WorldWideScience

Sample records for atomic conformational transition

  1. Conformal atoms in Supergravity

    Science.gov (United States)

    Jankowski, Jakub

    2016-01-01

    In this note, we summarize recent attempts to construct holographic models of atoms and lattices in the context of applications to solid state physics. The simplest setup turned out to impose strong constraints on the choice of matter interactions of dual gravitational theory.

  2. Transition probabilities for atoms

    International Nuclear Information System (INIS)

    Current status of advanced theoretical methods for transition probabilities for atoms and ions is discussed. An experiment on the f values of the resonance transitions of the Kr and Xe isoelectronic sequences is suggested as a test for the theoretical methods

  3. Atomic homodyne detection of weak atomic transitions.

    Science.gov (United States)

    Gunawardena, Mevan; Elliott, D S

    2007-01-26

    We have developed a two-color, two-pathway coherent control technique to detect and measure weak optical transitions in atoms by coherently beating the transition amplitude for the weak transition with that of a much stronger transition. We demonstrate the technique in atomic cesium, exciting the 6s(2)S(1/2) --> 8s(2)S(1/2) transition via a strong two-photon transition and a weak controllable Stark-induced transition. We discuss the enhancement in the signal-to-noise ratio for this measurement technique over that of direct detection of the weak transition rate, and project future refinements that may further improve its sensitivity and application to the measurement of other weak atomic interactions.

  4. Atomic cranks and levers control sugar ring conformations

    International Nuclear Information System (INIS)

    In this paper we review the conformational analysis of sugar rings placed under tension during mechanical manipulations of single polysaccharide molecules with the atomic force microscope and during steered molecular dynamics simulations. We examine the role of various chemical bonds and linkages between sugar rings in inhibiting or promoting their conformational transitions by means of external forces. Small differences in the orientation of one chemical bond on the sugar ring can produce significantly different mechanical properties at the polymer level as exemplified by two polysaccharides: cellulose, composed of β-1→4-linked D-glucose, and amylose, composed of α-1→4-linked D-glucose. In contrast to β-glucose rings, which are mechanically stable and produce simple entropic elasticity of the chain, α-glucose rings flip under tension from their chair to a boat-like structure and these transitions produce deviations of amylose elasticity from the freely jointed chain model. We also examine the deformation of two mechanically complementary 1→6-linked polysaccharides: pustulan, a β-1→6-linked glucan, and dextran, a α-1→6-linked glucan. Forced rotations about the C5-C6 bonds govern the elasticity of pustulan, and complex conformational transitions that involve simultaneous C5-C6 rotations and chair-boat transitions govern the elasticity of dextran. Finally, we discuss the likelihood of various conformational transitions in sugar rings in biological settings and speculate on their significance

  5. Nuclear effects in atomic transitions

    CERN Document Server

    Pálffy, Adriana

    2011-01-01

    Atomic electrons are sensitive to the properties of the nucleus they are bound to, such as nuclear mass, charge distribution, spin, magnetization distribution, or even excited level scheme. These nuclear parameters are reflected in the atomic transition energies. A very precise determination of atomic spectra may thus reveal information about the nucleus, otherwise hardly accessible via nuclear physics experiments. This work reviews theoretical and experimental aspects of the nuclear effects that can be identified in atomic structure data. An introduction to the theory of isotope shifts and hyperfine splitting of atomic spectra is given, together with an overview of the typical experimental techniques used in high-precision atomic spectroscopy. More exotic effects at the borderline between atomic and nuclear physics, such as parity violation in atomic transitions due to the weak interaction, or nuclear polarization and nuclear excitation by electron capture, are also addressed.

  6. Nuclear effects in atomic transitions

    OpenAIRE

    Pálffy, Adriana

    2011-01-01

    Atomic electrons are sensitive to the properties of the nucleus they are bound to, such as nuclear mass, charge distribution, spin, magnetization distribution, or even excited level scheme. These nuclear parameters are reflected in the atomic transition energies. A very precise determination of atomic spectra may thus reveal information about the nucleus, otherwise hardly accessible via nuclear physics experiments. This work reviews theoretical and experimental aspects of the nuclear effects ...

  7. Conformational transitions of a weak polyampholyte

    KAUST Repository

    Narayanan Nair, Arun Kumar

    2014-10-07

    Using grand canonical Monte Carlo simulations of a flexible polyelectrolyte where the charges are in contact with a reservoir of constant chemical potential given by the solution pH, we study the behavior of weak polyelectrolytes in poor and good solvent conditions for polymer backbone. We address the titration behavior and conformational properties of a flexible diblock polyampholyte chain formed of two oppositely charged weak polyelectrolyte blocks, each containing equal number of identical monomers. The change of solution pH induces charge asymmetry in a diblock polyampholyte. For diblock polyampholyte chains in poor solvents, we demonstrate that a discontinuous transition between extended (tadpole) and collapsed (globular) conformational states is attainable by varying the solution pH. The double-minima structure in the probability distribution of the free energy provides direct evidence for the first-order like nature of this transition. At the isoelectric point electrostatically driven coil-globule transition of diblock polyampholytes in good solvents is found to consist of different regimes identified with increasing electrostatic interaction strength. At pH values above or below the isoelectric point diblock chains are found to have polyelectrolyte-like behavior due to repulsion between uncompensated charges along the chain.

  8. Theoretical Studies of Atomic Transitions

    International Nuclear Information System (INIS)

    Atomic structure calculations were performed for properties such as energy levels, binding energies, transition probabilities, lifetimes, hyperfine structure, and isotope shifts. Accurate computational procedures were devised so that properties could be predicted even when they could not be obtained from experiment, and to assist in the identification of observed data. The method used was the multiconfiguration Hartree-Fock (MCHF) method, optionally corrected for relativistic effects in the Breit-Pauli approximation. Fully relativistic Dirac-Fock calculations also were performed using the GRASP code A database of energy levels, lifetimes, and transition probabilities was designed and implemented and, at present, includes many results for Be-like to Ar-like

  9. Atomic inner-shell transitions

    Science.gov (United States)

    Crasemann, B.; Chen, M. H.; Mark, H.

    1984-01-01

    Atomic inner-shell processes have quite different characteristics, in several important aspects, from processes in the optical regime. Energies are large, e.g., the 1s binding energy reaches 100 keV at Z = 87; relativistic and quantum-electrodynamic effects therefore are strong. Radiationless transitions vastly dominate over photon emission in most cases. Isolated inner-shell vacancies have pronounced single-particle character, with correlations generally contributing only approximately 1 eV to the 1s and 2p binding energies; the structure of such systems is thus well tractable by independent-particle self-consistent-field atomic models. For systems containing multiple deep inner-shell vacancies, or for highly stripped ions, the importance of relativistic intermediate coupling and configuration interaction becomes pronounced. Cancellation of the Coulomb interaction can lead to strong manifestations of the Breit interaction in such phenomena as multiplet splitting and hypersatellite X-ray shifts. Unique opportunities arise for the test of theory.

  10. Conformational Transition of Poly (Acrylic Acid) Detected by Microcantilever Sensing

    Institute of Scientific and Technical Information of China (English)

    LI Kai; LIU Hong; ZHANG Qing-Chuan; XUE Chang-Guo; WU Xiao-Ping

    2007-01-01

    Poly (acrylic acid) (PAA) chains are grafted on one side of a microcantilever by the self-assembled method and the deflections of the microcantilever are detected as a function of medium pH from 3 to 11. It is found that when the pH varies, the microcantilever deflects because of the changing surface stress. By analysing the electrostatic repulsive effect, the surface stress change is related to the conformation transition of PAA from a collapse state to a swelling state. This method offers the interaction information among the polymer chains during the conformational transition and affords an alternative way to study conformational change of polymers.

  11. Fluctuation Flooding Method (FFM) for accelerating conformational transitions of proteins

    Science.gov (United States)

    Harada, Ryuhei; Takano, Yu; Shigeta, Yasuteru

    2014-03-01

    A powerful conformational sampling method for accelerating structural transitions of proteins, "Fluctuation Flooding Method (FFM)," is proposed. In FFM, cycles of the following steps enhance the transitions: (i) extractions of largely fluctuating snapshots along anisotropic modes obtained from trajectories of multiple independent molecular dynamics (MD) simulations and (ii) conformational re-sampling of the snapshots via re-generations of initial velocities when re-starting MD simulations. In an application to bacteriophage T4 lysozyme, FFM successfully accelerated the open-closed transition with the 6 ns simulation starting solely from the open state, although the 1-μs canonical MD simulation failed to sample such a rare event.

  12. Quantum Hall transitions: An exact theory based on conformal restriction

    OpenAIRE

    Bettelheim, E.; Gruzberg, I. A.; Ludwig, A. W. W.

    2012-01-01

    We revisit the problem of the plateau transition in the integer quantum Hall effect. Here we develop an analytical approach for this transition, based on the theory of conformal restriction. This is a mathematical theory that was recently developed within the context of the Schramm-Loewner evolution which describes the stochastic geometry of fractal curves and other stochastic geometrical fractal objects in 2D space. Observables elucidating the connection with the plateau transition include t...

  13. Maximum Flux Transition Paths of Conformational Change

    CERN Document Server

    Zhao, Ruijun; Skeel, Robert D

    2009-01-01

    Given two metastable states A and B of a biomolecular system, the problem is to calculate the likely paths of the transition from A to B. Such a calculation is more informative and more manageable if done for a reduced set of collective variables chosen so that paths cluster in collective variable space. The computational task becomes that of computing the "center" of such a cluster. A good way to define the center employs the concept of a committor, whose value at a point in collective variable space is the probability that a trajectory at that point will reach B before A. The committor "foliates" the transition region into a collection of isocommittors. The maximum flux transition path is defined as a path that crosses each isocommittor at a point which (locally) has the highest crossing rate of distinct reactive trajectories. (This path is different from that of the MaxFlux method of Huo and Straub.) To make the calculation tractable, three approximations are introduced. It is shown that a maximum flux tra...

  14. Visualisation of xanthan conformation by atomic force microscopy.

    Science.gov (United States)

    Moffat, Jonathan; Morris, Victor J; Al-Assaf, Saphwan; Gunning, A Patrick

    2016-09-01

    Direct visual evidence obtained by atomic force microscopy demonstrates that when xanthan is adsorbed from aqueous solution onto the heterogeneously charged substrate mica, its helical conformation is distorted. Following adsorption it requires annealing for several hours to restore its ordered helical state. Once the helix state reforms, the AFM images obtained showed clear resolution of the periodicity with a value of 4.7nm consistent with the previously predicted models. In addition, the images also reveal evidence that the helix is formed by a double strand, a clarification of an ambiguity of the xanthan ultrastructure that has been outstanding for many years. PMID:27185152

  15. Many-Body Theory of Atomic Transitions

    Science.gov (United States)

    Holmes, Charles Potter

    This dissertation presents a systematic approach to the derivation of transition widths and cross sections for atomic radiative and/or nonradiative processes. By applying the transition theory of Goldberger and Watson ^1, all transition properties are derived from proper solutions of the time-dependent Schrodinger equation. The focus is on situations where initial and final wave functions are nonorthogonal functions that belong to different self-consistent fields. This approach is particularly useful in the treatment of ionizing transitions where the outgoing free electron sees a different atomic potential from that of the initial bound state. Transition amplitudes are expressed as perturbation expansions in which singularities have been removed algebraically. These singularities are due to states which are degenerate with the initial and final states and represent the competing transition channels. The perturbation expansions show clearly the role of the nonorthogonality of the participating states leading to terms representing "shake" processes competing with higher-order electron correlation processes. Transition amplitudes including all second-order processes, are derived for the following transitions: X-ray, Auger, photoionization, radiative recombination, dielectronic recombination, radiative -Auger. Comparisons are made with the expressions frequently used by other workers. Using a Hartree-Fock-Slater model K- and L-shell X-ray and Auger transition widths are calculated for the range 5 Z Theory, (John Wiley & Sons, New York, 1964), Chapter 8, page 424.

  16. Molecular motions and conformational transition between different conformational states of HIV-1 gp120 envelope glycoprotein

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The HIV-1 gp120 exterior envelope glycoprotein undergoes a series of conformational rearrangements while sequentially interacting with the receptor CD4 and coreceptor CCR5 or CXCR4 on the surface of host cells to initiate virus entry. Both the crystal structures of the HIV-1 gp120 core bound by the CD4 and antigen 17b and the SIV gp120 core prebound by CD4 are known. Despite the wealth of knowledge on these static snapshots of molecular conformations, the details of molecular motions involved in conformational transition that are crucial to intervention remain elusive. We presented comprehensive comparative analyses of the dynamics behaviors of the gp120 in its CD4-complexed, CD4-free and CD4-unliganded states based on the homology models with modeled V3 and V4 loops by means of CONCOORD computer simulation to generate ensembles of feasible protein structures that were subsequently analysed by essential dynamics analyses to identify preferred concerted motions. The revealed collective fluctuations are dominated by complex modes of combinational motions of the rotation/twisting, flexing/closure, and shortness/elongation between or within the inner, outer, and bridging-sheet domains, and these modes are related to the CD4 association and HIV neutralization avoidance. Further essential subspace overlap analyses were performed to quantitatively distinguish the preference for conformational transitions between the three states, revealing that the unliganded gp120 has a greater potential to translate its conformation into the conformational state adopted by the CD4-complexed gp120 than by the CD4-free gp120, whereas the CD4-free gp120 has a greater potential to translate its conformation into the unliganded state than the CD4-complexed gp120 does. These dy-namics data of gp120 in its different conformations are helpful in understanding the relationship be-tween the molecular motion/conformational transition and the function of gp120, and in gp120-structure-based subunit

  17. Continuum ionization transition probabilities of atomic oxygen

    Science.gov (United States)

    Samson, J. A. R.; Petrosky, V. E.

    1974-01-01

    The technique of photoelectron spectroscopy was employed in the investigation. Atomic oxygen was produced in a microwave discharge operating at a power of 40 W and at a pressure of approximately 20 mtorr. The photoelectron spectrum of the oxygen with and without the discharge is shown. The atomic states can be clearly seen. In connection with the measurement of the probability for transitions into the various ionic states, the analyzer collection efficiency was determined as a function of electron energy.

  18. Axion dark matter detection using atomic transitions.

    Science.gov (United States)

    Sikivie, P

    2014-11-14

    Dark matter axions may cause transitions between atomic states that differ in energy by an amount equal to the axion mass. Such energy differences are conveniently tuned using the Zeeman effect. It is proposed to search for dark matter axions by cooling a kilogram-sized sample to millikelvin temperatures and count axion induced transitions using laser techniques. This appears to be an appropriate approach to axion dark matter detection in the 10^{-4}  eV mass range.

  19. Axion Dark Matter Detection using Atomic Transitions

    CERN Document Server

    Sikivie, P

    2014-01-01

    Dark matter axions may cause transitions between atomic states that differ in energy by an amount equal to the axion mass. Such energy differences are conveniently tuned using the Zeeman effect. It is proposed to search for dark matter axions by cooling a kilogram-sized sample to milliKelvin temperatures and count axion induced transitions using laser techniques. This appears an appropriate approach to axion dark matter detection in the $10^{-4}$ eV mass range.

  20. Atomic transition probabilities of neutral samarium

    International Nuclear Information System (INIS)

    Absolute atomic transition probabilities from a combination of new emission branching fraction measurements using Fourier transform spectrometer data with radiative lifetimes from recent laser induced fluorescence measurements are reported for 299 lines of the first spectrum of samarium (Sm i). Improved values for the upper and lower energy levels of these lines are also reported. Comparisons to published transition probabilities from earlier experiments show satisfactory and good agreement with two of the four published data sets. (paper)

  1. Quantum Hall transitions: An exact theory based on conformal restriction

    Science.gov (United States)

    Bettelheim, E.; Gruzberg, I. A.; Ludwig, A. W. W.

    2012-10-01

    We revisit the problem of the plateau transition in the integer quantum Hall effect. Here we develop an analytical approach for this transition, and for other two-dimensional disordered systems, based on the theory of “conformal restriction.” This is a mathematical theory that was recently developed within the context of the Schramm-Loewner evolution which describes the “stochastic geometry” of fractal curves and other stochastic geometrical fractal objects in two-dimensional space. Observables elucidating the connection with the plateau transition include the so-called point-contact conductances (PCCs) between points on the boundary of the sample, described within the language of the Chalker-Coddington network model for the transition. We show that the disorder-averaged PCCs are characterized by a classical probability distribution for certain geometric objects in the plane (which we call pictures), occurring with positive statistical weights, that satisfy the crucial so-called restriction property with respect to changes in the shape of the sample with absorbing boundaries; physically, these are boundaries connected to ideal leads. At the transition point, these geometrical objects (pictures) become fractals. Upon combining this restriction property with the expected conformal invariance at the transition point, we employ the mathematical theory of “conformal restriction measures” to relate the disorder-averaged PCCs to correlation functions of (Virasoro) primary operators in a conformal field theory (of central charge c=0). We show how this can be used to calculate these functions in a number of geometries with various boundary conditions. Since our results employ only the conformal restriction property, they are equally applicable to a number of other critical disordered electronic systems in two spatial dimensions, including for example the spin quantum Hall effect, the thermal metal phase in symmetry class D, and classical diffusion in two

  2. Resonant quantum transitions in trapped antihydrogen atoms

    CERN Document Server

    Amole, C; Baquero-Ruiz, M; Bertsche, W; Bowe, P D; Butler, E; Capra, A; Cesar, C L; Charlton, M; Deller, A; Donnan, P H; Eriksson, S; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayden, M E; Humphries, A J; Isaac, C A; Jonsell, S; Kurchaninov, L; Little, A; Madsen, N; McKenna, J T K; Menary, S; Napoli, S C; Nolan, P; Olchanski, K; Olin, A; Pusa, P; Rasmussen, C Ø; Robicheaux, F; Sarid, E; Shields, C R; Silveira, D M; Stracka, S; So, C; Thompson, R I; van der Werf, D P; Wurtele, J S

    2012-01-01

    The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom’s stature lies in its simplicity and in the accuracy with which its spectrum can be measured1 and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and—by comparison with measurements on its antimatter counterpart, antihydrogen—the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state2, 3 of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave...

  3. Conformational and phase transitions in DNA--photosensitive surfactant solutions: Experiment and modeling.

    Science.gov (United States)

    Kasyanenko, N; Lysyakova, L; Ramazanov, R; Nesterenko, A; Yaroshevich, I; Titov, E; Alexeev, G; Lezov, A; Unksov, I

    2015-02-01

    DNA binding to trans- and cis-isomers of azobenzene containing cationic surfactant in 5 mM NaCl solution was investigated by the methods of dynamic light scattering (DLS), low-gradient viscometry (LGV), atomic force microscopy (AFM), circular dichroism (CD), gel electrophoresis (GE), flow birefringence (FB), UV-Vis spectrophotometry. Light-responsive conformational transitions of DNA in complex with photosensitive surfactant, changes in DNA optical anisotropy and persistent length, phase transition of DNA into nanoparticles induced by high surfactant concentration, as well as transformation of surfactant conformation under its binding to macromolecule were studied. Computer simulations of micelles formation for cis- and trans-isomers of azobenzene containing surfactant, as well as DNA-surfactant interaction, were carried out. Phase diagram for DNA-surfactant solutions was designed. The possibility to reverse the DNA packaging induced by surfactant binding with the dilution and light irradiation was shown.

  4. Conformational Transition Pathways in Signaling and Enzyme Catalysis Explored by Computational Methods

    Science.gov (United States)

    Pachov, Dimitar V.

    Biomolecules are dynamic in nature and visit a number of states while performing their biological function. However, understanding how they interconvert between functional substates is a challenging task. In this thesis, we employ enhanced computational strategies to reveal in atomistic resolution transition states and molecular mechanism along conformational pathways of the signaling protein Nitrogen Regulatory Protein C (NtrC) and the enzyme Adenylate Kinase (Adk). Targeted Molecular Dynamics (TMD) simulations and NMR experiments have previously found the active/inactive interconversion of NtrC is stabilized by non-native transient contacts. To find where along the conformational pathway they lie and probe the existence of multiple intermediates, a beyond 8mus-extensive mapping of the conformational landscape was performed by a multitude of straightforward MD simulations relaxed from the biased TMD pathway. A number of metastable states stabilized by local interactions was found to underline the conformational pathway of NtrC. Two spontaneous transitions of the last stage of the active-to-inactive conversion were identified and used in path sampling procedures to generate an ensemble of truly dynamic reactive pathways. The transition state ensemble (TSE) and mechanistic descriptors of this transition were revealed in atomic detail and verified by committor analysis. By analyzing how pressure affects the dynamics and function of two homologous Adk proteins - the P.Profundum Adk surviving at 700atm pressure in the deep sea, and the E. coli Adk that lives at ambient pressures - we indirectly obtained atomic information about the TSE of the large-amplitude rate-limiting conformational opening of the Adk lids. Guided by NMR experiments showing significantly decreased activation volumes of the piezophile compared to its mesophilic counterpart, TMD simulations revealed the formation of an extended hydrogen-bonded water network in the transition state of the piezophile

  5. Protein-segment universe exhibiting transitions at intermediate segment length in conformational subspaces

    Directory of Open Access Journals (Sweden)

    Hirokawa Takatsugu

    2008-08-01

    Full Text Available Abstract Background Many studies have examined rules governing two aspects of protein structures: short segments and proteins' structural domains. Nevertheless, the organization and nature of the conformational space of segments with intermediate length between short segments and domains remain unclear. Conformational spaces of intermediate length segments probably differ from those of short segments. We investigated the identification and characterization of the boundary(s between peptide-like (short segment and protein-like (long segment distributions. We generated ensembles embedded in globular proteins comprising segments 10–50 residues long. We explored the relationships between the conformational distribution of segments and their lengths, and also protein structural classes using principal component analysis based on the intra-segment Cα-Cα atomic distances. Results Our statistical analyses of segment conformations and length revealed critical dual transitions in their conformational distribution with segments derived from all four structural classes. Dual transitions were identified with the intermediate phase between the short segments and domains. Consequently, protein segment universes were categorized. i Short segments (10–22 residues showed a distribution with a high frequency of secondary structure clusters. ii Medium segments (23���26 residues showed a distribution corresponding to an intermediate state of transitions. iii Long segments (27–50 residues showed a distribution converging on one huge cluster containing compact conformations with a smaller radius of gyration. This distribution reflects the protein structures' organization and protein domains' origin. Three major conformational components (radius of gyration, structural symmetry with respect to the N-terminal and C-terminal halves, and single-turn/two-turn structure well define most of the segment universes. Furthermore, we identified several

  6. Electric quadrupole transition probabilities for atomic lithium

    International Nuclear Information System (INIS)

    Electric quadrupole transition probabilities for atomic lithium have been calculated using the weakest bound electron potential model theory (WBEPMT). We have employed numerical non-relativistic Hartree–Fock wavefunctions for expectation values of radii and the necessary energy values have been taken from the compilation at NIST. The results obtained with the present method agree very well with the Coulomb approximation results given by Caves (1975). Moreover, electric quadrupole transition probability values not existing in the literature for some highly excited levels have been obtained using the WBEPMT

  7. Surface immobilization of antibody on silk fibroin through conformational transition.

    Science.gov (United States)

    Lu, Qiang; Wang, Xiaoqin; Zhu, Hesun; Kaplan, David L

    2011-07-01

    In recent studies silk fibroin has been explored as a new material platform for biosensors. Based on these developments, a procedure for the immobilization of antibodies on silk fibroin substrates was developed as a route to functionalizing these biosensor systems. By controlling the conformational transition of the silk fibroin, a primary antibody was immobilized and enriched at the surface of silk fibroin substrates under mild reaction conditions to maintain antibody function. Compared to chemical crosslinking, the immobilization efficiency in the present approach was increased significantly. This method, achieving high loading of antibody while retaining function, improves the feasibility of silk fibroin as a platform material for biosensor applications.

  8. Atomic Transition Probabilities Scandium through Manganese

    International Nuclear Information System (INIS)

    Atomic transition probabilities for about 8,800 spectral lines of five iron-group elements, Sc(Z = 21) to Mn(Z = 25), are critically compiled, based on all available literature sources. The data are presented in separate tables for each element and stage of ionization and are further subdivided into allowed (i.e., electric dipole-E1) and forbidden (magnetic dipole-M1, electric quadrupole-E2, and magnetic quadrupole-M2) transitions. Within each data table the spectral lines are grouped into multiplets, which are in turn arranged according to parent configurations, transition arrays, and ascending quantum numbers. For each line the transition probability for spontaneous emission and the line strength are given, along with the spectroscopic designation, the wavelength, the statistical weights, and the energy levels of the upper and lower states. For allowed lines the absorption oscillator strength is listed, while for forbidden transitions the type of transition is identified (M1, E2, etc.). In addition, the estimated accuracy and the source are indicated. In short introductions, which precede the tables for each ion, the main justifications for the choice of the adopted data and for the accuracy rating are discussed. A general introduction contains a discussion of our method of evaluation and the principal criteria for our judgements

  9. Augmenting Transition Probabilities for Neutral Atomic Nitrogen

    Science.gov (United States)

    Terrazas-Salines, Imelda; Park, Chul; Strawa, Anthony W.; Hartman, G. Joseph (Technical Monitor)

    1996-01-01

    The transition probability values for a number of neutral atomic nitrogen (NI) lines in the visible wavelength range are determined in order to augment those given in the National Bureau of Standards Tables. These values are determined from experimentation as well as by using the published results of other investigators. The experimental determination of the lines in the 410 to 430 nm range was made from the observation of the emission from the arc column of an arc-heated wind tunnel. The transition probability values of these NI lines are determined to an accuracy of +/- 30% by comparison of their measured intensities with those of the atomic oxygen (OI) multiplet at around 615 nm. The temperature of the emitting medium is determined both using a multiple-layer model, based on a theoretical model of the flow in the arc column, and an empirical single-layer model. The results show that the two models lead to the same values of transition probabilities for the NI lines.

  10. Nuclear polarizability of helium isotopes in atomic transitions

    OpenAIRE

    Pachucki, K.; Moro, A. M.

    2006-01-01

    We estimate the nuclear polarizability correction to atomic transition frequencies in various helium isotopes. This effect is non-negligible for high precision tests of quantum electrodynamics or accurate determination of the nuclear charge radius from spectroscopic measurements in helium atoms and ions. In particular, it amounts to $28(3)$ kHz for 1S-2S transition in 4He+.

  11. Phase transitions, geometrothermodynamics and critical exponents of black holes with conformal anomaly

    CERN Document Server

    Liu, Jie-Xiong Mo Wen-Biao

    2013-01-01

    We investigate the phase transitions of black holes with conformal anomaly in canonical ensemble from different perspectives. Some interesting and novel phase transition phenomena have been discovered. Firstly, we discuss the behavior of the specific heat and the inverse of the isothermal compressibility. It is shown that there are striking differences in Hawking temperature and phase structure between black holes with conformal anomaly and those without it. In the case with conformal anomaly, there exists local minimum temperature corresponding to the phase transition point. Phase transitions take place not only from an unstable large black hole to a locally stable medium black hole but also from an unstable medium black hole to a locally stable small black hole. Secondly, we probe in details the dependence of phase transitions on the choice of parameters. The results show that black holes with conformal anomaly have much richer phase structure than those without it. There would be two, only one or no phase ...

  12. Electric Field-induced Conformational Transition of Bovine Serum Albumin from α -helix to β -sheet

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The irreversible conformational transition of bovine serum albumin (BSA) from α -helix to β -sheet, induced by electric field near the electrode surface, was monitored by circular dichroism (CD) with a long optical path thin layer cell (LOPTLC).

  13. Interplay of Nitrogen-Atom Inversion and Conformational Inversion in Enantiomerization of 1H-1-Benzazepines.

    Science.gov (United States)

    Ramig, Keith; Subramaniam, Gopal; Karimi, Sasan; Szalda, David J; Ko, Allen; Lam, Aaron; Li, Jeffrey; Coaderaj, Ani; Cavdar, Leyla; Bogdan, Lukasz; Kwon, Kitae; Greer, Edyta M

    2016-04-15

    A series of 2,4-disubstituted 1H-1-benzazepines, 2a-d, 4, and 6, were studied, varying both the substituents at C2 and C4 and at the nitrogen atom. The conformational inversion (ring-flip) and nitrogen-atom inversion (N-inversion) energetics were studied by variable-temperature NMR spectroscopy and computations. The steric bulk of the nitrogen-atom substituent was found to affect both the conformation of the azepine ring and the geometry around the nitrogen atom. Also affected were the Gibbs free energy barriers for the ring-flip and the N-inversion. When the nitrogen-atom substituent was alkyl, as in 2a-c, the geometry of the nitrogen atom was nearly planar and the azepine ring was highly puckered; the result was a relatively high-energy barrier to ring-flip and a low barrier to N-inversion. Conversely, when the nitrogen-atom substituent was a hydrogen atom, as in 2d, 4, and 6, the nitrogen atom was significantly pyramidalized and the azepine ring was less puckered; the result here was a relatively high energy barrier to N-inversion and a low barrier to ring-flip. In these N-unsubstituted compounds, it was found computationally that the lowest-energy stereodynamic process was ring-flip coupled with N-inversion, as N-inversion alone had a much higher energy barrier.

  14. Unified set of atomic transition probabilities for neutral argon

    OpenAIRE

    Wiese, W.; Brault, J.; Danzmann, K.; Helbig, V.; de Kock, M

    1989-01-01

    The atomic transition probabilities and radiative lifetimes of neutral argon have been the subject of numerous experiments and calculations, but the results exhibit many discrepancies and inconsistencies. We present a unified set of atomic transition probabilities, which is consistent with essentially all recent results, albeit sometimes only after critical reanalysis. The data consistency and scale confirmation has been achieved in two ways. (i) We have carried out some lifetime–branching-ra...

  15. Transition rates in proton - Rydberg atom collisions

    Science.gov (United States)

    Vrinceanu, Daniel

    2016-05-01

    Monte Carlo simulations for energy and angular momentum transfer processes in proton - Ryderg atom collisions were performed and the corresponding rates are reported.The relevance of these rates in the context of cosmological recombination is discussed. The rates are contrasted with the similar rates in electron - Rydberg atom collisions. This work has been supported by National Science Foundation through grants for the Center for Research on Complex Networks (HRD-1137732) and Research Infrastructure for Science and Engineering (RISE) (HRD-1345173).

  16. Coherent backscattering of light by resonant atomic dipole transitions

    International Nuclear Information System (INIS)

    We study coherent backscattering (CBS) of resonant light by cold atomic vapors, both experimentally and theoretically. The theory predicts a drastic reduction of the CBS enhancement factor when a degenerate internal structure is present in the ground state. We test this prediction in experiments using different atoms and various transitions

  17. Quantum phase transition and entanglement in Li atom system

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    By use of the exact diagonalization method, the quantum phase transition and en- tanglement in a 6-Li atom system are studied. It is found that entanglement appears before the quantum phase transition and disappears after it in this exactly solvable quantum system. The present results show that the von Neumann entropy, as a measure of entanglement, may reveal the quantum phase transition in this model.

  18. Investigating protein conformational energy landscapes and atomic resolution dynamics from NMR dipolar couplings: a review.

    Science.gov (United States)

    Salmon, Loïc; Blackledge, Martin

    2015-12-01

    Nuclear magnetic resonance spectroscopy is exquisitely sensitive to protein dynamics. In particular inter-nuclear dipolar couplings, that become measurable in solution when the protein is dissolved in a dilute liquid crystalline solution, report on all conformations sampled up to millisecond timescales. As such they provide the opportunity to describe the Boltzmann distribution present in solution at atomic resolution, and thereby to map the conformational energy landscape in unprecedented detail. The development of analytical methods and approaches based on numerical simulation and their application to numerous biologically important systems is presented. PMID:26517337

  19. Conformational Transitions in Silver Nanoparticals: DNA and Photoirradiation

    CERN Document Server

    Bregadze, Vasil G; Giorgadze, Tamar G

    2012-01-01

    Photoirradiation of silver nanoparticles in water solution of NaNO3 (0.01M) and in dissolved DNA was investigated by spectrophotometric and thermodynamic kinetic approaches. It is shown that only the irradiated complexes AgNPs-DNA have distinctly expressed isosbestic point. The test with the free AgNPs demonstrates that as a result of photo-irradiation desorption of silver atoms and their oxidation takes place. We have also observed that at photo-irradiation of the complexes by AgNPs-DNA desorption of silver atoms from the surface of AgNPs takes place. Kinetic study of photo-desorption of silver atoms has allowed to estimate desorption rate constant and the heat of adsorption for free AgNPs and AgNPs bound with DNA. On DNA example toxicity of AgNPs at their application to photo-chemo and photo-thermo therapy of cancer is discussed.

  20. Control of atomic transition rates via laser light shaping

    CERN Document Server

    Jauregui, R

    2015-01-01

    A modular systematic analysis of the feasibility of modifying atomic transition rates by tailoring the electromagnetic field of an external coherent light source is presented. The formalism considers both the center of mass and internal degrees of freedom of the atom, and all properties of the field: frequency, angular spectrum, and polarization. General features of recoil effects for internal forbidden transitions are discussed. A comparative analysis of different structured light sources is explicitly worked out. It includes spherical waves, Gaussian beams, Laguerre-Gaussian beams, and propagation invariant beams with closed analytical expressions. It is shown that increments in the order of magnitude of the transition rates for Gaussian and Laguerre-Gaussian beams, with respect to those obtained in the paraxial limit, requires waists of the order of the wavelength, while propagation invariant modes may considerably enhance transition rates under more favorable conditions. For transitions that can be natura...

  1. Observation of Aubry transition in finite atom chains via friction

    CERN Document Server

    Bylinskii, Alexei; Counts, Ian; Vuletic, Vladan

    2015-01-01

    The highly nonlinear many-body physics of a chain of mutually interacting atoms in contact with a periodic substrate gives rise to complex static and dynamical phenomena, such as structural phase transitions and friction. In the limit of an infinite chain incommensurate with the substrate, Aubry predicted a structural transition with increasing substrate potential, from the chain's intrinsic arrangement free to slide on the substrate, to a pinned arrangement favoring the substrate pattern. To date, the Aubry transition has not been observed. Here, using a chain of cold ions subject to a periodic optical potential we qualitatively and quantitatively establish a close relation between Aubry's sliding-to-pinned transition and superlubricity breaking in stick-slip friction. Using friction measurements with high spatial resolution and individual ion detection, we experimentally observe the Aubry transition and the onset of its hallmark fractal atomic arrangement. Notably, the observed critical lattice depth for a ...

  2. Allowed and forbidden transitions in artificial hydrogen and helium atoms.

    Science.gov (United States)

    Fujisawa, Toshimasa; Austing, David Guy; Tokura, Yasuhiro; Hirayama, Yoshiro; Tarucha, Seigo

    2002-09-19

    The strength of radiative transitions in atoms is governed by selection rules that depend on the occupation of atomic orbitals with electrons. Experiments have shown similar electron occupation of the quantized energy levels in semiconductor quantum dots--often described as artificial atoms. But unlike real atoms, the confinement potential of quantum dots is anisotropic, and the electrons can easily couple with phonons of the material. Here we report electrical pump-and-probe experiments that probe the allowed and 'forbidden' transitions between energy levels under phonon emission in quantum dots with one or two electrons (artificial hydrogen and helium atoms). The forbidden transitions are in fact allowed by higher-order processes where electrons flip their spin. We find that the relaxation time is about 200 micro s for forbidden transitions, 4 to 5 orders of magnitude longer than for allowed transitions. This indicates that the spin degree of freedom is well separated from the orbital degree of freedom, and that the total spin in the quantum dots is an excellent quantum number. This is an encouraging result for potential applications of quantum dots as basic entities for spin-based quantum information storage.

  3. Spectroscopy Investigation on Conformational Transition of Tea Glycoconjugate from Green Tea

    Institute of Scientific and Technical Information of China (English)

    CHEN,Hai-Xia(陈海霞); ZHANG,Min(张民); XIE,Bi-Jun(谢笔钧)

    2004-01-01

    The conformational transition of a new glycoconjugate,tea glycoconjugate(TGC),was investigated by spectroscopy techniques including circular dichroism(CD)and ultraviolet(UV)spectroscopy.The solution behaviors of TGC inthe mediums of different temperature,pH value,and ions were compared.Results showed that the native conformation of TGC was partially ordered.The CD value and UV absorbance of TGC altered with the change of pH value,temperature,the addition of ions,and also accompanied order-disorder transition.Especially the conditions with temperature higher than the glasstransition temperature(Tg=62℃),higher pH value orlower pH value will have the most impact on the conformation of TGC,which will destroy the hydrogen bonds between the TGC molecules.The results indicated that the outside factors playimportant roles onthe stability of the conformation of TGC.

  4. Pressure-induced conformation transition of o-phenylene solvated in bulk hydrocarbons.

    Science.gov (United States)

    Riello, Massimo; Doni, Giovanni; Filip, Sorin V; Gold, Martin; De Vita, Alessandro

    2014-11-26

    The conformational behavior of o-phenylene 8-mers and 10-mers solvated in a series of linear alkane solvents by means of classical molecular dynamics and first-principles calculations was studied. Irrespective of the solvent used, we find that at ambient pressure the molecule sits in the well-defined close-helical arrangement previously observed in light polar solvents. However, for pressures greater than 50 atm, and for tetradecane or larger solvent molecules, our simulations predict that o-phenylene undergoes a conformational transition to an uncoiled, extended geometry with a 35% longer head-to-tail distance and a much larger overlap between its lateral aromatic ring groups. The free energy barrier for the transition was studied as a function of pressure and temperature for both solute molecules in butane and hexadecane. Gas-phase density functional theory-based nudged elastic band calculations on 8-mer and 10-mer o-phenylene were used to estimate how the pressure-induced transition energy barrier changes with solute length. Our results indicate that a sufficiently large solvent molecule size is the key factor enabling a configuration transition upon pressure changes and that longer solute molecules associate with higher conformation transition energy barriers. This suggests the possibility of designing systems in which a solute molecule can be selectively "activated" by a controlled conformation transition achieved at a predefined set of pressure and temperature conditions.

  5. Anomalous conformational transitions in cytochrome C adsorbing to Langmuir-Blodgett films

    Science.gov (United States)

    Sankaranarayanan, Kamatchi; Nair, B. U.; Dhathathreyan, A.

    2013-05-01

    Helix to beta conformational transitions in proteins has attracted much attention due to their relevance to fibril formation which is implicated in many neurological diseases. This study reports on unusual conformational transition of cytochrome C adsorbing to hydrophilic surface containing pure cationic lipid and mixed Langmuir-Blodgett films (LB films) of cationic and neutral lipids. Evidence for conformational changes of the protein from its native helical state to beta sheet comes from Circular dichroic spectroscopy (CD spectroscopy). Analysis of these samples using High resolution TEM (HRTEM) shows a typical fibrillar pattern with each strand spacing of about 0.41 nm across which can be attributed to the repeat distance of interdigitated neighboring hydrogen-bonded ribbons in a beta sheet. Changes in contact angles of protein adsorbing to the LB films together with the increased mass uptake of water using quartz crystal microbalance (QCM) confirm the role of positive charges in the conformational transition. Dehydration of the protein resulting from the excess water entrainment in the polar planes of the cationic lipid in hydrophilic surface seems to trigger the refolding of the protein to beta sheet while it retains its native conformation in hydrophobic films. The results suggest that drastic conformational changes in CytC adsorbing to cationic lipids may be of significance in its role as a peripheral membrane protein.

  6. Conformational transitions of single polymer adsorption in poor solvent: Wetting transition due to molecular confinement induced line tension

    Science.gov (United States)

    Wei, Hsien-Hung; Li, Yen-Ching

    2016-07-01

    We report a theory capable of describing conformational transitions for single polymer adsorption in a poor solvent. We show that an additional molecular confinement effect near the contact line can act exactly like line tension, playing a critical role in the behavior of an absorbed polymer chain. Using this theory, distinct conformational states: desorbed globule (DG), surface attached cap (SAC), and adsorbed lens (AL), can be vividly revealed, resembling the drying-wetting transition of a nanodroplet. But the transitions between these states can behave rather differently from those in the usual wetting transitions. The DG-SAC transition is discrete, occurring at the adsorption threshold when the globule size at the desorbed state is equal to the adsorption blob. The SAC-AL transition is smooth for finite chain lengths, but can change to discontinuous in the infinite chain limit, characterized by the different end-to-end exponent 3/8 and the unique crossover exponent 1/4. Distinctive critical exponents near this transition are also determined, indicating that it is an additional universality class of phase transitions. This work also sheds light on nanodrop spreading, wherein the important role played by line tension might simply be a manifestation of the local molecular confinement near the contact line.

  7. Magnetism and electronic phase transitions in monoclinic transition metal dichalcogenides with transition metal atoms embedded

    Science.gov (United States)

    Lin, Xianqing; Ni, Jun

    2016-08-01

    First-principles calculations have been performed to study the energetic, electronic, and magnetic properties of substitutional 3d transition metal dopants in monoclinic transition metal dichalcogenides (TMDs) as topological insulators ( 1 T ' - MX 2 with M = (Mo, W) and X = (S, Se)). We find various favorite features in these doped systems to introduce magnetism and other desirable electronic properties: (i) The Mn embedded monoclinic TMDs are magnetic, and the doped 1 T ' - MoS 2 still maintains the semiconducting character with high concentration of Mn, while an electronic phase transition occurs in other Mn doped monoclinic TMDs with an increasing concentration of Mn. Two Mn dopants prefer the ferromagnetic coupling except for substitution of the nearest Mo atoms in 1 T ' - MoS 2 , and the strength of exchange interaction shows anisotropic behavior with dopants along one Mo zigzag chain having much stronger coupling. (ii) The substitutional V is a promising hole dopant, which causes little change to the energy dispersion around the conduction and valence band edges in most systems. In contrast, parts of the conduction band drop for the electron dopants Co and Ni due to the large structural distortion. Moreover, closing band gaps of the host materials are observed with increasing carrier concentration. (iii) Single Fe dopant has a magnetic moment, but it also dopes electrons. When two Fe dopants have a small distance, the systems turn into nonmagnetic semiconductors. (iv) The formation energies of all dopants are much lower than those in hexagonal TMDs and are all negative in certain growth conditions, suggesting possible realization of the predicted magnetism, electronic phase transitions as well as carrier doping in 1 T ' - MX 2 based topological devices.

  8. Supramolecular chemical shift reagents inducing conformational transitions: NMR analysis of carbohydrate homooligomer mixtures

    DEFF Research Database (Denmark)

    Beeren, Sophie; Meier, Sebastian

    2015-01-01

    We introduce the concept of supramolecular chemical shift reagents as a tool to improve signal resolution for the NMR analysis of homooligomers. Non-covalent interactions with the shift reagent can constrain otherwise flexible analytes inducing a conformational transition that results in signal...

  9. H/L transition time estimation in JET using conformal predictors

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, S., E-mail: sergio.gonzalez@ciemat.es [Asociacion EURATOM/CIEMAT para Fusion, Madrid 28040 (Spain); Vega, J. [Asociacion EURATOM/CIEMAT para Fusion, Madrid 28040 (Spain); Murari, A. [Consorzio RFX, Associazione EURATOM/ENEA per la Fusione, Padova 4-25127 (Italy); Pereira, A. [Asociacion EURATOM/CIEMAT para Fusion, Madrid 28040 (Spain); Dormido-Canto, S.; Ramirez, J.M. [Departamento de Informatica y Automatica, UNED, Madrid 28040 (Spain)

    2012-12-15

    Highlights: Black-Right-Pointing-Pointer H/L transitions have been predicted using H/L and L/H models. Black-Right-Pointing-Pointer Models have been built using conformal predictors to hedge the prediction with confidence and credibility measures. Black-Right-Pointing-Pointer Models have been trained using linear and radial basis function kernels. Black-Right-Pointing-Pointer Conformal measures have proven their usefulness to validate data-driven models. - Abstract: Recent advances in data mining allow the automatic recognition of physical phenomena in the databases of fusion devices without human intervention. This is important to create large databases of physical events (thereby increasing the statistical relevance) in an unattended manner. Important examples are the L/H and H/L transitions. In this contribution, a novel technique is introduced to automatically locate H/L transitions in JET by using conformal predictors. The focus is on H/L transitions because typically there is not a clear signature in the time series of the most widely available signals to recognize the change of confinement. Conformal predictors hedge their prediction by means of two parameters: confidence and credibility. The technique has been based on binary supervised classifiers to separate the samples of the respective confinement modes. Results with several underlying classifiers are presented.

  10. Parallel Cascade Selection Molecular Dynamics (PaCS-MD) to generate conformational transition pathway.

    Science.gov (United States)

    Harada, Ryuhei; Kitao, Akio

    2013-07-21

    Parallel Cascade Selection Molecular Dynamics (PaCS-MD) is proposed as a molecular simulation method to generate conformational transition pathway under the condition that a set of "reactant" and "product" structures is known a priori. In PaCS-MD, the cycle of short multiple independent molecular dynamics simulations and selection of the structures close to the product structure for the next cycle are repeated until the simulated structures move sufficiently close to the product. Folding of 10-residue mini-protein chignolin from the extended to native structures and open-close conformational transition of T4 lysozyme were investigated by PaCS-MD. In both cases, tens of cycles of 100-ps MD were sufficient to reach the product structures, indicating the efficient generation of conformational transition pathway in PaCS-MD with a series of conventional MD without additional external biases. Using the snapshots along the pathway as the initial coordinates, free energy landscapes were calculated by the combination with multiple independent umbrella samplings to statistically elucidate the conformational transition pathways.

  11. Induce magnetism into silicene by embedding transition-metal atoms

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Xiaotian; Wang, Lu, E-mail: lwang22@suda.edu.cn, E-mail: yyli@suda.edu.cn; Lin, Haiping; Hou, Tingjun; Li, Youyong, E-mail: lwang22@suda.edu.cn, E-mail: yyli@suda.edu.cn [Institute of Functional Nano and Soft Materials Laboratory (FUNSOM), Jiangsu Key Laboratory for Carbon-based Functional Materials and Devices, and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, Jiangsu (China)

    2015-06-01

    Embedding transition-metal (TM) atoms into nonmagnetic nanomaterials is an efficient way to induce magnetism. Using first-principles calculations, we systematically investigated the structural stability and magnetic properties of TM atoms from Sc to Zn embedded into silicene with single vacancy (SV) and double vacancies (DV). The binding energies for different TM atoms correlate with the TM d-shell electrons. Sc, Ti, and Co show the largest binding energies of as high as 6 eV, while Zn has the lowest binding energy of about 2 eV. The magnetic moment of silicene can be modulated by embedding TM atoms from V to Co, which mainly comes from the 3d orbitals of TM along with partly contributions from the neighboring Si atoms. Fe atom on SV and Mn atom on DV have the largest magnetic moment of more than 3 μB. In addition, we find that doping of N or C atoms on the vacancy site could greatly enhance the magnetism of the systems. Our results provide a promising approach to design silicene-based nanoelectronics and spintronics device.

  12. Electronic Relaxation Processes of Transition Metal Atoms in Helium Nanodroplets

    Science.gov (United States)

    Kautsch, Andreas; Lindebner, Friedrich; Koch, Markus; Ernst, Wolfgang E.

    2014-06-01

    Spectroscopy of doped superfluid helium nanodroplets (He_N) gives information about the influence of this cold, chemically inert, and least interacting matrix environment on the excitation and relaxation dynamics of dopant atoms and molecules. We present the results from laser induced fluorescence (LIF), photoionization (PI), and mass spectroscopy of Cr and Cu doped He_N. From these results, we can draw a comprehensive picture of the complex behavior of such transition metal atoms in He_N upon photo-excitation. The strong Cr and Cu ground state transitions show an excitation blueshift and broadening with respect to the bare atom transitions which can be taken as indication for the solvation inside the droplet. From the originally excited states the atoms relax to energetically lower states and are ejected from the He_N. The relaxation processes include bare atom spin-forbidden transitions, which clearly bears the signature of the He_N influence. Two-color resonant two-photon ionization (2CR2PI) also shows the formation of bare atoms and small Cr-He_n and Cu-He_n clusters in their ground and metastable states ^c. Currently, Cr dimer excitation studies are in progress and a brief outlook on the available results will be given. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, 2011. A. Kautsch, M. Koch, and W. E. Ernst, J. Phys. Chem. A, 117 (2013) 9621-9625, DOI: 10.1021/jp312336m F. Lindebner, A. Kautsch, M. Koch, and W. E. Ernst, Int. J. Mass Spectrom. (2014) in press, DOI: 10.1016/j.ijms.2013.12.022 M. Koch, A. Kautsch, F. Lackner, and W. E. Ernst, submitted to J. Phys. Chem. A

  13. Conformal nanocoating of zirconia nanoparticles by atomic layer deposition in a fluidized bed reactor

    Science.gov (United States)

    Hakim, Luis F.; George, Steven M.; Weimer, Alan W.

    2005-07-01

    Primary zirconia nanoparticles were conformally coated with alumina ultrathin films using atomic layer deposition (ALD) in a fluidized bed reactor. Alternating doses of trimethylaluminium and water vapour were performed to deposit Al2O3 nanolayers on the surface of 26 nm zirconia nanoparticles. Transmission Fourier transform infrared spectroscopy was performed ex situ. Bulk Al2O3 vibrational modes were observed for coated particles after 50 and 70 cycles. Coated nanoparticles were also examined with transmission electron microscopy, high-resolution field emission scanning electron microscopy and energy dispersive spectroscopy. Analysis revealed highly conformal and uniform alumina nanofilms throughout the surface of zirconia nanoparticles. The particle size distribution and surface area of the nanoparticles are not affected by the coating process. Primary nanoparticles are coated individually despite their high aggregation tendency during fluidization. The dynamic aggregation behaviour of zirconia nanoparticles in the fluidized bed plays a key role in the individual coating of nanoparticles.

  14. Highly conformal atomic layer deposition of tantalum oxide using alkylamide precursors

    Energy Technology Data Exchange (ETDEWEB)

    Hausmann, Dennis M.; Rouffignac, Philippe de; Smith, Amethyst; Gordon, Roy; Monsma, Douwe

    2003-10-22

    Atomic layer deposition of highly conformal films of tantalum oxide were studied using tantalum alkylamide precursors and water as the oxygen source. These films also exhibited a very high degree of conformality: 100% step coverage on vias with aspect ratios greater than 35. As deposited, the films were free of detectable impurities with the expected (2.5-1) oxygen to metal ratio and were smooth and amorphous. The films were completely uniform in thickness and composition over the length of the reactor used for depositions. Films were deposited at substrate temperatures from 50 to 350 deg. C from precursors that were vaporized at temperatures from 50 to 120 deg. C. As deposited, the films showed a dielectric constant of 28 and breakdown field consistently greater than 4.5 MV/cm.

  15. Atomic structure of non-stoichiometric transition metal carbides

    International Nuclear Information System (INIS)

    Different kinds of experimental studies of the atomic arrangement in non-stoichiometric transition metal carbides are proposed: the ordering of carbon vacancies and the atomic static displacements are the main subjects studied. Powder neutron diffraction on TiCsub(1-x) allowed us to determine the order-disorder transition critical temperature -Tsub(c) approximately 7700C- in the TiCsub(0.52-0.67) range, and to analyze at 300 K the crystal structure of long-range ordered samples. A neutron diffuse scattering quantitative study at 300 K of short-range order in TiCsub(0.76), TiCsub(0.79) and NbCsub(0.73) single crystals is presented: as in Ti2Csub(1+x) and Nb6C5 superstructures, vacancies avoid to be on each side of a metal atom. Besides, the mean-square carbon atom displacements from their sites are small, whereas metal atoms move radially about 0.03 A away from vacancies. These results are in qualitative agreement with EXAFS measurements at titanium-K edge of TiCsub(1-x). An interpretation of ordering in term of short-range interaction pair potentials between vacancies is proposed

  16. Multicanonical simulation of biomolecules and microcanonical statistical analysis of conformational transitions

    Science.gov (United States)

    Bachmann, Michael

    2013-05-01

    The simulation of biomolecular structural transitions such as folding and aggregation does not only require adequate models that reflect the key aspects of the cooperative transition behaviour. It is likewise important to employ thermodynamically correct simulation methods and to perform an accurate subsequent statistical analysis of the data obtained in the simulation. The efficient combination of methodology and analysis can be quite sophisticated, but also very instructive in their feedback to a better understanding of the physics of the underlying cooperative processes that drive the conformational transition. We here show that the density of states, which is the central result of multicanonical sampling and any other generalized-ensemble simulation, serves as the optimal basis for the microcanonical statistical analysis of transitions. The microcanonical inflection-point analysis method, which has been introduced for this purpose recently, is a perfect tool for a precise, unique identification and classification of all structural transitions.

  17. Transition Rates for a Rydberg Atom Surrounded by a Plasma

    CERN Document Server

    Lin, Chengliang; Röpke, Gerd; Reinholz, Heidi

    2016-01-01

    We derive a quantum master equation for an atom coupled to a heat bath represented by a charged particle many-body environment. In Born-Markov approximation, the influence of the plasma environment on the reduced system is described by the dynamical structure factor. Expressions for the profiles of spectral lines are obtained. Wave packets are introduced as robust states allowing for a quasi-classical description of Rydberg electrons. Transition rates for highly excited Rydberg levels are investigated. A circular-orbit wave packet approach has been applied, in order to describe the localization of electrons within Rydberg states. The calculated transition rates are in a good agreement with experimental data.

  18. Theory of rotational transition in atom-diatom chemical reaction

    Science.gov (United States)

    Nakamura, Masato; Nakamura, Hiroki

    1989-05-01

    Rotational transition in atom-diatom chemical reaction is theoretically studied. A new approximate theory (which we call IOS-DW approximation) is proposed on the basis of the physical idea that rotational transition in reaction is induced by the following two different mechanisms: rotationally inelastic half collision in both initial and final arrangement channels, and coordinate transformation in the reaction zone. This theory gives a fairy compact expression for the state-to-state transition probability. Introducing the additional physically reasonable assumption that reaction (particle rearrangement) takes place in a spatially localized region, we have reduced this expression into a simpler analytical form which can explicitly give overall rotational state distribution in reaction. Numerical application was made to the H+H2 reaction and demonstrated its effectiveness for the simplicity. A further simplified most naive approximation, i.e., independent events approximation was also proposed and demonstrated to work well in the test calculation of H+H2. The overall rotational state distribution is expressed simply by a product sum of the transition probabilities for the three consecutive processes in reaction: inelastic transition in the initial half collision, transition due to particle rearrangement, and inelastic transition in the final half collision.

  19. Finite-Size Conformational Transitions: A Unifying Concept Underlying Chromosome Dynamics

    International Nuclear Information System (INIS)

    Investigating average thermodynamic quantities is not sufficient to understand conformational transitions of a finite-size polymer. We propose that such transitions are better described in terms of the probability distribution of some finite-size order parameter, and the evolution of this distribution as a control parameter varies. We demonstrate this claim for the coil-globule transition of a linear polymer and its mapping onto a two-state model. In a biological context, polymer models delineate the physical constraints experienced by the genome at different levels of organization, from DNA to chromatin to chromosome. We apply our finite-size approach to the formation of plectonemes in a DNA segment submitted to an applied torque and the ensuing helix-coil transition that can be numerically observed, with a coexistence of the helix and coil states in a range of parameters. Polymer models are also essential to analyze recent in vivo experiments providing the frequency of pairwise contacts between genomic loci. The probability distribution of these contacts yields quantitative information on the conformational fluctuations of chromosome regions. The changes observed in the shape of the distribution when the cell type or the physiological conditions vary may reveal an epigenetic modulation of the conformational constraints experienced by the chromosomes. (condensed matter: structural, mechanical, and thermal properties)

  20. Conformational transition paths harbor structures useful for aiding drug discovery and understanding enzymatic mechanisms in protein kinases.

    Science.gov (United States)

    Wong, Chung F

    2016-01-01

    This short article examines the usefulness of fast simulations of conformational transition paths in elucidating enzymatic mechanisms and guiding drug discovery for protein kinases. It applies the transition path method in the MOIL software package to simulate the paths of conformational transitions between six pairs of structures from the Protein Data Bank. The structures along the transition paths were found to resemble experimental structures that mimic transient structures believed to form during enzymatic catalysis or conformational transitions, or structures that have drug candidates bound. These findings suggest that such simulations could provide quick initial insights into the enzymatic mechanisms or pathways of conformational transitions of proteins kinases, or could provide structures useful for aiding structure-based drug design.

  1. Self-limiting atomic layer deposition of conformal nanostructured silver films

    Science.gov (United States)

    Golrokhi, Zahra; Chalker, Sophia; Sutcliffe, Christopher J.; Potter, Richard J.

    2016-02-01

    The controlled deposition of ultra-thin conformal silver nanoparticle films is of interest for applications including anti-microbial surfaces, plasmonics, catalysts and sensors. While numerous techniques can produce silver nanoparticles, few are able to produce highly conformal coatings on high aspect ratio surfaces, together with sub-nanometre control and scalability. Here we develop a self-limiting atomic layer deposition (ALD) process for the deposition of conformal metallic silver nanoparticle films. The films have been deposited using direct liquid injection ALD with ((hexafluoroacetylacetonato)silver(I)(1,5-cyclooctadiene)) and propan-1-ol. An ALD temperature window between 123 and 128 °C is identified and within this range self-limiting growth is confirmed with a mass deposition rate of ∼17.5 ng/cm2/cycle. The effects of temperature, precursor dose, co-reactant dose and cycle number on the deposition rate and on the properties of the films have been systematically investigated. Under self-limiting conditions, films are metallic silver with a nano-textured surface topography and nanoparticle size is dependent on the number of ALD cycles. The ALD reaction mechanisms have been elucidated using in-situ quartz crystal microbalance (QCM) measurements, showing chemisorption of the silver precursor, followed by heterogeneous catalytic dehydrogenation of the alcohol to form metallic silver and an aldehyde.

  2. Conformal atomic layer deposition of alumina on millimeter tall, vertically-aligned carbon nanotube arrays.

    Science.gov (United States)

    Stano, Kelly L; Carroll, Murphy; Padbury, Richard; McCord, Marian; Jur, Jesse S; Bradford, Philip D

    2014-11-12

    Atomic layer deposition (ALD) can be used to coat high aspect ratio and high surface area substrates with conformal and precisely controlled thin films. Vertically aligned arrays of multiwalled carbon nanotubes (MWCNTs) with lengths up to 1.5 mm were conformally coated with alumina from base to tip. The nucleation and growth behaviors of Al2O3 ALD precursors on the MWCNTs were studied as a function of CNT surface chemistry. CNT surfaces were modified through a series of post-treatments including pyrolytic carbon deposition, high temperature thermal annealing, and oxygen plasma functionalization. Conformal coatings were achieved where post-treatments resulted in increased defect density as well as the extent of functionalization, as characterized by X-ray photoelectron spectroscopy and Raman spectroscopy. Using thermogravimetric analysis, it was determined that MWCNTs treated with pyrolytic carbon and plasma functionalization prior to ALD coating were more stable to thermal oxidation than pristine ALD coated samples. Functionalized and ALD coated arrays had a compressive modulus more than two times higher than a pristine array coated for the same number of cycles. Cross-sectional energy dispersive X-ray spectroscopy confirmed that Al2O3 could be uniformly deposited through the entire thickness of the vertically aligned MWCNT array by manipulating sample orientation and mounting techniques. Following the ALD coating, the MWCNT arrays demonstrated hydrophilic wetting behavior and also exhibited foam-like recovery following compressive strain.

  3. Path ensembles for conformational transitions in adenylate kinase using weighted--ensemble path sampling

    CERN Document Server

    Bhatt, Divesh

    2009-01-01

    We perform first path sampling simulations of conformational transitions of semi--atomistic protein models. We generate an ensemble of pathways for conformational transitions between open and closed forms of adenylate kinase using weighted ensemble path sampling method. Such an ensemble of pathways is critical in determining the important regions of configuration space sampled during a transition. To different semi--atomistic models are used: one is a pure Go model, whereas the other includes level of residue specificity via use of Miyajawa--Jernigan type interactions and hydrogen bonding. For both the models, we find that the open form of adenylate kinase is more flexible and the the transition from open to close is significantly faster than the reverse transition. We find that the transition occurs via the AMP binding domain snapping shut at a fairly fast time scale. On the other hand, the flexible lid domain fluctuates significantly and the shutting of the AMP binding domain does not depend upon the positi...

  4. Resolved atomic interaction sidebands in an optical clock transition

    CERN Document Server

    Bishof, Michael; Swallows, Matthew D; Gorshkov, Alexey V; Ye, Jun; Rey, Ana Maria

    2011-01-01

    We report the observation of resolved atomic interaction sidebands (ISB) in the ${}^{87}$Sr optical clock transition when atoms at microkelvin temperatures are confined in a two-dimensional (2D) optical lattice. The ISB are a manifestation of the strong interactions that occur between atoms confined in a quasi-one-dimensional geometry and disappear when the confinement is relaxed along one dimension. The emergence of ISB is linked to the recently observed suppression of collisional frequency shifts in [1]. At the current temperatures, the ISB can be resolved but are broad. At lower temperatures, ISB are predicted to be substantially narrower and usable as powerful spectroscopic tools in strongly interacting alkaline-earth gases.

  5. Steered molecular dynamics simulations of a type IV pilus probe initial stages of a force-induced conformational transition.

    Directory of Open Access Journals (Sweden)

    Joseph L Baker

    2013-04-01

    Full Text Available Type IV pili are long, protein filaments built from a repeating subunit that protrudes from the surface of a wide variety of infectious bacteria. They are implicated in a vast array of functions, ranging from bacterial motility to microcolony formation to infection. One of the most well-studied type IV filaments is the gonococcal type IV pilus (GC-T4P from Neisseria gonorrhoeae, the causative agent of gonorrhea. Cryo-electron microscopy has been used to construct a model of this filament, offering insights into the structure of type IV pili. In addition, experiments have demonstrated that GC-T4P can withstand very large tension forces, and transition to a force-induced conformation. However, the details of force-generation, and the atomic-level characteristics of the force-induced conformation, are unknown. Here, steered molecular dynamics (SMD simulation was used to exert a force in silico on an 18 subunit segment of GC-T4P to address questions regarding the nature of the interactions that lead to the extraordinary strength of bacterial pili. SMD simulations revealed that the buried pilin α1 domains maintain hydrophobic contacts with one another within the core of the filament, leading to GC-T4P's structural stability. At the filament surface, gaps between pilin globular head domains in both the native and pulled states provide water accessible routes between the external environment and the interior of the filament, allowing water to access the pilin α1 domains as reported for VC-T4P in deuterium exchange experiments. Results were also compared to the experimentally observed force-induced conformation. In particular, an exposed amino acid sequence in the experimentally stretched filament was also found to become exposed during the SMD simulations, suggesting that initial stages of the force induced transition are well captured. Furthermore, a second sequence was shown to be initially hidden in the native filament and became exposed upon

  6. A transferable coarse-grained model for diphenylalanine: How to represent an environment driven conformational transition

    International Nuclear Information System (INIS)

    One of the major challenges in the development of coarse grained (CG) simulation models that aim at biomolecular structure formation processes is the correct representation of an environment-driven conformational change, for example, a folding/unfolding event upon interaction with an interface or upon aggregation. In the present study, we investigate this transferability challenge for a CG model using the example of diphenylalanine. This dipeptide displays a transition from a trans-like to a cis-like conformation upon aggregation as well as upon transfer from bulk water to the cyclohexane/water interface. Here, we show that one can construct a single CG model that can reproduce both the bulk and interface conformational behavior and the segregation between hydrophobic/hydrophilic medium. While the general strategy to obtain nonbonded interactions in the present CG model is to reproduce solvation free energies of small molecules representing the CG beads in the respective solvents, the success of the model strongly depends on nontrivial decisions one has to make to capture the delicate balance between the bonded and nonbonded interactions. In particular, we found that the peptide's conformational behavior is qualitatively affected by the cyclohexane/water interaction potential, an interaction that does not directly involve the peptide at all but merely influences the properties of the hydrophobic/hydrophilic interface. Furthermore, we show that a small modification to improve the structural/conformational properties of the CG model could dramatically alter the thermodynamic properties

  7. A transferable coarse-grained model for diphenylalanine: How to represent an environment driven conformational transition

    Energy Technology Data Exchange (ETDEWEB)

    Dalgicdir, Cahit; Sensoy, Ozge; Sayar, Mehmet, E-mail: msayar@ku.edu.tr [College of Engineering, Koç University, 34450 Istanbul (Turkey); Peter, Christine [Max Planck Institute for Polymer Research, 55128 Mainz (Germany); Department of Chemistry, University of Konstanz, 78547 Konstanz (Germany)

    2013-12-21

    One of the major challenges in the development of coarse grained (CG) simulation models that aim at biomolecular structure formation processes is the correct representation of an environment-driven conformational change, for example, a folding/unfolding event upon interaction with an interface or upon aggregation. In the present study, we investigate this transferability challenge for a CG model using the example of diphenylalanine. This dipeptide displays a transition from a trans-like to a cis-like conformation upon aggregation as well as upon transfer from bulk water to the cyclohexane/water interface. Here, we show that one can construct a single CG model that can reproduce both the bulk and interface conformational behavior and the segregation between hydrophobic/hydrophilic medium. While the general strategy to obtain nonbonded interactions in the present CG model is to reproduce solvation free energies of small molecules representing the CG beads in the respective solvents, the success of the model strongly depends on nontrivial decisions one has to make to capture the delicate balance between the bonded and nonbonded interactions. In particular, we found that the peptide's conformational behavior is qualitatively affected by the cyclohexane/water interaction potential, an interaction that does not directly involve the peptide at all but merely influences the properties of the hydrophobic/hydrophilic interface. Furthermore, we show that a small modification to improve the structural/conformational properties of the CG model could dramatically alter the thermodynamic properties.

  8. A transferable coarse-grained model for diphenylalanine: How to represent an environment driven conformational transition

    Science.gov (United States)

    Dalgicdir, Cahit; Sensoy, Ozge; Peter, Christine; Sayar, Mehmet

    2013-12-01

    One of the major challenges in the development of coarse grained (CG) simulation models that aim at biomolecular structure formation processes is the correct representation of an environment-driven conformational change, for example, a folding/unfolding event upon interaction with an interface or upon aggregation. In the present study, we investigate this transferability challenge for a CG model using the example of diphenylalanine. This dipeptide displays a transition from a trans-like to a cis-like conformation upon aggregation as well as upon transfer from bulk water to the cyclohexane/water interface. Here, we show that one can construct a single CG model that can reproduce both the bulk and interface conformational behavior and the segregation between hydrophobic/hydrophilic medium. While the general strategy to obtain nonbonded interactions in the present CG model is to reproduce solvation free energies of small molecules representing the CG beads in the respective solvents, the success of the model strongly depends on nontrivial decisions one has to make to capture the delicate balance between the bonded and nonbonded interactions. In particular, we found that the peptide's conformational behavior is qualitatively affected by the cyclohexane/water interaction potential, an interaction that does not directly involve the peptide at all but merely influences the properties of the hydrophobic/hydrophilic interface. Furthermore, we show that a small modification to improve the structural/conformational properties of the CG model could dramatically alter the thermodynamic properties.

  9. A transferable coarse-grained model for diphenylalanine: How to represent an environment driven conformational transition

    OpenAIRE

    Dalgıçdir, Cahit; Şensoy, Özge; Sayar, Mehmet; Peter, Christine

    2013-01-01

    A transferable coarse-grained model for diphenylalanine: How to represent an environment driven conformational transition Cahit Dalgicdir, Ozge Sensoy, Christine Peter, and Mehmet Sayar Citation: The Journal of Chemical Physics 139, 234115 (2013); doi: 10.1063/1.4848675 View online: http://dx.doi.org/10.1063/1.4848675 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/139/23?ver=pdfcov Published by the AIP Publishing Articles you may be interested in...

  10. Solid-to-hybrid transitioning armature railgun with non-conforming-to-prejudice bore profile

    Science.gov (United States)

    Solberg, Jerome Michael

    2012-12-04

    An improved railgun, railgun barrel, railgun projectile, and railgun system for accelerating a solid-to-hybrid transitioning armature projectile using a barrel having a bore that does not conform to a cross-sectional profile of the projectile, to contact and guide the projectile only by the rails in a low pressure bore volume so as to minimize damage, failure, and/or underperformance caused by plasma armatures, insulator ablation, and/or restrikes.

  11. Distribution, transition and thermodynamic stability of protein conformations in the denaturant-induced unfolding of proteins.

    Directory of Open Access Journals (Sweden)

    Liujiao Bian

    Full Text Available BACKGROUND: Extensive and intensive studies on the unfolding of proteins require appropriate theoretical model and parameter to clearly illustrate the feature and characteristic of the unfolding system. Over the past several decades, four approaches have been proposed to describe the interaction between proteins and denaturants, but some ambiguity and deviations usually occur in the explanation of the experimental data. METHODOLOGY/PRINCIPAL FINDINGS: In this work, a theoretical model was presented to show the dependency of the residual activity ratio of the proteins on the molar denaturant concentration. Through the characteristic unfolding parameters ki and Δmi in this model, the distribution, transition and thermodynamic stability of protein conformations during the unfolding process can be quantitatively described. This model was tested with the two-state unfolding of bovine heart cytochrome c and the three-state unfolding of hen egg white lysozyme induced by both guanidine hydrochloride and urea, the four-state unfolding of bovine carbonic anhydrase b induced by guanidine hydrochloride and the unfolding of some other proteins induced by denaturants. The results illustrated that this model could be used accurately to reveal the distribution and transition of protein conformations in the presence of different concentrations of denaturants and to evaluate the unfolding tendency and thermodynamic stability of different conformations. In most denaturant-induced unfolding of proteins, the unfolding became increasingly hard in next transition step and the proteins became more unstable as they attained next successive stable conformation. CONCLUSIONS/SIGNIFICANCE: This work presents a useful method for people to study the unfolding of proteins and may be used to describe the unfolding and refolding of other biopolymers induced by denaturants, inducers, etc.

  12. Interface of transition metal oxides at the atomic scale

    Science.gov (United States)

    Shang, Tong-Tong; Liu, Xin-Yu; Gu, Lin

    2016-09-01

    Remarkable phenomena arise at well-defined heterostructures, composed of transition metal oxides, which is absent in the bulk counterpart, providing us a paradigm for exploring the various electron correlation effects. The functional properties of such heterostructures have attracted much attention in the microelectronic and renewable energy fields. Exotic and unexpected states of matter could arise from the reconstruction and coupling among lattice, charge, orbital and spin at the interfaces. Aberration-corrected scanning transmission electron microscopy (STEM) is a powerful tool to visualize the lattice structure and electronic structure at the atomic scale. In the present study some novel phenomena of oxide heterostructures at the atomic scale are summarized and pointed out from the perspective of electron microscopy.

  13. Laser Assisted Free-Free Transition in Electron - Atom Collision

    Science.gov (United States)

    Sinha, C.; Bhatia, A. K.

    2011-01-01

    Free-free transition is studied for electron-Hydrogen atom system in ground state at very low incident energies in presence of an external homogeneous, monochromatic and linearly polarized laser field. The incident electron is considered to be dressed by the laser in a non perturbative manner by choosing the Volkov solutions in both the channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the effect of electron exchange, short range as well as of the long range interactions. Laser assisted differential as well as elastic total cross sections are calculated for single photon absorption/emission in the soft photon limit, the laser intensity being much less than the atomic field intensity. A strong suppression is noted in the laser assisted cross sections as compared to the field free situations. Significant difference is noted in the singlet and the triplet cross sections.

  14. NMR chemical shift analysis of the conformational transition between the monomer and tetramer of melittin in an aqueous solution.

    Science.gov (United States)

    Miura, Yoshinori

    2016-05-01

    It is known that melittin in an aqueous solution undergoes a conformational transition between the monomer and tetramer by variation in temperature. The transition correlates closely with isomers of the proline residue; monomeric melittin including a trans proline peptide bond (trans-monomer) is involved directly in the transition, whereas monomeric melittin having a cis proline peptide bond (cis-monomer) is virtually not. The transition has been explored by using nuclear magnetic resonance spectroscopy in order to clarify the stability of the tetrameric conformation and the cooperativity of the transition. In the light of temperature dependence of chemical shifts of resonances from the isomeric monomers, we qualitatively estimate the temperature-, salt-, and concentration-dependence of the relative equilibrium populations of the trans-monomer and tetramer, and show that the tetramer has a maximum conformational stability at 30-45 °C and that the transition cooperativity is very low. PMID:26658745

  15. A conformation-dependent stereochemical library improves crystallographic refinement even at atomic resolution

    International Nuclear Information System (INIS)

    A script was created to allow SHELXL to use the new CDL v.1.2 stereochemical library which defines the target values for main-chain bond lengths and angles as a function of the residue’s ϕ/ψ angles. Test refinements using this script show that the refinement behavior of structures at resolutions even better than 1 Å is substantially enhanced by the use of the new conformation-dependent ideal geometry paradigm. To utilize a new conformation-dependent backbone-geometry library (CDL) in protein refinements at atomic resolution, a script was written that creates a restraint file for the SHELXL refinement program. It was found that the use of this library allows models to be created that have a substantially better fit to main-chain bond angles and lengths without degrading their fit to the X-ray data even at resolutions near 1 Å. For models at much higher resolution (∼0.7 Å), the refined model for parts adopting single well occupied positions is largely independent of the restraints used, but these structures still showed much smaller r.m.s.d. residuals when assessed with the CDL. Examination of the refinement tests across a wide resolution range from 2.4 to 0.65 Å revealed consistent behavior supporting the use of the CDL as a next-generation restraint library to improve refinement. CDL restraints can be generated using the service at http://pgd.science.oregonstate.edu/cdl_shelxl/

  16. Resonantly enhanced Bragg-scattering spectroscopy of an atomic transition

    Science.gov (United States)

    Yang, Xudong; Qiao, Cuifang; Li, Chuanliang; Chen, Fenghua

    2016-07-01

    A novel resonantly enhanced Bragg-scattering (REBS) spectroscopy from a population difference grating (PDG) is reported. The PDG is formed by a standing-wave (SW) pump field, which periodically modulates the space population distributions of two levels in the 87Rb D1 line. Then, a probe beam, having identical frequency and orthogonal polarization with the SW pump field, is Bragg-scattered by the PDG. The research achievement shows that the Bragg-scattered light is strongest at an atomic transition, and forms an REBS spectrum with a high signal-to-noise ratio and sub-natural linewidth. The observed REBS can be applied in precise frequency measurements.

  17. Conformational Transitions and Glycation of Serum Albumin in Patients with Minimal-Change Glomerulopathy

    Science.gov (United States)

    Hong, Sae Yong; Lee, Eun Young; Yang, Jong Oh; Kim, Tae Yeong; Kim, Eun Hee; Cheong, Mi Young; Kim, Soo Hyun; Cheong, Chae Joon

    2004-01-01

    Background There has been a lack of study on the structural changes of serum albumin in patients with minimal change disease (MCD). To determine whether glycation and/or conformational transitions of albumin are involved in the pathogenesis of albuminuria, nine patients with MCD were enrolled in a prospective follow-up study for comparison of these parameters in serum albumin during the remission and relapse of nephrotic syndrome. Methods Circular dichroism measurements were made with purified albumin. Ellipticities at each wavelength were transformed to mean residue ellipticity. Monosaccharide composition was analyzed by high-pH anion-exchange chromatography with pulsed amperometric detection. Results There was no difference in the proportions of α-helix, β-conformation, and β-turn of albumin between the sera of control patients and those with nephrotic syndrome. However, the proportion of the random configuration was slightly higher in the plasma albumin of patients in relapse than in those in remission. The proportion of the random configuration was lower in the albumin of the serum than in the urine of patients with nephrotic syndrome, but there was no difference in the proportions of α-helix, β-conformation, and β-turn of albumin between their plasma and urine. Conclusion Our results suggest that conformational changes in albumin are involved in albuminuria in patients with MCD. PMID:15481604

  18. Mechanism of Conformational Transition of Silk Fibroin in Alcohol-water Mixtures

    Institute of Scientific and Technical Information of China (English)

    Ma Lin; He Weiren; Huang Aimin; Li Lishuo; Wei Qiaona; Huang Zilun

    2011-01-01

    Circular dichroism, intrinsic fluorescence of protein and exogenous fluorescence probe of 8-anilino-l-naphtha-lenesulfonic acid hemimagnesium salt (ANS) was used to investigate the mechanism of conformational change of silk fibroin (SF) in aqueous alcohol including methanol and ethanol. The conformational transition of SF from ran-dom coil to β-sheet was found to be of a close relationship with the microstructure of the solvent. The alcohol-water mixture at low concentration had little effect on the solvation of the peptide unit, as the inherent water structure was conserved. At high alcohol concentration, the transition from the tetrahedral-like water structure to the chain-like alcohol structure in the mixtures induced a β-sheet conformation of SF, as a result of the formation of intramolecu-lar hydrogen bond between the peptide units in order to eliminate the thermodynamic unfavorite from the contact to the solvent molecules. Meanwhile, the aggregating of hydrophobic side chains was decreased by the alcohol via the destruction of hydrogen bond network of water by alcohol and the binding of alcohol to hydrophobic group.

  19. Conformational transitions of plasmid ds-DNA on ultrathin films of alkylamines on graphite

    Science.gov (United States)

    Falk, Caroline; Liang, Hua; Severin, Nikolai; Zhuang, Wei; Zauscher, Stefan; Rabe, Jürgen P.

    2015-03-01

    DNA replication is an important process in the human body. Replication of double-stranded (ds)-DNA requires its local melting into two single strands. DNA, when stretched in solution, overwinds and melts. This was argued to give insight onto the replication mechanism. It is difficult, however, to access the direct conformational changes during stretching in solution. Recent work demonstrated that this transition can be imaged with scanning force microscopy on a graphite surface that is coated with an alkylamine layer. ds-DNA can be controlled by an amphiphilic layer, since the DNA conformation depends on the amphiphile concentration. In particular we analyzed different DNA lengths on the same surface, and we found that at a specific concentration of octadecylamine the ds-DNA pUC19 plasmid ring splits into two single strands at one position. We will discuss methods to mark the DNA to determine the exact location at which the plasmid ring splits.

  20. Notes on Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities

    OpenAIRE

    Hyun-Kyung Chung; Per Jönsson; Alexander Kramida

    2013-01-01

    Atomic structure and transition probabilities are fundamental physical data required in many fields of science and technology. Atomic physics codes are freely available to other community users to generate atomic data for their interest, but the quality of these data is rarely verified. This special issue addresses estimation of uncertainties in atomic structure and transition probability calculations, and discusses methods and strategies to assess and ensure the quality of theoretical atomic...

  1. Shrinking light to allow forbidden transitions on the atomic scale

    Science.gov (United States)

    Rivera, Nicholas; Kaminer, Ido; Zhen, Bo; Joannopoulos, John D.; Soljačić, Marin

    2016-07-01

    The diversity of light-matter interactions accessible to a system is limited by the small size of an atom relative to the wavelength of the light it emits, as well as by the small value of the fine-structure constant. We developed a general theory of light-matter interactions with two-dimensional systems supporting plasmons. These plasmons effectively make the fine-structure constant larger and bridge the size gap between atom and light. This theory reveals that conventionally forbidden light-matter interactions—such as extremely high-order multipolar transitions, two-plasmon spontaneous emission, and singlet-triplet phosphorescence processes—can occur on very short time scales comparable to those of conventionally fast transitions. Our findings may lead to new platforms for spectroscopy, sensing, and broadband light generation, a potential testing ground for quantum electrodynamics (QED) in the ultrastrong coupling regime, and the ability to take advantage of the full electronic spectrum of an emitter.

  2. Giant modification of atomic transition probabilities induced by a magnetic field: forbidden transitions become predominant

    International Nuclear Information System (INIS)

    The magnetic field-induced giant modification of probabilities for seven components of 6S1/2, Fg = 3 → 6P3/2, Fe = 5 transition of the Cs D2 line, forbidden by selection rules, is observed experimentally for the first time. For the case of excitation with circularly polarized laser radiation, the probability of a Fg = 3, mF = −3 → Fe = 5, mF = −2 transition becomes the largest of 25 transitions of the Fg = 3 → Fe = 2,3,4,5 group in a wide-range magnetic field of 200–3200 G. Moreover, the modification is the largest among D2 lines of alkali metals. A half-wave-thick cell (the length along the beam propagation axis L = 426 nm) filled with Cs has been used in order to achieve sub-Doppler resolution, which allows the large number of atomic transitions that appear in the absorption spectrum to be separated when an external magnetic field is applied. For B > 3000 G the group of seven transitions Fg = 3 → Fe = 5 is completely resolved and is located at the high frequency level of Fg= 3 → Fe = 2,3,4 transitions. The applied theoretical model describes very well the experimental curves. (letters)

  3. Conformational transitions of cytochrome c in sub-micron-sized capsules at air/buffer interface.

    Science.gov (United States)

    Jaganathan, Maheshkumar; Dhathathreyan, Aruna

    2014-09-30

    This work presents the design of sub-micron-sized capsules of Cytochrome c (cyt c) in the range 300-350 nm and the conformational transitions of the protein that occur when the films of these capsules spread at the air/buffer interface are subjected to repeated compression-expansion cycles. Steady state fluorescence, time-resolved fluorescence, and circular dichroic (CD) spectra have been used to study the highly compact native conformation (70% helicity) of the protein in the capsules and its stability has been analyzed using cyclic voltammetry. The capsules have been characterized using zeta sizer and high resolution transmission electron microscopy (HRTEM). Surface concentration-surface pressure (Γ-π) isotherms of the films of the capsules spread at air/buffer interface following compression-expansion show destabilizing effect on cyt c. FTIR and CD spectra of these films skimmed from the surface show that the protein transitions gradually from its native helical to an anomalous beta sheet aggregated state. This results from a competition between stabilizing hydrated polar segments of the protein in the capsule and destabilizing nonspecific hydrophobic interactions arising at the air/buffer interface. This 2D model could further our understanding of the spatial and temporal roles of proteins in confined spaces and also in the design of new drug delivery vehicles using proteins.

  4. Identifying allosteric fluctuation transitions between different protein conformational states as applied to Cyclin Dependent Kinase 2

    Directory of Open Access Journals (Sweden)

    Gu Jenny

    2007-02-01

    Full Text Available Abstract Background The mechanisms underlying protein function and associated conformational change are dominated by a series of local entropy fluctuations affecting the global structure yet are mediated by only a few key residues. Transitional Dynamic Analysis (TDA is a new method to detect these changes in local protein flexibility between different conformations arising from, for example, ligand binding. Additionally, Positional Impact Vertex for Entropy Transfer (PIVET uses TDA to identify important residue contact changes that have a large impact on global fluctuation. We demonstrate the utility of these methods for Cyclin-dependent kinase 2 (CDK2, a system with crystal structures of this protein in multiple functionally relevant conformations and experimental data revealing the importance of local fluctuation changes for protein function. Results TDA and PIVET successfully identified select residues that are responsible for conformation specific regional fluctuation in the activation cycle of Cyclin Dependent Kinase 2 (CDK2. The detected local changes in protein flexibility have been experimentally confirmed to be essential for the regulation and function of the kinase. The methodologies also highlighted possible errors in previous molecular dynamic simulations that need to be resolved in order to understand this key player in cell cycle regulation. Finally, the use of entropy compensation as a possible allosteric mechanism for protein function is reported for CDK2. Conclusion The methodologies embodied in TDA and PIVET provide a quick approach to identify local fluctuation change important for protein function and residue contacts that contributes to these changes. Further, these approaches can be used to check for possible errors in protein dynamic simulations and have the potential to facilitate a better understanding of the contribution of entropy to protein allostery and function.

  5. Distinguishing Unfolding and Functional Conformational Transitions of Calmodulin Using Ultraviolet Resonance Raman Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Eric M.; Balakrishnan, G.; Squier, Thomas C.; Spiro, Thomas

    2014-06-14

    Calmodulin (CaM) is a ubiquitous moderator protein for calcium signaling in all eukaryotic cells. This small calcium-binding protein exhibits a broad range of structural transitions, including domain opening and folding-unfolding, that allow it to recognize a wide variety of binding partners in vivo. While the static structures of CaM associated with its various binding activities are fairly well known, it has been challenging to examine the dynamics of transition between these structures in real-time, due to a lack of suitable spectroscopic probes of CaM structure. In this paper, we examine the potential of ultraviolet resonance Raman (UVRR) spectroscopy for clarifying the nature of structural transitions in CaM. We find that the UVRR spectral change (with 229 nm excitation) due to thermal unfolding of CaM is qualitatively different from that associated with opening of the C-terminal domain in response to Ca2+ binding. This spectral difference is entirely due to differences in teritary contacts at the inter-domain tyrosine residue Tyr138, toward which other spectroscopic methods are not sensitive. We conclude that UVRR is ideally suited to identifying the different types of structural transitions in CaM and other proteins with conformation-sensitive tyrosine residues, opening a path to time-resolved studies of CaM dynamics using Raman spectroscopy.

  6. Enhancing coherence in molecular spin qubits via atomic clock transitions.

    Science.gov (United States)

    Shiddiq, Muhandis; Komijani, Dorsa; Duan, Yan; Gaita-Ariño, Alejandro; Coronado, Eugenio; Hill, Stephen

    2016-03-17

    Quantum computing is an emerging area within the information sciences revolving around the concept of quantum bits (qubits). A major obstacle is the extreme fragility of these qubits due to interactions with their environment that destroy their quantumness. This phenomenon, known as decoherence, is of fundamental interest. There are many competing candidates for qubits, including superconducting circuits, quantum optical cavities, ultracold atoms and spin qubits, and each has its strengths and weaknesses. When dealing with spin qubits, the strongest source of decoherence is the magnetic dipolar interaction. To minimize it, spins are typically diluted in a diamagnetic matrix. For example, this dilution can be taken to the extreme of a single phosphorus atom in silicon, whereas in molecular matrices a typical ratio is one magnetic molecule per 10,000 matrix molecules. However, there is a fundamental contradiction between reducing decoherence by dilution and allowing quantum operations via the interaction between spin qubits. To resolve this contradiction, the design and engineering of quantum hardware can benefit from a 'bottom-up' approach whereby the electronic structure of magnetic molecules is chemically tailored to give the desired physical behaviour. Here we present a way of enhancing coherence in solid-state molecular spin qubits without resorting to extreme dilution. It is based on the design of molecular structures with crystal field ground states possessing large tunnelling gaps that give rise to optimal operating points, or atomic clock transitions, at which the quantum spin dynamics become protected against dipolar decoherence. This approach is illustrated with a holmium molecular nanomagnet in which long coherence times (up to 8.4 microseconds at 5 kelvin) are obtained at unusually high concentrations. This finding opens new avenues for quantum computing based on molecular spin qubits. PMID:26983539

  7. Conformational Preference and Donor Atom Interaction Leading to Hexacoordination vs Pentacoordination in Bicyclic Tetraoxyphosphoranes(1).

    Science.gov (United States)

    Sherlock, David J.; Chandrasekaran, A.; Prakasha, T. K.; Day, Roberta O.; Holmes, Robert R.

    1998-01-12

    New bicyclic tetraoxyphosphoranes all containing a six-membered oxaphosphorinane ring, C(6)H(8)(CH(2)O)(2)P(OC(12)H(8))(OXyl) (1), (C(6)H(4)O)(2)P(OC(12)H(8))(OXyl) (2), CH(2)[(t-Bu)(2)C(6)H(2)O](2)P(OC(12)H(8))(OXyl) (3), O(2)S[(t-Bu)MeC(6)H(2)O](2)P(OC(12)H(8))(OXyl) (4), and S[(t-Bu)MeC(6)H(2)O](2)P(OC(12)H(8))(OXyl) (5), were synthesized by the oxidative addition reaction of the cyclic phosphine P(OC(12)H(8))(OXyl) (6) with an appropriate diol in the presence of N-chlorodiisopropylamine. X-ray analysis revealed trigonal bipyramidal (TBP) geometries for 1-4 where the dioxa ring varied in size from six- to eight-membered. With a sulfur donor atom as part of an eight-membered ring in place of a potential oxygen donor atom of a sulfone group as in 4, the X-ray study of 5 showed the formation of a hexacoordinated structure via a P-S interaction. Ring constraints are evaluated to give an order of conformational flexibility associated with the (TBP) tetraoxyphosphoranes 4 > 3 approximately 1 > 2 which parallels the degree of shielding from (31)P NMR chemical shifts: 4 > 3 > 1 > 2. The six- and seven-membered dioxa rings in 1 and 2, respectively, are positioned at axial-equatorial sites, whereas the eight-membered dioxa ring in 3 and 4 occupies diequatorial sites of a TBP. V-T (1)H NMR data give barriers to xylyl group rotation about the C-OXyl bond. The geometry of 5 is located along a coordinate from square pyramidal toward octahedral to the extent of 60.7%. Achieving hexacoordination in bicyclic tetraoxyphosphoranes of reduced electrophilicity relative to bicyclic pentaoxyphosphoranes appears to be dependent on the presence of a sufficiently strong donor atom.

  8. Special Issue on Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities

    OpenAIRE

    Per Jönsson; Hyun-Kyung Chung

    2013-01-01

    There exist several codes in the atomic physics community to generate atomic structure and transition probabilities freely and readily distributed to researchers outside atomic physics community, in plasma, astrophysical or nuclear physics communities. Users take these atomic physics codes to generate the necessary atomic data or modify the codes for their own applications. However, there has been very little effort to validate and verify the data sets generated by non-expert users. [...

  9. Growth of highly conformal ruthenium-oxide thin films with enhanced nucleation by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Park, Ji-Yoon; Yeo, Seungmin [School of Materials Science and Engineering, Yeungnam University, Gyeongsan-si 712-749 (Korea, Republic of); Cheon, Taehoon [School of Materials Science and Engineering, Yeungnam University, Gyeongsan-si 712-749 (Korea, Republic of); Center for Core Research Facilities, Daegu Gyeongbuk Institute of Science and Technology, Dalseong-gun, Daegu 711-873 (Korea, Republic of); Kim, Soo-Hyun, E-mail: soohyun@ynu.ac.kr [School of Materials Science and Engineering, Yeungnam University, Gyeongsan-si 712-749 (Korea, Republic of); Kim, Min-Kyu; Kim, Hyungjun [School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Hong, Tae Eun [Busan Center, Republic of Korea Basic Science Institute, 1275 Jisadong, Gangseogu, Busan 618-230 (Korea, Republic of); Lee, Do-Joong [School of Engineering, Brown University, Providence, RI 02912 (United States)

    2014-10-15

    Highlights: • Highly conformal RuO{sub 2} thin films were deposited using a zero-valent Ru precursor by atomic layer deposition (ALD). • Effects of deposition conditions on the formation of RuO{sub 2} phase were elucidated. • The performance as a bottom electrode of a metal–insulator-metal capacitor was evaluated. • The formation of a rutile-structured TiO{sub 2} on top of the ALD-RuO{sub 2} was demonstrated. - Abstract: Highly conformal and conductive RuO{sub 2} thin films were deposited without nucleation delay using atomic layer deposition (ALD) by zero-valent metallorganic precursor, (ethylbenzyl)(1,3-cyclohexadienyl)Ru(0) (EBCHDRu, C{sub 14}H{sub 18}Ru) and molecular oxygen (O{sub 2}) as a precursor and reactant, respectively. RuO{sub 2} thin films could be successfully prepared by controlling the process parameters, such as a reactant flow rate, a reactant pulsing time, a precursor pulsing time, and a deposition temperature. X-ray diffractometry, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry analysis revealed that the formation of a RuO{sub 2} phase became favorable with increasing both the reactant flow rate and the pulsing time and with decreasing the precursor pulsing time and the deposition temperature. With the optimized pulsing conditions, the RuO{sub 2} film deposited at 225 °C had a tetragonal structure and exhibited excellent properties such as the low resistivity of 118 μΩ-cm, the high density of 6.85 g/cm{sup 3} close to the bulk value, and the negligible roughness of 0.33 nm. The growth rate of ALD-RuO{sub 2} was as high as 0.186 nm/cycle on the SiO{sub 2} substrate and the number of incubation cycles was negligible as 2. The film showed excellent step coverage of ∼100% onto 25-nm-width trench structures with an aspect ratio of 4.5. The ALD-RuO{sub 2} was highly stable up to annealing at 700 °C in both O{sub 2} and N{sub 2} ambient. Finally, the ALD-RuO{sub 2} film was evaluated as a bottom electrode of a

  10. Interaction between cyclodextrin and neuronal membrane results in modulation of GABA(A) receptor conformational transitions.

    Science.gov (United States)

    Pytel, Maria; Mercik, Katarzyna; Mozrzymas, Jerzy W

    2006-06-01

    Cyclodextrins (CDs) are nanostructures widely applied in biotechnology and chemistry. Owing to partially hydrophobic character, CDs interact with biological membranes. While the mechanisms of CDs interactions with lipids were widely studied, their effects on proteins are less understood. In the present study we investigated the effects of beta cyclodextrin (betaCD) on GABA(A) receptor (GABA(A)R) gating. To reliably resolve the kinetics of conformational transitions, currents were elicited by ultrafast gamma-aminobutyric acid (GABA) applications to outside-out patches from rat cultured hippocampal neurons. betaCD increased the amplitude of responses to saturating GABA concentration ([GABA]) in a dose-dependent manner and this effect was accompanied by profound alterations in the current kinetics. Current deactivation was slowed down by betaCD but this effect was biphasic with a maximum at around 0.5 mM betaCD. While the fast deactivation time constant was monotonically slowed down within considered betaCD concentration range, the slow component first increased and then, at millimolar betaCD concentration, decreased. The rate and extent of desensitization was decreased by betaCD in a dose-dependent manner. The analysis of current responses to nonsaturating [GABA] indicated that betaCD affected the GABA(A)R agonist binding site by slowing down the unbinding rate. Modulation of GABA(A)R desensitization and binding showed different concentration-dependence suggesting different modualtory sites with higher affinity of the latter one. All the betaCD effects were fully reversible indicating that cholesterol uptake into betaCD was not the primary mechanism. We conclude that betaCD is a strong modulator of GABA(A)R conformational transitions.

  11. Interaction between cyclodextrin and neuronal membrane results in modulation of GABAA receptor conformational transitions

    Science.gov (United States)

    Pytel, Maria; Mercik, Katarzyna; Mozrzymas, Jerzy W

    2006-01-01

    Cyclodextrins (CDs) are nanostructures widely applied in biotechnology and chemistry. Owing to partially hydrophobic character, CDs interact with biological membranes. While the mechanisms of CDs interactions with lipids were widely studied, their effects on proteins are less understood. In the present study we investigated the effects of beta cyclodextrin (βCD) on GABAA receptor (GABAAR) gating. To reliably resolve the kinetics of conformational transitions, currents were elicited by ultrafast gamma-aminobutyric acid (GABA) applications to outside-out patches from rat cultured hippocampal neurons. βCD increased the amplitude of responses to saturating GABA concentration ([GABA]) in a dose-dependent manner and this effect was accompanied by profound alterations in the current kinetics. Current deactivation was slowed down by βCD but this effect was biphasic with a maximum at around 0.5 mM βCD. While the fast deactivation time constant was monotonically slowed down within considered βCD concentration range, the slow component first increased and then, at millimolar βCD concentration, decreased. The rate and extent of desensitization was decreased by βCD in a dose-dependent manner. The analysis of current responses to nonsaturating [GABA] indicated that βCD affected the GABAAR agonist binding site by slowing down the unbinding rate. Modulation of GABAAR desensitization and binding showed different concentration-dependence suggesting different modualtory sites with higher affinity of the latter one. All the βCD effects were fully reversible indicating that cholesterol uptake into βCD was not the primary mechanism. We conclude that βCD is a strong modulator of GABAAR conformational transitions. PMID:16702996

  12. Origin of the transition voltage in gold–vacuum–gold atomic junctions

    KAUST Repository

    Wu, Kunlin

    2012-12-13

    The origin and the distance dependence of the transition voltage of gold-vacuum-gold junctions are investigated by employing first-principles quantum transport simulations. Our calculations show that atomic protrusions always exist on the electrode surface of gold-vacuum-gold junctions fabricated using the mechanically controllable break junction (MCBJ) method. The transition voltage of these gold-vacuum-gold junctions with atomically sharp electrodes is determined by the local density of states (LDOS) of the apex gold atom on the electrode surface rather than by the vacuum barrier shape. More specifically, the absolute value of the transition voltage roughly equals the rising edge of the LDOS peak contributed by the 6p atomic orbitals of the gold atoms protruding from the electrode surface, whose local Fermi level is shifted downwards when a bias voltage is applied. Since the LDOS of the apex gold atom depends strongly on the exact shape of the electrode, the transition voltage is sensitive to the variation of the atomic configuration of the junction. For asymmetric junctions, the transition voltage may also change significantly depending on the bias polarity. Considering that the occurrence of the transition voltage requires the electrode distance to be larger than a critical value, the interaction between the two electrodes is actually rather weak. Consequently, the LDOS of the apex gold atom is mainly determined by its local atomic configuration and the transition voltage only depends weakly on the electrode distance as observed in the MCBJ experiments. © 2013 IOP Publishing Ltd.

  13. Derivation of the dipole approximation from the exact transition probabilities for hydrogen atoms

    International Nuclear Information System (INIS)

    The usual dipole approximation for the transition probabilities for hydrogen atoms is derived from the exact transition probabilities by considering j = 1 photons only, neglecting retardation, and using an identity derived from the wave equation for the radial wave function for the atom

  14. Transition from 2-D radiotherapy to 3-D conformal and intensity modulated radiotherapy

    International Nuclear Information System (INIS)

    Cancer is one of the leading causes of death globally and radiotherapy is currently an essential component in the management of cancer patients, either alone or in combination with surgery or chemotherapy, both for cure or palliation. It is now recognized that safe and effective radiotherapy service needs not only substantial capital investment in radiotherapy equipment and specially designed facilities but also continuous investment in maintenance and upgrading of the equipment to comply with the technical progress, but also in training the staff. The recent IAEA-TECDOC publication 'Setting up a Radiotherapy Programme: Clinical, Medical Physics, Radiation Protection and Safety Aspects' provides general guidelines for designing and implementing radiotherapy services in Member States. Advances in computer technology have enabled the possibility of transitioning from basic 2- dimensional treatment planning and delivery (2-D radiotherapy) to a more sophisticated approach with 3-dimensional conformal radiotherapy (3-D CRT). Whereas 2-D radiotherapy can be applied with simple equipment, infrastructure and training, transfer to 3-D conformal treatments requires more resources in technology, equipment, staff and training. A novel radiation treatment approach using Intensity Modulated Radiation Therapy (IMRT) that optimizes the delivery of radiation to irregularly shaped tumour volumes demands even more sophisticated equipment and seamless teamwork, and consequentially more resources, advanced training and more time for treatment planning and verification of dose delivery than 3-D CRT. Whereas 3-D CRT can be considered as a standard, IMRT is still evolving. Due to the increased interest of Member States to the modern application of radiotherapy the IAEA has received a number of requests for guidance coming from radiotherapy departments that wish to upgrade their facilities to 3-D CRT and IMRT through Technical Cooperation programme. These requests are expected to increase

  15. Thermoelectric material including conformal oxide layers and method of making the same using atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Jung Young; Ahn, Dongjoon; Salvador, James R.; Meisner, Gregory P.

    2016-06-07

    A thermoelectric material includes a substrate particle and a plurality of conformal oxide layers formed on the substrate particle. The plurality of conformal oxide layers has a total oxide layer thickness ranging from about 2 nm to about 20 nm. The thermoelectric material excludes oxide nanoparticles. A method of making the thermoelectric material is also disclosed herein.

  16. Lasing and high temperature phase transitions in atomic systems with dressed state polaritons

    CERN Document Server

    Chestnov, I Yu

    2013-01-01

    We consider the fundamental problem of high temperature phase transitions in the system of high density two-level atoms off-resonantly interacting with a pump field in the presence of optical collisions (OCs) and placed in the cavity. OCs are considered in the framework of thermalization of atomic dressed state (DS) population. For the case of a strong atom-field coupling condition we analyze the problem of thermodynamically equilibrium superradiant phase transition for the order parameter representing a real amplitude of cavity mode and taking place as a result of atomic DSs thermalization process. Such transition is also connected with condensed (coherent) properties of low branch (LB) DS-polaritons occurring in the cavity. For describing non-equilibrium phase transitions we derive Maxwell-Bloch like equations which account for cavity decay rate, collisional decay rate and spontaneous emission. Various aspects of transitions to laser field formation by using atomic DS levels for both positive and negative d...

  17. Blocking of diffusion transitions of metal atoms at excitation of weakly attenuating plasmons

    CERN Document Server

    Gorelov, B M; Ogenko, V M; Shalyapina, G M

    2001-01-01

    One studies blocking transitions of metal atoms in YBa sub 2 Cu sub 3 O sub 7 high-temperature superconductor at excitation of weakly attenuating acoustic plasmons and at thermodesorption of 01 atoms. Ni and Au atoms were as diffusates. YBa sub 2 Cu sub 3 O sub 7 sub - subdelta specimens were irradiated by 9.4 GHz frequency and 10 sup 4 W power pulsed UHF-field. Temperature dependences of diffusion coefficient of Ni and Au atoms prior and subsequent to UHF irradiation and thermodesorption of 0 atoms are analyzed. It is pointed out that subsequent to UHF irradiation resistance of a specimen increases near transition into superconducting state. One makes a conclusion that blocking of space and surface transitions of Ni and Au atoms results from accumulation a large number of interstitial atoms in the surface layer of crystallites

  18. Chiral phase transition at finite temperature and conformal dynamics in large Nf QCD

    CERN Document Server

    Miura, Kohtaroh

    2011-01-01

    We investigate the chiral phase transition at finite temperature (T) in colour SU(Nc=3) Quantum Chromodynamics (QCD) with six species of fermions (Nf=6) in the fundamental representation by using lattice QCD with improved staggered fermions. By considering lattices with several temporal extensions Nt, we observe asymptotic scaling for Nt > 4. We then extract the dimensionless ratio Tc/Lambda_L (Lambda_L = Lattice Lambda-parameter) for Nf = 6 and Nf = 8, the latter relying on our earlier results. Further, we collect the critical couplings beta^c for the chiral phase transition at Nf = 0 (quenched), and Nf = 4 at a fixed Nt = 6. The results are consistent with enhanced fermionic screening at larger Nf. The Tc/Lambda_L depends very mildly on Nf in the Nf = 0 - 4 region, starts increasing at Nf = 6, and becomes significantly larger at Nf = 8, close to the edge of the conformal window. We discuss interpretations of these results as well as their possible interrelation with preconformal dynamics in the light of a f...

  19. Magnetic anisotropies of late transition metal atomic clusters

    OpenAIRE

    Fernández-Seivane, Lucas; Ferrer, Jaime

    2006-01-01

    We analyze the impact of the magnetic anisotropy on the geometric structure and magnetic ordering of small atomic clusters of palladium, iridium, platinum and gold, using Density Functional Theory. Our results highlight the absolute need to include self-consistently the spin orbit interaction in any simulation of the magnetic properties of small atomic clusters, and a complete lack of universality in the magnetic anisotropy of small-sized atomic clusters.

  20. [Dynamics of electron-conformational transitions in proteins and physical mechanisms of biomacromolecule function].

    Science.gov (United States)

    Shaĭtan, K V

    1992-01-01

    The proteins can be considered as a microheterogeneous structured media possessing memory and feedback properties. The conformational energy surface depends on the chemical states of protein groups. Conformational motions are local diffusion with relaxation times much longer than vibrational relaxation times in condensed media. Owing to the hierarchy of relaxation times chemical reaction rates depend on conformation parametrically. Regulation of functional activity by conformational mobility is accomplished via transmission of information in the form of changes in the distribution functions of separate groups along the conformational substates. The interpretation of drastic effects on conformational mobility needs super-stochastic approaches. A possible mechanism of sharp conformational change are discussed in terms of the catastrophe theory.

  1. Enhancing pairwise state-transition weights: A new weighting scheme in simulated tempering that can minimize transition time between a pair of conformational states

    Science.gov (United States)

    Qiao, Qin; Zhang, Hou-Dao; Huang, Xuhui

    2016-04-01

    Simulated tempering (ST) is a widely used enhancing sampling method for Molecular Dynamics simulations. As one expanded ensemble method, ST is a combination of canonical ensembles at different temperatures and the acceptance probability of cross-temperature transitions is determined by both the temperature difference and the weights of each temperature. One popular way to obtain the weights is to adopt the free energy of each canonical ensemble, which achieves uniform sampling among temperature space. However, this uniform distribution in temperature space may not be optimal since high temperatures do not always speed up the conformational transitions of interest, as anti-Arrhenius kinetics are prevalent in protein and RNA folding. Here, we propose a new method: Enhancing Pairwise State-transition Weights (EPSW), to obtain the optimal weights by minimizing the round-trip time for transitions among different metastable states at the temperature of interest in ST. The novelty of the EPSW algorithm lies in explicitly considering the kinetics of conformation transitions when optimizing the weights of different temperatures. We further demonstrate the power of EPSW in three different systems: a simple two-temperature model, a two-dimensional model for protein folding with anti-Arrhenius kinetics, and the alanine dipeptide. The results from these three systems showed that the new algorithm can substantially accelerate the transitions between conformational states of interest in the ST expanded ensemble and further facilitate the convergence of thermodynamics compared to the widely used free energy weights. We anticipate that this algorithm is particularly useful for studying functional conformational changes of biological systems where the initial and final states are often known from structural biology experiments.

  2. Enhancing pairwise state-transition weights: A new weighting scheme in simulated tempering that can minimize transition time between a pair of conformational states.

    Science.gov (United States)

    Qiao, Qin; Zhang, Hou-Dao; Huang, Xuhui

    2016-04-21

    Simulated tempering (ST) is a widely used enhancing sampling method for Molecular Dynamics simulations. As one expanded ensemble method, ST is a combination of canonical ensembles at different temperatures and the acceptance probability of cross-temperature transitions is determined by both the temperature difference and the weights of each temperature. One popular way to obtain the weights is to adopt the free energy of each canonical ensemble, which achieves uniform sampling among temperature space. However, this uniform distribution in temperature space may not be optimal since high temperatures do not always speed up the conformational transitions of interest, as anti-Arrhenius kinetics are prevalent in protein and RNA folding. Here, we propose a new method: Enhancing Pairwise State-transition Weights (EPSW), to obtain the optimal weights by minimizing the round-trip time for transitions among different metastable states at the temperature of interest in ST. The novelty of the EPSW algorithm lies in explicitly considering the kinetics of conformation transitions when optimizing the weights of different temperatures. We further demonstrate the power of EPSW in three different systems: a simple two-temperature model, a two-dimensional model for protein folding with anti-Arrhenius kinetics, and the alanine dipeptide. The results from these three systems showed that the new algorithm can substantially accelerate the transitions between conformational states of interest in the ST expanded ensemble and further facilitate the convergence of thermodynamics compared to the widely used free energy weights. We anticipate that this algorithm is particularly useful for studying functional conformational changes of biological systems where the initial and final states are often known from structural biology experiments. PMID:27389209

  3. Inelastic scattering in atom-diatomic molecule collisions. II - Effect of rotation on vibrational transition

    Science.gov (United States)

    Stallcop, J. R.

    1975-01-01

    Rotational and vibrational transitions in a diatomic molecule caused by collisions with an atom are analyzed by a semiclassical method for conditions where the rotational transitions can be handled well by the sudden approximation and the vibrational transitions belong to the adiabatic regime. The contribution to the vibrational transition probability from the correction, which takes the finite value of the spacing between rotational energy levels into account, is examined.-

  4. Conformations of Carnosine in Aqueous Solutions by All-Atom Molecular Dynamics Simulations and 2D-NOSEY Spectrum

    Institute of Scientific and Technical Information of China (English)

    Rong Zhang; Dan Wang; Wen-juan Wu

    2013-01-01

    All-atom molecular simulations and two-dimensional nuclear overhauser effect spectrum have been used to study the conformations of carnosine in aqueous solution.Intramolecular distances,root-mean-square deviation,radius of gyration,and solvent-accessible surface are used to characterize the properties of the carnosine.Carnosine can shift between extended and folded states,but exists mostly in extended state in water.Its preference for extension in pure water has been proven by the 2D nuclear magnetic resonance (NMR) experiment.The NMR experimental results are consistent with the molecular dynamics simulations.

  5. Forbidden atomic transitions driven by an intensity-modulated laser trap.

    Science.gov (United States)

    Moore, Kaitlin R; Anderson, Sarah E; Raithel, Georg

    2015-01-20

    Spectroscopy is an essential tool in understanding and manipulating quantum systems, such as atoms and molecules. The model describing spectroscopy includes the multipole-field interaction, which leads to established spectroscopic selection rules, and an interaction that is quadratic in the field, which is not often employed. However, spectroscopy using the quadratic (ponderomotive) interaction promises two significant advantages over spectroscopy using the multipole-field interaction: flexible transition rules and vastly improved spatial addressability of the quantum system. Here we demonstrate ponderomotive spectroscopy by using optical-lattice-trapped Rydberg atoms, pulsating the lattice light and driving a microwave atomic transition that would otherwise be forbidden by established spectroscopic selection rules. This ability to measure frequencies of previously inaccessible transitions makes possible improved determinations of atomic characteristics and constants underlying physics. The spatial resolution of ponderomotive spectroscopy is orders of magnitude better than the transition frequency would suggest, promising single-site addressability in dense particle arrays for quantum computing applications.

  6. Critically evaluated atomic transition probabilities for Ba I and Ba II

    International Nuclear Information System (INIS)

    Atomic transition probabilities for allowed and forbidden lines of Ba I and Ba II are tabulated, based on a critical evaluation of recent literature sources. The data are presented in multiplet format and are ordered by increasing excitation energies. (author)

  7. Local Softening as a Universal Feature of Conformational Transitions of Biological Macromolecules

    OpenAIRE

    Qu, Hao

    2012-01-01

    Conformational changes are essential to biological macromolecules because they are tightly coupled to function and dynamics of these macromolecules. In cells, under most occasions, the macromolecules are deformed rather than in free states as in solution, due to mechanical stresses exposed. It is therefore of great interest and importance to understand conformational changes associated with the macromolecules. More in details, the conformational changes of two types of macromolecules, DNA and...

  8. COMPREHENSIVE SPECTROSCOPIC DATA TABULATIONS AND PROGRESS IN THE COMPILATION OF ATOMIC TRANSITION PROBABILITIES

    OpenAIRE

    Wiese, W.

    1991-01-01

    The critical data compilation work as well as the bibliographical efforts of two data centers on atomic spectroscopy at the National Institute of Standards and Technology (formerly the National Bureau of Standards) are briefly reviewed. A complete listing of all current compilations on wavelengths, energy levels and transition probabilities is given. A recently completed large tabulation of atomic transition probabilities for the Fe-group elements comprising about 18000 lines is discussed in ...

  9. An analysis of stable forms of CL-20: A DFT study of conformational transitions, infrared and Raman spectra

    Science.gov (United States)

    Kholod, Yana; Okovytyy, Sergiy; Kuramshina, Gulnara; Qasim, Mohammad; Gorb, Leonid; Leszczynski, Jerzy

    2007-10-01

    The most stable forms of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) were analyzed at the B3LYP/6-31G+(d,p) level of theory. The mechanism of conformational transformations was clarified. The activation energies of those transitions were found to be quite low and lie in the range 1.2-4.0 kcal mol -1. IR and Raman spectra of the studied CL-20 forms were simulated. The predicted vibrational modes were used for comparison with the experimental values. The unique peaks for each of the conformers in IR and Raman spectra were found. These peaks can be used as the "signatures" of the studied conformers and for identification of different polymorphs of CL-20 in mixtures.

  10. Atomic Structure of a Spinel-like Transition Al2O3 (100) Surface

    DEFF Research Database (Denmark)

    Jensen, Thomas Nørregaard; Meinander, Kristoffer; Helveg, Stig;

    2014-01-01

    We study a crystalline epitaxial alumina thin film with the characteristics of a spinel-type transition Al2O3(100) surface by using atom-resolved noncontact atomic force microscopy and density functional theory. It is shown that the films are terminated by an Al-O layer rich in Al vacancies...

  11. Bragg scattering as a probe of atomic wave functions and quantum phase transitions in optical lattices.

    Science.gov (United States)

    Miyake, Hirokazu; Siviloglou, Georgios A; Puentes, Graciana; Pritchard, David E; Ketterle, Wolfgang; Weld, David M

    2011-10-21

    We have observed Bragg scattering of photons from quantum degenerate ^{87}Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose position and momentum width is Heisenberg limited. The spatial coherence of the wave function leads to revivals in the Bragg scattered light due to the atomic Talbot effect. The decay of revivals across the superfluid to Mott insulator transition indicates the loss of superfluid coherence. PMID:22107532

  12. Some theoretical aspects of the group-IIIA-ion atomic clocks: Intercombination transition probabilities

    International Nuclear Information System (INIS)

    The main focus of this paper is the theoretical study of the 3P1→1S0 intercombination transition probabilities of the group-IIIA ions that are excellent candidates for high-accuracy atomic clocks. The importance of relativistic effects on the intercombination transition probabilities is made apparent by comparing their calculated values with those of the allowed 1P1→1S0 transition probabilities. In striking contrast to the allowed transition probabilities, the intercombination transition probabilities exhibit a strong Z dependence

  13. Observation of Electric Quadrupole Transitions to Rydberg nd States of Ultracold Rubidium Atoms

    CERN Document Server

    Tong, D; Van Kempen, E G M; Pavlovic, Z; Stanojevic, J; Côté, R; Eyler, E E; Gould, P L

    2008-01-01

    We report the observation of dipole-forbidden, but quadrupole-allowed, one-photon transitions to high Rydberg states in Rb. Using pulsed UV excitation of ultracold atoms in a magneto-optical trap, we excite $5s \\to nd$ transitions over a range of principal quantum numbers $n=27-59$. Compared to dipole-allowed (E1) transitions from $5s \\to np$, these E2 transitions are weaker by a factor of approximately 2000. We also report measurements of the anomalous $np_{3/2} : np_{1/2}$ fine-structure transition strength ratio for $n=28-75$. Both results are in agreement with theoretical predictions.

  14. Strong Coupling on a Forbidden Transition in Strontium and Nondestructive Atom Counting

    CERN Document Server

    Norcia, Matthew A

    2015-01-01

    We observe strong collective coupling between an optical cavity and the forbidden spin singlet to triplet optical transition $^1$S$_0$ to $^3$P$_1$ in an ensemble of $^{88}$Sr. Despite the transition being 1000 times weaker than a typical dipole transition, we observe a well resolved vacuum Rabi splitting. We use the observed vacuum Rabi splitting to make non-destructive measurements of atomic population with the equivalent of projection-noise limited sensitivity and minimal heating ($<0.01$ photon recoils/atom). This technique may be used to enhance the performance of optical lattice clocks by generating entangled states and reducing dead time.

  15. Forbidden atomic transitions driven by an intensity-modulated laser trap

    CERN Document Server

    Moore, Kaitlin R; Raithel, Georg

    2014-01-01

    Spectroscopy is an essential tool in understanding and manipulating quantum systems, such as atoms and molecules. The model describing spectroscopy includes a multipole-field interaction, which leads to established spectroscopic selection rules, and an interaction that is quadratic in the field, which is often neglected. However, spectroscopy using the quadratic (ponderomotive) interaction promises two significant advantages over spectroscopy using the multipole-field interaction: flexible transition rules and vastly improved spatial addressability of the quantum system. For the first time, we demonstrate ponderomotive spectroscopy by using optical-lattice-trapped Rydberg atoms, pulsating the lattice light at a microwave frequency, and driving a microwave atomic transition that would otherwise be forbidden by established spectroscopic selection rules. This new ability to measure frequencies of previously inaccessible transitions makes possible improved determinations of atomic characteristics and constants un...

  16. Off-resonant transitions in the collective dynamics of multi-level atomic ensembles

    DEFF Research Database (Denmark)

    Miroshnychenko, Yevhen; Mølmer, Klaus

    2013-01-01

    We study the contributions of off-resonant transitions to the dynamics of a system of N multi-level atoms sharing one excitation and interacting with the quantized vector electromagnetic field. The rotating wave approximation significantly simplifies the derivation of the equations of motion...... describing the collective atomic dynamics, but it leads to an incorrect expression for the dispersive part of the atom–atom interaction terms. For the case of two-level atoms and a scalar electromagnetic field, it turns out that the atom–atom interaction can be recovered correctly if integrals over the...... photon mode frequencies are extended to incorporate negative values. We explicitly derive the atom–atom interaction for multi-level atoms, coupled to the full vector electromagnetic field, and we recover also in this general case the validity of the results obtained by the extension to negative...

  17. Laboratory atomic transition data for precise optical quasar absorption spectroscopy

    CERN Document Server

    Murphy, Michael T

    2013-01-01

    Quasar spectra reveal a rich array of important astrophysical information about galaxies which intersect the quasar line of sight. They also enable tests of the variability of fundamental constants over cosmological time and distance-scales. Key to these endeavours are the laboratory frequencies, isotopic and hyperfine structures of various metal-ion transitions. Here we review and synthesize the existing information about these quantities for 43 transitions which are important for measuring possible changes in the fine-structure constant, alpha, using optical quasar spectra, i.e. those of Na, Mg, Al, Si, Ca, Cr, Mn, Fe, Ni and Zn. We also summarize the information currently missing that precludes more transitions being used. We present an up-to-date set of coefficients, q, which define the sensitivity of these transitions to variations in alpha. New calculations of isotopic structures and q coefficients are performed for SiII and TiII, including SiII 1808 and TiII 1910.6/1910.9 for the first time. Finally, s...

  18. Probing an Excited-State Atomic Transition Using Hyperfine Quantum Beat Spectroscopy

    CERN Document Server

    Wade, Christopher G; Keaveney, James; Adams, Charles S; Weatherill, Kevin J

    2014-01-01

    We describe a method to observe the dynamics of an excited-state transition in a room temperature atomic vapor using hyperfine quantum beats. Our experiment using cesium atoms consists of a pulsed excitation of the D2 transition, and continuous-wave driving of an excited-state transition from the 6P$_{3/2}$ state to the 7S$_{1/2}$ state. We observe quantum beats in the fluorescence from the 6P$_{3/2}$ state which are modified by the driving of the excited-state transition. The Fourier spectrum of the beat signal yields evidence of Autler-Townes splitting of the 6P$_{3/2}$, F = 5 hyperfine level and Rabi oscillations on the excited-state transition. A detailed model provides qualitative agreement with the data, giving insight to the physical processes involved.

  19. Analysis of the conformation of the androgen receptor in spinal bulbar muscular atrophy by atomic force microscopy.

    Science.gov (United States)

    Jochum, Tobias; Cato, Andrew C B

    2014-01-01

    Spinal bulbar muscular atrophy (SBMA) (also known as Kennedy's disease) is a motor degenerative disease caused by an amplification of the polyglutamine stretch at the N-terminus of the human androgen receptor (AR). Amplifications larger than 40 glutamine residues are thought to lead to the disease. A characteristic feature of this disease is a ligand-dependent misfolding and aggregation of the mutant receptor that lead to the death of motor neurons. Initially, large cytoplasmic and nuclear aggregates reaching sizes of 6 μm were thought to be the pathogenic agents. Later studies have suggested that oligomeric species with sizes of less than 1 μm that occur prior to the formation of the larger aggregates are the toxic agents. However, there have been disagreements regarding the shape of these oligomers, as most studies have been carried out with peptide fragments of the androgen receptor containing different lengths of polyglutamine stretch. We have isolated the wild-type AR with a polyglutamine stretch of 22 (ARQ22) and a mutant receptor with a stretch of 65 (ARQ65) using a baculovirus system and have analyzed the oligomeric structures formed by these receptors with atomic force microscopy. This method has allowed us to determine the conformations of the full-length wild-type and mutant AR and revealed the conformation of the mutant AR that causes SBMA.

  20. Role of the Subunits Interactions in the Conformational Transitions in Adult Human Hemoglobin: an Explicit Solvent Molecular Dynamics Study

    CERN Document Server

    Yusuff, Olaniyi K; Bussi, Giovanni; Raugei, Simone

    2012-01-01

    Hemoglobin exhibits allosteric structural changes upon ligand binding due to the dynamic interactions between the ligand binding sites, the amino acids residues and some other solutes present under physiological conditions. In the present study, the dynamical and quaternary structural changes occurring in two unligated (deoxy-) T structures, and two fully ligated (oxy-) R, R2 structures of adult human hemoglobin were investigated with molecular dynamics. It is shown that, in the sub-microsecond time scale, there is no marked difference in the global dynamics of the amino acids residues in both the oxy- and the deoxy- forms of the individual structures. In addition, the R, R2 are relatively stable and do not present quaternary conformational changes within the time scale of our simulations while the T structure is dynamically more flexible and exhibited the T\\rightarrow R quaternary conformational transition, which is propagated by the relative rotation of the residues at the {\\alpha}1{\\beta}2 and {\\alpha}2{\\b...

  1. The Lattice Kinetic Monte Carlo Simulation of Atomic Diffusion and Structural Transition for Gold

    Science.gov (United States)

    He, Xiang; Cheng, Feng; Chen, Zhao-Xu

    2016-01-01

    For the kinetic simulation of metal nanoparticles, we developed a self-consistent coordination-averaged energies for Au atoms based on energy properties of gold bulk phases. The energy barrier of the atom pairing change is proposed and holds for the microscopic reversibility principle. By applying the lattice kinetic Monte Carlo simulation on gold films, we found that the atomic diffusion of Au on the Au(111) surface undergoes a late transition state with an energy barrier of about 0.2 eV and a prefactor between 40~50 Å2/ps. This study also investigates the structural transition from spherical to faceted gold nanoparticles upon heating. The temperatures of structural transition are in agreement with the experimental melting temperatures of gold nanoparticles with diameters ranging from 2 nm to 8 nm. PMID:27629538

  2. The Lattice Kinetic Monte Carlo Simulation of Atomic Diffusion and Structural Transition for Gold.

    Science.gov (United States)

    He, Xiang; Cheng, Feng; Chen, Zhao-Xu

    2016-01-01

    For the kinetic simulation of metal nanoparticles, we developed a self-consistent coordination-averaged energies for Au atoms based on energy properties of gold bulk phases. The energy barrier of the atom pairing change is proposed and holds for the microscopic reversibility principle. By applying the lattice kinetic Monte Carlo simulation on gold films, we found that the atomic diffusion of Au on the Au(111) surface undergoes a late transition state with an energy barrier of about 0.2 eV and a prefactor between 40~50 Å(2)/ps. This study also investigates the structural transition from spherical to faceted gold nanoparticles upon heating. The temperatures of structural transition are in agreement with the experimental melting temperatures of gold nanoparticles with diameters ranging from 2 nm to 8 nm. PMID:27629538

  3. Effect of graphene oxide on the conformational transitions of amyloid beta peptide: A molecular dynamics simulation study.

    Science.gov (United States)

    Baweja, Lokesh; Balamurugan, Kanagasabai; Subramanian, Venkatesan; Dhawan, Alok

    2015-09-01

    The interactions between nanomaterials (NMs) and amyloid proteins are central to the nanotechnology-based diagnostics and therapy in neurodegenerative disorders such as Alzheimer's and Parkinson's. Graphene oxide (GO) and its derivatives have shown to modulate the aggregation pattern of disease causing amyloid beta (Aβ) peptide. However, the mechanism is still not well understood. Using molecular dynamics simulations, the effect of graphene oxide (GO) and reduced graphene oxide (rGO) having carbon:oxygen ratio of 4:1 and 10:1, respectively, on the conformational transitions (alpha-helix to beta-sheet) and the dynamics of the peptide was investigated. GO and rGO decreased the beta-strand propensity of amino acid residues in Aβ. The peptide displayed different modes of adsorption on GO and rGO. The adsorption on GO was dominated by electrostatic interactions, whereas on rGO, both van der Waals and electrostatic interactions contributed in the adsorption of the peptide. Our study revealed that the slight increase in the hydrophobic patches on rGO made it more effective inhibitor of conformational transitions in the peptide. Alpha helix-beta sheet transition in Aβ peptide could be one of the plausible mechanism by which graphene oxide may inhibit amyloid fibrillation.

  4. Conformal Coating of Three-Dimensional Nanostructures via Atomic Layer Deposition for Development of Advanced Energy Storage Devices and Plasmonic Transparent Conductors

    Science.gov (United States)

    Malek, Gary A.

    Due to the prodigious amount of electrical energy consumed throughout the world, there exists a great demand for new and improved methods of generating electrical energy in a clean and renewable manner as well as finding more effective ways to store it. This enormous task is of great interest to scientists and engineers, and much headway is being made by utilizing three-dimensional (3D) nanostructured materials. This work explores the application of two types of 3D nanostructured materials toward fabrication of advanced electrical energy storage and conversion devices. The first nanostructured material consists of vertically aligned carbon nanofibers. This three-dimensional structure is opaque, electrically conducting, and contains active sites along the outside of each fiber that are conducive to chemical reactions. Therefore, they make the perfect 3D conducting nanostructured substrate for advanced energy storage devices. In this work, the details for transforming vertically aligned carbon nanofiber arrays into core-shell structures via atomic layer deposition as well as into a mesoporous manganese oxide coated supercapacitor electrode are given. Another unique type of three-dimensional nanostructured substrate is nanotextured glass, which is transparent but non-conducting. Therefore, it can be converted to a 3D transparent conductor for possible application in photovoltaics if it can be conformally coated with a conducting material. This work details that transformation as well as the addition of plasmonic gold nanoparticles to complete the transition to a 3D plasmonic transparent conductor.

  5. Observation of Aubry-type transition in finite atom chains via friction.

    Science.gov (United States)

    Bylinskii, Alexei; Gangloff, Dorian; Counts, Ian; Vuletić, Vladan

    2016-07-01

    The highly nonlinear many-body physics of a chain of mutually interacting atoms in contact with a periodic substrate gives rise to complex static and dynamical phenomena, such as structural phase transitions and friction. In the limit of an infinite chain incommensurate with the substrate, Aubry predicted a transition with increasing substrate potential, from the chain's intrinsic arrangement free to slide on the substrate, to a pinned arrangement favouring the substrate pattern. So far, the Aubry transition has not been observed. Here, using spatially resolved position and friction measurements of cold trapped ions in an optical lattice, we observed a finite version of the Aubry transition and the onset of its hallmark fractal atomic arrangement. Notably, the observed critical lattice depth for few-ion chains agrees well with the infinite-chain prediction. Our results elucidate the connection between competing ordering patterns and superlubricity in nanocontacts-the elementary building blocks of friction. PMID:26998915

  6. The Calculations of Oscillator Strengths and Transition Probabilities for Atomic Fluorine

    OpenAIRE

    ÇELİK, Gültekin; KILIÇ, H. Şükür; Akin, Erhan

    2006-01-01

    Oscillator strengths for transitions between individual lines belonging to some doublet and quartet terms, and multiplet transition probabilities of atomic fluorine have been calculated using weakest bound electron potential model theory (WBEPMT). In the determination of relevant parameters, we employed numerical non-relativistic Hartree-Fock (NRHF) wave functions for expectation values of radii and the necessary energy values have been taken from experimental energy data in the liter...

  7. Mean field dynamics of superfluid-insulator phase transition in a gas of ultra cold atoms

    OpenAIRE

    Zakrzewski, Jakub

    2004-01-01

    A large scale dynamical simulation of the superfluid to Mott insulator transition in the gas of ultra cold atoms placed in an optical lattice is performed using the time dependent Gutzwiller mean field approach. This approximate treatment allows us to take into account most of the details of the recent experiment [Nature 415, 39 (2002)] where by changing the depth of the lattice potential an adiabatic transition from a superfluid to a Mott insulator state has been reported. Our simulations re...

  8. Accounting for conformational flexibility and torsional anharmonicity in the H + CH{sub 3}CH{sub 2}OH hydrogen abstraction reactions: A multi-path variational transition state theory study

    Energy Technology Data Exchange (ETDEWEB)

    Meana-Pañeda, Rubén; Fernández-Ramos, Antonio, E-mail: qf.ramos@usc.es [Department of Physical Chemistry and Center for Research in Biological Chemistry and Molecular Materials, University of Santiago de Compostela, 15706 Santiago de Compostela (Spain)

    2014-05-07

    This work reports a detailed theoretical study of the hydrogen abstraction reactions from ethanol by atomic hydrogen. The calculated thermal rate constants take into account torsional anharmonicity and conformational flexibility, in addition to the variational and tunneling effects. Specifically, the kinetics calculations were performed by using multi-path canonical variational transition state theory with least-action path tunneling corrections, to which we have added the two-dimensional non-separable method to take into account torsional anharmonicity. The multi-path thermal rate constant is expressed as a sum over conformational reaction channels. Each of these channels includes all the transition states that can be reached by internal rotations. The results show that, in the interval of temperatures between 250 and 2500 K, the account for multiple paths leads to higher thermal rate constants with respect to the single path approach, mainly at low and at high temperatures. In addition, torsional anharmonicity enhances the slope of the Arrhenius plot in this range of temperatures. Finally, we show that the incorporation of tunneling into the hydrogen abstraction reactions substantially changes the contribution of each of the transition states to the conformational reaction channel.

  9. 1 and 2 transitions in the ground-state configuration of atomic manganese

    Indian Academy of Sciences (India)

    S Kabakçi; B Karaçoban Usta; L Özdemir

    2015-10-01

    Using the multiconfiguration Hartree–Fock approximation within the framework of the Breit–Pauli Hamiltonian (MCHF+BP) and the relativistic Hartree–Fock (HFR) approximation, we have calculated the forbidden transition (1 and 2) parameters such as transition energies, logarithmic weighted oscillator strengths and transition probabilities between the fine-structure levels in the ground-state configuration of 3d5 4s2 for atomic manganese (Mn I, Z =25). A discussion of these calculations for manganese using MCHF+BP and HFR methods is given here.

  10. Conformation and dynamics of biopharmaceuticals: transition of mass spectrometry-based tools from academe to industry

    OpenAIRE

    Kaltashov, Igor A.; Bobst, Cedric E.; Abzalimov, Rinat R.; Berkowitz, Steven A; Houde, Damian

    2009-01-01

    Mass spectrometry plays a very visible role in biopharmaceutical industry, although its use in development, characterization and quality control of protein drugs is mostly limited to the analysis of covalent structure (amino acid sequence and post-translational modifications). Despite the centrality of protein conformation to biological activity, stability and safety of biopharmaceutical products, the expanding arsenal of mass spectrometry-based methods that are currently available to probe h...

  11. Interfacing transitions of different alkali atoms and telecom bands using one narrowband photon pair source

    CERN Document Server

    Schunk, Gerhard; Strekalov, Dmitry V; Förtsch, Michael; Sedlmeir, Florian; Schwefel, Harald G L; Göbelt, Manuela; Christiansen, Silke; Leuchs, Gerd; Marquardt, Christoph

    2015-01-01

    Photon-atom coupling, in particular for proposed quantum repeater schemes, requires pure and versatile sources of quantum light. Here we demonstrate coupling to alkali dipole transitions in the near-infrared with a tunable source of photon pairs generated via spontaneous parametric down-conversion in a whispering-gallery mode resonator (WGMR). We have developed novel wavelength tuning mechanisms, which allow for a coarse step-wise central wavelength tuning from 790 nm to 1630 nm as well as continuous tuning with MHz resolution. We demonstrate the compatibility of our source with atomic transitions, such as the D1 line of rubidium at 795 nm (idler at 1608 nm) and cesium at 895\\,nm (idler at 1312 nm). At the cesium D1 transition, we exemplarily show a continuous scanning of the signal wavelength over the Doppler-broadened absorption line, and finally a heralded single photon spectroscopy of the atomic decay. Providing this flexibility in connecting various atomic transitions with telecom wavelengths, we demonst...

  12. On cross sections of intercombination transitions between high-excited levels in electron-atom collisions

    International Nuclear Information System (INIS)

    The cross sections of intercombination transitions (ICT) between high-excited levels of atoms during the collisions of the latter with electrons are considered. A method is proposed for calculating ICT cross sections which are orbital quantum number totals. A comparison with the cross section calculated within the scope of quasiclassic approach is performed. Both methods yield close results

  13. Orientational invariance of the rotational transition probability in the sudden approximation. [atom-molecule collisions

    Science.gov (United States)

    Stallcop, J. R.

    1974-01-01

    Semiclassical collisions of an atom with a rigid-rotor molecule are examined in the sudden approximation. The rotational transition probability is shown to be invariant with respect to the choice of orientation for the molecular coordinate system; this fact contradicts recently reported results of a computer analysis. The present analysis may lead to an improved interpretation of recent molecular beam measurements.

  14. The substrate-driven transition to an inward-facing conformation in the functional mechanism of the dopamine transporter.

    Directory of Open Access Journals (Sweden)

    Jufang Shan

    Full Text Available BACKGROUND: The dopamine transporter (DAT, a member of the neurotransmitter:Na(+ symporter (NSS family, terminates dopaminergic neurotransmission and is a major molecular target for psychostimulants such as cocaine and amphetamine, and for the treatment of attention deficit disorder and depression. The crystal structures of the prokaryotic NSS homolog of DAT, the leucine transporter LeuT, have provided critical structural insights about the occluded and outward-facing conformations visited during the substrate transport, but only limited clues regarding mechanism. To understand the transport mechanism in DAT we have used a homology model based on the LeuT structure in a computational protocol validated previously for LeuT, in which steered molecular dynamics (SMD simulations guide the substrate along a pathway leading from the extracellular end to the intracellular (cytoplasmic end. METHODOLOGY/PRINCIPAL FINDINGS: Key findings are (1 a second substrate binding site in the extracellular vestibule, and (2 models of the conformational states identified as occluded, doubly occupied, and inward-facing. The transition between these states involve a spatially ordered sequence of interactions between the two substrate-binding sites, followed by rearrangements in structural elements located between the primary binding site and the cytoplasmic end. These rearrangements are facilitated by identified conserved hinge regions and a reorganization of interaction networks that had been identified as gates. CONCLUSIONS/SIGNIFICANCE: Computational simulations supported by information available from experiments in DAT and other NSS transporters have produced a detailed mechanistic proposal for the dynamic changes associated with substrate transport in DAT. This allosteric mechanism is triggered by the binding of substrate in the S2 site in the presence of the substrate in the S1 site. Specific structural elements involved in this mechanism, and their roles in the

  15. Hyperfine-induced electric dipole contributions to the electric octupole and magnetic quadrupole atomic clock transitions

    Science.gov (United States)

    Dzuba, V. A.; Flambaum, V. V.

    2016-05-01

    Hyperfine-induced electric dipole contributions may significantly increase probabilities of otherwise very weak electric octupole and magnetic quadrupole atomic clock transitions (e.g., transitions between s and f electron orbitals). These transitions can be used for exceptionally accurate atomic clocks, quantum information processing, and the search for dark matter. They are very sensitive to new physics beyond the standard model, such as temporal variation of the fine-structure constant, the Lorentz invariance, and Einstein equivalence principle violation. We formulate conditions under which the hyperfine-induced electric dipole contribution dominates and perform calculations of the hyperfine structure and E3, M2 and the hyperfine-induced E1 transition rates for a large number of atoms and ions of experimental interest. Due to the hyperfine quenching the electric octupole clock transition in +173Yb is 2 orders of magnitude stronger than that in currently used +171Yb. Some enhancement is found in 13+143Nd, 14+149Pm, 14+147Sm, and 15+147Sm ions.

  16. Giant perpendicular magnetic anisotropy of an individual atom on two-dimensional transition metal dichalcogenides

    Science.gov (United States)

    Odkhuu, Dorj

    2016-08-01

    Exploring magnetism and magnetic anisotropy in otherwise nonmagnetic two-dimensional materials, such as graphene and transition metal dichalcogenides, is at the heart of spintronics research. Herein, using first-principles calculations we explore the possibility of reaching an atomic-scale perpendicular magnetic anisotropy by carefully exploring the large spin-orbit coupling, orbital magnetism, and ligand field in a suitable choice of a two-dimensional structure with transition metal adatoms. More specifically, we demonstrate perpendicular magnetic anisotropy energies up to an order of 100 meV per atom in individual ruthenium and osmium adatoms at a monosulfur vacancy in molybdenum disulfide. We further propose a phenomenological model where a spin state transition that involves hybridization between molybdenum a1 and adatomic e' orbitals is a possible mechanism for magnetization reversal from an in-plane to perpendicular orientation.

  17. Temperature limits in laser cooling of free atoms with three-level cascade transitions

    CERN Document Server

    Cruz, Flavio C; Magno, Wictor C

    2013-01-01

    We employ semiclassical theoretical analysis to study laser cooling of free atoms using three-level cascade transitions, where the upper transition is much weaker than the lower one. This represents an alternate cooling scheme, particularly useful for group II atoms. We find that temperatures below the Doppler limits associated with each of these transitions are expected. The lowest temperatures arise from a remarkable increase in damping and reduced diffusion compared to two-level cooling. They are reached at the two-photon resonance, where there is a crossing between the narrow and the partially-dark dressed states, and can be estimated simply by the usual Doppler limit considering the decay rate of the optical coherence between these states.

  18. Tables of Transition Probabilities and Branching Ratios for Electric Dipole Transitions Between Arbitrary Levels of Hydrogen-Like Atoms

    Science.gov (United States)

    Omidvar, K.

    1980-01-01

    Branching ratios in hydrogen-like atoms due to electric-dipole transitions are tabulated for the initial principal and angular momentum quantum number n, lambda, and final principal and angular momentum quantum numbers n, lambda. In table 1, transition probabilities are given for transitions n, lambda, yields n, where sums have been made with respect to lambda. In this table, 2 or = n' or = 10, o or = lambda' or = n'-1, and 1 or = n or = n'-1. In addition, averages with respect to lambda' and sums with respect to n, and lifetimes are given. In table 2, branching ratios are given for transitions n' lambda' yields ni, where sums have been made with respect to lambda. In these tables, 2 or = n' or = 10, 0 or = lambda', n'-1, and 1 or = n or = n'-1. Averages with respect to lambda' are also given. In table 3, branching ratios are given for transitions n' lambda' yields in lambda, where 1 or = n or = 5, 0 or = lambda or = n-1, n n' or = 15, and 0 or = lambda' or = n(s), where n(s), is the smaller of the two numbers n'-1 and 6. Averages with respect to lambda' are given.

  19. Bose-Einstein condensation transition studies for atoms confined in Laguerre-Gaussian laser modes

    CERN Document Server

    Akin, T G; Dribus, Ben; Marzuola, Jeremy; Johnson, Lise; Alexander, Jason; Abraham, E R I

    2011-01-01

    Multiply-connected traps for cold, neutral atoms fix vortex cores of quantum gases. Laguerre-Gaussian laser modes are ideal for such traps due to their phase stability. We report theoretical calculations of the Bose-Einstein condensation transition properties and thermal characteristics of neutral atoms trapped in multiply connected geometries formed by Laguerre-Gaussian LG{p}{l} beams. Specifically, we consider atoms confined to the anti-node of a LG{0}{1} laser mode detuned to the red of an atomic resonance frequency, and those confined in the node of a blue-detuned LG{1}{1} beam. We compare the results of using the full potential to those approximating the potential minimum with a simple harmonic oscillator potential. We find that deviations between calculations of the full potential and the simple harmonic oscillator can be up to 3%-8% for trap parameters consistent with typical experiments.

  20. Generation of multi-atom W states via Raman transition in an optical cavity

    International Nuclear Information System (INIS)

    A simple scheme is proposed to generate the W state of N λ-type neutral atoms trapped in an optical cavity via Raman transition. Conditional on no photon leakage from the cavity, the N-qubit W state can be prepared perfectly by turning on a classical coupling field for an appropriate time. Compared with the previous ones, our scheme requires neither individual laser addressing of the atoms, nor demand for controlling N atoms to go through an optical cavity simultaneously with a constant velocity. We investigate the influence of cavity decay using the quantum jump approach and show that the preparation time decreases and the success probability increases with atom number because of a collective enhancement of the coupling. (general)

  1. Inhomogeneous broadening of optical transitions of 87Rb atoms in an optical nanofiber trap

    CERN Document Server

    Lee, J; Hoffman, J E; Orozco, L A; Rolston, S L

    2014-01-01

    We experimentally demonstrate optical trapping of 87Rb atoms using a two-color evanescent field around an optical nanofiber. In our trapping geometry, a blue-detuned traveling wave whose polarization is nearly parallel to the polarization of a red-detuned standing wave produce significant vector light shifts that lead to broadening of the absorption profile of a near-resonant beam at the trapping site. A model that includes scalar, vector, and tensor light shifts of the probe transition $5S_{1/2}$-$5P_{3/2}$ from the trapping beams; weighted by the temperature-dependent position of the atoms in the trap qualitatively describe the observed asymmetric profile, and explained differences with previous experiments that used Cs atoms. The model provides a consistent way to extract the number of atoms in the trap.

  2. Narrow-linewidth cooling of $^{6}$Li atoms using the 2S-3P transition

    CERN Document Server

    Chen, Hao-Ze; Wu, Yu-Ping; Liu, Xiang-Pei; Wang, Xiao-Qiong; Chen, Yu-Ao; Pan, Jian-Wei

    2016-01-01

    We report on a narrow-linewidth cooling of $^{6}$Li atoms using the $2S_{1/2}\\to 3P_{3/2}$ transition in the ultraviolet (UV) wavelength regime. By combining the traditional red magneto-optical trap (MOT) at 671 nm and the UV MOT at 323 nm, we obtain a cold sample of $1.3\\times10^9$ atoms with a temperature of 58 $\\mu$K. Furthermore, we demonstrate a high efficiency magnetic transport for $^{6}$Li atoms with the help of the UV MOT. Finally, we obtain $8.1\\times10^8$ atoms with a temperature of 296 $\\mu$K at a magnetic gradient of 198 G/cm in the science chamber with a good vacuum environment and large optical access.

  3. Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: opportunities and challenges.

    Science.gov (United States)

    Duan, Xidong; Wang, Chen; Pan, Anlian; Yu, Ruqin; Duan, Xiangfeng

    2015-12-21

    The discovery of graphene has ignited intensive interest in two-dimensional layered materials (2DLMs). These 2DLMs represent a new class of nearly ideal 2D material systems for exploring fundamental chemistry and physics at the limit of single-atom thickness, and have the potential to open up totally new technological opportunities beyond the reach of existing materials. In general, there are a wide range of 2DLMs in which the atomic layers are weakly bonded together by van der Waals interactions and can be isolated into single or few-layer nanosheets. The van der Waals interactions between neighboring atomic layers could allow much more flexible integration of distinct materials to nearly arbitrarily combine and control different properties at the atomic scale. The transition metal dichalcogenides (TMDs) (e.g., MoS2, WSe2) represent a large family of layered materials, many of which exhibit tunable band gaps that can undergo a transition from an indirect band gap in bulk crystals to a direct band gap in monolayer nanosheets. These 2D-TMDs have thus emerged as an exciting class of atomically thin semiconductors for a new generation of electronic and optoelectronic devices. Recent studies have shown exciting potential of these atomically thin semiconductors, including the demonstration of atomically thin transistors, a new design of vertical transistors, as well as new types of optoelectronic devices such as tunable photovoltaic devices and light emitting devices. In parallel, there have also been considerable efforts in developing diverse synthetic approaches for the rational growth of various forms of 2D materials with precisely controlled chemical composition, physical dimension, and heterostructure interface. Here we review the recent efforts, progress, opportunities and challenges in exploring the layered TMDs as a new class of atomically thin semiconductors. PMID:26479493

  4. Characterization of graphene and transition metal dichalcogenide at the atomic scale

    International Nuclear Information System (INIS)

    Edge structures and atomic defects are of fundamental importance since they can significantly affect the physical and chemical properties of low-dimensional materials, such as nanoribbons, and therefore merit thorough investigations at the atomic level. Recent developments of direct imaging and analytical techniques using an aberration-corrected scanning transmission electron microscope (STEM) have provided direct access to information on the local atomic structure and the chemical composition at the atomic scale. In this review, we report on the discrimination of single atoms including dopant atoms on a monolayered transition-metal dichalcogenide (TMD) nanoribbon and a single nitrogen adatom on graphene by time-resolved annular dark-field (ADF) imaging and spatially resolved electron energy loss spectroscopy (EELS). We also show that in situ scanning transmission electron microscopy can be used to monitor the structural transformation between semiconducting (2H) and metallic (1T) phases in monolayer MoS2, and can enable direct observation of in-plane graphene growth at a step edge of a bi-layer graphene and domain boundary formation during growth with atomic-resolution. (author)

  5. Characterization of Graphene and Transition Metal Dichalcogenide at the Atomic Scale

    Science.gov (United States)

    Liu, Zheng; Lin, Yung-Chang; Warner, Jamie H.; Teng, Po-Yuan; Yeh, Chao-Hui; Chiu, Po-Wen; Iijima, Sumio; Suenga, Kazu

    2015-12-01

    Edge structures and atomic defects are of fundamental importance since they can significantly affect the physical and chemical properties of low-dimensional materials, such as nanoribbons, and therefore merit thorough investigations at the atomic level. Recent developments of direct imaging and analytical techniques using an aberration-corrected scanning transmission electron microscope (STEM) have provided direct access to information on the local atomic structure and the chemical composition at the atomic scale. In this review, we report on the discrimination of single atoms including dopant atoms on a monolayered transition-metal dichalcogenide (TMD) nanoribbon and a single nitrogen adatom on graphene by time-resolved annular dark-field (ADF) imaging and spatially resolved electron energy loss spectroscopy (EELS). We also show that in situ scanning transmission electron microscopy can be used to monitor the structural transformation between semiconducting (2H) and metallic (1T) phases in monolayer MoS2, and can enable direct observation of in-plane graphene growth at a step edge of a bi-layer graphene and domain boundary formation during growth with atomic-resolution.

  6. Observation of parity-time symmetry breaking transitions in a dissipative Floquet system of ultracold atoms

    CERN Document Server

    Li, Jiaming; Liu, Ji; de Melo, Leonardo; Joglekar, Yogesh N; Luo, Le

    2016-01-01

    Open physical systems with balanced loss and gain exhibit a transition, absent in their solitary counterparts, which engenders modes that exponentially decay or grow with time and thus spontaneously breaks the parity-time PT symmetry. This PT-symmetry breaking is induced by modulating the strength or the temporal profile of the loss and gain, but also occurs in a pure dissipative system without gain. It has been observed that, in classical systems with mechanical, electrical, and electromagnetic setups with static loss and gain, the PT-symmetry breaking transition leads to extraordinary behavior and functionalities. However, its observation in a quantum system is yet to be realized. Here we report on the first quantum simulation of PT-symmetry breaking transitions using ultracold Li-6 atoms. We simulate static and Floquet dissipative Hamiltonians by generating state-dependent atom loss in a noninteracting Fermi gas, and observe the PT-symmetry breaking transitions by tracking the atom number for each state. W...

  7. Observation of four-wave mixing in caesium atoms using a noncycling transition

    Institute of Scientific and Technical Information of China (English)

    Wang Li-Rong; Ma Jie; Zhao Jian-Ming; Xiao Lian-Tuan; Jia Suo-Tang

    2006-01-01

    In this paper the generation of four-wave mixing (FWM) signal using a noncycling transition of caesium atoms is investigated when the pumping laser is locked to the transition 6S1/2F = 4 → 6P3/2F' = 4, and meanwhile the probe frequency is scanned across the 6S1/2F = 4 → 6P3/2 transition. The efficiency of the four-wave mixing signal as a function of the intensity of the pumping beams and the detuning of the pumping beams is also studied. In order to increase the detection efficiency, a repumping laser which is resonant with 6S1/2F = 3 → 6P3/2F' = 4 transition is used. A theoretical model is also introduced, and the theoretical results are in qualitative agreement with experimental ones.

  8. First Order Electroweak Phase Transition from (Non)Conformal Extensions of the Standard Model

    DEFF Research Database (Denmark)

    Sannino, Francesco; Virkajärvi, Jussi

    2015-01-01

    both, a first order electroweak phase transition, and a phenomenologically viable dark matter candidate requires to go beyond the simplest extensions of the Standard Model. Furthermore these extensions must all feature new degrees of freedom that are naturally lighter than a TeV and therefore...

  9. Circular dichroism in free-free transitions of high energy electron-atom scattering

    CERN Document Server

    Cionga, Aurelia; Zloh, Gabriela; 10.1103/PhysRevA.62.063406

    2013-01-01

    We consider high energy electron scattering by hydrogen atoms in the presence of a laser field of moderate power and higher frequencies. If the field is a superposition of a linearly and a circularly polarized laser beam in a particular configuration, then we can show that circular dichroism in two photon transitions can be observed not only for the differential but also for the integrated cross sections, provided the laser-dressing of the atomic target is treated in second order perturbation theory and the coupling between hydrogenic bound and continuum states is involved.

  10. Dicke-like quantum phase transition and vacuum entanglement with two coupled atomic ensembles

    Science.gov (United States)

    Zheng, Shi-Biao

    2011-09-01

    We study the coherent cooperative phenomena of the system composed of two interacting atomic ensembles in the thermodynamic limit. Remarkably, the system exhibits the Dicke-like quantum phase transition and entanglement behavior although the governing Hamiltonian is fundamentally different from the spin-boson Dicke Hamiltonian, offering the opportunity for investigating collective matter-light dynamics with pure matter waves. The model can be realized with two Bose-Einstein condensates or atomic ensembles trapped in two optical cavities coupled to each other. The interaction between the two separate samples is induced by virtual photon exchange.

  11. Dicke-like quantum phase transition and vacuum entanglement with two coupled atomic ensembles

    CERN Document Server

    Zheng, Shi-Biao

    2012-01-01

    We study the coherent cooperative phenomena of the system composed of two interacting atomic ensembles in the thermodynamic limit. Remarkably, the system exhibits the Dicke-like quantum phase transition and entanglement behavior although the governing Hamiltonian is fundamentally different from the spin-boson Dicke Hamiltonian, offering the opportunity for investigating collective matter-light dynamics with pure matter waves. The model can be realized with two Bose-Einstein condensates or atomic ensembles trapped in two optical cavities coupled to each other. The interaction between the two separate samples is induced by virtual photon exchange.

  12. Dicke-like quantum phase transition and vacuum entanglement with two coupled atomic ensembles

    Energy Technology Data Exchange (ETDEWEB)

    Zheng Shibiao [Department of Physics, Fuzhou University, Fuzhou 350002 (China)

    2011-09-15

    We study the coherent cooperative phenomena of the system composed of two interacting atomic ensembles in the thermodynamic limit. Remarkably, the system exhibits the Dicke-like quantum phase transition and entanglement behavior although the governing Hamiltonian is fundamentally different from the spin-boson Dicke Hamiltonian, offering the opportunity for investigating collective matter-light dynamics with pure matter waves. The model can be realized with two Bose-Einstein condensates or atomic ensembles trapped in two optical cavities coupled to each other. The interaction between the two separate samples is induced by virtual photon exchange.

  13. Dicke-like quantum phase transition and vacuum entanglement with two coupled atomic ensembles

    International Nuclear Information System (INIS)

    We study the coherent cooperative phenomena of the system composed of two interacting atomic ensembles in the thermodynamic limit. Remarkably, the system exhibits the Dicke-like quantum phase transition and entanglement behavior although the governing Hamiltonian is fundamentally different from the spin-boson Dicke Hamiltonian, offering the opportunity for investigating collective matter-light dynamics with pure matter waves. The model can be realized with two Bose-Einstein condensates or atomic ensembles trapped in two optical cavities coupled to each other. The interaction between the two separate samples is induced by virtual photon exchange.

  14. K-LL Auger transition probabilities for elements with low and intermediate atomic numbers

    Science.gov (United States)

    Chen, M. H.; Crasemann, B.

    1973-01-01

    Radiationless K-LL transition probabilities have been calculated nonrelativistically in j-j coupling and in intermediate coupling, without and with configuration interaction, for elements with atomic numbers from 13 to 47. The system is treated as a coupled two-hole configuration. The single-particle radial wave functions required in the calculation of radial matrix elements, and in the calculation of mixing coefficients in the intermediate-coupling scheme, were obtained from Green's atomic independent-particle model. Comparison with previous theoretical work and with experimental data is made. The effects of intermediate coupling, configuration interaction, and relativity are noted.

  15. Molecular dynamics simulation of phosphorylation-induced conformational transitions in the mycobacterium tuberculosis response regulator PrrA

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Guo [Los Alamos National Laboratory; Mcmahon, Benjamin H [Los Alamos National Laboratory; Tung, Chang - Shung [Los Alamos National Laboratory

    2008-01-01

    Phosphorylation-activated modulation of response regulators (RR) is predominantly used by bacteria as a strategy in regulating their two-component signaling (TCS) systems, the underlying molecular mechanisms are however far from fully understood. In this work we have conducted a molecular dynamics (MD) simulation of the phosphorylation-induced conformational transitions of RRs with the Mycobacterium Tuberculosis PrrA as a particular example. Starting from the full-length inactive structure of PrrA we introduced a local disturbance by phosphorylating the conserved aspartic acid residue, Asp-58, in the regulatory domain. A Go-model-type algorithm packaged with AMBER force fields was then applied to simulate the dynamics upon phosphorylation. The MD simulation shows that the phosphorylation of Asp-58 facilitates PrrA, whose inactive state has a compact conformation with a closed interdomain interface, to open up with its interdomain separation being increased by an average of about 1.5 {angstrom} for a simulation of 20 ns. The trans-activation loop, which is completely buried within the interdomain interface in the inactive PrrA, is found to become more exposed with the phosphorylated structure as well. These results provide more structural details of how the phosphorylation of a local aspartate activates PrrA to undergo a global conformational rearrangement toward its extended active state. This work also indicates that MD simulations can serve as a fast tool to unravel the regulation mechanisms of all RRs, which is especially valuable when the structures of full-length active RRs are currently unavailable.

  16. Anthrax Edema Factor: An Ion-Adaptive Mechanism of Catalysis with Increased Transition-State Conformational Flexibility.

    Science.gov (United States)

    Jara, Gabriel E; Martínez, Leandro

    2016-07-14

    Edema Factor (EF) is one of three major toxins of anthrax. EF is an adenylyl cyclase that disrupts cell signaling by accelerating the conversion of ATP into cyclic-AMP. EF has a much higher catalytic rate than that of mammalian adenylyl cyclases (mACs). Crystal structures were obtained for mACs and EF, but the molecular basis for different catalytic activities remained poorly understood. In particular, the arrangement of the active site in EF is unclear in what concerns the number of ions present and the conformation of the substrate. Here, we use quantum mechanics-molecular mechanics simulations to estimate the free-energy profiles for the reaction catalyzed by EF and a mAC. We found that EF catalysis is possible, and faster than that of mACs, in both one and two Mg(2+)-ion-binding modes, providing adaptive plasticity to host-cell environments. In both enzymes, the reaction mechanisms are highly associative. However, mechanistic differences exist. In the mAC, the nucleophile oxygen (ATP-O3') is consistently coordinated to one of the Mg(2+) ions, increasing its acidity. In EF, on the other hand, this coordination is eventual and not essential for the reaction to proceed. The persistent coordination of O3' to the ion is favored in mACs by a greater ion partial charge. In EF, the reduced acidity of the O3' oxygen is compensated by the presence of the His351 residue for proton abstraction. As proton transfer in EF does not require persistent attachment of the substrate to an ion, the substrate (ATP) and transition state display greater conformational flexibilities. These greater flexibilities allow the sampling of lower-energy conformations and might represent an entropic advantage for catalytic efficiency. PMID:27260163

  17. Spin-statistic selection rules for multiphoton transitions: Application to helium atoms

    Science.gov (United States)

    Zalialiutdinov, T.; Solovyev, D.; Labzowsky, L.; Plunien, G.

    2016-01-01

    A theoretical investigation of the three-photon transition rates 2 1P1→2 1S0,1 1S0 and 2 3P2→2 1S0,1 1S0 for the helium atom is presented. Photon energy distributions and precise values of the nonrelativistic transition rates are obtained with employment of correlated wave functions of the Hylleraas type. The possible experiments for the tests of the Bose-Einstein statistics for multiphoton systems are discussed.

  18. Spin-Statistic Selection Rules for Multiphoton Transitions: Application to Helium Atom

    CERN Document Server

    Zalialiutdinov, T; Labzowsky, L; Plunien, G

    2016-01-01

    A theoretical investigation of the three-photon transition rates $ 2^1P_1\\rightarrow 2^1S_0\\;,1^1S_0 $ and $ 2^3P_2\\rightarrow 2^1S_0\\;,1^1S_0 $ for the helium atom is presented. Photon energy distributions and precise values of the nonrelativistic transition rates are obtained with employment of correlated wave functions of the Hylleraas type. The possible experiments for the tests of the Bose-Einstein statistics for multiphoton systems are discussed.

  19. Saturation of atomic transitions using sub-wavelength diameter tapered optical fibers in rubidium vapor

    CERN Document Server

    Jones, D E; Pittman, T B

    2014-01-01

    We experimentally investigate ultralow-power saturation of the rubidium D2 transitions using a tapered optical fiber (TOF) suspended in a warm Rb vapor. A direct comparison of nonlinear absorption measurements for the TOF system with those obtained in a standard free-space vapor cell system highlights the differences in saturation behavior for the two systems. The effects of hyperfine pumping in the TOF system are found to be minimized due to the short atomic transit times through the highly confined evanescent optical mode guided by the TOF. The TOF system data is well-fit by a relatively simple empirical absorption model that indicates nanoWatt-level saturation powers.

  20. NiCo2O4@TiN Core-shell Electrodes through Conformal Atomic Layer Deposition for All-solid-state Supercapacitors

    KAUST Repository

    Wang, Ruiqi

    2016-03-04

    Ternary transition metal oxides such as NiCo2O4 show great promise as supercapacitor electrode materials. However, the unsatisfactory rate performance of NiCo2O4 may prove to be a major hurdle to its commercial usage. Herein, we report the development of NiCo2O4@TiN core–shell nanostructures for all-solid-state supercapacitors with significantly enhanced rate capability. We demonstrate that a thin layer of TiN conformally grown by atomic layer deposition (ALD) on NiCo2O4 nanofiber arrays plays a key role in improving their electrical conductivity, mechanical stability, and rate performance. Fabricated using the hybrid NiCo2O4@TiN electrodes, the symmetric all-solid-state supercapacitor exhibited an impressive stack power density of 58.205 mW cm−3 at a stack energy density of 0.061 mWh cm−3. To the best of our knowledge, these values are the highest of any NiCo2O4-based all-solid-state supercapacitor reported. Additionally, the resulting NiCo2O4@TiN all-solid-state device displayed outstanding cycling stability by retaining 70% of its original capacitance after 20,000 cycles at a high current density of 10 mA cm−2. These results illustrate the promise of ALD-assisted hybrid NiCo2O4@TiN electrodes for sustainable and integrated energy storage applications.

  1. Adsorption of Alkali, Alkaline Earth and Transition Metal Atoms on Silicene

    OpenAIRE

    Sahin, Hasan; Peeters, Francois M.

    2013-01-01

    The adsorption characteristics of alkali, alkaline earth and transition metal adatoms on silicene, a graphene-like monolayer structure of silicon, are analyzed by means of first-principles calculations. In contrast to graphene, interaction between the metal atoms and the silicene surface is quite strong due to its highly reactive buckled hexagonal structure. In addition to structural properties, we also calculate the electronic band dispersion, net magnetic moment, charge transfer, workfuncti...

  2. Immobilization of the distal hinge in the labile serpin plasminogen activator inhibitor 1: identification of a transition state with distinct conformational and functional properties.

    Science.gov (United States)

    De Taeye, Bart; Compernolle, Griet; Dewilde, Maarten; Biesemans, Wouter; Declerck, Paul J

    2003-06-27

    The serpin plasminogen activator inhibitor-1 (PAI-1) plays an important role in the regulation of the fibrinolytic activity in blood. In plasma, PAI-1 circulates mainly in the active conformation. However, PAI-1 spontaneously converts to a latent conformation. This conversion comprises drastic conformational changes in both the distal and the proximal hinge region of the reactive center loop. To study the functional and conformational rearrangements associated solely with the mobility of the proximal hinge, disulfide bonds were introduced to immobilize the distal hinge region. These mutants exhibited specific activities comparable with that of PAI-1-wt. However, the engineered disulfide bond had a major effect on the conformational and associated functional transitions. Strikingly, in contrast to PAI-1-wt, inactivation of these mutants yielded a virtually complete conversion to a substrate-like conformation. Comparison of the digestion pattern (with trypsin and elastase) of the mutants and PAI-1-wt revealed that the inactivated mutants have a conformation differing from that of latent and active PAI-1-wt. Unique trypsin-susceptible cleavage sites arose upon inactivation of these mutants. The localization of these exposed residues provides evidence that a displacement of alphahF has occurred, indicating that the proximal hinge is partly inserted between s3A and s5A. In conclusion, immobilization of the distal hinge region in PAI-1 allowed the identification of an "intermediate" conformation characterized by a partial insertion of the proximal hinge region. We hypothesize that locking PAI-1 in this transition state between active and latent conformations is associated with a displacement of alphahF, subsequently resulting in substrate behavior.

  3. Single-Molecule Analysis of Protein Large-Amplitude Conformational Transitions

    Science.gov (United States)

    Yang, Haw

    2011-03-01

    Proteins have evolved to harness thermal fluctuations, rather than frustrated by them, to carry out chemical transformations and mechanical work. What are, then, the operation and design principles of protein machines? To frame the problem in a tractable way, several basic questions have been formulated to guide the experimental design: (a) How many conformational states can a protein sample on the functionally important timescale? (b) What are the inter-conversion rates between states? (c) How do ligand binding or interactions with other proteins modulate the motions? (d) What are the structural basis of flexibility and its underlying molecular mechanics? Guided by this framework, we have studied protein tyrosine phosphatase B, PtpB, from M. tuberculosis (a virulence factor of tuberculosis and a potential drug target) and adenylate kinase, AK, from E. coli (a ubiquitous energy-balancing enzyme in cells). These domain movements have been followed in real time on their respective catalytic timescales using high-resolution single-molecule Förster resonance energy transfer (FRET) spectroscopy. It is shown quantitatively that both PtpB and AK are capable of dynamically sampling two distinct states that correlate well with those observed by x-ray crystallography. Integrating these microscopic dynamics into macroscopic kinetics allows us to place the experimentally measured free-energy landscape in the context of enzymatic turnovers.

  4. The influence of sodium perfluorooctanoate on the conformational transitions of human immunoglobulin.

    Science.gov (United States)

    Messina, Paula V; Prieto, Gerardo; Salgado, Francisco; Varela, Carla; Nogueira, Montserrat; Dodero, Verónica; Ruso, Juan M; Sarmiento, Félix

    2007-07-19

    In the field of bioscience, the study of the interactions between blood proteins and fluorinated materials is very important from both theoretical and applied points of view. Fluorinated materials have potential use in drug delivery, as blood substitutes, and in biotechnology. Using a combination of ultraviolet-visible (UV-vis) and ultraviolet-circular dichroism (UV-CD) spectroscopies and ion-selective electrodes, the complete interaction of sodium perfluorooctanoate (SPFO) and the most important immunoglobulin (on a quantitative basis) in human serum, immunoglobulin G (IgG), has been evaluated. The study has been focused on bulk solution. By the application of an SPFO selective electrode, it was determined that there were true specific unions between surfactant molecules and IgG structure. The experimental data were presented as Koltz and Scatchard plots and analyzed on the basis of an empirical Hill equation. The conformational changes at the bulk solution were well characterized by UV-vis and UV-CD spectroscopies. As a consequence of these changes, the protein structure was affected.

  5. First observation of the strongly forbidden transition 1S0 - 3P0 in Strontium, for an atomic clock with trapped atoms

    International Nuclear Information System (INIS)

    This thesis reports the first results towards the realization of an optical clock using trapped strontium atoms. This set up would combine advantages of the different approaches commonly used to develop an atomic frequency standard. The first part describes the cold atoms source which is implemented. A magneto-optical trap operating on the 1S0-1P1 transition at 461 nm is loaded from an atomic beam decelerated by a Zeeman slower. The 461 nm laser is obtained by sum-frequency mixing in a potassium titanyl phosphate (KTP) crystal. The second part is devoted to the different stages developed to achieve the direct excitation of the 1S0-3P0 clock transition in 87Sr. This line has a theoretical natural width of 10-3 Hz. Before this detection, we obtained an estimate of the resonance frequency by measuring absolute frequencies of several allowed optical transitions. (author)

  6. Conformation of Organic Chain in Phase Transition of Hybrid(Cl2H25NH3)2MnCl4

    Institute of Scientific and Technical Information of China (English)

    GUO Liling; SUN Yubing; MEI Ao; DAI Yadong; LIU Hanxing

    2008-01-01

    The structural change in phase transition of hybrid(C12H25NH3)2MnCl4 was investigated.The temperature and the structures of the phase transition is investigated by thermal gravimetry(TG)and differential scanning calorimetry(DSC),infrared spectrum(IR)and X-ray diffraction(XRD).The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain.The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase.This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs.Combining the experimental data with theoretical calculation,we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond alternating with trans bond(noted as GTG'TGTG'TGTG'T).

  7. Inner-shell magnetic dipole transition in Tm atom as a candidate for optical lattice clocks

    CERN Document Server

    Sukachev, D; Tolstikhina, I; Kalganova, E; Vishnyakova, G; Khabarova, K; Tregubov, D; Golovizin, A; Sorokin, V; Kolachevsky, N

    2016-01-01

    We consider a narrow magneto-dipole transition in the $^{169}$Tm atom at the wavelength of $1.14\\,\\mu$m as a candidate for a 2D optical lattice clock. Calculating dynamic polarizabilities of the two clock levels $[\\text{Xe}]4f^{13}6s^2 (J=7/2)$ and $[\\text{Xe}]4f^{13}6s^2 (J=5/2)$ in the spectral range from $250\\,$nm to $1200\\,$nm, we suggest the "magic" wavelength for the optical lattice at $807\\,$nm. Frequency shifts due to black-body radiation (BBR), the van der Waals interaction, the magnetic dipole-dipole interaction and other effects which can perturb the transition frequency are calculated. The transition at $1.14\\,\\mu$m demonstrates low sensitivity to the BBR shift corresponding to $8\\times10^{-17}$ in fractional units at room temperature which makes it an interesting candidate for high-performance optical clocks. The total estimated frequency uncertainty is less than $5 \\times 10^{-18}$ in fractional units. By direct excitation of the $1.14\\,\\mu$m transition in Tm atoms loaded into an optical dipole ...

  8. Atomic data from the Iron Project. LIII. Relativistic allowed and forbidden transition probabilities for Fe XVII

    CERN Document Server

    Nahar, S N; Chen, G X; Pradhan, A K; Nahar, Sultana N.; Eissner, Werner; Chen, Guo-Xin; Pradhan, Anil K.

    2003-01-01

    An extensive set of fine structure levels and corresponding transition probabilities for allowed and forbidden transitions in Fe XVII is presented. A total of 490 bound energy levels of Fe XVII of total angular momenta 0 <= J <= 7 of even and odd parities with 2 <= n <= 10, 0 <= l <= 8, 0 <= L <= 8, and singlet and triplet multiplicities, are obtained. They translate to over 2.6 x 10^4 allowed (E1) transitions that are of dipole and intercombination type, and about 3000 forbidden transitions that include electric quadrupole (E2), magnetic dipole (M1), electric octopole (E3), and magnetic quadrupole (M2) type representing the most detailed calculations to date for the ion. Oscillator strengths f, line strengths S, and coefficients A of spontaneous emission for the E1 type transitions are obtained in the relativistic Breit-Pauli R-matrix approximation. A valus for the forbidden transitions are obtained from atomic structure calculations using codes SUPERSTRUCTURE and GRASP. The energy le...

  9. The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds

    CERN Document Server

    Imara, Nia

    2016-01-01

    We characterize the column density probability distributions functions (PDFs) of the atomic hydrogen gas, HI, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic HI Survey to derive column density maps and PDFs. We find that the peaks of the HI PDFs occur at column densities ranging from ~1-2$\\times 10^{21}$ cm$^2$ (equivalently, ~0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of $\\sigma_{HI}\\approx 10^{20}$ cm$^2$ (~0.1 mag). We also investigate the HI-to-H$_2$ transition towards the cloud complexes and estimate HI surface densities ranging from 7-16 $M_\\odot$ pc$^{-2}$ at the transition. We propose that the HI PDF is a fitting tool for identifying the HI-to-H$_2$ transition column in Galactic MCs.

  10. The H I Probability Distribution Function and the Atomic-to-molecular Transition in Molecular Clouds

    Science.gov (United States)

    Imara, Nia; Burkhart, Blakesley

    2016-10-01

    We characterize the column-density probability distribution functions (PDFs) of the atomic hydrogen gas, H i, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic H i Survey to derive column-density maps and PDFs. We find that the peaks of the H i PDFs occur at column densities in the range ˜1-2 × 1021 {{cm}}-2 (equivalently, ˜0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of {σ }{{H}{{I}}}≈ {10}20 {{cm}}-2 (˜0.1 mag). We also investigate the H i-to-H2 transition toward the cloud complexes and estimate H i surface densities ranging from 7 to 16 {M}⊙ {{pc}}-2 at the transition. We propose that the H i PDF is a fitting tool for identifying the H i-to-H2 transition column in Galactic MCs.

  11. Laser-excitation technique for the measurement of absolute transition probabilities of weak atomic lines

    Science.gov (United States)

    Kwong, H. S.; Smith, P. L.; Parkinson, W. H.

    1982-01-01

    A new technique is presented for the measurement of transition probabilities for weak allowed, intersystem, and forbidden lines. The method exploits the fact that oscillator strength is proportional to the number of stimulated absorptions and emissions produced by a narrow-band laser pulse of known energy which is in resonance with an atomic transition. The method is tested for a particular transition of Mg I with a known oscillator strength value and of appropriate magnitude. The number densities are measured using a Mach-Zehnder interferometer and the hook method for the lower level population and by measuring an absorption-equivalent width for the other. The apparatus consisted of a high-power tunable laser and a magnesium oven to produce excited Mg vapor, and a laser-plasma background continuum. The results are in good agreement with theoretical and other experimental data.

  12. Atom-photon entanglement in the system with competing k-photon and l-photon transitions

    Institute of Scientific and Technical Information of China (English)

    Wu Qin; Fang Mao-Fa; Hu Yao-Hua

    2007-01-01

    We have investigated the evolution of the atomic quantum entropy and the entanglement of atom-photon in the system with competing k-photon and l-photon transitions by means of fully quantum theory, and examined the effects of competing photon numbers (k and l), the relative coupling strength between the atom and the two-mode field(λ/g),and the initial photon number of the field on the atomic quantum entropy and the entanglement of atom-photon.The results show that the multiphoton competing transitions or the large relative coupling strength can lead to the strong entanglement between atoms and photons. The maximal atom-photon entanglement can be prepared via the appropriate selection of system parameters and interaction time.

  13. Ballistic thermal transport in monolayer transition-metal dichalcogenides: Role of atomic mass

    Science.gov (United States)

    Ma, Jinlong; Li, Wu; Luo, Xiaobing

    2016-02-01

    We investigate the ballistic thermal transport of monolayer transition-metal dichalcogenides (TMDs), which is crucial for the thermal management of their potential applications in nanoelectronics. We find the thermal conductance is mainly affected by the atomic masses of TMDs. As a consequence, the temperature dependences of thermal conductances of different TMDs cross: At low temperatures below ˜50 K, the thermal conductance increases with the atomic mass, while it exhibits the opposite trend at high temperatures. The crossing behavior of temperature dependent thermal conductance is characteristic of the atomic mass effect, and TMDs provide a model system demonstrating that the thermal conductance can be effectively manipulated via the atomic mass by selecting appropriate atom. In addition, we clarify that in any two dimensional system such as monolayer TMDs and graphene, due to quadratic dispersion of the out-of-plane modes, the thermal conductance and specific heat in the low temperature limit are proportional to T3/2 and T, respectively. Mainly because of much smaller group velocities of in-plane acoustic phonons, the high temperature thermal conductances of monolayer TMDs are much smaller than graphene. However, due to comparable group velocities of out-of-plane acoustic phonons, below 100 K thermal conductances of monolayer TMDs are rather comparable to graphene if taking the same layer thickness for comparison.

  14. Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

    International Nuclear Information System (INIS)

    The electronic structure and magnetic properties of the transition-metal (TM) atoms (Sc—Zn, Pt and Au) doped zigzag GaN single-walled nanotubes (NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Co-doped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  15. Probing Magnetism in 2D Molecular Networks after in Situ Metalation by Transition Metal Atoms.

    Science.gov (United States)

    Schouteden, K; Ivanova, Ts; Li, Z; Iancu, V; Janssens, E; Van Haesendonck, C

    2015-03-19

    Metalated molecules are the ideal building blocks for the bottom-up fabrication of, e.g., two-dimensional arrays of magnetic particles for spintronics applications. Compared to chemical synthesis, metalation after network formation by an atom beam can yield a higher degree of control and flexibility and allows for mixing of different types of magnetic atoms. We report on successful metalation of tetrapyridyl-porphyrins (TPyP) by Co and Cr atoms, as demonstrated by scanning tunneling microscopy experiments. For the metalation, large periodic networks formed by the TPyP molecules on a Ag(111) substrate are exposed in situ to an atom beam. Voltage-induced dehydrogenation experiments support the conclusion that the porphyrin macrocycle of the TPyP molecule incorporates one transition metal atom. The newly synthesized Co-TPyP and Cr-TPyP complexes exhibit striking differences in their electronic behavior, leading to a magnetic character for Cr-TPyP only as evidenced by Kondo resonance measurements.

  16. An exacting transition probability measurement - a direct test of atomic many-body theories.

    Science.gov (United States)

    Dutta, Tarun; De Munshi, Debashis; Yum, Dahyun; Rebhi, Riadh; Mukherjee, Manas

    2016-01-01

    A new protocol for measuring the branching fraction of hydrogenic atoms with only statistically limited uncertainty is proposed and demonstrated for the decay of the P3/2 level of the barium ion, with precision below 0.5%. Heavy hydrogenic atoms like the barium ion are test beds for fundamental physics such as atomic parity violation and they also hold the key to understanding nucleo-synthesis in stars. To draw definitive conclusion about possible physics beyond the standard model by measuring atomic parity violation in the barium ion it is necessary to measure the dipole transition probabilities of low-lying excited states with a precision better than 1%. Furthermore, enhancing our understanding of the barium puzzle in barium stars requires branching fraction data for proper modelling of nucleo-synthesis. Our measurements are the first to provide a direct test of quantum many-body calculations on the barium ion with a precision below one percent and more importantly with no known systematic uncertainties. The unique measurement protocol proposed here can be easily extended to any decay with more than two channels and hence paves the way for measuring the branching fractions of other hydrogenic atoms with no significant systematic uncertainties. PMID:27432734

  17. Adsorption of alkali, alkaline-earth, and 3d transition metal atoms on silicene

    Science.gov (United States)

    Sahin, H.; Peeters, F. M.

    2013-02-01

    The adsorption characteristics of alkali, alkaline-earth, and transition metal adatoms on silicene, a graphene-like monolayer structure of silicon are analyzed by means of first-principles calculations. In contrast to graphene, interaction between the metal atoms and the silicene surface is quite strong due to its highly reactive buckled hexagonal structure. In addition to structural properties, we also calculate the electronic band dispersion, net magnetic moment, charge transfer, work function, and dipole moment of the metal adsorbed silicene sheets. Alkali metals, Li, Na, and K, adsorb to hollow sites without any lattice distortion. As a consequence of the significant charge transfer from alkalis to silicene, metalization of silicene takes place. Trends directly related to atomic size, adsorption height, work function, and dipole moment of the silicene/alkali adatom system are also revealed. We found that the adsorption of alkaline-earth metals on silicene is entirely different from their adsorption on graphene. The adsorption of Be, Mg, and Ca turns silicene into a narrow gap semiconductor. Adsorption characteristics of eight transition metals Ti, V, Cr, Mn, Fe, Co, Mo, and W are also investigated. As a result of their partially occupied d orbital, transition metals show diverse structural, electronic, and magnetic properties. Upon the adsorption of transition metals, depending on the adatom type and atomic radius, the system can exhibit metal, half-metal, and semiconducting behavior. For all metal adsorbates, the direction of the charge transfer is from adsorbate to silicene, because of its high surface reactivity. Our results indicate that the reactive crystal structure of silicene provides a rich playground for functionalization at nanoscale.

  18. Invited review: Mechanisms of GTP hydrolysis and conformational transitions in the dynamin superfamily.

    Science.gov (United States)

    Daumke, Oliver; Praefcke, Gerrit J K

    2016-08-01

    Dynamin superfamily proteins are multidomain mechano-chemical GTPases which are implicated in nucleotide-dependent membrane remodeling events. A prominent feature of these proteins is their assembly- stimulated mechanism of GTP hydrolysis. The molecular basis for this reaction has been initially clarified for the dynamin-related guanylate binding protein 1 (GBP1) and involves the transient dimerization of the GTPase domains in a parallel head-to-head fashion. A catalytic arginine finger from the phosphate binding (P-) loop is repositioned toward the nucleotide of the same molecule to stabilize the transition state of GTP hydrolysis. Dynamin uses a related dimerization-dependent mechanism, but instead of the catalytic arginine, a monovalent cation is involved in catalysis. Still another variation of the GTP hydrolysis mechanism has been revealed for the dynamin-like Irga6 which bears a glycine at the corresponding position in the P-loop. Here, we highlight conserved and divergent features of GTP hydrolysis in dynamin superfamily proteins and show how nucleotide binding and hydrolysis are converted into mechano-chemical movements. We also describe models how the energy of GTP hydrolysis can be harnessed for diverse membrane remodeling events, such as membrane fission or fusion. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 580-593, 2016. PMID:27062152

  19. Phase transitions due to interaction between photons and atoms in a cavity system

    CERN Document Server

    Shirai, Tatsuhiko; Miyashita, Seiji

    2012-01-01

    We survey phenomena of a cavity system in which many atoms coherently interact with a single quantized photon mode driven by the AC external field in a dissipative environment. It has been known that a strongly external field causes the so-called optical bistability which is a non-equilibrium phase transition for the balance of excitation and dissipation. On the other hand, a strong interaction causes the Dicke transition, which is a phase transition with a spontaneous appearance of excitations of atoms and photons in the equilibrium system as a consequence of the cooperative phenomena. We study the phenomena in full range of the strength of the interaction and the external field, and present a phase diagram of the stationary state. For the strong interaction region, in order to realize the ground state, appropriate form of the dissipative mechanism in the master equation is necessary instead of the conventional Lindblad form. We provide such an extended master equation. Moreover, the rotating wave approximat...

  20. Theoretical studies of atomic transitions. Progress report, March 15, 1982-March 14, 1985

    International Nuclear Information System (INIS)

    Allowed and forbidden transitions have been studied for a number of atomic systems, of interest in fusion research, using the multiconfiguration Hartree-Fock method with relativistic corrections in the Breit-Pauli approximation. To perform these studies, an atomic structure software package has been designed with computers such as the VAX 11/780 in mind. Numerical procedures are being developed which will extend the program capability to continuum functions which arise in photo-ionization calculations. Extensive studies have been performed of fine-structure splittings and transition rates (E2 and M1) for the ground configurations of the Boron, Nitrogen and Oxygen sequences within the MCHF + BP approximation. Allowed 2s → 2p transitions for the latter were also considered. Calculations for the Carbon sequence are in progress. In an attempt to improve the level of accuracy for few electron systems, programs were developed which would include the mass polarization correction, arising from the finite mass of the nucleus. A revised MCHF program has removed the restriction on the l-quantum number. Some preliminary results for He and Li II have been obtained. Unlike many studies which report results for an isoelectronic sequence, thereby providing fragments of information about a number of spectra, moderately accurate calculations of energy levels and lifetimes were performed for a large portion of a single spectrum. Some 30 quartet levels of Be II were determined. This lead to the identification of a number of lines that had been observed in fast-ion beam experiments

  1. Dynamic polarizability and electric multipolar transitions in two electron atoms under exponential cosine screened coulomb potential

    Science.gov (United States)

    Chaudhuri, Supriya K.; Modesto-Costa, Lucas; Mukherjee, Prasanta K.

    2016-05-01

    Detailed investigations on the frequency dependent polarizabilities, transition energies, oscillator strengths, and transition probabilities of two electron systems He, B e2 +, C4 + , and O6 + under electric dipolar (E1) and quadrupolar (E2) excitations have been performed using exponential cosine screened coulomb potential with a view to understand the structural behaviour of such systems due to external confinement produced by plasma environment. Time dependent coupled Hartree-Fock theory within a variational framework has been adopted for studying the first three low lying excited states 1 s2:1Se→1 s n p :1Po (n = 2, 3, 4) and 1 s n d :1De (n = 3, 4, 5) under such excitations. Quantitatively, the effect of confinement produced by the external plasma has been taken care of by considering the change in atomic potential through plasma screening, directly related to the coupling strength of the plasma with the atomic charge cloud. With increased plasma screening, a gradual destabilisation of the energy levels with subsequent reduction of the ionization potential and number of excited states has been observed. Behavioral pattern of the frequency dependent polarizabilities, excitation energies, oscillator strengths, and transition probabilities under systematic increase of the screening has been investigated. Results have been compared thoroughly with those available for free systems and under confinement by exponential cosine screened and screened Coulomb potential.

  2. Atomic data from plasma based measurements and compilations of transition probabilities

    Energy Technology Data Exchange (ETDEWEB)

    Griesmann, U.; Bridges, J.M.; Roberts, J.R.; Wiese, W.L.; Fuhr, J.R. [National Inst. of Standards and Technology, Gaithersburg, MD (United States)

    1996-12-31

    High efficiency electrical light sources used in lighting applications are based on electrical discharges in plasmas. The systematic search for improved lighting plasmas increasingly relies on plasma discharge modeling with computers and requires better and more comprehensive knowledge of basic atomic data such as radiative transition probabilities and collision cross sections. NIST has ongoing research programs aimed at the study of thermal equilibrium plasmas such as high pressure electric arcs and non-equilibrium plasmas in radio-frequency discharges and high current hallow cathode lamps. In emission experiments the authors have measured branching fractions and determined absolute transition probabilities for spectral lines in Ne I, Ne II, F I, O I and O II. Some measurements were aimed specifically at transitions where significant disagreement among advanced calculations exists. The experimental data thus serve as benchmarks for new critical data compilations at NIST which are largely based on comprehensive, sophisticated atomic structure calculations. Typical results of the recent measurements and of the new NIST data compilations will be shown.

  3. Coarse-grained simulations of transitions in the E2-to-E1 conformations for Ca ATPase (SERCA) show entropy-enthalpy compensation.

    Science.gov (United States)

    Nagarajan, Anu; Andersen, Jens Peter; Woolf, Thomas B

    2012-09-28

    SERCA is a membrane transport protein that has been extensively studied. There are a large number of highly resolved X-ray structures and several hundred mutations that have been characterized functionally. Despite this, the molecular details of the catalytic cycle, a cycle that includes large conformational changes, is not fully understood. In this computational study, we provide molecular dynamics descriptions of conformational changes during the E2→E1 transitions. The motivating point for these calculations was a series of insertion mutants in the A-M3 linker region that led to significant shifts in measured rates between the E2 and E1 states, as shown by experimental characterization. Using coarse-grained dynamic importance sampling within the context of a population shift framework, we sample on the intermediates along the transition pathway to address the mechanism for the conformational changes and the effects of the insertion mutations on the kinetics of the transition. The calculations define an approximation for the relative changes in entropy and enthalpy along the transition. These are found to be important for understanding the experimentally observed differences in rates. In particular, the interactions between cytoplasmic domains, water interactions, and the shifts in protein degrees of freedom with the insertion mutations show mutual compensation for the E2→E1 transitions in wild-type and mutant systems.

  4. An exacting transition probability measurement - a direct test of atomic many-body theories

    CERN Document Server

    Dutta, T; Yum, D; Rebhi, R; Mukherjee, M

    2016-01-01

    A new protocol for measuring the branching fraction of hydrogenic atoms with only statistically limited uncertainty is proposed and demonstrated for the decay of the P$_{3/2}$ level of the barium ion, with precision below $0.5\\%$. Heavy hydrogenic atoms like the barium ion are test beds for fundamental physics such as atomic parity violation and they also hold the key to understanding nucleo-synthesis in stars. To draw definitive conclusion about possible physics beyond the standard model by measuring atomic parity violation in the barium ion it is necessary to measure the dipole transition probabilities of low-lying excited states with precision better than $1\\%$. Furthermore, enhancing our understanding of the $\\it{barium-puzzle}$ in barium stars requires branching fraction data for proper modelling of nucleo-synthesis. Our measurements are the first to provide a direct test of quantum many-body calculations on the barium ion with precision below one percent and more importantly with no known systematic unc...

  5. Three-photon transitions from ground state to bound states in atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Thayyullathil, Ramesh Babu [Department of Physics, Cochin University of Science and Technology, Cochin 682 022 (India); Radhakrishnan, R [Department of Physics, Cochin University of Science and Technology, Cochin 682 022 (India); Seema, M [Department of Physics, Indian Institute of Technology, New Delhi 110 016 (India)

    2003-08-08

    In this paper, we present an efficient alternative method for the evaluation of the three-photon transition matrix element in the dipole approximation from the ground state to bound states in atomic hydrogen. This method is a variation of the Dalgarno-Lewis method for the treatment of the second-order Stark effect in the hydrogen atom. In this approach, the infinite double sum over the complete set of states including the continuum states present in the third-order perturbation theory result is treated exactly. The closed analytical expression obtained for the matrix element, as a function of incident photon energy, clearly displays all singularities present in the original third-order perturbation theory result.

  6. High-Resolution Photoassociation Spectroscopy of Ultracold Ytterbium Atoms by Using the Intercombination Transition

    International Nuclear Information System (INIS)

    We observed high-resolution photoassociation spectra of laser-cooled ytterbium (Yb) atoms in the spin-forbidden 1S0-3P1 intercombination line. The rovibrational levels in the 0u+ state were measured for red detunings of the photoassociation laser ranging from 2.9 MHz to 1.97 GHz with respect to the atomic resonance. The rotational splitting of the vibrational levels near the dissociation limit were fully resolved due to the sub-MHz linewidth of the spectra in contrast to previous measurements using the spin-allowed singlet transition. In addition, from a comparison between the spectra of 174Yb and those of 176Yb, a d-wave shape resonance for 174Yb is strongly suggested

  7. High-resolution photoassociation spectroscopy of ultracold ytterbium atoms by using the intercombination transition.

    Science.gov (United States)

    Tojo, Satoshi; Kitagawa, Masaaki; Enomoto, Katsunari; Kato, Yutaka; Takasu, Yosuke; Kumakura, Mitsutaka; Takahashi, Yoshiro

    2006-04-21

    We observed high-resolution photoassociation spectra of laser-cooled ytterbium (Yb) atoms in the spin-forbidden 1S0 - 3P1 intercombination line. The rovibrational levels in the 0u+ state were measured for red detunings of the photoassociation laser ranging from 2.9 MHz to 1.97 GHz with respect to the atomic resonance. The rotational splitting of the vibrational levels near the dissociation limit were fully resolved due to the sub-MHz linewidth of the spectra in contrast to previous measurements using the spin-allowed singlet transition. In addition, from a comparison between the spectra of 174Yb and those of 176Yb, a d-wave shape resonance for 174Yb is strongly suggested. PMID:16712155

  8. Charge exchange transition probability for collisions between unlike ions and atoms within the adiabatic approximation

    Science.gov (United States)

    Xu, Y. J.; Khandelwal, G. S.; Wilson, John W.

    1989-01-01

    A simple formula for the transition probability for electron exchange between unlike ions and atoms is established within the adiabatic approximation by employing the Linear Combination of Atomic Orbitals (LCAO) method. The formula also involves an adiabatic parameter, introduced by Massey, and thus the difficulties arising from the internal energy defect and the adiabatic approximation are avoided. Specific reactions Li(+++) + H to Li(++) + H(+) and Be(4+) + H to Be(3+) + H(+) are considered as examples. The calculated capture cross section results of the present work are compared with the experimental data and with the calculation of other authors over the velocity range of 10(7) cm/sec to 10(8) cm/sec.

  9. Inelastic scattering in atom-diatomic molecule collisions. I - Rotational transitions in the sudden approximation

    Science.gov (United States)

    Stallcop, J. R.

    1974-01-01

    The impact parameter method and the sudden approximation are applied to determine the total probability of inelastic rotational transitions arising from a collision of an atom and a homonuclear diatomic molecule at large impact parameters. An analytical approximation to this probability is found for conditions where the electron exchange or overlap forces dominate the scattering. An approximate upper bound to the range of impact parameters for which rotational scattering can be important is determined. In addition, an estimate of the total inelastic cross section is found at conditions for which a statistical model describes the scattering well. The results of this analysis are applied to Ar-O2 collisions and may be readily applied to other combinations of atoms and molecules.

  10. Magnetism of Metals, Alloys and of Clusters of Transition Metal Atoms

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A condition for local moment formation in metals derived by Stoddart and March (Ann. Phys.NY 1972 64, 174) is first used to discuss the ferromagnetism of body-centred-cubic Fe. A less detailed discussion is also added on Ni and Co. This leads into a treatment of the nonlinear response of such 3d ferromagnets to dilute substitutional impurities. Antiferromagnets responding to local changes in the exchange field caused by such impurities are also studied, Mn in Cr being one such system discussed. The paper concludes with a brief summary of clusters of transition metal atoms, with most attention devoted to Cr and to Mn.

  11. Theoretical studies of atomic transitions. Renewal progress report, April 1, 1994 - March 31, 1997

    International Nuclear Information System (INIS)

    With the aid of powerful workstations and our software modified for large-scale computation, considerable progress has been made during the last few years. This progress is in the form of increased accuracy for transition probability studies along with estimates of uncertainty, the study of nuclear effects on atomic properties such as hyperfine interactions and isotope shifts, the study of relativistic correlation in some large and small systems, and the extension of spline methods to regions of higher energy where multiple continuum channels are present. This paper highlights this research. The appendix lists grant related papers that appeared since 1994, papers presented at conferences, and the papers submitted

  12. Two-electron one-photon transitions in atoms with 12 {<=} Z {<=} 80

    Energy Technology Data Exchange (ETDEWEB)

    Kadrekar, Riddhi; Natarajan, L, E-mail: ln@mu.ac.i [Department of Physics, University of Mumbai, Mumbai 400 098 (India)

    2010-08-14

    Relativistic configuration interaction results are presented for the K{alpha}{alpha} x-rays arising from the decay of doubly ionized K shell of atoms with 12 {<=} Z {<=} 80. The x-ray energies and dipole rates are calculated in the active space approximation using multi-configuration Dirac-Fock wavefunctions with the inclusion of the Breit interaction and quantum electrodynamics corrections. The calculations include all single and double excitations from core-valence interactions. The resulting length and velocity gauge transition rates are well converged and are in good agreement with the allowed transition, while the intercombination line rate is seen to be gauge dependent. Conclusions concerning the relative importance of correlation and the Breit interaction on the intensity ratios are obtained in some detail. The sensitivity of the relative intensities of the fine structure lines to the coupling variations in both length and velocity gauges is analysed. The calculated results are compared with previous experimental and theoretical data.

  13. Two-electron one-photon transitions in atoms with 12 ≤ Z ≤ 80

    International Nuclear Information System (INIS)

    Relativistic configuration interaction results are presented for the Kαα x-rays arising from the decay of doubly ionized K shell of atoms with 12 ≤ Z ≤ 80. The x-ray energies and dipole rates are calculated in the active space approximation using multi-configuration Dirac-Fock wavefunctions with the inclusion of the Breit interaction and quantum electrodynamics corrections. The calculations include all single and double excitations from core-valence interactions. The resulting length and velocity gauge transition rates are well converged and are in good agreement with the allowed transition, while the intercombination line rate is seen to be gauge dependent. Conclusions concerning the relative importance of correlation and the Breit interaction on the intensity ratios are obtained in some detail. The sensitivity of the relative intensities of the fine structure lines to the coupling variations in both length and velocity gauges is analysed. The calculated results are compared with previous experimental and theoretical data.

  14. Semi-empirical studies of atomic transition probabilities, oscillator strengths and radiative lifetimes in Hf II

    International Nuclear Information System (INIS)

    Over the past few years, laser induced fluorescence and Fourier Transform techniques have been applied to measure radiative lifetimes and branching fractions in Hf II in order to derive oscillator strengths and transition probabilities. In the present work, we propose to compare for the first time these experimental data to computed values obtained by two different semi-empirical approaches, respectively based on a parametrization of the oscillator strengths and on a pseudo-relativistic Hartree–Fock model including core-polarization effects. The overall agreement between all sets of data is found to be good. We furthermore give radial integrals of the main atomic transitions in this study: 〈5d6s6p|r1|5d26s〉=0.1504 (0.0064), 〈6s26p|r1|5d6s2〉=1.299 (0.012), 〈5d26p|r1|5d26s〉=−0.298 (0.013), 〈5d26p|r1|5d3〉=2.025 (0.027). Finally a new set of oscillator strengths and transition probabilities is reported for many transitions in Hf II

  15. Dynamic non-reciprocal meta-surfaces with arbitrary phase reconfigurability based on photonic transition in meta-atoms

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Yu; Fan, Shanhui, E-mail: shanhui@stanford.edu [Ginzton Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States)

    2016-01-11

    We introduce a distinct class of dynamic non-reciprocal meta-surfaces with arbitrary phase-reconfigurability. This meta-surface consists of an array of meta-atoms, each of which is subject to temporal refractive index modulation, which induces photonic transitions between the states of the meta-atom. We show that arbitrary phase profile for the outgoing wave can be achieved by controlling the phase of the modulation at each meta-atom. Moreover, such dynamic meta-surfaces exhibit non-reciprocal response without the need for magneto-optical effects. The use of photonic transition significantly enhances the tunability and the possible functionalities of meta-surfaces.

  16. Dynamic non-reciprocal meta-surfaces with arbitrary phase reconfigurability based on photonic transition in meta-atoms

    International Nuclear Information System (INIS)

    We introduce a distinct class of dynamic non-reciprocal meta-surfaces with arbitrary phase-reconfigurability. This meta-surface consists of an array of meta-atoms, each of which is subject to temporal refractive index modulation, which induces photonic transitions between the states of the meta-atom. We show that arbitrary phase profile for the outgoing wave can be achieved by controlling the phase of the modulation at each meta-atom. Moreover, such dynamic meta-surfaces exhibit non-reciprocal response without the need for magneto-optical effects. The use of photonic transition significantly enhances the tunability and the possible functionalities of meta-surfaces

  17. Atoms

    Institute of Scientific and Technical Information of China (English)

    刘洪毓

    2007-01-01

    Atoms(原子)are all around us.They are something like the bricks (砖块)of which everything is made. The size of an atom is very,very small.In just one grain of salt are held millions of atoms. Atoms are very important.The way one object acts depends on what

  18. Quantum fluctuation and phase transition in a harmonic two-electron atomic model with variable dimensionality

    International Nuclear Information System (INIS)

    Witten's generalization to arbitrary dimension has afforded new insight into the correlated motion of quantum particles [Phys. Today 33, (7), 38 (1980)]. We have used a classically based method to understand the resultant dimensionality dependence of the ground-state energy of the helium atom in the approximation which regards the quantum fluctuations of the system as being harmonic oscillations about a classical, correlated state of minimum effective potential energy. Making an analogy with thermal systems, this provides a ''phase diagram'' of a single helium atom that features a first-order melting transition, with inverse dimensionality playing the role of temperature. Our approximation gives an understanding of the high-dimensionality behavior of the quantum solution found with a perturbation theory expansion in inverse dimensionality by Goodson and Herschbach [Phys. Rev. Lett. 58, 1628 (1987)]. From comparison with variational quantum ground-state solutions by Loeser and Herschbach [J. Chem. Phys. 84, 3882 (1986)] for atomic numbers 2, 3, and 6 we find that the harmonic description improves with decreasing nuclear charge

  19. Atomic structure of the adsorption of transition metals on silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Cocoletzi, G.H. [IF-BUAP, 72000 Puebla (Mexico); Takeuchi, N. [CCMC-UNAM, Ensenada, BCN (Mexico)

    2007-07-01

    Full text: Solid state devices are useful for their high sensitivity in a small volume. Applications of such devices as dose materials include semi-conducting dose-rate, and dose-reading measuring devices. Transition metals (TM) have electronic and atomic properties similar to those of rare earth elements when they are adsorbed on silicon surfaces. The interfaces of transition metals silicides with Si (111) have very small lattice mismatches, sharp interfaces, and low Schottky barrier, making them ideal in electronic devices, such as infrared detectors and rectifying contacts. In this work we shall describe our first principles total energy calculations to investigate structural properties of bulk ScSi and YSi, the two dimensional arrangement of ScSi{sub 2} and YSi{sub 2} on the Si(111) surface, and the growth of a few layers of ScSi{sub 1.7} and YSi{sub 1.7} on the Si(111) surface. Our calculated bulk structural parameters are in excellent agreement with experimental values. It will be shown that one monolayer of a TM on Si( l l 1) yields a two dimensional phase with (lxl) periodicity consisting of a layer of TM atoms on T4 sites and a Si bilayer on top. This double layer of Si atoms is very close to ideal Si(111)-(1x1) surface, but rotated 180 with respect to the rest of the crystal. More layers of TM silicide epitaxially grown on Si(l 11) result in a hexagonal structure similar to bulk ScSi2 and YSi2: graphite-like Si planes (with vacancies) intercalated with TM planes, and forming a ({radical}3x{radical}3) arrangement with a ScSi{sub 1.7} and YSi{sub 1.7} stoichiometry. The top Si layer does not contain vacancies and it does not present a graphite-like structure, but forms a bilayer arrangement as in bulk Si. (Author)

  20. To involvement the conformation of the adenine nucleotide translocase in opening the Tl(+)-induced permeability transition pore in Ca(2+)-loaded rat liver mitochondria.

    Science.gov (United States)

    Korotkov, Sergey M; Konovalova, Svetlana A; Brailovskaya, Irina V; Saris, Nils-Erik L

    2016-04-01

    The conformation of adenine nucleotide translocase (ANT) has a profound impact in opening the mitochondrial permeability transition pore (MPTP) in the inner membrane. Fixing the ANT in 'c' conformation by phenylarsine oxide (PAO), tert-butylhydroperoxide (tBHP), and carboxyatractyloside as well as the interaction of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) with mitochondrial thiols markedly attenuated the ability of ADP to inhibit the MPTP opening. We earlier found (Korotkov and Saris, 2011) that calcium load of rat liver mitochondria in medium containing TlNO3 and KNO3 stimulated the Tl(+)-induced MPTP opening in the inner mitochondrial membrane. The MPTP opening as well as followed increase in swelling, a drop in membrane potential (ΔΨmito), and a decrease in state 3, state 4, and 2,4-dinitrophenol-uncoupled respiration were visibly enhanced in the presence of PAO, tBHP, DIDS, and carboxyatractyloside. However, these effects were markedly inhibited by ADP and membrane-penetrant hydrophobic thiol reagent, N-ethylmaleimide (NEM) which fix the ANT in 'm' conformation. Cyclosporine A additionally potentiated these effects of ADP and NEM. Our data suggest that conformational changes of the ANT may be directly involved in the opening of the Tl(+)-induced MPTP in the inner membrane of Ca(2+)-loaded rat liver mitochondria. Using the Tl(+)-induced MPTP model is discussed in terms finding new transition pore inhibitors and inducers among different chemical and natural compounds. PMID:26835787

  1. Dynamics and Conformational Energetics of a Peptide Hormone: Vasopressin

    Science.gov (United States)

    Hagler, A. T.; Osguthorpe, D. J.; Dauber-Osguthorpe, P.; Hempel, J. C.

    1985-03-01

    A theoretical methodology for use in conjunction with experiment was applied to the neurohypophyseal hormone lysine vasopressin for elucidation of its accessible molecular conformations and associated flexibility, conformational transitions, and dynamics. Molecular dynamics and energy minimization techniques make possible a description of the conformational properties of a peptide in terms of the precise positions of atoms, their fluctuations in time, and the interatomic forces acting on them. Analysis of the dynamic trajectory of lysine vasopressin shows the ability of a flexible peptide hormone to undergo spontaneous conformational transitions. The excursions of an individual phenylalanine residue exemplify the dynamic flexibility and multiple conformational states available to small peptide hormones and their component residues, even within constraints imposed by a cyclic hexapeptide ring.

  2. Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd, E-mail: gerd.meyer@uni-koeln.de

    2014-11-15

    Comproportionation reactions of rare-earth metal trihalides (RX{sub 3}) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ((T{sub 3}R{sub 11})X{sub 15}-type, P6{sub 3}/m), tetramers ((T{sub 4}R{sub 16})X{sub 28}(R{sub 4}) (P-43m), (T{sub 4}R{sub 16})X{sub 20} (P4{sub 2}/nnm), (T{sub 4}R{sub 16})X{sub 24}(RX{sub 3}){sub 4} (I4{sub 1}/a) and (T{sub 4}R{sub 16})X{sub 23} (C2/m) types of structure) and pentamers ((Ru{sub 5}La{sub 14}){sub 2}Br{sub 39}, Cc) of (TR{sub r}){sub n} (n=2–5) clusters. These oligomers are further enveloped by inner (X{sup i}) as well as outer (X{sup a}) halido ligands, which possess diverse functionalities and interconnect like oligomers through i–i, i–a and/or a–i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of (TR{sub 6}) octahedra via common edges are more frequent than trimers and pentamers, in which the (TR{sub r}) clusters share common faces. - Graphical abstract: Rare earth-metal cluster complexes with endohedral transition metal atoms (TR{sub 6}) may connect via common edges or faces to form dimers, trimers, tetramers and pentamers of which the tetramers are the most prolific. Packing effects and electron counts play an important role. - Highlights: • Rare-earth metal cluster complexes encapsulate transition metal atoms. • Oligomers are built via connection of octahedral clusters via common edges or faces. • Dimers through pentamers with closed structures are known. • Tetramers including a tetrahedron of endohedral atoms are the most prolific.

  3. The Zα domain of fish PKZ facilitates the B-Z conformational transition of oligonucleotide DNAs with d(GC)n inserts

    Institute of Scientific and Technical Information of China (English)

    Puzhong Lu; Shoulong Deng; Youlin Zhu; Yongbin Yan; Yong Liu; Chengyu Hu

    2012-01-01

    PKZ (PKR-like) was discovered as a member of eIF2α kinase family in fish,which possesses a conserved catalytic domain of an eIF2α kinase in C-terminal and also two ZDNA-binding domains (Zα1 and Zα2) in N-terminal.PKZ can be activated through binding of Zα to Z-DNA.However,the regulatory function of PKZ Zα still remains unclear.To investigate a molecular mechanism of how PKZ Zα interacts with Z-DNA,we expressed Zα polypeptide Zα1α2 in Escherichia coli Rosetta strain and purified by affinity chromatography on Ni-NTA resin.Different lengths of oligonucleotide DNAs with various inserts,namely d(GC)n (n =6,8,10,13),d(TA)n (n =6,10),nond(GC),and non-d(TA),were designed and synthesized.Circular dichroism spectrum and gel mobility shift assays were used to investigate the effects of Zα1α2 on the conformational transition of different oligonucleotide DNAs.Results showed that oligonucleotide DNAs retained a conventional B-DNA conformation in the absence of Zα1α2.With the increasing amount of Zα1α2 titration,d(GC)n were recognized and converted to Z-DNA conformation to some degree.With increasing the repeat number (from n =6 to n =13),the tendency of conformational transition became more obvious.However,the conformation of oligonucleotides with d(TA)n inserts changed a little in the presence of Zα1α2,and Zα1α2 had no effect on conformational transition of oligonucleotides with non-d(GC) or non-d(TA) inserts.Gel mobility shift assays further showed that Zα1α2 could bind to oligonucleotide with d(GC)10.In other words,Zα1α2 can turn oligonucleotides with d(GC)n inserts into Z-DNA conformation and bind to it with high affinity.

  4. Influence of transition metal atoms doping on structural, electronic and nonlinear optical properties of Mg12O12 nanoclusters: A DFT study

    Science.gov (United States)

    Shamlouei, Hamid Reza; Nouri, Amin; Mohammadi, Asghar; Tehrani, Abbas Dadkhah

    2016-03-01

    Using density functional theory, we investigated the effect of transition metal doping on structural, electronic, energetic, linear and nonlinear optical properties of Mg12O12 nanocluster. The result revealed that transition metal atoms doping lead to reduce the Eg and increase the dipole moment. The doping of transition metal atom on Mg12O12 nanocluster enhances its polarizability value. Also polarizability values for doped nanoclusters decrease as the atomic number of transition metal increase. The first hyperpolarizability value dramatically increases as substitute a magnesium atom with a transition metal atom. Among the transition metal atom doped nanocage, scandium has the largest first hyperpolarizability value (β◦≈47,872 au). The stability and remarkable values of β◦ (for Sc, Ti and V doped of nanocage) suggest that these compounds may be applicable as NLO material in industrial.

  5. Atomically Thin Ordered Alloys of Transition Metal Dichalcogenides: Stability and Band Structures

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

    2016-01-01

    to be close to zero for several alloys and below 20 meV/atom for all the alloys. We explore to what extent the electronic properties like the band gap and band edge positions of the alloy can be evaluated by taking the weighted average of the corresponding properties of the pristine systems. In general......, this approach works well with the only exception being Cr containing compounds. Because the calculated properties of the alloys are very similar to the weighted averages, we expect that the trends observed for the ordered alloys will also hold for more realistic disordered alloys......We explore the possibility of modulating the electronic band edges of the transition metal dichalcogenides (TMD) via alloying of different semiconductors within the same group (intra-group alloying). The stability of the ordered alloys is assessed from the calculated mixing enthalpy which is found...

  6. Calculations of hydrogen atom multiphoton energy level shifts, transition amplitudes and ionization probabilities

    International Nuclear Information System (INIS)

    Analyses of the resonant multiphoton ionization of atoms require knowledge of ac Stark energy shifts and of multiphoton, bound-to-bound state, transition amplitudes. In this paper, we consider the three-photon photoionization of hydrogen atoms at frequencies that are at and surrounding the two-photon 1s to 2s resonance. AC energy shift sums of both the 1s and 2s states are calculated as a function of the laser frequency along with two-photon 1s → 2s resonant transition amplitude sums. These quantities are calculated using an extended version of a method, which has often been employed in a variety of ways, of calculating these sums by expressing them in terms of solutions to a variety of differential equations that are derived from the different sums being evaluated. We demonstrate how exact solutions are obtained to these differential equations, which lead to exact evaluations of the corresponding sums. A variety of different cases are analysed, some involving analytic continuation, some involving real number analysis and some involving complex number analysis. A dc Stark sum calculation of the 2s state is carried out to illustrate the case where analytic continuation, pole isolation and pole subtraction are required and where the calculation can be carried out analytically; the 2s state, ac Stark shift sum calculations involve a case where no analytic continuation is required, but where the solution to the differential equation produces complex numbers owing to the finite photoionization lifetime of the 2s state. Results from these calculations are then used to calculate three-photon ionization probabilities of relevance to an analysis of the multiphoton ionization data published by Kyrala and Nichols (1991 Phys. Rev. A 44, R1450)

  7. Dipole-forbidden atomic transitions induced by superintense x-ray laser fields

    Science.gov (United States)

    Simonsen, Aleksander Skjerlie; Førre, Morten

    2016-06-01

    A hydrogen atom, initially prepared in the 2 s and/or 2 p (m =±1 ) states, is assumed irradiated by 0.8 keV (1.5 nm) photons in pulses of 1 -250 fs duration and intensities in the range 1020 to 1023W /cm2 . Solving the corresponding time-dependent Schrödinger equation from first principles, we show that the ionization and excitation dynamics of the laser-atom system is strongly influenced by interactions beyond the electric dipole approximation. A beyond-dipole two-photon Raman-like transition between the 2 s and 2 p (m =±1 ) states is found to completely dominate the underlying laser-matter interaction. It turns out that the large difference in the ionization rates of the 2 s and 2 p (m =±1 ) states is important in this context, effectively leading to a symmetry breaking in the corresponding (beyond-dipole) bound-bound dynamics with the result that a net population transfer between the states occurs throughout the laser-matter interaction period. Varying the x-ray exposure time as well as the laser intensity, we probe the phenomenon as the bound wave packet oscillates between having 2 s and 2 p (m =±1 ) character, eventually giving rise to a Rabi-like oscillation pattern in the populations.

  8. Atomic force microscopy studies on phase transitions and surface morphology transformation of CMTC crystals

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, X.N.; Xu, D.; Yuan, D.R.; Sun, D.L.; Lu, M.K.; Jiang, M.H. [State Key Laboratory of Crystal Materials, Institute of Crystal Materials, Shandong University, Jinan (China)

    2002-11-01

    Atomic force microscopy (AFM) has been used to investigate the phase transitions and surface morphology transformation of cadmium mercury thiocyanate (CMTC) crystals, which are highly efficient nonlinear optical (NLO) materials for generating blue-violet light by laser frequency doubling. Amorphous aggregates at the crystalline steps become greatly contracted and much more crystalloid after the crystal was kept for one day. Elimination of dangling bonds, which lower the surface free energy at the crystal surface, and structural adjustment inside the crystal are assumed to cause this phase transition. Surface morphology transformations were also observed in CMTC crystals during and after multiple scanning by AFM tips. We have visualized the continuous translation process from two-dimensional nuclei to trigonal microcrystals with almost equal sizes during multiple scanning. In other cases, however, the surface morphology did not change at all during scanning, but became greatly altered hours after scanning. These experimental results suggest that reconstruction is a characteristic growth phenomenon on CMTC crystal surfaces. Reconstruction probably results from the formation of intervening metastable phases that have the potential to arrive at more stable stages; however, multiple scanning of AFM tips greatly affects this translation process. (orig.)

  9. Statistics of electromagnetic transitions as a signature of chaos in many-electron atoms

    CERN Document Server

    Flambaum, V V; Gribakin, G F

    1998-01-01

    Using a configuration interaction approach we study statistics of the dipole matrix elements (E1 amplitudes) between the 14 lower odd states with J=4 and 21st to 100th even states with J=4 in the Ce atom (1120 lines). We show that the distribution of the matrix elements is close to Gaussian, although the width of the Gaussian distribution, i.e. the root-mean-square matrix element, changes with the excitation energy. The corresponding line strengths are distributed according to the Porter-Thomas law which describes statistics of transition strengths between chaotic states in compound nuclei. We also show how to use a statistical theory to calculate mean squared values of the matrix elements or transition amplitudes between chaotic many-body states. We draw some support for our conclusions from the analysis of the 228 experimental line strengths in Ce [J. Opt. Soc. Am. v. 8, p. 1545 (1991)], although direct comparison with the calculations is impeded by incompleteness of the experimental data. Nevertheless, the...

  10. Optical trapping of ultracold dysprosium atoms: transition probabilities, dynamic dipole polarizabilities and van der Waals $C_6$ coefficients

    CERN Document Server

    Li, Hui; Dulieu, Olivier; Nascimbene, Sylvain; Lepers, Maxence

    2016-01-01

    The efficiency of optical trapping of ultracold atoms depend on the atomic dynamic dipole polarizability governing the atom-field interaction. In this article, we have calculated the real and imaginary parts of the dynamic dipole polarizability of dysprosium in the ground and first excited level. Due to the high electronic angular momentum of those two states, the polarizabilities possess scalar, vector and tensor contributions that we have computed, on a wide range of trapping wavelengths, using the sum-over-state formula. Using the same formalism, we have also calculated the $C_6$ coefficients characterizing the van der Waals interaction between two dysprosium atoms in the two lowest levels. We have computed the energies of excited states and the transition probabilities appearing in the sums, using a combination of \\textit{ab initio} and least-square-fitting techniques provided by the Cowan codes and extended in our group. Regarding the real part of the polarizability, for field frequencies far from atomic...

  11. Prospects for Forbidden-Transition Spectroscopy and Parity Violation Measurements using a Beam of Cold Stable or Radioactive Atoms

    CERN Document Server

    Sanguinetti, S; Lintz, M; Jacquier, P; Wasan, A; Bouchiat, M A; Jacquier, Ph.

    2003-01-01

    Laser cooling and trapping offers the possibility of confining a sample of radioactive atoms in free space. Here, we address the question of how best to take advantage of cold atom properties to perform the observation of as highly forbidden a line as the 6S-7S Cs transition for achieving, in the longer term, Atomic Parity Violation measurements in radioactive alkali isotopes. Another point at issue is whether one might do better with stable, cold atoms than with thermal atoms. To compensate for the large drawback of the small number of atoms available in a trap, one must take advantage of their low velocity. To lengthen the time of interaction with the excitation laser, we suggest choosing a geometry where the laser beam exciting the transition is colinear to a slow, cold atomic beam, either extracted from a trap or prepared by Zeeman slowing. We also suggest a new observable physical quantity manifesting APV, which presents several advantages:specificity, efficiency of detection, possibility of direct calib...

  12. Vibrational properties of vacancy in bcc transition metals using embedded atom method potentials

    Indian Academy of Sciences (India)

    Vandana Gairola; P D Semalty; P N Ram

    2013-06-01

    The embedded atom method (EAM) potentials, with the universal form of the embedding function along with the Morse form of pair potential, have been employed to determine the potential parameters for three bcc transition metals: Fe, Mo, and W, by fitting to Cauchy pressure $(C_{12} − C_{44})/2$, shear constants $G_{v} = (C_{11} − C_{12} + 3C_{44})/5$ and 44, cohesive energy and the vacancy formation energy. The obtained potential parameters are used to calculate the phonon dispersion spectra of these metals. Large discrepancies are found between the calculated results of phonon dispersion using the EAM and the experimental phonon dispersion results. Therefore, to overcome this inadequacy of the EAM model, we employ the modified embedded atom method (MEAM) in which a modified term along with the pair potential and embedding function is added in the total energy. The phonon dispersions calculated using potential parameters obtained from the MEAM show good agreement with experimental results compared to those obtained from the EAM. Using the calculated phonons, we evaluate the local density of states of the neighbours of vacancy using the Green’s function method. The local frequency spectrum of first neighbours of vacancy in Mo shows an increase at higher frequencies and a shift towards the lower frequencies whereas in Fe and W, the frequency spectrum shows a small decrease towards higher frequency and small shift towards lower frequency. For the second neighbours of vacancy in all the three metals, the local frequency spectrum is not much different from that of the host atom. The local density of states of the neighbours of the vacancy has been used to calculate the mean square displacements and the formation entropy of vacancy. The calculated mean square displacements of the first neighbours of vacancy are found to be higher than that of the host atom, whereas it is lower for the second neighbours. The calculated results of the formation entropy of the vacancy

  13. Highly Anti-UV Properties of Silk Fiber with Uniform and Conformal Nanoscale TiO2 Coatings via Atomic Layer Deposition.

    Science.gov (United States)

    Xiao, Xingfang; Liu, Xin; Chen, Fengxiang; Fang, Dong; Zhang, Chunhua; Xia, Liangjun; Xu, Weilin

    2015-09-30

    In this study, silk fiber was successfully modified via the application of a nanoscale titania coating using atomic layer deposition (ALD), with titanium tetraisopropoxide (TIP) and water as precursors at 100 °C. Scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscope, and field emission scanning electron microscope results demonstrated that uniform and conformal titania coatings were deposited onto the silk fiber. The thermal and mechanical properties of the TiO2 silk fiber were then investigated. The results showed that the thermal stability and mechanical properties of this material were superior to those of the uncoated substance. Furthermore, the titania ALD process provided the silk fiber with excellent protection against UV radiation. Specifically, the TiO2-coated silk fibers exhibited significant increases in UV absorbance, considerably less yellowing, and greatly enhanced mechanical properties compared with the uncoated silk fiber after UV exposure.

  14. Conformal SiO2 coating of sub-100 nm diameter channels of polycarbonate etched ion-track channels by atomic layer deposition.

    Science.gov (United States)

    Sobel, Nicolas; Hess, Christian; Lukas, Manuela; Spende, Anne; Stühn, Bernd; Toimil-Molares, M E; Trautmann, Christina

    2015-01-01

    Polycarbonate etched ion-track membranes with about 30 µm long and 50 nm wide cylindrical channels were conformally coated with SiO2 by atomic layer deposition (ALD). The process was performed at 50 °C to avoid thermal damage to the polymer membrane. Analysis of the coated membranes by small angle X-ray scattering (SAXS) reveals a homogeneous, conformal layer of SiO2 in the channels at a deposition rate of 1.7-1.8 Å per ALD cycle. Characterization by infrared and X-ray photoelectron spectroscopy (XPS) confirms the stoichiometric composition of the SiO2 films. Detailed XPS analysis reveals that the mechanism of SiO2 formation is based on subsurface crystal growth. By dissolving the polymer, the silica nanotubes are released from the ion-track membrane. The thickness of the tube wall is well controlled by the ALD process. Because the track-etched channels exhibited diameters in the range of nanometres and lengths in the range of micrometres, cylindrical tubes with an aspect ratio as large as 3000 have been produced.

  15. Conformal SiO2 coating of sub-100 nm diameter channels of polycarbonate etched ion-track channels by atomic layer deposition

    Directory of Open Access Journals (Sweden)

    Nicolas Sobel

    2015-02-01

    Full Text Available Polycarbonate etched ion-track membranes with about 30 µm long and 50 nm wide cylindrical channels were conformally coated with SiO2 by atomic layer deposition (ALD. The process was performed at 50 °C to avoid thermal damage to the polymer membrane. Analysis of the coated membranes by small angle X-ray scattering (SAXS reveals a homogeneous, conformal layer of SiO2 in the channels at a deposition rate of 1.7–1.8 Å per ALD cycle. Characterization by infrared and X-ray photoelectron spectroscopy (XPS confirms the stoichiometric composition of the SiO2 films. Detailed XPS analysis reveals that the mechanism of SiO2 formation is based on subsurface crystal growth. By dissolving the polymer, the silica nanotubes are released from the ion-track membrane. The thickness of the tube wall is well controlled by the ALD process. Because the track-etched channels exhibited diameters in the range of nanometres and lengths in the range of micrometres, cylindrical tubes with an aspect ratio as large as 3000 have been produced.

  16. Secondary structure of prothymosin alpha evidenced for conformational transitions induced by changes in temperature and concentration of n-dodecyltrimethylammonium bromide.

    Science.gov (United States)

    Pombo, C; Suarez, M J; Nogueira, M; Czarnecki, J; Ruso, J M; Sarmiento, F; Prieto, G

    2001-08-01

    Conformational changes of prothymosin alpha (ProTalpha) induced by changes in temperature and concentration of the denaturant n-dodecyltrimethylammonium bromide (C12TAB) were studied by difference spectroscopy. The conformational transition of ProTalpha by C12TAB was followed as a function of denaturant concentration by absorbance measurements at 230 nm and the data were analyzed to obtain the Gibbs energy of the transition in water (deltaG0(w)) and in a hydrophobic environment (deltaG0(hc)) for saturated protein-surfactant complexes. The value of deltaG0(w) was 6.38 kJ mol(-1) and that for deltaG0(hc), which is not affected by temperature, was -18.62 kJ mol(-1). Changes of absorbance at 230 nm of ProTalpha with temperature can be assumed to resemble a transition in the secondary structure. The parameters characterizing the thermodynamics of unfolding, melting temperature (Tm), enthalpy (deltaHm), entropy (deltaSm) and heat capacity (deltaCp) were determined. The values obtained for Tm, deltaHm, and deltaSm are smaller that those found for other globular proteins; deltaCp was found to be much smaller. These results suggest that ProTalpha exhibits some type of secondary structure under these conditions (10 mM glycine buffer, pH 2.4).

  17. Modeling the Atomic-to-Molecular Transition and Chemical Distributions of Turbulent Star-Forming Clouds

    CERN Document Server

    Offner, Stella S R; Viti, Serena; Bell, Thomas A

    2013-01-01

    We use 3D-PDR, a three-dimensional astrochemistry code for modeling photodissociation regions (PDRs), to post-process hydrodynamic simulations of turbulent, star-forming clouds. We focus on the transition from atomic to molecular gas, with specific attention to the formation and distribution of H, C+, C, H2 and CO. First, we demonstrate that the details of the cloud chemistry and our conclusions are insensitive to the simulation spatial resolution, to the resolution at the cloud edge, and to the ray angular resolution. We then investigate the effect of geometry and simulation parameters on chemical abundances and find weak dependence on cloud morphology as dictated by gravity and turbulent Mach number. For a uniform external radiation field, we find similar distributions to those derived using a one-dimensional PDR code. However, we demonstrate that a three-dimensional treatment is necessary for a spatially varying external field, and we caution against using one-dimensional treatments for non-symmetric probl...

  18. MODELING THE ATOMIC-TO-MOLECULAR TRANSITION AND CHEMICAL DISTRIBUTIONS OF TURBULENT STAR-FORMING CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Offner, Stella S. R. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Bisbas, Thomas G.; Viti, Serena [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6B (United Kingdom); Bell, Tom A., E-mail: stella.offner@yale.edu [Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir, km 4, E-28850 Madrid (Spain)

    2013-06-10

    We use 3D-PDR, a three-dimensional astrochemistry code for modeling photodissociation regions (PDRs), to post-process hydrodynamic simulations of turbulent, star-forming clouds. We focus on the transition from atomic to molecular gas, with specific attention to the formation and distribution of H, C{sup +}, C, H{sub 2}, and CO. First, we demonstrate that the details of the cloud chemistry and our conclusions are insensitive to the simulation spatial resolution, to the resolution at the cloud edge, and to the ray angular resolution. We then investigate the effect of geometry and simulation parameters on chemical abundances and find weak dependence on cloud morphology as dictated by gravity and turbulent Mach number. For a uniform external radiation field, we find similar distributions to those derived using a one-dimensional PDR code. However, we demonstrate that a three-dimensional treatment is necessary for a spatially varying external field, and we caution against using one-dimensional treatments for non-symmetric problems. We compare our results with the work of Glover et al., who self-consistently followed the time evolution of molecule formation in hydrodynamic simulations using a reduced chemical network. In general, we find good agreement with this in situ approach for C and CO abundances. However, the temperature and H{sub 2} abundances are discrepant in the boundary regions (A{sub v} {<=} 5), which is due to the different number of rays used by the two approaches.

  19. Electronic and magnetic properties of 1T-HfS2 by doping transition-metal atoms

    Science.gov (United States)

    Zhao, Xu; Wang, Tianxing; Wang, Guangtao; Dai, Xianqi; Xia, Congxin; Yang, Lin

    2016-10-01

    We explored the electronic and magnetic properties of 1T-HfS2 doped by transition metal (TM) atom using the first-principles calculation. We doped the transition metal atoms from the IIIB to VIB groups in nonmagnetic 1T-HfS2. Numerical results show that the pristine 1T-HfS2 is a semiconductor with indirect gaps of 1.250 eV. Magnetism can be observed for V, Cr, Mn, Fe, Co, and Cu doping. The polarized charges mainly arise from the localized 3d electrons of the TM atom. The strong p-d hybridization was found between the 3d orbitals of TM and 3p orbitals of S. The substituted 1T-HfS2 can be a metal, semiconductor or half-metal. Analysis of the band structure and magnetic properties indicates that TM-doped HfS2 (TM = V, Fe, Cu) are promising systems to explore two-dimensional diluted magnetic semiconductors. The formation energy calculations also indicate that it is energetically favorable and relatively easier to incorporate transition metal atom into the HfS2 under S-rich experimental conditions. In contrast, V-doped HfS2 has relatively wide half-metallic gap and low formation energy. So V-doped 1T-HfS2 is ideal for spin injection, which is important for application in semiconductor spintronics.

  20. A New Rb Lamp Exciter Circuit for Rb atomic clocks and Studies on Transition from Ring to Red mode

    CERN Document Server

    Singh, Savita; Saxena, G M

    2010-01-01

    In this paper we describe the development of novel RF exciter circuit for electrode less Rb lamp. The lamp exciter circuit is a RF oscillator with a a new configuration operating at 60 to 65 MHz frequency with 3 to 4 watt power. The Rb lamp is used in exciting the ground state hyperfine transitions in Rb atom in a glass cell placed inside a tuned microwave cavity, As the frequency of these hyperfine transitions is very stable it is used in the development of Rb atomic clock by phase locking the oven controlled crystal oscillator (OCXO) to this atomic transition frequency. The details of the Rb lamp exciter are presented in the paper.The Lamp is ideally operated in ring mode as in this mode the linewidth is narrow and there is no self reversal. However, high temperature and RF excitation power may drive the Rb lamp to red mode which gives rise to line broadening and self reversal. It is the experience that mode change from ring to red deteriorates the atomic signal strength and S/N. In this paper the reasons o...

  1. ac Stark shift measurements of the clock transition in cold Cs atoms: Scalar and tensor light shifts of the D2 transition

    Science.gov (United States)

    Costanzo, G. A.; Micalizio, S.; Godone, A.; Camparo, J. C.; Levi, F.

    2016-06-01

    The ac Stark shift, or light shift, is a physical phenomenon that plays a fundamental role in many applications ranging from basic atomic physics to applied quantum electronics. Here, we discuss experiments testing light-shift theory in a cold-atom cesium fountain clock for the Cs D2 transition (i.e., 6 2S1 /2→6 2P3 /2 at 852 nm). Cold-atom fountains represent a nearly ideal system for the study of light shifts: (1) The atoms can be perturbed by a field of arbitrary character (e.g., coherent field or nonclassical field); (2) there are no trapping fields to complicate data interpretation; (3) the probed atoms are essentially motionless in their center-of-mass reference frame, T ˜ 1 μK; and (4) the atoms are in an essentially collisionless environment. Moreover, in the present work the resolution of the Cs excited-state hyperfine splittings implies that the D2 ac Stark shift contains a nonzero tensor polarizability contribution, which does not appear in vapor phase experiments due to Doppler broadening. Here, we test the linearity of the ac Stark shift with field intensity, and measure the light shift as a function of field frequency, generating a "light-shift curve." We have improved on the previous best test of theory by a factor of 2, and after subtracting the theoretical scalar light shift from the experimental light-shift curves, we have isolated and tested the tensor light shift for an alkali D2 transition.

  2. Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra

    CERN Document Server

    Berengut, J C; Flambaum, V V; King, J A; Kozlov, M G; Murphy, M T; Webb, J K

    2010-01-01

    Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, alpha, could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Recent studies using 140 absorption systems from the Keck telescope and 153 from the Very Large Telescope, suggest that alpha varies spatially. That is, in one direction on the sky alpha seems to have been smaller at the time of absorption, while in the opposite direction it seems to have been larger. To continue this study we need accurate laboratory measurements of atomic transition frequencies. The aim of this paper is to provide a compilation of transitions of importance to the search for alpha variation. They are E1 transitions to the ground state in several different atoms and ions, with wavelengths ranging from around 900 - 6000 A, and require an accuracy of better than 10^{-4} A. We discuss isotope shift measurements that are...

  3. Conformational transitions and stop-and-go nanopore transport of single-stranded DNA on charged graphene

    Science.gov (United States)

    Shankla, Manish; Aksimentiev, Aleksei

    2014-10-01

    Control over interactions with biomolecules holds the key to applications of graphene in biotechnology. One such application is nanopore sequencing, where a DNA molecule is electrophoretically driven through a graphene nanopore. Here we investigate how interactions of single-stranded DNA and a graphene membrane can be controlled by electrically biasing the membrane. The results of our molecular dynamics simulations suggest that electric charge on graphene can force a DNA homopolymer to adopt a range of strikingly different conformations. The conformational response is sensitive to even very subtle nucleotide modifications, such as DNA methylation. The speed of DNA motion through a graphene nanopore is strongly affected by the graphene charge: a positive charge accelerates the motion, whereas a negative charge arrests it. As a possible application of the effect, we demonstrate stop-and-go transport of DNA controlled by the charge of graphene. Such on-demand transport of DNA is essential for realizing nanopore sequencing.

  4. A comparison of transition state of phenol in H-atom abstraction by methyl and methylperoxyl radicals

    Institute of Scientific and Technical Information of China (English)

    SUN YouMin; WU JunSen; LIU ChengBu

    2007-01-01

    DFT method was employed to locate transition state for H-atom transfer from phenol by methyl radical and methylperoxyl radical. The reaction pathway energy profiles and the structure of transition state show that a common feature is the out-of-plane structure of the transition state: in contrast to the energetic minima of a hydrogen-bonded intermediate, the hydrogen bond in transition structures is considerably twisted out of the aromatic ring. From the values of enthalpy (△H) and activation energy (Ea)obtained, it is found that the rate of the reaction of peroxyl radical with phenolic antioxidant is higher than that of alkyl radical with antioxidant. Spin density distributions show that the electron transmission is between methyl (methylperoxyl) radical and phenol.

  5. Demonstration of a Sagnac-Type Cold Atom Interferometer with Stimulated Raman Transitions

    Institute of Scientific and Technical Information of China (English)

    WANG Ping; LI Run-Bing; YAN Hui; WANG Jin; ZHAN Ming-Sheng

    2007-01-01

    @@ Cold-matter-wave Sagnac interferometers possess many advantages over their thermal atomic beam counterparts when they are used as precise inertial sensors. We report a realization of a Sagnac-type interferometer with cold atoms.

  6. Conformational ensembles of neuromedin C reveal a progressive coil-helix transition within a binding-induced folding mechanism

    OpenAIRE

    Roca Adrover, Miquel; Sanchis, Pilar; Vilanova, Bartolome; Pauwels, Kris; Martorell, Gabriel; Pérez González, Juan Jesús

    2015-01-01

    Neuromedin C (NMC) is a peptide that regulates various processes in the central nervous system and gastrointestinal tract through its interaction with the bombesin receptor subtype-2 (BB2R). Hence, BB2R antagonists hold the potential to treat disorders that occur as a result of NMC dysfunction or misregulation. However, their efficient design requires a detailed understanding of the structural features of NMC, which hitherto are unknown. Herein, we describe the conformational ensembles of NMC...

  7. Time-resolved fluorescence spectroscopy of matrix-isolated silver atoms after pulsed excitation of inner-shell transitions

    Science.gov (United States)

    Hebert, T.; Wiggenhauser, H.; Schriever, U.; Kolb, D. M.

    1990-02-01

    The energy dissipation in matrix-isolated silver atoms after pulsed vacuum ultraviolet (VUV) excitation of 4d-5p transitions has been studied by time-resolved fluorescence spectroscopy. The decay behavior of the various fluorescence bands has been analyzed and a model for the relaxation process proposed within the framework of a two-dimensional configuration-coordinate diagram. If minute quantities of Ag2 are present in the matrix, the analysis requires consideration of energy transfer between silver atoms and dimers.

  8. Tuning of Electron States of Transition Metal’s Catalysts Using Acceptor’s Atoms: ab initio Calculation

    Directory of Open Access Journals (Sweden)

    R.M. Balabai

    2016-06-01

    Full Text Available Within the methods of density functional theory and ab initio pseudopotential, we have obtained the spatial distributions of the density of valence electron and the electronic energy spectrum for the small clusters from the atoms of Cu, Ni, Co, O, Si with the aim to determine the mechanisms of their high catalytic activity. Electron’s levels of catalyst guide course of chemical reaction. We explored, that the organization of electronic states of nanocatalysts on the basis of transition metals possible control by changing the spatial organization of clusters and adding electronegative atoms.

  9. Residues Coevolution Guides the Systematic Identification of Alternative Functional Conformations in Proteins.

    Science.gov (United States)

    Sfriso, Pedro; Duran-Frigola, Miquel; Mosca, Roberto; Emperador, Agustí; Aloy, Patrick; Orozco, Modesto

    2016-01-01

    We present here a new approach for the systematic identification of functionally relevant conformations in proteins. Our fully automated pipeline, based on discrete molecular dynamics enriched with coevolutionary information, is able to capture alternative conformational states in 76% of the proteins studied, providing key atomic details for understanding their function and mechanism of action. We also demonstrate that, given its sampling speed, our method is well suited to explore structural transitions in a high-throughput manner, and can be used to determine functional conformational transitions at the entire proteome level. PMID:26688214

  10. Wafer-scale, conformal and direct growth of MoS2 thin films by atomic layer deposition

    Science.gov (United States)

    Jang, Yujin; Yeo, Seungmin; Lee, Han-Bo-Ram; Kim, Hyungjun; Kim, Soo-Hyun

    2016-03-01

    Molybdenum disulfide (MoS2) thin films were grown directly on SiO2 covered wafers by atomic layer deposition (ALD) at the deposition temperatures ranging from 175 to 225 °C using molybdenum hexacarbonyl [Mo(CO)6] and H2S plasma as the precursor and reactant, respectively. Self-limited film growth on the thermally-grown SiO2 substrate was observed with both the precursor and reactant pulsing time. The growth rate was ∼0.05 nm/cycle and a short incubation cycle of around 13 was observed at a deposition temperature of 175 °C. The MoS2 films formed nanocrystalline microstructure with a hexagonal crystal system (2H-MoS2), which was confirmed by X-ray diffraction and transmission electron microscopy. Single crystal MoS2 nanosheets, ∼20 nm in size, were fabricated by controlling the number of ALD cycles. The ALD-MoS2 thin films exhibited good stoichiometry with negligible C impurities, approximately 0.1 at.% from Rutherford backscattering spectrometry (RBS). X-ray photoelectron spectroscopy confirmed the formation of chemical bonding from MoS2. The step coverage of ALD-MoS2 was approximately 75% at a 100 nm sized trench. Overall, the ALD-MoS2 process made uniform deposition possible on the wafer-scale (4 in. in diameter).

  11. Cooper minima in the transitions from low-excited and Rydberg states of alkali-metal atoms

    CERN Document Server

    Beterov, I I; Yakshina, E A; Ryabtsev, I I; Tretyakov, D B; Entin, V M; MacCormick, C; Piotrowicz, M J; Kowalczyk, A; Bergamini, S

    2012-01-01

    The structure of the Cooper minima in the transition probabilities and photoionization cross-sections for low-excited and Rydberg nS, nP, nD and nF states of alkali-metal atoms has been studied using a Coulomb approximation and a quasiclassical model. The range of applicability of the quasiclassical model has been defined from comparison with available experimental and theoretical data on dipole moments, oscillator strengths, and photoionization cross-sections. A new Cooper minimum for transitions between rubidium Rydberg states has been found.

  12. Diode laser operating on an atomic transition limited by an isotope ⁸⁷Rb Faraday filter at 780 nm.

    Science.gov (United States)

    Tao, Zhiming; Hong, Yelong; Luo, Bin; Chen, Jingbiao; Guo, Hong

    2015-09-15

    We demonstrate an extended cavity Faraday laser system using an antireflection-coated laser diode as the gain medium and the isotope (87)Rb Faraday anomalous dispersion optical filter (FADOF) as the frequency selective device. Using this method, the laser wavelength works stably at the highest transmission peak of the isotope (87)Rb FADOF over the laser diode current from 55 to 140 mA and the temperature from 15°C to 35°C. Neither the current nor the temperature of the laser diode has significant influence on the output frequency. Compared with previous extended cavity laser systems operating at frequencies irrelevant to spectacular atomic transition lines, the laser system realized here provides a stable laser source with the frequency operating on atomic transitions for many practical applications. PMID:26371933

  13. Diode laser operating on an atomic transition limited by an isotope ⁸⁷Rb Faraday filter at 780 nm.

    Science.gov (United States)

    Tao, Zhiming; Hong, Yelong; Luo, Bin; Chen, Jingbiao; Guo, Hong

    2015-09-15

    We demonstrate an extended cavity Faraday laser system using an antireflection-coated laser diode as the gain medium and the isotope (87)Rb Faraday anomalous dispersion optical filter (FADOF) as the frequency selective device. Using this method, the laser wavelength works stably at the highest transmission peak of the isotope (87)Rb FADOF over the laser diode current from 55 to 140 mA and the temperature from 15°C to 35°C. Neither the current nor the temperature of the laser diode has significant influence on the output frequency. Compared with previous extended cavity laser systems operating at frequencies irrelevant to spectacular atomic transition lines, the laser system realized here provides a stable laser source with the frequency operating on atomic transitions for many practical applications.

  14. Roughness of the SiC/SiO{sub 2} vicinal interface and atomic structure of the transition layers

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Peizhi; Li, Guoliang; Duscher, Gerd, E-mail: gduscher@utk.edu [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996 (United States); Sharma, Yogesh K.; Ahyi, Ayayi C.; Isaacs-Smith, Tamara; Williams, John R.; Dhar, Sarit [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States)

    2014-11-01

    The SiC/SiO{sub 2} interface is generally considered to be the cause for the reduced electron mobility of SiC power devices. Previous studies have shown a correlation between the mobility and the transition layer width at the SiC/SiO{sub 2} interface. The authors investigated this interface with atomic resolution Z-contrast imaging and electron energy-loss spectroscopy, and discovered that this transition region was due to the roughness of the vicinal interface. The roughness of a vicinal interface consisted of atomic steps and facets deviating from the ideal off-axis cut plane. The authors conclude that this roughness is limiting the mobility in the channels of SiC MOSFETs.

  15. Atomic screening effects on electron-neutrino angular correlation and β-decay asymmetry in allowed transitions

    International Nuclear Information System (INIS)

    Atomic screening effects on the electron-neutrino angular correlation coefficient a0 and the β asymmetry coefficient A0, in allowed transitions, are studied. It has long been known that the dominant screening effect on the spectrum is the replacement, in the factor which represents the phase space of the β particle, of W, the energy with which the β particle emerges, by W-V0, the energy with which it is born; V0 is the energy of interaction of the β particle at the origin with the potential generated there by the atomic electrons. [One also replaces the momentum p=p(W) by p'=p(W-V0).] One might well expect a similar result for screening effects on a0 and A0, which include the influence of the nuclear Coulomb potential---and this intuitive expectation is shown to be the case. One need merely replace the velocity of emergence v=v(W) in the correlation functions by the velocity at birth, v'=v(W-V0). As for the case of the spectrum, the effect can be obtained by using a static approximation, with the atomic electrons unaffected by the β particle, and with the screening potential treated to second order; the effect of virtual or real excitation of the atomic electrons is negligible. The screening effect is of order 10-4 for most superallowed and mirror image transitions (presently, both theory and experiment for superallowed transitions---with implications for electro-weak theory and the standard model---give ft values accurate to about one part in 103); it can be as large as 20% for some pure Gamow-Teller transitions, for which the nuclear matrix element does not enter into the analysis of a0 and A0

  16. Effects of poly (ethylene glycol) chains conformational transition on the properties of mixed DMPC/DMPE-PEG thin liquid films and monolayers.

    Science.gov (United States)

    Georgiev, Georgi As; Sarker, Dipak K; Al-Hanbali, Othman; Georgiev, Georgi D; Lalchev, Zdravko

    2007-10-01

    Foam thin liquid films (TLF) and monolayers at the air-water interface formed by DMPC mixed with DMPE-bonded poly (ethylene glycol)s (DMPE-PEG(550), DMPE-PEG(2000) and DMPE-PEG(5000)) were obtained. The influence of both (i) PEG chain size (evaluated in terms of Mw) and mushroom-to-brush conformational transition and (ii) of the liposome/micelle ratio in the film-forming dispersions, on the interfacial properties of mixed DMPC/DMPE-PEG films was compared. Foam film studies demonstrated that DMPE-PEG addition to foam TLFs caused (i) delayed kinetics of film thinning and black spot expansion and (ii) film stabilization. At the mushroom-to-brush transition, due to steric repulsion increased DMPE-PEG films thickness reached 25 nm while pure DMPC films were only 8 nm thick Newton black films. It was possible to differentiate DMPE-PEG(2000/5000) from DMPE-PEG(550) by the ability to change foam TLF formation mechanism, which could be of great importance for "stealth" liposome design. Monolayer studies showed improved formation kinetics and equilibrium surface tension decrease for DMPE-PEG monolayers compared with DMPC pure films. SEM observations revealed "smoothing" and "sealing" of the defects in the solid-supported layer surface by DMPE-PEGs adsorption, which could explain DMPE-PEGs ability to stabilize TLFs and to decrease monolayer surface tension. All effects in monolayers, foam TLFs and solid-supported layers increased with the increase of PEG Mw and DMPE-PEG concentration. However, at the critical DMPE-PEG concentration (where mushroom-to-brush conformational transition occurred) maximal magnitude of the effects was reached, which only slightly changed at further DMPE-PEG content and micelle/liposome ratio increase.

  17. Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks.

    Science.gov (United States)

    Taichenachev, A V; Yudin, V I; Oates, C W; Hoyt, C W; Barber, Z W; Hollberg, L

    2006-03-01

    We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

  18. First application of superconducting transition-edge-sensor microcalorimeters to hadronic-atom x-ray spectroscopy

    CERN Document Server

    Okada, S; Curceanu, C; Doriese, W B; Fowler, J W; Gard, J; Gustafsson, F P; Hashimoto, T; Hayano, R S; Hirenzaki, S; Hays-Wehle, J P; Hilton, G C; Ikeno, N; Iliescu, M; Ishimoto, S; Itahashi, K; Iwasaki, M; Koike, T; Kuwabara, K; Ma, Y; Marton, J; Noda, H; O'Neil, G C; Outa, H; Reintsema, C D; Sato, M; Schmidt, D R; Shi, H; Suzuki, K; Suzuki, T; Swetz, D S; Tatsuno, H; Uhlig, J; Ullom, J N; Widmann, E; Yamada, S; Yamagata-Sekihara, J; Zmeskal, J

    2016-01-01

    High-resolution pionic-atom x-ray spectroscopy was performed with an x-ray spectrometer based on a 240-pixel array of superconducting transition-edge-sensor (TES) microcalorimeters at the piM1 beam line of the Paul Scherrer Institute. X-rays emitted by pionic carbon via the 4f->3d transition and the parallel 4d->3p transition were observed with a full-width-at-half-maximum energy resolution of 6.8 eV at 6.4 keV. Measured x-ray energies are consistent with calculated electromagnetic values which considered the strong-interaction effect assessed via the Seki-Masutani potential for the 3p energy level, and favor the electronic population of two filled 1s electrons in the K-shell. Absolute energy calibration with an uncertainty of 0.1 eV was demonstrated under a high-rate hadron beam condition of 1.45 MHz. This is the first application of a TES spectrometer to hadronic-atom x-ray spectroscopy and is an important milestone towards next-generation high-resolution kaonic-atom x-ray spectroscopy.

  19. The atomic parameter model for the fifth and sixth transition metal quasicrystal alloys (Mc=0.5)

    Institute of Scientific and Technical Information of China (English)

    LIAO ShuZhi; GUI XuChun; ZHANG Chun; PENG HaoJun; XIE HaoWen; OUYANG YiFang; ZHANG BangWei

    2009-01-01

    The forming ability of quasicrystal phase has a relationship with the atomic bond factors based on differences in atom size and electron factors.Usually,those factors or their combination are used to describe the forming ability,stability of alloys,etc.In this paper,the quasicrystal alloy forming abilities for the fifth and sixth transition metals (Y,Zr,Nb,Mo,Ru,Rh,Pd and La,Hf,Ta,W,Re,Os,Ir,Pt) based alloys have been studied by the size factor and the atomic parametric function.It has been found that an ellipse curve can be used to separate the quasicrystal formed area from the informed area in the size factor and atomic parameters functional graph.The ellipse curve can be defined by an equation(x-m)2/c2+(y-n)2/d2=1.The overall reliabilities for the model are up to 97.4% and 95.5% for the fifth and the sixth transition metals based quasicrystal alloys,respectively.Also,the ellipse parameters m,n,c and d can be paraphrased by some appropriate parameters for each host metal.

  20. The atomic parameter model for the fifth and sixth transition metal quasicrystal alloys(Mc=0.5)

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The forming ability of quasicrystal phase has a relationship with the atomic bond factors based on differences in atom size and electron factors.Usually,those factors or their combination are used to describe the forming ability,stability of alloys,etc.In this paper,the quasicrystal alloy forming abilities for the fifth and sixth transition metals(Y,Zr,Nb,Mo,Ru,Rh,Pd and La,Hf,Ta,W,Re,Os,Ir,Pt) based alloys have been studied by the size factor and the atomic parametric function.It has been found that an ellipse curve can be used to separate the quasicrystal formed area from the informed area in the size factor and atomic parameters functional graph.The ellipse curve can be defined by an equation(x-m)2/c2+(y?n)2/d2=1.The overall reliabilities for the model are up to 97.4% and 95.5% for the fifth and the sixth transition metals based quasicrystal alloys,respectively.Also,the ellipse parameters m,n,c and d can be paraphrased by some appropriate parameters for each host metal.

  1. Structures of the gauche conformers of somE substituted dimethyl ethers. Effect of adjacent atom lone pairs on methyl group asymmetry

    Science.gov (United States)

    Boggs, James E.; Altman, Michael; Cordell, Floyd R.; Dai, Yuanfang

    The complete equilibrium structures of CH 3OCH 3 and of the gauche conformers of CH 30CH 2F, HOCH,F, CH,OCH,Cl and CH,OCH,CN have been determined by ab initio gradient computation at the Hartree-Fock, double zeta-plus-polarization level. The very large asymmetries in CH bond distances previously reported from microwave substitution structures are shown to be non-existent in the equilibrium structures and are presumably artifacts. Small differences, different in direction from those reported from the experiments and nearly an order of magnitude smaller in size, do exist. They reflect three factors: (1) a lengthening of a CH bond which is trans to a lone pair on an adjacent atom, (2) a general shortening of CH bonds originating at a carbon atom bearing a highly electronegative substituent, and (3) a specific interaction in which a CX substituent shortens the nearly parallel CH bond on the other methyl group. The last interaction, not previously reported, is mediated by withdrawal of electron density from the oxygen lone pair which is trans to both groups. Other structural features derived from the microwave studies are supported by the new results. Inclusion of polarization functions in the basis set for oxygen is essential for correct determination of the COC angle and the dihedral angles. The dihedral angles of CH 3OCH 2F and HOCH 2F are not correctly determined by the computation even at this level, although the computed values are improved when d functions are used for oxygen and still more by use of two sets of oxygen d functions. Polarization functions on carbon or on fluorine have no effect on the computed torsional angles. There is no problem in computing the correct dihedral angles with the CI or CN derivatives.

  2. FTIR/PCA study of propanol in argon matrix: the initial stage of clustering and conformational transitions

    International Nuclear Information System (INIS)

    FTIR spectra of 1-propanol in an argon matrix were studied in the range 11 to 30 K. Principal component analysis of dynamic FTIR spectra and nonlinear band shape fitting has been carried out. The peaks of monomer, open dimer, mixed propanol-water dimer and those of higher H-bond clusters have been resolved and analyzed. The attribution of certain FTIR peaks has been supported by proper density functional theory calculations. Analyzing dependences of the integral band intensities of various aggregates on temperature it has been deduced that in the initial stage of clustering monomers and dimers are the basic building blocks forming higher H-bond clusters. The peaks assigned to two conformers of monomers and mixed propanol-water dimers were investigated processing the temperature dependences of their integral intensities in Arrhenius plot. The obtained values of 0.18 kJ.mol-1 for propanol monomer and 0.26 kJ.mol-1 for mixed dimer are well comparable with the energy differences between the global minimum conformation of 1-propanol (Gt) and some other energetically higher structures (Tt or Tg).

  3. An exacting transition probability measurement - a direct test of atomic many-body theories

    OpenAIRE

    Tarun Dutta; Debashis De Munshi; Dahyun Yum; Riadh Rebhi; Manas Mukherjee

    2016-01-01

    A new protocol for measuring the branching fraction of hydrogenic atoms with only statistically limited uncertainty is proposed and demonstrated for the decay of the P$_{3/2}$ level of the barium ion, with precision below $0.5\\%$. Heavy hydrogenic atoms like the barium ion are test beds for fundamental physics such as atomic parity violation and they also hold the key to understanding nucleo-synthesis in stars. To draw definitive conclusion about possible physics beyond the standard model by ...

  4. Self-Doping of Ultrathin Insulating Films by Transition Metal Atoms

    OpenAIRE

    Li, Zhe; Chen, H. -Y. T; Schouteden, Koen; Lauwaet, K; Giordano, L.; Trioni, M. I.; Janssens, Ewald; Iancu, Violeta; Van Haesendonck, Chris; Lievens, Peter; Pacchioni, G.

    2014-01-01

    Single magnetic Co atoms are deposited on atomically thin NaCl films on Au(111). Two different adsorption sites are revealed by high-resolution scanning tunneling microscopy (STM), i.e., at Na and at Cl locations. Using density functional based simulations of the STM images, we show that the Co atoms substitute with either a Na or Cl atom of the NaCl surface, resulting in cationic and anionic Co dopants with a high thermal stability. The dependence of the magnetic coupling between neighboring...

  5. Structure analysis and conformational transitions of the cell penetrating peptide transportan 10 in the membrane-bound state.

    Directory of Open Access Journals (Sweden)

    Susanne Fanghänel

    Full Text Available Structure analysis of the cell-penetrating peptide transportan 10 (TP10 revealed an exemplary range of different conformations in the membrane-bound state. The bipartite peptide (derived N-terminally from galanin and C-terminally from mastoparan was found to exhibit prominent characteristics of (i amphiphilic α-helices, (ii intrinsically disordered peptides, as well as (iii β-pleated amyloid fibrils, and these conformational states become interconverted as a function of concentration. We used a complementary approach of solid-state (19F-NMR and circular dichroism in oriented membrane samples to characterize the structural and dynamical behaviour of TP10 in its monomeric and aggregated forms. Nine different positions in the peptide were selectively substituted with either the L- or D-enantiomer of 3-(trifluoromethyl-bicyclopent-[1.1.1]-1-ylglycine (CF3-Bpg as a reporter group for (19F-NMR. Using the L-epimeric analogs, a comprehensive three-dimensional structure analysis was carried out in lipid bilayers at low peptide concentration, where TP10 is monomeric. While the N-terminal region is flexible and intrinsically unstructured within the plane of the lipid bilayer, the C-terminal α-helix is embedded in the membrane with an oblique tilt angle of ∼ 55° and in accordance with its amphiphilic profile. Incorporation of the sterically obstructive D-CF3-Bpg reporter group into the helical region leads to a local unfolding of the membrane-bound peptide. At high concentration, these helix-destabilizing C-terminal substitutions promote aggregation into immobile β-sheets, which resemble amyloid fibrils. On the other hand, the obstructive D-CF3-Bpg substitutions can be accommodated in the flexible N-terminus of TP10 where they do not promote aggregation at high concentration. The cross-talk between the two regions of TP10 thus exerts a delicate balance on its conformational switch, as the presence of the α-helix counteracts the tendency of the

  6. Repumping of ultracold strontium atoms using the ^3P2 - ^3D2 transition

    Science.gov (United States)

    Mickelson, P. G.; Martinez de Escobar, Y. N.; Traverso, A. J.; Killian, T. C.

    2008-05-01

    We discuss recent experiments involving ultracold strontium. Using a commercially-available 3 micron laser, we repump atoms out of the ^3P2 level via the ^3D2 state and gain almost a factor of 10 in the number of atoms in our system. This increase in the signal-to-noise ratio enables improved spectroscopy of strontium in our optical trap.

  7. Bonds Between Metal Atoms: A New Mode of Transition Metal Chemistry.

    Science.gov (United States)

    Cotton, F. Albert; Chisholm, Malcolm H.

    1982-01-01

    Discusses polynuclear metal clusters (containing two or more metal atoms bonded to one another as well as to nonmetallic elements), including their formation and applications. Studies of bonds between metal atoms reveal superconductors, organic-reaction catalysts, and photosensitive complexes that may play a role in solar energy. (JN)

  8. Specificity Rendering ‘Hot-Spots’ for Aurora Kinase Inhibitor Design: The Role of Non-Covalent Interactions and Conformational Transitions

    Science.gov (United States)

    Badrinarayan, Preethi; Sastry, G. Narahari

    2014-01-01

    The present study examines the conformational transitions occurring among the major structural motifs of Aurora kinase (AK) concomitant with the DFG-flip and deciphers the role of non-covalent interactions in rendering specificity. Multiple sequence alignment, docking and structural analysis of a repertoire of 56 crystal structures of AK from Protein Data Bank (PDB) has been carried out. The crystal structures were systematically categorized based on the conformational disposition of the DFG-loop [in (DI) 42, out (DO) 5 and out-up (DOU) 9], G-loop [extended (GE) 53 and folded (GF) 3] and αC-helix [in (CI) 42 and out (CO) 14]. The overlapping subsets on categorization show the inter-dependency among structural motifs. Therefore, the four distinct possibilities a) 2W1C (DI, CI, GE) b) 3E5A (DI, CI, GF) c) 3DJ6 (DI, CO, GF) d) 3UNZ (DOU, CO, GF) along with their co-crystals and apo-forms were subjected to molecular dynamics simulations of 40 ns each to evaluate the variations of individual residues and their impact on forming interactions. The non-covalent interactions formed by the 157 AK co-crystals with different regions of the binding site were initially studied with the docked complexes and structure interaction fingerprints. The frequency of the most prominent interactions was gauged in the AK inhibitors from PDB and the four representative conformations during 40 ns. Based on this study, seven major non-covalent interactions and their complementary sites in AK capable of rendering specificity have been prioritized for the design of different classes of inhibitors. PMID:25485544

  9. Data supporting the involvement of the adenine nucleotide translocase conformation in opening the Tl(+)-induced permeability transition pore in Ca(2+)-loaded rat liver mitochondria.

    Science.gov (United States)

    Korotkov, Sergey M

    2016-06-01

    There we made available information about the effects of the adenine nucleotide translocase (ANT) 'c' conformation fixers (phenylarsine oxide (PAO), tert-butylhydroperoxide (tBHP), and carboxyatractyloside) as well as thiol reagent (4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS)) on isolated rat liver mitochondria. We observed a decrease in A540 (mitochondrial swelling) and respiratory control rates (RCRADP [state 3/state 4] and RCRDNP [2,4-dinitrophenol-uncoupled state/basal state or state 4]), as well as an increase in Ca(2+)-induced safranin fluorescence (F485/590, arbitrary units), showed a dissipation in the inner membrane potential (ΔΨmito), in experiments with energized rat liver mitochondria, injected into the buffer containing 25-75 mM TlNO3, 125 mM KNO3, and 100 µM Ca(2+). The fixers and DIDS, in comparison to Ca(2+) alone, greatly increased A540 decline and the rate of Ca(2+)-induced ΔΨmito dissipation. These reagents also markedly decreased RCRADP and RCRDNP. The MPTP inhibitors (ADP, cyclosporin A, bongkrekic acid, and N-ethylmaleimide) fixing the ANT in 'm' conformation significantly hindered the above-mentioned effects of the fixers and DIDS. A more complete scientific analysis of these findings may be obtained from the manuscript "To involvement the conformation of the adenine nucleotide translocase in opening the Tl(+)-induced permeability transition pore in Ca(2+)-loaded rat liver mitochondria" (Korotkov et al., 2016 [1]). PMID:27054168

  10. Validation of Force Fields of Rubber through Glass-Transition Temperature Calculation by Microsecond Atomic-Scale Molecular Dynamics Simulation.

    Science.gov (United States)

    Sharma, Pragati; Roy, Sudip; Karimi-Varzaneh, Hossein Ali

    2016-02-25

    Microsecond atomic-scale molecular dynamics simulation has been employed to calculate the glass-transition temperature (Tg) of cis- and trans-1,4-polybutadiene (PB) and 1,4-polyisoprene (PI). Both all-atomistic and united-atom models have been simulated using force fields, already available in literature. The accuracy of these decade old force fields has been tested by comparing calculated glass-transition temperatures to the corresponding experimental values. Tg depicts the phase transition in elastomers and substantially affects various physical properties of polymers, and hence the reproducibility of Tg becomes very crucial from a thermodynamic point of view. Such validation using Tg also evaluates the ability of these force fields to be used for advanced materials like rubber nanocomposites, where Tg is greatly affected by the presence of fillers. We have calculated Tg for a total of eight systems, featuring all-atom and united-atom models of cis- and trans-PI and -PB, which are the major constituents of natural and synthetic rubber. Tuning and refinement of the force fields has also been done using quantum-chemical calculations to obtain desirable density and Tg. Thus, a set of properly validated force fields, capable of reproducing various macroscopic properties of rubber, has been provided. A novel polymer equilibration protocol, involving potential energy convergence as the equilibration criterion, has been proposed. We demonstrate that not only macroscopic polymer properties like density, thermal expansion coefficient, and Tg but also local structural characteristics like end-to-end distance (R) and radius of gyration (Rg) and mechanical properties like bulk modulus have also been equilibrated using our strategy. Complete decay of end-to-end vector autocorrelation function with time also supports proper equilibration using our strategy. PMID:26836395

  11. Structural Exploration and Conformational Transitions in MDM2 upon DHFR Interaction from Homo sapiens: A Computational Outlook for Malignancy via Epigenetic Disruption.

    Science.gov (United States)

    Banerjee, Arundhati; Ray, Sujay

    2016-01-01

    Structural basis for exploration into MDM2 and MDM2-DHFR interaction plays a vital role in analyzing the obstruction in folate metabolism, nonsynthesis of purines, and further epigenetic regulation in Homo sapiens. Therefore, it leads to suppression of normal cellular behavior and malignancy. This has been earlier documented via yeast two-hybrid assays. So, with a novel outlook, this study explores the molecular level demonstration of the best satisfactory MDM2 model selection after performing manifold modeling techniques. Z-scores and other stereochemical features were estimated for comparison. Further, protein-protein docking was executed with MDM2 and the experimentally validated X-ray crystallographic DHFR. Residual disclosure from the best suited simulated protein complex disclosed 18 side chain and 3 ionic interactions to strongly accommodate MDM2 protein into the pocket-like zone in DHFR due to the positive environment by charged residues. Lysine residues from MDM2 played a predominant role. Moreover, evaluation from varied energy calculations, folding rate, and net area for solvent accessibility implied the active participation of MDM2 with DHFR. Fascinatingly, conformational transitions from coils to helices and β-sheets after interaction with DHFR affirm the conformational strength and firmer interaction of human MDM2-DHFR. Therefore, this probe instigates near-future clinical research and interactive computational investigations with mutations. PMID:27213086

  12. Structural Exploration and Conformational Transitions in MDM2 upon DHFR Interaction from Homo sapiens: A Computational Outlook for Malignancy via Epigenetic Disruption

    Science.gov (United States)

    Banerjee, Arundhati; Ray, Sujay

    2016-01-01

    Structural basis for exploration into MDM2 and MDM2-DHFR interaction plays a vital role in analyzing the obstruction in folate metabolism, nonsynthesis of purines, and further epigenetic regulation in Homo sapiens. Therefore, it leads to suppression of normal cellular behavior and malignancy. This has been earlier documented via yeast two-hybrid assays. So, with a novel outlook, this study explores the molecular level demonstration of the best satisfactory MDM2 model selection after performing manifold modeling techniques. Z-scores and other stereochemical features were estimated for comparison. Further, protein-protein docking was executed with MDM2 and the experimentally validated X-ray crystallographic DHFR. Residual disclosure from the best suited simulated protein complex disclosed 18 side chain and 3 ionic interactions to strongly accommodate MDM2 protein into the pocket-like zone in DHFR due to the positive environment by charged residues. Lysine residues from MDM2 played a predominant role. Moreover, evaluation from varied energy calculations, folding rate, and net area for solvent accessibility implied the active participation of MDM2 with DHFR. Fascinatingly, conformational transitions from coils to helices and β-sheets after interaction with DHFR affirm the conformational strength and firmer interaction of human MDM2-DHFR. Therefore, this probe instigates near-future clinical research and interactive computational investigations with mutations. PMID:27213086

  13. Light-pulse atom interferometric device

    Science.gov (United States)

    Biedermann, Grant; McGuinness, Hayden James Evans; Rakholia, Akash; Jau, Yuan-Yu; Schwindt, Peter; Wheeler, David R.

    2016-03-22

    An atomic interferometric device useful, e.g., for measuring acceleration or rotation is provided. The device comprises at least one vapor cell containing a Raman-active chemical species, an optical system, and at least one detector. The optical system is conformed to implement a Raman pulse interferometer in which Raman transitions are stimulated in a warm vapor of the Raman-active chemical species. The detector is conformed to detect changes in the populations of different internal states of atoms that have been irradiated by the optical system.

  14. Theoretical modeling of UV-Vis absorption and emission spectra in liquid state systems including vibrational and conformational effects: explicit treatment of the vibronic transitions.

    Science.gov (United States)

    D'Abramo, Marco; Aschi, Massimiliano; Amadei, Andrea

    2014-04-28

    Here, we extend a recently introduced theoretical-computational procedure [M. D'Alessandro, M. Aschi, C. Mazzuca, A. Palleschi, and A. Amadei, J. Chem. Phys. 139, 114102 (2013)] to include quantum vibrational transitions in modelling electronic spectra of atomic molecular systems in condensed phase. The method is based on the combination of Molecular Dynamics simulations and quantum chemical calculations within the Perturbed Matrix Method approach. The main aim of the presented approach is to reproduce as much as possible the spectral line shape which results from a subtle combination of environmental and intrinsic (chromophore) mechanical-dynamical features. As a case study, we were able to model the low energy UV-vis transitions of pyrene in liquid acetonitrile in good agreement with the experimental data. PMID:24784250

  15. Atomic data from the Iron Project.XLIII. Transition probabilities for Fe V

    OpenAIRE

    Nahar, Sultana N.; Delahaye, Franck; Pradhan, Anil K.; Zeippen, C. J.

    2000-01-01

    An extensive set of dipole-allowed, intercombination, and forbidden transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM) method is used to calculate 1.46 x 10^6 oscillator strengths for the allowed and intercombination E1 transitions among 3,865 fine-structure levels dominated by configuration complexes with n

  16. Absolute Transition Probabilities of Lines in the Spectra of Astrophysical Atoms, Molecules, and Ions

    Science.gov (United States)

    Parkinson, W. H.; Smith, P. L.; Yoshino, K.

    1984-01-01

    Progress in the investigation of absolute transition probabilities (A-values or F values) for ultraviolet lines is reported. A radio frequency ion trap was used for measurement of transition probabilities for intersystem lines seen in astronomical spectra. The intersystem line at 2670 A in Al II, which is seen in pre-main sequence stars and symbiotic stars, was studied.

  17. Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter’s View

    OpenAIRE

    Elmar Träbert

    2014-01-01

    The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem need...

  18. Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter’s View

    Directory of Open Access Journals (Sweden)

    Elmar Träbert

    2014-03-01

    Full Text Available The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem needs more attention.

  19. The influence of atomic coherence and dipole–dipole interaction on entanglement of two qubits with nondegenerate two-photon transitions

    Indian Academy of Sciences (India)

    E K Bashkirov; M S Mastyugin

    2015-01-01

    Considering two artificial identical atoms interacting with two-mode thermal field through non-degenerate two-photon transitions, this paper studies the influence of atomic coherence and dipole–dipole interaction on the entanglement of two qubits. It is found that the entanglement is greatly enhanced by these mechanisms.

  20. Structural, electronic, and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

    Science.gov (United States)

    Luo, Jia; Xiang, Gang; Yu, Tian; Lan, Mu; Zhang, Xi

    2016-09-01

    By using first-principles calculations within the framework of density functional theory, the electronic and magnetic properties of 3d transitional metal (TM) atoms (from Sc to Zn) adsorbed monolayer GaAs nanosheets (GaAsNSs) are systematically investigated. Upon TM atom adsorption, GaAsNS, which is a nonmagnetic semiconductor, can be tuned into a magnetic semiconductor (Sc, V, and Fe adsorption), a half-metal (Mn adsorption), or a metal (Co and Cu adsorption). Our calculations show that the strong p-d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the GaAsNSs with Sc, V, and Fe adsorption. However, the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit, resulting in a stronger exchange interaction. Our results may be useful for electronic and magnetic applications of GaAsNS-based materials. Project supported by the National Natural Science Foundation of China (Grant No. 11174212).

  1. Determining the quantum-coherent to semiclassical transition in atomic-scale quasi-one-dimensional metals

    Science.gov (United States)

    Weber, Bent; Simmons, Michelle Y.

    2016-08-01

    Atomic-scale silicon wires, patterned by scanning tunneling microscopy (STM) and degenerately doped with phosphorus (P), have attracted significant interest owing to their exceptionally low resistivity and semiclassical Ohmic conduction at temperatures as low as T =4.2 K . Here, we investigate the transition from semiclassical diffusive to quantum-coherent conduction in a 4.6 nm wide wire as we decrease the measurement temperature. By analyzing the temperature dependence of universal conductance fluctuations (UCFs) and one-dimensional (1D) weak localization (WL)—fundamental manifestations of quantum-coherent transport in quasi-1D metals—we show that transport evolves from quantum coherent to semiclassical at T ˜4 K . Remarkably, our study confirms that universal concepts of mesoscopic physics such as UCF and 1D WL retain their validity in quasi-1D metallic conductors down to the atomic scale.

  2. Phase Transitions of PYR14-TFSI as a Function of Pressure and Temperature: the Competition between Smaller Volume and Lower Energy Conformer.

    Science.gov (United States)

    Capitani, F; Trequattrini, F; Palumbo, O; Paolone, A; Postorino, P

    2016-03-24

    A detailed Raman study has been carried out on the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI) over a wide pressure (0-8 GPa) and temperature (100-300 K) range. The explored thermodynamic region allowed us to study the evolution of the system across different solid and liquid phases. Calculated Raman spectra remarkably helped in the spectral data analysis. In particular, the pressure behavior of the most intense Raman peak and the shape analysis of the ruby fluorescence (used as a local pressure gauge) allowed us to identify a liquid-solid transition around 2.2 GPa at T = 300 K. The low-frequency Raman signal as well as the absence of remarkable spectral shape modifications on crossing the above threshold and the comparison with the spectra of the crystalline phase suggest a glassy nature of the high-pressure phase. A detailed analysis of the pressure dependence of the relative concentration of two conformers of TFSI allowed us to obtain an estimate of the volume variation between trans-TFSI and the smaller cis-TFSI, which is the favored configuration on applying the pressure. Finally, the combined use of both visual inspection and Raman spectroscopy confirmed the peculiar sequence of phase transitions observed as a function of temperature at ambient pressure and the different spectral/morphological characteristics of the two crystalline phases. PMID:26937556

  3. Satellites to Delta n = 1 transitions between high-lying levels of multiply ionized atoms

    Science.gov (United States)

    Koenig, R.; Kolk, K.-H.; Koshelev, K. N.; Kunze, H.-J.

    1989-04-01

    In a theta pinch discharge satellites to Delta n = 1 transitions between high-lying levels are observed for the ions Si IX, Si X, and Si XI, but not for Si XII. They are identified as Delta n = 1 transitions between the corresponding levels of doubly excited systems. At high densities, the series of Rydberg levels above their respective thermal limit are collisionally coupled to their ionization limit. The intensity ratio of a transition to that of its satellite thus offers the unique possibility of measuring the ratio of the population density in the ground energy level of the next ionization stage to that in the lowest excited levels of this ion.

  4. Valence state parameters of all transition metal atoms in metalloproteins--development of ABEEMσπ fluctuating charge force field.

    Science.gov (United States)

    Yang, Zhong-Zhi; Wang, Jian-Jiang; Zhao, Dong-Xia

    2014-09-01

    To promote accuracy of the atom-bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc-Zn, Y-Cd, and Lu-Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO-3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy.

  5. Valence state parameters of all transition metal atoms in metalloproteins--development of ABEEMσπ fluctuating charge force field.

    Science.gov (United States)

    Yang, Zhong-Zhi; Wang, Jian-Jiang; Zhao, Dong-Xia

    2014-09-01

    To promote accuracy of the atom-bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc-Zn, Y-Cd, and Lu-Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO-3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy. PMID:25042901

  6. Atomic Transition Frequencies, Isotope Shifts, and Sensitivity to Variation of the Fine Structure Constant for Studies of Quasar Absorption Spectra

    Science.gov (United States)

    Berengut, J. C.; Dzuba, V. A.; Flambaum, V. V.; King, J. A.; Kozlov, M. G.; Murphy, M. T.; Webb, J. K.

    Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, α = {e}2/hslash c , could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Recent studies using 140 absorption systems from the Keck telescope and 153 from the Very Large Telescope, suggest that α varies spatially (61). That is, in one direction on the sky α seems to have been smaller at the time of absorption, while in the opposite direction it seems to have been larger.

  7. Cooper minima in the transitions from low-excited and Rydberg states of alkali-metal atoms

    OpenAIRE

    Beterov, I. I.; Mansell, C. W.; Yakshina, E. A.; Ryabtsev, I. I.; Tretyakov, D. B.; Entin, V. M.; MacCormick, C.; Piotrowicz, M. J.; Kowalczyk, A.; S. Bergamini

    2012-01-01

    The structure of the Cooper minima in the transition probabilities and photoionization cross-sections for low-excited and Rydberg nS, nP, nD and nF states of alkali-metal atoms has been studied using a Coulomb approximation and a quasiclassical model. The range of applicability of the quasiclassical model has been defined from comparison with available experimental and theoretical data on dipole moments, oscillator strengths, and photoionization cross-sections. A new Cooper minimum for transi...

  8. Electronic and magnetic behaviors of graphene with 5d series transition metal atom substitutions: A first-principles study

    Science.gov (United States)

    Sun, Minglei; Tang, Wencheng; Ren, Qingqiang; Zhao, Yiming; Wang, Sake; Yu, Jin; Du, Yanhui; Hao, Yitong

    2016-06-01

    The electronic structures and magnetic behaviors of graphene with 5d series transition metal atom substitutions are investigated by performing first-principles calculations. All the impurities are tightly bonded to single vacancy in a graphene sheet. The substitutions of La and Ta lead to Fermi level shifting to valence and conduction band, respectively. Both the two substitutions result in metallic properties. Moreover, the Hf, Os and Pt-substituted systems exhibit semiconductor properties, while the Re and Ir-substituted ones exhibit robust half-metallic properties. Interestingly, W-substituted system shows dilute magnetic semiconductor property. On the other hand, the substitution of Ta, W, Re and Ir induce 0.86 μB, 2 μB, 1 μB and 0.99 μB magnetic moment, respectively. Our studies demonstrate that the 5d series transition metal substituted graphene have potential applications in nanoelectronics, spintronics and magnetic storage devices.

  9. Spectral distribution of the 2 → 1 two-photon transition in atoms and few-electron ions

    Indian Academy of Sciences (India)

    Ajay Kumar; S Trotsenko; A V Volotka; D Banaś; H F Beyer; H Bräuning; S Fritzsche; A Gumberidze; S Hagmann; S Hess; C Kozhuharov; R Reuschl; U Spillmann; M Trassinelli; G Weber; Th Stöhlker

    2011-02-01

    The two-photon decay of the 2 state to the ground state in dressed atoms and oneor two-electron ions has been studied for several decades. Relativistic calculations have shown an -dependence of the spectral shape of this two-photon transition in one- or two-electron ions. We have measured the spectral distribution of the 121 0 → 12 1 0 two-photon transition in He-like tin at the ESR storage ring using a new approach for such experiments. In this method, relativistic collisions of initially Li-like projectiles with a gaseous target were used to populate exclusively the first excited state, 12, of He-like tin, which provided a clean two-photon spectrum. The measured two-photon spectral distribution was compared with fully relativistic calculations. The obtained results show very good agreement with the calculations for He-like tin

  10. Spin-allowed and spin-forbidden transitions in excited He atoms induced by electron impact

    International Nuclear Information System (INIS)

    Cross sections σ and the corresponding Maxwellian rate coefficients have been calculated for spin-allowed and spin-forbidden n-n' transitions between excited states with the principal quantum number, n, n'=2,3 and 4 in He induced by electron impact. Calculations have been performed using the Coulomb-Born approximation with exchange (CBE) in the partial wave representation with orthogonalized wavefunctions of the initial and final states for the incident electron energies from threshold up to 2000 eV for spin-allowed transitions (ΔS=0) and up to 200 eV for spin-forbidden (intercombination, ΔS=1) transitions where the corresponding cross sections are still relatively large. The fitting parameters for σ and of spin-allowed transitions have been calculated as well. The results are compared with experimental data and other calculations available. (author). 23 refs, 4 figs, 2 tabs

  11. Spectroscopic data for atomic tungsten transitions of interest in fusion plasma research

    OpenAIRE

    Quinet, Pascal; Palmeri, P; Biémont, Emile

    2011-01-01

    Abstract Transition probabilities for W I lines of potential interest for fusion plasma diagnostics are reported in the present paper. They have been obtained using the relativistic Hartree-Fock approach including core-polarization effects. The accuracy of the results has been assessed through comparison between two different physical models and through detailed comparison with available experimental lifetimes and transition probabilities. These results represent the first complete set of ...

  12. Semiconductor-metal transition in thin VO2 films grown by ozone based atomic layer deposition

    OpenAIRE

    Rampelberg, Geert; Schaekers, Marc; Martens, Koen; Xie, Qi; Deduytsche, Davy; De Schutter, Bob; Blasco, Nicolas; Kittl, Jorge; Detavernier, Christophe

    2011-01-01

    Vanadium dioxide (VO2) has the interesting feature that it undergoes a reversible semiconductor-metal transition (SMT) when the temperature is varied near its transition temperature at 68°C.1 The variation in optical constants makes VO2 useful as a coating material for e.g. thermochromic windows,2 while the associated change in resistivity could be interesting for applications in microelectronics, e.g. for resistive switches and memories.3 Due to aggressive scaling and increasing integration ...

  13. Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

    International Nuclear Information System (INIS)

    Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9≥n>3, and (TiO2)x(HfO2)1−x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii) local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding

  14. Luminescence spectroscopy of matrix-isolated atomic manganese: Excitation of the 'forbidden' a6DJ↔a6S transitions

    International Nuclear Information System (INIS)

    Laser-induced excitation spectra recorded for the electric-quadrupole 3d64s a6DJ54s2a6S5/2 transitions of atomic Mn, allow assignment of the red emission features, previously observed in Mn/RG (RG=Ar, Kr and Xe) matrices with resonance 3d54s4pz6P5/254s2 a6S5/2 excitation, to the metastable a6D9/2 state. Narrow excitation bands recorded for the red site in the Mn/Kr system allow identification of all five spin-orbit levels (J=1/2, 3/2, 5/2, 7/2 and 9/2) in the a6D state. The coincidence of the lowest energy excitation band and the observed 585.75 nm (17 072 cm-1) emission band of atomic Mn in Kr matrices, yielded a definitive assignment of this emission to a transition from the J=9/2 spin-orbit level. Temperature dependent emission scans lead to the identification of the zero phonon line for the a6D9/2→a6S5/2 transition at 585.75 nm. The identified matrix-shift of +20 cm-1 allows an assessment of the extent of the ground state stabilization in the red (2 deg.) site of atomic Mn isolation in solid Kr. Emission produced with direct a6D state excitation yielded both the 585.75 and 626 nm features. The former band arises for Mn atoms occupying the red site--the latter from blue site occupancy in solid Kr. The excitation linewidths recorded for these two sites differ greatly, with the blue site yielding a broad featureless profile, in contrast to the narrow, structured features of the red site. The corresponding red site a6DJ↔a6S5/2 transitions in Ar and Xe matrices are broader than in Kr--a difference considered to originate from the site sizes available in these hosts and the interatomic Mn·RG potentials. The millisecond decay times recorded for the red emission bands in the Mn/RG systems are all much shorter than the 3 s value predicted for the gas phase a6D9/2→a6S5/2 transition. This enhancement allows optical pumping of the forbidden a6DJ↔a6S transitions with low laser powers when atomic manganese is isolated in the solid state. However all the emission

  15. DFT Conformation and Energies of Amylose Fragments at Atomic Resolution Part 2: “Band-flip” and “Kink” Forms of Alpha-Maltotetraose

    Science.gov (United States)

    In Part 2 of this series of DFT optimization studies of '-maltotetraose, we present results at the B3LYP/6-311++G** level of theory for conformations denoted “band-flips” and “kinks”. Recent experimental X-ray studies have found examples of amylose fragments with conformations distorted from the us...

  16. Protein Conformational Populations and Functionally Relevant Sub-states

    Energy Technology Data Exchange (ETDEWEB)

    Agarwal, Pratul K [ORNL; Burger, Virginia [University of Pittsburgh School of Medicine, Pittsburgh PA; Savol, Andrej [University of Pittsburgh School of Medicine, Pittsburgh PA; Ramanathan, Arvind [ORNL; Chennubhotla, Chakra [University of Pittsburgh School of Medicine, Pittsburgh PA

    2013-01-01

    Functioning proteins do not remain fixed in a unique structure, but instead they sample a range of conformations facilitated by motions within the protein. Even in the native state, a protein exists as a collection of interconverting conformations driven by thermodynamic fluctuations. Motions on the fast time scale allow a protein to sample conformations in the nearby area of its conformational landscape, while motions on slower time scales give it access to conformations in distal areas of the landscape. Emerging evidence indicates that protein landscapes contain conformational substates with dynamic and structural features that support the designated function of the protein. Nuclear magnetic resonance (NMR) experiments provide information about conformational ensembles of proteins. X-ray crystallography allows researchers to identify the most populated states along the landscape, and computational simulations give atom-level information about the conformational substates of different proteins. This ability to characterize and obtain quantitative information about the conformational substates and the populations of proteins within them is allowing researchers to better understand the relationship between protein structure and dynamics and the mechanisms of protein function. In this Account, we discuss recent developments and challenges in the characterization of functionally relevant conformational populations and substates of proteins. In some enzymes, the sampling of functionally relevant conformational substates is connected to promoting the overall mechanism of catalysis. For example, the conformational landscape of the enzyme dihydrofolate reductase has multiple substates, which facilitate the binding and the release of the cofactor and substrate and catalyze the hydride transfer. For the enzyme cyclophilin A, computational simulations reveal that the long time scale conformational fluctuations enable the enzyme to access conformational substates that allow

  17. Measurement of the 6s - 7p transition probabilities in atomic cesium and a revised value for the weak charge Q_W

    OpenAIRE

    Vasilyev, A. A.; Savukov, I. M.; Safronova, M. S.; Berry, H.G.

    2001-01-01

    We have measured the 6s - 7p_{1/2,3/2} transition probabilities in atomic cesium using a direct absorption technique. We use our result plus other previously measured transition rates to derive an accurate value of the vector transition polarizability \\beta and, consequently, re-evaluate the weak charge Q_W. Our derived value Q_W=-72.65(49) agrees with the prediction of the standard model to within one standard deviation.

  18. Spin-Statistic Selection Rules for Multi-Equal-Photon Transitions in Atoms: Extension of the Landau-Yang Theorem to Multiphoton Systems

    CERN Document Server

    Zalialiutdinov, T; Labzowsky, L; Plunien, G

    2014-01-01

    We establish the existence of spin-statistic selection rules (SSSR) for multi-equal-photon transitions in atomic systems. These selection rules are similar to those for systems of many equivalent electrons in atomic theory. The latter ones are the direct consequence of Pauli exclusion principle. In this sense the SSSR play the role of the exclusion principle for photons: they forbid some particular states for the photon systems. We established several SSSR for few-photon systems. 1) First rule (SSSR-1): two-equivalent photons involved in any atomic transition can have only even values of the total angular momentum J. This selection rule is an extension of the Landau-Yang theorem to the photons involved in atomic transitions. 2) second rule (SSSR-2): three equivalent dipole photons involved in any atomic transition can have only odd values of the total angular momentum J=1,3. 3) third rule (SSSR-3): four equivalent dipole photons involved in any atomic transition can have only even values of the total angular ...

  19. Interfacing transitions of different alkali atoms and telecom bands using one narrowband photon pair source

    DEFF Research Database (Denmark)

    Schunk, Gerhard; Vogl, Ulrich; Strekalov, Dmitry V.;

    2015-01-01

    Quantum information technology strongly relies on the coupling of optical photons with narrowband quantum systems, such as quantum dots, color centers, and atomic systems. This coupling requires matching the optical wavelength and bandwidth to the desired system, which presents a considerable pro...

  20. Conformal house

    DEFF Research Database (Denmark)

    Ryttov, Thomas Aaby; Sannino, Francesco

    2010-01-01

    fixed point. As a consistency check we recover the previously investigated bounds of the conformal windows when restricting to a single matter representation. The earlier conformal windows can be imagined to be part now of the new conformal house. We predict the nonperturbative anomalous dimensions...... at the infrared fixed points. We further investigate the effects of adding mass terms to the condensates on the conformal house chiral dynamics and construct the simplest instanton induced effective Lagrangian terms...

  1. Repumping and spectroscopy of laser-cooled Sr atoms using the (5s5p)3P2 - (5s4d)3D2 transition

    CERN Document Server

    Mickelson, P G; Anzel, P; DeSalvo, B J; Nagel, S B; Traverso, A J; Yan, M; Killian, T C

    2009-01-01

    We describe repumping and spectroscopy of laser-cooled strontium (Sr) atoms using the (5s5p)3P2 - (5s4d)3D2 transition. Atom number in a magneto-optical trap is enhanced by driving this transition because Sr atoms that have decayed into the (5s5p)3P2 dark state are repumped back into the (5s2)1S0 ground state. Spectroscopy of 84Sr, 86Sr, 87Sr, and 88Sr improves the value of the (5s5p)3P2 - (5s4d)3D2 transition frequency for 88Sr and determines the isotope shifts for the transition.

  2. Repumping and spectroscopy of laser-cooled Sr atoms using the (5s5p)3P2-(5s4d)3D2 transition

    Science.gov (United States)

    Mickelson, P. G.; Martinez de Escobar, Y. N.; Anzel, P.; De Salvo, B. J.; Nagel, S. B.; Traverso, A. J.; Yan, M.; Killian, T. C.

    2009-12-01

    We describe repumping and spectroscopy of laser-cooled strontium (Sr) atoms using the (5s5p)3P2-(5s4d)3D2 transition. Atom number in a magneto-optical trap is enhanced by driving this transition because Sr atoms that have decayed into the (5s5p)3P2 dark state are repumped back into the (5s2)1S0 ground state. Spectroscopy of 84Sr, 86Sr, 87Sr and 88Sr improves the value of the (5s5p)3P2-(5s4d)3D2 transition frequency and determines the isotope shifts for the transition accurately enough to guide laser-cooling experiments with less abundant isotopes.

  3. Tables of stark level transition probabilities and branching ratios in hydrogen-like atoms

    Science.gov (United States)

    Omidvar, K.

    1980-01-01

    The transition probabilities which are given in terms of n prime k prime and n k are tabulated. No additional summing or averaging is necessary. The electric quantum number k plays the role of the angular momentum quantum number l in the presence of an electric field. The branching ratios between stark levels are also tabulated. Necessary formulas for the transition probabilities and branching ratios are given. Symmetries are discussed and selection rules are given. Some disagreements for some branching ratios are found between the present calculation and the measurement of Mark and Wierl. The transition probability multiplied by the statistical weight of the initial state is called the static intensity J sub S, while the branching ratios are called the dynamic intensity J sub D.

  4. New Critical Compilations of Atomic Transition Probabilities for Neutral and Singly Ionized Carbon, Nitrogen, and Iron

    Science.gov (United States)

    Wiese, Wolfgang L.; Fuhr, J. R.

    2006-01-01

    We have undertaken new critical assessments and tabulations of the transition probabilities of important lines of these spectra. For Fe I and Fe II, we have carried out a complete re-assessment and update, and we have relied almost exclusively on the literature of the last 15 years. Our updates for C I, C II and N I, N II primarily address the persistent lower transitions as well as a greatly expanded number of forbidden lines (M1, M2, and E2). For these transitions, sophisticated multiconfiguration Hartree-Fock (MCHF) calculations have been recently carried out, which have yielded data considerably improved and often appreciably different from our 1996 NIST compilation.

  5. Electronic properties of transition metal atoms on Cu2 N/Cu(100): a DFT comparative study

    Science.gov (United States)

    Ferron, Alejandro; Lado, José; Fernández-Rossier, Joaquín

    2015-03-01

    We study the electronic and magnetic properties of individual transition metal atoms (Ti, V, Cr, Mn, Fe, Co and Ni) deposited on a Cu2N /Cu(100) surface by means of spin-polarized density functional theory (DFT) calculations. We focus our work on a comparative study of the various quantities, such as magnetic moment, orbital occupation, structural properties, hybridization with the substrate and spin polarization of the substrate, paying attention to the trends as the transition metal is changed. In this work we try to go beyond existing theoretical works by providing a comprehensive and comparative study of the electronic, magnetic and structural properties of these seven atoms including also Ni, for which there are no published calculations to the best of our knowledge. In the case of Mn, Fe and Co, we connect our results with the existing scanning tunneling microscope experiments. A.F. acknowledges funding from the European Union's Seventh Framework Programme for research, technological development and demonstration, under the PEOPLE programme, Marie Curie COFUND Actions, grant agreement number 600375 and CONICET.

  6. Estimation of Enthalpy of Formation of Liquid Transition Metal Alloys: A Modified Prescription Based on Macroscopic Atom Model of Cohesion

    Science.gov (United States)

    Raju, Subramanian; Saibaba, Saroja

    2016-09-01

    The enthalpy of formation Δo H f is an important thermodynamic quantity, which sheds significant light on fundamental cohesive and structural characteristics of an alloy. However, being a difficult one to determine accurately through experiments, simple estimation procedures are often desirable. In the present study, a modified prescription for estimating Δo H f L of liquid transition metal alloys is outlined, based on the Macroscopic Atom Model of cohesion. This prescription relies on self-consistent estimation of liquid-specific model parameters, namely electronegativity ( ϕ L) and bonding electron density ( n b L ). Such unique identification is made through the use of well-established relationships connecting surface tension, compressibility, and molar volume of a metallic liquid with bonding charge density. The electronegativity is obtained through a consistent linear scaling procedure. The preliminary set of values for ϕ L and n b L , together with other auxiliary model parameters, is subsequently optimized to obtain a good numerical agreement between calculated and experimental values of Δo H f L for sixty liquid transition metal alloys. It is found that, with few exceptions, the use of liquid-specific model parameters in Macroscopic Atom Model yields a physically consistent methodology for reliable estimation of mixing enthalpies of liquid alloys.

  7. The formation of the W43 complex: constraining its atomic-to-molecular transition and searching for colliding clouds

    CERN Document Server

    Motte, F; Schneider, N; Heitsch, F; Glover, S; Carlhoff, P; Hill, T; Bontemps, S; Schilke, P; Louvet, F; Hennemann, M; Didelon, P; Beuther, H

    2014-01-01

    Numerical simulations have explored the possibility to form molecular clouds through either a quasi-static, self-gravitating mechanism or the collision of gas streams or lower-density clouds. They also quantitatively predict the distribution of matter at the transition from atomic to molecular gases. We aim to observationally test these models by studying the environment of W43, a molecular cloud complex near the tip of the Galactic long bar. Using Galaxy-wide HI and 12CO surveys we searched for gas flowing toward the W43 molecular cloud complex. We also estimated the HI and H2 mass surface densities to constrain the transition from atomic to molecular gas around and within W43. We found 3 cloud ensembles within the position-velocity diagrams of 12CO and HI gases. They are separated by 20km/s along the line of sight and extend into the 13CO velocity structure of W43. Since their velocity gradients are consistent with free-fall, they could be nearby clouds attracted by, and streaming toward, the W43 10^7Msun p...

  8. Satellites to. delta. n = 1 transitions between high-lying levels of multiply ionized atoms

    Energy Technology Data Exchange (ETDEWEB)

    Konig, R.; Kolk, K.; Koshelev, K. N.; Kunze, H.

    1989-04-10

    In a theta pinch discharge satellites to ..delta../ital n/=1 transitionsbetween high-lying levels are observed for the ions Si ix, Six, and Si xi, but not for Si xii. They areidentified as ..delta../ital n/=1 transitions between the corresponding levels ofdoubly excited systems. At high densities, the series of Rydberg levels abovetheir respective thermal limit are collisionally coupled to their ionizationlimit: The intensity ratio of a transition to that of its satellite thus offersthe unique possibility of measuring the ratio of the population density in theground energy level of the next ionization stage to that in the lowest excitedlevels of this ion.

  9. Forbidden M1 and E2 transitions in monovalent atoms and ions

    CERN Document Server

    Safronova, U I; Johnson, W R

    2016-01-01

    We carried out a systematic high-precision relativistic study of the forbidden magnetic-dipole and electric-quadrupole transitions in Ca+, Rb, Sr+, Cs, Ba+, Fr, Ra+, Ac2+, and Th3+. This work is motivated by the importance of these transitions for tests of fundamental physics and precision measurements. The relative importance of the relativistic, correlation, Breit correction, and contributions of negative-energy states is investigated. Recommended values of reduced matrix elements are presented together with their uncertainties. The matrix elements and resulting lifetimes are compared with other theoretical values and with experiment where available.

  10. Spectroscopy of ^1S0 -- ^3P1^88Sr Atomic Transition in a 1.06 μm Optical Dipole Trap

    Science.gov (United States)

    Martinez de Escobar, Y. N.; Mickelson, P. G.; Traverso, A. J.; Killian, T. C.

    2008-05-01

    We studied the effects of laser light near-resonant with the ^1S0-- ^3P1^88Sr transition in an optical dipole trap (ODT). We observe laser cooling of our ODT atomic sample as the atoms collide in the presence of red-detuned 689 nm light. Heating of the atoms was also observed at a different range of frequency detunings while performing spectroscopy. Both processes were accompanied with atom loss, but the increase of phase space density observed during 689 nm laser cooling could aid pursuits of quantum degeneracy with Sr.

  11. Thermal and quantum phase transitions in atom-field systems: a microcanonical analysis

    Science.gov (United States)

    Bastarrachea-Magnani, M. A.; Lerma-Hernández, S.; Hirsch, J. G.

    2016-09-01

    The thermodynamical properties of a generalized Dicke model are calculated and related with the critical properties of its energy spectrum, namely the quantum phase transitions (QPT) and excited state quantum phase transitions (ESQPT). The thermal properties are calculated both in the canonical and the microcanonical ensembles. The latter deduction allows for an explicit description of the relation between thermal and energy spectrum properties. While in an isolated system the subspaces with different pseudospin are disconnected, and the whole energy spectrum is accessible, in the statistical ensemble the situation is radically different. The multiplicity of the lowest energy states for each pseudospin completely dominates the thermal behavior, making the set of degenerate states with the smallest pseudospin at a given energy the only ones playing a role in the thermal properties. As a result, the states in the region with positive thermal energy cannot be thermally populated because their negligible probability, making that energy region thermally unreachable at finite temperatures. The quantum phase transitions of the lowest energy states, from a normal to a superradiant phase, produce the thermal transition. The other critical phenomena, the ESQPTs occurring at excited energies, have no manifestation in the thermodynamics, although their effects could be seen in finite size corrections. A new superradiant phase is found, which only exists in the generalized model, and can be relevant in finite size systems.

  12. Collective vector method for calculation of E1 moments in atomic transition arrays

    International Nuclear Information System (INIS)

    The CV (collective vector) method for calculating E1 moments for a transition array is described and applied in two cases, herein denoted Z26A and Z26B, pertaining to two different configurations of iron VI. The basic idea of the method is to create a CV from each of the parent (''initial state'') state-vectors of the transition array by application of the E1 operator. The moments of each of these CV's, referred to the parent energy, are then the rigorous moments for that parent, requiring no state decomposition of the manifold of daughter state-vectors. Since, in cases of practical interest, the daughter manifold can be orders of magnitude larger in size than the parent manifold, this makes possible the calculation of many moments higher than the second in situations hitherto unattainable via standard methods. The combination of the moments of all the parents, with proper statistical weighting, then yields the transition array moments from which the transition strength distribution can be derived by various procedures. We describe two of these procedures: (1) The well-known GC (Gram-Charlier) expansion in terms of Hermite polynomials, (2) The Lanczos algorithm or Stieltjes imaging method, also called herein the delta expansion. Application is made in the cases of Z26A (50 lines) and Z26B (5523 lines) and the relative merits and shortcomings of the two procedures are discussed. 10 refs., 15 figs., 2 tabs

  13. A Computational Model of Word Segmentation from Continuous Speech Using Transitional Probabilities of Atomic Acoustic Events

    Science.gov (United States)

    Rasanen, Okko

    2011-01-01

    Word segmentation from continuous speech is a difficult task that is faced by human infants when they start to learn their native language. Several studies indicate that infants might use several different cues to solve this problem, including intonation, linguistic stress, and transitional probabilities between subsequent speech sounds. In this…

  14. NIR Laser Radiation Induced Conformational Changes and Tunneling Lifetimes of High-Energy Conformers of Amino Acids in Low-Temperature Matrices

    Science.gov (United States)

    Bazso, Gabor; Najbauer, Eszter E.; Magyarfalvi, Gabor; Tarczay, Gyorgy

    2013-06-01

    We review our recent results on combined matrix isolation FT-IR and NIR laser irradiation studies on glycine alanine, and cysteine. The OH and the NH stretching overtones of the low-energy conformers of these amino acids deposited in Ar, Kr, Xe, and N_{2} matrices were irradiated. At the expense of the irradiated conformer, other conformers were enriched and new, high-energy, formerly unobserved conformers were formed in the matrices. This enabled the separation and unambiguous assignment of the vibrational transitions of the different conformers. The main conversion paths and their efficiencies are described qualitatively showing that there are significant differences in different matrices. It was shown that the high-energy conformer decays in the matrix by H-atom tunneling. The lifetimes of the high-energy conformers in different matrices were measured. Based on our results we conclude that some theoretically predicted low-energy conformers of amino acids are likely even absent in low-energy matrices due to fast H-atom tunneling. G. Bazso, G. Magyarfalvi, G. Tarczay J. Mol. Struct. 1025 (Light-Induced Processes in Cryogenic Matrices Special Issue) 33-42 (2012). G. Bazso, G. Magyarfalvi, G. Tarczay J. Phys. Chem. A 116 (43) 10539-10547 (2012). G. Bazso, E. E. Najbauer, G. Magyarfalvi, G. Tarczay J. Phys. Chem. A in press, DOI: 10.1021/jp400196b. E. E. Najbauer, G. Bazso, G. Magyarfalvi, G. Tarczay in preparation.

  15. Interfacing transitions of different alkali atoms and telecom bands using one narrowband photon pair source

    DEFF Research Database (Denmark)

    Schunk, Gerhard; Vogl, Ulrich; Strekalov, Dmitry V.;

    2015-01-01

    Quantum information technology strongly relies on the coupling of optical photons with narrowband quantum systems, such as quantum dots, color centers, and atomic systems. This coupling requires matching the optical wavelength and bandwidth to the desired system, which presents a considerable...... major advance in controlling the spontaneous downconversion process, which makes our bright source of heralded single photons now compatible with a plethora of narrowband resonant systems....

  16. Intense laser interacting with a two level atom: WKB expressions for dipole transitions and population inversion

    OpenAIRE

    Lejarreta, J. D.; Cervero, J. M.

    2001-01-01

    In a previous paper, we have already considered the system composed by a two level atom interacting with a coherent external electromagnetic field. No application whatsoever has been made of the rotating wave approximation. Being specially interested in the problem of higher harmonic generations for the case of very intense laser fields, we have developed in this letter a much more efficient way to obtain these solutions as well as to carry out some calculations in a range in which the parame...

  17. Transition probabilities for lines of Cr II, Na II and Sb I by laser produced plasma atomic emission spectroscopy

    International Nuclear Information System (INIS)

    Absolute transition probabilities for lines of CR II, Na II and Sb I were determined by emission spectroscopy of laser induced plasmas. the plasma was produced focusing the emission of a pulsed Nd-Yag laser on solid samples containing the atom in study. the light arising from the plasma region was collected by and spectrometer. the detector used was a time-resolved optical multichannel analyzer (OMA III EG and G). The wavelengths of the measured transitions range from 2000 sto 4100 A. The spectral resolution of the system was 0. 2 A. The method can be used in insulators materials as Cl Na crystals and in metallic samples as Al-Cr and Sn-Sn alloys. to avoid self-absorption effects the alloys were made with low Sb or Cr content. Relative transition probabilities have been determined from measurements of emission-line intensities and were placed on an absolute scale by using, where possible, accurate experimental lifetime values form the literature or theoretical data. From these measurements, values for plasma temperature (8000-24000 K), electron densities (∼∼ 10''16 cm ''-3) and self-absorption coefficients have been obtained. (Author) 56 refs

  18. Search for Pauli Exclusion Principle Violating Atomic Transitions and Electron Decay with a P-type Point Contact Germanium Detector

    CERN Document Server

    Abgrall, N; Avignone, F T; Barabash, A S; Bertrand, F E; Bradley, A W; Brudanin, V; Busch, M; Buuck, M; Caldwell, A S; Chan, Y-D; Christofferson, C D; Chu, P -H; Cuesta, C; Detwiler, J A; Dunagan, C; Efremenko, Yu; Ejiri, H; Elliott, S R; Finnerty, P S; Galindo-Uribarri, A; Gilliss, T; Giovanetti, G K; Goett, J; Green, M P; Gruszko, J; Guinn, I S; Guiseppe, V E; Henning, R; Hoppe, E W; Howard, S; Howe, M A; Jasinski, B R; Keeter, K J; Kidd, M F; Konovalov, S I; Kouzes, R T; LaFerriere, B D; Leon, J; MacMullin, J; Martin, R D; Massarczyk, R; Meijer, S J; Mertens, S; Orrell, J L; O'Shaughnessy, C; Poon, A W P; Radford, D C; Rager, J; Rielage, K; Robertson, R G H; Romero-Romero, E; Shanks, B; Shirchenko, M; Suriano, A M; Tedeschi, D; Trimble, J E; Varner, R L; Vasilyev, S; Vetter, K; Vorren, K; White, B R; Wilkerson, J F; Wiseman, C; Xu, W; Yakushev, E; Yu, C -H; Yumatov, V; Zhitnikov, I

    2016-01-01

    A search for Pauli-exclusion-principle-violating K-alpha electron transitions was performed using 89.5 kg-d of data collected with a p-type point contact high-purity germanium detector operated at the Kimballton Underground Research Facility. A lower limit on the transition lifetime of 5.8x10^30 seconds at 90% C.L. was set by looking for a peak at 10.6 keV resulting from the x-ray and Auger electrons present following the transition. A similar analysis was done to look for the decay of atomic K-shell electrons into neutrinos, resulting in a lower limit of 6.8x10^30 seconds at 90 C.L. It is estimated that the MAJORANA DEMONSTRATOR, a 44 kg array of p-type point contact detectors that will search for the neutrinoless double-beta decay of 76-Ge, could improve upon these exclusion limits by an order of magnitude after three years of operation.

  19. Transition probabilities for lines of Cr II, Na II and Sb I by laser produced plasma atomic emission spectroscopy

    International Nuclear Information System (INIS)

    Absolute transition probabilities for lines of Cr II, Na II and Sb I were determined by emission spectroscopy of laser induced plasmas. The plasma was produced focusing the emission of a pulsed Nd-Yag laser on solid samples containing the atom in study. The light arising from the plasma region was collected by and spectrometer. the detector used was a time-resolved optical multichannel analyzer (OMA III EG and G). The wavelengths of the measured transitions range from 2000 to 4100 A. The spectral resolution of the system was 0.2 A. The method can be used in insulators materials as Cl Na crystals and in metallic samples as Al-Cr and Sn-Sb alloys. To avoid self-absorption effects the alloys were made with low Sb or Cr content. Relative transition probabilities have been determined from measurements of emission-line intensities and were placed on an absolute scale by using, where possible, accurate experimental lifetime values form the literature or theoretical data. From these measurements, values for plasma temperature (8000-24000K), electron densities (approx 10 ''16 cm''-3) and self-absorption coefficients have been obtained

  20. Controlling magnetism of MoS2 sheets by embedding transition-metal atoms and applying strain.

    Science.gov (United States)

    Zhou, Yungang; Su, Qiulei; Wang, Zhiguo; Deng, Huiqiu; Zu, Xiaotao

    2013-11-14

    Prompted by recent experimental achievement of transition metal (TM) atoms substituted in MoS2 nanostructures during growth or saturating existing vacancies (Sun et al., ACS Nano, 2013, 7, 3506; Deepak et al., J. Am. Chem. Soc., 2007, 129, 12549), we explored, via density functional theory, the magnetic properties of a series of 3d TM atoms substituted in a MoS2 sheet, and found that Mn, Fe, Co, Ni, Cu and Zn substitutions can induce magnetism in the MoS2 sheet. The localizing unpaired 3d electrons of TM atoms respond to the introduction of a magnetic moment. Depending on the species of TM atoms, the substituted MoS2 sheet can be a metal, semiconductor or half-metal. Remarkably, the applied elastic strain can be used to control the strength of the spin-splitting of TM-3d orbitals, leading to an effective manipulation of the magnetism of the TM-substituted MoS2 sheet. We found that the magnetic moment of the Mn- and Fe-substituted MoS2 sheets can monotonously increase with the increase of tensile strain, while the magnetic moment of Co-, Ni-, Cu- and Zn-substituted MoS2 sheets initially increases and then decreases with the increase of tensile strain. An instructive mechanism was proposed to qualitatively explain the variation of magnetism with elastic strain. The finding of the magnetoelastic effect here is technologically important for the fabrication of strain-driven spin devices on MoS2 nanostructures, which allows us to go beyond the current scope limited to the spin devices within graphene and BN-based nanostructures. PMID:24071945

  1. Controlling magnetism of MoS2 sheets by embedding transition-metal atoms and applying strain.

    Science.gov (United States)

    Zhou, Yungang; Su, Qiulei; Wang, Zhiguo; Deng, Huiqiu; Zu, Xiaotao

    2013-11-14

    Prompted by recent experimental achievement of transition metal (TM) atoms substituted in MoS2 nanostructures during growth or saturating existing vacancies (Sun et al., ACS Nano, 2013, 7, 3506; Deepak et al., J. Am. Chem. Soc., 2007, 129, 12549), we explored, via density functional theory, the magnetic properties of a series of 3d TM atoms substituted in a MoS2 sheet, and found that Mn, Fe, Co, Ni, Cu and Zn substitutions can induce magnetism in the MoS2 sheet. The localizing unpaired 3d electrons of TM atoms respond to the introduction of a magnetic moment. Depending on the species of TM atoms, the substituted MoS2 sheet can be a metal, semiconductor or half-metal. Remarkably, the applied elastic strain can be used to control the strength of the spin-splitting of TM-3d orbitals, leading to an effective manipulation of the magnetism of the TM-substituted MoS2 sheet. We found that the magnetic moment of the Mn- and Fe-substituted MoS2 sheets can monotonously increase with the increase of tensile strain, while the magnetic moment of Co-, Ni-, Cu- and Zn-substituted MoS2 sheets initially increases and then decreases with the increase of tensile strain. An instructive mechanism was proposed to qualitatively explain the variation of magnetism with elastic strain. The finding of the magnetoelastic effect here is technologically important for the fabrication of strain-driven spin devices on MoS2 nanostructures, which allows us to go beyond the current scope limited to the spin devices within graphene and BN-based nanostructures.

  2. Visualization of the evolution of charged droplet formation and jet transition in electrostatic atomization

    International Nuclear Information System (INIS)

    A detailed experimental study on the evolution of charged droplet formation and jet transition from a capillary is reported. By means of high-speed microscopy, special attention has been paid to the dynamics of the liquid thread and satellite droplets in the dripping mode, and a method for calculating the surface charge on the satellite droplet is proposed. Jet transition behavior based on the electric Bond number has been visualized, droplet sizes and velocities are measured to obtain the ejection characteristic of the spray plume, and the charge and hydrodynamic relaxation are linked to give explanations for ejection dynamics with different properties. The results show that the relative length is very sensitive to the hydrodynamic relaxation time. The magnitude of the electric field strength dominates the behavior of coalescence and noncoalescence, with the charge relationship between the satellite droplet and the main droplet being clear for every noncoalescence movement. Ejection mode transitions mainly depend on the magnitude of the electric Bond number, and the meniscus dynamics is determined by the ratio of the charge relaxation time to the hydrodynamic relaxation time

  3. Structure and Thermodynamic Properties of Liquid Transition Metals with Different Embedded-Atom Method Models

    Institute of Scientific and Technical Information of China (English)

    王金照; 陈民; 过增元

    2002-01-01

    Pair distribution functions and constant-volume heat capacities of liquid copper, silver and nickel have been calculated by molecular dynamics simulations with four different versions of the embedded-atom method (EAM) model, namely, the versions of Johnson, Mei, Cai and Pohlong. The simulated structural properties with the four potential models show reasonable agreement with experiments and have little difference with each other, while the calculated heat capacities with the different EAM versions show remarkable discrepancies. Detailed analyses of the energy of the liquid metallic system show that, to predict successfully the heat capacity, an EAM model should match the state equation first proposed by Rose.

  4. First observation of the strongly forbidden transition {sup 1}S{sub 0} - {sup 3}P{sub 0} in Strontium, for an atomic clock with trapped atoms; Premiere observation de la transition fortement interdite {sup 1}S{sub 0} - {sup 3}P{sub 0} du strontium, pour une horloge optique a atomes pieges

    Energy Technology Data Exchange (ETDEWEB)

    Courtillot, I

    2003-11-01

    This thesis reports the first results towards the realization of an optical clock using trapped strontium atoms. This set up would combine advantages of the different approaches commonly used to develop an atomic frequency standard. The first part describes the cold atoms source which is implemented. A magneto-optical trap operating on the {sup 1}S{sub 0}-{sup 1}P{sub 1} transition at 461 nm is loaded from an atomic beam decelerated by a Zeeman slower. The 461 nm laser is obtained by sum-frequency mixing in a potassium titanyl phosphate (KTP) crystal. The second part is devoted to the different stages developed to achieve the direct excitation of the {sup 1}S{sub 0}-{sup 3}P{sub 0} clock transition in {sup 87}Sr. This line has a theoretical natural width of 10{sup -3} Hz. Before this detection, we obtained an estimate of the resonance frequency by measuring absolute frequencies of several allowed optical transitions. (author)

  5. Nonlinear absorption in ionic liquids with transition metallic atoms in the anion

    Science.gov (United States)

    Nóvoa-López, José A.; López Lago, Elena; Seijas, Julio A.; Pilar Vázquez-Tato, M.; Troncoso, Jacobo; de la Fuente, Raúl; Salgueiro, José R.; Michinel, Humberto

    2016-02-01

    Nonlinear absorption has been investigated by open aperture Z-scan in ionic liquids obtained by combination of 1-butyl-3-methyl-imidazolium cations with anions containing a transition metal (Co, Zn, Cu or Ni) and thiocyanate groups. The laser source was a Ti:Sapphire oscillator (80-fs pulses, λ = 810 nm, repetition rate of 80.75 MHz). All liquids present quite low heat capacities that favor the development of strong thermal effects. Thermal effects and nonlinear absorption make them potential materials for optical limiting purposes.

  6. Improved adiabatic calculation of muonic-hydrogen-atom cross sections. II. Hyperfine transitions and elastic scattering in symmetric collisions

    International Nuclear Information System (INIS)

    The improved adiabatic representation is used in calculations of elastic and hyperfine-transition cross sections for symmetric collisions of pμ, dμ, and tμ with bare p, d, and t nuclei and with H, D, and T atoms, respectively. The cross sections for dμ+d and tμ+t are in excellent agreement with other recent determinations, while those for pμ+p are about 30% larger at low energies. The electronic screening is calculated nonperturbatively and found to be about 30% smaller in magnitude than the previously calculated value at large internuclear distances, and to deviate considerably from the asymptotic form in the molecular region. The resulting screened elastic cross sections are up to 60% smaller than those obtained using the old screening potential. The reactance matrices, needed for calculations of molecular-target effects, are given in tables

  7. Electromagnetic transition matrix elements in the continuous spectrum of atoms: theory and computation

    CERN Document Server

    Komninos, Yannis; Nicolaides, Cleanthes A

    2014-01-01

    In a variety of problems concerning the coupling of atomic and molecular states to strong and or short electromagnetic pulses, it is necessary to solve the time-dependent Schroedinger equation nonperturbatively. To this purpose, we have proposed and applied to various problems the state-specific expansion approach. Its implementation requires the computation of bound-bound, bound-free and free-free N-electron matrix elements of the operator that describes the coupling of the electrons to the external electromagnetic field. The present study penetrates into the mathematical properties of the free-free matrix elements of the full electric field operator of the multipolar Hamiltonian. kk is the photon wavenumber, and the field is assumed linearly polarized, propagating along the z axis. Special methods are developed and applied for the computation of such matrix elements using energy-normalized, numerical scattering wavefunctions. It is found that, on the momentum (energy) axis, the free-free matrix elements hav...

  8. Two-Atom Rydberg Blockade using a Single-Photon Transition

    CERN Document Server

    Hankin, A M; Parazzoli, L P; Chou, C W; Armstrong, D J; Landahl, A J; Biedermann, G W

    2014-01-01

    We explore a single-photon approach to Rydberg state excitation and Rydberg blockade. Using detailed theoretical models, we show the feasibility of direct excitation, predict the effect of background electric fields, and calculate the required interatomic distance to observe Rydberg blockade. We then measure and control the electric field environment to enable coherent control of Rydberg states. With this coherent control, we demonstrate Rydberg blockade of two atoms separated by 6.6(3) {\\mu}m. When compared with the more common two-photon excitation method, this single-photon approach is advantageous because it eliminates channels for decoherence through photon scattering and AC Stark shifts from the intermediate state while moderately increasing Doppler sensitivity.

  9. An Improved Limit on Pauli-Exclusion-Principle Forbidden Atomic Transitions

    CERN Document Server

    Elliott, S R; Gehman, V M; Kidd, M F; Chen, M

    2011-01-01

    We have examined the atomic theory behind recent constraints on the violation of the Pauli Exclusion Principle derived from experiments that look for x rays emitted from conductors while a large current is present. We also re-examine the assumptions underlying such experiments. We use the results of these studies to assess pilot measurements to develop an improved test of the Principle. We present an improved limit of $(1/2)\\beta^2 < 2.6\\times10^{-39}$ on the Pauli Exclusion Principle. This limit is the best to date for interactions between a system of fermions and a fermion that has not previously interacted with that given system. That is, for systems that do not obviously violate the Messiah-Greenberg symmetrization-postulate selection rule.

  10. A summary of transition probabilities for atomic absorption lines formed in low-density clouds

    Science.gov (United States)

    Morton, D. C.; Smith, W. H.

    1973-01-01

    A table of wavelengths, statistical weights, and excitation energies is given for 944 atomic spectral lines in 221 multiplets whose lower energy levels lie below 0.275 eV. Oscillator strengths were adopted for 635 lines in 155 multiplets from the available experimental and theoretical determinations. Radiation damping constants also were derived for most of these lines. This table contains the lines most likely to be observed in absorption in interstellar clouds, circumstellar shells, and the clouds in the direction of quasars where neither the particle density nor the radiation density is high enough to populate the higher levels. All ions of all elements from hydrogen to zinc are included which have resonance lines longward of 912 A, although a number of weaker lines of neutrals and first ions have been omitted.

  11. Direct observation of phase transition of GeSbTe thin films by Atomic Force Microscope

    Energy Technology Data Exchange (ETDEWEB)

    Yang Fei [National Laboratory of Solid State Microstructures and Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Sciences and Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Xu Ling, E-mail: xuling@nju.edu.cn [National Laboratory of Solid State Microstructures and Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Sciences and Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Zhang Rui; Geng Lei; Tong Liang; Xu Jun [National Laboratory of Solid State Microstructures and Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Sciences and Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Su Weining; Yu Yao [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Ma Zhongyuan; Chen Kunji [National Laboratory of Solid State Microstructures and Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Sciences and Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China)

    2012-10-01

    Graphical abstract: Nano-sized marks on GST thin film were fabricated using Conductive-AFM (Atomic Force Microscope). The AFM morphology images show that the marks are ablated at the center and a raised ring surrounding it. Highlights: Black-Right-Pointing-Pointer Microstructure of GeSbTe thin films was characterized by XRD and AFM. Black-Right-Pointing-Pointer Annealing and applying electrical field can induce crystallization on thin film. Black-Right-Pointing-Pointer Conductive-AFM was used to modify the surface of GeSbTe thin film. - Abstract: GeSbTe (GST) thin films were deposited on quartz substrates using electron beam evaporation system and then annealed in nitrogen atmosphere at different temperatures, ranging from 20 Degree-Sign C to 300 Degree-Sign C. X-ray diffraction (XRD) and Atomic Force microscope (AFM) measurements were used to characterize the as-deposited and post-annealed thin films. Annealing treatment was found to induce changes on microstructure, surface roughness and grain size, indicating that with the increase of annealing temperature, the amorphous GST films first changed to face-centered-cubic (fcc) phase and then the stable hexagonal (hex) phase. Meanwhile, conductive-AFM (C-AFM) was used to produce crystallized GST dots on thin films. I-V spectroscopy results show that GST films can switch from amorphous state to crystalline state at threshold voltage. After switching, I-V curve exhibits ohmic characteristic, which is usually observed in crystallized GST films. By applying repeated I-V spectroscopies on the thin films, crystallized nuclei were observed. As the times of I-V spectroscopies increases, the area of written dots increases, and the center of the mark begin to ablate. The AFM images show that the shape of marks is an ablated center with a raised ring surrounding it.

  12. Soft x-ray spectroscopy of Ba24Ge100: electronic phase transition and Ba-atom rattling.

    Science.gov (United States)

    Rachi, Takeshi; Kitajima, Masaki; Kobayashi, Kensuke; Guo, FangZhun; Nakano, Takehito; Ikemoto, Yuka; Kobayashi, Keisuke; Tanigaki, Katsumi

    2005-08-15

    The electronic states of Ba24Ge100 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy photon factory. A large reduction in the density of states (DOS) at the Fermi level is clearly shown before and after the electronic phase transition at 200 K. The changes in the spectrum widths and the fine structures of the core-level Ba 4d spectra give a very reasonable indication of the Ba-atom rattlings in the clathrate polyhedra. On-resonance experiments using the excitation from Ba 3d to 4f levels display that the wave functions of Ba 5d and 6s orbitals give only a small contribution to make a Fermi surface through the hybridization with the Ge20 cluster orbitals. Importantly, reliable values of the DOS at the Fermi level NEF are successfully deduced, using two data sets of DOS obtained from high-resolution XPS and the total magnetic susceptibilities by a superconducting quantum interference device, to be 0.149 and 0.0427 states eV(-1) (Ge atom)(-1) for a high-temperature and for a low-temperature phase.

  13. Co atoms on Bi2Se3 revealing a coverage dependent spin reorientation transition

    International Nuclear Information System (INIS)

    We investigate Co nanostructures on Bi2Se3 by means of scanning tunneling microscopy and spectroscopy (STM/STS), x-ray absorption spectroscopy, x-ray magnetic dichroism (XMCD) and calculations using the density functional theory (DFT). In the single adatom regime we find two different adsorption sites by STM. Our calculations reveal these to be the fcc and hcp hollow sites of the substrate. STS shows a pronounced peak for only one species of the Co adatoms indicating different electronic properties of both types. These are explained on the basis of our DFT calculations by different hybridizations with the substrate. Using XMCD we find a coverage dependent spin reorientation transition from easy-plane toward out-of-plane. We suggest clustering to be the predominant cause for this observation. (paper)

  14. Phase Transitions and Atomic-Scale Migration During the Preoxidation of a Titania/Ferrous Oxide Solution

    Science.gov (United States)

    Wang, Zhen-Yang; Zhang, Jian-Liang; Xing, Xiang-Dong; Liu, Zheng-Jian; Zhang, Ya-Peng; Liu, Xing-Le; Liu, Yi-Ran

    2016-02-01

    The non-isothermal preoxidation of the titania/ferrous oxide solution (TFOS) was investigated between 300°C and 1200°C. To explore the TFOS preoxidation mechanism, the phase transitions, crystal structure behavior, subreactions, and atomic-scale migration and enrichment of the TFOS during preoxidation were studied. Two different titanium and iron solutions were distinguished by scanning electron microscopy analysis. The phase transitions from titanomagnetite (TTM) to titanohematite to pseudobrookite (PSB) were indicated by the separation and enrichment of Ti and Fe, which migrated into PSB and hematite, respectively. This occurred alongside the generation and destruction of FeTiO3. Multiple local maxima and shoulders were observed in the double-derivative thermogravimetric curves during the preoxidation process, indicating the existence and initial reaction temperatures of five stages of subreactions. Compared with the theoretical mass gain (3.28 wt.%), only 80.8 at.% of the Fe2+ was oxidized to Fe3+, leaving unoxidized TTM in the solid solution during non-isothermal oxidation at 1200°C. The concentration of Ti gradually increased in the lamellar structures. However, Fe, Al, and O were mostly restricted to the homogeneous regions. The segregation of Mg only became obvious when TFOS was oxidized at high temperatures. The enrichment reduced the impact of Ti when O migrated during the reduction process, thus, enhancing the reducibility of the TFOS after preoxidation.

  15. Measurements of transition probabilities for spin-changing lines of atomic ions used in diagnostics of astrophysical plasmas

    Science.gov (United States)

    Smith, P. L.; Johnson, B. C.; Kwong, H. S.; Parkinson, W. H.; Knight, R. D.

    1984-01-01

    The intensities of ultraviolet, spin-changing, 'intersystem' lines of low-Z atomic ions are frequently used in determinations of electron densities and temperatures in astrophysical plasmas as well as in measurements of element abundances in the interstellar gas. The transition probabilities (A-values) of these lines, which are about five orders of magnitude weaker than allowed lines, have not been measured heretofore and various calculations produce A-values for these lines that differ by as much as 50 percent A radio-frequency ion trap has been used for the first measurements of transition probabilities for intersystem lines seen in astronomical spectra. The measurement procedure is discussed and results for Si III, O III, N II, and C III are reviewed and compared to calculated values. Discrepancies exist; these indicate that some of the calculated A-values may be less reliable than has been beleived and that revisions to the electron densities determined for some astrophysical plasmas may be required.

  16. Forbidden 2 P- nP and 2 P- nF transitions in the energy spectrum of ultracold Rydberg lithium-7 atoms

    Science.gov (United States)

    Zelener, B. B.; Saakyan, S. A.; Sautenkov, V. A.; Manykin, E. A.; Zelener, B. V.; Fortov, V. E.

    2016-04-01

    Forbidden 2 P- nP and 2 P- nF transitions in the ranges of the principal quantum number n = 42-114 and n = 38-48 have been detected in the optical spectra of ultracold highly excited lithium-7 atoms. The presence of forbidden transitions is due to induced external electric fields. The quantum defects and ionization energy obtained in various experiments and predicted theoretically have been discussed.

  17. Workers’ Conformism

    Directory of Open Access Journals (Sweden)

    Nikolay Ivantchev

    2013-10-01

    Full Text Available Conformism was studied among 46 workers with different kinds of occupations by means of two modified scales measuring conformity by Santor, Messervey, and Kusumakar (2000 – scale for perceived peer pressure and scale for conformism in antisocial situations. The hypothesis of the study that workers’ conformism is expressed in a medium degree was confirmed partly. More than a half of the workers conform in a medium degree for taking risk, and for the use of alcohol and drugs, and for sexual relationships. More than a half of the respondents conform in a small degree for anti-social activities (like a theft. The workers were more inclined to conform for risk taking (10.9%, then – for the use of alcohol, drugs and for sexual relationships (8.7%, and in the lowest degree – for anti-social activities (6.5%. The workers who were inclined for the use of alcohol and drugs tended also to conform for anti-social activities.

  18. Structures of 13-atom clusters of fcc transition metals by ab initio and semiempirical calculations

    Science.gov (United States)

    Longo, R. C.; Gallego, L. J.

    2006-11-01

    We report the results of ab initio calculations of the structures and magnetic moments of Ni13 , Pd13 , Pt13 , Cu13 , Ag13 , and Au13 that were performed using a density-functional method that employs linear combinations of pseudoatomic orbitals as basis sets (SIESTA). Our structural results for Pt13 , Cu13 , Ag13 , and Au13 show that a buckled biplanar structure (BBP) is more stable than the icosahedral configuration, in keeping with results obtained recently by Chang and Chou [Phys. Rev. Lett. 93, 133401 (2004)] using the Vienna ab initio simulation package with a plane-wave basis. However, for Ni13 and Pd13 we found that the icosahedral structure is more stable than BBP. For all these clusters, two semiempirical methods based on spherically symmetric potentials both found the icosahedral structure to be the more stable, while the modified embedded atom model method, which uses a direction-dependent potential, found BBP to be the more stable structure. When low-energy structures found in recent ab initio studies of Pt13 , Cu13 , and Au13 other than Chang and Chou were optimized with SIESTA, those reported for Pt13 and Cu13 were found to be less stable than BBP, but the two-dimensional planar configuration reported for Au13 proved to be more stable than BBP.

  19. Shock-Compressed Diamond: Melt, Insulator-Conductor and Polymeric-Atomic Transitions

    Energy Technology Data Exchange (ETDEWEB)

    Eggert, J; Hicks, D G; Celliers, P M; Bradley, D K; McWilliams, R S; Jeanloz, R; Miller, J E; Boehly, T R

    2007-08-16

    Temperatures measured on the shock-Hugoniot of diamond reveal melting between 650 ({+-} 60) GPa and 9000 ({+-} 800) K and 1090 ({+-} 50) GPa and 8400 ({+-} 800) K, with a heat of fusion of {approx} 25 {+-} 10 kJ/mole and a negative Clapeyron slope {partial_derivative}T/{partial_derivative}P|{sub melt} = -5 {+-} 3 K/GPa. Thus, the fluid is denser than the compressed solid, and optical reflectivity measurements show it to be metallic. Hugoniot-temperature measurements extending to over 4000 GPa (40 Mbar) and 115,000 K suggest de-polymerization of a dense covalently-bonded fluid to an atomic state between 10,000 and 30,000 K. These experimental results indicate that carbon present deep inside planets such as Uranus and Neptune could be solid for through-going convection, whereas stable stratification would allow for the presence of fluid metallic carbon at depth; in either case, the presence of carbon could potentially affect planetary seismic normal modes.

  20. Atomic-to-molecular gas phase transition triggered by the radio jet in Centaurus A

    CERN Document Server

    Salomé, Quentin; Combes, Françoise; Hamer, Stephen

    2016-01-01

    NGC 5128 (Centaurus A) is one of the best example to study AGN-feedback in the local Universe. At 13.5 kpc from the galaxy, optical filaments with recent star formation are lying along the radio-jet direction. We used the Atacama Pathfinder EXperiment (APEX) to map the CO(2-1) emission all along the filament structure. Molecular gas mass of 8.2x10^7 Msun was found over the 4.2 kpc-structure which represents about 3% of the total gas mass of the NGC 5128 cold gas content. Two dusty mostly molecular structure are identified, following the optical filaments. The region corresponds to the crossing of the radio jet with the Northern HI shell, coming from a past galaxy merger. One filament is located at the border of the HI shell, while the other is entirely molecular, and devoid of HI gas. The molecular mass is comparable to the HI mass in the shell, suggesting a scenario where the atomic gas was shocked and transformed in molecular clouds by the radio jet. Comparison with combined FIR Herschel and UV GALEX estima...

  1. Alkali metal and simple gas atom adsorption and coadsorption on transition metal surfaces

    CERN Document Server

    Norris, A G

    2000-01-01

    system is formed by adsorption of potassium or cesium on the Ni(100)c(2x2)-O overlayer. The difficulty of the structural fit is compounded' by the size of the unit cell. In this study, Anomalous Scattering was used to investigate whether there is a contribution from the nickel substrate to the reconstruction. Measurements of the fractional order rods at 10 eV and 200 eV below the nickel K edge (8333 eV) showed no discernible differences and involvement of the nickel substrate in the reconstruction can be eliminated. Alkali metal coadsorption systems represent a step along the pathway from simple model adsorbate overlayers to more technologically relevant real systems. Such is their complexity, however, that very few systems have been solved structurally. Presented here are SXRD and STM investigations of two such systems. The first study involves potassium adsorption on the Ni(100)(2x2)p4g-N surface, where a clock reconstruction is present with the nickel substrate atoms rotated in alternate clockwise and anti...

  2. Atomically thin arsenene and antimonene: semimetal-semiconductor and indirect-direct band-gap transitions.

    Science.gov (United States)

    Zhang, Shengli; Yan, Zhong; Li, Yafei; Chen, Zhongfang; Zeng, Haibo

    2015-03-01

    The typical two-dimensional (2D) semiconductors MoS2, MoSe2, WS2, WSe2 and black phosphorus have garnered tremendous interest for their unique electronic, optical, and chemical properties. However, all 2D semiconductors reported thus far feature band gaps that are smaller than 2.0 eV, which has greatly restricted their applications, especially in optoelectronic devices with photoresponse in the blue and UV range. Novel 2D mono-elemental semiconductors, namely monolayered arsenene and antimonene, with wide band gaps and high stability were now developed based on first-principles calculations. Interestingly, although As and Sb are typically semimetals in the bulk, they are transformed into indirect semiconductors with band gaps of 2.49 and 2.28 eV when thinned to one atomic layer. Significantly, under small biaxial strain, these materials were transformed from indirect into direct band-gap semiconductors. Such dramatic changes in the electronic structure could pave the way for transistors with high on/off ratios, optoelectronic devices working under blue or UV light, and mechanical sensors based on new 2D crystals.

  3. Atomic and molecular adsorption on transition-metal carbide (111) surfaces from density-functional theory: a trend study of surface electronic factors

    DEFF Research Database (Denmark)

    Vojvodic, Aleksandra; Ruberto, C.; Lundqvist, Bengt

    2010-01-01

    This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMCs) in NaCl structure by means of density-functional theory calculations. The investigated substrates are the TM-terminated TMC(111) surfaces, of interest because of the presence of different types...

  4. Application of an excited state LDA exchange energy functional for the calculation of transition energy of atoms within time-independent density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Shamim, Md; Harbola, Manoj K, E-mail: sami@iitk.ac.i, E-mail: mkh@iitk.ac.i [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India)

    2010-11-14

    Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.

  5. Conformal Infinity

    Directory of Open Access Journals (Sweden)

    Frauendiener Jörg

    2000-08-01

    Full Text Available The notion of conformal infinity has a long history within the research in Einstein's theory of gravity. Today, ``conformal infinity'' is related with almost all other branches of research in general relativity, from quantisation procedures to abstract mathematical issues to numerical applications. This review article attempts to show how this concept gradually and inevitably evolved out of physical issues, namely the need to understand gravitational radiation and isolated systems within the theory of gravitation and how it lends itself very naturally to solve radiation problems in numerical relativity. The fundamental concept of null-infinity is introduced. Friedrich's regular conformal field equations are presented and various initial value problems for them are discussed. Finally, it is shown that the conformal field equations provide a very powerful method within numerical relativity to study global problems such as gravitational wave propagation and detection.

  6. Conformal Infinity

    Directory of Open Access Journals (Sweden)

    Frauendiener Jörg

    2004-01-01

    Full Text Available The notion of conformal infinity has a long history within the research in Einstein's theory of gravity. Today, 'conformal infinity' is related to almost all other branches of research in general relativity, from quantisation procedures to abstract mathematical issues to numerical applications. This review article attempts to show how this concept gradually and inevitably evolved from physical issues, namely the need to understand gravitational radiation and isolated systems within the theory of gravitation, and how it lends itself very naturally to the solution of radiation problems in numerical relativity. The fundamental concept of null-infinity is introduced. Friedrich's regular conformal field equations are presented and various initial value problems for them are discussed. Finally, it is shown that the conformal field equations provide a very powerful method within numerical relativity to study global problems such as gravitational wave propagation and detection.

  7. Ab initio study of Ga-GaN system: Transition from adsorbed metal atoms to a metal–semiconductor junction

    Energy Technology Data Exchange (ETDEWEB)

    Witczak, Przemysław; Kempisty, Pawel; Strak, Pawel [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw (Poland); Krukowski, Stanisław, E-mail: stach@unipress.waw.pl [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, Poland and Interdisciplinary Centre for Modelling, University of Warsaw, Pawińskiego 5a, 02-106 Warsaw (Poland)

    2015-11-15

    Ab initio studies of a GaN(0001)-Ga system with various thicknesses of a metallic Ga layer were undertaken. The studied systems extend from a GaN(0001) surface with a fractional coverage of gallium atoms to a Ga-GaN metal–semiconductor (m–s) contact. Electronic properties of the system are simulated using density functional theory calculations for different doping of the bulk semiconductor. It is shown that during transition from a bare GaN(0001) surface to a m–s heterostructure, the Fermi level stays pinned at a Ga-broken bond highly dispersive surface state to Ga–Ga states at the m–s interface. Adsorption of gallium leads to an energy gain of about 4 eV for a clean GaN(0001) surface and the energy decreases to 3.2 eV for a thickly Ga-covered surface. The transition to the m–s interface is observed. For a thick Ga overlayer such interface corresponds to a Schottky contact with a barrier equal to 0.9 and 0.6 eV for n- and p-type, respectively. Bond polarization-related dipole layer occurring due to an electron transfer to the metal leads to a potential energy jump of 1.5 eV, independent on the semiconductor doping. Additionally high electron density in the Ga–Ga bond region leads to an energy barrier about 1.2 eV high and 4 Å wide. This feature may adversely affect the conductivity of the n-type m–s system.

  8. Coarse-grained simulations of proton-dependent conformational changes in lactose permease.

    Science.gov (United States)

    Jewel, Yead; Dutta, Prashanta; Liu, Jin

    2016-08-01

    During lactose/H(+) symport, the Escherichia coli lactose permease (LacY) undergoes a series of global conformational transitions between inward-facing (open to cytoplasmic side) and outward-facing (open to periplasmic side) states. However, the exact local interactions and molecular mechanisms dictating those large-scale structural changes are not well understood. All-atom molecular dynamics simulations have been performed to investigate the molecular interactions involved in conformational transitions of LacY, but the simulations can only explore early or partial global structural changes because of the computational limits (bridge dynamics agreed with all-atom simulations at early short time period, validating our simulations. From our microsecond simulations, we were able to observe the complete transition from inward-facing to outward-facing conformations of LacY. Our results showed that all helices have participated during the global conformational transitions and helical movements of LacY. The inter-helical distances measured in our simulations were consistent with the double electron-electron resonance experiments at both cytoplasmic and periplasmic sides. Our simulations indicated that the deprotonation of Glu325 induced the opening of the periplasmics side and partial closure of the cytoplasmic side of LacY, while protonation of the Glu269 caused a stable cross-domain salt-bridge (Glu130-Arg344) and completely closed the cytoplasmic side. Proteins 2016; 84:1067-1074. © 2016 Wiley Periodicals, Inc. PMID:27090495

  9. The conformal bootstrap

    Science.gov (United States)

    Poland, David; Simmons-Duffin, David

    2016-06-01

    The conformal bootstrap was proposed in the 1970s as a strategy for calculating the properties of second-order phase transitions. After spectacular success elucidating two-dimensional systems, little progress was made on systems in higher dimensions until a recent renaissance beginning in 2008. We report on some of the main results and ideas from this renaissance, focusing on new determinations of critical exponents and correlation functions in the three-dimensional Ising and O(N) models.

  10. Molecular insight into conformational transmission of human P-glycoprotein

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Shan-Yan [Department of Biochemical Engineering and Key Laboratory of Systems Bioengineering of the Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Liu, Fu-Feng, E-mail: fufengliu@tju.edu.cn, E-mail: ysun@tju.edu.cn; Dong, Xiao-Yan; Sun, Yan, E-mail: fufengliu@tju.edu.cn, E-mail: ysun@tju.edu.cn [Department of Biochemical Engineering and Key Laboratory of Systems Bioengineering of the Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072 (China)

    2013-12-14

    P-glycoprotein (P-gp), a kind of ATP-binding cassette transporter, can export candidates through a channel at the two transmembrane domains (TMDs) across the cell membranes using the energy released from ATP hydrolysis at the two nucleotide-binding domains (NBDs). Considerable evidence has indicated that human P-gp undergoes large-scale conformational changes to export a wide variety of anti-cancer drugs out of the cancer cells. However, molecular mechanism of the conformational transmission of human P-gp from the NBDs to the TMDs is still unclear. Herein, targeted molecular dynamics simulations were performed to explore the atomic detail of the conformational transmission of human P-gp. It is confirmed that the conformational transition from the inward- to outward-facing is initiated by the movement of the NBDs. It is found that the two NBDs move both on the two directions (x and y). The movement on the x direction leads to the closure of the NBDs, while the movement on the y direction adjusts the conformations of the NBDs to form the correct ATP binding pockets. Six key segments (KSs) protruding from the TMDs to interact with the NBDs are identified. The relative movement of the KSs along the y axis driven by the NBDs can be transmitted through α-helices to the rest of the TMDs, rendering the TMDs to open towards periplasm in the outward-facing conformation. Twenty eight key residue pairs are identified to participate in the interaction network that contributes to the conformational transmission from the NBDs to the TMDs of human P-gp. In addition, 9 key residues in each NBD are also identified. The studies have thus provided clear insight into the conformational transmission from the NBDs to the TMDs in human P-gp.

  11. Molecular insight into conformational transmission of human P-glycoprotein

    Science.gov (United States)

    Chang, Shan-Yan; Liu, Fu-Feng; Dong, Xiao-Yan; Sun, Yan

    2013-12-01

    P-glycoprotein (P-gp), a kind of ATP-binding cassette transporter, can export candidates through a channel at the two transmembrane domains (TMDs) across the cell membranes using the energy released from ATP hydrolysis at the two nucleotide-binding domains (NBDs). Considerable evidence has indicated that human P-gp undergoes large-scale conformational changes to export a wide variety of anti-cancer drugs out of the cancer cells. However, molecular mechanism of the conformational transmission of human P-gp from the NBDs to the TMDs is still unclear. Herein, targeted molecular dynamics simulations were performed to explore the atomic detail of the conformational transmission of human P-gp. It is confirmed that the conformational transition from the inward- to outward-facing is initiated by the movement of the NBDs. It is found that the two NBDs move both on the two directions (x and y). The movement on the x direction leads to the closure of the NBDs, while the movement on the y direction adjusts the conformations of the NBDs to form the correct ATP binding pockets. Six key segments (KSs) protruding from the TMDs to interact with the NBDs are identified. The relative movement of the KSs along the y axis driven by the NBDs can be transmitted through α-helices to the rest of the TMDs, rendering the TMDs to open towards periplasm in the outward-facing conformation. Twenty eight key residue pairs are identified to participate in the interaction network that contributes to the conformational transmission from the NBDs to the TMDs of human P-gp. In addition, 9 key residues in each NBD are also identified. The studies have thus provided clear insight into the conformational transmission from the NBDs to the TMDs in human P-gp.

  12. Conformational changes in glycine tri- and hexapeptide

    DEFF Research Database (Denmark)

    Yakubovich, Alexander V.; Solov'yov, Ilia; Solov'yov, Andrey V.;

    2006-01-01

    conformations and calculated the energy barriers for transitions between them. Using a thermodynamic approach, we have estimated the times of the characteristic transitions between these conformations. The results of our calculations have been compared with those obtained by other theoretical methods...... also investigated the influence of the secondary structure of polypeptide chains on the formation of the potential energy landscape. This analysis has been performed for the sheet and the helix conformations of chains of six amino acids....

  13. Distribution and Transition of Native and Completely Unfolded Conformations in the Unfolding of Bovine Heart Cytochrome c Induced by Urea and Guanidine Hydrochloride%Distribution and Transition of Native and Completely Unfolded Conformations in the Unfolding of Bovine Heart Cytochrome c Induced by Urea and Guanidine Hydrochloride

    Institute of Scientific and Technical Information of China (English)

    Yang, Jianting; Zhang, Tan; Lu, Cuizhu; Bian, Liujiao

    2011-01-01

    The unfolding of bovine heart cytochrome c induced by urea and guanidine hydrochloride was first studied through intrinsic fluorescence emission spectra and fluorescence phase diagram and the results showed that both of them separately followed a two-state model. As the simplest sample of the unfolding of protein molecules induced by denaturants, an equation was presented to show the effect of the denaturant concentrations in denaturation solu- tion on the residual activity ratios of bovine heart cytochrome c in their two-state unfolding. There are two charac- teristic unfolding parameters K and m in this equation. The former is the thermodynamic equilibrium constant of the unfolding of bovine heart cytochrome c induced by denaturants, the latter is the number of denaturant molecules associated with a bovine heart cytochrome c molecule during the unfolding procedure, and through them the distri- bution and transition of native and completely unfolded bovine heart cytochrome c conformations under different concentrations of urea or guanidine hydrochloride in denaturation solution can be accurately described.

  14. Conformational re-analysis of (+)-meptazinol: an opioid with mixed analgesic pharmacophores

    Institute of Scientific and Technical Information of China (English)

    Wei LI; Xing-hai WANG; Choi-wan LAU; Yun TANG; Qiong XIE; Zhui-bai QIU

    2006-01-01

    Aim: To further investigate the analgesic pharmacophore of (+)-meptazinol. Methods: Two different opioid pharmacophores, Pharm-Ⅰ and Pharm-Ⅱ, were established from structures of nine typical opiates and meperidine by using molecular modeling approaches according to their different structure activity relationship properties. They were further validated by a set of conformationally constrained arylpiperidines. Two conformers of (+)-meptazinol (Conformer-Ⅰ and Con-former-Ⅱ) detected in solution were then fitted into the pharmacophores, respectively, by Fit Atoms facilities available in SYBYL, a computational modeling tool kit for molecular design and analysis. Results: Conformer-Ⅰ fit Pharm-Ⅰ from typical opiates well. However, Conformer-Ⅱ fit none of these pharmacophores. Instead, it was found to be similar to another potent analgesic, benzofuro[2,3-c] pyridin-6-ol, whose pharmacophore was suggested to hold the transitional state between the two established pharmacophores. Unlike typical analgesics derived from 4-aryl piperidine (eg, meperidine) with one conformer absolutely overwhelming, the (+)-meptazinol exists in two conformers with similar amounts in solution. Furthermore, both conformers can not transform to each other freely in ordinary conditions based on our NMR results. Conclusion: (+)-meptazinol was suggested to be an opioid with mixed analgesic pharmacophores, which may account for the complicated pharmacological properties of meptazinol.

  15. Sensitive search for the temporal variation of the fine structure constant using radio-frequency E1 transitions in atomic dysprosium

    CERN Document Server

    Nguyen, A T; Lamoreaux, S K; Torgerson, J R

    2003-01-01

    It has been proposed that the radio-frequency electric-dipole (E1) transition between two nearly degenerate opposite-parity states in atomic dysprosium should be highly sensitive to possible temporal variation of the fine structure constant ($\\alpha$) [V. A. Dzuba, V. V. Flambaum, and J. K. Webb, Phys. Rev. A {\\bf 59}, 230 (1999)]. We discuss here an experimental realization of the proposed search, which involves monitoring the E1 transition frequency over a period of time using direct frequency counting techniques. We estimate that a statistical sensitivity of $|\\adota| \\sim 10^{-18}$/yr may be achieved and discuss possible systematic effects in such a measurement.

  16. Two-Photon Atomic Coherence Effect of Transition 5S1/2-5P3/2-4D5/2(4D3/2) of 85Rb atoms

    Institute of Scientific and Technical Information of China (English)

    DING Dong-Sheng; ZHOU Zhi-Yuan; SHI Bao-Sen; ZOU Xu-Bo; GUO Guang-Can

    2012-01-01

    We experimentally observe the counterintuitive absorption peaks in the transition spectra of 5S1/2-5P3/2-4D5/2 and 5S1/2-5.P3/2-4.D3/2 in a hot 85Rb vapor. These spectra are very different from the spectra observed via double resonance optical pumping or electromagnetically induced transparency in the same transitions. These absorption peaks are from electromagnetically induced absorption due to the two-photon atomic coherence effect. We also investigate the relations between these peaks and the powers of the coupling laser and the probe laser experimen tally.%We experimentally observe the counterintuitive absorption peaks in the transition spectra of 5S1/2-5P3/2-4D5/2 and 5S1/2-5P3/2-4D3/2 in a hot 85Rb vapor.These spectra are very different from the spectra observed via double resonance optical pumping or electromagnetically induced transparency in the same transitions.These absorption peaks are from electromagnetically induced absorption due to the two-photon atomic coherence effect.We also investigate the relations between these peaks and the powers of the coupling laser and the probe laser experimentally.

  17. Atomic sulfur: Frequency measurement of the J = 0 left arrow 1 fine-structure transition at 56.3 microns by laser magnetic resonance

    Science.gov (United States)

    Brown, John M.; Evenson, Kenneth M.; Zink, Lyndon R.

    1994-01-01

    The J = 0 left arrow 1 fine-structure transition in atomic sulfur (S I) in its ground (3)P state has been detected in the laboratory by far-infrared laser magnetic resonance. The fine-structure interval has been measured accurately as 5,322,492.9 +/- 2.8 MHz which corresponds to a wavelength of 56.325572 +/- 0.000030 micrometers.

  18. Adsorption of alkali, alkaline-earth, simple and 3d transition metal, and nonmetal atoms on monolayer MoS2

    Directory of Open Access Journals (Sweden)

    X. D. Li

    2015-05-01

    Full Text Available Single adsorption of different atoms on pristine two-dimensional monolayer MoS2 have been systematically investigated by using density functional calculations with van der Waals correction. The adatoms cover alkali metals, alkaline earth metals, main group metal, 3d-transition metals, coinage metal and nonmetal atoms. Depending on the adatom type, metallic, semimetallic or semiconducting behavior can be found in direct bandgap monolayer MoS2. Additionally, local or long-range magnetic moments of two-dimensional MoS2 sheet can also attained through the adsorption. The detailed atomic-scale knowledge of single adsorption on MoS2 monolayer is important not only for the sake of a theoretical understanding, but also device level deposition technological application.

  19. Luminescence spectroscopy of matrix-isolated atomic manganese: excitation of the "forbidden" a6D(J)a6S transitions.

    Science.gov (United States)

    Collier, Martin A; Ryan, Maryanne C; McCaffrey, John G

    2005-07-22

    Laser-induced excitation spectra recorded for the electric-quadrupole 3d(6)4s a6D(J)transitions of atomic Mn, allow assignment of the red emission features, previously observed in Mn/RG (RG=Ar, Kr and Xe) matrices with resonance 3d(5)4s4pz6P(5/2)transition from the J=9/2 spin-orbit level. Temperature dependent emission scans lead to the identification of the zero phonon line for the a6D(9/2)-->a6S(5/2) transition at 585.75 nm. The identified matrix-shift of +20 cm(-1) allows an assessment of the extent of the ground state stabilization in the red (secondary) site of atomic Mn isolation in solid Kr. Emission produced with direct a6D state excitation yielded both the 585.75 and 626 nm features. The former band arises for Mn atoms occupying the red site--the latter from blue site occupancy in solid Kr. The excitation linewidths recorded for these two sites differ greatly, with the blue site yielding a broad featureless profile, in contrast to the narrow, structured features of the red site. The corresponding red site a6D(J)a6S(5/2) transitions in Ar and Xe matrices are broader than in Kr--a difference considered to originate from the site sizes available in these hosts and the interatomic Mn x RG potentials. The millisecond decay times recorded for the red emission bands in the Mn/RG systems are all much shorter than the 3 s value predicted for the gas phase a6D(9/2)-->a6S(5/2) transition. This enhancement allows optical pumping of the forbidden a6D(J)a6S transitions with low laser powers when atomic manganese is isolated in the solid state. However all the emission decays are complex, exhibiting triple exponential decays. This behavior may be related to the dependence of the excitation linewidths on the J value, indicating removal of the J degeneracy due to weak matrix-induced, crystal field splitting.

  20. Structural, electronic and magnetic properties of 3d transition metal atom adsorbed germanene: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Pang, Qing, E-mail: pangqingjkd@163.com [College of Science, Xi' an University of Architecture and Technology, Xi' an 710055, Shaanxi (China); Li, Long; Zhang, Chun-Ling [College of Science, Xi' an University of Architecture and Technology, Xi' an 710055, Shaanxi (China); Wei, Xiu-Mei [College of Physics and Information Technology, Shaanxi Normal University, Xi' an 710062, Shaanxi (China); Song, Yu-Ling [College of Physics and Electronic Engineering, Nanyang Normal University, Nanyang 473061, Henan (China)

    2015-06-15

    The structural, electronic and magnetic properties of germanene adsorbed with 10 different 3d transition metal (TM) atoms have been investigated by using the spin-polarized DFT calculations. The 3d TM adatoms we considered prefer to bind to the hexagon hollow site of germanene, except Zn which favors to bind to the valley site. A strong covalent bonding character between TM adatom and germanene layer is found in most of TM/germanene adsorption systems. By means of adsorption, the germanene can exhibit various electronic and magnetic properties depending on the adatom species, such as nonmagnetic metal (Cu adsorption), nonmagnetic semiconductor (Ni or Zn adsorption), ferromagnetic metal (Cr or Mn adsorption), ferromagnetic semiconductor (V adsorption), and more particular, ferromagnetic half-metal (Sc, Ti, Fe or Co adsorption) with 100% spin-polarization at the Fermi level. In addition, Cr adatom introduces the largest magnetic moment in germanene, while Sc, Ti, V, Mn, Fe and Co adatoms all generate nearly integer magnetic moments. The effects of the on-site Coulomb interaction as well as the magnetic interaction between TM adatoms on the stability of the half-metallic TM/germanene systems are also considered, and the results show that the half-metallic states for the Sc/germanene and Ti/germanene are all robust. These ferromagnetic TM/germanene systems should have potential applications in the fields of two-dimensional spintronics devices. The analysis of the PDOS indicates the ferromagnetic property of the obtained TM/germanene systems mainly resulted from the spin-split of the TM 3d states. - Highlights: • Most of the 3d TM adatoms considered prefer to bind to the hexagon hollow site of germanene. • Strong covalent bonding between adatom and germanene is found in most of TM/germanene systems. • Germanene exhibits various electronic and magnetic properties depending on the adatom species. • The ferromagnetic property of TM/germanene systems mainly

  1. Structural stability and O2 dissociation on nitrogen-doped graphene with transition metal atoms embedded: A first-principles study

    Directory of Open Access Journals (Sweden)

    Mingye Yang

    2015-06-01

    Full Text Available By using first-principles calculations, we investigate the structural stability of nitrogen-doped (N-doped graphene with graphitic-N, pyridinic-N and pyrrolic-N, and the transition metal (TM atoms embedded into N-doped graphene. The structures and energetics of TM atoms from Sc to Ni embedded into N-doped graphene are studied. The TM atoms at N4V 2 forming a 4N-centered structure shows the strongest binding and the binding energies are more than 7 eV. Finally, we investigate the catalytic performance of N-doped graphene with and without TM embedding for O2 dissociation, which is a fundamental reaction in fuel cells. Compared to the pyridinic-N, the graphitic-N is more favorable to dissociate O2 molecules with a relatively low reaction barrier of 1.15 eV. However, the catalytic performance on pyridinic-N doped structure can be greatly improved by embedding TM atoms, and the energy barrier can be reduced to 0.61 eV with V atom embedded. Our results provide the stable structure of N-doped graphene and its potential applications in the oxygen reduction reactions.

  2. Conformational Transition of Threonine Molecules and Catalytic Mechanism of Water Molecules and Hydroxyl Radicals%苏氨酸分子的构象转变及水分子与羟基自由基的催化机理

    Institute of Scientific and Technical Information of China (English)

    闫红彦; 王佐成; 佟华; 李鑫峡; 张丹; 孙双双

    2016-01-01

    采用密度泛函理论的 B3LYP 方法和微扰论的 MP2方法,研究苏氨酸分子构象转变机制以及水分子与羟基自由基对氢迁移反应的催化作用.结果表明:S-苏氨酸向R-别苏氨酸的构象转变反应有4个通道,R-别苏氨酸向R-苏氨酸与 S-苏氨酸向 S-别苏氨酸的构象转变反应各有1个通道;S-苏氨酸向R-别苏氨酸构象转变反应的最高能垒为250.2 kJ/mol;R-别苏氨酸向 R-苏氨酸构象转变反应的最高能垒为335.0 kJ/mol;S-苏氨酸向 S-别苏氨酸构象转变反应的最高能垒为359.6 kJ/mol;2个水分子构成的链及水分子/羟基自由基构成的链对质子迁移反应有较好的催化作用,使 S-苏氨酸向 R-别苏氨酸构象转变反应的高能垒分别降为128.3 kJ/mol 和108.6 kJ/mol.%Using B3LYP methods of density functional theory and the MP2 methods of perturbation theory,we studied conformational transition mechanism of threonine molecules and catalytic action of water molecules and hydroxyl radicals in the hydrogen transfer reaction.The results show that there are four channels in the conformational transition reaction of S-Thr to R-allo-Thr.There is one channel in the conformational transitions of R-allo-Thr to R-Thr and S-Thr to S-allo-Thr.The highest energy barriers for the conformational transition of S-Thr to R-allo-Thr,R-allo-Thr to R-Thr and S-Thr to S-allo-Thr are 250.2,335.0,359.6 kJ/mol.Besides,the chain composed of two water molecules and the chain composed of hydroxyl radical and water molecules have a better catalytic effect in proton migration reaction,and the high-energy barriers are reduced to 128.3,108.6 kJ/mol for the conformational transition of S-Thr to R-allo-Thr respectively.

  3. Autler-Townes doublet in the absorption spectra for the transition between excited states of cold cesium atoms

    Institute of Scientific and Technical Information of China (English)

    Liang Qiang-Bing; Yang Bao-Dong; Yang Jian-Feng; Zhang Tian-Cai; Wang Jun-Min

    2010-01-01

    Autler-Townes splitting in absorption spectra of the excited states 6 2P3/2 - 82S1/2 of cold cesium atoms confined in a magneto-optical trap has been observed.Experimental data of the Autler-Townes splitting fit well to the dressedatom theory,by which the fact of the cold atoms dressed by cooling/trapping laser beams is revealed.The results of the theoretical fitting with experiment not only told us the effective Rabi frequency cold atoms experienced,but also could be used for measuring the probability amplitudes of the dressed states.

  4. Atomic-Resolution Visualization of Distinctive Chemical Mixing Behavior of Ni, Co and Mn with Li in Layered Lithium Transition-Metal Oxide Cathode Materials

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Pengfei [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Zheng, Jianming [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lv, Dongping [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wei, Yi [Peking Univ., Beijing (China); Zheng, Jiaxin [Peking Univ., Beijing (China); Wang, Zhiguo [Univ. of Electronic Science and Technology of China, Chengdu (China); Kuppan, Saravanan [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Yu, Jianguo [Idaho National Lab. (INL), Idaho Falls, ID (United States); Luo, Langli [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Edwards, Danny J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Olszta, Matthew J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Amine, Khalil [Argonne National Lab. (ANL), Argonne, IL (United States); Liu, Jun [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Xiao, Jie [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Pan, Feng [Peking Univ., Beijing (China); Chen, Guoying [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Zhang, Jiguang [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wang, Chong M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2015-07-06

    Capacity and voltage fading of layer structured cathode based on lithium transition metal oxide is closely related to the lattice position and migration behavior of the transition metal ions. However, it is scarcely clear about the behavior of each of these transition metal ions. We report direct atomic resolution visualization of interatomic layer mixing of transition metal (Ni, Co, Mn) and lithium ions in layer structured oxide cathodes for lithium ion batteries. Using chemical imaging with aberration corrected scanning transmission electron microscope (STEM) and DFT calculations, we discovered that in the layered cathodes, Mn and Co tend to reside almost exclusively at the lattice site of transition metal (TM) layer in the structure or little interlayer mixing with Li. In contrast, Ni shows high degree of interlayer mixing with Li. The fraction of Ni ions reside in the Li layer followed a near linear dependence on total Ni concentration before reaching saturation. The observed distinctively different behavior of Ni with respect to Co and Mn provides new insights on both capacity and voltage fade in this class of cathode materials based on lithium and TM oxides, therefore providing scientific basis for selective tailoring of oxide cathode materials for enhanced performance.

  5. Study of the 5p3/2 -> 6p3/2 electric dipole forbidden transition in atomic rubidium using optical-optical double resonance spectroscopy

    CERN Document Server

    Ponciano-Ojeda, Francisco; López-Hernández, Oscar; Mojica-Casique, Cristian; Colín-Rodríguez, Ricardo; Ramírez-Martínez, Fernando; Flores-Mijangos, Jesús; Sahagún, Daniel; Jáuregui, Rocío; Jiménez-Mier, José

    2015-01-01

    Direct evidence of excitation of the 5p3/2 -> 6p3/2 electric dipole forbidden transition in atomic rubidium is presented. The experiments were performed in a room temperature rubidium cell with continuous wave extended cavity diode lasers. Optical-optical double resonance spectroscopy with counterpropagating beams allows the detection of the non-dipole transition free of Doppler broadening. The 5p3/2 state is prepared by excitation with a laser locked to the maximum F cyclic transition of the D2 line, and the forbidden transition is produced by excitation with a 911 nm laser. Production of the forbidden transition is monitored by detection of the 420 nm fluorescence that results from decay of the 6p3/2 state. Spectra with three narrow lines (~ 13 MHz FWHM) with the characteristic F - 1, F and F + 1 splitting of the 6p3/2 hyperfine structure in both rubidium isotopes were obtained. The results are in very good agreement with a direct calculation that takes into account the 5s -> 5p3/2 preparation dynamics, the...

  6. Transition of radiative recombination channels from delocalized states to localized states in a GaInP alloy with partial atomic ordering: a direct optical signature of Mott transition?

    Science.gov (United States)

    Su, Z. C.; Ning, J. Q.; Deng, Z.; Wang, X. H.; Xu, S. J.; Wang, R. X.; Lu, S. L.; Dong, J. R.; Yang, H.

    2016-03-01

    Anderson localization is a predominant phenomenon in condensed matter and materials physics. In fact, localized and delocalized states often co-exist in one material. They are separated by a boundary called the mobility edge. Mott transition may take place between these two regimes. However, it is widely recognized that an apparent demonstration of Anderson localization or Mott transition is a challenging task. In this article, we present a direct optical observation of a transition of radiative recombination dominant channels from delocalized (i.e., local extended) states to Anderson localized states in the GaInP base layer of a GaInP/GaAs single junction solar cell by the means of the variable-temperature electroluminescence (EL) technique. It is found that by increasing temperature, we can boost a remarkable transition of radiative recombination dominant channels from the delocalized states to the localized states. The delocalized states are induced by the local atomic ordering domains (InP/GaP monolayer superlattices) while the localized states are caused by random distribution of indium (gallium) content. The efficient transfer and thermal redistribution of carriers between the two kinds of electronic states was revealed to result in both a distinct EL mechanism transition and an electrical resistance evolution with temperature. Our study gives rise to a self-consistent precise picture for carrier localization and transfer in a GaInP alloy, which is an extremely technologically important energy material for fabricating high-efficiency photovoltaic devices.

  7. Atomic-level Pseudo-degeneracy of Atomic Levels Giving Transitions Induced by Magnetic Fields, of Importance for Determining the Field Strengths in the Solar Corona

    Science.gov (United States)

    Li, Wenxian; Yang, Yang; Tu, Bingsheng; Xiao, Jun; Grumer, Jon; Brage, Tomas; Watanabe, Tetsuya; Hutton, Roger; Zou, Yaming

    2016-08-01

    We present a measured value for the degree of pseudo-degeneracy between two fine-structure levels in Fe9+ from line intensity ratios involving a transition induced by an external magnetic field. The extracted fine-structure energy difference between the 3{p}43d{}4{D}5/2 and {}4{D}7/2 levels, where the latter is the upper state for the magnetic-field induced line, is needed in our recently proposed method to measure magnetic-field strengths in the solar corona. The intensity of the 3{p}43d{}4{D}7/2\\to 3{p}5{}2{P}3/2 line at 257.262 Å is sensitive to the magnetic field external to the ion. This sensitivity is in turn strongly dependent on the energy separation in the pseudo-degeneracy through the mixing induced by the external magnetic field. Our measurement, which uses an Electron Beam Ion Trap with a known magnetic-field strength, indicates that this energy difference is 3.5 cm‑1. The high abundance of Fe9+ and the sensitivity of the line’s transition probability to field strengths below 0.1 T opens up the possibility of diagnosing coronal magnetic fields. We propose a new method to measure the magnetic field in the solar corona, from similar intensity ratios in Fe9+. In addition, the proposed method to use the line ratio of the blended line 3{p}43d{}4{D}7/{2,5/2}\\to 3{p}5{}2{P}3/2 with another line from Fe x as the density diagnostic should evaluate the effect of the magnetic-field-induced transition line.

  8. Atomic scale visualization of novel magnetic phase transitions in Fe-based superconductor Sr4V2O6Fe2As2

    Science.gov (United States)

    Choi, Seokhwan; Jang, Won-Jun; Ok, Jong Mok; Choi, Hyun Woo; Lee, Hyun Jung; Jung, Jin Oh; Son, Dong Hyun; Suh, Hwan Soo; Kim, Jun Sung; Semertzidis, Yannis K.; Lee, Jhinhwan

    Sr4V2O6Fe2As2 consists of superconducting FeAs layers and Mott insulating Sr2VO3 layers, and exhibits superconductivity with Tc near 30 K despite being a parent compound material. Unlike normal Fe-based superconductors, the magnetism of Sr4V2O6Fe2As2 has complexity due to the presence of two magnetic atomic layers of V and Fe; therefore, the issue of magnetism has been actively debated. In this work, we studied the orbital and magnetic phase transitions in the range of 4 K to 180 K using spin-polarized scanning tunneling microscope. We directly observed the changes of charge density waves of V atomic layer related to the nematicity at 150 K, and spin density waves of V atomic layer resulting from spin ordering of underlying Fe atomic layer below 50 K. Moreover, controlling the sample bias voltage, the hysteresis of magnetic domain is observed at 4 K. Our results show key clues to solve controversy about the magnetism of Sr4V2O6Fe2As2.

  9. An analysis of the shape of a luminescence band induced by free electron-to-carbon atom transitions in semi-insulating undoped GaAs crystals

    CERN Document Server

    Glinchuk, K D; Prokhorovich, A V; Strilchuk, O N

    2001-01-01

    The shape of a photoluminescence (band observed due to recombination of free electrons on carbon atoms) in semi-insulating undoped GaAs crystals is analyzed at different temperatures (T=4.8 to 77 K). It is shown that at low temperatures the shape essentially differs from the theoretical one while at high temperatures is very close to it for radiative transitions of free electrons to isolated shallow acceptors. The observed difference of the experimental and theoretical shapes of the photoluminescence band is connected with the broadening of carbon-induced acceptor levels, resulting from the influence of electric fields of randomly distributed ionized acceptors and donors on isolated carbon atoms. Coincidence of the shapes is connected with a considerable in the energy of free carriers

  10. High-resolution resonance Bragg-scattering spectroscopy of an atomic transition from a population difference grating in a vapour cell

    International Nuclear Information System (INIS)

    We present a novel high-resolution backward resonance Bragg-scattering (RBS) spectroscopy from a population difference grating (PDG). The PDG in thermal 87Rb vapour is formed by a standing-wave (SW) pump field, which periodically modulates the space population distributions of two levels in the 87Rb D1 line. A probe beam, having identical frequency and orthogonal polarization with the SW pump field, is Bragg-scattered by the PDG. The Bragg-scattered light is strongest at an atomic transition, and forms an RBS spectrum with a high signal-to-noise and sub-natural linewidth (60% of the natural linewidth). The observed RBS is a type of degenerate four-wave-mixing signal and can also be explained with the coherent superposition of the optical fields Rayleigh-scattered from the oscillating dipole moments of individual atoms on the PDG.

  11. High-resolution Resonance Bragg-scattering spectroscopy of an atomic transition from a population difference grating in a vapor cell

    CERN Document Server

    Wang*, Hai; Li, Shujing; Zhang, Chunhong; Xie, Changde; Peng, Kunchi

    2009-01-01

    The laser spectroscopy with a narrow linewidth and high signal to noise ratio (S/N) is very important in the precise measurement of optical frequencies. Here, we present a novel high-resolution backward resonance Bragg-scattering (RBS) spectroscopy from a population difference grating (PDG). The PDG is formed by a standing-wave (SW) pump field in thermal 87Rb vapor, which periodically modulates the space population distribution of two levels in the 87Rb D1 line. A probe beam, having the identical frequency and the orthogonal polarization with the SW pump field, is Bragg-scattered by the PDG. Such Bragg-scattered light becomes stronger at an atomic resonance transition, which forms the RBS spectrum with a high S/N and sub-natural linewidth. Using the scheme of the coherent superposition of the individual Rayleigh-scattered light emitted from the atomic dipole oscillators on the PDG, the experimentally observed RBS spectroscopy is theoretically explained.

  12. High-resolution resonance Bragg-scattering spectroscopy of an atomic transition from a population difference grating in a vapour cell

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hai; Yang, Xudong; Zhang, Ling; Li, Shujing; Zhang, Chunhong; Xie, Changde; Peng, Kunchi, E-mail: wanghai@sxu.edu.c [The State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006 (China)

    2010-07-14

    We present a novel high-resolution backward resonance Bragg-scattering (RBS) spectroscopy from a population difference grating (PDG). The PDG in thermal {sup 87}Rb vapour is formed by a standing-wave (SW) pump field, which periodically modulates the space population distributions of two levels in the {sup 87}Rb D1 line. A probe beam, having identical frequency and orthogonal polarization with the SW pump field, is Bragg-scattered by the PDG. The Bragg-scattered light is strongest at an atomic transition, and forms an RBS spectrum with a high signal-to-noise and sub-natural linewidth (60% of the natural linewidth). The observed RBS is a type of degenerate four-wave-mixing signal and can also be explained with the coherent superposition of the optical fields Rayleigh-scattered from the oscillating dipole moments of individual atoms on the PDG.

  13. Adsorption behavior of hexadecyltrimethylammonium bromide (CTAB) to mica substrates as observed by atomic force microscopy

    Institute of Scientific and Technical Information of China (English)

    ZHAO Feng; DU Yukou; YANG Ping; LI Xingchang; TANG Ji'an

    2005-01-01

    Atomic force microscopy is employed to study the adsorption behavior of CTAB to mica surfaces. Results show that conformational transitions from globular micelles→cylindrical micelles→flat films are observed in the process of the adsorption of CTAB to mica at twice the bulk critical concentration. However, in 0.5 cmc CTAB solution, the adsorbed CTAB molecules to mica form the layered film structures, and apparent conformational transitions do not appear. Meanwhile, the phenomena of the adsorption of CTAB to mica and the dissociation of mica surfaces are periodically observed.

  14. Interaction-induced quantum phase revivals and evidence for the transition to the quantum chaotic regime in 1D atomic Bloch oscillations.

    Science.gov (United States)

    Meinert, F; Mark, M J; Kirilov, E; Lauber, K; Weinmann, P; Gröbner, M; Nägerl, H-C

    2014-05-16

    We study atomic Bloch oscillations in an ensemble of one-dimensional tilted superfluids in the Bose-Hubbard regime. For large values of the tilt, we observe interaction-induced coherent decay and matter-wave quantum phase revivals of the Bloch oscillating ensemble. We analyze the revival period dependence on interactions by means of a Feshbach resonance. When reducing the value of the tilt, we observe the disappearance of the quasiperiodic phase revival signature towards an irreversible decay of Bloch oscillations, indicating the transition from regular to quantum chaotic dynamics.

  15. Optical to ultraviolet spectra of sandwiches of benzene and transition metal atoms: Time dependent density functional theory and many-body calculations

    DEFF Research Database (Denmark)

    Martinez, Jose Ignacio; García Lastra, Juan Maria; Lopez, M. J.;

    2010-01-01

    The optical spectra of sandwich clusters formed by transition metal atoms (titanium, vanadium, and chromium) intercalated between parallel benzene molecules have been studied by time-dependent density functional theory (TDDFT) and many-body perturbation theory. Sandwiches with different number...... the optical properties according to specific functionality targets. The differences in the spectra could be used to identify relative abundances of isomers with different spins in experimental studies. As a salient feature, this theoretical spectroscopic analysis predicts the metallization of the infinite (Ti...

  16. α-Helical to β-Helical Conformation Change in the C-Terminal of the Mammalian Prion Protein

    Science.gov (United States)

    Singh, Jesse; Whitford, Paul; Hayre, Natha; Cox, Daniel; Onuchic, José.

    2011-03-01

    We employ all-atom structure-based models with mixed basis contact maps to explore whether there are any significant geometric or energetic constraints limiting conjectured conformational transitions between the alpha-helical (α H) and the left handed beta helical (LHBH) conformations for the C-terminal (residues 166-226) of the mammalian prion protein. The LHBH structure has been proposed to describe infectious oligomers and one class of in vitro grown fibrils, as well as possibly self- templating the conversion of normal cellular prion protein to the infectious form. Our results confirm that the kinetics of the conformation change are not strongely limited by large scale geometry modification and there exists an overall preference for the LHBH conformation.

  17. Relativistic Configuration Interaction calculations of the atomic properties of selected transition metal positive ions; Ni II, V II and W II

    Science.gov (United States)

    Abdalmoneam, Marwa Hefny

    Relativistic Configuration Interaction (RCI) method has been used to investigate atomic properties of the singly ionized transition metals including Nickel (Ni II), Vanadium (V II), and Tungsten (W II). The methodology of RCI computations was also improved. Specifically, the method to shift the energy diagonal matrix of the reference configurations was modified which facilitated including the effects of many electronic configurations that used to be difficult to be included in the energy matrix and speeded-up the final calculations of the bound and continuum energy spectrum. RCI results were obtained for three different cases: i. Atomic moments and polarizabilities of Ni II; ii. Hyperfine structure constants of V II; iii. Lifetime, Lande g-values, and Oscillator strength of W II. Four atomic quantities of Ni II were calculated; scalar dipole polarizability, off-diagonal electric dipole polarizability, non-adiabatic scalar dipole polarizability, and quadrupole polarizability of Ni II. These quantities appear as effective parameters in an effective potential model. These quantities are computed for the first time. The two hyperfine structure (HFS) constants ; magnetic dipole interaction constant, A, and the electric quadrupole interaction constant, B, have been calculated for the V II 3d4, 3d3 4s, and 3d 2 4s2 J=1 to 5 even parity states . Analysis of the results shows the sum of HFS A of nearby energy levels to be conserved. The Lande g-value and the vector composition percentages for all the wavefunctions of those configurations have also been calculated. RCI results are in good agreement with most of the available experimental data. Lifetimes of 175 decay branches in W II have been calculated. Also, Lande g-values have been calculated for all measured W II odd parity levels J=1/2-11/2. The RCI oscillator strengths and branching fraction values of the lowest 10 energy levels for each odd parity J are presented. The calculated results are only in semi

  18. A double-interferometer laser system for cold 87Rb atom gyroscopes based on stimulated Raman transitions

    CERN Document Server

    Song, Ningfang; Li, Wei; Li, Yang; Liu, Jixun; Xu, Xiaobin; Pan, Xiong

    2014-01-01

    We proposed and implemented a double-interferometer laser system to manipulate cold 87Rb atoms to interfere. A frequency-modulated continuous-wave technique was applied to determine and compensate the optical path difference between the two Raman beams. With a coherent self-heterodyne method, the beat signal's FWHM linewidth was measured and the obtained linewidth of ~1Hz mainly limited by the resolution bandwidth of the spectrum analyzer indicates a good coherence degree of the two Raman beams, paving the way to realize a highly sensitive atom gyroscope.

  19. Combined Use of Residual Dipolar Couplings and Solution X-ray Scattering To Rapidly Probe Rigid-Body Conformational Transitions in a Non-phosphorylatable Active-Site Mutant of the 128 kDa Enzyme I Dimer

    Energy Technology Data Exchange (ETDEWEB)

    Takayama, Yuki; Schwieters, Charles D.; Grishaev, Alexander; Ghirlando, Rodolfo; Clore, G. Marius (NIH)

    2012-10-23

    The first component of the bacterial phosphotransferase system, enzyme I (EI), is a multidomain 128 kDa dimer that undergoes large rigid-body conformational transitions during the course of its catalytic cycle. Here we investigate the solution structure of a non-phosphorylatable active-site mutant in which the active-site histidine is substituted by glutamine. We show that perturbations in the relative orientations and positions of the domains and subdomains can be rapidly and reliably determined by conjoined rigid-body/torsion angle/Cartesian simulated annealing calculations driven by orientational restraints from residual dipolar couplings and shape and translation information afforded by small- and wide-angle X-ray scattering. Although histidine and glutamine are isosteric, the conformational space available to a Gln side chain is larger than that for the imidazole ring of His. An additional hydrogen bond between the side chain of Gln189 located on the EIN{sup {alpha}/{beta}} subdomain and an aspartate (Asp129) on the EIN{sup {alpha}} subdomain results in a small ({approx}9{sup o}) reorientation of the EIN{sup {alpha}} and EIN{sup {alpha}/{beta}} subdomains that is in turn propagated to a larger reorientation ({approx}26{sup o}) of the EIN domain relative to the EIC dimerization domain, illustrating the positional sensitivity of the EIN domain and its constituent subdomains to small structural perturbations.

  20. On the stochastic dynamics of molecular conformation

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    An important functioning mechanism of biological macromolecules is the transition between different conformed states due to thermal fluctuation. In the present paper, a biological macromolecule is modeled as two strands with side chains facing each other, and its stochastic dynamics including the statistics of stationary motion and the statistics of conformational transition is studied by using the stochastic averaging method for quasi Hamiltonian systems. The theoretical results are confirmed with the results from Monte Carlo simulation.

  1. The Transition from Atomic to Molecular Hydrogen in Interstellar Clouds: 21cm Signature of the Evolution of Cold Atomic Hydrogen in Dense Clouds

    CERN Document Server

    Goldsmith, P F; Krco, M; Goldsmith, Paul F.; Li, Di; Krco, Marko

    2006-01-01

    We have investigated the time scale for formation of molecular clouds by examining the conversion of HI to H2 using a time-dependent model. H2 formation on dust grains and cosmic ray and photo destruction are included in one-dimensional model slab clouds which incorporate time-independent density and temperature distributions. We calculate 21cm spectral line profiles seen in absorption against a background provided by general Galactic HI emission, and compare the model spectra with HI Narrow Self-Absorption, or HINSA, profiles absorbed in a number of nearby molecular clouds. The time evolution of the HI and H2 densities is dramatic, with the atomic hydrogen disappearing in a wave propagating from the central, denser regions which have a shorter H2 formation time scale, to the edges, where the density is lower and the time scale for H2 formation longer. The model 21cm spectra are characterized by very strong absorption at early times, when the HI column density through the model clouds is extremely large. The ...

  2. Theoretical investigation on the geometries of DOTA and DOTA-like complexes and on the transition states of their conformational equilibria

    International Nuclear Information System (INIS)

    Computations, mostly at the RHF level, have been performed on La3+ and Y3+ model complexes of the widely used DOTA ligand [DOTA 1,4,7,10-tetra-aza-1,4,7,10-tetrakis(carboxy-methyl)cyclo-dodecane] for the purpose of identifying properties of the transition states of geometrical isomer inter-conversions, which have been the object of numerous NMR studies. An analogous study has been carried out on model complexes of the same tri-cations formed by the DOTA-like ligand 1,7-bis(1-methyl-imidazole-2-ylmethyl)-4,10-bis(carboxy-methyl)-1 4,7,10-tetra-aza-cyclo-dodecane, LH2. Features of the transition states for the two types of systems are compared. (authors)

  3. Plastic-to-Elastic Transition in Aggregated Emulsion Networks, Studied with Atomic Force Microscopy-Confocal Scanning Laser Microscopy Microrheology

    NARCIS (Netherlands)

    Filip, D.; Duits, M.H.G.; Uricanu, V.I.; Mellema, J.

    2006-01-01

    In this paper, we demonstrate how the simultaneous application of atomic force microscopy (AFM) and confocal scanning laser microscopy (CSLM) can be used to characterize the (local) rheological properties of soft condensed matter at micrometer length scales. Measurement of AFM force curves as a func

  4. Atomic Spectral Methods for Ab Initio Molecular Electronic Energy Surfaces: Transitioning From Small-Molecule to Biomolecular-Suitable Approaches.

    Science.gov (United States)

    Mills, Jeffrey D; Ben-Nun, Michal; Rollin, Kyle; Bromley, Michael W J; Li, Jiabo; Hinde, Robert J; Winstead, Carl L; Sheehy, Jeffrey A; Boatz, Jerry A; Langhoff, Peter W

    2016-08-25

    Continuing attention has addressed incorportation of the electronically dynamical attributes of biomolecules in the largely static first-generation molecular-mechanical force fields commonly employed in molecular-dynamics simulations. We describe here a universal quantum-mechanical approach to calculations of the electronic energy surfaces of both small molecules and large aggregates on a common basis which can include such electronic attributes, and which also seems well-suited to adaptation in ab initio molecular-dynamics applications. In contrast to the more familiar orbital-product-based methodologies employed in traditional small-molecule computational quantum chemistry, the present approach is based on an "ex-post-facto" method in which Hamiltonian matrices are evaluated prior to wave function antisymmetrization, implemented here in the support of a Hilbert space of orthonormal products of many-electron atomic spectral eigenstates familiar from the van der Waals theory of long-range interactions. The general theory in its various forms incorporates the early semiempirical atoms- and diatomics-in-molecules approaches of Moffitt, Ellison, Tully, Kuntz, and others in a comprehensive mathematical setting, and generalizes the developments of Eisenschitz, London, Claverie, and others addressing electron permutation symmetry adaptation issues, completing these early attempts to treat van der Waals and chemical forces on a common basis. Exact expressions are obtained for molecular Hamiltonian matrices and for associated energy eigenvalues as sums of separate atomic and interaction-energy terms, similar in this respect to the forms of classical force fields. The latter representation is seen to also provide a long-missing general definition of the energies of individual atoms and of their interactions within molecules and matter free from subjective additional constraints. A computer code suite is described for calculations of the many-electron atomic eigenspectra and

  5. Non-conformable, partial and conformable transposition

    DEFF Research Database (Denmark)

    König, Thomas; Mäder, Lars Kai

    2013-01-01

    Although member states are obliged to transpose directives into domestic law in a conformable manner and receive considerable time for their transposition activities, we identify three levels of transposition outcomes for EU directives: conformable, partially conformable and non-conformable...... and the Commission regarding a directive’s outcome, play a much more strategic role than has to date acknowledged in the transposition literature. Whereas disagreement of a member state delays conformable transposition, it speeds up non-conformable transposition. Disagreement of the Commission only prolongs...

  6. Repumping and spectroscopy of laser-cooled Sr atoms using the (5s5p){sup 3}P{sub 2}-(5s4d){sup 3}D{sub 2} transition

    Energy Technology Data Exchange (ETDEWEB)

    Mickelson, P G; De Escobar, Y N Martinez; Anzel, P; DeSalvo, B J; Nagel, S B; Traverso, A J; Yan, M; Killian, T C, E-mail: killian@rice.ed [Department of Physics and Astronomy, Rice University, Houston, TX 77251 (United States)

    2009-12-14

    We describe repumping and spectroscopy of laser-cooled strontium (Sr) atoms using the (5s5p){sup 3}P{sub 2}-(5s4d){sup 3}D{sub 2} transition. Atom number in a magneto-optical trap is enhanced by driving this transition because Sr atoms that have decayed into the (5s5p){sup 3}P{sub 2} dark state are repumped back into the (5s{sup 2}){sup 1}S{sub 0} ground state. Spectroscopy of {sup 84}Sr, {sup 86}Sr, {sup 87}Sr and {sup 88}Sr improves the value of the (5s5p){sup 3}P{sub 2}-(5s4d){sup 3}D{sub 2} transition frequency and determines the isotope shifts for the transition accurately enough to guide laser-cooling experiments with less abundant isotopes.

  7. Remote sensing of atomic oxygen - Some observational difficulties in the use of the forbidden O I 1173-A and O I 1641-A transitions

    Science.gov (United States)

    Erdman, P. W.; Zipf, E. C.

    1987-01-01

    Recent sounding rocket and satellite studies suggest that simultaneous measurements of the O I 989-A and 1304-A resonance lines and of the forbidden 1172.6-A and 1641.3-A transitions would form the basis of a useful remote sensing technique for measuring the O I density and optical opacity of a planetary or stellar atmosphere. Because the 1172.6-A and 1641.3-A emissions are weak lines and are emitted in a wavelength region rich in spectral features, it is important to determine whether typical flight instruments can make measurements with sufficient spectral purity so that the remote sensing observations will yield accurate results. A detailed, high-resolution study of the far UV emission features in the regions surrounding the atomic oxygen transitions at 1172.6 and 1641.3 A was made. These spectra, which were excited by electron impact on O2 and N2, are presented in an attempt to display some potential sources of interference in aeronomical measurements of these O I lines. Both atomic and molecular emissions are found, and the spectral resolution necessary to make unambiguous measurements is discussed.

  8. Observation of the Forbidden Magnetic Dipole Transition 6{sup 2}P{sub ½} --> 7{sup 2}P{sub ½} in Atomic Thallium

    Science.gov (United States)

    Chu, S.

    1976-10-01

    A measurement of the 6{sup 2}P{sub ½} --> 7{sup 2}P{sub ½} forbidden magnetic dipole matrix element in atomic thallium is described. A pulsed, linearly polarized dye laser tuned to the transition frequency is used to excite the thallium vapor from the 6{sup 2}P{sub ½} ground state to the 7{sup 2}P{sub ½} excited state. Interference between the magnetic dipole M1 amplitude and a static electric field induced E1 amplitude results in an atomic polarization of the 7{sup 2}P{sub ½} state, and the subsequent circular polarization of 535 nm fluorescence. The circular polarization is seen to be proportional to / as expected, and measured for several transitions between hyperfine levels of the 6{sup 2}P{sub ½} and 7{sup 2}P{sub ½} states. The result is = -(2.11 +- 0.30) x 10{sup -5} parallel bar e parallel bar dirac constant/2mc, in agreement with theory.

  9. First-principles modeling of 3d-transition-metal-atom adsorption on silicene: a linear-response DFT  +  U approach

    International Nuclear Information System (INIS)

    By employing DFT  +  U calculations with the linear response method, we investigate the interactions between various 3d transition-metal atoms (Cr, Mn, Fe, Co) and silicene. In the cases of two-dimensional (2D) FeSi2 and CoSi2, the metal atoms tend to penetrate into the silicene layer. While CoSi2 is non-magnetic, FeSi2 exhibits a total magnetic moment of 2.21 μ B/cell. Upon the examination of 2D MSi6, a trend in anti-ferromagnetic (AFM) favorability in the z-direction is observed according to our DFT  +  U calculations. In the ferromagnetic (FM) states (less stable), each primary unit cell of CrSi6, MnSi6, and FeSi6 possesses different levels of total magnetization (4.01, 5.18, and 2.00 μ B/cell, respectively). The absolute magnetization given by AFM MSi6 structures varies in the range of 5.33–5.84 μ B/cell. A direct band gap in AFM MnSi6 (0.2 eV) is predicted, while the metastable FM FeSi6 structure has a wider band gap (0.85 eV). Interestingly, there are superexchange interactions between metal atoms in the MSi6 systems, which result in the AFM alignments. (paper)

  10. Excitation of the hyperfine transitions of atomic hydrogen, deuterium, and ionized helium 3 by Lyman-alpha radiation

    Energy Technology Data Exchange (ETDEWEB)

    Deguchi, S.; Watson, W.D.

    1985-03-01

    The profile of Lyman-alpha radiation in an expanding gas cloud is calculated in detail in order to determine the color temperature of the radiation scattered by an H I atom within the cloud. The basic methods used include a Sobolov-like treatment and the application of a redistribution function for the scattering that preserves detailed balance when the recoil of the atom is included. It is found that for hydrogen the color temperature approaches the kinetic temperature above tau(L) of 100,000, while for deuterium it tends to be well below the kinetic temperature for tau(L) of about a billion or less, becoming comparable to 3 K for some tau(L). For He-3 ion, the color temperature can become negative. 41 references.

  11. Conformal transformations and conformal invariance in gravitation

    CERN Document Server

    Dabrowski, Mariusz P; Blaschke, David B

    2008-01-01

    Conformal transformations are frequently used tools in order to study relations between various theories of gravity and Einstein relativity. Because of that, in this paper we discuss the rules of conformal transformations for geometric quantities in general relativity. In particular, we discuss the conformal transformations of the matter energy-momentum tensor. We thoroughly discuss the latter and show the subtlety of the conservation law (i.e., the geometrical Bianchi identity) imposed in one of the conformal frames in reference to the other. The subtlety refers to the fact that conformal transformation ``creates'' an extra matter term composed of the conformal factor which enters the conservation law. In an extreme case of the flat original spacetime the matter is ``created'' due to work done by the conformal transformation to bend the spacetime which was originally flat. We also discuss how to construct the conformally invariant gravity which, in the simplest version, is a special case of the Brans-Dicke t...

  12. Suppression of angular momentum transfer in cold collisions of transition metal atoms in ground States with nonzero orbital angular momentum.

    Science.gov (United States)

    Hancox, Cindy I; Doret, S Charles; Hummon, Matthew T; Krems, Roman V; Doyle, John M

    2005-01-14

    The Zeeman relaxation rate in cold collisions of Ti(3d(2)4s(2) 3F2) with He is measured. We find that collisional transfer of angular momentum is dramatically suppressed due to the presence of the filled 4s(2) shell. The degree of electronic interaction anisotropy, which is responsible for Zeeman relaxation, is estimated to be about 200 times smaller in the Ti-He complex than in He complexes with typical non-S-state atoms.

  13. Implementation of a k/k0 method to identify long-range structure in transition states during conformational folding/unfolding of proteins

    Science.gov (United States)

    Pradeep, Lovy; Kurinov, Igor; Ealick, Steven E.; Scheraga, Harold A.

    2007-01-01

    Summary A previously-introduced kinetic-rate constant (k/k0) method, where k and k0 are the folding (unfolding) rate constants in the mutant and the wild-type forms, respectively, of a protein, has been applied to obtain qualitative information about structure in the transition state (TS) ensemble of bovine pancreatic ribonuclease A (RNase A) which contains four native disulfide bonds. The method compares the folding (unfolding) kinetics of two versions of RNase A, with and without a covalent crosslink (in the form of a fifth disulfide bond); the method tests whether the crosslinked residues are associated in the folding (unfolding) transition state of the non-crosslinked version. To confirm that the fifth disulfide bond has not introduced a significant structural perturbation, we solved the crystal structure of the V43C-R85C mutant to 1.6 Å resolution. Our findings suggest that residues Val 43 and Arg 85 are not associated in the folding (unfolding) TS ensemble of RNase A, and also that Ala 4 and Val 118 may form non-native contacts in the folding (unfolding) TS ensemble. PMID:17937908

  14. Implementation of a k/k(0) method to identify long-range structure in transition states during conformational folding/unfolding of proteins.

    Science.gov (United States)

    Pradeep, Lovy; Kurinov, Igor; Ealick, Steven E; Scheraga, Harold A

    2007-10-01

    A previously introduced kinetic-rate constant (k/k(0)) method, where k and k(0) are the folding (unfolding) rate constants in the mutant and the wild-type forms, respectively, of a protein, has been applied to obtain qualitative information about structure in the transition state ensemble (TSE) of bovine pancreatic ribonuclease A (RNase A), which contains four native disulfide bonds. The method compares the folding (unfolding) kinetics of RNase A, with and without a covalent crosslink and tests whether the crosslinked residues are associated in the folding (unfolding) transition state (TS) of the noncrosslinked version. To confirm that the fifth disulfide bond has not introduced a significant structural perturbation, we solved the crystal structure of the V43C-R85C mutant to 1.6 A resolution. Our findings suggest that residues Val43 and Arg85 are not associated, and that residues Ala4 and Val118 may form nonnative contacts, in the folding (unfolding) TSE of RNase A. PMID:17937908

  15. Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods

    Science.gov (United States)

    Balabanov, Nikolai B.; Peterson, Kirk A.

    2006-08-01

    Recently developed correlation consistent basis sets for the first row transition metal elements Sc-Zn have been utilized to determine complete basis set (CBS) scalar relativistic electron affinities, ionization potentials, and 4s23dn -2-4s1dn -1 electronic excitation energies with single reference coupled cluster methods [CCSD(T), CCSDT, and CCSDTQ] and multireference configuration interaction with three reference spaces: 3d4s, 3d4s4p, and 3d4s4p3d'. The theoretical values calculated with the highest order coupled cluster techniques at the CBS limit, including extrapolations to full configuration interaction, are well within 1kcal/mol of the corresponding experimental data. For the early transition metal elements (Sc-Mn) the internally contracted multireference averaged coupled pair functional method yielded excellent agreement with experiment; however, the atomic properties for the late transition metals (Mn-Zn) proved to be much more difficult to describe with this level of theory, even with the largest reference function of the present work.

  16. Binding, conformational transition and dimerization of amyloid-β peptide on GM1-containing ternary membrane: insights from molecular dynamics simulation.

    Directory of Open Access Journals (Sweden)

    Moutusi Manna

    Full Text Available Interactions of amyloid-β (Aβ with neuronal membrane are associated with the progression of Alzheimer's disease (AD. Ganglioside GM1 has been shown to promote the structural conversion of Aβ and increase the rate of peptide aggregation; but the exact nature of interaction driving theses processes remains to be explored. In this work, we have carried out atomistic-scale computer simulations (totaling 2.65 µs to investigate the behavior of Aβ monomer and dimers in GM1-containing raft-like membrane. The oligosaccharide head-group of GM1 was observed to act as scaffold for Aβ-binding through sugar-specific interactions. Starting from the initial helical peptide conformation, a β-hairpin motif was formed at the C-terminus of the GM1-bound Aβ-monomer; that didn't appear in absence of GM1 (both in fluid POPC and liquid-ordered cholesterol/POPC bilayers and also in aqueous medium within the simulation time span. For Aβ-dimers, the β-structure was further enhanced by peptide-peptide interactions, which might influence the propensity of Aβ to aggregate into higher-ordered structures. The salt-bridges and inter-peptide hydrogen bonds were found to account for dimer stability. We observed spontaneous formation of intra-peptide D(23-K(28 salt-bridge and a turn at V(24GSN(27 region - long been accepted as characteristic structural-motifs for amyloid self-assembly. Altogether, our results provide atomistic details of Aβ-GM1 and Aβ-Aβ interactions and demonstrate their importance in the early-stages of GM1-mediated Aβ-oligomerisation on membrane surface.

  17. Two Keggin-type heteropolytungstates with transition metal as a central atom: Crystal structure and magnetic study with 2D-IR correlation spectroscopy

    International Nuclear Information System (INIS)

    Two Keggin-type heteropolytungstates, [Co(phen)3]3[CoW12O40]·9H2O 1 (phen=1,10-phenanthroline) and [Fe(phen)3]2[FeW12O40]·H3O·H2O 2, have been synthesized via the hydrothermal technique and characterized by single crystal X-ray diffraction analyses, IR, XPS, TG analysis, UV–DRS, XRD, thermal-dependent and magnetic-dependent 2D-COS IR (two-dimensional infrared correlation spectroscopy). Crystal structure analysis reveals that the polyanions in compound 1 are linked into 3D supramolecule through hydrogen bonding interactions between lattice water molecules and terminal oxygen atoms of polyanion units, and [Co(phen)3]2+ cations distributed in the polyanion framework with many hydrogen bonding interactions. The XPS spectra indicate that all the Co atoms in 1 are +2 oxidation state, the Fe atoms in 2 existing with +2 and +3 mixed oxidation states. - Graphical abstract: The magnetic-dependent synchronous 2D correlation IR spectra of 1 (a), 2 (b) over 0–50 mT in the range of 600–1000 cm−1, the obvious response indicate two Keggin polyanions skeleton susceptible to applied magnetic field. - Highlights: • Two Keggin-type heteropolytungstates with transition metal as a central atom has been obtained. • Compound 1 forms into 3D supramolecular architecture through hydrogen bonding between water molecules and polyanions. • Magnetic-dependent 2D-IR correlation spectroscopy was introduced to discuss the magnetism of polyoxometalate

  18. Four complete turns of a curved 3₁₀-helix at atomic resolution: the crystal structure of the peptaibol trichovirin I-4A in a polar environment suggests a transition to α-helix for membrane function.

    Science.gov (United States)

    Gessmann, Renate; Axford, Danny; Owen, Robin L; Brückner, Hans; Petratos, Kyriacos

    2012-02-01

    The first crystal structure of a member of peptaibol antibiotic subfamily 4, trichovirin I-4A (14 residues), has been determined by direct methods and refined at atomic resolution. The monoclinic unit cell has two molecules in the asymmetric unit. Both molecules assume a 3₁₀ right-handed helical conformation and are significantly bent. The molecules pack loosely along the crystallographic twofold axis, forming two large tunnels between symmetry-related molecules in which no ordered solvent could be located. Carbonyl O atoms which are not involved in intramolecular hydrogen bonding participate in close van der Waals interactions with apolar groups. The necessary amphipathicity for biological activity of peptaibols is not realised in the crystal structure. Hence, a structural change of trichovirin to an α-helical conformation is proposed for membrane integration and efficient water/ion transportation across the lipid bilayer.

  19. Conformal isoparametric hypersurfaces with two distinct conformal principal curvatures in conformal space

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The conformal geometry of regular hypersurfaces in the conformal space is studied.We classify all the conformal isoparametric hypersurfaces with two distinct conformal principal curvatures in the conformal space up to conformal equivalence.

  20. 锶原子互组跃迁中原子相干谱的实验观测%Observation of Atomic Coherence in Intercombination Transition Line of Strontium Atom

    Institute of Scientific and Technical Information of China (English)

    王叶兵; 丛东亮; 许朋; 田晓; 常宏

    2013-01-01

    在热原子束中利用锶原子互组跃迁塞曼子能级构成的V型能级结构,通过荧光观测实验研究了互组跃迁中的原子相干效应.对互组跃迁简并能级构成的V型能级结构的电磁诱导透明(EIT)效应进行了理论计算,且详细分析了耦合光失谐、线宽和拉比频率对互组跃迁EIT效应的影响.实验测量了不同耦合光失谐和功率条件下的互组跃迁电磁诱导透明效应.%The atomic coherence effect is investigated experimentally in the thermal strontium atomic beam by means of fluorescence observing, based on the V-type Zeeman-sublevel system of intercombination line of Sr. A theoretical calculation of the V-type electromagnetically induced transparency (EIT) has been elaborated, taking into account the effect of detuning, linewidth and Rabi frequency of the coupling laser on intercombination transition EIT. The V-type electromagnetically induced transparency of intercombination is measured experimentally under different condition of detuning and with different powers of the coupling laser.

  1. Ultracold lithium-6 atoms in the BEC-BCS crossover: experiments and the construction of a new apparatus; Atomes de lithium-6 ultra froids dans la transition BEC-BCS: experiences et construction d'un montage experimental

    Energy Technology Data Exchange (ETDEWEB)

    Teichmann, M

    2007-09-15

    We use a fermionic gas of Lithium-6 as a model system to study superfluidity. The limiting cases of superfluidity are Bose-Einstein condensation (BEC) and superconductivity, described by the theory by Bardeen, Cooper and Schrieffer (BCS). In Lithium-6 gases, we can explore the whole range between the two cases, known as the BEC-BCS crossover, using a Feshbach resonance. We study the change of the momentum distribution of the gas in this cross-over and compare to theoretical models. We also investigate the hydrodynamic expansion, characteristic for a superfluid gas. We observe a sudden change of the ellipticity of the gas close to the transition to the superfluid phase. Moreover, we localized heteronuclear Feshbach resonances between {sup 6}Li and {sup 7}Li. We are currently constructing a second generation of the experimental setup. An new laser system, based on high power laser diodes, was developed. Changes in the vacuum chamber, including a complete reconstruction of the Zeeman slower, have increased the atomic flux, allowing us to increase the repetition rate of our experiment. Modifications of the geometry of the magnetic traps lead to a higher number of trapped atoms. (author)

  2. Suppression of angular momentum transfer in cold collisions of transition metal atoms in ground States with nonzero orbital angular momentum.

    Science.gov (United States)

    Hancox, Cindy I; Doret, S Charles; Hummon, Matthew T; Krems, Roman V; Doyle, John M

    2005-01-14

    The Zeeman relaxation rate in cold collisions of Ti(3d(2)4s(2) 3F2) with He is measured. We find that collisional transfer of angular momentum is dramatically suppressed due to the presence of the filled 4s(2) shell. The degree of electronic interaction anisotropy, which is responsible for Zeeman relaxation, is estimated to be about 200 times smaller in the Ti-He complex than in He complexes with typical non-S-state atoms. PMID:15698077

  3. Reactivity of transition metal atoms supported or not on TiO2(110) toward CO and H adsorption

    KAUST Repository

    Helali, Zeineb

    2015-04-01

    Following our strategy to analyze the metal–support interaction, we present periodic DFT calculations for adsorption of metal atoms on a perfect rutile TiO2(110) surface (at low coverage, θ = 1/3) to investigate the interaction of an individual metal atom, M, with TiO2 and its consequence on the coadsorption of H and CO over M/TiO2. M under investigation varies in a systematic way from K to Zn. It is found that the presence of the support decreases or increases the strength of M–H or M–CO interaction according to the nature of M. The site of the adsorption for H and the formation of HCO/M also depend on M. From the left- to the right-hand side of the period, C and O both interact while O progressively detaches from M. On the contrary, for M = Fe–Cu, CO dissociation is more likely to happen. For CO and H coadsorption, two extreme cases emerge: For Ni, the hydrogen adsorbed should easily move on the support and CO dissociation is more likely. For Ti or Sc, H is easily coadsorbed with CO on the metal and CO hydrogenation could be the initial step. © 2015, Springer-Verlag Berlin Heidelberg.

  4. Real-time visualization of conformational changes within single MloK1 cyclic nucleotide-modulated channels.

    Science.gov (United States)

    Rangl, Martina; Miyagi, Atsushi; Kowal, Julia; Stahlberg, Henning; Nimigean, Crina M; Scheuring, Simon

    2016-09-20

    Eukaryotic cyclic nucleotide-modulated (CNM) ion channels perform various physiological roles by opening in response to cyclic nucleotides binding to a specialized cyclic nucleotide-binding domain. Despite progress in structure-function analysis, the conformational rearrangements underlying the gating of these channels are still unknown. Here, we image ligand-induced conformational changes in single CNM channels from Mesorhizobium loti (MloK1) in real-time, using high-speed atomic force microscopy. In the presence of cAMP, most channels are in a stable conformation, but a few molecules dynamically switch back and forth (blink) between at least two conformations with different heights. Upon cAMP depletion, more channels start blinking, with blinking heights increasing over time, suggestive of slow, progressive loss of ligands from the tetramer. We propose that during gating, MloK1 transitions from a set of mobile conformations in the absence to a stable conformation in the presence of ligand and that these conformations are central for gating the pore.

  5. Relativistic Calculation Of K$\\beta$ Hypersatellite Energies and Transition Probabilities for Selected Atoms with 13<=Z<=80

    CERN Document Server

    Costa, A M; Santos, J P; Indelicato, P J; Parente, F; Indelicato, Paul

    2006-01-01

    Energies and transition probabilities of K$\\beta$ hypersatellite lines are computed using the Dirac-Fock model for several values of $Z$ throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the K$\\beta\\_{1}^{\\rm h}$/K$\\beta\\_{3}^{\\rm h}$ intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.

  6. Calculation of total excitation cross section in the collision of bare ions with atomic hydrogen for transition from ground to and states using Born-Faddeev approximation

    Directory of Open Access Journals (Sweden)

    R Fathi

    2013-09-01

    Full Text Available  In this work, total excitation cross section of atomic hydrogen in the collision of bare ion was calculated employing a three body Faddeev formalism. In the present calculation, initially the first order electronic amplitude was calculated using the interaction potential which led to inelastic form factor. Secondly, the first order nuclear amplitude was calculated and added to the first order electronic amplitude. This second term was calculated employing the near-the-shell two body transition operator. The interaction energy was assumed to be in the intermediate and high energy limits . Finally, the results were compared with the relevant cross sections calculated under monocentric close-coupling data in the literature.

  7. Dopant-induced 2D-3D transition in small Au-containing clusters: DFT-global optimisation of 8-atom Au-Ag nanoalloys.

    Science.gov (United States)

    Heiles, Sven; Logsdail, Andrew J; Schäfer, Rolf; Johnston, Roy L

    2012-02-21

    A genetic algorithm (GA) coupled with density functional theory (DFT) calculations is used to perform global optimisations for all compositions of 8-atom Au-Ag bimetallic clusters. The performance of this novel GA-DFT approach for bimetallic nanoparticles is tested for structures reported in the literature. New global minimum structures for various compositions are predicted and the 2D-3D transition is located. Results are explained with the aid of an analysis of the electronic density of states. The chemical ordering of the predicted lowest energy isomers are explained via a detailed analysis of the charge separation and mixing energies of the bimetallic clusters. Finally, dielectric properties are computed and the composition and dimensionality dependence of the electronic polarizability and dipole moment is discussed, enabling predictions to be made for future electric beam deflection experiments.

  8. Magnetic dipolar and quadrupolar transitions in two-electron atoms under exponential-cosine-screened Coulomb potential

    Energy Technology Data Exchange (ETDEWEB)

    Modesto-Costa, Lucas; Canuto, Sylvio [Instituto de Física, Universidade de São Paulo, CP 66318, 05314-970 São Paulo (Brazil); Mukherjee, Prasanta K., E-mail: profpkmukherjee@gmail.com [Department of Physics, Ramakrishna Mission Vivekananda University, P.O. Belur Math, Howrah, West Bengal 711202 (India)

    2015-03-15

    A detailed investigation of the magnetic dipolar and quadrupolar excitation energies and transition probabilities of helium isoelectronic He, Be{sup 2+}, C{sup 4+}, and O{sup 6+} have been performed under exponential cosine screened Coulomb potential generated in a plasma environment. The low-lying excited states 1s{sup 2}:{sup 1}S{sup e} → 1sns:{sup 3}S{sup e}{sub 0}, and 1snp:{sup 3}P{sup o}{sub 2} (n = 2, 3, 4, and 5) are considered. The variational time-dependent coupled Hartree-Fock scheme has been used. The effect of the confinement produced by the potential on the structural properties is investigated for increasing coupling strength of the plasma. It is noted that there is a gradual destabilization of the energy of the system with the reduction of the ionization potential and the number of excited states. The effect of the screening enhancement on the excitation energies and transition probabilities has also been investigated and the results compared with those available for the free systems and under the simple screened Coulomb potential.

  9. Conformational Dependence of a Protein Kinase Phosphate Transfer Reaction

    CERN Document Server

    Henkelman, Graeme; Tung, Chang-Shung; Fenimore,, P W; McMahon, Benjamin H

    2004-01-01

    Atomic motions and energetics for a phosphate transfer reaction catalyzed by the cAMP-dependent protein kinase (PKA) are calculated by plane-wave density functional theory, starting from structures of proteins crystallized in both the reactant conformation (RC) and the transition-state conformation (TC). In the TC, we calculate that the reactants and products are nearly isoenergetic with a 0.2 eV barrier; while phosphate transfer is unfavorable by over 1.2 eV in the RC, with an even higher barrier. With the protein in the TC, the motions involved in reaction are small, with only P$_\\gamma$ and the catalytic proton moving more than 0.5 \\AA. Examination of the structures reveals that in the RC the active site cleft is not completely closed and there is insufficient space for the phosphorylated serine residue in the product state. Together, these observations imply that the phosphate transfer reaction occurs rapidly and reversibly in a particular conformation of the protein, and that the reaction can be gated by...

  10. Discovering Conformational Sub-States Relevant to Protein Function

    OpenAIRE

    Ramanathan, Arvind; Savol, Andrej J.; Langmead, Christopher J.; Agarwal, Pratul K.; Chennubhotla, Chakra S.

    2011-01-01

    Background Internal motions enable proteins to explore a range of conformations, even in the vicinity of native state. The role of conformational fluctuations in the designated function of a protein is widely debated. Emerging evidence suggests that sub-groups within the range of conformations (or sub-states) contain properties that may be functionally relevant. However, low populations in these sub-states and the transient nature of conformational transitions between these sub-states present...

  11. Valence correlation in the s2dn, sdn + 1, and dn + 2 states of the first-row transition metal atoms

    Science.gov (United States)

    Botch, Beatrice H.; Dunning, Thom. H., Jr.; Harrison, James F.

    1981-10-01

    The major differential valence correlation effects of the lowest lying states arising from the s2dn, sdn+1, and dn+2 configurations of the first-row transition metal atoms have been characterized using MCSCF and CI procedures. The important correlation effects are found to be, first, angular correlation of the 4s2 pair arising because of the near degeneracy of the 4s and 4p orbitals and, second, radial correlation of the 3d electron pairs. This large differential radial correlation of the 3d electrons can be interpreted as being due to nonequivalent d orbitals in the sdn+1 and dn+2 excited states. Both of these effects can be incorporated into a simple MCSCF wave function that reduces the error in the excited state atomic dissociation limits (˜0.2 eV in Sc-Cr and ˜0.5 eV in Mn-Cu for the sdn+1-s2dn excitation energy), yet still is of a form which lends itself easily to molecular calculations.

  12. EFFECTS OF METAL IONS ON THE CONFORMATIONAL CHANGES OF DNA

    Institute of Scientific and Technical Information of China (English)

    G. Q. Liu; Y.Y. Meng; S.H. Liu; Y.H. Hu

    2005-01-01

    DNA takes on multi-different conformations such as A-, B-, C-, D- and Z-form. These conformations can transit to one another when DNA deposited in some metal ions solutions or when changing the concentrations of the same metal ions. Here, several major conformational transitions of DNA induced by metal ions under different environment were introduced and the mechanism of the interaction of metal ions with DNA was discuss in detail.

  13. Electronic structures and magnetic properties of the transition-metal atoms (Mn, Fe, Co and Ni) doped WS2: A first-principles study

    Science.gov (United States)

    Xie, Ling-Yun; Zhang, Jian-Min

    2016-10-01

    The spin-polarized first-principles calculations are performed to study the electronic structures and magnetic properties of a single or double identical transition metal (TM) atoms X (X = Mn, Fe, Co and Ni) doped monolayer WS2 systems. Although the pristine monolayer WS2 system is a nonmagnetic semiconductor with a direct band gap of 1.820 eV, a single Mn, Fe, Co or Ni doped WS2 systems exhibit the magnetic half-metallic (HM) characters with the total magnetic moments Mtot of 1, 2, 3 and 4 μB and the smaller spin-down gaps Eg of 1.262, 1.154, 1.407 and 1.073 eV, respectively. For double identical TM atoms doped monolayer WS2 systems, except for the cases of two Ni atoms doped at the first (0,1), second (0,2) and third (0,3) nearest-neighbor cation configuration which are antiferromagnetic (AFM), ferromagnetic (FM) and FM metals, respectively, the other cases are all HM ferromagnets, and the total magnetic moment Mtot increases not only for double identical TM dopants Mn, Fe, Co and Ni (except for (0,1) AFM case) successively at the same nearest-neighbor cation configuration but also for each of the double identical TM dopants at the first (0,1), second (0,2) and third (0,3) nearest-neighbor cation configurations successively. These results provide a theoretical guide to choose new two-dimensional HM ferromagnetic materials in spintronic applications.

  14. Interlayer Transition and Infrared Photodetection in Atomically Thin Type-II MoTe₂/MoS₂ van der Waals Heterostructures.

    Science.gov (United States)

    Zhang, Kenan; Zhang, Tianning; Cheng, Guanghui; Li, Tianxin; Wang, Shuxia; Wei, Wei; Zhou, Xiaohao; Yu, Weiwei; Sun, Yan; Wang, Peng; Zhang, Dong; Zeng, Changgan; Wang, Xingjun; Hu, Weida; Fan, Hong Jin; Shen, Guozhen; Chen, Xin; Duan, Xiangfeng; Chang, Kai; Dai, Ning

    2016-03-22

    We demonstrate the type-II staggered band alignment in MoTe2/MoS2 van der Waals (vdW) heterostructures and an interlayer optical transition at ∼1.55 μm. The photoinduced charge separation between the MoTe2/MoS2 vdW heterostructure is verified by Kelvin probe force microscopy (KPFM) under illumination, density function theory (DFT) simulations and photoluminescence (PL) spectroscopy. Photoelectrical measurements of MoTe2/MoS2 vdW heterostructures show a distinct photocurrent response in the infrared regime (1550 nm). The creation of type-II vdW heterostructures with strong interlayer coupling could improve our fundamental understanding of the essential physics behind vdW heterostructures and help the design of next-generation infrared optoelectronics.

  15. Interlayer Transition and Infrared Photodetection in Atomically Thin Type-II MoTe₂/MoS₂ van der Waals Heterostructures.

    Science.gov (United States)

    Zhang, Kenan; Zhang, Tianning; Cheng, Guanghui; Li, Tianxin; Wang, Shuxia; Wei, Wei; Zhou, Xiaohao; Yu, Weiwei; Sun, Yan; Wang, Peng; Zhang, Dong; Zeng, Changgan; Wang, Xingjun; Hu, Weida; Fan, Hong Jin; Shen, Guozhen; Chen, Xin; Duan, Xiangfeng; Chang, Kai; Dai, Ning

    2016-03-22

    We demonstrate the type-II staggered band alignment in MoTe2/MoS2 van der Waals (vdW) heterostructures and an interlayer optical transition at ∼1.55 μm. The photoinduced charge separation between the MoTe2/MoS2 vdW heterostructure is verified by Kelvin probe force microscopy (KPFM) under illumination, density function theory (DFT) simulations and photoluminescence (PL) spectroscopy. Photoelectrical measurements of MoTe2/MoS2 vdW heterostructures show a distinct photocurrent response in the infrared regime (1550 nm). The creation of type-II vdW heterostructures with strong interlayer coupling could improve our fundamental understanding of the essential physics behind vdW heterostructures and help the design of next-generation infrared optoelectronics. PMID:26950255

  16. Atomic physics

    Energy Technology Data Exchange (ETDEWEB)

    Livingston, A.E.; Kukla, K.; Cheng, S. [Univ. of Toledo, OH (United States)] [and others

    1995-08-01

    In a collaboration with the Atomic Physics group at Argonne and the University of Toledo, the Atomic Physics group at the University of Notre Dame is measuring the fine structure transition energies in highly-charged lithium-like and helium-like ions using beam-foil spectroscopy. Precise measurements of 2s-2p transition energies in simple (few-electron) atomic systems provide stringent tests of several classes of current atomic- structure calculations. Analyses of measurements in helium-like Ar{sup 16+} have been completed, and the results submitted for publication. A current goal is to measure the 1s2s{sup 3}S{sub 1} - 1s2p{sup 3}P{sub 0} transition wavelength in helium-like Ni{sup 26+}. Measurements of the 1s2s{sup 2}S{sub 1/2} - 1s2p{sup 2}P{sub 1/2,3/2} transition wavelengths in lithium-like Kr{sup 33+} is planned. Wavelength and lifetime measurements in copper-like U{sup 63+} are also expected to be initiated. The group is also participating in measurements of forbidden transitions in helium-like ions. A measurement of the lifetime of the 1s2s{sup 3}S{sub 1} state in Kr{sup 34+} was published recently. In a collaboration including P. Mokler of GSI, Darmstadt, measurements have been made of the spectral distribution of the 2E1 decay continuum in helium-like Kr{sup 34+}. Initial results have been reported and further measurements are planned.

  17. Conformal transformations and conformal invariance in gravitation

    OpenAIRE

    Dabrowski, Mariusz P.; Garecki, Janusz; Blaschke, David B.

    2008-01-01

    Conformal transformations are frequently used tools in order to study relations between various theories of gravity and the Einstein relativity. In this paper we discuss the rules of these transformations for geometric quantities as well as for the matter energy-momentum tensor. We show the subtlety of the matter energy-momentum conservation law which refers to the fact that the conformal transformation "creates" an extra matter term composed of the conformal factor which enters the conservat...

  18. Hybrid compounds of Keggin polyoxotungstate with transition metal ion as the central atom. Synthesis, structure and properties

    Science.gov (United States)

    Li, Xiao-Min; Chen, Ya-Guang; Shi, Tian

    2016-02-01

    The compounds (Hbipy)2[Co(bipy)2(H2O)4]2(CoW12O40)·2bipy·7H2O (1) and [Ni2(Hbipy)2(bipy)(H2O)4(H2W12O40)]·5H2O (2) (bipy = 4,4-bipyridine) were synthesized hydrothermally and characterized by elemental analysis, IR spectroscopy, TG analyses, solid ultraviolet diffuse spectroscopy and single crystal X-ray diffraction method. In 1 the complex ions, [Co(bipy)2(H2O)4]2+, construct a supramolecular layer through π-π stacking interaction. The heteropolyanions with central Co atom and supramolecular layers are linked by hydrogen bonds. In 2 a 2D structure is formed from metatungstate anions and binuclear Ni-bipy complexes through the coordination of metatungstate anions and bipy to Ni ions. Between the layers and bipyridine molecules are the hydrogen bond interactions. The formation of 1 and 2 shows that the solution acidity and metal ions influence greatly the structure of the compounds. Solid ultraviolet diffusion results indicate that the compounds 1 and 2 are potential semiconductor materials. In 1 and 2 there exists a weak antiferromagnetic interaction.

  19. The Atomic to Molecular Transition and its Relation to the Scaling Properties of Galaxy Disks in the Local Universe

    CERN Document Server

    Fu, Jian; Kauffmann, Guinevere; Krumholz, Mark R

    2010-01-01

    We extend existing semi-analytic models of galaxy formation to track atomic and molecular gas in disk galaxies. Simple recipes for processes such as cooling, star formation, supernova feedback, and chemical enrichment of the stars and gas are grafted on to dark matter halo merger trees derived from the Millennium Simulation. Each galactic disk is represented by a series of concentric rings. We assume that surface density profile of infalling gas in a dark matter halo is exponential, with scale radius r_d that is proportional to the virial radius of the halo times its spin parameter $\\lambda$. As the dark matter haloes grow through mergers and accretion, disk galaxies assemble from the inside out. We include two simple prescriptions for molecular gas formation processes in our models: one is based on the analytic calculations by Krumholz, McKee & Tumlinson (2008), and the other is a prescription where the H_2 fraction is determined by the kinematic pressure of the ISM. Motivated by the observational result...

  20. Atomic Spectra Database (ASD)

    Science.gov (United States)

    SRD 78 NIST Atomic Spectra Database (ASD) (Web, free access)   This database provides access and search capability for NIST critically evaluated data on atomic energy levels, wavelengths, and transition probabilities that are reasonably up-to-date. The NIST Atomic Spectroscopy Data Center has carried out these critical compilations.

  1. Theoretical Investigation on Single-Wall Carbon Nanotubes Doped with Nitrogen, Pyridine-Like Nitrogen Defects, and Transition Metal Atoms

    Directory of Open Access Journals (Sweden)

    Michael Mananghaya

    2012-01-01

    Full Text Available This study addresses the inherent difficulty in synthesizing single-walled carbon nanotubes (SWCNTs with uniform chirality and well-defined electronic properties through the introduction of dopants, topological defects, and intercalation of metals. Depending on the desired application, one can modify the electronic and magnetic properties of SWCNTs through an appropriate introduction of imperfections. This scheme broadens the application areas of SWCNTs. Under this motivation, we present our ongoing investigations of the following models: (i (10, 0 and (5, 5 SWCNT doped with nitrogen (CNxNT, (ii (10, 0 and (5, 5 SWCNT with pyridine-like defects (3NV-CNxNT, (iii (10, 0 SWCNT with porphyrine-like defects (4ND-CNxNT. Models (ii and (iii were chemically functionalized with 14 transition metals (TMs: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt and Au. Using the spin-unrestricted density functional theory (DFT, stable configurations, deformations, formation and binding energies, the effects of the doping concentration of nitrogen, pyridine-like and porphyrine-like defects on the electronic properties were all examined. Results reveal that the electronic properties of SWCNTs show strong dependence on the concentration and configuration of nitrogen impurities, its defects, and the TMs adsorbed.

  2. Conformational Interconversions of Amino Acid Derivatives.

    Science.gov (United States)

    Kaminský, Jakub; Jensen, Frank

    2016-02-01

    Exhaustive conformational interconversions including transition structure analyses of N-acetyl-l-glycine-N-methylamide as well as its alanine, serine, and cysteine analogues have been investigated at the MP2/6-31G** level, yielding a total of 142 transition states. Improved estimates of relative energies were obtained by separately extrapolating the Hartree-Fock and MP2 energies to the basis set limit and adding the difference between CCSD(T) and MP2 results with the cc-pVDZ basis set to the extrapolated MP2 results. The performance of eight empirical force fields (AMBER94, AMBER14SB, MM2, MM3, MMFFs, CHARMM22_CMAP, OPLS_2005, and AMOEBAPRO13) in reproducing ab initio energies of transition states was tested. Our results indicate that commonly used class I force fields employing a fixed partial charge model for the electrostatic interaction provide mean errors in the ∼10 kJ/mol range for energies of conformational transition states for amino acid conformers. Modern reparametrized versions, such as CHARMM22_CMAP, and polarizable force fields, such as AMOEBAPRO13, have slightly lower mean errors, but maximal errors are still in the 35 kJ/mol range. There are differences between the force fields in their ability for reproducing conformational transitions classified according to backbone/side-chain or regions in the Ramachandran angles, but the data set is likely too small to draw any general conclusions. Errors in conformational interconversion barriers by ∼10 kJ/mol suggest that the commonly used force field may bias certain types of transitions by several orders of magnitude in rate and thus lead to incorrect dynamics in simulations. It is therefore suggested that information for conformational transition states should be included in parametrizations of new force fields. PMID:26691979

  3. Representation of target-bound drugs by computed conformers: implications for conformational libraries

    Directory of Open Access Journals (Sweden)

    Goede Andrean

    2006-06-01

    Full Text Available Abstract Background The increasing number of known protein structures provides valuable information about pharmaceutical targets. Drug binding sites are identifiable and suitable lead compounds can be proposed. The flexibility of ligands is a critical point for the selection of potential drugs. Since computed 3D structures of millions of compounds are available, the knowledge of their binding conformations would be a great benefit for the development of efficient screening methods. Results Integration of two public databases allowed superposition of conformers for 193 approved drugs with 5507 crystallised target-bound counterparts. The generation of 9600 drug conformers using an atomic force field was carried out to obtain an optimal coverage of the conformational space. Bioactive conformations are best described by a conformational ensemble: half of all drugs exhibit multiple active states, distributed over the entire range of the reachable energy and conformational space. A number of up to 100 conformers per drug enabled us to reproduce the bound states within a similarity threshold of 1.0 Å in 70% of all cases. This fraction rises to about 90% for smaller or average sized drugs. Conclusion Single drugs adopt multiple bioactive conformations if they interact with different target proteins. Due to the structural diversity of binding sites they adopt conformations that are distributed over a broad conformational space and wide energy range. Since the majority of drugs is well represented by a predefined low number of conformers (up to 100 this procedure is a valuable method to compare compounds by three-dimensional features or for fast similarity searches starting with pharmacophores. The underlying 9600 generated drug conformers are downloadable from the Super Drug Web site 1. All superpositions are visualised at the same source. Additional conformers (110,000 of 2400 classified WHO-drugs are also available.

  4. Are hydrogen bonds responsible for glycine conformational preferences?

    Energy Technology Data Exchange (ETDEWEB)

    Cormanich, Rodrigo A.; Ducati, Lucas C. [Chemistry Institute, State University of Campinas, P.O. Box 6154, 13083-970 Campinas, SP (Brazil); Rittner, Roberto, E-mail: rittner@iqm.unicamp.br [Chemistry Institute, State University of Campinas, P.O. Box 6154, 13083-970 Campinas, SP (Brazil)

    2011-08-25

    Highlights: {yields} Glycine conformational preferences in the isolated state were fully investigated. {yields} The lowest energy conformation is not stabilized by hydrogen bonding. {yields} Steric and hyperconjugative effects were analyzed for all conformers. {yields} Several theoretical methods were used to explain the conformational preferences. - Abstract: Glycine conformational preferences have mostly been explained as due to the formation of intramolecular hydrogen bonding, despite other possible relevant intramolecular interactions that may be present in this molecular system. This paper, within the framework of the quantum theory of atoms in molecules and natural bond orbital analysis, at the B3LYP/aug-cc-pVDZ level, shows that hydrogen bonding formally stabilizes just one of the glycine conformers. Indeed, these theoretical calculations suggest that both steric hindrance and hyperconjugative effects rule conformational preferences of this model compound and may not be ignored in discussions of amino acid conformational analyses.

  5. Principles of Atomic Structure and the Valence Electron Configurations of the Transition Elements%原子构造原理与过渡元素原子的价电子组态

    Institute of Scientific and Technical Information of China (English)

    刘承东

    2001-01-01

    According to the Aufbau build-up principle and the order of filling atomic orbits, the valence electron configuration of ground state atoms of the d-block transition elements seems only to be (n-1) dx-2ns2(x here denotes the number of the electron in (n-1) d and ns orbits). But the result of the spectra test shows that the atomic electron structure of the d-block transition elements also has the configurations (n-1) dx-1 ns1 and (n-1) dx nso. These two types of electron configurations are usually considered as "out of the ordinary". In addition, the another important phenomenon is that the electronic structure of the atoms for all of the elements can not attain the configuration (n-1)d6 ns1. The reasons why these exceptional electron configurations can be formed and why the configuration (n-1) d 6 ns1 can not exist are not properly understood and at present no theory of the many-electron atom structure is entirely satisfactory[1-7]. For this, it seems that the theoretical difficulty lies in accounting for the diversification of electron configurations and for the non-existence of configuration (n-1) d6 ns1 as we did not pay more attention to the control effect of symmetry principle in atom structure. We know that the stability of a mass system depends on the mechanics conservation law in the system and each conservation law is always relative to the invariance of the certain symmetry. In atom structure, the main interaction is the electromagnetic interaction. So the stability of atom structure system must be bounded up with the symmetry of the electromagnetic interaction in the atom system. The direct expression of this interconnection is that,when the electrons are allotted to the orbits with energy equivalent or close to one another in many-electron atoms, they would always distribute themselves in such a way that there is a relative highest symmetry configuration. That is to say, the way of the distribution of electrons(include electron spin states) in orbits is

  6. Conversion probabilities of low-energy (ℎω≤3 keV) nuclear transitions in the electron shells of free atoms. Article translated from Journal Yadernye Konstanty (Nuclear Constants). Series: Nuclear Constants, Issue No. 1, 1987

    International Nuclear Information System (INIS)

    Conversion of some low-energy transitions (ℎω≤3 keV) in the nuclei 90Nb, 99Tc, 103Ru, 110Ag, 140Pr, 142Pr, 153Gd, 159Gd, 160Tb, 165Tm, 171Lu, 173W, 188Re, 193Pt, 201Hg, 205Pb, 236Pa and 250Bk are investigated for the case of an isolated atom. The conversion transition probabilities are calculated using the electron wave functions, obtained through numerical integration of the Dirac equations in the atomic field within the framework of the Hartree-Fock-Slater method. The calculation is carried out for the normal configuration of the valence band of the aforementioned atoms. The calculation results are tabulated in this paper. (author)

  7. Atomizing nozzle and process

    Science.gov (United States)

    Anderson, Iver E.; Figliola, Richard S.; Molnar, Holly M.

    1992-06-30

    High pressure atomizing nozzle includes a high pressure gas manifold having a divergent expansion chamber between a gas inlet and arcuate manifold segment to minimize standing shock wave patterns in the manifold and thereby improve filling of the manifold with high pressure gas for improved melt atomization. The atomizing nozzle is especially useful in atomizing rare earth-transition metal alloys to form fine powder particles wherein a majority of the powder particles exhibit particle sizes having near-optimum magnetic properties.

  8. Atoms Talking to SQUIDs

    CERN Document Server

    Hoffman, J E; Kim, Z; Wood, A K; Anderson, J R; Dragt, A J; Hafezi, M; Lobb, C J; Orozco, L A; Rolston, S L; Taylor, J M; Vlahacos, C P; Wellstood, F C

    2011-01-01

    We present a scheme to couple trapped $^{87}$Rb atoms to a superconducting flux qubit through a magnetic dipole transition. We plan to trap atoms on the evanescent wave outside an ultrathin fiber to bring the atoms to less than 10 $\\mu$m above the surface of the superconductor. This hybrid setup lends itself to probing sources of decoherence in superconducting qubits. Our current plan has the intermediate goal of coupling the atoms to a superconducting LC resonator.

  9. Quadratic-nonlinear Landau-Zener transition for association of an atomic Bose-Einstein condensate with inter-particle elastic interactions included

    OpenAIRE

    Ishkhanyan, A.; Sokhoyan, R.; Suominen, K. -A.; Leroy, C.; Jauslin, H. -R.

    2009-01-01

    We study the strong coupling limit of a quadratic-nonlinear Landau-Zener problem for coherent photo- and magneto-association of cold atoms taking into account the atom-atom, atom-molecule, and molecule-molecule elastic scattering. Using an exact third-order nonlinear differential equation for the molecular state probability, we develop a variational approach which enables us to construct a highly accurate and simple analytic approximation describing the time dynamics of the coupled atom-molec...

  10. Superspace conformal field theory

    Energy Technology Data Exchange (ETDEWEB)

    Quella, Thomas [Koeln Univ. (Germany). Inst. fuer Theoretische Physik; Schomerus, Volker [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2013-07-15

    Conformal sigma models and WZW models on coset superspaces provide important examples of logarithmic conformal field theories. They possess many applications to problems in string and condensed matter theory. We review recent results and developments, including the general construction of WZW models on type I supergroups, the classification of conformal sigma models and their embedding into string theory.

  11. Superspace conformal field theory

    International Nuclear Information System (INIS)

    Conformal sigma models and WZW models on coset superspaces provide important examples of logarithmic conformal field theories. They possess many applications to problems in string and condensed matter theory. We review recent results and developments, including the general construction of WZW models on type I supergroups, the classification of conformal sigma models and their embedding into string theory.

  12. Conformal and non Conformal Dilaton Gravity

    CERN Document Server

    Alvarez, Enrique; Mart'\\in, C P

    2014-01-01

    The quantum dynamics of the gravitational field non-minimally coupled to an (also dynamical) scalar field is studied in the broken phase. For a particular value of the coupling the system is classically conformal, and can actually be understood as the group averaging of Einstein-Hilbert's action under conformal transformations. Contradicting cherished beliefs, a conformal anomaly is found in the trace of the equations of motion. To one loop order, this anomaly vanishes on shell. Arguments are given supporting the fact that this does not happen to two loop order, where the anomaly is argued to be a real physical effect.

  13. Conformation of 1,2-Dimethoxyethane in Water

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    To understand the conformation of 1,2-dimethoxyethane (DME) in water, a system of two kinds of molecules, DME and H2O, was focused. The interaction of various conformers of DME with water was studied by means of ab initio molecular orbital calculation with 6-31G(d)basis set. It is shown that there are two forms of interactions between the two molecules in the sys tem, the close touched (H2O attaches to the two oxygen atoms of DME) and the open touched (H2O attaches to one oxygen atom of DME) structures. The conformation of DME is remark ably influenced by the interactions. Instead the ttt conformer is preferred in the gas state, with a close touched H2O the tgt conformer becomes the most stable one. The obtained hydration ener gies show that the stabilized order of DME conformers by water is tgt>tgg'>ttt.

  14. Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries

    Science.gov (United States)

    Mohanty, Debasish; Dahlberg, Kevin; King, David M.; David, Lamuel A.; Sefat, Athena S.; Wood, David L.; Daniel, Claus; Dhar, Subhash; Mahajan, Vishal; Lee, Myongjai; Albano, Fabio

    2016-05-01

    The energy density of current lithium-ion batteries (LIBs) based on layered LiMO2 cathodes (M = Ni, Mn, Co: NMC; M = Ni, Co, Al: NCA) needs to be improved significantly in order to compete with internal combustion engines and allow for widespread implementation of electric vehicles (EVs). In this report, we show that atomic layer deposition (ALD) of titania (TiO2) and alumina (Al2O3) on Ni-rich FCG NMC and NCA active material particles could substantially improve LIB performance and allow for increased upper cutoff voltage (UCV) during charging, which delivers significantly increased specific energy utilization. Our results show that Al2O3 coating improved the NMC cycling performance by 40% and the NCA cycling performance by 34% at 1 C/‑1 C with respectively 4.35 V and 4.4 V UCV in 2 Ah pouch cells. High resolution TEM/SAED structural characterization revealed that Al2O3 coatings prevented surface-initiated layered-to-spinel phase transitions in coated materials which were prevalent in uncoated materials. EIS confirmed that Al2O3-coated materials had significantly lower increase in the charge transfer component of impedance during cycling. The ability to mitigate degradation mechanisms for Ni-rich NMC and NCA illustrated in this report provides insight into a method to enable the performance of high-voltage LIBs.

  15. Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries

    Science.gov (United States)

    Mohanty, Debasish; Dahlberg, Kevin; King, David M.; David, Lamuel A.; Sefat, Athena S.; Wood, David L.; Daniel, Claus; Dhar, Subhash; Mahajan, Vishal; Lee, Myongjai; Albano, Fabio

    2016-01-01

    The energy density of current lithium-ion batteries (LIBs) based on layered LiMO2 cathodes (M = Ni, Mn, Co: NMC; M = Ni, Co, Al: NCA) needs to be improved significantly in order to compete with internal combustion engines and allow for widespread implementation of electric vehicles (EVs). In this report, we show that atomic layer deposition (ALD) of titania (TiO2) and alumina (Al2O3) on Ni-rich FCG NMC and NCA active material particles could substantially improve LIB performance and allow for increased upper cutoff voltage (UCV) during charging, which delivers significantly increased specific energy utilization. Our results show that Al2O3 coating improved the NMC cycling performance by 40% and the NCA cycling performance by 34% at 1 C/−1 C with respectively 4.35 V and 4.4 V UCV in 2 Ah pouch cells. High resolution TEM/SAED structural characterization revealed that Al2O3 coatings prevented surface-initiated layered-to-spinel phase transitions in coated materials which were prevalent in uncoated materials. EIS confirmed that Al2O3-coated materials had significantly lower increase in the charge transfer component of impedance during cycling. The ability to mitigate degradation mechanisms for Ni-rich NMC and NCA illustrated in this report provides insight into a method to enable the performance of high-voltage LIBs. PMID:27226071

  16. Atomic physics in strong fields

    International Nuclear Information System (INIS)

    This report discusses: Microwave Driven Multiphoton Excitation Dynamics in Rydberg Atoms; Nonadiabatic Geometric Phases of Multiphoton Transitions in Dissipative Systems and Spin-j Systems; and Nonperturbative Treatments of Atomic and Molecular Processes in Intense Laser Fields

  17. Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging

    Science.gov (United States)

    Zaouris, D. K.; Wenge, A. M.; Murdock, D.; Oliver, T. A. A.; Richmond, G.; Ritchie, G. A. D.; Dixon, R. N.; Ashfold, M. N. R.

    2011-09-01

    The photodissociation dynamics of iodocyclohexane has been studied using velocity map imaging following excitation at many wavelengths within its A-band (230 ≤ λ ≤ 305 nm). This molecule exists in two conformations (axial and equatorial), and one aim of the present experiment was to explore the extent to which conformer-specific fragmentation dynamics could be distinguished. Ground (I) and spin-orbit excited (I*) state iodine atom products were monitored by 2 + 1 resonance enhanced multiphoton ionization, and total kinetic energy release (TKER) spectra and angular distributions derived from analysis of images recorded at all wavelengths studied. TKER spectra obtained at the longer excitation wavelengths show two distinct components, which can be attributed to the two conformers and the different ways in which these partition the excess energy upon C-I bond fission. Companion calculations based on a simple impulsive model suggest that dissociation of the equatorial (axial) conformer preferentially yields vibrationally (rotationally) excited cyclohexyl co-fragments. Both I and I* products are detected at the longest parent absorption wavelength (λ ˜ 305 nm), and both sets of products show recoil anisotropy parameters, β > 1, implying prompt dissociation following excitation via a transition whose dipole moment is aligned parallel to the C-I bond. The quantum yield for forming I* products, ΦI*, has been determined by time resolved infrared diode laser absorption methods to be 0.14 ± 0.02 (at λ = 248 nm) and 0.22 ± 0.05 (at λ = 266 nm). Electronic structure calculations indicate that the bulk of the A-band absorption is associated with transition to the 4A' state, and that the (majority) I atom products arise via non-adiabatic transfer from the 4A' potential energy surface (PES) via conical intersection(s) with one or more PESs correlating with ground state products.

  18. Conformation analysis of intermediates of analogues of Tamoxifen

    Science.gov (United States)

    Kapiller-Dezsőfi, Rita; Németh, Gábor; Lax, Györgyi; Simig, Gyula; Sohár, Pál

    1998-01-01

    The configuration and the conformation of two trifluoromethyl-triaryl-ethane diastereomer pairs and of some sole isomers were determined using the through-space spin-spin coupling between fluorine atoms and the hydrogen of the hydroxyl group. The molecule-mechanical calculations support the results of the conformation-analysis based on the NMR data.

  19. Frequency chain to measure the 2S-8S/8D transitions in atomic hydrogen: measurement of the Rydberg constant in frequency unit; Chaine de frequence optique pour mesurer les transitions 2S-8S/8D dans l'atome d'hydrogene: mesure de la constante de Rydberg en unite de frequence

    Energy Technology Data Exchange (ETDEWEB)

    Nez, F

    1993-10-15

    The aim of this thesis is to make a pure measurement of the frequency of the 2S-8S/8D two-photon transition in atomic hydrogen. In that purpose we have built a frequency chain in which hydrogen frequencies are compared with the difference of two optical standards, the methane stabilized He-Ne laser (3.39 {mu}m) and the iodine stabilized He-Ne laser (633 nm). The radiation from a home made Ti-sapphire laser (TS2) at 778 nm is mixed, in a LiIO{sub 3} crystal, with the one of a auxiliary He-Ne laser at 3.39 {mu}m to produce a synthesized radiation at 633 nm. The frequency of the Ti-sapphire (TS1) laser used for the two photon excitation is 89 GHz away from the one of TS2. To compare these two lasers, we have used a Schottky diode. The two lasers and a microwave radiation at 89 GHz, produced by a Gunn diode, are focused on the Schottky diode. The Gunn diode is phase locked on an ultra-stable quartz oscillator. In this way, we have linked an optical frequency of atomic hydrogen to the cesium clock without interferometry. From our measurements, we have deduced a new value of the Rydberg constant: R{sub {infinity}} equals 109737.3156834 (24) cm{sup -1} with an uncertainty of 2.2 10{sup -11}. Our uncertainty is near the one of the Q.E.D calculations giving the theoretical values of the energy levels. This value, which is currently the most precise available, is in good agreement with the recent result obtained from the 1S-2S and 2S-4D transitions. (author)

  20. Atomic-level characterization of the activation mechanism of SERCA by calcium.

    Directory of Open Access Journals (Sweden)

    L Michel Espinoza-Fonseca

    Full Text Available We have performed molecular dynamics (MD simulations to elucidate, in atomic detail, the mechanism by which the sarcoplasmic reticulum Ca(2+-ATPase (SERCA is activated by Ca(2+. Crystal structures suggest that activation of SERCA occurs when the cytoplasmic head-piece, in an open (E1 conformation stabilized by Ca(2+, undergoes a large-scale open-to-closed (E1 to E2 transition that is induced by ATP binding. However, spectroscopic measurements in solution suggest that these structural states (E1 and E2 are not tightly coupled to biochemical states (defined by bound ligands; the closed E2 state predominates even in the absence of ATP, in both the presence and absence of Ca(2+. How is this loose coupling consistent with the high efficiency of energy transduction in the Ca(2+-ATPase? To provide insight into this question, we performed long (500 ns all-atom MD simulations starting from the open crystal structure, including a lipid bilayer and water. In both the presence and absence of Ca(2+, we observed a large-scale open-to-closed conformational transition within 400 ns, supporting the weak coupling between structural and biochemical states. However, upon closer inspection, it is clear that Ca(2+ is necessary and sufficient for SERCA to reach the precise geometrical arrangement necessary for activation of ATP hydrolysis. Contrary to suggestions from crystal structures, but in agreement with solution spectroscopy, the presence of ATP is not required for this activating transition. Principal component analysis showed that Ca(2+ reshapes the free energy landscape of SERCA to create a path between the open conformation and the activated closed conformation. Thus the malleability of the free energy landscape is essential for SERCA efficiency, ensuring that ATP hydrolysis is tightly coupled to Ca(2+ transport. These results demonstrate the importance of real-time dynamics in the formation of catalytically competent conformations of SERCA, with broad

  1. Toward TeV Conformality

    Energy Technology Data Exchange (ETDEWEB)

    Appelquist, T; Avakian, A; Babich, R; Brower, R C; Cheng, M; Clark, M A; Cohen, S D; Fleming, G T; Kiskis, J; Neil, E T; Osborn, J C; Rebbi, C; Schaich, D; Soltz, R; Vranas, P

    2009-11-30

    We study the chiral condensate <{bar {psi}}{psi}> for an SU(3) gauge theory with N{sub f} massless Dirac fermions in the fundamental representation when N{sub f} is increased from 2 to 6. For N{sub f} = 2, our lattice simulations of <{bar {psi}}{psi}>/F{sup 3}, where F is the Nambu-Goldstone-boson decay constant, agree with the measured QCD value. For N{sub f} = 6, this ratio shows significant enhancement, presaging an even larger enhancement anticipated as N{sub f} increases further, toward the critical value for transition from confinement to infrared conformality.

  2. Toward TeV Conformality

    International Nuclear Information System (INIS)

    We study the chiral properties of an SU(3) gauge theory with Nf massless Dirac fermions in the fundamental representation when Nf is increased from 2 to 6. For Nf=2, our lattice simulations lead to a value of /F3, where F is the Nambu-Goldstone-boson decay constant and is the chiral condensate, which agrees with the measured QCD value. For Nf=6, this ratio shows significant enhancement, presaging an even larger enhancement anticipated as Nf increases further, toward the critical value for transition from confinement to infrared conformality.

  3. UV light induced insulator-metal transition in ultra-thin ZnO/TiOx stacked layer grown by atomic layer deposition

    Science.gov (United States)

    Saha, D.; Misra, P.; Joshi, M. P.; Kukreja, L. M.

    2016-08-01

    In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O2 and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ˜ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent

  4. DNA polymerase conformational dynamics and the role of fidelity-conferring residues: Insights from computational simulations

    Directory of Open Access Journals (Sweden)

    Massimiliano eMeli

    2016-05-01

    Full Text Available Herein we investigate the molecular bases of DNA polymerase I conformational dynamics that underlie the replication fidelity of the enzyme. Such fidelity is determined by conformational changes that promote the rejection of incorrect nucleotides before the chemical ligation step. We report a comprehensive atomic resolution study of wild type and mutant enzymes in different bound states and starting from different crystal structures, using extensive molecular dynamics (MD simulations that cover a total timespan of ~ 5 microseconds. The resulting trajectories are examined via a combination of novel methods of internal dynamics and energetics analysis, aimed to reveal the principal molecular determinants for the (destabilization of a certain conformational state. Our results show that the presence of fidelity-decreasing mutations or the binding of incorrect nucleotides in ternary complexes tend to favor transitions from closed towards open structures, passing through an ensemble of semi-closed intermediates. The latter ensemble includes the experimentally observed ajar conformation which, consistent with previous experimental observations, emerges as a molecular checkpoint for the selection of the correct nucleotide to incorporate. We discuss the implications of our results for the understanding of the relationships between the structure, dynamics and function of DNA polymerase I at the atomistic level.

  5. Relationship between SU Subdomains That Regulate the Receptor-Mediated Transition from the Native (Fusion-Inhibited) to the Fusion-Active Conformation of the Murine Leukemia Virus Glycoprotein

    OpenAIRE

    Lavillette, Dimitri; Ruggieri, Alessia; Boson, Bertrand; Maurice, Marielle; Cosset, François-Loïc

    2002-01-01

    Envelope glycoproteins (Env) of retroviruses are trimers of SU (surface) and TM (transmembrane) heterodimers and are expressed on virions in fusion-competent forms that are likely to be metastable. Activation of the viral receptor-binding domain (RBD) via its interaction with a cell surface receptor is thought to initiate a cascade of events that lead to refolding of the Env glycoprotein into its stable fusion-active conformation. While the fusion-active conformation of the TM subunit has bee...

  6. PubChem3D: Conformer generation

    Directory of Open Access Journals (Sweden)

    Bolton Evan E

    2011-01-01

    lower energy windows. Overall average accuracy of reproduction of bioactive conformations was remarkably linear with respect to both non-hydrogen atom count ("size" and effective rotor count ("flexibility". Using these as independent variables, a regression equation was developed to predict the RMSD accuracy of a theoretical ensemble to reproduce bioactive conformations. The equation was modified to give a minimum RMSD conformer sampling value to help ensure that 90% of the sampled theoretical models should contain at least one conformer within the RMSD sampling value to a "bioactive" conformation. Conclusion Optimal parameters for conformer generation using OMEGA were explored and determined. An equation was developed that provides an RMSD sampling value to use that is based on the relative accuracy to reproduce bioactive conformations. The optimal conformer generation parameters and RMSD sampling values determined are used by the PubChem3D project to generate theoretical conformer models.

  7. Ensemble refinement shows conformational flexibility in crystal structures of human complement factor D

    Energy Technology Data Exchange (ETDEWEB)

    Forneris, Federico; Burnley, B. Tom; Gros, Piet, E-mail: p.gros@uu.nl [Utrecht University, Padualaan 8, 3584 CH Utrecht (Netherlands)

    2014-03-01

    Ensemble-refinement analysis of native and mutant factor D (FD) crystal structures indicates a dynamical transition in FD from a self-inhibited inactive conformation to a substrate-bound active conformation that is reminiscent of the allostery in thrombin. Comparison with previously observed dynamics in thrombin using NMR data supports the crystallographic ensembles. Human factor D (FD) is a self-inhibited thrombin-like serine proteinase that is critical for amplification of the complement immune response. FD is activated by its substrate through interactions outside the active site. The substrate-binding, or ‘exosite’, region displays a well defined and rigid conformation in FD. In contrast, remarkable flexibility is observed in thrombin and related proteinases, in which Na{sup +} and ligand binding is implied in allosteric regulation of enzymatic activity through protein dynamics. Here, ensemble refinement (ER) of FD and thrombin crystal structures is used to evaluate structure and dynamics simultaneously. A comparison with previously published NMR data for thrombin supports the ER analysis. The R202A FD variant has enhanced activity towards artificial peptides and simultaneously displays active and inactive conformations of the active site. ER revealed pronounced disorder in the exosite loops for this FD variant, reminiscent of thrombin in the absence of the stabilizing Na{sup +} ion. These data indicate that FD exhibits conformational dynamics like thrombin, but unlike in thrombin a mechanism has evolved in FD that locks the unbound native state into an ordered inactive conformation via the self-inhibitory loop. Thus, ensemble refinement of X-ray crystal structures may represent an approach alternative to spectroscopy to explore protein dynamics in atomic detail.

  8. Universal bosonic tetramers of dimer-atom-atom structure

    OpenAIRE

    Deltuva, A

    2012-01-01

    Unstable four-boson states having an approximate dimer-atom-atom structure are studied using momentum-space integral equations for the four-particle transition operators. For a given Efimov trimer the universal properties of the lowest associated tetramer are determined. The impact of this tetramer on the atom-trimer and dimer-dimer collisions is analyzed. The reliability of the three-body dimer-atom-atom model is studied.

  9. Conformal Bootstrap in Embedding Space

    CERN Document Server

    Fortin, Jean-François

    2016-01-01

    It is shown how to obtain conformal blocks from embedding space with the help of the operator product expansion. The minimal conformal block originates from scalar exchange in a four-point correlation functions of four scalars. All remaining conformal blocks are simple derivatives of the minimal conformal block. With the help of the orthogonality properties of the conformal blocks, the analytic conformal bootstrap can be implemented directly in embedding space, leading to a Jacobi-like definition of conformal field theories.

  10. Conformal bootstrap in embedding space

    Science.gov (United States)

    Fortin, Jean-François; Skiba, Witold

    2016-05-01

    It is shown how to obtain conformal blocks from embedding space with the help of the operator product expansion. The minimal conformal block originates from scalar exchange in a four-point correlation function of four scalars. All remaining conformal blocks are simple derivatives of the minimal conformal block. With the help of the orthogonality properties of the conformal blocks, the analytic conformal bootstrap can be implemented directly in embedding space, leading to a Jacobi-like definition of conformal field theories.

  11. Conformational stability of calreticulin

    DEFF Research Database (Denmark)

    Jørgensen, Charlotte S; Trandum, Christa; Larsen, Nanna Brink;

    2005-01-01

    The conformational stability of calreticulin was investigated. Apparent unfolding temperatures (Tm) increased from 31 degrees C at pH 5 to 51 degrees C at pH 9, but electrophoretic analysis revealed that calreticulin oligomerized instead of unfolding. Structural analyses showed that the single C......-terminal alpha-helix was of major importance to the conformational stability of calreticulin....

  12. Conformational stability of calreticulin

    DEFF Research Database (Denmark)

    Jørgensen, C.S.; Trandum, C.; Larsen, N.;

    2005-01-01

    The conformational stability of calreticulin was investigated. Apparent unfolding temperatures (T-m) increased from 31 degrees C at pH 5 to 51 degrees C at pH 9, but electrophoretic analysis revealed that calreticulin oligomerized instead of unfolding. Structural analyses showed that the single C......-terminal a-helix was of major importance to the conformational stability of calreticulin....

  13. Microchip-Based Trapped-Atom Clocks

    CERN Document Server

    Vuletic, Vladan; Schleier-Smith, Monika H

    2011-01-01

    This is a chapter of a recently published book entitled Atom Chips, edited by Jakob Reichel and Vladan Vuletic. The contents of this chapter include: Basic Principles; Atomic-Fountain versus Trapped-Atom Clocks; Optical-Transition Clocks versus Microwave Clocks; Clocks with Magnetically Trapped Atoms--Fundamental Limits and Experimental Demonstrations; Readout in Trapped-Atom Clocks; and Spin Squeezing.

  14. Dimer-atom-atom recombination in the universal four-boson system

    OpenAIRE

    Deltuva, A

    2012-01-01

    The dimer-atom-atom recombination process in the system of four identical bosons with resonant interactions is studied. The description uses the exact Alt, Grassberger and Sandhas equations for the four-particle transition operators that are solved in the momentum-space framework. The dimer-dimer and atom-trimer channel contributions to the ultracold dimer-atom-atom recombination rate are calculated. The dimer-atom-atom recombination rate greatly exceeds the three-atom recombination rate.

  15. Discovering conformational sub-states relevant to protein function.

    Directory of Open Access Journals (Sweden)

    Arvind Ramanathan

    Full Text Available BACKGROUND: Internal motions enable proteins to explore a range of conformations, even in the vicinity of native state. The role of conformational fluctuations in the designated function of a protein is widely debated. Emerging evidence suggests that sub-groups within the range of conformations (or sub-states contain properties that may be functionally relevant. However, low populations in these sub-states and the transient nature of conformational transitions between these sub-states present significant challenges for their identification and characterization. METHODS AND FINDINGS: To overcome these challenges we have developed a new computational technique, quasi-anharmonic analysis (QAA. QAA utilizes higher-order statistics of protein motions to identify sub-states in the conformational landscape. Further, the focus on anharmonicity allows identification of conformational fluctuations that enable transitions between sub-states. QAA applied to equilibrium simulations of human ubiquitin and T4 lysozyme reveals functionally relevant sub-states and protein motions involved in molecular recognition. In combination with a reaction pathway sampling method, QAA characterizes conformational sub-states associated with cis/trans peptidyl-prolyl isomerization catalyzed by the enzyme cyclophilin A. In these three proteins, QAA allows identification of conformational sub-states, with critical structural and dynamical features relevant to protein function. CONCLUSIONS: Overall, QAA provides a novel framework to intuitively understand the biophysical basis of conformational diversity and its relevance to protein function.

  16. Inhibitory Effect of Curcumin on Metal Ions-induced Conformational Transition of Silk Fibroin and Its Mechanism%姜黄素抑制金属离子诱导的丝素蛋白构象转变及其作用机理

    Institute of Scientific and Technical Information of China (English)

    章月虹; 江腾; 赵学舟; 周平

    2013-01-01

    以丝素蛋白(SF)为神经退行性疾病相关蛋白的模型蛋白,分析了姜黄素(Curcumin)对Zn(Ⅱ)和Cu(Ⅱ)离子诱导的丝素蛋白构象转变的干预作用及其作用机理,试图探讨姜黄素在神经退行性疾病中的预防与治疗作用.结果表明,姜黄素可通过与Cu(Ⅱ)和Zn(Ⅱ)离子络合,干预金属离子诱导的丝素蛋白构象转变,并且所形成的络合物Cu(Ⅱ)-Curcumin可抑制丝素蛋白的构象转变,但是Zn(Ⅱ)-Curcumin络合物不具有这种能力.因此,基于姜黄素对于金属离子诱导的丝素蛋白构象转变具有良好的干预作用,可以将姜黄素作为神经退行性疾病预防和治疗的潜在候选药物.%The inhibitory effect of curcumin on the Cu ( II ) and Zn ( Ⅱ) -induced conformation transition of silk fibroin(SF) as a model protein of neurodegenerative diseases, was investigated for aiming at investigating the potency of curcumin in the prevention and treatment of neurodegenerative diseases. The results indicate that curcumin can inhibit Cu ( II ) and Zn ( II ) -induced conformational transition of SF through chelating Cu ( II ) and Zn ( II ), meanwhile, Cu ( Ⅱ ) -curcumin complex also has ability to inhibit the conformation transition of SF, but Zn ( II ) -curcumin complex does not. Therefore, based on those results about the .effective interference of curcumin on Cu ( II ) and Zn ( Ⅱ ) -induced conformation transition of SF, curcumin could be suggested as a potential agent for the prevention and treatment of neurodegenerative diseases.

  17. Nuclear physics: Elusive transition spotted in thorium

    Science.gov (United States)

    Safronova, Marianna

    2016-05-01

    The highly precise atomic clocks used in science and technology are based on electronic transitions in atoms. The discovery of a nuclear transition in thorium-229 raises hopes of making nuclear clocks a reality. See Article p.47

  18. Conformal expansions and renormalons

    CERN Document Server

    Gardi, E; Gardi, Einan; Grunberg, Georges

    2001-01-01

    The large-order behaviour of QCD is dominated by renormalons. On the other hand renormalons do not occur in conformal theories, such as the one describing the infrared fixed-point of QCD at small beta_0 (the Banks--Zaks limit). Since the fixed-point has a perturbative realization, all-order perturbative relations exist between the conformal coefficients, which are renormalon-free, and the standard perturbative coefficients, which contain renormalons. Therefore, an explicit cancellation of renormalons should occur in these relations. The absence of renormalons in the conformal limit can thus be seen as a constraint on the structure of the QCD perturbative expansion. We show that the conformal constraint is non-trivial: a generic model for the large-order behaviour violates it. We also analyse a specific example, based on a renormalon-type integral over the two-loop running-coupling, where the required cancellation does occur.

  19. [Conformers of carnosine].

    Science.gov (United States)

    Kliuev, S A

    2006-01-01

    The geometric and energetic parameters of most stable conformations of carnosine were calculated by the semiempirical guantum-chemical method PM3. The carnosine-water-zinc (II) clusters were simulated. PMID:16909845

  20. Quantum massive conformal gravity

    International Nuclear Information System (INIS)

    We first find the linear approximation of the second plus fourth order derivative massive conformal gravity action. Then we reduce the linearized action to separated second order derivative terms, which allows us to quantize the theory by using the standard first order canonical quantization method. It is shown that quantum massive conformal gravity is renormalizable but has ghost states. A possible decoupling of these ghost states at high energies is discussed. (orig.)

  1. Delineating the conformal window

    DEFF Research Database (Denmark)

    Frandsen, Mads Toudal; Pickup, Thomas; Teper, Michael

    2011-01-01

    We identify and characterise the conformal window in gauge theories relevant for beyond the standard model building, e.g. Technicolour, using the criteria of metric confinement and causal analytic couplings, which are known to be consistent with the phase diagram of supersymmetric QCD from Seiberg...... duality. Using these criteria we find perturbation theory to be consistent throughout the predicted conformal window for several of these gauge theories and we discuss recent lattice results in the light of our findings....

  2. Quantum massive conformal gravity

    OpenAIRE

    Faria, F. F.

    2016-01-01

    We first find the linear approximation of the second plus fourth order derivative massive conformal gravity action. Then we reduce the linearized action to separated second order derivative terms, which allows us to quantize the theory by using the standard first order canonical quantization method. It is shown that quantum massive conformal gravity is renormalizable but has ghost states. A possible decoupling of these ghost states at high energies is discussed.

  3. Quantum massive conformal gravity

    Science.gov (United States)

    Faria, F. F.

    2016-04-01

    We first find the linear approximation of the second plus fourth order derivative massive conformal gravity action. Then we reduce the linearized action to separated second order derivative terms, which allows us to quantize the theory by using the standard first order canonical quantization method. It is shown that quantum massive conformal gravity is renormalizable but has ghost states. A possible decoupling of these ghost states at high energies is discussed.

  4. Quantum massive conformal gravity

    Energy Technology Data Exchange (ETDEWEB)

    Faria, F.F. [Universidade Estadual do Piaui, Centro de Ciencias da Natureza, Teresina, PI (Brazil)

    2016-04-15

    We first find the linear approximation of the second plus fourth order derivative massive conformal gravity action. Then we reduce the linearized action to separated second order derivative terms, which allows us to quantize the theory by using the standard first order canonical quantization method. It is shown that quantum massive conformal gravity is renormalizable but has ghost states. A possible decoupling of these ghost states at high energies is discussed. (orig.)

  5. Excitonic splitting and vibronic coupling in 1,2-diphenoxyethane: Conformation-specific effects in the weak coupling limit

    Science.gov (United States)

    Buchanan, Evan G.; Walsh, Patrick S.; Plusquellic, David F.; Zwier, Timothy S.

    2013-05-01

    C atom in one of the rings is sufficient to localize the electronic excitation in one or the other ring. Dispersed fluorescence (DFL) spectra are used to provide assignments for all vibronic structure in the first 200 cm-1of both conformers. In the tgt conformer, both "a" and "b" symmetry fundamentals are observed, consistent with extensive vibronic coupling between the two dipole-allowed, nearly degenerate excited states. In the ttt conformer, the lowest frequency vibronic transition located 46 cm-1 above the Bu origin is assigned to a bu fundamental (labeled bar R) built off the dipole-forbidden Ag state origin. The DFL spectrum of the Ag(bar R^1) level contains strong transitions to v″(bar R) = 0, 1, and 2, seemingly at odds with vibronic coupling models. Studies of the DFL spectrum of this band as a function of distance from the nozzle reveal that much of the intensity in v″ = 1 arises from collisions of DPOE while in the excited state Ag(vb' = 1) level with He, producing Bu(bar R = 1) levels with large collision cross section. The remaining intensity in the fundamental at large x/D is ascribed to emission from the 13C isotopomer, for which this emission is dipole-allowed.

  6. An automated efficient conformation search of L-serine by the scaled hypersphere search method

    Science.gov (United States)

    Kishimoto, Naoki; Harayama, Manami; Ohno, Koichi

    2016-05-01

    Stable conformers of L-serine were automatically explored by applications of the scaled hypersphere search (SHS) method to equilibrium structures maintaining the chemical bond skeletons of serine. Energy barriers for conformational changes of L-serine were estimated from the heights of obtained transition structures. Zero-point-corrected electronic energies and Gibbs free energies of the 24 lowest energy conformers and 21 transition structures were calculated at 100, 298, and 400 K by a composite quantum chemistry method (Gaussian-4). Relative populations of 24 conformers including nine new conformers were calculated from the Gibbs energies assuming thermal equilibrium.

  7. Atomic physics and non-equilibrium plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Weisheit, J.C.

    1986-04-25

    Three lectures comprise the report. The lecture, Atomic Structure, is primarily theoretical and covers four topics: (1) Non-relativistic one-electron atom, (2) Relativistic one-electron atom, (3) Non-relativistic many-electron atom, and (4) Relativistic many-electron atom. The lecture, Radiative and Collisional Transitions, considers the problem of transitions between atomic states caused by interactions with radiation or other particles. The lecture, Ionization Balance: Spectral Line Shapes, discusses collisional and radiative transitions when ionization and recombination processes are included. 24 figs., 11 tabs.

  8. Atomic data from the Iron project. XIII. Electron excitation rates and emissivity ratios for forbidden transitions in NI II and Fe II.

    Science.gov (United States)

    Bautista, M. A.; Pradhan, A. K.

    1996-02-01

    Electron impact excitation rates and emissivity line ratios are reported for Optical and IR transitions in Ni II and Fe II arising from low-lying even parity levels. A total of 7 LS terms were included for Ni II, which result in 17 fine structure levels and 136 transitions. Coupling effects and resonance structures considered in the present calculations result in significant differences with the earlier distorted wave calculations by Nussbaumer & Storey (1982), although a reasonable agreement is found for the line diagnostics of some strong transitions in Ni II. Whereas an extensive set of collisional data has been presented earlier by Zhang & Pradhan for Fe II in the Iron Project series, in this paper we report collision strengths for some transitions missing from their dataset using an improved eigenfunction expansion for Fe II which includes the lowest 18 LS terms giving 52 fine structure levels and 1326 transitions. The present dataset provides a useful check on several forbidden transitions in Fe II and essentially confirms the diagnostics derived from the earlier work. The present calculations were carried out on the massively parallel processor Cray T3D with a parallelized version of the Iron Project R-matrix codes; to our knowledge these are the first such calculations.

  9. A reoptimized GROMOS force field for hexopyranose-based carbohydrates accounting for the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers.

    Science.gov (United States)

    Hansen, Halvor S; Hünenberger, Philippe H

    2011-04-30

    This article presents a reoptimization of the GROMOS 53A6 force field for hexopyranose-based carbohydrates (nearly equivalent to 45A4 for pure carbohydrate systems) into a new version 56A(CARBO) (nearly equivalent to 53A6 for non-carbohydrate systems). This reoptimization was found necessary to repair a number of shortcomings of the 53A6 (45A4) parameter set and to extend the scope of the force field to properties that had not been included previously into the parameterization procedure. The new 56A(CARBO) force field is characterized by: (i) the formulation of systematic build-up rules for the automatic generation of force-field topologies over a large class of compounds including (but not restricted to) unfunctionalized polyhexopyranoses with arbritrary connectivities; (ii) the systematic use of enhanced sampling methods for inclusion of experimental thermodynamic data concerning slow or unphysical processes into the parameterization procedure; and (iii) an extensive validation against available experimental data in solution and, to a limited extent, theoretical (quantum-mechanical) data in the gas phase. At present, the 56A(CARBO) force field is restricted to compounds of the elements C, O, and H presenting single bonds only, no oxygen functions other than alcohol, ether, hemiacetal, or acetal, and no cyclic segments other than six-membered rings (separated by at least one intermediate atom). After calibration, this force field is shown to reproduce well the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers. As a result, the 56A(CARBO) force field should be suitable for: (i) the characterization of the dynamics of pyranose ring conformational transitions (in simulations on the microsecond timescale); (ii) the investigation of systems where alternative ring conformations become significantly populated; (iii) the investigation of anomerization or epimerization in terms of free-energy differences

  10. Comment on "Conformally flat stationary axisymmetric metrics"

    CERN Document Server

    Barnes, A; Senovilla, José MM

    2003-01-01

    Garcia and Campuzano claim to have found a previously overlooked family of stationary and axisymmetric conformally flat spacetimes, contradicting an old theorem of Collinson. In both these papers it is tacitly assumed that the isometry group is orthogonally transitive. Under the same assumption, we point out here that Collinson's result still holds if one demands the existence of an axis of symmetry on which the axial Killing vector vanishes. On the other hand if the assumption of orthogonal transitivity is dropped, a wider class of metrics is allowed and it is possible to find explicit counterexamples to Collinson's result.

  11. Evanescent Wave Atomic Mirror

    Science.gov (United States)

    Ghezali, S.; Taleb, A.

    2008-09-01

    A research project at the "Laboratoire d'électronique quantique" consists in a theoretical study of the reflection and diffraction phenomena via an atomic mirror. This poster presents the principle of an atomic mirror. Many groups in the world have constructed this type of atom optics experiments such as in Paris-Orsay-Villetaneuse (France), Stanford-Gaithersburg (USA), Munich-Heidelberg (Germany), etc. A laser beam goes into a prism with an incidence bigger than the critical incidence. It undergoes a total reflection on the plane face of the prism and then exits. The transmitted resulting wave out of the prism is evanescent and repulsive as the frequency detuning of the laser beam compared to the atomic transition δ = ωL-ω0 is positive. The cold atomic sample interacts with this evanescent wave and undergoes one or more elastic bounces by passing into backward points in its trajectory because the atoms' kinetic energy (of the order of the μeV) is less than the maximum of the dipolar potential barrier ℏΩ2/Δ where Ω is the Rabi frequency [1]. In fact, the atoms are cooled and captured in a magneto-optical trap placed at a distance of the order of the cm above the prism surface. The dipolar potential with which interact the slow atoms is obtained for a two level atom in a case of a dipolar electric transition (D2 Rubidium transition at a wavelength of 780nm delivered by a Titane-Saphir laser between a fundamental state Jf = l/2 and an excited state Je = 3/2). This potential is corrected by an attractive Van der Waals term which varies as 1/z3 in the Lennard-Jones approximation (typical atomic distance of the order of λ0/2π where λ0 is the laser wavelength) and in 1/z4 if the distance between the atom and its image in the dielectric is big in front of λ0/2π. This last case is obtained in a quantum electrodynamic calculation by taking into account an orthornormal base [2]. We'll examine the role of spontaneous emission for which the rate is inversely

  12. Charged conformal Killing spinors

    Energy Technology Data Exchange (ETDEWEB)

    Lischewski, Andree, E-mail: lischews@mathematik.hu-berlin.de [Humboldt-Universität zu Berlin, Institut für Mathematik, Rudower Chaussee 25, Room 1.310, D12489 Berlin (Germany)

    2015-01-15

    We study the twistor equation on pseudo-Riemannian Spin{sup c}-manifolds whose solutions we call charged conformal Killing spinors (CCKSs). We derive several integrability conditions for the existence of CCKS and study their relations to spinor bilinears. A construction principle for Lorentzian manifolds admitting CCKS with nontrivial charge starting from CR-geometry is presented. We obtain a partial classification result in the Lorentzian case under the additional assumption that the associated Dirac current is normal conformal and complete the classification of manifolds admitting CCKS in all dimensions and signatures ≤5 which has recently been initiated in the study of supersymmetric field theories on curved space.

  13. Conformation of α,α,α'-Trisubstituted Cyclododecanone

    Institute of Scientific and Technical Information of China (English)

    WANG,Ming-An; ZHANG,Ning; LU,Hui-Zhe; WANG,Dao-Quan

    2007-01-01

    Ten α,α,α'-trisubstituted cyclododecanones were synthesized and characterized by elemental analyses, infrared,1H NMR and 13C NMR spectra, and X-ray diffraction. NMR data could not give conformational information clearly,but some of their ring skeleton conformations of cyclododecanone moiety were showed to remain the unchanged [3333]-2-one conformation with little distortion, while the others were changed to the [3324]-2-one conformation in their crystal structures. These are consistent with the results of molecular mechanics calculation with Sybyl 6.9 software and Tripos force field, and semi-empirical quantum calculation with AM1 method in Gaussian 98 software.Two geminal substituting groups are located at α-comer carbon atom, and the third group is at α-side-exo carbon atom in both conformations. Both [3333]-2-one and [3324]-2-one conformations are present in a dynamic equilibrium in the solution, but only one preferred conformation exists in the crystal solid.

  14. Atomic data from the Iron Project XLV. Relativistic transition probabilities for carbon-like Ar XIII and Fe XXI using Breit-Pauli R-matrix method

    OpenAIRE

    Nahar, Sultana N.

    2000-01-01

    The Breit-Pauli R-matrix method developed under the Iron Project has been used to obtain extensive sets of oscillator strengths and transition probabilities for dipole allowed and intercombination fine structure transitions in carbon like ions, Ar XIII and Fe XXI. The complete set consists of 1274 fine structure bound energy levels and 198,259 oscillator strengths for Ar XIII, and 1611 bound levels and 300,079 oscillator strengths for Fe XXI. These correspond to levels of total angular moment...

  15. Conformal special relativity

    International Nuclear Information System (INIS)

    It is shown that the information loss/recovery theorem based on the ADS/CFT correspondence is not consistent with the stability of the Schwarzschild or Reissner-Nordstrom black holes. Nonetheless, the conformal invariance of Yang-Mills theory points to new relativity principle compatible with quantum unitarity near those black holes

  16. Extende conformal field theories

    Energy Technology Data Exchange (ETDEWEB)

    Taormina, A. (Chicago Univ., IL (USA). Enrico Fermi Inst.)

    1990-08-01

    Some extended conformal field theories are briefly reviewed. They illustrate how non minimal models of the Virasoro algebra (c{ge}1) can become minimal with respect to a larger algebra. The accent is put on N-extended superconformal algebras, which are relevant in superstring compactification. (orig.).

  17. Extended conformal field theories

    Science.gov (United States)

    Taormina, Anne

    1990-08-01

    Some extended conformal field theories are briefly reviewed. They illustrate how non minimal models of the Virasoro algebra (c≥1) can become minimal with respect to a larger algebra. The accent is put on N-extended superconformal algebras, which are relevant in superstring compactification.

  18. Conformal General Relativity

    CERN Document Server

    Pervushin, V

    2001-01-01

    The inflation-free solution of problems of the modern cosmology (horizon, cosmic initial data, Planck era, arrow of time, singularity,homogeneity, and so on) is considered in the conformal-invariant unified theory given in the space with geometry of similarity where we can measure only the conformal-invariant ratio of all quantities. Conformal General Relativity is defined as the $SU_c(3)\\times SU(2)\\times U(1)$-Standard Model where the dimensional parameter in the Higgs potential is replaced by a dilaton scalar field described by the negative Penrose-Chernikov-Tagirov action. Spontaneous SU(2) symmetry breaking is made on the level of the conformal-invariant angle of the dilaton-Higgs mixing, and it allows us to keep the structure of Einstein's theory with the equivalence principle. We show that the lowest order of the linearized equations of motion solves the problems mentioned above and describes the Cold Universe Scenario with the constant temperature T and z-history of all masses with respect to an obser...

  19. Gamow-Teller transitions from Ni-58 to discrete states of Cu-51 - The study of isospin symmetry in atomic nuclei

    NARCIS (Netherlands)

    Fujita, Y; Fujita, H; Adachi, T; Berg, GPA; Caurier, E; Fujimura, H; Hara, K; Hatanaka, K; Janas, Z; Kamiya, J; Kawabata, T; Langanke, K; Martinez-Pinedo, G; Noro, T; Roeckl, E; Shimbara, Y; Shinada, T; van der Werf, SY; Yoshifuku, M; Yosoi, M; Zegers, RGT

    2002-01-01

    Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states of T = 1, T-z = +/-1 nuclei to the common excited states of the T-z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow

  20. Conformal Relativity versus Brans–Dicke and Superstring Theories

    Directory of Open Access Journals (Sweden)

    David B. Blaschke

    2012-10-01

    Full Text Available We show how conformal relativity is related to Brans–Dicke theory and to low-energy-effective superstring theory. Conformal relativity or the Hoyle–Narlikar theory is invariant with respect to conformal transformations of the metric. We show that the conformal relativity action is equivalent to the transformed Brans–Dicke action for ω = -3/2 (which is the border between standard scalar field and ghost in contrast to the reduced (graviton-dilaton low-energy-effective superstring action which corresponds to the Brans–Dicke action with ω = -1. We show that like in ekpyrotic/cyclic models, the transition through the singularity in conformal cosmology in the string frame takes place in the weak coupling regime. We also find interesting self-duality and duality relations for the graviton-dilaton actions.

  1. Logarithmic conformal field theory

    Science.gov (United States)

    Gainutdinov, Azat; Ridout, David; Runkel, Ingo

    2013-12-01

    Conformal field theory (CFT) has proven to be one of the richest and deepest subjects of modern theoretical and mathematical physics research, especially as regards statistical mechanics and string theory. It has also stimulated an enormous amount of activity in mathematics, shaping and building bridges between seemingly disparate fields through the study of vertex operator algebras, a (partial) axiomatisation of a chiral CFT. One can add to this that the successes of CFT, particularly when applied to statistical lattice models, have also served as an inspiration for mathematicians to develop entirely new fields: the Schramm-Loewner evolution and Smirnov's discrete complex analysis being notable examples. When the energy operator fails to be diagonalisable on the quantum state space, the CFT is said to be logarithmic. Consequently, a logarithmic CFT is one whose quantum space of states is constructed from a collection of representations which includes reducible but indecomposable ones. This qualifier arises because of the consequence that certain correlation functions will possess logarithmic singularities, something that contrasts with the familiar case of power law singularities. While such logarithmic singularities and reducible representations were noted by Rozansky and Saleur in their study of the U (1|1) Wess-Zumino-Witten model in 1992, the link between the non-diagonalisability of the energy operator and logarithmic singularities in correlators is usually ascribed to Gurarie's 1993 article (his paper also contains the first usage of the term 'logarithmic conformal field theory'). The class of CFTs that were under control at this time was quite small. In particular, an enormous amount of work from the statistical mechanics and string theory communities had produced a fairly detailed understanding of the (so-called) rational CFTs. However, physicists from both camps were well aware that applications from many diverse fields required significantly more

  2. Isotopic Selectivity of Pulsed Excitation of Zinc Atoms upon the 4s21S0 → 4p 3P01 Transition

    International Nuclear Information System (INIS)

    The spectral dependences of the isotopic selectivity of the optical excitation of zinc atoms in the course of an efficient photochemical reaction with molecules of a reagent gas are calculated within the framework of a simple model taking into account the gas mixture flow. At a certain frequency detuning of monochromatic laser radiation, a high selectivity of isotope separation is realized at the end of the interaction region under the condition that the isotopic shifts are smaller than the Doppler broadening

  3. Transition probabilities for lines of Cr II, Na II and Sb I by laser produced plasma atomic emission spectroscopy; Probabilidades de transicion de algunos niveles de Cr II, Na II y Sb I medediante espectroscopia de plasma producidos por laser

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, A. M.; Ortiz, M.; Campos, J.

    1995-07-01

    Absolute transition probabilities for lines of CR II, Na II and Sb I were determined by emission spectroscopy of laser induced plasmas. the plasma was produced focusing the emission of a pulsed Nd-Yag laser on solid samples containing the atom in study. the light arising from the plasma region was collected by and spectrometer. the detector used was a time-resolved optical multichannel analyzer (OMA III EG and G). The wavelengths of the measured transitions range from 2000 sto 4100 A. The spectral resolution of the system was 0. 2 A. The method can be used in insulators materials as Cl Na crystals and in metallic samples as Al-Cr and Sn-Sn alloys. to avoid self-absorption effects the alloys were made with low Sb or Cr content. Relative transition probabilities have been determined from measurements of emission-line intensities and were placed on an absolute scale by using, where possible, accurate experimental lifetime values form the literature or theoretical data. From these measurements, values for plasma temperature (8000-24000 K), electron densities ({approx}{approx} 10''16 cm ''-3) and self-absorption coefficients have been obtained. (Author) 56 refs.

  4. Measurement of the parity violating 6S-7S transition amplitude in cesium achieved within 2 \\times 10^{-13} atomic-unit accuracy by stimulated-emission detection

    CERN Document Server

    Guena, J; Bouchiat, M A

    2004-01-01

    We exploit the process of asymmetry amplification by stimulated emission which provides an original method for parity violation (PV) measurements in a highly forbidden atomic transition. The method involves measurements of a chiral, transient, optical gain of a cesium vapor on the 7S-6P_{3/2} transition, probed after it is excited by an intense, linearly polarized, collinear laser, tuned to resonance for one hyperfine line of the forbidden 6S-7S transition in a longitudinal electric field. We report here a 3.5 fold increase, of the one-second-measurement sensitivity, and subsequent reduction by a factor of 3.5 of the statistical accuracy compared with our previous result [J. Gu\\'ena et al., Phys. Rev. Lett. 90, 143001 (2003)]. Decisive improvements to the set-up include an increased repetition rate, better extinction of the probe beam at the end of the probe pulse and, for the first time to our knowledge, the following: a polarization-tilt magnifier, quasi-suppression of beam reflections at the cell windows, ...

  5. How to Distinguish Conformational Selection and Induced Fit Based on Chemical Relaxation Rates

    Science.gov (United States)

    2016-01-01

    Protein binding often involves conformational changes. Important questions are whether a conformational change occurs prior to a binding event (‘conformational selection’) or after a binding event (‘induced fit’), and how conformational transition rates can be obtained from experiments. In this article, we present general results for the chemical relaxation rates of conformational-selection and induced-fit binding processes that hold for all concentrations of proteins and ligands and, thus, go beyond the standard pseudo-first-order approximation of large ligand concentration. These results allow to distinguish conformational-selection from induced-fit processes—also in cases in which such a distinction is not possible under pseudo-first-order conditions—and to extract conformational transition rates of proteins from chemical relaxation data. PMID:27636092

  6. How to distinguish conformational selection and induced fit based on chemical relaxation rates

    CERN Document Server

    Paul, Fabian

    2016-01-01

    Protein binding often involves conformational changes. Important questions are whether a conformational change occurs prior to a binding event ('conformational selection') or after a binding event ('induced fit'), and how conformational transition rates can be obtained from experiments. In this article, we present general results for the chemical relaxation rates of conformational-selection and induced-fit binding processes that hold for all concentrations of proteins and ligands and, thus, go beyond the standard pseudo-first-order approximation of large ligand concentration. These results allow to distinguish conformational-selection from induced-fit processes - also in cases in which such a distinction is not possible under pseudo-first-order conditions - and to extract conformational transition rates of proteins from chemical relaxation data.

  7. A Conformal Extension Theorem based on Null Conformal Geodesics

    CERN Document Server

    Lübbe, Christian

    2008-01-01

    In this article we describe the formulation of null geodesics as null conformal geodesics and their description in the tractor formalism. A conformal extension theorem through an isotropic singularity is proven by requiring the boundedness of the tractor curvature and its derivatives to sufficient order along a congruence of null conformal geodesic. This article extends earlier work by Tod and Luebbe.

  8. Magnetoelectric Jones Dichroism in Atoms

    CERN Document Server

    Budker, D

    2003-01-01

    The authors suggest that atomic experiments measuring the interference between magnetic-dipole and electric-field-induced electric-dipole transition amplitudes may provide a valuable system to study magnetoelectric Jones effects.

  9. Determination of magic wavelengths for the $7s ~ {^2}S_{1/2}-7p ~ {^2}P_{3/2,1/2}$ transitions in Fr atom

    CERN Document Server

    Singh, Sukhjit; Arora, Bindiya

    2016-01-01

    Magic wavelengthsfor the $7S_{1/2}-7P_{1/2,3/2}$ transitions in Fr were reported by Dammalapati \\textit{et al.} in [Phys. Rev. A 93, 043407 (2016)]. These $\\lambda_{\\rm{magic}}$ were determined by plotting dynamic polarizabilities ($\\alpha$) of the involved states with the above transitions against a desired range of wavelength. Electric dipole (E1) matrix elements listed in [J. Phys. Chem. Ref. Data 36, 497 (2007)], from the measured lifetimes of the $7P_{1/2,3/2}$ states and from the calculations considering core-polarization effects in the relativistic Hartree-Fock (HFR) method, were used to determine $\\alpha$. However, contributions from core correlation effects and from the E1 matrix elements of the $7P-7S$, $7P-8S$ and $7P-6D$ transitions to $\\alpha$ of the $7P$ states were ignored. In this work, we demonstrate importance of these contributions and improve accuracies of $\\alpha$ further by replacing the E1 matrix elements taken from the HFR method by the values obtained employing relativistic coupled-cl...

  10. Computation of conformational coupling in allosteric proteins.

    Directory of Open Access Journals (Sweden)

    Brian A Kidd

    2009-08-01

    Full Text Available In allosteric regulation, an effector molecule binding a protein at one site induces conformational changes, which alter structure and function at a distant active site. Two key challenges in the computational modeling of allostery are the prediction of the structure of one allosteric state starting from the structure of the other, and elucidating the mechanisms underlying the conformational coupling of the effector and active sites. Here we approach these two challenges using the Rosetta high-resolution structure prediction methodology. We find that the method can recapitulate the relaxation of effector-bound forms of single domain allosteric proteins into the corresponding ligand-free states, particularly when sampling is focused on regions known to change conformation most significantly. Analysis of the coupling between contacting pairs of residues in large ensembles of conformations spread throughout the landscape between and around the two allosteric states suggests that the transitions are built up from blocks of tightly coupled interacting sets of residues that are more loosely coupled to one another.

  11. Versatile compact atomic source for high resolution dual atom interferometry

    CERN Document Server

    Müller, T; Gilowski, M; Jentsch, C; Rasel, E M; Ertmer, W

    2007-01-01

    We present a compact $^{87}$Rb atomic source for high precision dual atom interferometers. The source is based on a double-stage magneto-optical trap (MOT) design, consisting of a 2-dimensional (2D)-MOT for efficient loading of a 3D-MOT. The accumulated atoms are precisely launched in a horizontal moving molasses. Our setup generates a high atomic flux ($>10^{10}$ atoms/s) with precise and flexibly tunable atomic trajectories as required for high resolution Sagnac atom interferometry. We characterize the performance of the source with respect to the relevant parameters of the launched atoms, i.e. temperature, absolute velocity and pointing, by utilizing time-of-flight techniques and velocity selective Raman transitions.

  12. Multiscale conformal pattern transfer

    Science.gov (United States)

    Lodewijks, Kristof; Miljkovic, Vladimir; Massiot, Inès; Mekonnen, Addis; Verre, Ruggero; Olsson, Eva; Dmitriev, Alexandre

    2016-06-01

    We demonstrate a method for seamless transfer from a parent flat substrate of basically any lithographic top-down or bottom-up pattern onto essentially any kind of surface. The nano- or microscale patterns, spanning macroscopic surface areas, can be transferred with high conformity onto a large variety of surfaces when such patterns are produced on a thin carbon film, grown on top of a sacrificial layer. The latter allows lifting the patterns from the flat parent substrate onto a water-air interface to be picked up by the host surface of choice. We illustrate the power of this technique by functionalizing broad range of materials including glass, plastics, metals, rough semiconductors and polymers, highlighting the potential applications in in situ colorimetry of the chemistry of materials, anti-counterfeit technologies, biomolecular and biomedical studies, light-matter interactions at the nanoscale, conformal photovoltaics and flexible electronics.

  13. Conformational flexibility of aspartame.

    Science.gov (United States)

    Toniolo, Claudio; Temussi, Pierandrea

    2016-05-01

    L-Aspartyl-L-phenylalanine methyl ester, better known as aspartame, is not only one of the most used artificial sweeteners, but also a very interesting molecule with respect to the correlation between molecular structure and taste. The extreme conformational flexibility of this dipeptide posed a huge difficulty when researchers tried to use it as a lead compound to design new sweeteners. In particular, it was difficult to take advantage of its molecular model as a mold to infer the shape of the, then unknown, active site of the sweet taste receptor. Here, we follow the story of the 3D structural aspects of aspartame from early conformational studies to recent docking into homology models of the receptor. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 376-384, 2016. PMID:27038223

  14. Hot Conformal Gauge Theories

    DEFF Research Database (Denmark)

    Mojaza, Matin; Pica, Claudio; Sannino, Francesco

    2010-01-01

    We compute the nonzero temperature free energy up to the order g^6 \\ln(1/g) in the coupling constant for vector like SU(N) gauge theories featuring matter transforming according to different representations of the underlying gauge group. The number of matter fields, i.e. flavors, is arranged...... in such a way that the theory develops a perturbative stable infrared fixed point at zero temperature. Due to large distance conformality we trade the coupling constant with its fixed point value and define a reduced free energy which depends only on the number of flavors, colors and matter representation. We...... of flavors. Surprisingly this number, if computed to the order g^2, agrees with previous predictions for the lower boundary of the conformal window for nonsupersymmetric gauge theories. The higher order results tend to predict a higher number of critical flavors. These are universal properties, i...

  15. Conformal Complementarity Maps

    CERN Document Server

    Barbón, José L F

    2013-01-01

    We study quantum cosmological models for certain classes of bang/crunch singularities, using the duality between expanding bubbles in AdS with a FRW interior cosmology and perturbed CFTs on de Sitter space-time. It is pointed out that horizon complementarity in the AdS bulk geometries is realized as a conformal transformation in the dual deformed CFT. The quantum version of this map is described in full detail in a toy model involving conformal quantum mechanics. In this system the complementarity map acts as an exact duality between eternal and apocalyptic Hamiltonian evolutions. We calculate the commutation relation between the Hamiltonians corresponding to the different frames. It vanishes only on scale invariant states.

  16. Atom Chips

    CERN Document Server

    Folman, R; Cassettari, D; Hessmo, B; Maier, T; Schmiedmayer, J; Folman, Ron; Krüger, Peter; Cassettari, Donatella; Hessmo, Björn; Maier, Thomas

    1999-01-01

    Atoms can be trapped and guided using nano-fabricated wires on surfaces, achieving the scales required by quantum information proposals. These Atom Chips form the basis for robust and widespread applications of cold atoms ranging from atom optics to fundamental questions in mesoscopic physics, and possibly quantum information systems.

  17. Current-voltage curves of atomic-sized transition metal contacts: An explanation of why Au is ohmic and Pt is not

    DEFF Research Database (Denmark)

    Nielsen, S.K.; Brandbyge, Mads; Hansen, K.;

    2002-01-01

    We present an experimental study of current-voltage (I-V) curves on atomic-sized Au and Pt contacts formed under cryogenic vacuum (4.2 K). Whereas I-V curves for Au are almost Ohmic, the conductance G=I/V for Pt decreases with increasing voltage, resulting in distinct nonlinear I-V behavior....... The experimental results are compared with first principles density functional theory calculations for Au and Pt, and good agreement is found. The difference in conductance properties for Pt vs Au can be explained by the underlying electron valence structure: Pt has an open d shell while Au has not....

  18. Conformable light emitting modules

    OpenAIRE

    Jablonski, Michal

    2014-01-01

    As we become increasingly aware that there is more to light than the image it forms on our retina, and as we become more environmentally aware, the value of non-image-forming light increases along with the need for various new light related appliances. In particular, some lighting related applications are emerging which demand conformability (flexibility and stretchability). Well-being, automotive or wearable electronic applications are just a few examples where these trends can be observed. ...

  19. Conformal scalar field wormholes

    Science.gov (United States)

    Halliwell, Jonathan J.; Laflamme, Raymond

    1989-01-01

    The Euclidian Einstein equations with a cosmological constant and a conformally coupled scalar field are solved, taking the metric to be of the Robertson-Walker type. In the case Lambda = 0, solutions are found which represent a wormhole connecting two asymptotically flat Euclidian regions. In the case Lambda greater than 0, the solutions represent tunneling from a small Tolman-like universe to a large Robertson-Walker universe.

  20. Conformal boundaries of warped products

    DEFF Research Database (Denmark)

    Kokkendorff, Simon Lyngby

    2006-01-01

    In this note we prove a result on how to determine the conformal boundary of a type of warped product of two length spaces in terms of the individual conformal boundaries. In the situation, that we treat, the warping and conformal distortion functions are functions of distance to a base point....... The result is applied to produce examples of CAT(0)-spaces, where the conformal and ideal boundaries differ in interesting ways....

  1. Dynamics and quantum entanglement of two-level atoms in de Sitter spacetime

    CERN Document Server

    Tian, Zehua

    2014-01-01

    In the framework of open quantum systems, we study the internal dynamics of both freely falling and static two-level atoms interacting with quantized conformally coupled massless scalar field in de Sitter spacetime. We find that the atomic transition rates depend on both the nature of de Sitter spacetime and the motion of atoms, interestingly the steady states for both cases are always driven to being purely thermal, regardless of the atomic initial states. This thermalization phenomenon is structurally similar to what happens to an elementary quantum system immersed in a thermal field, and thus reveals the thermal nature of de Sitter spacetime. Besides, we find that the thermal baths will drive the entanglement shared by the freely falling atom (the static atom) and its auxiliary partner, a same two-level atom which is isolated from external fields, to being sudden death, and the proper time for the entanglement to be extinguished is computed. We also analyze that such thermalization and disentanglement phen...

  2. Random Conformal Weldings

    CERN Document Server

    Astala, K; Kupiainen, A; Saksman, E

    2009-01-01

    We construct a conformally invariant random family of closed curves in the plane by welding of random homeomorphisms of the unit circle. The homeomorphism is constructed using the exponential of $\\beta X$ where $X$ is the restriction of the two dimensional free field on the circle and the parameter $\\beta$ is in the "high temperature" regime $\\beta<\\sqrt 2$. The welding problem is solved by studying a non-uniformly elliptic Beltrami equation with a random complex dilatation. For the existence a method of Lehto is used. This requires sharp probabilistic estimates to control conformal moduli of annuli and they are proven by decomposing the free field as a sum of independent fixed scale fields and controlling the correlations of the complex dilation restricted to dyadic cells of various scales. For uniqueness we invoke a result by Jones and Smirnov on conformal removability of H\\"older curves. We conjecture that our curves are locally related to SLE$(\\kappa)$ for $\\kappa<4$.

  3. Entanglement analysis of a two-atom nonlinear Jaynes–Cummings model with nondegenerate two-photon transition, Kerr nonlinearity, and two-mode Stark shift

    International Nuclear Information System (INIS)

    An entangled state, as an essential tool in quantum information processing, may be generated through the interaction between light and matter in cavity quantum electrodynamics. In this paper, we study the interaction between two two-level atoms and a two-mode field in an optical cavity enclosed by a medium with Kerr nonlinearity in the presence of a detuning parameter and Stark effect. It is assumed that the atom–field coupling and third-order susceptibility of the Kerr medium depend on the intensity of the light. In order to investigate the dynamics of the introduced system, we obtain the exact analytical form of the state vector of the considered atom–field system under initial conditions which may be prepared for the atoms (in a coherent superposition of their ground and upper states) and the fields (in a standard coherent state). Then, in order to evaluate the degree of entanglement between the subsystems, we investigate the dynamics of the entanglement by employing the entanglement of formation. Finally, we analyze in detail the influences of the Stark shift, the deformed Kerr medium, the intensity-dependent coupling, and also the detuning parameter on the behavior of this measure for different subsystems. The numerical results show that the amount of entanglement between the different subsystems can be controlled by choosing the evolved parameters appropriately. (paper)

  4. Calculation of Electron-Impact 2s22p4 3P → 2p33s3SO Transition in Atomic Oxygen

    Institute of Scientific and Technical Information of China (English)

    WANG Yang; LI Yan-Hua; ZHOU Ya-Jun

    2005-01-01

    The inelastic scattering of electron from oxygen for the 2s22p4 3P → 2p33s 3SO transition is studied using the momentum-space coupled channel optical method at 15, 17.5, 20, 22.5, 25, 27.5, 30, 50, and 100eV. Direct ionization cross sections, i.e. differential and integral cross sections, are reported. Important continuum states are included in the coupled channel calculation via a complex equivalent-local optical potential. The present results are compared with the available experimental data and other theoretical calculation results.

  5. Absolute frequency measurement of 1S0 (F = 1/2) - 3P0 (F = 1/2) transition of 171Yb atoms in a one-dimensional optical lattice at KRISS

    CERN Document Server

    Park, Chang Yong; Lee, Won-Kyu; Park, Sang Eon; Kim, Eok Bong; Lee, Sun Kyung; Cho, Jun Woo; Yoon, Tai Hyun; Mun, Jongchul; Park, Sung Jong; Kwon, Taeg Yong; Lee, Sang-Bum

    2011-01-01

    We measured the absolute frequency of the optical clock transition 1S0 (F = 1/2) - 3P0 (F = 1/2) of 171Yb atoms confined in a one-dimensional optical lattice and it was determined to be 518 295 836 590 865.7 (9.2) Hz. The measured frequency was calibrated to the Coordinated Universal Time (UTC) by using an optical frequency comb of which frequency was phase-locked to a hydrogen maser as a flywheel oscillator traceable to the UTC. The magic wavelength was also measured as 394 798.48 (79) GHz. The results are in good agreement with two previous measurements of other institutes within the specified uncertainty of this work.

  6. Detection of the level of fluoride in the commercially available toothpaste using laser induced breakdown spectroscopy with the marker atomic transition line of neutral fluorine at 731.1 nm

    Science.gov (United States)

    Gondal, M. A.; Maganda, Y. W.; Dastageer, M. A.; Al Adel, F. F.; Naqvi, A. A.; Qahtan, T. F.

    2014-04-01

    Fourth harmonic of a pulsed Nd:YAG laser (wavelength 266 nm) in combination with high resolution spectrograph equipped with Gated ICCD camera has been employed to design a high sensitive analytical system. This detection system is based on Laser Induced Breakdown Spectroscopy and has been tested first time for analysis of semi-fluid samples to detect fluoride content present in the commercially available toothpaste samples. The experimental parameters were optimized to achieve an optically thin and in local thermo dynamic equilibrium plasma. This improved the limits of detection of fluoride present in tooth paste samples. The strong atomic transition line of fluorine at 731.102 nm was used as the marker line to quantify the fluoride concentration levels. Our LIBS system was able to detect fluoride concentration levels in the range of 1300-1750 ppm with a detection limit of 156 ppm.

  7. Conformal Janus on Euclidean Sphere

    CERN Document Server

    Bak, Dongsu; Rey, Soo-Jong

    2016-01-01

    We interpret Janus as an interface in a conformal field theory and study its properties. The Janus is created by an exactly marginal operator and we study its effect on the interface conformal field theory on the Janus. We do this by utilizing the AdS/CFT correspondence. We compute the interface free energy both from leading correction to the Euclidean action in the dual gravity description and from conformal perturbation theory in the conformal field theory. We find that the two results agree each other and that the interface free energy scales precisely as expected from the conformal invariance of the Janus interface.

  8. Direct Time-domain Observation of Conformational Relaxation in Gas-phase Cold Collisions

    OpenAIRE

    Drayna, Garrett K.; Hallas, Christian; Wang, Kenneth; Domingos, Sérgio R.; Eibenberger, Sandra; Doyle, John M.; Patterson, David

    2016-01-01

    Cooling molecules in the gas phase is important for precision spectroscopy, cold molecule physics, and physical chemistry. Measurements of conformational relaxation cross sections shed important light on potential energy surfaces and energy flow within a molecule. However, gas-phase conformational cooling has not been previously observed directly. In this work, we directly observe conformational dynamics of 1,2-propanediol in cold (6K) collisions with atomic helium using microwave spectroscop...

  9. Conformal superalgebras via tractor calculus

    Science.gov (United States)

    Lischewski, Andree

    2015-01-01

    We use the manifestly conformally invariant description of a Lorentzian conformal structure in terms of a parabolic Cartan geometry in order to introduce a superalgebra structure on the space of twistor spinors and normal conformal vector fields formulated in purely algebraic terms on parallel sections in tractor bundles. Via a fixed metric in the conformal class, one reproduces a conformal superalgebra structure that has been considered in the literature before. The tractor approach, however, makes clear that the failure of this object to be a Lie superalgebra in certain cases is due to purely algebraic identities on the spinor module and to special properties of the conformal holonomy representation. Moreover, it naturally generalizes to higher signatures. This yields new formulas for constructing new twistor spinors and higher order normal conformal Killing forms out of existing ones, generalizing the well-known spinorial Lie derivative. Moreover, we derive restrictions on the possible dimension of the space of twistor spinors in any metric signature.

  10. Conformal superalgebras via tractor calculus

    International Nuclear Information System (INIS)

    We use the manifestly conformally invariant description of a Lorentzian conformal structure in terms of a parabolic Cartan geometry in order to introduce a superalgebra structure on the space of twistor spinors and normal conformal vector fields formulated in purely algebraic terms on parallel sections in tractor bundles. Via a fixed metric in the conformal class, one reproduces a conformal superalgebra structure that has been considered in the literature before. The tractor approach, however, makes clear that the failure of this object to be a Lie superalgebra in certain cases is due to purely algebraic identities on the spinor module and to special properties of the conformal holonomy representation. Moreover, it naturally generalizes to higher signatures. This yields new formulas for constructing new twistor spinors and higher order normal conformal Killing forms out of existing ones, generalizing the well-known spinorial Lie derivative. Moreover, we derive restrictions on the possible dimension of the space of twistor spinors in any metric signature. (paper)

  11. Manipulating Higher Partial-Wave Atom-Atom Interaction by Strong Photoassoiative Coupling

    OpenAIRE

    Deb, Bimalendu; Hazra, Jisha

    2009-01-01

    We show that it is possible to change not only s-wave but also higher partial wave atom-atom interactions in cold collision in the presence of relatively intense laser fields tuned near a photoassociative transition.

  12. Preferred gauche conformation in N-(2-aminoethyl)pyridinium ions

    Science.gov (United States)

    Razenberg, Johannes A. S. J.; Nolte, Roeland J. M.; Drenth, Wiendelt; Kanters, Jan A.; Van Duijneveldt, Frans B.

    1984-01-01

    X-ray analysis of 1-[(2 S, 3 S)-2- N,N-dibenzylamino-3-methyl-1-pentyl]pyridinium p-toluenesulphonate and 1-[(2 S)-2- N,N-dibenzylamino-1-propyl]pyridinium p-toluenesulphonate reveals that in both compounds the central NCCN moiety is in the syn-clinal conformation. According to SCF-LCAO-MO calculations the syn-clinal conformation of the parent on, N-(2-aminomethyl)pyridinium is 23.4 kJ mol -1 lower in energy than the anti-periplanar conformation. The calculations suggest incipient bond formation between the amino nitrogen atom and the pyridinium ring in the syn-clinal conformation.

  13. Crystal structures and conformers of CyMe4-BTBP

    Directory of Open Access Journals (Sweden)

    Lyczko Krzysztof

    2015-12-01

    Full Text Available The crystal structure of new conformation of the CyMe4-BTBP ligand (ttc has been presented. The ttt conformer of this compound in a form of THF solvate has been also crystallized. The geometries of six possible conformations (ttt, ttc, tct, tcc, ctc and ccc of the CyMe4-BTBP ligand have been modeled in the gas phase and in solutions (MeOH and H2O by DFT calculations using B3LYP/6-31G(d,p method. According to the calculations, in the three different media the conformers with trans orientation of the N atoms in the bipyridyl moiety are the most stable.

  14. Conformational Study of Taurine in the Gas Phase

    Science.gov (United States)

    Cortijo, Vanessa; Sanz, M. Eugenia; López, Juan C.; Alonso, José L.

    2009-08-01

    The conformational preferences of the amino sulfonic acid taurine (NH2-CH2-CH2-SO3H) have been investigated in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MB-FTMW) in the 6-14 GHz frequency range. One conformer has been observed, and its rotational, centrifugal distortion, and hyperfine quadrupole coupling constants have been determined from the analysis of its rotational spectrum. Comparison of the experimental constants with those calculated theoretically identifies the detected conformer unambiguously. The observed conformer of taurine is stabilized by an intramolecular hydrogen bond O-H···N between the hydrogen of the sulfonic acid group and the nitrogen atom of the amino group.

  15. Potential Energy Surfaces for Reactions of X Metal Atoms (X = Cu, Zn, Cd, Ga, Al, Au, or Hg with YH4 Molecules (Y = C, Si, or Ge and Transition Probabilities at Avoided Crossings in Some Cases

    Directory of Open Access Journals (Sweden)

    Octavio Novaro

    2012-01-01

    Full Text Available We review ab initio studies based on quantum mechanics on the most important mechanisms of reaction leading to the C–H, Si–H, and Ge–H bond breaking of methane, silane, and germane, respectively, by a metal atom in the lowest states in Cs symmetry: X(2nd excited state, 1st excited state and ground state + YH4→ H3XYH → H + XYH3 and XH + YH3. with X = Au, Zn, Cd, Hg, Al, and G, and Y = C, Si, and Ge. Important issues considered here are (a the role that the occupation of the d-, s-, or p-shells of the metal atom plays in the interactions with a methane or silane or germane molecule, (b the role of either singlet or doublet excited states of metals on the reaction barriers, and (c the role of transition probabilities for different families of reacting metals with these gases, using the H–X–Y angle as a reaction coordinate. The breaking of the Y–H bond of YH4 is useful in the production of amorphous hydrogenated films, necessary in several fields of industry.

  16. Leaf growth is conformal

    Science.gov (United States)

    Alim, Karen; Armon, Shahaf; Shraiman, Boris I.; Boudaoud, Arezki

    2016-10-01

    Growth pattern dynamics lie at the heart of morphogenesis. Here, we investigate the growth of plant leaves. We compute the conformal transformation that maps the contour of a leaf at a given stage onto the contour of the same leaf at a later stage. Based on the mapping we predict the local displacement field in the leaf blade and find it to agree with the experimentally measured displacement field to 92%. This approach is applicable to any two-dimensional system with locally isotropic growth, enabling the deduction of the whole growth field just from observation of the tissue contour.

  17. Conformance and Deviance

    DEFF Research Database (Denmark)

    Gjerdrum Pedersen, Esben Rahbek; Neergaard, Peter; Thusgaard Pedersen, Janni;

    2013-01-01

    This paper analyses how large Danish companies are responding to new governmental regulation which requires them to report on corporate social responsibility (CSR). The paper is based on an analysis of 142 company annual reports required by the new Danish regulation regarding CSR reporting, plus ...... in CSR reporting practices. Finally, it is argued that non-conformance with the new regulatory requirements is not solely about conscious resistance but may also be caused by, for example, lack of awareness, resource limitations, misinterpretations, and practical difficulties....

  18. Calcul de haute précision d'énergies de transitions dans les atomes exotiques et les lithiumoïdes : corrections relativistes, corrections radiatives, structure hyperfine et interaction avec le cortège électronique résiduel

    OpenAIRE

    Boucard, Stéphane

    1998-01-01

    In this work we present the calculations of transition energies inlithiumlike and in exotics atoms : 1) With the use of new ions beamsource, it is now possible to produce highly charged ions. We thushave studied li-like ions hyperfine structure to obtain information onrelativistic many-body corrections and the magnetic sector of strongfield QED. In heavy ions these are of the order of a few percent ofthe total transition energy. We also evaluated the Bohr-Weisskopfcorrection, which depends on...

  19. Conformally symmetric traversable wormholes

    International Nuclear Information System (INIS)

    Exact solutions of traversable wormholes are found under the assumption of spherical symmetry and the existence of a nonstatic conformal symmetry, which presents a more systematic approach in searching for exact wormhole solutions. In this work, a wide variety of solutions are deduced by considering choices for the form function, a specific linear equation of state relating the energy density and the pressure anisotropy, and various phantom wormhole geometries are explored. A large class of solutions impose that the spatial distribution of the exotic matter is restricted to the throat neighborhood, with a cutoff of the stress-energy tensor at a finite junction interface, although asymptotically flat exact solutions are also found. Using the 'volume integral quantifier', it is found that the conformally symmetric phantom wormhole geometries may, in principle, be constructed by infinitesimally small amounts of averaged null energy condition violating matter. Considering the tidal acceleration traversability conditions for the phantom wormhole geometry, specific wormhole dimensions and the traversal velocity are also deduced

  20. Atom chips

    CERN Document Server

    Reichel, Jakob

    2010-01-01

    This book provides a stimulating and multifaceted picture of a rapidly developing field. The first part reviews fundamentals of atom chip research in tutorial style, while subsequent parts focus on the topics of atom-surface interaction, coherence on atom chips, and possible future directions of atom chip research. The articles are written by leading researchers in the field in their characteristic and individual styles.