 CFR 405.503 - Determining customary charges.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... charges for charity patients and substandard charges for welfare and other low income patients are to be... to determine the customary charge on the basis of reliable statistical data (for example, because...

  19. Experimental charge density of sucrose at 20K: bond topological, atomic, and intermolecular quantitative properties.

    PubMed

    Jaradat, Da'san M M; Mebs, Stefan; Checińska, Lilianna; Luger, Peter

    2007-08-13

    The charge density of sucrose was determined from a high-resolution X-ray data set measured at 20K. The density distribution so obtained was analyzed quantitatively by application of Bader's atoms in molecules (AIM) formalism, and a comparison was made with corresponding results from a B3LYP (6-311++G(3df,3pd)) calculation at the experimental geometry. Bond topological and atomic properties (volumes and charges) were derived and compared. The influence of hydrogen bonding on the experimental charge density was also studied qualitatively and quantitatively by means of topological properties. In terms of the hydrogen-bond energies, a grouping into strong, medium and very weak hydrogen bonds was made, the latter of which were involved in a bifurcated bond. PMID:17506999

  20. Interplay of pair density wave and charge density wave order in the cuprate pseudogap phase

    NASA Astrophysics Data System (ADS)

    Agterberg, Daniel; Amin, Adil

    Recent x-ray measurements in the cuprate YBCO suggest that the charge density wave (CDW) order seen at high-field has a different c-axis structure than that seen at zero-field and further suggests that CDW order breaks the c-axis mirror plane symmetry of the CuO2 layers. We examine pair density wave order that induces CDW order consistent with these observations.

  1. Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

    PubMed Central

    Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

    2010-01-01

    Abstract The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH3-(CH2)n-NH3]+, where n = 3–16 and 18, and then measuring d(001), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed. Key Words: Mars—Origin of life—Montmorillonite—Mineral catalysis—Layer charge density—X–ray diffractometry. Astrobiology 10, 743–749. PMID:20854214

  2. Interatomic potentials for ionic systems with density functional accuracy based on charge densities obtained by a neural network

    NASA Astrophysics Data System (ADS)

    Ghasemi, S. Alireza; Hofstetter, Albert; Saha, Santanu; Goedecker, Stefan

    2015-07-01

    Based on an analysis of the short-range chemical environment of each atom in a system, standard machine-learning-based approaches to the construction of interatomic potentials aim at determining directly the central quantity, which is the total energy. This prevents, for instance, an accurate description of the energetics of systems in which long-range charge transfer or ionization is important. We propose therefore not to target directly with machine-learning methods the total energy but an intermediate physical quantity, namely, the charge density, which then in turn allows us to determine the total energy. By allowing the electronic charge to distribute itself in an optimal way over the system, we can describe not only neutral but also ionized systems with unprecedented accuracy. We demonstrate the power of our approach for both neutral and ionized NaCl clusters where charge redistribution plays a decisive role for the energetics. We are able to obtain chemical accuracy, i.e., errors of less than a millihartree per atom compared to the reference density functional results for a huge data set of configurations with large structural variety. The introduction of physically motivated quantities which are determined by the short-range atomic environment via a neural network also leads to an increased stability of the machine-learning process and transferability of the potential.

  3. Charge Order Induced in an Orbital Density-Wave State

    NASA Astrophysics Data System (ADS)

    Singh, Dheeraj Kumar; Takimoto, Tetsuya

    2016-04-01

    Motivated by recent angle resolved photoemission measurements [D. V. Evtushinsky et al., Phys. Rev. Lett. 105, 147201 (2010)] and evidence of the density-wave state for the charge and orbital ordering [J. García et al., Phys. Rev. Lett. 109, 107202 (2012)] in La0.5Sr1.5MnO4, the issue of charge and orbital ordering in a two-orbital tight-binding model for layered manganite near half doping is revisited. We find that the charge order with the ordering wavevector 2{Q} = (π ,π ) is induced by the orbital order of d-/d+-type having B1g representation with a different ordering wavevector Q, where the orbital order as the primary order results from the strong Fermi-surface nesting. It is shown that the induced charge order parameter develops according to TCO - T by decreasing the temperature below the orbital ordering temperature TCO, in addition to the usual mean-field behavior of the orbital order parameter. Moreover, the same orbital order is found to stabilize the CE-type spin arrangement observed experimentally below TCE < TCO.

  4. Charge density waves in strongly correlated electron systems.

    PubMed

    Chen, Chih-Wei; Choe, Jesse; Morosan, E

    2016-08-01

    Strong electron correlations are at the heart of many physical phenomena of current interest to the condensed matter community. Here we present a survey of the mechanisms underlying such correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions. The focus is on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity. In addition to reviewing the CDW mechanisms in 1D, 2D, and 3D systems, we pay particular attention to the prevalence of this state in two particular classes of compounds, the high temperature superconductors (cuprates) and the layered transition metal dichalcogenides. The possibilities for quantum criticality resulting from the competition between magnetic fluctuations and electronic instabilities (CDW, unconventional superconductivity) are also discussed. PMID:27376547

  5. Charge density waves in strongly correlated electron systems

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Wei; Choe, Jesse; Morosan, E.

    2016-08-01

    Strong electron correlations are at the heart of many physical phenomena of current interest to the condensed matter community. Here we present a survey of the mechanisms underlying such correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions. The focus is on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity. In addition to reviewing the CDW mechanisms in 1D, 2D, and 3D systems, we pay particular attention to the prevalence of this state in two particular classes of compounds, the high temperature superconductors (cuprates) and the layered transition metal dichalcogenides. The possibilities for quantum criticality resulting from the competition between magnetic fluctuations and electronic instabilities (CDW, unconventional superconductivity) are also discussed.

  6. Topological analysis of the electronic charge density in the ethene protonation reaction catalyzed by acidic zeolite.

    PubMed

    Zalazar, M Fernanda; Peruchena, Nélida M

    2007-08-16

    In the present work, the distribution of the electronic charge density in the ethene protonation reaction by a zeolite acid site is studied within the framework of the density functional theory and the atoms in molecules (AIM) theory. The key electronic effects such as topological distribution of the charge density involved in the reaction are presented and discussed. The results are obtained at B3LYP/6-31G(**) level theory. Attention is focused on topological parameters such as electron density, its Laplacian, kinetic energy density, potential energy density, and electronic energy density at the bond critical points (BCP) in all bonds involved in the interaction zone, in the reactants, pi-complex, transition state, and alkoxy product. In addition, the topological atomic properties are determined on the selected atoms in the course of the reaction (average electron population, N(Omega), atomic net charge, q(Omega), atomic energy, E(Omega), atomic volume, v(Omega), and first moment of the atomic charge distribution, M(Omega)) and their changes are analyzed exhaustively. The topological study clearly shows that the ethene interaction with the acid site of the zeolite cluster, T5-OH, in the ethene adsorbed, is dominated by a strong O-H...pi interaction with some degree of covalence. AIM analysis based on DFT calculation for the transition state (TS) shows that the hydrogen atom from the acid site in the zeolitic fragment is connected to the carbon atom by a covalent bond with some contribution of electrostatic interaction and to the oxygen atom by closed shell interaction with some contribution of covalent character. The C-O bond formed in the alkoxy product can be defined as a weaker shared interaction. Our results show that in the transition state, the dominant interactions are partially electrostatic and partially covalent in nature, in which the covalent contribution increases as the concentration and accumulation of the charge density along the bond path between

  7. Density decrease in vanadium-base alloys irradiated in the dynamic helium charging experiment

    SciTech Connect

    Chung, H.M.; Galvin, T.M.; Smith, D.L.

    1996-04-01

    Combined effects of dynamically charged helium and neutron damage on density decrease (swelling) of V-4Cr-4Ti, V-5Ti, V-3Ti-1Si, and V-8Cr-6Ti alloys have been determined after irradiation to 18-31 dpa at 425-600{degrees}C in the Dynamic helium Charging Experiment (DHCE). To ensure better accuracy in density measurement, broken pieces of tensile specimens {approx} 10 times heavier than a transmission electron microscopy (TEM) disk were used. Density increases of the four alloys irradiated in the DHCE were <0.5%. This small change seems to be consistent with the negligible number density of microcavities characterized by TEM. Most of the dynamically produced helium atoms seem to have been trapped in the grain matrix without significant cavity nucleation or growth.

  8. Photoemission spectra of charge density wave states in cuprates

    NASA Astrophysics Data System (ADS)

    Tu, Wei-Lin; Chen, Peng-Jen; Lee, Ting-Kuo

    Angle-resolved photoemission spectroscopy(ARPES) experiments have reported many exotic properties of cuprates, such as Fermi arc at normal state, two gaps at superconducting state and particle-hole asymmetry at the antinodal direction. On the other hand, a number of inhomogeneous states or so-called charge density waves(CDW) states have also been discovered in cuprates by many experimental groups. The relation between these CDW states and ARPES spectra is unclear. With the help of Gutzwiller projected mean-field theory, we can reproduce the quasiparticle spectra in momentum space. The spectra show strong correspondence to the experimental data with afore-mentioned exotic features in it.

  9. Metal-insulator transition by holographic charge density waves.

    PubMed

    Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu; Zhang, Hongbao

    2014-08-29

    We construct a gravity dual for charge density waves (CDWs) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of CDWs, namely, the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDWs, which is further confirmed by the fact that dc conductivity decreases with the decreased temperature below the critical temperature. PMID:25215974

  10. Metal-insulator transition by holographic charge density waves.

    PubMed

    Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu; Zhang, Hongbao

    2014-08-29

    We construct a gravity dual for charge density waves (CDWs) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of CDWs, namely, the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDWs, which is further confirmed by the fact that dc conductivity decreases with the decreased temperature below the critical temperature.

  11. Shells of charge: a density functional theory for charged hard spheres

    NASA Astrophysics Data System (ADS)

    Roth, Roland; Gillespie, Dirk

    2016-06-01

    A functional for the electrostatic excess free-energy for charged, hard sphere fluids is proposed. The functional is derived from two complementary, but equivalent, interpretations of the mean spherical approximation (MSA). The first combines fundamental measure theory (FMT) from hard-core interactions with the idea that MSA can be interpreted in terms of the interaction spherical shells of charge. This formulation gives the free-energy density as a function of weighted densities. When all the ions have the same size, the functional adopts an FMT-like form. The second in effect ‘functionalizes’ the derivation of MSA; that is, it generalizes the MSA as a functional-based version of MSA (fMSA). This formulation defines the free-energy density as a function of a position-dependent MSA screening parameter and the weighted densities of the FMT approach. This FMT/fMSA functional is shown to give accurate density profiles, as compared to Monte Carlo simulations, under a wide range of ion concentrations, size asymmetries, and valences.

  12. Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

    NASA Astrophysics Data System (ADS)

    Ertem, Gözen; Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

    2010-09-01

    The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH3-(CH2)n-NH3]+, where n = 3-16 and 18, and then measuring d(001), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed.

  13. Correlation between the extent of catalytic activity and charge density of montmorillonites.

    PubMed

    Ertem, Gözen; Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

    2010-09-01

    The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH₃-(CH₂)(n)-NH₃](+), where n = 3-16 and 18, and then measuring d(₀₀₁), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed.

  14. Correlation between the extent of catalytic activity and charge density of montmorillonites.

    PubMed

    Ertem, Gözen; Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

    2010-09-01

    The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH₃-(CH₂)(n)-NH₃](+), where n = 3-16 and 18, and then measuring d(₀₀₁), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed. PMID:20854214

  15. Photoinduced Enhancement of the Charge Density Wave Amplitude.

    PubMed

    Singer, A; Patel, S K K; Kukreja, R; Uhlíř, V; Wingert, J; Festersen, S; Zhu, D; Glownia, J M; Lemke, H T; Nelson, S; Kozina, M; Rossnagel, K; Bauer, M; Murphy, B M; Magnussen, O M; Fullerton, E E; Shpyrko, O G

    2016-07-29

    Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well-defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom. PMID:27517781

  16. Photoinduced Enhancement of the Charge Density Wave Amplitude

    NASA Astrophysics Data System (ADS)

    Singer, A.; Patel, S. K. K.; Kukreja, R.; Uhlíř, V.; Wingert, J.; Festersen, S.; Zhu, D.; Glownia, J. M.; Lemke, H. T.; Nelson, S.; Kozina, M.; Rossnagel, K.; Bauer, M.; Murphy, B. M.; Magnussen, O. M.; Fullerton, E. E.; Shpyrko, O. G.

    2016-07-01

    Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well-defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom.

  17. Density determination from far-infrared lines

    NASA Technical Reports Server (NTRS)

    Rubin, Robert H.; Simpson, Janet P.; Erickson, Edwin F.; Haas, Michael R.; Lord, Steven D.; Colgan, Sean W. J.

    1995-01-01

    We demonstrate that when there are gas density variations within a nebula, various line ratios used to determine electron density (Ne) can give different results. When there are non-constant density conditions, it is shown that by using one (average) Ne, significant, systematic biases may occur in the derived chemical abundance ratios. The abundance ratio of a heavy element (when a collisionally excited line is used) to ionized hydrogen may be subject to a large underestimate in the presence of density fluctuations. The more Ne-diagnostic observations made, the more reliable will be the deciphering of the actual Ne variation throughout a nebula.

  18. PMSE dependence on aerosol charge number density and aerosol size

    NASA Astrophysics Data System (ADS)

    Rapp, Markus; Lübken, Franz-Josef; Hoffmann, Peter; Latteck, Ralph; Baumgarten, Gerd; Blix, Tom A.

    2003-04-01

    It is commonly accepted that the existence of polar mesosphere summer echoes (PMSEs) depends on the presence of charged aerosols since these are comparatively heavy and reduce the diffusion of free electrons due to ambipolar forces. Simple microphysical modeling suggests that this diffusivity reduction is proportional to rA2 (rA = aerosol radius) but only if a significant amount of charges is bound on the aerosols such that NA∣ZA∣/ne > 1.2 (NA = number of aerosols, ZA = aerosol charge, ne = number of free electrons). The fact that the background electron profile frequently shows large depletions ("biteouts") at PMSE altitudes is taken as a support for this idea since within biteouts a major fraction of free electrons is missing, i.e., bound on aerosols. In this paper, we show from in situ measurements of electron densities and from radar and lidar observations that PMSEs can also exist in regions where only a minor fraction of free electrons is bound on aerosols, i.e., with no biteout and with NA∣ZA∣/ne ≪ 1. We show strong experimental evidence that it is instead the product NA∣ZA∣rA2 that is crucial for the existence of PMSEs. For example, small aerosol charge can be compensated by large aerosol radius. We show that this product replicates the main features of PMSEs, in particular the mean altitude distribution and the altitude of PMSEs in the presence of noctilucent clouds (NLCs). We therefore take this product as a "proxy" for PMSE. The agreement between this proxy and the main characteristics of PMSEs implies that simple microphysical models do not satisfactorily describe PMSE physics and need to be improved. The proxy can easily be used in models of the upper atmosphere to better understand seasonal and geographical variations of PMSEs, for example, the long debated difference between Northern and Southern hemisphere PMSEs.

  19. Decay of Bloch oscillations in the charge-density-wave ordered phase of an all electronic charge density wave state

    NASA Astrophysics Data System (ADS)

    Matveev, Oleg; Shvaika, Andrij; Devereaux, Thomas; Freericks, James

    The charge-density-wave phase of the Falicov-Kimball model displays a number of anomalous behavior including the appearance of subgap density of states as the temperature increases. These subgap states should have a significant impact on transport properties, particularly the nonlinear response of the system to a large dc electric field. Using the Kadanoff-Baym-Keldysh formalism, we employ nonequilibrium dynamical mean-field theory to exactly solve for this nonlinear response. We examine both the current and the order parameter of the conduction electrons as the ordered system is driven by a dc electric field. Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, Lviv, Ukraine.

  20. Evidence against a charge density wave on Bi(111)

    DOE PAGES

    Kim, T. K.; Wells, J.; Kirkegaard, C.; Li, Z.; Hoffmann, S. V.; Gayone, J. E.; Fernandez-Torrente, I.; Häberle, P.; Pascual, J. I.; Moore, K. T.; et al

    2005-08-18

    The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW). The STM and TEM results to not support a CDW scenario at low temperatures. Thus the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electronmore » pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.« less

  1. Theory of charge-density-wave non-contact nanofriction

    NASA Astrophysics Data System (ADS)

    Tosatti, Erio; Pellegrini, Franco; Santoro, Giuseppe E.

    2014-03-01

    Bulk dissipation caused by charge-density-wave (CDW) voltage-induced depinning and sliding is a classic subject. We present a local, nanoscale mechanism describing the occurrence of distance-dependent dissipation in the dynamics of an atomic force microscope tip oscillating over the surface of a CDW material. A mechanical tip hysteresis is predicted in correspondence to localized 2 slips of the CDW phase, giving rise to large tip dissipation peaks at selected distances. Results of static and dynamic numerical simulations of the tip-surface interaction are believed to be relevant to recent experiments on the layer compound NbSe . Supported by SNF Contract CRSII2136287/1 and by ERC Advanced Grant 320796 - MODPHYSFRICT.

  2. Evidence against a charge density wave on Bi(111)

    SciTech Connect

    Kim, T. K.; Wells, J.; Kirkegaard, C.; Li, Z.; Hoffmann, S. V.; Gayone, J. E.; Fernandez-Torrente, I.; Häberle, P.; Pascual, J. I.; Moore, K. T.; Schwartz, A. J.; He, H.; Spence, J. C. H.; Downing, K. H.; Lazar, S.; Tichelaar, F. D.; Borisenko, S. V.; Knupfer, M.; Hofmann, Ph.

    2005-08-18

    The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW). The STM and TEM results to not support a CDW scenario at low temperatures. Thus the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electron pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.

  3. Evidence against a charge density wave on Bi(111)

    SciTech Connect

    Kim, T.K.; Wells, J.; Kirkegaard, C.; Li, Z.; Hoffmann, S.V.; Gayone, J.E.; Fernancez-Torrente, I.; Haberle, P.; Pascual, J.I.; Moore,K.T.; Schwartz, A.J.; He, H.; Spence, J.C.H.; Downing, K.H.; Lazar, S.; Tichelaar, F.D.; Borisenko, S.V.; Knupfer, M.; Hofmann, Ph.

    2005-05-01

    The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW) [Ch. R. Ast and H. Hoechst Phys. Rev. Lett. 90, 016403 (2003)]. The STM and TEM results to not support a CDW scenario at low temperatures. Furthermore, the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electron pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.

  4. Imaging Charge Density Wave Nucleation in NbSe2

    NASA Astrophysics Data System (ADS)

    Rosenthal, Ethan; Arguello, Carlos; Chockalingam, Subbaiah; Chung, Woo Chang; Zhao, Liuyan; Gutierrez, Christopher; Kang, Joon Ho; Pasupathy, Abhay; Jia, Shuang; Cava, Robert

    2012-02-01

    Understanding the effects of spatial inhomogeneity in complex materials is necessary to achieve a fundamental understanding of their quantum states. NbSe2 serves as a clean and relatively simple system for understanding the emergence of one such state -- the charge density wave (CDW) phase. Using variable temperature scanning tunneling microscopy (STM), we visualize the nucleation of CDWs about crystal defects at temperatures well above TCDW. The CDW correlation length increases with decreasing temperature, until global order is reached below TCDW. We also employ scanning tunneling spectroscopy in order to visualize the energy-dependent, spatial phase of the CDW state. With both topographic and spectroscopic data, we will provide a clear picture of the CDW transition and insight into the microscopic mechanisms at work.

  5. Fluctuating charge-density waves in a cuprate superconductor.

    PubMed

    Torchinsky, Darius H; Mahmood, Fahad; Bollinger, Anthony T; Božović, Ivan; Gedik, Nuh

    2013-05-01

    Cuprate materials hosting high-temperature superconductivity (HTS) also exhibit various forms of charge and spin ordering whose significance is not fully understood. So far, static charge-density waves (CDWs) have been detected by diffraction probes only at particular doping levels or in an applied external field . However, dynamic CDWs may also be present more broadly and their detection, characterization and relationship with HTS remain open problems. Here we present a method based on ultrafast spectroscopy to detect the presence and measure the lifetimes of CDW fluctuations in cuprates. In an underdoped La(1.9)Sr(0.1)CuO4 film (T(c) = 26 K), we observe collective excitations of CDW that persist up to 100 K. This dynamic CDW fluctuates with a characteristic lifetime of 2 ps at T = 5 K that decreases to 0.5 ps at T = 100 K. In contrast, in an optimally doped La(1.84)Sr(0.16)CuO4 film (T(c) = 38.5 K), we detect no signatures of fluctuating CDWs at any temperature, favouring the competition scenario. This work forges a path for studying fluctuating order parameters in various superconductors and other materials. PMID:23435216

  6. Breathing charge density waves in intrinsic Josephson junctions

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.; Abdelhafiz, H.

    2014-01-01

    We demonstrate the creation of a charge density wave (CDW) along a stack of coupled Josephson junctions (JJs) in layered superconductors. Electric charge in each superconducting layer oscillates around some average value, forming a breathing CDW. We show the transformation of a longitudinal plasma wave to CDW in the state corresponding to the outermost branch. Transition between different types of CDW's related to the inner branches of IV characteristic is demonstrated. The effect of the external electromagnetic radiation on the states corresponding to the inner branches differs crucially from the case of the single JJ. The Shapiro steps in the IV characteristics of the junctions in the stack do not correspond directly to the frequency of radiation ω. The system of JJs behaves like a single whole system: the Shapiro steps or their harmonics in the total IV characteristics appear at voltage , where V l is the voltage in the lth junction, N R is the number of JJs in the rotating state, and m and n are integers.

  7. Reentrant Solid-Liquid Transition in Ionic Colloidal Dispersions by Varying Particle Charge Density

    NASA Astrophysics Data System (ADS)

    Yamanaka, Junpei; Yoshida, Hiroshi; Koga, Tadanori; Ise, Norio; Hashimoto, Takeji

    1998-06-01

    The influence of the particle surface charge density on the solid-liquid phase transition in electrostatically stabilized colloidal silica and polymer latex dispersions is examined. Both systems show a reentrant transition with increasing charge density. This is not explainable in terms of the Yukawa potential and the charge-renormalization model.

  8. Investigation of surface charge density on solid-liquid interfaces by modulating the electrical double layer.

    PubMed

    Moon, Jong Kyun; Song, Myung Won; Pak, Hyuk Kyu

    2015-05-20

    A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid-liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid-liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid-liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid-liquid interfaces. PMID:25923410

  9. Study of surface charge density on solid/liquid interfaces by modulating the electrical double layer

    NASA Astrophysics Data System (ADS)

    Pak, Hyuk Kyu; Moon, Jong Kyun

    2014-11-01

    A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid/liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid/liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a DC bias voltage across the plates, an AC electric current can be generated. By measuring the voltage difference between the plates as a function of bias voltage, we can study the surface charge density on solid/liquid interfaces. Our experimental results agree very well with the simple equivalent circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. This work was supported by Center for Soft and Living Matter through IBS program in Korea.

  10. Investigation of surface charge density on solid-liquid interfaces by modulating the electrical double layer.

    PubMed

    Moon, Jong Kyun; Song, Myung Won; Pak, Hyuk Kyu

    2015-05-20

    A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid-liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid-liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid-liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid-liquid interfaces.

  11. Investigation of surface charge density on solid-liquid interfaces by modulating the electrical double layer

    NASA Astrophysics Data System (ADS)

    Moon, Jong Kyun; Song, Myung Won; Pak, Hyuk Kyu

    2015-05-01

    A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid-liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid-liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid-liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid-liquid interfaces.

  12. Phase transitions and charge ordering in a square spin ice model with conserved monopole density

    NASA Astrophysics Data System (ADS)

    Xie, Yunlong; Zhou, Xiaohui; Liu, Jun-Ming

    2015-03-01

    Artificial spin ices represent a class of highly interested frustrated magnetic systems under intensive investigations for fascinating ground states and thermodynamics/dynamics of spin excitations in recent years. As one of these issues, magnetic charge ordering and the corresponding phase transitions in the two-dimensional system are emerging topics in condensed matter physics. In this work, we investigate all the monopole-ordered phases of the square spin ice model using the conserved monopole density algorithm. In low monopole density (ρ ~ 0), the Coulomb potential determines the monopoles' dynamics. We test the Coulomb's law in a two-dimension lattice and justify the monopole dimerization which is quite different from the three-dimensional pyrochlore spin ice. These monopole dimers are charge neutral, and the interactions between them have also been investigated using our algorithm. In the cases of high monopole density (ρ ~ 1), the system is similar to the dipolar kagome spin ice model, and our simulation results show that there exists an intermediate phase between the paramagnetic phase and the ordered magnetic phase. Such intermediate phase can be distinguished by the order of magnetic charges. In a cooling process, the system undergoes a two-stage magnetic phase transition before freezing to the long range magnetic ordered phase via a staggered charge ordering. Furthermore, a liquefaction process of monopole dimers can be justified upon the increasing effective internal pressure in the isothermal condition.

  13. Comparative study of analytical techniques for determining protein charge.

    PubMed

    Filoti, Dana I; Shire, Steven J; Yadav, Sandeep; Laue, Thomas M

    2015-07-01

    As interest in high-concentration protein formulations has increased, it has become apparent that routine, accurate protein charge measurements are necessary. There are several techniques for charge measurement, and a comparison of the methods is needed. The electrophoretic mobility, effective charge, and Debye-Hückel-Henry charge have been determined for bovine serum albumin, and human serum albumin. Three different electrophoretic methods were used to measure the electrophoretic mobility: capillary electrophoresis, electrophoretic light scattering, and membrane confined electrophoresis. In addition, the effective charge was measured directly using steady-state electrophoresis. Measurements made at different NaCl concentrations, pH, and temperatures allow comparison with previous charge estimates based on electrophoresis, Donnan equilibrium, and pH titration. Similar charge estimates are obtained by all of the methods. The strengths and limitations of each technique are discussed, as are some general considerations about protein charge and charge determination.

  14. Fe(CN){sub 6}{sup 3-}/Fe(CN){sub 6}{sup 4-} redox in the interlayer determined by the charge density of Zn{sub n}Cr-layered double hydroxides

    SciTech Connect

    Zhang, Jia; Xu, Yunfeng; Liu, Jiangyong; Zhou, Jizhi; Xu, Zhi Ping; Qian, Guangren

    2013-02-15

    Redox of Fe(CN){sub 6}{sup 3-} and Fe(CN){sub 6}{sup 4-} in the ZnCr layered double hydroxide interlayer has been investigated. The conversion from Fe(CN){sub 6}{sup 3-} to Fe(CN){sub 6}{sup 4-} or from Fe(CN){sub 6}{sup 4-} to Fe(CN){sub 6}{sup 3-} in the ZnCr-LDH interlayer has been confirmed, depending on the Zn:Cr molar ratio. Both Fe(CN){sub 6}{sup 3-} and Fe(CN){sub 6}{sup 4-} are observed in all samples no matter whether the initial anion is Fe(CN){sub 6}{sup 3-} or Fe(CN){sub 6}{sup 4-} before precipitation. Deconvolution of the FTIR band around 2100 cm{sup -1} reveals that the relative amount of Fe(CN){sub 6}{sup 4-} and Fe(CN){sub 6}{sup 3-} in the LDH interlayer is considerably dependent on the Zn:Cr molar ratio. In brief, Fe(CN){sub 6}{sup 4-} is preferred at the ratio of 2:1 while there is more Fe(CN){sub 6}{sup 3-} in the ratio of 4:1. Therefore, it is our hypothesis that the charge density of the hydroxide layer is a key factor that directs the redox of Fe(CN){sub 6}{sup 3-}/Fe(CN){sub 6}{sup 4-}. The possible redox processes have also been proposed. - Graphical abstract: Redox reactions of Fe(CN){sub 6}{sup 3-} and Fe(CN){sub 6}{sup 4-} take place in the ZnCr layered double hydroxide (LDH) interlayer, which are reflected by Fe(CN){sub 6}{sup 3-}/Fe(CN){sub 6}{sup 4-} FTIR area ratio. Highlights: Black-Right-Pointing-Pointer An interlayer redox phenomena was observed in Fe(CN){sub 6}{sup 3/4-} intercalated ZnCr-LDHs. Black-Right-Pointing-Pointer The ratio of interlayer redox was examined by FTIR fitting analysis. Black-Right-Pointing-Pointer The tendency of redox was influenced by Zn:Cr molar ratio. Black-Right-Pointing-Pointer The mechanism relies on the charge density of metal hydroxyl layer.

  15. Comparison of charge and dopant densities for DX sites in AlGaAs:Sn

    NASA Astrophysics Data System (ADS)

    Lurio, L. B.; Hayes, T. M.; Pant, J.; Williamson, D. L.; Gibart, P.; Theis, T. N.

    1996-03-01

    X-ray absorption spectroscopy measurements using fluorescence detection have been performed on Sn dopant centers in Al_.33Ga_.77As:Sn. Absolute calibration of the fluorescence yield permits a comparison of dopant and charge carrier densities in the persistent photo-conducting (PPC) state. It is found that the ratio of dopants to carriers is significantly greater than 1:1. In order to understand this discrepancy, we have determined the average local environment of the dopants through analysis of the X-ray absorption fine structure. The reduced carrier density is explained by a combination of inactive donor sites and charge traps. Implications for the nature of the Sn donor sites will be discussed. This research is supported by NSF grant nos. DMR-9006956 and DMR-8902512. The measurements were made at SSRL which is funded by the DOE Office of Basic Energy Sciences and the NIH Biotechnology Research Resource Program.

  16. Bond length and charge density variations within extended arm chair defects in graphene.

    PubMed

    Warner, Jamie H; Lee, Gun-Do; He, Kuang; Robertson, Alex W; Yoon, Euijoon; Kirkland, Angus I

    2013-11-26

    Extended linear arm chair defects are intentionally fabricated in suspended monolayer graphene using controlled focused electron beam irradiation. The atomic structure is accurately determined using aberration-corrected transmission electron microscopy with monochromation of the electron source to achieve ∼80 pm spatial resolution at an accelerating voltage of 80 kV. We show that the introduction of atomic vacancies in graphene disrupts the uniformity of C-C bond lengths immediately surrounding linear arm chair defects in graphene. The measured changes in C-C bond lengths are related to density functional theory (DFT) calculations of charge density variation and corresponding DFT calculated structural models. We show good correlation between the DFT predicted localized charge depletion and structural models with HRTEM measured bond elongation within the carbon tetragon structure of graphene. Further evidence of bond elongation within graphene defects is obtained from imaging a pair of 5-8-5 divacancies.

  17. Determination of Top Quark charge in CDF experiment

    SciTech Connect

    Bednar, Peter

    2007-01-01

    This thesis deals with the problematic of top quark charge measurement in CDF experiment at Fermilab. The goal is to determine if the top quark observed on Tevatron experiments is the Standard Model particle with the predicted charge 2/3 or it is some exotic 4th generation quark with the charge of -4/3 as suggested by some alternative theories.

  18. Charge density wave transition in single-layer titanium diselenide

    DOE PAGES

    Chen, P.; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y.; Chou, M. Y.; Mo, S. -K.; Hussain, Z.; Fedorov, A. -V.; Chiang, T. -C.

    2015-11-16

    A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene--a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering.more » The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The behavior of the Bardeen-Cooper-Schrieffer (BCS) gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.« less

  19. Charge density wave transition in single-layer titanium diselenide

    SciTech Connect

    Chen, P.; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y.; Chou, M. Y.; Mo, S. -K.; Hussain, Z.; Fedorov, A. -V.; Chiang, T. -C.

    2015-11-16

    A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene--a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The behavior of the Bardeen-Cooper-Schrieffer (BCS) gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.

  20. Charge density wave transition in single-layer titanium diselenide.

    PubMed

    Chen, P; Chan, Y-H; Fang, X-Y; Zhang, Y; Chou, M Y; Mo, S-K; Hussain, Z; Fedorov, A-V; Chiang, T-C

    2015-01-01

    A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene-a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The observed Bardeen-Cooper-Schrieffer (BCS) behaviour of the gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk. PMID:26568512

  1. Superconductivity close to a charge-density-wave instability

    NASA Astrophysics Data System (ADS)

    Bourbonnais, Claude; Bakrim, Hassan

    2010-03-01

    The recent discovery of superconductivity (SC) in proximity of a Peierls distorted phase in the perylene based organic conductor Per2Au(mnt)2 [1] has raised once again the issue about the role of charge-density-wave (CDW) correlations in the mechanism of Cooper pairing. We have applied the renormalization group approach to a quasi-1D model of electrons interacting with acoustic phonons modes and studied the interplay between the two instabilities. From the one-loop flow equations for the momentum and frequency dependent interactions induced by phonons we analyze the stability of CDW and SC states vs the phonon frequency φD and the hopping parameter t' for nesting alterations. S-wave SC is demonstrated to be stabilyzed above some critical t'^*. In these conditions, the superconducting Tc˜φD^η exibits a non-BCS power law increase with φD(η˜0.7), as a result of quantum interfering CDW and SC pairings. The complete phase diagram is obtained as a function of both t' and φD and shown to agree with the one found for Per2Au(mnt)2 under pressure [1]. [1] D. Graf et al., Eur. Phys. Lett. 85, 27009 (2009).

  2. Semiclassical black holes expose forbidden charges and censor divergent densities

    NASA Astrophysics Data System (ADS)

    Brustein, Ram; Medved, A. J. M.

    2013-09-01

    Classically, the horizon of a Schwarzschild black hole (BH) is a rigid surface of infinite redshift; whereas the uncertainty principle dictates that the semiclassical (would-be) horizon cannot be fixed in space nor can it exhibit any divergences. We propose that this distinction underlies the BH information-loss paradox, the apparent absence of BH hair, the so-called trans-Planckian problem and the recent "firewall" controversy. We argue that the correct prescription is to first integrate out the fluctuations of the background geometry and only then evaluate matter observables. The basic idea is illustrated using a system of two strongly coupled harmonic oscillators, with the heavier oscillator representing the background. We then apply our proposal to matter fields near a BH horizon, initially treating the matter fields as classical and the background as semiclassical. In this case, the average value of the associated current does not vanish; so that it is possible, in pr inciple, to measure the global charge of the BH. Then the matter is, in addition to the background, treated quantum mechanically. We show that the average energy density of matter as seen by an asymptotic observer is finite and proportional to the BH entropy, rather than divergent. We discuss the implications of our results for the various controversial issues concerning BH physics.

  3. Relationship between critical charge density, holding current, and maximum current density in optically triggered silicon carbide thyristors

    NASA Astrophysics Data System (ADS)

    Yuferev, V. S.; Levinshtein, M. E.; Palmour, J. W.

    2013-10-01

    Relationship between critical charge density, holding current, and maximum current density has been studied by using an adequate numerical model for the axisymmetric configuration characteristic of the optical triggering of power silicon carbide thyristors. It is shown that the holding current Ih depends only weakly on the critical charge density of a thyristor, pc. At the same time, the maximum current density in the state corresponding to holding current grows very steeply with increasing pc. It is shown that the maximum current density can substantially increase with decreasing current in the axisymmetric configuration if the switched-on state occupies only a part of the total area of a thyristor.

  4. Fractional boundary charges in quantum dot arrays with density modulation

    NASA Astrophysics Data System (ADS)

    Park, Jin-Hong; Yang, Guang; Klinovaja, Jelena; Stano, Peter; Loss, Daniel

    2016-08-01

    We show that fractional charges can be realized at the boundaries of a linear array of tunnel-coupled quantum dots in the presence of a periodically modulated onsite potential. While the charge fractionalization mechanism is similar to the one in polyacetylene, here the values of fractional charges can be tuned to arbitrary values by varying the phase of the onsite potential or the total number of dots in the array. We also find that the fractional boundary charges, unlike the in-gap bound states, are stable against static random disorder. We discuss the minimum array size where fractional boundary charges can be observed.

  5. Device for determining frost depth and density

    NASA Technical Reports Server (NTRS)

    Huneidi, F.

    1983-01-01

    A hand held device having a forward open window portion adapted to be pushed downwardly into the frost on a surface, and a rear container portion adapted to receive the frost removed from the window area are described. A graph on a side of the container enables an observer to determine the density of the frost from certain measurements noted. The depth of the frost is noted from calibrated lines on the sides of the open window portion.

  6. Time-domain pumping a quantum-critical charge density wave ordered material

    NASA Astrophysics Data System (ADS)

    Matveev, O. P.; Shvaika, A. M.; Devereaux, T. P.; Freericks, J. K.

    2016-09-01

    We determine the exact time-resolved photoemission spectroscopy for a nesting driven charge density wave (described by the spinless Falicov-Kimball model within dynamical mean-field theory). The pump-probe experiment involves two light pulses: the first is an ultrashort intense pump pulse that excites the system into nonequilibrium, and the second is a lower amplitude, higher frequency probe pulse that photoexcites electrons. We examine three different cases: the strongly correlated metal, the quantum-critical charge density wave, and the critical Mott insulator. Our results show that the quantum critical charge density wave has an ultraefficient relaxation channel that allows electrons to be de-excited during the pump pulse, resulting in little net excitation. In contrast, the metal and the Mott insulator show excitations that are closer to what one expects from these systems. In addition, the pump field produces spectral band narrowing, peak sharpening, and a spectral gap reduction, all of which rapidly return to their field free values after the pump is over.

  7. Theoretical description of nonequilibrium behavior in charge density wave systems

    NASA Astrophysics Data System (ADS)

    Shen, Wen

    The fast development of time resolved photoemission (TRPES) techniques allow us to discover the rich features of nonequilibrium phenomena which may not appear in equilibrium. One of the most explored topics is the nonequilibrium behavior of a charge density wave (CDW) material. Being an ordered phase at low temperature, the CDW state provides a fertile ground to study electron-electron and electron-ion interactions. By driving this material out of equilibrium and taking ultrafast time resolution snapshots of its behavior, TRPES helps us understand these interactions and sheds light on the mechanisms behind these and other complex material properties, such as metal-insulator transitions, high temperature superconductivity, and magnetic phenomena. Recent experiments on TRPES in CDW materials show an ultrafast CDW gap closure in systems such as 1T--TaS2 and TbTe3 and the subsequent separation of time scales for the electron-electron interaction and the electron-lattice interaction. But it is still not clear what happens during the ultrashort period (in first 100 femtosecond). In this dissertation, we solve a two band model describing this ultrafast process in a CDW system. By fixing the lattice distortion effect in the CDW, we studied the nonequilibrium excitations of the electrons under a strong electric field. This research is performed by calculating nonequilibrium Green's functions (NGF) along the Kadanoff-Baym-Keldysh contour. We solved this nonequilibrium problem exactly. We show non-perturbative results and explore the nonlinear electronic behavior under an ultrashort light pulses. In addition to the TRPES problem, we also examined the behavior of Bloch oscillations under a large DC field, the response to an AC electric field, high harmonic generation from solids, and the crossover between frequency-driven excitation and amplitude-driven excitation.

  8. Void structure and density change of vanadium-base alloys irradiated in the dynamic helium charging experiment

    SciTech Connect

    Chung, H.M.; Nowicki, L.; Gazda, J.

    1995-04-01

    The objective of this work is to determine void structure, distribution, and density changes of several promising vanadium-base alloys irradiated in the Dynamic Helium Charging Experiment (DHCE). Combined effects of dynamically charged helium and neutron damage on density change, void distribution, and microstructural evolution of V-4Cr-4Ti alloy have been determined after irradiation to 18-31 dpa at 425-600{degree}C in the DHCE, and the results compared with those from a non-DHCE in which helium generation was negligible.

  9. Dental plaque microcosm response to bonding agents containing quaternary ammonium methacrylates with different chain lengths and charge densities

    PubMed Central

    Zhou, Han; Li, Fang; Weir, Michael D.; Xu, Hockin H.K.

    2013-01-01

    Objectives Antibacterial bonding agents are promising to combat bacteria and caries at tooth-restoration margins. The objectives of this study were to incorporate new quaternary ammonium methacrylates (QAMs) to bonding agent and determine the effects of alkyl chain length (CL) and quaternary amine charge density on dental plaque microcosm bacteria response for the first time. Methods Six QAMs were synthesized with CL = 3, 6, 9, 12, 16, 18. Each QAM was incorporated into Scotchbond Multi-purpose (SBMP). To determine the charge density effect, dimethylaminododecyl methacrylate (DMAHDM, CL = 16) was mixed into SBMP at mass fraction = 0%, 2.5%, 5%, 7.5%, 10%. Charge density was measured using a fluorescein dye method. Dental plaque microcosm using saliva from ten donors was tested. Bacteria were inoculated on resins. Early-attachment was tested at 4 hours. Biofilm colony-forming units (CFU) were measured at 2 days. Results Incorporating QAMs into SBMP reduced bacteria early-attachment. Microcosm biofilm CFU for CL = 16 was 4 log lower than SBMP control. Charge density of bonding agent increased with DMAHDM content. Bacteria early-attachment decreased with increasing charge density. Biofilm CFU at 10% DMAHDM was reduced by 4 log. The killing effect was similarly-strong against total microorganisms, total streptococci, and mutans streptococci. Conclusions Increasing alkyl chain length and charge density of bonding agent was shown for the first time to decrease microcosm bacteria attachment and reduce biofilm CFU by 4 orders of magnitude. Novel antibacterial resins with tailored chain length and charge density are promising for wide applications in bonding, cements, sealants and composites to inhibit biofilms and caries. PMID:23948394

  10. Ionic fluids: charge and density correlations near gas-liquid criticality.

    PubMed

    Patsahan, Oksana; Mryglod, Ihor; Caillol, Jean-Michel

    2005-06-29

    The correlation functions of an ionic fluid with charge and size asymmetry are studied within the framework of the random phase approximation. The results obtained for the charge-charge correlation function demonstrate that the second-moment Stillinger-Lovett (SL) rule is satisfied away from the gas-liquid critical point (CP) but not, in general, at the CP. However, in the special case of a model without size asymmetry the SL rules are satisfied even at the CP. The expressions for the density-density and charge-density correlation functions valid far from and close to the CP are obtained explicitly.

  11. Determining Atmospheric-Density Profile of Titan

    NASA Technical Reports Server (NTRS)

    Sarani, Siamak

    2010-01-01

    A method was developed for measuring the atmospheric density of Titan, the largest moon of Saturn, to create an accurate density profile as a function of altitude. This will allow mission planners to select safe flyby altitudes, and for navigation engineers to accurately predict the delta-v associated with those flybys. The spacecraft angular rate vector profile as a function of time is collected via telemetry from the onboard attitude estimator once every 2 seconds. The telemetry for thruster times, as a function of time, for eight Reaction Control System (RCS) thrusters is gathered, once a second, from the Propulsion Manager algorithm of the Cassini onboard attitude-control flight software. Using these data, the ground software computes the angular momentum vector profile and the per-axis external torque as a function of time imparted from the spacecraft only due to the atmospheric drag. The software can then determine the Titan atmospheric density profile as a function of time and altitude with the known values of spacecraft center of mass, the Titan-relative range and velocity data, the projected area, and the aerocenter, along with the estimated drag coefficient in a free molecular flow field.

  12. Topics in the Dynamics of Charge-Density

    NASA Astrophysics Data System (ADS)

    Ramakrishna, Sathyanarayan (Satish).

    This dissertation is an investigation into some interesting transport properties of charge-density-waves (CDWs). The field of CDW dynamics is an arena for the battle between mathematical analysis and random disorder. It is a very difficult physical situation to analyze. The theoretical study of CDW dynamics dates to the prescient suggestion of John Bardeen (in the 70s) that the nonlinear I-V characteristic of the quasi one-dimensional material TTF-TCNQ was a consequence of collective transport of condensate resulting from a Peierls instability. This instability, described first by Peierls, is studied in Chapter 1. Once the underlying physics of the instability was understood, the effects of coupling the CDW to impurities and to electric and magnetic fields were studied. The most striking effect of impurities is to produce CDW pinning, so that collective-mode transport ceases to occur if the applied electric field is smaller than a threshold field. Intensive research led to the Fukuyama-Lee-Rice model of CDW pinning. Experiments in the field are complicated by the difficulty in preparing well characterized samples of the relevant materials, among which are the trichalco-genides NbSe_3, TaS_3, the dichalcogenides (TaSe_4)_2I, TaS_2, NbSe_2 and blue bronze K_{0.3}MoO _3. Over the last decade, growth techniques have been perfected and intensive comparison between the various theoretical models and experiment is feasible. An outline of the dissertation is as follows. First, we review the theoretical ideas that underlie the subject. Then we discuss each new piece of work separately. First, this thesis presents one important theoretical approach to the study of CDW dynamics. The approach builds upon previous work on the microscopic theory of superconductors and results in a new formulation of the problem that seems likely to lend itself to non-perturbative approaches. The perturbative approach cannot provide answers to the question of what happens near the depinning

  13. Charge density wave formation in rare-earth tritellurides

    NASA Astrophysics Data System (ADS)

    Ru, Nancy

    Charge density wave formation is explored in the rare-earth tritelluride family of compounds (RTe3, R = Y, La-Nd, Sm, Gd-Tm). These quasi-two-dimensional compounds host a simple lattice modulation with very little variance across the series. They have an especially simple electronic structure, which can be easily tuned by chemical pressure via rare-earth substitution. The Fermi surface (FS) of RTe3 is derived mainly from the p-orbitals of the Te atoms, which are arranged in double layers of nearly square-planar sheets. Despite the nearly four-fold symmetry of the Fermi surface and electronic structure, it is energetically favorable for RTe3 to form an incommensurate CDW that is unidirectional, rather than bidirectional---that is, of "stripe" rather than "checkerboard" symmetry. This CDW wavevector lies along one of the in-plane directions and partially nests nearly-parallel regions of the FS. In this thesis, I present the results of resistivity and high resolution x-ray diffraction measurements that follow the CDW transition temperatures across the RTe3 series. Critical temperatures Tc1 were found to vary remarkably across the series, attributed to the subtle effects of chemical pressure on the electronic structure. For the compounds with the smallest lattice parameters (R = Dy, Ho, Er, Tm), second CDW transitions were observed at lower temperatures Tc2. X-ray diffraction measurements for ErTe3 revealed this to be the onset of a CDW with wavevector lying in the in-plane direction perpendicular to the first, which is reminiscent of bidirectional order. Yet, as this second CDW forms at a lower temperature than the first, and nests a Fermi surface that has been previous nested, this CDW state with two order parameters for perpendicular wavevectors may be more appropriately termed a "rectangular" state. Quantum oscillation studies are also presented that probe the reconstructed FS of LaTe3. Additionally, antiferromagnetism arising from the local moments on the rare

  14. Quantum coherent switch utilizing commensurate nanoelectrode and charge density periodicities

    DOEpatents

    Harrison; Neil , Singleton; John , Migliori; Albert

    2008-08-05

    A quantum coherent switch having a substrate formed from a density wave (DW) material capable of having a periodic electron density modulation or spin density modulation, a dielectric layer formed onto a surface of the substrate that is orthogonal to an intrinsic wave vector of the DW material; and structure for applying an external spatially periodic electrostatic potential over the dielectric layer.

  15. Tailoring Membrane Nanostructure and Charge Density for High Electrokinetic Energy Conversion Efficiency.

    PubMed

    Haldrup, Sofie; Catalano, Jacopo; Hinge, Mogens; Jensen, Grethe V; Pedersen, Jan S; Bentien, Anders

    2016-02-23

    The electrokinetic energy conversion (EKEC) of hydraulic work directly into electrical energy has been investigated in charged polymeric membranes with different pore charge densities and characteristic diameters of the nanoporous network. The membranes were synthesized from blends of nitrocellulose and sulfonated polystyrene (SPS) and were comprehensively characterized with respect to structure, composition, and transport properties. It is shown that the SPS can be used as a sacrificial pore generation medium to tune the pore size and membrane porosity, which in turn highly affects the transport properties of the membranes. Furthermore, it is shown that very high EKEC efficiencies (>35%) are encountered in a rather narrow window of the properties of the nanoporous membrane network, that is, with pore diameters of ca. 10 nm and pore charge densities of 4.6 × 10(2) to 1.5 × 10(3) mol SO3(-) m(-3) for dilute solutions (0.03 M LiCl). The high absolute value of the efficiency combined with the determination of the optimal membrane morphology makes membrane-based EKEC devices a step closer to practical applications and high-performance membrane design less empirical.

  16. Testing the concept of hypervalency: charge density analysis of K2SO4.

    PubMed

    Schmøkel, Mette S; Cenedese, Simone; Overgaard, Jacob; Jørgensen, Mads R V; Chen, Yu-Sheng; Gatti, Carlo; Stalke, Dietmar; Iversen, Bo B

    2012-08-01

    One of the most basic concepts in chemical bonding theory is the octet rule, which was introduced by Lewis in 1916, but later challenged by Pauling to explain the bonding of third-row elements. In the third row, the central atom was assumed to exceed the octet by employing d orbitals in double bonding leading to hypervalency. Ever since, polyoxoanions such as SO(4)(2-), PO(4)(3-), and ClO(4)(-) have been paradigmatic examples for the concept of hypervalency in which the double bonds resonate among the oxygen atoms. Here, we examine S-O bonding by investigating the charge density of the sulfate group, SO(4)(2-), within a crystalline environment based both on experimental and theoretical methods. K(2)SO(4) is a high symmetry inorganic solid, where the crystals are strongly affected by extinction effects. Therefore, high quality, very low temperature single crystal X-ray diffraction data were collected using a small crystal (∼30 μm) and a high-energy (30 keV) synchrotron beam. The experimental charge density was determined by multipole modeling, whereas a theoretical density was obtained from periodic ab initio DFT calculations. The chemical bonding was jointly analyzed within the framework of the Quantum Theory of Atoms In Molecules only using quantities derived from an experimental observable (the charge density). The combined evidence suggests a bonding situation where the S-O interactions can be characterized as highly polarized, covalent bonds, with the "single bond" description significantly prevailing over the "double bond" picture. Thus, the study rules out the hypervalent description of the sulfur atom in the sulfate group.

  17. DNA–DNA Interactions in Tight Supercoils Are Described by a Small Effective Charge Density

    PubMed Central

    Maffeo, Cristopher; Schöpflin, Robert; Brutzer, Hergen; Stehr, René; Aksimentiev, Aleksei; Wedemann, Gero; Seidel, Ralf

    2011-01-01

    DNA-DNA interactions are important for the assembly of DNA nanostructures and during biological processes such as genome compaction and transcription regulation. In studies of these complex processes, DNA is commonly modeled as a homogeneously charged cylinder and its electrostatic interactions are calculated within the framework of the Poisson-Boltzmann equation. Commonly, a charge adaptation factor is used to address limitations of this theoretical approach. Despite considerable theoretical and experimental efforts, a rigorous quantitative assessment of this parameter is lacking. Here, we comprehensively characterized DNA-DNA interactions in the presence of monovalent ions by analyzing the supercoiling behavior of single DNA molecules held under constant tension. Both a theoretical model and coarse-grained simulations of this process revealed a surprisingly small effective DNA charge of 40% of the nominal charge density. These findings were directly supported by atomic-scale molecular dynamics simulations that determined the effective force between two DNA molecules. Our new parameterization has direct impact on many physical models involving DNA-DNA interactions. PMID:21230940

  18. Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

    SciTech Connect

    Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro

    2009-03-01

    The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode (CPM) is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10{sup 18} cm{sup -3}. Beyond this defect level, a sublinear relation is found i

  19. Determination of Dusty Particle Charge Taking into Account Ion Drag

    SciTech Connect

    Ramazanov, T. S.; Dosbolayev, M. K.; Jumabekov, A. N.; Amangaliyeva, R. Zh.; Orazbayev, S. A.; Petrov, O. F.; Antipov, S. N.

    2008-09-07

    This work is devoted to the experimental estimation of charge of dust particle that levitates in the stratum of dc glow discharge. Particle charge is determined on the basis of the balance between ion drag force, gravitational and electric forces. Electric force is obtained from the axial distribution of the light intensity of strata.

  20. Determination of the Electronics Charge--Electrolysis of Water Method.

    ERIC Educational Resources Information Center

    Venkatachar, Arun C.

    1985-01-01

    Presents an alternative method for measuring the electronic charge using data from the electrolysis of acidified distilled water. The process (carried out in a commercially available electrolytic cell) has the advantage of short completion time so that students can determine electron charge and mass in one laboratory period. (DH)

  1. The effect of the charge density of microemulsion droplets on the bending elasticity of their amphiphilic film

    NASA Astrophysics Data System (ADS)

    Farago, B.; Gradzielski, M.

    2001-06-01

    Oil-in-water (O/W) microemulsion droplets have been investigated with respect to the effect of the electric charge density on the bending elasticity of the amphiphilic film. For this an originally uncharged microemulsion system became charged by the substitution of the nonionic by an ionic surfactant (up to 5 mol %). The sum of the bending constants, 2κ+κ¯, has been determined from the polydispersity index p of the droplets and alternatively from the macroscopic interfacial tension γ together with the maximum particle radius Rm. p and Rm were measured by means of small-angle neutron scattering (SANS) experiments in the shell contrast. Neutron spin echo (NSE) has been employed to measure directly the dynamics of the shape fluctuations of the droplets. This method enables a separate determination of κ on its own. It is found that the effect of the increasing charge density leads only to a fairly small increase for the sum of the bending constants 2κ+κ¯. Also the change of the ionic strength for a charged microemulsion system has almost no influence on this sum. NSE measurements show no measurable difference in the dynamics of the charged and uncharged system leading to the conclusion that not only the sum but separately the two bending constants stay within experimental error unchanged. This experimental observation is in contrast to simple electrostatic theories that would predict a much more pronounced influence of the electric charge density on the bending properties of the amphiphilic film.

  2. The effect of trap density on the space charge formation in polymeric photorefractive composites.

    PubMed

    Oh, Jin-Woo; Lee, Choongkeun; Kim, Nakjoong

    2009-04-01

    The effect of trap density on the space charge formation of polymeric photorefractive (PR) composites was studied using the modified Schildkraut differential equation. The densities of electrons, holes, and traps, as well as the rates of generation, recombination, trapping, and detrapping are examined. The steady-state and temporal behaviors of photocurrent and space charge field (E(sc)) formation dependence on the trap density are also discussed. The charge transport dynamics influenced by the presence of the trap molecules controls the formation of E(sc) via charge trapping, charge detrapping, and charge recombination. Experimental studies of photocurrent and E(sc) in poly[methyl-3-(9-carbazolyl) propylsiloxane]-based polymeric PR composites were carried out to demonstrate the applicability of the model.

  3. Determination of tunneling charge via current measurements

    NASA Astrophysics Data System (ADS)

    Safi, I.; Sukhorukov, E. V.

    2010-09-01

    We consider a tunnel junction between two arbitrary non-linear systems in any dimension, which can be different. We show that the tunneling charge can be detected using three alternative methods based on current measurements. Besides being technically easier compared to noise measurements, these methods present valuable advantages: they do not require the knowledge of the underlying models, and some are accessible in the experimentally convenient low-voltage regime, where heating effects are reduced. The first method is based on the AC conductance, while the two others are based on photo-assisted current (PAC) and can be implemented for any time dependence of the tunneling amplitude. These are promising for edge states in the regime of the fractional quantum Hall effect (FQHE): the Hamiltonian does not have to be specified and can incorporate non-universal interactions between the edges, and it is more convenient to use an AC gate voltage rather than an AC bias. These methods apply for instance to weak barriers in 1-D systems, Superconductor-Insulator-Normal (SIN) or graphene-like structures.

  4. Molecular Weight and Charge Density Asymmetry in Polyelectrolyte Complexation

    NASA Astrophysics Data System (ADS)

    Audus, Debra; Fredrickson, Glenn; Duechs, Dominik

    2009-03-01

    We investigate the phase diagram of oppositely charged polymers in a good solvent using a field-theoretic model. Mean-field solutions fail to predict the experimentally observed macroscopic phase separation into a solvent-rich phase and a dense liquid aggregate of polymers - a ``complex coacervate.'' We therefore study the model within a one-loop approximation, which accounts for Gaussian fluctuations in electrostatic and chemical potentials. Our particular focus is the effect of molecular weight, ionic strength, and charge asymmetry on the phase envelope. A set of dimensionless parameters is identified that dictate the size and shape of the two-phase region. Our results should be helpful in guiding experimental studies of coacervation.

  5. Growth dynamics, charge density, and structure of polyamide thin-film composite membranes

    NASA Astrophysics Data System (ADS)

    Matthews, Tamlin

    between 0.1 g/L TMC and 10 g/L TMC. The near-surface charge density also increases with increasing TMC concentration. Charge density was determined in the bulk RBS on membranes at varying pH between 3.5 and 10.5. These membranes show a good fit to a two pKa system, except the highest TMC concentration studied of 5 g/L which followed a one pKa system. Fitting the pH data using the pKa system shows that the total concentration of carboxylic acid groups decreases from 0.42 to 0.20 M with increasing MPD concentration. The decreasing carboxylic acid content is due to a higher concentration of MPD monomers. The total concentration of carboxylic acid groups increases with from 0.05 to 0.51 M with increasing TMC concentration. The concentration of TMC has a large effect on the charge density with the highest pH of 10.5 resulting in the highest measured charge density for each concentration increasing from 0.04 M to 0.55 M for 0.1 g/L to 5 g/L TMC. Grazing incidence small- and wide-angle X-ray scattering (GISAXS and GIWAXS) were successfully used to study the supported polysulfone ultrafiltration membrane and polyamide on polysulfone reverse osmosis membrane. Linear regions in GISAXS of I(Q) alpha Q-3.7 for polysulfone and Q -3.6 for polyamide on polysulfone were observed, which correspond to the Porod regime for smooth internal polymer interface sizes between 392.7 nm < d < 523.6 nm. The size of the interface is larger for higher incidence angles, which penetrate deeper into the porous structure of polysulfone. (Abstract shortened by UMI.).

  6. Method to obtain absolute impurity density profiles combining charge exchange and beam emission spectroscopy without absolute intensity calibrationa)

    NASA Astrophysics Data System (ADS)

    Kappatou, A.; Jaspers, R. J. E.; Delabie, E.; Marchuk, O.; Biel, W.; Jakobs, M. A.

    2012-10-01

    Investigation of impurity transport properties in tokamak plasmas is essential and a diagnostic that can provide information on the impurity content is required. Combining charge exchange recombination spectroscopy (CXRS) and beam emission spectroscopy (BES), absolute radial profiles of impurity densities can be obtained from the CXRS and BES intensities, electron density and CXRS and BES emission rates, without requiring any absolute calibration of the spectra. The technique is demonstrated here with absolute impurity density radial profiles obtained in TEXTOR plasmas, using a high efficiency charge exchange spectrometer with high etendue, that measures the CXRS and BES spectra along the same lines-of-sight, offering an additional advantage for the determination of absolute impurity densities.

  7. Precise and Accurate Density Determination of Explosives Using Hydrostatic Weighing

    SciTech Connect

    B. Olinger

    2005-07-01

    Precise and accurate density determination requires weight measurements in air and water using sufficiently precise analytical balances, knowledge of the densities of air and water, knowledge of thermal expansions, availability of a density standard, and a method to estimate the time to achieve thermal equilibrium with water. Density distributions in pressed explosives are inferred from the densities of elements from a central slice.

  8. Characterization of the internal ion environment of biofilms based on charge density and shape of ion.

    PubMed

    Kurniawan, Andi; Tsuchiya, Yuki; Eda, Shima; Morisaki, Hisao

    2015-12-01

    Biofilm polymers contain both electrically positively and negatively charged sites. These charged sites enable the biofilm to trap and retain ions leading to an important role of biofilm such as nutrient recycling and pollutant purification. Much work has focused on the ion-exchange capacity of biofilms, and they are known to adsorb ions through an exchange mechanism between the ions in solution and the ions adsorbed to the charged sites on the biofilm polymer. However, recent studies suggest that the adsorption/desorption behavior of ions in a biofilm cannot be explained solely by this ion exchange mechanism. To examine the possibility that a substantial amount of ions are held in the interstitial region of the biofilm polymer by an electrostatic interaction, intact biofilms formed in a natural environment were immersed in distilled water and ion desorption was investigated. All of the detected ion species were released from the biofilms over a short period of time, and very few ions were subsequently released over more time, indicating that the interstitial region of biofilm polymers is another ion reserve. The extent of ion retention in the interstitial region of biofilms for each ion can be determined largely by charge density, |Z|/r, where |Z| is the ion valence as absolute value and r is the ion radius. The higher |Z|/r value an ion has, the stronger it is retained in the interstitial region of biofilms. Ion shape is also a key determinant of ion retention. Spherical and non-spherical ions have different correlations between the condensation ratio and |Z|/r. The generality of these findings were assured by various biofilm samples. Thus, the internal regions of biofilms exchange ions dynamically with the outside environment.

  9. Determination of time zero from a charged particle detector

    DOEpatents

    Green, Jesse Andrew

    2011-03-15

    A method, system and computer program is used to determine a linear track having a good fit to a most likely or expected path of charged particle passing through a charged particle detector having a plurality of drift cells. Hit signals from the charged particle detector are associated with a particular charged particle track. An initial estimate of time zero is made from these hit signals and linear tracks are then fit to drift radii for each particular time-zero estimate. The linear track having the best fit is then searched and selected and errors in fit and tracking parameters computed. The use of large and expensive fast detectors needed to time zero in the charged particle detectors can be avoided by adopting this method and system.

  10. Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

    PubMed Central

    Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

    2016-01-01

    Local surface charge density of lipid membranes influences membrane–protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values. PMID:27561322

  11. Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy.

    PubMed

    Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

    2016-01-01

    Local surface charge density of lipid membranes influences membrane-protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values. PMID:27561322

  12. Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

    NASA Astrophysics Data System (ADS)

    Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

    2016-08-01

    Local surface charge density of lipid membranes influences membrane-protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values.

  13. Determining charge state of graphene vacancy by noncontact atomic force microscopy and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Weinert, M.; Li, L.

    2015-01-01

    Graphene vacancies are engineered for novel functionalities, however, the charge state of these defects, the key parameter that is vital to charge transfer during chemical reactions and carrier scattering, is generally unknown. Here, we carried out atomic resolution imaging of graphene vacancy defects created by Ar plasma using noncontact atomic force microscopy, and made the first determination of their charge state by local contact potential difference measurements. Combined with density functional theory calculations, we show that graphene vacancies are typically positively charged, with size-dependent charge states that are not necessarily integer-valued. These findings provide new insights into carrier scattering by vacancy defects in graphene, as well as its functionalization for chemical sensing and catalysis, and underline the tunability of these functions by controlling the size of vacancy defect.

  14. Surface electrochemical properties of red mud (bauxite residue): zeta potential and surface charge density.

    PubMed

    Liu, Yanju; Naidu, Ravendra; Ming, Hui

    2013-03-15

    The surface electrochemical properties of red mud (bauxite residue) from different alumina refineries in Australia and China were studied by electrophoresis and measuring surface charge density obtained from acid/base potentiometric titrations. The electrophoretic properties were measured from zeta potentials obtained in the presence of 0.01 and 0.001 M KNO(3) over a wide pH range (3.5-10) by titration. The isoelectric point (IEP) values were found to vary from 6.35 to 8.70 for the red mud samples. Further investigation into the surface charge density of one sample (RRM) by acid/base potentiometric titration showed similar results for pH(PZC) with pH(IEP) obtained from electrokinetic measurements. The pH(IEP) determined from zeta potential measurements can be used as a characteristic property of red mud. The minerals contained in red mud contributed to the different values of pH(IEP) of samples obtained from different refineries. Different relationships of pH(IEP) with Al/Fe and Al/Si ratios (molar basis) were also found for different red mud samples. PMID:23270758

  15. Determination of a vapor compression refrigeration system refrigerant charge

    NASA Astrophysics Data System (ADS)

    Yang, Chun-Xin; Dang, Chao-Bin

    1995-09-01

    A physical model is established in this paper to describe the heat transfer and two phase flow of a refrigerant in the evaporator and condenser of a vapor compression refrigeration system. The model is then used to determine the refrigerant charge in vapor compression units. The model is used for a sensitivity analysis to determine the effect that varing design parameters on the refrigerant charge. The model is also used to evaluate the effect of refrigerant charge and the thermal physical properties on the refrigeration cycle. The predicted value of the refrigerant charge and experimental data agree well. The model and the method presented in this paper could be used to design vapour compression units such as domestic refrigerators and air conditioners.

  16. Coaxial capacitor used to determine fluid density

    NASA Technical Reports Server (NTRS)

    Atkisson, E. A.

    1965-01-01

    Sensing device measures directly the density of compressible fluid existing simultaneously in both liquid and gaseous phases. The device is comprised of a capacitor connected as one leg of a bridge circuit, a power source, and an indicator calibrated to indicate density as a direct measurement.

  17. Dimensionality-driven phonon softening and incipient charge density wave instability in TiS2

    NASA Astrophysics Data System (ADS)

    Dolui, Kapildeb; Sanvito, Stefano

    2016-08-01

    Density functional theory and density functional perturbation theory are used to investigate the electronic and vibrational properties of TiS2. Within the local density approximation the material is a semimetal both in the bulk and in the monolayer form. Most interestingly we observe a Kohn anomaly in the bulk phonon dispersion, which turns into a charge density wave instability when TiS2 is thinned to less than four monolayers. Such instability, however, disappears when one calculates the electronic structure with a functional, such as the LDA+U, which returns an insulating ground state. In this situation charge-doping or strain does not bring back the charge density wave instability, whereas the formation of the TiSSe alloy does.

  18. 42 CFR 405.501 - Determination of reasonable charges.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... SERVICES MEDICARE PROGRAM FEDERAL HEALTH INSURANCE FOR THE AGED AND DISABLED Criteria for Determining... by entities that elect to be paid on a cost basis (including health maintenance organizations, rural... 42 Public Health 2 2010-10-01 2010-10-01 false Determination of reasonable charges....

  19. Cell density determines epithelial migration in culture.

    PubMed Central

    Rosen, P; Misfeldt, D S

    1980-01-01

    The dog kidney epithelial cell line (MDCK) has been shown to exhibit a density-correlated inhibition of growth at approxmately 6.6 X 10(5) cells per cm2. When a confluent monolayer at its maximal density was wounded by removal of a wide swath of cells, migration of the cell sheet into the denuded area occurred. Precise measurements of the rate of migration for 5 day showed that the cells accelerated at a uniform rate of 0.24 micrometer . hr-2 and, by extrapolation, possessed an apparent initial velocity of 2.8 micrometer . hr-1 at the time of wounding. The apparent initial velocity was considered to be the result of a brief (< 10 hr) and rapid acceleration dependent on cell density. To verify this, wounds were made at different densities below the maximum. In these experiments, the cells did not migrate until a "threshold" density of 2.0 X 10(5) cells per cm2 was reached regardless of the density at the time of wounding. At the threshold density, the cell sheet began to accelerate at the previously measured rate (0.24 micrometer . hr-2). Any increase in density by cell division was balanced by cell migration, so that the same threshold density was maintained by the migrating cells. Each migrating cell sustained the movement of the cell sheet at a constant rate of acceleration. It is proposed that an acceleration is, in general, characteristic of the vectorial movement of an epithelial cell sheet. Images PMID:6933523

  20. Implications of relativity on nonrelativistic Goldstone theorems: gapped excitations at finite charge density.

    PubMed

    Nicolis, Alberto; Piazza, Federico

    2013-01-01

    We adapt the Goldstone theorem to study spontaneous symmetry breaking in relativistic theories at finite charge density. It is customary to treat systems at finite density via nonrelativistic Hamiltonians. Here, we highlight the importance of the underlying relativistic dynamics. This leads to seemingly new results whenever the charge in question is spontaneously broken and does not commute with other broken charges. We find that that the latter interpolate gapped excitations. In contrast, all existing versions of the Goldstone theorem predict the existence of gapless modes. We derive exact nonperturbative expressions for their gaps, in terms of the chemical potential and of the symmetry algebra.

  1. Charge-density study of the nonlinear optical precursor DED-TCNQ at 20 K

    NASA Astrophysics Data System (ADS)

    Cole, Jacqueline M.; Copley, Royston C.; McIntyre, Garry J.; Howard, Judith A.; Szablewski, Marek; Cross, Graham H.

    2002-03-01

    A charge-density study of the nonlinear-optical (NLO) precursor \\{4-[bis(diethylamino)-methylium] phenyl\\}dicyanomethanide (DED-TCNQ), space group P21/c, a=11.174(2) Å b=12.859(2) Å c=12.486(2) Å β=112.00(1)°, is presented. The results derive from a suitable combination of complementary 20 K x-ray and neutron diffraction data, the latter being important for locating the hydrogen atoms precisely. The compound is one in a series of TCNQ derivatives that exhibit varying degrees of quinoidal and zwitterionic character, these two electronic states being very close energetically. Bond-length-alternation type calculations show that the molecule at 20 K exists in a mixture of the two states, the zwitterionic ground state being dominant (63:37% zwitterionic: quinoidal). A topological analysis of the bonding density within the benzenoid ring provides for a more direct, alternative method to calculate this ratio which utilizes ellipticity values derived from the charge-density study. Results are identical thus corroborating the validity of the ``strength-length'' relationship implicitly assumed in bond-length-alternation type calculations. The ratio determined corresponds well to the electronic configuration needed to meet the requirements of the general rule for obtaining a maximum value of β (a measure of the NLO response on the molecular scale) as a function of bond-length alternation. The promise of this class of compounds for nonlinear optics also lies partly in their high molecular dipole moments and so the pseudoatomic charges derived from this study were used to evaluate the nature of the molecular charge transfer in detail and the solid-state dipolar vector moment μ. Such measurements of μ are otherwise difficult in the solid state. A value of \\|μ\\|=91×10-30 Cm was deduced which compares with liquid and gas phase theoretical calculations of μ=66.71×10-30 Cm and μ=33.36×10-30 Cm, respectively. This comparison, combined with an analysis of the sense

  2. Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Campi, G.; Bianconi, A.; Poccia, N.; Bianconi, G.; Barba, L.; Arrighetti, G.; Innocenti, D.; Karpinski, J.; Zhigadlo, N. D.; Kazakov, S. M.; Burghammer, M.; Zimmermann, M. V.; Sprung, M.; Ricci, A.

    2015-09-01

    It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave `puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26, 27, 28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity.

  3. Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor.

    PubMed

    Campi, G; Bianconi, A; Poccia, N; Bianconi, G; Barba, L; Arrighetti, G; Innocenti, D; Karpinski, J; Zhigadlo, N D; Kazakov, S M; Burghammer, M; Zimmermann, M v; Sprung, M; Ricci, A

    2015-09-17

    It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave 'puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26-28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity. PMID:26381983

  4. Finite temperature bosonic charge and current densities in compactified cosmic string spacetime

    NASA Astrophysics Data System (ADS)

    Mohammadi, A.; Bezerra de Mello, E. R.

    2016-06-01

    In this paper, we study the expectation values of the induced charge and current densities for a massive bosonic field with nonzero chemical potential in the geometry of a higher-dimensional compactified cosmic string with magnetic fluxes along the string core and also enclosed by the compactified direction in thermal equilibrium at finite temperature T . These densities are calculated by decomposing them into the vacuum expectation values and finite temperature contributions coming from the particles and antiparticles. The only nonzero components correspond to the charge, azimuthal, and axial current densities. By using the Abel-Plana formula, we decompose the components of the densities into the part induced by the cosmic string and the one by the compactification. The charge density is an odd function of the chemical potential and even periodic function of the magnetic flux with a period equal to the quantum flux. Moreover, the azimuthal (axial) current density is an even function of the chemical potential and an odd (even) periodic function of the magnetic flux with the same period. In this paper, our main concern is the thermal effect on the charge and current densities, including some limiting cases, the low- and high-temperature approximations. We show that in all cases, the temperature enhances the induced densities.

  5. Comparison of density determination of liquid samples by density meters

    NASA Astrophysics Data System (ADS)

    Vámossy, C.; Davidson, S.; Zelenka, Z.

    2016-01-01

    This project was a European regional bilateral comparison of volume determination of stainless steel standards of 10 g, 20 g, and 200 g and 1 kg carried out under the auspices of EURAMET (project 1356, EURAMET.M.D-S3). The objectives of the present comparison were to check the measurement capabilities of the participants in the field of volume measurements of weights and provide a basis for the calibration measurement capabilities (CMC). BEV (Austria) was the pilot laboratory and the provider of the transfer standards. MKEH was the other participant in the bilateral comparison and NPL collected the measurement data ensuring the impartiality. The objectives of the comparison were achieved. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  6. Membrane interactions in nerve myelin: II. Determination of surface charge from biochemical data.

    PubMed Central

    Inouye, H; Kirschner, D A

    1988-01-01

    In our accompanying paper (Inouye and Kirschner, 1988) we calculated the surface charge density at the extracellular surfaces in peripheral and central nervous system (PNS; CNS) myelins from observations on the dependency of the width of the extracellular space on pH and ionic strength. Here, we have determined the surface charge density of the membrane surfaces in myelin from its chemical composition and the localization of some of its molecular components. We then analyzed the attractive and repulsive forces between the apposed surfaces and calculated equilibrium periods for comparison with the measured values. The biochemical model accounts for the observed isoelectric range of the myelin period and, with the surface charge reduced (possibly by divalent cation binding or a space charge approximation), the model also accounts for the dependency of period on pH above the isoelectric range. At the extracellular (and cytoplasmic) surfaces the contribution of lipid (with pI approximately 2) to the net surface charge is about the same in both PNS and CNS myelin, whereas the contribution of protein depends on which ones are exposed at the two surfaces. The protein conformation and localization modulate the surface charge of the lipid, resulting in positively-charged cytoplasmic surfaces (pI approximately 9) and negatively-charged extracellular surfaces (pI approximately 2-4). The net negative charge at the extracellular surface is due in CNS myelin to lipid, and in PNS myelin to both lipid and (PO) glycoprotein. The net positive charge at the cytoplasmic surface is due in CNS myelin mostly to basic protein, and in PNS myelin to PO glycoprotein and basic protein. The invariance of the cytoplasmic packing may be due to specific short-range interactions. Our models demonstrate how the particular myelin proteins and their localization and conformation can account for the differences in inter-membrane interactions in CNS and PNS myelins. PMID:3345333

  7. STM Studies of TbTe3: Evidence for a Fully Incommensurate Charge Density Wave

    SciTech Connect

    Fang, A.; Ru, N.; Fisher, I.R.; Kapitulnik, A.; /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept.

    2010-02-15

    We observe unidirectional charge density wave ordering on the cleaved surface of TbTe{sub 3} with a Scanning Tunneling Microscope at {approx}6 K. The modulation wave-vector q{sub CDW} as determined by Fourier analysis is 0.71 {+-} 0.02 x2{pi}/c. Where c is one edge of the in-plane 3D unit cell. Images at different tip-sample voltages show the unit cell doubling effects of dimerization and the layer below. Our results agree with bulk X-ray measurements, with the addition of (1/3) x2{pi}/a ordering perpendicular to the CDW. Our analysis indicates that the CDW is incommensurate.

  8. Charge-density-based analysis of the current–voltage response of polythiophene/fullerene photovoltaic devices

    PubMed Central

    Shuttle, C. G.; Hamilton, R.; O’Regan, B. C.; Nelson, J.; Durrant, J. R.

    2010-01-01

    A key challenge for organic electronics research is to develop device models that correctly account for the structural and energetic disorder typically present in such materials. In this paper we report an approach to analyze the electrical performance of an organic electronic device based upon charge extraction measurements of charge densities and transient optoelectronic measurements of charge carrier dynamics. This approach is applied to a poly(3-hexyl thiophene) (P3HT)/6,6 phenyl C61 butyric acid methyl ester (PCBM) blend photovoltaic device. These measurements are employed to determine the empirical rate law for bimolecular recombination losses, with the energetic disorder present in the materials being accounted for by a charge-density-dependent recombination coefficient. This rate law is then employed to simulate the current/voltage curve. This simulation assumes the only mechanism for the loss of photogenerated charges is bimolecular recombination and employs no fitting parameters. Remarkably the simulation is in good agreement with the experimental current/voltage data over a wide range of operating conditions of the solar cell. We thus demonstrate that the primary determinant of both the open-circuit voltage and fill factor of P3HT∶PCBM devices is bimolecular recombination. We go on to discuss the applicability of this analysis approach to other materials systems, and particularly to emphasize the effectiveness of this approach where the presence of disorder complicates the implementation of more conventional, voltage-based analyses such as the Shockley diode equation. PMID:20823262

  9. Structure/reactivity studies on an alpha-lithiated benzylsilane: chemical interpretation of experimental charge density.

    PubMed

    Ott, Holger; Däschlein, Christian; Leusser, Dirk; Schildbach, Daniel; Seibel, Timo; Stalke, Dietmar; Strohmann, Carsten

    2008-09-10

    Modern organic synthesis (e.g., of natural products) is virtually impossible without employment of enantiomerically enriched compounds. In many cases, alkyllithium compounds are key intermediates for the generation of these stereogenic substances. In recent years, the lithiated carbon atom in silicon-substituted benzyllithium compounds has become a focus of interest because it is possible to maintain its stereogenic information. Starting from a highly enantiomerically enriched benzylsilane, (R,S)-2 x quinuclidine could be obtained, and the absolute configuration at the metalated carbon atom was determined by X-ray diffraction analysis. In solution, a quartet was found in the (13)C NMR spectrum for the metalated carbon atom because of coupling between carbon and lithium, indicating a fixed lithium carbon contact at room temperature. After reaction of (R,S)-2 x quinuclidine with trimethylchlorostannane, the trapped product (S,S)-4 was obtained with a dr > or = 98:2 with inversion of the configuration at the metalated carbon. Multipole refinement against high-resolution diffraction data and subsequent topological analysis of the benchmark system (R,S)-2 x quinuclidine provide insight in the electronic situation and thus the observed stereochemical course of the transformations. Surprisingly, the negative charge generated at the carbanion hardly couples into the phenyl ring. The neighboring silicon atom counterbalances this charge by a pronounced positive charge. Therefore, the alpha-effect of the silicon atom is caused not just by a polarization of the electron density but also by an electrostatic bond reinforcement. Furthermore, the experimentally determined electrostatic potential unequivocally explains the observed back side attack of an electrophile under inversion of the stereogenic center with high diastereomeric ratios.

  10. A numerical study on charged-particle scattering and radiography of a steep density gradient

    NASA Astrophysics Data System (ADS)

    Shao, Guangchao; Wang, Xiaofang

    2016-09-01

    Electron and proton radiography of polystyrene planar targets with different density gradients is studied by Monte Carlo simulations in a regime that the incident charged-particle's kinetic energy is much higher than its energy loss in the targets. It is shown that by scattering of the electrons or protons, the density gradient causes modulations of the charged-particle beam transmitted from the target and the modulation contrast is sensitive only to a steep gradient, which suggests a novel diagnostic method wherein a steep density gradient could be distinguished from the scattering of a charged-particle beam in radiography. By using a 100-MeV charged-particle beam, it is found that the modulation is evident for a steep density gradient of width smaller than 1 μm for electron radiography and 0.6 μm for proton radiography, respectively, but almost negligible when the density gradient width is greater than 1 μm. The feasibility of diagnosing the steep density gradients in compressed matter is confirmed by the simulations of radiographing a laser-ablated planar foil. Simulations also show that it is possible to diagnose the density gradients inside a multilayered spherical capsule.

  11. Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM)

    PubMed Central

    Netzel, Jeanette; van Smaalen, Sander

    2009-01-01

    Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T ≃ 20 K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (l max = 1) for the H atoms. Topological properties at bond critical points (BCPs) are found to depend systematically on the bond length, but with different functions for covalent C—C, C—N and C—O bonds, and for hydrogen bonds together with covalent C—H and N—H bonds. Similar dependencies are known for AIM properties derived from static multipole densities. The ratio of potential and kinetic energy densities |V(BCP)|/G(BCP) is successfully used for a classification of hydrogen bonds according to their distance d(H⋯O) between the H atom and the acceptor atom. The classification based on MEM densities coincides with the usual classification of hydrogen bonds as strong, intermediate and weak [Jeffrey (1997) ▶. An Introduction to Hydrogen Bonding. Oxford University Press]. MEM and procrystal densities lead to similar values of the densities at the BCPs of hydrogen bonds, but differences are shown to prevail, such that it is found that only the true charge density, represented by MEM densities, the multipole model or some other method can lead to the correct characterization of chemical bonding. Our results do not confirm suggestions in the literature that the promolecule density might be sufficient for a characterization of hydrogen bonds. PMID:19767685

  12. Charge density wave order in 1D mirror twin boundaries of single-layer MoSe2

    NASA Astrophysics Data System (ADS)

    Barja, Sara; Wickenburg, Sebastian; Liu, Zhen-Fei; Zhang, Yi; Ryu, Hyejin; Ugeda, Miguel M.; Hussain, Zahid; Shen, Zhi-Xun; Mo, Sung-Kwan; Wong, Ed; Salmeron, Miquel B.; Wang, Feng; Crommie, Michael F.; Ogletree, D. Frank; Neaton, Jeffrey B.; Weber-Bargioni, Alexander

    2016-08-01

    We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe2. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe2 and MoS2. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent density of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.

  13. Direct Observation of Spin- and Charge-Density Waves in a Luttinger Liquid

    NASA Astrophysics Data System (ADS)

    Cao, Chenglin; Marcum, Andrew; Mawardi Ismail, Arif; Fonta, Francisco; O'Hara, Kenneth

    2016-05-01

    At low energy, interacting fermions in one dimension (e.g. electrons in quantum wires or fermionic atoms in 1D waveguides) should behave as Luttinger liquids. In stark contrast to Fermi liquids, the low-energy elementary excitations in Luttinger liquids are collective sound-like modes that propagate independently as spin-density and/or charge-density (i.e. particle-density) waves with generally unequal, and interaction-dependent, velocities. Here we aim to unambiguously confirm this hallmark feature of the Luttinger liquid - the phenomenon of spin-charge separation - by directly observing in real space the dynamics of spin-density and ``charge''-density waves excited in an ultracold gas of spin-1/2 fermions confined in an array of 1D optical waveguides. Starting from a two-component mixture of 6 Li atoms harmonically confined along each of the 1D waveguides, we excite low lying normal modes of the trapped system - namely the spin dipole and density dipole and quadrupole modes - and measure their frequency as a function of interaction strength. Luttinger liquid theory predicts that the spin dipole frequency is strongly dependent on interaction strength whereas the density dipole and quadrupole mode frequencies are relatively insensitive. We will also discuss extending our approach to exciting localized spin density and particle density wavepackets which should propagate at different velocities. Supported by AFOSR and NSF.

  14. Low Density Phases in a Uniformly Charged Liquid

    NASA Astrophysics Data System (ADS)

    Knüpfer, Hans; Muratov, Cyrill B.; Novaga, Matteo

    2016-07-01

    This paper is concerned with the macroscopic behavior of global energy minimizers in the three-dimensional sharp interface unscreened Ohta-Kawasaki model of diblock copolymer melts. This model is also referred to as the nuclear liquid drop model in the studies of the structure of highly compressed nuclear matter found in the crust of neutron stars, and, more broadly, is a paradigm for energy-driven pattern forming systems in which spatial order arises as a result of the competition of short-range attractive and long-range repulsive forces. Here we investigate the large volume behavior of minimizers in the low volume fraction regime, in which one expects the formation of a periodic lattice of small droplets of the minority phase in a sea of the majority phase. Under periodic boundary conditions, we prove that the considered energy {Γ}-converges to an energy functional of the limit "homogenized" measure associated with the minority phase consisting of a local linear term and a non-local quadratic term mediated by the Coulomb kernel. As a consequence, asymptotically the mass of the minority phase in a minimizer spreads uniformly across the domain. Similarly, the energy spreads uniformly across the domain as well, with the limit energy density minimizing the energy of a single droplet per unit volume. Finally, we prove that in the macroscopic limit the connected components of the minimizers have volumes and diameters that are bounded above and below by universal constants, and that most of them converge to the minimizers of the energy divided by volume for the whole space problem.

  15. Charged Group Surface Accessibility Determines Micelleplexes Formation and Cellular Interaction

    PubMed Central

    Zhang, Yu; Liu, Yang; Sen, Soumyo; Král, Petr; Gemeinhart, Richard A.

    2015-01-01

    Micelleplexes are a class of nucleic acid carriers that have gained acceptance due to their size, stability, and ability to synergistically carry small molecules. MicroRNAs (miRNAs) are small non-coding RNA gene regulator that is consists of 19–22 nucleotides. Altered expression of miRNAs plays an important role in many human diseases. Using a model 22-nucleotide miRNA sequence, we investigated the interaction between charged groups on the micelle surface and miRNA. The model micelle system was formed from methoxy-poly(ethylene glycol)-b-poly(lactide) (mPEG-PLA) mixed with methoxy-poly(ethylene glycol)-b-poly(lactide)-b-oligoarginine (mPEG-PLA-Rx, x = 8 or 15). Surface properties of the micelles were varied by controlling the oligoarginine block length and conjugation density. Micelles were observed to have a core-shell conformation in the aqueous environment where the PLA block constituted the hydrophobic core, mPEG and oligoarginine formed a hydrophilic corona. Significantly different thermodynamic behaviors were observed during the interaction of single stranded miRNA with micelles of different surface properties, and the resulting micelleplexes mediated substantial cellular association. Depending upon the oligoarginine length and density, micelles exhibited miRNA loading capacity directly related to the presentation of charged groups on the surface. The effect of charged group accessibility of cationic micelle on micelleplex properties provides guidance on future miRNA delivery system design. In this article, we investigated charged group presentation on the micelle surfaces and their interaction with miRNA using thermodynamics, biochemistry, and molecular dynamics simulation. Charged group accessibility on cationic micelle surfaces was shown as a mechanism to alter micelleplex formation and stability. PMID:25866141

  16. Autonomous gauge for blast impulse determination close to explosive charges

    NASA Astrophysics Data System (ADS)

    Kisters, T.; Kuder, J.; Nau, S.

    2016-03-01

    This paper reports on a new gauge for blast impulse determination close to explosive charges. The gauge is based on the autonomous data recorder g-rec developed at the Ernst-Mach-Institute for data acquisition in harsh environments. Combined with an acceleration sensor these data recorders allow for the direct determination of the momentum transferred to an object by a blast wave even in the immediate vicinity of the explosive charge. From this the blast impulse can be determined. Using autonomous electronics distinct advantages are gained compared to classical passive momentum traps. The paper summarizes the properties of the g-rec recorder and describes the setup of the autonomous momentum trap in detail. Numerical simulations are presented which illustrate the gauge performance and its limitations. Tests with 1 kg charges demonstrate the feasibility of the approach. Good agreement was found between simulations and tests. The application range of the gauges is determined by the measurement range of the built-in acceleration sensor and its overall dimensions and weight. The present configuration is designed for distances between ˜ 0.3 and 1 m from charges between several 100 g and several kilograms. Data were successfully collected down to reduced distances of 0.25 m/kg^{1/3}. Minor changes in gauge dimensions, weight, or measurement range enable the gauges to be deployed at even closer distances.

  17. Transport and Attenuation of Particles of Different Density and Surface Charge: A Karst Aquifer Field Study.

    PubMed

    Schiperski, Ferry; Zirlewagen, Johannes; Scheytt, Traugott

    2016-08-01

    Although karst aquifers are far more susceptible to contamination than porous aquifers, with the transport of particulate matter being an important factor, little is known about the attenuation of solutes within karst aquifers and even less about the attenuation of particulate matter. These in situ investigations have therefore aimed to systematically identify the processes that influence the transport and attenuation of particles within a karst aquifer through multitracer testing, using four different types of 1 μm fluorescent particles and the fluorescent dye uranine. Each of the types of particles used were detected at the observed spring, which drains the investigated aquifer. However, the transport behavior varied significantly between the various particles and the uranine dye, with the breakthrough of particles occurring slightly earlier than that of uranine. Attenuation was determined from the tracer recovery and attributed to filtration processes. These processes were affected by the hydrophobicity and surface charge of the particles. Carboxylated polystyrene particles with a density and surface charge comparable to pathogenic microorganisms were found to be mobile in groundwater over a distance of about 3 km. No attenuation was observed for plain silica particles. Particles with these characteristics thus pose a major threat to karst spring water as they might occur as contaminants themselves or facilitate the transport of other contaminants.

  18. Transport and Attenuation of Particles of Different Density and Surface Charge: A Karst Aquifer Field Study.

    PubMed

    Schiperski, Ferry; Zirlewagen, Johannes; Scheytt, Traugott

    2016-08-01

    Although karst aquifers are far more susceptible to contamination than porous aquifers, with the transport of particulate matter being an important factor, little is known about the attenuation of solutes within karst aquifers and even less about the attenuation of particulate matter. These in situ investigations have therefore aimed to systematically identify the processes that influence the transport and attenuation of particles within a karst aquifer through multitracer testing, using four different types of 1 μm fluorescent particles and the fluorescent dye uranine. Each of the types of particles used were detected at the observed spring, which drains the investigated aquifer. However, the transport behavior varied significantly between the various particles and the uranine dye, with the breakthrough of particles occurring slightly earlier than that of uranine. Attenuation was determined from the tracer recovery and attributed to filtration processes. These processes were affected by the hydrophobicity and surface charge of the particles. Carboxylated polystyrene particles with a density and surface charge comparable to pathogenic microorganisms were found to be mobile in groundwater over a distance of about 3 km. No attenuation was observed for plain silica particles. Particles with these characteristics thus pose a major threat to karst spring water as they might occur as contaminants themselves or facilitate the transport of other contaminants. PMID:27348254

  19. Method of measuring a profile of the density of charged particles in a particle beam

    DOEpatents

    Hyman, L.G.; Jankowski, D.J.

    1975-10-01

    A profile of the relative density of charged particles in a beam is obtained by disposing a number of rods parallel to each other in a plane perpendicular to the beam and shadowing the beam. A second number of rods is disposed perpendicular to the first rods in a plane perpendicular to the beam and also shadowing the beam. Irradiation of the rods by the beam of charged particles creates radioactive isotopes in a quantity proportional to the number of charged particles incident upon the rods. Measurement of the radioactivity of each of the rods provides a measure of the quantity of radioactive material generated thereby and, together with the location of the rods, provides information sufficient to identify a profile of the density of charged particles in the beam.

  20. Density-based Energy Decomposition Analysis for Intermolecular Interactions with Variationally Determined Intermediate State Energies

    SciTech Connect

    Wu, Q.; Ayers, P.W.; Zhang, Y.

    2009-10-28

    The first purely density-based energy decomposition analysis (EDA) for intermolecular binding is developed within the density functional theory. The most important feature of this scheme is to variationally determine the frozen density energy, based on a constrained search formalism and implemented with the Wu-Yang algorithm [Q. Wu and W. Yang, J. Chem. Phys. 118, 2498 (2003) ]. This variational process dispenses with the Heitler-London antisymmetrization of wave functions used in most previous methods and calculates the electrostatic and Pauli repulsion energies together without any distortion of the frozen density, an important fact that enables a clean separation of these two terms from the relaxation (i.e., polarization and charge transfer) terms. The new EDA also employs the constrained density functional theory approach [Q. Wu and T. Van Voorhis, Phys. Rev. A 72, 24502 (2005)] to separate out charge transfer effects. Because the charge transfer energy is based on the density flow in real space, it has a small basis set dependence. Applications of this decomposition to hydrogen bonding in the water dimer and the formamide dimer show that the frozen density energy dominates the binding in these systems, consistent with the noncovalent nature of the interactions. A more detailed examination reveals how the interplay of electrostatics and the Pauli repulsion determines the distance and angular dependence of these hydrogen bonds.

  1. Long-range order and pinning of charge-density waves in competition with superconductivity

    NASA Astrophysics Data System (ADS)

    Caplan, Yosef; Wachtel, Gideon; Orgad, Dror

    2015-12-01

    Recent experiments show that charge-density-wave correlations are prevalent in underdoped cuprate superconductors. The correlations are short ranged at weak magnetic fields but their intensity and spatial extent increase rapidly at low temperatures beyond a crossover field. Here we consider the possibility of long-range charge-density-wave order in a model of a layered system where such order competes with superconductivity. We show that in the clean limit, low-temperature long-range order is stabilized by arbitrarily weak magnetic fields. This apparent discrepancy with the experiments is resolved by the presence of disorder. Like the field, disorder nucleates halos of charge-density wave, but unlike the former it also disrupts interhalo coherence, leading to a correlation length that is always finite. Our results are compatible with various experimental trends, including the onset of longer range correlations induced by interlayer coupling above a characteristic field scale.

  2. Suppression of Three-Dimensional Charge Density Wave Ordering via Thickness Control

    NASA Astrophysics Data System (ADS)

    Kim, Gideok; Neumann, Michael; Kim, Minu; Le, Manh Duc; Kang, Tae Dong; Noh, Tae Won

    2015-11-01

    Barium bismuth oxide (BaBiO3 ) is the end member of two families of high-Tc superconductors, i.e., BaPb1 -xBix O3 and Ba1 -xKx BiO3 . The undoped parent compound is an insulator, exhibiting a charge density wave that is strongly linked to a static breathing distortion in the oxygen sublattice of the perovskite structure. We report a comprehensive spectroscopic and x-ray diffraction study of BaBiO3 thin films, showing that the minimum film thickness required to stabilize the breathing distortion and charge density wave is ≈11 unit cells, and that both phenomena are suppressed in thinner films. Our results constitute the first experimental observation of charge density wave suppression in bismuthate compounds without intentionally introducing dopants.

  3. Improving the charge density normalization in Korringa Kohn Rostoker Green-function calculations

    NASA Astrophysics Data System (ADS)

    Zeller, Rudolf

    2008-01-01

    The truncation of angular momentum expansions in the Korringa-Kohn-Rostoker Green-function method introduces a charge normalization error and disallows calculation of the Fermi level and the charge density in a consistent manner. It is shown how this error can be compensated by Lloyd's formula, in particular if this formula is applied to normalize the Green function everywhere along the complex energy contour used for the integration of the charge density. The advantages of the improved normalization over the conventional one are illustrated by density-functional calculations for CrAs, the dilute magnetic semiconductor Ga1-xMnxN and a Si12Fe8 multilayer. It is shown that only the improved normalization leads to correct integer values of the magnetic moments in the half-metallic state of CrAs and Ga1-xMnxN and to a correct band alignment of Fe and Si states in the multilayer.

  4. Charge and magnetization densities in transverse coordinate and impact parameter space

    NASA Astrophysics Data System (ADS)

    Kumar, Narinder; Dahiya, Harleen

    2014-11-01

    Electromagnetic form factors obtained from the overlap of light front wave functions have been used to study the transverse densities of charge and magnetization. The calculations have been carried out to develop a relation between the charge distribution of the quarks inside the nucleon in the transverse coordinate space as well as in the impact parameter space. When a comparison is carried out, it is found that the transverse distribution in the impact parameter space, where the longitudinal momentum fraction x can be fixed, falls off faster than the spatial distribution in the transverse coordinate space where there is some contribution from the longitudinal momentum as well. The anomalous magnetization density of the nucleon has also been discussed. Further, we have also presented the results of the QCD transverse Anti-de Sitter charge density inspired from the holographic QCD model.

  5. Superconductivity in Pd-intercalated charge-density-wave rare earth poly-tellurides RETe n

    NASA Astrophysics Data System (ADS)

    He, J. B.; Wang, P. P.; Yang, H. X.; Long, Y. J.; Zhao, L. X.; Ma, C.; Yang, M.; Wang, D. M.; Shangguan, X. C.; Xue, M. Q.; Zhang, P.; Ren, Z. A.; Li, J. Q.; Liu, W. M.; Chen, G. F.

    2016-06-01

    Charge density waves (CDWs) are periodic modulations of the conduction electron density in solids, which are generally considered to remove electrons from the Fermi level, and thus preclude a superconducting state. However, in a variety of CDW materials, such as the prototypical transition metal chalcogenides, superconductivity has also been observed at very low temperature (Yokoya et al 2001 Science 294 2518; Morosan et al 2006 Nat. Phys. 2 544; Kiss et al 2007 Nat. Phys. 3 720), in which, although the two electronic correlated states are believed to occur in different parts of Fermi surface sheets derived mainly from chalcogen p-states and transition metal d-states, the nature of the relationship between them has not yet been unambiguously determined. Here we report the discovery of superconductivity in Pd-intercalated RETe n (RE = rare earth; n = 2.5, 3) CDW systems, in which the chalcogen layers alone are responsible for both superconductivity and CDW instability. Our finding could provide an ideal model system for comprehensive study of the interplay between CDW and superconductivity due to the remarkable simplicity of the electronic structure of Te planes.

  6. Spatially separated charge densities of electrons and holes in organic-inorganic halide perovskites

    SciTech Connect

    Li, Dan; Liang, Chunjun E-mail: zhqhe@bjtu.edu.cn; Zhang, Huimin; You, Fangtian; He, Zhiqun E-mail: zhqhe@bjtu.edu.cn; Zhang, Chunxiu

    2015-02-21

    Solution-processable methylammonium lead trihalide perovskites exhibit remarkable high-absorption and low-loss properties for solar energy conversion. Calculation from density functional theory indicates the presence of non-equivalent halogen atoms in the unit cell because of the specific orientation of the organic cation. Considering the 〈100〉 orientation as an example, I{sub 1}, one of the halogen atoms, differs from the other iodine atoms (I{sub 2} and I{sub 3}) in terms of its interaction with the organic cation. The valance-band-maximum (VBM) and conduction-band-minimum (CBM) states are derived mainly from 5p orbital of I{sub 1} atom and 6p orbital of Pb atom, respectively. The spatially separated charge densities of the electrons and holes justify the low recombination rate of the pure iodide perovskite. Chlorine substitution further strengthens the unique position of the I{sub 1} atom, leading to more localized charge density around the I{sub 1} atom and less charge density around the other atoms at the VBM state. The less overlap of charge densities between the VBM and CBM states explains the relatively lower carrier recombination rate of the iodine-chlorine mixed perovskite. Chlorine substitution significantly reduces the effective mass at a direction perpendicular to the Pb-Cl bond and organic axis, enhancing the carrier transport property of the mixed perovskite in this direction.

  7. Spatially resolved charge-state and current-density distributions at the extraction of an electron cyclotron resonance ion source

    SciTech Connect

    Panitzsch, Lauri; Peleikis, Thies; Stalder, Michael; Wimmer-Schweingruber, Robert F.

    2011-09-15

    In this paper we present our measurements of charge-state and current-density distributions performed in very close vicinity (15 mm) of the extraction of our hexapole geometry electron cyclotron resonance ion source. We achieved a relatively high spatial resolution reducing the aperture of our 3D-movable extraction (puller) electrode to a diameter of only 0.5 mm. Thus, we are able to limit the source of the extracted ion beam to a very small region of the plasma electrode's hole (O = 4 mm) and therefore to a very small region of the neutral plasma sheath. The information about the charge-state distribution and the current density in the plane of the plasma electrode at each particular position is conserved in the ion beam. We determined the total current density distribution at a fixed coaxial distance of only 15 mm to the plasma electrode by remotely moving the small-aperture puller electrode which contained a dedicated Faraday cup (FC) across the aperture of the plasma electrode. In a second measurement we removed the FC and recorded m/q-spectra for the different positions using a sector magnet. From our results we can deduce that different ion charge-states can be grouped into bloated triangles of different sizes and same orientation at the extraction with the current density peaking at centre. This confirms observations from other groups based on simulations and emittance measurements. We present our measurements in detail and discuss possible systematic errors.

  8. Topology of the spin-polarized charge density in bcc and fcc iron.

    PubMed

    Jones, Travis E; Eberhart, Mark E; Clougherty, Dennis P

    2008-01-11

    We report the first investigation of the topology of spin-polarized charge density, specifically in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical. In these cases, the two spin densities are correlated: the spin-minority electrons have directional bond paths and deep minima, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of distinct spin topologies allows us to show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter involves a topological catastrophe. PMID:18232817

  9. Topology of the Spin-Polarized Charge Density in bcc and fcc Iron

    NASA Astrophysics Data System (ADS)

    Jones, Travis E.; Eberhart, Mark E.; Clougherty, Dennis P.

    2008-01-01

    We report the first investigation of the topology of spin-polarized charge density, specifically in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical. In these cases, the two spin densities are correlated: the spin-minority electrons have directional bond paths and deep minima, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of distinct spin topologies allows us to show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter involves a topological catastrophe.

  10. Topology of the spin-polarized charge density in bcc and fcc iron.

    PubMed

    Jones, Travis E; Eberhart, Mark E; Clougherty, Dennis P

    2008-01-11

    We report the first investigation of the topology of spin-polarized charge density, specifically in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical. In these cases, the two spin densities are correlated: the spin-minority electrons have directional bond paths and deep minima, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of distinct spin topologies allows us to show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter involves a topological catastrophe.

  11. Charge density waves in exfoliated films of van der Waals materials: evolution of Raman spectrum in TiSe2.

    PubMed

    Goli, Pradyumna; Khan, Javed; Wickramaratne, Darshana; Lake, Roger K; Balandin, Alexander A

    2012-11-14

    A number of the charge-density-wave materials reveal a transition to the macroscopic quantum state around 200 K. We used graphene-like mechanical exfoliation of TiSe(2) crystals to prepare a set of films with different thicknesses. The transition temperature to the charge-density-wave state was determined via modification of Raman spectra of TiSe(2) films. It was established that the transition temperature can increase from its bulk value to ~240 K as the thickness of the van der Waals films reduces to the nanometer range. The obtained results are important for the proposed applications of such materials in the collective-state information processing, which require room-temperature operation.

  12. Determination of nuclear level densities from experimental information

    SciTech Connect

    Cole, B.J. ); Davidson, N.J. , P.O. Box 88, Manchester M60 1QD ); Miller, H.G. )

    1994-10-01

    A novel information theory based method for determining the density of states from prior information is presented. The energy dependence of the density of states is determined from the observed number of states per energy interval, and model calculations suggest that the method is sufficiently reliable to calculate the thermal properties of nuclei over a reasonable temperature range.

  13. Directly mapping the surface charge density of lipid bilayers under physiological conditions

    NASA Astrophysics Data System (ADS)

    Fuhs, Thomas; Klausen, Lasse Hyldgaard; Besenbacher, Flemming; Dong, Mingdong

    2015-03-01

    The surface charge density of lipid bilayers governs the cellular uptake of charged particles and guides cell-cell and cell-surface interactions. Direct probing of the potential requires sub nanometer distances as the electrostatic potential is screened by high physiological salt concentrations. This prevented direct measurement of the SCD under physiological conditions. In this study we investigate supported bilayers of lipid mixtures that form domains of distinct surface charges, submerged in 150mM NaCl. We use a scanning ion-conductance microscope (SICM) setup to measure the ionic current through a nanopipette as the pipette is scanned several nanometers above the sample. The charged headgroups of the lipids attract counter ions leading to a charge dependent enhancement of the ion concentration near the surface. This creates a measurable change of conductivity in the vicinity of the surface. As the dependency of the current on the SCD and pipette potential is non-trivial we characterized it using numerical solutions to Poisson and Nernst-Planck equations. Based on the simulation results we propose an imaging method. We confirm feasibility of the proposed method by experimentally mapping the local surface charge density of phase separated lipid bilayers.

  14. Density of states determination in organic donor-acceptor blend layers enabled by molecular doping

    NASA Astrophysics Data System (ADS)

    Fischer, Janine; Ray, Debdutta; Kleemann, Hans; Pahner, Paul; Schwarze, Martin; Koerner, Christian; Vandewal, Koen; Leo, Karl

    2015-06-01

    Charge carrier transport is a key parameter determining the efficiency of organic solar cells, and is closely related to the density of free and trapped states. For trap characterization, impedance spectroscopy is a suitable, non-invasive method, applicable to complete organic semiconductor devices. In order to contribute to the capacitive signal, the traps must be filled with charge carriers. Typically, trap filling is achieved by illuminating the device or by injecting charge carriers through application of a forward bias voltage. However, in both cases, the exact number of charge carriers in the device is not known and depends strongly on the measurement conditions. Here, hole trap states of the model blend layer ZnPc:C60 are filled by weak p-doping, enabling trap characterization in a blend layer at a controlled hole density. We evaluate impedance spectra at different temperatures in order to determine the density of occupied states (DOOS) directly from the capacitance-frequency spectra by assuming a simple energy diagram. The reconstructed DOOS distribution is analyzed at different doping concentrations and device thicknesses and compared to thermally stimulated current measurements performed on the same devices. In both methods, a pronounced Gaussian peak at about 0.4 eV below the transport level is found as well as deep, exponential tail states, providing a deeper insight into the density of states distribution of this donor-acceptor blend layer. Additionally, the effect of doping-induced trap filling on the solar cell characteristics is studied in these devices.

  15. Tuning nucleation density of metal island with charge doping of graphene substrate

    SciTech Connect

    Ming, Wenmei; Liu, Feng

    2014-08-18

    We have demonstrated that the island nucleation in the initial stage of epitaxial thin film growth can be tuned by substrate surface charge doping. This charge effect was investigated using spin density functional theory calculation in Fe-deposition on graphene substrate as an example. It was found that hole-doping can noticeably increase both Fe-adatom diffusion barrier and Fe inter-adatom repulsion energy occurring at intermediate separation, whereas electron-doping can decrease Fe-adatom diffusion barrier but only slightly modify inter-adatom repulsion energy. Further kinetic Monte Carlo simulation showed that the nucleation island number density can be increased up to six times larger under hole-doping and can be decreased down to ten times smaller under electron doping than that without doping. Our findings indicate a route to tailor the growth morphology of magnetic metal nanostructure for spintronics and plasmonic applications via surface charge doping.

  16. Charged group surface accessibility determines micelleplexes formation and cellular interaction

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Liu, Yang; Sen, Soumyo; Král, Petr; Gemeinhart, Richard A.

    2015-04-01

    Micelleplexes are a class of nucleic acid carriers that have gained acceptance due to their size, stability, and ability to synergistically carry small molecules. MicroRNAs (miRNAs) are small non-coding RNA gene regulator that is consists of 19-22 nucleotides. Altered expression of miRNAs plays an important role in many human diseases. Using a model 22-nucleotide miRNA sequence, we investigated the interaction between charged groups on the micelle surface and miRNA. The model micelle system was formed from methoxy-poly(ethylene glycol)-b-poly(lactide) (mPEG-PLA) mixed with methoxy-poly(ethylene glycol)-b-poly(lactide)-b-oligoarginine (mPEG-PLA-Rx, x = 8 or 15). Surface properties of the micelles were varied by controlling the oligoarginine block length and conjugation density. Micelles were observed to have a core-shell conformation in the aqueous environment where the PLA block constituted the hydrophobic core, mPEG and oligoarginine formed a hydrophilic corona. Significantly different thermodynamic behaviors were observed during the interaction of single stranded miRNA with micelles of different surface properties, and the resulting micelleplexes mediated substantial cellular association. Depending upon the oligoarginine length and density, micelles exhibited miRNA loading capacity directly related to the presentation of charged groups on the surface. The effect of charged group accessibility of cationic micelle on micelleplex properties provides guidance on future miRNA delivery system design.Micelleplexes are a class of nucleic acid carriers that have gained acceptance due to their size, stability, and ability to synergistically carry small molecules. MicroRNAs (miRNAs) are small non-coding RNA gene regulator that is consists of 19-22 nucleotides. Altered expression of miRNAs plays an important role in many human diseases. Using a model 22-nucleotide miRNA sequence, we investigated the interaction between charged groups on the micelle surface and miRNA. The

  17. A self-consistent method for the determination of neutral density from X-ray impurity spectra

    NASA Astrophysics Data System (ADS)

    Rosmej, F. B.; Lisitsa, V. S.

    1998-07-01

    A new method for the determination of neutral densities and the electron lifetime from X-ray line spectra through charge exchange processes is proposed. The non-equilibrium population of neutrals and the charge exchange from their excited states in plasma regimes of high density and temperature have been calculated in a self-consistent manner through the introduction of an “effective diffusion rate”.

  18. Reversible Electrochemical Sensor for Detection of High-Charge Density Polyanion Contaminants in Heparin.

    PubMed

    Lester, Jacob; Chandler, Timothy; Gemene, Kebede L

    2015-11-17

    We present a simple, rapid, and inexpensive electrochemical sensor based on a reversible pulsed chronopotentiometric polyanion-selective membrane electrode for the detection and quantification of oversulfated chondroitin sulfate (OSCS) and other high charge-density polyanions that could potentially be used to adulterate heparin. The membrane is free of ion exchanger and is formulated with plasticized poly(vinyl chloride) (PVC) and an inert lipophilic salt, tridodecylmethylammonium-dinonylnaphthaline sulfonate (TDMA-DNNS). The neutral salt is used to reduce membrane resistance and to ensure reversibility of the sensor. More importantly, TDMA(+) is used as the recognition element for the polyanions. Here an anodic galvanostatic current pulse is applied across the membrane to cause the extraction of the polyanions from the sample into the membrane and potential is measured at the sample-membrane interface. The measured electromotive force (emf) is proportional to the concentration and the charge density of the polyanions. High charge-density polyanion contaminants and impurities in heparin can be detected using this method since the overall equilibrium potential response of polyions increases with increasing charge density of the polyions. Here, first the potential response of pure heparin is measured at a saturation concentration, the concentration beyond which further addition of heparin does not produce a change in potential response. Then the potential response of heparin tainted with different quantities of the high charge-density contaminant is measured at a fixed total polyion concentration (heparin concentration + contaminant concentration). The latter gives a greater negative potential response due to the presence of the high charge-density contaminant. The increase in the negative potential response can be used for detection and quantification of high charge-density contaminants in heparin. We demonstrate here that 0.3% (w/w) OSCS as well as 0.1% (w

  19. 42 CFR 405.509 - Determining the inflation-indexed charge.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 42 Public Health 2 2011-10-01 2011-10-01 false Determining the inflation-indexed charge. 405.509... Reasonable Charges § 405.509 Determining the inflation-indexed charge. (a) Definition. For purposes of this section, inflation-indexed charge means the lowest of the fee screens used to determine reasonable...

  20. 42 CFR 405.509 - Determining the inflation-indexed charge.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 42 Public Health 2 2013-10-01 2013-10-01 false Determining the inflation-indexed charge. 405.509... Reasonable Charges § 405.509 Determining the inflation-indexed charge. (a) Definition. For purposes of this section, inflation-indexed charge means the lowest of the fee screens used to determine reasonable...

  1. 42 CFR 405.509 - Determining the inflation-indexed charge.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 42 Public Health 2 2014-10-01 2014-10-01 false Determining the inflation-indexed charge. 405.509... Reasonable Charges § 405.509 Determining the inflation-indexed charge. (a) Definition. For purposes of this section, inflation-indexed charge means the lowest of the fee screens used to determine reasonable...

  2. 42 CFR 405.509 - Determining the inflation-indexed charge.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 42 Public Health 2 2012-10-01 2012-10-01 false Determining the inflation-indexed charge. 405.509... Reasonable Charges § 405.509 Determining the inflation-indexed charge. (a) Definition. For purposes of this section, inflation-indexed charge means the lowest of the fee screens used to determine reasonable...

  3. Charged nanoparticle attraction in multivalent salt solution: A classical-fluids density functional theory and molecular dynamics study

    DOE PAGES

    Salerno, K. Michael; Frischknecht, Amalie L.; Stevens, Mark J.

    2016-04-08

    Here, negatively charged nanoparticles (NPs) in 1:1, 1:2, and 1:3 electrolyte solutions are studied in a primitive ion model using molecular dynamics (MD) simulations and classical density functional theory (DFT). We determine the conditions for attractive interactions between the like-charged NPs. Ion density profiles and NP–NP interaction free energies are compared between the two methods and are found to be in qualitative agreement. The NP interaction free energy is purely repulsive for monovalent counterions, but can be attractive for divalent and trivalent counterions. Using DFT, the NP interaction free energy for different NP diameters and charges is calculated. The depthmore » and location of the minimum in the interaction depend strongly on the NPs’ charge. For certain parameters, the depth of the attractive well can reach 8–10 kBT, indicating that kinetic arrest and aggregation of the NPs due to electrostatic interactions is possible. Rich behavior arises from the geometric constraints of counterion packing at the NP surface. Layering of counterions around the NPs is observed and, as secondary counterion layers form the minimum of the NP–NP interaction free energy shifts to larger separation, and the depth of the free energy minimum varies dramatically. We find that attractive interactions occur with and without NP overcharging.« less

  4. Charged Nanoparticle Attraction in Multivalent Salt Solution: A Classical-Fluids Density Functional Theory and Molecular Dynamics Study.

    PubMed

    Salerno, K Michael; Frischknecht, Amalie L; Stevens, Mark J

    2016-07-01

    Negatively charged nanoparticles (NPs) in 1:1, 1:2, and 1:3 electrolyte solutions are studied in a primitive ion model using molecular dynamics (MD) simulations and classical density functional theory (DFT). We determine the conditions for attractive interactions between the like-charged NPs. Ion density profiles and NP-NP interaction free energies are compared between the two methods and are found to be in qualitative agreement. The NP interaction free energy is purely repulsive for monovalent counterions, but can be attractive for divalent and trivalent counterions. Using DFT, the NP interaction free energy for different NP diameters and charges is calculated. The depth and location of the minimum in the interaction depend strongly on the NPs' charge. For certain parameters, the depth of the attractive well can reach 8-10 kBT, indicating that kinetic arrest and aggregation of the NPs due to electrostatic interactions is possible. Rich behavior arises from the geometric constraints of counterion packing at the NP surface. Layering of counterions around the NPs is observed and, as secondary counterion layers form the minimum of the NP-NP interaction free energy shifts to larger separation, and the depth of the free energy minimum varies dramatically. We find that attractive interactions occur with and without NP overcharging. PMID:27057763

  5. Quantifying the nucleon’s pion cloud with transverse charge densities

    SciTech Connect

    Strikman, M.; Weiss, C.

    2010-10-01

    The transverse densities in a fast-moving nucleon offer a model-independent framework for analyzing the spatial structure of the pion cloud and its role in current matrix elements. We calculate the chiral large-distance component of the charge density in a dispersion representation of the form factor and discuss its partonic interpretation. It dominates over the nonchiral density only at surprisingly large distances above ~2 fm. The chiral component can be probed in precision low-Q^2 elastic eN scattering or in peripheral deep-inelastic processes that resolve its quark/gluon content.

  6. Rigorous surface charge method for determining electrostatic interaction energies in biomolecular systems

    NASA Astrophysics Data System (ADS)

    Doerr, T. P.; Obolensky, O. I.; Ogurtsov, A. Y.; Yu, Yi-Kuo

    2014-03-01

    Classical electrostatics plays a crucial role in bimolecular systems, dominating the interactions that determine the formation and dissolution of complexes responsible for the operation of cells. For systems that can be modeled as a set of piecewise-constant dielectric bodies, surface charge methods are usually preferable in both analytical and numerical contexts. We present a numerical implementation of a surface charge method previously used in analytical contexts. The method is applied to a realistic model of trypsin, an important protein involved in digesting other proteins, and one of its inhibitors, benzamidine. The classical calculations are complemented by density function theory calculations at short separations for which the classical model is inappropriate. We find that the surface charge method correctly distinguishes between correct and incorrect docking sites. This research was supported by the Intramural Research Program of the NIH, National Library of Medicine.

  7. Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR.

    PubMed

    Bastardo, Luis A; Iruthayaraj, Joseph; Lundin, Maria; Dedinaite, Andra; Vareikis, Ausvydas; Makuska, Ricardas; van der Wal, Albert; Furó, István; Garamus, Vasil M; Claesson, Per M

    2007-08-01

    A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO(45)MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 A. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO(45)MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements. PMID:17547922

  8. Theoretical description of charge migration with a single Slater-determinant and beyond

    NASA Astrophysics Data System (ADS)

    Kuleff, Alexander I.; Dreuw, Andreas

    2009-01-01

    Triggered by the interest to study charge migration in large molecular systems, a simple methodology has recently been proposed based on straightforward density functional theory calculations. This approach describes the time evolution of the initially created hole density in terms of the time evolution of the ionized highest occupied molecular orbital (HOMO). Here we demonstrate that this time-dependent analog of Koopmans' theorem is not valid, and instead of the time evolution of the HOMO, the time evolution of the orbitals that remain occupied in the cation determines the evolution of the initially created hole in the framework of time-dependent single-determinant theories. Numerical examples underline that for a proper description of charge migration processes, an explicit treatment of the electron correlation is indispensable. Moreover, they also demonstrate that the attempts to describe charge migration based on Kohn-Sham density functional theory using conventional exchange-correlation functionals are doomed to fail due to the well-known self-interaction error.

  9. Application of charge density methods to a protein model compound: Calculation of Coulombic intermolecular interaction energies from the experimental charge density

    PubMed Central

    Li, Xue; Wu, Guang; Abramov, Yuriy A.; Volkov, Anatoliy V.; Coppens, Philip

    2002-01-01

    A combined experimental and theoretical charge density study of the pentapeptide Boc-Gln-d-Iva-Hyp-Ala-Phol (Boc, butoxycarbonyl; Gln, glutamine; Iva, isovaline; Hyp, hydroxyproline; Ala, ethylalanine; Phol, phenylalaninol) is described. The experimental analysis, based on synchrotron x-ray data collected at 20 K, is combined with ab initio theoretical calculations. The topologies of the experimental and theoretical densities are analyzed in terms of the atoms in molecules quantum theory. Topological parameters, including atomic charges and higher moments integrated over the atomic basins, have been evaluated with the program topxd and are used to calculate the electrostatic interactions between the molecules in the crystal. The interaction energies obtained after adding dispersive and repulsive van der Waals contributions agree quite well with those based on M-B3LYP/6–31G** dimer calculations for two of the three dimers in the crystal, whereas for the third a larger stabilization is obtained than predicted by the calculation. The agreement with theory is significantly better than that obtained with multipole moments derived directly from the aspherical atom refinement. The convergence of the interaction as a function of addition of successively higher moments up to and including hexadecapoles (l = 4) is found to be within 2–3 kJ/mol. Although shortcomings of both the theoretical and experimental procedures are pointed out, the agreement obtained supports the potential of the experimental method for the evaluation of interactions in larger biologically relevant molecules. PMID:12221293

  10. Application of charge density methods to a protein model compound: calculation of Coulombic intermolecular interaction energies from the experimental charge density.

    PubMed

    Li, Xue; Wu, Guang; Abramov, Yuriy A; Volkov, Anatoliy V; Coppens, Philip

    2002-09-17

    A combined experimental and theoretical charge density study of the pentapeptide Boc-Gln-d-Iva-Hyp-Ala-Phol (Boc, butoxycarbonyl; Gln, glutamine; Iva, isovaline; Hyp, hydroxyproline; Ala, ethylalanine; Phol, phenylalaninol) is described. The experimental analysis, based on synchrotron x-ray data collected at 20 K, is combined with ab initio theoretical calculations. The topologies of the experimental and theoretical densities are analyzed in terms of the atoms in molecules quantum theory. Topological parameters, including atomic charges and higher moments integrated over the atomic basins, have been evaluated with the program topxd and are used to calculate the electrostatic interactions between the molecules in the crystal. The interaction energies obtained after adding dispersive and repulsive van der Waals contributions agree quite well with those based on M-B3LYP/6-31G** dimer calculations for two of the three dimers in the crystal, whereas for the third a larger stabilization is obtained than predicted by the calculation. The agreement with theory is significantly better than that obtained with multipole moments derived directly from the aspherical atom refinement. The convergence of the interaction as a function of addition of successively higher moments up to and including hexadecapoles (l = 4) is found to be within 2-3 kJ/mol. Although shortcomings of both the theoretical and experimental procedures are pointed out, the agreement obtained supports the potential of the experimental method for the evaluation of interactions in larger biologically relevant molecules. PMID:12221293

  11. Wet and dry bacterial spore densities determined by buoyant sedimentation.

    PubMed Central

    Tisa, L S; Koshikawa, T; Gerhardt, P

    1982-01-01

    The wet densities of various types of dormant bacterial spores and reference particles were determined by centrifugal buoyant sedimentation in density gradient solutions of three commercial media of high chemical density. With Metrizamide or Renografin, the wet density values for the spores and permeable Sephadex beads were higher than those obtained by a reference direct mass method, and some spore populations were separated into several density bands. With Percoll, all of the wet density values were about the same as those obtained by the direct mass method, and only single density bands resulted. The differences were due to the partial permeation of Metrizamide and Renografin, but not Percoll, into the spores and the permeable Sephadex beads. Consequently, the wet density of the entire spore was accurately represented only by the values obtained with the Percoll gradient and the direct mass method. The dry densities of the spores and particles were determined by gravity buoyant sedimentation in a gradient of two organic solvents, one of high and the other of low chemical density. All of the dry density values obtained by this method were about the same as those obtained by the direct mass method. PMID:6285824

  12. Laser-Induced Charge-Density-Wave Transient Depinning in Chromium

    NASA Astrophysics Data System (ADS)

    Jacques, V. L. R.; Laulhé, C.; Moisan, N.; Ravy, S.; Le Bolloc'h, D.

    2016-10-01

    We report on time-resolved x-ray diffraction measurements following femtosecond laser excitation in pure bulk chromium. Comparing the evolution of incommensurate charge-density-wave (CDW) and atomic lattice reflections, we show that, a few nanoseconds after laser excitation, the CDW undergoes different structural changes than the atomic lattice. We give evidence for a transient CDW shear strain that breaks the lattice point symmetry. This strain is characteristic of sliding CDWs, as observed in other incommensurate CDW systems, suggesting the laser-induced CDW sliding capability in 3D systems. This first evidence opens perspectives for unconventional laser-assisted transport of correlated charges.

  13. Density functional theory study of neutral, singly, and multiply charged Polycylcic Aromatic Hydrocarbon molecules

    NASA Astrophysics Data System (ADS)

    Zettergren, Henning; Holm, Anne I. S.; Johansson, Henrik; Cederquist, Henrik

    2012-11-01

    We have studied multiply ionization for a range of Polycyclic Aromatic Hydrocarbons (PAHs) and their charge dependent stabilities with respect to H-, H+-, C2H2- and C2H2+-emissions by means of Density Functional Theory. The adiabatic dissociation energies reveal information about the competition between these channels as functions of PAH charge state and provide predictions of the thermodynamical stability limits, while the sequences of ionization energies may e.g. be used to extract absolute ionization cross sections of astrophysical relevance.

  14. Differences in cationic and anionic charge densities dictate zwitterionic associations and stimuli responses.

    PubMed

    Shao, Qing; Mi, Luo; Han, Xia; Bai, Tao; Liu, Sijun; Li, Yuting; Jiang, Shaoyi

    2014-06-19

    Zwitterionic materials have shown their excellent performance in many biological and chemical applications. Zwitterionic materials possess moieties that own both cationic and anionic groups. The associations among zwitterionic moieties through electrostatic interactions play an important role in properties of zwitterionic materials. However, the relationship between the molecular structures and associations of zwitterionic moieties are still not well understood. This work compared thermal- and salt-responsive behaviors of sulfobetaine and carboxybetaine polymers by examining their rheological properties as a function of temperature and their hydrodynamic sizes as a function of salt concentration. Results showed that carboxybetaine polymers do not exhibit stimuli responses as expected from the antipolyelectrolyte behavior of zwitterionic polymers as observed in sulfobetaine polymers. We studied and compared the associations among zwitterionic moieties in these two zwitterionic polymers using molecular dynamic simulations. Simulation results show that the charge-density difference between cationic and anionic groups determines the associations among zwitterionic moieties, which are responsible for different stimuli responses of carboxybetaine and sulfobetaine polymers. PMID:24885910

  15. Cholesterol improves the transfection efficiency of lipoplexes by increasing the effective membrane charge density

    NASA Astrophysics Data System (ADS)

    Safinya, Cyrus R.; Zidovska, Alexandra; Evans, Heather M.; Ewert, Kai K.

    2008-03-01

    Motivated by its important role in lipid-mediated gene delivery, we have studied the effect of cholesterol on the transfection efficiency (TE) of lamellar, cationic lipid-DNA (CL-DNA) complexes. A successful in vivo liposome mixture seems to require cholesterol. Recent work in our group has identified the membrane charge density (σ) as a universal parameter for TE of lamellar, DOPC containing CL-DNA complexes (A.J. Lin et al, Biophys. J., 2003, K. Ewert et al, J. Med. Chem., 2002, A. Ahmad et al., J. Gene Med., 2005), with TE following a universal bell-shaped curve as a function of σ. Theoretical calculations considering the headgroup area of cholesterol and thus necessarily counting for an increase in σ, when DOPC is replaced by cholesterol, show that TE strongly deviates from the TE universal curve. However, experimental determination of σ via X-ray diffraction shows full agreement with the TE universal curve demonstrating that the real σ is higher as predicted, therefore the effective headgroup area of cholesterol is lower as expected by theory, suggesting that cholesterol is inserted deep into lipid bilayer partially hidden by the neighboring lipids. Funding provided by NIH GM-59288 and NSF DMR-0503347.

  16. A Quick Method for Determining the Density of Single Crystals.

    ERIC Educational Resources Information Center

    Roman, Pascual; Gutierrez-Zorrilla, Juan M.

    1985-01-01

    Shows how the Archimedes method is used to determine the density of a single crystal of ammonium oxalate monohydrate. Also shows how to calculate the density of other chemicals when they are available as single crystals. Experimental procedures and materials needed are included. (JN)

  17. On determining defects identity in carbon nanotubes using charge probes

    NASA Astrophysics Data System (ADS)

    Kostyrko, T.; García-Suárez, V. M.; Wawrzyniak-Adamczewska, M.; Ferrer, J.

    2016-06-01

    A metallic carbon nanotube with point-like defects under influence of a local potential due to a point charge probe is theoretically studied. A combination of density functional theory and the Landauer-Büttiker formalism is used to compute the electronic conductance in the zero-voltage limit. From a collection of the results obtained by varying the probe position around different defects the conductance maps are created. The analysis of the conductance maps allows us to formulate conditions under which several point-like defects (the Stone-Wales defect, a simple carbon vacancy, hydrogen-passivated vacancies) can be distinguished and identified in experiments with the help of scanning probe microscopy.

  18. X-ray derived experimental charge density distribution in GaF3 and VF3 solid systems

    NASA Astrophysics Data System (ADS)

    Sujatha, K.; Israel, S.; Anzline, C.; Niranjana Devi, R.; Sheeba, R. A. J. R.

    2016-09-01

    The electronic structure and bonding features of metal and transition metal fluorides in low oxidation states, GaF3 and VF3, have been studied from precise single crystal X-ray diffraction data using multipole and maximum entropy methods. The topology of the charge density is analyzed and the (3,-1) bond critical points are determined. Existences of ionic nature of bonding in low valent fluorine compounds are clearly evident. The spherical core of metal atom and aspherical or twisted core of transition metal atom reveal the fact that GaF3 is much more rigid than VF3. Aspherical cores of the polarized ligand atoms are also visible in the two-dimensional density distribution pictures. The true valence charge density surfaces with encapsulating the atomic basins maps are elucidated. An elongated saddle with mid-bond density of 0.6191 e/Å3, observed in the compound VF3, shows that its lattice is less rigid and has more ionic character than GaF3.

  19. Photophysical properties of charge transfer pairs encapsulated inside macrocycle cage: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Arkamita; Pati, Swapan K.

    2015-03-01

    Density functional theory calculations have been performed on three charge transfer donor-acceptor (D-A) molecular pairs, i.e. naphthalene-diamine (Naph) and tetrathiafulvalene (TTF) molecules as electron donors and benzene-diimide (Diimide) and tetracyanoquinodimethane (TCNQ) as electron acceptors. Structural, charge transfer and optical properties of the systems have been studied. The D-A pairs then has been considered inside a macrocycle (cucurbit[8]uril) cavity and Naph-Diimide and TTF-Diimide pairs have been shown to exhibit changes in their structures and orientations, TTF-TCNQ pair does not show any significant structural change. Our work suggests that these changes in structures or orientations are result of electronic repulsion between the keto group oxygen atoms and it can lead to tuning of charge transfer and optical properties of the systems.

  20. Charged-Particle Pseudorapidity Density Distributions from Au+Au Collisions at

    SciTech Connect

    Back, B. B.; Baker, M. D.; Barton, D. S.; Betts, R. R.; Bindel, R.; Budzanowski, A.; Busza, W.; Carroll, A.; Decowski, M. P.; Garcia, E.

    2001-09-03

    The charged-particle pseudorapidity density dN{sub ch}/d{eta} has been measured for Au+Au collisions at s{sub NN}=130 GeV at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the 3% most-central Au+Au collisions for |{eta}|{<=}5.4 is found to be 4200{+-}470 . The evolution of dN{sub ch}/d{eta} with centrality is discussed, and compared to model calculations and to data from proton-induced collisions. The data show an enhancement in charged-particle production at midrapidity, while in the fragmentation regions, the results are consistent with expectations from pp and pA scattering.

  1. Modulating the fixed charge density in silicon nitride films while monitoring the surface recombination velocity by photoluminescence imaging

    NASA Astrophysics Data System (ADS)

    Bazilchuk, Molly; Haug, Halvard; Marstein, Erik Stensrud

    2015-04-01

    Several important semiconductor devices such as solar cells and photodetectors may be fabricated based on surface inversion layer junctions induced by fixed charge in a dielectric layer. Inversion layer junctions can easily be fabricated by depositing layers with a high density of fixed charge on a semiconducting substrate. Increasing the fixed charge improves such devices; for instance, the efficiency of a solar cell can be substantially increased by reducing the surface recombination velocity, which is a function of the fixed charge density. Methods for increasing the charge density are therefore of interest. In this work, the fixed charge density in silicon nitride layers deposited by plasma enhanced chemical vapor deposition is increased to very high values above 1 × 1013 cm-2 after the application of an external voltage to a gate electrode. The effect of the fixed charge density on the surface recombination velocity was experimentally observed using the combination of capacitance-voltage characterization and photoluminescence imaging, showing a significant reduction in the surface recombination velocity for increasing charge density. The surface recombination velocity vs. charge density data was analyzed using a numerical device model, which indicated the presence of a sub-surface damage region formed during deposition of the layers. Finally, we have demonstrated that the aluminum electrodes used for charge injection may be chemically removed in phosphoric acid without loss of the underlying charge. The injected charge was shown to be stable for a prolonged time period, leading us to propose charge injection in silicon nitride films by application of soaking voltage as a viable method for fabricating inversion layer devices.

  2. A method of determining spectral dye densities in color films

    NASA Technical Reports Server (NTRS)

    Friederichs, G. A.; Scarpace, F. L.

    1977-01-01

    A mathematical analysis technique called characteristic vector analysis, reported by Simonds (1963), is used to determine spectral dye densities in multiemulsion film such as color or color-IR imagery. The technique involves examining a number of sets of multivariate data and determining linear transformations of these data to a smaller number of parameters which contain essentially all of the information contained in the original set of data. The steps involved in the actual procedure are outlined. It is shown that integral spectral density measurements of a large number of different color samples can be accurately reconstructed from the calculated spectral dye densities.

  3. Gas pycnometry for density determination of plutonium parts

    SciTech Connect

    Collins, S.; Randolph, H.W.

    1997-08-19

    The traditional method for plutonium density determination is by measuring the weight loss of the component when it is immersed in a liquid of known density, Archimedes` Principle. The most commonly used heavy liquids that are compatible for plutonium measurement are freon and monobromobenzene, but these pose serious environmental and health hazards. The contaminated liquid is also a radiological waste concern with difficult disposition. A gaseous medium would eliminate these environmental and health concerns. A collaborative research effort between the Savannah River Technology Center and Los Alamos National Laboratory was undertaken to determine the feasibility of a gaseous density measurement process for plutonium hemishells.

  4. Wavelike charge density fluctuations and van der Waals interactions at the nanoscale.

    PubMed

    Ambrosetti, Alberto; Ferri, Nicola; DiStasio, Robert A; Tkatchenko, Alexandre

    2016-03-11

    Recent experiments on noncovalent interactions at the nanoscale have challenged the basic assumptions of commonly used particle- or fragment-based models for describing van der Waals (vdW) or dispersion forces. We demonstrate that a qualitatively correct description of the vdW interactions between polarizable nanostructures over a wide range of finite distances can only be attained by accounting for the wavelike nature of charge density fluctuations. By considering a diverse set of materials and biological systems with markedly different dimensionalities, topologies, and polarizabilities, we find a visible enhancement in the nonlocality of the charge density response in the range of 10 to 20 nanometers. These collective wavelike fluctuations are responsible for the emergence of nontrivial modifications of the power laws that govern noncovalent interactions at the nanoscale.

  5. Wavelike charge density fluctuations and van der Waals interactions at the nanoscale.

    PubMed

    Ambrosetti, Alberto; Ferri, Nicola; DiStasio, Robert A; Tkatchenko, Alexandre

    2016-03-11

    Recent experiments on noncovalent interactions at the nanoscale have challenged the basic assumptions of commonly used particle- or fragment-based models for describing van der Waals (vdW) or dispersion forces. We demonstrate that a qualitatively correct description of the vdW interactions between polarizable nanostructures over a wide range of finite distances can only be attained by accounting for the wavelike nature of charge density fluctuations. By considering a diverse set of materials and biological systems with markedly different dimensionalities, topologies, and polarizabilities, we find a visible enhancement in the nonlocality of the charge density response in the range of 10 to 20 nanometers. These collective wavelike fluctuations are responsible for the emergence of nontrivial modifications of the power laws that govern noncovalent interactions at the nanoscale. PMID:26965622

  6. Charge density waves in the graphene sheets of the superconductor CaC(6).

    PubMed

    Rahnejat, K C; Howard, C A; Shuttleworth, N E; Schofield, S R; Iwaya, K; Hirjibehedin, C F; Renner, Ch; Aeppli, G; Ellerby, M

    2011-01-01

    Graphitic systems have an electronic structure that can be readily manipulated through electrostatic or chemical doping, resulting in a rich variety of electronic ground states. Here we report the first observation and characterization of electronic stripes in the highly electron-doped graphitic superconductor, CaC(6), by scanning tunnelling microscopy and spectroscopy. The stripes correspond to a charge density wave with a period three times that of the Ca superlattice. Although the positions of the Ca intercalants are modulated, no displacements of the carbon lattice are detected, indicating that the graphene sheets host the ideal charge density wave. This provides an exceptionally simple material-graphene-as a starting point for understanding the relation between stripes and superconductivity. Furthermore, our experiments suggest a strategy to search for superconductivity in graphene, namely in the vicinity of striped 'Wigner crystal' phases, where some of the electrons crystallize to form a superlattice. PMID:22127054

  7. Collective modes in charge-density waves and long-range Coulomb interactions

    NASA Astrophysics Data System (ADS)

    Virosztek, Attila; Maki, Kazumi

    1993-07-01

    We study theoretically the collective modes in charge-density waves in the presence of long-range Coulomb interaction. We find that earlier works by Takada and his collaborators are inadequate since they introduced inconsistent approximations in evaluating a variety of correlation functions. The amplitude mode is unaffected by the Coulomb interaction, while the phase mode splits into the phason with linear dispersion (i.e., acoustic mode) and the optical mode with an energy gap in the presence of the Coulomb interaction. In particular, we establish the temperature dependence of the phason velocity vφ. A comparison with recent neutron-scattering data on the phason velocity in the charge-density wave of a single crystal of blue bronze K0.3MoO3 indicates that mean-field theory which includes the long-range Coulomb interaction gives an excellent description of the observed phason velocity.

  8. Ionic density distributions near the charged colloids: Spherical electric double layers

    SciTech Connect

    Kim, Eun-Young; Kim, Soon-Chul

    2013-11-21

    We have studied the structure of the spherical electric double layers on charged colloids by a density functional perturbation theory, which is based both on the modified fundamental-measure theory for the hard spheres and on the one-particle direct correlation functional (DCF) for the electronic residual contribution. The contribution of one-particle DCF has been approximated as the functional integration of the second-order correlation function of the ionic fluids in a bulk phase. The calculated result is in very good agreement with the computer simulations for the ionic density distributions and the zeta potentials over a wide range of macroion sizes and electrolyte concentrations, and compares with the results of Yu et al. [J. Chem. Phys. 120, 7223 (2004)] and modified Poisson-Boltzmann approximation [L. B. Bhuiyan and C. W. Outhwaite, Condens. Matter Phys. 8, 287 (2005)]. The present theory is able to provide interesting insights about the charge inversion phenomena occurring at the interface.

  9. Electron Charge and Current Densities, the Geometrie Phase and Cellular Automata

    NASA Astrophysics Data System (ADS)

    Sukumar, N.; Deb, B. M.; Singh, Harjinder

    1993-02-01

    Some consequences of the quantum fluid dynamics formulation are discussed for excited states of atoms and molecules and for time-dependent processes. It is shown that the conservation of electronic current density j(r) allows us to manufacture a gauge potential for each excited state of an atom, molecule or atom in a molecule. This potential gives rise to a tube of magnetic flux carried around by the many-electron system. In time-dependent situations, the evolution of the electronic density distribution can be followed with simple, site-dependent cellular automaton (CA) rules. The CA consists of a lattice of sites, each with a finite set of possible values, here representing finite localized elements of electronic charge and current density (since the charge density r no longer suffices to fully characterize a time-dependent system, it needs to be supplemented with information about the current density j).Our numerical results are presented elsewhere and further development is in progress.

  10. Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions

    SciTech Connect

    Oberhofer, Harald; Blumberger, Jochen

    2009-08-14

    We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following the earlier work of Wu and Van Voorhis [Phys. Rev. A 72, 024502 (2005)], the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the charge constrained state. We investigate the dependence of the constrained energy and of the energy gap on the definition of the charge and present expressions for the constraint forces. The method is applied to the Ru{sup 2+}-Ru{sup 3+} electron self-exchange reaction in aqueous solution. Sampling the vertical energy gap along CDFT-MD trajectories and correcting for finite size effects, a reorganization free energy of 1.6 eV is obtained. This is 0.1-0.2 eV lower than a previous estimate based on a continuum model for solvation. The smaller value for the reorganization free energy can be explained by the fact that the Ru-O distances of the divalent and trivalent Ru hexahydrates are predicted to be more similar in the electron transfer complex than for the separated aqua ions.

  11. Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Oberhofer, Harald; Blumberger, Jochen

    2009-08-01

    We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following the earlier work of Wu and Van Voorhis [Phys. Rev. A 72, 024502 (2005)], the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the charge constrained state. We investigate the dependence of the constrained energy and of the energy gap on the definition of the charge and present expressions for the constraint forces. The method is applied to the Ru2+-Ru3+ electron self-exchange reaction in aqueous solution. Sampling the vertical energy gap along CDFT-MD trajectories and correcting for finite size effects, a reorganization free energy of 1.6 eV is obtained. This is 0.1-0.2 eV lower than a previous estimate based on a continuum model for solvation. The smaller value for the reorganization free energy can be explained by the fact that the Ru-O distances of the divalent and trivalent Ru hexahydrates are predicted to be more similar in the electron transfer complex than for the separated aqua ions.

  12. Charge density measurement and bonding character in LiNiO{sub 2}

    SciTech Connect

    Cao Jiefeng Guo Chao; Zou Huamin

    2009-03-15

    Accurate low-order structure factors of LiNiO{sub 2} were measured by quantitative convergent-beam electron diffraction (QCBED), and then transformed into X-ray structure factors with Mott formula. Combining the structure factors measured by electron diffraction with the structure factors from X-ray diffraction measurements, accurate charge density maps based on a multipole model were obtained. The parameters of the bond critical points (BCP) were calculated for topological analyses. It shows that closed-shell interactions exist between Ni and O atoms, and that the Ni-O and Ni-Ni bonds exhibit some covalent character. The calculated d-orbital occupancies show the charge deficiency at e{sub g}(e{sub g}) orbital and charge surplus at e{sub g}(t{sub 2g}) orbital. The remaining 29.12% population of e{sub g}(e{sub g}) is also an indication of covalent component in the Ni-O bond. The unusual small {kappa}{sub defv} value of the O atom is also discussed. - Graphical Abstract: Combining electron and X-ray diffraction data of LiNiO{sub 2} in multipole refinement, charge density distribution, topological properties at bond critical points and 3d orbital populations of Ni atoms were obtained.

  13. Determining density of maize canopy. 1: Digitized photography

    NASA Technical Reports Server (NTRS)

    Stoner, E. R.; Baumgardner, M. F.; Swain, P. H.

    1972-01-01

    The relationship between different densities of maize (Zea mays L.) canopies and the energy reflected by these canopies was studied. Field plots were laid out, representing four growth stages of maize, on a dark soil and on a very light colored surface soil. Spectral and spatial data were obtained from color and color infrared photography taken from a vertical distance of 10 m above the maize canopies. Estimates of ground cover were related to field measurements of leaf area index. Ground cover was predicted from leaf area index measurements by a second order equation. Color infrared photography proved helpful in determining the density of maize canopy on dark soils. Color photography was useful for determining canopy density on light colored soils. The near infrared dye layer is the most valuable in canopy density determinations.

  14. Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

    PubMed Central

    Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

    2011-01-01

    Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

  15. New Density Estimation Methods for Charged Particle Beams With Applications to Microbunching Instability

    SciTech Connect

    Balsa Terzic, Gabriele Bassi

    2011-07-01

    In this paper we discuss representations of charge particle densities in particle-in-cell (PIC) simulations, analyze the sources and profiles of the intrinsic numerical noise, and present efficient methods for their removal. We devise two alternative estimation methods for charged particle distribution which represent significant improvement over the Monte Carlo cosine expansion used in the 2d code of Bassi, designed to simulate coherent synchrotron radiation (CSR) in charged particle beams. The improvement is achieved by employing an alternative beam density estimation to the Monte Carlo cosine expansion. The representation is first binned onto a finite grid, after which two grid-based methods are employed to approximate particle distributions: (i) truncated fast cosine transform (TFCT); and (ii) thresholded wavelet transform (TWT). We demonstrate that these alternative methods represent a staggering upgrade over the original Monte Carlo cosine expansion in terms of efficiency, while the TWT approximation also provides an appreciable improvement in accuracy. The improvement in accuracy comes from a judicious removal of the numerical noise enabled by the wavelet formulation. The TWT method is then integrated into Bassi's CSR code, and benchmarked against the original version. We show that the new density estimation method provides a superior performance in terms of efficiency and spatial resolution, thus enabling high-fidelity simulations of CSR effects, including microbunching instability.

  16. Chiral Charge Density Wave and Superconductivity in CuxTiSe2 Single Crystals

    NASA Astrophysics Data System (ADS)

    Karapetrov, Goran; Husanikova, P.; Cambel, V.; Szabó, P.; Samuely, P.; Fedor, J.; Iavarone, M.

    2015-03-01

    We investigate atomic scale scanning tunneling microscopy and spectroscopy in CuxTiSe2 single crystals at low temperatures. We map the CDW and superconducting phase diagram as a function of copper doping. STM measurements reveal coexistence of chiral charge density wave and superconductivity. In case of optimally doped and overdoped cases we find that the amplitude of charge density wave modulation is strongly suppressed with respect to strongly underdoped case (x < 0 . 06) with the chiral domain size remaining approximately the same. Superconductivity exhibits BCS character at variety of dopings with 2 Δ / kTc ~ 3 . 6 ÷ 3 . 7 indicating an intermediate coupling strength. Application of the external magnetic field introduces the Abrikosov vortex lattice that is weakly pinned. The size of the vortex core extracted from vortex images corresponds to the one extracted from the magnetization measurements. Our results suggest that, if charge density wave quantum critical point exist, it should be well above the optimal copper concentration of x=0.08. This work is supported by the Army Research Office Grant #W911NF-14-1-0567.

  17. [Study on structure, charge and spectrum for para-halogenated diphenyl ethers through density functional theory].

    PubMed

    Jiang, Long; Cai, Xiao-Yu; Zhang, Chen; Zou, Qiao; Li, Yu

    2013-11-01

    The present paper mainly researched the molecular geometry, charge distribution and spectrum vibration of diphenyl ether and its 3 kinds of para-halogenated diphenyl ethers based on density functional theory (DFT). The infrared and Raman spectrum vibration frequency for para-halogenated diphenyl ethers was calculated based on respective optimal molecular geometry with the same method which was carried out at the B3LYP/6-31(d) level, then spectrum vibration of para-halogenated diphenyl ethers was assigned in detail for the first time. Combined with charge distribution of diphenyl ether and by the nuclear magnetic resonance and Milliken charge distribution, the authors also analyzed the effect of different para-halogenated substituent on charge distribution, at last the vibration mechanism and change rule of of para-halogenated diphenyl ethers' characteristic vibrations were analyzed in the view of charge distribution innovatively. From the research we can see that the more the electronegativity of para-halogenated substituent, the bigger the atomic radius, and the longer the C-X bond, the easier they are degraded in the environment; para-halogenated substituent affected the charge distribution greatly especially to para-carbon relative to ether bond, and meta-carbon was controlled by the combination electronic effect of para-halogenated substituent and oxygen atom, meanwhile ortho-carbon didn't have distinct change; charge gap between bond atoms played significant role in the stability of bonds and vibration frequency of characteristic vibration, and the larger the electronegativity of para-halogenated substituent, the larger the vibration frequency. PMID:24555401

  18. Sequential tentacle grafting and charge modification for enhancing charge density of mono-sized beads for facilitated protein refolding and purification from inclusion bodies.

    PubMed

    Dong, Xiao-Yan; Chen, Ran; Yang, Chun-Yan; Sun, Yan

    2014-06-20

    We have previously found that addition of like-charged media in a refolding solution can greatly enhance the refolding of pure proteins by suppressing protein aggregation. Herein, negatively charged mono-sized microspheres with sulfonic groups were fabricated to explore the facilitating effect of like-charged media on the refolding of enhanced green fluorescent protein (EGFP) expressed as inclusion bodies (IBs). A sequential polymer-tentacle grafting and sulfonate modification strategy was developed to increase the charge density of mono-sized poly(glycidyl methacrylate) (pGMA) beads (2.4μm). Namely, GMA was first grafted onto the beads by grafting polymerization to form poly(GMA) tentacles on the pGMA beads, and then the epoxy groups on the tentacles were converted into sulfonic groups by modification with sodium sulfite. By this fabrication strategy, the charge density of the beads reached 793μmol/g, about 2.8 times higher than that modified without prior grafting of the pGMA beads (285μmol/g). The negatively charged beads of different charge densities were used for facilitating the refolding of like-charged EGFP from IBs. The refolding yield as well as refolding rate increased with increasing charge density. The anti-aggregation effects of urea and like-charged microspheres were synergetic. In addition, partial purification of EGFP was achieved because the ion-exchange adsorption led to 52% removal of positively charged contaminant proteins in the refolded solution. Finally, reusability of the tentacle beads was demonstrated by repetitive EGFP refolding and recovery cycles.

  19. Effective thermal conductivity determination for low-density insulating materials

    NASA Technical Reports Server (NTRS)

    Williams, S. D.; Curry, D. M.

    1978-01-01

    That nonlinear least squares can be used to determine effective thermal conductivity was demonstrated, and a method for assessing the relative error associated with these predicted values was provided. The differences between dynamic and static determination of effective thermal conductivity of low-density materials that transfer heat by a combination of conduction, convection, and radiation were discussed.

  20. First Determination of the Weak Charge of the Proton

    SciTech Connect

    Androic, D.

    2013-10-01

    The Qweak experiment has measured the parity-violating asymmetry in polarized e-p elastic scattering at Q2 = 0.025(GeV/c)2, employing 145 microamps of 89% longitudinally polarized electrons on a 34.4cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run are reported here, constituting approximately 4% of the data collected in the experiment. From these initial results the measured asymmetry is Aep = -279 +- 35 (statistics) +- 31 (systematics) ppb, which is the smallest and most precise asymmetry ever measured in polarized e-p scattering. The small Q2 of this experiment has made possible the first determination of the weak charge of the proton, QpW, by incorporating earlier parity-violating electron scattering (PVES) data at higher Q2 to constrain hadronic corrections. The value of QpW obtained in this way is QnW(PVES) = 0.064 +- 0.012, in good agreement with the Standard Model prediction of QpW(SM) = 0.0710 +- 0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES+APV analysis reveals the neutron's weak charge to be QnW(PVES+APV) = -0.975 +- 0.010.

  1. XPAD X-ray hybrid pixel detector for charge density quality diffracted intensities on laboratory equipment.

    PubMed

    Wenger, Emmanuel; Dahaoui, Slimane; Alle, Paul; Parois, Pascal; Palin, Cyril; Lecomte, Claude; Schaniel, Dominik

    2014-10-01

    The new generation of X-ray detectors, the hybrid pixel area detectors or `pixel detectors', is based on direct detection and single-photon counting processes. A large linearity range, high dynamic and extremely low noise leading to an unprecedented high signal-to-noise ratio, fast readout time (high frame rates) and an electronic shutter are among their intrinsic characteristics which render them very attractive. First used on synchrotron beamlines, these detectors are also promising in the laboratory, in particular for pump-probe or quasi-static experiments and accurate electron density measurements, as explained in this paper. An original laboratory diffractometer made from a Nonius Mach3 goniometer equipped with an Incoatec Mo microsource and an XPAD pixel area detector has been developed at the CRM2 laboratory. Mo Kα accurate charge density quality data up to 1.21 Å(-1) resolution have been collected on a sodium nitroprusside crystal using this home-made diffractometer. Data quality for charge density analysis based on multipolar modelling are discussed in this paper. Deformation electron densities are compared to those already published (based on data collected with CCD APEXII and CAD4 diffractometers). PMID:25274511

  2. Expanding the Scope of Density Derived Electrostatic and Chemical Charge Partitioning to Thousands of Atoms.

    PubMed

    Lee, Louis P; Limas, Nidia Gabaldon; Cole, Daniel J; Payne, Mike C; Skylaris, Chris-Kriton; Manz, Thomas A

    2014-12-01

    The density derived electrostatic and chemical (DDEC/c3) method is implemented into the onetep program to compute net atomic charges (NACs), as well as higher-order atomic multipole moments, of molecules, dense solids, nanoclusters, liquids, and biomolecules using linear-scaling density functional theory (DFT) in a distributed memory parallel computing environment. For a >1000 atom model of the oxygenated myoglobin protein, the DDEC/c3 net charge of the adsorbed oxygen molecule is approximately -1e (in agreement with the Weiss model) using a dynamical mean field theory treatment of the iron atom, but much smaller in magnitude when using the generalized gradient approximation. For GaAs semiconducting nanorods, the system dipole moment using the DDEC/c3 NACs is about 5% higher in magnitude than the dipole computed directly from the quantum mechanical electron density distribution, and the DDEC/c3 NACs reproduce the electrostatic potential to within approximately 0.1 V on the nanorod's solvent-accessible surface. As examples of conducting materials, we study (i) a 55-atom Pt cluster with an adsorbed CO molecule and (ii) the dense solids Mo2C and Pd3V. Our results for solid Mo2C and Pd3V confirm the necessity of a constraint enforcing exponentially decaying electron density in the tails of buried atoms. PMID:26583221

  3. METHOD AND APPARATUS FOR DETERMINING CHARGED PARTICLE MOTION

    DOEpatents

    Kerns, Q.A.

    1959-08-01

    An analog system for determining the motion of charged particles in three dimensional electrical fields is described. A model electrode structure is formed and potentials are applied to the electrodes to provide an analog of the field which is to be studied. To simulate charged particles within the model, conducting spheres are placed at points from which particle motion is to be traced. To free the spheres from gravitational attraction in order that they will be electrostatically accelerated through the model, the apparatus is suspended and dropped. During the pericd that the model is dropping the spheres move through the electrcde structure with a motion corresponding to that of particles in the real system. The model is photographed in the course of falling so that the instantaneous position of the spheres within the simulated field at selected times may be observed and measured. The device thus gives data of particles in the real system. The model is photographed in the course of falling so that the instantaneous position of the spheres within the simulated field at selected times may be observed and measured. The device thus gives data which frequently can otherwise be obtained only with a digital computer.

  4. Determination of Thermal State of Charge in Solar Heat Receivers

    NASA Technical Reports Server (NTRS)

    Glakpe, E. K.; Cannon, J. N.; Hall, C. A., III; Grimmett, I. W.

    1996-01-01

    The research project at Howard University seeks to develop analytical and numerical capabilities to study heat transfer and fluid flow characteristics, and the prediction of the performance of solar heat receivers for space applications. Specifically, the study seeks to elucidate the effects of internal and external thermal radiation, geometrical and applicable dimensionless parameters on the overall heat transfer in space solar heat receivers. Over the last year, a procedure for the characterization of the state-of-charge (SOC) in solar heat receivers for space applications has been developed. By identifying the various factors that affect the SOC, a dimensional analysis is performed resulting in a number of dimensionless groups of parameters. Although not accomplished during the first phase of the research, data generated from a thermal simulation program can be used to determine values of the dimensionless parameters and the state-of-charge and thereby obtain a correlation for the SOC. The simulation program selected for the purpose is HOTTube, a thermal numerical computer code based on a transient time-explicit, axisymmetric model of the total solar heat receiver. Simulation results obtained with the computer program are presented the minimum and maximum insolation orbits. In the absence of any validation of the code with experimental data, results from HOTTube appear reasonable qualitatively in representing the physical situations modeled.

  5. Control of the surface charge density of colloidal silica by sodium hydroxide in salt-freeand low-salt dispersions

    NASA Astrophysics Data System (ADS)

    Yamanaka, Junpei; Hayashi, Yoshihiro; Ise, Norio; Yamaguchi, Takuji

    1997-03-01

    Electrical conductivity measurements and conductometric titrations were performed on dilute salt-free aqueous dispersion of a colloidal silica (diameter: 0.11+/-0.01×10-6nm) whose charge number can be varied with the quantity of coexisting sodium hydroxide. In the absence of sodium hydroxide, the silica particle had an effective (net) surface charge density σe of 8×10-8nC cm-2. Titrations by hydrochloric acid were performed in the presence of sodium hydroxide. When the NaOH concentration was sufficiently high, the titration curve could be divided into three regions with regard to slope values. These regions could be ascribed to titrations of excess sodium hydroxide, ionizable surface groups having Na ions as counterions, and excess hydrochloric acid. The analytical surface charge density σa, estimated from the titration curves, increased with increasing [NaOH]. It was found that the concentrations of Na and OH ions in excess were negligible when the [NaOH] was smaller than 2.5×10-4nM and the volume fraction of the silica, φ, was larger than 2.6×10-3. The value of σa at this threshold was 1.8×10-5nC cm-2. Under these conditions we could control the σa value by varying [NaOH]. The present system provides larger possibilities in studying the influence of charge density on the physico-chemical properties of ionic colloidal systems. Viscosity measurements were performed for salt-free and low-salt dispersions at [NaOH]'s where its excess concentration was found to be negligible. The σa dependence of the viscosity was in good agreement with previous results obtained from ionic latices having various σa's. A relationship between the effective charge density at an infinite dilution, σe\\|φ=0, and σa was examined for latex systems. An empirical relation, ln σe\\|φ=0=0.49 ln σa-1.0, was obtained by using σe\\|φ=0 values determined by the conductivity for latices with various σa's from 0.21×10-6 to 5.6×10-6nC cm-2. By assuming that this relation holds

  6. Picosecond charge transport in rutile at high carrier densities studied by transient terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Zajac, V.; Němec, H.; Kužel, P.

    2016-09-01

    We study terahertz photoconductivity of a rutile single crystal between 10 and 300 K under strong photoexcitation by femtosecond pulses at 266 nm. A marked dependence of the carrier mobility on the carrier density is observed leading to highly complex transport phenomena on a picosecond time scale. We develop a general model of carrier photoconductive response in the case of time dependent inhomogeneous distribution of carrier density and mobility. This allows us to assess an important role of both electrons and holes in the response of photoexcited rutile. At low temperatures, the carrier mobility is initially reduced due to the electron-hole scattering and increases by one order of magnitude upon ambipolar diffusion of the carriers into deeper regions of the sample. At room temperature, contributions of transient hot optical phonons and/or of midinfrared polaron excitations with charge-density-dependent dielectric strength emerge in the photoconductivity spectra.

  7. Light-emitting quantum dot transistors: emission at high charge carrier densities.

    PubMed

    Schornbaum, Julia; Zakharko, Yuriy; Held, Martin; Thiemann, Stefan; Gannott, Florentina; Zaumseil, Jana

    2015-03-11

    For the application of colloidal semiconductor quantum dots in optoelectronic devices, for example, solar cells and light-emitting diodes, it is crucial to understand and control their charge transport and recombination dynamics at high carrier densities. Both can be studied in ambipolar, light-emitting field-effect transistors (LEFETs). Here, we report the first quantum dot light-emitting transistor. Electrolyte-gated PbS quantum dot LEFETs exhibit near-infrared electroluminescence from a confined region within the channel, which proves true ambipolar transport in ligand-exchanged quantum dot solids. Unexpectedly, the external quantum efficiencies improve significantly with current density. This effect correlates with the unusual increase of photoluminescence quantum yield and longer average lifetimes at higher electron and hole concentrations in PbS quantum dot thin films. We attribute the initially low emission efficiencies to nonradiative losses through trap states. At higher carrier densities, these trap states are deactivated and emission is dominated by trions.

  8. Ground-state and transition charge densities in /sup 192/Os

    SciTech Connect

    Reuter, W.; Shera, E.B.; Hoehn, M.V.; Hersman, F.W.; Milliman, T.; Finn, J.M.; Hyde-Wright, C.; Lourie, R.; Pugh, B.; Bertozzi, W.

    1984-11-01

    Elastic and inelastic electron-scattering cross sections of an Os-Pt transition region nucleus, /sup 192/Os, have been measured in a momentum transfer range from 0.6 to 2.9 fm/sup -1/. The data for the ground and the J/sup ..pi../ = 2/sup +/, 2/sup +/', 4/sup +/, and 3/sup -/ states were analyzed model independently with a Fourier-Bessel parametrization of the ground state and transition charge densities. The normalization of the (e,e') cross sections was obtained from a combined analysis with muonic-atom data for the ground and first 2/sup +/ states. The densities and their radial moments are compared with theoretical predictions of the Davydov model and with axially symmetric deformed density-matrix-expansion Hartree-Fock calculations (including the Legendre expansion and the small-amplitude vibration model extensions).

  9. Determination of Jupiter's electron density profile from plasma wave observations

    NASA Astrophysics Data System (ADS)

    Gurnett, D. A.; Scarf, F. L.; Kurth, W. S.; Shaw, R. R.; Poynter, R. L.

    1981-09-01

    The electron density measurements obtained in the Jovian magnetosphere from the plasma wave instruments on the Voyager 1 and 2 spacecraft are summarized. Three basic techniques for determining the electron density are discussed. They are (1) local measurements from the low-frequency cutoff of continuum radiation, (2) local measurements from the frequency of upper hybrid resonance emissions, and (3) integral measurements from the dispersion of whistlers. The limitations and advantages of each technique are reviewed.

  10. [Spectrophotometric determination of cinnarizine based on charge-transfer reaction].

    PubMed

    Xu, B; Zhao, F; Tong, S

    1999-12-01

    The charge-transfer (CT) complex formed between cinnarizine as the donor and 7, 7, 8, 8-Tetracyanoquinodimethane (TCNQ) as the acceptor in acetone-methanol has been studied by spectrophotometric method. Beer's law is obeyed in the range of 0-18 microg x mL(-1) of cinnarizine. The apparent molar absorptivity of CT complex at 743 nm is 1.58 x 10(4) L x mol(-1) x cm(-1). The composition of CT complex is found to be 1 : 1 by Bent-French and Job's methods. The relative standard deviation is less than 3% (n = 10). The method has been applied to the determination of cinnarizine in tablets with satisfactory results. PMID:15822327

  11. Long-range charge-density-wave proximity effect at cuprate/manganate interfaces

    NASA Astrophysics Data System (ADS)

    Frano, A.; Blanco-Canosa, S.; Schierle, E.; Lu, Y.; Wu, M.; Bluschke, M.; Minola, M.; Christiani, G.; Habermeier, H. U.; Logvenov, G.; Wang, Y.; van Aken, P. A.; Benckiser, E.; Weschke, E.; Le Tacon, M.; Keimer, B.

    2016-08-01

    The interplay between charge density waves (CDWs) and high-temperature superconductivity is currently under intense investigation. Experimental research on this issue is difficult because CDW formation in bulk copper oxides is strongly influenced by random disorder, and a long-range-ordered CDW state in high magnetic fields is difficult to access with spectroscopic and diffraction probes. Here we use resonant X-ray scattering in zero magnetic field to show that interfaces with the metallic ferromagnet La2/3Ca1/3MnO3 greatly enhance CDW formation in the optimally doped high-temperature superconductor YBa2Cu3O6+δ (δ ~ 1), and that this effect persists over several tens of nanometres. The wavevector of the incommensurate CDW serves as an internal calibration standard of the charge carrier concentration, which allows us to rule out any significant influence of oxygen non-stoichiometry, and to attribute the observed phenomenon to a genuine electronic proximity effect. Long-range proximity effects induced by heterointerfaces thus offer a powerful method to stabilize the charge-density-wave state in the cuprates and, more generally, to manipulate the interplay between different collective phenomena in metal oxides.

  12. Long-range charge-density-wave proximity effect at cuprate/manganate interfaces.

    PubMed

    Frano, A; Blanco-Canosa, S; Schierle, E; Lu, Y; Wu, M; Bluschke, M; Minola, M; Christiani, G; Habermeier, H U; Logvenov, G; Wang, Y; van Aken, P A; Benckiser, E; Weschke, E; Le Tacon, M; Keimer, B

    2016-08-01

    The interplay between charge density waves (CDWs) and high-temperature superconductivity is currently under intense investigation. Experimental research on this issue is difficult because CDW formation in bulk copper oxides is strongly influenced by random disorder, and a long-range-ordered CDW state in high magnetic fields is difficult to access with spectroscopic and diffraction probes. Here we use resonant X-ray scattering in zero magnetic field to show that interfaces with the metallic ferromagnet La2/3Ca1/3MnO3 greatly enhance CDW formation in the optimally doped high-temperature superconductor YBa2Cu3O6+δ (δ ∼ 1), and that this effect persists over several tens of nanometres. The wavevector of the incommensurate CDW serves as an internal calibration standard of the charge carrier concentration, which allows us to rule out any significant influence of oxygen non-stoichiometry, and to attribute the observed phenomenon to a genuine electronic proximity effect. Long-range proximity effects induced by heterointerfaces thus offer a powerful method to stabilize the charge-density-wave state in the cuprates and, more generally, to manipulate the interplay between different collective phenomena in metal oxides. PMID:27322824

  13. Humic substance charge determination by titration with a flexible cationic polyelectrolyte

    NASA Astrophysics Data System (ADS)

    Tan, Wen-Feng; Norde, Willem; Koopal, Luuk K.

    2011-10-01

    The anionic charge of humic substances (HS) plays a major role in the interaction of HS with other components. Therefore, the potential of the polyelectrolyte titration technique to obtain the charge density of HS in simple 1-1 electrolyte solutions has been investigated. Titrations are carried out with an automatic titrator combined with the "Mütek particle charge detector" which allows determination of the Mütek potential and the pH as a function of the added amount of titrant which is a solution of poly-diallyldimethylammonium chloride (polyDADMAC), a cationic strong polyelectrolyte. When the Mütek potential reverses its sign the iso-electric point (IEP) of the polyDADMAC-HS complex is reached. The polyDADMAC/HS mass ratio at the IEP gives information on the HS charge density and from the pH changes in solution an estimate of the charge regulation in the HS-polyDADMAC complex can be obtained. In general, for polyDADMAC-HS complexes an increase in the dissociation of the acid groups of HS is found (charge regulation). The charge regulation decreases with increasing concentration of 1-1 background electrolyte. Cation incorporation can be neglected at 1-1 electrolyte concentrations ⩽ 1 mmol L -1 and a 1-1 stoichiometry exists between the polyDADMAC and HS charge. However, at these low salt concentrations the charge regulation is substantial. A detailed analysis of purified Aldrich humic acid (PAHA) at pH 5 and a range of KCl concentrations reveals that the anionic charge of PAHA in the complex increases at 5 mmol L -1 KCl by 30% and at 150 mmol L -1 KCl by 12%. On the other hand, increasing amounts of K + become incorporated in the complex: at 5 mmol L -1 KCl 5% and at 150 mmol L -1 KCl 24% of the PAHA charge is balanced by K +. By comparing at pH 5 the mass ratios polyDADMAC/PAHA in the complex at the IEP with the theoretical mass ratios of polyDADMAC/PAHA required to neutralize PAHA in the absence of charge regulation and K + incorporation, it is found that

  14. Electric Double Layer electrostatics of spherical polyelectrolyte brushes with pH-dependent charge density

    NASA Astrophysics Data System (ADS)

    Li, Hao; Chen, Guang; Sinha, Shayandev; Das, Siddhartha; Soft Matter, Interfaces,; Energy Laboratory (Smiel) Team

    Understanding the electric double layer (EDL) electrostatics of spherical polyelectrolyte (PE) brushes, which are spherical particles grafted with PE layers, is essential for appropriate use of PE-grfated micro-nanoparticles for targeted drug delivery, oil recovery, water harvesting, emulsion stabilization, emulsion breaking, etc. Here we elucidate the EDL electrostatics of spherical PE brushes for the case where the PE exhibits pH-dependent charge density. This pH-dependence necessitates the consideration of explicit hydrogen ion concentration, which in turn dictates the distribution of monomers along the length of the grafted PE. This monomer distribution is shown to be a function of the nature of the sphere (metallic or a charged or uncharged dielectric or a liquid-filled sphere). All the calculations are performed for the case where the PE electrostatics can be decoupled from the PE elastic and excluded volume effects. Initial predictions are also provided for the case where such decoupling is not possible.

  15. Investigation of asymmetric alcohol dehydrogenase (ADH) reduction of acetophenone derivatives: effect of charge density.

    PubMed

    Naik, Hemantkumar G; Yeniad, Bahar; Koning, Cor E; Heise, Andreas

    2012-07-01

    In an effort to study the effect of substituent groups of the substrate on the alcohol dehydrogenase (ADH) reductions of aryl-alkyl ketones, several derivatives of acetophenone have been evaluated against ADHs from Lactobacillus brevis (LB) and Thermoanaerobacter sp. (T). Interestingly, ketones with non-demanding (neutral) para-substituents were reduced to secondary alcohols by these enzymes in enantiomerically pure form whereas those with demanding (ionizable) substituents could not be reduced. The effect of substrate size, their solubility in the reaction medium, electron donating and withdrawing properties of the ligand and also the electronic charge density distribution on the substrate molecules have been studied and discussed in detail. From the results, it is observed that the electronic charge distribution in the substrate molecules is influencing the orientation of the substrate in the active site of the enzyme and hence the ability to reduce the substrate.

  16. Dusty plasma diagnostics methods for charge, electron temperature, and ion density

    SciTech Connect

    Liu Bin; Goree, J.; Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F.; Morfill, G. E.; Thomas, H. M.; Ivlev, A. V.

    2010-05-15

    Diagnostic methods are developed to measure the microparticle charge Q and two plasma parameters, electron temperature T{sub e}, and ion density n{sub i}, in the main plasma region of a dusty plasma. Using video microscopy to track microparticles yields a resonance frequency, which along with a charging model allows an estimation of Q and T{sub e}. Only measurements of microparticle position and velocity are required, unlike other methods that use measurements of T{sub e} and plasma parameters as inputs. The resonance frequency measurement can also be used with an ion drag model to estimate n{sub i}. These methods are demonstrated using a single-layer dusty plasma suspension under microgravity conditions.

  17. Density-functional theory for an electrolyte confined by thin charged walls.

    PubMed

    Henderson, D; Bryk, P; Sokołowski, S; Wasan, D T

    2000-04-01

    Results are reported for the primitive model of an electrolyte and for the solvent primitive model of an electrolyte for the case where these fluids are confined by two charged walls. When the walls are thin, the confined electrolyte inside the walls is affected by the charge on both the inside and the outside of the walls. In the case of the primitive model (PM), this system has been studied previously using a singlet integral equation. Our density-functional (DF) study is more general because the fluids inside and outside the walls are constrained to have the same chemical potential and because solvent effects are considered, albeit at a crude level. The singlet integral equation does not consider the chemical potential constraint explicitly. We find that for the low density PM, the DF and integral equation approaches yield, except for a very narrow pore, very similar results. When solvent molecules are considered, the profiles become oscillatory. The co-ion density profiles are particularily interesting because the repulsive electrostatic potential and the effect of the increased pressure in "pushing" the co-ions against the wall compete. PMID:11088170

  18. PEDOT-CNT coated electrodes stimulate retinal neurons at low voltage amplitudes and low charge densities

    NASA Astrophysics Data System (ADS)

    Samba, R.; Herrmann, T.; Zeck, G.

    2015-02-01

    Objective. The aim of this study was to compare two different microelectrode materials—the conductive polymer composite poly-3,4-ethylenedioxythiophene (PEDOT)-carbon nanotube(CNT) and titanium nitride (TiN)—at activating spikes in retinal ganglion cells in whole mount rat retina through stimulation of the local retinal network. Stimulation efficacy of the microelectrodes was analyzed by comparing voltage, current and transferred charge at stimulation threshold. Approach. Retinal ganglion cell spikes were recorded by a central electrode (30 μm diameter) in the planar grid of an electrode array. Extracellular stimulation (monophasic, cathodic, 0.1-1.0 ms) of the retinal network was performed using constant voltage pulses applied to the eight surrounding electrodes. The stimulation electrodes were equally spaced on the four sides of a square (400 × 400 μm). Threshold voltage was determined as the pulse amplitude required to evoke network-mediated ganglion cell spiking in a defined post stimulus time window in 50% of identical stimulus repetitions. For the two electrode materials threshold voltage, transferred charge at threshold, maximum current and the residual current at the end of the pulse were compared. Main results. Stimulation of retinal interneurons using PEDOT-CNT electrodes is achieved with lower stimulation voltage and requires lower charge transfer as compared to TiN. The key parameter for effective stimulation is a constant current over at least 0.5 ms, which is obtained by PEDOT-CNT electrodes at lower stimulation voltage due to its faradaic charge transfer mechanism. Significance. In neuroprosthetic implants, PEDOT-CNT may allow for smaller electrodes, effective stimulation in a safe voltage regime and lower energy-consumption. Our study also indicates, that the charge transferred at threshold or the charge injection capacity per se does not determine stimulation efficacy.

  19. Space Charge Neutralization of DEMO Relevant Negative Ion Beams at Low Gas Density

    SciTech Connect

    Surrey, Elizabeth; Porton, Michael

    2011-09-26

    The application of neutral beams to future power plant devices (DEMO) is dependent on achieving significantly improved electrical efficiency and the most promising route to achieving this is by implementing a photoneutralizer in place of the traditional gas neutralizer. A corollary of this innovation would be a significant reduction in the background gas density through which the beam is transported between the accelerator and the neutralizer. This background gas is responsible for the space charge neutralization of the beam, enabling distances of several metres to be traversed without significant beam expansion. This work investigates the sensitivity of a D{sup -} beam to reduced levels of space charge compensation for energies from 100 keV to 1.5 MeV, representative of a scaled prototype experiment, commissioning and full energy operation. A beam transport code, following the evolution of the phase space ellipse, is employed to investigate the effect of space charge on the beam optics. This shows that the higher energy beams are insensitive to large degrees of under compensation, unlike the lower energies. The probable degree of compensation at low gas density is then investigated through a simple, two component beam-plasma model that allows the potential to be negative. The degree of under-compensation is dependent on the positive plasma ion energy, one source of which is dissociation of the gas by the beam. The subsequent space charge state of the beam is shown to depend upon the relative times for equilibration of the dissociation energy and ionization by the beam ions.

  20. Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

    PubMed

    Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

    2015-08-11

    The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

  1. Direct experimental determination of spectral densities of molecular complexes

    NASA Astrophysics Data System (ADS)

    Pachón, Leonardo A.; Brumer, Paul

    2014-11-01

    Determining the spectral density of a molecular system immersed in a proteomic scaffold and in contact to a solvent is a fundamental challenge in the coarse-grained description of, e.g., electron and energy transfer dynamics. Once the spectral density is characterized, all the time scales are captured and no artificial separation between fast and slow processes need to be invoked. Based on the fluorescence Stokes shift function, we utilize a simple and robust strategy to extract the spectral density of a number of molecular complexes from available experimental data. Specifically, we show that experimental data for dye molecules in several solvents, amino acid proteins in water, and some photochemical systems (e.g., rhodopsin and green fluorescence proteins), are well described by a three-parameter family of sub-Ohmic spectral densities that are characterized by a fast initial Gaussian-like decay followed by a slow algebraic-like decay rate at long times.

  2. Direct experimental determination of spectral densities of molecular complexes

    SciTech Connect

    Pachón, Leonardo A.; Brumer, Paul

    2014-11-07

    Determining the spectral density of a molecular system immersed in a proteomic scaffold and in contact to a solvent is a fundamental challenge in the coarse-grained description of, e.g., electron and energy transfer dynamics. Once the spectral density is characterized, all the time scales are captured and no artificial separation between fast and slow processes need to be invoked. Based on the fluorescence Stokes shift function, we utilize a simple and robust strategy to extract the spectral density of a number of molecular complexes from available experimental data. Specifically, we show that experimental data for dye molecules in several solvents, amino acid proteins in water, and some photochemical systems (e.g., rhodopsin and green fluorescence proteins), are well described by a three-parameter family of sub-Ohmic spectral densities that are characterized by a fast initial Gaussian-like decay followed by a slow algebraic-like decay rate at long times.

  3. Stochasticity and determinism: how density-independent and density-dependent processes affect population variability.

    PubMed

    Ohlberger, Jan; Rogers, Lauren A; Stenseth, Nils Chr

    2014-01-01

    A persistent debate in population ecology concerns the relative importance of environmental stochasticity and density dependence in determining variability in adult year-class strength, which contributes to future reproduction as well as potential yield in exploited populations. Apart from the strength of the processes, the timing of density regulation may affect how stochastic variation, for instance through climate, translates into changes in adult abundance. In this study, we develop a life-cycle model for the population dynamics of a large marine fish population, Northeast Arctic cod, to disentangle the effects of density-independent and density-dependent processes on early life-stages, and to quantify the strength of compensatory density dependence in the population. The model incorporates information from scientific surveys and commercial harvest, and dynamically links multiple effects of intrinsic and extrinsic factors on all life-stages, from eggs to spawners. Using a state-space approach we account for observation error and stochasticity in the population dynamics. Our findings highlight the importance of density-dependent survival in juveniles, indicating that this period of the life cycle largely determines the compensatory capacity of the population. Density regulation at the juvenile life-stage dampens the impact of stochastic processes operating earlier in life such as environmental impacts on the production of eggs and climate-dependent survival of larvae. The timing of stochastic versus regulatory processes thus plays a crucial role in determining variability in adult abundance. Quantifying the contribution of environmental stochasticity and compensatory mechanisms in determining population abundance is essential for assessing population responses to climate change and exploitation by humans. PMID:24893001

  4. Nuclear charge and neutron radii and nuclear matter: Trend analysis in Skyrme density-functional-theory approach

    NASA Astrophysics Data System (ADS)

    Reinhard, P.-G.; Nazarewicz, W.

    2016-05-01

    Background: Radii of charge and neutron distributions are fundamental nuclear properties. They depend on both nuclear interaction parameters related to the equation of state of infinite nuclear matter and on quantal shell effects, which are strongly impacted by the presence of nuclear surface. Purpose: In this work, by studying the correlation of charge and neutron radii, and neutron skin, with nuclear matter parameters, we assess different mechanisms that drive nuclear sizes. Method: We apply nuclear density functional theory using a family of Skyrme functionals obtained by means of optimization protocols, which do not include any radius information. By performing the Monte Carlo sampling of reasonable functionals around the optimal parametrization, we scan all correlations between nuclear matter properties and observables characterizing charge and neutron distributions of spherical closed-shell nuclei 48Ca,208Pb, and 298Fl. Results: By considering the influence of various nuclear matter properties on charge and neutron radii in a multidimensional parameter space of Skyrme functionals, we demonstrate the existence of two strong relationships: (i) between the nuclear charge radii and the saturation density of symmetric nuclear matter ρ0, and (ii) between the neutron skins and the slope of the symmetry energy L . The impact of other nuclear matter properties on nuclear radii is weak or nonexistent. For functionals optimized to experimental binding energies only, proton and neutron radii are found to be weakly correlated due to canceling trends from different nuclear matter characteristics. Conclusion: The existence of only two strong relations connecting nuclear radii with nuclear matter properties has important consequences. First, by requiring that the nuclear functional reproduces the empirical saturation point of symmetric nuclear matter practically fixes the charge (or proton) radii, and vice versa. This explains the recent results of ab initio calculations

  5. Recoil separator ERNA: charge state distribution, target density, beam heating, and longitudinal acceptance

    NASA Astrophysics Data System (ADS)

    Schürmann, D.; Strieder, F.; Di Leva, A.; Gialanella, L.; De Cesare, N.; D'Onofrio, A.; Imbriani, G.; Klug, J.; Lubritto, C.; Ordine, A.; Roca, V.; Röcken, H.; Rolfs, C.; Rogalla, D.; Romano, M.; Schümann, F.; Terrasi, F.; Trautvetter, H. P.

    2004-10-01

    For improved cross section measurements of the reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with high efficiency. The 16O recoils are produced by the 12C projectiles in a windowless 4He gas target. We report on the charge state distribution of the 16O recoils, the gas target density, the beam heating of the gas target, and the acceptance of the separator along the extended gas target.

  6. Restoring The Azimuthal Symmetry Of Charged Particle Lateral Density In The Range Of KASCADE-Grande

    SciTech Connect

    Sima, O.; Rebel, H.; Apel, W. D.; Bekk, K.; Bozdog, H.; Daumiller, K.; Doll, P.; Engel, R.; Engler, J.; Finger, M.; Gils, H. J.; Haungs, A.; Heck, D.; Huege, T.; Isar, P. G.; Klages, H. O.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Nehls, S.

    2010-11-24

    KASCADE-Grande, an extension of the former KASCADE experiment, is a multi-component Extensive Air Shower (EAS) experiment located in Karlsruhe Institute of Technology (Campus North), Germany. An important observable for analyzing the EAS is the lateral density of charged particles in the intrinsic shower plane. This observable is deduced from the basic information provided by the Grande scintillators - the energy deposit - first in the observation plane, by using a Lateral Energy Correction Function (LECF), then in the intrinsic shower plane, by applying an adequate mapping procedure. In both steps azimuthal.

  7. Instability and charge density wave of metallic quantum chains on a silicon surface

    SciTech Connect

    Yeom, H.W.; Takeda, S.; Rotenberg, E.; Matsuda, I.; Horikoshi, K.; Schaefer, J.; Lee, C.M.; Kevan, S.D.; Ohta, T.; Nagao, T.; Hasegawa, S.

    1999-06-14

    Self-assembled indium linear chains on the Si(111) surface are found to exhibit instability of the metallic phase and 1D charge density wave (CDW). The room-temperature metallic phase of these chains undergoes a temperature-induced, reversible transition into a semiconducting phase. The 1D CDW along the chains is observed directly in real space by scanning tunneling microscopy at low temperature. The Fermi contours of the metallic phase measured by angle-resolved photoemission exhibit a perfect nesting predicting precisely the CDW periodicity.

  8. Charge transfer in time-dependent density-functional theory via spin-symmetry breaking

    SciTech Connect

    Fuks, Johanna I.; Maitra, Neepa T.

    2011-04-15

    Long-range charge-transfer excitations pose a major challenge for time-dependent density-functional approximations. We show that spin-symmetry breaking offers a simple solution for molecules composed of open-shell fragments, yielding accurate excitations at large separations when the acceptor effectively contains one active electron. Unrestricted exact-exchange and self-interaction-corrected functionals are performed on one-dimensional models and on the real LiH molecule within the pseudopotential approximation to demonstrate our results.

  9. Effect of the surface charge density on the creep of copper

    NASA Astrophysics Data System (ADS)

    Zhmakin, Yu. D.; Rybyanets, V. A.; Nevskii, S. A.; Gromov, V. E.

    2015-01-01

    The creep of polycrystalline copper under the action of high and low electric potentials is studied. At potentials of ±4 kV and ±5 V, the steady-state creep rate decreases, and the effect in the former case is weaker than in the latter by a factor of 2.5. This difference is caused by the fact that the charge density in the sample-capacitor bank system at the high electric potentials is lower than at the low potentials.

  10. Instability and Charge Density Wave of Metallic Quantum Chains on a Silicon Surface

    SciTech Connect

    Takeda, S.; Rotenberg, E.; Matsuda, I.; Horikoshi, K.; Schäfer, J.; Lee, C. M.; Kevan, S. D.; Ohta, T.; Nagao, T.; Hasegawa, S.

    1999-06-14

    Self-assembled indium linear chains on the Si(111) surface are found to exhibit instability of the metallic phase and 1D charge density wave (CDW). The room-temperature metallic phase of these chains undergoes a temperature-induced, reversible transition into a semiconducting phase. The 1D CDW along the chains is observed directly in real space by scanning tunneling microscopy at low temperature. The Fermi contours of the metallic phase measured by angle-resolved photoemission exhibit a perfect nesting predicting precisely the CDW periodicity.

  11. Accurate vibrational frequencies using the self-consistent-charge density-functional tight-binding method

    NASA Astrophysics Data System (ADS)

    Małolepsza, Edyta; Witek, Henryk A.; Morokuma, Keiji

    2005-09-01

    An optimization technique for enhancing the quality of repulsive two-body potentials of the self-consistent-charge density-functional tight-binding (SCC-DFTB) method is presented and tested. The new, optimized potentials allow for significant improvement of calculated harmonic vibrational frequencies. Mean absolute deviation from experiment computed for a group of 14 hydrocarbons is reduced from 59.0 to 33.2 cm -1 and maximal absolute deviation, from 436.2 to 140.4 cm -1. A drawback of the new family of potentials is a lower quality of reproduced geometrical and energetic parameters.

  12. Nanogyroids incorporating multivalent lipids: enhanced membrane charge density and pore forming ability for gene silencing.

    PubMed

    Leal, Cecília; Ewert, Kai K; Shirazi, Rahau S; Bouxsein, Nathan F; Safinya, Cyrus R

    2011-06-21

    The self-assembly of a custom-synthesized pentavalent cationic lipid (MVL5) and glycerol monooleate (GMO) with small interfering RNA (siRNA) results in the formation of a double-gyroid bicontinuous inverted cubic phase with colocalized lipid/siRNA domains as shown by synchrotron X-ray scattering and fluorescence microscopy. The high charge density (due to MVL5) and positive Gaussian modulus of the GMO-containing membranes confer optimal electrostatic and elastic properties for endosomal escape, enabling efficient siRNA delivery and effective, specific gene silencing.

  13. Nanogyroids Incorporating Multivalent Lipids: Enhanced Membrane Charge Density and Pore Forming Ability for Gene Silencing

    PubMed Central

    Leal, Cecília; Ewert, Kai K.; Shirazi, Rahau S.; Bouxsein, Nathan F.; Safinya, Cyrus R.

    2011-01-01

    The self-assembly of a custom-synthesized pentavalent cationic lipid (MVL5) and glycerol monooleate (GMO) with small interfering RNA (siRNA) results in the formation of a double-gyroid bicontinuous inverted cubic phase with co-localized lipid/siRNA domains as shown by synchrotron X-ray scattering and fluorescence microscopy. The high charge density (due to MVL5) and positive Gaussian modulus of the GMO-containing membranes confer optimal electrostatic and elastic properties for endosomal escape, enabling efficient siRNA delivery and effective, specific gene silencing. PMID:21612245

  14. Pressure Dependence of the Charge-Density-Wave Gap in Rare-Earth Tri-Tellurides

    SciTech Connect

    Sacchetti, A.; Arcangeletti, E.; Perucchi, A.; Baldassarre, L.; Postorino, P.; Lupi, S.; Ru, N.; Fisher, I.R.; Degiorgi, L.; /Zurich, ETH

    2009-12-14

    We investigate the pressure dependence of the optical properties of CeTe{sub 3}, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe{sub 3}.

  15. 42 CFR 405.509 - Determining the inflation-indexed charge.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Reasonable Charges § 405.509 Determining the inflation-indexed charge. (a) Definition. For purposes of this... factor, that is, the annual change in the level of the consumer price index for all urban consumers,...

  16. Cell-penetrating compounds preferentially bind glycosaminoglycans over plasma membrane lipids in a charge density- and stereochemistry-dependent manner.

    PubMed

    Prevette, Lisa E; Benish, Nicolas C; Schoenecker, Amber R; Braden, Kristin J

    2015-12-01

    Cell-penetrating compounds (CPCs) are often conjugated to drugs and genes to facilitate cellular uptake. We hypothesize that the electrostatic interaction between the positively charged amines of the cell-penetrating compounds and the negatively charged glycosaminoglycans (GAGs) extending from cell surfaces is the initiating step in the internalization process. The interactions of generation 5 PAMAM dendrimer, Tat peptide and 25 kDa linear PEI with four different GAGs have been studied using isothermal titration calorimetry to elucidate structure-function relationships that could lead to improved drug and gene delivery methods to a wide variety of cell types. Detailed thermodynamic analysis has determined that CPC-GAG binding constants range from 8.7×10(3) to 2.4×10(6)M(-1) and that affinity is dependent upon GAG charge density and stereochemistry and CPC molecular weight. The effect of GAG composition on affinity is likely due to hydrogen bonding between CPC amines and amides and GAG hydroxyl and amine groups. These results were compared to the association of CPCs with lipid vesicles of varying composition as model plasma membranes to finally clarify the relative importance of each cell surface component in initial cell recognition. CPC-lipid affinity increases with anionic lipid content, but GAG affinity is higher for all cell-penetrating compounds, confirming the role these heterogeneous polysaccharides play in cellular association and clustering.

  17. Electronic Structure and Charge-Density Wave Instabilities in Monolayers of Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Darancet, Pierre; Millis, Andrew J.; Marianetti, Chris A.

    2013-03-01

    Transition metal dichalcogenides (TMDC) are layered materials displaying a variety of charge-density wave (CDW) instabilities and complex phase diagrams for group IV & V transition metals. Recent progress in mechanical exfoliation and device fabrication now allow for electrical characterization and gating of individual, 3-atom thick layers of TMDCs, providing new probes of the complex many-body interactions arising in these compounds. In this talk, I will present our investigations using density functional and dynamical mean-field theory regarding the electronic structure and electronic correlations arising in distorted monolayers, bilayers, and trilayers of octahedral group V TMDCs. We will examine the importance of doping, crystal fields, and many-body interactions, and their influence on the transport and optical properties of these materials upon distortion. Computational resources provided by New York Center for Computational Sciences at SBU/BNL supported by the U.S. DOE under Contract No. DE-AC02-98CH10886

  18. Charge-density distribution in hydrogen methylphosphonates of calcium and lithium.

    PubMed

    Mermer, Adrian; Starynowicz, Przemysław

    2011-10-01

    Two new crystal structures, calcium bis(hydrogen methylphosphonate), Ca(CH(3)PO(3)H)(2), and lithium hydrogen methylphosphonate, Li(CH(3)PO(3)H), have been obtained, and the experimental and theoretical charge densities, as well as their topological properties, are reported. Both compounds display layered structures. Each hydrogen methylphosphonate anion coordinates three metal cations in the calcium compound and four in the lithium one. Weak polarization of oxygen lone pairs is observed, with lithium showing somewhat stronger polarization strength than calcium. The reported topological properties from the density functional theory (DFT) and X-ray approach are consistent with each other. In both structures the P-O bonds have a significant share of ionic character. The hyperconjugation effects within the phosphonate group are quenched upon coordination of the metal cations.

  19. Charge density wave fluctuations, heavy electrons, and superconductivity in KNi2S2

    NASA Astrophysics Data System (ADS)

    Neilson, James R.; McQueen, Tyrel M.; Llobet, Anna; Wen, Jiajia; Suchomel, Matthew R.

    2013-01-01

    Understanding the complexities of electronic and magnetic ground states in solids is one of the main goals of solid-state physics. Materials with the canonical ThCr2Si2-type structure have proved particularly fruitful in this regard, as they exhibit a wide range of technologically advantageous physical properties described by “many-body physics,” including high-temperature superconductivity and heavy fermion behavior. Here, using high-resolution synchrotron x-ray diffraction and time-of-flight neutron scattering, we show that the isostructural mixed valence compound KNi2S2 displays a number of highly unusual structural transitions, most notably the presence of charge density wave fluctuations that disappear on cooling. This behavior occurs without magnetic or charge order, in contrast to expectations based on other known materials exhibiting related phenomena. Furthermore, the low-temperature electronic state of KNi2S2 is found to exhibit many characteristics of heavy-fermion behavior, including a heavy electron state (m*/me˜ 24), with a negative coefficient of thermal expansion, and superconductivity below Tc=0.46(2) K. In the potassium nickel sulfide, these behaviors arise in the absence of localized magnetism, and instead appear to originate in proximity to charge order.

  20. Application of double-hybrid density functionals to charge transfer in N-substituted pentacenequinones

    NASA Astrophysics Data System (ADS)

    Sancho-García, J. C.

    2012-05-01

    A set of N-heteroquinones, deriving from oligoacenes, have been recently proposed as n-type organic semiconductors with high electron mobilities in thin-film transistors. Generally speaking, this class of compounds self-assembles in neighboring π-stacks linked by weak hydrogen bonds. We aim at theoretically characterizing here the sequential charge transport (hopping) process expected to take place across these arrays of molecules. To do so, we need to accurately address the preferred packing of these materials simultaneously to single-molecule properties related to charge-transfer events, carefully employing dispersion-corrected density functional theory methods to accurately extract the key molecular parameters governing this phenomenon at the nanoscale. This study confirms the great deal of interest around these compounds, since controlled functionalization of model molecules (i.e., pentacene) allows to efficiently tune the corresponding charge mobilities, and the capacity of modern quantum-chemical methods to predict it after rationalizing the underlying structure-property relationships.

  1. Charged-particle rapidity density in Au+Au collisions in a quark combination model

    NASA Astrophysics Data System (ADS)

    Shao, Feng-Lan; Yao, Tao; Xie, Qu-Bing

    2007-03-01

    Rapidity/pseudorapidity densities for charged particles and their centrality, rapidity, and energy dependence in Au+Au collisions at the Relativistic Heavy Ion Collider are studied in a quark combination model. Using a Gaussian-type rapidity distribution for constituent quarks as a result of Landau hydrodynamic evolution, the data at sNN=130,200 GeV at various centralities in full pseudorapidity range are well described, and the charged-particle multiplicities are reproduced as functions of the number of participants. The energy dependence of the shape of the dNch/dη distribution is also described at various collision energies sNN=200,130,62.4 GeV in central collisions with same value of parameters except 19.6 GeV. The calculated rapidity distributions and yields for the charged pions and kaons in central Au+Au collisions at sNN=200 GeV are compared with experimental data of the BRAHMS Collaboration.

  2. Superconductivity and Charge Density Wave in ZrTe3-xSex.

    PubMed

    Zhu, Xiangde; Ning, Wei; Li, Lijun; Ling, Langsheng; Zhang, Ranran; Zhang, Jinglei; Wang, Kefeng; Liu, Yu; Pi, Li; Ma, Yongchang; Du, Haifeng; Tian, Minglian; Sun, Yuping; Petrovic, Cedomir; Zhang, Yuheng

    2016-01-01

    Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe3 when the long range CDW order is gradually suppressed. Superconducting critical temperature Tc(x) in ZrTe3-xSex (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase in Se content results in diminishing Tc and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe3 CDW order in resistivity vanishes. The electronic-scattering for high Tc crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy. PMID:27253150

  3. Superconductivity and Charge Density Wave in ZrTe3-xSex.

    PubMed

    Zhu, Xiangde; Ning, Wei; Li, Lijun; Ling, Langsheng; Zhang, Ranran; Zhang, Jinglei; Wang, Kefeng; Liu, Yu; Pi, Li; Ma, Yongchang; Du, Haifeng; Tian, Minglian; Sun, Yuping; Petrovic, Cedomir; Zhang, Yuheng

    2016-06-02

    Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe3 when the long range CDW order is gradually suppressed. Superconducting critical temperature Tc(x) in ZrTe3-xSex (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase in Se content results in diminishing Tc and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe3 CDW order in resistivity vanishes. The electronic-scattering for high Tc crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy.

  4. Superconductivity and Charge Density Wave in ZrTe3−xSex

    PubMed Central

    Zhu, Xiangde; Ning, Wei; Li, Lijun; Ling, Langsheng; Zhang, Ranran; Zhang, Jinglei; Wang, Kefeng; Liu, Yu; Pi, Li; Ma, Yongchang; Du, Haifeng; Tian, Minglian; Sun, Yuping; Petrovic, Cedomir; Zhang, Yuheng

    2016-01-01

    Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe3 when the long range CDW order is gradually suppressed. Superconducting critical temperature Tc(x) in ZrTe3−xSex (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase in Se content results in diminishing Tc and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe3 CDW order in resistivity vanishes. The electronic-scattering for high Tc crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy. PMID:27253150

  5. Superconductivity and Charge Density Wave in ZrTe3‑xSex

    NASA Astrophysics Data System (ADS)

    Zhu, Xiangde; Ning, Wei; Li, Lijun; Ling, Langsheng; Zhang, Ranran; Zhang, Jinglei; Wang, Kefeng; Liu, Yu; Pi, Li; Ma, Yongchang; Du, Haifeng; Tian, Minglian; Sun, Yuping; Petrovic, Cedomir; Zhang, Yuheng

    2016-06-01

    Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe3 when the long range CDW order is gradually suppressed. Superconducting critical temperature Tc(x) in ZrTe3‑xSex (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase in Se content results in diminishing Tc and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe3 CDW order in resistivity vanishes. The electronic-scattering for high Tc crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy.

  6. Charge Density Wave Behavior of Ionic Liquid Gated Strontium Titanate Nanowires

    NASA Astrophysics Data System (ADS)

    Bretz-Sullivan, Terence; Goldman, Allen

    2015-03-01

    Measurements of the current-voltage characteristics of ionic liquid gated nanometer scale channels of strontium titanate have been carried out. These characteristics exhibit a large voltage threshold for conduction and a nonlinear power law behavior at all temperatures measured. The source-drain current of these nanowires scales as a power law of the difference between the source-drain voltage and the threshold voltage. The temperature dependence of the threshold voltage appears to be related to the inverse of the temperature dependent dielectric constant of strontium titanate in qualitative agreement with a simple model of charge density wave depinning. These observations, when taken together, are evidence that a gate induced charge density wave has been induced, and is depinned by strong electric fields. This work was supported by DOE Basic Energy Sciences Grant DE-FG02-02ER46004. Samples were fabricated at the Minnesota Nanofabrication Center. Parts of this work were carried out in the University of Minnesota Characterization Facility, a member of the Materials Research Facilities Network (www.mrfn.org) funded via the NSF MRSEC program.

  7. Charge density wave in layered La1 -xCexSb2

    NASA Astrophysics Data System (ADS)

    Luccas, R. F.; Fente, A.; Hanko, J.; Correa-Orellana, A.; Herrera, E.; Climent-Pascual, E.; Azpeitia, J.; Pérez-Castañeda, T.; Osorio, M. R.; Salas-Colera, E.; Nemes, N. M.; Mompean, F. J.; García-Hernández, M.; Rodrigo, J. G.; Ramos, M. A.; Guillamón, I.; Vieira, S.; Suderow, H.

    2015-12-01

    The layered rare-earth diantimonides R Sb2 are anisotropic metals with generally low electronic densities whose properties can be modified by substituting the rare earth. LaSb2 is a nonmagnetic metal with a low residual resistivity presenting a low-temperature magnetoresistance that does not saturate with the magnetic field. It has been proposed that the latter can be associated to a charge density wave (CDW), but no CDW has yet been found. Here we find a kink in the resistivity above room temperature in LaSb2 (at 355 K) and show that the kink becomes much more pronounced with substitution of La by Ce along the La1 -xCexSb2 series. We find signatures of a CDW in x-ray scattering, specific heat, and scanning tunneling microscopy (STM) experiments in particular for x ≈0.5 . We observe a distortion of rare-earth-Sb bonds lying in-plane of the tetragonal crystal using x-ray scattering, an anomaly in the specific heat at the same temperature as the kink in resistivity and charge modulations in STM. We conclude that LaSb2 has a CDW which is stabilized in the La1 -xCexSb2 series due to substitutional disorder.

  8. In situ unravelling structural modulation across the charge-density-wave transition in vanadium disulfide.

    PubMed

    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.

  9. Superconductivity and charge density wave in ZrTe3–xSex

    DOE PAGES

    Zhu, Xiangde; Ning, Wei; Li, Lijun; Ling, Langsheng; Zhang, Ranran; Zhang, Jinglei; Wang, Kefeng; Liu, Yu; Pi, Li; Ma, Yongchang; et al

    2016-06-02

    Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe3 when the long range CDW order is gradually suppressed. Superconducting critical temperature Tc(x) in ZrTe3–xSex (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase in Se content results inmore » diminishing Tc and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe3 CDW order in resistivity vanishes. As a result, the electronic-scattering for high Tc crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy.« less

  10. Low temperature thermoelectric properties of Cu intercalated TiSe2: a charge density wave material

    NASA Astrophysics Data System (ADS)

    Bhatt, Ranu; Basu, Ranita; Bhattacharya, S.; Singh, A.; Aswal, D. K.; Gupta, S. K.; Okram, G. S.; Ganesan, V.; Venkateshwarlu, D.; Surgers, C.; Navaneethan, M.; Hayakawa, Y.

    2013-05-01

    In this communication, we investigate the thermoelectric properties of a charge density wave material TiSe2 upon Cu intercalation. Polycrystalline Cu x TiSe2 ( x=0-0.11) alloys were synthesized using solid state sintering process and their morphological and structural properties were investigated. The material grows in layered morphology and the c-lattice parameter increases linearly with x. The temperature dependent resistivity measured in the 300-5 K range, shows that increasing x leads to a systematic transition from charge density wave state to the metallic state. For x=0.11, the room temperature thermoelectric figure-of-merit is found to be 0.104, which is higher by seven orders in magnitude (i.e. 1.93×10-8) measured for pristine TiSe2 and comparable to the other reported thermoelectric materials. These results show that Cu x TiSe2 are a potential material for the low temperature thermoelectric applications.

  11. Superficial Collagen Fibril Modulus and Pericellular Fixed Charge Density Modulate Chondrocyte Volumetric Behaviour in Early Osteoarthritis

    PubMed Central

    Turunen, Siru M.; Han, Sang Kuy; Herzog, Walter; Korhonen, Rami K.

    2013-01-01

    The aim of this study was to investigate if the experimentally detected altered chondrocyte volumetric behavior in early osteoarthritis can be explained by changes in the extracellular and pericellular matrix properties of cartilage. Based on our own experimental tests and the literature, the structural and mechanical parameters for normal and osteoarthritic cartilage were implemented into a multiscale fibril-reinforced poroelastic swelling model. Model simulations were compared with experimentally observed cell volume changes in mechanically loaded cartilage, obtained from anterior cruciate ligament transected rabbit knees. We found that the cell volume increased by 7% in the osteoarthritic cartilage model following mechanical loading of the tissue. In contrast, the cell volume decreased by 4% in normal cartilage model. These findings were consistent with the experimental results. Increased local transversal tissue strain due to the reduced collagen fibril stiffness accompanied with the reduced fixed charge density of the pericellular matrix could increase the cell volume up to 12%. These findings suggest that the increase in the cell volume in mechanically loaded osteoarthritic cartilage is primarily explained by the reduction in the pericellular fixed charge density, while the superficial collagen fibril stiffness is suggested to contribute secondarily to the cell volume behavior. PMID:23634175

  12. Brownian dynamics determine universality of charge transport in ionic liquids

    SciTech Connect

    Sangoro, Joshua R; Iacob, Ciprian; Mierzwa, Michal; Paluch, Marian; Kremer, Friedrich

    2012-01-01

    Broadband dielectric spectroscopy is employed to investigate charge transport in a variety of glass-forming ionic liquids over wide frequency, temperature and pressure ranges. Using a combination of Einstein, Einstein-Smoluchowski, and Langevin relations, the observed universal scaling of charge transport in ionic liquids is traced back to the dominant role of Brownian dynamics.

  13. Determination of layer-charge characteristics of smectites

    USGS Publications Warehouse

    Christidis, G.E.; Eberl, D.D.

    2003-01-01

    A new method for calculation of layer charge and charge distribution of smectites is proposed. The method is based on comparisons between X-ray diffraction (XRD) patterns of K-saturated, ethylene glycol-solvated, oriented samples and calculated XRD patterns for three-component, mixed-layer systems. For the calculated patterns it is assumed that the measured patterns can be modeled as random interstratifications of fully expanding 17.1 A?? layers, partially expanding 13.5 A?? layers and non-expanding 9.98 A?? layers. The technique was tested using 29 well characterized smectites. According to their XRD patterns, smectites were classified as group 1 (low-charge smectites) and group 2 (high-charge smectites). The boundary between the two groups is at a layer charge of -0.46 equivalents per half unit-cell. Low-charge smectites are dominated by 17.1 A?? layers, whereas high-charge smectites contain only 20% fully expandable layers on average. Smectite properties and industrial applications may be dictated by the proportion of 17.1 A?? layers present. Non-expanding layers may control the behavior of smectites during weathering, facilitating the formation of illite layers after subsequent cycles of wetting and drying. The precision of the method is better than 3.5% at a layer charge of -0.50; therefore the method should be useful for basic research and for industrial purposes.

  14. Kinetic theory and atomic physics corrections for determination of ion velocities from charge-exchange spectroscopy

    NASA Astrophysics Data System (ADS)

    Muñoz Burgos, J. M.; Burrell, K. H.; Solomon, W. M.; Grierson, B. A.; Loch, S. D.; Ballance, C. P.; Chrystal, C.

    2013-09-01

    Charge-exchange spectroscopy is a powerful diagnostic tool for determining ion temperatures, densities and rotational velocities in tokamak plasmas. This technique depends on detailed understanding of the atomic physics processes that affect the measured apparent velocities with respect to the true ion rotational velocities. These atomic effects are mainly due to energy dependence of the charge-exchange cross-sections, and in the case of poloidal velocities, due to gyro-motion of the ion during the finite lifetime of the excited states. Accurate lifetimes are necessary for correct interpretation of measured poloidal velocities, specially for high density plasma regimes on machines such as ITER, where l-mixing effects must be taken into account. In this work, a full nl-resolved atomic collisional radiative model coupled with a full kinetic calculation that includes the effects of electric and magnetic fields on the ion gyro-motion is presented for the first time. The model directly calculates from atomic physics first principles the excited state lifetimes that are necessary to evaluate the gyro-orbit effects. It is shown that even for low density plasmas where l-mixing effects are unimportant and coronal conditions can be assumed, the nl-resolved model is necessary for an accurate description of the gyro-motion effects to determine poloidal velocities. This solution shows good agreement when compared to three QH-mode shots on DIII-D, which contain a wide range of toroidal velocities and high ion temperatures where greater atomic corrections are needed. The velocities obtained from the model are compared to experimental velocities determined from co- and counter-injection of neutral beams on DIII-D.

  15. Normal mode analysis of single bunch, charge density dependent behavior in electron/positron beams

    NASA Astrophysics Data System (ADS)

    Ehrlichman, Michael

    Accelerator science in coming years will be increasingly dependent upon high single-bunch charges and/or small emittances. Under these conditions, single-particle dynamics are not a sufficient description of beam behavior and interactions between the beam particles must be taken into account. One such interaction is when collisions between the particles that compose a bunch perturb the motion of the colliding particles significantly and frequently enough to impact the beam dynamics. Multiple, small-angle, collisions blow up the emittance of the bunch and are referred to as intrabeam scattering (IBS). Here are documented the theoretical and experimental studies of IBS in storage rings undertaken as part of the CesrTA program. Under the conditions where IBS becomes dominant, other multi-particle effects can also appear. The additional effects we investigate include potential well distortion, coherent current-dependent tune shift, and direct space charge. CesrTA design and analysis is conducted in a normal mode coordinates environment which allows for natural handling of coupling. To that end, we develop a 6D normal modes decomposition of the linear beam optics. Multi-particle effects are also important for Energy Recovery Linear Accelerators (ERLs). Because the beam circulates for only a short period of time in an ERL, the beam lifetime imposed by Touschek scattering is not significant. However, the particles scattered out of the bunch can generate a radiation hazard where they collide with the beam pipe. We re-derive Piwinski's original Touschek scattering equation to check its validity when applied to ERL beams, then repurpose the formula to generate a profile of where scattered particles are generated and where they are lost. The results presented here advance our understanding of charge-dependent behavior in the sorts of high charge-density accelerators that will be implemented in coming years.

  16. Determining density of maize canopy. 2: Airborne multispectral scanner data

    NASA Technical Reports Server (NTRS)

    Stoner, E. R.; Baumgardner, M. F.; Cipra, J. E.

    1971-01-01

    Multispectral scanner data were collected in two flights over a light colored soil background cover plot at an altitude of 305 m. Energy in eleven reflective wavelength band from 0.45 to 2.6 microns was recorded. Four growth stages of maize (Zea mays L.) gave a wide range of canopy densities for each flight date. Leaf area index measurements were taken from the twelve subplots and were used as a measure of canopy density. Ratio techniques were used to relate uncalibrated scanner response to leaf area index. The ratios of scanner data values for the 0.72 to 0.92 micron wavelength band over the 0.61 to 0.70 micron wavelength band were calculated for each plot. The ratios related very well to leaf area index for a given flight date. The results indicated that spectral data from maize canopies could be of value in determining canopy density.

  17. Using line broadening to determine the electron density in an argon surface-wave discharge at atmospheric pressure

    SciTech Connect

    Christova, M.; Christov, L.; Castanos-Martinez, E.; Moisan, M.; Dimitrijevic, M. S.

    2008-10-22

    Broadening due to collisions with charged particles (Stark broadening ) and neutral atoms, was determined for Ar I 522.1, 549.6 and 603.2 nm spectral lines from the spectral series 3p{sup 5}nd-3p{sup 5}4p, in order to evaluate the electron density in a surface-wave discharge at atmospheric pressure.

  18. Interplay of charge density wave and multiband superconductivity in 2H-PdxTaSe2.

    PubMed

    Bhoi, D; Khim, S; Nam, W; Lee, B S; Kim, Chanhee; Jeon, B-G; Min, B H; Park, S; Kim, Kee Hoon

    2016-04-05

    2H-TaSe2 has been one of unique transition metal dichalcogenides exhibiting several phase transitions due to a delicate balance among competing electronic ground states. An unusual metallic state at high-T is sequentially followed by an incommensurate charge density wave (ICDW) state at ≈122 K and a commensurate charge density wave (CCDW) state at ≈90 K, and superconductivity at TC ~ 0.14 K. Upon systematic intercalation of Pd ions into TaSe2, we find that CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x ~ 0.09-0.10. Moreover, TC shows a dramatic enhancement up to 3.3 K at x = 0.08, ~24 times of TC in 2H-TaSe2, in proportional to the density of states N(EF). Investigations of upper critical fields Hc2 in single crystals reveal evidences of multiband superconductivity as temperature-dependent anisotropy factor γH = , quasi-linear increase of , and an upward, positive-curvature in near TC. Furthermore, analysis of temperature-dependent electronic specific heat corroborates the presence of multiple superconducting gaps. Based on above findings and electronic phase diagram vs x, we propose that the increase of N(EF) and effective electron-phonon coupling in the vicinity of CDW quantum phase transition should be a key to the large enhancement of TC in PdxTaSe2.

  19. Interplay of charge density wave and multiband superconductivity in 2H-PdxTaSe2

    PubMed Central

    Bhoi, D.; Khim, S.; Nam, W.; Lee, B. S.; Kim, Chanhee; Jeon, B.-G.; Min, B. H.; Park, S.; Kim, Kee Hoon

    2016-01-01

    2H-TaSe2 has been one of unique transition metal dichalcogenides exhibiting several phase transitions due to a delicate balance among competing electronic ground states. An unusual metallic state at high-T is sequentially followed by an incommensurate charge density wave (ICDW) state at ≈122 K and a commensurate charge density wave (CCDW) state at ≈90 K, and superconductivity at TC ~ 0.14 K. Upon systematic intercalation of Pd ions into TaSe2, we find that CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x ~ 0.09–0.10. Moreover, TC shows a dramatic enhancement up to 3.3 K at x = 0.08, ~24 times of TC in 2H-TaSe2, in proportional to the density of states N(EF). Investigations of upper critical fields Hc2 in single crystals reveal evidences of multiband superconductivity as temperature-dependent anisotropy factor γH = , quasi-linear increase of , and an upward, positive-curvature in near TC. Furthermore, analysis of temperature-dependent electronic specific heat corroborates the presence of multiple superconducting gaps. Based on above findings and electronic phase diagram vs x, we propose that the increase of N(EF) and effective electron-phonon coupling in the vicinity of CDW quantum phase transition should be a key to the large enhancement of TC in PdxTaSe2. PMID:27045426

  20. Resonant plasmon-axion excitations induced by charge density wave order in a Weyl semimetal

    NASA Astrophysics Data System (ADS)

    Redell, Matthew D.; Mukherjee, Shantanu; Lee, Wei-Cheng

    2016-06-01

    We investigate the charge excitations of a Weyl semimetal in the axionic charge density wave (axionic CDW) state. While it has been shown that the topological response (anomalous Hall conductivity) is protected against the CDW state, we find that the long-wavelength plasmon excitation is radically influenced by the dynamics of the CDW order parameter. In the normal state, we show that an undamped collective mode should exist at q ⃗≈Q⃗CDW if there is an attractive interaction favoring the formation of the CDW state. The undamped nature of this collective mode is attributed to a gaplike feature in the particle-hole continuum at q ⃗≈Q⃗CDW due to the chirality of the Weyl nodes, which is not seen in other materials with CDW instability. In the CDW state, the long-wavelength plasmon excitations become more dispersive due to the additional interband scattering not allowed in the normal state. Moreover, because the translational symmetry is spontaneously broken, umklapp scattering, the process conserving the total momentum only up to n Q⃗CDW , with n an integer and Q⃗CDW the ordering wave vector, emerges in the CDW state. We find that the plasmon excitation couples to the phonon mode of the CDW order via the umklapp scattering, leading to two branches of resonant collective modes observable in the density-density correlation function at q ⃗≈0 and q ⃗≈Q⃗CDW . Based on our analysis, we propose that measuring these resonant plasmon-axion excitations around q ⃗≈0 and q ⃗≈Q⃗CDW by momentum-resolved electron energy loss spectroscopy could serve as a reliable way to detect the axionic CDW state in Weyl semimetals.

  1. The role of surface charge density in cationic liposome-promoted dendritic cell maturation and vaccine-induced immune responses

    NASA Astrophysics Data System (ADS)

    Ma, Yifan; Zhuang, Yan; Xie, Xiaofang; Wang, Ce; Wang, Fei; Zhou, Dongmei; Zeng, Jianqiang; Cai, Lintao

    2011-05-01

    Cationic liposomes have emerged as a novel adjuvant and antigen delivery system to enhance vaccine efficacy. However, the role of surface charge density in cationic liposome-regulated immune responses has not yet been elucidated. In the present study, we prepared a series of DOTAP/DOPC cationic liposomes with different surface densities by incorporating varying amounts of DOPC (a neutral lipid) into DOTAP (a cationic lipid). The results showed that DOTAP/DOPC cationic liposome-regulated immune responses relied on the surface charge density, and might occur through ROS signaling. The liposomes with a relatively high charge density, such as DOTAP/DOPC 5 : 0 and 4 : 1 liposomes, potently enhanced dendritic cell maturation, ROS generaion, antigen uptake, as well as the production of OVA-specific IgG2a and IFN-γ. In contrast, low-charge liposomes, such as DOTAP/DOPC 1 : 4 liposome, failed to promote immune responses even at high concentrations, confirming that the immunoregulatory effect of cationic liposomes is mostly attributable to their surface charge density. Moreover, the DOTAP/DOPC 1 : 4 liposome suppressed anti-OVA antibody responses in vivo. Overall, maintaining an appropriate surface charge is crucial for optimizing the adjuvant effect of cationic liposomes and enhancing the efficacy of liposome-based vaccines.

  2. EXPERIMENTAL INVESTIGATIONS OF ION CHARGE DISTRIBUTIONS, EFFECTIVE ELECTRON DENSITIES, AND ELECTRON-ION CLOUD OVERLAP IN ELECTRON BEAM ION TRAP PLASMA USING EXTREME-ULTRAVIOLET SPECTROSCOPY

    SciTech Connect

    Liang, G. Y.; Crespo Lopez-Urrutia, J. R.; Baumann, T. M.; Epp, S. W.; Gonchar, A.; Mokler, P. H.; Simon, M. C.; Tawara, H.; Maeckel, V.; Ullrich, J.; Lapierre, A.; Yao, K.; Zou, Y.; Zhao, G. E-mail: crespojr@mpi-hd.mpg.de

    2009-09-10

    Spectra in the extreme ultraviolet range from 107 to 353 A emitted from Fe ions in various ionization stages have been observed at the Heidelberg electron beam ion trap (EBIT) with a flat-field grating spectrometer. A series of transition lines and their intensities have been analyzed and compared with collisional-radiative simulations. The present collisional-radiative model reproduces well the relative line intensities and facilitates line identification of ions produced in the EBIT. The polarization effect on the line intensities resulting from nonthermal unidirectional electron impact was explored and found to be significant (up to 24%) for a few transition lines. Based upon the observed line intensities, relative charge state distributions (CSD) of ions were determined, which peaked at Fe{sup 23+} tailing toward lower charge states. Another simulation on ion charge distributions including the ionization and electron capture processes generated CSDs which are in general agreement with the measurements. By observing intensity ratios of specific lines from levels collisionally populated directly from the ground state and those starting from the metastable levels of Fe XXI, Fe X and other ionic states, the effective electron densities were extracted and found to depend on the ionic charge. Furthermore, it was found that the overlap of the ion cloud with the electron beam estimated from the effective electron densities strongly depends on the charge state of the ion considered, i.e. under the same EBIT conditions, higher charge ions show less expansion in the radial direction.

  3. Tests of QCD at HERA: determination of the gluon density

    SciTech Connect

    Repond, J.

    1996-12-31

    An overview is given of the various methods available to the colliding beam experiments at HERA to determine the gluon density of the proton. The article includes a description of fits to the structure function F{sub 2}, of studies of dijet and open charm production in deep inelastic scattering, of elastic and inelastic {psi} photoproduction, and of inclusive diffractive scattering. 13 refs., 8 figs.

  4. Use of calorimetry for end of charge determination

    NASA Technical Reports Server (NTRS)

    Johnson, Chris J.

    1994-01-01

    To perform heat flow measurements on batteries, it is necessary to consider the following requirements: establish thermal neutral potential; identify inefficient charging; understand self discharge mechanisms; and provide accurate voltage/temperature data. A discussion is provided in viewgraph format.

  5. Suppressing a charge density wave by changing dimensionality in the ferecrystalline compounds ([SnSe]1.15)1(VSe2)n with n = 1, 2, 3, 4.

    PubMed

    Falmbigl, Matthias; Fiedler, Andreas; Atkins, Ryan E; Fischer, Saskia F; Johnson, David C

    2015-02-11

    The compounds, ([SnSe]1.15)1(VSe2)n with n = 1, 2, 3, and 4, were prepared using designed precursors in order to investigate the influence of the thickness of the VSe2 constituent on the charge density wave transition. The structure of each of the compounds was determined using X-ray diffraction and scanning transmission electron microscopy. The charge density wave transition observed in the resistivity of ([SnSe]1.15)1(VSe2)1 was confirmed. The electrical properties of the n = 2 and 3 compounds are distinctly different. The magnitude of the resistivity change at the transition temperature is dramatically lowered and the temperature of the resistivity minimum systematically increases from 118 K (n = 1) to 172 K (n = 3). For n = 1, this temperature correlates with the onset of the charge density wave transition. The Hall-coefficient changes sign when n is greater than 1, and the temperature dependence of the Hall coefficient of the n = 2 and 3 compounds is very similar to the bulk, slowly decreasing as the temperature is decreased, while for the n = 1 compound the Hall coefficient increases dramatically starting at the onset of the charge density wave. The transport properties suggest an abrupt change in electronic properties on increasing the thickness of the VSe2 layer beyond a single layer.

  6. The charge-asymmetric nonlocally determined local-electric (CANDLE) solvation model.

    PubMed

    Sundararaman, Ravishankar; Goddard, William A

    2015-02-14

    Many important applications of electronic structure methods involve molecules or solid surfaces in a solvent medium. Since explicit treatment of the solvent in such methods is usually not practical, calculations often employ continuum solvation models to approximate the effect of the solvent. Previous solvation models either involve a parametrization based on atomic radii, which limits the class of applicable solutes, or based on solute electron density, which is more general but less accurate, especially for charged systems. We develop an accurate and general solvation model that includes a cavity that is a nonlocal functional of both solute electron density and potential, local dielectric response on this nonlocally determined cavity, and nonlocal approximations to the cavity-formation and dispersion energies. The dependence of the cavity on the solute potential enables an explicit treatment of the solvent charge asymmetry. With four parameters per solvent, this "CANDLE" model simultaneously reproduces solvation energies of large datasets of neutral molecules, cations, and anions with a mean absolute error of 1.8 kcal/mol in water and 3.0 kcal/mol in acetonitrile. PMID:25681887

  7. The charge-asymmetric nonlocally determined local-electric (CANDLE) solvation model

    SciTech Connect

    Sundararaman, Ravishankar; Goddard, William A.

    2015-02-14

    Many important applications of electronic structure methods involve molecules or solid surfaces in a solvent medium. Since explicit treatment of the solvent in such methods is usually not practical, calculations often employ continuum solvation models to approximate the effect of the solvent. Previous solvation models either involve a parametrization based on atomic radii, which limits the class of applicable solutes, or based on solute electron density, which is more general but less accurate, especially for charged systems. We develop an accurate and general solvation model that includes a cavity that is a nonlocal functional of both solute electron density and potential, local dielectric response on this nonlocally determined cavity, and nonlocal approximations to the cavity-formation and dispersion energies. The dependence of the cavity on the solute potential enables an explicit treatment of the solvent charge asymmetry. With four parameters per solvent, this “CANDLE” model simultaneously reproduces solvation energies of large datasets of neutral molecules, cations, and anions with a mean absolute error of 1.8 kcal/mol in water and 3.0 kcal/mol in acetonitrile.

  8. On the Control of the Fixed Charge Densities in Al2O3-Based Silicon Surface Passivation Schemes.

    PubMed

    Simon, Daniel K; Jordan, Paul M; Mikolajick, Thomas; Dirnstorfer, Ingo

    2015-12-30

    A controlled field-effect passivation by a well-defined density of fixed charges is crucial for modern solar cell surface passivation schemes. Al2O3 nanolayers grown by atomic layer deposition contain negative fixed charges. Electrical measurements on slant-etched layers reveal that these charges are located within a 1 nm distance to the interface with the Si substrate. When inserting additional interface layers, the fixed charge density can be continuously adjusted from 3.5 × 10(12) cm(-2) (negative polarity) to 0.0 and up to 4.0 × 10(12) cm(-2) (positive polarity). A HfO2 interface layer of one or more monolayers reduces the negative fixed charges in Al2O3 to zero. The role of HfO2 is described as an inert spacer controlling the distance between Al2O3 and the Si substrate. It is suggested that this spacer alters the nonstoichiometric initial Al2O3 growth regime, which is responsible for the charge formation. On the basis of this charge-free HfO2/Al2O3 stack, negative or positive fixed charges can be formed by introducing additional thin Al2O3 or SiO2 layers between the Si substrate and this HfO2/Al2O3 capping layer. All stacks provide very good passivation of the silicon surface. The measured effective carrier lifetimes are between 1 and 30 ms. This charge control in Al2O3 nanolayers allows the construction of zero-fixed-charge passivation layers as well as layers with tailored fixed charge densities for future solar cell concepts and other field-effect based devices.

  9. Adsorption of weak polyelectrolytes on charged nanoparticles. Impact of salt valency, pH, and nanoparticle charge density. Monte Carlo simulations.

    PubMed

    Carnal, Fabrice; Stoll, Serge

    2011-10-27

    Complex formation between a weak flexible polyelectrolyte chain and one positively charged nanoparticle in presence of explicit counterions and salt particles is investigated using Monte Carlo simulations. The influence of parameters such as the nanoparticle surface charge density, salt valency, and solution property such as the pH on the chain protonation/deprotonation process and monomer adsorption at the nanoparticle surface are systematically investigated. It is shown that the nanoparticle presence significantly modifies chain acid/base and polyelectrolyte conformational properties. The importance of the attractive electrostatic interactions between the chain and the nanoparticle clearly promotes the chain deprotonation leading, at high pH and nanoparticle charge density, to fully wrapped polyelectrolyte at the nanoparticle surface. When the nanoparticle bare charge is overcompensated by the polyelectrolyte charges, counterions and salt particles condense at the surface of the polyelectrolyte-nanoparticle complex to compensate for the excess of charges providing from the adsorbed polyelectrolyte chain. It is also shown that the complex formation is significantly affected by the salt valency. Indeed, with the presence of trivalent salt cations, competition is observed between the nanoparticle and the trivalent cations. As a result, the amount of adsorbed monomers is less important than in the monovalent and divalent case and chain conformations are different due to the collapse of polyelectrolyte segments around trivalent cations out of the nanoparticle adsorption layer.

  10. Impurity-Mediated Early Condensation of a Charge Density Wave in an Atomic Wire Array.

    PubMed

    Yeom, Han Woong; Oh, Deok Mahn; Wippermann, Stefan; Schmidt, Wolf Gero

    2016-01-26

    We directly show how impurity atoms induce the condensation of a representative electronic phase, the charge density wave (CDW) phase, in atomic scale with scanning tunneling microscopy. Oxygen impurity atoms on the self-assembled metallic atomic wire array on a silicon crystal condense the CDW locally above the pristine transition temperature. More interestingly, the CDW along the wires is induced not by a single atomic impurity but by the cooperation of multiple impurities. First-principles calculations disclose the mechanism of the cooperation as the coherent superposition of the local lattice strain induced by impurities, stressing the coupled electronic and lattice degrees of freedom for the CDW. This opens the possibility of the strain engineering over electronic phases of atomic-scale systems.

  11. Evidence for Charge-Density-Wave in Underdoped Bi2201 from ARPES and LEED

    NASA Astrophysics Data System (ADS)

    Rosen, J. A.; Comin, R.; Levy, G.; Fournier, D.; Zhu, Z.-H.; Ludbrook, B.; Veenstra, C. N.; Wong, D.; Dosanjh, P.; Yoshida, Y.; Eisaki, H.; Petaccia, L.; Damascelli, A.

    2012-02-01

    While there is mounting evidence for a broken symmetry in the pseudogap state of the high-Tc cuprates, the identification of a specific phase remains elusive. Through the combination of electronic (ARPES) and structural (LEED) probes, we uncover a temperature dependent evolution of the CuO2 plane band dispersion in highly-ordered Bi2201, which is directly associated with a hitherto-undetected evolution of the incommensurate superstructure. The quasilinear, continuous variation of the modulation wavelength 2π/Q2 from ˜ 6 to 43,elow a characteristic TQ2 30,, provides evidence for an electronically-driven charge-density-wave ordering. This points to a remarkable electron-lattice coupling, in which the footprint of the BiO-layer-induced superstructure is found in the modulated electronic structure of the CuO2 plane.

  12. Descreened Fröhlich mode in charge density wave systems

    NASA Astrophysics Data System (ADS)

    Baier, T.; Wonneberger, W.

    1989-11-01

    The Fukuyama-Lee-Rice approach to the a.c. response problem of pinned charge density waves in quasi one-dimensional solids requires perfect screening by quasi particles. We account for descreening at low temperatures by using a frequency dependent damping function appearing only in internal lines of the phason propagator. It is shown that this procedure agrees with Littlewood's prescription of descreening. Phason self energies are evaluated within the self-consistent Born approximation for strong and weak pinning. Quantitative results for σ(ω)are obtained for spatial dimensions d = 1 and d = 3. Two new frequency scales appear in σ(ω): the dielectric screening frequency of the quasi particles and the frequency of the longitudinal optical phason. The latter frequency modifies the pinning frequency and its concentration dependence and the former the low frequency tail of the Fröhlich mode absorption profile Re σ(ω).

  13. Metastability, Adaptability and Memory in Charge Density Waves. I. Resetting Property

    NASA Astrophysics Data System (ADS)

    Ito, Hiroyuki

    1989-06-01

    We give a possible interpretation of the adaptation of the charge density waves (CDW) to the pulse fields, which is observed to be accompanied with the memory of the width of the applied pulses (Ido step memory effect). When the identical pulse fields are repeatedly applied, successive state transitions are induced among metastable states. By the numerical simulations with the use of the Fukuyama-Lee-Rice model, we have found that only the state can be a fixed point in the transitions where the sliding motion under the pulse field satisfies a certain condition. Selecting the adequate state for a fixed point, the system adapts itself to the applied pulse width so that the current response has a common regularity regardless of the pulse width.

  14. Cooperative interplay between impurities and charge density wave in the phase transition of atomic wires

    NASA Astrophysics Data System (ADS)

    Shim, Hyungjoon; Lee, Geunseop; Hyun, Jung-Min; Kim, Hanchul

    2015-09-01

    Impurities interact with a charge density wave (CDW) and affect the phase transitions in low-dimensional systems. By using scanning tunneling microscopy, we visualize the interaction between oxygen impurities and the CDW in indium atomic wires on Si(111), a prototypical one-dimensional electronic system, and unveil the microscopic mechanism of the intriguing O-induced increase of the transition temperature (Tc). Driven by the fluctuating CDW, the O atoms adopt an asymmetric structure. By adjusting the asymmetry, a pair of O impurities in close distance can pin the one-dimensional CDW, which develops into the two-dimensional domains. First-principles calculations showed that the asymmetric interstitially-incorporated O defects induce shear strains, which assists the formation of hexagon structure of the CDW phase. The cooperative interplay between the O impurities and the CDW is responsible for the enhancement of the CDW condensation and the consequent increase in Tc.

  15. Monte Carlo studies of diamagnetism and charge density wave order in the cuprate pseudogap regime

    NASA Astrophysics Data System (ADS)

    Hayward Sierens, Lauren; Achkar, Andrew; Hawthorn, David; Melko, Roger; Sachdev, Subir

    2015-03-01

    The pseudogap regime of the hole-doped cuprate superconductors is often characterized experimentally in terms of a substantial diamagnetic response and, from another point of view, in terms of strong charge density wave (CDW) order. We introduce a dimensionless ratio, R, that incorporates both diamagnetic susceptibility and the correlation length of CDW order, and therefore reconciles these two fundamental characteristics of the pseudogap. We perform Monte Carlo simulations on a classical model that considers angular fluctuations of a six-dimensional order parameter, and compare our Monte Carlo results for R with existing data from torque magnetometry and x-ray scattering experiments on YBa2Cu3O6+x. We achieve qualitative agreement, and also propose future experiments to further investigate the behaviour of this dimensionless ratio.

  16. Persistent order due to transiently enhanced nesting in an electronically excited charge density wave

    PubMed Central

    Rettig, L.; Cortés, R.; Chu, J.-H.; Fisher, I. R.; Schmitt, F.; Moore, R. G.; Shen, Z.-X.; Kirchmann, P. S.; Wolf, M.; Bovensiepen, U.

    2016-01-01

    Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time- and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of the dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. Our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order. PMID:26804717

  17. Vertical variations of charged-particle temperature and density in quiet conditions

    NASA Astrophysics Data System (ADS)

    Apati, I.; Semerei, T.; Afonin, V.; Bezrukikh, V.; Shiutte, N.; Bentse, P.

    1983-09-01

    Electrostatic analyzers aboard the Vertical-6 rocket were used to study vertical variations of charged-particle temperature and density at heights of 200-1200 km during quiet-solar conditions on October 25, 1977. The heating of the electron-ion gas was found to have an essentially nonmonotonic character. Above the F-region maximum, significant fluctuations of ion-gas temperature were observed, apparently associated with vertical variations of cooling and heating due to the excitation of the fine structure of atomic-oxygen levels as well as due to the effect of ion-exchange reactions. The maximum heating of ion gas occurs at heights where hydrogen ions begin to predominate. It is noted that the results obtained can be used to improve existing ionospheric models relating to periods of low solar activity.

  18. Coexistence of bulk superconductivity and charge density wave in CuxZrTe3.

    PubMed

    Zhu, Xiangde; Lei, Hechang; Petrovic, C

    2011-06-17

    We report the coexistence of bulk superconductivity with T(c)=3.8  K and charge density wave (CDW) in Cu intercalated quasi-two-dimensional crystals of ZrTe(3). The Cu intercalation results in the expansion of the unit cell orthogonal to the Zr-Zr metal chains and partial filling of CDW energy gap. We present anisotropic parameters of the superconducting state. We also show that the contribution of CDW to the scattering mechanism is anisotropic in the a-b plane. The dominant scattering mechanism in the normal state for both ZrTe(3) and Cu(0.05)ZrTe(3) along the b axis is the electron-electron umklapp scattering.

  19. Atomistic view of impurities interacting with a quasi-one-dimensional charge density wave

    NASA Astrophysics Data System (ADS)

    Oh, Deok Mahn; Yeom, Han Woong

    2016-06-01

    Atomistic details of the interaction of impurities with quasi-one-dimensional charge density wave (CDW) are revealed by scanning tunneling microscopy. Oxygen and pentacene adsorbates are utilized as strongly and weakly interacting impurities, respectively, on the well-known CDW state of the In atomic wire array on the Si(111) surface. Distinct CDW pinning configurations are identified for oxygen impurities with different atomic structures, indicating the strong pinning. The governing role of local strain field for the strong pinning is elucidated. In contrast, a few different pinning configurations occur for a unique adsorption structure of pentacene indicating a weak pinning. Pentacene molecules commonly induce characteristic phase shifts, which readily couple with other phase defects, in particular, solitons in order to avoid interwire phase misfits. This work provides the mechanism and methodology for the atomic scale control over phases, solitons, and domain boundaries of CDW.

  20. Dynamical properties of bidirectional charge-density waves in ErTe3

    NASA Astrophysics Data System (ADS)

    Sinchenko, A. A.; Lejay, P.; Leynaud, O.; Monceau, P.

    2016-06-01

    We report a strong difference in the sliding properties of the bidirectional charge-density wave (CDW) in the two-dimensional rare-earth tritelluride ErTe3 which occurs below TCDW1=265 K with a wave vector along the c axis and below TCDW2=165 K with a wave vector along the a axis; the excess current carried by the motion of the CDW is 10 times less for the lower CDW compared with the value of the upper one. We tentatively explain this result by a stronger pinning of the lower temperature CDW intricated with the upper one, which inhibits its motion and may generate a phase slippage lattice.

  1. Impurity-Mediated Early Condensation of a Charge Density Wave in an Atomic Wire Array.

    PubMed

    Yeom, Han Woong; Oh, Deok Mahn; Wippermann, Stefan; Schmidt, Wolf Gero

    2016-01-26

    We directly show how impurity atoms induce the condensation of a representative electronic phase, the charge density wave (CDW) phase, in atomic scale with scanning tunneling microscopy. Oxygen impurity atoms on the self-assembled metallic atomic wire array on a silicon crystal condense the CDW locally above the pristine transition temperature. More interestingly, the CDW along the wires is induced not by a single atomic impurity but by the cooperation of multiple impurities. First-principles calculations disclose the mechanism of the cooperation as the coherent superposition of the local lattice strain induced by impurities, stressing the coupled electronic and lattice degrees of freedom for the CDW. This opens the possibility of the strain engineering over electronic phases of atomic-scale systems. PMID:26634634

  2. Synthetic polycations with controlled charge density and molecular weight as building blocks for biomaterials.

    PubMed

    Kleinberger, Rachelle M; Burke, Nicholas A D; Zhou, Christal; Stöver, Harald D H

    2016-01-01

    A series of polycations prepared by RAFT copolymerization of N-(3-aminopropyl)methacrylamide hydrochloride (APM) and N-(2-hydroxypropyl)methacrylamide, with molecular weights of 15 and 40 kDa, and APM content of 10-75 mol%, were tested as building blocks for electrostatically assembled hydrogels such as those used for cell encapsulation. Complexation and distribution of these copolymers within anionic calcium alginate gels, as well as cytotoxicity, cell attachment, and cell proliferation on surfaces grafted with the copolymers were found to depend on composition and molecular weight. Copolymers with lower cationic charge density and lower molecular weight showed less cytotoxicity and cell adhesion, and were more mobile within alginate gels. These findings aid in designing improved polyelectrolyte complexes for use as biomaterials.

  3. 3. QUANTUM DOTS AND WELLS, MESOSCOPIC NETWORKS : Submicron charge-density-wave devices

    NASA Astrophysics Data System (ADS)

    van der Zant, H. J. S.; Markovic, N.; Slot, E.

    2001-10-01

    We review our fabrication methods to produce submicron charge-density-wave (CDW) structures and present measurements of CDW dynamics on a microscopic scale. Our data show that mesoscopic CDW dynamics is different from bulk behavior. We have studied current-conversion and found a size-effect that can not be accounted for by existing models. An explanation might be that the removal and addition of wave fronts becomes correlated in time when probe spacing is reduced below a few µm. On small segments we occasionally observe negative differential resistance in the I(V) characteristics and sometimes the resistance may even become negative. We believe that the interplay between CDW deformations (strain) and quasi-particles may yield non-equilibrium effects that play a crucial role in this new phenomenon. No detailed theoretical calculations are available. Our measurements clearly show the need of a microscopic model for CDW dynamics.

  4. Chiral and nonchiral edge states in quantum Hall systems with charge density modulation

    NASA Astrophysics Data System (ADS)

    Szumniak, Paweł; Klinovaja, Jelena; Loss, Daniel

    2016-06-01

    We consider a system of weakly coupled wires with quantum Hall effect (QHE) and in the presence of a spatially periodic modulation of the chemical potential along the wire, equivalent to a charge density wave (CDW). We investigate the competition between the two effects which both open a gap. We show that by changing the ratio between the amplitudes of the CDW modulation and the tunneling between wires, one can switch between nontopological CDW-dominated phase to topological QHE-dominated phase. Both phases host edge states of chiral and nonchiral nature robust to on-site disorder. However, only in the topological phase, the edge states are immune to disorder in the phase shifts of the CDWs. We provide analytical solutions for filling factor ν =1 and study numerically effects of disorder as well as present numerical results for higher filling factors.

  5. Possibility of charge density wave transition in a SrPt2Sb2 superconductor.

    PubMed

    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.

  6. Charging of mesospheric particles - Implications for electron density and particle coagulation

    NASA Technical Reports Server (NTRS)

    Jensen, Eric J.; Thomas, Gary E.

    1991-01-01

    The relationship between N(e) and mesospheric aerosols near the mesopause is studied. The full distribution of charges on mesospheric aerosols is calculated, including dust and ice particles with radii ranging from 1 to 400 nm. The N(e) and ion density N(i) are obtained and ionization height profiles are calculated. The effects of dust and ice particles on N(e) and N(i) are studied for a wide range of assumed conditions. The results indicate that aerosol concentrations associated with visible polar mesospheric clouds are unlikely to cause a severe N(e) depletion. The pronounced 'bite-out' of N(e) at about 87 km in the summertime may be caused by a large concentration of small ice particles in a narrow cold layer near the mesosphere. Net negative charge on mesospheric aerosols may severely inihibit coagulation, so that mesospheric dust would not grow significantly. A higher supersaturation with respect to water vapor would be needed for heterogeneous nucleation of ice crystals.

  7. The amplitudes and the structure of the charge density wave in YBCO

    NASA Astrophysics Data System (ADS)

    Kharkov, Y. A.; Sushkov, O. P.

    2016-10-01

    We find unknown s- and d-wave amplitudes of the recently discovered charge density wave (CDW) in underdoped cuprates. To do so we perform a combined analysis of experimental data for ortho-II YBa2Cu3Oy. The analysis includes data on nuclear magnetic resonance, resonant inelastic X-ray scattering, and hard X-ray diffraction. The amplitude of doping modulation found in our analysis is 3.5 · 10‑3 in a low magnetic field and T = 60 K, the amplitude is 6.5 · 10‑3 in a magnetic field of 30T and T = 1.3 K. The values are in units of elementary charge per unit cell of a CuO2 plane. We show that the data rule out a checkerboard pattern, and we also show that the data might rule out mechanisms of the CDW which do not include phonons.

  8. The amplitudes and the structure of the charge density wave in YBCO

    PubMed Central

    Kharkov, Y. A.; Sushkov, O. P.

    2016-01-01

    We find unknown s- and d-wave amplitudes of the recently discovered charge density wave (CDW) in underdoped cuprates. To do so we perform a combined analysis of experimental data for ortho-II YBa2Cu3Oy. The analysis includes data on nuclear magnetic resonance, resonant inelastic X-ray scattering, and hard X-ray diffraction. The amplitude of doping modulation found in our analysis is 3.5 · 10−3 in a low magnetic field and T = 60 K, the amplitude is 6.5 · 10−3 in a magnetic field of 30T and T = 1.3 K. The values are in units of elementary charge per unit cell of a CuO2 plane. We show that the data rule out a checkerboard pattern, and we also show that the data might rule out mechanisms of the CDW which do not include phonons. PMID:27721385

  9. Quantum Tunneling of Charge-Density Waves in Quasi One-Dimensional Conductors

    NASA Astrophysics Data System (ADS)

    Miller, John Harris, Jr.

    The charge-density wave (CDW) dynamics of the linear chain compound orthorhombic TaS(,3) is characterized by extensive measurements of dc conductivity, ac admittance, direct mixing, harmonic mixing, second harmonic generation, and third harmonic generation as functions of dc bias voltage, applied frequencies, and, in some cases, the amplitude of an additional ac signal. Measurements of the direct and harmonic mixing responses of NbSe(,3) are also reported. The results are analyzed in terms of an extension of the tunneling theory of CDW depinning, proposed by John Bardeen, coupled to the theory of photon-assisted tunneling (PAT). Where possible, the results are also compared with predictions of the classical overdamped oscillator model of CDW transport. The tunneling model is shown to provide a complete and semiquantitative interpretation of the entire small -signal ac dynamics at megahertz frequencies, using only the measured dc I-V curve and an experimentally inferred frequency-voltage scaling parameter, and also accounts for much of the large-signal behavior studied thus far. The observation of both an induced ac harmonic mixing current and a third harmonic generation current whose amplitudes peak at output frequencies far below the measured "cross -over frequency" for ac conductivity agrees with the phenomenological tunneling model, but is in serious disagreement with the classical overdamped oscillator model of CDW motion. Furthermore, the absence of any observed quadrature component in the harmonic mixing response, even though the measured linear response at the applied frequencies has substantial frequency -dependent in-phase and quadrature components, is probably impossible to reconcile with any classical theory. The results reported here thus provide compelling evidence in favor of collective, coherent quantum tunneling as the mechanism of charge-density wave depinning, and indicate that macroscopic quantum effects are observed in the megahertz frequency

  10. The cis-effect using the topology of the electronic charge density

    NASA Astrophysics Data System (ADS)

    Jenkins, Samantha; Kirk, Steven R.; Rong, Chunying; Yin, Dulin

    2013-03-01

    We provide a physics-inspired coupling mechanism explaining the cis-effect in terms of electronic and nuclear degrees of freedom and explore the implications for three families of molecules. The cis- or trans-effect is related to the tendency of electronic charge density to move away from the bond critical point (BCP) and towards the associated nuclear attractors. A quantitative measure of this effect is given by the λ 3 eigenvalue of the Hessian matrix of the electronic charge density. The physical origin of the cis-effect is tied to the observation that the central X=X, X=C or N bond-paths of the cis-isomers are more bent (they are up to 1.5% longer than the internuclear distance) than the bond-paths of the corresponding trans-isomers. Greater bond-path bending is associated with a stronger cis-effect; the direction of bond deformation can in all cases be predicted by the most facile (least compressible) mode of the electronic stress tensor. Further to this, the ellipticity ε of the X=X BCPs of a molecule displaying the cis-effect is lower in the cis-isomer than for the corresponding trans-isomer, suggesting that the cis-effect is less counterintuitive than previously thought. The molecules that exhibit the greatest cis-effect are those with fluorinated double bonds; this is because the most facile modes of the C-F bond couple with the highest-symmetry normal mode of vibration. Qualitative agreement is found with existing experimental data and predictions are made where experimental data is lacking.

  11. Topology of electron charge density for chemical bonds from valence bond theory: a probe of bonding types.

    PubMed

    Zhang, Lixian; Ying, Fuming; Wu, Wei; Hiberty, Philippe C; Shaik, Sason

    2009-01-01

    To characterize the nature of bonding we derive the topological properties of the electron charge density of a variety of bonds based on ab initio valence bond methods. The electron density and its associated Laplacian are partitioned into covalent, ionic, and resonance components in the valence bond spirit. The analysis provides a density-based signature of bonding types and reveals, along with the classical covalent and ionic bonds, the existence of two-electron bonds in which most of the bonding arises from the covalent-ionic resonance energy, so-called charge-shift bonds. As expected, the covalent component of the Laplacian at the bond critical point is found to be largely negative for classical covalent bonds. In contrast, for charge-shift bonds, the covalent part of the Laplacian is small or positive, in agreement with the weakly attractive or repulsive character of the covalent interaction in these bonds. On the other hand, the resonance component of the Laplacian is always negative or nearly zero, and it increases in absolute value with the charge-shift character of the bond, in agreement with the decrease of kinetic energy associated with covalent-ionic mixing. A new interpretation of the topology of the total density at the bond critical point is proposed to characterize covalent, ionic, and charge-shift bonding from the density point of view.

  12. SEMICONDUCTOR TECHNOLOGY: Influence of nitrogen dose on the charge density of nitrogen-implanted buried oxide in SOI wafers

    NASA Astrophysics Data System (ADS)

    Zhongshan, Zheng; Zhongli, Liu; Ning, Li; Guohua, Li; Enxia, Zhang

    2010-02-01

    To harden silicon-on-insulator (SOI) wafers fabricated using separation by implanted oxygen (SIMOX) to total-dose irradiation, the technique of nitrogen implantation into the buried oxide (BOX) layer of SIMOX wafers can be used. However, in this work, it has been found that all the nitrogen-implanted BOX layers reveal greater initial positive charge densities, which increased with increasing nitrogen implantation dose. Also, the results indicate that excessively large nitrogen implantation dose reduced the radiation tolerance of BOX for its high initial positive charge density. The bigger initial positive charge densities can be ascribed to the accumulation of implanted nitrogen near the Si-BOX interface after annealing. On the other hand, in our work, it has also been observed that, unlike nitrogen-implanted BOX, all the fluorine-implanted BOX layers show a negative charge density. To obtain the initial charge densities of the BOX layers, the tested samples were fabricated with a metal-BOX-silicon (MBS) structure based on SIMOX wafers for high-frequency capacitance-voltage (C-V) analysis.

  13. Magnetic properties of the charge density wave compounds RTe3, R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er & Tm

    SciTech Connect

    Ru, N.; Chu, J.-H.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2009-12-14

    The antiferromagnetic transition is investigated in the rare-earth (R) tritelluride RTe{sub 3} family of charge density wave (CDW) compounds via specific heat, magnetization and resistivity measurements. Observation of the opening of a superzone gap in the resistivity of DyTe{sub 3} indicates that additional nesting of the reconstructed Fermi surface in the CDW state plays an important role in determining the magnetic structure.

  14. Spectroscopic analysis and charge transfer interaction studies of 4-benzyloxy-2-nitroaniline insecticide: A density functional theoretical approach

    NASA Astrophysics Data System (ADS)

    Arul Dhas, D.; Hubert Joe, I.; Roy, S. D. D.; Balachandran, S.

    2015-01-01

    A widespread exploration on the intra-molecular charge transfer interaction through an efficient π-conjugated path from a strong electron-donor group (amino) to a strong electron-acceptor group (nitro) has been carried out using FTIR, FT-Raman, UV-Vis, fluorescence and NMR spectra on insecticide compound 4-benzyloxy-2-nitroaniline. Density functional theory method is used to determine optimized molecular geometry, harmonic vibrational wavenumbers and intensities using 6-311G(d,p) basis set by means of Gaussian 09W program suit. A comprehensive investigation on the sp2 to sp3 hybridization and non-planarity property has been performed. Natural bond orbital analysis is used to study the existence of C-H⋯O, N-H⋯O and C-H⋯π proper and improper hydrogen bonds. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. A complete assignment of the experimental absorption peaks in the ultraviolet region has also been performed. Isotropic chemical shifts of 13C, 1H, 15N and 18O NMR and nuclear spin-spin coupling constants have been computed using the gauge-invariant atomic orbital method. The biological activity of substituent amino and nitro groups are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.

  15. Local Structure and Vibrational Properties of alpha-Pu, alpha-U, and the alpha-U Charge Density Wave

    SciTech Connect

    Nelson, E J; Allen, P G; Blobaum, K M; Wall, M A; Booth, C H

    2004-08-10

    The local atomic environment and vibrational properties of atoms in monoclinic pure {alpha}-plutonium as well as orthorhombic pure {alpha}-uranium and its low-temperature charge-density-wave (CDW) modulation are examined by extended x-ray absorption fine structure spectroscopy (EXAFS). Pu L{sub III}-edge and U L{sub III}-edge EXAFS data measured at low temperatures verify the crystal structures of {alpha}-U and {alpha}-Pu samples previously determined by x-ray diffraction and neutron scattering. Debye-Waller factors from temperature-dependent EXAFS measurements are fit with a correlated Debye model. The observed Pu-Pu bond correlated Debye temperature of {theta}{sub cD}({alpha}-Pu) = 162 {+-} 5 K for the pure {alpha}-Pu phase agrees with our previous measurement of the correlated Debye temperature of the gallium-containing {alpha}'-Pu phase in a mixed phase 1.9 at% Ga-doped {alpha}'-Pu/{delta}-Pu alloy. The temperature dependence of the U-U nearest neighbor Debye-Waller factor exhibits a sharp discontinuity in slope near T{sub CDW} = 43 K, the transition temperature at which the charge-density wave (CDW) in {alpha}-U condenses from a soft phonon mode along the (100) direction. Our measurement of the CDW using EXAFS is the first observation of the structure of the CDW in polycrystalline {alpha}-U. The different temperature dependence of the Debye-Waller factor for T < T{sub CDW} can be modeled by the change in bond length distributions resulting from condensation of the charge density wave. For T > T{sub CDW}, the observed correlated Debye temperature of {theta}{sub cD}({alpha}-U) = 199 {+-} 3 K is in good agreement with other measurements of the Debye temperature for polycrystalline {alpha}-U. CDW structural models fit to the {alpha}-U EXAFS data support a squared CDW at the lowest temperatures, with a displacement amplitude of {var_epsilon} = 0.05 {+-} 0.02 {angstrom}.

  16. Charge-density studies of energetic materials: CL-20 and FOX-7.

    PubMed

    Meents, A; Dittrich, B; Johnas, S K J; Thome, V; Weckert, E F

    2008-02-01

    Experimental electron densities and derived properties have been determined for the two energetic materials CL-20 (3,5,9,11-tetraacetyl-14-oxo-1,3,5,7,9,11-hexaazapentacyclo-[5.5.3.02,6.04,10.08,12]pentadecane), and FOX-7 (1,1-diamino-2,2-dinitroethylene) from single-crystal diffraction. Synchrotron data extending to high scattering angles were measured at low temperature. Low figures-of-merit and excellent residuals were obtained. The Hansen & Coppens multipole-model electron density was compared with results from theoretical calculations via structure factors simulating an experiment. Chemical bonding in the molecules is discussed and a topological analysis gives insight especially into the character of those bonds that are thought to play a key role in the decomposition of the molecules. A comparison of theoretical and experimental electrostatic potentials shows no obvious evidence supporting earlier findings on other nitroheterocyclic molecules that electron-density maxima near the C-NO(2) bonds mapped on the electron-density isosurface can be correlated with impact sensitivities. For FOX-7 periodic Hartree-Fock calculations were performed to investigate the influence of the crystal field on the electron density distribution. PMID:18204210

  17. Correlating Thin-Film Radical Density with Charge Transport in Open-Shell Conducting Macromolecules

    NASA Astrophysics Data System (ADS)

    Hay, Martha; Jergens, Elizabeth; Boudouris, Bryan

    Within the class of radical polymers, stable open-shell species serve as the medium for charge transport by undergoing oxidation-reduction (redox) reactions. The kinetics of these reactions are rapid enough that they are not considered rate-limiting in the electronic interactions of these materials. Rather, the proximity of these radical sites is paramount as a synthetic handle. Unfortunately, controlling the density of radicals has proven challenging in radical polymer systems. Often radical functionality is imparted to a polymer, rather than polymerizing a radical-containing monomer unit. This can prove troublesome as longer reaction times, in the interest of higher radical functionality, can lead to the elimination of radicals. Thus, the consequential altering of the radical electronic interactions is not well understood. We have synthesized a series of polynorbornene-based radical monomers at controlled radical loadings such that the radical density was preserved from monomer to polymer synthesis. As such, we attribute any change in the macroscopic transport properties to a change in the spacing between radical sites. These results elucidate the role of radical site distribution on the electronic performance of nitroxide-based radical polymers.

  18. Effect of spin-orbit nuclear charge density corrections due to the anomalous magnetic moment on halonuclei

    SciTech Connect

    Ong, A.; Berengut, J. C.; Flambaum, V. V.

    2010-07-15

    In this paper we consider the contribution of the anomalous magnetic moments of protons and neutrons to the nuclear charge density. We show that the spin-orbit contribution to the mean-square charge radius, which has been neglected in recent nuclear calculations, can be important in light halonuclei. We estimate the size of the effect in helium, lithium, and beryllium nuclei. It is found that the spin-orbit contribution represents a approx2% correction to the charge density at the center of the {sup 7}Be nucleus. We derive a simple expression for the correction to the mean-square charge radius due to the spin-orbit term and find that in light halonuclei it may be larger than the Darwin-Foldy term and comparable to finite size corrections. A comparison of experimental and theoretical mean-square radii including the spin-orbit contribution is presented.

  19. Syntheses, structures, characterizations and charge-density matching of novel amino-templated uranyl selenates

    SciTech Connect

    Ling Jie; Sigmon, Ginger E.; Burns, Peter C.

    2009-02-15

    Five hybrid organic-inorganic uranyl selenates have been synthesized, characterized and their structures have been determined. The structure of (C{sub 2}H{sub 8}N){sub 2}[(UO{sub 2}){sub 2}(SeO{sub 4}){sub 3}(H{sub 2}O)] (EthylAUSe) is monoclinic, P2{sub 1}, a=8.290(1), b=12.349(2), c=11.038(2) A, {beta}=104.439(4){sup o}, V=1094.3(3) A{sup 3}, Z=2, R{sub 1}=0.0425. The structure of (C{sub 7}H{sub 10}N){sub 2}[(UO{sub 2})(SeO{sub 4}){sub 2}(H{sub 2}O)]H{sub 2}O (BenzylAUSe) is orthorhombic, Pna2{sub 1}, a=24.221(2), b=11.917(1), c=7.4528(7) A, V=2151.1(3) A{sup 3}, Z=4, R{sub 1}=0.0307. The structure of (C{sub 2}H{sub 10}N{sub 2})[(UO{sub 2})(SeO{sub 4}){sub 2}(H{sub 2}O)](H{sub 2}O){sub 2} (EDAUSe) is monoclinic, P2{sub 1}/c, a=11.677(2), b=7.908(1), c=15.698(2) A, {beta}=98.813(3){sup o}, V=1432.4(3) A{sup 3}, Z=4, R{sub 1}=0.0371. The structure of (C{sub 6}H{sub 22}N{sub 4})[(UO{sub 2})(SeO{sub 4}){sub 2}(H{sub 2}O)](H{sub 2}O) (TETAUSe) is monoclinic, P2{sub 1}/n, a=13.002(2), b=7.962(1), c=14.754(2) A, {beta}=114.077(2){sup o}, V=1394.5(3) A{sup 3}, Z=4, R{sub 1}=0.0323. The structure of (C{sub 6}H{sub 21}N{sub 4})[(UO{sub 2})(SeO{sub 4}){sub 2}(HSeO{sub 4})] (TAEAUSe) is monoclinic, P2{sub 1}/m, a=9.2218(6), b=12.2768(9), c=9.4464(7) A, {beta}=116.1650(10){sup o}, V=959.88(12) A{sup 3}, Z=2, R{sub 1}=0.0322. The inorganic structural units in these compounds are composed of uranyl pentagonal bipyramids and selenate tetrahedra. In each case, tetrahedra link bipyramids through vertex-sharing, resulting in chain or sheet topologies. The charge-density matching principle is discussed relative to the orientations of the organic molecules between the inorganic structural units. - Graphical abstract: The structures of five new inorganic-organic hybrid uranyl selenates present new structural topologies based upon chains and sheets of uranyl pentagonal bipyramids and selenate tetrahedra.

  20. Evaluation of semiempirical atmospheric density models for orbit determination applications

    NASA Technical Reports Server (NTRS)

    Cox, C. M.; Feiertag, R. J.; Oza, D. H.; Doll, C. E.

    1994-01-01

    This paper presents the results of an investigation of the orbit determination performance of the Jacchia-Roberts (JR), mass spectrometer incoherent scatter 1986 (MSIS-86), and drag temperature model (DTM) atmospheric density models. Evaluation of the models was performed to assess the modeling of the total atmospheric density. This study was made generic by using six spacecraft and selecting time periods of study representative of all portions of the 11-year cycle. Performance of the models was measured for multiple spacecraft, representing a selection of orbit geometries from near-equatorial to polar inclinations and altitudes from 400 kilometers to 900 kilometers. The orbit geometries represent typical low earth-orbiting spacecraft supported by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD). The best available modeling and orbit determination techniques using the Goddard Trajectory Determination System (GTDS) were employed to minimize the effects of modeling errors. The latest geopotential model available during the analysis, the Goddard earth model-T3 (GEM-T3), was employed to minimize geopotential model error effects on the drag estimation. Improved-accuracy techniques identified for TOPEX/Poseidon orbit determination analysis were used to improve the Tracking and Data Relay Satellite System (TDRSS)-based orbit determination used for most of the spacecraft chosen for this analysis. This paper shows that during periods of relatively quiet solar flux and geomagnetic activity near the solar minimum, the choice of atmospheric density model used for orbit determination is relatively inconsequential. During typical solar flux conditions near the solar maximum, the differences between the JR, DTM, and MSIS-86 models begin to become apparent. Time periods of extreme solar activity, those in which the daily and 81-day mean solar flux are high and change rapidly, result in significant differences between the models. During periods of high

  1. Application of Polychromatic µCT for Mineral Density Determination

    PubMed Central

    Zou, W.; Hunter, N.; Swain, M.V.

    2011-01-01

    Accurate assessment of mineral density (MD) provides information critical to the understanding of mineralization processes of calcified tissues, including bones and teeth. High-resolution three-dimensional assessment of the MD of teeth has been demonstrated by relatively inaccessible synchrotron radiation microcomputed tomography (SRµCT). While conventional desktop µCT (CµCT) technology is widely available, polychromatic source and cone-shaped beam geometry confound MD assessment. Recently, considerable attention has been given to optimizing quantitative data from CµCT systems with polychromatic x-ray sources. In this review, we focus on the approaches that minimize inaccuracies arising from beam hardening, in particular, beam filtration during the scan, beam-hardening correction during reconstruction, and mineral density calibration. Filtration along with lowest possible source voltage results in a narrow and near-single-peak spectrum, favoring high contrast and minimal beam-hardening artifacts. More effective beam monochromatization approaches are described. We also examine the significance of beam-hardening correction in determining the accuracy of mineral density estimation. In addition, standards for the calibration of reconstructed grey-scale attenuation values against MD, including K2PHO4 liquid phantom, and polymer-hydroxyapatite (HA) and solid hydroxyapatite (HA) phantoms, are discussed. PMID:20858779

  2. Determination of Energy Independent Neutron Densities using Dirac Phenomenology based on the RIA

    NASA Astrophysics Data System (ADS)

    Clark, B. C.; Kerr, L. J.; Hama, S.; Mercer, R. L.

    2002-04-01

    A new method for extracting neutron densities from intermediate energy elastic proton-nucleus scattering observables using a global Dirac phenomenological (DP) approach based on the Relativistic Impulse Approximation (RIA) is presented. (B. C. Clark, et al.) BAPS Vol 46, No. 7 pg.139, 2001. We have considered data sets for ^40Ca, ^48Ca and ^208Pb and energies from 500 MeV to 1040 MeV. The global fits are successful in reproducing the data and in predicting data sets not included in the analysis. Using this global DP approach we have obtained energy independent neutron densities. The vector point proton density distribution, ρ^p_v, is determined from the empirical charge density after unfolding the proton form factor. The other densities, ρ^n_v, ρ^p_s, ρ^n_s, are parameterized using the cosh form given in our paper on global DP optical potentials.(E. D. Cooper, et al.) Phys Rev. 47C, pg. 297, 1993 Neutron skin thicknesses extracted using the global analysis are compared to predictions from theoretical models.

  3. Evidence for a Peierls phase-transition in a three-dimensional multiple charge-density waves solid

    PubMed Central

    Mansart, Barbara; Cottet, Mathieu J. G.; Penfold, Thomas J.; Dugdale, Stephen B.; Tediosi, Riccardo; Chergui, Majed; Carbone, Fabrizio

    2012-01-01

    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. PMID:22451898

  4. Effects of interaction and polarization on spin-charge separation: A time-dependent spin-density-functional theory study

    NASA Astrophysics Data System (ADS)

    Xianlong, Gao

    2010-03-01

    We calculate the nonequilibrium dynamic evolution of a one-dimensional system of two-component fermionic atoms after a strong local quench by using a time-dependent spin-density-functional theory. The interaction quench is also considered to see its influence on the spin-charge separation. It is shown that the charge velocity is larger than the spin velocity for the system of on-site repulsive interaction (Luttinger liquid), and vise versa for the system of on-site attractive interaction (Luther-Emery liquid). We find that both the interaction quench and polarization suppress the spin-charge separation.

  5. Attosecond pumping of nonstationary electronic states of LiH: Charge shake-up and electron density distortion

    SciTech Connect

    Remacle, F.; Levine, R. D.

    2011-01-15

    Electronic reorganization during and after excitation by an intense ultrashort pulse is computed for LiH in a many-electron multireference time-dependent approach at a fixed nuclear geometry. The electronic dipole moment is used to probe the temporal response of the charge density. Above a field-strength threshold, there is an extensive Stark shifting and Rabi broadening of levels with corresponding distortion of the charge distribution whose response at strong fields is neither adiabatic nor diabatic. A nonresonant IR pulse is more effective in inducing charge shake-up during the pulse.

  6. Transport studies of ions across polystyrene based composite membrane: Evaluation of fixed charge density using theoretical models

    NASA Astrophysics Data System (ADS)

    Imteyaz, Shahla; Rafiuddin

    2016-11-01

    Polystyrene (PS) dispersed tin molybdate (TM) composite was prepared by sol-gel method. The membrane was characterized for its thermal stability by TG-DTA. SEM reveals the formation of composite material with uniform surface morphology. Crystallinity and phosphorylation of the membrane was confirmed by X-RD and FT-IR. Membrane potential of different monovalent electrolytes with varying concentration followed the order LiCl > NaCl > NH4Cl > KCl. Membrane potential increases with dilution of electrolytes confirming it to be cation selective in nature. The theoretical value of fixed charge density for the membrane was also evaluated from membrane potential using different approaches proposed by (a) Teorell-Meyer-Sievers (b) Kobatake and (c) Nagasawa, which are comparable with the experimental values. Fixed charge density examined for the electrolytes follows the order LiCl > NaCl > NH4Cl > KCl. Li+ ion shows highest value of fixed charge density in all the methods as the Donnan exclusion is highest for the electrolyte of smaller cation size. Transport number and mobility ratio for ion selectivity also increases with dilution. Membrane shows the lowest permselectivity for K+ while highest for Li+. The strong binding affinity of K+ counter-ion with fixed charge groups on the polymer decreases the membrane charge density and permselectivity. Thus, the membrane shows its applicability in various electro-membrane processes.

  7. A structural study of charge-density-wave perturbations in mixed-halide MX solids

    NASA Astrophysics Data System (ADS)

    Scott, Brian; Johnson, Sabina R.; Swanson, Basil I.

    Mixed-halide crystals have been formed by co-crystallizing pure (Pt(en)2Cl2)(Pt(en)2)(ClO4)4(PtCl) and (Pt(en)2I2)(Pt(en)2)(ClO4)4(PtI), where en = 1,2 diaminoethane. Single crystal x-ray diffraction reveals that these crystals are of high quality. The pure PtI and PtCl contain chains of alternating Pt and halogen atoms that have undergone a Peierls distortion and commensurate charge disproportionation, resulting in alternating valence states on the platinum atoms: X-Pt(IV)-X---Pt(II)---X. The Peierls distortion results in a charge-density-wave (CDW), the strength of which is measured as the ratio, rho, of the short Pt(IV)-X bond distance to the long Pt(II)---X bond distance. PtCl is a strong CDW system with rho = 0.750 and PtI is a weak CDW system with rho = 0.919. The mixed-halide systems have the stoichiometry PtCl(1-x)I(x), with x = 0.1, 0.15, 0.2, 0.3, 0.7, 0.8, 0.85, and 0.90. A Chain lattice constant versus composition study strongly suggests distorted PtI and PtCl chains in these solids. A single crystal diffraction study on PtCl(0.85)I(0.15) shows significant perturbations in the PtCl and PtI chain CDW strengths, with the PtI segment showing no Peierls distortion (rho = 1). This control of the CDW strength, which is strongly tied to electron-electron and electron-phonon interactions in these solids, potentially allows tuning of electronic and optical properties on a nanometer scale.

  8. Time-dependent transition density matrix for visualizing charge-transfer excitations in photoexcited organic donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    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

  9. 40 CFR Appendix C to Subpart Nnn... - Method for the Determination of Product Density

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Product Density C Appendix C to Subpart NNN of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Determination of Product Density 1. Purpose The purpose of this test is to determine the product density of... thickness. 3.5Calculate the product density: Density (lb/ft3) = area weight (lb/ft2)/thickness (ft)...

  10. Effects of the internal structure of spheroidal divalent ions on the charge density profiles of the electric double layer.

    PubMed

    Ibarra-Armenta, José Guadalupe; Martín-Molina, Alberto; Bohinc, Klemen; Quesada-Pérez, Manuel

    2012-12-14

    In this work, the effects of the internal structure of charge for ions are analyzed by means of Monte Carlo simulations within a modified primitive model of electric double layer with spheroidal ions. The simulation results are compared to those obtained from a generalized Poisson-Boltzmann theory, where the separation of the charges within the spheroidal ions is considered. The spheroidal divalent ions have finite dimensions and two identical unitary charges separated by a distance of one diameter. Two structurally equivalent but oppositely charged ionic species are considered: coions and counterions. In the simulation, the number of particles is not fixed and the grand canonical ensemble is employed to reach the thermodynamic equilibrium. Meanwhile, the variational theory is applied to the analytical density functional. The fixed separation between charges within the spheroidal ions causes the orientational ordering of the spheroidal ions (with quadrupolar charge distributions) leading to very different charge distributions than those of the regular divalent ions from the primitive model of electrolyte. The internal structure of ions could be dramatically relevant for the modelling of large molecules, which are known to posses complex charge distributions. PMID:23249020

  11. Modeling of Optical Waveguide Poling and Thermally Stimulated Discharge (TSD) Charge and Current Densities for Guest/Host Electro Optic Polymers

    NASA Technical Reports Server (NTRS)

    Watson, Michael D.; Ashley, Paul R.; Abushagur, Mustafa

    2004-01-01

    A charge density and current density model of a waveguide system has been developed to explore the effects of electric field electrode poling. An optical waveguide may be modeled during poling by considering the dielectric charge distribution, polarization charge distribution, and conduction charge generated by the poling field. These charge distributions are the source of poling current densities. The model shows that boundary charge current density and polarization current density are the major source of currents measured during poling and thermally stimulated discharge These charge distributions provide insight into the poling mechanisms and are directly related to E(sub A), and, alpha(sub r). Initial comparisons with experimental data show excellent correlation to the model results.

  12. Ab initio Determination of Formation Energies and Charge Transfer Levels of Charged Ions in Water

    NASA Astrophysics Data System (ADS)

    Vatti, Anoop Kishore; Todorova, Mira; Neugebauer, Joerg

    The ability to describe the complex atomic and electronic structure of liquid water and hydrated ions on a microscopic level is a key requirement to understand and simulate electro-chemical and biological processes. Identifying theoretical concepts which enable us to achieve an accurate description in a computationally efficient way is thereby of central importance. Aiming to unravel the importance and influence of different contributions on the hydration energy of ions we perform extensive ab-initio molecular dynamics simulations for charged and neutral cations (Zn, Mg) and anions (Cl, Br, I) in water. The structural correlations and electronic properties of the studied ions are analysed and compared to experimental observations. Following an approach inspired by the defect chemistry in semiconductors and aligning the water band edges on an absolute scale allows us to benchmark the calculated formation energies, identify transition states and compare the results to experiment. Based on these results we discuss the performance of various DFT xc-functionals to predict charge transfer levels and photo-emission experiments.

  13. First-principles studies on the charge density wave in uranium

    NASA Astrophysics Data System (ADS)

    Qiu, Ruizhi; Lu, Haiyan; Ao, Bingyun; Tang, Tao; Chen, Piheng

    2016-06-01

    The charge density wave (CDW) state of α-U (called {α1} -U) was studied through a first-principles total-energy minimization using the conjugate gradient algorithm. The optimized crystal structure of {α1} -U was found to have the space group Pbnm, which was proposed in the earlier Landau-type theory and is isostructural with the α-Np structure. In particular, the changes in the lattice parameters of Pbnm-U with respect to α-U are consistent with the experimental observations. In addition, the energetic stability of Pbnm-U with respect to α-U was confirmed by enthalpy calculations, and the value of the critical pressure in the pressure-induced quantum transition from Pbnm-U to α-U is in good agreement with the experimental result. Moreover, the phonon calculation verified the dynamical instability of α-U and the stability of Pbnm-U. Finally, the calculated electronic structures exhibit features of the CDW state.

  14. Non-thermal separation of electronic and structural orders in a persisting charge density wave.

    PubMed

    Porer, M; Leierseder, U; Ménard, J-M; Dachraoui, H; Mouchliadis, L; Perakis, I E; Heinzmann, U; Demsar, J; Rossnagel, K; Huber, R

    2014-09-01

    The simultaneous ordering of different degrees of freedom in complex materials undergoing spontaneous symmetry-breaking transitions often involves intricate couplings that have remained elusive in phenomena as wide ranging as stripe formation, unconventional superconductivity or colossal magnetoresistance. Ultrafast optical, X-ray and electron pulses can elucidate the microscopic interplay between these orders by probing the electronic and lattice dynamics separately, but a simultaneous direct observation of multiple orders on the femtosecond scale has been challenging. Here we show that ultrabroadband terahertz pulses can simultaneously trace the ultrafast evolution of coexisting lattice and electronic orders. For the example of a charge density wave (CDW) in 1T-TiSe2, we demonstrate that two components of the CDW order parameter--excitonic correlations and a periodic lattice distortion (PLD)--respond very differently to 12-fs optical excitation. Even when the excitonic order of the CDW is quenched, the PLD can persist in a coherently excited state. This observation proves that excitonic correlations are not the sole driving force of the CDW transition in 1T-TiSe2, and exemplifies the sort of profound insight that disentangling strongly coupled components of order parameters in the time domain may provide for the understanding of a broad class of phase transitions.

  15. Superior Charge Storage and Power Density of a Conducting Polymer-Modified Covalent Organic Framework

    PubMed Central

    2016-01-01

    The low conductivity of two-dimensional covalent organic frameworks (2D COFs), and most related coordination polymers, limits their applicability in optoelectronic and electrical energy storage (EES) devices. Although some networks exhibit promising conductivity, these examples generally lack structural versatility, one of the most attractive features of framework materials design. Here we enhance the electrical conductivity of a redox-active 2D COF film by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) within its pores. The resulting poly(3,4-ethylenedioxythiophene) (PEDOT)-infiltrated COF films exhibit dramatically improved electrochemical responses, including quantitative access to their redox-active groups, even for 1 μm-thick COF films that otherwise provide poor electrochemical performance. PEDOT-modified COF films can accommodate high charging rates (10–1600 C) without compromising performance and exhibit both a 10-fold higher current response relative to unmodified films and stable capacitances for at least 10 000 cycles. This work represents the first time that electroactive COFs or crystalline framework materials have shown volumetric energy and power densities comparable with other porous carbon-based electrodes, thereby demonstrating the promise of redox-active COFs for EES devices. PMID:27725966

  16. Persistent order due to transiently enhanced nesting in an electronically excited charge density wave

    DOE PAGES

    Rettig, L.; Cortés, R.; Chu, J. -H.; Fisher, I. R.; Schmitt, F.; Moore, R. G.; Shen, Z. -X.; Kirchmann, P. S.; Wolf, M.; Bovensiepen, U.

    2016-01-25

    Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time-and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of themore » dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. In conclusion, our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order.« less

  17. 1/f noise anomalies in nanoribbons of charge density wave materials

    NASA Astrophysics Data System (ADS)

    Shi, Zhenzhong; Stabile, Adam; Marley, Peter M.; Banerjee, Sarbajit; Sambandamurthy, Ganapathy

    2013-03-01

    Charge density wave (CDW) as an ordered form of matter has attracted attention for many decades. Below a critical temperature (TP), CDW materials undergo a Peierls transition and enter the CDW ground state, where the energy is minimized by a collectively pinning mechanism. Under a moderate electric field, CDWs can be depinned and they start sliding. An onset of a large broad band noise (BBN) has been observed in bulk CDW materials as a signature of this depinning process. We report low frequency conductance fluctuation (1/f noise) measurements on single nanoribbon devices of single-crystalline NbSe3, across both Peierls transitions. In the CDW state, a non-monotonic behavior in the noise magnitude was observed when approaching the threshold electric field for depinning: while increasing voltage from the zero-bias limit, the magnitude of BBN first decreases before increasing sharply near the threshold voltage. This unusually large BBN magnitude and the non-monotonic behavior below the depinning threshold suggest some inherent instability that could be suppressed by a small bias field, and is clearly different from results from bulk materials. Transport and noise studies from individual nanoribbons of NbSe3, Ta-doped NbSe3 and o-TaS3 will be presented.

  18. Topology of charge density and elastic properties of Ti3SiC2 polymorphs

    SciTech Connect

    Yu, Rong; Zhang, Xiao Feng; He, Lian Long; Ye, Heng Qiang

    2004-06-24

    Using an all-electron, full potential first-principles method, we have investigated the topology of charge density and elastic properties of the two polymorphs, alpha and beta, of Ti3SiC2. The bonding effect was analyzed based on Bader's quantum theory of ''atoms in molecules'' (AIM). It was found that the Ti-Si bonding effect is significantly weaker in beta than in alpha, giving less stabilizing effect for beta. The Si-C bonds, which are absent in alpha, are formed in beta and provide additional stabilizing effect for beta. In contrast to conventional thinking, there is no direction interaction between Ti atoms in both alpha and beta. The calculated elastic properties are in good agreement with the experimental results, giving the bulk modulus of about 180 GPa and the Poisson's ratio of 0.2. The beta phase is generally softer than the alpha phase. As revealed by the direction dependent Young's modulus, there is only slight elastic anisotropy in Ti3SiC2. For alpha, Young's modulus is minimum in the c direction and maximum in the directions 42o from c. For beta, the maximum lies in the c direction, in part due to the formation of Si-C bonds in this direction.

  19. Density functional investigation of the electronic structure and charge transfer excited states of a multichromophoric antenna

    NASA Astrophysics Data System (ADS)

    Basurto, Luis; Zope, Rajendra R.; Baruah, Tunna

    2016-05-01

    We report an electronic structure study of a multichromophoric molecular complex containing two of each borondipyrromethane dye, Zn-tetraphenyl-porphyrin, bisphenyl anthracene and a fullerene. The snowflake shaped molecule behaves like an antenna capturing photon at different frequencies and transferring the photon energy to the porphyrin where electron transfer occurs from the porphyrin to the fullerene. The study is performed within density functional formalism using large polarized Guassian basis sets (12,478 basis functions in total). The energies of the HOMO and LUMO states in the complex, as adjudged by the ionization potential and the electron affinity values, show significant differences with respect to their values in participating subunits in isolation. These differences are also larger than the variations of the ionization potential and electron affinity values observed in non-bonded C60-ZnTPP complexes in co-facial arrangement or end-on orientations. An understanding of the origin of these differences is obtained by a systematic study of the effect of structural strain, the presence of ligands, the effect of orbital delocalization on the ionization energy and the electron affinity. Finally, a few lowest charge transfer energies involving electronic transitions from the porphyrin component to the fullerene subunit of the complex are predicted.

  20. Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tri-Tellurides

    SciTech Connect

    Lee, W.S.; Sorini, A.P.; Yi, M.; Chuang, Y.D.; Moritz, B.; Yang, W.L.; Chu, J.-H.; Kuo, H.H.; Gonzalez, A.G.Cruz; Fisher, I.R.; Hussain, Z.; Devereau, T.P.; Shen, Z.X.

    2012-05-15

    We performed resonant soft X-ray diffraction on known charge density wave (CDW) compounds, rare earth tri-tellurides. Near the M{sub 5} (3d - 4f) absorption edge of rare earth ions, an intense diffraction peak is detected at a wavevector identical to that of CDW state hosted on Te{sub 2} planes, indicating a CDW-induced modulation on the rare earth ions. Surprisingly, the temperature dependence of the diffraction peak intensity demonstrates an exponential increase at low temperatures, vastly different than that of the CDW order parameter. Assuming 4f multiplet splitting due to the CDW states, we present a model to calculate X-ray absorption spectrum and resonant profile of the diffraction peak, agreeing well with experimental observations. Our results demonstrate a situation where the temperature dependence of resonant X-ray diffraction peak intensity is not directly related to the intrinsic behavior of the order parameter associated with the electronic order, but is dominated by the thermal occupancy of the valence states.

  1. Thickness dependent charge transfer states and dark carriers density in vacuum deposited small molecule organic photocell

    NASA Astrophysics Data System (ADS)

    Shekhar, Himanshu; Tzabari, Lior; Solomeshch, Olga; Tessler, Nir

    2016-10-01

    We have investigated the influence of the active layer thickness on the balance of the internal mechanisms affecting the efficiency of copper phthalocyanine - fullerene (C60) based vacuum deposited bulk heterojunction organic photocell. We fabricated a range of devices for which we varied the thickness of the active layer from 40 to 120 nm and assessed their performance using optical and electrical characterization techniques. As reported previously for phthalocyanine:C60, the performance of the device is highly dependent on the active layer thickness and of all the thicknesses we tried, the 40 nm thin active layer device showed the best solar cell characteristic parameters. Using the transfer matrix based optical model, which includes interference effects, we calculated the optical power absorbed in the active layers for the entire absorption band, and we found that this cannot explain the trend with thickness. Measurement of the cell quantum efficiency as a function of light intensity showed that the relative weight of the device internal processes changes when going from 40 nm to 120 nm thick active layer. Electrical modeling of the device, which takes different internal processes into account, allowed to quantify the changes in the processes affecting the generation - recombination balance. Sub gap external quantum efficiency and morphological analysis of the surface of the films agree with the model's result. We found that as the thickness grows the density of charge transfer states and of dark carriers goes up and the uniformity in the vertical direction is reduced.

  2. Magnetic field controlled charge density wave coupling in underdoped YBa2Cu3O6+x

    PubMed Central

    Chang, J.; Blackburn, E.; Ivashko, O.; Holmes, A. T.; Christensen, N. B.; Hücker, M.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Rütt, U.; Zimmermann, M. v.; Forgan, E. M.; Hayden, S M

    2016-01-01

    The application of magnetic fields to layered cuprates suppresses their high-temperature superconducting behaviour and reveals competing ground states. In widely studied underdoped YBa2Cu3O6+x (YBCO), the microscopic nature of field-induced electronic and structural changes at low temperatures remains unclear. Here we report an X-ray study of the high-field charge density wave (CDW) in YBCO. For hole dopings ∼0.123, we find that a field (B∼10 T) induces additional CDW correlations along the CuO chain (b-direction) only, leading to a three-dimensional (3D) ordered state along this direction at B∼15 T. The CDW signal along the a-direction is also enhanced by field, but does not develop an additional pattern of correlations. Magnetic field modifies the coupling between the CuO2 bilayers in the YBCO structure, and causes the sudden appearance of the 3D CDW order. The mirror symmetry of individual bilayers is broken by the CDW at low and high fields, allowing Fermi surface reconstruction, as recently suggested. PMID:27146255

  3. Magnetic field controlled charge density wave coupling in underdoped YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Chang, J.; Blackburn, E.; Ivashko, O.; Holmes, A. T.; Christensen, N. B.; Hücker, M.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Rütt, U.; Zimmermann, M. V.; Forgan, E. M.; Hayden, S. M.

    2016-05-01

    The application of magnetic fields to layered cuprates suppresses their high-temperature superconducting behaviour and reveals competing ground states. In widely studied underdoped YBa2Cu3O6+x (YBCO), the microscopic nature of field-induced electronic and structural changes at low temperatures remains unclear. Here we report an X-ray study of the high-field charge density wave (CDW) in YBCO. For hole dopings ~0.123, we find that a field (B~10 T) induces additional CDW correlations along the CuO chain (b-direction) only, leading to a three-dimensional (3D) ordered state along this direction at B~15 T. The CDW signal along the a-direction is also enhanced by field, but does not develop an additional pattern of correlations. Magnetic field modifies the coupling between the CuO2 bilayers in the YBCO structure, and causes the sudden appearance of the 3D CDW order. The mirror symmetry of individual bilayers is broken by the CDW at low and high fields, allowing Fermi surface reconstruction, as recently suggested.

  4. Direct observation of many-body charge density oscillations in a two-dimensional electron gas.

    PubMed

    Sessi, Paolo; Silkin, Vyacheslav M; Nechaev, Ilya A; Bathon, Thomas; El-Kareh, Lydia; Chulkov, Evgueni V; Echenique, Pedro M; Bode, Matthias

    2015-01-01

    Quantum interference is a striking manifestation of one of the basic concepts of quantum mechanics: the particle-wave duality. A spectacular visualization of this effect is the standing wave pattern produced by elastic scattering of surface electrons around defects, which corresponds to a modulation of the electronic local density of states and can be imaged using a scanning tunnelling microscope. To date, quantum-interference measurements were mainly interpreted in terms of interfering electrons or holes of the underlying band-structure description. Here, by imaging energy-dependent standing-wave patterns at noble metal surfaces, we reveal, in addition to the conventional surface-state band, the existence of an 'anomalous' energy band with a well-defined dispersion. Its origin is explained by the presence of a satellite in the structure of the many-body spectral function, which is related to the acoustic surface plasmon. Visualizing the corresponding charge oscillations provides thus direct access to many-body interactions at the atomic scale. PMID:26498368

  5. Direct observation of many-body charge density oscillations in a two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Sessi, Paolo; Silkin, Vyacheslav M.; Nechaev, Ilya A.; Bathon, Thomas; El-Kareh, Lydia; Chulkov, Evgueni V.; Echenique, Pedro M.; Bode, Matthias

    2015-10-01

    Quantum interference is a striking manifestation of one of the basic concepts of quantum mechanics: the particle-wave duality. A spectacular visualization of this effect is the standing wave pattern produced by elastic scattering of surface electrons around defects, which corresponds to a modulation of the electronic local density of states and can be imaged using a scanning tunnelling microscope. To date, quantum-interference measurements were mainly interpreted in terms of interfering electrons or holes of the underlying band-structure description. Here, by imaging energy-dependent standing-wave patterns at noble metal surfaces, we reveal, in addition to the conventional surface-state band, the existence of an `anomalous' energy band with a well-defined dispersion. Its origin is explained by the presence of a satellite in the structure of the many-body spectral function, which is related to the acoustic surface plasmon. Visualizing the corresponding charge oscillations provides thus direct access to many-body interactions at the atomic scale.

  6. Electroosmotic transport in polyelectrolyte-grafted nanochannels with pH-dependent charge density

    NASA Astrophysics Data System (ADS)

    Chen, Guang; Das, Siddhartha

    2015-05-01

    "Smart" polyelectrolyte-grafted or "soft" nanochannels with pH-responsiveness have shown great promise for applications like manipulation of ion transport, ion sensing and selection, current rectification, and many more. In this paper, we develop a theory to study the electroosmotic transport in a polyelectrolyte-grafted (or soft) nanochannel with pH-dependent charge density. In one of our recent studies, we have identified that explicit consideration of hydrogen ion concentration is mandatory for appropriately describing the electrostatics of such systems and the resulting monomer concentration must obey a non-unique, cubic distribution. Here, we use this electrostatic calculation to study the corresponding electroosmotic transport. We establish that the effect of pH in the electroosmotic transport in polyelectrolyte-grafted nanochannels introduces two separate issues: first is the consideration of the hydrogen and hydroxyl ion concentrations in describing the electroosmotic body force, and second is the consideration of the appropriate drag force that bears the signature of this cubic monomeric distribution. Our results indicate that the strength of the electroosmotic velocity for the pH-dependent case is always smaller than that for the pH-independent case, with the extent of this difference being a function of the system parameters. Such nature of the electroosmotic transport will be extremely significant in suppressing the electroosmotic flow strength with implications in large number applications such as capillary electrophoresis induced separation, electric field mediated DNA elongation, electrophoretic DNA nanopore sequencing, and many more.

  7. Collective modes in quasi-one-dimensional charge-density wave systems probed by femtosecond time-resolved optical studies

    NASA Astrophysics Data System (ADS)

    Schaefer, H.; Kabanov, V. V.; Demsar, J.

    2014-01-01

    The interplay between the electronic and structural subsystems has strong implications on the character of collective excitations in cooperative systems. Their detailed understanding can provide important information on the coupling mechanisms and coupling strengths in such systems. With the recent developments in femtosecond time-resolved optical probes, numerous advantages with respect to conventional time-integrated probes have been put forward. Owing to their high dynamic range, high-frequency resolution, fast data acquisition, and an inherent access to phases of coherent excitations, they provide direct access to the interplay between various degrees of freedom. In this paper, we present a detailed analysis of time-resolved optical data on blue bronzes (K0.3MoO3 and Rb0.3MoO3), prototype quasi-one-dimensional charge-density wave (CDW) systems. Numerous coherent (Raman active) modes appear upon the phase transition into the CDW state. We analyze the temperature dependence of mode frequencies, their damping times, as well as their oscillator strengths and phases using the time-dependent Ginzburg-Landau model. We demonstrate that these low-temperature modes are a result of linear coupling between the Fermi surface nesting driven modulation of the conduction electron density and the normal-state phonons at the CDW wave vector, and determine their coupling strengths. Moreover, we are able to identify the nature of excitation of these coupled modes, as well as the nature of the probing mechanisms in this type of experiments. We demonstrate that in incommensurate CDW systems, femtosecond optical excitation initially suppresses the electronic density modulation, while the reflectivity changes at frequencies far above the CDW induced gap in the single-particle excitation spectrum are governed by the modulation of interband transitions caused by lattice motion. This approach can be readily extended to more complex systems with spatially modulated ground states.

  8. Metal-Organic Coordination Number Determined Charge Transfer Magnitude

    NASA Astrophysics Data System (ADS)

    Yang, Hung-Hsiang; Chu, Yu-Hsun; Lu, Chun-I.; Yang, Tsung-Han; Yang, Kai-Jheng; Kaun, Chao-Cheng; Hoffmann, Germar; Lin, Minn-Tsong

    2014-03-01

    By the appropriate choice of head groups and molecular ligands, various metal-organic coordination geometries can be engineered. Such metal-organic structures provide different chemical environments for molecules and give us templates to study the charge redistribution within the metal-organic interface. We created various metal-organic bonding environment by growing self-assembly nanostructures of Fe-PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) chains and networks on a Au(111) surface. Bonding environment dependent frontier molecular orbital energies are acquired by low temperature scanning tunneling microscopy and scanning tunneling spectroscopy. By comparing the frontier energies with the molecular coordination environments, we conclude that the specific coordination affects the magnitude of charge transfer onto each PTCDA in the Fe-PTCDA hybridization system. H.-H. Yang, Y.-H. Chu, C.-I Lu, T.-H. Yang, K.-J. Yang, C.-C. Kaun, G. Hoffmann, and M.-T. Lin, ACS Nano 7, 2814 (2013).

  9. Anisotropy-induced crossover from Drude conductivity to charge-density-wave excitations in a stripe-type charge-ordered manganite

    NASA Astrophysics Data System (ADS)

    Rana, Rakesh; Pandey, Parul; Rana, D. S.; Mavani, K. R.; Kawayama, I.; Murakami, H.; Tonouchi, M.

    2013-06-01

    The half-doped Pr0.5Sr0.5MnO3 (PSMO) manganite represents a unique stripe type of charge orbital order that induces transport and magnetic anisotropy. Low-energy charge dynamics in PSMO (110) epitaxial film were investigated along and across two dissimilar in-plane orthogonal axes, [1-10] and [001], by recording the complex refractive index in the energy range of 1-7 meV. We report a novel observation of a gradual crossover from Drude-like metallic conductivity to charge-density-wave (CDW)-like collective excitations as the polarized terahertz excitation field is swept across the orthogonal in-plane axes. This is a rare manifestation of a CDW mode in a highly conducting stripe-type charge-ordered (CO) system, which is fundamentally different from the CDW modes of checkerboard CO. Interestingly, the contrasting charge dynamics along orthogonal in-plane axes form an intrinsic electronic switch, apparently a consequence of the unique CO of PSMO.

  10. The surface charge density of plant cell membranes: an attempt to resolve conflicting values for intrinsic s.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The electrical potentials at membrane surfaces (Psi) may be computed with electrostatic models incorporating the intrinsic surface charge density of the membrane (Sigma), the ion composition of the bathing medium, and ion binding to the membrane. Ion activities at membrane surfaces may be computed ...

  11. Membrane effects of Vitamin E deficiency: bioenergetic and surface-charge-density studies of skeletal muscle and liver mitochondria

    SciTech Connect

    Quintanilha, A.T.; Packer, L.; Szyszlo Davies, J.M.; Racanelli, T.L.; Davies, K.J.A.

    1981-12-01

    Vitamin E (dl-..cap alpha..-tocopherol) deficiency in rats increased the sensitivity of liver and muscle mitochondria to damage during incubation at various temperatures, irradiation with visible light, or steady state respiration with substrates. In all cases, vitamin E deficient mitochondria exhibited increased lipid peroxidation, reduced transmembrane potential, decreased respiratory coupling, and lower rates of electron transport, compared to control mitochondria. Muscle mitochondria always showed greater negative inner membrane surface charge density, and were also more sensitive to damage than were liver mitochondria. Vitamin E deficient mitochondria also showed slightly more negative inner membrane surface charge density compared to controls. The relationship between greater negative surface potential and increased sensitivity to damage observed, provides for a new and sensitive method to further probe the role of surface charge in membrane structure and function. Implications of these new findings for the well known human muscle myopathies and those experimentally induced by Vitamin E deficiency in animals, are discussed.

  12. Molecular-scale quantitative charge density measurement of biological molecule by frequency modulation atomic force microscopy in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Umeda, Kenichi; Kobayashi, Kei; Oyabu, Noriaki; Matsushige, Kazumi; Yamada, Hirofumi

    2015-07-01

    Surface charge distributions on biological molecules in aqueous solutions are essential for the interactions between biomolecules, such as DNA condensation, antibody-antigen interactions, and enzyme reactions. There has been a significant demand for a molecular-scale charge density measurement technique for better understanding such interactions. In this paper, we present the local electric double layer (EDL) force measurements on DNA molecules in aqueous solutions using frequency modulation atomic force microscopy (FM-AFM) with a three-dimensional force mapping technique. The EDL forces measured in a 100 mM KCl solution well agreed with the theoretical EDL forces calculated using reasonable parameters, suggesting that FM-AFM can be used for molecular-scale quantitative charge density measurements on biological molecules especially in a highly concentrated electrolyte.

  13. Spin-Fluctuation-Driven Nematic Charge-Density Wave in Cuprate Superconductors: Impact of Aslamazov-Larkin Vertex Corrections.

    PubMed

    Yamakawa, Youichi; Kontani, Hiroshi

    2015-06-26

    We present a microscopic derivation of the nematic charge-density wave (CDW) formation in cuprate superconductors based on the three-orbital d-p Hubbard model by introducing the vertex correction (VC) into the charge susceptibility. The CDW instability at q=(Δ(FS),0), (0,Δ(FS)) appears when the spin fluctuations are strong, due to the strong charge-spin interference represented by the VC. Here, Δ(FS) is the wave number between the neighboring hot spots. The obtained spin-fluctuation-driven CDW is expressed as the "intra-unit-cell orbital order" accompanied by the charge transfer between the neighboring atomic orbitals, which is actually observed by the scanning tunneling microscope measurements. We predict that the cuprate CDW and the nematic orbital order in Fe-based superconductors are closely related spin-fluctuation-driven phenomena. PMID:26197139

  14. Spin-Fluctuation-Driven Nematic Charge-Density Wave in Cuprate Superconductors: Impact of Aslamazov-Larkin Vertex Corrections.

    PubMed

    Yamakawa, Youichi; Kontani, Hiroshi

    2015-06-26

    We present a microscopic derivation of the nematic charge-density wave (CDW) formation in cuprate superconductors based on the three-orbital d-p Hubbard model by introducing the vertex correction (VC) into the charge susceptibility. The CDW instability at q=(Δ(FS),0), (0,Δ(FS)) appears when the spin fluctuations are strong, due to the strong charge-spin interference represented by the VC. Here, Δ(FS) is the wave number between the neighboring hot spots. The obtained spin-fluctuation-driven CDW is expressed as the "intra-unit-cell orbital order" accompanied by the charge transfer between the neighboring atomic orbitals, which is actually observed by the scanning tunneling microscope measurements. We predict that the cuprate CDW and the nematic orbital order in Fe-based superconductors are closely related spin-fluctuation-driven phenomena.

  15. Far infrared conductivity of charge density wave materials and the oxygen isotope effect in high-T sub c superconductors

    SciTech Connect

    Creager, W.N.

    1991-09-01

    The far infrared reflectance and conductivity of (Ta{sub 1-x}Nb{sub x}Se{sub 4}){sub 2}I and TaS{sub 3} have been measured to determine the origin of a huge infrared resonance that dominates the charge density wave (CDW) dynamics along with the pinned acoustic phason mode in the related materials (TaSe{sub 4}){sub 2}I and K{sub 0. 3}MoO{sub 3}. The measurements cover frequencies from 3 to 700cm{sup {minus}1} and the temperature range from 15K to 300K. In the niobium-doped alloys (Ta{sub 1-x}Nb{sub x}Se{sub 4}){sub 2}I, the size and frequency of the giant infrared mode remain nearly constant as the impurity concentration x is increased. For TaS{sub 3}, the pinned acoustic phason near 0.5cm{sup {minus}1} dominates {var epsilon}({omega}) and an additional small mode lies near 9cm{sup {minus}1}. The latter mode is much smaller than the infrared mode in other CDW materials. These results rule out several models of a generic infrared mode'' in CDW excitations. They are compared in detail to the predictions of a recent theory attributing the infrared mode to a bound collective mode localized at impurity sites within the crystal. The transmittance of K{sub 0.3}MoO{sub 3} has been measured at 1.2K with a strong dc electric field applied across the crystal. Under these conditions, the charge density wave depins abruptly and carries large currents with near-zero differential resistance. For some samples, the low-frequency transmittance is enhanced slightly when the CDW depins. The magnitude of the oxygen isotope effect in the high-{Tc} superconductor YBa{sub 2}Cu{sub 3}O{sub 7} has been determined by substitution of {sup 18}O for {sup 16}O. A series of cross-exchanges was performed on high-quality polycrystalline specimens to eliminate uncertainties due to sample heat treatments and sample inhomogeneities.

  16. Origin of charge density at LaAlO3-on-SrTiO3 heterointerfacespossibility of intrinsic doping

    SciTech Connect

    Siemons, W.

    2010-04-29

    As discovered by Ohtomo et al., a large sheet charge density with high mobility exists at the interface between SrTiO{sub 3} and LaAlO{sub 3}. Based on transport, spectroscopic and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies introduced by the pulsed laser deposition process used by all researchers to date to make these samples is the source of the large carrier densities. Annealing experiments show a limiting carrier density. We also present a model that explains the high mobility based on carrier redistribution due to an increased dielectric constant.

  17. Kinetic theory of current and density drift instabilities with weak charged-neutral collisions. [in space plasmas

    NASA Technical Reports Server (NTRS)

    Gary, S. P.

    1984-01-01

    This paper describes the linear kinetic theory of electrostatic instabilities driven by a density gradient drift and a magnetic-field-aligned current in a plasma with weak charged neutral collisions. The configuration is that of a uniform magnetic field B, a weak, uniform density gradient in the x direction and a weak, uniform electric field in the z direction. Collisions are represented by the BGK model. The transition from the (kinetic) universal density drift instability to the (fluidlike) current convective instability is studied in detail, and the short wavelength properties of the latter mode are investigated.

  18. Density and capacitance profiles and edge effects in a two-dimensional charge layer on a dielectric surface

    NASA Astrophysics Data System (ADS)

    Mehrotra, Ravi

    1987-04-01

    The density and capacitance profiles and edge effects in a two-dimensional (2D) layer of electrons held on a liquid helium surface between two horizontal plates of a parallel-plate capacitor are studied by solving Laplace's equation on a computer. An effective length for experimental cells is defined to take into account nonuniform charge density and capacitance near the edges of the cells. The profiles and edge effects are studied as a function of charge density on the helium surface, helium depth inside the cell, repelling voltages on guard electrodes around the capacitor plates, and the frequency of excitation. The results should be useful in designing cells for experiments and better analyzing the results of measurements.

  19. Refinement of crystal structural parameters and charge density using convergent-beam electron diffraction--the rhombohedral phase of LaCrO3.

    PubMed

    Tsuda, Kenji; Ogata, Yoichiro; Takagi, Kazunari; Hashimoto, Takuya; Tanaka, Michiyoshi

    2002-11-01

    Atom positions and anisotropic Debye-Waller factors of the rhombohedral phase of LaCrO(3) have been refined simultaneously with the low-order structure factors, using a structure-analysis method of convergent-beam electron diffraction (CBED) proposed by Tsuda & Tanaka [Acta Cryst. (1999), A55, 939-954]. The method is based on the least-squares fitting between full dynamical calculations and energy-filtered intensities of two-dimensional higher-order Laue-zone (HOLZ) and zeroth-order Laue-zone (ZOLZ) CBED patterns. The positions of the oxygen atoms have been determined with a high precision. Clear anisotropy of the thermal vibrations of the oxygen atoms has been successfully determined by the CBED method for the first time. The charge transfer from the La and Cr atoms to the O atoms has been found from the deformation charge-density map.

  20. Superlattice Structure in Chalcogen Square-Net Charge Density Wave Phases.

    NASA Astrophysics Data System (ADS)

    Foran, Brendan John

    Superstructures in materials with chalcogen square lattices are accounted for in terms of charge density waves associated with quasi-one-dimensional electronic structure. Two new compounds, DySe_{1.84} and Rb_{0.33}DySe _{2.67}, were grown in a RbCl/LiCl eutectic flux. Rb_{0.33}DySe _{2.67} has an orthorhombic subcell, space group Cmcm, a = 4.0579(6)A, b =26.47(1)A and c = 3.8909(6)A; the selenium square lattice has site occupancy waves and charge density waves. The average substructure of DySe_{1.84} is tetragonal, P4/nmm, but the complete modulated structure is better described in a 3 + 2 dimensional space group C_sp{c"m"m1}{Pm2 _1n}. The basic cell is a = 3.9912(3)A, b = 3.9863(1)A, and c = 8.206(1)A, with modulation wave vectors at q_1 = alpha{ bf a}^* + beta{bf b} ^* + 1/2{bf c}^*, and {bf q}_2 = alpha{ bf a}^* - beta{bf b} ^* + 1/2{bf c}^* where alpha = 0.33338(12), and beta = 0.27284(6). Refinement on main reflections plus first and second order satellites produced four solutions that could not be differentiated by R-factors. An energy minimum structure is predicted by mu_2 -scaled Huckel theory, and the superstructures found in elemental selenium, and LnQ_2(Ln=La,Ce; Q=S,Se) phases are rationalized. The concept of an effective band filling is introduced as a means of generating a model for the Fermi surface of a defective lattice from that of an ideal non-defective lattice. By this method the superstructures of La_{10}Se _{19}, Cs_3Te_{22 }, RbDy_3Se_8 and DySe _{1.84} are rationalized and predicted. The synthesis, structure and band structure analysis of the quaternary compound K_{0.33 }rm Ba_{0.67}AgTe_2 are reported. Crystals were obtained by reaction of K _2Te, BaTe, Ag and Te in a K _2Te/BaTe/Te flux cooling from 450 ^circC. The substructure is tetragonal, 14/mmm, a_{sub} = 4.624(2) A, {bf c}_{sub } = 23.326(4) A, 172 independent data, 13 variables, R/R_{w} = 0.054/0.067. A (Te_2]^{4/3-} square net should be metallic, but transport measurements show

  1. Charge-density oscillations on Be(10{bar 1}0): Screening in a non-free two-dimensional electron gas

    SciTech Connect

    Briner, B.G.; Hofmann, P. ||; Doering, M.; Rust, H.; Plummer, E.W. |; Bradshaw, A.M.

    1998-11-01

    The surface state on Be(10{bar 1}0) has been investigated using a low-temperature scanning tunneling microscope (STM). The Fermi contour of this surface state is located at one boundary of the surface Brillouin zone, and surface-state electrons provide the main part of the charge density near the Fermi energy. Be(10{bar 1}0), therefore, corresponds closely to a non-free two-dimensional electron gas. We have observed standing waves of the surface charge density on Be(10{bar 1}0) near step edges and point defects. Such wave patterns derive from the interference of incoming and scattered electrons; they demonstrate the screening characteristics of the surface state. On Be(10{bar 1}0) these waves were found to be highly anisotropic. It is shown that calculating the Fourier transforms of topographic STM images is a powerful method for determining the Fermi contour of the surface state. This method could even be applied to images that display a complex wave pattern arising from a random distribution of point scatterers. Fourier analysis also revealed that the charge density oscillations on Be(10{bar 1}0) contain multiple periods that differ by reciprocal lattice vectors. These multiperiodic oscillations relate to the non-free character of the surface-state electrons and constitute an interference pattern of Bloch states. Fourier filtering was used to separate the charge-density oscillations from the topographic corrugation and to visualize their shape and spatial range. The experimental data are qualitatively discussed using a model calculation based on the scattering of Bloch electrons from planar obstacles in a two-dimensional conductor. Experimental results and model calculations highlight how the screening characteristics on Be(10{bar 1}0) significantly deviate from the behavior expected for a free two-dimensional electron gas. {copyright} {ital 1998} {ital The American Physical Society}

  2. Multiple charge density wave transitions in the antiferromagnets R NiC2 (R =Gd ,Tb)

    NASA Astrophysics Data System (ADS)

    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.

  3. Unconventional Charge-Density-Wave Transition in Monolayer 1T-TiSe2.

    PubMed

    Sugawara, Katsuaki; Nakata, Yuki; Shimizu, Ryota; Han, Patrick; Hitosugi, Taro; Sato, Takafumi; Takahashi, Takashi

    2016-01-26

    Reducing the dimension in materials sometimes leads to unexpected discovery of exotic and/or pronounced physical properties such as quantum Hall effect in graphene and high-temperature superconductivity in iron-chalcogenide atomically thin films. Transition-metal dichalcogenides (TMDs) provide a fertile ground for studying the interplay between dimensionality and electronic properties, since they exhibit a variety of electronic phases like semiconducting, superconducting, and charge-density-wave (CDW) states. Among TMDs, bulk 1T-TiSe2 has been a target of intensive studies due to its unusual CDW properties with the periodic lattice distortions characterized by the three-dimensional (3D) commensurate wave vector. Clarifying the ground states of its two-dimensional (2D) counterpart is of great importance not only to pin down the origin of CDW, but also to find unconventional physical properties characteristic of atomic-layer materials. Here, we show the first experimental evidence for the realization of 2D CDW phase without Fermi-surface nesting in monolayer 1T-TiSe2. Our angle-resolved photoemission spectroscopy (ARPES) signifies an electron pocket at the Brillouin-zone corner above the CDW-transition temperature (TCDW ∼ 200 K), while, below TCDW, an additional electron pocket and replica bands appear at the Brillouin-zone center and corner, respectively, due to the back-folding of bands by the 2 × 2 superstructure potential. Similarity in the spectral signatures to bulk 1T-TiSe2 implies a common driving force of CDW, i.e., exciton condensation, whereas the larger energy gap below TCDW in monolayer 1T-TiSe2 suggests enhancement of electron-hole coupling upon reducing dimensionality. The present result lays the foundation for the electronic-structure engineering based with atomic-layer TMDs.

  4. Variable temperature neutron diffraction and x-ray charge density studies of tetraacetylethane.

    SciTech Connect

    Piccoli, P. M. B.; Koetzle, T. F.; Schultz, A. J.; Zhurova, E. A.; Stare, J.; Pinkerton, A. A.; Eckert, J.; Hadzi, D.; Univ. of Toledo; National Inst. of Chemistry; Univ. of California at Santa Barbara

    2008-07-24

    Single crystal neutron diffraction data have been collected on a sample of enolized 3,4-diacetyl-2,5-hexanedione (tetraacetylethane, TAE) at five temperatures between 20 and 298 K to characterize the temperature-dependent behavior of the short, strong, intramolecular hydrogen bond. Upon decreasing the temperature from 298 K to 20 K, the O2-H1 distance decreases from 1.171(11) to 1.081(2) {angstrom} and the O1 {hor_ellipsis} H1 distance increases from 1.327(10) to 1.416(6) {angstrom}. The convergence of the C?O bond lengths from inequivalent distances at low temperature to identical values (1.285(4) {angstrom}) at 298 K is consistent with a resonance-assisted hydrogen bond. However, a rigid bond analysis indicates that the structure at 298 K is disordered. The disorder vanishes at lower temperatures. Short intermolecular C?H {hor_ellipsis} O contacts may be responsible for the ordering at low temperature. The intramolecular O {hor_ellipsis} O distance (2.432 0.006 {angstrom}) does not change with temperature. X-ray data at 20 K were measured to analyze the charge density and to gain additional insight into the nature of the strong hydrogen bond. Quantum mechanical calculations demonstrate that periodic boundary conditions provide significant enhancement over gas phase models in that superior agreement with the experimental structure is achieved when applying periodicity. One-dimensional potential energy calculations followed by quantum treatment of the proton reproduce the location of the proton nearer to the O2 site reasonably well, although they overestimate the O?H distance at low temperatures. The choice of the single-point energy calculation strategy for the proton potential is justified by the fact that the proton is preferably located nearer to O2 rather than being equally distant to O1 and O2 or evenly distributed (disordered) between them.

  5. 42 CFR 414.320 - Determination of reasonable charges for physician renal transplantation services.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... renal transplantation services. 414.320 Section 414.320 Public Health CENTERS FOR MEDICARE & MEDICAID... Determination of reasonable charges for physician renal transplantation services. (a) Comprehensive payment for... a renal transplantation, including the usual preoperative and postoperative care, and...

  6. 42 CFR 414.320 - Determination of reasonable charges for physician renal transplantation services.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... AND OTHER HEALTH SERVICES Determination of Reasonable Charges Under the ESRD Program § 414.320... payment levels established under the ESRD program and adjusted to give effect to variations in...

  7. The effect of charge density in tropospheric thunderclouds on production of sprites and terrestrial gamma ray flashes

    NASA Astrophysics Data System (ADS)

    Babich, Leonid; Haldoupis, Christos; Kudryavtsev, Andrei; Kutsyk, Igor

    2011-09-01

    We demonstrate that positive cloud-to-ground lightning flash (most often responsible for sprites) from stratiform tropospheric thundercloud leading to charge moment change iΔMq high above the sprite “threshold” 500 C km really triggers the high-altitude discharge exciting the air luminescence at sprite altitudes with brightness close to the observed brightness. Specifically, we present results for three configurations with the same charges Qcl = 200 C located at altitudes 6 and 8 km (iΔMq = 1200 C km for +Qcl at 6 km and iΔMq = 1600 C km for +Qcl at 8 km) differing by a magnitude of charge density, namely, σ = 1.86, 2.88, and 4.41 C km-2. All three configurations produce luminescence at sprite altitudes with brightness close to the observed one. In addition, the configuration with σ = 2.88 C km-2 produces observable γ emission, which can be detected in near space as terrestrial gamma-ray flashes (TGFs). The configuration with σ = 4.41 C km-2, provided it really could develop, would produce a blue fluorescence directly near the cloud top and extremely intensive γ emission not observed till now. The results obtained for smaller σ prove that too small-charge density in stratiform thunderclouds and consequently too weak electric field above them could account for the lack of Reuven Ramaty High Energy Solar Spectroscopic Imager TGFs correlated with large-charge moment change.

  8. Charge Density and Molecular Weight of Polyphosphoramidate Gene Carrier Are Key Parameters Influencing Its DNA Compaction Ability and Transfection Efficiency

    PubMed Central

    Ren, Yong; Jiang, Xuan; Pan, Deng; Mao, Hai-Quan

    2011-01-01

    A series of polyphosphoramidates (PPA) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293 and HepG2 cells). An increase in MW and/or net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for non-viral gene delivery. PMID:21067136

  9. 40 CFR Appendix C to Subpart Nnn... - Method for the Determination of Product Density

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Product Density C Appendix C to Subpart NNN of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION... Product Density 1. Purpose The purpose of this test is to determine the product density of cured blanket... product density: Density (lb/ft3) = area weight (lb/ft2)/thickness (ft)...

  10. Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D

    NASA Astrophysics Data System (ADS)

    Haskey, S. R.; Grierson, B. A.; Burrell, K. H.; Chrystal, C.; Groebner, R. J.; Kaplan, D. H.; Pablant, N. A.; Stagner, L.

    2016-11-01

    Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region in H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. These challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model.

  11. Nuclear Charge Radii of Li-8,Li-9 Determined by Laser Spectroscopy

    SciTech Connect

    Ewald, G; Nortershauser, W.; Dax, A ..; Gotte, S; Kirchner, Rolf; Kluge, H J.; Kuhl, T H.; Sanchez, R J.; Wojtasek, Alesia S.; Bushaw, Bruce A.; Drake, Gordon W. F.; Yan, Z C.; Zimmerman, Colin H.

    2004-09-09

    The 2S ' 3S transition of 6,7,8,9 Li was studied by high-resolution laser spectroscopy using two-photon Doppler-free excitation and resonance-ionization detection. The hyperfine structure splitting and the isotope shift were determined with precision at the 100 kHz level. Combined with recent theoretical work, the changes in nuclear charge radii of 8,9Li were determined. These are now the lightest short-lived isotopes for which the charge radii have been measured. It is found that the charge radii monotonically decrease with increasing neutron number from 6Li to 9Li.

  12. Shale volume determination using sonic, density and neutron data

    NASA Astrophysics Data System (ADS)

    Mabrouk, Walid M.; Kamel, Mostafa H.

    2011-06-01

    The volume of shale calculation based on naturally occurring gamma rays frequently overestimates shale volume when radioactive material other than shale is present, for example where sand appears to be shale. In this situation, shale volume calculations from other methods are highly recommended in order to avoid overestimation or underestimation of shale volume. This paper introduces an equation relating shale volume to porosity logs (neutron, density and acoustic logs), which takes into account the effect of matrix, fluid and shale parameters. This equation, which is based on the effective porosity definition and the Dresser Atlas (1982) equation, has been successfully applied to many shaly formations, regardless of the type and distribution of shale. Solved examples are used to test and compare this equation and the results come close to what actually exists, with the amount of error ranging from -5 to +5%. The advantages of the proposed equation can be summarised as: (1) it is a function of several parameters that affect the determination of shale volume in one formula; (2) it collects the three porosity tools for a more accurate calculation; and (3) it works best where radioactive material other than shale is present.

  13. Characterization of exfoliated TaS{sub 2} thin films and the existence of charge density waves

    SciTech Connect

    Manivannan, A.; Cabrera, C.R.; Fujishima, A.

    1995-05-01

    Restacked single molecular layers of the layer compound TaS{sub 2} from suspensions was deposited on titanium substrates by using a lithium intercalation-exfoliation method. These exfoliated thin films on titanium substrates have been characterized by scanning electron microscopy and Raman spectroscopy, and x-ray diffraction techniques are also investigated for the existence of charge density wave (CDW) phases using scanning tunneling microscopy (STM). All these techniques revealed that TaS{sub 2} crystallites tend to orient mostly with their basal planes parallel to the titanium substrate. TaS{sub 2} thin films are chosen with the understanding that the CDW states could mostly be determined because of intralayer interactions in comparison to bulk single crystals where inter- and intralayer interactions are considered. STM images showed strong CDWs with a hexagonal array having periodicity of {approximately}12{angstrom} and {open_quotes}corrugations{close_quotes} of {approximately}15{angstrom}, respectively. The existence of a CDW superlattice, together with the surface atomic structure observed at room temperature, on these thin films (thickness, ca. 300 {angstrom}) of single layers, allows us to understand the intralayer effects on the CDWs. The existence of CDWs in these films was not observed by transmission electron microscopy even at 25 K. 27 refs., 10 figs.

  14. Adsorption of carbon dioxide on Al12X clusters studied by density functional theory: effect of charge and doping.

    PubMed

    Zhao, Jian-Ying; Zhang, Yu; Zhao, Feng-Qi; Ju, Xue-Hai

    2013-11-27

    The adsorption of a CO2 molecule on neutral and charged X-centered icosahedron Al12X(±z) clusters (X = Al, Be, Zn, Ni, Cu, B, P; z = 0, 1) was investigated by the density functional PW91 and PWC methods. Optimized configurations corresponding to physisorption and chemisorption of CO2 were identified. The adsorption energies, activation barriers, and binding energies involving both the physisorption (Al12X(±z)·CO2-I) and chemisorption (Al12X(±z)·CO2-II) for CO2 were determined. The chemisorption of a CO2 molecule on the Al12X clusters (X is a metallic doping element) requires relatively low activation barriers. The lowest barrier was found to be with the Al12Be cluster. For the Al12X(-) clusters, the barriers are all higher than those of the neutral analogues. For the Al12X(+) clusters, two corresponding configurations are linked by a low-energy barrier, and CO2 molecule chemisorption on the Al12Be(+) cluster has the lowest barrier. The adsorption energies are larger than the energy barriers, which facilitates the chemisorption. The results show that carbon dioxide adsorbed on the Al12X(±z) clusters can be tuned by controllable X doping and the total number of valence electrons and suggest the potential application of Al12X(±z) nanostructures for carbon dioxide capture and activation.

  15. First experimental charge density study using a Bruker CMOS-type PHOTON 100 detector: the case of ammonium tetraoxalate dihydrate.

    PubMed

    Jarzembska, Katarzyna N; Kamiński, Radosław; Dobrzycki, Lukasz; Cyrański, Michał K

    2014-10-01

    The aim of this study was to test the applicability of a Bruker AXS CMOS-type PHOTON 100 detector for the purpose of a fine charge density quality data collection. A complex crystal containing oxalic acid, ammonium oxalate and two water molecules was chosen as a test case. The data was collected up to a resolution of 1.31 Å(-1) with high completeness (89.1%; Rmrg = 0.0274). The multipolar refinement and subsequent quantum theory of atoms in molecules (QTAIM) analysis resulted in a comprehensive description of the charge density distribution in the crystal studied. The residual density maps are flat and almost featureless. It was possible to derive reliable information on intermolecular interactions to model the anharmonic motion of a water molecule, and also to observe the fine details of the charge density distribution, such as polarization on O and H atoms involved in the strongest hydrogen bonds. When compared with our previous statistical study on oxalic acid data collected with the aid of CCD cameras, the complementary metal-oxide semiconductor (CMOS) detector can certainly be classified as a promising alternative in advanced X-ray diffraction studies.

  16. Influence of defects on the charge density wave of ([SnSe]1+δ)1(VSe2)1 ferecrystals

    DOE PAGES

    Falmbigl, Matthias; Putzky, Daniel; Ditto, Jeffrey; Esters, Marco; Bauers, Sage R.; Ronning, Filip; Johnson, David C.

    2015-07-14

    A series of ferecrystalline compounds ([SnSe]1+δ)1(VSe2)1 with varying Sn/V ratios were synthesized using the modulated elemental reactant technique. Temperature-dependent specific heat data reveal a phase transition at 102 K, where the heat capacity changes abruptly. An abrupt increase in electrical resistivity occurs at the same temperature, correlated with an abrupt increase in the Hall coefficient. Combined with the magnitude and nature of the specific heat discontinuity, this suggests that the transition is similar to the charge density wave transitions in transition metal dichalcogenides. An ordered intergrowth was formed over a surprisingly wide compositional range of Sn/V ratios of 0.89 ≤more » 1 + δ ≤ 1.37. X-ray diffraction and transmission electron microscopy reveal the formation of various volume defects in the compounds in response to the nonstoichiometry. The electrical resistivity and Hall coefficient data of samples with different Sn/V ratios show systematic variation in the carrier concentration with the Sn/V ratio. There is no significant change in the onset temperature of the charge density wave transition, only a variation in the carrier densities before and after the transition. Given the sensitivity of the charge density wave transitions of transition metal dichalcogenides to variations in composition, it is very surprising that the charge density wave transition observed at 102 K for ([SnSe]1.15)1(VSe2)1 is barely influenced by the nonstoichiometry and structural defects. As a result, this might be a consequence of the two-dimensional nature of the structurally independent VSe2 layers.« less

  17. Influence of Defects on the Charge Density Wave of ([SnSe](1+δ))1(VSe2)1 Ferecrystals.

    PubMed

    Falmbigl, Matthias; Putzky, Daniel; Ditto, Jeffrey; Esters, Marco; Bauers, Sage R; Ronning, Filip; Johnson, David C

    2015-08-25

    A series of ferecrystalline compounds ([SnSe]1+δ)1(VSe2)1 with varying Sn/V ratios were synthesized using the modulated elemental reactant technique. Temperature-dependent specific heat data reveal a phase transition at 102 K, where the heat capacity changes abruptly. An abrupt increase in electrical resistivity occurs at the same temperature, correlated with an abrupt increase in the Hall coefficient. Combined with the magnitude and nature of the specific heat discontinuity, this suggests that the transition is similar to the charge density wave transitions in transition metal dichalcogenides. An ordered intergrowth was formed over a surprisingly wide compositional range of Sn/V ratios of 0.89 ≤ 1 + δ ≤ 1.37. X-ray diffraction and transmission electron microscopy reveal the formation of various volume defects in the compounds in response to the nonstoichiometry. The electrical resistivity and Hall coefficient data of samples with different Sn/V ratios show systematic variation in the carrier concentration with the Sn/V ratio. There is no significant change in the onset temperature of the charge density wave transition, only a variation in the carrier densities before and after the transition. Given the sensitivity of the charge density wave transitions of transition metal dichalcogenides to variations in composition, it is very surprising that the charge density wave transition observed at 102 K for ([SnSe]1.15)1(VSe2)1 is barely influenced by the nonstoichiometry and structural defects. This might be a consequence of the two-dimensional nature of the structurally independent VSe2 layers.

  18. Charge-density analysis of an iron-sulfur protein at an ultra-high resolution of 0.48 Å.

    PubMed

    Hirano, Yu; Takeda, Kazuki; Miki, Kunio

    2016-06-01

    The fine structures of proteins, such as the positions of hydrogen atoms, distributions of valence electrons and orientations of bound waters, are critical factors for determining the dynamic and chemical properties of proteins. Such information cannot be obtained by conventional protein X-ray analyses at 3.0-1.5 Å resolution, in which amino acids are fitted into atomically unresolved electron-density maps and refinement calculations are performed under strong restraints. Therefore, we usually supplement the information on hydrogen atoms and valence electrons in proteins with pre-existing common knowledge obtained by chemistry in small molecules. However, even now, computational calculation of such information with quantum chemistry also tends to be difficult, especially for polynuclear metalloproteins. Here we report a charge-density analysis of the high-potential iron-sulfur protein from the thermophilic purple bacterium Thermochromatium tepidum using X-ray data at an ultra-high resolution of 0.48 Å. Residual electron densities in the conventional refinement are assigned as valence electrons in the multipolar refinement. Iron 3d and sulfur 3p electron densities of the Fe4S4 cluster are visualized around the atoms. Such information provides the most detailed view of the valence electrons of the metal complex in the protein. The asymmetry of the iron-sulfur cluster and the protein environment suggests the structural basis of charge storing on electron transfer. Our charge-density analysis reveals many fine features around the metal complex for the first time, and will enable further theoretical and experimental studies of metalloproteins. PMID:27279229

  19. Charge-density analysis of an iron-sulfur protein at an ultra-high resolution of 0.48 Å.

    PubMed

    Hirano, Yu; Takeda, Kazuki; Miki, Kunio

    2016-05-18

    The fine structures of proteins, such as the positions of hydrogen atoms, distributions of valence electrons and orientations of bound waters, are critical factors for determining the dynamic and chemical properties of proteins. Such information cannot be obtained by conventional protein X-ray analyses at 3.0-1.5 Å resolution, in which amino acids are fitted into atomically unresolved electron-density maps and refinement calculations are performed under strong restraints. Therefore, we usually supplement the information on hydrogen atoms and valence electrons in proteins with pre-existing common knowledge obtained by chemistry in small molecules. However, even now, computational calculation of such information with quantum chemistry also tends to be difficult, especially for polynuclear metalloproteins. Here we report a charge-density analysis of the high-potential iron-sulfur protein from the thermophilic purple bacterium Thermochromatium tepidum using X-ray data at an ultra-high resolution of 0.48 Å. Residual electron densities in the conventional refinement are assigned as valence electrons in the multipolar refinement. Iron 3d and sulfur 3p electron densities of the Fe4S4 cluster are visualized around the atoms. Such information provides the most detailed view of the valence electrons of the metal complex in the protein. The asymmetry of the iron-sulfur cluster and the protein environment suggests the structural basis of charge storing on electron transfer. Our charge-density analysis reveals many fine features around the metal complex for the first time, and will enable further theoretical and experimental studies of metalloproteins.

  20. Theory of space-charge polarization for determining ionic constants of electrolytic solutions.

    PubMed

    Sawada, Atsushi

    2007-06-14

    A theoretical expression of the complex dielectric constant attributed to space-charge polarization has been derived under an electric field calculated using Poisson's equation considering the effects of bound charges on ions. The frequency dependence of the complex dielectric constant of chlorobenzene solutions doped with tetrabutylammonium tetraphenylborate (TBATPB) has been analyzed using the theoretical expression, and the impact of the bound charges on the complex dielectric constant has been clarified quantitatively in comparison with a theory that does not consider the effect of the bound charges. The Stokes radius of TBA+(=TPB-) determined by the present theory shows a good agreement with that determined by conductometry in the past; hence, the present theory should be applicable to the direct determination of the mobility of ion species in an electrolytic solution without the need to measure ionic limiting equivalent conductance and transport number.

  1. Density-Gradient Determination of Osmotic Potential in Plant Cells

    ERIC Educational Resources Information Center

    Nabors, Murray W.

    1973-01-01

    Describes a method for measuring osmotic potential which is suitable for high school and college biology classes. This method introduces students to the hard-to-visualize technique of using density gradients to separate cells or cell constituents of differing densities. (JR)

  2. Limitations of the potentiometric titration technique in determining the proton active site density of goethite surfaces

    NASA Astrophysics Data System (ADS)

    Lützenkirchen, Johannes; Boily, Jean-François; Lövgren, Lars; Sjöberg, Staffan

    2002-10-01

    Density of proton active surface sites at mineral surfaces is a property of fundamental importance in equilibrium modeling of surface complexation reactions. In this article, methods for an experimental determination of these sites at the surface of α-FeOOH (goethite) are explored. It is shown that previously obtained saturation data of goethite with respect to protons do not yield a site density that can be considered as an intrinsic sorbent property: the results are below crystallographically expected values and values for different ionic media in terms of composition and concentration yield different numbers - for example, chloride would yield higher values than nitrate at the same concentration, and higher electrolyte concentration would favor higher apparent maxima. Although site saturation might be explained by electrostatic repulsion, which is more efficient at high electrolyte concentration or for certain ions, further independent experimental results show that no saturation occurs on goethite down to ph ≡ -log[H +] = 2.2 and possibly to ph = 1.0 in 0.6 M NaCl. For those very low pH values, the experimental charging curve was obtained by coulometric back titration (using the Gran plot) or titrations with tris (hydroxymethyl)-aminomethane of the supernatant of acidified goethite suspension. These experimental data are to our knowledge the first high quality data at such low pHs. However, small errors in the determination of proton concentrations (1%) are shown to strongly affect the shape of the charging curve for ph < 2. Furthermore, goethite dissolution (proton consumption and iron reduction in coulometric titrations) and liquid junction effects interfere at low ph, hampering the straightforward application of coulometric Gran titrations over the whole pH range. From these experiments, it can nonetheless be ascertained that a minimum of 2.5 protons/nm 2 can be adsorbed at the goethite surface from the point of zero charge (ph 9.4) to pH 0.9. Although

  3. ACTIVE CATHODES FOR SUPER-HIGH POWER DENSITY SOLID OXIDE FUEL CELLS THROUGH SPACE CHARGE EFFECTS

    SciTech Connect

    Anil V. Virkar

    2004-05-17

    This report summarizes the work done during the sixth quarter of the project. Effort was directed in three areas: (1) Further development of the model on the role of connectivity on ionic conductivity of porous bodies, including the role of grain boundaries and space charge region. (2) Calculation of the effect of space charge and morphology of porous bodies on the effective charge transfer resistance of porous composite cathodes. (3) The investigation of the three electrode system for the measurement of cathodic polarization using amperometric sensors.

  4. Modeling and simulation of centroid and inversion charge density in cylindrical surrounding gate MOSFETs including quantum effects

    NASA Astrophysics Data System (ADS)

    Vimala, P.; Balamurugan, N. B.

    2013-11-01

    An analytical model for surrounding gate metal—oxide—semiconductor field effect transistors (MOSFETs) considering quantum effects is presented. To achieve this goal, we have used a variational approach for solving the Poissonand Schrodinger equations. This model is developed to provide an analytical expression for the inversion charge distribution function for all regions of the device operation. This expression is used to calculate the other important parameters like the inversion charge centroid, threshold voltage and inversion charge density. The calculated expressions for the above parameters are simple and accurate. The validity of this model was checked for the devices with different device dimensions and bias voltages. The calculated results are compared with the simulation results and they show good agreement.

  5. Polarization curve measurements combined with potential probe sensing for determining current density distribution in vanadium redox-flow batteries

    NASA Astrophysics Data System (ADS)

    Becker, Maik; Bredemeyer, Niels; Tenhumberg, Nils; Turek, Thomas

    2016-03-01

    Potential probes are applied to vanadium redox-flow batteries for determination of effective felt resistance and current density distribution. During the measurement of polarization curves in 100 cm2 cells with different carbon felt compression rates, alternating potential steps at cell voltages between 0.6 V and 2.0 V are applied. Polarization curves are recorded at different flow rates and states of charge of the battery. Increasing compression rates lead to lower effective felt resistances and a more uniform resistance distribution. Low flow rates at high or low state of charge result in non-linear current density distribution with high gradients, while high flow rates give rise to a nearly linear behavior.

  6. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe2.

    PubMed

    Arguello, C J; Rosenthal, E P; Andrade, E F; Jin, W; Yeh, P C; Zaki, N; Jia, S; Cava, R J; Fernandes, R M; Millis, A J; Valla, T; Osgood, R M; Pasupathy, A N

    2015-01-23

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe2 that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe2. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe2, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.

  7. Charge density dependent two-channel conduction in organic electric double layer transistors (EDLTs).

    PubMed

    Xie, Wei; Liu, Feilong; Shi, Sha; Ruden, P Paul; Frisbie, C Daniel

    2014-04-23

    A transport model based on hole-density-dependent trapping is proposed to explain the two unusual conductivity peaks at surface hole densities above 10(13) cm(-2) in rubrene electric double layer transistors (EDLTs). Hole transport in rubrene is described to occur via multiple percolation pathways, where conduction is dominated by transport in the free-site channel at low hole density, and in the trap-site channel at larger hole density. PMID:24496822

  8. An effective longitudinal space-charge impedance model for beamswith non-uniform and non-axissymmetric transverse density

    SciTech Connect

    Venturini, Marco

    2007-06-29

    Use of a one-dimensional model of longitudinal space-charge(SC) impedance has been proposed for studying the microbunchinginstability in single-pass delivery systems relevant for the nextgeneration of FELs. For beams with uniform transverse density andcircular cross-section of radius r_b the SC impedance can be expressed ina handy analytical form, making this model particularly convenient. Inthis report we show how with an appropriate choice of r_b one can usethis as an effective-beam model to approximate beams with non-axissymmetric and non-uniform transverse densities.

  9. Temperature Dependence of the Magnetic Penetration Depth in the Case of the Coexistence of Charge Density Waves and Superconductivity

    NASA Astrophysics Data System (ADS)

    Eremin, M. V.; Sunyaev, D. A.

    2015-12-01

    An analytical expression for the temperature dependence of the superfluid density in the regime of the coexistence of charge density waves (CDW) and superconductivity has been derived beyond the effective mass approximation. In contrast to the previous research on this subject, possible dispersions of both order parameters have been taken into account. In particular, it was found that when the CDW gap parameter depends on the wave vector, London's type current is nonzero even above T_c , i.e., in the interval T_c

  10. Conducting polymer/graphite fiber composites for high charge density battery electrodes

    SciTech Connect

    Coffey, B.; Madsen, P.V.; Poehler, T.O.; Searson, P.C.

    1994-12-31

    A porous graphite fiber matrix (Toray Graphite Paper) provides a practical substrate into which electropolymerization of conducting Polymers, such as Polypyrrole, may be carried out to form composite, porous electrode structures. The graphite matrix provides a lightweight, intrinsically conducting structure with high surface area. The resultant porous electrode structures offer possibilities for enhanced charge capacity and current availability characteristics over dense films produced on planar substrates. Polypyrrole/graphite composites prepared by anodic electropolymerization are characterized for their charge capacity and overall morphology as a function of polymerization time. Reversible charge capacities in excess of 4.0 C/cm{sup 2} or 70 mAh/g have been obtained for these polypyrrole/graphite composite electrodes. Charge release for thick films is slow due to mass transport limitations.

  11. Stretching the limits of membrane charge density using Dendrimer Lipids - New Highly Transfecting Hexagonal Phases for Gene Delivery

    NASA Astrophysics Data System (ADS)

    Ewert, Kai; Zidovska, Alexandra; Evans, Heather M.; Safinya, Cyrus R.

    2006-03-01

    Newly designed multivalent lipids ranging in head group charge from 4+ to 16+ have been synthesized and investigated as DNA delivery vectors. These dendritic lipids (DLs) allow a controlled study of the relationship between membrane charge density (σ) and transfection efficiency (TE). An earlier report from our group described that TE of different cationic lipids of charge 1+ to 5+ follows a common, bell shaped curve as a function of membrane charge density [1]. To further probe this universal behavior, the dendritic lipids with higher valence were designed in order to reach higher values of σ. Structural studies using x-ray diffraction reveal new phases, where cylindrical micelles of DLs form a hexagonal lattice which holds together a continuous DNA network, described as HI^C [2]. The new hexagonal phase is highly transfecting in the regime where the TE of lamellar complexes follows a decrease in the bell curve. Small angle x-ray scattering studies have revealed a rich phase diagram of micelles made from DL/DOPC mixtures. Funding provided by NIH GM-59288 and NSF DMR-0503347. [1] A. Ahmad et al., J. Gene Med., 2005, V7:739-748. [2] K. Ewert et al., J. Am. Chem. Soc., (submitted).

  12. De Haas-van Alphen oscillations in the charge-density wave compound lanthanum tritelluride (LaTe3)

    SciTech Connect

    Ru, N.; Borzi, R.A.; Rost, A.; Mackenzie, A.P.; Laverock, J.; Dugdale, S.B.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2009-12-14

    De Haas-van Alphen oscillations were measured in lanthanum tritelluride (LaTe{sub 3}) to probe the partially gapped Fermi surface resulting from charge density wave (CDW) formation. Three distinct frequencies were observed, one of which can be correlated with a FS sheet that is unaltered by CDW formation. The other two frequencies arise from FS sheets that have been reconstructed in the CDW state.

  13. Nonequilibrium Dynamical Mean-Field Theory for the Charge-Density-Wave Phase of the Falicov-Kimball Model

    SciTech Connect

    Matveev, O. P.; Shvaika, A. M.; Devereaux, T. P.; Freericks, J. K.

    2015-12-08

    Nonequilibrium dynamical mean-field theory (DMFT) is developed for the case of the charge-density-wave ordered phase. We consider the spinless Falicov-Kimball model which can be solved exactly. This strongly correlated system is then placed in an uniform external dc electric field. We present a complete derivation for nonequilibrium dynamical mean-field theory Green’s functions defined on the Keldysh-Schwinger time contour. We also discuss numerical issues involved in solving the coupled equations.

  14. ACTIVE CATHODES FOR SUPER-HIGH POWER DENSITY SOLID OXIDE FUEL CELLS THROUGH SPACE CHARGE EFFECTS

    SciTech Connect

    Anil V. Virkar

    2003-12-12

    This report summarizes the work done during the fourth quarter of the project. Effort was directed in two areas, namely, continued further development of the model on the role of connectivity on ionic conductivity of porous bodies, including the role of grain boundaries and space charge, and its relationship to cathode polarization; and fabrication of samaria-doped ceria porous (SDC). The work on the model development involves calculation of the effect of space charge on transport through porous bodies. Three specific cases have been examined: (1) Space charge resistivity greater than the grain resistivity, (2) Space charge resistivity equal to the grain resistivity, and (3) Space charge resistivity lower than the grain resistivity. The model accounts for transport through three regions: the bulk of the grain, the space charge region, and the structural part of the grain boundary. The effect of neck size has been explicitly incorporated. In future work, the effective resistivity will be incorporated into the effective cathode polarization resistance. The results will then be compared with experiments.

  15. Determination of concentration of charged particles in various regions of thunderstorms

    NASA Astrophysics Data System (ADS)

    Detwiler, A. G.; Mo, Q.

    2015-12-01

    During the Severe Thunderstorm Precipitation and Electrification Study in 2000, data on hydrometeor sizes and charges were obtained in thunderstorms using an optical array probe modified by the New Mexico Institute of Mining and Technology and mounted on the South Dakota School of Mines and Technology armored T-28 research aircraft. Analysis yielded quantitative observations of hydrometeor size and charge data in selected regions of storms with relatively low concentrations of charged particles. In most regions hydrometeor concentrations were so high that there were multiple charged particles in the probe sample volume at the same time and quantitative charge analysis was not possible. While it is impossible to reliably determine individual particle charges in these high concentration regions, we can use Poisson statistics to estimate the total number concentration of charged particles based on the fraction of records with just one particle in them. We compare these number concentrations for different thunderstorm regions, including updrafts, flanking cells, core precipitation regions, and trailing stratiform regions, at approximately the -10 C level, in several thunderstorms. We will discuss the implications of these results for understanding charge-separation processes in thunderstorms.

  16. Preliminary results of experimental measurements to determine microparticle charge in a complex plasma

    NASA Astrophysics Data System (ADS)

    Gillman, Eric; Amatucci, Bill

    2015-09-01

    Microparticles in a dusty plasma typically collect many of the more mobile electrons as they charge up and therefore typically attain a net negative potential. The charge on these microparticles is typically estimated by calculating the charge on a spherical capacitor at the floating potential or by making measurements of particles levitating in the plasma sheath. However, secondary processes can alter the charging process and are significantly altered in the plasma sheath. Currently there is no reliable method to measure microparticle surface charge in the bulk region of complex or dusty plasmas. A novel, non-invasive, experimental method of measuring the charging of microparticles in the bulk region of a plasma will be presented. Ions impinging directly upon the microparticle surface and interacting electrostatically with the charged microparticle, known as collisional and electrostatic Coulomb ion drag, respectively, slows particle acceleration due to gravity as the particle falls through a plasma discharge. Since ion and neutral drag are commonly the dominant forces on microparticles in complex plasmas, the reduced acceleration is measured without a plasma to determine the neutral drag. By repeating the measurement with a plasma and subtracting the neutral drag, the ion drag is obtained. The microparticle net charge is then ascertained from the ion drag on isolated grains falling through a plasma discharge. This work was supported by the Naval Research Laboratory Base Program.

  17. Complex coacervation of hyaluronic acid and chitosan: effects of pH, ionic strength, charge density, chain length and the charge ratio.

    PubMed

    Kayitmazer, A B; Koksal, A F; Kilic Iyilik, E

    2015-11-28

    Hyaluronic acid (HA) and chitosan (CH) can form nanoparticles, hydrogels, microspheres, sponges, and films, all with a wide range of biomedical applications. This variety of phases reflects the multiple pathways available to HA/CH complexes. Here, we use turbidimetry, dynamic light scattering, light microscopy and zeta potential measurements to show that the state of the dense phase depends on the molar ratio of HA carboxyl to CH amines, and is strongly dependent on their respective degrees of ionization, α and β. Due to the strong charge complementarity between HA and CH, electrostatic self-assembly takes place at very acidic pH, but is almost unobservable at ionic strength (I) ≥ 1.5 M NaCl. All systems display discontinuity in the I-dependence of the turbidity, corresponding to a transition from coacervates to flocculates. An increase in either polymer chain length or charge density enhances phase separation. Remarkably, non-stoichiometric coacervate suspensions form at zeta potentials far away from zero. This result is attributed to the entropic effects of chain semi-flexibility as well as to the charge mismatch between the two biopolymers. PMID:26406548

  18. Percolation threshold determines the optimal population density for public cooperation

    NASA Astrophysics Data System (ADS)

    Wang, Zhen; Szolnoki, Attila; Perc, Matjaž

    2012-03-01

    While worldwide census data provide statistical evidence that firmly link the population density with several indicators of social welfare, the precise mechanisms underlying these observations are largely unknown. Here we study the impact of population density on the evolution of public cooperation in structured populations and find that the optimal density is uniquely related to the percolation threshold of the host graph irrespective of its topological details. We explain our observations by showing that spatial reciprocity peaks in the vicinity of the percolation threshold, when the emergence of a giant cooperative cluster is hindered neither by vacancy nor by invading defectors, thus discovering an intuitive yet universal law that links the population density with social prosperity.

  19. ISS FPP Ionospheric Electron Density and Temperature Measurements: Results, Comparison with the IRI-90 Model, and Implications for ISS Charging

    NASA Technical Reports Server (NTRS)

    Ferguson, D. C.; Hillard, G. B.; Morton, T. L.; Personen, R.

    2003-01-01

    We give measurement results of electron temperature and electron density from the Floating Potential Probe (FPP) on the International Space Station (ISS), and relate them to the electron current collection of the ISS solar arrays and the degree of charging of ISS when its Plasma Contacting Units (PCUs) are not operating. We show that on days of high solar activity index Kp, high levels of ISS charging are significantly more probable than on days of low solar activity, due to some abnormally low morning electron temperatures. Although the FPP electron temperatures measured are almost always higher than predicted by the International Reference Ionosphere 90 model (IRI-90), it is shown that the CHAMP satellite Langmuir Probe (PLP) also shows low dawn electron temperatures on the same day as those found by FPP. It is further shown that similar high levels of predicted charging, accompanied by vxB charging on the ISS structure, could exceed the -40 V specification on ISS charging, and could be dangerous to ISS astronauts if the PCUs fail to operate.

  20. A geometric method to determine the electric field due to a uniformly charged line segment

    NASA Astrophysics Data System (ADS)

    Zuo, Fulin

    2015-06-01

    A geometrical method to calculate the electric field due to a uniformly charged rod is presented. The result is surprisingly simple and elegant. Using only lengths and angles, the direction of the electric field at any point due to this charge configuration can be graphically determined. The method is not new but seems to have been all but forgotten. A full understanding of this result can lead to a deeper appreciation of symmetry in a seemingly un-symmetric system.

  1. Effect of Siloxane Ring Strain and Cation Charge Density on the Formation of Coordinately Unsaturated Metal Sites on Silica: Insights from DFT Studies

    SciTech Connect

    Das, Ujjal; Zhang, Guanghui; Hu, Bo; Hock, Adam S.; Redfern, Paul C.; Miller, Jeffrey T.; Curtiss, Larry A.

    2015-12-01

    Amorphous silica (SiO2) is commonly used as a support in heterogeneous catalysis. However, due to the structural disorder and temperature induced change of surface morphology, the structures of silica supported metal catalysts are difficult to determine. Most studies are primarily focused on understanding the interactions of different types of surface hydroxyl groups with metal ions. In comparison, the effect of siloxane ring size on the structure of silica supported metal catalysts and how it affects catalytic activity is poorly understood. Here, we have used density functional theory calculations to understand the effect of siloxane ring strain on structure and activity of different monomeric Lewis acid metal sites on silica. In particular, we have found that large siloxane rings favor strong dative bonding interaction between metal ion and surface hydroxyls, leading to the formation of high-coordinate metal sites. In comparison, metal-silanol interaction is weak in small siloxane rings, resulting in low-coordinate metal sites. The physical origin of this size dependence is associated with siloxane ring strain, and, a correlation between metal-silanol interaction energy and ring strain energy has been observed. In addition to ring strain, the strength of the metal-silanol interaction also depends on the positive charge density of the cations. In fact, a correlation also exists between metal-silanol interaction energy and charge density of several first-row transition and post-transition metals. The theoretical results are compared with the EXAFS data of monomeric Zn(II) and Ga(III) ions grafted on silica. The molecular level insights of how metal ion coordination on silica depends on siloxane ring strain and cation charge density will be useful in the synthesis of new catalysts.

  2. Electric response of a magnetic colloid to periodic external excitation for different nanoparticles concentrations: Determination of the particles' effective charge

    NASA Astrophysics Data System (ADS)

    Batalioto, F.; Barbero, G.; Sehnem, A. L.; Figueiredo Neto, A. M.

    2016-08-01

    The effective electric charge of a nanoparticle in an ionic magnetic colloidal system (an ionic ferrofluid) is determined by using the impedance spectroscopy technique. The electric response of the samples to a harmonic external electric field excitation is described by means of the Poisson-Nernst-Planck model. The model proposed for the theoretical interpretation of the impedance spectroscopy data considers that the magnetic particles are electrically charged with H+ and have in their vicinity Cl- counterions, resulting in an effective charge Qeff. In the presence of an harmonic, in time, external field (frequency bigger than 10 4 Hz ) particles are assumed to be at rest, due to inertial reason. In this framework, the response of the cell is due to the H+ and Cl- present in the solution. From the spectra of the real and imaginary components of the electric impedance of the cell, by means of a best fit procedure to our model, we derive the effective electric charge of the magnetic particles and the bulk density of ions. From an independent measurement of the ζ-potential of the suspension, it is possible to calculate the hydrodynamic radius of the particle, in good agreement with that independently measured.

  3. Coarse-grained density functional theories for metallic alloys: Generalized coherent-potential approximations and charge-excess functional theory

    NASA Astrophysics Data System (ADS)

    Bruno, Ezio; Mammano, Francesco; Fiorino, Antonino; Morabito, Emanuela V.

    2008-04-01

    The class of the generalized coherent-potential approximations (GCPAs) to the density functional theory (DFT) is introduced within the multiple scattering theory formalism with the aim of dealing with ordered or disordered metallic alloys. All GCPA theories are based on a common ansatz for the kinetic part of the Hohenberg-Kohn functional and each theory of the class is specified by an external model concerning the potential reconstruction. Most existing DFT implementations of CPA-based theories belong to the GCPA class. The analysis of the formal properties of the density functional defined by GCPA theories shows that it consists of marginally coupled local contributions. Furthermore, it is shown that the GCPA functional does not depend on the details of the charge density and that it can be exactly rewritten as a function of the appropriate charge multipole moments to be associated with each lattice site. A general procedure based on the integration of the qV laws is described that allows for the explicit construction of the same function. The coarse-grained nature of the GCPA density functional implies a great deal of computational advantages and is connected with the O(N) scalability of GCPA algorithms. Moreover, it is shown that a convenient truncated series expansion of the GCPA functional leads to the charge-excess functional (CEF) theory [E. Bruno , Phys. Rev. Lett. 91, 166401 (2003)], which here is offered in a generalized version that includes multipolar interactions. CEF and the GCPA numerical results are compared with status of art linearized augmented plane wave (LAPW) full-potential density functional calculations for 62 bcc- and fcc-based ordered CuZn alloys, in all the range of concentrations. Two facts clearly emerge from these extensive tests. In the first place, the discrepancies between GCPA and CEF results are always within the numerical accuracy of the calculations, both for the site charges and the total energies. In the second place, the

  4. Comparison of Classical and Charge Storage Methods for Determining Conductivity of Thin Film Insulators

    NASA Technical Reports Server (NTRS)

    Swaminathan, Prasanna; Dennison, J. R.; Sim, Alec; Brunson, Jerilyn; Crapo, Eric; Frederickson, A. R.

    2004-01-01

    Conductivity of insulating materials is a key parameter to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. Classical ASTM and IEC methods to measure thin film insulator conductivity apply a constant voltage to two electrodes around the sample and measure the resulting current for tens of minutes. However, conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator. Charge decay methods expose one side of the insulator in vacuum to sequences of charged particles, light, and plasma, with a metal electrode attached to the other side of the insulator. Data are obtained by capacitive coupling to measure both the resulting voltage on the open surface and emission of electrons from the exposed surface, as well monitoring currents to the electrode. Instrumentation for both classical and charge storage decay methods has been developed and tested at Jet Propulsion Laboratory (JPL) and at Utah State University (USU). Details of the apparatus, test methods and data analysis are given here. The JPL charge storage decay chamber is a first-generation instrument, designed to make detailed measurements on only three to five samples at a time. Because samples must typically be tested for over a month, a second-generation high sample throughput charge storage decay chamber was developed at USU with the capability of testing up to 32 samples simultaneously. Details are provided about the instrumentation to measure surface charge and current; for charge deposition apparatus and control; the sample holders to properly isolate the mounted samples; the sample carousel to rotate samples into place; the control of the sample environment including sample vacuum, ambient gas, and sample temperature; and the computer control and data acquisition systems. Measurements are compared here for a number of thin film insulators using both

  5. Determining the local dark matter density with LAMOST data

    NASA Astrophysics Data System (ADS)

    Xia, Qiran; Liu, Chao; Mao, Shude; Song, Yingyi; Zhang, Lan; Long, R. J.; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Wu, Yue

    2016-06-01

    Measurement of the local dark matter density plays an important role in both Galactic dynamics and dark matter direct detection experiments. However, the estimated values from previous works are far from agreeing with each other. In this work, we provide a well-defined observed sample with 1427 G- and K-type main-sequence stars from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope spectroscopic survey, taking into account selection effects, volume completeness, and the stellar populations. We apply a vertical Jeans equation method containing a single exponential stellar disc, a razor thin gas disc, and a constant dark matter density distribution to the sample, and obtain a total surface mass density of 78.7 ^{+3.9}_{-4.7} M_{{⊙}} pc^{-2} up to 1 kpc and a local dark matter density of 0.018± 0.0054 M_{{⊙}} pc^{-3}. We find that the sampling density (i.e. number of stars per unit volume) of the spectroscopic data contributes to about two-third of the uncertainty in the estimated values. We discuss the effect of the tilt term in the Jeans equation and find it has little impact on our measurement. Other issues, such as a non-equilibrium component due to perturbations and contamination by the thick-disc population, are also discussed.

  6. Ionic liquid based lithium battery electrolytes: charge carriers and interactions derived by density functional theory calculations.

    PubMed

    Angenendt, Knut; Johansson, Patrik

    2011-06-23

    The solvation of lithium salts in ionic liquids (ILs) leads to the creation of a lithium ion carrying species quite different from those found in traditional nonaqueous lithium battery electrolytes. The most striking differences are that these species are composed only of ions and in general negatively charged. In many IL-based electrolytes, the dominant species are triplets, and the charge, stability, and size of the triplets have a large impact on the total ion conductivity, the lithium ion mobility, and also the lithium ion delivery at the electrode. As an inherent advantage, the triplets can be altered by selecting lithium salts and ionic liquids with different anions. Thus, within certain limits, the lithium ion carrying species can even be tailored toward distinct important properties for battery application. Here, we show by DFT calculations that the resulting charge carrying species from combinations of ionic liquids and lithium salts and also some resulting electrolyte properties can be predicted. PMID:21591707

  7. Absolute measurement of electron-cloud density in a positively charged particle beam.

    PubMed

    Kireeff Covo, Michel; Molvik, Arthur W; Friedman, Alex; Vay, Jean-Luc; Seidl, Peter A; Logan, Grant; Baca, David; Vujic, Jasmina L

    2006-08-01

    Clouds of stray electrons are ubiquitous in particle accelerators and frequently limit the performance of storage rings. Earlier measurements of electron energy distribution and flux to the walls provided only a relative electron-cloud density. We have measured electron accumulation using ions expelled by the beam. The ion energy distribution maps the depressed beam potential and gives the dynamic cloud density. Clearing electrode current reveals the static background cloud density, allowing the first absolute measurement of the time-dependent electron-cloud density during the beam pulse.

  8. Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Rak, Zs.; Rost, C. M.; Lim, M.; Sarker, P.; Toher, C.; Curtarolo, S.; Maria, J.-P.; Brenner, D. W.

    2016-09-01

    Density functional theory calculations were carried out for three entropic rocksalt oxides, (Mg0.1Co0.1Ni0.1Cu0.1Zn0.1)O0.5, termed J14, and J14 + Li and J14 + Sc, to understand the role of charge neutrality and electronic states on their properties, and to probe whether simple expressions may exist that predict stability. The calculations predict that the average lattice constants of the ternary structures provide good approximations to that of the random structures. For J14, Bader charges are transferable between the binary, ternary, and random structures. For J14 + Sc and J14 + Li, average Bader charges in the entropic structures can be estimated from the ternary compositions. Addition of Sc to J14 reduces the majority of Cu, which show large displacements from ideal lattice sites, along with reduction of a few Co and Ni cations. Addition of Li to J14 reduces the lattice constant, consistent with experiment, and oxidizes some of Co as well as some of Ni and Cu. The Bader charges and spin-resolved density of states (DOS) for Co+3 in J14 + Li are very different from Co+2, while for Cu and Ni the Bader charges form continuous distributions and the two DOS are similar for the two oxidation states. Experimental detection of different oxidation states may therefore be challenging for Cu and Ni compared to Co. Based on these results, empirical stability parameters for these entropic oxides may be more complicated than those for non-oxide entropic solids.

  9. ACTIVE CATHODES FOR SUPER-HIGH POWER DENSITY SOLID OXIDE FUEL CELLS THROUGH SPACE CHARGE EFFECTS

    SciTech Connect

    Anil V. Virkar

    2004-03-08

    This report summarizes the work done during the fifth quarter of the project. Effort was directed in two areas: (1) Further development of the model on the role of connectivity on ionic conductivity of porous bodies, including the role of grain boundaries and space charge region. (2) Fabrication of porous samaria-doped ceria (SDC) and investigation of the effect of thermal treatment on its conductivity. The model developed accounts for transport through three regions: (a) Transport through the bulk of the grain, RI, which includes parallel transport through space charge region. (b) Transport through the space charge region adjacent to the neck (grain boundary), RII. (c) Transport through the structural part of the neck (grain boundary), RIII. The work on the model development involves calculation RI, RII, RIII, and the sum of these three terms, which is the total resistance, as a function of the grain radius ranging between 0.5 and 5 microns and as a function of the relative neck size, described in terms of the angle theta, ranging between 5 and 45{sup o}. Three values of resistivity of the space charge region were chosen; space charge resistivity greater than grain resistivity, equal to grain resistivity, and lower than grain resistivity. Experimental work was conducted on samaria (Sm{sub 2}O{sub 3})-doped ceria (SDC) samples of differing porosity levels, before and after thermal treatment at 1200 C. The conductivity in the annealed samples was lower, consistent with enhanced Debye length. This shows the important role of space charge on ionic transport, and its implications concerning cathode polarization.

  10. The use of CCD area detectors in charge-density research. Application to a mineral compound: the alpha-spodumene LiAl(SiO3)2.

    PubMed

    Kuntzinger; Dahaoui; Ghermani; Lecomte; Howard

    1999-12-01

    X-ray diffraction data sets collected on both Nonius and Siemens (Bruker) goniometers equipped with charge-coupled device (CCD) area detectors have been tested for the electron-density determination of the aluminosilicate mineral compound alpha-spodumene LiAl(SiO(3))(2), aluminium lithium silicon oxide. Data collection strategies, reflection intensity peak integration methods and experimental error estimates are different for the two instruments. Therefore, the consistency and quality of the two types of CCD measurements have been carefully compared to each other and to high-resolution data collected on a conventional CAD-4 point-detector diffractometer. Multipole density model refinements were carried out against the CCD data and the statistical factors analysed in terms of experimental weighting schemes based on the standard uncertainties of the diffraction intensities derived by the Nonius and Siemens software programs. Consistent experimental electron-density features in the Si-O-Si and Si-O-Al bridges were found from both CCD data sets. The net atomic charges obtained from the kappa refinements against each CCD data set are also in good agreement and quite comparable with the results of the conventional CAD-4 experiment.

  11. 40 CFR Appendix C to Subpart Nnn... - Method for the Determination of Product Density

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Density C Appendix C to Subpart NNN of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY..., Subpt. NNN, App. C Appendix C to Subpart NNN of Part 63—Method for the Determination of Product Density 1. Purpose The purpose of this test is to determine the product density of cured blanket...

  12. 40 CFR Appendix C to Subpart Nnn... - Method for the Determination of Product Density

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Density C Appendix C to Subpart NNN of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY..., Subpt. NNN, App. C Appendix C to Subpart NNN of Part 63—Method for the Determination of Product Density 1. Purpose The purpose of this test is to determine the product density of cured blanket...

  13. Determination of the atomic density of rubidium-87

    NASA Astrophysics Data System (ADS)

    Zhao, Meng; Zhang, Kai; Chen, Li-Qing

    2015-09-01

    Atomic density is a basic and important parameter in quantum optics, nonlinear optics, and precision measurement. In the past few decades, several methods have been used to measure atomic density, such as thermionic effect, optical absorption, and resonance fluorescence. The main error of these experiments stemmed from depopulation of the energy level, self-absorption, and the broad bandwidth of the laser. Here we demonstrate the atomic density of 87Rb vapor in paraffin coated cell between 297 K and 334 K mainly using fluorescence measurement. Optical pumping, anti-relaxation coating, and absorption compensation approaches are used to decrease measurement error. These measurement methods are suitable for vapor temperature at dozens of degrees. The fitting function for the experimental data of 87Rb atomic density is given. Project supported by the Natural Science Foundation of China (Grant Nos. 11274118 and 11474095), the Innovation Program of Shanghai Municipal Education Commission of China (Grant No. 13ZZ036), and the Fundamental Research Funds for the Central Universities of China.

  14. Ionic Wind Phenomenon and Charge Carrier Mobility in Very High Density Argon Corona Discharge Plasma

    NASA Astrophysics Data System (ADS)

    Nur, M.; Bonifaci, N.; Denat, A.

    2014-04-01

    Wind ions phenomenon has been observed in the high density argon corona discharge plasma. Corona discharge plasma was produced by point to plane electrodes and high voltage DC. Light emission from the recombination process was observed visually. The light emission proper follow the electric field lines that occur between point and plane electrodes. By using saturation current, the mobilities of non-thermal electrons and ions have been obtained in argon gas and liquid with variation of density from 2,5 1021 to 2 1022 cm-3. In the case of ions, we found that the behaviour of the apparent mobility inversely proportional to the density or follow the Langevin variation law. For non-thermal electron, mobility decreases and approximately follows a variation of Langevin type until the density <= 0,25 the critical density of argon.

  15. High-density CAMAC and FASTBUS charge integrating ADC for use at the LEP OPAL detector

    SciTech Connect

    Bourgeois, F.; Corre, A.; Marcelin, J.P.; Meyrier, A.; Schuler, G.

    1987-02-01

    This work shows that conventional techniques can be used for the design and manufacture of high-accuracy, cheap and densely packed charge digitizers. A factor of two more sensitive than other designs, the CIAFB appears to be very reliable and well matched to most HEP detectors.

  16. Femtosecond x rays link melting of charge-density wave correlations and light-enhanced coherent transport in YBa2Cu3O6.6

    DOE PAGES

    Först, M.; Frano, A.; Kaiser, S.; Mankowsky, R.; Hunt, C. R.; Turner, J. J.; Dakovski, G. L.; Minitti, M. P.; Robinson, J.; Loew, T.; et al

    2014-11-17

    In this study, we use femtosecond resonant soft x-ray diffraction to measure the optically stimulated ultrafast changes of charge density wave correlations in underdoped YBa₂Cu₃O₆.₆. We find that when coherent interlayer transport is enhanced by optical excitation of the apical oxygen distortions, at least 50% of the in-plane charge density wave order is melted. These results indicate that charge ordering and superconductivity may be competing up to the charge ordering transition temperature, with the latter becoming a hidden phase that is accessible only by nonlinear phonon excitation.

  17. Microtubule Protofilament Number Is Modulated in a Step-Wise Fashion By the Charge of Density of An Enveloping Layer

    SciTech Connect

    Raviv, U.; Nguyen, T.; Ghafouri, R.; Needleman, D.J.; Li, Y.; Miller, H.P.; Wilson, L.; Bruinsma, R.F.; Safinya, C.R.; /UC, Santa Barbara /UCLA

    2007-07-12

    Microtubules are able to adjust their protofilament (PF) number and, as a consequence, their dynamics and function, to the assembly conditions and presence of cofactors. However, the principle behind such variations is poorly understood. Using synchrotron x-ray scattering and transmission electron microscopy, we studied how charged membranes, which under certain conditions can envelop preassembled MTs, regulate the PF number of those MTs. We show that the mean PF number, , is modulated primarily by the charge density of the membranes. decreases in a stepwise fashion with increasing membrane charge density. does not depend on the membrane-protein stoichiometry or the solution ionic strength. We studied the effect of taxol and found that increases logarithmically with taxol/tubulin stoichiometry. We present a theoretical model, which by balancing the electrostatic and elastic interactions in the system accounts for the trends in our findings and reveals an effective MT bending stiffness of order 10-100 k{sub B}T/nm, associated with the observed changes in PF number.

  18. A Technique to Determine Billet Core Charge Weight for P/M Fuel Tubes

    SciTech Connect

    Peacock, H.B.

    2001-07-02

    The core length in an extruded tube depends on the weight of powder in the billet core. In the past, the amount of aluminum powder needed to give a specified core length was determined empirically. This report gives a technique for calculating the weight of aluminum powder for the P/M core. An equation has been derived which can be used to determine the amount of aluminum needed for P/M billet core charge weights. Good agreement was obtained when compared to Mark 22 tube extrusion data. From the calculated charge weight, the elastomeric bag can be designed and made to compact the U3O8-Al core.

  19. A surface structural model for ferrihydrite I: Sites related to primary charge, molar mass, and mass density

    NASA Astrophysics Data System (ADS)

    Hiemstra, Tjisse; Van Riemsdijk, Willem H.

    2009-08-01

    A multisite surface complexation (MUSIC) model for ferrihydrite (Fh) has been developed. The surface structure and composition of Fh nanoparticles are described in relation to ion binding and surface charge development. The site densities of the various reactive surface groups, the molar mass, the mass density, the specific surface area, and the particle size are quantified. As derived theoretically, molecular mass and mass density of nanoparticles will depend on the types of surface groups and the corresponding site densities and will vary with particle size and surface area because of a relatively large contribution of the surface groups in comparison to the mineral core of nanoparticles. The nano-sized (˜2.6 nm) particles of freshly prepared 2-line Fh as a whole have an increased molar mass of M ˜ 101 ± 2 g/mol Fe, a reduced mass density of ˜3.5 ± 0.1 g/cm 3, both relatively to the mineral core. The specific surface area is ˜650 m 2/g. Six-line Fh (5-6 nm) has a molar mass of M ˜ 94 ± 2 g/mol, a mass density of ˜3.9 ± 0.1 g/cm 3, and a surface area of ˜280 ± 30 m 2/g. Data analysis shows that the mineral core of Fh has an average chemical composition very close to FeOOH with M ˜ 89 g/mol. The mineral core has a mass density around ˜4.15 ± 0.1 g/cm 3, which is between that of feroxyhyte, goethite, and lepidocrocite. These results can be used to constrain structural models for Fh. Singly-coordinated surface groups dominate the surface of ferrihydrite (˜6.0 ± 0.5 nm -2). These groups can be present in two structural configurations. In pairs, the groups either form the edge of a single Fe-octahedron (˜2.5 nm -2) or are present at a single corner (˜3.5 nm -2) of two adjacent Fe octahedra. These configurations can form bidentate surface complexes by edge- and double-corner sharing, respectively, and may therefore respond differently to the binding of ions such as uranyl, carbonate, arsenite, phosphate, and others. The relatively low PZC of

  20. Energy density inhomogeneities in charged radiating stars with generalized CDTT model

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Yousaf, Z.

    2014-12-01

    In this paper, we analyze the role of electromagnetic field and generalized Carrol-Duvvuri-Trodden-Turner (CDTT) model on the existence of homogeneous energy density. For this purpose, we model spherical star with anisotropic matter distribution dissipating in the mode of heat and radiation density. To develop a relationship between the Weyl tensor and matter parameters, we construct two evolution equations. We explore inhomogeneity parameters for particular cases of non-dissipative and dissipative matter distributions. It is concluded that in addition to other fluid variables higher order f( R) corrections, relaxation processes and electromagnetic field affect the energy density inhomogeneity of spherical stars.

  1. Dimensionality effect on the charge density wave and superconductivity of molecular beam epitaxy grown monolayer NbSe2

    NASA Astrophysics Data System (ADS)

    Ryu, Hyejin; Zhang, Yi; Hussain, Zahid; Mo, Sung-Kwan; Shen, Z.-X.; Ugeda, Miguel M.; Bradley, Aaron J.; Onishi, Seita; Chen, Yi; Ruan, Wei; Ojeda-Aristizabal, Claudia; Edmonds, Mark T.; Tsai, Hsin-Zon; Riss, Alexander; Lee, Dunghai; Zettl, Alex; Crommie, Michael F.

    Transition metal dichalcogenides are ideal compounds to investigate dimensionality effect since the weak coupling between layers enables to study single-layer material which removes interlayer interactions and introduces quantum confinement. We investigate dimensionality effect of NbSe2 in which the bulk phase shows charge density wave (CDW) (TCDW = 33 K) and superconductivity (Tc = 7.2 K). We report electronic band structure of MBE grown monolayer NbSe2 measured by Angel-resolved photoemission spectroscopy compared with bulk. We find the number of bands crossing the Fermi energy reduces from three (bulk) to one (monolayer). Based on the significant suppression of superconducting Tc = 0.65 K with robust CDW in monolayer NbSe2, our results imply the band remained at the Fermi level in monolayer NbSe2 may play a crucial role in CDW formation and the disappeared bands are possibly in charge of superconductivity.

  2. Parametric study of a high current-density EBIS Charge Breeder regarding Two Stream plasma Instability (TSI)

    NASA Astrophysics Data System (ADS)

    Shornikov, Andrey; Mertzig, Robert; Breitenfeldt, Martin; Lombardi, Alessandra; Wenander, Fredrik; Pikin, Alexander

    2016-06-01

    In this paper we report on our results from the design study of an advanced Electron Beam Ion Source (EBIS) based Charge Breeder (ECB). The ECB should fulfill the requirements of the HIE-ISOLDE upgrade, and if possible be adapted for ion injection into TSR@ISOLDE, as well as serve as an early prototype of a future EURISOL ECB. Fulfilling the HIE-ISOLDE/TSR@ISOLDE specifications requires simultaneous increase in electron beam energy, current and current density in order to provide the requested beams with proper charge state, high intensity and with a specified pulse repetition rate. We have carried out a study on the technical requirements of the ECB. The obtained parameters were optimized to comply with technical limitations arising from the electron beam technology and plasma physics in an ECB.

  3. Electrostatic correlations in colloidal suspensions: Density profiles and effective charges beyond the Poisson-Boltzmann theory

    NASA Astrophysics Data System (ADS)

    dos Santos, Alexandre P.; Diehl, Alexandre; Levin, Yan

    2009-03-01

    A theory is proposed which allows us to calculate the distribution of the multivalent counterions around a colloidal particle using the cell model. The results are compared with the Monte Carlo simulations and are found to be very accurate in the two asymptotic regimes, close to the colloidal particle and far from it. The theory allows to accurately calculate the osmotic pressure and the effective charge of colloidal particles with multivalent counterions.

  4. Formation and stability of water-soluble, molecular polyelectrolyte complexes: effects of charge density, mixing ratio, and polyelectrolyte concentration.

    PubMed

    Shovsky, Alexander; Varga, Imre; Makuska, Ricardas; Claesson, Per M

    2009-06-01

    The formation of complexes with stoichiometric (1:1) as well as nonstoichiometric (2:1) and (1:2) compositions between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights is reported in this contribution. Poly(sodium styrenesulfonate) (NaPSS) was used as polyanion, and a range of copolymers with various molar ratios of the poly(methacryloxyethyltrimethylammonium) chloride, poly(METAC), and the nonionic poly(ethylene oxide) ether methacrylate, poly(PEO45MEMA), were used as polycations. Formation and stability of PECs have been investigated by dynamic and static light scattering (LS), turbidity, and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration, charge density of the cationic polyelectrolyte, and mixing ratio. The data obtained demonstrate that in the absence of PEO45 side chains the 100% charged polymer (polyMETAC) formed insoluble PECs with PSS that precipitate from solution when exact stoichiometry is achieved. In nonstoichiometric complexes (1:2) and (2:1) large colloidally stable aggregates were formed. The presence of even a relatively small amount of PEO45 side chains (25%) in the cationic copolymer was sufficient for preventing precipitation of the formed stoichiometric and nonstoichiometric complexes. These PEC's are sterically stabilized by the PEO45 chains. By further increasing the PEO45 side-chain content (50 and 75%) of the cationic copolymer, small, water-soluble molecular complexes could be formed. The data suggest that PSS molecules and the charged backbone of the cationic brush form a compact core, and with sufficiently high PEO45 chain density (above 25%) molecular complexes are formed that are stable over prolonged times.

  5. Determination of the muon charge sign with the dipolar spectrometers of the OPERA experiment

    NASA Astrophysics Data System (ADS)

    Agafonova, N.; Aleksandrov, A.; Anokhina, A.; Aoki, S.; Ariga, A.; Ariga, T.; Bender, D.; Bertolin, A.; Bozza, C.; Brugnera, R.; Buonaura, A.; Buontempo, S.; Büttner, B.; Chernyavsky, M.; Chukanov, A.; Consiglio, L.; D'Ambrosio, N.; De Lellis, G.; De Serio, M.; Del Amo Sanchez, P.; Di Crescenzo, A.; Di Ferdinando, D.; Di Marco, N.; Dmitrievski, S.; Dracos, M.; Duchesneau, D.; Dusini, S.; Dzhatdoev, T.; Ebert, J.; Ereditato, A.; Fini, R. A.; Fukuda, T.; Galati, G.; Garfagnini, A.; Giacomelli, G.; Göllnitz, C.; Goldberg, J.; Goloubkov, D.; Gornushkin, Y.; Grella, G.; Guler, M.; Gustavino, C.; Hagner, C.; Hara, T.; Hollnagel, A.; Hosseini, B.; Ishida, H.; Ishiguro, K.; Jakovcic, K.; Jollet, C.; Kamiscioglu, C.; Kamiscioglu, M.; Kawada, J.; Kim, J. H.; Kim, S. H.; Kitagawa, N.; Klicek, B.; Kodama, K.; Komatsu, M.; Kose, U.; Kreslo, I.; Lauria, A.; Lenkeit, J.; Ljubicic, A.; Longhin, A.; Loverre, P.; Malgin, A.; Malenica, M.; Mandrioli, G.; Matsuo, T.; Matveev, V.; Mauri, N.; Medinaceli, E.; Meregaglia, A.; Meyer, M.; Mikado, S.; Monacelli, P.; Montesi, M. C.; Morishima, K.; Muciaccia, M. T.; Naganawa, N.; Naka, T.; Nakamura, M.; Nakano, T.; Nakatsuka, Y.; Niwa, K.; Ogawa, S.; Okateva, N.; Olshevsky, A.; Omura, T.; Ozaki, K.; Paoloni, A.; Park, B. D.; Park, I. G.; Pasqualini, L.; Pastore, A.; Patrizii, L.; Pessard, H.; Pistillo, C.; Podgrudkov, D.; Polukhina, N.; Pozzato, M.; Pupilli, F.; Roda, M.; Rokujo, H.; Roganova, T.; Rosa, G.; Rostovtseva, I.; Ryazhskaya, O.; Sato, O.; Sato, Y.; Schembri, A.; Shakiryanova, I.; Shchedrina, T.; Sheshukov, A.; Shibuya, H.; Shiraishi, T.; Shoziyoev, G.; Simone, S.; Sioli, M.; Sirignano, C.; Sirri, G.; Spinetti, M.; Stanco, L.; Starkov, N.; Stellacci, S. M.; Stipcevic, M.; Strolin, P.; Takahashi, S.; Tenti, M.; Terranova, F.; Tioukov, V.; Tufanli, S.; Vilain, P.; Vladimirov, M.; Votano, L.; Vuilleumier, J. L.; Wilquet, G.; Wonsak, B.; Yoon, C. S.; Zaitsev, Y.; Zemskova, S.; Zghiche, A.

    2016-07-01

    The OPERA long-baseline neutrino-oscillation experiment has observed the direct appearance of ντ in the CNGS νμ beam. Two large muon magnetic spectrometers are used to identify muons produced in the τ leptonic decay and in νμ CC interactions by measuring their charge and momentum. Besides the kinematic analysis of the τ decays, background resulting from the decay of charmed particles produced in νμ CC interactions is reduced by efficiently identifying the muon track. A new method for the charge sign determination has been applied, via a weighted angular matching of the straight track-segments reconstructed in the different parts of the dipole magnets. Results obtained for Monte Carlo and real data are presented. Comparison with a method where no matching is used shows a significant reduction of up to 40% of the fraction of wrongly determined charges.

  6. Determination of the topological charge of a twisted beam with a Fresnel bi-prism

    NASA Astrophysics Data System (ADS)

    Emile, Olivier; Emile, Janine; Brousseau, Christian

    2014-12-01

    The self-interference pattern of a Laguerre Gaussian beam using a Fresnel bi-prism is shown to be very different from what could be expected from a usual laser beam. It resembles the interference pattern that could be obtained using a double slit experiment. The interferences are shifted and the topological charge and its sign can be readily determined considering the shift order of the pattern only. However, since there is no diffraction nor absorption losses unlike in a double slit interference, such a set up could be used even for low power twisted beams or beams with high topological charge. Even fractional topological charges could be determined with an absolute precision of 0.05.

  7. Use of emission-line intensities for a self-consistent determination of the particle densities in a transient plasma.

    PubMed

    Gregorian, L; Bernshtam, V A; Kroupp, E; Davara, G; Maron, Y

    2003-01-01

    A method for a self-consistent determination of the time history of the electron density, electron temperature, and ionic charge-state composition in a multicomponent plasma, using time-dependent measurements and calculations of absolute emission-line intensities, is presented. The method is applied for studying the properties of an imploding gas-puff Z-pinch plasma that contains several oxygen ions up to the fifth ionization stage. Furthermore, by using intensity ratios of lines from different ion species, the electron temperature was determined with a much improved accuracy, in comparison to previous spectroscopic studies of the same plasma. The ion-density history obtained, together with the known time-dependent radial boundaries of the plasma shell, allowed for tracking the rise in time of the mass swept by the magnetic field during the implosion. PMID:12636608

  8. Use of emission-line intensities for a self-consistent determination of the particle densities in a transient plasma.

    PubMed

    Gregorian, L; Bernshtam, V A; Kroupp, E; Davara, G; Maron, Y

    2003-01-01

    A method for a self-consistent determination of the time history of the electron density, electron temperature, and ionic charge-state composition in a multicomponent plasma, using time-dependent measurements and calculations of absolute emission-line intensities, is presented. The method is applied for studying the properties of an imploding gas-puff Z-pinch plasma that contains several oxygen ions up to the fifth ionization stage. Furthermore, by using intensity ratios of lines from different ion species, the electron temperature was determined with a much improved accuracy, in comparison to previous spectroscopic studies of the same plasma. The ion-density history obtained, together with the known time-dependent radial boundaries of the plasma shell, allowed for tracking the rise in time of the mass swept by the magnetic field during the implosion.

  9. Communication: a density functional with accurate fractional-charge and fractional-spin behaviour for s-electrons.

    PubMed

    Johnson, Erin R; Contreras-García, Julia

    2011-08-28

    We develop a new density-functional approach combining physical insight from chemical structure with treatment of multi-reference character by real-space modeling of the exchange-correlation hole. We are able to recover, for the first time, correct fractional-charge and fractional-spin behaviour for atoms of groups 1 and 2. Based on Becke's non-dynamical correlation functional [A. D. Becke, J. Chem. Phys. 119, 2972 (2003)] and explicitly accounting for core-valence separation and pairing effects, this method is able to accurately describe dissociation and strong correlation in s-shell many-electron systems.

  10. Amplitude modulation of charge-density-wave domains in 1T-TaS sub 2 at 300 K

    SciTech Connect

    Coleman, R.V.; McNairy, W.W.; Slough, C.G.

    1991-01-01

    Measurements of the charge-density-wave (CDW) amplitude modulation in 1T-TaS{sub 2} at room temperature have been made using a scanning tunneling microscope (STM) operating in the constant current mode. The amplitude profiles are in good agreement with the profile predicated by the CDW domain model of Nakanishi and Shiba. Interference effects between the atomic and CDW lattices have been analyzed and do not modify these profiles significantly. They represent the true CDW amplitude variation connected with the CDW domain structure.

  11. Amplitude modulation of charge-density-wave domains in 1T-TaS{sub 2} at 300 K

    SciTech Connect

    Coleman, R.V.; McNairy, W.W.; Slough, C.G.

    1991-12-31

    Measurements of the charge-density-wave (CDW) amplitude modulation in 1T-TaS{sub 2} at room temperature have been made using a scanning tunneling microscope (STM) operating in the constant current mode. The amplitude profiles are in good agreement with the profile predicated by the CDW domain model of Nakanishi and Shiba. Interference effects between the atomic and CDW lattices have been analyzed and do not modify these profiles significantly. They represent the true CDW amplitude variation connected with the CDW domain structure.

  12. Optical Properties of the Charge-Density-Wave Polychalcogenide Compounds R2Te5 (R=Nd, Sm and Gd)

    SciTech Connect

    Pfuner, F.; Degiorgi, L.; Shin, K.Y.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2010-02-15

    We investigate the rare-earth polychalcogenide R{sub 2}Te{sub 5} (R = Nd, Sm and Gd) charge-density-wave (CDW) compounds by optical methods. From the absorption spectrum we extract the excitation energy of the CDW gap and estimate the fraction of the Fermi surface which is gapped by the formation of the CDW condensate. In analogy to previous findings on the related RTe{sub n} (n = 2 and 3) families, we establish the progressive closing of the CDW gap and the moderate enhancement of the metallic component upon chemically compressing the lattice.

  13. Pressure-induced quenching of the charge-density-wave state observed by x-ray diffraction

    SciTech Connect

    Sacchetti, A.

    2010-05-03

    We report an x-ray diffraction study on the charge-density-wave (CDW) LaTe{sub 3} and CeTe{sub 3} compounds as a function of pressure. We extract the lattice constants and the CDW modulation wave-vector, and provide direct evidence for a pressure-induced quenching of the CDW phase. We observe subtle differences between the chemical and mechanical compression of the lattice. We account for these with a scenario where the effective dimensionality in these CDW systems is dependent on the type of lattice compression and has a direct impact on the degree of Fermi surface nesting and on the strength of fluctuation effects.

  14. A simple apparatus for determining the density of solids

    NASA Astrophysics Data System (ADS)

    Marinder, Bengt-Olov

    1996-11-01

    A gas volumenometer for solid material is described. Using helium as a pressure medium an accuracy of about 1% or better is achieved for sample volumes of 0957-0233/7/11/004/img1. The relative standard deviations range from 0.2 to 0.3%. A novel feature of the method is that a set of pressure and volume readings are collected and used in Boyle's law in the form 0957-0233/7/11/004/img2. Plotting these data gives a straight line whose slope is used to calculate 0957-0233/7/11/004/img3. A standard volume is used for calibration of the apparatus. Sources of experimental error are discussed, and an error analysis of the obtained sample volume is performed. Air, argon, and helium have been used and are compared as pressure media. Mass and volume measurements have been obtained for six substances, and their observed densities are compared with x-ray densities taken from the literature.

  15. Colloid Titration--A Rapid Method for the Determination of Charged Colloid.

    ERIC Educational Resources Information Center

    Ueno, Keihei; Kina, Ken'yu

    1985-01-01

    "Colloid titration" is a volumetric method for determining charged polyelectrolytes in aqueous solutions. The principle of colloid titration, reagents used in the procedure, methods of endpoint detection, preparation of reagent solutions, general procedure used, results obtained, and pH profile of colloid titration are considered. (JN)

  16. 18 CFR 11.11 - Energy gains method of determining headwater benefits charges.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... power generation is not a function of the headwater project, section 10(f) costs will be apportioned... 18 Conservation of Power and Water Resources 1 2013-04-01 2013-04-01 false Energy gains method of determining headwater benefits charges. 11.11 Section 11.11 Conservation of Power and Water Resources...

  17. 18 CFR 11.11 - Energy gains method of determining headwater benefits charges.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... power generation is not a function of the headwater project, section 10(f) costs will be apportioned... 18 Conservation of Power and Water Resources 1 2012-04-01 2012-04-01 false Energy gains method of determining headwater benefits charges. 11.11 Section 11.11 Conservation of Power and Water Resources...

  18. 18 CFR 11.11 - Energy gains method of determining headwater benefits charges.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... power generation is not a function of the headwater project, section 10(f) costs will be apportioned... 18 Conservation of Power and Water Resources 1 2010-04-01 2010-04-01 false Energy gains method of determining headwater benefits charges. 11.11 Section 11.11 Conservation of Power and Water Resources...

  19. Quantum lattice fluctuations in a 1-dimensional charge-density-wave material: Luminescence and resonance Raman studies of an MX solid

    SciTech Connect

    Long, F.H.; Love, S.P.; Swanson, B.I.

    1993-01-01

    Luminescence spectra, both emission and excitation, and the excitation dependence of the resonance Raman (RR) spectra were measured for a 1-dimensional charge-density-wave solid, [Pt(L)[sub 2]Cl[sub 2

  20. ACTIVE CATHODES FOR SUPER-HIGH POWER DENSITY SOLID OXIDE FUEL CELLS THROUGH SPACE CHARGE EFFECTS

    SciTech Connect

    Anil V. Virkar

    2003-11-03

    This report summarizes the work done during the third quarter of the project. Effort was directed in two areas: (1) Further development of the model on the role of connectivity on ionic conductivity of porous bodies, including the role of grain boundaries, and its relationship to cathode polarization. Included indirectly through the grain boundary effect is the effect of space charge. (2) Synthesis of LSC + SDC composite cathode powders by combustion synthesis. (3) Fabrication and testing of anode-supported single cells made using synthesized LSC + ScDC composite cathodes.

  1. Alternative Method for the Thermospheric Atomic Oxygen Density Determination

    NASA Technical Reports Server (NTRS)

    Bennett, A. C.; Omidvar, K.; Atlas, Robert (Technical Monitor)

    2001-01-01

    Atomic oxygen density in the upper thermosphere (approximately 300 km) can be calculated using ground based incoherent scatter radar and Fabry-Perot interferometer measurements. Burnside et al. was the first to try this method, but Buonsanto et al. provided an extensive treatment of the method in 1997. This paper further examines the method using 46 nights of data collected over six years and the latest information on the oxygen collision frequency. The method is compared with the MSIS (Mass Spectrometer Incoherent Scatter)-86 atomic oxygen prediction values, which are based upon in situ rocket born and satellite measurements from the 70s to the mid-80s. In general, the method supports the MSIS-86 model, but indicates several areas of discrepancy. Furthermore, no direct correlation is found between the geomagnetic conditions and the difference between the method and MSIS-86 predictions.

  2. Alternative Methods of the Thermospheric Atomic Oxygen Density Determination

    NASA Technical Reports Server (NTRS)

    Bennett. Adam C.; Omidvar, Kazem; Einaudi, Franco (Technical Monitor)

    2000-01-01

    Atomic oxygen density in the upper thermosphere (approximately 300 km) can be calculated using ground based incoherent scatter radar and Fabry-Perot interferometer measurements. Burnside et al. [1991] was the first to try this method, but Buonsanto et al. provided an extensive treatment of the method in 1997. This paper further examines the method using 46 nights of data collected over six years and the latest information on the oxygen collision frequency. The method is compared with the MSIS-86 atomic oxygen prediction values, which are based upon in situ rocket born and satellite measurements from the 70's to the mid-80's In general, the method supports the MSIS-86 model, but indicates several areas of discrepancy. Furthermore, no direct correlation is found between the geomagnetic conditions and the difference between the method and MSIS-86 predictions.

  3. Possibility of determination of the asymptotic level-density parameter

    SciTech Connect

    Kudyaev, G.A.; Ostapenko, Y.B.; Svirin, M.I.; Smirenkin, G.N.

    1988-02-01

    We investigate the sensitivity of the fissility of nuclei to the parameters of the density of excited levels and conclude that the nuclei in the region of Pb are most favorable for an experimental estimate of the asymptotic parameter a-italic-tilde = ..cap alpha..A. The mean value ..cap alpha.. = 0.086 +- 0.009 MeV/sup -1/ is found from analysis of the fission of seven nuclei from /sup 201/Tl to /sup 213/At. This value is in agreement with the phenomenological description of the energy dependence a(U) (..cap alpha.. = 0.093 MeV/sup -1/) and with the theoretical prediction ..cap alpha.. = 0.09 MeV/sup -1/ obtained for a Woods-Saxon potential.

  4. Determining electron temperature and density in a hydrogen microwave plasma

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.; Farhat, Samir; Gicquel, Alix; Hassouni, Khaled; Lefebvre, Michel

    1993-01-01

    A three-temperature thermo-chemical model is developed for analyzing the chemical composition and energy states of a hydrogen microwave plasma used for studying diamond deposition. The chemical and energy exchange rate coefficients are determined from cross section data, assuming Maxwellian velocity distributions for electrons. The model is reduced to a zero-dimensional problem to solve for the electron temperature and ion mole fraction, using measured vibrational and rotational temperatures. The calculations indicate that the electron temperature may be determined to within a few percent error even though the uncertainty in dissociation fraction is many times larger.

  5. ‘Living’ PEGylation on gold nanoparticles to optimize cancer cell uptake by controlling targeting ligand and charge densities

    NASA Astrophysics Data System (ADS)

    Chen, Hongwei; Paholak, Hayley; Ito, Masayuki; Sansanaphongpricha, Kanokwan; Qian, Wei; Che, Yong; Sun, Duxin

    2013-09-01

    We report and demonstrate biomedical applications of a new technique—‘living’ PEGylation—that allows control of the density and composition of heterobifunctional PEG (HS-PEG-R; thiol-terminated poly(ethylene glycol)) on gold nanoparticles (AuNPs). We first establish ‘living’ PEGylation by incubating HS-PEG5000-COOH with AuNPs (˜20 nm) at increasing molar ratios from zero to 2000. This causes the hydrodynamic layer thickness to differentially increase up to 26 nm. The controlled, gradual increase in PEG-COOH density is revealed after centrifugation, based on the ability to re-suspend the pellet and increase the AuNP absorption. Using a fluorescamine-based assay we quantify differential HS-PEG5000-NH2 binding to AuNPs, revealing that it is highly efficient until AuNP saturation is reached. Furthermore, the zeta potential incrementally changes from -44.9 to +52.2 mV and becomes constant upon saturation. Using ‘living’ PEGylation we prepare AuNPs with different ratios of HS-PEG-RGD (RGD: Arg-Gly-Asp) and incubate them with U-87 MG (malignant glioblastoma) and non-target cells, demonstrating that targeting ligand density is critical to maximizing the efficiency of targeting of AuNPs to cancer cells. We also sequentially control the HS-PEG-R density to develop multifunctional nanoparticles, conjugating positively charged HS-PEG-NH2 at increasing ratios to AuNPs containing negatively charged HS-PEG-COOH to reduce uptake by macrophage cells. This ability to minimize non-specific binding/uptake by healthy cells could further improve targeted nanoparticle efficacy.

  6. ‘Living’ PEGylation on gold nanoparticles to optimize cancer cell uptake by controlling targeting ligand and charge densities

    PubMed Central

    Chen, Hongwei; Paholak, Hayley; Ito, Masayuki; Sansanaphongpricha, Kanokwan; Qian, Wei; Che, Yong; Sun, Duxin

    2013-01-01

    We report and demonstrate biomedical applications of a new technique – ‘living’ PEGylation – that allows control of the density and composition of heterobifunctional PEG (HS-PEG-R) on gold nanoparticles (AuNPs). We first establish ‘living’ PEGylation by incubating HS-PEG5000-COOH with AuNPs (~20 nm) at increasing molar ratios from zero to 2000. This causes the hydrodynamic layer thickness to differentially increase up to 26 nm. The controlled, gradual increase in PEG-COOH density is revealed after centrifugation, based on the ability to re-suspend the pellet and increase the AuNP absorption. Using a fluorescamine-based assay we quantify differential HS-PEG5000-NH2 binding to AuNPs, revealing it is highly efficient until AuNP saturation. Furthermore, the zeta potential incrementally changes from −44.9 to +52.2 mV and becomes constant upon saturation. Using ‘living’ PEGylation we prepare AuNPs with different ratios of HS-PEG-RGD and incubate them with U-87 MG and non-target cells, demonstrating that targeting ligand density is critical to maximizing the targeting efficiency of AuNPs to cancer cells. We also sequentially control the HS-PEG-R density to develop multifunctional nanoparticles, conjugating positively-charged HS-PEG-NH2 at increasing ratios to AuNPs containing negatively-charged HS-PEG-COOH to reduce uptake by macrophage cells. This ability to minimize non-specific binding/uptake by healthy cells could further improve targeted nanoparticle efficacy. PMID:23940104

  7. Sandwich-structured polymer nanocomposites with high energy density and great charge-discharge efficiency at elevated temperatures.

    PubMed

    Li, Qi; Liu, Feihua; Yang, Tiannan; Gadinski, Matthew R; Zhang, Guangzu; Chen, Long-Qing; Wang, Qing

    2016-09-01

    The demand for a new generation of high-temperature dielectric materials toward capacitive energy storage has been driven by the rise of high-power applications such as electric vehicles, aircraft, and pulsed power systems where the power electronics are exposed to elevated temperatures. Polymer dielectrics are characterized by being lightweight, and their scalability, mechanical flexibility, high dielectric strength, and great reliability, but they are limited to relatively low operating temperatures. The existing polymer nanocomposite-based dielectrics with a limited energy density at high temperatures also present a major barrier to achieving significant reductions in size and weight of energy devices. Here we report the sandwich structures as an efficient route to high-temperature dielectric polymer nanocomposites that simultaneously possess high dielectric constant and low dielectric loss. In contrast to the conventional single-layer configuration, the rationally designed sandwich-structured polymer nanocomposites are capable of integrating the complementary properties of spatially organized multicomponents in a synergistic fashion to raise dielectric constant, and subsequently greatly improve discharged energy densities while retaining low loss and high charge-discharge efficiency at elevated temperatures. At 150 °C and 200 MV m(-1), an operating condition toward electric vehicle applications, the sandwich-structured polymer nanocomposites outperform the state-of-the-art polymer-based dielectrics in terms of energy density, power density, charge-discharge efficiency, and cyclability. The excellent dielectric and capacitive properties of the polymer nanocomposites may pave a way for widespread applications in modern electronics and power modules where harsh operating conditions are present. PMID:27551101

  8. Sandwich-structured polymer nanocomposites with high energy density and great charge-discharge efficiency at elevated temperatures.

    PubMed

    Li, Qi; Liu, Feihua; Yang, Tiannan; Gadinski, Matthew R; Zhang, Guangzu; Chen, Long-Qing; Wang, Qing

    2016-09-01

    The demand for a new generation of high-temperature dielectric materials toward capacitive energy storage has been driven by the rise of high-power applications such as electric vehicles, aircraft, and pulsed power systems where the power electronics are exposed to elevated temperatures. Polymer dielectrics are characterized by being lightweight, and their scalability, mechanical flexibility, high dielectric strength, and great reliability, but they are limited to relatively low operating temperatures. The existing polymer nanocomposite-based dielectrics with a limited energy density at high temperatures also present a major barrier to achieving significant reductions in size and weight of energy devices. Here we report the sandwich structures as an efficient route to high-temperature dielectric polymer nanocomposites that simultaneously possess high dielectric constant and low dielectric loss. In contrast to the conventional single-layer configuration, the rationally designed sandwich-structured polymer nanocomposites are capable of integrating the complementary properties of spatially organized multicomponents in a synergistic fashion to raise dielectric constant, and subsequently greatly improve discharged energy densities while retaining low loss and high charge-discharge efficiency at elevated temperatures. At 150 °C and 200 MV m(-1), an operating condition toward electric vehicle applications, the sandwich-structured polymer nanocomposites outperform the state-of-the-art polymer-based dielectrics in terms of energy density, power density, charge-discharge efficiency, and cyclability. The excellent dielectric and capacitive properties of the polymer nanocomposites may pave a way for widespread applications in modern electronics and power modules where harsh operating conditions are present.

  9. Zone-Folded Phonons and the Commensurate-Incommensurate Charge-Density-Wave Transition in 1T-TaSe2 Thin Films.

    PubMed

    Samnakay, R; Wickramaratne, D; Pope, T R; Lake, R K; Salguero, T T; Balandin, A A

    2015-05-13

    Bulk 1T-TaSe2 exhibits unusually high charge density wave (CDW) transition temperatures of 600 and 473 K below which the material exists in the incommensurate (I-CDW) and the commensurate (C-CDW) charge-density-wave phases, respectively. The (13)(1/2) × (13)(1/2) C-CDW reconstruction of the lattice coincides with new Raman peaks resulting from zone-folding of phonon modes from middle regions of the original Brillouin zone back to Γ. The C-CDW transition temperatures as a function of film thickness are determined from the evolution of these new Raman peaks, and they are found to decrease from 473 to 413 K as the film thicknesses decrease from 150 to 35 nm. A comparison of the Raman data with ab initio calculations of both the normal and C-CDW phases gives a consistent picture of the zone-folding of the phonon modes following lattice reconstruction. The Raman peak at ∼154 cm(-1) originates from the zone-folded phonons in the C-CDW phase. In the I-CDW phase, the loss of translational symmetry coincides with a strong suppression and broadening of the Raman peaks. The observed change in the C-CDW transition temperature is consistent with total energy calculations of bulk and monolayer 1T-TaSe2. PMID:25927475

  10. 5 CFR 2423.12 - Settlement of unfair labor practice charges after a Regional Director determination to issue a...

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... charges after a Regional Director determination to issue a complaint but prior to issuance of a complaint... charges after a Regional Director determination to issue a complaint but prior to issuance of a complaint. (a) Alternative Dispute Resolution (ADR). After a merit determination to issue a complaint,...

  11. Method for determining transport critical current densities and flux penetration depth in bulk superconductors

    NASA Technical Reports Server (NTRS)

    Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)

    1992-01-01

    A contact-less method for determining transport critical current density and flux penetration depth in bulk superconductor material. A compressor having a hollow interior and a plunger for selectively reducing the free space area for distribution of the magnetic flux therein are formed of superconductor material. Analytical relationships, based upon the critical state model, Maxwell's equations and geometrical relationships define transport critical current density and flux penetration depth in terms of the initial trapped magnetic flux density and the ratio between initial and final magnetic flux densities whereby data may be reliably determined by means of the simple test apparatus for evaluating the current density and flux penetration depth.

  12. The multi-configurational adiabatic electron transfer theory and its invariance under transformations of charge density basis functions

    NASA Astrophysics Data System (ADS)

    Basilevsky, M. V.; Chudinov, G. E.; Newton, M. D.

    1994-02-01

    The continuum multi-configurational dynamical theory of electron transfer (ET) reactions in a chemical solute immersed in a polar solvent is developed. The solute wave function is represented as a CI expansion. The corresponding decomposition of the solute charge density generates a set of dynamical variables, the discrete medium coordinates. A new expression for the free energy surface in terms of these coordinates is derived. The stochastic equations of motion derived earlier are shown to be invariant under unitary transformations of orbitals used to build the CI expansion provided the latter is complete over the corresponding orbital subspace, and also under general linear transformations of the bases employed in expanding the charge density. The interrelation between the present general treatment and the reduced theory applied previously in terms of the two-level ET model is investigated. Finally, the explicit expression for the screening potential of medium electrons is derived in the electronic Born-Oppenheimer approximation (fast (slow) electronic timescale for solvent (solute)). The theory leads to a self-consistent scheme for practical calculations of rate constants for ET reactions involving complex solutes. Illustrative test calculations for two-level ET systems are presented, and the importance of proper boundary conditions for realistic molecular cavities is demonstrated.

  13. Nature of the charged headgroup determines the fusogenic potential and membrane properties of lithocholic acid phospholipids.

    PubMed

    Bhargava, Priyanshu; Singh, Manish; Sreekanth, Vedagopuram; Bajaj, Avinash

    2014-08-01

    Phospholipids play a crucial role in many cellular processes ranging from selective membrane permeability, to membrane fission and fusion, to cellular signaling. Headgroups of phospholipids determine the membrane properties and fusogenicity of these lipids with target cell membranes. We studied the fusogenic and membrane properties of phospholipids possessing unnatural charged headgroups with model membranes using laurdan based membrane hydration studies, DPH based membrane fluidity, and differential scanning calorimetry. We unravel that fusogenicity, membrane hydration, and fluidity of membranes are strongly contingent on the nature of the phospholipid charged headgroup. Our studies unraveled that introduction of bulky headgroups like dimethylamino pyridine induces maximum membrane hydration and perturbations with high fusogenicity as compared to small headgroup based phospholipids. These phospholipids also have the capability of high retention in DPPC membranes. Hydration and fluidity of these phospholipid-doped DPPC membranes are contingent on the nature of the charged headgroup. This study would help in future design of phospholipid based nanomaterials for effective drug delivery.

  14. Density determination of nail polishes and paint chips using magnetic levitation

    NASA Astrophysics Data System (ADS)

    Huang, Peggy P.

    Trace evidence is often small, easily overlooked, and difficult to analyze. This study describes a nondestructive method to separate and accurately determine the density of trace evidence samples, specifically nail polish and paint chip using magnetic levitation (MagLev). By determining the levitation height of each sample in the MagLev device, the density of the sample is back extrapolated using a standard density bead linear regression line. The results show that MagLev distinguishes among eight clear nail polishes, including samples from the same manufacturer; separates select colored nail polishes from the same manufacturer; can determine the density range of household paint chips; and shows limited levitation for unknown paint chips. MagLev provides a simple, affordable, and nondestructive means of determining density. The addition of co-solutes to the paramagnetic solution to expand the density range may result in greater discriminatory power and separation and lead to further applications of this technique.

  15. Structure-property relationships in non-epitaxial chalcogenide heterostructures: the role of interface density on charge exchange

    NASA Astrophysics Data System (ADS)

    Bauers, S. R.; Ditto, J.; Moore, D. B.; Johnson, D. C.

    2016-07-01

    A homologous series of quasi-2D ([PbSe]1+δ)m(TiSe2)m nanolayered heterostructures are prepared via self-assembly of designed precursors with 1 <= m <= 4 and their structures and properties investigated. All heterostructures have the same global composition but vary in their interface density. X-ray diffraction and electron microscopy studies show that the structures consist of rock salt structured PbSe layers alternating with TiSe2 layers, and that grain size increases with m. The compounds are all metallic with upturns in resistivity at low temperature suggesting electron localization, with room temperature resistivity of 1-3 10-5 Ω m, negative Hall coefficients and Seebeck coefficients between -50 and -100 μV K-1. A decrease in the mobile carrier concentration with temperature is observed for all m and the rate increases with increasing low-dimensionality. Decreasing the interface density also decreases the average carrier concentration while increasing the electron mobility. The Seebeck coefficients systematically increase in magnitude as m is increased, but the net effect to the power factor is small due to a compensating increase in resistivity. The observed transport behavior is not described by the simple rigid band models with charge transfer between constituents used previously. Charge exchange between constituents stabilizes the intergrowth, but also introduces mobile carriers and interfacial band bending that must play a role in the transport behavior of the heterostructures. As chemical potentials equilibrate in high m heterostructures there is a decrease in total coulombic stabilization as there are fewer interfaces, so m = 1 is likely to be most stable. This rationalizes why the structurally similar misfit layer compounds with m = 1 are often the only intergrowths that can be prepared. Charge transfer and band bending at interfaces should occur in other heterostructures with similar type II broken-gap band alignments and are important

  16. Turbo charging time-dependent density-functional theory with Lanczos chains.

    PubMed

    Rocca, Dario; Gebauer, Ralph; Saad, Yousef; Baroni, Stefano

    2008-04-21

    We introduce a new implementation of time-dependent density-functional theory which allows the entire spectrum of a molecule or extended system to be computed with a numerical effort comparable to that of a single standard ground-state calculation. This method is particularly well suited for large systems and/or large basis sets, such as plane waves or real-space grids. By using a superoperator formulation of linearized time-dependent density-functional theory, we first represent the dynamical polarizability of an interacting-electron system as an off-diagonal matrix element of the resolvent of the Liouvillian superoperator. One-electron operators and density matrices are treated using a representation borrowed from time-independent density-functional perturbation theory, which permits us to avoid the calculation of unoccupied Kohn-Sham orbitals. The resolvent of the Liouvillian is evaluated through a newly developed algorithm based on the nonsymmetric Lanczos method. Each step of the Lanczos recursion essentially requires twice as many operations as a single step of the iterative diagonalization of the unperturbed Kohn-Sham Hamiltonian. Suitable extrapolation of the Lanczos coefficients allows for a dramatic reduction of the number of Lanczos steps necessary to obtain well converged spectra, bringing such number down to hundreds (or a few thousands, at worst) in typical plane-wave pseudopotential applications. The resulting numerical workload is only a few times larger than that needed by a ground-state Kohn-Sham calculation for a same system. Our method is demonstrated with the calculation of the spectra of benzene, C(60) fullerene, and of chlorophyll a.

  17. Switching of Slow Magnetic Relaxation Dynamics in Mononuclear Dysprosium(III) Compounds with Charge Density.

    PubMed

    Lim, Kwang Soo; Baldoví, José J; Lee, Woo Ram; Song, Jeong Hwa; Yoon, Sung Won; Suh, Byoung Jin; Coronado, Eugenio; Gaita-Ariño, Alejandro; Hong, Chang Seop

    2016-06-01

    The symmetry around a Dy ion is recognized to be a crucial parameter dictating magnetization relaxation dynamics. We prepared two similar square-antiprismatic complexes, [Dy(LOMe)2(H2O)2](PF6) (1) and Dy(LOMe)2(NO3) (2), where LOMe = [CpCo{P(O)(O(CH3))2}3], including either two neutral water molecules (1) or an anionic nitrate ligand (2). We demonstrated that in this case relaxation dynamics is dramatically affected by the introduction of a charged ligand, stabilizing the easy axis of magnetization along the nitrate direction. We also showed that the application of either a direct-current field or chemical dilution effectively stops quantum tunneling in the ground state of 2, thereby increasing the relaxation time by over 3 orders of magnitude at 3.5 K. PMID:27186802

  18. Microcapsules through polymer complexation. II. By complex coacervation of polymers containing a low charge density.

    PubMed

    Shao, W; Yin, X; Stevenson, W T; Alexander, H

    1991-07-01

    Relationships between ionizable group content, structure and molecular weight, solubility and solution behaviour, and the efficacy of ionic complex formation through complex coacervation, have been established for a range of sparingly soluble synthetic weak polyelectrolyte polymers with low charge content, based on hydroxyalkyl methacrylates. Selected polymers containing methacrylic acid (acidic) and dimethylaminoethyl methacrylate (basic) functionality show promise as capsule-forming pairs for the entrapment of mammalian cells. The solubility of basic polymers and their ability to form microcapsules with structural integrity is enhanced through quaternization of the N-methyl functionality to the quaternary ammonium group. The survival of guinea-pig erythrocytes encapsulated for 4 d in this promising system was shown by the Drabkin's test to be about 41% of the control sample.

  19. Determination of Points of Zero Charge of Natural and Treated Adsorbents

    NASA Astrophysics Data System (ADS)

    Nasiruddin Khan, M.; Sarwar, Anila

    Although particle size and its measurement are intuitively familiar to particle technologists, the concept of point of zero charge (pzc) is less widely understood and applied. This is unfortunate since it is at least as fundamentally important as particle size in determining the behavior of particulate materials, especially those with sizes in the colloidal range below a micrometer. pzc is related to the charge on the surface of the particle and strongly depends on the pH of the material; so it influences a wide range of properties of colloidal materials, such as their stability, interaction with electrolytes, suspension rheology, and ion exchange capacity. The pH dependence of surface charges was quantified for four different adsorbent-aqueous solution interfaces. The points of zero charge were determined for activated charcoal, granite sand, lakhra coal, and ground corn cob materials using three methods: (1) the pH drift method, measuring pH where the adsorbent behaves as a neutral specie; (2) potentiometric titration, measuring the adsorption of H+ and OH- on surfaces in solutions of varying ionic strengths; (3) direct assessment of the surface charge via nonspecific ion adsorption as a function of pH. The intrinsic acidity constants for acid and base equilibria, pK a1 s and pK a2 s, were also calculated. Lakhra coal was found to have the lowest pzc value among all other adsorbents studied owing to the presence of a large amount of humus material. The results were used to explain general connections among points of zero charges, cation exchange capacity, and base saturation % of adsorbents.

  20. Percolation, tie-lines, and the microstructural determinants of charge transport in semicrystalline conjugated polymers

    NASA Astrophysics Data System (ADS)

    Spakowitz, Andrew

    2015-03-01

    Semiconducting polymers play an important role in a wide range of optical and electronic material applications. It is widely accepted that the polymer ordering impacts charge transport in such devices. However, the connection between molecular ordering and device performance is difficult to predict due to the current need for a mathematical theory of the physics that dictates charge transport in semiconducting polymers. Here, we present a new analytical and computational description in which the morphology of individual polymer chains is dictated by well-known statistical models and the electronic coupling between units is determined using Marcus theory. This effort combines our research group's modeling efforts in polymer conformational properties and reaction-diffusion phenomena to address the multiscale dynamics of charge transport in a heterogeneous material. The resulting model is capable of bridging molecular-level charge transport mechanisms to large scale transport behavior, thus facilitating direct comparison with experiments. The multiscale transport of charges in these materials (high mobility at short length scales, low mobility at long length scales) is naturally described with our framework. Additionally, the dependence of mobility with electric field and temperature is explained in terms of conformational variability and spatial correlation. Our model offers a predictive approach to connecting processing conditions with transport behavior.

  1. Determination of edge and screw dislocation density in single crystals of high-purity iron

    SciTech Connect

    Park, Y.K.; Waber, J.T.; Snead, C.L. Jr.

    1985-01-01

    The trapping of positrons in dislocation-associated traps has been studied and the density of traps has been demonstrated to be in close agreement with the density of dislocations determined by TEM and etch-pit measurements on the same specimens. The specific trapping rates were determined.

  2. Atomic charges of Cl- ions confined in a model Escherichia coli ClC-Cl-/H+ ion exchanger: a density functional theory study

    NASA Astrophysics Data System (ADS)

    Nieto-Delgado, P. G.; Arreola, J.; Guirado-López, R. A.

    2013-11-01

    We present extensive semi-empirical and pseudo-potential density functional theory calculations dedicated to analyse the stability, charge density distribution and migration behaviour of Cl- ions confined in model Escherichia coli (ec) ClC-Cl-/H+ ion-exchangers. Following recent high-resolution crystal structure determination in these kinds of systems, we use a finite-cluster model approach and construct various chemically simplified pore structures made of a glutamate residue -CH2-CH2-COO- (E148) and its closets 15, 19, 23 and 26 amino acids into which the Cl- ions will be confined. We reveal the sequence of molecular rearrangements induced on the E148 chain, which blocks the middle of the conduction pathway, leading to the pore opening. The -CH2-CH2-COO- fragment shows notable variations in its average charge density for small changes in the intra-cellular environment varying from -0.4e to -0.3e to -0.1e in the presence of zero, one and two confined Cl- ions, respectively, a result that reveals an interesting functionality of the E148 chain during Cl- conduction. We also obtain complex fluctuations in the ionic charge of the confined Cl- ions varying from ∼-0.7e to -0.2e, which deviate significantly from the value (-1e) usually used in classical simulations. By attaching a single H species to one of the oxygens of the glutamate group, we obtain that the -CH2-CH2-COOH fragment has now a small effective charge of ∼+0.25e. The energy barriers opposing the exit of the Cl- ions from our considered ion-exchangers vary from 0.65 eV to 4.7 eV, the smallest values being obtained for model structures exhibiting a high degree of flexibility and having protonated E148 fragments. Our results reinforce previous findings and provide additional physical insight, at the atomic level, on the gating process. Finally, we underline the importance of using electronically polarisable force fields to describe the transport of anionic species through this kind of molecular

  3. Determining density of maize canopy. 3: Temporal considerations

    NASA Technical Reports Server (NTRS)

    Stoner, E. R.; Baumgardner, M. F.; Anuta, P. E.; Cipra, J. E.

    1972-01-01

    Multispectral scanner data were collected in two flights over ground cover plots at an altitude of 305 m. Eight ground reflectance panels in close proximity to the ground cover plots were used to normalize the scanner data obtained on different dates. Separate prediction equations were obtained for both flight dates for all eleven reflective wavelength bands of the multispectral scanner. Ratios of normalized scanner data were related to leaf area index over time. Normalized scanner data were used to plot relative reflectance versus wavelength for the ground cover plots. Spectral response curves were similar to those for bare soil and green vegetation as determined by laboratory measurements. The spectral response curves from the normalized scanner data indicated that reflectance in the 0.72 to 1.3 micron wavelength range increased as leaf area index increased. A decrease in reflectance was observed in the 0.65 micron chlorophyll absorption band as leaf area index increased.

  4. A simple approach to the determination of the charging state of photovoltaic-powered storage batteries

    NASA Astrophysics Data System (ADS)

    Hamdy, M. A.

    Stand-alone photovoltaic (PV) applications, such as domestic and street lighting systems, usually include a storage battery which is subjected to a daily charge/discharge cycle. During such cycle the battery chargesduring the day and loses a percentage of its charge to the load at night. A knowledge of the battery state-of-charge (SOC) during charging is important since it leads to design information about the desired size of the PV array and battery capacity to satisfy a given load. A simple approach to the theoretical determination of the battery SOC in stand-alone PV systems is presented in this paper. The approach is based on the graphical determination of the system operating points found from the intersection between the I-V curves representing the power source (PV) under varying solar radiation and temperature conditions with the I-V curves representing the load (battery) under varying SOC conditions. The study is restricted to locally manufactured lead/acid batteries used to power TV sets in some of the rural areas of Egypt. It takes into consideration the different factors affecting battery performance. Conclusions are drawn from the analysis that permit a better design of the system for full utilization of the PV output power leading to the appropriate PV size that ensures proper system operation for the designed period.

  5. Preparation and Charge Density in (Co, Fe)-Doped La-Ca-Based Chromite

    NASA Astrophysics Data System (ADS)

    Saravanan, R.; Thenmozhi, N.; Fu, Yen-Pei

    2016-08-01

    Transition metal-doped lanthanum chromites (La0.8Ca0.2)(Cr0.9- x Co0.1Fe x )O3 ( x = 0.03, 0.06, 0.09, 0.12) have been synthesized by solid state reaction method. The synthesized samples were characterized for their structural properties using powder x-ray diffraction analysis, which shows that the grown samples are orthorhombic in structure with single phase. The nature of bonding and the charge distribution of the grown samples have been analyzed by maximum entropy method. Further, the samples were characterized for their optical and magnetic properties using ultraviolet-visible spectra and vibrating sample magnetometry. The microstructural studies were carried by scanning electron microscopy/electron dispersive x-ray spectroscopy techniques. From the optical absorption spectra, it was found that the energy band gap of the samples ranges from 2.135 eV to 2.405 eV. From vibrating sample magnetometer measurements, ferromagnetic like behaviour with large coercive field was observed for Fe doping concentration of x = 0.12. Since the doped lanthanum chromites have good mechanical properties and electrical conductivity at high temperature, these materials are used in solid oxide fuel cells.

  6. Subgap tunneling via a quantum interference effect: Insulators and charge density waves

    NASA Astrophysics Data System (ADS)

    Duhot, S.; Mélin, R.

    2007-11-01

    A quantum interference effect is discussed for subgap tunneling over a distance comparable to the coherence length, which is a consequence of “advanced-advanced” and “retarded-retarded” transmission modes [Altland and Zirnbauer, Phys. Rev. B 55, 1142 (1997)]. Effects typical of disorder are obtained from the interplay between multichannel averaging and higher order processes in the tunnel amplitudes. Quantum interference effects similar to those occurring in normal tunnel junctions explain magnetoresistance oscillations of a CDW pierced by nanoholes [Latyshev , Phys. Rev. Lett. 78, 919 (1997)], having periodicity h/2e as a function of the flux enclosed in the nanohole. Subgap tunneling is coupled to the sliding motion by charge accumulation in the interrupted chains. The effect is within the same trend as random matrix theory for normal metal-CDW hybrids [Visscher , Phys. Rev. B 62, 6873 (2000)]. We suggest that the experiment by Latyshev probes weak localizationlike properties of evanescent quasiparticles, not an interference effect related to the quantum-mechanical ground state.

  7. Universal bulk charge-density-wave (CDW) correlations in the cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Tabis, Wojciech

    2014-03-01

    The recent observation of bulk CDW order in YBa2Cu3O8+δ(YBCO) in competition with superconductivity is a significant development. Using Cu L-edge resonant X-ray scattering, we also observe bulk CDW order in HgBa2CuO4+δ(Hg1201 Tc = 72K). The correlations appear below TCDW ~ 200K, well below the pseudogap temperature T* ~ 320K associated with unusual magnetism, but coincident with the onset of Fermi-liquid-like charge transport. In contrast to YBCO, we observe no decrease of the CDW amplitude below Tc, and the correlation length is short and temperature independent. CDW correlations therefore are a universal property of underdoped cuprates, enhanced by low structural symmetry and a magnetic field, but fundamentally not in significant competition with superconductivity. We also discuss the relationship between the CDW modulation wave vector and the Fermi surface area extracted from QO experiments. Work supported by DOE-BES. In collaboration with Y. Li, M. Le Tacon, L. Braicovich, A. Kreyssig, M. Minola, G. Dellea, E. Weschke, M. Veit, A. Goldman, T. Schmitt, G. Ghiringhelli, N. Barisic, M.K. Chan, C. Dorow, G. Yu, X. Zhao, B. Keimer, M. Greven.

  8. Determination of the “NiOOH” charge and discharge mechanisms at ideal activity

    SciTech Connect

    Merrill, Matthew; Worsley, Marcus; Wittstock, Arne; Biener, Juergen; Stadermann, Michael

    2014-01-24

    Here, optimization of electrodeposition conditions produced Ni(OH)2 deposits chargeable up to 1.84 ± 0.02 e per Ni on and the resulting nickel oxide/hydroxide active material could subsequently deliver 1.58 ± 0.02 e per Ni ion (462 mA h/g) over a potential range <0.2 V. The ability of the “NiOOH” active material to deliver an approximately ideal charge and discharge facilitated a coulometric and thermodynamic analysis through which the charge/discharge mechanisms were determined from known enthalpies of formation. The (dis)charge states were confirmed with in situ Raman spectroscopy. The mechanisms were additionally evaluated with respect to pH and potential dependence, charge quantities, hysteresis, and fluoride ion partial inhibition of the charge mechanism. The results indicate that the “NiOOH” (dis)charges as a solid-state system with mechanisms consistent with known nickel and oxygen redox reactions. A defect chemistry mechanism known for the LiNiO2 system also occurs for “NiOOH” to cause both high activity and hysteresis. Similar to other cation insertion nickel oxides, the activity of the “NiOOH” mechanism is predominantly due to oxygen redox activity and does not involve the Ni4+ oxidation state. The “NiOOH” was produced from cathodic electrodeposition of Ni(OH)2 from nickel nitrate solutions onto highly oriented pyrolytic graphite at ideal electrodeposition current efficiencies and the deposition mechanism was also characterized.

  9. HIEN-LO: An experiment for charge determination of cosmic rays of interplanetary and solar origin

    NASA Technical Reports Server (NTRS)

    Klecker, B.; Hovestadt, D.; Mason, G. M.; Blake, J. B.; Nicholas, J.

    1988-01-01

    The experiment is designed to measure the heavy ion environment at low altitude (HIEN-LO) in the energy range 0.3 to 100 MeV/nucleon. In order to cover this wide energy range a complement of three sensors is used. A large area ion drift chamber and a time-of-flight telescope are used to determine the mass and energy of the incoming cosmic rays. A third omnidirectional counter serves as a proton monitor. The analysis of mass, energy and incoming direction in combination with the directional geomagnetic cut-off allows the determination of the ionic charge of the cosmic rays. The ionic charge in this energy range is of particular interest because it provides clues to the origin of these particles and to the plasma conditions at the acceleration site. The experiment is expected to be flown in 1988/1989.

  10. Photoemission study of the electronic structure and charge density waves of Na₂Ti₂Sb₂O

    SciTech Connect

    Tan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L.

    2015-04-30

    The electronic structure of Na₂Ti₂Sb₂O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na₂Ti₂Sb₂O in the non-magnetic state, which indicates that there is no magnetic order in Na₂Ti₂Sb₂O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na₂Ti₂Sb₂O. Photon energy dependent ARPES results suggest that the electronic structure of Na₂Ti₂Sb₂O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV at 7 K, indicating that Na₂Ti₂Sb₂O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime. (author)

  11. Unusual dimensionality effects and surface charge density in 2D Mg(OH)2

    PubMed Central

    Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M.; Tongay, Sefaattin

    2016-01-01

    We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics. PMID:26846617

  12. Unusual dimensionality effects and surface charge density in 2D Mg(OH)2

    NASA Astrophysics Data System (ADS)

    Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M.; Tongay, Sefaattin

    2016-02-01

    We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics.

  13. Extraction of high charge density of states in electrolyte-gated polymer thin-film transistor with temperature-dependent measurements

    NASA Astrophysics Data System (ADS)

    Lee, Jiyoul

    2016-05-01

    Using temperature-dependent charge transport measurements, we investigated spectral density of states (DOS) in the bandgap of polythiophene thin-films under high carrier densities (<3.5 × 1020 cm-3) induced by electrochemical doping. The thermally activated charge transport indicates that the electrical currents in the polymer thin-film under high charge density state follow the Meyer-Neldel rule. The spectral DOS extracted from the electrolyte-gated polymer film lie in the range of 8.0 × 1019 cm-3 eV-1-8.0 × 1021 cm-3 eV-1, which are at least two orders of magnitude larger than the DOS extracted from the same polymer film at relatively low induced carrier densities by general oxide dielectrics.

  14. Mass determination of megadalton-DNA electrospray ions using charge detection mass spectrometry.

    PubMed

    Schultz, J C; Hack, C A; Benner, W H

    1998-04-01

    Charge detection mass spectrometry (CD-MS) has been used to determine the mass of double-stranded, circular DNA and single-stranded, circular DNA in the range of 2500 to 8000 base pairs (1.5-5.0 MDa). Simultaneous measurement of the charge and velocity of an electrostatically accelerated ion allows a mass determination of the ion, with instrument calibration determined independently of samples. Positive ion mass spectra of electrosprayed commercial DNA samples supplied in tris(hydroxymethyl)ethylenediaminetetraacetic acid buffer, diluted in 50 vol. % acetonitrile, were obtained without cleanup of the sample. A CD mass spectrum constructed from 3000 ion measurements takes 10 min to acquire and yields the DNA molecular mass directly (mass resolution = 6). The data collected represent progress toward a more automatable alternative to sizing of DNA by gel electrophoresis. In addition to the mass spectra, CD-MS generates charge versus mass plots, which provide another means to investigate the creation and fate of large electrospray ions.

  15. Mass determination of megadalton-DNA Electrospray Ions usingCharge Detection Mass Spectrometry

    SciTech Connect

    Schultz, Jocelyn C.; Hack, Christopher; Benner, Henry W.

    1997-10-01

    Charge detection mass spectrometry (CD-MS) has been used to determine the mass of double-stranded, circular DNA and single-stranded, circular DNA in the range of 2500 to 8000 base pairs (1.5-5.0 MDa). Simultaneous measurement of the charge and velocity of an electrostatically accelerated ion allows a mass determination of the ion, with instrument calibration determined independently of samples. Positive ion mass spectra of electrosprayed commercial DNA samples supplied in tris(hydroxymethyl)ethylenediamine tetraacetic acid buffer, diluted in 50 vol. percent acetonitrile, were obtained without cleanup of the sample. ACD mass spectrum constructed from 3000 ion measurements takes 10 min to acquire and yields the DNA molecular mass directly (mass resolution = 6). The data collected represent progress toward a more automatable alternative to sizing of DNA by gel electrophoresis. In addition to the mass spectra, CD-MS generates charge versus mass plots, which provide another means to investigate the creation and fate of large electrospray ions.

  16. Determination of Interfacial Charge-Transfer Rate Constants in Perovskite Solar Cells.

    PubMed

    Pydzińska, Katarzyna; Karolczak, Jerzy; Kosta, Ivet; Tena-Zaera, Ramon; Todinova, Anna; Idígoras, Jesus; Anta, Juan A; Ziółek, Marcin

    2016-07-01

    A simple protocol to study the dynamics of charge transfer to selective contacts in perovskite solar cells, based on time-resolved laser spectroscopy studies, in which the effect of bimolecular electron-hole recombination has been eliminated, is proposed. Through the proposed procedure, the interfacial charge-transfer rate constants from methylammonium lead iodide perovskite to different contact materials can be determined. Hole transfer is faster for CuSCN (rate constant 0.20 ns(-1) ) than that for 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD; 0.06 ns(-1) ), and electron transfer is faster for mesoporous (0.11 ns(-1) ) than that for compact (0.02 ns(-1) ) TiO2 layers. Despite more rapid charge separation, the photovoltaic performance of CuSCN cells is worse than that of spiro-OMeTAD cells; this is explained by faster charge recombination in CuSCN cells, as revealed by impedance spectroscopy. The proposed direction of studies should be one of the key strategies to explore efficient hole-selective contacts as an alternative to spiro-OMeTAD. PMID:27253726

  17. Discovery of an Unconventional Charge Density Wave at the Surface of K_{0.9}Mo_{6}O_{17}.

    PubMed

    Mou, Daixiang; Sapkota, A; Kung, H-H; Krapivin, Viktor; Wu, Yun; Kreyssig, A; Zhou, Xingjiang; Goldman, A I; Blumberg, G; Flint, Rebecca; Kaminski, Adam

    2016-05-13

    We use angle resolved photoemission spectroscopy, Raman spectroscopy, low energy electron diffraction, and x-ray scattering to reveal an unusual electronically mediated charge density wave (CDW) in K_{0.9}Mo_{6}O_{17}. Not only does K_{0.9}Mo_{6}O_{17} lack signatures of electron-phonon coupling, but it also hosts an extraordinary surface CDW, with T_{S_CDW}=220  K nearly twice that of the bulk CDW, T_{B_CDW}=115  K. While the bulk CDW has a BCS-like gap of 12 meV, the surface gap is 10 times larger and well in the strong coupling regime. Strong coupling behavior combined with the absence of signatures of strong electron-phonon coupling indicates that the CDW is likely mediated by electronic interactions enhanced by low dimensionality. PMID:27232028

  18. Three-dimensional charge density wave order in YBa2Cu3O6.67 at high magnetic fields.

    PubMed

    Gerber, S; Jang, H; Nojiri, H; Matsuzawa, S; Yasumura, H; Bonn, D A; Liang, R; Hardy, W N; Islam, Z; Mehta, A; Song, S; Sikorski, M; Stefanescu, D; Feng, Y; Kivelson, S A; Devereaux, T P; Shen, Z-X; Kao, C-C; Lee, W-S; Zhu, D; Lee, J-S

    2015-11-20

    Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured with x-ray scattering at zero and low fields. We combined a pulsed magnet with an x-ray free-electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields of up to 28 tesla. While the zero-field CDW order, which develops at temperatures below ~150 kelvin, is essentially two dimensional, at lower temperature and beyond 15 tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked. PMID:26541608

  19. Seebeck coefficient of underdoped LSCO in high magnetic fields : Fermi-surface reconstruction by charge-density-wave order

    NASA Astrophysics Data System (ADS)

    Badoux, Sven; Afshar, Arezoo; Michon, Bastien; Ouellet, Alexandre; Fortier, Simon; Doiron-Leyraud, Nicolas; Taillefer, Louis; Leboeuf, David; Croft, Thomas; Hayden, Stephen; Takagi, Hidenori; Yamada, Kazuyoshi; Graf, David

    The Seebeck coefficient S of the hole-doped cuprate La2-xSrxCuO4 (LSCO) was measured in magnetic fields large enough to suppress superconductivity, for a range of Sr concentrations x in the underdoped regime. For x = 0 . 12 , 0.125 and 0.13, S / T is seen to drop upon cooling and become negative at low temperature. The same behavior is observed in the Hall coefficient RH (T) . In analogy with other hole-doped cuprates at similar hole concentrations, the sign change in S and RH shows that the Fermi surface of LSCO undergoes a reconstruction caused by the onset of charge-density-wave modulations. Such modulations have indeed been detected in LSCO by X-ray diffraction in precisely the same doping range.

  20. Evidence for coupling between collective state and phonons in two-dimensional charge-density-wave systems

    SciTech Connect

    Lavagnini, M.; Baldini, M.; Sacchetti, A.; Castro, D.Di; Delley, B.; Monnier, R.; Chu, J.-H.; Ru, N.; Fisher, I.R.; Postorino, P.; Degiorgi, L.; /Zurich, ETH

    2010-02-15

    We report on a Raman scattering investigation of the charge-density-wave (CDW), quasi two-dimensional rare-earth tri-tellurides RTe{sub 3} (R = La, Ce, Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe{sub 3} and CeTe{sub 3} under externally applied pressure. The observed phonon peaks can be ascribed to the Raman active modes for both the undistorted as well as the distorted lattice in the CDW state by means of a first principles calculation. The latter also predicts the Kohn anomaly in the phonon dispersion, driving the CDW transition. The integrated intensity of the two most prominent modes scales as a characteristic power of the CDW-gap amplitude upon compressing the lattice, which provides clear evidence for the tight coupling between the CDW condensate and the vibrational modes.

  1. Discovery of an Unconventional Charge Density Wave at the Surface of K_{0.9}Mo_{6}O_{17}.

    PubMed

    Mou, Daixiang; Sapkota, A; Kung, H-H; Krapivin, Viktor; Wu, Yun; Kreyssig, A; Zhou, Xingjiang; Goldman, A I; Blumberg, G; Flint, Rebecca; Kaminski, Adam

    2016-05-13

    We use angle resolved photoemission spectroscopy, Raman spectroscopy, low energy electron diffraction, and x-ray scattering to reveal an unusual electronically mediated charge density wave (CDW) in K_{0.9}Mo_{6}O_{17}. Not only does K_{0.9}Mo_{6}O_{17} lack signatures of electron-phonon coupling, but it also hosts an extraordinary surface CDW, with T_{S_CDW}=220  K nearly twice that of the bulk CDW, T_{B_CDW}=115  K. While the bulk CDW has a BCS-like gap of 12 meV, the surface gap is 10 times larger and well in the strong coupling regime. Strong coupling behavior combined with the absence of signatures of strong electron-phonon coupling indicates that the CDW is likely mediated by electronic interactions enhanced by low dimensionality.

  2. Three-Dimensional Charge Density Wave Order in YBa2Cu3O6.67 at High Magnetic Fields

    SciTech Connect

    Gerber, S.; Jang, H.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Bonn, D. A.; Liang, R.; Hardy, W.; Islam, Z.; Lee, W. -S.; Zhu, D.; Lee, J. -S.

    2015-11-20

    Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW onsets around the zero-field superconducting transition temperature, yet the incommensurate inplane ordering vector is field-independent. This implies that the two forms of CDW and hightemperature superconductivity are intimately linked.

  3. Remarkable Stability of Charge Density Wave Order in La1.875 Ba0.125 CuO4

    NASA Astrophysics Data System (ADS)

    Chen, X. M.; Thampy, V.; Mazzoli, C.; Barbour, A. M.; Miao, H.; Gu, G. D.; Cao, Y.; Tranquada, J. M.; Dean, M. P. M.; Wilkins, S. B.

    2016-10-01

    The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.825 Ba0.125 CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2 ¾ h . We discuss the implications of these results for some of the competing theories.

  4. Electronic structure of novel charge transfer compounds: application of Fermi orbital self-interaction corrected density functional theory

    NASA Astrophysics Data System (ADS)

    Hahn, Torsten; Rückerl, Florian; Liebing, Simon; Pederson, Mark

    We present our experimental and theoretical results on novel Picene/F4TCNQ and Manganese-Phthalocyanine/F4TCNQ donor / acceptor systems. We apply the recently developed Fermi-orbital based approach for self-interaction corrected density functional theory (FO-SIC DFT) to these materials and compare the results to standard DFT calculations and to experimental data obtained by photoemission spectroscopy. We focus our analysis on the description of the magnitude of the ground state charge transfer and on the details of the formed hybrid orbitals. Further, we show that for weakly bound donor / acceptor systems the FO-SIC approach delivers a more realistic description of the electronic structure compared to standard DFT calculations Support by DFG FOR1154 is greatly acknowledged.

  5. Controlling charge-density-wave states in nano-thick crystals of 1T-TaS2.

    PubMed

    Yoshida, Masaro; Zhang, Yijin; Ye, Jianting; Suzuki, Ryuji; Imai, Yasuhiko; Kimura, Shigeru; Fujiwara, Akihiko; Iwasa, Yoshihiro

    2014-12-03

    Two-dimensional crystals, especially graphene and transition metal dichalcogenides (TMDs), are attracting growing interests because they provide an ideal platform for novel and unconventional electronic band structures derived by thinning. The thinning may also affect collective phenomena of electrons in interacting electron systems and can lead to exotic states beyond the simple band picture. Here, we report the systematic control of charge-density-wave (CDW) transitions by changing thickness, cooling rate and gate voltage in nano-thick crystals of 1T-type tantalum disulfide (1T-TaS2). Particularly the clear cooling rate dependence, which has never been observed in bulk crystals, revealed the nearly-commensurate CDW state in nano-thick crystals is a super-cooled state. The present results demonstrate that, in the two-dimensional crystals with nanometer thickness, the first-order phase transitions are susceptible to various perturbations, suggestive of potential functions of electronic phase control.

  6. Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey

    NASA Technical Reports Server (NTRS)

    Dyall, Kenneth G.; Arnold, James (Technical Monitor)

    1999-01-01

    The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

  7. Structure and control of charge density waves in two-dimensional 1T-TaS2

    PubMed Central

    Tsen, Adam W.; Hovden, Robert; Wang, Dennis; Kim, Young Duck; Okamoto, Junichi; Spoth, Katherine A.; Liu, Yu; Lu, Wenjian; Sun, Yuping; Hone, James C.; Kourkoutis, Lena F.; Kim, Philip; Pasupathy, Abhay N.

    2015-01-01

    The layered transition metal dichalcogenides host a rich collection of charge density wave phases in which both the conduction electrons and the atomic structure display translational symmetry breaking. Manipulating these complex states by purely electronic methods has been a long-sought scientific and technological goal. Here, we show how this can be achieved in 1T-TaS2 in the 2D limit. We first demonstrate that the intrinsic properties of atomically thin flakes are preserved by encapsulation with hexagonal boron nitride in inert atmosphere. We use this facile assembly method together with transmission electron microscopy and transport measurements to probe the nature of the 2D state and show that its conductance is dominated by discommensurations. The discommensuration structure can be precisely tuned in few-layer samples by an in-plane electric current, allowing continuous electrical control over the discommensuration-melting transition in 2D. PMID:26598707

  8. Pressure-induced continuous phase transition of charge-density-wave state in a linear-chain complex

    NASA Astrophysics Data System (ADS)

    Kuroda, Noritaka; Sakai, Masamichi; Nishina, Yuichiro; Sasaki, Kazuo

    1992-05-01

    [Pt(en)2][Pt(en)2Cl2](ClO4)4 (en=ethylenediamine) is found to undergo a novel phase transition from the charge-density-wave (CDW) state to a new phase under hydrostatic pressure. The new phase appears at 3 GPa and coexists with the CDW state up to 6 GPa, at least. The volume ratio between the two coexisting phases measured by Raman scattering spectroscopy changes continuously with pressure. The result is discussed in terms of the theoretical approach to the polymorphic phase transition developed recently by Bassler, Sasaki, and Griffiths. It is suggested that kink solitons play an important role in this phase transition.

  9. Three-dimensional charge density wave order in YBa2Cu3O6.67 at high magnetic fields

    DOE PAGES

    Gerber, S.; Jang, H.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Islam, Z.; Mehta, A.; et al

    2015-11-20

    In this study, charge density wave (CDW) correlations have recently been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW onsetsmore » around the zero-field superconducting transition temperature, yet the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.« less

  10. Discovery of an unconventional charge density wave at the surface of K0.9Mo6O17

    DOE PAGES

    Mou, Daixiang; Sapkota, Aashish; Kung, H. -H.; Krapivin, Viktor; Wu, Yun; Kreyssig, A.; Zhou, Xingjiang; Goldman, A. I.; Blumberg, G.; Flint, Rebecca; et al

    2016-05-13

    In this study, we use angle resolved photoemission spectroscopy, Raman spectroscopy, low energy electron diffraction, and x-ray scattering to reveal an unusual electronically mediated charge density wave (CDW) in K0.9Mo6O17. Not only does K0.9Mo6O17 lack signatures of electron-phonon coupling, but it also hosts an extraordinary surface CDW, with TS_CDW = 220 K nearly twice that of the bulk CDW, TB_CDW = 115 K. While the bulk CDW has a BCS-like gap of 12 meV, the surface gap is 10 times larger and well in the strong coupling regime. Strong coupling behavior combined with the absence of signatures of strong electron-phononmore » coupling indicates that the CDW is likely mediated by electronic interactions enhanced by low dimensionality.« less

  11. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H–NbSe2

    DOE PAGES

    Arguello, C. J.; Rosenthal, E. P.; Andrade, E. F.; Jin, W.; Yeh, P. C.; Zaki, N.; Jia, S.; Cava, R. J.; Fernandes, R. M.; Millis, A. J.; et al

    2015-01-21

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe₂, that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe₂. Thus, we demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiologymore » and the interactions. In 2H-NbSe₂, we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.« less

  12. Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide: Power-law decay of the charge density exchange

    SciTech Connect

    Wen, Rui-Tao Granqvist, Claes G.; Niklasson, Gunnar A.

    2014-10-20

    Ni-oxide-based thin films were produced by reactive direct-current magnetron sputtering and were characterized by X-ray diffraction and Rutherford backscattering spectroscopy. Intercalation of Li{sup +} ions was accomplished by cyclic voltammetry (CV) in an electrolyte of LiClO{sub 4} in propylene carbonate, and electrochromism was documented by spectrophotometry. The charge density exchange, and hence the optical modulation span, decayed gradually upon repeated cycling. This phenomenon was accurately described by an empirical power law, which was valid for at least 10{sup 4} cycles when the applied voltage was limited to 4.1 V vs Li/Li{sup +}. Our results allow lifetime assessments for one of the essential components in an electrochromic device such as a “smart window” for energy-efficient buildings.

  13. Short-ranged and short-lived charge-density-wave order and pseudogap features in underdoped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Greco, Andrés; Bejas, Matías

    2011-06-01

    The pseudogap phase of high-Tc cuprates is controversially attributed to preformed pairs or to a phase which coexists and competes with superconductivity. One of the challenges is to develop theoretical and experimental studies in order to distinguish between both proposals. Very recently, researchers at Stanford have reported [M. Hashimoto , Nat. Phys.PRLTAO1745-247310.1038/nphys1632 6, 414 (2010); R.-H. He , ScienceSCIEAS0036-807510.1126/science.1198415 331, 1579 (2011)] angle-resolved photoemission spectroscopy experiments on Pb-Bi2201 supporting the point of view that the pseudogap is distinct from superconductivity and associated to a spacial symmetry breaking without long-range order. In this paper, we show that many features reported by these experiments can be described in the framework of the t-J model considering self-energy effects in the proximity to a d charge-density-wave instability.

  14. Time-Dependent Ginzburg-Landau Equation and Boltzmann Transport Equation for Charge-Density-Wave Conductors

    NASA Astrophysics Data System (ADS)

    Takane, Yositake; Hayashi, Masahiko; Ebisawa, Hiromichi

    2016-08-01

    The time-dependent Ginzburg-Landau equation and the Boltzmann transport equation for charge-density-wave (CDW) conductors are derived from a microscopic one-dimensional model by applying the Keldysh Green's function approach under a quasiclassical approximation. The effects of an external electric field and impurity pinning of the CDW are fully taken into account without relying on a phenomenological argument. These equations simultaneously describe the spatiotemporal dynamics of both the CDW and quasiparticles; thus, they serve as a starting point to develop a general framework to analyze various nonequilibrium phenomena, such as current conversion between the CDW condensate and quasiparticles, in realistic CDW conductors. It is shown that, in typical situations, the equations correctly describe the nonlinear behavior of electric conductivity in a simpler manner.

  15. Discovery of an Unconventional Charge Density Wave at the Surface of K0.9Mo6O17

    NASA Astrophysics Data System (ADS)

    Mou, Daixiang; Sapkota, A.; Kung, H.-H.; Krapivin, Viktor; Wu, Yun; Kreyssig, A.; Zhou, Xingjiang; Goldman, A. I.; Blumberg, G.; Flint, Rebecca; Kaminski, Adam

    2016-05-01

    We use angle resolved photoemission spectroscopy, Raman spectroscopy, low energy electron diffraction, and x-ray scattering to reveal an unusual electronically mediated charge density wave (CDW) in K0.9 Mo6 O17 . Not only does K0.9 Mo6 O17 lack signatures of electron-phonon coupling, but it also hosts an extraordinary surface CDW, with TS _CDW =220 K nearly twice that of the bulk CDW, TB _CDW =115 K . While the bulk CDW has a BCS-like gap of 12 meV, the surface gap is 10 times larger and well in the strong coupling regime. Strong coupling behavior combined with the absence of signatures of strong electron-phonon coupling indicates that the CDW is likely mediated by electronic interactions enhanced by low dimensionality.

  16. Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide: Power-law decay of the charge density exchange

    NASA Astrophysics Data System (ADS)

    Wen, Rui-Tao; Granqvist, Claes G.; Niklasson, Gunnar A.

    2014-10-01

    Ni-oxide-based thin films were produced by reactive direct-current magnetron sputtering and were characterized by X-ray diffraction and Rutherford backscattering spectroscopy. Intercalation of Li+ ions was accomplished by cyclic voltammetry (CV) in an electrolyte of LiClO4 in propylene carbonate, and electrochromism was documented by spectrophotometry. The charge density exchange, and hence the optical modulation span, decayed gradually upon repeated cycling. This phenomenon was accurately described by an empirical power law, which was valid for at least 104 cycles when the applied voltage was limited to 4.1 V vs Li/Li+. Our results allow lifetime assessments for one of the essential components in an electrochromic device such as a "smart window" for energy-efficient buildings.

  17. Density functional studies on wurtzite piezotronic transistors: influence of different semiconductors and metals on piezoelectric charge distribution and Schottky barrier

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Zhang, Aihua; Zhang, Yan; Wang, Zhong Lin

    2016-05-01

    The mechanical-electrical coupling properties of piezoelectric semiconductors endow these materials with novel device applications in microelectromechanical systems, sensors, human-computer interfaces, etc. When an applied strain is exerted on a piezoelectric semiconductor, piezoelectric charges are generated at the surface or interface of the semiconductor, which can be utilized to control the electronic transport characteristics. This is the fundamental working mechanism of piezotronic devices, called the piezotronic effect. In the present report, a series of piezotronic transistors composed of different electrode metals and semiconductors is examined using density functional theory calculation. It is found that the influence of semiconductors on the piezotronic effect is larger than the impact of metals, and GaN and CdS are promising candidates for piezotronic and piezo-phototronic devices, respectively. The width of the piezoelectric charge distribution obtained in the present study can be used as a parameter in classical finite-element-method based simulations, which provide guidance on designing high-performance piezotronic devices.

  18. Density functional studies on wurtzite piezotronic transistors: influence of different semiconductors and metals on piezoelectric charge distribution and Schottky barrier.

    PubMed

    Liu, Wei; Zhang, Aihua; Zhang, Yan; Wang, Zhong Lin

    2016-05-20

    The mechanical-electrical coupling properties of piezoelectric semiconductors endow these materials with novel device applications in microelectromechanical systems, sensors, human-computer interfaces, etc. When an applied strain is exerted on a piezoelectric semiconductor, piezoelectric charges are generated at the surface or interface of the semiconductor, which can be utilized to control the electronic transport characteristics. This is the fundamental working mechanism of piezotronic devices, called the piezotronic effect. In the present report, a series of piezotronic transistors composed of different electrode metals and semiconductors is examined using density functional theory calculation. It is found that the influence of semiconductors on the piezotronic effect is larger than the impact of metals, and GaN and CdS are promising candidates for piezotronic and piezo-phototronic devices, respectively. The width of the piezoelectric charge distribution obtained in the present study can be used as a parameter in classical finite-element-method based simulations, which provide guidance on designing high-performance piezotronic devices. PMID:27053577

  19. Density functional studies on wurtzite piezotronic transistors: influence of different semiconductors and metals on piezoelectric charge distribution and Schottky barrier.

    PubMed

    Liu, Wei; Zhang, Aihua; Zhang, Yan; Wang, Zhong Lin

    2016-05-20

    The mechanical-electrical coupling properties of piezoelectric semiconductors endow these materials with novel device applications in microelectromechanical systems, sensors, human-computer interfaces, etc. When an applied strain is exerted on a piezoelectric semiconductor, piezoelectric charges are generated at the surface or interface of the semiconductor, which can be utilized to control the electronic transport characteristics. This is the fundamental working mechanism of piezotronic devices, called the piezotronic effect. In the present report, a series of piezotronic transistors composed of different electrode metals and semiconductors is examined using density functional theory calculation. It is found that the influence of semiconductors on the piezotronic effect is larger than the impact of metals, and GaN and CdS are promising candidates for piezotronic and piezo-phototronic devices, respectively. The width of the piezoelectric charge distribution obtained in the present study can be used as a parameter in classical finite-element-method based simulations, which provide guidance on designing high-performance piezotronic devices.

  20. The unusual normal state and charge-density-wave order in 2H-NbSe2.

    PubMed

    Koley, S; Mohanta, N; Taraphder, A

    2015-05-13

    Competition between collective states like charge-density-wave and superconductivity, unencumbered by the spin degrees of freedom, is played out in some of the transition metal dichalcogenides. Although 2H-NbSe2 has received much less attention than some of the other members of the family (such as 1T-TiSe2 and 2H-TaSe2) of late, it shows superconductivity at 7.2 K and incommensurate charge ordering at 33 K. Recent experiments, notably angle resolved photoemission spectroscopy, have cast serious doubts on the theories based on Fermi surface nesting and electron-phonon interaction. The normal state has been found to be a poor, incoherent metal and remarkably, the coherence increases in the broken symmetry state. From a preformed excitonic liquid scenario, we show that there exists a natural understanding of the experimental data on 2H-NbSe2, based on electron-electron interaction. The collective instabilities, in this scenario, are viewed as a condensation of an incoherent excitonic liquid already present at high temperature. PMID:25880453