On the Aharonov-Bohm effect with neutrons
Peshkin, M.
1994-11-01
The neutron interferometry phenomenon called scalar Aharonov-Bohm effect (SAB) follows from an ordinary local interaction, contrary to the usual Aharonov-Bohm effect with electrons (AB). I argue that SAB is not a topological effect by any useful definition. SAB in fact measures an apparently novel spin autocorrelation whose operator equations of motion contain the local torque in the magnetic field. The Aharonov-Casher effect shares these properties with SAB.
Thermoelectric effect in Aharonov-Bohm structures
NASA Astrophysics Data System (ADS)
Lu, Xin; Wang, Jian-Sheng; Morrel, William G.; Ni, Xiaoxi; Wu, Chang-Qin; Li, Baowen
2015-01-01
The thermoelectric effects of a single Aharonov-Bohm (SAB) ring and coupled double Aharonov-Bohm (DAB) rings have been investigated on a theoretical basis, taking into account the contributions of both electrons and phonons to the transport process by using the nonequilibrium Green's function technique. The thermoelectric figure of merit of the coupled DAB rings cannot be predicted directly by combining the values of two SAB ring systems due to the contribution of electron-phonon interaction to coupling between the two sites connecting the rings. We find that thermoelectric efficiency can be optimized by modulating the phases of the magnetic flux threading the two rings.
The electric Aharonov-Bohm effect
Weder, Ricardo
2011-05-15
The seminal paper of Aharonov and Bohm [Phys. Rev. 115, 485 (1959)] is at the origin of a very extensive literature in some of the more fundamental issues in physics. They claimed that electromagnetic fields can act at a distance on charged particles even if they are identically zero in the region of space where the particles propagate, that the fundamental electromagnetic quantities in quantum physics are not only the electromagnetic fields but also the circulations of the electromagnetic potentials; what gives them a real physical significance. They proposed two experiments to verify their theoretical conclusions. The magnetic Aharonov-Bohm effect, where an electron is influenced by a magnetic field that is zero in the region of space accessible to the electron, and the electric Aharonov-Bohm effect where an electron is affected by a time-dependent electric potential that is constant in the region where the electron is propagating, i.e., such that the electric field vanishes along its trajectory. The Aharonov-Bohm effects imply such a strong departure from the physical intuition coming from classical physics that it is no wonder that they remain a highly controversial issue after more than fifty years, in spite of the fact that they are discussed in most of the text books in quantum mechanics. The magnetic case has been studied extensively. The experimental issues were settled by the remarkable experiments of Tonomura et al. [Phys. Rev. Lett. 48, 1443 (1982); Phys. Rev. Lett. 56, 792 (1986)] with toroidal magnets, that gave a strong evidence of the existence of the effect, and by the recent experiment of Caprez et al. [Phys. Rev. Lett. 99, 210401 (2007)] that shows that the results of the Tonomura et al. experiments cannot be explained by the action of a force. The theoretical issues were settled by Ballesteros and Weder [Commun. Math. Phys. 285, 345 (2009); J. Math. Phys. 50, 122108 (2009); Commun. Math. Phys. 303, 175 (2011)] who rigorously proved that quantum
Macroscopic Test of the Aharonov-Bohm Effect
Caprez, Adam; Barwick, Brett; Batelaan, Herman
2007-11-23
The Aharonov-Bohm (AB) effect is a purely quantum mechanical effect. The original (classified as type-I) AB-phase shift exists in experimental conditions where the electromagnetic fields and forces are zero. It is the absence of forces that makes the AB effect entirely quantum mechanical. Although the AB-phase shift has been demonstrated unambiguously, the absence of forces in type-I AB effects has never been shown. Here, we report the observation of the absence of time delays associated with forces of the magnitude needed to explain the AB-phase shift for a macroscopic system.
Aharonov-Bohm effect without closing a loop
Retzker, A.; Nussinov, S.; Reznik, B.; Aharonov, Y.; Botero, A.
2006-03-15
We discuss the consequences of the Aharonov-Bohm (AB) effect in setups involving several charged particles, wherein none of the charged particles encloses a closed loop around the magnetic flux. We show that in such setups, the AB phase is encoded either in the relative phase of a bipartite or multipartite entangled photons states, or alternatively, gives rise to an overall AB phase that can be measured relative to another reference system. These setups involve processes of annihilation or creation of electron-hole pairs. We discuss the relevance of such effects in 'vacuum birefringence' in QED, and comment on their connection to other known effects.
Aharonov-Bohm Effect in a Rotating Acoustic Black Hole
NASA Astrophysics Data System (ADS)
Oliveira, E. S.; Crispino, L. C. B.; Dolan, S. R.
2015-01-01
A classical analogue to the Aharonov-Bohm (AB) effect occurs in a (idealized) draining bathtub (DBT) vortex system. The DBT vortex presents a sonic horizon, at which the flow rate exceeds the speed of sound. The sonic horizon is the analogue of a black hole event horizon. The DBT vortex also presents an ergoregion, similar to a rotating black hole. Because of the sonic event horizon, the AB effect is modified and has two tuning coefficients proportional to the flow draining and circulation couplings with the perturbation frequency.
Noncommutative analogue Aharonov-Bohm effect and superresonance
NASA Astrophysics Data System (ADS)
Anacleto, M. A.; Brito, F. A.; Passos, E.
2013-06-01
We consider the idea of modeling a rotating acoustic black hole by an idealized draining bathtub vortex which is a planar circulating flow phenomenon with a sink at the origin. We find the acoustic metric for this phenomenon from a noncommutative Abelian Higgs model. As such the acoustic metric not only describes a rotating acoustic black hole but also inherits the noncommutative characteristic of the spacetime. We address the issues of superresonance and analogue Aharonov-Bohm (AB) effect in this background. We mainly show that the scattering of planar waves by a draining bathtub vortex leads to a modified AB effect and due to spacetime noncommutativity, the phase shift persists even in the limit where the parameters associated with the circulation and draining vanish. Finally, we also find that the analogue AB effect and superresonance are competing phenomena at a noncommutative spacetime.
Global analogue of the Aharonov-Bohm effect
Navin, R.L.
1993-12-31
This thesis deals with a global analogue of the Aharonov-Bohm effect previously pointed out by other authors. The effect was not well understood because the pure Aharonov-Bohm cross section was thought to be merely an approximate low energy limit. This thesis provides a detailed analysis and reveals that in the particular model considered, there is an exact Aharonov-Bohm cross section over the energy range that a mass splitting occurs. At energies slightly above the mass splitting, the effect has completely disappeared and there is effectively no scattering at large distances. This is a curious observation as it was previously thought that a global theory would not act exactly like a local one over an extended range of energies. It begs the heretical speculation that experimentally observed forces modelled with Lagrangians possessing local symmetries may have an underlying global theory.
Non-traditional Aharonov-Bohm effects in condensed matter
Krive, I.V. ); Rozhavsky, A.S. )
1992-05-10
In 1959, Aharonov and Bohm proposed an elegant experiment demonstrating observability of electromagnetic potentials (or, which is the same, the non-locality of the wave function of charged particles) in quantum mechanics. This paper discusses the Aharonov-Bohm effect, based on the fundamental principles of quantum theory, as the superposition principles, the quantum character of motion of particles and locality of the interaction of a charge with an electromagnetic potential L{sub int} = j{sub {mu}}A{sup {mu}}. It is thus no wonder that the Aharonov-Bohm's paper aroused much dispute which is still ongoing. Originally, the Aharonov-Bohm effect (ABE) means the dependence of the interference pattern on the magnetic fluid flux {phi} in a Gendaken experiment on a coherent electron beam in the field of an infinitely thin solenoid. Later, however, it became common to refer to the Aharonov-Bohm phenomenon wherever the characteristics of systems under study appear to depend on the flux {phi} in the absence of electric and magnetic fields. In this sense, it was highly interesting to analyze the ABE in condensed media (the many-particle Aharonov-Bohm effect), in particular to study the dependence of the thermodynamic and kinetic characteristics, e.g., of metal on the flux. Such a problem was first discussed by Byers and Yang who formulated the general theorems related to the ABE in conducting condensed media. The next important step was the work of Kulik who formulated a concrete model and calculated the flux-dependent contribution to the metal free energy and provided a first clear formulation of the requirements to reveal.
Topological Aharonov-Bohm Effect and Pseudo-Particle Bundles
NASA Astrophysics Data System (ADS)
Payandeh, Farrin
2016-10-01
Exploiting a topological approach, we discuss the outstanding Aharonov-Bohm effect and try to explain it in the context of the principal P(M, U(1)) bundle. We show that this could be done by excluding a specific region from the main manifold which acts as the solenoid around which the effect is observed. Moreover, we discuss the impacts of pseudo-particles in this topological approach.
Scalar Aharonov-Bohm effect with longitudinally polarized neutrons
Allman, B. E.; Lee, W.-T.; Motrunich, O. I.; Werner, S. A.
1999-12-01
In the scalar Aharonov-Bohm effect, a charged particle (electron) interacts with the scalar electrostatic potential U in the field-free (i.e., force-free) region inside an electrostatic cylinder (Faraday cage). Using a perfect single-crystal neutron interferometer we have performed a ''dual'' scalar Aharonov-Bohm experiment by subjecting polarized thermal neutrons to a pulsed magnetic field. The pulsed magnetic field was spatially uniform, precluding any force on the neutrons. Aligning the direction of the pulsed magnetic field to the neutron magnetic moment also rules out any classical torque acting to change the neutron polarization. The observed phase shift is purely quantum mechanical in origin. A detailed description of the experiment, performed at the University of Missouri Research Reactor, and its interpretation is given in this paper. (c) 1999 The American Physical Society.
Aharonov-Bohm and Aharonov-Casher tunneling effects and edge states in double-barrier structures
Bogachek, E.N.; Landman, U. )
1994-07-15
The simultaneous occurrence of Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects due to edge states in double-barrier two-dimensional wires formed by an electrostatic confinement potential, in the quantum Hall effect regime, is discussed. The AC effect is manifested via a shift of the AB conductance oscillations, and a method for measurement of the effect is proposed.
Analogue Aharonov-Bohm effect in neo-Newtonian theory
NASA Astrophysics Data System (ADS)
Anacleto, M. A.; Salako, I. G.; Brito, F. A.; Passos, E.
2015-12-01
We address the issues of the scattering of massless planar scalar waves by an acoustic black hole in neo-Newtonian hydrodynamics. We then compute the differential cross section through the use of the partial wave approach in the neo-Newtonian theory which is a modification of the usual Newtonian theory that correctly incorporates the effects of pressure. We mainly show that the scattering of planar waves leads to a modified analogue Aharonov-Bohm effect due to a nontrivial response of the parameters defining the equation of state.
Non-Abelian Aharonov-Bohm effect with the time-dependent gauge fields
NASA Astrophysics Data System (ADS)
Hosseini Mansoori, Seyed Ali; Mirza, Behrouz
2016-04-01
We investigate the non-Abelian Aharonov-Bohm (AB) effect for time-dependent gauge fields. We prove that the non-Abelian AB phase shift related to time-dependent gauge fields, in which the electric and magnetic fields are written in the adjoint representation of SU (N) generators, vanishes up to the first order expansion of the phase factor. Therefore, the flux quantization in a superconductor ring does not appear in the time-dependent Abelian or non-Abelian AB effect.
What did we learn from the Aharonov-Bohm effect? Is spin 1/2 different?
Peshkin, M.
1994-06-01
I review what has been learned about fundamental issues in quantum mechanics from the Aharonov-Bohm effect. Following that, I consider the Aharonov-Casher effect and the Scalar Aharonov-Bohm effect, in both of which a spin-1/2 particle interacts with a local electromagnetic field through its magnetic moment, and conclude that those effects can be described as observable effects of local torques.
Experimental test for approximately dispersionless forces in the Aharonov-Bohm effect
NASA Astrophysics Data System (ADS)
Becker, Maria; Batelaan, Herman
2016-07-01
A new class of forces, approximately dispersionless forces, were recently predicted as part of a semiclassical description of the Aharonov-Bohm effect. Electron time-of-flight measurements have been performed that test for such forces. Magnetized iron cores used in the previous time-of-flight experiment may affect potential back-action forces and have, therefore, been eliminated. We report that no forces were detected. This finding supports the local and nonlocal, quantum descriptions of the AB effect and rules out local, semiclassical descriptions.
Relativistic Aharonov-Bohm effect in the presence of planar Coulomb potentials
Khalilov, V.R.
2005-01-01
Exact analytic solutions are found to the Dirac equation in 2+1 dimensions for a combination of an Aharonov-Bohm potential and the Lorentz three-vector and scalar Coulomb potentials. By means of the solutions obtained the relativistic quantum Aharonov-Bohm effect is studied for the free (in the presence of a Lorentz three-vector Coulomb potential) and bound fermion states. We obtain the total scattering amplitude in a combination of the Aharonov-Bohm and Lorentz three-vector Coulomb potentials as a sum of two scattering amplitudes. This modifies the expression for the standard Aharonov-Bohm cross section due to the interference of these two amplitudes with each other. We discuss that the observable quantities can be the phases of electron wave functions or the energies of bound states.
Absence of the Electric Aharonov-Bohm Effect due to Induced Charges
Wang, Rui-Feng
2015-01-01
This paper states that the induced charge should not be neglected in the electric Aharonov-Bohm (A-B) effect. If the induced charge is taken into account, the interference pattern of the moving charge will not change with the potential difference between the two metal tubes. It means that the scalar potential itself can not affect the phase of the moving charge, and the true factor affecting the phase of the moving charge is the energy of the system including the moving charge and the induced charge. PMID:26392302
Time-dependent Aharonov-Bohm effect on the noncommutative space
NASA Astrophysics Data System (ADS)
Ma, Kai; Wang, Jian-Hua; Yang, Huan-Xiong
2016-08-01
We study the time-dependent Aharonov-Bohm effect on the noncommutative space. Because there is no net Aharonov-Bohm phase shift in the time-dependent case on the commutative space, therefore, a tiny deviation from zero indicates new physics. Based on the Seiberg-Witten map we obtain the gauge invariant and Lorentz covariant Aharonov-Bohm phase shift in general case on noncommutative space. We find there are two kinds of contribution: momentum-dependent and momentum-independent corrections. For the momentum-dependent correction, there is a cancellation between the magnetic and electric phase shifts, just like the case on the commutative space. However, there is a non-trivial contribution in the momentum-independent correction. This is true for both the time-independent and time-dependent Aharonov-Bohm effects on the noncommutative space. However, for the time-dependent Aharonov-Bohm effect, there is no overwhelming background which exists in the time-independent Aharonov-Bohm effect on both commutative and noncommutative space. Therefore, the time-dependent Aharonov-Bohm can be sensitive to the spatial noncommutativity. The net correction is proportional to the product of the magnetic fluxes through the fundamental area represented by the noncommutative parameter θ, and through the surface enclosed by the trajectory of charged particle. More interestingly, there is an anti-collinear relation between the logarithms of the magnetic field B and the averaged flux Φ / N (N is the number of fringes shifted). This nontrivial relation can also provide a way to test the spatial noncommutativity. For BΦ / N ∼ 1, our estimation on the experimental sensitivity shows that it can reach the 10 GeV scale. This sensitivity can be enhanced by using stronger magnetic field strength, larger magnetic flux, as well as higher experimental precision on the phase shift.
Against a proposed alternative explanation of the Aharonov-Bohm effect.
Peshkin, M.; Physics
2010-09-03
The Aharonov-Bohm (AB) effect is understood to demonstrate that the Maxwell fields can act nonlocally in some situations. However it has been suggested from time to time that the AB effect is somehow a consequence of a local classical electromagnetic field phenomenon involving energy that is temporarily stored in the overlap between the external field and the field of which the beam particle is the source. That idea was shown in the past not to work for some models of the source of the external field. Here a more general proof is presented for the magnetic AB effect to show that the overlap energy is always compensated by another contribution to the energy of the magnetic field in such a way that the sum of the two is independent of the external flux. Therefore no such mechanism can underlie the AB effect.
Photon mass and quantum effects of the Aharonov-Bohm type
Spavieri, G.; Rodriguez, M.
2007-05-15
The magnetic field due to the photon rest mass m{sub ph} modifies the standard results of the Aharonov-Bohm effect for electrons, and of other recent quantum effects. For the effect involving a coherent superposition of beams of particles with opposite electromagnetic properties, by means of a tabletop experiment, the limit m{sub ph}{approx_equal}10{sup -51} g is achievable, improving by 6 orders of magnitude that derived by Boulware and Deser for the Aharonov-Bohm effect.
Flux effect in superconducting hybrid Aharonov-Bohm rings
Stoof, T.H.; Nazarov, Y.V.
1996-07-01
We have extended the circuit theory of Andreev conductance [Phys. Rev. Lett. {bold 73}, 1420 (1994)] to diffusive superconducting hybrid structures that contain an Aharonov-Bohm ring. The electrostatic potential distribution in the system is predicted to be flux dependent with a period of the superconducting flux quantum {Phi}{sub 0}={ital h}/2{ital e}. When at least one tunnel barrier is present, the conductance of the system oscillates with the same period. {copyright} {ital 1996 The American Physical Society.}
Cloaking of matter waves under the global Aharonov-Bohm effect
Lin, D.-H.; Luan, P.-G.
2009-05-15
We discuss the Aharonov-Bohm effect of a magnetic flux for its influence on a two-dimensional quantum cloak. It is shown that the matter wave of a charged particle under the global influence of the Aharonov-Bohm effect can still be perfectly cloaked and guided by the quantum cloak. Since the presence of the global influence of a magnetic flux on charged particles is universal, the perfect cloaking and guiding nature not only provides an ideal setup to cloak an object from matter waves but also provides an ideal setup to test the global physics of charged matter waves in the presence of a bare magnetic flux.
Globalism of commutation relation and mechanism of momentum transfer in the Aharonov-Bohm effect
NASA Astrophysics Data System (ADS)
Li, Chun-Fang
1997-09-01
After examining the domain of an operator that has classical analog, which is shown to be the whole spatial space, the concept of globalism of a commutation relation is introduced through analyzing the quantization of the kinetic angular momentum in the Aharonov-Bohm effect. Its applications are also given to explain in an elegant and precise way, the mechanism of momentum transfer in the Aharonov-Bohm scattering and to study the probability distribution of the momentum for a particle in a one-dimensional infinitely deep square potential well.
Nucleon statistics in holographic QCD: Aharonov-Bohm effect in a matrix model
Hashimoto, Koji; Iizuka, Norihiro
2010-11-15
We show that the Aharonov-Bohm effect in the nuclear matrix model [K. Hashimoto, N. Iizuka, and P. Yi, J. High Energy Phys. 10 (2010), 3.] derives the statistical nature of nucleons in holographic QCD. For N{sub c}=odd (even), the nucleon is shown to be a fermion (boson).
Nucleon statistics in holographic QCD: Aharonov-Bohm effect in a matrix model
NASA Astrophysics Data System (ADS)
Hashimoto, Koji; Iizuka, Norihiro
2010-11-01
We show that the Aharonov-Bohm effect in the nuclear matrix model [K. Hashimoto, N. Iizuka, and P. Yi, J. High Energy Phys.JHEPFG1029-8479 10 (2010), 3.10.1007/JHEP10(2010)003] derives the statistical nature of nucleons in holographic QCD. For Nc=odd (even), the nucleon is shown to be a fermion (boson).
Line of magnetic monopoles and an extension of the Aharonov-Bohm effect
NASA Astrophysics Data System (ADS)
Chee, J.; Lu, W.
2016-10-01
In the Landau problem on the two-dimensional plane, physical displacement of a charged particle (i.e., magnetic translation) can be induced by an in-plane electric field. The geometric phase accompanying such magnetic translation around a closed path differs from the topological phase of Aharonov and Bohm in two essential aspects: The particle is in direct contact with the magnetic field and the geometric phase has an opposite sign from the Aharonov-Bohm phase. We show that magnetic translation on the two-dimensional cylinder implemented by the Schrödinger time evolution truly leads to the Aharonov-Bohm effect. The magnetic field normal to the cylinder's surface corresponds to a line of magnetic monopoles of uniform density whose simulation is currently under investigation in cold atom physics. In order to characterize the quantum problem, one needs to specify the value of the magnetic flux (modulo the flux unit) that threads but not in touch with the cylinder. A general closed path on the cylinder may enclose both the Aharonov-Bohm flux and the local magnetic field that is in direct contact with the charged particle. This suggests an extension of the Aharonov-Bohm experiment that naturally takes into account both the geometric phase due to local interaction with the magnetic field and the topological phase of Aharonov and Bohm.
Stokes' theorem, gauge symmetry and the time-dependent Aharonov-Bohm effect
Macdougall, James Singleton, Douglas
2014-04-15
Stokes' theorem is investigated in the context of the time-dependent Aharonov-Bohm effect—the two-slit quantum interference experiment with a time varying solenoid between the slits. The time varying solenoid produces an electric field which leads to an additional phase shift which is found to exactly cancel the time-dependent part of the usual magnetic Aharonov-Bohm phase shift. This electric field arises from a combination of a non-single valued scalar potential and/or a 3-vector potential. The gauge transformation which leads to the scalar and 3-vector potentials for the electric field is non-single valued. This feature is connected with the non-simply connected topology of the Aharonov-Bohm set-up. The non-single valued nature of the gauge transformation function has interesting consequences for the 4-dimensional Stokes' theorem for the time-dependent Aharonov-Bohm effect. An experimental test of these conclusions is proposed.
The Aharonov-Bohm effect and Tonomura et al. experiments: Rigorous results
Ballesteros, Miguel; Weder, Ricardo
2009-12-15
The Aharonov-Bohm effect is a fundamental issue in physics. It describes the physically important electromagnetic quantities in quantum mechanics. Its experimental verification constitutes a test of the theory of quantum mechanics itself. The remarkable experiments of Tonomura et al. ['Observation of Aharonov-Bohm effect by electron holography', Phys. Rev. Lett 48, 1443 (1982) and 'Evidence for Aharonov-Bohm effect with magnetic field completely shielded from electron wave', Phys. Rev. Lett 56, 792 (1986)] are widely considered as the only experimental evidence of the physical existence of the Aharonov-Bohm effect. Here we give the first rigorous proof that the classical ansatz of Aharonov and Bohm of 1959 ['Significance of electromagnetic potentials in the quantum theory', Phys. Rev. 115, 485 (1959)], that was tested by Tonomura et al., is a good approximation to the exact solution to the Schroedinger equation. This also proves that the electron, that is, represented by the exact solution, is not accelerated, in agreement with the recent experiment of Caprez et al. in 2007 ['Macroscopic test of the Aharonov-Bohm effect', Phys. Rev. Lett. 99, 210401 (2007)], that shows that the results of the Tonomura et al. experiments can not be explained by the action of a force. Under the assumption that the incoming free electron is a Gaussian wave packet, we estimate the exact solution to the Schroedinger equation for all times. We provide a rigorous, quantitative error bound for the difference in norm between the exact solution and the Aharonov-Bohm Ansatz. Our bound is uniform in time. We also prove that on the Gaussian asymptotic state the scattering operator is given by a constant phase shift, up to a quantitative error bound that we provide. Our results show that for intermediate size electron wave packets, smaller than the ones used in the Tonomura et al. experiments, quantum mechanics predicts the results observed by Tonomura et al. with an error bound smaller than 10
Scattering theory and the Aharonov-Bohm effect in quasiclassical physics
Sitenko, Yurii A.; Vlasii, Nadiia D.
2011-06-15
Research Highlights: > Scattering Aharonov-Bohm effect. > Short-wavelength limit of scattered nonrelativistic particles. > Fraunhofer diffraction in the forward direction. > Fresnel diffraction in the forward region in conical space. > Enclosed magnetic flux is a gate for the propagation of quasiclassical particles. - Abstract: Scattering of a nonrelativistic quantum-mechanical particle by an impenetrable magnetic vortex is considered. The nonvanishing transverse size of the vortex is taken into account, and the limit of short, as compared to this size, wavelengths of the scattered particle is analyzed. We show that the scattering Aharonov-Bohm effect persists in the quasiclassical limit owing to the diffraction persisting in the short-wavelength limit. As a result, the vortex flux serves as a gate for the propagation of short-wavelength, almost classical, particles. This quasiclassical effect is more feasible to experimental detection in the case when space outside the vortex is conical.
Aharonov-Bohm effect in quantum-to-classical correspondence of the Heisenberg principle
Lin, D.-H.; Chang, J.-G.; Hwang, C.-C.
2003-04-01
The exact energy spectrum and wave function of a charged particle moving in the Coulomb field and Aharonov-Bohm's magnetic flux are solved by the nonintegrable phase factor. The universal formula for the matrix elements of the radial operator r{sup {alpha}} of arbitrary power {alpha} is given by an analytical solution. The difference between the classical limit of matrix elements of inverse radius in quantum mechanics and the Fourier components of the corresponding quantity for the pure Coulomb system in classical mechanics is examined in reference to the correspondence principle of Heisenberg. Explicit calculation shows that the influence of nonlocal Aharonov-Bohm effect exists even in the classical limit. The semiclassical quantization rule for systems containing the topological effect is presented in the light of Heisenberg's corresponding principle.
Aharonov-Bohm effect and resonances in the circular quantum billiard with two leads
Ree, S.; Reichl, L.E.
1999-03-01
We calculate the conductance through a circular quantum billiard with two leads and a point magnetic flux at the center. The boundary element method is used to solve the Schr{umlt o}dinger equation of the scattering problem, and the Landauer formula is used to calculate the conductance from the transmission coefficients. We use two different shapes of leads, straight and conic, and find that the conductance is affected by lead geometry, the relative positions of the leads and the magnetic flux. The Aharonov-Bohm effect can be seen from shifts and splittings of fluctuations. When the flux is equal to h/2e and the angle between leads is 180{degree}, the conductance tends to be suppressed to zero in the low-energy range due to the Aharonov-Bohm effect. {copyright} {ital 1999} {ital The American Physical Society}
The Aharonov-Bohm effect in Möbius rings
NASA Astrophysics Data System (ADS)
Li, Zehao; Ram-Mohan, L.; CenterComputational NanoScience Team
2013-03-01
Electron transmission through finite-width 2D ring structures is calculated for cylindrical, flat (Aharonov-Bohm), and Möbius rings. In the presence of an external magnetic field, curves of constructive transmission display a pattern similar to that for a 1D ring. The periodicity in the magnetic flux, in units of h / e , is weakly broken on 2D rings of finite width, so that a description with a 1D-path is very acceptable. The unusual states with half-integer values of
Reply to "Comment on `Role of potentials in the Aharonov-Bohm effect' "
NASA Astrophysics Data System (ADS)
Vaidman, Lev
2015-08-01
The preceding Comment challenged my claim that potentials might be just auxiliary mathematical tools and that they are not necessary for explaining physical phenomena. The Comment did not confront my explanation without the potentials of the Aharonov-Bohm effects that appeared in the original article, but stated that I cannot apply this explanation for seven other examples. In my reply, using my method, I provide explanations of one of the examples, show that two other examples are not relevant, and agree that the remaining examples require further analysis. However, I argue that none of the examples provides robust counterexamples to my claim, similar to the original Aharonov-Bohm setups which were explained in my article, so the Comment does not refute my claim.
Spin accumulation assisted by the Aharonov-Bohm-Fano effect of quantum dot structures
2012-01-01
We investigate the spin accumulations of Aharonov-Bohm interferometers with embedded quantum dots by considering spin bias in the leads. It is found that regardless of the interferometer configurations, the spin accumulations are closely determined by their quantum interference features. This is mainly manifested in the dependence of spin accumulations on the threaded magnetic flux and the nonresonant transmission process. Namely, the Aharonov-Bohm-Fano effect is a necessary condition to achieve the spin accumulation in the quantum dot of the resonant channel. Further analysis showed that in the double-dot interferometer, the spin accumulation can be detailedly manipulated. The spin accumulation properties of such structures offer a new scheme of spin manipulation. When the intradot Coulomb interactions are taken into account, we find that the electron interactions are advantageous to the spin accumulation in the resonant channel. PMID:22985404
Time-dependent Pauli equation in the presence of the Aharonov-Bohm effect
Bouguerra, Y.; Bounames, A.; Maamache, M.; Saadi, Y.
2008-04-15
We use the Lewis-Riesenfeld theory to determine the exact form of the wavefunctions of a two-dimensional Pauli equation of a charged spin 1/2 particle with time-dependent mass and frequency in the presence of the Aharonov-Bohm effect and a two-dimensional time-dependent harmonic oscillator. We find that the irregular solution at the origin as well as the regular one contributes to the phase of the wavefunction.
Atomic multiple-wave interferometer phase-shifted by the scalar Aharonov-Bohm effect
Aoki, Takatoshi; Yasuhara, Makoto; Morinaga, Atsuo
2003-05-01
A time-domain atomic multiple-wave interferometer using laser-cooled and trapped sodium atoms has been developed under pulsed magnetic fields. Each atomic phase was shifted due to the scalar Aharonov-Bohm effect by applying spatially homogeneous pulsed magnetic fields between numerous Raman excitation laser pulses. Interference fringes with a finesse of 11 were demonstrated for 11 successive Raman pulses and ten magnetic-field pulses.
Effects of nongauge potentials on the spin-1/2 Aharonov-Bohm problem
Hagen, C.R. )
1993-12-15
Some recent work has attempted to show that the singular solutions which are known to occur in the Dirac description of spin-1/2 Aharonov-Bohm scattering can be eliminated by the inclusion of strongly repulsive potentials inside the flux tube. It is shown here that these calculations are generally unreliable since they necessarily require potentials which lead to the occurrence of Klein's paradox. To avoid that difficulty the problem is solved within the framework of the Galilean spin-1/2 wave equation which is free of that particular complication. It is then found that the singular solutions can be eliminated provided that the nongauge potential is made energy dependent. The effect of the inclusion of a Coulomb potential is also considered with the result being that the range of flux parameter for which singular solutions are allowed is only one-half as great as in the pure Aharonov-Bohm limit. Expressions are also obtained for the binding energies which can occur in the combined Aharonov-Bohm-Coulomb system.
A solenoidal synthetic field and the non-Abelian Aharonov-Bohm effects in neutral atoms
NASA Astrophysics Data System (ADS)
Huo, Ming-Xia; Nie, Wei; Hutchinson, David A. W.; Kwek, Leong Chuan
2014-08-01
Cold neutral atoms provide a versatile and controllable platform for emulating various quantum systems. Despite efforts to develop artificial gauge fields in these systems, realizing a unique ideal-solenoid-shaped magnetic field within the quantum domain in any real-world physical system remains elusive. Here we propose a scheme to generate a ``hairline'' solenoid with an extremely small size around 1 micrometer which is smaller than the typical coherence length in cold atoms. Correspondingly, interference effects will play a role in transport. Despite the small size, the magnetic flux imposed on the atoms is very large thanks to the very strong field generated inside the solenoid. By arranging different sets of Laguerre-Gauss (LG) lasers, the generation of Abelian and non-Abelian SU(2) lattice gauge fields is proposed for neutral atoms in ring- and square-shaped optical lattices. As an application, interference patterns of the magnetic type-I Aharonov-Bohm (AB) effect are obtained by evolving atoms along a circle over several tens of lattice cells. During the evolution, the quantum coherence is maintained and the atoms are exposed to a large magnetic flux. The scheme requires only standard optical access, and is robust to weak particle interactions.
A solenoidal synthetic field and the non-Abelian Aharonov-Bohm effects in neutral atoms.
Huo, Ming-Xia; Nie, Wei; Hutchinson, David A W; Kwek, Leong Chuan
2014-08-08
Cold neutral atoms provide a versatile and controllable platform for emulating various quantum systems. Despite efforts to develop artificial gauge fields in these systems, realizing a unique ideal-solenoid-shaped magnetic field within the quantum domain in any real-world physical system remains elusive. Here we propose a scheme to generate a "hairline" solenoid with an extremely small size around 1 micrometer which is smaller than the typical coherence length in cold atoms. Correspondingly, interference effects will play a role in transport. Despite the small size, the magnetic flux imposed on the atoms is very large thanks to the very strong field generated inside the solenoid. By arranging different sets of Laguerre-Gauss (LG) lasers, the generation of Abelian and non-Abelian SU(2) lattice gauge fields is proposed for neutral atoms in ring- and square-shaped optical lattices. As an application, interference patterns of the magnetic type-I Aharonov-Bohm (AB) effect are obtained by evolving atoms along a circle over several tens of lattice cells. During the evolution, the quantum coherence is maintained and the atoms are exposed to a large magnetic flux. The scheme requires only standard optical access, and is robust to weak particle interactions.
A solenoidal synthetic field and the non-Abelian Aharonov-Bohm effects in neutral atoms
Huo, Ming-Xia; Nie, Wei; Hutchinson, David A. W.; Kwek, Leong Chuan
2014-01-01
Cold neutral atoms provide a versatile and controllable platform for emulating various quantum systems. Despite efforts to develop artificial gauge fields in these systems, realizing a unique ideal-solenoid-shaped magnetic field within the quantum domain in any real-world physical system remains elusive. Here we propose a scheme to generate a “hairline” solenoid with an extremely small size around 1 micrometer which is smaller than the typical coherence length in cold atoms. Correspondingly, interference effects will play a role in transport. Despite the small size, the magnetic flux imposed on the atoms is very large thanks to the very strong field generated inside the solenoid. By arranging different sets of Laguerre-Gauss (LG) lasers, the generation of Abelian and non-Abelian SU(2) lattice gauge fields is proposed for neutral atoms in ring- and square-shaped optical lattices. As an application, interference patterns of the magnetic type-I Aharonov-Bohm (AB) effect are obtained by evolving atoms along a circle over several tens of lattice cells. During the evolution, the quantum coherence is maintained and the atoms are exposed to a large magnetic flux. The scheme requires only standard optical access, and is robust to weak particle interactions. PMID:25103877
Eckle, H.-P.; Johannesson, H.; Stafford, C. A.
2001-07-02
We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a sidebranch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo resonance interferes with the spin-dependent Aharonov-Casher effect to induce a current which, in the strong-coupling limit, is independent of the number of electrons in the ring.
Tunable Pseudogap Kondo Effect and Quantum Phase Transitions in Aharonov-Bohm Interferometers
Dias Da Silva, Luis G; Sandler, Nancy; Simon, Pascal; Ingersent, Kevin; Ulloa, Sergio E
2009-01-01
We study two quantum dots embedded in the arms of an Aharonov-Bohm ring threaded by a magnetic flux. This system can be described by an effective one-impurity Anderson model with an energy- and flux- dependent density of states. For specific values of the flux, this density of states vanishes at the Fermi energy, yielding a controlled realization of the pseudogap Kondo effect. The conductance and trans- mission phase shifts reflect a nontrivial interplay between wave interference and interactions, providing clear signatures of quantum phase transitions between Kondo and non-Kondo ground states.
Anyonic strings and membranes in anti-de Sitter space and dual Aharonov-Bohm effects.
Hartnoll, Sean A
2007-03-16
It is observed that strings in AdS(5) x S(5) and membranes in AdS(7) x S(4) exhibit long range phase interactions. Two well separated membranes dragged around one another in anti-de Sitter space (AdS) acquire phases of 2 pi/N. The same phases are acquired by a well separated F and D string dragged around one another. The phases are shown to correspond to both the standard and a novel type of Aharonov-Bohm effect in the dual field theory.
Anyonic Strings and Membranes in Anti-de Sitter Space and Dual Aharonov-Bohm Effects
Hartnoll, Sean A.
2007-03-16
It is observed that strings in AdS{sub 5}xS{sup 5} and membranes in AdS{sub 7}xS{sup 4} exhibit long range phase interactions. Two well separated membranes dragged around one another in anti-de Sitter space (AdS) acquire phases of 2{pi}/N. The same phases are acquired by a well separated F and D string dragged around one another. The phases are shown to correspond to both the standard and a novel type of Aharonov-Bohm effect in the dual field theory.
Excitonic Aharonov-Bohm effect in a two-dimensional quantum ring
Gonzalez-Santander, C.; Dominguez-Adame, F.; Roemer, R. A.
2011-12-15
We study theoretically the optical properties of an exciton in a two-dimensional ring threaded by a magnetic flux. We model the quantum ring by a confining potential that can be continuously tuned from strictly one-dimensional to truly two-dimensional with finite radius-to-width ratio. We present an analytic solution of the problem when the electron-hole interaction is short ranged. The oscillatory dependence of the oscillator strength as a function of the magnetic flux is attributed to the Aharonov-Bohm effect. The amplitude of the oscillations changes upon increasing the width of the quantum ring. We find that the Aharonov-Bohm oscillations of the ground state of the exciton decrease with increasing the width, but, remarkably, the amplitude remains finite down to radius-to-width ratios less than unity. We attribute this resilience of the excitonic oscillations to the nonsimple connectedness of our chosen confinement potential with its centrifugal core at the origin.
Eskin, G.
2008-02-15
We consider the inverse boundary value problem for the Schroedinger operator with time-dependent electromagnetic potentials in domains with obstacles. We extend the resuls of the author's works [Inverse Probl. 19, 49 (2003); 19, 985 (2003); 20, 1497 (2004)] to the case of time-dependent potentials. We relate our results to the Aharonov-Bohm effect caused by magnetic and electric fluxes.
NASA Technical Reports Server (NTRS)
Trammel, G. T.
1964-01-01
Aharonov-bohm paradox involving charge particle interaction with stationary current distribution showing that vector potential term in canonical momenta expression represents electromagnetic field momentum
Jones-Smith, Katherine; Mathur, Harsh; Vachaspati, Tanmay
2010-02-15
A solenoid oscillating in vacuum will pair produce charged particles due to the Aharonov-Bohm (AB) interaction. We calculate the radiation pattern and power emitted for charged scalar particles. We extend the solenoid analysis to cosmic strings and find enhanced radiation from cusps and kinks on loops. We argue by analogy with the electromagnetic AB interaction that cosmic strings should emit photons due to the gravitational AB interaction of fields in the conical spacetime of a cosmic string. We calculate the emission from a kink and find that it is of similar order as emission from a cusp, but kinks are vastly more numerous than cusps and may provide a more interesting observational signature.
Induced current and Aharonov-Bohm effect in graphene
NASA Astrophysics Data System (ADS)
Jackiw, R.; Milstein, A. I.; Pi, S.-Y.; Terekhov, I. S.
2009-07-01
The effect of vacuum polarization in the field of an infinitesimally thin solenoid at distances much larger than the radius of solenoid is investigated. The induced charge density and induced current are calculated. Though the induced charge density turned out to be zero, the induced current is a finite periodical function of the magnetic flux Φ . The expression for this function is found exactly in a value of the flux. The induced current is equal to zero at the integer values of Φ/Φ0 as well as at half-integer values of this ratio, where Φ0=2πℏc/e is the elementary magnetic flux. The latter is a consequence of the Furry theorem and periodicity of the induced current with respect to magnetic flux. As an example we consider the graphene in the field of solenoid perpendicular to the plane of a sample.
Magneto-optical properties in inhomogeneous quantum dot: The Aharonov-Bohm oscillations effect
NASA Astrophysics Data System (ADS)
Nasri, Djillali; Bettahar, N.
2016-11-01
In this study, we investigated theoretically the effect of a magnetic field B on the linear, nonlinear, and total absorption coefficients (ACs) and the refractive index changes (RICs) associated with intersubband transitions in the HgS quantum shell. In the calculations, a diagonalization method was employed within the effective-mass approximation. We find that a three kinds of optical transitions (S-P, P-D and D-F) between the ground state and the first excited state appear, resulting from the oscillation of the ground state with B (Aharonov-Bohm effect). In the other hand, the magnetic field enhances and diminishes their related RICs and ACs intensities respectively for the three kinds of optical transitions, and shifts their peaks towards low energy (blue shift).
On solutions of Coulomb system and its generalization to the Aharonov-Bohm effect
Lin, D.-H.
2009-02-15
The paper numerically analyzes the Aharonov-Bohm effect of an infinitely thin magnetic flux for its influence on a two- or three-dimensional (3d) solutions of Coulomb system in momentum and coordinate spaces. For any definitive eigenstate, it is shown that the flux shifts the position of the most probable radius (MPR) of a probability distribution inward or outward in momentum or coordinate spaces, respectively. Moreover, the probability density of the shifted MPR is amplified in the momentum space, while reduced in the coordinate space. Since the Coulomb force among charged particles dominate the structure of matter, shifting of the MPR controlling by the flux effect may be beneficial to the construction of nanostructure by manipulating the atomic and molecular bonds.
Electromagnetism, Local Covariance, the Aharonov-Bohm Effect and Gauss' Law
NASA Astrophysics Data System (ADS)
Sanders, Ko; Dappiaggi, Claudio; Hack, Thomas-Paul
2014-06-01
We quantise the massless vector potential A of electromagnetism in the presence of a classical electromagnetic (background) current, j, in a generally covariant way on arbitrary globally hyperbolic spacetimes M. By carefully following general principles and procedures we clarify a number of topological issues. First we combine the interpretation of A as a connection on a principal U(1)-bundle with the perspective of general covariance to deduce a physical gauge equivalence relation, which is intimately related to the Aharonov-Bohm effect. By Peierls' method we subsequently find a Poisson bracket on the space of local, affine observables of the theory. This Poisson bracket is in general degenerate, leading to a quantum theory with non-local behaviour. We show that this non-local behaviour can be fully explained in terms of Gauss' law. Thus our analysis establishes a relationship, via the Poisson bracket, between the Aharonov-Bohm effect and Gauss' law - a relationship which seems to have gone unnoticed so far. Furthermore, we find a formula for the space of electric monopole charges in terms of the topology of the underlying spacetime. Because it costs little extra effort, we emphasise the cohomological perspective and derive our results for general p-form fields A ( p < dim( M)), modulo exact fields, for the Lagrangian density . In conclusion we note that the theory is not locally covariant, in the sense of Brunetti-Fredenhagen-Verch. It is not possible to obtain such a theory by dividing out the centre of the algebras, nor is it physically desirable to do so. Instead we argue that electromagnetism forces us to weaken the axioms of the framework of local covariance, because the failure of locality is physically well-understood and should be accommodated.
Valley Zeeman energy in monolayer MoS2 quantum rings: Aharonov-Bohm effect
NASA Astrophysics Data System (ADS)
Oliveira, D.; Fu, Jiyong; Villegas-Lelovsky, L.; Dias, A. C.; Qu, Fanyao
2016-05-01
We investigate the valley Zeeman energy (VZE) in monolayer MoS2 quantum rings, subjected to a magnetic flux Φ only passing through a hole region enclosed by the inner circle of the ring. To gain insight on our numerical outcomes for finite two-dimensional rings, an analytic solution in the one-dimensional limit (zero ring width) is also presented. Although no magnetic field is applied inside the ring region, we observe finite VZEs. Interestingly, in contrast to the usual linear scenario, the VZE of the rings exhibits an oscillatory dependence on Φ with possible vanishing valley Zeeman effect even in a nonzero magnetic flux due to Aharonov-Bohm type effect. On the other hand, within one period of oscillations the VZE increases linearly with Φ . Furthermore, for a given magnetic flux, the valley Zeeman effect is more pronounced in a ring with a stronger quantum confinement. Thus the VZE can be tuned by either magnetic flux or ring confinement or both of them. This opens a new route for controlling the valley Zeeman effect using a nonmagnetic means.
Correa, Francisco Jakubsky, Vit Plyushchay, Mikhail S.
2009-05-15
We explain the origin and the nature of a special nonlinear supersymmetry of a reflectionless Poeschl-Teller system by the Aharonov-Bohm effect for a non-relativistic particle on the AdS{sub 2}. A key role in the supersymmetric structure appearing after reduction by a compact generator of the AdS{sub 2} isometry is shown to be played by the discrete symmetries related to the space and time reflections in the ambient Minkowski space. We also observe that a correspondence between the two quantum non-relativistic systems is somewhat of the AdS/CFT holography nature.
Magnetically tunable Kondo-Aharonov-Bohm effect in a triangular quantum dot.
Kuzmenko, T; Kikoin, K; Avishai, Y
2006-02-01
The role of discrete orbital symmetry in mesoscopic physics is manifested in a system consisting of three identical quantum dots forming an equilateral triangle. Under a perpendicular magnetic field, this system demonstrates a unique combination of Kondo and Aharonov-Bohm features due to an interplay between continuous [spin-rotation SU(2)] and discrete (permutation C3v) symmetries, as well as U(1) gauge invariance. The conductance as a function of magnetic flux displays sharp enhancement or complete suppression depending on contact setups.
Electron Interferometry in the Quantum Hall Regime: Aharonov-Bohm Effect of Interacting Electrons
Lin, P.V.; Camino, F.; Goldman, V.J.
2009-09-01
An apparent h/fe Aharonov-Bohm flux period, where f is an integer, has been reported in coherent quantum Hall devices. Such subperiod is not expected for noninteracting electrons and thus is thought to result from interelectron Coulomb interaction. Here we report experiments in a Fabry-Perot interferometer comprised of two wide constrictions enclosing an electron island. By carefully tuning the constriction front gates, we find a regime where interference oscillations with period h/2e persist throughout the transition between the integer quantum Hall plateaus 2 and 3, including half-filling. In a large quantum Hall sample, a transition between integer plateaus occurs near half-filling, where the bulk of the sample becomes delocalized and thus dissipative bulk current flows between the counterpropagating edges ('backscattering'). In a quantum Hall constriction, where conductance is due to electron tunneling, a transition between forward and backscattering is expected near the half-filling. In our experiment, neither period nor amplitude of the oscillations show a discontinuity at half-filling, indicating that only one interference path exists throughout the transition. We also present experiments and an analysis of the front-gate dependence of the phase of the oscillations. The results point to a single physical mechanism of the observed conductance oscillations: Aharonov-Bohm interference of interacting electrons in quantum Hall regime.
Schütz, G; Rembold, A; Pooch, A; Prochel, H; Stibor, A
2015-11-01
We propose an experiment for the first proof of the type I electric Aharonov-Bohm effect in an ion interferometer for hydrogen. The performances of three different beam separation schemes are simulated and compared. The coherent ion beam is generated by a single atom tip (SAT) source and separated by either two biprisms with a quadrupole lens, two biprisms with an einzel-lens or three biprisms. The beam path separation is necessary to introduce two metal tubes that can be pulsed with different electric potentials. The high time resolution of a delay line detector allows to work with a continuous ion beam and circumvents the pulsed beam operation as originally suggested by Aharonov and Bohm. We demonstrate that the higher mass and therefore lower velocity of ions compared to electrons combined with the high expected SAT ion emission puts the direct proof of this quantum effect for the first time into reach of current technical possibilities. Thereby a high detection rate of coherent ions is crucial to avoid long integration times that allow the influence of dephasing noise from the environment. We can determine the period of the expected matter wave interference pattern and the signal on the detector by determining the superposition angle of the coherent partial beams. Our simulations were tested with an electron interferometer setup and agree with the experimental results. We determine the separation scheme with three biprisms to be most efficient and predict a total signal acquisition time of only 80s to measure a phase shift from 0 to 2π due to the electric Aharonov-Bohm effect. PMID:26188995
Numazaki, Kazuya; Imai, Hiromitsu; Morinaga, Atsuo
2010-03-15
The second-order Zeeman effect of the sodium clock transition in a weak magnetic field of less than 50 {mu}T was measured as the scalar Aharonov-Bohm phase by two-photon stimulated Raman atom interferometry. The ac Stark effect of the Raman pulse was canceled out by adopting an appropriate intensity ratio of two photons in the Raman pulse. The Ramsey fringes for the pulse separation of 7 ms were obtained with a phase uncertainty of {pi}/200 rad. The nondispersive feature of the scalar Aharonov-Bohm phase was clearly demonstrated through 18 fringes with constant amplitude. The Breit-Rabi formula of the sodium clock transition was verified to be {Delta}{nu}=(0.222{+-}0.003)x10{sup 12}xB{sup 1.998{+-}0.004} in a magnetic field of less than 50 {mu}T.
A charged particle in a homogeneous magnetic field accelerated by a time-periodic Aharonov-Bohm flux
Kalvoda, T.; Stovicek, P.
2011-10-15
We consider a nonrelativistic quantum charged particle moving on a plane under the influence of a uniform magnetic field and driven by a periodically time-dependent Aharonov-Bohm flux. We observe an acceleration effect in the case when the Aharonov-Bohm flux depends on time as a sinusoidal function whose frequency is in resonance with the cyclotron frequency. In particular, the energy of the particle increases linearly for large times. An explicit formula for the acceleration rate is derived with the aid of the quantum averaging method, and then it is checked against a numerical solution and a very good agreement is found. - Highlights: > A nonrelativistic quantum charged particle on a plane. > A homogeneous magnetic field and a periodically time-dependent Aharonov-Bohm flux. > The quantum averaging method applied to a time-dependent system. > A resonance of the AB flux with the cyclotron frequency. > An acceleration with linearly increasing energy; a formula for the acceleration rate.
NASA Astrophysics Data System (ADS)
Kondo, Kenji
2016-01-01
Many researchers have reported on spin filters using linear Rashba spin-orbit interactions (SOI). However, spin filters using square and cubic Rashba SOIs have not yet been reported. We consider that this is because the Aharonov-Casher (AC) phases acquired under square and cubic Rashba SOIs are ambiguous. In this study, we try to derive the AC phases acquired under square and cubic Rashba SOIs from the viewpoint of non-Abelian SU(2) gauge theory. These AC phases can be derived successfully from the non-Abelian SU(2) gauge theory without the completing square methods. Using the results, we investigate the spin filtering in a double quantum dot (QD) Aharonov-Bohm (AB) ring under linear, square, and cubic Rashba SOIs. This AB ring consists of elongated QDs and quasi-one-dimensional quantum nanowires under an external magnetic field. The spin transport is investigated from the left nanowire to the right nanowire in the above structure within the tight-binding approximation. In particular, we focus on the difference of spin filtering among linear, square, and cubic Rashba SOIs. The calculation is performed for the spin polarization by changing the penetrating magnetic flux for the AB ring subject to linear, square, and cubic Rashba SOIs. It is found that perfect spin filtering is achieved for all of the Rashba SOIs. This result indicates that this AB ring under general Rashba SOIs can be a promising device for spin current generation. Moreover, the AB rings under general Rashba SOIs behave in totally different ways in response to penetrating magnetic flux, which is attributed to linear, square, and cubic behaviors in the in-plane momentum. This result enables us to make a clear distinction between linear, square, and cubic Rashba SOIs according to the peak position of the perfect spin filtering.
Magnetic edge states in Aharonov-Bohm graphene quantum rings
Farghadan, R. Heidari Semiromi, E.; Saffarzadeh, A.
2013-12-07
The effect of electron-electron interaction on the electronic structure of Aharonov-Bohm (AB) graphene quantum rings (GQRs) is explored theoretically using the single-band tight-binding Hamiltonian and the mean-field Hubbard model. The electronic states and magnetic properties of hexagonal, triangular, and circular GQRs with different sizes and zigzag edge terminations are studied. The results show that, although the AB oscillations in the all types of nanoring are affected by the interaction, the spin splitting in the AB oscillations strongly depends on the geometry and the size of graphene nanorings. We found that the total spin of hexagonal and circular rings is zero and therefore, no spin splitting can be observed in the AB oscillations. However, the non-zero magnetization of the triangular rings breaks the degeneracy between spin-up and spin-down electrons, which produces spin-polarized AB oscillations.
Lin, D.-H.
2004-05-01
Partial wave theory of a three dimensional scattering problem for an arbitrary short range potential and a nonlocal Aharonov-Bohm magnetic flux is established. The scattering process of a 'hard sphere'-like potential and the magnetic flux is examined. An anomalous total cross section is revealed at the specific quantized magnetic flux at low energy which helps explain the composite fermion and boson model in the fractional quantum Hall effect. Since the nonlocal quantum interference of magnetic flux on the charged particles is universal, the nonlocal effect is expected to appear in a quite general potential system and will be useful in understanding some other phenomena in mesoscopic physics.
Tokuno, Akiyuki; Oshikawa, Masaki; Demler, Eugene
2008-04-11
We study one-dimensional Bose liquids of interacting ultracold atoms in the Y-shaped potential when each branch is filled with atoms. We find that the excitation packet incident on a single Y junction should experience a negative density reflection analogous to the Andreev reflection at normal-superconductor interfaces, although the present system does not contain fermions. In a ring-interferometer-type configuration, we find that the transport is completely insensitive to the (effective) flux contained in the ring, in contrast with the Aharonov-Bohm effect of a single particle in the same geometry.
Miyamoto, Satoru; Ishikawa, Toyofumi; Eto, Mikio; Itoh, Kohei M.; Moutanabbir, Oussama; Haller, Eugene E.; Sawano, Kentarou; Shiraki, Yasuhiro
2010-08-15
We report on a magnetophotoluminescence study of isotopically pure {sup 70}Ge/Si self-assembled type-II quantum dots. Oscillatory behaviors attributed to the Aharonov-Bohm effect are simultaneously observed for the emission energy and intensity of excitons subject to an increasing magnetic field. When the magnetic flux penetrates through the ringlike trajectory of an electron moving around each quantum dot, the ground state of an exciton experiences a change in its angular momentum. Our results provide the experimental evidence for the phase coherence of localized electron wave functions in group-IV Ge/Si self-assembled quantum structures.
The Aharonov-Bohm Effect and Transport Properties in Graphene Nanostructures
NASA Astrophysics Data System (ADS)
Lungu, Mihai; Giugiulan, Raluca; Lungu, Antoanetta; Bunoiu, Madalin; Neculae, Adrian
2013-12-01
This paper investigates the possibility to improve the filtering process of flue gas by separation of suspended nanoparticle using dielectrophoresis. The study focuses on the particles having an average radius of about 50-150 nm, that cannot be filtrated by classical techniques but have a harmful effect for environment and human health. The size distribution nanoparticles collected from the flue gas filters of a hazardous waste incinerator plant were evaluated. Based on obtained experimental data and a proposed mathematical model, the concentration distribution of nanoparticle suspended in flue gas inside a microfluidic separation device was analyzed by numerical simulations, using the finite element method. The performances of the device were described in terms of three new specific quantities related to the separation process, namely Recovery, Purity and Separation Efficiency. The simulations could provide the optimal values of control parameters for separation process, and aim to be a useful tool in designing microfluidic devices for separating nanoparticle from combustion gases.
Group-theoretical derivation of Aharonov-Bohm phase shifts
Hagen, C. R.
2013-02-15
The phase shifts of the Aharonov-Bohm effect are generally determined by means of the partial wave decomposition of the underlying Schroedinger equation. It is shown here that they readily emerge from an o(2,1) calculation of the energy levels employing an added harmonic oscillator potential which discretizes the spectrum.
Aharonov-Bohm interactions of a vector unparticle
Kobakhidze, Archil
2007-11-01
Recently Georgi argued that a hypothetical conformally invariant hidden sector weakly interacting with ordinary particles will have unusual manifestations at low energies in terms of effective degrees of freedom called unparticles. In this paper we consider Aharonov-Bohm type of interactions due to the vector unparticle coupled to elementary fermions. We have found that the quantum mechanical phase shift is path dependent.
Polarization and Aharonov-Bohm oscillations in quantum-ring magnetoexcitons
Dias da Silva, Luis G.G.V.; Ulloa, Sergio E.; Shahbazyan, Tigran V.
2005-09-15
We study interaction and radial polarization effects on the absorption spectrum of neutral bound magnetoexcitons confined in quantum-ring structures. We show that the size and orientation of the exciton's dipole moment, as well as the interaction screening, play important roles in the Aharonov-Bohm (AB) oscillations. In particular, the excitonic absorption peaks display AB oscillations both in position and amplitude for weak electron-hole interaction and large radial polarization. The presence of impurity scattering induces anticrossings in the exciton spectrum, leading to a modulation in the absorption strength. These properties could be used in experimental investigations of the effect in semiconductor quantum-ring structures.
NASA Astrophysics Data System (ADS)
Ji, Haojie
In this thesis I develop understanding of the fundamental physical and material properties of type-II ZnTe/ZnSe submonolayer quantum dots (QDs), grown via combination of molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). I use magneto-photoluminescence, including excitonic Aharonov-Bohm (AB) effect and polarized optical spectroscopy as the primary tools in this work. I present previous studies as well as the background of optical and magneto-optical processes in semiconductor nanostructures and introduce the experimental methods in Chapters 1 - 3. In Chapter 4 I focus on the excitonic AB effect in the type-II QDs. I develop a lateral tightly-bound exciton model for ZnTe/ZnSe type-II QDs, using analytical methods and numerical calculations. This explained the magneto-PL observation and allowed for establishing the size and density of the QDs in each sample based on the results of PL and magneto-PL measurements. For samples with larger QDs, I observe behaviors that fall between properties of quantum-dot and quantum-well-like systems due to increased QD densities and their type-II nature. Finally, the decoherence mechanisms of the AB excitons are investigated via the temperature dependent studies of the magneto-PL. It is determined that the AB exciton decoherence is due to transport-like (acoustic phonon) scattering of the electrons moving in the ZnSe barriers, but with substantially smaller magnitude of electron-phonon coupling constant due to relatively strong electron-hole coupling within these type-II QDs. In Chapter 5 I discuss the results of circularly polarized magneto-PL measurements. A model with ultra-long spin-flip time of holes confined to submonolayer QDs is proposed. The g-factor of type-II excitons was extracted from the Zeeman splitting and the g-factor of electrons was obtained by fitting the temperature dependence of the degree of circular polarization (DCP), from which g-factor of holes confined within ZnTe QDs was found. It is shown
Inelastic transport through Aharonov-Bohm interferometer in Kondo regime
Yoshii, Ryosuke; Eto, Mikio; Sakano, Rui; Affleck, Ian
2013-12-04
We formulate elastic and inelastic parts of linear conductance through an Aharonov-Bohm (AB) ring with an embedded quantum dot in the Kondo regime. The inelastic part G{sub inel} is proportional to T{sup 2} when the temperature T is much smaller than the Kondo temperature T{sub K}, whereas it is negligibly small compared with elastic part G{sub el} when T ≫ T{sub K}. G{sub inel} weakly depends on the magnetic flux penetrating the AB ring, which disturbs the precise detection of G{sub el}/(G{sub el}+G{sub inel}) by the visibility of AB oscillation.
Nguyen, V Hung; Niquet, Y-M; Dollfus, P
2014-05-21
We report on a numerical study of the Aharonov-Bohm (AB) effect and parity selective tunneling in pn junctions based on rectangular graphene rings where the contacts and ring arms are all made of zigzag nanoribbons. We find that when applying a magnetic field to the ring, the AB interference can reverse the parity symmetry of incoming waves and hence can strongly modulate the parity selective transmission through the system. Therefore, the transmission between two states of different parity exhibits the AB oscillations with a π-phase shift, compared to the case of states of the same parity. On this basis, it is shown that interesting effects, such as giant (both positive and negative) magnetoresistance and strong negative differential conductance, can be achieved in this structure. Our study thus presents a new property of the AB interference in graphene nanorings, which could be helpful for further understanding the transport properties of graphene mesoscopic systems. PMID:24785639
Analytic Aharonov-Bohm rings — Currents readout from Zeeman spectrum
NASA Astrophysics Data System (ADS)
Xiao, Mufei; Reyes-Serrato, Armando
2016-06-01
This paper reports the work on the development and analysis of a model for quantum rings in which persistent currents are induced by Aharonov-Bohm (AB) or other similar effects. The model is based on a centric and annual potential profile. The time-independent Schrödinger equation including an external magnetic field and an AB flux is analytically solved. The outputs, namely energy dispersion and wavefunctions, are analyzed in detail. It is shown that the rotation quantum number m is limited to small numbers, especially in weak confinement, and a conceptual proposal is put forward for acquiring the flux and eventually estimating the persistent currents in a Zeeman spectroscopy. The wavefunctions and electron distributions are numerically studied and compared to one-dimensional (1D) quantum well. It is predicated that the model and its solutions, eigen energy structure and analytic wavefunctions, would be a powerful tool for studying various electric and optical properties of quantum rings.
Relativistic persistent currents in ideal Aharonov-Bohm rings
NASA Astrophysics Data System (ADS)
Cotăescu, Ion I.; Băltăţeanu, Doru-Marcel; Cotăescu, Ion
2016-11-01
The exact solutions of the complete Dirac equation for fermions moving in ideal Aharonov-Bohm rings are used for deriving the exact expressions of the relativistic partial currents. It is shown that as in the nonrelativistic case, these currents can be related to the derivative of the fermion energy with respect to the flux parameter. A specific relativistic effect is the saturation of the partial currents for high values of the total angular momentum. Based on this property, the total relativistic persistent current at T = 0 is evaluated giving its analytical expression and showing how this depends on the ring parameters.
Recovery of the Aharonov-Bohm oscillations in asymmetrical quantum rings
NASA Astrophysics Data System (ADS)
Voskoboynikov, O.
2016-07-01
We theoretically investigate suppression and recovery of the Aharonov-Bohm oscillations of the diamagnetic response of electrons (holes) confined in self-assembled IncGa1-cAs/GaAs semiconductor reflection asymmetrical quantum rings. Based on the mapping method and gauge-origin-independent definition for the magnetic vector potential we simulate the energies and wave functions of the electron (hole) under external magnetic and electric fields. We examine the transformation of the ground state wave function of the electron (hole) in reflection asymmetrical rings from localized in one of the potential valleys (dotlike shape of the wave function) to distributed over all volume of the ring (ringlike shape) under an appropriate lateral electric field. This transformation greatly recovers the electron (hole) diamagnetic coefficient and Aharonov-Bohm oscillations of the diamagnetic response of the ring. However, the recovering electric field for the first Aharonov-Bohm diamagnetic oscillation of the electron is a suppressing one for the hole (and vice versa). This can block the recovery of the optical Aharonow-Bohm effect in IncGa1-cAs/GaAs asymmetrically wobbled rings. However, the recovery of the Aharonov-Bohm oscillations for the independent electron (hole) by the external electric field remains interesting and feasible objective for the asymmetric rings.
Aharonov-Bohm radiation of fermions
Chu Yizen; Mathur, Harsh; Vachaspati, Tanmay
2010-09-15
We analyze Aharonov-Bohm radiation of charged fermions from oscillating solenoids and cosmic strings. We find that the angular pattern of the radiation has features that differ significantly from that for bosons. For example, fermionic radiation in the lowest harmonic is approximately isotropically distributed around an oscillating solenoid, whereas for bosons the radiation is dipolar. We also investigate the spin polarization of the emitted fermion-antifermion pair. Fermionic radiation from kinks and cusps on cosmic strings is shown to depend linearly on the ultraviolet cutoff, suggesting strong emission at an energy scale comparable to the string energy scale.
NASA Astrophysics Data System (ADS)
Vaidman, Lev; Dennis, Mark; Popescu, Sandu
2010-01-01
This is a call for contributions to a special issue of Journal of Physics A: Mathematical and Theoretical dedicated to the subject of quantum phases and highlighting the impact of the discovery of the Aharonov--Bohm effect and of the Berry phase across physics. Researchers working in the area are invited to submit papers of original research to this issue. Editorial policy The Editorial Board has invited Lev Vaidman, Mark Dennis and Sandu Popescu to serve as Guest Editors for the special issue. The criteria for acceptance of contributions are as follows: Contributions will be refereed and processed according to the usual procedure and high standards of the journal. Papers should be original and should contain substantial new results. All contributions will be refereed and processed according to the usual procedure of the journal. Papers should report original and significant research that has not already been published. Guidelines for preparation of contributions The DEADLINE for contributed papers will be 1 February 2010. This deadline will allow the special issue to appear in September 2010. Advice on publishing your work in Journal of Physics A: Mathematical and Theoretical www.iop.org/Journals/jphysa. Contributions to the special issue should be submitted electronically, if possible, by web upload at www.iop.org/Journals/jphysa, or by email to jphysa@iop.org, quoting 'JPhysA Special Issue— Quantum Phases'. Submissions should ideally be in standard LaTeX form. Please see the website for further information on electronic submissions. Authors unable to submit electronically may send hard-copy contributions to: Publishing Administrators, Journal of Physics A, IOP Publishing, Dirac House, Temple Back, Bristol BS1 6BE, UK. Please quote 'JPhysA Special Issue— Quantum Phases'. All contributions should be accompanied by a read-me file or covering letter giving the postal and e-mail addresses for correspondence. The Publishing Office should be notified of any
Nonlinear Aharonov-Bohm Scattering by Optical Vortices
Neshev, Dragomir; Nepomnyashchy, Alexander; Kivshar, Yuri S.
2001-07-23
We study linear and nonlinear wave scattering by an optical vortex in a self-defocusing nonlinear Kerr medium. In the linear case, we find a splitting of a plane-wave front at the vortex proportional to its circulation, similar to what occurs in the scattered wave of electrons for the Aharonov-Bohm effect. For larger wave amplitudes, we study analytically and numerically the scattering of a dark-soliton stripe (a nonlinear analog of a small-amplitude wave packet) by a vortex and observe a significant asymmetry of the scattered wave. Subsequently, a wave-front splitting of the scattered wave develops into transverse modulational instability, ''unzipping'' the stripe into trains of vortices with opposite charges.
Calculation of the Aharonov-Bohm wave function
Alvarez, M.
1996-08-01
A calculation of the Aharonov-Bohm wave function is presented. The result is an asymptotic series of confluent hypergeometric functions which is finite at the forward direction. {copyright} {ital 1996 The American Physical Society.}
Falaye, Babatunde James; Sun, Guo-Hua; Silva-Ortigoza, Ramón; Dong, Shi-Hai
2016-05-01
This study presents the confinement influences of Aharonov-Bohm (AB) flux and electric and magnetic fields directed along the z axis and encircled by quantum plasmas on the hydrogen atom. The all-inclusive effects result in a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that the combined effect of the fields is stronger than a solitary effect and consequently there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for the hydrogen atom in quantum plasmas, a strong electric field and weak magnetic field are required, whereas the AB flux field can be used as a regulator. The application of the perturbation technique utilized in this paper is not restricted to plasma physics; it can also be applied in molecular physics.
Falaye, Babatunde James; Sun, Guo-Hua; Silva-Ortigoza, Ramón; Dong, Shi-Hai
2016-05-01
This study presents the confinement influences of Aharonov-Bohm (AB) flux and electric and magnetic fields directed along the z axis and encircled by quantum plasmas on the hydrogen atom. The all-inclusive effects result in a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that the combined effect of the fields is stronger than a solitary effect and consequently there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for the hydrogen atom in quantum plasmas, a strong electric field and weak magnetic field are required, whereas the AB flux field can be used as a regulator. The application of the perturbation technique utilized in this paper is not restricted to plasma physics; it can also be applied in molecular physics. PMID:27300989
Scattering of spin 1/2 particles by the 2+1 dimensional noncommutative Aharonov-Bohm potential
Ferrari, A. F.; Gomes, M.; Stechhahn, C. A.
2007-10-15
In this work we study modifications in the Aharonov-Bohm effect for relativistic spin 1/2 particles due to the noncommutativity of spacetime in 2+1 dimensions. The noncommutativity gives rise to a correction to the Aharonov-Bohm potential which is highly singular at the origin, producing divergences in a perturbative expansion around the usual solution of the free Dirac equation. This problem is surmounted by using a perturbative expansion around the exact solution of the commutative Aharonov-Bohm problem. We calculate, in this setting, the scattering amplitude and the corrections to the differential and total cross sections for a spin 1/2 particle, in the small-flux limit.
Noncommutative correction to Aharonov-Bohm scattering: A field theory approach
Anacleto, M.A.; Gomes, M.; Silva, A.J. da; Spehler, D.
2004-10-15
We study a noncommutative nonrelativistic theory in 2+1 dimensions of a scalar field coupled to the Chern-Simons field. In the commutative situation this model has been used to simulate the Aharonov-Bohm effect in the field theory context. We verified that, contrary to the commutative result, the inclusion of a quartic self-interaction of the scalar field is not necessary to secure the ultraviolet renormalizability of the model. However, to obtain a smooth commutative limit the presence of a quartic gauge invariant self-interaction is required. For small noncommutativity we fix the corrections to the Aharonov-Bohm scattering and prove that up to one loop the model is free from dangerous infrared/ultraviolet divergences.
Beating of Aharonov-Bohm oscillations in a closed-loop interferometer
Jo, Sanghyun; Chang, Dong-In; Lee, Hu-Jong; Khym, Gyong Luck; Kang, Kicheon; Chung, Yunchul; Mahalu, Diana; Umansky, Vladimir
2007-07-15
One of the points at issue with closed-loop-type interferometers is beating in the Aharonov-Bohm (AB) oscillations. Recent observations suggest the possibility that the beating results from the Berry-phase pickup by the conducting electrons in materials with the strong spin-orbit interaction (SOI). In this study, we also observed beats in the AB oscillations in a gate-defined closed-loop interferometer fabricated on a GaAs/Al{sub 0.3}Ga{sub 0.7}As two-dimensional electron-gas heterostructure. Since this heterostructure has very small SOI, the picture of the Berry-phase pickup is ruled out. The observation of beats in this study, with the controllability of forming a single transverse subband mode in both arms of our gate-defined interferometer, also rules out the often-claimed multiple transverse subband effect. It is observed that nodes of the beats with an h/2e period exhibit a parabolic distribution for varying the side gate. These results are shown to be well interpreted, without resorting to the SOI effect, by the existence of two-dimensional multiple longitudinal modes in a single transverse subband. The Fourier spectrum of measured conductance, despite showing multiple h/e peaks with the magnetic-field dependence that are very similar to that from strong-SOI materials, can also be interpreted as the two-dimensional multiple-longitudinal-modes effect.
Quantum anholonomies in time-dependent Aharonov-Bohm rings
Tanaka, Atushi; Cheon, Taksu
2010-08-15
Anholonomies in eigenstates are studied through time-dependent variations of a magnetic flux in an Aharonov-Bohm ring. The anholonomies in the eigenenergy and the expectation values of eigenstates are shown to persist beyond the adiabatic regime. The choice of the gauge of the magnetic flux is shown to be crucial to clarify the relationship of these anholonomies to the eigenspace anholonomy, which is described by a non-Abelian connection in the adiabatic limit.
Levinson theorem for Aharonov-Bohm scattering in two dimensions
Sheka, Denis D.; Mertens, Franz G.
2006-11-15
We apply the recently generalized Levinson theorem for potentials with inverse-square singularities [Sheka et al., Phys. Rev. A 68, 012707 (2003)] to Aharonov-Bohm systems in two dimensions (2D). By this theorem, the number of bound states in a given mth partial wave is related to the phase shift and the magnetic flux. The results are applied to 2D soliton-magnon scattering.
Enhanced spin figure of merit in an Aharonov-Bohm ring with a double quantum dot
Zhou, Xingfei; Qi, Fenghua; Jin, Guojun
2014-04-21
We theoretically investigate the thermoelectric effects in an Aharonov-Bohm ring with a serially coupled double quantum dot embedded in one arm. An external magnetic field is perpendicularly applied to the two dots. Using the nonequilibrium Green's function method in the linear-response regime, we calculate the charge and spin figures of merit. When the energy levels of the two quantum dots are equal and the system is connected to two normal leads, a large spin figure of merit (Z{sub s}T ≈ 4.5) accompanying with a small charge figure of merit (Z{sub c}T ≈ 0) can be generated due to the remarkable bipolar effect. Further, when the system is connected to two ferromagnetic leads, the spin figure of merit can reach even a higher value about 9. Afterwards, we find that Z{sub s}T is enhanced while Z{sub c}T is reduced in the coaction of the Aharonov-Bohm flux and Rashba spin-orbit coupling. It is argued that the bipolar effect is positive (negative) to spin (charge) figure of merit in the presence of level detuning of the two quantum dots and intradot Coulomb interactions, respectively. Also, we propose a possible experiment to verify our results.
Aharonov-Bohm oscillations in a quasi-ballistic three-dimensional topological insulator nanowire.
Cho, Sungjae; Dellabetta, Brian; Zhong, Ruidan; Schneeloch, John; Liu, Tiansheng; Gu, Genda; Gilbert, Matthew J; Mason, Nadya
2015-07-09
Aharonov-Bohm oscillations effectively demonstrate coherent, ballistic transport in mesoscopic rings and tubes. In three-dimensional topological insulator nanowires, they can be used to not only characterize surface states but also to test predictions of unique topological behaviour. Here we report measurements of Aharonov-Bohm oscillations in (Bi1.33Sb0.67)Se3 that demonstrate salient features of topological nanowires. By fabricating quasi-ballistic three-dimensional topological insulator nanowire devices that are gate-tunable through the Dirac point, we are able to observe alternations of conductance maxima and minima with gate voltage. Near the Dirac point, we observe conductance minima for zero magnetic flux through the nanowire and corresponding maxima (having magnitudes of almost a conductance quantum) at magnetic flux equal to half a flux quantum; this is consistent with the presence of a low-energy topological mode. The observation of this mode is a necessary step towards utilizing topological properties at the nanoscale in post-CMOS applications.
Forward-smooth high-order uniform Aharonov-Bohm asymptotics
NASA Astrophysics Data System (ADS)
Berry, M. V.
2016-07-01
The Aharonov-Bohm (AB) function, describing a plane wave scattered by a flux line, is expanded asymptotically in a Fresnel-integral based series whose terms are smooth in the forward direction and uniformly valid in angle and flux. Successive approximations are valid for large distance r from the flux (or short wavelength) but are accurate even within one wavelength of it. Coefficients of all the terms are exhibited explicitly for the forward direction, enabling the high-order asymptotics to be understood in detail. The series is factorally divergent, with optimal truncation error exponentially small in r. Systematic resummation gives further exponential improvement. Terms of the series satisfy a resurgence relation: the high orders are related to the low orders. Discontinuities in the backward direction get smaller order by order, with systematic cancellation by successive terms. The relation to an earlier scheme based on the Cornu spiral is discussed.
Goldhaber, Alfred Scharff; Requist, Ryan
2003-07-01
As a consequence of the Aharonov-Bohm effect, there is a quantum-induced attraction between a charged particle and a rigid, impenetrable hoop made from an arbitrarily thin tube containing a superconductor quantum of magnetic flux. This is remarkable because in classical physics there is no force between the two objects, and quantum-mechanical effects (associated with uncertainty-principle energy) generally are repulsive rather than attractive. For an incident spinless charged particle in a P wave (in a configuration with total angular momentum zero) we verify a resonance just above threshold using the Kohn variational principle in its S-matrix form. Even if optimistic choices of parameters describing a model system with these properties were feasible, the temperature required to observe the resonance would be far lower than has yet been attained in the laboratory.
Goldhaber, Alfred S.
2003-01-09
As a consequence of the Aharonov-Bohm effect, there is a quantum-induced attraction between a charged particle and a rigid impenetrable hoop made from an arbitrarily thin tube containing a superconductor quantum of magnetic flux. This is remarkable because in classical physics there is no force between the two objects, and quantum-mechanical effects (associated with uncertainty-principle energy) generally are repulsive rather than attractive. For an incident spinless charged particle in a P wave, in a configuration with total angular momentum zero, we verify a resonance just above threshold using the Kohn variational principle in its S-matrix form. Even if optimistic choices of parameters describing a model system with these properties turned out to be feasible, the temperature required to observe the resonance would be far lower than has yet been attained in the laboratory.
An Aharonov-Bohm interferometer for determining Bloch band topology.
Duca, L; Li, T; Reitter, M; Bloch, I; Schleier-Smith, M; Schneider, U
2015-01-16
The geometric structure of a single-particle energy band in a solid is fundamental for a wide range of many-body phenomena and is uniquely characterized by the distribution of Berry curvature over the Brillouin zone. We realize an atomic interferometer to measure Berry flux in momentum space, in analogy to an Aharonov-Bohm interferometer that measures magnetic flux in real space. We demonstrate the interferometer for a graphene-type hexagonal optical lattice loaded with bosonic atoms. By detecting the singular π Berry flux localized at each Dirac point, we establish the high momentum resolution of this interferometric technique. Our work forms the basis for a general framework to fully characterize topological band structures. PMID:25525160
NASA Astrophysics Data System (ADS)
Roy, Bidisha; Ji, Haojie; Dhomkar, Siddharth; Cadieu, Fred J.; Peng, Le; Moug, Richard; Tamargo, Maria C.; Kuskovsky, Igor L.
2013-02-01
A spectral analysis of the Aharonov-Bohm (AB) oscillations in photoluminescence intensity was performed for stacked type-II ZnTe/ZnSe quantum dots (QDs) fabricated within multilayered Zn-Se-Te system with sub-monolayer insertions of Te. Robust AB oscillations allowed for fine probing of distinguishable QDs stacks within the ensemble of QDs. The AB transition magnetic field, B AB , changed from the lower energy side to the higher energy side of the PL spectra revealing the presence of different sets of QDs stacks. The change occurs within the spectral range, where the contributing green and blue bands of the spectra overlapped. "Bundling" in lifetime measurements is seen at transition spectral regions confirming the results.
Induced vacuum charge of massless fermions in Coulomb and Aharonov-Bohm potentials in 2+1 dimensions
NASA Astrophysics Data System (ADS)
Mamsurov, I. V.; Khalilov, V. R.
2016-08-01
We study the vacuum polarization of zero-mass charged fermions in Coulomb and Aharonov-Bohm potentials in 2+1 dimensions. For this, we construct the Green's function of the two-dimensional Dirac equation in the considered field configuration and use it to find the density of the induced vacuum charge in so-called subcritical and supercritical regions. The Green's function is represented in regular and singular (in the source) solutions of the Dirac radial equation for a charged fermion in Coulomb and Aharonov-Bohm potentials in 2+1 dimensions and satisfies self-adjoint boundary conditions at the source. In the supercritical region, the Green's function has a discontinuity related to the presence of singularities on the nonphysical sheet of the complex plane of "energy," which are caused by the appearance of an infinite number of quasistationary states with negative energies. Ultimately, this situation represents the neutral vacuum instability. On the boundary of the supercritical region, the induced vacuum charge is independent of the self-adjoint extension. We hope that the obtained results will contribute to a better understanding of important problems in quantum electrodynamics and will also be applicable to the problem of screening the Coulomb impurity due to vacuum polarization in graphene with the effects associated with taking the electron spin into account.
Berry's phase manifestation in Aharonov-Bohm oscillations in single Bi nanowires
NASA Astrophysics Data System (ADS)
Gitsu, D. V.; Huber, T. E.; Konopko, L. A.; Nikolaeva, A. A.
2009-02-01
Here we report on Aharonov-Bohm oscillations of magnetoresistance (MR) of the single Bi nanowires with diameter d<80 nm. The samples were prepared by Ulitovsky technique and represented cylindrical single crystals with the 1011 orientation along the wire axis. Due to semimetal-to-semiconductor transformation and big density of surface states with strong spin-orbit interactions Bi nanowire should effectively become a conducting tube. The equidistant oscillations of the MR have been observed in a wide range of magnetic fields up to 14 T at various temperatures (1.5 K< T< 4.2 K) and angles θ (0< θ < 90°) of the sample orientation relative to the magnetic field. We have obtained longitudinal MR oscillations with periods ΔB1=Φ0/S and ΔB2=Φ0/2S, where Φ0=h/e is the flux quantum and S is the wire cross section. From B approx 8 T down to B=0 the extremums of Φ0/2S oscillations are shifted up to 3π at B=0 which is the manifestation of Berry phase shift due to carriers moving in inhomogeneous magnetic field. An interpretation of the MR oscillations in terms of a subband structure in the surface state band caused by quantum interference is presented.
NASA Astrophysics Data System (ADS)
Aharony, Amnon; Tokura, Yasuhiro; Cohen, Guy Z.; Entin-Wohlman, Ora; Katsumoto, Shingo
2011-07-01
Spin-1/2 electrons are scattered through one or two diamond-like loops, made of quantum dots connected by one-dimensional wires, and subject to both an Aharonov-Bohm flux and (Rashba and Dresselhaus) spin-orbit interactions. With some symmetry between the two branches of each diamond, and with appropriate tuning of the electric and magnetic fields (or of the diamond shapes), this device completely blocks electrons with one polarization and allows only electrons with the opposite polarization to be transmitted. The directions of these polarizations are tunable by these fields, and do not depend on the energy of the scattered electrons. For each range of fields one can tune the site and bond energies of the device so that the transmission of the fully polarized electrons is close to unity. Thus, these devices perform as ideal spin filters, and these electrons can be viewed as mobile qubits; the device writes definite quantum information on the spinors of the outgoing electrons. The device can also read the information written on incoming polarized electrons: The charge transmission through the device contains full information on this polarization. The double-diamond device can also act as a realization of the Datta-Das spin field-effect transistor.
On the Aharonov-Bohm Operators with Varying Poles: The Boundary Behavior of Eigenvalues
NASA Astrophysics Data System (ADS)
Noris, Benedetta; Nys, Manon; Terracini, Susanna
2015-11-01
We consider a magnetic Schrödinger operator with magnetic field concentrated at one point (the pole) of a domain and half integer circulation, and we focus on the behavior of Dirichlet eigenvalues as functions of the pole. Although the magnetic field vanishes almost everywhere, it is well known that it affects the operator at the spectral level (the Aharonov-Bohm effect, Phys Rev (2) 115:485-491, 1959). Moreover, the numerical computations performed in (Bonnaillie-Noël et al., Anal PDE 7(6):1365-1395, 2014; Noris and Terracini, Indiana Univ Math J 59(4):1361-1403, 2010) show a rather complex behavior of the eigenvalues as the pole varies in a planar domain. In this paper, in continuation of the analysis started in (Bonnaillie-Noël et al., Anal PDE 7(6):1365-1395, 2014; Noris and Terracini, Indiana Univ Math J 59(4):1361-1403, 2010), we analyze the relation between the variation of the eigenvalue and the nodal structure of the associated eigenfunctions. We deal with planar domains with Dirichlet boundary conditions and we focus on the case when the singular pole approaches the boundary of the domain: then, the operator loses its singular character and the k-th magnetic eigenvalue converges to that of the standard Laplacian. We can predict both the rate of convergence and whether the convergence happens from above or from below, in relation with the number of nodal lines of the k-th eigenfunction of the Laplacian. The proof relies on the variational characterization of eigenvalues, together with a detailed asymptotic analysis of the eigenfunctions, based on an Almgren-type frequency formula for magnetic eigenfunctions and on the blow-up technique.
Graphene under the influence of Aharonov-Bohm flux and constant magnetic field
NASA Astrophysics Data System (ADS)
Stepanov, E. A.; Zhukovsky, V. Ch.
2016-09-01
Investigation of real two-dimensional systems with Dirac-like electronic behavior under the influence of magnetic field is challenging and leads to many interesting physical results. In this paper we study a 2D graphene model with a particular form of magnetic field as a superposition of a homogeneous field and an Aharonov-Bohm vortex. For this configuration, electronic wave functions and the energy spectrum are obtained and it is shown that the magnetic Aharonov-Bohm vortex plays the role of a charge impurity. As a demonstration of vacuum properties of the system, vacuum current, as well as an electric current, is calculated and their representation for particular limiting cases of a magnetic field is obtained.
Scattering of spin-polarized electron in an Aharonov-Bohm potential
Khalilov, V.R.; Ho, C.-L.
2008-05-15
The scattering of spin-polarized electrons in an Aharonov-Bohm vector potential is considered. We solve the Pauli equation in 3 + 1 dimensions taking into account explicitly the interaction between the three-dimensional spin magnetic moment of electron and magnetic field. Expressions for the scattering amplitude and the cross section are obtained for spin-polarized electron scattered off a flux tube of small radius. It is also shown that bound electron states cannot occur in this quantum system. The scattering problem for the model of a flux tube of zero radius in the Born approximation is briefly discussed.
NASA Astrophysics Data System (ADS)
Barseghyan, M. G.; Manaselyan, A. Kh.; Laroze, D.; Kirakosyan, A. A.
2016-07-01
In this work we study the electronic states in quantum dot-ring complex nanostructures with an on-center hydrogenic impurity. The influence of the impurity on Aharonov-Bohm energy spectra oscillations and intraband optical absorption is investigated. It is shown that in the presence of a hydrogenic donor impurity the Aharonov-Bohm oscillations in quantum dot-ring structures become highly tunable. Furthermore, the presence of the impurity drastically changes the intraband absorption spectra due to the strong controllability of the electron localization type.
Aharonov-Bohm effect on Aharonov-Casher scattering
Lin Qionggui
2010-01-15
The scattering of relativistic spin-1/2 neutral particles with a magnetic dipole moment by a long straight charged line and a magnetic flux line at the same position is studied. The scattering cross sections for unpolarized and polarized particles are obtained by solving the Dirac-Pauli equation. The results are in general the same as those for pure Aharonov-Casher scattering (by the charged line alone) as expected. However, in special cases when the incident energy, the line charge density, and the magnetic flux satisfy some relations, the cross section for polarized particles is dramatically changed. Relations between the polarization of incident particles and that of scattered ones are presented, both in the full relativistic case and the nonrelativistic limit. The characteristic difference between the general and special cases lies in the backward direction: in the general cases the incident particles are simply bounced while in the special cases their polarization is turned over simultaneously. For pure Aharonov-Casher scattering there exist cases where the helicities of all scattered particles are reversed. This seems to be remarkable but appears unnoticed previously. Two mathematical approaches are employed to deal with the singularity of the electric and magnetic field and it turns out that the physical results are essentially the same.
Transmission through a quantum dot molecule embedded in an Aharonov-Bohm interferometer.
Lovey, Daniel A; Gomez, Sergio S; Romero, Rodolfo H
2011-10-26
We study theoretically the transmission through a quantum dot molecule embedded in the arms of an Aharonov-Bohm four quantum dot ring threaded by a magnetic flux. The tunable molecular coupling provides a transmission pathway between the interferometer arms in addition to those along the arms. From a decomposition of the transmission in terms of contributions from paths, we show that antiresonances in the transmission arise from the interference of the self-energy along different paths and that application of a magnetic flux can produce the suppression of such antiresonances. The occurrence of a period of twice the quantum of flux arises at the opening of the transmission pathway through the dot molecule. Two different connections of the device to the leads are considered and their spectra of conductance are compared as a function of the tunable parameters of the model.
Aharonov-Bohm oscillations in Dirac semimetal Cd3As2 nanowires.
Wang, Li-Xian; Li, Cai-Zhen; Yu, Da-Peng; Liao, Zhi-Min
2016-01-01
Three-dimensional Dirac semimetals, three-dimensional analogues of graphene, are unusual quantum materials with massless Dirac fermions, which can be further converted to Weyl fermions by breaking time reversal or inversion symmetry. Topological surface states with Fermi arcs are predicted on the surface and have been observed by angle-resolved photoemission spectroscopy experiments. Although the exotic transport properties of the bulk Dirac cones have been demonstrated, it is still a challenge to reveal the surface states via transport measurements due to the highly conductive bulk states. Here, we show Aharonov-Bohm oscillations in individual single-crystal Cd3As2 nanowires with low carrier concentration and large surface-to-volume ratio, providing transport evidence of the surface state in three-dimensional Dirac semimetals. Moreover, the quantum transport can be modulated by tuning the Fermi level using a gate voltage, enabling a deeper understanding of the rich physics residing in Dirac semimetals. PMID:26902716
Aharonov-Bohm oscillations in Dirac semimetal Cd3As2 nanowires
NASA Astrophysics Data System (ADS)
Wang, Li-Xian; Li, Cai-Zhen; Yu, Da-Peng; Liao, Zhi-Min
2016-02-01
Three-dimensional Dirac semimetals, three-dimensional analogues of graphene, are unusual quantum materials with massless Dirac fermions, which can be further converted to Weyl fermions by breaking time reversal or inversion symmetry. Topological surface states with Fermi arcs are predicted on the surface and have been observed by angle-resolved photoemission spectroscopy experiments. Although the exotic transport properties of the bulk Dirac cones have been demonstrated, it is still a challenge to reveal the surface states via transport measurements due to the highly conductive bulk states. Here, we show Aharonov-Bohm oscillations in individual single-crystal Cd3As2 nanowires with low carrier concentration and large surface-to-volume ratio, providing transport evidence of the surface state in three-dimensional Dirac semimetals. Moreover, the quantum transport can be modulated by tuning the Fermi level using a gate voltage, enabling a deeper understanding of the rich physics residing in Dirac semimetals.
Aharonov-Bohm scattering of relativistic Dirac particles with an anomalous magnetic moment
Lin Qionggui
2005-10-15
The Aharonov-Bohm scattering of relativistic spin-1/2 particles with an anomalous magnetic moment are studied. The scattering cross sections for unpolarized and polarized particles are obtained by solving the Dirac-Pauli equation. It is somewhat unexpected that the results are in general the same as those for particles without an anomalous magnetic moment. However, when the incident energy takes some special values, the cross section for polarized particles is dramatically changed. In these cases the helicity of scattered particles is not conserved. In particular, the helicity of particles scattered in the backward direction is all reversed. In the nonrelativistic limit, a very simple relation between the polarized directions of the incident and scattered particles is found, for both general and special incident energies. For particles without an anomalous magnetic moment this relation can be drawn from previous results but it appears to be unnoticed.
Topological phases reviewed: The Aharonov Bohm, Aharonov Casher, and He McKellar Wilkens phases
McKellar, B. H. J.; He, X-G.; Klein, A. G.
2014-03-05
There are three topological phases related to electromagnetic interactions in quantum mechanics: 1. The Aharonov Bohm phase acquired when a charged particle encircles a magnetic field but travels through a field free region. 2. The Aharonov Casher phase acquired when a magnetic dipole encircles electric charges but travels through a charge free region. 3. The He McKellar Wilkens phase acquired when an electric dipole encircles magnetic charges but travels through a charge free region. We review the conditions under which these phases are indeed topological and their experimental realisation. Because the He McKellar Wilkens phase has been recently observed we pay particular attention to how the basic concept of 'an electric dipole encircles magnetic charges' was realised experimentally, and discuss possible future experimental realisations.
Levinson's theorem and higher degree traces for Aharonov-Bohm operators
Kellendonk, Johannes; Pankrashkin, Konstantin; Richard, Serge
2011-05-15
We study Levinson-type theorems for the family of Aharonov-Bohm models from different perspectives. The first one is purely analytical involving the explicit calculation of the wave-operators and allowing to determine precisely the various contributions to the left hand side of Levinson's theorem, namely, those due to the scattering operator, the terms at 0-energy and at energy +{infinity}. The second one is based on non-commutative topology revealing the topological nature of Levinson's theorem. We then include the parameters of the family into the topological description obtaining a new type of Levinson's theorem, a higher degree Levinson's theorem. In this context, the Chern number of a bundle defined by a family of projections on bound states is explicitly computed and related to the result of a 3-trace applied on the scattering part of the model.
Spin transport in an Aharonov-Bohm ring with exchange interaction
NASA Astrophysics Data System (ADS)
Savenko, I. G.; Polozkov, R. G.; Shelykh, I. A.
2013-11-01
We investigate spin-dependent conductance through a quantum Aharonov-Bohm ring containing localized electrons which interact with the propagating flow of electrons via exchange interaction of the ferromagnetic or antiferromagnetic type. We analyze the conductance oscillations as a function of both the chemical potential (particle concentration) and external magnetic field. It is demonstrated that the amplitude of the conductance oscillations in the ballistic regime is determined by the value of the noncompensated spin localized in the ring. The results are in agreement with the concept of fractional quantization of the ballistic conductance, proposed by us earlier [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.71.113311 71, 113311 (2005)].
NASA Astrophysics Data System (ADS)
Georgiev, Lachezar S.
2004-02-01
Using the effective conformal field theory for the quantum Hall edge states we propose a compact and convenient scheme for the computation of the periods, amplitudes, and temperature behavior of the chiral persistent currents and the magnetic susceptibilities in the mesoscopic disk version of the Zk parafermion quantum Hall states in the second Landau level. Our numerical calculations show that the persistent currents are periodic in the Aharonov Bohm flux with period exactly one flux quantum and have a diamagnetic nature. In the high-temperature regime their amplitudes decay exponentially with increasing the temperature and the corresponding exponents are universal characteristics of non-Fermi liquids. Our theoretical results for these exponents are in perfect agreement with those extracted from the numerical data and demonstrate that there is in general a nontrivial contribution coming from the neutral sector. We emphasize the crucial role of the nonholomorphic factors, first proposed by Cappelli and Zemba in the context of the conformal field theory partition functions for the quantum Hall states, which ensure the invariance of the annulus partition function under the Laughlin spectral flow.
Bulgakov, Evgeny N; Sadreev, Almas F
2016-07-01
We consider the trapping of electrons with a definite spin polarization by bound states in the continuum (BSC) in the open Aharonov-Bohm rings in the presence of the Rashba spin-orbit interaction (RSOI). Neglecting the Zeeman term we show the existence of BSCs in the one-dimensional ring when the eigenstates of the closed ring are doubly degenerate. With account of the Zeeman term BSCs occur only at the points of threefold degeneracy. The BSCs are found in the parametric space of flux and RSOI strength in close pairs with opposite spin polarization. Thereby the spin polarization of electrons transmitted through the ring can be altered by minor variation of magnetic or electric field at the vicinity of these pairs. Numerical simulations of the two-dimensional open ring show similar results for the BSCs. Encircling the BSC points in the parametric space of the flux and the RSOI constant gives rise to a geometric phase. PMID:27165662
NASA Astrophysics Data System (ADS)
Bulgakov, Evgeny N.; Sadreev, Almas F.
2016-07-01
We consider the trapping of electrons with a definite spin polarization by bound states in the continuum (BSC) in the open Aharonov-Bohm rings in the presence of the Rashba spin-orbit interaction (RSOI). Neglecting the Zeeman term we show the existence of BSCs in the one-dimensional ring when the eigenstates of the closed ring are doubly degenerate. With account of the Zeeman term BSCs occur only at the points of threefold degeneracy. The BSCs are found in the parametric space of flux and RSOI strength in close pairs with opposite spin polarization. Thereby the spin polarization of electrons transmitted through the ring can be altered by minor variation of magnetic or electric field at the vicinity of these pairs. Numerical simulations of the two-dimensional open ring show similar results for the BSCs. Encircling the BSC points in the parametric space of the flux and the RSOI constant gives rise to a geometric phase.
Bruno, Patrick
2012-06-15
The (Berry-Aharonov-Anandan) geometric phase acquired during a cyclic quantum evolution of finite-dimensional quantum systems is studied. It is shown that a pure quantum state in a (2J+1)-dimensional Hilbert space (or, equivalently, of a spin-J system) can be mapped onto the partition function of a gas of independent Dirac strings moving on a sphere and subject to the Coulomb repulsion of 2J fixed test charges (the Majorana stars) characterizing the quantum state. The geometric phase may be viewed as the Aharonov-Bohm phase acquired by the Majorana stars as they move through the gas of Dirac strings. Expressions for the geometric connection and curvature, for the metric tensor, as well as for the multipole moments (dipole, quadrupole, etc.), are given in terms of the Majorana stars. Finally, the geometric formulation of the quantum dynamics is presented and its application to systems with exotic ordering such as spin nematics is outlined. PMID:23004240
Bruno, Patrick
2012-06-15
The (Berry-Aharonov-Anandan) geometric phase acquired during a cyclic quantum evolution of finite-dimensional quantum systems is studied. It is shown that a pure quantum state in a (2J+1)-dimensional Hilbert space (or, equivalently, of a spin-J system) can be mapped onto the partition function of a gas of independent Dirac strings moving on a sphere and subject to the Coulomb repulsion of 2J fixed test charges (the Majorana stars) characterizing the quantum state. The geometric phase may be viewed as the Aharonov-Bohm phase acquired by the Majorana stars as they move through the gas of Dirac strings. Expressions for the geometric connection and curvature, for the metric tensor, as well as for the multipole moments (dipole, quadrupole, etc.), are given in terms of the Majorana stars. Finally, the geometric formulation of the quantum dynamics is presented and its application to systems with exotic ordering such as spin nematics is outlined.
Khatua, Pradip; Bansal, Bhavtosh; Shahar, Dan
2014-01-10
In a "thought experiment," now a classic in physics pedagogy, Feynman visualizes Young's double-slit interference experiment with electrons in magnetic field. He shows that the addition of an Aharonov-Bohm phase is equivalent to shifting the zero-field wave interference pattern by an angle expected from the Lorentz force calculation for classical particles. We have performed this experiment with one slit, instead of two, where ballistic electrons within two-dimensional electron gas diffract through a small orifice formed by a quantum point contact (QPC). As the QPC width is comparable to the electron wavelength, the observed intensity profile is further modulated by the transverse waveguide modes present at the injector QPC. Our experiments open the way to realizing diffraction-based ideas in mesoscopic physics. PMID:24483873
Khatua, Pradip; Bansal, Bhavtosh; Shahar, Dan
2014-01-10
In a "thought experiment," now a classic in physics pedagogy, Feynman visualizes Young's double-slit interference experiment with electrons in magnetic field. He shows that the addition of an Aharonov-Bohm phase is equivalent to shifting the zero-field wave interference pattern by an angle expected from the Lorentz force calculation for classical particles. We have performed this experiment with one slit, instead of two, where ballistic electrons within two-dimensional electron gas diffract through a small orifice formed by a quantum point contact (QPC). As the QPC width is comparable to the electron wavelength, the observed intensity profile is further modulated by the transverse waveguide modes present at the injector QPC. Our experiments open the way to realizing diffraction-based ideas in mesoscopic physics.
NASA Astrophysics Data System (ADS)
Khatua, Pradip; Bansal, Bhavtosh; Shahar, Dan
2014-01-01
In a "thought experiment," now a classic in physics pedagogy, Feynman visualizes Young's double-slit interference experiment with electrons in magnetic field. He shows that the addition of an Aharonov-Bohm phase is equivalent to shifting the zero-field wave interference pattern by an angle expected from the Lorentz force calculation for classical particles. We have performed this experiment with one slit, instead of two, where ballistic electrons within two-dimensional electron gas diffract through a small orifice formed by a quantum point contact (QPC). As the QPC width is comparable to the electron wavelength, the observed intensity profile is further modulated by the transverse waveguide modes present at the injector QPC. Our experiments open the way to realizing diffraction-based ideas in mesoscopic physics.
Two-dimensional quantum ring in a graphene layer in the presence of a Aharonov-Bohm flux
NASA Astrophysics Data System (ADS)
Amaro Neto, José; Bueno, M. J.; Furtado, Claudio
2016-10-01
In this paper we study the relativistic quantum dynamics of a massless fermion confined in a quantum ring. We use a model of confining potential and introduce the interaction via Dirac oscillator coupling, which provides ring confinement for massless Dirac fermions. The energy levels and corresponding eigenfunctions for this model in graphene layer in the presence of Aharonov-Bohm flux in the centre of the ring and the expression for persistent current in this model are derived. We also investigate the model for quantum ring in graphene layer in the presence of a disclination and a magnetic flux. The energy spectrum and wave function are obtained exactly for this case. We see that the persistent current depends on parameters characterizing the topological defect.
Smirnov, A. G.
2015-12-15
We develop a general technique for finding self-adjoint extensions of a symmetric operator that respects a given set of its symmetries. Problems of this type naturally arise when considering two- and three-dimensional Schrödinger operators with singular potentials. The approach is based on constructing a unitary transformation diagonalizing the symmetries and reducing the initial operator to the direct integral of a suitable family of partial operators. We prove that symmetry preserving self-adjoint extensions of the initial operator are in a one-to-one correspondence with measurable families of self-adjoint extensions of partial operators obtained by reduction. The general scheme is applied to the three-dimensional Aharonov-Bohm Hamiltonian describing the electron in the magnetic field of an infinitely thin solenoid. We construct all self-adjoint extensions of this Hamiltonian, invariant under translations along the solenoid and rotations around it, and explicitly find their eigenfunction expansions.
An experimental proposal to test the physical effect of the vector potential.
Wang, Rui-Feng
2016-01-01
There are two interpretations of the Aharonov-Bohm (A-B) effect. One interpretation asserts that the A-B effect demonstrates that the vector potential is a physical reality that can result in the phase shift of a moving charge in quantum mechanics. The other interpretation asserts that the phase shift of the moving charge results from the interaction energy between the electromagnetic field of the moving charge and external electromagnetic fields. This paper briefly reviews these two interpretations and analyzes their differences. In addition, a new experimental scheme is proposed to determine which interpretation is correct.
Exciton storage in type-II quantum dots using the optical Aharonov-Bohm effect
Climente, Juan I.; Planelles, Josep
2014-05-12
We investigate the bright-to-dark exciton conversion efficiency in type-II quantum dots subject to a perpendicular magnetic field. To this end, we take the exciton storage protocol recently proposed by Simonin and co-workers [Phys. Rev. B 89, 075304 (2014)] and simulate its coherent dynamics. We confirm the storage is efficient in perfectly circular structures subject to weak external electric fields, where adiabatic evolution is dominant. In practice, however, the efficiency rapidly degrades with symmetry lowering. Besides, the use of excited states is likely unfeasible owing to the fast decay rates. We then propose an adaptation of the protocol which does not suffer from these limitations.
Decoherence in a double-dot Aharonov-Bohm interferometer: Numerical renormalization group study
NASA Astrophysics Data System (ADS)
Kubala, Björn; Roosen, David; Sindel, Michael; Hofstetter, Walter; Marquardt, Florian
2014-07-01
Coherence in electronic interferometers is typically believed to be restored fully in the limit of small voltages, frequencies, and temperatures. However, it is crucial to check this essentially perturbative argument by nonperturbative methods. Here we use the numerical renormalization group to study ac transport and decoherence in an experimentally realizable model interferometer, a parallel double quantum dot coupled to a phonon mode. The model allows us to clearly distinguish renormalization effects from decoherence. We discuss finite-frequency transport and confirm the restoration of coherence in the dc limit.
Half-period Aharonov-Bohm oscillations in disordered rotating optical ring cavities
NASA Astrophysics Data System (ADS)
Li, Huanan; Kottos, Tsampikos; Shapiro, Boris
2016-09-01
There exists an analogy between Maxwell equations in a rotating frame and the Schrödinger equation for a charged particle in the presence of a magnetic field. We exploit this analogy to point out that electromagnetic phenomena in the rotating frame, under appropriate conditions, can exhibit periodicity with respect to the angular velocity of rotation. In particular, in disordered ring cavities one finds the optical analog of the Al'tshuler-Aronov-Spivak effect well known in mesoscopic physics of disordered metals.
NASA Astrophysics Data System (ADS)
Englman, R.
2016-08-01
The recent phase shift data of Takada et al. (Phys. Rev. Lett. 113 (2014) 126601) for a two level system are reconstructed from their current intensity curves by the method of Hilbert transform, for which the underlying Physics is the principle of causality. An introductory algebraic model illustrates pedagogically the working of the method and leads to newly derived relationships involving phenomenological parameters, in particular for the sign of the phase slope between the resonance peaks. While the parametrization of the experimental current intensity data in terms of a few model parameters shows only a qualitative agreement for the phase shift, due to the strong impact of small, detailed variations in the experimental intensity curve on the phase behavior, the numerical Hilbert transform yields a satisfactory reproduction of the phase.
Dmitriev, A P; Gornyi, I V; Kachorovskii, V Yu; Polyakov, D G
2010-07-16
We study the effect of electron-electron interaction on transport through a tunnel-coupled single-channel ring. We find that the conductance as a function of magnetic flux shows a series of interaction-induced resonances that survive thermal averaging. The period of the series is given by the interaction strength α. The physics behind this behavior is the blocking of the tunneling current by the circular current. The main mechanism of dephasing is due to circular-current fluctuations. The dephasing rate is proportional to the tunneling rate and does not depend on α.
ERIC Educational Resources Information Center
Matteucci, G.
2007-01-01
In the so-called electric Aharonov-Bohm effect, a quantum interference pattern shift is produced when electrons move in an electric field free region but, at the same time, in the presence of a time-dependent electric potential. Analogous fringe shifts are observed in interference experiments where electrons, travelling through an electrostatic…
The Aharanov-Bohm effect, magnetic monopoles and reversal in spin-ice lattices.
Pollard, Shawn D; Zhu, Yimei
2013-06-01
The proof of the Aharonov-Bohm (AB) effect has been one of the most important experiments of the last century and used as essential evidence for the theory of gauge fields. In this article, we look at its fundamental relation to the Dirac monopole and string. Despite the Dirac string being invisible to the AB effect, it can be used to study emergent quasiparticles in condensed matter settings that behave similar to the fundamental monopoles and strings between them. We utilize phase-imaging method based on the AB effect to study the ordering in a one-model system - that of frustrated spin ice - to understand the ordering processes that occur during a magnetic field reversal cycle. The reversal is linked to the propagation of monopole defects linked by flux channels, reminiscent of Dirac strings. Monopole interactions govern the defect densities within the lattice. Furthermore, we exploit these interactions to propose a new ordering method in which high degrees of ground-state ordering can be achieved in a frustrated system.
The Aharanov-Bohm effect, magnetic monopoles and reversal in spin-ice lattices.
Pollard, Shawn D; Zhu, Yimei
2013-06-01
The proof of the Aharonov-Bohm (AB) effect has been one of the most important experiments of the last century and used as essential evidence for the theory of gauge fields. In this article, we look at its fundamental relation to the Dirac monopole and string. Despite the Dirac string being invisible to the AB effect, it can be used to study emergent quasiparticles in condensed matter settings that behave similar to the fundamental monopoles and strings between them. We utilize phase-imaging method based on the AB effect to study the ordering in a one-model system - that of frustrated spin ice - to understand the ordering processes that occur during a magnetic field reversal cycle. The reversal is linked to the propagation of monopole defects linked by flux channels, reminiscent of Dirac strings. Monopole interactions govern the defect densities within the lattice. Furthermore, we exploit these interactions to propose a new ordering method in which high degrees of ground-state ordering can be achieved in a frustrated system. PMID:23549453
Topological insulator Bi2Te3 nanowire field effect devices
NASA Astrophysics Data System (ADS)
Jauregui, Luis A.; Zhang, Genqiang; Wu, Yue; Chen, Yong P.
2012-02-01
Bismuth telluride (Bi2Te3) has been studied extensively as one of the best thermoelectric materials and recently shown to be a prototype topological insulator with nontrivial conducting surface states. We have grown Bi2Te3 nanowires by a two-step solution phase reaction and characterized their material and structural properties by XRD, TEM, XPS and EDS. We fabricate both backgated (on SiO2/Si) and top-gated (with ALD high-k gate dielectric such as Al2O3 or HfO2) field effect devices on such nanowires with diameters ˜50nm. Ambipolar field effect and a resistance modulation of up to 600% at low temperatures have been observed. The 4-terminal resistance shows insulating behavior (increasing with decreasing temperature) from 300 K to 50K, then saturates in a plateau for temperatures below 50K, consistent with the presence of metallic surface state. Aharonov--Bohm (AB) oscillations are observed in the magneto-resistance with a magnetic field parallel to the nanowire, providing further evidence of the presence of surface state conduction Finally, a prominent weak anti-localization (WAL) feature that weakens with increasing magnetic field and/or temperature is observed in the magneto-resistance with a magnetic field perpendicular to the nanowire.
Fano-Rashba effect in thermoelectricity of a double quantum dot molecular junction.
Liu, Ys; Hong, Xk; Feng, Jf; Yang, Xf
2011-01-01
We examine the relation between the phase-coherent processes and spin-dependent thermoelectric effects in an Aharonov-Bohm (AB) interferometer with a Rashba quantum dot (QD) in each of its arm by using the Green's function formalism and equation of motion (EOM) technique. Due to the interplay between quantum destructive interference and Rashba spin-orbit interaction (RSOI) in each QD, an asymmetrical transmission node splits into two spin-dependent asymmetrical transmission nodes in the transmission spectrum and, as a consequence, results in the enhancement of the spin-dependent thermoelectric effects near the spin-dependent asymmetrical transmission nodes. We also examine the evolution of spin-dependent thermoelectric effects from a symmetrical parallel geometry to a configuration in series. It is found that the spin-dependent thermoelectric effects can be enhanced by controlling the dot-electrode coupling strength. The simple analytical expressions are also derived to support our numerical results.PACS numbers: 73.63.Kv; 71.70.Ej; 72.20.Pa. PMID:22151740
Quantum Phenomena Observed Using Electrons
Tonomura, Akira
2011-05-06
Electron phase microscopy based on the Aharonov-Bohm (AB) effect principle has been used to illuminate fundamental phenomena concerning magnetism and superconductivity by visualizing quantitative magnetic lines of force. This paper deals with confirmation experiments on the AB effect, the magnetization process of tiny magnetic heads for perpendicular recording, and vortex behaviors in high-Tc superconductors.
NASA Astrophysics Data System (ADS)
Varma, Ram K.
2013-01-01
The article should include the following section: Acknowledgment This work was supported by the Platinum Jubilee Fellowship of the National Academy of Sciences of India, which is gratefully acknowledged.
Measurement of Aharonov-Casher effect in a Josephson junction chain
NASA Astrophysics Data System (ADS)
Pop, Ioan Mihai; Lecocq, Florent; Pannetier, Bernard; Buisson, Olivier; Guichard, Wiebke
2011-03-01
We have recently measured the effect of superconducting phase-slips on the ground state of a Josephson junction chain and a rhombi chain. Here we report clear evidence of Aharonov-Casher effect in a chain of Josephson junctions. This phenomenon is the dual of the well known Aharonov-Bohm interference. Using a capacitively coupled gate to the islands of the chain, we induce oscillations of the supercurrent by tuning the polarization charges on the islands. We observe complex interference patterns for different quantum phase slip amplitudes, that we understand quantitatively as Aharonov-Casher vortex interferences. European STREP MIDAS.
On the effects of a screw dislocation and a linear potential on the harmonic oscillator
NASA Astrophysics Data System (ADS)
Bueno, M. J.; Furtado, C.; Bakke, K.
2016-09-01
Quantum effects on the harmonic oscillator due to the presence of a linear scalar potential and a screw dislocation are investigated. By searching for bound states solutions, it is shown that an Aharonov-Bohm-type effect for bound states and a restriction of the values of the angular frequency of the harmonic oscillator can be obtained, where the allowed values are determined by the topology of the screw dislocation and the quantum numbers associated with the radial modes and the angular momentum. As particular cases, the angular frequency and the energy levels associated with the ground state and the first excited state of the system are obtained.
Bose-Einstein condensates in strong electric fields: Effective gauge potentials and rotating states
Kailasvuori, J.M.; Hansson, T.H.; Kavoulakis, G.M.
2002-11-01
Magnetically trapped atoms in Bose-Einstein condensates are spin polarized. Since the magnetic field is inhomogeneous, the atoms acquire Berry phases of the Aharonov-Bohm type during adiabatic motion. In the presence of an electric field, there is an additional Aharonov-Casher effect. Taking into account the limitations on the strength of the electric fields due to the polarizability of the atoms, we investigate the extent to which these effects can be used to induce rotation in a Bose-Einstein condensate.
NASA Astrophysics Data System (ADS)
Shech, Elay
2015-09-01
This paper looks at the nature of idealizations and representational structures appealed to in the context of the fractional quantum Hall effect, specifically, with respect to the emergence of anyons and fractional statistics. Drawing on an analogy with the Aharonov-Bohm effect, it is suggested that the standard approach to the effects—(what we may call) the topological approach to fractional statistics—relies essentially on problematic idealizations that need to be revised in order for the theory to be explanatory. An alternative geometric approach is outlined and endorsed. Roles for idealizations in science, as well as consequences for the debate revolving around so-called essential idealizations, are discussed.
Casimir force between two Aharonov-Bohm solenoids
Duru, I.H. )
1993-05-01
The vacuum structure for the massive charged scalar field in the region of two parallel, infinitely long and thin solenoids confining the fluxes n[sub 1] and n[sub 2] is studied. By using the Green function method, it is found that the vacuum expectation value of the system's energy has a finite mutual interaction term depending on the distance a between the solenoids, which implies an attractive force per unit length given by F[sub n1n2] = [minus]([h bar]c/[pi][sup 2])(n[sub 1]n[sub 2])[sup 2]/a[sup 3]. 11 refs.
Quantum gates with topological phases
Ionicioiu, Radu
2003-09-01
We investigate two models for performing topological quantum gates with the Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and two-qubit Abelian phases can be enacted with the AB effect using charge qubits, whereas the AC effect can be used to perform all single-qubit gates (Abelian and non-Abelian) for spin qubits. Possible experimental setups suitable for a solid-state implementation are briefly discussed.
Joe, Yong S; Lee, Sun H; Hedin, Eric R; Kim, Young D
2013-06-01
We utilize a two-dimensional four-channel DNA model, with a tight-binding (TB) Hamiltonian, and investigate the temperature and the magnetic field dependence of the transport behavior of a short DNA molecule. Random variation of the hopping integrals due to the thermal structural disorder, which partially destroy phase coherence of electrons and reduce quantum interference, leads to a reduction of the localization length and causes suppressed overall transmission. We also incorporate a variation of magnetic field flux density into the hopping integrals as a phase factor and observe Aharonov-Bohm (AB) oscillations in the transmission. It is shown that for non-zero magnetic flux, the transmission zero leaves the real-energy axis and moves up into the complex-energy plane. We also point out that the hydrogen bonds between the base pair with flux variations play a role to determine the periodicity of AB oscillations in the transmission.
Optical analog of the Iordanskii force in a Bose-Einstein condensate
Leonhardt, U.; Oehberg, P.
2003-05-01
A vortex in a Bose-Einstein condensate generates the optical analog of the Aharonov-Bohm effect when illuminated with slow light. In contrast to the original Aharonov-Bohm effect the vortex will exchange forces with the light that leads to a measurable motion of the vortex.
Experimental Realization of Strong Effective Magnetic Fields in an Optical Lattice
Aidelsburger, M.; Atala, M.; Trotzky, S.; Chen, Y.-A.; Bloch, I.; Nascimbene, S.
2011-12-16
We use Raman-assisted tunneling in an optical superlattice to generate large tunable effective magnetic fields for ultracold atoms. When hopping in the lattice, the accumulated phase shift by an atom is equivalent to the Aharonov-Bohm phase of a charged particle exposed to a staggered magnetic field of large magnitude, on the order of 1 flux quantum per plaquette. We study the ground state of this system and observe that the frustration induced by the magnetic field can lead to a degenerate ground state for noninteracting particles. We provide a measurement of the local phase acquired from Raman-induced tunneling, demonstrating time-reversal symmetry breaking of the underlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single atoms in the lattice exposed to the magnetic field is directly revealed.
Quantum mechanics : Intellectually delicious;
Peshkin, M.; Vaidman, L.
2010-03-01
It is 50 years since the discovery of the Aharonov-Bohm effect, and 25 years since that of the Berry phase. A celebration of this double anniversary at the University of Bristol made evident that these discoveries still offer much food for thought. The meeting celebrating the fiftieth anniversary of the Aharonov-Bohm effect and the twenty-fifth anniversary of the Berry phase was held on 14-15 December 2009 in the historic H. H.
Conductance phases in the quantum dots of an Aharonov-Bohm ring
NASA Astrophysics Data System (ADS)
Yahalom, A.; Englman, R.
2006-09-01
The regimes of growing phases (for electron numbers N≈0 8 ) that pass into regions of self-returning phases (for N>8 ), found recently in quantum dot conductances by Heiblum and co-workers are accounted for by an elementary Green’s function formalism, appropriate to an equi-spaced ladder structure (with at least three rungs) of electronic levels in the quantum dot. The key features of the theory are physically a dissipation rate that increases linearly with the level number (and is tentatively linked to coupling to longitudinal optical phonons) and a set of Fano-like metastable levels, which disturb the unitarity, and mathematically the changeover of the position of the complex transmission amplitude zeros from the upper half in the complex gap-voltage plane to the lower half of that plane. The two regimes are identified with (respectively) the Blaschke term and the Kramers-Kronig integral term in the theory of complex variables.
Exciton Storage in a Nanoscale Aharonov-Bohm Ring with Electric Field Tuning
Fischer, Andrea M.; Roemer, Rudolf A.; Campo, Vivaldo L. Jr.; Portnoi, Mikhail E.
2009-03-06
We study analytically the optical properties of a simple model for an electron-hole pair on a ring subjected to perpendicular magnetic flux and in-plane electric field. We show how to tune this excitonic system from optically active to optically dark as a function of these external fields. Our results offer a simple mechanism for exciton storage and readout.
Quantum interference in an electron-hole graphene ring system
Smirnov, D.; Schmidt, H.; Haug, R. J.
2013-12-04
Quantum interference is observed in a graphene ring system via the Aharonov Bohm effect. As graphene is a gapless semiconductor, this geometry allows to study the unique situation of quantum interference between electrons and holes in addition to the unipolar quantum interference. The period and amplitude of the observed Aharonov-Bohm oscillations are independent of the sign of the applied gate voltage showing the equivalence between unipolar and dipolar interference.
NASA Astrophysics Data System (ADS)
Saharian, A. A.
2016-09-01
We investigate the vacuum expectation value of the current density for a charged scalar field on a slice of anti-de Sitter (AdS) space with toroidally compact dimensions. Along the compact dimensions periodicity conditions are imposed on the field operator with general phases and the presence of a constant gauge field is assumed. The latter gives rise to Aharonov-Bohm-like effects on the vacuum currents. The current density along compact dimensions is a periodic function of the gauge field flux with the period equal to the flux quantum. It vanishes on the AdS boundary and, near the horizon, to the leading order, it is conformally related to the corresponding quantity in Minkowski bulk for a massless field. For large values of the length of the compact dimension compared with the AdS curvature radius, the vacuum current decays as power-law for both massless and massive fields. This behavior is essentially different from the corresponding one in Minkowski background, where the currents for a massive field are suppressed exponentially.
Zeeman effect on surface electron transport in topological insulator Bi2Se3 nanoribbons
NASA Astrophysics Data System (ADS)
Wang, Li-Xian; Yan, Yuan; Zhang, Liang; Liao, Zhi-Min; Wu, Han-Chun; Yu, Da-Peng
2015-10-01
Topological insulators have exotic surface states that are massless Dirac fermions, manifesting special magnetotransport properties, such as the Aharonov-Bohm effect, Shubnikov-de Haas oscillations, and weak antilocalization effects. In the surface Dirac cone, the band structures are typically closely related to the p-orbitals and possess helical orbital texture. Here we report on the tunability of the transport properties via the interaction between the magnetic field and the spin-orbital angular momentum of the surface states in individual Bi2Se3 nanoribbons. Because the surface states have a large Landé factor and helical spin-orbital texture, the in-plane magnetic field induced Zeeman energy will result in the deformation of the Dirac cone, which gives rise to spin polarization of the surface states. The spin-dependent scattering of the conducting electrons on the existing local magnetic moments produces a giant negative magnetoresistance. The negative magnetoresistance is robust with a ratio of -20% at 2 K and -0.5% at 300 K under 14 T. The results are valuable for possible orbital-electronics based on topological insulators.Topological insulators have exotic surface states that are massless Dirac fermions, manifesting special magnetotransport properties, such as the Aharonov-Bohm effect, Shubnikov-de Haas oscillations, and weak antilocalization effects. In the surface Dirac cone, the band structures are typically closely related to the p-orbitals and possess helical orbital texture. Here we report on the tunability of the transport properties via the interaction between the magnetic field and the spin-orbital angular momentum of the surface states in individual Bi2Se3 nanoribbons. Because the surface states have a large Landé factor and helical spin-orbital texture, the in-plane magnetic field induced Zeeman energy will result in the deformation of the Dirac cone, which gives rise to spin polarization of the surface states. The spin-dependent scattering of
Deletion of nfnAB in Thermoanaerobacterium saccharolyticum and Its Effect on Metabolism
Lo, Jonathan; Zheng, Tianyong; Olson, Daniel G.; Ruppertsberger, Natalie; Tripathi, Shital A.; Guss, Adam M.
2015-01-01
ABSTRACT NfnAB catalyzes the reversible transfer of electrons from reduced ferredoxin and NADH to 2 NADP+. The NfnAB complex has been hypothesized to be the main enzyme for ferredoxin oxidization in strains of Thermoanaerobacterium saccharolyticum engineered for increased ethanol production. NfnAB complex activity was detectable in crude cell extracts of T. saccharolyticum. Activity was also detected using activity staining of native PAGE gels. The nfnAB gene was deleted in different strains of T. saccharolyticum to determine its effect on end product formation. In wild-type T. saccharolyticum, deletion of nfnAB resulted in a 46% increase in H2 formation but otherwise little change in other fermentation products. In two engineered strains with 80% theoretical ethanol yield, loss of nfnAB caused two different responses: in one strain, ethanol yield decreased to about 30% of the theoretical value, while another strain had no change in ethanol yield. Biochemical analysis of cell extracts showed that the ΔnfnAB strain with decreased ethanol yield had NADPH-linked alcohol dehydrogenase (ADH) activity, while the ΔnfnAB strain with unchanged ethanol yield had NADH-linked ADH activity. Deletion of nfnAB caused loss of NADPH-linked ferredoxin oxidoreductase activity in all cell extracts. Significant NADH-linked ferredoxin oxidoreductase activity was seen in all cell extracts, including those that had lost nfnAB. This suggests that there is an unidentified NADH:ferredoxin oxidoreductase (distinct from nfnAB) playing a role in ethanol formation. The NfnAB complex plays a key role in generating NADPH in a strain that had become reliant on NADPH-ADH activity. IMPORTANCE Thermophilic anaerobes that can convert biomass-derived sugars into ethanol have been investigated as candidates for biofuel formation. Many anaerobes have been genetically engineered to increase biofuel formation; however, key aspects of metabolism remain unknown and poorly understood. One example is the
Deletion of nfnAB in Thermoanaerobacterium saccharolyticum and Its Effect on Metabolism
Lo, Jonathan; Zheng, Tianyong; Olson, Daniel G.; Ruppertsberger, Natalie; Tripathi, Shital A.; Guss, Adam M.; Lynd, Lee R.
2015-06-29
NfnAB catalyzes the reversible transfer of electrons from reduced ferredoxin and NADH to 2 NADP^{+}. The NfnAB complex has been hypothesized to be the main enzyme for ferredoxin oxidization in strains of Thermoanaerobacterium saccharolyticum engineered for increased ethanol production. NfnAB complex activity was detectable in crude cell extracts of T. saccharolyticum. In this paper, activity was also detected using activity staining of native PAGE gels. The nfnAB gene was deleted in different strains of T. saccharolyticum to determine its effect on end product formation. In wild-type T. saccharolyticum, deletion of nfnAB resulted in a 46% increase in H_{2} formation but otherwise little change in other fermentation products. In two engineered strains with 80% theoretical ethanol yield, loss of nfnAB caused two different responses: in one strain, ethanol yield decreased to about 30% of the theoretical value, while another strain had no change in ethanol yield. Biochemical analysis of cell extracts showed that the ΔnfnAB strain with decreased ethanol yield had NADPH-linked alcohol dehydrogenase (ADH) activity, while the ΔnfnAB strain with unchanged ethanol yield had NADH-linked ADH activity. Deletion of nfnAB caused loss of NADPH-linked ferredoxin oxidoreductase activity in all cell extracts. Significant NADH-linked ferredoxin oxidoreductase activity was seen in all cell extracts, including those that had lost nfnAB. This suggests that there is an unidentified NADH:ferredoxin oxidoreductase (distinct from nfnAB) playing a role in ethanol formation. The NfnAB complex plays a key role in generating NADPH in a strain that had become reliant on NADPH-ADH activity. Importance: Thermophilic anaerobes that can convert biomass-derived sugars into ethanol have been investigated as candidates for biofuel formation. Many anaerobes have been genetically engineered to increase biofuel formation; however, key aspects of metabolism remain unknown and poorly
Deletion of nfnAB in Thermoanaerobacterium saccharolyticum and Its Effect on Metabolism
Lo, Jonathan; Zheng, Tianyong; Olson, Daniel G.; Ruppertsberger, Natalie; Tripathi, Shital A.; Guss, Adam M.; Lynd, Lee R.
2015-06-29
NfnAB catalyzes the reversible transfer of electrons from reduced ferredoxin and NADH to 2 NADP+. The NfnAB complex has been hypothesized to be the main enzyme for ferredoxin oxidization in strains of Thermoanaerobacterium saccharolyticum engineered for increased ethanol production. NfnAB complex activity was detectable in crude cell extracts of T. saccharolyticum. In this paper, activity was also detected using activity staining of native PAGE gels. The nfnAB gene was deleted in different strains of T. saccharolyticum to determine its effect on end product formation. In wild-type T. saccharolyticum, deletion of nfnAB resulted in a 46% increase in H2 formation butmore » otherwise little change in other fermentation products. In two engineered strains with 80% theoretical ethanol yield, loss of nfnAB caused two different responses: in one strain, ethanol yield decreased to about 30% of the theoretical value, while another strain had no change in ethanol yield. Biochemical analysis of cell extracts showed that the ΔnfnAB strain with decreased ethanol yield had NADPH-linked alcohol dehydrogenase (ADH) activity, while the ΔnfnAB strain with unchanged ethanol yield had NADH-linked ADH activity. Deletion of nfnAB caused loss of NADPH-linked ferredoxin oxidoreductase activity in all cell extracts. Significant NADH-linked ferredoxin oxidoreductase activity was seen in all cell extracts, including those that had lost nfnAB. This suggests that there is an unidentified NADH:ferredoxin oxidoreductase (distinct from nfnAB) playing a role in ethanol formation. The NfnAB complex plays a key role in generating NADPH in a strain that had become reliant on NADPH-ADH activity. Importance: Thermophilic anaerobes that can convert biomass-derived sugars into ethanol have been investigated as candidates for biofuel formation. Many anaerobes have been genetically engineered to increase biofuel formation; however, key aspects of metabolism remain unknown and poorly understood. One
Magnetic doping and kondo effect in bi(2)se(3) nanoribbons.
Cha, Judy J; Williams, James R; Kong, Desheng; Meister, Stefan; Peng, Hailin; Bestwick, Andrew J; Gallagher, Patrick; Goldhaber-Gordon, David; Cui, Yi
2010-03-10
A simple surface band structure and a large bulk band gap have allowed Bi2Se3 to become a reference material for the newly discovered three-dimensional topological insulators, which exhibit topologically protected conducting surface states that reside inside the bulk band gap. Studying topological insulators such as Bi2Se3 in nanostructures is advantageous because of the high surface-to-volume ratio, which enhances effects from the surface states; recently reported Aharonov-Bohm oscillation in topological insulator nanoribbons by some of us is a good example. Theoretically, introducing magnetic impurities in topological insulators is predicted to open a small gap in the surface states by breaking time-reversal symmetry. Here, we present synthesis of magnetically doped Bi2Se3 nanoribbons by vapor-liquid-solid growth using magnetic metal thin films as catalysts. Although the doping concentration is less than approximately 2%, low-temperature transport measurements of the Fe-doped Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K, confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The capability to dope topological insulator nanostructures magnetically opens up exciting opportunities for spintronics.
Zeeman effect on surface electron transport in topological insulator Bi2Se3 nanoribbons.
Wang, Li-Xian; Yan, Yuan; Zhang, Liang; Liao, Zhi-Min; Wu, Han-Chun; Yu, Da-Peng
2015-10-28
Topological insulators have exotic surface states that are massless Dirac fermions, manifesting special magnetotransport properties, such as the Aharonov-Bohm effect, Shubnikov-de Haas oscillations, and weak antilocalization effects. In the surface Dirac cone, the band structures are typically closely related to the p-orbitals and possess helical orbital texture. Here we report on the tunability of the transport properties via the interaction between the magnetic field and the spin-orbital angular momentum of the surface states in individual Bi2Se3 nanoribbons. Because the surface states have a large Landé factor and helical spin-orbital texture, the in-plane magnetic field induced Zeeman energy will result in the deformation of the Dirac cone, which gives rise to spin polarization of the surface states. The spin-dependent scattering of the conducting electrons on the existing local magnetic moments produces a giant negative magnetoresistance. The negative magnetoresistance is robust with a ratio of -20% at 2 K and -0.5% at 300 K under 14 T. The results are valuable for possible orbital-electronics based on topological insulators. PMID:26400635
Zeeman effect on surface electron transport in topological insulator Bi2Se3 nanoribbons.
Wang, Li-Xian; Yan, Yuan; Zhang, Liang; Liao, Zhi-Min; Wu, Han-Chun; Yu, Da-Peng
2015-10-28
Topological insulators have exotic surface states that are massless Dirac fermions, manifesting special magnetotransport properties, such as the Aharonov-Bohm effect, Shubnikov-de Haas oscillations, and weak antilocalization effects. In the surface Dirac cone, the band structures are typically closely related to the p-orbitals and possess helical orbital texture. Here we report on the tunability of the transport properties via the interaction between the magnetic field and the spin-orbital angular momentum of the surface states in individual Bi2Se3 nanoribbons. Because the surface states have a large Landé factor and helical spin-orbital texture, the in-plane magnetic field induced Zeeman energy will result in the deformation of the Dirac cone, which gives rise to spin polarization of the surface states. The spin-dependent scattering of the conducting electrons on the existing local magnetic moments produces a giant negative magnetoresistance. The negative magnetoresistance is robust with a ratio of -20% at 2 K and -0.5% at 300 K under 14 T. The results are valuable for possible orbital-electronics based on topological insulators.
NASA Astrophysics Data System (ADS)
Moulopoulos, K.
2015-06-01
A quantum system that lies nearby a magnetic or time-varying electric field region, and that is under periodic boundary conditions parallel to the interface, is shown to exhibit a "hidden" Aharonov-Bohm effect (magnetic or electric), caused by fluxes that are not enclosed by, but are merely neighboring to our system - its origin being the absence of magnetic monopoles in 3D space (with corresponding spacetime generalizations). Novel possibilities then arise, where a field-free system can be dramatically affected by manipulating fields in an adjacent or even distant land, provided that these nearby fluxes are not quantized (i.e. they are fractional or irrational parts of the flux quantum). Topological effects (such as Quantum Hall types of behaviors) can therefore be induced from outside our system (that is always field-free and can even reside in simply-connected space). Potential novel applications are outlined, and exotic consequences in solid state physics are pointed out (i.e. the possibility of field-free quantum periodic systems that violate Bloch's theorem), while formal analogies with certain high energy physics phenomena and with some rather under-explored areas in mechanics and thermodynamics are noted.
Resonant Transmission through Serially Connected Hexagonal Nanorings with Magnetic Flux Effects
NASA Astrophysics Data System (ADS)
Hedin, Eric; Joe, Yong
Nanostructures composed of six quantum dots (QDs) connected in a ring are linked together in a linear chain with each ring separated by a coupling segment from adjoining rings. A tight-binding model is used to obtain the electron transmission through an arbitrary number of rings in series as a function of energy, external magnetic field, coupling parameters, and QD site energy values. Modifications of the transmission band structure as a function of external field, due to the Aharonov-Bohm and Zeeman effects, demonstrate control over the conductance properties of the linear chain of nano-rings. Resonant transmission effects (with electron energy equal to the QD site energy values) show a complex dependence upon an interplay of magnetic flux, inter-ring coupling, and the strength of the coupling between the ring system and the external leads. For specific values of lead and ring couplings, nearly full transmission (ballistic transport) is seen to occur across a broad energy range, independent of the number of rings in series. Partially supported by BSU ASPiRE program.
Moulopoulos, Konstantinos; Constantinou, Martha
2004-12-15
By using a Green's function procedure we determine exactly the energy spectrum and the associated eigenstates of a system of two oppositely charged particles interacting through a contact potential and moving in a one-dimensional ring threaded by a magnetic flux. Critical interactions for the appearance of bound states are analytically determined and are viewed as limiting cases of many-body results from the area of interaction-induced metal-insulator transitions in charged quantal mixtures. Analytical expressions on one-body probability and charge current densities for this overall neutral system are derived and their single-valuedness leads to the possibility of states with broken symmetry, with possible experimental signatures in exciton spectra. Persistent currents are analytically determined and their properties investigated from the point of view of an interacting mesoscopic system. A cyclic adiabatic process on the interaction potential is also identified, with the associated Berry's phase directly linked to the electric (persistent) currents, the probability currents having no contribution for a neutral system.
Monoclonal antibody, mAb 4C13, an effective detoxicant antibody against ricin poisoning.
Dong, Na; Luo, Longlong; Wu, Junhua; Jia, Peiyuan; Li, Qian; Wang, Yuxia; Gao, Zhongcai; Peng, Hui; Lv, Ming; Huang, Chunqian; Feng, Jiannan; Li, Hua; Shan, Junjie; Han, Gang; Shen, Beifen
2015-07-31
Ricin is a glycoprotein produced in castor seeds and consists of two polypeptide chains named Ricin Toxin A Chain (RTA) and Ricin Toxin B Chain (RTB), linked via a disulfide bridge. Due to its high toxicity, ricin is regarded as a high terrorist risk for the public. However, antibodies can play a pivotal role in neutralizing the toxin. In this research, the anti-toxicant effect of mAb 4C13, a monoclonal antibody (mAb) established using detoxicated ricin as the immunized antigen, was evaluated. Compared with mAb 4F2 and mAb 5G6, the effective mechanism of mAb 4C13 was analyzed by experiments relating to its cytotoxicity, epitope on ricin, binding kinetics with the toxin, its blockage on the protein synthesis inhibition induced by ricin and the intracelluar tracing of its complex with ricin. Our result indicated that mAb 4C13 could recognize and bind to RTA, RTB and exert its high affinity to the holotoxin. Both cytotoxicity and animal toxicity of ricin were well blocked by pre-incubating the toxin with mAb 4C13. By intravenous injection, mAb 4C13 could rescue the mouse intraperitoneally (ip) injected with a lethal dose of ricin (20μg/kg) even at 6h after the intoxication and its efficacy was dependent on its dosage. This research indicated that mAb 4C13 could be an excellent candidate for therapeutic antibodies. Its potent antitoxic efficiency was related to its recognition on the specific epitope with very high affinity and its blockage of protein synthesis inhibition in cytoplasm followed by cellular internalization with ricin.
Dynamic spin-flip shot noise of mesoscopic transport through a toroidal carbon nanotube
NASA Astrophysics Data System (ADS)
Zhao, H. K.; Zhang, J.; Wang, J.
2015-01-01
The shot noise in a toroidal carbon nanotube (TCN) interferometer under the perturbation of a rotating magnetic field (RMF) has been investigated. A general shot noise formula has been derived by calculating the current correlation. It was found that photon absorption and emission induce novel features of dynamic shot noise. The oscillatory behavior of shot noise and Fano factor vary with the Aharonov-Bohm (AB) magnetic flux, and they are sensitively dependent on the Zeeman energy, frequency of RMF, and source-drain bias. By adjusting the Zeeman energy, the AB oscillation structures of shot noise and Fano factor show valley-to-peak transformation. The shot noise increases nonlinearly with increasing the Zeeman energy and photon energy. The enhancement and asymmetry of shot noise can be attributed to the spin-flip effect.
NASA Astrophysics Data System (ADS)
Wu, Dianxing; Ye, Qingfu; Wang, Zhonghua; Xia, Yingwu
2004-01-01
The effects of gamma irradiation on the transgenic rice containing a synthetic cry1Ab gene from Bacillus thuringiensis were investigated. There was almost no difference in the content of the major nutritional components, i.e. crude protein, crude lipid, eight essential amino acids and total ash between the irradiated grains and the non-irradiated transgenic rice. However, the amounts of Cry1Ab protein and apparent amylose in the irradiated transgenic rice were reduced significantly by the doses higher than 200 Gy. In vivo observation showed that Cry1Ab protein contents also decreased in the fresh leaf tissues of survival seedlings after irradiation with 200 Gy or higher doses and showed inhibition of seedling growth. The results indicate that gamma irradiation might improve the quality of transgenic rice due to removal of the toxic Cry1Ab protein.
Topological quantum scattering under the influence of a nontrivial boundary condition
NASA Astrophysics Data System (ADS)
Mota, Herondy
2016-04-01
We consider the quantum scattering problem of a relativistic particle in (2 + 1)-dimensional cosmic string spacetime under the influence of a nontrivial boundary condition imposed on the solution of the Klein-Gordon equation. The solution is then shifted as consequence of the nontrivial boundary condition and the role of the phase shift is to produce an Aharonov-Bohm-like effect. We examine the connection between this phase shift and the electromagnetic and gravitational analogous of the Aharonov-Bohm effect and compare the present results with previous ones obtained in the literature, also considering non-relativistic cases.
Effective pair potentials using an ab initio variational approach
NASA Astrophysics Data System (ADS)
Faussurier, Gérald; Blancard, Christophe; Silvestrelli, Pier Luigi
2010-01-01
We used a variational approach adapted to a quantum molecular-dynamics code to determine the best reference potential for warm dense aluminum. This ab initio variational approach was based on the Gibbs-Bogolyubov inequality. We used many-body reference systems interacting through inverse-power-law potentials, among which the Coulomb potential was a particular case defining the classical one-component plasma model. By comparisons with full quantum molecular-dynamics simulations, we found that the Coulomb potential was not always the best reference potential. We calculated the self-diffusion coefficient and the shear viscosity and discussed the results obtained using the Chisolm-Wallace relation in the warm dense matter regime.
Topological effects in quantum mechanics
Peshkin, M.; Lipkin, H.J. |
1995-08-01
We completed our analysis of experiments, some completed, some planned, and some only conceptual at present, that purport to demonstrate new kinds of non-local and topological effects in the interaction of a neutron with an external electromagnetic field. In the Aharonov-Casher effect (AC), the neutron interacts with an electric field and in the Scalar Aharonov-Bohm effect (SAB) the neutron interacts with a magnetic field. In both cases, the geometry can be arranged so that there is no force on the neutron but an interference experiment nevertheless finds a phase shift proportional to the applied field and to the neutron`s magnetic moment. Previously, we showed that the accepted interpretation of these phenomena as topological effects due to a non-local interaction between the neutron and the electromagnetic field is incorrect. Both AC and SAB follow from local torques on the neutron whose expectation values vanish at every instant but which have non-vanishing effect on the measurable spin-correlation variables S(t) = (1/2) [{sigma}{sub x}{sigma}{sub x}(t) + {sigma}{sub y}(0){sigma}{sub y}(t) + h.c.] and V(t) = [{sigma}{sub x}(0){sigma}{sub y}(t) - {sigma}{sub y}(0){sigma}{sub x}(t) + h.c.]. We have now completed this work by observing that a criterion often used for identifying a topological effect, energy independence of the phase shift between two arms of an interferometer, is only a necessary condition, and by describing a phase shifter which obeys the energy-independence condition but whose interaction with the neutron is neither topological nor even non-local.
Marusich, Julie A.; Lefever, Timothy W.; Antonazzo, Kateland R.; Wallgren, Michael T.; Cortes, Ricardo A.; Patel, Purvi R.; Grabenauer, Megan; Moore, Katherine N.
2015-01-01
Diversion of synthetic cannabinoids for abuse began in the early 2000s. Despite legislation banning compounds currently on the drug market, illicit manufacturers continue to release new compounds for recreational use. This study examined new synthetic cannabinoids, AB-CHMINACA (N-[1-amino-3-methyl-oxobutan-2-yl]-1-[cyclohexylmethyl]-1H-indazole-3-carboxamide), AB-PINACA [N-(1-amino-3-methyl-1-oxobutan-2-yl)-1-pentyl-1H-indazole-3-carboxamide], and FUBIMINA [(1-(5-fluoropentyl)-1H-benzo[d]imadazol-2-yl)(naphthalen-1-yl)methanone], with the hypothesis that these compounds, like those before them, would be highly susceptible to abuse. Cannabinoids were examined in vitro for binding and activation of CB1 receptors, and in vivo for pharmacological effects in mice and in Δ9-tetrahydrocannabinol (Δ9-THC) discrimination. AB-CHMINACA, AB-PINACA, and FUBIMINA bound to and activated CB1 and CB2 receptors, and produced locomotor suppression, antinociception, hypothermia, and catalepsy. Furthermore, these compounds, along with JWH-018 [1-pentyl-3-(1-naphthoyl)indole], CP47,497 [rel-5-(1,1-dimethylheptyl)-2-[(1R,3S)-3-hydroxycyclohexyl]-phenol], and WIN55,212-2 ([(3R)-2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenyl-methanone, monomethanesulfonate), substituted for Δ9-THC in Δ9-THC discrimination. Rank order of potency correlated with CB1 receptor-binding affinity, and all three compounds were full agonists in [35S]GTPγS binding, as compared with the partial agonist Δ9-THC. Indeed, AB-CHMINACA and AB-PINACA exhibited higher efficacy than most known full agonists of the CB1 receptor. Preliminary analysis of urinary metabolites of the compounds revealed the expected hydroxylation. AB-PINACA and AB-CHMINACA are of potential interest as research tools due to their unique chemical structures and high CB1 receptor efficacies. Further studies on these chemicals are likely to include research on understanding cannabinoid receptors
Wiley, Jenny L; Marusich, Julie A; Lefever, Timothy W; Antonazzo, Kateland R; Wallgren, Michael T; Cortes, Ricardo A; Patel, Purvi R; Grabenauer, Megan; Moore, Katherine N; Thomas, Brian F
2015-09-01
Diversion of synthetic cannabinoids for abuse began in the early 2000s. Despite legislation banning compounds currently on the drug market, illicit manufacturers continue to release new compounds for recreational use. This study examined new synthetic cannabinoids, AB-CHMINACA (N-[1-amino-3-methyl-oxobutan-2-yl]-1-[cyclohexylmethyl]-1H-indazole-3-carboxamide), AB-PINACA [N-(1-amino-3-methyl-1-oxobutan-2-yl)-1-pentyl-1H-indazole-3-carboxamide], and FUBIMINA [(1-(5-fluoropentyl)-1H-benzo[d]imadazol-2-yl)(naphthalen-1-yl)methanone], with the hypothesis that these compounds, like those before them, would be highly susceptible to abuse. Cannabinoids were examined in vitro for binding and activation of CB1 receptors, and in vivo for pharmacological effects in mice and in Δ(9)-tetrahydrocannabinol (Δ(9)-THC) discrimination. AB-CHMINACA, AB-PINACA, and FUBIMINA bound to and activated CB1 and CB2 receptors, and produced locomotor suppression, antinociception, hypothermia, and catalepsy. Furthermore, these compounds, along with JWH-018 [1-pentyl-3-(1-naphthoyl)indole], CP47,497 [rel-5-(1,1-dimethylheptyl)-2-[(1R,3S)-3-hydroxycyclohexyl]-phenol], and WIN55,212-2 ([(3R)-2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenyl-methanone, monomethanesulfonate), substituted for Δ(9)-THC in Δ(9)-THC discrimination. Rank order of potency correlated with CB1 receptor-binding affinity, and all three compounds were full agonists in [(35)S]GTPγS binding, as compared with the partial agonist Δ(9)-THC. Indeed, AB-CHMINACA and AB-PINACA exhibited higher efficacy than most known full agonists of the CB1 receptor. Preliminary analysis of urinary metabolites of the compounds revealed the expected hydroxylation. AB-PINACA and AB-CHMINACA are of potential interest as research tools due to their unique chemical structures and high CB1 receptor efficacies. Further studies on these chemicals are likely to include research on understanding cannabinoid
Ab initio study of piezomagnetic effect in Mn-antiperovskites
NASA Astrophysics Data System (ADS)
Sandeman, Karl; Gercsi, Zsolt; Zemen, Jan
2015-03-01
The magnetocaloric and magnetoelastic coupling that often occur together in magnetically frustrated materials have great potential for practical applications ranging from magnetic refrigeration to data processing and storage. Here we focus on the manganese antiperovskite family. Negative thermal expansion (NTE) close to the Néel temperature and a large magnetovolume effect have been measured recently in Mn3NiN using temperature dependent neutron powder diffraction. A large piezomagnetic effect has been predicted in Mn3GaN from Density Functional Theory (DFT) calculations. We perform a computational study of the piezomagnetic effect in three metallic Mn3XN antiperovskites, based our recent DFT model of anisotropic thermal expansions and large magnetoelastic coupling. We confirm the existence of a fully compensated non-collinear antiferromagnetic ground state and predict canting and the change of magnitude of the Mn local magnetic moments as a function of applied biaxial strain, finding that the induced net magnetization reaches values of 0.1 μB per Mn per 1% of strain. The research leading to these results has received funding from the European Community's 7th Framework Programme under Grant agreement 310748 ``DRREAM.''
NASA Astrophysics Data System (ADS)
Timko, Jeff; Kuyucak, Serdar
2012-11-01
Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K+ ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K+ ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K+ ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K+ ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.
Timko, Jeff; Kuyucak, Serdar
2012-11-28
Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K(+) ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K(+) ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K(+) ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K(+) ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.
Solution of Coulomb system in momentum space
Lin, D.-H.
2008-02-15
The solution of D-dimensional Coulomb system is solved in momentum space by path integral. From which the topological effect of a magnetic flux in the system is given. It is revealed that the flux effect represented by the two-dimensional field of Aharonov-Bohm covers any space-dimensions.
Suppression of decoherence in a graphene monolayer ring
Smirnov, D. Rode, J. C.; Haug, R. J.
2014-08-25
The influence of high magnetic fields on coherent transport is investigated. A monolayer graphene quantum ring is fabricated and the Aharonov-Bohm effect is observed. For increased magnitude of the magnetic field, higher harmonics appear. This phenomenon is attributed to an increase of the phase coherence length due to reduction of spin flip scattering.
Nontrivial systems and the necessity of the scalar quantum mechanics axioms
Kotulek, Jan
2009-06-15
We discuss the necessity of the axioms of scalar quantum mechanics introduced by Paschke and clearly demonstrate their geometric and/or physical meaning. We show that reasonable nonrelativistic quantum mechanics is exactly specified by the axioms. A system describing the electric Aharonov-Bohm effect is presented. It illustrates the topological obstructions for the existence of a Hamiltonian.
How to Test Atom and Neutron Neutrality with Atom Interferometry
Arvanitaki, Asimina; Dimopoulos, Savas; Geraci, Andrew A.; Hogan, Jason; Kasevich, Mark
2008-03-28
We propose an atom-interferometry experiment based on the scalar Aharonov-Bohm effect which detects an atom charge at the 10{sup -28}e level, and improves the current laboratory limits by 8 orders of magnitude. This setup independently probes neutron charges down to 10{sup -28}e, 7 orders of magnitude below current bounds.
Testing Atom and Neutron Neutrality with Atom Interferometry
Arvanitaki, Asimina; Dimopoulos, Savas; Geraci, Andrew A.; Hogan, Jason; Kasevich, Mark; /Stanford U., Phys. Dept.
2008-01-07
We propose an atom-interferometry experiment based on the scalar Aharonov-Bohm effect which detects an atom charge at the 10{sup -28} e level, and improves the current laboratory limits by 8 orders of magnitude. This setup independently probes neutron charges down to 10{sup 28} e, 7 orders of magnitude below current bounds.
Usui, Masaru; Nagai, Hidetaka; Hiki, Mototaka; Tamura, Yutaka; Asai, Tetsuo
2013-01-01
Understanding the impact of antimicrobial use on the emergence of resistant bacteria is imperative to prevent its emergence. For instance, activation of the AcrAB efflux pumps is responsible for the emergence of antimicrobial-resistant Salmonella strains. Here, we examined the expression levels of acrB and its multiple regulator genes (RamA, SoxS, MarA, and Rob) in 17 field isolates of S. Choleraesuis by using quantitative PCR methods. The expression of acrB increased in eight of the field isolates (P < 0.05). The expression of acrB was associated with that of ramA in one isolate, soxS in one isolate, and both these genes in six isolates. Thereafter, to examine the effect of selected antimicrobials (enrofloxacin, ampicillin, oxytetracycline, kanamycin, and spectinomycin) on the expression of acrB and its regulator genes, mutants derived from five isolates of S. Choleraesuis were selected by culture on antimicrobial-containing plates. The expression of acrB and ramA was higher in the mutants selected using enrofloxacin (3.3–6.3- and 24.5–37.7-fold, respectively), ampicillin (1.8–7.7- and 16.1–55.9-fold, respectively), oxytetracycline (1.7–3.3- and 3.2–31.1-fold, respectively), and kanamycin (1.6–2.2- and 5.6–26.4-fold, respectively), which are AcrAB substrates, than in each of the parental strains (P < 0.05). In contrast, in AcrAB substrate-selected mutants, the expression of soxS, marA, and rob remained similar to that in parental strains. Of the four antimicrobials, the level of ramA expression was significantly higher in the enrofloxacin- and ampicillin-selected mutants than in the oxytetracycline- and kanamycin-selected mutants (P < 0.05), whereas the expression levels of acrB and multiple regulator genes in spectinomycin-selected mutants were similar to those in each parental strain. These data suggest that exposure to antimicrobials that are AcrAB substrates enhance the activation of the AcrAB efflux pump via RamA, but not via Sox
Casimir effect for scalar current densities in topologically nontrivial spaces
NASA Astrophysics Data System (ADS)
Bellucci, S.; Saharian, A. A.; Saharyan, N. A.
2015-08-01
We evaluate the Hadamard function and the vacuum expectation value (VEV) of the current density for a charged scalar field, induced by flat boundaries in spacetimes with an arbitrary number of toroidally compactified spatial dimensions. The field operator obeys the Robin conditions on the boundaries and quasiperiodicity conditions with general phases along compact dimensions. In addition, the presence of a constant gauge field is assumed. The latter induces Aharonov-Bohm-type effect on the VEVs. There is a region in the space of the parameters in Robin boundary conditions where the vacuum state becomes unstable. The stability condition depends on the lengths of compact dimensions and is less restrictive than that for background with trivial topology. The vacuum current density is a periodic function of the magnetic flux, enclosed by compact dimensions, with the period equal to the flux quantum. It is explicitly decomposed into the boundary-free and boundary-induced contributions. In sharp contrast to the VEVs of the field squared and the energy-momentum tensor, the current density does not contain surface divergences. Moreover, for Dirichlet condition it vanishes on the boundaries. The normal derivative of the current density on the boundaries vanish for both Dirichlet and Neumann conditions and is nonzero for general Robin conditions. When the separation between the plates is smaller than other length scales, the behavior of the current density is essentially different for non-Neumann and Neumann boundary conditions. In the former case, the total current density in the region between the plates tends to zero. For Neumann boundary condition on both plates, the current density is dominated by the interference part and is inversely proportional to the separation.
Quantum fluctuations and isotope effects in ab initio descriptions of water
Wang, Lu; Markland, Thomas E.; Ceriotti, Michele
2014-09-14
Isotope substitution is extensively used to investigate the microscopic behavior of hydrogen bonded systems such as liquid water. The changes in structure and stability of these systems upon isotope substitution arise entirely from the quantum mechanical nature of the nuclei. Here, we provide a fully ab initio determination of the isotope exchange free energy and fractionation ratio of hydrogen and deuterium in water treating exactly nuclear quantum effects and explicitly modeling the quantum nature of the electrons. This allows us to assess how quantum effects in water manifest as isotope effects, and unravel how the interplay between electronic exchange and correlation and nuclear quantum fluctuations determine the structure of the hydrogen bond in water.
Ab initio molecular dynamics of solvation effects on reactivity at electrified interfaces.
Herron, Jeffrey A; Morikawa, Yoshitada; Mavrikakis, Manos
2016-08-23
Using ab initio molecular dynamics as implemented in periodic, self-consistent (generalized gradient approximation Perdew-Burke-Ernzerhof) density functional theory, we investigated the mechanism of methanol electrooxidation on Pt(111). We investigated the role of water solvation and electrode potential on the energetics of the first proton transfer step, methanol electrooxidation to methoxy (CH3O) or hydroxymethyl (CH2OH). The results show that solvation weakens the adsorption of methoxy to uncharged Pt(111), whereas the binding energies of methanol and hydroxymethyl are not significantly affected. The free energies of activation for breaking the C-H and O-H bonds in methanol were calculated through a Blue Moon Ensemble using constrained ab initio molecular dynamics. Calculated barriers for these elementary steps on unsolvated, uncharged Pt(111) are similar to results for climbing-image nudged elastic band calculations from the literature. Water solvation reduces the barriers for both C-H and O-H bond activation steps with respect to their vapor-phase values, although the effect is more pronounced for C-H bond activation, due to less disruption of the hydrogen bond network. The calculated activation energy barriers show that breaking the C-H bond of methanol is more facile than the O-H bond on solvated negatively biased or uncharged Pt(111). However, with positive bias, O-H bond activation is enhanced, becoming slightly more facile than C-H bond activation. PMID:27503889
Ab initio molecular dynamics of solvation effects on reactivity at electrified interfaces
NASA Astrophysics Data System (ADS)
Herron, Jeffrey A.; Morikawa, Yoshitada; Mavrikakis, Manos
2016-08-01
Using ab initio molecular dynamics as implemented in periodic, self-consistent (generalized gradient approximation Perdew-Burke-Ernzerhof) density functional theory, we investigated the mechanism of methanol electrooxidation on Pt(111). We investigated the role of water solvation and electrode potential on the energetics of the first proton transfer step, methanol electrooxidation to methoxy (CH3O) or hydroxymethyl (CH2OH). The results show that solvation weakens the adsorption of methoxy to uncharged Pt(111), whereas the binding energies of methanol and hydroxymethyl are not significantly affected. The free energies of activation for breaking the C-H and O-H bonds in methanol were calculated through a Blue Moon Ensemble using constrained ab initio molecular dynamics. Calculated barriers for these elementary steps on unsolvated, uncharged Pt(111) are similar to results for climbing-image nudged elastic band calculations from the literature. Water solvation reduces the barriers for both C-H and O-H bond activation steps with respect to their vapor-phase values, although the effect is more pronounced for C-H bond activation, due to less disruption of the hydrogen bond network. The calculated activation energy barriers show that breaking the C-H bond of methanol is more facile than the O-H bond on solvated negatively biased or uncharged Pt(111). However, with positive bias, O-H bond activation is enhanced, becoming slightly more facile than C-H bond activation.
Ab Initio Classical Dynamics Simulations of CO_2 Line-Mixing Effects in Infrared Bands
NASA Astrophysics Data System (ADS)
Lamouroux, Julien; Hartmann, Jean-Michel; Tran, Ha; Snels, Marcel; Stefani, Stefania; Piccioni, Giuseppe
2013-06-01
Ab initio calculations of line-mixing effects in CO_2 infrared bands are presented and compared with experiments. The predictions were carried using requantized Classical Dynamics Molecular Simulations (rCDMS) based on an approach previously developed and successfully tested for CO_2 isolated line shapes. Using classical dynamics equations, the force and torque applied to each molecule by the surrounding molecules (described by an ab initio intermolecular potential) are computed at each time step. This enables, using a requantization procedure, to predict dipole and isotropic polarizability auto-correlation functions whose Fourier-Laplace transforms yield the spectra. The quality of the rCDMS calculations is demonstrated by comparisons with measured spectra in the spectral regions of the 3ν_3 and 2ν_1+2ν_2+ν_3 Infrared bands. J.-M. Hartmann, H. Tran, N. H. Ngo, et al., Phys. Rev. Lett. A {87} (2013), 013403. H. Tran, C. Boulet, M. Snels, S. Stefani, J. Quant. Spectrosc. Radiat. Transfer {112} (2011), 925-936.
Yu, Kuang; Carter, Emily A
2014-03-28
The density functional theory (DFT)+U method is an efficient and effective way to calculate the ground-state properties of strongly correlated transition metal compounds, with the effective U parameters typically determined empirically. Two ab initio methods have been developed to compute the U parameter based on either constrained DFT (CDFT) or unrestricted Hartree-Fock (UHF) theory. Previous studies have demonstrated the success of both methods in typical open-shell materials such as FeO and NiO. In this Communication we report numerical instability issues that arise for the CDFT method when applied to closed-shell transition metals, by using ZnO and Cu2O as examples. By contrast, the UHF method behaves much more robustly for both closed- and open-shell materials, making it more suitable for treating closed-shell transition metals, as well as main group elements. PMID:24697417
NASA Astrophysics Data System (ADS)
Yu, Kuang; Carter, Emily A.
2014-03-01
The density functional theory (DFT)+U method is an efficient and effective way to calculate the ground-state properties of strongly correlated transition metal compounds, with the effective U parameters typically determined empirically. Two ab initio methods have been developed to compute the U parameter based on either constrained DFT (CDFT) or unrestricted Hartree-Fock (UHF) theory. Previous studies have demonstrated the success of both methods in typical open-shell materials such as FeO and NiO. In this Communication we report numerical instability issues that arise for the CDFT method when applied to closed-shell transition metals, by using ZnO and Cu2O as examples. By contrast, the UHF method behaves much more robustly for both closed- and open-shell materials, making it more suitable for treating closed-shell transition metals, as well as main group elements.
Schroyen, M; Goddeeris, B M; Stinckens, A; Verhelst, R; Janssens, S; Cox, E; Georges, M; Niewold, T; Buys, N
2013-03-15
Diarrhoea in neonatal and early-weaned piglets due to enterotoxigenic Escherichia coli-F4 (ETEC-F4) is an important problem in the pig farming industry. There is substantial evidence for a genetic basis for susceptibility to ETEC-F4 since not all pigs suffer from diarrhoea after an ETEC-F4 infection. A region on SSC13 has been found to be in close linkage to the susceptibility of piglets for ETEC-F4ab,ac. Potential candidate genes on SSC13 have been examined and although some polymorphisms were found to be in linkage disequilibrium with the phenotype, the causative mutation has not yet been found. In this study we are looking at the expression of porcine genes in relation to ETEC-F4ab,ac. With the aid of the Affymetrix GeneChip Porcine Genome Array we were able to find differentially expressed genes between ETEC-F4ab,ac receptor positive (Fab,acR(+)) piglets without diarrhoea and F4ab,acR(+) piglets with diarrhoea or F4ab,acR(-) animals. Since the susceptibility to ETEC-F4ab,ac was described as a Mendelian trait, it is not so surprisingly that only two differentially expressed genes, transferrin receptor (TFRC) and trefoil factor 1 (TFF1), came out of the analysis. Although both genes could pass for functional candidate genes only TFRC also mapped to the region on SSC13 associated with susceptibility for ETEC-F4, which makes TFRC a positional functional candidate gene. Validation by qRT-PCR confirmed the differential expression of TFRC and TFF1. In piglets without diarrhoea, the expression of both genes was higher in F4ab,acR(+) than in F4ab,acR(-) piglets. Similarly, TFRC and TFF1 expression in F4ab,acR(+) piglets without diarrhoea was also higher than in F4ab,acR(+) piglets with diarrhoea. Consequently, although both genes might not play a role as receptor for F4 fimbriae, they could be of great importance during an ETEC-F4 outbreak. An upregulation of TFRC can be a consequence of the piglets ability to raise an effective immune response. An elevation of TFF1, a
Ab initio Approach to Effective Single-Particle Energies in Doubly Closed Shell Nuclei
Duguet, T.
2012-01-01
The present work discusses, from an ab initio standpoint, the definition, the meaning, and the usefulness of effective single-particle energies (ESPEs) in doubly closed shell nuclei. We perform coupled-cluster calculations to quantify to what extent selected closed-shell nuclei in the oxygen and calcium isotopic chains can effectively be mapped onto an effective independent-particle picture. To do so, we revisit in detail the notion of ESPEs in the context of strongly correlated many-nucleon systems and illustrate the necessity of extracting ESPEs through the diagonalization of the centroid matrix, as originally argued by Baranger. For the purpose of illustration, we analyze the impact of correlations on observable one-nucleon separation energies and nonobservable ESPEs in selected closed-shell oxygen and calcium isotopes. We then state and illustrate the nonobservability of ESPEs. Similarly to spectroscopic factors, ESPEs can indeed be modified by a redefinition of inaccessible quantities while leaving actual observables unchanged. This leads to the absolute necessity of employing consistent structure and reaction models based on the same nuclear Hamiltonian to extract the shell structure in a meaningful fashion from experimental data.
Ab initio study of the effect of vacancies on the thermal conductivity of boron arsenide
NASA Astrophysics Data System (ADS)
Protik, Nakib Haider; Carrete, Jesús; Katcho, Nebil A.; Mingo, Natalio; Broido, David
2016-07-01
Using a first principles theoretical approach, we show that vacancies give anomalously strong suppression of the lattice thermal conductivity κ of cubic Boron arsenide (BAs), which has recently been predicted to have an exceptionally high κ . This effect is tied to the unusually large phonon lifetimes in BAs and results in a stronger reduction in the BAs κ than occurs in diamond. The large changes in bonding around vacancies cannot be accurately captured using standard perturbative methods and are instead treated here using an ab initio Green function approach. As and B vacancies are found to have similar effects on κ . In contrast, we show that commonly used mass disorder models for vacancies fail for large mass ratio compounds such as BAs, incorrectly predicting much stronger (weaker) phonon scattering when the vacancy is on the heavy (light) atom site. The quantitative treatment given here contributes to fundamental understanding of the effect of point defects on thermal transport in solids and provides guidance to synthesis efforts to grow high quality BAs.
Wang, Zhi; Tian, Yun; Tan, Shuduan; Dong, Shengzhang; Song, Qisheng
2013-01-01
To assess the safety of transgenic rice expressing Cry1Ab protein to vertebrates, the effect of Cry1Ab rice on broad health indicators in blood and various organs of Swiss rats were analyzed. The 30 and 90 day safety studies of Cry1Ab rice on female Swiss rats revealed that Cry1Ab rice had no significant effect on the several elements of blood lymph including hemogram, calcium ion concentration and apoptosis rate of lymphocytes, indicating that Cry1Ab protein could not affect the blood lymph of Swiss rat. Similarly, Cry1Ab rice had no effect on enzyme activities in a variety of organs of Swiss rat. However, Cry1Ab rice did have significant effects on the blood biochemistry indexes including urea, triglyceride (TG), glutamic oxalacetic transaminase (AST) and alkaline phosphatase (ALP) after the rats were fed with Cry1Ab rice for 30 days, but not after 90 days, indicating that Cry1Ab protein may influence blood metabolism for a short duration. Quantitative real-time PCR (qPCR) analysis of the 6 genes encoding enzymes responsible for the major detoxification functions of liver revealed that Cry1Ab rice exerted no influences on the levels of these transcripts in liver of Swiss rat, indicating that significant differences registered in part of the blood biochemical parameters in the 30 day study might result from other untested organs or tissues in response to the stress of exogenous Cry1Ab protein. The results suggest that Cry1Ab protein has no significant long-term (90 day) effects on female Swiss rat. PMID:24312218
Wang, Yang; Wei, Baoyang; Tian, Yixing; Wang, Zhi; Tian, Yun; Tan, Shuduan; Dong, Shengzhang; Song, Qisheng
2013-01-01
To assess the safety of transgenic rice expressing Cry1Ab protein to vertebrates, the effect of Cry1Ab rice on broad health indicators in blood and various organs of Swiss rats were analyzed. The 30 and 90 day safety studies of Cry1Ab rice on female Swiss rats revealed that Cry1Ab rice had no significant effect on the several elements of blood lymph including hemogram, calcium ion concentration and apoptosis rate of lymphocytes, indicating that Cry1Ab protein could not affect the blood lymph of Swiss rat. Similarly, Cry1Ab rice had no effect on enzyme activities in a variety of organs of Swiss rat. However, Cry1Ab rice did have significant effects on the blood biochemistry indexes including urea, triglyceride (TG), glutamic oxalacetic transaminase (AST) and alkaline phosphatase (ALP) after the rats were fed with Cry1Ab rice for 30 days, but not after 90 days, indicating that Cry1Ab protein may influence blood metabolism for a short duration. Quantitative real-time PCR (qPCR) analysis of the 6 genes encoding enzymes responsible for the major detoxification functions of liver revealed that Cry1Ab rice exerted no influences on the levels of these transcripts in liver of Swiss rat, indicating that significant differences registered in part of the blood biochemical parameters in the 30 day study might result from other untested organs or tissues in response to the stress of exogenous Cry1Ab protein. The results suggest that Cry1Ab protein has no significant long-term (90 day) effects on female Swiss rat.
Sumner, Isaiah; Iyengar, Srinivasan S
2007-10-18
We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.
NASA Astrophysics Data System (ADS)
Miwa, R. H.; Kagimura, R.; Lima, Matheus P.; Fazzio, A.
2015-05-01
We have performed an ab initio theoretical study of the energetic stability and the electronic properties of pristine and hydrogen-adsorbed grain boundaries (GBs) in silicene. We find that GBs in silicene present lower formation energy when compared with their counterparts in graphene. Removing the inversion symmetry, by applying an external electric field perpendicular to the silicene sheet, we verify the formation of valley-indexed metallic states lying along the GBs, characterizing the quantum valley Hall effect (QVHE). Here, we find the maintenance of the QVHE upon the presence of disordered and asymmetric geometries along the GBs. Those metallic states are suppressed upon the adsorption of H adatoms along the GBs. The H adatoms promote an unbalance on the electronic occupation of the unsaturated π electrons beside the hydrogenated GB rows, giving rise to (i) a net magnetic moment on the Si atoms along the edge sites of the hydrogenated GBs and (ii) an electronic band structure characterized by spin-polarized valley states protected against backscattering processes.
NASA Astrophysics Data System (ADS)
Katayama-Yoshida, Hiroshi; Nakanishi, Akitaka; Uede, Hiroki; Takawashi, Yuki; Fukushima, Tetsuya; Sato, Kazunori
2014-03-01
Based upon ab initio electronic structure calculation, I will discuss the general rule of negative effective U system by (1) exchange-correlation-induced negative effective U caused by the stability of the exchange-correlation energy in Hund's rule with high-spin ground states of d5 configuration, and (2) charge-excitation-induced negative effective U caused by the stability of chemical bond in the closed-shell of s2, p6, and d10 configurations. I will show the calculated results of negative effective U systems such as hole-doped CuAlO2 and CuFeS2. Based on the total energy calculations of antiferromagnetic and ferromagnetic states, I will discuss the magnetic phase diagram and superconductivity upon hole doping. I also discuss the computational materials design method of high-Tc superconductors by ab initio calculation to go beyond LDA and multi-scale simulations.
Detection and Characterization of the Effect of AB-FUBINACA and Its Metabolites in a Rat Model.
Hsin-Hung Chen, Michael; Dip, Aybike; Ahmed, Mostafa; Tan, Michael L; Walterscheid, Jeffrey P; Sun, Hua; Teng, Ba-Bie; Mozayani, Ashraf
2016-04-01
Synthetic cannabinoids were originally developed by academic and pharmaceutical laboratories with the hope of providing therapeutic relief from the pain of inflammatory and degenerative diseases. However, recreational drug enthusiasts have flushed the market with new strains of these potent drugs that evade detection yet endanger public health and safety. Although many of these drug derivatives were published in the medical literature, others were merely patented without further characterization. AB-FUBINACA is an example of one of the new indazole-carboxamide synthetic cannabinoids introduced in the past year. Even though AB-FUBINACA has become increasingly prominent in forensic drug and toxicology specimens analyses, little is known about the pharmacology of this substance. To study its metabolic fate, we utilized Wistar rats to study the oxidative products of AB-FUBINACA in urine and its effect on gene expressions in liver and heart. Rats were injected with 5 mg/kg of AB-FUBINACA each day for 5 days. Urine samples were collected every day at the same time. On day 5 after treatment, we collected the organs such as liver and heart. The urine samples were analyzed by mass spectrometry, which revealed several putative metabolites and positioning of the hydroxyl addition on the molecule. We used quantitative PCR gene expression array to analyze the hepatotoxicity and cardiotoxicity on these rats and confirmed by real-time quantitative RT-PCR. We identified three genes significantly associated with dysfunction of oxidation and inflammation. Our study reports in vivo metabolites of AB-FUBINACA in urine and its effect on the gene expressions in liver and heart.
Marsalek, Ondrej; Markland, Thomas E
2016-02-01
Path integral molecular dynamics simulations, combined with an ab initio evaluation of interactions using electronic structure theory, incorporate the quantum mechanical nature of both the electrons and nuclei, which are essential to accurately describe systems containing light nuclei. However, path integral simulations have traditionally required a computational cost around two orders of magnitude greater than treating the nuclei classically, making them prohibitively costly for most applications. Here we show that the cost of path integral simulations can be dramatically reduced by extending our ring polymer contraction approach to ab initio molecular dynamics simulations. By using density functional tight binding as a reference system, we show that our ring polymer contraction scheme gives rapid and systematic convergence to the full path integral density functional theory result. We demonstrate the efficiency of this approach in ab initio simulations of liquid water and the reactive protonated and deprotonated water dimer systems. We find that the vast majority of the nuclear quantum effects are accurately captured using contraction to just the ring polymer centroid, which requires the same number of density functional theory calculations as a classical simulation. Combined with a multiple time step scheme using the same reference system, which allows the time step to be increased, this approach is as fast as a typical classical ab initio molecular dynamics simulation and 35× faster than a full path integral calculation, while still exactly including the quantum sampling of nuclei. This development thus offers a route to routinely include nuclear quantum effects in ab initio molecular dynamics simulations at negligible computational cost.
Detection and Characterization of the Effect of AB-FUBINACA and Its Metabolites in a Rat Model.
Hsin-Hung Chen, Michael; Dip, Aybike; Ahmed, Mostafa; Tan, Michael L; Walterscheid, Jeffrey P; Sun, Hua; Teng, Ba-Bie; Mozayani, Ashraf
2016-04-01
Synthetic cannabinoids were originally developed by academic and pharmaceutical laboratories with the hope of providing therapeutic relief from the pain of inflammatory and degenerative diseases. However, recreational drug enthusiasts have flushed the market with new strains of these potent drugs that evade detection yet endanger public health and safety. Although many of these drug derivatives were published in the medical literature, others were merely patented without further characterization. AB-FUBINACA is an example of one of the new indazole-carboxamide synthetic cannabinoids introduced in the past year. Even though AB-FUBINACA has become increasingly prominent in forensic drug and toxicology specimens analyses, little is known about the pharmacology of this substance. To study its metabolic fate, we utilized Wistar rats to study the oxidative products of AB-FUBINACA in urine and its effect on gene expressions in liver and heart. Rats were injected with 5 mg/kg of AB-FUBINACA each day for 5 days. Urine samples were collected every day at the same time. On day 5 after treatment, we collected the organs such as liver and heart. The urine samples were analyzed by mass spectrometry, which revealed several putative metabolites and positioning of the hydroxyl addition on the molecule. We used quantitative PCR gene expression array to analyze the hepatotoxicity and cardiotoxicity on these rats and confirmed by real-time quantitative RT-PCR. We identified three genes significantly associated with dysfunction of oxidation and inflammation. Our study reports in vivo metabolites of AB-FUBINACA in urine and its effect on the gene expressions in liver and heart. PMID:26517302
Marsalek, Ondrej; Markland, Thomas E
2016-02-01
Path integral molecular dynamics simulations, combined with an ab initio evaluation of interactions using electronic structure theory, incorporate the quantum mechanical nature of both the electrons and nuclei, which are essential to accurately describe systems containing light nuclei. However, path integral simulations have traditionally required a computational cost around two orders of magnitude greater than treating the nuclei classically, making them prohibitively costly for most applications. Here we show that the cost of path integral simulations can be dramatically reduced by extending our ring polymer contraction approach to ab initio molecular dynamics simulations. By using density functional tight binding as a reference system, we show that our ring polymer contraction scheme gives rapid and systematic convergence to the full path integral density functional theory result. We demonstrate the efficiency of this approach in ab initio simulations of liquid water and the reactive protonated and deprotonated water dimer systems. We find that the vast majority of the nuclear quantum effects are accurately captured using contraction to just the ring polymer centroid, which requires the same number of density functional theory calculations as a classical simulation. Combined with a multiple time step scheme using the same reference system, which allows the time step to be increased, this approach is as fast as a typical classical ab initio molecular dynamics simulation and 35× faster than a full path integral calculation, while still exactly including the quantum sampling of nuclei. This development thus offers a route to routinely include nuclear quantum effects in ab initio molecular dynamics simulations at negligible computational cost. PMID:26851913
Liang, Yan; Wu, Xueqiong; Zhang, Junxian; Xiao, Li; Yang, Yourong; Bai, Xuejuan; Yu, Qi; Li, Zhongming; Bi, Lan; Li, Ning; Wu, Xiaoli
2012-12-01
The situation of tuberculosis (TB) is very severe in China. New therapeutic agents or regimens to treat TB are urgently needed. In this study, Mycobacterium tuberculosis-infected mice were given immunotherapy intramuscularly with Ag85A/B chimeric DNA or saline, plasmid vector pVAX1, or Mycobacterium vaccae vaccine. The mice treated with Ag85A/B chimeric DNA showed significantly higher numbers of T cells secreting interferon-gamma (IFN-γ), more IFN-γ in splenocyte culture supernatant, more Th1 and Tc1 cells, and higher ratios of Th1/Th2 and Tc1/Tc2 cells in whole blood, indicating a predominant Th1 immune response to treatment. Infected mice treated with doses of 100 μg Ag85A/B chimeric DNA had an extended time until death of 50% of the animals that was markedly longer than the saline and vector control groups, and the death rate at 1 month after the last dose was lower than that in the other groups. Compared with the saline group, 100 μg Ag85A/B chimeric DNA and 100 μg Ag85A DNA reduced the pulmonary bacterial loads by 0.79 and 0.45 logs, and the liver bacterial loads by 0.52 and 0.50 logs, respectively. Pathological changes in the lungs were less, and the lesions were more limited. These results show that Ag85A/B chimeric DNA was effective for the treatment of TB, significantly increasing the cellular immune response and inhibiting the growth of M. tuberculosis.
Metformin Enhances the Therapy Effects of Anti-IGF-1R mAb Figitumumab to NSCLC
Cao, Hongxin; Dong, Wei; Qu, Xiao; Shen, Hongchang; Xu, Jun; Zhu, Linhai; Liu, Qi; Du, Jiajun
2016-01-01
The insulin-like growth factor (IGF) signaling system plays a critical role in tumorigenesis, highlighting the potential of targeting IGF-1R as an anti-cancer therapy. Although multiple anti-IGF-1R monoclonal antibody (mAb) drugs have been developed, challenges remain in the validation of the therapeutic effects and understanding the molecular mechanism of these mAbs. Herein, we conducted a study to validate the effect of Figitumumab (CP), an anti-IGF-1R mAb, in a panel of non-small cell lung cancer (NSCLC) cell lines. We found all tested cell lines were sensitive to CP, and CP could block IGF-1R and the downstream PI3K/AKT pathway activation. Unexpectedly, we found CP could activate ERK signaling pathway in IGF-1R kinase independent manner, which we further verified was mainly mediated by β-arrestin2. We also investigated the anti-tumor effect of metformin alone as well as its combination with CP to target NSCLC. Metformin could target IGF-1R signaling pathway by attenuating PI3K/AKT and MEK/ERK signaling pathways and down-regulating IGF-1R. Finally, we found that combining metformin with CP could further induce IGF-1R down-regulation and was more effective to target NSCLC cells. Our data suggests the combining of metformin with CP has additive therapeutic value against NSCLC. PMID:27488947
NASA Astrophysics Data System (ADS)
Sælen, L.; Birkeland, T.; Sisourat, N.; Hansen, J. P.; Dubois, A.
2009-11-01
Following ab initio 1D and 2D calculations by Sisourat et. al. [1] we here report full three dimensional calculations of the single ionization of an H2-molecule by a highly charged Kr+34 ion at high velocity impact (60 MeV/u). Prior theoretical investigations have all failed to account for any second order interference effects. Final results will be presented at the conference.
Dane Morgan
2010-06-10
The project began March 13, 2006, allocated for three years, and received a one year extension from March 13, 2009 to March 12, 2010. It has now completed 48 of 48 total months. The project was focused on using ab initio methods to gain insights into radiation induced segregation (RIS) in Ni-Fe-Cr alloys. The project had the following key accomplishments • Development of a large database of ab initio energetics that can be used by many researchers in the future for increased understanding of this system. For example, we have the first calculations showing a dramatic stabilization effect of Cr-Cr interstitial dumbbells in Ni. • Prediction of both vacancy and interstitial diffusion constants for Ni-Cr and Ni-Fe for dilute Cr and Fe. This work included generalization of widely used multifrequency models to make use of ab initio derived energetics and thermodynamics. • Prediction of qualitative trends of RIS from vacancy and interstitial mechanisms, suggesting the two types of defect fluxes drive Cr RIS in opposite directions. • Detailed kinetic Monte Carlo modeling of diffusion by vacancy mechanism in Ni-Cr as a function of Cr concentration. The results demonstrate that Cr content can have a significant effect on RIS. • Development of a quantitative RIS transport model, including models for thermodynamic factors and boundary conditions.
Barker, John R; Nguyen, Thanh Lam; Stanton, John F
2012-06-21
Calculations were carried out for 25 isotopologues of the title reaction for various combinations of (35)Cl, (37)Cl, (12)C, (13)C, (14)C, H, and D. The computed rate constants are based on harmonic vibrational frequencies calculated at the CCSD(T)/aug-cc-pVTZ level of theory and X(ij) vibrational anharmonicity coefficients calculated at the CCSD(T) /aug-cc-pVDZ level of theory. For some reactions, anharmonicity coefficients were also computed at the CCSD(T)/aug-cc-pVTZ level of theory. The classical reaction barrier was taken from Eskola et al. [J. Phys. Chem. A 2008, 112, 7391-7401], who extrapolated CCSD(T) calculations to the complete basis set limit. Rate constants were calculated for temperatures from ∼100 to ∼2000 K. The computed ab initio rate constant for the normal isotopologue is in good agreement with experiments over the entire temperature range (∼10% lower than the recommended experimental value at 298 K). The ab initio H/D kinetic isotope effects (KIEs) for CH(3)D, CH(2)D(2), CHD(3), and CD(4) are in very good agreement with literature experimental data. The ab initio (12)C/(13)C KIE is in error by ∼2% at 298 K for calculations using X(ij) coefficients computed with the aug-cc-pVDZ basis set, but the error is reduced to ∼1% when X(ij) coefficients computed with the larger aug-cc-pVTZ basis set are used. Systematic improvements appear to be possible. The present SCTST results are found to be more accurate than those from other theoretical calculations. Overall, this is a very promising method for computing ab initio kinetic isotope effects.
Effects of Mg II and Ca II ionization on ab-initio solar chromosphere models
NASA Technical Reports Server (NTRS)
Rammacher, W.; Cuntz, M.
1991-01-01
Acoustically heated solar chromosphere models are computed considering radiation damping by (non-LTE) emission from H(-) and by Mg II and Ca II emission lines. The radiative transfer equations for the Mg II k and Ca II K emission lines are solved using the core-saturation method with complete redistribution. The Mg II k and Ca II K cooling rates are compared with the VAL model C. Several substantial improvements over the work of Ulmschneider et al. (1987) are included. It is found that the rapid temperature rises caused by the ionization of Mg II are not formed in the middle chromosphere, but occur at larger atmospheric heights. These models represent the temperature structure of the 'real' solar chromosphere much better. This result is a major precondition for the study of ab-initio models for solar flux tubes based on MHD wave propagation and also for ab-initio models for the solar transition layer.
Postural Change Effects on Infants' AB Task Performance: Visual, Postural, or Spatial?
ERIC Educational Resources Information Center
Lew, Adina R.; Hopkins, Brian; Owen, Laura H.; Green, Michael
2007-01-01
Smith and colleagues (Smith, L. B., Thelen, E., Titzer, R., & McLin, D. (1999). Knowing in the context of acting: The task dynamics of the A-not-B error. "Psychological Review, 106," 235-260) demonstrated that 10-month-olds succeed on a Piagetian AB search task if they are moved from a sitting position to a standing position between A and B…
NASA Astrophysics Data System (ADS)
Auer, Alexander A.
2009-01-01
In this contribution high-level ab-initio calculations of the chemical shifts of methanol including zero-point vibrational and temperature corrections are presented. For the first time, secondary isotope effects have been calculated via second order vibrational perturbation theory. In comparison with recent experimental gas-phase data and in contrast to other quantum-chemical methods the results are consistent and in very good agreement with the experimental 13C, 17O and 1H chemical shifts reported by Makulski [W. Makulski, J. Mol. Struct. 872 (2008) 81]. Secondary isotope effects can be calculated with remarkable accuracy of a few hundredths of a ppm in comparison to experiment.
Lesinski, T.; Meyer, J.
2006-10-15
We study the effect of the splitting of neutron and proton effective masses with isospin asymmetry on the properties of the Skyrme energy density functional. We discuss the ability of the latter to predict observables of infinite matter and finite nuclei, paying particular attention to controlling the agreement with ab initio predictions of the spin-isospin content of the nuclear equation of state, as well as diagnosing the onset of finite size instabilities, which we find to be of critical importance. We show that these various constraints cannot be simultaneously fulfilled by the standard Skyrme force, calling at least for an extension of its P-wave part.
General relativity in electrical engineering
NASA Astrophysics Data System (ADS)
Leonhardt, U.; Philbin, T. G.
2007-05-01
In electrical engineering metamaterials have been developed that offer unprecedented control over electromagnetic fields. Here we show that general relativity lends the theoretical tools for designing devices made of such versatile materials. We consider media that facilitate space-time transformations and include negative refraction. Our theory unifies the concepts operating behind the scenes of perfect invisibility devices, perfect lenses, the optical Aharonov-Bohm effect and electromagnetic analogs of the event horizon, and may lead to further applications.
Bound on the Photon Charge from the Phase Coherence of Extragalactic Radiation
Altschul, Brett
2007-06-29
If the photon possessed a nonzero charge, then electromagnetic waves traveling along different paths would acquire Aharonov-Bohm phase differences. The fact that such an effect has not hindered interferometric astronomy places a bound on the photon charge estimated to be at the 10{sup -32}e level if all photons have the same charge and 10{sup -46}e if different photons can carry different charges.
Berry's phase for coherent states of Landau levels
Yang, Wen-Long; Chen, Jing-Ling
2007-02-15
The Berry phases for coherent states and squeezed coherent states of Landau levels are calculated. Coherent states of Landau levels are interpreted as a result of a magnetic flux moved adiabatically from infinity to a finite place on the plane. The Abelian Berry phase for coherent states of Landau levels is an analog of the Aharonov-Bohm effect. Moreover, the non-Abelian Berry phase is calculated for the adiabatic evolution of the magnetic field B.
Schuman, Joel S.; Brown, Eric N.
2016-01-01
Purpose To compare intraocular pressure (IOP) reduction and to develop a predictive surgery calculator based on the results between trabectome-mediated ab interno trabeculectomy in pseudophakic patients versus phacoemulsification combined with trabectome-mediated ab interno trabeculectomy in phakic patients. Methods This observational surgical cohort study analyzed pseudophakic patients who received trabectome-mediated ab interno trabeculectomy (AIT) or phacoemulsification combined with AIT (phaco-AIT). Follow up for less than 12 months or neovascular glaucoma led to exclusion. Missing data was imputed by generating 5 similar but non-identical datasets. Groups were matched using Coarsened Exact Matching based on age, gender, type of glaucoma, race, preoperative number of glaucoma medications and baseline intraocular pressure (IOP). Linear regression was used to examine the outcome measures consisting of IOP and medications. Results Of 949 cases, 587 were included consisting of 235 AIT and 352 phaco-AIT. Baseline IOP between groups was statistically significant (p≤0.01) in linear regression models and was minimized after Coarsened Exact Matching. An increment of 1 mmHg in baseline IOP was associated with a 0.73±0.03 mmHg IOP reduction. Phaco-AIT had an IOP reduction that was only 0.73±0.32 mmHg greater than that of AIT. The resulting calculator to determine IOP reduction consisted of the formula -13.54+0.73 × (phacoemulsification yes:1, no:0) + 0.73 × (baseline IOP) + 0.59 × (secondary open angle glaucoma yes:1, no:0) + 0.03 × (age) + 0.09 × (medications). Conclusions This predictive calculator for minimally invasive glaucoma surgery can assist clinical decision making. Only a small additional IOP reduction was observed when phacoemulsification was added to AIT. Patients with a higher baseline IOP had a greater IOP reduction. PMID:27077914
León, G; Stiles, B; Alape, A; Rojas, G; Gutiérrez, J M
1999-08-01
A comparative study was performed on the ability of IgG and F(ab')2 antivenoms to neutralize lethal and myotoxic activities of Micrurus nigrocinctus venom. Both antivenoms were adjusted to a similar neutralizing potency in experiments where venom and antivenoms were preincubated prior to injection. No significant differences were observed between IgG and F(ab')2 antivenoms concerning neutralization of lethal effect in rescue experiments, i.e., when antivenom was administered intravenously after envenomation. However, F(ab')2 antivenom was more effective in prolonging the time of death when subneutralizing doses were administered immediately after venom injection. Both products partially reversed the binding of M. nigrocinctus alpha-neurotoxins to acetylcholine receptor in vitro. The IgG and F(ab')2 antivenoms effectively neutralized venom-induced myotoxicity when administered intravenously immediately after envenomation, although neutralization was poor if antivenom injections were delayed. Intramuscular injection of venom promoted diffusion of antivenom antibodies throughout muscle tissue, and F(ab')2 diffused to a higher extent than IgG molecules. Thus, despite the observation that F(ab')2 antivenom was more effective than IgG antivenom in prolonging the time of death when subneutralizing doses were administered immediately after envenomation, no major differences were observed in antivenom neutralization of lethal and myotoxic effects or in their capacity to reverse neurotoxin binding to the acetylcholine receptor.
Higher-order elastic constants and megabar pressure effects of bcc tungsten: Ab initio calculations
NASA Astrophysics Data System (ADS)
Vekilov, Yu. Kh.; Krasilnikov, O. M.; Lugovskoy, A. V.; Lozovik, Yu. E.
2016-09-01
The general method for the calculation of n th (n ≥2 ) order elastic constants of the loaded crystal is given in the framework of the nonlinear elasticity theory. For the crystals of cubic symmetry under hydrostatic compression, the two schemes of calculation of the elastic constants of second, third, and fourth order from energy-finite strain relations and stress-finite strain relations are implemented. Both techniques are applied for the calculation of elastic constants of orders from second to fourth to the bcc phase of tungsten at a 0-600 GPa pressure range. The energy and stress at the various pressures and deformations are obtained ab initio in the framework of projector augmented wave+generalized gradient approximation (PAW+GGA) method, as implemented in Vienna Ab initio Simulation Package (VASP) code. Using the obtained results, we found the pressure dependence of Grüneisen parameters for long-wave acoustic modes in this interval. The Lamé constants of second and third order were estimated for polycrystalline tungsten. The proposed method is applicable for crystals with arbitrary symmetry.
Weston, Ralph E; Nguyen, Thanh Lam; Stanton, John F; Barker, John R
2013-02-01
Ab initio microcanonical rate constants were computed using Semi-Classical Transition State Theory (SCTST) and used in two master equation formulations (1D, depending on active energy with centrifugal corrections, and 2D, depending on total energy and angular momentum) to compute temperature-dependent rate constants for the title reactions using a potential energy surface obtained by sophisticated ab initio calculations. The 2D master equation was used at the P = 0 and P = ∞ limits, while the 1D master equation with centrifugal corrections and an empirical energy transfer parameter could be used over the entire pressure range. Rate constants were computed for 75 K ≤ T ≤ 2500 K and 0 ≤ [He] ≤ 10(23) cm(-3). For all temperatures and pressures important for combustion and for the terrestrial atmosphere, the agreement with the experimental rate constants is very good, but at very high pressures and T ≤ 200 K, the theoretical rate constants are significantly smaller than the experimental values. This effect is possibly due to the presence in the experiments of dimers and prereactive complexes, which were not included in the model calculations. The computed H/D kinetic isotope effects are in acceptable agreement with experimental data, which show considerable scatter. Overall, the agreement between experimental and theoretical H/D kinetic isotope effects is much better than in previous work, and an assumption of non-RRKM behavior does not appear to be needed to reproduce experimental observations.
van der Merwe, Frances; Bezuidenhout, Carlos; van den Berg, Johnnie; Maboeta, Mark
2012-01-01
A 28-day study was conducted to determine the effects of the Bacillus thuringiensis Cry1Ab toxin on the earthworm Eisenia andrei. Previously, investigations have been limited to life-cycle level effects of this protein on earthworms, and mostly on E. fetida. In this study several endpoints were compared which included biomass changes, cocoon production, hatching success, a cellular metal-stress biomarker (Neutral Red Retention Time; NRRT) and potential genotoxic effects in terms of Randomly Amplified Polymorphic DNA sequences (RAPDs). NRRT results indicated no differences between treatments (p > 0.36), and NRRT remained the same for both treatments at different times during the experiment (p = 0.18). Likewise, no significant differences were found for cocoon production (p = 0.32) or hatching success (p = 0.29). Conversely, biomass data indicated a significant difference between the control treatment and the Bt treatment from the second week onwards (p < 0.001), with the Bt treatment losing significantly more weight than the isoline treatment. Possible confounding factors were identified that might have affected the differences in weight loss between groups. From the RAPD profiles no conclusive data were obtained that could link observed genetic variation to exposure of E. andrei to Cry1Ab proteins produced by Bt maize. PMID:23235452
Bondzio, Angelika; Lodemann, Ulrike; Weise, Christoph; Einspanier, Ralf
2013-01-01
In vitro testing can contribute to reduce the risk that the use of genetically modified (GM) crops and their proteins show unintended toxic effects. Here we introduce a porcine intestinal cell culture (IPEC-J2) as appropriate in vitro model and tested the possible toxic potential of Cry1Ab protein, commonly expressed in GM-maize. For comprehensive risk assessment we used WST-1 conversion and ATP content as metabolic markers for proliferation, lactate dehydrogenase release as indicator for cells with compromised membrane and transepithelial electrical resistance as parameter indicating membrane barrier function. The results were compared to the effects of valinomycin, a potassium ionophore, known to induce cytotoxic effects in most mammalian cell types. Whereas no toxicity was observed after Cry1Ab treatment, valinomycin induced a decrease in IPEC-J2 viability. This was confirmed by dynamic monitoring of cellular responses. Additionally, two dimensional differential in-gel electrophoresis was performed. Only three proteins were differentially expressed. The functions of these proteins were associated with responses to stress. The up-regulation of heat shock protein Hsp70 was verified by Western blotting as well as by enzyme-linked immunosorbent assay and may be related to a protective function. These findings suggest that the combination of in vitro testing and proteomic analysis may serve as a promising tool for mechanism based safety assessment. PMID:23861753
Wikfeldt, K T; Michaelides, A
2014-01-28
Ab initio simulations that account for nuclear quantum effects have been used to examine the order-disorder transition in squaric acid, a prototypical H-bonded antiferroelectric crystal. Our simulations reproduce the >100 K difference in transition temperature observed upon deuteration as well as the strong geometrical isotope effect observed on intermolecular separations within the crystal. We find that collective transfer of protons along the H-bonding chains - facilitated by quantum mechanical tunneling - is critical to the order-disorder transition and the geometrical isotope effect. This sheds light on the origin of isotope effects and the importance of tunneling in squaric acid which likely extends to other H-bonded ferroelectrics.
Wikfeldt, K. T.; Michaelides, A.
2014-01-28
Ab initio simulations that account for nuclear quantum effects have been used to examine the order-disorder transition in squaric acid, a prototypical H-bonded antiferroelectric crystal. Our simulations reproduce the >100 K difference in transition temperature observed upon deuteration as well as the strong geometrical isotope effect observed on intermolecular separations within the crystal. We find that collective transfer of protons along the H-bonding chains – facilitated by quantum mechanical tunneling – is critical to the order-disorder transition and the geometrical isotope effect. This sheds light on the origin of isotope effects and the importance of tunneling in squaric acid which likely extends to other H-bonded ferroelectrics.
Mahmoud, A.; Erba, A. Dovesi, R.; Doll, K.
2014-06-21
A general methodology has been devised and implemented into the solid-state ab initio quantum-mechanical CRYSTAL program for studying the evolution under geophysical pressure of the elastic anisotropy of crystalline materials. This scheme, which fully exploits both translational and point symmetry of the crystal, is developed within the formal frame of one-electron Hamiltonians and atom-centered basis functions. Six silicate garnet end-members, among the most important rock-forming minerals of the Earth's mantle, are considered, whose elastic anisotropy is fully characterized under high hydrostatic compressions, up to 60 GPa. The pressure dependence of azimuthal anisotropy and shear-wave birefringence of seismic wave velocities for these minerals are accurately simulated and compared with available single-crystal measurements.
Ab initio study of the effect of vacancies on the thermal conductivity
NASA Astrophysics Data System (ADS)
Protik, Nakib; Carrete, Jesus; Mingo, Natalio; Katcho, Nebil; Broido, David
Point defects and vacancies in particular can have a profound impact on phonon thermal transport. Examples are seen in diamond and cubic boron arsenide where large C and As vacancy concentrations give much lower thermal conductivity than expected. Here, we calculate the phonon-vacancy scattering rates using an ab initioGreen's function approach, which treats the scattering to all orders in contrast to standard perturbation theory approaches. The lattice thermal conductivity, k, is calculated from first principles by solving the Boltzmann transport equation for phonons, with interatomic force constants determined using density functional theory. The reduction in k with vacancy defect density is assessed. The phonon-vacancy scattering can show significant differences using the Green's function method compared to what would be predicted from the perturbative Born approximation, consistent with previous findings for diamond.
Burns, Andrea; Raybould, Alan
2014-12-01
Event 5307 transgenic maize produces the novel insecticidal protein eCry3.1Ab, which is active against certain coleopteran pests such as Western corn rootworm (Diabrotica virgifera virgifera). Laboratory tests with representative nontarget organisms (NTOs) were conducted to test the hypothesis of no adverse ecological effects of cultivating Event 5307 maize. Estimates of environmental eCry3.1Ab concentrations for each NTO were calculated from the concentrations of eCry3.1Ab produced by 5307 maize in relevant plant tissues. Nontarget organisms were exposed to diets containing eCry3.1Ab or diets comprising Event 5307 maize tissue and evaluated for effects compared to control groups. No statistically significant differences in survival were observed between the control group and the group exposed to eCry3.1Ab in any organism tested. Measured eCry3.1Ab concentrations in the laboratory studies were equal to or greater than the most conservative estimates of environmental exposure. The laboratory studies corroborate the hypothesis of negligible ecological risk from the cultivation of 5307 maize.
Bai, Y Y; Yan, R H; Ye, G Y; Huang, F N; Cheng, J A
2010-02-01
During 2005-2008, field studies were conducted at two locations in Chongqing, China, to assess the potential effects of transgenic rice expressing Bacillus thuringiensis (Bt) Cry1Ab protein on the nontarget ground-dwelling collembolan community in three postharvest seasons. Collembolans in non-Bt and Bt rice fields were sampled with pitfall traps during each of two postharvest seasons of 2005/2006 and 2006/2007 and litterbag traps during each of three postharvest seasons of 2005/2006, 2006/2007, and 2007/2008. Ground-dwelling collembolans in rice fields during the postharvest seasons were abundant, whereas community densities varied considerably between the two locations and among the three seasons. A total of 67,310 collembolans, representing three species, Entomobrya griseoolivata, Hypogastrura matura, and Bourletiella christianseni, were captured during the three postharvest seasons. E. griseoolivata was the predominant species, accounting for 87.7% of the total captures, followed by H. matura (10.7%) and B. christianseni (1.6%). In general, there were no significant differences in species compositions and abundances of each species between Bt and non-Bt paddy fields, suggesting no significantly impact of plant residues of Cry1Ab rice on collembolan communities during postharvest seasons.
Jin, K.; Xiao, H. Y.; Zhang, Y.; Weber, W. J.
2014-05-19
Ab initio molecular dynamics simulations are performed to investigate the effects of a boron nitride (BN) substrate on Stone-Wales (SW) defect formation and recovery in graphene. It is found that SW defects can be created by an off-plane recoil atom that interacts with the BN substrate. A mechanism with complete bond breakage for formation of SW defects in suspended graphene is also revealed for recoils at large displacement angles. In addition, further irradiation can result in recovery of the SW defects through a bond rotation mechanism in both graphene and graphene/BN, and the substrate has little effect on the recovery process. This study indicates that the BN substrate enhances the irradiation resistance of graphene.
NASA Astrophysics Data System (ADS)
Seijo, Luis
1995-05-01
Presented in this paper, is a practical implementation of the use of the Wood-Boring Hamiltonian [Phys. Rev. B 18, 2701 (1978)] in atomic and molecular ab initio core model potential calculations (AIMP), as a means to include spin-orbit relativistic effects, in addition to the mass-velocity and Darwin operators, which were already included in the spin-free version of the relativistic AIMP method. Calculations on the neutral and singly ionized atoms of the halogen elements and sixth-row p-elements Tl-Rn are presented, as well as on the one or two lowest lying states of the diatomic molecules HX, HX+, (X=F, Cl, Br, I, At) TlH, PbH, BiH, and PoH. The calculated spin-orbit splittings and bonding properties show a stable, good quality, of the size of what can be expected from an effective potential method.
Pisani, Cesare; Erba, Alessandro; Ferrabone, Matteo; Dovesi, Roberto
2012-07-28
In the frame of the Born-Oppenheimer approximation, nuclear motions in crystals can be simulated rather accurately using a harmonic model. In turn, the electronic first-order density matrix (DM) can be expressed as the statistically weighted average over all its determinations each resulting from an instantaneous nuclear configuration. This model has been implemented in a computational scheme which adopts an ab initio one-electron (Hartree-Fock or Kohn-Sham) Hamiltonian in the CRYSTAL program. After selecting a supercell of reasonable size and solving the corresponding vibrational problem in the harmonic approximation, a Metropolis algorithm is adopted for generating a sample of nuclear configurations which reflects their probability distribution at a given temperature. For each configuration in the sample the "instantaneous" DM is calculated, and its contribution to the observables of interest is extracted. Translational and point symmetry of the crystal as reflected in its average DM are fully exploited. The influence of zero-point and thermal motion of nuclei on such important first-order observables as x-ray structure factors and Compton profiles can thus be estimated.
NASA Astrophysics Data System (ADS)
Kamelian, Fariba Sadat; Mousavi, Seyed Mahmoud; Ahmadpour, Ali
2015-12-01
The present study focuses on the aluminum oxide (Al2O3) and titanium oxide (TiO2) entrapped acrylonitrile-butadiene-styrene (ABS) membranes prepared from phase inversion method. The effect of Al2O3 and TiO2 nanoparticles on the hydrophilicity, tensile strength, thermal stability, permeate flux, and rejection of wastewater pollution indices was investigated. Some of the membranes were exposed to ultraviolet (UV) irradiation. Al2O3 and TiO2 nanoparticles generally improved performance of the membranes. Thermal stability and tensile strength of the membranes were also enhanced in the presence of the nanoparticles. Increasing the nanoparticles concentration increased viscosity of the casting solutions. The UV irradiated membranes had better performance than the non-irradiated ones.
Colciago, Alessandra; Celotti, Fabio; Casati, Lavinia; Giancola, Rinaldo; Castano, Stefano M.; Antonini, Guido; Sacchi, Maria Cristina; Negri-Cesi, Paola
2009-01-01
PDGF is a major constituent of platelet rich plasma (PRP), responsible of chemotactic and possibly of mitogenic effects of PRP on osteoblasts. PDGF family includes 5 isoforms: PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD, all expressed in platelets except PDGF-DD. Aim of this study was to analyze the effect of recombinant hPDGF-A, -AB, -B and -C, on migration and proliferation of a human osteoblastic cell line, SaOS-2. Preliminary observations on cell migration were also done in primary cultures of human osteoblasts. In vitro microchemotaxis and 3H-thymidine mitogenic assays were used. While PDGF-AB is active at concentrations present in PRP, PDGF-AA and BB are chemotactic only at much higher doses. PDGF-C is totally inactive alone or together with the active isoforms. PDGF-AA, PDGF-BB and PDGF-C stimulate SaOS-2 proliferation only at the highest dose tested, while PDGF-AB is ineffective. Primary osteoblasts are less sensitive than SaOS-2 and progressively lose responsiveness with increasing passages in culture, in line with loss of cell differentiation. The different PDGF isoforms act differentially on osteoblasts, the-AB isoform appearing the major responsible of the PRP chemiotaxis. PDGF, at the concentrations present in PRP, does not affect cell proliferation. PMID:23675162
Wang, Yingying; Hu, Zhaonong; Wu, Wenjun
2015-12-15
Bacillus thuringiensis (Bt) Cry toxins from the Cry1A family demonstrate significantly different toxicities against members of the family Noctuidae for unknown reasons. In this study, membrane potential was measured and analyzed in freshly isolated midgut samples from Mythimna separata and Agrotis ipsilon larvae under oral administration and in vitro incubation with Bt toxin Cry1Ab to elucidate the mechanism of action for further control of these pests. Bioassay results showed that the larvae of M. separata achieved a LD50 of 258.84 ng/larva at 24 h after ingestion; M. separata larvae were at least eightfold more sensitive than A. ipsilon larvae to Cry1Ab. Force-feeding showed that the observed midgut apical-membrane potential (V(am)) of M. separata larvae was significantly depolarized from -82.9 ± 6.6 mV to -19.9 ± 7.2 mV at 8 h after ingestion of 1 μg activated Cry1Ab, whereas no obvious changes were detected in A. ipsilon larvae with dosage of 5 μg Cry1Ab. The activated Cry1Ab caused a distinct concentration-dependent depolarization of the apical membrane; V(am) was reduced by 50% after 14.7 ± 0.2, 9.8 ± 0.4, and 7.6 ± 0.6 min of treatment with 1, 5, and 10 μg/mL Cry1Ab, respectively. Cry1Ab showed a minimal effect on A. ipsilon larvae even at 20 μg/mL, and V(am) decreased by 26.3% ± 2.3% after 15 min. The concentrations of Cry1Ab displayed no significant effect on the basolateral side of the epithelium. The V(am) of A. ipsilon (-33.19 ± 6.29 mV, n = 51) was only half that of M. separata (-80.94 ± 6.95 mV, n = 75). The different degrees of sensitivity to Cry1Ab were speculatively associated with various habits, as well as the diverse physiological or biochemical characteristics of the midgut cell membranes.
Wang, Yingying; Hu, Zhaonong; Wu, Wenjun
2015-01-01
Bacillus thuringiensis (Bt) Cry toxins from the Cry1A family demonstrate significantly different toxicities against members of the family Noctuidae for unknown reasons. In this study, membrane potential was measured and analyzed in freshly isolated midgut samples from Mythimna separata and Agrotis ipsilon larvae under oral administration and in vitro incubation with Bt toxin Cry1Ab to elucidate the mechanism of action for further control of these pests. Bioassay results showed that the larvae of M. separata achieved a LD50 of 258.84 ng/larva at 24 h after ingestion; M. separata larvae were at least eightfold more sensitive than A. ipsilon larvae to Cry1Ab. Force-feeding showed that the observed midgut apical-membrane potential (Vam) of M. separata larvae was significantly depolarized from −82.9 ± 6.6 mV to −19.9 ± 7.2 mV at 8 h after ingestion of 1 μg activated Cry1Ab, whereas no obvious changes were detected in A. ipsilon larvae with dosage of 5 μg Cry1Ab. The activated Cry1Ab caused a distinct concentration-dependent depolarization of the apical membrane; Vam was reduced by 50% after 14.7 ± 0.2, 9.8 ± 0.4, and 7.6 ± 0.6 min of treatment with 1, 5, and 10 μg/mL Cry1Ab, respectively. Cry1Ab showed a minimal effect on A. ipsilon larvae even at 20 μg/mL, and Vam decreased by 26.3% ± 2.3% after 15 min. The concentrations of Cry1Ab displayed no significant effect on the basolateral side of the epithelium. The Vam of A. ipsilon (−33.19 ± 6.29 mV, n = 51) was only half that of M. separata (−80.94 ± 6.95 mV, n = 75). The different degrees of sensitivity to Cry1Ab were speculatively associated with various habits, as well as the diverse physiological or biochemical characteristics of the midgut cell membranes. PMID:26694463
Wang, Yingying; Hu, Zhaonong; Wu, Wenjun
2015-12-01
Bacillus thuringiensis (Bt) Cry toxins from the Cry1A family demonstrate significantly different toxicities against members of the family Noctuidae for unknown reasons. In this study, membrane potential was measured and analyzed in freshly isolated midgut samples from Mythimna separata and Agrotis ipsilon larvae under oral administration and in vitro incubation with Bt toxin Cry1Ab to elucidate the mechanism of action for further control of these pests. Bioassay results showed that the larvae of M. separata achieved a LD50 of 258.84 ng/larva at 24 h after ingestion; M. separata larvae were at least eightfold more sensitive than A. ipsilon larvae to Cry1Ab. Force-feeding showed that the observed midgut apical-membrane potential (V(am)) of M. separata larvae was significantly depolarized from -82.9 ± 6.6 mV to -19.9 ± 7.2 mV at 8 h after ingestion of 1 μg activated Cry1Ab, whereas no obvious changes were detected in A. ipsilon larvae with dosage of 5 μg Cry1Ab. The activated Cry1Ab caused a distinct concentration-dependent depolarization of the apical membrane; V(am) was reduced by 50% after 14.7 ± 0.2, 9.8 ± 0.4, and 7.6 ± 0.6 min of treatment with 1, 5, and 10 μg/mL Cry1Ab, respectively. Cry1Ab showed a minimal effect on A. ipsilon larvae even at 20 μg/mL, and V(am) decreased by 26.3% ± 2.3% after 15 min. The concentrations of Cry1Ab displayed no significant effect on the basolateral side of the epithelium. The V(am) of A. ipsilon (-33.19 ± 6.29 mV, n = 51) was only half that of M. separata (-80.94 ± 6.95 mV, n = 75). The different degrees of sensitivity to Cry1Ab were speculatively associated with various habits, as well as the diverse physiological or biochemical characteristics of the midgut cell membranes. PMID:26694463
Quantum oblivion: A master key for many quantum riddles
NASA Astrophysics Data System (ADS)
Elitzur, Avshalom C.; Cohen, Eliahu
2014-02-01
A simple quantum interaction is analyzed, where the paths of two superposed particles asymmetrically cross, while a detector set to detect an interaction between them remains silent. Despite this negative result, the particles' states leave no doubt that a peculiar interaction has occurred: One particle's momentum is changed while the other's remains unaffected, in apparent violation of momentum conservation. Revisiting the foundations of the standard quantum measurement process offers the resolution. Prior to the macroscopic recording of no interaction, a brief critical interval (CI) prevails, during which the particles and the detector's pointer form a subtle entanglement which immediately dissolves. It is this self-cancellation, henceforth "quantum oblivion (QO)," that lies at the basis of some well-known intriguing quantum effects. Such is interaction-free measurement (IFM)1 and its more paradoxical variants like Hardy's Paradox2 and the quantum liar paradox.3 Even the Aharonov-Bohm (AB) effect4 and weak measurement (WM)5 turn out to belong to this group. We next study interventions within the CI that produce some other peculiar effects. Finally, we discuss some of the conceptual issues involved. Under a greater time-resolution of the CI, some non-local phenomena turn out to be local. Momentum is conserved due to the quantum uncertainties inflicted by the particle-pointer interaction, which sets the experiment's final boundary condition.
John, Christopher; Spura, Thomas; Habershon, Scott; Kühne, Thomas D
2016-04-01
We present a simple and accurate computational method which facilitates ab initio path-integral molecular dynamics simulations, where the quantum-mechanical nature of the nuclei is explicitly taken into account, at essentially no additional computational cost in comparison to the corresponding calculation using classical nuclei. The predictive power of the proposed quantum ring-polymer contraction method is demonstrated by computing various static and dynamic properties of liquid water at ambient conditions using density functional theory. This development will enable routine inclusion of nuclear quantum effects in ab initio molecular dynamics simulations of condensed-phase systems. PMID:27176426
NASA Astrophysics Data System (ADS)
John, Christopher; Spura, Thomas; Habershon, Scott; Kühne, Thomas D.
2016-04-01
We present a simple and accurate computational method which facilitates ab initio path-integral molecular dynamics simulations, where the quantum-mechanical nature of the nuclei is explicitly taken into account, at essentially no additional computational cost in comparison to the corresponding calculation using classical nuclei. The predictive power of the proposed quantum ring-polymer contraction method is demonstrated by computing various static and dynamic properties of liquid water at ambient conditions using density functional theory. This development will enable routine inclusion of nuclear quantum effects in ab initio molecular dynamics simulations of condensed-phase systems.
Huri, Emre; Beyazit, Yavuz; Mammadov, Rashad; Toksoz, Sila; Tekinay, Ayse B.; Guler, Mustafa O.; Ustun, Huseyin; Kekilli, Murat; Dadali, Mumtaz; Celik, Tugrul; Astarci, Müzeyyen; Haznedaroglu, Ibrahim C.
2013-01-01
Purpose. Using the classical Ankaferd Blood Stopper (ABS) solution to create active hemostasis during partial nephrectomy (PN) may not be so effective due to insufficient contact surface between the ABS hemostatic liquid agent and the bleeding area. In order to broaden the contact surface, we generated a chimeric hemostatic agent, ABS nanohemostat, via combining a self-assembling peptide amphiphile molecule with the traditional Ankaferd hemostat. Materials and Methods. In order to generate ABS nanohemostat, a positively charged Peptide Amphiphile (PA) molecule was synthesized by using solid phase peptide synthesis. For animal experiments, 24 Wistar rats were divided into the following 4 groups: Group 1: control; Group 2: conventional PN with only 0.5 ml Ankaferd hemostat; Group 3: conventional PN with ABS + peptide gel; Group 4: conventional PN with only 0.5 ml peptide solution. Results. Mean warm ischemia times (WITs) were 232.8 ± 56.3, 65.6 ± 11.4, 75.5 ± 17.2, and 58.1 ± 17.6 seconds in Group 1 to Group 4, respectively. Fibrosis was not different among the groups, while inflammation was detected to be significantly different in G3 and G4. Conclusions. ABS nanohemostat has comparable hemostatic efficacy to the traditional Ankaferd hemostat in the partial nephrectomy experimental model. Elucidation of the cellular and tissue effects of this chimeric compound may establish a catalytic spark and open new avenues for novel experimental and clinical studies in the battlefield of hemostasis. PMID:23509463
Huri, Emre; Beyazit, Yavuz; Mammadov, Rashad; Toksoz, Sila; Tekinay, Ayse B; Guler, Mustafa O; Ustun, Huseyin; Kekilli, Murat; Dadali, Mumtaz; Celik, Tugrul; Astarci, Müzeyyen; Haznedaroglu, Ibrahim C
2013-01-01
Purpose. Using the classical Ankaferd Blood Stopper (ABS) solution to create active hemostasis during partial nephrectomy (PN) may not be so effective due to insufficient contact surface between the ABS hemostatic liquid agent and the bleeding area. In order to broaden the contact surface, we generated a chimeric hemostatic agent, ABS nanohemostat, via combining a self-assembling peptide amphiphile molecule with the traditional Ankaferd hemostat. Materials and Methods. In order to generate ABS nanohemostat, a positively charged Peptide Amphiphile (PA) molecule was synthesized by using solid phase peptide synthesis. For animal experiments, 24 Wistar rats were divided into the following 4 groups: Group 1: control; Group 2: conventional PN with only 0.5 ml Ankaferd hemostat; Group 3: conventional PN with ABS + peptide gel; Group 4: conventional PN with only 0.5 ml peptide solution. Results. Mean warm ischemia times (WITs) were 232.8 ± 56.3, 65.6 ± 11.4, 75.5 ± 17.2, and 58.1 ± 17.6 seconds in Group 1 to Group 4, respectively. Fibrosis was not different among the groups, while inflammation was detected to be significantly different in G3 and G4. Conclusions. ABS nanohemostat has comparable hemostatic efficacy to the traditional Ankaferd hemostat in the partial nephrectomy experimental model. Elucidation of the cellular and tissue effects of this chimeric compound may establish a catalytic spark and open new avenues for novel experimental and clinical studies in the battlefield of hemostasis. PMID:23509463
NASA Astrophysics Data System (ADS)
Aquino, Fredy; Rodriguez, Jorge H.
2007-03-01
Zero-Field Splittings (ZFS) in metalloproteins and other metal complexes arise from the combined action of crystalline fields acting on the metal valence electrons and spin-orbit coupling (SOC), a relativistic effect. The ab-initio calculation of ZFS parameters of metal-containing (bio)molecules is a challenging computational problem of practical relevance to metalloenzyme biochemistry, inorganic chemistry, and molecular-based bio- nanotechnology. We have implemented a methodology which treats the nonrelativistic electronic structure of magnetic (bio) molecules within the framework of spin density functional theory (SDFT) and adds the relativistic effects of SOC via perturbation theory (PT). This combined SDFT-PT approach allowed us to compute the ZFS parameters of iron-containing complexes and non-heme iron proteins with a good degree of accuracy. We also developed a semiquantitative approach to elucidate the physico-chemical origin of the magnitudes of ZFS parameters. We present results for biochemically relevant iron complexes and for nitric oxide-containing non-heme iron proteins, such as isopenicillin N synthase, which have unusually large ZFS. The computed ZFS parameters are in good agreement with experiment. Supported by NSF CAREER Award CHE- 0349189 (JHR).
Lin, Hui; Hurt, Jr., Richard Ashley; Johs, Alexander; Parks, Jerry M; Morrell-Falvey, Jennifer L; Liang, Liyuan; Elias, Dwayne A; Gu, Baohua
2014-01-01
The hgcA and hgcB gene pair is essential for mercury (Hg) methylation by certain anaerobic bacteria,1 but little is known about how deletion of hgcAB affects cell surface interactions and intracellular uptake of Hg. Here, we compare hgcAB mutants with the wild-type (WT) strains of both Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132 and observe differences in Hg redox transformations, adsorption, and uptake in laboratory incubation studies. In both strains, deletion of hgcAB increased the reduction of Hg(II) but decreased the oxidation of Hg(0) under anaerobic conditions. The measured cellular thiol content in hgcAB mutants was lower than the WT, accounting for decreased adsorption and uptake of Hg. Despite the lack of methylation activity, Hg uptake by the hgcAB continued, albeit at a slower rate than the WT. These findings demonstrate that deletion of the hgcAB gene not only eliminates Hg methylation but also alters cell physiology, resulting in changes to Hg redox reactions, sorption, and uptake by cells.
Wong, Kin-Yiu; Xu, Yuqing; York, Darrin M
2014-06-30
Detailed understandings of the reaction mechanisms of RNA catalysis in various environments can have profound importance for many applications, ranging from the design of new biotechnologies to the unraveling of the evolutionary origin of life. An integral step in the nucleolytic RNA catalysis is self-cleavage of RNA strands by 2'-O-transphosphorylation. Key to elucidating a reaction mechanism is determining the molecular structure and bonding characteristics of transition state. A direct and powerful probe of transition state is measuring isotope effects on biochemical reactions, particularly if we can reproduce isotope effect values from quantum calculations. This article significantly extends the scope of our previous joint experimental and theoretical work in examining isotope effects on enzymatic and nonenzymatic 2'-O-transphosphorylation reaction models that mimic reactions catalyzed by RNA enzymes (ribozymes), and protein enzymes such as ribonuclease A (RNase A). Native reactions are studied, as well as reactions with thio substitutions representing chemical modifications often used in experiments to probe mechanism. Here, we report and compare results from eight levels of electronic-structure calculations for constructing the potential energy surfaces in kinetic and equilibrium isotope effects (KIE and EIE) computations, including a "gold-standard" coupled-cluster level of theory [CCSD(T)]. In addition to the widely used Bigeleisen equation for estimating KIE and EIE values, internuclear anharmonicity and quantum tunneling effects were also computed using our recently developed ab initio path-integral method, that is, automated integration-free path-integral method. The results of this work establish an important set of benchmarks that serve to guide calculations of KIE and EIE for RNA catalysis.
Wong, Kin-Yiu; Yuqing, Xu; York, Darrin M.
2014-01-01
Detailed understandings of the reaction mechanisms of RNA catalysis in various environments can have profound importance for many applications, ranging from the design of new biotechnologies to the unraveling of the evolutionary origin of life. An integral step in the nucleolytic RNA catalysis is self-cleavage of RNA strands by 2′-O-transphosphorylation. Key to elucidating a reaction mechanism is determining the molecular structure and bonding characteristics of transition state. A direct and powerful probe of transition state is measuring isotope effects on biochemical reactions, particularly if we can reproduce isotope effect values from quantum calculations. This paper significantly extends the scope of our previous joint experimental and theoretical work in examining isotope effects on enzymatic and non-enzymatic 2′-O-transphosphorylation reaction models that mimic reactions catalyzed by RNA enzymes (ribozymes), and protein enzymes such as ribonuclease A (RNase A). Native reactions are studied, as well as reactions with thio substitutions representing chemical modifications often used in experiments to probe mechanism. Here, we report and compare results from eight levels of electronic-structure calculations for constructing the potential energy surfaces in kinetic and equilibrium isotope effects (KIE and EIE) computations, including a “gold-standard” coupled-cluster level of theory [CCSD(T)]. In addition to the widely-used Bigeleisen equation for estimating KIE and EIE values, internuclear anharmonicity and quantum tunneling effects were also computed using our recently-developed ab initio path-integral method, i.e., automated integration-free path-integral (AIF-PI) method. The results of this work establish an important set of benchmarks that serve to guide calculations of KIE and EIE for RNA catalysis. PMID:24841935
Aharonov-casher effect in Bi2Se3 square-ring interferometers.
Qu, Fanming; Yang, Fan; Chen, Jun; Shen, Jie; Ding, Yue; Lu, Jiangbo; Song, Yuanjun; Yang, Huaixin; Liu, Guangtong; Fan, Jie; Li, Yongqing; Ji, Zhongqing; Yang, Changli; Lu, Li
2011-07-01
Electrical control of spin dynamics in Bi(2)Se(3) was investigated in ring-type interferometers. Aharonov-Bohm and Altshuler-Aronov-Spivak resistance oscillations against a magnetic field, and Aharonov-Casher resistance oscillations against the gate voltage were observed in the presence of a Berry phase of π. A very large tunability of spin precession angle by the gate voltage has been obtained, indicating that Bi(2)Se(3)-related materials with strong spin-orbit coupling are promising candidates for constructing novel spintronic devices.
Magnon Hall effect in AB-stacked bilayer honeycomb quantum magnets
NASA Astrophysics Data System (ADS)
Owerre, S. A.
2016-09-01
Motivated by the fact that many bilayer quantum magnets occur in nature, we generalize the study of thermal Hall transports of spin excitations to bilayer magnetic systems. It is shown that bilayer magnetic systems can be coupled either ferromagnetically or antiferromagnetically. We study both scenarios on the honeycomb lattice and show that the system realizes topologically nontrivial magnon bands induced by alternating next-nearest-neighbor Dzyaloshinsky-Moriya interaction. As a result, the bilayer system realizes both magnon Hall effect and magnon spin Nernst effect. We show that antiferromagnetically coupled layers differ from ferromagnetically coupled layers by a sign change in the conductivities as the magnetic field is reversed. Furthermore, Chern number protected magnon edge states are observed and propagate in the same direction on the top and bottom layers in ferromagnetically coupled layers, whereas the magnon edge states propagate in opposite directions for antiferromagnetically coupled layers.
NASA Astrophysics Data System (ADS)
Rout, G. C.; Sahu, Sivabrata; Panda, S. K.
2016-04-01
We report here a microscopic tight-binding model calculation for AB-stacked bilayer graphene in presence of biasing potential between the two layers and the impurity effects to study the evolution of the total density of states with special emphasis on opening of band gap near Dirac point. We have calculated the electron Green's functions for both the A and B sub-lattices by Zubarev technique. The imaginary part of the Green's function gives the partial and total density of states of electrons. The density of states are computed numerically for 1000 × 1000 grid points of the electron momentum. The evolution of the opening of band gap near van-Hove singularities as well as near Dirac point is investigated by varying the different interlayer hoppings and the biasing potentials. The inter layer hopping splits the density of states at van-Hove singularities and produces a V-shaped gap near Dirac point. Further the biasing potential introduces a U shaped gap near Dirac point with a density minimum at the applied potential(i.e. at V/2).
Ab initio simulation of single- and few-layer MoS2 transistors: Effect of electron-phonon scattering
NASA Astrophysics Data System (ADS)
Szabó, Áron; Rhyner, Reto; Luisier, Mathieu
2015-07-01
In this paper, we present full-band atomistic quantum transport simulations of single- and few-layer MoS2 field-effect transistors (FETs) including electron-phonon scattering. The Hamiltonian and the electron-phonon coupling constants are determined from ab initio density-functional-theory calculations. It is observed that the phonon-limited electron mobility is enhanced with increasing layer thicknesses and decreases at high charge concentrations. The electrostatic control is found to be crucial even for a single-layer MoS2 device. With a single-gate configuration, the double-layer MoS2 FET shows the best intrinsic performance with an ON current, ION=685 μ A /μ m , but with a double-gate contact the transistor with a triple-layer channel delivers the highest current with ION=1850 μ A /μ m . The charge in the channel is almost independent of the number of MoS2 layers, but the injection velocity increases significantly with the channel thickness in the double-gate devices due to the reduced electron-phonon scattering rates in multilayer structures. We demonstrate further that the ballistic limit of transport is not suitable for the simulation of MX 2 FETs because of the artificial negative differential resistance it predicts.
NASA Astrophysics Data System (ADS)
Dhayal, Suman; Rostovtsev, Yuri
2011-03-01
Recent progress in ultrashort, e.g. attosecond, laser technology allows to obtain ultra-strong fields which can be of the same order of magnitude as the electric field created by an atomic nucleus. Interaction of such strong and broadband field with atomic systems even under the action of a far-off resonance strong pulse of laser radiation should be revisited. As we have shown, such pulses can excite remarkable coherence on high frequency transitions. We have found and analyzed analitical solutions for various pulse shapes. We have developed new mechanisms of efficient atomic coherent excitation by using two-frequency laser pulses and via tunneling through electric fields. We have done ab initio calculations using TDDFT for several atoms and simple molecules interacting with strong optical fields. We compare efficiency generation with the efficiency of high harmonic generation approach, and discuss the CEP effects and possible applications of the results obtained to cooperative generation of XUV radiation. The efficiency of XUV generation is calculated for particular candidates for XUV radiation such as H (100 nm) and He (50 nm) atoms and H-like ions (Li 2+ (30 nm), as well as Ar 8+ and Xe 8+ (30-50 nm).
NASA Astrophysics Data System (ADS)
Ko, Hsin-Yu; Distasio, Robert A., Jr.; Santra, Biswajit; Car, Roberto
Molecular crystal structure prediction has posed a substantial challenge to first-principles methods and requires sophisticated electronic structure methods to determine the stabilities of nearly degenerate polymorphs. In this work, we demonstrate that the anharmonicity from van der Waals interactions is relevant to the finite-temperature structures of pyridine and pyridine-like molecular crystals. Using such an approach, we find that the equilibrium structures are well captured with classical ab initio molecular dynamics (AIMD), despite the presence of light atoms such as hydrogen. Employing path integral AIMD simulations, we demonstrate that the success of classical AIMD results from a separation of nuclear quantum effects between the intermolecular and intramolecular degrees of freedom. In this separation, the quasiclassical and anharmonic intermolecular degrees of freedom determine the equilibrium structure, while the quantum and harmonic intramolecular degrees of freedom are averaging to the correct intramolecular structure. This work has been supported by the Department of Energy under Grants No. DE-FG02-05ER46201 and DE-SC0008626.
NASA Astrophysics Data System (ADS)
Hüter, Claas; Friák, Martin; Weikamp, Marc; Neugebauer, Jörg; Goldenfeld, Nigel; Svendsen, Bob; Spatschek, Robert
2016-06-01
We investigate nonlinear elastic deformations in the phase field crystal model and derived amplitude equation formulations. Two sources of nonlinearity are found, one of them is based on geometric nonlinearity expressed through a finite strain tensor. This strain tensor is based on the inverse right Cauchy-Green deformation tensor and correctly describes the strain dependence of the stiffness for anisotropic and isotropic behavior. In isotropic one- and two-dimensional situations, the elastic energy can be expressed equivalently through the left deformation tensor. The predicted isotropic low-temperature nonlinear elastic effects are directly related to the Birch-Murnaghan equation of state with bulk modulus derivative K'=4 for bcc. A two-dimensional generalization suggests K2D '=5 . These predictions are in agreement with ab initio results for large strain bulk deformations of various bcc elements and graphene. Physical nonlinearity arises if the strain dependence of the density wave amplitudes is taken into account and leads to elastic weakening. For anisotropic deformation, the magnitudes of the amplitudes depend on their relative orientation to the applied strain.
AB069. Effect of osteogenesis imperfecta on children and their families
Dung, Vu Chi; Armstrong, Kate; Ngoc, Can Thi Bich; Thao, Bui Phuong; Khanh, Nguyen Ngoc; Trang, Nguyen Thu; Hoan, Nguyen Thi; Dat, Nguyen Phu; Munns, Craig
2015-01-01
Osteogenesis imperfecta (OI) is a heterogeneous genetic disorder, with features that include increased bone fragility, pathological fractures, blue sclera, dentinogenesis imperfecta and conductive or mixed hearing loss. Clinical variability is wide from children with few fractures and normal stature to children with multiple fractures, long bone deformity, scoliosis and extreme short stature. Although there is no curative treatment, there are several therapeutic tools capable of improving the course of the condition and patient quality of life. We aim to evaluate the effect of OI on the well-being of children with the disorder and their families through a family-centered questionnaire. Sixty children with OI from the Vietnam National Hospital of Pediatrics and/or their parent(s), who attended the first annual family support group in 2011, completed a child and parent questionnaire. Sixty patients participated, 26 female and 34 male. The median age was 6.0 years [interquartile range (IQR), 0.25-18 years]. Of these, 36 (60%) had dentinogenesis imperfect and 23 (38.3%) had a scoliosis. The median number of fractures was 6.0 (IQR 0-30) and median number of hospitalizations due to OI was 5.0 (IQR 0-30). Among patients of school age, 9 (15%) could not go to school due to OI. Almost all parents (93.7%) worried about school social communication of the patients. Among these parents, 100% fear of inferiority with friends and 98.3% fear of broken bones. Most parents (76.2%) were significantly concerned about their child’s health. The parents’ themselves reported psychological concerns, with feelings of desperation (58.4%), anxiety (81.7%) and depression (56.7%). OI appeared to have a significant deleterious effect on the life of the patients and their families. These data provide a baseline from which to evaluate the effectiveness of interventions to improve the medical and psychological needs of this cohort and their families.
Relativistic Killingbeck energy states under external magnetic fields
NASA Astrophysics Data System (ADS)
Eshghi, M.; Mehraban, H.; Ikhdair, S. M.
2016-07-01
We address the behavior of the Dirac equation with the Killingbeck radial potential including the external magnetic and Aharonov-Bohm (AB) flux fields. The spin and pseudo-spin symmetries are considered. The correct bound state spectra and their corresponding wave functions are obtained. We seek such a solution using the biconfluent Heun's differential equation method. Further, we give some of our results at the end of this study. Our final results can be reduced to their non-relativistic forms by simply using some appropriate transformations. The spectra, in the spin and pseudo-spin symmetries, are very similar with a slight difference in energy spacing between different states.
Ab initio theory of the scattering-independent anomalous Hall effect.
Weischenberg, Jürgen; Freimuth, Frank; Sinova, Jairo; Blügel, Stefan; Mokrousov, Yuriy
2011-09-01
We report on first-principles calculations of the side-jump contribution to the anomalous Hall conductivity (AHC) directly from the electronic structure of a perfect crystal. We implemented our approach for a short-range scattering disorder model within the density functional theory and computed the full scattering-independent AHC in elemental bcc Fe, hcp Co, fcc Ni, and L1(0) FePd and FePt alloys. The full AHC thus calculated agrees systematically with experiment to a degree unattainable so far, correctly capturing the previously missing elements of side-jump contributions, hence paving the way to a truly predictive theory of the anomalous Hall effect and turning it from a characterization tool to a probing tool of multiband complex electronic band structures.
Sulphur diffusion in β-NiAl and effect of Pt additive: an ab initio study
NASA Astrophysics Data System (ADS)
Chen, Kuiying
2016-02-01
Diffusivities of detrimental impurity sulfur (S) in stoichiometric and Pt doped β-NiAl were evaluated using density functional theory calculations. The apparent activation energy and the pre-exponential factor of diffusivity via the next nearest neighbour (NNN) and interstitial jumps were evaluated to identify possible preferred diffusion mechanism(s). By calculating the electron localization function (ELF), the bonding characteristics of S with its surrounding atoms were assessed for the diffusion process. By comparison with the experimental results, the S diffusion through the NNN vacancy-mediated mechanism is found to be favoured. Addition of Pt in β-NiAl was found to significantly reduce the S diffusivity, and an associated electronic effect was explored. The elucidation of the above mechanisms may shed light on the development of new Pt-modified doped β-NiAl bond coats that can extend the life of oxidation resistant and thermal barrier coatings.
NASA Astrophysics Data System (ADS)
DiStasio, Robert A.; Santra, Biswajit; Li, Zhaofeng; Wu, Xifan; Car, Roberto
2014-08-01
In this work, we report the results of a series of density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations of ambient liquid water using a hierarchy of exchange-correlation (XC) functionals to investigate the individual and collective effects of exact exchange (Exx), via the PBE0 hybrid functional, non-local van der Waals/dispersion (vdW) interactions, via a fully self-consistent density-dependent dispersion correction, and an approximate treatment of nuclear quantum effects, via a 30 K increase in the simulation temperature, on the microscopic structure of liquid water. Based on these AIMD simulations, we found that the collective inclusion of Exx and vdW as resulting from a large-scale AIMD simulation of (H2O)128 significantly softens the structure of ambient liquid water and yields an oxygen-oxygen structure factor, SOO(Q), and corresponding oxygen-oxygen radial distribution function, gOO(r), that are now in quantitative agreement with the best available experimental data. This level of agreement between simulation and experiment demonstrated herein originates from an increase in the relative population of water molecules in the interstitial region between the first and second coordination shells, a collective reorganization in the liquid phase which is facilitated by a weakening of the hydrogen bond strength by the use of a hybrid XC functional, coupled with a relative stabilization of the resultant disordered liquid water configurations by the inclusion of non-local vdW/dispersion interactions. This increasingly more accurate description of the underlying hydrogen bond network in liquid water also yields higher-order correlation functions, such as the oxygen-oxygen-oxygen triplet angular distribution, POOO(θ), and therefore the degree of local tetrahedrality, as well as electrostatic properties, such as the effective molecular dipole moment, that are in much better agreement with experiment.
DiStasio, Robert A.; Santra, Biswajit; Li, Zhaofeng; Wu, Xifan; Car, Roberto
2014-08-28
In this work, we report the results of a series of density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations of ambient liquid water using a hierarchy of exchange-correlation (XC) functionals to investigate the individual and collective effects of exact exchange (Exx), via the PBE0 hybrid functional, non-local van der Waals/dispersion (vdW) interactions, via a fully self-consistent density-dependent dispersion correction, and an approximate treatment of nuclear quantum effects, via a 30 K increase in the simulation temperature, on the microscopic structure of liquid water. Based on these AIMD simulations, we found that the collective inclusion of Exx and vdW as resulting from a large-scale AIMD simulation of (H{sub 2}O){sub 128} significantly softens the structure of ambient liquid water and yields an oxygen-oxygen structure factor, S{sub OO}(Q), and corresponding oxygen-oxygen radial distribution function, g{sub OO}(r), that are now in quantitative agreement with the best available experimental data. This level of agreement between simulation and experiment demonstrated herein originates from an increase in the relative population of water molecules in the interstitial region between the first and second coordination shells, a collective reorganization in the liquid phase which is facilitated by a weakening of the hydrogen bond strength by the use of a hybrid XC functional, coupled with a relative stabilization of the resultant disordered liquid water configurations by the inclusion of non-local vdW/dispersion interactions. This increasingly more accurate description of the underlying hydrogen bond network in liquid water also yields higher-order correlation functions, such as the oxygen-oxygen-oxygen triplet angular distribution, P{sub OOO}(θ), and therefore the degree of local tetrahedrality, as well as electrostatic properties, such as the effective molecular dipole moment, that are in much better agreement with experiment.
Effect of Sulfuric and Triflic Acids on the Hydration of Vanadium Cations: An ab Initio Study.
Sepehr, Fatemeh; Paddison, Stephen J
2015-06-01
Vanadium redox flow batteries (VRFBs) may be a promising solution for large-scale energy storage applications, but the crossover of any of the redox active species V(2+), V(3+), VO(2+), and VO2(+) through the ion exchange membrane will result in self-discharge of the battery. Hence, a molecular level understanding of the states of vanadium cations in the highly acidic environment of a VRFB is needed. We examine the effects of sulfuric and triflic (CF3SO3H) acids on the hydration of vanadium species as they mimic the electrolyte and functional group of perfluorosulfonic acid (PFSA) membranes. Hybrid density functional theory in conjunction with a continuum solvation model was utilized to obtain the local structures of the hydrated vanadium cations in proximity to H2SO4, CF3SO3H, and their conjugate anions. The results indicate that none of these species covalently bond to the vanadium cations. The hydration structure of V(3+) is more distorted than that of V(2+) in an acidic medium. The oxo-group of VO2(+) is protonated by either acid, in contrast to VO(2+) which is not protonated. The atomic partial charge of the four oxidation states of vanadium varies from +1.7 to +2.0. These results provide the local solvation structures of vanadium cations in the VRFBs environment that are directly related to the electrolytes stability and diffusion of vanadium ions into the membrane. PMID:25954916
AB101. Therapeutic effect of low intensity pulsed ultrasound in stress urinary incontinence
Yang, Bicheng; Lei, Hongen; Guan, Ruili; Li, Huixi; Xin, Zhongcheng
2016-01-01
Objective Stress urinary incontinence, a major type of urinary incontinence, increases with age and is often developed after partum injury. Low intensity pulsed ultrasound (LIPUS) has been investigated in the treatment of many diseases showing its ability of restoring soft tissue injury. We investigated the therapeutic effect of low intensity pulsed ultrasound in stress urinary incontinence. Methods Thirty-two Sprague Dawley rats in SUI group underwent vaginal distension (VD) and bilateral ovariectomy mimicking partum injury. Eight rats served as mock operation control. Eight rats each in SUI group was treated with low-dosage LESW (0.03 mJ/mm2), medium-dosage LESW (0.06 mJ/mm2), or high-dosage LESW (0.09 mJ/mm2). The rest eight rats served as none-treatment group. For functional study, leak point pressure test (LPP) was performed 2 weeks after the last LESW. Masson trichrome staining was performed to validate the pathological changes. Results The LPP was restored in medium-dosage LESW and high-dosage LESW groups, but not in low-dosage LESW group. More robust striated muscle regeneration was found in these two groups comparing with the none-treatment group. Conclusions LIPUS ameliorate the symptom of SUI via activating striated muscle regeneration.
Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion.
Zhou, Jiawei; Liao, Bolin; Qiu, Bo; Huberman, Samuel; Esfarjani, Keivan; Dresselhaus, Mildred S; Chen, Gang
2015-12-01
Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect--a coupling phenomenon between electrons and nonequilibrium phonons--in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ∼ 0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons.
Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion.
Zhou, Jiawei; Liao, Bolin; Qiu, Bo; Huberman, Samuel; Esfarjani, Keivan; Dresselhaus, Mildred S; Chen, Gang
2015-12-01
Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect--a coupling phenomenon between electrons and nonequilibrium phonons--in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ∼ 0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons. PMID:26627231
Effect of Sulfuric and Triflic Acids on the Hydration of Vanadium Cations: An ab Initio Study.
Sepehr, Fatemeh; Paddison, Stephen J
2015-06-01
Vanadium redox flow batteries (VRFBs) may be a promising solution for large-scale energy storage applications, but the crossover of any of the redox active species V(2+), V(3+), VO(2+), and VO2(+) through the ion exchange membrane will result in self-discharge of the battery. Hence, a molecular level understanding of the states of vanadium cations in the highly acidic environment of a VRFB is needed. We examine the effects of sulfuric and triflic (CF3SO3H) acids on the hydration of vanadium species as they mimic the electrolyte and functional group of perfluorosulfonic acid (PFSA) membranes. Hybrid density functional theory in conjunction with a continuum solvation model was utilized to obtain the local structures of the hydrated vanadium cations in proximity to H2SO4, CF3SO3H, and their conjugate anions. The results indicate that none of these species covalently bond to the vanadium cations. The hydration structure of V(3+) is more distorted than that of V(2+) in an acidic medium. The oxo-group of VO2(+) is protonated by either acid, in contrast to VO(2+) which is not protonated. The atomic partial charge of the four oxidation states of vanadium varies from +1.7 to +2.0. These results provide the local solvation structures of vanadium cations in the VRFBs environment that are directly related to the electrolytes stability and diffusion of vanadium ions into the membrane.
Karwat, Darshan M A; Wooldridge, Margaret S; Klippenstein, Stephen J; Davis, Michael J
2015-01-29
Experimental, time-resolved species profiles provide critical tests in developing accurate combustion models for biofuels such as n-butanol. A number of such species profiles measured by Karwat et al. [ Karwat, D. M. A.; et al. J. Phys. Chem. A 2011 , 115 , 4909 ] were discordant with predictions from a well-tested chemical kinetic mechanism developed by Black et al. [ Black, G.; et al. Combust. Flame 2010 , 157 , 363 ]. Since then, significant theoretical and experimental efforts have focused on determining the rate coefficients of primary n-butanol consumption pathways in combustion environments, including H atom abstraction reactions from n-butanol by key radicals such as HO2 and OH, as well as the decomposition of the radicals formed by these H atom abstractions. These reactions not only determine the overall reactivity of n-butanol, but also significantly affect the concentrations of intermediate species formed during n-butanol ignition. In this paper we explore the effect of incorporating new ab initio predictions into the Black et al. mechanism on predictions of ignition delay time and species time histories for the experimental conditions studied by Karwat et al. The revised predictions for the intermediate species time histories are in much improved agreement with the measurements, but some discrepancies persist. A rate of production analysis comparing the effects of various modifications to the Black et al. mechanism shows significant changes in the predicted consumption pathways of n-butanol, and of the hydroxybutyl and butoxy radicals formed by H atom abstraction from n-butanol. The predictions from the newly revised mechanism are in very good agreement with the low-pressure n-butanol pyrolysis product species measurements of Stranic et al. [ Stranic, I.; et al. Combust. Flame 2012 , 159 , 3242 ] for all but one species. Importantly, the changes to the Black et al. mechanism show that concentrations of small products from n-butanol pyrolysis are
NASA Astrophysics Data System (ADS)
Xin, Yan; Hou, S. C.; Xiang, Lan; Yu, Yang-Xin
2015-12-01
Calcium sulfate hemihydrate (CaSO4·0.5H2O, CSH) whiskers with high aspect ratio are promising reinforce materials which have drawn much attention. In order to obtain high quality CSH materials, effect of Mg2+ ions on properties of the (0 0 2), (2 0 0)1 and (2 0 0)2 planes of CSH is investigated using an ab initio density functional theory (DFT) with a van der Waals (vdW) dispersion-correction. The computed results show that strong adsorption and substitution effects take place between Mg2+ ion and (2 0 0)1 plane. The adsorption energies of an Mg2+ ion on the (0 0 2), (2 0 0)1 and (2 0 0)2 planes are -0.066, -0.571 and -0.047 eV, respectively. An insight into the electrostatic potential of pristine CSH planes has demonstrated that the (2 0 0)1 plane is much more negatively charged than the (0 0 2) and (2 0 0)2 planes. The energies of the substitution of a Ca atom with an Mg atom on the CSH (0 0 2), (2 0 0)1 and (2 0 0)2 planes are 1.572, 0.063 and 1.349 eV, respectively. It is found that Ca atoms on the (2 0 0)1 plane are relatively easy to be substituted by Mg atoms. The calculation results of a Ca2+ ion adsorption on the Mg-doped (2 0 0)1 plane indicate that the adsorption energies increase apparently as the doping ratio varies from 0 to 1.0. Compared with K+, Na+ and Al3+ ions, Mg2+ ion is the most promising additive to promote the growth of CSH along c axis.
Ab initio molecular dynamics studies on effect of Zr on oxidation resistance of TiAlN coatings
NASA Astrophysics Data System (ADS)
Pi, Jingwu; Kong, Yi; Chen, Li; Du, Yong
2016-08-01
It was demonstrated experimentally that doping Zr into TiAlN coatings at room temperature will detriment its oxidation resistance. On the other hand, there are evidences that doping Zr into TiAlN at high temperature will improve coating's oxidation resistance. In the present work, we address the effect of Zr on the oxidation resistance of TiAlN by means of ab initio molecular dynamics simulations. The TiAlN and TiAlZrN (1 Zr atom replacing 1 Ti atom) surfaces covered with 4 oxygen atoms at 300 K and 1123 K were simulated. Based on the analysis of the atomic motion, bond formation after relaxation, and the charge density difference maps we find that at 300 K, the addition of Zr induces escape of Ti atoms from the surface, resulting in formation of surface vacancies and subsequently TiO2. Comparison of metal-oxygen dimers in the vacuum and above the TiAlZrN surface further shows that the addition of Zr in the TiAlN surface will change the lowest bonding energy sequence from Zrsbnd O < Tisbnd O < Alsbnd O in the vacuum to Tisbnd O < Zrsbnd O < Alsbnd O above the TiAlZrN surface. From Molecular Dynamics simulations at 1123 K, it is find that no Ti vacancies were generated in the surface. Moreover, less charge is transferred from metal to N atoms and the bond lengths between Ti and O atoms become shorter at 1123 K as compared with 300 K, suggesting that the addition of Zr atom promotes the interaction of Ti and O at TiAlZrN surface at 1123 K, leading to a more stable surface. Our simulation explains why Zr-doping at 1123 K increases TiAlN coating's oxidation resistance while at 300 K reduces its oxidation resistance.
Ab initio study of shear strain effects on ferroelectricity at PbTiO3 thin films
NASA Astrophysics Data System (ADS)
Van Truong, Do; Hung, Nguyen Tuan; Shimada, Takahiro; Kitamura, Takayuki
2012-08-01
Ferroelectric thin film with the perovskite ABO3 structure have been widely used in technology applications, e.g., actuators in MEMS/NEMS and nonvolatile random access memories (FeRAM). In order to clarify the effect of the shear strain on the ferroelectricity, the PbTiO3 thin film as a typical one is chosen. The focus of this study is to put on the PbO-terminated (1 × 1) and c(2 × 2) surfaces and the TiO2-terminated (1 × 1) surface. Based on ab initio density functional theory calculations with the local density approximation, we have found out that in both the PbO and TiO2-terminated (1 × 1) models, the ferroelectricity in the PbO layers was enhanced under the positive shear strain while it was suppressed under the negative one. For the TiO2 layers, the ferroelectricity was slightly enhanced and sharply suppressed under the positive and negative shear strains, respectively. In the PbO-terminated (2 × 2) model, the AFE phase was suppressed by the FE phase under the positive shear strain while the opposite trend was found under the negative shear strain. For the PbO layers, the ferroelectricity was enhanced under the positive and negative shear strains. For the TiO2 layers, the influence of the negative shear strain on the ferroelectricity was larger than that of the positive one. In addition, the ideal strength of the PbTiO3 thin film with the different terminations was investigated as well.
Li, Zeyang; Gao, Yang; Zhang, Minhong; Feng, Jinghai; Xiong, Yandan
2015-01-01
The aim of this study was to evaluate the effect of feeding Bacillus thuringiensis (Bt) rice expressing the Cry1Ab/1Ac protein on broiler chicken. The genetically modified (GM) Bt rice was compared with the corresponding non-GM rice regarding performance of feeding groups, their health status, relative organ weights, biochemical serum parameters and occurrence of Cry1Ab/1Ac gene fragments. One hundred and eighty day-old Arbor Acres female broilers with the same health condition were randomly allocated to the two treatments (6 replicate cages with 15 broilers in each cage per treatment). They received diets containing GM rice (GM group) or its parental non-GM rice (non-GM group) at 52-57% of the air-dried diet for 42 days. The results show that the transgenic rice had a similar nutrient composition as the non-GM rice and had no adverse effects on chicken growth, biochemical serum parameters and necropsy during the 42-day feeding period. In birds fed the GM rice, no transgenic gene fragments were detected in the samples of blood, liver, kidneys, spleen, jejunum, ileum, duodenum and muscle tissue. In conclusion, the results suggest that Bt rice expressing Cry1Ab/1Ac protein has no adverse effects on broiler chicken. Therefore, it can be considered as safe and used as feed source for broiler chicken.
Li, Zeyang; Gao, Yang; Zhang, Minhong; Feng, Jinghai; Xiong, Yandan
2015-01-01
The aim of this study was to evaluate the effect of feeding Bacillus thuringiensis (Bt) rice expressing the Cry1Ab/1Ac protein on broiler chicken. The genetically modified (GM) Bt rice was compared with the corresponding non-GM rice regarding performance of feeding groups, their health status, relative organ weights, biochemical serum parameters and occurrence of Cry1Ab/1Ac gene fragments. One hundred and eighty day-old Arbor Acres female broilers with the same health condition were randomly allocated to the two treatments (6 replicate cages with 15 broilers in each cage per treatment). They received diets containing GM rice (GM group) or its parental non-GM rice (non-GM group) at 52-57% of the air-dried diet for 42 days. The results show that the transgenic rice had a similar nutrient composition as the non-GM rice and had no adverse effects on chicken growth, biochemical serum parameters and necropsy during the 42-day feeding period. In birds fed the GM rice, no transgenic gene fragments were detected in the samples of blood, liver, kidneys, spleen, jejunum, ileum, duodenum and muscle tissue. In conclusion, the results suggest that Bt rice expressing Cry1Ab/1Ac protein has no adverse effects on broiler chicken. Therefore, it can be considered as safe and used as feed source for broiler chicken. PMID:26414482
Alam, Todd
2013-07-29
The impacts of local polymer chain conformations on the methine and carbonyl 13C-NMR chemical shifts for polyethylene acrylic acid p(E-AA) copolymers were predicted using ab initio methods. Using small molecular cluster models, the magnitude and sign of the γ-gauche torsional angle effect, along with the impact of local tetrahedral structure distortions near the carbonyl group, on the 13C-NMR chemical shifts were determined. These 13C-NMR chemical shift variations were compared to the experimental trends observed for precise p(E-AA) copolymers as a function acid group spacing and degree of zinc-neutralization in the corresponding p(E-AA) ionomers. These ab initio calculations address the future ability of 13C-NMR chemical shift variations to provide information about the local chain conformations in p(E-AA) copolymer materials.
Brebu, Mihai; Bhaskar, Thallada; Murai, Kazuya; Muto, Akinori; Sakata, Yusaku; Uddin, Md Azhar
2004-08-01
Acrylonitrile-butadiene-styrene (ABS) copolymers without and with a polybrominated epoxy type flame retardant were thermally degraded at 450 degrees C alone (10 g) and mixed with polyvinylchloride (PVC) (8 g/2 g). Gaseous and liquid products of degradation were analysed by various gas chromatographic methods (GC with TCD, FID, AED, MSD) in order to determine the individual and cumulative effect of bromine and chlorine on the quality and quantity of degradation compounds. It was found that nitrogen, chlorine, bromine and oxygen are present as organic compounds in liquid products, their quantity depends on the pyrolysed polymer or polymer mixture. Bromophenol and dibromophenols were the main brominated compounds that come from the flame retardant. 1-Chloroethylbenzene was the main chlorine compound observed in liquid products. It was also determined that interactions appear at high temperatures during decomposition between the flame retardant, PVC and the ABS copolymer.
NASA Astrophysics Data System (ADS)
Vaks, V. G.
2013-06-01
I had the good fortune to be a student of A. B. Migdal - AB, as we called him in person or in his absence - and to work in the sector he headed at the Kurchatov Institute, along with his other students and my friends, including Vitya Galitsky, Spartak Belyayev and Tolya Larkin. I was especially close with AB in the second half of the 1950s, the years most important for my formation, and AB's contribution to this formation was very great. To this day, I've often quoted AB on various occasions, as it's hard to put things better or more precisely than he did; I tell friends stories heard from AB, because these stories enhance life as AB himself enhanced it; my daughter is named Tanya after AB's wife Tatyana Lvovna, and so on. In what follows, I'll recount a few episodes in my life in which AB played an important or decisive role, and then will share some other memories of AB...
The Effect of CdS/organic Nanostructure as Additive on the Thermal Stability of ABS Polymer
NASA Astrophysics Data System (ADS)
Ghanbari, Davood; Salavati-Niasari, Masoud
2012-04-01
Flower like cadmium sulfide/organic (CdS-or) nanostructures were synthesized via a simple reaction between CdCl2 · 2H2O and thioglycolic acid using water solvent at room temperature, then CdS-or nanostructures were added to Acrylonitrile-Butadiene-Styrene (ABS) copolymer. The influence of inorganic phase on the thermal properties of ABS matrix was studied using thermogravimetry analysis and limiting oxygen index (LOI). Nanostructures and nanocomposite materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Fourier transform infrared (FT-IR) spectra. Cone calorimeter measurements showed that the heat release rate (HRR) significantly decreased in the presence of CdS-or nanostructures.
Rein, David B; Weinbaum, Cindy M
2008-10-01
Previous studies estimated that vaccinating high-risk heterosexuals (HRH) with combination hepatitis A/B vaccine was a cost-effective alternative to vaccinating HRH against hepatitis B alone. Since then, the incidence of hepatitis A has declined dramatically in the United States. We re-estimate the cost-effectiveness of this policy accounting for modern declines in incidence. According to our estimates, vaccinating with combination vaccine resulted in a cost of $120,000 per quality adjusted life year gained (2.79 times the 2005 United States Gross Domestic Product per capita), a ratio that is less favorable than those for most other vaccination strategies.
Lavilla Lerma, Leyre; Benomar, Nabil; Valenzuela, Antonio Sánchez; Casado Muñoz, María del Carmen; Gálvez, Antonio; Abriouel, Hikmate
2014-12-01
Enterococcus faecalis and Enterococcus faecium isolated from various traditional fermented foods of both animal and vegetable origins have shown multidrug resistance to several antibiotics and tolerance to biocides. Reduced susceptibility was intra and inter-species dependent and was due to specific and unspecific mechanisms such as efflux pumps. EfrAB, a heterodimeric ABC transporter efflux pump, was detected in 100% of multidrug resistant (MDR) E. faecalis strains and only in 12% of MDR E. faecium strains. EfrAB expression was induced by half of minimum inhibitory concentration (MIC) of gentamicin, streptomycin and chloramphenicol. However, expression of efrA and efrB genes was highly dependent on the strain tested and on the antimicrobial used. Our results indicated that 3 mM EDTA highly reduced the MICs of almost all drugs tested. Nevertheless, the higher reductions (>8 folds) were obtained with gentamicin, streptomycin, chlorhexidine and triclosan. Reductions of MICs were correlated with down-regulation of EfrAB expression (10-140 folds) in all three MDR enterococci strains. This is the first report describing the role of EfrAB in the efflux of antibiotics and biocides which reflect also the importance of EfrAB in multidrug resistance in enterococci. EDTA used at low concentration as food preservative could be one of the best choices to prevent spread of multidrug resistant enterococci throughout food chain by decreasing EfrAB expression. EfrAB could be an attractive target not only in enterococci present in food matrix but also those causing infections as well by using EDTA as therapeutic agent in combination with low doses of antibiotics.
NASA Astrophysics Data System (ADS)
Faria Junior, Paulo E.; Campos, Tiago; Bastos, Carlos M. O.; Gmitra, Martin; Fabian, Jaroslav; Sipahi, Guilherme M.
2016-06-01
Semiconductor nanowires based on non-nitride III-V compounds can be synthesized under certain growth conditions to favor the appearance of the wurtzite crystal phase. Despite reports in the literature of ab initio band structures for these wurtzite compounds, we still lack effective multiband models and parameter sets that can be simply used to investigate physical properties of such systems, for instance, under quantum confinement effects. In order to address this deficiency, in this study we calculate the ab initio band structure of bulk InAs and InP in the wurtzite phase and develop an 8 ×8 k .p Hamiltonian to describe the energy bands around the Γ point. We show that our k .p model is robust and can be fitted to describe the important features of the ab initio band structure. The correct description of the spin-splitting effects that arise due to the lack of inversion symmetry in wurtzite crystals is obtained with the k -dependent spin-orbit term in the Hamiltonian, often neglected in the literature. All the energy bands display a Rashba-like spin texture for the in-plane spin expectation value. We also provide the density of states and the carrier density as functions of the Fermi energy. Alternatively, we show an analytical description of the conduction band, valid close to the Γ point. The same fitting procedure is applied to the 6 ×6 valence band Hamiltonian. However, we find that the most reliable approach is the 8 ×8 k .p Hamiltonian for both compounds. The k .p Hamiltonians and parameter sets that we develop in this paper provide a reliable theoretical framework that can be easily applied to investigate electronic, transport, optical, and spin properties of InAs- and InP-based nanostructures.
Souza, Raphael S S; Almeida, Marcela C; Manoel, Cristiano V; Santos-Filho, Sebastião D; Fonseca, Adenilson S; Bernardo Filho, Mario
2009-01-01
Stannous chloride (SnC12) is used in nuclear medicine as a reducing agent to obtain technetium-99m-radiopharmaceuticals. It have been reported that natural products might reduce the genotoxic and cytotoxic effects related to SnC12. This work evaluated the biological effects of an aqueous extract of Salix alba on the survival of Escherichia coli (E. coli) AB1157 (wild type) cultures submitted to the action of SnC12. E. coli AB1157 cultures (exponential growth phase) were collected by centrifugation, washed and resuspended in 0.9% NaCl. Samples were incubated in water bath shaker with: (a) SnC12 (25 microg/ml), (b) Salix alba extract(11.6 mg/ml) and (c) SnC12 (25 microg/ml) + Salix alba extract (11.6 mg/ml). Incubation with 0.9% NaCl was also carried out (control). At 60 min intervals, aliquots were withdrawn, diluted, spread onto Petri dishes with solid LB medium and incubated overnight. The colonies formed were counted and the survival fractions calculated. The extract was not able to protect the E. coli cultures against the lesive action of SnC12. The extract also did not interfere with the survival of the cultures. It suggested that the substances present in the Salix alba aqueous extract did not interfere strongly with cellular metabolism and did not alter the survival fractions of E. coli AB 1157. It is speculated that this extract cannot interfere with the generation of free radicals, the possible main agent responsible for SnC12 lesive action.
NASA Astrophysics Data System (ADS)
Dash, S.; Joshi, N.; Drera, G.; Ghosh, P.; Magnano, E.; Bondino, F.; Galinetto, P.; Mozzati, M. C.; Salvinelli, G.; Aguekian, V.; Sangaletti, L.
2016-03-01
The electronic properties of the Mn:GaSe interface, produced by evaporating Mn at room temperature on a ɛ -GaSe(0001) single-crystal surface, have been studied by soft x-ray spectroscopies, and the experimental results are discussed at the light of ab initio DFT+U calculations of a model Ga1 -xMnxSe (x =0.055 ) surface alloy. Consistently with these calculations that also predict a high magnetic moment for the Mn ions (4.73 -4.83 μB), XAS measurements at the Mn L edge indicate that Mn diffuses into the lattice as a Mn2 + cation with negligible crystal-field effects. Ab initio calculations also show that the most energetically favorable lattice sites for Mn diffusion are those where Mn substitutes Ga cations in the Ga layers of the topmost Se-Ga-Ga-Se sandwich. Mn s and p states are found to strongly hybridize with Se and Ga p states, while weaker hybridization is predicted for Mn d states with Se s and p orbitals. Furthermore, unlike other Mn-doped semiconductors, there is strong interaction between the Ga -s and Mn -dz2 states. The effects of hybridization of Mn 3 d electrons with neighboring atoms are still clearly detectable from the characteristic charge-transfer satellites observed in the photoemission spectra. The Mn 3 d spectral weight in the valence band is probed by resonant photoemission spectroscopy at the Mn L edge, which also allowed an estimation of the charge transfer (Δ =2.95 eV) and Mott-Hubbard (U =6.4 eV) energies on the basis of impurity-cluster configuration-interaction model of the photoemission process. The Mott-Hubbard correlation energy U is consistent with the Ueff on-site Coulomb repulsion parameter (5.84 eV) determined for the ab initio calculations.
Karvelas, D.E.; Jody, B.J.; Pomykala, J.A.; Daniels, E.J.
1996-07-01
This paper presents the results of research being conducted at Argonne National Laboratory, to develop a cost-effective and environmentally acceptable process for the separation of high-value plastics from discarded household appliances. The process under development has separated high-purity (greater than 99.5%) acrylonitrile-butadiene-styrene (ABS) and high-impact polystyrene (HIPS) from commingled plastics generated by appliance-shredding and metal recovery operations. Plastics of similar densities, such as ABS and HIPS are further separated by using a chemical solution. By controlling the surface tension, the density and the temperature of the chemical solution, we are able to selectively float/separate plastics that have equivalent densities. In laboratory-scale tests, this technique has proven highly effective in recovering high-purity plastics materials from discarded household appliances and other obsolete durable goods. A pilot plant is under construction to demonstrate and assess the technical and economic performance of this process. In this paper, we examine the technical and economic issues that affect the recovery and separation of plastics and provide an update on Argonne`s plastics separation research and development activities.
Nonquantized dirac monopoles and strings in the berry phase of anisotropic spin systems.
Bruno, Patrick
2004-12-10
The Berry phase of an anisotropic spin system that is adiabatically rotated along a closed circuit C is investigated. It is shown that the Berry phase consists of two contributions: (i) a geometric contribution which can be interpreted as the flux through C of a nonquantized Dirac monopole, and (ii) a topological contribution which can be interpreted as the flux through C of a Dirac string carrying a nonquantized flux, i.e., a spin analogue of the Aharonov-Bohm effect. Various experimental consequences of this novel effect are discussed. PMID:15697856
Nonlocal Pancharatnam phase in two-photon interferometry
Mehta, Poonam; Samuel, Joseph; Sinha, Supurna
2010-09-15
We propose a polarized intensity interferometry experiment, which measures the nonlocal Pancharatnam phase acquired by a pair of Hanbury-Brown-Twiss photons. The setup involves two polarized thermal sources illuminating two polarized detectors. Varying the relative polarization angle of the detectors introduces a two-photon geometric phase. Local measurements at either detector do not reveal the effects of the phase, which is an optical analog of the multiparticle Aharonov-Bohm effect. The geometric phase sheds light on the three-slit experiment and suggests ways of tuning entanglement.
Cloaking two-dimensional fermions
Lin, De-Hone
2011-09-15
A cloaking theory for a two-dimensional spin-(1/2) fermion is proposed. It is shown that the spinor of the two-dimensional fermion can be cloaked perfectly through controlling the fermion's energy and mass in a specific manner moving in an effective vector potential inside a cloaking shell. Different from the cloaking of three-dimensional fermions, the scaling function that determines the invisible region is uniquely determined by a nonlinear equation. It is also shown that the efficiency of the cloaking shell is unaltered under the Aharonov-Bohm effect.
Shu, Yinghua; Zhang, Yanyan; Feng, Yuanjiao; Wang, Jianwu
2015-01-01
The cultivation of genetically modified plants (GMP) has raised concerns regarding the plants’ ecological safety. A greenhouse experiment was conducted to assess the impact of five seasons of continuous Bt (Bacillus thuringiensis) maize cultivation on the colonisation and community structure of the non-target organisms arbuscular mycorrhizal fungi (AMF) in the maize roots, bulk soils and rhizospheric soils using the terminal restriction fragment length polymorphism (T-RFLP) analysis of the 28S ribosomal DNA and sequencing methods. AMF colonisation was significantly higher in the two Bt maize lines that express Cry1Ab, 5422Bt1 (event Bt11) and 5422CBCL (MON810) than in the non-Bt isoline 5422. No significant differences were observed in the diversity of the AMF community between the roots, bulk soils and rhizospheric soils of the Bt and non-Bt maize cultivars. The AMF genus Glomus was dominant in most of the samples, as detected by DNA sequencing. A clustering analysis based on the DNA sequence data suggested that the sample types (i.e., the samples from the roots, bulk soils or rhizospheric soils) might have greater influence on the AMF community phylotypes than the maize cultivars. This study indicated that the Cry1Ab protein has minor effects on the AMF communities after five seasons of continuous Bt maize cultivation. PMID:26717324
Zeng, Huilan; Tan, Fengxiao; Shu, Yinghua; Zhang, Yanyan; Feng, Yuanjiao; Wang, Jianwu
2015-01-01
The cultivation of genetically modified plants (GMP) has raised concerns regarding the plants' ecological safety. A greenhouse experiment was conducted to assess the impact of five seasons of continuous Bt (Bacillus thuringiensis) maize cultivation on the colonisation and community structure of the non-target organisms arbuscular mycorrhizal fungi (AMF) in the maize roots, bulk soils and rhizospheric soils using the terminal restriction fragment length polymorphism (T-RFLP) analysis of the 28S ribosomal DNA and sequencing methods. AMF colonisation was significantly higher in the two Bt maize lines that express Cry1Ab, 5422Bt1 (event Bt11) and 5422CBCL (MON810) than in the non-Bt isoline 5422. No significant differences were observed in the diversity of the AMF community between the roots, bulk soils and rhizospheric soils of the Bt and non-Bt maize cultivars. The AMF genus Glomus was dominant in most of the samples, as detected by DNA sequencing. A clustering analysis based on the DNA sequence data suggested that the sample types (i.e., the samples from the roots, bulk soils or rhizospheric soils) might have greater influence on the AMF community phylotypes than the maize cultivars. This study indicated that the Cry1Ab protein has minor effects on the AMF communities after five seasons of continuous Bt maize cultivation.
Tong, Xin; Cerný, Jirí; Müller-Dethlefs, Klaus; Dessent, Caroline E H
2008-07-01
Two conformational isomers of the aromatic hydrocarbon n-butylbenzene have been studied using two-color MATI (mass analyzed threshold ionization) spectroscopy to explore the effect of conformation on ionization dynamics. Cationic states of g auche-conformer III and anti- conformers IV were selectively produced by two-color excitation via the respective S 1 origins. Adiabatic ionization potentials of the gauche- and anti-conformations were determined to be 70146 and 69872 +/- 5 cm (-1) respectively. Spectral features and vibrational modes are interpreted with the aid of MP2/cc-pVDZ ab initio calculations, and ionization-induced changes in the molecular conformations are discussed. Complete basis set (CBS) ab initio studies at MP2 level reveal reliable energetics for all four n-butylbenzene conformers observed in earlier two-color REMPI (resonance enhanced multiphoton ionization) spectra. For the S 0 state, the energies of conformer III, IV and V are above conformer I by 130, 289, 73 cm (-1), respectively. Furthermore, the combination of the CBS calculations with the measured REMPI, MATI spectra allowed the determination of the energetics of all four conformers in the S 1 and D 0 states.
Tong, Xin; Cerný, Jirí; Müller-Dethlefs, Klaus; Dessent, Caroline E H
2008-07-01
Two conformational isomers of the aromatic hydrocarbon n-butylbenzene have been studied using two-color MATI (mass analyzed threshold ionization) spectroscopy to explore the effect of conformation on ionization dynamics. Cationic states of g auche-conformer III and anti- conformers IV were selectively produced by two-color excitation via the respective S 1 origins. Adiabatic ionization potentials of the gauche- and anti-conformations were determined to be 70146 and 69872 +/- 5 cm (-1) respectively. Spectral features and vibrational modes are interpreted with the aid of MP2/cc-pVDZ ab initio calculations, and ionization-induced changes in the molecular conformations are discussed. Complete basis set (CBS) ab initio studies at MP2 level reveal reliable energetics for all four n-butylbenzene conformers observed in earlier two-color REMPI (resonance enhanced multiphoton ionization) spectra. For the S 0 state, the energies of conformer III, IV and V are above conformer I by 130, 289, 73 cm (-1), respectively. Furthermore, the combination of the CBS calculations with the measured REMPI, MATI spectra allowed the determination of the energetics of all four conformers in the S 1 and D 0 states. PMID:18533642
Zeng, Huilan; Tan, Fengxiao; Shu, Yinghua; Zhang, Yanyan; Feng, Yuanjiao; Wang, Jianwu
2015-01-01
The cultivation of genetically modified plants (GMP) has raised concerns regarding the plants' ecological safety. A greenhouse experiment was conducted to assess the impact of five seasons of continuous Bt (Bacillus thuringiensis) maize cultivation on the colonisation and community structure of the non-target organisms arbuscular mycorrhizal fungi (AMF) in the maize roots, bulk soils and rhizospheric soils using the terminal restriction fragment length polymorphism (T-RFLP) analysis of the 28S ribosomal DNA and sequencing methods. AMF colonisation was significantly higher in the two Bt maize lines that express Cry1Ab, 5422Bt1 (event Bt11) and 5422CBCL (MON810) than in the non-Bt isoline 5422. No significant differences were observed in the diversity of the AMF community between the roots, bulk soils and rhizospheric soils of the Bt and non-Bt maize cultivars. The AMF genus Glomus was dominant in most of the samples, as detected by DNA sequencing. A clustering analysis based on the DNA sequence data suggested that the sample types (i.e., the samples from the roots, bulk soils or rhizospheric soils) might have greater influence on the AMF community phylotypes than the maize cultivars. This study indicated that the Cry1Ab protein has minor effects on the AMF communities after five seasons of continuous Bt maize cultivation. PMID:26717324
Van der Wielen, Marie; Van Damme, Pierre; Chlibek, Roman; Smetana, Jan; von Sonnenburg, Frank
2006-06-29
Challenged by contrasting data on low immune responses in the elderly with a combined hepatitis A/B vaccine, a randomised, controlled study was conducted to assess the immunogenicity of three hepatitis A and B vaccination regimens (group 1: combined hepatitis A/B vaccine Twinrix [GSK]; group 2: co-administered hepatitis A vaccine, Havrix [GSK]+hepatitis B vaccine Engerix -B [GSK], group 3: co-administered hepatitis A vaccine, Vaqta [Sanofi-Pasteur MSD]+hepatitis B vaccine HB VAX PRO [Sanofi-Pasteur MSD]) and the effect of influencing factors in subjects >40 years. On completion of the full vaccination course, anti-HBs seroprotection (SP) rates were 92, 80 and 71% in groups 1, 2 and 3, respectively; anti-HAV seropositivity (S+) rates were 97, 99 and 99%, respectively. In group 1, anti-HBs SP rate was non-inferior as well as superior and anti-HAV S+ rate was non-inferior to that in groups 2 and 3. Anti-HBs response was most significantly influenced by the vaccine regimen, followed by age, gender and BMI (stepwise multiple regression analysis). BMI had the most significant influence on HAV response followed by age, gender and vaccine regimen. In conclusion, Twinrix induced superior hepatitis B SP rates and similar hepatitis A S+ rates compared to concomitant administration of monovalent vaccines in subjects aged >40 years.
General relativity in electrical engineering
NASA Astrophysics Data System (ADS)
Leonhardt, Ulf; Philbin, Thomas G.
2006-10-01
In electrical engineering metamaterials have been developed that offer unprecedented control over electromagnetic fields. Here, we show that general relativity provides the theoretical tools for designing devices made of such versatile materials. Given a desired device function, the theory describes the electromagnetic properties that turn this function into fact. We consider media that facilitate space-time transformations and include negative refraction. Our theory unifies the concepts operating behind the scenes of perfect invisibility devices, perfect lenses, the optical Aharonov Bohm effect and electromagnetic analogues of the event horizon, and may lead to further applications.
On a relation of the angular frequency to the Aharonov-Casher geometric phase in a quantum dot
NASA Astrophysics Data System (ADS)
Barboza, P. M. T.; Bakke, K.
2016-09-01
By analysing the behaviour of a neutral particle with permanent magnetic dipole moment confined to a quantum dot in the presence of a radial electric field, Coulomb-type and linear confining potentials, then, an Aharonov-Bohm-type effect for bound states and a dependence of the angular frequency of the system on the Aharonov-Casher geometric phase and the quantum numbers associated with the radial modes, the angular momentum and the spin are obtained. In particular, the possible values of the angular frequency and the persistent spin currents associated with the ground state are investigated in two different cases.
Observation of localized flat-band modes in a quasi-one-dimensional photonic rhombic lattice.
Mukherjee, Sebabrata; Thomson, Robert R
2015-12-01
We experimentally demonstrate the photonic realization of a dispersionless flat band in a quasi-one-dimensional photonic lattice fabricated by ultrafast laser inscription. In the nearest neighbor tight binding approximation, the lattice supports two dispersive and one nondispersive (flat) band. We experimentally excite superpositions of flat-band eigenmodes at the input of the photonic lattice and show the diffractionless propagation of the input states due to their infinite effective mass. In the future, the use of photonic rhombic lattices, together with the successful implementation of a synthetic gauge field, will enable the observation of Aharonov-Bohm photonic caging.
Tunable strength saddle-point contacts impact on quantum rings transmission
NASA Astrophysics Data System (ADS)
González, J. J.; Diago-Cisneros, L.
2016-09-01
A particular subject of investigation is the role of several sadle-point contact (QPC) parameters on the scattering properties of an Aharonov-Bohm-Aharonov-Casher quantum ring (QR) under Rashba-type spin orbit interaction. We discuss the interplay of the conductance with the confinement strengths and height of the QPC, which yields new and tunable harmonic and non-harmonics patterns, while one manipulates these constriction parameters. This phenomenology may be of utility to implement a novel way to modulate spin interference effects in semiconducting QRs, providing an appealing test-platform for spintronics applications.
Cold Atoms in Non-Abelian Gauge Potentials: From the Hofstadter Moth to Lattice Gauge Theory
Osterloh, K.; Baig, M.; Santos, L.; Zoller, P.; Lewenstein, M.
2005-07-01
We demonstrate how to create artificial external non-Abelian gauge potentials acting on cold atoms in optical lattices. The method employs atoms with k internal states, and laser assisted state sensitive tunneling, described by unitary kxk matrices. The single-particle dynamics in the case of intense U(2) vector potentials lead to a generalized Hofstadter butterfly spectrum which shows a complex mothlike structure. We discuss the possibility to realize non-Abelian interferometry (Aharonov-Bohm effect) and to study many-body dynamics of ultracold matter in external lattice gauge fields.
Electromagnetic potential vectors and the Lagrangian of a charged particle
NASA Technical Reports Server (NTRS)
Shebalin, John V.
1992-01-01
Maxwell's equations can be shown to imply the existence of two independent three-dimensional potential vectors. A comparison between the potential vectors and the electric and magnetic field vectors, using a spatial Fourier transformation, reveals six independent potential components but only four independent electromagnetic field components for each mode. Although the electromagnetic fields determined by Maxwell's equations give a complete description of all possible classical electromagnetic phenomena, potential vectors contains more information and allow for a description of such quantum mechanical phenomena as the Aharonov-Bohm effect. A new result is that a charged particle Lagrangian written in terms of potential vectors automatically contains a 'spontaneous symmetry breaking' potential.
Fedin, Igor; Talapin, Dmitri V
2016-08-10
Semiconductor quantum rings are of great fundamental interest because their non-trivial topology creates novel physical properties. At the same time, toroidal topology is difficult to achieve for colloidal nanocrystals and epitaxially grown semiconductor nanostructures. In this work, we introduce the synthesis of luminescent colloidal CdSe nanorings and nanostructures with double and triple toroidal topology. The nanorings form during controlled etching and rearrangement of two-dimensional nanoplatelets. We discuss a possible mechanism of the transformation of nanoplatelets into nanorings and potential utility of colloidal nanorings for magneto-optical (e.g., Aharonov-Bohm effect) and other applications.
Surface state dominated transport in topological insulator Bi{sub 2}Te{sub 3} nanowires
Hamdou, Bacel Gooth, Johannes; Dorn, August; Nielsch, Kornelius; Pippel, Eckhard
2013-11-04
We report on low temperature magnetoresistance measurements on single-crystalline Bi{sub 2}Te{sub 3} nanowires synthesized via catalytic growth and post-annealing in a Te-rich atmosphere. The observation of Aharonov-Bohm oscillations indicates the presence of topological surface states. Analyses of Subnikov-de Haas oscillations in perpendicular magnetoresistance yield extremely low two-dimensional carrier concentrations and effective electron masses, and very high carrier mobilities. All our findings are in excellent agreement with theoretical predictions of massless Dirac fermions at the surfaces of topological insulators.
Dirac oscillator interacting with a topological defect
Carvalho, J.; Furtado, C.; Moraes, F.
2011-09-15
In this work we study the interaction problem of a Dirac oscillator with gravitational fields produced by topological defects. The energy levels of the relativistic oscillator in the cosmic string and in the cosmic dislocation space-times are sensible to curvature and torsion associated to these defects and are important evidence of the influence of the topology on this system. In the presence of a localized magnetic field the energy levels acquire a term associated with the Aharonov-Bohm effect. We obtain the eigenfunctions and eigenvalues and see that in the nonrelativistic limit some results known in standard quantum mechanics are reached.
Quantum Electronic Transport of Topological Surface States in β-Ag2Se Nanowire.
Kim, Jihwan; Hwang, Ahreum; Lee, Sang-Hoon; Jhi, Seung-Hoon; Lee, Sunghun; Park, Yun Chang; Kim, Si-In; Kim, Hong-Seok; Doh, Yong-Joo; Kim, Jinhee; Kim, Bongsoo
2016-04-26
Single-crystalline β-Ag2Se nanostructures, a new class of 3D topological insulators (TIs), were synthesized using the chemical vapor transport method. The topological surface states were verified by measuring electronic transport properties including the weak antilocalization effect, Aharonov-Bohm oscillations, and Shubnikov-de Haas oscillations. First-principles band calculations revealed that the band inversion in β-Ag2Se is caused by strong spin-orbit coupling and Ag-Se bonding hybridization. These investigations provide evidence of nontrivial surface state about β-Ag2Se TIs that have anisotropic Dirac cones.
Liu, Lihong; Liu, Jian; Martinez, Todd J.
2015-12-17
Here, we investigate the photoisomerization of a model retinal protonated Schiff base (trans-PSB3) using ab initio multiple spawning (AIMS) based on multi-state second order perturbation theory (MSPT2). Discrepancies between the photodynamical mechanism computed with three-root state-averaged complete active space self-consistent field (SA-3-CASSCF, which does not include dynamic electron correlation effects) and MSPT2 show that dynamic correlation is critical in this photoisomerization reaction. Furthermore, we show that the photodynamics of trans-PSB3 is not well described by predictions based on minimum energy conical intersections (MECIs) or minimum energy conical intersection (CI) seam paths. Instead, most of the CIs involved in the photoisomerization are far from MECIs and minimum energy CI seam paths. Thus, both dynamical nuclear effects and dynamic electron correlation are critical to understanding the photochemical mechanism.
Liu, Lihong; Liu, Jian; Martinez, Todd J.
2015-12-17
Here, we investigate the photoisomerization of a model retinal protonated Schiff base (trans-PSB3) using ab initio multiple spawning (AIMS) based on multi-state second order perturbation theory (MSPT2). Discrepancies between the photodynamical mechanism computed with three-root state-averaged complete active space self-consistent field (SA-3-CASSCF, which does not include dynamic electron correlation effects) and MSPT2 show that dynamic correlation is critical in this photoisomerization reaction. Furthermore, we show that the photodynamics of trans-PSB3 is not well described by predictions based on minimum energy conical intersections (MECIs) or minimum energy conical intersection (CI) seam paths. Instead, most of the CIs involved in the photoisomerizationmore » are far from MECIs and minimum energy CI seam paths. Thus, both dynamical nuclear effects and dynamic electron correlation are critical to understanding the photochemical mechanism.« less
Yamamoto, S. Faculty of Liberal Arts, Chukyo University, Kaizu-cho, Toyota 470-03 ); Yamaguchi, K. ); Nasu, K. )
1990-07-01
{ital Ab} {ital initio} molecular-orbital calculations for CuO{sub 6} clusters have been performed to elucidate the electronic structures of undoped and doped copper oxides, which are of current interest in relation to high-{ital T}{sub {ital c}} superconductivity. The electron correlation effects for these species are thoroughly investigated by the full-valence configuration-interaction method and the complete-active-space self-consistent-field method. The electron correlation effect is relatively simple for the {ital A}{sub {ital g}} state ({sigma} hole), whereas pair excitations and spin-flip excitations give sizable contributions to the configuration-interaction wave function for the {ital B} state (in-plane {pi} hole). Implications of these results are discussed in relation to the mechanisms of the high-{Tc} superconductivity.
NASA Astrophysics Data System (ADS)
Brambila, Danilo S.; Harvey, Alex G.; Mašín, Zdeněk; Gorfinkiel, Jimena D.; Smirnova, Olga
2015-12-01
We present the first ab initio photoionization calculations for the NO2 molecule in its equilibrium geometry using the multichannel R-matrix method and a multiconfigurational description of the system. We focus on the role of correlation in NO2 photoionization and find that it plays a key role, both at the level of partial cross sections and asymmetry parameters. For the most sophisticated model used here, we achieve excellent agreement with the experimental data of Baltzer et al (2009 Chem. Phys. 237 451-70) for the asymmetry parameters of angle-resolved photo-electron spectra. We also present and analyse the angle-resolved photoionization dipoles for photon energies up to 90 eV and for the two lowest-energy ionization channels. Our results should advance the analysis of experiments in the field of attosecond spectroscopy, especially high harmonic generation, where angle-resolved photorecombination dipoles become crucial for the interpretation of experiments, even for randomly oriented molecular ensembles, due to coherent addition of signals from different orientations.
NASA Astrophysics Data System (ADS)
Gillard, Timothy; Hickey, Robert; Habersberger, Brian; Lodge, Timothy; Bates, Frank
2015-03-01
Fluctuations profoundly influence the phase behavior of block polymer-based soft materials. In ternary blends of an AB diblock copolymer with A- and B-type homopolymers, fluctuations destroy a mean-field predicted higher-order multicritical Lifshitz point and lead to the formation of the technologically important polymeric bicontinuous microemulsion phase (B μE). Here we report a fascinating change in character of the lamellar-to-disorder phase transition as the composition of homopolymer in the ternary blend is increased from zero (neat diblock) to the onset of the B μE channel. As the B μE channel is approached, the transition exhibits increasingly second-order character with the development of large-scale fluctuating smectic correlations in the disordered state near the transition. This change in character of the transition is documented with a combination of scattering, optical transmission, rheology, and TEM experiments in model blends of poly(cyclohexylethylene- b-ethylene) with the constituent homopolymers.
Omura, Y; Losco, M
1993-01-01
The effects, on normal human subjects, of 3 minutes exposure to electro-magnetic fields (EMFs) emitted from: A) personal computers, B) color television sets, or C) microwave-ovens, or cellular phones were compared by placing the same large sheet of aluminum foil with a square hole or rectangular band-shaped hole at the chest level (or at the side of the head with the cellular phone), with or without grounding the aluminum foil, using the Bi-Digital O-Ring Test Dysfunction Localization and Molecular Identification Methods with cancer related substances (i.e., Oncogen C-fos Ab2 and mercury in the cell nucleus, Integrin alpha 5 beta 1 in the cell & nuclear membranes, and disappearance of Acetylcholine) as reference control substances. All the above sources of the EMFs not only induced the following various transitional abnormalities on the EMF entry area, but also induced similar abnormalities at the EMF exit area on the back (where the abnormality was found in the same shape as exposed EMF entry area, and the effect lasted for a shorter time than the entry point of the EMF): A) Exposure of the body at about 50 cm from the monitor of some of the typical personal computers resulted in: A1) decrease in Acetylcholine; A2) appearance of circulatory disturbance with the appearance of Thromboxane B2; A3) short-lasting appearance of Oncogen C-fos Ab2; A4) short-lasting appearance of Oncogen C-fos Ab1, though it lasted longer than C-fos Ab2; A5) no appearance of Integrin alpha 5 beta 1. B) part of the chest was exposed at a distance between 1 meter and up to 3 meters from a color television sized anywhere from 13'' to 21'', resulting in: B1) decrease in Acetylcholine; B2) appearance of circulatory disturbance with the appearance of Thromboxane B2; B3) short-lasting appearance of Oncogen C-fos Ab2; B4) short-lasting appearance of Oncogen C-fos Ab1, though it lasted longer than C-fos Ab2; B5) very short-lasting appearance of Integrin alpha 5 beta 1. C) When body was exposed, at
Pantcheva, Mina B; Kahook, Malik Y
2010-10-01
Anterior chamber drainage angle surgery, namely trabeculotomy and goniotomy, has been commonly utilized in children for many years. Its' reported success has ranged between 68% and 100% in infants and young children with congenital glaucoma. However, the long-term success of these procedures has been limited in adults presumably due to the formation of anterior synechiae (AS) in the postoperative phase. Recently, ab interno trabeculectomy with the Trabectome™ has emerged as a novel surgical approach to effectively and selectively remove and ablate the trabecular meshwork and the inner wall of the Schlemm's canal in an attempt to avoid AS formation or other forms of wound healing with resultant closure of the cleft. This procedure seems to have an appealing safety profile with respect to early hypotony or infection if compared to trabeculectomy or glaucoma drainage device implantation. This might be advantageous in some of the impoverish regions of the Middle East and Africa where patients experience difficulties keeping up with their postoperative visits. It is important to note that no randomized trial comparing the Trabectome to other glaucoma procedures appears to have been published to date. Trabectome surgery is not a panacea, however, and it is associated with early postoperative intraocular pressure spikes that may require additional glaucoma surgery as well as a high incidence of hyphema. Reported results show that postoperative intraocular pressure (IOP) remains, at best, in the mid-teen range making it undesirable in patients with low-target IOP goals. A major advantage of Trabectome surgery is that it does not preclude further glaucoma surgery involving the conjunctiva, such as a trabeculectomy or drainage device implantation. As prospective randomized long-term clinical data become available, we will be better positioned to elucidate the exact role of this technique in the glaucoma surgical armamentarium. PMID:21180426
Siirola, John D.; Slepoy, Alexander; Sprigg, Jr., James A.; Jorgensen, Craig R.; Selzler, Gene; Pryor, Richard J.
2007-05-01
A hierarchical, modular modeling environment for hybrid simulations of sequential-modular, systems dynamics, discrete-event, and agent-based paradigms Omega-AB models contain a hierarchically-defined module tree that specifies the execution logic for the simulation, and a multi-network graph that defines the environment within which the simulation occurs. Modules are the fundamental buildinig blocks of an Omega-AB model and can define anything from a basic mathematical operation to a complex behavioral response model. Modules rely on the "plug-in" concept which allows developers to build independent module libraries that are gathered, linked, and instantiated by the Omega-AB engine at run time. Inter-module communication occurs through two complimentary systems: pull-based "ports" for general computation patterns and push-based "plugs" for event processing. The simulation environment is an abstract graph of nodes and links. Agents (module sub-trees headed up by an Agent module) reside at nodes and relate to their neighbors through typed links. To facilitate the construction and visualization of complex, interacting networks with dramatically different structure, Omega-AB provides a system for organizing the nodes into hierarchica trees that describe "slices" of the overall network.
2007-05-01
A hierarchical, modular modeling environment for hybrid simulations of sequential-modular, systems dynamics, discrete-event, and agent-based paradigms Omega-AB models contain a hierarchically-defined module tree that specifies the execution logic for the simulation, and a multi-network graph that defines the environment within which the simulation occurs. Modules are the fundamental buildinig blocks of an Omega-AB model and can define anything from a basic mathematical operation to a complex behavioral response model. Modules rely on the "plug-in" conceptmore » which allows developers to build independent module libraries that are gathered, linked, and instantiated by the Omega-AB engine at run time. Inter-module communication occurs through two complimentary systems: pull-based "ports" for general computation patterns and push-based "plugs" for event processing. The simulation environment is an abstract graph of nodes and links. Agents (module sub-trees headed up by an Agent module) reside at nodes and relate to their neighbors through typed links. To facilitate the construction and visualization of complex, interacting networks with dramatically different structure, Omega-AB provides a system for organizing the nodes into hierarchica trees that describe "slices" of the overall network.« less
Niu, Zhen-Wei; Zeng, Zhao-Yi; Hu, Cui-E; Cai, Ling-Cang; Chen, Xiang-Rong
2015-01-07
The thermodynamic properties of CeO{sub 2} have been reevaluated by a simple but accurate scheme. All our calculations are based on the self-consistent ab initio lattice dynamical (SCAILD) method that goes beyond the quasiharmonic approximation. Through this method, the effects of phonon-phonon interactions are included. The obtained thermodynamic properties and phonon dispersion relations are in good agreement with experimental data when considering the correction of phonon-phonon interaction. We find that the correction of phonon-phonon interaction is equally important and should not be neglected. At last, by comparing with quasiharmonic approximation, the present scheme based on SCAILD method is probably more suitable for high temperature systems.
Matsubara, Toshiaki; Dupuis, Michel; Aida, Misako
2008-02-01
We applied the ONIOM-molecular dynamics (MD) method to cytosine deaminase to examine the environmental effects of the amino acid residues in the pocket of the active site on the substrate taking account of their thermal motion. The ab initio ONIOM-MD simulations show that the substrate uracil is strongly perturbed by the amino acid residue Ile33, which sandwiches the uracil with His62, through the steric contact due to the thermal motion. As a result, the magnitude of the thermal oscillation of the potential energy and structure of the substrate uracil significantly increases. TM and MA were partly supported by grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan.MD was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, and by the Office of Biological and Environmental Research of the U.S. Department of Energy DOE. Battelle operates Pacific Northwest National Laboratory for DOE.
NASA Astrophysics Data System (ADS)
Kudashov, A. D.; Petrov, A. N.; Skripnikov, L. V.; Mosyagin, N. S.; Isaev, T. A.; Berger, R.; Titov, A. V.
2014-11-01
Relativistic ab initio calculations have been performed to assess the suitability of RaF for experimental search of P - and T -and-P -violating interactions. The parameters of P - and T ,P -odd terms of the spin-rotational Hamiltonian have been calculated for the 2Σ electronic ground state of the 223RaF molecule. They include the Wa parameter, which is critical in the experimental search for nuclear anapole moment, and the parameters Wd and WSP required to obtain restrictions on the electric dipole moment of the electron and T ,P -odd scalar-pseudoscalar interactions, respectively. The parameter X corresponding to the "volume effect" in the T ,P -odd interaction of the 223Ra nuclear Schiff moment with electronic shells of RaF has also been computed. Spectroscopic and hyperfine structure constants for 223RaF and 223Ra+ have been computed as well, demonstrating the accuracy of the methods employed.
NASA Astrophysics Data System (ADS)
Pamuk, Betül; Allen, Philip B.; Soler, Jose M.; Fernández-Serra, Marivi
2014-03-01
The contributions of nuclear zero point vibrations to the structures of liquid water and ice are not negligible. Recently, we have explained the source of an anomalous isotope shift in hexagonal ice, representing itself as an increase in the lattice volume when H is replaced by D, by calculating free energy within the quasiharmonic approximation, with ab initio density functional theory. In this work, we extend our studies to analyze the zero point effect in other ice-like structures under different densities: clathrate hydrates, LDL and HDL-like amorphous ices with different densities, and a highly dense ice phase, ice VIII. We show that there is a transition from anomalous isotope effect to normal isotope effect as the density increases. We also analyze nuclear zero point effects in liquid water using different vdW-DFs and make connections to this anomalous-normal isotope effect transition in ice. This work is supported by DOE Early Career Award No. DE-SC0003871.
NASA Astrophysics Data System (ADS)
Vigil-Fowler, Derek; Malone, Brad; Louie, Steven
2014-03-01
Understanding the effect of semicore electrons on ab initiioPW-PP GW calculations is currently of great interest due to the increasing importance of complex materials with active semicore electrons, e.g.,the transition metal dichalcogenides. While past research has found a significant effect due to the inclusion of semicore electrons, it did not fully explore the nature of the various deviations of traditional valence-only PW-PP GW calculations from calculations that include the semicore electrons. We study this issue in the simple system of the Si atom, where the effect is more easily isolated, and then extend our results to bulk Si, and other bulk systems. We present results showing the effect of semicore electrons on various contributions to the GW self energy, and discuss the nature of differences with the traditional PW-PP approach. We present methods to efficiently include the effect of semicore electrons in a hierarchy of computational cost and accuracy. This work was supported by NSF Grant No. DMR10-1006184 and U.S. DOE Contract No. DE-AC02-05CH11231. Computational resources have been provided by the NERSC and NICS. D.V-F. acknowledges funding from the DOD's NDSEG fellowship.
Laasonen, Kari
2013-01-01
In this chapter, an introduction to ab initio molecular dynamics (AIMD) has been given. Many of the basic concepts, like the Hellman-Feynman forces, the difference between the Car-Parrinello molecular dynamics and AIMD, have been explained. Also a very versatile AIMD code, the CP2K, has been introduced. On the application, the emphasis was on the aqueous systems and chemical reactions. The biochemical applications have not been discussed in depth.
Zhu, Hua; Fan, Gao-Chao; Abdel-Halim, E S; Zhang, Jian-Rong; Zhu, Jun-Jie
2016-03-15
A novel, enhanced photoelectrochemical immunoassay was established for sensitive and specific detection of carbohydrate antigen 19-9 (CA19-9, Ag). In this protocol, TiO2 nanowires (TiO2NWs) were first decorated with Au nanoparticles to form TiO2NWs/Au hybrid structure, and then coated with CdSe@ZnS quantum dots (QDs) via the layer-by-layer method, producing TiO2NWs/Au/CdSe@ZnS sensitized structure, which was employed as the photoelectrochemical matrix to immobilize capture CA19-9 antibodies (Ab1); whereas, bipyridinium (V(2+)) molecules were labeled on signal CA19-9 antibodies (Ab2) to form Ab2@V(2+) conjugates, which were used as signal amplification elements. The TiO2NWs/Au/CdSe@ZnS sensitized structure could adequately absorb light energy and dramatically depress electron-hole recombination, resulting in evidently enhanced photocurrent intensity of the immunosensing electrode. While target Ag were detected, the Ab2@V(2+) conjugates could significantly decrease the photocurrent detection signal because of strong electron-withdrawing property of V(2+) coupled with evident steric hindrance of Ab2. Thanks to synergy effect of TiO2NWs/Au/CdSe@ZnS sensitized structure and quenching effect of Ab2@V(2+) conjugates, the well-established photoelectrochemical immunoassay exhibited a low detection limit of 0.0039 U/mL with a wide linear range from 0.01 U/mL to 200 U/mL for target Ag detection. This proposed photoelectrochemical protocol also showed good reproducibility, specificity and stability, and might be applied to detect other important biomarkers. PMID:26433066
Zhu, Hua; Fan, Gao-Chao; Abdel-Halim, E S; Zhang, Jian-Rong; Zhu, Jun-Jie
2016-03-15
A novel, enhanced photoelectrochemical immunoassay was established for sensitive and specific detection of carbohydrate antigen 19-9 (CA19-9, Ag). In this protocol, TiO2 nanowires (TiO2NWs) were first decorated with Au nanoparticles to form TiO2NWs/Au hybrid structure, and then coated with CdSe@ZnS quantum dots (QDs) via the layer-by-layer method, producing TiO2NWs/Au/CdSe@ZnS sensitized structure, which was employed as the photoelectrochemical matrix to immobilize capture CA19-9 antibodies (Ab1); whereas, bipyridinium (V(2+)) molecules were labeled on signal CA19-9 antibodies (Ab2) to form Ab2@V(2+) conjugates, which were used as signal amplification elements. The TiO2NWs/Au/CdSe@ZnS sensitized structure could adequately absorb light energy and dramatically depress electron-hole recombination, resulting in evidently enhanced photocurrent intensity of the immunosensing electrode. While target Ag were detected, the Ab2@V(2+) conjugates could significantly decrease the photocurrent detection signal because of strong electron-withdrawing property of V(2+) coupled with evident steric hindrance of Ab2. Thanks to synergy effect of TiO2NWs/Au/CdSe@ZnS sensitized structure and quenching effect of Ab2@V(2+) conjugates, the well-established photoelectrochemical immunoassay exhibited a low detection limit of 0.0039 U/mL with a wide linear range from 0.01 U/mL to 200 U/mL for target Ag detection. This proposed photoelectrochemical protocol also showed good reproducibility, specificity and stability, and might be applied to detect other important biomarkers.
New challenges to medicare beneficiary access to mAbs
Wilson, Andrew
2009-01-01
Precision binding of monoclonal antibodies (mAbs) to biological targets, their relative clinical success, and expansion of indications following initial approval, are distinctive clinical features. The relatively high cost of mAbs, together with the absence of a regulatory pathway to generics, stand out as distinctive economic features. Based on both literature review and primary data collection we enumerated mAb original approvals, supplemental indications and off-label uses, assessed payer formulary management of mAbs, and determined new challenges to Medicare beneficiary access to mAbs. We found that the FDA has approved 22 mAbs and 30 supplemental indications pertaining to the originally approved mAbs. In addition, there are 46 off-label use citations in officially recognized pharmaceutical compendia. Across Part B carriers and Part D plans, we found considerable variation in terms of coverage and conditions of reimbursement related to on- and off-label uses of mAbs. Our results point to four major challenges facing mAb developers, health care providers, Medicare beneficiaries, payers and policymakers. These include administrative price controls, coverage variation, projected shift from physician- to self-administered mAbs, and comparative effectiveness. We suggest more systematic use of “coverage with evidence development” as a means of optimally addressing these challenges. PMID:20046575
NASA Astrophysics Data System (ADS)
Nattino, Francesco; Galparsoro, Oihana; Costanzo, Francesca; Díez Muiño, Ricardo; Alducin, Maite; Kroes, Geert-Jan
2016-06-01
Accurately modeling surface temperature and surface motion effects is necessary to study molecule-surface reactions in which the energy dissipation to surface phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-surface results. Furthermore, the GLO model and the AIMD method predict very similar energy transfer to the lattice degrees of freedom in the non-reactive events, and similar dissociation dynamics.
van der Poll, T; Levi, M; ten Cate, H; Jansen, J; Biemond, B J; Haagmans, B L; Eerenberg, A; van Deventer, S J; Hack, C E; ten Cate, J W
1995-04-01
TNF is considered to be an intermediate factor in endotoxin-induced release of other cytokines and endotoxin-induced neutrophil degranulation. Little is known about the effect of postponed treatment with anti-TNF in primate endotoxin models. To assess the effect of delayed treatment with anti-TNF in endotoxaemia, six healthy adult chimpanzees were intravenously injected with Escherichia coli endotoxin (4 ng/kg). In three of these animals the administration of endotoxin was followed after 30 min by a bolus i.v. injection of the anti-TNF F(ab')2 fragment MAK 195F (0.1 mg/kg). Post-treatment with MAK 195F completely prevented the appearance of TNF activity in serum elicited by endotoxin, and markedly reduced the rises in the serum concentrations of IL-6 and IL-8. In addition, the endotoxin-induced increases in the type I and type II soluble TNF receptors were also profoundly inhibited by MAK 195F, suggesting that TNF is involved in the release of its own soluble receptors in endotoxaemia. Neutrophilic leucocytosis was not affected by MAK 195F. In contrast, MAK 195F did significantly abrogate neutrophil degranulation, as measured by the plasma concentrations of lactoferrin. These results indicate that treatment with anti-TNF 30 min after the administration of endotoxin is still effective in attenuating the induction of the cytokine network and of neutrophil degranulation.
Nattino, Francesco; Galparsoro, Oihana; Costanzo, Francesca; Díez Muiño, Ricardo; Alducin, Maite; Kroes, Geert-Jan
2016-06-28
Accurately modeling surface temperature and surface motion effects is necessary to study molecule-surface reactions in which the energy dissipation to surface phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-surface results. Furthermore, the GLO model and the AIMD method predict very similar energy transfer to the lattice degrees of freedom in the non-reactive events, and similar dissociation dynamics.
NASA Astrophysics Data System (ADS)
Wolff, Stephen K.; Jayatilaka, Dylan; Chandler, Graham S.
1995-09-01
Spin-orbit interaction plays a significant role in determining the magnetic density in some transition metal complexes. We present a new ab initio technique, based on an extension of unrestricted Hartree-Fock theory, which includes nonperturbatively these spin-orbit effects, and simultaneously also the effects of a finite magnetic field. We also present a new and efficient method for calculating magnetic structure factors, based on the current density rather than magnetic dipole moment density, for a crystal composed of noninteracting molecular fragments. These structure factors are directly comparable to polarized neutron diffraction experiments. Results for the Cs3CoCl5 crystal are compared with experiment and previous studies. Without one-electron spin-orbit coupling terms, the magnitudes of the predicted structure factors are on average 10-15 % too low, whereas, with the spin-orbit terms, the magnitudes are 25-30% too high. Using an effective nuclear charge for Co in the spin-orbit term brings the results into much better agreement, and suggests that the two-electron spin-orbit shielding terms omitted in the present work are important. For over one quarter of the reflections studied, the magnetic contribution to the structure factors is more than 20% of the nuclear contribution.
Li, Yunhe; Romeis, Jörg; Wang, Ping; Peng, Yufa; Shelton, Anthony M.
2011-01-01
The ladybird beetle, Coleomegilla maculata (DeGeer), is a common and abundant predator in many cropping systems. Its larvae and adults are predaceous, feeding on aphids, thrips, lepidopteran larvae and plant tissues, such as pollen. Therefore, this species is exposed to insecticidal proteins expressed in insect-resistant, genetically engineered cotton expressing Cry proteins derived from Bacillus thuringiensis (Bt). A tritrophic bioassay was conduced to evaluate the potential impact of Cry2Ab- and Cry1Ac-expressing cotton on fitness parameters of C. maculata using Bt-susceptible and -resistant larvae of Trichoplusia ni as prey. Coleomegilla maculata survival, development time, adult weight and fecundity were not different when they were fed with resistant T. ni larvae reared on either Bt or control cotton. To ensure that C. maculata were not sensitive to the tested Cry toxins independent from the plant background and to add certainty to the hazard assessment, C. maculata larvae were fed artificial diet incorporated with Cry2Ab, Cry1Ac or both at >10 times higher concentrations than in cotton tissue. Artificial diet containing E-64 was included as a positive control. No differences were detected in any life-table parameters between Cry protein-containing diet treatments and the control diet. In contrast, larvae of C. maculata fed the E-64 could not develop to the pupal stage and the 7-d larval weight was significantly negatively affected. In both feeding assays, the stability and bioactivity of Cry proteins in the food sources were confirmed by ELISA and sensitive-insect bioassays. Our results show that C. maculata is not affected by Bt cotton and is not sensitive to Cry2Ab and Cry1Ac at concentrations exceeding the levels in Bt cotton, thus demonstrating that Bt cotton will pose a negligible risk to C. maculata. More importantly, this study demonstrates a comprehensive system for assessing the risk of genetically modified plants on non-target organisms. PMID
Okamoto, Akisumi; Yano, Atsushi; Nomura, Kazuya; Higai, Shin'ichi; Kurita, Noriyuki
2014-05-01
The molecular pathogenesis of Alzheimer's disease (AD) is deeply involved in aggregations of amyloid β-proteins (Aβ) in a diseased brain. The recent experimental studies indicated that the mutation of Asp23 by Asn (D23N) within the coding sequence of Aβ increases the risk for the pathogeny of cerebral amyloid angiopathy and early-onset familial ADs. Fibrils of the D23N mutated Aβs can form both parallel and antiparallel structures, and the parallel one is considered to be associated with the pathogeny. However, the structure and the aggregation mechanism of the mutated Aβ fibrils are not elucidated at atomic and electronic levels. We here investigated solvated structures of the two types of Aβ dimers, each of which is composed of the wild-type or the D23N mutated Aβ, using classical molecular mechanics and ab initio fragment molecular orbital (FMO) methods, in order to reveal the effect of the D23N mutation on the structure of Aβ dimer as well as the specific interactions between the Aβ monomers. The results elucidate that the effect of the D23N mutation is significant for the parallel structure of Aβ dimer and that the solvating water molecules around the Aβ dimer have significant contribution to the stability of Aβ dimer.
On the Strain Rate Sensitivity of Abs and Abs Plus Fused Deposition Modeling Parts
NASA Astrophysics Data System (ADS)
Vairis, A.; Petousis, M.; Vidakis, N.; Savvakis, K.
2016-06-01
In this work the effect of strain rate on the tensile strength of fused deposition modeling parts built with Acrylonitrile-butadiene-styrene (ABS) and ABS plus material is presented. ASTM D638-02a specimens were built with ABS and ABS plus and they were tested on a Schenck Trebel Co. tensile test machine at three different test speeds, equal, lower, and higher to the test speed required by the ASTM D638-02a standard. The experimental tensile strength results were compared and evaluated. The fracture surfaces of selected specimens were examined with a scanning electron microscope, to determine failure mode of the filament strands. It was found that, as the test speed increases, specimens develop higher tensile strength and have higher elastic modulus. Specimens tested in the highest speed of the experiment had on average about 10% higher elastic modulus and developed on average about 11% higher tensile strength.
On the Strain Rate Sensitivity of Abs and Abs Plus Fused Deposition Modeling Parts
NASA Astrophysics Data System (ADS)
Vairis, A.; Petousis, M.; Vidakis, N.; Savvakis, K.
2016-09-01
In this work the effect of strain rate on the tensile strength of fused deposition modeling parts built with Acrylonitrile-butadiene-styrene (ABS) and ABS plus material is presented. ASTM D638-02a specimens were built with ABS and ABS plus and they were tested on a Schenck Trebel Co. tensile test machine at three different test speeds, equal, lower, and higher to the test speed required by the ASTM D638-02a standard. The experimental tensile strength results were compared and evaluated. The fracture surfaces of selected specimens were examined with a scanning electron microscope, to determine failure mode of the filament strands. It was found that, as the test speed increases, specimens develop higher tensile strength and have higher elastic modulus. Specimens tested in the highest speed of the experiment had on average about 10% higher elastic modulus and developed on average about 11% higher tensile strength.
Ab initio studies on the mechanism for linear and nonlinear optical effects in YAl3(BO3)4
NASA Astrophysics Data System (ADS)
He, Ran; Lin, Z. S.; Lee, M.-H.; Chen, C. T.
2011-05-01
First-principles studies of the linear and nonlinear optical properties for YAl3(BO3)4 (YAB) are presented. Based upon the electronic band structure, the optical refractive indices, birefringence, and second harmonic generation (SHG) coefficients of YAB are calculated, which are in good agreement with experimental values. In addition, the SHG-weighted electron density analysis and the real-space atom-cutting method are adopted to elucidate the origin of the linear and nonlinear optical effects in YAB. The results show that the anionic (BO3) groups have dominant contributions to the birefringence. The contribution of the Al cations to the optical effects is negligibly small. However, the Y cations bond to the neighbor O anions and form the deformed (YO6) octahedra, which results in the large SHG effects in YAB.
NASA Astrophysics Data System (ADS)
Ebert, D.; Klimenko, K. G.; Kolmakov, P. B.; Zhukovsky, V. Ch.
2016-08-01
In this paper we consider a class of (2+1)D schematic models with four-fermion interactions that are effectively used in studying condensed-matter systems with planar crystal structure, and especially graphene. Symmetry breaking in these models occurs due to a possible appearance of condensates. Special attention is paid to the symmetry properties of the appearing condensates in the framework of discrete chiral and C, P and T transformations. Moreover, boundary conditions corresponding to carbon nanotubes are considered and their relations with the effect of an applied external magnetic field are studied. To this end we calculated the effective potential for the nanotube model including effects of finite temperature, density and an external magnetic field. As an illustration we made numerical calculations of the chiral symmetry properties in a simpler Gross-Neveu model with only one condensate taken into account. We also investigated the phase structure of the nanotube model under the influence of the Aharonov-Bohm effect and demonstrated that there is a nontrivial relation between the magnitude of the Aharonov-Bohm phase, compactification of the spatial dimension and thermal restoration of the originally broken chiral symmetry.
NASA Astrophysics Data System (ADS)
Dariavach, Nader Guseinovich
The effect of high-density electrical pulses on mechanical and structural properties of sintered aluminum SiC metal-matrix composites, fabricated by standard powder-metallurgy compaction and sintering, was investigated. Three types of phenomena where investigated during transverse rupture testing of the samples: a consolidation effect (increasing of the transverse rupture strength (TRS)), an electroplastic effect (decreasing of the flow stresses), and an increasing of the stress intensity factor by electric pulse application. It was observed, that an increase in the TRS strength of sintered powder metallurgy (PM) aluminum and aluminum metal matrix composite (MMC) compacts is a result of the electric pulse consolidation effect due to non-uniform temperature distribution around the grain boundaries. Three analytical models of the thermal effect of electric pulses on aluminum samples where considered: total temperature change of the sample due to a one electric pulse, one-dimensional steady state model and transient 2D thermal analysis of the temperature distribution around the grain boundary. The 2D transient analysis shows that the temperature rise in the grain boundary of a sintered PM aluminum sample due to an electric pulse can exceed the melting point. At the same time the temperature of the bulk material has an insignificant (<28°C) change. It was found that the electroplastic effect, due to electric pulse application, can account for up to a 40% load drop in aluminum MMC PM compacts. Reduction of flow stresses during plastic deformation could reduce the risk of structural damage, micro-cracks, SiC particle fracture and delamination of the aluminum MMC. These results may find practical application for manufacturing processes such as forging, extrusion, rolling, which involve plastic deformation. It was experimentally proven that a non-uniform temperature distribution around the crack could re-melt the crack tip and increase the strength of the damaged material
NASA Astrophysics Data System (ADS)
Li, Xiaojie; Schönecker, Stephan; Li, Ruihuan; Li, Xiaoqing; Wang, Yuanyuan; Zhao, Jijun; Johansson, Börje; Vitos, Levente
2016-07-01
To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1‑x‑y Re x Os y (0 ⩽ x, y ⩽ 6%) random alloys in body centered cubic (bcc) structure are investigated systematically using the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA). The calculated lattice constant and elastic properties of pure W are consistent with available experiments. Both Os and Re additions reduce the lattice constant and increase the bulk modulus of W, with Os having the stronger effect. The polycrystalline shear modulus, Young’s modulus and the Debye temperature increase (decrease) with the addition of Re (Os). Except for C 11, the other elastic parameters including C 12, C 44, Cauchy pressure, Poisson ratio, B/G, increase as a function of Re and Os concentration. The variations of the latter three parameters and the trend in the ratio of cleavage energy to shear modulus for the most dominant slip system indicate that the ductility of the alloy enhances with increasing Re and Os content. The calculated elastic anisotropy of bcc W slightly increases with the concentration of both alloying elements. The estimated melting temperatures of the W–Re–Os alloy suggest that Re or Os addition will reduce the melting temperature of pure W solid. The classical Labusch–Nabarro model for solid-solution hardening predicts larger strengthening effects in W1‑y Os y than in W1‑x Re x . A strong correlation between C‧ and the fcc–bcc structural energy difference for W1‑x‑y Re x Os y is revealed demonstrating that canonical band structure dictates the alloying effect on C‧. The structural energy difference is exploited to estimate the alloying effect on the ideal tensile strength in the [0 0 1] direction.
NASA Astrophysics Data System (ADS)
Li, Xiaojie; Schönecker, Stephan; Li, Ruihuan; Li, Xiaoqing; Wang, Yuanyuan; Zhao, Jijun; Johansson, Börje; Vitos, Levente
2016-07-01
To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1-x-y Re x Os y (0 ⩽ x, y ⩽ 6%) random alloys in body centered cubic (bcc) structure are investigated systematically using the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA). The calculated lattice constant and elastic properties of pure W are consistent with available experiments. Both Os and Re additions reduce the lattice constant and increase the bulk modulus of W, with Os having the stronger effect. The polycrystalline shear modulus, Young’s modulus and the Debye temperature increase (decrease) with the addition of Re (Os). Except for C 11, the other elastic parameters including C 12, C 44, Cauchy pressure, Poisson ratio, B/G, increase as a function of Re and Os concentration. The variations of the latter three parameters and the trend in the ratio of cleavage energy to shear modulus for the most dominant slip system indicate that the ductility of the alloy enhances with increasing Re and Os content. The calculated elastic anisotropy of bcc W slightly increases with the concentration of both alloying elements. The estimated melting temperatures of the W-Re-Os alloy suggest that Re or Os addition will reduce the melting temperature of pure W solid. The classical Labusch-Nabarro model for solid-solution hardening predicts larger strengthening effects in W1-y Os y than in W1-x Re x . A strong correlation between C‧ and the fcc-bcc structural energy difference for W1-x-y Re x Os y is revealed demonstrating that canonical band structure dictates the alloying effect on C‧. The structural energy difference is exploited to estimate the alloying effect on the ideal tensile strength in the [0 0 1] direction.
Tummanapelli, Anil Kumar; Vasudevan, Sukumaran
2014-11-26
The theoretical estimation of the dissociation constant, or pKa, of weak acids continues to be a challenging field. Here, we show that ab initio Car-Parrinello molecular dynamics simulations in conjunction with metadynamics calculations of the free-energy profile of the dissociation reaction provide reasonable estimates of the pKa value. Water molecules, sufficient to complete the three hydration shells surrounding the acid molecule, were included explicitly in the computation procedure. The free-energy profiles exhibit two distinct minima corresponding to the dissociated and neutral states of the acid, and the difference in their values provides the estimate for pKa. We show for a series of organic acids that CPMD simulations in conjunction with metadynamics can provide reasonable estimates of pKa values. The acids investigated were aliphatic carboxylic acids, chlorine-substituted carboxylic acids, cis- and trans-butenedioic acid, and the isomers of hydroxybenzoic acid. These systems were chosen to highlight that the procedure could correctly account for the influence of the inductive effect as well as hydrogen bonding on pKa values of weak organic acids. In both situations, the CPMD metadynamics procedure faithfully reproduces the experimentally observed trend and the magnitudes of the pKa values.
NASA Astrophysics Data System (ADS)
Music, Denis; Chirita, Valeriu; Schneider, Jochen M.; Helmersson, Ulf
2004-03-01
The effect of chemical composition on the elastic and electrical properties is studied for the BOxYz system with 0.27⩽x⩽1.14 and 0.36⩽z⩽0.08. We use ab initio calculations to obtain the elastic constants and density of states for BO1.5 and the BOY phase (yttrium substituting for oxygen in the boron suboxide structure). For decreasing x values, the elastic modulus is predicted to increase from 11 to 340 GPa, while electronic structure calculations suggest a shift in electrical properties from insulating to metallic. Thin films in the B-O-Y system are grown by reactive rf magnetron sputtering. As x decreases from 1.14 to 0.27, the elastic modulus increases from 12 to 282 GPa, which is a factor of 24, while resistivity decreases from 7.6±0.4 to (3.8±0.1)×10-2 Ωm. The observed shifts in elasticity and resistivity are shown to be induced by the associated changes in chemical bonding from van der Waals type in BO1.5 to icosahedral type in the BOY phase.
NASA Astrophysics Data System (ADS)
Reyes-Lillo, Sebastian E.; Rangel, Tonatiuh; Bruneval, Fabien; Neaton, Jeffrey B.
2016-07-01
The Ruddlesden-Popper (RP) homologous series Srn +1TinO3 n +1 provides a useful template for the study and control of the effects of dimensionality and quantum confinement on the excited state properties of the complex oxide SrTiO3. We use ab initio many-body perturbation theory within the G W approximation and the Bethe-Salpeter equation approach to calculate quasiparticle energies and absorption spectra of Srn +1TinO3 n +1 for n =1 -5 and ∞ . Our computed direct and indirect optical gaps are in excellent agreement with spectroscopic measurements. The calculated optical spectra reproduce the main experimental features and reveal excitonic structure near the gap edge. We find that electron-hole interactions are important across the series, leading to significant exciton binding energies that increase for small n and reach a value of 330 meV for n =1 , a trend attributed to increased quantum confinement. We find that the lowest-energy singlet exciton of Sr2TiO4 (n =1 ) localizes in the two-dimensional plane defined by the TiO2 layer, and we explain the origin of its localization.
Farhat, Ayman; Abdul-Al, Saleh N
2015-06-15
The electronic structures with spin-orbit effects of the zirconium nitride ZrN molecule are investigated by the methods of multireference single and double configuration interaction. The potential energy curves are calculated along with the spectroscopic constants for the lowest-lying 34 spin-orbit states Ω in ZrN. A good agreement is displayed by comparing the calculated spectroscopic constants with those available experimentally. The permanent dipole moments are calculated along with the vibrational energies. New results are obtained in this work for 29 spin-orbit states and their spectroscopic constants calculated. PMID:25899865
Alinia, F; Ghareyazie, B; Rubia, L; Bennett, J; Cohen, M B
2000-04-01
The resistance of vegetative, booting, and flowering stage plants of a variety of an aromatic rice, Oryza sativa L., transformed with a Bacillus thuringiensis Berliner cry1Ab gene under control of the maize phosphoenolpyruvate carboxylase (PEPC) promoter was evaluated against four lepidopterous rice pests--the stem borers Chilo suppressalis (Walker) (Lepidoptera: Crambidae) and Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae), and the foliage feeders Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) and Naranga aenescens Moore (Lepidoptera: Noctuidae). Plants of the cry1Ab-transformed line (no. 827) were more resistant to young larvae of S. incertulas, C. suppressalis, and C. medinalis than control plants at the vegetative stage but not at the flowering stage. Survival of 10-d-old stem borer larvae did not differ on cry1Ab plants and control plants at either the vegetative or flowering stage, but the development of 10-d-old C. suppressalis larvae was retarded on the vegetative stage cry1Ab plants. Immunological analysis also showed an apparent decline in Cry1Ab titer in leaf blades and leaf sheaths at the reproductive stage. In experiments comparing three fertilizer treatments (NPK, PK, and none), there was a significant interaction between fertilizer treatment and variety on larval survival only in whole-plant assays at booting stage with C. suppressalis. On cry1Ab plants, larval survival did not differ significantly among the three fertilizer levels, whereas on control plants survival was highest with the NPK treatment. cry1Ab plants tested at the sixth and seventh generations after transformation were more resistant than control plants to N. aenescens and C. suppressalis, respectively, suggesting that gene silencing will not occur in line 827. The results of the experiments are discussed in terms of resistance management for B. thuringiensis toxins in rice. PMID:10826204
Lau, E Y; Lightstone, F C; Colvin, M E
2006-02-10
Quantum mechanical calculations were performed to study the differences between the important radiopharmaceutical metals yttrium (Y) and indium (In) bound by DOTA and modified DOTA molecules. Energies were calculated at the MP2/6-31+G(d)//HF/6-31G(d) levels, using effective core potentials on the Y and In ions. Although the minimum energy structures obtained are similar for both metal ion-DOTA complexes, changes in coordination and local environment significantly affect the geometries and energies of these complexes. Coordination by a single water molecule causes a change in the coordination number and a change in the position of the metal ion in In-DOTA; but, Y-DOTA is hardly affected by water coordination. When one of the DOTA carboxylates is replaced by an amide, the coordination energy for the amide arm shows a large variation between the Y and In ions. Optimizations including water and guandinium moieties to approximate the effects of antibody binding indicate a large energy cost for the DOTA-chelated In to adopt the ideal conformation for antibody binding.
Full 3D ab initio studies of interference effects in high-energy ion-molecule collisions
NASA Astrophysics Data System (ADS)
Sælen, L.; Birkeland, T.; Sisourat, N.; Hansen, J. P.; Dubois, A.
2009-11-01
We present an investigation of the interference effects which have been observed experimentally and predicted for ionizing collisions between highly charged projectiles and molecular hydrogen targets. The present data have been obtained from a non perturbative treatment of the collision system, using the semiclassical impact parameter method and solving the time-dependent Schrödinger equation fully numerically, the scattering wavefunction being discretized in the electron position space and, for detailed analysis, on spaces of reduced dimensionality. We discuss the oscillatory structures observed in differential cross sections as function of outgoing electron energy and angle in Kr34+ - H2 collisions. Emphasis is placed on the discussion on Young-type interference pattern as well as extra high frequency oscillations which have been observed experimentally but not confirmed by theoretical calculations.
Ab initio investigation of helium in Y2Ti2O7: Mobility and effects on mechanical properties
NASA Astrophysics Data System (ADS)
Danielson, T.; Tea, E.; Hin, C.
2016-08-01
Oxide nanoclusters (NCs) in nanostructured ferritic alloys (NFAs) are known to be efficient trapping sites for the transmutation product helium. In this study, the migration barriers and potential energy surfaces of helium in Y2Ti2O7 are presented to explain the mobility of helium through oxide NCs and shed light on the accumulation of helium and the trapping mechanisms of the oxides. A complex tunnel-shaped potential energy surface is identified and gives rise to relatively large migration barriers. Subsequently, the effect of helium accumulation on the mechanical properties of Y2Ti2O7 oxide nanoclusters is investigated and it is shown that the mechanical properties of the oxide do not significantly degrade as helium accumulates.
Shields, Ashley E; van Mourik, Tanja
2007-12-20
We establish that routine B3LYP and MP2 methods give qualitatively wrong conformations for flexible organic systems containing pi systems and that recently developed methods can overcome the known inadequacies of these methods. This is illustrated for a molecule (a conformer of the Tyr-Gly dipeptide) for which B3LYP/6-31+G(d) and MP2/6-31+G(d) geometry optimizations yield strikingly different structures [Mol. Phys. 2006, 104, 559-570]: MP2 predicts a folded "closed-book" conformer with the glycine residue located above the tyrosine ring, whereas B3LYP predicts a more open conformation. By employing different levels of theory, including the local electron correlation methods LMP2 (local MP2) and LCCSD(T0) (local coupled cluster with single, double, and noniterative local triple excitations) and large basis sets (aug-cc-pVnZ, n=D, T, Q), it is shown that the folded MP2 minimum is an artifact caused by large intramolecular BSSE (basis set superposition error) effects in the MP2/6-31+G(d) calculations. The B3LYP functional gives the correct minimum, but the potential energy apparently rises too steeply when the glycine and tyrosine residues approach each other, presumably due to missing dispersion effects in the B3LYP calculations. The PWB6K and M05-2X functionals, designed to give good results for weak interactions, remedy this to some extent. The reduced BSSE in the LMP2 calculations leads to faster convergence with increasing basis set quality, and accurate results can be obtained with smaller basis sets as compared to canonical MP2. We propose LMP2 as a suitable method to study interactions with pi-electron clouds.
NASA Astrophysics Data System (ADS)
Chakrabarty, Aurab; Bouhali, Othmane; Mousseau, Normand; Becquart, Charlotte S.; El-Mellouhi, Fedwa
2016-08-01
Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps on the path to carburization, eventually leading to dusting corrosion. While adsorption of CO molecules on Fe surface is a barrier-less exothermic process, this is not the case for the dissociation of CO into C and O adatoms and the diffusion of C beneath the surface that are found to be associated with large energy barriers. In practice, these barriers can be affected by numerous factors that combine to favour the CO-Fe reaction such as the abundance of CO and other hydrocarbons as well as the presence of structural defects. From a numerical point of view, studying these factors is challenging and a step-by-step approach is necessary to assess, in particular, the influence of the finite box size on the reaction parameters for adsorption and dissociation of CO on metal surfaces. Here, we use density functional theory (DFT) total energy calculations with the climbing-image nudged elastic band method to estimate the adsorption energies and dissociation barriers for different CO coverages with surface supercells of different sizes. We further compute the effect of periodic boundary condition for DFT calculations and find that the contribution from van der Waals interaction in the computation of adsorption parameters is important as they contribute to correcting the finite-size error in small systems. The dissociation process involves carbon insertion into the Fe surface causing a lattice deformation that requires a larger surface system for unrestricted relaxation. We show that, in the larger surface systems associated with dilute CO-coverages, C-insertion is energetically more favourable, leading to a significant decrease in the dissociation barrier. This observation suggests that a large surface system with dilute coverage is necessary for all similar metal-hydrocarbon reactions in order to study their fundamental electronic mechanisms, as an isolated phenomenon, free from
Towards Accurate Ab Initio Predictions of the Spectrum of Methane
NASA Technical Reports Server (NTRS)
Schwenke, David W.; Kwak, Dochan (Technical Monitor)
2001-01-01
We have carried out extensive ab initio calculations of the electronic structure of methane, and these results are used to compute vibrational energy levels. We include basis set extrapolations, core-valence correlation, relativistic effects, and Born- Oppenheimer breakdown terms in our calculations. Our ab initio predictions of the lowest lying levels are superb.
NASA Astrophysics Data System (ADS)
Santoyo-Castillo, I.; Ramírez-Solís, A.
2010-10-01
The X 2Π g, 2Σ g+ and 2Δ g states of AgBr 2 have been studied through benchmark ab initio CASSCF + Averaged Coupled Pair Functional (ACPF) and DFT calculations using especially developed valence basis sets to study the transition energies, geometries, vibrational frequencies, Mulliken charges and spin densities. The spin-orbit (SO) effects were included through the effective hamiltonian formalism using the |ΛSΣ> ACPF energies as diagonal elements. At the ACPF level, the ground state is 2Π g, in contradiction with ligand-field theory and Hartree-Fock results. The ACPF adiabatic excitation energies of the 2Σ g+ and 2Δ g states are 3825 and 20 152 cm -1, respectively. The inclusion of the SO effects leads to a pure Ω = 3/2 ( 2Π g) ground state, a Ω = 1/2 (97% 2Π g + 3% 2Σ g+) A state, a Ω = 1/2 (3% 2Π g + 97% 2Σ g+) B state, a Ω = 5/2 ( 2Δ g) C state and a Ω = 3/2 (99% 2Δ g) D state. The B97, B3LYP and PBE0 functionals, which were shown to yield accurate transition energies for CuCl 2, overestimate the X 2Π g- 2Σ g+ T e by around 25% but provide a qualitative energetic ordering in agreement with CASSCF and ACPF results. The nature of the bonding in the X 2Π g ground state is different from that of AgCl 2 since the Mulliken charge on the metal is 0.95 while the spin density is only 0.39. DFT strongly delocalizes the spin density providing even smaller values of around 0.13 on Ag not only for the ground state, but also for the 2Σ g+ state.
Pérez, Astrid; Poza, Margarita; Aranda, Jesús; Latasa, Cristina; Medrano, Francisco Javier; Tomás, María; Romero, Antonio; Lasa, Iñigo
2012-01-01
Control of membrane permeability is a key step in regulating the intracellular concentration of antibiotics. Efflux pumps confer innate resistance to a wide range of toxic compounds such as antibiotics, dyes, detergents, and disinfectants in members of the Enterobacteriaceae. The AcrAB-TolC efflux pump is involved in multidrug resistance in Enterobacter cloacae. However, the underlying mechanism that regulates the system in this microorganism remains unknown. In Escherichia coli, the transcription of acrAB is upregulated under global stress conditions by proteins such as MarA, SoxS, and Rob. In the present study, two clinical isolates of E. cloacae, EcDC64 (a multidrug-resistant strain overexpressing the AcrAB-TolC efflux pump) and Jc194 (a strain with a basal AcrAB-TolC expression level), were used to determine whether similar global stress responses operate in E. cloacae and also to establish the molecular mechanisms underlying this response. A decrease in susceptibility to erythromycin, tetracycline, telithromycin, ciprofloxacin, and chloramphenicol was observed in clinical isolate Jc194 and, to a lesser extent in EcDC64, in the presence of salicylate, decanoate, tetracycline, and paraquat. Increased expression of the acrAB promoter in the presence of the above-described conditions was observed by flow cytometry and reverse transcription-PCR, by using a reporter fusion protein (green fluorescent protein). The expression level of the AcrAB promoter decreased in E. cloacae EcDC64 derivates deficient in SoxS, RobA, and RamA. Accordingly, the expression level of the AcrAB promoter was higher in E. cloacae Jc194 strains overproducing SoxS, RobA, and RamA. Overall, the data showed that SoxS, RobA, and RamA regulators were associated with the upregulation of acrAB, thus conferring antimicrobial resistance as well as a stress response in E. cloacae. In summary, the regulatory proteins SoxS, RobA, and RamA were cloned and sequenced for the first time in this species. The
NASA Astrophysics Data System (ADS)
Şaşıoğlu, Ersoy; Galanakis, Iosif; Friedrich, Christoph; Blügel, Stefan
2013-10-01
Correlation effects play an important role in the electronic structure of half-metallic (HM) magnets. In particular, they give rise to nonquasiparticle states above (or below) the Fermi energy at finite temperatures that reduce the spin polarization and, as a consequence, the efficiency of spintronics devices. Employing the constrained random-phase approximation (cRPA) within the full-potential linearized augmented-plane-wave (FLAPW) method using maximally localized Wannier functions, we calculate the strength of the effective on-site Coulomb interaction (Hubbard U and Hund exchange J) between localized electrons in different classes of HM magnets considering: (i) sp-electron ferromagnets in rock-salt structure, (ii) zinc-blende 3d binary ferromagnets, as well as (iii) ferromagnetic and ferrimagnetic semi- and full-Heusler compounds. For HM sp-electron ferromagnets, the calculated Hubbard U parameters are between 2.7 and 3.9 eV, while for transition-metal-based HM compounds, they lie between 1.7 and 3.8 eV, being smallest for MnAs (Mn-3d orbitals) and largest for Cr2CoGa (Co-3d orbitals). For the HM full-Heusler compounds, the Hubbard U parameters are comparable to the ones in elementary 3d transition metals, while for semi-Heusler compounds, they are slightly smaller. We show that the increase of the Hubbard U with structural complexity, i.e., from MnAs to Cr2CoGa, stems from the screening of the p electrons of the nonmagnetic sp atoms. The p-electron screening turns out to be more efficient for MnAs than for Cr2CoGa. The calculated Hubbard U parameters for CrAs, NiMnSb, and Co2MnSi are about two times smaller than previous estimates based on the constrained local-density approximation (cLDA) method. Furthermore, the width of the correlated d or p bands of the studied compounds is usually smaller than the calculated Hubbard U parameters. Thus these HM magnets should be classified as weakly correlated materials.
Hydrogen effect on electronic and magnetic properties of Cd1-xMnxTe: Ab initio study
NASA Astrophysics Data System (ADS)
Larabi, A.; Merad, G.; Abdelaoui, I.; Sari, A.
2016-07-01
Hydrogen effect on electronic and magnetic properties of diluted magnetic semiconductor (DMS) Cd1-xMnxTe for x composition of 0.125 has been investigated using the projected augmented wave (PAW) based on density functional theory (DFT) formalism within the generalized gradient approximation (GGA). The results show that the Mn dopant is spin-polarized with magnetic moment of 4.189 μB per Mn atom at x≈0.125. The calculated formation energies indicate that the hydrogen is not stable in CdTe and the lowest energy position for H is at the Cd-Mn bond center in Cd0.875Mn0.125Te. We find also that the existence of interstitial hydrogen decreases the magnetic moment of Cd0.875Mn0.125Te diluted magnetic semiconductor. From the calculated density of state, we observed that the presence of hydrogen does not cause a change in electronic properties of Cd0.875Mn0.125Te.
Ab initio, theoretical and Monte Carlo approaches for the magnetocaloric effect in DyNi4Si
NASA Astrophysics Data System (ADS)
Laghrissi, Ayoub; Salmani, El Mehdi; Ez-Zahraouy, Hamid; Benyoussef, Abdelilah
2016-08-01
The magnetic and magnetocaloric properties of DyNi4Si alloys in YNi4Si-type orthorhombic structure have been investigated by using a combination of first-principles calculations and mean field theory, effective field theory, and Monte Carlo simulation. We find that Magnetic results of DyNi4Si compound show ferromagnetic-type ordering at 19 K, the magnetization-field isotherms for DyNi4Si exhibit hysteresis loop at 2 K due to strong magnetic anisotropy. The non-saturating behavior and the value of the magnetic moment of 7.7 μB/fu in 140 kOe at 2 K where the theoretical value for DyNi4Si only is about 10 μB, this suggest a not completely ordered ferromagnetic state of DyNi4Si (Morozkin et al., 2015) [2]. The isothermal entropy changes for H=14 T at T=22 K is -ΔS=15.6 J/(kg K). The obtained results are in good agreement with available experimental data. This study allows the suggestion of the compatible Ising model for a new class of compound YNi4Si-type, which shows magnetocaloric behavior at low temperature.
Zheng, Tao; Wang, Rui; Zhang, Tian-Biao; Jia, Dong-Hui; Wang, Chao-Liang; Sun, Yang; Zhang, Wei-Xing
2016-01-01
Background To investigate the effects and its potential mechanisms of Cox-2 inhibitors on ejaculation latency of rat with experimental autoimmune prostatitis (EAP). Methods Thirty six male Wistar rats with normal sexual function were screened by using the copulatory test, and were randomly divided into 3 groups: the model group (n=16), the normal control group (n=10) and the celecoxib treatment group (n=10). EAP rat model was established in the model group and the celecoxib treatment group by subcutaneous multiple point’s injection of male prostate gland extract emulsified in an equal volume of Freund’s adjuvant at the 0 and 21th day. Control animals received equal volume of saline. From the 0th day, the celecoxib treatment group was given a gavage of celecoxib (18 mg·kg-1·d-1), the model group and the normal control group were given a gavage of saline (0.1 mL·kg-1·d-1). Eight weeks later, the sexual behavior was investigated by the copulatory test, the morphological change of prostatic tissue was observed by light microscopy after HE staining, cytokines (TNF-α, IL-1β) in serum were detected by ELISA, the levels of 5-HT, 5-HT1A receptor, 5-HT2C receptor and SERT in T13-L2 and L5-S2 spinal cord tissue were detected by immunohistochemical staining and Western Blot. Results In model group, prostatic inflammation was found in 12 rats, and not in another 4 rats. The 4 rats were not included in the statistical analysis. In normal control group, prostatic inflammation was not found. In the celecoxib treatment group, there was a small amount of interstitial infiltration of inflammatory cells in rat’s prostate. In the copulatory test, compared with normal control group, mount latency (ML) and intromission latency (IL) in the model group were significantly prolonged (P<0.05); ejaculation latency (EL) in the model group was significantly shortened (P<0.05). There was no significant difference in these sexual behavior parameters between the normal control group and
Ming, Simon Wan Yau; Small, Iain; Wolfe, Stephanie; Hamil, John; Gruffydd-Jones, Kevin; Daly, Cathal; Soriano, Joan B.; Gardner, Liz; Skinner, Derek; Price, David
2016-01-01
Background Treatment of asthmatics with an inhaled corticosteroid (ICS) and long-acting beta agonist (LABA) is recommended for maintenance treatment according to Step 3 in the GINA guidelines. Fixed-dose combination (FDC) inhalers simplify the dosing regimen and may improve adherence over their separate components. However, the effectiveness and cost impact of FDC devices containing fluticasone propionate/formoterol (FP/FOR) compared to fluticasone/salmeterol (FP/SAL) in asthma patients who initiate or switch to FDC ICS/LABA inhalers have not been studied in real-life patients in the United Kingdom. To determine whether FP/FOR is non-inferior to FP/SAL in patients who initiate or switch to a FDC ICS/LABA therapy with respect to decreasing the occurrence of asthma exacerbations and overall cost impact. Methods This study used a matched, historical cohort design to compare the two FDC ICS/LABA treatments using the Optimal Patient Care Database. Based on a 1-year exploratory analysis of baseline variables such as comorbidities, current treatment, demographics and clinical measurements, cohorts were matched to ensure similar patients were compared over a 1-year outcome. Two cohorts of patients were studied: one of patients initiated on combination therapy (either FP/FOR or FP/SAL) and one of patients either switched from FP/SAL to FP/FOR or who remained on FP/SAL. The primary outcome studied non-inferiority in terms of percentage of patients who were free from severe asthma exacerbations (defined by ATS/ERS position statements) for patients prescribed FP/FORversusFP/SAL in the outcome year. Secondary outcomes included the rate of asthma exacerbations, clinical exacerbations, asthma control, treatment stability, and lower respiratory tract hospitalisations. Cost impact outcomes included a comparison of resource costs, drug costs and combined drug and resource costs. Results The study included 2,472 patients (618 patients in FP/FOR and 1,854 patients in FP/SAL cohorts
Arango, Yulieth C; Huang, Liubing; Chen, Chaoyu; Avila, Jose; Asensio, Maria C; Grützmacher, Detlev; Lüth, Hans; Lu, Jia Grace; Schäpers, Thomas
2016-01-01
We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires. PMID:27581169
Arango, Yulieth C.; Huang, Liubing; Chen, Chaoyu; Avila, Jose; Asensio, Maria C.; Grützmacher, Detlev; Lüth, Hans; Lu, Jia Grace; Schäpers, Thomas
2016-01-01
We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires. PMID:27581169
NASA Astrophysics Data System (ADS)
Arango, Yulieth C.; Huang, Liubing; Chen, Chaoyu; Avila, Jose; Asensio, Maria C.; Grützmacher, Detlev; Lüth, Hans; Lu, Jia Grace; Schäpers, Thomas
2016-09-01
We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires.
Arango, Yulieth C; Huang, Liubing; Chen, Chaoyu; Avila, Jose; Asensio, Maria C; Grützmacher, Detlev; Lüth, Hans; Lu, Jia Grace; Schäpers, Thomas
2016-09-01
We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires.
Magnetosymmetries of nonlinear transport in dissipative conductors
NASA Astrophysics Data System (ADS)
Bedkihal, Salil; Segal, Dvira
2014-03-01
We demonstrate with numerically exact simulations that nonlinear transport coefficients obey certain magnetic field symmetries. Our model includes a two terminal Aharonov-Bohm interferometer with a quantum dot located at each of its arms. One quantum dot is interacting electrostatically with a reservoir, a fermionic environment made of a quantum dot coupled to one or more leads. We study the dynamics and steady state properties of this many-body out of equilibrium setup, by using a numerically exact influence functional path integral technique (Phys. Rev.B 82, 205323 (2010)). We show that, in agreement with phenomenological treatments of dephasing and mean field approaches, even (odd) conductance terms obey odd (even) symmetry with threading magnetic flux, as long as system acquires spatial inversion symmetry. When spatial asymmetry is introduced, magnetic field symmetries are broken, but more general symmetries with respect to left-right interchange are obeyed. Finally we also numerically demonstrate that double quantum dot Aharonov-Bohm interferometer coupled electrostatically to a fermionic environment can act as a charge current rectifier when two conditions are met simultaneously (I)broken time reversal and (II) many body effects. Authors acknowledge funding from NSERC, University of Toronto Department of Chemistry, Queen Elizabeth II graduate scholarship, Gilchrist fellowship.
Vázquez, Hilda; Olvera, Felipe; Alagón, Alejandro; Sevcik, Carlos
2013-12-15
We separated whole IgG, Fab and F(ab')2 fragments from horse plasma. We previously studied the pharmacokinetics of these immunoglobulins and fragments in rabbits and shown that Fab and F(ab')2 pharmacokinetics were well described by a three-exponential kinetics, while IgG and IgG(T) pharmacokinetics, however, deviated from the three-exponential kinetics 120 h after injecting a bolus of the immunotherapeutics; this departure was shown to be due to a surge of anti-horse antibodies occurring after 120 h, peaking at ≈260 h and decaying slowly afterward (Vázquez et al., 2010). We now describe antivenom pharmacokinetics and anti-horse IgG production in rabbits receiving three boluses (300 μg/kg, I.V.) of Fab, F(ab')2 or IgG separated by 21 days.
NASA Astrophysics Data System (ADS)
Berdiñas, Z. M.; Amado, P. J.; Anglada-Escudé, G.; Rodríguez-López, C.; Barnes, J.
2016-07-01
Understanding the sources of instrumental systematic noise is a must to improve the design of future spectrographs. In this study, we alternated observations of the well-suited pair of M-stars GJ 725A+B to delve into the sub-night High Accuracy Radial Velocity Planet Searcher for the Northern hemisphere (HARPS-N) response. Besides the possible presence of a low-mass planet orbiting GJ 725B, our observations reveal changes in the spectral energy distribution (SED) correlated with measurements of the width of the instrumental line profile and, to a lower degree, with the Doppler measurements. To study the origin of these effects, we searched for correlations among several quantities defined and measured on the spectra and on the acquisition images. We find that the changes in apparent SED are very likely related to flux losses at the fibre input. Further tests indicate that such flux losses do not seriously affect the shape of the instrumental point spread function of HARPS-N, but identify an inefficient fitting of the continuum as the most likely source of the systematic variability observed in the full width at half-maximum. This index, accounting for the HARPS-N cross-correlation profiles width, is often used to decorrelate Doppler time series. We show that the Doppler measurement obtained by a parametric least-squares fitting of the spectrum accounting for continuum variability is insensitive to changes in the slope of the SED, suggesting that forward modelling techniques to measure moments of the line profile are the optimal way to achieve higher accuracy. Remaining residual variability at ˜1 m s-1 suggests that for M-stars Doppler surveys the current noise floor still has an instrumental origin.
NASA Astrophysics Data System (ADS)
Moynier, Frédéric; Fujii, Toshiyuki; Wang, Kun; Foriel, Julien
2013-05-01
Iron is one of the most abundant transition metal in higher plants and variations in its isotopic compositions can be used to trace its utilization. In order to better understand the effect of plant-induced isotopic fractionation on the global Fe cycling, we have estimated by quantum chemical calculations the magnitude of the isotopic fractionation between different Fe species relevant to the transport and storage of Fe in higher plants: Fe(II)-citrate, Fe(III)-citrate, Fe(II)-nicotianamine, and Fe(III)-phytosiderophore. The ab initio calculations show firstly, that Fe(II)-nicotianamine is ˜3‰ (56Fe/54Fe) isotopically lighter than Fe(III)-phytosiderophore; secondly, even in the absence of redox changes of Fe, change in the speciation alone can create up to ˜1.5‰ isotopic fractionation. For example, Fe(III)-phytosiderophore is up to 1.5‰ heavier than Fe(III)-citrate2 and Fe(II)-nicotianamine is up to 1‰ heavier than Fe(II)-citrate. In addition, in order to better understand the Fe isotopic fractionation between different plant components, we have analyzed the iron isotopic composition of different organs (roots, seeds, germinated seeds, leaves and stems) from six species of higher plants: the dicot lentil (Lens culinaris), and the graminaceous monocots Virginia wild rye (Elymus virginicus), Johnsongrass (Sorghum halepense), Kentucky bluegrass (Poa pratensis), river oat (Uniola latifolia), and Indian goosegrass (Eleusine indica). The calculations may explain that the roots of strategy-II plants (Fe(III)-phytosiderophore) are isotopically heavier (by about 1‰ for the δ56Fe) than the upper parts of the plants (Fe transported as Fe(III)-citrate in the xylem or Fe(II)-nicotianamine in the phloem). In addition, we suggest that the isotopic variations observed between younger and older leaves could be explained by mixing of Fe received from the xylem and the phloem.
Chikayama, Eisuke; Shimbo, Yudai; Komatsu, Keiko; Kikuchi, Jun
2016-04-14
NMR spectroscopy is a powerful method for analyzing metabolic mixtures. The information obtained from an NMR spectrum is in the form of physical parameters, such as chemical shifts, and construction of databases for many metabolites will be useful for data interpretation. To increase the accuracy of theoretical chemical shifts for development of a database for a variety of metabolites, the effects of sets of conformations (structural ensembles) and the levels of theory on computations of theoretical chemical shifts were systematically investigated for a set of 29 small molecules in the present study. For each of the 29 compounds, 101 structures were generated by classical molecular dynamics at 298.15 K, and then theoretical chemical shifts for 164 (1)H and 123 (13)C atoms were calculated by ab initio quantum chemical methods. Six levels of theory were used by pairing Hartree-Fock, B3LYP (density functional theory), or second order Møller-Plesset perturbation with 6-31G or aug-cc-pVDZ basis set. The six average fluctuations in the (1)H chemical shift were ±0.63, ± 0.59, ± 0.70, ± 0.62, ± 0.75, and ±0.66 ppm for the structural ensembles, and the six average errors were ±0.34, ± 0.27, ± 0.32, ± 0.25, ± 0.32, and ±0.25 ppm. The results showed that chemical shift fluctuations with changes in the conformation because of molecular motion were larger than the differences between computed and experimental chemical shifts for all six levels of theory. In conclusion, selection of an appropriate structural ensemble should be performed before theoretical chemical shift calculations for development of an accurate database for a variety of metabolites.
Yin, Haiqing; Kang, Han Chang; Huh, Kang Moo; Bae, You Han
2014-01-01
In our previous study, a histidine-based AB2 miktoarm polymer, methoxy poly(ethylene glycol)-b-poly(l-histidine)2 (mPEG-b-(PolyHis)2), was designed to construct pH-sensitive polymersomes that transform in acidic pH; the polymer self-assembles into a structure that mimics phospholipids. In this study, the polymersomes further imitated liposomes due to the incorporation of cholesterol (CL). The hydrodynamic radii of the polymersomes increased with increasing CL wt% (e.g., 70 nm for 0 wt% vs. 91 nm for 1 wt%), resulting in an increased capacity for encapsulating hydrophilic drugs (e.g., 0.92 µL/mg for 0 wt% vs. 1.42 µL/mg for 1 wt%). The CL incorporation enhanced the colloidal stability of the polymersomes in the presence of serum protein and retarded their payload release. However, CL-incorporating polymersomes still demonstrated accelerated release of a hydrophilic dye (e.g., 5(6)-carboxyfluorescein (CF)) below pH 6.8 without losing their desirable pH sensitivity. CF-loaded CL-incorporating polymersomes showed better cellular internalization than the hydrophilic CF, whereas doxorubicin (DOX)-loaded CL-incorporating polymersomes presented similar or somewhat lower anti-tumor effects than free hydrophobic DOX. The findings suggest that CL-incorporating mPEG-b-(PolyHis)2-based polymersomes may have potential for intracellular drug delivery of chemical drugs due to their improved colloidal stability, lower drug loss during circulation, acidic pH-induced drug release, and endosomal disruption. PMID:24463148
Zhou, Xia; Guo, Yunling; Kong, Hua; Zuo, Jiao; Huang, Qixing; Jia, Ruizong; Guo, Anping; Xu, Lin
2016-01-01
Micraspis discolor (Fabricius) (Coleoptera: Coccinellidae) is a widely distributed coleoptera predator in southern Asia in rice ecosystem, and adult M. discolor feed on both rice pollen and soft-bodied arthropods. Bitrophic bioassay and tritrophic bioassay were conducted to evaluate the potential impact of Cry1Ac/Cry1Ab-expressing rice Huahui 1 and its non-transgenic counterpart Minghui 63 on fitness parameters of adult M. discolor. The results showed that the survival, and fecundity of this beetle’ adults were not different when they fed on Bt rice or non-Bt rice pollen or Nilaparvata lugens (Stål) reared on Bt rice or non-Bt rice. Toxicity assessment to ensure M. discolor adults were not sensitive to Cry1Ab or Cry1Ac protein independent from the pollen background, M. discolor adults were fed with an artificial diet containing Cry1Ac, Cry1Ab or both protein approximately 10 times higher concentration than in Huahui 1 rice pollen. No difference was detected for any of the life-table parameters tested between Cry protein-containing and pure diet. Artificial diet containing E-64 (N-(trans-Epoxysuccinyl)-L-leucine 4-guanidinobutylamide) was included as a positive control. In contrast, the pre-oviposition and fecundity of M. discolor were significantly adversely affected by feeding on E-64-containing diet. In both bioassays, the uptakes of Cry protein by adult M. discolor were tested by ELISA measurements. These results indicated that adults of M. discolor are not affected by Cry1Ab- or Cry1Ac-expressing rice pollen and are not sensitive to Cry protein at concentrations exceeding the levels in rice pollen in Huahui1. This suggests that M. discolor adults would not be harmed by Cry1Ac/Cry1Ab rice if Bt rice Huahui 1 were commercialized. PMID:26914608
Zhou, Xia; Guo, Yunling; Kong, Hua; Zuo, Jiao; Huang, Qixing; Jia, Ruizong; Guo, Anping; Xu, Lin
2016-01-01
Micraspis discolor (Fabricius) (Coleoptera: Coccinellidae) is a widely distributed coleoptera predator in southern Asia in rice ecosystem, and adult M. discolor feed on both rice pollen and soft-bodied arthropods. Bitrophic bioassay and tritrophic bioassay were conducted to evaluate the potential impact of Cry1Ac/Cry1Ab-expressing rice Huahui 1 and its non-transgenic counterpart Minghui 63 on fitness parameters of adult M. discolor. The results showed that the survival, and fecundity of this beetle' adults were not different when they fed on Bt rice or non-Bt rice pollen or Nilaparvata lugens (Stål) reared on Bt rice or non-Bt rice. Toxicity assessment to ensure M. discolor adults were not sensitive to Cry1Ab or Cry1Ac protein independent from the pollen background, M. discolor adults were fed with an artificial diet containing Cry1Ac, Cry1Ab or both protein approximately 10 times higher concentration than in Huahui 1 rice pollen. No difference was detected for any of the life-table parameters tested between Cry protein-containing and pure diet. Artificial diet containing E-64 (N-(trans-Epoxysuccinyl)-L-leucine 4-guanidinobutylamide) was included as a positive control. In contrast, the pre-oviposition and fecundity of M. discolor were significantly adversely affected by feeding on E-64-containing diet. In both bioassays, the uptakes of Cry protein by adult M. discolor were tested by ELISA measurements. These results indicated that adults of M. discolor are not affected by Cry1Ab- or Cry1Ac-expressing rice pollen and are not sensitive to Cry protein at concentrations exceeding the levels in rice pollen in Huahui1. This suggests that M. discolor adults would not be harmed by Cry1Ac/Cry1Ab rice if Bt rice Huahui 1 were commercialized.
Li, Jia; Zhang, Zhiming; Lv, Lianjie; Qiao, Haibo; Chen, Xiuju; Zou, Changlin
2016-04-01
Antibody-based targeted therapy of cancers requires the antibody targeting of specific molecules inducing tumor cells apoptosis or death. Angiopoietin-2 (Agn-2) and translocator protein (TSPO) are identified as potential target molecules for glioblastoma therapy. The single chain anti-Agn-2 antibody (Anag-2) and anti-TSPO antibody (ATSPO) were obtained by monoclonal antibody screening. In the present study, for specific targeting and killing, we generated a recombinant bispecific antibody comprising a single-chain Fragment variable (ScFv) of anti-human Agn-2 and anti-human TSPO (ScBsAbAgn-2/TSPO), which is the mediator for mitochondrial apoptosis and tumor angiogenesis. In vitro, ScBsAbAgn-2/TSPO simultaneously bounded to both targets with a high antigen-binding affinity to Anag-2 and TSPO compared to the individual antibody. The higher expression of Ang-2 and TSPO was observed in bevacizumab-treated glioblastoma compared to normal rat brain endothelium. We also observed apoptosis-mediated cytotoxicity was improved, which resulted in the elimination of up to 90% of the target cells within 72 h. ScBsAbAgn-2/TSPO inhibited tumor growth, decreased vascular permeability, led to extended survival, improved pericyte coverage, depletion of tumor-associated macrophages, and increased numbers of intratumoral T lymphocytes infiltration in a murine bevacizumab-treated glioblastoma model. These findings were also confirmed ex vivo using glioblastoma cells from bevacizumab-treated rats with glioblastoma. We conclude that ScBsAbAgn-2/TSPO targeting of glioblastoma cell lines can be achieved in vitro and in vivo that the efficient elimination of glioblastoma cells supports the potential of ScBsAbAgn-2/TSPO as a potent, novel immunotherapeutic agent. PMID:26898800
Zhou, Xia; Guo, Yunling; Kong, Hua; Zuo, Jiao; Huang, Qixing; Jia, Ruizong; Guo, Anping; Xu, Lin
2016-01-01
Micraspis discolor (Fabricius) (Coleoptera: Coccinellidae) is a widely distributed coleoptera predator in southern Asia in rice ecosystem, and adult M. discolor feed on both rice pollen and soft-bodied arthropods. Bitrophic bioassay and tritrophic bioassay were conducted to evaluate the potential impact of Cry1Ac/Cry1Ab-expressing rice Huahui 1 and its non-transgenic counterpart Minghui 63 on fitness parameters of adult M. discolor. The results showed that the survival, and fecundity of this beetle' adults were not different when they fed on Bt rice or non-Bt rice pollen or Nilaparvata lugens (Stål) reared on Bt rice or non-Bt rice. Toxicity assessment to ensure M. discolor adults were not sensitive to Cry1Ab or Cry1Ac protein independent from the pollen background, M. discolor adults were fed with an artificial diet containing Cry1Ac, Cry1Ab or both protein approximately 10 times higher concentration than in Huahui 1 rice pollen. No difference was detected for any of the life-table parameters tested between Cry protein-containing and pure diet. Artificial diet containing E-64 (N-(trans-Epoxysuccinyl)-L-leucine 4-guanidinobutylamide) was included as a positive control. In contrast, the pre-oviposition and fecundity of M. discolor were significantly adversely affected by feeding on E-64-containing diet. In both bioassays, the uptakes of Cry protein by adult M. discolor were tested by ELISA measurements. These results indicated that adults of M. discolor are not affected by Cry1Ab- or Cry1Ac-expressing rice pollen and are not sensitive to Cry protein at concentrations exceeding the levels in rice pollen in Huahui1. This suggests that M. discolor adults would not be harmed by Cry1Ac/Cry1Ab rice if Bt rice Huahui 1 were commercialized. PMID:26914608
Li, Jia; Zhang, Zhiming; Lv, Lianjie; Qiao, Haibo; Chen, Xiuju; Zou, Changlin
2016-04-01
Antibody-based targeted therapy of cancers requires the antibody targeting of specific molecules inducing tumor cells apoptosis or death. Angiopoietin-2 (Agn-2) and translocator protein (TSPO) are identified as potential target molecules for glioblastoma therapy. The single chain anti-Agn-2 antibody (Anag-2) and anti-TSPO antibody (ATSPO) were obtained by monoclonal antibody screening. In the present study, for specific targeting and killing, we generated a recombinant bispecific antibody comprising a single-chain Fragment variable (ScFv) of anti-human Agn-2 and anti-human TSPO (ScBsAbAgn-2/TSPO), which is the mediator for mitochondrial apoptosis and tumor angiogenesis. In vitro, ScBsAbAgn-2/TSPO simultaneously bounded to both targets with a high antigen-binding affinity to Anag-2 and TSPO compared to the individual antibody. The higher expression of Ang-2 and TSPO was observed in bevacizumab-treated glioblastoma compared to normal rat brain endothelium. We also observed apoptosis-mediated cytotoxicity was improved, which resulted in the elimination of up to 90% of the target cells within 72 h. ScBsAbAgn-2/TSPO inhibited tumor growth, decreased vascular permeability, led to extended survival, improved pericyte coverage, depletion of tumor-associated macrophages, and increased numbers of intratumoral T lymphocytes infiltration in a murine bevacizumab-treated glioblastoma model. These findings were also confirmed ex vivo using glioblastoma cells from bevacizumab-treated rats with glioblastoma. We conclude that ScBsAbAgn-2/TSPO targeting of glioblastoma cell lines can be achieved in vitro and in vivo that the efficient elimination of glioblastoma cells supports the potential of ScBsAbAgn-2/TSPO as a potent, novel immunotherapeutic agent.
Coulomb stability of the 4π-periodic Josephson effect of Majorana fermions
NASA Astrophysics Data System (ADS)
van Heck, B.; Hassler, F.; Akhmerov, A. R.; Beenakker, C. W. J.
2011-11-01
The Josephson energy of two superconducting islands containing Majorana fermions is a 4π-periodic function of the superconducting phase difference. If the islands have a small capacitance, their ground state energy is governed by the competition of Josephson and charging energies. We calculate this ground-state energy in a ring geometry, as a function of the flux Φ enclosed by the ring, and show that the dependence on the Aharonov-Bohm phase 2eΦ/ℏ remains 4π periodic regardless of the ratio of charging and Josephson energies—provided that the entire ring is in a topologically nontrivial state. If part of the ring is topologically trivial, then the charging energy induces quantum phase slips that restore the usual 2π periodicity.
Coulomb stability of the 4π-periodic Josephson effect of Majorana fermions
NASA Astrophysics Data System (ADS)
Hassler, Fabian; van Heck, Bernard; Akhmerov, Anton R.; Beenakker, C. W. J.
2012-02-01
The Josephson energy of two superconducting islands containing Majorana fermions is a 4π-periodic function of the superconducting phase difference. If the islands have a small capacitance, their ground state energy is governed by the competition of Josephson and charging energies. We calculate this ground state energy in a ring geometry, as a function of the flux φ enclosed by the ring, and show that the dependence on the Aharonov-Bohm phase 2eφ/ remains 4π-periodic regardless of the ratio of charging and Josephson energies---provided that the entire ring is in a topologically nontrivial state. If part of the ring is topologically trivial, then the charging energy induces quantum phase slips that restore the usual 2π-periodicity [B. van Heck, F. Hassler, A. R. Akhmerov, and C. W. J. Beenakker, Phys. Rev. B 84, 180502(R) (2011)].
Berns, Veronica M; Engelkemier, Joshua; Guo, Yiming; Kilduff, Brandon J; Fredrickson, Daniel C
2014-08-12
The notion of atomic size poses an important challenge to chemical theory: empirical evidence has long established that atoms have spatial requirements, which are summarized in tables of covalent, ionic, metallic, and van der Waals radii. Considerations based on these radii play a central role in the design and interpretation of experiments, but few methods are available to directly support arguments based on atomic size using electronic structure methods. Recently, we described an approach to elucidating atomic size effects using theoretical calculations: the DFT-Chemical Pressure analysis, which visualizes the local pressures arising in crystal structures from the interactions of atomic size and electronic effects. Using this approach, a variety of structural phenomena in intermetallic phases have already been understood in terms that provide guidance to new synthetic experiments. However, the applicability of the DFT-CP method to the broad range of the structures encountered in the solid state is limited by two issues: (1) the difficulty of interpreting the intense pressure features that appear in atomic core regions and (2) the need to divide space among pairs of interacting atoms in a meaningful way. In this article, we describe general solutions to these issues. In addressing the first issue, we explore the CP analysis of a test case in which no core pressures would be expected to arise: isolated atoms in large boxes. Our calculations reveal that intense core pressures do indeed arise in these virtually pressure-less model systems and allow us to trace the issue to the shifts in the voxel positions relative to atomic centers upon expanding and contracting the unit cell. A compensatory grid unwarping procedure is introduced to remedy this artifact. The second issue revolves around the difficulty of interpreting the pressure map in terms of interatomic interactions in a way that respects the size differences of the atoms and avoids artificial geometrical
Autonomous Biological System (ABS) experiments.
MacCallum, T K; Anderson, G A; Poynter, J E; Stodieck, L S; Klaus, D M
1998-12-01
Three space flight experiments have been conducted to test and demonstrate the use of a passively controlled, materially closed, bioregenerative life support system in space. The Autonomous Biological System (ABS) provides an experimental environment for long term growth and breeding of aquatic plants and animals. The ABS is completely materially closed, isolated from human life support systems and cabin atmosphere contaminants, and requires little need for astronaut intervention. Testing of the ABS marked several firsts: the first aquatic angiosperms to be grown in space; the first higher organisms (aquatic invertebrate animals) to complete their life cycles in space; the first completely bioregenerative life support system in space; and, among the first gravitational ecology experiments. As an introduction this paper describes the ABS, its flight performance, advantages and disadvantages.
Ab initio phonon limited transport
NASA Astrophysics Data System (ADS)
Verstraete, Matthieu
We revisit the thermoelectric (TE) transport properties of two champion materials, PbTe and SnSe, using fully first principles methods. In both cases the performance of the material is due to subtle combinations of structural effects, scattering, and phase space reduction. In PbTe anharmonic effects are completely opposite to the predicted quasiharmonic evolution of phonon frequencies and to frequently (and incorrectly) cited extrapolations of experiments. This stabilizes the material at high T, but also tends to enhance its thermal conductivity, in a non linear manner, above 600 Kelvin. This explains why PbTe is in practice limited to room temperature applications. SnSe has recently been shown to be the most efficient TE material in bulk form. This is mainly due to a strongly enhanced carrier concentration and electrical conductivity, after going through a phase transition from 600 to 800 K. We calculate the transport coefficients as well as the defect concentrations ab initio, showing excellent agreement with experiment, and elucidating the origin of the double phase transition as well as the new charge carriers. AH Romero, EKU Gross, MJ Verstraete, and O Hellman PRB 91, 214310 (2015) O. Hellman, IA Abrikosov, and SI Simak, PRB 84 180301 (2011)
Omidi, Mahboubeh Faizabadi, Edris
2015-03-21
Magnetic susceptibility is investigated in a man-made elliptical quantum ring in the presence of Rashba spin-orbit interactions and the magnetic flux. It is shown that magnetic susceptibility as a function of magnetic flux changes between negative and positive signs periodically. The periodicity of the Aharonov-Bohm oscillations depends on the geometry of the region where magnetic field is applied, the eccentricity, and number of sites in each chain ring (the elliptical ring is composed of chain rings). The magnetic susceptibility sign can be reversed by tuning the Rashba spin-orbit strength as well. Both the magnetic susceptibility strength and sign can be controlled via external spin-orbit interactions, which can be exploited in spintronics and nanoelectronics.
Boiling treatment of ABS and PS plastics for flotation separation.
Wang, Chong-qing; Wang, Hui; Wu, Bao-xin; Liu, Qun
2014-07-01
A new physical method, namely boiling treatment, was developed to aid flotation separation of acrylonitrile-butadiene-styrene (ABS) and polystyrene (PS) plastics. Boiling treatment was shown to be effective in producing a hydrophilic surface on ABS plastic. Fourier Transform Infrared analysis was conducted to investigate the mechanism of boiling treatment of ABS. Surface rearrangement of polymer may be responsible for surface change of boiling treated ABS, and the selective influence of boiling treatment on the floatability of boiling treated plastics may be attributed to the difference in the molecular mobility of polymer chains. The effects of flotation time, frother concentration and particle size on flotation behavior of simple plastic were investigated. Based on flotation behavior of simple plastic, flotation separation of boiling treatment ABS and PS with different particle sizes was achieved efficiently. The purity of ABS and PS was up to 99.78% and 95.80%, respectively; the recovery of ABS and PS was up to 95.81% and 99.82%, respectively. Boiling treatment promotes the industrial application of plastics flotation and facilitates plastic recycling.
Current techniques for AB0-incompatible living donor liver transplantation.
Rummler, Silke; Bauschke, Astrid; Bärthel, Erik; Jütte, Heike; Maier, Katrin; Ziehm, Patrice; Malessa, Christina; Settmacher, Utz
2016-09-24
For a long time, it was considered medical malpractice to neglect the blood group system during transplantation. Because there are far more patients waiting for organs than organs available, a variety of attempts have been made to transplant AB0-incompatible (AB0i) grafts. Improvements in AB0i graft survival rates have been achieved with immunosuppression regimens and plasma treatment procedures. Nevertheless, some grafts are rejected early after AB0i living donor liver transplantation (LDLT) due to antibody mediated rejection or later biliary complications that affect the quality of life. Therefore, the AB0i LDLT is an option only for emergency situations, and it requires careful planning. This review compares the treatment possibilities and their effect on the patients' graft outcome from 2010 to the present. We compared 11 transplant center regimens and their outcomes. The best improvement, next to plasma treatment procedures, has been reached with the prophylactic use of rituximab more than one week before AB0i LDLT. Unfortunately, no standardized treatment protocols are available. Each center treats its patients with its own scheme. Nevertheless, the transplant results are homogeneous. Due to refined treatment strategies, AB0i LDLT is a feasible option today and almost free of severe complications. PMID:27683633
Current techniques for AB0-incompatible living donor liver transplantation
Rummler, Silke; Bauschke, Astrid; Bärthel, Erik; Jütte, Heike; Maier, Katrin; Ziehm, Patrice; Malessa, Christina; Settmacher, Utz
2016-01-01
For a long time, it was considered medical malpractice to neglect the blood group system during transplantation. Because there are far more patients waiting for organs than organs available, a variety of attempts have been made to transplant AB0-incompatible (AB0i) grafts. Improvements in AB0i graft survival rates have been achieved with immunosuppression regimens and plasma treatment procedures. Nevertheless, some grafts are rejected early after AB0i living donor liver transplantation (LDLT) due to antibody mediated rejection or later biliary complications that affect the quality of life. Therefore, the AB0i LDLT is an option only for emergency situations, and it requires careful planning. This review compares the treatment possibilities and their effect on the patients’ graft outcome from 2010 to the present. We compared 11 transplant center regimens and their outcomes. The best improvement, next to plasma treatment procedures, has been reached with the prophylactic use of rituximab more than one week before AB0i LDLT. Unfortunately, no standardized treatment protocols are available. Each center treats its patients with its own scheme. Nevertheless, the transplant results are homogeneous. Due to refined treatment strategies, AB0i LDLT is a feasible option today and almost free of severe complications. PMID:27683633
Current techniques for AB0-incompatible living donor liver transplantation
Rummler, Silke; Bauschke, Astrid; Bärthel, Erik; Jütte, Heike; Maier, Katrin; Ziehm, Patrice; Malessa, Christina; Settmacher, Utz
2016-01-01
For a long time, it was considered medical malpractice to neglect the blood group system during transplantation. Because there are far more patients waiting for organs than organs available, a variety of attempts have been made to transplant AB0-incompatible (AB0i) grafts. Improvements in AB0i graft survival rates have been achieved with immunosuppression regimens and plasma treatment procedures. Nevertheless, some grafts are rejected early after AB0i living donor liver transplantation (LDLT) due to antibody mediated rejection or later biliary complications that affect the quality of life. Therefore, the AB0i LDLT is an option only for emergency situations, and it requires careful planning. This review compares the treatment possibilities and their effect on the patients’ graft outcome from 2010 to the present. We compared 11 transplant center regimens and their outcomes. The best improvement, next to plasma treatment procedures, has been reached with the prophylactic use of rituximab more than one week before AB0i LDLT. Unfortunately, no standardized treatment protocols are available. Each center treats its patients with its own scheme. Nevertheless, the transplant results are homogeneous. Due to refined treatment strategies, AB0i LDLT is a feasible option today and almost free of severe complications.
Safety assessment of Cry1Ab/Ac fusion protein.
Xu, Wentao; Cao, Sishuo; He, Xiaoyun; Luo, Yunbo; Guo, Xing; Yuan, Yanfang; Huang, Kunlun
2009-07-01
Cry1ab/ac gene was fused by both the cry1ab gene (GenBank Accession No. X54939) and the cry1ac gene (GenBank Accession No. Y09787), which was widely used in genetically modified (GM) rice, cotton, maize and so on. In order to support the safety assessment of GM food or feed products containing Cry1Ab/Ac protein, sufficient quantities of Cry1Ab/Ac protein were produced in Escherichia coli for in vitro evaluation and animal studies. The Cry1Ab/Ac protein does not possess the characteristics associated with food toxins or allergens, i.e., it has no sequence homology with any known allergens or toxins, and no N-glycosylation sites, can be rapidly degraded in gastric and intestinal fluids, and is devoid of adverse effects in mice by gavage at a high dose level of 5g (Cry1Ab/Ac protein)/kg body weight. In conclusion, there is a reasonable certainty of no harm resulting from the inclusion of the Cry1Ab/Ac protein in human food or animal feed.
Masses and activity of AB Doradus B a/b. The age of the AB Dor quadruple system revisited
NASA Astrophysics Data System (ADS)
Wolter, U.; Czesla, S.; Fuhrmeister, B.; Robrade, J.; Engels, D.; Wieringa, M.; Schmitt, J. H. M. M.
2014-10-01
We present a multiwavelength study of the close binary AB Dor Ba/b (Rst137B). Our study comprises astrometric orbit measurements, optical spectroscopy, X-ray and radio observations. Using all available adaptive optics images of AB Dor B taken with VLT/NACO from 2004 to 2009, we tightly constrain its orbital period to 360.6 ± 1.5 days. We present the first orbital solution of Rst 137B and estimate the combined mass of AB Dor Ba+b as 0.69+0.02-0.24 M⊙, slightly exceeding previous estimates based on IR photometry. Our determined orbital inclination of Rst 137B is close to the axial inclination of AB Dor A inferred from Doppler imaging. Our VLT/UVES spectra yield high rotational velocities of ≥30 km s-1 for both components Ba and Bb, in accord with previous measurements, which corresponds to rotation periods significantly shorter than one day. Our combined spectral model, using PHOENIX spectra, yields an effective temperature of 3310 ± 50 K for the primary and approximately 60 K less for the secondary. The optical spectra presumably cover a chromospheric flare and show that at least one component of Rst 137B is significantly active. Activity and weak variations are also found in our simultaneous XMM-Newton observations, while our ATCA radio data yield constant fluxes at the level of previous measurements. Using evolutionary models, our newly determined stellar parameters confirm that the age of Rst 137B is between 50 and 100 Myr. Based on observations collected at the European Southern Observatory, Paranal, Chile, 383.D-1002(A) and the ESO Science Archive Facility. Using data obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member states and NASA. Using data obtained with the Australia Telescope Compact Array (ATCA) operated by the Commonwealth Scientific and Industrial Research Organisation (CSIRO).
NASA Astrophysics Data System (ADS)
Abe, Akihiro; Furuya, Hidemine; Ichimura, Noriko; Kawauchi, Susumu
1997-02-01
The gas-phase NMR analysis of 5-methoxy-1,3-dioxanes was carried out. The conformational energies estimated from the observed coupling constant data were compared with the results of ab initio MO calculations using d95 + (2df,p) basis set at the MP2 level. While the energy difference between the axial-out and equatorial-out forms was in a reasonable agreement, the 1,5 interaction energy between the methoxy methyl and the ring oxygens was not in accord.
Structural Basis of Subtilase Cytotoxin SubAB Assembly*
Le Nours, Jérôme; Paton, Adrienne W.; Byres, Emma; Troy, Sally; Herdman, Brock P.; Johnson, Matthew D.; Paton, James C.; Rossjohn, Jamie; Beddoe, Travis
2013-01-01
Pathogenic strains of Escherichia coli produce a number of toxins that belong to the AB5 toxin family, which comprise a catalytic A-subunit that induces cellular dysfunction and a B-pentamer that recognizes host glycans. Although the molecular actions of many of the individual subunits of AB5 toxins are well understood, how they self-associate and the effect of this association on cytotoxicity are poorly understood. Here we have solved the structure of the holo-SubAB toxin that, in contrast to other AB5 toxins whose molecular targets are located in the cytosol, cleaves the endoplasmic reticulum chaperone BiP. SubA interacts with SubB in a similar manner to other AB5 toxins via the A2 helix and a conserved disulfide bond that joins the A1 domain with the A2 helix. The structure revealed that the active site of SubA is not occluded by the B-pentamer, and the B-pentamer does not enhance or inhibit the activity of SubA. Structure-based sequence comparisons with other AB5 toxin family members, combined with extensive mutagenesis studies on SubB, show how the hydrophobic patch on top of the B-pentamer plays a dominant role in binding the A-subunit. The structure of SubAB and the accompanying functional characterization of various mutants of SubAB provide a framework for understanding the important role of the B-pentamer in the assembly and the intracellular trafficking of this AB5 toxin. PMID:23921389
Wang, Ran; Tetreau, Guillaume; Wang, Ping
2016-01-01
Fitness costs associated with resistance to Bacillus thuringiensis (Bt) toxins critically impact the development of resistance in insect populations. In this study, the fitness costs in Trichoplusia ni strains associated with two genetically independent resistance mechanisms to Bt toxins Cry1Ac and Cry2Ab, individually and in combination, on four crop plants (cabbage, cotton, tobacco and tomato) were analyzed, in comparison with their near-isogenic susceptible strain. The net reproductive rate (R0) and intrinsic rate of increase (r) of the T. ni strains, regardless of their resistance traits, were strongly affected by the host plants. The ABCC2 gene-linked mechanism of Cry1Ac resistance was associated with relatively low fitness costs, while the Cry2Ab resistance mechanism was associated with higher fitness costs. The fitness costs in the presence of both resistance mechanisms in T. ni appeared to be non-additive. The relative fitness of Bt-resistant T. ni depended on the specific resistance mechanisms as well as host plants. In addition to difference in survivorship and fecundity, an asynchrony of adult emergence was observed among T. ni with different resistance mechanisms and on different host plants. Therefore, mechanisms of resistance and host plants available in the field are both important factors affecting development of Bt resistance in insects. PMID:26868936
Brereton, Jacqueline
2016-01-01
Background The Salford Lung Study (SLS) involves two prospective patient cohorts—one patients with asthma; the other patients with COPD. SLS is believed to be the first pre-license, prospective randomised controlled trial (RCT) to use electronic healthcare records to monitor patient safety. Safety events are processed in near real-time, and a linked database system creates daily summaries that alert a specialist safety team to potential treatment-related adverse events. SLS is a ‘world first’ in effectiveness research. To synthesise the learnings from the SLS and experiences from leading experts in real-world research in a White Paper to help guide the future design and feasibility of pragmatic RCTs. Methods Hold an advisory board involving representatives from: the pioneering SLS collaboration (between the UK National Health Service, The University of Manchester, GlaxoSmithKline); the Pharmaceutical Industry, Government, regulatory and health technology appraisal agencies as well as clinical experts, social scientists and information technology specialists to pool expertise in effectiveness and cost-effectiveness research. Through shared experiences, discussion and consensus, develop a joint stakeholder position on the value of effectiveness and cost-effectiveness research and clear standards to guide the future design and delivery of meaningful, affordable and implementable pragmatic RCTs in the future. Results None available at the time of writing. Conclusions There have been significant advances in effectiveness and cost-effectiveness research in recent years and important learnings resulting from the SLS. Current expertise must be shared, documented and discussed by experts and used to develop standards to guide optimised use of research resource in the future.
Interferometer-Based Studies of Quantum Hall Phenomena
NASA Astrophysics Data System (ADS)
McClure, Douglas Templeton, III
The fractional quantum Hall (FQH) effect harbors a wealth of unique phenomena, many of which remain mysterious. Of particular interest is the predicted existence of quasi-particles with unusual topological properties, especially in light of recent proposals to observe these properties using electronic interferometers. An introduction to quantum Hall physics and electronic interferometry is given in Chapter 1 of this thesis. The remaining chapters, summarized below, describe a set of experiments in which FQH systems are studied using electronic Fabry-Perot interferometry and related techniques. Since prior studies of electronic Fabry-Perot interferometers revealed unexpected behavior even in the integer quantum Hall (IQH) regime, we began our measurements there. Our initial experiment, presented in Chapter 2, disentangles signatures of Coulomb interaction effects from those of Aharonov-Bohm (AB) interference and provides the first measurement of pure AB interference in these devices. In our next experiment, presented in Chapter 3, we measure AB interference oscillations as a function of an applied dc bias, use their period to study the velocity of the interfering electrons, and study how the oscillations decay as a function of bias and magnetic field. Moving to the FQH regime, applying a similar-sized bias to a quantum point contact leads to long-lasting changes in the strengths and positions of FQH plateaus. The involvement of lattice nuclear spins in this effect, suggested by the long persistence times, is confirmed using NMR-type measurements. Although the exact physical process responsible for the effect remains unclear, its filling-factor dependence provides a striking illustration of composite fermion physics. These measurements are described in Chapter 4. In certain devices, interference oscillations associated with several FQH states are observed. Interpretation of their magnetic-field and gate-voltage periods provides a measurement of quasi-particle charge
AB 1725: A Comprehensive Analysis.
ERIC Educational Resources Information Center
California Community Colleges, Sacramento. Board of Governors.
A summary and analysis is provided of California Assembly Bill (AB) 1725, a reform bill that provides new direction and support for the state's community colleges. The analysis addresses each of the eight sections of the bill: (1) mission, highlighting reforms related to mission statements, transfer core curriculum, remedial limits, articulation…
Li, Zi; Li, Chuanying; Wang, Cong; Zhang, Ping; Kang, Wei
2015-11-15
Ultrafast laser experiments on metals usually induce a high electron temperature and a low ion temperature and, thus, an energy relaxation process. The electron heat capacity and electron-phonon coupling factor are crucial thermal quantities to describe this process. We perform ab initio theoretical studies to determine these thermal quantities and their dependence on density and electron temperature for the metals aluminum and beryllium. The heat capacity shows an approximately linear dependence on the temperature, similar to free electron gas, and the compression only slightly affects the capacity. The electron-phonon coupling factor increases with both temperature and density, and the change observed for beryllium is more obvious than that for aluminum. The connections between thermal quantities and electronic/atomic structures are discussed in detail, and the different behaviors of aluminum and beryllium are well explained.
NASA Astrophysics Data System (ADS)
Li, Zi; Wang, Cong; Kang, Wei; Li, Chuanying; Zhang, Ping
2015-11-01
Ultrafast laser experiments on metals usually induce a high electron temperature and a low ion temperature and, thus, an energy relaxation process. The electron heat capacity and electron-phonon coupling factor are crucial thermal quantities to describe this process. We perform ab initio theoretical studies to determine these thermal quantities and their dependence on density and electron temperature for the metals aluminum and beryllium. The heat capacity shows an approximately linear dependence on the temperature, similar to free electron gas, and the compression only slightly affects the capacity. The electron-phonon coupling factor increases with both temperature and density, and the change observed for beryllium is more obvious than that for aluminum. The connections between thermal quantities and electronic/atomic structures are discussed in detail, and the different behaviors of aluminum and beryllium are well explained.
NASA Astrophysics Data System (ADS)
MacDonell, Ryan J.; Schalk, Oliver; Geng, Ting; Thomas, Richard D.; Feifel, Raimund; Hansson, Tony; Schuurman, Michael S.
2016-09-01
We report a joint experimental and theoretical study on the photoinitiated ultrafast dynamics of acrylonitrile (AN) and two methylated analogs: crotonitrile (CrN) and methacrylonitrile (MeAN). Time-resolved photoelectron spectroscopy (TRPES) and ab initio simulation are employed to discern the conical intersection mediated vibronic dynamics leading to relaxation to the ground electronic state. Each molecule is pumped with a femtosecond pulse at 200 nm and the ensuing wavepackets are probed by means of one and two photon ionization at 267 nm. The predominant vibrational motions involved in the de-excitation process, determined by ab initio trajectory simulations, are an initial twisting about the C=C axis followed by pyramidalization at a carbon atom. The decay of the time-resolved photoelectron signal for each molecule is characterized by exponential decay lifetimes for the passage back to the ground state of 60 ± 10, 86 ± 11, and 97 ± 9 fs for AN, CrN, and MeAN, respectively. As these results show, the excited state dynamics are sensitive to the choice of methylation site and the explanation for the observed trend may be found in the trajectory simulations. Specifically, since the pyramidalization motion leading to the conical intersection with the ground state is accompanied by the development of a partial negative charge at the central atom of the pyramidal group, the electron donation of the cyano group ensures that this occurs exclusively at the medial carbon atom. In this way, the donated electron density from the cyano group "directs" the wavepacket to a particular region of the intersection seam. The excellent agreement between the experimental and simulated TRPES spectra, the latter determined by employing trajectory simulations, demonstrates that this mechanistic picture is consistent with the spectroscopic results.
Testing Distributed ABS System with Fault Injection
NASA Astrophysics Data System (ADS)
Trawczyński, Dawid; Sosnowski, Janusz; Gawkowski, Piotr
The paper deals with the problem of adapting software implemented fault injection technique (SWIFI) to evaluate dependability of reactive microcontroller systems. We present an original methodology of disturbing controller operation and analyzing fault effects taking into account reactions of the controlled object and the impact of the system environment. Faults can be injected randomly (in space and time) or targeted at the most sensitive elements of the controller to check it at high stresses. This approach allows identifying rarely encountered problems, usually missed in classical approaches. The developed methodology has been used successfully to verify dependability of ABS system. Experimental results are commented in the paper.
Josefsson, Ida; Kunnus, Kristjan; Schreck, Simon; Föhlisch, Alexander; de Groot, Frank; Wernet, Philippe; Odelius, Michael
2012-12-01
A new ab initio approach to the calculation of X-ray spectra is demonstrated. It combines a high-level quantum chemical description of the chemical interactions and local atomic multiplet effects. We show here calculated L-edge X-ray absorption (XA) and resonant inelastic X-ray scattering spectra for aqueous Ni(2+) and XA spectra for a polypyridyl iron complex. Our quantum chemical calculations on a high level of accuracy in a post-Hartree-Fock framework give excellent agreement with experiment. This opens the door to reliable and detailed information on chemical interactions and the valence electronic structure in 3d transition-metal complexes also in transient excited electronic states. As we combine a molecular-orbital description with a proper treatment of local atomic electron correlation effects, our calculations uniquely allow, in particular, identifying the influence of interatomic chemical interactions versus intra-atomic correlations in the L-edge X-ray spectra.
Chaudhuri, D; Jin, W; Lefkidis, G; Hübner, W
2015-11-01
We present a systematic analysis of the ab initio controlled femtosecond spin dynamics in Ni3(CH3OH) and Co3(+)(CH3OH) clusters achieved by a spin-orbit-coupling enabled Λ process. The distortion caused by the attachment of CH3OH to one of the active magnetic centers of the Ni3 and the Co3(+) clusters induces asymmetric geometries which result in well localized spin densities on the magnetic centers. With the use of high-level quantum chemistry methods, successful spin-flip scenarios are demonstrated for both clusters. In order to assess the experimental accessibility of those effects, we compute their tolerance with respect to two laser pulse parameters, i.e., the energy detuning as well as the deviation of the polar angle ϕ from its optimized value. Finally, we calculate the magneto-optical Kerr effect in order to connect to the susceptibility tensor χ as an experimentally measurable quantity.
Jiang, M.; Peng, S. M.; Zhang, H. B.; Xu, C. H.; Xiao, H. Y.; Zhao, F. A.; Liu, Z. J.; Zu, X. T.
2016-01-01
In this study, an ab initio molecular dynamics method is employed to investigate how the existence of stacking faults (SFs) influences the response of SiC to low energy irradiation. It reveals that the C and Si atoms around the SFs are generally more difficult to be displaced than those in unfaulted SiC, and the corresponding threshold displacement energies for them are generally larger, indicative of enhanced radiation tolerance caused by the introduction of SFs, which agrees well with the recent experiment. As compared with the unfaulted state, more localized point defects are generated in faulted SiC. Also, the efficiency of damage production for Si recoils is generally higher than that of C recoils. The calculated potential energy increases for defect generation in SiC with intrinsic and extrinsic SFs are found to be higher than those in unfaulted SiC, due to the stronger screen-Coulomb interaction between the PKA and its neighbors. The presented results provide a fundamental insight into the underlying mechanism of displacement events in faulted SiC and will help to advance the understanding of the radiation response of SiC with and without SFs. PMID:26880027
Tong, Xin; Cerný, Jirí; Müller-Dethlefs, Klaus
2008-07-01
Clusters of Ar bound to isomers of the aromatic hydrocarbon n-butylbenzene (BB) have been studied using two-color REMPI (resonance enhanced multiphoton ionization) and MATI (mass analyzed threshold ionization) spectroscopy to explore noncovalent vdW interactions between these two moieties. Blue shifts of excitation energy were observed for gauche-BB...Ar clusters, and red shifts for anti-BB...Ar clusters were observed. Adiabatic ionization energies (IEs) of the conformer BB-I...Ar and BB-V...Ar were determined as 70052 and 69845 +/- 5 cm (-1), respectively. Spectral features and vibrational modes were interpreted with the aid of UMP2/cc-pVDZ ab initio calculations. Data of complexation shifts of the alkyl-benzenes and their argon clusters were collected and discussed. Using the CCSD(T) method at complete basis set (CBS) level, interaction energies for the neutral ground states of BB-I...Ar and BB-V...Ar were obtained as 650 and 558 cm (-1), respectively. Combining the CBS calculation results and the REMPI and MATI spectra allowed further the determination of the interaction energies and the energetics of BB...Ar in the excited neutral S 1 and the D 0 cationic ground states.
Tong, Xin; Cerný, Jirí; Müller-Dethlefs, Klaus
2008-07-01
Clusters of Ar bound to isomers of the aromatic hydrocarbon n-butylbenzene (BB) have been studied using two-color REMPI (resonance enhanced multiphoton ionization) and MATI (mass analyzed threshold ionization) spectroscopy to explore noncovalent vdW interactions between these two moieties. Blue shifts of excitation energy were observed for gauche-BB...Ar clusters, and red shifts for anti-BB...Ar clusters were observed. Adiabatic ionization energies (IEs) of the conformer BB-I...Ar and BB-V...Ar were determined as 70052 and 69845 +/- 5 cm (-1), respectively. Spectral features and vibrational modes were interpreted with the aid of UMP2/cc-pVDZ ab initio calculations. Data of complexation shifts of the alkyl-benzenes and their argon clusters were collected and discussed. Using the CCSD(T) method at complete basis set (CBS) level, interaction energies for the neutral ground states of BB-I...Ar and BB-V...Ar were obtained as 650 and 558 cm (-1), respectively. Combining the CBS calculation results and the REMPI and MATI spectra allowed further the determination of the interaction energies and the energetics of BB...Ar in the excited neutral S 1 and the D 0 cationic ground states. PMID:18533640
Sillar, Kaido; Sauer, Joachim
2012-11-01
A hybrid method that combines density functional theory for periodic structures with wave function-based electron correlation methods for finite-size models of adsorption sites is employed to calculate energies for adsorption of CH(4) onto different sites in the metal-organic framework (MOF) CPO-27-Mg (Mg-MOF-74) with chemical accuracy. The adsorption energies for the Mg(2+), linker, second layer sites are -27.8, -18.3, and -15.1 kJ/mol. Adsorbate-adsorbate interactions increase the average CH(4) adsorption energy by about 10% (2.4 kJ/mol). The free rotor-harmonic oscillator-ideal gas model is applied to calculate free energies/equilibrium constants for adsorption on the individual sites. This information is used in a multisite Langmuir model, augmented with a Bragg-Williams model for lateral interactions, to calculate adsorption isotherms. This ab initio approach yields the contributions of the individual sites to the final isotherms and also of the lateral interactions that contribute about 15% to the maximum excess adsorption capacity. Isotherms are calculated for both absolute amounts, for calculation of isosteric heats of adsorption as function of coverage, and excess amounts, for comparison with measured isotherms. Agreement with observed excess isotherms is reached if the experimentally determined limited accessibility of adsorption sites (78%) is taken into account.
Pi, Xiaodong; Ni, Zhenyi; Yang, Deren E-mail: christophe.delerue@isen.fr; Delerue, Christophe E-mail: christophe.delerue@isen.fr
2014-11-21
In contrast to the conventional doping of bulk silicon (Si), the doping of Si nanocrystals (NCs) that are often smaller than 5 nm in diameter may lead to serious structural changes. Since the electronic and optical properties of Si NCs are intimately associated with their structures, it is critical to understand how doping impacts the structures of Si NCs. By means of ab initio calculation we now compare 1.4 nm phosphorus (P)-doped Si NCs without structural relaxation and those with structural relaxation. Structural changes induced by structural relaxation are manifested by the stretching and compressing of bonds and apparent variations in bond angles. With the increase of the concentration of P structural changes induced by structural relaxation become more serious. It is found that structural relaxation makes differences in the energy-level schemes of P-doped Si NCs. Structural relaxation also causes the binding energy of an electron in a P-doped Si NC to more significantly increase as the concentration of P increases. With the increase of the concentration of P structural relaxation leads to more pronounced changes in the optical absorption of P-doped Si NCs.
Control of tripod-scheme cold-atom wavepackets by manipulating a non-Abelian vector potential
Zhang Qi; Gong Jiangbin; Oh, C.H.
2010-06-15
Tripod-scheme cold atoms interacting with laser beams have attracted considerable interest for their role in synthesizing effective non-Abelian vector potentials. Such effective vector potentials can be exploited to realize an all-optical imprinting of geometric phases onto matter waves. By working on carefully designed extensions of our previous work, we show that coherent lattice structure of cold-atom sub-wavepackets can be formed and that the non-Abelian Aharonov-Bohm effect can be easily manifested via the translational motion of cold atoms. We also show that by changing the frame of reference, effects due to a non-Abelian vector potential may be connected with a simple dynamical phase effect, and that under certain conditions it can be understood as an Abelian geometric phase in a different frame of reference. Results should help design better schemes for the control of cold-atom matter waves.
NASA Astrophysics Data System (ADS)
Hayashi, S.; Léonard, C.; Chambaud, G.
2009-11-01
On the basis of highly correlated ab initio calculations, an accurate determination of the electronic structure and of the rovibrational spectroscopy has been performed for the electronic ground state of the HZnF system. Using effective core pseudopotentials for the Zn and F atoms and associated aug-cc-pVQZ basis sets, we have calculated, at the multireference configuration interaction level including the Davidson correction, the three-dimensional potential energy surface of the X1Σ+ ground state. The rovibrational energy levels have been obtained variationally, and the results have been discussed and compared with existing experimental data on the ground state of the close system HZnCl, which exhibits a complicated vibration-rotation spectrum. Our analysis shows that the nature of the H-ZnF bond is quite similar to that of the H-ZnCl bond, according to their bond lengths, harmonic frequencies of the H-Zn stretching mode, and dissociation energies into H and ZnF/ZnCl. The ab initio study of the electronic ground and excited states of ZnH and ZnH+ are also presented using similar level of calculations. Characteristic constants are given for the first bounded electronic states correlating to the first two dissociation asymptotes of the neutral and ionic diatomics.
Longitudinal wheel slip during ABS braking
NASA Astrophysics Data System (ADS)
Hartikainen, Lassi; Petry, Frank; Westermann, Stephan
2015-02-01
Anti-lock braking system (ABS) braking tests with two subcompact passenger cars were performed on dry and wet asphalt, as well as on snow and ice surfaces. The operating conditions of the tyres in terms of wheel slip were evaluated using histograms of the wheel slip data. The results showed different average slip levels for different road surfaces. It was also found that changes in the tyre tread stiffness affected the slip operating range through a modification of the slip value at which the maximum longitudinal force is achieved. Variation of the tyre footprint length through modifications in the inflation pressure affected the slip operating range as well. Differences in the slip distribution between vehicles with different brake controllers were also observed. The changes in slip operating range in turn modified the relative local sliding speeds between the tyre and the road. The results highlight the importance of the ABS controller's ability to adapt to changing slip-force characteristics of tyres and provide estimates of the magnitude of the effects of different tyre and road operating conditions.
Black holes with quantum massive spin-2 hair
Dvali, Gia
2006-08-15
We show that black holes can posses a long range quantum-mechanical hair associated with a massive spin-2 field, which can be detected by a stringy generalization of the Aharovon-Bohm effect, in which a string loop lassoes the black hole. The long distance effect persist for arbitrarily high mass of the spin-2 field. An analogous effect is exhibited by a massive antisymmetric two-form field. We make a close parallel between the two and the ordinary Aharonov-Bohm phenomenon, and also show that in the latter case the effect can be experienced even by the electrically-neutral particles, provided some boundary terms are added to the action.
Magneto Transport of Graphene Monolayer with Antidot Arrays
NASA Astrophysics Data System (ADS)
Wang, Lei; Yin, Ming; Datta, Timir; Mbamalu, Godwin; Alameri, Dheyaa
Graphene has a significant potential for electronics application as well as in high precision resistive metrological standard. Here we report magneto transport studies of monolayer graphene with antidot in hexagonal arrays on SiO2/Si substrate. The choice of antidot array was motivated by the potential to enhance quantum interference effect amongst charge carriers. The graphene-antidot arrays were fabricated by electron beam lithography followed by reactive ion etching. In our samples the dc magnetic field (B) was applied continuously up to 18 Tesla while the measurement temperature (T) was held steady at desired set points, ranging from 200 mK to 20 K. The effect of nanoarrays on the temperature and field dependence of the electrical properties (MR) and quantum hall effect with particular attention to Aharonov-Bohm oscillations will be reported.
Controlling local currents in molecular junctions
NASA Astrophysics Data System (ADS)
Yadalam, Hari Kumar; Harbola, Upendra
2016-09-01
The effects of nonequilibrium constraints and dephasing on the circulating currents in molecular junctions are analyzed. Circulating currents are manifestations of quantum effects and can be induced either by externally applied bias or an external magnetic field through the molecular system. In a symmetric Aharonov-Bohm ring, bond currents have two contributions, bias driven and magnetic field driven. We analyze the competition between these two contributions and show that, as a consequence, current through one of the branches can be completely suppressed. We then study the effect of asymmetry (as a result of chemical substitution) on the current pathways inside the molecule and study asymmetry-induced circulating currents (without magnetic field) by tuning the coupling strength of the substituent (at finite bias).
Wheel slip control of ABS using ER valve pressure modulator
NASA Astrophysics Data System (ADS)
Choi, Seung-Bok; Cho, Myung-Soo; Kim, Yong-Il; Choi, Young-Tai; Wereley, Norman M.
2004-07-01
This paper presents a wheel slip control via sliding mode controller for a new anti-lock brake system (ABS) of a passenger vehicle using electrorheological (ER) valve pressure modulator. The principal design parameters of the ER valves and hydraulic booster are appropriately determined by considering braking pressure variation during ABS operation. An electrically controllable pressure modulator using the ER valves is then constructed and its governing equations are derived. Subsequently, the pressure control performance of the new pressure modulator is experimentally evaluated. The governing equations of motion for a quarter car wheel model are derived and the sliding mode controller is formulated for wheel slip control. Hardware in the loop simulation (HILS) for braking performance evaluation is undertaken in order to demonstrate the effectiveness of the proposed ABS associated with the ER valve pressure modulator.
AB INITIO AND CALPHAD THERMODYNAMICS OF MATERIALS
Turchi, P A
2004-04-14
Ab initio electronic structure methods can supplement CALPHAD in two major ways for subsequent applications to stability in complex alloys. The first one is rather immediate and concerns the direct input of ab initio energetics in CALPHAD databases. The other way, more involved, is the assessment of ab initio thermodynamics {acute a} la CALPHAD. It will be shown how these results can be used within CALPHAD to predict the equilibrium properties of multi-component alloys.
Detecting Majorana nonlocality using strongly coupled Majorana bound states
NASA Astrophysics Data System (ADS)
Rubbert, S.; Akhmerov, A. R.
2016-09-01
Majorana bound states (MBS) differ from the regular zero energy Andreev bound states in their nonlocal properties, since two MBS form a single fermion. We design strategies for detection of this nonlocality by using the phenomenon of Coulomb-mediated Majorana coupling in a setting which still retains falsifiability and does not require locally separated MBS. Focusing on the implementation of MBS based on the quantum spin Hall effect, we also design a way to probe Majoranas without the need to open a magnetic gap in the helical edge states. In the setup that we analyze, long range MBS coupling manifests in the h /e magnetic flux periodicity of tunneling conductance and supercurrent. While h /e is also the periodicity of Aharonov-Bohm effect and persistent current, we show how to ensure its Majorana origin by verifying that switching off the charging energy restores h /2 e periodicity conventional for superconducting systems.
Steer, Daniele A.; Vachaspati, Tanmay
2011-02-15
The time-dependent metric of a cosmic string leads to an effective interaction between the string and photons--the ''gravitational Aharonov-Bohm'' effect--and causes cosmic strings to emit light. We evaluate the radiation of pairs of photons from cosmic strings and find that the emission from cusps, kinks and kink-kink collisions occurs with a flat spectrum at all frequencies up to the string scale. Further, cusps emit a beam of photons, kinks emit along a curve, and the emission at a kink-kink collision is in all directions. The emission of light from cosmic strings could provide an important new observational signature of cosmic strings that is within reach of current experiments for a range of string tensions.
Is Quantum Mechanics Incompatible with Newton's First Law?
NASA Astrophysics Data System (ADS)
Rabinowitz, Mario
2008-04-01
Quantum mechanics (QM) clearly violates Newton’s First Law of Motion (NFLM) in the quantum domain for one of the simplest problems, yielding an effect in a force-free region much like the Aharonov-Bohm effect. In addition, there is an incompatibility between the predictions of QM in the classical limit, and that of classical mechanics (CM) with respect to NFLM. A general argument is made that such a disparity may be found commonly for a wide variety of quantum predictions in the classical limit. Alternatives to the Schrödinger equation are considered that might avoid this problem. The meaning of the classical limit is examined. Critical views regarding QM by Schrödinger, Bohm, Bell, Clauser, and others are presented to provide a more complete perspective.
Dynamical features of interference phenomena in the presence of entanglement
Kaufherr, T.; Aharonov, Y.; Nussinov, S.; Popescu, S.; Tollaksen, J.
2011-05-15
A strongly interacting, and entangling, heavy nonrecoiling external particle effects a significant change of the environment. Described locally, the corresponding entanglement event is a generalized electric Aharonov-Bohm effect, which differs from the original one in a crucial way. We propose a gedanken interference experiment. The predicted shift of the interference pattern is due to a self-induced or ''private'' potential difference experienced while the particle is in vacuum. We show that all nontrivial Born-Oppenheimer potentials are ''private'' potentials. We apply the Born-Oppenheimer approximation to interference states. Using our approach, we calculate the relative phase of the external heavy particle as well as its uncertainty throughout an interference experiment or entanglement event. We thus complement the Born-Oppenheimer approximation for interference states.
A-B Distinction in a Sample of Prominent Psychotherapists
ERIC Educational Resources Information Center
Geller, Jesse D.; Berzins, Juris I.
1976-01-01
A sample of prominent psychotherapists were asked to fill out the A-B therapist "type" scale and comment on their possible differential effectiveness in treating schizoid/schizophrenic versus neurotic patients. The data suggest that B therapists desire and seek more complex and exciting sensory-cognitive inputs during therapy hours than A…
Alternative Expression for the Electromagnetic Lagrangian
NASA Astrophysics Data System (ADS)
Saldanha, Pablo L.
2016-06-01
We reintroduce an alternative expression for the Lagrangian density that governs the interaction of a charged particle with external electromagnetic fields, proposed by Livens about one century ago. This Lagrangian is written in terms of the local superposition of the particle fields with the applied electromagnetic fields, not in terms of the particle charge and of the electromagnetic potentials as is usual. Here, we show that the total Lagrangian for a set of charged particles assumes a simple elegant form with the alternative formulation, giving an aesthetic support for it. We also show that the alternative Lagrangian is equivalent to the traditional one in their domain of validity and that it provides an interesting description of the Aharonov-Bohm effect.
NASA Astrophysics Data System (ADS)
Matsunaga, Ryusuke; Matsuda, Kazunari; Kanemitsu, Yoshihiko
2009-03-01
We have performed micro-photoluminescence (PL) spectroscopy for single carbon nanotubes under magnetic fields at various temperatures. Sharp PL spectra of single carbon nanotubes allow us to directly observe the dark exciton PL peak a few meV below the bright exciton PL peak due to the Aharonov-Bohm effect [1]. From the PL intensity ratio of the dark to the bright excitons under magnetic fields, we found that the non-equilibrium (non-Boltzmann) distribution occurs between the bright and dark states, because phonons cannot scatter excitons between the two states with different parities [2]. Furthermore, we discuss the diameter dependence of the exciton population of the bright and dark states in single carbon nanotubes. [1] R. Matsunaga, K. Matsuda, and Y. Kanemitsu, Phys. Rev. Lett. 101, 147404 (2008). [2] V. Perebeinos, J. Tersoff, and Ph. Avouris, Nano Lett. 5, 2495 (2005).
Quantum oscillations and wave packet revival in conical graphene structure
NASA Astrophysics Data System (ADS)
Sinha, Debabrata; Berche, Bertrand
2016-03-01
We present analytical expressions for the eigenstates and eigenvalues of electrons confined in a graphene monolayer in which the crystal symmetry is locally modified by replacing a hexagon by a pentagon, square or heptagon. The calculations are performed in the continuum limit approximation in the vicinity of the Dirac points, solving Dirac equation by freezing out the carrier radial motion. We include the effect of an external magnetic field and show the appearance of Aharonov-Bohm oscillations and find out the conditions of gapped and gapless states in the spectrum. We show that the gauge field due to a disclination lifts the orbital degeneracy originating from the existence of two valleys. The broken valley degeneracy has a clear signature on quantum oscillations and wave packet dynamics.
Reprint of : Flux sensitivity of quantum spin Hall rings
NASA Astrophysics Data System (ADS)
Crépin, F.; Trauzettel, B.
2016-08-01
We analyze the periodicity of persistent currents in quantum spin Hall loops, partly covered with an s-wave superconductor, in the presence of a flux tube. Much like in normal (non-helical) metals, the periodicity of the single-particle spectrum goes from Φ0 = h / e to Φ0 / 2 as the length of the superconductor is increased past the coherence length of the superconductor. We further analyze the periodicity of the persistent current, which is a many-body effect. Interestingly, time reversal symmetry and parity conservation can significantly change the period. We find a 2Φ0-periodic persistent current in two distinct regimes, where one corresponds to a Josephson junction and the other one to an Aharonov-Bohm setup.
Three Attempts at Two Axioms for Quantum Mechanics
NASA Astrophysics Data System (ADS)
Rohrlich, Daniel
The axioms of nonrelativistic quantum mechanics lack clear physical meaning. In particular, they say nothing about nonlocality. Yet quantum mechanics is not only nonlocal, it is twice nonlocal: there are nonlocal quantum correlations, and there is the Aharonov-Bohm effect, which implies that an electric or magnetic field here may act on an electron there. Can we invert the logical hierarchy? That is, can we adopt nonlocality as an axiom for quantum mechanics and derive quantum mechanics from this axiom and an additional axiom of causality? Three versions of these two axioms lead to three different theories, characterized by "maximal nonlocal correlations", "jamming" and "modular energy". Where is quantum mechanics in these theories?
Vortex dynamics in self-dual Chern-Simons-Higgs systems
Kim, Y. ); Lee, K. )
1994-02-15
We consider vortex dynamics in self-dual Chern-Simons-Higgs systems. We show that the naive Aharonov-Bohm phase is the inverse of the statistical phase expected from the vortex spin, and that the self-dual configurations of vortices are degenerate in energy but not in angular momentum. We also use the path integral formalism to derive the dual formulation of Chern-Simons-Higgs systems in which vortices appear as charged particles. We argue that in addition to the electromagnetic interaction, there is an additional interaction between vortices, the so-called Magnus force, and that these forces can be put together into a single dual electromagnetic'' interaction. This dual electromagnetic interaction leads to the right statistical phase. We also derive and study the effective action for slowly moving vortices, which contains terms both linear and quadratic in the vortex velocity. We show that vortices can be bounded to each other by the Magnus force.
Random Matrix Theory for Closed Quantum Dots with Weak Spin-Orbit Coupling
NASA Astrophysics Data System (ADS)
Held, K.; Eisenberg, E.; Altshuler, B. L.
2003-03-01
To lowest order in the coupling strength, the spin-orbit coupling in quantum dots results in a spin-dependent Aharonov-Bohm flux. This flux decouples the spin-up and spin-down random matrix theory ensembles of the quantum dot. We employ this ensemble and find significant changes in the distribution of the Coulomb blockade peak height, in particular, a decrease of the width of the distribution. The puzzling disagreement between standard random matrix theory and the experimental distributions by Patel et al. [
NASA Astrophysics Data System (ADS)
Onorato, P.
2011-03-01
An introduction to quantum mechanics based on the sum-over-paths (SOP) method originated by Richard P Feynman and developed by E F Taylor and coworkers is presented. The Einstein-Brillouin-Keller (EBK) semiclassical quantization rules are obtained following the SOP approach for bounded systems, and a general approach to the calculation of propagation amplitude is discussed for unbounded systems. These semiclassical results are obtained when the SOP is limited to the trajectories classically allowed. EBK semiclassical quantization and the topological Maslov index are used to deduce the correct quantum mechanical results for systems which live in a two-dimensional world as quantum dots and quantum rings. In the latter systems, the semiclassical propagation amplitude is used to discuss the Aharonov-Bohm effect. The development involves only elementary calculus and also provides a theoretical introduction to the quantum nature of low-dimensional nanostructures.
Experimental Demonstration of a Synthetic Lorentz Force by Using Radiation Pressure
Šantić, N.; Dubček, T.; Aumiler, D.; Buljan, H.; Ban, T.
2015-01-01
Synthetic magnetism in cold atomic gases opened the doors to many exciting novel physical systems and phenomena. Ubiquitous are the methods used for the creation of synthetic magnetic fields. They include rapidly rotating Bose-Einstein condensates employing the analogy between the Coriolis and the Lorentz force, and laser-atom interactions employing the analogy between the Berry phase and the Aharonov-Bohm phase. Interestingly, radiation pressure - being one of the most common forces induced by light - has not yet been used for synthetic magnetism. We experimentally demonstrate a synthetic Lorentz force, based on the radiation pressure and the Doppler effect, by observing the centre-of-mass motion of a cold atomic cloud. The force is perpendicular to the velocity of the cold atomic cloud, and zero for the cloud at rest. Our novel concept is straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries. PMID:26330327
Experimental Demonstration of a Synthetic Lorentz Force by Using Radiation Pressure
NASA Astrophysics Data System (ADS)
Šantić, N.; Dubček, T.; Aumiler, D.; Buljan, H.; Ban, T.
2015-09-01
Synthetic magnetism in cold atomic gases opened the doors to many exciting novel physical systems and phenomena. Ubiquitous are the methods used for the creation of synthetic magnetic fields. They include rapidly rotating Bose-Einstein condensates employing the analogy between the Coriolis and the Lorentz force, and laser-atom interactions employing the analogy between the Berry phase and the Aharonov-Bohm phase. Interestingly, radiation pressure - being one of the most common forces induced by light - has not yet been used for synthetic magnetism. We experimentally demonstrate a synthetic Lorentz force, based on the radiation pressure and the Doppler effect, by observing the centre-of-mass motion of a cold atomic cloud. The force is perpendicular to the velocity of the cold atomic cloud, and zero for the cloud at rest. Our novel concept is straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries.
Decoherence of high-energy electrons in weakly disordered quantum Hall edge states
NASA Astrophysics Data System (ADS)
Nigg, Simon E.; Lunde, Anders Mathias
2016-07-01
We investigate theoretically the phase coherence of electron transport in edge states of the integer quantum Hall effect at filling factor ν =2 , in the presence of disorder and inter edge state Coulomb interaction. Within a Fokker-Planck approach, we calculate analytically the visibility of the Aharonov-Bohm oscillations of the current through an electronic Mach-Zehnder interferometer. In agreement with recent experiments, we find that the visibility is independent of the energy of the current-carrying electrons injected high above the Fermi sea. Instead, it is the amount of disorder at the edge that sets the phase space available for inter edge state energy exchange and thereby controls the visibility suppression.
NASA Astrophysics Data System (ADS)
Haroz, Erik; Kono, Junichiro; Searles, Thomas; Tu, Xiaomin; Zheng, Ming; Fagan, Jeffrey; McGill, Stephen; Smirnov, Dmitry
2012-02-01
We studied magnetic susceptibility anisotropy, via magnetic linear dichroism spectroscopy, of aqueous suspensions of single-walled carbon nanotubes in high magnetic fields up to 22T using a unique magnet system (Split-Florida Helix magnet). Specifically, we measured magnetic susceptibility anisotropies, δχ, of several armchair species ranging from (5,5)-(13,13) at room temperature over an excitation wavelength range of 400-900 nm. For large diameter armchairs such as (12,12) and (13,13), we have observed some of the strongest alignment in a static magnetic field due to their large diameters. Results will be discussed in comparison with detailed calculations involving the Aharonov-Bohm effect.
Observation of interaction-induced modulations of a quantum Hall liquid's area
NASA Astrophysics Data System (ADS)
Sivan, I.; Choi, H. K.; Park, Jinhong; Rosenblatt, A.; Gefen, Yuval; Mahalu, D.; Umansky, V.
2016-07-01
Studies of electronic interferometers, based on edge-channel transport in the quantum Hall effect regime, have been stimulated by the search for evidence of abelian and non-abelian anyonic statistics of fractional charges. In particular, the electronic Fabry-Pérot interferometer has been found to be Coulomb dominated, thus masking coherent Aharonov-Bohm interference patterns: the flux trapped within the interferometer remains unchanged as the applied magnetic field is varied, barring unobservable modulations of the interference area. Here we report on conductance measurements indicative of the interferometer's area `breathing' with the variation of the magnetic field, associated with observable (a fraction of a flux quantum) variations of the trapped flux. This is the result of partial (controlled) screening of Coulomb interactions. Our results introduce a novel experimental tool for probing anyonic statistics.
Reprint of : Thermodynamic properties of a quantum Hall anti-dot interferometer
NASA Astrophysics Data System (ADS)
Levy Schreier, Sarah; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand I.
2016-08-01
We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop. We show that in the Aharonov-Bohm regime, in which effects of fractional statistics should be visible, is easier to access in interferometers based on anti-dots than in those based on dots. We discuss the relevance of our results to recent measurements on anti-dots interferometers.
On a relation of the angular frequency to the Aharonov-Casher geometric phase in a quantum dot
NASA Astrophysics Data System (ADS)
Barboza, P. M. T.; Bakke, K.
2016-09-01
By analysing the behaviour of a neutral particle with permanent magnetic dipole moment confined to a quantum dot in the presence of a radial electric field, Coulomb-type and linear confining potentials, then, an Aharonov-Bohm-type effect for bound states and a dependence of the angular frequency of the system on the Aharonov-Casher geometric phase and the quantum numbers associated with the radial modes, the angular momentum and the spin are obtained. In particular, the possible values of the angular frequency and the persistent spin currents associated with the ground state are investigated in two different cases.
Geometric diffusion of quantum trajectories.
Yang, Fan; Liu, Ren-Bao
2015-07-16
A quantum object can acquire a geometric phase (such as Berry phases and Aharonov-Bohm phases) when evolving along a path in a parameter space with non-trivial gauge structures. Inherent to quantum evolutions of wavepackets, quantum diffusion occurs along quantum trajectories. Here we show that quantum diffusion can also be geometric as characterized by the imaginary part of a geometric phase. The geometric quantum diffusion results from interference between different instantaneous eigenstate pathways which have different geometric phases during the adiabatic evolution. As a specific example, we study the quantum trajectories of optically excited electron-hole pairs in time-reversal symmetric insulators, driven by an elliptically polarized terahertz field. The imaginary geometric phase manifests itself as elliptical polarization in the terahertz sideband generation. The geometric quantum diffusion adds a new dimension to geometric phases and may have applications in many fields of physics, e.g., transport in topological insulators and novel electro-optical effects.
Adiabatic Edge Channel Transport in a Nanowire Quantum Point Contact Register.
Heedt, S; Manolescu, A; Nemnes, G A; Prost, W; Schubert, J; Grützmacher, D; Schäpers, Th
2016-07-13
We report on a prototype device geometry where a number of quantum point contacts are connected in series in a single quasi-ballistic InAs nanowire. At finite magnetic field the backscattering length is increased up to the micron-scale and the quantum point contacts are connected adiabatically. Hence, several input gates can control the outcome of a ballistic logic operation. The absence of backscattering is explained in terms of selective population of spatially separated edge channels. Evidence is provided by regular Aharonov-Bohm-type conductance oscillations in transverse magnetic fields, in agreement with magnetoconductance calculations. The observation of the Shubnikov-de Haas effect at large magnetic fields corroborates the existence of spatially separated edge channels and provides a new means for nanowire characterization. PMID:27347816
Induced vacuum current and magnetic field in the background of a vortex
NASA Astrophysics Data System (ADS)
Gorkavenko, Volodymyr M.; Ivanchenko, Iryna V.; Sitenko, Yurii A.
2016-02-01
A topological defect in the form of the Abrikosov-Nielsen-Olesen vortex is considered as a gauge-flux-carrying tube that is impenetrable for quantum matter. Charged scalar matter field is quantized in the vortex background with the perfectly reflecting (Dirichlet) boundary condition imposed at the side surface of the vortex. We show that a current circulating around the vortex and a magnetic field directed along the vortex are induced in the vacuum, if the Compton wavelength of the matter field exceeds considerably the transverse size of the vortex. The vacuum current and magnetic field are periodic in the value of the gauge flux of the vortex, providing a quantum-field-theoretical manifestation of the Aharonov-Bohm effect. The total flux of the induced vacuum magnetic field attains notable finite values even for the Compton wavelength of the matter field exceeding the transverse size of the vortex by just three orders of magnitude.
Experimental Demonstration of a Synthetic Lorentz Force by Using Radiation Pressure.
Šantić, N; Dubček, T; Aumiler, D; Buljan, H; Ban, T
2015-01-01
Synthetic magnetism in cold atomic gases opened the doors to many exciting novel physical systems and phenomena. Ubiquitous are the methods used for the creation of synthetic magnetic fields. They include rapidly rotating Bose-Einstein condensates employing the analogy between the Coriolis and the Lorentz force, and laser-atom interactions employing the analogy between the Berry phase and the Aharonov-Bohm phase. Interestingly, radiation pressure - being one of the most common forces induced by light - has not yet been used for synthetic magnetism. We experimentally demonstrate a synthetic Lorentz force, based on the radiation pressure and the Doppler effect, by observing the centre-of-mass motion of a cold atomic cloud. The force is perpendicular to the velocity of the cold atomic cloud, and zero for the cloud at rest. Our novel concept is straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries. PMID:26330327
Point-contact spectroscopy of hopping transport : efffects of a magnetic field.
Kozub, V. I.; Zyuzin, A. A.; Entin-Wohlman, O.; Aharony, A.; Galperin, Y. M.; Vinokur, V.; Materials Science Division; Russian Acad. Sci.; Ben Gurion Univ.; Univ. Oslo
2007-01-01
The conductance of a point contact between two hopping insulators is expected to be dominated by the individual localized states in its vicinity. Here, we study the additional effects due to an external magnetic field. Combined with the measured conductance, the measured magnetoresistance provides detailed information on these states (e.g., their localization length, the energy difference, and the hopping distance between them). We also calculate the statistics of this magnetoresistance, which can be collected by changing the gate voltage in a single device. Since the conductance is dominated by the quantum interference of particular mesoscopic structures near the point contact, it is predicted to exhibit Aharonov-Bohm oscillations, which yield information on the geometry of these structures. These oscillations also depend on local spin accumulation and correlations, which can be modified by the external field. Finally, we also estimate the mesoscopic Hall voltage due to these structures.
Bellucci, S.; Saharian, A. A.; Bardeghyan, V. M.
2010-09-15
The vacuum expectation value of fermionic current is evaluated for a massive spinor field in spacetimes with an arbitrary number of toroidally compactified spatial dimensions in the presence of a constant gauge field. By using the Abel-Plana type summation formula and the zeta-function technique we present the fermionic current in two different forms. Nontrivial topology of the background spacetime leads to the Aharonov-Bohm effect for the fermionic current induced by the gauge field. The current is a periodic function of the magnetic flux with the period equal to the flux quantum. In the absence of gauge field it vanishes for special cases of untwisted and twisted fields. Applications of general formulas to Kaluza-Klein type models and to cylindrical and toroidal carbon nanotubes are given. In the absence of magnetic flux the total fermionic current in carbon nanotubes vanishes, due to the cancellation of contributions from two different sublattices of the hexagonal lattice of graphene.
Gauge invariance and reciprocity in quantum mechanics
Leung, P. T.; Young, K.
2010-03-15
Reciprocity in wave propagation usually refers to the symmetry of the Green's function under the interchange of the source and the observer coordinates, but this condition is not gauge invariant in quantum mechanics, a problem that is particularly significant in the presence of a vector potential. Several possible alternative criteria are given and analyzed with reference to different examples with nonzero magnetic fields and/or vector potentials, including the case of a multiply connected spatial domain. It is shown that the appropriate reciprocity criterion allows for specific phase factors separable into functions of the source and observer coordinates and that this condition is robust with respect to the addition of any scalar potential. In the Aharonov-Bohm effect, reciprocity beyond monoenergetic experiments holds only because of subsidiary conditions satisfied in actual experiments: the test charge is in units of e and the flux is produced by a condensate of particles with charge 2e.
Colloquium: Artificial gauge potentials for neutral atoms
Dalibard, Jean; Gerbier, Fabrice; Juzeliunas, Gediminas; Oehberg, Patrik
2011-10-01
When a neutral atom moves in a properly designed laser field, its center-of-mass motion may mimic the dynamics of a charged particle in a magnetic field, with the emergence of a Lorentz-like force. In this Colloquium the physical principles at the basis of this artificial (synthetic) magnetism are presented. The corresponding Aharonov-Bohm phase is related to the Berry's phase that emerges when the atom adiabatically follows one of the dressed states of the atom-laser interaction. Some manifestations of artificial magnetism for a cold quantum gas, in particular, in terms of vortex nucleation are discussed. The analysis is then generalized to the simulation of non-Abelian gauge potentials and some striking consequences are presented, such as the emergence of an effective spin-orbit coupling. Both the cases of bulk gases and discrete systems, where atoms are trapped in an optical lattice, are addressed.
Recoherence by squeezed states in electron interferometry
Hsiang, J.-T.; Ford, L. H.
2008-09-15
Coherent electrons coupled to the quantized electromagnetic field undergo decoherence which can be viewed as due either to fluctuations of the Aharonov-Bohm phase or to photon emission. When the electromagnetic field is in a squeezed vacuum state, it is possible for this decoherence to be reduced, leading to the phenomenon of recoherence. This recoherence effect requires electrons which are emitted at selected times during the cycle of the excited mode of the electromagnetic field. We show that there are bounds on the degree of recoherence which are analogous to quantum inequality restriction on negative energy densities in quantum field theory. We make some estimates of the degree of recoherence, and show that although small, it is in principle observable.
Geometric phase in Bohmian mechanics
Chou, Chia-Chun; Wyatt, Robert E.
2010-10-15
Using the quantum kinematic approach of Mukunda and Simon, we propose a geometric phase in Bohmian mechanics. A reparametrization and gauge invariant geometric phase is derived along an arbitrary path in configuration space. The single valuedness of the wave function implies that the geometric phase along a path must be equal to an integer multiple of 2{pi}. The nonzero geometric phase indicates that we go through the branch cut of the action function from one Riemann sheet to another when we locally travel along the path. For stationary states, quantum vortices exhibiting the quantized circulation integral can be regarded as a manifestation of the geometric phase. The bound-state Aharonov-Bohm effect demonstrates that the geometric phase along a closed path contains not only the circulation integral term but also an additional term associated with the magnetic flux. In addition, it is shown that the geometric phase proposed previously from the ensemble theory is not gauge invariant.
Ab Initio Calculation of the Hoyle State
Epelbaum, Evgeny; Krebs, Hermann; Lee, Dean; Meissner, Ulf-G.
2011-05-13
The Hoyle state plays a crucial role in the helium burning of stars heavier than our Sun and in the production of carbon and other elements necessary for life. This excited state of the carbon-12 nucleus was postulated by Hoyle as a necessary ingredient for the fusion of three alpha particles to produce carbon at stellar temperatures. Although the Hoyle state was seen experimentally more than a half century ago nuclear theorists have not yet uncovered the nature of this state from first principles. In this Letter we report the first ab initio calculation of the low-lying states of carbon-12 using supercomputer lattice simulations and a theoretical framework known as effective field theory. In addition to the ground state and excited spin-2 state, we find a resonance at -85(3) MeV with all of the properties of the Hoyle state and in agreement with the experimentally observed energy.
Ab initio alpha-alpha scattering.
Elhatisari, Serdar; Lee, Dean; Rupak, Gautam; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Luu, Thomas; Meißner, Ulf-G
2015-12-01
Processes such as the scattering of alpha particles ((4)He), the triple-alpha reaction, and alpha capture play a major role in stellar nucleosynthesis. In particular, alpha capture on carbon determines the ratio of carbon to oxygen during helium burning, and affects subsequent carbon, neon, oxygen, and silicon burning stages. It also substantially affects models of thermonuclear type Ia supernovae, owing to carbon detonation in accreting carbon-oxygen white-dwarf stars. In these reactions, the accurate calculation of the elastic scattering of alpha particles and alpha-like nuclei--nuclei with even and equal numbers of protons and neutrons--is important for understanding background and resonant scattering contributions. First-principles calculations of processes involving alpha particles and alpha-like nuclei have so far been impractical, owing to the exponential growth of the number of computational operations with the number of particles. Here we describe an ab initio calculation of alpha-alpha scattering that uses lattice Monte Carlo simulations. We use lattice effective field theory to describe the low-energy interactions of protons and neutrons, and apply a technique called the 'adiabatic projection method' to reduce the eight-body system to a two-cluster system. We take advantage of the computational efficiency and the more favourable scaling with system size of auxiliary-field Monte Carlo simulations to compute an ab initio effective Hamiltonian for the two clusters. We find promising agreement between lattice results and experimental phase shifts for s-wave and d-wave scattering. The approximately quadratic scaling of computational operations with particle number suggests that it should be possible to compute alpha scattering and capture on carbon and oxygen in the near future. The methods described here can be applied to ultracold atomic few-body systems as well as to hadronic systems using lattice quantum chromodynamics to describe the interactions of
Ab initio alpha-alpha scattering.
Elhatisari, Serdar; Lee, Dean; Rupak, Gautam; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Luu, Thomas; Meißner, Ulf-G
2015-12-01
Processes such as the scattering of alpha particles ((4)He), the triple-alpha reaction, and alpha capture play a major role in stellar nucleosynthesis. In particular, alpha capture on carbon determines the ratio of carbon to oxygen during helium burning, and affects subsequent carbon, neon, oxygen, and silicon burning stages. It also substantially affects models of thermonuclear type Ia supernovae, owing to carbon detonation in accreting carbon-oxygen white-dwarf stars. In these reactions, the accurate calculation of the elastic scattering of alpha particles and alpha-like nuclei--nuclei with even and equal numbers of protons and neutrons--is important for understanding background and resonant scattering contributions. First-principles calculations of processes involving alpha particles and alpha-like nuclei have so far been impractical, owing to the exponential growth of the number of computational operations with the number of particles. Here we describe an ab initio calculation of alpha-alpha scattering that uses lattice Monte Carlo simulations. We use lattice effective field theory to describe the low-energy interactions of protons and neutrons, and apply a technique called the 'adiabatic projection method' to reduce the eight-body system to a two-cluster system. We take advantage of the computational efficiency and the more favourable scaling with system size of auxiliary-field Monte Carlo simulations to compute an ab initio effective Hamiltonian for the two clusters. We find promising agreement between lattice results and experimental phase shifts for s-wave and d-wave scattering. The approximately quadratic scaling of computational operations with particle number suggests that it should be possible to compute alpha scattering and capture on carbon and oxygen in the near future. The methods described here can be applied to ultracold atomic few-body systems as well as to hadronic systems using lattice quantum chromodynamics to describe the interactions of
Ultrasound Biomicroscopy Comparison of Ab Interno and Ab Externo Intraocular Lens Scleral Fixation.
Horiguchi, Lie; Garcia, Patricia Novita; Malavazzi, Gustavo Ricci; Allemann, Norma; Gomes, Rachel L R
2016-01-01
Purpose. To compare ab interno and ab externo scleral fixation of posterior chamber intraocular lenses (PCIOL) using ultrasound biomicroscopy (UBM). Methods. Randomized patients underwent ab externo or ab interno scleral fixation of a PCIOL. Ultrasound biomicroscopy was performed 3 to 6 months postoperatively, to determine PCIOL centration, IOL distance to the iris at 12, 3, 6, and 9 hours, and haptics placement in relation to the ciliary sulcus. Results. Fifteen patients were enrolled in the study. The ab externo technique was used in 7 eyes (46.6%) and the ab interno in 8 eyes (53.3%). In the ab externo technique, 14 haptics were located: 4 (28.57%) in the ciliary sulcus; 2 (14.28%) anterior to the sulcus; and 8 (57.14%) posterior to the sulcus, 6 in the ciliary body and 2 posterior to the ciliary body. In the ab interno group, 4 haptics (25.0%) were in the ciliary sulcus, 2 (12.50%) anterior to the sulcus, and 10 (75.0%) posterior to the sulcus, 4 in the ciliary body and 6 posterior to the ciliary body. Conclusions. Ab externo and ab interno scleral fixation techniques presented similar results in haptic placement. Ab externo technique presented higher vertical tilt when compared to the ab interno.
Ultrasound Biomicroscopy Comparison of Ab Interno and Ab Externo Intraocular Lens Scleral Fixation
Horiguchi, Lie; Garcia, Patricia Novita; Malavazzi, Gustavo Ricci; Allemann, Norma
2016-01-01
Purpose. To compare ab interno and ab externo scleral fixation of posterior chamber intraocular lenses (PCIOL) using ultrasound biomicroscopy (UBM). Methods. Randomized patients underwent ab externo or ab interno scleral fixation of a PCIOL. Ultrasound biomicroscopy was performed 3 to 6 months postoperatively, to determine PCIOL centration, IOL distance to the iris at 12, 3, 6, and 9 hours, and haptics placement in relation to the ciliary sulcus. Results. Fifteen patients were enrolled in the study. The ab externo technique was used in 7 eyes (46.6%) and the ab interno in 8 eyes (53.3%). In the ab externo technique, 14 haptics were located: 4 (28.57%) in the ciliary sulcus; 2 (14.28%) anterior to the sulcus; and 8 (57.14%) posterior to the sulcus, 6 in the ciliary body and 2 posterior to the ciliary body. In the ab interno group, 4 haptics (25.0%) were in the ciliary sulcus, 2 (12.50%) anterior to the sulcus, and 10 (75.0%) posterior to the sulcus, 4 in the ciliary body and 6 posterior to the ciliary body. Conclusions. Ab externo and ab interno scleral fixation techniques presented similar results in haptic placement. Ab externo technique presented higher vertical tilt when compared to the ab interno. PMID:27293878
Banister, Samuel D; Moir, Michael; Stuart, Jordyn; Kevin, Richard C; Wood, Katie E; Longworth, Mitchell; Wilkinson, Shane M; Beinat, Corinne; Buchanan, Alexandra S; Glass, Michelle; Connor, Mark; McGregor, Iain S; Kassiou, Michael
2015-09-16
Synthetic cannabinoid (SC) designer drugs based on indole and indazole scaffolds and featuring l-valinamide or l-tert-leucinamide side chains are encountered with increasing frequency by forensic researchers and law enforcement agencies and are associated with serious adverse health effects. However, many of these novel SCs are unprecedented in the scientific literature at the time of their discovery, and little is known of their pharmacology. Here, we report the synthesis and pharmacological characterization of AB-FUBINACA, ADB-FUBINACA, AB-PINACA, ADB-PINACA, 5F-AB-PINACA, 5F-ADB-PINACA, ADBICA, 5F-ADBICA, and several analogues. All synthesized SCs acted as high potency agonists of CB1 (EC50 = 0.24-21 nM) and CB2 (EC50 = 0.88-15 nM) receptors in a fluorometric assay of membrane potential, with 5F-ADB-PINACA showing the greatest potency at CB1 receptors. The cannabimimetic activities of AB-FUBINACA and AB-PINACA in vivo were evaluated in rats using biotelemetry. AB-FUBINACA and AB-PINACA dose-dependently induced hypothermia and bradycardia at doses of 0.3-3 mg/kg, and hypothermia was reversed by pretreatment with a CB1 (but not CB2) antagonist, indicating that these SCs are cannabimimetic in vivo, consistent with anecdotal reports of psychoactivity in humans. PMID:26134475
Nam, Kikyung; Kim, Yongho
2009-04-14
We performed high-level quantum mechanical calculations and direct ab initio reaction dynamics calculations for multiple proton transfers in ClONO(2)+HCl-->HNO(3)+Cl(2) with water clusters containing one to two water molecules, which can be used as a model of the reactions occurring on ice surface in stratospheric clouds. The energy barriers of these reactions depend on the number of water molecules involved. Two and three protons in these reactions with one and two water molecules, respectively, were transferred concertedly and asynchronously. The potential energy barrier at the MP2/6-311++(3df,3pd)//MP2/6-31G(d,p) level was 4.8 kcal/mol for the triple proton transfer involving two water molecules with a rate constant of 1.6x10(3) s(-1) at 197 K. The potential energy curve near the saddle points was very flat and the tunneling effect on the proton transfer was negligible. The primary HH/DH kinetic isotope effect for the double proton transfer involving one water molecule was lower than unity due to the enhanced force constant at the transition state. The rule of the geometric mean for the concerted proton transfer does not hold in these reactions because the zero-point energy changes of each proton in flight at the transition state are not the same in the highly asynchronous processes.
NASA Astrophysics Data System (ADS)
Ostojic, Bojana; Schwerdtfeger, Peter; Bunker, Phil; Jensen, Per
2016-06-01
We present the results of ab initio calculations for the lower electronic states of the Group 15 (pnictogen) dihydrides, SbH_2 and BiH_2. For each of these molecules the two lowest electronic states become degenerate at linearity and are therefore subject to the Renner effect. Spin-orbit coupling is also strong in these two heavy-element containing molecules. For the lowest two electronic states of SbH_2, we construct the three dimensional potential energy surfaces and corresponding dipole moment and transition moment surfaces by multi-reference configuration interaction techniques. Including both the Renner effect and spin-orbit coupling, we calculate term values and simulate the rovibrational and rovibronic spectra of SbH_2. Excellent agreement is obtained with the results of matrix isolation infrared spectroscopic studies and with gas phase electronic spectroscopic studies in absorption [1,2]. For the heavier dihydride BiH_2 we calculate bending potential curves and the spin-orbit coupling constant for comparison. For SbH_2 we further study the local mode vibrational behavior and the formation of rovibronic energy level clusters in high angular momentum states. [1] X. Wang, P. F. Souter and L. Andrews, J. Phys. Chem. A 107, 4244-4249 (2003) [2] N. Basco and K. K. Lee, Spectroscopy Letters 1, 13-15 (1968)
NASA Astrophysics Data System (ADS)
Tarighi Ahmadpour, Mahdi; Hashemifar, S. Javad; Rostamnejadi, Ali
2016-07-01
We use density functional computations to study the zero temperature structural, electronic, magnetic, and optical properties of (5,0) finite carbon nanotubes (FCNT), with length in the range of 4-44 Å. It is found that the structural and electronic properties of (5,0) FCNTs, in the ground state, converge at a length of about 30 Å, while the excited state properties exhibit long-range edge effects. We discuss that curvature effects enhance energy gap of FCNTs, in contrast to the known trend in the periodic limit. It is seen that compensation of curvature effects in two special small sizes may give rise to spontaneous magnetization. The obtained cohesive energies provide some insights into the effects of environment on the growth of FCNTs. The second-order difference of the total energies reveals an important magic size of about 15 Å. The optical and dynamical magnetic responses of the FCNTs to polarized electromagnetic pulses are studied by time dependent density functional theory. The results show that the static and dynamic magnetic properties mainly come from the edge carbon atoms. The optical absorption properties are described in terms of local field effects and characterized by Casida linear response method.
Takeuchi, Hiroshi; Enmi, Jun-ichiro; Onozaki, Manabu; Egawa, Toru; Konaka, Shigehiro
1994-09-01
Gas electron diffusion and HF/4-21 G calculations on geometric parameters and harmonic force constants are used to study the molecular structure of tert-butyl acetate. This determined that C{sub 1} = O{sub 2} is (cis) to O{sub 4}-C{sub 5} and the tert-butyl group is staggered to the C{sub 1}-O{sub 4} bond. The structural parameters are also determined. C{sub 1}-O{sub 4} bond length shortening is rationalized in terms of the resonance effect and the electron-releasing inductive effect of substituents. 29 refs., 4 figs., 4 tabs.
Ab initio study of radiation effects on the Li4Ti5O12 electrode used in lithium-ion batteries
NASA Astrophysics Data System (ADS)
Samin, Adib; Kurth, Michael; Cao, Lei
2015-04-01
Lithium-ion batteries are currently in wide use owing to their high energy density and enhanced capabilities. Li4Ti5O12 is a promising anode material for lithium-ion batteries because of its advantageous properties. Lithium-ion batteries could be exposed to radiation occurring in various conditions such as during outer space exploration and nuclear accidents. In this study, we apply density functional theory to explore the effect of radiation damage on this electrode and, ultimately, on the performance of the battery. It was found that radiation could affect the structural stability of the material. Furthermore, the electrode was shown to undergo a transition from insulator to metal, following the defects due to radiation. In addition, the effect of radiation on the intercalation potential was found to be highly dependent on the nature of the defect induced.
Samin, Adib E-mail: cao.152@osu.edu; Kurth, Michael; Cao, Lei E-mail: cao.152@osu.edu
2015-04-15
Lithium-ion batteries are currently in wide use owing to their high energy density and enhanced capabilities. Li{sub 4}Ti{sub 5}O{sub 12} is a promising anode material for lithium-ion batteries because of its advantageous properties. Lithium-ion batteries could be exposed to radiation occurring in various conditions such as during outer space exploration and nuclear accidents. In this study, we apply density functional theory to explore the effect of radiation damage on this electrode and, ultimately, on the performance of the battery. It was found that radiation could affect the structural stability of the material. Furthermore, the electrode was shown to undergo a transition from insulator to metal, following the defects due to radiation. In addition, the effect of radiation on the intercalation potential was found to be highly dependent on the nature of the defect induced.
Sun, Wei; Dai, Zuyang; Wang, Jia; Mo, Yuxiang
2015-05-21
The spin-vibronic energy levels of the chloroacetylene cation up to 4000 cm(-1) above the ground state have been measured using the one-photon zero-kinetic energy photoelectron spectroscopic method. The spin-vibronic energy levels have also been calculated using a diabatic model, in which the potential energy surfaces are expressed by expansions of internal coordinates, and the Hamiltonian matrix equation is solved using a variational method with harmonic basis functions. The calculated spin-vibronic energy levels are in good agreement with the experimental data. The Renner-Teller (RT) parameters describing the vibronic coupling for the H-C≡C bending mode (ε4), Cl-C≡C bending mode (ε5), the cross-mode vibronic coupling (ε45) of the two bending vibrations, and their vibrational frequencies (ω4 and ω5) have also been determined using an effective Hamiltonian matrix treatment. In comparison with the spin-orbit interaction, the RT effect in the H-C≡C bending (ε4) mode is strong, while the RT effect in the Cl-C≡C bending mode is weak. There is a strong cross-mode vibronic coupling of the two bending vibrations, which may be due to a vibronic resonance between the two bending vibrations. The spin-orbit energy splitting of the ground state has been determined for the first time and is found to be 209 ± 2 cm(-1).
Shen, Hongchang; Xu, Jun; Zhu, Linhai; Liu, Qi; Du, Jiajun
2015-01-01
Background Small cell lung cancer (SCLC) is a recalcitrant malignancy with distinct biologic properties. Antibody targeting therapy has been actively investigated as a new drug modality. Methods We tested the expression of IGF-1R and calculated the survival in 61 SCLC patients. We also evaluated the anti-tumor effects of anti-IGF-1R monoclonal antibody Figitumumab (CP) on SCLC, and tried two drug combinations to improve CP therapy. Results Our clinical data suggested that high IGF-1R expression was correlated with low SCLC patient survival. We then demonstrated the effect of CP was likely through IGF-1R blockage and down-regulation without IGF-1R auto-phosphorylation and PI3K/AKT activation. However, we observed elevated MEK/ERK activation upon CP treatment in SCLC cells, and this MEK/ERK activation was enhanced by ß-arrestin1 knockdown while attenuated by ß-arrestin2 knockdown. We found both MEK/ERK inhibitor and metformin could enhance CP treatment in SCLC cells. We further illustrated the additive effect of metformin was likely through promoting further IGF-1R down-regulation. Conclusion Our results highlighted the potential of anti-IGF-1R therapy and the adjuvant therapy strategy with either MEK/ERK inhibitor or metformin to target SCLC, warranting further studies. PMID:26287334
Surface Segregation Energies of BCC Binaries from Ab Initio and Quantum Approximate Calculations
NASA Technical Reports Server (NTRS)
Good, Brian S.
2003-01-01
We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy method. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameterization. Quantum approximate segregation energies are computed with and without atomistic relaxation. The ab initio calculations are performed without relaxation for the most part, but predicted relaxations from quantum approximate calculations are used in selected cases to compute approximate relaxed ab initio segregation energies. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with other quantum approximate and ab initio theoretical work, and available experimental results.
Boda, Anil; Ali, Sk Musharaf; Rao, Hanmanth; Ghosh, Sandip K
2012-08-01
The structures, energetic and thermodynamic parameters of model crown ethers with different donor, cavity and electron donating/ withdrawing functional group have been determined with ab initio MP2 and density functional theory in gas and solvent phase. The calculated values of binding energy/ enthalpy for lithium ion complexation are marginally higher for hard donor based aza and oxa crown compared to soft donor based thia and phospha crown. The calculated values of binding enthalpy for lithium metal ion with 12C4 at MP2 level of theory is in good agreement with the available experimental result. The binding energy is altered due to the inductive effect imparted by the electron donating/ withdrawing group in crown ether, which is well correlated with the values of electron transfer. The role of entropy for extraction of hydrated lithium metal ion by different donor and functional group based ligand has been demonstrated. The HOMO-LUMO gap is decreased and dipole moment of the ligand is increased from gas phase to organic phase because of the dielectric constant of the solvent. The gas phase binding energy is reduced in solvent phase as the solvent molecules weaken the metal-ligand binding. The theoretical values of extraction energy for LiCl salt from aqueous solution in different organic solvent is validated by the experimental trend. The study presented here should contribute to the design of model host ligand and screening of solvent for metal ion recognition and thus can contribute in planning the experiments.
NASA Astrophysics Data System (ADS)
Ziat, Younes; Zarhri, Zakaryaa; Hammi, Maryama; Slassi, Amine; Echihi, Siham; El Kenz, Abdallah; Benyoussef, Abdelilah
2016-07-01
The ab-initio calculations, based on the Korringa-Kohn-Rostoker approximation combined with Coherent Potential Approximation (KKR-CPA) and the local density approximation (LDA) have been used to study the electronic and magnetic properties of 3% of N-doped Fe0.98TM0.02S2 (TM=V or Cr) pyrite. The N is occurred as a non-metallic impurity to evaluate its effect on conductivity type and the stability of the studied systems. Our investigation confirms the p-type conductivity. The stabilization of the ferromagnetic state in N-doped Fe0.98V0.02S2 is observed due to the incorporation of N impurity. The majority-spin related to t2g+ is located around the Fermi level. And the ferromagnetic state connected to the half metal is potentially utilized in spintronic field. In Fe0.98Cr0.02S1.97N0.03, the 3% of N induced a hybridization between (Cr[3d] and N[2p]). We predicted an enlargement of the peak of the Cr[3d]. In addition, the total moment of the studied systems is augmented as well as the Curie temperature (TC).
Moon, Jiwon; Kim, Joonghan
2016-09-29
Density functional theory (DFT) and ab initio calculations, including spin-orbit coupling (SOC), were performed to investigate the spin-orbit (SO) effect on the molecular properties of tellurium halides, TeXn (X = F, Cl, Br, and I; n = 1, 2, and 4). SOC elongates the Te-X bond and slightly reduces the vibrational frequencies. Consideration of SOC leads to better agreement with experimental values. Møller-Plesset second-order perturbation theory (MP2) seriously underestimates the Te-X bond lengths. In contrast, B3LYP significantly overestimates them. SO-PBE0 and multireference configuration interactions with the Davidson correction (MRCI+Q), which include SOC via a state-interaction approach, give the Te-I bond length of TeI2 that matches the experimental value. On the basis of the calculated thermochemical energy and optimized molecular structure, TeI4 is unlikely to be stable. The use of PBE0 including SOC is strongly recommended for predicting the molecular properties of Te-containing compounds.
Okuno, Yukihiro; Ushirogata, Keisuke; Sodeyama, Keitaro; Tateyama, Yoshitaka
2016-03-28
Additives in the electrolyte solution of lithium-ion batteries (LIBs) have a large impact on the performance of the solid electrolyte interphase (SEI) that forms on the anode and is a key to the stability and durability of LIBs. We theoretically investigated effects of fluoroethylene carbonate (FEC), a representative additive, that has recently attracted considerable attention for the enhancement of cycling stability of silicon electrodes and the improvement of reversibility of sodium-ion batteries. First, we intensively examined the reductive decompositions by ring-opening, hydrogen fluoride (HF) elimination to form a vinylene carbonate (VC) additive and intermolecular chemical reactions of FEC in the ethylene carbonate (EC) electrolyte, by using density functional theory (DFT) based molecular dynamics and the blue-moon ensemble technique for the free energy profile. The results show that the most plausible product of the FEC reductive decomposition is lithium fluoride (LiF), and that the reactivity of FEC to anion radicals is found to be inert compared to the VC additive. We also investigated the effects of the generated LiF on the SEI by using two model systems; (1) LiF molecules distributed in a model aggregate of organic SEI film components (SFCs) and (2) a LiF aggregate interfaced with the SFC aggregate. DFT calculations of the former system show that F atoms form strong bindings with the Li atoms of multiple organic SFC molecules and play as a joint connecting them. In the latter interface system, the LiF aggregate adsorbs the organic SFCs through the F-Li bindings. These results suggest that LiF moieties play the role of glue in the organic SFC within the SEI film. We also examined the interface structure between a LiF aggregate and a lithiated silicon anode, and found that they are strongly bound. This strong binding is likely to be related to the effectiveness of the FEC additive in the electrolyte for the silicon anode.
Okuno, Yukihiro; Ushirogata, Keisuke; Sodeyama, Keitaro; Tateyama, Yoshitaka
2016-03-28
Additives in the electrolyte solution of lithium-ion batteries (LIBs) have a large impact on the performance of the solid electrolyte interphase (SEI) that forms on the anode and is a key to the stability and durability of LIBs. We theoretically investigated effects of fluoroethylene carbonate (FEC), a representative additive, that has recently attracted considerable attention for the enhancement of cycling stability of silicon electrodes and the improvement of reversibility of sodium-ion batteries. First, we intensively examined the reductive decompositions by ring-opening, hydrogen fluoride (HF) elimination to form a vinylene carbonate (VC) additive and intermolecular chemical reactions of FEC in the ethylene carbonate (EC) electrolyte, by using density functional theory (DFT) based molecular dynamics and the blue-moon ensemble technique for the free energy profile. The results show that the most plausible product of the FEC reductive decomposition is lithium fluoride (LiF), and that the reactivity of FEC to anion radicals is found to be inert compared to the VC additive. We also investigated the effects of the generated LiF on the SEI by using two model systems; (1) LiF molecules distributed in a model aggregate of organic SEI film components (SFCs) and (2) a LiF aggregate interfaced with the SFC aggregate. DFT calculations of the former system show that F atoms form strong bindings with the Li atoms of multiple organic SFC molecules and play as a joint connecting them. In the latter interface system, the LiF aggregate adsorbs the organic SFCs through the F-Li bindings. These results suggest that LiF moieties play the role of glue in the organic SFC within the SEI film. We also examined the interface structure between a LiF aggregate and a lithiated silicon anode, and found that they are strongly bound. This strong binding is likely to be related to the effectiveness of the FEC additive in the electrolyte for the silicon anode. PMID:26948716
NASA Astrophysics Data System (ADS)
Salmani, E.; Mounkachi, O.; Ez-Zahraouy, H.; El Kenz, A.; Hamedoun, M.; Benyoussef, A.
2013-03-01
Based on first-principles spin-density functional calculations, using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of (Ga, Fe)N co-doped with carbon within the self-interaction-corrected local density approximation. Mechanism of hybridization and interaction between magnetic ions in p-type (Ga, Fe)N is investigated. Stability energy of ferromagnetic and disorder local moment states was calculated for different carbon concentration. The local density and the self-interaction-corrected approximations have been used to explain the strong ferromagnetic interaction observed and the mechanism that stabilizes this state. The transition temperature to the ferromagnetic state has been calculated within the effective field theory, with a Honmura-Kaneyoshi differential operator technique.
NASA Astrophysics Data System (ADS)
Pairor, P.; Nilmoung, S.
2004-11-01
We study the effect of gap suppression near the surface on the conductance spectra of normal metal-{100} and {110} da2-b2 -wave superconductor junctions using the scattering method. We find that for {100} junctions the positions of the maxima of the spectra are not always at the gap maximum of the bulk. The positions depend on the degree of the gap suppression at the interface. For {110} junctions, we find that the width of zero-bias conductance peaks (ZBCPs) in the spectra depends on the magnitude of the gap function at the interface of the junction. The ZBCP is absent when the gap function is totally suppressed at the interface. We also find that the shape of the spectra depends on the slope of the order parameter at the interface.
Setyawan, Wahyu; Kurtz, Richard J.
2014-03-13
Density functional theory calculations were performed to study the effects of H, He, Li and Be on the cohesion of W Σ3<110>{112} and Σ27<110>{552} grain boundaries (GBs). In Σ3, Li causes the strongest embrittlement, while in Σ27 it is He. In both GBs, H slightly reduces the cohesion. Compared to He and Li, H exhibits much stronger attractive binding with W that may inhibit subsequent segregation of Li and He to the GBs. In Σ3, Be decreases the cohesion. However, in Σ27, Be strengthens the cohesion in several interstitial positions by increasing the bonding across the interface or by inducing GB restructuring.
Superconductivity of the magnetized electron gas of a quantum cylinder
Eminov, P. A. Sezonov, Yu. I.
2008-10-15
A microscopic theory of superconductivity is developed for the magnetized electron gas on a cylindrical surface. The Gibbs free energy is calculated for the superconducting system. A gap equation is derived that determines the critical temperature as a function of the quantum-cylinder dimensions and the Aharonov-Bohm parameter. It is shown that the gap not only exhibits Aharonov-Bohm oscillations, but also oscillates with varying curvature of the cylindrical surface.
Ab initio calculations of nitramine dimers
NASA Astrophysics Data System (ADS)
Koh-Fallet, Sharon; Schweigert, Igor
2015-06-01
Elevated temperatures and pressures are typically thought to have opposing effects on the reaction channels of nitramine decomposition. These high temperatures promote reactions with loose transition structures (positive activation entropies and volumes), such as N-N bond homolysis. Elevated pressures promote reactions with tight transition structures (negative activation entropies and volumes), such as intramolecular and intermolecular H transfer. However, no quantitative data exists regarding the range of temperatures and pressures at which these effects become pronounced. We are pursuing ab initio calculations of the corresponding unimolecular and bimolecular transition structures with the objective of estimating the relevant thermochemical parameters and quantifying the effects of elevated temperature and pressures on the corresponding rate constants. Here, we present density functional theory and complete active space calculations of gas-phase molecular dimers of nitramines as an intermediate step toward modeling transition structures directly in the condensed phase. This work was supported by the Naval Research Laboratory via the American Society for Engineering and Education and by the Office of Naval Research, both directly and through the Naval Research Laboratory.
Park, Hyun Jun; Moon, Du Guen; Park, Nam Cheol
2016-01-01
Objectives 5ARIs have sexual side effects, including erectile dysfunction (ED), loss of libido and ejaculatory dysfunction due to their action mechanism which decreases serum DHT levels. We examined whether concomitant dutasteride reduced the efficacy of testosterone replacement therapy (TRT) in men with late-onset hypogonadism. Methods This was a 24-week, randomized, parallel study of the clinical outcomes in men age >40 years with symptomatic benign prostatic hypertrophy [BPH; International Prostate Symptom Score (IPSS) th], prostate volume Prostate Symptom Score (IPSS) 300 ng/dL with aging male symptoms, who were taking stable doses of alpha-blockers 4 weeks before participation. Eligible patients received a combination of dutasteride 0.5 mg once daily and a transdermal gel containing 10 g testosterone (T) (DT group, n=30) or the transdermal gel alone (T group, n=30). The primary outcomes were the change in the aging male symptom (AMS) score, sexual desire (question 17, AMS score), and erectile function (International Index of Erectile Function-5). Secondary outcomes were the post-treatment IPSS, peak urinary flow rate, post-void residual urine volume (PVR), and prostate volume. Results Both groups showed significant improvements from baseline in all primary outcome parameters. However, there were no significant differences in the changes in the AMS total score (DT −5.2 vs. T −5.0; P=0.55), sexual desire (DT −2.5 vs. T −2.3; P=0.23), and IIEF-5 score (DT −2.1 vs. T −1.9; P=0.13) between groups. The extent of IPSS improvement from baseline to 24 weeks was the same in both groups (DT −1.2 vs. T −1.0; P=0.64). In addition, the changes in Q(max) and PVR from baseline were very similar in both groups. However, prostate volume decreased significantly (P<0.01) in the DT group (DT −6.1 cc vs. T +0.6 cc). Conclusions Concomitant dutasteride did not reduce the effect of testosterone replacement therapy in men with late-2onset hypogonadism. Otherwise it
Hahn, Konstanze R; Seitsonen, Ari P; Baiker, Alfons
2015-11-01
The cinchona alkaloids cinchonidine and cinchonine belong to the most efficient chiral modifiers for the noble metal-catalyzed enantioselective hydrogenation of C=O and C=C bonds. Under reaction conditions these modifiers are coadsorbed on the noble metal surface with hydrogen. Using density functional theory, we studied the effect of coadsorbed hydrogen on the adsorption mode of cinchonidine and cinchonine on a Pt(111) surface at different hydrogen coverages. The theoretical study indicates that the presence of coadsorbed hydrogen affects both the adsorption geometry as well as the stability of the adsorbed cinchona alkaloids. At all hydrogen coverages the cinchona alkaloids are found to be adsorbed via anchoring of the quinoline moiety. In the absence of hydrogen as well as at low hydrogen coverage the quinoline moiety adsorbs nearly parallel to the surface, whereas at higher hydrogen coverage it becomes tilted. Higher hydrogen coverage as well as partial hydrogenation of the quinoline part of the cinchona alkaloid and hydrogen transfer to the C[double bond, length as m-dash]C double bond at 10, 11 position of the quinuclidine moiety destabilize the adsorbed cinchona alkaloid, whereas hydrogen transfer to the nitrogen atom of the quinoline and the quinuclidine moiety stabilizes the adsorbed molecule. The stability as well as the adsorption geometry of the cinchona alkaloids are affected by the coadsorbed hydrogen and are proposed to influence the efficiency of the enantiodifferentiating ability of the chirally modified platinum surface.
Hahn, Konstanze R; Seitsonen, Ari P; Baiker, Alfons
2015-11-01
The cinchona alkaloids cinchonidine and cinchonine belong to the most efficient chiral modifiers for the noble metal-catalyzed enantioselective hydrogenation of C=O and C=C bonds. Under reaction conditions these modifiers are coadsorbed on the noble metal surface with hydrogen. Using density functional theory, we studied the effect of coadsorbed hydrogen on the adsorption mode of cinchonidine and cinchonine on a Pt(111) surface at different hydrogen coverages. The theoretical study indicates that the presence of coadsorbed hydrogen affects both the adsorption geometry as well as the stability of the adsorbed cinchona alkaloids. At all hydrogen coverages the cinchona alkaloids are found to be adsorbed via anchoring of the quinoline moiety. In the absence of hydrogen as well as at low hydrogen coverage the quinoline moiety adsorbs nearly parallel to the surface, whereas at higher hydrogen coverage it becomes tilted. Higher hydrogen coverage as well as partial hydrogenation of the quinoline part of the cinchona alkaloid and hydrogen transfer to the C[double bond, length as m-dash]C double bond at 10, 11 position of the quinuclidine moiety destabilize the adsorbed cinchona alkaloid, whereas hydrogen transfer to the nitrogen atom of the quinoline and the quinuclidine moiety stabilizes the adsorbed molecule. The stability as well as the adsorption geometry of the cinchona alkaloids are affected by the coadsorbed hydrogen and are proposed to influence the efficiency of the enantiodifferentiating ability of the chirally modified platinum surface. PMID:26426825
Jutier, Laurent; Léonard, Céline
2010-05-11
A new variational methodology for the treatment of the Renner-Teller effect in tetra-atomic molecules has been developed in valence coordinates. The kinetic-energy operator of Bramley et al. [Mol. Phys. 1991, 73, 1183] for any sequentially bonded four-atom molecule, A-B-C-D, in the singlet nondegenerate electronic state has been adapted to the Renner-Teller and spin couplings by modifying the expression of the nuclear angular momentum. The total Schrödinger equation is solved by diagonalizing the Hamiltonian matrix in a three-step contraction scheme. The main advantage of this new theoretical development is the possibility of studying different isotopomers using the same potential-energy surfaces. This procedure has been tested on HCCH(+) and its deuterated derivatives DCCD(+) and DCCH(+). The calculated rovibronic band origins were compared with previous data deduced from the Jacobi coordinates methodology, dimensionality reduced variational treatment, and photoelectron spectra with a good global agreement. Rotational structures for these systems are also tackled.
Zabidi, Noriza Ahmad; Kassim, Hasan Abu; Shrivastava, Keshav N.
2008-05-20
Polonium is the only element with a simple cubic (sc) crystal structure. Atoms in solid polonium sit at the corners of a simple cubic unit cell and no where else. Polonium has a valence electron configuration 6s{sup 2}6p{sup 4} (Z = 84). The low temperature {alpha}-phase transforms into the rhombohedral (trigonal) {beta} structure at {approx}348 K. The sc {alpha}-Po unit cell constant is a = 3.345 A. The beta form of polonium ({beta}-Po) has the lattice parameters, a{sub R} = 3.359 A and a rhombohedral angle 98 deg. 13'. We have performed an ab initio electronic structure calculation by using the density functional theory. We have performed the calculation with and without spin-orbit (SO) coupling by using both the LDA and the GGA for the exchange-correlations. The k-points in a simple cubic BZ are determined by R (0.5, 0.5, 0.5), {gamma} (0, 0, 0), X (0.5, 0, 0), M (0.5, 0.5, 0) and {gamma} (0, 0, 0). Other directions of k-points are {gamma} (0, 0, 0), X (0.5, 0, 0), R (0.5, 0.5, 0.5) and {gamma} (0, 0, 0). The SO splittings of p states at the {gamma} point in the GGA+SO scheme for {alpha}-Po are 0.04 eV and 0.02 eV while for the {beta}-Po these are 0.03 eV and 0.97 eV. We have also calculated the vibrational spectra for the unit cells in both the structures. We find that exchanging of a Po atom by Pb atom produces several more bands and destabilizes the {beta} phase.
Zhang, Wenbiao; Li, Qiang E-mail: dhm@xju.edu.cn; Duan, Haiming E-mail: dhm@xju.edu.cn
2015-03-14
In order to understand the effects of the metalloid elements M (M: P, C, B) on the atomic structure, glass formation ability (GFA) and magnetic properties of Fe-based amorphous alloys, Fe{sub 80}P{sub 13}C{sub 7}, Fe{sub 80}P{sub 14}B{sub 6} and Fe{sub 80}B{sub 14}C{sub 6} amorphous alloys are chosen to study through first-principle simulations in the present work. The atomic structure characteristic of the three amorphous alloys is investigated through the pair distribution functions (PDFs) and Voronoi Polyhedra (VPs) analyses. The PDFs and VPs analyses suggest that the GFA of the three alloys dropped in the order of Fe{sub 80}P{sub 13}C{sub 7}, Fe{sub 80}P{sub 14}B{sub 6}, and Fe{sub 80}B{sub 14}C{sub 6}, which is well consistent with the experimental results. The density of state (DOS) of the three amorphous alloys is calculated to investigate their magnetic properties. Based on the DOS analysis, the average magnetic moment of Fe atom in Fe{sub 80}P{sub 13}C{sub 7} and Fe{sub 80}P{sub 14}B{sub 6} amorphous alloys can be estimated to be 1.71 μ{sub B} and 1.70 μ{sub B}, respectively, which are in acceptable agreement with the experimental results. However, the calculated average magnetic moment of Fe atom in Fe{sub 80}B{sub 14}C{sub 6} amorphous alloy is about 1.62 μ{sub B}, which is far less than the experimental result.
Braden, M.L.
1987-01-01
A new method of determining kinetic isotope effects (KIE) has been developed based upon optical rotation of isotopically engendered chiral compounds. This method can not only measure primary (1{degree}) KIE but also secondary (2{degree}) KIE which are not possible by mass spectral techniques. The mechanisms of the Hoffman, Cope, and E2 elimination reactions were studied using the optical rotation method to determine the 1{degree} and 2{degree} KIE. The syn 1{degree} KIE of (1S,2S)-N-n-butyl-N,N-dimethylcyclooctyl ammonium iodide-2d{sub 1} by a Hoffmann elimination (syn 1{degree} k{sub H}/k{sub D} = 1.40) or E2 elimination (syn 1{degree} d{sub H}/k{sub D} = 3.28) were measured for the formation of E-cyclooctene via a early transition state. Primary and secondary KIE provided evidence for a late transition state for the Cope elimination of syn (2R,3R)-3-amino-N,N,6,6-tetramethylbicyclo (3.1.1)heptane-N-oxide-2d{sub 1} (syn 1{degree} k{sub H}/k{sub D} = 2.22) and the anti-(2S,3R)-3-amino-N,N,6,6-tetramethylbicyclo (3.1.1) heptane-N-oxide-2d{sub 1} (2{degree} k{sub H}/k{sub D}) = 1.061. The mechanism of the E2 elimination of the corresponding bicyclic ammonium iodides and the bicyclic chlorides and bromides were also studied using 1{degree} and 2{degree} KIE determined by the optical rotation method. A study of the anionic oxy-Cope rearrangement using divinyl carbonols revealed that a chair transition state is more favorable that an boat revealed that a chair transition state is more favorable than a boat transition state. A theoretical study of the anti E2 elimination of HF from ethyl fluoride with hydride and cyanide anion and HCl from ethyl chloride with hydride ion provided evidence that the four electron three molecular orbital interactions are involved. These interactions help contribute to phase cancellation in the molecular orbitals leading to the transition state.
Modeling study of the ABS relay valve
NASA Astrophysics Data System (ADS)
Lei, Ming; Lin, Min; Guo, Bin; Luo, Zai; Xu, Weidong
2011-05-01
The ABS (anti-lock braking system) relay valve is the key component of anti-lock braking system in most commercial vehicles such as trucks, tractor-trailers, etc. In this paper, structure of ABS relay valve and its work theory were analyzed. Then a mathematical model of ABS relay valve, which was investigated by dividing into electronic part, magnetic part, pneumatic part and mechanical part, was set up. The displacement of spools and the response of pressure increasing, holding, releasing of ABS relay valve were simulated and analyzed under conditions of control pressure 500 KPa, braking pressure 600 KPa, atmospheric pressure 100 KPa and air temperature 310 K. Thisarticle provides reliable theory for improving the performance and efficiency of anti-lock braking system of vehicles.
Modeling study of the ABS relay valve
NASA Astrophysics Data System (ADS)
Lei, Ming; Lin, Min; Guo, Bin; Luo, Zai; Xu, Weidong
2010-12-01
The ABS (anti-lock braking system) relay valve is the key component of anti-lock braking system in most commercial vehicles such as trucks, tractor-trailers, etc. In this paper, structure of ABS relay valve and its work theory were analyzed. Then a mathematical model of ABS relay valve, which was investigated by dividing into electronic part, magnetic part, pneumatic part and mechanical part, was set up. The displacement of spools and the response of pressure increasing, holding, releasing of ABS relay valve were simulated and analyzed under conditions of control pressure 500 KPa, braking pressure 600 KPa, atmospheric pressure 100 KPa and air temperature 310 K. Thisarticle provides reliable theory for improving the performance and efficiency of anti-lock braking system of vehicles.
Verbruggen, Erik; Kuramae, Eiko E; Hillekens, Remy; de Hollander, Mattias; Kiers, E Toby; Röling, Wilfred F M; Kowalchuk, George A; van der Heijden, Marcel G A
2012-10-01
The cultivation of genetically modified (GM) crops has increased significantly over the last decades. However, concerns have been raised that some GM traits may negatively affect beneficial soil biota, such as arbuscular mycorrhizal fungi (AMF), potentially leading to alterations in soil functioning. Here, we test two maize varieties expressing the Bacillus thuringiensis Cry1Ab endotoxin (Bt maize) for their effects on soil AM fungal communities. We target both fungal DNA and RNA, which is new for AM fungi, and we use two strategies as an inclusive and robust way of detecting community differences: (i) 454 pyrosequencing using general fungal rRNA gene-directed primers and (ii) terminal restriction fragment length polymorphism (T-RFLP) profiling using AM fungus-specific markers. Potential GM-induced effects were compared to the normal natural variation of AM fungal communities across 15 different agricultural fields. AM fungi were found to be abundant in the experiment, accounting for 8% and 21% of total recovered DNA- and RNA-derived fungal sequences, respectively, after 104 days of plant growth. RNA- and DNA-based sequence analyses yielded most of the same AM fungal lineages. Our research yielded three major conclusions. First, no consistent differences were detected between AM fungal communities associated with GM plants and non-GM plants. Second, temporal variation in AMF community composition (between two measured time points) was bigger than GM trait-induced variation. Third, natural variation of AMF communities across 15 agricultural fields in The Netherlands, as well as within-field temporal variation, was much higher than GM-induced variation. In conclusion, we found no indication that Bt maize cultivation poses a risk for AMF.
Kuramae, Eiko E.; Hillekens, Remy; de Hollander, Mattias; Kiers, E. Toby; Röling, Wilfred F. M.; Kowalchuk, George A.; van der Heijden, Marcel G. A.
2012-01-01
The cultivation of genetically modified (GM) crops has increased significantly over the last decades. However, concerns have been raised that some GM traits may negatively affect beneficial soil biota, such as arbuscular mycorrhizal fungi (AMF), potentially leading to alterations in soil functioning. Here, we test two maize varieties expressing the Bacillus thuringiensis Cry1Ab endotoxin (Bt maize) for their effects on soil AM fungal communities. We target both fungal DNA and RNA, which is new for AM fungi, and we use two strategies as an inclusive and robust way of detecting community differences: (i) 454 pyrosequencing using general fungal rRNA gene-directed primers and (ii) terminal restriction fragment length polymorphism (T-RFLP) profiling using AM fungus-specific markers. Potential GM-induced effects were compared to the normal natural variation of AM fungal communities across 15 different agricultural fields. AM fungi were found to be abundant in the experiment, accounting for 8% and 21% of total recovered DNA- and RNA-derived fungal sequences, respectively, after 104 days of plant growth. RNA- and DNA-based sequence analyses yielded most of the same AM fungal lineages. Our research yielded three major conclusions. First, no consistent differences were detected between AM fungal communities associated with GM plants and non-GM plants. Second, temporal variation in AMF community composition (between two measured time points) was bigger than GM trait-induced variation. Third, natural variation of AMF communities across 15 agricultural fields in The Netherlands, as well as within-field temporal variation, was much higher than GM-induced variation. In conclusion, we found no indication that Bt maize cultivation poses a risk for AMF. PMID:22885748
An ab initio MO study of butalene
NASA Astrophysics Data System (ADS)
Ohta, Katsuhisa; Shima, Toru
1994-01-01
Butalene as a structural isomer of p-benzyne has been studied by using an ab initio GVB wavefunction. The geometry of butalene, which is shown to be almost rectangular, is first optimized as a local minimum on the energy surface at the ab initio level. However, the energy barrier of conversion to p-benzyne is as small as 1.6 kcal/mol, and experimental isolation of butalene is predicted to be difficult from a force-constant analysis.
Ab-initio modeling of an anion C- 60 pseudopotential for fullerene-based compounds
NASA Astrophysics Data System (ADS)
Vrubel, Ivan I.; Polozkov, Roman G.; Ivanov, Vadim K.
2016-08-01
An anion C- 60 pseudopotential is determined from an ab-initio-based approach. First, ab-initio calculations are performed to calculate the electronic charge density and the total electrostatic potential. Second, the effective dependence of the pseudopotential on the radial degree of freedom is extracted from the angular average of the total electrostatic potential. Finally, the resulting effective pseudopotential is fitted to a simple analytical form which can be applied in further dynamical simulations of fullerene-based compounds.
Heats of Segregation of BCC Binaries from ab Initio and Quantum Approximate Calculations
NASA Technical Reports Server (NTRS)
Good, Brian S.
2004-01-01
We compare dilute-limit heats of segregation for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent LMTO-based parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation, while the ab initio calculations are performed without relaxation. Results are discussed within the context of a segregation model driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.
Ab initio two-component Ehrenfest dynamics
Ding, Feizhi; Goings, Joshua J.; Liu, Hongbin; Lingerfelt, David B.; Li, Xiaosong
2015-09-21
We present an ab initio two-component Ehrenfest-based mixed quantum/classical molecular dynamics method to describe the effect of nuclear motion on the electron spin dynamics (and vice versa) in molecular systems. The two-component time-dependent non-collinear density functional theory is used for the propagation of spin-polarized electrons while the nuclei are treated classically. We use a three-time-step algorithm for the numerical integration of the coupled equations of motion, namely, the velocity Verlet for nuclear motion, the nuclear-position-dependent midpoint Fock update, and the modified midpoint and unitary transformation method for electronic propagation. As a test case, the method is applied to the dissociation of H{sub 2} and O{sub 2}. In contrast to conventional Ehrenfest dynamics, this two-component approach provides a first principles description of the dynamics of non-collinear (e.g., spin-frustrated) magnetic materials, as well as the proper description of spin-state crossover, spin-rotation, and spin-flip dynamics by relaxing the constraint on spin configuration. This method also holds potential for applications to spin transport in molecular or even nanoscale magnetic devices.
Ab initio two-component Ehrenfest dynamics
NASA Astrophysics Data System (ADS)
Ding, Feizhi; Goings, Joshua J.; Liu, Hongbin; Lingerfelt, David B.; Li, Xiaosong
2015-09-01
We present an ab initio two-component Ehrenfest-based mixed quantum/classical molecular dynamics method to describe the effect of nuclear motion on the electron spin dynamics (and vice versa) in molecular systems. The two-component time-dependent non-collinear density functional theory is used for the propagation of spin-polarized electrons while the nuclei are treated classically. We use a three-time-step algorithm for the numerical integration of the coupled equations of motion, namely, the velocity Verlet for nuclear motion, the nuclear-position-dependent midpoint Fock update, and the modified midpoint and unitary transformation method for electronic propagation. As a test case, the method is applied to the dissociation of H2 and O2. In contrast to conventional Ehrenfest dynamics, this two-component approach provides a first principles description of the dynamics of non-collinear (e.g., spin-frustrated) magnetic materials, as well as the proper description of spin-state crossover, spin-rotation, and spin-flip dynamics by relaxing the constraint on spin configuration. This method also holds potential for applications to spin transport in molecular or even nanoscale magnetic devices.
Technology Transfer Automated Retrieval System (TEKTRAN)
Blended seed mixtures containing various ratios of transgenic Bt maize expressing the mCry3A + eCry3.1Ab proteins and non-Bt maize (near-isoline maize) were deployed alone and in combination with a soil applied insecticide (Force CS) to evaluate the survivorship of the western corn rootworm, Diabrot...
High Yield Chemical Vapor Deposition Growth of High Quality Large-Area AB Stacked Bilayer Graphene
Liu, Lixin; Zhou, Hailong; Cheng, Rui; Yu, Woo Jong; Liu, Yuan; Chen, Yu; Shaw, Jonathan; Zhong, Xing; Huang, Yu; Duan, Xiangfeng
2012-01-01
Bernal stacked (AB stacked) bilayer graphene is of significant interest for functional electronic and photonic devices due to the feasibility to continuously tune its band gap with a vertical electrical field. Mechanical exfoliation can be used to produce AB stacked bilayer graphene flakes but typically with the sizes limited to a few micrometers. Chemical vapor deposition (CVD) has been recently explored for the synthesis of bilayer graphene but usually with limited coverage and a mixture of AB and randomly stacked structures. Herein we report a rational approach to produce large-area high quality AB stacked bilayer graphene. We show that the self-limiting effect of graphene growth on Cu foil can be broken by using a high H2/CH4 ratio in a low pressure CVD process to enable the continued growth of bilayer graphene. A high temperature and low pressure nucleation step is found to be critical for the formation of bilayer graphene nuclei with high AB stacking ratio. A rational design of a two-step CVD process is developed for the growth of bilayer graphene with high AB stacking ratio (up to 90 %) and high coverage (up to 99 %). The electrical transport studies demonstrated that devices made of the as-grown bilayer graphene exhibit typical characteristics of AB stacked bilayer graphene with the highest carrier mobility exceeding 4,000 cm2/V·s at room temperature, comparable to that of the exfoliated bilayer graphene. PMID:22906199
Thermophysical Modeling of WISE Data on 2010 AB78
NASA Astrophysics Data System (ADS)
Wright, Edward L.; Mainzer, A.; Grav, T.
2010-10-01
2010 AB78 was the first NEO discovered by WISE in early January. It came back through the WISE scan path in February and again in July, appearing in a total of 89 frames. The lines-of-sight to the asteroid cover 180 deg in RA and 70 deg in Dec. These data are used to constrain the rotation rate, rotation axis, thermal inertia and size of 2010 AB78 using the rotating cratered thermophysical model of Wright (2007). All data were obtained on the same side of the WISE scan circle, limiting our ability to constrain the thermal inertia. The effect of poorly constrained parameters on the size is handled using a Monte Carlo Markov Chain approach.
Ab Initio Calculations Of Light-Ion Reactions
Navratil, P; Quaglioni, S; Roth, R; Horiuchi, W
2012-03-12
The exact treatment of nuclei starting from the constituent nucleons and the fundamental interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of nuclear forces, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in ab initio nuclear structure and reaction calculations based on input from QCD employing Hamiltonians constructed within chiral effective field theory. In this contribution, we present one of such promising techniques capable of describing simultaneously both bound and scattering states in light nuclei. By combining the resonating-group method (RGM) with the ab initio no-core shell model (NCSM), we complement a microscopic cluster approach with the use of realistic interactions and a microscopic and consistent description of the clusters. We discuss applications to light nuclei scattering, radiative capture and fusion reactions.
NASA Astrophysics Data System (ADS)
Ramírez-Solís, A.; Poteau, R.; Daudey, J. P.
2006-01-01
The XΠg2, Σg+2, and Δg2 states of AgCl2 have been studied through benchmark ab initio complete active space self-consistent field plus second-order complete active space multireference Möller-Plesset algorithm (CASSCF +CASPT2) and complete active space self-consistent field plus averaged coupled pair functional (CASSCF +ACPF) and density-functional theory (DFT) calculations using especially developed basis sets to study the transition energies, geometries, vibrational frequencies, Mulliken charges, and spin densities. The spin-orbit (SO) effects were included through the effective Hamiltonian formalism using the ΛSΣ ACPF energies as diagonal elements. At the ACPF level, the ground state is Πg2 in contradiction with ligand-field theory, SCF, and large CASSCF; the adiabatic excitation energies for the Σg+2 and Δg2 states are 1640 and 18230cm-1, respectively. The inclusion of the SO effects leads to a pure Ω =3/2(Πg2) ground state, a Ω =1/2 (66%Πg2 and 34%Σg+2) A state, a Ω =1/2 (34%Πg2 and 66%Σg+2) B state, a Ω =5/2(Δg2)C state, and a Ω =3/2(99%Δg2)D state. The X-A, X-B, X-C, and X-D transition energies are 485, 3715, 17 246, and 20110cm-1, respectively. The B97-2, B3LYP, and PBE0 functionals overestimate by ≈100% the XΠg2-Σg+2Te but provide a qualitative energetic ordering in good agreement with ACPF results. B3LYP with variable exchange leads to a 42% optimal Hartree-Fock exchange for transition energies but all equilibrium geometries get worsened. Asymptotic corrections to B3LYP do not provide improved values. The nature of the bonding in the XΠg2 state is very different from that of CuCl2 since the Mulliken charge on the metal is 1.1 while the spin density is only 0.35. DFT strongly delocalizes the spin density providing even smaller values of around 0.18 on Ag not only for the ground state, but also for the Σg+2 state.
The end of a myth—Bt (Cry1Ab) maize does not harm green lacewings
Romeis, Jörg; Meissle, Michael; Naranjo, Steven E.; Li, Yunhe; Bigler, Franz
2014-01-01
A concern with Bt-transgenic insect-resistant plants is their potential to harm non-target organisms. Early studies reported that Cry1Ab-producing Bt maize and purified Cry1Ab harmed larvae of the green lacewing, Chrysoperla carnea. Although these effects could not be confirmed in subsequent studies, some authors still refer to them as evidence that Bt maize harms beneficial species. We provide a comprehensive review of the studies evaluating the effects of Bt (Cry1Ab) maize on C. carnea. The evidence indicates that this important predator is not affected by Bt maize or by the produced Cry1Ab protein. We discuss how conceptual models can assist environmental risk assessments, and we emphasize the importance of robust and reproducible studies. PMID:25161661
The end of a myth-Bt (Cry1Ab) maize does not harm green lacewings.
Romeis, Jörg; Meissle, Michael; Naranjo, Steven E; Li, Yunhe; Bigler, Franz
2014-01-01
A concern with Bt-transgenic insect-resistant plants is their potential to harm non-target organisms. Early studies reported that Cry1Ab-producing Bt maize and purified Cry1Ab harmed larvae of the green lacewing, Chrysoperla carnea. Although these effects could not be confirmed in subsequent studies, some authors still refer to them as evidence that Bt maize harms beneficial species. We provide a comprehensive review of the studies evaluating the effects of Bt (Cry1Ab) maize on C. carnea. The evidence indicates that this important predator is not affected by Bt maize or by the produced Cry1Ab protein. We discuss how conceptual models can assist environmental risk assessments, and we emphasize the importance of robust and reproducible studies.
Serum PDGF-AB in pleural mesothelioma.
Filiberti, Rosa; Marroni, Paola; Neri, Monica; Ardizzoni, Andrea; Betta, Pier Giacomo; Cafferata, Mara A; Canessa, Pier Aldo; Puntoni, Riccardo; Ivaldi, Giovanni Paolo; Paganuzzi, Michela
2005-01-01
Overexpression of platelet-derived growth factor (PDGF) has been observed in lung and pleural tumors. The aim of this study was to evaluate the diagnostic and prognostic role of serum PDGF in pleural mesothelioma (PM). Four groups of subjects were studied: 93 malignant PM patients, 33 primary non small cell lung cancer patients, 51 subjects exposed to asbestos, defined as high-risk controls, and 24 healthy controls. PDGF-AB mean concentration was higher in PM patients (45.8 ng/ml) than in high-risk controls (33.1 ng/ml) and healthy controls (26.8 ng/ml). Using the cut-off level of 49.8 ng/ml, corresponding to the mean+2SD of PDGF-AB in healthy controls, 43% of PM patients showed positive PDGF-AB levels. Survival was evaluated in 82 PM patients. At the end of the follow-up (median 9.8 months) 80.5% of patients had died. Median survival was 13.1 and 7.9 months for patients with PDGF-AB lower and higher than the cut-off, respectively. Adjusting for age, sex, histology and platelet count, positive PDGF-AB levels were associated with lower survival (OR=1.2, 95%CI: 0.9-1.6), even if not significantly so. In conclusion, serum PDGF may represent a useful additional parameter to prognostic factors already available for PM.
Ab-Initio Shell Model with a Core
Lisetskiy, A F; Barrett, B R; Kruse, M; Navratil, P; Stetcu, I; Vary, J P
2008-06-04
We construct effective 2- and 3-body Hamiltonians for the p-shell by performing 12{h_bar}{Omega} ab initio no-core shell model (NCSM) calculations for A=6 and 7 nuclei and explicitly projecting the many-body Hamiltonians onto the 0{h_bar}{Omega} space. We then separate these effective Hamiltonians into 0-, 1- and 2-body contributions (also 3-body for A=7) and analyze the systematic behavior of these different parts as a function of the mass number A and size of the NCSM basis space. The role of effective 3- and higher-body interactions for A > 6 is investigated and discussed.
Ab interno trabeculectomy: patient selection and perspectives.
Vinod, Kateki; Gedde, Steven J
2016-01-01
Ab interno trabeculectomy is one among several recently introduced minimally invasive glaucoma surgeries that avoid a conjunctival incision and full-thickness sclerostomy involved in traditional glaucoma surgery. Ablation of the trabecular meshwork and inner wall of Schlemm's canal is performed in an arcuate fashion via a clear corneal incision, alone or in combination with phacoemulsification cataract surgery. Intraocular pressure reduction following ab interno trabeculectomy is limited by resistance in distal outflow pathways and generally stabilizes in the mid-to-high teens. Relief of medication burden has been demonstrated by some studies. A very low rate of complications, most commonly transient hyphema and intraocular pressure elevations in the immediate postoperative period, have been reported. However, available data are derived from small retrospective and prospective case series. Randomized, controlled trials are needed to better elucidate the potential merits of ab interno trabeculectomy in the combined setting versus phacoemulsification cataract surgery alone and to compare it with other minimally invasive glaucoma surgeries. PMID:27574396
The end of a myth – Bt(Cry1Ab) maize does not harm green lacewings
Technology Transfer Automated Retrieval System (TEKTRAN)
A concern with Bt-transgenic insect-resistant plants is their potential to harm non-target organisms. Early studies reported that Cry1Ab-producing Bt maize and purified Cry1Ab harmed larvae of the green lacewing, Chrysoperla carnea. Although these effects could not be confirmed in subsequent studies...
A highly accurate ab initio potential energy surface for methane
NASA Astrophysics Data System (ADS)
Owens, Alec; Yurchenko, Sergei N.; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-09-01
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art ab initio theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of 12CH4 reproduced with a root-mean-square error of 0.70 cm-1. The computed ab initio equilibrium C-H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as J (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate ab initio surface to date and will serve as a good starting point for empirical refinement.
A highly accurate ab initio potential energy surface for methane.
Owens, Alec; Yurchenko, Sergei N; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-09-14
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art ab initio theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of (12)CH4 reproduced with a root-mean-square error of 0.70 cm(-1). The computed ab initio equilibrium C-H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as J (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate ab initio surface to date and will serve as a good starting point for empirical refinement. PMID:27634258
Pressure tracking control of vehicle ABS using piezo valve modulator
NASA Astrophysics Data System (ADS)
Jeon, Juncheol; Choi, Seung-Bok
2011-03-01
This paper presents a wheel slip control for the ABS(anti-lock brake system) of a passenger vehicle using a controllable piezo valve modulator. The ABS is designed to optimize for braking effectiveness and good steerability. As a first step, the principal design parameters of the piezo valve and pressure modulator are appropriately determined by considering the braking pressure variation during the ABS operation. The proposed piezo valve consists of a flapper, pneumatic circuit and a piezostack actuator. In order to get wide control range of the pressure, the pressure modulator is desired. The modulator consists of a dual-type cylinder filled with different substances (fluid and gas) and a piston rod moving vertical axis to transmit the force. Subsequently, a quarter car wheel slip model is formulated and integrated with the governing equation of the piezo valve modulator. A sliding mode controller to achieve the desired slip rate is then designed and implemented. Braking control performances such as brake pressure and slip rate are evaluated via computer simulations.
Ab initio calculations for industrial materials engineering: successes and challenges.
Wimmer, Erich; Najafabadi, Reza; Young, George A; Ballard, Jake D; Angeliu, Thomas M; Vollmer, James; Chambers, James J; Niimi, Hiroaki; Shaw, Judy B; Freeman, Clive; Christensen, Mikael; Wolf, Walter; Saxe, Paul
2010-09-29
Computational materials science based on ab initio calculations has become an important partner to experiment. This is demonstrated here for the effect of impurities and alloying elements on the strength of a Zr twist grain boundary, the dissociative adsorption and diffusion of iodine on a zirconium surface, the diffusion of oxygen atoms in a Ni twist grain boundary and in bulk Ni, and the dependence of the work function of a TiN-HfO(2) junction on the replacement of N by O atoms. In all of these cases, computations provide atomic-scale understanding as well as quantitative materials property data of value to industrial research and development. There are two key challenges in applying ab initio calculations, namely a higher accuracy in the electronic energy and the efficient exploration of large parts of the configurational space. While progress in these areas is fueled by advances in computer hardware, innovative theoretical concepts combined with systematic large-scale computations will be needed to realize the full potential of ab initio calculations for industrial applications.
A highly accurate ab initio potential energy surface for methane.
Owens, Alec; Yurchenko, Sergei N; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-09-14
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art ab initio theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of (12)CH4 reproduced with a root-mean-square error of 0.70 cm(-1). The computed ab initio equilibrium C-H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as J (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate ab initio surface to date and will serve as a good starting point for empirical refinement.
MELCOR 1.8.2 assessment: Aerosol experiments ABCOVE AB5, AB6, AB7, and LACE LA2
Souto, F.J.; Haskin, F.E.; Kmetyk, L.N.
1994-10-01
The MELCOR computer code has been used to model four of the large-scale aerosol behavior experiments conducted in the Containment System Test Facility (CSTF) vessel. Tests AB5, AB6 and AB7 of the ABCOVE program simulate the dry aerosol conditions during a hypothetical severe accident in an LMFBR. Test LA2 of the LACE program simulates aerosol behavior in a condensing steam environment during a postulated severe accident in an LWR with failure to isolate the containment. The comparison of code results to experimental data show that MELCOR is able to correctly predict most of the thermal-hydraulic results in the four tests. MELCOR predicts reasonably well the dry aerosol behavior of the ABCOVE tests, but significant disagreements are found in the aerosol behavior modelling for the LA2 experiment. These results tend to support some of the concerns about the MELCOR modelling of steam condensation onto aerosols expressed in previous works. During these analyses, a limitation in the MELCOR input was detected for the specification of the aerosol parameters for more than one component. A Latin Hypercube Sampling (LHS) sensitivity study of the aerosol dynamic constants is presented for test AB6. The study shows the importance of the aerosol shape factors in the aerosol deposition behavior, and reveals that MELCOR input/output processing is highly labor intensive for uncertainty and sensitivity analyses based on LHS.
NASA Technical Reports Server (NTRS)
Phillips, W. P.
1981-01-01
Subsonic longitudinal andd laternal directional characteristics were obtained for several modified configurations of the 140 A/B orbiter (0.010 scale). These modifications, designed to extend longitudinal trim capability forward of the 65 percent fuselage length station, consisted of modified wing planform fillet and a canard. Tests were performed in the Langley Low Turbulence Pressure Tunnel at Reynolds numbers from about 4.2 million to 14.3 million based on the fuselage reference length.
Ab Initio Calculations of Water Line Strengths
NASA Technical Reports Server (NTRS)
Schwenke, David W.; Partridge, Harry
1998-01-01
We report on the determination of a high quality ab initiu potential energy surface (PES) and dipole moment function for water. This PES is empirically adjusted to improve the agreement between the computed line positions and those from the HITRAN 92 data base with J less than 6 for H2O. The changes in the PES are small, nonetheless including an estimate of core (oxygen 1s) electron correlation greatly improves the agreement with experiment. Using this adjusted PES, we can match 30,092 of the 30,117 transitions in the HITRAN 96 data base for H2O with theoretical lines. The 10,25,50,75, and 90 percentiles of the difference between the calculated and tabulated line positions are -0.11, -0.04, -0.01, 0.02, and 0.07 l/cm. Non-adiabatic effects are not explicitly included. About 3% of the tabulated line positions appear to be incorrect. Similar agreement using this adjusted PES is obtained for the oxygen 17 and oxygen 18 isotopes. For HDO, the agreement is not as good, with root-mean-square error of 0.25 l/cm for lines with J less than 6. This error is reduced to 0.02 l/cm by including a small asymmetric correction to the PES, which is parameterized by simultaneously fitting to HDO md D2O data. Scaling this correction by mass factors yields good results for T2O and HTO. The intensities summed over vibrational bands are usually in good agreement between the calculations and the tabulated results, but individual lines strengths can differ greatly. A high temperature list consisting of 307,721,352 lines is generated for H2O using our PES and dipole moment function.
Hepatoma-Targeted Radionuclide Immune Albumin Nanospheres: (131)I-antiAFPMcAb-GCV-BSA-NPs.
Lin, Mei; Huang, Junxing; Zhang, Dongsheng; Jiang, Xingmao; Zhang, Jia; Yu, Hong; Xiao, Yanhong; Shi, Yujuan; Guo, Ting
2016-01-01
An effective strategy has been developed for synthesis of radionuclide immune albumin nanospheres ((131)I-antiAFPMcAb-GCV-BSA-NPs). In vitro as well as in vivo targeting of (131)I-antiAFPMcAb-GCV-BSA-NPs to AFP-positive hepatoma was examined. In cultured HepG2 cells, the uptake and retention rates of (131)I-antiAFPMcAb-GCV-BSA-NPs were remarkably higher than those of (131)I alone. As well, the uptake rate and retention ratios of (131)I-antiAFPMcAb-GCV-BSA-NPs in AFP-positive HepG2 cells were also significantly higher than those in AFP-negative HEK293 cells. Compared to (131)I alone, (131)I-antiAFPMcAb-GCV-BSA-NPs were much more easily taken in and retained by hepatoma tissue, with a much higher T/NT. Due to good drug-loading, high encapsulation ratio, and highly selective affinity for AFP-positive tumors, the (131)I-antiAFPMcAb-GCV-BSA-NPs are promising for further effective radiation-gene therapy of hepatoma.
Hepatoma-Targeted Radionuclide Immune Albumin Nanospheres: 131I-antiAFPMcAb-GCV-BSA-NPs
Lin, Mei; Huang, Junxing; Zhang, Dongsheng; Jiang, Xingmao; Zhang, Jia; Yu, Hong; Xiao, Yanhong; Shi, Yujuan; Guo, Ting
2016-01-01
An effective strategy has been developed for synthesis of radionuclide immune albumin nanospheres (131I-antiAFPMcAb-GCV-BSA-NPs). In vitro as well as in vivo targeting of 131I-antiAFPMcAb-GCV-BSA-NPs to AFP-positive hepatoma was examined. In cultured HepG2 cells, the uptake and retention rates of 131I-antiAFPMcAb-GCV-BSA-NPs were remarkably higher than those of 131I alone. As well, the uptake rate and retention ratios of 131I-antiAFPMcAb-GCV-BSA-NPs in AFP-positive HepG2 cells were also significantly higher than those in AFP-negative HEK293 cells. Compared to 131I alone, 131I-antiAFPMcAb-GCV-BSA-NPs were much more easily taken in and retained by hepatoma tissue, with a much higher T/NT. Due to good drug-loading, high encapsulation ratio, and highly selective affinity for AFP-positive tumors, the 131I-antiAFPMcAb-GCV-BSA-NPs are promising for further effective radiation-gene therapy of hepatoma. PMID:26981334
An investigation of ab initio shell-model interactions derived by no-core shell model
NASA Astrophysics Data System (ADS)
Wang, XiaoBao; Dong, GuoXiang; Li, QingFeng; Shen, CaiWan; Yu, ShaoYing
2016-09-01
The microscopic shell-model effective interactions are mainly based on the many-body perturbation theory (MBPT), the first work of which can be traced to Brown and Kuo's first attempt in 1966, derived from the Hamada-Johnston nucleon-nucleon potential. However, the convergence of the MBPT is still unclear. On the other hand, ab initio theories, such as Green's function Monte Carlo (GFMC), no-core shell model (NCSM), and coupled-cluster theory with single and double excitations (CCSD), have made many progress in recent years. However, due to the increasing demanding of computing resources, these ab initio applications are usually limited to nuclei with mass up to A = 16. Recently, people have realized the ab initio construction of valence-space effective interactions, which is obtained through a second-time renormalization, or to be more exactly, projecting the full-manybody Hamiltonian into core, one-body, and two-body cluster parts. In this paper, we present the investigation of such ab initio shell-model interactions, by the recent derived sd-shell effective interactions based on effective J-matrix Inverse Scattering Potential (JISP) and chiral effective-field theory (EFT) through NCSM. In this work, we have seen the similarity between the ab initio shellmodel interactions and the interactions obtained by MBPT or by empirical fitting. Without the inclusion of three-body (3-bd) force, the ab initio shell-model interactions still share similar defects with the microscopic interactions by MBPT, i.e., T = 1 channel is more attractive while T = 0 channel is more repulsive than empirical interactions. The progress to include more many-body correlations and 3-bd force is still badly needed, to see whether such efforts of ab initio shell-model interactions can reach similar precision as the interactions fitted to experimental data.
Frank, Daniel L; Kurtz, Ryan; Tinsley, Nicholas A; Gassmann, Aaron J; Meinke, Lance J; Moellenbeck, Daniel; Gray, Michael E; Bledsoe, Larry W; Krupke, Christian H; Estes, Ronald E; Weber, Patrick; Hibbard, Bruce E
2015-06-01
Seed blends containing various ratios of transgenic Bt maize (Zea mays L.) expressing the mCry3A+eCry3.1Ab proteins and non-Bt maize (near-isoline maize) were deployed alone and in combination with a soil applied pyrethroid insecticide (Force CS) to evaluate the emergence of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in a total of nine field environments across the Midwestern United States in 2010 and 2011. Northern corn rootworm, Diabrotica barberi Smith & Lawrence emergence was also evaluated in four of these environments. Both western and northern corn rootworm beetle emergence from all Bt treatments was significantly reduced when compared with beetle emergence from near-isoline treatments. Averaged across all environments, western corn rootworm beetle emergence from 95:5, 90:10, and 80:20 seed blend ratios of mCry3A+eCry3.1Ab: near-isoline were 2.6-, 4.2-, and 6.7-fold greater than that from the 100:0 ratio treatment. Northern corn rootworm emergence from the same seed blend treatments resulted in 2.8-, 3.2-, and 4.2-fold more beetles than from the 100:0 treatment. The addition of Force CS (tefluthrin) significantly reduced western corn rootworm beetle emergence for each of the three treatments to which it was applied. Force CS also significantly delayed the number of days to 50% beetle emergence in western corn rootworms. Time to 50% beetle emergence in the 100% mCry3A+eCry3.1Ab treatment with Force CS was delayed 13.7 d when compared with western corn rootworm beetle emergence on near-isoline corn. These data are discussed in terms of rootworm resistance management.
Frank, Daniel L; Kurtz, Ryan; Tinsley, Nicholas A; Gassmann, Aaron J; Meinke, Lance J; Moellenbeck, Daniel; Gray, Michael E; Bledsoe, Larry W; Krupke, Christian H; Estes, Ronald E; Weber, Patrick; Hibbard, Bruce E
2015-06-01
Seed blends containing various ratios of transgenic Bt maize (Zea mays L.) expressing the mCry3A+eCry3.1Ab proteins and non-Bt maize (near-isoline maize) were deployed alone and in combination with a soil applied pyrethroid insecticide (Force CS) to evaluate the emergence of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in a total of nine field environments across the Midwestern United States in 2010 and 2011. Northern corn rootworm, Diabrotica barberi Smith & Lawrence emergence was also evaluated in four of these environments. Both western and northern corn rootworm beetle emergence from all Bt treatments was significantly reduced when compared with beetle emergence from near-isoline treatments. Averaged across all environments, western corn rootworm beetle emergence from 95:5, 90:10, and 80:20 seed blend ratios of mCry3A+eCry3.1Ab: near-isoline were 2.6-, 4.2-, and 6.7-fold greater than that from the 100:0 ratio treatment. Northern corn rootworm emergence from the same seed blend treatments resulted in 2.8-, 3.2-, and 4.2-fold more beetles than from the 100:0 treatment. The addition of Force CS (tefluthrin) significantly reduced western corn rootworm beetle emergence for each of the three treatments to which it was applied. Force CS also significantly delayed the number of days to 50% beetle emergence in western corn rootworms. Time to 50% beetle emergence in the 100% mCry3A+eCry3.1Ab treatment with Force CS was delayed 13.7 d when compared with western corn rootworm beetle emergence on near-isoline corn. These data are discussed in terms of rootworm resistance management. PMID:26470254
GQ Lup Ab Visible & Near-Infrared Photometric Analysis
Marois, C; Macintosh, B; Barman, T
2006-08-07
We have re-analyzed archival HST R and I band images and Subaru CH{sub 4}, H, Ks and L{prime} data of the recently discovered planetary mass companion (PMC) GQ Lup Ab. With these we produce the first R and I band photometry of the companion and fit a radius and effective temperature using detailed model atmospheres. We find an effective temperature of 2338 {+-} 100K, and a radius of 0.37 {+-} 0.05R{sub {circle_dot}} and luminosity of log(L/L{sub {circle_dot}}) = -2.43 {+-} 0.07 (at 140pc). Since we fit wavelengths that span most of the emitted radiation from GQ Lup this luminosity estimate is robust, with uncertainty dominated by the distance uncertainty. The radius obtained for 140pc (0.37R{sub {circle_dot}}) is significantly larger than the one originally derived. The mass of the object is much more model-dependent than the radiative properties, but for the GAIA dusty models we find a mass between 9-20 M{sub Jup}, in the range of the brown dwarf and PMC deuterium burning boundary. Assuming a distance of 140pc, observations fit to 1{sigma} the Baraffe evolution model for a {approx} 15 M{sub Jup} brown dwarf. Additionally, the F606W photometric band is significantly overluminous compared to model predictions. Such overluminosity could be explained by a bright H{alpha} emission from chromospheric activity, interaction with another undetected companion, or accretion. Assuming that GQ Lup Ab has a bright H{alpha} emission line, its H{alpha} emission strength is 10{sup -1.71 {+-} 0.10} L{sub bol}, significantly larger than field late-type dwarfs. GQ Lup Ab might be strongly accreting and still be in its formation phase.
Ab initio infrared and Raman spectra
NASA Technical Reports Server (NTRS)
Fredkin, D. R.; White, S. R.; Wilson, K. R.; Komornicki, A.
1983-01-01
It is pointed out that with increased computer power and improved computational techniques, such as the gradients developed in recent years, it is becoming practical to compute spectra ab initio, from the fundamental constants of nature, for systems of increasing complexity. The present investigation has the objective to explore several possible ab initio approaches to spectra, giving particular attention to infrared and nonresonance Raman. Two approaches are discussed. The sequential approach, in which first the electronic part and then later the nuclear part of the Born-Oppenheimer approximation is solved, is appropriate for small systems. The simultaneous approach, in which the electronic and nuclear parts are solved at the same time, is more appropriate for many-atom systems. A review of the newer quantum gradient techniques is provided, and the infrared and Raman spectral band contours for the water molecule are computed.
Barrett, B R; Navratil, P; Vary, J P
2011-04-11
A long-standing goal of nuclear theory is to determine the properties of atomic nuclei based on the fundamental interactions among the protons and neutrons (i.e., nucleons). By adopting nucleon-nucleon (NN), three-nucleon (NNN) and higher-nucleon interactions determined from either meson-exchange theory or QCD, with couplings fixed by few-body systems, we preserve the predictive power of nuclear theory. This foundation enables tests of nature's fundamental symmetries and offers new vistas for the full range of complex nuclear phenomena. Basic questions that drive our quest for a microscopic predictive theory of nuclear phenomena include: (1) What controls nuclear saturation; (2) How the nuclear shell model emerges from the underlying theory; (3) What are the properties of nuclei with extreme neutron/proton ratios; (4) Can we predict useful cross sections that cannot be measured; (5) Can nuclei provide precision tests of the fundamental laws of nature; and (6) Under what conditions do we need QCD to describe nuclear structure, among others. Along with other ab initio nuclear theory groups, we have pursued these questions with meson-theoretical NN interactions, such as CD-Bonn and Argonne V18, that were tuned to provide high-quality descriptions of the NN scattering phase shifts and deuteron properties. We then add meson-theoretic NNN interactions such as the Tucson-Melbourne or Urbana IX interactions. More recently, we have adopted realistic NN and NNN interactions with ties to QCD. Chiral perturbation theory within effective field theory ({chi}EFT) provides us with a promising bridge between QCD and hadronic systems. In this approach one works consistently with systems of increasing nucleon number and makes use of the explicit and spontaneous breaking of chiral symmetry to expand the strong interaction in terms of a dimensionless constant, the ratio of a generic small momentum divided by the chiral symmetry breaking scale taken to be about 1 GeV/c. The resulting NN
Ab interno trabeculectomy: patient selection and perspectives
Vinod, Kateki; Gedde, Steven J
2016-01-01
Ab interno trabeculectomy is one among several recently introduced minimally invasive glaucoma surgeries that avoid a conjunctival incision and full-thickness sclerostomy involved in traditional glaucoma surgery. Ablation of the trabecular meshwork and inner wall of Schlemm’s canal is performed in an arcuate fashion via a clear corneal incision, alone or in combination with phacoemulsification cataract surgery. Intraocular pressure reduction following ab interno trabeculectomy is limited by resistance in distal outflow pathways and generally stabilizes in the mid-to-high teens. Relief of medication burden has been demonstrated by some studies. A very low rate of complications, most commonly transient hyphema and intraocular pressure elevations in the immediate postoperative period, have been reported. However, available data are derived from small retrospective and prospective case series. Randomized, controlled trials are needed to better elucidate the potential merits of ab interno trabeculectomy in the combined setting versus phacoemulsification cataract surgery alone and to compare it with other minimally invasive glaucoma surgeries. PMID:27574396
An activin A/BMP2 chimera, AB204, displays bone-healing properties superior to those of BMP2.
Yoon, Byung-Hak; Esquivies, Luis; Ahn, Chihoon; Gray, Peter C; Ye, Sang-Kyu; Kwiatkowski, Witek; Choe, Senyon
2014-09-01
Recombinant bone morphogenetic protein 2 (rhBMP2) has been used clinically to treat bone fractures in human patients. However, the high doses of rhBMP2 required for a therapeutic response can cause undesirable side effects. Here, we demonstrate that a novel Activin A/BMP2 (AB2) chimera, AB204, promotes osteogenesis and bone healing much more potently and effectively than rhBMP2. Remarkably, 1 month of AB204 treatment completely heals tibial and calvarial defects of critical size in mice at a concentration 10-fold lower than a dose of rhBMP2 that only partially heals the defect. We determine the structure of AB204 to 2.3 Å that reveals a distinct BMP2-like fold in which the Activin A sequence segments confer insensitivity to the BMP2 antagonist Noggin and an affinity for the Activin/BMP type II receptor ActRII that is 100-fold greater than that of BMP2. The structure also led to our identification of a single Activin A-derived amino acid residue, which, when mutated to the corresponding BMP2 residue, resulted in a significant increase in the affinity of AB204 for its type I receptor BMPRIa and a further enhancement in AB204's osteogenic potency. Together, these findings demonstrate that rationally designed AB2 chimeras can provide BMP2 substitutes with enhanced potency for treating non-union bone fractures.
Valley-symmetry-preserved transport in ballistic graphene layers with gate-defined carrier guiding
NASA Astrophysics Data System (ADS)
Kim, Minsoo; Choi, Ji-Hae; Lee, Sang-Hoon; Watanabe, Kenji; Taniguchi, Takashi; Jhi, Seung-Hoon; Lee, Hu-Jong
Zigzag graphene nanoribbons are predicted to exhibit interesting electronic properties stemming from its Dirac band structure. However, to date, investigation of them is highly limited because of the defects and the roughness at the edges, which mix different valley properties of graphene. Here, we report the signature of conservation of valley symmetry in two types of quasi-1D ballistic graphene transport devices; one is a quantum point contact (QPC) and another is an Aharonov-Bohm (AB) interferometer. In measurements, charge carriers were confined in a potential well formed by the dual gates operation and the four-terminal magnetoconductance (MC) was measured with varying the carrier density, dc bias, and temperature. It exhibits the conductance quantization in steps of ΔG = 4e2/ h starting from G = (2, 6), 10 ×e2 / h in a constricted conducting channel of QPC-type devices. This behavior is similar to the one observed in zigzag graphene nanoribbons having edge localized channels. Our tight-binding calculation shows that quasi-1D charge flow on a graphene plane acts a zigzag-type nanoribbon, unless it is perfectly aligned along the armchair direction. In the AB interferometry, we observed h/ e periodic modulation of MC and the zero-field conductance minimum with a negative MC background.
YaxAB, a Yersinia enterocolitica Pore-Forming Toxin Regulated by RovA
Wagner, Nikki J.; Lin, Carolina P.; Borst, Luke B.
2013-01-01
The transcriptional regulator RovA positively regulates transcription of the Yersinia enterocolitica virulence gene inv. Invasin, encoded by inv, is important for establishment of Y. enterocolitica infection. However, a rovA mutant is more attenuated for virulence than an inv mutant, implying that RovA regulates additional virulence genes. When the Y. enterocolitica RovA regulon was defined by microarray analysis, YE1984 and YE1985 were among the genes identified as being upregulated by RovA. Since these genes are homologous to Xenorhabdus nematophila cytotoxin genes xaxA and xaxB, we named them yaxA and yaxB, respectively. In this work, we demonstrate the effects of YaxAB on the course of infection in the murine model. While a yaxAB mutant (ΔyaxAB) is capable of colonizing mice at the same level as the wild type, it slightly delays the course of infection and results in differing pathology in the spleen. Further, we found that yaxAB encode a probable cytotoxin capable of lysing mammalian cells, that both YaxA and YaxB are required for cytotoxic activity, and that the two proteins associate. YaxAB-mediated cell death occurs via osmotic lysis through the formation of distinct membrane pores. In silico tertiary structural analysis identified predicted structural homology between YaxA and proteins in pore-forming toxin complexes from Bacillus cereus (HBL-B) and Escherichia coli (HlyE). Thus, it appears that YaxAB function as virulence factors by inducing cell lysis through the formation of pores in the host cell membrane. This characterization of YaxAB supports the hypothesis that RovA regulates expression of multiple virulence factors in Y. enterocolitica. PMID:24002058
Islet biology, the CDKN2A/B locus and type 2 diabetes risk.
Kong, Yahui; Sharma, Rohit B; Nwosu, Benjamin U; Alonso, Laura C
2016-08-01
Type 2 diabetes, fuelled by the obesity epidemic, is an escalating worldwide cause of personal hardship and public cost. Diabetes incidence increases with age, and many studies link the classic senescence and ageing protein p16(INK4A) to diabetes pathophysiology via pancreatic islet biology. Genome-wide association studies (GWASs) have unequivocally linked the CDKN2A/B locus, which encodes p16 inhibitor of cyclin-dependent kinase (p16(INK4A)) and three other gene products, p14 alternate reading frame (p14(ARF)), p15(INK4B) and antisense non-coding RNA in the INK4 locus (ANRIL), with human diabetes risk. However, the mechanism by which the CDKN2A/B locus influences diabetes risk remains uncertain. Here, we weigh the evidence that CDKN2A/B polymorphisms impact metabolic health via islet biology vs effects in other tissues. Structured in a bedside-to-bench-to-bedside approach, we begin with a summary of the evidence that the CDKN2A/B locus impacts diabetes risk and a brief review of the basic biology of CDKN2A/B gene products. The main emphasis of this work is an in-depth look at the nuanced roles that CDKN2A/B gene products and related proteins play in the regulation of beta cell mass, proliferation and insulin secretory function, as well as roles in other metabolic tissues. We finish with a synthesis of basic biology and clinical observations, incorporating human physiology data. We conclude that it is likely that the CDKN2A/B locus influences diabetes risk through both islet and non-islet mechanisms. PMID:27155872
An Absolute Index (Ab-index) to Measure a Researcher’s Useful Contributions and Productivity
Biswal, Akshaya Kumar
2013-01-01
Bibliographic analysis has been a very powerful tool in evaluating the effective contributions of a researcher and determining his/her future research potential. The lack of an absolute quantification of the author’s scientific contributions by the existing measurement system hampers the decision-making process. In this paper, a new metric system, Absolute index (Ab-index), has been proposed that allows a more objective comparison of the contributions of a researcher. The Ab-index takes into account the impact of research findings while keeping in mind the physical and intellectual contributions of the author(s) in accomplishing the task. The Ab-index and h-index were calculated for 10 highly cited geneticists and molecular biologist and 10 young researchers of biological sciences and compared for their relationship to the researchers input as a primary author. This is the first report of a measuring method clarifying the contributions of the first author, corresponding author, and other co-authors and the sharing of credit in a logical ratio. A java application has been developed for the easy calculation of the Ab-index. It can be used as a yardstick for comparing the credibility of different scientists competing for the same resources while the Productivity index (Pr-index), which is the rate of change in the Ab-index per year, can be used for comparing scientists of different age groups. The Ab-index has clear advantage over other popular metric systems in comparing scientific credibility of young scientists. The sum of the Ab-indices earned by individual researchers of an institute per year can be referred to as Pr-index of the institute. PMID:24391941
NASA Technical Reports Server (NTRS)
Phillips, W. P.
1984-01-01
Aerodynamic characteristics at M=5.97 for the 140 A/B Space Shuttle Orbiter configuration and for the configuration modified by geometric changes in the wing planform fillet region and the fuselage forebody are presented. The modifications, designed to extend the orbiter's longitudinal trim capability to more forward center of gravity locations, include reshaping the baseline wing fillet, changing the fuselage forebody camber, and adding canards. The Langley 20 inch Mach 6 Tunnel at a Reynolds number of approximately 6 million based on fuselage reference length was used. The angle of attack range of the investigation varied from about 15 deg to 35 deg at 0 deg and -5 deg sideslip angles. Data are obtained with the elevators and body flap deflected at appropriate negative and positive conditions to assess the trim limits.
Undoing Gender Through Legislation and Schooling: the Case of AB 537 and AB 394 IN California, USA
NASA Astrophysics Data System (ADS)
Knotts, Greg
2009-11-01
This article investigates California laws AB 537: The Student Safety and Violence Prevention Act of 2000, and the recently enacted AB 394: Safe Place to Learn Act. Both demand that gender identity and sexual orientation be added to the lexicon of anti-harassment protection in public education. However, despite these progressive measures, schools have an unconscious acceptance of heteronormativity and gendered norms, which undermines both the spirit and language of these laws. This paper examines how California schools can both change standard practices and realise the transformative social change that laws like AB 537 and AB 394 can instigate. I assert that the systemic implementation of these laws, through the adoption, enforcement and evaluation of existing AB 537 Task Force Recommendations, is necessary for their success. My second assertion is that AB 537 and AB 394 have the potential to change and reconstitute gender-based and heteronormative standards at school sites.
Possible Future Monoclonal Antibody (mAb)-Based Therapy against Arbovirus Infections
Mancini, Nicasio; Gorini, Giacomo; Clementi, Massimo; Burioni, Roberto
2013-01-01
More than 150 arboviruses belonging to different families are known to infect humans, causing endemic infections as well as epidemic outbreaks. Effective vaccines to limit the occurrence of some of these infections have been licensed, while for the others several new immunogens are under development mostly for their improvements concerning safety and effectiveness profiles. On the other hand, specific and effective antiviral drugs are not yet available, posing an urgent medical need in particular for emergency cases. Neutralizing monoclonal antibodies (mAbs) have been demonstrated to be effective in the treatment of several infectious diseases as well as in preliminary in vitro and in vivo models of arbovirus-related infections. Given their specific antiviral activity as well-tolerated molecules with limited side effects, mAbs could represent a new therapeutic approach for the development of an effective treatment, as well as useful tools in the study of the host-virus interplay and in the development of more effective immunogens. However, before their use as candidate therapeutics, possible hurdles (e.g., Ab-dependent enhancement of infection, occurrence of viral escape variants) must be carefully evaluated. In this review are described the main arboviruses infecting humans and candidate mAbs to be possibly used in a future passive immunotherapy. PMID:24058915
Code of Federal Regulations, 2013 CFR
2013-07-01
... Cry35Ab1 proteins in corn; exemption from the requirement of a tolerance. 174.506 Section 174.506... thuringiensis Cry34Ab1 and Cry35Ab1 proteins in corn; exemption from the requirement of a tolerance. Residues of Bacillus thuringiensis Cry34Ab1 and Cry35Ab1 proteins in corn are exempted from the requirement of...
Code of Federal Regulations, 2014 CFR
2014-07-01
... Cry35Ab1 proteins in corn; exemption from the requirement of a tolerance. 174.506 Section 174.506... thuringiensis Cry34Ab1 and Cry35Ab1 proteins in corn; exemption from the requirement of a tolerance. Residues of Bacillus thuringiensis Cry34Ab1 and Cry35Ab1 proteins in corn are exempted from the requirement of...
Code of Federal Regulations, 2012 CFR
2012-07-01
... Cry35Ab1 proteins in corn; exemption from the requirement of a tolerance. 174.506 Section 174.506... thuringiensis Cry34Ab1 and Cry35Ab1 proteins in corn; exemption from the requirement of a tolerance. Residues of Bacillus thuringiensis Cry34Ab1 and Cry35Ab1 proteins in corn are exempted from the requirement of...
Ab initio melting curve of osmium
NASA Astrophysics Data System (ADS)
Burakovsky, L.; Burakovsky, N.; Preston, D. L.
2015-11-01
The melting curve of osmium up to a pressure P of 500 GPa is obtained from an extensive suite of ab initio quantum molecular dynamics (QMD) simulations using the Z method. The ab initio P =0 melting point of Os is 3370 ±75 K; this range encompasses all of the available data in the literature and corroborates the conclusion of J. W. Arblaster [Platinum Metals Rev. 49, 166 (2005)], 10.1595/147106705X70264 that the melting temperature of pure Os is 3400 ±50 K and that the 3300 K typically quoted in the literature is the melting point of impure Os. The T =0 equation of state (EOS) of Os and the P dependence of the optimized c /a ratio for the hexagonal unit cell, both to pressures ˜900 GPa, are obtained in the ab initio approach as validation of its use. Although excellent agreement with the available experimental data (P ≲80 GPa) is found, it is the third-order Birch-Murnaghan EOS with B0'=5 rather than the more widely accepted B0'=4 that describes the QMD data to higher pressures, in agreement with the more recent experimental EOS by Godwal et al. The theoretical melting curve of Os obtained earlier by Joshi et al. is shown to be inconsistent with our QMD results, and the possible reason for this discrepancy is suggested. Regularities in the melting curves of Os and five other third-row transition metals (Ta, W, Re, Pt, Au) could be used to estimate the currently unknown melting curves of Hf and Ir.
Ab-initio phasing in protein crystallography
NASA Astrophysics Data System (ADS)
van der Plas, J. L.; Millane, Rick P.
2000-11-01
The central problem in the determination of protein structures form x-ray diffraction dada (x-ray crystallography) corresponds to a phase retrieval problem with undersampled amplitude data. Algorithms for this problem that have an increased radius of convergence have the potential for reducing the amount of experimental work, and cost, involved in determining protein structures. We describe such an algorithm. Application of the algorithm to a simulated crystallographic problem shows that it converges to the correct solution, with no initial phase information, where currently used algorithms fail. The results lend support to the possibility of ab initio phasing in protein crystallography.
Three-cluster dynamics within an ab initio framework
Quaglioni, Sofia; Romero-Redondo, Carolina; Navratil, Petr
2013-09-26
In this study, we introduce a fully antisymmetrized treatment of three-cluster dynamics within the ab initio framework of the no-core shell model/resonating-group method. Energy-independent nonlocal interactions among the three nuclear fragments are obtained from realistic nucleon-nucleon interactions and consistent ab initio many-body wave functions of the clusters. The three-cluster Schrödinger equation is solved with bound-state boundary conditions by means of the hyperspherical-harmonic method on a Lagrange mesh. We discuss the formalism in detail and give algebraic expressions for systems of two single nucleons plus a nucleus. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we apply the method to amore » 4He+n+n description of 6He and compare the results to experiment and to a six-body diagonalization of the Hamiltonian performed within the harmonic-oscillator expansions of the no-core shell model. Differences between the two calculations provide a measure of core (4He) polarization effects.« less
Rescue of failed filtering blebs with ab interno trephination.
Shihadeh, Wisam A; Ritch, Robert; Liebmann, Jeffrey M
2006-06-01
We evaluated the effectiveness of ab interno automated trephination as a technique for rescuing failed mature filtering blebs. A retrospective chart review of 40 failed blebs of 38 patients who had a posttrephination follow-up period of at least 3 months was done. With success defined as intraocular pressure (IOP) <21 mm Hg and at least a 20% reduction from baseline on the same or fewer number of pretrephination medications, 30/40 eyes (75%) fit these criteria over the entire course of follow-up. Among all 40 eyes, there was a significant reduction of IOP from pretrephination to 3 months (P<.001). The percentage of patients requiring 2 or more medications declined from 90% pretrephination to 21% at 3 months (P<.0001), and was stable thereafter. Some patients were able to eliminate all medications. Patients who did not meet the criteria of success regained successful IOP control with other modalities of management. Complications were few. We believe that ab interno trephination is an excellent option for rescuing selected failed filtering blebs.