Spin-phonon coupling and exchange interaction in Gd substituted YFe0.5Cr0.5O3

NASA Astrophysics Data System (ADS)

Singh, Karan; Sharma, Mohit K.; Mukherjee, K.

2018-02-01

We report the evolution of physical properties due to partial substitution of Gd on the Y site in a mixed metal oxide YFe0.5Cr0.5O3. This compound exhibits negative magnetization at low applied fields. Our investigations on Y1-xGdxFe0.5Cr0.5O3 (x = 0.0, 0.2, 0.4 and 0.6) compounds is carried out through magnetization and Raman spectroscopy studies. It is observed that even with 20% Gd substitution, the negative magnetization observed in YFe0.5Cr0.5O3 is suppressed. Due to magnetic rare earth ion Gd3+, additional exchange interaction of the form Gd-O-Fe/Cr dominates the magnetic interaction arising due to the transition metal ions. This results in positive magnetization in Gd-substituted compounds. Temperature dependent Raman spectroscopy along with magnetization studies revealed that the observed shifts of Raman mode is due to spin-phonon coupling. Hardening of Raman mode observed below 240 K in YFe0.5Cr0.5O3 weakens and softening of phonon modes was observed for Y0.4Gd0.6Fe0.5Cr0.5O3 compound. This implies that additional magnetic interactions due to Gd ions play a dominating role in dictating the behavior of the Gd-substituted compounds.

The double-soft limit in cosmological correlation functions and graviton exchange effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alinea, Allan L.; Kubota, Takahiro; Misumi, Nobuhiko, E-mail: alinea@het.phys.sci.osaka-u.ac.jp, E-mail: kubota@celas.osaka-u.ac.jp, E-mail: misumi.nobu@gmail.com

The graviton exchange effect on cosmological correlation functions is examined by employing the double-soft limit technique. A new relation among correlation functions that contain the effects due to graviton exchange diagrams in addition to those due to scalar-exchange and scalar-contact-interaction, is derived by using the background field method and independently by the method of Ward identities associated with dilatation symmetry. We compare these three terms, putting small values for the slow-roll parameters and (1− n {sub s} ) ≈ 0.042, where n {sub s} is the scalar spectral index. It is argued that the graviton exchange effects are more dominantmore » than the other two and could be observed in the trispectrum in the double-soft limit. Our observation strengthens the previous work by Seery, Sloth and Vernizzi, in which it has been argued that the graviton exchange dominates in the counter-collinear limit for single field slow-roll inflation.« less

Better band gaps for wide-gap semiconductors from a locally corrected exchange-correlation potential that nearly eliminates self-interaction errors

DOE PAGES

Singh, Prashant; Harbola, Manoj K.; Johnson, Duane D.

2017-09-08

Here, this work constitutes a comprehensive and improved account of electronic-structure and mechanical properties of silicon-nitride (more » $${\\rm Si}_{3}$$ $${\\rm N}_{4}$$ ) polymorphs via van Leeuwen and Baerends (LB) exchange-corrected local density approximation (LDA) that enforces the exact exchange potential asymptotic behavior. The calculated lattice constant, bulk modulus, and electronic band structure of $${\\rm Si}_{3}$$ $${\\rm N}_{4}$$ polymorphs are in good agreement with experimental results. We also show that, for a single electron in a hydrogen atom, spherical well, or harmonic oscillator, the LB-corrected LDA reduces the (self-interaction) error to exact total energy to ~10%, a factor of three to four lower than standard LDA, due to a dramatically improved representation of the exchange-potential.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orlenko, E. V., E-mail: eorlenko@mail.ru; Evstafev, A. V.; Orlenko, F. E.

A formalism of exchange perturbation theory (EPT) is developed for the case of interactions that explicitly depend on time. Corrections to the wave function obtained in any order of perturbation theory and represented in an invariant form include exchange contributions due to intercenter electron permutations in complex multicenter systems. For collisions of atomic systems with an arbitrary type of interaction, general expressions are obtained for the transfer (T) and scattering (S) matrices in which intercenter electron permutations between overlapping nonorthogonal states belonging to different centers (atoms) are consistently taken into account. The problem of collision of alpha particles with lithiummore » atoms accompanied by the redistribution of electrons between centers is considered. The differential and total charge-exchange cross sections of lithium are calculated.« less

Effect of ferromagnetic exchange field on band gap and spin polarisation of graphene on a TMD substrate

NASA Astrophysics Data System (ADS)

Goswami, Partha

2018-03-01

We calculate the electronic band dispersion of graphene monolayer on a two-dimensional transition metal dichalcogenide substrate (GrTMD) around K and K^' } points by taking into account the interplay of the ferromagnetic impurities and the substrate-induced interactions. The latter are (strongly enhanced) intrinsic spin-orbit interaction (SOI), the extrinsic Rashba spin-orbit interaction (RSOI) and the one related to the transfer of the electronic charge from graphene to substrate. We introduce exchange field ( M) in the Hamiltonian to take into account the deposition of magnetic impurities on the graphene surface. The cavalcade of the perturbations yield particle-hole symmetric band dispersion with an effective Zeeman field due to the interplay of the substrate-induced interactions with RSOI as the prime player. Our graphical analysis with extremely low-lying states strongly suggests the following: The GrTMDs, such as graphene on WY2, exhibit (direct) band-gap narrowing / widening (Moss-Burstein (MB) gap shift) including the increase in spin polarisation ( P) at low temperature due to the increase in the exchange field ( M) at the Dirac points. The polarisation is found to be electric field tunable as well. Finally, there is anticrossing of non-parabolic bands with opposite spins, the gap closing with same spins, etc. around the Dirac points. A direct electric field control of magnetism at the nanoscale is needed here. The magnetic multiferroics, like BiFeO3 (BFO), are useful for this purpose due to the coupling between the magnetic and electric order parameters.

Highly anisotropic exchange interactions of j eff = 1 2 iridium moments on the fcc lattice in La 2 B IrO 6   ( B = Mg , Zn )

DOE PAGES

Aczel, A. A.; Cook, A. M.; Williams, T. J.; ...

2016-06-20

Here we have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites Lamore » $$_2$$ZnIrO$$_6$$ and La$$_2$$MgIrO$$_6$$, which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated $$j_{\\rm eff}=1/2$$ Mott insulators provide clear evidence for gapped spin wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in $$j_{\\rm eff}=1/2$$ Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly-directional Kitaev interaction is a type of exchange anisotropy which is symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry-lowering due to lattice distortions can pin the order and enhance the magnon gap. In conclusion, our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling.« less

The exchange interaction effects on magnetic properties of the nanostructured CoPt particles

NASA Astrophysics Data System (ADS)

Komogortsev, S. V.; Iskhakov, R. S.; Zimin, A. A.; Filatov, E. Yu.; Korenev, S. V.; Shubin, Yu. V.; Chizhik, N. A.; Yurkin, G. Yu.; Eremin, E. V.

2016-03-01

Various manifestations of the exchange interaction effects in magnetization curves of the CoPt nanostructured particles are demonstrated and discussed. The inter-grain exchange constant A in the sponge-like agglomerates of crystallites is estimated as A=(7±1) pJ/m from the approach magnetization to saturation curves that is in good agreement with A=(6.6±0.5) pJ/m obtained from Bloch T 3/2 law. The fractal dimensionality of the exchange coupled crystallite system in the porous media of the disordered CoPt alloy d=(2.60±0.18) was estimated from the approach magnetization to saturation curve. Coercive force decreases with temperature as Hc T 3/2 which is assumed to be a consequence of the magnetic anisotropy energy reduction due to the thermal spin wave excitations in the investigated CoPt particles.

Removal of Carbon Dioxide from Gas Mixtures Using Ion-Exchanged Silicoaluminophosphates

NASA Technical Reports Server (NTRS)

Hernandez-Maldonado, Arturo J (Inventor); Rivera-Ramos, Milton E (Inventor); Arevalo-Hidalgo, Ana G (Inventor)

2017-01-01

Na+-SAPO-34 sorbents were ion-exchanged with several individual metal cations for CO2 absorption at different temperatures (273-348 K) and pressures (<1 atm). In general, the overall adsorption performance of the exchanged materials increased as follows: Ce3+

Effects of the spaces available for cations in strongly acidic cation-exchange resins on the exchange equilibria by quaternary ammonium ions and on the hydration states of metal ions.

PubMed

Watanabe, Yuuya; Ohnaka, Kenji; Fujita, Saki; Kishi, Midori; Yuchi, Akio

2011-10-01

The spaces (voids) available for cations in the five exchange resins with varying exchange capacities and cross-linking degrees were estimated, on the basis of the additivity of molar volumes of the constituents. Tetraalkylammonium ions (NR(4)(+); R: Me, Et, Pr) may completely exchange potassium ion on the resin having a larger void radius. In contrast, the ratio of saturated adsorption capacity to exchange capacity of the resin having a smaller void radius decreased with an increase in size of NR(4)(+) ions, due to the interionic contacts. Alkali metal ions could be exchanged quantitatively. While the hydration numbers of K(+), Rb(+), and Cs(+) were independent of the void radius, those of Li(+) and Na(+), especially Na(+), decreased with a decrease in void radius. Interionic contacts between the hydrated ions enhance the dehydration. Multivalent metal ions have the hydration numbers, comparable to or rather greater than those in water. A greater void volume available due to exchange stoichiometry released the interionic contacts and occasionally promoted the involvement of water molecules other than directly bound molecules. The close proximity between ions in the conventional ion-exchange resins having higher exchange capacities may induce varying interactions.

Magnetic exchange bias of more than 1 Tesla in a natural mineral intergrowth.

PubMed

McEnroe, Suzanne A; Carter-Stiglitz, Brian; Harrison, Richard J; Robinson, Peter; Fabian, Karl; McCammon, Catherine

2007-10-01

Magnetic exchange bias is a phenomenon whereby the hysteresis loop of a 'soft' magnetic phase is shifted by an amount H(E) along the applied field axis owing to its interaction with a 'hard' magnetic phase. Since the discovery of exchange bias fifty years ago, the development of a general theory has been hampered by the uncertain nature of the interfaces between the hard and soft phases, commonly between an antiferromagnetic phase and a ferro- or ferrimagnetic phase. Exchange bias continues to be the subject of investigation because of its technological applications and because it is now possible to manipulate magnetic materials at the nanoscale. Here we present the first documented example of exchange bias of significant magnitude (>1 T) in a natural mineral. We demonstrate that exchange bias in this system is due to the interaction between coherently intergrown magnetic phases formed through a natural process of phase separation during slow cooling over millions of years. Transmission electron microscopy studies show that these intergrowths have a known crystallographic orientation with a known crystallographic structure and that the interfaces are coherent.

Effect of Annealing Temperature on Broad Luminescence of Silver-Exchanged Zeolites Y and A

NASA Astrophysics Data System (ADS)

Gui, Sa Chu Rong; Lin, H.; Bao, W.; Wang, W.

2018-05-01

The annealing temperature dependence of luminescence properties of silver (Ag)-exchanged zeolites Y and A was studied. It was found that the absorbance and excitation/emission bands are strongly affected by the thermal treatments. With increase in annealing temperature, the absorbance of Ag in zeolite Y increases at first and then decreases. However, the position of the excitation/emission band in zeolite Y was found to be insensitive to the annealing temperature. In contrast, the excitation/emission bands in zeolite A are particularly sensitive to the annealing temperature. The difference of such temperature dependence in zeolites Y and A may be due to the different microporous structure of the two minerals. Moreover, the fact that this dependence is not observed in Ag-exchanged zeolite Y is likely to be due to the difficulty in dehydration of zeolite Y in air or due to the weak Ag+-Ag+ interaction in zeolite Y.

Energy exchange between a laser beam and charged particles using inverse transition radiation and method for its use

DOEpatents

Kimura, Wayne D.; Romea, Richard D.; Steinhauer, Loren C.

1998-01-01

A method and apparatus for exchanging energy between relativistic charged particles and laser radiation using inverse diffraction radiation or inverse transition radiation. The beam of laser light is directed onto a particle beam by means of two optical elements which have apertures or foils through which the particle beam passes. The two apertures or foils are spaced by a predetermined distance of separation and the angle of interaction between the laser beam and the particle beam is set at a specific angle. The separation and angle are a function of the wavelength of the laser light and the relativistic energy of the particle beam. In a diffraction embodiment, the interaction between the laser and particle beams is determined by the diffraction effect due to the apertures in the optical elements. In a transition embodiment, the interaction between the laser and particle beams is determined by the transition effect due to pieces of foil placed in the particle beam path.

Evolution of magnetic Dirac bosons in a honeycomb lattice

NASA Astrophysics Data System (ADS)

Boyko, D.; Balatsky, A. V.; Haraldsen, J. T.

2018-01-01

We examine the presence and evolution of magnetic Dirac nodes in the Heisenberg honeycomb lattice. Using linear spin theory, we evaluate the collinear phase diagram as well as the change in the spin dynamics with various exchange interactions. We show that the ferromagnetic structure produces bosonic Dirac and Weyl points due to the competition between the interactions. Furthermore, it is shown that the criteria for magnetic Dirac nodes are coupled to the magnetic structure and not the overall crystal symmetry, where the breaking of inversion symmetry greatly affects the antiferromagnetic configurations. The tunability of the nodal points through variation of the exchange parameters leads to the possibility of controlling Dirac symmetries through an external manipulation of the orbital interactions.

Flow-Induced New Channels of Energy Exchange in Multi-Scale Plasma Dynamics - Revisiting Perturbative Hybrid Kinetic-MHD Theory.

PubMed

Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go

2016-05-10

It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle's Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas.

Ion-exchange selectivity of diclofenac, ibuprofen, ketoprofen, and naproxen in ureolyzed human urine.

PubMed

Landry, Kelly A; Sun, Peizhe; Huang, Ching-Hua; Boyer, Treavor H

2015-01-01

This research advances the knowledge of ion-exchange of four non-steroidal anti-inflammatory drugs (NSAIDs) - diclofenac (DCF), ibuprofen (IBP), ketoprofen (KTP), and naproxen (NPX) - and one analgesic drug-paracetamol (PCM) - by strong-base anion exchange resin (AER) in synthetic ureolyzed urine. Freundlich, Langmuir, Dubinin-Astakhov, and Dubinin-Radushkevich isotherm models were fit to experimental equilibrium data using nonlinear least squares method. Favorable ion-exchange was observed for DCF, KTP, and NPX, whereas unfavorable ion-exchange was observed for IBP and PCM. The ion-exchange selectivity of the AER was enhanced by van der Waals interactions between the pharmaceutical and AER as well as the hydrophobicity of the pharmaceutical. For instance, the high selectivity of the AER for DCF was due to the combination of Coulombic interactions between quaternary ammonium functional group of resin and carboxylate functional group of DCF, van der Waals interactions between polystyrene resin matrix and benzene rings of DCF, and possibly hydrogen bonding between dimethylethanol amine functional group side chain and carboxylate and amine functional groups of DCF. Based on analysis of covariance, the presence of multiple pharmaceuticals did not have a significant effect on ion-exchange removal when the NSAIDs were combined in solution. The AER reached saturation of the pharmaceuticals in a continuous-flow column at varying bed volumes following a decreasing order of DCF > NPX ≈ KTP > IBP. Complete regeneration of the column was achieved using a 5% (m/m) NaCl, equal-volume water-methanol solution. Results from multiple treatment and regeneration cycles provide insight into the practical application of pharmaceutical ion-exchange in ureolyzed urine using AER.

Measurement of the Parity-Violating Neutron Spin Rotation in 4He

PubMed Central

Bass, C. D.; Dawkins, J. M.; Luo, D.; Micherdzinska, A.; Sarsour, M.; Snow, W. M.; Mumm, H. P.; Nico, J. S.; Huffman, P. R.; Markoff, D. M.; Heckel, B. R.; Swanson, H. E.

2005-01-01

In the meson exchange model of weak nucleon-nucleon (NN) interactions, the exchange of virtual mesons between the nucleons is parameterized by a set of weak meson exchange amplitudes. The strengths of these amplitudes from theoretical calculations are not well known, and experimental measurements of parity-violating (PV) observables in different nuclear systems have not constrained their values. Transversely polarized cold neutrons traveling through liquid helium experience a PV spin rotation due to the weak interaction with an angle proportional to a linear combination of these weak meson exchange amplitudes. A measurement of the PV neutron spin rotation in helium (φPV (n,α)) would provide information about the relative strengths of the weak meson exchange amplitudes, and with the longitudinal analyzing power measurement in the p + α system, allow the first comparison between isospin mirror systems in weak NN interaction. An earlier experiment performed at NIST obtained a result consistent with zero: φPV (n,α) = (8.0 ±14(stat) ±2.2(syst)) ×10−7 rad / m[1]. We describe a modified apparatus using a superfluid helium target to increase statistics and reduce systematic effects in an effort to reach a sensitivity goal of 10−7 rad/m. PMID:27308122

The tight binding model study of the role of anisotropic AFM spin ordering in the charge ordered CMR manganites

NASA Astrophysics Data System (ADS)

Kar, J. K.; Panda, Saswati; Rout, G. C.

2017-05-01

We propose here a tight binding model study of the interplay between charge and spin orderings in the CMR manganites taking anisotropic effect due to electron hoppings and spin exchanges. The Hamiltonian consists of the kinetic energies of eg and t2g electrons of manganese ion. It further includes double exchange and Heisenberg interactions. The charge density wave interaction (CDW) describes an extra mechanism for the insulating character of the system. The CDW gap and spin parameters are calculated using Zubarev's Green's function technique and computed self-consistently. The results are reported in this communication.

Stopping powers and cross sections due to two-photon processes in relativistic nucleus-nucleus collision

NASA Technical Reports Server (NTRS)

Cheung, Wang K.; Norbury, John W.

1992-01-01

The radiation dose received from high energy galactic cosmic rays (GCR) is a limiting factor in the design of long duration space flights and the building of lunar and martian habitats. It is of vital importance to have an accurate understanding of the interactions of GCR in order to assess the radiation environment that the astronauts will be exposed to. Although previous studies have concentrated on the strong interaction process in GCR, there are also very large effects due to electromagnetic (EM) interactions. In this report we describe our first efforts at understanding these EM production processes due to two-photon collisions. More specifically, we shall consider particle production processes in relativistic heavy ion collisions (RHICs) through two-photon exchange.

A second-order theory for transverse ion heating and momentum coupling due to electrostatic ion cyclotron waves

NASA Technical Reports Server (NTRS)

Miller, Ronald H.; Winske, Dan; Gary, S. P.

1992-01-01

A second-order theory for electrostatic instabilities driven by counterstreaming ion beams is developed which describes momentum coupling and heating of the plasma via wave-particle interactions. Exchange rates between the waves and particles are derived, which are suitable for the fluid equations simulating microscopic effects on macroscopic scales. Using a fully kinetic simulation, the electrostatic ion cyclotron instability due to counterstreaming H(+) beams has been simulated. A power spectrum from the kinetic simulation is used to evaluate second-order exchange rates. The calculated heating and momentum loss from second-order theory is compared to the numerical simulation.

Flow-Induced New Channels of Energy Exchange in Multi-Scale Plasma Dynamics – Revisiting Perturbative Hybrid Kinetic-MHD Theory

PubMed Central

Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go

2016-01-01

It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle’s Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas. PMID:27160346

Collective behavior of stock price movements in an emerging market

NASA Astrophysics Data System (ADS)

Pan, Raj Kumar; Sinha, Sitabhra

2007-10-01

To investigate the universality of the structure of interactions in different markets, we analyze the cross-correlation matrix C of stock price fluctuations in the National Stock Exchange (NSE) of India. We find that this emerging market exhibits strong correlations in the movement of stock prices compared to developed markets, such as the New York Stock Exchange (NYSE). This is shown to be due to the dominant influence of a common market mode on the stock prices. By comparison, interactions between related stocks, e.g., those belonging to the same business sector, are much weaker. This lack of distinct sector identity in emerging markets is explicitly shown by reconstructing the network of mutually interacting stocks. Spectral analysis of C for NSE reveals that, the few largest eigenvalues deviate from the bulk of the spectrum predicted by random matrix theory, but they are far fewer in number compared to, e.g., NYSE. We show this to be due to the relative weakness of intrasector interactions between stocks, compared to the market mode, by modeling stock price dynamics with a two-factor model. Our results suggest that the emergence of an internal structure comprising multiple groups of strongly coupled components is a signature of market development.

Genetic exchange of fimbrial alleles exemplifies the adaptive virulence strategy of Porphyromonas gingivalis.

PubMed

Kerr, Jennifer E; Abramian, Jared R; Dao, Doan-Hieu V; Rigney, Todd W; Fritz, Jamie; Pham, Tan; Gay, Isabel; Parthasarathy, Kavitha; Wang, Bing-yan; Zhang, Wenjian; Tribble, Gena D

2014-01-01

Porphyromonas gingivalis is a gram-negative anaerobic bacterium, a member of the human oral microbiome, and a proposed "keystone" pathogen in the development of chronic periodontitis, an inflammatory disease of the gingiva. P. gingivalis is a genetically diverse species, and is able to exchange chromosomal DNA between strains by natural competence and conjugation. In this study, we investigate the role of horizontal DNA transfer as an adaptive process to modify behavior, using the major fimbriae as our model system, due to their critical role in mediating interactions with the host environment. We show that P. gingivalis is able to exchange fimbrial allele types I and IV into four distinct strain backgrounds via natural competence. In all recombinants, we detected a complete exchange of the entire fimA allele, and the rate of exchange varies between the different strain backgrounds. In addition, gene exchange within other regions of the fimbrial genetic locus was identified. To measure the biological implications of these allele swaps we compared three genotypes of fimA in an isogenic background, strain ATCC 33277. We demonstrate that exchange of fimbrial allele type results in profound phenotypic changes, including the quantity of fimbriae elaborated, membrane blebbing, auto-aggregation and other virulence-associated phenotypes. Replacement of the type I allele with either the type III or IV allele resulted in increased invasion of gingival fibroblast cells relative to the isogenic parent strain. While genetic variability is known to impact host-microbiome interactions, this is the first study to quantitatively assess the adaptive effect of exchanging genes within the pan genome cloud. This is significant as it presents a potential mechanism by which opportunistic pathogens may acquire the traits necessary to modify host-microbial interactions.

Nuclear quantum effects in water exchange around lithium and fluoride ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilkins, David M.; Manolopoulos, David E.; Dang, Liem X.

2015-02-14

We employ classical and ring polymer molecular dynamics simulations to study the effect of nuclear quantum fluctuations on the structure and the water exchange dynamics of aqueous solutions of lithium and fluoride ions. While we obtain reasonably good agreement with experimental data for solutions of lithium by augmenting the Coulombic interactions between the ion and the water molecules with a standard Lennard-Jones ion-oxygen potential, the same is not true for solutions of fluoride, for which we find that a potential with a softer repulsive wall gives much better agreement. A small degree of destabilization of the first hydration shell ismore » found in quantum simulations of both ions when compared with classical simulations, with the shell becoming less sharply defined and the mean residence time of the water molecules in the shell decreasing. In line with these modest differences, we find that the mechanisms of the exchange processes are unaffected by quantization, so a classical description of these reactions gives qualitatively correct and quantitatively reasonable results. We also find that the quantum effects in solutions of lithium are larger than in solutions of fluoride. This is partly due to the stronger interaction of lithium with water molecules, partly due to the lighter mass of lithium and partly due to competing quantum effects in the hydration of fluoride, which are absent in the hydration of lithium.« less

Incorporating water-release and lateral protein interactions in modeling equilibrium adsorption for ion-exchange chromatography.

PubMed

Thrash, Marvin E; Pinto, Neville G

2006-09-08

The equilibrium adsorption of two albumin proteins on a commercial ion exchanger has been studied using a colloidal model. The model accounts for electrostatic and van der Waals forces between proteins and the ion exchanger surface, the energy of interaction between adsorbed proteins, and the contribution of entropy from water-release accompanying protein adsorption. Protein-surface interactions were calculated using methods previously reported in the literature. Lateral interactions between adsorbed proteins were experimentally measured with microcalorimetry. Water-release was estimated by applying the preferential interaction approach to chromatographic retention data. The adsorption of ovalbumin and bovine serum albumin on an anion exchanger at solution pH>pI of protein was measured. The experimental isotherms have been modeled from the linear region to saturation, and the influence of three modulating alkali chlorides on capacity has been evaluated. The heat of adsorption is endothermic for all cases studied, despite the fact that the net charge on the protein is opposite that of the adsorbing surface. Strong repulsive forces between adsorbed proteins underlie the endothermic heat of adsorption, and these forces intensify with protein loading. It was found that the driving force for adsorption is the entropy increase due to the release of water from the protein and adsorbent surfaces. It is shown that the colloidal model predicts protein adsorption capacity in both the linear and non-linear isotherm regions, and can account for the effects of modulating salt.

First-principles study of the giant magnetic anisotropy energy in bulk Na4IrO4

NASA Astrophysics Data System (ADS)

Wang, Di; Tang, Feng; Du, Yongping; Wan, Xiangang

2017-11-01

In 5 d transition-metal oxides, novel properties arise from the interplay of electron correlations and spin-orbit interactions. Na4IrO4 , where the 5 d transition-metal Ir atom occupies the center of the square-planar coordination environment, has attracted research interest. Based on density functional theory, we present a comprehensive investigation of electronic and magnetic properties of Na4IrO4 . We propose the magnetic ground-state configuration, and find that the magnetic easy axis is perpendicular to the IrO4 plane. The magnetic anisotropy energy (MAE) of Na4IrO4 is found to be giant. We estimate the magnetic parameters in the generalized symmetry-allowed spin model, and find that the next-nearest-neighbor exchange interaction J2 is much larger than other intersite exchange interactions and results in the magnetic ground-state configuration. The numerical results reveal that the anisotropy of interatomic spin-exchange interaction is quite small and the huge MAE comes from the single-ion anisotropy. This compound has a large spin gap but very narrow spin-wave dispersion, due to the large single-ion anisotropy and quite small intersite exchange couplings. We clarify that these remarkable magnetic features are originated from its highly isolated and low-symmetry IrO4 moiety. We also explore the possibility to further enhance the MAE.

Influences of Ru-doping on the magnetic properties of Ca0.85Pr0.15Mn1- x Ru x O3

NASA Astrophysics Data System (ADS)

Phan, T. L.; Zhang, Y. D.; Yu, S. C.; Thanh, P. Q.; Yen, P. D. H.

2012-11-01

CaMnO3 is an antiferromagnet, in which the super-exchange interaction taking place between Mn4+ ions plays an important role. The doping of a small amount of 15% Pr into the Ca site, Ca0.85Pr0.15MnO3, leads to the appearance of Mn3+ ions, and introduces the ferromagnetic (FM) double-exchange interaction between Mn3+ and Mn4+ ions, which is dominant in a narrow temperature range of 90 ˜ 115 K. The FM interaction becomes strong for Ca0.85Pr0.15MnO3 doped with 4 and 8% Ru into the Mn site ( i.e., Ca0.85Pr0.15Mn1- x Ru x O3 with x = 0.04 and 0.08). The Curie temperature obtained for x = 0.04 and 0.08 are about 135 and 180 K, respectively. While the FM interaction in the former is dominant due to Mn3+-Mn4+ exchange pairs, the latter has the contribution of Ru ions. This results in remarkable differences in the features of their FM-paramagnetic phase transitions and their coercive fields H c .

Thermal relaxation and collective dynamics of interacting aerosol-generated hexagonal NiFe2O4 nanoparticles.

PubMed

Ortega, D; Kuznetsov, M V; Morozov, Yu G; Belousova, O V; Parkin, I P

2013-12-28

This article reports on the magnetic properties of interacting uncoated nickel ferrite (NiFe2O4) nanoparticles synthesized through an aerosol levitation-jet technique. A comprehensive set of samples with different compositions of background gas and metal precursors, as well as applied electric field intensities, has been studied. Nanoparticles prepared under a field of 210 kV m(-1) show moderately high-field irreversibility and shifted hysteresis loops after field-cooling, also exhibiting a joint temperature decrease of the exchange field and coercivity. The appearance of memory effects has been checked using the genuine ZFC protocol and the observed behavior cannot be fully explained in terms of thermal relaxation. Although dipolar interactions prevail, exchange interactions occur to a certain extent within a narrow range of applied fields. The origin of the slow dynamics in the system is found to be given by the interplay of the distribution of energy barriers due to size dispersion and the cooperative dynamics associated with frustrated interactions.

Ionization energies and electron affinities from a random-phase-approximation many-body Green's-function method including exchange interactions

NASA Astrophysics Data System (ADS)

Heßelmann, Andreas

2017-06-01

A many-body Green's-function method employing an infinite order summation of ring and exchange-ring contributions to the self-energy is presented. The individual correlation and relaxation contributions to the quasiparticle energies are calculated using an iterative scheme which utilizes density fitting of the particle-hole, particle-particle and hole-hole densities. It is shown that the ionization energies and electron affinities of this approach agree better with highly accurate coupled-cluster singles and doubles with perturbative triples energy difference results than those obtained with second-order Green's-function approaches. An analysis of the correlation and relaxation terms of the self-energy for the direct- and exchange-random-phase-approximation (RPA) Green's-function methods shows that the inclusion of exchange interactions leads to a reduction of the two contributions in magnitude. These differences, however, strongly cancel each other when summing the individual terms to the quasiparticle energies. Due to this, the direct- and exchange-RPA methods perform similarly for the description of ionization energies (IPs) and electron affinities (EAs). The coupled-cluster reference IPs and EAs, if corrected to the adiabatic energy differences between the neutral and charged molecules, were shown to be in very good agreement with experimental measurements.

Solar Wind Charge Exchange During Geomagnetic Storms

NASA Technical Reports Server (NTRS)

Robertson, Ina P.; Cravens, Thomas E.; Sibeck, David G.; Collier, Michael R.; Kuntz, K. D.

2012-01-01

On March 31st. 2001, a coronal mass ejection pushed the subsolar magnetopause to the vicinity of geosynchronous orbit at 6.6 RE. The NASA/GSFC Community Coordinated Modeling Center (CCMe) employed a global magnetohydrodynamic (MHD) model to simulate the solar wind-magnetosphere interaction during the peak of this geomagnetic storm. Robertson et aL then modeled the expected 50ft X-ray emission due to solar wind charge exchange with geocoronal neutrals in the dayside cusp and magnetosheath. The locations of the bow shock, magnetopause and cusps were clearly evident in their simulations. Another geomagnetic storm took place on July 14, 2000 (Bastille Day). We again modeled X-ray emission due to solar wind charge exchange, but this time as observed from a moving spacecraft. This paper discusses the impact of spacecraft location on observed X-ray emission and the degree to which the locations of the bow shock and magnetopause can be detected in images.

Insufficient Hartree–Fock Exchange in Hybrid DFT Functionals Produces Bent Alkynyl Radical Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oyeyemi, Victor B.; Keith, John A.; Pavone, Michele

2012-01-11

Density functional theory (DFT) is often used to determine the electronic and geometric structures of molecules. While studying alkynyl radicals, we discovered that DFT exchange-correlation (XC) functionals containing less than ~22% Hartree–Fock (HF) exchange led to qualitatively different structures than those predicted from ab initio HF and post-HF calculations or DFT XCs containing 25% or more HF exchange. We attribute this discrepancy to rehybridization at the radical center due to electron delocalization across the triple bonds of the alkynyl groups, which itself is an artifact of self-interaction and delocalization errors. Inclusion of sufficient exact exchange reduces these errors and suppressesmore » this erroneous delocalization; we find that a threshold amount is needed for accurate structure determinations. Finally, below this threshold, significant errors in predicted alkyne thermochemistry emerge as a consequence.« less

Probing Low-Mass Vector Bosons with Parity Nonconservation and Nuclear Anapole Moment Measurements in Atoms and Molecules

NASA Astrophysics Data System (ADS)

Dzuba, V. A.; Flambaum, V. V.; Stadnik, Y. V.

2017-12-01

In the presence of P -violating interactions, the exchange of vector bosons between electrons and nucleons induces parity-nonconserving (PNC) effects in atoms and molecules, while the exchange of vector bosons between nucleons induces anapole moments of nuclei. We perform calculations of such vector-mediated PNC effects in Cs, Ba+ , Yb, Tl, Fr, and Ra+ using the same relativistic many-body approaches as in earlier calculations of standard-model PNC effects, but with the long-range operator of the weak interaction. We calculate nuclear anapole moments due to vector-boson exchange using a simple nuclear model. From measured and predicted (within the standard model) values for the PNC amplitudes in Cs, Yb, and Tl, as well as the nuclear anapole moment of 133Cs, we constrain the P -violating vector-pseudovector nucleon-electron and nucleon-proton interactions mediated by a generic vector boson of arbitrary mass. Our limits improve on existing bounds from other experiments by many orders of magnitude over a very large range of vector-boson masses.

Delineation of spatial-temporal patterns of groundwater/surface-water interaction along a river reach (Aa River, Belgium) with transient thermal modeling

NASA Astrophysics Data System (ADS)

Anibas, Christian; Tolche, Abebe Debele; Ghysels, Gert; Nossent, Jiri; Schneidewind, Uwe; Huysmans, Marijke; Batelaan, Okke

2018-05-01

Among the advances made in analytical and numerical analysis methods to quantify groundwater/surface-water interaction, one methodology that stands out is the use of heat as an environmental tracer. A large data set of river and riverbed temperature profiles from the Aa River in Belgium has been used to examine the spatial-temporal variations of groundwater/surface-water interaction. Exchange fluxes were calculated with the numerical heat-transport code STRIVE. The code was applied in transient mode to overcome previous limitations of steady-state analysis, and allowed for the calculation of model quality. In autumn and winter the mean exchange fluxes reached -90 mm d-1, while in spring and early summer fluxes were -42 mm d-1. Predominantly gaining conditions occurred along the river reach; however, in a few areas the direction of flow changed in time. The river banks showed elevated fluxes up to a factor of 3 compared to the center of the river. Higher fluxes were detected in the upstream section of the reach. Due to the influence of exchange fluxes along the river banks, larger temporal variations were found in the downstream section. The exchange fluxes at the river banks seemed more driven by variable local exchange flows, while the center of the river was dominated by deep and steady regional groundwater flows. These spatial and temporal differences in groundwater/surface-water exchange show the importance of long-term investigations on the driving forces of hyporheic processes across different scales.

Minimizing back exchange in the hydrogen exchange-mass spectrometry experiment.

PubMed

Walters, Benjamin T; Ricciuti, Alec; Mayne, Leland; Englander, S Walter

2012-12-01

The addition of mass spectrometry (MS) analysis to the hydrogen exchange (HX) proteolytic fragmentation experiment extends powerful HX methodology to the study of large biologically important proteins. A persistent problem is the degradation of HX information due to back exchange of deuterium label during the fragmentation-separation process needed to prepare samples for MS measurement. This paper reports a systematic analysis of the factors that influence back exchange (solution pH, ionic strength, desolvation temperature, LC column interaction, flow rates, system volume). The many peptides exhibit a range of back exchange due to intrinsic amino acid HX rate differences. Accordingly, large back exchange leads to large variability in D-recovery from one residue to another as well as one peptide to another that cannot be corrected for by reference to any single peptide-level measurement. The usual effort to limit back exchange by limiting LC time provides little gain. Shortening the LC elution gradient by 3-fold only reduced back exchange by ~2%, while sacrificing S/N and peptide count. An unexpected dependence of back exchange on ionic strength as well as pH suggests a strategy in which solution conditions are changed during sample preparation. Higher salt should be used in the first stage of sample preparation (proteolysis and trapping) and lower salt (<20 mM) and pH in the second stage before electrospray injection. Adjustment of these and other factors together with recent advances in peptide fragment detection yields hundreds of peptide fragments with D-label recovery of 90% ± 5%.

Minimizing Back Exchange in the Hydrogen Exchange-Mass Spectrometry Experiment

NASA Astrophysics Data System (ADS)

Walters, Benjamin T.; Ricciuti, Alec; Mayne, Leland; Englander, S. Walter

2012-12-01

The addition of mass spectrometry (MS) analysis to the hydrogen exchange (HX) proteolytic fragmentation experiment extends powerful HX methodology to the study of large biologically important proteins. A persistent problem is the degradation of HX information due to back exchange of deuterium label during the fragmentation-separation process needed to prepare samples for MS measurement. This paper reports a systematic analysis of the factors that influence back exchange (solution pH, ionic strength, desolvation temperature, LC column interaction, flow rates, system volume). The many peptides exhibit a range of back exchange due to intrinsic amino acid HX rate differences. Accordingly, large back exchange leads to large variability in D-recovery from one residue to another as well as one peptide to another that cannot be corrected for by reference to any single peptide-level measurement. The usual effort to limit back exchange by limiting LC time provides little gain. Shortening the LC elution gradient by 3-fold only reduced back exchange by ~2 %, while sacrificing S/N and peptide count. An unexpected dependence of back exchange on ionic strength as well as pH suggests a strategy in which solution conditions are changed during sample preparation. Higher salt should be used in the first stage of sample preparation (proteolysis and trapping) and lower salt (<20 mM) and pH in the second stage before electrospray injection. Adjustment of these and other factors together with recent advances in peptide fragment detection yields hundreds of peptide fragments with D-label recovery of 90 % ± 5 %.

Rapid onset of decoherence in driven-dissipative Rydberg systems

NASA Astrophysics Data System (ADS)

Magnan, Eric; Boulier, Thomas; Bracamontes, Carlos; Maslek, James; Young, Jeremy; Gorshkov, Alexei; Porto, Trey; Rolston, Steven; JQI-Rubidium One Team

2017-04-01

Rydberg atoms have been strong candidates for the realization of quantum information processing and quantum simulation. Recently, however, there has been concerns about this approach due to the observation of a rapid onset of decoherence in large ensembles. In we provide experimental support for the hypothesis that this is due to the avalanche-like onset of exchange dipole interactions, fueled by blackbody transitions to nearby Rydberg states of opposite parity. Making a fully microscopic model has proven difficult as it requires beyond mean-field arguments, but the ubiquitousness of Rydberg-Rydberg blackbody transitions at room temperature and the always-resonant nature of dipole exchange interactions make it an interesting challenge, and argues for deeper study into the matter. In this poster, we present complementary measurements and analysis that confirm this mechanism. We also discuss several possibilities to reduce its impact on the system's coherence. This work was partially supported by NSF PIF, AFOSR, ARO, ARL-CDQI, and NSF PFC at JQI.

Spectroscopic study of carbaryl sorption on smectite from aqueous suspension.

PubMed

de Oliveira, Maurilio Fernandes; Johnston, Cliff T; Premachandra, G S; Teppen, Brian J; Li, Hui; Laird, David A; Zhu, Dongqiang; Boyd, Stephen A

2005-12-01

Sorption of carbaryl (1-naphthyl-N-methyl-carbamate) from aqueous suspension to smectite was studied using Fourier transform infrared (FTIR), high-performance liquid chromatography (HPLC) (for batch sorption), and quantum chemical methods. The amount of carbaryl sorbed was strongly dependent on the surface-charge density of the smectite with more sorption occurring on the two "low" surface-charge density smectites (SHCa-1 and SWy-2) compared to that of the high surface-charge SAz-1 smectite. In addition, the amount of carbaryl sorbed was strongly dependent on the nature of the exchangeable cation and followed the order of Ba approximately Cs approximately Ca > Mg approximately K > Na approximately Li for SWy-2. A similartrend was found for hectorite (SHCa-1) of Cs > Ba > Ca > K approximately Mg > Na approximately Li. Using the shift of the carbonyl stretching band as an indicator of the strength of interaction between carbaryl and the exchangeable cation, the observed order was Mg > Ca > Ba approximately K > Na > Cs. The position of the carbonyl stretching band shifted to lower wavenumbers with increasing ionic potential of the exchangeable cation. Density functional theory predicted a cation-induced lengthening of the C=O bond, resulting from the carbonyl group interacting directly with the exchangeable cation in support of the spectroscopic observations. Further evidence was provided by a concomitant shift in the opposite direction by several vibrational bands in the 1355-1375 cm(-1) region assigned to stretching bands of the carbamate N-Ccarbonyl and Oether-Ccarbonyl bonds. These data indicate that carbaryl sorption is due, in part, to site-specific interactions between the carbamate functional group and exchangeable cations, as evidenced by the FTIR data. However, these data suggest that hydrophobic interactions also contribute to the overall amount of carbaryl sorbed. For example, the FTIR data indicated thatthe weakest interaction occurred when Cs+ was the exchangeable cation. In contrast, the highest amount of carbaryl sorption was observed on Cs-exchanged smectite. Of all the cations studied, Cs has the lowest enthalpy of hydration. It is suggested that this low hydration energy provides the carbaryl with greater access to the hydrophobic regions of the siloxane surface.

Effect of Sr doping on the magnetic exchange interactions in manganites of type L a 1 - x S r x M n y A 1 - y O 3 ( A = Ga , Ti ; 0.1 ≤ y ≤ 1 )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furrer, Albert; Podlesnyak, Andrey A.; Pomjakushina, Ekaterina

Strontium doping transforms manganites of type La 1 - x Sr x Mn O 3 from an insulating antiferromagnet ( x = 0 ) to a metallic ferromagnet ( x > 0.16 ) due to the induced charge carriers (holes). We employed neutron scattering experiments in order to investigate the effect of Sr doping on a tailor-made compound of composition La 0.7 S r 0.3 M n 0.1 Ti 0.3 G a 0.6 O 3 . By the simultaneous doping with S r 2 + and Ti 4 + ions, the compound remains in the insulating state so thatmore » the magnetic interactions for large Sr doping can be studied in the absence of charge carriers. At T C = 215 K , there is a first-order reconstructive phase transition from the trigonal R - 3 c structure to the orthorhombic Pnma structure via an intermediate virtual configuration described by the common monoclinic subgroup P2 1 / c . The magnetic excitations associated with Mn 3 + dimers give evidence for two different nearest-neighbor ferromagnetic exchange interactions, in contrast to the undoped compound LaM n y A 1 - y O 3 where both ferromagnetic and antiferromagnetic interactions are present. Furthemore, the doping-induced changes of the exchange coupling originates from different Mn-O-Mn bond angles determined by neutron diffraction. The large fourth-nearest-neighbor interaction found for metallic manganites is absent in the insulating state. Here, we argue that the Ruderman-Kittel-Kasuya-Yosida interaction reasonably accounts for all the exchange couplings derived from the spin-wave dispersion in metallic manganites.« less

A quantum dot close to Stoner instability: The role of the Berry phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, Arijit, E-mail: arijitsahahri@gmail.com; Gefen, Yuval; Burmistrov, Igor

2012-10-15

The physics of a quantum dot with electron-electron interactions is well captured by the so called 'Universal Hamiltonian' if the dimensionless conductance of the dot is much higher than unity. Within this scheme interactions are represented by three spatially independent terms which describe the charging energy, the spin-exchange and the interaction in the Cooper channel. In this paper we concentrate on the exchange interaction and generalize the functional bosonization formalism developed earlier for the charging energy. This turned out to be challenging as the effective bosonic action is formulated in terms of a vector field and is non-abelian due tomore » the non-commutativity of the spin operators. Here we develop a geometric approach which is particularly useful in the mesoscopic Stoner regime, i.e., when the strong exchange interaction renders the system close to the Stoner instability. We show that it is sufficient to sum over the adiabatic paths of the bosonic vector field and, for these paths, the crucial role is played by the Berry phase. Using these results we were able to calculate the magnetic susceptibility of the dot. The latter, in close vicinity of the Stoner instability point, matches very well with the exact solution [I.S. Burmistrov, Y. Gefen, M.N. Kiselev, JETP Lett. 92 (2010) 179]. - Highlights: Black-Right-Pointing-Pointer We consider a conducting QD whose dynamics is governed by exchange interaction. Black-Right-Pointing-Pointer We study the model within the 'Universal Hamiltonian' framework. Black-Right-Pointing-Pointer The ensuing bosonic action is non-abelian (hence non-trivial). Black-Right-Pointing-Pointer We find that the low energy dynamics is governed by a fluctuating Berry phase term. Black-Right-Pointing-Pointer We calculate the partition function and the zero frequency magnetic susceptibility.« less

Effect of Sr doping on the magnetic exchange interactions in manganites of type L a 1 - x S r x M n y A 1 - y O 3 ( A = Ga , Ti ; 0.1 ≤ y ≤ 1 )

DOE PAGES

Furrer, Albert; Podlesnyak, Andrey A.; Pomjakushina, Ekaterina; ...

2017-03-14

Strontium doping transforms manganites of type La 1 - x Sr x Mn O 3 from an insulating antiferromagnet ( x = 0 ) to a metallic ferromagnet ( x > 0.16 ) due to the induced charge carriers (holes). We employed neutron scattering experiments in order to investigate the effect of Sr doping on a tailor-made compound of composition La 0.7 S r 0.3 M n 0.1 Ti 0.3 G a 0.6 O 3 . By the simultaneous doping with S r 2 + and Ti 4 + ions, the compound remains in the insulating state so thatmore » the magnetic interactions for large Sr doping can be studied in the absence of charge carriers. At T C = 215 K , there is a first-order reconstructive phase transition from the trigonal R - 3 c structure to the orthorhombic Pnma structure via an intermediate virtual configuration described by the common monoclinic subgroup P2 1 / c . The magnetic excitations associated with Mn 3 + dimers give evidence for two different nearest-neighbor ferromagnetic exchange interactions, in contrast to the undoped compound LaM n y A 1 - y O 3 where both ferromagnetic and antiferromagnetic interactions are present. Furthemore, the doping-induced changes of the exchange coupling originates from different Mn-O-Mn bond angles determined by neutron diffraction. The large fourth-nearest-neighbor interaction found for metallic manganites is absent in the insulating state. Here, we argue that the Ruderman-Kittel-Kasuya-Yosida interaction reasonably accounts for all the exchange couplings derived from the spin-wave dispersion in metallic manganites.« less

Quantifying hyporheic exchange dynamics in a highly regulated large river reach.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hammond, Glenn Edward; Zhou, T; Huang, M

Hyporheic exchange is an important mechanism taking place in riverbanks and riverbed sediments, where river water and shallow groundwater mix and interact with each other. The direction, magnitude, and residence time of the hyporheic flux that penetrates the river bed are critical for biogeochemical processes such as carbon and nitrogen cycling, and biodegradation of organic contaminants. Many approaches including field measurements and numerical methods have been developed to quantify the hyporheic exchanges in relatively small rivers. However, the spatial and temporal distributions of hyporheic exchanges in a large, regulated river reach remain less explored due to the large spatial domains,more » complexity of geomorphologic features and subsurface properties, and the great pressure gradient variations at the riverbed created by dam operations.« less

One-dimensional magnetic fluctuations in the spin-2 triangular lattice alpha-NaMnO2.

PubMed

Stock, C; Chapon, L C; Adamopoulos, O; Lappas, A; Giot, M; Taylor, J W; Green, M A; Brown, C M; Radaelli, P G

2009-08-14

The S=2 anisotropic triangular lattice alpha-NaMnO2 is studied by neutron inelastic scattering. Antiferromagnetic order occurs at T< or =45 K with opening of a spin gap. The spectral weight of the magnetic dynamics above the gap (Delta approximately equal to 7.5 meV) has been analyzed by the single-mode approximation. Excellent agreement with the experiment is achieved when a dominant exchange interaction (|J|/k(B) approximately 73 K), along the monoclinic b axis and a sizable easy-axis magnetic anisotropy (|D|/k(B) approximately 3 K) are considered. Despite earlier suggestions for two-dimensional spin interactions, the dynamics illustrate strongly coupled antiferromagnetic S=2 chains and cancellation of the interchain exchange due to the lattice topology. alpha-NaMnO2 therefore represents a model system where the geometric frustration is resolved through the lowering of the dimensionality of the spin interactions.

Crystal Structure of the Caged Magnetic Compound DyFe2Zn20 at Low Temperature Magnetic Ordering State

NASA Astrophysics Data System (ADS)

Kishii, Nobuya; Tateno, Shota; Ohashi, Masashi; Isikawa, Yosikazu

We have carried out X-ray powder diffraction and thermal expansion measurements of the caged magnetic compound DyFe2Zn20. Even though a strong magnetic anisotropy exists in the magnetization and magnetic susceptibility due to strong exchange interaction between Fe and Dy, almost all X-ray powder diffraction peaks at 14 K correspond to Bragg reflections of the cubic structural models not only at room temperature paramagnetic state but also at low temperature magnetic ordering state. Although the temperature change of the lattice constant is isotropic, an anomalous behavior was observed in the thermal expansion coefficient around 15 K, while the anomaly around TC = 53 K is not clear. The results indicate that the volume change is not caused by the ferromagnetic interaction between Fe and Dy but by the exchange interaction between two Dy ions.

A simple chip free-flow electrophoresis for monosaccharide sensing via supermolecule interaction of boronic acid functionalized quencher and fluorescent dye.

PubMed

Yin, Xiao-Yang; Dong, Jing-Yu; Wang, Hou-Yu; Li, Si; Fan, Liu-Yin; Cao, Cheng-Xi

2013-08-01

Here, a simple micro free-flow electrophoresis (μFFE) was developed for fluorescence sensing of monosaccharide via supermolecule interaction of synthesized boronic acid functionalized benzyl viologen (ο-BBV) and fluorescent dye. The μFFE contained two open electrode cavities and an ion-exchange membrane was sandwiched between two polymethylmethacrylate plates. The experiments demonstrated the following merits of developed μFFE: (i) up to 90.5% of voltage efficiency due to high conductivity of ion-exchange membrane; (ii) a strong ability against influence of bubble produced in two electrodes due to open design of electrode cavities; and (iii) reusable and washable separation chamber (45 mm × 17 mm × 100 μm, 77 μL) avoiding the discard of μFFE due to blockage of solute precipitation in chamber. Remarkably, the μFFE was first designed for the sensing of monosaccharide via the supermolecule interaction of synthesized ο-BBV, fluorescent dye, and monosaccharide. Under the optimized conditions, the minimum concentration of monosaccharide that could be detected was 1 × 10(-11) M. Finally, the developed device was used for the detection of 0.3 mM glucose spiked in human urine. All of the results demonstrated the feasibility of monosaccharide detection via the μFFE. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced asymmetric magnetization reversal in nanoscale Co/CoO arrays: competition between exchange bias and magnetostatic coupling.

PubMed

Girgis, E; Portugal, R D; Loosvelt, H; Van Bael, M J; Gordon, I; Malfait, M; Temst, K; Van Haesendonck, C; Leunissen, L H A; Jonckheere, R

2003-10-31

Magnetization reversal was studied in square arrays of square Co/CoO dots with lateral size varying between 200 and 900 nm. While reference nonpatterned Co/CoO films show the typical shift and increased width of the hysteresis loop due to exchange bias, the patterned samples reveal a pronounced size dependence. In particular, an anomaly appears in the upper branch of the magnetization cycle and becomes stronger as the dot size decreases. This anomaly, which is absent at room temperature in the patterned samples, can be understood in terms of a competition between magnetostatic interdot interaction and exchange anisotropy during the magnetic switching process.

Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

DOE PAGES

Christianson, Andrew D.; Hahn, Steven E.; Fishman, Randy Scott; ...

2016-05-09

Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientationmore » that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.« less

Variability in benthic exchange rate, depth, and residence time beneath a shallow coastal estuary

NASA Astrophysics Data System (ADS)

Russoniello, C. J.; Michael, H. A.; Heiss, J.

2017-12-01

Hydrodynamically-driven exchange of water between the water column and shallow seabed aquifer, benthic exchange, is a significant and dynamic component of coastal and estuarine fluid budgets, but wave-induced benthic exchange has not been measured in the field. Mixing between surface water and groundwater solutes promotes ecologically important chemical reactions, so quantifying benthic exchange rates, depths, and residence times, constrains estimates of coastal chemical cycling. In this study, we present the first field-based direct measurements of wave-induced exchange and compare it to exchange induced by the other primary drivers of exchange - tides, and currents. We deployed instruments in a shallow estuary to measure benthic exchange and temporal variability over an 11-day period. Differential pressure sensors recorded pressure gradients across the seabed, and up-and down-looking ADCPs recorded currents and pressures from which wave parameters, surface-water currents, and water depth were determined. Wave-induced exchange was calculated directly from 1) differential pressure measurements, and indirectly with an analytical solution based on wave parameters from 2) ADCP and 3) weather station data. Groundwater flow models were used to assess the effects of aquifer properties on benthic exchange depth and residence time. Benthic exchange driven by tidal pumping or current-bedform interaction was calculated from tidal stage variation and from ADCP-measured currents at the bed, respectively. Waves were the primary benthic exchange driver (average = 20.0 cm/d, maximum = 92.3 cm/d) during the measurement period. Benthic exchange due to tides (average = 3.7 cm/d) and current-bedform interaction (average = 6.5x10-2 cm/d) was much lower. Wave-induced exchange calculated from pressure measurements and ADCP-measured wave parameters matched well, but wind-based rates underestimated wave energy and exchange. Groundwater models showed that residence time and depth increased in high-permeability, incompressible aquifers, and exchange rates increased in low-permeability, compressible aquifers. These findings support and extend the utility of existing wave-induced exchange solutions and will help managers assess the importance of benthic exchange on coastal chemical cycling.

Developing Collaborative Cyber Communities to Prepare Tomorrow's Teachers

ERIC Educational Resources Information Center

Lord, Gillian; Lomicka, Lara L.

2004-01-01

Computer-mediated exchange and interaction have become topics of debate and discussion in the past several years due to the growing interest in synchronous and asynchronous communication and their role in language acquisition, learning, and teaching (Liu, Moore, Graham, & Lee, 2002). This article offers a model for a collaborative course on…

The interactions of sorbates with gallosilicates and alkali-metal exchanged gallosilicates

NASA Astrophysics Data System (ADS)

Limtrakul, J.; Kuno, M.; Treesukol, P.

1999-11-01

Structures, energetics and vibrational frequencies of the interaction of adsorbates with H-aluminosilicates (H-AlZ), H-gallosilicates (H-GaZ), alkali-metal exchanged aluminosilicates (X-AlZ) and alkali-metal exchanged gallosilicates (X-GaZ), where X being Li, Na, or K, have been carried out at B3LYP and HF levels of theory with 6-31G(d) as the basis set. The charge compensating alkali-metal ions can affect the catalytically active site (Si-O-T where T=Al or Ga) by weakening the Si-O, Al-O, and Ga-O bonds as compared to their anionic frameworks. Comparing the net stabilization energies, Δ ENSE, of the naked alkali-metal/H 2O adducts with those of the alkali-metal exchanged zeolite/H 2O systems, the latter amounts only to about 50% of the former, which is partly due to the destabilizing role of the negative zeolitic oxygen frameworks surrounding the cations. The interaction of sorbates with the alkali-metal exchanged gallosilicates can be employed to probe the field strength inside the catalytic frameworks as indicated by the plot of the binding energy, Δ E, versus 1/ RX-O w2, with R(X-O w) being the distance between the cationic nucleus and the oxygen atom of the adsorbate. The IR spectra of H 2O adsorbed on Na-AlZ are calculated to be 3584, 3651, and 1686 cm -1. The obtained results are in excellent agreement with the very recent experimental IR spectra of water adsorbed on Na-ZSM-5 of Zecchina et al. (J. Phys. Chem., 100 (1996) 16 484). Other important features, i.e. the correlation between Δ νOH and, Δ E, R(X-O w) , and 1/ RX-O w2, cationic size, demonstrate that the interactions of sorbates with alkali-metal exchanged gallosilicates are well approximated by electrostatic contribution.

Magnetic spiral induced by strong correlations in MnAu2

NASA Astrophysics Data System (ADS)

Glasbrenner, J. K.; Bussmann, K. M.; Mazin, I. I.

2014-10-01

The compound MnAu2 is one of the oldest known spin-spiral materials, yet the nature of the spiral state is still not clear. The spiral cannot be explained via relativistic effects due to the short pitch of the spiral and the weakness of the spin-orbit interaction in Mn, and another common mechanism, nesting, is ruled out as direct calculations show no features at the relevant wave vector. We propose that the spiral state is induced by a competition between the short-range antiferromagnetic exchange and a long-range interaction induced by the polarization of Au bands, similar to double exchange. We find that, contrary to earlier reports, the ground state in standard density functional theory is ferromagnetic, i.e., the latter interaction dominates. However, an accounting for Coulomb correlations via a Hubbard U suppresses the Schrieffer-Wolff-type s-d magnetic interaction between Mn and Au faster than the superexchange interaction, favoring a spin-spiral state. For realistic values of U, the resulting spiral wave vector is in close agreement with experiment.

The effects of intramolecular H-bond formation on the stability constant and water exchange rate of the Gd(III)-diethylenetriamine-N'-(3-amino-1,1-propylenephosphonic)-N, N,N'',N''-tetraacetate complex.

PubMed

Baranyai, Zsolt; Gianolio, Eliana; Ramalingam, Kondareddiar; Swenson, Rolf; Ranganathan, Ramachandran; Brücher, E; Aime, Silvio

2007-01-01

The binding interaction of metal chelates to biological macromolecules, though driven by properly devoted recognition synthons, may cause dramatic changes in some property associated with the coordination cage such as the thermodynamic stability or the exchange rate of the metal coordinated water. Such changes are due to electrostatic and H-bonding interactions involving atoms of the coordination cage and atoms of the biological molecule at the binding site. To mimic this type of H-bonding interactions, lanthanide(III) complexes with a DTPA-monophosphonate ligand bearing a propylamino moiety (H6NP-DTPA) were synthesized. Their thermodynamic stabilities and the exchange lifetime of the coordinated water molecule (for the Gd-complex) were compared with those of the analog complexes with DTPA and the parent DTPA-monophosphonate derivative (H6P-DTPA). It was found that the intramolecular H-bond between the epsilon-amino group and the phosphonate moiety in NP-DTPA complexes causes displacements of electric charges in their coordination cage that are markedly pH dependent. In turn, this affects the characteristic properties of the coordination cage. In particular it results in a marked elongation of the exchange lifetime of the coordinated water molecule. (c) 2007 John Wiley & Sons, Ltd.

Polyanion Driven Antiferromagnetic and Insulating Ground State of Olivine Phosphates: LiMPO4

NASA Astrophysics Data System (ADS)

Jena, Ajit Kumar; Nanda, B. R. K.; Condensed Matter Theory; Computation Team

Through density functional calculations we have investigated the electronic and magnetic properties of LiMPO4, where M is a 3d transition metal element. We find that contrary to many transition metal oxides, in these Olivine phosphates the band gap is originated due to crystal field anisotropy as well as weak O-p - M-d covalent interaction. Both of them are attributed to the presence of PO43- polyanion. The anisotropic crystal field, in the absence of covalent interactions, creates atomically localized non-degenerate M-d states and therefore the gap is a natural outcome. Onsite repulsion, due to strong correlation effect, further enhances the gap. These localized d states favor high-spin configuration which leads to antiferromagnetic ordering due to Hund's coupling. Experimentally observed low Neel temperature of this family of compounds is explained from the DFT obtained spin exchange interaction parameters. Work supported by Nissan Research Program.

Neutrino nuclear responses for double beta decays and astro neutrinos by charge exchange reactions

NASA Astrophysics Data System (ADS)

Ejiri, Hiroyasu

2014-09-01

Neutrino nuclear responses are crucial for neutrino studies in nuclei. Charge exchange reactions (CER) are shown to be used to study charged current neutrino nuclear responses associated with double beta decays(DBD)and astro neutrino interactions. CERs to be used are high energy-resolution (He3 ,t) reactions at RCNP, photonuclear reactions via IAR at NewSUBARU and muon capture reactions at MUSIC RCNP and MLF J-PARC. The Gamow Teller (GT) strengths studied by CERs reproduce the observed 2 neutrino DBD matrix elements. The GT and spin dipole (SD) matrix elements are found to be reduced much due to the nucleon spin isospin correlations and the non-nucleonic (delta isobar) nuclear medium effects. Impacts of the reductions on the DBD matrix elements and astro neutrino interactions are discussed.

Early-stage aggregation in three-dimensional charged granular gas.

PubMed

Singh, Chamkor; Mazza, Marco G

2018-02-01

Neutral grains made of the same dielectric material can attain considerable charges due to collisions and generate long-range interactions. We perform molecular dynamic simulations in three dimensions for a dilute, freely cooling granular gas of viscoelastic particles that exchange charges during collisions. As compared to the case of clustering of viscoelastic particles solely due to dissipation, we find that the electrostatic interactions due to collisional charging alter the characteristic size, morphology, and growth rate of the clusters. The average cluster size grows with time as a power law, whose exponent is relatively larger in the charged gas than the neutral case. The growth of the average cluster size is found to be independent of the ratio of characteristic Coulomb to kinetic energy, or equivalently, of the typical Bjerrum length. However, this ratio alters the crossover time of the growth. Both simulations and mean-field calculations based on Smoluchowski's equation suggest that a suppression of particle diffusion due to the electrostatic interactions helps in the aggregation process.

Early-stage aggregation in three-dimensional charged granular gas

NASA Astrophysics Data System (ADS)

Singh, Chamkor; Mazza, Marco G.

2018-02-01

Neutral grains made of the same dielectric material can attain considerable charges due to collisions and generate long-range interactions. We perform molecular dynamic simulations in three dimensions for a dilute, freely cooling granular gas of viscoelastic particles that exchange charges during collisions. As compared to the case of clustering of viscoelastic particles solely due to dissipation, we find that the electrostatic interactions due to collisional charging alter the characteristic size, morphology, and growth rate of the clusters. The average cluster size grows with time as a power law, whose exponent is relatively larger in the charged gas than the neutral case. The growth of the average cluster size is found to be independent of the ratio of characteristic Coulomb to kinetic energy, or equivalently, of the typical Bjerrum length. However, this ratio alters the crossover time of the growth. Both simulations and mean-field calculations based on Smoluchowski's equation suggest that a suppression of particle diffusion due to the electrostatic interactions helps in the aggregation process.

Effect of exact Coulomb-exchange calculations on band-head spectra of odd-proton nuclei

NASA Astrophysics Data System (ADS)

Koh, Meng-Hock; Nurhafiza, Mohamad Nor

2017-10-01

Previous calculations of band-head energy spectra of odd-mass heavy nuclei in the Hartree-Fock-plus-Bardeen-Cooper-Schrieffer (HF-BCS) framework showed that the agreement with data is better for odd-neutron as compared to odd-proton nuclei. The reason for a poorer agreement with data for the latter have been ascribed to the possible usage of the Slater approximation in calculating the Coulomb-exchange term. In this work, we report the effect of exact Coulomb-exchange calculations on band-head energy spectra of two odd-proton nuclei (namely 237Np and 241Am) as compared to the results obtained using the Slater approximation. We performed self-consistent blocking calculations while taking the breaking of time-reversal symmetry at the mean-field level into account due to the unpaired nucleon. The SkM* and SIII parametrizations of the Skyrme interaction have been employed to approximate the effective nucleon-nucleon interaction while a seniority force is used for the pairing channel. Contrary to what was expected, our preliminary results show no improvement on the band-head spectra as compared to data when the Coulomb-exchange term is calculated exactly.

Chromosome damage in human cells by γ rays, α particles and heavy ions: track interactions in basic dose-response relationships.

PubMed

Loucas, Bradford D; Durante, Marco; Bailey, Susan M; Cornforth, Michael N

2013-01-01

We irradiated normal human lymphocytes and fibroblasts with (137)Cs γ rays, 3.5 MeV α particles and 1 GeV/amu (56)Fe ions and measured the subsequent formation of chromosome-type aberrations by mFISH at the first mitosis following irradiation. This was done for the purposes of characterizing the shape of dose-response relationships and determining the frequency distribution of various aberration types with respect to the parameters of dose, radiation quality and cell type. Salient results and conclusions include the following. For low-LET γ rays, lymphocytes showed a more robust dose response for overall damage and a higher degree of upward curvature compared to fibroblasts. For both sources of high-LET radiation, and for both cell types, the response for simple and complex exchanges was linear with dose. Independent of all three parameters considered, the most likely damage outcome was the formation of a simple exchange event involving two breaks. However, in terms of the breakpoints making up exchange events, the majority of damage registered following HZE particle irradiation was due to complex aberrations involving multiple chromosomes. This adds a decidedly nonlinear component to the overall breakpoint response, giving it a significant degree of positive curvature, which we interpret as being due to interaction between ionizations of the primary HZE particle track and long-range δ rays produced by other nearby tracks. While such track interaction had been previously theorized, to the best of our knowledge, it has never been demonstrated experimentally.

Chromosome Damage in Human Cells by γ Rays, α Particles and Heavy Ions: Track Interactions in Basic Dose-Response Relationships

PubMed Central

Loucas, Bradford D.; Durante, Marco; Bailey, Susan M.; Cornforth, Michael N.

2013-01-01

We irradiated normal human lymphocytes and fibroblasts with 137Cs γ rays, 3.5 MeV α particles and 1 GeV/amu 56Fe ions and measured the subsequent formation of chromosome-type aberrations by mFISH at the first mitosis following irradiation. This was done for the purposes of characterizing the shape of dose-response relationships and determining the frequency distribution of various aberration types with respect to the parameters of dose, radiation quality and cell type. Salient results and conclusions include the following. For low-LET γ rays, lymphocytes showed a more robust dose response for overall damage and a higher degree of upward curvature compared to fibroblasts. For both sources of high-LET radiation, and for both cell types, the response for simple and complex exchanges was linear with dose. Independent of all three parameters considered, the most likely damage outcome was the formation of a simple exchange event involving two breaks. However, in terms of the breakpoints making up exchange events, the majority of damage registered following HZE particle irradiation was due to complex aberrations involving multiple chromosomes. This adds a decidedly nonlinear component to the overall breakpoint response, giving it a significant degree of positive curvature, which we interpret as being due to interaction between ionizations of the primary HZE particle track and long-range δ rays produced by other nearby tracks. While such track interaction had been previously theorized, to the best of our knowledge, it has never been demonstrated experimentally. PMID:23198992

Nuclear quantum effects in water exchange around lithium and fluoride ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilkins, David M.; Manolopoulos, David; Dang, Liem X.

2015-02-14

We employ classical and ring polymer molecular dynamics simulations to study the effect of nuclear quantum fluctuations on the structure and the water exchange dynamics of aqueous solutions of lithium and fluoride ions. While we obtain reasonably good agreement with experimental data for solutions of lithium by augmenting the Coulombic interactions between the ion and the water molecules with a standard Lennard-Jones ion-oxygen potential, the same is not true for solutions of fluoride, for which we find that a potential with a softer repulsive wall gives much better agreement. A small degree of destabilization of the first hydration shell ismore » found in quantum simulations of both ions when compared with classical simulations, with the shell becoming less sharply defined and the mean residence time of the water molecules in the shell decreasing. In line with these modest differences, we find that the mechanisms of the water exchange reactions are unaffected by quantization, so a classical description of these reactions gives qualitatively correct and quantitatively reasonable results. We also find that the quantum effects in solutions of lithium are larger than in solutions of fluoride. This is partly due to the stronger interaction of lithium with water molecules, partly due to the lighter mass of lithium, and partly due to competing quantum effects in the hydration of fluoride, which are absent in the hydration of lithium. LXD was supported by US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.« less

Cation-Exchanged Zeolitic Chalcogenides for CO2 Adsorption.

PubMed

Yang, Huajun; Luo, Min; Chen, Xitong; Zhao, Xiang; Lin, Jian; Hu, Dandan; Li, Dongsheng; Bu, Xianhui; Feng, Pingyun; Wu, Tao

2017-12-18

We report here the intrinsic advantages of a special family of porous chalcogenides for CO 2 adsorption in terms of high selectivity of CO 2 /N 2 , large uptake capacity, and robust structure due to their first-ever unique integration of the chalcogen-soft surface, high porosity, all-inorganic crystalline framework, and the tunable charge-to-volume ratio of exchangeable cations. Although tuning the CO 2 adsorption properties via the type of exchangeable cations has been well-studied in oxides and MOFs, little is known about the effects of inorganic exchangeable cations in porous chalcogenides, in part because ion exchange in chalcogenides can be very sluggish and incomplete due to their soft character. We have demonstrated that, through a methodological change to progressively tune the host-guest interactions, both facile and nearly complete ion exchange can be accomplished. Herein, a series of cation-exchanged zeolitic chalcogenides (denoted as M@RWY) were studied for the first time for CO 2 adsorption. Samples were prepared through a sequential ion-exchange strategy, and Cs + -, Rb + -, and K + -exchanged samples demonstrated excellent CO 2 adsorption performance. Particularly, K@RWY has the superior CO 2 /N 2 selectivity with the N 2 adsorption even undetected at either 298 or 273 K. It also has the large uptake of 6.3 mmol/g (141 cm 3 /g) at 273 K and 1 atm with an isosteric heat of 35-41 kJ mol -1 , the best among known porous chalcogenides. Moreover, it permits a facile regeneration and exhibits an excellent recyclability, as shown by the multicycling adsorption experiments. Notably, K@RWY also demonstrates a strong tolerance toward water.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Prashant; Harbola, Manoj K.; Johnson, Duane D.

Here, this work constitutes a comprehensive and improved account of electronic-structure and mechanical properties of silicon-nitride (more » $${\\rm Si}_{3}$$ $${\\rm N}_{4}$$ ) polymorphs via van Leeuwen and Baerends (LB) exchange-corrected local density approximation (LDA) that enforces the exact exchange potential asymptotic behavior. The calculated lattice constant, bulk modulus, and electronic band structure of $${\\rm Si}_{3}$$ $${\\rm N}_{4}$$ polymorphs are in good agreement with experimental results. We also show that, for a single electron in a hydrogen atom, spherical well, or harmonic oscillator, the LB-corrected LDA reduces the (self-interaction) error to exact total energy to ~10%, a factor of three to four lower than standard LDA, due to a dramatically improved representation of the exchange-potential.« less

A weak cation-exchange monolith as stationary phase for the separation of peptide diastereomers by CEC.

PubMed

Ludewig, Ronny; Nietzsche, Sandor; Scriba, Gerhard K E

2011-01-01

A CEC weak cation-exchange monolith has been prepared by in situ polymerization of acrylamide, methylenebisacrylamide and 4-acrylamidobutyric acid in a decanol-dimethylsulfoxide mixture as porogen. The columns were evaluated by SEM and characterized with regard to the separation of diastereomers and α/β-isomers of aspartyl peptides. Column preparation was reproducible as evidenced by comparison of the analyte retention times of several columns prepared simultaneously. Analyte separation was achieved using mobile phases consisting of acidic phosphate buffer and ACN. Under these conditions the peptides migrated due to their electrophoretic mobility but the EOF also contributed as driving force as a function of the pH of the mobile phase due to increasing dissociation of the carboxyl groups of the polymer. Raising the pH of the mobile phase also resulted in deprotonation of the peptides reducing analyte mobility. Due to these mechanisms each pair of diastereomeric peptides displayed the highest resolution at a different pH of the buffer component of the mobile phase. Comparing the weak-cation exchange monolith to an RP monolith and a strong cation-exchange monolith different elution order of some peptide diastereomers was observed, clearly illustrating that interactions with the stationary phase contribute to the CEC separations. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The ground state of metallic nano-structures in heavily irradiated NaCl-KBF4

NASA Astrophysics Data System (ADS)

Cherkasov, F. G.; L'Vov, S. G.; Tikhonov, D. A.; den Hartog, H. W.; Vainshtein, D. I.

ESR, NMR and static magnetic susceptibility measurements of heavily irradiated NaCl-K and NaCl-KBF4 are reported. Up to 10% of the NaCl-molecules are transformed into metallic Na nanoparticles and Cl-2 precipitates. In addition, there are paramagnetic F- and F-aggregates, which are coupled by exchange interactions to the conduction electrons in the nanoparticles. Above 160 K the NMR and ESR signals of NaCl-K and NaCl-KBF4 show Pauli paramagnetism and the properties of the Na nanoparticles are similar to bulk sodium. A single ESR line is observed revealing exchange interaction between conduction electrons in the nano-particles and F-aggregates. The observed decrease of the ESR susceptibility with decreasing temperature is due to a metal-insulator transition. The conduction electrons are localized below 40 K and the above mentioned F-aggregate centers contribute significantly to the overall ESR signal. For NaCl-KBF4 we observed that with decreasing temperature the ESR line shifts towards lower fields due to antiferromagnetic ordering and internal magnetic fields.

Ultrafast Magnetism of Multi-component Ferromagnets and Ferrimagnets on the Time Scale of the Exchange Interaction

NASA Astrophysics Data System (ADS)

Radu, Ilie

2012-02-01

Revealing the ultimate speed limit at which magnetic order can be controlled, is a fundamental challenge of modern magnetism having far reaching implications for the magnetic recording industry [1]. Exchange interaction is the strongest force in magnetism, being ultimately responsible for ferromagnetic or antiferromagnetic spin order. How do spins react after being optically excited on a timescale of or even faster than the exchange interaction? Here, we demonstrate that femtosecond (fs) measurements of ferrimagnetic and ferromagnetic alloys using X-ray magnetic circular dichroism provide revolutionary new insights into the problem of ultrafast magnetism on timescales pertinent to the exchange interaction. In particular, we show that upon fs optical excitation the ultrafast spin reversal of GdFeCo - a material with antiferromagnetic coupling of spins - occurs via a transient ferromagnetic state [2]. The latter emerges due to different dynamics of the Gd and Fe magnetic moments: Gd switches within 1.5 ps while it takes only 300 fs for Fe. Thus, by using a single fs laser pulse one can force the spin system to evolve via an energetically unfavorable way and temporarily switch from an antiferromagnetic to a ferromagnetic type of ordering. In order to understand whether the observation of this temporarily decoupled and element-specific dynamics is a general phenomenon or just something strictly related to the case of ferrimagnetic GdFeCo, we have investigated the demagnetization of the archetypal ferromagnetic NiFe alloys. Essentially, we observe the same distinct magnetization dynamics of the constituent magnetic moments: Ni demagnetizes within ˜300 fs being much faster than the demagnetization of Fe of ˜800 fs. This distinct demagnetization behavior leads to an apparent decoupling of the Fe and Ni magnetic moments on a few hundreds of fs time scale, despite the strong exchange interaction of 260meV (˜16 fs) that couples them. These observations supported by atomistic simulations, present a novel concept of manipulating magnetic order on different classes of magnetic materials on timescales of the exchange interaction [3]. [4pt] [1] A. Kirilyuk, A.V. Kimel and Th. Rasing, Rev. Mod. Phys. 82, 2731 (2010). [0pt] [2] I. Radu et al., Nature 472, 205 (2011). [0pt] [3] I. Radu et al., submitted (2011).

High Performance Non-Dispersive X-Ray Spectrometers for Charge Exchange Measurements

NASA Technical Reports Server (NTRS)

Porter Frederick; Adams, J.; Beiersdorfer, P.; Brown, G. V.; Karkatoua, D.; Kelley, R. L.; Kilbourne, C. A.; Lautenagger, M.

2010-01-01

Currently, the only measurements of cosmological charge exchange have been made using low resolution, non-dispersive spectrometers like the PSPC on ROSAT and the CCD instruments on Chandra and XMM/Newton. However, upcoming cryogenic spectrometers on Astro-H and IXO will add vast new capabilities to investigate charge exchange in local objects such as comets and planetary atmospheres. They may also allow us to observe charge exchange in extra-solar objects such as galactic supernova remnants. With low spectral resolution instruments such as CCDs, x-ray emission due to charge exchange recombination really only provides information on the acceptor species, such as the solar wind. With the new breed of x-ray calorimeter instruments, emission from charge exchange becomes highly diagnostic allowing one to uniquely determine the acceptor species, ionization state, donor species and ionization state, and the relative velocity of the interaction. We will describe x-ray calorimeter instrumentation and its potential for charge exchange measurements in the near term. We will also touch on the instrumentation behind a decade of high resolution measurements of charge exchange using an x-ray calorimeter at the Lawrence Livermore National Laboratory.

Physical Forces between Humans and How Humans Attract and Repel Each Other Based on Their Social Interactions in an Online World

PubMed Central

Thurner, Stefan; Fuchs, Benedikt

2015-01-01

Physical interactions between particles are the result of the exchange of gauge bosons. Human interactions are mediated by the exchange of messages, goods, money, promises, hostilities, etc. While in the physical world interactions and their associated forces have immediate dynamical consequences (Newton’s laws) the situation is not clear for human interactions. Here we quantify the relative acceleration between humans who interact through the exchange of messages, goods and hostilities in a massive multiplayer online game. For this game we have complete information about all interactions (exchange events) between about 430,000 players, and about their trajectories (movements) in the metric space of the game universe at any point in time. We use this information to derive “interaction potentials" for communication, trade and attacks and show that they are harmonic in nature. Individuals who exchange messages and trade goods generally attract each other and start to separate immediately after exchange events end. The form of the interaction potential for attacks mirrors the usual “hit-and-run" tactics of aggressive players. By measuring interaction intensities as a function of distance, velocity and acceleration, we show that “forces" between players are directly related to the number of exchange events. We find an approximate power-law decay of the likelihood for interactions as a function of distance, which is in accordance with previous real world empirical work. We show that the obtained potentials can be understood with a simple model assuming an exchange-driven force in combination with a distance-dependent exchange rate. PMID:26196505

Physical Forces between Humans and How Humans Attract and Repel Each Other Based on Their Social Interactions in an Online World.

PubMed

Thurner, Stefan; Fuchs, Benedikt

2015-01-01

Physical interactions between particles are the result of the exchange of gauge bosons. Human interactions are mediated by the exchange of messages, goods, money, promises, hostilities, etc. While in the physical world interactions and their associated forces have immediate dynamical consequences (Newton's laws) the situation is not clear for human interactions. Here we quantify the relative acceleration between humans who interact through the exchange of messages, goods and hostilities in a massive multiplayer online game. For this game we have complete information about all interactions (exchange events) between about 430,000 players, and about their trajectories (movements) in the metric space of the game universe at any point in time. We use this information to derive "interaction potentials" for communication, trade and attacks and show that they are harmonic in nature. Individuals who exchange messages and trade goods generally attract each other and start to separate immediately after exchange events end. The form of the interaction potential for attacks mirrors the usual "hit-and-run" tactics of aggressive players. By measuring interaction intensities as a function of distance, velocity and acceleration, we show that "forces" between players are directly related to the number of exchange events. We find an approximate power-law decay of the likelihood for interactions as a function of distance, which is in accordance with previous real world empirical work. We show that the obtained potentials can be understood with a simple model assuming an exchange-driven force in combination with a distance-dependent exchange rate.

Correlated lateral phase separations in stacks of lipid membranes

NASA Astrophysics Data System (ADS)

Hoshino, Takuma; Komura, Shigeyuki; Andelman, David

2015-12-01

Motivated by the experimental study of Tayebi et al. [Nat. Mater. 11, 1074 (2012)] on phase separation of stacked multi-component lipid bilayers, we propose a model composed of stacked two-dimensional Ising spins. We study both its static and dynamical features using Monte Carlo simulations with Kawasaki spin exchange dynamics that conserves the order parameter. We show that at thermodynamical equilibrium, due to strong inter-layer correlations, the system forms a continuous columnar structure for any finite interaction across adjacent layers. Furthermore, the phase separation shows a faster dynamics as the inter-layer interaction is increased. This temporal behavior is mainly due to an effective deeper temperature quench because of the larger value of the critical temperature, Tc, for larger inter-layer interaction. When the temperature ratio, T/Tc, is kept fixed, the temporal growth exponent does not increase and even slightly decreases as a function of the increased inter-layer interaction.

Spin Qubits in Germanium Structures with Phononic Gap

NASA Technical Reports Server (NTRS)

Smelyanskiy, V. N.; Vasko, F. T.; Hafiychuk, V. V.; Dykman, M. I.; Petukhov, A. G.

2014-01-01

We propose qubits based on shallow donor electron spins in germanium structures with phononic gap. We consider a phononic crystal formed by periodic holes in Ge plate or a rigid cover / Ge layer / rigid substrate structure with gaps approximately a few GHz. The spin relaxation is suppressed dramatically, if the Zeeman frequency omegaZ is in the phononic gap, but an effective coupling between the spins of remote donors via exchange of virtual phonons remains essential. If omegaZ approaches to a gap edge in these structures, a long-range (limited by detuning of omegaZ) resonant exchange interaction takes place. We estimate that ratio of the exchange integral to the longitudinal relaxation rate exceeds 10(exp 5) and lateral scale of resonant exchange 0.1 mm. The exchange contribution can be verified under microwave pumping through oscillations of spin echo signal or through the differential absorption measurements. Efficient manipulation of spins due to the Rabi oscillations opens a new way for quantum information applications.

Exchange and correlation energies in silicene illuminated by circularly polarized light

NASA Astrophysics Data System (ADS)

Iurov, Andrii; Gumbs, Godfrey; Huang, Danhong

2017-05-01

Both the exchange and correlation energies due to Coulomb and spin-orbit interactions in a monolayer silicene with a buckled honeycomb lattice are calculated. We use Lindhard formalism for the polarizability. Many-body effects in such Dirac-like materials are studied with an emphasis on the influence of on-site potential difference ? between two sublattices. Our calculations have shown that the presence of an energy bandgap ? leads to a reduced exchange energy, which has some potential applications, such as, tunability of entanglement of electrons for quantum information devices. Since silicene acquires two energy gaps associated with up- and down-pseudospin, we can adjust its electronic properties in a wider range by varying these two bandgaps as compared to graphene. Another way to tune silicene electronic properties is through impurity doping. Our numerical results demonstrate the dependence of exchange and correlation energies on the energy bandgaps, doping and temperature under circularly polarized light.

Temperature Ddependence of Anomalous Hall Conductivity in Rashba-type Ferromagnets

NASA Astrophysics Data System (ADS)

Sakuma, Akimasa

2018-03-01

We theoretically investigated the anomalous Hall conductivity (AHC) of Rashba-type ferromagnets at a finite temperature, taking into account spin fluctuation. We observed that the intrinsic AHC increases with increasing temperature. This can be understood from the characteristic nature of the spin chirality in the k-space, which increases with decreasing exchange splitting (EXS) when the spin-orbit interaction is much smaller than the EXS. The extrinsic part of the AHC also increases with temperature owing to the enhancement of the scattering strength of electrons due to the thermal fluctuation of the exchange field.

Excitation energies of molecules within time-independent density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hemanadhan, M., E-mail: hemanadh@iitk.ac.in; Harbola, Manoj K., E-mail: hemanadh@iitk.ac.in

2014-04-24

Recently proposed exchange energy functional for excited-states is tested for obtaining excitation energies of diatomic molecules. The functional is the ground-state counterpart of the local-density approximation, the modified local spin density (MLSD). The MLSD functional is tested for the N{sub 2} and CO diatomic molecules. The excitation energy obtained with the MLSD functional for the N{sub 2} molecule is in close vicinity to that obtained from the exact exchange orbital functional, Krieger, Li and Iafrate (KLI). For the CO molecule, the departure in excitation energy is observed and is due to the overcorrection of self-interaction.

Excitation energies of molecules within time-independent density functional theory

NASA Astrophysics Data System (ADS)

Hemanadhan, M.; Harbola, Manoj K.

2014-04-01

Recently proposed exchange energy functional for excited-states is tested for obtaining excitation energies of diatomic molecules. The functional is the ground-state counterpart of the local-density approximation, the modified local spin density (MLSD). The MLSD functional is tested for the N2 and CO diatomic molecules. The excitation energy obtained with the MLSD functional for the N2 molecule is in close vicinity to that obtained from the exact exchange orbital functional, Krieger, Li and Iafrate (KLI). For the CO molecule, the departure in excitation energy is observed and is due to the overcorrection of self-interaction.

Release behavior and toxicity profiles towards A549 cell lines of ciprofloxacin from its layered zinc hydroxide intercalation compound.

PubMed

Abdul Latip, Ahmad Faiz; Hussein, Mohd Zobir; Stanslas, Johnson; Wong, Charng Choon; Adnan, Rohana

2013-01-01

Layered hydroxides salts (LHS), a layered inorganic compound is gaining attention in a wide range of applications, particularly due to its unique anion exchange properties. In this work, layered zinc hydroxide nitrate (LZH), a family member of LHS was intercalated with anionic ciprofloxacin (CFX), a broad spectrum antibiotic via ion exchange in a mixture solution of water:ethanol. Powder x-ray diffraction (XRD), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) confirmed the drug anions were successfully intercalated in the interlayer space of LZH. Specific surface area of the obtained compound was increased compared to that of the host due to the different pore textures between the two materials. CFX anions were slowly released over 80 hours in phosphate-buffered saline (PBS) solution due to strong interactions that occurred between the intercalated anions and the host lattices. The intercalation compound demonstrated enhanced antiproliferative effects towards A549 cancer cells compared to the toxicity of CFX alone. Strong host-guest interactions between the LZH lattice and the CFX anion give rise to a new intercalation compound that demonstrates sustained release mode and enhanced toxicity effects towards A549 cell lines. These findings should serve as foundations towards further developments of the brucite-like host material in drug delivery systems.

Controlling ferromagnetism of (In,Fe)As semiconductors by electron doping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dang Vu, Nguyen; Fukushima, Tetsuya; Katayama-Yoshida, Hiroshi

2014-02-21

Based on experimental results, using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method and Monte Carlo simulation, we study the mechanism of ferromagnetic behavior of (In,Fe)As. We show that with doped Be atoms occupying in interstitial sites, chemical pair interactions between atoms and magnetic exchange interactions between Fe atoms change due to electron concentration. Therefore, by controlling the doping process, magnetic behavior of (In,Fe)As is controlled and ferromagnetism is observed in this semiconductor.

High-field magnetization and magnetic phase diagram of α -Cu2V2O7

NASA Astrophysics Data System (ADS)

Gitgeatpong, G.; Suewattana, M.; Zhang, Shiwei; Miyake, A.; Tokunaga, M.; Chanlert, P.; Kurita, N.; Tanaka, H.; Sato, T. J.; Zhao, Y.; Matan, K.

2017-06-01

High-field magnetization of the spin-1 /2 antiferromagnet α -Cu2V2O7 was measured in pulsed magnetic fields of up to 56 T in order to study its magnetic phase diagram. When the field was applied along the easy axis (the a axis), two distinct transitions were observed at Hc 1=6.5 T and Hc 2=18.0 T. The former is a spin-flop transition typical for a collinear antiferromagnet and the latter is believed to be a spin-flip transition of canted moments. The canted moments, which are induced by the Dzyaloshinskii-Moriya interactions, anti-align for Hc 1

Collider effects of unparticle interactions in multiphoton signals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aliev, T. M.; Frank, Mariana; Turan, Ismail

2009-12-01

A new model of physics, with a hidden conformal sector which manifests itself as an unparticle coupling to standard model particles effectively through higher dimensional operators, predicts strong collider signals due to unparticle self-interactions. We perform a complete analysis of the most spectacular of these signals at the hadron collider, pp(p){yields}{gamma}{gamma}{gamma}{gamma} and {gamma}{gamma}gg. These processes can go through the three-point unparticle self-interactions as well as through some s and t channel diagrams with one and/or two unparticle exchanges. We study the contributions of individual diagrams classified with respect to the number of unparticle exchanges and discuss their effect on themore » cross sections at the Tevatron and the LHC. We also restrict the Tevatron bound on the unknown coefficient of the three-point unparticle correlator. With the availability of data from the Tevatron, and the advent of the data emerging from the LHC, these interactions can provide a clear and strong indication of unparticle physics and distinguish this model from other beyond the standard model scenarios.« less

Acetone and Water on TiO₂(110): H/D Exchange

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henderson, Michael A.

2005-04-12

Isotopic H/D exchange between coadsorbed acetone and water on the TiO?(110) surface was examined using temperature programmed desorption (TPD) as a function of coverage and two surface pretreatments (oxidation and reduction). Coadsorbed acetone and water interact repulsively on reduced TiO?(110) based on results from the companion paper to this study, with water exerting a greater influence in destabilizing acetone and acetone having only a nominal influence on water. Despite the repulsive interaction between these coadsorbates, about 0.02 ML of a 1 ML d6-acetone on the reduced surface exhibits H/D exchange with coadsorbed water, with the exchange occurring exclusively in themore » high temperature region of the d?-acetone TPD spectrum at {approx}340 K. The effect was confirmed with combinations of d?-acetone and D?O. The extent of exchange decreased on the reduced surface with water coverages above {approx}0.3 ML due to the ability of water to displace coadsorbed acetone from first layer sites to the multilayer. In contrast, the extent of exchange increased by a factor of 3 when the surface was pre-oxidized prior to coadsorption. In this case, there was no evidence for the negative influence of high water coverages on the extent of H/D exchange. Comparison of the TPD spectra from the exchange products (either d?- or d?-acetone depending on the coadsorption pairing) suggests that, in addition to the 340 K exchange process seen on the reduced surface, a second exchange process was observed on the oxidized surface at {approx}390 K. In both cases (oxidized and reduced), desorption of the H/D exchange products appeared to be reaction limited and to involve the influence of OH/OD groups (or water formed during recombinative desorption of OH/OD groups) instead of molecularly adsorbed water. The 340 K exchange process is assigned to reaction at step sites and the 390 K exchange process is attributed to the influence of oxygen adatoms deposited during surface oxidation. The H/D exchange mechanism likely involves an enolate or propenol surface intermediate formed transiently during the desorption of oxygen-stabilized acetone molecules.« less

Resuspension and Shelf-Deep Ocean Exchange in the Northern California Current: New Insights From Underwater Gliders

NASA Astrophysics Data System (ADS)

Erofeev, A.; Barth, J. A.; Shearman, R. K.; Pierce, S. D.

2016-02-01

Shelf-deep ocean exchange is dominated by wind-driven upwelling and downwelling in the northern California Current. The interaction of strong, along-shelf jets with coastline and bottom topographic features can also create significant cross-margin exchange. We are using data from over 60,000 kilometers of autonomous underwater glider tracks to understand the temporal and spatial distribution of shelf-deep ocean exchange off central Oregon. Year-round glider observations of temperature, salinity, depth-averaged currents, chlorophyll fluorescence, light backscatter, and colored dissolved organic matter fluorescence from a single cross-margin transect are used to examine shelf-deep ocean exchange mechanisms. During summer, cross-margin exchange is dominated by wind-driven upwelling and the relaxation or reversal of the dominant southward winds. This process has been fairly well observed and studied due to the relatively low sea states and winds during summer. There is far less data from fall and winter off Oregon, a time of strong winds and large waves. We use autonomous underwater gliders to sample during the winter, including through the fall and spring transitions. Glider observations of suspended material detected via light backscatter, show time-space variations in resuspension in the bottom boundary layer due to winds, waves and currents. Examples of shelf-deep ocean exchange are shown by layers with high light backscatter separating from the bottom near the shelf break and extending into the interior along isopycnals. We describe these features and events in relationship to wind-forcing, along-shelf flows, and other forcing mechanisms.

Oligonucleotide gas-phase hydrogen/deuterium exchange with D2S in the collision cell of a quadrupole-Fourier transform ion cyclotron resonance mass spectrometer.

PubMed

Mo, Jingjie; Håkansson, Kristina

2007-10-15

We have implemented gas-phase hydrogen/deuterium exchange (HDX) experiments in the external collision cell of a hybrid quadrupole-Fourier transform ion cyclotron resonance mass spectrometer. In this configuration, multiply charged oligonucleotide anions undergo significant exchange with D(2)S at reaction intervals ranging from 0.11 to 60.1 s. For DNA homohexamers, relative exchange rates were dC(6) approximately dA(6) > dG(6) > dT(6), correlating with the gas-phase acidities of nucleobases (C > A > T > G), except for guanine. Our results are consistent with a relay mechanism in which D(2)S interacts with both a backbone phosphate group and a neutral nucleobase through hydrogen bonding. We propose that the faster exchange of polyguanosine compared to polythymidine is due to the larger size of guanine and the orientation of its labile hydrogens, which may result in gas-phase conformations more favorable for forming complexes with D(2)S. Similar trends were observed for RNA homohexamers, although their HDX rates were faster than for DNA, suggesting they can also exchange via another relay process involving the 2'-hydroxyl group. HDX of DNA duplexes further supports the involvement of nucleobase hydrogens because duplexes exchanged slower than their corresponding single strands, presumably due to the intermolecular hydrogen bonds between nucleobases. This work constitutes the first investigation of the mechanisms of oligonucleotide gas-phase HDX. Our results on duplexes show promise for application of this strategy to the characterization of structured nucleic acids.

Magnetic and magnetoresistance properties of La0.7Sr0.3(Mn,Сo)O3

NASA Astrophysics Data System (ADS)

Troyanchuk, I. O.; Karpinsky, D. V.; Bushinsky, M. V.; Sikolenko, V. V.; Gavrilov, S. A.; Silibin, M. V.

2017-11-01

Magnetic and magnetotransport properties of La0.7Sr0.3Mn1-xCoxO3 ceramics have been investigated by neutron powder diffraction, magnetization and electrical measurements. It is shown that substitution by cobalt ions leads to a decrease of magnetic transition temperature down to 140 K for the compound with x = 0.33. The compounds with cobalt content 0.4 < x < 0.6 are characterized by a presence of small ferromagnetic component due to exchange interactions between cobalt and manganese ions with maximal transition temperature of about 190 K observed for x = 0.5. Further increase of the dopant concentration diminishes ferromagnetic interactions. An evolution of electronic configuration of manganese and cobalt ions upon chemical substitution as well as related changes in the exchange interactions which determine the type of the magnetic state are discussed. Based on the neutron diffraction results and magnetometry data the preliminary magnetic phase diagram has been constructed.

Numerical Simulation of Flow Features and Energy Exchange Physics in Near-Wall Region with Fluid-Structure Interaction

NASA Astrophysics Data System (ADS)

Zhang, Lixiang; Wang, Wenquan; Guo, Yakun

Large eddy simulation is used to explore flow features and energy exchange physics between turbulent flow and structure vibration in the near-wall region with fluid-structure interaction (FSI). The statistical turbulence characteristics in the near-wall region of a vibrating wall, such as the skin frictional coefficient, velocity, pressure, vortices, and the coherent structures have been studied for an aerofoil blade passage of a true three-dimensional hydroturbine. The results show that (i) FSI greatly strengthens the turbulence in the inner region of y+ < 25; and (ii) the energy exchange mechanism between the flow and the vibration depends strongly on the vibration-induced vorticity in the inner region. The structural vibration provokes a frequent action between the low- and high-speed streaks to balance the energy deficit caused by the vibration. The velocity profile in the inner layer near the vibrating wall has a significant distinctness, and the viscosity effect of the fluid in the inner region decreases due to the vibration. The flow features in the inner layer are altered by a suitable wall vibration.

Exchange interaction in hexagonal MnRhP from first-principles studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, X. B., E-mail: liuxubo@uta.edu; Zhang, Qiming; Ping Liu, J., E-mail: pliu@uta.edu

2014-05-07

Electronic structure and magnetic properties for MnRhP have been studied from a first-principles density functional calculation. The calculated lattice constants, a = 6.228 Å and c = 3.571 Å, are in good agreement with the experimental values of a = 6.223 Å and c = 3.585 Å. The calculated moment of Mn is 3.1 μ{sub B}/atom, resulting in a total moment of 3.0 μ{sub B}/atom due to small moments induced at Rh and P sites. The magnetic moment of Mn decreases with unit cell size. The exchange interactions are dominated by positive Mn-Mn exchange coupling (J{sub Mn−Mn}), implying a stable ferromagnetic ordering in Mn sublattice. In particular, J{sub Mn−Mn} showsmore » a maximum value (1.5 mRy) at the the optimized unit cell size. The structural distortion or unit cell size change will affect J{sub Mn−Mn}, which is intimately related to the magneto-elastic and magneto-caloric effect.« less

Spatio-temporal variability of hyporheic exchange through a pool-riffle-pool sequence

Treesearch

Frank P. Gariglio; Daniele Tonina; Charles H. Luce

2013-01-01

Stream water enters and exits the streambed sediment due to hyporheic fluxes, which stem primarily from the interaction between surface water hydraulics and streambed morphology. These fluxes sustain a rich ecotone, whose habitat quality depends on their direction and magnitude. The spatio-temporal variability of hyporheic fluxes is not well understood over several...

High field ESR study of the pi-d interaction effect in beta-(BDA-TTP)2MCl4 (M=Fe, Ga)

NASA Astrophysics Data System (ADS)

Tokumoto, Takahisa; Vantol, J.; Brunel, L.-C.; Choi, E. S.; Brooks, J. S.; Kaihatsu, T.; Akutsu, H.; Yamada, J.

2007-03-01

Novel magnetic organic conductors with pi-d interaction have commanded attention since the discovery of field induced superconductivity. One of them, beta-(BDA-TTP)2FeCl4, has alternating donor molecules and quasi 2D electrical properties. Previous studies of electrical and magnetic properties show an M-I transition at 120K and an AF transition at TN=8.5K, suggesting an exchange interaction between the conduction electrons and the Fe^3+ d-electrons. The properties of beta-(BDA-TTP)2GaCl4 are similar with exception of the absence of the AF transition, which is apparently due to the absence of pi-d exchange interaction. We report angular/temperature dependent 240GHz quasi optical ESR measurements on both compounds to probe the magnetic properties. The Ga compound signals follow the donor molecule structure, and show no magnetic order at any temperature. The Fe compound signals are quite different from the Ga compound, and exhibit AF behavior below TN. The difference of Fe and Ga compounds will be discussed in terms of the interaction between localized and itinerant magnetic moments.

Interplay of Dzyaloshinsky-Moriya and dipole-dipole interactions and their joint effects upon vortical structures on nanodisks

NASA Astrophysics Data System (ADS)

Liu, Zhaosen; Ciftja, Orion; Ian, Hou

2017-06-01

In transition metal oxides, magnetic dipole-dipole (DD) and chiral Dzyaloshinsky-Moriya (DM) interactions between nearest neighboring spins are comparable in magnitude. In particular, the effects of the DD interaction on the physical properties of magnetic nanosystems cannot be simply neglected due to its long-range character. For these reasons, we employed here a new quantum simulation approach in order to investigate the interplay of these two interactions and study their combined effects upon the magnetic vortical structures of monolayer nanodisks. Consequently, we found out from our computational results that, in the presence of Heisenberg exchange interaction, a sufficiently strong DD interaction is also able to induce a single magnetic vortex on a small nanodisk; a strong DM interaction usually gives rise to a multi-domain structure which evolves with changing temperature; In this circumstance, if a weak DD interaction is further considered, the multi-domains merge to form a single vortex in the whole magnetic phase. Moreover, if only the Heisenberg exchange and chiral DM interactions are considered in simulations, our results from calculations with different spin values show that the transition temperature TM is simply proportional to S (S + 1) ; if the temperature is scaled with TM, and the calculated magnetizations are divided by the spin value S, their curves exhibit very similar features in the whole temperature region below TM.

High-field Overhauser dynamic nuclear polarization in silicon below the metal-insulator transition.

PubMed

Dementyev, Anatoly E; Cory, David G; Ramanathan, Chandrasekhar

2011-04-21

Single crystal silicon is an excellent system to explore dynamic nuclear polarization (DNP), as it exhibits a continuum of properties from metallic to insulating as a function of doping concentration and temperature. At low doping concentrations DNP has been observed to occur via the solid effect, while at very high-doping concentrations an Overhauser mechanism is responsible. Here we report the hyperpolarization of (29)Si in n-doped silicon crystals, with doping concentrations in the range of (1-3) × 10(17) cm(-3). In this regime exchange interactions between donors become extremely important. The sign of the enhancement in our experiments and its frequency dependence suggest that the (29)Si spins are directly polarized by donor electrons via an Overhauser mechanism within exchange-coupled donor clusters. The exchange interaction between donors only needs to be larger than the silicon hyperfine interaction (typically much smaller than the donor hyperfine coupling) to enable this Overhauser mechanism. Nuclear polarization enhancement is observed for a range of donor clusters in which the exchange energy is comparable to the donor hyperfine interaction. The DNP dynamics are characterized by a single exponential time constant that depends on the microwave power, indicating that the Overhauser mechanism is a rate-limiting step. Since only about 2% of the silicon nuclei are located within 1 Bohr radius of the donor electron, nuclear spin diffusion is important in transferring the polarization to all the spins. However, the spin-diffusion time is much shorter than the Overhauser time due to the relatively weak silicon hyperfine coupling strength. In a 2.35 T magnetic field at 1.1 K, we observed a DNP enhancement of 244 ± 84 resulting in a silicon polarization of 10.4 ± 3.4% following 2 h of microwave irradiation.

Diclofenac removal in urine using strong-base anion exchange polymer resins.

PubMed

Landry, Kelly A; Boyer, Treavor H

2013-11-01

One of the major sources of pharmaceuticals in the environment is wastewater effluent of which human urine contributes the majority of pharmaceuticals. Urine source separation has the potential to isolate pharmaceuticals at a higher concentration for efficient removal as well as produce a nutrient byproduct. This research investigated the efficacy of using strong-base anion exchange polymer resins to remove the widely detected and abundant pharmaceutical, diclofenac, from synthetic human urine under fresh and ureolyzed conditions. The majority of experiments were conducted using a strong-base, macroporous, polystyrene resin (Purolite A520E). Ion-exchange followed a two-step removal rate with rapid removal in 1 h and equilibrium removal in 24 h. Diclofenac removal was >90% at a resin dose of 8 mL/L in both fresh and ureolyzed urine. Sorption of diclofenac onto A520E resin was concurrent with desorption of an equivalent amount of chloride, which indicates the ion-exchange mechanism is occurring. The presence of competing ions such as phosphate and citrate did not significantly impact diclofenac removal. Comparisons of three polystyrene resins (A520E, Dowex 22, Dowex Marathon 11) as well as one polyacrylic resin (IRA958) were conducted to determine the major interactions between anion exchange resin and diclofenac. The results showed that polystyrene resins provide the highest level of diclofenac removal due to electrostatic interactions between quaternary ammonium functional groups of resin and carboxylic acid of diclofenac and non-electrostatic interactions between resin matrix and benzene rings of diclofenac. Diclofenac was effectively desorbed from A520E resin using a regeneration solution that contained 4.5% (m/m) NaCl in an equal-volume mixture of methanol and water. The greater regeneration efficiency of the NaCl/methanol-water mixture over the aqueous NaCl solution supports the importance of non-electrostatic interactions between resin matrix and benzene rings of diclofenac. Experiments with ketoprofen, in addition to diclofenac, suggest that polystyrene anion exchange resins can be used to selectively remove other acidic pharmaceuticals from urine. Copyright © 2013 Elsevier Ltd. All rights reserved.

The exact solution of a four-body Coulomb problem

NASA Astrophysics Data System (ADS)

Ray, Hasi

2018-03-01

The elastic collision between two H-like atoms utilizing an ab initio static-exchange model (SEM) in the center of mass (CM) frame considering the system as a four-body Coulomb problem where all the Coulomb interaction terms in the direct and exchange channels are treated exactly, is studied thoroughly. A coupled-channel methodology in momentum space is used to solve Lippman-Schwinger equation following the integral approach. The new SEM code [Ray, Pramana 83, 907 (2014)] in which the Born-Oppenheimer (BO) scattering amplitude acts as input to derive the SEM amplitude using partial wave analysis, is utilized to study the s-, p-, d-wave elastic phase shifts and the corresponding partial cross sections. An augmented-Born approximation is used to include the contribution of higher partial waves more accurately to determine the total/integrated elastic cross sections. The effective range theory is used to determine the scattering lengths and effective ranges in the s-wave elastic scattering. The systems studied are Ps-Ps, Ps-Mu, Ps-H, Ps-D, Ps-T, Mu-Mu, Mu-H, Mu-D, Mu-T, H-H, H-D, H-T, D-D, D-T, T-T. The SEM includes the non-adiabatic short-range effects due to exchange. The MSEM code [Ray, Pramana 83, 907 (2014)] is used to study the effect of the long-range van der Waals interaction due to induced dipole polarizabilities of the atoms in H(1s)-H(1s) elastic collision. The dependence of scattering length on the reduced mass of the system and the dependence of scattering length on the strength of long-range van der Waals interaction that varies with the minimum interatomic distance are observed. Contribution to the Topical Issue "Low Energy Positron and Electron Interactions", edited by James Sullivan, Ron White, Michael Bromley, Ilya Fabrikant, and David Cassidy.

Restructuring of a Peat in Interaction with Multivalent Cations: Effect of Cation Type and Aging Time

PubMed Central

Kunhi Mouvenchery, Yamuna; Jaeger, Alexander; Aquino, Adelia J. A.; Tunega, Daniel; Diehl, Dörte; Bertmer, Marko; Schaumann, Gabriele Ellen

2013-01-01

It is assumed to be common knowledge that multivalent cations cross-link soil organic matter (SOM) molecules via cation bridges (CaB). The concept has not been explicitly demonstrated in solid SOM by targeted experiments, yet. Therefore, the requirements for and characteristics of CaB remain unidentified. In this study, a combined experimental and molecular modeling approach was adopted to investigate the interaction of cations on a peat OM from physicochemical perspective. Before treatment with salt solutions of Al3+, Ca2+ or Na+, respectively, the original exchangeable cations were removed using cation exchange resin. Cation treatment was conducted at two different values of pH prior to adjusting pH to 4.1. Cation sorption is slower (>>2 h) than deprotonation of functional groups (<2 h) and was described by a Langmuir model. The maximum uptake increased with pH of cation addition and decreased with increasing cation valency. Sorption coefficients were similar for all cations and at both pH. This contradicts the general expectations for electrostatic interactions, suggesting that not only the interaction chemistry but also spatial distribution of functional groups in OM determines binding of cations in this peat. The reaction of contact angle, matrix rigidity due to water molecule bridges (WaMB) and molecular mobility of water (NMR analysis) suggested that cross-linking via CaB has low relevance in this peat. This unexpected finding is probably due to the low cation exchange capacity, resulting in low abundance of charged functionalities. Molecular modeling demonstrates that large average distances between functionalities (∼3 nm in this peat) cannot be bridged by CaB-WaMB associations. However, aging strongly increased matrix rigidity, suggesting successive increase of WaMB size to connect functionalities and thus increasing degree of cross-linking by CaB-WaMB associations. Results thus demonstrated that the physicochemical structure of OM is decisive for CaB and aging-induced structural reorganisation can enhance cross-link formation. PMID:23750256

Restructuring of a peat in interaction with multivalent cations: effect of cation type and aging time.

PubMed

Kunhi Mouvenchery, Yamuna; Jaeger, Alexander; Aquino, Adelia J A; Tunega, Daniel; Diehl, Dörte; Bertmer, Marko; Schaumann, Gabriele Ellen

2013-01-01

It is assumed to be common knowledge that multivalent cations cross-link soil organic matter (SOM) molecules via cation bridges (CaB). The concept has not been explicitly demonstrated in solid SOM by targeted experiments, yet. Therefore, the requirements for and characteristics of CaB remain unidentified. In this study, a combined experimental and molecular modeling approach was adopted to investigate the interaction of cations on a peat OM from physicochemical perspective. Before treatment with salt solutions of Al(3+), Ca(2+) or Na(+), respectively, the original exchangeable cations were removed using cation exchange resin. Cation treatment was conducted at two different values of pH prior to adjusting pH to 4.1. Cation sorption is slower (>2 h) than deprotonation of functional groups (<2 h) and was described by a Langmuir model. The maximum uptake increased with pH of cation addition and decreased with increasing cation valency. Sorption coefficients were similar for all cations and at both pH. This contradicts the general expectations for electrostatic interactions, suggesting that not only the interaction chemistry but also spatial distribution of functional groups in OM determines binding of cations in this peat. The reaction of contact angle, matrix rigidity due to water molecule bridges (WaMB) and molecular mobility of water (NMR analysis) suggested that cross-linking via CaB has low relevance in this peat. This unexpected finding is probably due to the low cation exchange capacity, resulting in low abundance of charged functionalities. Molecular modeling demonstrates that large average distances between functionalities (∼3 nm in this peat) cannot be bridged by CaB-WaMB associations. However, aging strongly increased matrix rigidity, suggesting successive increase of WaMB size to connect functionalities and thus increasing degree of cross-linking by CaB-WaMB associations. Results thus demonstrated that the physicochemical structure of OM is decisive for CaB and aging-induced structural reorganisation can enhance cross-link formation.

Atomistic modelling of magnetic nano-granular thin films

NASA Astrophysics Data System (ADS)

Agudelo-Giraldo, J. D.; Arbeláez-Echeverry, O. D.; Restrepo-Parra, E.

2018-03-01

In this work, a complete model for studying the magnetic behaviour of polycrystalline thin films at nanoscale was processed. This model includes terms as exchange interaction, dipolar interaction and various types of anisotropies. For the first term, exchange interaction dependence of the distance n was used with purpose of quantify the interaction, mainly in grain boundaries. The third term includes crystalline, surface and boundary anisotropies. Special attention was paid to the disorder vector that determines the loss of cubic symmetry in the crystalline structure. For the case of the dipolar interaction, a similar implementation of the fast multiple method (FMM) was performed. Using these tools, modelling and simulations were developed varying the number of grains, and the results obtained presented a great dependence of the magnetic properties on this parameter. Comparisons between critical temperature and magnetization of saturation depending on the number of grains were performed for samples with and without factors as the surface and boundary anisotropies, and the dipolar interaction. It was observed that the inclusion of these parameters produced a decrease in the critical temperature and the magnetization of saturation; furthermore, in both cases, including and not including the disorder parameters, not only the critical temperature, but also the magnetization of saturation exhibited a range of values that also depend on the number of grains. This presence of a critical interval is due to each grain can transit toward the ferromagnetic state at different values of critical temperature. The processes of Zero field cooling (ZFC), Field cooling (FCC) and field cooling in warming mode (FCW) were necessary for understanding the mono-domain regime around of transition temperature, due to the high probabilities of a Super-paramagnetic (SPM) state.

Modification of ocean-estuary salt fluxes by density-driven advection of a headland eddy

NASA Astrophysics Data System (ADS)

Fram, J. P.; Stacey, M. T.

2005-05-01

Scalar exchange between San Francisco Bay and the coastal ocean is examined using shipboard observations made across the Golden Gate Channel. Ocean-estuary exchange is often described as a combination of two independent types of mechanisms: density-driven exchange such as gravitational circulation and tidal asymmetries such as tidal trapping. In this study we found that exchange is also governed by an interaction between these mechanisms. Tidally trapped eddies created in shallow shoals are mixed into the main channel earlier in the tidal cycle during the rainy season because the eddies are pushed seaward by gravitational circulation. This interaction increases the tidally averaged dispersive salt flux into the bay. The study consists of experiments during each of three 'seasons': winter/spring runoff (March 2002), summer upwelling (July 2003), and fall relaxation (October 2002). Within each experiment, transects across the channel were repeated approximately every 12 minutes for 25 hours during both spring tide and the following neap tide. Velocity was measured from a boat-mounted ADCP. Scalar concentrations were measured from a tow-yoed SeaSciences Acrobat. Salinity exchange over each spring-neap cycle is quantified with harmonic analysis. Harmonic results are decomposed into flux mechanisms using temporal and spatial correlations. The temporal correlation of cross-sectional averaged salinity and velocity (tidal pumping flux) is the largest part of the dispersive flux of salinity into the bay. From the tidal pumping portion of the dispersive flux, it is shown that there is less exchange than was found in earlier studies. Furthermore, tidal pumping flux scales strongly with flow due to density-driven movement of tidally trapped eddies and density-driven increases in ebb-flood frictional phasing. Complex bathymetry makes salinity exchange scale differently with flow than would be expected from simple tidal pumping and gravitational circulation models.

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine.

PubMed

Wu, Wei

2014-06-14

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-½) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

Spin-wave dynamics and exchange interactions in multiferroic NdFe3(BO3)4 explored by inelastic neutron scattering

NASA Astrophysics Data System (ADS)

Golosovsky, I. V.; Ovsyanikov, A. K.; Aristov, D. N.; Matveeva, P. G.; Mukhin, A. A.; Boehm, M.; Regnault, L.-P.; Bezmaternykh, L. N.

2018-04-01

Magnetic excitations and exchange interactions in multiferroic NdFe3(BO3)4 were studied by inelastic neutron scattering in the phase with commensurate antiferromagnetic structure. The observed spectra were analyzed in the frame of the linear spin-wave theory. It was shown that only the model, which includes the exchange interactions within eight coordination spheres, describes satisfactorily all observed dispersion curves. The calculation showed that the spin-wave dynamics is governed by the strongest antiferromagnetic intra-chain interaction and three almost the same inter-chain interactions. Other interactions, including ferromagnetic exchange, appeared to be insignificant. The overall energy balance of the antiferromagnetic inter-chain exchange interactions, which couple the moments from the adjacent ferromagnetic layers as well as within a layer, stabilizes ferromagnetic arrangement in the latter. It demonstrates that the pathway geometry plays a crucial role in forming of the magnetic structure.

Social exchange as a framework for client-nurse interaction during public health nursing maternal-child home visits.

PubMed

Byrd, Mary E

2006-01-01

The purpose of this paper was to develop a nursing-focused use of social exchange theory within the context of maternal-child home visiting. The nature of social exchange theory, its application to client-nurse interaction, and its fit with an existing data set from a field research investigation were examined. Resources exchanged between the nurse and clients were categorized and compared across the patterns of home visiting, nursing strategies based on exchange notions were identified, and variations in exchange were linked with client outcomes. The nurse provided resources within the categories of information, status, service, and goods. Clients provided time, access to the home, space within the home to conduct the visit, opportunities to observe maternal-child interaction, access to the infant, and information. The ease and breadth of resource exchange varied across the patterns of home visiting. The social exchange perspective was useful in categorizing resources, specifying and uncovering new resource categories, understanding nursing strategies to initiate and maintain the client-nurse relationship, and linking client-nurse interactive phenomena with client outcomes. Social exchange theory is potentially useful for understanding client-nurse interaction in the context of maternal-child home visits.

Asymmetric band gaps in a Rashba film system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carbone, C.; Moras, P.; Sheverdyaeva, P. M.

The joint effect of exchange and Rashba spin-orbit interactions is examined on the surface and quantum well states of Ag 2 Bi -terminated Ag films grown on ferromagnetic Fe(110). The system displays a particular combination of time-reversal and translational symmetry breaking that strongly influences its electronic structure. Angle-resolved photoemission reveals asymmetric band-gap openings, due to spin-selective hybridization between Rashba-split surface states and exchange-split quantum well states. This results in an unequal number of states along positive and negative reciprocal space directions. We suggest that the peculiar asymmetry of the discovered electronic structure can have significant influence on spin-polarized transport properties.

Redox Sorption of Oxygen Dissolved in Water on Copper Nanoparticles in an Ion Exchange Matrix

NASA Astrophysics Data System (ADS)

Vakhnin, D. D.; Pridorogina, V. E.; Polyanskii, L. N.; Kravchenko, T. A.; Gorshkov, V. S.

2018-01-01

The redox sorption of molecular oxygen from water by a thin granular layer of a copper-ion exchanger nanocomposite in the currentless mode and under cathodic polarization is studied. The speed of propagation of the boundaries of the chemical reaction of stepwise oxidation of copper nanoparticles under the conditions of polarization slows considerably. At the same time, the amount of electrochemically regenerated copper from the resulting oxides that is capable of interacting with oxygen again grows. The stationarity of the redox sorption of oxygen is due to the equality of the rates of oxidation and reduction of the metallic component of the composite.

Effect of magnetism and atomic order on static atomic displacements in the Invar alloy Fe-27 at.% Pt

NASA Astrophysics Data System (ADS)

Sax, C. R.; Schönfeld, B.; Ruban, A. V.

2015-08-01

Fe-27 at.% Pt was aged at 1123 K and quenched to room temperature (RT) to set up a state of thermal equilibrium. The local atomic arrangement was studied by diffuse x-ray scattering above (at 427 K) and below (at RT) the Curie temperature as well as at RT under a saturating magnetic field. The separated short-range order scattering remained unchanged for all three states, with maxima at 100 positions. Effective pair interaction parameters determined by the inverse Monte Carlo method gave an order-disorder transition temperature of about 1088 K, close to direct experimental findings. The species-dependent static atomic displacements for the first two shells show large differences, with a strong increase in magnitude from the state at 427 K over RT to the state under saturating magnetic field. This outcome is in agreement with an increase in atomic volume of Fe with increasing local magnetic moment. Electronic-structure calculations closely reproduce the values for the static atomic displacements in the ferromagnetic state, and predict their dependence on the atomic configuration. They also reveal a strong dependence of the magnetic exchange interactions in Fe-Pt on the atomic configuration state and lattice parameter. In particular, the increase of the Curie temperature in a random state relative to that in the ordered one is demonstrated to be related to the corresponding change of the magnetic exchange interactions due to the different local atomic chemical environment. There exists a similar strong concentration dependence of the chemical interactions as in the case of magnetic exchange interactions. Theoretical effective interactions for Fe-27 at.% Pt alloy are in good agreement with experimental results, and they also reproduce well the L1 2-A1 transition temperature.

Signature of Griffith phase in (Tb1-xCex)MnO3

NASA Astrophysics Data System (ADS)

Kumar, Abhishek; Dwivedi, G. D.; Singh, A.; Singh, R.; Shukla, K. K.; Yang, H. D.; Ghosh, A. K.; Chatterjee, Sandip

2016-05-01

Griffith phase phenomena is attributed to existence of FM (ferromagnetic) cluster in AFM (antiferromagnetic) ordering which usually occurs in ferromagnetic and antiferromagnetic bilayers or multilayers. In (Tb1-xCex)MnO3 evolution of Griffith phase have been observed. The observed Griffith phase might be due to the exchange interaction between Mn3+/Mn2+ states.

Effects of polymer graft properties on protein adsorption and transport in ion exchange chromatography: a multiscale modeling study.

PubMed

Basconi, Joseph E; Carta, Giorgio; Shirts, Michael R

2015-04-14

Multiscale simulation is used to study the adsorption of lysozyme onto ion exchangers obtained by grafting charged polymers into a porous matrix, in systems with various polymer properties and strengths of electrostatic interaction. Molecular dynamics simulations show that protein partitioning into the polymer-filled pore space increases with the overall charge content of the polymers, while the diffusivity in the pore space decreases. However, the combination of greatly increased partitioning and modestly decreased diffusion results in macroscopic transport rates that increase as a function of charge content, as the large concentration driving force due to enhanced pore space partitioning outweighs the reduction in the pore space diffusivity. Matrices having greater charge associated with the grafted polymers also exhibit more diffuse intraparticle concentration profiles during transient adsorption. In systems with a high charge content per polymer and a low protein loading, the polymers preferentially partition toward the surface due to favorable interactions with the surface-bound protein. These results demonstrate the potential of multiscale modeling to illuminate qualitative trends between molecular properties and the adsorption equilibria and kinetic properties observable on macroscopic scales.

Mirror Neuron System and Mentalizing System connect during online social interaction.

PubMed

Sperduti, Marco; Guionnet, Sophie; Fossati, Philippe; Nadel, Jacqueline

2014-08-01

Two sets of brain areas are repeatedly reported in neuroimaging studies on social cognition: the Mirror Neuron System and the Mentalizing System. The Mirror System is involved in goal understanding and has been associated with several emotional and cognitive functions central to social interaction, ranging from empathy to gestural communication and imitation. The Mentalizing System is recruited in tasks requiring cognitive processes such as self-reference and understanding of other's intentions. Although theoretical accounts for an interaction between the two systems have been proposed, little is known about their synergy during social exchanges. In order to explore this question, we have recorded brain activity by means of functional MRI during live social exchanges based on reciprocal imitation of hand gestures. Here, we investigate, using the method of psychophysiological interaction, the changes in functional connectivity of the Mirror System due to the conditions of interest (being imitated, imitating) compared with passive observation of hand gestures. We report a strong coupling between the Mirror System and the Mentalizing System during the imitative exchanges. Our findings suggest a complementary role of the two networks during social encounters. The Mirror System would engage in the preparation of own actions and the simulation of other's actions, while the Mentalizing System would engage in the anticipation of the other's intention and thus would participate to the co-regulation of reciprocal actions. Beyond a specific effect of imitation, the design used offers the opportunity to tackle the role of role-switching in an interpersonal account of social cognition.

Cation-exchanged SAPO-34 for adsorption-based hydrocarbon separations: predictions from dispersion-corrected DFT calculations.

PubMed

Fischer, Michael; Bell, Robert G

2014-10-21

The influence of the nature of the cation on the interaction of the silicoaluminophosphate SAPO-34 with small hydrocarbons (ethane, ethylene, acetylene, propane, propylene) is investigated using periodic density-functional theory calculations including a semi-empirical dispersion correction (DFT-D). Initial calculations are used to evaluate which of the guest-accessible cation sites in the chabazite-type structure is energetically preferred for a set of ten cations, which comprises four alkali metals (Li(+), Na(+), K(+), Rb(+)), three alkaline earth metals (Mg(2+), Ca(2+), Sr(2+)), and three transition metals (Cu(+), Ag(+), Fe(2+)). All eight cations that are likely to be found at the SII site (centre of a six-ring) are then included in the following investigation, which studies the interaction with the hydrocarbon guest molecules. In addition to the interaction energies, some trends and peculiarities regarding the adsorption geometries are analysed, and electron density difference plots obtained from the calculations are used to gain insights into the dominant interaction types. In addition to dispersion interactions, electrostatic and polarisation effects dominate for the main group cations, whereas significant orbital interactions are observed for unsaturated hydrocarbons interacting with transition metal (TM) cations. The differences between the interaction energies obtained for pairs of hydrocarbons of interest (such as ethylene-ethane and propylene-propane) deliver some qualitative insights: if this energy difference is large, it can be expected that the material will exhibit a high selectivity in the adsorption-based separation of alkene-alkane mixtures, which constitutes a problem of considerable industrial relevance. While the calculations show that TM-exchanged SAPO-34 materials are likely to exhibit a very high preference for alkenes over alkanes, the strong interaction may render an application in industrial processes impractical due to the large amount of energy required for regeneration. In this respect, SAPOs exchanged with alkaline earth cations could provide a better balance between selectivity and energy cost of regeneration.

Finite-size corrections to the excitation energy transfer in a massless scalar interaction model

NASA Astrophysics Data System (ADS)

Maeda, Nobuki; Yabuki, Tetsuo; Tobita, Yutaka; Ishikawa, Kenzo

2017-05-01

We study the excitation energy transfer (EET) for a simple model in which a massless scalar particle is exchanged between two molecules. We show that a finite-size effect appears in EET by the interaction energy due to overlapping of the quantum waves in a short time interval. The effect generates finite-size corrections to Fermi's golden rule and modifies EET probability from the standard formula in the Förster mechanism. The correction terms come from transition modes outside the resonance energy region and enhance EET probability substantially.

Spatial interactions between urban areas and cause-specific mortality differentials in France.

PubMed

Ghosn, Walid; Kassie, Daouda; Jougla, Eric; Rican, Stéphane; Rey, Grégoire

2013-11-01

Spatial interactions constitute a challenging but promising approach for investigation of spatial mortality inequalities. Among spatial interactions measures, between-spatial unit migration differentials are a marker of socioeconomic imbalance, but also reflect discrepancies due to other factors. Specifically, this paper asks whether population exchange intensities measure differentials or similarities that are not captured by usual socioeconomic indicators. Urban areas were grouped pairwise by the intensity of connection estimated from a gravity model. The mortality differences for several causes of death were observed to be significantly smaller for strongly connected pairs than for weakly connected pairs even after adjustment on deprivation. © 2013 Published by Elsevier Ltd.

Release behavior and toxicity profiles towards A549 cell lines of ciprofloxacin from its layered zinc hydroxide intercalation compound

PubMed Central

2013-01-01

Background Layered hydroxides salts (LHS), a layered inorganic compound is gaining attention in a wide range of applications, particularly due to its unique anion exchange properties. In this work, layered zinc hydroxide nitrate (LZH), a family member of LHS was intercalated with anionic ciprofloxacin (CFX), a broad spectrum antibiotic via ion exchange in a mixture solution of water:ethanol. Results Powder x-ray diffraction (XRD), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) confirmed the drug anions were successfully intercalated in the interlayer space of LZH. Specific surface area of the obtained compound was increased compared to that of the host due to the different pore textures between the two materials. CFX anions were slowly released over 80 hours in phosphate-buffered saline (PBS) solution due to strong interactions that occurred between the intercalated anions and the host lattices. The intercalation compound demonstrated enhanced antiproliferative effects towards A549 cancer cells compared to the toxicity of CFX alone. Conclusions Strong host-guest interactions between the LZH lattice and the CFX anion give rise to a new intercalation compound that demonstrates sustained release mode and enhanced toxicity effects towards A549 cell lines. These findings should serve as foundations towards further developments of the brucite-like host material in drug delivery systems. PMID:23849189

Ionic regulation of the cardiac sodium-calcium exchanger.

PubMed

Reeves, John P; Condrescu, Madalina

2008-01-01

The Na(+)-Ca(2+) exchanger (NCX) links transmembrane movements of Ca(2+) ions to the reciprocal movement of Na(+) ions. It normally functions primarily as a Ca(2+) efflux mechanism in excitable tissues such as the heart, but it can also mediate Ca(2+) influx under certain conditions. Na(+) and Ca(2+) ions exert complex regulatory effects on NCX activity. Ca(2+) binds to two regulatory sites in the exchanger's central hydrophilic domain, and this interaction is normally essential for activation of exchange activity. High cytosolic Na(+) concentrations, however, can induce a constitutive activity that by-passes the need for allosteric Ca(2+) activation. Constitutive NCX activity can also be induced by high levels of phopshotidylinositol-4,5-bisphosphate (PIP₂) and by mutations affecting the regulatory calcium binding domains. In addition to promoting constitutive activity, high cytosolic Na(+) concentrations also induce an inactivated state of the exchanger (Na(+)-dependent inactivation) that becomes dominant when cytosolic pH and PIP₂ levels fall. Na(+)-dependent inactivation may provide a means of protecting cells from Ca(2+) overload due to NCX-mediated Ca(2+) influx during ischemia.

A spin exchange model for singlet fission

NASA Astrophysics Data System (ADS)

Yago, Tomoaki; Wakasa, Masanobu

2018-03-01

Singlet fission has been analyzed with the Dexter model in which electron exchange occurs between chromophores, conserving the spin for each electron. In the present study, we propose a spin exchange model for singlet fission. In the spin exchange model, spins are exchanged by the exchange interaction between two electrons. Our analysis with simple spin functions demonstrates that singlet fission is possible by spin exchange. A necessary condition for spin exchange is a variation in exchange interactions. We also adapt the spin exchange model to triplet fusion and triplet energy transfer, which often occur after singlet fission in organic solids.

Do π-conjugative effects facilitate SN2 reactions?

PubMed

Wu, Chia-Hua; Galabov, Boris; Wu, Judy I-Chia; Ilieva, Sonia; Schleyer, Paul von R; Allen, Wesley D

2014-02-26

Rigorous quantum chemical investigations of the SN2 identity exchange reactions of methyl, ethyl, propyl, allyl, benzyl, propargyl, and acetonitrile halides (X = F(-), Cl(-)) refute the traditional view that the acceleration of SN2 reactions for substrates with a multiple bond at Cβ (carbon adjacent to the reacting Cα center) is primarily due to π-conjugation in the SN2 transition state (TS). Instead, substrate-nucleophile electrostatic interactions dictate SN2 reaction rate trends. Regardless of the presence or absence of a Cβ multiple bond in the SN2 reactant in a series of analogues, attractive Cβ(δ(+))···X(δ(-)) interactions in the SN2 TS lower net activation barriers (E(b)) and enhance reaction rates, whereas repulsive Cβ(δ(-))···X(δ(-)) interactions increase E(b) barriers and retard SN2 rates. Block-localized wave function (BLW) computations confirm that π-conjugation lowers the net activation barriers of SN2 allyl (1t, coplanar), benzyl, propargyl, and acetonitrile halide identity exchange reactions, but does so to nearly the same extent. Therefore, such orbital interactions cannot account for the large range of E(b) values in these systems.

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wei, E-mail: wei.wu@ucl.ac.uk

2014-06-14

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-1/2 ) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by themore » long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.« less

Triangular arbitrage as an interaction among foreign exchange rates

NASA Astrophysics Data System (ADS)

Aiba, Yukihiro; Hatano, Naomichi; Takayasu, Hideki; Marumo, Kouhei; Shimizu, Tokiko

2002-07-01

We first show that there are in fact triangular arbitrage opportunities in the spot foreign exchange markets, analyzing the time dependence of the yen-dollar rate, the dollar-euro rate and the yen-euro rate. Next, we propose a model of foreign exchange rates with an interaction. The model includes effects of triangular arbitrage transactions as an interaction among three rates. The model explains the actual data of the multiple foreign exchange rates well.

Exchange interactions and magnetocaloric effects of the Heusler alloys Ni-Mn-In-R (R = Fe, Co)

NASA Astrophysics Data System (ADS)

Li, Yan-Ru; Su, Hui-Ling; Sun, Ji-Bing; Li, Ying

2018-05-01

The magnetic interactions and magnetocaloric effects in Ni2Mn1.4In0.6‑xRx (x = 0-0.2) (R = Fe, Co) Heusler alloys are investigated by the first-principles and Monte Carlo method. The ab initio calculations provide a basic understanding of the competition of ferromagnetic and antiferromagnetic interactions due to the chemical disorder of the alloy compositions. The thermodynamic properties including magnetization, specific heat and magnetic entropy change are calculated by the finite-temperature Monte Carlo simulations using the exchange couplings and magnetic moments from ab initio calculation as input parameters. The results show that the Fe or Co doping in Ni2Mn1.4In0.6 leads to an increase of magnetic moment and magnetic entropy change but a decrease of magnetic transition temperature with the increase in the Fe or Co contents. This indicates that the transition temperature and magnetocaloric properties of Ni2Mn1.4In0.6 alloy can be tuned by substituting In atom by Fe or Co with different contents.

The influence of compressibility on nonlinear spectral energy transfer - Part 1: Fundamental mechanisms

NASA Astrophysics Data System (ADS)

Praturi, Divya Sri; Girimaji, Sharath

2017-11-01

Nonlinear spectral energy transfer by triadic interactions is one of the foundational processes in fluid turbulence. Much of our current knowledge of this process is contingent upon pressure being a Lagrange multiplier with the only function of re-orienting the velocity wave vector. In this study, we examine how the nonlinear spectral transfer is affected in compressible turbulence when pressure is a true thermodynamic variable with a wave character. We perform direct numerical simulations of multi-mode evolution at different turbulent Mach numbers of Mt = 0.03 , 0.6 . Simulations are performed with initial modes that are fully solenoidal, fully dilatational and mixed solenoidal-dilatational. It is shown that solenoidal-solenoidal interactions behave in canonical manner at all Mach numbers. However, dilatational and mixed mode interactions are profoundly different. This is due to the fact that wave-pressure leads to kinetic-internal energy exchange via the pressure-dilatation mechanism. An important consequence of this exchange is that the triple correlation term, responsible for spectral transfer, experiences non-monotonic behavior resulting in inefficient energy transfer to other modes.

Electrically facilitated molecular transport. Analysis of the relative contributions of diffusion, migration, and electroosmosis to solute transport in an ion-exchange membrane.

PubMed

Bath, B D; White, H S; Scott, E R

2000-02-01

Electrically facilitated molecular transport in an ion-exchange membrane (Nafion, 1100 equiv wt) has been studied using a scanning electrochemical microscope. The transport rates of ferrocenylmethyltrimethylammonium (a cation), acetaminophen (a neutral molecule), and ascorbate (an anion) through approximately 120-micron-thick membranes were measured as a function of the iontophoretic current passed across the membrane (-1.0 to +1.0 A/cm2). Transport rates were analyzed by employing the Nernst-Planck equation, modified to account for electric field-driven convective transport. Excellent agreement between experimental and theoretical values of the molecular flux was obtained using a single fitting parameter for each molecule (electroosmotic drag coefficient). The electroosmotic velocity of the neutral molecule, acetaminophen, was shown to be a factor of approximately 500 larger than that of the cation ferrocenylmethyltrimethylammonium, a consequence of the electrostatic interaction of the cation with the negatively charged pore walls of the ion-exchange membrane. Electroosmotic transport of ascorbate occurred at a negligible rate due to repulsion of the anion by the cation-selective membrane. These results suggest that electroosmotic velocities of solute molecules are determined by specific chemical interactions of the permeant and membrane and may be very different from the average solution velocity. The efficiency of electroosmotic transport was also shown to be a function of the membrane thickness, in addition to membrane/solute interactions.

Microscopic theory of the Coulomb based exchange coupling in magnetic tunnel junctions.

PubMed

Udalov, O G; Beloborodov, I S

2017-05-04

We study interlayer exchange coupling based on the many-body Coulomb interaction between conduction electrons in magnetic tunnel junction. This mechanism complements the known interaction between magnetic layers based on virtual electron hopping (or spin currents). We find that these two mechanisms have different behavior on system parameters. The Coulomb based coupling may exceed the hopping based exchange. We show that the Coulomb based exchange interaction, in contrast to the hopping based coupling, depends strongly on the dielectric constant of the insulating layer. The dependence of the interlayer exchange interaction on the dielectric properties of the insulating layer in magnetic tunnel junction is similar to magneto-electric effect where electric and magnetic degrees of freedom are coupled. We calculate the interlayer coupling as a function of temperature and electric field for magnetic tunnel junction with ferroelectric layer and show that the exchange interaction between magnetic leads has a sharp decrease in the vicinity of the ferroelectric phase transition and varies strongly with external electric field.

Observation of two-orbital spin-exchange interactions with ultracold SU(N)-symmetric fermions

NASA Astrophysics Data System (ADS)

Scazza, F.; Hofrichter, C.; Höfer, M.; de Groot, P. C.; Bloch, I.; Fölling, S.

2014-10-01

Spin-exchanging interactions govern the properties of strongly correlated electron systems such as many magnetic materials. When orbital degrees of freedom are present, spin exchange between different orbitals often dominates, leading to the Kondo effect, heavy fermion behaviour or magnetic ordering. Ultracold ytterbium or alkaline-earth ensembles have attracted much recent interest as model systems for these effects, with two (meta-) stable electronic configurations representing independent orbitals. We report the observation of spin-exchanging contact interactions in a two-orbital SU(N)-symmetric quantum gas realized with fermionic 173Yb. We find strong inter-orbital spin exchange by spectroscopic characterization of all interaction channels and demonstrate SU(N = 6) symmetry within our measurement precision. The spin-exchange process is also directly observed through the dynamic equilibration of spin imbalances between ensembles in separate orbitals. The realization of an SU(N)-symmetric two-orbital Hubbard Hamiltonian opens the route to quantum simulations with extended symmetries and with orbital magnetic interactions, such as the Kondo lattice model.

Zero-range effective field theory for resonant wino dark matter. Part III. Annihilation effects

NASA Astrophysics Data System (ADS)

Braaten, Eric; Johnson, Evan; Zhang, Hong

2018-05-01

Near a critical value of the wino mass where there is a zero-energy S-wave resonance at the neutral-wino-pair threshold, low-energy winos can be described by a zero-range effective field theory (ZREFT) in which the winos interact nonperturbatively through a contact interaction and through Coulomb interactions. The effects of wino-pair annihilation into electroweak gauge bosons are taken into account through the analytic continuation of the real parameters for the contact interaction to complex values. The parameters of ZREFT can be determined by matching wino-wino scattering amplitudes calculated by solving the Schrödinger equation for winos interacting through a real potential due to the exchange of electroweak gauge bosons and an imaginary potential due to wino-pair annihilation into electroweak gauge bosons. ZREFT at leading order gives an accurate analytic description of low-energy wino-wino scattering, inclusive wino-pair annihilation, and a wino-pair bound state. ZREFT can also be applied to partial annihilation rates, such as the Sommerfeld enhancement of the annihilation rate of wino pairs into monochromatic photons.

Reduced-Order Biogeochemical Flux Model for High-Resolution Multi-Scale Biophysical Simulations

NASA Astrophysics Data System (ADS)

Smith, Katherine; Hamlington, Peter; Pinardi, Nadia; Zavatarelli, Marco

2017-04-01

Biogeochemical tracers and their interactions with upper ocean physical processes such as submesoscale circulations and small-scale turbulence are critical for understanding the role of the ocean in the global carbon cycle. These interactions can cause small-scale spatial and temporal heterogeneity in tracer distributions that can, in turn, greatly affect carbon exchange rates between the atmosphere and interior ocean. For this reason, it is important to take into account small-scale biophysical interactions when modeling the global carbon cycle. However, explicitly resolving these interactions in an earth system model (ESM) is currently infeasible due to the enormous associated computational cost. As a result, understanding and subsequently parameterizing how these small-scale heterogeneous distributions develop and how they relate to larger resolved scales is critical for obtaining improved predictions of carbon exchange rates in ESMs. In order to address this need, we have developed the reduced-order, 17 state variable Biogeochemical Flux Model (BFM-17) that follows the chemical functional group approach, which allows for non-Redfield stoichiometric ratios and the exchange of matter through units of carbon, nitrate, and phosphate. This model captures the behavior of open-ocean biogeochemical systems without substantially increasing computational cost, thus allowing the model to be combined with computationally-intensive, fully three-dimensional, non-hydrostatic large eddy simulations (LES). In this talk, we couple BFM-17 with the Princeton Ocean Model and show good agreement between predicted monthly-averaged results and Bermuda testbed area field data (including the Bermuda-Atlantic Time-series Study and Bermuda Testbed Mooring). Through these tests, we demonstrate the capability of BFM-17 to accurately model open-ocean biochemistry. Additionally, we discuss the use of BFM-17 within a multi-scale LES framework and outline how this will further our understanding of turbulent biophysical interactions in the upper ocean.

Variability in Benthic Exchange Rate, Depth, and Residence Time Beneath a Shallow Coastal Estuary

NASA Astrophysics Data System (ADS)

Russoniello, Christopher J.; Heiss, James W.; Michael, Holly A.

2018-03-01

Hydrodynamically driven benthic exchange of water between the water column and shallow seabed aquifer is a significant and dynamic component of coastal and estuarine fluid budgets. Associated exchange of solutes promotes ecologically important chemical reactions, so quantifying benthic exchange rates, depths, and residence times constrains coastal chemical cycling estimates. We present the first combined field, numerical, and analytical modeling investigation of wave-induced exchange. Temporal variability of exchange was calculated with data collected by instruments deployed in a shallow estuary for 11 days. Differential pressure sensors recorded pressure gradients across the seabed, and up- and down-looking ADCPs recorded currents and pressures to determine wave parameters, surface-water currents, and water depth. Wave-induced exchange was calculated (1) directly from differential pressure measurements, and indirectly with an analytical model based on wave parameters from (2) ADCP and (3) wind data. Wave-induced exchange from pressure measurements and ADCP-measured wave parameters matched well, but both exceeded wind-based values. Exchange induced by tidal pumping and current-bed form interaction—the other primary drivers in shallow coastal waters were calculated from tidal stage variation and ADCP-measured currents. Exchange from waves (mean = 20.0 cm/d; range = 1.75-92.3 cm/d) greatly exceeded exchange due to tides (mean = 3.7 cm/d) and current-bed form interaction (mean = 6.5 × 10-2 cm/d). Groundwater flow models showed aquifer properties affect wave-driven benthic exchange: residence time and depth increased and exchange rates decreased with increasing hydraulic diffusivity (ratio of aquifer permeability to compressibility). This new understanding of benthic exchange will help managers assess its control over chemical fluxes to marine systems.

Hole pairing and thermodynamic properties of the two dimensional frustrated t-J model

NASA Astrophysics Data System (ADS)

Roy, K.; Pal, P.; Nath, S.; Ghosh, N. K.

2018-04-01

The frustrated t-J model is investigated by using the exact-diagonalization (ED) method on an 8-site cluster. The effect on next-nearest-neighbor (NNN) exchange interaction J' (frustration) on the hole pairing and the thermodynamic properties of the system is considered. Two holes initially remain unbound at smaller value of J'/t, but tend to bind at larger value. The maximum possibility of pair formation has been observed to be at NNN sites. Entropy calculation shows that the system goes to more disordered state with J'. The specific heat curves show a single peak structure. A decrease in effective exchange energy is observed due to the frustration.

Merging and energy exchange between optical filaments

NASA Astrophysics Data System (ADS)

Georgieva, D. A.; Kovachev, L. M.

2015-10-01

We investigate nonlinear interaction between collinear femtosecond laser pulses with power slightly above the critical for self-focusing Pcr trough the processes of cross-phase modulation (CPM) and degenerate four-photon parametric mixing (FPPM). When there is no initial phase difference between the pulses we observe attraction between pulses due to CPM. The final result is merging between the pulses in a single filament with higher power. By method of moments it is found that the attraction depends on the distance between the pulses and has potential character. In the second case we study energy exchange between filaments. This process is described through FPPM scheme and requests initial phase difference between the waves.

Long-range spin-singlet proximity effect for a Josephson system with a single-crystal ferromagnet due to its band-structure features

NASA Astrophysics Data System (ADS)

Avdeev, M. V.; Proshin, Yu. N.

2018-03-01

A possible explanation for the long-range proximity effect observed in single-crystalline cobalt nanowires sandwiched between two tungsten superconducting electrodes [Nat. Phys. 6, 389 (2010), 10.1038/nphys1621] is proposed. The theoretical model uses properties of a ferromagnet band structure. Specifically, to connect the exchange field with the momentum of quasiparticles the distinction between the effective masses in majority and minority spin subbands and the Fermi-surface anisotropy are considered. The derived Eilenberger-like equations allowed us to obtain a renormalized exchange interaction that is completely compensated for some crystallographic directions under certain conditions. The proposed theoretical model is compared with previous approaches.

Merging and energy exchange between optical filaments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Georgieva, D. A., E-mail: dgeorgieva@tu-sofia.bg; Kovachev, L. M.

2015-10-28

We investigate nonlinear interaction between collinear femtosecond laser pulses with power slightly above the critical for self-focusing P{sub cr} trough the processes of cross-phase modulation (CPM) and degenerate four-photon parametric mixing (FPPM). When there is no initial phase difference between the pulses we observe attraction between pulses due to CPM. The final result is merging between the pulses in a single filament with higher power. By method of moments it is found that the attraction depends on the distance between the pulses and has potential character. In the second case we study energy exchange between filaments. This process is describedmore » through FPPM scheme and requests initial phase difference between the waves.« less

Laboratory Measurements of Solar-Wind/Comet X-Ray Emission and Charge Exchange Cross Sections

NASA Technical Reports Server (NTRS)

Chutjian, A.; Cadez, I.; Greenwood, J. B.; Mawhorter, R. J.; Smith, S. J.; Lozano, J.

2002-01-01

The detection of X-rays from comets such as Hyakutake, Hale-Bopp, d Arrest, and Linear as they approach the Sun has been unexpected and exciting. This phenomenon, moreover, should be quite general, occurring wherever a fast solar or stellar wind interacts with neutrals in a comet, a planetary atmosphere, or a circumstellar cloud. The process is, O(+8) + H2O --> O(+7*) + H2O(+), where the excited O(+7*) ions are the source of the X-ray emissions. Detailed modeling has been carried out of X-ray emissions in charge-transfer collisions of heavy solar-wind Highly Charged Ions (HCIs) and interstellar/interplanetary neutral clouds. In the interplanetary medium the solar wind ions, including protons, can charge exchange with interstellar H and He. This can give rise to a soft X-ray background that could be correlated with the long-term enhancements seen in the low-energy X-ray spectrum of ROSAT. Approximately 40% of the soft X-ray background detected by Exosat, ROSAT, Chandra, etc. is due to Charge Exchange (CXE): our whole heliosphere is glowing in the soft X-ray due to CXE.

Giant exchange interaction in mixed lanthanides

PubMed Central

Vieru, Veacheslav; Iwahara, Naoya; Ungur, Liviu; Chibotaru, Liviu F.

2016-01-01

Combining strong magnetic anisotropy with strong exchange interaction is a long standing goal in the design of quantum magnets. The lanthanide complexes, while exhibiting a very strong ionic anisotropy, usually display a weak exchange coupling, amounting to only a few wavenumbers. Recently, an isostructural series of mixed (Ln = Gd, Tb, Dy, Ho, Er) have been reported, in which the exchange splitting is estimated to reach hundreds wavenumbers. The microscopic mechanism governing the unusual exchange interaction in these compounds is revealed here by combining detailed modeling with density-functional theory and ab initio calculations. We find it to be basically kinetic and highly complex, involving non-negligible contributions up to seventh power of total angular momentum of each lanthanide site. The performed analysis also elucidates the origin of magnetization blocking in these compounds. Contrary to general expectations the latter is not always favored by strong exchange interaction. PMID:27087470

ROSAT Observations of Solar Wind Charge Exchange with the Lunar Exosphere

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Snowden, S. L.; Benna, M.; Carter, J. A.; Cravens, T. E.; Hills, H. Kent; Hodges, R. R.; Kuntz, K. D.; Porter, F. Scott; Read, A.;

Monte Carlo simulations of the spin-2 Blume-Emery-Griffiths model with four-spin interactions

NASA Astrophysics Data System (ADS)

Jabar, A.; Masrour, R.; Jetto, K.; Bahmad, L.; Benyoussef, A.; Hamedoun, M.

2016-12-01

The magnetic properties of a spin S = 2 Ising system with bilinear exchange interaction J1, the biquadratic exchange interaction K, four-spin exchange interactions J4 and crystal field Δ are discussed using the Monte Carlo simulation. The lattice is divided into two sublattices: A and B, for which we compute the magnetizations mA and mB. The phase obtained diagrams of this system are deduced in the planes: (T, Δ/J1), (K/J1, Δ/J1), (Δ/J1, J4/J1) and (J4/J1, K/J1). In addition to the usual phases, we found a new phase called nonmagnetic quadratic, for which the magnetizations are mA ≠ mB and the quadrupolar moments are so that are qA = qB. Furthermore, the behavior of the magnetizations as a function of temperature, crystal field, four-spin exchange interactions and biquadratic exchange interaction are deduced.

The role of dynamic surface water-groundwater exchange on streambed denitrification in a first-order, low-relief agricultural watershed

NASA Astrophysics Data System (ADS)

Rahimi, Mina; Essaid, Hedeff I.; Wilson, John T.

2015-12-01

The role of temporally varying surface water-groundwater (SW-GW) exchange on nitrate removal by streambed denitrification was examined along a reach of Leary Weber Ditch (LWD), Indiana, a small, first-order, low-relief agricultural watershed within the Upper Mississippi River basin, using data collected in 2004 and 2005. Stream stage, GW heads (H), and temperatures (T) were continuously monitored in streambed piezometers and stream bank wells for two transects across LWD accompanied by synoptic measurements of stream stage, H, T, and nitrate (NO3) concentrations along the reach. The H and T data were used to develop and calibrate vertical two-dimensional, models of streambed water flow and heat transport across and along the axis of the stream. Model-estimated SW-GW exchange varied seasonally and in response to high-streamflow events due to dynamic interactions between SW stage and GW H. Comparison of 2004 and 2005 conditions showed that small changes in precipitation amount and intensity, evapotranspiration, and/or nearby GW levels within a low-relief watershed can readily impact SW-GW interactions. The calibrated LWD flow models and observed stream and streambed NO3 concentrations were used to predict temporal variations in streambed NO3 removal in response to dynamic SW-GW exchange. NO3 removal rates underwent slow seasonal changes, but also underwent rapid changes in response to high-flow events. These findings suggest that increased temporal variability of SW-GW exchange in low-order, low-relief watersheds may be a factor contributing their more efficient removal of NO3.

The role of dynamic surface water-groundwater exchange on streambed denitrification in a first-order, low-relief agricultural watershed

USGS Publications Warehouse

Rahimi Kazerooni, Mina N.; Essaid, Hedeff I.; Wilson, John T.

2015-01-01

The role of temporally varying surface water-groundwater (SW-GW) exchange on nitrate removal by streambed denitrification was examined along a reach of Leary Weber Ditch (LWD), Indiana, a small, first-order, low-relief agricultural watershed within the Upper Mississippi River basin, using data collected in 2004 and 2005. Stream stage, GW heads (H), and temperatures (T) were continuously monitored in streambed piezometers and stream bank wells for two transects across LWD accompanied by synoptic measurements of stream stage, H, T, and nitrate (NO3) concentrations along the reach. The H and T data were used to develop and calibrate vertical two-dimensional, models of streambed water flow and heat transport across and along the axis of the stream. Model-estimated SW-GW exchange varied seasonally and in response to high-streamflow events due to dynamic interactions between SW stage and GW H. Comparison of 2004 and 2005 conditions showed that small changes in precipitation amount and intensity, evapotranspiration, and/or nearby GW levels within a low-relief watershed can readily impact SW-GW interactions. The calibrated LWD flow models and observed stream and streambed NO3 concentrations were used to predict temporal variations in streambed NO3 removal in response to dynamic SW-GW exchange. NO3 removal rates underwent slow seasonal changes, but also underwent rapid changes in response to high-flow events. These findings suggest that increased temporal variability of SW-GW exchange in low-order, low-relief watersheds may be a factor contributing their more efficient removal of NO3.

Understanding Groundwater and Surface Water Exchange Processes Along a Controlled Stream Using Thermal Remote Sensing and In-Situ Measurements

NASA Astrophysics Data System (ADS)

Varli, D.; Yilmaz, K. K.

2016-12-01

Effective management of water resources requires understanding and quantification of interaction between groundwater and surface water bodies. Moreover, the exchange processes have recently received increasing attention due to important influences on biogeochemical and ecological status of watersheds. In this study we investigated the exchange processes between surface water and groundwater along Kirmir stream - a controlled stream nearby Kizilcahamam, Ankara, Turkey. At the first stage, potential stream reaches where the exchange processes could occur were pinpointed using geological and geomorphological information. Then, thermal remote sensing was utilized to further narrow down the potential locations in which interaction could occur at a smaller scale. Nested piezometers were installed at identified locations to observe the variations in vertical hydraulic gradient over time. Differential discharge measurements were performed to understand the gains and losses along the stream reach. Streambed temperature measurements were taken at two different depths for a period of time using temperature loggers to calculate the vertical fluid fluxes through the streambed at various locations. Basic water quality field parameters (temperature, electrical conductivity, total dissolved solid amount, dissolved oxygen, pH and oxidation - reduction potential) were measured along the stream reach, from surface water and the piezometers as wells as from the nearby springs and wells. Chloride mass balance was performed to find the contribution of groundwater and chloride concentrations were associated with the geology of the area. This hierarchical, multi-scale methodology provided an efficient and effective way to determine the locations and the direction of groundwater and surface water exchange processes within the study area.

Electron energy spectrum and magnetic interactions in high-Tc superconductors

NASA Technical Reports Server (NTRS)

Turshevski, S. A.; Liechtenstein, A. I.; Antropov, V. P.; Gubanov, V. A.

1991-01-01

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T(sub N1) and T(sub N2). The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T(sub N2) reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T(sub N1) and T(sub N2) which depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg Hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J(sub ij) parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

Electron energy spectrum and magnetic interactions in high-T(sub c) superconductors

NASA Technical Reports Server (NTRS)

Turshevski, S. A.; Liechtenstein, A. I.; Antropov, V. P.; Gubanov, V. A.

1990-01-01

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T sub N1 and T sub N2. The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T sub N2 reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T sub N1 and T sub N2 depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J sub ij parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

Interaction of coeval felsic and mafic magmas from the Kanker granite, Pithora region, Bastar Craton, Central India

NASA Astrophysics Data System (ADS)

Elangovan, R.; Krishna, Kumar; Vishwakarma, Neeraj; Hari, K. R.; Ram Mohan, M.

2017-10-01

Field and petrographic studies are carried out to characterize the interactions of mafic and felsic magmas from Pithora region of the northeastern part of the Bastar Craton. The MMEs, syn-plutonic mafic dykes, cuspate contacts, magmatic flow textures, mingling and hybridization suggest the coeval emplacement of end member magmas. Petrographic evidences such as disequilibrium assemblages, resorption textures, quartz ocelli, rapakivi and poikilitic textures suggest magma mingling and mixing phenomena. Such features of mingling and mixing of the felsic and mafic magma manifest the magma chamber processes. Introduction of mafic magmas into the felsic magmas before initiation of crystallization of the latter, results in hybrid magmas under the influence of thermal and chemical exchange. The mechanical exchange occurs between the coexisting magmas due to viscosity contrast, if the mafic magma enters slightly later into the magma chamber, then the felsic magma starts to crystallize. Blobs of mafic magma form as MMEs in the felsic magma and they scatter throughout the pluton due to convection. At a later stage, if mafic magma enters the system after partial crystallization of felsic phase, mechanical interaction between the magmas leads to the formation of fragmented dyke or syn-plutonic mafic dyke. All these features are well-documented in the study area. Field and petrographic evidences suggest that the textural variations from Pithora region of Bastar Craton are the outcome of magma mingling, mixing and hybridization processes.

Exchange interaction effects on waves in magnetized quantum plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trukhanova, Mariya Iv., E-mail: mar-tiv@yandex.ru; Andreev, Pavel A., E-mail: andreevpa@physics.msu.ru

2015-02-15

We have applied the many-particle quantum hydrodynamics that includes the Coulomb exchange interaction to magnetized quantum plasmas. We considered a number of wave phenomena that are affected by the Coulomb exchange interaction. Since the Coulomb exchange interaction affects the longitudinal and transverse-longitudinal waves, we focused our attention on the Langmuir waves, the Trivelpiece-Gould waves, the ion-acoustic waves in non-isothermal magnetized plasmas, the dispersion of the longitudinal low-frequency ion-acoustic waves, and low-frequency electromagnetic waves at T{sub e} ≫ T{sub i}. We have studied the dispersion of these waves and present the numeric simulation of their dispersion properties.

Spin and orbital exchange interactions from Dynamical Mean Field Theory

NASA Astrophysics Data System (ADS)

Secchi, A.; Lichtenstein, A. I.; Katsnelson, M. I.

2016-02-01

We derive a set of equations expressing the parameters of the magnetic interactions characterizing a strongly correlated electronic system in terms of single-electron Green's functions and self-energies. This allows to establish a mapping between the initial electronic system and a spin model including up to quadratic interactions between the effective spins, with a general interaction (exchange) tensor that accounts for anisotropic exchange, Dzyaloshinskii-Moriya interaction and other symmetric terms such as dipole-dipole interaction. We present the formulas in a format that can be used for computations via Dynamical Mean Field Theory algorithms.

Spin-electron acoustic soliton and exchange interaction in separate spin evolution quantum plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreev, Pavel A., E-mail: andreevpa@physics.msu.ru

Separate spin evolution quantum hydrodynamics is generalized to include the Coulomb exchange interaction, which is considered as interaction between the spin-down electrons being in quantum states occupied by one electron. The generalized model is applied to study the non-linear spin-electron acoustic waves. Existence of the spin-electron acoustic soliton is demonstrated. Contributions of concentration, spin polarization, and exchange interaction to the properties of the spin electron acoustic soliton are studied.

Hyporheic Zone Residence Time Distributions in Regulated River Corridors

NASA Astrophysics Data System (ADS)

Song, X.; Chen, X.; Shuai, P.; Gomez-Velez, J. D.; Ren, H.; Hammond, G. E.

2017-12-01

Regulated rivers exhibit stage fluctuations at multiple frequencies due to both natural processes (e.g., seasonal cycle) and anthropogenic activities (e.g., dam operation). The interaction between the dynamic river flow conditions and the heterogeneous aquifer properties results in complex hydrologic exchange pathways that are ubiquitous in free-flowing and regulated river corridors. The dynamic nature of the exchange flow is reflected in the residence time distribution (RTD) of river water within the groundwater system, which is a key metric that links river corridor biogeochemical processes with the hydrologic exchange. Understanding the dynamics of RTDs is critical to gain the mechanistic understanding of hydrologic exchange fluxes and propose new parsimonious models for river corridors, yet it is understudied primarily due to the high computational demands. In this study, we developed parallel particle tracking algorithms to reveal how river flow variations affect the RTD of river water in the alluvial aquifer. Particle tracking was conducted using the velocity outputs generated by three-dimensional groundwater flow simulations of PFLOTRAN in a 1600 x 800 x 20m model domain within the DOE Hanford Site. Long-term monitoring data of inland well water levels and river stage were used for eight years of flow simulation. Nearly a half million particles were continually released along the river boundary to calculate the RTDs. Spectral analysis of the river stage data revealed high-frequency (sub-daily to weekly) river stage fluctuations caused by dam operations. The higher frequencies of stage variation were progressively filtered to generate multiple sets of flow boundary conditions. A series of flow simulations were performed by using the filtered flow boundary conditions and various degrees of subsurface heterogeneity to study the relative contribution of flow dynamics and physical heterogeneity on river water RTD. Our results revealed multimodal RTDs of river water as a result of the highly variable exchange pathways driven by interactions between dynamic flow and aquifer heterogeneity. A relationship between the RTD and frequency of flow variation was built for each heterogeneity structure, which can be used to assess the potential ecological consequences of dam operations in regulated rivers.

Piezoelectric and Electrostrictive Materials for Transducer Applications. Volume 2

DTIC Science & Technology

1991-01-31

field cooled (ZFC) state the structure of a relaxor appears cubic indicating that the scale of the polar behavior is smaller than the coherence length of...inhomogeneity. The glassy behavior is believed to arise due to competing interactions between magnetic moments resulting in a freezing of the magnetization...between ferromagnetic and antiferromagnetic exchanges (16,17). The FC state exhibits behavior resembling a normal ferromagnet below Tf, i.e

Theoretical modeling of the electronic structure and exchange interactions in Cu(II)Pc

NASA Astrophysics Data System (ADS)

Wu, Wei; Fisher, A. J.; Harrison, N. M.; Wang, Hai; Wu, Zhenlin; Gardener, Jules; Heutz, Sandrine; Jones, Tim; Aeppli, Gabriel

2012-12-01

We calculate the electronic structure and exchange interactions in a copper(II)phthalocyanine (Cu(II)Pc) crystal as a one-dimensional molecular chain using hybrid exchange density functional theory (DFT). In addition, the intermolecular exchange interactions are also calculated in a molecular dimer using Green's function perturbation theory (GFPT) to illustrate the underlying physics. We find that the exchange interactions depend strongly on the stacking angle, but weakly on the sliding angle (defined in the text). The hybrid DFT calculations also provide an insight into the electronic structure of the Cu(II)Pc molecular chain and demonstrate that on-site electron correlations have a significant effect on the nature of the ground state, the band gap and magnetic excitations. The exchange interactions predicted by our DFT calculations and GFPT calculations agree qualitatively with the recent experimental results on newly found η-Cu(II)Pc and the previous results for the α- and β-phases. This work provides a reliable theoretical basis for the further application of Cu(II)Pc to molecular spintronics and organic-based quantum information processing.

Theoretical modeling of the electronic structure and exchange interactions in a Cu(II)Pc one-dimensional chain

NASA Astrophysics Data System (ADS)

Wu, Wei; Fisher, A. J.; Harrison, N. M.

2011-07-01

We calculate the electronic structure and exchange interactions in a copper(II)phthalocyanine [Cu(II)Pc] crystal as a one-dimensional molecular chain using hybrid exchange density functional theory (DFT). In addition, the intermolecular exchange interactions are also calculated in a molecular dimer using Green’s function perturbation theory (GFPT) to illustrate the underlying physics. We find that the exchange interactions depend strongly on the stacking angle, but weakly on the sliding angle (defined in the text). The hybrid DFT calculations also provide an insight into the electronic structure of the Cu(II)Pc molecular chain and demonstrate that on-site electron correlations have a significant effect on the nature of the ground state, the band gap, and magnetic excitations. The exchange interactions predicted by our DFT calculations and GFPT calculations agree qualitatively with the recent experimental results on newly found η-Cu(II)Pc and the previous results for the α and β phases. This work provides a reliable theoretical basis for the further application of Cu(II)Pc to molecular spintronics and organic-based quantum information processing.

Influence of exchange group of modified glycidyl methacrylate polymer on phenol removal: A study by batch and continuous flow processes.

PubMed

Aversa, Thiago Muza; da Silva, Carla Michele Frota; da Rocha, Paulo Cristiano Silva; Lucas, Elizabete Fernandes

2016-11-01

Contamination of water by phenol is potentially a serious problem due to its high toxicity and its acid character. In this way some treatment process to remove or reduce the phenol concentration before contaminated water disposal on the environment is required. Currently, phenol can be removed by charcoal adsorption, but this process does not allow easy regeneration of the adsorbent. In contrast, polymeric resins are easily regenerated and can be reused in others cycles of adsorption process. In this work, the interaction of phenol with two polymeric resins was investigated, one of them containing a weakly basic anionic exchange group (GD-DEA) and the other, a strongly basic group (GD-QUAT). Both ion exchange resins were obtained through chemical modifications from a base porous resin composed of glycidyl methacrylate (GMA) and divinyl benzene (DVB). Evaluation tests with resins were carried out with 30 mg/L of phenol in water solution, at pH 6 and 10, employing two distinct processes: (i) batch, to evaluate the effect of temperature, and (ii) continuous flow, to assess the breakthrough of the resins. Batch tests revealed that the systems did not follow the model proposed by Langmuir due to the negative values obtained for the constant b and for the maximum adsorption capacity, Q0. However, satisfactory results for the constants KF and n allowed assuming that the behavior of systems followed the Freundlich model, leading to the conclusion that resin GD-DEA had the best interaction with the phenol when in a solution having pH 10 (phenoxide ions). The continuous flow tests corroborated this conclusion since the performance of GD-DEA in removing phenol was also best at pH 10, indicating that the greater availability of the electron pair in the resin with the weakly basic donor group contributed to enhance the resin's interaction with the phenoxide ions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Water adsorption on surface-modified cellulose nanocrystals

NASA Astrophysics Data System (ADS)

Wei, Zonghui; Sinko, Robert; Keten, Sinan; Luijten, Erik

Cellulose nanocrystals (CNCs) have attracted much attention as a filler phase for polymer nanocomposites due to their impressive mechanical properties, low cost, and environmental sustainability. Despite their promise for this application, there are still numerous obstacles that prevent optimal performance of CNC-polymer nanocomposites, such as poor filler dispersion and high levels of water absorption. One way to mitigate these negative effects is to modify CNC surfaces. Computational approaches can be utilized to obtain direct insight into the properties of modified CNC surfaces and probe the interactions of CNCs with other materials to facilitate the experimental design of nanocomposites. We use atomistic grand-canonical Monte Carlo simulations to study how surface modification of ion-exchanged sulfated cellulose nanocrystals (Na-CNCs) impacts water adsorption. We find that methyl(triphenyl)phosphonium-exchanged CNCs adsorb less water than Na-CNCs at the same relative humidity, supporting recent experimental dynamic vapor sorption measurements. By characterizing the distribution and configuration of water molecules near the modified CNC surfaces we determine how surface modifications disrupt CNC-water interactions.

Quantitative analysis of protein-ligand interactions by NMR.

PubMed

Furukawa, Ayako; Konuma, Tsuyoshi; Yanaka, Saeko; Sugase, Kenji

2016-08-01

Protein-ligand interactions have been commonly studied through static structures of the protein-ligand complex. Recently, however, there has been increasing interest in investigating the dynamics of protein-ligand interactions both for fundamental understanding of the underlying mechanisms and for drug development. NMR is a versatile and powerful tool, especially because it provides site-specific quantitative information. NMR has widely been used to determine the dissociation constant (KD), in particular, for relatively weak interactions. The simplest NMR method is a chemical-shift titration experiment, in which the chemical-shift changes of a protein in response to ligand titration are measured. There are other quantitative NMR methods, but they mostly apply only to interactions in the fast-exchange regime. These methods derive the dissociation constant from population-averaged NMR quantities of the free and bound states of a protein or ligand. In contrast, the recent advent of new relaxation-based experiments, including R2 relaxation dispersion and ZZ-exchange, has enabled us to obtain kinetic information on protein-ligand interactions in the intermediate- and slow-exchange regimes. Based on R2 dispersion or ZZ-exchange, methods that can determine the association rate, kon, dissociation rate, koff, and KD have been developed. In these approaches, R2 dispersion or ZZ-exchange curves are measured for multiple samples with different protein and/or ligand concentration ratios, and the relaxation data are fitted to theoretical kinetic models. It is critical to choose an appropriate kinetic model, such as the two- or three-state exchange model, to derive the correct kinetic information. The R2 dispersion and ZZ-exchange methods are suitable for the analysis of protein-ligand interactions with a micromolar or sub-micromolar dissociation constant but not for very weak interactions, which are typical in very fast exchange. This contrasts with the NMR methods that are used to analyze population-averaged NMR quantities. Essentially, to apply NMR successfully, both the type of experiment and equation to fit the data must be carefully and specifically chosen for the protein-ligand interaction under analysis. In this review, we first explain the exchange regimes and kinetic models of protein-ligand interactions, and then describe the NMR methods that quantitatively analyze these specific interactions. Copyright © 2016 Elsevier B.V. All rights reserved.

Relationship between radiation-induced aberrations in individual chromosomes and their DNA content: effects of interaction distance

NASA Technical Reports Server (NTRS)

Wu, H.; Durante, M.; Lucas, J. N.

2001-01-01

PURPOSE: To study the effect of the interaction distance on the frequency of inter- and intrachromosome exchanges in individual chromosomes with respect to their DNA content. Assumptions: Chromosome exchanges are formed by misrejoining of two DNA double-strand breaks (DSB) induced within an interaction distance, d. It is assumed that chromosomes in G(0)/G(1) phase of the cell cycle occupy a spherical domain in a cell nucleus, with no spatial overlap between individual chromosome domains. RESULTS: Formulae are derived for the probability of formation of inter-, as well as intra-, chromosome exchanges relating to the DNA content of the chromosome for a given interaction distance. For interaction distances <1 microm, the relative frequency of interchromosome exchanges predicted by the present model is similar to that by Cigarran et al. (1998) based on the assumption that the probability of interchromosome exchanges is proportional to the "surface area" of the chromosome territory. The "surface area" assumption is shown to be a limiting case of d-->0 in the present model. The present model also predicts that the probability of intrachromosome exchanges occurring in individual chromosomes is proportional to their DNA content with correction terms. CONCLUSION: When the interaction distance is small, the "surface area" distribution for chromosome participation in interchromosome exchanges has been expected. However, the present model shows that for the interaction distance as large as 1 microm, the predicted probability of interchromosome exchange formation is still close to the surface area distribution. Therefore, this distribution does not necessarily rule out the formation of complex chromosomal aberrations by long-range misrejoining of DSB.

Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty, Subrata; Vijay, Amrendra, E-mail: avijay@iitm.ac.in

Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, whichmore » is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romera, M.; Monteblanco, E.; Garcia-Sanchez, F.

The influence of dynamic coupling in between magnetic layers of a standard spin torque nano-oscillator composed of a synthetic antiferromagnet (SyF) as a polarizer and an in-plane magnetized free layer has been investigated. Experiments on spin valve nanopillars reveal non-continuous features such as kinks in the frequency field dependence that cannot be explained without such interactions. Comparison of experiments to numerical macrospin simulations shows that this is due to non-linear interaction between the spin torque (STT) driven mode and a damped mode that is mediated via the third harmonics of the STT mode. It only occurs at large applied currentsmore » and thus at large excitation amplitudes of the STT mode. Under these conditions, a hybridized mode characterized by a strong reduction of the linewidth appears. The reduced linewidth can be explained by a reduction of the non-linear contribution to the linewidth via an enhanced effective damping. Interestingly, the effect depends also on the exchange interaction within the SyF. An enhancement of the current range of reduced linewidth by a factor of two and a reduction of the minimum linewidth by a factor of two are predicted from simulation when the exchange interaction strength is reduced by 30%. These results open directions to optimize the design and microwave performances of spin torque nano-oscillators taking advantage of the coupling mechanisms.« less

Interference of 1:1 and 2:1 layered phyllosilicates as excipients with ranitidine.

PubMed

Li, Zhaohui; Fitzgerald, Nicole M; Albert, Zachary; Jiang, Wei-Teh

2016-04-01

As natural ingredients and excipients, kaolinite and talc were frequently studied for their interactions with drugs in pharmaceutical formulations. In this study, the uptake of ranitidine (RT) on these two minerals was studied under different physic-chemical conditions and the mechanism of RT uptake on these two minerals contrasted. Although the thermodynamic and kinetic RT uptake on these two minerals was similar and the RT uptake on both minerals were limited to the external surfaces only, drastic difference in RT uptake was found under different equilibrium solution pH and ionic strength conditions. As cation exchange process was strongly affected by solution pH and ionic strength, the RT uptake on kaolinite was dominated by cation exchange and electrostatic interactions, while the RT uptake on talc was more controlled by inter- and intra- molecular hydrogen bonding interactions. For kaolinite, the limiting factor for RT uptake was the specific surface area due to monolayer RT adsorption. In contract, multilayer RT uptake was found on talc surfaces. No matter which mechanism dominated RT uptake on these minerals, the interaction should not be neglected in pharmaceutical formulations should these minerals be used as additives and/or excipients. Copyright © 2015 Elsevier B.V. All rights reserved.

Interactions between benzylamiloride and fura-2: studies in vitro and in cardiac myocytes.

PubMed

Hudson, C A; Rojas, J D; Sarvazyan, N; Wesson, D E; Martínez-Zaguilán, R

1998-08-01

Amiloride derivatives are commonly used inhibitors of Na+/H+- and Na+/Ca2+-exchange. Because they are fluorescent molecules the use of benzylamiloride (BZA), an inhibitor of Na+/Ca2+ exchange, in conjunction with Fura-2, a commonly used fluorescent Ca2+ indicator, might complicate interpretation of fluorescence data obtained. In vitro data show that BZA decreases the Fura-2 fluorescence at all useful wavelengths in a concentration-dependent manner. The Fura-2 ratio 340/380 (used to estimate intracellular Ca2+ ([Ca2+]in)) also decreased with increasing BZA concentrations. The Stern-Volmer relation suggests that this phenomenon is due to either static or dynamic quenching. Varying temperatures from 4 to 37 degreesC did not alter Stern-Volmer constants, consistent instead with fluorescence resonance energy transfer (FRET). The in situ relevance of these interactions was evaluated in adult rat cardiac myocytes which exhibit Na+/Ca2+ exchange reflected by rapid [Ca2+]in increase following Na+ removal. Pretreatment with BZA >/= 25 microM decreased the magnitude of Fura-2 changes induced by Na+ removal. Analysis of the individual Fura-2 useful wavelengths indicated that >/= 25 microM BZA altered the Fura-2 signal in a manner consistent with the quenching effects noted in vitro. Together, these data show that BZA interacts with Fura-2 in vitro and in situ and suggest caution when interpreting Fura-2 fluorescence data derived in conjunction with BZA. Copyright 1998 Academic Press.

Ordered bimetallic ferromagnets of chromium(III): [Cr(NH 3) 6][Cr(CN) 6], [Cr(H 2O)(NH 3) 5][Cr(CN) 6], and trans-[Cr(en) 2(H 2O) 2]trans-[Cr(en) 2(OH)F] 2(CIO 4) 5·2H 2O

NASA Astrophysics Data System (ADS)

Burriel, Ramón; Casabó, Jaime; Pons, Josefina; Carnegie, David W.; Carlin, Richard L.

1985-07-01

The magnetic bahavior of the isomorphous compounds [Cr(NH 3) 6][Cr(CN) 6] and [Cr(H 2O)(NH 3) 5][Cr(CN) 6] has been studied by means of zero-field susceptibility measurements. The materials order ferromagnetically at 0.60 and 0.38K, respectively. The compounds behave as examples of the ferromagnetic ( S=3/2) Heisenberg body-center-cubic lattice. The susceptibilities have been analyzed and compared to the Padé approximants of the high-temperature series expansion for this model, a remarkably good fit being obtained with exchange constants 0.042 and 0.022 K, respectively. Another bimetallic substance, trans-[Cr(en) 2(H 2O) 2] trans-[Cr(en) 2(OH)F] 2(CIO 4) 5·2H 2O, with a dominant Heisenberg ferromagnetic interaction J/ kB=0.122 K in one dimension, orders antiferromagnetically at 0.14 K due to a weaker interchain interaction with exchange constant z‧ J‧/ kB=-0.019 K. The three sets of measurements have been carried out on powdered samples for which demagnetization effects are important. The exchange interactions are remarkably weak for such concentrated magnetic materials, yet they are stronger than those found in a number of other such Cr/Cr compounds.

Unveiling magnetic interactions of ruthenium trichloride via constraining direction of orbital moments: Potential routes to realize a quantum spin liquid

NASA Astrophysics Data System (ADS)

Hou, Y. S.; Xiang, H. J.; Gong, X. G.

2017-08-01

Recent experiments reveal that the honeycomb ruthenium trichloride α -RuC l3 is a prime candidate of the Kitaev quantum spin liquid (QSL). However, there is no theoretical model which can properly describe its experimental dynamical response due to the lack of a full understanding of its magnetic interactions. Here, we propose a general scheme to calculate the magnetic interactions in systems (e.g., α -RuC l3 ) with nonnegligible orbital moments by constraining the directions of orbital moments. With this scheme, we put forward a minimal J1-K1-Γ1-J3-K3 model for α -RuC l3 and find that: (I) The third nearest neighbor (NN) antiferromagnetic Heisenberg interaction J3 stabilizes the zigzag antiferromagnetic order; (II) The NN symmetric off-diagonal exchange Γ1 plays a pivotal role in determining the preferred direction of magnetic moments and generating the spin wave gap. An exact diagonalization study on this model shows that the Kitaev QSL can be realized by suppressing the NN symmetric off-diagonal exchange Γ1 and the third NN Heisenberg interaction J3. Thus, we not only propose a powerful general scheme for investigating the intriguing magnetism of Jeff=1 /2 magnets, but also point out future directions for realizing the Kitaev QSL in the honeycomb ruthenium trichloride α -RuC l3 .

Short-range second order screened exchange correction to RPA correlation energies

NASA Astrophysics Data System (ADS)

Beuerle, Matthias; Ochsenfeld, Christian

2017-11-01

Direct random phase approximation (RPA) correlation energies have become increasingly popular as a post-Kohn-Sham correction, due to significant improvements over DFT calculations for properties such as long-range dispersion effects, which are problematic in conventional density functional theory. On the other hand, RPA still has various weaknesses, such as unsatisfactory results for non-isogyric processes. This can in parts be attributed to the self-correlation present in RPA correlation energies, leading to significant self-interaction errors. Therefore a variety of schemes have been devised to include exchange in the calculation of RPA correlation energies in order to correct this shortcoming. One of the most popular RPA plus exchange schemes is the second order screened exchange (SOSEX) correction. RPA + SOSEX delivers more accurate absolute correlation energies and also improves upon RPA for non-isogyric processes. On the other hand, RPA + SOSEX barrier heights are worse than those obtained from plain RPA calculations. To combine the benefits of RPA correlation energies and the SOSEX correction, we introduce a short-range RPA + SOSEX correction. Proof of concept calculations and benchmarks showing the advantages of our method are presented.

Short-range second order screened exchange correction to RPA correlation energies.

PubMed

Beuerle, Matthias; Ochsenfeld, Christian

2017-11-28

Direct random phase approximation (RPA) correlation energies have become increasingly popular as a post-Kohn-Sham correction, due to significant improvements over DFT calculations for properties such as long-range dispersion effects, which are problematic in conventional density functional theory. On the other hand, RPA still has various weaknesses, such as unsatisfactory results for non-isogyric processes. This can in parts be attributed to the self-correlation present in RPA correlation energies, leading to significant self-interaction errors. Therefore a variety of schemes have been devised to include exchange in the calculation of RPA correlation energies in order to correct this shortcoming. One of the most popular RPA plus exchange schemes is the second order screened exchange (SOSEX) correction. RPA + SOSEX delivers more accurate absolute correlation energies and also improves upon RPA for non-isogyric processes. On the other hand, RPA + SOSEX barrier heights are worse than those obtained from plain RPA calculations. To combine the benefits of RPA correlation energies and the SOSEX correction, we introduce a short-range RPA + SOSEX correction. Proof of concept calculations and benchmarks showing the advantages of our method are presented.

Intra- and inter-shell Kondo effects in carbon nanotube quantum dots

NASA Astrophysics Data System (ADS)

Krychowski, Damian; Lipiński, Stanisław

2018-01-01

The linear response transport properties of carbon nanotube quantum dot in the strongly correlated regime are discussed. The finite-U mean field slave boson approach is used to study many-body effects. Magnetic field can rebuilt Kondo correlations, which are destroyed by the effect of spin-orbit interaction or valley mixing. Apart from the field induced revivals of SU(2) Kondo effects of different types: spin, valley or spin-valley, also more exotic phenomena appear, such as SU(3) Kondo effect. Threefold degeneracy occurs due to the effective intervalley exchange induced by short-range part of Coulomb interaction or due to the intershell mixing. In narrow gap nanotubes the full spin-orbital degeneracy might be recovered in the absence of magnetic field opening the condition for a formation of SU(4) Kondo resonance.

Spin Exchange Interaction in Substituted Copper Phthalocyanine Crystalline Thin Films

NASA Astrophysics Data System (ADS)

Rawat, Naveen; Pan, Zhenwen; Lamarche, Cody J.; Wetherby, Anthony; Waterman, Rory; Tokumoto, Takahisa; Cherian, Judy G.; Headrick, Randall L.; McGill, Stephen A.; Furis, Madalina I.

2015-11-01

The origins of spin exchange in crystalline thin films of Copper Octabutoxy Phthalocyanine (Cu-OBPc) are investigated using Magnetic Circular Dichroism (MCD) spectroscopy. These studies are made possible by a solution deposition technique which produces highly ordered films with macroscopic grain sizes suitable for optical studies. For temperatures lower than 2 K, the contribution of a specific state in the valence band manifold originating from the hybridized lone pair in nitrogen orbitals of the Phthalocyanine ring, bears the Brillouin-like signature of an exchange interaction with the localized d-shell Cu spins. A comprehensive MCD spectral analysis coupled with a molecular field model of a σπ - d exchange analogous to sp-d interactions in Diluted Magnetic Semiconductors (DMS) renders an enhanced Zeeman splitting and a modified g-factor of -4 for the electrons that mediate the interaction. These studies define an experimental tool for identifying electronic states involved in spin-dependent exchange interactions in organic materials.

Spin Exchange Interaction in Substituted Copper Phthalocyanine Crystalline Thin Films

PubMed Central

Rawat, Naveen; Pan, Zhenwen; Lamarche, Cody J.; Wetherby, Anthony; Waterman, Rory; Tokumoto, Takahisa; Cherian, Judy G.; Headrick, Randall L.; McGill, Stephen A.; Furis, Madalina I.

2015-01-01

The origins of spin exchange in crystalline thin films of Copper Octabutoxy Phthalocyanine (Cu-OBPc) are investigated using Magnetic Circular Dichroism (MCD) spectroscopy. These studies are made possible by a solution deposition technique which produces highly ordered films with macroscopic grain sizes suitable for optical studies. For temperatures lower than 2 K, the contribution of a specific state in the valence band manifold originating from the hybridized lone pair in nitrogen orbitals of the Phthalocyanine ring, bears the Brillouin-like signature of an exchange interaction with the localized d-shell Cu spins. A comprehensive MCD spectral analysis coupled with a molecular field model of a σπ − d exchange analogous to sp-d interactions in Diluted Magnetic Semiconductors (DMS) renders an enhanced Zeeman splitting and a modified g-factor of −4 for the electrons that mediate the interaction. These studies define an experimental tool for identifying electronic states involved in spin-dependent exchange interactions in organic materials. PMID:26559337

Spin Exchange Interaction in Substituted Copper Phthalocyanine Crystalline Thin Films.

PubMed

Rawat, Naveen; Pan, Zhenwen; Lamarche, Cody J; Wetherby, Anthony; Waterman, Rory; Tokumoto, Takahisa; Cherian, Judy G; Headrick, Randall L; McGill, Stephen A; Furis, Madalina I

2015-11-12

The origins of spin exchange in crystalline thin films of Copper Octabutoxy Phthalocyanine (Cu-OBPc) are investigated using Magnetic Circular Dichroism (MCD) spectroscopy. These studies are made possible by a solution deposition technique which produces highly ordered films with macroscopic grain sizes suitable for optical studies. For temperatures lower than 2 K, the contribution of a specific state in the valence band manifold originating from the hybridized lone pair in nitrogen orbitals of the Phthalocyanine ring, bears the Brillouin-like signature of an exchange interaction with the localized d-shell Cu spins. A comprehensive MCD spectral analysis coupled with a molecular field model of a σπ - d exchange analogous to sp-d interactions in Diluted Magnetic Semiconductors (DMS) renders an enhanced Zeeman splitting and a modified g-factor of -4 for the electrons that mediate the interaction. These studies define an experimental tool for identifying electronic states involved in spin-dependent exchange interactions in organic materials.

Density Anomalies in the Mantle and the Gravitational Core-Mantle Interaction

NASA Technical Reports Server (NTRS)

Kuang, Weijia; Liu, Lanbo

2003-01-01

Seismic studies suggest that the bulk of the mantle is heterogeneous, with density variations in depth as well as in horizontal directions (latitude and longitude). This density variation produces a three- dimensional gravity field throughout the Earth. On the other hand, the core density also varies in both time and space, due to convective core flow. Consequently, the fluid outer core and the solid mantle interact gravitationally due to the mass anomalies in both regions. This gravitational core-mantle interaction could play a significant role in exchange of angular momentum between the core and the mantle, and thus the change in Earth's rotation on time scales of decades and longer. Aiming at estimating the significance of the gravitational core-mantle interaction on Earth's rotation variation, we introduce in our MoSST core dynamics model a heterogeneous mantle, with a density distribution derived from seismic results. In this model, the core convection is driven by the buoyancy forces. And the density variation is determined dynamically with the convection. Numerical simulation is carried out with different parameter values, intending to extrapolate numerical results for geophysical implications.

Interactive Modelling of Salinity Intrusion in the Rhine-Meuse Delta

NASA Astrophysics Data System (ADS)

Baart, F.; Kranenburg, W.; Luijendijk, A.

2015-12-01

In many delta's of the world salinity intrusion imposes limits to fresh water availability. With increasing population and industry, the need for fresh water increases. But also salinity intrusion is expected to increase due to changes in river discharge, sea level and storm characteristics. In the Rhine-Meuse delta salt intrusion is impacted by human activities as well, like deepening of waterways and opening of delta-branches closed earlier. All these developments call for increasing the understanding of the system, but also for means for policy makers, coastal planners and engineers to assess effects of changes and to explore and design measures. In our presentation we present the developments in interactive modelling of salinity intrusion in the Rhine-Meuse delta. In traditional process-based numerical modelling, impacts are investigated by researchers and engineers by following the steps of pre-defining scenario's, running the model and post-processing the results. Interactive modelling lets users adjust simulations while running. Users can for instance change river discharges or bed levels, and can add measures like changes to geometry. The model will take the adjustments into account immediately, and will directly compute the effect. In this way, a tool becomes available with which coastal planners, policy makers and engineers together can develop and evaluate ideas and designs by interacting with the numerical model. When developing interactive numerical engines, one of the challenges is to optimize the exchange of variables as e.g. salt concentration. In our case we exchange variables on a 3D grid every time step. For this, the numerical model adheres to the Basic Model Interface (http://csdms.colorado.edu/wiki), which allows external control and the exchange of variables through pointers while the model is running. In our presentation we further explain our method and show examples of interactive design of salinity intrusion measures in the Rhine-Meuse delta.

A Search for Freshwater in the Saline Aquifers of Coastal Bangladesh

NASA Astrophysics Data System (ADS)

Peters, C.; Hornberger, G. M.

2017-12-01

Can we locate pockets of freshwater amidst brackish groundwater in remote villages in Bangladesh? This study explores what we can infer about local groundwater-surface water (GW-SW) interactions in the polders of coastal Bangladesh. In this underdeveloped region, the shallow groundwater is primarily brackish with unpredictable apportioning of freshwater pockets. We use transects of piezometers, cores, electromagnetic induction, and water chemistry surveys to explore two sources of potential fresh groundwater: (1) tidal channel-aquifer exchange and (2) meteoric recharge. Freshwater is difficult to find due to disparate subsurface lithology, asymmetrical tidal dynamics, extreme seasonal fluctuations in rainfall, and limited field data. Observations suggest substantial lateral variability in shallow subsurface conductivity profiles as well as tidal pressure signals in piezometers. Nevertheless, active exchange of freshwater may be limited due to low permeability of banks and surface sediments limits. Small scale heterogeneity in delta formation likely caused much of the groundwater salinity variation. Without adequate ground truthing of groundwater quality, the ability to deduce the exact location of freshwater pockets may be restricted.

Characterization of xenon ion and neutral interactions in a well-characterized experiment

NASA Astrophysics Data System (ADS)

Patino, Marlene I.; Wirz, Richard E.

2018-06-01

Interactions between fast ions and slow neutral atoms are commonly dominated by charge-exchange and momentum-exchange collisions, which are important to understanding and simulating the performance and behavior of many plasma devices. To investigate these interactions, this work developed a simple, well-characterized experiment that accurately measures the behavior of high energy xenon ions incident on a background of xenon neutral atoms. By using well-defined operating conditions and a simple geometry, these results serve as canonical data for the development and validation of plasma models and models of neutral beam sources that need to ensure accurate treatment of angular scattering distributions of charge-exchange and momentum-exchange ions and neutrals. The energies used in this study are relevant for electric propulsion devices ˜1.5 keV and can be used to improve models of ion-neutral interactions in the plume. By comparing these results to both analytical and computational models of ion-neutral interactions, we discovered the importance of (1) accurately treating the differential cross-sections for momentum-exchange and charge-exchange collisions over a large range of neutral background pressures and (2) properly considering commonly overlooked interactions, such as ion-induced electron emission from nearby surfaces and neutral-neutral ionization collisions.

Speaker transfer in children's peer conversation: completing communication-aid-mediated contributions.

PubMed

Clarke, Michael; Bloch, Steven; Wilkinson, Ray

2013-03-01

Managing the exchange of speakers from one person to another effectively is a key issue for participants in everyday conversational interaction. Speakers use a range of resources to indicate, in advance, when their turn will come to an end, and listeners attend to such signals in order to know when they might legitimately speak. Using the principles and findings from conversation analysis, this paper examines features of speaker transfer in a conversation between a boy with cerebral palsy who has been provided with a voice-output communication aid (VOCA), and a peer without physical or communication difficulties. Specifically, the analysis focuses on turn exchange, where a VOCA-mediated contribution approach completion, and the child without communication needs is due to speak next.

Tuning the stability and the skyrmion Hall effect in magnetic skyrmions by adjusting their exchange strengths with magnetic disks

NASA Astrophysics Data System (ADS)

Sun, L.; Wu, H. Z.; Miao, B. F.; Wu, D.; Ding, H. F.

2018-06-01

Magnetic skyrmion is a promising candidate for the future information technology due to its small size, topological protection and the ultralow current density needed to displace it. The applications, however, are currently limited by its narrow phase diagram and the skyrmion Hall effect which prevents the skyrmion motion at high speed. In this work, we study the Dzyaloshinskii-Moriya interaction induced magnetic skyrmion that exchange coupled with magnetic nano-disks utilizing the micromagnetic simulation. We find that the stability and the skyrmion Hall effect of the created skyrmion can be tuned effectively with the coupling strength, thus opens the space to optimize the performance of the skyrmion based devices.

Effect of pressure on the magnetic properties of TM3[Cr(CN)6]2·12H2O

NASA Astrophysics Data System (ADS)

Zentková, M.; Arnold, Z.; Kamarád, J.; Kavecanský, V.; Lukácová, M.; Mat'aš, S.; Mihalik, M.; Mitróová, Z.; Zentko, A.

2007-07-01

We present the results of magnetization and AC susceptibility measurements performed on ferrimagnetic Mn32+[CrIII(CN)6]2·12H2O and ferromagnetic Ni32+[CrIII(CN)6]2·12H2O systems under pressures up to 0.9 GPa in a commercial SQUID magnetometer. The magnetization process is affected by pressure: magnetization saturates at higher magnetic field, saturated magnetization μs of Ni3[Cr(CN)6]2 is reduced and almost unaffected for Mn3[Cr(CN)6]2 at low temperatures. The Curie temperature TC of Mn3[Cr(CN)6]2 increases with the applied pressure, ΔTC/Δp = 25.5 K GPa-1, due to a strengthened super-exchange antiferromagnetic interaction JAF, but it is not affected significantly in the case of Ni3[Cr(CN)6]2 with a dominant ferromagnetic JF super-exchange interaction. The increase in the JAF interaction is attributed to the enhanced value of the single electron overlapping integral S and the energy gap Δ of the mixed molecular orbitals t2g (Mn2+) and t2g (CrIII) induced by pressure.

Snohomish RARE project update for Tulalip Tribes | Science ...

EPA Pesticide Factsheets

Rising atmospheric CO2 due to anthropogenic emissions alters local atmospheric gas exchange rates in estuaries, causing alterations of the seawater carbonate system and reductions in pH broadly described as coastal acidification. These changes in marine chemistry have been demonstrated to negatively affect a variety of coastal and estuarine organisms. The naturally dynamic carbonate chemistry of estuaries driven by biological activity, hydrodynamic processes, and intensive biogeochemical cycling has led to uncertainty regarding the role of rising atmospheric CO2 as a driver in these systems, and the suggestion that altered atmospheric exchange may be relatively unimportant to estuarine biogeochemistry. In this presentation, we illustrate how rising atmospheric CO2 from 1765 through 2100 interacts with the observed local carbonate chemistry dynamics of a seagrass bed, and calculated how pHT, pCO2, and Ωaragonite respond. This presentation is part of an informal meeting with the Tulalip Tribes of Tulalip, WA to update them on the progress of the ORD/Region 10 RARE project in the Snohomish estuary to study drivers of coastal acidification. Multiple processes, including primary production and respiration, river runoff, cultural eutrophication, oceanic upwelling, and atmospheric exchange contribute to the characteristically dynamic carbonate conditions in these habitats, with potential interactions amongst these processes leading to coastal acidification. As a

An NMR-based quenched hydrogen exchange investigation of model amyloid fibrils formed by cold shock protein A.

PubMed

Alexandrescu, A T

2001-01-01

Acid-denatured cold shock protein A (CspA) self-assembles into polymers with properties typical of amyloid fibrils. In the present work, a quenched hydrogen exchange experiment was used to probe the interactions of CspA fibrils with solvent. Exchange was initiated by incubating suspensions of fibrils in D2O, and quenched by flash freezing. Following lyophilization, exchange-quenched samples were dissolved in 90% DMSO/10% D2O, giving DMSO-denatured monomers. Intrinsic exchange rates for denatured CspA in 90% DMSO/10% D2O (pH* 4.5) were sufficiently slow (approximately 1 x 10(-3) min-1) to enable quantification of NMR signal intensity decays due to H/D exchange in the fibrils. Hydrogen exchange rate constants for CspA fibrils were found to vary less than 3-fold from a mean value of 5 x 10(-5) min-1. The uniformity of rate constants suggests that exchange is in the EX1 limit, and that the mechanism of exchange involves a cooperative dissociation of CspA monomers from fibrils, concomitant with unfolding. Previous studies indicated that the highest protection factors in native CspA are approximately 10(3), and that protection factors for the acid-denatured monomer precursors of CspA fibrils are close to unity. Because exchange in is in the EX1 regime, it is only possible to place a lower limit of at least 10(5) on protection factors in CspA fibrils. The observation that all amide protons are protected from exchange indicates that the entire CspA polypeptide chain is structured in the fibrils.

Kondo blockade due to quantum interference in single-molecule junctions

PubMed Central

Mitchell, Andrew K.; Pedersen, Kim G. L.; Hedegård, Per; Paaske, Jens

2017-01-01

Molecular electronics offers unique scientific and technological possibilities, resulting from both the nanometre scale of the devices and their reproducible chemical complexity. Two fundamental yet different effects, with no classical analogue, have been demonstrated experimentally in single-molecule junctions: quantum interference due to competing electron transport pathways, and the Kondo effect due to entanglement from strong electronic interactions. Here we unify these phenomena, showing that transport through a spin-degenerate molecule can be either enhanced or blocked by Kondo correlations, depending on molecular structure, contacting geometry and applied gate voltages. An exact framework is developed, in terms of which the quantum interference properties of interacting molecular junctions can be systematically studied and understood. We prove that an exact Kondo-mediated conductance node results from destructive interference in exchange-cotunneling. Nonstandard temperature dependences and gate-tunable conductance peaks/nodes are demonstrated for prototypical molecular junctions, illustrating the intricate interplay of quantum effects beyond the single-orbital paradigm. PMID:28492236

Negative exchange interactions in coupled few-electron quantum dots

NASA Astrophysics Data System (ADS)

Deng, Kuangyin; Calderon-Vargas, F. A.; Mayhall, Nicholas J.; Barnes, Edwin

2018-06-01

It has been experimentally shown that negative exchange interactions can arise in a linear three-dot system when a two-electron double quantum dot is exchange coupled to a larger quantum dot containing on the order of one hundred electrons. The origin of this negative exchange can be traced to the larger quantum dot exhibiting a spin tripletlike rather than singletlike ground state. Here we show using a microscopic model based on the configuration interaction (CI) method that both tripletlike and singletlike ground states are realized depending on the number of electrons. In the case of only four electrons, a full CI calculation reveals that tripletlike ground states occur for sufficiently large dots. These results hold for symmetric and asymmetric quantum dots in both Si and GaAs, showing that negative exchange interactions are robust in few-electron double quantum dots and do not require large numbers of electrons.

Simulation of alnico coercivity

DOE PAGES

Ke, Liqin; Skomski, Ralph; Hoffmann, Todd D.; ...

2017-07-10

Micromagnetic simulations of alnico show substantial deviations from Stoner-Wohlfarth behavior due to the unique size and spatial distribution of the rod-like Fe-Co phase formed during spinodal decomposition in an external magnetic field. Furthemore, the maximum coercivity is limited by single-rod effects, especially deviations from ellipsoidal shape, and by interactions between the rods. In both the exchange interaction between connected rods and magnetostatic we consider the interaction between rods, and the results of our calculations show good agreement with recent experiments. Unlike systems dominated by magnetocrystalline anisotropy, coercivity in alnico is highly dependent on size, shape, and geometric distribution of themore » Fe-Co phase, all factors that can be tuned with appropriate chemistry and thermal-magnetic annealing.« less

Creation and Annihilation of Skyrmions in the Frustrated Magnets with Competing Exchange Interactions.

PubMed

Hu, Yong; Chi, Xiaodan; Li, Xuesi; Liu, Yan; Du, An

2017-11-22

In triangular-lattice magnets, the coexistence of third-neighbor antiferromagnetic and nearest-neighbor ferromagnetic exchange interactions can induce rich magnetic phases including noncoplanar skyrmion crystals. Based on Monte Carlo simulation, we studied the dependence of magnetic phase transition on exchange interaction strength. Under the consideration of uniaxial anisotropy and magnetic field both perpendicular to the film plane, a large antiferromagnetic exchange interaction induces a high frustration. When the value of antiferromagnetic exchange interaction is one and a half times larger than the ferromagnetic one, a magnetic phase composed of canting spin stripes, never observed in the chiral magnets, forms. Interestingly, different canting spin stripes along three 120 degree propagation directions may coexist randomly in a magnetic phase, attesting that the canting spin stripes are three-fold degenerate states akin to helices and the multiple state of canting spin stripes is a circular configuration with zero skyrmion charge number. Moreover, skyrmions and antiskyrmions can be observed simultaneously in the configuration at the low temperature nearly close to 0 K, and their configuration and diameter properties are discussed. Finally, the mechanisms of skyrmion creation and annihilation are properly interpreted by comparing exchange and Zeeman energy terms.

Competition of Dzyaloshinskii-Moriya and Higher-Order Exchange Interactions in Rh /Fe Atomic Bilayers on Ir(111)

NASA Astrophysics Data System (ADS)

Romming, Niklas; Pralow, Henning; Kubetzka, André; Hoffmann, Markus; von Malottki, Stephan; Meyer, Sebastian; Dupé, Bertrand; Wiesendanger, Roland; von Bergmann, Kirsten; Heinze, Stefan

2018-05-01

Using spin-polarized scanning tunneling microscopy and density functional theory we demonstrate the occurrence of a novel type of noncollinear spin structure in Rh /Fe atomic bilayers on Ir(111). We find that higher-order exchange interactions depend sensitively on the stacking sequence. For fcc-Rh /Fe /Ir (111 ) , frustrated exchange interactions are dominant and lead to the formation of a spin spiral ground state with a period of about 1.5 nm. For hcp-Rh /Fe /Ir (111 ) , higher-order exchange interactions favor an up-up-down-down (↑↑↓↓) state. However, the Dzyaloshinskii-Moriya interaction at the Fe /Ir interface leads to a small angle of about 4° between adjacent magnetic moments resulting in a canted ↑↑↓↓ ground state.

Magnetic Yoking and Tunable Interactions in FePt-Based Hard/Soft Bilayers

PubMed Central

Gilbert, Dustin A.; Liao, Jung-Wei; Kirby, Brian J.; Winklhofer, Michael; Lai, Chih-Huang; Liu, Kai

2016-01-01

Magnetic interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations. Here we demonstrate an extremely sensitive magnetic yoking effect and tunable interactions in FePt based hard/soft bilayers mediated by the soft layer. Below the exchange length, a thin soft layer strongly exchange couples to the perpendicular moments of the hard layer; above the exchange length, just a few nanometers thicker, the soft layer moments turn in-plane and act to yoke the dipolar fields from the adjacent hard layer perpendicular domains. The evolution from exchange to dipolar-dominated interactions is experimentally captured by first-order reversal curves, the ΔM method, and polarized neutron reflectometry, and confirmed by micromagnetic simulations. These findings demonstrate an effective yoking approach to design and control magnetic interactions in wide varieties of magnetic nanostructures and devices. PMID:27604428

Construction of exchange-correlation functionals through interpolation between the non-interacting and the strong-correlation limit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Yongxi; Ernzerhof, Matthias, E-mail: Matthias.Ernzerhof@UMontreal.ca; Bahmann, Hilke

Drawing on the adiabatic connection of density functional theory, exchange-correlation functionals of Kohn-Sham density functional theory are constructed which interpolate between the extreme limits of the electron-electron interaction strength. The first limit is the non-interacting one, where there is only exchange. The second limit is the strong correlated one, characterized as the minimum of the electron-electron repulsion energy. The exchange-correlation energy in the strong-correlation limit is approximated through a model for the exchange-correlation hole that is referred to as nonlocal-radius model [L. O. Wagner and P. Gori-Giorgi, Phys. Rev. A 90, 052512 (2014)]. Using the non-interacting and strong-correlated extremes, variousmore » interpolation schemes are presented that yield new approximations to the adiabatic connection and thus to the exchange-correlation energy. Some of them rely on empiricism while others do not. Several of the proposed approximations yield the exact exchange-correlation energy for one-electron systems where local and semi-local approximations often fail badly. Other proposed approximations generalize existing global hybrids by using a fraction of the exchange-correlation energy in the strong-correlation limit to replace an equal fraction of the semi-local approximation to the exchange-correlation energy in the strong-correlation limit. The performance of the proposed approximations is evaluated for molecular atomization energies, total atomic energies, and ionization potentials.« less

Direct measurement of the long-range p -d exchange coupling in a ferromagnet-semiconductor Co/CdMgTe/CdTe quantum well hybrid structure

NASA Astrophysics Data System (ADS)

Akimov, I. A.; Salewski, M.; Kalitukha, I. V.; Poltavtsev, S. V.; Debus, J.; Kudlacik, D.; Sapega, V. F.; Kopteva, N. E.; Kirstein, E.; Zhukov, E. A.; Yakovlev, D. R.; Karczewski, G.; Wiater, M.; Wojtowicz, T.; Korenev, V. L.; Kusrayev, Yu. G.; Bayer, M.

2017-11-01

The exchange interaction between magnetic ions and charge carriers in semiconductors is considered to be a prime tool for spin control. Here, we solve a long-standing problem by uniquely determining the magnitude of the long-range p -d exchange interaction in a ferromagnet-semiconductor (FM-SC) hybrid structure where a 10-nm-thick CdTe quantum well is separated from the FM Co layer by a CdMgTe barrier with a thickness on the order of 10 nm. The exchange interaction is manifested by the spin splitting of acceptor bound holes in the effective magnetic field induced by the FM. The exchange splitting is directly evaluated using spin-flip Raman scattering by analyzing the dependence of the Stokes shift ΔS on the external magnetic field B . We show that in a strong magnetic field, ΔS is a linear function of B with an offset of Δp d=50 -100 μ eV at zero field from the FM induced effective exchange field. On the other hand, the s -d exchange interaction between conduction band electrons and FM, as well as the p -d contribution for free valence band holes, are negligible. The results are well described by the model of indirect exchange interaction between acceptor bound holes in the CdTe quantum well and the FM layer mediated by elliptically polarized phonons in the hybrid structure.

Exchange-Correlation Effects for Noncovalent Interactions in Density Functional Theory.

PubMed

Otero-de-la-Roza, A; DiLabio, Gino A; Johnson, Erin R

2016-07-12

In this article, we develop an understanding of how errors from exchange-correlation functionals affect the modeling of noncovalent interactions in dispersion-corrected density-functional theory. Computed CCSD(T) reference binding energies for a collection of small-molecule clusters are decomposed via a molecular many-body expansion and are used to benchmark density-functional approximations, including the effect of semilocal approximation, exact-exchange admixture, and range separation. Three sources of error are identified. Repulsion error arises from the choice of semilocal functional approximation. This error affects intermolecular repulsions and is present in all n-body exchange-repulsion energies with a sign that alternates with the order n of the interaction. Delocalization error is independent of the choice of semilocal functional but does depend on the exact exchange fraction. Delocalization error misrepresents the induction energies, leading to overbinding in all induction n-body terms, and underestimates the electrostatic contribution to the 2-body energies. Deformation error affects only monomer relaxation (deformation) energies and behaves similarly to bond-dissociation energy errors. Delocalization and deformation errors affect systems with significant intermolecular orbital interactions (e.g., hydrogen- and halogen-bonded systems), whereas repulsion error is ubiquitous. Many-body errors from the underlying exchange-correlation functional greatly exceed in general the magnitude of the many-body dispersion energy term. A functional built to accurately model noncovalent interactions must contain a dispersion correction, semilocal exchange, and correlation components that minimize the repulsion error independently and must also incorporate exact exchange in such a way that delocalization error is absent.

Size and diluted magnetic properties of diamond shaped graphene quantum dots: Monte Carlo study

NASA Astrophysics Data System (ADS)

Masrour, R.; Jabar, A.

2018-05-01

The magnetic properties of diamond shaped graphene quantum dots have been investigated by varying their sizes with the Monte Carlo simulation. The magnetizations and magnetic susceptibilities have been studied with dilutions x (magnetic atom), several sizes L (carbon atom) and exchange interaction J between the magnetic atoms. The all magnetic susceptibilities have been situated at the transitions temperatures of each parameters. The obtained values increase when increases the values of x, L and J. The effect of exchanges interactions and crystal field on the magnetization has been discussed. The magnetic hysteresis cycles for several dilutions x, sizes L, exchange interactions J and temperatures T. The magnetic coercive increases with increasing the exchange interactions and decreases when the temperatures values increasing.

PT -symmetric gain and loss in a rotating Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Haag, Daniel; Dast, Dennis; Cartarius, Holger; Wunner, Günter

2018-03-01

PT -symmetric quantum mechanics allows finding stationary states in mean-field systems with balanced gain and loss of particles. In this work we apply this method to rotating Bose-Einstein condensates with contact interaction which are known to support ground states with vortices. Due to the particle exchange with the environment transport phenomena through ultracold gases with vortices can be studied. We find that even strongly interacting rotating systems support stable PT -symmetric ground states, sustaining a current parallel and perpendicular to the vortex cores. The vortices move through the nonuniform particle density and leave or enter the condensate through its borders creating the required net current.

Ferromagnetic interactions in chromium (III) doped YMnO3

NASA Astrophysics Data System (ADS)

Thakur, Rajesh K.; Thakur, Rasna; Kaurav, N.; Okram, G. S.; Gaur, N. K.

2016-05-01

Both of the reported compounds with compositions YMn1-xCrxO3 (x = 0.1 and 0.2) are synthesized by using the conventional solid state reaction method and their magnetic properties are analyzed vigilantly. The XRD pattern reveals the hexagonal structure of the reported compounds with space group P63cm (25-1079). The in-depth analysis of the magnetic measurements reveals the enhancement in the ferromagnetic character with Cr doping in YMnO3 compounds. The observed enhancement in the ferromagnetism is found to be due to the increased double exchange interactions among the Cr3+ and Mn3+ ions with Cr doping.

First-Principles Evaluation of the Dzyaloshinskii-Moriya Interaction

NASA Astrophysics Data System (ADS)

Koretsune, Takashi; Kikuchi, Toru; Arita, Ryotaro

2018-04-01

We review recent developments of formulations to calculate the Dzyaloshinskii-Moriya (DM) interaction from first principles. In particular, we focus on three approaches. The first one evaluates the energy change due to the spin twisting by directly calculating the helical spin structure. The second one employs the spin gauge field technique to perform the derivative expansion with respect to the magnetic moment. This gives a clear picture that the DM interaction can be represented as the spin current in the equilibrium within the first order of the spin-orbit couplings. The third one is the perturbation expansion with respect to the exchange couplings and can be understood as the extension of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction to the noncentrosymmetric spin-orbit systems. By calculating the DM interaction for the typical chiral ferromagnets Mn1-xFexGe and Fe1-xCoxGe, we discuss how these approaches work in actual systems.

Quantum statistics and squeezing for a microwave-driven interacting magnon system.

PubMed

Haghshenasfard, Zahra; Cottam, Michael G

2017-02-01

Theoretical studies are reported for the statistical properties of a microwave-driven interacting magnon system. Both the magnetic dipole-dipole and the exchange interactions are included and the theory is developed for the case of parallel pumping allowing for the inclusion of the nonlinear processes due to the four-magnon interactions. The method of second quantization is used to transform the total Hamiltonian from spin operators to boson creation and annihilation operators. By using the coherent magnon state representation we have studied the magnon occupation number and the statistical behavior of the system. In particular, it is shown that the nonlinearities introduced by the parallel pumping field and the four-magnon interactions lead to non-classical quantum statistical properties of the system, such as magnon squeezing. Also control of the collapse-and-revival phenomena for the time evolution of the average magnon number is demonstrated by varying the parallel pumping amplitude and the four-magnon coupling.

Final state interactions and the transverse structure of the pion using non-perturbative eikonal methods

DOE PAGES

Gamberg, Leonard; Schlegel, Marc

2010-01-18

In the factorized picture of semi-inclusive hadronic processes the naive time reversal-odd parton distributions exist by virtue of the gauge link which renders it color gauge invariant. The link characterizes the dynamical effect of initial/final-state interactions of the active parton due soft gluon exchanges with the target remnant. Though these interactions are non-perturbative, studies of final-state interaction have been approximated by perturbative one-gluon approximation in Abelian models. We include higher-order contributions by applying non-perturbative eikonal methods incorporating color degrees of freedom in a calculation of the Boer-Mulders function of the pion. Lastly, using this framework we explore under what conditionsmore » the Boer Mulders function can be described in terms of factorization of final state interactions and a spatial distribution in impact parameter space.« less

Constraint on the second functional derivative of the exchange-correlation energy

NASA Astrophysics Data System (ADS)

Joubert, D. P.

2012-09-01

Using the density functional adiabatic connection approach for an N-electron system it is shown that ? γ is the coupling constant that scales the electron-electron interaction strength. For the non-interacting Kohn-Sham Hamiltonian γ = 0 and for the fully interacting system γ = 1. ? is the Hartree plus exchange-correlation energy while f 0(r) and fγ(r) are the Fukui functions of the non-interacting and interacting systems, respectively. This identity can serve to test the internal self-consistency or quality of approximate functionals. The quality of some popular approximate exchange and correlation functionals are tested for a simple model system.

Magnetism and exchange interaction of small rare-earth clusters; Tb as a representative

PubMed Central

Peters, Lars; Ghosh, Saurabh; Sanyal, Biplab; van Dijk, Chris; Bowlan, John; de Heer, Walt; Delin, Anna; Di Marco, Igor; Eriksson, Olle; Katsnelson, Mikhail I.; Johansson, Börje; Kirilyuk, Andrei

2016-01-01

Here we follow, both experimentally and theoretically, the development of magnetism in Tb clusters from the atomic limit, adding one atom at a time. The exchange interaction is, surprisingly, observed to drastically increase compared to that of bulk, and to exhibit irregular oscillations as a function of the interatomic distance. From electronic structure theory we find that the theoretical magnetic moments oscillate with cluster size in exact agreement with experimental data. Unlike the bulk, the oscillation is not caused by the RKKY mechanism. Instead, the inter-atomic exchange is shown to be driven by a competition between wave-function overlap of the 5d shell and the on-site exchange interaction, which leads to a competition between ferromagnetic double-exchange and antiferromagnetic super-exchange. This understanding opens up new ways to tune the magnetic properties of rare-earth based magnets with nano-sized building blocks. PMID:26795239

Model simulations of a field experiment on cation exchange-affected multicomponent solute transport in a sandy aquifer

NASA Astrophysics Data System (ADS)

Bjerg, Poul L.; Ammentorp, Hans C.; Christensen, Thomas H.

1993-04-01

A large-scale and long-term field experiment on cation exchange in a sandy aquifer has been modelled by a three-dimensional geochemical transport model. The geochemical model includes cation-exchange processes using a Gaines-Thomas expression, the closed carbonate system and the effects of ionic strength. Information on geology, hydrogeology and the transient conservative solute transport behaviour was obtained from a dispersion study in the same aquifer. The geochemical input parameters were carefully examined. CEC and selectivity coefficients were determined on the actual aquifer material by batch experiments and by the composition of the cations on the exchange complex. Potassium showed a non-ideal exchange behaviour with KCa selectivity coefficients indicating dependency on equivalent fraction and K + concentration in the aqueous phase. The model simulations over a distance of 35 m and a period of 250 days described accurately the observed attenuation of Na and the expelled amounts of Ca and Mg. Also, model predictions of plateau zones, formed by interaction with the background groundwater, in general agreed satisfactorily with the observations. Transport of K was simulated over a period of 800 days due to a substantially attenuation in the aquifer. The observed and the predicted breakthrough curves showed a reasonable accordance taking the duration of the experiment into account. However, some discrepancies were observed probably caused by the revealed non-ideal exchange behaviour of K +.

Urban legacies and soil management affect the concentration and speciation of trace metals in Los Angeles community garden soils.

PubMed

Clarke, Lorraine Weller; Jenerette, G Darrel; Bain, Daniel J

2015-02-01

Heavy metals in urban soils can compromise human health, especially in urban gardens, where gardeners may ingest contaminated dust or crops. To identify patterns of urban garden metal contamination, we measured concentrations and bioavailability of Pb, As, and Cd in soils associated with twelve community gardens in Los Angeles County, CA. This included sequential extractions to partition metals among exchangeable, reducible, organic, or residual fractions. Proximity to road increased all metal concentrations, suggesting vehicle emissions sources. Reducible Pb increased with neighborhood age, suggesting leaded paint as a likely pollutant source. Exchangeable Cd and As both increased with road proximity. Only cultivated soils showed an increase in exchangeable As with road proximity, potentially due to reducing humic acid interactions while Cd bioavailability was mitigated by organic matter. Understanding the geochemical phases and metal bioavailability allows incorporation of contamination patterns into urban planning. Copyright © 2014 Elsevier Ltd. All rights reserved.

Evidence of exchange-coupled behavior in chromium-cobalt ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Tanbir, Kamar; Sharma, Lalit Kumar; Aakash; Singh, Rakesh Kumar; Choubey, Ravi Kant; Mukherjee, Samrat

2018-06-01

Cr doped cobalt ferrite nanoparticles were synthesized with the generic formula Co1-xCrxFe2O4 (x = 0, 0.05, 0.15, 0.25) through standard chemical co-precipitation method. XRD studies confirmed the pure spinel cubic structure belonging to Fd 3 bar m space group. From the Williamson-Hall plots, crystallite sizes were found to lie within the range (42 ± 1) nm for the different doped samples. The lattice parameter was found to decrease linearly with increase in the concentration of Cr3+ ion. The magnetic behavior of the samples was determined by M-H studies at 300 K, field cooled (5 T) at 5 K and temperature dependent studies. The M-H at 300 K show soft magnetic behavior whereas the M-H plots at 5 K predict the existence of in-homogeneity of the exchange interactions due to strong exchange coupling between the spins at the core and the surface of the nanoparticles.

Thermal adaptation of net ecosystem exchange

DOE PAGES

Yuan, W.; Luo, Y.; Liang, S.; ...

2011-06-06

Thermal adaptation of gross primary production and ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of net ecosystem exchange of carbon (NEE). Here in this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland ecosystems located at latitudes ranging from ~29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (T b) at which ecosystem transfer from carbon source to sinkmore » and optimal temperature (T o) at which carbon uptake is maximized. T b was strongly correlated with annual mean air temperature. T o was strongly correlated with mean temperature during the net carbon uptake period across the study ecosystems. Our results imply that the net ecosystem exchange of carbon adapts to the temperature across the geographical range due to intrinsic connections between vegetation primary production and ecosystem respiration.« less

Thermal adaptation of net ecosystem exchange

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, W.; Luo, Y.; Liang, S.

Thermal adaptation of gross primary production and ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of net ecosystem exchange of carbon (NEE). Here in this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland ecosystems located at latitudes ranging from ~29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (T b) at which ecosystem transfer from carbon source to sinkmore » and optimal temperature (T o) at which carbon uptake is maximized. T b was strongly correlated with annual mean air temperature. T o was strongly correlated with mean temperature during the net carbon uptake period across the study ecosystems. Our results imply that the net ecosystem exchange of carbon adapts to the temperature across the geographical range due to intrinsic connections between vegetation primary production and ecosystem respiration.« less

Nonbolometric bottleneck in electron-phonon relaxation in ultrathin WSi films

NASA Astrophysics Data System (ADS)

Sidorova, Mariia V.; Kozorezov, A. G.; Semenov, A. V.; Korneeva, Yu. P.; Mikhailov, M. Yu.; Devizenko, A. Yu.; Korneev, A. A.; Chulkova, G. M.; Goltsman, G. N.

2018-05-01

We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique, we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide. We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in τe -ph˜14 0 -19 0 ps at TC=3.4 K , supporting the results of earlier measurements by independent techniques.

Water on BN doped benzene: A hard test for exchange-correlation functionals and the impact of exact exchange on weak binding

DOE PAGES

Al-Hamdani, Yasmine S.; Alfè, Dario; von Lilienfeld, O. Anatole; ...

2014-10-22

Density functional theory (DFT) studies of weakly interacting complexes have recently focused on the importance of van der Waals dispersion forces, whereas the role of exchange has received far less attention. Here, by exploiting the subtle binding between water and a boron and nitrogen doped benzene derivative (1,2-azaborine) we show how exact exchange can alter the binding conformation within a complex. Benchmark values have been calculated for three orientations of the water monomer on 1,2-azaborine from explicitly correlated quantum chemical methods, and we have also used diffusion quantum Monte Carlo. For a host of popular DFT exchange-correlation functionals we showmore » that the lack of exact exchange leads to the wrong lowest energy orientation of water on 1,2-azaborine. As such, we suggest that a high proportion of exact exchange and the associated improvement in the electronic structure could be needed for the accurate prediction of physisorption sites on doped surfaces and in complex organic molecules. Meanwhile to predict correct absolute interaction energies an accurate description of exchange needs to be augmented by dispersion inclusive functionals, and certain non-local van der Waals functionals (optB88- and optB86b-vdW) perform very well for absolute interaction energies. Through a comparison with water on benzene and borazine (B₃N₃H₆) we show that these results could have implications for the interaction of water with doped graphene surfaces, and suggest a possible way of tuning the interaction energy.« less

The Effects of Interaction Management and Background Similarity on Perceived Communication Competence and Attraction during Initial Interaction.

ERIC Educational Resources Information Center

Harris, Linda

Although most information exchanged in an initial interaction is superficial, relationships often develop or terminate depending on the evaluations made during the first three to four minutes of a conversation. In order to investigate the content and process levels of the information exchanged during the initial interactions, 90 subjects watched…

Eccentricity Evolution of Extrasolar Multiple Planetary Systems Due to the Depletion of Nascent Protostellar Disks

NASA Astrophysics Data System (ADS)

Nagasawa, M.; Lin, D. N. C.; Ida, S.

2003-04-01

Most extrasolar planets are observed to have eccentricities much larger than those in the solar system. Some of these planets have sibling planets, with comparable masses, orbiting around the same host stars. In these multiple planetary systems, eccentricity is modulated by the planets' mutual secular interaction as a consequence of angular momentum exchange between them. For mature planets, the eigenfrequencies of this modulation are determined by their mass and semimajor axis ratios. However, prior to the disk depletion, self-gravity of the planets' nascent disks dominates the precession eigenfrequencies. We examine here the initial evolution of young planets' eccentricity due to the apsidal libration or circulation induced by both the secular interaction between them and the self-gravity of their nascent disks. We show that as the latter effect declines adiabatically with disk depletion, the modulation amplitude of the planets' relative phase of periapsis is approximately invariant despite the time-asymmetrical exchange of angular momentum between planets. However, as the young planets' orbits pass through a state of secular resonance, their mean eccentricities undergo systematic quantitative changes. For applications, we analyze the eccentricity evolution of planets around υ Andromedae and HD 168443 during the epoch of protostellar disk depletion. We find that the disk depletion can change the planets' eccentricity ratio. However, the relatively large amplitude of the planets' eccentricity cannot be excited if all the planets had small initial eccentricities.

Suppression of Magnetic Quantum Tunneling in a Chiral Single-Molecule Magnet by Ferromagnetic Interactions.

PubMed

Lippert, Kai-Alexander; Mukherjee, Chandan; Broschinski, Jan-Philipp; Lippert, Yvonne; Walleck, Stephan; Stammler, Anja; Bögge, Hartmut; Schnack, Jürgen; Glaser, Thorsten

2017-12-18

Single-molecule magnets (SMMs) retain a magnetization without applied magnetic field for a decent time due to an energy barrier U for spin-reversal. Despite the success to increase U, the difficult to control magnetic quantum tunneling often leads to a decreased effective barrier U eff and a fast relaxation. Here, we demonstrate the influence of the exchange coupling on the tunneling probability in two heptanuclear SMMs hosting the same spin-system with the same high spin ground state S t = 21/2. A chirality-induced symmetry reduction leads to a switch of the Mn III -Mn III exchange from antiferromagnetic in the achiral SMM [Mn III 6 Cr III ] 3+ to ferromagnetic in the new chiral SMM RR [Mn III 6 Cr III ] 3+ . Multispin Hamiltonian analysis by full-matrix diagonalization demonstrates that the ferromagnetic interactions in RR [Mn III 6 Cr III ] 3+ enforce a well-defined S t = 21/2 ground state with substantially less mixing of M S substates in contrast to [Mn III 6 Cr III ] 3+ and no tunneling pathways below the top of the energy barrier. This is experimentally verified as U eff is smaller than the calculated energy barrier U in [Mn III 6 Cr III ] 3+ due to tunneling pathways, whereas U eff equals U in RR [Mn III 6 Cr III ] 3+ demonstrating the absence of quantum tunneling.

Homogeneously dispersed CeO2 nanoparticles on exfoliated hexaniobate nanosheets

NASA Astrophysics Data System (ADS)

Marques, Thalles M. F.; Strayer, Megan E.; Ghosh, Anupama; Silva, Alexandre; Ferreira, Odair P.; Fujisawa, Kazunori; Alves da Cunha, Jose R.; Abreu, Guilherme J. P.; Terrones, Mauricio; Mallouk, Thomas E.; Viana, Bartolomeu C.

2017-12-01

Hexaniobate nanosheets derived from the parent compound K4Nb6O17 have been decorated with CeO2 nanoparticles by ion exchange with aqueous cerium (IV) solution. Very homogeneous CeO2 nanoparticle decoration of the hexaniobate sheets can be achieved by this method and the resulting composites may absorb visible light. HRTEM images show that ∼3.0 nm diameter CeO2 nanoparticles adhere to hexaniobate nanosheets that are exfoliated and then restacked prior to Ce deposition. The interfacial interaction between CeO2 nanoparticles and nanosheets would be due to an electrostatic attraction mechanism. Raman and XRD measurements have given strong evidence that CeO2 nanoparticles have fluorite structure. EDS, FTIR and XPS results suggest almost complete exchange of TBA+ and K+ by Ce4+. Cerium ion exchange on the acid exchanged parent compound, H2.9K1.1Nb6O17, revealed that the extent of Ce ion exchange is much greater in case of nanosheets, which may be rationalized by the larger surface area available after exfoliation. XPS measurements show that the ratio of Ce4+/Ce3+ is around 4.4, in agreement with the formation of fluorite structure (CeO2). Thus, these CeO2 nanoparticle/nanosheet composites may be useful for catalytic processes.

Probing of the interfacial Heisenberg and Dzyaloshinskii-Moriya exchange interaction by magnon spectroscopy.

PubMed

Zakeri, Khalil

2017-01-11

This Topical Review presents an overview of the recent experimental results on the quantitative determination of the magnetic exchange parameters in ultrathin magnetic films and multilayers grown on different substrates. The experimental approaches for probing both the symmetric Heisenberg and the antisymmetric Dzyaloshinskii-Moriya exchange interaction in ultrathin magnetic films and at interfaces are discussed in detail. It is explained how the experimental spectrum of magnetic excitations can be used to quantify the strength of these interactions.

Teaching Interactions between Foreign Exchange Markets and Balance-of-Payments Flows: An Alternative Graphical Approach.

ERIC Educational Resources Information Center

Gaske, Dan

1992-01-01

Provides a graphical framework for presenting interactions among current account flows, capital account flows, and exchange rates. Suggests that the two type of flows must be considered separately in discussions of foreign exchange equilibrium and balance of payments flows. Supplies sample graphs and instructions for applying the framework to real…

Triangular Arbitrage as an Interaction in Foreign Exchange Markets

NASA Astrophysics Data System (ADS)

Aiba, Yukihiro; Hatano, Naomichi

Analyzing correlation in financial time series is a topic of considerable interest [1]-[17]. In the foreign exchange market, a correlation among the exchange rates can be generated by a triangular arbitrage transaction. The purpose of this article is to review our recent study [18]-[23] on modeling the interaction generated by the triangular arbitrage.

Interacting quantum dot coupled to a kondo spin: a universal Hamiltonian study.

PubMed

Rotter, Stefan; Türeci, Hakan E; Alhassid, Y; Stone, A Douglas

2008-04-25

We study a Kondo spin coupled to a mesoscopic interacting quantum dot that is described by the "universal Hamiltonian." The problem is solved numerically by diagonalizing the system Hamiltonian in a good-spin basis and analytically in the weak and strong Kondo coupling limits. The ferromagnetic exchange interaction within the dot leads to a stepwise increase of the ground-state spin (Stoner staircase), which is modified nontrivially by the Kondo interaction. We find that the spin-transition steps move to lower values of the exchange coupling for weak Kondo interaction, but shift back up for sufficiently strong Kondo coupling. The interplay between Kondo and ferromagnetic exchange correlations can be probed with experimentally tunable parameters.

Electric-field-induced modification of the magnon energy, exchange interaction, and curie temperature of transition-metal thin films.

PubMed

Oba, M; Nakamura, K; Akiyama, T; Ito, T; Weinert, M; Freeman, A J

2015-03-13

The electric-field-induced modification in the Curie temperature of prototypical transition-metal thin films with the perpendicular magnetic easy axis, a freestanding Fe(001) monolayer and a Co monolayer on Pt(111), is investigated by first-principles calculations of spin-spiral structures in an external electric field (E field). An applied E field is found to modify the magnon (spin-spiral formation) energy; the change arises from the E-field-induced screening charge density in the spin-spiral states due to p-d hybridizations. The Heisenberg exchange parameters obtained from the magnon energy suggest an E-field-induced modification of the Curie temperature, which is demonstrated via Monte Carlo simulations that take the magnetocrystalline anisotropy into account.

On the physical origins of interaction-induced vibrational (hyper)polarizabilities.

PubMed

Zaleśny, Robert; Garcia-Borràs, Marc; Góra, Robert W; Medved', Miroslav; Luis, Josep M

2016-08-10

This paper presents the results of a pioneering exploration of the physical origins of vibrational contributions to the interaction-induced electric properties of molecular complexes. In order to analyze the excess nuclear relaxation (hyper)polarizabilities, a new scheme was proposed which relies on the computationally efficient Bishop-Hasan-Kirtman method for determining the nuclear relaxation contributions to electric properties. The extension presented herein is general and can be used with any interaction-energy partitioning method. As an example, in this study we employed the variational-perturbational interaction-energy decomposition scheme (at the MP2/aug-cc-pVQZ level) and the extended transition state method by employing three exchange-correlation functionals (BLYP, LC-BLYP, and LC-BLYP-dDsC) to study the excess properties of the HCN dimer. It was observed that the first-order electrostatic contribution to the excess nuclear relaxation polarizability cancels with the negative exchange repulsion term out to a large extent, resulting in a positive value of Δα(nr) due to the contributions from the delocalization and the dispersion terms. In the case of the excess nuclear relaxation first hyperpolarizability, the pattern of interaction contributions is very similar to that for Δα(nr), both in terms of their sign as well as relative magnitude. Finally, our results show that the LC-BLYP and LC-BLYP-dDsC functionals, which yield smaller values of the orbital relaxation term than BLYP, are more successful in predicting excess properties.

Interaction of bacteria and ion-exchange particles and its potential in separation for matrix-assisted laser desorption/ionization mass spectrometric identification of bacteria in water.

PubMed

Guo, Zhongxian; Liu, Ying; Li, Shuping; Yang, Zhaoguang

2009-12-01

Identification of microbial contaminants in drinking water is a challenge to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) due to low levels of microorganisms in fresh water. To avoid the time-consuming culture step of obtaining enough microbial cells for subsequent MALDI-MS analysis, a combination of membrane filtration and nanoparticles- or microparticles-based magnetic separation is a fast and efficient approach. In this work, the interaction of bacteria and fluidMAG-PAA, a cation-exchange superparamagnetic nanomaterial, was investigated by MALDI-MS analysis and transmission electron microscopy. FluidMAG-PAA selectively captured cells of Salmonella, Bacillus, Enterococcus and Staphylococcus aureus. This capture was attributed to the aggregation of negatively charged nanoparticles on bacterial cell regional surfaces that bear positive charges. Three types of non-porous silica-encapsulated anion-exchange magnetic microparticles (SiMAG-Q, SiMAG-PEI, SiMAG-DEAE) were capable of concentrating a variety of bacteria, and were compared with silica-free, smaller fluidMAG particles. Salmonella, Escherichia coli, Enterococcus and other bacteria spiked in aqueous solutions, tap water and reservoir water were separated and concentrated by membrane filtration and magnetic separation based on these ion-exchange magnetic materials, and then characterized by whole cell MALDI-MS. By comparing with the mass spectra of the isolates and pure cells, bacteria in fresh water can be rapidly detected at 1 x 10(3) colony-forming units (cfu)/mL. Copyright 2009 John Wiley & Sons, Ltd.

Influence of the four-photon parametric processes and cross-phase modulation on the relative motion of optical filaments

NASA Astrophysics Data System (ADS)

Kovachev, L. M.; Georgieva, D. A.; Dakova, A. M.

2015-10-01

We investigate two types of nonlinear interaction between collinear femtosecond laser pulses with power slightly above the critical for self-focusing {{P}\\text{cr}} . In the first case we study energy exchange between filaments. The model describes this process through a degenerate four-photon parametric mixing (FPPM) scheme and requests initial phase difference between the waves. When there is no initial phase difference between the pulses, the FPPM process does not work. In this case the second type of interaction is obtained as merging between two, three or four filaments in a single filament with higher power. It is found that in the second case the interflow between the filaments has the potential for interaction due to cross-phase modulation (CPM).

Methods for characterizing convective cryoprobe heat transfer in ultrasound gel phantoms.

PubMed

Etheridge, Michael L; Choi, Jeunghwan; Ramadhyani, Satish; Bischof, John C

2013-02-01

While cryosurgery has proven capable in treating of a variety of conditions, it has met with some resistance among physicians, in part due to shortcomings in the ability to predict treatment outcomes. Here we attempt to address several key issues related to predictive modeling by demonstrating methods for accurately characterizing heat transfer from cryoprobes, report temperature dependent thermal properties for ultrasound gel (a convenient tissue phantom) down to cryogenic temperatures, and demonstrate the ability of convective exchange heat transfer boundary conditions to accurately describe freezing in the case of single and multiple interacting cryoprobe(s). Temperature dependent changes in the specific heat and thermal conductivity for ultrasound gel are reported down to -150 °C for the first time here and these data were used to accurately describe freezing in ultrasound gel in subsequent modeling. Freezing around a single and two interacting cryoprobe(s) was characterized in the ultrasound gel phantom by mapping the temperature in and around the "iceball" with carefully placed thermocouple arrays. These experimental data were fit with finite-element modeling in COMSOL Multiphysics, which was used to investigate the sensitivity and effectiveness of convective boundary conditions in describing heat transfer from the cryoprobes. Heat transfer at the probe tip was described in terms of a convective coefficient and the cryogen temperature. While model accuracy depended strongly on spatial (i.e., along the exchange surface) variation in the convective coefficient, it was much less sensitive to spatial and transient variations in the cryogen temperature parameter. The optimized fit, convective exchange conditions for the single-probe case also provided close agreement with the experimental data for the case of two interacting cryoprobes, suggesting that this basic characterization and modeling approach can be extended to accurately describe more complicated, multiprobe freezing geometries. Accurately characterizing cryoprobe behavior in phantoms requires detailed knowledge of the freezing medium's properties throughout the range of expected temperatures and an appropriate description of the heat transfer across the probe's exchange surfaces. Here we demonstrate that convective exchange boundary conditions provide an accurate and versatile description of heat transfer from cryoprobes, offering potential advantages over the traditional constant surface heat flux and constant surface temperature descriptions. In addition, although this study was conducted on Joule-Thomson type cryoprobes, the general methodologies should extend to any probe that is based on convective exchange with a cryogenic fluid.

Carbon Dioxide-Lubricant Two-Phase Flow Patterns in Small Horizontal Wetted Wall Channels: The Effects of Refrigerant/Lubricant Thermophysical Properties

ERIC Educational Resources Information Center

Seeton, Christopher John

2009-01-01

Microchannel heat exchangers are gaining popularity due to their ability to handle high pressures, reduce refrigerant charge, and reduce heat exchanger package size. These heat exchanger designs provide better heat exchange performance due to increased refrigerant side heat transfer coefficients and geometries that allow for a denser packing…

Fragility of ferromagnetic double exchange interactions and pressure tuning of magnetism in 3 d -5 d double perovskite Sr2FeOsO6

NASA Astrophysics Data System (ADS)

Veiga, L. S. I.; Fabbris, G.; van Veenendaal, M.; Souza-Neto, N. M.; Feng, H. L.; Yamaura, K.; Haskel, D.

2015-06-01

The ability to tune exchange (magnetic) interactions between 3 d transition metals in perovskite structures has proven to be a powerful route to discovery of novel properties. Here we demonstrate that the introduction of 3 d -5 d exchange pathways in double perovskites enables additional tunability, a result of the large spatial extent of 5 d wave functions. Using x-ray probes of magnetism and structure at high pressure, we show that compression of Sr2FeOsO6 drives an unexpected continuous change in the sign of Fe-Os exchange interactions and a transition from antiferromagnetic to ferrimagnetic order. We analyze the relevant electron-electron interactions, shedding light into fundamental differences with the more thoroughly studied 3 d -3 d systems.

Fragility of ferromagnetic double exchange interactions and pressure tuning of magnetism in 3d–5d double perovskite Sr₂FeOsO₆

DOE PAGES

Veiga, L. S. I.; Fabbris, G.; van Veenendaal, M.; ...

2015-06-19

The ability to tune exchange (magnetic) interactions between 3d transition metals in perovskite structures has proven to be a powerful route to discovery of novel properties. Here we demonstrate that the introduction of 3d-5d exchange pathways in double perovskites enables additional tunability, a result of the large spatial extent of 5d wave functions. Using x-ray probes of magnetism and structure at high pressure, we show that compression of Sr₂FeOsO₆ drives an unexpected continuous change in the sign of Fe-Os exchange interactions and a transition from antiferromagnetic to ferrimagnetic order. We analyze the relevant electron-electron interactions, shedding light into fundamental differencesmore » with the more thoroughly studied 3d-3d systems.« less

Multi-excitonic (N=1,2 and 3) quantum dots in magnetic field: Analytical mapping of correlations (exchange) by multipole expansion

NASA Astrophysics Data System (ADS)

Singh, Sunny; Kaur, Harsimran; Sharma, Shivalika; Aggarwal, Priyanka; Hazra, Ram Kuntal

2017-04-01

The understanding of the physics of exciton, bi-exciton, tri-exciton and the subsequent insight into controlling the properties of mesoscopic systems holds the key to various exotic optical, electrical and magnetic phenomena like superconductivity, Mott insulation, Quantum Hall effect etc. Many of exciton properties are similar to atomic hydrogen that attracts researchers to explore electronic structure of exciton in quantum dots, but nontriviality arises due to coulombic interactions among electrons and holes. We propose an exact integral of coulomb (exchange) correlation in terms of finitely summed Lauricella functions to examine 3-D exciton of harmonic dots confined in zero and non-zero arbitrary magnetic field. The highlight of our work is the use of exact variational solution for coloumbic interaction between the hole and the electron and evaluation of the cross terms arising out of the coupling among centre-of-mass and relative coordinates. We also have extended the size of the system to generalized N-body problem with N=3,4 for tri-exciton (e-e-h/e-h-h)

3D Localized Trions in Monolayer WSe2 in a Charge Tunable van der Waals Heterostructure.

PubMed

Chakraborty, Chitraleema; Qiu, Liangyu; Konthasinghe, Kumarasiri; Mukherjee, Arunabh; Dhara, Sajal; Vamivakas, Nick

2018-05-09

Monolayer transition metal dichalcogenides (TMDCs) have recently emerged as a host material for localized optically active quantum emitters that generate single photons. (1-5) Here, we investigate fully localized excitons and trions from such TMDC quantum emitters embedded in a van der Waals heterostructure. We use direct electrostatic doping through the vertical heterostructure device assembly to generate quantum confined trions. Distinct spectral jumps as a function of applied voltage bias, and excitation power-dependent charging, demonstrate the observation of the two different excitonic complexes. We also observe a reduction of the intervalley electron-hole exchange interaction in the confined trion due to the addition of an extra electron, which is manifested by a decrease in its fine structure splitting. We further confirm this decrease of exchange interaction for the case of the charged states by a comparative study of the circular polarization resolved photoluminescence from individual excitonic states. The valley polarization selection rules inherited by the localized trions will provide a pathway toward realizing a localized spin-valley-photon interface.

Explicit modeling of groundwater-surface water interactions using a simple bucket-type model

NASA Astrophysics Data System (ADS)

Staudinger, Maria; Carlier, Claire; Brunner, Philip; Seibert, Jan

2017-04-01

Longer dry spells can become critical for water supply and groundwater dependent ecosystems. During these dry spells groundwater is often the most relevant source for streams. Hence, the hydrological behavior of a catchment is often dominated by groundwater surface water interactions, which can vary considerably in space and time. While classical hydrological approaches hardly consider this spatial dependence, quantitative, hydrogeological modeling approaches can couple surface runoff processes and groundwater processes. Hydrogeological modeling can help to gain an improved understanding of catchment processes during low flow. However, due to their complex parametrization and large computational requirements, such hydrogeological models are difficult to employ at catchment scale, particularly for a larger set of catchments. Then bucket-type hydrological models remain a practical alternative. In this study we combine the strengths of both the hydrogeological and bucket-type hydrological models to better understand low flow processes and ultimately to use this knowledge for low flow projections. Bucket-type hydrological models have traditionally not been developed with focus on the simulation of low flow. One consequence is that interactions between surface and groundwater are not explicitly considered. Water fluxes in bucket-type hydrological models are commonly simulated only in one direction, namely from the groundwater to the stream but not from the stream to the groundwater. This latter flux, however, can become more important during low flow situations. We therefore further developed the bucket-type hydrological model HBV to simulate low flow situations by allowing for exchange in both directions i.e. also from the stream to the groundwater. The additional HBV exchange box is developed by using a variety of synthetic hydrogeological models as training set that were generated using a fully coupled, physically based hydrogeological model. In this way processes that occur in different spatial settings within the catchment are translated to functional relationships and effective parameter values for the conceptual exchange box can be extracted. Here, we show the development and evaluation of the HBV exchange box. We further show a first application in real catchments and evaluate the model performance by comparing the simulations to benchmark models that do not consider groundwater surface water interaction.

On-tissue Direct Monitoring of Global Hydrogen/Deuterium Exchange by MALDI Mass Spectrometry: Tissue Deuterium Exchange Mass Spectrometry (TDXMS)*

PubMed Central

Quanico, Jusal; Franck, Julien

2016-01-01

Hydrogen/deuterium exchange mass spectrometric (H/DXMS) methods for protein structural analysis are conventionally performed in solution. We present Tissue Deuterium Exchange Mass Spectrometry (TDXMS), a method to directly monitor deuterium uptake on tissue, as a means to better approximate the deuterium exchange behavior of proteins in their native microenvironment. Using this method, a difference in deuterium uptake behavior was observed when the same proteins were monitored in solution and on tissue. The higher maximum deuterium uptake at equilibrium for all proteins analyzed in solution suggests a more open conformation in the absence of interacting partners normally observed on tissue. We also demonstrate a difference in the deuterium uptake behavior of a few proteins across different morphological regions of the same tissue section. Modifications of the total number of hydrogens exchanged, as well as the kinetics of exchange, were both observed. These results provide information on the implication of protein interactions with partners as well as on the conformational changes related to these interactions, and illustrate the importance of examining protein deuterium exchange behavior in the presence of its specific microenvironment directly at the level of tissues. PMID:27512083

Phase coexistence and exchange-bias effect in LiM n2O4 nanorods

NASA Astrophysics Data System (ADS)

Zhang, X. K.; Yuan, J. J.; Xie, Y. M.; Yu, Y.; Kuang, F. G.; Yu, H. J.; Zhu, X. R.; Shen, H.

2018-03-01

In this paper, the magnetic properties of LiM n2O4 nanorods with an average diameter of ˜100 nm and length of ˜1 μ m are investigated. The temperature dependences of dc and ac susceptibility measurements show that LiM n2O4 nanorods experience multiple magnetic phase transitions upon cooling, i.e., paramagnetic (PM), antiferromagnetic (AFM), canted antiferromagnetic (CAFM), and cluster spin glass (SG). The coexistence between a long-range ordered AFM phase due to a M n4 +-M n4 + interaction and a cluster SG phase originating from frozen AFM clusters at low temperature in LiM n2O4 nanorods is elucidated. Field-cooled hysteresis loops (FC loops) and magnetic training effect (TE) measurements confirm the presence of an exchange-bias (EB) effect in LiM n2O4 nanorods below the Néel temperature (TN˜60 K ) . Furthermore, by analyzing the TE, we conclude that the observed EB effect originates completely from an exchange coupling interaction at the interface between the AFM and cluster SG states. A phenomenological model based on phase coexistence is proposed to interpret the origin of the EB effect below 60 K in the present compound. In turn, the appearance of the EB effect further supports the coexistence of AFM order along with a cluster SG state in LiM n2O4 nanorods.

Underground Pumped Storage Hydropower using abandoned open pit mines: influence of groundwater seepage on the system efficiency

NASA Astrophysics Data System (ADS)

Pujades, Estanislao; Bodeux, Sarah; Orban, Philippe; Dassargues, Alain

2016-04-01

Pumped Storage Hydropower (PSH) plants can be used to manage the production of electrical energy according to the demand. These plants allow storing and generating electricity during low and high demand energy periods, respectively. Nevertheless, PSH plants require a determined topography because two reservoirs located at different heights are needed. At sites where PSH plants cannot be constructed due to topography requirements (flat regions), Underground Pumped Storage Hydropower (UPSH) plants can be used to adjust the electricity production. These plants consist in two reservoirs, the upper one is located at the surface (or at shallow depth) while the lower one is underground (or deeper). Abandoned open pit mines can be used as lower reservoirs but these are rarely isolated. As a consequence, UPSH plants will interact with surrounding aquifers exchanging groundwater. Groundwater seepage will modify hydraulic head inside the underground reservoir affecting global efficiency of the UPSH plant. The influence on the plant efficiency caused by the interaction between UPSH plants and aquifers will depend on the aquifer parameters, underground reservoir properties and pumping and injection characteristics. The alteration of the efficiency produced by the groundwater exchanges, which has not been previously considered, is now studied numerically. A set of numerical simulations are performed to establish in terms of efficiency the effects of groundwater exchanges and the optimum conditions to locate an UPSH plant.

Effects of the U boson on the inner edge of neutron star crusts

NASA Astrophysics Data System (ADS)

Zheng, Hao; Chen, Lie-Wen

2012-02-01

We explore effects of the light vector U boson, which is weakly coupled to nucleons, on the transition density ρt and pressure Pt at the inner edge separating the liquid core from the solid crust of neutron stars. Three methods, i.e., the thermodynamical approach, the curvature matrix approach, and the Vlasov equation approach, are used to determine the transition density ρt with the Skyrme effective nucleon-nucleon interactions. We find that the ρt and Pt depend on not only the ratio of coupling strength to mass squared of the U boson g2/μ2 but also its mass μ due to the finite-range interaction from the U-boson exchange. In particular, our results indicate that the ρt and Pt are sensitive to both g2/μ2 and μ if the U-boson mass μ is larger than about 2 MeV. Furthermore, we show that both g2/μ2 and μ can have significant influence on the mass-radius relation and the crustal fraction of total moment of inertia of neutron stars. In addition, we study the exchange term contribution of the U boson based on the density matrix expansion method, and demonstrate that the exchange term effects on the nuclear matter equation of state as well as the ρt and Pt are generally negligible.

Band gap narrowing in BaTiO{sub 3} nanoparticles facilitated by multiple mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramakanth, S.; James Raju, K. C., E-mail: kcjrsp@uohyd.ernet.in; School of Physics, University of Hyderabad, Hyderabad 500046

2014-05-07

In the present work, BaTiO{sub 3} nanoparticles of four different size ranges were prepared by sol-gel method. The optical band gap of these particles at some size ranges has come down to 2.53 eV from 3.2 eV, resulting in substantial increase in optical absorption by these ferroelectric nanoparticles making them potential candidates for light energy harvesting. XRD results show the presence of higher compressive strain in 23 nm and 54 nm size particles, they exhibit a higher band gap narrowing, whereas tensile strain is observed in 31 nm and 34 nm particles, and they do not show the marginal band gap narrowing. The 23 nm and 54 nmmore » particles also show a coupling of free carriers to phonons by increasing the intensity of LO phonon mode at 715 cm{sup −1}. The higher surface charge density is expected in case of enhanced surface optical Raman modes (638 cm{sup −1}) contained in 31 and 34 nm size particles. In addition to this, the red shift in an LO mode Raman spectral line at 305 cm{sup −1} with decrease in particle size depicts the presence of phonon confinement in it. The enhanced optical absorption in 23 nm and 54 nm size particles with a narrowed band gap of 3 eV and 2.53 eV is due to exchange correlation interactions between the carriers present in these particles. In 31 nm and 34 nm range particles, the absorption got bleached exhibiting increased band gaps of 3.08 eV and 3.2 eV, respectively. It is due to filling up of conduction band resulting from weakening of exchange correlation interactions between the charge carriers. Hence, it is concluded that the band gap narrowing in the nanoparticles of average size 23 nm/54 nm is a consequence of multiple effects like strain, electron-phonon interaction, and exchange correlation interactions between the carriers which is subdued in some other size ranges like 31 nm/34 nm.« less

The effect of band Jahn-Teller distortion on the magnetoresistivity of manganites: a model study.

PubMed

Rout, G C; Panda, Saswati; Behera, S N

2011-10-05

We present a model study of magnetoresistance through the interplay of magnetisation, structural distortion and external magnetic field for the manganite systems. The manganite system is described by the Hamiltonian which consists of the s-d type double exchange interaction, Heisenberg spin-spin interaction among the core electrons, and the static and dynamic band Jahn-Teller (JT) interaction in the e(g) band. The relaxation time of the e(g) electron is found from the imaginary part of the Green's function using the total Hamiltonian consisting of the interactions due to the electron and phonon. The calculated resistivity exhibits a peak in the pure JT distorted insulating phase separating the low temperature metallic ferromagnetic phase and the high temperature paramagnetic phase. The resistivity is suppressed with the increase of the external magnetic field. The e(g) electron band splitting and its effect on magnetoresistivity is reported here. © 2011 IOP Publishing Ltd

Ultracoherent operation of spin qubits with superexchange coupling

NASA Astrophysics Data System (ADS)

Rančić, Marko J.; Burkard, Guido

2017-11-01

With the use of nuclear-spin-free materials such as silicon and germanium, spin-based quantum bits (qubits) have evolved to become among the most coherent systems for quantum information processing. The new frontier for spin qubits has therefore shifted to the ubiquitous charge noise and spin-orbit interaction, which are limiting the coherence times and gate fidelities of solid-state qubits. In this paper we investigate superexchange, as a means of indirect exchange interaction between two single electron spin qubits, each embedded in a single semiconductor quantum dot (QD), mediated by an intermediate, empty QD. Our results suggest the existence of "supersweet spots", in which the qubit operations implemented by superexchange interaction are simultaneously first-order-insensitive to charge noise and to errors due to spin-orbit interaction. The proposed spin-qubit architecture is scalable and within the manufacturing capabilities of semiconductor industry.

Assessing the performance of the random phase approximation for exchange and superexchange coupling constants in magnetic crystalline solids

NASA Astrophysics Data System (ADS)

Olsen, Thomas

2017-09-01

The random phase approximation (RPA) for total energies has previously been shown to provide a qualitatively correct description of static correlation in molecular systems, where density functional theory (DFT) with local functionals are bound to fail. This immediately poses the question of whether the RPA is also able to capture the correct physics of strongly correlated solids such as Mott insulators. Due to strong electron localization, magnetic interactions in such systems are dominated by superexchange, which in the simplest picture can be regarded as the analog of static correlation for molecules. In this paper, we investigate the performance of the RPA for evaluating both superexchange and direct exchange interactions in the magnetic solids NiO, MnO, Na3Cu2SbO6,Sr2CuO3,Sr2CuTeO6 , and a monolayer of CrI3, which were chosen to represent a broad variety of magnetic interactions. It is found that the RPA can accurately correct the large errors introduced by Hartree-Fock, independent of the input orbitals used for the perturbative expansion. However, in most cases, accuracies similar to RPA can be obtained with DFT+U, which is significantly simpler from a computational point of view.

Effects of stomata clustering on leaf gas exchange.

PubMed

Lehmann, Peter; Or, Dani

2015-09-01

A general theoretical framework for quantifying the stomatal clustering effects on leaf gaseous diffusive conductance was developed and tested. The theory accounts for stomatal spacing and interactions among 'gaseous concentration shells'. The theory was tested using the unique measurements of Dow et al. (2014) that have shown lower leaf diffusive conductance for a genotype of Arabidopsis thaliana with clustered stomata relative to uniformly distributed stomata of similar size and density. The model accounts for gaseous diffusion: through stomatal pores; via concentration shells forming at pore apertures that vary with stomata spacing and are thus altered by clustering; and across the adjacent air boundary layer. Analytical approximations were derived and validated using a numerical model for 3D diffusion equation. Stomata clustering increases the interactions among concentration shells resulting in larger diffusive resistance that may reduce fluxes by 5-15%. A similar reduction in conductance was found for clusters formed by networks of veins. The study resolves ambiguities found in the literature concerning stomata end-corrections and stomatal shape, and provides a new stomata density threshold for diffusive interactions of overlapping vapor shells. The predicted reduction in gaseous exchange due to clustering, suggests that guard cell function is impaired, limiting stomatal aperture opening. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes

USGS Publications Warehouse

McGuire, A.D.; Wirth, C.; Apps, M.; Beringer, J.; Clein, J.; Epstein, H.; Kicklighter, D.W.; Bhatti, J.; Chapin, F. S.; De Groot, B.; Efremov, D.; Eugster, W.; Fukuda, M.; Gower, T.; Hinzman, L.; Huntley, B.; Jia, G.J.; Kasischke, E.; Melillo, J.; Romanovsky, V.; Shvidenko, A.; Vaganov, E.; Walker, D.

2002-01-01

The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes.

Phase transitions and thermal entanglement of the distorted Ising-Heisenberg spin chain: topology of multiple-spin exchange interactions in spin ladders

NASA Astrophysics Data System (ADS)

Arian Zad, Hamid; Ananikian, Nerses

2017-11-01

We consider a symmetric spin-1/2 Ising-XXZ double sawtooth spin ladder obtained from distorting a spin chain, with the XXZ interaction between the interstitial Heisenberg dimers (which are connected to the spins based on the legs via an Ising-type interaction), the Ising coupling between nearest-neighbor spins of the legs and rungs spins, respectively, and additional cyclic four-spin exchange (ring exchange) in the square plaquette of each block. The presented analysis supplemented by results of the exact solution of the model with infinite periodic boundary implies a rich ground state phase diagram. As well as the quantum phase transitions, the characteristics of some of the thermodynamic parameters such as heat capacity, magnetization and magnetic susceptibility are investigated. We prove here that among the considered thermodynamic and thermal parameters, solely heat capacity is sensitive versus the changes of the cyclic four-spin exchange interaction. By using the heat capacity function, we obtain a singularity relation between the cyclic four-spin exchange interaction and the exchange coupling between pair spins on each rung of the spin ladder. All thermal and thermodynamic quantities under consideration should be investigated by regarding those points which satisfy the singularity relation. The thermal entanglement within the Heisenberg spin dimers is investigated by using the concurrence, which is calculated from a relevant reduced density operator in the thermodynamic limit.

Competition between Bose-Einstein Condensation and Spin Dynamics.

PubMed

Naylor, B; Brewczyk, M; Gajda, M; Gorceix, O; Maréchal, E; Vernac, L; Laburthe-Tolra, B

2016-10-28

We study the impact of spin-exchange collisions on the dynamics of Bose-Einstein condensation by rapidly cooling a chromium multicomponent Bose gas. Despite relatively strong spin-dependent interactions, the critical temperature for Bose-Einstein condensation is reached before the spin degrees of freedom fully thermalize. The increase in density due to Bose-Einstein condensation then triggers spin dynamics, hampering the formation of condensates in spin-excited states. Small metastable spinor condensates are, nevertheless, produced, and they manifest in strong spin fluctuations.

Orbital-free bond breaking via machine learning

NASA Astrophysics Data System (ADS)

Snyder, John C.; Rupp, Matthias; Hansen, Katja; Blooston, Leo; Müller, Klaus-Robert; Burke, Kieron

2013-12-01

Using a one-dimensional model, we explore the ability of machine learning to approximate the non-interacting kinetic energy density functional of diatomics. This nonlinear interpolation between Kohn-Sham reference calculations can (i) accurately dissociate a diatomic, (ii) be systematically improved with increased reference data and (iii) generate accurate self-consistent densities via a projection method that avoids directions with no data. With relatively few densities, the error due to the interpolation is smaller than typical errors in standard exchange-correlation functionals.

Optical Orientation of Mn2+ Ions in GaAs in Weak Longitudinal Magnetic Fields

NASA Astrophysics Data System (ADS)

Akimov, I. A.; Dzhioev, R. I.; Korenev, V. L.; Kusrayev, Yu. G.; Sapega, V. F.; Yakovlev, D. R.; Bayer, M.

2011-04-01

We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins.

Optical orientation of Mn2+ ions in GaAs in weak longitudinal magnetic fields.

PubMed

Akimov, I A; Dzhioev, R I; Korenev, V L; Kusrayev, Yu G; Sapega, V F; Yakovlev, D R; Bayer, M

2011-04-08

We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100  mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins.

Effect of Pd substitution for Ni on magnetism in UNiAl

NASA Astrophysics Data System (ADS)

Dremov, R. V.; Andreev, A. V.; Šebek, J.; Mushnikov, N. V.; Goto, T.; Havela, L.; Sechovský, V.; Shiokawa, Y.; Homma, Y.

1999-01-01

Itinerant 5f-electron antiferromagnet UNiAl ( TN=19.3 K) undergoes a metamagnetic transition in fields ( Bc≈11 T) applied along the c-axis of the hexagonal ZrNiAl-type structure. The same structure is preserved in the UNi 1- xPd xAl solid solutions x⩽0.4 characterized by isotropic lattice expansion with increasing x. The gradual increase of Bc and TN due to the Pd doping can be tentatively attributed to enhancement of antiferromagnetic exchange interactions.

The improvement of the effectiveness of using natural gas in hot-water boilers by means of condensing economizers

NASA Astrophysics Data System (ADS)

Vnukov, A. K.; Rozanova, F. A.

2013-07-01

The paper describes the results of the study of the mathematical model of a condensing economizer (CE) interacting with the technological parameter of the particular district heating station. This model has been developed by the authors. It is shown that the CE, due to condensation of water vapor and augmentation of convective heat exchange between products of natural gas combustion, makes it possible to save up to 8% of fuel.

The ground state magnetic moment and susceptibility of a two electron Gaussian quantum dot

NASA Astrophysics Data System (ADS)

Boda, Aalu; Chatterjee, Ashok

2018-04-01

The problem of two interacting electrons moving in a two-dimensional semiconductor quantum dot with Gaussian confinement under the influence of an external magnetic field is studied by using a method of numerical diagonalization of the Hamiltonian matrix with in the effective-mass approximation. The energy spectrum is calculated as a function of the magnetic field. We find the ground state magnetic moment and the magnetic susceptibility show zero temperature diamagnetic peaks due to exchange induced singlet-triplet oscillations. The position and the number of these peaks depend on the size of the quantum dot and also strength of the electro-electron interaction. The theory is applied to a GaAs quantum dot.

Modelling copper-phthalocyanine/cobalt-phthalocyanine chains: towards magnetic quantum metamaterials.

PubMed

Wu, Wei

2014-07-23

The magnetic properties of a theoretically designed molecular chain structure CuCoPc2, in which copper-phthalocyanine (CuPc) and cobalt-phthalocyanine (CoPc) alternate, have been investigated across a range of chain structures. The computed exchange interaction for the α-phase CuCoPc2 is ∼ 5 K (ferromagnetic), in strong contrast to the anti-ferromagnetic interaction recently observed in CuPc and CoPc. The computed exchange interactions are strongly dependent on the stacking angle but weakly on the sliding angle, and peak at 20 K (ferromagnetic). These ferromagnetic interactions are expected to arise from direct exchange with the strong suppression of super-exchange interaction. These first-principles calculations show that π-conjugated molecules, such as phthalocyanine, could be used as building blocks for the design of magnetic materials. This therefore extends the concept of quantum metamaterials further into magnetism. The resulting new magnetic materials could find applications in the studies such as organic spintronics.

Magnetism of metallacrown single-molecule magnets: From a simplest model to realistic systems

NASA Astrophysics Data System (ADS)

Pavlyukh, Y.; Rentschler, E.; Elmers, H. J.; Hübner, W.; Lefkidis, G.

2018-06-01

Electronic and magnetic properties of molecular nanomagnets are determined by competing energy scales due to the crystal field splitting, the exchange interactions between transition metal atoms, and relativistic effects. We present a comprehensive theory embracing all these phenomena based on first-principles calculations. In order to achieve this goal, we start from the FeNi4 cluster as a paradigm. The system can be accurately described on the ab initio level yielding all expected electronic states in a range of multiplicities from 1 to 9, with a ferromagnetic ground state. By adding the spin-orbit coupling between them we obtain the zero-field splitting. This allows to introduce a spin Hamiltonian of a giant spin model, which operates on a smaller energy scale. We compare the computed parameters of this Hamiltonian with the experimental and theoretical magnetic anisotropy energies of the monolayer Ni/Cu(001). In line with them, we find that the anisotropy almost entirely originates from the second-order spin-orbit coupling, the spin-spin coupling constitutes only a small fraction. Finally, we include the ligand atoms in our consideration. This component has a decisive role for the stabilization of molecules in experimental synthesis and characterization, and also substantially complicates the theory by bringing the superexchange mechanisms into play. Since they are higher-order effects involving two hopping matrix elements, not every theory can describe them. Our generalization of the corresponding perturbation theory substantiates the use of complete active space methods for the description of superexchange. At the same time, our numerical results for the {CuFe4} system demonstrate that the Goodenough-Kanamori rules, which are often used to determine the sign of these exchange interactions, cannot deliver quantitative predictions due to the interplay of other mechanisms, e. g., involving multicenter Coulomb integrals. We conclude by comparing ab initio values of the exchange interaction constants for the {CuCu4} and {CuFe4} metallacrown magnetic molecules with experimental values determined by fitting of the magnetic susceptibility curves χMT (T ) , and attribute the remaining discrepancy between them to the role of virtual electron excitations into and out of the active space (dynamical correlations).

Tuning antiferromagnetic exchange interaction for spontaneous exchange bias in MnNiSnSi system

NASA Astrophysics Data System (ADS)

Jia, Liyun; Shen, Jianlei; Li, Mengmeng; Wang, Xi; Ma, Li; Zhen, Congmian; Hou, Denglu; Liu, Enke; Wang, Wenhong; Wu, Guangheng

2017-12-01

Based on almost all the data from the literature on spontaneous exchange bias (SEB), it is expected that the system will show SEB if it meets two conditions simultaneously: (i) there are the coexistence and competition of antiferromagnetic (AFM) and ferromagnetic (FM) interactions and (ii) AFM interaction should dominate but not be too strong in this competition. In order to verify this view, a systematic study on SEB has been performed in this work. Mn50Ni40Sn10 with strong FM interaction and without SEB is chosen as the mother composition, and the negative chemical pressure is introduced by the substitution of Sn by Si to enhance AFM interaction. It is found that a long-range FM ordering window is closed, and a long-range AFM ordering window is opened. As a result, SEB is triggered and a continuous tuning of the spontaneous exchange bias field (HSEB) from 0 Oe to 1300 Oe has been realized in a Mn50Ni40Sn10-xSix system by the enhanced AFM interaction.

Dynamic spin injection into a quantum well coupled to a spin-split bound state

NASA Astrophysics Data System (ADS)

Maslova, N. S.; Rozhansky, I. V.; Mantsevich, V. N.; Arseyev, P. I.; Averkiev, N. S.; Lähderanta, E.

2018-05-01

We present a theoretical analysis of dynamic spin injection due to spin-dependent tunneling between a quantum well (QW) and a bound state split in spin projection due to an exchange interaction or external magnetic field. We focus on the impact of Coulomb correlations at the bound state on spin polarization and sheet density kinetics of the charge carriers in the QW. The theoretical approach is based on kinetic equations for the electron occupation numbers taking into account high order correlation functions for the bound state electrons. It is shown that the on-site Coulomb repulsion leads to an enhanced dynamic spin polarization of the electrons in the QW and a delay in the carriers tunneling into the bound state. The interplay of these two effects leads to nontrivial dependence of the spin polarization degree, which can be probed experimentally using time-resolved photoluminescence experiments. It is demonstrated that the influence of the Coulomb interactions can be controlled by adjusting the relaxation rates. These findings open a new way of studying the Hubbard-like electron interactions experimentally.

The hydrophilicity vs. ion interaction selectivity plot revisited: The effect of mobile phase pH and buffer concentration on hydrophilic interaction liquid chromatography selectivity behavior.

PubMed

Iverson, Chad D; Gu, Xinyun; Lucy, Charles A

2016-08-05

This work systematically investigates the selectivity changes on many HILIC phases from w(w)pH 3.7-6.8, at 5 and 25mM buffer concentrations. Hydrophilicity (kcytosine/kuracil) vs. ion interaction (kBTMA/kuracil) selectivity plots developed by Ibrahim et al. (J. Chromatogr. A 1260 (2012) 126-131) are used to investigate the effect of mobile phase changes on the selectivity of 18 HILIC columns from various classes. "Selectivity change plots" focus on the change in hydrophilicity and ion interaction that the columns exhibit upon changing mobile phase conditions. In general, the selectivity behavior of most HILIC columns is dominated by silanol activity. Minimal changes in selectivity are observed upon changing pH between w(w)pH 5 and 6.8. However, a reduction in ionic interaction is observed when the buffer concentration is increased at w(w)pH≥5.0 due to ionic shielding. Reduction of the w(w)pH to<5.0 results in decreasing cation exchange activity due to silanol protonation. Under all eluent conditions, the majority of phases show little change in their hydrophilicity. Copyright © 2016 Elsevier B.V. All rights reserved.

Design of tubesheet for U-tube heat exchangers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paliwal, D.N.; Saxena, R.M.

1993-02-01

Thorough analysis of two-side integral tubesheet of U-tube heat exchanger is carried out, using Panc's component theory of plates. Effects of solid annular rim and interaction between tubesheet and shell/channel are considered. A design procedure based on foregoing analysis is proposed. Fictive elastic constants due to Osweiller, as well as effective elastic constants due to Slot and O'Donnell, are employed. Deformations, internal forces and primary stress intensities are evaluated in both pitch and diagonal directions. Stress category concept of ASME Sect. VIII Div. 2 is used. Design thickness obtained by this method is compared with the thicknesses calculated, using ASMEmore » Sect. VIII Div. 1, TEMA and BS-5500. This method enables us to calculate stresses in shell and channel in the junction region as well. Present analysis and design procedure thoroughly investigates the tubesheet behavior and leads to a thinner tubesheet. It is concluded that though all the codes based on Gardner's work provide safe and efficient design rules, and lie on firm footing, still there is further scope for reducing the design thickness of tubesheet by about ten percent.« less

Three-dimensional Features of the Outer Heliosphere Due to Coupling between the Interstellar and Heliospheric Magnetic Field. V. The Bow Wave, Heliospheric Boundary Layer, Instabilities, and Magnetic Reconnection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pogorelov, N. V.; Heerikhuisen, J.; Roytershteyn, V.

The heliosphere is formed due to interaction between the solar wind (SW) and local interstellar medium (LISM). The shape and position of the heliospheric boundary, the heliopause, in space depend on the parameters of interacting plasma flows. The interplay between the asymmetrizing effect of the interstellar magnetic field and charge exchange between ions and neutral atoms plays an important role in the SW–LISM interaction. By performing three-dimensional, MHD plasma/kinetic neutral atom simulations, we determine the width of the outer heliosheath—the LISM plasma region affected by the presence of the heliosphere—and analyze quantitatively the distributions in front of the heliopause. Itmore » is shown that charge exchange modifies the LISM plasma to such extent that the contribution of a shock transition to the total variation of plasma parameters becomes small even if the LISM velocity exceeds the fast magnetosonic speed in the unperturbed medium. By performing adaptive mesh refinement simulations, we show that a distinct boundary layer of decreased plasma density and enhanced magnetic field should be observed on the interstellar side of the heliopause. We show that this behavior is in agreement with the plasma oscillations of increasing frequency observed by the plasma wave instrument onboard Voyager 1. We also demonstrate that Voyager observations in the inner heliosheath between the heliospheric termination shock and the heliopause are consistent with dissipation of the heliospheric magnetic field. The choice of LISM parameters in this analysis is based on the simulations that fit observations of energetic neutral atoms performed by Interstellar Boundary Explorer .« less

Exploring cavity-mediated long-range interactions in a dilute quantum gas

NASA Astrophysics Data System (ADS)

Landig, Renate; Mottl, Rafael; Brennecke, Ferdinand; Baumann, Kristian; Donner, Tobias; Esslinger, Tilman

2013-05-01

We report on the observation of a characteristic change in the excitation spectrum of a Bose-Einstein condensate and increased density fluctuations due to cavity-mediated atom-atom interactions. Increasing the strength of the interaction leads to a softening of an excitation mode at finite momentum, preceding a superfluid to supersolid phase transition. The observed behavior is reminiscent of a roton minimum, as predicted for quantum gases with long-range interactions. We create long-range interactions in the BEC using a non-resonant transverse pump beam which induces virtual photon exchange via the vacuum field of an optical cavity. The mode softening is spectroscopically studied across the phase transition using a variant of Bragg spectroscopy. At the phase transition a diverging density response is observed which is linked to increased density fluctuations. Using the cavity dissipation channel we monitor these fluctuations in real-time and identify the influence of measurement backaction onto the critical behavior of the system.

Interaction theory of mammalian mitochondria.

PubMed

Nakada, K; Inoue, K; Hayashi, J

2001-11-09

We generated mice with deletion mutant mtDNA by its introduction from somatic cells into mouse zygotes. Expressions of disease phenotypes are limited to tissues expressing mitochondrial dysfunction. Considering that all these mice share the same nuclear background, these observations suggest that accumulation of the mutant mtDNA and resultant expressions of mitochondrial dysfunction are responsible for expression of disease phenotypes. On the other hand, mitochondrial dysfunction and expression of clinical abnormalities were not observed until the mutant mtDNA accumulated predominantly. This protection is due to the presence of extensive and continuous interaction between exogenous mitochondria from cybrids and recipient mitochondria from embryos. Thus, we would like to propose a new hypothesis on mitochondrial biogenesis, interaction theory of mitochondria: mammalian mitochondria exchange genetic contents, and thus lost the individuality and function as a single dynamic cellular unit. Copyright 2001 Academic Press.

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

NASA Astrophysics Data System (ADS)

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

2018-04-01

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2 Pt2 Pb , a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S =1 /2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.

Electron-electron interaction in Multiple Quantum Wells

NASA Astrophysics Data System (ADS)

Zybert, M.; Marchewka, M.; Tomaka, G.; Sheregii, E. M.

2012-07-01

The complex investigation of the magneto-transport effects in structures containing multiple quantum well (MQWs) based on the GaAs/AlGaAs-heterostructures has been performed. The MQWs investigated have different electron densities in QWs. The parameters of 2DEG in MQWs were determined from the data of the Integer Quantum Hall Effect (IQHE) and Shubnikov-de Haas oscillations (SdH) observed at low temperatures (0.6-4.2 K). The method of calculation of the electron states energies in MQWs has been developed which is based on the splitting of these states due to the exchange interaction (SAS-splitting, see D. Płoch et al., Phys. Rev. B 79 (2009) 195434) including the screening of this interaction. The IQHE and SdH observed in these multilayer structures with the third degree of freedom for electrons are interpreted from this.

Type 2 Diabetes Education and Support in a Virtual Environment: A Secondary Analysis of Synchronously Exchanged Social Interaction and Support

PubMed Central

2018-01-01

Background Virtual environments (VEs) facilitate interaction and support among individuals with chronic illness, yet the characteristics of these VE interactions remain unknown. Objective The objective of this study was to describe social interaction and support among individuals with type 2 diabetes (T2D) who interacted in a VE. Methods Data included VE-mediated synchronous conversations and text-chat and asynchronous emails and discussion board posts from a study that facilitated interaction among individuals with T2D and diabetes educators (N=24) in 2 types of sessions: education and support. Results VE interactions consisted of communication techniques (how individuals interact in the VE), expressions of self-management (T2D-related topics), depth (personalization of topics), and breadth (number of topics discussed). Individuals exchanged support more often in the education (723/1170, 61.79%) than in the support (406/1170, 34.70%) sessions or outside session time (41/1170, 3.50%). Of all support exchanges, 535/1170 (45.73%) were informational, 377/1170 (32.22%) were emotional, 217/1170 (18.55%) were appraisal, and 41/1170 (3.50%) were instrumental. When comparing session types, education sessions predominately provided informational support (357/723, 49.4%), and the support sessions predominately provided emotional (159/406, 39.2%) and informational (159/406, 39.2%) support. Conclusions VE-mediated interactions resemble those in face-to-face environments, as individuals in VEs engage in bidirectional exchanges with others to obtain self-management education and support. Similar to face-to-face environments, individuals in the VE revealed personal information, sought information, and exchanged support during the moderated education sessions and unstructured support sessions. With this versatility, VEs are able to contribute substantially to support for those with diabetes and, very likely, other chronic diseases. PMID:29467118

Reverse Estuarine Circulation Due to Local and Remote Wind Forcing, Enhanced by the Presence of Along-Coast Estuaries

NASA Astrophysics Data System (ADS)

Giddings, S. N.; MacCready, P.

2017-12-01

Estuarine exchange flow governs the interaction between oceans and estuaries and thus plays a large role in their biogeochemical processes. This study investigates the variability in estuarine exchange flow due to offshore oceanic conditions including upwelling/downwelling, and the presence of a river plume offshore (from a neighboring estuary). We address these processes via numerical simulations at the mouth of the Salish Sea, a large estuarine system in the Northeast Pacific. An analysis of the Total Exchange Flow indicates that during the upwelling season, the exchange flow is fairly consistent in magnitude and oriented in a positive (into the estuary at depth and out at the surface) direction. However, during periods of downwelling favorable winds, the exchange flow shows significantly more variability including multiple reversals, consistent with observations, and surface intrusions of the Columbia River plume which originates 250 km to the south. Numerical along-strait momentum budgets show that the exchange flow is forced dominantly by the pressure gradients, particularly the baroclinic. The pressure gradient is modified by Coriolis and sometimes advection, highlighting the importance of geostrophy and local adjustments. In experiments conducted without the offshore river plume, reversals still occur but are weaker, and the baroclinic pressure gradient plays a reduced role. These results suggest that estuaries along strong upwelling coastlines should experience significant modulation in the exchange flow during upwelling versus downwelling conditions. Additionally, they highlight the importance of nearby estuaries impacting one-another, not only in terms of connectivity, but also altering the exchange flow.